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 Re-187/Os-188 versus Os-187/Os-188 isochron age of 93.2 +/- 2.6 Ma (MSWD = 1.3) and the Re-187 versus Os-187 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.