An Early Cretaceous Ag-Pb-Zn mineralization at Halasheng in the South Erguna Block, NE China: Constraints from U-Pb and Rb-Sr geochronology, geochemistry and Sr-Nd-Hf isotopes

Abstract

The Halasheng deposit, located in the southern Erguna Block, is a vein-type Ag-Pb-Zn deposit in the Derbugan metallogenic belt. The orebodies, hosted in Middle-Late Jurassic volcanic rocks, show a close spatial and temporal relationship with Early Cretaceous granites. Zircon U-Pb dating suggests that the granites were emplaced at 134–128 Ma. Rb-Sr dating of ore-related sphalerite gives an imprecise age of 122 ± 18 Ma, indicating that the Halasheng deposit formed in the Early Cretaceous. Whole-rock major and trace element analyses show that the Cretaceous granites belong to the metaluminous to peraluminous, shoshonite to high-K calc-alkaline series, and can be classified as A-type granites. They are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE), but depleted in high field-strength elements (HFSE) and heavy rare earth elements (HREE). The quartz monzonite, which has a spatial relationship with mineralization, has low initial 87Sr/86Sr (0.7058–0.7069), and positive εNd (t) (0.42–0.61) and εHf (t) (3.47–6.45), with Nd and Hf two-stage model ages of 0.81–0.85 Ga and 0.69–0.86 Ga, respectively. These geochemical features are similar to those of major Mesozoic granite intrusions in the Erguna Block. We propose that these graintes originated from partial melting of juvenile crust in an intraplate extensional setting. Taken together, the Halasheng Ag-Pb-Zn deposit formed in the Early Cretaceous after the orogeny related to closure of the Mongol-Okhotsk Ocean. The relatively low-temperature of Ag-Pb-Zn ore and alteration mineralogy suggest that there is only a distal relationship, if any, to nearby potentially-causative granite intrusions.