Mid‐Late Jurassic Skarn Au Polymetallic Mineralisation and Associated Magmatism in Nanling Range (South China): Constraints From the Dafang Deposit

ABSTRACT Southern Hunan Province, located at the intersection of the Nanling and Qin‐Hang metallogenic belts of South China, hosts numerous Jurassic magmatic‐hydrothermal W–Sn and Cu polymetallic deposits. However, the contemporaneous gold mineralisation is notably scarce and remains poorly understood. To address this issue, we integrate multi‐mineral geochronology and Pb isotope, coupled with the whole‐rock geochemistry of the Dafang deposit, which stands out as the only skarn gold deposit in the district. The Dafang mineralisation can be divided into prograde skarn (I), retrograde alteration (II), quartz–sulfide (III), and calcite–sulfide (IV) stages. The two granodiorite porphyry stocks at Dafang, Maoerling and Lashuxia, yield zircon U–Pb ages of 156.3 ± 0.6 Ma (MSWD = 0.7) and 160.3 ± 0.7 Ma (MSWD = 1.0), consistent with its magmatic apatite U–Pb age of 159.2 ± 3.7 Ma (MSWD = 1.5), respectively. The U–Pb age of Stage I vesuvianite (160.9 ± 2.2 Ma, MSWD = 1.8) and the similar Pb isotopic compositions between the Lashuxia granodiorite porphyry and Stage IV galena demonstrate that the Lashuxia granodiorite porphyry, rather than the Maoerling one, is the most likely causative intrusion for the Dafang mineralisation. The whole‐rock Pb isotopes, zircon ε Hf ( t ) (−13.4 to −1.9), Nb/Ta (9.5–11.8), and Zr/Hf (30.2–32.9), along with the listric‐shaped normalised REE patterns with weak or absent Eu anomalies, indicate that the Maoerling and Lashuxia granodiorite porphyries with I‐type affinity were likely mainly derived from partial melting of the ancient crust. However, the more heterogeneous ε Hf ( t ) (−13.4 to −1.9) of the Lashuxia compared to Maoerling (−12.3 to −6.8) suggests that the fertile Lashuxia granodiorite porphyry may have incorporated more or less mantle‐derived components during its formation. While the zircon trace element geochemistry reveals that the oxygen fugacity and H 2 O contents of the magma are not conducive to W–Sn or porphyry Cu mineralisation, the granodiorites' strong similarities to intrusions genetically associated with skarn Cu mineralisation in southern Hunan Province point to the potential for deeper skarn Cu mineralisation. These findings may provide new potential targets for skarn Cu–Au polymetallic deposits exploration in South China.