Search Results (205)

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

Basin-scale dolomitization of carbonate sequences occurs over long time spans and results from diagenesis, burial, and tectonically driven fluid fluxes. Depicting the different geological processes producing dolomitized carbonate sequences requires combining accurate field, petrographic, and geochemical analyses. Here, we investigate the dolomitization processes in carbonates of the Norian to Toarcian age exposed in the Gran Sasso Massif, Central Apennines of Italy, by integrating field observations, standard and CL petrography, carbon, oxygen, strontium and clumped isotopes, minor elements, and X-ray diffractometry. The carbonates show pervasive replacive dolomitization, and dolomite cements are observed in bed-parallel and thrust-related veins. Replacive dolomites show incomplete replacement from modified seawater in oxidizing conditions, with minimum temperatures of 40–65 °C and a ⁸⁷Sr/⁸⁶Sr lower than coeval seawater. The first dolomitization event started at shallow burial in the Late Triassic–Early Jurassic and was later affected by replacement at intermediate burial depths. Bedding-parallel dolomite veins crystallized due to fluid overpressures at deep burial depths in a rock-buffered system without variations in geochemistry. Fault-related dolomites cemented thrust-related fractures during compressional deformation in the Messinian–Early Pliocene from seawater modified by mixing with external fluids. Precipitation temperatures of replacive, bedding-parallel, and fault-related dolomite veins are similar. Despite the dolomite types being characterized by different textures and petrographic features, rock-buffered conditions resulted in insignificant variations of their geochemical properties. Full article

In the presented paper, an approach to assessing the size of the plastic deformation zone around a circular cavity intersecting a crushed disintegrated layer in tectonically stressed massive rock is suggested. Fractured rock zones of different quality and spatial configurations are investigated in order to predict the size of dangerous plastic deformation zones or zones of potential rock collapses. The analysis is performed by means of numerical modeling after preliminary verification of the model by in situ and monitoring data. The paper explores the impact of such parameters of the fractured rock zone as the GSI index, the true thickness of the zone, and its inclination angle relative to the plane perpendicular to the axis of the excavation. It was found that with the increase in the thickness and angle of inclination of the fractured rock zone, the size of the hazardous zone in the vicinity of the excavation increases, while with the increase in its strength characteristics, the size of the potential failure zone decreases. According to the results of the study, qualitative dependencies are established, which localize and predict the size of the danger zone, or the potential failure zone in the vicinity of an unfixed excavation. Full article

Berthierine was found in a natrolite vein intersecting volcanogenic-sedimentary rocks on the slope of Mt. Quamdespakh in the upper reaches of the Suolwai River, Lovozero alkaline massif, Kola peninsula, Russian Arctic. The mineral occurs as well-formed translucent pyramidal crystals up to 250 μm in size. The chemical composition determined by electron microprobe analysis corresponds to the empirical formula ^VI(Fe²⁺_1.99Al_0.94Mg_0.03Mn_0.04)_Σ3.00[^IV(Si_1.15Al_0.85)_Σ2.00O₅] [(OH)_3.92O_0.08]_Σ4.00; the idealized formula is ^VI(Fe²⁺₂Al)[^IV(SiAl)O₅](OH)₄. The crystal-structure determination (the first detailed crystal-structure characterization of berthierine) shows that the Lovozero mineral is hexagonal, P6₃cm (a = 5.3903(4), c = 14.0146(10) Å, V = 352.64(6) ų, R₁ = 0.053 for 338 unique observed reflections), and corresponds to the 2H₁ polytype of serpentine-group minerals with 1:1 tetrahedral-octahedral layers. The unit cell contains two M₃[T₂O₅](OH)₄ layers (M = Fe²⁺,Al; T = Si,Al) stacked along the c axis. The calculations of information-based structural and topological complexity parameters indicate that berthierine is structurally and topologically simpler than its chlorite-group polymorph chamosite. Since berthierine usually crystallizes metastably in the stability field of chamosite, the complexity analysis is agreement with the Goldsmith rule that states that, in Ostwald sequences of crystallization, metastable phases are simpler and more disordered than their stable counterparts. This observation can be applied to a general case of the metastable formation of serpentine-group minerals prior to the crystallization of chlorites. Full article

