鄂尔多斯盆地西南缘镇原地区洛河组沉积环境对铀成矿的制约

The Constraints of the Depositional Environment of the Luohe Formation on Uranium Mineralization in the Zhenyuan Area of the Southwestern Ordos Basin

含铀岩系沉积环境制约着铀储层的空间分布以及铀成矿作用,其在铀成矿潜力评价中具有重要的意义。鄂尔多斯西南缘洛河组含铀岩系沉积环境存在争议,其与铀成矿的关系不明确,制约了区域铀成矿规律的认识。笔者通过碎屑组分分析、粒度分析等方法,对鄂尔多斯盆地西南缘上白垩统洛河组含铀岩系进行了沉积环境分析。研究发现洛河组含铀岩系铀储层主要为红色、灰色、灰绿色细–粗砂岩,碎屑成分主要由石英、长石、岩屑组成,砂岩主要为岩屑石英砂岩和长石石英砂岩。砂岩粒度平均值(Mz)的均值为2.01。标准偏差(σ)平均值为0.49,表明分选好。偏度(Sk)平均值为0.11,表明洛河组沉积以较粗物质为主,且留有一个细物质的尾部。峰度(Kg)平均值为1.05,峰度变化幅度不大。频率曲线显示较好的正态分布特征,频率直方图多呈单峰式,概率值累积曲线为高斜率一段跳跃式、一跳一悬两段式和一滚一跳一悬三段式。综合分析认为,研究区上白垩统洛河组含铀岩系沉积环境为风成沉积体系,其中包括风成砂丘、丘间沉积、河道沉积和浅湖沉积等成因相,成因相的岩性组合、粒度特征有其各自特征。研究区上白垩统洛河组含铀岩系中的河流沉积和小型湖泊沉积制约着铀成矿作用,风成–水成相互作用,形成了富含有机质、发育有较为稳定“泥–砂–泥”结构的铀储层,这为后期大规模的铀成矿作用提供了前提条件。因此,盆地边缘的风成–水成交互沉积作用区域为有利的砂岩型铀成矿区域。

The sedimentary environment of uranium bearing rock series restricts the spatial distribution of uranium reservoirs and uranium mineralization,which is of great significance in the evaluation of uranium mineralization potential.There is controversy over the sedimentary environment of the Luohe Formation uranium bearing rock series in the southwestern edge of Ordos,and its relationship with uranium mineralization is unclear,which restricts the understanding of regional uranium mineralization laws.This article analyzes the sedimentary environment of the Upper Cretaceous Luohe Formation uranium bearing rock series in the southwestern edge of the Ordos Basin through methods such as debris composition analysis and particle size analysis.Research has found that the uranium bearing rock series in the Luohe Formation are mainly composed of red,gray,and grayish green fine coarse sandstone,with detrital components mainly composed of quartz,feldspar,and rock debris.The sandstone is mainly composed of rock debris quartz sandstone and feldspar quartz sandstone.The average particle size(Mz)of sandstone is 2.01.The average value of standard deviation(σ)is 0.49,indicating good sorting.The average skewness(Sk)value is 0.11,indicating that the sedimentation of the Luohe Formation is mainly composed of coarse material,with a tail of fine material remaining.The average kurtosis(Kg)is 1.05,and the change in kurtosis is not significant.The frequency curve shows good normal distribution characteristics,and the frequency histogram mostly shows a unimodal pattern.The probability value accumulation curve is a high slope one segment jump,one jump one suspension two segment,and one roll one jump one suspension three segment.Based on comprehensive analysis,it is believed that the sedimentary environment of the Upper Cretaceous Luohe Formation uranium bearing rock series in the study area is an aeolian sedimentary system,including aeolian sand dunes,inter hill sediments,channel sediments,and shallow lake sediments.The lithological combination and particle size characteristics of the genetic facies have their own characteristics.The river sediments and small lake sediments in the Upper Cretaceous Luohe Formation uranium bearing rock series in the research area constrain uranium mineralization,and the interaction between wind and water forms uranium reservoirs rich in organic matter with a relatively stable"mud sand mud"structure,which provides a prerequisite for large-scale uranium mineralization in the later stage.Therefore,the area of wind water interaction sedimentation at the edge of the basin is a favorable area for sandstone type uranium mineralization.