Isotope geochronology study of the granitoid intrusions in the Changshanhao gold deposit and its geological implications
内蒙古长山壕金矿区花岗岩同位素年代学研究及地质意义

The Changshanhao gold deposit is super large gold deposit found in the western part of Inner Mongolia in recent years. Although gold mineralization occurs in the metamorphic rocks of the Proterozoic Bayan Obo Group as stratoid layer, stratiform and lenticular, the gold mineralization has a close spatial relationship with various types of granitoid intrusions. The paper has systematically studied the chronology of granitoid intrusions with LA-ICP-MS. The zircon grains separated from the altered granite porphyry and monzonitic granite porphyry samples have given average LA-ICP-MS U-Pb ages of 290.9±2.8Ma, with MSWD value of 1.4 and 287.5±1.9Ma, with MSWD value of 2.4 respectively. Meanwhile, the zircon grains separated from the two fresh biotite granite samples have given average LA-ICP-MS U-Pb ages of 267.9±1.2Ma, with MSWD value of 0.95 and 274.0±2.3Ma, with MSWD value of 1.4 respectively. Based on the zircon LA-ICP-MS U-Pb age data mentioned above and combined with other geological evidences, it has been suggested that the granite porphyry, the monzonitic granite porphyry and their related gold deposit were formed in the early period of Early Permian, and which suffered the superposition of the tectonic-magmatic activity between the late period of Early Permian and the early period of Middle Permian. The presence of the biotite granite cutting through the gold-bearing veins is a good example. The granitoid intrusions were probably the products of Hercynian tectonic-magmatic activities, and played an important role during the ore-forming processes of the Changshanhao gold deposit. Preliminary results show that the Changshanhao gold deposit is a product of Hercynian tectonic-magmatic and fluid-related activities, and belongs to mesothermal vein-type gold deposit related to intrusive rocks.