摘要
对新疆北山地区红石山镁铁-超镁铁质岩体中含铜镍的硫化物矿石和岩石进行了铂族元素和Re-Os同位素地球化学特征研究,结果表明,矿石及岩石的铂族元素(PGE)总量较低,变化于0.54×10-9~15.84×10-9之间。较低的Pd/Ir比值表明岩石主要受岩浆作用控制,后期热液作用影响不明显。较高的Cu/Pd和Ti/Pd比值表明岩浆在演化过程中发生了硫化物的熔离。岩体的母岩浆为有早期结晶橄榄石加入的高镁的玄武质岩浆。γOs(t)的变化较大,变化于-282^+282之间,表明有较多的地壳物质混入。地壳物质混染和橄榄石等矿物的分离结晶可能是引起岩浆中的S达到饱和进而熔离的重要因素。红石山岩体是经历了结晶分异和硫化物熔离后橄榄石的堆积体与残余岩浆演化的混合体。
The Pobei mafic-ultramafic belt is an impotant Ni-Cu sulfide metallogenic prospective province in Beishan area,eastern Xinjiang.About 20 intrusions（e.g.,Bijiashan,Hongshishan,Cihai,Poyi,Poshi and Luodong） were recognized along the fault in this area and almost all the intrusions are associated with Ni-Cu sulfide deposits.The Hongshishan mafic-ultramafic complexs are located in the eastern part of the Pobei mafic-ultramafic belt and the southern part of the Baidiwa-Yunihe fault in this area.They intruded into quartz schist of the Lower Carboniferous Hongliuhe Formation.They are mainly composed of dunite,peridotite,troctolite,pyrox-enite,olivine gabbro,gabbro and diorite.These rocks were emplaced in two stages.The first stage consists of peridotite and olivine gabbro,and the second stage comprises gabbro and diorite.The dunite,pyroxene peridotite and troctolite are the host rocks for Ni-Cu sulfide ores.The platinum-group elements and Re-Os isotopic compositions of ore and rocks from the Hongshishan Ni-Cu sulfide-bearing mafic-ultramafic intrusions were analyzed,and the result shows that the total PGE content is quite low,ranging from 0.54×10-9 to 15.84×10-9 and increasing with the increase of sulfide content.The PGE primitive mantle-normalized patterns display a positive slope and low fractionation between IPGE and PPGE.PGE,Cu and Ni are depleted relative to the primitive mantle with low and a narrow Pd/Ir range（3.19~10.5）,indicating a weak influence of later hydrothermal alteration.Furthermore,the Ir displays positive correlations with Pt,Pd,Os,Ru and Rh,indicating a weak contribution of the fractionation and the partial melt to PGE depletion.The Cu/Pd ratios（73×103~1 670×103）and Ti/Pd ratios（87×103~2 857×103）of these rocks suggest that sulfur in the primary magmas had reached saturation,and immiscible sulfides droplets were segregated from silicate magmas before their emplacement.The relationship between Ni/Cu and Pd/Ir indicates that the parental magma was high-magnesium basaltic magmas.Their γOs（t） and（187Os/188Os）i are variable,ranging from ＋18 to ＋282 and from 0.148 3 to 0.481 3,respectively,suggesting that abundant crustal material was mixed with the ascending magma.The fractionation of olivine and contamination by crustal material probably triggered the sulfide saturation and segregation and the Ni-Cu-（PGE） mineralization as well.The intrusions were generated from the magma that had undergone crystallization differentiation of olivine and segregation of sulfides.
出处
《岩石矿物学杂志》
CAS
CSCD
北大核心
2012年第1期1-12,共12页
Acta Petrologica et Mineralogica
基金
国家自然科学基金项目(40863001
40973028
40972069)
新疆维吾尔自治区自然科学基金项目(2010211A08)
新疆大学"天山学者"特聘教授(陈斌)启动经费资助
