Pete Siegfried

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

High purity fluorite veins (acid grade > 97 % CaF 2) are generally rare in a global context. The fluorite-(±quartz-calcite) veins in the Aukam Valley mining district in SW Namibia have not previously been studied but due to their excellent exposure they are an ideal natural laboratory to study such mineralization. These veins cross-cut Mesoproteroz...

Carbonatites exist as intrusive and extrusive rocks, with the former dominating the rock record. The geochemical link between intrusive and extrusive equivalents and the processes during eruption of carbonatite melt are essentially unknown. This contribution aims at providing new insights into the transition from intrusive to extrusive carbonatites...

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...

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...

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...

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...

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...

Collation of new geochronology results in Mozambique

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...

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...

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...

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...

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...

The Southern Irumide Belt (SIB) records over one and a half billion years ( c . 2000–500 Ma) of tectonic evolution along the southern Congo Craton margin. To understand this evolution we present U–Pb, Lu–Hf, REE zircon and structural data for the SIB of Zambia, which are used to investigate its formation, evolution and relationship to the Irumide B...

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...

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...

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...

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...

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...

Mineral Deposits: Processes to Processing January 1999Ore Geology Reviews 17(1) DOI: 10.1016/S0169-1368(00)00005-6

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...

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...

Summary in English. Word processed copy. Thesis (M.Sc. (Geology))--University of Cape Town, 1990. Includes bibliography.