湘南铜山岭矽卡岩铜铅锌矿床形成过程

The genesis and ore-forming process of skarn deposits have attracted a great interest of geologists around the world over the centuries. Different from most Cu-Pb-Zn skarn deposits, the Tongshanling Cu-Pb-Zn skarn deposit in southern Hunan Province shows a distinctive outward zonation of proximal endoskarn, proximal exoskarn, sulfide-quartz vein, and distal skarn from the contact zone between intrusion and wall rocks. This proposal aims to investigate the ore-forming process of the Tongshanling deposit based on comprehensive studies of wall-rock metamorphism and deformation and resulting permeability variation, structural control, and fluid migration and evolution. RSCM (Raman spectra of carbonaceous material) geothermometer and EBSD (electron backscatter diffraction) mapping will be used to determine the metamorphic temperatures of wall rocks and the lattice-preferred orientation of calcite, respectively, and then delineate the border of wall-rock metamorphism and deformation induced by magma emplacement. Permeability experiments of different wall rocks will be conducted by an internal heated Paterson gas apparatus to study the permeability variation during wall-rock metamorphism and deformation. Distinct structural controls on different types of ore bodies will be revealed and distinguished through structural analysis. Combined with the sequence of different mineralization types, the process of ore-forming fluid migration will be constructed. The processes of fluid evolution and water-rock interaction will be revealed by the variation of trace elements in different generations of garnet and quartz. Finally, the formation mechanism of the unusual zonation in the Tongshanling deposit will be discussed based on the processes of fluid migration and evolution and water-rock interaction.

矽卡岩矿床成因及其形成过程一直是地质学家高度关注的科学问题。与多数矽卡岩铜铅锌矿床不同，湘南铜山岭矽卡岩铜铅锌矿床呈现出从岩体接触带向外依次为近端内矽卡岩、近端外矽卡岩、硫化物石英脉和远端矽卡岩的独特成矿分带。本项目将通过围岩变质变形及其引起的渗透性变化、构造控矿和流体迁移与演化等研究综合探讨铜山岭矿床的形成过程。利用围岩RSCM（含碳物质拉曼光谱）测温和EBSD（电子背散射衍射）面扫分别揭示围岩变质温度和方解石晶轴定向程度，据此限定岩浆侵位对围岩变质和变形的影响范围。利用Paterson高温高压流变仪研究围岩变质变形过程中渗透性的变化规律。通过构造解析厘清不同类型矿体的构造控制，结合矿体形成顺序揭示成矿流体的迁移过程。通过不同期次石榴子石和石英的微量元素变化揭示成矿流体演化与水岩反应过程。基于流体迁移演化与水岩反应过程探讨铜山岭矿床特殊成矿分带的形成机制。

湘南铜山岭矽卡岩铜铅锌矿床产出于铜山岭花岗闪长斑岩体北东缘隐伏接触带及其外围地层中，表现出独特的成矿分带，从接触带向外依次发育近端内矽卡岩、近端外矽卡岩、硫化物-石英脉和远端矽卡岩矿体。根据切穿关系、交代结构和矿物组合可以把铜山岭铜铅锌矿床划分为四个蚀变和成矿阶段，从早到晚依次为进变质矽卡岩、退变质矽卡岩、石英-硫化物和碳酸盐阶段，其中石英-硫化物阶段为主成矿阶段。近端内矽卡岩型团块状硫化物矿石的闪锌矿成分压力计计算结果为3.1±1.0kbar，与花岗闪长斑岩中角闪石全铝压力计制约的岩浆侵位压力（3.0±0.4kbar）一致，说明铜山岭铜铅锌矿床形成于较大深度。含碳物质拉曼光谱温度计和绿泥石成分温度计研究表明近端内矽卡岩、近端外矽卡岩和远端矽卡岩的形成温度分别为390–620℃、380–610℃和340–500℃，成矿温度分别为270–318℃、209–238℃和200–223℃。区域和矿床构造解析结合渗透性实验研究揭示岩浆侵位引起的围岩变质变形对流体迁移与成矿具有重要影响，围岩变形过程中产生的构造裂隙控制了近端外矽卡岩脉和硫化物-石英脉的产出。铜山岭多金属矿田中铜山岭铜铅锌矿床的石榴子石U-Pb年龄和辉钼矿Re-Os年龄分别为162.0±3.7Ma和161.8±1.7Ma，江永铅锌银矿床的方解石U-Pb年龄为159.8±5.4Ma，玉龙钼矿床的辉钼矿Re-Os年龄为160.0±5.8Ma，与铜山岭岩体的锆石U-Pb年龄（164–160Ma）一致，指示三个矿床在成因上与铜山岭花岗闪长斑岩密切相关。三个矿床的硫化物δ34S值变化于–0.3‰至6.3‰，具有岩浆硫特征，硫化物206Pb/204Pb比值为18.610–18.969，207Pb/204Pb比值为15.712–15.875，208Pb/204Pb比值为38.837–39.535，与岩体Pb同位素组成一致，石英δDH2O值变化于–70‰至–48‰，δ18OH2O值变化于4.4‰至7.3‰，具有岩浆水特征，指示成矿物质和成矿流体都主要来自铜山岭花岗闪长斑岩。