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A. B. Roy ¹, P. R. Golani ², B. R. Bejarniya ¹

Affiliations
1 Department of Geology, University of Rajasthan, Udaipur 313 001, IN
2 Geological Survey of India, Assam-Meghalaya Circle, Shillong 793003, IN

Abstract

The Ahar River granite near Udaipur city, considered by Heron as intrusive into the Aravalli rocks of early Proterozoic age, is a coarse-grained, massive, leucocratic rock except along the outcrop margins. The granite ranges in composition from alkali granite to granodiorite and tonalite, with about 5% ferromagnesian minerals. The enveloping Aravalli metasediments form a continuous sequence starting with greenschist (metavolcanics) and quartzite (locally conglomerate) along the granite contact. The stratigraphic position of the Ahar River granite in relation to the surrounding metasediments suggests that the granite is the basement rock. The granite characteristically shows post-crystalline deformation of the constituent grains, specially quartz and feldspar; and the granite-cover contacts are marked by ductile shear zones developed during the earliest deformation of the Aravalli rocks.

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P. R. Golani ¹

Affiliations
1 G.S.I., D-23, Saraswati Marg, Bani Park, Jaipur-302016, IN

Abstract

A zone of fault breccia. gouge, silicification and rare mylonite reveals the presence of a 20 km long north-south trending tensional fault in the granitoid-gneiss terrain of Western Meghalaya. Emplacement of alkaline magmatic rocks including carbonatite, in the form of thin dykes along the fault and associated fractures in the vicinity, indicate deep seated nature of the dislocation. Changes in the drainage pattern in recent past and high microseismicity along the fault zone provide evidences of recent reactivation.

Keywords

Fault, Meghalaya, Carbonatite, Geomorphology.

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P. R. Golani ¹, R. C. Gathania ¹, A. K. Grover ¹, J. Bhattacharjee ¹

Affiliations
1 Geological Survey of India, Jhalana Dungri Complex, Jaipur 302 004, IN

Abstract

Felsic volcanics in the south Khetri Copper Belt (KCB) occur interlayered with fine grey banded phyllitic quartzite which often contains fine carbonaceous matter. The volcanics include crystal tuff, ultrafinely laminated grey tuff and pumice. They have been recognised in field on the basis of vesicles and rare amygdules; and under microscope by embayed and resorbed quartz phenocrysts. Glass is altered and incipiently recrystallised. Devitrification textures like spherulites are intact in rare cases. The relatively unaltered tuffs fall in dacitic field of Total Alkali-Silica (TAS) diagram. The tuffs are intimately associated with baryte and ironstone layers at places. Recent work in the south KCB indicates that sulfide mineralisation is polymetaHic. It is stratabound hosted by felsic volcanics and fine carbonaceous phyllite and quartzite. The mineralised zones show wall-rock alteration in the form of profuse silicification and sericitisation. These features when seen in conjunction with the occurrence of concordant baryte and ironstone layers, indicate that the sulfide mineralisation is volcanic-exhalative type.

Keywords

Felsic Volcanics, Khetri Copper Belt, Rajasthan, Economic Geology.

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P. R. Golani ¹, M. K. Pandit ²

Affiliations
1 A.M.S.E. Wing, Central Zone, GSI, Seminary Hills, Nagpur 440 006, IN
2 Department of Geology, University of Rajasthan, Jaipur 302004, IN

Abstract

The geological, geochemical and C- and Pb-isotopic evidence available on the Newania Carbonatitic Body (NCB) in southern Rajasthan are not entirely incontrovertible from the point of view of carbonatite magmatism. Based on recognition of calcite-lined vugs, 'dog-tooth spar' and 'jig-saw puzzle' structure, the hematite bearing ankeritic carbonates (the ankeritic 'carbonatite') are considered as epithermal emplacements into dolomitic (magnesio-) carbonatite. Seven samples collected from hematite bearing ankeritic (±sideritic) carbonates, which constitute an important component of the NCB, have given gold values ranging between 0.93 to 1.36 ppm. The significance of this find lies in the association of gold with oxides and carbonates of hydrothermal affinity.

