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Kaukonen, R. J.
- Chemistry of Cr-Spinels from Ultramafic Complexes of Western Dharwar Craton and its Petrogenetic Implications
Authors
1 Rajamangala', Saptapur, Haliyal Rd., Dharwad-580 00 1, IN
2 Institute of Geosciences, University of Oulu, P.O. Box 3000, SF-9057, Oulu -57, FI
3 Institute of Geosciences, University of Oulu, P.O. Box 3000, SF-9057, Oulu-57, FI
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 69, No 6 (2007), Pagination: 1161-1175Abstract
Ultramafic complexes containing chromite-bearing units occur scattered over a large area of the Western Dharwar Craton (WDC). They are broadly separated into two groups; the older complexes, forming a part of the oldest known Sargur Group and occurring as dismembered enclaves within the Peninsular Gneissic Complex, and the younger, forming part of greenstone belt sequence having emplaced in the early stages of basin formation. In this study, chromitebearing units of the ultramafic complexes of the older group forming the Nuggihalli belt and Rangapura-Shivani complex and the younger group forming the ultramafic complexes of Channagiri, Shankaraghatta and Usgao, have been selectively examined. While Shankaraghatta ultramafite contains sparse disseminations, the other complexes include in addition mm-cm scale bands and lenses\pods of chromite; commercially workable deposits of chromite are confined only to the Nuggihalli belt. Further, whereas PGE mineralization of possible commercial value is recognized in the Channagiri complex, the Shankaraghatta complex encloses Ni-Au-PGE mineralization.
Almost 200 spot analyses of chromite grains occurring in the five different ultramafic complexes of WDC have been obtained. Although it is the most resistant mineral of the rocks, in the intensely altered Channagiri complex it shows deep alteration whereas in the other less altered complexes the alterations are localized to outer zones and margins of the mineral. The least altered Cr-spinel composition (Spl) with XMg0.01-0.656, Xcr 0.553-0.955 and X, 0.014-0.215 is on the whole in the range of aluminian chromite, but, it shows significant variations from one cornplex to the other and even within the limits of a single complex, related to primary magmatic processes. An interesting finding is the presence of occasional relics of titanium chromite in the PGE mineralized Channagiri complex.In addition to common alteration of Spl to ferrian chromite (SpII) (with A12O3:0.47-6.46 %; MgO: 1.4-4.196; Cr20,: 36.1-54.9 %; Fe20,: 11.6-23.1 %), alteration of the mineral to chromian magnetite and magnetite (with A1203,: 0.01-0.84 %; MgO: 0.01-0.07 %; Cr2O3,: 1.17-28.81 %; Fe2O3,: 34.7-63.6 %) is also recorded. These alterations, as well as near total conversion of olivine and pyroxenes into antigorite and chlorite, were brought about by pervasive low-grade regional metamorphism which accompanied penetrative fluid action and deformation. The alteration comprised of two way diffusion of elements. While the formation of ferrian chrornite was associated with quantitative outward migration of Al, Mg and very moderate Cr into the surrounding and inward migration of iron from the surrounding and oxidation of iron, the conversion of chromite into Cr-magnetite/magnetite was brought about by quantitative outward migration of Cr, A1 and Mg into the surrounding and inward diffusion of iron.
As has been the case with many of the examples studied world over, the Cr-spinels of WDC too have chemical characteristics which largely overlap with those of both layered and ophiolitic/podiform examples and do not permit their characterization exclusively as layered or podiform types.
