鄂尔多斯盆地北部东胜铀矿区沉积有机质中脂肪酸甲酯的检出及意义

从鄂尔多斯盆地北部东胜铀矿区侏罗系沉积有机质中检出了丰富的脂肪酸甲酯系列化合物。脂肪酸甲酯系列化合物与相应样品中的正构烷烃化合物在分布特征上极为相似。在碳同位素组成方面，脂肪酸甲酯系列化合物与相应样品中正构烷烃系列也具有完全相同的变化范围。因此，脂肪酸甲酯系列化合物很可能就是正构烷烃系列化合物十分重要的母质来源。地质体中脂肪酸甲酯化合物的存在需要在相应的沉积体中维持一个比较严格的弱碱性—中性的环境。这种弱碱性—中性的成岩环境不仅对该地区有机质中脂肪酸甲酯化合物的形成和保存产生重要影响，而且有可能对该地区砂岩型铀矿床的形成产生了某些积极的作用。

The Content and Significance of Fatty Acid Methylesters in Dongsheng Sedimentary Uranium Ore Deposits, Ordos basin, China

Organic matter associated with Dongsheng uranium ore interbedded organic matter-rich layers was investigated by gas chromatographic-mass spectrometery and carbon isotopic analysis.n-Alkanes in organic matter-rich strata are characteristic of a higher relative abundance of heavy-molecular-weight(HMW) homologues and are dominated by the C_(25),C_(27) or C_(29) with distinct odd-to-even carbon number predominance from C_(23) to C_(29.) n-Fatty acid methylesters in the organic matter-rich layers are characterized by a higher relative abundance of heavy-molecular-weight(HMW) homologues,maximizing at C_(24),C_(26)or C_(28) with distinct even-overodd carbon number predominance above C_(22) homologue range.All of the results indicate that the organic matter in Dongsheng uranium ore interbedded organic matter-rich layers are mainly derived from terrestrial high plants,very similar distribution patterns and consistent carbon isotopic variations between n-alkanes and n-fatty acid methylesters in corresponding samples suggest a product-precursor relationship between these two series of compounds.Thus,we assumed that n-fatty acid methylesters could be the diagenetic intermediates for the formation of n-alkanes from n-fatty acids in the samples studied,or at least,they are derived from the same source precursors.n-Fatty acid methylesters can be formed and preserved in a strict mild-alkali to neuter geological environment.So a geologically mild-alkali to neuter environment probably also is a favorable factor for the formation and preservation of the uranium ore deposit in this region.