Ar-Ar Dating on the Metallogenesis of the Dongchuang Gold Deposit in the Xiaoqinling Area

摘要

The Dongchuang gold deposit in the Xiaoqinling area is an orogenic-type lode gold deposit. It is one of the few superlarge (>100 t Au) deposits in China. Although it has been argued that it was formed in the Mesozoic, related isotopic age data have not been reported in previous studies. Based on detailed geological study, the authors have carried out isotopic dating on various metallogenic generations. The ore-forming process of the Dongchuang gold deposit consists of four stages: coarse-grained pyrite-bearing quartz veins (stage Ⅰ), fine-grained pyrite-quartz veinlets (stage Ⅱ), multi-sulfides (stage Ⅲ) and carbonate-quartz veinlets (stage Ⅳ). Ar-Ar dating on mineral separates of stages Ⅰ, Ⅱ and Ⅲ yields plateau ages of 142.9+-2.9 Ma, 132.2+-2.6 Ma and 128.3+-6.2 Ma, respectively. Sericite separates from stage Ⅱ assemblage also yield an Ar-Ar isochron age of 132.6+-2.7 Ma, similar to the Ar-Ar plateau age. These results suggest that the Dongchuang gold deposit was mainly formed during 143-128 Ma, coinciding with the authors' geological observations and previous hypothesis. This ore formation is coeval with the regional-tectonic transition from collisional compression to extension, strongly showing that the decompression-geothermal increase regime during compression-to-extension transition is the most conducive geodynamic environment to orogenic-type gold mineralization.