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

S. Jaireth ¹

Affiliations
1 Department of Earth Sciences, University of Roorkee, Roorkee, IN

Abstract

δ³⁴S values of chalcopyrite and pyrrhotite from the two deposits have been interpreted following 'Ohmoto-procedure'. Analysis of appropriate log^aO₂-log^aS₂ diagram shows that a hydrothermal fluid having sulfur with δ³⁴S values varying between + 3‰ to +5‰ explains best the recorded range of δ³⁴S values. Such a sulfur in hydrothermal fluid can be derived frem an igneous source only.

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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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