Search Results (151)

This article presents a technology for the production of magnesium hydroxide from serpentinite via sulfuric acid leaching of magnesium and purification of the resulting sulfate solution from impurity metals using thermally activated serpentinite (TA-SP) at 750 °C for one hour. Purifying the leach solution is one of the key challenges in obtaining high-purity magnesium compounds from serpentinite. It has been established that the use of thermally activated serpentinite to neutralize the acidic suspension of serpentinite to pH 8.3, prior to treatment with an alkaline agent (sodium hydroxide), has a positive effect on the purity of the precipitated magnesium hydroxide. The influence of the thermal treatment on the acid–base properties of serpentinite, its phase composition, and adsorbent structure parameters, such as specific surface area and micropore distribution, was studied, revealing improvements in the adsorption properties. Flowcharts for the acid leaching and magnesium hydroxide precipitation processes are provided. The flow-sheet that we propose is shown to reduce the number of steps in the process and amount of equipment required for the purification of sulfate solution while ensuring that the magnesium hydroxide product has a purity of at least 99.5%. Full article

In this study, the neutron and gamma radiation-shielding properties of serpentinites from the Guleman ophiolite complex were investigated, and results were evaluated in comparison with rare earth element (REE) content. The linear and mass attenuation coefficients (LAC and MAC), half-value layer (HVL), mean free path (MFP), and effective atomic numbers (Z_eff) of serpentinite samples were experimentally measured in the energy range of 80.99–383.85 keV. Theoretical MAC values were calculated. Additionally, fast neutron removal cross-sections, as well as thermal and fast neutron macroscopic cross-sections, were theoretically determined. The absorbed equivalent dose rates of serpentinite samples were also measured. The radiation protection efficiency (RPE) for gamma rays and neutrons were determined. It was observed that the presence of rare earth elements within serpentinite structure has a significant impact on thermal neutron cross-sections, while crystalline water content (LOI) plays an influential role in fast neutron cross-sections. Moreover, it has been observed that the concentration of gadolinium exerts a more substantial influence on the macroscopic cross-sections of thermal neutrons than on those of fast neutrons. The research results reveal the mineralogical, geochemical, morphological and radiation-shielding properties of serpentinite rocks contribute significantly to new visions for the use of this naturally occurring rock as a geological repository for nuclear waste or as a wall-covering material in radiotherapy centers and nuclear facilities instead of concrete. Full article

This study investigates the weathering crust composite of serpentine, pyroxenite and granite in the Niangniangmiao area, the weathering crusts inside and outside the mining area were compared respectively, systematically revealing the distribution patterns, migration pathways, and ecological element activity characteristics of high-background elements (e.g., chromium (Cr) and nickel (Ni)) through precise sampling, the Tessier five-step sequential extraction method, and a migration coefficient model. Key findings include: (1) Element distribution and controlling mechanisms: The average Cr and Ni contents in the serpentinite profile are significantly higher than those in pyroxenite. However, the semi-weathered pyroxenite layer exhibits an inverted Cr enrichment ratio in relation to serpentinite, 1.8× and 1.2×, respectively, indicating that mineral metasomatic sequences driven by hydrothermal alteration dominate element differentiation; the phenomenon of inverted enrichment of high-background elements occurs in the weathering crust profiles of the two basic rocks. (2) Dual impacts of mining activities on heavy metal enrichment: Direct mining increases topsoil Cr content in serpentinite by 40% by disrupting parent material homology, while indirect activities introduce exogenous Zn and Cd (Spearman correlation coefficients with Cr/Ni are from ρ = 0.58 to ρ = 0.72). Consequently, the bioavailable fraction ratio value of Ni outside the mining area (21.14%) is significantly higher than that within the area (14.30%). (3) Element speciation and ecological element activity: Over 98% of Cr in serpentine exists in residual fractions, whereas the Fe-Mn oxide-bound fraction (F3) of Cr in extra-mining pyroxenite increases to 5.15%. The element activity in ecological systems ranking of Ni in soil active fractions (F1 + F2 = 15%) follows the order: granite > pyroxenite > serpentine. Based on these insights, a scientific foundation for targeted remediation in high-background areas (e.g., prioritizing the treatment of semi-weathered pyroxenite layers) can be provided. Full article

