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

Key words: 
• nfatty acid methylester /
• nalkane /
• individual compound carbon isotopic composition

Abstract: 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overodd 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. 