Search Results (295)

Isotopic investigations focused on determining the mobility and provenance of ancient human civilizations and sourcing of archeological artifacts continue to gain prominence in archeology. Most studies focus on the premise that the geographic variation in isotope systems of interest (e.g., Sr, Pb, Nd, O) in the natural environment is recorded in both human hard tissues of local individuals and raw materials sourced for artifacts within the same region. The introduction of multi-collection–inductively coupled plasma mass spectrometry (MC-ICP-MS) and laser ablation systems are techniques that consume smaller sample sizes compared to previous mass spectrometric approaches due to their higher ionization efficiency and increased sensitivity. This development has facilitated the isotopic measurement of trace elements present at low abundances (e.g., Pb, Nd, <1-to-low ppm range) particularly in human tooth enamel. Accurate interpretation of any isotope ratio measurement for the proveniencing of such low-abundance samples requires the adequate evaluation of post-mortem diagenetic alteration. A synopsis of practices currently in use for identifying post-mortem alteration in human archeological samples is discussed here. Post-mortem shifts in radiogenic isotope signatures resulting from secondary alteration are distinct from those potentially related to the impact of climate change on the bioavailable budgets for these elements. This topic is of interest to the archeological community and discussed here in the context of Holocene-aged samples from burial sites within the Nile River Valley System, and preferred dust source areas from the neighboring Sahara Desert. Full article

As a pivotal clean energy source with considerable reserves, geothermal water plays an indispensable role in diminishing reliance on fossil fuels and accomplishing carbon neutrality. This study employed conventional electrical prospecting and radon gas surveys in the Lantian area of Ningdu, aimed at curtailing geothermal development costs by precise targeting of resource locations. The investigations successfully delineated fracture structures within the Lantian region. Distinct anomalies were identified in the electrical profiling along Survey Lines 1, 2, and 4, with the most pronounced features observed on Line 4. Accordingly, characteristic peak anomalies were exhibited by the radon gas measurement profiles S1, S2, and S4 corresponding to Lines 1, 2, and 4, respectively. The synergistic interpretation of resistivity and radon survey data recognized two primary fracture zones: the NE-trending zone F1 and the NEE-trending zone F2. This integrated approach not only ascertained the efficacy of the radon gas measurement, but also lays a robust basis for future geothermal water exploration targeting. Full article

The Hida Belt in central Japan is a key geological unit for understanding the crustal growth of the Eurasian continent in the Mesozoic. However, while previous studies have focused primarily on geochronology, the geochemical characteristics of its rocks and minerals remain largely unexplored. This study investigates the geochemical characteristics and magmatic processes of the Hida granitoids, including adakitic rocks, distributed in the Unazuki and Katakaigawa areas. Whole-rock major oxides and trace elements, as well as Rb-Sr isotopes, were analyzed. Based on Rb–Sr isotopic compositions, the Hida granitoids are classified into two types. The younger and older granitoids in the Unazuki area, categorized as Type I, exhibit a narrow range of isotopic ratios, whereas the older granitoids in the Katakaigawa area, classified as Type II, display significantly higher values than those of Type I. The geochemical data suggest that the adakitic rocks in the older granitoids originated from interaction with alkali-rich melts or fluids, while those in the younger granitoids were derived from hydrous felsic magmas sourced from subducted oceanic crust. These findings provide new insights into the formation and evolution of granitic magmatism in the Hida Belt. Full article

The Sidi Aissa Pb-Zn-(Ag) District, located within the Nappe Zone of northern Tunisia, has been reinterpreted as a typical intermediate-sulfidation (IS) epithermal mineralization system based on field observations and lithogeochemical analyses. Previously described as vein-style Pb-Zn deposits, the local geological framework is dominated by extensional normal faults forming half-grabens. These faults facilitated the exhumation of deep Triassic autochthonous rocks and the extrusion of 8-Ma rhyodacites and Messinian basalts. These structures, functioning as pathways for magmatic-hydrothermal fluids, facilitated the upward migration of acidic fluids, which interacted with the surrounding wall rocks, forming a subsurface alteration zone. The mineralization, shaped by Miocene extensional tectonics and magmatic activity, occurred in three stages: early quartz-dominated veins, an intermediate barite-rich phase, and late-stage supergene oxidation. Hydrothermal alteration, characterized by silicification, argillic, and propylitic zones, is closely associated with the deposition of base metals (Pb, Zn) and silver. The mineral assemblage, including barite, galena, sphalerite, and quartz, reflects dynamic processes such as fluid boiling, mixing, and pressure changes. Full article

