Fe-rich Minerals Research Articles

Rhizosphere modifications of iron-rich minerals and forms of heavy metals encapsulated in sulfidic tailings hardpan

Hardpan caps formed after extensive weathering of the top layer of sulfidic tailings have been advocated to serve as physical barriers separating reactive tailings in depth and root zones above. However, in a hardpan-based root zone reconstructed with the soil cover, roots growing into contact with hardpan surfaces may induce the transformation of Fe-rich minerals and release potentially toxic elements for plant uptake. For evaluating this potential risk, two representative native species, Turpentine bush (Acacia chisholmii, AC) and Red Flinders grass (Iseilema vaginiflorum, RF), of which pre-cultured root mats were interfaced with thin discs of crushed hardpan minerals in the rhizosphere (RHIZO) test. After 35 days, the surface dissolution of hardpan minerals occurred and Fe-rich cement minerals were transformed from ferrihydrite-like minerals to goethite-like and Fe(III)-carboxylic complexes, as revealed by scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS) and synchrotron-based X-ray absorption fine structure spectroscopy (XAFS) analysis. This transformation may result from the functions of root exudates. The transformation of hardpan cement minerals caused the co-dissolution of Cu and Zn initially encapsulated in the cements and their uptake by plants. Nevertheless, only was the minority of the plant Cu and Zn transported into shoots.

Recycling reduced iron at the base of magmatic orogens

The Earth's continental crust is thought to originate from melting of the mantle, but it is too felsic and depleted in Fe relative to a primary mantle melt. This depletion in Fe is also commonly found in continental arc magmas and is often attributed to magnetite crystallization. However, Fe depletion in arc magmas coincides with an enrichment in ferric Fe relative to ferrous Fe, which cannot be explained by removal of a ferric Fe-rich mineral like magnetite. Deep-seated garnet pyroxenite arc cumulates (arclogites) have Fe-rich compositions that complement the Fe-depleted nature of the continental crust and continental arc magmas, and are likely candidates for the “missing link” between basaltic mantle magmas and the felsic continental crust. To test this suggestion, we present high precision in-situ Fe valence data for garnets in arclogites and reconstruct whole rock Fe valence states. We show that arclogites have low bulk Fe3+/∑Fe due to the low Fe3+/∑Fe of garnets and the lack of magnetite. At high pressures, garnet crystallizes, but magnetite does not, the former causing preferential accumulation of ferrous Fe at the base of magmatic orogens. Arclogite fractionation thus leads to the formation of oxidized felsic residual liquids (Fe3+/∑Fe of 0.2-0.4). Such oxidation may profoundly influence the speciation of magmatic volatiles as well as the oxidative weathering capacity of the crust.

Magnetic and radar surveys at Locri Epizephyrii: A comparison between expectations from geophysical prospecting and actual archaeological findings

Abstract In recent years, geophysical methods have been increasingly applied as a preliminary mapping tool to guide archaeological excavations. Despite the reported growing case histories of geophysical prospections for archaeological purposes, direct comparison between expectations arising from the geophysical results and actual findings is not always systematically performed. A critical comparison between pre-excavation geophysical-guided hypotheses and post-excavation archeological evidences is proposed in this work. A test site within the archaeological area of Locri Epizephyrii (Calabria, southern Italy) was chosen for this purpose. An unsurveyed rectangular area (31 × 26 m) was investigated with high-density ground-penetrating radar (GPR) and magnetic profiles. Several anomalous alignments, both compatible and oblique with respect to the orientation of the Greek-Roman city plan, were preliminarly observed in the geophysical results. The use of two different techniques allowed for comparison of anomalous areas, enhancing the likelihood of finding features of significance. Two archaeological soundings were later carried out in the areas showing the most peculiar geophysical anomalies. Several structures revealing the same orientation of the ancient city plan and belonging to at least two different building phases were unearthed from a depth of 15–25 cm below the ground surface. A systematic comparison between geophysical and archeological results was then carried out. In general, walls showing different construction typologies (opus testaceum, opus incertum or opus caementicium) were found to generate similar radar anomalies. Artifacts made with materials similar to the background sandy alluvial deposits were not identified by both geophysical techniques, as in the case of an unearthed channel bank, made of local sandstone blocks. GPR was globally observed to detect buried structures better than the magnetic method, probably due to background geological variables linked to the presence of Fe-rich minerals within the background sediments, generating noisier and scattered magnetic gradient maps.

