Mineral Textures Research Articles

Ultrapotassic dykes in the Moldanubian Zone and their significance for understanding of the post-collisional mantle dynamics during Variscan orogeny in the Bohemian Massif

We report mineral textures, geochemistry and age relations of two ultrapotassic dykes from a dyke swarm in the Western part of the Moldanubian Zone at contact to the Teplá-Barrandian Block. The dykes have orientation almost perpendicular to the NNE–SSW trending Central Bohemian plutonic complex and cross cut metamorphic foliation in basement gneisses and migmatites. Based on mineral compositions and geochemistry, the dykes show close relations to Mg-K syenite plutons in the Moldanubian Zone. The two dykes are vaugnerite and syenite in compositions and contain talc pseudomorphs after olivine within a fine-grained matrix that consists of K-feldspar, phlogopite with small amounts of clinopyroxene and accessory quartz, apatite, titanite and sulphides of Fe, Cu, Ni. The syenite porphyry dyke cross cuts the vaugnerite. It contains quartz phenocrysts and comparing to vaugnerite has lower modal content of talc pseudomorphs.The vaugnerite and syenite porphyry have high K2O (6 to 7wt.%) and mg-number (0.66–0.74), but low CaO and Na2O contents. The vaugnerite is markedly rich in P2O5 (>2wt.%) and comparing to syenite porphyry has higher amount of mantle-incompatible elements (e.g. Rb, Cs, Ba, Pb, Th, U), V and Cr. ID-TIMS analyses on titanite in vaugnerite and on zircon in syenite porphyry yielded 338.59±0.68 and 337.87±0.21Ma, respectively. Mineral and bulk rock chemistry of the dykes indicates that the source magma was formed by a low degree of partial melting of a highly anomalous domain in the upper mantle which subsequently fractionated and was contaminated with crustal material during its ascent. Formation of ultrapotassic magma is explained by transcurrent shear zones in the mantle lithosphere that occurred due to block rotation and post-collisional mantle dynamics initiated by slab break-off and asthenosphere upwelling into the Moldanubian accretionary complex during the Variscan Orogeny.

Early Mesozoic retrograded eclogite and mafic granulite from the Badu Complex of the Cathaysia Block, South China: Petrology and tectonic implications

The high-grade metamorphic terrane in the Badu region along the northeastern Cathaysia Block in South China preserves retrograded eclogites and mafic granulites. Here we present the petrology, mineral phase equilibria and P-T conditions based on pseudosection computations, as well as zircon U-Pb ages of these rocks. Mineral textures and reaction relationships suggest four metamorphic stages for the retrograded eclogite as follows: (1) eclogite facies stage (M1), (2) clinopyroxene retrograde stage (M2), (3) amphibole retrograde stage (M3), and (4) chlorite retrograde stage (M4). For the mafic granulite, three stages are identified as: (1) plagioclase-absent stage (M1), (2) granulite facies stage (M2) and (3) amphibolite facies stage (M3). Metamorphic evolution of both of the rock types follows clockwise P-T path. Conventional geothermometers and geobarometers in combination with phase equilibria modelling yield metamorphic P-T conditions for each metamorphic stage for the eclogite as 500–560°C, 23–24kbar (M1), 640–660°C, 14–16kbar (M2), 730–750°C, and 11–13kbar (M3). The chlorite retrograde stage (M4) is inferred to have occurred at lower amphibolite to greenschist facies conditions. Phase equilibria modelling of the mafic granulite shows P-T conditions for each metamorphic stage as 600–720°C, >13kbar (M1) and 860–890°C, 5–6kbar (M2) and M3 at amphibolite facies conditions. LA-ICPMS zircon U-Pb dating and trace element analysis show that the high pressure metamorphism occurred at 245–251Ma. Protolith age of the mafic granulite is 997Ma, similar to that of the mafic to ultramafic rocks widely distributed in the Cathaysia Block and also along the Jiangnan belt. Subduction of ancient oceanic lithospheric materials (or crustal thickening) during Mesozoic and formation of eclogites suggest that the Cathaysia Block was perhaps in the Tethyan oceanic domain at this time. The granulite formation might have been aided by Mesozoic mafic magma underplating associated with lithospheric delamination, heating and retrogression of the eclogite accompanied by rapid uplift.

