Petrographical and geochemical study of the Eboundja nepheline syenite–derived regolith (Southwest Cameroon): evidence of changes at mineral scale during tropical weathering

Studies have been made of the Abai alkaline rocks massif, located in the northeastern part of the ChingizTarbagatai zone of Eastern Kazakhstan. The Chingiz-Tarbagatai zone of Eastern Kazakhstan is located in the western part of the Central Asian Orogenic Belt (CAOB), the lithospheric evolution of which continued during the Paleozoic and was associated with the basin closure in the system of the Paleoasian Ocean. The 9 km² massif is characterized by an isometric shape with a clearly defined concentric zonal structure and represents a multiphase intrusion composed of several varieties of syenite. Potassium feldspar is the most prevalent mineral in syenite, while plagioclase, pyroxene (5 to 15 vol. %), and amphibole (5 to 20 vol. %) are less common. Most of the massif is composed of nepheline syenite rocks containing 5–10 vol. % of nepheline. Accessory minerals include apatite, zircon, and ilmenite. Studies of mineral composition and geochemical characteristics of the rocks revealed that the syenites formed during the evolution of a single magma melt composed of alkali-syenite or monzonite. This magma was formed probably as a result of primary alkaline-mafic magma differentiation. The U-Pb LA-ICP-MS dating of magmatic zircon grains for the first time yielded a relibale rock age estimate of 401–398 Ma, which corresponds to the Emsian stage of the Early Devonian. This refutes the previously accepted ideas about the Early Permian age of the massif and its intraplate geodynamic nature. When the data on the composition and age of the massif are compared with the data on the geological evolution of the region, it is apparent that the Abai syenite massif formation is related to the extensional processes in response to subduction of the Junggar-Balkhash oceanic lithosphere underneath the Chingiz-Tarbagatai zone.

ABSTRACT The study aims to delineate the small intrusive bodies, intrusive zones, shear related sympathetic structures and add inputs in tectonic history at the contact zone of tectonically contrasting geological terranes, i.e., the Nallamallai group of Cuddapah Basin (CB), Nellore Schist Belt (NSB) and Eastern Ghats Mobile Belt (EGMB), which are not evident in earlier regional scale studies. Detailed gravity, total field magnetic and radiometric surveys at station spacing of 500 m were collected over 700 km 2 area with 1486 stations. The Bouguer gravity anomaly and total‐field magnetic anomaly map intuitively delimits the contacts between these three geological terranes. Bouguer gravity anomaly reveal NE–SW trending weak zones that host low‐density granitic intrusions and denser gabbroic–dolomitic bodies, while total field magnetic data clearly delineate the CB–NSB–EGMB boundaries, major shear zones and localized high‐susceptibility BIF and mafic intrusive bodies in the studied area. Residual Bouguer gravity anomaly, radiometric total‐count and ternary data delineate younger granites, nepheline syenites, their subsurface extensions and uranium‐rich zones in the Vellikonda Shear Zone (VSZ). The results reveal that the VSZ and sympathetic structures in the EGMB extend from 0.5 to 3 km with eastward‐dipping geometries, consistent with oblique thrust and transpressional tectonics. Granitic intrusions occur at depths of 2 to 5 km, while relict NSB patches are observed at 1 to 3 km. Shallow intrusive roots along the VSZ range from 0.5 to 1 km, with maximum crustal involvement reaching approximately 5.13 km, highlighting emplacement along pre‐existing structural weaknesses and progressive shearing and faulting. Joint 2D gravity‐magnetic modelling and 3D density inversion are employed to delineate the subsurface geometry of intrusive bodies and the depth‐dependent dip variations of major shear zones across the EGMB. The conceptual geological model provides a detailed tectonic perspective, emphasizing the imprint of younger tectono‐thermal events on the pre‐existing crustal architecture. The findings suggest that low‐density intrusions are emplaced along shear‐related sympathetic structures, serving as pathways for both younger felsic plutons and mineral‐enriched hydrothermal fluids within a complex tectonic architecture of continental collision and accretion.

