FIG. 1. Regional geology of the western Superior province, illustrating the boundaries of subprovinces, the locations of the Nipigon plate and the Lac des Iles mine (modified from Ontario Geological Survey, 1991). The subprovince names are shown in italics. The Nipigon plate is the northern extension of the igneous province related to the Midcontinental rift. The inset displays a simplified map of the Superior province. The square outlines the area shown in the figure.