Keywords
Cr-Spinels, Aluminian chromite, Ferrian chromite, Western Dharwar Craton, Karnataka.- Petrological and PGE Mineralisation Study of the Channagiri Mafic-Ultramafic Complex, Shimoga Supracrustal Belt, Karnataka
Authors
1 'Rajamangala', Saptapur, Haliyal Road, Dharwad - 580 001, IN
2 Institute of Geosciences, University of Oulu, PO Box 3000, FIN-90014, Oulu, FI
3 MSPL Limited, Nehru Co-Operative Colony, Hospet - 583 203, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 70, No 4 (2007), Pagination: 535-556Abstract
The Channagiri mafic-Ultramafic complex constitutes the main lithounit of Hegdale Gudda Formation of the Shimoga Supracrustal Belt. Mapping at a scale of 1 2000 coupled with detailed petrological examination of the Platinum Group Element (PGE) mineralized 3 5 km x 0 3 km. Hanumalapur segment of the complex has revealed that it is composed of outer gabbroic zone and central 100-150 m ultramafic zone. While V-Ti magnetite seams occupy the outer boundary of the ultramafic zone, several small isolated lenses/pods of anorthositic variation occur within the ultramafic zone itself. The complex is affected by penetrative deformation, hydrothermal alteration and low-grade metamorphism, which together have caused complete replacement of olivine and pyroxenes by chlorite, amphibole, epidote and carbonate. The gabbro forming outer zone is in the range of quartz gabbro-melagabbro and is strongly banded/foliated. The ultramafite in the central zone is a complex mix of the dominant fine (chromite-chlorite Schist) and subordinate coarse grained units. The magnetite occupying the western interface zone is the typically coarse grained V-Ti variety whereas that on the eastern side includes narrow chromiferous lenses. PGE data obtained for the different units of Hanumalapur segment has revealed that only the central fine-grained ultramafite and the chromiferous lenses in the eastern magnetite seam host PGE mineralization of commercial interest with Pt+Pd values ranging from 1 5 to 6 ppm, the other lithologies of the segment as well as those constituting the remaining segments of Channagiri ultramafic complex and Hegdale Gudda Formation have not yielded positive anomalies of PGE mineralization. The governing control of chromite over the separation of PGE in the very early stages of magmatic crystallization is inferred taking into account the close association of PGE with the chromite-bearing units. The recorded textural relationships suggest that the PGEs remained virtually immobile during later penetrative alterations of the host rock.
Geochemically, the PGE mineralized ultramafic units of Hanumalapur segment carry signatures of basaltic komatiite to Fe-Rich tholerite and in terms of Pd/Ir Ni/Cu, Pd/Pt Ni/Cu and Ni/Pd Cu/Pt ratios they compare with layered intrusions.
The chromite controlled PGE mineralization of Hanumalapura roughly resembles the UG2 of the Bushveld complex and a part of the SJ reef of the Penikat Detailed logging of a 252 m deep drill core has revealed the existence of three ore reefs of 20, 30 and 35cm thickness, analyzing 37,50 and 40 ppm Pt+Pd respectively located within a 5 m zone and 5 lower grade reefs of 035 m to 10 m thickness analyzing 1 3 to 1 8 ppm Pt+Pd (and 07 to 1 8% Cu), located in a 50 m wide zone, just above the main ore zone. The PGE reefs of Hanumalapur segment include both Pt- and Pd rich ones but the latter dominate.
Keywords
Channagiri Mafic-Ultramafic Complex, PGE Distribution, Chromite-Controlled, Hanumalapur Segment, Shimoga Belt, Karnataka.- Petrology, Geochemistry, Model Sm-Nd Ages and Pedogenesis of the Granitoids of the Northern Block of Western Dharwar Craton
Authors
1 Rajamangala, Saptapui, Hahyal Road, Dharwad - 580 001, IN
2 Geological Survey of Finland, PO Box 96, FI-02151, Espoo, FI
3 MSPL Limited, Baldota Enclave, Hospet - 583 203, IN
4 Department ol Geosciences, University of Oulu, PO Box 3000, FI-90014, Oulu, FI
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 70, No 6 (2007), Pagination: 889-911Abstract
