Search Results (47)

The high extraction of natural resources and the limited use of mining waste as alternative mineral resources are intensifying the depletion of natural reserves. The linear economic structure used by industrial sectors needs to be replaced with more sustainable models, such as the one proposed in the circular economy. This study aimed to evaluate strategies for the valorization of nepheline syenite waste (NSW) as an alternative mineral resource to natural and conventional ones. To this end, a set of criteria was adopted, consisting of a systematic approach for waste valorization, namely classification, potentiality, quantity/viability, and applicability (CPQvA). This involved investigating the properties of NSW, including its environmental, physical, chemical, morphological, and durability characteristics. The findings provide evidence of several potential applications for NSW, including the civil construction (fine aggregate and supplementary cementitious material), metallurgical (segregation of the iron fraction), and agricultural (segregation of the alkaline fraction) sectors. Methodologies for the beneficiation of NSW are suggested for each of the investigated applications. The valorization of NSW not only reduces the environmental impact of mining but also contributes to sustainable development by creating new products and economic opportunities, thereby promoting industrial symbiosis and advancement in the circular economy. Full article

The Mesoproterozoic alkaline Grønnedal-Íka complex (1325 ± 6 Ma) is intruded into old Archean gneissic bedrock between Ikka Fjord and Kangilinnguit (Grønnedal) by Arsuk Fjord in Southwestern Greenland. This 8 × 2.8 km oval-shaped complex constitutes the oldest part of the Gardar Province, representing a failed continental rift across southern Greenland. It comprises outer rings of mainly nepheline syenites with a central plug of Fe- and Ca-rich carbonatites. Here, we present petrological data on the syenites and carbonatites combined with geochemical modelling of groundwater percolating through the Grønnedal-Íka complex and the secondary minerals and fluid chemistry arising from these fluid–rock reactions. The results show that modelling using input data of (1) meteoric water in a closed system with respect to atmospheric CO₂ can (2) dissolve the primary minerals of the syenites and carbonatites and (3) simulate the fluid chemistry of the natural sodium carbonate springs of 3–4 °C and pH 10–11 seeping up through fractures at the bottom of Ikka Fjord, which (4) leads to the deposition of nearly a thousand tufa columns of the cold carbonate mineral ikaite (CaCO₃•6H₂O). Our results thereby support the geochemical relationship between fluid–rock reactions inside the Grønnedal-Íka alkaline complex and the precipitation of ikaite in the shape of submarine tufa columns in Ikka Fjord. The modelling indicates that the groundwater itself can be supersaturated with respect to ikaite and provide the seed crystals that lead to the columnar growth of ikaite up to 20 m tall in the seawater of Ikka Fjord. Full article

U-Pb and Lu-Hf isotopes, by inductively coupled plasma mass spectrometry and laser ablation (ICP-MS-LA), are reported in zircon grains from the Peixe Alkaline Suite. This unit comprises alkaline rocks such as syenites with nepheline, albite-oligoclase-biotite, and pegmatitic bodies. The zircon grain was imaged by cathodoluminescence (CL), which allowed the characterization of features within the crystal. These features comprise complex zone crosscuts, showing the existence of pulses that caused the intrusion of isotopically younger phases into the interior of the grain on a millimetric scale. The U-Pb results suggest a metamorphic event with Pb loss at 579 ± 3 Ma. They can be interpreted because of the collisional regional event of the Brasilia Orogen (Mara Rosa Orogeny). A second age grouping at 548 ± 2.5 Ma (MSWD = 8), obtained in areas with high luminescence fading laterally to oscillatory zoned domains with variations in the abundance of isotopes, is 33 Ma younger, demonstrating a rejuvenation of these areas through Pb loss. It is interpreted here as a second metamorphic event related to a collisional event (Santa Terezinha de Goiás arc). The Lu-Hf results for these areas indicate ƐHf values between −10 and −17, suggesting the existence of magmatic isotopic rework in a crustal environment. Full article

