Temperatures and Oxygen Isotopic Compositions of Hydrothermal Fluids for the Takatori Tungsten-copper Deposit, Japan

Abstract. Fluid inclusion and oxygen isotope studies are performed to obtain temperatures and oxygen isotopic compositions of hydrothermal fluids for the vein-type tungsten-copper deposit at Takatori in Ibaraki Prefecture, Japan. Temperatures of the hydrothermal fluids are calculated from fluid inclusion data. The calculation incorporates the effects of the salinity, gas concentration, and fluid pressure. The fluid temperatures range from 370 to 460C. For these calculations, this study obtains a density equation for H₂O-NaCl-CO₂ solution at the vapor-liquid two-phase boundary. Then the present study combines the obtained equation with the equation of state by Bowers and Helgeson (1983).
The fluid temperatures determined in this study are applied to the calculation of oxygen isotopic compositions of the hydrothermal fluids. The calculation of the oxygen isotopic compositions is based on the oxygen isotope analyses of vein quartz. The oxygen isotopic compositions of vein quartz range from +13.5 to +14.4 % relative to SMOW. Then, the oxygen isotopic compositions of the hydrothermal fluids in equilibrium with the vein quartz are calculated to be from +9.7 to +10.5 %. These δ¹⁸O_fluid values agree with those of magmatic fluids derived from the ilmenite-series granitic rock, which is related to the mineralization. Keywords: Takatori tungsten-copper deposit, fluid inclusion, oxygen isotope, vein quartz, H₂O-NaCl-CO₂ solution, density     

Chemical compositions of tourmaline in the vein-type tungsten deposits of the kaneuchi mine,Japan

Chemical compositions of tourmaline from the vein-type tungsten deposits of the Kaneuchi mine in Japan are obtained with an electron probe microanalyzer. Tourmaline occurring at this mine belongs to the dravite-schorl series. Magnesium contents are high compared with tourmaline from granitic zones. This suggests that ore-forming solutions are not formed directly from magmatic fluid and reacted with sedimentary rocks. Compositions of tourmaline in quartz veins are similar to those in host rocks, and the bulk compositions of host rocks do not indicate magnesium metasomatic reactions. It can therefore be concluded that water/rock interactions occurred at a deeper level which remains unexplored.