Study on the geochemical evolution of hydrothermal fluid using Sr isotope as a tracer

Sr isotope method was applied as a tool to reconstruct the geochemical evolution of fossil hydrothermal system and to explore mineral deposit.The low Ii D187 Iedimentary rocks of the Yakushima Island，southern Japan，suggests that significant amounts of magmatic fluid were responsible for the formation of the Yakushima tungsten deposit。Volcanic rocks of dacite to andesite composition in the epithermal gold deposit in the Hishikari area can be divided into two groups，the northern Kurosonsan-group and the southern Shishimano one。It is concluded from the Sr，Nd and Pb isotope systematics that the Kurosonsan volcanic rocks formed by the crystallization from a series of magma which progressively contaminated with surrounding Shimanto sedimentary rocks with age，while in the Shishimano volcanic rocks，significant amounts of mantle materials with low y D187i D1Sr/I D 186 I D 1 Sr ratio and high i D 1143。Lower crust was suggested as the ultimate source of gold and other metals in the Hishikari gol-producing fluid。The integrated approach using the Sr isotope and conventional elemental analysis methods is useful for the exploration of skarn deposits.I also examined Sr isotope as a tool to determine the age of marine sediments and to evaluate its potential for the exploration of crude oils.

Sr isotope method was applied as a tool to reconstruct the geochemical evolution of fossil hydrothermal system and to explore mineral deposit. The low ィイD187ィエD1Sr/ィイD186ィエD1Sr ratio of hydrothermal quartz hosted in sedimentary rocks of the Yakushima Island, southern Japan, suggests that significant amounts of magmatic fluid were responsible for the formation of the Yakushima tungsten deposit. Volcanic rocks of dacite to andesite composition in the epithermal gold deposit in the Hishikari area can be divided into two groups, the northern Kurosonsan-group and the southern Shishimano one. It is concluded from the Sr, Nd and Pb isotope systematics that the Kurosonsan volcanic rocks formed by the crystallization from a series of magma which progressively contaminated with surrounding Shimanto sedimentary rocks with age, while in the Shishimano volcanic rocks, significant amounts of mantle materials with low ィイD187ィエD1Sr/ィイD186ィエD1Sr ratio and high ィイD1143ィエD1Nd/ィイD1144ィエD1Nd ratio were involved in the late-stage of magma related to the gold mineralization. Lower crust was suggested as the ultimate source of gold and other metals in the Hishikari gol-producing fluid. The integrated approach using the Sr isotope and conventional elemental analysis methods is useful for the exploration of skarn deposits. I also examined Sr isotope as a tool to determine the age of marine sediments and to evaluate its potential for the exploration of crude oils.