Polymetallic mineralization in the periphery of cratonic margin extensional basins: Cases study of the Qibaoshan ore district and the Hubu and Yangjiayu deposits at the southern margin of the Jiaolai Basin

The mineralization characteristics, geodynamic setting and dynamic driving mechanisms of porphyry-epithermal polymetallic deposits developed along margins of cratonic continental basins remain poorly understood. In this study, the Qibaoshan Cu-Pb-Zn ore district, the Hubu Mo-Pb-Zn and Yangjiayu Cu-Pb-Zn deposits, located along the southern margin of the Jiaolai Basin, were selected as cases for a systematic investigation on their mineralization processes and geodynamic setting by using comparative analyses of hydrothermal alteration, mineral assemblages and geochronological data. The Qibaoshan Cu-Pb-Zn ore district is controlled by regional crypto-explosive breccia pipes and faults, and is characterized by chalcopyrite, galena and sphalerite metal assemblages, accompanied by quartz-sericite and carbonate alteration, resembling intermediate-sulfidation epithermal systems. The Hubu Mo-Pb-Zn deposit is structurally controlled by regional faults and dominated by molybdenite, quartz, sericite and K-feldspar mineral assemblages, representing porphyry-type Mo mineralization. The Yangjiayu Cu-Pb-Zn deposit is characterized by chalcopyrite, galena and sphalerite, with quartz-sericite and carbonate alteration, indicative of a fault-controlled epithermal hydrothermal deposit. Zircon U-Pb isotopic dating yields ages of 117.0±0.8Ma for the Hubu granitic porphyry and 119.1±2.1Ma for the Yangjiayu granodiorite porphyry, which are comparable to the ~120Ma sub-volcanic complexes in the Qibaoshan ore district. These results suggest that the magmatic events in Qibaoshan, Hubu and Yangjiayu were coeval and related to a common tectono-magmatic process. Integrating our data with previous tectonic studies, we infer that the polymetallic mineralization along the southern margin of the Jiaolai Basin formed in an extensional setting associated with slab rollback or stress-field reorganization of the subducting Paleo-Pacific Plate. Volcanic edifices and faults at the basin margins can serve as regional prospecting indicators, whereas differences in metal assemblages across mineralization zones and specificity of magma and mineralization require further investigation.