Complex base-metal mineralization (Cu-Pb-Zn-Co-Ni) in Palaeo-proterozoic black shales: the Browns deposit, N.T., Australia

摘要

The Browns deposit (70 Mt) occurs in the Rum Jungle Mineral Field, Northern Territory, Australia. It comprises galena, chalcopyrite, sphalerite, pyrite and siegenite ((Co, Ni)_3S_4), within a matrix of carbonaceous pelites. Ore minerals occur as fine-grained flasers parallel to the bedding-parallel foliation, and as coarse-grained assemblages that crosscut the foliation. Values of δ~(34)S for sulphides range from -5 to +15 per mil, indicating sulphur has been derived from a mixed source, inorganic thermochemical reduction of seawater and bacterial activity. Homogeneous lead isotope signatures indicate one source of lead and cross-cutting galena has been remobilized from bedding-parallel galena. Primary mineralization is linked to basin formation, whereas remobilization is the product of regional metamorphism.