Ore genesis of the Baiyun gold deposit in Liaoning province, NE China: constraints from fluid inclusions and zircon U–Pb ages

Abstract

The Baiyun gold deposit in the Liaodong gold province, NE, North China Craton (NCC), is a lode gold deposit hosted within the Paleoproterozoic metamorphic rocks. Disseminated and vein-hosted gold mineralization occurs along NWW-trending interlayer faults and NE-trending normal faults. Crosscutting relationships and mineral assemblages indicate hydrothermal process of the gold deposit can be divided into three stages, characterized by pyrite–quartz (stage 1), quartz–pyrite–chalcopyrite (stage 2), and quartz–carbonate (stage 3) assemblages. Gold is observed within stage 1 and 2 veins. Hessite is observed within stage 2 veins. Fluid inclusion petrography and microthermometry indicate that the ore fluid evolved from moderate salinities to low salinities, likely due to fluid mixing. The precipitation of gold and hessite is attributed to fluid mixing. Fluid inclusion compositions present the minimum trapping temperatures of the ore fluid were between 200 and 290 °C. Minimum trapping pressures estimated from H2O–CO2–NaCl inclusions were 58–139 and 24–68 MPa for stage 1 and 2 assemblages, respectively. The δ18Owater (‰ SMOW) values of ore fluid in stage 1 range from 3.9 to 7.8 ‰, and the δD (‰ SMOW) values are between − 92 and − 69‰, indicating that the ore fluid was dominantly magmatic water. Zircon from a pre-ore quartz porphyry yielded a weighted mean zircon 206Pb/238U age of 127.8 ± 0.8 Ma, and the emplacement of a post-ore microdiorite is constrained to 125.6 ± 1.3 Ma. These results suggest that the Baiyun gold deposit is an intrusion-related vein gold deposit formed at ~ 126 Ma, which coincides with extension and a peak in magmatism within the NCC, indicating that gold mineralization in this region might have resulted from the breakup of the NCC.