Carbon isotopes in magmatic systems serve as powerful tracers for understanding magma evolution, mantle processes, the deep carbon cycle, and the origin of Earth’s carbon. This review provides a comprehensive overview of carbon isotope measurements and behavior in magmatic systems, highlighting recent technological advancements and scientific insights. We begin by examining methods for measuring δ¹³C in volcanic gases, vesicles, glasses, melt, and fluid inclusions. We then explore the behavior of carbon isotopes in magmatic systems, especially during magmatic degassing. Finally, we evaluate what recent advances mean for our understanding of the carbon isotope signature of the Earth’s upper mantle. Full article

Mineral fluorescence under different portions of the visible and invisible light spectrum has a long history of scientific study. In our study of marine sediments from the Georgia Bight, we have utilized the blue portion of the light spectrum in the 445 nanometer (nm) range. The use of fluorescence has proven very useful in microscopic analyses of carbonate minerals. While the sediment prism of the inner-to-mid continental shelf in the southeastern Atlantic is predominantly siliceous, the dissolution and deterioration of marine shell contribute a significant amount to the fabric of any sediment sample. Together with carbonate minerals such as dolomite, eroded from basement rock and redeposited on the shelf, a potentially robust fluorescent response was expected and observed in samples. In marine sediments, blue light illumination has produced an easily observed fluorescent response in both underwater and in laboratory settings. This fluorescence can be attributed to carbonate minerals—calcite/aragonite. Feldspars are major accessory minerals in the sediment prism of the Georgia Bight, and much of the observed fluorescence in our samples can be attributed to their presence. To identify specific minerals responsible for any observed fluorescence, X-ray diffraction and energy dispersive spectroscopy were utilized. This combined methodology of luminescent excitation, X-ray diffractometry and spectroscopy has produced the results reported herein. Full article

Researchers are exploring eco-friendly alternatives to Portland cement, such as geopolymers, which require reactive aluminosilicate sources. This study evaluated the reactivity of six calcined clays (heated at 700 °C) in the presence of an alkaline solution. The calcined samples from kaolinite quarries in Kamboinsé, Kandarfa, Saaba, Sabcé, Selogo, and Tougou were subjected to chemical and mineralogical analyses. The results indicated a high aluminosilicate content (>50%), with kaolinite reaching up to 83.1%, and an amorphous fraction of up to 31.8%, a key factor influencing reactivity. Geopolymer pastes, prepared using a 12 M NaOH solution and each of these calcined clays, exhibited varying setting times: 24 h for the Saaba clay (the most reactive) compared with 48 h or even up to 7 days for the least reactive. The evaluation of the compressive strength of the geopolymer pastes revealed varying performances depending on the composition of clay. The Saaba clay showed the highest strength (14 MPa), attributed to its high kaolinite content (83.1%) and amorphous phase (31.8%), and thus reactivity. This was followed by Kamboinsé with 10.5 MPa (58.3% kaolinite; 24.3% amorphous phase), Selogo with 4.6 MPa (42.9%; 20.4%), Tougou with 1.4 MPa (44.1%; 20.4%), Kandarfa with only 0.7 MPa (31.3%; 19.2%), and Sabcé, which did not set with 0 MPa (24.1%; 13.7%). A discussion between the chemical and mineralogical compositions of the different clays and the mechanical characteristics of the synthesized pastes highlighted the importance of kaolinite content and its amorphous nature on the reactivity of the geopolymer binders. These findings highlight its potential for applications such as stabilized bricks or geopolymer concrete, offering a low-carbon alternative to traditional materials. Full article

The Central Depression of the Junggar Basin relies heavily on Permian lacustrine mudstone for deep-seated hydrocarbon sealing. This research investigated how the fluorescence parameters of caprock samples responded to the leakage of palaeo-oil zones based on measurements from SEM, Rock-Eval, and X-ray diffraction analysis. First, two sets of control experiments were conducted to establish the proper grain-size range of 100–140 mesh for testing caprock samples in the research area using quantitative fluorescence technology. Subsequently, based on the examination of the rock pyrolysis parameters and the fluorescence parameters against TOC values, the conjecture was formed that the quantitative fluorescence technology test results were mostly unaffected by the primary hydrocarbons. Lastly, four fluorescence parameters were used to assess seal integrity: quantitative grain fluorescence intensity of the extract (QGF E intensity, the meaning of QGF is the same in this study), QGF spectral peaks (QGF λmax), the ratio of QGF intensity to fluorescence intensity at 300 nm on the QGF spectrum (QGF index), and total scanning fluorescence spectral ratio R₁ (TSF R₁). The Permian caprock can effectively seal hydrocarbons as evidenced by the decrease of QGF E intensity and QGF index values with depth. When hydraulic fracturing causes caprock failure, it can lead to complete leakage of hydrocarbons from the palaeo-oil zones. As the depth becomes shallower, the QGF E intensity value increases, the QGF index value decreases. Due to the differences in the migration pathways of hydrocarbons in the caprock, those leaked from the Permian palaeo-oil zone into the well PD1 caprock are mainly condensate and light–normal crude oil, while the hydrocarbons from the Carboniferous palaeo-oil zone into the well MS1 caprock consist predominantly of light–normal crude oil and medium–heavy crude oil. Full article

