Formation of the Laowan Gold Field in the Tongbai–Dabie Orogen, Central China: Constraints From Geochronology, Whole‐Rock and Mineral Geochemistry, and Lu–Hf–Sr–Nd Isotopes of Ore‐Related Granite

ABSTRACT

The Tongbai–Dabie orogen constitutes the eastern segment of the Qinling–Dabie orogen. The orogen contains many large Mo and Au deposits, with a proven reserve of over 3 Mt. Mo and 300 t Au. Ore genesis of these magmatic‐hydrothermal Mo and Au deposits has been widely debated, and the geochemical difference of the ore‐forming magma remains unclear. Here, we present new data on the age, geochemistry, and Lu–Hf and Sr–Nd isotopes of the ore‐related granite from the Laowan gold field in the Tongbai orogen. The Laowan Au ore‐related granites were zircon U–Pb dated at 129.9 ± 0.9 Ma. The granites feature LREE enrichments and HREE depletions. They are classified as oxidised magnetite‐type. Geochemical and multi‐isotope data show that the Laowan granite was formed by partial melting of the ancient lower crust with varying lithospheric mantle input. Mafic magma from depth could serve as an Au source. Compared with the Mo‐related granites in the Dabie orogen, the Au‐related granites from Laowan were likely formed from a less hydrous (2.2–3.8 wt.% H ₂ O) and S‐poor (26.8–51.0 ppm), F‐rich (706.44–1106.67 ppm), oxidised magma with low temperature and viscosity. The Au ore‐forming fluids may have exsolved from this oxidised magma at a later stage.