Japan Geoscience Union Meeting 2023

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[J] Online Poster

H (Human Geosciences ) » H-RE Resource and Engineering Geology

[H-RE11] Earth Resource Science

Tue. May 23, 2023 1:45 PM - 3:15 PM Online Poster Zoom Room (1) (Online Poster)

convener:Tsubasa Otake(Division of Sustainable Resources Engineering, Faculty of Engineering, Hokkaido University), Kenzo Sanematsu(Mineral Resource Research Group, Institute for Geo-Resources and Environment, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology), Ryohei Takahashi(Graduate School of International Resource Sciences, Akita University), Tatsuo Nozaki(Submarine Resources Research Center, Research Institute for Marine Resources Utilization, Japan Agency for Marine-Earth Science and Technology)

On-site poster schedule(2023/5/22 17:15-18:45)

1:45 PM - 3:15 PM

[HRE11-P08] Nitrogen isotope geochemistry of ion adsorption-type REE mineralization: Insights from the weathered granitoid rocks in the Sancheong district, south Korea

*Jaeguk Jo1, Toshiro Yamanaka2, Dongbok Shin1 (1.Kongju National University, 2.Tokyo University of Marine Science and Technology)

Keywords:ammonium-nitrogen, nitrogen isotope, kaolin group minerals, Rare earth elements, Ion-adsorption type

Ion adsorption-type rare earth deposits formed by the weathering of igneous rocks have drawn attention in recent years as an important source of REEs. We studied for the mechanism of REE enrichment on clay fractions formed in weathered crusts of granitic orthogneiss, gabbroic anorthosite, and syenite rocks in the Sancheong district, South Korea, based on trace element and ammonium-nitrogen behavior. Ion adsorption-type REE mineralization commonly occurs with kaolinite and halloysite in the B-horizon layer, which reflects a series of pH changes from wholly weathered surface soil (A-horizon) to slightly weathered rock (C-horizon). The REEs of clay fractions separated from weathered crusts under weakly acidic conditions (pH 5-7) were higher than those of the bulk rocks. In contrast, the REEs of the clay fractions decreased sharply under more acidic conditions (pH < 4). The enrichment of REEs in both the bulk rocks and clay fractions correlate with negative Eu/Eu* and a positive Th(n) and U(n) trend, which indicates that the REEs were gradually concentrated during igneous and weathering processes. Ammonium-nitrogen concentrations correlate with the enrichment of REEs as well as the increasing δ15N values in the weathered crusts of each rock type. The δ15N values of the clay fractions (av. 5.1‰, av. 3.5‰, av. 1.1‰), which are heavier than those of the bulk rocks (av. 4.0‰, av. 1.4‰, av. -0.7‰) for granitic orthogneiss, gabbroic orthogneiss, and syenite rocks, respectively, are mostly attributed to the influence of sedimentary organic matter, in addition to nitrogen isotope fractionation. The geochemical characteristics and the features of nitrogen behavior in the bulk rock and its clay fraction contribute to our understanding of the genesis of ion adsorption-type REEs mineralization on the weathered crusts of granitoid rocks.