二连盆地脑木更凹陷赛汉组砂岩地球化学特征及沉积环境

Geochemical Characteristics and Sedimentary Environment of Saihan Formation Sandstone in Naomugeng Depression,Erlian Basin

二连盆地的脑木更凹陷发育砂岩型铀矿,赋矿地层为下白垩统赛汉组。通过镜下观察和岩石地球化学,查明了赛汉组砂岩的岩石特征,论证了研究区赛汉组的沉积母岩,讨论了赛汉组形成的沉积环境。研究表明,赛汉组砂岩主要为岩屑砂岩和杂砂岩,主要由斜长石、钾长石、石英及岩屑组成,填隙物主要为泥质为主,其次为黏土矿物。赛汉组含矿砂岩和不含矿砂岩主量元素、稀土元素、微量元素组成相近,砂岩的含矿与否主要受控于体系的氧化-还原条件。砂岩具明显负铕异常,为轻稀土富集的右倾型,具有Ba、Ta、Ce、Sm富集,Sr、K、Zr、Hf适度亏损,Ti强烈亏损的特征,总体变化特征与平均上地壳差别不大。元素地球化学特征指示赛汉组砂岩的沉积母岩主要为花岗质岩石,形成与干热的气候条件,为偏碱性、过渡-还原的陆相淡水环境,Fe^(2+)/Fe^(3+)值为0.2~0.33时,U含量达到最高值,反映了氧化-还原状态控制了铀的富集或贫化。

Sandstone-type uranium deposits are developed in the Naomugeng depression of the Erlian Basin.The ore-bearing strata is the Lower Cretaceous Saihan Formation.In this paper,the rock characteristics of the sandstones of the Saihan Formation have been identified through microscopic observation and rock geochemistry,the sedimentary parent rocks of the Saihan formation in the study area have been demonstrated,and the sedimentary environment of the Saihan Formation has been discussed.The research shows that the sandstone of Saihan Formation is mainly composed of lithic sandstone and gritstone,which are mainly composed of plagioclase,potassium feldspar,quartz and debris.The interstitial material is mainly argillaceous,followed by clay minerals.The composition of major elements,rare earth elements and trace elements is similar between ore-bearing sandstones and non-ore-bearing sandstones,and the ore-bearing sandstones are mainly controlled by the oxidation-reduction conditions of the system.The sandstone has obvious negative Eu anomaly and is a right-leaning type of light rare earth enrichment,enriched in Ba,Ta,Ce,Sm enrichment,moderate depleted in Sr,K,Zr,Hf,and strong depleted of Ti.The overall variation characteristics are not different from the average upper crust.The element geochemical characteristics indicate that the sedimentary parent rocks of Saihan Formation sandstone are mainly granitic rocks,formed in a dry and hot climate,more alkaline,transition-reduction terrestrial freshwater environment.When Fe^(2+)/Fe^(3+)values are 0.2~0.3,the U content reaches the highest value,indicating the REDOX state controls the enrichment or depletion of uranium.