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Godhavari, K. S.
- Carbonaceous Metaexhalite of Shungitic Affinity in Palaeoproterozoic Aravalli Supergroup, Dugocha Area, Rajasthan
Authors
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
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 63, No 5 (2004), Pagination: 522-532Abstract
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.
- Lamprophyre Dykes in Chotanagpur Gneissic Comlex, Near Simdega, Gumla District, Jharkhand
Authors
1 Geological Survey of India, Central Zone, AMSE Wing, Ranchi, IN
2 Geological Survey of India, AMSE Wing, 40th Cross, Eshwar Nagar, Bangalore - 560 078, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 63, No 6 (2004), Pagination: 655-658Abstract
Lamprophyre dykes are reported from the Precambrian metamorphites of the Chotanagpur Gneissic Complex near Simdega, Gumla district, Jharkhand. Petrological and petrochemical studies indicate that they are calc-Alkaline lamprophyres. The economic significance of these lamprophyres is discussed in light of their proximity to (i) the gold prospects in its strike continuity and (ii) reported occurrences of diamonds in the major drainage basins of the region.Full Text
- Three New Candidate Rock Standards: Granite, Dunite and Anorthosite from Geological Survey of India, Bangalore
Authors
1 PPOD Division, AMSE Wing, Geological Survey of India, Bangalore - 560 070, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 59, No 3 (2002), Pagination: 273-275Abstract
Petrology, Petrochemistry and Ore Dressing (PPOD) Laboratories of the Airborne Mineral Surveys and Exploration (AMSE) Wing, Geological Survey of India, Bangalore has taken up the preparation of three International Rock Standards/Geostandards of a granite from Chamundi Hills, Mysore (designated as GSI-CG-1), a serpentinised dunite from Dodkanya dunite/magnesite mines, Mysore District (designated as GSI-DD-1) and an anorthosite from the Sittampundi Anorthosite Complex, Salem District, Tamil Nadu (designated as GSI-SA-1). Details of the three rock-standards are provided here for participative collaboration of interested geochemcial laboratories.Full Text
- Dr. S. V. P. Iyengar (1921-2012)
Authors
1 Bangalore, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 80, No 1 (2012), Pagination: 136-138Abstract
No Abstract.Full Text
- Earth Day-22 April, 2012: 'Every Day is an Earth Day, Earth's History and Human Impact-Related Challenges'
Authors
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 79, No 6 (2012), Pagination: 559-662Abstract
No Abstract.Full Text