新疆额尔齐斯金成矿带的^(40)Ar/^(39)Ar年龄及其地质意义

^(40)Ar/^(39)Ar Dating and Its Significance of the Ertix Gold Metallogenic Belt in the Altay Orogen, Xinjiang

额尔齐斯大型剪切构造带是目前阿尔泰古生代造山带内最重要的金成矿带。对其玛尔卡库里段的多拉那萨依和赛都两个剪切带型金矿床含金蚀变岩中的云母类矿物进行了 4 0 Ar/39Ar快中子活化法同位素测年 ,获得坪年龄分别为 2 92 .8± 1.0 Ma和 2 89.2± 3.1Ma,对应的等时线年龄分别为 2 93.1± 4 .8Ma和 2 91.9± 8.4 Ma,表明含金剪切带韧脆性剪切活动的时代或主成矿期为 2 90 Ma左右。结合区域地质资料说明控矿剪切带经历了由深部构造层次的韧性变形到浅部构造层次的韧脆性变形的演化过程 ,并伴随两次构造—岩浆热事件 ,而成矿作用主要发生于造山带构造演化的后碰撞伸展构造环境 。

The Ertix shear zone is currently one of the most important gold metallogenic belts in the Paleozoic Altay Orogen, but there remain disputes both in genesis and geodynamic setting of the mineralization. Through field investigations and isotope chronological studies of two typical gold deposits (e.g. Duolanasayi and Saidu) in the Ma'erkakuli shear zone northwest of the Ertix belt, the authors obtained a group of Ar/Ar chronological data of altered auriferous rocks, i.e., a plateau age of 292.8±1.0 Ma and isochronal age of 293.13±4.84 Ma for muscovite from the Duolanasayi deposit, and a plateau age of 289.2±3.1 Ma and isochronal age of 291.93±8.37 Ma for muscovite from the Saidu deposit, suggesting that the ductile-brittle shearing of the Ertix belt and shear zone-hosted gold deposits were chiefly formed at the time around 290 Ma. These chronological data together with regional geology show that the ore-controlling shear zone experienced a structural evolution from ductile deformation in the deeper tectonic domain to brittle deformation in the shallower tectonic domain, and was coupled with two magmatic events, and the gold-forming process mainly occurred during the post-collisional extensional environment of the Altay Orogen and genetically related to the late stage of the tectono-magmatism.