Paleomagnetism and the evolution of fluids in the Proterozoic Athabasca Basin, northern Saskatchewan, Canada

Abstract

In the Athabasca Basin, diagenetic hematite of variable paragenesis occurs throughout the sandstones and underlying paleoregolith. This hematite carries three distinct, single-component magnetizations: A (D = 158", 1 = 62", a,, = 5", n = 21); B (D = 11°, I = -36", a,, = 7", n = 6); and C (D = 18", I = 79", a,, = 3", n = 27). In some areas of the sandstones, such as near reactivated fault zones, the diagenetic hematite has been altered to goethite which yields a very lowintensity, incoherent D magnetization. Ages for the A, B, and C magnetizations, inferred from comparisons with paleomagnetic directions in Precambrian rocks whose ages are known approximately, are 1750-1600, 1600-1450, and about 900 Ma, respectively. The A magnetization is carried by the earliest formed hematite, and its estimated age compares well with U-Pb ages of 1650-1700 Ma for early diagenetic apatite. U-Pb and Rb-Sr ages of approximately 1500 and 900 Ma for uraninite and illite coeval with hematite that carries the B and C magnetizations compare well with their ages estimated from paleomagnetism. The development of B magnetization appears to be coeval with high-grade, unconformitytype uranium mineralization.Petrographic and field relationships indicate that the A magnetization is carried by hematite formed during initial diagenesis of the Athabasca sandstones, the B magnetization is carried by hematite formed during peak diagenesis, and the C magnetization is carried by hematite formed during subsequent high-temperature hydrothermal alteration. The incoherent D magnetizations have resulted from degradation of hematite to goethite as a result of incursion of low-temperature meteoric waters along fault zones that have been continuously reactivated since the late Precambrian. 6180 values of clay minerals and of the coeval hematite which carries the B and C magnetization indicate that they were formed from a fluid having temperatures of 150-200°C and 6180 values near 1.0%,. Fluids that deposited the early formed hematite carrying the A magnetism are relatively 180 depleted, with values of approximately 0.8%, and somewhat lower temperatures of 120-160°C. Intermingling of A, B, and C magnetizations indicates either that hematite may be deposited by one fluid and reprecipitated by a subsequent fluid, or that fluid flow was controlled by local variations in permeability. Evidently, fluid flow has been episodic and basin wide and has occurred over a time span on the order of lo8 years. It is suggested that the stratigraphy of the sandstones controlled the basin-wide lateral migration of the basinal fluids and that faults facilitated interformational fluid flow.Dans le bassin d'Athabasca, I'hCmatite diagtnCtique de paragenhe variable est distribuke au travers les grks et le palCortgolithe sous-jacent. Cette hCmatite porte trois composantes discrktes d'aimantation bien distinctes : A (D = 158", 1 = 62", a,, = 5 " , n = 21);B(D = 11°, I = -36",a9, = 7 " , n = 6 ) ; e t C ( D = 18", I = 79",a,, = 3 " , n = 27). Danscertaines parties de ces grks, comme da...

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).…”

Oxygenation of the Earth's atmosphere–ocean system: A review of physical and chemical sedimentologic responses

“…The paragenesis of diagenetic and metamorphic mineral assemblages in Proterozoic sedimentary basin-hosted uranium and PbeZn deposits demonstrate that periods of elevated fluid flow and concomitant alteration are driven by tectonic events that changed basin hydrology (Kotzer et al, 1992;Polito et al, 2004Polito et al, , 2011Alexandre and Kyser, 2005;Alexandre et al, 2009;Hiatt et al, 2010;Polito et al, 2011). In these systems the punctuated recrystallization of iron oxides (Kotzer et al, 1992) and uraninite (Polito et al, 2004(Polito et al, , 2011Alexandre and Kyser, 2005;Polito et al, 2011) as well as the precipitation of diagenetic illite (Polito et al, 2004;Alexandre et al, 2009;Hiatt et al, 2010;and Polito et al, 2011) indicate fluid/rock ratios increased during regionalscale tectonic events, which created the hydraulic gradients necessary for fluid flow. All successions used to interpret the nature of the GOE have been subjected to these conditions.…”

An evaporated seawater origin for the ore-forming brines in unconformity-related uranium deposits (Athabasca Basin, Canada): Cl/Br and δ37Cl analysis of fluid inclusions

“…Thus, in order to evaluate the possibility of evaporitic environments during formation of the Athabasca Basin, the paleolatitudes of Northern Saskatchewan must be considered between 1.5 Ga (approximate age for the Carswell Formation) and 1.3 Ga (minimum age for primary uranium mineralizations) (Cumming and Krstic, 1992;Fayek et al, 2002;Alexandre et al, 2009). Paleomagnetic reconstructions suggest that Northern Saskatchewan was located within 30°of the equator between 1.5 and 1.3 Ga and possibly within 5°during periods (Kotzer et al, 1992;Buchan et al, 2000;Meert, 2002;Pesonen et al, 2003;Zhao et al, 2004). Thus, low latitudes of the Northern Saskatchewan area during sedimentation of the Athabasca Basin could have favoured evaporitic environments and the production of halite deposits and evaporated seawater.…”