The article presents a comprehensive analysis of long-term studies on hydrogen-hydrocarbon free gases (FGs) in the rocks of the Khibiny massif, systematically organized and generalized for the first time. Gasometric observations were predominantly conducted within underground mine workings, with occasional measurements taken during the drilling of exploration boreholes at the surface or in subsurface air within loose sediments. Methane is the primary component of these gases, followed in descending order by hydrogen, ethane, helium, other methane homologs, and alkenes. Nitrogen is also presumed to be present, although its proportions remain undefined. The carbon and hydrogen in FGs exhibit relatively heavy isotopic compositions, which progressively lighten from methane to ethane. The intensity of gas emissions is characterized by a gas flow rate from shot holes and boreholes, reaching up to 0.5 L/min but generally decreasing significantly within an hour of reservoir exposure. Gas-bearing areas, ranging in size from a few meters to tens of meters, are distributed irregularly and without discernible patterns. The FG content in rocks and ores varies from trace amounts to approximately 1 m³ of gas per cubic meter of undisturbed rock. These gases are primarily residual, preserved within microfractures and cavities following the isolation of fluid inclusions. Their distribution and composition may fluctuate due to the dynamic geomechanical conditions of the rock mass. The release of flammable and explosive FGs presents a significant hazard during ore deposit exploration and development, necessitating the implementation of rigorous safety measures for mining and drilling operations. Additionally, the environmental implications and potential applications of gas emissions warrant attention. Future comprehensive studies of the Khibiny gases using advanced methodologies and equipment are expected to address various scientific and practical challenges. Full article

We herein present a comprehensive investigation of the eudialyte group minerals from the nepheline syenites of Rouma Island in the Los Archipelago, Conakry region, Guinea. Two distinct mineral phases were identified: an oneillite-like phase, associated with the agpaitic rock suite, and, for the first time in this locality, kentbrooksite, occurring in pegmatites. The oneillite-like phase crystallizes in the trigonal system (space group R3), with unit cell parameters a = 14.1489(2) Å, c = 30.1283(5) Å and an idealized crystal chemical formula of Na₁₅(Mn,REE)₃(Ca,Mn)₃(Fe,Mn)₃Zr₃(Zr,Si,Al,Nb,Ti)₁ (Si₂₅O₇₃)(O,OH,H₂O)₃(OH,Cl,F)₂. Kentbrooksite also exhibits trigonal symmetry (space group R3m), with unit cell parameters a = 14.2037(3) Å c = 30.1507(9) Å and an idealized formula of (Na,REE)₁₅(Ca,Mn)₆(Mn,Fe)₃Zr₃(Nb,Si)₁(Si₂₅O₇₃)(O,OH,H₂O)₃(F,Cl,OH)₂. Compared to the oneillite-like phase, kentbrooksite is markedly enriched in Mn and rare earth elements (REE). This geochemical distinction aligns with the progressive mineralogical evolution of the system, transitioning from the miaskitic to agpaitic suite (oneillite-like phase) and subsequently to pegmatites (kentbrooksite). These findings are consistent with the broader-scale observations regarding the syenite ring structure of the Los Archipelago. Full article

This article presents the results of studies on the distribution of rare metals among the products of the alkali sulfate processing of nepheline syenites. In response to the limited reserves of Bayer bauxite in the alumina industrial production region of Kazakhstan, the feasibility of using alternative alumina-containing nonbauxite raw materials was investigated. The most promising nonbauxite raw materials in Kazakhstan are nepheline and kaolinite clays. At present, there is no effective technology for processing nepheline ores. This article describes a proposed complex technology involving nepheline processing with the associated extraction of gallium and vanadium. The technology includes the activation of raw materials, followed by two-stage leaching, where potassium is extracted in the first stage. The sludge and solution obtained from the second stage of the leaching process are utilized for calcium silicate production and two-stage carbonization, respectively. In the first stage, aluminum hydroxide is extracted, and, in the second stage, a concentration of rare metals, such as gallium and vanadium, is obtained. Vanadium is extracted from the solution via crystallization, and gallium is extracted via electrodeposition. Overall, 38.48% of the Ga₂O₃ and 56.12% of the V₂O₅ are recovered from raw nepheline syenite. A technological scheme of the developed technology is presented in this article. Full article

The origin of the carbonatites that appear on Earth is one of the most controversial current topics in the petrogenesis of igneous rocks. Situated in the northern sector of the Basal Complex of Fuerteventura (Canary Islands), the Miocene Esquinzo ultra-alkaline plutonic rock complex is composed of pyroxenites, melteigites-ijolites-urtites, malignites-nepheline syenites, carbonatites, silicocarbonatites, nephelinites and nepheline phonolites. This work tries to establish the genesis of this massif of ultra-alkaline rocks with associated carbonatites from Fuerteventura (which are very rare in the oceans). The geochemical characteristics of these rocks and the minerals that are included in them have allowed us to establish their origin. This complex was generated by three successive magmatic events associated with differentiation of melanephelinite magmas emplaced in the oceanic crust. Silicocarbonatite and calciocarbonatite (sövites) dykes are related to the first magmatic event and were formed by fractional crystallization of H₂O- and CO₂-rich ijolite magmas. The melanephelinite magmas that formed these plutonic ultra-alkaline rocks were apparently generated as partial melts of asthenospheric mantle, which assimilated enriched lithospheric mantle material as they ascended. The upwelling of this large body of anomalous asthenospheric Miocene material exceeded the deformation associated with plate motions and led to an oceanic rifting event in Fuerteventura. Full article

