| The new studies indicate that the Jinchuan ultramafic intrusion is composed of eastern and western portions which are originally two separate intrusions and characterized by different petrology,mineralogy and geochemistry.The research on the mineralization mechanism of Eastern and Western intrusion has made some new understandings.For instance,sulfides were deposited in the Western intrusion when sulfide-bearing magmas passed through the intrusion;the Eastern intrusion was formed by injections of sulfide-free and sulfide-bearing olivine-crystal mushes from a deep-seated staging chamber;the sulfides of the Upper and Lower units segregated from PGE-undepleted and-depleted magmas,respectively.However,the metal oge-nic process of different portions of No.1 Orebody have not been well known and the researches of this area are still very weak.For most magmatic sulfide deposits,platinum-group elements,especially Pt and Pd are strongly correlate with semimetal elements,such as As,Bi,Sb,Se,and Te.The majority of platinum group minerals(PGM)consist of one or more of As,Bi,Sb,Se and Te complexed with Pt and Pd.Predecessors have reported and explained semimetal elements and its genetic significance of No.24 orebody and Longshoushan mine.However,the researches on semimetal elements of No.1 Orebody are still very weak.This dissertation is funded by National Natural Science Foundation of C hina(No:40973038,41003022,and 41172090)and cooperative projiect of Jinchuan Group Ltd(No : JC12008).Combined with previous research results and by means of rock geochemistry,the spatial distribution of the semimetal elements,PGE and their genetic significance of No.1 ore body are focused.To achieve the goal,we firstly judge the nature of the primitive magma and assume the chalcophile element compositions of the parental magmas.Then we used models to modify the sulfide segregation and fractionation of west extension,western,central,and eastern portions of No.1 ore body.They will enrich the petrogenetic of Jinchuan deposits and provid e a theory bases for seeking new orebodies in depth and border and ore-bearing magmatic plumbing system.The achievements and views are as follows:1.The primitive magma of No.1 Ore body is high MgO picritic and the sulfide ores formed from the silicate magmas that had already experienced prior-sulfide separation.Our calculations indicate that 0.007% sulfide removal would result in PGE-depletion in the residual magma.The Jinchuan sulfides were formed by a second stage of sulfide segregation from a PGE-depleted magma under silicate/sulfide liquid ratios(R-factor)ranging from 100 to 1000 in a deep-seated staging chamber.2.The parental magma of No.1 Orebody contains only ~0.28 ppb Ir,~0.26 ppb Ru,~1.74 ppb Pd,and ~344 ppm N i.The disseminated sulfides of the No.24 orebodies were segregated from a less PGE-depleted parental magma due to smaller amount of prior sulfide liquids removal at depth.Moreover,the higher PGE concentrations of the disseminated sulfides in the No.1 orebody relative to those of the No.2 orebody are attributed to greater R factors.3.The greater R factors of middle,west portion of the No.1 orebody re lative to those of east portion of the No.1 orebody has something with magmatic conduit and middle,west portion of the No.1 orebody may have deep prospecting prospect well.4.The net-textured sulfides of west portion formed by ~30 to 70% fractionation of the residual sulfide melt and some net-textured sulfides of middle portion formed by ~20 to 40% fractionation of the residual sulfide melt,whereas the net-textured sulfides of east and west extension portion were formed by 0 to ~30% and 0 to ~20% fractionation of the sulfide melt,respectively.5.Platinum relative to Pd has better chemical affinity with semimetal elements. |
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