GEOCHEMICAL EXPLORATION FOR POLYMETALLIC ORES IN VOLCANO-SEDIMENTARY ROCKSStudies in China and Finland

XIPINGZHANG

Institute of Geosciences,University of Oulu

OULU 2000

XIPING ZHANG

GEOCHEMICAL EXPLORATION FOR POLYMETALLIC ORES IN VOLCANO-SEDIMENTARY ROCKSStudies in China and Finland

Academic Dissertation to be presented with the assent ofthe Faculty of Science, University of Oulu, for publicdiscussion in the Auditorium of the Department ofGeology (GO 101), Linnanmaa, on December 1st, 2000,at 12 noon.

OULUN YLIOPISTO, OULU 2000

Copyright © 2000University of Oulu, 2000

Manuscript received: 10 November 2000Manuscript accepted: 20 November 2000

Communicated byProfessor Ouyang ZongqiDoctor Raimo Lahtinen

ISBN 951-42-5787-1 (URL: http://herkules.oulu.fi/isbn9514257871/)

ALSO AVAILABLE IN PRINTED FORMATISBN 951-42-5786-3ISSN 0355-3191 (URL: http://herkules.oulu.fi/issn03553191/)

OULU UNIVERSITY PRESSOULU 2000

To my mother

Zhang, Xiping, Geochemical exploration for polymetallic ores in volcano-sedimentary rocks: studies in China and FinlandInstitute of Geoscienses, University of Oulu, P.O.Box 3000, FIN-90014 University ofOulu, Finland2000Oulu, Finland(Manuscript received 10 November 2000)

Abstract

A comparison between the two very important sulfide belts Raahe-Ladoga Ore Zone (RLZ) inFinland and Southern Edge of Altay (SEA) in China, including geological setting, metallogeniccharacters and geochemical exploration has been made.

The two sulfide belts share similarities but differ from each other in the tectonic setting andmetallogenic epoch. Polymetallic ores in RLZ and SEA are the products of the submarinevolcanism, but mainly Zn-Cu type is present in RLZ and Pb-Zn, Cu-Pb-Zn and Cu-Zn types occurin SEA. A main Ni-Cu ore belt related to the mafic-ultramafic intrusions is also present in the RLZ.RLZ is metamorphosed to a higher grade than SEA.

The Viholanniemi Zn-Au deposit is a veinlet-disseminated type, possibly beneath thestratabound sulphide ores, and the Keketale Pb-Zn deposit is a stratabound sulphide ore hosted bysedimentary rocks in the volcano-sedimentary formation. They show many differences. It issuggested that stratabound sulphide ores overlie stratigraphically the Viholanniemi stringer ores andAu-bearing stringers underlie the Keketale stratabound ores. Geochemical explorations of the twodeposits exhibit different methods, subjects and procedures. Boulder tracing and till geochemicalexploration proved to be very effective in finding the Viholanniemi deposit while stream sedimentand soil geochemical surveys were the major and effective tools in finding the Keketale deposit.

An extensional environment and the intensity of volcanism are the essential conditions for theformation of polymetallic ores related to the volcanism. It is feasible to classify the ores into theores hosted by volcanics and sedimentary rocks in a volcano-sedimentary formation. Thestratigraphical thickness of volcanic rocks and the amount of agglomerates are the two most crucialfactors needed to be considered in prospecting. The chemical variations of the host rocks canindicate the sulphide ores hosted by sedimentary rocks in some circumstances.

Keywords: Raahe-Ladoga Ore Zone (RLZ), Southern Edge of Altay (SEA), metallogene-sis, volcanism

A short preface to the study

I was in Finland as an exchange scholar through an agreement between the FinnishAcademy and the Chinese Academy of Sciences in 1997. The invitation came from theGeological Survey of Finland (GTK) and the Institute of Geosciences and Astronomy ofthe Oulu University. Before that I knew that Finland enjoyed a high reputation inPrecambrian research and geochemical explorations.

The facts, however, are not merely as I had learned before. Two of the greatestgeologists, Sederholm, J.J. and Eskola, P. are well known over the world for theirpioneering studies and contributions to the anatexis, as well as migmatization andexperiment petrology. Before 1998, I knew almost nothing about them when I read theirfamous works on the advice of Prof. Cheng Yuqi, the pioneer of metamorphic geology ofChina. Of course, Finnish geologists have also made by far the most outstanding researchon Quaternary Geology and Economic Geology which resulted in the finding of manyimportant ore deposits e.g. the Main Sulphide Ore Belt including Outokumpu Cu-Co-Zn-Ni deposits.

The following study has been carrying out in the way of cherishing a feeling of greatreverence for Finland and Finnish geologists. With the results of the study, the authorwould like to express his sincere thanks to Finland and Finnish friends for the invitationand giving me the chance to do the study.

Acknowledgements

In January 1997, Geological Survey of Finland and Institute of Geosciences andAstronomy, at the University of Oulu invited me to Finland as a junior scientist as part ofthe agreement of co-operation in a scientific exchange program between Finland andChina. The Academy of Finland provided financial support. Geological Survey ofFinland and Institute of Geosciences and Astronomy, at the University of Oulu providedsupport, including field, laboratory and office work, as well as analyses of samples. TheGeological Survey of Finland has also given me permission to use and publish thevaluable data including unpublished data. The Research Center of Mineral ResourcesExploration, the Chinese Academy of Sciences and the Beijing Institute of Geology andMineral Resources have supported me with this program. I am very grateful to all theseinstitutes.

I am deeply indebted to Dr. Elias Ekdahl, Professor Risto Aario, Dr. Hannu Makkonenand Professor Vesa Peuraniemi. Dr. Elias Ekdahl and Professor Risto Aario arranged andsupervised the programs in Finland and Dr. Hannu Makkonen followed the study withenthusiasm. Professor Vesa Peuraniemi also supervised part of the program. Theirknowledge and experiences were so invaluable both in field and subsequent discussions,as well as in directing the course of the study. The manuscript was also checked andreviewed by them and I acknowledge with gratitude for their numerous suggestions andcomments.

Professor Jiang Fuzhi has given me many valuable suggestions during discussions. Dr.Raimo Lahtinen and Professor Ouyang Zongqi read and checked the manuscript andmade comments and many important suggestions. Drs. Li Yanhe and Juha Karhureviewed the part with the isotope studies. Mr. Rauli Lempiäinen assisted me with fieldwork in Finland. Mr. Gordon Roberts M.A. reviewed the English of the manuscripts.

I am additionally grateful to Professor Markku Mäkelä, the Research Director of theGeological Survey of Finland, Dr. Anssi Lonka and Mr. Kari Pääkkönen, the Director ofthe Kuopio Regional Office of the Geological Survey of Finland, Professor Risto Aarioand Professor Tuomo Alapieti, the Director of the Institute of Geosciences andAstronomy, at the University of Oulu, for allowing me to use the facilities of institutes.Also I wish to thank Mr. Tuomo Korkalo, the General Manager of Exploration,Outokumpu Mining Oy, for allowing me to use some unpublished data.

The author wishes to express his specific thanks to Professors Cheng Yuqi, HuangDingcheng, Sun Zhaojun, Wang Jingbin, Wang Dongbo, Ms.Yin Xiuzhu, Dr. HuangZhen, Mr. Yang Bing, as well as many friends from Finland for their help and support indifferent ways.

I would like here also to thank my mother, brothers, sister and my close friends fortheir great support.

List of original publications

The following previously published papers are reviewed and revised in this study:1. Zhang X (1992) Geochemical anomalies of rock-forming elements reflecting

precipitation environments of ore substances - an important indicator for prognosis ofblind ore deposits in geochemical exploration. Geoph Geoch Explor 16(3): 208-215(in Chinese with English Summary).

2. Zhang X & Chen W (1995) Preliminary research on REE geochemistry of theKeketale Pb-Zn deposit, Xinjiang. Geol Expl Non-Ferrous Metals 4(4): 219-222 (inChinese with English Summary).

3. Zhang X, Chen W & Wang S (1996) Geochemical investigation of the Keketale Pb-Zn deposits in Xinjiang and its anomaly model. Geol Expl Non-Ferrous Metals 5(1):48-53 (in Chinese with English Summary).

This thesis consists of the following parts:

Part I Early Proterozoic metavolcano-sedimentary formation and zinc-gold deposit inthe Viholanniemi area, south-eastern Finland.

Part II Boulder prospecting and till geochemistry in the search for zinc-gold ore in theViholanniemi area, south-eastern Finland.

Part III Geochemical exploration and study of Keketale lead-zinc deposit hosted by sedi-mentary rocks in a volcano-sedimentary formation, north-western China (reviewof previous studies including papers 2 and 3).

Part IV Geochemical anomalies of rock-forming elements: an important indicator ofblind ore deposits (revised version of the previously published paper 1).

Contents

Abstract A short preface to the studyAcknowledgementsList of original publications1 Polymetallic ores in the RLZ, Finland and the SEA, China . . . . . . . . . . . . . . . . . . . 15

1.1 Volcano-sedimentary formations and related polymetallic oresin the Viholanniemi and Maizi areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

1.2 Essential genetic conditions of polymetallic ores in volcano-sedimentary formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

1.3 Geochemical exploration for polymetallic ores in volcanic terrains . . . . . . . . . 201.4 Prospecting and interpretation of polymetallic ores in volcanic terrains . . . . . . 24

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25PART I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27Early Proterozoic metavolcano-sedimentary formation and zinc-gold deposit in the Viholanniemi Area, South-eastern Finland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Location and physiography of the study area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Background to the research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31Methods and objectives of the study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

The regional geological setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Geology of the Viholanniemi area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Lithology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Stratigraphical relationships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38The volcanic cycle, rock assemblage and paleovolcanic center. . . . . . . . . . . . . . . 40Metamorphism, deformation and structural features . . . . . . . . . . . . . . . . . . . . . . . 41

Lithogeochemistry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41Whole rock geochemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41Classification of volcanic rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46Tectonomagmatic affinities of volcanic rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Viholanniemi Zn-Au deposit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52Wall rocks and host rock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52Ore occurrence and metal contents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53Ore mineralogy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55Isotope studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64Geotectonic setting of the Viholanniemi volcano-sedimentary formation. . . . . . . 64Viholanniemi Zn-Au mineralization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

Summary and conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Appendices 1-4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75PART II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87Boulder prospecting and till geochemistry in the search for zinc (gold) ore in the Viholanniemi area, South-eastern Finland. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89Bedrock geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90Glacial geology and boulder prospecting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93Till geochemistry and geochemical exploration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

Mineralogy of Till. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95Chemical composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97Till geochemical exploration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Conclusions and discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

PART III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109Geochemical exploration and study of the Keketale lead-zinc deposit hosted by sedimentary rocks in the volcano-sedimentary formation in North-Western China . . . 111

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111The geological setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112Ore deposit geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114Geochemical exploration and the discovery of the deposit. . . . . . . . . . . . . . . . . . . . 116Deposit geochemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119Summary and conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

PART IV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131Geochemical anomalies of rock-forming elements: an important indicator of blind ore deposits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133The case of anomalous models of rock-forming elements . . . . . . . . . . . . . . . . . . . . 134

Porphyry copper deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134Stratabound sulfide deposits hosted by volcanic rocks . . . . . . . . . . . . . . . . . . . . 136Stratabound sulfide deposits hosted by sedimentary rocks in the volcano-sedimentary formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136

Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139Acknowledgement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139

1 Polymetallic ores in the RLZ, Finland and the SEA, China

For the author it was very useful to take part in geochemical exploration for polymetallicores and make studies on deposits, for instance the Keketale Pb-Zn deposit, found involcanic terrain within the Southern Edge of Altay (SEA) in China from 1985, andcontinue the studies in the Viholanniemi Zn-Au deposit within the Raahe-Ladoga OreZone (RLZ) in Finland from 1997. This made it possible to understand better thepolymetallic ores related to volcanism, their genesis and geological setting, as well asshare the experiences on exploration both in Finland and China through the studies andcomparison. The Viholanniemi Zn-Au deposit is not a typical VMS deposit but can beconsidered as a stringer type (also see Makkonen 1991) with superimposition ofmetamophism according to its distinct characters, while the Keketale Pb-Zn deposit isone of the stratabound deposits hosted by sedimentary rocks in the volcano-sedimentaryformation (also see Jiang & Liu 1992, Jiang 1994). This however does not hinder thecomparison of SEA and RLZ, which both contain a variety of ores in volcanic terrains.The studies greatly help to learn the characteristics of VHMS deposits and also theprospecting.

RLZ and SEA seem to share similarities in many respects, although they differ fromeach other in the tectonic setting and metallogenic epoch. RLZ is a boundary zonebetween the Finnish Archaean and Proterozoic, which has been interpreted as a colli-sional zone of the Archaean continent and Palaeoproterozoic, Svecofennian lithosphere(see Ekdahl1993, Weihed & Mäki 1997). Several epochs of mineralization and also met-allogenic provinces are related to the Palaeoproterozoic intracratonic rifting (Outo-kumpu), island arc volcanism (Pyhäsalmi-Vihanti), locally arc-rifting (Viholanniemi) andalso the mafic-ultramafic intrusions (Kotalahti Ni-belt) (Ekdahl 1993) (Fig. 1).

16

Fig. 1. Metallogenic provinces and epochs within the Raahe-Ladoga zone, central Finland. 1.Kotalahti Ni-Belt; 2. Pyhäsalmi Island Arc; 3. Kainuu-Outokumpu Back Arc. (Ekdahl 1993).

SEA is a part of the southern margin of the Siberia plate. The regional tectonicevolution is characterised by splitting-collision regims from Proterozoic to Paleozoic (Li1983, Huang et al. 1990, Han & He 1991, Xiao et al. 1990, Chen et al. 1996). Accordingto Chen et al. (1996), the protolith of the Proterozoic basement is a volcanic-terrigenousformation indicating an extensional environment. Altai massif was accreted to the Siberiaplate on its southern margin in Early Ordovician. During the Early-Middle Devonian, anepicontinental extensional rift was formed beginning at the eastern part of the area. It wasaccompanied by ongoing rifting, submarine volcanism associated with massive sulphidemineralizations along three basins Maizi (Mongku-Keketale)-Altay-Ashele (Chen et al.1996) (Fig. 2).

Polymetallic ores in RLZ and SEA were the products of the submarine volcanism.Volcanic rocks related to the massive sulphides in RLZ are mainly tholeiitic and calc-alkaline, and also the products of bimodal volcanism, while in SEA the rocks aretholeiitic, calc-alkaline and alkaline, and the bimodal volcanism seem to have a closerelationship with Cu-Zn ores. Deposits in RLZ are Zn-Cu type, however, in SEA, depositsare Pb-Zn, Cu-Pb-Zn and Cu-Zn types. In addition, except for VMS deposits, a main Ni-Cu ore belt related to the mafic-ultramafic intrusions is also present in the RLZ; these areabsent in SEA except for locally mafic intrusions and one related Cu-Ni deposit. Bothzones have experienced deformation and metamorphism, but the effects seem to be

17

stronger in RLZ than in SEA. Detailed comparison is listed in Table 1 according to thedata of Ekdahl (1993), Weihed and Mäki (1997), Jiang (1993), Jiang and Liu (1992),Jiang (1994), Zhang (1992), Zhang et al. (1996), Wang et al. (1998, 1999), Chen et al.(1995, 1996), Ding (1999).

Fig. 2. Metallogenic belts and epochs in the southern edge of Altay, north-western China. Themap is simplified after Chen et al. (1996) and Wang et al. (1998). The data is from Chen et al.(1996) and Ding (1999). 1. Volcanic-sedimentary basin; 2. Fault.

18

Table 1. Comparison between the VHMS deposits in Finnish RLZ and Chinese SEA.

1.1 Volcano-sedimentary formations and related polymetallic ores in the Viholanniemi and Maizi areas

A comparison between the Viholanniemi Zn-Au deposit and Keketale Pb-Zn deposit ismade in Table 2 (the data are from Wu 1992, Jiang 1993, Han and He 1991, Han 1992,He et al. 1994, Jiang & Liu 1992, Jiang 1994, Zhang et al. 1990, Zhang 1992, Zhang etal. 1996, Wang et al. 1998 and 1999, Chen et al. 1995 and 1996).

RLZ in Finland SEA in ChinaBimodal submarine volcanism in island arc system, volcanics are tholeiitic and calc-alkaline

Volcanic complexes and zones are associated with gravimetric highs or sharp gradients and medium-to high-grade metamorphism

Ores are mainly Zn-Cu type

Footwall rocks include dolomite/carbonate, calc-silicate rocks, felsic volcanics, chert, U-P horizon, black schist, ( BIF )

Sericitization, Silicification and Chloritization are general

Mg, Fe, H2O and S increase towards the ore, and conversely, Si, Ca, Na and K decrease

Cyprus-type (Outokumpu) deposits (�1.96Ga ) are presentThe geometry of the deposits is intensely tectonically controlled

c. 2.0-1.9 Ga in ages

Amphibolite-granulite facies metamorphism

Bimodal-unimodal submarine volcanism in continental margin rift, volcanics are tholeiitic, calc-alkaline and alkaline

Volcanic-sedimentary formations are associated with gravimetric gradients

Ores are mainly Cu-Zn, Cu-Pb-Zn and Pb-Zn types

Quartz-Keratophyrite-Keratophyric pyroclastics, carbonate, tuffaceous clastics compose the footwall of Cu-Zn ores, Na-K rich rhyolitic lava and felsic pyroclastics compose the footwall of Pb-Zn ores.

Commonly underlain by a zone of alteration enclosing the stringer ores, silicification, sericitization, pyritization as well as chloritization, epidotization and carbonatization are general

Si, K, H2O and S increase and Ca, Na decrease towards Ore in Cu-Zn type; Mg, Fe, Ca increase and Na decrease towards Ore in Pb-Zn type

Cyprus-type deposits absent

The geometry of the deposits is tectonically controlled

c. 404.6-352.3 Ma in ages

Greenschist facies metamorphism

19

Table 2. Comparison between the Viholanniemi Zn-Au deposit, south-eastern Finland andthe Keketale Pb-Zn deposits, north-western China.

Comparing the two areas of Viholanniemi and Keketale, the volcanic rocks in theViholanniemi area seem to be the products of bimodal volcanism, if only concerning thestratigraphical sequence, and in fact the rocks of calc-alkaline and tholeiitic series are notfractionates from the same parent magma. The tectonic setting is interpreted as anincipient arc-rifting, and the felsic volcanics are mainly pyroclastics. In contrast to these,the volcanic rocks of the calc-alkaline series in the Maizi area were formed by bimodalvolcanism fractionated from the same parent magma in the continental margin rift. Thelarge quantity of felsic lava is peculiar to the formation. Secondly, the stratigraphicalthickness is less and the period of inactivity of volcanism is shorter in Viholanniemi areathan in Maizi area. The sedimentary rocks formed in hot water (here it means asedimentary basin near the volcanic center, in which the water may have been about100oC in temperature) are present in both areas, only a small volume of siliceous rock hasbeen found in Viholanniemi. Siliceous rock and iron bearing carbonate rocks, however,are common in the Maizi area, particularly in Keketale. Thirdly, ore sulphide �34S valuesvary between 5.4� to 15.3�, and no carbon concentration has been documented inKeketale (Han 1992), while sulphide �34S values in Viholanniemi are mainly positive and

Viholanniemi Zn-Au deposit Keketale Pb-Zn deposit

Bimodal submarine volcanism seen from the stratigraphical sequence but not fractionated from the same parent magma in arc-rifting, volcanics are tholeiitic and calc-alkaline

Bimodal submarine volcanism fractionated from the same parent magma in continental margin rift, volcanics are calc-alkaline

The volcano-sedimentary formation has a relative small stratigraphical thickness

The volcano-sedimentary formation has a stratigraphical thickness over 300m

Volcanic breccia and agglomerate are common Volcanic breccia and agglomerate are common

Felsic volcanics are mainly pyroclastics Felsic volcanics including large voluminous lava underlie the host rocks

The host rocks are mainly quartz-carbonate-tremolite rocks (the protolith includes siliceous rock, tuffaceous siltstone and tuff)

The host rocks are mainly composed of biotite quartz schist, granoblasite with interlayers of marbles, meta-tuff, meta-tuffaceous siltsone and meta-siltstone. (The protoliths include calcareous-argillaceous sandstone, siliceous rock and iron-bearing carbonates)

Ores are veinlet and disseminated Ores are mainly disseminated, taxitic, massive, banded, breccia and net-veined

Sericitization and locally epidotization are general Sericitization, carbonatization and silicification are general

Ore sulphide �34S values vary from -0.5� to 10.4� and no sulphate mineral is present

Ore sulphide �34S values vary from �5.4� to �15.3� and sulphate minerals are present

Calcite has �18O values of 7.6-20� and �13C values of �3.6 � � 8.1�, and graphite is present

One carbonate has �13C value of �11.6� and no graphite is present

Not intense primary geochemical patterns and no depleted Na2O

Clear and coherent primary geochemical patterns with typical depleted Na2O

Intense metamorphic overprinting Evident metamorphic overprinting has not been found

20

vary between -0.5� to10.4� and also graphite is very common. In addition, an intenseoverprinting of metamorphism is present in Viholanniemi, but this is not evident inKeketale.

However, although a big difference, including an economic significance, between thetwo deposits is obvious, they share common features connected by stratabound sulphidesrelated to marine volcanism. The volcano-sedimentary formations are composed ofmarine volcanics and clastics, and volcanic agglomerate and breccia are general in twoareas, which indicates that both deposits were formed in the sedimentary basin near thevolcanic center. The most important factor is that both of them were formed in anextension environment, and this is perhaps the volcanogenic sulphide ore proper.Therefore the Viholanniemi Zn-Au deposit could be considered as a veinlet-disseminatedtype possibly beneath the strata bound sulphide ores which experienced metamorphicoverprinting, and the Keketale Pb-Zn deposit is a stratabound sulphide ore hosted bysedimentary rocks in the volcano-sedimentary formation. It is noteworthy perhaps here topoint out the possibility of the presence of stratabound sulphide ores stratigraphicallyabove the Viholanniemi stringer ores and of Au bearing stringer below the Keketale stratabound ores.

1.2 Essential genetic conditions of polymetallic ores in volcano-sedimentary formation

As the geological setting of the polymetallic ores are related to the volcanism, anextensional environment seems to be essential. In this case, the magma in the depth mayprovide good conditions to differentiate and gather the volatile component needed byintense eruption. It is easy to understand why most of important polymetallic sulphideores are associated with the intense felsic or felsic-intermediate volcanism.

Other essential conditions could contribute to the intensity of volcanism. According toJiang (1994), the intensity of volcanism in the same time with the mineralization is thecrucial factor affecting the genetic type of polymetallic ores. The ores hosted by volcanicrocks are generally the products of intense volcanism in which the extensive fluidactivities also happened. In contrast to this, the ores hosted by sedimentary rocks in thevolcano-sedimentary formation were formed in the periods of small volcanic activityfollowing mainly felsic eruptions. The sedimentary basin near the volcanic center andrelative strict conditions, such as reducing environment or bacteria activity, would beneeded.

1.3 Geochemical exploration for polymetallic ores in volcanic terrains

Boulder tracing and till geochemical exploration have been proved to be very effectivetools in the prospecting of mineral deposits in Finland. One must, however investigate theQuaternary framework before the exploration, because the erosion, entrainment,

21

transportation and depositional history and the resulting composition of sediments arevery important factors in considering sampling, analysis of glacial sediments andinterpretation of the data.

Preglacial weathering in the Viholanniemi area was intense, but its products preservedwell only in the bottommost layers, immediately above the bedrock. The till in thebottom-most layer is composed of more local material illustrated by identical mineralcomposition including the ore minerals in the mineralized sites presented both in till andweathered bedrock. Trace elements presented in till in the area are generally related to theadsorption of clay minerals, secondary oxides and hydroxides, but high concentrations ofZn, Cu, Pb, Au, Ag, Ni and Co in till in the project area are mainly related to the residualore minerals.

The ore-bearing boulder train that indicated ores related to quartz-carbonate rocks andfelsic volcanics is composed of long and narrow boulder clusters of about 20 km (Fig. 3).Following the till geochemical, together with geophysical exploration led to the discoveryof the Viholanniemi Zn-Au deposit. All metals detected in the till show clear and coherentanomalous distribution patterns which reflect the mineralization sites well in the area withAg and Zn having the strongest anomalies (Fig. 4).

Differing from Finland, stream sediment and locally soil geochemical surveys are themajor and effective tools in prospecting of mineral deposits in China. Stream sedimentgeochemical exploration is the first choice in most mountain areas and this was wellillustrated in the SEA, in NW China. Generally, the testing of selecting the fraction offavorable size is necessary before the exploration. Stream sediment geochemicalexploration carried out in the central part of SEA exhibits an associated anomalous areaof about 200 km2 composed of Pb, Zn, Ag, As, Cu, Cd and Mn in the Maizi area (Fig. 5).Detailed exploration of the anomalies of Cd and coherent Pb, Zn, As, Ag and Mn occur tothe south-eastern part of the Maizi area (Fig. 6) brought about the finding of stratiformgossan at Keketale and a ring of soil anomalies of Pb and Zn corresponding to thevolcano-sedimentary formation of Lower Devonian. The Keketale Pb-Zn deposit wasfound by following geochemical and geophysical anomalies.

Fig. 3. Ore boulder train from Viholanniemi, south-eastern Finland (modified after Makkonen1991).

22

Fig. 4. Map of the areal distribution of zinc concentration in till at Viholanniemi, south-easternFinland.

Obviously, the Quaternary framework is the main subject of the till geochemistry inFinland. In China, however, most exploration geochemists are not concerned with theQuaternary framework but only the favorable sample size (and the horizon in soil survey).The geochemical surveys of the Viholanniemi Zn-Au deposit were started with theboulder tracing. Then, it transited to the close-spaced sampling along lines with distancesof 200 m, 50 m and 25 m, and the sample spacing of 40 m, 20 m, 10 m and 5 m.Meanwhile, a geophysical survey was also carried out. It was composed of two mainstages before the drilling. Compared to these, the geochemical surveys of the KeketalePb-Zn deposit began with the stream sediment survey, and then with the anomaly tracingand at the same time sampling with a grid of 200 m by 40 m was also carried out. At thelast step, it transited to a more detailed sampling with a grid of 100 m by 20 m and thegeophysical exploration. These two parts of detailed sampling and the geophysicalexploration should have been combined into one for economic reasons and for a rationalprospecting procedure. Trace elements, particularly Cd associated closely with the oreminerals, were successfully applied in the interpretation of geochemical anomalies inKeketale.

23

Fig. 5. Anomaly of lead in stream sediments in the Maizi district, north-western China(modified after Wang et al. 1998).

Fig. 6. Anomalies of selected elements in stream sediments at Keketale, north-western China.The sample site is marked by small point. a) Pb (solid line): 30,60,120,240ppm; Ag (dotted line):0.05,0.1,0.2,0.4ppm; b) Zn (solid line): 120,240,480,1000ppm; Cd (dotted line): 0.6,1.2,2.4ppm.

24

1.4 Prospecting and interpretation of polymetallic ores in volcanic terrains

Concerning prospecting and interpretation of polymetallic ores, it is feasible to classifythe sulphide polymetallic ores related to volcanism into the ores hosted by volcanics andsedimentary rocks in a volcano-sedimentary formation (Jiang & Liu 1992, Jiang 1994).The stratigraphical thickness of volcanic rocks and the amount of agglomerates are thetwo most crucial factors. Intense alteration, including an alteration pipe in the footwall,occurs mainly in the ores hosted by volcanics and is characterized by the absence of afeldspar zone (Lambert 1974, Riverin & Hodgson 1980, Larson 1984, Jiang & Liu 1992,Jiang 1994). Alteration is typically shown as enrichment of Fe and Mg (K and Si) and asdepletion of Na and Ca in chemical composition (Lambert & Sato 1974, Riverin andHodgson 1980, Frater 1983, Larson 1984, Peterson 1988, Ekdahl 1993, Chen et al. 1996).The alteration present in the ores hosted by sedimentary rocks is commonly weaker andthe alteration pipe is seldom met. The chemical variations, however, are obvious: forinstance the increase of Fe, Mg and Ca and the decrease of Na correspond to thealteration and ore bodies (Zhang et al. 1990, 1996, Zhang 1992). Consequently, thechemical variations of the host rocks would give a good indication of prospecting ofsulphide ores hosted by sedimentary rocks in the volcano-sedimentary formation, in thecase where alteration can not be used as a good indicator of the presence of sulphide oreshosted by sedimentary rocks.

Elements associated to the major minerals in the polymetallic ores should be givenmuch attention in the interpretation of geochemical exploration, for example, theindication of Cd in the discovery of the Keketale Pb-Zn deposit. Rock-forming elementsand their variations can be used as good indicators of blind ores, no matter what type ofsulphide ore it is (Zhang et al. 1990, 1996, Zhang 1992).

References

Ekdahl E (1993) Early Proterozoic Karelian and Svecofennian formations and the evolution of theRaahe-Ladoga Ore Zone, based on the Pielavesi area, central Finland. Geol Surv Finland, Bull373, 137 p.

Chen Y, Ye Q, Feng J, Mu C, Zhou L, Wang Q, Huang G, Zhuang D & Ren B (1996) Ore-formingconditions and metallogenic prognosis of the Ashele Copper-Zinc metallogenic belt, Xinjiang,China. Geol Publ House, Beijing, 330 p (in Chinese with English Summary).

Chen Y, Ye Q, Wang J & Rei J (1995) Metallogenic conditions and evaluation of mineral resourcesof Altay gold and non-ferrous metals provinces. Unpublished research report, 483 p (in Chinese).

Ding R (1999) Evolution of ore-bearing fluid and prospect forecasting in Keketale metallogenic belt,Xinjiang. Unpubl. PhD thesis. China University of Geosciences, Beijing, 100 p (in Chinese).

Frater KM (1983) Geology of the Golden Grove prospect, Western Australia: A volcanogenicmassive sulfide-magnetite deposit. Econ Geol 78: 75-919.

Han B & He G (1991) The tectonic nature of the Devonian volcanic belt on the Southern Edge ofAltay Mountains in China. Geosc Xinjiang, No 3: 89-100 (in Chinese).

Han D (1992) Keketale lead-zinc deposit. In: Jiang Q, Liu Y, Wen H, Deng Y & Chen H (eds)Geological, geophysical and geochemical studies of Cu-Fe-polymetallic ore belt in Southern Edgeof Altay and the prospecting targets. Unpublished research report, 251 p (in Chinese).

He G, Li M, Liu D, Tang Y & Zhou R (1994) Paleozoic crustal evolution and mineralization inXinjiang of China. People�s Publ House of Xinjiang, 437 p (in Chinese with English Summary).

Huang J, Jiang C & Wang Z (1990) On the opening-closing tectonics and accordion movement ofplate in Xinjiang and adjacent. Geosc Xinjiang, No 1: 3-16 (in Chinese).

Jiang F (1993) Petrochemical characters of ore-bearing volcanic formation in massive sulfidedeposits. In: Li Z & Wang B (eds) Volcanic rocks, volcanism and related mineral resources.Collection of Papers of Geo Soc China 1: 31-38 (in Chinese).

Jiang Q & Liu Y (1992) Geological features of Cu-polymetallic ore deposits in Southern Edge ofAltay. In: Jiang Q, Liu Y, Wen H, Deng Y & Chen H (eds) Geological, geophysical andgeochemical studies of Cu-Fe-polymetallic ore belt in Southern Edge of Altay and the prospectingtargets. Unpublished research report, 251 p (in Chinese).

Jiang Q (1994) Types, evaluation criteria and geneses of the massive sulfide deposits in the volcanicterrain. Geol Expl Non-Ferrous Metals 3(1): 4-9. (in Chinese).

Lambert IB & Sato T (1974) The Kuroko and associated ore deposits of Japan: A review of theirfeatures and metallogenesis. Econ Geol 69: 1215-1236.

Larson PB (1984) Geochemisry of the alteration pipe at the Bruce Cu-Zn volcanogenic massivesulfide deposit. Arizona. Econ Geol 79: 1880-1896.

26

Li C (1983) Contributions to the project of plate tectonics in Northern China. N1. Geol Publ House,Beijing, p 3-6 (in Chinese).

Makkonen H (1991) Studies of the Viholanniemi Zn deposit in Joroinen, 1984-1988. Geol SurvFinland, unpublished research report, 22 p.

Peterson JA (1988) Distribution of selected trace and major elements around the massive sulfidedeposit at the Penn Mine, California. Econ Geol 83: 419-427.

Riverin G & Hodgson CJ (1980) Wall-rock alteration at the Millenbach Cu-Zn Mine, Noranda,Quebec. Econ Geol 75: 424-444.

Wang J, Qin K, Wu Z, Hu J, Deng J, Zhang J, Bian, Y & Li S (1998) Volcanic-exhalative-sedimentary lead-zinc deposits in the Southern Margin of the Altai, Xinjiang. Geol Publ House,Beijing, 210 p (in Chinese).

Wang J, Li B, Zhang J, Yin Y, Wang J, Wang Z & Zheng G (1999) Metallogenesis and prognosis ofgold and copper deposits in Ertix Metallogenic Belt, Xinjiang. Metallurgical Industry Press,Beijing, 178 p (in Chinese).

