Mineral chemistry and alteration of rare earth element (REE) carbonates from alkaline pegmatites of Mount Malosa, Malawi

Guastoni, Alessandro; Nestola, Fabrizio; Giaretta, A.

doi:10.2138/am.2009.3185

Cited by 36 publications

(24 citation statements)

References 20 publications

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“…The first is stabilised by high X(CO 2 ) and/ or low Ca activity and the second by lower X(CO 2 ) and higher Ca activity. A limit to the Ca activity might have been given, however, by reactions of the type: 2CeCO 3 F + CaO = CaF 2 + Ce 2 O 3 + CO 2 (Hsu 1992;Guastoni et al 2009). …”

Section: Relationships Between Cgm Composition and Nature Of Accessoriesmentioning

confidence: 99%

Hydrothermal alteration of a chevkinite-group mineral to a bastnäsite-(Ce)-ilmenite- columbite-(Fe) assemblage: interaction with a F-, CO2-rich fluid

et al. 2015

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The results are presented of a textural and mineral chemical study of a previously undescribed type of hydrothermal alteration of chevkinite-(Ce) which occurs in a syenitic pegmatite from the Vishnevye Mountains, Urals Region, Russia. The progressive alteration of the chevkinite to a bastnäsite-(Ce)-ilmenite-columbite-(Fe) assemblage through a series of texturally complex intermediate stages is described and electron microprobe analyses are given of all the major phases. Unusual Nb±Th-rich phases formed late in the alteration sequence provide evidence of local Nb mobility. The main compositional fluxes are traced, especially of the REE, HFSE, Th and U. It appears that almost all elements, with the exception of La, released from the chevkinite-(Ce) were reincorporated into later phases, such that they did not leave the alteration crust in significant amounts. The hydrothermal fluids are inferred to have been F-and CO 2 -rich, with variable levels of Ca activity, and with fO 2 mainly between the nickelnickel oxide and magnetite-hematite buffers. This occurrence represents a new paragenesis for a columbite-group mineral.

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Section: Relationships Between Cgm Composition and Nature Of Accessoriesmentioning

confidence: 99%

Hydrothermal alteration of a chevkinite-group mineral to a bastnäsite-(Ce)-ilmenite- columbite-(Fe) assemblage: interaction with a F-, CO2-rich fluid

et al. 2015

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“…In contrast, carbonatite-hosted synchysite has average La/Nd and La/Ce ratios of 2.471 and 0.617, respectively [42,43]. Pegmatite-hosted synchysite [44] has average La/Nd and La/Ce ratios of 1.692 of 0.524; synchysite precipitated in basalts has average ratios of La/Nd = 1.459 and La/Ce = 0.543 [45]. Lastly, synchysite from hydrothermal fluorite veins, where REE are thought not to have been sourced not from the host rocks but rather from the basement, has average La/Nd as 1.238 and La/Ce 0.525 [46].…”

Section: Comparison With Published Compositional Datamentioning

confidence: 98%

Rare Earth Element Fluorocarbonate Minerals from the Olympic Dam Cu-U-Au-Ag Deposit, South Australia

et al. 2017

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Abstract:Olympic Dam is a world-class breccia-hosted iron-oxide copper-gold-uranium ore deposit located in the Gawler Craton, South Australia. It contains elevated concentrations of rare earth elements (REE) which occur as the REE minerals bastnäsite, synchysite, florencite, monazite, and xenotime. This is the first study to focus on the mineralogy and composition of the most abundant REE mineral at Olympic Dam, bastnäsite, and subordinate synchysite. The sample suite extends across the deposit and represents different sulfide mineralization styles (chalcopyrite-bornite and bornite-chalcocite) and breccias of various types, ranging from those dominated by clasts of granite, dykes, and hematite. The REE-fluorocarbonates (bastnäsite and synchysite) typically occur as fine-grained (<50 µm) disseminations in Cu-Fe-sulfides and gangue minerals, and also within breccia matrix. They are also locally concentrated within macroscopic REE-mineral-rich pockets at various locations across the deposit. Such coarse-grained samples formed the primary target of this study. Three general textural groups of bastnäsite are recognized: matrix (further divided into disseminated, fine-grained, and stubby types), irregular (sulfide-associated), and clast replacement. Textures are largely driven by the specific location and prevailing mineral assemblage, with morphology and grain size often controlled by the associated minerals (hematite, sulfides). Major element concentration data reveal limited compositional variation among the REE-fluorocarbonates; all are Ce-dominant. Subtle compositional differences among REE-fluorocarbonates define a spectrum from relatively La-enriched to (Ce + Nd)-enriched phases. Granite-derived hydrothermal fluids were the likely source of F in the REE-fluorocarbonates, as well as some of the CO 2 , which may also have been contributed by associated mafic-ultramafic magmatism. However, transport of REE by Cl-ligands is the most likely scenario. Stubby bastnäsite and synchysite may have formed earlier, coincident with hydrothermal alteration of granite releasing Ca from feldspars. Other categories of bastnäsite, notably those co-existing with sulfides, and reaching the top of the IOCG mineralization at Olympic Dam (chalcocite + bornite zone) are relatively younger. Such an interpretation is concordant with subtle changes in the REE patterns for the different categories. The common association of bastnäsite and fluorite throughout the deposit is typical of the hematite breccias and can be deposited from neutral, slightly acidic fluids (sericite stability) at T ≈ 300 • C.

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“…Evidence of large-scale, latestage alteration and/or replacement activity (as seen in the Woodland Drive pegmatite) is lacking. Guastoni, Nestola, and Giaretta (2009) suggested that decomposition of early-formed primary REE minerals by fluid interactions could mobilize the REE to form other minerals, including cerianite-(Ce), due to increasing f O 2 . Zaitsev et al (2011) noted the incorporation of REE 3+ in cerianite-(Ce) from the Kerimasi volcano in northern Tanzania.…”

Section: Referencementioning

confidence: 99%

Forty-Second Rochester Mineralogical Symposium: Contributed Papers in Specimen Mineralogy—Part 1

2016

Rocks & Minerals

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Mineral chemistry and alteration of rare earth element (REE) carbonates from alkaline pegmatites of Mount Malosa, Malawi

Cited by 36 publications

References 20 publications

Hydrothermal alteration of a chevkinite-group mineral to a bastnäsite-(Ce)-ilmenite- columbite-(Fe) assemblage: interaction with a F-, CO2-rich fluid

Hydrothermal alteration of a chevkinite-group mineral to a bastnäsite-(Ce)-ilmenite- columbite-(Fe) assemblage: interaction with a F-, CO2-rich fluid

Rare Earth Element Fluorocarbonate Minerals from the Olympic Dam Cu-U-Au-Ag Deposit, South Australia

Forty-Second Rochester Mineralogical Symposium: Contributed Papers in Specimen Mineralogy—Part 1

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