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大山头南铜镍矿化基性-超基性杂岩体位于北山褶皱带东段,侵位于长城系古硐井群变质岩中。岩相分带明显,主要包括花岗闪长岩-闪长岩相、辉长岩-橄榄苏长辉长岩相和橄榄二辉岩-纯橄岩相。铜镍矿化主要赋存于橄榄二辉岩-纯橄岩相中。岩石化学特征显示K2O、Na2O、TiO2含量较低,Mg#值介于0.74~0.85之间,MgO/FeOT的值介于1.6~3.1之间,属于铁质镁铁-超镁铁岩;AFM图解显示该岩体具拉斑玄武岩的演化趋势;稀土元素总量较低,介于6.37×10-6~37.51×10-6之间;稀土元素标准化配分曲线表现为轻稀土元素稍富集的右倾型,LREE/HREE比值介于3.03~4.11之间,轻重稀土发生了明显的分馏;采用SHRIMP锆石U-Pb方法,获得杂岩体辉长岩中锆石U-Pb年龄为374.3±3 Ma(MSWD=0.92),表明该岩体侵位于中晚泥盆世,与形成大型镍矿床的黑山岩体年龄一致,形成于洋壳俯冲阶段。该年龄的获得不仅对北山乃至中亚造山带地质构造演化具有重要意义,而且也为北山褶皱带东段铜镍找矿提供了新的方向。
The Dashanntou copper-nickel basement-ultrabasic complex is located in the eastern section of the Beishan fold belt and invaded the metamorphic rocks of the Gujing well group in the Great Wall. The lithofacies zoning is obvious, including mainly granodiorite-diorite facies, gabbro-olivine-gabbro feldspathic phase and olivine-pyroxene-dulpidite facies. Copper-nickel mineralization mainly occurs in olivine-dunite facies. The petrochemical characteristics show that the K2O, Na2O and TiO2 contents are relatively low, the Mg # values range from 0.74 to 0.85, and the MgO / FeOT values range from 1.6 to 3.1, belonging to the ferrous mafic-ultramafic rocks. The AFM Showing that the rock body has the evolution trend of tholeiitic basalt; the total amount of rare earth elements is relatively low, ranging from 6.37 × 10-6 to 37.51 × 10-6; the normalized distribution pattern of rare earth elements shows a right enrichment of light rare earth elements Type and the LREE / HREE ratios ranged from 3.03 to 4.11. The fractional fractionation of light and heavy rare earths occurred. By using the SHRIMP zircon U-Pb method, the U-Pb zircon ages of zircons from the complex gabbro bodies were 374.3 ± 3 Ma (MSWD = 0.92), indicating that the intrusive rock intrusion is in the middle Devlo-Late Devonian and coincides with the age of the Heishan pluton forming a large nickel deposit and formed in the subduction of the oceanic crust. This age is of great significance not only for the geological evolution of the orogenic belt in the Beishan area but also for the Central Asia. It also provides a new direction for Cu-Ni prospecting in the eastern part of the Beishan fold belt.