柴达木北缘东段呼德生镁铁-超镁铁质岩体锆石U-Pb年代学、地球化学及成岩成矿分析

呼德生岩体位于柴北缘造山带欧龙布鲁克微陆块东南缘,侵位于古元古代金水口变质岩群中。该岩体从中心到边缘依次出现橄榄岩→辉石岩→辉长岩的岩相分带特征,岩石主要类型有纯橄岩、橄榄二辉岩和辉长岩,各岩石之间多为过渡接触关系,镍铜矿化主要赋存于辉石岩中。锆石LAICP-MS U-Pb年代学研究表明,岩体形成年龄为425.2±5.8Ma,为柴北缘晚志留世-晚泥盆世后造山伸展阶段岩浆作用的产物。岩石镁铁比值(m/f)为2.51~5.37,属于铁质系列基性-超基性岩。各类岩石富集轻稀土元素(LREE)和大离子亲石元素(Ba、Sr、Rb),而亏损高场强元素(Zr、Hf、Nb、Ta)。岩相学、矿物学及岩石地球化学研究表明岩浆在演化过程中发生了一定程度的结晶分异作用和同化混染作用。结合岩体形成年代及区域地质资料,呼德生岩体应形成于大陆边缘伸展阶段,原始岩浆在演化过程中经历了地幔流体的交代作用。通过对岩浆结晶分异程度及同化混染情况等方面的综合评价,认为呼德生岩体具有良好的铜镍硫化物矿床形成条件。

Zircon U-Pb geochronology, geochemistry and metallogensis of the Hudesheng mafic-ultramafic intrusion in the eastern section of northern Qaidam Basin

The Hudengsheng mafic-ultramafic intrusion, located in the southeastern margin of the Oulongbuluke micro-continent in the northern Qaidam orogenic belt, intruded into the Paleoproterozoic Jinshuikou group. From the core to its edge, this complex is composed of peridotite, pyroxenite and gabbro. In rock types, it is dominated by dunite, olivine websterite and gabbro, which contact each other mostly in gradual transition. The nickel and copper mineralization occurred primarily in pyroxenolite. Zircon LA-ICP-MS U-Pb geochronology shows that this intrusion (425.2±5.8Ma) resulted from magma activity during the Late Silurian to Late Devonian in a setting of post-orogenic extension. The m/f ratios range from 2.51 to 5.37, indicative of iron series of basic-ultrabasic rocks. All kinds of rocks in the intrusion are enriched in light rare earth elements (LREE) and large ion lithophile elements (Ba, Sr, Rb) and depleted in high field strength element (Zr, Hf, Nb, Ta). In combination with data of petrography, mineralogy and geochemistry, it is inferred that the crystallization differentiation and crustal contamination occurred during the process of magma evolution. Integrated with the age of the intrusion and regional geological setting, it is considered that this intrusion formed in the extensional stage of a continental margin. The primitive magma experienced the metasomatism of mantle fluids in the evolution process. According to the degree of magmatic differentiation and the characteristics of assimilation contamination, it is comprehensively concluded that the Hudesheng intrusion has good conditions for nickel and copper mineralization.