Lower Cambrian black rock series and associated stratiform deposits in Southern China

Abstract

Widespread in more than ten provinces of southern China are the Lower Cambrian black argillaceous-arenaceous rock series consisting of black carbonaceous shales, black carbonaceous-argillo-siliceous rocks, black carbonaceous silicolite and black silicolite and black carbonaceous-argillaceous siltstone. The Ni, Mo, V, Cu, U, Ba, Ag, P contents of these series are usually several to tens of times higher than their average values in shales.

As viewed from lithological sequence, element association and evolution, these black series can be divided into two types.

There occur a variety of deposits in the black rock series, such as phosphorite deposits, Ni-Mo-V polymetal deposits and “stone coal” seams. According to ore composition, texture and structure, the phosphorite deposits fall into three types, i.e., thick-bedded, lenticular and nodular. The Ni-Mo-V polymetal deposits, V deposits and reworked sedimentary Cu-U-Cd polymetal deposits in terms of their element association and ore genesis. As for the stratiform deposits in the black rock series, three mineralization stages have been recognized, i.e., the formation of phosphorite deposits, of Ni-Mo polymetal deposits and of V-Cu-U-Cd polymetal deposits as well as of “stone coal” seams.

Evidence strongly suggests that lower organisms have played an important role in mineralization. Our studies indicate that the Lower Cambrian black argillaceous-arenaceous rock series in southern China and their associated stratiform deposits occur generally in the basal parts of a big sedimentary cycle, i.e., the initial period of a transgression, or in the fine detrital-siliceous formation between two carbonate formations, formed in a humid climatic zone between two arid ones. As for the environment of deposition, it is suggested that the Lower Cambrian black argillaceous-arenaceous rock series and associated stratiform deposits (excluding thick-bedded phosphorite deposits) were formed mainly in a restricted and poorly-fed sea basin of stagnant shallow water containing abundant lower organisms and organic matter under statically hydrodynamic conditions.