Geochemical study of seafloor hydrothermal systems as modern analogue of kuroko-type are deposits

为了从古黑古型火山块状硫化物矿床矿石样品中的流体包裹体中获得成矿过程的关键信息，本研究对现代海底热液系统中采集的热液流体和硫化物/硫酸盐矿石流体包裹体的化学成分进行了比较，并试图探讨流体化学与构造环境的关系。我们开发了分析系统，一个是用气相色谱仪测定气体成分，另一个是用高效液相色谱法分析微量阴离子。利用这些仪器，我们测定了大量硫化物矿石样品中流体包裹体的气体组成。另一方面，我们也进行了实地研究，参与了一些潜水项目，从西南和西北太平洋的海底热液系统中收集样本。分析了活热液样品的气体种类和元素种类，以及同一地点硫化物/硫酸盐矿石样品的矿物组成和流体包裹体性质。在此基础上，发现了反映特定构造背景的地球化学特征，如在弧后活动密切的构造背景下，热液中不相容元素明显富集，在大陆边缘构造背景下，沉积层内存在广泛的相分离和流体运移。利用新研制的仪器获得的地球化学数据也有助于微生物学的合作研究。

In order to obtain the key information for ore forming process from fluid inclusions in ore samples of ancient kuroko-type VMSD (volcanic massive sulfide deposits), this research aimed to compare chemical composition of hydrothermal fluid and of fluid inclusion of sulfide/sulfate ores, both are collected from modern seafloor hydrothermal systems and tried to discuss relationship between the fluid chemistry and the tectonic setting. We developed analytical systems, the one is for gas composition determination using a gas chromatograph and the other is for minor anions analysis using a HPLC. Using these apparatuses, we determined gas composition of fluid inclusions in a massive sulfide ore sample. On the other hand, we also conducted field studies participating into some dive program to collect samples from seafloor hydrothermal systems in southwestern and northwestern Pacific. We analyzed both gas species and elemental species of the hydrothermal fluid samples obtained from active venting, and also mineral composition and fluid inclusion properties of the sulfide/sulfate ore samples collected from the same site. Based on these results, we found some geochemical signature reflecting the specific tectonic setting, such as significant enrichment in incompatible elements of the hydrothermal fluid in the tectonic setting where arc and backarc activities occur closely, and as extensive phase separation and fluid migration within sediment layer in the tectonic setting of continental margin. The geochemical data obtained in this study using the newly developed apparatuses also contributed to the collaborative microbiological studies.