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

Ashok Ballurkar ¹, P. C. Pal ¹

Affiliations
1 Centre of Exploration Geophysics, Osmania University, Hyderabad-500 007, IN

Abstract

The ultramafics of Roro are layered bodies comprising two major lithological units-serpentinised pyroxenites (SPX) and serpentinised saxonites (SSX). Ribbon zones of chrysotile mineralisation are found localised in thin granular serpentinite (SR) horizons at the contacts of 'the SPX and SSX layers in cross folded portions of these ultramafic bodies.

The SSX rock is typically a clot-bearing one, comprising poikilitic clots of saxonitic composition embedded in relatively olivine-rich and more serpentinised groundmass. Two controls for chrysotile localisation can be readily identified in the Roro ultramafics. The lithological control is provided by extensively serpentinised interfaces of the already partially serpentinisied pyroxenitic and saxonitic layers. These horizons of secondary serpentinisation (viz., the SR horizons) appear to have resulted from either a fusion of the SPX and SSX rocks at their contacts or, alternately, from the segregation of the SSX clots at the interfaces of these layers and their subsequent serpentinisation. The composition of the SSX rock therefore appears to have been a vital factor in fibre development in the SR horizons. The structural control is considered to have been provided by the superposition of structural deformations due to Singhbhum orogeny over those caused by the older Iron ore orogeny.

Fibre development is indicated to be a dynamothermal process in the structure-restricted zones of secondary serpentinisation in an already serpentinised ultramafic body.

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Abhijeet Mukherjee ¹, Ashok Ballurkar ²

Affiliations
1 National Mineral Development Corporation Ltd., Masab Tank, Hyderabad-500 028, IN
2 Centre for Exploration Geophysics, Osmania University, Hyderabad-500007, IN

Abstract

The δ³⁴S X-CDT values for barite and pyrite range from +23.6 to +25.5 per mil and -0.9 to +1.9 per mil respectively. Data of fluid inclusion studies enable temperature of deposition to be 250°C after pressure correction of homogenization temperatures (Th). The δ³⁴S X-CDT values of pyrite and barite suggest igneous source for pyrite and marine for barite implying that they are not formed together. The δ³⁴S X-CDT values of barite agree with δ³⁴S X-CDT values for contemporaneous Proterozoic sea water.

Keywords

Sulphur Isotopes, Barite, Pyrite, Cuddapah Basin, Andhra Pradesh.

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Abhijeet Mukherjee ¹, Ashok Ballurkar ²

Affiliations
1 National Mineral Development Corporation, Khanij Bhavan, Masab Tank, Hyderabad-500028, IN
2 Centre of Exploration Geophysics, Osmania University, Hyderabad-500007, IN

Abstract

Fluid inclusion study is carried out on the vein and bedded-type barite of the Proterozoic Cuddapah basin of Andhra Pradesh. In the case of vein barite, primary inclusions are mostly monophase and liquid-rich biphase (L+ V), with their freezing temperatures indicating their composition as H₂O+NaCI±KCl and density of the ore forming fluids as 0.901 to 0.944 g/cm³. The primary liquid-rich biphase (L+V) inclusions of the hydrothermal vein barite shows homogenization temperatures in the range of 230° to 260°C. The primary inclusions of the bedded (volcanogenic) barite deposits of Mangampeta are monophase carbonic with densities corresponding to 0.76 to 0.88 g/cm³. A conceptual mobilization-deposition model for the vein-type barite mineralization is given.

Keywords

Fluid Inclusion, Barite, Geochemistry, Cuddapah Basin, Andhra Pradesh.

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