Copper-bearing clay minerals of the oxidized zone of the Rakha-Chapri Block, Singhbhum Copper Belt, India

Abstract

In the oxidized zone of Rakha-Chapri Block of the Singhbhum Copper Belt, alteration of biotite, chlorite and muscovite extends down to ∼ 60 m. Below this level, these minerals are not altered, implying a supergene origin for the clay alteration products. The altered host-rock profile consists of an upper, predominantly kaolinitic zone and a lower illite-chlorite rich zone, with the clay minerals showing an overall tendency to decrease with depth. Kaolinite is the dominant clay mineral, the proportion of which varies considerably with depth, and chlorite, illite and halloysite are the other clay minerals of the oxidized zone. Incipient removal of copper even from the cap rocks, in-situ transformation of sulphides to oxidized compounds, and the unusual mode of occurrence of copper in the oxidized zone are the characteristic features of the Rakha-Chapri Block. Insufficient localized hydrolysis of silicates is considered responsible for relatively low acidity in the oxidized zone as a whole. Copper forms a component of the clay minerals probably as surface adsorbed or/lattice-bound ions.