Thorium-poor monazite and columbite-(Fe) mineralization in the Gleibat Lafhouda carbonatite and its associated iron-oxide-apatite deposit of the Ouled Dlim Massif, South Morocco

Recent exploration work in South Morocco revealed the occurrence of several carbonatite bodies, including the Paleoproterozoic Gleibat Lafhouda magnesiocarbonatite and its associated iron oxide mineralization, recognized here as iron-oxide-apatite (IOA) deposit type. The Gleibat Lafhouda intrusion is hosted by Archean gneiss and schist and not visibly associated with alkaline rocks. Metasomatized micaceous rocks occur locally at the margins of the carbonatite outcrop and were identified as glimmerite fenite type. Rare earth element (REE) and Nb mineralization is mainly linked to the associated IOA mineralization and is represented by monazite-(Ce) and columbite-(Fe) as major ore minerals. The IOA mineralization mainly consists of magnetite and hematite that usually contain large apatite crystals, quartz and some dolomite. Monazite-(Ce) is closely associated with fluorapatite and occurs as inclusions within the altered parts of apatite and along cracks or as separate phases near apatite. Monazite shows no zonation patterns and very low Th contents (<0.4 wt%), which would be beneficial for commercial extraction of the REE and which indicates monazite formation from apatite as a result of hydrothermal volatile-rich fluids. Similar monazite-apatite mineralization and chemistry also occurs at depth within the carbonatite, although the outcropping carbonatite is barren, suggesting an irregular REE ore distribution within the carbonatite body. The barren carbonatite contains some tiny unidentified secondary Nb-Ta-U phases, synchysite and monazite. Niobium mineralization is commonly represented by anhedral minerals of columbite-(Fe) which occur closely associated with magnetite-hematite and host up to 78 wt% Nb2O5, 7 wt% Ta2O5 and 1.6 wt% Sc2O3. This association may suggest that columbite-(Fe) precipitated by an interaction of Nb-rich fluids with pre-existing Fe-rich minerals or as pseudomorphs after pre-existing Nb minerals like pyrochlore. Our results most strongly suggest that the studied mineralization is economically important and warrants both, further research and exploration with the ultimate goal of mineral extraction.

Shallow-marine ironstones formed by microaerophilic iron-oxidizing bacteria in terminal Paleoproterozoic

The microbial origin of Precambrian iron formations is debated due to the lack of direct fossil evidence. In order to reveal the genesis of ironstones under low-oxygen levels, integrative studies of sedimentology, petrography, mineralogy, and geochemistry were conducted on the intertidal to shallow subtidal ooidal and stromatolitic ironstones from the terminal Paleoproterozoic Chuanlinggou Formation (ca. 1.65–1.64 Ga) of North China, using microscopy, SEM, EDS, ICP-OES, ICP-MS and MC-ICP-MS techniques. Mineralogical study shows that the Fe-rich mineral is predominantly hematite that resulted from dehydration of amorphous Fe-oxyhydroxide during diagenesis. Petrographic observation indicates that the iron was oxidized and precipitated from seawater rather than sourced from terrestrial detritus. Basinward increases of the ironstone abundance, Eu anomalies (from 1.39 to 1.56) and δ56Fe values of the ironstones (from +0.5‰ to +1.0‰) suggest that the iron was mainly sourced from seafloor hydrothermal fluids, and partially oxidized and precipitated in shallow subtidal to intertidal environments. The common existence of Fe-oxide coated sheaths, spiral stalks, residual extracellular polymer substances (EPS) and other biogenic fabrics indicates that microaerophilic iron-oxidizing bacteria (FeOB) may have played an important role in precipitating the Chuanlinggou ironstones. The extremely low oxygen concentrations implied by the proliferation of microaerophilic FeOB in the shallow waters, the weak positive Ce anomalies (0.94–1.12) and low Mn concentrations in the ironstones are broadly consistent with the previous result of a Cr isotope study. Thus the establishment of a microaerophilic FeOB genetic model for the widespread Chuanlinggou ironstones in North China provides new insight into the origin of Precambrian iron formations and the redox evolution of ocean-atmosphere systems during the “Boring Billion”.

