Plutonic xenoliths in volcaniclastic rocks from the Laacher See (LS), East Eifel and the Rockeskyller Kopf Volcanic Complex (RKVC), West Eifel, were studied. They show different ways of magmatic carbonate formation at plutonic levels.

Well-preserved original igneous textures of carbonate-bearing syenites were observed in LS plutonic xenoliths. Calcite is often crystallised in “micropegmatitic texture” with sanidine and nosean. These structures argue for syngenetic crystallisation of calcite and main silicate minerals in alkali syenite melts in the case of the LS volcano. Different proportions of euhedral calcite and silicate minerals point to calcite cumulate formation.

Occurrence of calcite associated to apatite, magnetite, phlogopite and pyrochlore in nosean syenite from xenoliths of the RKVC is in line with the assumption of magmatic carbonate formation in a highly fractionated undersaturated silicate magma.

Next to carbonatite - nosean syenite xenoliths and sanidinite, a series of different mafic xenoliths were found around the RKVC, from amphibolite to pyroxenite and magnetite cumulates, that could indicate one or more magma chambers below the volcano.

A comprehensive data set for geochemistry, mineralogy and mineral chemistry of the carbonates of LS and RKVC volcanoes is provided. Characteristic carbonate and whole rock trace element patterns are presented. Different chondrite normalised REE signatures of RKVC and LS argue for different ways of fractionation in these volcanic systems.

Complex field relationships and association to alkaline ultramafic rocks, textural diversity and locally marked isotopic heterogeneity of ijolites lead to contrasting petrogenetic concepts for these rocks. They may either be formed by magmatic differentiation from nephelinitic magmas or by assimilation of silicate wall rocks in a carbonatite melt formed after metasomatic reaction during its’ ascent from mantle to crustal levels. We show new petrographic and mineral chemical results from the ijolite type locality, Iivaara. It is the aim of this presentation to set constraints to ijolite formation in the Iivaara alkaline complex and to discuss applicability of contrasting petrogenetic concepts. Pegmatitic growth, comb layering or brecciation indicate ijolite crystallization from a low viscosity and volatile rich melt. Small scale textural heterogeneity reveals locally highly variable crystallization conditions characterized by steep temperature gradients and sudden pressure drop. Irregular clinopyroxene zonation points to repeated disturbance of magmatic crystallization at depth prior to emplacement at the actual erosion level. Veins and matrices of breccia are dominated by clinopyroxene next to titanite and apatite attesting to the high Ca-concentration of a fluid that is violently expelled from the magma. The transitional zone between wall rocks and ijolite, too, is dominated by pyroxenitic compositions. Lack of a clearly defined contact between ijolite and wall rock is in line with the observation of migmatitic textures in high grade fenites, which probably obtained plastic behavior with increasing degree of fenitization. Such fenites with syenitic composition or partial melts of them may have been assimilated by ijolite.

The study aims to provide valuable insights into the dynamics of the interaction between carbonate melts and silicate wall-rocks during ascent and emplacement of carbonatitic intrusions. A specific focus is given to potential processes leading to rare earth element (REE) enrichment. It can be assumed that the interaction of silicate rocks with carbonate melt is diverse. Therefore, a study of granites interacting with a carbonatite melt was used to carefully assess the effects of a specific lithology.

The research centers the Bulhoek carbonatite complex, a bi-partite intrusion (Bulhoek North and South) situated in the eastern central region of the Bushveld Complex, approximately 35km west of Pilanesberg (South Africa), where it intruded the Nebo-granite (an integral part of the Bushveld Complex). The key characteristics of this intrusion are reflected by volcanic breccia, finitized Nebo-granite and beforsite (fine-grained magnesio-carbonatite) containing abundant apatite and strongly disaggregated granite xenoliths. Textural evaluation indicates that the element budget of the granites was resorbed by the carbonate melt. An integrated analytical approach, involving scanning electron microscopy (SEM), X-ray fluorescence (XRF), X-ray diffraction (XRD), and whole-rock analysis, is currently in progress to reveal the intricacies of the carbonate melt – granite interaction. While previous field studies have touched upon the fenitization of the Nebo-granite, a comprehensive understanding of the entire (and mutual) interaction remains a significant research gap. This study bridges this gap and will deepen our knowledge of carbonatite formation.

