Serpentinite Rocks Research Articles

Evaluation of the agricultural potential of the serpentinite rock as a soil remineralizer.

Magnesium is one of the essential elements for the plant growth. However, when the supply of magnesium is required exclusively, few economically feasible options are available. Serpentinite represents an alternative source of magnesium, although little is known about its potential and efficiency under tropical soil conditions. This work aimed to evaluate the use of serpentinite as a soil remineralizer, as well as magnesium fertilizer. The study was conducted in a greenhouse, using a completely randomized design, with seven treatments and four replications, as follows: three levels of serpentinite, mix of serpentinite and phonolite, and the controls with dolomitic limestone and without fertilization. Two plant species (Zea mays L. corn hybrid BRS - 1055 and Phaseolus vulgaris L. common bean variety BRS - Estilo) and two contrasting soils (clayey and sandy texture), were used in pots. Results showed that serpentinite's free silica and toxic element contents fitted the legal requirements. No statistically significant difference was observed for the plant dry matter weight production in the serpentinite and dolomitic limestone control, as well as in the pure serpentinite and the mix with phonolite treatments. The serpentinite was able to supply and to fullfil magnesium requirements for growth and development of corn and bean plants.

Compositional Variations and Tectonic Settings of Podiform Chromitites Associated with Ultramafic Rocks of the Pan‐African Proterozoic Ophiolites from South Eastern Desert, Egypt

AbstractThe Precambrian podiform chromitites associated with ophiolites are abundant in Pan‐African belt in central Eastern Desert (CED) and south Eastern Desert (SED), Egypt and range from 690 to 890 Ma in age. The studied chromitites associated with Neoproterozoic ophiolites are distributed in southern Eastern Desert, Egypt in Baranis ‐ Shalaten sheet and occur as lenticular bodies with variable dimensions in ultramafic component (serpentinites). We present geochemical and mineralogical data from three areas of ophiolites and associated chromitites namely Gebel Abu Dahr (D), Gebel Arais (A) and Gebel Anbat in the Wadi Hodein area (H) (Fig. 1). The paper studies the compositional variations and tectonic settings of podiform chromitites associated with ultramafic rocks, in addition to the alteration process of chromite during metamorphism.The ophiolite in the present areas is composed of the ultramafic rocks (mainly serpentinites) with minor relics of fresh dunite and harzburgite. All these rocks are affected by metamorphism and subsequent retrograde during subduction and exhumation.Six samples selected from the serpentinites geochemically analyzed for major, trace and some REE elements and the geochemical results reflect that harzburgite and dunite compositions are typical of depleted mantle peridotite. Microprobe analyses and SIMS investigations were carried out for three massive podiform chromitite ore bodies and disseminated chromites in serpentinites (1215 spot probe analyses), and silicate minerals in serpentinite rocks such as serpentine and olivine (102 spots). Serpentine minerals are mainly antigorite with some chrysotile in serpentinite rocks and in chromitites, mainly filling cross‐cutting veins.In this study, we consider that the alteration occurred in two stages: during the first one chromite reacted with olivine and water to form Cr‐ and Fe‐rich, porous chromite and chlorite; during the second event magnetite filled the pores, created in the porous chromite and defused into this chromite to form homogeneous magnetite.According to this, the composition of chromite is a key factor controlling the metamorphic reaction between olivine and chromite because if the primary chromite is very poor in Al, the chlorite‐forming reaction hardly takes place. In this case, during the second event, the addition of magnetite only contributes to create a magnetite corona around the former chromite grains without any diffusion at the chromite‐magnetite boundary as suggested by Gerbilla et al. (2012).Barnes (2000) studied the chromite in komatiites and modification during green schist to mid amphibolite facies metamorphism. He suggested that the chromite cores continually equilibrated with magnetite rims document metamorphic grade conditions. Barnes (2000) suggested that the relative proportions of Cr3+, Al3+ and Fe3+ of chromite are not affected by metamorphism up to lower temperature amphibolite facies implying restricted mobility of these elements occurred under lower amphibolite facies. So, the chromite in lower temperature amphibolite facies preserves its primary igneous chemistry and can be used to estimate the metamorphic grade. Sack and Ghiorso (1991) and Barnes (2000) suggested that all chromite cores are equilibrated at temperature below ∼ 500–550°C corresponding to lowest amphibolite facies metamorphism and reflect magmatic composition not influenced by metamorphism. In this study, there is no alteration but only nearly pure magnetite deposition and development with restricted Cr‐solubility at < 500°C in the chromite rims on crystal boundaries and within fractures as shown in Fig 2a, b. Also magnetite alters later to hematite.The podiform chromitites are common in the Moho transition zone (MTZ) to the mantle section of ophiolites or harzburgite dominant peridotite massifs (e.g., Arai, 1997; Miura et al., 2012). They have been interpreted as a product of peridotite / melt reaction and subsequent melt mixing within the MTZ to the upper mantle; they are basically magmatic cumulates that formed at the upper mantle level (e.g., Arai and Yurimoto, 1994; Zhou et al., 1994). They are thus a good marker of peridotite / melt reaction (e.g., Arai, 1997). The Pan‐African podiform chromitites may have formed in the same way as the Phanerozoic, namely by melt‐ harzburgite reaction and subsequent melt mixing. The podiform chromatites and disseminated chromites are high‐Cr chromites and have range in Cr#(Cr/Cr+Al) atomic ratio from 0.75 to 0.95 and low Ti with boninitic affinity (Fig. 3a), indicating an island arc setting in supra ‐ subduction zone setting. The present massive chromitites and disseminated chromites in serpentinites fall in the field of chromites de Bou Azer, chromites de Cordoba, Argentinia in the Cr# versus Mg# diagram (Fig. 3b, c) (Gervilla et al., 2012)The studied chromatites contain some grains of platinum‐group minerals (PGM) such as sulfides (Os‐rich laurite) and Os–Ir alloy as shown in Fig. 4 and as reported in South Eastern Desert by Ahmed (2007).