High-enthalpy geothermal resources in volcanic settings often lack clear surface manifestations, requiring integrated, data-driven approaches to identify hidden reservoirs. In this study, we apply a multivariate clustering technique—genetic K-Means clustering (GKMC)—to a comprehensive soil gas dataset collected from 1050 sampling sites across the ~100 km² Garehagua mining license, located in the southern rift zone of Tenerife (Canary Islands). The survey included diffuse CO₂ flux measurements and concentrations of key soil gases (He, H₂, CH₄, O₂, N₂, Ar isotopes, and ²²²Rn, among others). Statistical-graphical analysis using the Sinclair method allowed for an objective classification of geochemical anomalies relative to background populations. The GKMC algorithm segmented the dataset into geochemically coherent clusters. One cluster, defined by elevated CO₂, helium, and ²²²Rn levels, showed a clear spatial correlation with inferred tectonic lineaments in the southern rift zone. These anomalies are interpreted as structurally controlled conduits for the ascent of deep magmatic-hydrothermal fluids. The findings support the presence of a concealed geothermal system structurally constrained in the southern region of Tenerife. This study demonstrates that integrating GKMC clustering with soil gas geochemistry offers a robust methodology for detecting hidden geothermal anomalies. By enhancing anomaly detection in areas with subtle or absent surface expression, this approach contributes to reducing exploration risk and provides a valuable decision-support tool for targeting future drilling operations in volcanic terrains. Full article

The greisens discussed in the present study are associated with the Homrit Akarem post-collisional granites, which are exposed near the western edge of the Egyptian Nubian Shield in the Southeastern Desert of Egypt. The Homrit Akarem granites intruded into Neoproterozoic country rocks, with sharp intrusive contacts. The marginal parts of the Homrit Akarem intrusion underwent extensive post-magmatic metasomatism, resulting in the formation of albitized granite and greisens. The Homrit Akarem greisens occur as veins and stockworks, which can be classified into four types: muscovite-rich, cassiterite-rich, topaz-rich, and beryl-rich greisens. Based on petrographic inspection, we identified ore minerals (cassiterite, beryl, topaz, muscovite, Nb-Ta oxides, tourmaline, fluorite, and corundum) in the greisens using electron probe microanalysis. The Homrit Akarem mineralized greisens were formed in a magmatic cupola above A-type magma, where fluid–rock interactions played a significant role in their formation. The accumulation of residual volatile-rich melt and exsolved fluids in the apical part of the magma chamber produced albitized granite, greisens, and quartz veins that intruded into the peripheries of the granitic intrusion and its surrounding country rocks. The variation in the mineralogy of the studied greisens indicates the diverse chemical composition of both the hydrothermal/magmatic fluids and the host granites. The simultaneous decrease in temperature and pressure is considered a crucial factor that controlled mineralization in the apical parts of the magma chamber. The occurrence of cassiterite, beryl, topaz, tourmaline, muscovite, and Nb-Ta oxides in the studied greisens suggests a potential polymetallic deposit of industrial minerals. Full article

Integrated ⁴⁰Ar/³⁹Ar and U-Pb geochronology, combined with microstructural analysis of Early Cretaceous volcanics from eastern China, challenge conventional interpretations of flat ⁴⁰Ar/³⁹Ar age spectra. K-feldspar sample JD-1K (122.12 ± 0.81 Ma) preserves magmatic sanidine characteristics (homogeneous composition, disordered monoclinic structure), while hydrothermally altered perthite JD-2K yields a flat plateau age of 99.83 ± 0.73 Ma (~20 Ma younger than coeval K-feldspar, biotite, and zircon samples). Microstructural analyses using energy dispersive spectroscopy (SEM−EDS), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM) methods unequivocally demonstrate that the concordant ⁴⁰Ar/³⁹Ar age spectrum of sample JD-2K is a result of isotopic resetting during fluid-mediated recrystallization processes, rather than primary post-crystallization thermal stability. In step-heating experiments, contrasting argon release patterns correlate with microstructural heterogeneities. This study challenges the paradigm that flat ⁴⁰Ar/³⁹Ar spectra uniquely signify post-crystallization thermal histories, demonstrating that hydrothermal alteration can fully reset argon systems to produce misleadingly concordant ages. This study highlights the complexity of interpreting isotopic data in hydrothermally altered rocks, emphasizing the necessity of integrated petrological-geochemical analyses to differentiate primary magmatic signals from secondary overprints. Full article

