安徽铜陵马山金硫矿床稀土元素和稳定同位素地球化学研究

REE and Stable Isotope Geochemical Characteristics of the Mashan Au-S Deposit in Tongling, Anhui Province

安徽铜陵铜官山铜矿田是中国长江中、下游铁、铜、硫、金成矿带中著名的矽卡岩型矿床。马山金硫矿床位于安徽铜陵铜官山矿田,侵入岩体为天鹅抱蛋山石英闪长岩。文章通过对马山金硫矿床的氢、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、碳、硅和硫的来源以及成矿溶液的演化问题。研究表明,稀土元素球粒陨石标准化组成模式为右倾型,矿石的稀土配分曲线类似于天鹅抱蛋山石英闪长岩,认为形成该矿床的热液流体主要来源于闪长质熔体。马山金硫矿床矿石中石英的δ18OH2OV-SMOW变化范围为6.9‰~10.7‰,平均为8.7‰,与岩体的δ18OV-SMOW值(9.3‰~11.1‰,平均为10.0‰)比较接近,而矿石中石英的δDV-SMOW变化范围为-69‰^-62‰,表明矿石成矿流体主要来自岩浆。矿石中方解石的碳、氧同位素组成与矿区围岩的碳、氧同位素组成明显不同,其δ13CV-PDB、δ18OV-SMOW值分别为-5.2‰^-3.6‰和12.2‰~12.9‰,与岩浆作用形成的CO2的碳、氧同位素组成一致,表明矿石中方解石的碳、氧来源于岩浆作用。硅和硫具深部岩浆或岩浆热液水来源的特点。

The Tongguanshan copper field in Tongling, Anhui, is one of the typical skarn orefields in the middle-lower Yangtze River iron, copper, sulfur and gold metallogenic belt of China. The Mashan Au-S deposit located in the Tongguanshan field is related to the Tian＇ebaotanshan quartz diorite. A lot of research work has been done in such aspects as mineral deposit, mineralogy, tectonics, isotope geochemistry and fluid inclusions. Based on the work done, this paper mainly studied hydrogen, oxygen, carbon, sulfur, silicon isotopic compositions and REE geochemistry of the Mashan Au-S deposit. The results show that chondrite-normalized REE patterns are right-inclined, and the REE distribution patterns for ores are similar to those of the Tian＇ebaotanshan quartz diorite, which indicates that the hydrothermal fluids of the deposit were mainly derived from dioritic melt. The O isotopic compositions of quartzes in ore range from 6.9‰-10.7‰ with average of 8.7‰, which are approximate to those of the pluton （9.3‰~ 11.1‰, with the average of 10. 0‰）. Together with the D isotopic compositions of quartzes in ore （-69‰--62‰）, it shows that the metallogenic fluids were mainly derived from magmatism. The C and O isotopic compositions of calcites in ore are different from those of country rocks in the orefield. The C and O isotopic compositions range from -5.2‰--3.6‰and 12.2‰~ 12.9‰, respectively, which are similar to the C and O isotopic compositions of magmatigm. Therefore, C and O in ores might have come from magmatism. Silicon and sulfur isotopes are quite similar to those in magma or magmatic hydrothermal solutions.