Investigation of dependences of physical and mechanical properties of serpentinites of the Dzhetygarinsky deposit

Introduction. The study of the rock stability properties and parameters is an integral part of ensuring safe subsurface use in the process of human impact on the rock mass. In order to understand the spatial variability of serpentinite rocks properties and parameters, research has been carried out, including laboratory tests with subsequent determination and analysis of laws governing the changes in their physical and mechanical properties. Research methodology. In this study, physical and mechanical properties of rocks of the Zhitikarinsky (Dzhetygarisnky) quarry were determined and analysed. The research methods included laboratory uniaxial compression-tensile tests, direct measurements of dry unit weigh, and the statistical analysis of the data obtained. Research result. According to the results of tests and statistical data processing, the values of physical and mechanical properties were obtained for ten rock types collected at the marginal area of the Zhitikarinsky quarry. The graphs show an analysis of laws governing the changes. With an increase in the degree of serpentinization, the values of strength characteristics decrease significantly. Correlations of physical and mechanical properties of serpentinite rocks of the Zhitikarinsky deposit are established.

Origin, diversity and geothermal potentiality of thermal and mineral waters in Vrnjačka Banja, Serbia

Based on the results of 15 years of research on the physical and chemical parameters of 11 occurrences of thermal and mineral water in the extended area of the spa town of Vrnjacka Banja, diverse hydrochemical types of water have been identified, originating from different lithological formations (serpentinite, schist, marble, etc.). Currently, the total amount of abstracted thermo-mineral water is close to 70 L/s, with water temperatures up to 33.8 °C. However, interpretation of collected data indicates that the chemical composition of the mineral water is not exclusively related to the mineralogical composition of the host rock, i.e., aquifer material. To better understand the genesis of these waters, multivariate statistical analysis was undertaken in combination with hydrochemical interpretation of different ionic ratios. This approach revealed the existence of three distinct clusters of thermal and mineral waters: (1) low temperature, low mineral content and mild alkaline; (2) slightly acidic, with a moderate mineral content and elevated iron and fluoride concentrations; and (3) thermal, rich in CO2, with elevated mineral content and iron, manganese and fluoride concentrations. Two primary hydrogeochemical processes, which influence the composition of the thermo-mineral waters, were also identified: dissolution of serpentinite rocks and dissolution of schists, both enhanced by the presence of CO2 gas, circulating through fault zones. Estimates of available geothermal energy suggest a significant potential for expanding current uses of thermal waters of this most popular spa center in Serbia.

