Search Results (15)

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

This study presents the first comprehensive investigation of perovskite from its type locality (Mineral Mines of Southern Urals, Russia), where this mineral was first described by Gustav Rose in 1839. The new data includes results from precise chemical analyses (electron-probe microanalyzer, LA-ICP-MS) and U-Pb ages (SHRIMP-II) of perovskite. Perovskite occurs in silicate-carbonate veins that transect the marginal parts of the Middle Riphaean Kusinsko-Kopanskaya layered intrusion, previously thought to be skarns. The perovskite crystals range from micrometer-scale grains to up to 11 cm in size. Chemical investigations revealed a low content of trace elements (rare earth elements, Y, Nd, U, Th) compared to perovskites from alkaline ultramafic rocks, silica-undersaturated basic rocks, carbonatites, and kimberlites. The determined age of the perovskite, 535 ± 43 Ma, significantly differs from the 1379 ± 8 Ma age of the Kusinsko-Kopanskaya intrusion, challenging the skarn-origin hypothesis for perovskite. Instead, the findings suggest a carbonatite origin for the perovskite mineralization. This timing indicates a previously unknown stage of endogenic activity on the Western Slope of the Southern Urals. Full article

Nepheline, ideally Na₃K(Al₄Si₄O₁₆) is a key mineral of silica-undersaturated igneous rocks. Under subsolidus conditions, nepheline is intensively replaced by numerous secondary minerals, of which various zeolites (mainly natrolite, analcime, gonnardite), as well as cancrinite, muscovite and Al-O-H phases (gibbsite, böhmite, nordstrandite) are the most common. In the rocks of the Lovozero alkaline massif (Kola Peninsula, NW Russia), nepheline is extensively replaced by the association natrolite + nordstrandite ± böhmite ± paranatrolite. To reproduce the conditions for the formation of such a mineral association, a series of experiments were carried out on the dissolution of nepheline in deionized water, 0.5 mol/L NaCl, 0.5 mol/L NaOH, and 0.1 mol/L HCl at 230 °C for 1/5/15 days. When nepheline is partially dissolved, phases and mixtures of phases precipitate on the surface of its grains, and these phases were diagnosed using X-ray powder diffraction and Raman spectroscopy. Observations in natural samples and experimental studies have shown that the nepheline alteration in the rocks of the Lovozero massif with the formation of natrolite and Al-O-H phases occurred under the influence of a high to medium salinity solution at a pH of near 6. 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

The blue color of glass and ceramic glazes produced in Apulia and Basilicata (Southern Italy) between the 13th and 14th centuries and connected to the Norman-Swabian Emperor Frederick II, has been, for a long time, under archaeometric investigation. On the one hand, it has usually been associated with lapis lazuli, due to the finding of the polysulphide blue chromophores typical of lazurite. Moreover, the observation that the mineral haüyne, which belongs to the sodalite group as well as lazurite, can be blue and/or can gain a blue color after heating, due to the same chromophores, has caused this automatic attribution to be questioned, and also considering that the mineral is characteristic of the rock haüynophyre of Melfi (Potenza, Southern Italy), a location of interest for glass and pottery findings. In this paper, for the first time, several haüyne crystals were found in the blue glaze of a ceramic dish found at Melfi Castle, leading to the hypothesis that, in this case, the local haüyne-bearing source could have been used as the coloring raw material. The discovery was possible thanks to SEM-EDS and Raman analyses that, respectively, highlighted the typical numerous presence of very fine sulphur-based inclusions in the crystals and the characteristic Raman signal of blue haüyne. This study was also focused on the composition of the crystals inclusions, aided by SEM-EDS and Raman maps, since the original very fine pyrrhotite was transformed into Cu and Pb phases (copper sulphates, copper sulphides, and lead oxide) due to reactions with cations that had mobilized from the glaze, while the migration of Si from the glass allowed the transformation of the rim of the haüyne, a silica-undersaturated mineral, into a corona of small euhedral and neomorphic Pb-rich feldspars, a silica-saturated phase. Full article

