Geological mapping of carbonatites and related ores from the Oulad Dlim massif (Dakhla Province, Morocco) using remote sensing, portable X-ray fluorescence, and mineralogical data

Abstract and Poste

Widespread Cadomian–Pan-African Ediacaran magmatism across the Moroccan Meseta: Implication for the geodynamic evolution of the NW Gondwana margin

The Moroccan Meseta constitutes a key peri-Gondwanan and Variscan terranes linking the branches between the SW European Cadomian and the north West African Craton (WAC), anti-Atlas metacratonic Pan-African terranes. While the Paleozoic sedimentary and tectono-magmatic record of the different blocks of the Moroccan Meseta is well documented, there is still a lack of systematic absolute ages and geochemical isotopic data of putative Precambrian basement rocks from different Meseta blocks. Here we present new U–Pb zircon ages, petrological, and whole-rock major, trace, and Sr–Nd–Pb isotope geochemical data of (meta)igneous rocks from the Bou-Acila, Jbel-Hadid, Goaïda, Midelt and El Jadida, constituting the basement of two main Moroccan Meseta blocks. Basaltic rocks, unconformably overlain by Cambrian platform sediments, in the Western Meseta Bou-Acila basement yield U–Pb zircon age of c. 581 ± 9 Ma that unveils the existence of Ediacaran magmatism in the Moroccan basement of this area. Alleged early Paleozoic mafic sills in the metasedimentary series of the Midelt Sidi-Saïd yield U–Pb zircon ages of c. 554 ± 12 Ma reveals, for the first time, the presence of Ediacaran magmatism in the basement of the Moroccan Eastern Meseta. U–Pb zircon ages in the Jbel-Hadid and El Jadida rhyolitic basement rocks (c. 604–543 Ma and c. 575–559 Ma, respectively), as well as granitic pebbles (c. 573 Ma) in the Goaïda Cambrian limestone series, further attest for coeval Ediacaran magmatism in the basement of Western Meseta. The geochemical affinity of the investigated Moroccan Meseta Ediacaran magmatic rocks is mainly metaluminous, low-K tholeiites for mafic rocks, and peraluminous, high-K calc-alkaline for the felsic rocks, consistent with a back-arc tectonic setting. Geochemical and Sr–Nd–Pb isotopic data indicate that the source of the Moroccan Meseta Ediacaran magmatism involved sources from the depleted mantle and old WAC crustal basement. Altogether, these data show widespread Ediacaran magmatism in the Moroccan Meseta mostly likely formed in a back-arc south of the Cadomian active margin along the NW Gondwana during the waning stages of the Cadomian–Pan-African orogeny, recording a transitional stage between the Ediacaran subduction and early Paleozoic rifting.The authors have been supported by CSIC grant n°COOPB20619 from the “Programa de cooperación científica para el desarrollo – Convocatoria 2021, Modalida B”. The authors also acknowledge funding from the “Junta de Andalucia” research group RNM–131. Research infrastructure grants used in this research have been co-funded by the European Regional Development Fund (ERFD) of the European Commission

Alkali-Hydrothermal Treatment of K-Rich Igneous Rocks for Their Direct Use as Potassic Fertilizers

