Zircon U-Pb dating and geochemical characteristics of the plagiogranite porphyry from the Xiaoyuanshan iron-polymetallic ore district in East Kunlun Mountains

Abstract: Qimantag in East Kunlun Mountains is an important skarn-type iron-polymetallic metallogenic belt in Qinghai Province, and the Xiaoyuanshan iron-polymetallic ore district is located in the eastern Qimantag, Qinghai. The mineralization has close relationship with plagiogranite porphyry, and the orebody occurs in the outer contact zone of plagiogranite porphyry. LA-MC-ICP-MS zircon U-Pb dating shows that the weighted mean age of plagiogranite porphyry is 216.9±1.9 Ma (n=16，MSWD=2.9), suggesting Late Triassic. Detailed petrogeochemical studies show that the plagiogranite porphyry belongs to the peraluminous high-K calc-alkaline series. This suite of rocks are enriched in LILE (such as Rb, K), LREE and more mobile incompatible elements (such as U, Th) and relatively depleted in HFSE (such as Nb, Ta, Ti, P). The plagiogranite porphyry is rich in LREE and poor in HREE, with obviously negative Eu anomalies. Based on a combined study of geochronology and evolutionary characteristics of regional structures, the authors consider that the plagiogranite porphyry was formed at the post-collisional development stage of the orogen, corresponding to the late stage of the Late Paleozoic-Early Mesozoic tectonic event in eastern Kunlun orogenic belt．