Weihed P & Mäki T (1997) Volcanic hosted massive sulfide deposits and gold deposits in theSkellefte district, Sweden and Western Finland. Research and exploration-where do they meet?4th Biennial SGA Meeting, Aug. 11-13, 1997, Turku, Finland, excursion guidebook A2. GeolSurv Finland, Guide 41, 81 p.

Wu Z (1992) The volcano-sedimentary formations of lower Devonian in major districts, SouthernEdge of Altay. In: Jiang Q, Liu Y, Wen H, Deng Y & Chen H (eds) Geological, geophysical andgeochemical studies of Cu-Fe-polymetallic ore belt in Southern Edge of Altay and the prospectingtargets. Unpublished research report, 251 p (in Chinese).

Xiao X, Tang Y, Li J, Zhao M, Feng Y & Zhu B (1990) On the tectonic evolution of the NorthernXinjiang, Northwest China. Geosc Xinjiang, No 1: 47-68 (in Chinese).

Zhang X, Chen W & Wang S (1990) Studies of the polymetallic ores, their geochemical anomalouspatterns and interpretation, Beijing Institute of Geology for Mineral Resources, China.Unpublished research report with three accessary, 98 p (in Chinese).

Zhang X (1992) Geochemical anomalies of rock-forming elements reflecting precipitationenvironments of ore substances-an important indicator for prognosis of blind ore deposits ingeochemical exploration. Geoph & Geoch Explor 16(3): 208-215 (in Chinese).

Zhang X & Chen W (1995) Preliminary research on REE geochemistry of the Keketale Pb-Zndeposit, Xinjiang. Geol Expl Non-Ferrous Metals 4(4): 219-222 (in Chinese).

Zhang X, Chen W & Wang S (1996) Geochemical investigation of the Keketale Pb-Zn deposits inXinjiang and its anomaly model. Geol Expl Non-Ferrous Metals 5(1): 48-53 (in Chinese).

PART I

I

29

Early Proterozoic metavolcano-sedimentary formation and zinc-gold deposit in the Viholanniemi Area, South-eastern

Finland

Xiping Zhang

Abstract

The Viholanniemi metavolcanic-sedimentary formation is composed of mainly clastics with volcanicsof a shallow marine environment. This formation includes felsic pyroclastics with minor intermediateintercalations, mafic pyroclastics associated with pillow lava, siliceous rock and fine tuffacoussiltstone between the felsic and mafic pyroclastics, as well as flychoid clastics in the bottom and toprespectively. The volcanism began with mainly felsic explosive eruption of the central type and endedwith mafic effusive eruption of the fissure type. Pyroclastics of the Viholanniemi formation occurconcordantly with the flychoid clastic rocks of the Svecofennian. Chemical composition of thevolcanics suggests that felsic-intermediate rocks are calc-alkaline, while mafic rocks belong totholeiitic series of low potassium. The volcanic rocks of the area are products of mantle-derived meltand its induced anatextic melt, and also their mixing instead of fractionates from the same parentmagma.

The mafic rocks of the Viholanniemi area are the products of volcanism within plate. Evidenceincludes: (1) chemical variations share a few features of arc-tholeiite but display a clear trending ofalkalic; (2) high contents of TiO2 of mafic volcanics differ clearly from those of island arc as well asoutside the RLZ and are similar to ridge tholeiite; (3) multi-element distribution patterns includingREE patterns exhibit characteristics both of volcanism related to subduction and within plate basalts;(4) discrimination diagrams using immobile elements indicate affinities to within plate setting andMORB. The inference has been deduced that an incipient arc-rifting system was presented in theViholanniemi area.

Viholanniemi Zn-Au deposit shows distinctive features that are not typical of VHMS deposits inmany respects. These features include: (1) ore host rocks are mainly vein like quartz-carbonate-tremolite rocks and ore is disseminated, or is as open fillings. Sulphur contents in the ore are very lowand no sulphate mineral has been found; (2) ore sulphide �34S values are mainly positive and vary in arelatively wide range: �34Ssp 0.2 -10.4�, �34Spy -0.5 -10.2�. Sulphur came from mainly a magmaticsource mixed with a sea water source; (3) Calcite analysed has �18O values of 7.6-20 per mill and�

13C values of -3.6 � -8.1 per mill showing a clear affinity of mantle-derived carbon and possiblymixed carbon coming from marine sediments and organic materials, and also considerableinvolvement of meteoric water and metamorphic water; (4) ore bearing fluids have relatively lowsalinities of 0.7-9.2wt% NaCl and different Th temperatures ranging from 170�C to 335�C (notcorrected for pressure); (5) ores experienced intense deformation and superimposition ofmetamorphism, and part of the metals were remobilized; (6) geochemical patterns of the deposit donot show intense anomalies and the typical Na2O depletion of the massive sulphides proper. Thedeposit is considered as a veinlet-disseminated type that experienced intense metamorphicsuperimposition.

The mineralization involves possibly convective cells developed immediately after the felsiceruptions in the early stage of the arc-rift environment, driven by ascending mafic magma, and thensuperimposed by metamorphism. A tentative geological model of the Viholanniemi Zn-Au deposit hasbeen established.

I

30

Keywords: Palaeoproterozoic, metavolcanic-sedimentary formation, pyroclastics, within-plate,MORB, island arc, subduction, incipient arc-rifting, Viholanniemi Zn-Au deposit, veinlet, carbonisotopes, oxygen isotopes, sulphur isotopes, carbon sources, sulphur sources, superimposition ofmetamorphism, geological model, Finland.

Introduction

The Main Sulphide Ore Belt (Kahma 1973) or the Raahe-Ladoga Ore Zone (see Ekdahl1993), which runs diagonally across central Finland from Lake Ladoga to the northerncoast of the Gulf of Bothnia, is a typical belt occurring at ancient convergent plateboundaries. Within the belt occur many sulphide deposits such as Outokumpu Cu-Co-Zn-Ni deposits, Vihanti and Pyhäsalmi as well as Virtasalmi stratabound Zn-Cu (-Pb)deposits, Hitura and Kotalahti Ni-Cu deposits and small occurrences including porphyrytype Cu�Mo�Au occurrences, stratiform U-P occurrences and epigenetic Au-Asoccurrences etc. (Simonen 1980, Ekdahl 1993).

The Viholanniemi Zn-Au deposit is a small deposit in the belt hosted by felsic-intermediate pyroclastic rocks and was interpreted as the possible representation of dykesystems under a massive ore (Makkonen 1991). Due to its unique features, theViholanniemi deposit can be distinguished in many respects from sulphide Zn-Cu-Pbdeposits within the Pyhäsalmi volcanic arc (Ekdahl 1993), although it is a small one. It isreally worthy of further study due to varied and interesting metallogeny in the MainSulphide Ore Belt between the two main geotectonic units of the Finnish Precambrian.

This study represents the results of field and laboratory works carried out by the writerin Finland and later in China during 1997 and 1998-1999 respectively, in the course ofexecuting the agreement of co-operation in a scientific exchange program betweenFinland and China.

Location and physiography of the study area

The Viholanniemi Zn-Au deposit is located in Joroinen village and covers a total area ofabout 70 km2. The area is a flat terrain consisting mainly of till with heavy forestcovering and boulders on the surface. There are many drumlins and lakes with northwestorientation due to the influence of glaciation and these in turn result in a slightly variabletopography with general level of 85-100 m and the highest 130.9 m above the sea levelwithin the area. The outcrops, therefore, are not abundant, but it is easy to find them inplaces such as drumlin tops and lake banks.

I

31

Fig. 1. Location of the study area on the geological map of Finland (simplified after the bedrockmap of Finland 1:1 000 000, Korsman et al. 1997).

Background to the research

According to the report of the Viholanniemi Zn deposit (studied in 1984-1988, Makkonen1991), the Geological Survey of Finland (GTK) carried out exploration that led to thediscovery of the Viholanniemi Zn-Au deposit.

The first three ore bearing boulders were found on the west bank of Lake Kolkonjärviabout 20 km southeast of the Viholanniemi deposit in 1971 with significant contents ofZn (1.65-2.25%), Au (3.2 ppm), Cu (0.42-1.08%), Ag (133 ppm). In autumn 1984, four

I

32

more boulders of the same rock type (Zn: 4.15-24.16%, Au:0.21-1.50 ppm, Cu:0.03-0.51%, Ag:10-63 ppm, Pb:0.05-1.65%) were discovered at Pirttiselkä, about 7 kmnorthwest of the first boulders.

After this initial period of boulder tracing, a multimethod program including bouldertracing, mapping, geophysical and geochemical exploration, pitting and deep drilling andalso research work had been executed by GTK from 1985 to 1988. Dr. E. Ekdahl and Dr.H. Makkonen were responsible for the overall supervision of the program and fieldwork,respectively.

It was in spring 1985 that a galena-sphalerite boulder (Zn: 1.66%, Au:0.93 ppm,Cu:0.10%, Pb:1.66%, Ag:130 ppm) was found at Viholanniemi after discovering asphalerite and galena-bearing quartz-carbonate rock (Zn:1.04%, Au:7.30 ppm, Cu:0.06%,Pb:0.43%, Ag:12 ppm) in an outcrop at the north-western end of Vuotsinsuo mire. Thus,the boulder fan starting from the Viholanniemi deposit is about 20 km in length. Theresult of bedrock mapping carried out in 1985-1986 confirmed that the bedrock in theViholanniemi area is mainly composed of volcanics, although they have been marked asmica schists on the 1:100 000 bedrock geology map (Korsman 1973). The majority of thevolcanics is felsic-intermediate pyroclastics and associated with mafic volcanics(Makkonen 1991). A geophysical survey (1985-1988) made it possible to distinguishmica schists from volcanics (magnetic, EM, gravimetric). The ore can be distinguished insome way by IP-surveying. Based on information of outcrops, boulders and geophysics,totalling 886 geochemical samples of till and weathered bedrock were collected in an areaof about 6 km2. All elements detected (Zn, Au, Cu, Pb, Ag, Co, Ni) show clear andcoherent anomalies and reflect the deposit well.

In addition to the all information shown above, four pits were dug and 22 drill holestotalling 3759.00 m were drilled in 1986-1987; the Viholanniemi Zn-Au depositcomposed of a southern part (600 m�100 m�1.1 m) and a northern part (100 m�100 m�2m) was then discovered. The quartz-carbonate rock is the major host rock and othermineral assemblages such as quartz, quartz-carbonate-tremolite, tremolite-carbonate,quartz-tremolite-chlorite and quartz-sericite rocks are the minor host rocks. The amountof ore was estimated to be about 250 000 tonnes.

Methods and objectives of the study

The objective of this study is to compare and describe the metallogenic environment andthe type of the Viholanniemi Zn-Au deposit. The study area is one part of the Raahe-Ladoga ore zone which is the most important ore zone in Finland running near theArchaean margin in the south-eastern part. In some respects, the Viholanniemi deposit isdifferent from the stratabound Zn-Cu-Pb sulphide deposits within the belt, and theKuroko deposits as well, and demonstrates some unique features.

One specific aim of the present study is also try to make a contribution to establishingthe metallogenic diversity in this main ore belt in central Finland. A comparison betweenthe main sulphide deposits of RLZ in Finland and a selected belt in China will also bemade.

I

33

The methods involved in this study include mainly bedrock mapping, lithogeochmistryand deposit geochemistry. All thin sections (47) examined were prepared at the GTK inKuopio and Espoo. Samples (98) were collected by the author from metavolcanics,metasedimentary rocks, ore and host rocks in the study area for geochemical analyses. Allof those samples were also analyzed at the GTK in Kuopio and Espoo.

X-ray fluorescence spectrometry (XRF: SiO2, Al2O3, TiO2, Fe2O3, MgO, MnO, CaO,Na2O, K2O,P2O5, Rb, Ba, Sr, Pb, Th, Zr, Ga, Sc, La, Ce, Nb, Y, V, Cr, Cu, Zn, S, seeAppendix 1) and inductively coupled plasma mass spectrometry (ICP-MS: REE, Nb,Rb,Sc, Ta, Th, U, Y, Zr, see Appendix 2) as well as inductively coupled plasma atomicemission spectrometry (ICP-AES), graphite-furnace atomic absorption spectrophotometry(GAAS) and infrared spectroscopy (IR) (see Appendix 3) analyses were performed at theGTK in Espoo and Kuopio. The sulphur isotope analyse was made at the Technical HighSchool in Espoo. Carbon and oxygen isotopes and fluid inclusions were analyzed at theChinese Academy of Geosciences and the Institute of Geology, at the Chinese Academyof Sciences in Beijing, respectively. The electron microprobe analysis was performed atthe University of Oulu.

In addition, there is much material from the GTK and the Exploration Department ofOutokumpu Mining Company, which includes thin sections and unpublished data. All ofthem are employed in the present study.

The regional geological setting

As all rocks in the study area are metamorphic the prefix meta has been dropped.According to studies and descriptions of Finnish geologists (Simonen 1980, Korsman

et al. 1984, Vaasjoki & Sakko 1988, Kilpeläinen 1988, Korsman et al. 1988, Luukkonen& Lukkarinen 1986, Ekdahl 1993, Lahtinen 1994, Makkonen 1996, Nurmi & Sorjonen-Ward 1996, Weihed & Mäki 1997), the Precambrian in southern and central Finland ismainly composed of Archaean basement and the Palaeoproterozoic Svecofenniansupergroup. The latter comprise ca. 1.9 Ga old orogenic terrains in southern and westernFinland including volcanic-sedimentary belts and migmatitic gneiss belts. TheViholanniemi area belongs to this supergroup and lies within the south-eastern part of theRLZ which has already been regarded as a representation of Palaeoproterozoic collisionalsuture (Koistinen 1981, Korsman et al. 1988, also see Ekdahl 1993). The collision ofProterozoic oceanic and Archaean continental plates is responsible for the generation ofnew Svecofennian crust between 1930Ma and 1850 Ma ago (Vaasjoki & Sakko 1988) andthe Kolkonjärvi shear zone (Kosman et al. 1984, 1988) that passes through the easternpart of the Viholanniemi district.

According to Ekdahl (1993) and Nurmi and Sorjonen-Ward (1996), continuedvolcanism within Svecofennian oceanic island arc at 1920-1890 Ma resulted in theformation of Kuroko-type deposits; the synorogenic basic and ultrabasic intrusions atabout 1890-1880 Ma led to syngenetic Ni-Cu deposits; and the late phase calc-alkalineintrusions host porphyry type occurrences and epigenetic Au-As deposits.

I

34

There are several deposits surrounding the Viholanniemi area such as the Virtasalmistratabound Zn-Cu-Pb deposit (about 15 km west) (Ekdahl 1993), the Pirilä Au-bearingquartz vein (about 18 km southeast, Makkonen & Ekdahl 1988), Osikonmäki Au depositoccurring in a shear zone (about 24 km southeast, Kontoniemi & Ekdahl 1990), and somesmaller mineral occurrences.

Geology of the Viholanniemi area

Lithology

Mica schists and mica gneisses are the major rocks in the eastern-south-eastern parts ofViholanniemi (Fig. 2). The primary sedimentary characteristics of turbidites include grad-ing, graded bedding, and cross bedding. Some thin but discontinuous intercalations ofpyroclastics and carbonate occur within the turbiditic sequences, and graphite-bearingpelitic intercalations can also be observed.

Fig. 2. Principal geological features of the study area (based on the mapping and the data fromPapunen 1990, Makkonen 1991).

Within the study area, the mineral composition of the pelitic component shows sometrends of decreasing in the amount of muscovite to east and south, although biotite ispresent together with muscovite. To the south-eastern outside of Fig. 2, in the Pirilä dis-trict, sillimanite, garnet and K-feldspar are common. Pegmatites with coarse grain beryl

I

35

and quartz veins also can be met. According to Korsman et al. (1984, 1988), there areprogressive metamorphic zones towards the south: andalusite - muscovite, K-feldspar-sil-limanite, cordierite-K-feldspar, garnet-cordierite-sillimanite-biotite and garnet-cordierite-sillimanite (Fig. 3). As a result of this progressive metamorphism, mica gneisses or gran-ites are present in south-eastern and south-western-southern parts of the area.

Fig. 3. Location of the study area on the tectonometamorphic map of southern Savo (Korsmanet al. 1988).

In addition, a narrow iron formation has been observed in Pirilä, which includessilicate, oxide, and sulphide facies (Makkonen & Ekdahl 1988).

Volcanics are the predominant rocks in the study area and most of them are felsic-intermediate and mafic. The felsic and also sometimes the intermediate volcanics togethershow a pale weathering surface. In most circumstances, they are changed into anothergradually or appear in the form of intercalations instead of clear boundaries betweenthem.

I

36

Lapilli and agglomerate structures are common in the study area (Fig. 4, 5a). In manyplaces the primary structure is nevertheless destroyed by the strong S2 schistosity so thatthe stretched ejectae can be as much as 50 cm long and the intermediate ejectae have alsobeen stretched to be longer than the felsic ejectae (Makkonen 1991).

Fig. 4. a) Intermediate volcanic rock with lapilli structure containing disseminated pyrite,R305/46.10, single nicol. b) Felsic porphyrite volcanic rock with plagioclase phenocrysts, HVM-86-M3.4, single nicol (Makkonen 1991).

Fig. 5. a) Felsic agglomerate with stretched ejectae from the Suurisaareke. b) Basaltic pillowlava with recognizable fumaroles and deformed pillow from the Lahnalahti.

Quartz and biotite are generally the major minerals in felsic rocks but in intermediaterocks plagioclase and amphibole are additional major minerals. The minor minerals aresericite, chlorite, K-feldspar, epidote, actinolite, carbonate, and sometimes amphibole andgarnet. Accessory minerals include opaques, apatite, zircon, sphene. In felsic porphyriticvolcanics, phenocrysts are plagioclase (An10 and quartz, and quartz or plagioclase alone(Fig. 4). The phenocrysts are usually >2 mm in size. The groundmass is mainly composedof quartz and biotite or quartz alone. The minor minerals are plagioclase, K-feldspar,chlorite, sericite, carbonate, epidote, amphibole with accessory minerals such as zircon,apatite, rutile and sphene. In intermediate intercalations the porphyritic or porphyritic-liketextures are also present. The phenocrysts are plagioclase and quartz as well as amphibole

a b

a b

I

37

(biotite and garnet mainly as the porphyroblasts), and the groundmass containsplagioclase, quartz, biotite, sericite, chlorite, and carbonate with accessories of apatite,opaques and occasionally cordierite.

Mafic volcanics usually occur as intercalations but in the southern part of the arearelative thick mafic layers can be encountered. They seem to connect mainly with felsicvolcanics. Basaltic pillow lava has been observed in Lahnalahti (Fig. 5b). Occasionally,the pillow structure can also be found in amphibolites, but the pillows are elongated andsometimes become obscure due to the intense deformation. Hornblende, biotite,plagioclase, as well as diopside and quartz are the main minerals. Chlorite, epidote,carbonate, hypersthene are the minor composition and opaques, zircon, apatite andsphene are the accessories. Most of these rocks are homogenous in texture but there aresome porphyritic-like and porphyroblastic types with phenocrysts of diopside andporphyroblasts of hornblende and biotite as well. An amygdaloidal structure appearsoccasionally and is filled by carbonate.

Agglomeratic, breccia and tuff textures as well as the relict structure of sedimentarysuch as bedded structure are general in volcanic rocks. Thus the majority of volcanicrocks of the area are volcaniclastic rocks.

Sericitization, epidotization, chloritization and disseminated pyrite are also verycommon in the volcanics (Fig. 6). Particularly, the sericitization and disseminated pyritemainly occur in felsic-intermediate and epidotization and chloritization in intermediate-mafic volcanics. Potassium feldspathization was observed in the western-south-westernparts of the area.

The majority of rocks in the study area therefore can be named as follows according tothe observations:

� pelitic siltstone � turbidite

Sedimentary rocks � tuffaceous siltstone�� intermediate-felsic crystal-lithic tuff � siliceous rock

� stratified tuff (basic-intermediate-felsic)Volcaniclastic rocks� breccia tuff (basic-intermediate-felsic)

� agglomerate (intermediate-felsic)

� basaltic lavaVolcanic rocks �

� dacitic-(ryodacitic) lava (?)

Mica gneisses and migmatite together with quartz veins and pegmatitic veins werefound to be associated with the diopside-bearing amphibolites in the south-western part ofthe area. Amphibolite is possibly metamorphosed from the volcanogenic rocks(Makkonen 1996). The diopside-bearing amphibolites show features of granulite by theirhomeoblast structure and minerals.

I

38

Fig. 6. a) Sericitized volcanic rock with disseminated pyrite, R301/33.75, crossed nicol. b)Epidotised intermediate volcanic rock, HVM-86-M3.1, crossed nicol (Makkonen 1991).

Granite intrusions are present in the western part of Viholanniemi (Papunen 1990).Granodiorites intruded on the mica schist and granite gneisses in the south-eastern andsouth-western parts.

Diabase, possibly comagmatic, with mafic volcanies intruded on the intermediate-felsic volcanics in the southern part of the area.

Stratigraphical relationships

According to Luukkonen and Lukkarinen (1986), the rocks of the area belong to thelower Bothnia subgroup which consists of mica schist and mica gneisses, mafic and acidvolcanics and their weathering products, and also arkosites, limestones and skarns.

Many stratigraphical interpretations for the surrounding areas of Viholanniemiconsidered the mica schist and mica gneisses (with emphasising on pelitic lithologies) asthe lower-most rocks (see Luukkonen & Lukkarinen 1986, Makkonen & Ekdahl 1988,Makkonen 1996). Hyvärinen (1969; see Makkonen 1996) delimited the stratigraphicalsequence in the Virtasalmi district as follows: mica gneisses with graphitic schistintercalations in the bottom, overlain sucessively by diopside-and quartz-feldspargneisses including calc-silicate intervals, amphibolites, principally diopside amphibolites,and finally by more mica gneisses (top). Makkonen (1988, 1996) proposed two similarstratigraphical sequences which include mica schist (bottom), iron formation, felsicvolcanics, intermediate volcanics, mafic volcanics and komatiite (top) in Pirilä and micagneisses and mica schists (bottom), marbles and cherts and iron formations, felsicvolcanics (quartz-feldspar gnesses), mafic volcanics (diopside amphibolites) ultramaficvolcanics (top) in Juva.

The author proposes a tentative stratigraphical sequence in the Viholanniemi areabased on mapping and observations as well as above sequences as following:

a b

I

39

mica schist and gneisses� basic tuff� basaltic lava

basic volcanics � basic tuff (with weak sulphide mineralization)� basic breccia tuff

� siliceous rock (with minor tuffaceous siltstone) �n-Au� occurrence� felsic-intermediate breccia tuff +tuff �

felsic volcanics � felsic-intermediate agglomerate� felsic-intermediate breccia tuff� intermediate-felsic stratified tuff

� intermediate-felsic crystal-lithic tuffmica schist � tuffaceous siltstonemetaturbidite � turbidite

� pelitic siltstone

It is worth mentioning here about the observations made by Makkonen (1991) andMakkonen and the present author that include:1. There are some thin pyroclastic intercalations in the mica schist area, which are

mainly intermediate-felsic. The tuffaceous material can be observed in fine clasticrocks.

2. Volcanics in the area overlay directly the so-called mica schist and begin with mainintermediate stratified tuff. The aeromagnetic map of the area also shows a clearanomalous magnetic belt but not very high in intensity corresponding to thoseintermediate (including thin mafic intercalations) volcanic rocks that contact with themica schist (Fig. 7).

3. The majority of volcanics is mainly felsic and mafic with minor intermediate felsic.The felsic volcanics are mainly pyroclastic rocks, and the mafic are mainly composedof basaltic lava with pillow structure and pyroclastic rocks.

4. Mica gneisses (and migmatite) with diopside amphibolite intercalations wereobserved to be contacted with the mafic volcanics in the southwestern part of thestudy area.

5. Basaltic lava with pillow structure and mafic pyroclastic rocks suggest a relativelyshallow eruptive environment (Condie 1986).

I

40

Fig. 7. Aeromagnetic map of the study area (Geological Survey of Finland, compiled by JLerssi).

Isotopic age determinations in samples from the areas surrounding Viholanniemi haveprovided some reasonable U-Pb ages which are very helpful to understand thestratigraphical relationships of the area. The 207Pb/206Pb ages of the zircons from themetasediments in the mica schist area of the Vuotsinsuo range from 2200 to 2300 Ma andone felsic metavolcanic rock from Viholanniemi has a zircon age of 1906�4 Ma (Vaasjoki& Sakko 1988). To the south-eastern part, Tuusmäki tonalite which intrudes the maficvolcanics (Makkonen & Ekdahl 1988) has the U-Pb zircon age of 1888�15 Ma (Korsmanet al. 1984).

The volcanic cycle, rock assemblage and paleovolcanic center

The above mentioned geological features of the study area suggest that the volcanic cycleof the area began with minor intermediate and major felsic eruptions and terminated withmafic eruptions. The volcanic cycle can be described as:

mafic �intermediate alternatingfelsic

felsic �felsic alternatingintermediate

I

41

The volcanic rocks in the area can be sorted into two facies of explosion and overflow inwhich the explosion facies includes mainly volcanic agglomerate, breccia tuff and tuffand the overflow facies are composed of basaltic lava. According to outcrop and thinsection investigations, the volcanic rock assemblage is of basalt, andesite, dacite and(rhyolite).

From the occurrences of volcanic agglomerate and pillow lava in the area, it can besaid that there is a paleovolcanic center in the Viholanniemi area. Obviously, the site ofthe center is not easy to recognize now due to the complex and strong tectonism.

Metamorphism, deformation and structural features

According to Korsman et al. (1984) and Korsman et al. (1988), the Viholanniemi area isan area in which the metamorphism is characteristic by the transition of metamorphosedblocks in the north to progressive metamorphosed belts in the southern (Fig. 3). Themetamorphism in the northern part of the area is characterized by intenselymetamorphosed and migmatized areas often separated from the environment by faults.Accompanied with the granulite facies metamorphism in the so-called complex areas, theprogressive stage of metamorphism was associated with the D1 and D2 deformations (seeKorsman et al. 1988). From the Viholanniemi area to the Sulkava area, well-developedzones caused by progressive metamorphism have been established by Korsman et al.(1984); the metamorphic grade is increasing towards the Sulkava thermal dome. Theevolution of the zonal metamorphism took place mainly during the D2 deformation (1880Ma ago) and was affected and culminated during D3 deformation at 1830-1810 Ma ago.The D3 deformation is cut by the ca.1800 Ma post-tectonic granites (Vaasjoki & Sakko1988) and the later in turn were partly folded by the D4 deformation (Kilpeläinen 1988).

The D3 deformation has manifested itself as asymmetric folds of varying size andshear zones that locally disrupt metamorphic zoning. The primary axial planes of thefolds trend northwest-southeast and the axis plunges southeast at 45o. F1 folds occurringonly in the andalusite-muscovite zone are tight and usually of 10-20 m in amplitude witha few degrees of S1 schistosity on their limbs. F2 folds are also tight and their wave lengthis a few hundred metres and S2 schistosity is penetrative throughout the K-feldspar-sillimanite zone (Kilpeläinen 1988, Makkonen 1996).

Lithogeochemistry

Whole rock geochemistry

The chemical compositions of volcanic rocks in the Viholanniemi area are listed in Table1. The data of intermediate and acid rocks are mean values, c.f. details in Appendix 1.

Acid rocks are those of SiO2 > 63%. The values of Na2O, K2O as well as Na2O+K2Oare the highest in three groups. Average An values calculated from CIPW norms are 3-34.Intermediate rocks have SiO2 of 52-63% and the highest average values of Al2O3, P2O5and TiO2 in the groups. Na2O+K2O=3.69-5.39 and average An values are 19-32.

I

42

Basic rocks are those of SiO2 < 52%. Considering the effects of alteration, samplehvm-86-24.5a, xz-97-4.2 as well as xz-97-4.1 should be excluded here. The contents ofFe2O3

*, CaO and TiO2 are very high, while K2O is very low; Na2O+K2O=2.15-5.02. Allsamples contain normative di, mt, il, ap and some samples have normative ne, hy and ol.Q valnus are almost zero, except one is 9.1, and the average An values vary from 36 to100. These suggest that the basic rocks of the area show some distinctions such as Ca, Fe,Ti-rich and alkalic trend.

The variation diagrams (Fig. 8) show that, Fe2O3*, MgO, CaO and MnO decrease

coherently with the increasing of SiO2. Na2O and K2O display scattered charactersinstead of clear positive correlation relationships with SiO2. The inflections however, canbe observed in Al2O3, TiO2 and P2O5 variations correlated with SiO2. TiO2 is similar tothe case of tholeiitic basalts by increasing and reaching maxima between 50% and 57%SiO2 (Gill 1981). They may also imply here that volcanics of the area are not fractionatesfrom the same parent magma otherwise a clear negative correlation relationships withSiO2 should be present (see Liu et al. 1984). Variations of Na2O and K2O might partly beaffected by the weak alterations such as sericitization, chloritization as well as potassiumfeld spathization presented in the volcanics, on the other hand, they may also confirmwhat has been indicated by TiO2 and P2O5 as a lack of clear positive correlationrelationships with SiO2 (also see Liu et al. 1984).

The trace elements Rb, Ba, Zr, Nb and Y have their highest values in acid rocks, whileelements Sr, V, Cr and Ni are mainly concentrated in basic rocks. K-group elements (K,Rb, Ba, Sr, Gill 1981) in the basic rocks correlate positively with each other except for Srwhich in contrast has a negative correlation with others. The basic rocks also have lowRb/Sr and high Ba/Rb ratios respectively.

Concentrations of REE of volcanic rocks and their chondrite normalized distributionpatterns (Table 2, Fig. 9) show varied total REE contents (61.5-201.6 ppm) and �Ce/�Yratios (3.72-16.19) with a small negative Eu anomaly. Acid rocks have relatively high�REE and �Ce/�Y with an apparent Eu negative anomaly showing slightly strongfractionated patterns. In these respects, they represent those rocks of modern arc volcanics(Jakes & Gill 1970, Jakes & White 1971, Garcia 1978, Cullers & Graf 1984, Condie1986). In contrast, mafic rocks have flat and weak fractionated patterns.

I

43

Table 1. Representative analyses and average chemical compositions of the volcanic rocksof the Viholanniemi area.

1hvm-86-

24.2

2hvm-86-

24.3

3hvm-86-

24.4

4 hvm-86-

24.5a

5xz-97-

4.1

6xz-97-

4.2

7xz-97-

8.1

8xz-97-20.1

9xz-97-22.1

10 11

wt%SiO2 47.3 54.7 49.8 43.4 46.4 37.7 49.3 48.3 45.1 57.75 70.18TiO2 1.5 1.82 1.65 1.02 1.74 1.18 1.74 1.19 1.38 1.52 0.63Al2O3 16.3 16.1 12.9 9.46 14.1 9.16 14.9 13.9 14.9 15.50 13.65Fe2O3 9.6 11.4 12.9 16 7.86 12.3 12.8 12 12.3 9.45 4.30MnO 0.399 0.29 0.223 1.04 0.137 0.194 0.168 0.225 0.162 0.19 0.12MgO 7.75 4.81 6.47 5.71 3.74 9.47 4.71 5.8 7.73 4.46 1.82CaO 11.1 6.77 10.5 18.1 13.2 17.5 9.34 12.3 12.8 5.33 2.72Na2O 2.74 3.08 3 0.16 5.1 1.69 4.29 3.32 2.08 4.02 4.34K2O 0.813 0.508 0.292 0.019 0.125 0.085 0.726 0.396 0.071 0.73 1.24P2O5 0.23 0.244 0.29 0.253 0.184 0.244 0.342 0.117 0.173 0.40 0.15total 97.76 99.75 98.06 95.38 92.62 89.66 98.37 97.59 96.78

ppmRb 22 8 7 1 3 2 10 8 5 21.90 37.35Ba 66 105 150 34 98 21 189 161 26 116 246Sr 325 306 305 446 319 179 423 154 689 191 116Pb 37 78 <30 <30 <30 <30 <30 <30 <30 <30 <30Zr 146 166 241 145 113 100 172 74 80 278 370La 18 24 32 23 6 10 11 10 13 29.10 41.77Ce 44 49 74 45 37 48 68 33 46 76.60 99.08Nb 16 17 21 14 17 9 20 5 15 24.70 30.65Y 19 24 28 20 20 23 26 23 18 29.50 34.81V 251 365 300 204 264 267 345 363 305 226 56.46

Cr 74 22 22 17 85 1216 64 88 557 27.60 15.92Ni 38 23 53 34 99 569 33 82 321 38.20 7.62Cu 45 35 18 2024 86 67 222 77 180 114 61.19Zn 545 473 194 290 50 115 115 130 97 93.40 68.96S 50 30 40 590 310 370 180 90 1370 105 856 Na2O+K2O 3.55 3.59 3.29 0.18 5.23 1.78 5.02 3.72 2.15 4.75 5.58Na2O/K2O 3.37 6.06 10.27 8.42 40.80 19.88 5.91 8.38 29.30 8.34 6.18K/Rb 306.77 527.13 346.28 157.72 345.89 352.81 602.67 410.91 117.88 279.25 308.95Rb/Sr 0.068 0.026 0.023 0.002 0.009 0.011 0.024 0.052 0.007 0.125 0.408Ba/Rb 3.00 13.13 21.43 34.00 32.67 10.50 18.90 20.13 5.20 5.44 7.77Q 0 9.13 0 0 0 0 0 0 0or 4.97 3.04 1.78 0.12 0.81 0 4.42 2.43 0.44ab 22.68 26.39 26.19 1.44 23.47 0 33.92 24.78 18.4an 30.74 28.99 21.55 26.7 16.56 19.4 19.82 22.65 32.55ne 0.67 0 0 0 12.72 8.75 1.85 2.34 0di 20.03 2.94 25.05 56.52 37 39.06 21.43 32.95 26.94hy 0 22.96 17.86 8.8 0 0 0 0 0.97ol 15.3 0 0.79 0 0 17.12 11.52 9.55 14.67mt 2.15 2.51 2.89 3.71 1.86 3.02 2.86 2.7 2.8il 2.94 3.5 3.23 2.06 3.59 2.53 3.4 2.34 2.74hm 0 0 0 0 0 0 0 0 0ap 0.56 0.59 0.71 0.64 0.47 0.65 0.83 0.29 0.43

Total iron as Fe2O3. 1-9 are mafic rocks, 10=mean value of intermediate rocks (10 samples), 11=mean value of acid rocks (26 samples), Sampling sites see App. 4.

