High-resolution aeromagnetic data from the Larder Lake – Kirkland Lake region have been analyzed to develop optimum maps for geologic interpretation. The use of the apparent susceptibility technique has led to a map that shows clearly the major lithologies in a major synclinorium in the Abitibi Greenstone Belt. Calc-alkaline volcanics of the Blake River group are weakly magnetic, but show ring-like anomalies associated with intrusives where magnetite has been generated in the country rock. Alternating bands of Mg-rich and Fe-rich tholeiites of the Kinojevis Group show a strong magnetization associated with the Fe-rich phases. Gabbroic intrusions underlain by serpentine and peridotite give strong levels of magnetization.These various units have been sampled and it is shown that the susceptibility is not high enough to account for the anomalies. Rather, the anomalies are associated with the mean natural remanent magnetization in the formations sampled. These studies have led to a revised geological map of this region.