The Bourlamaque batholith, of Archean age, outcrops in the Val d'Or mining camp of northwest Quebec. In order to describe its geochemistry and interpret its origin, 82 samples of the main igneous body, of synplutonic dykes, and of related later dykes were studied petrographically and analysed for 21 elements. Geochemical interpretation was based mainly on petrochemical variation (Larsen) diagrams and on abundance ratios calculated for several element pairs. The batholith is composed of at least two consanguineous and differentiated dioritic intrusions, probably introduced as sills into surrounding flat-lying volcanic rocks, and now metamorphosed to the greenschist facies. Local metamorphism appears to have been essentially isochemical except for CO2 and Cu. The redistribution of copper during metamorphism seems potentially important for mineral exploration. The Bourlamaque batholith, poor in K, Rb, Sr, Mg, Cr, and Ni, seems chemically very like the enclosing Archean volcanic rocks and similar but not identical to Phanerozoic calc-alkaline suites.