| About 90%of the world's platinum group elements(PGE)resources are contained in magmatic Cu-Ni sulfide deposits.PGE list as key or strategic minerals by many countries and have received great attention.However,China's magmatic Cu-Ni sulfide deposits are short of PGE,highly dependent on foreign countries and greatly affected by the international environment.Jinchuan Cu-Ni-(PGE)deposit and Xiarihamu Ni-Co deposit are the only two super large magmatic sulfide deposits in China,which play an important role in Cu-Ni-Co-PGE resources.Previous studies on the occurrence background,metallogenic age,ore-forming elements and ore grade of the two have been carried out in detail,but there is no systematic comparative study on the characteristics of PGE.PGE is not only an important resource,but also a good indicator of magmatic process.The study of their differences is of great significance for sorting out the similarities and differences of magmatic evolution and metallogenic processes of the two deposits,and condenses the important metallogenic theories such as the evolution law,migration mechanism and metallogenic conditions of platinum group elements in China.According to the research idea of comparative science and on the basis of deep understanding of geological and geochemical characteristics of the deposit,the whole rock platinum group elements and trace elements analysis,electron microprobe major elements test,LA-ICP-MS in-situ micro area trace elements test and in-situ sulfur isotope method are adopted in this work.This paper systematically analyzes,compares and studies the PGE concentration of rocks,ores and minerals of the two magmatic sulfide deposits to find out their similarities and differences.Therefore,the similarities and differences of magmatic evolution and metallogenic process between the two deposits are further recognized.Furthermore,according to their different occurrence characteristics of PGE,the occurrence state,migration mechanism and metallogenic conditions of PGE are compared and summarized,which can provide guidance for PGE prospecting in the future.Through systematic comparative study,the following understandings are obtained:(1)The contents of platinum group elements(PGE)and semimetal elements(TAB)in the rocks of different mining areas of Jinchuan deposit are relatively uniform,showing the characteristics of homologous magmatic evolution,which can basically represent the element composition of Jinchuan mafic ultramafic pluton.The contents of PGEs and TABs in ores areas I,II and IV gradually decrease,and the enrichment degree of Pt and Pd is much higher than Ir,Ru and Rh.However,Pt and Pd have inconsistent changes,while Ru,Rh and Ir have basically the same changes;Bi,Se and Te are significantly enriched,but As has no obvious change.In contrast,the content of PGEs in the whole rock of Xiarihamu deposit is very low,but As and Bi are high.(2)According to the relationship between TABs and PGEs,and the correlation between TABs,PGEs and S,the expression of PGM in magma can be well indicated.PGE are mainly as simple substance or alloy,and a small number of platinum metal compounds and isomorphic substitution of sulfides in Jinchuan Mining Area I;they mainly form platinum metal compounds and isomorphic substitution of sulfides in mining area II;PGE in Mining Area IV is similar to Xiarihamu deposit,without platinum group minerals,mainly isomorphic substitution of sulfides.(3)Based on the different characteristics of spinel in Jinchuan and xiahamu deposits and the comparison with the spinel types of typical PGE deposits at home and abroad,it is suggested that alchromite may be the indicator mineral of PGE mineralization,which represents specific magma source or physicochemical condition.(4)The important features of the different metallogenic elements of the two deposits are that platinum group minerals,gold and silver minerals are widely developed in Jinchuan deposit;there has developed widely nickel and cobalt minerals such as nickeline,cobaltite,gersdorffite,violarite,maucherite in Xiarihamu deposit.(5)Pt(possibly Ir)in magmatic copper-nickel sulfide deposit only occurs in platinum group minerals,which tends to directly form Pt As2(possibly Ir As S)or form platinum group element monoelement or alloy in poor semi-metallic environment;Besides the platinum group minerals,Pd also replaced Fe in chalcopyrite and chalcopyrite;Rh mainly replaced Fe in chalcopyrite and chalcopyrite.(6)Whether PGEs can enrich mainly depends on the number of platinum group minerals formed by magmatism.The main reasons of Jinchuan and Xiarihamu different PGE content are less sulfide in the source area,low degree of partial melting,low oxygen fugacity,higher degree of magma crystallization differentiation,stronger deep melting and lower R factor in Xirarihamu deposit.(7)PGM in magmatic copper nickel sulfide deposits are mainly magmatic.Because Pt is not easy to enter sulfide,the residual Pt after the early formation of platinum group minerals can enter into hydrothermal solution,and Pt hydrothermal mineralization will occur under appropriate conditions.(8)Through the comparative study of the two deposits,the metallogenic conditions of platinum group elements are summarized as follows:there are a lot of sulphides in the magma source area,high degree partial melting,continuous supply of magma,limited deep melting and dissociation,the"catcher"of platinum group elements and good differentiation and accumulation process. |
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