Wapikopa Lake is an elliptical complex covering 98 km2, intruded into Precambrian orthogneisses. It consists of a core of pyroxene syenite with an outer zone, best developed in the southeast, of a mafic pyroxene syenite. The mafic syenite consists of 25-70% augite/aegirine-augite in crystals up to 1 cm in length and sometimes rimmed by amphibole, perthite, up to 15% apatite, abundant sphene and a little quartz. The core syenites are mineralogically similar but with only 5-35% pyroxene. Dykes of amphibole syenite occur on the northwestern margin of the complex. The syenites are highly potassic and BaO values approach 1.5%.