上扬子地块东缘凹子岗锌矿床成矿流体特征

Characteristics of Ore-forming Fluid of the Aozigang Zinc Deposit in the East Margin of the Upper Yangtze Block

凹子岗锌矿床位于上扬子地块东缘,该矿床经历了两个成矿期：沉积成岩期和热液期,形成两种不同岩相学特征的闪锌矿。流体包裹体岩相学研究显示,存在盐水包裹体（W型）、烃类包裹体（G型）和含石盐子矿物多相包裹体（S型）。有机流体活动与成矿存在耦合关系,其中烃类包裹体（G型）赋存于白云石和自形粗粒闪锌矿中,具有黄色荧光效应,激光拉曼测试显示其成分为沥青质、CH4、C3H8和H2O;此外,沥青与闪锌矿密切共生。显微测温结果显示热液期流体包裹体均一温度集中于160-180℃,盐度集中于8%~14%NaCl（eqv）,部分可达30%NaCl（eqv）左右。成矿流体除含有机质外,还含有NaCl、KCl、CaCl2、MgCl2、H2O,为多元共存的流体体系,成矿压力为22~84 MPa。

The Aozigang deposit in the Hubei province, in the east margin of the Upper Yangtze Block, is a zinc deposit hosted in the Dengying Formation. The mineralization process is composed of depositional stage and hydrothermal stage. The reseda fine-grained sphalerites are recognized as the typical layered-laminated ore of the depositional stage, whereas reddish brown coarse-grained sphalerites occur in the hydrothermal stage. Primary fluid inclusions（FIs） in dolomite, quartz and sphalerite include three compositional types, i.e. aqueous（W-type） inclusions, gaseous hydrocarbon（G-type）, and daughter mineral-bearing（S-type）. The Laser Raman microspectroscopy results indicate that CH4, C3H8 and bitumen dominate G-type inclusions in the dolomite and reddish brown coarse-grained sphalerite, and G-type inclusions show yellow fluorescence color. The coexistence of bitumen and sphalerite also indicates that organic fluids have potential relationship with zinc mineralization in the Aozigang Zn deposit. At the hydrothermal stage, microthermometric data show the FIs are totally homogenized mainly at 160–180 ℃ and with salinities of 8%–14%NaCl（eqv）, and S-type FIs have salinities of 30%NaCl（eqv）. Ore-forming fluids are a multicomponent system, which contains not only organic material, but also NaCl, KCl, CaCl2, MgCl2, H2O. The estimated trapping pressures are 22–84 MPa.