The rocks of the Tazin Lake region, north of Lake Athabasca, have been subdivided into three major complexes: the Northeastern basement complex, mainly composed of a syn-to-late tectonic granodiorite-diorite series; a central meta-sedimentary and gneissic belt; and the Western granodiorite complex. Mylonitization, folding, and faulting are common in the centrally located meta-sedimentary and gneissic belt. Twenty new radiometric age determinations by the K–Ar method on biotite and amphibole of the granodiorite–diorite series average 2370 ± 40 m.y. Fragmentation of late tectonic basic dikes and remobilization of the granodiorite–diorite series have been provisionally correlated with this established minimum age. The Western granodiorite complex was intruded 1900 m.y. ago. One biotite sample from White Lake granite of the meta-sedimentary and gneissic belt indicates an apparent K–Ar age of 1800 m.y.