Geology and mineralization of the Nakatenjo ore deposit in the Nakatatsu area

Zonal arrangement of skarn and ore minerals

Abstract

The Nakatenjo lead and zinc deposit, 3.5 kilometers south of the Nakatatsu mine, belongs to the pyrometasomatic type, embedded in the Akiu Formation of middle Permian age.
The formation of the deposit appears to be controlled by the inferred fault with N-S trend, and syncline, anticline and related fissures with E-W trend. The main mineralized zone is formed at the boundary between the limestone and sandstone-slate members on the south flank of anticline.
The nickel content and chemical composition of the country rocks and skarns suggest the followings. Limestone is replaced to clinopyroxene skarn, and sandstone, slate and schalstein to epidote skarn causing the exchange of CaO, CO₂, SiO₂, Fe₂O₃, FeO and MnO. Furthermore, clinopyroxene skarn is partly altered to rhodonite skarn resulting from the ascension of fCO₂ and concentration of MnO.
The metal elements are arranged in the deposit as the followings. Ag, Pb, Zn and Co contents of ores increase toward the depth of deposit, while Mn content decreases. Thulite (Mn₂" (Al, Fe "')₃Si₃O₁₂(OH)) mol% in epidote and quantity of rhodonite vary in accord with Mn content. From the viewpoint of zonal arrangement, the deposit may be divided into a part of surface (the Mn zone), a part of anticline and syncline (the transitional zone into the Pb-Zn zone), and a part of south flank of anticline (the Pb-Zn zone).