Trace Element and Isotopic Analysis by Laser Ablation ICP-MS of Ore Deposit Bitumens: A Test Case with Uranium Ores from Oklo, Gabon

Carbonaceous substances (CS) such as kerogen and derivative bitumens are closely linked to the origin of various types of ore deposits. Examples are metal accumulations in living organisms, black shales, crude oils, solid bitumens, and coals. Although presently a marginal economic proposition, the uranium ores of Oklo provide a classic case. At Oklo, solid bitumen occurs closely associated with the several main uranium ore types and also as discrete veinlets in the 2.1 Ga old country rock shales. These bitumen occurrences have been distinguished on the basis of field evidence, petrography, carbon isotopic signatures, and degree of thermal maturation. Chemical analysis by laser ablation inductively coupled plasma-mass spectrometry (ICP-MS) now allows detailed chemical characterization of CS such as these solid bitumens. For the first time, the technique has been used to produce quantitative in situ trace element and isotopic analysis of bitumen. There is a potential here to make major contributions to the understanding of Oklo and other ore deposits associated with carbonaceous substances.