贵州西部晚二叠世富稀土岩系沉积相分析

Analysis of sedimentary facies of the Late Permian REE-rich rock series in the western Guizhou

贵州西部晚二叠世玄武岩顶部新发现的“古陆相沉积型”稀土资源具有富矿岩系分布广泛,连续性好的特点,其厚度在2~16 m之间,平均品位为0.12%~0.15%,最高可达1.60%。作为一种全新的稀土矿床类型,相关研究较为薄弱,含矿的岩性组合和沉积相带尚未明确,阻碍了成矿理论的研究和该地区的找矿预测。本文在收集大量基础地质资料与前人研究成果的基础上,结合野外调查与微量元素测试结果,对该套富稀土岩系开展了沉积相分析。研究表明,贵州西部玄武岩顶部富稀土岩系从下往上由3个岩性段组成,即铁质岩段、铝质岩段和宣威组底部的碎屑岩段。其中,铁质岩段为残积平原相、铝质岩段为湖泊相、宣威组底部的碎屑岩段为河流-三角洲平原相。由此提出富矿铝质岩段为“隆凹相间”的古地形地貌控制下的湖泊相沉积,并识别出了铝质岩段沉积期贵州西部由西往东分别为湖泊-隆起-湖泊-潮坪的沉积格局,从而建立了峨眉山玄武岩经风化剥蚀基底形成-湿热气候湖泊沉积-河流发育3阶段稀土岩系沉积模式。

The newly discovered"paleocontinental sedimentary type"rare earth elements(REE)resources in the REE-rich rocks are widely and continuously distributed on the top of Late Permian basalt in the western Guizhou,with thicknesses of 2-16m,average REO grades of 0.12%-0.15%,and the highest REO grade of 1.60%.As a new type of the REE deposit,it has been relative poorly researched,and its ore-bearing lithologic association and sedimentary facies belts are not clear.These shortcomings hinder the theoretical study and ore-prospecting prediction of the REE resources in this area.On the basis of collecting a lot of basic geological data and previous research results,combined with field investigation and trace elements test results,we have carried out the analysis of sedimentary facies of the REE-rich rock series in this paper.The study shows that the REE-rich rock series on the top of basalt in the western Guizhou is composed of three lithologic segments from bottom to top,namely,the ferruginous rock segment,the aluminous rock segment and the clastic rock segment at the bottom of the Xuanwei Formation.Especially,the ferruginous,aluminous,and clastic rocks belong to the eluvial plain,the lacustrine,and the river-delta plain facies,respectively.Therefore,we have proposed that the REE ore-rich aluminous rock is of the lacustrine facies sedimented under the control of paleotopography and landform,then have identified that the sedimentary patterns of the aluminous rock in the western Guizhou from west to east are the lake,uplift,lake,tidal flat facies,respectively,and finally have estabblished a model of the three-stage sedimentary facies of the REE-rich rock series from the base one formed by the weathering and denudation of the Emeishan basalt,to the middle one formed by the lake sedimentation in hot and humid climate,to the top one formed by the river sedimentation.