Eco. Lec. No.1 & 2 , 2011
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Transcript of Eco. Lec. No.1 & 2 , 2011
8/13/2019 Eco. Lec. No.1 & 2 , 2011
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Economic Geology
Lec. No. 1 & 2
Introduction to Economic Geology
!Introduction and aims
! What is economic geology?
! Brief history of Economic geology
! A simple classification scheme for mineral deposits
! Magmatic Ore Deposits
! What make a viable mineral deposit?
! Terminology
! Some relevant compilations: [Periodic table of the elements, Table
of the main ore and gangue minerals]
Topics
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Introduction and Objectives:
Given the unprecedented growth of human population over the past
century, as well as the related increase in demand for and production of
natural resource, it is evident that understanding the nature, origin, and
distribution of the world's mineral deposits remains a strategic topic.
The discipline of economic geology which covers all aspects pertaining
to description and understanding of mineral resource is therefore, one
which traditionally has been and should remain a core component of the
University earth science curriculum.
This lecture intended to provide a comprehensive glossary term used
in economic geology and brief history of economic geology as well as
classification scheme for ore deposits.
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What is economic geology?
Economic geology involves the study of mineral resources and their
geological environments. You will learn about the geological
processes that lead to the formation of ore deposits, and how we
explore for new deposits using geochemistry and geophysics.
Economic geology is concerned with earth materials that can be used
for economic and/or industrial purposes. These materials include1- precious and base metals,2- nonmetallic minerals, construction-
grade stone,3- petroleum, coal, and 4- water.
The term commonly refers to metallic mineral deposits and mineral
resources.
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Brief history of Economic geology
These Ages refer to different periods in human cultural development
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A classification scheme for ore deposits
There are many different way of categorizing ore deposits, and the
best classification schemes are probably those that remain asindependent of genetic linkage as possible these are:
Igneous, Metamorphic, and Sedimentary ore deposits (Fig 1, a, b)
Einaudi, (2000), stated that all mineral deposits can be classified
into three types based on process, namely
magmatic deposits, hydrothermal deposits, and surfacial deposits
formed by surface and groundwater.
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Fig 1 classification of the principle rock types (a) and an analogous, but
much simplified, classification of ore deposit types (b) photograph show
interplay between ore forming processes
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Magmatic Ore Deposits
Magmatic ore deposits are those which are formed during
crystallization of a magma, deep underground. The host rock forthe mineralization can range from ultramafic to felsic. The deposit
can consist of massive ores in some cases, and disseminations of rare
minerals in others. In the case of more massive ores, there are three
primary means of concentrating minerals of value during the
formation of these deposits (Fig. 3.38):
• gravitational settling
• differentiation
• immiscible separations
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immiscible separations
Oil and water don’t mix …
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High T
Desirable element preferentially concentrated into low-volume melt
Low T
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• Types of Immiscible Melts
•Oxide melts can be rich in Fe (Fe2O3, hematite) and Ti(FeTiO3, ilmanite).
• Sulfide melts can be rich in Ni, Cu, and the platinum-group elements, in addition to iron sulfur (FeS,
pyrrhotite).
• Carbonate melts can be rich in niobium, tantalum, rareearths, copper, thorium, and phosphorous.
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What make a viable mineral deposit?
Table 1 average crustal abundance for selected metal and typical concentration
factors that need to be achieved in order to produce a viable ore deposits
(From Evan, A.M, 1993) Note: 1 ppm is the same as 1 gt -1
* 12505 gt -14 ppbAu
* 1000
* 2500
* 700
* 130
* 180
* 10* 4
Approximate
concentration
factor
5 gt -15 ppbPt
0.5 %2 ppmSn
5 %70 ppmZn
1 %75 ppmNi
1 %55 ppmCu
50 %5.60%Fe30 %8.20%Al
Typical exploitable
grade or \
(Av.minimum exploitable
grade)
Average Crutal
abundance
Elements
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Terminology:
Ore: any naturally occurring material from which a mineral or
aggregate of value can be extracted at profit.
To be ore must be ,1-Payable, 2- Involve economic consideration, 3- involving geologic
consideration.
Economic Consideration:
• Mineral exploration
• Economic evaluation
• Mine development• Mine extraction
• Ore dressing
• Smelting
• Refining
• Marketing
• Power supplies• 10-Eqipments cost
• 11-water supplies
• 12-Transport metal cost
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Gangue minerals: Usually worthless, non metallic minerals of adeposit that may be:
Introduced minerals, b- The inclosing rocks c- are discarded inthe treatment of the ore
Economic minerals: Are natural resources which, once extracted
and used, are not renewable.
Grade: The concentration of an element in a mineral deposit is termed
grade usually expressed as % or in ppm
Cut-off grade: The lowest percentage at which deposits can beeconomically worked is termed cut-off grade.
