三江多才玛超大型铅锌矿床同位素地球化学及矿源研究

多才玛超大型铅锌矿床是三江北段铅锌铜银多金属成矿带中的典型矿床,其主要硫化物的δ34S值变化范围大,主要集中于-26.72‰~-4.1‰之间,具塔式分布特征;其中,方铅矿的δ34S最高值大于黄铁矿的相应值。这表明成矿过程中硫同位素未达到平衡,硫主要是细菌还原硫酸盐的产物。矿区208Pb/204Pb=38.985~39.253,206Pb/204Pb=18.825~18.918;铅同位素构造环境演化图解和Δβ-Δγ成因分类图解显示铅的来源复杂多样,不仅来自上地壳和造山带,还来自壳幔混合的俯冲带。δ13CV-PDB=1.2‰~6.7‰,而δ18OV-SMOW=16.4‰~23.4‰,碳氧同位素明显来源于海相碳酸盐岩,成矿过程中应伴随有碳酸盐岩的溶解作用。综上,多才玛大型铅锌矿成矿物质来源复杂,碳酸岩围岩和深部物质都有可能提供成矿物质来源,生物作用参与成矿的痕迹明显。

Isotopic Geochemistry and Origin of the Duocaima Lead-Zinc Deposit in the Northtern Sanjiang Area

The Duocaima Pb-Zn deposit is located in the northern Sanjiang polymetallic metallogenic belt. The values of δ³⁴S in main sulfides are significantly variable, mainly ranging in between-26.72 ‰ and-4.1 ‰ with a normal distribution. The maximum δ³⁴S value of galena is larger than the corresponding value of pyrite, indicating that the sulfur isotopes are in disequilibrium during the process of mineralization and that sulfur is originated mainly from bacterial sulfate reduction. The ²⁰⁸Pb/²⁰⁴Pb values vary from 38.985 to 39.253, and ²⁰⁶Pb/²⁰⁴Pb from 18.825 to 18.918 Tectonic evolution and Δβ~Δγ genetic classification diagrams of lead isotope show that the source of lead is complex and diverse. It is not only originated from the upper crust and orogenic belts, but also from the subducted zone with crust and mantle mixed. The values of δ¹³C_V-PDB =1.2‰~6.7‰ and δ¹⁸O_V-SMOW=16.4‰~23.4‰ show that the C and O are derived from marine carbonates, accompanied by carbonate dissolution. The origin of the Duocaima Pb Zn deposit is complex, The hosting carbonates and the mantle may provide metals, while biomineralization may play an important role in the ore forming process.