Search Results (110)

Between approximately 725 and 518 Ma, a suite of specialized felsic plutons and granitic stocks were emplaced across the Arabian Shield, many of which are now recognized as highly mineralized prospects enriched in rare earth elements (REEs), rare metals, and radioactive elements bearing mineralizations. The current investigation focused on the radiological and geochemical characterization of naturally occurring radionuclides, specifically ²³⁸U, ²²⁶Ra, ²³²Th, and ⁴⁰K, within three strategically selected granitic prospects, namely, J. Tawlah albite granite (TW), J. Hamra (HM), and J. Abu Al Dod alkali feldspar syenite and granites (AD). Concerning the radioactivity levels of the investigated granitic stocks, specifically the activity concentrations of ²³⁸U, ²²⁶Ra, ²³²Th, and ⁴⁰K, the measured average values demonstrate significant variability across the TW, HM, and AD stocks. The average ²³⁸U concentrations are 195 (SD = 38.7), 88.66 (SD = 25.6), and 214.3 (SD = 140.8) Bq/kg for TW, HM, and AD granitic stocks, respectively. Corresponding ²²⁶Ra levels are recorded at 172.4 (SD = 34.6), 75.62 (SD = 25.9), and 198.4 (SD = 139.5) Bq/kg. For ²³²Th, the concentrations are markedly elevated in TW at 5453.8 (SD = 2182.9) Bq/kg, compared to 77.16 (SD = 27.02) and 160.2 (SD = 103.8) Bq/kg in HM and AD granitic stocks, respectively. Meanwhile, ⁴⁰K levels are reported at 1670 (SD = 535.9), 2846.2 (SD = 249.9), and 3225 (SD = 222.3) Bq/kg for TW, HM, and AD granitic plutons, respectively. Notably, these values exceed the global average background levels, indicating an anomalous enrichment of the studied granitic occurrences. The mean radiological hazard indices for each granitic unit generally exceed global benchmarks, except for AEDE_out in the HM and AD stocks, which remain below international limits. The geochemical disparities observed are indicative of post-magmatic alteration processes, as substantiated by the interpretation of remote sensing datasets. In light of the significant radiological burden presented by these granitic stocks, it is essential to implement a rigorous precautionary framework for any future mining. These materials must be categorically excluded from uses that entail direct human exposure, especially in residential construction or infrastructure projects. Full article

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

Cenozoic alkali-rich porphyries are widely distributed in the junction zone between the Sanjiang Orogenic belt and the Yangtze Plate. They are of great significance for understanding the regional geodynamics, tectonic evolution, and metallogenesis. However, the origin of these porphyries remains controversial. In this study, new petrological, geochemical, and geochronological data are presented for Cenozoic syenite porphyry from the Beiya porphyry Au-polymetallic deposit in western Yunnan. Zircon U-Pb dating results show that the Beiya syenite porphyries formed around 36.3–35.0 Ma, coinciding with the magmatic peak in the Jinshajiang-Red River (JSJ-RR) alkali-rich porphyry belt. Geochemical analyses indicate that the Beiya porphyries have potassic characteristics and an arc-like geochemical affinity, with C-type adakite affinity, suggesting a post-collisional setting. The JSJ-RR fault zone is unlikely to be the primary mechanism responsible for the formation of this alkali-rich porphyry magmatism. Instead, the development of the Beiya alkali-rich porphyries is likely associated with the convective removal of the lower part of the overthickened lithospheric mantle and asthenospheric upwelling during the Eocene–Oligocene. Their magmas probably originated from the partial melting of Paleo–Mesoproterozoic garnet amphibolite facies rocks in the thickened lower continental crust, with the addition of shoshonitic mafic magmas produced by the partial melting of metasomatized lithospheric mantle triggered by asthenospheric upwelling. This study provides additional reliable evidence to further constrain the origin of Cenozoic alkali-rich porphyries in the JSJ-RR belt. Full article