Dissolution behaviour of radiocaesium-bearing microparticles released from the Fukushima nuclear plant

Radiocaesium-bearing microparticles (CsMPs) composed of silicate glass were released by the Fukushima Daiichi Nuclear Power Plant accident in March 2011. Since CsMPs contain a high concentration of radiocaesium, their dynamics and fate in the environment are urgent issues to be investigated. Here, we show that CsMPs are dissolved by weathering in the environment and that their radioactivity is more rapidly decreased by dissolution than the physical decay of radiocaesium. We conducted dissolution experiments with CsMPs in pure water that absorbed CO2 from the atmosphere and in artificial seawater at several temperatures. The dissolution progress was monitored by the decrease in the 137Cs radioactivity in CsMPs, and the dissolution rate was estimated. The activation energy for the dissolution of CsMPs was estimated to be 65 and 88 kJ/mol and the dissolution rate at 13 °C (approximate annual mean temperature in Fukushima City) was 0.014 and 0.140 μm/y for pure water and seawater, respectively, assuming that radiocaesium is uniformly distributed in spherical CsMPs. The shapes of the CsMPs dissolved in pure water were considerably altered, suggesting that the dissolution proceeded without maintaining the geometry. Tin oxide and iron oxide nanoparticulates formed on the surfaces. Such features were similar to those observed in CsMPs recently collected in Fukushima Prefecture, indicating that weathering dissolution of CsMPs is also occurring in the environment. For the CsMPs dissolved in seawater, a crust of secondary Mg- and Fe-rich minerals was formed, and the glass matrix inside the crust decreased, creating space between the crust and the glass matrix.

Calibration of the production rate of cosmogenic 36Cl from Fe

Abstract We present a new calibration of the in-situ production rate of cosmogenic 36Cl from Fe with the aim of enabling the use of Fe-oxides and other Fe-rich minerals as 36Cl target materials. The calibration was conducted using magnetite mineral separates from rocks with well-constrained exposure histories, including late-Pleistocene glacial erratic boulders from the Sierra Nevada, California, USA and samples from a slowly eroding ridgetop in the Quadrilatero Ferrifero, Minas Gerais, Brazil. At both sites the 36Cl production rate from Fe was calibrated against the production rate of 10Be in co-occurring quartz, while in the Sierra Nevada the calibration was also conducted against 14C-based deglaciation ages. The data produce a mean 36ClFe to 10BeQtz production ratio of 0.417 ± 0.010 at the calibration sites. This ratio may depend on altitude and latitude. A reaction-specific scaling model predicts that the calibrated ratio scales to a reference value at sea level and high latitude of 0.326 ± 0.008. When considering uncertainties in reference 10Be production rate, this is equivalent to a sea level and high latitude production rate of 1.28 ± 0.11 atoms g Fe−1 yr−1. Additional data are needed to confirm the scaling behavior.

Mineralogy, solid-phase fractionation and chemical extraction to assess the mobility and availability of arsenic in an urban environment

A multi-disciplinary approach, using chemical extraction and analytical structural techniques, has been used to assess the mobility and availability of arsenic in urban soil samples from two current housing sites. Arsenic concentrations in each site varied between 126 and 1660 mg/kg (Site A) and 40–24,900 mg/kg (Site B). Using a non-specific sequential extraction approach, it was possible to identify two distinct, site specific, As-containing fractions i.e. Fe-As-Ca (Site A) and As-Fe (Site B), in the soils. Further investigation using a sequential extraction approach identified the main As component in the reducible fraction, linking As with Fe-oxides in the soils. Further investigation of the crystalline mineral phases, by X-ray diffraction, within the most As-contaminated soils (up to 24,000 mg/kg) identified no As-bearing minerals but identified the major component as quartz (SiO2) with an array of minor and trace minerals. Further mineralogical investigation, using micro-Raman in the major As-contaminated soils (from Site B) as well as re-confirming the presence of the major mineral (quartz) additionally identified the As-bearing minerals pharmacosiderite (KFe4[(H2O)4(AsO4)3].6H2O) and mimetite (Pb5(AsO4)3Cl) in the trace mineral component, alongside amorphous carbon, chromite (FeCr2O4), goethite (α-FeO(OH)), gypsum (CaSO4.H2O), muscovite (KAl2(AlSi3O10)(F,OH)2), magnetite (Fe3O4), martite (α-Fe2O3), psilomelane (Ba,H2O)2Mn5O10), pyrrhotite (Fe7S8) and rutile (TiO2). The identification and presence of several Fe-rich minerals could be considered as the major hosts of As in the soil matrix. It is concluded that while the soil contains elevated levels of As, it's lack of mobility in the soil, means that minimal remedial action is required provided the sites are left undisturbed and free of human endeavour and activity.

