Anatomy of a Porphyry Copper Deposit - Malanjkhand, Madhya Pradesh

Abstract The Malanjkhand ore body consists of rnineralised quartz veins, mainly of two generations, emplaced in altered and silicified granitoids. Hypogene wall rock alteration includes silicification, potassic alteration, chloritisation and biotitisation, Sassuritisation and sericitisation of plagioclase are common. Hydrothermal alteration has modified the composition of granitoids. Oxidation and supergene enrichment have resulted in distinct supergene mineral zoning. Leached zone, supergene oxide zone and supergene sulphide zone have been identified. Supergene enrichment has increased >22% copper in the supergene sulphide zone. Localisation of copper in the deposit is related to intensity of fracturing in Stage-II veins as well as volumetric proportion of the silicified granitoid patches. The ore body contains >2000 ppm Mo on the northern side. Mo mineralisation is independent of copper concentration. Gold and silver show positive correlation with copper. The mode of occurrence of sulphide mineralisation suggests its genesis under variable hydrothermal conditions. The localisation of quartz veins in long and narrow zones as well as limited hydrothermal alteration suggests that fluids must have followed permeable zones provided by the sheared and fractured granitoids.