I

44

Fig. 8. Harker diagrams showing compositional ranges of selected major elements in volcanicrocks from the study area.

I

45

Table 2. Representative analyses of trace elements (ppm) of volcanic rocks of theViholanniemi area.

1hvm-85-

11.1

2r312/

183.15

3r321/132.0

4r359/234.0

5hvm-85-

11.2

6xz-97-

5.3

7r312/142.3

8xz-97-

4.1

9xz-97-

4.2

10xz-97-8.1

La 30.9 41 40.3 21.3 16.7 63.5 29 8.07 10.1 17Ce 63.5 83.1 77.5 41.8 35.7 134 59.9 20.4 24.2 40.4Pr 7.16 9.47 8.56 4.8 4.37 16.4 7.13 2.89 3.51 5.52Nd 25.7 35.7 30 17.4 16.9 61.5 27.3 12.9 15.7 22.2Sm 4.94 6.88 4.93 3.13 3.98 10.7 5.5 3.21 3.98 5.02Eu 1.21 1.77 1.37 0.59 1.32 2.76 1.69 1.01 1.19 1.59Gd 4.64 6.93 4.01 2.72 4.27 7.79 5.17 3.65 4.59 4.79Tb 0.71 1.09 0.54 0.38 0.65 0.98 0.82 0.57 0.66 0.73Dy 3.86 6.26 2.42 2 3.87 3.89 4.41 3.56 3.9 4.55Ho 0.75 1.24 0.43 0.38 0.78 0.68 0.88 0.71 0.78 0.86Er 2.34 3.64 1.23 1.03 2.25 1.74 2.56 2.04 2.14 2.38Tm 0.35 0.55 0.18 0.17 0.33 0.22 0.38 0.3 0.28 0.35Yb 2.44 3.44 1.09 1.04 2.03 1.47 2.41 1.9 1.86 2.26Lu 0.38 0.53 0.15 0.16 0.31 0.22 0.35 0.29 0.24 0.3�REE 148.88 201.6 172.71 96.9 93.46 305.85 147.5 61.5 73.13 107.95�Ce 133.41 177.92 162.66 89.02 78.97 288.86 130.52 48.48 58.68 91.73�Y 15.47 23.68 10.05 7.88 14.49 16.99 16.98 13.02 14.45 16.22�Ce/�Y 8.62 7.51 16.19 11.30 5.45 17.00 7.69 3.72 4.06 5.66dEu 0.76 0.78 0.92 0.61 0.98 0.89 0.96 0.90 0.85 0.98La/Yb 12.66 11.92 36.97 20.48 8.23 43.20 12.03 4.25 5.43 7.52Y 23.4 39.6 14.1 11.9 23 20.9 27.3 21.1 22.1 24.3Th 6.51 5.29 5.4 6.13 1.93 6.17 2.52 0.76 1.01 1.4U 2.14 2.14 2.52 1.84 0.74 3.63 0.89 0.3 0.37 0.59Zr 261 353 198 115 161 173 194 76.6 78.2 120Nb 20.8 25.2 18.1 4.75 13.3 14 16.7 13.9 6.97 15.5Ta 1.58 1.65 1.12 0.4 0.89 0.65 1.04 0.9 0.44 0.96Rb 44.1 21.3 51.4 73.9 30.3 86.9 30.7 2.13 0.49 9.2Sc 8.6 11.8 8.57 5.42 25.7 15 21.7 30.2 25.4 32.5La/Th 4.75 7.75 7.46 3.47 8.65 10.29 11.51 10.62 10.00 12.14La/Nb 1.49 1.63 2.23 4.48 1.26 4.54 1.74 0.58 1.45 1.101-4: felsic, 5-7: intermediate, 8-10: mafic. Sampling sites see App. 4.

I

46

Fig. 9. Chondrite-normalized rare-earth element patterns of selected volcanic rocks from thestudy area. a) felsic rocks; b) intermediate rocks; c) mafic rocks.

Classification of volcanic rocks

Considering the cases of low grade metamorphism and non visible strong alteration in thesalmpes studied, it should be feasible to classify volcanic rocks by means of geochemicalschemes. This in turn will show some relationships between elements which haveresulted from the varied geochemical processes.

I

47

Fig. 10. Geochemical characteristics of Viholanniemi volcanics on (a) TAS diagram (Le Maitreet al. 1989) showing subalkaline (tholeiitic) series and (b) the Jensen cation plot (Jensen 1976).

Volcanic rocks of the area are mainly of the subalkaline (or tholeiitic) series in the TASdiagram (Fig. 10a). According to Rollinson (1993), the Jensen plot has a distinctadvantage over other classification schemes for volcanic rocks especially for those thatexperienced metamorphism. Thus the volcanic rocks of the area are mainly basalt,andesite and dacite of calc-alkaline series and high-Fe tholeiite basalt (Fig. 10b).

On the AFM diagram, the volcanic rocks display a calc-alkaline trend in most of thefelsic and intermediate volcanic rocks, while mafic volcanic rocks show a tholeiiticaffinity (Fig. 11a). On the K2O vs. SiO2 diagram, the rocks fall in the low-K and medium-K areas (Fig. 11b). The number of the rocks falling in the low-K area are more than thatof medium-K area particularly those that are mafic and intermediate, and thus, they canbe considered to mainly belong to the low-K tholeiite magma series.

I

48

Fig. 11. Geochemical characteristics of Viholanniemi volcanics on (a) AFM diagram afterIrvine & Baragar (1971) and (b) K2O vs silica diagram after Le Maitre et al. (1989). Symbolsas in Fig. 10.

Tectonomagmatic affinities of volcanic rocks

Before considering the use of the chemical composition of volcanic rocks for theirtectonomagmatic affinity discrimination, it is necessary to evaluate the rock alterationfirst, even though the low grade metamorphism in the area has been established. On theMgO/10-CaO/Al2O3-SiO2/100 diagram, which has been suggested by Davies et al.(1978), most of mafic and intermediate rock samples studied fall within the field ofunaltered magmatic rocks (Fig. 12). Three mafic rock samples (xz-97-4.1, xz-97-4.2 andhvm-86-24.5a) and also a few intermediate samples show an alteration trend (also seeTable 1).

I

49

Fig. 12. Field for unaltered magmatic rocks (Davis et al. 1978). Symbols as in Fig. 10.

Compared with the volcanic rocks from the arc system, the mafic and intermediaterocks of the study area (Table 2) have a unique La/Yb ratio (Jakes & Gill 1970), and theyalso show affinities to those of the back arc or MORB by La/Th and La/Nb ratios (Gill1981, Table 5.4). The mafic samples of the area may be considered further by theirslightly LREE enriched patterns and La/Nb ratio as the E-MORB (Saunders 1984, Gill1981).

Considering the MORB-normalized multi-element diagram, some elements such as Sr,K, Rb and Ba might have been enriched during metamorphism (Saunders & Tarney1984); the rest of the elements however belong to those unaffected or immobile (Saunders& Tarney 1984, Brewer & Atkin 1989) which are mainly controlled by the chemistry ofthe source and the crystal/melt processes (Rollinson 1993). The mafic rocks excluding xz-97-4.1,xz-97-4.2 and hvm-86-24.5a showing alteration trend on figure 12 exhibit somenotable features resembling those basalts of within plate (Pearce 1983, Condie 1986) bytheir patterns and lack of Nb depletion which is proper for volcanic arc basalts (Pearce1982) (Fig. 13). In Virtasalmi (about 15 km west), Lawrie (1992) observed basalts withsimilar MORB-normalized multi-element patterns.

I

50

Fig. 13. MORB-normalized trace element patterns for the different metavolcanic rock types: a)felsic rocks; b) intermediate rocks; c) mafic rocks.

The discriminating diagrams are presented with trace elements such as Cr, Ni, Ti, Y,Zr, Ta, Nb which were considered to be immobile during secondary processes (Condie1982, Saunders & Tarney 1984, Brewer & Atkin 1989). On the Cr-Ti diagram (Fig. 14a),

I

51

Fig. 14. Composition of mafic rocks on tectonomagmatic discrimination diagrams. a) Oceanfloor basalts (OFB) and low potassium tholeiites after Pearce (1975). b) Ocean floor basalts(OFB) and island arc tholeiites after Beccaluva et al. (1979). c) Arc volcanics (ARC) and oceanfloor basalts (OFB) after Shervais (1982). d) Mid ocean ridge basalts (MORB),within platebasalts (WPB) and arc lavas (AL) after Pearce (1982). e) Fields for island arc tholeiites (A),ocean floor basalts (B), calc-alkali basalts (B,C) and within plate basalts (D) after Pearce &Cann (1973). f) Fields for within plate basalts (AI), within plate alkaline basalts and within platetholeiites (A), E-MORB (B), within plate tholeiites and volcanic arc basalts (C) and N-MORBand volcanic arc basalts (D) after Meschede (1986). g) Fields for MORB and volcanic arcbasalts (dashed line) and within plate basalts after Pearce (1982), Thol=tholeiitic basalts,Trans=transitional basalts, Alk=alkaline basalts. h) Fields for within plate basalts (A), islandarc basalts (B) and mid-ocean ridge basalts (MORB) after Pearce & Norry (1979).

I

52

the mafic samples are divided into ocean-floor basalts and low potassium tholeiites. Thelatter group includes mainly the mafic pyroclastics indicating that some differences maybe present between them and those of basaltic lava. The same situation is also obtainedon Ni-Ti/Cr diagram (Fig. 14b), but almost all samples are ocean-floor basalts and notisland arc tholeiites. The Ti-V diagram (Fig. 14c) shows that all mafic samples are withinthe field of Ti/V ratios of 20-50 and are those of MORB and back arc basin basalts.Further indication is shown on plots of Zr-Ti (Fig. 14d), Ti-Zr-Y (Fig. 14e), Zr-Nb-Y(Fig. 14f), Nb/Y-Ti/Y (Fig. 14g) and Zr-Zr/Y (Fig. 14h), they not only display the mainaffinities to within-plate basalts with the samples studied, but the Nb/Y-Ti/Y alsosubdivides most samples into the transitional basalts area. The latter three diagramsclearly show that the basalt and basaltic rocks of the study area differ from those of thevolcanic arc and MORB.

Obviously, the varieties of chemical composition are present among the volcanic rocksand particularly those of mafic rocks. These features imply the compositional character ofmagma on the one hand, and the character of tectonic setting on the other. In conclusionsthe affinities to within plate suggested by the majority of the samples of mafic volcanicrocks in the study area seem to be clear and these show further a possible enriched mantlesource.

Viholanniemi Zn-Au deposit

Wall rocks and host rock

The wall rocks are mainly siliceous rock and tuffaceous siltstone that weremetamorphosed to quartz (-feldspar) schist with a recognizable blastobedding structure,and felsic-intermediate volcanics as well with some lapilli, agglomerate and alsoblastobedding structures. The strong sericitization and abundant disseminated pyrite arecharacteristic in the rocks particularly in the felsic ones. Less abundant carbonate andlocal epidotization is also present, and casually disseminated magnetite occurs inintermediate rocks. The wall rocks are sometimes crushed by shearing.

Makkonen (1991) has named the majority of host rock as quartz-carbonate rock. Themost common mineral assemblage is quartz-carbonate-tremolite and the others include:quartz, quartz-carbonate-tremolite-chlorite-biotite, tremolite-carbonate, quartz-tremolite-chlorite, quartz-sericite, quartz-biotite-chlorite and chlorite. Other accessory minerals areopaques, epidote, garnet, titanite and tourmaline. Sometimes graphite is abundant. In thehost rocks, carbonate and amphibole are mostly of about 1 mm in grain size and quartz ismore fine-grained, coarse-grained types are about 5 mm in grain size. The orientation andplastic deformation of quartz can be observed frequently in host rocks. In mostcircumstances the host rocks occur as conformable dykes and sometimes as stockworkveinlet. They vary in thickness from under 1 cm to 5 m.

The microanalyses of carbonate carried out (Makkonen 1991) indicate that thecarbonate is a manganese-bearing calcite. The composition of the center of somecarbonate grains is probably different because it is fractured while other parts of the grainare whole and gold is often present in this part of the grain.

I

53

Ore occurrence and metal contents

Ore occurs in the host rocks as mainly disseminated and veinlet. The ore bodies strikealong the directions from NW to NNW and dip into SW. According to Makkonen (1991),the form of ore bodies is defined by F3 folds and partly in the depth the dip is nearlyhorizontal. In the southern part, the ore body extents up to over 300 m in the depth and itsaverage thickness in the first 100 m is c. 1.1 m (Fig. 15, 16). The length was assumed tobe 600 m. In the northern part, the dimensions of the ore body were assumed to be100�100�2 m (Fig. 17).

Fig. 15. Cross-section of the southern ore body on profile R301-303, 320. The ore (quartz-carbonate rock) is marked with black. Other rocks consist of felsic to mafic volcanics(Makkonen 1991).

The most important elements in the ore are Zn and Au, and then Pb, Cu, Ag and S. Theaverage contents of Zn and Au are 2.31% and 0.7 ppm in the southern part, and 1.97%and 1.11 ppm in the northern part. Zn and Au have their highest concentrations in a onemeter drill core of 12.26% and 10.48 ppm in the southern part and 11.61% and 7.84 ppmin the northern part, respectively. Cu, Pb and Ag are nevertheless low in the oreoccurrence but Pb has its highest content of 11.17% and the highest Ag is in the northernore body. However, with regard to the economic benefits, the very important factor is thatthe sulphur concentration in both the southern and northern ore bodies is low, and thus themetal contents are high in the sulphide fraction (Table 3). Estimated ore amounts of190 080 and 57 600 tonnes in the southern and northern parts, respectively, were obtained(Makkonen 1991).

I

54

Fig. 16. Cross-section of the southern ore body on profile R304-305, R321. Rock types as infigure 15 (Makkonen 1991).

I

55

Fig. 17. Cross-section of the northern ore body on profile R310-312. Rock types as in figure 15(Makkonen 1991).

Table 3. The thickness of ore intersections and their main composition.

Ore mineralogy

Sphalerite is the most important and most common ore mineral. It occurs as adisseminated form and dykes that brecciate the silicate and carbonate material. In mostcircumstances, the grain size of sphalerite in the dykes is coarse and the grain boundariesare not observable. Haematite often replaces sphalerite from the rims of the grains.

Galena appears as small xenomorphic inclusions in sphalerite and dykes but is morerare than sphalerite. Chalcopyrite occurs either as single grains (<0.1 mm) inxenomorphic form, or most often as inclusions in sphalerite. Cubanite is associated withsome chalcopyrite grains and haematite is also presented as the replacement ofchalcopyrite. Pyrite occurs most often as idiomorphic grains (<2 mm) in sphalerite dykes

borehole thickness(m) Zn % Cu % Pb % Ag ppm Au ppm S %301 1.95 3.31 0.36 0.03 22 0.2 3.98302 3.00 0.23 0.04 0.00 3 1.8 2.47303 1.85 3.50 0.23 0.02 15 0.1 4.03304 0.85 1.17 0.05 0.62 16 <0.1 3.09305 1.00 3.09 0.05 0.4 16 <0.1 3.34306 0.70 6.49 0.07 0.12 64 1.2 3.88307 0.90 3.05 0.19 0.01 140 <0.1 2.29308 0.40 0.04 0.71 0.00 14 1.7 2.09321 1.00 1.88 0.01 0.00 2 <0.1 n.d.

mean in southern part 1.29 2.31 0.19 0.10 26 0.7 3.21311 7.35 1.34 0.09 0.95 140 1.29 0.37311 1.20 1.97 0.26 0.02 41 1.55 2.15312 0.90 8.28 0.27 0.05 86 0.60 n.d.316 1.55 1.27 0.06 0.00 2 0.19 n.d.

mean in northern part 2.75 1.97 0.12 0.64 105 1.11 0.62

I

56

and disseminated in the host rocks. It is sometimes slightly altered to marcasite orhydrated pyrrhotite. Pyrrhotite grains are also xenomorphic and appear as inclusions insphalerite. Ilmenite is present as acicular grains (�1 mm long) and usually as mixedgrains consisting of ilmenite and rutile. Gold is present as small (<10µ) grains of electrumwithin silicates and carbonate. Silver can be observed as metallic silver and dyscrasiteinclusions in galena (Ag3Sb) and possibly other compounds (Fig. 18).

Besides the previously mentioned ore minerals, magnetite, mackinawite, covellite,arsenopyrite and tetrahedrite can also casually be found.

Fig. 18. Ore minerals and their occurrences. a) Sphalerite (brown in quartz-carbonate-amphibole rock, R302/79.70, single nicol. b) Chalcopyrite-bearing sphalerite, R312/83.10,single nicol. c) Gold-electrum grains in carbonate, R301/37.25, single nicol. d) Metallic silver instrongly altered volcanic rock, R311/96.75, single nicol. (Makkonen 1991).

Isotope studies

Sulphur

Sulphur isotope measurements have been made on different disseminated sulphideminerals from the Viholanniemi Zn-Au deposit. The results are shown in Table 4 and Fig.19. The sulphides of the deposit have �34S values in a relative wide range from 1.7 to10.4 per mil, with a median value around 5 per mil (average value 5.13 per mil).

a b

c d

I

57

Table 4. Sulphur Isotope Composition of Sulphides from Ore Occurrences in theViholanniemi Area.

Fig. 19. The �34S values for sulphides in Viholanniemi Zn-Au deposit. Comparison data fromRollinson (1993).

Sample Location Rock* Minerals* d34S Notes*py po ga sp ch

R311/99.6 Viholanniemi inter ga+sp+py** 8.7 8.2 8.5 strongly altered (ep+ca), filling ores

R311/101.8 Viholanniemi c-a ga+sp 7.0 8.4 filling ores R312/82.8 Viholanniemi q-a-chl py 10.2 disseminated py ( sp )R312/83.5 Viholanniemi q-a-chl py 6.5 disseminated py ( sp )R319/95.1 Viholanniemi felsic py -0.5 strongly altered ( ser ), dis-

spminated pyR319/96.35 Viholanniemi felsic py -1.7 strongly altered ( ser ), dis-

seminated pyR319/188.1 Viholanniemi inter py 6.0 disseminated py ( ch )R319/196.5 Viholanniemi mafic py+ch 4.6 disseminated py ( ch )R319/203.0 Viholanniemi felsic py 4.7 disseminated pyR306/229.95 Viholanniemi q-c sp 10.4 disseminated sp ( ga )R301/33.75 Viholanniemi q-c-a ga+sp -0.5 disseminated ga+spR303/71.80 Viholanniemi q-c sp** 7.4 disseminated sp ( py+ch )R304/101.00 Viholanniemi q-c sp 0.2 disseminated sp ( ga+ch )HVM-86-24.5b Viholanniemi mafic py+ch 2.2 disseminated py ( ch )ZX-97-6.1 Joroisenniemi po -4.6 disseminated ZX-97-6.2 Joroisenniemi po+py -6.3 disseminatedRock and Mineral abbreviations: inter=intermediate, C=carbonate, a=amphibol, chl=chlorite, q=quartz,ga=galena, sp=sphalerite, py=pyrite, ch=chalcopyrite, ep=epidotization, ca=carbonatization, ser=sericitization. **Mixed sample. Analytic precision: ±0.2� -: the amount of mineral is not enough.

I

58

Similar ranges of �34S are presented in pyrite and sphalerite, between 1.7 and 10.2 permil and 0.2 and 10.4 per mil, respectively. These �34S values of sulphides are similar tothose of the massive sulphide deposits of the Kuroko type (Rye & Ohmoto 1974, Ohmoto& Rye 1979, Hoefs 1980, Rollinson 1993) and of the later Archaen (Ohmoto 1986, Taylor1987). The relatively wide range of �34S and mainly positive values of sulphides isnevertheless distinguished.

The disseminated pyrite from strongly sericitized felsic volcanies have �34S values of1.7 to 0.5 per mil differing from that of sulphides in quartz-carbonate rock or volcanieswith a strong carbonatization and epidotization. The later group of sulphides includingpyrite, sphalerite and galena have �34S values of 0.2 to 10.4 per mil. It shows that thesulphur of pyrite in volcanies with only sericitization is more reduced sulphur comingfrom the rock itself, and sulphur of sulphides in quartz-carbonate rocks may come frommainly a magmatic source mixed with sea water. Two samples of pyrite and pyrrhotitefrom meta-sedimentary rocks in the south-eastern part of the area have �34S values of 6.3and 4.6 per mil showing quite clear sulphur source of rocks themselves.

A narrow variation of �34S in sulphides from the northern part of the deposit aredistinguished from that of the southern part of the deposit. With calculations usingsphalerite-galena pair (Hulston 1980, see Wei et al. 1988), the crystallization temperatureis 473°C.

Carbon and Oxygen

Eight calcite samples from the deposit were analysed for carbon and oxygen isotopes(Table 5 and Fig. 20). Carbon isotope compositions vary in a quite narrow range: the�13C range between -3.6 and -8.1 per mil, but oxygen isotope vary in a wide range: the�18O range between 7.6 and 20.0 per mil. Most of the calcite analysed has �18O values of7-11 per mil and �13C values of -3 -5 per mil.

Table 5. Carbon and oxygen isotope composition of calcite from the Viholanniemi Zn-Auoccurrence.

Sample Rock* �13CPDB(�)

�18OPDB(�)

�18OSMOW(�)

Notes*

R312/82.95-83.35 q-a-chl -8.1 -22.5 7.6 disseminated sp+pyR315/84.25-84.75 q-c -4.0 -21.8 8.4 disseminated pyR316/81.55-82.05 q-c -6.1 -12.8 17.7 disseminated pyR301/37.00-37.50 q-c-a -5.0 -10.8 20.0 disseminated sp+py+chR303/70.90-71.40 q-c -4.2 -22.0 8.2 disseminated sp+py+chR304/100.80-101.30 q-c -4.7 -20.0 10.2 disseminated sp+py+ga+chR302/79.70 q-c-a -4.0 -20.5 9.8 disseminated sp+pyR306/229.85 q-c -3.6 -19.7 10.5 disseminated sp+ga* Rock and mineral abbreviation see table 4. Analytic precision:±0.2�

I

59

Fig. 20. Carbon and oxygen isotope composition of carbonate from the Viholanniemi Zn-Audeposit.

Comparing the northern part to the southern part of the deposit, the �13C values varyfrom -4.2 to -8.1 per mil in the northern part, and in contrast, the �13C values are quitehomogeneous in the southern part varying from -3.6 to -5.0 per mil. In combining the dataof �13C with �18O, the majority of samples fall in the field of carbonatites in Rollinsons(1993) �18O-�13C plot (Fig. 21). Two samples fall within the hydrothermal calcite area,showing mixing between mantle-derived carbon and seawater and within the MississippiValley-type hydrothermal area respectively, as well as one within the ordinary chondritefield. These characteristicss indicate a main deep-seated origin of the carbon and also thepossible mixing with carbonate-derived and organically derived CO2 (Ohomoto & Rye1979, Hoefs 1980, Taylor 1987).

The �18O range between 7.6 and 20.0 per mil in calcite may reflect the effect ofmetamorphic fluids with a wide range of �18O due to different rock types andmetamorphic grade (Hoefs 1980, Wei et al. 1988).

I

60

Fig. 21. �18O vs �13C plot showing the composition of carbonates from a variety ofenvironments after Rollinson (1993). �18O is plotted relative to both the SMOW and PDB scalesand the isotopic composition of a number of different carbon is plotted along the right-handside of the diagram.

Fluid inclusions

Fluid inclusion measurements were carried out on quartz from the quartz-carbonate rockof the deposit and the results are listed in Table 6. The results show that the smallinclusions presented in quartz include liquid inclusion, pure CO2 inclusion, CO2-H2O

I

61

inclusion and gas-liquid inclusion. Inclusions distributed randomly, especially thoseisolated are the oldest (Crawford & Hollister 1986) and most possibly original, whilethose appearing as clusters or oriented along recognizable planes of healed fractures areclearly later, possibly pseudosecondary or secondary (Fig. 22). Homogenizationtemperatures (Tn) were found to have three ranges of 170ºC-175ºC, 318ºC -335ºC and268ºC -272ºC (not corrected for pressure). The original inclusions have the highesthomogenization temperature range in measured samples and they concentrate mainlyarround 320ºC. Middle salinities were also obtained in original inclusions by 8.4-9.2 wt%NaCl. Possibly secondary inclusions have lower temperatures of 170ºC-175ºC andsalinities of 0.7-1.1 wt% NaCl.

Table 6. Measurement results of fluid inclusion in quartz from the Viholanniemi Zn-Auoccurrence.

Fig. 22. Fluid inclusions and their distributions. a) CO2-H2O inclusions isolated; b) CO2inclusions distribute along fractures.

Sample Type Form Size(µ) GLR*(%)

Dis-tribution

Genesis Th*(°C)

Fp*(°C)

Salinity(wt% NaCl)

R305/126.20

liquid elliptical major 1-2minor 4-6 <10 orientated

172170173174174175

-0.6~-0.8-0.6-0.8

0.7-1.1

Pure CO2ellipticalnegativecrystale

4-8 100 random original

R307/37.90

CO2-H2O elliptical 4-8 20-30 random original

318320321321320335330

8.4-9.2

gas-liquid elliptical 3-6 10 orientated

265268268270272272

* GLR=gas liquid ratio, Th=homogenization temperature, Fp=freezing point.

a b

I

62

Observations of the several generations of fluid inclusions suggest that themineralization of the deposit originated through mixing of fluids, or there were multi-stage fluid activities and the maximum temperature was about 335ºC (Crawford &Hollister 1986). The ore-bearing fluids are therefore middle salinity and of hightemperatures of 268-335ºC if original inclusions are related to the mineralization. Inconnection with the plastic deformation of quartz, the observations may also reflect thepresence of metamorphic fluids accompanied by recrystallization of quartz.

According to Ohmoto (1986), the sphalerite-galena pair usually gives isotopictemperatures very close to the fluid inclusion temperatures in low P environments. If thiscould be used here in combining with the observations of inclusion temperatures, the ore-bearing fluids in which the major sulphides were precipitated from might havetemperatures of more than 300ºC.

As already mentioned above, if the temperature is 318ºC -335ºC, the �18O value ofwater in the fluids can be calculated using the �18O value of calcite. The calculation givesthe � 18O value varying in a range of 1.9per mil to 15.37 per mil but most of which varyfrom 1.9 per mil to 5.87 per mil. Similarly, the calculation with the temperature of 268ºC -272ºC gives the results of the �18O value varying from 0.99 per mil to 13.53 per mil andmost of which range in 0.99 per mil to 4.03 per mil. Also the �18O values reached bytemperatures of 170ºC -175ºC are 3.68 per mil to 9.36 per mil with most of the negativevalues. Those calculated �18O values of water in the fluids may be tentative. Consideringthe facts of � 18O values of calcite and the inclusion features mentioned above, all theseimply that metamorphic fluids could have been involved during the whole mineralization.

Geochemical patterns

Most of the metals analysed (see Appendix 1 and 2) are very low in their concentrationsin the volcanic rocks of the Viholanniemi area. Taking away the samples near the oreoccurrences and some abnormally high data, the average contents of Zn, Pb and Cucalculated in felsic-intermediate volcanics are 63 ppm, 23 ppm and 22 ppm, respectively.Only Pb is somewhat higher, Zn and Cu are lower compared to their abundances in theearth crust. It is noteworthy that Zn is lower in felsic rocks than intermediate rocks.

Figure 23 shows geochemical patterns of selected elements on the section of R312-R311-R310 in the northern ore body (see Fig. 2, 17). Zn and Cu show anomalies withpartly correspondent concentration patterns, whereas Pb and Mn display weak anomalouspatterns. Unfortunately, although the weak anomalies of Zn, Cu and Mn can reflect theplaces where ore bodies occur, these primary geochemical patterns especially those ofmajor oxides do not show intense anomalies. Coherent patterns are those of CaO andMgO as well as Fe2O3 with good correspondance to that of Zn. Concentrated SiO2appears mainly both in the upper and lower sides of the enriched Zn, CaO and MgO parts.K2O and Na2O have the patterns showing banded concentration and indistinguishabledepletion of Na2O.

I

63

Fig. 23. Geochemical patterns of selected elements on profile R312-311-310.

I

64

Apparently the patterns of CaO, MgO, Fe2O3, SiO2, K2O and Na2O with unclearvariations in their concentrations are possibly a reflection of the protolith. In addition,SiO2, Na2O (and K2O) may also indicate the alteration.

Discussion

Geotectonic setting of the Viholanniemi volcano-sedimentary formation

An island arc system, including the Pyhäsalmi Island Arc (PIA) and Kainuu-Outokumpuback-arc related to the subduction in the Raahe-Ladoga Zone (RLZ) has been suggested(see Ekdahl 1993). A totally opposite model with subduction from the NE without anyconnection to Kainuu-Outokumpu area was also interpreted (e.g. Ward 1987, Lahtinen1994, Nironen 1997). Geochemical studies of early Proterozoic volcanic rocks in theRLZ display considerable varieties in their chemical compositions (Kousa et al. 1994,Viluksela 1994, Vaarma & Kähkonen 1994, Lawrie 1992, also see Ekdahl 1993) andpossibly very complex geological processes.

The Viholanniemi volcanic cycle began with minor intermediate pyroclastic eruption,succeeded by major felsic productions with an intermediate interlude; it ended with maficproductions. The majority of volcanics are volcanic clastics with minor lava. Pyroclasticsof the cycle contact concordantly with the sequence of flychoid clastic rocks which arenow called mica schist in the eastern side of the Viholanniemi area. A clear temporarybreak after the felsic eruptions is now confirmed by the presence of siliceous rockaccompanied by fine tuffaceous rocks. All this, together with the pillow structure,indicates a shallow marine environment on the one hand, and, on the other hand, theexplosiue eruption of central type in the early stage, and an effusive eruption of a possiblefissure type in the later stage. According to their chemical compositions, felsic andintermediate rocks are calc-alkaline, and mafic rocks are of low potassium tholeiitic serieswith Fe-enrichment. The volcanic rock association is basalt, andesite, dacite and rhyolite.

A notable factor that should be mentioned here is that the majority of the volcanics inthe area are felsic and mafic rocks and they connect directly in the southern area.Together with the variations of major elements, especially TiO2 and P2O5 in the rocks,they may imply that the volcanics are not fractionates from the same parent magma.

Jakes and White (1971) subdivided the calc-alkaline series related to the subductionzone into three sub-series: the arc-tholeiite, calc-alkaline and shoshonite sub-series.Compared to arc-tholeiite (Jakes & White 1971, table 2), the mafic rocks of the studyarea, particularly those occurring in the southern-most area (late products) exhibit somedifferences by their very high TiO2, MnO, P2O5, Sr, La, Ce, Na2O/K2O, La/Yb values. Itseems that the mafic rocks of the area did not share the features of arc-tholeiite. Condie(1982) considered that tholeiites may be mixed with calc-alkaline volcanics from the arcproper in a relatively small back-arc basin. In addition, the Cr, Ni contents in the maficrocks obviously increase from earlier products to later ones. Particularly, two samples(Table 1) have surprisingly high values of Cr and Ni as well as very high MgO and CaOcontents. One sample (xz-97-4.2) is the cement of pillow lava and the other (xz-97-22.1)is amphibolite. If these contents are absolutely true, they may imply that some material

I

65

came from the mantle at shallow depths. Unfortunately, from this two samples, it isdifficult to confirm the presence of mafic cumulate. Lawrie (1992) however, hasconsidered some amphibolites in Virtasalmi (about 15 km west) as tectonised relics ofhigh-level magma chambers.

