Geochemistry, geochronology, and petrogenesis of leucogranites in the Xiaogouli gold deposit in the West Qinling Orogen

摘要

Gold metallogenesis is closely related to orogeny. The Qinling-Dabie Orogen is the most important part of the Central China Orogen. The West Qinling Orogen was formed during the Indosinian period, the main period of amalgamation of the continent of China. The Xiaogouli gold deposit in the West Qinling Orogen has unique geological characteristics, with a unique albite-quartz-vein ore type and mineralization correlate well with the granites. The granites have relatively low concentrations of Sr and Yb (Sr<400ppm and Yb<2ppm) but relatively high Al content, with average Na2O/K2O of 1.86, indicating that they are Na-rich Himalayan type leucogranites. The minimum temperature of the initial magma was 804 degrees C; amphibolite-facies hornfelsization occurred in the contact zone, and there was micrographic texture widely developed in the potassium feldspar, indicating an initial high-temperature magma. The granites have low Mg# content (4.07-14.28) and are strongly enriched in light rare earth elements [(La/Yb)(N)=(101.57-355.49)], suggesting that they had experienced some fractional crystallization. The zircon SHRIMP U-Pb granite ages of 217.4 +/- 1.5Ma indicate that the granites were formed during the late stage of Indosinian magmatic activity in the area. The Xiaogouli leucogranites are believed to be products of partial melting of crust-mantle mixing rocks under the condition of high temperature, induced by asthenosphere upwelling during delamination and thinning of the lithosphere in the extensional environment in the late stage of orogenesis of the West Qinling Orogen. The magma formation depth was 30-50km. Then, the magma experienced crystal differentiation, and the metallogenic materials and fluids were mainly from the crust-mantle magmas.