Isotope geochemistry and genesis of the Liyuan gold deposit, Shanxi, North China

Abstract

The Liyuan lode gold deposit is located in the Shanxi province, central North China Craton. Gold orebodies are mainly hosted in Archean metamorphic rocks and structurally controlled by the NNE-trending faults. Gold occurs in disseminated and auriferous quartz-sulfide veins and veinlets within hydrothermally altered rocks. Mineralization can be divided into three intervals: (1) quartz-pyrite stage, (2) quartz-polymetallic sulfides stage, and (3) quartz-carbonate stage. Gold formed mainly in the middle stage. Sericite sample associated with the middle stage pyrite from phyllic alteration zones yields an well-defined 40Ar/39Ar plateau age of 133.3 ± 1.2 Ma, which is remarkably consistent with zircon U-Pb age (133.4 ± 1.1 Ma) of the quartz porphyry dikes in the Liyuan mine, indicating a close relationship between gold mineralization and granitic magmatism in the area. The sulfur isotopic compositions of pyrite (Py1-2) from the early stage have a narrow range from −0.3 to 4.1‰, indicating a deep-seated magmatic source. However, the sulfides (Py3-5, sphalerite, galena) from the middle stage have lower δ34SV-CDT values of −7.2 to 3.0‰, which is thought to be a result of fluid oxidation during gold mineralization. The Pb isotopic compositions of sulfides from Liyuan ores have 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of 16.671–16.860, 15.236–15.255, and 41.452–44.159, respectively, indicting a high-thorium lower continental crust source of ore-forming materials. The δ13CVPDB and δ18OVSMOW values of late stage calcite ranging from −7.1 to −5.8‰ and 12.2 to 13.7‰, respectively, illustrating a deep-seated magmatic source of carbon-bearing portion. Given the absence of granite bodies at the present mining levels, we speculate that the ore-forming fluids may have been exsolved from a concealed granite pluton at greater depth. Based on the regional tectono-magmatic events, ore geology, geochronologic and isotopic data obtained in this study together with the previous published fluid inclusion data, we suggest that the Liyuan deposit is an orogenic gold deposit that is probably related to the early Cretaceous granite magmatism in the interior of the North China Craton.