The deep rare metal metallogenic characteristics of the Jiajika lithium polymetallic deposit in Sichuan Province, China: Revealed by the Jiajika Scientific Drilling

Abstract

Jiajika, located in the Songpan–Ganzi orogenic belt in western Sichuan Province, is the largest pegmatite-type lithium polymetallic deposit in China. Nanjing University has completed a 3211.21 m scientific drilling (JSD-1) in the Jiajika lithium polymetallic deposit. Pegmatite samples from core of this hole were investigated with the aim of decreasing the bottleneck of upstream exploration and development of lithium resources. Base on the JSD-1 drill core, the pegmatite is poorly zoned, but mineral assemblages reflect a gradual evolution from bottom to top. The dominant feldspar in pegmatites evolve from microcline to albite, and the content of biotite decreases. Muscovite and tourmaline are present in the pegmatite at various depths. Spodumene is the only primary lithium mineral observed in the drill core samples, and is present at 1123 m to 56 m, especially near the surface in albite-spodumene pegmatites. U–Pb dating of columbite in pegmatites, indicate that the main ore-forming age of Jiajika pegmatites is 213.0 ± 1.6 Ma. In addition to lithium, beryllium, niobium and tantalum elements are also enriched in the drill core. Beryllium is dominantly contained in beryl and occurs mainly in pegmatites at depths of 863 m to 56 m. Niobium and tantalum are mainly enriched in columbite-group minerals, and can also occur in Nb–Ta-rich rutile associated biotite. Columbite-group minerals were observed at depths of 1728 m to 56 m. An addition intersection of columbite-group minerals mineralization occurred at a depth of 3186 m. U–Pb dating of the deeper occurrence of columbite minerals yielded a mineralization age of 190.6 ± 2.5 Ma. There are variable concentrations of lithium in muscovite, tourmaline and beryl in the drill core. However, there is a clear negative correlation of lithium concentrations with the depth, indicating the progressive lithium enrichment in the granitic magma. Although the main rare metal mineralization of Jiajika occurred at 213.0 ± 1.6 Ma, another niobium and tantalum mineralization event (190.6 ± 2.5 Ma) in-depth, which is discovered for the first time in this area, deserves also further attention.