Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

T. C. Devaraju ¹, T. T. Alapieti ², A. A. Halkoaho ², K. A. Jayaraj ¹, S. D. Khanadali ¹

Affiliations
1 Dept of Studies in Geology, Karnatak University, Dharwad 580 003, IN
2 Dept of Geology, University of Oulu, Linnanmaa, SF 905 070, Oulu, FI

Abstract

No Abstract.

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T. C. Devaraju ¹, T. T. Alapieti ², R. J. Kaukonen ³, T. L. Sudhakara ³

Affiliations
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

Abstract

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 X_Mg0.01-0.656, 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.

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T. C. Devaraju ¹, T. T. Alapieti ², R. J. Kaukonen ², T. L. Sudhakara ³

Affiliations
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

Abstract

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.

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T. C. Devaraju ¹, R. J. Kaukonen ², T. L. Sudhakara ¹, T. T. Alapieti ²

Affiliations
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

Abstract

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.

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T. C. Devaraju ¹, T. T. Alapieti ², R. J. Kaukonen ²

Affiliations
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

Abstract

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.

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T. C. Devaraju ¹, T. T. Alapieti ², R. J. Kaukonen ²

Affiliations
1 Department of Studies in Geology, Karnatak University, Dharwad - 580 003, IN
2 Institute of Geosciences, University of Oulu, P.O.Box 3000, FI

Abstract

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.

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T. C. Devaraju ¹, T. T. Alapieti ², R. J. Kaukonen ²

Affiliations
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

Abstract

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.

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K. T. Vidyadharan ¹, S. Paranthaman ¹, K. N. Rao ², T. C. Devaraju ³, T. T. Alapieti ⁴, R. J. Kaukonen ⁴

Affiliations
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

Abstract

No Abstract.

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T. C. Devaraju ¹, T. L. Sudhakara ², R. J. Kaukonen ³, R. P. Viljoen ⁴, T. T. Alapieti ³, S. A. Ahmed ², S. Sivakumar ⁵

Affiliations
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

Abstract

Late Archaean Supracrustals of the Goa-Dharwar sector (GDS) are composed of a thick sequence of greywacke sequence with narrow intercalations of quartzite, BIF and carbonates. Mafic volcanics occupy the base of the sequence. The greywackes are predominantly tuffacious containing chlorite-sericite and hornblende. Arkosic variations containing biotite dominate the western part of the sector. Fine-grained variations occur as isolated narrow lenses within other types of greywackes. The conglomeratic greywackes are localized along the western and the eastern margins of the sector. All of the greywackes are all typically immature containing coarser clasts of mostly plagioclase (18-23%) and quartz (32-34%). Lithic fragments of felsic volcanic rocks are common. The matrix is dominated by mafic material. Biotite and amphibole are related to metamorphic recrystallization. Chlorite, sericite, epidote, carbonate and chert are products of the interplay of diagenesis and low-grade metamorphism. Fe-Ti oxide, sphene, apatite and zircon are usual accessories. But for slight enrichment in K₂O, the major element chemistry of the GDS greywackes is similar to the chemistry of Late Archaean greywackes. They also compare in respect of V, Co, Hf contents, K₂O/Na₂O, SiO₂/Al₂O₃, Na₂O/Al₂O₃, Ba/Rb, Th/U, La/Th, Sm/Nd ratios, steep REE patterns with distinct LREE enrichment and HREE depletion. The GDS greywackes however are distinctly enriched in Rb, Ba, Sr, Th, U, Cu, Zr, Ce/Ce^* and depleted in Cr, Ni, and Zn. The conglomeritic and biotite bearing verities contain considerable proportions of clasts derived from the basement tonalitic/granitic terrain. The common tuffacious greywackes containing hornblende and biotite-sericite however include only volcanic clasts and bear evidence of derivation from submarine weathering of predominantly felsic volcanics erupted on a large scale to form a magmatic arc in the later stages of geosynclinal deposition. Geochemical data suggest that the GDS greywackes were laid down in progressively changing basin geometry from a passive to active continental margin and island arc setting.

Keywords

Greywackes, Felsic Volcanic Source, Continental Island Arc, Submarine Weathering, Goa-Dharwar Sector.

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T. C. Devaraju ¹, T. T. Alapieti ², K. S. Ananthamurthy ³

Affiliations
1 Department of Studies in Geology, Karnatak University, Dharwad - 580 003, IN
2 Institute of Geosciences and Astronomy, University of Oulu, Linnanmaa, SF-90570, Oulu, FI
3 Department of Environmental Sciences, Bangalore University, Jnanabharati, Bangalore - 560 056, IN

Abstract

No Abstract.

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T. C. Devaraju ¹, T. T. Alapieti ²

Affiliations
1 Department of studies in Geology, Karnataka University, Dharwad - 580003, IN
2 Department of Geology, Institute of Geoscience and Astronomy, University of Oulu, Linnanmaa SF-90570, Oulu, FI

Abstract

No Abstract.

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