A petrographic, geochemical, and geochronological study of rare earth element mineralization in the red wine intrusive suite, Labrador, Canada

Abstract

The Red Wine Intrusive Suite is located in central Labrador, in the Grenville Province front zone. This suite consists of two peralkaline silica-undersaturated (agpaitic) bodies which are enveloped by a larger oversaturated component, which previously yielded a U-Pb zircon crystallization age of 1330 +40/-20 Ma. The agpaitic units include melanocratic and leucocratic units that occur both as igneous textured and gneissic rocks, and host two varieties of rare earth element (REE) mineralization. The essential mineral assemblage of these units includes variable amounts of K-feldspar, albite, nepheline, pyroxene, amphibole, and aenigmatite, with local occurrence of eudialyte and britholite as the key REE-bearing minerals. Petrographic, geochemical and geochronological data indicate that the two key REEminerals crystallized at very different times. Eudialyte occurs in an igneous texture but has yielded a U-Pb age of 976 ± 3 Ma, which implies closure of the U-Pb system during cooling after Grenvillian metamorphism. Britholite exhibits a variety of textures, all of which indicate secondary crystallization, agreeing with a U-Pb age of 929 Ma which is considerably younger than the host rocks. Britholite mineralization was likely due to fluid flow within highly deformed melanocratic syenites during a period of orogenic collapse after the Grenvillian Orogeny.