Considering the bulk chemical compositions of the volcanics in the area, the content ofNa2O is very high in almost all rocks. Plagioclase phenocrysts in felsic rocks are mainlyalbite (An 10) (Makkonen 1991) and the Ti, Fe, Ca bearing minerals such as diopside,ilmenite are also general in mafic rocks. Average An values of the mafic rocks calculatedby CIPW norms range mostly from 22 to 47, and particularly, normative nefeline ispresent in some samples. It should be noted here that the volcanics particularly those ofmafic share a clear trend of alkalic features, although they are not alkaline series. Weknow that the alkaline series occur usually within a plate environment (Condie 1982,Cong 1978, Qiu 1985). Smellie (1987) has interpreted the volcanic rocks with distinctlyalkaline composition in the Antarctic Peninsula as the products of a post-subductiontensional environment.

Another distinct characteristic of the mafic (including intermediate) rocks of the studyarea is their high TiO2 content (mostly>1.5%). These values are near to or higher thanthat of the average composition of ridge tholeiite (Condie 1982, table 7.3). Maficvolcanics in the arc are generally thought to be characterised by low contents of Ti(Pearce & Cann 1973, Pearce & Norry 1979, Wood et al. 1979) and rarely haveTiO2>1.3% (Gill 1981). Augustithis (1978) connected Ti to the petrogenic significance.Chaye�s (1964, 1965; also see Augustithis 1978) data showed that the circum-oceanicbasalt usually has TiO2 of <1.5%, and ocean basalt has TiO2 of >2.0%. The same casesare also presented in the mafic volcanics in south-eastern Finland and the Tampere SchistBelt (Lawrie 1992, Viluksela 1994). Kähkonen (1987, see Viluksela 1994) has attributedthis feature to a temporary extensional stage during the geological evolution of TheTampere Schist Belt. Pekkarinen and Lukkarinen (1991) documented the metalava andlava with TiO2 of >1.5% in the Koljola formation, the Kiihtelysvaara-Tohmajärvi districtwhich was interpreted as a rift environment. Similarly, Lawrie (1992) suggested anintracratonic rift in Virtasalmi where the amphibolites have also high TiO2. However, inthe Pielavesi and Rautalampi areas the content of TiO2 in the mafic rocks is varied(Ekdahl 1993, Lahtinen 1994).

The mafic volcanics of the Viholanniemi area are characterised by enrichment of Sr,K, Rb, Ba, Nb, Ce, and P on MORB-normalized plots. They show features similar tothose basalts within the plate by their distribution patterns and absence of Nb depletionwhich is proper for volcanic arc basalts (Pearce 1982). The chondrite normalized REEpatterns of the volcanics suggest the calc-alkaline rocks in modern island arc (Garcia1978, Jakes & Gill 1970, Jalles & White 1971) on one hand, and on the other, mafic rockshave their REE patterns with a slight enrichment of LREE similar to those of within platesuch as Hawaiian basalts, ridge basalts and E-MORB (Condie 1982, Jakes & White 1971,Jakes & Gill 1970, Saunders 1984).

Discrimination diagrams using elements Cr, Ni, Ti, Y, Zr, Ta and Nb which wereconsidered to be immobile during secondary processes (Condie 1982, Saunders & Tarney1984, Brewer & Atkin 1989) indicate that most mafic samples (including intermediatesamples in some case) have affinities to the setting within the plate and MORB or E-

I

66

MORB on Ti-Zr, Nb/Y-Ti/Y, Zr-Zr/Y and Nb-Zr-Y diagrams. On Cr-Ti, Ni-Ti/Cr and Ti-V diagrams, the mafic rock samples are also subdivided into MORB or back arc basingroups and low-K tholeiites.

Korsman et al. (1988) have established a clear tectono-metamorphic discordancebetween the northern and southern parts of the Savo schist belt. The discordance,particularly the abrupt changes in metamorphic facies can be encounted in theViholanniemi area which belongs to the Rantasalmi-Sulkava progressive metamorphismarea (Fig. 3). According to Korsman et al. (1988), the isolated Haukivuori area was thrustover the blocks of the Kiuruvesi-Haukivesi complex. The conglomerate with plutonicclasts of 1885±6Ma encountered in the Haukivuori area indicate that the sedimentationmight still have been going on in the Rantasalmi-Sulkava area when erosion was alreadyaffecting the Kiuruvesi-Haukivesi complex. Therefore the Viholanniemi area could bepart of a possible subsiding basin.

The mafic and ultramafic sill-like intrusions of c.1.9Ga in the Juva district representingmantle-derived magma intruded into metapelitic sediments prior to deformation andreorientation into their present steeply dipping attitudes (Makkonen 1996). Theseintrusions, together with volcanics in the Viholanniemi area, should be the products of co-magmatism caused of similar geochronological and compositional characters. In thisrespect, the volcanism of the study area could be explained as the basaltic magma-induced crustal melting so that felsic melts erupted first, followed by the mafic melts.

In fact, Svecofennian basalts of the early Proterozoic seem to be identical in the LILelement enrichment and slightly enriched LREE concentration (Colley & Westra 1987,Ekdahl 1993, Lahtinen 1994, Kousa et al. 1994, Vaarma & Kähkönen 1994, Kähkönen &Nironen 1994, Viluksela 1994, Makkonen 1996). However, not only in the Viholanniemi,but also in the RLZ, especially in the southestern part, the negative anomaly of Nb (Ta) inthe basalts can not be observed (Ekdahl 1993, Viluksela 1994), but they appear in thebasalts in the TSB (Tampere Schist Belt). This also may indicate here that the crustalinvolment in magma of RLZ at least in its south-eastern part is limited.

It is clear from the discussion above that the volcanics of the Viholanniemi area exhibitconsiderable variety in their compositional characteristics. This could contribute to thehybrid magma resulting from the mixing of mantle-derived melt with its inducedanatextic melt (Fyfe 1981). The volcanic cycle developed mainly from explosive eruptionof the central type in the early stage to effusive in the later stage. The volcanism mostpossibly took place in a temporary tensional environment.

Allen et al. (1996) considered the Bergslagen and Skellefteå areas in Sweden as acontinental back-arc region and a transitional area between renewed arc volcanism of amore continental character to the north and subsidence basin to the south, respectively.Lawrie (1992) interpreted the Virtasalmi area as an intracratonic rift (passive margin?).Considering the cases of post-subduction tensional events in the Antarctic Peninsula(Smellie 1987), intra-arc rifting in the Skellefteå district in Sweden (Rickard 1987,Vivallo & Claesson 1987) and an aborted marginal basin in the Western Peruvian(Aguirre & Offler 1985), it could be envisaged here that an incipient arc-rifting systemwas presented in the Viholanniemi area and the subsiding basin was aborted shortly afterit formed. The rift might have developed in the temporary period of stress changing due

I

67

to the decreasing subduction rate and this in turn induced a transtension stress regime.Thus, the Viholanniemi volcanic-sedimentary formation was formed in an incipient arc-rifting environment.

Viholanniemi Zn-Au mineralization

Distinctive characteristics

The Viholanniemi Zn-Au deposit is not a typical volcanic host massive sulphide deposit(VHMS) because there is no stratified or massive ore. However, the deposit shares somesimilarities with VHMS deposits on the one hand, and displays distinctive characteristicsin many respects on the other.

With regard to the VHMS deposits, the Viholanniemi Zn-Au deposit have characters ingeneral as follows: (1) the volcanic-sedimentary formation is the production of an arc-riftenvironment; (2) the deposit occurs in those places where the felsic pyroclastics transitsto sedimentary rocks; (3) Sericitization, disseminated pyrite as well as chloritization andsecondary quartz are very common; (4) Cu-Pb-Zn metal relationships in ores representthose of VHMS deposits (Ekdahl 1993); (5) Ore sulphide �34S is between 1.7 to 10.4 permil similar to that of VHMS deposits (Rye & Ohmoto 1974, Ohmoto & Rye 1979, Hoefs1980, Ohmoto 1986, Taylor 1987).

On the other hand, the deposit shows its distinctive characteristics in many respectsthat include:

� The ore host rocks are mainly vein like quartz-carbonate-tremolite rocks and the oreoccurs disseminated or as open fillings.

� The sulphur contents in the ore are very low and no sulphate mineral has been found.� Ore bearing fluids have been observed to be extensively but less intensely activated

in the area. Apart from the Viholanniemi Zn-Au occurrence, there are also smalloccurrences elsewhere surrounding Lahnalahti both in mafic and felsic rocks.

� Ore bearing fluids were possibly composed mainly of CO2 and H2O with relativelylow salinity. However, the values of 8.4-9.2 wt% NaCl of the fluid inclusion mayresemble that of stockwork beneath the massive ore (Sawkins 1990). Clearly, therewere different fluids with variety of temperatures which range from 170ºC to 335ºC(not corrected for pressure).

� Ore sulphide �34S values are mainly positive and vary in a relatively wide range:�34Ssp 0.2�10.4�, �34Spy -0.5�10.2�.

� Carbon and oxygen isotopes together show a clear affinity of mantle-derived carbon(Hoefs 1980, Kerrich 1989, Rollinson 1993) and also possibly another carbon sourcecoming from the mixing between marine sediments and organic materials. The�18OSMOW values of calcite vary greatly and may indicate a wide range of tempera-tures. Calculated �18OSMOW values of water in the fluids varying from 3.68 per milto 15.37 per mil suggest a considerable involvement of atomspheric water and meta-morphic water.

� Ores experienced intense deformation and overprints of metamorphism. The remobi-lization of metals during the metamophism is present.

I

68

� Geochemical patterns of the deposit do not show typical Na2O depletion of the mas-sive sulphides proper, particularly in the altered footwall.

Sulphur and base metal sources

Due to no sulphate mineral present in the ores, the ore sulphide �34S values could beconsidered as representative of �34S�S of fluid. The positive and varied sulphide �34Svalues of ores indicate that the sulphur came from mixed sources including mainlymagmatic, seawater and partly sulphides in the rocks (Hoefs 1980, Ohmoto 1986,Rollinson 1993). Disseminated sulphides in volcanics derived clearly their sulphur fromthe rocks themselves. The variations of sulphide �34S values might also be the result ofthe various degrees of mixing between sulphur of magmatic and ocean water. A widespread of disseminated pyrite in the volcanics in the study area and lower contents of Znand Cu, especially in the felsic volcanics, imply that the main base metals of the depositpossibly came from those volcanics.

Carbon sources

Marine limestones have �13C values close to 0 per mill and decarbonation of thelimestones would produce CO2 with �13C values between +3 per mill and +5 per mil(Hoefs 1980). The marine carbonates and also the organic origin should not be consideredas the major carbon sources of the deposit. Considering the presence of graphite in thehost rock and also the high concentration of MnO in carbonate of the deposit however,part of the carbon coming from sediments and organic materials cannot be absolutelyexcluded.

Calcite from calc-silicate has mean �18O and �13C values of +16.5 per mill and -6 permill (Hoefs 1980). Stakes and ONeil (1982, see Rollinson 1993) documented calcite in agreenstone breccia having mantle-like �13C values and forming in a rock-dominatedenvironment (low water/rock ratio) at high temperature. The diagram after Rollinson(1993) (Fig. 21) shows the characteristics of carbonatites in most of samples. Consideringthe alkalic trend of the mafic volcanics of the area, the main carbon sources of the depositcould be (1) mantle-derived and partly mixed with carbonate-derived and organicoriginated CO2, and possibly (2) mixing between carbonate-derived and organicoriginated CO2.

Water in the fluids

The calculated �18O values of water in the fluids range in three groupes: 1.9�15.37 permil, 0.99�13.53 per mil and 3.68�9.36 per mil corresponding respectively to thetemperatures of 318ºC-335ºC, 268ºC -272ºC and 170ºC -175ºC. Regardless of the �18Ovalues of ocean water at that time, it could be deduced that the water in the fluids fromwhich the major sulphides precipitated was mainly composed of ocean water and alsosome magmatic water. During the metamorphism, the meteoric water and also themetamorphic water might have been involved.

I

69

Superimposition of metamorphic fluids

Although the majority of carbon of the carbonate in the deposit can hardly be expected tobe derived from the decarbonation of marine limestones during the metamorphism, thesuperimposition of metamorphic fluids on mineralization is significant. The evidence isas follows:

(1) Fluid inclusions measured in the deposit exhibit obvious multi-stage fluid activitiesaccording to inclusion types, distributions and different salinities and temperature alongwith the plastic deformation of quartz. (2) The presence of graphite in the host rocks andpossibly part of carbon coming from the mixing of morine carbonate-derived and organicoriginated CO2. (3) Involvement of meteoric water and also the metamorphic watersuggested by the �18O values of calcite. (4) Some sulphides (e.g. chalcopyrite andsphalerite) have been remobilized and reprecipitated along the fractures in garnet duringmetamorphism (Fig. 24).

Therefore, many of the distinctive characteristics of the Viholanniemi Zn-Au depositcould be the results of metamorphic superimposition.

Fig. 24. Remobilized sulphides in the Viholanniemi Zn-Au deposit. a) Chalcopyrite fillings inthe fractures of garnet, R301/36.55, single nicol. Magnification x 200. b) Sphalerite andchalcopyrite fillings in the fractures of garnet R301/36.55, single nicol. Magnification x 200.

Mineralization type

All the above mentioned factors indicate that the Viholanniemi Zn-Au deposit is aveinlet-disseminated type deposit related to volcanism, and it experienced intensemetamophic superimposition. Compared to the mafic volcanics, the relatively smallervolume of felsic volcanics in the study area and surroundings may be considered to be themain reason of the limited mineralization. If there are typical stratabound massive orebodies, not yet found in the area, the sedimentary rocks stratigraphically overlying felsicvolcanics should be considered further.

a b

I

70

Summary and conclusion

The Viholanniemi metavolcanic-sedimentary formation is composed of mainly clasticrocks with volcanics of the shallow marine environment. The formation includes felsicpyroclastics with minor intermediate intercalations, siliceous rock and fine tuffacoussiltstone, mafic pyroclastics associated with pillow lava, as well as flychoid clastics in thebottom and top respectively. The volcanism of the Viholanniemi area is characterised byan explosive eruption of the central type in the early stage and effusive eruption of afissure type in the later stage. Volcanics of the area are products of mantle-derived meltand its induced anatextic melt as well as their mixing instead of fractionates from thesame parent magma. Pyroclastics of the formation occur concordantly with the flychoidclastic rocks of the Svecofennian. Chemical compositions of the volcanics suggest thatthe felsic-intermediate rocks are calc-alkaline, while mafic rocks belong to a tholeiiticseries of low potassium with a trend of Fe-enrichment.

The tholeiitic rocks of the Viholanniemi area are the products of volcanism withinplate. Evidence includes: (1) chemical variations share few features of arc-tholeiite but aclear alkalic trend; (2) high contents of TiO2 of mafic volcanics differ clearly from thoseof the island arc and are also outside the RLZ, but are similar to those of ridge tholeiite;(3) multi-element distribution patterns including REE patterns exhibit characteristics bothof volcanism related to subduction and within plate basalts; (4) discrimination diagramsusing immobile elements indicate affinities to within plate setting and MORB. Theconclusion could be deduced here that an incipient arc-rifting system was presented in theViholanniemi area and the basin was aborted shortly after it formed. Therefore thegeotectonic setting of the Viholanniemi volcanic-sedimentary formation is of an incipientarc-rifting system.

Observations of the presence of siliceous rock and fine tuffaceous rocks indicate atemporary break between the mainly felsic and mafic volcanic eruptions. TheViholanniemi Zn-Au mineralizations started during this short period.

The Viholanniemi veinlet-disseminated Zn-Au deposit shares some features of VHMSdeposits on the one hand, and exhibits also distinctive features in many respects on theother. The mineralization involves possibly convective cells developed immediately afterthe felsic pyroclastic eruptions in the early stage of the arc-rift environment, driven byascending mafic magma, and then superimposed by metamorphism. Those distinctivecharacteristics of the Viholanniemi Zn-Au deposit lead the author to assume a tentativegeological model as follows:

(1) In the early stage of the arc-rifting, extrusion of mainly felsic pyroclastic materialaccumulated a relatively thick volcanic pile. Infiltrated and inverted seawater along thesynvolcanic faults downflowed into the deep and led to the initial development ofconvective cells.

(2) As the ongoing of temporary extension, the initiatially convective cells were drivenby the ascending mafic magma. Thus, the convective hydrothermal systems were formedand circulated throughout the volcanic pile. Ore bearing fluids might reach the seafloorforming small scale stratified ores, or they formed mainly vein type sulphide ores anddisseminated sulphides in volcanics.

I

71

(3) During the metamorphism, the deposit experienced intense superimposition,sulphides present in volcanics and ores were partly remobilized. Some distinctivecharaceristics of the deposit may also be attributed to this secondary processing.

Acknowledgements

Dr. Elias Ekdahl and Professor Risto Aario arranged and supervised the programs, andDr. Hannu Makkonen followed the study in Finland. The manuscript was also checkedand reviewed by them and I acknowledge with gratitude their invaluable suggestions andcomments.

Professor Jiang Fuzhi checked part of thin sections that I had examined in Finland andgave me many valuable suggestions during discussions. Dr. Li Yanhe reviewed the part ofisotope studies. Mr. Rauli Lempiäinen assisted me with field work. Dr. Jouko Paasohelped me with electron microprobe analysis. Mr. Heikki Puustjärvi, senior geologist, andDr. Lauri Pekkarinen introduced me to the geological background of the Outokumpudistrict and Lahnalahti area. Mr. Li Shengqi helped me with the data processing. I wouldlike to express my heartfelt thanks to them all.

References

Aguirre L & Offler R (1985) Burial metamorphism in the western Peruvian trough:its relation toAndean magmatism and tectonics. In: Pitcher WS, Atherton MP, Cobbing EJ & Beckinsale RD,Magmatism at a plate edge: the Peruvian Andes. Blackie Halsted Press, 59-71.

Allen RL, Lundström I, Ripa M, Simeonov A & Christofferson H (1996) Facies analysis of a 1.9 Ga,Continental margin, back-arc, felsic caldera province with diverse Zn-Pb-Ag-(Cu-Au) sulfide andFe oxide deposits, Bergslagen region, Sweden. Econ Geol 91: 979-1008.

Allen RL, Weihed P & Svenson S-Å (1996b) Setting of Zn-Cu-Au-Ag massive sulfide deposits in theevolution and facies architecture of a 1.9 Ga marine volcanic arc, Skellefteå district, Sweden.Econ Geol 91: 1022-1053.

Augustithis SS (1978) Atlas of the textural patterns of basalts and their genetic significance. Elsevier,Amsterdam, 320 p (Chinese translation).

Beccaluva L, Ohnenstetter D & Ohnenstetter M (1979) Geochemical discrimination between ocean-floor and island-arc tholeiites-application to some ophiolites. Can J Earth Sci 16: 1874-1882.

Brewer TS & Atkin BP (1989) Element mobilities produced by low grade metamorphic events. Acase study from the Proterozoic of southern Norway. Precamb Res 45: 143-158.

Colley H & Westra L (1987) The volcanic-tectonic setting and mineralization of the early ProterozoicKemiö-Orijärvi-Lohja belt, SW Finland. In: Pharaoh TC, Beckinsale RD & Rickard D (eds)Geochemistry and mineralization of Proterozoic volcanic suites. Geol Soc Spec Publ, No 33: 95-107.

Condie KC (1986) Geochemistry and tectonic setting of early Proterozoic supracrustal rocks in theSouthwestern United states. J Geol 94: 845-864.

Condie KC (1982) Plate tectonics and crustal evolution. 2nd ed. New York: Pergamon Press. 310 p.Cong B (1979) Magmatic activities and igneous rock associations. Geol Publ House, Beijing, 335 p

(in Chinese).

I

72

Crawford ML & Hollister LS (1986) Metamorphic fluids: The evidence from fluid inclusions. In:Walther JV & Wood BJ (eds) Fluid-rock interactions during metamorphism. Springer-Verlag,Berlin, p 1-35.

Cullers RL & Graf J (1984) Rare earth elements in igneous rocks of the continental crust: intermediateand silicic rocks-ore petrogenesis. In: Henderson P (ed) Rare earth element geochemistry.Elsevier, 275-316.

Davies A, Blackburn WH, Brown WR & Ehmann WD (1978) Trace element geochemistry and originof late Precambrian-early Cambrian Catoctin greenstones of the Appalachian Mountains. Univ. ofCalifornia at Davies, Calif. Rep. (unpubl). In: Schweitzer J & Kroner A (eds) Geochemistry andpetrogenesis of early Proterozoic intracratonic volcanic rocks of the vendersdorp Supergroup,South Africa. Chem Geol 51: 265-288.

Ekdahl E (1993) Early Proterozoic Karelian and Svecofennian formations and the evolution of theRaahe-Ladoga Ore Zone, based on the Pielavesi area, central Finland. Geol Surv Finland, Bull373, 137 p.

Fyfa WS (1981) How do we recognize plate tectonics in very old rocks. In: Kroner A (ed)Precambrian plate tectonics. Elsevier Sci Publ Com, Amsterdam, 549-560.

Garcia MO (1978) Criteria for the identification of ancient volcanic arcs. Earth Sci Rev 14: 147-165.Gill JB (1981) Orogenic andesites and plate tectonics. Springer-Verlag, Berlin, 390 p.Hoefs J (1980) Stable isotope geochemistry. 2nd ed. Springer-Verlag, Berlin, 208 p.Holm PE (1985) The geochemical fingerprints of different tectonomagmatic environments using

hygromagmatophile element abundances of tholeiitic basalts and basaltic andesites. Chem Geol51: 303-323.

Irvine TN & Baragar WRA (1971) A guide to the chemical classification of the common volcanicrocks. Can J Earth Sci 8: 523-548.

Jakes P & White AJR (1971) Composition of island arcs and continental growth. Earth planet. SciLett 12: 224-230.

Jakes P & Gill J (1970) Rare earth elements and the island arc tholeiitic series. Earth planet. Sci Lett9: 17-28.

Jensen LS (1976) A new cation plot for classifying subalkalic volcanic rocks. Ontario Div MinesMisc Pap 66.

Kähkönen Y & Nironen M (1994) Supracrustal rocks around the Paleoproterozoic Haveri Au-Cudeposit, southern Finland: evolution from a spreading center to a volcanic arc environment. In:Nironen M & Kähkönen Y (eds) Geochemistry of Proterozoic supracrustal rocks in Finland. GeolSurv Finland, Spec Pap 19: 141-160.

Kahma A (1973) The main metallogenic features of Finland. Geol Surv Finland, Bull 265, 29p.Kilpeläinen T (1988) Evolution of deformation and metamorphism as a function of time in the

Rantasalmi-Sulkava area, south-eastern Finland. In: Korsman K (ed.) Tectono-metamorphicevolution of the Raahe-Ladoga zone. Geol Surv Finland, Bull 343: 77-88.

Koistinen TJ (1981) Structural evolution of an Early Proterozoic strata-bound Cu-Co-Zn deposit,Outokumpu, Finland. Trans R Soc Earth Sci 72: 115-158.

Kontoniemi O & Ekdahl E (1990) Tonalite-hosted Early Proterozoic gold deposit at Osikonmäki,south-eastern Finland. Bull Geol Soc Finland 62 part 1: 61-70.

Korsman K, Niemelä R and Wasenius P (1988) Multistage evolution of the Proterozoic crust in theSavo schist belt, eastern Finland. In: Korsman K (ed) Tectono-metamorphic evolution of theRaahe-Ladoga zone. Geol Surv Finland, Bull 343: 89-96.

Korsman K, Holttä P, Hautala T and Wasenius P (1984) Metamorphism as an indicator of evolutionand structure of the crust in Eastern Finland. Geol Surv Finland, Bull 328, 40 p.

Korsman K (1973) Rantasalmi. Geological map of Finland, Pre-quaternary rocks, Sheet 3233. GeolSurv Finland.

I

73

Korsman K, Koistinen T, Kohonen J, Wennerström M, Ekdahl E, Honkamo M, Idman H & PekkalaY (eds) (1997) Bedrock map of Finland 1:1 000 000. Espoo: Geol Surv Finland.

Kousa J, Marttila E & Vaasjoki M (1994) Petrology, geochemistry and dating of paleoproterozoicmetavolcanic rocks in the Pyhäjärvi area, central Finland. In: Nironen M & Kähkönen Y (eds)Geochemistry of Proterozoic supracrustal rocks in Finland. Geol Surv Finland, Spec Pap 19: 7-28.

Lahtinen R (1994) Crustal evolution of the Svecofennian and Karelian domains during 2.1-1.79 Ga,with special emphasis on the geochemistry and origin of 1.93-1.91 Ga gneissic tonalites andassociated supracrustal rocks in the Rautalampi area, central Finland. Geol Surv Finland, Bull 378,128 p.

Lawrie KC (1992) Geochemical characterisation of a polyphase deformed, altered, and high grademetamorphosed volcanic terrane: implications for the tectonic setting of the Svecofennides south-central Finland. Precamb Res 59: 171-205.

Le Maitre RW, Bateman P, Dudek A, Keller J, Lameyre Le Bas MJ, Sabine PA, Schmid R, SorensenH, Streckeisen A, Wooley AR & Zanettin B (1989) A classification of igneous rocks and glossaryof terms. Blackwell, Oxford, 193 p.

Liu Y, Cao L, Li Z, Wang H, Chu T & Zhang J (1984) Element Geochemistry. Sci Publ House,Beijing, 548 p (in Chinese).

Luukkonen E & Lukkarinen H (1986) Explanation to the stratigraphic map of Middle Finland. GeolSurv Finland, Rep of Invest 74, 47 p.

Makkonen H (1996) 1.9 Ga tholeiitic magmatism and related Ni-Cu deposition in the Juva area, SEFinland. Geol Surv Finland, Bull 386, 101 p.

Makkonen H (1991) Studies of the Viholanniemi Zn deposit in Joroinen, 1984-1988. Geol SurvFinland, unpublished research report, 22 p.

Makkonen H & Ekdahl E (1988) Petrology and structure of the early Proterozoic Pirilä gold depositin south-eastern Finland. Bull Geol Soc Finland 60: 55-66.

Meschede M (1986) A method of discriminating between different types of mid-ocean ridge basaltsand continental tholeiites with the Nb-Zr-Y DIAGRAM. Chem Geol 56: 207-218.

Nironen M (1997) The Svecofennian Orogen: a tectonic model. Precamb Res 86: 21-44.Nurmi P A & Sorjonen-Ward P (1996) Mining and exploration in Finland. SGA News, Nov. 1996,

No 2: 1-11.Ohmoto H (1986) Stable isotope geochemistry of ore deposits. In: Valley JW, Taylor HP & O�Neil

JR (eds) Stable isotopes in high temperature geological processes. Reviews in Mineralogy 16.Mineral Soc Amer 460-491.

Ohmoto H & Rye RO (1979) Isotopes of sulfur and carbon. In: Barnes HL (ed.) Geochemistry ofhydrothermal ore deposits. 2nd ed. J Wiley and Sons, New York, p 509-567.

Papunen H (ed) (1990) Report of the zinc project. Univ Turku, Publ N 22, 143 p.Pearce JA (1983) Role of sub-continental lithosphere in magma genesis at active continental margins.

In: Hawkesworth CJ & Norry MJ (eds) Continental Basalts and Mantle Xenolits. Cheshire: Shiva.230-249.

Pearce JA (1982) Trace element characteristics of lavas from destructive plate boundaries. In: ThorpeRS (ed) Andesites, Orogenic Andesites and Related Rocks. Chichester: John Wiley and Sons, p525-548.

Pearce JA & Norry MJ (1979) Petrogenetic implications of Ti,Zr,Y, and Nb variations in volcanicrocks. Contrib Mineral Petrol 69: 33-47.

Pearce JA (1975) Basalt geochemistry used to investigate past tectonic environments on Cyprus.Tectonophysics 25: 41-67.

Pearce JA & Cann jr (1973) Tectonic setting of basic volcanic rocks determined using trace elementanalyses. Earth Planet Sci Lett 19: 290-300.

Pekkarinen LJ & Lukkarinen H (1991) Paleoproterozoic volcanism in the Kiihtelysvaara-Tohmajarvidistrict, eastern Finland. Geol Surv Finland, Bull 357, 30 p.

I

74

Qiu J (ed ) (1985) Petrology of igneous rocks. Geol Publ House, Beijing, 340 p (in Chinese).Rickard D (1987) Proterozoic volcanogenic mineralization styles. In: Pharaoh TC, Beckinsale RD &

Rickard D (eds) Geochemistry and mineralization of Proterozoic volcanic suites. Geol Soc SpecPubl No 33: 23-35.

Rollinson HR (1993) Using geochemical data: evaluation, presentation, interpretation. New York:Longman Sci & Tech, 343 p.

Rye RO & Ohmoto H (1974) Sulfur and carbon isotopes and ore genesis: A review. Econ Geol 69:826-842.

Saunders AD (1984) The rare earth element characteristics of igneous rocks from the ocean basins.In: Henderson P (ed) Rare earth element geochemistry. Elsevier, Amsterdam, p 205-236.

Saunders AD & Tarney J (1984) Geochemistry characteristics of basaltic volcanism within back-arcbasins. In: Kokelaar BP & Howells MF (eds)Marginal basin geology. Spec Publ Geol Soc London16: 59-76.

Sawkins FJ (1990) Metal deposits in relation to plate tectonics. 2nd ed. Springer-Verlag, Berlin, 459p.

Shervais JW (1982) Ti-V plots and the petrogenesis of modern and ophiolitic lavas. Earth Planet SciLett 59: 101-118.

Simonen A (1980) The Precambrian in Finland. Geol Surv Finland, Bull 304, 58 p.Smellie JL (1987) Geochemistry and tectonic setting of alkaline volcanic rocks in the Antarctic

Peninsula: A review. In: Weaver SD & Johnson RW (eds) Tectonic controls on magma chemistry.Elsevier, Amsterdam, p 269-285.

Taylor BE (1987) Stable isotope geochemistry of ore-forming fluids. In: Kyser TK (ed) Short couresin stable isotope geochemistry of low temperature fluids. Mineralogical Assoc Canada 13: 337-445.

Vaarma M & Kähkönen Y (1994) Geochemistry of Paleoproterozoic metavolcanic rocks at Evijärvi,western Finland. In: Nironen M & Kähkönen Y (eds) Geochemistry of Proterozoic supracrustalrocks in Finland. Geol Surv Finland, Spec Pap 19: 47-60.

Vaasjoki M & Sakko M (1988) The evolution of Raahe-Ladoga zone in Finland: isotopic constraints.In: Korsman K (ed) Tectono-metamorphic evolution of the Raahe-Ladoga zone. Geol SurvFinland, Bull 343, p 7-32.

Viluksela A (1994) Geochemistry of calc-alkaline metavolcanic rocks in the Parikkala-Punkaharjuarea, south-eastern Finland. In: Nironen M & Kähkönen Y (eds) Geochemistry of Proterozoicsupracrustal rocks in Finland. Geol Surv Finland, Spec Pap 19: 61-69.

VivalloW & Claesson L-A (1987) Intra-arc rifting and massive sulphide mineralization in an earlyProterozoic volcanic arc, Skellefteå district, northern Sweden. In: Pharaoh TC, Beckinsale RD &Rickard D (eds) Geochemistry and mineralization of Proterozoic volcanic suites. Geol Soc SpecPubl No 33: 69-79.

Ward P (1987) Early Proterozoic deposition and deformation at the Karelian craton margin in south-eastern Finland. Precamb Res 35: 71-93.

Wei J & Wang G. (1988) Isotope geochemistry. Geol Publ House, Beijing, 166 p (in Chinese).Weihed P & Mäki T (1997) Volcanic hosted massive sulfide deposits and gold deposits in the

Skellefteå district, Sweden and Western Finland. Research and exploration-where do they meet?4th Biennial SGA Meeting, Aug. 11-13, 1997, Turku, Finland, excursion guidebook A2. GeolSurv Finland, Guide 41, 81 p.

Wood DA, Joron J-L & Treuil M (1979) A re-appraisal of the use of trace elements to classify anddiscriminate between magma series erupted in different tectonic settings. Earth planet. Sci Lett 45:326-336.

Appendices 1-4

76

Appendix 1 W

hole rock chemical com

positions of selected rocks in the Viholanniem

i area. Ox-

ides and others are all in wt%

. Sampling sites are presented at the A

pp.4.1

26

714

1516

1721

2223

2425

2627

SiO2

65.453.3

70.755.1

47.354.7

49.843.4

66.877

65.471.3

76.864.8

46.4TiO

21.13

2.470.701

1.641.5

1.821.65

1.020.859

0.1480.738

0.9260.255

0.81.74

Al2 O3

14.814.7

13.915.5

16.316.1

12.99.46

13.912

12.911.9

9.1612.2

14.1Fe2 O

35.87

124.48

11.29.6

11.412.9

166.62

2.236.03

5.752.81

4.97.86

MnO

0.0880.165

0.1030.22

0.3990.29

0.2231.04

0.1970.287

0.1930.096

0.0980.166

0.137MgO

2.185.35

1.744.43

7.754.81

6.475.71

2.551.09

1.140.73

0.561.2

3.74CaO

3.915.56

0.7695.25

11.16.77

10.518.1

1.61.45

6.443.41

3.86.42

13.2Na2 O

4.324.27

54.32

2.743.08

30.16

4.382.51

3.683.78

2.713.46

5.1K2 O

1.540.779

2.171.28

0.8130.508

0.2920.019

2.552.76

1.30.954

0.9551.75

0.125P2 O

50.327

1.040.182

0.2840.23

0.2440.29

0.2530.212

0.0140.162

0.280.044

0.2150.184

total99.57

99.6399.75

99.2297.73

99.7298.03

95.1699.67

99.4997.98

99.1397.19

95.9192.59

C0.22

0.03<0.01

0.060.01

<0.01<0.01

<0.01<0.01

0.020.92

0.330.62

0.941.73

Rb

0.00370.0022

0.00510.0033

0.00220.0008!

