LIPS and Proterozoic uranium (U) deposits of the Canadian Shield

Abstract

Most large igneous provinces (LIPs) are associated with lithospheric extension driven by mantle upwelling. The Dubawnt Supergroup LISP (Large Igneous and Sedimentary Province) contains two LIPs and a BLIP of mantle-sourced magmatism likely driven by lithosphere plateau collapse and strike-slip deformation rather than plumes. LIP #1, the mafic/ultrapotassic Christopher Island Formation, was intercalated from 1845 ± 12 to 1785 ± 3 Ma with siliciclastic rocks of the trans-extensional Baker Lake Basin that partly covers the vein-style, unconformity associated, 1828 ± 29 Ma Lac Cinquante U deposit and correlates temporally with the Martin Basin of Saskatchewan's Beaverlodge district. LIP #2, granite/gabbro/basalt/rhyolite of the 1.75 Ga Nueltin Suite, was intercalated with siliciclastic rocks of the Wharton Group, invaded pre-Thelon Basin faults, and prepared the ground for basement hosted, unconformity associated U deposits inferred as <1667 ± 5 Ma (fluorapatite cement within Thelon Basin). Five to 10 km aeromagnetic rings are being investigated as potential, shallow bimodal volcanic centres that powered epithermal precious metals systems. The two LIPs broadly mobilized U, moving it upward in the crust and available to paleoweathering, basinal fluid alteration and transport, particularly by leaching incompatible element-rich volcanic detritus. The thin, ultrapotassic mafic Kuungmi lavas cap the Thelon Basin and this BLIP provides a 1540 ± 30 Ma (micro-baddeleyite) upper age for the LISP. The proposed-plume-related 1.27 Ga Mackenzie event re-set unconformity U deposits in the Athabasca and Thelon basins, and developed new alteration vectors in the Athabasca Basin such as a third generation of chlorite. U-rich phosphate minerals in the Hornby Bay Basin dated as 1282 ± 11 and 1158 ± 80 Ma suggest the Mackenzie event drove sandstone U mineralization. New ages of mafic igneous events constrain the tectonic development of siliciclastic basins and hydrothermal fluid events that formed U deposits. Once covered by more than 2 km of Hornby Bay Group strata, Port Radium's classic uraninite veins cut the 1.74 Ga Cleaver diabase dykes and are, in turn, cut by the 1.59 Ga Western Channel diabase; thus implying U mineralization beneath the Hornby Bay Basin unconformity. Dating of Mackenzie diabase sills in the largely sub-surface Dessert Lake basin west of Yellowknife confirms its Paleoproterozoic age and supports correlation with the Hornby Bay and Athabasca basins. An outstanding question is the cause of the regional 1.4 Ga re-setting of U and precious metal deposit ages in the Athabasca and Thelon regions.