Origin of hydrothermal fluid of mineralization

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The purpose of this research is to understand the relationship between magmatism and mineralization, and to consider the contribution rate of magmatic water, seawater, meteoric water, and others.l) We survey the hydrothermal ore deposits and geology in the Hokusatsu district, Kagoshima Prefecture. The hydrothermal fluid was produced at the top of cupola shaped felsic magma that supplied dacitic volcanics, and was rich in chlorine and oxidized sulfur species such as SOィイD22ィエD2. Chlorine has joined with gold and other metals to form chloro-complex. The fluid has emanated and was cooled in the overlying anoxic Shimanto Supergroup, where the chloro-complex of gold was destroyed, and the SOィイD22ィエD2 was converted to HS-. The gold released from chlorine reacted with HS- to form Au(HS)ィイD22ィエD2-. At the most top of the Shimanto Supergroup, hydrothermal fluid was oxidized by meteoric water and by volcanic rocks of magnetite series. In this process, magmatic water played essentially important role to mineralization, and meteoric water played as oxidant to precipitate the gold. Similar phenomena can be confirmed at the Ladolam ore deposits, Papua New Guinea.2) The origin of hydrothermal fluid was also examined on the fumarole in Kagoshima Bay. Volcanic gas added to the seawater, and bio-activity played important role to change the sea water to ore fluid. The bio-activity was also recognized in the Tizapa VMS mine in Mexico.3) The contribution of felsic magma was also confirmed by the research on the granitic rocks in Kyushu area. The asymmetrical zonation of the Tertiary granite could be recognized from the aspects of halogen geochemistry, REE distribution, and isotopic phenomena. The source area of ore fluid can be expected at the middle and/or lower crust.During the research, the isotopic compositions contribute for consideration. The methodology of measurement was developed through this research.