Chemical composition of tetrahedrite-tennantite minerals and the chemical environments of some Japanese ore deposits.

Abstract

Chemical compositions of tetrahedrite group minerals from some Japanese ore deposits are summarized. It is clarified that the chemical compositions (Cu, Ag, Zn, Fe, Sb, As) are different in different types of oredeposits. For example, zinc content of the minerals increases in the order, skarn and epithermal Cu-Pb-Zn <epithermal Au-Ag<kuroko.
Summarizing analytical data on the tetrahedrite group minerals, chemical formula for the minerals is regarded as (Cu, Ag) ₁₀ (Fe, Zn) ₂ (As, Sb) ₄S ₁₃ Using this chemical formula, the relationship between zinc and iron contents and physicochemical variables (fo ₂, pH, ΣS etc.) is derived. It is considered that Zn/Fe ratio in the minerals is largely dependent on fo ₂ as well as the other variables and has maximum value at the boundary between the predominance field of oxidized sulfur species and that of reduced sulfur species at constant other variables. This consideration and zinc and iron content of the minerals from kuroko type deposits suggest that kuroko type deposition has occurred near at the boundary between the predominance field of reduced sulfur species and that of oxidized sulfur species. The fo ₂ ranges at the time of formations of the other types ore depositions are also estimated. These estimations are in good agreement with those previously made by the other geochemical data such as mineral assemblages and iron content of sphalerite.