Performance Analysis of Local Pekanbaru Bentonite for Reactive Solid Application of Mud Drilling

In oil and gas drilling activities, drilling mud is one of the most important commodities. The main mineral used as a reactive solid that works to suck fresh water and form drilling mud is bentonite. Bentonite which is used as a drilling mud in the market is mostly imported from the United States. In Indonesia there are several areas that have enough potential for bentonite minerals, namely Java, Sumatra, parts of Kalimantan and Sulawesi with reserves estimated to be more than 380 million tons. (Riyanto A, 1994). This study uses bentonite in Kulim area, Tenayan Raya City, Pekanbaru, in hopes of providing useful information input, especially in the use of bentonite minerals in drilling mud. Using local bentonite the price is cheaper and more efficient.&#x0D; The object observed was the effect and number of bentonite mixed with fresh water so that the rheological properties of drilling mud such as viscosity, gel strength, mud cake and filtration loss were obtained and would be in accordance with API specification 13A standards. Whereas to find out the composition and structure of local mineral clay, SEM and EDX analyzes were performed to determine the characteristics and composition of these minerals. From these tests add additives NaCO3 and NaOH as ion exchangers and add the element Na to the sludge.&#x0D; From SEM and EDX analysis, two samples taken in central Sumatra Sumatra can be categorized as clay Illite fe-rich and Clay Illite Platty. Rheological testing of drilling mud and chemical composition analysis of clay Illite fe-rich minerals and Clay Illite Platty in Riau, Central Sumatra and with the addition of additives NaCO3 and NaOH to local Clay, Rheology in mud based on Clay Illite Platty is obtained with Bentonite. commonly used as a basic material for the manufacture of oil and gas drilling mud with API Spec13 A.

Mobility and natural attenuation of metals and arsenic in acidic waters of the drainage system of Timok River from Bor copper mines (Serbia) to Danube River.

Bor, Krivelj, and Bela Rivers belong to the watershed of Timok River, which is a tributary of transboundary Danube River. These rivers receive metal-rich acidic wastewater from metallurgical facilities and acid mine drainage (AMD) from mine wastes around Bor copper mines. The aim of this study was to determine the mobility and natural attenuation of metals and arsenic in rivers from Bor copper mines to Danube River during the year 2015. The results showed that metallurgical facilities had the largest impact on Bor River by discharging about 400t of Cu per year through highly acidic wastewater (pH = 2.6). The highest measured concentrations of Cu in river water and sediments were 40mgL-1 and 1.6%, respectively. Dissolution of calcite from limestone bedrock and a high concentration of bicarbonate ions in natural river water (about 250mgL-1) enhanced the neutralization of acidic river water and subsequent chemical precipitation of metals and arsenic. Decreases in the concentrations of Al, Fe, Cu, As, and Pb in river water were mainly due to precipitation on the river bed. On the other hand, dilution played an important role in the decreases in concentrations of Mn, Ni, Zn, and Cd. Chemically precipitated materials and flotation tailings containing Fe-rich minerals (fayalite, magnetite, and pyrite) were transported toward Danube River during the periods of high discharge. This study showed that processes of natural attenuation in catchments with limestone bedrock play an important role in reducing concentrations of metals and arsenic in AMD-bearing river water.

Radiative forcing by light-absorbing aerosols of pyrogenetic iron oxides

Iron (Fe) oxides in aerosols are known to absorb sun light and heat the atmosphere. However, the radiative forcing (RF) of light-absorbing aerosols of pyrogenetic Fe oxides is ignored in climate models. For the first time, we use a global chemical transport model and a radiative transfer model to estimate the RF by light-absorbing aerosols of pyrogenetic Fe oxides. The model results suggest that strongly absorbing Fe oxides (magnetite) contribute a RF that is about 10% of the RF due to black carbon (BC) over East Asia. The seasonal average of the RF due to dark Fe-rich mineral particles over East Asia (0.4–1.0 W m−2) is comparable to that over major biomass burning regions. This additional warming effect is amplified over polluted regions where the iron and steel industries have been recently developed. These findings may have important implications for the projection of the climate change, due to the rapid growth in energy consumption of the heavy industry in newly developing countries.

