Comparative Molecular, Elemental, and U-Pb Isotopic Composition of Stratiform and Dispersed-Globular Matter in the Paleoproterozoic Uraniferous Metasediments, Elliot Lake, Canada

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Abstract
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 convened by heat into a solid, consisting of highly condensed aromatic hydrocarbons, preventing Pb mobility U-Pb isotopic data from individual kerogen grains form an approximately linear array that intersects concordia at 2139 ± 100 Ma and 550 ± 260 Ma. The upper intersection is within error of the 2219 ± 4 Ma Nipissing diabase event, which suggests that this was responsible for almost totally resetting the U-Pb systems in the uraninite. The U-Pb systems show subsequent partial mobility of both U and Pb at a variety of times. The lower concordia intercept probably represents an average age for U and Pb mobility. 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 Rn into the same openings, leading to the 206Pb anomaly Bitumens contain lower abundances of trace elements and rare earth elements REE) than kerogen, except for As and ore-grade concentrarions of Au. Pt, and Pd. Between kerogen and bitumen REE distributions vary sympathetically, and Eu and heavy rare earth element (HREE) depletion occurs in both. Uraniferous kerogen occurs mainly in stmtifom layers. l'he kerogen has Ro- - 2.63 to 7.31 1; it is highly aromatic in molecular composition, contains large clusters of aromatic hydrocarbon moieties, and its H/C atom'c ratios range from 0.41 to 0.60. Bitumen, derived from the syngenetic kerogen, occurs as solid pore and frocture fillings, has Ro,, - 0. R to 1.32%. H/C atom'c ratios of 0.71-0.81, and contains more alkyl substitution$ on aromatic molecular components than the kerogen. A functional rehionship between these two groups of organic maner is supported by their molecular compositions and 613c signatures