潮水盆地砂岩型铀矿地质特征及找矿方向探讨

Discussion on geological characteristics and prospecting direction of sandstone-type uranium deposits in Chaoshui basin

潮水盆地是我国北方发育砂岩型铀矿的中新生代盆地之一,地处华北板块阿拉善地块之上。总结了盆地目的层岩性-岩相、砂体、后生氧化及典型矿点特征,分析了控矿因素,并指出了盆地下一步找矿方向。认为下白垩统庙沟群和中侏罗统青土井组是潮水盆地主要产铀层位,也是找矿目的层位,发育扇三角洲、辫状河有利相带,砂体规模较大,具备形成砂岩型铀矿的岩性-岩相及砂体等有利条件,U与∑S、Corg及Fe3+/Fe2+等地球化学环境参数关系密切,后生改造作用对铀的叠加富集成矿非常有利,目的层形成之后发生了多期抬升掀斜改造作用,在潜水氧化带底部和层间氧化带前锋线附近形成砂岩型铀矿化。通过综合分析,指出下白垩统庙沟群杂色层的找矿方向为长期隆升的富铀花岗岩体周缘、红色建造中富含炭屑的灰色层扇三角洲相砂体及潜水氧化叠加部位,以寻找沉积成岩叠加潜水氧化带型铀矿为主;中侏罗统青土井组的找矿方向为宽缓的构造斜坡带、富铀花岗岩体、含煤的辫状河相灰色砂体及层间氧化后生改造部位,以寻找层间氧化带型铀矿为主。

s:Chaoshui basin is one of the Mesozoic-Cenozoic basins where sandstone-type uranium mineralization are developed in northern China.It is located in the Alashan block of the North China plate.The characteristics of lithology-lithofacies,sand bodies epigenetic oxidation and typical occurrences in the target layer are summarized and the prospecting direction of the basin is proposed.The Lower Cretaceous Miaogou group and the Middle Jurassic Qingtujing formation were regared as the main uranium-producing horizons in Chaoshui basin and also the target horizons for prospecting.The target horizons developed fan delta and braided river facies,and the sand bodies are large,and has favorable conditions such as litholoy-lithofacies and sand bodies for the formation of sandstone-tyoe uranium deposits.Uranium is closely related to geochemical environmental parameters such as∑S,Corg and valence iron.The epigenetic transformation is very favorable for the superposition and enrichment of uranium mineralization.After the formation of the target horizon,multi-stage uplift and tilt transformation occurred,and sandstone-type uranium mineralization was formed near the bottom of the phreatic oxidation zone and the front line of the interlayer oxidation zone.Through comprehensive analysis,it was pointed out that the prospecting direction of the Lower Cretaceous Miaogou group variegated layer is of relatively stable and moderately uplifted monoclinic structure,long-term uplifted uranium-rich granite body periphery,carbon-rich gray layer in the red formation.Fan delta facies sand body and phreatic oxidation superposition site,and the prospecting type is sedimentary diagenetic superimposed phreatic oxidation zone type uranium deposits;The prospecting direction of the Middle Jurassic Qingtujing formation is the wide and gentle structural slope zone,uranium-rich geological body,coal-bearing braided river facies gray sand body and interlayer oxidation epigenetic transformation site,mainly to find interlayer oxidation zone type uranium deposits.