Magnetic susceptibility of Variscan granite-types of the Spanish Central System and the redox state of magma

Magnetic susceptibility (MS) has been measured in Variscan granites from central Spain. They yield values in the order of 15 to 180µSI units for S- and I-type granites, indicating that both types belong to the ilmenite series. Only samples from magnetite-bearing leucogranites from the I-type La Pedriza massif show high MS values, in the order of 500-1400µSI, reflecting the presence of this ferromagnetic mineral. Mineral chemistry of magmatic Fe-rich minerals (mainly biotite) suggests similar oxidation values for both granite types. MS values change in highly fractionated granites accordingly either with the presence of rare new Fe-oxide phases (some I-type leucogranites) or with the marked modal amount decrease of Fe-rich minerals (I- and S-type leucogranites). The redox state in highly fractionated granite melts is mostly controlled by magmatic processes that modify redox conditions inherited from the source region. Thus, the occurrence of magnetite or ilmenite in granites is primarily controlled by the oxidation state of the source material but also by the differentiation degree of the granite melt. The presence of magnetite in some Variscan I-type leucogranites might be a consequence of crystal fractionation processes in a more limited mafic mineral assemblage than in S-type granite melts.

Residues from the Upper Permian carnivore coprolites from Vyazniki in Russia - key questions in reconstruction of feeding habits

Residues of twenty-five coprolite fragments collected from the Upper Permian of Vyazniki (European Russia) were studied in detail. The phosphatic composition, general shape and size, and bone inclusions of these specimens indicate that medium to large-sized carnivores, such as therocephalian therapsids or early archosauriforms, were the most likely coprolite producers. The contents of the examined fossils (i.e. scale, bone and tooth fragments, mineral grains, and microbial structures) do not differ significantly among the samples, implying fairly comparable feeding habits of their producers. Fragments of large tooth crowns in two of the analyzed samples imply that either (1) the coprolite producer swallowed the cranial elements of its prey or (2) the coprolite producer broke and swallowed its own tooth while feeding (such tooth damage is known in archosaurs that have tooth replacement, e.g. crocodiles and dinosaurs). Indeed, the most complete tooth fragment in these fossils is serrated, most likely belonging to an early archosauriform known from skeletal records from the Late Permian of Vyazniki. Another coprolite fragment contains the etched tooth of a lungfish, while putative actinopterygian fish remains (scales and small fragments of bones) are abundant in some samples. Mineral particles (mostly quartz grains, feldspars and mica) may have been swallowed accidentally. The preserved microbial colonies (mineralized fossil fungi and bacteria or their pseudomorphs), manifested in the coprolites as Fe-rich mineral structures, seem to have developed on the expelled feces rather than on the items before they were swallowed.

Iron isotope fractionation in subduction-related high-pressure metabasites (Ile de Groix, France)

Characterisation of mass transfer during subduction is fundamental to understand the origin of compositional heterogeneities in the upper mantle. Fe isotopes were measured in high-pressure/low-temperature metabasites (blueschists, eclogites and retrograde greenschists) from the Ile de Groix (France), a Variscan high-pressure terrane, to determine if the subducted oceanic crust contributes to mantle Fe isotope heterogeneities. The metabasites have δ56Fe values of +0.16 to +0.33‰, which are heavier than typical values of MORB and OIB, indicating that their basaltic protolith derives from a heavy-Fe mantle source. The δ56Fe correlates well with Y/Nb and (La/Sm)PM ratios, which commonly fractionate during magmatic processes, highlighting variations in the magmatic protolith composition. In addition, the shift of δ56Fe by +0.06 to 0.10‰ compared to basalts may reflect hydrothermal alteration prior to subduction. The δ56Fe decrease from blueschists (+0.19 ± 0.03 to +0.33 ± 0.01‰) to eclogites (+0.16 ± 0.02 to +0.18 ± 0.03‰) reflects small variations in the protolith composition, rather than Fe fractionation during metamorphism: newly-formed Fe-rich minerals allowed preserving bulk rock Fe compositions during metamorphic reactions and hampered any Fe isotope fractionation. Greenschists have δ56Fe values (+0.17 ± 0.01 to +0.27 ± 0.02‰) similar to high-pressure rocks. Hence, metasomatism related to fluids derived from the subducted hydrothermally altered metabasites might only have a limited effect on mantle Fe isotope composition under subsolidus conditions, owing to the large stability of Fe-rich minerals and low mobility of Fe. Subsequent melting of the heavy-Fe metabasites at deeper levels is expected to generate mantle Fe isotope heterogeneities.

