Temporal evolution, tectonic exhumation and preservation potential of the giant Zaozigou Au deposit in West Qinling Orogen, China

The study of metallogeny includes origin, development, modification, and preservation of mineralisation. The understanding of temporal evolution, and post-mineralisation modification and preservation of mineralisation are vital for building metallogenic theory and mineral prospecting, but they remain poorly understood and controversial. The Zaozigou deposit is the largest Au deposit in the West Qinling Orogen of central China with a resource of 142 t Au, and offers an excellent opportunity for deciphering the post-mineralisation exhumation and preservation of Au deposit in orogens. Here, we present integrated results from zircon U-Pb(ZUPb), apatite U-Pb(AUPb), apatite fission-track(AFT) and apatite(U-Th-Sm)/He(AHe)dating, thermal history modelling, biotite thermobarometer, and pyrite thermoelectricity of the deposit. The aims of the study are to decipher the temporal history, and post-mineralisation tectonic evolution and exhumation, and to evaluate the degree of exhumation and preservation potential of the deposit. Integrating the newly determined ZUPb(ca. 242–238 and 218–201 Ma),AUPb(ca. 247–235 Ma), AFT(ca. 237–186 Ma), and AHe(ca. 131–52 Ma) ages with multiple geo-thermochronological dates published from the Zaozigou deposit, major magmatic and hydrothermal events are recognised during ca. 250–233 and230–203 Ma, with two Au mineralisation being deposited at ca. 230 and 211 Ma. The Zaozigou area underwent rapid postmagma cooling during ca. 250–228 Ma, rapid hydrothermal cooling at ca. 219–211 Ma, and episodic post-Triassic cooling pulses. Thermal history modelling indicates rapid cooling at ca. 210–170 Ma, slow reheating at ca. 170–60 Ma, and enhanced cooling during ca. 60–35 and 20–9 Ma at the Zaozigou deposit. In conjunction with the Triassic to Cenozoic tectonic evolution of the West Qinling Orogen, the ca. 250–233 Ma magmatism, ca. 230 Ma Au mineralisation, and ca. 250–228 Ma rapid postmagma cooling are related to the northward subduction of the Mianlue Ocean(Paleo-Tethys Ocean). The ca. 211 Ma Au mineralisation and rapid hydrothermal cooling during ca. 210–170 Ma are correlated with the collision between the South Qinling Belt and South China Block during ca. 220–210 Ma and the post-collisional gravitational collapse during the Jurassic.Prolonged reheating during ca. 170–60 Ma is associated with the unconformable deposition of coeval sedimentary sequences.The ca. 60–35 and 20–9 Ma enhanced cooling relates to the India-Eurasia collision, the northward growth of Tibetan Plateau, and the intensive East Asian summer monsoon during the Cenozoic. ～28%–68% amounts of the Au orebodies in the Zaozigou deposit have been eroded away. In contrast with the estimated post-mineralisation exhumation depth of ～4.8 km and reported ore-forming depth of 2–6 km, local portions of the deposit are indicated to be preserved to a depth of over 1 km for Au exploration. Timely supply of post-mineralisation sediments and regional peneplanation during the Jurassic to Cenozoic are important factors for preservation of the deposit. During rapid uplift and exhumation of orogens, sediment-hosted Au mineralisation has highly prospective for prospecting. The study also highlights that multidisciplinary approaches of geo-thermochronology, thermobarometer, and thermoelectricity are effective tools in determining post-mineralisation modification and preservation of orebodies.