Ca-rich Minerals Research Articles

Supplementing Low-Sodium Bicarbonate-Calcic (Lete)® Water: Effects in Women on Bone and Systemic Metabolism.

Calcium (Ca) represents about 40% of the total mineral mass, mainly in the bone, providing mechanical strength to the skeleton and teeth. An adequate Ca intake is necessary for bone growth and development in children and adolescents and for maintaining bone mineral loss in elderly age. Ca deficiency predisposes to osteopenia and osteoporosis. Healthy nutrition, including an adequate intake of Ca-rich food, is paramount to prevent and cure osteoporosis. Recently, several clinical studies have demonstrated that, in conditions of Ca dysmetabolism, Ca-rich mineral water is beneficial as a valuable source of Ca to be used as an alternative to caloric Ca-rich dairy products. Although promising, these data have been collected from small groups of participants. Moreover, they mainly regard the effect of Ca-rich mineral water on bone metabolism. In contrast, an investigation of the effect of Ca supplementation on systemic metabolism is needed to address the spreading of systemic metabolic dysfunction often associated with Ca dysmetabolism. In the present study, we analyzed urine and blood sera of 120 women in perimenopausal condition who were subjected for six months to 2l daily consumption of bicarbonate-calcium mineral water marketed under ®Lete. Remarkably, this water, in addition to being rich in calcium and bicarbonate, is also low in sodium. A complete set of laboratory tests was carried out to investigate whether the specific water composition was such to confirm the known therapeutic effects on bone metabolism. Second, but not least, urine and blood sera were analyzed using NMR-based metabolomic procedures to investigate, other than the action on Ca metabolism, potential system-wide metabolic effects. Our data show that Lete water is a valid supplement for compensating for Ca dysmetabolism and preserving bone health and integrity.

Investigating weathering signatures in terrestrial muds: Can climatic signatures be separated from provenance?

Siliciclastic muds (clay- and silt-sized sediment) concentrate physical and chemical weathering products. However, both rock composition and climate can affect the mineralogy and geochemistry of these sediments. We quantitatively assessed the influence of provenance and climate on muds collected from end-member climates to test, which, if any, of these potential weathering signatures are indicative of climate in fine-grained, fluvial sediments. Granulometry, mineralogy, and geochemistry of the studied muds indicated that provenance and mineral sorting hinder interpretation of (paleo)climate signals. These issues also affect chemical index of alteration (CIA) values, as well as mafic-felsic-weathering (MFW), Al2O3−(CaO* + Na2O)−K2O (A-CN-K), and Al2O3−(CaO* + Na2O + K2O)−(FeOT + MgO) (A-CNK-FM) ternary plots, decreasing their utility as paleoclimate proxies. CaO content is heavily weighted within the calculations, resulting in even felsic-sourced sediment commonly plotting as mafic owing to the relative enrichment in CaO from preferential sorting of Ca-rich minerals into the mud-sized fraction during transport. These results cast doubt on the indiscriminate use of CIA values and ternary plots for interpreting chemical weathering and paleoclimate within muds, particularly from glacial systems. Most notably, the positive correlations between CIA and climatic parameters (mean annual temperature and mean annual precipitation) diminished when sediments that had formed in nonglacial settings were filtered out from the data sets. This implies that CIA may only be applicable when used in nonglacial systems in which the composition of the primary source material is well constrained—such as soil/paleosol profiles. Within this end-member climate data set, CIA was only useful in discriminating hot-humid climates.

Retention of trivalent actinides (Am, Cm) and lanthanides (Eu) by Ca feldspars

Abstract. The transport of radionuclides in the environment is a major problem for the safety assessment of radioactive waste repositories. Storage in deep geological repositories is considered a safe disposal strategy because of their ability to isolate hazardous components from the biosphere for hundreds of thousands of years. Minor actinides (i.e. Am, Cm and Np) dominate the radiotoxicity of spent nuclear fuel over geological timescales. In underground repositories, reducing conditions are expected, and therefore the trivalent oxidation state is dominant for Am and Cm as well as possibly for Pu. For investigations of the mobility of the trivalent actinides Am3+ and Cm3+, the less toxic trivalent rare earth elements, in particular Eu3+, are commonly used. Besides clay and salt, crystalline rock is considered a possible host rock for deep geological repositories. Crystalline rock (e.g. granite) consists mainly of quartz, mica and feldspar. The latter forms common aluminosilicates making up ∼60 vol. % of the earth's crust, but their sorption behaviour is not well understood, especially for the Ca-bearing members of the group. Here, we study the sorption of trivalent actinides and their rare earth element homologues on plagioclase which are Ca-bearing feldspars, quantitatively and mechanistically. Zeta potentials of various Ca feldspars show an unexpected increase at pH 4–7, which becomes more pronounced as the amount of Ca in the crystal lattice increases. This can be interpreted by assuming uptake of Al3+ and/or the precipitation of an Al phase, where Al originates from feldspar dissolution at different pH values. Nevertheless, only minor differences were found in the retention and surface speciation of Cm3+ on Ca and K feldspars (Neumann et al., 2021). Ca feldspar has a slightly higher potential to retain trivalent metal ions compared to K feldspar. An inner-sphere (IS) complex and its two hydrolysis forms have been identified on both minerals, but the hydrolysis of the IS complex is stronger in the Ca-rich mineral. A surface complexation model for Ca feldspar was developed by combining the batch sorption data and the spectroscopically identified surface complexes to describe the experimental data. These data will be the basis for the improvement of transport simulations for a reliable safety assessment of potential radioactive waste repositories in crystalline rock.

