Duffett, and 5 co-aurthors, reported in 2020 that 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 high lights 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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