Variations in the U-and Th-bearing Mineralogy of the Grenvillian granitic pegmatites of Fort-Coulonge, Quebec,Canada

Abstract

The Fort-Coulonge area is located in the Central Metasedimentary Belt (CMB) in the western part of the Grenville Province. For this study, two different types of uraniferous and thoriferous pegmatite, a white granitic and a pink granitic pegmatite. Thorium is frequently more abundant than U and Th/U ratio varies from 0.77 to 25.2, but is usually closer to 2 to 4, indicative of both extensive fractionation and magmatic hydrothermal processes. Thorium is mainly concentrated in thorite or uranothorite, thorogummite, allanite, zircon, monazite, and xenotime, whereas U is included in several minerals, such as uraninite, uranothorite, gummite, swamboite, allanite, zircon, and monazite.