新疆东天山剪切带型金矿床时代研究

Study on the age of the shear zone-type gold deposit of East Tianshan,Xinjiang,China.

东天山造山带中部的秋格明塔什-黄山巨型韧性剪切带内三个典型的剪切带型金矿床——康古尔金矿床、红石金矿床和红山金矿床的同位素年代学研究表明,金矿床成矿作用和剪切带后期的走滑剪切变形作用在时间上具有强烈的耦合关系。秋格明塔什-黄山韧性剪切带剪切变形作用主活动期的时代为262.9～242.8Ma,而剪切带型金矿床金成矿作用发生在261.0～246.5Ma 之间,恰好落在剪切变形作用主活动期的时代范围之内。这种强烈的耦合关系证明了秋格明塔什-黄山韧性剪切带晚期的右行走滑剪切变形作用才是剪切带内一系列金矿床成矿作用的主因。金成矿和右行走滑剪切变形之间的时间耦合关系在不同部位还有不同的表现。在剪切带中-西段的康古尔地区,快速抬升发生在261.5～262.9Ma,而康古尔金矿床主成矿期时代范围是261.0～252.5Ma,可以看出,康古尔金矿床成矿作用刚好发生于剪切带中-西段快速抬升之后。在剪切带东段,快速抬升发生在247.1～246.9Ma 期间,位于该剪切带东段北外带的红山金矿床主成矿期的年龄范围是246.9～246.5Ma,表明该金矿也是在剪切带东段快速抬升冷却之后形成的。金矿石 Ar-Ar 同位素年代学研究未能得到可靠的和早期韧性推覆剪切变形事件相对应的年龄,推测在晚石炭世—早二叠世发生的韧性推覆剪切变形事件可能仅导致了包括金在内的金属元素的初步富集,但由于高温不利于金属元素沉淀和挤压环境不易存在容矿空间等不利因素的影响,导致此阶段并没有形成有工业开采价值的金矿床。只是到了华力西晚期—印支早期,在原韧性推覆剪切带内发生了走滑剪切变形活动,并产生了快速抬升冷却降温到350℃后,在地体缓慢冷却阶段,在脆-韧性剪切带内才有足够的空间和时间形成金矿床。

Abstract The isotope geochronological study of the Kanggur, Hongshi and Hongshan, three typical shear zone-type gold deposit located in Qiugemingtashi-Huangshan large-scale ductile shear zone in the middle of the East Tianshan orogenic belt, shows that the time of the gold deposit mineralization is in agreement with that of the strike-slip shear deformation of the shear zone in its late period. The main shear deformation time of the Qiugemingtashi-Huangshan ductile shear zone is between 262.9 ～ 242.8Ma, while the gold mineralization time of the shear zone-type gold deposit is between 261.0 ～ 246.5Ma. This high concordance proves that the late right lateral strike-slip shear deformation is the main reason for the gold mineralization. The agreement between the gold mineralization time and the right lateral strike-slip shear deformation time shows diversity in different part of the shear zone. The fast uplift of middle-western part of shear zone happened in 261.5 ～ 262.9Ma while the main mineralization time of the Kanggur gold deposit is between 261.0～252.5Ma, which indicates that the mineralization of the Kanggur gold deposit began just after the fast uplift of the middle-western shear zone. In the eastern shear zone, the fast uplift happened in 247.1 ～246.9Ma while the main mineralization time of the Hongshan gold deposit, situated in the north area of the eastern shear zone, is between 246.9～246.5Ma, which indicates that the mineralization of this gold deposit also began after the fast uplift of the eastern shear zone. The Ar-Ar age of the gold ore obtained in this study is not in agreement with the time of the early ductile nappe Shear deformation, which is inferred that the ductile nappe shear deformation happening in late Carboniferous-early Permian may only result in the primary concentration of metal element including gold. Because the high temperature is unfavorable to the metal element precipitation and the compression environment is unfavorable for forming space to hold ore, gold deposit is not formed during this period. Until late Variscan to Early Indo-sinian epoch, the strike-slip shear deformation resulting in fast uplift and cooling to 350℃, then the brittle-ductile shear zone had enough space and time for forming gold deposit during the slowly cooling period below 350℃.