A review of the geochronology of the Precambrian of Saskatchewan—some clues to uranium mineralization

Abstract

Assessment of available geochronological information, as well as new whole-rock Rb-Sr data from several granitoid rocks of Saskatchewan, shows a close relationship between magmatic-metamorphic events in the Hudsonian orogen and uranium mineralization. Most uranium deposits lie to the west of the Needle Falls Shear Zone and occur as either: (i) vein-type deposits or (ii) unconformity-type deposits close to the contact between the Athabasca sediments and their basement. At least two metamorphisms have affected the pre-Athabasca rocks: the Kenoran at about 2500 Ma ago, and the more pervasive ‘main’ Hudsonian event at 1740 Ma. A much younger thermal event (perhaps associated with uplift and cooling) at 1540 Ma is also indicated. The post-Kenoran K-Ar dates suggest prolonged thermal activity from about 1900 Ma through to about 1500 Ma ago. Granitoid events at 1870 Ma and 1740 Ma ago are outlined by both U-Pb zircon and Rb-Sr whole-rock isochron data. Whole-rock Rb-Sr data from the unmetamorphosed Athabasca sediments suggest an approximate depositional age of 1450±50 Ma, a figure that is consistent with the age of the underlying Hudsonian basement and the truncation of the sediments by the Cree Lake diabase dyke swarm at about 1200–1300 Ma ago. Although several episodes of uranium deposition have been documented, the main ones seem to have occurred at 1860 Ma (syngenetic uraninite in pegmatites), 1740 Ma (the Beaverlodge vein-type deposits) and between 1300 and 800 Ma (the epigenetic uranium of the unconformity-type deposits). Whereas the two earlier episodes can be correlated with periods of either magmatic or metamorphic activity, the late Proterozoic episodes cannot. The close agreement between the age of the Cree Lake dyke swarm and the late Proterozoic mineralization suggests that at about 1300 Ma ago possible hydrothermal activity from relatively deep-seated fractures may have been responsible for the solution and transportation of the uranium of the unconformity-type deposits. The period 1300 Ma to about 900 Ma, in other parts of the Canadian Shield, was a time of crustal rifting, basic magmatism, carbonatite activity, and intense deformation. Prior to the deposition of the Athabasca sediments uranium was concentrated by Hudsonian magmatic and metamorphic processes whereas subsequently, transportation and intermittent deposition of the unconformity-type deposits were related to fairly long-lived, low-temperature hydrothermal activity.

Isotopic composition of lead in galena and Ni-arsenides of the Midwest deposit, northern Saskatchewan

“…In addition, we know that the basement rocks are Aphebian to Archean in age , and Pb derived directly from those rocks should have a slope age characteristic of that time, whereas if the Pb were derived from the altered regolith it would have compositions more characteristic of the time of regolith formation, which is likely close to 1400 Ma (Bell 1981). Our data are consistent with this latter time, and thus a regolith source is indicated.…”

The case of the carbonatite-like dyke of the Madenska River complex at the Kriva Lakavica section in the Republic of Macedonia: oxygen and carbon isotopic constraints

“…The observed δ 18 O and δ 13 C values are clearly much higher than the range of the suggested values reported by Taylor et al (1967), implying that the carbonatite-like dyke is not a normal "carbonatite" related to any carbonatitic magmatism. Preliminary geochemical data on the carbonatite-like dyke of the Madenska River revealed Ba, U, Th, Na, Pb, and REE content and slightly higher values of Sr in the range from 1470 to 3588 pm, which are not typical for normal carbonatites (Pirc et al, 2007) and are much lower than the normal abundance levels for carbonatites (Bell, 1981;Xu et al, 2010). Similar δ 18 O and δ 13 C values ranging from 8‰ to 24.4‰ and 0.80‰ to 3.55‰, respectively, described by Liu et al (2006) in carbonatite-like dykes from the eastern Himalayan syntaxes, were formed as melts from sedimentary carbonates at the crustal levels.…”

Stratigraphic variations in carbon and oxygen isotopes in the dolostone of the Carswell Formation (Proterozoic) of northern Saskatchewan

“…The basement rocks are composed of paragneisses and granitic rocks that have been metamorphosed to upper amphibolite to granulite facies and intruded by the Cluff Breccias. The sediments of the Athabasca Group have been dated radiometrically by the Rb-Sr method at 1350 + 50 Ma (Ramaekers and Dunn 1977), 1428 f 30 Ma (Ramaekers 1981), 1430 f 30 Ma (Armstrong and Ramaekers 1985), and 1512 f 24 Ma (Bell 1981). Laser probe 40Ar/39Ar and conventional K-Ar dates on illites in the Wolverine Point Formation (Table 1) gave dates of 1484 f 55 and 1459 f 4 (Bray et al 1987).…”

“…The ring structure of exposed Carswell Formation and Douglas Formation sediments is the consequence of an early Phanerozoic event, with evidence (Innes 1964;Harper 1978;Page1 et al 1985) of a meteorite impact, but Currie (1969) and Page1 et al (1985) argued that the shock features associated with the underlying igneous rocks but absent from the Carswell dolomites could indicate an explosive event originating from below-a cryptovolcanic event. The Cluff Breccias are considered as having formed at the same time as the ring structure that exposed the Carswell Formation and have yielded K-Ar dates of 515-365 Ma, setting a lower limit for the age of the Carswell Formation (Bell 1985). The Carswell Formation is considered, on the basis of these dates and its association with the Douglas Formation, as having an age of 1200-1300 Ma.…”