The nature of orthomagmatic, carbonatitic fluids precipitating REE,Sr-rich fluorite: fluid-inclusion evidence from the Okorusu fluorite deposit, Namibia

Bühn, Bernhard; Rankin, A. H.; Schneider, Jens; Dulski, Peter

doi:10.1016/s0009-2541(01)00421-1

Cited by 99 publications

(47 citation statements)

References 37 publications

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“…Syn-fenitising fluid inclusions trails at Chilwa Island are recognised by their spatial coincidence within distinctive low-luminescent CL zones (Dowman, 2014), similar to that seen by Bühn et al (2002) at the Okorusu fluorite deposit in Namibia.…”

Section: Fluid Inclusion Datamentioning

confidence: 62%

Granitoid zircon forms the nucleus for minerals precipitated by carbonatite-derived metasomatic fluids at Chilwa Island, Malawi

et al. 2017

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Mineralogical assemblages are fundamental to the interpretation of geological processes. Zircon is an integral petrographic component of the mineral assemblages present in fenites (rocks formed by alkaline metasomatism) associated with the 136 Ma-aged Chilwa Island carbonatite complex, Malawi. Zircon exhibits contrasting characteristics and properties across the fenite aureole that surrounds the carbonatite stock. It shows intense grain dissolution and subsequent replacement by pyrochlore in the more intensely metasomatised 'high-grade' fenite of the innermost part of the aureole. By contrast, relict zircon crystals form the nucleus for the development of apatite-ilmenite-REE mineral assemblages in less altered zones. These changes in zircon properties are considered to be evidence of the diverse nature of fluids that metasomatised the Chilwa Islands fenite aureole. Although zircon is a principal component of the fenite mineral assemblages, when dated by LA-ICP-MS techniques it was found to predate the other minerals present in the mineral assemblages and, thus, the age of carbonatite intrusion, by over 380 Ma. Instead of co-crystallising with the assemblage, zircon is therefore interpreted as providing a focus around which the minerals in the fenite assemblage formed. This implies that caution is needed both in the interpretation of Zr mobility in metasomatic assemblages, and also in attributing a zircon age to the assemblage as a whole in such sequences.

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Section: Fluid Inclusion Datamentioning

confidence: 62%

Granitoid zircon forms the nucleus for minerals precipitated by carbonatite-derived metasomatic fluids at Chilwa Island, Malawi

et al. 2017

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“…The three main subsystems were modeled with variable temperature (150 and 350 ∘ C), initial XCO 2 (0.01-0.1), and salinity (0.5 and 20 wt.% NaCl). The initial REE concentration was set to 100 ppm, within the upper range of concentrations retrieved from natural fluid inclusion data [10,23,25,39,69,70], and used in previous numerical modeling studies [71]. Variable pH values were fixed in the speciation model by titrating different amounts of NaOH into the starting fluids to reach saturation with calcite.…”

Section: Simulation Setupmentioning

confidence: 99%

“…Quartz-hosted fluid inclusions are generally used within mineralized carbonatites and peralkaline igneous complexes to determine the salinity, metal concentrations, and temperature of such ore-forming fluids [4,16,[21][22][23][24][25][26]. Another approach that can be used to understand the evolution of fluids in REE mineral deposits is the study of fluid-mineral trace element partitioning.…”

Section: Introductionmentioning

confidence: 99%

Rare Earth Elements in Mineral Deposits: Speciation in Hydrothermal Fluids and Partitioning in Calcite

Perry

Gysi

2018

Geofluids

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is properly cited.Studying the speciation and mineral-fluid partitioning of the rare earth elements (REE) allows us to delineate the key processes responsible for the formation of economic REE mineral deposits in natural systems. Hydrothermal REE-bearing calcite is typically hosted in carbonatites and alkaline rocks, such as the giant Bayan Obo REE deposit in China and potential REE deposits such as Bear Lodge, WY. The compositions of these hydrothermal veins yield valuable information regarding pressure ( ), temperature ( ), salinity, and other physicochemical conditions under which the REE can be fractionated and concentrated in crustal fluids. This study presents numerical simulation results of the speciation of REE in aqueous NaCl-H 2 O-CO 2 -bearing hydrothermal fluids and a new partitioning model between calcite and fluids at different --conditions. Results show that, in a high CO 2 and low salinity system, bicarbonate/carbonate are the main transporting ligands for the REE, but predominance shifts to chloride complexes in systems with high CO 2 and high salinity. Hydroxyl REE complexes may be important for the solubility and transport of the REE in alkaline fluids. These numerical predictions allow us to make quantitative interpretations of hydrothermal processes in REE mineral deposits, particularly in carbonatites, and show where future experimental work will be essential in improving our modeling capabilities for these ore-forming processes.

