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Journal article
Hydrothermal mineral replacement of bastnäsite by rhabdophane and monazite: effects of temperature on mineralogy, REE immobilisation, and fractionation
Contributions to mineralogy and petrology, Vol.179(11), 101
2024
Abstract
The rare-earth elements (REEs, La–Lu, Y) are essential for the development of renewable technologies. Bastnäsite (REECO3F) is a common REE ore mineral that is often subject to hydrothermal alteration at all crustal levels. Mechanisms of hydrothermal bastnäsite alteration therefore govern the evolution of REE deposits, though these mechanisms remain poorly understood. This experimental work investigates the hydrothermal replacement of bastnäsite by rhabdophane (REEPO4∙xH2O, x = 0–1) and monazite (REEPO4) in phosphatic fluids. Two temperature-dependent alteration pathways were identified; both follow the coupled dissolution-reprecipitation (CDR) mechanism. At 90 °C, bastnäsite was replaced by highly-porous metastable rhabdophane which was then replaced by monazite, forming an inner layer of rhabdophane and an outer layer of monazite. At 220 °C, bastnäsite was replaced directly by monazite. Although replacement initiated more quickly at 220 °C, greater overall replacement occurred at 90 °C (~ 61 wt.% after 500 h, compared to ~ 13 wt.% at 220 °C) due to surface passivation by monazite at 220 °C. Geochemical analyses showed REE fractionation during bastnäsite alteration. At 90 °C, rhabdophane was enriched in heavy REEs (Eu–Lu, Y), likely due to the evolving fluid chemistry, while at 220 °C secondary monazite was enriched in Sm and Ho compared to bastnäsite. These results indicate that: 1) the hydrothermal alteration of bastnäsite by rhabdophane and monazite in ore deposits leads to REE immobilisation, with little net loss of REEs to solution; 2) rhabdophane is metastable relative to monazite at 90 °C, and; 3) variable temperatures can cause different mineral textures and REE fractionation trends during hydrothermal alteration and mineral replacement.
Details
- Title
- Hydrothermal mineral replacement of bastnäsite by rhabdophane and monazite: effects of temperature on mineralogy, REE immobilisation, and fractionation
- Authors/Creators
- Manuel Knorsch - Sustainable Geochemistry and Mineral Sciences, School of Mathematics, Statistics, Chemistry and Physics, Murdoch University, Australian Resources Research Centre, CSIRO Mineral Resources, RSCTobias G. Bamforth - Murdoch UniversityFang Xia - Murdoch University, Centre for Water, Energy and WasteArtur P. Deditius - Murdoch University, Centre for Water, Energy and WasteMark A. Pearce - Mineral ResourcesLouise Schoneveld - Mineral ResourcesMalcolm P. Roberts - The University of Western Australia
- Publication Details
- Contributions to mineralogy and petrology, Vol.179(11), 101
- Publisher
- Springer Berlin Heidelberg
- Number of pages
- 23
- Grant note
- DP170101893; DP200102284 / Australian Research Council (http://dx.doi.org/10.13039/501100000923)
- Identifiers
- 991005717068507891
- Copyright
- © The Author(s) 2024
- Murdoch Affiliation
- School of Mathematics, Statistics, Chemistry and Physics
- Language
- English
- Resource Type
- Journal article
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