The conducted study shows that apatite is one of the key accessory minerals in the ultramafic-mafic rocks of the Khudolaz differentiated complex in the Southern Urals, including late pegmatoid gabbro. Petrographic and mineralogical investigations determine apatite crystallizing simultaneously with hornblende in pegmatoid gabbro from the residual water-saturated melt after plagioclase crystallization at a temperature of 990–800 °C, a pressure of 1–3 kbar, oxygen fugacity from −13.9 to −10.7, and water content of 3.9–5.5 wt. %. Pegmatoid gabbro apatite (Ap_pg) from the Severnyi Buskun composite massif differs from early ultramafic-mafic apatite having a fairly high potential for sulfide-platinum metal mineralization in low chlorine and high fluorine content. Low sulfur concentrations in Ap_pg testify to the lack of sulfide-platinum metal mineralization potential of pegmatoid gabbro, but a scanty potential for rare-metal mineralization (e.g., REE) is possible. Ap_pg is quite poor in REE despite the enrichment of pegmatoid gabbros in REE relative to early ultramafic-mafics, which indicates REE accumulation in the fluid. The ratios of cerium and europium anomalies characterize the Ap_pg crystallization under conditions transitional from the magmatic to the hydrothermal stage. Generally, apatite is a good indicator of the difference in the conditions of formation of late pegmatoid gabbro and early ultramafic-mafic rocks, which determines the importance of this mineral in mineralogical and petrological studies. Full article

When excavating tunnels and underground openings with the drill-and-blast method, minimizing excavation overbreak is vital, as it reduces the costs associated with excavation stability, mucking, and rock support. Overbreak in excavations not only causes safety concerns but also increases the cost of construction and completion time. This paper proposes a contour blasting design in which the parameters are optimized based on the rock’s structural properties. Numerical modeling was used to identify the possible damage zones of rock with a change of the seismic load due to blasting. The results were used as input for the design of the proposed contour blasting with a low-brisance explosive. Experimental blasting tests were conducted at the Akbakai mine, located in Kazakhstan, and the performance of the design was examined. The proposed contour blasting was compared with the standard blasting method. The results indicated that the cross-section of excavation with the conventional blasting method varied between 10.5 and 12.1 m², indicating an overbreak between 17 and 34%. However, with the suggested contour blasting, the overbreak was less than 13%. It was concluded that charging contour boreholes with low-brisance explosives is an effective method of reducing overbreak due to excessive explosive loads on the contour massif, which can improve the safety and profitability of mining operations. Full article

