京都府鐘打・大谷タングステン鉱床における鉱液の水素同位体比 : 鉱液へのマグマ水とorganic water の寄与 Hydrogen isotopic ratios of the ore-forming fluids responsible for the Kaneuchi and Ohtani tungsten deposits, Kyoto Prefecture : Involvement of magmatic fluid and organic water in the ore-forming fluids.
The possible roles of hydrothermal solutions of magmatic and sedimentary-rock origins in the mineralization of the Kaneuchi and Ohtani tungsten deposits, Kyoto Prefecture, are evaluated on the basis of hydrogen isotope geochemistry of the host rocks and hydrothermal muscovite. The hydrogen isotopic ratios of the Ohtani granitic rocks range from -53 to -87‰. Based on the isotopic ratios of the granitic rocks, the δD values of the magmatic fluid related to the Ohtani and Kaneuchi deposits are estimated to be from -42 to -766‰.<BR>The δD values of hydrothermal muscovite from the Ohtani deposit range from -90 to -94‰. The δD values of the hydrothermal solution in equilibrium with muscovite are calculated to be from -62 to -80‰ at precipitation temperatures of 368° to 488°C. Therefore, the δD values of the hydrothermal solution for the muscovite mineralization agree with the range of the magmatic fluid.<BR>On the other hand, the δD values of the hydrothermal solution in equilibrium with the Kaneuchi muscovite agree with the δD range of the magmatic fluid at 530°C or below. However, the δD values are lower than the magmatic value when calculated above 550°C. The magmatic fluid probably mixed with a deuterium-depleted hydrothermal solution at the early stage of the mineralization. It is suggested that the deuterium-depleted hydrothermal solution is originated from organic materials in the host rocks.<BR>Previous results on gas compositions of fluid inclusions from both deposits are interpreted as the mixing of a magmatic fluid with a relatively carbon-enriched hydrothermal solution. Carbon in the hydrothermal solution responsible for the Kaneuchi deposit partly originated from organic materials in the host sedimentary rocks.
資源地質 46(5), 255-266, 1996-10-31
The Society of Resource Geology