Does Exposure to Naturally Occurring Asbestos (NOA) During Dam Construction Increase Mesothelioma Risk?

ABSTRACT The Calaveras Dam Replacement Project, a major construction project completed in 2019, involved hundreds of workers using heavy earth-moving equipment and mining operations, including blasting, drilling, rock crushing, and other operations designed to move millions of cubic yards of earth. Much of the material was composed of serpentinite, blueschist, and other rocks that contain chrysotile and a variety of amphibole minerals, including glaucophane, winchite, actinolite, tremolite, and other asbestos-related amphiboles. This article explores the unique characteristics of the blueschist that required extensive protective measures to be undertaken by the contractor to protect workers and surrounding sensitive receptors. This article will provide an overall summary of the dimensional characteristics of the airborne blueschist elongate mineral particles encountered during construction activities to compare and contrast current understanding of cleavage fragments versus asbestiform mineral fibers.

Application of 2D resistivity method to determine serpentinite rocks in Kuta Cot Glie, Aceh Besar

Abstrak. Kuta Cot Glie di Aceh Besar, merupakan salah satu daerah yang memiliki potensi batuan metamorf serpentinit. Batuan ini dapat digunakan sebagai bahan baku untuk pembuatan pupuk, batu hias, dan beberapa manfaat lainnya. Penelitian ini bertujuan untuk menginterpretasi model bawah permukaan dan memperkirakan ketebalan lapisan batuan serpentinit. Metode geofisika yang digunakan adalah metode geolistrik resistivitas dengan konfigurasi Wenner-Schlumberger. Pengukuran dilakukan pada dua lintasan sepanjang 275 m untuk masing-masing lintasan dengan 56 buah elektroda dan jarak spasi setiap elektroda adalah 5 m. Prinsip metode geolistrik tersebut memanfaatkan sifat kelistrikan suatu material untuk mengetahui karakteristik material. Hasil penelitian menunjukkan bahwa nilai resistivitas adalah 50 - 150 Ωm yang diperkirakan lapisan batuan serpentinit dengan ketebalan 10 - 35 m.Abstract. Kuta Cot Glie located in Aceh Besar, Aceh Province, has a natural potential of serpentine. The metamorphic rocks used as a raw material for making fertilizer, ornamental stones, and other benefits. This research aims to interpret sub-surface models and estimate the thickness of the rock layers. The geophysical method used in this study was the resistivity geoelectric method with a Wenner-Schlumberger configuration. Measurements were carried out on two lines with 275 m for each line and the spacing of the electrode was 5m using 56 electrodes. The physical approach utilizes the electrical properties of a material to determine the characteristics of its material. The result show that the resistivity of 50 to 150 Ωm can be interpreted as serpentinite rock layers with the thickness of 10 m to 35 m.Keywords: Serpentinite, resistivity, geoelectric method, Wenner-Schlumberger configuration.

