The metasomatic changes that accompany uranium mineralization in the nonorogenic rhyolites of the Upper Aillik Group, Labrador

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Authors:White, M. V. W.; Martin, Robert F.
Author Affiliations:Primary:
X-Plor Int., Oakville, ON, Canada
McGill Univ., Canada
Volume Title:Canadian Mineralogist
Source:The Canadian Mineralogist, Vol.18(Part 4), p.459-479. Publisher: Mineralogical Association of Canada, Ottawa, ON, Canada. ISSN: 0008-4476
Publication Date:1980
Note:In English with French summary. 59 refs.; illus. incl. 3 anals., 2 tables, geol. sketch map
Summary:Textures and mineral assemblages of the porphyritic rhyolites and tuffs of the Upper Aillik group (Labrador) are interpreted as indicating very low-P crystallization in a rift-related environment. 18 XRF rock analyses are reported (including contents of Zr, Pb, Zn, and Cu) as well as NAA values for U, Th and, for 8 samples, RE. These data along with analytical data from Gandhi are considered to suggest these rocks are products of highly evolved pre-orogenic granitic melts. The tuffs were probably originally mostly glassy and enriched in alkalis, U, Th, and other incompatible elements whose primary concentrations have been disturbed by autometasomatic reactions: K-metasomatism that did not affect primary U/Th ratios; and somewhat higher temperature Na- metasomatism and desilication associated with important U mineralization in a mildly peralkaline environment. Feldspar textures and mineralogy indicate the direction of metasomatic enrichment which is suggestive of fenitization-type reactions: Zr, Pb, CO2, Cl and F increasing and Th, Cu, and S decreasing with desilication. The mobilization of the residual elements probably accompanied devitrification of glass shards and pumice fragments in the ash. Rock-fluid interaction may have been long-lived, as the ignimbrites and plugs may have been surface expressions of an epizonal granitic complex. Distinctly later orogenies may have been important factors in the development of economic concentrations of U. [L.C.C.]
Subjects:Alkali feldspar; Autometamorphism; Chemical composition; Controls; Devitrification; Economic geology; Feldspar group; Framework silicates; Geochemistry; Igneous rocks; Ions; Metal ores; Metals; Metamorphism; Metasomatism; Mineral deposits, genesis; Minerals; Petrology; Processes; Pyroclastics; Rare earths; Rhyolites; Silicates; Thorium ores; Tuff; Uranium ores; Volcanic rocks; Canada; Eastern Canada; Labrador; Newfoundland; Burnt Lake; Central Mineral Belt; Michelin; Upper Aillik Group; White Bear Mountain
Coordinates:N520000 N520000 W0630000 W0630000
Abstract Numbers:82M/0227
Record ID:1981052185
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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