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坡北岩体位于塔里木板块东北部,由5个阶段的岩浆作用形成,其中,第二阶段岩浆作用形成的侵入体岩石类型单一,主要为橄榄辉长苏长岩,局部有零星的辉长苏长岩和斜长岩。岩石的SiO_2—FeO/MgO图解显示其化学组成为钙碱性系列,但单斜辉石的Al_2O_3—SiO_2及n(Si)—n(Al~Ⅳ)图解表明母岩浆为拉斑玄武质岩浆。岩浆演化方向与岩石化学系列的转化是同化混染作用的结果,侵入体遭受了长城系古硐井岩群1.38%～3.15%的混染。原生岩浆为MgO含量约7.31%的玄武质岩浆。岩石的TiO_2、Na_2O、K_2O、稀土元素、大离子亲石元素丰度均很低;除一件样品外,其余岩石的ε_(Nd)(t)值为+2.54～+2.81,这些特征表明岩浆源区属亏损型大陆岩石圈地幔。岩浆在结晶过程中处于物理化学条件相对稳定的近平衡状态,局部不平衡分离结晶形成堆晶结构和纹层状构造,岩浆结晶温度约为1070℃。由于岩浆源区熔融程度低,导致原生岩浆贫硫,且岩浆在演化过程中没有经历充分的分离结晶作用,这些因素使得橄榄辉长苏长岩侵入体不具备硫达到过饱和进而发生铜镍硫化物熔离成矿的潜力。
The Pauobei pluton is located in the northeastern part of the Tarim plate and is formed by five stages of magmatism. In the second stage, the intrusive rocks formed by the magmatic activity are of a single type, mainly olivine-long magmatic rocks, sporadic subducted magnesia and oblique Long rock. The SiO_2-FeO / MgO diagram shows that the chemical composition of the rock is calc-alkaline. However, the diagrams of Al_2O_3-SiO_2 and n (Si) -n (Al_IV) of clinopyroxene show that the parent magma is tholeiitic basaltic magma. The evolution direction of magmatic rocks and the conversion of petrochemical series are the result of assimilation and contamination, and the invaders suffer from 1.38% -3.15% contamination of the ancient cave system in the Great Wall. Primary magma is basaltic magma with a MgO content of about 7.31%. The abundances of TiO_2, Na_2O, K_2O, rare earth elements and large ion lithophile rocks are very low. The ε_ (Nd) (t) values of the remaining rocks are + 2.54 ~ + 2.81 except for one sample, indicating that the magma The source area is a depleted continental lithosphere mantle. During the crystallization process, the magma is in a nearly equilibrium condition with relatively stable physicochemical conditions. The local imbalance separates and crystallizes to form a stacked crystal structure and a lamellar structure, and the crystallization temperature of the magma is about 1070 ° C. Due to the low degree of melting in the magma source zone, the primary magma is depleted in sulfur, and the magma did not undergo sufficient separation and crystallization in the evolutionary process. These factors make the Oligocene somatic intrusions not supersaturated with sulfur to produce copper-nickel sulfide melts Potential of mineralization.