Hydrothermal gold mineralisation in the Bhukia gold prospect of the lower Proterozoic Aravalli fold belt of Rajasthan
Garhia, S.S.; Jat, R.L.; Guha, D.B.; Harpawat, C.L.
Special Publication Series - Geological Survey of India 58: 375-384
Auriferous sulphides in Bhukia prospect are hosted by the Delwara Group made up of dolomitic marble, quartzite, keratophyre, meta-pyroxenite, amphibolite, meta-pelite and pegmatite litho-assemblage constituting the lower part of the Aravalli Supergroup. The ore bodies and their oxidised equivalents (gossans) developed after massive, semi-massive to disseminated sulphides, occur as a series of isolated to continuous bodies exhibiting discordant relationship with the folded schistosity (S (sub 1) = S (sub 0) ). The sulphide hosted gold mineralisation and associated hydrothermally altered zones characterised by intense carbonation, amphibolisation and tourmalinisation formed synchronously with early to late AF (sub 2) -deformation. Gold occurs as a native metal in arsenopyrite, lollingite, chalcopyrite and rarely in pyrrhotite. Besides, the sulphide-hosted native gold, its presence in the alteration zones without sulphides or along the criss-crossing micro-fractures permeating through the host rocks or sulphide is recorded. Fluid inclusions having characteristic affiliation with mineralisation are aqueous and non-aqueous in nature and can be classified in general terms of CO (sub 2) -rich, CH (sub 4) -rich, NaCl-rich and H (sub 2) O-rich types. The average homogeneisation temperature varied from 131 degrees C to 562 degrees C. Sulphur isotope (d (super 34) S) ratios exhibit a very narrow range between +5.87 and +16.01% with an average of 12.01 per mil, thus correlatable with modern hydrothermal fluid system.