江西永平铜多金属矿床流体包裹体及硫同位素研究

摘要

永平铜多金属矿床位于华南地区十杭裂谷带南侧,是一个与晚侏罗世二长花岗斑岩侵入体有关的斑岩-矽卡岩矿床。矿区存在斑岩型钼矿和矽卡岩型铜矿两种矿化类型。其中,斑岩型钼矿含矿石英脉中主要发育I型气液两相包裹体、II型CO2三相包裹体和III型含子矿物多相包裹体,早期石英-硫化物阶段流体包裹体的形成温度介于202~359℃之间,盐度介于4.62~36.68 wt%NaCl之间；晚期石英-碳酸盐-硫化物阶段均一温度介于211~318℃之间,盐度范围为2.07~11.47 wt%NaCl。矽卡岩铜矿主要发育I型气液两相包裹体,早期矽卡岩阶段均一温度达到406~486℃,盐度为9.21~9.89 wt%NaCl；石英-硫化物阶段均一温度介于137~335℃之间,盐度值范围为4.98~13.20 wt%NaCl；晚期碳酸盐阶段包裹体均一温度只有89~151℃,盐度范围介于2.07~19.13 wt%NaCl之间。激光拉曼结果显示两者流体包裹体中具有相似的气相成分,都以CO2和H2O为主,成矿流体总体上属于H2O-CO2-NaCl体系。含Mo成矿流体中存在CH4,具有低氧逸度特征,在流体演化早期形成Mo矿化中心,石英-硫化物阶段含Mo流体相对于含Cu流体具有更高的温度和压力。矿石中金属硫化物的δ34S值变化于–0.2‰~+1.9‰之间,这表明成矿物质硫源主要来自深源岩浆。结合地质特征,认为该矿床是与晚侏罗世花岗质岩浆密切相关的斑岩钼-矽卡岩铜矿床,铜和钼矿化存在分带现象,岩浆系统的中心部位具有斑岩型钼矿化,外围及和碳酸盐岩的接触带形成斑岩-矽卡岩型铜钨铅锌矿化。%The Yongping copper-polymetallic deposit, located in the southern segment of Shi-Hang rift zone, is a porphyry-skarn type deposit related to the late Jurassic monzogranite intrusions. The mineralization at Yongping can be divided into two types: porphyry type and skarn type. Petrographic study of fluid inclusions suggests that three dominant types of fluid inclusions related to metallogensis are present in the porphyry Mo deposit: I-type gas-liquid inclusion, II-type CO2-bearing three-phase inclusion and III-type daughter-minerals bearing inclusion. Homogenization temperatures and salinities of fluid inclusions at the quartz-sulfide stage range from 202℃ to 359℃ and 4.62 wt%NaCl to 36.68 wt%NaCl. The quartz-carbonate-sulfide stage yielded homogenization temperatures of 211~318℃ and salinities of 2.07~11.47 wt%NaCl. Fluid inclusions in minerals of the skarn Cu deposit are mainly I-type gas-liquid inclusions. The homogenization temperatures and salinity of fluid inclusions at the skarn stage vary in the range of 406~486℃ and 9.21~9.89 wt%NaCl. The fluid inclusions of middle-stage have the homogenization temperatures of 137~335℃ and the salinity of 4.98~13.20 wt%NaCl. The late stage fluid has the homogenization temperatures of 89~151℃ and the salinity of 2.07~19.13 wt%NaCl. Raman microspectroscopic studies of the fluid inclusions of the skarn deposit and the porphyry deposit show that the main components are CO2 and H2O, and the ore-forming fluid belongs to the H2O-CO2-NaCl system. CH4 in the Mo fluid indicates condition of low oxygen fugacity. Therefore, Mo mineralization center is formed in the early stage of fluid evolution. Mo fluid has a higher temperature and pressure with respect to the Cu fluid at the quartz-sulfide stage. Most sulfur isotope values of the sulfides give a narrowδ34S range from –0.2‰ to +1.9‰, indicating a predominant magmatic sulfur origin. The authors hold that the Yongping copper-polymetallic deposit is a porphyry-skarn type deposit resulting from the emplacement of the Late Jurassic monzogranite intrusions. From the intrusion through the contact zone to the host rocks, the mineralization is demonstrated by zoning of Mo-Cu-W-Pb-Zn.