0.0007!0.0001!

0.00670.0064

0.00430.0038

0.00390.0049

0.0003!Ba

0.02790.0072

0.06750.0221

0.00660.0105

0.0150.0034

0.02980.0847

0.03720.0214

0.03240.0323

0.0098Sr

0.01490.0166

0.0070.0202

0.03250.0306

0.03050.0446

0.00710.0047

0.01570.0149

0.01170.0171

0.0319Pb

0.0020!0.0023!

0.0015!0.0020!

0.00370.0078

0.0024!0.0027!

0.0016!0.0015!

0.0023!0.0020!

0.0018!0.0024!

0.0020!Th

0.0004!0.0000!

0.0007!0.0000!

0.0000!0.0000!

0.0003!0.0003!

0.0005!0.0010!

0.0005!0.0002!

0.0006!0.0003!

0.0002!Zr

0.05060.0326

0.03250.0193

0.01460.0166

0.02410.0145

0.0450.0179

0.03150.0279

0.02920.0263

0.0113Ga

0.00310.0025

0.0020!0.0027

0.00250.0027

0.0019!0.0018!

0.00270.0022

0.00230.0016!

0.0015!0.0018!

0.0012!Sc

0.0010!0.0017!

0.0004!0.0020!

0.00310.0029!

0.0026!0.0028!

0.0005!0.0000!

0.0010!0.0006!

0.0000!0.0010!

0.0036La

0.00550.0033

0.00370.0021!

0.0018!0.0024!

0.00320.0023!

0.00460.0057

0.00420.0032

0.00380.0026!

0.0006!Ce

0.01480.0118

0.00920.0053

0.00440.0049

0.00740.0045

0.00990.0115

0.01020.0066

0.00890.0082

0.0037Nb

0.0050.0036

0.00260.0018

0.00160.0017

0.00210.0014

0.00350.0025

0.00330.0028

0.00250.0022

0.0017Y

0.00470.0035

0.00230.0024

0.00190.0024

0.00280.002

0.00410.0032

0.00390.0028

0.00270.0027

0.002V

0.00610.0269

0.00770.0323

0.02510.0365

0.030.0204

0.00530.0009!

0.00930.007

0.00330.0124

0.0264Cr

0.0012!0.0011!

0.0023!0.0019!

0.00740.0022!

0.0022!0.0017!

0.0009!0.0018!

0.0028!0.0015!

0.0016!0.0020!

0.0085Ni

0.0005!0.0013!

0.0017!0.0023

0.00380.0023

0.00530.0034

0.0000!0.0000!

0.00210.0005!

0.0002!0.0018!

0.0099Cu

0.0003!0.0008!

0.0016!0.0171

0.00450.0035

0.0018!0.2024

0.0009!0.0018!

0.0009!0.1037

0.0150.004

0.0086Zn

0.0120.0175

0.01370.0125

0.05450.0473

0.01940.029

0.0180.0038

0.01050.0083

0.0050.0181

0.005S

0.009!0.006!

0.003!0.032

0.005!0.003!

0.004!0.059

0.001!0.000!

0.0220.175

0.0220.041

0.031U

0.0003!0.0002!

0.0000!0.0000!

0.0001!0.0000!

0.0000!0.0002!

0.0002!0.0000!

0.0002!0.0004!

0.0000!0.0000!

0.0001!Sb

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!Sn

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!As

0.0002!0.0000!

0.0000!0.0001!

0.0000!0.0000!

0.0000!0.0006!

0.0002!0.0001!

0.0000!0.0001!

0.0000!0.0000!

0.0003!Bi

0.0003!0.0002!

0.0003!0.0002!

0.0000!0.0002!

0.0000!0.0000!

0.0001!0.0001!

0.0000!0.0001!

0.0000!0.0000!

0.0000!Cl

0.0070.004!

0.0060.004!

0.003!0.004!

0.004!0.003!

0.0120.004!

0.0120.01

0.010.008

0.006!Mo

0.0000!0.0000!

0.0000!0.0001!

0.0000!0.0000!

0.0000!0.0000!

0.0001!0.0004!

0.0000!0.0000!

0.0000!0.0000!

0.0000!

77

Appendix 1 C

ontinued.28

3031

3233

3436

3738

3940

4142

4344

SiO2

37.749.3

60.157

56.871.9

76.167.8

72.968.7

48.361.9

45.175.9

74.4TiO

21.18

1.741.08

0.7421.24

0.5080.6

0.6180.503

0.6861.19

0.7081.38

0.3530.044

Al2 O3

9.1614.9

15.719.1

15.912.6

12.114.4

12.313.5

13.917

14.911.8

14.7Fe2 O

312.3

12.88.01

7.98.94

4.353.54

5.584.78

5.9812

7.0112.3

3.330.78

MnO

0.1940.168

0.0760.039

0.1380.042

0.0240.07

0.0590.074

0.2250.061

0.1620.083

0.057MgO

9.474.71

3.42.98

4.112.42

0.992.42

1.992.8

5.82.66

7.731.55

0.19CaO

17.59.34

3.170.381

6.690.861

0.5742.45

1.721.7

12.31.01

12.81.35

1.32Na2 O

1.694.29

2.961.36

2.31.69

1.763.44

3.312.8

3.322.09

2.082.79

5.95K2 O

0.0850.726

2.725.17

1.523.23

3.542.19

23.24

0.3964.1

0.0712

1.83P2 O

50.244

0.3420.5

0.0930.61

0.1360.118

0.1660.148

0.1390.117

0.0860.173

0.0530.036

total89.52

98.3297.72

94.7798.25

97.7499.35

99.1399.71

99.6297.55

96.6396.70

99.2199.31

C1.97

0.160.02

0.210.02

0.630.03

<0.010.02

0.030.23

0.360.33

0.050.21

Rb

0.0002!0.0010!

0.01710.0222

0.00950.0103

0.01340.0105

0.00910.0146

0.0008!0.0173

0.0005!0.0062

0.0044Ba

0.00210.0189

0.02470.0686

0.06040.0535

0.06880.0313

0.04230.0756

0.01610.0989

0.00260.0202

0.0651Sr

0.01790.0423

0.04410.0111

0.13030.0111

0.01190.0248

0.02330.0177

0.01540.0197

0.06890.005

0.02Pb

0.0018!0.0013!

0.00360.004

0.00320.0017!

0.0026!0.0033

0.0029!0.0027!

0.0017!0.0041

0.0015!0.0018!

0.0027!Th

0.0000!0.0001!

0.0005!0.001

0.0006!0.0010!

0.0007!0.0008!

0.00130.0008!

0.0000!0.0015

0.0000!0.0006!

0.0000!Zr

0.010.0172

0.02040.0164

0.02140.0181

0.02550.0178

0.02160.0197

0.00740.0193

0.0080.0367

0.0037Ga

0.0020!0.0023

0.00290.004

0.00260.0023

0.0020.0025

0.00230.0024

0.00220.0027

0.00240.0019!

0.0026Sc

0.00350.0030!

0.0009!0.0015!

0.0014!0.0008!

0.0000!0.0010!

0.0007!0.0010!

0.00470.0013!

0.0040.0002!

0.0000!La

0.0010!0.0011!

0.00490.0031

0.00690.0029!

0.00380.0032

0.00360.0032

0.0010!0.0052

0.0013!0.0049

0.0009!Ce

0.00480.0068

0.01360.0097

0.01640.0084

0.00850.0066

0.01080.0087

0.00330.012

0.00460.0106

0.0036Nb

0.0009!0.002

0.00160.0017

0.00160.0009!

0.00160.0012

0.0008!0.0012

0.0005!0.0015

0.00150.0032

0.0007!Y

0.00230.0026

0.00250.0029

0.00210.0017

0.00230.0022

0.00240.0023

0.00230.0026

0.00180.0041

0.0001!V

0.02670.0345

0.01720.0169

0.02020.0106

0.00790.0117

0.01060.0127

0.03630.0128

0.03050.0027!

0.0006!Cr

0.12160.0064

0.00570.0144

0.00460.0079

0.01040.0157

0.01320.0106

0.00880.0111

0.05570.0018!

0.0014!Ni

0.05690.0033

0.00460.0066

0.0050.0046

0.00230.0051

0.00370.0036

0.00820.0036

0.03210.0007!

0.0005!Cu

0.00670.0222

0.00740.0051

0.00830.0055

0.0010!0.0037

0.0017!0.0003!

0.00770.0019!

0.0180.0016!

0.0007!Zn

0.01150.0115

0.0140.0164

0.01340.0069

0.00720.0082

0.00570.0084

0.0130.0128

0.00970.0095

0.0027S

0.0370.018

0.3170.063

0.3341.56

0.0350.154

0.1270.008!

0.009!0.031

0.1370.004!

0.011U

0.0001!0.0000!

0.0003!0.0003!

0.0001!0.0000!

0.0000!0.0002!

0.0000!0.0003!

0.0002!0.0003!

0.0001!0.0000!

0.0000!Sb

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!Sn

0.0003!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!As

0.0000!0.0002!

0.0000!0.0008!

0.0001!0.0003!

0.0000!0.0000!

0.0008!0.0003!

0.0002!0.0000!

0.0006!0.0001!

0.0000!Bi

0.0000!0.0001!

0.0000!0.0002!

0.0000!0.0000!

0.0000!0.0002!

0.0000!0.0000!

0.0004!0.0002!

0.0003!0.0000!

0.0002!Cl

0.0070.008

0.004!0.006

0.004!0.006

0.006!0.005!

0.004!0.007

0.004!0.003!

0.002!0.003!

0.004!Mo

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!

78

Appendix 1 C

ontinued.45

4647

4849

5051

5253

5455

5657

5859

SiO2

64.356.1

74.869.7

68.672.8

71.672.2

67.759.5

59.262.1

68.154.8

64.7TiO

21.09

1.090.38

0.6120.609

0.5640.465

0.4830.85

1.791.33

1.090.826

1.470.889

Al2 O3

15.116.6

13.314.3

14.412.9

13.713.9

15.114.6

15.115.4

14.616.2

15.1Fe2 O

36.88

9.323.01

55.28

4.144.51

2.694.15

9.389.03

7.535.54

10.95.19

MnO

0.170.223

0.0480.076

0.1270.083

0.1290.133

0.0860.192

0.2180.15

0.1070.263

0.152MgO

4.415.33

1.021.73

2.021.68

1.432.45

2.183.87

4.324.28

1.745.16

3.26CaO

2.645.19

1.141.78

4.042.77

2.131.46

3.55.67

3.763.61

2.675.79

5.15Na2 O

4.245.21

4.754.7

2.253.42

4.625.56

5.863.59

4.024.01

4.664.17

4.13K2 O

0.7150.18

1.131.12

1.841.18

1.070.467

0.140.712

1.020.689

1.330.296

0.635P2 O

50.238

0.2670.044

0.140.143

0.1250.087

0.0860.241

0.4590.238

0.280.234

0.3670.217

total99.78

99.5199.62

99.1699.31

99.6699.74

99.4399.81

99.7698.24

99.1499.81

99.4299.42

C0.02

0.030.06

<0.010.02

0.020.11

0.020.06

0.030.04

0.010.05

0.050.06

Rb

0.00270.0004!

0.00250.0035

0.00620.0034

0.00360.0014

0.0001!0.0027

0.00340.002

0.00450.0012

0.0022Ba

0.00650.0053

0.03390.0192

0.02560.023

0.01860.0048

0.00360.0058

0.03090.0084

0.02590.0047

0.0055Sr

0.01120.0219

0.00860.009

0.01270.013

0.00690.008

0.01930.0179

0.0150.0172

0.01240.0194

0.0225Pb

0.0027!0.0021!

0.0014!0.0031

0.0023!0.0016!

0.0016!0.0020!

0.0025!0.0029!

0.00310.0029!

0.00320.0019!

0.0021!Th

0.0005!0.0000!

0.0006!0.0007!

0.0006!0.0003!

0.0007!0.0006!

0.0004!0.0001!

0.0001!0.0002!

0.0005!0.0001!

0.0005!Zr

0.02980.022

0.05570.0365

0.03520.0373

0.04480.0468

0.04010.028

0.0310.034

0.040.0228

0.0256Ga

0.00220.0024

0.0020!0.0024

0.00240.0021

0.00330.0025

0.00260.0025

0.00270.0026

0.00250.0025

0.0023Sc

0.0013!0.0015!

0.0000!0.0003!

0.0004!0.0001!

0.0004!0.0003!

0.0009!0.0023!

0.0017!0.0015!

0.0011!0.0019!

0.0013!La

0.00350.0025!

0.00520.0047

0.00450.0035

0.00410.0051

0.0040.0031

0.00330.0042

0.0040.0020!

0.0036Ce

0.00740.0055

0.01380.0102

0.01010.0101

0.00880.0109

0.00930.007

0.00770.0091

0.01120.0065

0.0078Nb

0.00240.002

0.00440.0027

0.00310.0027

0.00350.0035

0.00340.0026

0.00260.0027

0.00310.0022

0.0022Y

0.00280.0026

0.00490.0029

0.00390.0032

0.00550.0043

0.00350.003

0.00330.0032

0.00340.0025

0.0025V

0.01410.0195

0.0019!0.0062

0.00570.0051

0.0024!0.0031

0.00650.0249

0.02250.0133

0.00670.0234

0.0131Cr

0.0025!0.0063

0.0010!0.0020!

0.0023!0.0021!

0.0016!0.0010!

0.0006!0.0016!

0.0011!0.0024!

0.0010!0.004

0.0026!Ni

0.0018!0.0096

0.0010!0.0015!

0.0009!0.0010!

0.0001!0.0001!

0.0002!0.0010!

0.00230.0036

0.0003!0.0077

0.0029Cu

0.0005!0.0009!

0.00880.0095

0.00540.0007!

0.0000!0.0000!

0.0002!0.0005!

0.08540.0005!

0.0011!0.007

0.0000!Zn

0.00740.0081

0.0016!0.0022

0.00230.0028

0.00230.0098

0.00230.0134

0.01050.0091

0.00310.0075

0.0045S

0.003!0.003!

0.002!0.907

0.0310.003!

0.000!0.001!

0.004!0.003!

0.0380.004!

0.005!0.009!

0.002!U

0.0001!0.0000!

0.0000!0.0001!

0.0002!0.0000!

0.0000!0.0000!

0.0000!0.0001!

0.0001!0.0000!

0.0000!0.0001!

0.0000!Sb

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!Sn

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!As

0.0000!0.0000!

0.0001!0.0002!

0.0001!0.0000!

0.0001!0.0000!

0.0002!0.0001!

0.0000!0.0000!

0.0000!0.0000!

0.0001!Bi

0.0002!0.0003!

0.0006!0.0002!

0.0002!0.0003!

0.0001!0.0005!

0.0002!0.0002!

0.0003!0.0000!

0.0003!0.0003!

0.0003!Cl

0.004!0.006!

0.003!0.005!

0.006!0.005!

0.003!0.004!

0.006!0.006!

0.006!0.006!

0.005!0.006!

0.004!Mo

0.0000!0.0000!

0.0000!0.0011

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0001!

0.0000!0.0000!

0.0001!0.0000!

0.0000!

79

Appendix 1 C

ontinued60

6162

6364

6566

6768

6970

7172

7374

SiO2

61.371.3

72.870

67.658.6

57.573.4

66.661.8

61.665.5

67.659.7

81.6TiO

21.16

0.4960.463

0.4730.816

1.841.31

0.4810.855

0.690.699

0.8830.661

0.7650.246

Al2 O3

15.714.3

13.113.7

14.715.3

15.913.5

15.915.3

15.215.8

14.916.7

8.91Fe2 O

36.35

3.82.82

3.255.53

8.989.84

2.834.49

5.986.21

5.345.94

8.542.28

MnO

0.1520.077

0.1540.166

0.0590.144

0.1970.063

0.0890.087

0.0930.047

0.0750.061

0.03MgO

3.761.34

1.373.48

1.563.44

4.631.85

2.745.64

5.882.07

2.333.71

0.7CaO

5.631.93

3.291.83

2.187.32

5.561.31

2.484.77

4.713.28

1.580.959

0.699Na2 O

4.175.92

3.62.96

6.093.25

3.195.75

5.744.3

4.154.02

3.462.22

1.92K2 O

0.60.445

1.111.58

0.5570.444

1.330.479

0.6470.908

0.9692.11

3.043.67

3.25P2 O

50.28

0.0990.096

0.0990.22

0.4560.33

0.0810.241

0.180.176

0.2850.142

0.1540.072

total99.10

99.7198.80

97.5499.31

99.7799.79

99.7499.78

99.6699.69

99.3499.73

96.4899.71

C0.06

0.090.2

0.020.03

<0.01<0.01

<0.010.02

<0.01<0.01

<0.01<0.01

<0.010.03

Rb

0.00170.0018

0.00520.0058

0.00120.0017

0.00330.0014

0.00220.0026

0.00310.0058

0.0150.0179

0.0081Ba

0.00530.0057

0.00650.0075

0.01890.0023

0.02420.0089

0.00750.0338

0.0370.0458

0.04950.0506

0.0824Sr

0.02380.0087

0.01020.0081

0.01170.0261

0.01320.0094

0.01070.0612

0.06550.0698

0.02530.0159

0.0169Pb

0.0022!0.0017!

0.00480.0087

0.0016!0.0025!

0.0020!0.0016!

0.0030!0.0033

0.00410.0024!

0.00360.0045

0.0048Th

0.0004!0.0005!

0.0005!0.0007!

0.0005!0.0002!

0.0001!0.0005!

0.0004!0.0003!

0.0001!0.0005!

0.0007!0.0007!

0.0005!Zr

0.03480.0475

0.04410.0456

0.03920.0288

0.02490.05

0.04120.0166

0.01620.0234

0.01430.0151

0.0144Ga

0.00260.0026

0.0019!0.0019!

0.00230.0023

0.00270.0019!

0.0018!0.0019!

0.00250.0029

0.00250.0029

0.0015!Sc

0.0016!0.0000!

0.0003!0.0000!

0.0000!0.0018!

0.0020!0.0000!

0.0004!0.0010!

0.0008!0.0000!

0.0009!0.0015!

0.0000!La

0.00320.0046

0.00540.0043

0.0040.0027!

0.0027!0.0051

0.00390.0026!

0.0020!0.0047

0.0027!0.0034

0.0023!Ce

0.00910.0108

0.01040.0114

0.01080.0077

0.00690.011

0.01010.006

0.00670.0108

0.00780.0072

0.0073Nb

0.00280.0037

0.00360.0034

0.00320.0024

0.0020.0034

0.00310.0011

0.0010.0023

0.00130.0015

0.0007!Y

0.0030.0041

0.00410.0042

0.00310.0035

0.00250.0035

0.00410.0012

0.00130.0015

0.00230.0026

0.0013V

0.01470.0030!

0.0024!0.0033

0.00740.0265

0.02190.0026!

0.0080.0127

0.01260.013

0.01090.0175

0.005Cr

0.00490.0013!

0.0016!0.0012!

0.0013!0.0015!

0.0028!0.0010!

0.0010!0.0274

0.02820.0069

0.01040.0149

0.0057Ni

0.00430.0000!

0.0002!0.0007!

0.0003!0.0012!

0.00490.0001!

0.0007!0.0157

0.01730.0034

0.00450.0079

0.0024Cu

0.0000!0.0009!

0.0000!0.0005!

0.0010!0.0009!

0.0007!0.0000!

0.0000!0.0034

0.0014!0.0049

0.00380.0074

0.0002!Zn

0.00450.0022

0.00620.0262

0.0019!0.0051

0.00520.0031

0.00330.0076

0.00740.0063

0.00960.0153

0.0055S

0.000!0.001!

0.003!0.004!

0.9630.005!

0.005!0.002!

0.007!0.006!

0.004!0.037

0.0120.014

0.002!U

0.0002!0.0000!

0.0000!0.0000!

0.0004!0.0001!

0.0000!0.0000!

0.0000!0.0003!

0.0001!0.0003!

0.0002!0.0004!

0.0000!Sb

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!Sn

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0000!

0.0000!As

0.0002!0.0004!

0.0000!0.0000!

0.0005!0.0000!

0.0000!0.0002!

0.0000!0.0183

0.0290.0004!

0.0000!0.0003!

0.0012!Bi

0.0000!0.0000!

0.0000!0.0001!

0.0000!0.0000!

0.0002!0.0001!

0.0003!0.0003!

0.0004!0.0003!

0.0000!0.0004!

0.0000!Cl

0.005!0.004!

0.005!0.006!

0.0070.004!

0.004!0.004!

0.005!0.005!

0.005!0.006

0.006!0.074

0.005!Mo

0.0000!0.0001!

0.0003!0.0001!

0.0000!0.0000!

0.0000!0.0004!

0.0000!0.0000!

0.0000!0.0000!

0.0000!0.0001!

0.0000!

80

Appendix 2 G

eochemical com

positions of selected rocks in the Viholanniem

i area. Elem

ents are in ppm

. Samplins sites are presented at A

pp.4.

67

2728

3031

3233

3639

4166

6871

7374

Ce

63.535.7

20.424.2

40.4118

77.6134

64.866.6

8759.9

83.177.5

62.441.8

Dy

3.863.87

3.563.9

4.553.84

4.443.89

3.313.44

4.534.41

6.262.42

3.882

Er2.34

2.252.04

2.142.38

1.972.43

1.741.89

1.852.32

2.563.64

1.232.05

1.03Eu

1.211.32

1.011.19

1.592.4

1.172.76

1.041.02

1.181.69

1.771.37

1.080.59

Gd

4.644.27

3.654.59

4.797.24

5.17.79

4.754.62

5.815.17

6.934.01

4.542.72

Ho

0.750.78

0.710.78

0.860.7

0.860.68

0.650.69

0.870.88

1.240.43

0.760.38

La30.9

16.78.07

10.117

57.240.6

63.532.1

32.844.7

2941

40.331.1

21.3Lu

0.380.31

0.290.24

0.30.22

0.370.22

0.280.26

0.340.35

0.530.15

0.290.16

Nb

20.813.3

13.96.97

15.513

12.514

10.69.01

1416.7

25.218.1

10.74.75

Nd

25.716.9

12.915.7

22.256

33.561.5

28.129.4

36.527.3

35.730

27.117.4

Pr7.16

4.372.89

3.515.52

14.79.34

16.47.72

7.6310.4

7.139.47

8.567.32

4.8Rb

44.130.3

2.130.49

9.2157

20686.9

117133

15930.7

21.351.4

16173.9

Sc8.6

25.730.2

25.432.5

14.423.7

1510.5

15.118

21.711.8

8.5722.5

5.42Sm

4.943.98

3.213.98

5.029.31

6.2610.7

5.15.31

6.895.5

6.884.93

5.323.13

Ta1.58

0.890.9

0.440.96

0.730.97

0.650.77

0.610.95

1.041.65

1.120.81

0.4Tb

0.710.65

0.570.66

0.730.85

0.780.98

0.60.66

0.830.82

1.090.54

0.660.38

Th6.51

1.930.76

1.011.4

6.510.9

6.178.84

8.8614.4

2.525.29

5.48.84

6.13Tm

0.350.33

0.30.28

0.350.26

0.360.22

0.250.28

0.350.38

0.550.18

0.290.17

U2.14

0.740.3

0.370.59

3.533.56

3.633.18

2.283.49

0.892.14

2.522.95

1.84Y

23.423

21.122.1

24.320.9

25.520.9

20.220.6

2627.3

39.614.1

22.511.9

Yb2.44

2.031.9

1.862.26

1.72.68

1.471.76

1.772.27

2.413.44

1.092.09

1.04Zr

261161

76.678.2

120178

140173

218175

169194

353198

134115

81

Appendix 3 G

eochemical com

positions of rocks in the Viholanniem

i area. Ca, Fe, M

g and S in w

t%; A

u, Pd, Pt, Te in ppb; others in ppm

.Sampling sites are presented in A

pp.4. 1

23

45

67

89

1011

1213

1415

1617

1819

Ag

<1.0<1.0

2.6<1.0

<1.01.2

<1.01.6

<1.0<1.0

1.5<1.0

<1.0<1.0

<1.0<1.0

<1.05.9

<1.0A

s<30

<30<30

<30<30

<30<30

<30<30

<30<30

<30<30

<30<30

<30<30

<30<30

Ca

0.941.38

1.031.97

0.410.21

0.921.02

0.341.83

0.320.27

0.571.55

1.111.57

3.911.24

0.3C

d<0.5

<0.5<0.5

<0.5<0.5

<0.5<0.5

<0.5<0.5

<0.5<0.5

<0.5<0.5

<0.5<0.5

<0.5<0.5

1.6<0.5

Co

516

3128

1413

1918

627

418

213

2616

1122

4C

r<5

58

77

86

6<5

135

12,5

1711

7<5

10<5

Cu

85

4661

622

16170

3129

3810

749

3514

19907250

39Fe

3.453.78

4.794.25

3.782.84

3.043.8

1.156.4

2.526.79

0.531.52

4.323.16

3.274.87

1.5M

g1.23

1.511.86

1.540.91

0.981.12

1.890.69

2.740.25

2.290.16

1.131.33

1.190.33

1.280.47

Mn

327226

10301360

438535

347991

8511230

320958

216617

625449

13301010

349M

o<5

<5<5

<5<5

<5<5

<5<5

<5<5

<5<5

<5<5

<5<5

<5<5

Ni

57

3227

1117

1410

49

89

312

1120

711

2P

13104120

14201260

1270785

12001020

1853880

2391400

192907

10101240

1130721

150Pb

<10<10

<10<10

<10<10

<1015

<10<10

<10<10

<10<10

20<10

<1031

<10S

<0.01<0.01

<0.01<0.01

<0.01<0.01

0.030.19

0.020.05

0.04<0.01

<0.01<0.01

<0.01<0.01

0.060.61

<0.01Sr

10.79.3

6.313.6

3.3<2.0

4.519.2

416.6

4.2<2.0

13.934.5

26.143.6

74.645.5

17.1Ti

24902860

39503400

29002930

26803830

8856180

5415090

982660

20003350

30902030

831V

20120

145150

9644

14496

<5148

<5255

<553

17188

72169

5Zn

9075

9773

75120

49133

28184

44291

31179

25655

34295

30A

u<10

<10<10

<1011

<10<10

<10<10

<10<10

<10<10

<10<10

<10<10

<10<10

Pd<25

<25<25

<25<25

<25<25

<25<25

<25<25

<25<25

<25<25

<25<25

<25<25

Pt<50

<50<50

<50<50

<50<50

<50<50

<50<50

<50<50

<50<50

<50<50

<50<50

Te<50

<50<50

<50<50

<50<50

<50<50

<50<50

<50<50

<50<50

<50<50

1360<50

82

Appendix 3 C

ontinued.

2021

2223

2425

2627

2829

3031

3233

3435

3637

38

Ag

<1.0<1.0

<1.0<1.0

4.8<1.0

<1.0<1.0

<1.0<1.0

<1.0<1.0

<1.0<1.0

<1.0<1.0

<1.0<1.0

<1.0A

s<30

<30<30

<30<30

<30<30

<30<30

<30<30

<30<30

<30<30

<30<30

<30<30

Ca

0.920.27

0.183.18

1.412.01

2.995.72

6.911.71

2.360.53

0.072.18

0.130.16

0.10.18

0.16C

d<0.5

<0.5<0.5

<0.5<0.5

<0.5<0.5

<0.5<0.5

<0.5<0.5

<0.5<0.5

<0.5<0.5

1.8<0.5

<0.5<0.5

Co

3212

617

118

1718

1922

2023

1725

1224

818

14C

r10

<5<5

15<5

<514

17162

1824

4773

2628

7740

133112

Cu

55422

3518

1020153

5188

72248

21672

4679

62149

1037

23Fe

5.94.29

1.293.74

3.461.78

3.151.32

1.743.76

3.475.08

4.943.67

2.853.68

2.133.74

3.23M

g2.84

1.520.59

0.620.43

0.310.71

0.521.1

1.241.11

1.971.62

1.541.19

1.520.49

1.451.21

Mn

7881050

1010946

398566

945431

510379

428370

219368

247361

123439

381M

o<5

<5<5

<5<5

<5<5

<5<5

<5<5

<5<5

<5<5

<5<5

<5<5

Ni

143

219

84

1942

15025

1744

6444

3991

2447

33P

1440965

136752

1180241

873722

11201590

14402080

5572490

637640

508826

685Pb

<10<10

<10<10

<10<10

<10<10

<10<10

<10<10

<1012

<10<10

<10<10

<10S

0.040.01

0.010.02

0.20.03

0.040.03

0.040.02

0.020.34

0.060.37

1.452.34

0.040.15

0.12Sr

8.5<2.0

2.419.4

17.518.3

18.241.4

81.723.3

28.722.6

<2.0502

3.9<2.0

<2.04.8

4.4Ti

44603620

4731590

1680489

27202000

12603630

40902440

24602210

642804

19903100

2600V

11918

<558

3215

9049

47135

130141

8097

28198

29100

85Zn

277154

3388

6338

1529

1556

44115

13874

52241

5269

45A

u<10

<10<10

<10<10

<10<10

<10<10

<10<10

<10<10

<10<10

<10<10

<10<10

Pd<25

<25<25

<25<25

<25<25

<25<25

<25<25

<25<25

<25<25

29<25

<25<25

Pt<50

<50<50

<50<50

<50<50

<50<50

<50<50

<50<50

<50<50

<50<50

<50<50

Te<50

<50<50

<50<50

<50<50

<50<50

<50<50

<50<50

<5068

123<50

<50<50

83

Appendix 3 C

ontinued.

3940

4142

4344

4546

4748

4950

5152

5354

5556

57

Ag

<1.0<1.0

<1.0<1.0

<1.0<1.0

<1.0<1.0

<1.01.1

<1.0<1.0

<1.0<1.0

<1.0<1.0

6.2<1.0

<1.0A

s<30

<30<30

<30<30

<30<30

<30<30

<30<30

<30<30

<30<30

<30<30

<30<30

Ca

0.121.87

0.043.09

0.340.65

0.360.83

0.280.24

1.350.39

0.530.25

0.621.21

0.860.66

0.46C

d<0.5

<0.5<0.5

<0.5<0.5

<0.5<0.5

<0.5<0.5

1.6<0.5

<0.5<0.5

<0.5<0.5

1.8<0.5

<0.5<0.5

Co

1715

1020

62

1917

712

1311

57

720

2821

12C

r87

2284

97<5

<513

37<5

99

8<5

<5<5

811

13<5

Cu

972

17162

2713

917

9393

5916

1113

48

84715

18Fe

3.911.89

4.551.73

2.010.42

4.162.98

1.843.16

3.372.8

2.81.79

2.434.22

4.874.04

3.42M

g1.66

0.761.51

0.840.84

0.062.36

1.320.52

1.011.17

1.020.74

1.380.71

1.472.09

2.070.97

Mn

441443

367231

468295

639484

282361

578443

696725

295638

833567

438M

o<5

<5<5

<5<5

<5<5

<5<5

7<5

<5<5

<5<5

<5<5

<5<5

Ni

3520

26132

52

1344

213

119

23

25

1727

3P

639529

411693

265157

10401200

251660

692580

387424

10101890

11301180

949Pb

<10<10

<10<10

<10<10

<10<10

<1013

<10<10

<10<10

<10<10

<10<10

<10S

<0.01<0.01

0.030.14

<0.01<0.01

<0.01<0.01

<0.010.98

0.04<0.01

<0.01<0.01

<0.01<0.01

0.04<0.01

<0.01Sr

3.88.9

7.4308

3.99.9

4.18.7

3.62.0

36.211.4

5.23.4

15.518.8

16.113.8

7Ti

33602170

32501290

112024

19901330

2871290

18601890

1090974

13402270

24901560

2080V

10397

9949

8<5

9893

<534

3733

77

33131

15775

36Zn

7042

10413

7616

5529

812

1716

1576

875

7163

24A

u<10

<10<10

<10<10

<10<10

<10<10

13<10

<10<10

<10<10

<10<10

<10<10

Pd<25

<25<25

<25<25

<25<25

<25<25

<25<25

<25<25

<25<25

<25<25

<25<25

Pt<50

<50<50

<50<50

<50<50

<50<50

<50<50

<50<50

<50<50

<50<50

<50<50

Te<50

<50<50

<50<50

<50<50

<50<50

224<50

<50<50

<50<50

<50<50

<50<50

84

Appendix 3 C

ontinued

5859

6061

6263

6465

6667

6869

7071

7273

74

Ag

<1.0<1.0

<1.0<1.0

<1.0<1.0

<1.0<1.0

<1.0<1.0

<1.0<1.0

<1.0<1.0

<1.0<1.0

<1.0

As

<30<30

<30<30

<30<30

<30<30

<30<30

<30171

281<30

<30<30

<30

Ca

1.141

1.140.43

10.24

0.371.94

1.240.2

0.340.33

0.330.33

0.120.13

0.14

Cd

<0.5<0.5

<0.5<0.5

<0.5<0.5

<0.5<0.5

<0.5<0.5

<0.5<0.5

<0.5<0.5

<0.5<0.5

<0.5

Co

2210

127

79

1115

237

1116

1913

1923

6

Cr

209

27<5

<5<5

<55

20<5

<5144

15857

85129

38

Cu

8812

1211

1518

1417

199

1235

1748

8062

9

Fe3.85

2.133.01

2.41.7

2.163.57

3.545.06

1.842.77

1.311.42

3.453.88

5.451.73

Mg

1.481.26

1.570.73

0.731.92

0.91.02

2.071.07

1.51.08

1.211.18

1.372.03

0.43

Mn

530545

575368

753942

239507

668337

41377

83283

466382

208

Mo

<5<5

<5<5

<5<5

<5<5

<5<5

<5<5

<5<5

<5<5

<5

Ni

4321

35<2

32

<26

412

392

10434

4675

23

P1530

8881200

450412

493925

18201400

363959

745742

1170521

683312

Pb<10

<10<10

<1014

15<10

<10<10

<10<10

<10<10

<10<10

<10<10

S<0.01

<0.01<0.01

<0.01<0.01

<0.011.15

<0.01<0.01

<0.01<0.01

<0.01<0.01

0.030.01

<0.01<0.01

Sr11.6

27.228.6

2.712.5

3.84.5

53.920.7

2.2<2.0

21.624.2

25.44.3

<2.05.4

Ti1940

17002000

7301290

11001900

29802990

11401550

18501960

36203280

39801100

V126

6176

77

1038

120151

1035

6265

9293

15345

Zn28

2126

1651

21011

2032

1719

1520

11680

12544

Au

<10<10

<10<10

<10<10

<10<10

<10<10

<10<10

<10<10

<10<10

<10

Pd<25

<25<25

<25<25

<25<25

<25<25

<25<25

<25<25

<25<25

<25<25

Pt<50

<50<50

<50<50

<50<50

<50<50

<50<50

<50<50

<50<50

<50<50

Te<50

<50<50

<50<50

<50<50

<50<50

<50<50

<50<50

<50<50

<50<50

85

Appendix 4 Sample sites and rock types.