Trace Element Analysis of Minerals in Magmatic-Hydrothermal Ores by Laser Ablation Inductively-Coupled Plasma Mass Spectrometry: Approaches and Opportunities

Laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) has rapidly established itself as the method of choice for generation of multi-element datasets for specific minerals, with broad applications in Earth science. Variation in absolute concentrations of different trace elements within common, widely distributed phases, such as pyrite, iron-oxides (magnetite and hematite), and key accessory minerals, such as apatite and titanite, can be particularly valuable for understanding processes of ore formation, and when trace element distributions vary systematically within a mineral system, for a vector approach in mineral exploration. LA-ICP-MS trace element data can assist in element deportment and geometallurgical studies, providing proof of which minerals host key elements of economic relevance, or elements that are deleterious to various metallurgical processes. This contribution reviews recent advances in LA-ICP-MS methodology, reference standards, the application of the method to new mineral matrices, outstanding analytical uncertainties that impact on the quality and usefulness of trace element data, and future applications of the technique. We illustrate how data interpretation is highly dependent on an adequate understanding of prevailing mineral textures, geological history, and in some cases, crystal structure.

Mineralogy and Metal Zoning of the Cambrian Zn-Pb-Cu-Ag-Au Lemarchant Volcanogenic Massive Sulfide (VMS) Deposit, Newfoundland

The Lemarchant deposit is a Cambrian bimodal felsic Zn-Pb-Cu-Ag-Au volcanogenic massive sulfide (VMS) deposit located in the Central Mobile Belt, Newfoundland, Canada. Despite regional greenschist metamorphism and faulting, primary mineralogy and mineral textures are well preserved. The deposit is a type example of a precious metal-enriched VMS deposit in the Appalachians. Mineralization consists of a stratiform massive sulfide zone that lies at the contact between a rhyolitic footwall and a basaltic hanging wall. A stringer sulfide zone that is hosted in footwall rhyolite breccia underlies the massive sulfide lens. The stratiform sulfide zone contains massive baryte that is heterogeneously replaced by sphalerite and pyrite, lesser galena, and trace chalcopyrite. The stringer zone contains chalcopyrite, pyrite, and lesser sphalerite and galena. Sphalerite ranges in color from white (low-Fe) to red (high-Fe). The palest sphalerite (<1 mol.% FeS) occurs in the baryte-rich stratiform zone and is associated with early stage exhalative mineralization, intermediate sulfidation epithermal suite minerals (tetrahedrite, bornite, colusite, Ag-bearing gold, covellite) and sulfide minerals enriched in the epithermal trace element suite (Au, Ag, As, Bi, Co, Cr, In, Mo, Ni, Sb, Sn, Te). Darker sphalerite (4.7–13.6 mol.% FeS) in the stratiform zone overprints early stage mineralization and occurs with chalcopyrite; high-Fe sphalerite is also present in the stringer zone. Early exhalative/epithermal-type VMS mineralization was deposited from low temperature (150–250 °C), oxidized, acidic to near-neutral hydrothermal fluids with high sulfur activity. Early mineralization was likely deposited in relatively shallow water ( 300 °C), less oxidized, near-neutral hydrothermal fluids, likely in deeper water (>1500 mbsl). Abundant epithermal suite minerals and epithermal trace element suite-enriched sulfides at Lemarchant suggest a direct magmatic contribution to the hydrothermal fluid.

