新疆阿尔泰南缘托库孜巴依金矿成矿演化:石英脉系、同位素地球化学及其Ar-Ar年代学证据

Metallogenic evolution of Tuokuzibayi gold deposit in southern Altay,north Xinjiang:Evidence from characteristics of quartz vein systems,isotopic geochemistry and Ar-Ar chronology

托库孜巴依金矿区赋存于玛尔卡库里大型韧性剪切带及其次级构造中,含矿构造演化经历了5个主要变形阶段:D1推覆挤压变形与紧闭褶皱,D2左行走滑韧性剪切带,D3造山带的抬升与脆-韧性变形,D4伸展体制下的张性构造,伴生有多金属硫化物-石英脉充填与闪长岩脉贯入;D5晚期近东西向及北西向等多组压扭或张扭性次级断裂。相应地,在构造变形过程中形成一系列形态和矿物组合各异的石英脉,初步划分出8种脉系、4个主要成矿阶段,识别出两个主要成矿事件:①与脆-韧性剪切作用有关的含金黄铁矿-石英脉,②与走滑-伸展转换体制有关的含金多金属-石英脉。氢、氧同位素研究结果显示从早阶段向晚阶段,成矿流体由以变质热液为主向以大气降水为主的方向演化,硫同位素主要为深源硫特征,铅同位素分析结果显示来源于造山带和上地幔之间,并向造山带演化,且与阿舍勒铜矿的围岩和矿石有一定的成因联系,说明早期的火山作用对成矿有一定的贡献。对构造变形形成的黑云母进行Ar-Ar法定年,获得黑云母的坪年龄为(269.94±2.54)Ma,反等时线年龄为(269.38±2.63)Ma,结合已发表的年龄数据,该矿床可能由两个成矿事件形成,分别为290Ma左右和270Ma左右,对应于额尔齐斯构造带的两幕变形,早期主要与其大规模左行走滑有关,而第二成矿事件可能与后碰撞走滑-伸展转换体制有关。

The gold ore bodies of the Tuokuzibayi gold field, located in southern Altay, Xinjiang, are hosted by NW- SE trending, steeply NE-dipping and 1000 m wide Ma＇ erkakuli large-size ductile shear zone （MDSZ） and its secondary structures, which transect Middle and Lower Devonian metamorphic rocks of lower greensehist facies. Studies indicate that tectonic evolution of the ductile shear zone that hosts ore bodies has gone through mainly five deformation stages. D1 event is represented by tight folds, which were generated by compression deformation. But it is quite difficult to recognize these folds because of subsequent deformation. Ductile D2 shearing is associated with a sinistral strike-slip deformation, which formed intense deformation zone. D3 eyent is characterized by transition of ductile shearing to brittle-ductile shearing in continual development and uplift of the Altay orogen. In the post-collision period, compression was transformed to the extension domain, which formed tension structures and brittle faults filled with polymetallic sulfide-quartz veins and diorite dikes （134）. D5 is associated with superimposing late EW and NE trending brittle faults in the shear zone. Accordingly, at least eight multifacies quartz veins, each with its own characteristic geometry and mineral paragenesis, were formed in the evolution of the Ma＇ erkakuli ductile shear zone. On the basis of the relationships between various types of quartz veins as well as the characteristics of their mineral composition, gold mineralization of this gold deposit is divided into four stages, and two main ore-forming events are recognized： brittle-ductile deformationrelated pyrite-quartz veins and transition of strike-slip deformation to extension domain-related polymetallic quartz veins. Hydrogen and oxygen isotope studies show that ore-forming fluids varied from metamorphic fluids to meteoric water-dominant fluids from early to late stages. δ34 S‰ （CDT） values of sulfides from this gold deposit range from -2. 71‰ to 5.6‰, showing a deep source. Pb isotope analyses reveal that ore-forming materials were generated between the orogen and the upper mantle, in the direction of the orogen. This must have had some genetic relations with host rocks and ores in the Ashele massive sulfide Cu-Zn deposit, indicating that early volcanism contributed to gold mineralization in the gold deposit. Ar-Ar dating of biotite from mylonite in the shear zone yields a plateau age of 269.94±2.54 Ma and inverse isochron age of 269.38±2.63 Ma. According to this result in combination with age data available, it is held that the gold deposit must have resulted from two main gold ore-forming events at 290 Ma and 270 Ma, respectively, corresponding to two deformation stages of the Ertix tectonic belt. It is presumed that early gold mineralization was related to large-scale sinistral strike-slip whereas late gold mineralization resulted from post-collisional structural transition.