U–Pb, Pb–Pb, and K–Ar isotopic study and petrography of uraniferous phosphate-bearing rocks in the Thelon Formation, Dubawnt Group, Northwest Territories, Canada

Abstract

The Thelon Formation, uppermost unit of the Dubawnt Group, overlies a regionally extensive paleoweathered zone developed on a wide range of lithochronological units including formations in the lower Dubawnt Group. Authigenic uraniferous phosphate minerals, fluorapatite and goyazite, cementing Thelon conglomerate–sandstone and filling fractures in the underlying paleoweathered zone, were dated in an attempt to better constrain the age of Thelon sedimentation and diagenesis. The oldest age, 1720 ± 6 Ma, derived from phosphate-cemented sediments, is interpreted as a minimum age for diagenesis and therefore brackets initial Thelon sedimentation between emplacement of fluorite-bearing granites at 1753 Ma and authigenic phosphate cementation at 1720 Ma. Additional ages of 1685 ± 4 and 1647 Ma are interpreted as remobilization or subsequent cementation events. K–Ar ages on illite, 1386 ± 37 and 1266 ± 31 Ma, from the paleoweathered zone and basal conglomerate, respectively, are significantly younger than ages derived from coexisting phosphate. These K–Ar ages record hydrothermal events that may be related to processes associated with unconformity-type uranium mineralization at approximately 1400–1300 Ma.Ages from the Thelon Basin permit geochronologic correlations with the Athabasca and Hornby basins, long correlated on the basis of similarities in sedimentation, stratigraphy, and tectonic setting.

Geochronology at the Namew Lake Ni–Cu orebody, Flin Flon area, Manitoba, Canada: thermal history of a metamorphic terrane

“…It is worthwhile to contrast this evidence for slow cooling and the slow uplift that is therefore implied with the rapid peneplane formation followed by basin filling in the Athabasca and Thelon basins to the northwest of this study area (Cumming and Krstic 1987;Hoffman 1989;Miller et al 1989). There, the evidence indicates that only a very few tens of million of years are available between late Hudsonian activity (volcanism and high-level intrusions) and the cementation of sandstone sediments emplaced in a basin that had already developed over eroded Hudsonian mountain belts.…”

Numerical modeling of hydrothermal fluid flow in the Paleoproterozoic Thelon Basin, Nunavut, Canada

“…The youngest age for the last magmatic event in the basement is 1753 Ma, which limits the beginning of Thelon Formation sedimentation (Miller et al, 1989). Argon-argon ages of peak-diagenetic (highest temperature) illite reveal a peak diagenesis period of ca.…”

Diagenetic fluorapatite and aluminum phosphate–sulphate in the Paleoproterozoic Thelon Formation and Hornby Bay Group, northwestern Canadian Shield

“…Fluorapatite cement was identified in Thelon Formation sandstone, and the underlying Thelon paleosol, by LeCheminant et al (1981), Miller (1983) and Miller et al (1989). U-Pb isotope analyses of fluorapatite cement from basal sandstone and conglomerate of the Thelon Formation by Miller et al (1989), yielded ages of 1720 ± 6 Ma, interpreted as a minimum age for diagenetic cementation, and 1685 ± 4 and 1647 Ma, interpreted as subsequent remobilization or cementation ages.…”

“…U-Pb isotope analyses of fluorapatite cement from basal sandstone and conglomerate of the Thelon Formation by Miller et al (1989), yielded ages of 1720 ± 6 Ma, interpreted as a minimum age for diagenetic cementation, and 1685 ± 4 and 1647 Ma, interpreted as subsequent remobilization or cementation ages.…”

“…However, phosphatic cements are widespread within continental Paleoproterozoic sedimentary rocks of the northwestern part of the Canadian Shield (LeCheminant et al 1981;Miller et al 1989). This paper further documents the unusual occurrence of diagenetic fluorapatite and, for the first time, documents a rare hydrated aluminum phosphatesulphate mineral (APS) in the correlative Paleoproterozoic sandstones of the Thelon Formation (Thelon Basin) and Hornby Bay Group (Hornby Bay Basin).…”