多硫同位素示踪金川铜镍硫化物矿床硫的源区

The Jinchuan Ni-Cu sulfide deposit is the largest magmatic sulfide deposit in China. According to the deep exploration for the Jinchuan deposit, the pyrite was found in the country rock (Paleoproterozoic Baijiazuizi formation, from 1500 to 1900m), and the δ34S values of pyrite are from -4.8 to 13.1 ‰. In addition, small amount of ∆33S values (0–0.22‰) for the sulfide ores may indicate a contribution of S from Archean crustal rocks. In order to accurately determine the potential S sources of Jinchuan Ni-Cu sulfide deposit, the multiple S isotope measurement will be carried on the disseminated and massive sulfide ores from the segment I and II of the Jinchuan deposit and the pyrite from the country rock. The combination of ∆33S and δ34S values will indicate the potential S sources of the Jinchuan deposit, and provide an effective means of evaluating the proportion of S deriving from Archean or Paleoproterozoic country rocks in the process of magmatic Ni-Cu sulfide mineralization. Based on the spatial variability of ∆33S and δ34S values within different types of sulfide ores in the Segment I and II, the similarity and difference of S source between two types of sulfide ores will be discussed, which will reveal the ore-forming process.

金川矿床是中国最大的岩浆铜镍硫化物矿床。近年科学深钻研究发现，在1500–1900m深度范围内，矿区围岩古元古代地层白家咀子组混合花岗岩中黄铁矿δ34S值为-4.8–13.1‰。经申请者初步研究，金川硫化物矿石∆33S值为0–0.22‰，表明硫化物熔离过程中可能有太古代硫加入。本项目针对金川矿床成矿过程中硫的来源进行研究，通过I、II矿区浸染状和块状硫化物矿石及白家咀子组混合花岗岩中黄铁矿多硫同位素分析，依据∆33S和δ34S示踪金川矿床中硫的来源，模拟计算成矿过程中太古代地层硫和古元古代地层硫加入的相对含量；通过I、II矿区浸染状和块状硫化物矿石∆33S、δ34S研究，探讨两类硫化物矿石中硫源的异同，揭示成矿过程。

金川岩浆铜镍矿床是中国最大的铜镍硫化物矿床。关于该矿床中硫的来源一直存在争议。传统硫同位素（δ34S值）指示金川矿床中硫应源自于地幔岩浆，而研究表明单纯的幔源硫难以形成如此巨大的硫化物矿床。本项目将多硫同位素（δ34S、Δ33S）和Fe同位素（δ56Fe）联合使用示踪金川矿床成矿过程硫可能的源区。金川铜镍硫化物矿床I、II矿区中硫化物矿物Δ33S值为-0.07 ~ 0.22，远超出了幔源岩浆Δ33S值的参考值，表明金川岩体母岩浆同化混溶了太古代沉积岩中硫化物。I、II矿区中磁黄铁矿δ56Fe值为-1.07 ~ -0.33 ‰，计算表明与硫化物熔体处于平衡的母岩浆δ56Fe值为-2.18‰，远低于正常的幔源玄武质岩浆范围。此外，具有低的δ56Fe值硫化物样品通常具有正异常的Δ33S值，表明金川母岩浆中低的δ56Fe值是由于同化混染太古代沉积岩所致。金川矿床围岩中黄铁矿Δ33S值为-0.04 ~ -0.08 ‰，范围远小于金川矿石中硫化物的Δ33S值，表明金川岩体母岩浆发生同化混染以及硫饱和应发生在深部岩浆房中，与矿床当前围岩无关。