新疆阿舍勒VMS型铜锌矿床元素活化富集作用初步研究

A Preliminary Study on the Ore Metal Remobilization of the Ashele VMS Cu-Zn Deposit, Xinjiang

新疆阿舍勒铜锌矿床位于阿尔泰增生型造山带南缘阿舍勒盆地内,受褶皱控制的透镜状矿体产于阿舍勒组地层中,矿体与围岩一起发生协和变形。成矿过程可分为两个成矿期：以条带状–块状矿石为代表的VMS成矿期和以脉状矿石为代表的热液成矿期。局部可见脉状矿石切穿条带状矿石,表明热液成矿期明显晚于VMS成矿期。大部分VMS成矿期矿石同生沉积特征保存较好。脉状矿石穿插条带状矿石时,会出现硫化物矿物颗粒变粗的现象,并伴随定向构造、压力影构造、碎裂结构、变斑晶结构、交代残余结构和港湾交代结构等现象。以上证据表明,后期变质变形导致矿石中局部硫化物品位提高。脉状矿石中的石英广泛发育流体包裹体,可分为水溶液包裹体（W型）、纯CO2包裹体（PC型）、CO2-H2O包裹体（C型）及含子矿物多相包裹体（S型）四类。显微测温表明,均一温度集中在220~280℃,流体盐度集中于4%~8%Na Cleqv之间。激光拉曼结果证实,流体包裹体中普遍富含CO2,甚至出现少量纯液相和纯气相的CO2包裹体。脉状矿石成矿流体具有中温、低盐度和富CO2的特征,与造山型金矿的变质流体特征一致。联系区域构造演化历史,晚古生代洋陆俯冲背景有利于形成VMS型矿石,而印支期碰撞拼贴过程的变形–变质流体作用导致阿舍勒铜锌矿床进一步加富。因此,新疆阿舍勒铜锌矿可作为变质加富VMS型矿床的典例,区域上火山岩地层和褶皱复合部位是寻找此类矿床的理想靶区。

The Ashele Cu-Zn deposit is located in the Ashele Devonian volcanic-sedimentary basin to the south of the Altay accretionary orogenic belt. The ore bodies are lens like hosted in the Ashele Formation. Orebodies show deformations concordant with the host rocks. The ore-forming process can be divided into two stages： the first VMS stage represented by banded and massive ores, while the second hydrothermal stage represented by Cu-polymatellic veins. Most of primary ores are preserved, but locally some veins cut across the earlier banded ores accompany with the coarse grains and pressure-solution, crushed, meta-porphyry, replacing textures, indicating metallic remobilization of primary VMS ores. Four types of fluid inclusions are distinguished, which include aqueous water（W-type）, pure CO2（PC-type）, CO2-H2O（C-type） and daughter mineral-bearing（S-type）. The primary fluid inclusions have homogenization temperatures of 220–280 ℃ and salinities of 4% to 8% Na Cl equivalent. Gases in fluid inclusions are CO2, CH4 and N2. The low salinity and high CO2 content indicate the ore-forming fluid may be metamorphic fluid. The hydrostatic-lithostatic pressure of boiling fluid assemblage fluctuates is range of 85–295 MPa, corresponding to the depth of 8.5–10.9 km. Considering the regional tectonic evolution, we conclude that the VMS mineralization was formed in the arc-basin under extensional setting, whereas the late stage hydrothermal remobilization was formed in continental-arc collision setting. Therefore, the Ashele Cu-Zn deposit is a modified VMS deposit.