Potential Slow Release Fertilizers Based on K2MgSiO4 Obtained from Serpentinite

In this work, a potassium magnesium silicate mineral based on phase K2MgSiO4 was prepared from serpentinite rock and studied as a potential K and Mg slow-release fertilizer. The material was prepared by impregnation of serpentinite/KOH and calcination at 700 °C to produce K2MgSiO4 phase, olivine and forsterite. The release patterns of K and Mg in the stirred-flow trial and leaching through the soil columns showed that K2MgSiO4-based materials released K on lower rates than KCl and MgSO4.7H2O, however, there was no evidence of Mg release. The extraction with 1 mol L-1 NH4OAc showed a considerable content of Mg and K for K2MgSiO4-based materials, due to exchange of NH4+ and Mg2+. X-ray diffraction (XRD) analysis of materials impregnated with K and calcined showed peaks relative to K2MgSiO4. After leaching, the peaks intensity diminished, supporting that part of K leached. Therefore, the samples showed great potential as slow-release K-fertilizers when compared with KCl source.

Shallow reworking of magmatic zircon grains of latest Neoproterozoic (Timanian) age in serpentinite of the Voykar Massif, Polar Urals: new constraints from U-Pb isotopic data, and first trace elements and Lu-Hf isotopic data

ABSTRACTThe Voykar Massif of the Polar Urals in Russia consists of an ultramafic complex (mantle section) in the northwest, followed by a late Cambrian to Silurian mafic complex (intra-oceanic primitive island arc) and early Devonian intrusive rocks of an evolved island arc to the southeast. These complexes represent tectonic nappes thrust over the East European continental margin during the late Palaeozoic Uralian Orogeny. LA-ICP-MS U-Pb dating of zircon grains (n = 42) from an antigorite-serpentinite lens within the mafic complex yielded a Concordia age of 542 ± 2 Ma with an age range of 549–527 Ma. Additionally, few grains contain inherited domains with ages between ~990 and 3277 Ma. Hafnium isotopic data of the main age group show 176Hf/177Hft from 0.28242 to 028249 and εHft ranging from +1.9 to −6.5. The evolved Hf isotope data and the trace-element composition of the zircon grains point to an involvement of a continental crustal component in the parental magma. The zircon grains originate from igneous rocks formed during the Timanian Orogeny that affected the East European margin in the latest Neoproterozoic. During the Timanian or Uralian Orogeny, the magmatic zircons were eroded and shallowly recycled into the serpentinised mantle above the subduction zone. Finally, Uralian thrusting led to juxtaposition and imbrication of the zircon-bearing serpentinite and intra-oceanic volcanic rocks of the mafic complex.

Role of structural inheritance in the gravitational deformation of the Monviso meta-ophiolite Complex: the Pui-Orgiera serpentinite landslide (Varaita Valley, Western Alps)

ABSTRACT Depending on its chemical and mineralogical composition, the serpentinite represents a peculiar rocky material, which plays a significant role in influencing pedogenetic weathering, vegetation ecology, geo-mechanical and tectonic processes, as well as gravitational slope failure. In serpentinite-bearing environments the response to gravitational stress is more effective than in other rock types. In the Monviso meta-ophiolite Complex (Western Alps), a close relation between landsliding and serpentinite rock occurrences is particularly evident. Our geological map (Main Map), at a scale 1:10,000, illustrates the geology and geomorphological features of the Pui-Orgiera giant (2.98 km2) complex landslide, located on the southern slope of the Monviso Massif. This map clearly documents that the characteristics and kinematics of the landslide are closely associated to the anomalous thickening and widening increase of the Baracun Shear Zone, a remnants of an intra-oceanic detachment fault which separates serpentinite and meta-intrusives from metabasalt and metasediments of the Monviso meta-ophiolite Complex.

Mineralogical Asbestos Assessment in the Southern Apennines (Italy): A Review

This paper deals with petrography and mineralogy of serpentinitic rocks occurring in the Southern Apennines (Italy) with the aim to review the already available literature data and furnish new details on asbestos minerals present in the studied area. Two sites of Southern Italy were taken into account: the Pollino Massif, at the Calabrian-Lucanian border, and the surroundings of the Gimigliano and Mt. Reventino areas where serpentinites of Frido Unit are mainly exposed. Textural and mineralogical features of the studied rocks point to a similar composition for both sites including asbestos minerals such as chrysotile and tremolite-actinolite series mineral phases. Only in the Pollino Massif serpentinites edenite crystals have been detected as well; they are documented here for the first time. This amphibole forms as fibrous and/or prismatic crystals in aggregates associated with serpentine, pyroxene, and calcite. Metamorphism and/or metasomatic alteration of serpentinites are the most probable processes promoting the edenite formation in the Southern Apennine ophiolitic rocks.