The Syum-Keu massif is the northernmost ophiolite complex of the Ural mobile belt. It differs from other massifs of the Polar Urals due to the prominent distribution of lherzolites in the upper mantle section. This feature aligns it more closely to some massifs in the southern part of the belt (Kraka). Thus, a comparison of the ultramafic rock compositions in these massifs is highly relevant. Thus, comparing the compositions of ultramafic rocks from these massifs is highly relevant and is one of the primary objectives of this study. Our second objective is to study the microstructural features of ultramafic rocks from the upper mantle, as they can indicate modes of subsolidus processes that played a key role in the formation of this massif. Our study utilizes optical microscopy, assessments of bulk rock composition using X-ray fluorescence and ICP-MS, as well as mineralogical methods, such as scanning electron microscopy with energy dispersive spectroscopy and electron backscattered diffraction, for the microstructural analysis of peridotites. In addition to ultramafic rocks from the upper mantle section, the composition and mineralogy of mafic rocks from the crustal section were studied. The microstructural analysis of ultramafic rocks indicates their two-stage evolution. The first is associated with plastic flow under the upper mantle conditions dominated by the olivine slip along the {0kl}[100] system, while the second reflects formation in the lower crust, with lower-temperature deformation along the {110}[001] slip system. Comparing the mineralogy of the Syum-Keu peridotites to lherzolite massifs in the Southern Urals reveals a significant difference in accessory Cr-spinel composition; the former show elevated iron content (Fe trend), indicating intense crustal metamorphism. Similarly, amphiboles in Syum-Keu ultramafic rocks exhibit a significant crustal (metamorphic) component, while the same minerals in the Kraka massif suggest a mantle (magmatic) origin. Mafic rocks in the Syum-Keu massif also typically display a high degree of metamorphism. The obtained results generally corroborate prior findings on a longer evolution of the upper mantle ultramafic rocks of the Syum-Keu massif compared to those of the Kraka massif. Our results are also consistent with the suprasubduction nature of these ultramafic rocks. Our findings can be utilized in further studies of the microstructure and composition of ophiolites from the Polar Urals to provide a more detailed characterization of the partial melting conditions of the mantle source, the plastic flow of peridotites, and their interaction with melts and fluids. Full article

Karst areas are characteristic landscapes formed by the dissolution of soluble rocks, whose hydrology is largely influenced by rapid infiltration through the karst massif. These areas are often hotspots of biodiversity, especially for epikarst and cave fauna. The epikarst, the uppermost layer of the unsaturated zone, plays a crucial role in regulating water flow in karst aquifers. The aim of this study was to investigate the extent of microplastic (MP) pollution, its relationship with precipitation and its correlation with copepod populations in karst areas. The study was conducted between April 2021 and October 2022 in the Postojna–Planina karst area in SW Slovenia at surface and underground sampling sites to determine the pathways of MP pollution from the surface to the depth of the karst massif. The results indicate that heavier rainfall flushes out more MP contaminants from the surface and epikarst environment. The transport dynamics of MP pollution are similar to the dynamics of copepods, which are the baseline organisms for the food chain in caves. One MP sample contained only polyamide particles, which could indicate clothing as a possible source of pollution, but the results are inconclusive. With this study, we provide the first insight into the transport of MP pollution from the surface environment to deeper karst massifs. Full article

A geochemical study was conducted on the Touro deposit, which is situated within the Iberian Variscan Massif on the allochthonous terrain of the Galicia–Tras-os-Montes Zone. This study encompassed both mineralogical and geochemical analyses of the host rocks, with a particular focus on the high-grade Fornás metamorphic unit of the Órdenes Complex. The deposit is composed of massive and semi-massive sulfides, the host rocks are amphibolites and paragneisses, and the ore is hosted in garnet amphibolites and mineralized paragneisses. A microscopic study of thin sections and over 300 electron probe microanalyses on various minerals were conducted with the objective of geochemical characterization. Furthermore, a study of approximately 6000 samples processed by mining companies for multielement analyses of over 1350 drill cores was conducted to geochemically characterize the host and mineralized rocks for use as exploration guides. Additionally, five samples underwent Sm-Nd isotope analysis. The data from the Touro Cu (Zn-Co) deposit are consistent with its classification as a mafic–siliciclastic (Besshi-type) VMS deposit constructed in a back-arc environment during the Ordovician period. Following burial and high-grade metamorphism during the Middle Devonian period, these rocks were subsequently exposed during the later Variscan deformation phases, resulting in the formation of the Arinteiro antiform. Full article

