Kirkland Lake

Alkaline lavas and tuffs occur in the Timiskaming Group of the Abitibi Volcanic Belt, which is perhaps the largest continuous greenstone belt in the world. The Timiskaming Group comprises a sequence of conglomerates, lithic sandstones, greywackes and argillites, andesites and pyroclastic rocks. They vary in thickness from 2200 to 4500 m, extend east-west over 45 km and dip to the south between 30° and 60°. Contemporaneous small intrusions of syenite penetrate both sedimentary and volcanic units. All the rocks have been moderately metamorphosed but primary textures and mineralogy generally still survive. There are four principal volcanic sequences, each separated by a considerable thickness of sedimentary rocks, and each contains lavas and pyroclastics though the proportions differ from area to area. Rock types include andesite, trachyte and quartz trachyte, what are probably leucite-bearing rocks, and minor basalt. The trachytes vary from rocks consisting of sodic plagioclase, sanidine, augite, magnetite and apatite to mafic varieties with 25-60% of olivine, augite/aegirine-augite, hornblende and biotite. Fresh leucite does not occur, but pseudoleucites from 0.5-2 cm in diameter constitute 5-90% of the leucitic lavas, which vary from leucite tephrite through trachyte to phonolitic types. The pseudoleucites comprise varying proportions of alkali feldspar, carbonate and sericite and other minerals include orthoclase, sodic plagioclase, biotite and chlorite. All the rock types are represented among the pyroclastics with crystals of feldspar, pyroxene, hornblende and pseudoleucite in crystal tuffs. Conglomerates overlying the volcanics contain a high proportion of volcanic cobbles including leucitic lavas with fresh melanite, which have not been found in the flows, probably because of alteration. Carbonate-rich rocks lying immediately south of the alkaline volcanics in the eastern part of the outcrop were thought to be carbonatites by Stricker (1978), but this interpretation is disputed (Hyde, 1980; Stricker, 1980). Rock analyses will be found in Cooke and Moorhouse (1969), Basu et al. (1984) and Ujike (1985).