巴音戈壁盆地砂岩型铀矿找矿新发现与意义

砂岩型铀矿是全球最重要的铀矿类型之一，一般以表生流体的氧化还原成矿作用为主。虽然在勘查中发现部分砂岩型铀矿中存在热液流体活动的痕迹，但热液流体与铀成矿之间的关系仍不明确。本研究以巴音戈壁盆地下白垩统巴音戈壁组下段底部砂质砾岩中新发现的铀矿化为研究对象，通过镜下鉴定、电子探针(EPMA)、铀含量、铀价态和微量元素分析等手段，研究了铀矿石的岩石学、矿物学和地球化学特征。结果显示，铀矿化产出于巴音戈壁组下段的紫红色砂岩中，与不整合界面及次级断层有关；铀呈分散状态分布在胶磷矿中，并伴生有方铅矿、闪锌矿等金属硫化物；微量元素分析显示矿石中Sr、Y、Mo、W和REE等显著富集，指示其形成与深部流体密切相关。研究认为，苏红图组玄武岩喷发形成的火山热液在上升过程中与地表大气降水混合形成弱酸性氧化流体，流体沿不整合和断层向上运移并不断萃取地层中的U和P,当其遇到上覆巴音戈壁组砂砾岩中的菱铁矿等还原物质时，形成酸碱度和氧化还原接触界面，进而诱发铀、磷的沉淀。本次在新层位发现的铀矿化拓宽了巴音戈壁盆地铀矿勘查的找矿空间和方向。

New discovery and significance of sandstone type uranium deposit prospecting in the Bayingebi basin

Sandstone type uranium deposit is one of the most important type of uranium mineralization in the world, which is generally dominated by redox mineralization of supergene fluids. Although traces of hydrothermal fluid activity were found in some sandstone type uranium deposits, the relationship between the hydrothermal fluids and uranium mineralization is still unclear. In this study, the newly discovered uranium mineralization in the sandy conglomerate of the lower Bayingebi Formation of Lower Cretaceous in the Bayingebi basin is selected as the research object. The petrology, mineralogy and geochemistry of uranium ore were studied by means of microscopic identification, electron microprobe (EPMA), uranium content, uranium valence and trace element analysis.The results show that uranium mineralization occurs in the purplish red sandstone in the lower Bayingebi Formation, which is related to unconformity interface and secondary faults. Uranium is dispersed in collophanite and associated with metal sulfides such as galena and sphalerite. The Sr, Y, Mo, W and REE are significantly enriched in the ore. All these indicate that the formation of ore is closely related to deep fluids.Our research shows that the volcanic hydrothermal solution formed by the eruption of the Suhongtu Formation basalt mixes with the surface atmospheric precipitation to form a weak acidic oxidizing fluid during the rising process. The fluid moves upward along the unconformity and fault and continuously extracts U and P from the surrounding rocks. When it meets the reducing substances such as siderite in the overlying Bayingobi Formation glutenite, it forms the acid- alkali and redox contact interface, which then induces the precipitation of uranium and phosphorus.The uranium mineralization found in the new horizon widens the prospecting space and direction of uranium exploration in Bayingebi basin.