Hierapolis of Phrygia, an archaeological site in southwestern Turkey, has been a UNESCO World Heritage Site since 1988. During archaeological campaigns, 71 mortar samples from public buildings were collected, dating from the Julio-Claudian to the Middle Byzantine period. The samples were analyzed using a multi-analytical approach including polarized optical microscopy (POM), digital image analysis (DIA), X-ray powder diffraction (XRPD) and SEM–EDS to trace the raw materials and understand the evolution of mortar composition and technology over time. During the Roman period, travertine and marble were commonly used in binder production, while marble dominated in the Byzantine period. The aggregates come mainly from sands of the Lycian Nappe and Menderes Massif, with carbonate and silicate rock fragments. Variations in composition, average size and circularity suggest changes in raw material sources in both Roman and Byzantine periods. Cocciopesto mortar was used in water-related structures from the Flavian to the Severan period, but, in the Byzantine period, it also appeared in non-hydraulic contexts. Straw became a common organic additive in Byzantine renders, marking a shift from the exclusively inorganic aggregates of Roman renders. This study illustrates the evolving construction technologies and material sources used throughout the city’s history. Full article

The present research’s main objective was to apply thorough exploration approaches that combine remote sensing data with geochemical sampling and analysis to predict and identify potential chromitite locations in a complex geological site, particularly in rugged mountainous terrain, and differentiate the ultramafic massif containing chromitite orebodies from other lithologies. The ultramafic massif forming the mantle section of the Kırdağ ophiolite, located within the Erzurum–Kars Ophiolite Zone and emerging in the east of Oltu district (Erzurum, NE Turkey), was selected as the study area. Optimum index factor (OIF), false-color composite (FCC), decorrelation stretch (DS), band rationing (BR), minimum noise fraction (MNF), and principal and independent component analyses (PCA-ICA) were performed to differentiate the lithological features and identify the chromitite host formations. The petrography, mineral chemistry, and whole-rock geochemical properties of the harzburgites, which are the host rocks of chromitites in the research area, were evaluated to verify and confirm the remote sensing results. In addition, detailed petrographic properties of the pyroxenite and chromitite samples are presented. The results support the existence of potential chromitite formations in the mantle section of the Kırdağ ophiolite. Our remote sensing results also demonstrate the successful detection of the spectral anomalies of this ultramafic massif. The mineral and whole-rock geochemical features provide clear evidence of petrological processes, such as partial melting and melt–peridotite interactions during the harzburgite formation. The chromian spinels’ Cr#, Mg#, Fe³⁺, Al₂O₃, and TiO₂ concentrations indicate that the harzburgite formed in a fore-arc environment. The Al₂O₃ content and Mg# of the pyroxenes and the whole-rock Al₂O₃/MgO ratio and V contents of the harzburgite are also compatible with these processes. Consequently, the combined approaches demonstrated clear advantages over conventional chromitite exploration techniques, decreasing the overall costs and supporting the occurrence of chromite production at the site. Full article

A comprehensive study (monitoring, thermodynamic modeling) of natural and anthropogenically polluted waters of the Lovozero Massif has been carried out. A thermodynamic study of the weathering of the Lovozero Massif within the “water-rock-atmosphere” system at a temperature of 5 °C showed that the elements contained in the rocks of the studied massif influence the formation of the chemical composition of natural waters. It has been established that an increase in the degree of “water-rock” interaction leads to an increase in the concentrations of F⁻, Cl⁻, SO₄²⁻, and HCO₃⁻ in the solution. This affects the mobility of lanthanum, cerium, and other elements due to the formation of complex compounds with them. The relatively high content of fluorine, phosphorus, and HCO₃⁻ (weak and medium acids) in the solution promotes the dissolution of silicates while Si, Al, and P are released into the solution. Monitoring of water from a flooded mine in which there is an increase in the degree of interaction of water with rock showed higher pH values for the concentrations of Na, HCO₃⁻, F⁻, P, Al, Si, V, U, La, and Ce. The conclusions are relevant in the context of the use of groundwater for drinking water supply purposes. The obtained information is useful to evaluate the health of the population of the region under study. Full article