The Saima alkaline rock-hosted niobium–tantalum deposit (hereafter referred to as the Saima Deposit) is situated in the Liaodong Peninsula, which constitutes the eastern segment of the northern margin of the North China Craton. The rock types of the Saima Deposit include phonolite, nepheline syenite, and aegirine nepheline syenite, which hosts niobium–tantalum ore bodies. In this study, the primary niobium-bearing minerals identified include loparite, betafite, and fersmite. The Saima pluton is characterized as a potassium-rich, low-sodium, and peraluminous alkaline pluton. Trace element characteristics reveal that the metallization-associated syenite is enriched in large-ion lithophile elements (LILEs) such as K and Rb but is relatively depleted in high-field strength elements (HFSEs). As indicated by the rare earth element (REE) profile, the Saima pluton exhibits a high total REE content (∑REE), dominance of light REEs (LREEs), and scarcity of heavy REEs (HREEs). The Sr-Nd-Pd isotopic data suggest that aegirine nepheline syenite and nepheline syenite share consistent isotopic signatures, indicating a common origin. The Saima alkaline pluton displays elevated I_Sr values ranging from 0.70712 to 0.70832 coupled with low ε_Nd(t) values between −12.84 and −11.86 and two-stage model ages (t_DM2) from 1967 to 2047 Ma. These findings indicate that the metallogenic materials for the Saima Deposit derive from both an enriched mantle source and some crustal components. The lithium (Li) isotopic fractionation observed during the genesis of the Saima pluton could be attributed to the differential diffusion rates of ⁶Li and ⁷Li under non-equilibrium fluid–rock interactions. Full article

A mineralogical mapping (terrain analysis) based on micro-mounts has been performed in the Archipelago of the Canary Islands, Spain. The rare elements Be, F, Li, Nb, Ta, Zr, Hf, and rare earth elements (REE) were investigated on the largest island of the Canary Islands Archipelago, Tenerife, Spain. This study forms a contribution to the metallogenetic evolution of the offshore area of the NW African Rare Mineral Province. The finds made at Tenerife were correlated by means of minero-stratigraphy with the adjacent islands La Gomera, Gran Canaria and Fuerteventura, where typical critical element host rocks, e.g., carbonatites, are exposed. At Tenerife, these hidden rock types are only indicated by a wealth of 128 compositional first-order marker minerals hosting Be, F, Zr, Nb, Ta, Zr, Hf, Li, Cs, Sn, W, Ti and REE plus Y and another 106 structural second-order marker minerals describing the geodynamic and morpho-structural evolution of Tenerife (Mn, Fe, Pb, U, Th, As, Sb, V, S, B, Cu, Zn, Mo, Au). Based upon the quantitative micro-mineralogical mapping of lithoclasts and mineralogical xenoliths (foid-bearing monzodiorite/gabbro, (nepheline) syenite, phonolite trachyte) in volcanic and volcaniclastic rocks, hidden intrusive/subvolcanic bodies can be delineated that are associated with contact-metasomatic, zeolitic and argillic alteration zones, as well as potential ore zones. Two potential types of deposits are determined. These are pegmatite-syenites with minor carbonatites bound to a series of agpaitic intrusive rocks that are genetically interlocked with rift zones and associated with a hotspot along a passive continental margin. Towards the east, the carbonatite/alkali magmatite ratio reverses at Fuerteventura in favor of carbonatites, while at Gran Canaria and La Gomera, shallow hypogene/supergene mineral associations interpreted as a marginal facies to Tenerife occur and a new REE discovery in APS minerals has been made. There are seven mineralizing processes different from each other and representative of a peculiar metallogenic process (given in brackets): Protostage 1 (rifting), stages 2a to 2d (differentiation of syenite–pegmatite), stages 3 to 4b (contact-metasomatic/hydrothermal mineralization), stages 5a to 5b (hydrothermal remobilization and zeolitization), stage 6 (shallow hypogene-supergene transition and kaolinization), and stage 7 (auto-hydrothermal-topomineralic mineralization). The prerequisites to successfully take this holistic approach in economic geology are a low maturity of the landscapes in the target area, a Cenozoic age of endogenous and exogenous processes amenable to sedimentological, geomorphological, volcano-tectonic and quantitative mineralogical investigations. The volcanic island’s mineralogical mapping is not primarily designed as a proper pre-well-site study on the Isle of Tenerife, but considered a reference study area for minero-stratigraphic inter-island correlation (land–land) and land–sea when investigating the seabed and seamounts around volcanic archipelagos along the passive margin, as exemplified by the NW African Craton and its metallogenic province. This unconventional exploration technique should also be tested for hotspot- and rift-related volcanic islands elsewhere on the globe for mineral commodities different from the ones under study. Full article

