Genetic features of Gold Ore Deposit at Kolar, Dharwar Craton, India

Twenty-five ore minerals have been identified from a study of ore-bearing samples from different reefs of the Kolar Goldfields. The mineral association includes fifteen minerals being reported for the first time: altaite, hessite hedleyite, tzumoite, volynskyite gudmundite, ullmannite, brethauptite, tetrahedrite, hawleyite, cotunite, electrum and native bismuth. Besides, two new minerals, as yet unnamed, have been determined through electronprobe - Pb₃Te₉Cl₄S₂ and PbTeCI₂ They occur along with cotunite (PbCI₂) and altaite.

The study of time relations of different ore and vein mineral assemblages in the Kolar gold-quartz reefs has revealed six stages of mineralization: 1) Early quartz, 2) quartz-feldspar (Pegmatite), 3) scheelite, 4) early sulphides with gold, 5) sulphide-gold-tellurides (with quartz) and 6) quartz-carbonate. Fluid inclusions indicate that the mineral association of quartz-feldspar stage has developed under high TP-conditions of 250-300°C and 1.8 and 3.5 kb. Isotope composition of sulphur in the sulphides indicate the juvenile nature of sulphur. Available data suggest that the quartz of first stage is of metasomatic origin, derived possibly from host amphibolites; gold-sulphide and gold-telluride mineralization took place through hydrothermal processes.