<p indent="0mm">Lithology recognition is one of the fundamental skills for geologists. With the rise of artificial intelligence (AI), a fundamental challenge and opportunity in geosciences is translating expert geological knowledge into AI models capable of delivering intelligent lithological recognition services, enabling geoscience enthusiasts or non-geologists to more accurately identify rock types. In natural environments, the spatial distribution of surface rocks is highly heterogeneous, resulting in rock image datasets that typically exhibits a long-tailed distribution. Taking plutonic rocks as an example, this study adopts the classification and nomenclature scheme from the textbook Petrology (edited by Yu Bingsong et al.), and introduces PlutonicRocks-13, an imbalanced dataset for rock image recognition. The dataset comprises 13 common types of plutonic rocks, containing a total of 4,785 images with a data size of 2.49 GB. The rock types represented in this dataset are: olivine, pyroxenite, hornblendite, gabbro, diorite, monzonite, syenite, nepheline syenite, granodiorite, monzogranite, syenogranite, plagiogranite and graphic granite. Rock images were primarily collected from field outcrops and hand specimens from museums, supplemented by online sources. After careful screening, processing, and annotation, these images were curated into PlutonicRocks-13, a dataset tailored for rock image classification. To ensure annotation quality, quality control and evaluation procedures were applied, including thin-section petrographic verification and bias detection based on explainable deep learning techniques. Furthermore, by converting annotated labels into question-answer pairs, this dataset can be used for instruction tuning of multimodal models, enabling them to perform rock image classification through natural language instructions. This image dataset provides reliable data support for research on automated rock image recognition and holds significant reference value for geological surveys, surficial substrate investigations, and public geoscience education.

Abstract Rare earth elements (REE) are strategic resources critical for advanced technologies. Although their enrichment in peralkaline systems is widely attributed to magmatic-hydrothermal processes, the key mechanisms controlling REE enrichment and LREE-HREE fractionation remain poorly constrained. This study investigates a near-continuous Ca-Sr solid solution series in apatite from the Saima peralkaline complex to track REE behavior from magmatic through hydrothermal stages. All analyzed apatites exhibit homogeneous initial ⁸⁷Sr/⁸⁶Sr (0.7083–0.7089) and εNd(t) (-10.5 to -14.4) values, indicating a stable Sr-Nd isotopic system during both crystallization and late alteration. Throughout the early magmatic sequence from primitive lamprophyre to syenite and nepheline syenite, the REE budget and LREE-HREE fractionation were dominantly controlled by apatite crystallization. This is evidenced by positive correlations between whole-rock P₂O₅ and total REE contents, together with whole‑rock REE patterns that resemble those of magmatic apatite. Concurrent decreases in apatite SO₃ contents and volatile ratios (XCl/XOH, XCl/XF) record a decline in melt oxygen fugacity and an increase in H₂O saturation, which efficiently promoted REE and volatile enrichment in the residual melt. These processes culminated in the most evolved lujavrite, where intense REE mineralization produced relatively HREE-enriched silicates such as eudialyte. Subsequently, an autometasomatic fluid enriched in Na⁺, Sr2⁺, LREE3⁺, CO₃2⁻, PO₄3⁻, and F⁻ exsolved from the lujavrite system, decomposing earlier REE-bearing phases and precipitating hydrothermal LREE-phosphates and carbonates at 220.0 ± 2.4 Ma. Hydrothermal apatite from this stage exhibits coupled Sr and REE enrichment, accomplished through fluid-mediated substitutions Ca2⁺ ↔ Sr2⁺, 2Ca2⁺ ↔ REE3⁺ + Na⁺, and Ca2⁺ + P⁵⁺ ↔ REE3⁺ + Si⁴⁺. The pronounced LREE-HREE fractionation observed in hydrothermal apatite is ascribed to the prior magmatic removal of HREE into early silicates and the preferential compatibility and mobility of LREE in alkaline, carbonate-rich fluids. This study highlights the utility of apatite as a petrogenetic indicator for deciphering REE mineralization processes in alkaline igneous systems.