Late Mesozoic magmatism in Southeast China extensively reworked the Cathaysia Block’s crust, linked to the Paleo-Pacific Plate subduction beneath East Asia. The northeastern Cathaysia Block, largely covered by Cretaceous volcanic-sedimentary basins, has limited Jurassic exposure to Early Cretaceous intrusions, which provides critical insights into deep crust-mantle processes. In this study, we present zircon U-Pb geochronology and Hf isotope, whole-rock geochemistry, and Sr-Nd isotopes of the Middle Jurassic syenite-granite suites and Early Cretaceous granites with enclaves in the Qingyuan area (SW Zhejiang Province) to constrain their petrogenesis and tectonic significance. Middle Jurassic syenites and alkali-feldspar granites (169–167 Ma) exhibit calc-alkaline to shoshonitic affinities and weakly peraluminous compositions. Early Cretaceous granites (134 Ma) and their enclaves (136 Ma) are high-K calc-alkaline and weakly peraluminous to metaluminous. All samples show LILE and LREE enrichment, HFSE depletion, and negative Eu and Sr anomalies, with only syenites displaying negative Ce anomalies. We suggest that the Middle Jurassic syenites originated from the partial melting of an enriched lithospheric mantle influenced by subduction-related metasomatism. Alkali-feldspar granites derived from partial melting of the basement of the Cathaysia Block. Early Cretaceous granites formed by partial melting of lower crustal mafic rocks, with enclaves representing earlier crystallization products, which were then mechanically mixed with granites. We propose the NE Cathaysia Block underwent significant reworking from the Middle Jurassic to the Early Cretaceous. Middle Jurassic syenites formed in a compressional setting linked to Paleo-Pacific Plate subduction, while Early Cretaceous magmatism reflects lithospheric extension and crust-mantle interaction triggered by slab rollback. Full article

Gejiu, a prominent tin–polymetallic ore district, is distinguished by its diverse mineral complexes. However, the genesis of these complexes and their relationship with mineralization remain inadequately studied. This study utilized whole-rock geochemical analyses to investigate the magmatic sources and petrogenesis of different complex types, aiming to elucidate their implications for tin–polymetallic mineralization. The results indicate that gabbro, monzonite, diorite, and syenite are derived from enriched mantle-derived magmas and have undergone limited crustal contamination. Granites are formed by the mixing of mantle- and crust-derived magmas, involving both physical mixing and chemical diffusion. Major and trace element characteristics suggest that the Gejiu granites predominantly exhibit features of both A-type and I-type granites. Harker diagrams and whole-rock indicators, such as Nb/Ta and Zr/Hf, suggest that granites experienced a two-stage fractional crystallization process, ultimately forming highly evolved biotite monzogranite. Fractional crystallization is the dominant mechanism controlling magmatic evolution, while high-temperature melting and biotite decomposition reactions are critical for the formation of the world-class Gejiu tin deposit. Full article

This study focused on identifying Th-, Nb-Ta-, Zr-, and REE-bearing minerals with a multivariate statistical approach in alkaline syenite to evaluate their radiological risks, at Nikeiba, Egypt. Through microchemical analyses, by utilizing electron probe microanalysis, horite, microlite, monazite, zircon, columbite, and fergusonite were shown to bear uranium and thorium. These minerals have played an important role in higher radioactive zones in the studied alkaline syenite. REE-minerals comprising bastnäsite, monazite, and fluorite and apatite are well recorded. The total rare earth elements (TREE₂O₃) reveal higher concentrations in bastnäsite than monazite, with averages 74.87 and 63.8 wt%. Ce is considered the most predominant LREE in the analyzed bastnäsite and monazite. The mean values of radionuclide activity concentrations of ²³⁸U, ²³²Th, and ⁴⁰K are 108 ± 20 Bq/kg, 107 ± 9 Bq/kg, and 1255 ± 166 Bq/kg, respectively. Radiological assessments revealed a radium equivalent activity of 357 Bq/kg, below global limits, but an air-absorbed dose rate (166 nGy/h) and annual effective doses (0.81 mSv/y indoors, 0.20 mSv/y outdoors) exceeding safe thresholds. Additionally, the excess lifetime cancer risk (ELCR) was calculated at 0.00071, surpassing the acceptable limit of 0.00029, making these rocks unsafe for construction use. Statistical analyses further underscored the relationships between radionuclide concentrations and associated risks, highlighting the necessity for continuous monitoring and mitigation. 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

