摘要:
北祁连造山带内的红川铜镍矿床是近年找矿的重要发现。为了查明该矿床的赋矿岩体形成时代、岩石成因和岩浆源区性质，对其开展了岩石学、岩石地球化学、锆石U-Pb同位素年代学和Hf同位素地球化学研究。红川铜镍矿床中赋矿岩体主要由橄榄岩相和角闪石岩相组成，橄榄岩相分布在岩体下部，是主要赋矿岩相。岩石地球化学特征显示，主量元素具有低SiO2（39.13~46.35%），高MgO（13.69~27.47%），高Mg#值（68.28~79.91），属亚碱性拉斑玄武岩系列。微量稀土元素蛛网图显示平坦型特征，富集Rb、Ba、Pb和K等元素，亏损Nb、Ta、P和Ti。对Ⅳ号赋矿岩体中的含斜长石橄榄岩进行了LA-ICP-MS锆石U-Pb同位素测年，获得锆石206Pb/238U加权平均年龄为486.9 ±5.9 Ma，锆石εHf(t)值介于-0.19~7.12之间，结合岩石地球化学数据和区域地质背景对比分析，该岩体形成于岛弧环境，岩浆源区为经历了俯冲板片流体交代作用的亏损地幔，岩浆侵位过程中经历了微弱的下地壳物质混染。
Abstract:
The Hongchuan Cu-Ni sulphide deposit within the North Qilian orogenic belt is an important discovery in recent years. In order to find out the age of intrusion, petrogenesis and nature of the source area of this deposit, petrology, geochemistry, zircon U-Pb isotope chronology and Hf isotope geochemistry studies have been carried out. The mineralized intrusions of Hongchuan Cu-Ni deposit mainly consists of peridotite and hornblende phases, and the peridotite phase is distributed in the lower part of the intrusion, which is the main mineralized rock phase. The geochemical characterization of the rocks shows that the major elements of the Hongchuan intrusion have low SiO2 (39.13-46.35%), high MgO (13.69-27.47%), high Mg# (68.28-79.91), and belong to the subalkaline series and the island arc zebra basalt series. The spider diagram of trace rare earth elements shows flat-type characteristics, enriched in Rb,Ba,Pb and K,and deficient in Nb,Ta,P and Ti.LA-ICP-MS zircon U-Pb isotope dating of plagioclase-bearing peridotite in the intrusion No. Ⅳ was carried out, and the weighted average age of zircon 206Pb/238U was obtained to be 486.9±5.9 Ma, the zircon εHf(t) values ranged between -0.19 and 7.12. Combined with the comparative analysis of the rock geochemical data and the regional geologic background, it is concluded that the intrusion was formed in an island arc environment, the source area of the magma is a lossy mantle that underwent subducted slab fluid accounting, and the magma intrusion process underwent weak mixing of lower crustal materials.
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