Petrology, geothermobarometry and C-O-H-S fluid compositions in the environs of Rampura-Agucha Zn-(Pb) ore deposit, Bhilwara District, Rajasthan |
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| Authors: | M Deb Uma Sehgal |
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| Institution: | (1) Department of Geology, Delhi University, 110 007 Delhi, India;(2) Present address: Central Ground Water Board, Man Singh Road, 110011 New Delhi, India |
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| Abstract: | The massive Zn-(Pb) sulfide ore body at Rampura-Agucha in Bhilwara district, Rajasthan, occurs within graphitic metapelites
surrounded by garnet-biotite-sillimanite gneiss containing concordant bodies of amphibolite. These rocks and the sulfide ores
have been studied to estimate the pressure, temperature and fluid composition associated with upper amphibolite facies metamorphism.
Geothermobarometric calculations involving garnet-biotite and garnet-hornblende pairs, as well as sphalerite-hexagonal pyrrhotite-pyrite
and garnet-plagioclase-sillimanite-quartz assemblages indicate that the most pervasive P-T condition during peak of regional
metamorphism was 650°C and 6 kb, and was attained between the first and second deformations in the region. Some temperature-pressure
estimates also cluster around 500°C–5.1 kb which probably represent retrograde cooling during unloading.
Consideration of devolatilization equilibria in the C-O-H-S system at the pervasive metamorphic conditions mentioned above
shows that the metamorphic fluid was H2O-rich (
) but also had a substantial component of
.
and
were the other important phases in the fluid. CO (XCO = 0.002) and
were the minor phases in the fluid. It is probable that a part of this aqueous fluid was consumed by re-/neocrystallization
of hydrous silicate phases like chlorite during the retrogressive metamorphic path, so that fluid entrapped in quartz below
450°C was rendered CO2-rich (Holleret al 1996). |
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| Keywords: | Rajasthan mineral chemistry geothermobarometry metamorphic fluids C-O-H-S equilibria |
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