Keywords

Economic Geology, Gold Mineralization, Carbonatite, Hematite, Ankerite, Rajasthan.

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P. R. Golani ¹, R. S. Rajawat ¹, N. C. Pant ², M. S. Rao ³

Affiliations
1 Geological Survey of India, AMSE Wing, Central Zone, Seminary Hills, Nagpur - 440 006, IN
2 Geological Survey of India, EPMA Laboratory, NIT-5, Faridabad - 121 001, IN
3 Geological Survey of India, PPOD, AMSE Wing, Bangalore - 560 078, IN

Abstract

Primary gold occurs with sulfides in Paleoproterozoic Aravalli rocks in the Bhukia area of Banswara District, Rajasthan. It occurs as microscopic grains of various shapes, mainly in arsenopyrite and lollingite. With a combined approach of ore petrologic and EPMA studies, we report high purity gold, native bismuth and alloys of gold-bismuth and bismuth-tellurium which best approximate to the rare minerals maldonite and wehrlite respectivety. The fineness of gold ranges between 934 and 995. Preliminary estimates on temperature using arsenopyrite composition coupled with rare presence of spherulitic graphite indicate the temperature of equilibration of around 550°C for the coexisting mineral phases of pyrrhotite, arsenopyrite and lollingite.

Keywords

Economic Geology, Gold Mineralogy, Bismuth, Maldonite, Wehrlite, Lollingite, Bhukia, Aravalli, Rajasthan.

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P. R. Golani ¹

Affiliations
1 Geol Surv India, Jaipur - 302 004, IN

Abstract

No Abstract.

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P. R. Golani ¹, D. Bhattacharyya ², S. Sanyal ², I. R. Kirmani ², G. Malhotra ², S. Bhattacharyya ², A. K. Grover ², J. L. Narang ²

Affiliations
1 Geological Survey of India, A.M.S.E. Wing, Central Zone, Seminary Hills, Nagpur - 440 006, IN
2 Geological Survey of India, Western Region, 15-16, Jhalana Dungri, Jaipur - 302 004, IN

Abstract

The Deldar-Kui-Chitrasani (DKC) fault is a brittle structure manifested by anastomosing system of fractures in the southwestern part of the South Delhi Fold Belt (SDFB). Based on the identification of cross-fibre and 'jigsaw puzzle' type structures, presence of vugs lined with cryptocrystalline quartz, replacement of calcite by chalcedonic quartz and evidences of argillic alteration, the breccia along the fault is recognised by present workers as epithermal breccia. Lithogeochemical sampling of the breccia reveals that, besides moderate base metal signatures, gold values are consistently present in significant concentrations comparable to regional anomalies associated with epithermal gold deposits in the United States. In view of the high proportion of magmatic rocks in the southwestern part of the SDFB, the DKC fault zone is considered a favourable target for searching epithermal type of gold mineralisation.

Keywords

Economic Geology, Epithermal Breccia, Lithogeochemistry, Gold Anomaly, Faults, Shear Zone, South Delhi Fold Belt, Rajasthan, Gujarat.

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P. R. Golani ¹, M. L. Dora ¹, B. K. Bandyopadhyay ¹

Affiliations
1 Geological Survey of Indra, Project Thematic Mapping, Op Maharashtra, Seminary Hills, Nagpur - 440 006, IN

