The double S Zone deposit on the north shore of the St. Lawrence Seaway in eastern Quebec, Canada mineralogic, petrogenetic, and geochronologic constraints

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University of New Brunswick


The Main Double S Zone is an alaskite-type uranium deposit located on the north shore of the St. Lawrence Seaway in eastern Quebec, approximately 9 km northwest of the town of Baie Johan Beetz. The uraniferous aplitic and pegmatitic alaskites occur within the late tectonic Lac Turgeon granitic intrusion, which is hosted by metasedimentary units of the Grenvillian Wakeham Bay Group. Several episodes of U mineralization occur within the granite and crosscutting pegmatite dikes. The granite is similar to the pegmatite dikes in petrology, chemistry, and age. SEM-BSE images show uraninite and thorite/uranothorite are the major uranium-bearing minerals and are usually surrounded by chloritic minerals. These uraniferous minerals also occur as inclusions in xenotime, monazite, and zircon and are also be associated with magnetite, rutile, and allanite. Some U minerals are secondary (non-magmatic) occurring within fractures. The geochemical compositions of Rb ranges from 66 to 369 ppm, Nb ranges from 1.2 to 35 ppm, and Y ranges from 3.4 to 130 ppm typify of syn-collisional, peraluminous (ASI =1.15 to 1.26) granitic intrusions of S-type affinity, with evidence of extensive fractionation into the (crustal) A-type granite field. Earlier age dating by U-Pb concordia intercept indicates an age of primary U mineralization formed between 980 and 1000 Ma. The U-Th-Pb CHIME monazite ages obtained indicate average U (2202 ppm) and Th (113066 ppm) in granite and average U (4148 ppm) and Th (118933 ppm) in pegmatite yield ages of 961± 7 Ma and 962 ± 9 Ma, respectively. The pegmatite is probably derived from an evolved phase of the host granite.