Strontium Isotopic Evidence for the Genesis of Fluorite from Takatori Mine, Japan

Abstract

The fluorite from veins in the Takatori tungsten deposit, central Japan, has a distinct ⁸⁷Sr/⁸⁶Srr composition ranging from 0.7260 to 0.7270. This ratio is significantly higher than the initial ⁸⁷Sr/⁸⁶Srr ratio of the granitoids (0.7095-0.7136) in the Tsukuba and Yamizo areas probably related to the ore formation but rather approaching that of the wall sandstone (0.7250). Sr content in the wall sandstone composed mainly of quartz, feldspars (alkali feldspar+plagioclase) and sericite, shows a strong positive correlation with Na content, indicating that the Sr is mostly included in feldspars. The Sr content in the wall psammitic rocks decreases successively toward the vein from 200 ppm to several tens ppm with the increasing degree of sericitization of feldspars. Therefore, it is presumed that the Sr in the mineralizing fluid is essentially derived from feldspars in the nearby wall rocks through the sericitization.