COPPER MINERALIZATION IN MACHANUR AREA OF THE DHARWAR CRATON, KARNATAKA

Copper mineralization in Machanur is confined to the fracture and brec cia zone (shear zone) traversing mainly pink porphyritic granite of th e Closepet granite suite (2,400-2,000 m.y.) including minor diabase dy kes and pegmatites. The mineralization is fracture-controlled cavity f illing epigenetic hydrothermal type. The associated wall-rock alterati ons are chloritization, saussuritization, sericitization and silicific ation of the host-rocks. The mineralization consists essentially of ch alcopyrite and pyrite with subordinate bornite, chalcocite, covellite, digenite and linnaeite. Native copper occurs but rarely. Hematite (sp ecularite) and magnetite are commonly associated with the mineralizati on. Three stages of mineralization have been inferred. It is suggested that the second stage has been dominated by precipitation of chalcopy rite. The paragenetic sequence is suggestive of high fO2 condition in fluid at the beginning and progressive increase of Cu/Fe ratio and hig h fS2 condition in fluid during the main Cu-deposition stage.