Comparative molecular, elemental, and U-Pb isotopic composition of stratiform and dispersed-globular matter in the paleoproterozoic uraniferous metasediments, Elliot Lake, Canada

Uraninite and other uranium minerals at the Elliot Lake-Blind River uranium ore deposits are held mainly within syngenetic kerogen. Bitumen was generated from kerogen by hydrothermal solutions, through a process similar to hydrous pyrolysis. Liquid bitumen migrated away from its parent kerogen, but transported virtually no U and Th. However, bitumen has a large excess of 206Pb, which indicates that the liquid bitumen must have acted as a sink for mobile intermediate decay products of 238U, probably the noble gas, 222Rn. Bitumen was then converted by heat into a solid, consisting of highly condensed aromatic hydrocarbons, preventing Pb mobility. The upper intersection of U-Pb isotopic data is within error of the Nipissing diabase event, which suggests that this was responsible for almost totally resetting the U-Pb systems in the uraninite. The tectonic and thermal anomaly associated with emplacement of the Nipissing diabase may have also been responsible for formation and migration of bitumen into pores and fissures and for outgassing of 222Rn into the same openings, leading to the 206Pb anomaly. Uraniferous kerogen occurs mainly in stratiform layers. The kerogen has Romax = 2.63 to 7.31%; it is highly aromatic in molecular composition, contains large clusters of aromatic hydrocarbon moieties, and its H/C atomic ratios range from 0.41 to 0.60. Bitumen, derived from the syngenetic kerogen, occurs as solid pore and fracture fillings, has Romax = 0.72 to 1.32%, H/C atomic ratios of 0.71-0.81, and contains more alkyl substitutions on aromatic molecular components than the kerogen. A functional relationship between these two groups of organic matter is supported by their molecular compositions and δ13C signatures