In this study, water-rock interaction, salinity sources, evolution, and the mixing of groundwater were modelled. The objectives of this research are to understand the hydrogeochemical factors that govern groundwater composition in a shallow aquifer system, Jazan Province, Saudi Arabia. The study aquifer is called a Quaternary aquifer, which is composed of gravel, sand, sandstone, and intercalated with some shale. In this study, 80 groundwater samples have been collected and analyzed for major ions and 30 representative samples were analyzed for Oxygen-18 (δ¹⁸O) and Deuterium (δD). NETPATH and environmental isotopes were integrated and applied to study the overall geochemical processes and to identify the salinity source in the groundwater. Saturation indices calculated for carbonates minerals indicates that 49%, 74%, and 61% of groundwater samples are undersaturated in terms of calcite, aragonite, and dolomite minerals, respectively. The remaining groundwater samples (51%, 39%, and 26%) are close to saturation with calcite, dolomite, and aragonite minerals, respectively. The saturation indices of gypsum, anhydrite, silica, strontionite, and sepiolite minerals show undersaturation in all groundwater samples, which is likely due to the dilution through the groundwater recharge from the surface runoff. In this study, water-rock interaction models were employed with the concentration of major ions of all selected groundwater samples, in addition to reference waters such as rain and sea waters, to evaluate the chemistry of groundwater in the flow path. Mixing calculations suggested that there is a variable contribution of rainwater (5% to 53%) in groundwater samples. The results indicate that evaporation and infiltration have a major impact on water chemistry in the study site. The intrusion of seawater at the coastal zone is well identified in some wells. Stable isotope data (δ¹⁸O and δD) support the results and underline the impact of evaporation processes on the groundwater and infiltration of evaporated water. Full article

Groundwater is increasingly being used to help meet the Sustainable Development Goals (SDGs) 2 and 6 in many parts of the world, including Ghana. Against this background, hydrogeochemical and multivariate statistical studies were conducted to determine the physicochemical characteristics and suitability of groundwater in some agrarian communities in the Upper East Region of Ghana for drinking and irrigational farming. Additional analyses were also performed to identify potential health risks associated with the groundwater use and to better understand the hydrogeochemical processes controlling groundwater evolution for its effective management. The results showed that the groundwater is typically fresh; moderate to very hard in character; undersaturated with calcite, dolomite, halite, and gypsum; and supersaturated with quartz and amorphous silica. The physicochemical characteristics of the groundwater are controlled by both anthropogenic and natural activities/processes, such as fertilizer application, irrigation return flows, rock weathering, and forward/reverse cation exchange. The total dissolved solids (TDS) (165–524 mg/L), electrical conductivity (EC) (275–873 μS/cm), sodium percentage (Na%; 9.05–17.74%), magnesium ratios (MR) (29.25–53.3%), permeability index (PI) (36.6–74.6%), and sodium adsorption ratio (SAR) (0.20–0.51) point to the possibility of using the groundwater for irrigation, however, with some salinity control. The water quality and health risk analysis also revealed that the groundwater can be used for drinking; however, the high concentrations of fluoride, which can cause noncarcinogenic health issues such as dental and skeletal fluorosis in both adults and children, must be reduced to the WHO required level of 1.5 mg/L. Full article

Titanite is an important mineral in petrochronology studies. Understanding chemical signatures of titanite from different environments can provide significant data in unraveling the complex histories recorded in their textures and compositions. Using a database of over 8500 titanite analyses from both the literature (3829) and our own data (4900), we found that the ratio of Fe/Al is useful for separating igneous titanite (Fe/Al is typically close to 1:1 and almost always > 1:2) from metamorphic titanite (Fe/Al ratio is < 1:2) with few exceptions. Volcanic titanite grains can also be separated from plutonic titanite grains due to their shorter crystallization histories with compositions clustered more tightly in terms of Fe, Al, and F. Compositions of titanite from plutonic rocks often have later metamorphic or hydrothermal overgrowths that are not found on volcanic titanite. Fe/Al ratios in titanite from silica-undersaturated volcanic and plutonic rocks are typically > 1:2 and include titanite with the highest Fe/Al ratios. Although they overlap the field for normal igneous titanite, other elements (particularly high levels of Nb and low levels of Y) allow them to be separated. In most metamorphic rocks, the Fe/Al ratio is < 1:2 except for a few metamorphic titanite grains that formed in mafic rocks. Titanite from ultrahigh pressure metamorphic rocks (eclogite facies) tend to have the lowest Fe/Al ratios, typically < 1:8. Titanite from hydrothermal and pegmatitic environments scatter widely in terms of Fe/Al even within single grains due to crystallization from fluids with highly variable compositions. Charge balancing in metamorphic, hydrothermal, and pegmatitic titanite due to Fe⁺³ and Al⁺³ substitution into the Ti⁺⁴ site is largely accomplished by the coupled substitution of F⁻ for O⁻². However, in volcanic and plutonic titanite, the charge imbalance due to Fe⁺³ and Al⁺³ substitution appears to be mainly coupled with REE⁺³ or Y⁺³ substitution into the Ca⁺² site with a lesser contribution from F⁻. Full article

