| 其他摘要 | 广西大厂矿田处于江南古陆西南缘与右江盆地北东侧所夹持的丹池褶皱带中部。矿田内褶皱紧闭，断裂构造发育，岩浆活动强烈，以笼箱盖花岗岩侵入体为中心，在矿田中部产出有拉么、杉木冲锌铜矿床，东西两侧分别产出有铜坑—长坡、巴里、龙头山和大福楼、灰乐、亢马等锡多金属矿床。在前人研究和野外地质观察的基础上，本论文重点选择大厂矿田东成矿带灰乐和亢马这两个研究程度低的矿床为研究对象，运用矿石显微岩相学结构、矿物学与地球化学、电子探针、单颗粒石英扫描电镜-X射线激发荧光（SEM-CL）、同位素地球化学、流体包裹体岩相学与显微测温学、激光Raman光谱等方法手段，对其主要矿物微区化学成分、成矿物质与成矿流体来源、成矿流体物理化学性质、演化及成矿机制等进行了较为系统的研究，取得了以下认识：（1）矿物学和电子探针分析表明，灰乐和亢马矿床矿石矿物主要由锡石、毒砂、磁黄铁矿、闪锌矿组成，其次为黄铁矿、黄铜矿、黄锡矿等，脉石矿物则由石英、方解石和少量萤石、白云石等组成。锡石成分较为纯净，SnO2含量为98.97 ~ 99.69%，平均99.19%，FeO含量相对较高，平均达0.29%；磁黄铁矿以高温六方磁黄铁矿为主，少量低温的单斜磁黄铁矿也存在于亢马矿床中；除了闪锌矿以外，毒砂、磁黄铁矿、黄铁矿中Au含量均较高，分别为300 ~1100ppm，300 ~ 900ppm，300 ~ 900ppm。（2）流体包裹体分析表明，灰乐矿床主成矿期锡石—硫化物阶段（石英—锡石—毒砂—磁黄铁矿—闪锌矿矿物组合）锡石中主要发育含子晶流体包裹体，石英中主要发育富CO2气相包裹体，两者的均一温度和盐度分别为375 ~ 498°C、28.6 ~ 43.9 wt% NaCl eqv.和353 ~ 437°C、0.2 ~ 7.8 wt% NaCl eqv.；而同一石英中次生气—液两相盐水流体包裹体的均一温度和盐度为114 ~ 215°C、3.6 ~ 9.2 wt% NaCl eqv.。亢马矿床主成矿期锡石—硫化物阶段（石英—锡石—毒砂—黄铁矿—磁黄铁矿—闪锌矿—黄铜矿矿物组合）石英中同时发育含子晶流体包裹体和富CO2气相流体包裹体，其均一温度和盐度分别为314 ~ 420°C、35.5 ~ 48.1 wt% NaCl eqv.和304 ~ 392°C、0 ~ 8.1 wt% NaCl eqv.，成矿晚期碳酸盐岩—硫盐阶段方解石中仅发育气—液两相盐水流体包裹体，具有较低的均一温度（108 ~ 197°C）和盐度（6.3 ~ 11.6 wt% NaCl eqv.）。两矿床主成矿阶段含子晶流体包裹体和富CO2气相包裹体组合共存、具相近的均一温度以及不同的盐度，认为成矿流体经历了流体不混溶（沸腾）过程并控制了成矿元素的沉淀。而成矿晚期碳酸盐岩阶段的成矿作用可能主要来自于富含CO2气相流体的冷凝过程。（3）硫同位素研究显示，灰乐、亢马矿床成矿热液总硫同位素分别在-13.51‰ ~ -13.04‰和-10.81‰ ~ -9.47‰之间，主要为地层来源硫；亢马矿床黄铁矿的原位微区铅同位素组成（206Pb/204Pb=18.230 ~ 18.545，平均18.441； 207Pb/204Pb=15.499 ~ 17.777，平均15.685；208Pb/204Pb=38.304 ~ 39.030，平均38.810）和笼箱盖花岗岩中长石（206Pb/204Pb=18.416 ~ 18.682，平均18.525；207Pb/204Pb=15.591 ~ 17.803，平均15.711；208Pb/204Pb=38.724 ~ 39.263，平均39.008）相似，认为两者具有相同的铅源，主要来源上地壳，可能有部分幔源铅的参与；碳同位素数据分析表明，灰乐矿床的δ13CPDB范围在-9.4‰ ~ -8.1‰之间，亢马矿床δ13CPDB范围为-9.2‰ ~ -7.1‰，两矿床的δ13CPDB值均跟岩浆的δ13CPDB值（-7.0‰ ~ -5.0‰）相近，但稍稍偏负，推测其碳除了来自岩浆热液以外，还有赋矿围岩有机质热分解的部分碳；通过计算获得灰乐、亢马矿床流体中水的δ18OSMOW分别为6.94‰ ~ 13.65‰和8.50‰ ~ 13.53‰，与笼箱盖岩体岩浆水的δ18OSMOW（8.7‰ ~ 12.2‰）相近，认为灰乐、亢马矿床成矿流体中的水主要来自于高δ18OSMOW值的岩浆水。（4）提出了矿床的成矿模式：燕山晚期，从矿田中部笼箱盖岩体或者灰乐、亢马矿床深部隐伏花岗岩分异出的富含Sn、Zn、Sb、W、Bi等成矿物质的岩浆流体沿丹池大断裂的次级构造—车河断裂向上迁移。迁移过程中，高温岩浆流体可能萃取地层中的部分成矿物质（如S等）。当这种富含成矿物质的流体运移到NW向派生的断裂构造裂隙时，由于压力的骤降，成矿流体发生不混溶（沸腾）作用，导致原始成矿流体相分离形成高盐度的卤水相和低密度的CO2气相两个端元。以Cl的络合物搬运的Sn、Zn、Fe 、Sb、Pb等成矿元素主要富集在高盐度的卤水之中，随后CO2还原SnCl2的过程导致了锡石的沉淀富集（如4SnCl2 + CO2 + 6H2O = 4SnO2 + CH4 + 8HCl），Zn、Fe等成矿元素与流体中H2S（可能为地层同生黄铁矿高温热分解成因）的反应则导致了硫化物的沉淀。; The Dachang district, Guangxi, China, located in the middle of the Danchi (Nandan-Hechi) fold belt, is one of the largest tin-polymetallic ore field in the world. The district contains the Lamo and Shamuchong Cu-Zn skarn deposits in the central, Tongkeng-Changpo, Bali, and Longtoushan tin-base metal carbonate replacement deposits in the west, and Dafulou, Huile, and Kangma tin-base metal veins deposits in the east.This thesis focus on mineralogy and geochemistry of ores, fluid inclusion, isotopic studies from Huile and Kangma tin-polymetallic deposits, using petrography, electron probe, scanning electron microscope cathodoluminescence (SEM-CL), microthermometry, and laser Raman spectroscopy analyses to constrain chemistry and source of ore fluid components that formed these deposits, and to understand the formation of tin-polymetallic deposits in this region. The results and conclusions are as follows:(1) The deposits are located at the eastern part of the Dachang ore field and the orebodies mainly occur as veins hosted in Devonian black shale. The mineralization includes: the proximal skarn stage of garnet-pyroxene, the