The Long Lake Diorite and Associated Rocks, Sudbury District, Ontario

The igneous petrology of an area near the Long Lake gold mine, Sudbury district. Ontario, is described. The area lies at the contact of a region of folded sediments and one of granite-gneiss. Two rock types, Keweenawan diabase and Long Lake diorite, resulted from the injection of basic magma into the sediments. Later a large granitic batholith invaded the region. Reaction between the magma and the quartz-rich sediments is postulated to account for a border phase of very quartz-rich tonalite. The Long Lake diorite grades into a more acidic phase and this phase is explained as due to emanations from the batholith affecting the diorite and adding silica and soda.