Release and fate of Cr(VI) in the ophiolitic aquifers of Italy: the role of Fe(III) as a potential oxidant of Cr(III) supported by reaction path modelling

Reaction path modelling of serpentinite dissolution in meteoric water was performed, varying Fe2O3/(FeO + Fe2O3) weight ratios of serpentine and reproducing the analytical concentrations of relevant solutes, including Cr(VI), in the Mg-HCO3 groundwaters hosted in the ophiolitic aquifers of Italy. The occurrence of geogenic Cr(VI) in these groundwaters appears to be potentially controlled by the oxidation of trivalent Cr to the hexavalent redox state, driven by the reduction of trivalent Fe to the divalent redox state. In fact, trivalent Fe is the only oxidant present in suitable amounts in serpentinite rock, and even serpentine contains a high content of trivalent Fe as proven by recent studies. In contrast, the generally accepted hypothesis that geogenic Cr(VI) in waters interacting with serpentinites is driven by the reduction of trivalent and tetravalent Mn is questionable, since serpentinite rock has a low Mn content and it is necessary to invoke adsorption of trivalent Cr ions onto the surface of Mn oxides, which are oxidised as a surface complex to hexavalent Cr. Moreover, Mn oxides are present in the aqueous solution as suspended particles or in rocks as coatings or nodules.

Estimation of tensile strength of ultramafic rocks using indirect approaches

Because the estimation of the tensile strength is very important in any geotechnical project, many attempts have been made to determine. But the immediate determination of the tensile strength is usually difficult owing to well-shaped specimens, time-consuming, expensive and sometimes unreliable. In this study, engineering properties of several ultramafic rock samples were measured to assess the correlations between the Brazilian Tensile Strength (BTS) and degree of serpentinization, physical, dynamic and mechanical characteristics. For this purpose, a comprehensive laboratory testing program was conducted after collecting thirty-two peridotite and fifty-one serpentinite rock samples, taken from central Greece, in accordance with ASTM and ISRM standards. In addition, a representative number of them were subjected to petrographic studies and the obtained results were statistically described and analysed. Simple and multiple regression analyses were used to investigate the relationships between the Brazilian Tensile Strength and the other measured properties. Thus, empirical equations were developed and they showed that all of the properties are well correlated with Brazilian Tensile Strength. The curves with the 45o line (y = x) were extracted for evaluating the validity degree of concluded empirical equations which approved approximately close relationships between Brazilian Tensile Strength and the measured properties.

Ambient geochemical baselines for trace elements in Chernozems\u2014approximation of geochemical soil transformation in an agricultural area

