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Authors
Affiliations
1 Wadia Institute of Himalayan Geology, 33, G. M. S. Road, Dehra Dun - 248001, IN
2 Geological Survey of India, Jawaharlal Nehru Marg, Kolkata - 700 016, IN
3 Department of Geology, University of Rajasthan, Jaipur - 302004, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 61, No 1 (2003), Pagination: 37-50
Abstract
The S-type, high-level, biotite granite (Sewariya Granite) intruding the metasediments of the South Delhi Fold Belt in central Rajasthan hosts W-mineralization that occurs within the shear controlled late-stage quartz veins. The fluid inclusion data of the observed type 1 to type 4 inclusions in mineralized quartz veins and type 1, type 2 inclusions in fluorite reveal that the high to low temperature alkali chloride solution was in equilibrium with syn to post W-mineralization events. Boiling at a temperature range of 373 to 417°C is recorded in the earliest fluid inclusions viz. gas rich type 2 and liquid rich type 3 inclusions, which together show a continuum in the fluid density from 0,2 to 0.85 g/cm3. Dominance of high saline aqueous fluid with 32.5 to 43.3 equiv. wt percent NaCl is represented in type 1 inclusions. The increase in salinity to the extent of Tm NaCl> Th L-V is attributed to the boiling of fluid and successive influx of high saline hydrothermal fluid exsolved from crystallizing granite source rocks. Type 1 inclusions of fluorite show a difference from type 1 inclusions of mineralized quartz in terms of their lower temperature and a common Th> Tm NaCl homogenization trend. Type 4 inclusions are secondary mostly homogenized below 170°C,these are unrelated to the mineralization event. The observed conditions favour the interpretation that tungsten was transported as tungstic acid in the CI and vapour rich hot hydrothermal solution. A low pressure of 250-350 bars at about 400°C is suggested for this W-mineralization.
Keywords
Tungsten Mineralization, Sewariya Granite, Fluid Inclusions, Delhi Fold Belt, Rajasthan.
