二连盆地赛汉塔拉凹陷宝拉格地区赛汉组层序地层与砂岩型铀成矿关系

Relationship Between Sequence Stratigraphy of Saihan Formation and Sandstone Type Uranium Mineralization in Baolage Area,Saihantala Sag,Erlian Basin

赛汉塔拉凹陷是二连盆地主要的油-煤-铀富集凹陷之一,近年来在凹陷北东部宝拉格地区落实了一处砂岩型铀矿产地。文章应用层序地层学基本理论,以典型钻孔为例对宝拉格地区含矿建造赛汉组进行了沉积旋回划分和剖面对比,并结合地震资料,在下白垩统赛汉组中识别出3个层序界面,以此将赛汉组划分为1个长期旋回、4个中期旋回,建立了研究区下白垩统赛汉组层序地层格架。通过层序内部沉积体系、砂体、氧化带及铀矿化特征研究,提出赛汉组下段扇三角洲砂体、赛汉组上段辫状河三角洲砂体在垂向上相互叠置,在平面上具有一定的连通性,砂岩渗透性好,富含有机质,有利于垂向的潜水氧化、侧向的潜水-层间氧化和层间氧化作用发育。潜水-层间氧化带发育在赛汉组上段下降体系域(FST)中,矿体主要赋存于辫状河三角洲平原-前缘(水下)分流河道砂体中,层间氧化带发育在赛汉组下段湖侵-高位体系域(TST-HST)中,矿体主要赋存于扇三角洲平原-前缘(水下)分流河道砂体中,具有较大的勘探潜力。

Saihantala sag is one of the main oil coal uranium enrichment sag in Erlian Basin.In recent years,a sandstone type uranium occurrence has been identified in Baolage area in the northeast of the sag.According to the theory of sequence stratigraphy,this paper selected some typical boreholes to study the sedimentary cycles of the Saihan Formation in Baolage area.Combined with seismic data,three sequence boundaries were identified in the Saihan Formation of Lower Cretaceous.And the Saihan Formation was divided into a long-term cycle and four medium-term cycles.By studying the sedimentary system,sand body,oxidation zone and uranium mineralization characteristics in the sequence,it was proposed that the fan delta sand body in the lower Saihan Formation and the braided river delta sand body in the upper Saihan Formation overlap each other in the vertical direction,but have certain connectivity in horizon,which caused the sandstone good in permeability and rich in organic matters,and conducive to the development of vertical phreatic oxidation and lateral interlayer oxidation.The phreatic interlayer oxidation zone was found developed in the descending system tract(FST)of the upper Saihan Formation,the ore bodies are mainly hosted in the braided river delta(underwater)distributary channel sand body formed under the low accommodation space.The interlayer oxidation zone was developed in the lake transgressive high stand system tract(TST-HST)of the lower Saihan Formation,and the ore bodies are mainly hosted in the fan delta(underwater)distributary channel sand body.Therefor,there is great exploration potential for sandstone uranium resources jn Baolage area.