Paragenesis of the Dazzler Heavy Rare Earth (HREE) and Uranium Deposit, Browns Range, Western Australia
Date
2022
Authors
Cillins, B. N.
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Abstract
Unconformity-related rare earth (REE) mineralisation occurs at Browns Range, Western Australia, where hydrothermal basinal brines mobilise REE from the Archean Browns Range Metamorphics (BRM) to interact with phosphorus-bearing meteoric fluids permeating from the unconformably overlying Paleoproterozoic Birrindudu Group. Significant contributions to the understanding of these systems have been made with a principal focus on the Wolverine heavy rare earth (HREE) deposit, which is situated completely within the BRM, with no real known proximity to the overlying sandstones that play a major role in ore formation. The Dazzler HREE deposit, discovered in 2018, is situated on the unconformity across three lithologies, the BRM, an argillaceous metasediment at the base of the Birrindudu Group’s Gardiner Sandstone, and within fractures immediately overlying. Investigation into the paragenesis of the Dazzler deposit opens the opportunity to revisit the unconformity-related REE model. This study investigates the major element geochemical composition of the host lithologies using major element geochemical and hyperspectral drill core analysis to determine alteration assemblages, petrographical analysis with SEM-EDS, and U-Pb dating of xenotime with LA-ICPMS.
Major element geochemistry constrains host BRM to an arkose (sublitharenite) and the argillaceous metasediment to a wacke (shale). HREE mineralisation predominantly occurs as clay-replacement of the argillaceous metasediment host with perching into the fractures of the overlying GSS and a mineral assemblage of xenotime ± florencite ± rutile ± torbernite. Minor breccia hosted REE mineralisation within the BRM is enriched in light rare earths (LREE) with a florencite ± xenotime ± rutile assemblage. Florencite abundance in the underlying breccias provide further insight into LREE – HREE fractionation. Torbernite is localised in fractures within the clay-replacement xenotime, appears texturally later than REE and may be precipitating using local Fe as a reductant. K-feldspar – muscovite alteration is evident within the BRM, consistent with that of Wolverine. Additional intermediate argillic – phyllic alteration of the already mica-rich argillaceous metasediment occurs syn-REE deposition. Age ranges of xenotime of 1679 – 1633 Ma are presented and were generally discordant, with a concordant age of 1641 ± 10.4 Ma (MSWD = 12). These coincide with the main- breccia hosted REE mineralising event seen at Wolverine. Exploration targets were provided, with a focus to the south of Dazzler and Rogue prospects recommended.
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School of Physical Sciences
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Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, YEAR
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