SAMPLE LOCATION X Y ROCK TYPE1 hvm-85-33.1 viholanniemi 6893.850 3541.550 felsic2 hvm-85-33.2 viholanniemi 6893.850 3541.550 intermediate3 hvm-85-32.1 viholanniemi 6893.400 3541.290 felsic4 hvm-85-32.2 viholanniemi 6893.400 3541.290 intermediate5 hvm-85-24.1 viholanniemi 6893.300 3541.250 intermediate6 hvm-85-11.1 viholanniemi 6893.290 3541.120 felsic7 hvm-85-11.2 viholanniemi 6893.290 3541.116 intermediate8 hvm-85-3.1 viholanniemi 6893.170 3541.210 felsic9 hvm-85-2.2 viholanniemi 6893.112 3541.230 felsic10 hvm-85-2.3 viholanniemi 6893.112 3541.228 intermediate11 hvm-85-37.a.1 viholanniemi 6891.430 3540.330 felsic12 hvm-85-37.b.1 viholanniemi 6891.390 3540.330 intermediate13 hvm-86-24.1 viholanniemi 6891.110 3540.085 felsic14 hvm-86-24.2 viholanniemi 6891.110 3540.055 mafic15 hvm-86-24.3 viholanniemi 6891.110 3540.035 mafic16 hvm-86-24.4 viholanniemi 6891.170 3539.910 mafic17 hvm-86-24.5a viholanniemi 6891.180 3539.925 mafic18 hvm-86-24.5b viholanniemi 6891.180 3539.925 mafic19 hvm-86-26.1 viholanniemi 6891.050 3539.900 felsic20 hvm-86-29.1 viholanniemi 6890.900 3540.160 mafic21 xz-97-13.1 viholanniemi 6891.240 3540.320 felsic22 xz-97-17.1 viholanniemi 6890.360 3540.300 felsic23 xz-97-18.1 viholanniemi 6890.650 3541.245 felsic24 xz-97-18.2 viholanniemi 6890.650 3541.245 felsic25 xz-97-18.3 viholanniemi 6890.650 3541.245 felsic26 xz-97-18.4 viholanniemi 6890.615 3541.230 felsic27 xz-97-4.1 lahnalahti 6888.680 3541.520 mafic28 xz-97-4.2 lahnalahti 6888.680 3541.520 mafic29 xz-97-9.1 lahnalahti 6889.380 3540.360 mafic30 xz-97-8.1 lahnalahti 6888.750 3540.560 mafic31 xz-97-5.1 joroisniemi 6892.685 3544.190 graywacke32 xz-97-5.2 joroisniemi 6892.665 3544.200 pellitic33 xz-97-5.3 joroisniemi 6892.700 3544.190 intermediate34 xz-97-6.1 joroisniemi 6892.910 3546.030 sedimentary35 xz-97-6.2 joroisniemi 6892.910 3546.030 sedimentary36 xz-97-7.1 joroisniemi 6892.020 3545.540 sedimentary37 xz-97-14.1 kotkatlahti 6888.280 3544.380 sedimentary38 xz-97-14.2 kotkatlahti 6888.280 3544.380 sedimentary39 xz-97-19.1 katajamäki 6889.730 3536.840 gneiss40 xz-97-20.1 katajamäki 6888.700 3537.700 mafic41 xz-97-21.1 katajamäki 6887.920 3538.260 gneiss42 xz-97-22.1 katajamäki 6886.500 3539.540 mafic43 r306/20.40 viholanniemi felsic44 r306/174.45 viholanniemi felsic45 r310/11.85 viholanniemi felsic46 r310/41.70 viholanniemi intermediate

86

Appendix 4 Continued.

47 r310/79.35 viholanniemi felsic48 r310/118.75 viholanniemi felsic49 r310/135.40 viholanniemi felsic50 r310/162.55 viholanniemi felsic51 r311/11.00 viholanniemi felsic52 r311/31.80 viholanniemi felsic53 r311/51.70 viholanniemi felsic54 r311/70.70 viholanniemi intermediate55 r311/88.65 viholanniemi intermediate56 r311/109.65 viholanniemi intermediate57 r311/128.90 viholanniemi felsic58 r311/140.80 viholanniemi intermediate59 r312/24.70 viholanniemi felsic60 r312/42.70 viholanniemi intermediate61 r312/68.15 viholanniemi felsic62 r312/81.40 viholanniemi felsic(gr)63 r312/84.40 viholanniemi felsic64 r312/103.60 viholanniemi felsic65 r312/122.10 viholanniemi intermediate66 r312/142.30 viholanniemi intermediate67 r312/164.10 viholanniemi felsic68 r312/183.15 viholanniemi felsic69 r321/7.50 pirilä intermediate70 r321/12.85 pirilä intermediate71 r321/132.00 pirilä felsic72 r321/204.10 pirilä mic schist73 r359/38.15 pirilä mic schist74 r359/234.00 pirilä felsic

PART II

II

89

Boulder prospecting and till geochemistry in the search for zinc (gold) ore in the Viholanniemi area,

South-eastern Finland

Xiping Zhang

Abstract: Preglacial weathering proved to be intense in the study area and also the weatheringproducts variated but were well preserved in the bottommost layers immediately above the bedrock.As a result of transportation and deposition, but not very much erosion of the last glacial processes,the till in the bottommost layer has a high proportion of local material in the Viholanniemi area.

The fines of till and weathered bedrock have identical mineral composition. They containprimary rock-forming minerals such as quartz, albite/microcline, hornblende/tremolite, muscovite/phlogopite, calcite; clay minerals such as chlorite in general, as well as some ore minerals includingsphalerite, pyrite and magnetite in the mineralized sites. The chemical composition of till showssome similarities to that of weathered and unweathered bedrock. Elements Na and Ca wereremoved during the decomposition of primary minerals and the formation of clay minerals, but Al,Na, Ca were enriched in till. Fe, Mg, Mn, P might be partly lost during the weathering. The mode ofoccurrence of trace elements Zn, Cu, Pb, Au, Ag, Ni and Co in till in the non-anomalous area is dueto the adsorption onto clay minerals, secondary oxides and hydroxides, but high concentrations ofthose elements in the area are related mainly to the residual ore minerals.

Till geochemical prospecting showed a clear and coherent anomalous distribution pattern of Zn,Ag, Au, Pb, Cu, Ni and Co that reflect the Viholanniemi Zn(Au) ore occurrences well. Ag and Znare the best indicators of the ore occurrences. The anomalies proved to be local and related to thedeposit.

Introduction

Boulder prospecting and till geochemical exploration in the glaciated terrains ofFennoscandia, Canada and mountainous areas of South America have long beenextensively adopted and proved to be very effective tools in prospecting for mineraldeposits since the beginning of the 20th century (Peuraniemi 1982,1990a, Ekdahl 1982,Stigzelius 1987, Koljonen 1992, Saltikoff 1992, McClenaghan et al. 1993, 1997,McClenaghan 1994, Gustavsson et al. 1994, Salminen & Tarvainen 1995, Salminen1995, Klassen 1997). The famous Outokumpu Cu-Ni-Co deposit in Finland was found byboulder tracing and also the earliest Finnish till geochemical investigation was carried outthere (Kauranne 1951, 1959, Stigzelius 1987, Koljonen 1992, Saltikoff 1992).

Unlike other geochemical methods, till geochemical prospecting needs knowledge ofthe glacial history, morainic landforms as well as till characteristics, i.e. Quaternaryframework (Klassen & Murton 1996). The erosion, entrainment, transportation anddepositional history, and the resulting composition of sediments are the crucial factors,not only in the sampling and analysis of glacial sediments (McClenaghan et al. 1997), butalso in the interpretation of prospecting results. A detailed investigation of the glacialhistory, and especially of the ice movement directions is the only way that can lead to thesource.

II

90

The Viholanniemi Zn-Au deposit is located about 5 km southwest of the Joroinenvillage, in south-eastern Finland (Fig. 1, 4) and the flat terrain in the area consists mainlyof till. From the year 1985 to 1988, exploration in the Viholanniemi area includingboulder tracing, till geochemical exploration, bedrock mapping and drilling was carriedout by the Geological Survey of Finland (GTK) (Makkonen 1991, unpublished researchreport). The main objective of the present study is to make further investigation of the tillgeochemistry, and in connection with ore prospecting, to make the plausibleinterpretations of till geochemical survey in the area. All the samples and data involved inthe study were provided by GTK.

Bedrock geology

The Viholanniemi area is within the Raahe- Ladoga zone, which forms part of the socalled Savo schist belt (Fig. 1), a transition belt between the Svecofennian and Kareliansupracrustal domains in Finland (Vaasjoki & Sakko 1988, Ekdahl 1993). The bedrock iscomposed mainly of meta-volcanics, metasediments and granitoids with the strike ofNNW-SSE to NW-SE. The volcanics are chiefly felsic-intermediate pyroclastics with thinmafic intercalations in the northern and central part of the area. In the southern part, thereoccur more mafic volcanics which have been metamorphosed to amphibolite. Also pillowlava can be found there. Mica schist and turbidity greywacke occur in the eastern part,and granite, granite gneiss and mylonite (Papunen 1990) in the western and south-westernpart. Sericitization, disseminated pyrite are widespread in volcanics especially in felsic-intermediate volcanics; in mafic volcanics epidotization is general.

The sulphide Zn-Au mineralizations were observed to be associated mainly withfelsic-intermediate pyroclastics and the host rocks are quartz-carbonate-tremolite veinsand lenses, that can be called the skarn-like rock, as well as felsic (- intermediate)volcanics with sericitization, carbonatization and pyritization. Ore mineralization occursas two main parts: the northern and southern ore occurrences having about NW-SE trends.The average contents of metals in the ore bodies are as follows: southern ore-body: Zn2.31%, Cu 0.19%, Pb <0.1%, Au 0.7 ppm, Ag 26 ppm; northern ore body: Zn 1.97%, Cu0.12%, Pb 0.64%, Au 1.11 ppm, Ag 105 ppm (Makkonen 1991).

Postglacial weathering resulted in the pale surface of the bedrocks and the colourchange in the surficial parts of the drift. Preglacial weathering however, had affectedgreatly both the bedrock and glacial deposits as it was throughout Finland. For example,the occurrences of weathered bedrock have been found immediately underlyingPleistocene till deposits all over Finland and the entire eastern part of Fennoscandia hadbeen covered by an old weathering crust before the Pleistocene glaciations (see Nenonen1995). As a result of intense preglacial chemical weathering, the occurrences of Kaolinand other clay minerals have been found in many places in Finland (Peuraniemi 1990c,Peuraniemi et al. 1993, 1997, Saarnisto & Salonen 1995, Lintinen 1995, Nenonen 1995,Sarapää 1996).

II

91

Fig. 1. Location of the study area on the geological map of Finland (simplified after the bedrockmap of Finland 1:1 000 000, Korsman et al. 1997).

In the study area, Niemelä (unpublished research report 1992) observed the kaolinoccurrences at Tervajoensuo and also at places around Virtasalmi (also see Nenonen1995, Sarapää 1996). In order to confirm the observation, some samples were re-analysedby X-ray diffraction (Siemens Diffractometer D5000), differential thermal (DTA) andthermogravimetric(TGA) techniques (Netzsch Simultaneous Thermal Analyzer STA 409Ep) at the University of Oulu. The XRD traces and DTA curves of samples are shown inFigs 2-3. Kaolinite gives two XRD peaks at 7.1 and 3.5Å (Fig. 2) and typical DTA curves(Norton 1939, Huang 1987) with a sharp endothermic peak at 520-530 �C and exothermicpeak at 990-1000 �C (Fig. 3), and is amorphous or less crystallized (Huang 1987). It isalso possible that kaolinite was formed mainly by the weathering of plagioclase becausethe latter can not be detected in the case of the presence of kaolinite (Fig. 2 a,b,d) but isdetectable in the absence of kaolinite (Fig. 2 c). From the TG curves showing about 3%-7% weight loss it can be estimated that the total content of water bearing secondaryminerals in the weathered bedrock is not very high.

II

92

Fig. 2. X-ray diffraction traces of fines of the weathered bedrock samples from Viholanniemi.Mc=muscovite, K=kaolinite, Ch=chlorite, Q=quartz, M=microcline, Ab=albite, a=R374/12.8m-13.8m, b=R248/13.4m-14.5m, c=R373/17.8m-18.4m, d=R373/10.8m-12.8m.

Fig. 3. DTA-TGA graphs of fines of the weatheredbedrock samples from Viholanniemi. Solid line=DTA,dashed line=TGA, a=R373/10.8m-12.8, b=R248/13.4m-14.5m, c=R374/12.8m-13.8m.

II

93

Glacial geology and boulder prospecting

The study area belongs to the area covered by the activity of the Finnish Lake District IceLobe during the Later Weichselian Deglaciation (Punkari 1980, Glückert 1987, Salonen1986). According to Saarnisto and Salonen (1995), there was a long ice-free period insouthern and central Finland in the Early Weichselian period. During the deglaciation ofsouthern and central Finland, the ice sheet was divided into six different ice lobes(Punkari 1979, 1980). An actively flowing ice of the Finnish Lake District Lobe flowedtowards the Salpausselka ice-marginal belt and created strong drumlinisation (Glückert1987). The Pieksamäki drumlin field (Glückert 1987) inside of the former ice lobe with11000 drumlins is one of the largest in the world. The Viholanniemi area is a part of thedrumlin field (Fig. 4, 5).

The drumlins have been extensively investigated in Finland by Aario et al. (1974,1979a,b, 1990a, 1992), Glückert (1987), Salonen (1987), Peuraniemi (1990a), Nenonen(1995) and many others.

Till sampling carried out by GTK during 1986-1987 (Makkonen 1991) indicated thatthe thickness of till in the Viholanniemi project area can reach 16 m. The thickness of tillvaries greatly and the drumlins in the study area appear often to be rock- cored. Theridges of those drumlins have the same trend of NW-SE. This direction is related to theice movement direction of the last advance of the Weichselian Ice Sheet that moved fromthe northwest and north (300-360°) (Glückert 1987).

The first ore-bearing boulders with high concentrations of Zn, Au, Ag, Cu were foundon the west bank of lake Kolkonjärvi, about 20 km southeast of the Viholanniemi deposit.During the following years of 1984-1985, several boulders which were quartz-carbonaterocks and felsic volcanics containing sphalerite were found in Pirttiselkä, at the north-

Fig. 4. Ice lobes of the Scandinavian icesheet in Finland during deglaciation(from Nenonen 1995). Fan shaped linesindicate major ice flow directions.Location of Viholanniemi area isoutlined by rectangle.

II

94

western end of the Vuotsinsuo mire and the western side of Highway 5 respectively, and,finally, a sphalerite bearing exposure at Viholanniemi by GTK (Makkonen 1991).Together with an ore boulder at the west side of the exposure found during the bedrockmapping, it showed a boulder train that is long and narrow with the length of about 20kmand composed of separate boulder clasters (Fig. 6). It can be estimated from the bouldertrain that the direction of ice movement in the area is about 310°. A narrow ore bouldertrain about 50 km long at Virtasalmi had been reported by Glückert (1973) (cf., Aario &Peuraniemi 1992) (Fig. 5). Salonen (1986) also estimated that the boulder transportdistance in drumlin areas is about 5-17 km.

Fig. 5. Copper ore boulder train in a drumlin landscape (afterGlückert 1973 and cf Aario & Peuraniemi 1992) at Virtasalmi inPieksämäki drumlin field, central Finland.

Fig. 6. Ore boulder train from Viholanniemi(modified after Makkonen 1991).

II

95

All the above suggest on the one hand an active ice flow from the northwest (about310°) with a relatively long transport distance in the study area, and obviously thedominant transportation and deposition of this ice flow on the other.

Till geochemistry and geochemical exploration

Mineralogy of Till

Extensive research into the mineralogy of till in Finland has been published byPeuraniemi (1982, 1987, 1990b,c, 1991), Aario and Peuraniemi (1990), Peuraniemi andIslam (1993), Peuraniemi and Pulkkinen (1993), Lintinen (1995), Peuraniemi et al.(1997) and also many others. In order to investigate the composition of fines of till in thearea, and then to determine the origin of till material, and also to get a detailed andreasonable interpretation of the prospecting results, some chosen samples of till andweathered bedrock were analyzed further by XRF and XRD in the University of Oulu.

The minerals observed in fines of till and weathered bedrock can be classified intothree groups: (1) primary rock-forming minerals; (2) clay minerals; and (3) ore minerals(Fig. 7, 8).

Fig. 7. X-ray diffraction traces of fines of the till samples from Viholanniemi. H=hornblende,T=tremolite, Ph=phlogopite, Sp=sphalerite, Ca=calcite, the rest of the symbols are the same asin Fig. 4.

II

96

Fig. 8. X-ray diffraction traces of fines of the weathered bedrock samples from Viholanniemi.H=hornblende, T=tremolite, Sp=sphalerite, Py=pyrite, Ma=magnetite, the rest of the symbolsare the same as in Fig. 4.

Rock-forming minerals are quartz, feldspars, amphiboles and micas. The presence ofquartz is shown as peaks at 3.34Å and 4.26Å in almost all the samples studied. Feldspars,which are also common minerals in the samples, are mainly albite that has the peaks at3.19Å and sometimes 4.03Å, and microcline that has the peaks at 3.25Å and 3.47Å.Amphiboles present in some samples appear at 3.12Å and 8.42-8.51Å as hornblende and/or tremolite. Muscovite was detected on the basis of peaks at 10.1Å, 5.0Å, as well as3.31Å in some samples and phlogopite was recorded in one sample at 10.1Å and 5.1Å.Clay mineral detectable in samples is mainly chlorite which was found in some sampleswith the d values of 7.1Å, 4.7Å and 3.5Å. From the case of kaolin occurrences showed inFig. 2-3, it is clear that the partial resolution of two peaks of kaolinite and chlorite at3.58Å and 3. 55Å, respectively (Duance & Robert 1989) is present when both of themwere detectable in the samples. It can be inferred that the kaolinite is possibly absent orundetectable in the samples from the project area although it is present in surroundings(Niemelä 1992, Sarapää 1996).

Ore minerals found are sphalerite, pyrite and magnetite that could be measured insome weathered bedrock and till samples. All of the samples were collected in or near themineralized sites and the concentrations of base metals in them all are very high. Calcitewas detected in one sample from the mineralized site by its d values of 3.86Å, 3.03Å and2.46Å (Fig. 7, 30837).

According to the investigations of Finnish tills (Lintinen 1995, Peuraniemi et al. 1993,1997), the mineral composition of till and its variation are mainly controlled by thecomposition of the bedrock from which the till material was derived. The till material in

II

97

the bottommost layer just above the bedrock in the Viholanniemi area shared a highproportion of local material because the mineral compositions of till and weatheredbedrock in the area are quite the same. Generally, the till material in the higher levels ofthe drumlins have been transported far.

Chemical composition

The chemical compositions of the samples studied are listed in tables 1, 2, and 3. Theyshow that the till has contents of SiO2, K2O and TiO2 similar to that of weatheredbedrock, and the contents of SiO2, Al2O3 and TiO2 similar to that of mainly felsic rocks.

Compared to felsic-intermediate volcanics, the weathered bedrock from themineralized area has lower contents of Al, Na, Ca and Ti, but higher of K, Mn and Mg. Inspite of the mixed mineral composition including stable and undecomposed primaryminerals and also secondary minerals (Fig. 7, 8), it is obvious that the removal of therelatively soluble elements Na and Ca accompanied the formation of clay minerals (seeRose et al. 1979) during the weathering. Probably, the decomposed mineral is dominantlyplagioclase. This is evident in the XRD traces of samples with kaolin occurrences in Fig.2 and in their chemical composition. Silicon, Al and K were relatively enriched, whereasMg, Fe, Na, Ca, Mn, Ti and P depleted while the kaolinite (and also possible illite)formed.

On the other hand, the contents of Al, Ca, Na, K and Ti are higher and Fe, Mg, Mn andP are lower in till compared to the weathered bedrock. This is possibly the result of arelative gathering of primary minerals including secondary minerals as well as a smallamount of calcite while the leaching of Fe, Mg, Mn and P as soluble products ofweathering. Åström and Björklund (1995) reported the case of extensive leaching andhigh concentations of Mg, Mn, Fe in solution in western Finland.

The fact is, however, that the preglacial weathering in the study area was relativelyintense but areally varying, particularly variated and controlled by the rock types andtopographic relief and also drainage (Rose et al. 1979).

The presence of trace elements Zn, Cu, Pb, Ni, as well as Au and Ag in till can beattributed to the residual primary ore minerals and to their adsorption onto clay mineralsand secondary oxides and hydroxides (Rose et al. 1979, Jenkins et al. 1980). But thoseelements in the area of no anomalies are related mainly to biotite/phlogopite, feldsparsand secondary minerals. Peuraniemi (1991) reported gold occurring inside goethite inKotkajärvi, southern Finland. Nikkarinen (1991), Lestinen et al. (1991) also cited thepossible supergene gold in Ilomantsi, eastern Finland and Seinäjoki, western Finland.Dilabio (1985) (see Bernier et al. 1989) has documented gold related to the oxidizedfractions of till in Canada. Almost all of the high concentrations of trace elements in thestudy area were detected in the weathered bedrock and only a few till samples had hightrace element contents in the anomalous areas (Table 1, Fig. 7, 8).

II

98

Table 1. Arithmetic m

ean and variation of the chemical elem

ents in the till and weathered bedrock samples from

the project area.

Table 2. Chem

ical composition of w

eathered bedrock with kaolin occurrences.

Table 3. Arithmetic m

eans of the chemical elem

ents in the volcanics in Viholanniemi area.

nSiO

2TiO

2A

l2 O3

Fe2 O3

MnO

MgO

CaO

Na2 O

K2 O

P2 O

5Cu

Ni

Co

ZnPb

Ag

Au

(%)

(%)

(%)

(%)

(%)

(%)

(%)

(%)

(%)

(%)

(ppm)

(ppm)

(ppm)

(ppm)

(ppm)

(ppm)

(ppb)

Till from non-anom

alous area3

73.32 0.42

12.24 2.92

0.051.15

2.59 3.26

1.990.13

1614.3

6 24.7

6.30.40

0.667

Till from anom

aly area9

63.260.73

12.716.38

0.384.27

4.242.37

2.500.18

7432.3

17.7703

18.21.21

2.33

Till from anom

aly area2

65.350.61

12.235.45

0.233.01

2.263.00

2.190.18

9924

171985

615811.3

5

Mean

1465.71

0.6512.54

5.500.29

3.423.60

2.652.35

0.17

Weathered bedrock from

anomaly area

566.21

0.6010.90

7.68 0.32

4.622.53

1.622.10

0.221010

41.817.6

1462105

6.4818.2

nSiO

2TiO

2A

l2 O3

Fe2 O3

MnO

MgO

CaO

Na2 O

K2 O

P2 O

5

(%)

(%)

(%)

(%)

(%)

(%)

(%)

(%)

(%)

(%)

R373/10.8-12.8m

168.39

0.8219.68

1.790.01

1.890.18

0.172.38

0.04

R374/12.8-13.8m

179.38

0.1613.64

0.330.00

0.360.03

0.062.36

0.03

R248/13.4-14.5m

175.36

0.1814.10

1.750.02

2.600.04

0.332.78

0.03

Mean

374.38

0.3915.80

1.290.01

1.620.08

0.192.51

0.03

nSiO

2TiO

2A

l2 O3

Fe2 O3

MnO

MgO

CaO

Na2 O

K2 O

P2 O

5C

uN

iC

oZn

PbA

gA

u

(%)

(%)

(%)

(%)

(%)

(%)

(%)

(%)

(%)

(ppm)

(ppm)

(ppm)

(ppm)

(ppm)

(ppm)

(ppm)

(ppb)

Felsic rocks26

70.20.63

13.64.30

0.121.82

2.724.34

1.240.15

61.27.62

9.6969

24.40.72

5.11

Intermediate rocks

1057.8

1.5215.5

9.45 0.19

4.46 5.33

4.020.73

0.40114

38.219.3

93.423.9

1.075

II

99

Till geochemical exploration

Till geochemical exploration in Viholanniemi was carried out in the winter of 1986 byGTK. All samples were taken by a percussion drilling machine (Cobra) and total of 886samples was collected in an area of about 6 km2. The sampling lines were chosen on thebasis of information shown by outcrops, ore boulders and geophysics. The line distanceswere 25, 50 or 200 m, and the sample spacing along the lines 5, 10, 20 or 40 m. Tillmaterial was the main sampling media but the weathered bedrock, sorted materials andglaciofluvial sand might be taken in some places as the substitution. Sampling alwaystried to reach the interface between the till and underlying bedrock. It gave the depths of0.4-5.4 m. Sample size was small (100-200 g).

Samples were first dried at room temperature in open bags and then in +70oC in thelaboratory. A sieving procedure was not employed, only the large bedrock pieces weretaken away for storing. The rest of the sample was ground in a carbon steel vessel.

Hot aqua regia leaching was adopted for all elements except for Au that was leachedby aqua regia at room temperature before analysis. Cu, Zn, Pb, Co, Ni and Ag wereanalysed by atomic absorption spectrometry (AAS) and Au by graphite-furnace atomicabsorption spectrometry (GAAS). Sulphur was determined with a Leco-sulphur-analyser.

Statistical parameters of the metals measured in the till are presented in Table 4. Allelements seem to be positively skewed, amongst which the marked skewness of Zn, Cuand Pb are notable. It suggests the anomalous distributions of those metals, especially Zn,Cu and Pb in the project area.

Table 4. Statistical parameters for metals in the till at Viholanniemi (x= arithmetic mean, s= standard deviation, c = coefficient of variation, n = number of samples).

The areal distributions of various metals are presented as maps in Fig. 9-15.Apparently, all the metals detected show quite clear and coherent anomalous distributionpatterns and the main parts of those patterns reflect well the Zn mineralization sites in theViholanniemi area. Anomalous contents are also found outside the presently knownmineralization. The main anomalies have dispersal trends of NW to SE, and the totallength of the anomalous area, which is composed of many different local anomalies, isabout 3.4 km.

The strongest anomalies of almost all elements analysed, except for Pb, were found inthe mineralized areas. Silver and Zn are the best two of all, by which their coherent andstrongest anomaly patterns delineate precisely the ore occurrences and the highest

min max x s c n

Co(ppm) 1 54 12 8.1 0.7 886

Cu(ppm) 5 8700 75 431 5.7 886

Ni(ppm) 0.5 439 25 31 1.3 886

Pb(ppm) 1 12300 26 416 16 886

Zn(ppm) 10 11600 129 534 4.1 886

Ag(ppm) 0 127 0.87 4.5 5.2 886

Au(ppb) 0 198 2.8 10 3 6 886

II

100

contents are 127 and 11600 ppm, respectively. A less coherent anomaly belt of Ag and Znparallel to the ore occurrences is located in the eastern part of the area and the highestcontents of them in the belt are 21.4 and 3060 ppm. Pb, Ni and Co have about the sameanomalous patterns of which the main parts not only reflect ore occurrences well, but alsoextend north-west from the northern ore occurrence for about 250 m. In addition, Pb, Coand Ni also show another anomalous belt in the same area with the eastern anomalies ofAg and Zn. Lead gives its highest content of 12300 ppm there. The anomaly patterns ofAu and Cu can be divided into two parts: the southern part is stronger and correspondswell to the southern ore occurrences with the highest contents of 198 ppb and 8700 ppm;the northern part appears as discontinued but widely distributed anomalous points in thenorthern area including the northern ore occurrence.

Fig. 9. Map of the areal distribution of zinc concentration in till at Viholanniemi.

It can be deduced that the principal parts of anomalies which reflect well themineralized sites are related directly to the ore materials coming from ore bodies of theViholanniemi Zn (Au) deposit. In addition, those anomalies did not show evidentdisplacement. Apparently, the materials from the bottom-most layer of till and theweathered bedrock have been well preserved. It is consistent with the reflections of tillcomposition and thus favour the till geochemical prospecting of ore. The practice offinding a deposit in the area has already corroborated the effectiveness of the tillgeochemical survey.

II

101

Fig. 10. Map of the areal distribution of silver concentration in till at Viholanniemi..

Fig. 11. Map of the areal distribution of gold concentration in till at Viholanniemi.

II

102

Fig. 12. Map of the areal distribution of copper concentration in till at Viholanniemi.

Fig. 13. Map of the areal distribution of lead concentration in till at Viholanniemi.

II

103

Fig. 14. Map of the areal distribution of cobalt concentration in till at Viholanniemi.

Fig. 15. Map of the areal distribution of nickel concentration in till at Viholanniemi.

II

104

Conclusions and discussion

The ore boulder train in the Viholanniemi area is about 20 km long and composed ofnarrow and separate boulder clusters with a direction of about 310°. The trends ofdrumlin ridges and also some of the distal axes of lakes in the area are about the same asthe boulder train (Fig. 5, 6). Long and narrow boulder trains are general in the drumlinfields resulting from an active ice flow. The ice movement direction in the area is about310°.

Rock-cored drumlins (Glückert 1987) composed of mainly basal till (also see Nenonen1995) at least at the bottom are dominant in the Viholanniemi area. The preservation ofkaolin occurrences reported by Niemelä (1992) and confirmed by the present studysuggests an intense preglacial chemical weathering and the glacial deposition prevailingover erosion. The relatively small amount of water-bearing minerals (Fig. 3) and thecompositional variation of weathering products suggest that the intensity of the preglacialweathering is areally varied. It is also possible that preglacial weathering products arepreserved only in fracture zones where weathering reached deeper down than in thesurroundings (cf. Sarapää 1996).

The fines of till samples from the project area contain primary minerals such as quartz,microcline, hornblende and/or tremolite, muscovite or phlogopite; clay minerals such aschlorite. Some till samples collected in the mineralized sites also contain sphalerite, orpyrite, or magnetite and calcite. The weathered bedrock has about the same mineralcomposition as till. It is apparent that minerals which are unsusceptible to weathering orare undecomposed during the weathering are presented together with the new mineralssuch as clay minerals and secondary Fe-Mn minerals (see Tarvainen 1995) in till.

Till and weathered bedrock samples have similar contents of SiO2, K2O and TiO2, andthe similar levels of SiO2, Al2O3 and TiO2 are also obvious between till and unweatheredfelsic rocks. During the weathering process, the relatively soluble elements Na, Ca wereremoved while rock-forming minerals decomposed and secondary minerals formed (seeRose et al. 1979). Particularly, Si, Al and K were concentrated, whereas Mg, Fe, Na, Ca,Mn, Ti and P depleted when kaolinite formed in places. Due to the relative concentrationcaused by mixed mineral composition (possibly including carbonates) and the leaching ofFe, Mg, Mn and P, elements Al, Na and Ca were enriched in till in the project area.

