Two mineralization events in the Laozuoshan Au deposit, north‐east China: Evidence from Re–Os geochronology and trace element geochemistry

The Laozuoshan deposit, located in the central Jiamusi Block of north‐east China, is characterized by two types of mineralization, including principal skarn‐type Au mineralization occurring along the contact zone between granite and migmatite, and minor auriferous quartz‐arsenopyrite veins hosting in plagiogranite and granite. Re–Os dating of auriferous pyrrhotite and arsenopyrite were performed to determine the metallogenic ages of the Laozuoshan gold deposit. Analyses of arsenopyrite from quartz vein‐type ores yield a weighted average model age of 89.0 ± 3.1 Ma (mean standard weighted deviation（MSWD） = 9.3), which is within uncertainty in agreement with the 187Re/188Os versus 187Os/188Os isochron age of 93.2 ± 2.6 Ma (MSWD = 1.3) and the 187Re versus 187Os isochron age of 97 ± 14 Ma (MSWD = 7.4). Pyrrhotite samples from skarn‐type ores have model ages from 82.6 Ma to 424.8 Ma, indicating an unclosed Re–Os isotope system. However, the skarn‐type Au mineralization likely occurred during the Permian following the emplacement of the Laozuoshan granite. Results of laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) trace element analysis show that element contents in sulphides from different types of ores are systematically different. Au, Ag, Bi, Pb, Co, and Ni are significantly enriched in skarn‐type arsenopyrite. These data suggest that the Laozuoshan deposit formed from two gold mineralization events. Combined with previous studies, we suggest that the skarn‐type Au mineralization was associated with the subduction of the Panthalassic oceanic plate, whereas the rollback of the Palaeo‐Pacific Plate was responsible for the quartz vein‐type Au mineralization in the Laozuoshan deposit. The multiple mineralization events have important implications for regional exploration. The Laozuoshan gold deposit formed from two mineralization events, including Permian skarn‐type Au mineralization and Cretaceous quartz vein‐type Au mineralization. Trace element compositions in sulphides from different types of ores are systematically different.