The Paleoproterozoic Amer supergroup, Amer Fold Belt, Nunavut: stratigraphy, structure, correlations and uranium metallogeny

Abstract

The Amer Belt, hosting eleven informal formations of the Amer supergroup, is proposed as type area for four regional Paleoproterozoic sequences (Ps1-Ps4) in central Rae Craton, western Churchill Province. The ca. 1.9-1.865 Ga Snowbird orogeny (DP1) affected only Ps1-Ps3, whereas the ca. 1.87-1.81 Ga Hudsonian orogeny (DP2) affected all four. Sequence Ps1 Ayagaq Lake formation (<2.3 Ga quartzite) initiates as schistose basal polymict orthoconglomerate unconformably overlying paleoweathered Neoarchean rocks. It transitions upward to lower Ps2 Resort Lake formation: gossanous, recessive, graphitic, pyritic-metalliferous phyllite (Re-Os age 2126 ± 24 Ma). Ps2 conductors beneath the <1.74 Ga Thelon Formation have been drilled for unconformity-related uranium. Gradationally overlying siliceous dolomitic marble (Aluminium River formation) completes Ps2. The gradationally overlying lower Ps3 is either foliated calcareous tholeiitic basalt (Five Mile Lake formation) or grey phyllite (Three Lakes formation). These lateral equivalents host strong linear aeromagnetic markers. The Oora Lake formation foliated feldspathic calcareous sandstone gradationally overlies only the Three Lakes formation and underlies the upper Ps3 Showing Lake formation (interbedded phyllite and foliated calcareous arkose) whose two arkose members host laterally continuous disseminated uraninite + magnetite forming linear aeromagnetic markers. Pristine sequence Ps4 molasse, deposited and later deformed during DP2, comprises four formations of rhythmically interbedded, deep maroon to pink and green, feldspathic-lithic arenite, conglomerate and mudstone that unconformably overlie and include clasts of DP1-deformed Ps1 – Ps3 + Neoarchean basement. Ps4 detrital zircon (3.05 to 1.90 Ga) suggest local + distal provenance from south Rae and Slave cratons, and Taltson-Thelon magmatic zone.