Assessment of Hydrogeochemical Characteristics and Seawater Intrusion in Coastal Aquifers by Integrating Statistical and Graphical Techniques: Quaternary Aquifer, West Nile Delta, Egypt

The Quaternary aquifer in the western Nile Delta is threatened by seawater intrusion. Few studies have integrated diverse techniques for the assessment of seawater intrusion in this aquifer. The present study aims to determine the geochemical processes and impact of seawater intrusion on this aquifer. To accomplish this investigation, the integration of hydrogeochemical, statistical, multivariate statistical, and graphical tools were implemented on 75 groundwater samples and 5 soil samples. The physicochemical variables were analyzed using hierarchical cluster analysis (HCA), saturation index (SI), ionic ratios, ionic relationships, the seawater intrusion index (SWI) and the correlations among 16 hydrochemical parameters, to identify the influencing processes of groundwater quality in the study area. According to the statistical study, the groundwater is divided into four groups. Those are distributed, from north to south: Group1 (G1), Group2 (G2), Group4 (G4), and Group3 (G3). The samples of G1 and G2 are distinguished by Na–Cl chemical type. While G4 has two main ion associations, HCO3–Ca–Mg and Cl–SO4–Na, G3 is characterized by HCO3–Cl–SO4–Ca–Na type. The processes that affect the chemistry of the groundwater are the seawater intrusion, ion exchange, silicate and Ca-rich mineral weathering, and mineral deposition. G1 and G2 groups are primarily influenced by seawater incursion, evaporation, and the ion exchange mechanism. In addition, the weathering of silicate minerals has a substantial effect on G3 and G4 groups, resulting in the creation of carbonate minerals.

Rodingites in the Darbut Ophiolitic Mélange, West Junggar: New Insights into Rodingitization and Tectonic Evolution

The Darbut ophiolitic mélange is located in the central West Junggar area, southwestern Central Asian Orogenic Belt (CAOB), and rodingites are widespread within serpentinized peridotites in the mélange. Here, we conducted field, structural, mineralogical, and geochemical investigations of the Darbut rodingites for the first time to constrain their metasomatic processes. Rodingites usually occur as strongly sheared blocks surrounded by chloritic blackwall, and their preferred axial surface orientations are subparallel to the serpentinite foliations. Based on the petrology and geochemistry of these metasomatic rocks, two stages of metasomatic processes, namely rodingitization and derodingitization, were recognized: (1) rodingitization of gabbroic protolith was characterized by the input of Ca and the release of Si, K, Na, and LILE; this stage was related to the diapiric emplacement of the Darbut ophiolitic mélange in the Late Carboniferous; and (2) derodingitization of rodingites led to the replacement of Ca-rich minerals by chlorite, accompanied by Mg increase, and depletions of Ca and REE; the derodingitization stage occurred under enhanced CO2/H2O ratio conditions and was likely associated with regional postcollision volcanism in the Early Permian. Hence, the rodingite in the Darbut ophiolitic mélange provides important fingerprints recording the tectonic evolution.

Co-genetic formation of scheelite- and wolframite-bearing quartz veins in the Chuankou W deposit, South China: Evidence from individual fluid inclusion and wall-rock alteration analysis

