Zircon U-Pb geochronology,geochemistry and petrogenesis of the granites from the Xiaoliugou deposit in the western of the North Qilian

The Xiaoliugou W-Mo deposit in Gansu is a porphyry-skarn-quartz type deposit related to granitoids. Xiaoliugou granitoids are comprised of monzogranite and granodiorite. In this paper,zircon U-Pb dating and geochemistry of the Xiaoliugou granite are studied to constrain its geochronology and petrogenesis. Zircon LA-ICP-MS dating yields concordant ages of 454. 0 ± 2. 0 and 417. 7 ± 1. 7Ma respectively indicating that the two plutons were formed at Caledonian,later affected by Hercynian and Yanshanian magmaticthermal event. Geochemical data shows that,Xiaoliugou granite is silica enriched in composition with high content of alkali. It's a peraluminous granite and belongs to the high-K calc-alkaline series,enriched in Rb,Th,U,K,Pb,depleted in Ba,Sr,Ti,P with strong negative abnormal of Eu,especially,the monzogranite has intensely negative Eu abnormality( δEu = 0. 08 ～ 0. 19) and should be ascribed to highly fractionated I-type granite. The Hf isotope shows that the e Hf( t) value of the monzogranite range from- 4. 45 to 4. 04,with t DM2 ages between 1176Ma and 1714Ma,while the e Hf( t) value of the granodiorite range from-4. 18 to 4. 43,with t DM2 ages between 1124Ma and 1670Ma,indicating that the Xiaoliugou granitoids were most likely generated by mixing of a depleted mantlederived and an induced crustal-melted felsic magma in the deep crust. We suggested that the source region of granite were likely from the Paleoproterozoic-Mesoproterozoic ancient crustal rocks and the granodiorite is relatively deeper than monzogranite,the ore-forming metals such as tungsten in the deposit may have likely derived from the Beidahe Group and the Zhulongguan Group. Comprehensive studies indicate that Xiaoliugou W-Mo deposit has a closely temporal relationship with the monzogranite. Combine with the tectonic evolution of the North Qilian,we speculate the monzogranite was generated in a continental arc tectonic setting triggered by slab subduction,the granodiorite probably have been generated in syn-collison setting.