Deformation in the upper mantle is localized in shear zones. In order to localize strain, weakening has to occur, which can be achieved by a reduction in grain size. In order for grains to remain small and preserve shear zones, phases have to mix. Phase mixing leads to dragging or pinning of grain boundaries which slows down or halts grain growth. Multiple phase mixing processes have been suggested to be important during shear zone evolution. The importance of a phase mixing process depends on the geodynamic setting. This study presents detailed microstructural analysis of spinel bearing shear zones from the Erro-Tobbio peridotite (Italy) that formed during pre-alpine rifting. The first stage of deformation occurred under melt-free conditions, during which clinopyroxene and olivine porphyroclasts dynamically recrystallized. With ongoing extension, silica-undersaturated melt percolated through the shear zones and reacted with the clinopyroxene neoblasts, forming olivine–clinopyroxene layers. Furthermore, the melt reacted with orthopyroxene porphyroclasts, forming fine-grained polymineralic layers (ultramylonites) adjacent to the porphyroclasts. Strain rates in these layers are estimated to be about an order of magnitude faster than within the olivine-rich matrix. This study demonstrates the importance of melt-rock reactions for grain size reduction, phase mixing and strain localization in these shear zones. Full article

General information is presented on ten agpaitic occurrences located in southern Brazil and at the border between Brazil and Paraguay. All the Brazilian agpaitic rocks are Late Cretaceous in age, whereas the Paraguayan ones are older than Early Triassic. The most significant occurrence is Poços de Caldas, the largest alkaline massif in South America. In general, these agpaitic rocks contain mineral assemblages that indicate presence of typical halogen-bearing Na–Ca–HFSE phases, eudialyte-, rinkite- and wöhlerite-group minerals being the most frequent ones. However, these associations are indeed more complex in terms of composition, with accessory phases in some cases consisting of various minerals, including U–Th oxides/silicates, Nb oxides, REE–Sr–Ba bearing carbonates–fluorocarbonates–phosphates–silicates and Zr–Na rich silicates. They usually form late magmatic stage to hydrothermal/deuteric assemblages linked with coarse and fine-grained, mainly silica-undersaturated evolved rocks. Data also indicate significant differences in type, amount and composition of agpaitic minerals in all investigated occurrences. Full article

In this paper, we provide insight into the evolution of syenite magmas based on geological data and petrographic, geochemical, and O-Nd isotope parameters of rocks of the Saibar intrusion located within the Minusinsk Trough, Altay-Sayan area. The intrusive suite includes predominant syenites, few bodies of melanocratic and leucocratic nepheline syenites (foyaites), and granites. In addition, dykes of granites and mafic rocks are present. The U-Pb zircon age from the melanocratic foyaites was determined to be 457 ± 10 Ma? Examined rocks show fractionated light rare earth element patterns, normalized to chondrite, with (La/Sm)_n varying from 4 to 9, and a weakly fractionated distribution of medium and heavy rare elements, with (Dy/Yb)_n from 0.35 to 1.23 and (Sm/Yb)_n from 0.63 to 2.62. The spidergram normalized to the primitive mantle shows negative Ba, Sr, Nb, Ta, Ti, and Eu anomalies (Eu* = 0.48–0.60) and positive Rb, Th, and U anomalies. The δ¹⁸O values vary within 6.3 to 10.2‰, and εNd(t) from +4.1 to +5.0. We observe gradual transitions from syenites to foyaites. Assimilation by syenite magma of the host carbonate rocks was followed to transition from silica-saturated to silica-undersaturated conditions and removal of anorthite from the melt, which then led to nepheline. Granites of the main phase show depleted lithophile incompatible elements in comparison with syenites and foyaites. They originate via interaction of magmas at the marginal part (endocontact zone) of the intrusion, corresponding to north contact of the granites with the host felsic rocks. In comparison, the rock composition of granite dykes is enriched in lithophile incompatible elements, except for Zr, Hf, and Ti. These rocks are formed due to the differentiation of syenite magma without a significant effect of host rock assimilation. Mantle magmas must be used as parent magmas for syenites based on analysis of the formation model of other alkaline intrusions, which are similar in age to the Saibar intrusion. In the line of syenite intrusions of the Altai-Sayan province, the Saibar intrusion is no exception, and its origin is related to the evolution of mafic magmas that arose during the melting of the mantle under the influence of a mantle plume. Full article

Corundum-bearing anatectic aluminous rocks are exposed in the deeply subducted North Dabie complex zone (NDZ), of Central China. The rocks consist of corundum, biotite, K-feldspar and plagioclase, and show clear macro- and micro-structural evidence of anatexis by dehydration melting of muscovite in the absence of quartz. Mineral textures and chemical data integrated with phase equilibria modeling, indicate that coarse-grained corundum in leucosome domains is a peritectic phase, reflecting dehydration melting of muscovite through the reaction: Muscovite = Corundum + K-feldspar + Melt. Aggregates of fine-grained, oriented, corundum grains intergrown with alkali feldspar in the mesosome domains are, instead, formed by the dehydration melting of muscovite with aluminosilicate, through the reaction: Muscovite + Al-silicate = Corundum + K-feldspar + Melt. P-T pseudosections modeling in the Na₂O-CaO-K₂O-FeO-MgO-Al₂O₃-SiO₂-H₂O-TiO₂ system constrains peak pressure-temperature (P-T) conditions at 900–950 °C, 9–14 kbar. The formation of peritectic corundum in the studied rocks is a robust petrographic evidence of white mica decompression melting that has occurred during the near-isothermal exhumation of the NDZ. Combined with P-T estimates for the other metamorphic rocks in the area, these new results further confirm that the NDZ experienced a long-lived high-T evolution with a near-isothermal decompression path from mantle depths to lower-crustal levels. Furthermore, our new data suggest that white mica decompression melting during exhumation of the NDZ was a long-lasting process occurring on a depth interval of more than 30 km. Full article