Tenor: The grade or amount of commodity actually present
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Factors controlling cut-off grade limit:
A-Geological factor, B-Geochemical factors, C-Other factors
The point B and C depend on the following factors:
1-By product2-Undesirable substance
3-Mineralogical form
4-Grain size and shape
5-Size and shape of ore body
6-Mineral charactersThe other factors controlling the classification of Cut-off grade are:
• 1-Commodity price
• 2-Cost of capital
• 3-Location
• 4-Environmental consideration
• 5-Taxation
• 6-Political factors
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Syngenetic: refers to ore deposits that form at the same time as their hostrocks.
Epigenetic: refers to ore deposits that form after their host rocks.
Hypogene: refers to mineralization caused by ascending hydrothermalsolution.
Supergene: refers to mineralization caused by descending solutions.
Generally refers to the enrichment process accompanying the
weathering and oxidation of sulfide and oxide ores at or near the
surface.
Metallogeny: the study of genesis of mineral deposits, with emphasis
on their relationship in space and time to geological features of the
Earths crust.
Metallotect:any geological, tectonic, lithological, or geochemicalfeature that has played a role in the concentration of one or more
elements in the Earths crust.
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Metallogeneic Epoch: a unit of geologic time favorable fordeposition of ores or characterized by a particular assemblage of
deposit types.Metallogenic Province: a region characterized by a particular
assemblage of mineral deposit type.
Epithermal: hydrothermal ore deposits formed at shallow depth (lessthan 1500 m) and fairly low temperature (50-200 !C)
Mesothermal: hydrothermal ore deposits formed at intermediatedepth (1500 – 4500 m) and temperature 200 - 400!C)
Hypothermal: hydrothermal ore deposits formed at substantial depth
(grater than 4500 m) and elevated temperature (400-600 !C)
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Periodic table of the elements:
Fig 2 Periodic table showing the 92 geologically relevant elements classified on
the basis of their rock and mineral associations ( From Robb, 2005)
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Common Ore and Gangue mineral
1- Native element
Metals Non-Metals
Gold - Au Sulfur –
S
Silver - Ag Diamond – C
Platinum - Pt Graphite - C
Palladium - Pd
Copper - Cu
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2- Halides
•
Halite –
NaCl• Sylvite – Kcl
• Chloragyrite – AgCl
• Fluorite - CaF2• Atacmite Cu2 Cl(OH)3
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4- Oxides:
Oxides
Cuprite- Cu2OHematite – Fe2O3
Illminite – FeTiO3
Hercynite – FeAl2O4
Gahnite – ZnAl2O4
Magnetite – Fe3O4
Chromite –
FeCr2O4
Rutile – TiO2
Anatase – TiO2
Pyrlucite – MnO2
Casseterite – SnO2
Uraninite –
UO2Thorianite – ThO2
Hydroxide (or Oxyhydroxide)
Geothite FeO(OH)
Gibbsite – Al(OH)3
Boehemite – MnO(OH)
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Salts-Oxy- 5
Azurite Cu3(OH)2(CO3)2
Cerussite PbCO3
Simthonite ZnCo3
Epsomite
MgSO4.7H2O
Rhodochrosite MnCO3
Malachite Cu2(OH)2 CO3
Gypsum
CASO4.2H2O
Siderite FeCO3
Apatite
Ca5(PO4)3(F,Cl,OH)
Alunite
KAl3(OH)6
(SO4)2
Ankerite CaFe(CO3)2
Monazite
(Ce,La,Th)PO4
Anhydrite CaSO4Wolformite
(Fe,Mn)WO4
Dolomite CaMg(CO3
Carnotite
K2(UO2)(VO4)2.3H2O
Xenotime YPO4Barytes BaSO4Scheelite
CaWO4
Calcite CaCo3
Vanadates PhosphatesSalfatesTungestatesCarbonates
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6- Silicate
Spodumene,
Wollastonite
Biotite, ChloriteEpidoteTourmalineGarnet,
Sillimanite
Albite,Orthoclase
ChrysocollaTremoliteKaolinite,
Montmorilionite,
Illite,Talc
LawsoniteBerylZirconOuartz
Unknown
structure
Ino (Chain) Phyllo(Sheet)Soro (Di)Cyclo
(Ring)
Neso (Ortho)Tekto (Framework)
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References:
! Evans, A.M., 1993, Ore Geology and Industrial Minerals
An Introduction, Third Edition, Blackwell Publishing,
PP.84-95
! Jensen, M. L and Batman, A. M., 1979, Economic mineral
deposits 3rd edition, New York, 593p.
!Robb, L., Introduction to ore-forming process, (2005)Blackwell Publishing, 373p.
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End of the Lecture
Good Luck
Instructor
Dr. Tola A. Mirza
Assistant Professor