Geological characteristics and geochronology of the Huayagou Au deposit, Western Qinling: Implication for regional ore genesis

Abstract

The Huayagou gold deposit, situated at Longnan-Fengtai mineral field (LMF) within the Western Qinling Orogen (WQO) of central China, is a newly identified deposit, representative of major deposits within Gansu section that hold significant geological and economic value. Its geological similarities to major deposits in Fengtai district underscore its importance for advancing regional mining exploration and metallogenic studies. However, the lack of robust geochronological data and detailed geological characterization hampers our comprehensive understanding of the deposit’s genesis and regional metallogenic significance. To address this, research was carried out, involving detailed geological and mineralogical examination of ore samples from the Huayagou and subsequently robust chronology. Two distinct stages of mineralisation have been identified based on mineral association. The U-Pb dating of hydrothermal apatite that is closely associated with mineralisation yielded a ²⁰⁷Pb-corrected age of 205 ± 23 Ma (MSWD = 0.4) on Tera-Wasserburg concordia diagram, interpreted as the timing for primary mineralisation event. Microscopic and geochemical analyses confirmed the hydrothermal origin of apatite, which intergrows with arsenopyrite and gold, providing a reliable chronological framework for the deposit’s formation. These findings align with the 230–210 Ma mineralisation period established for major deposits in the LMF, such as Pangjiahe, Baguamiao, and Shuangwang. The ca. 248 Ma and ca. 163 Ma ages obtained from in situ Rb-Sr of sericite correspond to two rapid regional cooling events, possibly caused by uplifting and related metamorphism. Integrating these results into the regional geological context, we classify the Huayagou deposit as an orogenic gold deposit. This deposit, like others in the LMF, supports the spatial zoning model correlating uplift rates and erosion intensities with the distribution of epizonal, mesozonal, and hypozonal orogenic deposits across the western, central, and eastern regions of the field, respectively. The Late Triassic period in the WQO, characterized by the transition from subduction to collision to post-collision extension of the Paleo-Tethys Ocean, was a key phase for tectonic-magmatic activity and large-scale, multi-stage ore formation. Our findings reinforce this metallogenic framework and suggest significant potential for further gold exploration in the region.