The large-scale Chuankou W deposit is located in the north part of the Nanling metallogenic belt, South China. It comprises independent quartz vein-type scheelite and wolframite mineralization, both associated with the underlying granitic intrusion spatially. The scheelite-bearing quartz veins occur invariably in sandstone and slate to the west, whereas the wolframite-bearing quartz veins are mainly hosted by the granite to the east. To reveal the fluid characteristics of the two mineralizing vein systems, detailed petrography, microthermometry, and Raman spectroscopic analyses were carried out on fluid inclusions in scheelite, wolframite and their coexisting quartz. Major and trace element concentrations of fluids were obtained from individual fluid inclusions in quartz via LA-ICP-MS analysis. Wall-rock alteration of both vein systems were evaluated by TESCAN Integrated Mineral Analyser (TIMA) analysis, and based on which the bulk geochemical data of wall-rock as a function of distance from the vein were obtained for scheelite-bearing quartz vein. These data aid elucidation on the nature of fluids in the two types of W mineralization. Fluid inclusions in quartz and its coexisting tungsten minerals share similar homogenization temperature and salinity, suggesting near concurrent formation of quartz and ore minerals. LA-ICP-MS analyses on pseudosecondary fluid inclusions in quartz associated with ore minerals show considerable concentrations of W in both mineralizing fluids, whereas Fe, Mn and Ca are generally absent irrespective of their higher detection limits. This may imply that Ca, Fe, and Mn were not initially derived from the granitic magma. The fluid compositions of both types of W mineralization display similar Rb/Na, K/Na, and Rb/Cs ratios, indicating a similar initial fluid source. The TIMA image shows that the host rock (sandstone) of scheelite-bearing quartz vein contains abundant Ca-rich minerals, such as apatite and calcium feldspar, indicating wall-rock as potential source providing Ca for the precipitation of scheelite. This assumption is strongly supported by bulk geochemical data of wall rock as a function of distance from hydrothermal quartz vein. In contrast, the tourmaline-rich granite hosting wolframite quartz veins may be a potential source of Fe for the precipitation of wolframite. Study on fluid composition combined with wall rock alteration suggest that the magmatic-sourced fluids and fluid–wall-rock interactions exerted primary control on the large-scale variations in mineralization types in the deposit, with scheelite- and wolframite-bearing quartz veins being both genetically and spatially related. Results of this study provide new guidelines for mineral exploration, suggesting a homologous scheelite-dominated deposit being likely to exist in association with a wolframite-dominated deposit, where the lithology of Ca-bearing formations may indicate potential prospecting areas.

Measurement and modeling of heavy metal behaviors during the incineration of RDF in a pilot-scale kiln incinerator–Part 2: Incineration test

This paper is part of the studies that examine the performance of multizonal thermodynamic equilibrium calculation applied to waste incineration, and the primary objective was to obtain experimental data on the fate of elements in a waste incinerator under a controlled condition for comparison with the results of the calculation. We conducted an incineration test of refuse dried fuel (RDF) made from municipal solid waste (MSW) using a pilot-scale kiln incinerator, which enables us to control the combustion condition and reduce the fluctuation of the waste composition during the incineration test. The second objective was to obtain the fundamental characteristics of RDF incineration residues, as there was limited information about RDF incineration in the literature. The incineration residues obtained had uniform appearance, and the recovery ratios of total ash and individual elements were around 100%, which is suitable for use in the checking of the performance of the calculations. The elemental and mineralogical composition of the RDF incineration residues was analyzed. The fate of elements in the RDF incinerations was similar to those of ordinary MSW incinerations in the literature, whereas the RDF ash contained more Ca-rich minerals than MSW, reflecting the composition of the RDF.

Ash deposition mechanism of shoe manufacturing waste combustion in a full-scale CFB boiler

China is the largest shoe production country and the disposal of large amounts of shoe manufacturing waste (SMW) has become a rising problem. Incineration is regarded as a promising route for the utilization of SMW, since there exist considerable amounts of carbonaceous compounds in SMW. However, there are still some challenges for SMW incineration plant, such as corrosion, ash deposition, and pollution issues. This work investigated the ash deposition behavior in a full-scale SMW CFB boiler with 576 t/d treatment capability. Results suggest that submicron particles and uncooled inorganic vapors are the deposit precursors during initial deposition stage, and they are normally rich in alkali chlorides. Therefore, inner ash deposit layer contains a high concentration of alkali chlorides, even though alkali content in original fuel is negligible. The alkali chlorides in initial deposits can further aggravate tube surface corrosion and cause Fe enrichment in the initial layer. In contrast with inner layer deposits, the outer deposit layer shows relatively uniform characteristics and is mainly composed of Ca-rich minerals since raw ash in SMW is dominated by CaO. Overall, the ash deposition rate in SMW combustion is fairly high compared to other solid waste and biomass, and the deposition propensity increases when the flue gas temperature increases. The ash deposits are observed to have high compressive strength and hard to be removed through soot-blowing during operation. This work sheds the light on the ash deposition behavior of SMW during circulating fluidized bed combustion, which facilitates the design and optimization of industrial boilers.

Influence of lime, calcium silicate and portlandite on alkali activation of calcined common clays

The application of calcite rich common clays has marked impact on the formation of alkali-activated binders. Experiments have shown that the carbonate decomposition can be well controlled via the calcination procedure, whereby the majority of the decomposition and the subsequent CO2 release occurs above the calcination temperature of 750 ​°C. The decarbonation of the calcite can mostly be separated from the dehydroxylation of the layered silicates. Depending on the composition of the raw clay material, the CaCO3 decomposition leads either to the formation of lime or other Ca rich minerals. The mechanical properties of the alkali-activated binders were investigated and despite the very low amounts of layered silicates of the clay raw materials and the high content of unreactive minerals, compressive strengths of above 20 ​MPa of the mortars could be obtained. The presence of lime in calcined clays up to an adequate amount has a positive effect on post-solidification and the carbonation resistance of the mortars.

