东天山黄山东铜镍矿床铂族元素地球化学特征及其意义

摘要

黄山东岩体位于东天山北部的土墩-黄山-镜儿泉-图拉尔根镁铁-超镁铁质岩带中段,受康古尔塔格-黄山深大断裂控制,是由二辉橄榄岩、橄榄辉长岩、辉长苏长岩和辉长闪长岩组成的复式岩体.黄山东铜镍硫化物矿床镁铁质岩石和矿石中的铂族元素(PGE)含量很低,其中IPGE(Os, Ir, Ru, Rh)与PPGE(Pt, Pd)含量相近,PPGE略高于IPGE.岩石平均2×10~(-9),矿石平均86×10~(-9).在矿石中,PGE含量与硫含量呈正相关关系.在原始地幔标准化图解上,岩石和矿石具有相似的分配模式,PPGE和IPGE之间分异很弱.Ni/Cu-Pd/Ir关系图以及岩石地球化学资料显示,形成黄山东岩体的原始岩浆为MgO含量较高的PGE不亏损的拉斑玄武质岩浆.岩浆在上升的过程中发生过早期硫化物深部熔离,带走了岩浆中大部分的PGE,可能是造成黄山东矿床母岩浆中PGE明显亏损的主要原因.矿石低的Pd/Ir比值(为4.22～17.24,平均值为8.49)及高的Ir含量(为2.04×10~(-9)～21.45×10~(-9),平均值为8.79×10~(-9))显示黄山东矿床成矿过程中后期热液作用不明显.铂族元素地球化学特征和岩石地球化学资料显示了地壳物质的混染以及橄榄石、辉石等矿物的分离结晶是引起该矿床硫饱和并发生硫化物熔离作用而成矿的主要因素.%The Huangshandong intrusion, is located in the centre segment of Tudun-Huangshan-Jing'erquan- Tulaergen mafic-ultramafic rock belt, the northern of the East Tianshan, controlled by the Kangurtag- Huangshan ductile sheer zone, and it is a multiple intrusion and composes of lherzolite, olivine gabbro, gabbro norite, and gabbro diorite. The total concentration of platinum-group elements (PGE) in rocks and ores is very low, which average value is 2×10~(-9) and 86×10~(-9) respectively and it increases with sulfur content increases in ores. Rocks and ores samples have similar mantle-normalized PGE patterns, the fractionation between IPGE and PPGE is low.Diagram of Ni/Cu verses Pd/Ir and petrochemistry reveal that the initial magma of Huangshandong is high MgO tholeiitic magma, which should be undepleted in PGE. Compared with continental tholeiite, simulating result reveals that the parental magma is visibly depleted in PGE, possibly duing to the sulfide pre-segregation of initial magma in deep crust. The lower Pd/Ir ratio (4.22×10~(-9)～17.24×10~(-9), 8.49×10~(-9)in average) and higher Ir content (2.04×10~(-9)～21.45×10~(-9), average 8.79×10~(-9)) in ores suggest that the later hydrothermal alteration in the mineralized process is weak.The platinum-group elements geochemical character and petrochemical data show that crustal contamination and the fractionation of olivine and pyroxene may be the main factors leading to S-saturation and sulfide segregation in deep crust.