The peridotite massifs of New Caledonia are characterised by complex hydrodynamics influenced by intense inherited fracturing, uplift, and erosion. Following the formation of the erosion surfaces and alteration processes, these processes drive chemical redistribution during weathering; particularly lateritisation and saprolitisation. Magnesium, silica, and trace elements such as nickel and cobalt—released as the dissolution front advances—are redistributed through the system. New observations and interpretations reveal how lateritic paleo-land surfaces evolved, and their temporal relationship with alteration processes since the Oligocene. Considering the geometry of discontinuity networks ranging from micro-fractures to faults, the transfers occur in dual-permeability environments. Olivine dissolution rates are heterogeneously due to differential solution renewal caused by erosion and valley deepening. Differential mass transfer occurs between mobile regions of highly transmissive faults, while immobile areas correspond to the rock matrix and the secondary fracture network. The progression of alteration fronts controls the formation of boulders and the distribution of nickel across multiple scales. In the saprolite, nickel reprecipitates mostly in talc-like phases, as well as minor nontronite and goethite with partial diffusion in inherited serpentine. The current nickel distribution results from a complex interplay of climatic, hydrological and structural factors integrated into a model across different scales and times. Full article

The Taimyr Peninsula in the Russian High Arctic comprises a late Paleozoic-early Mesozoic collisional belt where several porphyry-type mineralization occurrences were identified during the last decade, making this area a potential exploration target for Cu-Mo deposits. In order to further evaluate the metallogenic potential of the poorly outcropped northeastern part of Taimyr, samples from seven granitoid intrusions were investigated in this study aimed to evaluate the granite fertility based on petrography, geochemistry, and composition of porphyry indicator minerals (zircon, apatite, and titanite). The studied intrusions represent small to moderate-sized bodies (40–800 km²) composed of biotite (±amphibole) quartz monzonites, granodiorites, granites, and biotite leucogranites that formed in the course of late Paleozoic-early Mesozoic tectono-magmatic events at the Siberian margins. The late Carboniferous Tessemsky massif represents suprasubduction granitoid series, while the Pekinskiy, Shirokinskiy, Dorozhinskiy, Kristifensenskiy, and Yuzhno-Lodochnikovskiy massifs are correlated with the early Triassic Siberian Traps LIP. The rocks of intrusions comprise a relatively uniform geochemically, predominantly magnesian, slightly peraluminous, calc-alkaline high-K amphibole-bearing I-type granitoid series with adakitic affinity, where Triassic plume-related granitoids inherit geochemical signatures of Carboniferous supra-subduction granitoids, and all rock types are marked by enrichment in LILE and negative Ta, Nb, and Ti anomalies. It is suggested that the adakitic geochemical characteristics of the Taimyr granites are a result of derivation from a relatively homogeneous mafic lower crustal source that formed at the stage of Carboniferous continental subduction and continued to produce granitic melts in the course of the early Mesozoic magmatic evolution. Whole rock geochemistry and composition of porphyry mineral indicators (zircon, apatite, and titanite) indicate that the Taimyr granites crystallized from oxidized water-saturated magmas at moderate temperatures, with the majority of samples showing characteristics typical for porphyry-fertile granites worldwide (fO₂ = ΔFMQ +1 to +3 with zircon Eu/Eu* > 0.4 and apatite SO₃ > 0.2 wt.%). Data from Dorozhinskiy, Kristifensenskiy, Pekinskiy, and Tessemskiy intrusions fully match geochemical criteria for porphyry-fertile granitoids, and these massifs are considered the most prospective for Cu-Mo mineralization. Granites from Shirokinskiy and Yuzhno-Lodochnikovskiy intrusions only partially match compositional constraints for fertile melts and can be considered as second-tier exploration targets. Finally, available data for the Simsovsky massif preclude its classification as a porphyry-fertile body. These conclusions are in line with previously developed exploration criteria for the northeastern Taimyr, showing that geochemical indicators of granite-fertility can be used on a regional scale in parallel with other exploration methods. Full article