15:00 〜 15:15
[HTT16-18] 対馬花崗岩と鉛-亜鉛鉱床に関する放射起源同位体研究
キーワード：放射起源同位体、対馬花崗岩、鉛－亜鉛鉱床
The Tsushima granite was studied in detail in my doctoral thesis, and some of the results were published (Shin et al., 2009). This granite is composed of granite and numerous mafic microgranular enclaves (MMEs). There are also numerous small miarolitic cavities and few small quartz veins and aplite dikes. However, it was revealed that hydrothermal fluids containing many metal components were generated as the granite cooled (Kurosawa et al., 2016). Considerations using Sr-Nd-Pb isotopes revealed that the granite was formed by mixing mafic magma derived from the mantle and felsic magma derived from the lower crust. However, the relationship between the granite and the formation of the Pb-Zn ore deposits has not yet been clarified. This is because TIMS was used to measure the isotope ratio, and the Pb isotope results, which cannot be internally corrected, could not achieve sufficient accuracy.
With the spread of MC-ICP-MS, it has become possible to measure Pb isotope ratios with high accuracy and precision by using Tl as an internal standard. Therefore, I am re-measuring lead isotope ratios and re-examining the behavior of metallic elements in fluids formed by magma cooling and the formation of ore deposits.
Part of the results will be presented here. There is no significant difference between the existing data and the newly measured data in terms of Sr-Nd isotopes, but some differences are becoming apparent in lead isotopes. The samples measured included dolerite, which is believed to be derived from the mantle, volcanic rocks (dacite and rhyolite) that were active before the granite, granites and magma-related fluids, and sedimentary rocks. The Sr-Pb diagram revealed the relationship between dolerite, volcanic rocks, and granite, and also clarified the characteristics of the fluids. Components related to the granite and those thought to have come directly from the mantle are now visible. Sr-Nd-Pb isotopic values of Galena revealed the influence of granitic magma and sedimentary rocks on the formation of the Pb-Zn deposit.
With the spread of MC-ICP-MS, it has become possible to measure Pb isotope ratios with high accuracy and precision by using Tl as an internal standard. Therefore, I am re-measuring lead isotope ratios and re-examining the behavior of metallic elements in fluids formed by magma cooling and the formation of ore deposits.
Part of the results will be presented here. There is no significant difference between the existing data and the newly measured data in terms of Sr-Nd isotopes, but some differences are becoming apparent in lead isotopes. The samples measured included dolerite, which is believed to be derived from the mantle, volcanic rocks (dacite and rhyolite) that were active before the granite, granites and magma-related fluids, and sedimentary rocks. The Sr-Pb diagram revealed the relationship between dolerite, volcanic rocks, and granite, and also clarified the characteristics of the fluids. Components related to the granite and those thought to have come directly from the mantle are now visible. Sr-Nd-Pb isotopic values of Galena revealed the influence of granitic magma and sedimentary rocks on the formation of the Pb-Zn deposit.