Abstract The petrogenetic link between carbonatites and associated silicate rocks remains a longstanding debate in igneous petrology. Some minerals, such as apatite and calcite, which crystallize across diverse lithologies during magmatic differentiation, can record geochemical changes in their crystallizing environments, thereby providing valuable insights into the genesis of these rock suites. The Wajilitage Carbonatite Complex (WCC) in northwest China, part of the Tarim Large Igneous Province, is a typical carbonatite–alkaline complex composed of calcite and dolomite carbonatites, aillikite, nephelinite, and nepheline syenite. In this study, in situ geochemical and C–O isotope analyses of apatite and calcite are utilized to investigate their genetic relationships. The Mg content of apatite (Mgap) serves as an effective recorder of the magmatic evolution of this carbonatite–alkaline complex. Apatite in the carbonatite has higher Mg contents than apatite in the nephelinite and nepheline syenite, precluding an origin via fractional crystallization or liquid immiscibility from these silicate melts. Although the Mg contents of apatite in the carbonatites overlap with those of apatite phenocrysts in aillikite, their distinct trace-element compositions (e.g. La, Sr, and Y) and δ18OV-SMOW values rule out a direct genetic relationship between these rocks. We propose that the carbonatites formed independently by low-degree partial melting of a carbonated mantle source. Subsequent fractional crystallization of calcite and dolomite from this parental magma produced the calcite and dolomite carbonatites, respectively. Trace elements and δ18OV-SMOW values of apatite suggest that nephelinite evolved to nepheline syenite, the latter of which assimilated the aillikite. Differentiation of the carbonatite magma generated distinct styles of rare earth element (REE) mineralization, with light REE (LREE) being enriched in dolomite carbonatite, and both LREE and heavy REE (HREE) being enriched in calcite carbonatite. This study presents an integrated petrogentic model for the WCC, highlighting the utility of apatite geochemistry in unraveling the complex magmatic evolution of carbonatite–alkaline complexes.

Quartz syenite and nepheline syenite occur as massive bodies and dikes within the Bulfat complex in the Zagros Suture Zone, located in the Kurdistan region of northeastern Iraq, within the Penjween-Walash Subzone. This study examines the petrogenesis, geochemistry, and tectonic implications of these rocks. Petrographic analysis identified two intrusions: quartz syenite, which is silica-saturated, dominated by alkali feldspar, plagioclase, quartz, and garnet, with inequigranular, porphyritic, poikilitic, myrmekitic, and perthitic intergrowth textures. Nepheline syenite is silica-undersaturated, containing a significant amount of feldspar and feldspathoid, and mafic minerals such as amphibole, biotite, and aegirine-augite. It displays holocrystalline, inequigranular, poikilitic, and perthitic intergrowth textures, with alterations including cancrinite pseudomorphs, albitization, and sericitization. Whole-rock geochemistry classifies both as alkaline, characterized by higher SiO2 content in quartz syenite (64.2 to 68 wt.%) compared to nepheline syenite (57 to 59.3 wt.%), and elevated alkalis. Both show enrichment in Light Rare Earth Elements relative to Heavy Rare Earth Elements, but quartz syenite has a higher total ∑REE =106.6–383 ppm than nepheline syenite, 7.7–145.3 ppm. Negative Eu anomalies indicate plagioclase fractionation and limit crustal contamination, while two nepheline syenite samples show positive Eu anomalies, indicating plagioclase accumulation. High Rb/Sr ratios suggest that the crust was contaminated from pelitic and psammitic sources. Tectonic discriminant diagrams reveal a volcanic arc field, characterized by enrichment in large ion lithophile elements, reflecting mantle-derived magmas modified by subduction during the closure of the Neo-Tethys. The elevated Zr/Y ratio further supports a continental arc setting, reflecting partial melting and magmatic differentiation. This study highlights the roles of magmatic fractionation, crustal assimilation, and subduction-related processes in the formation of nepheline syenite and quartz syenite.

This study investigated lithium beneficiation from nepheline syenite ore containing 242.57 ppm Li, identifying biotite as the primary lithium-bearing mineral. A high-intensity dry magnetic separation produced a pre-concentrate assaying at approximately 850–1000 ppm Li, and flotation tests were conducted on both the run-of-mine ore and this magnetic product. Flotation performance was systematically evaluated using two top sizes (−500 and −300 µm), six size fractions (−500 + 75, −500 + 53, −500 + 38, −300 + 75, −300 + 53, −300 + 38 µm), four pH values (2.5, 4.0, 6.5, 9.5), and three collectors (DAHC, Derna 7, and Der A4). Among the reagents, Der A4 yielded the most promising results. Optimization using sodium silicate as a depressant demonstrated that, at 20 g/t Der A4, 500 g/t Na2SiO3, and pH 4.0, the −300 + 75 µm fraction of the run-of-mine ore reached approximately 5300 ppm Li. Applying the same parameters to the magnetic pre-concentrate resulted in a 6326.46 ppm Li concentrate with roughly 80% of flotation recovery. Mineralogical characterization using MLA, XRD, modal mineralogy, and SEM-EDS confirmed that the optimized product consisted predominantly of biotite, accompanied by K-feldspar, nepheline, and albite. Liberation results showed high liberation levels and the free surface, supporting the efficiency of combining magnetic separation with flotation for upgrading nepheline syenite as a potential lithium resource.