Gianitoids comprising the northern block of Western Dharwar Craton (WDC), enclosed within the 225 km long and 40 km wide transect corridor stretching from East of Gadag to the Goa coast, have been examined in the field, mapped and interpreted on the basis of petrological, geochemical and Sm-Nd isotopic data. The rocks constitute 43% of the corridor lithology and include 5 large plutons of batholithic dimensions and two Stock-Like bodies. Those are classified as Anmod Ghat trondhjemite(AGT), Chandranath granite(CNG), Dudhsagar granite(DSG) Ramnagar migmatite (RNM), Ramnagar granite gneiss(RNGn), Ramanagar porphyntic granite(RNPG), Annigen-Majjigudda granite(AMG) and Hatalgen-Naregal migmatite(HNM) Of these, only RNM and HNM show the typical polyphase migmatitic character, the remaining are lather homogeneous with only localized occurrence of tectomcally emplacedmahc rocks and pegmatiteaphte. Modal mineral compositions coupled with geochemical parameters especially the combination of K, Rb, Sr, Sr/Ba, LaN/YN and Eu/Eu* values, serve as the distinctive features of the granitoids. The granitoids and greenstone belts of the corridor show overall structural conformity and evidence of Low-Grade metamorphism in the range of Greenschistlow-Amphibohte facies. There is no obvious evidence of their diapinc emplacement and contact metamorphism the granitoids bear essentially a basement relation towards the associated greenstone belts. The results of Sm-Nd isotopic analyses have indicated existence of mainly three groups viz , (I) the older trondhjemite (AGT) - Tonahte (RNM) - Monzogranite (HNM) providing model ages (TDM) of around 3 3 Ga, (ii) a suite of granitoids viz CNG, DSG, RNGn and RNPG with TDM between 2 96 and 2 83 Ga and (in) younger granite viz AMG, dating 2 68 Ga The isotopic data suggests that the protohth of AGT was different from that of CNG, RNGn and RNPG Higher soda and Na2O K20 ratio of 1 1 or more and marked depletion in REE of all the younger granitoids of the tiansect are distinctive chemical features as compared to Closepet Granite, Hyderabad Gianite and other younger K rich granites in the Eastern Dharwar Craton The geochemical characteristics recorded place the granitoids of the corridor closer to those constituting Peninsular Gneissic Complex in the Southern part of WDC.Various chemical parameters suggest derivation of the transect granitoids from predominantly igneous protohths and their emplacement in syncolhsional volcanic arc regime In addition, their lithogeochemical features suggest that they constitute separate plutons AGT is related to a 3 3-3 4 Ga old crust forming event RNM and HNM are products of reworking of old crust whereas the remaining granitoids of the corridor appear to be plume related.
Keywords
Geochemistry, Granitoids, Gadag-Goa Transect, Model Sm-Nd Isotopic Data Igneous Protoliths, Postorogenic, Syn-Colhsional Regime, Western Dharwar Craton.- Tremolite-Olivine-Phlogopite-Bearing Ultramafic Enclaves in The Archaean Migmatite Gneiss near Naregal, Gadag District, Karnataka
Authors
1 Department of Applied Geology, Kuvempu University, Jnanasahyadri Shankaraghatta, Shimoga- 577 45 1, IN
2 Institute of Geosciences, University of Oulu, PO Box 3000, Oulu, FI
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 67, No 3 (2006), Pagination: 312-316Abstract
The polyphase migmatite gneiss exposed in the vicinity of Naregal contains unusual ultramafic enclaves with the modal composition of 50% tremolite, 21% olivine, 16% phlogopite, 10% Cr-magnetite(with 5 6 wt% Cr2O3) and 2% anthophyllite. Geochemically the enclaves resemble 'Barberton komatite' in respect of high MgO, Ni, Cr and Low Al2O3, and TiO2, and one of 'Wajrakarur kimberlite' plug rocks with reference to'high K2O, Rb Zr and Ba. The finding suggests the possible existence of pristine crust in the northern part of the Western Dharwar Craton.Keywords
Ultramafic Enclaves, Polyphase Gneiss, Fresh Olivine, Phlogopite, Pristine Crust, Naregal Karnataka.- SEM-EDS Study of the Platinum-Group Minerals in the PGE Mineralized Hanumalapura Segment of the Layered Mafic-Ultramafic Complex of Channagifu, Davangere District, Karnataka
Authors
1 Department of Applied Geology, Kuvempu University, Jnanasahyadri, Shankaraghatta, Shimoga - 577 451, IN
2 institute of Geosciences, University of Oulu, P.O.Box 3000, Oulu, FI
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 65, No 6 (2005), Pagination: 745-752Abstract
