Pre-Athabasca Supergroup structures played an important role in channelizing reduced fluids into the Athabasca Basin of Saskatchewan, Canada [1].Although the life-cycle of these structures is undoubtly long-lived -spanning 100s of Myrs or more [1], they under went a critical rheological change from a ductile to semi-brittle regime ca.1800-1700 Ma [2].This change allowed higher volumes of carbonic-rich fluid to pass through these long-lived shear zones and precipitate graphite and pyrite that could later serve as a reductant for uranium mineralization [1].Underlying the eastern flanks of the Athabasca Basin are graphitic ± pyritic shear zones hosted in Wollaston Domain basement rocks and spatially associated with some of the largest unconformity uranium deposits in the world (e.g.McArthur River and Cigar Lake).Martz et al. (2017) and others attributed the preciptation of these minerals to a carbonic-fluid flow event triggered by post-orogenic uplift and cooling that is indirectly bracketed to ca. 1770-1715 Ma.Here we present preliminary Re-Os pyrite dates from Wollaston Domain basment shear zones straddling the eastern flanks of the Athabasca Basin.Our Re-Os pyrite dates (ca.1750-1720 Ma) place the first absolute age constraints on carbonicpyritic fluid flow in Wollaston structures and confirm existing models by Martz et al. (2017) and others that this fluid flow event was synchronous with a major dewatering event following the Trans-Hudson Orogeny that was previously only constrained by Ar-Ar muscovite and Rb-Sr biotite dating (ca.1770-1715 Ma) [4].In addition to this, we contextualize the timing of carbonic fluid flow in eastern Pre-Athabasca Supergroup structures with similar structures in the west [5].
Recent discoveries of basement-hosted uranium deposits in the Patterson Lake corridor in the southwestern Athabasca Basin of Canada have brought vigorous exploration interest to the region. New lithostratigraphic constraints, geochronology and airborne geophysical surveys have dramatically improved the understanding of the host basement geology, warranting a re-examination of the remote predictive mapping and geophysical responses of the buried basement rocks. This study took a two-step approach to examine the regional basement geology and architecture. First, a mosaic of the long-wavelength response of potential field (gravity and magnetic) datasets was examined to divide the basement into regional domains based on bulk physical property variations. The interpretive geological model was then refined using textural and lineament analysis of new airborne gravity and magnetic datasets, geological drill hole logs and magnetic susceptibility measurements. The new basement map identifies and updates major features including a crustal-scale structure that separates the southern Tantato Domain from the newly defined eastern Taltson Domain. This structure may have played a role in localizing fluid flow in the Patterson Lake corridor, defining the spatial extents of structurally controlled buried felsic intrusions, and redefines the boundaries of the Taltson, Clearwater and Tantato Domains. In addition, the potential field enhancements delineated significant regional faults that controlled the geometry of Paleoproterozoic cover sequences and have implications for understanding the crustal architecture of the southern Rae Province. These new interpretations shed light on the tectonic history of the region to support on-going exploration activities and delineate regionally prospective areas in this understudied area of the Canadian Shield. Thematic collection: This article is part of the Uranium Fluid Pathways collection available at: https://www.lyellcollection.org/cc/uranium-fluid-pathways
The southeastern portion of the Athabasca basin hosts the largest high-grade unconformity-related uranium deposits in the world, including the McArthur River and Key Lake deposits. As a first step of an effort to reconstruct and model the fluid flow related to uranium mineralization, a 3D model of the sub-Athabasca unconformity and basin stratigraphy has been constructed using publicly available geological, geophysical and drill-hole data. Several cross-sections have been built and integrated into the 3D model to constrain the spatial configuration of Athabasca Group units. Faults have been identified using an iterative approach where potential fault lineaments were identified using the basement geophysical signature then confirmed by the presence of spatial relationships to offsets of the unconformity surface. Using this approach, three dominant sets of faults, inferred to be subvertical, have been identified in the study area: northeast trending, north-northwest trending and northwest trending. In the 3D model, the unconformity surface shows an approximately northeasttrending zone of elevated topography where elevations change abruptly (SE to NW) from about -100 m to +200 m (referenced to mean sea level). This topographic ridge of the unconformity surface is associated with the Phoenix - McArthur River deposits trend. A preliminary cross-section illustrates that this topographic high may be controlled by northeast-trending reverse faults that have uplifted the basement. Regional clay anomalies in the Athabasca Group and the majority of deposits and prospects are also broadly coincident with this feature. Future work will be focussed on increasing resolution of the model in this and other key areas to gain a better understanding of the geometry and kinematics of regional plus local structures and their control on fluid flow and uranium mineralization.
The basement to the Athabasca Basin comprises rocks of the Rae and Hearne provinces and the Taltson magmatic zone. The Rae Province is characterized by mainly metasedimentary supracrustal sequences, including the Murmac Bay Group, and Archean and Proterozoic granitoid rocks. The Hearne Province contains Archean granitoid gneiss with interleaved supracrustal belts including the Archean Ennadai Group, the Paleoproterozoic Hurwitz Group, and other rocks of unknown age. The eastern Hearne Province is dominated by Wollaston Supergroup metasedimentary rocks. The Taltson magmatic zone contains a basement complex that was intruded by ca. 1.99 - 1.96 Ga continental magmatic arc granitoid rocks and 1.95 - 1.92 Ga peraluminous granitoid rocks. Numerous structural features affected the Athabasca Group and its basement rocks. Their histories were generally protracted and included multiple displacements under ductile and brittle conditions. Mackenzie diabase dykes cut the Athabasca Group, providing its minimum age. The Carswell Structure is thought to be the result of an Ordovician meteorite impact.
Much of the basement to the southwest Athabasca Basin comprises rocks of the Lloyd Domain. These include the Careen Lake Group, a melange of metasedimentary rocks, parts of which are correlative with Archean Murmac Bay Group and Rutledge River Basin rocks. These rocks were intruded by ca. 1985 - 1968 Ma plutons of the Taltson magmatic zone. The Lloyd Domain was divided by weakly deformed 1843 Ma granite and 2500 Ma granitic gneiss of the Clearwater Domain. To the east, supracrustal rocks of the 'Virgin schist group' are at the boundary between the Virgin River and Lloyd domains. Most basement rocks to the western Athabasca Basin were subjected to multiple deformational and metamorphic events. The Virgin River shear zone was subjected to multiple displacement episodes under ductile, brittle-ductile, and brittle conditions. Brittle reactivation of the Virgin River shear zone, along the Dufferin Lake Fault, played a role in concentrating uranium at the basal unconformity of the Athabasca Basin.
Zircons from seven granitoid samples from the southern and southwestern margins of the Athabasca Basin were dated using the SHRIMP II ion microprobe. A granite from the Virgin River shear zone was imprecisely dated at ca. 1.83 Ga. Two samples from the eastern Lloyd Domain both crystallized at ca. 1.98 Ga. These rocks were either sourced within, or intruded, 2.4 - 2.0 Ga crust. The Clearwater Domain comprises 1.843 Ga granite and 2.53 Ga granitic gneiss. Two granodioritic rocks within the basement at the western edge of the basin crystallized at 1.97 Ga. The new ages indicate that a considerable proportion of the basement to the western half of the Athabasca Basin is underlain by rocks related to the Taltson magmatic zone.
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