Textural and compositional complexities resulting from coupled dissolution–reprecipitation reactions in geomaterials

Altree-Williams, Alexander; Pring, Allan; Ngothai, Yung; Brugger, Joël

doi:10.1016/j.earscirev.2015.08.013

Cited by 129 publications

(67 citation statements)

References 197 publications

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“…Localities such as Tsumeb (Namibia), Långban (Sweden), Lengenbach (Switzerland), Shinkolobwe (Democratic Republic of Congo), and Franklin Accessibility to the nano-to microscale domain has permitted a better understanding of the critical mechanisms involved in fluid-mineral reaction. Coupled dissolution replacement reaction (CDRR) [170][171][172] is recognised as a widespread phenomenon that is responsible for local-scale mineral transformation in hydrothermal ores. In our work on the Olympic Dam deposit, evidence for CDRR is recorded in feldspars [36,46], uraninite [76,77,173], hematite [162], and REE-fluorocarbonates [43].…”

Section: Discovery Of New Mineralsmentioning

confidence: 99%

Advances and Opportunities in Ore Mineralogy

et al. 2017

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Abstract:The study of ore minerals is rapidly transforming due to an explosion of new microand nano-analytical technologies. These advanced microbeam techniques can expose the physical and chemical character of ore minerals at ever-better spatial resolution and analytical precision. The insights that can be obtained from ten of today's most important, or emerging, techniques and methodologies are reviewed: laser-ablation inductively-coupled plasma mass spectrometry; focussed ion beam-scanning electron microscopy; high-angle annular dark field scanning transmission electron microscopy; electron back-scatter diffraction; synchrotron X-ray fluorescence mapping; automated mineral analysis (Quantitative Evaluation of Mineralogy via Scanning Electron Microscopy and Mineral Liberation Analysis); nanoscale secondary ion mass spectrometry; atom probe tomography; radioisotope geochronology using ore minerals; and, non-traditional stable isotopes. Many of these technical advances cut across conceptual boundaries between mineralogy and geochemistry and require an in-depth knowledge of the material that is being analysed. These technological advances are accompanied by changing approaches to ore mineralogy: the increased focus on trace element distributions; the challenges offered by nanoscale characterisation; and the recognition of the critical petrogenetic information in gangue minerals, and, thus the need to for a holistic approach to the characterization of mineral assemblages. Using original examples, with an emphasis on iron oxide-copper-gold deposits, we show how increased analytical capabilities, particularly imaging and chemical mapping at the nanoscale, offer the potential to resolve outstanding questions in ore mineralogy. Broad regional or deposit-scale genetic models can be validated or refuted by careful analysis at the smallest scales of observation. As the volume of information at different scales of observation expands, the level of complexity that is revealed will increase, in turn generating additional research questions. Topics that are likely to be a focus of breakthrough research over the coming decades include, understanding atomic-scale distributions of metals and the role of nanoparticles, as well how minerals adapt, at the lattice-scale, to changing physicochemical conditions. Most importantly, the complementary use of advanced microbeam techniques allows for information of different types and levels of quantification on the same materials to be correlated.

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Section: Discovery Of New Mineralsmentioning

confidence: 99%

Advances and Opportunities in Ore Mineralogy

et al. 2017

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“…A study by Xia et al (2009) has shown that during mineral replacement reactions, when the ratecontrolling step is dissolution, there may be perfect preservation of the mineral microstructure inherited from the parent phase (micro and nano-scale pseudomorphism). The relevance of coupled dissolution-precipitation reactions to a wide range of fluid-solid reactions has been recently reviewed by Ruiz-Agudo et al (2014) and Altree-Williams et al (2015). As well as describing reequilibration reactions occurring in the Earth, these reactions may be used to design new materials with specific engineered and functionalized properties.…”

