陕西略阳南部何家垭镍钴含矿岩体铂族元素特征——对硫化物熔离过程的约束

Platinum-group elements characteristics of the Hejiaya Ni-Co intrusion inthe south of Lüeyang County,Shaanxi Province:Constraints on the process of sulfide melting segregation

陕西何家垭镍钴含矿岩体位于南秦岭碧口地块,是近年来秦岭造山带中镍、钴战略性矿产找矿取得的重要新发现之一。该岩体由辉长岩、辉长闪长岩和少量辉石岩、角闪石岩组成,矿(化)体主要赋存在蚀变辉长岩中。基于对不同结构类型矿石铂族元素地球化学和硫化物原位硫同位素分析,探讨了岩浆性质和硫化物熔离过程。结果表明,各类矿石铂族元素(PGE)丰度均较低(3.93×10^(-9)~87.85×10^(-9),平均为27.88×10^(-9))。铂族元素地球化学特征反映,岩体母岩浆为高镁玄武质岩浆,受后期热液作用影响较弱。铂族元素和原位硫同位素特征显示,镁铁质矿物分离结晶是引起矿床中硫演化至饱和并发生深部硫化物熔离的重要因素。矿石中Pt元素的显著亏损可能是含Pt矿物结晶导致。南秦岭略阳何家垭岩体具有较好的镍钴成矿条件和找矿潜力,有望在秦岭造山带岩浆型铜镍硫化物矿床勘查评价方面取得重大突破。

Hejiaya Ni−Co mineralized intrusion is located in Bikou block of South Qinling.It is one of the important new discoveries ofnickel,cobalt and other strategic minerals in Qinling orogenic belt in recent years.The rock mass is mainly composed of gabbro,gabbro−diorite and a small amount of pyroxenite,amphibolite,and the mineral bodies is mainly hosted by the altered gabbro.Based onthe analysis of platinum−group element geochemistry and in situ sulfur isotope of sulfide in ores of different structural types,themagmatic properties and the process of sulfide melting segregation are discussed.The results showed that the abundance ofplatinum−group elements(PGE)was low in all kinds of ores(3.93×10^(−9)~87.85×10^(−9),average 27.88×10^(−9)).The geochemicalcharacteristics of platinum−group elements indicate that the primary magma of the rock mass is high magnesium basaltic magma,which is weakly affected by the late hydrothermal process.The characteristics of platinum−group elements and in situ sulfur isotopesindicate that the separation and crystallization of mafic minerals is an important factor that causes sulfur evolution to saturation and deep sulfide melting segregation.The significant depletion of Pt element in the ore may be the result of Pt−containing mineralcrystallization. The Lüeyang Hejiaya rock mass in South Qinling has good Ni−Co metallogenic conditions and prospecting potential,which is expected to make a major breakthrough in the exploration and evaluation of magmatic Cu−Ni sulfide deposit in Qinlingorogenic belt.