Genesis of the volcanic-related Be-U-Mo Baiyanghe deposit, West Junggar (NW China), constrained by mineralogical, trace element and U-Pb isotope signatures of the primary U mineralisation

The Volcanic-related Be-U-Mo Baiyanghe deposit is located in the Paleozoic Xuemisitan Volcanic Belt in West Junggar (NW China). It is the largest Be deposit in Asia which is dominantly hosted in late Devonian rhyolitic tuff and in the late Carboniferous Yangzhuang granite (313 ± 2 Ma) that were emplaced after the closure of the Junggar oceanic domain. The late Devonian rhyolitic tuff is a strongly fractionated peralkaline A1-type volcanic rock with a major magmatic enrichment in Nb, Y, Th, Be, Ta and U. Highly fractionated REE patterns and significant concentrations of Pb, Nb, Zr, Y, Th and Ta in the primary U mineralisation identified these tuffs as the dominant U and probably Be source for Be-U ore genesis in West Junggar. The primary high U concentrations (6.5 < Umean < 15.0 ppm) were released through volcanic glass devitrification and mobilised by oxidising fluids for the formation of hydrothermal mineralisation. The Yangzhuang granite is to the contrary a moderately fractionated moderate- to high-K calc-alkaline A2-type granite characterised by low magmatic U and Be enrichment (Umean = 2.9 ppm; Bemean = 4.7 ppm), and thus constituted a minor U source for the mineralisation as demonstrated by U release and remobilisation from metamict U-bearing accessory minerals.In the Baiyanghe deposit, structurally-controlled primary U mineralisation was temporally constrained by an in situ U-Pb isotopic minimum crystallisation age of 240 ± 7 Ma on pitchblende. This event represents the hydrothermal stage of U mineralisation that occurred during the early Permian–middle Triassic post-accretion event in West Junggar and paragenetically postdates the Be ore stage (ca. 303–265 Ma). The hydrothermal U mineralisation is mainly characterised by Pb-Nb-Ti-Zr-Mo-rich pitchblende veins associated with calcite and quartz, which crosscut Be-stage fluorite veins. During this episode of crustal extension, the Be-U-Mo ore therefore formed in a two-stage hydrothermal model within the same mineralising event: (i) oxidising meteoric and possibly basinal waters percolated downward into the basement through structures and mixed with CO2-bearing magmatic fluids derived from early generations of mafic dykes that intruded the host rocks in the Baiyanghe area. During the circulation of these thermal solutions along faults and fractured zones, Be was leached mainly from the Devonian rhyolitic tuff during hydrothermal alteration and dominantly transported as fluoride complexes in the fluids. These low-temperature (130–150 °C) ore solutions then reacted with Ca-rich minerals of the host rocks, which resulted in a pH increase that triggered fluorite precipitation in turn promoting Be deposition as bertrandite; and (ii) in a second stage, additional oxidising surface-derived fluids including meteoric waters and possibly basinal brines infiltrated the basement. U was also leached mainly from the late Devonian rhyolitic tuff and likely transported as chlorine and/or uranyl carbonate complexes in the fluids. U precipitated as pitchblende due to fO2 decrease when these low-temperature (120–125 °C) oxidising U-bearing solutions encountered favourable reducing environments mainly represented by dolerite and diabase dykes crosscutting the host rocks and/or carbonaceous shales at the contact with the Devonian rhyolitic tuff. Pitchblende then locally experienced dyke-emplacement related post-ore hydrothermal potassic alteration characterised by abundant illite crystallisation, significant Si gain and in situ relative enrichment of Nb, Ti, Th, and Ta due to strong U and Pb depletion. The primary U mineralisation was then largely oxidised into uranophane due to supergene alteration related to further meteoric water infiltration during late Mesozoic–Cenozoic crustal extension in West Junggar.The characteristics of the volcanic-related hydrothermal Be-U mineralisation in the Baiyanghe deposit show key similarities with Streltsovka (U-Mo-F) and Spor Mountain (Be-U) world-class districts, although Baiyanghe has much smaller resources than the ones in Streltsovka.

