Magmatic and tectonic setting of the Permian Au mineralization in the Xing-Meng Orogenic Belt: constraints from the U-Pb ages, Hf-O isotopes and geochemistry of granitic intrusions in the Bilihe and Hadamiao gold deposits

摘要

The Xing-Meng Orogenic Belt (XMOB) hosts significant Au-dominant polymetallic mineral deposits. Although these deposits mostly formed in the Mesozoic, Permian Au deposits are also present but less well studied. In the Bilihe and Hadamiao gold mining areas, granitic intrusions that are associated with gold mineralization were dated by LA-ICP-MS at 272.7-259.7Ma. These intrusions consist of granodioritic porphyry and quartz diorite that both represent calc-alkaline metaluminous I-type granites. These granitoids exhibit enrichment in LREEs and LILEs, depletion in HREEs and HFSEs, and low Sr/Y ratios, suggesting that these rocks have an island-arc affinity. The epsilon(Hf)(t) values of the Bilihe granodioritic porphyry and Hadamiao quartz diorite range from -0.3 to +8.9, with T-DM2 values ranging from 0.7 to 1.3Ga, and from +2.5 to +13.5, with T-DM2 values ranging from 0.4 to 1.1Ga, respectively. The zircon O-18 values of the granitic porphyry and quartz diorite range from 6.9 to 7.6 parts per thousand and from 5.0 to 6.4 parts per thousand, respectively. A simple binary Hf-O isotope mixing model shows that the assimilation of 10-15% sediments by MORB could have generated the Bilihe granodioritic porphyry, and that the assimilation of less than 5% sediments by MORB could have generated the Hadamiao quartz diorite. Combined with previous studies of the Late Carboniferous to Permian igneous rocks in the southern region of the XMOB, these new data suggest that the Bilihe and Hadamiao ore-related intrusive rocks formed in a continental-arc setting associated with the subduction of the Paleo-Asian oceanic slab. This setting indicates the potential existence of subduction-related gold deposits that are related to contemporaneous igneous activity.