Arsenic (As) contamination in groundwater represents a major global public health threat, particularly in alluvial aquifer systems where redox-sensitive geochemical processes facilitate the mobilization of naturally occurring trace elements. This study investigates groundwater quality, particularly focusing on the origin of arsenic contamination in shallow and deep alluvial aquifers of the Lower Sakarya River Basin, which are crucial for drinking, domestic, and agricultural uses. Groundwater samples were collected from 34 wells—7 tapping the shallow aquifer (<60 m) and 27 tapping the deep aquifer (>60 m)—during wet and dry seasons for the hydrogeochemical characterization of groundwater. Environmental isotope analysis (δ¹⁸O, δ²H, ³H) was conducted to characterize origin and groundwater residence times, and the possible hydraulic connection between shallow and deep alluvial aquifers. Mineralogical and geochemical characterization of the sediment core samples were carried out using X-ray diffraction and acid digestion analyses to identify mineralogical sources of As and other metals. Pearson correlation coefficient analyses were also applied to the results of the chemical analyses to determine the origin of metal enrichments observed in the groundwater, as well as related geochemical processes. The results reveal that 33–41% of deep groundwater samples contain arsenic concentrations exceeding the WHO and Turkish drinking water standard of 10 µg/L, with maximum values reaching 373 µg/L. Manganese concentrations exceeded the 50 µg/L limit in up to 44% of deep aquifer samples, reaching 1230 µg/L. On the other hand, iron concentrations were consistently low, remaining below the detection limit in nearly all samples. The co-occurrence of As and Mn above their maximum contaminant levels was observed in 30–33% of the wells, exhibiting extremely low sulfate concentrations (0.2–2 mg/L), notably low dissolved oxygen concentration (1.45–3.3 mg/L) alongside high bicarbonate concentrations (450–1429 mg/L), indicating localized varying reducing conditions in the deep alluvial aquifer. The correlations between molybdenum and As (rdry = 0.46, rwet = 0.64) also indicate reducing conditions, where Mo typically mobilizes with As. Arsenic concentrations also showed significant correlations with bicarbonate (HCO₃⁻) (rdry = 0.66, rwet = 0.80), indicating that alkaline or reducing conditions are promoting arsenic mobilization from aquifer materials. All these correlations between elements indicate that coexistence of As with Mn above their MCLs in deep alluvial aquifer groundwater result from reductive dissolution of Mn/Fe(?) oxides, which are primary arsenic hosts, thereby releasing arsenic into groundwater under reducing conditions. In contrast, the shallow aquifer system—although affected by elevated nitrate, sulfate, and chloride levels from agricultural and domestic sources—exhibited consistently low arsenic concentrations below the maximum contaminant level. Seasonal redox fluctuations in the shallow zone influence manganese concentrations, but the aquifer’s more dynamic recharge regime and oxic conditions suppress widespread As mobilization. Mineralogical analysis identified that serpentinite, schist, and other ophiolitic/metamorphic detritus transported by river processes into basin sediments were identified as the main natural sources of arsenic and manganese in groundwater of deep alluvium aquifer. Full article

