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WELCOME TAGADUR CHROMITE MINE NUGGIHALLI SCHIST BELT

Dissertation onSubmitted by,VENKATAKRISHNAIAH.C4 th Sem, M.Sc[Geology]Reg.No : 09TUSG4008Department of Geology Bangalore University.Submitted to,Dr. B.C.PRABHAKARProfessor Department of GeologyBangalore University .

Ultra-mafic rocks also referred as ultra-basics are igneous and meta-igneous rocks with very low silica content (less than 45%), greater than 18% MgO, high FeO, low potassium. These are composed of usually greater than 90% mafic minerals, which are dark coloured , and high magnesium and iron content. The earths mantle is usually composed of ultra-mafic rocks. Many of them are found in the lower parts of the thick sills, flows and lopoliths, where they grade upward into basic rocks. INTRODUCTION ULTRAMAFIC ROCKSMost ultra-mafic rocks are formed due to early formed crystals , some of them are of remelting of crystal differentiates and some of them are due to metasomatic alteration of pre-existing , less mafic igneous rocks and intrusions are due to perhaps largely crystalline. Perodotite magma rising from beneath the basaltic substratum. Most of the coarse-grained types are made up principally of olivine and iron ores. A few coarse-grained ultra-mafics carry a small amount of calcic plagioclase and devoid of Feldspar.Examples: 1.Dunite 2. Peridotite 3. Pyroxenite 4. Serpentinite etc..

continueLayered intrusion is a large sill like body of igneous rock which exhibits vertical layering or differences in composition or texture. These intrusions are typically of many km`s in area covering from around 100km2 to over 50,000km2 and several hundred meters to over a kilometer in thickness .Layered intrusions are found in typically ancient cratons and are rare but worldwide in distribution. The intrusive complexes exhibit evidence of fractional crystallization and crystal segregation by settling or floating of minerals from a melt.

LAYERED INTRUSION

Mafic-ultramafic layered intrusions occur at all levels within the crust, from depths in excess of 50km to depths of as little as 1.5 to 5km. The depth at which an intrusion is formed is dependent on several factors: Convection, Diffusion , settings of phenocrysts, assimilation of Wall rocks and Fractional crystallization.

DISTRIBUTION OF ULTRAMAFIC ROCKS The majority of ultramafic rocks are exposed in orogenic belts, and predominate in Archaeanand Proterozoic terraines. Ultramafic magmas in the Phanerozoic are rare, and there are very few recognised true ultramafic lavas in the Phanerozoic.CAUSES OF LAYERING 1. Bushveld Igneous Complex Transvall , South Africa 2. The Koillisma Layered Igneous Complex Finland 3. Pindos Ophiolite Complex - North-west Greece 4. Giles Layered Igneous Complex - Central Australia

Layered Complexes in India 1.Sukinda Ultramafic Complex Orissa 2. Baula-Nausahi Ultramafic Complex Orissa 3.Jojohatu-Roroburu Ultramafic Complex Jharkhand 4. Bhandara -Nagpur Belt Maharashtra 5. Kondapalli Igneous Complex Andhrapradesh 6. Sittampundi Igneous Complex Tamil Nadu

Layered Complexes in Karnataka 1. Nuggihalli Schist Belt - Hassan District 2. Sindhuvalli Talur belt - Mysore district

Layered Complexes in the World The Nuggihalli Schist Belt is situated in the western part of the Dharwar Craton. The Western Dharwar Craton is composed of older supracrustals known as the Sargur Group (3.33.1 Ga) that are enclosed within the associated tonalitetrondhjemitegranodiorites . The rocks in the Nuggihalli schist belt belong to the Sargur Group.

The Sargur Group of rocks occur as linear ultramaficmafic belt, containing minor classic sediments and banded iron formation (BIF), in the Nuggihalli area The ultramaficmafic rocks of the Sargur Group occur both as intrusive bodies as well as volcanics. This belt has received considerable attention in view of gold, copper, chromite, and vanadiferous ,titano-magnatite mineralization in different places. NUGGIHALLI SCHIST BELTFirstly , Bruce Foote [1900] made a passing mention of possible Dharma outliers near Tagadur betta and Belagumba. In 1906 , Sampath Iyengar discovered the Nuggihalli schist belt and correlated it with the Chithradurga schist belt. Sampath iyengar observed that this belt comoposed of mainly hornblende schists , ultrabasics and quartz reefs . Again in 1922, Sampath Iyengar described the chromite and titanomagnatite bodies and made a breif mention of the kyanite occurance of Malavanaghatta. Pichamuthu in 1956, described the ultramafics of the alpine type and included them as a part of the major ultramafic zone in karnataka, and he compared this zone to the Great dyke of the Rhodesia.