The legal regulatory/action levels of trace elements in soils are established at high concentrations, at which the crucial functions of soil are at risk or are eliminated. However, concentrations below these action levels, but above presumed natural levels, may also limit particular ecosystem services, including organic food production. Thus, defining the (ambient) background concentrations is an essential part of environmental or health risk assessment, e.g., on Chernozems, which are considered to be the most productive soils and ones that should be protected against all forms of contamination. Based on 28 profiles of chernozemic soils developed from loess in an agricultural region of SW Poland presumed to be free of industrial contamination, ambient geochemical baselines have been derived for Fe and six trace metals for four standardized soil layers, including the topsoil (plow layer) and parent material layers. The median values for the plow layer (1.89% for Fe, and 537, 49, 17, 14, and 26 mg kg−1 for Mn, Zn, Pb, Cu, and Ni, respectively) are lower than the values reported for other Chernozems in SE Poland/Europe/the world, and thus may serve as a general geochemical baseline for chernozemic soils developed from loess. The concentration of Cd, although lower than in other Chernozems around the world, is higher than in Ukrainian Chernozems and thus may serve as a local (or Central European) baseline only. The median concentrations of Fe, Cu, Mn, and Zn are very close to their concentrations in the Chernozem buried under the Neolithic kurgan. However, Pb and Cd concentrations are two times higher than in the buried soil, indicating the scale of general contamination of the topsoil horizons of arable soils. Concentrations of the elements under study, excluding Fe, in both the buried and surface soils are significantly higher in the topsoil layer compared to parent material (loess), and this justifies the separate baseline values for topsoil horizons, instead of background values derived universally for parent rock types. This is essential, in particular in soils texturally differentiated within profiles, where the subsoil material has a different origin and cannot be considered the parent material for topsoil horizons. Underlying or locally outcropped bedrock (e.g., serpentinite rocks) may naturally enhance the total concentration of trace elements in the entire soil profile by the addition of metal-rich regolith particles during the formation of surface covers, e.g., by eolian processes under periglacial conditions (Late Pleistocene). Such soils are naturally enriched with metals (with nickel in the case of serpentinite bedrock), cannot be considered contaminated, and thus require a separate legal treatment, including separate (or individually suited) background baselines for health risk assessments.

Development of Concurrent grinding for application in aqueous mineral carbonation

Vast reserves of peridotite and serpentinite rocks can be utilised for the safe and permanent sequestration of global CO2 emissions via aqueous mineral carbonation. These, and indeed most feedstocks used in mineral carbonation require ultrafine grinding and/or heat-activation, to engender significantly enhanced reactivity in the rock such that it can then be carbonated. Both activation processes are energy intensive and present significant obstacles to the commercial application of mineral carbonation. Here we show that these limitations can be addressed, at least in part, through the application of a concurrent or in operando grinding technique which does not require feedstocks which have been subjected to prior ultrafine grinding nor heat-activation.Concurrent grinding is shown to result in a significant increase in magnesite yields for non-heat activated feedstock, prepared such that fines (<20 μm particles) were excluded from the feed. We assert that concurrent grinding may be a suitable technique for the processing of feedstocks such as those containing significant proportions of forsterite and pyroxene, minerals which are unresponsive to thermal activation for use in aqueous mineral carbonation. This study also investigates the effect of different grinding media particle size on reducing the particle size distribution (PSD) of the feed. Optimum ratio of grinding media size to feed particle size, optimum grinding media and slurry concentrations, optimum time for grinding and optimum impeller designs are determined for the system under study. The quantitative effect of grinding media concentration, slurry concentration, pressure and temperature on magnesite yield has been investigated.

Study of the kinetics of the magnesium leaching from serpentine bearing chromite overburden rocks for mineral carbonation

ABSTRACT Characterisation and leaching studies have been carried out on serpentinite rock samples collected from Sukinda mines, India. Dissolution characteristics of samples have been studied using HCl, H2SO4 and HNO3 acid. Effect of particle sizes, solvent concentrations, reaction temperatures and reaction time have been investigated. It was found that Mg recoveries vary between 54.95% and 98.12%. Leaching of fine particles of <53 µm sizes using H2SO2 solution of 1 M at 70°C for 2 h can recover maximum 93% Mg with lowest Si content (6.6%). Kinetic studies indicated that dissolution of Mg follows product layer diffusion mechanism and activation energy calculated was 37.88 kJ mol−1. CO2 treatment of leach liquor resulted in precipitation of magnesium carbonates and hydroxides at a solution pH adjustment between 7 and 10. The study revealed that these rocks can be used for CO2 fixation and H2SO4 can be the best solvent.