The Aghbar-Bou Azzer East mining district (ABED) is located between the Bou Azzer East and Aghbar deposits. It is an area of approximately 7 km long towards ENE–WSW and 2 km wide towards N–S. In this barren area, volcano-sedimentary rocks are attributed to the Ouarzazate group outcrop (Ediacarian age): they are composed of volcanic rocks (ignimbrite, andesite, rhyolite, dacite, etc.) covered by the Adoudou detritic formation in angular unconformity. Given the absence of serpentinite outcrops, exploration investigation in this area has been very limited. This paper aims to use ionic leach geochemistry (on samples of soil) to detect the presence of Co-bearing arsenides above hidden ore deposits in this unexplored area of the Bou Azzer inlier. In addition, a detailed structural analysis allowed the identification of four families of faults and fractures with or without filling. Three directional major fault systems of several kilometers in length and variable orientation in both the Cryogenian basement and the Ediacaran cover have been identified: (i) ENE–WSW, (ii) NE–SW, and (iii) NW–SE. Several geochemical anomalies for Co, As, Ni, Ag, and Cu are aligned along three main directions, including NE–SW, NW–SE, and ENE–WSW. They are particularly well-defined in the western zone but are only minor in the central and eastern zones. Some of these anomalies correlate with the primary structural features observed in the studied area. These trends are consistent with those known under mining exploitation in nearby ore deposits, supporting the potential for similar mineralization in the ABED. Based on structural analysis and ionic leach geochemistry, drilling programs were conducted in the study area, confirming the continuity of serpentinites at depth beneath the Ediacaran cover and the presence of Co–Fe-bearing arsenide ores. This validates the ionic geochemistry technique as a reliable method for exploring buried ore deposits. Full article

Serpentinite is a common lithology in Greece with significant geotectonic and petrogenetic implications, yet its archaeometric study remains limited. This also applies to the Ras serpentinite outcrop on Tinos Island—an enigmatic ancient quarry with no prior documentation of its exploitation. This study aims to provide a holistic provenance analysis and full material characterization to establish a unique fingerprint for future comparative research. A multidisciplinary methodology was applied, including petrography, XRD, FTIR, BET, LA-ICP-MS, electron microprobe analyses, and lichenometry—the latter used to estimate the quarry’s period of activity. The Ras serpentinite consists of a dark-green, brecciated lizardite matrix cut by a pale-green chrysotile network, and notably hosts the first recorded occurrence of minnesotaite in Greece. Relict antigorite within the matrix indicates high-pressure, high-temperature metamorphism preceding a greenschist facies overprint. Geochemical data classify the Ras occurrence as a subduction-related serpentinite derived from a depleted ultrabasic protolith. The aforementioned traits distinguish it from other Greek examples. Lichenometric analysis suggests the quarry was active in the 13th century A.D., with evidence of deliberate extraction techniques. These findings offer valuable insights into archaeometric studies and the provenance of serpentinites in the Aegean. Full article

The Paleoproterozoic Kovdozero complex, one of largest in the Fennoscandian Shield, was emplaced in a peripheral region of the SB–TB–LBB (Serpentinite Belt–Tulppio Belt–Lapland–Belomorian Belt) megastructure. Coronitic rocks of ultrabasic–basic compositions, investigated along a cross-section in the Gabrish area, are members of a cryptically layered series. They crystallized from the northern margin inward, as indicated by variations in mineral compositions and geochemical trends. Unsteady conditions of crystallization arose because of uneven cooling of the shallowly emplaced complex. Rapid drops in temperature likely caused the forced deposition of different generations of variously textured pyroxenes and chromian spinel or resulted in the unique development of narrow recurrent rims of orthopyroxene hosted by olivine. The unstable conditions of crystallization are expressed by (1) textural diversity, (2) broad variations in values of Mg#, and (3) virtual presence of double trends of Mg# as a function of distance. The coronitic textures are intimately associated with interstitial grains of plagioclase (An_≤65), also present as relics in a rim of calcic amphibole. The coronas are results of (1) rapid cooling leading to unsteady conditions of crystallization, which caused the sudden cessation of olivine crystallization and the development of an orthopyroxene rim on olivine and (2) an intrinsic enrichment in H₂O (and essential Cl in scapolite) coupled with a progressive accumulation of Al and alkalis, giving rise to fluid-rich environments in the intercumulus melt at advances stages of crystallization. These processes were followed by deuteric composite rims of calcic amphibole and reaction of fluid with early rims or grains of pyroxenes and late plagioclase. The coronitic sequences Ol → Opx → Cpx → calcic Amp → Pl (plus Qz + Mca) observed at a microscopic scale reproduce, in miniature, the normal order of crystallization in an ultrabasic–basic complex. A composite orthopyroxene + calcic amphibole corona resembles some rocks in complexes of the Serpentinite Belt. The prominence of such coronas may well be characteristic of the crystallization of komatiite-derived melts. Full article

