Bismuth minerals from the W–Mo–Sn deposits hosted in the Iwafune granitoids, Niigata Prefecture, Japan

摘要

Bismuth minerals are described in 10 W–Mo–Sn deposits (Wakikawa, Shintoku, Takane, Shionomachi, Juseki, Nabekura, Nogeyama, Kanamaru, Kanzeon, and Daitoku) in the ilmenite–series Iwafune granitoids, located in the Uetsu region, Niigata Prefecture, Japan. The results are compared with those in the Cu–Pb–Zn–Bi deposits hosted in the magnetite–series Wasada granodiorite in the same region. Native bismuth and bismuthinite occur as major Bi minerals, accompanied by minor Pb–Bi–S sulfosalts (cannizzarite, cosalite, and lillianite) and Bi–tellurosulfides (joséite–A, joséite–B, ingodite, tetradymite, and ikunolite) in the Iwafune deposits. The Bi mineralogy of the Iwafune and Wasada deposits shows the following three characteristics: Native bismuth and bismuthinite are abundant in the Iwafune deposits; Pb–Bi–S sulfosalts and Bi–tellurosulfides are common in the Iwafune and Wasada deposits; and Cu–rich Bi–sulfosalts are restricted to the Wasada deposits. Since the major mineralization in the Iwafune deposits (W–Mo–Sn) and Wasada deposits (Cu–Pb–Zn–Bi) is largely controlled by the related granitoid–series, the difference in Bi minerals between the Iwafune and Wasada deposits might reflect the oxidized/reduced mineralization associated with the granitioid–series.