安徽铜陵小铜官山铜矿床稀土元素和稳定同位素地球化学研究

REE and stable isotope geochemistry of the Xiaotongguanshan copper deposit,Tongling,Anhui

安徽铜陵铜官山铜矿田是中国长江中、下游铁、铜、硫、金成矿带中著名的夕卡岩型矿床。小铜官山铜矿床位于安徽铜陵铜官山矿田,侵入岩体为铜官山石英二长闪长岩。成矿过程包括夕卡岩阶段、石英-硫化物阶段和石英-碳酸盐阶段3个主要成矿阶段。笔者通过对小铜官山铜矿床的氢、氧、碳、硫、硅同位素组成和稀土元素地球化学特征研究,探讨成矿溶液中水、硅和硫的来源以及成矿溶液的演化问题。研究表明,成矿热液早期以岩浆热液为主,随着成矿过程的进行,加入的大气降水比重越来越大,到晚期可能主要以大气降水为主。硫的来源主要有两个方面,即地层和岩浆热液,但以后者为主。硅具深部岩浆或岩浆热液水来源的特点。稀土元素球粒陨石标准化组成模式为右倾型,夕卡岩、矿石的稀土配分曲线类似于铜官山岩体石英二长闪长岩,故认为形成本区的夕卡岩型矿床的热液流体主要来源于闪长质熔体。

The Tongguanshan copper field in Tongling, Anhui, is one of the typical skam orefields in the middie-lower Yangtze Valley iron, copper, sulfur and gold metallogenic belt of China. The Xiaotongguanshan copper deposit located in the Tongguanshan copper field is related to the Tongguanshan quartz monzodiorite. The formation of the copper deposit progresses through the skarn stage, quartz-sulfide stage and quartz-carbonate stage. Based on the geological setting, mineralogy and tectonics of the deposit, combined with the hydrogen, oxygen, carbon, sulfur and silicon isotopic compositions and REE geochemistry of the ore-forming fluids, this paper deals mainly with the sources of water, silicon and sulfur in the ore-forming fluids and their evolution. The results show that the ore-forming fluids were dominated by magrnatic water at the early stage, whereas with an increase in meteoric water entering the mineralizing system, the meteoric water might predominate at the late stage. Sulfur has two sources, i. e. strata and magrnatic hydrothermal fluids, with the latter predominating. Silicon shows the features of deep-seated magma or magmatic hydrothermal fluids. Chondrite-normalized REE patterns are right-inclined, and the REE distribution patterns for skarn and ores are similar to those of the Tongguanshan quartz monzodiorite, which indicates that the hydrothermal fluids of the skam deposit in the study area were mainly derived from dioritic melt.