The discovery of the Wuluqiong magnetite deposit in Tibet and its geological characteristics

A relatively large magnetite (including copper) deposit was newly discovered during the 1:50, 000 regional geological survey in Wuluqiong area, Tibet, following the discovery of the Nixiong iron mine, Fuye iron deposit, Caima iron deposit, and some other deposits. Located in the western part of Bangong Co-Nujiang River mineralization belt, this ore deposit has not been studied in such aspects as geological features, genesis, age and formation structural environment. According to the field survey, the authors found that the Wuluqiong magnetite ore deposit was formed in the exo-contact zone between the intermediate-acid intrusive rocks in Middle-Late Jurassic and carbonate rock in 2^nd member of Riganpeicuo Group in Upper Triassic (T₃R²). It was reconstructed by the later NS-trending high-angle normal fault and showed characteristics of multiple phases and stages of mineralization. Based on the LA-ICPMS zircon U-Pb geochronological study of the quartz diorite and the monzogranite adjacent to the orebody and the isostructural carbonate veins in the fault controlling the orebody, the authors obtained two weighted mean ²⁰⁶Pb/²³⁸U ages of (161.3±0.72) Ma, (157.5±1.7) Ma for the crystallized zircons in the quartz diorite and the monzogranite, and obtained a weighted mean ²⁰⁶Pb/²³⁸U age of (84.2±1.1) Ma for the hydrothermal zircons in the isostructural carbonate veins. Combined with the previous research and 1:50, 000 geological survey, the authors hold that the Wuluqiong magnetite ore deposit was initially concentrated in skarn-type magnetite during the process of northward subduction of Bangong Co-Nujiang River in Middle-Late Jurassic (157.5-161.3 Ma), and then underwent another enrichment in the process of intracontinental stretch in Late Cretaceous (84.2 Ma). It is considered that mineralization events related to the intracontinental stretch occurred in the middle of Late Cretaceous in Bangong Co area and mineralization might have existed on both north and south sides of the Bangong Co ophiolitic mélange belt. The mineralization, together with the diapirism of asthenosphere after the closure of Bangong Co-Nujiang River and related linearly thermal uplift and stretch of the crust, constituted a system of correlative mechanism.