云南保山黑牛凹金矿地质特征及成因研究

发布时间：2018-04-27 00:24

  本文选题：矽卡岩矿物 + 金的赋存状态　； 参考：《中国地质大学(北京)》2017年硕士论文

【摘要】：云南保山黑牛凹金矿床位于三江造山带西侧,核桃坪矿集区西北侧的一个金矿床。构造位置为保山-永德褶皱束北段的核桃坪复式背斜核部,矿床主要受近南北向的F12、F3、F4次级断层控制。矿体呈脉状、似层状赋存于上寒武统核桃坪组上段的构造破碎带及石英硫化物脉中。本文依据野外矿体穿插关系与镜下观测矿物共生关系,将金矿床成矿分为早期矽卡岩化阶段、退化蚀变阶段、石英-硫化物阶段、石英-碳酸盐化阶段等四个阶段。区内早期矽卡岩矿物主要为石榴石、辉石,属于钙质矽卡岩,分布较少。其中,石榴石主要为钙铁榴石-钙铝榴石系列,石榴石环带中元素组分变化显示,成矿环境由弱氧化、偏碱性环境→中酸性、偏还原环境。辉石为钙铁辉石,闪石族矿物为阳起石、铁闪石、铁阳起石、绿泥石等。绿泥石以铁镁绿泥石为主,形成于250℃~330℃,相对还原环境。黑牛凹金矿矿体中的金主要有以下3种赋存状态:(1)呈粒间金的形式与石英、磁黄铁矿共生;(2)呈包裹金包裹于石英或硫化物中,载金矿物为石英、磁黄铁矿和毒砂;(3)呈纳米级自然金(Au0)的形式存在于黄铁矿、闪锌矿、磁黄铁矿、毒砂等载金矿物中。对成矿前到成矿后3个阶段的石英、方解石中的包裹体进行测温,温度变化范围为:260-320℃、190-270℃、170-250℃,成矿温度逐渐降低。主成矿阶段的温度变化范围为230-280℃,平均为257℃,说明金矿结晶沉淀的温度较低,为中温环境。成矿各阶段的流体盐度变化较大,沸腾作用强烈,CO2的溢出作用随着成矿作用进行逐渐减弱。随着CO2的溢出,溶液pH值变高,加之温度、压力的下降,导致硫金络合物稳定性下降,可能是金的主要富集机制。矿区同位素结果表明:δDV-SMOW变化范围是-132‰~-109‰,平均为-114.4‰;δ18O水值为1.89‰~3.79‰,平均为2.60‰,表明其成矿热液可能来源于深部岩浆水与大气降水的混合。δ13CV-PDB变化范围为-3‰~1.5‰,平均-2.53‰,碳质主要来源于深源岩浆,部分碳来源于碳酸盐岩的热解作。δ34SV-CDT的变化范围为-0.9‰~2.7‰,平均为1.02‰,δ34S值的分布范围很窄,集中在0±1‰,2-3‰之间,与核桃坪、金厂河铅锌矿中硫同位素总体分布范围基本一致,反应了成矿物质主要来自于深部流体,可能与中酸性岩浆密切相关。
[Abstract]:The HeiNiuao gold deposit in Baoshan Yunnan is located in the west side of the Sanjiang orogenic belt and a gold deposit in the northwestern side of the Juzuping ore concentration area. The tectonic location is the Juzuping complex anticline in the northern segment of Baoshan-Yongde fold bundle, and the deposit is mainly controlled by the near north-south F12F3F4 secondary fault. The orebody is veined and stratiform in the structural fracture zone and quartz sulphide vein of the upper member of the Upper Cambrian Juzuping formation. Based on the relationship between the intercalation of ore bodies in the field and the mineral symbiosis observed under the microscope, the mineralization of gold deposits is divided into four stages: early skarn stage, degenerative alteration stage, quartz sulphide stage, quartz carbonization stage. The early skarn minerals in the area are mainly garnet and pyroxene, which belong to calcareous skarn. Among them, garnet is mainly composed of calcium iron garnet and calcium aluminite series. The change of element composition in garnet ring shows that the ore-forming environment is weakly oxidized, the alkalinity environment is slightly acidic, and the partial reduction environment is partial. Pyroxene is calcium ferroxene, amphibole group minerals are actinolite, iron amphibole, iron actinite, chlorite and so on. Chlorite is mainly iron and magnesium chlorite, formed at 250 鈩，

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