SEM-EDS study of outcrop samples from the PGE mineralized, layered Hanumalapura segment of the Channagiri Mafic-Ultramafic complex, has revealed that they contain a variety of Platinum-Group mineral inclusions. Among more than 25 different PGM's distinguished, sperrylite, stibiopalladinite, hollingworthite, keithconnite, mertieite II, laurite, ruarsite together with a suite of Pt and Pd alloys, constitute the more important carriers of PGE in the ore reefs. From the close association of PGM's with chromite-bearing host rocks, it is inferred that crystallization of chromite had the governing control over the concentration of PGE.- Geochemistry of Ultramafic Lenses in the Granitoids of the Southeastern Flanks of Shimoga Supracrustal Belt (karnataka) with a Note on the Distribution of Platinum Group Elements and Minerals
Authors
1 Department of Studies in Geology, Karnatak University, Dharwad - 580 003, IN
2 Institute of Geosciences, University of Oulu, P.O.Box 3000, FI
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 63, No 4 (2004), Pagination: 371-386Abstract
Almost Thirty Individual Lenses of Ultramatites Occur Within about 150 Km2of the Basement Granitords of the Peninsular Gneiss forming Southeastern flanks of the Shimoga Supracrustal Belt. They form Small elongated Bodies (<50 M X l Km) which are most Commonly Oriented Parallel to the General Northwesterly Strike of the Basement Granitoids.The Ultramafites fall Mainly in the Range of Chromitite-dunite-peridotite-pyroxenite. the Original Textures as well as Mineralogy of the Rocks are Considerably Modified by Pervasive Deuteric and Low-grade Metamorphic Alterations. Chlorite (and/or Antigorite) and Fe-cr Oxides are the Ubiquitous Minerals. Amphibole is abundant only in Hornblendite. Carbonate, Epidote, talc, Magnetite and Sphene Occur in Minor Amounts. The Re1ics of the Original Olivine and Pyroxenes are very Rare.
Geochemically, the Ultramafites include High-cr, High-mg, High-a1 and High-fe Types. of the Four, High-cr and -Mg types Account for the Largest Proportion, whereas High-A1 and Fe-types Constitute only Local Variations. the overall High Magnesia (25.6 Wt%) and Alumina (9.5%), Iow Lime (2.8 %) and very Low Alkalis (< 0.1%) are Distinctive Major Element Geochemical Features. Marked Enrichment of Ni (1317 Pprn) in High-Cr and -Mg Types, Ti (3.9%) and V (1176 ppm) in High-fe Type and Zr (291 Ppm) in High-A1 Type are among Distinctive Trace Element Geochemical Features. Low REE (3.2 - 18.5 Ppm) and Nearly Flat Chondrite Normalized Patterns Characterize High-Cr and -Mg Types. the High-A1 Type has Contrastingly High REE (141.6 Ppm) and Markedly Enriched in LREE.The High-Cr and -Mg Types Bear Geochemical Signatures of Derivation from Higher Degree of Partial Melting of Garnet-lherzolite Layer of the Mantle. Mixing of Primitive and Evolved Magmas is Indicated by the Composite Association of High-Cr, -Mg, and -Fe Units Noted in some of the Ultramafic Bodies. the High-a1 Type with Strong Enrichment in Ree and Zr Bears Evidence of Derivation from Segregation of Late Stage Residual Liquids. Kornatiitic Bulk Composition of the Parental Magma is Indicated by some of the High-Cr and -Mg Ulyarnafites. the Chromite-dunlte-peridotite-pyroxentite Association Strongly Suggests that the Ultramafite Lenses of the Area Constitute Parts of a Tectonically Emplaced Layered Body.
Analysis of as many as 27 Samples of Ultramafites, Covering all the important Petrographic Variations has not Revealed either Anomalies in the Content of Pt and Pd or Possible Potential of PGE minerailzation. Samples from the layered Ultrarnafite body to the East of Rangapura, Containing Variable Proportions of Chromite Bands, However, have Yielded Significantly High Os, Ir, Ru and Rh Values (the Total of these Ranges from 130 to 240 Ppb). these Samples also Contain Minute Platinum Group Mineral (pgm) Inclusions, Mainly in the Range of Ladrite-irarsile and less Frequently those Corresponding to Erlichmanite, Osarsite, Irarsite and Bowieite. the Pge Mineral Inclusions are Early formed Phases of Deep Seated Crystallization which became Entrapped in Later Crystallized Chrornite and Silicates. the Ubiquitous Hydrothermal and Low-grade Metamorphic Alterations have not Apparently Caused Significant Migration of Pge.
