Enrichment of heavy REE and Th in carbonatite-derived fenite breccia

Broom-Fendley, Sam; Elliott, Holly A. L.; Beard, Charles D.; Wall, Frances; Armitage, Paul E.B.; Brady, Aoife E.; Deady, Eimear; Dawes, William

doi:10.1017/s0016756821000601

Cited by 15 publications

(8 citation statements)

References 55 publications

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“…We therefore suggest that REE fractionation could be a better explanation for the lower (La/Nd) cn ratios of fenite, particularly noting that the best mixing results came from quartz rock monazite-(Ce), which is of non-primary magmatic origin, and which might have formed from REE-fractionating fluids. This accords with the view of Broom-Fendley et al (2021a) and Broom-Fendley et al (2021b) who suggested that, subsequent to precipitation of LREE minerals in carbonatite, the more incompatible HREE are expelled in residual hydrothermal fluids, and that REE fractionation occurs in most cases of fenitisation.…”

Section: Ree Fractionation Further Investigatedsupporting

confidence: 91%

“…These authors also linked increasing solubility of the MREE and HREE over time to fluids with falling temperature and a change from CO 2 to H 2 O dominance, which may have promoted (re)mobilisation of the MREE and HREE (Andrade et al , 1999; Broom-Fendley et al , 2013). This was possibly via a dissolution–reprecipitation process (Broom-Fendley et al , 2021a; 2021b) as evidenced by the presence of porous fluorapatite containing sub-micrometre zircon in medium-grade fenite and breccia at Kangankunde, and skeletal zircon in breccia at Chilwa Island.…”

Section: Discussionmentioning

confidence: 99%

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A comparison of the fenites at the Chilwa Island and Kangankunde carbonatite complexes, Malawi

Dowman

Wall²,

Treloar³

2022

MinMag

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Carbonatites are igneous carbonate rocks. They are the main source of the rare earth elements (REE) that are essential in low carbon and high technology applications.Exploration targeting and mine planning would both benefit from a better understanding of the processes that create the almost ubiquitous alkaline and rare earth (RE)-bearing metasomatic aureoles in the surrounding country rocks.Using SEM-based analysis and whole rock geochemistry, we investigated the composition and mineralogy of the fenite aureoles developed around the RE-poor Chilwa Island carbonatite and the RE-rich Kangankunde carbonatite, which intrude similar country rocks in the Chilwa Alkaline Province of Southern Malawi. Although common characteristics and trends in their mineralogy and composition may be typical of fenites in general, there are significant differences in their petrography and petrogenesis. For instance, the mineralogically diverse breccia at Kangankunde contrasts with the intensely altered

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Section: Ree Fractionation Further Investigatedsupporting

confidence: 91%

Section: Discussionmentioning

confidence: 99%

A comparison of the fenites at the Chilwa Island and Kangankunde carbonatite complexes, Malawi

Dowman

Wall²,

Treloar³

2022

MinMag

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“…The alkali metasomatic aureoles that surround alkaline-silicate and carbonatite intrusions are termed "fenite." Because fenite composition is controlled by protolith mineralogy, fluid composition, pressure, and temperature, it has potential for use as a vectoring tool during exploration (Elliott et al, 2018;Broom-Fendley et al, 2021). The extent of fenite is additionally controlled by country-rock permeability.…”

Section: Wall-rock Influences and Fenite Alteration Halosmentioning

confidence: 99%

“…The potassium enrichment in fenite can be mapped by radiometric surveys and used as a vector toward mineralization (Simandl, 2015;Simandl and Paradis, 2018). Because fenite aureoles are formed via fluid expulsion from a parental intrusion, their extent, mineralogy, and geochemistry record information about the metal tenor of the parent intrusion (Dowman et al, 2017;Broom-Fendley et al, 2021). This effect is not yet characterized to a sufficient level for widespread use in exploration.…”