PREVIOUS WORK Radhakrishna in 1957 , described the chromite deposits and the associated rocks of Byrapur. Varadarajan in 1964, described the ultramafites and associated rocks of this belt.. Phene in 1969 described amphibolite,green schist and quarzyte from this belt.Unpublished works by the GSI officers made the sequence of the rock formations such as the horneblende schist, quartz mica schist and ferruginuos quartz [lower Dharwar ] followed by the ultrabasics and talc- chlorite schists. Viswanadha in 1971 , examined the vermiculite occurrence of malavanaghatta and ponnasamudra. Ramakrishna in 1972, described the ultramafic bands of the belt in relation to asbestos mineralization.continueAfter a detailed Literature survey of geology , geomorphology and tectonic features of the Nuggihalli belt area, chromite mine pits near Tagadur were selected for the study. - Geological mapping was carried out on a Scale of 1:25000 using survey of India . Tope sheet number : 57C/8 and all the litho section were mapped on their map. - Dip and Strike of the schistose foliation using Brinton Clinometers compass were measured - GPS was used for the precise spot and sample locations. - Fresh samples at different places with in the mine area of both host rocks and mineralization were representative samples of different rocktypes were prepared for thin section and polished section of ores were prepared for ore microscope studies.

METHODOLOGY

Nuggihalli Schist Belt is a prominent, linear and narrow belt of schistose and ultramafic rocks situated in the western part of the Dharwar craton in Hassan district of Karnataka state. This belt has considerable attention in view of the chromite, vanadiferous titanomagnetite and gold.The Nuggihalli schist belt trends in a NNW-SSE direction with the length of 60 kms starting from Arasikere in the North (13058l:76017l) to Kempinakote in the south (12054l:76031l) and with average width of about 1km, with a maximum width at central bulge near Nuggihalli of over 3km.

REGIONAL GEOLOGY OF NUGGIHALLI SCHIST BELT

TAGADUR MINE 13The ultramafic rocks especially the amphibolites schists, were considered to belong to greenschist facies in view of the mineral assemblage of tremolite, actinolite and chlorite. Even where gneissic intrusions are seen in the ultramafics and where the ultramafics isolated as enclaves, the mineralogy is of actinolite, tremolite and chlorite. It is well known that ultramafic schists in all grades of metamorphism show similar low grade mineralogy when fluids like water are involved and therefore are not diagnostic indicators of P-T conditions.

METAMORPHISM

Topography and Drainage The Tagadur mining area is an undulating terrain having gentle slope both Eastrly and Westerly. The general area ranges from 911 to 973 mtrs above MeanSeaLevel. Few seasonal Nallahs are observed in the area towards North West, North East and Central part of the area and flow only during monsoon and remains dry during other seasons. The surrounding area of the Mining block is using for cultivation of Coconut, Sugar cane and seasonal crops such as Ragi and Maize. This area receives a moderate rainfall ranging from 500-600 mm annually and under sub-tropical climate.GEOLOGICAL SETTINGS OF THE TAGADUR AREA

The Tagadur Chromite Mine is a part of Nuggihalli Schist belt received considerable attention in view of the Chromite, Gold and Vanadiferrous Titano-Magnetite mineralization. Recently an interesting discovery of Copper mineralization has been made.The foliation of the Schist is predominantly NNW-SSW with steep dip towards East. The Tentative sequence as identified in the region / area is indicated below. Dolerite dyke , Amphibolite , Quartz vein ,Sepiolite Granitic Gneisses, Titano Magnetite Serpentinite, Tonalitic Gneiss , Talc Chlorite Schist , Chromite Ore Gabbro .

MINEROLOGY - Tagadur area is one of the ore producing mines of chromite in Nuggihalli Schist Belt. It is in the southern part of the Nuggihalli Schist Belt .Interesting lithological characteristics and structural features are observed here , the chief lithological varieties here include strongly schistose serpentinite , serpentinized dunite, chromite rich serpentinite and talc-chlorite rich schistose rocks.

1. Strongly Schistose Serpentinite2. Chromite Bearing Schistose Serpentinites3. Dunite with Sepentinized Sequence4. Talc- Chlorite Schist with poor Chromite concentration

GEOLOGICAL SETTINGS OF TAGADUR CHROMITE MINE - SOUTH BLOCK

FIELD PHOTOS

Schistose Serpenitinite with Magnasite veins

Dunite cleavages with poor Chromite concentration

Chromite body enclosed in Ultramafics

Chromite occurance in Lensoid body

Chromite occurance in Vein types In this study, detailed investigation in the chromite deposits of the Nuggihalli Schist Belt and detailed petrographic investigation of the Tagadur chromite mine has been carried out by systematic sampling from the mine sections of open cut and outcrops, by using petrographic and mineral analyses. Important rock types observed petrographically are serpentine, Dunite , amphibolites, talc-chlorite schist, peridotite etc.In this chapter petrographic description of the different rock types observed and sampled in the field is produced Variations in the comopositions of the different lithologies and their textural patterns are also observed.