Serpentinites are metamorphic rocks constituted primarily by serpentine-group minerals (antigorite, chrysotile, lizardite) resulting from the transformation and low-temperature hydration of previous olivine-rich ultramafic rocks, such as dunite, lherzolite, wehrlite, and harzburgite. The peculiar features of the serpentinites such as the greenish color and the intricate vein and mesh-like texture, as well as their role in CO₂ sequestration when carbonated, have hugely increased interest in studying these rocks over recent decades. Moreover, since antiquity, serpentinites have long been exploited, traded, and exported worldwide as daily tools, as well as in buildings and decorative stones in both internal and external architectural elements, because of their aesthetic appeal, attractiveness, and durability. In this work, we analyzed and compared petrographic features, geochemical signatures, and physical–mechanical properties of serpentinites from historical quarries from Andalusia (southern Spain), Basilicata, and Calabria (southern Italy) where they have been used as dimension stones in religious and civil buildings and as construction materials. We aim to evaluate and assess differences in petrographic, carbonation, uniaxial compressive strength, and seismic behavior, that could affect the efficiency when these serpentinites are used as either building and construction materials or for preservation/renovation purposes in cultural heritage. Results obtained from petrophysical investigations of serpentinites from these regions highlight that these materials are suitable for use in construction to various extents and are considered a valuable georesource, behind a detailed characterization carried out before their implementation in construction or conservation/restoration of architectural heritage. Full article

‘Whitestone’ is a characteristic raw material in the Late Neolithic (Tisza and Lengyel culture) polished stone tool (chisel, adze, macehead) archaeological record in Southern Hungary. However, the lithology—the technical term not reflecting a petrographic definition—needs detailed petrographic-analytical investigations (by optical microscopy, PGAA, and SEM-EDS) to determine the exact rock types and to connect them to specific geological sources. This article identifies the main types of ‘whitestone’ and, furthermore, focuses on the predominant ‘silicified magnesite’ type and the secondary ‘silicified limestone/dolomite’ type. Based on our results, both types originated from the alteration of serpentinized ultramafic assemblages, most probably from the closest magnesitic alteration zones of serpentinite outcrops in Serbia. Thus, the most possible provenance of the Late Neolithic ‘whitestone’ polished stone tools is the Serbian magnesite. These lithologies are in the territory of the Late Neolithic Vinča culture, which was engaged in mass production of ‘whitestone’ tools. This fact indicates the strong relationship of that population with the Tisza and Lengyel communities. Full article

The geochemical maps and geochemical anomaly maps produced based on the data in the databases of the Regional Geochemistry–National Reconnaissance (RGNR) and the National Multipurpose Regional Geochemistry Survey (NMPRGS) projects have played a crucial role in China’s geochemical exploration. A geochemical survey of the Mojiang area, Yunnan Province, China, has been completed and reveals potential new regions for Ni exploration related to occurrences of serpentinite melanges. The geochemical maps and geochemical anomaly maps need to be drawn in this area. Traditional geochemical maps, heavily dependent on data quantity, are less suitable for consistent comparisons across distinct regions and elements. Here, a fixed value method is proposed to contour the Ni geochemical map on 19 levels, which is convenient for the comparison among elements. On the geochemical maps, the two known Ni deposits are located in a region with Ni surely screening risk level (on the national standard of pollution risk of heavy metals in China) and a region with Ni economic level (Ni as an associate or main economic metal on the national standard of Ni deposit in China), respectively. In addition, we have determined that the Sn and Li levels in this area are at (low or high) background levels compared to other regions. Then, the method of seven levels of classification, which is also suitable for the comparison across different areas or elements, is used to draw the geochemical anomaly maps in the Mojiang area. On the anomaly maps, the two known Ni deposits are located in the regions with Ni anomaly levels not less than four, while the anomaly areas of Sn and Li are sporadic, with anomaly levels not larger than two in this area. These consistent results with the known facts of Ni, Sn, and Li deposits in the Mojiang area not only consolidate the roles of geochemical maps and geochemical anomaly maps but also illustrate the comparison among elements in mineral exploration. Furthermore, we predicted three Ni potential regions in the Mojiang area on the geochemical survey. Full article

