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

V. K. Singh ¹, O. P. Varma ¹

Affiliations
1 Indian School of Mines, Dhanbad, IN

Abstract

The paper, describes the structure and tectonic environments of the tungsten mineralization at Chhendapathar, India's largest tungsten mining district. The main structural configuration of the district developed as a result of early, cross and later fold movements during the Singhbhum Orogeny (2000-850 m.y.). The early folding generated axial plane schistosity, whereas cross fold movements produced asymmetrical folds, and the later folding gave rise to a broad zone of culmination, that was the site of an intrusion-the source of tungsten-bearing solutions, responsible for the ore deposits. Ore controlling structures like shear-slips, shear-fractures and fault-fractures were primarily formed during the period of cross folding. On mineralization, they developed into vein patterns trending: (i) N70°E, (ii) N50°w, (iii) N70°w, (iv) N50°E, and (v) N10°E. Post-ore faults have dislocated the veins, sometimes rotating their strike by about 25°.

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V. K. Singh ¹, O. P. Varma ²

Affiliations
1 Central Mine Planning and Design Institute, Dhanbad, IN
2 Indian School of Mines, Dhanbad 826004, IN

Abstract

Based on the available data, relationship between chemical composition and depositional temperature of wolframites is illustrated by means of a curve, which provides information about the temperatures of deposition of wolframites from their estimated iron-manganese ratios, whose validity as reliable geothermometers, hitherto controversial, is re-established by this study.

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S. Jaireth ¹, A. K. Sen ², O. P. Varma ²

Affiliations
1 Gold Research Group, Geology Department, James Cook University, Townsville, AU
2 Department of Earth Sciences, University of Roorkee, Roorkee, IN

Abstract

The Sung Valley carbonatite complex of Cretaceous age has a core of serpentinized peridotite rimmed by pyroxenite. The complex is intruded by small- to medium-sized bodies of uncompahgrite, ijolite, syenite and carbonatite. The carbonatites occur as stocks, lenses, dykes and veins. Apatite grains in the apatite-magnetite sovite are characterized by three varieties of apparently syngenetic primary inclusions: The type S (solidified) inclusions contain highly birefringent and anisotropic solids along with some gas and liquid; the co-existing type F (fluid) inclusions are of two types-low to moderate salinity gas-liquid inclusions (gas= 15 to 35% by volume) and high salinity gas-liquid inclusions with one or more daughter minerals (halite, sylvite, carbonates). Type S inclusions homogenize into a relatively viscous, melt-like liquid at temperatures between 740 and 806°C whereas type F inclusions homogenize into a liquid phase at temperatures between 177 and 488°C. The large variation in homogenization temperatures between type S and type F inclusions and the difference in their composition are interpreted to be the result of a liquid immiscibility between a volatilerich carbonate melt and a saline aqueous fluid, though contribution of necking down of some original inclusions in generating clusters of type S and type F inclusions cannot be ruled out completely.

Keywords

Carbonatite, Apatite, Fluid Inclusions, Liquid-Immiscibility, Sung Valley.

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O. P. Varma ¹

Affiliations
1 Indian Geological Congress, B. No. 114, 35A, Civil Lines, Roorkee - 247 667, IN

Abstract

No Abstract.

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O. P. Varma ¹, T. R. Sreedhara Murthy ¹

Affiliations
1 Indian Geological Congress, RB. No. 114 35 A Civil Lines, Roorkee - 247 667, IN

Abstract

No Abstract.

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M. S. Pandian ¹, O. P. Varma ²

Affiliations
1 Department of Earth Sciences, Pondicherry University, Pondicherry- 605 014, IN
2 35-A, Civil Lines, Roorkee-247 667, IN

Abstract

Post-Delhi acid magmatism at Degana has yielded three intrusive bodies of topaz granite, the earliest one emplaced within phyllite of Delhi Supergroup and the other two successively in the core of previous intrusive, along with two generations of aplites. Wolframite mineralisation has occurred at two different stages during the magmatism: (1) greisen-bordered vein-type ore bodies hosted by the earliest granite intrusive and adjoining phyllite rcpresent the first stage, and (2) stockwork ore bodies hosted by an intrusion breecia developed at a later stage following the emplacement of other two granite bodies. Presence of topaz, Li-mica and fluorite is a characteristic feature of these granites and wolframite deposits. The granites are strongly peraluminous and geochemically specialised with enrichment of Li, F, Rb and depleted in Sr, K-As dating of zinnwaldite from wolframite bearing lode indicates an age of 860±25 Ma.

Keywords

Neoproterozoic, Topaz Granite, Tungsten Deposit, Delhi Fold Belt, Degana, Rajasthan.

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