ABSTRACT

Physico-chemical properties of ore-forming solution responsible for the formation of Toyoha Pb-Zn vein type deposits, Japan are estimated on the basis of the studies on mineral assemblage and fluid inclusions. The concentration of total dissolved sulfur is estimated in a range from 10^-2 to 10^-3 mol/l which is consistent with that of hot springs accompanying sulfide deposition. The probable ranges of the other variables such as pH, NaCl and base metal contents of ore-forming solution are also calculated. These estimated values are compared with those of hot springs, Broadland geothermal area, New Zealand, now depositing sulfide minerals. It is concluded that both hydrothermal solutions are very similar with respect to physico-chemical properties and both are characterized by (1) total dissolved sulfur in excess over base metals, (2) neutral to slightly alkaline pH, and (3) low NaCl content. These characteristic features are very different from those of Salton Sea geothermal brine which is now depositing sulfide minerals with total dissolved sulfur insufficient for base metals, slightly acid to neutral, and has high NaCl content.