A Preliminary Study on the Roles of Fe Content and Neoformed Ca-rich Minerals in the Coloration of Ceramic Glazes

Iron oxides are the essential coloring oxides in traditional ceramic glazes. However, when Fe is involved in the coloration in the form of ions or colloids in glazes with low Fe content, it is difficult to identify the iron oxide phases. Generally, in many these glazes, Ca-rich minerals are observed by X-ray diffraction (XRD) or microscopic images, owing to their devitrification by the high Ca content. This study attempts to elucidate the correlation between the crystalline structure and coloration in the glazes while mainly focusing on neoformed Ca-rich minerals and Fe content. An experimental firing was carried out to produce tree ash glazes, with pine tree ash and Buyeo feldspar. In the case of oxidation glazes, the scanning electron microscopy (SEM) images and XRD patterns did not exhibit any Ca-rich crystals, and all the visible light reflectance spectra lines exhibited a similar shape. In contrast, the reduction glazes divided into blue glazes and other colored glazes according to the shapes of their reflectance spectra. It was confirmed that the influence of Ca-rich minerals on the glaze color was more pronounced than the blue color of the reduction glazes when the Ca and feldspar contents were sufficiently high and low, respectively, to form wollastonite. As the Ca content increased and the elemental composition of the reduction glazes changed, the neoformation of the Ca-rich minerals, such as wollastonite, anorthite, diopside, and akermanite was sequentially observed.

Structural Controls on Shallow Cenozoic Fluid Flow in the Otago Schist, New Zealand

The Otago Schist in the South Island of New Zealand represents an exhumed Mesozoic accretionary prism. Two coastal areas (Akatore Creek and Bruce Rocks) south of Dunedin preserve structural and geochemical evidence for the development of postmetamorphic hydrothermal systems that involved widespread fluid-rock reaction at shallow crustal depths. The Jurassic to Triassic pumpellyite-actinolite (Akatore Creek) to upper greenschist facies (Bruce Rocks) metamorphic fabrics were crosscut by sets of regionally extensive Cretaceous exhumation joints. Many of the joints were subsequently reactivated to form networks of small-displacement (&lt;metres) strike-slip faults containing cemented fault breccias and veins composed of hydrothermal calcite, siderite, and ankerite. Paleostress analysis performed on infrequent fault slickenlines indicates an overall strike-slip paleostress regime and a paleo-σ1 orientation (azimuth 094°) similar to the contemporary σ1 orientation in Otago and Canterbury (azimuth c. 110°-120°). High δ18O values in vein calcite (δ18OVPDB=21 to 28‰), together with the predominance of Type I calcite twins, suggest that vein formation occurred at low temperatures (&lt;200°C) in the shallow crust and was associated with strongly channelized fluid flow along the joint and fault networks. Mass-balance calculations performed on samples from carbonate alteration zones show that significant mobilisation of elements occurred during fluid flow and fluid-rock reaction. Whole-rock and in situ carbonate 87Sr/86Sr data indicate varying degrees of interaction between the hydrothermal fluids and the host rock schists. Fluids were likely derived from the breakdown of metamorphic Ca-rich mineral phases with low 87Rb in the host schists (e.g., epidote or calcite), as well as more radiogenic components such as mica. Overall, the field and geochemical data suggest that shallow fluid flow in the field areas was channelized along foliation surfaces, exhumation joints, and networks of brittle faults, and that these structures controlled the distribution of fluid-rock reactions and hydrothermal veins. The brittle fault networks and associated hydrothermal systems are interpreted to have formed after the onset of Early Miocene compression in the South Island and may represent the manifestation of fracturing and fluid flow associated with reverse reactivation of regional-scale faults such as the nearby Akatore Fault.

Paleotethys-related water-rocks interactions in gabbros of the Anarak ophiolite (Central Iran): constraints from mineralogy and geochemistry

The Anarak Paleozoic ophiolite with nearly east-west trend is located in the western part of the Central-East Iranian Microcontinent (CEIM). There are some leucocratic gabbros which are found as stocks and dykes and cross-cut the Anarak ophiolite. The studied gabbros are composed of clinopyroxene, amphibole, biotite, plagioclase, chlorite, epidote, garnet, sphene, apatite, prehnite, calcite, magnetite and ilmenite. Presence of a very high amount of hydrous minerals in the studied rocks reveal high activity of H 2 O in the involved fluids. Very low values of HREEs and light color of the studied gabbros indicate a non-peridotitic source rock. Geochemical features of the studied rocks indicate the melting of a mafic protolith. These hydrous phases are possible products of the reaction between oceanic crust and the fluids of seawater derivation, rich in calcium ingredients. Ingression of seawater through the oceanic crust and its downward penetration into the gabbros, caused the dissolution of a large amount of Ca and alkali components. At the lower, the Ca was added to the gabbro and produced new Ca-rich minerals. The Anarak samples show geochemical signatures of melts derived from a subducted oceanic slab. Distinct trace-element signatures, show the similarity of the studied gabbros to "adakite-like" rocks. According to the age and location of the studied gabbros, it is suggested that the primary magma of the studied gabbros should be created by partial melting of Paleo-Tethys subducting oceanic crust.