Magma plumbing for the 2014–2015 Holuhraun eruption, Iceland

AbstractThe 2014–2015 Holuhraun eruption on Iceland was located within the Askja fissure swarm but was accompanied by caldera subsidence in the Bárðarbunga central volcano 45 km to the southwest. Geophysical monitoring of the eruption identified a seismic swarm that migrated from Bárðarbunga to the Holuhraun eruption site over the course of two weeks. In order to better understand this lateral connection between Bárðarbunga and Holuhraun, we present mineral textures and compositions, mineral‐melt‐equilibrium calculations, whole rock and trace element data, and oxygen isotope ratios for selected Holuhraun samples. The Holuhraun lavas are compositionally similar to recorded historical eruptions from the Bárðarbunga volcanic system but are distinct from the historical eruption products of the nearby Askja system. Thermobarometry calculations indicate a polybaric magma plumbing system for the Holuhraun eruption, wherein clinopyroxene and plagioclase crystallized at average depths of ∼17 km and ∼5 km, respectively. Crystal resorption textures and oxygen isotope variations imply that this multilevel plumbing system facilitated magma mixing and assimilation of low‐δ18O Icelandic crust prior to eruption. In conjunction with the existing geophysical evidence for lateral migration, our results support a model of initial vertical magma ascent within the Bárðarbunga plumbing system followed by lateral transport of aggregated magma batches within the upper crust to the Holuhraun eruption site.

Radiation damage-controlled localization of alteration haloes in albite: implications for alteration types and patterns vis-à-vis mineralization and element mobilization

Uraninite, besides occurring in other modes, occurs as inclusions in albite in feldspathic schist in the Bagjata uranium deposits, Singhbhum shear zone, India. The feldspathic schist, considered the product of Na-metasomatism, witnessed multiple hydrothermal events, the signatures of which are preserved in the alteration halo in albite surrounding uraninite. Here we report radiation damage-controlled localization of alteration halo in albite and its various geological implications. Microscopic observation and SRIM/TRIM simulations reveal that the dimension of the alteration halo is dependent collectively on the zone of maximum cumulative α dose that albite was subjected to and by the extent of dissolution of uraninite during alteration. In well-preserved alteration haloes, from uraninite to the unaltered part of albite, the alteration minerals are systematically distributed in different zones; zone-1: K-feldspar; zone-2: chlorite; zone-3: LREE-phase/pyrite/U-Y-silicate. Based on textures of alteration minerals in the alteration microdomain, we propose a generalized Na+➔K+➔H+ alteration sequence, which is in agreement with the regional-scale alteration pattern. Integrating distribution of ore and alteration minerals in the alteration zone and their geochemistry, we further propose multiple events of U, REE, and sulfide mineralization/mobilization in the Bagjata deposit. The alteration process also involved interaction of the hydrothermal fluid with uraninite inclusions resulting in resorption of uraninite, redistribution of elements, including U and Pb, and resetting of isotopic clock. Thus, our study demonstrates that alteration halo is a miniature scale-model of the regional hydrothermal alteration types and patterns vis-a-vis mineralization/mobilization. This study further demonstrates that albite is vulnerable to radiation damage and damage-controlled fluid-assisted alteration, which may redistribute metals, including actinides, from radioactive minerals included in albite. This has important implications in geochronology. Such a study can also provide important clues to the chemical behavior of granite, in which albite is a common constituent, in a physico-chemical ambience analogous to a site of deep borehole disposal of radioactive waste.