Platinum-group element and gold enrichment in soils monitored by chromium stable isotopes during weathering of ultramafic rocks

Weathering of ultramafic rocks can lead to the formation of soil profiles with high contents of Fe, Ni, Co, platinum-group elements (PGE) and gold. Traditionally, these metal-rich soils are known as “laterites” and are formed under tropical climates and stable tectonic conditions. However, little is known about their possible development in cold/humid regions, and the factors governing PGE and gold mobility and enrichment under these weathering conditions are poorly constrained. In this study, five soil profiles developed on serpentinized, chromite-bearing ultramafic rocks at La Cabaña, located in the Coastal Range of south-central Chile (38° S) were studied by combining major and trace element geochemistry with chromium stable isotope data. The results show that the soils developed at La Cabaña have higher PGE and Au contents than the parent serpentinite rock, with ∑PGE and Au reaching up to 160 ppb and 29 ppb in a limonitic soil horizon and clay saprolite, respectively. Most soil samples have slightly negative δ53/52CrSRM979 values, within a range of −0.089 ± 0.012‰ to −0.320 ± 0.013‰ (average of −0.178‰), and are in agreement with previous data reported for modern soils. A noteworthy relation between δ53/52Cr data and PGE + Au contents is observed in the studied soil horizons, where isotopically lighter values of δ53/52Cr match the higher contents of PGE and gold. These results show that pedogenetic processes operating at the cold and humid La Cabaña area are capable of increasing the total PGE and Au contents of certain soil horizons. Such processes are complex and multivariate but are primarily modulated by chromite dissolution and the formation of secondary phases such as clay minerals and oxy-hydroxide phases in the soil. These findings provide evidence that important weathering and PGE + Au supergene accumulation are not only restricted to tropical latitudes, and that the chromium isotope system is a useful proxy to track surface redox process and noble metal enrichment during pedogenesis.

Review on the adverse health effects of asbestiform antigorite, a non-regulated asbestiform serpentine mineral.

Although antigorite is generally described as platy, its fibrous (asbestiform) variant is present widespread in serpentinite rocks. In addition to its primarily fibrous occurrence, asbestiform antigorite may also be formed from serpentinite with massive appearance during tunneling and mining. It is not of commercial interest, but exposure may occur in the certain environments. Detailed studies of the structural features of this antigorite type revealed characteristics closely related to those of chrysotile. Therefore, it is plausible that this serpentine mineral may present a similar health risk for exposed subjects. This is in agreement with results from clinical and animal studies, as well as in vitro experiments showing the cytotoxic, fibrogenic, and carcinogenic potential of antigorite, similar to that of chrysotile and amphibole asbestos. Current evidence supports a need for an update to existing regulations to include unregulated asbestiform antigorite, similar to regulatory measures taken for asbestos.

The late Neoproterozoic Pan-African low-grade metamorphic ophiolitic and island-arc assemblages at Gebel Zabara area, Central Eastern Desert, Egypt: Petrogenesis and remote sensing - Based geologic mapping

The late Neoproterozoic Pan-African basement rocks of the Gebel Zabara area, Central Eastern Desert of Egypt is of particular interest where the medium-grade Hafafit gneisses juxtapose the low-grade ophiolitic and island-arc assemblages along major structural contacts. The area comprises important mineral deposits including gold, base metal vein-type deposits as well as emerald and talc. In the current work, various image processing algorithms including Principal Component Analyses (PCA), Minimum Noise Fraction (MNF) and Decorrelation Stretch (DS) were proposed and applied on Landsat-8, ASTER and Sentinel-2 data to delineate and discriminate the different rock units. Several ASTER mineral indices are successfully used in the mapping process to detect the alteration zones, which are mainly confined to the NNW-SSE and N-S trending structures. The petrogenesis studies for the different rock unites in the study area indicate that the ophiolitic assemblage include serpentinite-talc carbonate, metagabbros complex and metabasalts. Serpentinite rocks represent the hydrated low temperature form of a harzburgite precursor, while the talcose serpentinites evolved via SiO2 aqueou metasomatic alteration. Geochemically, the ophiolitic rocks exhibit N-MORB tholeiitic affinity and imply a back-arc setting. The island-arc rock assemblages encompass calc-alkaline meta-andesite, metadacite and metarhyolite, which imply a normal continental island-arc setting, i.e. less mature than the proper active continental margin. Apart from serpentinites, the ophiolitic and island-arc assemblages experienced regional greenschist facies metamorphism. The ophiolitic metagabbros exhibit the metamorphic assemblage: actinolite + albite (An < 5%)/oligoclase (An 19–20%) + chlorite + epidote + quartz. The coexistence of albite and oligoclase may indicate either: (1) disequilibria association, or (2) a possible greenschist-amphibolite facies transition. The P-T metamorphic condition of the metagabbros was constrained at about 5 kbar and 430 to 452°C.

