11:00 〜 13:00
[SGL23-P03] LA-ICP-MSによる釜石スカルン鉱床中のザクロ石U-Pb年代測定
キーワード：ザクロ石、U-Pb年代、LA-ICP-MS、スカルン
Garnet is a common mineral in metamorphic, metasonatic and igneous rocks. In-situ U-Pb dating of garnet is recently applied to understand the timing of skarn mineralizations at various locations.
In this study, we present U-Pb age of the garnets in the skarn of the Kamaishi deposit, Japan. The Kamaishi deposit is the largest Fe-Cu skarn deposit in Japan, and is located in the Kitakami Mountains, Northeastern Japan. Early Cretaceous igneous complexes, the Ganidake granodiorite and diorite, and the Kurihashi granodiorite are occurred in the Kamaishi mine. The Ganidake granodiorite is considered to have formed Fe-Cu mineralization and zonal skarn of the Kamaishi deposit. The zonal skarn was formed at the boundaries between limestones and sedimentary rocks or at granodiorite. The chemical composition of garnets from the Kamaishi mine can be grouped in to grossular-rich (Grs50-60And32-43Hgr4-6Pyp0-2Sps1) with 15-57 μg/g of REE or andradite-rich (And66-80Grs16-33Pyp0-3Sps0-1Hgr0-1) with 92-223 μg/g of REE. The U concentrations of the garnet correlates with those of HREE.
The U-Pb dating of garnet was attempted with the LA-ICP-MS utilize a New Wave Research 193UC excimer laser ablation system, coupled to an Agilent 7700 quadru-pole ICP-MS at Akita University. Our preliminary result of the U-Pb garnet dating show 129.5 ± 5.8 Ma which is consistent with the U-Pb zircon age of the Ganidake granodiorite, and support the model that the Ganidake granodiorite formed the skarn.
In this study, we present U-Pb age of the garnets in the skarn of the Kamaishi deposit, Japan. The Kamaishi deposit is the largest Fe-Cu skarn deposit in Japan, and is located in the Kitakami Mountains, Northeastern Japan. Early Cretaceous igneous complexes, the Ganidake granodiorite and diorite, and the Kurihashi granodiorite are occurred in the Kamaishi mine. The Ganidake granodiorite is considered to have formed Fe-Cu mineralization and zonal skarn of the Kamaishi deposit. The zonal skarn was formed at the boundaries between limestones and sedimentary rocks or at granodiorite. The chemical composition of garnets from the Kamaishi mine can be grouped in to grossular-rich (Grs50-60And32-43Hgr4-6Pyp0-2Sps1) with 15-57 μg/g of REE or andradite-rich (And66-80Grs16-33Pyp0-3Sps0-1Hgr0-1) with 92-223 μg/g of REE. The U concentrations of the garnet correlates with those of HREE.
The U-Pb dating of garnet was attempted with the LA-ICP-MS utilize a New Wave Research 193UC excimer laser ablation system, coupled to an Agilent 7700 quadru-pole ICP-MS at Akita University. Our preliminary result of the U-Pb garnet dating show 129.5 ± 5.8 Ma which is consistent with the U-Pb zircon age of the Ganidake granodiorite, and support the model that the Ganidake granodiorite formed the skarn.