Abstract
Stannite was found in the Otoge kaolin-pyrophyllite deposits of ca. 4Ma(K-Ar), which are localized in rhyolitic pyroclastic rocks of middle Miocene time. Stannite occurs exclusively in pyrite-rich silicified portion within the sericite zone. Under the microscope, stannite, strongly anisotropic, shows a close association with sphalerite and pyrite. Microprobe analysis of stannite reveal that it is of Zn-rich variety with Fe/Fe+Zn atomic ratios of 0.49 to 0.71. It is noted that the atomic contents of the (Fe+Zn) site exceed 1.000 by up to 30% for stannite which contains more than 6 wt. % of Zn, suggesting a possibility of non-stoichiometry. The temperatures estimated based on the Fe and Zn partition are 300°to 340°C with Log fS2 of ca. -10 to -8, approximately corresponding to the corrected filling temperatures of fluid inclusions in quartz nearby stannite.