Trace and Rare Earth Elements Compositional Change on Andesite Alteration in Kaligesing, Purworejo

The change of chemical composition because of hydrothermal alteration process is related to the modification on mineralogy and elements mobility. Different alteration conditions could lead to dissimilar geochemical character. This study aims to discuss the alteration effect on trace and rare earth elements composition of an andesite outcrop with hydrothermal alteration in Kaligesing, Purworejo, Central Java Province. Microscopic analysis at Central for Geological Survey was applied to determine the modal mineral composition of the selected samples whilst trace and rare earth elements abundances was measured using Inductively Coupled Plasma – Mass Spectrometry. Plagioclase is the major phenocryst embedded in the fine-grained feldspar and glass groundmass of relatively fresh andesite. On the other hand, sericite, chlorite, epidote, and iron oxide are detected in the altered rock. The more Sr and Rb compositions on unaltered sample exhibit their common existence in plagioclase. The bigger Rb/Sr and the lower Ba/Sr ratios inward to the center of alteration might indicate the more degree of K-bearing mineral formation than Ca-rich mineral alteration. The Ba/Zr escalation and Zr/Y reduction from relatively fresh rock through to the vein of the studied samples are parallel to the previous investigation about andesite alteration. Chondrite-normalized rare-earth elements (REE) pattern of unaltered, altered, and vein samples depicts similar patterns: strong enrichment of Low REE, positive Eu anomaly, and relatively flat high REE. The decrease of Eu anomaly may reflect the reduction of plagioclase modal composition because of alteration and might indicate a reductive alteration state.Keywords: Alteration, andesite, geochemistry, trace and rare earth elements.

In-site mineral geochemistry and whole-rock Fe isotopes of the quartz-magnetite-pyroxene rocks in the Wuyang area, North China Craton: Constraints on the genesis of the pyroxene-rich BIF

Quartz-magnetite-pyroxene (QMP) rocks with high Fe contents are of greatly economic and petrological importance and generally occur within the oldest and largest exposures of supracrustal rocks preserved on Earth. However, the chemical composition and genesis of QMP rocks remain unclear. To constrain the protolith and genesis, we present new whole-rock geochemistry and Fe isotopic data, mineral EPMA and LA-ICP-MS analysis and X-ray mapping for the QMP rocks in the Wuyang area, North China Craton. The Wuyang QMP rocks have undergone high-temperature metamorphism and have special mineral assemblages with coexisting magnetite, quartz, clinopyroxene and variable orthopyroxene. Pyroxenes of the Wuyang QMP rocks show very distinct major, trace and rare earth element (REE) compositions from those of the nearby pyroxene-marbles and pyroxenite intrusions. Such difference excludes a contact metamorphic origin for pyroxenes of the QMP rocks. X-ray elemental mapping suggests that Fe-poor carbonate minerals (dolomite and calcite) and quartz inclusions are well preserved in these pyroxene grains and no reaction phenomenon can be observed between them, indicating that these pyroxenes are not the product of metamorphic decarbonation reactions of pre-existing sedimentary silica and Fe-rich carbonate phase. Shale-normalized REE + Y patterns of the whole-rock samples and pyroxenes display geochemical features consistent with classic banded iron formations (BIFs), which show light REE depletion, positive LaSN, EuSN and YSN anomalies. This indicates that the geochemical features are compositionally inherited from their original pure chemical sediments. The Wuyang QMP rocks are therefore considered as pyroxene-rich BIF. Neotocite and hisingerite inclusions in pyroxene grains from the QMP rocks could be metamorphic products of some early Fe- and Mn-rich silicates before pyroxene. Moreover, the Wuyang QMP rocks are enriched in light iron isotopes similar to other Fe- and Ca-rich minerals in Archean BIFs. Therefore, we inferred that pyroxene from the QMP rocks could result from dehydration of initial sedimentary hydrous Ca-, Mg- and Mn-containing Fe(II)-silicate gel during diagenesis and re-crystallization in later metamorphism, providing a new interpretation for the origin of pyroxene-rich BIF.