SEM morphological studies of carbonates and the search for ancient life on Mars

AbstractNext space missions will investigate the possibility of extinct or extant life on Mars. Studying the infrared spectral modifications, induced by thermal processing on different carbonate samples (recent shells and fossils of different ages), we developed a method able to discriminate biogenic carbonates from their abiogenic counterparts. The method has been successfully applied to microbialites, i.e. bio-induced carbonates deposits, and particularly to stromatolites, the laminated fabric of microbialites, some of which can be ascribed to among the oldest traces of biological activity known on Earth. These results are of valuable importance since such carbonates are linked to primitive living organisms that can be considered as good analogues for putative Martian life forms. Considering that the microstructures of biogenic carbonate are different from those of abiogenic origin, we investigated the micromorphology of shells, skeletal grains and microbialites at different scale with a scanning electron microscope. The results show that this line of research may provide an alternative and complementary approach to other techniques developed in the past by our group to distinguish biotic from abiotic carbonates. In this paper, we present some results that can be of valuable interest since they demonstrate the utility for a database of images concerning the structures and textures of relevant carbonate minerals. Such data may be useful for the analysis of Martian samples, coming from sample return missions or investigated by futurein situexplorations, aimed to characterize the near-subsurface of Mars in search for past or present life.

Resolving the Relative Timing of Au Enrichment in Volcanogenic Massive Sulfide Deposits Using Scanning Electron Microscopy-Mineral Liberation Analyzer: Empirical Evidence from the Ming Deposit, Newfoundland, Canada

The metamorphosed Cambro-Ordovician Ming volcanogenic massive sulfide deposit in northern Newfoundland, Canada, is locally overlain by a unit consisting of mafic to intermediate medium- to coarse-grained volcaniclastic breccia with up to 10 vol % sulfide clasts. Analysis via mineral liberation analyzer of two sulfide clasts, completed using scanning electron microscope observations, allowed the identification of a number of microscopic and submicroscopic electrum grains. These electrum grains occur in three types of textural settings: (1) free electrum grains with tellurides within gangue minerals, (2) inclusions of electrum with tellurides in pyrrhotite grains, and (3) free electrum grains with base metals and tellurides interstitial between base metals and along cataclastic fractures in pyrite. These three textural settings are similar to those in the underlying massive sulfide orebodies that represent very likely sources to the sulfide clasts. The polylithic nature and angularity of the volcaniclastic fragments in the breccia suggest a postmineralization gravity-controlled debris flow proximal to its source. The mineral assemblage and textures of electrum in the sulfide clasts implies evidence in support of syngenetic and predeformation Au introduction in the volcanogenic massive sulfide deposit, and argues against an orogenic overprint as the cause for Au enrichment.

OPAQUE MINERAL CONTENT OF DUTLUCA VOLCANICS (BURHANİYE - BALIKESİR): THE EFFECT OF HYDROTHERMAL ALTERATION ON THESE MINERALS

Dutluca volcanics, which are known as Hallaclar Formation in regional scale in the study area (Kurshens- ky, 1976), are composed of hydrothermally altered andesite and basaltic andesite. In these rocks, sulfidic minerals such as pyrite, enargite and chalcosine, and oxide and hydroxide minerals such as magnetite, hematite and goethite were detected as opaque minerals. The presence of enargite in opaque mineral para- genesis, and the changes observed in structures and textures of opaque and silicate minerals indicate that examined volcanics have been altered by highly sulfidic hydrothermal solutions. During the hydrothermal alteration process, which indicates at least in two phases, a diffuse pyritization rich in H S in reducing conditions and enargite mineral, which is known as pathfinder minerals in such processes, formed in the first phase. Later on; the extensive martitization developed in oxidizing conditions.

Modelling of Dynamic Rock Fracture Process with a Rate-Dependent Combined Continuum Damage-Embedded Discontinuity Model Incorporating Microstructure

This paper deals with numerical modelling of rock fracture under dynamic loading. For this end, a combined continuum damage-embedded discontinuity model is applied in finite element modelling of crack propagation in rock. In this model, the strong loading rate sensitivity of rock is captured by the rate-dependent continuum scalar damage model that controls the pre-peak nonlinear hardening part of rock behaviour. The post-peak exponential softening part of the rock behaviour is governed by the embedded displacement discontinuity model describing the mode I, mode II and mixed mode fracture of rock. Rock heterogeneity is incorporated in the present approach by random description of the rock mineral texture based on the Voronoi tessellation. The model performance is demonstrated in numerical examples where the uniaxial tension and compression tests on rock are simulated. Finally, the dynamic three-point bending test of a semicircular disc is simulated in order to show that the model correctly predicts the strain rate-dependent tensile strengths as well as the failure modes of rock in this test. Special emphasis is laid on modelling the loading rate sensitivity of tensile strength of Laurentian granite.

