The Evolution of Metasomatic Uranium Ore Systems in the Central Mineral Belt of Labrador

Abstract

In quantitative LA-ICP-MS maps of uraninite from the Kitts-Post Hill belt in Central Labrador, remobilization of U and LREE along grain boundaries/fractures support the varying degrees of alteration recorded in major/trace element chemistry. Primary uraninite contains elevated Th, Zr, and REE contents implying crystallization from high-temperature fluids capable of transporting HFSE. Altered grains are characterized by elevated Zr, low Th and low REE contents, indicating potential remobilization in response to regional tectonic-magmatic events. In chondritenormalized plots of uraninite, contrasting REE signatures imply three populations, formed under different temperatures/physico-chemical conditions. Magnetite geochemistry reveals at least two events, characterized by both magmatic-like V contents, and hydrothermal Ni/Cr ratios. The inferred contrasting fluid sources, reflected in the major/trace element compositions, reveal a fluid history complicated by post-ore magmatism and metamorphism. Potential syn-uranium mineralization hydrothermal zircon grains from the Kitts and Gear deposits were analyzed by SHRIMP and record isotopic re-setting ca. 1800 Ma.