The Kumishi ophiolitic mélange contains well-preserved large-scale serpentinites and their accompanying granulites in the eastern South Tianshan Accretionary Complex (STAC), southwestern Altaids. Previous studies have mainly focused on the thermodynamic conditions and tectonic setting of granulites. However, the petrogenesis of the widespread serpentinites in the Kumishi ophiolitic mélange remains largely unexplored. In this paper, petrological, geochemical, and geochronological studies were carried out on the Kumishi serpentinites, as well as the host sediment and intermediate–felsic volcanic rocks. The serpentinites show variable LOI values of 8.3–16.5 wt% and relatively consistent SiO₂/(sum oxides) ratios of 0.81, which demonstrate that the major elements of their protoliths have been preserved well during serpentinization. Multi-trace element and REE diagrams suggest that the protoliths of the Kumishi serpentinites have experienced varying degrees of refertilization, with distinct natures seen between the Yushugou, Tonghuashan, and Liuhuangshan serpentinites. Zircon U-Pb chronology of the Tonghuahsan serpentinites yields a mean age of 355.8 ± 7.3 Ma (MSWD = 1.0, N = 26). Detrital zircons from the host sediment record a maximum depositional age of 375 ± 10 Ma (MSWD = 0.4, N = 3), with a peak at ca.419 Ma. Subduction-related volcanic rocks yield ages of ca.437 Ma. Hence, clues are provided to the petrogenesis of the Kumishi serpentinites, with calls for future in-depth works from an isotopic perspective. Full article

Experiments were conducted to evaluate domestic low-grade laterites and serpentinite waste as potential secondary sources of nickel and magnesium and to assess leaching residues for carbon dioxide adsorption. Solids were leached chemically using sulfuric acid, while bioreductive dissolution under anoxic conditions employed a consortium of microorganisms dominated by Sulfobacillus. The efficiency of laterite bioreduction was 26.81% for Ni and 63.92% for Mg. In the case of serpentinite, 20.54% Ni and 92.88% Mg were extracted. The chemical dissolution yielded 26.73% Ni and 61.37% Mg in the case of laterites and 16.20% Ni and 77.49% Mg for serpentinite waste. Specific surface area was analyzed during the processes, showing a systematic increase over time. Based on the changes in this parameter, a mathematical description of the process was proposed using a shrinking particle model (SPM). Except for laterite bioreduction, leaching was shown to be a two-stage process controlled by a chemical reaction. The serpentinite solid processed in the presence of microorganisms exhibited the highest surface area (267 m²/g) and a CO₂ adsorption capacity of 19.9 cm³/g. Full article

