Study on C-O-S isotopic characteristics and genesis of the Nancha Gold Deposit in Jilin Province

The Nancha gold deposit, discovered in the 1980 s in southern Jilin Province, is a large vein-type gold deposit hosted in fractured marble of the Mesoproterozoic Zhenzhumen Formation. Field investigations, cross-cutting relationships, and mineral paragenetic associations indicate three hydrothermal stages at Nancha: pyrite-quartz stage (I), polymetallic sulfide-quartz stage (II), and sulfide-poor quartz-calcite stage (III). The δ¹³C and δ¹⁸O values of ore-stage calcite range from −3.1 ‰ to −5.2 ‰ and 6.3 ‰ to 7.4 ‰, respectively. The C−O isotopic compositions are similar to those of granitic magmas, which indicates that the carbon component was primarily derived from magmatic fluids. Moreover, in-situ sulfur isotopes of sulfides are concentrated in the range of 1.26 ‰ to 2.69 ‰, with a weak δ³⁴S enrichment. They obviously differ from the scattered δ³⁴S values of the wall rocks, but are similar to the homogeneous δ³⁴S composition of evolved felsic magmatic fluids. These features suggest that the magmatic fluids provided the primary source for the gold mineralization of the Nancha deposit. In conclusion, the Nancha gold deposit is genetically associated with the magmatism, and can thus be classified as a magmatic-hydrothermal vein-type gold deposit.