东昆仑夏日哈木矿床镍黄铁矿、磁黄铁矿成因认识及钴赋存特征

继世界第三大金川铜镍矿床之后,东昆仑夏日哈木是中国境内发现的又一超大型岩浆镍钴硫化物矿床,也是造山带背景发现的最大规模的同类矿床。前人在矿物学方面的研究主要集中在硅酸盐矿物上,而对成矿物质本身--硫化物矿物学研究较为薄弱,限制了镍钴矿体深部成矿过程的客观认识和区域找矿新突破。通过系统划分镍黄铁矿的产出状态,结合Ni/Fe原子比及Co元素的分布和对磁黄铁矿种类的划分,初步判断夏日哈木矿床经历了至少两期岩浆成矿作用。其中早一期的岩浆活动熔离出少量的高钴硫化物,硫化物结晶温度较高,而晚一期的岩浆活动熔离出大量的硫化物,且结晶温度较低。综合镍黄铁矿中金属原子与硫原子比值变化特点,发现在硫化物结晶过程中硫逸度是逐渐增高的,可能受到硫化物和硅酸盐矿物的结晶以及外来硫加入等因素的共同影响。在夏日哈木矿床中,Co在金属硫化物中主要赋存在镍黄铁矿内,在磁黄铁矿中主要赋存在陨硫铁和六方磁黄铁矿内;在砷化物中主要赋存在辉砷钴矿内,相比于硫化物,Co更倾向在砷化物中富集,这些特征可以为Co元素的选冶研究与综合利用提供技术支撑。

The Genetic Significance of Pentlandite and Pyrrhotite and the Characteristics of Cobalt Occurrence in Xiarihamu Cobalt-Nickel Deposit of Eastern Kunlun

Jinchuan copper-nickel deposit being the world’s third-largest deposit found in China,Xirihamu in Eastern Kunlun is another super large magmatic nickel-cobalt-sulfide deposit,and it is also the largest deposit in orogenic belts.Previous mineralogical research focused mainly on silicate minerals,studies on ore-forming materials(sulfide)is relatively less.Through systematic division of the output of pentlandite,based on the atomic ratio of Ni/Fe,the distribution of Co elements and the classification of pyrrhotite types,we infer that Xiarihamu deposit has experienced at least two stages of magmatism.At the first magmatic stage,some high-cobalt content sulfide crystallized at higher temperature;at the second magmatic stage,some sulfide with low-cobalt content crystallized at a relatively low temperature.Combined with the ratio change of metal atom to sulfur atom in pentlandite,we found that the sulfur fugacity increases gradually in the process of sulfide crystallization.This may be affected by such factors as the crystallization of sulfide and silicate minerals and the sulfur contamination.In the Xiarihamu deposit,cobalt exists mainly in pentlandite.In pyrrhotite,cobalt mainly exists in meteorite pyrite and hexagonal pyrrhotite.In arsenide,cobalt mainly exists in cobaltite.The arsenide contains more cobalt than the sulfides.These characteristics give scientific support to the extraction and synthetic use of cobalt.