| Summary: | The CAGE district was discovered during an exploration survey made in 2005 in Northern Québec, by Claude Caillat (AREVA) and Serge Genest (Omegalpha). The district is located in the northeastern Canadian Shield, at the eastern margin of Ungava Bay. The U showings are located in Paleoproterozoic metasedimentary rocks (Lake Harbour Group) that were deposited on a passive margin epicontinental platform setting. High-grade metamorphism with partial melting occurred during the Torngat collision (1.86–1.74 Ga). Several pegmatoid generations were injected into the metasedimentary rocks. The strongly differing structural, mineralogical and geochemical characteristics of each generation reflect derivation by partial melting from a variety of protoliths. The pegmatoid bodies are generally poorly mineralized in U, except for some located outside the CAGE district (e.g., Amaujaq). Two types of mineralization have been distinguished according to their geological setting, mineralogical, and geochemical characteristics, but both give the same age on uraninite (1790 ± 10 Ma). The first type is hosted by impure dolomitic marble (with phlogopite – olivine – K-feldspar) and skarnoids (diopside – tremolite – phlogopite – K-feldspar – scapolite), resulting from nearly isochemical metamorphism of impure dolomitic limestone or marl. The ore mineral is pure uraninite with REE patterns characterized by a decreasing fractionation from the LREE to HREE, with neutral or a slightly positive Eu anomaly and a low total REE. The uraninite is consistently associated with enriched Ba (Ba-rich K-feldspar and phlogopite, celsiane, kampfite, baryte), V (coulsonite Fe++V+++2O4, V-pyroxene), Zn(sphalerite), Pb (non-radiogenic galena), S-Cu (pyrite, pyrrhotite, chalcopyrite, chalcosite), As (arsenopyrite), Sb (ullmannite NiSSb) and Mo (molybdenite). The scapolite composition (40 < marialite % < 60) and kampfite [Ba12(Si11Al5)O31(CO3)8Cl5] suggest the influence of evaporitic fluids. Graphite is locally observed in the marble. Organic matter ...
|
|---|