Basin evolution, diagenesis and uranium mineralization in the Paleoproterozic Thelon Basin, Nunavut, Canada

Abstract

The Paleoproterozoic (Statherian) Thelon Basin is located in the Churchill Province of the Canadian Shield, formed following the Trans‐Hudson Orogeny. Basin formation followed an interval of felsic volcanism and weathering of underlying bedrock. The diagenetic evolution of the Thelon lasted about one billion years and was punctuated by fluid movement influenced by tectonic events. Early quartz cements formed in well‐sorted, quartz‐rich facies during diagenetic stage 1; fluids in which these overgrowths formed had δ18O values near 0‰ (Vienna Standard Mean Ocean Water). Uranium‐rich apatite cement (P1) also formed during diagenetic stage 1 indicating that oxygenated, uranium‐bearing pore water was present in the basin early in its diagenetic history. Syntaxial quartz cement (Q1) formed in water with δ18O from −4 to −0.8‰ in diagenetic stage 2. Diagenetic stage 3 occurred when the Thelon Formation was at ca. 5 km depth, and was marked by extensive illitization, alteration of detrital grains, and uranium mineralization. Basin‐wide, illite crystallized at ∼200 °C by fluids with δ18O values of 5–9‰ and δD values of −60 to −31‰, consistent with evolved basinal brines. Tectonism caused by the accretion of Nena at ca. 1600 Ma may have provided the mechanism for brine movement during deep burial. Diagenetic stage 4 is associated with fracturing and emplacement of mafic dikes at ca. 1300 Ma, quartz cement (Q3) in fractures and vugs, further illitization, and recrystallization of uraninite (U2). Q3 cements have fluid inclusions that suggest variable salinities, δ18O values of 1.5–9‰, and δD values of −97 to −83‰ for stage 4 brines. K‐feldspar and Mg‐chlorite formed during diagenetic stage 5 at ca. 1000 Ma in upper stratigraphic sequences, and in the west. These phases precipitated from low‐temperature, isotopically distinct fluids. Their distribution indicates that the basin hydrostratigraphy remained partitioned for >600 Ma.

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

“…Hayes et al, 1983;Ayalon and Longstaffe, 1988;Crusius and Thomson, 2000;Shields and Stille, 2001;Petsch et al, 2005;Gonzalez Alvarez and Kerrich, 2010;Hiatt et al, 2010). Thus, it is difficult to reconcile why so few studies of Precambrian depositional systems attempt to understand alteration of what are primarily metamorphic rocks and minerals before interpreting geochemical data.…”

“…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.…”

“…Hiatt and Budd, 2003). Widespread lateral flow of diagenetic fluids can occur over distances of hundreds of kilometers and at temperatures >200 C Alexandre et al, 2009;Hiatt et al, 2010). Diagenetic fluids flow most intensively within coarse-grained facies that have not experienced intense cementation and are situated above unconformities or along internal discordances such as parasequence boundaries .…”

“…Stratigraphic boundaries often allow preferential diagenetic and metamorphic fluid flow that can reset relatively robust geochemical proxies, such as d 34 S . This long-term diagenetic hydrostratigraphy can involve multiple diagenetic events and can persist into deep burial settings (>5 km) over long periods of basin evolution, which in the case of Proterozoic basins can extend over 500 Ma (Holk et al, 2003;Hiatt et al, , 2010Alexandre et al, 2009;Hiatt et al, 2010).…”

Meso-Neoproterozoic Grenville-Sveconorwegian intracontinental orogen: history, tectonics, geodynamics

“…1). Бассейны Телон (1.72-1.00 млрд лет) и Атабаска (1.74-1.50 млрд лет) расположены на за-паде Лавроскандии в центральной и западной ча-сти Северо-Американского кратона [Jefferson et al, 2007;Hiatt et al, 2010;Allen et al, 2015]. Онежская и Прионежская депрессии (2.20-1.86 и ~1.77 млрд лет соответственно) расположены на востоке Лав-роскандии в юго-восточной части Фенносканди-навского щита.…”