Formation, exhumation, and preservation of the superlarge Dashui goldfield, West Qinling orogen, China

Abstract Understanding postmineralization exhumation and preservation is crucial to better decipher ore-forming processes and optimize mineral exploration strategies. The Dashui goldfield is an archetypal epithermal goldfield in the world-class West Qingling gold province of central China, with a total resource of >120 tonnes (t) grading 6 g/t. Early studies have focused on genetic type, ore-forming materials and fluids, and age of Au-bearing calcite generations and coeval mineralizing dikes of the goldfield. However, ore-forming age and genetic type remain debated. Additionally, postmineralization exhumation, modification, and preservation of the goldfield has not been investigated, hampering gold exploration. In this study, we conducted same-sample apatite U-Pb (AUPb), apatite fission-track (AFT), and apatite (U-Th)/He (AHe) thermochronology and thermal history modeling to determine the timing of ore formation and postmineralization modification of the Dashui goldfield, allowing us to better focus future exploration for gold in the West Qinling orogen. AUPb and AFT dates (ca. 239–212 Ma) in this study, combined with published multiple geo-thermochronometric data, indicate that the Dashui goldfield formed through multiple episodes of gold mineralization during ca. 211–189 Ma. This corresponds to regional Triassic–Early Jurassic (ca. 249–194 Ma) gold mineralization in the West Qinling orogen. AFT (ca. 239–225 Ma) and AHe (ca. 176–107 Ma) dates, along with thermal history modeling, reveal rapid cooling (>5 °C/m.y.) during ca. 237–205 Ma, prolonged reheating (0.05–0.14 °C/m.y.) from ca. 205 Ma to 70 Ma, and multiple episodes of accelerated cooling (0.26–0.67 °C/m.y.) after 70 Ma at Dashui. Furthermore, published geo-thermochronometric data at Dashui also indicate an Early Jurassic (ca. 189–183 Ma) rapid cooling (>30 °C/m.y.) phase. Combining these results with the Mesozoic–Cenozoic tectonic evolution of the Qinling orogen, we interpret that ca. 237–205 Ma rapid cooling corresponds to the subduction of the Mianlue Ocean and the collision between the South Qinling terrane and Yangtze block. Early Jurassic rapid cooling (ca. 189–183 Ma) is attributed to the postcollisional extensional collapse and exhumation of the Qinling orogen during the Early to Middle Jurassic. Protracted reheating at ca. 205–70 Ma reflects coeval sedimentary burial of the Qinling orogen. Multiple episodes of accelerated cooling during ca. 70–50 Ma and 37–24 Ma are associated with coeval rapid exhumation (>0.01 mm/yr) of the Qinling orogen, the India-Eurasia collision, and the northward growth and lateral expansion of the Tibetan Plateau. Prolonged sedimentary burial between ca. 205 Ma and 70 Ma and episodic peneplanation events of the orogen during ca. 100–50 Ma, 47–38 Ma, and 33–13 Ma contributed to the preservation of gold mineralization at Dashui. Consequently, the West Qinling orogen is highly prospective for gold resources. We also propose that postmineralization sedimentary burial enhances the preservation of primary gold deposits, whereas rapid exhumation transfers gold to secondary reservoirs through erosional redistribution.