Formation mechanisms and sequence response of authigenic grain-coating chlorite: evidence from the Upper Triassic Xujiahe Formation in the southern Sichuan Basin, China

Authigenic grain-coating chlorite is widely distributed in the clastic rocks of many sedimentary basins around the world. These iron minerals were mainly derived from flocculent precipitates formed when rivers flow into the ocean, especially in deltaic environments with high hydrodynamic conditions. At the same time, sandstone sequences with grain-coating chlorites also tend to have relatively high glauconite and pyrite content. EPMA composition analysis shows that glauconites with “high Al and low Fe” content indicate slightly to semi-saline marine environments with weak alkaline and weakly reducing conditions. By analyzing the chlorite-containing sandstone bodies of the southern Sichuan Xujiahe Formation, this study found that chlorite was mainly distributed in sedimentary microfacies, including underwater distributary channels, distributary channels, shallow lake sandstone dams, and mouth bars. Chlorite had a tendency to form in the upper parts of sandstone bodies with signs of increased base level, representing the influence of marine (lacustrine) transgression. This is believed to be influenced by megamonsoons in the Middle and Upper Yangtze Region during the Late Triassic Epoch. During periods of abundant precipitation, river discharges increased and more Fe particulates flowed into the ocean (lake). In the meantime, increases or decreases in lake level were only affected by precipitation for short periods of time. The sedimentary environment shifted from weakly oxidizing to weak alkaline, weakly reducing conditions as sea level increased, and Fe-rich minerals as authigenic chlorite and glauconite began to form and deposit.

Dissolution of nontronite in chloride brines and implications for the aqueous history of Mars

Increasing evidence suggests the presence of recent liquid water, including brines, on Mars. Brines have therefore likely impacted clay minerals such as the Fe-rich mineral nontronite found in martian ancient terrains. To interpret these interactions, we conducted batch experiments to measure the apparent dissolution rate constant of nontronite at 25.0°C at activities of water (aH2O) of 1.00 (0.01M CaCl2 or NaCl), 0.75 (saturated NaCl or 3.00molkg−1 CaCl2), and 0.50 (5.00molkg−1 CaCl2). Experiments at aH2O=1.00 (0.01M CaCl2) were also conducted at 4.0°C, 25.0°C, and 45.0°C to measure an apparent activation energy for the dissolution of nontronite.Apparent dissolution rate constants at 25.0°C in CaCl2-containing solutions decrease with decreasing activity of water as follows: 1.18×10−12±9×10−14molmineralm−2s−1 (aH2O=1.00)>2.36×10−13±3.1×10−14molmineralm−2s−1 (aH2O=0.75)>2.05×10−14±2.9×10−15molmineralm−2s−1 (aH2O=0.50). Similar results were observed at 25.0°C in NaCl-containing solutions: 1.89×10−12±1×10−13molmineralm−2s−1 (aH2O=1.00)>1.98×10−13±2.3×10−14molmineral m−2s−1 (aH2O=0.75). This decrease in apparent dissolution rate constants with decreasing activity of water follows a relationship of the form: logkdiss=3.70±0.20×aH2O−15.49, where kdiss is the apparent dissolution rate constant, and aH2O is the activity of water. The slope of this relationship (3.70±0.20) is within uncertainty of that of other minerals where the relationship between dissolution rates and activity of water has been tested, including forsteritic olivine (logR=3.27±0.91×aH2O−11.00) (Olsen et al., 2015) and jarosite (logR=3.85±0.43×aH2O−12.84) (Dixon et al., 2015), where R is the mineral dissolution rate. This result allows prediction of mineral dissolution as a function of activity of water and suggests that with decreasing activity of water, mineral dissolution will decrease due to the role of water as a ligand in the reaction.Apparent dissolution rate constants in the dilute NaCl solution (1.89×10−12±1×10−13molmineralm−2s−1) are slightly greater than those in the dilute CaCl2 solutions (1.18×10−12±9×10−14molmineralm−2s−1). We attribute this effect to the exchange of Na with Ca in the nontronite interlayer. An apparent activation energy of 54.6±1.0kJ/mol was calculated from apparent dissolution rate constants in dilute CaCl2-containing solutions at temperatures of 4.0°C, 25.0°C, and 45.0°C: 2.33×10−13±1.3×10−14molmineralm−2s−1 (4.0°C), 1.18×10−12±9×10−14molmineralm−2s−1 (25.0°C), and 4.98×10−12±3.8×10−13molmineralm−2s−1 (45.0°C).The greatly decreased dissolution of nontronite in brines and at low temperatures suggests that any martian nontronite found to be perceptibly weathered may have experienced very long periods of water–rock interaction with brines at the low temperatures prevalent on Mars, with important implications for the paleoclimate and long-term potential habitability of Mars.

