开鲁盆地钱家店地区姚家组还原剂特征及铀成矿作用

在开鲁盆地钱家店地区发现超大型铀矿床,为了界定储层还原剂对铀成矿作用的影响,通过岩心、镜下观察及相关测试技术的应用,进行了还原剂特征研究。结果表明: 研究区铀储层内部的还原剂主要以有机质-碳化植物碎屑、烃类、黄铁矿等形式为主。其中,有机质中常见的黄铁矿可以为铀成矿提供大量优质的还原剂; 矿化砂岩中甲烷含量及烃类总量较其他类型的砂岩高,并且随着铀的富集,气烃/重烃的比值明显升高,表明铀的富集与烃类也具有密切关系; 铀储层内部常见的黄铁矿类型包括莓球状黄铁矿、胶状黄铁矿、自形和它形黄铁矿,其作为还原剂以多种形式与铀共存。矿化层位的砂岩中,总有机碳(total organic carbon, TOC)含量与S全含量普遍较高,而Fe2O3/FeO值则明显偏低; 与此相反,在非矿化层位的砂岩中,TOC含量与S全含量普遍较低,而Fe2O3/FeO值较高,表明铀矿化与TOC、S全含量具有一定的正相关关系,而与Fe2O3/FeO值呈负相关。对铀储层内部还原剂特征的深入研究,反映出还原剂对铀成矿作用的制约机理具有重要意义,为砂岩型铀矿的勘查预测提供理论指导。

Characteristics of reducing agent and uranium mineralization of Yaojia Formation in Qianjiadian area of Kailu Basin

A super-large uranium deposit was discovered in Qianjiadian area of Kailu Basin. In order to define the influence of reservoir reducing agent on uranium mineralization, the authors defined the characteristics of reducing agent through the application of core, microscopic observation and related testing techniques. The results show that reducing agent in uranium reservoir in the study area is mainly in the form of organic-carbonized plant debris, hydrocarbons and pyrite. The pyrite in organic matter can provide a lot of high-quality reducing agent for uranium mineralization. The methane content and total amount of hydrocarbons in the mineralized sandstone are higher than those in other types of sandstone, and the ratio of gas hydrocarbon to heavy hydrocarbon increase obviously with uranium enrichment, indicating that uranium enrichment is also closely related to hydrocarbons. The common pyrite types in uranium reservoirs include raspberry pyrite, colloidal pyrite, idiomorphic pyrite and alloomorphic pyrite, which coexist with uranium in various forms as reducing agents. The TOC content and S content are generally higher, while Fe₂O₃/FeO ratio is obviously lower in sandstone with mineralized horizon. On the contrary, TOC content and S content are generally lower in the non-mineralized sandstone, while Fe₂O₃/FeO ratio is higher, indicating that uranium mineralization is positively correlated with TOC content and total S content, and is negatively correlated with Fe₂O₃/FeO. Therefore, the reducing agent is of great significance on restricting mechanism of uranium mineralization by the in-depth study on the characteristics of reducing agent in uranium reservoir, which provides theoretical guidance for the exploration and prediction of sandstone type uranium deposits.