International audienceDue to the increasing demand for conventional sources of potassium (K) and their inaccessibility by African countries, K-rich igneous rocks are increasingly studied as potential alternative sources. In this study, six potassic igneous rocks (syenites and trachytes) from the Tamazeght, Jbel Boho, Ait Saoun, and El Glo’a regions (Morocco) were sampled and characterized. Then they were hydrothermally treated to enhance their K release for potential use as potassic fertilizers. The raw materials are mainly formed by microcline (up to 74%), orthoclase (20–68%), albite (36–57%), biotite-muscovite (15–23%), and titanite, calcite, hematite, and apatite as accessory minerals. These samples were crushed and milled to reach a particle size <150 µm and mixed with 4 N NaOH solution in an autoclave. The liquid/solid (L/S) ratio was about 44 mL/50 g. The powders were allowed to react with the solution at 170 °C for 7 h. For all tests, NaOH reacted completely with the powders and no liquid was observed after the treatment. X-ray diffraction (XRD), thermal gravimetric analysis (TGA), infrared spectroscopy (IRTF), and scanning electron microscopy (SEM-EDS) were carried out on treated samples to characterize the mineralogical and structural changes due to the alkali-hydrothermal treatment. Indeed, the treated samples revealed the presence of sodic neoformed phases such as thermonatrite, sodalite, analcime, and cancrinite. The treated material was leached for a week using deionized water and the elements released were measured using inductively coupled plasma–atomic emission spectroscopy (ICP-AES). The hydrothermal process showed a strong effect on structure breakdown as well as on the release of K and other nutrients such as P, Fe, Si, Mg, and Ca. Therefore, the alkali-hydrothermal treatment allowed the release of 50.5 wt% K. Moreover, the release of Mg, Ca, Fe, P, K, and Si were significantly increased. Mg, Ca, Fe, P, K, and Si release within raw materials was about (0.5–3.6), (3.5–31.4), (0.01–0.4), (0.01–0.3), (20–55), and (4.6–8) mg/kg, respectively, whereas treated samples showed a higher release of these elements. Quantitatively, Mg, Ca, Fe, P, K, and Si releases were about (10–11.8), (60–70), (7–20), (1.2–15), (218–1278), and (1119–2759) mg/kg, respectively. Consequently, the treated igneous rocks (syenite and trachyte) could be directly used as potassic fertilizers that would also be a source of other nutrients

An Integrated Approach for Rapid Delineation of K-Rich Syenites Suitable as Unconventional Potash Resources

Potassium (K)-rich igneous rocks include a variety of silica-undersaturated and alkaline rocks, which distinguished by their elevated KO contents. These rocks have attracted attention for decades and motivated various studies focused either on geodynamic implications or on their association with mineral resources. Recently, further studies of K-rich igneous suites were dedicated to assessing their potential as unconventional potash resource for agricultural K fertilization. These works led many countries to reassess their geological resources in K by including suitable igneous suites, hence promoting detailed geological survey and lithological/geochemical mapping of key areas. In this study, we present an integrated approach coupling remote sensing, GIS, and field data to identify and map K-rich igneous rocks over wide areas. Based on the thermal infrared (TIR) spectral properties of silicate K-bearing minerals commonly found in igneous rocks (e.g., syenites and trachytes), the ASTER TIR emissivity band ratio (B10/B11) was selected to identify potential areas of K-rich rocks. Then, a supervised mapping-based classification was applied to high potential areas using field data (field observations and portable X-ray fluorescence analyses) and petrographic characterization as training data. This approach was applied successfully at a large scale in two different areas in Morocco where potential areas of K-rich syenites have been reported. The accuracy and detail of preliminary band ratio mapping were enhanced, and several K-rich lithologies were differentiated using the spectral angle mapper algorithm. This approach for integrating easily accessible data has proven to be relatively rapid and cost-effective

Petrogenesis and crustal evolution of the Tasiast TTG suite (SW Reguibat Shield, Mauritania). Implication for crustal growth in the West African craton

