松辽盆地铁法地区砂岩型铀矿关键控矿因素的时空耦合

Spatial-Temporal Coupling of Key Ore-Controlling Factors for Sandstone-Type Uranium Deposits in Tiefa Area,Songliao Basin

松辽盆地东南部的铁法地区白垩系新发现一处铀矿产地和多个铀矿化点.本文结合区域地质背景调查和1000余个钻孔资料分析,由源到汇对研究区铀成矿系统的铀储层砂体、层间氧化带及还原介质等关键控矿因素进行了定量化系统研究.研究表明铁法地区铀成矿作用主要经历了沉积阶段的预富集期和层间氧化阶段主成矿期两个重要阶段.区域构造驱动下的盆山耦合作用不仅控制着铀源的形成与迁移,也是两个成矿阶段之间构造反转作用的驱动力.研究区铀矿化分布规律与铀储层砂体非均质性、氧化砂体规模、还原介质等控矿因素具有明显的空间耦合关系.泉头组三段(泉三段)含铀岩系的“泥‒砂‒泥”结构完整,铀矿化线索明显,是该区砂岩型铀矿成矿最有利层位,其次是研究区西部阜新组底部的砂砾岩.泉三段铀储层砂体由厚变薄,含砂率由高变低,氧化砂体厚度与氧化砂体比率变小,以及灰色泥岩和煤层等外部还原地质体由薄变厚的部位是该区砂岩型铀矿成矿最有利区域.

A new uranium deposit and many uranium mineralization spots have been discovered in the Cretaceous strata of the Tiefa area in the southeastern Songliao basin.Based on the regional geological background investigation and the analysis of more than 1 ooo drilling data,the author conducts a quantitative and systematic study on the key ore-controlling factors,such as uranium reservoir,interlayer oxidation zone and reducing medium in the uranium metallogenic system from source to sink in the study area.The sandstone-type uranium deposits in the study area have experienced two important stages:the pre-enrichment stage in the depositional stage and the main metallogenic stage in the interlayer oxidation stage.The basin-mountain coupling driven by regional tectonic evolution not only controls the formation and migration of uranium sources,but also drives the tectonic inversion between the two metallogenic stages.The distribution law of uranium mineralization in the study area has obvious spatial coupling relationship with ore control factors such as uranium reservoir heterogeneity,oxidized sand body size,and reducing medium,etc.The gray mudstone at the bottom of the 3rd member of Quantou Formation and the coal seam at the top of the Fuxin Formation restrict the scale of the interlayer oxidation zone and the distribution of uranium mineralization.The 3rd member of Quantou Formation has developed uranium reservoir sand bodies with a complete"mud-sand-mud"structure and obvious clues of uranium mineralization.It is the most favorable layer for sandstone-type uranium mineralization in this area,followed by the glutenite at the bottom of the Fuxin Formation in the western margin of the depression.The most favorable parts for sandstone-type uranium mineralization is in the west of the depression,where the sandstone body of uranium reservoir in the 3rd member of Quantou Formation has changed from thick to thin,the sand content has changed from high to low,the ratio of the thickness to the oxidized sand body decreased,and the external reducing geological bodies such as gray mudstone and coal seams have changed from thin to thick.