Genesis of the Lishupo gold deposit in the Jiangnan Orogen, NE Hunan (South China): Biotite Ar-Ar, zircon U-Pb ages and H-O-S-Pb isotopic constraints

Abstract

The Lishupo gold deposit is located in the central Jiangnan Orogen (South China). Gold ore occurs mainly as quartz veins and altered slates, hosted by faults and shear zones in the low-grade metamorphosed Neoproterozoic Lengjiaxi Group. Metallic minerals include pyrite, arsenopyrite, pyrrhotite, chalcopyrite, sphalerite and galena, and the major alteration styles include silicification, sericitization, chloritization and carbonatization. Based on its vein crosscutting relationships and mineral assemblages and paragenetic sequence, mineralization at Lishupo comprises three stages: (1) quartz (Q1)–dolomite–pyrite (Py1)–arsenopyrite; (2) quartz (Q2)–dolomite–pyrite (Py2)–polymetallic sulfides; (3) quartz (Q3)–carbonate. Biotite from the sulfide-bearing ores of Stage 2 yielded a 40Ar–39Ar plateau age of 208.67 ± 1.25 Ma, and pre-ore granodiorite yielded a zircon U-Pb age of 430.8 ± 3.2 Ma. The dating results indicate that the Lishupo gold mineralization occurred at ∼ 210 Ma, coeval with the Late Triassic regional gold mineralization event in NE Hunan. Stage 1 to 3 quartz has δ18OVSMOW = +15.5 to + 17.6‰ and δDVSMOW = –81.2 to –70.3‰, and the ore-fluids were calculated to have δ18OFluid = +2.9 to + 10.9‰. This suggests that the ore-forming fluids were derived from a metamorphic source with magmatic input. The auriferous sulfides (pyrite containing invisible gold) have δ34SCDT = –13.7 to –4.6‰, 206Pb/204Pb = 18.230–18.642, 207Pb/204Pb = 15.615–15.755, and 208Pb/204Pb = 38.582–39.100. These isotopic data indicate that the ore-forming fluids and metals were derived from a deeper metamorphic source. The Lishupo deposit exhibits many features of orogenic gold mineralization, such as control by ductile shear zones, mineralization styles (quartz veins with abundant sulfide minerals), and H–O–S–Pb isotopic features indicating deeper metamorphic source. Based on similarities to other orogenic gold deposits, the Lishupo deposit is best classified as orogenic type formed at ∼ 210 Ma, in response to the Late Triassic extensional tectonics caused by the Paleo-Pacific plate, or the post-orogenic tectonics after the South China-Indochina and/or North China-South China collision.