Tracking magmatic and hydrothermal Nb–Ta–W–Sn fractionation using mineral textures and composition: A case study from the late Cretaceous Jiepailing ore district in the Nanling Range in South China

The Jiepailing mining district in the Nanling range in South China is well-known for its granite-related Sn–Be–F-mineralization. Recently, drill holes have exposed an Nb–Ta–W–Sn mineralized granitic porphyry and topaz-bearing granite–greisen at depth, which we have studied here, using mineral (columbite, rutile, wolframite, cassiterite, zircon, and mica) major- and trace-element compositional data, mineral textures, and zircon and columbite U–Pb geochronology. Our age data shows that the porphyry and the granite and their mineralization formed at ~91–89±1Ma in the late-Cretaceous, and thus subsequent to the main ore-forming events of the region. Continuous mineral compositional trends indicate that the studied granitoids are related by progressive fractionation. We propose that: (1) subhedral–euhedral, low-Ta columbite crystallized from melt; (2) euhedral–subhedral rutile and wolframite and subhedral and subhedral cassiterite up to ~30μm in size formed at the magmatic–hydrothermal transition of the system; and (3) high-Ta columbite and subhedral cassiterite up to ~10μm in size formed from subsolidus hydrothermal fluids. In combination with the Nb, Ta, W, and Sn compositions of zircon and mica, their textures and compositional variation allow us to track the magmatic to hydrothermal rare-metal fractionation (concentration, mobilization, and deposition) of the system in detail, despite our limited access to it through only two exploration drill cores. Using the Nb, Ta, W, and Sn concentrations in zircon (refractory, early-crystallized) and in micas (late equilibrated), respectively, was particularly useful for tracing the partial loss of Sn and W ore components from the intrusion, and to constrain the information which is crucial for any rigorous ore exploration.

Texture-based analysis of liberation behaviour using Voronoi tessellations

A liberation simulation is outlined based on image analysis of mineral texture images such as those produced by automated mineralogical analysis. The method relies on a freeware image analysis programme, Fiji, and uses Voronoi tessellations to represent a fragmentation pattern. This pattern is superimposed onto a mineral texture image and the mineralogical composition of each tile is analysed separately to produce a liberation spectrum.A comparison is presented between actual and simulated data in terms of liberation, shape and size distribution. The correlation (r2) of simulated to measured liberation data exceeded 0.98 for all minerals assessed but for optimum confidence further validation is required over a larger size range. Comparing real and simulated particle shape gave a correlation exceeding 0.95, and it is shown the particle size distribution of Voronoi patterns can accurately reproduce that of scalped feeds (i.e. a narrow size fraction) of comminution products. Repeatability of the process is shown to be dependent on particle size, but overall is very good. To demonstrate potential applications of this analysis method, quartz liberation spectra for three granites of different grain sizes are included and discussed, and a simulated grade–recovery curves for an Au-bearing pyrite is demonstrated.

