渤海湾盆地大港探区明化镇组多级别层序格架及砂岩型铀成矿条件

Sequence stratigraphic frameworks in different scales and sandstone-type uranium ore-formation of Minghuazhen Formation in Dagang area, Bohai Bay Basin

渤海湾盆地位于世界两大砂岩型铀矿成矿带之一的欧亚成矿带内,具有砂岩型铀成矿的潜力。大港探区测井结果显示明化镇组发育着大范围的高伽马异常,为探究其铀成矿条件并指明找矿方向,建立了大港探区明化镇组多级别层序格架,并开展了层序内沉积微相研究,对氧化还原带进行了划分。研究表明,依据测井曲线特征和岩石性质,将明化镇组划分为五级层序,铀异常主要见于明化镇组下段上亚段和上段下亚段2个五级层序内。其沉积微相主要发育曲流河河道、边滩、溢岸沉积和泛滥平原4种,其中铀异常主要发育于边滩、河道砂体。2个层序内的氧化还原带可划分出氧化带、过渡带和还原带,其中铀异常主要位于过渡带内。叠合沉积微相、氧化还原带展布、铀异常展布和油气分布等特征,认为油气富集带附近的过渡带中,边滩和河道微相砂体中均具有良好的铀成矿条件。综合分析认为,港东港西地区西7-14-2、西1603、港3-6-20和港8-15-1井区是大港探区砂岩型铀矿的有利找矿位置,研究结果为渤海湾盆地砂岩型铀矿勘探提供了启示意义。

[Objective]The Bohai Bay Basin,situated within the Eurasian metallogenic belt,is one of the world′s two largest belts for sandstone-type uranium deposits,exhibiting significant potential for uranium mineralization.Well logging data indicate the development of extensive high gamma-ray anomalies within the Minghuazhen Formation in the Dagang area.[Methods]To investigate uranium ore formation and guide exploration efforts,a multiscale sequence stratigraphic framework of the Minghuazhen Formation was established,including a detailed study of sedimentary microfacies and the delineation of redox zones.[Results]The Minghuazhen Formation was subdivided into five sequences based on variations in log responses and lithological characteristics.Gamma-ray anomalies predominantly occur in the upper part of the lower member(SPN xs m)and the lower part of the upper member(SPN sx m)of the Minghuazhen Formation.Four sedimentary microfacies were identified:meandering river channel,levee,overbank,and floodplain.Uranium anomalies are primarily associated with the levee and channel sand bodies.The redox zones in these sections were classified into oxidation,transition,and reduction zones,with uranium anomalies mainly occurring in the transition zone.[Conclusion]The integration of sedimentary facies,redox zone distribution,uranium anomaly distribution,and oil and gas distribution suggests that the most favorable conditions for uranium mineralization are present in the levee and river channel microfacies within the transition zone near oil-gas enrichment areas.Consequently,the X7-14-2,X1603,G3-6-20,and G8-15-1 well areas are identified as the most prospective targets for sandstone-type uranium deposits in the Dagang area.This study provides valuable insights for the exploration of sandstone-type uranium deposits in the Bohai Bay Basin.