C, H, O, S, Pb isotopic geochemistry of the Jianchaling gold deposit, Shaanxi province

The Jianchaling gold deposit in Shaanxi province, China, is located to the south of the Mianlue suture zone. The ore bodies were controlled by fault F1-45 and the secondary faults. The hydrothermal ore-forming processes can be divided into three stages according to the mineral assemblages and the crosscutting relationships of the veinlets as follows: (I) quartz-pyrite-dolomite vein with poor sulfides which was strongly deformed in a compressional or transcompressional setting; (II) quartz-polymetallic sulfides vein, characterized by large amount of fuchsite; and (III) dolomite-calcite-quartz-orpiment-realgar veinlets. The δ18OW and δD values of early stage fluids range from 7.5‰ to 21.1‰, with an average of 13.3‰, and from -85‰ to -70‰, with an average of -77‰, respectively; while the δ18OW of late stage fluids range from 2.5‰ to 7.7‰, with an average of 6.5‰, and the average value of δD is -81‰. This H-O isotopic signature suggests a shift from metamorphic water towards meteoric water. (13CCO2 values of the ore-forming fluid range from -2.4‰ to 2.6‰ in stage I, from -1.9‰ to 0.4‰ in stage II, and from -5.0‰ to 1.6‰ in stage III, respectively, indicating that the ore-forming fluids were derived from metamorphic devolatilisation of carbonate strata. The (34S values of the Jianchaling ores (10.0‰~14.3‰) suggest that the sulfur was mainly sourced from evaporation strata. The Pb isotope ratios of the ores have less radiogenic Pb isotope than the host rocks, and suggest that the ore-forming fluids, which interacted with the wallrocks to form ores, must have been sourced from a depleted mantle or a depleted subducting oceanic slab. In combination with the H, O, C, S and Pb geochemical signatures of the mineral systems, we argue that the initial ore-forming fluid is mainly metamorphic extracted from the dehydration of the wall rocks, and the ore-forming materials might have derived mainly from the wall rocks with mantle input.