云南大红山铁铜矿床碳、氧同位素和微量元素地球化学特征及成矿意义

Geochemical Characteristics of Carbon and Oxygen Isotopes and Trace Elements of the Dahongshan Cu-Fe Deposit in Yunnan and Their Metallogenic Significances

云南大红山铁铜矿床产于古元古界大红山群变质火山-沉积岩建造中,主要由火山沉积型矿体和热液型矿体组成,为查明热液型矿体的形成机制,开展了热液方解石的碳、氧同位素以及磁铁矿、围岩和岩体的微量元素分析。结果显示,热液方解石的δ13CPDB值为-5.78‰^-0.53‰,δ18OSMOW值为4.55‰~9.77‰。磁铁矿与围岩和辉长辉绿岩体均相对亏损Sr、相对富集LREE,具有不同程度的Eu正异常和微弱的Ce负异常。粗粒磁铁矿中Ti、V、Cr含量低,Co、Ni含量较高,Ni/Cr值远大于1,具有典型热液成因特征。研究认为,与围岩呈过渡关系的细粒磁铁矿体由海底火山喷发作用形成,而与围岩呈截然接触关系的粗粒磁铁矿体可能是与辉长辉绿岩同源的岩浆热液充填交代含矿围岩的结果。

The Dahongshan Cu-Fe deposit is hosted within metavolcanic to metasedimentary rocks of the Paleoproterozoic Dahongshan group.There are two types of orebodies including the strata-bound metavolcanic type and hydrothermal type of orebodies in the deposit.In this paper,carbon and oxygen isotopic compositions of the hydrothermal calcites,trace and rare earth elements of different types of magnetite,wallrocks,and gabbro-diabases are analyzed in order to reveal the formation mechanism of hydrothermal ore bodies in the Dahongshan copper iron deposit.The results show thatδ13CPDB andδ18OSMOW values of calcites in orebodies range from-5.78‰to-0.53‰and from 4.55‰to 9.77‰,respectively.The magnetites,wallrocks,and gabbro-diabase are relatively depleted in Sr,but relatively enriched in LREE,with various degrees of positive Eu anomalies and weak negative Ce anomalies.The coarse grained magnetites are characterized with low contents of Ti,V and Cr,high contents Co and Ni,and Ni/Cr values of far larger than 1,indicating characteristics of the typically hydrothermal genesis.Based on the comprehensive study,it is believed that the fine-grained magnetites,which are transitionally associated with wallrocks,could be formed by submarine volcanism,while the coarse-grained magnetites,which are in sharp contact with wallrocks,could be the result of infilling and metasomatism in wallrocks by the magmatic hydrothermal fluids sourced from the magma of gabbro-diabase.