Tectonomagmatic Evolution And Metallogenesis In The Cenozoic Jinping-Fan Si Pan Metallogenic Province, Southeastern Tibet

The Indian-Eurasian collision had profound effects on Tibet and surrounding areas. In southeastern Tibet large scale strike-slip shear zones (e.g., Ailaoshan and Sagaing fault zones) and alkaline intrusions were genetically associated with post-collisional tectonic evolution. The Jinsha Jiang - Ailaoshan is a mobile zone which experienced several stages of tectonic evolution. It is generally regarded as a remnant of the Jinsha Jiang– Ailao Shan Palaeotethyan Basin of Early Carboniferous to Late Triassic. Strike-slip shearing along the Ailaoshan-Red River fault zone with displacement of over a thousand kilometers accommodated the southeastward extrusion of the Indochina block during Indian-Eurasian convergence since the Paleogene. Pre-shearing Cenozoic potassic alkaline magmatic rocks were formed along a belt encompassing the Ailaoshan - Red River shear zone (and also the Jinsha Jiang - Ailaoshan suture zone), forming a 1000-km-long alkaline magmatisim-mineralisation belt. The latter hosts a large number of various Cu-Mo-Au deposits related to high potassic alkaline porphyry plutons formed between 40 and 33 Ma.The Jinping - Fan Si Pan metallogenic belt located in the southeastern part of the Ailaoshan shear zone and consists of five Cu-Mo-Au deposits: Tongchang Cu-Mo deposit, Chang’an gold deposit, Habo Cu-(Mo)-Au deposit O Quy Ho Mo deposit and Chinh Sang Cu-(Mo)-Au deposit. Structural geology and ore deposit geology investigations (including fluid inclusion and stable isotopic compositions studies), zircon U-Pb and molybdenite Re-Os chronological constraints suggest that these deposits form an integrated epithermal porphyry Cu-Mo-Au mineralisation system associated with potassic alkaline magmarism. The zircon U-Pb ages and Re-Os dating of molybdenite suggest that metallogenic epoch of The Jinping - Fan Si Pan metallogenic belt took place during the 36~33Ma.The Jinping - Fan Si Pan metallogenic province (JPF) potassic alkaline rocks are characterized by relatively low TiO2 (<0.8 wt %), P2O5 (<0.64 wt %) and FeO* (<8.1 wt %) and high Na2O (1-4.5 wt %) and K2O (5.1-9.1 wt %), coupled with high contents of incompatible trace elements. They are ultrapotassic or shoshonitic being enriched in LILE (Rb, Ba, K, Sr), LREE and compatible elements (Cr, Ni, V, Sc), and have marked Nb, Ta, Ti depletion. These characteristics are similar to Neogene potassic igneous rocks in Eastern Tibet area, northern Ailaoshan belt. From the age data and structural relationships of ore mineralisation with left-lateral ductile shearing, it is suggested that the Jinping - Fan Si Pan Cenozoic Cu-Mo-Au mineralisation occurred prior to the initiation of left-lateral shearing along the Ailaoshan shear zone. The remnant of the subduction of Yangtze plate beneath the Indochina plate during the closure of the Jinsha Jiang– Ailao Shan Paleotethyan oceanic basin, and the Cenozoic continental collision between Indian and Eurasian plates provide a broad tectonic background for the Jinping– Fan Si Pan Cenozoic potassic alkaline magmatism and Cu-Mo-Au mineralisation...