The Argor body is an elongate intrusion of pyroxenite and carbonatite about 2.5 km long, although the ends were not reached in drilling, with a maximum width of 300 m. It is emplaced into garnet-hornblende-plagioclase gneisses and augen gneisses but is overlain by 13-35 m of Lower Devonian sedimentary rocks of the Sextant Formation. The carbonatite is a complex body of several phases, the principal type comprising 60-68% dolomite, 5-10% riebeckite, 5-15% apatite, 5-10% phlogopite and 2-15% titaniferous magnetite, together with pyrochlore and zircon. Another carbonatite phase forms bands up to 6 m thick consisting of calcite with some apatite and phlogopite; olivine-bearing carbonatite is also present. Pyroxenite appears to have been intruded before the carbonatite and is principally found to the west of it. The pyroxenite consists of augite, salite, with amphibole, sometimes after pyroxene, biotite, and accessory sphene, apatite, titaniferous magnetite and sulphides, including pyrite, pyrrhotine and chalcopyrite.