The Key Lake uranium-nickel deposits

CIM Bulletin, Vol. 72, No. 807, 1979

R. GATZWEILER, K. LEHNERT-THIEL D. CLASEN, B. TAN, V. VOULTSIDIS, J.G. STRNAD and J. RICH, Uranerzbergbau, Bonn, West Germany, and Uranerz Exploration and Mining, Saskatoon, Saskatchewan

The Key Lake nickel-uranium deposits are situated within the Wollaston domain of the Churchill structural province. The host rocks of the two orebodies are of Aphebian and Helikian age. The orebodies occur mainly within a 5.2-km-long, northeast-trending zone which coincides with the intersection of the sub-Athabasca unconformity and a reverse fault striking east-northeast. The principal controls of mineralization are structural and lithostratigraphic (i.e., post-Athabasca faults, the sub-Athabasca unconformity and graphitic metapelites in the lower Aphebian, close to the Aphebian/Archean unconformity).Grades of up to 35% U3O8 and 20% Ni are recorded over intervals of up to 2 m. Some hypogene zonation exists and the nickel mineralization tends to underlie the high-grade uranium ore. The ore minerals include pitchblende, α-U3O7, coffinite, gersdorffite, millerite, niccolite, bravoite, zoisite, sericite, chlorite and kaolinite. The kaolinite is a post-ore, supergene alteration product. Chemical studies of the sub-Athabasca paleoweathering profile show that regolithization is characterized by depletion in SiO2 and K2O and concomitant enrichment in Al2O3 and perhaps MgO. In the paleoweathering profile the ferromagnesian minerals are chloritized, the K-feldspars sericitized and the plagioclase saussuritized.Preliminary geochronologic data from the ores reveal U/Pb ages of ~ 1228 my, ~ 960 my and 89 my, and Rb/Sr data indicate basement ages of ~ 1850 my and ~ 1372 my. Aphebian pelitic protoliths, carrying U and Ni, may have released some metals during post-Hudsonian weathering, and minor concentration in structural and geochemical traps may have taken place prior to the deposition of the Athabasca strata. However, it is felt that the bulk of the ore-grade mineralization was generated after the deposition of the Athabasca formation and after faulting, probably during a major regional thermal/intrusive episode of Grenvillian age. Several episodes of remobilization took place between 1228 and 89 my ago.
Keywords: Exploration, Uranium exploration, Key Lake deposits, Nickel, Mineralization, Alteration, Geochronology, Paragenesis, Saskatchewan, Wollaston belt, Gaertner orebody, Deilmann orebody.