鄂尔多斯盆地北部大营铀矿床砂岩元素地球化学特征及指示意义

Elementary geochemical feature of sandstone and their indicating significance in Daying uranium deposit,northern Ordos Basin

在大营铀矿床内进行系统取样,根据各地球化学分带砂岩的主量、微量、稀土元素和全岩C-O同位素分析结果,对各类砂岩的地球化学组成进行分析,厘定与铀伴生的元素的种类及其与铀含量的关系,建立含矿砂岩特有的地球化学标志,并查明砂岩中碳酸盐胶结物的成因类型。分析结果显示:含矿砂岩中CaO、有机C和全岩S的含量较古氧化砂岩和还原带砂岩高,Fe在还原带砂岩中含量最高,与黄铁矿关系密切;各地球化学分带砂岩的稀土元素表现为轻稀土富集,重稀土相对亏损,稀土元素配分曲线呈"右倾"型,未出现Eu的异常;微量元素Li、 Ba在含矿砂岩中含量较古氧化砂岩和还原带砂岩低,W、 Mo、 V、 Ce、 La在含矿砂岩中强烈富集,且Mo、 V、 Ce、 La与U具有明显的正相关关系;C-O同位素分析结果表明碳酸盐胶结物中的碳为大气降水中的碳和有机碳的混合产物,碳酸盐胶结物的形成与有机质的脱羧作用关系密切。通过研究对含矿砂岩的地球化学特征有更进一步的认识,同时为其他伴生元素矿产的勘查提供线索。

Based on the analysis results of major,trace and rare earth elements and C-O isotope of sandstone samples from different geochemical zones of Daying uranium deposit,the geochemical feature and their relationship to uranium content were analyzed,the unique geochemical indicators of ore host sandstones were established and the genesis types of carbonate cement in sandstone were also ascertained.The results showed that the content of CaO,organic C and total S in ore host sandstone is higher than that in paleo-oxidized sandstone and reduction zone sandstone,and the content of Fe is the highest in reduction zone sandstone because of the occurrence of the pyrite;The REE is enriched in LREE and relatively deficient in HREE of sandstone in different zone.The REE pattern is right inclined but without Eu depletion;The content of Li and Ba in ore hosting sandstone are lower than that in green sandstone and grey sandstone,and W,Mo,V,Ce,La are strongly enriched in ore hosting sandstones and positively correlated with U except W;The results of C-O isotope analysis showed that carbon in the cement is the mixture of organic carbon and meteoric carbon and the formation of carbonate cement is closely related to the decarboxylation of organic matter.