The complex interaction of hydrothermal fluids and carbonate rocks is recognized to promote significant impacts on petroleum systems, reservoir porosity, and potential. The objective of this study is to investigate the fluid phases entrapped in the mineral phases of the Barra Velha Formation (Santos Basin), including their petrographic paragenetic relationships, relative timing, temperatures of migration events, and maximum temperature reached by the sedimentary section. The petrographic descriptions (387), Rock-Eval pyrolysis (107), fluid inclusion petrography (14), and microthermometry (428) were performed on core and sidewall samples from two wells from one field of the Santos Basin. Hydrocarbon source intervals were primarily identified in lithologies with high argillaceous content. Chert samples still retain some organic remnants indicative of their original composition prior to extensive silicification. Redeposited intraclastic rocks exhibit the lowest organic content and oil potential. A hydrothermal petroleum system is identified by fluids consisting in gas condensate, light to heavy undersaturated oil, occasionally accompanied by aqueous fluids influenced by juvenile and evaporitic sources, and localized flash vaporization events. These hydrothermal fluids promoted silicification and dolomitization, intense brecciation, and lead to enhanced porosity in different compartments of the reservoir. The relative ordering of paleo-hydrothermal oils and the main oil migration and accumulation events has improved our understanding of the petroleum systems in the basin. This contribution is significant for future regional research on the evolution of fluid systems and their implications for carbonate reservoirs. 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

This study explores the generation of natural hydrogen through the serpentinization of onshore ultramafic rocks, highlighting its potential as a clean energy resource. By investigating critical factors such as mineral composition, temperature, and pressure, the research develops an empirical model using multiple regression analysis to predict hydrogen generation rates under varying geological conditions. A novel five-stage volumetric calculation methodology is introduced to estimate hydrogen production from ultramafic rock bodies. The application of this framework to the Giles Complex, an ultramafic-mafic intrusion in Australia, suggests a hydrogen generation potential of approximately 2.24 × 10¹³ kg of hydrogen through partial serpentinization. This estimate is based on the assumed mineral composition, depth, and temperature conditions within the intrusion, which influence the extent of serpentinization reactions. The findings demonstrate the significant potential of ultramafic complexes for natural hydrogen production and provide a foundation for advancing natural hydrogen exploration, refining predictive models, and supporting sustainable energy development. Full article

So far, published geochronological data poorly constrain the Late Pleistocene glacial fluctuations in the Făgăraş Mts (Southern Carpathians, Romania). The deglaciation chronology in the central Făgăraş Mts is supported by new (n = 5) and recalculated (n = 5) ¹⁰Be exposure ages from a southern and two northern valleys. Cosmic ray exposure (CRE) ages were calculated considering the effects of surface denudation, uplift and snow-shielding. A ¹⁰Be exposure age obtained from a glacial landform representing the last glacierets of the central Făgăraş Mts yielded an age of 13.3 ± 1.2 ka. A polished bedrock sample and a moraine boulder constrain the age of a cirque glacier stage to 14.5 ± 1.5 ka, while quite coherent CRE ages from two erratic boulders place the previous stage at ~18.7 ka (18.6 ± 1.7 ka and 18.7 ± 1.7 ka). These glacial stages coincide with major deglaciation stages M4 and M2a reconstructed in the Retezat Mts, derived from comparable CRE ages calculated using the same methodology; however, geomorphological and/or geochronological evidence of the intermediate stages is still not found in the central Făgăraş Mts. All CRE ages gathered from the landforms corresponding to the more extended glacial stages are younger than expected from their morphostratigraphic position and thus considered as minimum age constraints. However, considering the coherent CRE ages of the above morphostratigraphic stage, it is likely that the balanced-budget glaciological conditions corresponding to these more extended stages prevailed before ~19 ka and likely coincided with the cold peaks of the Marine Isotope Stage 2. The currently available in situ ¹⁰Be data do not support the existence of a period of glacier advance during the Holocene or Greenland Stadial-1 (Younger Dryas) in the central Făgăraş Mts. Full article