Genesis of gold deposits in the Wulong orefield, Liaodong Peninsula, North China Craton: Constraints from ore deposit geology, REE, and C-H-O-S-Pb isotopes

The Wulong gold orefield is located in the eastern part of the Liaodong Peninsula, and contains the large Sidaogou and Wulong gold deposits, as well as several small gold deposits with a total of >100 tonnes of gold reserves. These deposits are hosted within Paleoproterozoic metamorphic rocks of the Liaohe Group and Mesozoic granitoids, and are structurally controlled by NNE-SSW- and NNW-SSE-trending faults and interlayer fractures. The Sidaogou deposit is characterized by altered-rock-type mineralization occurring within interlayer fracture zones, whereas the mineralization in the Wulong deposit occurs as auriferous quartz veins along subsidiary faults. These two types of gold mineralization are representative of the mineralization in the Wulong orefield. The REE contents of quartz and calcite, together with previous studies of fluid inclusions, indicate that the ore-forming fluids of the Sidaogou deposit were reduced NaCl-H2O-CO2 fluids. Quartz yielded delta O-18(H2O-SMOW), delta D-SMOW, and delta C-13(CO2) values of +4.7 parts per thousand to +6.6 parts per thousand, -82.2 parts per thousand to -79.0 parts per thousand, and - 13.1 parts per thousand to -6.6 parts per thousand, respectively, and calcite yielded delta C-13(CO2) and delta O-18(V-SMOW) values of -2.3 parts per thousand to -2.0 parts per thousand and + 7.4 parts per thousand to +7.9 parts per thousand, respectively. These results indicate that the ore-forming fluids of the Sidaogou deposit were derived primarily from magmatic water, and the C was sourced mainly from deep-seated magma with a minor contribution from sedimentary organic matter. Pyrite crystals have delta S-34(CDT) values of +4.9 parts per thousand to +12.9 parts per thousand, indicating the S source was a combination of the magmatic system and ore-bearing metamorphic rocks. Pyrite has Pb-208/Pb-204 ratios of 38.226-38.336, Pb-207/Pb-204 ratios of 15.606-15.683, and Pb-206/Pb-204 ratios of 18.345-18.492, suggesting that the Pb in the Sidaogou deposit was derived primarily from the upper crust, with minor input from the mantle. Taking into account previous studies of the Wulong deposit, we propose a metallogenic model for the Wulong gold orefield. Deep-seated ore-forming fluids were released from different intrusions hidden below the Wulong orefield for each of the deposits. The ore-forming fluids moved through the metamorphic rocks of the Gaixian Formation along interlayer fracture zones, where intensive water-wallrock reactions, and episodic temperature and pressure drops resulted in the formation of altered-rock-type Sidaogou deposit. The fluids ascended to the Wulong and Sanguliu intrusions along NNE-SSW- and NNW-SSE-trending faults, where temperature and pressure dropping, water-wallrock reactions, and fluid immiscibility generated the vein-type Wulong deposit. The gold deposits in the Wulong orefield share many similarities with the Linglong- and Jiaojia-type gold deposits in the Jiaodong Peninsula, including geological setting, mineralization style and age, and sources of ore-forming fluids and metal.