17:15 〜 19:15
[SCG53-P10] Re-Os放射年代法による兵庫県生野鉱床の生成年代：多金属鉱化作用の解明に向けた示唆
キーワード：生野鉱床、熱水性多金属鉱床、硫化鉱物、局所化学組成、Re-Os放射年代
Hydrothermal deposits serve as major sources of industrially important metals. Especially, a significant portion of the deposits can be classified as polymetallic vein-type deposits that exhibit high-grade enrichment of multiple metallic elements. Therefore, in proposing exploration guidelines for new deposits, it is crucial to elucidate the formation processes of such hydrothermal polymetallic vein-type deposits. To understand the formation process of ore deposits, a chronological framework by determining the ages of both the magma involved in ore genesis and the mineralization of the deposit itself provides a key constraint.
This study focuses on the Ikuno deposit, located in the Tajima region of Hyogo Prefecture, where hydrothermal polymetallic vein-type deposits are densely distributed. The Ikuno deposit is known as one of the Japan's three major silver mines, which produced large amounts of gold and silver from the Muromachi to Edo periods. Additionally, from the Meiji period onward, the Ikuno deposit supported domestic industries through the production of various metals, including copper, lead, zinc, and tin, contributing significantly to Japan’s modernization. Thus, the deposit is of high importance both geologically and historically.
Previous studies reported the formation age of the deposit based on K-Ar dating of adularia from the veins, yielding ages of 74–63 Ma [1]. However, the formation age of ore minerals containing useful metals remains poorly understood. Moreover, no intrusive bodies directly associated with the mineralization have been identified among the igneous rocks surrounding the Ikuno deposit. While the surrounding granitic rocks have yielded reliable age data, the closest granitic unit, the Ohata Granites, has an age of 61.3 Ma determined only by whole-rock K-Ar dating on a sample that had undergone alteration. Thus, it is necessary to obtain more reliable age data of the Ohata Granite.
The Re-Os radiometric dating method, which utilizes the radioactive decay of 187Re to 187Os, is applicable to sulfide ore samples from hydrothermal deposits [2]. In this study, to determine the age of the Ikuno deposit, local Re analysis using LA-ICP-MS was first performed on ore samples with well-characterized mineral assemblages to determine the distribution of Re. Then, the Re-Os isotope measurements was implemented for the samples showing distinct Re signals. Additionally, U-Pb dating was conducted on zircon samples collected from the Ohata Granites to obtain a reliable magmatic age for the granitic unit. In this presentation, we compare the formation age of the Ikuno deposit with the emplacement age of the surrounding granitic rocks and attempt to place more direct constraints on the timing of mineralization and the source magma of the deposit.
[1] MITI. (1988) Report of the regional geological and tectonic survey:Bantan regio
[2] Dana et al. (2023) Economic Geology. 118(6), 1341-1370.
This study focuses on the Ikuno deposit, located in the Tajima region of Hyogo Prefecture, where hydrothermal polymetallic vein-type deposits are densely distributed. The Ikuno deposit is known as one of the Japan's three major silver mines, which produced large amounts of gold and silver from the Muromachi to Edo periods. Additionally, from the Meiji period onward, the Ikuno deposit supported domestic industries through the production of various metals, including copper, lead, zinc, and tin, contributing significantly to Japan’s modernization. Thus, the deposit is of high importance both geologically and historically.
Previous studies reported the formation age of the deposit based on K-Ar dating of adularia from the veins, yielding ages of 74–63 Ma [1]. However, the formation age of ore minerals containing useful metals remains poorly understood. Moreover, no intrusive bodies directly associated with the mineralization have been identified among the igneous rocks surrounding the Ikuno deposit. While the surrounding granitic rocks have yielded reliable age data, the closest granitic unit, the Ohata Granites, has an age of 61.3 Ma determined only by whole-rock K-Ar dating on a sample that had undergone alteration. Thus, it is necessary to obtain more reliable age data of the Ohata Granite.
The Re-Os radiometric dating method, which utilizes the radioactive decay of 187Re to 187Os, is applicable to sulfide ore samples from hydrothermal deposits [2]. In this study, to determine the age of the Ikuno deposit, local Re analysis using LA-ICP-MS was first performed on ore samples with well-characterized mineral assemblages to determine the distribution of Re. Then, the Re-Os isotope measurements was implemented for the samples showing distinct Re signals. Additionally, U-Pb dating was conducted on zircon samples collected from the Ohata Granites to obtain a reliable magmatic age for the granitic unit. In this presentation, we compare the formation age of the Ikuno deposit with the emplacement age of the surrounding granitic rocks and attempt to place more direct constraints on the timing of mineralization and the source magma of the deposit.
[1] MITI. (1988) Report of the regional geological and tectonic survey:Bantan regio
[2] Dana et al. (2023) Economic Geology. 118(6), 1341-1370.