Petrology of the "northern granitic rocks" : Wanipigow River area, southeast Manitoba

Abstract

The Northern Granitic Rocks comprise a group of leucocratIc to mesocratic, plutonIc rocks which occur immediately to the north of the Rice Lake Greenstone Belt. An area of two hundred square miles has been mapped at a scale of 1:50,000 and several hundred samples have been studied to provide data on mineralogy, texture, specific gravity and chemical composition. This appears to be a group of truly igneous rocks which are intrusive into the rocks of the Rice Lake Greenstone Belt. Compositional variation exists from an area of homogeneous trondhjemite, characterised by a high silica content and a high soda to potash ratio west of Wallace Lake, to more mafic, hornblende-bearing quartz diorites and diorites east of Wallace Lake. Both field relationships and mineralogical characteristics suggest that the Northern Granitic Rocks are synkinematic intrusions. This suite of rocks bears a strong resemblance to the other quartz diorite plutons in the area and to granitic intrusions bordering greenstone belts in many shield areas of the world.