mentioning

confidence: 99%

The replacement of a carbonate rock by fluorite: Kinetics and microstructure

Pedrosa

Boeck

Putnis

et al. 2017

American Mineralogist

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Understanding the mechanism and kinetics of the replacement of carbonates by fluorite has application in Earth sciences and engineering. Samples of Carrara marble were reacted with an ammonium fluoride (NH 4 F) solution for different reaction times and temperatures. The microstructure of the product phase (fluorite) was analyzed using SEM. The kinetics of replacement was monitored using Rietveld analysis of X-ray powder diffraction patterns of the products. After reaction, all samples preserved their size and external morphology (a pseudomorphic replacement). The grain boundaries of the original marble were preserved although each calcite grain was replaced by multiple fine crystals of fluorite creating inter-crystal porosity. The empirical activation energy E a (kJ/mol) of the replacement reaction was determined by both model-fitting and model-free methods. The isoconversional method yielded an empirical activation energy of 41 kJ/mol, and a statistical approach applied to the modelfitting method revealed that the replacement of Carrara marble by fluorite is better fitted to a diffusion-controlled process. These results suggest that the replacement reaction is dependent on the ion diffusion rate in the fluid phase through the newly formed porosity.

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“…In detail, the model predicts that bornite (±chalcocite) is usually accompanied by uraninite enrichment, while chalcopyrite is accompanied by fluorite enrichment. Li et al [94] demonstrated experimentally that reactions among sulfide minerals create microenvironments that result in efficient scavenging of U from solution and provide evidence that kinetic factors also favor the enrichment predicted by the equilibrium thermodynamic calculations [95]. Results from the step-flow reactor model are consistent with mineralogical observations from OD.…”

Section: Remobilization and Upgrading Of Uranium Bymentioning

confidence: 65%

Uranium Transport in F-Cl-Bearing Fluids and Hydrothermal Upgrading of U-Cu Ores in IOCG Deposits

et al. 2018

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Uranium mineralization is commonly accompanied by enrichment of fluorite and other F-bearing minerals, leading to the hypothesis that fluoride may play a key role in the hydrothermal transport of U. In this paper, we review the thermodynamics of U(IV) and U(VI) complexing in chloride-and fluoride-bearing hydrothermal fluids and perform mineral solubility and reactive transport calculations to assess equilibrium controls on the association of F and U. Calculations of uraninite and U 3 O 8 (s) solubility in acidic F-rich (Cl : F = 100 [ppm-based]) hydrothermal fluids at 25-450°C, 600 bar, show that U(IV)-F complexes (reducing conditions) and uranyl-F complexes (oxidizing conditions) predominate at low temperature (T <~200°C), while above~250°C, chloride complexes predominate in acidic solutions. In the case of uraninite, solubility is predicted to decrease dramatically as U(IV)Cl 2 2+ becomes the predominant U species at T > 260°C. In contrast, the solubility of U 3 O 8 (s) increases with increasing temperatures. We evaluated the potential of low-temperature fluids to upgrade U and F concentrations in magnetite-chalcopyrite ores. In our model, an oxidized (hematite-rich) granite is the primary source of F and has elevated U concentration. Hydrothermal fluids (15 wt.% NaCl equiv.) equilibrated with this granite at 200°C react with low-grade magnetite-chalcopyrite ores. The results show that extensive alteration by these oxidized fluids is an effective mechanism for forming ore-grade Cu-U mineralization, which is accompanied by the coenrichment of fluorite. Fluorite concentrations are continuously upgraded at the magnetite-hematite transformation boundary and in the hematite ores with increasing fluid : rock (F/R) ratio. Overall, the model indicates that the coenrichment of F and U in IOCG ores reflects mainly the source of the oreforming fluids, rather than an active role of F in controlling the metal endowment of these deposits. Our calculations also show that the common geochemical features of hematite-dominated IOCG deposits can be related to a two-phase process, whereby a magnetite-hematite-rich orebody (formed via a number of processes/tectonic settings) is enriched in Cu ± U and F during a second stage (low temperature, oxidized) of hydrothermal circulation.

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Textural and compositional complexities resulting from coupled dissolution–reprecipitation reactions in geomaterials

Cited by 129 publications

References 197 publications

Advances and Opportunities in Ore Mineralogy

Advances and Opportunities in Ore Mineralogy

The replacement of a carbonate rock by fluorite: Kinetics and microstructure

Uranium Transport in F-Cl-Bearing Fluids and Hydrothermal Upgrading of U-Cu Ores in IOCG Deposits

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