新疆西南天山阿万达金矿区赋矿围岩物源及形成时代：碎屑锆石U-Pb年代学制约

Sedimentary Provenance and Age of the Ore-hosting Strata in the Awanda Gold Deposit in the Southwest Tianshan Area, Xinjiang:Constraints from Detrital Zircon U-Pb Dating

阿万达金矿位于西南天山造山带内。此次研究在简要总结其矿床地质特征基础上,对与阿万达金矿成矿密切相关的阿克苏群中硅质片岩围岩分别进行了岩石地球化学分析和LA-ICP-MS碎屑锆石U-Pb定年研究,以期对围岩的沉积环境、物源及形成时代进行讨论。岩石地球化学分析结果显示,阿万达金矿赋矿围岩中硅质片岩的原岩可能为一套成熟度较低的泥岩或砂岩,物源主要为石英岩质沉积物,沉积环境可能处于活动大陆弧内的沉积盆地内。U-Pb定年结果显示,其碎屑锆石定年数据主要形成了加权平均年龄值为405 Ma或406 Ma的年龄峰,其谐和年龄最小峰值即405 Ma可以作为其最大沉积年龄。因此笔者认为阿克苏群中硅质片岩的沉积时代并不是前人所定的长城纪,而是不老于早泥盆世。另外,这一地层的物源组成具有多样性,～405 Ma碎屑锆石占主体,可能与哈尔克山北缘火山弧内的早泥盆世岩浆活动有关;～745Ma的碎屑锆石的出现,表明其物源有少部分来自新元古代岩石;极少数～2.50 Ga的碎屑锆石的出现,反映了华北地台对本地层有物源上的贡献。

The Awanda gold deposit is located in the Southwestern Tianshan Orogenic Belt. On the basis of the geologicalcharacteristics of the Awanda gold deposit, the authors applied petrological geochemistry and LA-ICP-MS detrital zircon U-Pb dating of the siliceous schist wall rocks from the So-called Aksu Group, which is closely related to the mineralization of Awanda gold deposit,with an aim to understand depositional environment, provenance and age of these rocks. The results of petrochemistrical analysis showthat the protoliths of the ore-hosting strata are possibly composed of mudstones and sandstones with low maturity. Most of the provenances are quartzose sediments and the depsotional environment is likely related to depositional basin nearby the active continentmargin. LA-ICP-MS detrital zircon U-Pb date indicates that the zircon ages have peaks of weighted age of 405 or 406 Ma. The youngest peak age of these concordant age data is 405 Ma which could be regarded as the maximum sedimentary age. Therefore, it wasconsidered that the sedimentary age of the so-called Aksu group ore-hosting strata is not older than the Early Devonian, rather than the Changcheng period as previously reported. In addition, the provenances of the strata are multiform. Among the analytic data, the ~405Ma detrital zircons occupy the principal part, which could be related to the magmatic activity in the northern rim of the Early Devonianvolcanic arc of the Haerke Mountain. The ~745 Ma detrital zircons suggest that small part of the material source comes fromNeoproterozoic rocks. Several ~2.50 Ga detrital zircons reflect that North China block makes few contributions of material sources tothe strata.