Abstract

The pyritic ores of the Yanahara district occur as irregular masses in felsic pyroclastic rocks (locally hornfels) of Permian age. Quartz porphyry and granite porphyry dikes cut both the ore deposits and country rock; zones of magnetite (with chlorite and plagioclase) are found adjacent to the dikes and country rock, and pyrrhotite (with small amounts of other sulfides, chlorite, and quartz) occurs between the magnetite zones and the pyritic ore, and also forms veinlike masses within the ore. Formation of the magnetite and pyrrhotite is attributed to processes of diffusion metasomatism as a result of interaction between the pyritic ore (and wall rocks) and ascending fluids associated with dike emplacement.

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