Genesis of carbonate-rich veins in the serpentinites at the Calabria-Lucania boundary (southern Apennines)

In the northern sector of the Pollino massif (southern Apennines, Italy) well-exposed lens-shaped bodies of serpentinites and sediments of the Frido Unit belonging to the Liguride Complex crop-out. Most serpentinite rocks are cross-cut by carbonate and quartz-carbonate veins with different thickness. This study focuses on petrographic, mineralogical, geochemical, and isotopic analysis of the carbonate veins embedded in serpentinite rocks, collected at the Fosso Arcangelo site and at the Pietrapica quarry (Calabria-Lucanian boundary). The paragenesis of the carbonate veins from the Fosso Arcangelo site is dominantly made by calcite and aragonite with minor amount of rhodochrosite. In quartz-carbonate veins from Pietrapica quarry, dolomite, Mg-calcite, quartz, with minor ankerite were observed.The δ13CV-PDB isotope ratios of carbonates in the carbonate veins are in the range from +2.16‰ to -3.66‰ and corresponding δ18OV-SMOW values are between +15.02‰ and +21.53‰. The δ13CV-PDB values of carbonates in quartz-carbonate veins are in the range from -3.60‰ to -1.78‰ and the corresponding δ18OV-SMOW average value is around +21.3‰. The results suggest that the carbonate at both site occurredunder the same environmental conditions from crustal-derived andlow-moderate temperatures hydrothermal fluids having different chemical composition.

The early Earth geochemical and isotope record of serpentinizing environments from Archean stichtite (Mg6Cr2(OH)16[CO3]·4H2O)

A record of the conditions and duration of Archean serpentinization is preserved as chemical, isotopic, and textural properties of the magnesium-chromium hydroxycarbonate mineral stichtite. This provides a window into the conditions associated with a potentially habitable environment on early Earth and Mars. Stichtite is associated with Archean chromite-rich serpentinite rocks of South Africa, Western Australia and Southern India. Stichtite compositions range within the Cr-Fe-Al hydrotalcite group, with trends unique to each discrete serpentinite host body. Elemental and textural analysis of stichtite-associated chromite indicates that stichtite forms in fore-arc/layered intrusive/boninite setting rocks through interaction of chromite and methane-rich serpentinizing fluids. The degree to which chromite is replaced by stichtite is inferred to correlate with the length of time that the host rocks spent within the “stichtite window.” Carbon stable-isotope values of Archean stichtite suggest carbon sourcing from marine kerogen with minor marine dissolved inorganic carbonate in most samples, as opposed to the strongly kerogen-dominated Phanerozoic stichtite. The carbon and hydrogen stable isotope profile of Archean stichtite ranges from the methane fields of active serpentinizing zones, to geothermal, with trends suggestive of methane oxidation rather than the substrate depletion noted in Phanerozoic stichtite. Thus, isotope values of stichtite appear to record oceanic oxygenation levels. The association of the stichtite 2H polytype (nee barbertonite) with aragonite ± antigorite suggests this is a higher pressure/temperature polytype of stichtite. Reaction textures, isotopic values, and qualitative mineral thermobarometric indicators indicate that stichtite forms during serpentinization in a methane/H2-rich environment within fluid conduits, ranging from near the surface, to depths where pressure is up to 2.8 GPa and temperature is up to ∼300 °C.