鄂尔多斯盆地东北部砂岩型铀矿常量元素地球化学特征及地质意义

鄂尔多斯盆地东北部是我国砂岩型铀矿的重要矿集区,区内铀矿床的含矿主岩为中侏罗统直罗组砂岩。本文以该区含铀砂岩为对象,研究了紫红色砂岩、绿色砂岩、矿化砂岩、铀矿石及灰色砂岩中常量元素含量变化特征,分析了铀成矿过程中常量元素迁移规律,并讨论了成岩成矿背景。研究表明:在铀成矿过程中,SiO2、Al2O3表现为带出组分,CaO、MgO、K2O、Na2O及TFe2O3表现为带入组分,说明水-岩作用过程中常量元素具有明显的活动性。根据元素迁入迁出强度,将常量元素划分为活动组分(SiO2、Fe2O3、FeO、CaO)、次活动组分(Al2O3、MgO、K2O、Na2O)及惰性组分(TiO2、MnO、P2O5)三类。含铀砂岩构造环境主要为活动大陆边缘和大陆岛弧,鄂尔多斯盆地北侧阴山褶皱带中的花岗闪长岩可能是其主要的物质来源。不同类型砂岩样品的Fe2+/Fe3+值与铀元素含量具有一定的正相关性,铀矿化严格受灰绿色-灰色砂岩控制,主要发生在氧化-还原过渡环境偏还原一侧,部分灰绿色含矿砂岩具有弱氧化环境的特征,说明该区成矿环境的特殊性,灰绿色砂岩可作为区内重要的找矿标志。

Major elements geochemical characteristics of sandstone-type uranium deposit in north-east Ordos basin and its geological implactions

The north-east Ordos basin is an important sandstone-type uranium mineralization province in our country. Uranium depostis are mainly hosted in the sandstones of the Jurassic Zhiluo formation. The characteristics of the major elements contents and its migration patterns during the uranium mineralization process of the purple red sandstone, green sandstone, mineralization stone, uranium ore and the gray sandstone were studied in this article. And the diagenesis and mineralization setting was also discussed based on the characteristics of the relevant major elements. The study indicats that SiO2, Al2O3 are the migration out components and CaO, MgO, K2O, Na2O, TFe2O3 are the migration in components which showing obvious activities of the major elements during the water-rock process. These major elements can be divided into 3 parts as activity (SiO2、Fe2O3、FeO、CaO), sub-activity (Al2O3、MgO、K2O、Na2O) and non-activity (TiO2、MnO、P2O5) based on the density of migration in and out. The tectonic setting of the uranium sandstone is active continental margin and continental island arc. The granodiorite in the Yinshan fold belt of the north Ordos basin may be its main sourcematerial. There is a certain positive correlation between the ratio of Fe2+/Fe3+and the uranium content in different types of sandstone samples. Uranium mineralization is strictly controlled by sage green, gray sandstone and it mainly occurred in the partial reduction on one side of the redox transitional environment. Part of the sage green sandstone has the characteristics of weak oxidizing environment which indicats a special metallogenic environment of the study area. The sage green sandstone can be used as important prospecting mark in this area.