云南金顶超大型铅锌矿床碳、氧、锶、铅同位素地球化学

Carbon, oxygen, strontium and lead isotopic geochemistry in the Jinding super-large Zn-Pb deposit, Yunnan Province

云南金顶铅锌矿是目前中国最大的铅锌矿,也是铅锌矿金属储量超过千万吨的世界级超大型矿床之一。对该矿床主矿化期和矿化后期方解石进行了系统的碳、氧、锶同位素分析,结果表明,主矿化期脉状方解石碳同位素变化范围大(δ13C-23.0‰^-2.6‰),显示有机沉积物与海相碳酸盐岩混合碳的特征,氧同位素相对集中(δ18O 22.1‰~23.5‰),类似于沉积岩,Sr含量较高(Sr 163~1920μg/g),富放射成因锶(87Sr/86Sr0.709860~0.710362);而矿化后期结核状方解石碳同位素分布集中(δ13C-7.0‰^-6.2‰),氧同位素(δ18O20.2‰~22.4‰)类似于沉积岩,在150~200℃时,据公式1000 lnα方解石-水=4.01×106/T2-4.66×103/T+1.71计算,与矿化后期结核状方解石平衡的流体的δ18O流体介于7.1‰~12.7‰之间,此外,结核状方解石Sr含量较高(Sr 240~817μg/g),富放射成因Sr(87Sr/86Sr 0.710235~0.710347)。金属硫化物铅同位素(206Pb/204Pb18.373~18.452,207Pb/204Pb 15.605~15.668,208Pb/204Pb 38.524~38.726)在铅演化图解上位于造山带演化线与上地壳演化线之间,变化范围类似于兰坪盆地上地壳沉积岩系和喜马拉雅期岩浆岩。综合分析认为,金顶铅锌矿至少存在两期热液矿化事件,主矿化期成矿流体主要来源于富含有机质的上三叠统三合洞组灰岩中的地层水,可能有深源组分的加入;矿化后期成矿流体系大气降水。成矿流体在盆地中迁移时与围岩(含膏岩)发生了强烈的水岩反应。成矿金属可能来源于上三叠统三合洞组灰岩和喜马拉雅期岩浆岩。

The Jinding Zn-Pb deposit in Yunnan Province, is the largest Zn-Pb deposit in China, and one of the world-class super-large deposits with Zn＋Pb reserves more than 10 Mt. A systematic study of carbon, oxygen and strontium isotopes has been carried out on main mineralization vein calcites and post-mineralization nodule calcites. The main mineralization vein calcites show a large variation of δ^l3C （-23.0‰--2.6‰）, indicating mixed carbon source of sedimentary organics and marine carbonates, with high δ^l8O （22.1‰ - 23.5‰） similar to the sediments, and high Sr contents （163 - 1920 μg/g）, as well as ^87Sr/^86Sr （0.709860 - 0.710362）. The post-mineralization nodule calcites have homogeneous δ^l3C （-7.0‰ - -6.2‰） and δ^l8O （20.2‰ - 22.4‰）, high contents of Sr （240 - 817 μg/g） and ^87Sr/^86Sr （0.710235 - 0.710347）. Besides, the calculated δ^l8O of the ore-forming fluid equilibrated with the post-mineralization nodule calcites, range from 7.1‰ to 12.7‰ at 150 -200℃ by the equation 1000 In acalcit ter = 4.01×106/T^2 - 4.66×10^3/T＋1.71 （Zheng, 1991）. Pb isotopes in sulfides （^206pb/^204pb 18.373 - 18.452, ^207pb/^204pb 15.605 - 15.668, ^208pb/^204pb 38.524 - 38.726） plot between the line of orogenic Pb and the line of upper crustal Pb in Pb evolution diagram （Zartman and Doe, 1981）, consistent with the Himalayan magmatisms and partially overlapping with the upper crustal sedimentary rocks in the Lanping basin. These indicate that there were at least two episodes of hydrothermal mineralization in Jinding. The ore-forming fluid at the main mineralization stage might be the formation water originating from organic-rich limestones of the Upper Triassic Sanhedong Formation, apart from some involvement of deep-sourced components, whereas the ore-forming fluid at the post-mineralization stage is dominated by meteoric water. During migrating in the basin, the ore-forming fluids reacted with wall rocks and acquired high contents of radiogenic S7Sr. Metals were likely provided by the Upper Triassic Sanhedong Formation limestones and Himalayan igneous rocks.