The Mauritanian Tasiast unit in the Southwestern Reguibat Archean Shield (North of the West African craton = WAC) consists mainly of gneiss dated between 3.07 and 2.91 Ga. We present new field and petrographic observations combined with whole-rock geochemical data on gneisses of Tasiast to understand their petrogenesis, tectonic setting, and the evolution of the continental crust of WAC. These data provide firm evidence of two distinct orthogneisses: trondhjemite and high-K granite affinities. Geochemical characters suggest that (1) trondhjemites magma source were originally derived from polybaric partial melting at the thickened crust occurred over a range of P–T conditions, covering the stability fields of garnet amphibolite and rutile eclogite. The trondhjemite composition is attributed to mixing of two major melts: one originating from eclogitic facies source region (high Nb/Ta) and the other from a garnet-amphibolite facies (low Nb/Ta) leaving garnet, amphibole, and rutile in the residue. (2) Compared to trondhjemite, the granites with high KO and Rb contents, and low NaO, AlO and Sr contents suggest that basaltic oceanic crust was not their source material. Moreover, field relationships suggest that the granites were derived from partial melting of trondhjemites. Hence, the trondhjemite and high-K granites marked together two distinct stages during the growth of the continental crust in the Tasiast area.This paper is a contribution part of the PhD project of M. Bouha funded and supported by the FP7-PEOPLE-2013-IRSES project MEDYNA: Maghreb-Eu research staff exchange on geodynamics, geohazards, and applied geology in Northwest Africa 2014–2017, WP3–Deep structures and mantle processes. We would like to thank Carlos J. Garrido, co-coordinator of MEDYNA, for using the analytical facilities of Petrology, Geochemistry, and Geochronology department (PGG), IACT-CSIC, Granada. We also thank all the PGG members for their help in sample preparation and assistance in laboratory work. We would like to thank François Chabaux for editorial handling, and reviewers for their corrections and constructive remarks

Phosphate Rocks: A Review of Sedimentary and Igneous Occurrences in Morocco

International audiencePhosphate rocks are a vital resource for world food supply and security. They are the primary raw material for phosphoric acid and fertilizers used in agriculture, and are increasingly considered to be a potential source of rare earth elements. Phosphate rocks occur either as sedimentary deposits or igneous ores associated with alkaline rocks. In both cases, the genesis of high-grade phosphate rocks results from complex concentration mechanisms involving several (bio)geochemical processes. Some of these ore-forming processes remain poorly understood and subject to scientific debate. Morocco holds the world’s largest deposits of sedimentary phosphate rocks, and also possesses several alkaline complexes with the potential to bear igneous phosphate ores that are still largely underexplored. This paper summarizes the main geological features and driving processes of sedimentary and igneous phosphates, and discusses their global reserve/resource situation. It also provides a comprehensive review of the published data and information on Moroccan sedimentary and igneous phosphates. It reveals significant knowledge gaps and a lack of data, inter alia, regarding the geochemistry of phosphates and basin-scale correlations. Owing to the unique situation of Moroccan phosphates on the global market, they clearly deserve more thorough studies that may, in turn, help to constrain future resources and/or reserves, and answer outstanding questions on the genesis of phosphates

An Integrated Approach for Rapid Delineation of K-Rich Syenites Suitable as Unconventional Potash Resources

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Neogene basins in Eastern Rif of Morocco and their potential to host native sulphur

International audienceSediment-hosted sulphur deposits provide valuable information on sedimentary biogeochemical processes related to microbial activity and are paleoenvironmental proxy records. They are also used as markers for oil exploration and the largest ones may represent exploitable economic resources of sulphur. Biogenic sulphur occurrences associated with Neogene formations are found around the Western Mediterranean, in Southern Europe (e.g. Hellin, Lorca, and Teruel, Spain, and Sicily, Italy). In northern Morocco, similar geological settings are present where several sediment-hosted sulphur occurrences were reported by unpublished studies. In this study, we provide the first description of such occurrences selected from two Neogene basins in the Eastern Rif (Taza-Guercif and Boudinar) and studied using sedimentological facies analysis and mineralogical data. The studied facies occur as yellowish sub-spherical concretions, nodules, and laminated structures associated with gypsiferous marls or organic-matterrich marly clays and gypsum lenses. Mineralogical analysis revealed a mineralogical assemblage composed mainly jarosite, gypsum, and native sulphur. These geo-markers are indicative of bacterially mediated sulphate reduction and favourable conditions for the formation of sulphur, especially at the level of the Guercif basin. In contrast, Ras Tarf volcanism probably contributed to the observed facies in the Boudinar basin through different processes

Petrological and geochemical constraints on the origin of apatite ores from Mesozoic alkaline intrusive complexes, Central High-Atlas, Morocco

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