Geology of the Bayonet, Ashton, Potts and Charles Lakes Districts, Alberta

The geology of 308.5 square miles of Precambrian Shield in northeastern Alberta is presented on six colored maps of scale 2 inches to 1 mile. Some 22 rock-types have been distinguished on the maps. Their characteristics are systematically described and modal analyses are given. The older granite gneiss complex of biotite and hornblende granite gneisses with minor amphibolite and metasedimentary rocks forms the predominant terrain. Biotite granite is petrologically distinct and unique in its close association with certain metasedimentary rock bands. All of these rock-types have been locally subjected to intensive cataclasis to give rise to four major mylonite zones, which generally extend tens of miles in length and up to one mile in width. Post-cataclastic intrustions of massive to foliated granites are concentrated in a band to the west. The last phase of igneous activity is recorded by uncommon small basic dykes. Later confined fault movements have developed secondary mylonites and breccias which are aligned within the major mylonite zones, and a late series of transverse faults offsets some rock contacts. A northerly regional structural trend prevails, expressed as a general alignment of gneissosity and schistosity, of metasedimentary, amphibolite and granite bonds and masses, and of major mylonite zones.