Section: Wall-rock Influences and Fenite Alteration Halosmentioning

confidence: 99%

Alkaline-Silicate REE-HFSE Systems

et al. 2023

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Development of renewable energy infrastructure requires critical raw materials, such as the rare earth elements (REEs, including scandium) and niobium, and is driving expansion and diversification in their supply chains. Although alternative sources are being explored, the majority of the world’s resources of these elements are found in alkaline-silicate rocks and carbonatites. These magmatic systems also represent major sources of fluorine and phosphorus. Exploration models for critical raw materials are comparatively less well developed than those for major and precious metals, such as iron, copper, and gold, where most of the mineral exploration industry continues to focus. The diversity of lithologic relationships and a complex nomenclature for many alkaline rock types represent further barriers to the exploration and exploitation of REE-high field strength element (HFSE) resources that will facilitate the green revolution. We used a global review of maps, cross sections, and geophysical, geochemical, and petrological observations from alkaline systems to inform our description of the alkaline-silicate REE + HFSE mineral system from continental scale (1,000s km) down to deposit scale (~1 km lateral). Continental-scale targeting criteria include a geodynamic trigger for low-degree mantle melting at high pressure and a mantle source enriched in REEs, volatile elements, and alkalies. At the province and district scales, targeting criteria relate to magmatic-system longevity and the conditions required for extensive fractional crystallization and the residual enrichment of the REEs and HFSEs. A compilation of maps and geophysical data were used to construct an interactive 3-D geologic model (25-km cube) that places mineralization within a depth and horizontal reference frame. It shows typical lithologic relationships surrounding orthomagmatic REE-Nb-Ta-Zr-Hf mineralization in layered agpaitic syenites, roof zone REE-Nb-Ta mineralization, and mineralization of REE-Nb-Zr associated with peralkaline granites and pegmatites. The resulting geologic model is presented together with recommended geophysical and geochemical approaches for exploration targeting, as well as mineral processing and environmental factors pertinent for the development of mineral resources hosted by alkaline-silicate magmatic systems.

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“…Elliott et al (2018) explain that the occurrence of breccias at several carbonatite complexes corroborates the explosive release of fluids and volatiles from an evolving magma underneath. For Songwe carbonatite, Broom-Fendley et al (2021) stress that based on the angular nature of the clasts and the comminuted groundmass, the breccia formed by in situ rapid volume expansion, most likely as a result of subsurface explosive release of volatiles from the proposed underlying carbonatite bodies. Thus, the explosive hydrothermal brecciation and the metasomatic action of hydrothermal fluids can indeed be considered responsible for the generation of the breccia.…”

Section: Location and Geology Of The Study Areamentioning

confidence: 99%

Slope design in brecciated carbonatite complexes under high-stress regimes

Moses

Shimada²,

Onyango³

et al. 2022

Bull Eng Geol Environ

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Carbonatites are generally competent rock masses with Rock Mass Rating class II rating 60-74. In spite of their competency, they tend to be affected by weak features like Mn-Fe veins and/or in situ rock damage due to brecciation associated with carbonatite complexes. Rock slope failure in such hard rocks is complex since such structures within the rock mass form weak links that could potentially control slope instability. In this contribution, a numerical simulation using phase 2 v 7.0 was carried out to investigate the influence of in situ rock damage on the stability of mine pit walls. The outcome reveals that, the existence of breccia in the competent rock mass has the capability to reduce the slope stability performance particularly at gentle dipping angle of emplacement in close range to the slope toe. However, as the emplacement position of breccia moves away from the pit wall, the stability performance increases at gentle dipping angle < 50º. On the contrary, at the dipping angle of 50° the performance of slope reduced, and at steeper angle >50° the impact becomes negligible. Thus, from a series of analyses, mine design in brecciated rock masses, the ratio of 1:5 between the breccia distance from slope toe and pit depth should be implemented to counter its impact. If the breccia is within or close to the pit limit, a deliberate effort must be made to mine out or truncate it.

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Enrichment of heavy REE and Th in carbonatite-derived fenite breccia

Cited by 15 publications

References 55 publications

A comparison of the fenites at the Chilwa Island and Kangankunde carbonatite complexes, Malawi

A comparison of the fenites at the Chilwa Island and Kangankunde carbonatite complexes, Malawi

Alkaline-Silicate REE-HFSE Systems

Slope design in brecciated carbonatite complexes under high-stress regimes

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