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＜紀要論文＞
田口鉱山の吉村石および共生鉱物のRb-Sr年代
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| 概要 | The Taguchi mine, situated about fifty kilometers north of the Toyohashi City, Central Japan, is a manganese ore deposit in the Ryoke metamorphic complex composed mainly of banded quartz gneiss, bande...d biotite gneiss, and coarse-grained massive quartzite with small amounts of basic rocks. The ore bodies, extending about eighty meters to the strike side and about three meters in maximum thickness, are composed of layers of various mineral assemblages generally conformable with the Ryoke metamorphic rocks. The hanging wall rock is banded biotite gneiss while the foot wall rock is coarse grained massive quartzite. Yoshimuraite, a barium, titanium, manganese silicate mineral containing more than 2 percent strontium, occurs in the quartz-potassium feldspar-yoshimuraite-richterite-manganophyllite-rhodonite gneissic rock near the boundary of the ore bodies of the hanging wall rock side. Yoshimuraite, rhodonite, and manganophyllite separated from this rock, and rhodonite and manganophyllite from potassium feldspar-manganophyllite-rhodonite gneissic rock-a transitional layer of yoshimuraite bearing rock to the hanging wall rock-, were analysed on rubidium and strontium by the isotopic dilution method. The yoshimuraite, rhodonite and manganophyllite give an isochron age of 71±3m.y. with an initial strontium ratio Sr (87/86)_0=0.7092±0.0006 which equal to the ratio of Sr 87 /86 of yoshimuraite and rhodonite. The rhodonite and manganophyllite of the transitional zone give an isochron age of 80±3m.y. with an initial strontium ratio Sr (87 /86)_0 = 0.7084±0.0007 which equal to the ratio of Sr 87 /86 of rhodonite. The ages of the manganese minerals are close to the late stage of the Ryoke metamorphism and the intrusions of granodiorites around this region, the yoshimuraite bearing rock being slightly younger than the rocks of the transitional zone. It has been reported that a Ryoke biotite schist has a ratio Sr(87/86)_0=0.718and granodiorites have a ratio Sr(87/86)_0=0.7075 (OZIMA et al, 1967). At present, the low isotope ratios of Sr(87/86)_0 ofthe manganese minerals may be interpreted in either ways: the manganese minerals are closely related to the intrusions of the granodiorites, or derived from some basic igneous rocks, or formed by the incorporation of both basic rocks and the intrusions of the granodiorites.続きを見る |
| 目次 | I. 序言 II. 田口鉱山周辺の地質概説 III. 吉村石および共生鉱物の産状 IV. Rb, Srの同位体分析と年令 v. 考察 |
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| 登録日 | 2021.11.24 |
| 更新日 | 2022.06.20 |