Unconformity-type uranium deposits are characterized by mineralization developed along the contact between younger sandstone cover and underlying crystalline basement rocks. Mineralization may extend up to 400 m into the underlying basement rocks. Whereas sandstone-hosted unconformity-type deposits have been well studied, deposits hosted primarily in the basement have not. This study examines the deposits at Rabbit Lake, Dawn Lake, and McArthur River, in the Athabasca basin of Canada, which are hosted by the metamorphic Archean and Early Paleoproterozoic rocks forming the basement to younger Late Paleoproterozoic sandstones. Alteration is similar in the three deposits and is characterized by three distinct paragenetic stages: (1) preore alteration involving illitization of plagioclase and amphibole, followed by chloritization of biotite and illite, which formed at ca. 230°C; (2) ore-stage alteration, characterized by uraninite and coarse-grained illite, which formed at ca. 240°C; (3) postore alteration comprising spherulitic dravite, vein chlorite, quartz, calcite, and Fe, Cu, Co, and Pb sulfides, which formed at ca. 135°C. Fluid circulation associated with emplacement of later Mackenzie dikes initiated partial recrystallization of uraninite. A later stage of alteration includes kaolinite and iron hydroxide precipitation formed at much lower temperatures of ca. 50°C.Stable isotope compositions of the alteration minerals in conjunction with their paragenesis indicate that oxidized basinal fluids (δD = -43 to -21‰ . , δ 18 O = 3-8‰) were derived primarily from evolved seawater and leached uranium from the overlying sandstones of the Athabasca Formation and transported it into the basement via infiltration along fracture zones associated with reverse faults. Graphitic units in the basement and preore alteration served as both physical (fractured zones) and chemical (reductants) traps for the uranium mineralization. The basinal fluids were responsible for the preore illite-chlorite, synore uraninite-illite, and the early postore alteration events; this differs from many other sandstone-hosted deposits, where both oxidized basinal and reduced basement-derived fluids were responsible for uranium precipitation.

Numerous environmental pressures have precipitated long-term population reductions of many insect species. Population declines in aerially foraging insectivorous birds have also been detected, but the cause remains unknown partly because of a dearth of long-term monitoring data on avian diets. Chimney swifts (Chaetura pelagica) are a model aerial insectivore to fill such information gaps because their roosting behaviour makes them easy to sample in large numbers over long time periods. We report a 48-year-long (1944 -1992) dietary record for the chimney swift, determined from a well-preserved deposit of guano and egested insect remains in Ontario (Canada). This unique archive of palaeo-environmental data reflecting past chimney swift diets revealed a steep rise in dichlorodiphenyltrichloroethane (DDT) and metabolites, which were correlated with a decrease in Coleoptera remains and an increase in Hemiptera remains, indicating a significant change in chimney swift prey. We argue that DDT applications decimated Coleoptera populations and dramatically altered insect community structure by the 1960s, triggering nutritional consequences for swifts and other aerial insectivores.

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A new technique has been developed to assess the mobility and site of specific elements in complex natural materials such as rocks. Concentration profiles during leaching were obtained by pumping reagents (water, 1% HNO3, 10% HNO3, 30% HNO3), either continuously or with flow injection, through a microcolumn of sample while continuously monitoring analyte signals by inductively coupled plasma mass spectrometry (ICPMS). Compared to batch extraction procedures normally used, the approach involves minimal sample preparation and reduced contamination since the leaching is performed in a closed system. Continuous on-line monitoring also allows a greater resolution of the various phases reacting with given reagent. Compared to continuous leaching, flow injection increased the resolution of the various phases using discrete injections of reagents while reducing reagent consumption and minimizing etching of the MS interface. Furthermore, sensitivity was preserved by injecting into air instead of an aqueous carrier. Whether in the continuous or flow injection modes, the proposed approach provides real-time data on what phases are breaking down and what metals are released. It can therefore be used to design effective leaching strategies and to trace isotopic compositions. However, the resulting spectra are complex and the correct determination of some elements requires high-resolution ICPMS.