阿尔金西段卡尔恰尔—库木塔什超大型萤石矿带矿床地质、控矿花岗岩特征及找矿远景

Geological characteristics,associated granites and the prospecting potential of the super-large Kaerqiaer-Kumutashi fluorite mineralization belt in the West Altyn-Tagh Orogen,NW China

【研究目的】阿尔金西段近年来萤石找矿取得重大突破,新发现卡尔恰尔、库木塔什、小白河沟、布拉克北等矿床(点),已达超大型规模,初步形成西部重要的萤石大型资源基地。有关萤石成矿机制的研究非常薄弱,本文选择区内的典型矿床开展研究,以期揭示阿尔金西段超大型萤石成矿带矿床地质、控矿因素与找矿远景,深化矿床成因研究并指导区域找矿。【研究方法】本文在详尽野外调查的基础上,利用LA-ICP-MS锆石定年、岩石地球化学和Hf同位素分析,探讨成岩成矿时代、控矿碱长花岗岩成因及萤石成矿机制,总结区内控矿要素和找矿标志,通过地质、地球化学和遥感等数据进行成矿预测,分析区域找矿远景。【研究结果】研究发现,区内萤石成矿与碱长花岗岩密切相关,矿体明显受控于北东向及次级北东东、东西向断裂构造,赋矿地层主要为阿尔金岩群斜长片麻岩和大理岩,矿石类型主要有块状、脉状、角砾状矿石,矿物组成主要为萤石、方解石、少量石英及磷灰石,早期萤石呈白色,晚期萤石呈紫色,伴生含锂的带云母,属于岩浆热液充填型脉状萤石矿床。库木塔什萤石矿区控矿碱长花岗岩锆石U-Pb年龄为(450.0±2.7)Ma,εHf(t)为-5.33~+6.45,二阶段模式年龄(TDM2)为1020~1767 Ma,具有钾玄质、准铝质、高分异特点,具有富F、高ΣREE特征,明显富集大离子亲石元素Rb、Th、U、La、Ce、Nd、Zr、Hf等,强烈亏损Ta、Nb、Sr、P、Ti等,属于A型花岗岩,与奥陶纪造山后伸展背景下壳幔岩浆混合作用密切相关。【结论】区域广泛分布的高氟碱长花岗岩对于萤石-锡-稀有-稀土成矿十分有利。矿带萤石控矿要素主要为碱长花岗岩+北东向断裂及次级构造系+阿尔金岩群富钙地层,叠加“F化探异常+碳酸根离子异常”等重要找矿标志,成矿预测显示具有巨大的萤石找矿潜力,北东向与东西向构造系、碳酸根离子异常、F化探异常等套合区域具有较大找矿远景。

[Objective]Significant breakthroughs have recently been made in fluorite prospecting in the western part of the Altyn-Tagh Orogen in NW China.The newly discovered super-large mineralized belt,which includes the Kaerqiaer,Kumutashi,Xiaobaihegou and North Bulake deposits,is an important fluorite resource base.Research on the genesis of fluorite mineralization is lacking.This paper selects typical deposits in the area for research,to reveal the geological characteristics,ore-controlling factors and prospecting potentials of the super-large fluorite mineralization belt in the West Altyn-Tagh Orogen,thus increasing our knowledge of the genesis and improving regional prospecting for the mineralization.[Methods]Based on detailed field investigation,this paper uses LA-ICP-MS zircon dating,geochemistry and Hf isotope analysis to define:(1)The age of rock formation and mineralization;(2)The genesis of ore-controlling alkali-feldspar granite and fluorite mineralization;(3)Summarises the ore-controlling elements and prospecting characteristics of the area;(4)Conducts mineralisation prediction through geological,geochemical and remote sensing data;(5)Analyses the prospectivity of the region.[Results]The fluorite mineralization is of hydrothermal origin closely related to alkali feldspar granites,and is controlled largely by NE-trending faults and,to a lesser extent,NEE-and E-trending faults.The host rocks are plagioclase gneiss and carbonate rocks in Altyn Group.The main types of ore include massive,vein and breccia containing early white and later purple fluorite,calcite and minor amounts of quartz,apatite and tainiolite.The alkali feldspar granite at the Kumutashi fluorite deposit has a zircon U-Pb age of(450.0±2.7)Ma,εHf(t)values ranges from-5.33 to+6.45,and TDM2 age between 1767 Ma and 1020 Ma.The geochemical data also shows that the alkali feldspar granite is potassic,metaluminous,high differentiated and genetically related with F-rich rocks.The granite is enriched in Rb,Th,U,La,Ce,Nd,Zr and Hf,depleted in Ta,Nb,Sr,P,and Ti,and has a highΣREE content.These characteristics are indicative of A-type granites emplaced during the Late Ordovician and derived from a mixed crustal and mantle magma during post-orogenic extension.[Conclusions]The widely distributed alkali feldspar granite with high F andΣREE contents have high prospectivity for fluorite,tin,rare metals,and REE.Thus,the combination of alkali granites,NE-trending faults,and carbonates in the Altyn Group are consisted prospective for large fluorite deposits.