The conclusion is that the till in the bottom-most layer just above the bedrock in theproject area consists mainly of local material, although the till materials in the drumlinfields are overal far-transported (Glückert 1987, Aario & Peuraniemi 1992).

Trace elements Zn, Cu, Pb, Au, Ag, Ni and Co are related to residual primary mineralsand secondary minerals. The main part of those elements present in till in the non-anomalous area can be attributed mainly to the adsorption onto clay minerals, secondaryoxides and hydroxides. The high contents of those elements in the project area weredetected in weathered bedrock samples and a few till samples, and they are relateddirectly to the ore material.

Boulder tracing, and till geochemical exploration in the area, proved to be effective inprospecting for ore. All metals show clear and coherent anomalies in till and well reflectthe Zn mineralization bodies in the Viholanniemi. The anomalies occur as a beltcomposed of different local anomalies with a dispersal trend of NW to SE and a total

II

105

length of about 3.4 km. Almost all elements, except Pb have their strongest anomalies juston or near to ore sub-outcrops. Ag and Zn are the most crucial indicators of oreoccurrences compared to Au, Cu, Pb, Ni and Co.

The anomalies are of quite a local nature and they closely reflect the ore occurrences,anomalies in the eastern part of the project area are worth further study, because Zn, Ag,Pb, Ni and Co altogether show anomalies there. Moreover, the highest content of Pb isalso there.

However, it should be taken into account also that most of the strongly anomaloussamples in mineralized sites are from the weathered bedrock, while only a few of themare from till. In contrast, the anomalous samples in the eastern anomaly are mainly fromtill. Besides, Au and Cu show no regular distribution patterns, as in mineralized sites.Thereby the differences between two anomalous areas are appreciable.

In addition, it is obvious that the coherent anomalous distribution patterns of Ag, Zn,Pb, Au, Cu reflecting the mineralized sites are well correspondent to the anomalouspatterns of IP if we consider the geophysical exploration in the area carried out by GTK.Unfortunately, these identically anomalous patterns outside the mineralized sites cannotbe found. So, as far as the information goes, the clear potential significance of the easternanomalies is still difficult to figure out.

On the other hand, however, from the prospecting point of view, those anomalies in theeastern part and northern part shown by Cu and Au are all still worth detailedinvestigation. Most anomalous points of Cu and Au in the northern area were detected inthe weathered bedrock samples and there appears no evidence to connect those of Au tothe "nugget effect".

Acknowledgements

The Geological Survey of Finland has given me the permission to do the study andprovided all samples and data involved, bedrock samples were also analysed there.Mineralogical and geochemical analyses have been performed in the laboratories of theDepartments of Geoscience and Electron Optics of the University of Oulu. I wish toexpress my sincere thanks to the institutes involved.

I would like to thank Dr. Elias Ekdahl, Prof. Risto Aario, Prof. Vesa Peuraniemi andDr. Hannu Makkonen for their invaluable help. Risto and Vesa instructed me in doing thisstudy and made useful comments on the text. Elias and Hannu also made many usefulsuggestions and checked the manuscript. Dr. Kauko Holappa and Mr. Olli Taikina-Ahoassisted me with my laboratory work. Ms. Fan Jiao, Ms. Li Chunxia and Ms. Qu Lilihelped me to draw the figures. I also wish to express my gratitude to all other personsinvolved.

References

Aario R, Forsström L & Lahermo P (1974) Glacial landforms with special reference to drumlins andfluting in Koillismaa, Finland. Geol Surv Finland Bull 273, 30 p.

II

106

Aario R & Forsström L (1979a) Glacial stratigraphy of Koillismaa and north Kainuu, Finland. Fennia157(2): 1-49.

Aario R & Forsström L (1979b) Deglaciation stratigraphy of Koillismaa and north Kainuu, Finland.Nordia 13(3): 3-11.

Aario R (1990) Morainic landforms in northern Finland. In: Aario R (ed) Glacial heritage of northernFinland. Excursion guide: 13-28.

Aario R & Peuraniemi V (1990) Secondary copper iodide in till in the Löytösuo area, Ylikiiminki,Finland. Applied Geol 5: 347-355.

Aario R & Peuraniemi V (1992) Glacial dispersal of till constituents in morainic landforms ofdifferent types. Geomor 6: 9-25.

Bernier MA & Webber GR (1989) Mineralogical and geochemical analysis of shallow overburden asan aid to gold exploration in south western Gaspesie, Quebec, Canada. J Geoch Explor 34: 115-145.

Ekdahl E (1982) Glacial history and geochemistry of the till/bedrock interface in prospecting in thePielavesi area of central Finland. In: Davenport PH (ed) Prospecting in areas of glaciated terrain-1982. The Can Inst of Min & Metal, p 213-227.

Ekdahl E (1993) Early proterozoic Karelian and Svecofennian formations and the evolution of theRaahe-Ladoge Ore Zone, based on the Pielavesi area, central Finland, Geol Surv Finland Bull 373,137 p.

Glückert G (1987) The drumlins of central Finland. In: Menzies J & Rose J (eds) DrumlinSymposium, Proceedings of the drumlin symposium/First international conference onGeomorphology/Manchester 1985, p 291-294.

Huang B (1987) Mineral identification handbook of differential thermal analysis (in Chinese),Scientific Publishing House.

Jenkins DA & Jones RGW (1980) Trace elements in rock, soil, plants and animals, Introduction. In:Davies BE (ed) Applied soil trace elements. John Wiley & Sons, p 1-18.

Kauranne LK (1951) Outokummun lohkarevastan moreenin mineraalikoostumuksesta. Manuscr.Arch Univ Helsinki, Dept Geol, 20 p (in Finnish).

Kauranne LK (1959) Pedogeochemical prospecting in glaciated terrain. Geol Surv Finland, Bull 184:1-10.

Klassen RA & Murton Jb (1996) Quaternary geology of the Buchans area, Newfoundland,implication for mineral exploration. Can J Earth Sci 33: 363-377.

Koljonen T (1992) Historical development of geochemistry in Finland. In: Koljonen T (ed) Thegeochemical atlas of Finland, Part 2: Till, Geol Surv Finland. Espoo, 13.

Korsman K, Koistinen T, Kohonen J. Wennerström M, Ekdahl E, Honkamo M, Idman H & PekkalaY (eds) (1997) Bedrock map of Finland 1:1 000 000. Espoo: Geol Surv Finland.

Lestinen P, Kontas E, Niskavaara H & Virtasalo J (1991) Till geochemistry of gold, arsnic andantimony in the Seinäjoki district, Western Finland. J Geoch Explor 39: 343-361.

Lintinen P (1995) Origin and physical characteristics of till fines in Finland. Geol Surv Finland Bull379. 83 p.

Makkonen H (1991) Studies of the Viholanniemi Zn deposit in Joroinen 1984-1988. Unpublishedresearch report, Geol Surv Finland.

McClenaghan MB (1994) Till geochemistry in areas of thick drift and its application to goldexploration, Matheson Area, Northeastern Ontario. Explor Min Geol 3, No. 1: 17-30.

McClenaghan MB & Dilabio RNW (1993) Till geochemistry and its implications for mineralexploration:south-eastern cape breton island, nova scotia, Canada. Quater Inter 20: 107-122.

McClenaghan MB, Thorleifson LH & Dilabio RNW (1997) Till geochemical and indicator mineralmethods in mineral exploration. In: Gubins AG (ed) Proceeding of exploration 97: fourthdecennial international conference on mineral exploration, p 233-248.

II

107

Moore DM & Reynolds JrRC (1989) X- ray diffraction and the identification and analysis of clayminerals, Oxford. New York, 332 p.

Nenonen K (1995) Pleistocene stratigraphy of southern Finland. In: Ehlers J, Kozarski S & GibbardP (eds) Glacial deposits in northeast Europe, p 11-28.

Niemelä M (1992) Joroisten Tervajoensuon kaoliinitutkimukset vuosina 1990-1991 (in Finnish).Unpublished research report, Geol Surv Finland, 47 p.

Nikkarinen M (1991) Size, form and composition of gold grains in glacial drift in Ilomantsi,easternFinland. J Geoch Explor 39: 295-302.

Norton FH (1939) Critical study of the differential method for the identification of the clay minerals,J. Am. Ceram, Soc., 22: 54-63. In: Wendlandt WW & Collins LW (eds) 1976, Thermal analysis,Dowden, Hutchinson & Ross, Inc.

Papunen H (ed) (1990) Report of the zinc project. Inst. of Geol. and Mineralogy. Publ n 22, Universityof Turku, Finland, 143 p.

Peuraniemi V (1982) Geochemistry of till and mode of occurrence of metals in some moraine typesin Finland. Geol Surv Finland, Bull 332, 75p.

Peuraniemi V (1987) Interpretation of heavy mineral geochemical results from till. Geol SurvFinland, Spec Pap 3, p 169-179.

Peuraniemi V (1990a) On boulder transport in drumlins, Rogen moraines and Sevetti moraines. In:Aario R (ed) Glacial heritage of northern Finland, Excursion guide, 29-32.

Peuraniemi V (1990b) Heavy minerals in glacial material. In: Kujansuu R & Saarnisto M (eds)Geological indicator tracing: 165-185.

Peuraniemi V (1990c) The weathering crust in Finnish Lapland and its influence on the compositionof glacial deposits. In: Aario R (ed) Glacial heritage of northern Finland. Excursion guide: 7-11.

Peuraniemi V (1991) Geochemistry of till and humus in the Kotkajärvi Cu-Co-Au prospect, Kalvola,southern Finland. J Geoch Explor 39: 363-378.

Peuraniemi V & Islam MR (1993) The weathering crust in the Vuotso - Tankavaara area - The firstevidence on the occurrence of halloysite in Finland. Chem Geol 107: 307-311.

Peuraniemi V & Pulkkinen P (1993) Preglacial weathering crust in Ostrobothnia, western Finlandwith special reference to the Raudaskylä occurrence. Chem Geol 107: 313-316.

Peuraniemi V, Aario R & Pulkkinen P (1997) Mineralogy and geochemistry of the clay fraction oftill in northern Finland. Sediment Geol 111: 313-327.

Punkari M (1980) The ice lobes of the Scandinavian ice sheet during the deglaciation in southFinland. Boreas 9: 307-310.

Rose AW, Hawks HE & Webb JS (1979) Geochemistry in mineral exploration (second edition).Academic Press (London), 657 p.

Saarnisto M & Salonen V-P (1995) Glacial history of Finland. In: Ehlers J, Kozarski S & Gibbard P(eds) Glacial deposits in north-east Europe, p 3-10.

Salminen R (1995) Alueellinen geokemiallinen kartoitus Suomessa vuosina 1982-1994. Summary:Regional geochemical mapping in Finland in 1982-1994. Geol Surv Finland, Report ofinvestigation 130, 47 p.

Salminen R & Tarvainen T (1995) Geochemical mapping and databases in Finland. J Geoch Explor55, Nos 1-3: 321-327.

Salonen V-P (1986) Glacial transport distance distributions of surface boulders in Finland. Geol SurvFinland, Bull 338, 57 p.

Saltikoff B (1992) Glacial ore boulders in mineral exploration, in Koljonen, T. (ed), The geochemicalatlas of Finland, Part 2: Till. Geol Surv Finland, Espoo, 13.

Sarapää O (1996) Proterozoic primary kaolin deposits at Virtasalmi, south-eastern Finland. Geol SurvFinland, Espoo, 12 p.

Stigzelius H (1987) Otto Trustedt and his impact on the Finnish mining industry, Geol Surv Finland,Spec Pap 1: 5-14.

II

108

Tarvainen T (1995) The geochemical correlation between coarse and fine fractions of till in southernFinland. J Geoch Explor 54: 187-198.

Vaasjoki M & Sakko M (1988) Evolution of the Raahe-Ladoga zone in Finland: Isotopic constrains.In: Korsman K (ed) Tectono-metamorphic evolution of the Raahe-Ladoga zone. Geol SurvFinland, Bull 343: 7-32.

Åström M & Björklund A (1995) Impact of acid sulfate soils on stream water geochemistry in westernFinland. J Geoch Explor 55: 163-170.

PART III

III

111

Geochemical exploration and study of the Keketale lead-zinc deposit hosted by sedimentary rocks in the volcano-

sedimentary formation in North-Western China(A review of previous studies including papers 2 and 3)

Xiping Zhang

ABSTRACT: The Keketale Pb-Zn deposit is a stratabound sulphide deposit hosted by sedimentaryrocks in the volcano-sedimentary formation of the Devonian age in the Maizi syncline within theSouthern Edge of Altay. Volcanic rocks of a calc-alkaline series are the products of bimodalvolcanism and the Pb-Zn mineralization is related to the felsic eruptions in the early stage ofvolcanism. The original host rocks are those of sedimentary rocks such as silicalite and iron bearingcarbonate rocks formed in hot water. Meta-volcanic breccia, meta-agglomerate, meta-breccic tuffand meta-felsic lava as well as meta-tuff and mica quartz schist underlie the host rocks.Disseminated ores dominate and other types include taxitic and massive, also banded, breccia aswell as net-veined. The alteration includes carbonation, sericitization, silicification anddisseminated pyrite. Epidotization appears outside the ore bodies.

Stream sediment and soil surveys showed a geochemical anomaly area of about 200 km2

composed of coherent Pb, Zn, As, Ag, Cu, Cd and Mn and a ring anomalous belt of Pb and Zncorresponding to the Maizi syncline and the volcano-sedimentary formation respectively. Theappearance of a Cd anomaly together with a concentrated center of Pb, Zn, As, Ag and Mn indicatesin most circumstances the ore outcrop. The element concentrations of volcano-sedimentaryformation and the chondrite-normalized REE patterns of ores and felsic lava below the host rockssuggest clearly a leaching out of Pb, Zn etc. and the metal sources of the deposit thus could beconnected to this leaching process. The deposit was formed in the sedimentary basin near thevolcanic center with extensive bacterial activity.

Coherent primary geochemical anomalies of the deposit include (1) Pb, Zn, Ag, As, Sb, Hg, Mn,Cd, Mo, TFe, CaO and MgO; and (2) depleted Na2O.The rock-forming element patterns reflect themain wall-rock alteration and also possibly the environment characters of ore precipitation. Theanomalies of Cd, Mo and Na2O have their distinct significance on ore deposit siting and also onprospecting.

Introduction

Several important deposits have been found in the Southern Edge of Altay (SEA) innorth-western China during extensive explorations in the past twenty years. Thosedeposits include Ashele Cu-Zn deposit, Tiemierte and Abagong polymetallic ore deposits,Keketale Pb-Zn deposit, Duolanasayi Au deposit, Saerbulake and Saidu Au deposits.Keketale Pb-Zn deposit was found by China National Non-ferrous Metals IndustryCorporation (CNNC) in 1986. In 1985, a project of stream sediment geochemicalexploration over 3250km2 in SEA was carried out by CNNC and an associatedgeochemical anomaly of Pb, Zn, Ag, As, Cu, Cd and Mn, which is about 3-8 km wideand 40 km long in the Maizi district was discovered. At the same time as detailedgeochemical exploration in the Maizi district, a stratiform gossan was met in the district.It was corroborated later, by drilling, that the existence of a stratabound Pb-Zn sulphide

III

112

deposit hosted by sedimentary rocks in the volcano-sedimentary formation of LowerDevonian. Now the reserves of the deposit have been estimated at about 300 0000 t(Pb+Zn) (Wang et al. 1998).

The author took part in the geochemical exploration in 1985 and made geochemicalstudy after the deposit had been found.

Fig. 1. Location of the study area (outlined by rectangle) on simplified geological map of theAltay area, north-western China (after Chen et al. 1996). 1, Cenozoic; 2, Cretaceous; 3,Jurassic; 4, Permian; 5, Carboniferous; 6, Devonian; 7, Devonian-Silurian; 8, Silurian-Ordovician; 9, Proterozoic; 10, Paleoproterozoic(1-10 are all supracrustal); 11, Granitoids; 12,Diabase; 13, Faults.

The geological setting

SEA is one of the most important metallogenic belts of Hercynian orogeny in China andhas attracted the attention of geologists from the 80's. During the past twenty years, it hasbeen considered to connect to the island arc and continental margin although the viewsare divergent on geotectonic setting. Li et al. (1982) and Li and Wang (1983) suggestedthat SEA is an active continental margin accreted from the southern part of the Siberiaplate; Liu (1984) interpreted the belt as an island arc of active continental marginproduced by subduction of Junggar paleo-oceanic crust. Based on these interpretations,

III

113

the Ashele Cu-Zn zone related to the marine bimodal volcanism of the early-midDevonian has been considered as the island arc belt, and also the extension of marginal-Ertix belt of Kazakhstan; the Keketale Pb-Zn zone related to the marine felsic-intermediate volcanism of the early Devonian was considered as the northern edge of theback arc basin (Jiang & Liu 1992, Jiang 1994, Zhang 1987). Recently, however, thevolcano-sedimentary formation of the late Paleozoic in SEA was interpreted as theproduction of continental margin rift (Han & He 1991, He et al. 1994, Chen et al. 1995,1996, Wang et al. 1998, 1999).

Polymetallic ore deposits found in SEA occur mainly in four volcano- sedimentarybasins of the Devonian. From east to west, those basins are Maizi, Kelang,Chonhuer andAshele (Fig. 2). The Keketale Pb-Zn deposit is situated in the south-eastern part of theMaizi syncline, about 95 km southeast to Aletai. The volcano-sedimentary formation inKeketale has its greatest stratigraphical thickness in the basin, and volcanic breccia andagglomerate are also mainly found there. According to Jiang and Liu (1992) and Chen etal. (1995), the thickness of the formation in the north-western part of the basin is less thanthat in Keketale, and the sedimentary rocks, particularly those of carbonate, are dominantthere.

Fig. 2. Metallogenic belts and epochs in the southern edge of Altay. The map is simplified afterChen et al. (1996) and Wang et al. (1998). The data is from Chen et al. (1996) and Ding (1999).1. Volcanic-sedimentary basin; 2. Fault.

III

114

Volcanic eruption in the Maizi basin is mainly felsic in early stage and felsic,intermediate and mafic in later, and the rocks are of bimodal assemblage of calc-alkalineseries (Wu 1992, Jiang 1993). Volcanic rocks include felsic breccia, agglomerate, lavaand pyroclastics, as well as mafic lava and pyroclastics. There was a relative long periodof inactivity between the early and later eruptions. The volcano-sedimentary formation isabout 3000 m in stratigraphical thickness (Wu 1992). The Keketale Pb-Zn deposit occursin the sedimentary rocks with several thin layers of volcanics formed during the inactiveperiod of volcanism. The stratigraphical thickness of the sedimentary rocks is up to 300m.The deposit has been suggested as a transitional type between the stratabound depositshosted by volcanics and sedimentary rocks (Jiang & Liu 1992, Jiang 1994). The volcano-sedimentary formation experienced regional metamorphism of greenschist-lowamphibolite facies (Wu 1992).

Ore deposit geology

The host rocks of the Keketale Pb-Zn deposit are mainly composed of biotite quartzschist with granoblasite (contains calcite, diopside and garnet locally) intercalations, andintercalated also diopside marble, garnet epidote marble, meta-tuff, meta- tuffaceoussiltstone and meta-siltstone (Han 1992, Wang et al. 1998). The protoliths are sedimentaryrocks such as calcareous-argillaceous sandstone, and siliceous rock and iron bearingcarbonate rocks formed in hot water (Jiang,1992, 1994) (see the explanation in Synopsis).Meta-volcanic breccia, meta-agglomerate, meta-breccia tuff and meta-felsic lava as wellas meta tuff and mica quartz schist underlie the host rocks (Han 1992, Wang et al. 1998)(Fig. 3).

Fig. 3. Simplified geological map of the Keketale area (after Han 1990 and Wang et al. 1998).�=Granite; CT=Meta crystal tuff; FL=Meta felsic lava; BA=Volcanic breccia and agglomerate;Tu=Tuff; Ss=Meta calcareous sandstone and siltstone; Mb=Marble; Bsc=Biotite schist;PbZn=Pb-Zn ore.

III

115

Ore bodies that occur as stratiform and stratiform-like with the NE direction of dip(turning to SW in deep) are 50-1350 m in length, 5-80 m in breadth and extend down to200-750 m in inclined depth (Fig. 4). On the surface, they appear as gossan of reddish andyellowish brown and the gossan belt extends up to 810 m along its strike. Disseminatedores are dominant and then taxitic and massive, and also sometimes banded, breccia aswell as net-veined. Pyrite, pyrrhotite, sphalerite and galena constitute major ore mineralsand arsenopyrite, chalcopyrite, tetrahedrite, bornite and marcasite make up the minors.Quartz, calcite, plagioclase, sericite, diopside, tremolite, epidote, biotite and less barite,fluorite and gypsum compose the gangue. Metal contents are Pb: 0.379-4.95%, Zn: 0.40-10.79% and associated elements are S, Ag (max:222g/t) and Cd as well (Han 1992, Wanget al. 1998).

Fig. 4. Cross-section of the ore body on profile of No.7 in the Keketale lead-zinc deposit, north-western China (after Han, 1990 and Wang et al, 1998). 1, Meta felsic lava; 2, Meta breccia tuff;3, Meta tuffite; 4, Leucogranoblasite; 5, Biotite granoblasite; 6, Biotite-quartz schist; 7, Marble;8, Meta calcareous sandstone; 9, Meta sandstone; 10, Mica schist; 11, Plagioclase-biotite schist;12, Biotite-epidote granoblasite; 13, Pegmatite; 14, Garnet, epidote, tremolite, actinolite,chlorite and diopside; 15, Silification, muscovite and calcite; 16, Oxidized zone of Pb-Zn ore;17, Pb-Zn ore; 18, High-grade Pb-Zn ore; 19, Inferred primary Pb-Zn ore.

III

116

Carbonation, sericitization, silicification and disseminated pyrite occur with themineralization. Epidotization appears outside the ore bodies and sericitization as well aspotassium feldspar are present in the volcanics below the host rocks (Han 1992, Wang etal. 1998).

Geochemical exploration and the discovery of the deposit

Stream sediment geochemical exploration in an area more than 3250 km2 in the centralpart of SEA was carried out by CNNC in 1985. A total of 12250 samples were taken,mainly in the first-order and second-order streams, and a few in the third-order streams,with average density of about 4 samples/km2. After taking away big fragments of rocks,the samples were dried outside and sieved. Part of the <0.42mm fraction was ground to0.097mm and the rest stored. Samples were analyzed by inductively coupled plasmaatomic emission spectrometry (ICP-AES: Zn, Cu, Cd, Mn, V, Ti, Cr, Co, Be, Ba and Sr),atomic absorption spectrophotometry (AAS: Pb, Ag, Au, Ni,), atomic fluorescencespectrometry (AFS: As and Hg), polarography (POL: W and Sn) as well. Some rocksamples were analyzed by ICP-AES for TFe, SiO2, CaO, MgO, MnO, Na2O, K2O andAl2O3. Before analyses, HF+H2SO4 and HF+HNO3 leaching for ICP-AES and AASrespectively, hot aqua regia leaching for AFS as well as Na2O2 leaching for POL analyseswere employed. For deposit geochemical study, except for the elements mentioned abovethe samples were also analyzed Se and REE(ICP-MS), Tl, In, Ga and Ge(AAS), Sb andBi(AFS), Mo(POL), S and Fe(Volumetry).

The elements analyzed were calculated for their average values using 2000 randomsamples (excluded very high and low values) and thresholds using the average value plustwo times the standard deviation. An anomaly area of about 40 km long and 3-8 km widecomposed of Pb, Zn, Ag, As, Cu, Cd, Mn was found in the Maizi district (Fig. 5,6).Extremely coherent anomalies of Pb, Zn, As, Ag, Mn correspond in their concentratedcenter to small anomalies of Cd. The eastern part of the anomaly area is about 27 km by4-8 km and the concentrated center of Pb, Zn, Ag, As anomalies (max: 270 ppm, 1608ppm, 0.476 ppm, 59 ppm) correspond well to Cd anomalies appearing in six sites evenlyspaced (Fig. 7). Because a similar anomalous association was met in the Tiemuerte Pb-Znpolymetallic occurrence about 80km northwest of Keketale and also a Pb occurrence ispresent near to the anomalies, the attention of the explorers was therefore by analogyattracted to the anomalies in Keketale.

III

117

Fig. 5. Anomaly of lead in stream sediments in the Maizi district (modified after Wang et al.1998).

Fig. 6. Anomaly of zinc in stream sediments in the Maizi district (modified after Wang et al.1998).

III

118

Fig. 7. Anomalies of selected elements in stream sediments at Keketale. The sample site ismarked by a small round point (modified after Zhang et al. 1990). a) Pb (solid line): 30, 60, 120,240 ppm; Ag (dotted line): 0.05, 0.1, 0.2, 0.4ppm; b) Zn (solid line): 120, 240, 480, 1000 ppm; Cd(dotted line): 0.6, 1.2, 2.4 ppm.

Detailed explorations including a soil geochemical survey with a grid of 200 m by 40m and mapping were made in 1986. The results not only showed a round anomalous beltof Pb, Zn related to the volcano-sedimentary formation of the lower Devonian in theMaizi syncline (Fig. 8), but also indicated a clear correlation between the anomalous areaof the stream sediment survey and the syncline. At the same time, a stratiform gossan ofreddish and yellowish brown colour was found some hundreds of meters northeast to a Cdanomaly. A gossan sample gave the metal contents of Pb+Zn>10%, and thus it wasconcluded that the anomalies of the area originate mainly from a Pb-Zn mineralization.Explorations followed, such as trenching, a geochemical survey with a grid of 100m by20m and geophysical survey (SP) indicated the anomalies of high polarization, lowresistivity, negative SP and concentrated Pb and Zn above the gossan. The informationabove led to the first drilling and the primary Pb-Zn sulphide ore body was met.

Fig. 8. Anomaly of lead (solid line) and zinc (dotted line) in soil at Keketale (modified afterWang 1996).

III

119

Deposit geochemistry

An interesting phenomenon is seen from the element variations in the time-strata profilewithin the area of 3250 km2. The major ore-forming elements including Pb, Zn, Cu, (Au)and some trace elements such as Sb, Cr, Ni, Co display a clear valley floor correspondingto the Lower Devonian in variation curves of elements in the time-strata profile. A similarsituation is also seen from the variations of TFe, MgO and MnO. However, the curve ofSiO2 has its highest point at the Lower Devonian (Fig. 9) (Zhang et al. 1990). Becausethe Pb-Zn mineralization related to the volcanism of the Lower Devonian is verycommon, it is reasonable to assume that the eluviation of sediments by leaking sea-waterwas general in the region at that time.

Fig. 9. Variation of elements in the time-strata profile within the exploration area (3250 km) inSouthern Edge of Altay. S2-3 =Mid-upper Silurian; D1=Lower Devonian; D2=Mid Devonian;C3K=Upper Carboniferous; P=Permian (data after Zhang et al. 1990).

120

Table 1. Averaged element contents of rocks from

the No. 7 profile in the Keketale ore district. Number of sam

ples in parentheses (Zhang etal. 1990).

Table 2. Representative analyses of trace elements in sulphides of K

eketale Pb-Zn deposit (ppm).

No

Rock

Cu

PbZn

WSn

Mo

As

SbBe

Hg

Au

Ag

Ba

Mn

Cr

Ni

Co

Cd

1M

arble (5)14.2

219425

2.430.508

0.314

2.180.786

43.60.48

0.48235

404619.3

10.73.39

2.222

Meta tuff (8)

35.527.9

2353.34

2.780.391

3.590.675

2.5737.2

<0.30.121

504945

42.718.5

11.70.439

3Epidote biotite quartz schist (7)

74.749.9

3342.49

2.843.50

7.542.47

22.70.807

0.2831671

60.225.7

21.52.43

4G

arnet biotite quartz schist (4)22.1

220708

4.142.2

1.2112.2

3.363.33

381.39

0.8511696

228579.2

34.021.1

0.2595

Meta tuff (5)

19.622.2

2994.21

1.390.98

13.30.958

2.0420

0.240.083

6161281

41.519.6

13.00.259

6M

eta breccia tuff (4)15.2

20.578

2.272.83

1.5917.3

0.3432.30

32.50.538

0.103119

56832.6

18.611.7

0.0347

Meta felsic lava (8)

16.219.4

362.75

2.621.66

5.050.244

1.3526

0.2690.071

644462

20.315.5

5.870.045

8R

egional average value (1000)20.2

40.565.2

1.152.83

0.643.92

0.371.10

400.6

0.043346

46.024.4

12.71.28

Crustal abundance (Taylor, 1964)

5512.5

701.5

21.5

1.50.2

2.880

4.000.07

425950

75.025.0

0.2A

u and Hg:

�10 -9, K2 O

and Na2 O

: %, O

thers: �10 -6, 4 and 5 are hanging w

all and footwall rock respectively.

Sample

Mineral

PositionN

otesS(%

)Se

CoN

iA

gPb

ZnSn

As

TlSb

InC

dBi

Ga

Ge

Mo

CuM

nFe(%

)V

S/SeC

o/Ni

15-8607

pyriteZK

7-7,412.39-466.0m

massive

48.321.1

915

6>3000

4050105

48020

4392730.6

25-8601

pyriteZK

7-7,136.66-149.15m

massive

47.010.8

>30015

10.5>3000

>3000102

210021

587625>20

3ZK

7-9-26pyrite

ZK7-9,585.49m

banded48.27

10.0>200

51<3

34.525

4.248

1.2<3

9.666

<1048270

>4.04

ZK93-3-5

pyriteZK

9-3,277.40mbanded

48.369.5

>20090

0.45150

25<2

114<1

<342

45<10

50905>2.0

5ZK

7-9-18pyrite

ZK7-9,420.0m

massive

49.090.62

3321

0.3810

7503.6

7801.98

2413.2

43<10

7917441.57

6ZK

7-2-2pyrite

ZK7--2,64.0m

dissemi-

nated48.97

2.639

1021.1

450<20

3480

3.9<3

3630

<10188346

0.38

7ZK

15-3-10pyrite

ZK15-3,284.68m

banded48.87

2.121

450.45

870180

2.1168

2.4<3

8742

<10232714

0.478

ZK7-9-28

pyriteZK

7-9,622.10mdissem

i-nated

48.107.9

16245

<0.342

99<2

301

<372

42<10

608863.6

9ZK

7-2-1pyrite

ZK7-2,53.9m

veined48.40

2.03

<30.51

45075

<2315

1.2<3

78<10

<10242000

1.010

ZK15-7-26

pyriteZK

15-7,404.52mm

assive47.99

0.730

1912

96002040

2840

951

24.660

<10685571

1.5811

ZK15-7-

27Agalena

ZK15-7,425.0m

veined13.14

<0.1<3

<3>30

>10000126

33120

>30>300

<1>100

<127

<100<10

>13140001.0

12ZK

3-7-9galena

ZK3-7,232.0m

veined12.67

0.2<3

<3>30

>1000020

4.2330

12>300

20>100

138

<100<10

6335001.0

13ZK

7-0-4sphalerite

ZK7-0,33.25m

veined30.89

0.521

6.62.7

5400>10000

<26.9

7.515.6

>30>300

<3<1

19266

>10000<10

33617800

3.1814

ZK15-7-

25Asphalerite

ZK15-7,399.0m

massive

31.351.2

2410.2

<0.372

>10000<2

31

319

>300<3

<115.6

78>10000

<10<10

2612502.35

1-2 from Zhang et al. (1990), 3-14 from

Han (1992).

III

121

The geochemical cross-section (Table 1, excluded the samples above the ore bodies)displays in most of the rocks in the volcano-sedimentary formation high contents of Pb,Zn, As, Sb, Cd, Ba, Mn and W, and low contents of Cr, Ni, Co, Cu, Mo and Sn.Compared to the average concentrations of unmineralized rocks taken within the area of3250 km2, Pb, Zn, Ag, As, Sb, Ba and W are concentrated in the rocks of the upper partof the formation including the host rocks (Table 1:1-5); Pb, Zn, Sb, Cd, however, havetheir lowest contents particularly in felsic meta-lava below the host rocks. It clearlysuggests a leaching out of Pb and Zn etc. from the felsic volcanics (Zhang et al. 1990,1996).

Trace elements in the ores are listed in Table 2. Ag, Tl, Sb, Bi are mainly found ingalena and In, Cd and Mn in sphalerite. Pyrite in the ore bodies has varying Co/Ni ratiosand high S/Se ratios, which indicates on one hand a variety of origins of pyrite and on theother dominantly sedimentary origins (Tu et al. 1984, Tu 1987, Xu & Shao 1980). It isalso confirmed that Ag, Sb, Cd, Tl, Bi, Mn, As, In, Cu, Mo, Hg are associated with thePb-Zn mineralization (Zhang et al. 1990, 1996, Han 1992).

