内蒙古乌拉特后旗查干花钼矿锆石U-Pb和辉钼矿Re-Os同位素年龄及其地质意义

内蒙古乌拉特后旗查干花钼多金属矿为华北陆块宝音图岩浆弧内的一处具有大型规模的隐伏矿床。钼矿体呈隐伏状赋存于二叠纪花岗闪长岩体与宝音图群二云石英片岩外接触带,大致呈不规则厚层状、脉状及网脉状,近NW向展布。发育钾化、云英岩化和绿泥石化等围岩蚀变,具斑岩型矿床蚀变分带特征。对与钼成矿关系密切的花岗闪长岩开展LA-ICP-MS锆石U-Pb定年,获得加权平均年龄为(257.2±1.3)Ma,表明查干花花岗闪长岩体形成于晚二叠世。对辉钼矿开展了Re-Os同位素测年,获得辉钼矿Re-Os等时线年龄为(238.6±4.4) Ma,模式年龄为(240.0±1.6) Ma,限定查干花钼矿是印支早期构造-岩浆活动的产物。辉钼矿Re含量为64 502×10^-9~245 621×10^-9,推测其成矿物质为壳幔混合来源。

Zircon U-Pb and Molybdenite Re-Os Ages and Geological Significance of the Chaganhua Molybdenum Deposit,Urad Rear Banner,Inner Mongolia

The Chaganhua molybdenum (Mo) polymetallic deposit is a large concealed deposit in the Baoyintu magmatic arc of North China Craton. The Mo orebody is hosted within the exo-contact between the Permian granodiorite and the two-mica quartz schist of the Baoyintu Group. The orebodies are NW-trending, and occur as irregularly-thick layers, veins,or stockworks. The wall-rock alteration styles include potassic, greisen, and chlorite, consistent with the typical porphyry-type deposit. In this study, we separated and LA-ICP-MS U-Pb dated zircons from the Mo-mineralized granodiorite from Chaganhua. Our results yielded a weighted mean ²⁰⁶Pb/²³⁸U age of (257.2±1.3) Ma (n=32, MSWD=1.6),indicating that the Chaganhua granodiorite was formed in the Late Permian.In addition, molybdenite Re-Os dating yielded an isochron age of (238.6±4.4) Ma and a model age of (240.0±1.6) Ma (n=9, MSWD=0.27),which reveals that the Chaganhua Mo mineralization was the product of the Early Indosinian magmatism.Furthermore, the Re content of molybdenite ranges from 64 502×10^-9 to 245 6 21×10^-9, suggesting that the ore-forming material was sourced from a mixture of crust and mantle.