Stability of Slopes and Embankments of Coarse Man-made Soils

The suitability of soils for the construction of subgrade is determined by their road-building properties. For this purpose coarse, sandy and sandy loam soils are the most suitable. Many coarse man-made soils are formed during mining. These soils undergo significant changes in composition, structure and texture of natural minerals under the influence of weather and climatic factors. Coarse man-made soils may differ by petrographic composition and metamorphism of minerals. These multi-component systems are composed of fine-grained components and large particles varying in strength, water and frost resistance. The aggregate strength characteristic was taken as an integrated criterion for the assessment of embankment subgrade based in part on the capabilities of the test and also the need for the creation of a dense structure for multi-component coarse soils. From this, a technological classification for coarse soils was developed. The problem of using coarse soil in embankments is the possibility of soil settlements occurrence due to the large space between the particles and due to the impact of weather and climate factors. For ensuring a stable structure of subgrade, such coarse soils should be either isolated from the influence of weather and climatic factors or the structure of the subgrade should be made dense non-settling properties by means of technological solutions that envisage filling the entire space between the large particles with fine-grained materials (e.g. pit-run fines). The design solutions are developed depending on the type of coarse soil. This will protect the embankment body from the effects of weather and climatic factors, namely: wetting-drying and freezing- thawing.To ensure durability and stability of the embankment slopes, technological solutions for creating a single strong structure were developed. Effective subgrade structures that take into account the characteristics of these materials and ensure their sustainability and stability were developed basing on the results of coal waste research.

Composition and origin of the sabkha brines, and their environmental impact on infrastructure in Jizan area, Red Sea Coast, Saudi Arabia

The sulfate evaporite minerals (gypsum and anhydrite) and brines of Jizan sabkha cause corrosion of the steel reinforcement and deterioration of the concrete, and consequently hinder the development activity for building new urban communities and industrial zones in Jizan area, Red Sea coastal plain of Saudi Arabia. The sabkha evaporite minerals below the sediment surface are represented by displacive and inclusive growth of lenticular and rosette gypsum, and nodular anhydrite. In small saline pans, halite precipitates form rafts, chevrons and cornets. The salinity (TDS) of the groundwater in the sabkha area is highly variable, and ranges from 12,900 to 495,000 mg/l, compared to the average value of the Red Sea water of 40,366 mg/l. The low salinity values of the sabkha brines are most probably caused by localized influx of groundwater of meteoric origin from direct rain fall and/or temporary floods, in addition to seepage of sewage water from septic tanks. The electric conductivity (EC) values range from 20,000 to 199,100 µS/cm which are conformable to the salinity values of the brine. The dominant cation concentration order in seawater and brines of the sabkha is Na+ > Mg2+ > Ca2+ > K+, or Na+ > Mg2+ > K+ > Ca2+. The dominant anion concentration order is Cl− > SO4 2− > HCO3 −. The dominant brine type for most samples is sodium chloride, with variable proportions of the major cations Ca2+ and Mg2+ and the major anion SO4 2−. Most brine samples indicate their source is of modified marine water having an elevated CaCl2 content, which may be derived from dissolution of mixed salt from the Miocene salt dome in Jizan area. The chemical composition and origin of the brines, and mineralogy and textures of the evaporite minerals in Jizan sabkha help in understanding the nature of the corrosive factors to the foundations in Jizan area.

Serpentinization, element transfer, and the progressive development of zoning in veins: evidence from a partially serpentinized harzburgite

Serpentinization is an important geochemical process that affects the chemistry and petrophysical properties of the oceanic lithosphere and supports life through abiogenic formation of hydrogen. Here, we document through detailed mineralogical evidence and equilibrium thermodynamic models the importance of water (H2O) and silica (SiO2) activities on mineral assemblages produced during progressive serpentinization of a harzburgite. We describe a harzburgite from the Santa Elena Ophiolite in Costa Rica that is ~30 % serpentinized. Serpentine + brucite ± magnetite veins occur in olivine, Al-rich serpentine + talc veins occur in orthopyroxene, and Al-rich serpentine ± talc ± brucite veins occur at the boundary of orthopyroxene and olivine. Bulk vein chemistry and element distribution maps demonstrate distinct chemical zonations within veins and chemical gradients between orthopyroxene- and olivine-dominated areas. Specifically, the sample records (1) varying brucite composition depending on whether or not it is associated with magnetite, (2) formation of magnetite from Fe-rich brucite (±Fe-rich serpentine) during olivine hydration, where magnetite coexists with brucite Mg#96 and serpentine Mg#99, (3) chemical gradients in Si, Al, Cr, and Ca within and between orthopyroxene- and olivine-hosted veins, and 4) local (different) equilibrium assemblages within different zones of veins. The studied sample preserves rarely observed textures documenting continuous replacement of olivine, rather than individual vein generations and overprinting that is typically observed in more intensely serpentinized peridotites. Furthermore, the presence of a discrete sequence of vein textures and mineralogy allows direct comparison between mineral textures and equilibrium thermodynamic models and permits new insights into mineral reactions during serpentinization.