The Tanguá Massif (TM) is an alkaline intrusion that is part of the Poços de Caldas-Cabo Frio Alignment (PCCFA), which comprises more than 25 intrusive bodies and extends over 1000 km along a WNW-ESE trend in southeastern Brazil. This study presents new insights into the evolution and genesis of the TM based on updated geological mapping, combined with mineralogical, petrographic, lithogeochemical, geochronological, and isotopic analyses. A new lithofacies map is proposed for the Tanguá Massif, subdividing the massif into five main units: i) central nepheline syenite; ii) intermediate nepheline syenite; iii) syenite; iv) breccias; v) undivided nepheline syenite. Additionally, phonolites and trachytes occur as dikes crosscutting the massif. U-Pb geochronological data reveal two distinct age groups: an older Cenomanian phase (94.8 Ma) and a younger Danian-Maastrichtian phase (ca. 60-70 Ma). The presence of an older syenite aged than previously reported – the oldest age for the PCCFA – suggests that the conventional mantle plume model may not adequately explain the origin of this province. Sr-Nd and Lu-Hf isotopic signatures indicate that the syenites and nepheline-syenites plot in the DMM-EMI array, whereas phonolite in the DMM-EMII array, suggesting mixing of different mantle components according to other studies. Geochemical and isotopic parameters (e.g., SSI, Zr/TiO2, REE sum, and εNd) highlight the significant role of crustal assimilation during the evolution of the TM, a process also proposed for other PCCFA bodies. Furthermore, ratios such as Th/Yb and Ba/La, combined with Nd-Hf isotopic decoupling, suggest the involvement of oceanic sediments associated with subducted slabs in the genesis of the magmas. These findings provide new insights into the magmatic evolution of the Tanguá Massif and contribute to a broader understanding of the processes controlling the formation of the PCCFA alkaline province.

ABSTRACT The Lugiin Gol deposit is one of four REE deposits (Khalzan Burged, Mushigai Khudag, and Khotor) in Mongolia. It consists of a nepheline syenite stock, equivalent dike rocks, and more than 400 carbonatite veins within an area of approximately 13 km 2 . This study focuses mainly on the western part of the Lugiin Gol deposit. The western Lugiin Gol deposit consists of many carbonatites that fill NE‐trending fractures in sedimentary rock. The minerals in the carbonatites include calcite, dolomite, strontianite, kutnohorite, ankerite, fluorite, synchysite‐(Ce), bastnaesite‐(Ce), parisite‐(Ce), synchysite‐bastnaesite intergrowths, rutile, apatite, goyazite, quartz, K‐feldspar, muscovite, chlorite, Al‐Si mineral, Na‐Si mineral, pyrite, sphalerite, chalcopyrite, galena, Fe hydroxide, and graphite. Synchysite‐(Ce), bastnaesite‐(Ce), parisite‐(Ce), and synchysite‐bastnaesite intergrowths are REE fluorocarbonates. Synchysite‐(Ce), the most abundant REE fluorocarbonate, occurs as disseminated euhedral crystals in carbonates, Fe hydroxide, and K‐feldspar. It is LREE‐dominant, with La/Ce ratios ranging from 0.47 to 0.84, and its LREE abundance decreases in the order Ce &gt; La &gt; Nd &gt; Gd &gt; Sm &gt; Eu. Bastnasesite‐(Ce), the second most abundant REE fluorocarbonate, occurs as granular crystals closely intergrown with synchysite‐(Ce). It is also LREE‐dominant, with La/Ce ratios ranging from 0.68 to 0.91, and LREE abundances in the order Ce &gt; La &gt; Nd &gt; Gd &gt; Eu &gt; Sm. Parisite‐(Ce), the third most abundant REE fluorocarbonate, occurs as anhedral or granular crystals that are closely intergrown with or replaced by synchysite‐(Ce). It is LREE‐dominant, with La/Ce ratios ranging from 0.38 to 0.61, and LREE abundances in the order Ce &gt; La &gt; Nd &gt; Gd &gt; Sm &gt; Eu. The synchysite‐bastnaesite intergrowths occur as granular crystals and are LREE‐dominant, with La/Ce ratios ranging from 0.81 to 0.97, and LREE abundances in the order Ce &gt; La &gt; Nd &gt; Gd &gt; Eu. The grain size and intergrowth textures of the REE minerals govern the grinding fineness required to achieve sufficient mineral liberation. REE mineral grains in this deposit range from fine (&lt; 150 μm) to moderately coarse (&lt; 400 μm), but they commonly occur locked with gangue minerals. This indicates that the ore must be ground sufficiently fine to break the intergrowths and liberate the REE minerals. Based on the observed REE mineral textures, REE mineralization was formed by the addition of Ca and a decrease in temperature in ore‐bearing fluids (from approximately 100°C to over 400°C) at relatively low pressures. Therefore, information on the occurrence and chemical composition of REE minerals can be used as basic data for understanding REE minerals genesis and improving their recovery rates.

