甘肃北山大山头铜镍矿化基性-超基性岩成矿潜力研究

Metallogenic Potential of Copper and Nickel Mineralization in the Mafic-Ultramafic Rocks in Dashantou,Beishan,Gansu Province

为了研究甘肃北山大山头含铜镍硫化物基性、超基性岩的成矿潜力，通过野外调查和室内综合对比研究，取得如下认识及成果：（1）大山头岩体侵位于前寒武系中深变质碎屑岩与片麻状花岗岩中，为多期次侵位的杂岩体，早期以中细粒辉长岩岩基为主，晚期为橄榄苏长辉长岩-二辉橄榄岩相基性-超基性岩，岩体分异明显，橄榄二辉岩全岩铜镍矿化（Cu含量0.08%-0.46%，Ni含量0.2%-0.37%）：（2）岩体常量和微量元素具岛弧基性超基性岩浆特征（例如岩体亏损高场强元素Nb， Ta，Ti，Hf及Y和P，富集大离子亲石元素Ba，Rb，Th，U，K及La等）；（3）磁法异常与岩体地表矿化一致，电法结果显示岩体深部矿化更好（最大磁场强度值600nT，视极化率（ηs）显示最大值可达7.5%-12.1%）；（4）岩体岩石地球化学特征与金川、喀拉通克、红旗岭等相似，与甘肃黑山一致。因此，大山头有望成为储量规模不亚于甘肃黑山的铜镍硫化物矿床。

In order to study the ore-forming potential of mafic-ultramafic rocks with Cu-Ni sulfide in Dashantou, Beishan,Gansu Province, we have conducted the field investigation and comprehensive comparison, and made the following achievements ： （1） the Dashantou rock was emplaced in Precambrian middle-deep metamorphic clastic rocks and gneissic granite, and is characterized by many episodes of magmatism. Early stage was dominated by the fine-grained gabbro rock foundation and the olivine, gabbro-two pyroxene peridotite mafic ultramafic rocks become dominant in later period. Rocks were differentiated obviously, and the Cu-Ni mineralization of lherzolite completely （Cu content 0.08%-0.46%, Ni content 0.2%-0.37%）;（2） The major and trace elements have the characteristics of arc ultramafic basic magma （such as lack of high field intensity elements Nb, Ta, Ti, Hf , Y and P, enrichment of large ion lithophile elements Ba, Rb, Th, U, K and La）; （3） Magnetic anomaly and rock surface mineralization are uniform. The results of electric conductivity show that the mineralization in deep rock is better.（the maximum value of the magnetic field strength 600nT, apparent polarizability （ηs） shows a maximum value of 7.5%-12.1%）; （4） the geochemical characteristics are similar to those of Jinchuan, Kalatongke, Hongqiling deposit, and the Heishan deposit in Gansu Provice. Therefore, Dashantou is expected to become the Cu-Ni sulfide deposit with reserve scale not less than that of the Heishan deposit.