The Ossa-Morena Zone (SW Iberian Massif) hosts the largest set of Cambro–Ordovician alkaline magmatic plutons related to the Palaeozoic rifting of the northern Gondwana margin so far described. An organized framework for their classification at different scales is proposed through data-driven ranks based on their distinctive petrological features relative to other rift-related magmatic rocks found throughout western Europe. The classification method aims to enhance geological mapping at different scales, regional- and continental-scale correlations, and, as such, facilitate the petrogenetic interpretation of this magmatism. The hierarchical scheme, from highest to lowest rank, is as follows: rank-1 (supersuite) assembles rocks that have distinctive characteristics from other magmatic units emplaced in the same magmatic event; rank-2 (suite) categorizes the units based on their major textural features, indicating if the body is plutonic, sub-volcanic, or a strongly deformed magmatic-derived unit; rank-3 (subsuite) clusters according to their spatial arrangement (magmatic centres) or association to larger structures (e.g., shear zones or alignments); rank-4, the fundamental mapping unit, characterizes the lithotype (alkaline granite, alkaline gabbro, syenite, albitite, etc.) by considering higher ranks (alkalinity and textural aspects); rank-5 characterizes the geometry of individual plutons (with several intrusions) or swarms; rank-6 (smallest mappable unit) corresponds to each intrusion or individual body from a swarm. Although this classification scheme is currently presented solely for the Ossa-Morena Zone, the scheme can be easily extended to incorporate other co-magmatic alkaline bodies, such as those in the NW Iberian allochthonous units or other peri-Gondwanan zones or massifs, in order to facilitate regional correlations of the rift-related magmatism. Full article

This article presents the results of fractal texture analyses of selected minerals (aegirine, eudialyte, orthoclase) in the northwestern part of the Lovozero intrusion. This intrusion is located in northeastern Scandinavia and is a massif made of alkaline rocks. There are rocks such as massive syenites and porphyrtes, as well as iiolites, urtites, and foyaites, accompanied by metasomatic rocks of the contact zone. A box-counting fractal dimension was used to numerically represent the texture of these minerals. In the further part, this coefficient was visualized in the form of maps superimposed on the study area, and some simple arithmetic calculations were performed to highlight the common features of this dimension for the selected rock-forming minerals. In conjunction with the geological interpretation of these results, rock-forming processes in this massif were depicted. This work is preliminary, showing the potential of this calculation method in petrological applications. Full article

Feldspars are essential components in the ceramic industry, and the increasing demand for high-grade fluxes has recently elevated their status as critical raw materials for the European Union. This survey aims to evaluate, for the first time, Italy’s mining potential for the production of ceramic fluxes through a methodological approach that considers lithology, technological value, degree of alteration and potential for mining exploitation. The most promising resources are identified in the Alps, the Apennines, Sardinia and the Calabro–Peloritan Arc, based on the chemical composition of rocks without any beneficiation. Key parameters include the equivalent feldspar content and the sum of Fe₂O₃ + TiO₂. Factors that may influence the feasibility of exploitation are critically discussed for granitoids and syenites, acidic volcanics, aplites and pegmatites, albitites, felsic metamorphics, silica-saturated and silica-undersaturated volcanics, arkosic sandstones and rocks that have undergone epithermal alteration. All resources are compared with deposits currently under extraction and assessed against benchmarks or well-recognized raw materials used as market proxies. This review lays the groundwork for operational mining exploration by clearly defining Italy’s potential for feldspathic fluxes. The exploratory assessment approach to feldspathic resources can also be applied in other countries. Full article

