Newly discovered Ordovician Li-Be deposits at Tugeman in the Altyn-Tagh Orogen, NW China
Yongbao Gao, Yongbao Gao, Zhao Xinmin, Leon Bagas, Yalei Wang, Jin Moushun, Jiangwei Zhang, Lin Lü, Yijie Gao, Yijie Gao, Zhouquan Yan, Jiaxin Teng, Zhiquan Yang
Abstract
Magmatism was widespread in the Proterozoic to Early Paleozoic Altyn-Tagh Orogen of NW China. Rare metal deposits hosted by ca. 472 Ma pegmatite dykes with a monzogranitic geochemistry have recently been discovered in the orogen, including the Tugeman Li-Be deposit. The pegmatites contain spodumene – beryl (– columbite – tantalite – cassiterite), and are coeval with the ca. 482 Ma biotite monzogranite as a late-stage phase of the monzogranite, and both the monzogranite and pegmatite intrude orthogneiss and gneissic syenogranite. Two samples of biotite monzogranite yield weighted mean Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) U–Pb zircon dates of 482 ± 5 and 475 ± 5 Ma, and columbite-tantalite dates of 472 ± 8 Ma for the pegmatite, and minimum dates of 438–412 Ma for hosts of the columbite-tantalite. The gneissic syenogranite and orthogneiss in the deposit’s wallrocks have zircon U–Pb ages of ca. 900 Ma. The geochemistry and Hf-Lu isotopic systematics indicated that the protoliths for the gneissic syenogranite and orthogneiss have a mantle source with a contribution from the Proterozoic crust, and the biotite monzogranite has a Proterozoic crustal source. The Tugeman Li-Be deposit, therefore, has a Precambrian crustal source and was deposited during the Ordovician, which we propose was a post-collision extensional event and a previously unknown mineralising event in China.