Hyperspectral remote sensing applied to uranium exploration: A case study at the Mary Kathleen metamorphic-hydrothermal U-REE deposit, NW, Queensland, Australia

The HyMap airborne hyperspectral scanner provides 128 spectral bands between Visible-Near Infrared (VNIR) and Short Wave Infrared (SWIR) wavelengths (0.45–2.5μm). It transcends any currently operational orbital multispectral sensor (ASTER, WV3, Landsat-8) for mineral mapping in exposed areas. Here we employ HyMap data to study the type and spatial distribution of mineral assemblages in the world-class Mary Kathleen metamorphic-hydrothermal Uranium (U) - Rare Earth Elements (REE) deposit, situated in the Mount Isa Province, Australia. The focus is on Ca-bearing silicates and Fe-rich minerals. Two spectral libraries were built for the task based on publicly available data. The VNIR library comprises goethite and andradite. The SWIR library includes hornblende, epidote, calcite, kaolinite and montmorillonite. Scapolite SWIR spectra were yielded autonomously. These mineral spectra were used as endmembers for HyMap data classification and production of mineral abundance maps. Spectral Angle Mapper (SAM) and Mixture Tuned Matched Filtering (MTMF) were the methods employed for image classification. Results were combined in RGB color composites and enhanced to provide high quality maps of Ca-bearing silicates and other minerals associated with the Ca-skarn hosted U-REE mineralization. The spatial correlation of mineral abundance maps produced here and known exposed surfaces of equivalent minerals in the open pit mine proved plausible. Wallrock alteration halos show characteristic zonal arrangements. Andradite occurs in the outer alteration halo. Selectively pervasive alteration is characterized by calcite, scapolite, epidote and hornblende. These specific mineral types and their distribution in the Mary Kathleen deposit indicate multiple stages of metasomatic processes, resulting in high-temperature and retrograde Ca-bearing silicates associations. In addition, kaolinite, montmorillonite and goethite are the surface footprint of the skarn-hosted U-REE mineralization. HyMap proved to be a solid tool to characterize exposed hydrothermal mineral systems associated to skarns enriched in U and REE, providing the framework for advanced geologic interpretation and conception of a regional exploration model. The occurrence of goethite, kaolinite and montmorillonite and their zonal relationship with the U-REE mineralization, as also mapped here with HyMap, may be also an additional guide for U exploration in the Mount Isa Province, especially if combined with other exploration methods.

Biofilm adaptation to iron availability in the presence of biotite and consequences for chemical weathering.

Bacteria in nature often live within biofilms, exopolymeric matrices that provide a favorable environment that can differ markedly from their surroundings. Biofilms have been found growing on mineral surfaces and are expected to play a role in weathering those surfaces, but a clear understanding of how environmental factors, such as trace-nutrient limitation, influence this role is lacking. Here, we examine biofilm development by Pseudomonas putida in media either deficient or sufficient in Fe during growth on biotite, an Fe rich mineral, or on glass. We hypothesized that the bacteria would respond to Fe deficiency by enhancing biotite dissolution and by the formation of binding sites to inhibit Fe leaching from the system. Glass coupons acted as a no-Fe control to investigate whether biofilm response depended on the presence of Fe in the supporting solid. Biofilms grown on biotite, as compared to glass, had significantly greater biofilm biomass, specific numbers of viable cells (SNVC), and biofilm cation concentrations of K, Mg, and Fe, and these differences were greater when Fe was deficient in the medium. Scanning electron microscopy (SEM) confirmed that biofilm growth altered the biotite surface, smoothing the rough, jagged edges of channels scratched by hand on the biotite, and dissolving away small, easy-to-access particles scattered across the planar surface. High-resolution magic angle spinning proton nuclear magnetic resonance (HRMAS 1 H NMR) spectroscopy showed that, in the Fe-deficient medium, the relative amount of polysaccharide nearly doubled relative to that in biofilms grown in the medium amended with Fe. The results imply that the bacteria responded to the Fe deficiency by obtaining Fe from biotite and used the biofilm matrix to enhance weathering and as a sink for released cation nutrients. These results demonstrate one mechanism by which biofilms may help soil microbes overcome nutrient deficiencies in oligotrophic systems.

