神岡鉱山石英斑岩脈の地球化学的研究

抄録

A geochemical investigation has been performed on the whole rock specimens from a quartz porphyry dyke of about 10 m width which intrudes into the Tochibora area of the Kamioka Mine, central Japan. This Kamioka quartz porphyry is high in SiO₂(76-77 wt.%) and K₂O(>5wt.%) with per-metaluminous signature and enriched in Rb, Cs, Y, Nb, Ta, Th, U and HREE. The REE patterns are almostfl at (LREE≅HREE) with pronounced negative Eu anomalies. These features are identical to non-alkalic A-type granites or Topaz Rhyolites in the western United States of America.
The concentrations of Na, K, Ba and Sr change substantially from specimen to specimen. Sodium correlates negatively with other three elements. This elemental variation may be due to the hydrothermal metasomatism which occurred after the intrusion of the quartz porphyry dyke.
A specimen from open-cut region, where Pb-Zn ores are mined, shows distinct depletions of La, Sm and Y and great enrichments of Zn and Pb. The depletions of La, Sm and Y are supposed to be related to the formations of Pb-Zn ores or penetrations of fluids into the quartz porphyry.
The geochemical characteristics demonstrate that the intrusion of the Kamioka quartz porphyry with hydrothermal activity may be closely related to Mo deposit rather than Pb-Zn deposits.