Geological, mineralogical, and petrological observations are reported for hornfels-like fine-grained granular mafic rocks in the Early Paleozoic Olkhon collisional orogen (West Baikal area, Russia). The rocks are composed of orthopyroxene, clinopyroxene, amphibole, plagioclase, and ilmenite; some samples also contain olivine, phlogopite, spinel, and titanomagnetite (Opx+Cpx+Amp+Pl+Ilm±Ol±Bt±Spl±Ti-Mag). There are three occurrences of these rocks in the area: a 500 m × 1000 m field in the Shirokaya Valley, another occurrence within the Tazheran Massif (a complex of igneous and metamorphic rocks), and dismembered dikes on the southern margin of the Birkhin gabbro intrusion. The Shirokaya field is located between two 500 Ma intrusions of the Birkhin gabbro; the Tazheran occurrence coexists with syenite, including nepheline syenite, subalkaline gabbro, and marble protrusions; and the dismembered dikes coexist with carbonates and display progressive alteration of dolerite through typical granular varieties. The dikes associated with granite and marble veins mark a part of a large arc-shaped shear zone that traverses the whole intrusive body produced by rotation of a rigid gabbro block during the peak of tectonic deformation at 470–460 Ma. All three occurrences of the hornfels-like rocks lack any evident source of heat that would be responsible for the thermal alteration of the igneous protolith. We hypothesize that the precursor, subvolcanic dolerite, may have undergone autometamorphism maintained by self-generated heat. Mafic magma intruded during high-rate strike–slip faulting, which caused rapid recrystallization of magmatic minerals and produced the observed metamorphic structures. Proceeding from the controversy in the formation mechanisms, with a heat source required for hornfels but lacking from the sampled occurrences of hornfels-like rocks, we suggest identifying the latter as beerbachite, though the term has mostly fallen into disuse. The reason is that the Olkhon rocks we study have a mineralogy, structure, and texture that are perfectly identical to those of beerbachites described in publications from the first half of the 20th century. Full article

The 360–370 Ma old Lovozero massif (NW Russia) is a layered nepheline syenitic-foidolitic pluton. Despite its huge size (650 km²), the massif is surrounded by a narrow fenite aureole, and the most intensive fenitization is associated with pegmatites and hydrothermal veins that have intruded into the wall rocks. We studied petrography, petrochemistry, mineralogy and fluid inclusions along a profile crossing the direct contact of the Lovozero massif with country Archean gneiss. We found that the fluid responsible for fenitization was a heterogeneous mixture of two coexisting phases, an aqueous fluid with salinity 8.6–15.1 eq. wt.% NaCl and a methane fluid. The coexistence of these two fluids indicates immiscibility conditions at (or below) CH₄–H₂O solvus. The aqueous fluid affected both the endocontact alkaline rocks and country gneiss. In the endocontact, intense autometasomatic alterations of the early crystallized minerals occurred, for example, the natrolitization of nepheline and sodalite. Besides, the aqueous fluid transported Na₂O, K₂O, as well as P₂O₅, TiO₂, H₂O, F, Cl and S into the exocontact. These components were precipitated in the immediate vicinity of the massif contact, and the salinity of the aqueous fluid decreased to 0.53–3.06 eq. wt.% NaCl. We assume that there are two reasons for a narrow fenite aureole in the Lovozero massif: intense autometasomatic alterations and a decrease in the permeability of country rocks due to fluid immiscibility. Full article

This study investigates the coupling effect of mechanically activated nepheline-syenite (NS) and mineral wool melt waste (MWMW) on the physical–mechanical properties of a ceramic body. The results indicate that an optimal amount (10–20%) of NS additive promotes the formation of the smallest pore size from 0.001 to 0.01 µm, as well as improves physical, mechanical, and durability properties of the ceramic samples with MWMW, when fired at temperatures between 1000 and 1080 °C. As the NS content increases, the composition becomes more alkaline, leading to enhanced vitrification and the formation of a glass phase during firing. This reduces open porosity, modifies pore size distribution, and enhances compressive strength and frost resistance. An NS content of 15% produces the best results, increasing the smallest pore fraction and yielding favourable properties, such as reduced open porosity, water absorption and density, increased compressive strength, and does not affect the linear shrinkage. The frost resistance test demonstrates that the coupling effect of NS additive and MWMW improves the samples’ resistance to freeze–thaw cycles, with the best performance observed at 15% NS content. The study also highlights the usefulness of structural parameters and ultrasound testing for assessing and predicting the frost resistance of ceramic samples. Full article