Initial subduction of Neo-Tethyan ocean: Geochemical records in chromite and mineral inclusions in the Pozantı-Karsantı ophiolite, southern Turkey

Chromitites in the Pozantı-Karsantı ophiolite in Turkey mainly occur as podiform chromitites within mantle harzburgite and stratiform-like chromitites in mantle-crust transition zone. Chromites in chromitites have varing Cr# from 62.8 to 80.3 and can be divided into two types, namely; intermediate (Cr#: 62.8 – 69.2) and high-Cr (Cr#: 73.9 – 80.3) types. Major elements of the high-Cr chromitite have an affinity with boninite, whereas the intermediate chromitite shows transitional features between MORB and boninite. The compositional differences in clinopyroxene inclusions between intermediate- and high-Cr chromitite, coupled with the relatively high trace element contents (e.g. V, Ga) in the high-Cr chromitite, indicate distinctive parental magmas. Trace elemental profile analysis of a nodular chromite grain in one nodular chromitite sample PK14-41 demonstrates significant but non-systematic variations from the core to the rim, which also confirmed the compositional heterogeneity of the parental magmas. The presence of primary hydrous mineral inclusions such as amphibole in chromite, together with Ca-rich minerals (e.g. calcite), reflect the water-rich and Ca-rich characteristics of the parental magma. The higher fO2 of high-Cr chromitite evidenced by the lower V/Mn values may be due to more oxidized fluids released from downgoing crustal materials. Thus, we conclude that the parental magmas of the Pozantı-Karsantı chromitite were derived from a proto-forearc mantle and evolved to higher fO2 with the subduction initiation at that time, but were water- and Ca-rich in general.

Origin of the high-temperature Olserum-Djupedal REE-phosphate mineralisation, SE Sweden: A unique contact metamorphic-hydrothermal system

The Swedish part of the Fennoscandian Shield hosts a variety of rare earth element (REE) deposits, including magmatic to magmatic-hydrothermal types. This paper focuses on the origin of the Olserum-Djupedal REE-phosphate mineralisation located in the sparsely studied Västervik region, SE Sweden. Here, mineralisation occurs in three main areas, Olserum, Djupedal and Bersummen. Primary hydrothermal REE mineralisation formed at high temperatures (about 600 °C), leading to precipitation of monazite-(Ce), xenotime-(Y), fluorapatite and minor (Y,REE,U,Fe)-(Nb,Ta)-oxides in veins and vein zones dominated by biotite, amphibole, magnetite and quartz. The veins are hosted primarily by metasedimentary rocks present close to, or within, the contact aureole of a local 1.8 Ga ferroan alkali feldspar granite pluton, but also occur within in the chemically most primitive granite in the outermost part of that pluton. In the Djupedal area, REE-mineralised metasedimentary bodies are extensively migmatised, with migmatisation post-dating the main stage of mineralisation. In the Olserum and Bersummen areas, the REE-bearing veins are cross-cut by abundant pegmatitic to granitic dykes. The field relationships demonstrate a protracted magmatic evolution of the granitic pluton and a clear spatial and temporal relationship of the REE mineralisation to the granite.The major and trace element chemistry of ore-associated biotite and magnetite support genetic links between all mineralised areas. Biotite mineral chemistry data further demonstrate a distinct chemical trend from metasediment-hosted ore-associated biotite distal to the major contact of the granite to the biotite in the granite-hosted veins. This trend is characterised by a systematic decrease in Mg and Na and a coupled increase in Fe and Ti with proximity to the granite-hosted veins. The halogen compositions of ore-associated biotite indicate elevated contents of HCl and HF in the primary REE mineralising fluid. Calculated log(fHF/fHCl) values in the Olserum area suggest a constant ratio of about −1 at temperatures of 650–550 °C during the evolution of the primary hydrothermal system. In the Djupedal and Bersummen areas, the fluid locally equilibrated at lower log(fHF/fHCl) values down to −2. High Na contents in ore-associated biotite and amphibole, and the abundance of primary ore-associated biotite indicate a K- and Na-rich character of the primary REE mineralising fluid and suggest initial high-temperature K-Na metasomatism. With subsequent cooling of the system, the fluid evolved locally to more Ca-rich compositions as indicated by the presence of the Ca-rich minerals allanite-(Ce) and uvitic tourmaline and by the significant calcic alteration of monazite-(Ce). The later Ca-rich stages were probably coeval with low to medium-high temperature (200–500 °C) Na-Ca metasomatism variably affecting the granite and the wall rocks, producing distinct white quartz-plagioclase rocks.All observations and data lead us to discard the prevailing model that the REE mineralisation in the Olserum-Djupedal district represents assimilated and remobilised former heavy mineral-rich beds. Instead, we propose that the primary REE mineralisation formed by granite-derived fluids enriched in REE and P that were expelled early during the evolution of a local granitic pluton. The REE mineralisation developed primarily in the contact aureole of this granite and represents the product of a high temperature contact metamorphic-hydrothermal mineralising system. The REE mineralisation probably formed synchronously with K-Na and subsequent Na-Ca metasomatism affecting the granite and the wall rocks. The later Na-Ca metasomatic stage is probably related to a regional Na ± Ca metasomatic and associated U ± REE mineralising system operating concurrently with granitic magmatism at c. 1.8 Ga in the Västervik region. This highlights the potential for discovering hitherto unknown REE deposits and for the reappraisal of already known deposits in this part of the Fennoscandian Shield.

