[H-RE12] 資源地質学

[HRE12-02] MC-ICP-MSと気化法による硫化物の迅速Re-Os同位体測定手法: 東北日本釜石鉱床への適用

*小笠原 瑞姫¹、大田 隼一郎^1,2、石田 美月¹、矢野 萌生^2,1、牧 亮太¹、野崎 達生^3,1,4,2、高谷 雄太郎^5,3,2、藤永 公一郎^2,1、安川 和孝^1,2、加藤 泰浩^1,2 (1.東京大学大学院工学系研究科、2.千葉工業大学次世代海洋資源研究センター、3.海洋研究開発機構、4.神戸大学、5.早稲田大学)

キーワード：Re-Os同位体、マルチコレクターICP-MS、気化法、硫化物鉱床

The Re-Os isotope system is a powerful tool in geological/geochemical studies, especially in radiometric dating of sulfide minerals, black shale and meteorite. Since both Re and Os are siderophile and chalcophile elements enriched in various sulfide minerals, the Re-Os isotope geochronology has been applied to the direct age determination of sulfide mineralization. However, the conventional analytical method of the Re-Os isotope dating using a N-TIMS is time-consuming and requires some reagents harmful to the human body. Also, the simpler, more rapid and safer sparging method for Os isotope analysis using a MC-ICP-MS [1,2] had not been applied to sulfide minerals.

Here, we present an improved analytical method for the Re-Os isotope and its first application to the Kamaishi skarn sulfide deposits in NE Japan. In our method, 0.4 g of powdered sulfide was digested by 1 mL of HClO₄ and 4 mL of inverse aqua regia in the Carius tube, which was analyzed using a MC-ICP-MS. The isotopic compositions of ¹⁸⁷Os/¹⁸⁸Os and ¹⁸⁷Re/¹⁸⁸Os obtained in the present study showed good agreements with those obtained by the conventional method digesting 0.5 g of the same powdered sample using 10 mL of inverse aqua regia and measuring with a N-TIMS. The less volume of sample solution is favorable for Re-Os isotope analysis by the sparging method using a MC-ICP-MS to accomplish low blank level, which enables us a simpler and more efficient analytical procedure for Re-Os dating on sulfide deposits.



1: Nozaki, T. et al. (2012) Geostand. Geoanal. Res. 36, 131-148.

2: Kimura, J.-I. et al. (2014) J. Anal. Atom. Spectr. 29, 1483-1490.