The Geology of the Cenex Mine: Beaverlodge, Saskatchewan
Tortosa, Delio J.J.
The Cenex uranium deposit occurs in gneisses and schists of the Tazin Group which represent supracrustal rocks folded and metamorphosed to amphibolite rank during the Hudsonian orogeny. During the late stages of the orogenic uplift, cataclastic deformation caused partial retrogression of the rocks to greenschist facies assemblages and their transformation into mylonites, ultramylonites, and mylonite schist. Continued uplift of these rocks led to their brittle fracture, and, contemporaneous erosion on surface resulted in the formation of successor basins in the area. The orebody occurs at the intersection of northwest and northeast-trending fault zones and the ore is localized in breccia zones, along faults, and in veins and the adjacent wallrocks. The host rocks are quartzo-feldspathic mylonites and ultramylonites and chlorite, sericite, quartz, graphite, feldspar mylonite schist. The uranium-bearing minerals are pitchblende and a uraniferous titanate, which commonly occur finely disseminated in the host rocks. Cross-cutting relationships between mineralized structures indicate five stages of uranium mineralization separated by fracturing events· The earliest episode of mineralization is associated with late-stage retrograde metamorphic processes in the mylonite schist, whereas later stages of mineralization are dominated by the intense hematization, carbonatization, and chloritization of the quartzo-feldspathic mylonites and ultramylonites. Traditional genetic models, which metamorphic-hydrothermal sources propose magmatic for the uranium and ore-bearing fluid, have been evaluated and found to be ·inconsistent with the geological history of the rocks and the relative time of emplacement of uranium mineralization. In the Cenex mine area there appears to have been contemporaneity of late uplift, erosion, and deposition of continental clastics on the one hand, and· brittle fracture and uranium mineralization in the basement, on the other. This suggests that the hydrologic system, during and after sedimentation, may have played an important role as a source for ore-bearing fluids- This source would be most important in areas of the basement which were faulted, fractured, and occurred close to the continental clastics - hence the close spatial relationship of the uranium deposits in the Beaverlodge area with the basal unconformity of the Martin Group.
DegreeMaster of Science (M.Sc.)