The Early Cretaceous Weilasituo Zn–Cu–Ag vein deposit in the southern Great Xing'an Range, northeast China: Fluid inclusions, H, O, S, Pb isotope geochemistry and genetic implications

Abstract

The Weilasituo vein-type deposit hosted in Hercynian (Middle to Late Paleozoic) quartz diorite and Palaeozoic gneiss occurs on the western slopes of the southern Great Xing'an Range. In this paper, we present results from fluid inclusion and isotope (H, O, S, Pb) investigations on the Weilasituo deposit. We identify three stages during the ore formation: a barren pre-ore stage (stage 1), a main-ore stage with economic grade Cu–Zn–Ag mineralization (stage 2), and a barren post-ore stage (stage 3). Fluid inclusion and mineral thermometry constrain temperature intervals of approximately 243 to 333°C, 192 to 425°C, and 141 to 261°C, for the three stages, respectively. Fluids in the main-ore stage are characterized by complex NaCl–H2O–CH4–CO2 low-salinity (3.55 to 8.68wt.% NaCl equiv.) with isotopic signatures consistent with a magmatic source. These fluids evolved by mixing with local meteoric water (δ18Ofluid=1.15 to 5.15‰, δDfluid=−139.4 to −88.2‰). Measured and calculated sulfur isotope compositions of hydrothermal fluids (δ34Sfluid=−3.0 to 3.4‰) indicate that the ore sulfur was derived mainly from a magmatic source. The lead isotope ratios from the ores show mean values of 18.326, 15.553, and 38.242 for 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb, respectively, indicating a mantle source. Our study shows that fluid mixing and/or dilution played an important role in copper, zinc, and silver mineralization in the Weilasituo deposit. The Weilasituo and Bairendaba deposits represent a linked ore system genetically related to the late Mesozoic magmatism. The ore-forming fluids associated with the Early Cretaceous mineralization in the southern Great Xing'an Range are of magmatic in origin, and evolved by mixing with local meteoric water. These deposits preserve the signature of a mantle source for lead. However, the deposits formed at ca. 177–160Ma possess a dominantly magmatic signature with less radiogenic lead.