Lanping Basin Full Of Gold - Citylink Vein-type Copper Deposit Genesis

The Tibetan Plateau is an ideal area for understanding metallogenesis of continent-continent collision because it yields many mineral deposits with clear tectonic setting. Lanping basin is located in the east of the Tibetan Plateau, clamping between Lancang River suture and Jinshajiang-Ailaoshan suture. Along the Lancang River development a hydrothermal vein-type Cu deposits in the western basin. All of the deposits were formed in the intense deformation foreland basin of the collision belt, which were epigenetic deposits. The distribution of these deposits were controlled by the thrust-nappe structure system, and orebody occurrence strictly controlled by the steep dip of the fault. To the vein-type deposits, which formation mechanism and relationship with collision orogenesis are poorly understood. Meantime, how distribution of different mineral deposits in spatial and temporal? How is its transport and drive of the ore-forming fluid? Where were metal components and other elements in fluid from? How precipitation of metal component, and so on, these questions neither be explained by the known mineralization theory nor be futher clarified by the work of the past. So, this study aims to investigate their developed characteristics and establish the preliminary genetic models.Jinman and Liancheng copper deposits located at the eastern of the Lancang River suture, which major structural patterns was the double reverse anticline of the Jinman-Liancheng, and the anticline axial was NNE. The exposed stratus mainly are middle Jurassic Huakaizuo formation (J2h) and upper Jurassic Bazhulu formation (J3b). Among both of them, quartz sandstone, siltstone, mudstone and other clastic rocks, and sericite slate, calcareous slate and other weak metamorphic rocks of the Jurassic Huakaizuo formations are main host rocks for ores.Ores mainly consisted of quartz, carbonate minerals, and Cu-bearing sulfides. Main ore structure are subhedral-xenomorphic granular texture and replacement texture, vein-type, disseminated, and block structure. Molybdenite Re-Os dating showed that the Liancheng deposit formed at 48-49Ma. Fluid inclusion studies show that the ore-forming fluids of the Jinman and Liancheng ore deposits is a rich in CO2 with middle-low temperature (170-350℃) and low salinity (<10-15 wt% NaCl) fluid system. The results of isotope geochemistry show that the value ofδ18OH2O and 8D were 3.7%o to 10.3%o and-111‰to-89%o, which demonstrated the fluids come from metamorphic water and/or magmatic water. However, because it was no mineralization magmatic activity of the Lanping basin, so the ore-forming fluid was source of metamorphic fluid. The carbon-oxygen-strontium isotopic composition of calcite display that the value ofδ13CPDB were between-7‰and-4%o,δ18OPDB were between-18.0%o and-13.0%o, and the value of 87Sr/86Sr were changes between 0.709 and 0.714, all of these datas reflected that metamorphic carbonate and marine carbonate were the main source of carbon in hydrothermal calcite. The value ofδ34S were between-11‰and-2%o,206Pb/204Pb were changes between 18.137 and 18.724, 207Pb/204Pb were changes between 15-517 and 15.677,208Pb/204Pb were changes between 38.213 and 38.983, show that the sulfur and metal components of the ore-forming fluids drived from the basement metamorphic rocks and host rocks.According to the results of the geologic features with fluid inclusions and isotope geochemistry, we think that the metamorphic fluid which was formed by the Lancang River suture reactive again formed the Jinman and Liancheng ore deposits. In the process of the metamorphic fluid rised up and migration, it extracted metal and other components from deep metamorphic rocks and shallow stratus. When the superficial stratus formed faults in the fold-thrust events, the ore-forming fluid rapid rise up in place. If the suddenly changed in surrounding environmental pressure such as from static rock pressure to hydrostatic pressure, the ore-forming fluid taken place boiling and CO2-immiscibility, thus results metal sulfides precipitation.