Archean geology and silver mineralization controls at Cobalt, Ontario

CIM Bulletin, Vol. 81, No. 910, 1988

R.S. NICHOLS Esso Resources Canada Limited

During 1973 to 1978, Canadaka Mines Limited, a subsidiary of St. Joseph Explorations Ltd., undertook an extensive exploration and development program in the Cobalt area. This program resulted in the delineation of previously unknown stratigraphic units in the Archean volcanic sequence. During this time period, significant ore controls related to area silver deposits were also identified. The Archean geology is comprised of a volcanic pile conformably overlain by sediments. The volcanics contain at least two felsic volcanic centres near the stratigraphic top of the pile. The bulk of the pile consists of mafic flows and interflow sediments. Interflow sediments around silver ore shoots contain mineralized halos of base metal sulphides. The halos exhibit lateral and vertical metal zoning with Cu, Pb and Zn mineralization decreasing away from an ore shoot. Silver mineralization controls determined during the Canadaka program agree with the historically well established importance of Coleman sediments as well as Archean contacts for hosting silver deposits. The vertical extent of ore shoots is typically 150 to 250ft. A strong correlation was found to exist in the Cobalt area between Archean strike and the strike of ore veins. Finally, all Cobalt area ore deposits appear to be associated with a distinct volcanic pile at the top of a sequence of Archean flows.

Mots Clés: Exploration, Development, Mineralization, Archean geology, Cobalt, Canadaka Mines Limited, Silver ore controls.