海南高通岭石英脉型钼矿床成矿流体来源与成矿机制研究

Study on Ore-forming Fluid Source and Metallogenic Mechanism of the Gaotongling Quartz Vein Type Mo Deposit,Hainan Province

高通岭矿床是海南岛典型的石英脉型钼矿床。基于流体包裹体以及H、O、S、Pb同位素研究,本文对高通岭石英脉型钼矿床成矿流体性质、成矿物质来源及成矿机制进行了讨论。结果表明,①流体包裹体以富液两相水溶液(A-L型)为主,次为富液两相含CO_(2)水溶液(AC-L型)和富气两相含CO_(2)溶液(AC-V型);A-L及AC-L型包裹体均一成液相,AC-V型包裹体均一成气相。均一成液相和均一成气相的包裹体共生指示流体不混溶或沸腾。拉曼结果显示流体成分以H_(2)O为主,其次是CO_(2),含微量N2、CH4和H_(2)等气体;成矿期流体包裹体均一温度为180~280℃,盐度为4.0%~8.2%NaCleqv;②H-O同位素组成显示成矿流体具有岩浆水与大气降水混合特点;δ34S值域为-0.9‰~5.5‰,均值2.8‰,属于深源硫;③Pb同位素组成及特征参数暗示其具有岩浆作用带来的地幔Pb与上地壳Pb混合成因。据此,高通岭钼矿床成矿流体主体来源于壳幔岩浆源区,上升过程可能萃取了少量壳源岩石的Mo;来自壳幔源区的初始流体与大气降水的混合发生在成矿部位及其附近,其作用主要是导致成矿流体温度、压力、盐度降低,是高通岭钼矿成矿的主要机制。断裂作用及其引起沸腾、排气作用进一步促进了成矿物质的结晶沉淀。

The Gaotongling Mo deposit in Hainan Island is a typical quartz vein type Mo deposit.Based on the study of fluid inclusions and H,O,S and Pb isotopes,this paper examines the properties of the ore-forming fluids,the sources of ore-forming materials and the ore-forming mechanisms of the Gaotongling deposit.(1)The fluid inclusions are dominated by the aqueous liquid-rich(A-L)type,with lesser aqueous-CO_(2) liquid-rich(AC-L)type and the aqueous-CO_(2) vapor-rich AC-V type.A-L and AC-L inclusions are homogenized into liquid phase,and AC-V inclusions are homogenized into gas phase.The co-occurrence of inclusions in homogeneous liquid and gas phases indicates immiscibility or boiling of the fluid.Raman analyses show that H_(2)O is the main component of the fluid,followed by CO_(2),with trace amounts of N2,CH4 and H_(2).The homogenization temperatures of the fluid inclusions range from 180℃to 280℃,and the salinities range from 4.0%to 8.2%.(2)H-O isotopes suggest that the ore-forming fluids are mixtures of magmatic water and meteoric water.Theδ34S values of sulfides range from–0.9‰to 5.5‰,with an average value of 2.8‰,suggestive of deep-sourced sulfur.(3)Pb isotopic compositions and characteristic parameters indicate that Pb is of mixed mantle and upper crust origin during the magmatism.Thus it is believed that the ore-forming fluids of the Gaotongling deposit were mainly derived from the crust-mantle magma source,and that a small amount of Mo may have been extracted from the crust during the magma ascending process.The mixing of the magmatic fluids with meteoric water took place at the sites of mineralization,and the decrease of temperature,pressure and salinity of ore-forming fluid are the main metallogenic mechanism of the Gaotongling molybdenum deposit.Boiling and exhaust caused by fracture promote the crystallization and precipitation of ore-forming materials.