东天山三宫铜镍矿化岩体年代学、岩石地球化学特征及对Cu-Ni找矿的启示

三宫岩体是近几年新发现的铜镍矿化镁铁-超镁铁岩体,位于哈尔里克山东段。岩石类型主要为辉长岩、斜长辉石岩和含长橄榄辉石岩,局部有零星铜镍矿化。锆石U-Pb谐和年龄为(281.7±2.6)Ma,表明岩体形成于早二叠世。样品MgO与FeO~T呈正相关关系,与CaO、SiO_2和Al_2O_3之间呈负相关关系,岩体主量元素成分主要受橄榄石和单斜辉石含量的控制;样品明显富集轻稀土元素(La/Yb)N=5.02~7.04,重稀土元素之间具有明显的分馏(Gd/Yb)N=2.36~2.87,δEu为0.98~1.09多具弱的正铕异常,富集大离子亲石元素(Cs、Sr、Ba),相对亏损高场强元素,具明显的Nb、Ta、Ti负异常。Sr-Nd同位素模拟计算表明母岩浆上升过程中遭受了约10%的下地壳物质混染。岩浆源区遭受了明显的熔体交代作用,部分熔融主要发生在石榴子石稳定域。综合区域构造演化历史认为三宫岩体形成于后碰撞伸展环境,该岩体的发现初步表明哈尔里克地区也具有寻找早二叠世铜镍矿的潜力。

Chronological and Geochemical Characteristics of Sangong Cu-Ni Mineralization Intrusion in Eastern Tianshan of Xinjiang and Their Implications for Cu-Ni Mineralization

The Sangong Ni-Cu mineralization intrusion is a newly-discovered intrusion located in the eastern section of Harlik Mountain, Eastern Tianshan Mountains. The intrusion was emplaced in biotite granite and granodiorite and mainly consists of gabbro, plagioclase pyroxenite and plagioclase-bearing olivine pyroxenite. Zircon LA-ICP-MS U-Pb age of plagioclase-bearing olivine pyroxenite is (281.7±2.6) Ma, indicating that the mafic intrusion was formed in the Early Permian. The values of MgO and FeOT show positive correlation, and there is a negative relationship between MgO and SiO2, CaO, Al2O3, implying that the major element compositions are mainly controlled by the abundances of olivine and pyroxenes. The chondrite-normalized REE patterns show significant enrichment of light REE relative to heavy REE ((La/Yb)N=5.02~7.04). Most of the mafic rocks are characterized by positive Eu anomalies. The rocks are enriched in LILE (Cs, Sr, Ba) and depleted in HFSE (Nb, Ta, Ti). Sr-Nd isotopic simulation indicates that the parental magma of the rocks experienced about 10% contamination of lower crust material. The magma source was replaced by melt fluid, and partial melting mainly occurred in the granet stability field. The chronological and geochemical characteristics, together with regional evolution history of Harlik Mountain, indicate that the Sangong Cu-Ni mineralization intrusion might be the product of post-collision extension. The Harlik area may have a huge potential for Cu-Ni ore exploration.