Uranium mineralization in the Kitts-Post Hill belt of the Central Mineral Belt (CMB) of Labrador, Canada is concentrated in the upper portion of the Paleoproterozoic Post Hill Group, along a structurally complex shear zone that developed during ca. 1860–1800 Ma orogenic events. Recent research in the CMB highlights regional-to deposit-scale features such as Na-, Ca-Fe-, K- and K-Fe- alteration and hydrothermal breccia zones characteristic of iron oxide and alkali-calcic alteration systems that host iron oxide-copper–gold (IOCG) and affiliated deposits. Potential genetic links between the CMB uranium district and metasomatic systems hosting IOCG deposits was explored through petrography and trace element chemistry of uraninite. The least-altered uraninite grains from mineral occurrences in the Kitts-Post Hill belt contain elevated Th, Zr, Y and rare earth element (REE) contents, implying primary uranium mineralization from high temperature, alkaline fluids capable of transporting high field-strength elements – similar to deposits in iron oxide and alkali-calcic alteration systems. Quantitative LA-ICP-MS mapping of uraninite at the Kitts deposit demonstrates remobilization of U, Pb and light-REE along grain boundaries and fractures, coupled with zones of elevated Zr, and lower Th and REE contents that record element leaching during alteration and/or recrystallization. In chondrite-normalized REE plots of uraninite, contrasting REE patterns define three populations of uraninite grains that formed under different temperature and physico-chemical conditions. Leaching of light-REE from uraninite grains support recent studies that indicate light-REE signatures of uraninite can be disturbed under certain conditions, whereas the primary signatures of heavy-REE remain preserved. The inferred contrasting fluid sources revealed by the major and trace element composition of uraninite suggest that metasomatism and mineralization involved a complex and evolving fluid history, complicated by post-ore magmatism and metamorphism.

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Ore Geology Reviews
Ottawa-Carleton Geoscience Centre

Duffett, C.L. (Charlene L.), Potter, E.G. (Eric G.), Petts, D.C. (Duane C.), Acosta-Gongóra, P. (Pedro), Cousens, B, & Sparkes, G.W. (Greg W.). (2020). The evolution of metasomatic uranium ore systems in the Kitts-Post Hill belt of the Central Mineral Belt, Labrador, Canada. Ore Geology Reviews, 126. doi:10.1016/j.oregeorev.2020.103720