PETROGRAPHY

In handspecimen it is green coloured and coarse grained. The mineral grains have stretching effects. It shows strong alterations and is traversed by thin magnasite veins . In thin sections well developed schistosity is observed , serpentine grains are abundant , olivine grains mostly occur as relict grains [ fig1] ,they are greysih to greenish colour . Magnasite show aciculars with in serpentinized rock and is developed due to the alteration [metasomatism]. Fine fissility is developed along with schistose magnasite veins and shows micro level sheath folding and stretching effects . Pyroxene grains are less in abundance and they are invariably altered to Hornblende and shows strong pleochroism [ dark green-yellow-brown] and its pseudomorphs are observed here.

Schistose Sepentinite

The lithosection is the schistose serpentinite and shows transition features. In hand specimen it is generally green or greenish grey in colour . Here, the podiform chromite has been found , they are found as thin or thick veins and these are stretched up and shows boudinage texture , which is due to the deformation. In thin sections this serpentinite shows schistosity and is mainly made top of altered olivine and pyroxenes with enstatite grains and the boundaries shows plenty of alterations . Chromite grains appear as dark grey to brownish coloured , they are rounded to subhedral in shape and at places they also show pinch and swell structures .

Podiform Chromite bearing Sepentinite

26 In handspecimen , the periditite is dark grey in colour and is coarse grained. Pyroxene minerals display strong orientation to produce schistosity . Foliation planes are well developed , sometimes dotted with chromite grains , veins of chromite are also sometimes observed. In thin section , peridotite shows the composition of pyroxenes ,olivine and minor plagioclase . Pyroxene which are both augite and hypersthene shows subhedral to euhedral and cumulus nature. Strong alteration is also commonly observed to hornblende and some extent to chlorite . Olivine shows irregular cracks. It occurs rounded to subrounded grains and is strongly altered to serpentine , talc and carbonates. Chromite shows chain textures which are wider at interstices and narrowing at the margins.

Schistose PeridotiteTalc chlorite schist shows light grey to greenish grey coloured , which is easily identified by its softness and it is closely associated with chlorite and tremolite . The rock has been derived from the alteration of dunite and pyroxene.Under microscope, schistosity is commonly seen. Grains of talc and sheaths of chlorite are chief minerals of this rock. Fine aggregates of talc are aligning along the schistose planes. Sheaths of chlorite are closely intertwined with talc grains.Chlorite under plane polarizer light is green coloured and can be seen chlorite coatings on ultramafics , under crossnicols , it shows strong bluish grey colour. Chromite also shows alignment along schistosity , it indicates that the deformation was post dating chromite mineralization.

Talc-Chlorite Schist THIN SECTION PHOTOS

Schistose texture

Schistose rock showing flowage of Chromite grains

Schistose rock showing inclusion of Chromite in HornblendeIn this section the important ore microscopic characteristics of chromite and its association with host rocks of tagadur mine have been described.Chromite Chromite generally exhibits fine granular to massive texture in polished specimens. It is deep brown to black in colour . It is subhedral to anhedral in shape and occasionally euhedral. The grain size of the chromite is varies considerably with the amount of gangue minerals. Normally it occurs either as lensoid or podiform ore. Under microscope it show high relief and poor reflectance Colour varies from grey to grayish brown . Pleochroism is not observed .It occurs as isotropic and brownish red internal reflectance are normally observed . Sometimes silicate inclusions especially are serpentine grains are observed.

ORE PETROGRAPHY STUDY

1.Schistose Texture Chromite is highly deformed zones shows stretching and flowage along the schistosity . At that places , it show microlevel pinch and swell structure . This kind of texture are important to understand the post-depositional structural important on the ore and its state at that time . [fig .4.1] 2.Net TextureIn net textured chromites inter cumulus chromite grains are joined together to form net-texture . Due to shearing the net-textured chromite grains locally are fragmented and both silicate and chromite grains show orientation in a planar fabric. [fig 4.5]

A detailed description of the different structures found in chromite ores of tagadur area are described below.

Photograph showing strongly Schistose rock with foliations

Chromite grains showing Net texture in Host rock Near many cumulus zones chromite shows panidiomorphic texture , medium to coarse grained . Euhedral grains are displayed in the silicate matrix which is mostly made up of serpentines. This texture is commonly noticed in dunite and peridotite varieties.