Abstract

The southeastern part of the Proterozoic Betul Belt exposes a Felsic-Dominated sequence around Bhuyari in the Kanhan river sector. The felsic volcanic rocks, identified as rhyolite occur in the form of two mappable bands in a milieu of biotite ± hornblende bearing Quartzo-Feldspathic rocks of subvolcanic affinity. A very well developed zone of hydrothermal alteration is recognized in rhyolite that occurs to the immediate south of Bhuyan village. The hydrothermal facies mapped in the alteration zone include sericite - muscovite-bearing rhyolite, phlogopite± spessartite biotite schist and trernolite (± actinolite) - rich rock with serpentine, talc, epidote and dolomitic carbonates. Discrete grains of fluorite and REE bearing flour carbonates form part of the hydrothermal mineral assemblage. Apart from the magnesian enrichment, the occurrence of spessartite garnet, epidote and sporadic development of staurolite indicate significant fluxes of manganese, calcium and alumina in the zone of hydrothermal alteration. The alteration is attendant with polymetallic base metal mieralisation which is invariably Zinc-Dominated. Bedrock samples and selected channel sampling indicate that the Tremolite-Rich facies is intensely mineralized, followed by phlogopite ± garnet biotite schist. Primary sulphides observed in a dug well section are pyrite, sphalerite galena and chalcopyrite which occur as disseminations and also as several millimeter thick semiconformable veins Rare quartz Phenocryst-Groundmass relationship in the mineralized host rock from the dug well provide incontrovertible evidence for the volcanic affinity of the base metal mineralisation.

Keywords

Base Metal Mineralisation, Hydrothermal Alteration, Volcanic Rocks, Chhrndwara District, Madhya Pradesh.

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P. R. Golani ¹

Affiliations
1 Geological Survey of India Training Institute, 15-16 Jhalana Dungri, Jaipur - 302 004, IN

Abstract

No Abstract.

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Fareeduddin ¹, Susmita Gupta ¹, P. R. Golani ², I. R. Kirmani ³, Suresh Chander ⁴

Affiliations
1 Geological Survey of India, PPOD Division, RSAS Wing, Kumaraswamy Layout, Bangalore - 560 078, IN
2 Geological Survey of India, Training Institute, Jaipur, IN
3 Geological Survey of India, Operations Rajasthan, Jaipur, IN
4 Geological Survey of India, WZ, RSAS, Jaipur, IN

Abstract

Petrology and mineral chemistry of ten types of tourmalines from Pb-Zn bearing strata-bound exhalative deposits and Cu-Au-Fe deposits, presumably of IOCG-type, from Rajasthan are presented. The Pb-Zn deposits studied include Agucha, Kayar and Dariba areas in central Rajasthan, each of which is widely separated in space and occurs in isolated but coeval basins within the Archaean basement. The Cu-Au deposits include Ghagri, Bada Talav, Dugocha and Bhukia areas in southeast Rajasthan. The syngenetic Pb-Zn type and the epigenetic Cu-Au-Fe type of deposits are formed during the initial phase of Paleoproterozoic Aravalli Basin evolution with dominant deposition of shelf facies pelite-carbonate sequence of Debari Group. The post-depositional tectono-metamorphic history of the host rocks of Pb- Zn type and Cu-Au type deposits differ significantly with the former deposits showing higher metamorphic impress (amphibolite to lower granulite facies) than the latter (green schist facies).

This study suggests that tourmalines on individual deposit scale exhibit both similarities and differences in optical and chemical features that are in accordance to their bulk host mineral assemblages. But on individual belt-scale, despite significant differences in the post-depositional metamorphic alterations, there is an overall chemical similarity of tourmalines that suggests prevalence of similar hydrothermal conditions during the formation of the tourmalines of individual deposits in each of the Pb-Zn and Cu-Au belts. In many of the discriminant diagrams using the critical elements, the tourmalines of these two belts maintain a distinct identity and assert their role as metal-type indicator in contemporaneous (Paleoproterozoic) deposits formed in different hydrothermal conditions.

This study also tests the reported role of tetrahedral alumina (Al^iv) and X-site vacancies (X^£) in the tourmaline in indicating the grade of metamorphism of the host rocks. Whereas this study confirms the assertions regarding the covariance of Al^iv with respect to the grade of metamorphism in calcareous and metapelitic sediments, the same assertions could not be made in respect of X^£ for the tourmalines from different ore deposits of Rajasthan. The latter is attributed to the diffusion of Na in the tourmaline structure from the abundantly available Na⁺-rich host rocks (albitites) in a postore formation event.

