Abstract

Several zoned skarns are found in the Nakatatsu mine, which consists of several zinc-lead skarn deposits in the vicinity of the contact between the Paleozoic Fujikuradani Formation and granite porphyry intrusions of Tertiary age. The skarns are mainly composed of manganoan hedenbergite of limestone origin and grandite-andradite of dolerite and limestone origin. Clinopyroxene was altered in the vicinity of the orebodies to nontronite, and clinopyroxene in the same skarn below the orebodies was transformed into garnet. Thus, the relationship between skarns and ores seems to be one of the key points in considering a possible mechanism for ore formation.The mode of occurrence of the ores, the mineral compositions, and the estimated physicochemical environment during ore formation suggest that the principal causes of ore formation are a reduction of the ore-forming fluid and a decrease in temperature.

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