中天山白石泉含Ni镁铁质岩与含Ni-Cu超镁铁质岩体的成因研究

We choose Permian nickel sulfide-bearing mafic intrusion, and coeval nickel-copper sulfide-bearing mafic-ultramafic complexes of Baishiquan, located in Central Tianshan area, as research object. Based on the plane and section observation of various lithofacies from different plus of magmas, distinguish the emplacement sequence, identify the occurrence and shape of the intrusions and orebodies, and further determine the location and their formation condition of different rocks in the magma conduit. We use electron probe, Laser inductively coupled plasma mass spectrometer and solution Sr-Nd isotope method of orthopyroxene and clinopyroxene to analysis major oxides, trace elements and Sr-Nd isotope data of the silicate minerals (pyroxene and magnetite) and sulfides, then indicate the rocks or layers which underwent multi stage magma injection, magma evolution, immiscible sulfide segregation. Summary the minerals and whole rocks geochemical characteristic, we want to find the key factors which control the Ni-Cu sulfide orebody formation of both mafic intrusion and mafic-ultramafic complex in Baishiquan deposits. We want to identify the mechanism of magma evolution and sulfide fractionation of the nickel sulfide-bearing mafic intrusion by comparison geological feature and key factor of mineralizaiton between mafic and ultramafic intrusions. We also want to reveal the component of parental magma and the partial melting degree of source by the composition of melt inclusion in Permian basalts and the PGE, Sr-Nd isotopic results of basalt and mafic dyke in this area and further judge the tectonic setting and emplacement mechanism of the Baishiquan mafic-ultramafic complexes in Central Tianshan.

以中天山白石泉17#含镍镁铁质岩为研究的切入点，对比1#和8#含镍铜矿镁铁-超镁铁质岩。在多期次岩相平面、剖面上野外观察的基础上，识别出侵位次序、追溯岩体及矿体形态，进而判别不同期次岩相位于通道式成矿模型的部位及形成条件。针对不同期次岩体中的贯通矿物辉石和磁铁矿，运用电子探针、LA-ICP-MS及矿物的Sr-Nd同位素分析，进行剖面上矿物微区主量、微量元素、同位素成分分析，厘定多期次岩浆注入、硫化物发生熔离的机制及层位。结合全岩地球化学特征，查明白石泉镁铁-超镁铁质岩体分别成矿的关键性因素。详细对比北疆含铜镍硫化物的基性岩的地质特征及控矿因素，查明基性岩含富镍矿的岩浆演化和硫化物熔离机制。利用同期玄武岩熔融包裹体成分，结合邻区玄武岩、基性岩墙的PGE、Sr-Nd同位素特征，揭示母岩浆的性质、部分熔融程度，在此基础上推断白石泉岩体产出的构造背景。

白石泉矿区位于东疆中天山地块，原来发现有1号和17号岩体镁铁-超镁铁杂岩体，矿体主要赋存在两个岩体的底部，近年勘探工作发现了8号超镁铁质岩体，侵位于17号岩体的南侧。该矿区以镁铁岩和超镁铁岩同时赋矿为特色，但是这些岩体之间的联系、成矿性差异的控制因素仍然不清，查明这些岩体的成矿作用将加深中天山乃至东疆铜镍矿床成矿机理的认识。.基于最新地质资料和详细的野外探槽、钻孔岩心的观测，将白石泉三个主要岩体对应着三期岩浆侵位，并且均发育不同程度的铜镍硫化物矿化，可细分为三期成矿：第一期主要为辉石岩相、含长橄辉岩相，主要包括整个1号超基性岩体、17号基性岩体内部的多个小的超基性岩捕虏体；第二期主要岩相为辉长岩相、辉长苏长岩相、辉长闪长岩相，主要为17号岩体；第三期为辉石岩和橄榄岩相，形成8号岩体。锆石年代学指示白石泉三个岩体年龄分别为：8号岩体291.2±1.2Ma；17号岩体277.8±1.7Ma；1号岩体267.9±1.9Ma。三期岩浆活动形成的岩体都含矿且侵位时间差异较大，不同于区域上其他多期岩浆成矿，例如黄山东、黄山矿床，这些矿床的多期岩浆在SIMS测年误差范围内无法区分。全岩主微量元素、矿物成分对比指示8#和17#虽为非同期岩浆结晶产物，但是可能为相同地幔熔融，不同期次侵位的产物。.白石泉硫化物含量高的样品普遍蚀变较强，贫矿化二辉橄榄岩样品的橄榄石水含量较低，浸染状和海绵陨铁状样品中橄榄石水含量高，矿化程度和橄榄石的蚀变程度及水含量呈正相关；1号和8号岩体橄榄石的δ7Li值随着矿化变富而增大，这与富水熔体/流体扩散作用有直接的关系。玄武质岩浆演化的后期，硫饱和及不混溶液态硫化物形成的同时产生了相对富含水的残余岩浆。从原始岩浆中结晶出来的橄榄石并不富含Li或H2O，随着晶间富水熔体的水扩散，Li或H2O会进入橄榄石。水在白石泉铜镍矿床硫化物聚集过程中起到了重要的作用，含水的玄武质岩浆可能是造山带铜镍矿床成矿的一个重要特色，影响了硫化物饱和、运移、聚集等多种重要过程。