LAUSR

Abstract The Erguna metallogenic belt is a large Erdaohezi epithermal polymetallic sulfide Pb-Zn deposit in the northern Great Xing’an Range that is associated with andesitic porphyry. Mineralization mainly occurs at the edges of andesitic porphyry and adjacent Jurassic quartz porphyry and volcanic strata. Hydrothermal alteration minerals mainly include quartz, sericite, adularia, chlorite and calcite, while ore minerals include pyrite, galena and sphalerite, with minor argentite, chalcopyrite and tetrahedrite. Three hydrothermal-mineralization stages are recognized. Three categories of fluid inclusions (FIs) are distinguished in quartz, fluorite and sphalerite veins: liquid-rich, gas-rich and a few H2O–CO2 inclusions. The stage I FIs include all three inclusion types and present high homogenization temperatures (197–233℃) and salinities (0.7–6.8 wt% NaCl eq.). The stage II FIs mainly comprise liquid-rich inclusions with a few H2O–CO2 types and present higher homogenization temperatures (167–190℃) and slightly higher salinities (0.9–7.6 wt% NaCl eq.) than those of stage I. Stage III only contains liquid-rich inclusions and presents the lowest homogenization temperatures (120–157℃) and salinities (0.5–4.8 wt% NaCl eq.). The ore-forming fluids have low temperatures and salinities in an H2O–NaCl–CO2 ± CH4 system. The O–H isotope data (-2.2 to −5.0‰ and −160.0 to −152.5‰, respectively) suggest that ore-forming fluids gradually evolved from mantle primary water to meteoric water. Sulfur, strontium and lead isotopes imply a mixed crustal and mantle source for the ore-forming materials. Sulfide Rb–Sr dating yields a well-defined isochron age of 130.5 ± 3.6 Ma from the main mineralization stage, which is similar to the zircon age of 134.9 ± 0.9 Ma for the andesitic porphyry related to mineralization. We therefore proposed that Erdaohezi is a low-sulfidation epithermal Pb-Zn polymetallic deposit, and fluid immiscibility was the dominant mechanism of ore deposition. Mineralization occurred in an Early Cretaceous back-arc extensional setting that was related to the subduction of the Paleo-Pacific Plate.