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“…In the latter deposits, the carbonatites were strongly overprinted by hydrothermal fluids resulting in remobilization and precipitation of the REE in vug-and vein-hosted assemblages. Although it is widely believed that these fluids originate from the carbonatite (Currie and Ferguson, 1971;Kresten 1988;Wyllie, 1989;Gittins et al, 1990) and fluid inclusion studies (e.g., Bühn and Rankin, 1999;Bühn et al, 2002; have documented the nature of the fluids exsolving from carbonatites, the controls on the REE mineralization are poorly understood. In many carbonatite-hosted deposits, there is a close association of the REE mineralization with fluorite (e.g., Amba Dongar, Doroshkevich et al, 2009;Bear Lodge, Moore et al, 2015), and this has led some authors (Möller et al, 1980;Salvi and Williams-Jones, 1990;Williams-Jones et al, 2000) to suggest that the REE are transported as fluoride complexes, particularly as such complexes are known to be extremely stable (Migdisov et al, 2009 i.e., REE-fluorocarbonates that are associated with barite, fluorite, and quartz (Doroshkevich et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

The Nature and Origin of the REE Mineralization in the Wicheeda Carbonatite, British Columbia, Canada

et al. 2016

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In response to rising demand of the rare earth elements (REE), recent exploration of the British Columbia alkaline province has identified the Wicheeda Carbonatite, which contains an estimated 11.3 million tons of light REE-enriched ore grading 1.95 wt.% TREO, to be the highest-grade prospect known in British Columbia. However, research of the deposit is restricted to one paper describing mineralization in carbonatite dikes adjacent to the main plug. This study describes the nature and origin of REEmineralization in the Wicheeda plug.The carbonatite was emplaced in metasedimentary limestone and argillaceous limestone belonging to the Kechika Group, which has been altered to potassic fenite immediately adjacent to the carbonatite and to sodic fenite at greater distances from it. The carbonatite comprises a ferroan dolomite core, which passes outwards gradationally into calcite carbonatite. Three texturally distinct varieties of dolomite have been recognized. Un modèle est proposé dans lequel la carbonatite calcitique est la phase magmatique la plus précoce. Cette phase a atteint la saturation en niobium très tôt, entrainant la précipitation du pyrochlore. Le magma a évolué plus tardivement vers une composition de carbonatite dolomitique qui, lors de son refroidissement, a exsolvé un fluide aquocarbonique altérant les métasédiments de Kechika en fénite potassique et se mélangeant avec les eaux formationelles, plus distales, pour produire les fénites sodiques.Le fluide aquo-carbonique a mobilisé et transporté les ETR sous la forme de complexes chlorurés, au sein de la porosité et des fractures de la carbonatite dolomitique. A la suite des interactions fluide-roche prolongées, les ETR ont précipité du fait du refroidissement et de l'augmentation du pH ; la présence d'apatite a entrainé la formation de monazite-(Ce). La concentration hydrothermale a permis une répartition homogène des teneurs, avec la carbonatite dolomitique contenant dans son ensemble plus de 1 % TREO, faisant de Wicheeda un gisement très attrayant. Contributions of AuthorsThis thesis has been written in manuscript format in accordance with the regulations put

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The nature of orthomagmatic, carbonatitic fluids precipitating REE,Sr-rich fluorite: fluid-inclusion evidence from the Okorusu fluorite deposit, Namibia

Cited by 99 publications

References 37 publications

Granitoid zircon forms the nucleus for minerals precipitated by carbonatite-derived metasomatic fluids at Chilwa Island, Malawi

Granitoid zircon forms the nucleus for minerals precipitated by carbonatite-derived metasomatic fluids at Chilwa Island, Malawi

Rare Earth Elements in Mineral Deposits: Speciation in Hydrothermal Fluids and Partitioning in Calcite

The Nature and Origin of the REE Mineralization in the Wicheeda Carbonatite, British Columbia, Canada

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