Abstract:Western Sichuan is one of the most important rare metal mining regions in China, composed mainly of Jiajika, Keryin, Shiqu and Jiulong deposit clusters. In the Jiajika and Keryin deposit clusters, lithium- beryllium deposits have been discovered in Lijiagou, Dangba and Jiajika, while only medium- sized lithium- beryllium deposits have been discovered in Daqianggou in the Jiulong deposit cluster. In this paper, petrological, geochemical and U- Pb chronological studies of zircon and monazite were conducted to determine the genesis and structural setting of Qiaopengzi and its peripheral granite, as well as its spatiotemporal relationship with pegmatite, providing a basis for the prospecting and exploration of rare metals in the Jiulong River Basin and its surrounding areas. The results show that Qiaopengzi granite, which is rich in SiO2(69. 98%~76. 80%), Al2O3 (13. 72%~15. 29%) and K2O+Na2O(6. 71%~7. 24%), is a peraluminous and calc- alkali- high- K calc- alkaline series that is low in REE, Sr, δEu and HFSE, but rich in LREE/HREE, Yb and LILE, boasts a high differentiation index (79. 67~91. 73) and high Ga/Al ratios (10000×Ga/Al=2. 45~3. 11). The diagenetic age of Qiaopengzi granite and Landiao- Shitizi granite are 168. 2±0. 9 Ma, 157. 1±1. 6~152. 5±0. 5 Ma, respectively. It underwent magmatic or tectonic thermal events at 143. 5±1. 0 Ma. The temperature of Landiao- Shitizi granite (696℃~729℃) is lower than that of Qiaopengzi granite 766~804℃. The oxygen fugacity parameter of zircon shows the Qiaopengzi granite (lgf O2=-18. 71±1. 84, ΔFMQ=-4. 75±1. 84) and the Landiao granite (lgf O2 =-17. 19±1. 29, ΔFMQ=-1. 87±1. 29) are both low oxygen fugacity. Combined with the regional geological background, about 170 ~ 140 Ma, the lithosphere in the southern margin of Songpan Ganzi block is in the extension stage, with three stages of magmatic activity or tectonic thermal events recorded. The granite magma activity dominated in the early stage (168 Ma) by Qiaopengzi granite, and in the middle stage 157~152 Ma by Landiao- Shitizi granite, and in the late stage (144 Ma) by magmatism or tectonic thermal events. The metallogenic age of rare metals, such as Daqianggou and Luomo lithium beryllium deposit, is limited to 167~157 Ma, which is basically consistent with the early and medium- term time of the above magmatism within the error range. In the Jiulong region, the Yanshanian granites are discovered to be associated with rare metal mineralization, and this is obviously different from the Jiajika, Zhawulong and Keryin deposit clusters in geochemistry and chronology. This discovery points out the direction of rare metal prospecting in the Jiulong region.