Panidiomorphic Texture

Euhedral to Sub hedral grains in Chromite It is a very common texture in ultramafic rocks. Thayer (1969) used the term to describe texture small euhedral to subhedral of chromite crystals join ends together to form chains encircling silicate minerals . Sometimes the chains occur at the margins of serpentine pseudomorphs. The chain texture is more prevalent in disseminated ores where the crystals are joined along the long diagonals of the grains and encircle the serpentine pseudomorph. This type of textures indicate development of crystals under the condition of free growthChain Texture

Chain like Chromite grains in Hostrock Tagadur mining area is an important tract from the point of chromite productivity in Nuggihalli Schist Belt, an ancient ultramafic supercrustal belt. Field and petrographic study of this area has revealed that chromite occurs in different lithological setup. The host rock lithologies of chromite ore include 1.strongly schistose serpentinite 2.serpentinite with chromite 3. Dunite bearing enclaves and 4. Talc- Chlorite schist . Amongst them serpentinite with dunite enclaves is a formable unit from the chromite deposit . Petrographically all these litho units are strongly altered usually to serpentine and less to chlorite and talc.Some of the ultramafic varieties are strongly schistose and some show local effects deformation . Chromite is occur as veins , pods and lensoid bodies , thier localization and size are highly valuable. Their deposition appears to be strongly evolutioned by deformation effects . They have been dragged, stretched , boudinazed and localized.When studies under microscope chromite displays variety of textures like 1.panidiomorphic 2.cumulus 3.chain 4.mesh textures .

SUMMARY AND CONCLUSIONS

Early formed chromite layers display cumulus and mesh textures where as the subsequent chromite layers display Panidiomorphic texture. In the highly schistose and deformed zones chromite also show stretching at microscopic level. Though chromite in handspecimen display massive habit several structural imprints of deformation are evident under microscope, especially when chromite occurs with schistose serpentinite. However, in granular variety the effects of deformation is minimum.

In the overall study , it is informed that the chromite of the study has been formed as a result of early segregation of ultrabasic magma was evolving in the magma chamber , to start with they were formed as early crystal fractionates and basal layers of magma enriched in chromite and it distributed in the later sequences. However successive batches of the ultrabasic magma produced by partial wetting of periditite magma ,probably produced , chromite rich layers in different horizons . All of them have been subsequently tilted and metamorphoshosed during regional scale foldingcontinueMaibam Bidyananda and Sachinadh Mithra, Room Temperature characteristics of the chromites from the Nuggihalli Schist Belt ,Dharwar craton ,Southern India. Jour.Geo.Soc.India,vol . 86, pp.9 R.Nijagunnappa and C. Naganna ,(1983) , Archean meta lamphropyres from Nuggihalli Schist Belt: An arechean layered complex as interpreted from chromite distribution , Jour.Geo.Soc.India , vol.78, pp.507-513. S.Varadarajan and C.Pande , (1969), Metamorphic history of Nuggihalli Schist Belt,Hassan district, Mysore state.,Journal of the Indian geo sciences association,vol-10,p-81.R.K.Sahoo ,J.K.Mohanthy,S.K.Das and A.K.Paul, (2009)Chromites of India , their textural and mineralogical characteristics , ISMOMinik.T.Rosing, Robert Frei , Sisir.K.Mandal and Ria Mukhejee ,2010,Compositional variations in the Meso Archean chromites of the Nuggihalli Schist Belt, Western Dharwar craton India: potential parental melts and implications for tectonic setting ,Jour.Geo.Soc.India, vol-10,pp-865-888.perumala V.S.raju, V.S.S.K.Babu, and Ronald K.W.Merkley,(2011),New data on the mineralogy of chromite from the Nuggihalli Schist Belt, J.K.Mohanty , A.K.Paul, R.K.Sahoo, (2001) , Sequence of Chromite crystallization from the Baula-Nausahi igneous complex,Orissa,india

REFERENCE

K.L.Chakraborthy ,Chromite ores associated with the ultrabasic rocks of Baula-Nausahi ,OrissaIndia : Their mineragraphy and genisis. Jour. Geo.Soc.India , vol 24, a, no.1

T.C.Devaraju, R.P.Viljoein , R.H.Sawkhar,(2010),Magic and Ultramafic magmatism and associated mineralization in the DharwarCraton , Southern IndiaChromite data from wikipediaK.T.Damodaran and B.Somasekhar,chrome chlorite from the Nuggihalli Schist Belt. C.Naganna and S.G.Phene, 1969, Study of opaque minerals associated with the Ultrabasic rocks of Nuggihalli Schist Belt, Mysore state, The Indian mineralogist , vol-10,pp.227-235.S.V.Srikanta and S.Jayaram, 1983,Report on the Geology and Geochemistry of part of Nuggihalli supracrustal Belt and adjacent areas , Karnataka,India.C.Naganna and S.G.Phene, 1971, Study of the distribution on the trace elements in the rocks of Nuggihalli Schist Belt, Hassan district, Mysore state.

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