湖南香花岭锡多金属矿床C、O、Sr同位素地球化学

Carbon, Oxygen and Strontium Isotope Geochemistry of Calcites from the Xianghualing Tin-Polymetallic Deposit, Hunan Province

对湖南香花岭锡多金属矿床成矿早、晚两期方解石进行了系统的C、O、Sr同位素研究。结果表明,成矿早期方解石具有相对较低的δ13CPDB(-5.4‰^-1.4‰)、δ18OSMOW(+6.1‰^+13.9‰)和较高的87Sr/86Sr值(0.7101~0.7230);而成矿晚期方解石则具有相对较高的δ13CPDB(+0.2‰^+0.6‰)、δ18OSMOW(+19.4‰^+21.5‰)和较低的87Sr/86Sr值(0.7101)。分析认为,成矿早期方解石为岩浆热液与海相碳酸盐岩相互作用的产物,成矿流体中的碳源于岩浆碳和海相碳酸盐岩;模拟计算结果显示,成矿早期方解石为成矿溶液发生0.05~0.1摩尔分数的CO2去气作用的产物。而成矿晚期方解石主要为矿区碳酸盐岩低温淋滤的产物,流体中的碳主要源于矿区碳酸盐岩围岩。成矿流体中的Sr源于矿区花岗岩和碳酸盐岩,从成矿早期到晚期,岩浆来源的Sr逐渐减少,而碳酸盐岩围岩提供的Sr比例不断增大。

Carbon, oxygen and strontiumisotope studies have been performed on hydrothermal calcites from the Xianghualing tin-polymetallic deposit to investigate the sources of ore-forming fluids and the mechanism of mineralization. The results show that there are light carbon （δ^13 CPDB = - 5.4‰ ～ - 1.4‰） and oxygen isotope compositions （δ^18 OSMOW = ＋6.1‰ ～＋ 13.9‰） and higher strontium isotope compositions （0. 7101 ～ 0. 7230） for the calcites formed in the early stage of mineralization, while for the calcites formed in late stage of mineralization, the δ^13CPDB, δ^18SMOW and ^87Sr/^86 Sr values are ＋0.2‰ ～ ＋ 0.6‰, ＋ 19.4‰～ ＋21.5‰ and 0. 7101 respectively. It is suggested that the calcites formed in the early stage of mineralization resulted from the water/rock interaction of magmatic hydrothermal fluid and marine carbonate, and the carbon in ore-forming fluids are mainly derived from magmatic fluids and marine carbonates. It is revealed from simulation calculation that the calcites formed in the early stage of mineralization resulted from CO2 degassing where 5 to 10 percent of CO2 was lost. In contrast, the calcites precipitated in late stage of mineralization may be formed by leaching marine carbonate host rock in this area at lower temperatures, and the carbon in ore-forming fluids are mainly derived from the marine carbonate rocks. Strontium in the ore-forming fluid is mainly of granite and marine carbonate rock origin and there is a decrease in the proportion of strontium originated from granite and an increase for the strontium of marine carbonate origin during mineralization.