Chromite in the amphibolites of the Myanmar jadeite deposits has not been well studied. Mineralogical studies on chromite and related kosmochlor and Cr-omphacite in the amphibolite of the Myanmar jadeite deposits were conducted. Compared to the chromite in the adjacent serpentinized peridotite, the chromite had higher Cr₂O₃ (45.67–54.25 wt.%) and MnO (1.82–1.90 wt.%) but lower MgO (1.00–1.96 wt.%) and Al₂O₃ (1.05–15.09 wt.%), similar to the published chromite compositions in jadeitite. Serpentinite was derived from a highly depleted mantle peridotite. There were at least two stages of metasomatism during the transformation of serpentinite + chromite to magnesio-katophorite + chromite + thin kosmochlor (and/or Cr-omphacite cortex). The first stage was the Ca-rich metasomatism of serpentinite, resulting in sodic-calcic amphibole (magnesio-katophorite), which preceded the formation of jadeite. The second stage of Na-rich metasomatism was produced by the Na-Al-Si-rich fluids with the magnesio-katophorite + chromite (contemporaneous with the formation of jadeite). The composition of the fluid was altered by a reaction with magnesio-katophorite, increasing the Ca-Mg content and resulting in the formation of kosmochlor rich in Ca-Mg and/or peripheral Cr-omphacite. This kosmochlor–Cr-omphacite belongs to the Jd-Kos-Di ternary join, which differs from the kosmochlor–Cr-jadeite (which belongs to the Jd-Kos join in jadeitite). The formation of jadeitite with chromite + kosmochlor + Cr-jadeite occurs when large amounts of Na-Al-Si-rich fluids have wrapped the pieces of chromite-bearing amphibolite. This also explains the proverbial “moss spray green” given that amphibole (with chromite) brings out the green color in jadeitite. Full article

Oxygen-bearing platinum group minerals (O-bearing PGMs) are intergrown with base metal sulfides (BMS, e.g., pentlandite–[NiFe]₉S₈) within fractures in chromite grains from chromitite bodies on Ouen Island, New Caledonia. These PGMs are hosted in chlorite and serpentine, which formed during serpentinization of olivine and pyroxene. The O-bearing PGM grains are polygonal, show microfracturing (indicating volume loss), and contain Pt-Pd-rich sulfide remnants, suggesting pseudomorphic replacement of primary (magmatic) sulfides. They display chemical zonation, with Pt(-Pd-Ni-Fe) relict sulfide cores replaced by Pt-Fe-Ni oxidized alloy mantles and Pt-Cu-Fe(-Pd) alloy rims (tulameenite), indicating desulfurization. The core and mantle show a nanoporous structure, interpreted as the result of coupled dissolution–reprecipitation reactions between magmatic sulfides and low fO₂–fS₂ serpentinite-related fluids, probably formed during olivine transformation to serpentine + magnetite (early stages of serpentinization). This fluid infiltrated magmatic sulfides (PGE-rich and BMS), degrading them to secondary products and releasing S and metals that were accommodated in the mantle and rim of O-bearing PGMs. Upon olivine exhaustion, an increase in fO₂ might have stabilized Pt-Fe-O compounds (likely Pt⁰/Pt-Fe + Fe oxyhydroxides) alongside Ni-Fe alloys. Our results show that post-magmatic desulfurization of primary sulfides produces complex nano-scale intergrowths, mainly driven by changes in the fluid’s physicochemical properties during serpentinization. Full article

Serpentinite refers to a group of hydrated magnesium-rich natural silicate rocks. Because serpentinite contains metallic elements and has a layered structure, it can release magnesium ions when immersed in water. Garlic is a widely cultivated crop characterized by a rich chemical composition and many health benefits. Magnesium and manganese are essential nutrients for the human body. In garlic, magnesium stabilizes allicin and prevents its decomposition and release, and manganese promotes polysaccharide metabolism. In this study, serpentinite powder was modified using immersion plating and sintering to improve its crystallinity and ion release capability and enable the cultivation of magnesium–manganese-enriched garlic. An experimental analysis of growth characteristics confirmed the layered structure of serpentinite powder, with sintering effectively reducing impurities and enhancing the powder’s crystallinity and ion release capability. An evaluation of the powder’s specific surface area and ion release capability after surface treatment revealed that Mg-Si-Mn-O sintered at 400 °C for 1 h was the optimal powder for preparing magnesium–manganese ion water. Magnesium–manganese garlic grown with this water contained magnesium and manganese at concentrations of 38–43 and 11–17 mg/L, respectively, and had a higher concentration of allicin and sulfur compounds relative to garlic grown with distilled water. After natural drying, the allicin in the magnesium–manganese-enriched garlic remained stable, and the garlic was found to have a high moisture content. These findings jointly demonstrate the high nutritional value and antioxidant properties of garlic in applications involving serpentinite technology. Full article