Abstract

The chemical compositions of pyroxenes from 46 skarn deposits in Japan were statistically examined after compiling published and newly analyzed compositional data in order to put constraints on skarn metallogeny. The Mn/Fe ratio and Zn content of pyroxene in each deposit are relatively constant and tend to vary regionally in accordance with metal type. Most pyroxenes of Cu-Fe deposits are characterized by a low Mn/Fe ratio (<0.1) and a low Zn content (<200 ppm), whereas those of Pb-Zn deposits have a high Mn/Fe ratio (>0.2) and a high Zn content (>200 ppm). Pyroxenes of W deposits have an intermediate Mn/Fe ratio (around 0.15) and a very high Zn content, especially those of W-Sn-F deposits (>500 ppm). The systematic relation between the pyroxene composition and the metal type extends to the Mn/Fe ratio and Cd content of skarn sphalerites. These compositional features of pyroxenes and sphalerites seem to indicate that the proportion of Fe, Mn, Zn, and Cd contents in hydrothermal fluids did not change significantly from the time of pyroxene formation to the period of the later sulfide deposition, on the scale of the deposit. The Mn/Fe ratio and Zn content of skarn pyroxene can serve as an additional aid in the classification and defining of the environment of skarn formation.

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