Abstract
Trace metal compositions of single fluid inclusions in quartz from pegmatites and hydrothermal veins were analyzed by micro-PIXE to elucidate the compositional change of granite-derived fluids during a pegmatite and hydrothermal stages. Quartz samples were collected from a pegmatite at Kurobera, a hydrothermal vein at Suisyo-toge, and a hydrothermal vein near Fe-Cu ore deposit at Kawahage, central Japan. Three veins are genetically related to a Miocene granite body. The quartz sample from Kurobera includes two-phase fluid inclusions, and the Suisyo-toge sample and the Kawahage sample include two-phase inclusions and polyphase inclusions including halite crystals. Salinity (NaCl eq %) of the polyphase inclusions are ~30% for the Suisyo-toge sample and 30-38% for the Kawahage sample. Determined concentrations are as follows: 200 ppm for Fe, 150-500 ppm Cu, 150-250 ppm Ge, 20-100 ppm for Br, Rb, and Pb from Kurobera; 900 ppm for Fe, 2300 ppm for Mn, 250-400 ppm Cu, 120 ppm Ge, 10-350 ppm for Br, Rb, Sr, Zn, and Pb from Suisyo-toge; 2000-90000 ppm for Ca and Fe, 300-8000 ppm for Mn and Zn, 40-3000 ppm for Cu, 100-4000 ppm for Br, Rb, Sr, and Pb, less than 100 ppm for Ge, from Kawahage. The contents of Mn, Fe, Cu, Pb, Zn, Rb, Sr, and Br increase from the pegmatite to the hydrothermal veins, whereas the Ge contents decrease. Since the salinity of the inclusions also increases in the hydrothermal vein, the base-metal enrichment could relate to a formation of hyper saline water and a metal separation by boiling of fluids after the pegmatite stage.