The research focus on the use of glass cullet (GW) and nepheline syenite (NS) in the development of linings for petrochemical reactors walls. The ash used was rice husk ash (RHA) obtained from rice husk after burning at 7000C. The Chemical profile of GW and NS were evaluated using Atomic Absorption Spectroscopy (AAS) and result obtained showed lower percentage of SiO2 (56.23%) in NS than in GW (71.13%). The physical tests showed higher flexural strength (FS) of ?35mpa for GW linings (RHAGW) which was within the ISO 13006 B1a standard at 11000C. Thermal conductivity values were higher for NS linings (RHANS) (0.32 – 1.98w/mK) than RHAGW (0.22 – 1.91) which is probably due to more closure of pores, higher content of Fe2O3 and conductive metallic impurities making NS very unsuitable for linings production. Thermal gravimetric analysis (TGA) showed higher weight loss with RHANS (26%) than with RHAGW (17%) making only RHAGW suitable for production of linings. The X-ray diffractogram (XRD) shows the presence of quartz and mullite while RHANS showed the presence of microcline, albite hermatite, andalusite, orthoclase and nepheline. Results obtained showed that GW formulations gave better porcelain linings suitable for corrosion resistant reactors

The Arkansas alkaline province (AAP), southeastern US, consists of seven intrusions or intrusive complexes that lie along a NE–SW trend that falls on the extension of the Mississippi Valley graben. There are three distinct magmatic events: (1) emplacement of lamproites at ~104 Ma, (2) emplacement of lamprophyres, phonolites, carbonatites, ijolites, and a variety of nepheline syenites between 100 and 98 Ma, and (3) emplacement of a large nepheline syenite body at ~88 Ma. Unpublished and published mineralogical, elemental, and isotope data are used to develop an integrated model for the AAP magmatic activity. The lamproites were derived from ancient enriched subcontinental lithosphere. The carbonatite–lamprophyre–phonolite–ijolite–nepheline syenite association comprises several intrusive complexes (Magnet Cove, Potash Sulphur Springs, V-intrusive) and the Benton lamprophyre–felsic dike swarm. Magmatic evolution is controlled by fractional crystallization of pyroxene and nepheline. The carbonatites may be the result of liquid immiscibility between carbonate and lamprophyric liquids. The large nepheline syenite body (Granite Mountain and Saline County) evolved through fractional crystallization of feldspar and nepheline. Event 2 and 3 magmas were derived from an OIB-like asthenospheric source. The most likely model for the origin of the AAP is the reactivation of a zone of crustal weakness by far field stresses.

The article presents the results of 40Ar/39Ar dating of rocks (quartz and alkali syenites, nepheline syenites with REE-Nb-Zr mineralization) from the Burpala massif using feldspar, phlogopite, and amphibole. The obtained results limit the closure of the K-Ar isotope system in feldspars of quartz and alkali syenites to 274–283 Ma, while the age of closure of the K-Ar isotope system in amphibole of alkali syenite and in phlogopite of ore-bearing nepheline syenite is 298±4 Ma and 301±4 Ma, respectively. Estimates of the formation pressure using the plagioclase–hornblende geobarometer show that the massif rocks were formed at a depth of about 10 km. Comparison with zircon age values indicates a simultaneous closure of the U-Pb and K-Ar isotope systems in zircons, phlogopite and amphibole, respectively. The closure of the K-Ar isotope system in feldspars occurred 12–15 million years later.

