东昆仑别里赛北铁矿床石英闪长岩LA-ICP-MS锆石U-Pb测年、地球化学及其地质意义

Geochemistry,LA-ICP-MS zircon U-Pb dating and geological significance of quartz diorite in the Bielisaibei iron ore deposit,East Kunlun Mountains,Qinghai Province

别里赛北铁矿床是近几年在东昆仑成矿带上新发现的一处小型矿床,在对矿区地质背景及矿床特征分析的基础上,对与成矿关系最密切的石英闪长岩进行了LA-ICP-MS锆石U-Pb定年,岩石地球化学研究。研究结果显示石英闪长岩LA-ICP-MS锆石U-Pb年龄为（242.9±0.6）Ma,MSWD值为0.6,n=22;Si O2的含量在53.62%~63.83%,Al2O3含量在14.55%~17.57%,Na2O含量在2.95%~4.06%,K2O含量在1.60%~3.83%,为准铝质中-高钾钙碱性岩石系列;稀土元素总量中等,轻稀土元素富集,中等负铕异常;强不相容元素K、Rb、Th强烈富集,高场强元素Ta、Nb、Zr、Hf及轻稀土元素Ce、Sm中等富集,Ba、Sr富集不明显,贫P、Ti而Sm、Y、Yb元素含量高出球粒陨石值不多,反映了岩浆具有壳源为主的特点。

The Bielisaibei iron deposit is a small deposit recently discovered in the East Kunlun metallogenic belt. Based on an analysis of the geological background and ore deposit characteristics, the authors studied petrological geochemistry of the deposit and conducted LA-ICP-MS zircon U-Pb dating of the quartz diorite which is most closely related to mineralization. According to the results obtained, the LA-ICP-MS zircon U-Pb age of the quartz diorite is 242.9 ± 0.6 Ma（MSWD = 0.6, n=22）, and the majorelements of the quartz diorite have the data Si O2（51.98%- 63.83%）, Al2O3（14.55%- 17.57%）, Na2O（2.95%- 4.21%）, and K2O（1.60%- 3.83%）, indicating that the quartz diorite belongs to the metaluminous medium- high potash calc- alkaline series. Other characteristics of the quartz diorite include moderate ΣREE values, enrichment of LREE, moderate negative Eu anomalies, strong enrichment of K, Rb, Th, moderate enrichment of Ta, Nb, Zr, Hf, Ce, Sm, insignificant enrichment of Ba and Sr, depletion of P and Ti, and somewhat higher Sm, Y and Yb values than chondritic values, suggesting that the magma was dominated by crustal rocks.