Pleistocene alkaline basaltic lavas crop out in the region of Volos at the localities of Microthives and Porphyrio. Results from detailed petrographic study show porphyritic textures with varying porosity between 15% and 23%. Data from deep and shallow water samples were analysed and belong to the Ca-Mg-Na-HCO₃-Cl and the Ca-Mg-HCO₃ hydrochemical types. Irrigation wells have provided groundwater temperatures reaching up to ~30 °C. Water samples obtained from depths ranging between 170 and 250 m. The enhanced temperature of the groundwater is provided by a recent-inactive magmatic heating source. Comparable temperatures are also recorded in adjacent regions in which basalts of similar composition and age crop out. Estimations based on our findings indicate that basaltic rocks from the region of Volos have the appropriate physicochemical properties for the implementation of a financially feasible CO₂ capture and storage scenario. Their silica-undersaturated alkaline composition, the abundance of Ca-bearing minerals, low alteration grade, and high porosity provide significant advantages for CO₂ mineral carbonation. Preliminary calculations suggest that potential pilot projects at the Microthives and Porphyrio basaltic formations can store 64,800 and 21,600 tons of CO₂, respectively. Full article

Cenozoic volcanic rocks were recently discovered during full-coring kilometer-scale major scientific drilling in the Xisha Islands, northwestern South China Sea. A systematic mineralogical study of these samples was performed for this paper. The results show that the volcanic rock samples are basaltic pyroclastic. The major elements demonstrate that the clinopyroxenes are diopside and fassaite, which contain high Al₂O₃ (5.33–11.2 wt. %), TiO₂ (2.13–4.78 wt. %) and CaO (22.5–23.7 wt. %). Clinopyroxenes have high REE abundances (104–215 ppm) and are strongly enriched in LREE (LREE/HREE = 3.56–5.14, La/Yb_N = 2.61–5.1). Large-ion lithophile elements show depleted characteristics. Nb/Ta shows obvious fractionation features: Nb is lightly enriched, relative to primitive mantle, but Ta is heavily depleted, relative to primitive mantle. The parental magma of the basaltic pyroclastic rocks belongs to a silica-undersaturated alkaline series, characterized by a high temperature, low pressure, and low oxygen fugacity. The Al^IV content increases with decreasing Si concentration. The Si-unsaturated state causes Si-Al isomorphic replacement during the formation of clinopyroxene. The electric charge imbalance caused by the replacement of Si by Al is mainly compensated by Fe³⁺. The clinopyroxene discrimination diagrams show that the parental magma formed in an intraplate tectonic setting environment. Full article

Zircon macrocrysts in (sub)volcanic silica-undersaturated rocks are an important source of information about mantle processes and their relative timing with respect to magmatism. The present work describes variations in trace element (Sc, Ti, Y, Nb, lanthanides, Hf, Ta, Pb, Th, and U) and isotopic (U-Pb) composition of zircon from the Drybones Bay kimberlite, Northwest Territories, Canada. These data were acquired at a spatial resolution of ≤100 µm and correlated to the internal characteristics of macrocrysts (imaged using cathodoluminescence, CL). Six types of zircon were distinguished on the basis of its luminescence characteristics, with the majority of grains exhibiting more than one type of CL response. The oscillatory-zoned core and growth sectors of Drybones Bay zircon show consistent variations in rare-earth elements (REE), Hf, Th, and U. Their chondrite-normalized REE patterns are typical of macrocrystic zircon and exhibit extreme enrichment in heavy lanthanides and a positive Ce anomaly. Their Ti content decreases slightly from the core into growth sectors, but the Ti-in-zircon thermometry gives overlapping average crystallization temperatures (820 ± 26 °C to 781 ± 19 °C, respectively). There is no trace element or CL evidence for Pb loss or other forms of chemical re-equilibration. All distinct zircon types are concordant and give a U-Pb age of 445.6 ± 0.8 Ma. We interpret the examined macrocrysts as products of interaction between a shallow (<100 km) mantle source and transient kimberlitic melt. Full article