Structural And Performance Characteristics Of Glasses Derived From Processed Nepheline Syenite Of Kaleibar

Data are presented on the historical aspects of geological research and the structural and mineral composition of rocks in the Zhovtnevy alkaline massif of the Azov region. The uniqueness of its structure and petrography, genetic characteristics, and the vast diversity of rock-forming minerals, textures, and rare-earth elements are highlighted. Polish researcher Yu. Morozevich describes mariupolite as an extreme alkaline facies of nepheline syenites, primarily composed of albite, nepheline, and aegirine. Therefore, it is commonly referred to as aegirine-albitic nepheline syenite. Other minerals that lead to the classification of mariupolites into different types include zircon, hastingsite, lepidomelane, and beckelite or cerium brytholite. Among the researchers studying the alkaline massif, A.S. Ginzburg stands out for his detailed examination of the composition and structure of mariupolites. He describes the components of these rocks and discusses their distribution. He also addresses the genesis of the Mariupol (Zhovtnevy) nepheline massif, suggesting that the formation of nepheline syenites results from the assimilation of limestones by magma and subsequent differentiation. The ideas of Yu. Morozevich were further developed by Liya Falkovna Einberg. Based on field research conducted by the Polish researcher between 1927 and 1929, Einberg created a detailed topographic map that illustrates the geological structure, relief elements, and names of streams and their tributaries – many of which have been lost on contemporary maps (Einberg, 1933). Structurally, the massif exhibits zonation: nepheline rocks are situated at the core, surrounded by nepheline syenites, with pyroxene-amphibole granites occurring on the periphery. Mariupolites are integral to the massif and form distinct zones and bodies of various shapes and sizes within it. The primary rock-forming minerals in mariupolites include nepheline, albite, aegirine, and lepidomelan, while secondary and accessory minerals consist of zircon, apatite, sodalite, amphiboles, calcite, cancrinite, zeolite, pyrochlore, brytholite, magnetite, and iron sulfides, among others. All rock complexes in the Zhovtnevy massif are largely ferruginous. Zirconium, rare earth elements, tantalum, and niobium mineralisation are associated with nepheline syenites, mariupolites, and albitites, which may have industrial significance in certain areas. Sodalite varieties of mariupolite are regarded as promising raw materials for the stone-working industry. The main decorative minerals found in them are sodalite, albite, and nepheline, occurring in various ratios and textural combinations. The ability of sodalite mariupolites to be processed, ground, polished, and utilised in producing jewellery, haber-dashery, and souvenir items has been studied. The results of these tests have been positive, and the demand for products made from this material has exceeded expectations. The authors recommend that when planning the development of the Zhovtnevy massif deposits, an integrated approach should be taken, ensuring that the extraction of critically important minerals occurs alongside the harvesting of sodalite varieties of mariupolite for the stone-working industry.

ABSTRACT Ornamental stone is extensively utilised in architectural structures due to its resistance and longevity. Nevertheless, exposure to atmospheric pollutants, in conjunction with the improper use of chemical products, both in isolation and as components of cleaning agents, has the potential to compromise its structural and aesthetic properties over time. This study aims to evaluate the effects of acidic and alkaline solutions and cleaning products on Ás de Paus Granite, a nepheline syenite from the state of Rio de Janeiro, Brazil, which is widely used in buildings. Laboratory tests were conducted to ascertain physical indices (bulk density, apparent porosity and water absorption), water absorption by capillarity, water absorption with a Karsten tube, ultrasonic wave propagation velocity, colour analysis by spectrophotometry and accelerated weathering tests by partial immersion in acidic and alkaline solutions and cleaning products. The results indicated structural alterations to the stone, represented by mineral corrosion and salt crystallisation, and mainly chromatic alteration, characterised by intense yellowing, and locally accentuated whitening. The conclusion drawn from this analysis is that when selecting cleaning products, it is imperative to conduct preliminary tests on the stone surface and ensure meticulous selection and adequate dilution to guarantee enhanced durability and preservation of ornamental stones.

Due to the rapid advancement of technology, lithium carbonate has become a crucial raw material for battery storage applications. Brines remain the primary source, while lithium carbonate production from ores is limited. Therefore, expanding resources, identifying potential deposits, and characterizing existing sources are essential. Direct lithium detection via MLA is challenging due to its atomic number being below 6; however, it can be indirectly identified through lithium-bearing biotite. This study characterizes lithium-bearing biotite in nepheline syenite ore, considering biotite as the primary lithium source. Analytical methods included MLA, modal mineralogy, XRD, ICP-OES, XRF, SEM-BSE, and EDS. The ore contained 4% biotite, with a liberation degree exceeding 70% in particles finer than 500 µm. Biotite formed binary, ternary, and complex associations with K-feldspar, nepheline, and albite. Finer particle sizes increased biotite liberation while reducing associations; no binary biotite–nepheline associations were detected below 75 µm. EDS spectra confirmed biotite as the sole lithium-bearing mineral.

