The Kirkland-Larder Lake stratiform carbonatite

Abstract

The auriferous zone long known as the “Larder Lake Break” and more recently as the “Larder Lake Exhalite” is here interpreted as an exhalative kimberlitic carbonatite on the basis of its K, Ba, Sr, Mg, Fe, Cr, Ni and Co contents, and by comparison with similar younger rocks. Gold is believed to have been deposited syngenetically with this stratiform carbonatite and to be genetically related to late Archean tectonic, volcanic, petrochemical, sedimentary and exhalative processes. Rocks of the Timiskaming Series which host the carbonatite appear to represent a post-uplift graben assemblage of sedimentary and alkalic igneous rocks analagous to modern alkalic-carbonatitic complexes located in rifted upwarps. Preliminary data seems to indicate that carbonatite in general has a higher gold abundance than any other rock type, including iron formations and ultramafic rocks. Ferromagnesian carbonatites, the least common variety, may be worthy untested targets for gold exploration programs, particularly if some pyrite or other sulphide mineral is present.