Na/K ratios and fluorine contents of micas from the skarn-type tungsten deposits of the Fujigatani, Kiwada, and Kuga mines, Southwest Japan.

Abstract

Chemical compositions of micas from the Fujigatani, Kiwada, and Kuga tungsten mines, Yamaguchi Prefecture, Southwest Japan are obtained, and are compared with those from the vein-type tungsten deposits of the Kaneuchi, Ohtani, and Takatori mines.Activity ratios of NaCl/KCl in hydrothermal solutions for the formation of the Fujigatani, Kiwada, and Kuga deposits are estimated from Na/K atomic ratios of muscovites. The ratios range from 5.5 to 2.9 at 400°C during the formation of muscovites. Na/K atomic ratios in muscovites from the Fujigatani, Kiwada, and Kuga mines are similar to those in muscovites from the Kaneuchi, Ohtani, and Takatori mines. Fluorine contents of muscovites from the studied tungsten mices are above 0.1 wt%, and those of biotites from the Kuga mine are above 3 wt%. These values are comparable to those in muscovites from the vein-type tungsten deposits of the Kaneuchi and Ohtani mines. Fluorine contents of micas from the three mices are higher than those from several porphyry copper deposits. High fluorine contents of micas are characteristic features of skarn-type tungsten deposits as well as vein-type tungsten deposits.