新疆东天山红石岗北铜镍矿化镁铁质岩体岩石成因及成矿潜力分析

摘要

The Hongshigangbei mafic intrusion was discovered by No.704 Geological Party,Xinjiang GeologicalExploration Bureau for Nonferrous Metals in 2014.It is located in East Tianshan,and controlled by theKangguer-Huangshan ductile shear zone.The mafic intrusion is composed predominantly of diorite,hornblende gabbro and olivine gabbro,with a minor amount of sufide droplets in gabbro occasionally.Sulfide mineral assemblages are composed of pyrrhotite,pentlandite and chalcopyrite.In order toaccurately evaluate the prospecting potential of the intrusion,we investigated the zircon U-Pb chronology,mineral chemistry,geochemical and Sr-Nd isotopic characters of the intrusion.Combining with thegeophysical characteristics,we compared the Hongshigangbei intrusion with the typical Ni-Cu sulfidedeposit in East Tianshan area.The zircon U-Pb isotope age of 276.1 ± 5.4 Ma reveals that the maficintrusion was formed in Early Permian.Olivine crystals in the Hongshigangbei rocks have a narrow range(Fo=69.9～72.6) and the Ni content of 101× 10-6 ～1326× 10-6.The clinopyrexene and orthopyroxenebelong to endiopside-diopside and enstatite respectively.The values of MgO (5.95％～13.06％) and FeOTshow positive correlation,but there is negative relation between MgO and SiO2,CaO and Al2O3.All thesamples are slightly enriched in LREE and positive Eu anomaly.Trace elements show a LILE-rich andHFSE-depleted(Nb,Ta) pattern.The (87Sr/86Sr)i and εNd(t) rations range from 0.70342～0.70349 and +7.51～+8.25(t=276Ma) respectively,indicating that the source of intrusion was depleted mantle.TheSr-Nd isotope trend reveals that the parental magma of the Hongshigangbei intrusion experienced about5％ crustal contamination during upwelling.Compared with the typical Ni-Cu sulfide deposits in EastTianshan,the Eo contents and major elements contents of the Hongshigangbei intrusion are in a low andnarrow range.But they are similar in isotope age,trace elements,Sr-Nd isotopic characteristics,degree ofcrustal contamination and material.This indicates that the characteristics of magma sources,tectonicsetting,composition of parental magma and evolution process may have obvious similarity betweenHongshigangbei intrusion and Huangshandong,Huangshan deposit.On the basis of the study above,wespeculate that the deep of intrusion may exist ultramfic rocks.Geophysical data also indicate that theHongshigangbei intrusion has lower polarization rate than the typical Ni-Cu sulfide deposit in EastTianshan.But they have similarity in surface magnetic anomaly,residual gravity anomaly and resistivity.These characters show that the deep of the Hongshigangbei intrusion may exist ore-bearing ultramaficintrusion.In conclusion,we believe that the deep of Hongshigangbei intrusion has large Ni-Cu prospectingpotential.%红石岗北岩体是新疆有色地质勘查局704队于2014年新发现的,产于东天山康古尔—黄山韧性剪切带内.岩体地表主要岩性为闪长岩、角闪辉长岩和橄榄辉长岩,硫化物主要由磁黄铁矿、镍黄铁矿和黄铜矿组成.为准确评价岩体深部找矿潜力,本文在对该岩体开展系统的锆石U-Pb年代学、矿物晶体化学、岩石地球化学及Sr-Nd同位素研究基础上,结合其地球物理特征,将其与东天山已知典型铜镍矿床进行了系统对比研究.结果表明红石岗北岩体锆石U-Pb谐和年龄为276.1±5.4Ma,表明其形成于早二叠世.橄榄石Fo值为69.9～72.6,属贵橄榄石,Ni含量变化范围为101×10-6～1326×10-6;单斜辉石主要为顽透辉石—透辉石;斜方辉石主要为古铜辉石.MgO与SiO2、CaO和Al2O3之间呈明显的负相关性,与FeOT呈明显的正相关性.在稀土元素球粒陨石标准化图解上,所有样品均呈轻稀土略富集的右倾型,相对富集大离子亲石元素(Cs、Sr、Ba),具有明显的Nb、Ta负异常.样品(87Sr/86 Sr)i=0.70342～0.70349,εNd (t) =+7.51～+8.25(t=276Ma),Sr、Nd同位素模拟计算表明母岩浆上升过程中遭受了约5％的地壳物质混染.与东天山地区已知典型铜镍矿床相比,红石岗北岩体中橄榄石Fo值及主量元素含量明显偏低,且变化范围较小,但其形成时代、微量元素和Sr-Nd同位素特征和同化混染程度均相似,表明红石岗北岩体与黄山东、黄山等矿床的岩浆源区性质、构造背景、母岩浆成分及演化过程具有相似性,暗示红石岗北岩体深部应存在超镁铁质岩石.红石岗北岩体地表磁异常、剩余重力异常和视电阻率均与东天山已知铜镍矿床具有相似性,表明其深部可能存在赋矿的超镁铁质岩体.综上所述,我们认为红石岗北岩体深部具有较大的铜镍找矿潜力.