Mechanisms of Co enrichment in the Zhubu Ni–Co–PGE deposit in the Emeishan LIP, SW China: Constraints from mineral geochemistry and Fe–S isotopes of sulfides

IF 3.2 2区 地球科学 Q1 GEOLOGY
Yawen Bao , Mingjie Zhang , Hongfu Zhang , Yantong Feng , Xiaofei Li , Jie He
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引用次数: 0

Abstract

The Zhubu Ni–Co–PGE sulfide deposit in the Permian Emeishan Large Igneous Province (LIP), SW China is hosted by a mafic–ultramafic intrusion that comprises two morphologically distinct ore-forming spaces: a central, layered sequence that represents a magma chamber surrounded by a marginal sub-vertical conduit zone. The marginal conduit zone contains significant Ni–Co–PGE sulfide mineralization, suggesting that high volumes of sulfide-bearing silicate melt flowed through the magma conduit system. Determining the hosts of Co is key to understanding the Co enrichment process in the Zhubu deposit, as well as in the Emeishan LIP as a whole. We assess this here using the geochemistry and Fe–S isotope compositions of sulfides in the Zhubu deposit. Cobalt is mainly concentrated in pentlandite sulfide in the websterite, with Co contents increasing in the order pyrrhotite < chalcopyrite < pyrite < pentlandite < violarite; the abundance of violarite, however, is notably lower than that of the other sulfides. The Co contents of pentlandite, pyrite, and chalcopyrite are negatively correlated with their Ni and Fe contents, suggesting that Co substitutes isomorphically for Ni and Fe in the sulfide structure. The δ56Fe values of sulfides increase in the order pyrrhotite < chalcopyrite < pentlandite < pyrite resulted from kinetic fractionation of Fe isotopes. The δ56Fe values of pentlandite and chalcopyrite in lherzolite are higher than those in websterite, implying that lherzolite and websterite formed in compositionally distinct magmas, Fe isotope compositions become heavier with crystal fractionation. The δ34S values of sulfides increase in the order pyrrhotite < pentlandite < chalcopyrite < pyrite, similar to the fractionation sequence of sulfide melts, suggesting that externally derived S was added to the magma and contributed to its sulfide saturation. The Co contents of chalcopyrite and pyrite vary positively with δ56Fe values, and negatively with δ34S values, indicating that the addition of externally derived S and resulting sulfide segregation were critical to Co enrichment.

Abstract Image

中国西南部峨眉山陆相沉积带竹埠镍钴铅锌矿床的钴富集机制:矿物地球化学和硫化物Fe-S同位素的制约因素
位于中国西南部二叠纪峨眉山大火成岩省(LIP)的竹埠镍钴卟啉硫化物矿床由一个黑云母-超黑云母侵入体所孕育,该侵入体包括两个形态截然不同的成矿空间:一个是代表岩浆室的中央层序,周围是边缘次垂直导管带。边缘导管区含有大量镍-钴-PGE硫化物矿化物,表明大量含硫化物的硅酸盐熔体流经岩浆导管系统。要了解竹埠矿床以及整个峨眉山LIP的钴富集过程,确定钴的赋存地是关键。在此,我们利用竹步矿床硫化物的地球化学和Fe-S同位素组成来评估这一问题。钴主要集中在网纹石中的辉铜矿硫化物中,钴含量按照黄铁矿、黄铜矿、黄铁矿、辉铜矿、辉铜矿、辉绿岩的顺序递增,但辉绿岩的丰度明显低于其他硫化物。辉铜矿、黄铁矿和黄铜矿的钴含量与镍和铁的含量呈负相关,这表明钴在硫化物结构中以同构方式取代了镍和铁。硫化物的 δ56Fe 值按照黄铁矿 < 黄铜矿 < 辉铜矿 < 黄铁矿 < 黄铁矿 < 黄铁矿 < 的顺序增加,这是由于铁同位素的动力学分馏所致。蛭石中的戊铁矿和黄铜矿的δ56Fe值高于钨铁矿,这意味着蛭石和钨铁矿形成于成分不同的岩浆中,铁同位素组成随晶体分馏而变重。硫化物的δ34S值按照黄铁矿< 辉铜矿< 黄铜矿< 黄铁矿的顺序增加,这与硫化物熔体的分馏顺序相似,表明外部衍生的S被添加到岩浆中,并促使其硫化物饱和。黄铜矿和黄铁矿的钴含量与δ56Fe值呈正向变化,而与δ34S值呈负向变化,这表明外源S的加入以及由此产生的硫化物偏析对钴的富集至关重要。
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来源期刊
Ore Geology Reviews
Ore Geology Reviews 地学-地质学
CiteScore
6.50
自引率
27.30%
发文量
546
审稿时长
22.9 weeks
期刊介绍: Ore Geology Reviews aims to familiarize all earth scientists with recent advances in a number of interconnected disciplines related to the study of, and search for, ore deposits. The reviews range from brief to longer contributions, but the journal preferentially publishes manuscripts that fill the niche between the commonly shorter journal articles and the comprehensive book coverages, and thus has a special appeal to many authors and readers.
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