Impact of SO2 on Alteration of Reservoir Rock with Ca-Deficient Conditions and Poor Buffering Capacity under a CO2 Geologic Storage Condition

The objective of this study is to evaluate the impact of SO2-CO2-water-rock interaction on the alteration of a reservoir rock having Ca-deficient conditions and little buffering capacity and its implication for porosity change near the injection well from a CO2 storage pilot site, Republic of Korea. For our study, three cases of experimental and geochemical modeling were carried out (pure CO2, 0.1% SO2 in CO2, and 1% SO2 in CO2, resp.) under realistic geologic storage conditions. Our results show that SO2 accelerated water-rock interactions by lowering the pH. In the 1% SO2 case, pH remained less than 2 during the experiments because of insufficient buffering capacity. Sulfate minerals were not precipitated because of an insufficient supply of Ca. Because the total volume of precipitated secondary minerals was less than that of the dissolved primary minerals, the porosity of rock increased in all cases. Chlorite largely contributed to the decrease in total rock volume although it formed only 4.8 wt.% of the rock. Our study shows that the coinjection of a certain amount of SO2 at CO2 storage reservoirs without carbonate and Ca-rich minerals can significantly increase the porosity by enhancing water-rock interactions. This procedure can be beneficial to CO2 injection under some conditions.

Advancements in cosmogenic 38Ar exposure dating of terrestrial rocks

Cosmogenic exposure dating of Ca-rich minerals using 38Ar on terrestrial rocks could be a valuable new dating tool to determine timescales of geological surface processes on Earth. Here, we show that advancement in analytical precision, using the new generation multi-collector ARGUSVI mass spectrometer on irradiated pyroxene and apatite samples, allows determination of cosmogenic 38Ar abundances above background values, as well as discrimination of 38Ar/36Ar ratios (1σ absolute precision of ±0.3%) from the non-cosmogenic background value. Four statistically significant cosmochron (38Ar/36Ar vs37Ar/36Ar) diagrams could be constructed for southeast Australian pyroxene samples from the Mt Elephant scoria cone for which a combined apparent exposure age of 313±179ka (2σ) was obtained when using a 38Ar production rate (Ca) of 250 atoms /g Ca/ yr. This exposure age overlaps within error with the known 40Ar/39Ar eruption age of 184±15ka (2σ). Although apatite shows much larger 38Ar abundances than pyroxene, our modelling and analyses of unirradiated apatite suggest that apatite suffers from both natural and reactor-derived chlorogenic as well as natural nucleogenic contributions of 38Ar. Hence, we suggest that cosmogenic 38Ar exposure dating on irradiated Ca-rich (and eventually K-rich), but Cl-free, terrestrial minerals is a potential valuable and accessible tool to determine geological surface processes on timescales of a few Ma. Calculations show that with the new generation multi-collector mass spectrometers an analytical uncertainty better than 5% (2σ) can be achieved on samples with expected exposure ages of >4Ma.

CO2-induced geochemical reactions in heterogeneous sandstone and potential conditions causing the tight cementation

The contribution of tight gas, stored in sandstone reservoirs, to hydrocarbon production has been increasing. However, the formation mechanisms of these tight sandstone reservoirs remain unclear and the conditions leading to them are not well-understood. It is generally thought that early CO2 emission may have caused the sandstones of the Permian Shihezi Formation in the Ordos Basin, China, to become tight. In this study, we quantitatively investigate the effects of CO2 intrusion on reservoir evolution, choosing three factors thought to dominate this process (i.e. detrital mineral assemblage, formation water, and intruded CO2 volume) for sensitivity analyses. We constructed eight two-dimensional models to investigate CO2-water-rock reactions and reservoir porosity changes under various conditions. Subsequent to determination of the potential conditions leading to the formation of tight reservoirs, we then constructed a three-dimensional model applying given heterogeneities in porosity (Φ), permeability (K), and mineral assemblages to evaluate porosity distribution. Results show that the processes underlying the formation of tight reservoirs are controlled by various factors rather than any single one. Reservoirs containing Ca-rich minerals (i.e. calcite and anorthite) and Ca2+-rich formation water are apt to become tight as a result of CO2 intrusion because of large-scale carbonate precipitation. In addition, under primary geological and geochemically heterogeneous conditions, CO2-water-rock reactions vary spatially, which further enhances reservoir heterogeneities. Although minerals are heterogeneously distributed, they exhibit some similar characteristics as their common ions link them. Results show that it is possible to predict both high-quality and tight reservoirs. In the study area, favorable reservoirs are found in regions with initially high Φ, high K, and high feldspar mineral contents, while regions that are characterized by low Φ and K as well as Ca2+-rich formation water and a high content of Ca-rich minerals tend to become tight after CO2 intrusion.