The Thor–Odin dome of the Monashee complex, in the southeastern Canadian Cordillera, comprises Paleoproterozoic basement gneiss with infolds of unconformably overlying rocks of a supracrustal cover sequence and is the deepest exposed structural level in the Omineca belt. Orthogneiss and paragneiss of the basement are migmatitic and contain ubiquitous stromatic leucosome and discrete phenocrystic and pegmatitic vein-type leucosome, which are all interpreted to have formed as a result of in situ melting. The stromatic leucosome is infolded with the country rock (F2), contains a weakly developed foliation, and has a biotite-rich melanosome. The phenocrystic and pegmatitic vein-type leucosome crosscut the stromatic leucosome and the transposition foliation (S2). Evidence to support an igneous and anatectic source for the leucosome includes (i) petrography, (ii) major and trace element chemistry, (iii) zircon morphology, and (iv) peak pressure–temperature (P–T) conditions. Sensitive high-resolution ion microprobe (SHRIMP) 206Pb/238U zircon dates range from ca. 56 to 54 Ma and are interpreted to represent the age of leucosome crystallization. Zircon commonly contains discrete ca. 2.6-1.8 Ga cores that are interpreted as detrital grains inherited from the host paragneiss. Anatexis was ongoing by ca. 56 Ma, as a result of regional prograde metamorphism, and was coincident, at least in part, with the formation of the penetrative S2 transposition foliation and large recumbent F2 tight to isoclinal folds. Anatexis continued during F3 and F4 folding. Melting may have continued until ca. 51 Ma, driven by decompression reactions, and was concomitant with the D5 extensional deformation.

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Surficial geochemical methods were applied to delineate zones of anomalous uranium and related element concentrations in areas overlain by an extensive blanket of glacial sediments and dense vegetation cover in the Jacque’s Lake area of the Central Mineral Belt, Labrador, Canada. The study involved sampling and analyses of vegetation including black spruce twigs and bark, Labrador tea shoots, and humus. Ash derived from the vegetation samples was analyzed using inductively coupled plasma – mass spectrometry (ICP–MS) following ignition at 450 °C, and humus was analyzed with delayed neutron counting (DNC) for a suite of 35 elements. B-horizon soil was analyzed using aqua regia digestion to investigate potential chemical signatures of bedrock mineralization at the surface. Uranium concentration in humus varied from 0.05 to 885 ppm. Zones exhibiting anomalous U responses were associated with areas proximal to anoxic peat and sphagnum bogs where mobile U species were sequestered. Uranium and pathfinder element (e.g., Pb, V, Sr, and Mo) concentrations were low in the <250 μm fraction of B-horizon soils. The soil geochemistry delineated bedrock U mineralization in areas with <15 cm of overburden and U concentration varied from 50 to 405 ppm. Biogeochemical signatures of the bedrock mineralization in black spruce twigs produced greater anomaly to background contrasts for U and pathfinder elements (e.g., Be, Ag, Pb, Ca, and Sb) and correlated more precisely with the detected radiometric U/Th anomaly than did those of soil and humus. Principal component analysis of spruce twig data discriminated three major components, including plant nutrients, ore-related elements, and a mobile species. Uranium concentration varied from below detection limit to 23 ppm U in black spruce bark and from below detection limit in ∼40% of samples to 18 ppm in Labrador tea stem.