Discovery of Kimberlites in the Kirkland Lake Area Northern Ontario, Canada PART I: Early Surveys and the Surficial Geology

Exploration & Mining Geology, Vol. 1, No. 4, 1992

J.J. BRUMMER, Toronto, Ontario, Canada, D.A. MacFADYEN, Scarborough, Ontario, Canada, and C.C. PEGG, LAC Minerals Ltd., Toronto, Ontario, Canada

The first record of a kimberlite found in Canada (1946) was the identification of thin dykes intersected while drilling for gold in Michaud Township, Ontario. Sampling of the Munro Esker (1964) in the Kirkland Lake area, Ontario, by the Geological Survey of Canada identified the occurrence of detrital grains of pyrope garnets along a length of 35 km of the 113 km tested. A search for the source of the garnets resulted in the identification (1968) of a narrow subsurface kimberlite dyke in the Upper Canada Mine. This discovery resulted in a staking rush. Unfortunately, subsequent work did not identify the source of the kimberlite indicator minerals. During 1978 the Ontario Geological Survey started a multi-discipline study of 29 townships (2560 km2) in the Kirkland Lake area, to encourage exploration for gold, base metals, and kim-berlites. Back-hoe sampling (1979 to 1982), where the overburden was thin, and reverse circulation drilling, in areas of thicker drift, yielded samples of the till. These were analyzed for several elements and a mineralogical identification of the heavy minerals was completed. Pyrope and chrome diopside grains were identified. Studies of the Pleistocene geology indicated only the most recent direction (167 degrees) of ice advance (Matheson) and the associated deposits, out of a possible three advances known to occur in the general region straddling the Ontario-Quebec boundary, is present in the immediate area of Kirkland Lake. Contouring the distribution of pyrope grains (1990) showed a concentration centered over an area of 616 km2 extending down-ice from Gauthier Township. This included a smaller area containing chrome diopside grains. Kimberlite boulders were identified (1981) in gravel pits on the Munro and Misema River Eskers located within this anomalous area. The next step would be to use the airborne geophysical data to locate the kimberlite pipes which yielded the indicator minerals and boulders. The source area is likely to be in the northern half of the Ontario Geological Survey study area.