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

M. S. Rao ¹, Fareeduddin ¹, K. S. Godhavari ¹, Suresh Chander ², C. P. Sisodia ²

Affiliations
1 PROD Division, AMSE Wing, Geological Survey of India, Eshwar Nagar, Bangalore -560 082, IN
2 AMSE Wing, WZ, Geological Survey of India, Jhalana Dungri, Jaipur - 302 004, IN

Abstract

The Palaeoproterozoic Debari Group of Aravalli Supergroup near Dugocha, Rajasthan exposes carbonalbite-tourmaline bearing exhalite rock termed carbonaceous metaexhalite. This unit occurs within dolomites of Jagpura Formation and hosts gold-bismuth bearing sulphide mineralisation either within it or along dolomite-metaexhalite contact zones. Polyphase deformation and mineral recrystallisation under green schist facies of metamorphism characterise these rocks.

Geochemically, the carbonaceous metaexhalites have a wide silica range (51 wt% to 63 wt%) and high total alkali (7.85 wt % to 13.20 wt%). EPMA studies of silicates indicate that the main feldspar in the rock is albite and the tourmalines are richer in titanium and chromium. The associated sulphides possess high salinity fluid inclusions (up to 19 wt% NaCl equivalent) and δ³⁴S isotopic values of 12-14 permil. The latter values match well with those of the modern hydrotherms along Discovery Deep median trench of Red Sea.

The most outstanding feature of the rock is abundant carbon and its distribution pattern vis-a-vis associated silicates. The carbon distributed mainly as tiny graphite flakes of low order crystallinity often exceeds 30% by volume and analyses upto 15% by weight. There is an intimate intergrowth of the carbonaceous matter and the composite silicates that gives unique identity to the rock as for the texture and constituent minerals. These features together with their similar age and geological set-up have been discussed in terms of these rocks being similar to the multi-utility carbonaceous rocks with high economic significance found in Shunga Region, Karelia, Russia called Shungites. These high sodacarbon rocks are interpreted here as metamorphic products of mixed volcanic-clastic-exhalite facies rocks (felsic lavas, tuffs, exhalite and carbonate rocks) or the metamorphosed product of the original soda-carbonate volcanic flows during initial stages of Aravalli ensialic rifts.

Keywords

Carbon, Shungite, Albite-Graphite-Tourmaline Metaexhalite, Gold, Proterozoic, Aravalli, Debari, Dugocha, Rajasthan.

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Suresh Chander ¹, C. P. Sisodia ¹

Affiliations
1 Geological Survey of India, AMSE Wing (Western Zone), GSI Complex, 15-16, Jhalana Dungn, Jaipur - 302 004, IN

Abstract

Ground re-evaluation of airborne electromagnetic and magnetic anomaly zones associated with geological and geochemical studies has brought to light the presence of two significant zones of gold mineralisation at Baratalav- Dugocha and Manpur-Lohagarh in Sanjela-Manpur-Dugocha belt of Salumbar area, Udaipur district, Rajasthan The area exposes a Palaeoproterozoic carbonate dominated volcano-sedimentary sequence including quartzite, dolomite and meta-exhahte of the Debari Group forming a part of the Aravalh Supergroup This sequence shows polyphase deformation and greenschist facies metamorphism and shows presence of shear zones trending in northwest- southeast direction in conformity with the general foliation trend of the rocks in the area The shear zones are characterized by siltcification, brecciation, and hydrothermal alteration

Auriferous sulphide mineralisation occurs in the Jagpura Formation of the Debari Group in the Sanjela Manpur- Dugocha belt The Baratalav-Dugocha mineralised zone characterized by occurrence of gossan and presence of ancient workings is confined to a shear zone Bedrock samples from a thick band of meta-exhahte within the dolomite horizon occurring northwest of Dugocha have analysed 1 to 4 ppm of gold The gold values in dolomite range between 0 10 ppm and 2 70 ppm in Baratalav and between 0 15 ppm and 8 52 ppm in Dugocha area The Manpur Lohagarh mineralised zone, characterised by linear ancient workings and gossans, also occurs in the proximity of a shear zone Richer concentration of gold mineralisation can be expected along shear zones that are believed to have offered easy passage for gold-sulphide mineralising fluids.

Keywords

Gold Mineralisation, Palaeoproterozoic, Meta-Exhahtes, Dugocha area, Rajasthan.

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K. R. Raghu Nandan ¹, Suresh Chander ², C. P. Sisodia ²

Affiliations
1 787, 7th Cross, M.C. Layout, Viyayanagar, Bangalore - 560 040, IN
2 AMSE Wing, Geological Survey of India, WZ, Jaipur - 302 004, IN

Abstract

No Abstract.

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