Mineralogy, geochemistry, and geotectonic significance of the Neoproterozoic ophiolite of Wadi Arais area, south Eastern Desert, Egypt

ABSTRACTThe dismembered ophiolites in Wadi Arais area of the south Eastern Desert of Egypt are one of a series of Neoproterozoic ophiolites found within the Arabian–Nubian Shield (ANS). We present new major, trace, and rare earth element analyses and mineral composition data from samples of the Wadi Arais ophiolitic rocks with the goal of constraining their geotectonic setting. The suite includes serpentinized ultramafics (mantle section) and greenschist facies metagabbros (crustal section). The major and trace element characteristics of the metagabbro unit show a tholeiitic to calc-alkaline affinity. The serpentinized ultramafics display a bastite, or less commonly mesh, texture of serpentine minerals reflecting harzburgite and dunite protoliths, and unaltered relics of olivine, orthopyroxene, clinopyroxene, and chrome spinel can be found. Bulk-rock chemistry confirms harzburgite as the main protolith. The high Mg# (91.93–93.15) and low Al2O3/SiO2 ratios (0.01–0.02) of the serpentinized peridotite, together with the high Cr# (>0.6) of their Cr-spinels and the high NiO contents (0.39–0.49 wt.%) of their olivines, are consistent with residual mantle rocks that experienced high degrees of partial melt extraction. The high Cr# and low TiO2 contents (0.02–0.34 wt.%) of the Cr-spinels are most consistent with modern highly refractory fore-arc peridtotites and suggest that these rocks probably developed in a supra-subduction zone environment.

A mineralogical investigation of the Late Permian Doba gabbro, southern Chad: Constraints on the parental magma conditions and composition

The late Permian Doba (257 ± 1 Ma) gabbro was discovered at the base of an exploration well through the Cretaceous Doba Basin of Southern Chad. The gabbro is at least 250 m thick, has cumulus mineral textures and consists of plagioclase, clinopyroxene, orthopyroxene, Fe–Ti oxide, apatite and quartz. The composition of the silicate minerals (i.e. plagioclase, pyroxenes) from the lowest part of the intrusion tend to be more primitive (i.e. An59, Wo40-44En33-47Fs12-25) than the upper part (i.e. An41, Wo39-43En30-44Fs14-29) suggesting the magmatic system differentiated internally by crystal fractionation and crystal redistribution. Based on the chemistry of the pyroxenes, the parental magma was compositionally similar to a Ti-rich, within-plate continental tholeiite that had a bulk Mg# of ∼44. The relative oxidation state of the magma was initially moderately reducing (i.e. ΔFMQ-0.3) and then became more reducing after a period of fractionation (i.e. ΔFMQ-1.2). The estimated initial magma temperature was at least 1100 °C. The within-plate composition suggests there was rifting-related magmatism near the boundary of the Saharan Metacraton that could be related to edge-driven mantle convection.

Role of the texture of fibrous clay minerals in the plasticity behavior of host materials (Plateau du Kik, Western High Atlas, Morocco)

Seven samples (MB2 to MB8) collected from the clays and silty clays formations belonging to the Paleogene sedimentary series of the Plateau du Kik (Western High Atlas, Morocco) were characterized for granulometric analysis, mineral composition, clay composition and textures and for Atterberg limits. All the studied samples are classified as MH–OH type soils according to the ASTM international standard. Palygorskite usually constitutes the more abundant mineral phase in all the samples (35 to 64). The liquid limit for the most samples is well above 50 indicating the highly plastic nature of the studied sediment. This work clearly evidences that fibrous clay rich clayey materials having similar grain distribution and identical mineral composition and contents can have very different plasticity behaviors. This suggests that the fibrous clay textures play a role of prime importance in the plasticity behavior of the studied materials.

