高温岩浆过程中的钴镍解耦机制及其成矿指示  

Decoupling of cobalt and nickel in high-temperature magmatic processes and its metallogenic indication

作　　者：苏本勋[1,2] 崔梦萌 袁庆晗 王静 白洋 SU BenXun;CUI MengMeng;YUAN QingHan;WANG Jing;BAI Yang(Key Laboratory of Mineral Resources,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;University of Chinese Academy of Sciences,Beijing 100049,China;College of Mining Engineering,Taiyuan University of Technology,Taiyuan 030024,China)

机构地区：[1]中国科学院地质与地球物理研究所,中国科学院矿产资源研究重点实验室,北京100029 [2]中国科学院大学,北京100049 [3]太原理工大学矿业工程学院,太原030024

出　　处：《岩石学报》2023年第10期2867-2878,共12页Acta Petrologica Sinica

基　　金：国家重点研发计划项目(2022YFC2903501);中国科学院青促会项目联合资助.

摘　　要：钴(Co)和镍(Ni)具有相似的地球化学行为,在自然界多协同变化,然而在某些地质过程(尤其是成矿作用)中二者可发生解耦现象,解耦机制尚不清楚。本文对不同成因类型的镁铁-超镁铁岩石样品开展了主要造岩矿物中Co、Ni元素分布特征和迁移行为的研究。地幔橄榄石的Ni(2500×10^(-6)~3400×10^(-6))和Co(110×10^(-6)~160×10^(-6))含量均高于原始地幔,其Ni含量与Fo值无明显相关性,而Co含量与Fo及Ni/Co比值呈较好的负相关关系。这表明部分熔融并不造成橄榄石中Ni含量的系统变化,但可控制Co含量和改变Ni/Co比值,其原因主要与两种元素在橄榄石中的相容性差异有关。熔-岩反应可引起矿物间及矿物内显著的Co-Ni解耦,但机制有所差异:在与玄武质熔体反应的过程中,橄榄石以吸收Co、丢失Ni为主,同时受到共结矿物尖晶石的影响;与碳酸盐熔体反应的过程中,橄榄石以丢失Co而Ni基本不变为特征。在幔源玄武质岩浆底侵麻粒岩相下地壳时,辉石中Co、Ni元素的迁移受控于浓度梯度和硫化物结晶,而Co的局部富集为地壳深熔形成富Co熔体提供了重要物质基础。镁铁-超镁铁质岩浆分异演化过程中,铬铁矿分离结晶、硫化物熔离均可造成岩石和/或矿物尺度的Co、Ni解耦。同时,铬铁矿聚集沉淀及硫化物熔体固结过程中释放的富水流体将大大促进亚固相状态下的元素交换效率,尤其加强Co的活动性,从而引起橄榄石甚至铬铁矿的Co、Ni负相关。对比研究发现,成矿与不成矿岩体以及含矿与不含矿岩石中矿物的Co、Ni含量变化趋势明显不同或截然相反,为识别岩体成矿潜力和指导找矿提供了依据。Cobalt(Co)and nickel(Ni)have similar geochemical behaviors and commonly co-vary in nature,but they may undergo decoupling in certain geological processes,especially in ore-forming processes,and the decoupling mechanism is not yet clear.This paper analyzes the distribution characteristics and migration behaviors of Co and Ni in major rock-forming minerals in different types of mafic-ultramafic rocks.The Ni(2500×10^(-6)-3400×10^(-6))and Co(110×10^(-6)-160×10^(-6))contents of mantle olivine are both higher than those of the primitive mantle.The Ni content shows no obvious correlation with the Fo value,while the Co content has a strong negative correlation with both the Fo value and the Ni/Co ratio.This indicates that partial melting does not cause significant changes in Ni content of olivine,but can control the Co content and the Ni/Co ratio,mainly due to the differences in compatibility between the two elements in olivine.Melt-rock reactions can cause significant Co-Ni decoupling between minerals and within minerals,but the mechanisms differ.In the process of reacting with basaltic magma,olivine mainly absorbs Co and loses Ni,while being affected by coexisting spinel minerals.When reacting with carbonatite melt,olivine loses Co,but Ni remains almost unchanged.As mantle-derived basaltic magma intrudes into the lower crust,the migration of Co and Ni in pyroxenes is controlled by concentration gradients and sulfide crystallization.The local enrichment of Co provides an important material basis for the formation of Co-rich melts in deep crustal melting.During the differentiation and evolution of mafic-ultramafic magma,the chromite fractional crystallization and sulfide segregation can cause Co-Ni decoupling at both rock and/or mineral scales.Meanwhile,the enriched hydrous fluids released during chromite aggregation and sulfide melt solidification can significantly promote the efficiency of element exchange in sub-solidus state,especially strengthening the activity of Co,thus causing negative correlations between Co

关 键 词：钴镍矿床 钴镍解耦 熔/流体-岩石反应 镁铁-超镁铁岩 

分 类 号：P588.11[天文地球—岩石学] P588.125[天文地球—地质学] P618.62P618.63