Gold mineralization in the Atikokan area

CIM Bulletin, Vol. 76, No. 851, 1983

B.R. SCHNIEDERS, Resource Geologist, Ontario Ministry of Natural Resources, Thunder Bay, Ontario

Atikokan is 200 km west of Thunder Bay and earned its mining fame from the discovery of the Steep Rock Iron Range in the late 1930s. Gold, however, was discovered in the Atikokan and Mine Centre areas in the late 1800s and eventually led to one of Ontario's first gold camps, and a total production of approximately 52,000 oz of gold and 174,000 oz of silver from 218,000 tons milled. The general geology of the area consists of Early Precam-brian rocks of the Wabigoon and Quetico subprovinces, separated by the east-trending Quetico Fault. The Wabigoon Subprovince, to the north, consists of metavolcanics, minor metasediments and granitic batholiths. The Quetico Sub-province consists of metasediments and granitoids. Small ultramafic plutons occur throughout the metasediments. Within a 50-km radius of Atikokan, more than 50 gold occurrences, prospects and past producers have been discovered since the 1800s. The Atikokan Gold Study performed by the Ontario Geological Survey (Wilkinson, 1980, 1982) defined three types of gold mineralization in which gold is concentrated in quartz and quartz-carbonate veins: 1) Metavolcanic-Hosted, Stratabound Type—associated with altered felsic fragmental units and chemical sedimentary rocks; possible gold mineralization source rocks. The mineralization is due to metamorphogenic (epigenetic) enrichment, associated with dynamic metamorphism events and/or felsic intrusive events.2) Marmion Lake Batholith Type—occurs within the gneissic core of the batholith associated with northeast-trending lineaments, representing faults or shear zones. Mineralized veins are related to several periods of deformation and shearing, suggesting that metamorphogenic veins were produced during dynamic metamorphism.3) Contact Zone Type—occurs in the contact zone rocks between gneissic batholiths and metavolcanic belts. Hydrother-mal solutions produced during several deformational periods acted to leach and concentrate gold mineralization. Localized, discontinuous shear zones host the epigenetic (metamorphogenic) veins. Twenty-one properties in the area were mapped and sampled, and researched petrographically and geochemically. Geological data from the Atikokan Economic Geologist Program of the Ontario Geological Survey are used in discussing the types of mineralization, genetic models, and exploration targets and techiques.

Keywords: Gold deposits, Gold mineralization, Atikokan area, Wabigoon subprovince, Quetico subprovince, Vein mineralization.