Formation and evolution of the Cigar Lake uranium deposit based on U–Pb and K–Ar isotope systematics

Abstract

A systematic geochronological study was conducted on the Cigar Lake uranium deposit. U–Pb and Pb–Pb systematics were applied to different types of uranium ore, and various associated sheet silicates were dated by the K–Ar method. These two approaches define a widespread retrograde metamorphic event in the basement, which occurred at about 1780 Ma during the Hudsonian orogeny, and a four-stage evolutionary model for the ore deposit. This model is compatible with the history of other unconformity-type, uranium deposits in the Athabasca Basin.The first stage in the evolution of the Cigar Lake uranium deposit is marked by uraninite crystallization at 1341 ± 17 Ma, which, in association with arsenides and sulpharsenides, constitutes the mineralization of economic interest (main orebody). The second stage, characterized by a Fe-kaolinite and Fe-illite paragenesis, occurred locally at about 900 Ma. The third stage involved uranium mobilization at about 325 Ma and is characterized by (i) preferential loss of radiogenic lead from primary uraninite and crystallization of pitchblende at the rims of uraninite grains and (ii) formation of pitchblende associated with Fe-sulphides or hematite in the main and perched orebodies. The last stage is characterized by recent alteration and coffinitization which have affected all ore types.

Low long-term erosion rates and extreme continental stability documented by ancient (U-Th)/He dates

“…Basinal fluid inclusion and clay mineralogy studies, U-Pb and Pb-Pb analyses of U-rich minerals, and 40 Ar/ 39 Ar and K-Ar investigation of Fe-rich clay paragenesis indicate an early 150 ЊC diagenetic event at 1.7-on July 23, 2015 geology.gsapubs.org Downloaded from 1.6 Ga, Ͼ150 ЊC burial diagenesis between 1.6 and 1.45 Ga, fluid remobilization ca. 0.9 Ga, and Phanerozoic fluid incursion at Ͻ50 ЊC (Kotzer et al 1992;Philippe et al, 1993;Fayek et al, 2002). Continental reconstructions have proposed that the Paleozoic seas that deposited sedimentary sequences preserved in much of the North American interior also inundated most of the western Canadian shield currently lacking Phanerozoic cover, including our area of study (Ziegler, 1989;Scotese and Golonka, 1992).…”

Alteration Mineralogy and Stable Isotope Geochemistry of Paleoproterozoic Basement-Hosted Unconformity-Type Uranium Deposits in the Athabasca Basin, Canada

“…Reported mineralization ages vary from 900 to 1400 Ma from U/Pb dating of uraninite and pitchblende from the Key Lake (Carl et al, 1991), Cigar Lake (Philippe et al, 1993), and Midwest deposits (Badsgaard et al, 1984;Worden et al, 1985), and from 40 Ar/ 39 Ar and K-Ar dating of illite associated with mineralization at the McClean Lake deposit (Bray et al, 1988). More recent U-Pb ages of uraninite using an ion probe have upper intercept ages of 1598 ± 25 Ma for the McArthur River sandstone-hosted deposit, 1543 ± 8 Ma for the Sue C zone deposit (M. Fayek, pers.…”

Effects of Cationic Substitutions and Alteration in Uraninite, and Implications for the Dating of Uranium Deposits

“…found throughout the Athabasca Basin (Carl et al 1991, Philippe et al 1993, Baadsgard et al 1984. The difference in substitution-based intercept ages obtained for calcium and for iron indicates that there was a significant change in fluid composition moving along the fracture system with time, as should be expected.…”