Deep Geological Controls on Formation of the Highest‐Grade Uranium Deposits in the World: Magnetotelluric Imaging of Unconformity‐Related Systems From the Athabasca Basin, Canada

• Published in: Geophysical research letters 2022-08, Vol.49 (15), p.n/a
• Main Authors: Tschirhart, V., Potter, E. G., Powell, J. W., Roots, E. A., Craven, J. A.
• Format: Article
• Language: English
• Subjects: Athabasca Basin; Brines; Cells; Connecting; Corridors; Deposits; Earth; Earth crust; Earth surface; Electrical conductivity; Electrical resistivity; Fluid dynamics; Fluid flow; Fluids; Geological processes; Geological structures; Geology; Geophysical methods; Gravity; Heat; Identification; Igneous intrusions; Intrusion; Lakes; Magnetic field; Magnetic fields; magnetotelluric; Modelling; Shear zone; Three dimensional models; Unconformity; Uranium; Uranium ores
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2022GL098208

Unconformity‐related uranium (URU) deposits in the Athabasca Basin, Canada, include the highest grade, large tonnage deposits in the world. Recent studies of the Patterson Lake corridor uranium deposits suggest a deep heat source enhances hydrothermal fluid flow and incursion of basinal brines along brittlely reactivated ductile shear zones. However, the spatial extent of the ore systems and lower crustal features capable of driving the hydrothermal cells remained largely unresolved. Three‐dimensional electrical conductivity models derived from inversion of magnetotelluric data and coincident gravity modeling identified a voluminous conductivity anomaly and corresponding gravity low related to a belt of high‐heat producing intrusions that dips below the deposit. Shallow conductive bodies are identified below the deposits and similarly prospective corridors. The volume and location of the intrusive bodies may have provided a source of radiogenic heat that helped drive remobilization of fluids along reactivated structures, redefining the spatial extent of URU systems. Plain Language Summary The western Athabasca Basin, straddling the border of Saskatchewan and Alberta in Canada, is home to some of the highest‐grade, large tonnage uranium deposits in the world. Recent studies have suggested a spatial connection between uranium ore systems that are found near the earth’s surface and geological processes occurring deep within the crust. However, the processes connecting the lower crust to these shallow deposits is poorly understood. This study used 3D models created from magnetotelluric data, a passive a geophysical technique that measures the earth’s natural electric and magnetic fields, to image the earth from surface to a depth of 40 km. We identified a voluminous igneous intrusion that extends from the surface to great depths in the earth’s crust. We propose that this intrusion may have contributed to the uranium endowment of the basin, and that radiogenic heat from the large igneous body helped circulate uranium‐bearing fluids through the shallow crust along reactivated geologic structures. The modeling, when combined with other geoscientific datasets, showcases the role of high‐heat producing granitic intrusions in driving the hydrothermal fluid cells that formed the deposits. Key Points Integrated resistivity—gravity modeling over the Arrow uranium deposit in Canada Magnetotelluric inversion images deep‐seated thermal source and fluid pathways that forme