新疆阿尔泰造山带中伟晶岩型稀有金属矿床成矿 规律、找矿模型及其找矿方向

文章对阿尔泰造山带中的主要伟晶岩类型、时空分布特征、形成物源以及稀有金属矿化类型、形成条件(包括温度、压力、侵位深度)、可能控制因素等进行了归纳和总结,进而提出了阿尔泰伟晶岩成因模式、稀有金属矿化机制、伟晶岩型稀有金属矿床找矿模型及其找矿方向。阿尔泰稀有金属伟晶岩显示2个期次(同造山和后造山)和4个阶段(泥盆纪—早石炭世、二叠纪、三叠纪、早侏罗世)的成岩成矿特征。其中,以后造山阶段的三叠纪伟晶岩成岩及其Be、Li成矿作用最为显著。不同期次和阶段的伟晶岩显示规律的时空分布特征,稀有金属伟晶岩的成岩成矿明显受"构造-变质-物源-岩浆"的控制,而伟晶岩与周边花岗岩存在时代或物源上的解耦,表明阿尔泰伟晶岩不是由花岗质岩浆分异演化晚期的残余岩浆固结形成,由此提出阿尔泰不同时代伟晶岩的成因模式,即造山过程中加厚的不成熟地壳物质在伸展减压背景下发生小比例部分熔融(深熔)形成独立伟晶岩。通过对形成伟晶岩初始岩浆中磷含量、伟晶岩分异演化程度的评价以及基于围岩蚀变过程中全岩及蚀变矿物电气石中稀有金属Li、Rb、Cs含量特征,建立了阿尔泰伟晶岩型稀有金属矿床找矿模型、地质-地球化学找矿指标体系,并提出不同尺度的找矿方向。

Metallogeny and prospecting model as well as prospecting direction of pegma-tite-type rare metal ore deposits in Altay orogenic belt, Xinjiang

The dominant type, temporal-spatial distribution and source of pegmatites as well as the mineralization type, formation conditions (temperature, pressure and emplacement depth) and potential controlling factors of the rare metal ore deposits in the Altay orogenic belt are summarized in this paper, and the petrogenesis model of pegmatites, mineralization mechanism of rare metals, and prospecting model as well as prospecting direction for rare metal ore deposits in China''s Altay are further proposed. Rare metal pegmatites show two stages (syn-and postorogeny) and four generations (Devonian-Early Carboniferous, Permian, Triassic and Early Jurassic) of petrogenesis and metallogenesis, with peak age and Be-Li mineralization in Triassic. Different generations of pegmatites show evident temporal-spatial distributions, and the petrogenesis and metallogenesis of rare metal pegmatites are significantly controlled by "tectonism-metamorphism-source-magma". The decoupling in temporal or source between pegmatites and neighboring granites indicate that pegmatites in China''s Altay were not derived from differentiated granitic melts. The authors therefore propose the petrogenesis model of pegmatites, i.e., low percentage partial melting of the thickened immature crust (anatexis) gave rise to the formation of isolated pegmatites in China''s Altay. Finally, the models, geological-geochemical indicators and the prospecting direction of rare metal ore deposits are built and proposed based on the phosphorus content in the initial pegmatite-forming melts, the differentiation degrees of pegmatites and the content of Li, Rb and Cs in the altered wall rocks and tourmaline minerals.