main ore stage of cassiterite-sulfides, and the late ore stage of carbonate-sulfosalt. The ore minerals in the Huile and Kangma deposits mainly contain cassiterite, arsenopyrite, pyrrhotite, sphalerite, with minor pyrite, chalcopyrite and stannite. The gangue minerals are quartz, calcite with a small amount of fluorite and dolomite. The EPMA results show that cassiterite (SnO2=98.97 ~ 99.69%) contains an average of 0.29% FeO. Pyrrhotite is dominated by hexagonal pyrrhotite in the deposits that formed high temperature. EMPA results also show that arsenopyrite, pyrrhotite, and pyrite have high contens of Au, ranging from 300 ~1100ppm, 300 ~ 900ppm, 300 ~ 900ppm, respectively.(2) Fluid inclusions studies show that the quartz and cassiterite associated with the main ore stage of cassiterite-sulfides veins only contains two-phase, CO2 vapor-rich and daughter-bearing fluid inclusion assemblages. The vapor-rich fluid inclusion assemblage yield homogenization temperatures of 304 ~ 437°C and salinities of 0 ~ 8.1 wt% NaCl eqv.. The daughter-bearing inclusion assemblages have similar range of homogenization temperatures of 314~498°C, but high salinities of 28.6 ~ 43.9 wt% NaCl eqv., whereas the fluid inclusions in quartz and calcite associated with the late ore stage of carbonate-sulfosalt veins are only two-phase, liquid-rich aqueous fluid inclusions, with low homogenization temperatures of 108 ~ 215°C and medium salinities of 3.6 ~ 11.6 wt% NaCl eqv.. The coexistence, similar homogenization temperature, contrasting salinity of the vapor-rich and daughter-bearing fluid inclusion assemblages in the main ore stage of cassiterite-sulfides indicate that boiling and redox of ore fluids are key process for deposition of cassiterite and sulfides. The late ore fluids may be sourced from cooling and contraction of vapor phase of the main stage to liquid that deposited carbonates and sulfosalts in the late ore stage.(3) Sulfur isotopes of sulfides from the deposits range from -13.51 ~ -9.47‰, suggesting derivation from a sedimentary source. Carbon and oxygen isotopes of calcite and water range from -9.4‰ ~-7.1%, 6.9‰ ~ 13.7‰, respectively, indicating that ore fluids were mainly derived from magmatic fluids in origin. In situ Pb isotopic compositons of sulfides (206Pb/204Pb=18.230 ~ 18.545,207Pb/204Pb=15.499 ~ 17.777, 208Pb/204Pb=38.304 ~ 39.030) measured by fsLA-MC-ICP-MS are similar to plagioclase in the Longxianggai granite (206Pb/204Pb=18.416 ~ 18.682, 207Pb/204Pb=15.591 ~ 17.803, 208Pb/204Pb=38.724 ~ 39.263), suggesting that the metals were mainly sourced from the granite. (4) A model is proposed in which the ore fluids enriched Sn, Zn, Sb, W and Bi directly exsolved from a crystallizing granitic magma and migrated upwards along the faults during the Late Yanshanian, where the opening of the faults caused significant decrease of pressure that promoted the ore fluids to be separated into high salinity of brine and low-salinity CO2-bearing vapor. Elements that formed as chloride complexes, such as Sn, Zn, Fe, and Pb, were distributed preferentially into brine. The redox of the brine by resolved CO2 is the key process for deposition of cassiterite, whereas Zn, Pb, and Fe in the ore fluids reacted with reduced sulfur (e.g. H2S) to deposit base-metal sulfides. |
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