九瑞矿集区城门山斑岩型钼铜矿床流体包裹体研究

Fluid inclusion Study of the Chengmenshan Porphyry Mo-Cu Deposit in the Jiujiang-Ruichang District

城门山钼铜矿床位于江西省九江市,是一座铜、硫、钼、铁、锌,金、银等多矿种大型综合性矿床,由矽卡岩型矿床、块状硫化物型矿床和斑岩型矿床组成。本文对其斑岩型钼铜矿床中的成矿岩体(石英斑岩)斑晶石英和三个阶段热液石英中的流体包裹体系统开展了包裹体岩相学、激光拉曼探针(LRM)、显微测温研究。根据产状和岩相学特征识别出的三个阶段热液石英从早到晚分别为:与辉钼矿伴生的不规则细脉状石英(Ⅰ阶段)、与黄铁矿和黄铜矿伴生的网状脉石英(Ⅱ阶段)以及与黄铁矿和零星黄铜矿伴生的平直粗脉型石英(Ⅲ阶段)。岩相学观测和激光拉曼探针分析显示,矿区石英中流体包裹体可划分为富液相(Ⅰ型)、含子晶(Ⅱ型)、富气相(Ⅲ型)、纯气相(Ⅳ型)和富二氧化碳(Ⅴ型)五种类型,其中Ⅱ型包裹体中子矿物复杂,主要有石盐、钾盐、方解石、硬石膏、黄铁矿、黄铜矿、斑铜矿等子矿物,反映出成矿流体组成复杂,岩浆分异出的热液流体中可能含大量成矿元素,原始斑岩岩浆可能是重要成矿物质来源,与前人同位素资料相吻合。三阶段脉石英中流体包裹体显微测温结果为:Ⅰ阶段均一温度范围310～486℃,盐度范围[w(NaCleq.)]6.2%～41.7%;Ⅱ阶段均一温度范围251～489℃,盐度范围[w(NaCleq.)]1.2%～46.9%;Ⅲ阶段均一温度范围209～386℃,盐度范围[w(NaCleq.)]10.4%～45.7%。斑晶石英中流体包裹体密集,关系复杂,总体均一温度范围为230～590℃,盐度范围为[w(NaCleq.)]1.9%～47.4%,可能反映了多阶段流体叠加特征。流体包裹体岩相学特征和测温结果揭示,斑岩钼铜矿成矿流体演化过程中发生过多次沸腾,沸腾可能是导致矿质沉淀的主要因素。根据Ⅰ阶段沸腾包裹体群估算的成矿深度约1.3km,显示该区140Ma成矿以来剥蚀作用不强,指示该区存在较好的矿床保存条件。

The Chengmenshan Cu-Mo deposit, located near the Jiujiang city, Jiangxi Province, is a large comprehensive deposit, which is enriched in ore-forming elements of Cu, S, Mo, Fe, Zn, Au and Ag. The deposit is composed of skarn-, massive sulfide- and porphyry-type ore bodies. Petrographic, microthermometric and Laser Raman Probe studies have been carried out on fluid inclusions （FI） in various kinds of quartz from the Chengmenshan deposit. Five types of fluid inclusions including liquid-rich fluid inclusions （FI） （Ⅰ）, daughter mineral-bearing FI （Ⅱ）, gas-rich FI （Ⅲ）, pure gas FI （Ⅳ） and carbon dioxide-rich （Ⅴ）, respectively, have been observed. The daughter minerals mainly include halite,sylvite, calcite,anhydrite, pyrite, chalcopyrite and bornite, suggesting that the original magma was important material source of the deposit. This is consistent with the stable isotopic results of previous researchers. Three mineralization stages were recognized in the Chengmenshan porphyry deposit. Quartz-molybdenite mineralization stage （stage I） is associated with K-feldspar alteration. The fluid inclusions of stage I are characterized by high temperatures （310 - 486℃） and low to high salinity （[-w （NaCleq.） ] 6. 2 % - 41. 7%）. Stockwork quartz-pyrite mineralization （stage Ⅱ） may be related to hydraulic brecciation. The fluid inclusions of stage Ⅱ exhibit medium to high temperatures （251-489℃） and low to high salinity （[w （NaCleq.）]1. 2% -46. 9%）. The straight filling vein-style quartz-pyrite mineralization （stage Ⅲ） developed in phyllic zone may occur in an extensional environment. The fluid inclusions of stage Ⅲ have medium temperatures （209-386℃） and medium to high salinity （[w（NaCleq.）]10.4-45.7%）. From early to late stages, the temperature of mineralization gradually decreased, showing that it is a continuous evolutionary sequence. Boiling had already occurred several times during ore-forming evolution and may be the dominated factor for metal precipitation.