Magma emplacement, differentiation and cooling in the middle crust: Integrated zircon geochronological–geochemical constraints from the Bergell Intrusion, Central Alps

U–Th–Pb zircon geochronology is an essential tool for quantifying the emplacement, differentiation and thermal evolution of crustal magmatic systems. However, the power of U–Pb zircon dates can be enhanced through complementary characterization of mineral texture and geochemistry, as this permits more detailed interpretations of geochronological datasets than conventionally achieved. Our approach to better relating zircon dates and geological processes consists of a multi-method analytical workflow, including cathodoluminescence imaging (CL), in situ LA-ICPMS/EPMA zircon geochemistry, U–Pb zircon ID-TIMS geochronology, and solution ICPMS zircon Trace Element Analysis (U–Pb TIMS-TEA). These methods are here applied to zircon from the Bergell Intrusion, a composite Alpine pluton preserving a ~10km mid-crustal transect. Hand samples of tonalite, granodiorite and hybridized granitoid each record 250–700kyr of autocrystic zircon growth. Bergell zircons are ubiquitously zoned with ca. 104–106yr growth histories, as evidenced by ID-TIMS analysis of microsampled fragments from single crystals. U–Pb TIMS-TEA data exhibit compositional trends on multiple spatiotemporal scales, including the handsample-scale, representing in situ differentiation at the emplacement level (e.g., Th/U); lithology-scale, defining trajectories corresponding to the production of tonalitic versus granodioritic magmas (Lu/Hf); and pluton-scale, indicating increasingly-evolved melts over ~1.6Myr of pluton assembly (Zr/Hf). These absolute TIMS-TEA temporal trends are corroborated by relative LA-ICPMS/EPMA core-to-rim geochemistry. We compare records of trace element evolution from TIMS-TEA, Bergell whole-rock geochemistry, and a global compilation of whole-rock geochemical data. These findings support zircon compositional evolution as a robust indicator of differentiation at local and crustal scales, and provide key empirical constraints on melt differentiation and cooling timescales in the middle crust.

CO2 sequestration utilizing basic-oxygen furnace slag: Controlling factors, reaction mechanisms and V–Cr concerns

Basic-oxygen furnace slag (BOF-slag) contains >35% CaO, a potential component for CO2 sequestration. In this study, slag–water–CO2 reaction experiments were conducted with the longest reaction duration extending to 96hr under high CO2 pressures of 100–300kg/cm2 to optimize BOF-slag carbonation conditions, to address carbonation mechanisms, and to evaluate the extents of V and Cr release from slag carbonation. The slag carbonation degree generally reached the maximum values after 24hr slag–water–CO2 reaction and was controlled by slag particle size and reaction temperature. The maximum carbonation degree of 71% was produced from the experiment using fine slag of ≤0.5mm under 100°C and a CO2 pressure of 250kg/cm2 with a water/slag ratio of 5. Vanadium release from the slag to water was significantly enhanced (generally >2 orders) by slag carbonation. In contrast, slag carbonation did not promote chromium release until the reaction duration exceeded 24hr. However, the water chromium content was generally at least an order lower than the vanadium concentration, which decreased when the reaction duration exceeded 24hr. Therefore, long reaction durations of 48–96hr are proposed to reduce environmental impacts while keeping high carbonation degrees. Mineral textures and water compositions indicated that Mg-wüstite, in addition to CaO-containing minerals, can also be carbonated. Consequently, the conventional expression that only considered carbonation of the CaO-containing minerals undervalued the CO2 sequestration capability of the BOF-slag by ~20%. Therefore, the BOF-slag is a better CO2 storage medium than that previously recognized.