Uraninite-Albite Veins from the Mistamisk Valley of the Labrador Trough, Quebec

L. Kish and M. Cuney*
Ministère de l'Energie et des Ressources, 1620 boul. de l'Entente, Quebec G1S 4N6, Canada
Centre de Recherches sur la Géologe de l'Uranium, B.P. 23, 54500 Vandoeuvre lès Nancy, France
*And Centre de Recherches Pétrographiques et Géochimiques C.O. no. 1, 54500 Vandoeuvre lès Nancy, France.

Abstract: The uraninite-albite veins of the Mistamisk area occur in the argillite member of the Dunphy Formation, which is near the base of the slightly meta-morphosed Lower Proterozoic sequence of the central Labrador Trough. The vein minerals are albite, uraninite, dolomite, and chlorite, and minor quantities of quartz, tellurides, sulphides, gold, and organic material. Pitchblende and calcite are related to late remobilization.

The veins were deposited in fractures by hydrothermal solutions, and metasomatism caused albitization of wall rocks. Fluid inclusions have an unusual composition, described here for the first time in connection with soda-metasomatism; the aqueous solution of the inclusions is oversaturated in NaCl and contains Ca2+ and Mg2+, and the gas phase mostly consists of N2, CO and CO2. The presence of hematite and absence of hydrocarbons indicates that the vein-forming solution was oxidizing.

The temperature and pressure of vein formation, estimated from fluid inclusion data, was 300°–350° and 2.5 kbar respectively consistent with the composition of the phengite which is a common metamorphic mineral of the host rock. Vein emplacement occurred in the waning stages of the Hudsonian Orogeny, the hydrothermal solution possibly originating by metamorphism of sodic schists of the Mistamisk area, which are possibly of evaporitic origin.

Mineralogical Magazine; December 1981 v. 44; no. 336; p. 471-483; DOI: 10.1180/minmag.1981.044.336.13
© 1981, The Mineralogical Society
Mineralogical Society (www.minersoc.org)