The Zhueryu Au deposit is one of the important quartz-vein type Au deposits. It is located at the western margin of the Jidong gold belt in China and characterized by ore bodies hosted in structural fractures within the Zhueryu syenite. The H, O, and S isotopes as well as the Rb–Sr isotope age of fluid inclusions from the quartz-polymetallic sulfide ore bodies (main stage) and the zircon U–Pb isotope age from the syenite were analyzed so as to discuss the source of ore-forming fluids and constrain the Au’s mineralization age. The textural characteristics of the fluid inclusions indicate that the fluid inclusions in the quartz (QzII) are from the same stage, with no evidence of secondary fluid inclusions from the later stage. Fluid inclusion microthermometry performed on the quartz (QzII) reveals a predominance of vapor–liquid two-phase inclusions, with homogenization temperatures ranging from 177 °C to 337 °C (average: 260 °C), characteristic of a medium-low temperature hydrothermal system. Furthermore, H, O, and S isotope analyses of the ore-forming fluids yielded δD, δ¹⁸O, and δ³⁴S values ranging from +12.8‰ to +14.8‰, +9.15‰ to +9.51‰, and −8.395‰ to -1.918‰ (average: −5.826‰), respectively. These isotopic signatures, particularly the distinctly positive δD values, strongly suggest that the Zhueryu ore-forming fluids were primarily derived from metamorphic sources, contrasting with the magmatic-hydrothermal fluids implicated in the formation of many other Au deposits within the Jidong belt. The LA–ICP–MS zircon U–Pb dating yielded a concordia age of 242 ± 2 Ma (MSWD = 0.17), indicating a Middle Triassic crystallization age for the Zhueryu syenite. In contrast, the Rb–Sr dating of primary fluid inclusions hosted within quartz (QzII) yielded an isochron age of 181 ± 12 Ma (MSWD = 2.5), placing the Au mineralization event firmly within the Early Jurassic. This demonstrates that the Au mineralization is significantly younger than the host syenite, representing a distinct mineralization event. These results might have certain significance for studying the dynamics of Au mineralization in the Jidong gold belt. Full article

The Anwangshan gold deposit is located in the northwestern part of the Fengtai Basin, Western Qinling Orogen (WQO). The gold ore is hosted within quartz syenite and its contact zone. The U–Pb weighted mean age of the quartz syenite is 231 ± 1.8 Ma. It is characterized by high potassium (K₂O = 10.13%, K₂O/Na₂O > 1) and high magnesium (Mg^# = 55.31 to 72.78) content, enriched in large ion lithophile elements (Th, U, and Ba) and light rare earth elements (LREE), with a typical “TNT” (Ti, Nb, and Ta) deficiency. The geochemical features and Hf isotope compositions (ε_Hf(t) = −6.68 to +2.25) suggest that the quartz syenite would form from partial melting of an enriched lithospheric mantle under an extensional setting. Three generations of gold mineralization have been identified, including the quartz–sericite–pyrite (Py1) stage I, the quartz–pyrite (Py2)–polymetallic sulfide–early calcite stage II, and the epidote–late calcite stage III. In situ sulfur isotope analysis of pyrite shows that Py1 (δ³⁴S = −1.1 to +3.8‰) possesses mantle sulfur characteristics. However, Py2 has totally different δ³⁴S (+5.1 to +6.7‰), which lies between the typical orogenic gold deposits in the WQO (δ³⁴S = +8 to +12‰) and mantle sulfur. This suggests a mixed source of metamorphosed sediments and magmatic sulfur during stage II gold mineralization. The fluid inclusions in auriferous quartz have three different types, including the liquid-rich phase type, pure (gas or liquid)-phase type, and daughter-minerals-bearing phase type. Multiple-stage fluid inclusions indicate that the ore fluids are medium-temperature (concentrated at 220 to 270 °C), medium-salinity (7.85 to 13.80% NaCleq) CO₂–H₂O–NaCl systems. The salinity is quite different from typical orogenic gold deposits in WQO and worldwide, and this is more likely to be a mixture of magmatic and metamorphic fluids as well. In summary, the quartz syenite should have not only a spatio-temporal but also a genetical relationship with the Anwangshan gold deposit. It could provide most of the gold and ore fluids at the first stage, with metamorphic fluids and/or gold joining in during the later stages. Full article