The Soarinho Alkaline Intrusion, southeastern Brazil, makes up part of the Serra do Mar Igneous Province, and it is composed of alkali feldspar syenite, alkali feldspar trachyte, quartz syenite, and monzonite. Geochemical and geochronological analyses of the Soarinho were compared with data from its neighbors, Rio Bonito and Tanguá. Zircon U-Pb Laser Ablation ages show that Soarinho is younger than Rio Bonito and Tanguá. Ages obtained from the monzonite (60 ± 2 Ma), alkali feldspar syenite (58 ± 2 Ma), and quartz syenite (58 ± 2 Ma) are indistinguishable within error. One nepheline syenite sample from Tanguá gives an age equal to those of Rio Bonito already published (65 ± 1 Ma). Petrographic and geochemical data show a clear contrast among Soarinho, Rio Bonito, and Tanguá. Lu-Hf isotopic data for the three alkaline intrusions (all negative) point to some similarities in their sources. The data suggest an enriched mantle source for Soarinho; however, an older continental crust contribution cannot be discarded. Full article

Carbonatite complexes and associated fenite zones are famous for their high-grade rare metal ores. The carbonatite–fenite complexes generally contain high concentrations of light rare earth elements (LREE), thorium (Th), and uranium (U). While most carbonatites are closely related to continental rift zones, some complexes can be observed in post-collisional tectonic environments. The Özvatan nepheline syenite–carbonatite complex is an example of post-collisional carbonatitic magmatism in Central Anatolia, Turkey. The magmatic suite is generally composed of silica-undersaturated ultra-alkaline rocks and carbonatite dikes accompanied by high-intensity fenite zones. The carbonatites of the complex are generally dominated by coarse-grained calcite minerals accompanied by fluorite phenocrysts and may also contain minor amounts of rock-forming silicate minerals. The metasomatic aureole zones (fenites) are mainly composed of euhedral nephelines, K-feldspars, aegirines, augites, and garnets. Carbonatites of the Özvatan complex show enrichments in Ca and F with depletion of alkaline (K and Na) elements. Carbonatites and fenite zones of the Özvatan complex host a variety of incompatible elements, including La, Ce, Nd, Th, U, and Nb. The isotopic composition and general geochemical properties of carbonatites in the study area represent mantle-derived carbonatites rather than crustal limestones/skarns. Full article

In Mongolia, rare earth element (REE) mineralization of economic significance is related either to the Mesozoic carbonatites or to the Paleozoic peralkaline granitoid rocks. Carbonatites occur as part of alkaline silicate-carbonatite complexes, which are composed mainly of nepheline syenites and equivalent volcanic rocks. The complexes were emplaced in the Gobi-Tien Shan rift zone in southern Mongolia where carbonatites usually form dikes, plugs or intruded into brecciated rocks. In mineralized carbonatites, REE occur mainly as fluorocarbonates (bastnäsite, synchysite, parisite) and apatite. Apatite is also present in the carbonatite-hosted apatite-magnetite (mostly altered to hematite) bodies. Alkaline silicate rocks and carbonatites show common geochemical features such as enrichment of light REE but relative depletion of Ti, Zr, Nb, Ta and Hf and similar Sr and Nd isotopic characteristics suggesting the involvement of the heterogeneous lithospheric mantle in the formation of both carbonatites and associated silicate rocks. Hydrothermal fluids of magmatic origin played an important role in the genesis of the carbonatite-hosted REE deposits. The REE mineralization associated with peralkaline felsic rocks (peralkaline granites, syenites and pegmatites) mainly occurs in Mongolian Altai in northwestern Mongolia. The mineralization is largely hosted in accessory minerals (mainly elpidite, monazite, xenotime, fluorocarbonates), which can reach percentage levels in mineralized zones. These rocks are the results of protracted fractional crystallization of the magma that led to an enrichment of REE, especially in the late stages of magma evolution. The primary magmatic mineralization was overprinted (remobilized and enriched) by late magmatic to hydrothermal fluids. The mineralization associated with peralkaline granitic rocks also contains significant concentrations of Zr, Nb, Th and U. There are promising occurrences of both types of rare earth mineralization in Mongolia and at present, three of them have already established significant economic potential. They are mineralization related to Mesozoic Mushgai Khudag and Khotgor carbonatites in southern Mongolia and to the Devonian Khalzan Buregtei peralkaline granites in northwestern Mongolia. Full article