天山—阿尔泰东部地区海西晚期后碰撞铜镍硫化物矿床:主要特点及可能与地幔柱的关系

Late Variscan Post-collisional Cu—Ni Sulfide Deposits in East Tianshan and Altay in China:Principal Characteristics and Possible Relationship with Mantle Plume

天山-阿尔泰东部地区是中国重要的铜镍成矿区，近年来针对区内的铜镍矿床和相关岩体的研究不断取得进展，找矿也取得了一系列新突破，已经探明了十几个矿床和矿点。笔者基于以往研究成果，结合目前地质勘查和找矿评价的新进展，比较详细地全面总结了后碰撞铜镍硫化物矿床的基本特点、成矿规律和成矿过程，并建立了描述性成矿模型。这些矿床沿一组平行的走向近东西的深大断裂分布，与成矿有关的镁铁质超镁铁质杂岩体一般不大于5km^2，小的可为一个岩墙。矿化分两种类型：通道型和熔离型。成矿时代为298～270Ma，为中亚成矿带大规模成矿期的组成部分，形成于后碰撞伸展阶段。与这组铜镍硫化物矿床有关的镁铁质-超镁铁质杂岩体可能是早二叠世大面积喷溢岩浆的残留根部或通道部分，可能与地幔柱活动有关。另外，针对区内的地质特征，结合以往找矿的成功经验，对区内进一步的找矿工作提出了一些设想和建议。

In the past twenty years 18 Cu-Ni sulfide deposits and occurrences were discovered in the Chinese Tianshan and Altay orogenic belts in northern Xinjiang, China. There are several belts and ore districts along several parallel deep faults. The Kelatongke and several other Cu--Ni mineralized intrusions are located along the Etrix fault, which separates the Altay orogenic belt and Junggar Basin. The Huangshan, Huangshandong, Xiangshan, Tudun, Erhongwa, Tula＇ ergen and Hongling deposits distribute along the Kanggurtag suture, which separates the Qol Tag orogenic belt and Turpan--Hami Basin. The Baishiquan, Tianyu, and Tianxiang deposits are located along the Aqikkuduk fault, which separates the Qol Tag orogenic belt and Middle Tianshan Precambrian terrane. The Poyi, Poshi and Luodong deposits are located along the Hongliuhe fault, which separates the Middle Tianshan Precambrian terrane and the Baishan Variscan rift. Re-Os dating for Cu--Ni sulfide ores reveals that the various ore belts formed in a small age range of 298-282 Ma. This age range is almost identical to the ages of related intrusions and dikes dated by the SHRIMP U-Pb zircon method. Tectonic and geochronological studies explain that the amalgamation of continental blocks mainly occurred during the Late Carboniferous in the Central Asian Orogenic Belt. Large-scale metallogenesis in this region was developed during post-collisional tectonism in the latest Carboniferous to Early Permian. The Cu--Ni sulfide deposits are one component of this large-scale metallogenesis. The Cu--Ni sulfide deposits in northern Xinjiang can be divided into： （1） magma conduit type and （2） differentiated sill type. Some mafic-ultramafic systems exhibit lithological zoning caused by strong differentiation. Stratiform ore bodies are hosted by ultramafic rocks at the base of the magma chamber. Good examples are provided by the Kelatongke, Huangshandong and Poshi deposits. Others, such as the Xiangshan, Baishiquan, Tianyu, and Tula＇ergen deposits, are hosted by magma conduits consisting of peridotite, troctolite, and pyroxenite. These ultramafic rocks either occur within faults or are surrounded by slightly younger diorite intrusions. These two types of orthomagmatic Cu--Ni sulfide deposits are also distributed along the same ore belts. For instance, the differentiated sill-related Huangshandong coexists with the magma conduit type of the Tula＇ergen deposit in the Qol Tag orogenic belt. Orthomagmatic Cu--Ni sulfide deposits in northern Xinjiang were formed during post-collisional extensional tectonism and possibly related to a Late Carboniferous--Early Permian mantle plume event. The mafic-- ultramafic systems and associated Cu--Ni deposits are commonly accompanied by dike swarms and are characterized by elongated outcrops developed along several parallel regional faults. These mafic--ultramafic systems and accompanying dikes are generally fractionated, hinting that they were feeders of now eroded flood basalts.