Fahlores from Porphyry Cu-(Mo) Deposits of the Urals

The typomorpic features of the minerals of the fahlore group from three porphyry deposits of the Urals: the Mikheevskoe and Tomino porphyry copper deposits (the Southern Urals) and Talitsa porphyry Mo deposit (the Middle Urals) are studied. In the deposits studied, the fahlore- group minerals belong either to late mineral assemblages of the porphyry stage or to subepithermal veins. They vary in composition from tennantite to tetrahedrite with variable Fe and Zn contents. Contents of Cd, Co, Te, Bi, Ag, and Se are usually insignificant. However, an exception is fahlore of late generation from the Mikheevskoe deposit, which is represented by argentotetrahedrite-(Fe) and fahlore associated with bornite from the Tomino deposit, which corresponds to tennantite-tetrahedrite-(Cd) in composition. Most of the studied fahlore-group minerals are not characterized by complicated chemical zoning: they are either homogeneous or comprise a homogeneous core of intermediate tennantite-tetrahedrite composition and a rim with a dominating tetrahedrite end member. This evidences a relatively quiet deposition environment with no sharp variations of physicochemical parameters of ore-forming fluid, which in general is typical of porphyry deposits. Comparison with published data shows that the studied fahlores are similar in composition to those from "transitional" subepithermal mineralization.