Abstract Alkaline igneous rocks are one of the most important sources of rare earth elements (REE) worldwide, due to their elevated contents of HFSE (e.g. Zr, Nb, REE), in particular the heavy rare earth elements. This study presents detailed geochemical and geochronological characteristics of a REE-bearing mineral assemblage forming Zr–REE–Nb mineralisation in nepheline syenite dykes at the contact zone of the Čistá granodiorite pluton (Czech Republic). The primary REE-bearing accessory minerals, monazite-(Ce), pyrochlore, fergusonite-(Y) and gadolinite-(Ce), underwent multiple alteration driven by hydrothermal fluids. Fine-scale investigation of the alteration assemblages, using a combination of electron probe microanalysis (EPMA), transmission electron microscopy (TEM), and laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS), revealed the occurrence of two main stages of alteration and provided insights into the relationships among the primary and secondary REE-bearing minerals and the replacement mechanisms. The first alteration stage took place when the pluton cooled below 600°C. This was marked by monazite-(Ce) breakdown and its replacement by allanite-(Ce) and fluorcalciobritholite-(Ce), as well as alteration of primary pyrochlore and the formation of U-rich oxide inclusions. The second alteration stage involved alkali-fluid-induced metasomatism at ∼200–450°C, affecting the majority of the REE-bearing assemblage and leading to the formation of new secondary minerals such as bastnäsite-(Ce), britholite-(Ce) and gadolinite-(Y), and a second generation of pyrochlore. Age determination of primary monazite-(Ce) yielded a lower intercept U–Pb age of 376.5 ± 9.9 Ma, consistent with mean 208 Pb/ 232 Th age of 375 ± 3.2 Ma, which constrains the timing of the late magmatic hydrothermal processes related to the main magmatic event in the Čistá pluton. This study provides new insights into stability relations of REE-bearing accessory minerals in an alkali-rich environment. It also highlights the advantages of using comprehensive analytical methods from microscale to submicron-scale as a fundamental approach in the petrochronological investigation of metasomatic processes.

Bio Waste Application for Potassium Extraction from Nepheline Syenite

Abstract Agpaitic nepheline syenite complexes are globally rare, yet their unique mineralogy and potential for critical metal mineralization make them an important focus of research. Here we investigate the Yangyuan Alkaline Complex from the circum-cratonic Triassic alkaline belt of the North China Craton. The complex mainly comprises sills divided into two series: an early phase of aegirine nepheline syenite series (ANS) and a late phase of alkali-feldspar syenite series (AFS). The ANS features agpaitic mineral assemblages, high alkalinity index (most &amp;gt;1.0), and high Na/K molar ratios (&amp;gt;2.0), whereas the AFS is orthoclase dominated and potassic. Both series are enriched in incompatible elements and have δ66Zn ranging from 0.37‰ to 0.39‰ for ANS and 0.29‰ to 0.43‰ for AFS, and an average εNd(t) of −3.23 for ANS and −4.43 for AFS. The Sr–Nd–Zn isotopes, together with in situ zircon Hf–O isotopic systematics, indicate that both the ANS and AFS are derived from an enriched lithospheric mantle source that was previously metasomatized by fluids/melts from recycled carbonate-bearing sediments. Phase-equilibrium relations and isotope mixing models indicate that the AFS cannot be evolved from the ANS via crystal fractionation and assimilation at upper crustal levels. In contrast, a combination of lower continental crustal assimilation and potential kaersutite fractionation may be important factors driving the transition from agpaitic-silica-undersaturated to potassic-silica-saturated magma systems. During ascent and emplacement at upper crustal levels, extensive fractional crystallization of sanidine, ±eudialyte, ±nepheline, and ±apatite resulted in an enrichment in high-field-strength elements (HFSE), Rb, Th U and rare earth elements (REE). Two different types of zircons—magmatic and hydrothermal—yield indistinguishable ages at c. 223–221 Ma, indicating near contemporaneous igneous crystallization and hydrothermal alteration. Hydrothermal metasomatism may have introduced post-magmatic HFSE−REE mineralization.