花岗伟晶岩分异演化与含矿性评价——从造岩矿物组构视角  

Indication of magma evolution and ore-bearing potential on granitic pegmatite in the view of texture-composition of rock-forming minerals

作　　者：秦克章[1,2] 刘宇超 赵俊兴 赵永能[1,2] 周起凤 施睿哲 朱丽群 何畅通 李俊瑜 曹明坚 QIN Kezhang;LIU Yuchao;ZHAO Junxing;ZHAO Yongneng;ZHOU Qifeng;SHI Ruizhe;ZHU Liqun;HE Changtong;LI Junyu;CAO Mingjian(Key Laboratory of Mineral Resources,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China;Institute of Mineral Resources Research,China Metallurgical Geology Bureau,Beijing 101300,China)

机构地区：[1]中国科学院矿产资源研究重点实验室,中国科学院地质与地球物理研究所,北京100029 [2]中国科学院大学地球与行星科学学院,北京100049 [3]中国冶金地质总局矿产资源研究院,北京101300

出　　处：《地质学报》2024年第5期1527-1549,共23页Acta Geologica Sinica

基　　金：第二次青藏高原科学考察任务八之综合和稀有专题(编号2019QZKK0806、2019QZK0802);国家重点研发计划青年科学家项目(编号2023YFC2908400)联合资助的成果。

摘　　要：高演化稀有金属伟晶岩的成矿过程是复杂和苛刻的,涉及到岩浆-热液过程热历史、岩浆迁移路径与成矿空间、侵位环境的过冷程度以及岩浆组分中稀有金属元素的初始富集等条件。而伟晶岩的分带特征是其形成过程的一种综合体现,不论是伟晶岩区域分带还是伟晶岩内部结构分带,都反映了伟晶岩岩浆结晶分异过程中岩浆的性质与形成环境,而这同时也赋予了造岩矿物在组构上的特殊性,形成遗传代码,对其进行解密,从而能够用于示踪与评估花岗伟晶岩的演化程度与成矿潜力。对于区域伟晶岩群的成矿潜力评估,由于含矿熔体在组分上的跨度较大,随着远离母体花岗岩体距离的增大,伟晶岩群演化程度增加,熔体中铁镁质组分以及Ca、Ba、Sr等碱土金属含量迅速降低,而挥发分、助熔剂组分、碱金属含量在残余熔体中逐渐增加,长石、云母与石英在类别和组构上产生显著变化;其中长石向钾-钠端元演化,且钠长石相对钾长石占据主导地位,云母由黑云母向白云母以及锂白云母转变,石英阴极发光特征与晶体结构及微量元素成分也表现出规律性的变化。受矿物晶格的限制,长石的K/Rb、K/Cs以及云母的K/Rb、K/Cs、Nb/Ta等比值特征能有效区分不同矿化潜力的伟晶岩群。石英的阴极发光特征能够揭示其生长环境与历史,石英的Li、Al、Ti、Ge等微量元素组成可以用来区分不同类型的伟晶岩矿床,并提供关于岩浆演化和成矿过程的重要线索。伟晶岩内部分带的形成主要受成矿熔体规模、过冷度以及成矿空间的封闭性等因素的控制,但在初始熔体成分上可以具有较大的变化。其中强分带型稀有金属伟晶岩记录了完整的岩浆-热液演化过程,不同阶段石英、长石和云母在晶体形态、微观结构以及微量元素组成上都具有显著变化。弱分带型稀有金属伟晶岩(钠长石-锂辉石伟晶岩)�The genesis of highly evolved rare-metal pegmatites,characterized by extreme element fractionation,is a complex and demanding process influenced by a multifaceted array of geological factors.These include the thermal history of magmatic-hydrothermal systems,magma migration paths,the availability of oreforming spaces,the degree of undercooling during emplacement,and the initial enrichment of rare-metal elements within the parental magma.The distinctive zoning patterns observed within pegmatite,both at the regional scale of pegmatite groups and at the internal structural level within individual pegmatite vein,provide valuable insights into the dynamic evolution of magmatic environments during the crystallization and differentiation processes.These zoning patterns manifest as unique characteristics in the rock-forming minerals,thereby establishing a genetic code that can be deciphered to trace and assess the magma evolution and ore-forming potential and evolutionary history of granitic pegmatites.In the assessment of the ore-forming potential of regional pegmatite groups,the evolution of pegmatite groups and the potential for mineralization are influenced by the wide compositional range of ore-bearing melts.As the distance from the parent granite body increases and the pegmatite group undergoes further evolution,the content of iron-magnesium components and alkali-earth metals,such as Ca,Ba,and Sr,rapidly decreases in the melt.In contrast,volatile components,solvents,and alkali metal content gradually increase in the residual melt.This compositional evolution leads to significant changes in the categories and composition of feldspars,micas,and quartz.Feldspar evolves towards the potassium-sodium end-member,with albite dominating over K-feldspar.Micas undergo a transition from biotite to muscovite and lithium muscovite.Meanwhile,quartz exhibits systematic variations in cathodoluminescence characteristics,crystal structure,and trace element composition.Certain element ratios,such as K/Rb and K/Cs in feldspar,and K/Rb,K

关 键 词：花岗伟晶岩 造岩矿物长石-石英-云母 组构特征 岩浆分异演化 含矿性评价 

分 类 号：P618.6[天文地球—矿床学] P588.131[天文地球—地质学]