攀西地区与二叠纪镁铁-超镁铁岩有关的钒钛磁铁矿床和铜镍硫化物矿床伴生有可观的钴资源。为实现对铜镍硫化物矿床中钴的资源评价与综合利用,本文选取攀西地区的羊合五铜镍矿床为例,阐述钴在全岩和矿物中的分布特征,查明其赋存状态,在此基础上讨论了岩浆作用过程中钴的富集机制。在全岩层面,辉石岩带具有最高的钴含量(177×10^-6),其次为斜长辉石岩带(133×10^-6)、橄榄辉石岩带(103×10^-6)、辉长岩带(63.4×10^-6)。在矿物层面,各类矿物平均钴含量从高到低依次为镍黄铁矿(3.56%)、橄榄石(175×10^-6)、磁黄铁矿(96.6×10^-6)、角闪石(54.8×10^-6)、钛铁矿(34.2×10^-6)、辉石(31.0×10^-6)、黄铜矿(1.15×10^-6)、斜长石(0.05×10^-6)。矿物微区原位分析结果结合镜下观察发现镍黄铁矿为矿床中最重要的载钴矿物。镍黄铁矿根据其形态、分布位置可分为三类:(1)分布于硫化物颗粒边缘,呈棒状或楔状充填于硫化物颗粒中的填隙状镍黄铁矿(PnI);(2)分布于硫化物颗粒内部,呈规则或较规则状的颗粒状镍黄铁矿(PnII);(3)分布于硫化物颗粒内部和边缘,呈出溶针状、毛刷状或火焰状的出溶状镍黄铁矿(PnIII)。这三类镍黄铁矿的钴含量依次降低,分别为5.44%、3.54%、1.70%,反映了随着成矿过程推进,岩浆温度降低,结晶出的镍黄铁矿形态也发生变化,钴含量越来越低。矿物中的Co-Ni(Fe)负相关表明钴主要以类质同象形式替换Ni²⁺、Fe²⁺等二价阳离子。钴富集机制主要包括硫化物熔离、硫化物熔体结晶和硅酸盐熔体的分异结晶作用。硫化物熔离过程的钴富集系数为28~35,根据母岩浆与镍黄铁矿钴含量计算得硫化物熔体结晶过程中钴富集系数为10~12。硫化物熔离和硫化物熔体结晶对钴的富集效率最高,是最重要的富集机制。本文依据上述地质、地球化学和矿物学研究提出了攀西地区铜镍硫化物矿床中钴的富集机制模型。

The study of the occurrence state and enrichment mechanism of cobalt in Cu-Ni-Fe-Ti paragenetic deposits is critical for precise ore blending and comprehensive utilization of associated cobalt resources. This work investigates the Xiangshanxi Cu-Ni-Fe-Ti deposit (eastern Tianshan) using petrogeochemistry, petrographic mineralogy and element-partitioning calculations to decipher cobalt’s temporal–spatial distribution and partitioning behavior at the rock–mineral scale. The Xiangshanxi intrusion comprises peridotite, Ti-Fe gabbro and gabbro rock types. Cobalt peaks in peridotite rock type (113–146 ppm) followed by Ti-Fe gabbro rock type (67–115 ppm). Mineralogical analyses reveal the highest Co contents in independent minerals (cobaltite, siegenite, gersdorffite) and then isomorphous cobalt-rich pentlandite. Pyrite and pyrrhotite contain <1 wt.% Co, whereas silicate and Fe-Ti oxide minerals have low Co content. Cobalt occurs as independent minerals, isomorphous substitution (replacing Fe, Ni in sulfide lattices) and micro-inclusions. Pentlandite preferentially crystallizes from monosulfide solid solution (MSS). Cobaltite–siegenite–gersdorffite formed in late-magmatic–hydrothermal overprinting. Sulfide melt liquation–exsolution drives initial Co pre-enrichment, and later hydrothermal overprinting triggers Co mineral precipitation. Combined processes control Co enrichment; an evolutionary model for Co enrichment is proposed for the Xiangshanxi deposit.