Keywords

Tourmaline, Pb-Zn Ore Deposit, Cu-Au Ore Deposit, Stratabound, Evaporitic, Paleoproterozoic, Aravalli, Rajasthan.

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Vadlamani Ravikant ¹, P. R. Golani ²

Affiliations
1 Institute Instrumentation Center, Indian Institute of Technology, Roorkee – 247 667, IN
2 Geological Survey of India Training Institute, Jaipur – 302 004, IN

Abstract

In unaltered volcanogenic massive sulfide (VMS) ore deposits, variable Rb/Sr ratios in the ore mineral permits application of the Rb-Sr isotopic method to directly date the time of ore formation. In contrast, post-crystallization deformation and metamorphism would open the system to metamorphic fluids that would alter elemental ratios. To test whether the Rb-Sr isotopic systematics in the ore minerals had preserved the formation time in the ∼800 Ma metamorphosed VMS ores within the ∼1 Ga Ambaji-Sendra arc terrain, Rajasthan, NW India, common sulfides, pyrite and sphalerite from the Pipela Cu-Zn prospect, were analyzed for their geochemistry and Rb-Sr isotopic systematics. Trace and rare earth elements in these minerals are resident probably at crystal defects, whereas all inclusions (including those from metamorphic fluids) were removed by a simple crush leach method. Results of direct dating by the Rb-Sr method to the hydrothermal pyrite yielded an isochron age of 1025 ± 76 Ma with an initial Sr ratio of 0.7051 ± 0.0006, similar to previously determined zircon U-Pb age of 987 Ma from associated rhyolites. This suggests the applicability of the crush leach method to date formation time of metamorphosed pyrite ores.

Keywords

Hydrothermal Pyrite, Rb-Sr Dating, Pipela VMS Cu-Zn Prospect, Rajasthan.

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Vadlamani Ravikant ¹, A. Dharwadkar ², P. R. Golani ³, R. Ravindra ⁴

Affiliations
1 Geochronology and Isotope Geology Division, Geological Survey of India, 15 A&B Kyd Street, Kolkata – 700 016, IN
2 Antarctica Division, Geological Survey of India, NH-5P, NIT, Faridabad - 121001, IN
3 Airborne Mineral and Surveys and Exploration Wing, WR, Geological Survey of India, Jhalana Dungri, Jaipur, IN
4 National Centre for Antarctic and Ocean Research, Headland Sada, Vasco-da-Gama, Goa - 403 004, IN

Abstract

The Grubergebirge anorthosite, a Late Neoproterozoic massif-type anorthosite, was emplaced into Late Mesoproterozoic-aged metamorphosed orthogneisses and supracrustal rocks in the Wohlthat Mountains. Mineralogically and chemically, the marginal rocks to the anorthosite massif classify as ferromonzodiorite and ferromonzonite.

Variations in trace and rare earth element abundances and normalized patterns between the anorthosite and associated marginal ferromonzodiorite (and minor ferromonzonite) and distinct differences between the ferromonzodiorite and ferromonzonite have been observed. Whereas the magmas from which the anorthosite crystallized have been slightly contaminated by incorporating crustal material (now occurring as enclaves), the marginal ferromonzodiorite represent rocks that originated due to mixing (hybridization) of injected primitive ferrodiorite magma(s) with preexisting crustal material, resulting in the hybrid ferromonzodiorite.

These events at the margin of the massif anorthosite represent a widespread Late Neoproterozoic magmatic event with accompanying crustal mixing; all these rocks were thereafter metamorphosed under amphibolite- to granulite-facies conditions during the Early Cambrian Period. In contrast, unmetamorphosed dykes with a ferrodiorite mineralogy, of Late Cambro-Ordovician age, have been found that probably represent a part of the late magmatic suites of the south Petermannketten (Zwiesel).

Keywords

Gruber Anorthosite-Ferrodiorite, Neoproterozoic Magmatism, East Antarctica.

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