Except for the fluorite and barite bearing ore which have the highest �REE, ores havelower �REE than rocks. The taxitic and massive ores that are mainly composed ofsulphides show the lowest �REE. The chondrite-normalized patterns of ores (most have�Eu<1 and two have �Ce<1, Table 3, Fig. 10a) (Zhang et al. 1990, Zhang & Chen 1995)are clearly different from each other due to their geneses and compositions. Massive anddisseminated ores have similar patterns with those of felsic lava (�Eu<1, �Ce<1) belowthe host rocks in the Maizi area (Fig. 11) although their �REE differ greatly( mostlycaused of added sulphides). It has been found that the lava below the host rocks ischaracterized by negative anomalies of Eu and Ce, however the lava above the host rockshas positive Ce and negative Eu anomalies (Wang et al. 1998). Rocks, including alteredones, nevertheless show quite similar patterns (Fig. 10b), but altered rocks display thetrend of depletion of Eu (Fig. 10c) relative to unaltered ones. These characters implyfurther a close relationship between the Pb-Zn mineralization and felsic lava below thehost rocks, and also possibly the leaching of Eu during the wall-rock alteration.

III

122

Fig. 10. Chondrite-normalized REE patterns of (a) ores, (b) rocks and (c) Curves showing REEratio of altered rocks to unaltered rocks (r1: to hanging wallrock; r2: to the bottom-most rockof the volcano-sedimentary formation) from the Keketale Pb-Zn deposit (data after Zhang etal. 1990 and Zhang & Chen 1995).

III

123

Fig. 11. Chondrite-normalized REE patterns of volcanics in the Maizi district (after Wang et al.1998).

Statistical data of the elements analysed in the rock samples of drill cores shows thatthe variations of Pb and Zn are related to that of rock-forming elements: from the rocks� wall rocks near ores � ore body, Na2O drops, and CaO and MgO increase graduallyas Pb and Zn increase (Table 4, Fig. 12).

The primary geochemical anomalies of the deposit are composed of concentrated traceand major elements such as Pb, Zn, Ag, As, Sb, Cd, Mo, Hg, Mn, Au, Cu, W, Be, Ca , Mgand (TFe), and depleted major elements of Na (Fig. 12, 13).

Fig. 12. Variation of selected elements in the drill core of ZK7-7 at the Keketale Pb-Zn deposit.1=Meta tuffite; 2=Plagioclase-biotite schist; 3=Biotite schist; 4=Granoblasite; 5=Marble;6=Mica schist; 7=Garnet, epidote, silification; 8=Pb-Zn ores (after Zhang et al. 1990).

124

Table 3. Representative analyses of REE in the samples from

the Keketale district (ppm

) (Zhang et al. 1990).

Table 4. Statistical data of elements in the Keketale Pb-Zn deposit (Zhang et al. 1990).

12

34

56

78

910

11La

3.984.47

11.2915.72

76.7120.56

17.1319.57

16.6218.62

15.66C

e7.55

9.9825.21

36.60139.62

48.1640.00

48.8742.86

45.2535.92

Pr0.83

0.983.01

4.0215.25

4.734.37

4.825.09

4.343.86

Nd

3.234.33

14.6416.20

57.1219.59

18.3319.65

20.9920.26

16.78Sm

0.791.16

3.733.14

10.283.93

4.274.11

3.964.69

3.92Eu

0.150.37

1.270.39

4.640.71

0.930.69

0.791.07

0.97G

d0.91

1.253.60

3.239.81

4.535.01

5.033.68

5.124.39

Tb<0.3

<0.30.67

0.471.08

0.570.88

0.670.46

0.710.62

Dy

0.660.98

3.582.38

4.523.85

5.294.65

2.224.18

3.82H

o0.11

0.210.77

0.510.73

0.881.08

0.970.52

0.880.84

Er0.45

0.632.00

2.101.44

2.933.46

3.052.26

2.772.76

Tm<0.1

<0.10.28

0.370.13

0.450.51

0.450.41

0.410.40

Yb

0.350.59

1.632.43

0.603.02

3.222.83

3.072.58

2.74Lu

<0.1<0.1

<0.10.20

<0.10.40

0.580.51

0.220.29

0.25Y

3.424.74

19.5414.58

27.7224.42

33.4927.01

15.3622.75

22.53�R

EE22.68

29.9491.27

102.34349.70

138.73138.55

142.88118.51

133.92115.46

LREE/H

REE

2.692.46

1.842.90

6.592.38

1.592.16

3.202.37

2.01�C

e0.95

1.101.02

1.080.93

1.131.09

1.181.11

1.171.08

�Eu0.54

0.931.05

0.371.39

0.510.61

0.460.62

0.660.71

1. massive ore, 2. taxitic ore, 3. banded ore, 4. dissem

inated ore, 5. fluorite and barite bearing disseminated ore, 6. hanging w

all rock (garnet-biotite-quartzschist), 7. silicificated m

ica schist, 8. footwall rock (altered granoblasite), 9. footw

all rock (leucogranoblasite), 10. biotite quartz schist (in the bottom of the

formation), 11. m

eta sandstone (in the top of the formation), chondrite values from

Boynton (1984).

K2 O

(%)

Na2 O

(%)

A12 O

3 (%)

TFe(%)

CaO

(%)

MgO

(%)

Pb(ppm)

Zn(ppm)

wall rocks

0.n�����

0.n�6

11�13.5

2�10

0.n�4

0.n�4

nx10�100

nx10�100

wall rocks

2�8

0.1�4

5�14

>6>3

1�4

>100>100

near oresorebodies

0.n�4

<0.1<6

>20>5

>3>3000

>3000

III

125

Fig. 13. Geochemical patterns of selected elements in the profile of No.7 in the Keketale lead-zinc deposit, north-western China (after Zhang et al. 1990, 1996). 1=Meta felsic lava; 2=Metabreccia tuff; 3=Meta felsic lava and tuff; 4=Biotite-quartz schist and Biotite granoblasite withcarbonate and meta tuff intercalations; 5=Pb-Zn ore.

Strongly concentrated Pb, Zn, Ag, As, Sb have a broad anomaly area respectively. Thepatterns of Pb, Ag, As, Sb are also quite similar (Fig. 13). A distinct pattern is seen fromthe element As, which exhibits clear trends of high concentration both in the hanging walland foot wall rocks immediate to ores. Similar trends but mainly appearing in the hangingwall rocks are shown by Sb and Cu (Fig. 12). Cd, Mo, Hg and Mn distribute in arelatively narrow area corresponding to ores, particularly, Cd and Mo illustrate a narrowbut coherent pattern confined exactly to the shape of ore bodies. Major elements CaO,MgO and (TFe) show anomalies of enrichment and TFe correspond well to ores. CaO(and Mn) also seems to reflect the character of the host rocks: iron bearing carbonaterocks. Depleted and coherent Na2O patterns are nevertheless typical of strata boundsulphide deposit related to volcanism, particularly the depletion of Na2O well reflects awhole stratiform space where the ores are enveloped (Fig. 13).

The variations and the patterns of rock-forming elements are clearly the reflections ofthe main alteration although the alteration in the deposit is not intense, and possiblyreflections of the environmental characteristicss of ore precipitation (also see Zhang1992). Obviously, the host rocks are characteristic of unusually high Fe, Ca and Mg

III

126

bearing sediments. From the point of view of prospecting, therefore, high concentrationsof Ca and Mg can lead the attention to the promise of the strata position; and theanomalies of Cd, Mo and Na2O however have a great significance on ore deposit sitingand also ore body finding.

According to Han (1992), sulphides in the deposit have �34S values, varying between�5.4 to �15.3 per mill and high S/Se ratios (also see Zhang et al. 1990). Such data suggesta main sulphur source of sea water sulphate reduced by bacteria. One carbon isotopeanalysis gave the �13C values of �11.6 per mill, and lead isotope data showed the sameage as the host rocks. Also no carbon concentration has been found both in ores and hostrocks. All this data, together with the characteristics above lead to the conclusion that theKeketale Pb-Zn deposit was formed in the sedimentary basin near the volcanic centerduring the sedimentary process of the host rocks. At the same time of the processing, thebacteria activity was also extensive. As one type of the stratabound sulphide depositrelated to the volcanism, the Keketale Pb-Zn deposit may imply that the deposit hosted bythe sedimentary rocks in the volcano-sedimentary formation would prefer relatively strictconditions for the sedimentary basin in addition to the volcanism during their formation.

Summary and conclusions

1. The Keketale Pb-Zn deposit is a stratabound sulphide deposit hosted by sedimentaryrocks in the volcano-sedimentary formation (Jiang 1992, 1994). The deposit occurs inthe south-eastern part of the Maizi volcano-sedimentary basin within the SEA in theplace with the greatest stratigraphical thickness of the basin. Volcanic rocks of thecalc-alkaline series including felsic breccia, agglomerate, lava and pyroclastics, aswell as mafic lava and pyroclastics are the products of bimodal volcanism (Wu 1992).The Pb-Zn mineralization took place after the felsic eruption in the early stage of thevolcanism.

2. The host rocks of the Keketale Pb-Zn deposit are mainly composed of biotite quartzschist and granoblasite intercalations with interlayers of diopside marble, garnetepidote marble, meta-tuff, meta- tuffaceous siltestone and meta-siltestone (Han 1992,Wang et al. 1998). The protoliths are those sedimentary rocks including calcareous-argillaceous sandsone, siliceous rock and iron- bearing carbonate rocks formed in hotwater (Jiang 1992, 1994). Meta-volcanic breccia, meta-agglomerate, meta-breccictuff and meta-felsic lava as well as meta tuff and mica quartz schist underlying thehost rocks (Han 1992, Wang et al. 1998).

3. Ore bodies are present as stratiform or are stratiform-like. Dominant ores aredisseminated and then taxitic and massive, also banded, breccia as well as net-veined.Carbonation, sericitization, silicification and disseminated pyrite appear with themineralization. Epidotization occurs outside the ore bodies and sericitization as wellas potassium feldspar are met in the volcanics below the host rocks (Han 1992, Wanget al. 1998).

4. Stream sediment and soil surveys showed a geochemical anomaly area of about 200km2 composed of coherent Pb, Zn, As, Ag, Cu, Cd and Mn and a round anomalousbelt of Pb and Zn corresponding to the Maizi syncline and the volcano-sedimentary

III

127

formation of the lower Devonian in the syncline, respectively. The appearance of theCd anomaly together with a coherent concentrated center of Pb, Zn, As, Ag and Mnindicate in most cases the ore outcrop.

5. The major ore-forming elements including Pb, Zn, Cu, (Au) and some trace elementssuch as Sb, Cr, Ni, Co display a clear valley floor corresponding to the lowerDevonian in variation curves of elements in the time-strata profile. Because the Pb-Znmineralization related to the volcanism of lower Devonian is very common, it isreasonable to assume that the eluviation of sediments by leaking sea-water wasgeneral in the region in that time.

6. The volcano-sedimentary formation has high contents of Pb, Zn, As, Sb, Cd, Ba, Mnand W and low contents of Cr, Ni, Co, Cu, Mo and Sn. Pb, Zn, Ag, As, Sb, Ba and Ware concentrated in the rocks of the upper part of the formation, including the hostrocks. On the other hand, Pb, Zn, Sb, Cd have their lowest contents particularly infelsic meta-lava compared to the average concentrations of unmineralized rockswithin the area of 3250 km2. The similar chondrite normalized REE patternsespecially the values of �Eu and �Ce of ores and felsic lava below the host rocks inthe Maizi area (Wang et al. 1998) suggest clearly a leaching out of Pb and Zn etc. andthe metal sources of the deposit thus could be connected to the leaching of felsiclavas. The leaching of Eu in the rocks during the alteration is also possible.

7. The coherent primary geochemical anomalies of the deposit are characteristic of (1)broad and strongly concentrated of Pb, Zn, Ag, As and Sb; (2) concentrated butnarrow Cd, Mo, Hg, Mn especially for Cd and Mo corresponding exactly to the orebodies; and (3) concentrated CaO and MgO and depleted Na2O; (4) a distinct trend ofAs which exhibits clear trends of high concentration both in the hanging wall and footwall rocks immediate to ores, and similar trends but mainly appearing in the hangingwall rocks of Sb and Cu.

8. The variations and geochemical patterns of rock-forming elements reflect the mainwall-rock alteration and also possibly the environment characteristics of oreprecipitation such as Ca and Mg bearing sediments formed in hot water. Theanomalies of Cd, Mo, Na2O have a great significance on ore deposit siting and alsoore body finding.

9. Sulphides in the deposit have �34S values varying between �5.4 to �15.3 per mill andhigh S/Se ratios, showing a main sulphur source of sea water sulphate reduced bybacteria. One carbon isotope with the �13C values of �11.6 per mill and lead isotopedata showing the same age as the host rocks, and also no carbon concentration both inores and host rocks (Han 1992), together with the characters of the deposit suggestthat the Keketale Pb-Zn deposit was formed in the sedimentary basin near thevolcanic center with extensive bacterial activity.

Acknowledgements

The author would like to express appreciation to the Xinjiang Geochemical ExplorationTeam of Geology for Nonferrous Metals for providing some data, and Dr. HannuMakkonen for reviewing the manuscript.

III

128

References

Chen Y, Ye Q, Feng J, Mu C, Zhou L, Wang Q, Huang G, Zhuang D & Ren B (1996) Ore-formingconditions and metallogenic prognosis of the Ashele Copper-Zinc metallogenic belt, Xinjiang,China. Geol Publ House, Beijing, 330 p (in Chinese with English Summary).

Chen Y, Ye Q, Wang J, Rei J and the research group (1995) Metallogenic conditions and evaluationof mineral resources of Altay gold and non-ferrous metals provinces. Unpublished research report,483 p (in Chinese).

Han B & He G. (1991) The tectonic nature of the Devonian volcanic belt on the Southern Edge ofAltay Mountains in China. Geosc Xinjiang, No 3: 89-100 (in Chinese).

Han D (1992) Keketale lead-zinc deposit. In: Jiang Q, Liu Y, Wen H, Deng Y & Chen H (eds),Geological, geophysical and geochemical studies of Cu-Fe-polymetallic ore belt in Southern Edgeof Altay and the prospecting targets, unpublished research report, 251 p (in Chinese).

He G, Li M, Liu D, Tang Y & Zhou R (1994) Paleozoic crustal evolution and mineralization inXinjiang of China, Peoples Publ. Hose of Xinjiang, 437 p (in Chinese with English Summary)

Jiang F (1993) Petrochemical characters of ore-bearing volcanic formation in massive sulfidedeposits. In: Li Z & Wang B (eds) Volcanic rocks, volcanism and related mineral resources.Collection of Papers of Geo Soc China, vol 1: 31-38 (in Chinese).

Jiang Q & Liu Y (1992) Geological features of Cu-polymetallic ore deposits in Southern Edge ofAltay. In: Jiang Q, Liu Y, Wen H, Deng Y & Chen H (eds) Geological, geophysical andgeochemical studies of Cu-Fe-polymetallic ore belt in Southern Edge of Altay and the prospectingtargets. Unpublished research report, 251 p (in Chinese).

Jiang Q (1994) Types, evaluation criteria and geneses of the massive sulfide deposits in the volcanicterrain. Geol Expl Non-Ferrous Metals, Vol 3, No 1: 4-9. (in Chinese).

Li C, Wang Q, Liu X & Tang Y (1982) Explanation to tectonic map of Asia. Map Publ House, Beijing(in Chinese).

Li C & Wang Q (1983) Contributions to the project of plate tectonics in Northern China, N1. GeolPubl House, Beijing: 3-6 (in Chinese).

Liu F (1984) Altay paleo-plate and endogenetic deposits, Northwest Geol. N4: 14-21 (in Chinese).Tu G., Ou Z, Zhu B, Fan C, Zhong F, Yu J, Zhao Z, Fu J, Hong Y, Lu J, Wang Y & Guo Q (1984)

Geochemistry. Shanghai Sci. & Tec. Publ. House, Shanghai, 447 p (in Chinese).Tu G. (1987) Geochemistry of Chinese stratabound ore deposits, vol. 2. Sci Publ House, Beijing, 298

p (in Chinese).Wang J, Qin K, Wu Z, Hu J, Deng J, Zhang J, Bian Y & Li S (1998) Volcanic-exhalative-sedimentary

lead-zinc deposits in the Southern Margin of the Altai, Xinjiang. Geol Publ House, Beijing, 210 p(in Chinese).

Wang J, Li B, Zhang J, YinY, Wang J, Wang Z & Zheng G (1999) Metallogenesis and prognosis ofgold and copper deposits in Ertix Metallogenic Belt, Xinjiang. Metallurgical Industry Press,Beijing, 178 p (in Chinese).

Wang Z (1996) Exploration and discovery of Keketale Pb-Zn deposit. In: Xong G, Deng Z & Xie D(eds) The discovery of important metal deposits in Xinjiang, Geol Publ House, Beijing, pp 105-114 (in Chinese).

Wu Z (1992) The volcano-sedimentary formations of lower Devonian in major districts, SouthernEdge of Altay. In: Jiang Q, Liu Y, Wen H, Deng Y & Chen H (eds) Geological, geophysical andgeochemical studies of Cu-Fe-polymetallic ore belt in Southern Edge of Altay and the prospectingtargets. Unpublished research report, 251 p (in Chinese).

Xu G & Shao J (1980) On the type pecularities of pyrite and their practical significance. Geol Revvol 26: 541-546 (in Chinese).

Zhang J (1987) Abagong-Monku marine volcanic rocks and associated Fe deposit, Xinjiang.Northwest Geoscience, N 20: 89-100 (in Chinese).

III

129

Zhang X, Chen W & Wang S (1990) Studies of the polymetallic ores, their geochemical anomalouspatterns and interpretation, Beijing Institute of Geology for Mineral Resources, China.Unpublished research report with three accessary, 98 p (in Chinese).

Zhang X (1992) Geochemical anomalies of rock-forming elements reflecting precipitationenvironments of ore substances-an important indicator for prognosis of blind ore deposits ingeochemical exploration. Geoph & Geoch Explor 16(3): 208-215 (in Chinese with EnglishSummary).

Zhang X, Chen W (1995) Preliminary research on REE geochemistry of the Keketale Pb-Zn deposit,Xinjiang. Geol Expl Non-Ferrous Metals l 4(4): 219-222 (in Chinese with English Summary).

Zhang X, Chen W & Wang S (1996) Geochemical investigation of the Keketale Pb-Zn deposit inXinjiang and its anomaly model. Geol Expl Non-Ferrous Metals 5(1): 48-53 (in Chinese withEnglish Summary).

PART IV

IV

133

Geochemical anomalies of rock-forming elements: an important indicator of blind ore deposits

(Revised version of previously published paper 1)

Xiping Zhang

Abstract. Traditionally, geochemical explorationists have relied overwhelmingly on trace elementsand ignored major rock-forming elements. It is, however, the major rock-forming elements thatdictate the physio-chemical parameters of the ore-forming system which favors or prevents theprecipitation of ore elements. The much researched wall-rock alteration is the result ofredistribution of rock-forming elements to form new minerals under changed conditions. A certainportion of wall rock alteration is actually the product of ore forming processes. Wall rock alterationthat took place before ore-forming processes may have created a favorable condition for oreprecipitation.

Major element anomaly patterns are well developed and best investigated in porphyry Cudeposits and Kuroko type deposits, where the distribution and quantitative variation of the majorelements show a close spatial relationship to the extent of mineralization and the rich ore beds. Thefactor that rock-forming elements control the migration, accumulation and precipitation of oreelements is confirmed by the following observations: the composition of fluid inclusions in both oreminerals and gangue, the theory of transportation in complex ions, the mass exchange between orefluids and wall rocks and the existence of metasomatic plumes at the early stages of ore formingprocesses in a number of pyrite deposits. Geochemical anomaly of rock-forming elements istherefore not only a subject of academic interest, but a practical indicator in geochemicalprospecting, especially in the search for blind ore deposits.

Introduction

Geochemical prospecting in the past was almost always direct. Essential and associatedelements were used for finding blind deposits and these were mainly trace elements.Geochemical prospecting is now developing in new directions, which involve studyingclosely the geochemical reflection of ore precipitation environments, conditions and ore-forming processes.

The ore-forming system, a very complex system, not only concentrates usefulelements but also leaves information and marks of the ore-forming process. Anomalies ofore-forming elements and associated elements comprise part of, but not all, theinformation and marks. Information on environmental changes before and during theprecipitation of ore-forming elements can be useful in finding blind deposits.

Experienced geologists commonly consider the wall rock alteration to be a useful oredeposit indicator since it plays a part in mineralization. Geochemically, wall rockalteration reflects the environmental preconditions for ore substance precipitation. Onrelationships of alteration and ore, Burt (1972, see Rose & Burt 1979) indicated thatalteration and ore probably have closer relationships if early stage alteration enlarged theporosity and permeability of rocks, and thus provided the feeder for mineralizing fluid; or,the mineral assemblage of early stage alteration made it possible in chemistry to acceptthe precipitation of ore substances. Actually, the most important factor in the relationship

IV

134

between early stage alteration and ore is that the mineral assemblage of the former canchemically accept the precipitation of the latter. It is impossible that ore will precipitatewhen there is a chemical balance between the hydrothermal solution and wall rocks (Rose& Burt 1979). Thus the mineral assemblage of early stage alteration is essential to oreprecipitation.

Because it is so essential to alteration, the re-allotment of rock-forming elements mustbe related to element anomalies. So studying rock-forming elements and their anomalieswill enrich the study of deposit geochemistry, and at the same time reveal themineralization process and the geochemical environments favorable to the settling of ore,as well as establishing a most useful indicator for prospecting. Alterations around orereflect that mineral assemblage necessary for the precipitation of ore substances andmedia, and indicate geochemical environments favorable to the precipitation of oresubstances.

The case of anomalous models of rock-forming elements

The relationship of wall rock alteration to ore shows clear patterns of lateral and verticalzoning, and one or two types of these are intimately associated with ore.

Alterations studied thoroughly are porphyry copper deposits and a Kuroko deposit.The closed alteration zoning of the San Manuel Kalamazoo porphyry deposit is a typicalexample (Lowell & Guilbert 1970), the ore bodies were located on the border of potassicalteration of the central zone, and toward the outside it transits to a sericitization zone andpropylitization zone.

The alteration enveloped Kuroko deposit can be divided into four zones (Matsukuma1970): from the wall rock to the ore body there are: 1) the montmorillonite and zeolitezone (zone of transition to unaltered rocks), 2) the sericite, chlorite and pyrite zone (insideof strata above ore bodies), 3) sericite, chlorite and quartz zone (in the ore bodies), and 4)silication zone (footwall and middle part of ore bodies).

The Baiyin massive sulphide deposit (Gansu, China), Jiang et al. (1968) indicated thatthe features of alteration were no feldspar zone (silication and sericitize) +decolourisation process (chloritization, decolourisation and titanic hematite becamerutile) + pyrite (pyritization).

Carbonation, sericitization, silicification and disseminated pyrite occur with themineralization of the Keketale Pb-Zn deposit, one strata bound sulfide deposit hosted bysedimentary rocks in the volcano-sedimentary formation in Xinjiang (NW China).

There must be regular anomalous patterns of rock-forming elements in response to thetypical alteration zoning.

Porphyry copper deposits

The Fujiawu porphyry copper deposit (Jiangxi, China, Li et al. 1978) showsconcentration of K2O and depletion of Na2O in response to metallogenic elements Cuand Mo. The K2O/Na2O ratio shows low value(<1) in the centre no ore body zone,

IV

135

medium value (1-10) in the ore bodies, and high value (10-30) on the periphery of the orebodies. It indicates an intimate relationship between alkaline alteration and concentrationof copper and also the precipitation of ore substances (Fig. 1).

Fig. 1. Geochemical patterns of selected elements in the Fujiawu porphyry copper deposit(modified after Li et al. 1978).

The Duobaoshan porphyry copper deposit (Heilongjiang, China, Li et al. 1979) showsthe same patterns and that K2O/Na2O�1, by means of a plan view. The study carried outby The Research Group (1978) had also showed the enrichment of K, OH and the loss ofNa, Ca, (Al) in each alteration zone, and concentration of Si only in the silication zone(Fig. 2).

Fig. 2. Geochemical patterns of selectedelements in the Duobaoshan porphyrycopper deposit (modified after Li et al.

IV

136

Obviously, anomalies of rock-forming elements of porphyry copper deposits are notonly clear, but also typical. Actually no exceptions to this type deposit have been found inthe world.

Stratabound sulfide deposits hosted by volcanic rocks

We are all familiar with the depletion of sodium in Kuroko ore. It was documented thatthe content of Na and Ca is decreased but Fe and Mg (K and Si) is increased from wallrock to the centre of ore body (Lambert & Sato 1974, Riverin & Hodgson 1980, Frater1983, Larson 1984, Peterson 1988, Chen et al. 1996).

Stratabound sulfide deposits hosted by sedimentary rocks in the volcano-sedimentary formation

In studying the Keketale Pb-Zn deposit, the author devoted much attention to thedistribution of rock-forming elements in the deposit. The deposit is a volcanogenic Pb-Znore deposit related to the mainly felsic marine volcanism of the lower Devonian.Anomalies of rock-forming elements are regular (Fig. 3). The ore bodies are in the zoneof CaO and MgO enrichment and Na2O depletion. The patterns of depletion are veryspecial, but the anomaly of K2O is not regular.

Fig. 3. Geochemical patterns of selected elements in the Keketale lead-zinc deposit (modifiedafter Zhang et al. 1990).

IV

137

According to the anomalous models of Na2O, Pb and Zn, an inference about deep orebody and the occurrence of deposit was made and confirmed by drilling.

Discussion

The concentration and precipitation of ore substances is due to the change of physio-chemical conditions in the ore solution and environment. It is impossible to induce theconcentration and precipitation of a large scale and complex component without changingthe chemistry and exchange of chemical components.

Rei (1984) calculated the exchange capacity of chemical components in rock pillars ata depth of 1 km from altered porphyry bodies in Yulong, Malasongduo and Tongchang. Itshows that the amount of SiO2 added to the pillars is about hundred million tons, twentymillion tons and forty million tons, respectively. The amount of K2O added to the pillarsof Yulong and Malasongduo is about six million tons, and the amount of Na2O depleted isfifty million tons, ten million tons and forty million tons, respectively. As a result of theexchange, the amount of Cu and Mo added to the porphyry bodies is five million tons,one million tons, three million tons and three hundred thousand tons, seventy thousandtons and fifty thousand tons respectively.

The composition of fluid inclusions shows that the ore solution contains a great deal ofCl, K, and Na etc., with mostly heavy metal such as Cu, Pb and Zn etc. These can formcomplexes and move stably under acid or slightly acid conditions, and low concentrationsof H2S. The complexes can be decomposed and heavy metals precipitated in some wayswhen the conditions change.

In discussing the mineralization epoch of pyrite deposits, Smirnov (1970) indicatedthat: True vaporous solution with high temperatures in the initial stage of mineralizationchanged the mineral composition of volcanic rocks as it moved through, and formed thehydrothermal altered rock pillar. The temperature reduced from 400 to 200 degreesCelsius from the quartz zone to the chlorite zone, the acidity-alkalinity (Ph) increasedfrom 4-5 to 6-7-8, and rock-forming elements were diluted from or added to the differentzones (Fig. 4). The following pyrite stage caused the iron sulfide to dissociate from theflowing strongly leached quartzite and quartz-sericitelite hydrothermal solution, and thenformed sediment. The Ural-orefield terrain proved that the porosity of altered rocks hadbeen enlarged by 2-4 times, and showed a direct ratio with the increase in the amount ofsericite and chlorite.

IV

138

Fig. 4. General sketch of reallotment of elements in the replacement pillar of volcanic rockscaused by fell off in energy (t°C) and acidity (pH) in the replacement front of the early periodof pyrite mineralization (after Smirnov 1976).

Actually, heavy metal mineralization (Cu, Pb, Zn etc.) works in the same way. Thehydrothermal altered rock pillar of the initial stages of mineralization of pyrite oredeposits is significant, because it always takes place before the ore precipitation and isnecessary for this precipitation. Therefore the rock pillar shown in figure 4 is just apreparation stage of the concentration and precipitation of pyrite; it not only produces anew mineral assemblage favorable to pyrite precipitation but also greatly enlarges theporosity of protolith. The major cause of formation of altered mineral assemblage is thedecrease in the temperature and acidity of the solution. Decreasing acidity is due to thechemical exchange between solution and wall rock, especially for the replacement of ionsof alkaline metals, alkaline-earth metals and iron.

The formation of sericite, chlorite (and quartz) is as follows (Department of Geology1979):

3KAl3SiO8 + 2H+ � KAl2AlSi3O10 (OH)2 + 2K+ + 6SiO2 (1)(orthoclase) (sericite) (quartz)

2K(Mg,Fe)3AlSi3O10(OH)2 + 4H+ � Al(Mg,Fe)5AlSi3O10(OH)8 + 2K+

(biotite) (chlorite)

+ (Mg,Fe)2+ + 3SiO2 (2)(quartz)

IV

139

Action (1) shows that the OH-/H+ ratio increases with the H+/K+ exchange, and thus theacidity drops. At the beginning of the exchange, the decrease in acidity and thecontinuing action are interdependent. The result of action (2) is the same as (1). Theexchange causes the recombination of the component of the protolith, changes thecharacter of the solution, and also breaks the chemical balance between the solution andthe wall rocks. As a result, the complexes with ore elements are dissociated, and thereleased elements together with the elements from wall rocks are precipitated. Therecombination of components of the protolith causes the enlargement of porosity of theprotolith and geochemical anomalies of rock-forming elements. In this way, the favorableconditions for ore-forming element precipitation come about, confirming the intimaterelationships of wall rock alteration and ore substance precipitation.

Conclusions

Early stage alteration can have a significant effect on mineralization. The altered mineralassemblage makes it chemically possible to accept the precipitation of ore substances,and the alteration can enlarge the porosity of rocks. That is to say early stage alterationhas created chemical and physical conditions favorable to the precipitation of ore.

The second significant effect of the alteration is that it can promote the concentrationof ore further through chemical material exchange.

Wall rock alteration is the re-allotment of rock-forming elements, and thus causesanomalies of the elements. That is to say the anomalies of rock-forming elements are thereflection of geochemical environments favorable to ore precipitation.

Rock-forming elements control the geochemical behavior of ore-forming elements,and therefore merit further study.

Anomalies of rock-forming elements are practical indicators of deposit particularlyblind deposits.

Acknowledgement

The author expresses his thanks here to Ms. Tracy Lyons Shupp for checking the Englishof the manuscript.

References

Chen Y, Ye Q, Feng J, Mu C, Zhou L, Wang Q, Huang G, Zhuang D & Ren B (1996) Ore-formingconditions and metallogenic prognosis of the Ashele Copper-Zinc metallogenic belt, Xinjiang,China. Geol Publ House, Beijing, 330 p (in Chinese with English Summary).

Department of Geology, The University of Nanjing (1979) Geochemistry, Sci. Publ. House, Beijing,514 p (in Chinese).

Frater KM (1983) Geology of the Golden Grove prospect, Western Australia: A volcanogenic mas-sive sulfide-magnetite deposit. Econ Geol 78: 875-919.

IV

140

Jiang Q and the research group (1968) Rocks and alteration of pyrite type deposits and prospectingtargets in Baiyin district. Beijing Institute of Geology for mineral Resource. Unpublished researchreport.

Lambert IB & Sato T (1974) The Kuroko and associated ore deposits of Japan: A review of their fea-tures and metallogenesis. Econ Geol 69: 1215-1236.

Larson PB (1984) Geochemisry of the alteration pipe at the Bruce Cu-Zn volcanogenic massivesulfide deposit, Arizona. Econ Geol 79: 1880-1896.

Li H et al. (1978) Geochemical character and evaluation marks of Fujiawu porphyry deposit. Geol &Prospe14: 29-36 (in Chinese).

Li H et al. (1979) Geochemical character and zoning of Duobaoshan porphyry deposit. Geol & Prospe15: 72-79 (in Chinese).

Lowell JD & JM Guilbert (1970) Lateral and vertical alteration-mineralization zoning in porphyrycopper deposits. Econ Geol 65: 373-408.

Matsukuma (1970) Summary of Kuroko deposits. In: Tachimi (ed) Volcanism and ore genesis, Chi-nese version (1974).

Peterson JA (1988) Distribution of selected trace and major elements around the massive sulfide de-posit at the Penn Mine, California. Econ Geol 83: 419-427.

Riverin G. & Hodgson CJ (1980) Wall-rock alteration at the Millenbach Cu-Zn Mine, Noranda, Que-bec. Econ Geol 75: 424-444.

Rei Z, Huang C, Qi G, Xu J & Zhang H (1984) Porphyry copper (moleybdenum) deposits of China.Geol Publ House, Beijing, 350 p(in Chinese).

The Research Group (1978) Study on alteration and mineralization of Duobaoshan porphyry copperdeposit, Heilongjiang. Guilin Institute of Geology for Mineral Resources. Unpublished researchreport.

Rose AW & Burt DM (1979) Alteration. In: Barnes HL (ed) Geochemistry of hydrothermal ore de-posits (2d edition). John Wiley & Sons.

Smirnov, BI (1976) Ore deposit geology, Chinese version (1981) Geol Publ House, Beijing, 514 p.