Context of the Deilmann orebody, Key Lake mine, Saskatchewan

The Deilmann orebody was formed at the intersection of the unconformity underlying Athabasca Group and an east-northeast-trending anastomosing zone of deformation centred on graphite-bearing metasedimentary rocks of the Daly Lake Group. Four ductile to brittle-ductile deformational events predated deposition of the Athabasca Group, whereas two brittle deformational events occurred during and after deposition. Alteration and mineralization were intimately related to D5 faults, the most prominent of which is the Key Lake Fault. These formed by the brittle reactivation of older (predating Athabasca Group) fault structures. In a paleovalley on the unconformity surface underlying the Athabasca Group, the basal Athabasca Group sandstone onlaps the erosion surface, indicating early valley-fill deposition. Overlying strata are characterized by horizontal, laterally continuous (sheet-like) bedding. The location and pattern of mineralization suggests that this feature, in part, affected fluid flow. Near-infrared reflectance spectrometry analyses on samples from the Deilmann pit allowed identification of a number of alteration patterns revealing a clear relationship with faults postdating the Athabasca Group. The relative abundance of these different alteration signatures is a useful exploration tool.