Keywords
Ultramafic lenses, Geochemistry, PGE and PGM, Shimoga Schist Belt, Karnataka.- Ni-Au-PGE Mineralization in the Ultramafic Body at Shankaraghatta, Shimoga Schist Belt, Karnataka: A Mineralogical and Geochemical Study
Authors
1 Department of Applied Geology, Kuvempu University, Jnanasahyadri, Shankaraghatta, Shimoga - 577 45 1, IN
2 Institute of Geosciences, University of Oulu, P.O.Box 3000, FI
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 63, No 6 (2004), Pagination: 611-624Abstract
Association of Ni and PGE with the already known gold mineralization is recognized in about 5 m wide sulphide zone in the ultramafic rock exposed between Bhadra Reservoir and northern border of Kuvempu University Campus. The mineralization is picked up over a strike length of almost 3 km. The mineralized ultramafite, which is a metadunite, contains about 94% serpentine, 3% sulphides, 1% magnesite and 0.5% Fe-Cr oxide. Millerite and pentlandite are the main carriers of Ni. Gold varies from native gold to electrum. Melonite greatly dominates michenerite, merenskyite and Pd-Ti-Bi-Sb alloy among Pd minerals identified. Pt is present both as sperrylite and as irarsite. Au as well as Pd-Pt minerals occur as minute inclusions of 1 to 10 microns in size. About 50% of these inclusions are in sulphides, 10% in silicates and the remaining are located along the contacts between the sulphides and silicates.
The ultramafite contains isolated pods and patches of chlorite-Rock which are contrastingly enriched in Al, Fe, Ti, Mn, REE, Y, Th, U, Zn and Zr and depleted in Si, Mg, Ni, Cr, As and Bi. These chlorite pods are interpreted as products of late stage residual liquid of ultramafic magma.
The Shankaraghatta ultramafite is not a layered intrusion. The primary economic target in this case is Au and Ni and not PGE as in stratabound deposits. Here the distribution of Ni, Au and PGE is controlled by sulphides. Concentration of the metals in sulphide melt by liquid immiscibility is suggested. Very high MgO and contrastingly low Al2O3 and TiO2 of the mineralized metadunite of Shankaraghatta suggest its formation from ultramafic magma derived from high degree (20-25%) of partial melting of fertile mantle associated with plume activity.
Keywords
Late Archaean, Metadunite, Ni-Au-PGE Mineralization, Millerite, Pentlandite, Melonite, Liquid Immiscibility, Shimoga Schist Belt, Karnataka.- Geochemistry of Ultramafic Lenses in the Granitoids of the Southeastern Flanks of Shimoga Supracrustal Belt [karnataka] with a Note on the Distribution of Platinum Group Elements and Minerals
Authors
1 Geological Survey of India, Bangalore, IN
2 Geological Survey of India, Hyderabad, IN
3 Department of Studies in Geology, Karnatak University, Dharwad - 580 003, IN
4 Institute of Geosciences, University of Oulu, P 0 Box 3000, FI
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 64, No 5 (2004), Pagination: 702-704Abstract
No Abstract.- Petrology and Geochemistry of Greywackes from Goa-Dharwar Sector, Western Dharwar Craton: Implications for Volcanoclastic Origin
Authors
1 'Rajamangala' Saptapur, Haliyal Road, Dharwad - 580 001, IN
2 Department of Applied Geology, Kuvempu University, Jnanasahyadri, Shankaraghatta - 577 451, IN
3 Institute of Geosciences, University of Oulu, P.O.Box 3000, FIN-90014, Oulu, FI
4 School of Geosciences, University of Witwatersrand, Johannesburg, ZA
5 Ashapura Minechem Ltd., 'Sita Kunj', # 4-119C, Kunjibettu, Udupi - 576 102, IN