Geology, fluid inclusion geochemistry, and 40Ar/39Ar geochronology of the Wulasigou Cu deposit, and their implications for ore genesis, Altay, Xinjiang, China
Geology, fluid inclusion geochemistry, and 40Ar/39Ar geochronology of the Wulasigou Cu deposit, and their implications for ore genesis, Altay, Xinjiang, China
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DOI：
10.1016/j.oregeorev.2012.09.005
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发表时间：
2012-12
影响因子：
3.3
通讯作者：
Yi Zheng;Li Zhang;Yan‐jing Chen;Ya-Jing Qin;Chunfa Liu
中科院分区：
文献类型：
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作者：
Yi Zheng;Li Zhang;Yan‐jing Chen;Ya-Jing Qin;Chunfa Liu
乌拉斯沟铜存款矿床产于阿尔泰造山带泥盆纪火山-沉积盆地中，呈脉状，受北西向构造控制。区内出露的火成岩和沉积岩均经历了绿片岩相变质作用。成矿作用可分为早、中、晚三个阶段，分别以黄铁矿石英、多金属硫化物石英和碳酸盐石英脉、细脉和交代体为代表。早期脉体在挤压或压扭作用中变形和角砾化。中期细脉充填在早期脉和蚀变组合中的裂缝中，并且未变形，表明张性剪切环境。晚期细脉主要是切割脉体和早期形成的交代体的开放空间裂隙充填物。乌拉斯沟存款中与铜有关的石英和方解石中的流体包裹体有4种类型，即水相（W型）、碳水混合相（M型）、纯碳相（C型）和含子矿物（S型）。早期石英含有M型和W型原生矿物，在322-412°C温度下完全均匀化，盐度低，为0.9-6.5wt.% NaCl当量晚期石英或方解石仅含W型矿物，均一温度101-234 ℃，盐度0.9-2.9wt.% NaCl当量这表明成矿系统经历了富CO2变质-贫CO2的大气降水流体输入过程。所有四种类型的FI只能在中期矿物中观察到，在那里它们显示出在流体不可渗透性事件期间形成脉的证据。这些FI均质化的温度范围主要为230 - 347°C，盐度聚集在2.7-10.2wt.% W-、M-和C-型的NaCl当量，和34.7-38.2wt.% NaCl当量的S型。金属沉淀是由于在流体不渗透期铜的溶解度降低所致。中期流体的捕获压力为1.55-3.55kbar，为岩石静力学-流体静力学交替流体系统，受13-15.5km深度的断层阀活动控制。中期多金属石英细脉中白云母的40 Ar/39 Ar坪年龄为219.41±2.10Ma，39 Ar/36 Ar-40 Ar/36 Ar等时线年龄为219.73±2.17Ma。这一年龄晚于古亚洲洋最终闭合（约1000年）。表明乌拉斯沟铜矿化形成于三叠纪大陆碰撞环境。因此，乌拉斯沟铜存款可能是第一个在增生造山作用或大陆碰撞作用下形成的造山矿脉型铜矿床。
The Wulasigou Cu deposit occurs as veins controlled by a NW-trending structure in a Devonian volcano-sedimentary basin of the Altay orogenic belt, Xinjiang, China. Igneous and sedimentary rocks exposed in the area have undergone greenschist-facies metamorphism. The ore-forming process can be divided into early, middle, and late stages, represented by, respectively, pyrite-quartz, polymetallic sulfide-quartz, and carbonate–quartz veins, veinlets, and/or replacement bodies. The early veins were deformed and brecciated during a compressional or transpressional event. The middle-stage veinlets filled fractures in the early-stage vein and alteration assemblages, and are undeformed, suggesting a tensional shear setting. The late-stage veinlets are mainly open-space fissure fillings that cut veins and replacement bodies formed in the earlier stages. Four types of fluid inclusions (FIs), including aqueous (W-type), mixed carbonic-aqueous (M-type), purely carbonic (C-type) and daughter mineral-bearing (S-type), have been identified in copper-related quartz and calcite from the Wulasigou deposit. The early-stage quartz contains M- and W-type primary FIs that completely homogenized at temperatures of 322–412°C with low salinities of 0.9–6.5wt.% NaCl equiv. In contrast, the late-stage quartz or calcite contains only the W-type FIs with homogenization temperatures of 101–234°C, and salinities of 0.9–2.9wt.% NaCl equiv. This indicates that the metallogenic system evolved from CO2-rich, metamorphic to CO2-poor, through input of meteoric fluids. All four types of FIs can only be observed in the middle-stage minerals, where they show evidence of vein formation during an episode of fluid immiscibility. These FIs homogenized at temperatures ranging mainly from 230 to 347°C, with salinities clustering 2.7–10.2wt.% NaCl equiv for the W-, M- and C-types, and 34.7–38.2wt.% NaCl equiv for the S-type, respectively. The metal precipitation resulted from a decrease in copper solubility during the fluid immiscibility episode. The estimated trapping pressures for the middle-stage fluids are 1.55–3.55kbar, suggesting an alternating lithostatic-hydrostatic fluid-system, controlled by fault-valve activity at a depth of 13–15.5km. Muscovite separates from the middle-stage polymetallic-quartz veinlets yield a well-defined40Ar/39Ar isotopic plateau age of 219.41±2.10Ma, and an39Ar/36Ar -40Ar/36Ar isochron age of 219.73±2.17Ma. This age postdates the final Paleo-Asia Ocean closure (at ca. 250Ma) by about 30Ma, and indicates that the Cu mineralization at Wulasigou has occurred in the Triassic continental collision setting. Hence, the Wulasigou Cu deposit may be the first example of orogenic lode Cu deposits formed in accretionary orogeny or continental collision.