Geochemical Characteristics Of Chalcophile Elements In Jinchuan Deposit And Their Constraints On Genesis Of Ore Deposit

The Jinchuan Cu-Ni sulfide deposit is located in the Longshoushan uplift belt.As the largest Cu-Ni sulfide deposit in China and the third largest in the world,the Jinchuan deposit has attracted extensive attention from scholars.In recent years,scholars have found that platinumgroup elements among the chalcophile elements have a strong affinity for chalcophile semimatal elements,and the two will combine to form platinum-group element minerals during the separation and crystallization of sulfide melts.But as an important element in the formation of platinumgroup minerals,the occurrence mechanism of chalcophile semimetal elements,the differences of their contents among mining areas as well as their significance in indicating the characteristics of magma channels are still controversial.Therefore,this article comprehensively collected geological data and previous research results,the ultramafic rocks and sulfide ores at Jincuhan and analyzed the geochemical characteristics of the platinum-group elements and chalcophile semimetal elements using the whole rock;electron probe;LA-ICPMS and energy spectrum analysis.Discussing the occurrence mechanism of chalcophile semimetal elements,the genesis of ore,the sulfide liquation and crystallization differentiation process,the differences in the chalcophile elements’ content of various ore zones and magma channel entrance position of the Jinchuan deposit.The main findings ars as following:(1)Mass balance calculations of chalcophile semimetal elements in the Jinchuan deposit indicate that Te,As and Bi in disseminated and nettextured ores tend to form platinum-group element minerals(PGMs)with platinum-group elements,while in massive ores,Te,As and Bi are mostly hosted in base metal sulfides(BMS),and only a small portion of Bi will form PGMs,implying that the hosting state of chalcophile semimetal elements is mainly distributed in BMS or crystallized to form PGMs.The BMS is formes by magma melting and PGE enrichment,so magma melting controls the state of chalcophile elements,and the factors controlling the state of chalcophile elements are as follows: crystallization of PGMs,differentiation of sulfide melts and diffusion of chalcophile elements at high temperatures.(2)The R factor can be used to simulate and quantitatively trace the mineralization of the main ore types in the Jinchuan deposit,Cu/Te-Te and Bi/Pd-Bi simulation results are consistent with Cu/Pd-Pd.So the semimetallic elements such as Te and Bi can also be used to simulate the sulfide dissociation process of the Cu-Ni sulfide deposit.Quantitative R factor simulation analysis shows that the net-texture ore is formed after the deep melting of sulfide melt.A small amount of PGM in massive ore indicates that the massive ore experienced a high degree of separation crystallizationis and the rich copper ore is formed by the condensation crystallization of Bi and Cu-rich residual sulfide melt.(3)According to various sample geochemical differences jinchuan ore body can be divided into three parts :the western intrusion,segments Ⅱ-W and Ⅱ-E.The similar geochemical characteristics of the west side of the segment Ⅱ-E and the segment Ⅱ-W suggest that the two segments evoloed in the same magma channel in the early stage,and the first mentioned of two were formed by the emplacement of magma along different magma channels.(4)The metallogenic model of Jinchuan deposit is a multi-channel magmatic channel metallogenic model,where the metallogenic material is intruded in the form of “melt-fluid”.The entrances of magmatic channels are row Ⅲ-6,Ⅱ-2 and Ⅱ-36.In summary,this paper not only clarifies the state of chalcophile semimetal elements and their controlling factors,but also analyzes the control of chalcophile semimetal elements during the melting and separation and crystallization of sulfide melt,and points out the genesis of each type of ore in the Jinchuan deposit.Finally,on the basis of the previous study,obtains the characteristics of the metallogenic pattern of the Jinchuan deposit through the difference of chalcophile elements content in each mining area,points out the location of the entrance of magma channel,which has certain indicative significance for future ore search and prospecting.