Pete Siegfried

Pete Siegfried
University of Exeter | UoE · Camborne School of Mines (CSM)

B.Sc (hons), M.Sc

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29
Publications
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402
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Publications

Publications (29)
Article
Full-text available
Exploration for rare earth element (REE)-deposits hosted in carbonatites and associated rocks is challenging because of the heterogeneous distribution of REE and the variable and often complex mineralogy of such REE mineralisation. The Kieshöhe in southwestern Namibia is a subvolcanic intrusion consisting of calcite-carbonatite, dolomite-carbonatit...
Article
Full-text available
Development of renewable energy infrastructure requires critical raw materials, such as the rare-earth elements (REE, incl. 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-silicat...
Conference Paper
Full-text available
Alkaline igneous rocks and carbonatites form important resources for technology metals such as rare earths elements (REE), Nb, Ta, Li and P. These metals appear on the European list of Critical Raw Materials 2020, due to continued growth in demand and ongoing supply concerns [1]. Angola hosts a series of Cretaceous to Tertiary alkaline igneous rock...
Article
Full-text available
Carbonate-bearing fluorapatite rocks occur at over 30 globally distributed carbonatite complexes and represent a substantial potential supply of phosphorus for the fertiliser industry. However, the process(es) involved in forming carbonate-bearing fluorapatite at some carbonatites remain equivocal, with both hydrothermal and weathering mechanisms i...
Article
Fluid inclusion and mineral thermobarometric study supplemented by U-Th-total Pb monazite dating has been carried out in country rocks of the Evate carbonatite, which is an example of a Neoproterozoic (~590 Ma) orogenic carbonatite formed within a post-collisional tectonic setting in the Monapo granulite complex of NE Mozambique. The fluid inclusio...
Conference Paper
Full-text available
Effective exploration methodology is today driven by a robust and detailed mineral systems approach model for tracing the route of the target element from its source to its end location (Hronsky, 2011, McCuaig, et al., 2010). With forced residence of fluids responsible for mineralisation produced through an impermeable trap or seal, the concentrati...
Conference Paper
Full-text available
Development of renewable energy infrastructure requires critical raw materials, such as REE and Nb, and is driving expansion and diversification in their supply chains. Although alternative sources are being explored, the majority of the world's resources are found in alkaline silicate rocks and carbonatites (hereafter 'alkaline'). These unusual ma...
Article
Full-text available
Two types of scapolite occur in the Evate carbonatite deposit – the largest resource of apatite in south-east Africa. Calc-silicate rocks composed of amphiboles (hastingsite, hornblende, actinolite, and pargasite), diopside, Ba-rich phlogopite, allanite, epidote, apatite, K-feldspar, titanite, and minor calcite, also contain scapolite with 62–74 mo...
Conference Paper
Full-text available
A contextual, probabilistic REE-HFSE mineral system approach is being developed by the authors to enable any REE-HFSE mineral system's extent to be defined, mapped and risked in 4D. This will enable systematic investigation of the crustal pathways and potential trap locations along which a mantle-derived REE-HFSE 'batch' may now be distributed. A w...
Article
Full-text available
Security of supply of “hi-tech” raw materials (including the rare earth elements (REE) and some high-field-strength elements (HFSEs)) is a concern for the European Union. Exploration and research projects mostly focus on deposit- to outcrop-scale description of carbonatite- and alkaline igneous-associated REE-HFSE mineralization. The REE-HFSE miner...
Article
The Southern Irumide Belt (SIB) records over one and a half billion years (c. 2000 to 500 Ma) of tectonic evolution along the southern Congo Craton margin. To understand this evolution we present U–Pb, Lu–Hf, rare earth element zircon and structural data for the SIB of Zambia, which are used to investigate its formation, evolution, and relationship...
Article
Full-text available
The Southern Irumide Belt (SIB) is an orogenic belt consisting of a number of lithologically varied Mesoproterozoic and Neoproterozoic terranes that were thrust upon each other. The belt lies along the southwest margin of the Archaean to Proterozoic Congo Craton, and bears a Neoproterozoic tectono-thermal overprint relating to the Neoproterozoic–Ca...
Article
Full-text available
Zirconolite is documented from the Evate apatite-magnetite-carbonate deposit in the circular Monapo Klippe (eastern Mozambique)—a relic of Neoproterozoic nappe thrusted over the Mesoproterozoic basement of the Nampula block. Zirconolite enriched in rare earth elements—REE = Y + Lu+ΣLa–Yb (up to 24.11 wt% REE2O3, 0.596 apfu REE) creates thin rims ar...
Article
Full-text available
Carbonatites and alkaline-silicate rocks are the most important sources of rare earth elements (REE) and niobium (Nb), both of which are metals imperative to technological advancement and associated with high risks of supply interruption. Cooling and crystallizing carbonatitic and alkaline melts expel multiple pulses of alkali-rich aqueous fluids w...
Article
The Evate deposit represents the largest resource of apatite in south-east Africa (155 Mt. ore grading 9.3 wt.% P2O5) accumulated in up to 100 m thick magnetite-carbonate-apatite horizons conformable to the granulitic gneiss of the Monapo Klippe. Baddeleyite and zircon from early iron-oxide (magnetite, geikielite, spinel), apatite- and forsterite-b...
Article
The Monapo Klippe in north-east Mozambique is an ovoid-shaped outcrop measuring approximately 35 × 40 km and is clearly visible on satellite and geophysical images. Based on recent field mapping, geo-chemical studies and new geochronological data, we present a revision of the lithostratigraphy of the klippe and offer a model for its origin and empl...
Article
Full-text available
Mineral Deposits: Processes to Processing January 1999Ore Geology Reviews 17(1) DOI: 10.1016/S0169-1368(00)00005-6
Article
Full-text available
Dating of single zircons from low-grade metamorphosed rhyolites in the Rosh Pinah Formation of the Gariep Belt in southwestern Namibia, using the Pb evaporation technique, yielded a primary crystallization age of $741 \pm 6 Ma$. Both the stratigraphic position and the geochemistry of the volcanic rocks indicate an early continental rift environment...
Article
Full-text available
The Diaz Point Formation is a highly sheared, late Proterozoic diamictite which crops out along the Namibian coast from Lüderitz to Wolf Bay. It lies with a marked structural discontinuity on gneissic basement, which forms part of the Namaqua Metamorphic Complex. Three units can be distinguished from each other by thrust faults. All lithologies are...
Article
Full-text available
Summary in English. Word processed copy. Thesis (M.Sc. (Geology))--University of Cape Town, 1990. Includes bibliography.

