The fluorspar deposits of Saint Lawrence, Newfoundland

Abstract

Fluorspar from Newfoundland, eighth ranking producer of the world, comes entirely from the St. Lawrence district. Here pre-Cambrian lavas and pyroclastics, Cambrian sedimentary rocks, Ordovician (?) volcanic and sedimentary rocks, and a Paleozoic alaskite-granite comprise the bedrock.Epithermal fluorite veins occupy steeply dipping fault fissures in granite, rhyolite porphyry, and lamprophyre. Eleven veins show walls bearing nearly horizontal striations; one vein bears only vertical striations; and the walls of three veins show both horizontal and vertical striations. The strikes of nearly all veins are within 45 degrees of the normal to the walls of the elongated granite mass. Some veins are more than a mile long and contain numerous workable lenses. Veins are of two types: high-grade containing over 95 per cent CaF 2 and averaging about 5 feet thick, and lower grade containing about 75 per cent CaF 2 and averaging between 15 and 20 feet thick.Sulphides, present in small quantities, include pyrite, chalcopyrite, sphalerite, and argentiferous galena. Non-metallic gangue minerals are quartz, calcite, and rarely barite. Blastonite, a local name for material composed of microcrystalline quartz and brecciated fluorite, in some places forms as much as 10 per cent of a vein. A nodular type of fluorspar probably formed by alternate rotation of fragments of breccia and deposition of fluorite.Regional zoning is shown by the distribution of barite and green fluorite. Barite shows a distinct zone of localization, and green fluorite predominates in veins both near the granite margins and farther from the granite body.This district will undoubtedly occupy a still more prominent position among producers of fluorspar.