Late Triassic lithium pegmatites in Northwest China: A response to continental collision during Paleo-Tethys Ocean closure

Spodumene-bearing pegmatite dyke swarms have recently been discovered in the Chaqiabeishan area, at the northeastern margin of the Qinghai-Tibet Plateau in northwest China. In order to elucidate the connection between the Chaqiabeishan lithium pegmatites and Triassic magmatism and mineralization within the West Kunlun - Songpan -Garz & ecirc; rare-metal belt, this study presents new columbite-group mineral and monazite U-Pb dating results, mineral chemistry, monazite in situ Nd isotope analyses and gamma-ray spectrometric measurements. Magmatism and mineralization at Chaqiabeishan mainly occurred ca. 216 Ma, and the mineralized pegmatites (Mn-rich columbite-group minerals, highly evolved monazite compositions and high effective uranium contents in the gamma-ray survey) were generated from the high degree of the fractional crystallization in a volatile-rich granitic magma. The source material of the Chaqiabeishan lithium pegmatites (epsilon Nd(t) values from -14.4 to -12.8) was more enriched than that of other pegmatite-type lithium deposits (Jiajika and Bailongshan) in the West Kunlun - Songpan - Garz & ecirc; rare-metal belt and is ascribed to melting of ancient crustal materials in the basement. These late-Triassic mineralizing events were closely related to the collision-related tectonic setting at the northeastern margin of the Tibetan-Qinghai Plateau, a product of Paleo-Tethys Ocean closure. Geochronology, mineral chemistry-Nd isotopes and gamma-ray spectrometry document the Chaqiabeishan Li pegmatites on the northeastern margin of the Qinghai-Tibet Plateau were formed from a highly evolved, volatile-rich granitic magma, derived by partial melting of basement materials in the Quanji Massif. image