Fluid inclusion study on the Itaga tungsten deposit, Ashio district, Japan.

Abstract

Fluid inclusion study on the Itaga tungsten deposit is carried out in order to characterize the hydrothermal solution responsible for this deposit. Polyphase fluid inclusions and vapor-rich ones as well as liquid-rich inclusions are found in quartz of the disseminated ore in the Itaga granite. Vapor-rich and liquid-rich inclusions are found in vein quartz, scheelite, and topaz from this deposit, but polyphase inclusions are not found in these minerals. Homogenization temperatures of primary fluid inclusions in quartz of the disseminated ore, vein quartz, scheelite, and topaz range from 518° to 261°C, from 388° to 265°C, from 336° to 301°C, and from 420° to 370°C, respectively. Salinities of primary fluid inclusions in quartz of the disseminated ore, vein quartz, scheelite, and topaz range from 45.1 to 0.9, from 21.0 to 8.3, from 7.9 to 5.3, and from 14.3 to 3.1 NaCl eq. wt%, respectively. The highest temperature and salinity reported in the present study are higher than any other data previously obtained for the Japanese tungsten deposits. Based on the plots of homogenization temperature against salinity, it is suggested that there were at least two hydrothermal solutions, i.e., very saline and dilute ones, responsible for the mineralization of the Itaea deoosit.