Unusual manganese enrichment in the Mesoarchean Mozaan Group, Pongola Supergroup, South Africa

An unusual sediment-hosted manganese deposit is described from the Mesoarchean Mozaan Group, Pongola Supergroup, South Africa. MnO contents up to 15wt.% were observed in marine clastic and chemical sedimentary rocks. Mn enrichment is interpreted to have resulted from the hydrothermal alteration of manganiferous shale and BIF parent rocks, the primary MnO contents of which are as high as 8.5wt.%. A detailed mineralogical and petrographic study shows that these parent rocks are characterized by manganoan siderite, ferroan rhodochrosite and other Mn–Fe-rich mineral phases, such as kutnohorite and Fe–Mn-chlorite. Their hypogene alteration gave rise to a diversification of mineral assemblages where ferroan tephroite, calcian rhodochrosite, rhodochrosite, pyrochroite, pyrophanite, cronstedtite, manganoan Fe-rich chlorite and manganoan phlogopite partially or totally replaced the previous mineral assemblage. Thermodynamic modeling performed on chlorite phases associated with the described mineral assemblages illustrates a decrease of average crystallization temperatures from ca. 310°C during early metamorphic stages to ca. 250°C during a hydrothermal stage. Mineral transformation processes were thus related to retrograde metamorphism and/or hydrothermal alteration post-dating metamorphism and gave rise to progressive Mn enrichment from unaltered parent to altered rocks. The timing of hypogene alteration was constrained by 40Ar/39Ar dating to between about 1500 and 1100Ma ago, reflecting tectonic processes associated with the Namaqua-Natal orogeny along the southern Kaapvaal Craton margin. Manganiferous shale and BIF of the Mozaan Group may represent the oldest known examples of primary sedimentary Mn deposition, related to oxidation of dissolved Mn(II) by free oxygen in a shallow marine environment. Oxygenic photosynthesis would have acted as a first-order control during Mn precipitation. This hypothesis opens a new perspective for better constraining secular evolution of sediment-hosted mineral deposits linked to oxygen levels in the atmosphere-hydrosphere system during the Archean Eon.

Characterization of Fe(III)-saturated montmorillonite and evaluation its sorption behavior for U(VI)

Abstract Radioactive waste is usually sealed in steel canisters surrounded by a layer of compacted clay back-fill, and permanent buried in a deep geological repository. Unavoidably, the radionuclide contaminants can be released from repository and then sorbed onto the waste container corrosion products or the Fe-rich minerals. Herein, we characterized the Fe(III)-saturated montmorillonite (Fe(III)-MMT) by using Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET), and found the changes of the surface incorporating Fe(III) and surface micropores. The sorption of U(VI) on Fe(III)-MMT and Na-montmorillonite (Na-MMT) was investigated by batch experiments. The larger surface area and cation exchange capacity, and the existence of Fe(III) (hydr)oxide phases in Fe(III)-MMT contributed greatly to its sorption capacity. In the whole pH range, the sorption of U(VI) on Fe(III)-MMT was higher than on Na-MMT, and the sorption was strongly depended on pH and ionic strength. The sorption isotherms were simulated well by the Langmuir and Freundlich models. The thermodynamic parameters (ΔH, ΔS and ΔG) calculated from the temperature dependent sorption isotherms indicated that the sorption of U(VI) on Fe(III)-MMT was an endothermic and spontaneous process. The observations suggest that the interactions between U(VI) and Fe(III)-MMT are important in controlling U(VI) retention. The phenomena need to be considered in risk assessment and reactive transport modeling.