Carbonatites are igneous rocks with significant concentrations of rare earth elements (REEs) and other important metals. Despite their economic potential, their origin and evolution are poorly understood. Crustal contamination can significantly modify REE abundance in carbonatites. The current study provides new petrographic, geochemical, and stable isotopic insight into the processes that led to the formation of high field strength element (HFSE) bearing carbonatites i.e. pyrochlore-calcite carbonatite, and rare earth element (REE) bearing carbonatite i.e. quartz-ankerite-calcite carbonatite in the Nooitgedacht Volcano.

The Nooitgedacht Volcano is an oval-shaped body with approximately a 3 km diameter situated in the Kaapvaal Craton in South Africa. It comprises mostly calcite carbonatite with enclosures of dolomite carbonatite. Petrographically, calcite carbonatite is divided into pyrochlore-calcite carbonatite and quartz-ankerite-calcite carbonatite. The mineral assemblage of pyrochlore, apatite, magnetite, and forsterite indicate an ortho-magmatic origin while the mineral association of monazite, ankerite, and quartz represents a post-magmatic/ hydrothermal origin for the quartz-ankerite calcite carbonatite. Stable isotope data (δ¹³C = -5 to -4) and (δ¹⁸O = +7 to +16) indicate a primary mantle source for the carbonatite with subsequent crustal contamination.

In summary, petrographic, mineralogical, geochemical, and isotopic data provide significant insight into the evolution of the Nooitgedacht Volcano, highlighting a complex history of magmatic differentiation, mineral fractionation, and crustal contamination.

Carbonatites are mantle-derived igneous rocks which may comprise economically important mineralizations of REE and HFSE. Their emplacement into the crust is usually accompanied by fenitization, alkali metasomatism of country rocks caused by fluids expelled during cooling and crystallization. Often, carbonatites are associated with diverse silicate rocks like syenites, nepheline syenites or phonolites. Understanding magmatic differentiation and late-stage processes after emplacement, such as hydrothermal alteration and element remobilization and re-precipitation, is of great importance to understand the formation of HFSE and especially REE deposits.

Carbonatites and associated silicate rocks (syenites, phonolites, fenites) of the Kalkfeld group in Northern Namibia show a large range in whole-rock REE contents, heterogeneity and textural variety and are therefore perfectly suited to study the phenomena named above. Detailed petrographic and microtextural analysis of the samples was done and focused on understanding the paragenetic sequence and evolution of the samples. Within the carbonatites, the typical sequence sövite -> beforsite -> ferrocarbonatite is observed, as well as late-stage, hydrothermal mineralization of REE- bearing phases like ancylite and bastnäsite. Currently, the study focuses on mineral chemistry by means of EMPA to further differentiate processes involved in the formation and evolution of the observed assemblages. Furthermore, silicate minerals like pyroxene, biotite and feldspar observed in carbonatites of the Kalkfeld group may indicate wall-rock interaction and crustal contamination of the carbonatitic magma during ascent and emplacement. The importance of silica contamination on REE enrichment in the carbonatites of Kalkfeld group will be discussed.

Rare Earth elements (REE) belong to the most strategic materials of the 21st century with steadily growing economic importance. PRISMA, the hyperspectral satellite data, is used for the very first time to test its capability of detecting REE contents from space using distinct subtle diagnostic spectral absorption features of REE. The PRISMA hyperspectral sensor acquired 234 spectral bands over VNIR/SWIR optical regions (400–2500 nm) of the electromagnetic spectrum at a spatial resolution of 30 m and a spectral resolution ranging from 11 to 15 nm. The carbonatite occurences within the Ondoto area in North Namibia were selected as the test site. To detect the REE-related diagnostic spectral absorption parameters (absorption wavelength position and depth) the in-house toolbox (QUANTools) developed at the Czech Geological Survey was tested and four absorption features placed within 700–900 nm range were found to correlate with the carbonatites containing high loads of REE. As a result, three perspective carbonatite areas were identified as the most promising, with one site validated using the laboratory geochemical data from collected samples. The results showed a good correlation between the high REE loads mapped using PRISMA data and the ground truth data highlighting the future potential of state-of-the-art satellite hyperspectral data to explore REE deposits using contactless Earth Observation data and methods.

Funded by the Czech Science Foundation project 19-29124X.