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Projects (5)
Project
The genesis of carbonatites is typically explained by a combination of factors, including low-degree partial melting of an enriched mantle source, crystal fractionation and carbonate-silicate liquid immiscibility. Previous work by the applicants indicate that carbonatite magmas can be significantly modified by crustal contamination. The relation between emplacement depth, multiple reuse of pathways and carbonatite generation was, however, given only limited attention. In an ideal case study, we would investigate spatially related intrusions covering broad range of igneous silicate rocks and carbonatites. In such an ideal natural laboratory we could study the effect of emplacement depth-related variations and the multiple reuse of pathways which can be evaluated against crustal contamination in a carbonatitic-alkaline igneous province. Such an ideal system with an excellent outcrop situation can be found at the Namibian- South African border at the Kuboos-Bremen Line (KBL). The Kuboos-Bremen-Line complexes show highly variable rock associations, some of them include carbonatites. Two important observations lead to research questions of scientific and economic significance: 1) While the carbonatites of the Marinkas Quellen complex are strongly enriched in HFSE, the eastern carbonatites are barren. 2) Many of the silicate rocks associated with the carbonatites are granites and syenites, but their genetic relations towards each other are not clear. The proposed study will therefore investigate the genetic relationships between granites, quartz syenites, syenites, foid syenites and carbonatites and will be guided by the following hypotheses: (i) The behaviour of HFSE and REE in carbonatitic magmas is influenced by source contamination and silicate wall-rock interaction. (ii) The crosscutting relationships of the individual complexes and available age data suggest progressive evolution of the province from SW to NE evolving from granitic to foid-syenitic/carbonatitic compositions with time and location. (iii) The rock associations represent two magma suites derived from variable sources that used the same zone of weakness for ascent and emplacement. To test these alternative scenarios, textural, mineral chemical, isotopic and geochronological data will be gathered and compared for the representative intrusions of the Kuboos-Bremen Line. The expected results will allow to characterize the magmatic to hydrothermal evolution of the whole system in great detail and to reconstruct the genesis of carbonatites in alkaline silicate dominated igneous provinces.
Project
High levels of REE in carbonatites are generally explained by a combination of factors, including low-degree melting of geochemically enriched mantle sources, crystal fractionation, carbonate-silicate melt immiscibility, melt-aqueous brine immiscibility and hydrothermal alteration. Crustal contamination, however, is a process that is typically not considered to play an important role during carbonatite magmatism. Nevertheless, a recent study of the applicants demonstrated that the interaction of carbonatite magma with silicate wall rocks can enable strong REE enrichment in apatite via a coupled substitution mechanism involving Si. Having shown this for the Kaiserstuhl, the applicants suggest that such processes may be of general importance in carbonatitic systems. This project will investigate the impact of carbonatite-wall rock interaction on REE enrichment in carbonatites. The study will be performed using field examples from the Damaraland Province (Namibia), because these carbonatites show variable REE enrichment and REE mineralogy and contain variable amounts of silicate minerals (amphibole, clinopyroxene, quartz, feldspar) that may indicate crustal contamination. To test this hypothesis, textural, mineral chemical and geochronological data (microscopy, EMPA, LA-ICP-MS) as well as fluid inclusion data (microthermometry including numerical liquidus-surface modeling for quantification, Raman spectroscopy) for the different carbonatites which are probably genetic related will be gathered and compared with each other. The expected results will allow for (1) characterizing the magmatic to hydrothermal evolution of the carbonatites in great detail and (2) reconstructing the genesis of the REE mineralizations including the potential influence of wall-rock interaction and hydrothermal overprint.
Project
The project is aimed to provide mineralogical, geochemical and genetic characteristics of the Evate deposit in NE Mozambique, which is one of the largest phosphate deposits of Africa, with estimated reserves of 155 Mt of ore grading 9.3 % P2O5 calculated to the depth of 100 m from recent surface. The deposit is intended to supply apatite for the fertilizer complex to be built in the nearby coastal district of Nacala-a-Velha. In spite of prepared exploitation, mineralogy of the deposit is poorly elucidated and its origin remains controversial. Recent models include metamorphogenic or magmatogenic origin linked with Precambrian alkalic intrusions. Magmatic deposits of similar types (e.g. Kovdor, Kola), however, also serve as a source of rare earth elements and rare metals bound in apatite and other specific minerals. Detailed mineralogy as well as genetic information have a profound importance for the exploitation and beneficiation strategy, and economic assessment of the deposit.