2004 年 54 巻 2 号 p. 139-144
The Takara ore deposit is located in the Misaka Mountain, Yamanashi Prefecture in central Japan and formed at Miocene as volcanogenic massive sulfide ore deposit. In the Takara ore deposit, gold exists in the pyrite type ore that is mainly composed of pyrite. The Au-bearing pyrite type ore shows a massive structure, and pyrite has the zoning structure by alternating As or Sb contents. Especially, the As-zoning structure is predominant in pyrite from the Au-bearing pyrite type ore. On the other hand, the pyrite type ore without gold shows a disseminated texture with quartz, and pyrite has uniform chemical composition. Gold is not observed under the microscope and by the back-scattered microprobe image. Gold could exist as invisible Au. As (and probably Sb) contents in pyrite show negative correlation with S and Fe contents. As is considered to replace both S and Fe. It seems to be that the zoning structure by alternating As or Sb contents in pyrite from the Aubearing pyrite type ore was formed at low temperature.