Iron Oxide Mineralogy Research Articles

Shear zone-hosted hypogene high-grade iron deposit: The Cuité case study

The Cuité iron ore deposit consists of high-grade schistose lenses (>60 wt% Fe) hosted in a tectonic sliver of iron formation associated to mica schist (Serra da Serpentina Group). It is located at the southeastern border of the São Francisco Craton, enclosed by sheared Sthaterian granitoids (Borrachudos Suite), Neoarchean ortogneiss (Guanhães Complex), quartz and pegmatite veins. The iron formation encloses schistose to massive high-grade ore lenses, with a pervasively, continuous to anastomosed schistosity defined by millimetric elongated hematite plates and quartz grains enclosing hematite granoblastic domains. Kenomagnetite/maghemite and martite pseudomorphs (after magnetite) overgrow the foliation and intergrow with granoblastic hematite. Three high-grade iron ore types are identified, according to the fabric and mineralogy of the main iron oxides: lamellar-granular hematitic (LGO), magnetitic (MO), and granular hematitic ore (GO). Intrusive pegmatite bodies related to the swarms of the Eastern Brazilian Province (late Ediacaran to early Cambrian) and to post-collisional Cambrian vents of the Brasiliano Orogeny caused extensive hydrothermal alteration in the country rocks, encompassing recrystallization of the detrital zircon grains from the associated psammopelitic units, which yielded Cambrian ages, formation of kaolinite-rich lenses, and generation of granoblastic ore bodies. The association of intense stretching along foliation and circulation of hydrothermal fluids from pegmatite intrusion is responsible for the ore formation.

Influence of iron (hydr)oxide mineralogy and contents in aquifer sediments on dissolved organic carbon attenuations during aquifer storage and recovery

Aquifer storage and recovery (ASR) is a promising approach for managing water resources that enhances water quality through biogeochemical reactions occurring within aquifers. Iron (hydr)oxides, which are the predominant metallic oxides in soil, play a crucial role in degrading dissolved organic carbon (DOC), primarily through a process known as dissimilatory iron reduction (DIR). However, the efficiency of this reaction varies depending on the mineralogy and composition of the aquifer, and this understanding is essential for adequate water quality in ASR. The objective of this study is to investigate the impact of iron (hydr)oxide on acetate, as an organic carbon source, attenuation during the ASR. To achieve this, three sets of laboratory sediment columns were prepared, each containing a different type of iron (hydr)oxide minerals: ferrihydrite, goethite, and hematite. Following an acclimation period of 28 days to simulate the microcosm within an aquifer, the columns were continuously supplied with the simulated river water spiked with acetate (DOC 40–60 mg L−1), and the acetate concentration in the effluent was monitored. The result revealed that the column containing ferrihydrite achieved 97% acetate attenuation through DIR with anoxic conditions (DO < 0.1 mg L−1), while the goethite and hematite columns exhibited limited attenuation rates of 40 and 50%, respectively. Furthermore, the efficiency of acetate attenuation in the ferrihydrite columns increased with the content of ferrihydrite but experienced a rapidly declined at higher contents (3–4%), possibly due to the partial conversion of ferrihydrite to goethite as a result of the interaction between ferrihydrite and the Fe(II) produced during DIR. Additionally, an analysis of the microbial community demonstrated that microorganisms known to possess the ability to reduce iron (hydr)oxides under anaerobic conditions were abundant in the ferrihydrite columns.

How Weather Affects over Time the Repeatability of Spectral Indices Used for Geological Remote Sensing

Geologic remote sensing studies often targets surface cover that is supposed to be invariant or only changing on a geological timescale. In terms of surface material characteristics, this holds for rocks and minerals, but only to a lesser degree for soils (including alluvium, colluvium, regolith or weathered outcrop) and not for vegetation cover, for example. A view unobstructed by clouds, vegetation or fire scars is essential for a persistent observation of surface mineralogy. Sensors with a continuous multi-temporal operation (e.g., Landsat 8 OLI and Sentinel-2 MSI) can provide the data volume needed to come to an optimal seasonal acquisition and the application of data fusion approaches to create an unobstructed view. However, the acquisition environment always changes over time, driven by seasonal changes, illumination changes and the weather. Consequently, the creation of an unobstructed view does not necessarily lead to a repeatable measurement. In this paper, we evaluate the influence of weather and resulting soil moisture conditions over a 3-year period, with alternating dry and wet periods, on the variance of several “geological” spectral indices in a semi-arid area. Sentinel-2 MSI data are chosen to calculate band ratios for green vegetation, ferric and ferrous iron oxide mineralogy and hydroxyl bearing alteration (clay) mineralogy. The data were used “as provided”, meaning that the performance of the atmospheric correction and geometric accuracy is not changed. The results are shown as time-series for selected areas that include solid rock, beach sand, bare soil and natural vegetation surfaces. Results show that spectral index values vary not only between dry and wet periods, but also within dry periods longer than 45 days, as a result of changing soil moisture conditions long after a last rain event has passed. In terms of repeatability of measurements, an overall low soil-moisture level is more important for long-term stability of spectral index values than the occurrence of minor rain events. In terms of creating an unobstructed view, we found that thresholds for NDVI should not be higher than 0.1 when masking vegetation in geological remote sensing, which is lower than what usually is indicated in literature. In conclusion, multi-temporal data are not only important to study dynamic Earth processes, but also to improve mapping of surfaces that are seemingly invariant. As this work is based on a few selected pixels, the obtained results should be considered only indicative and not as a numerical truth. We conclude that multi-temporal data can be used to create an unobstructed view, but also to select the data that give the most repeatability of measurements. Images selection should not be based on a certain number of days without rain in the days preceding data acquisition but aim for the lowest soil moisture conditions. Consequently, weather data should be incorporated to come to an optimal selection of remote sensing imagery, and also when analyzing multi-temporal data.

Environmental controls of soil fungal abundance and diversity in Australia's diverse ecosystems

Soil fungi are vital for ecosystem functioning, but an understanding of their ecology is still growing. A better appreciation of their ecological preferences and the controls on the composition and distribution of fungal communities at macroecological scales is needed. Here, we used one of the most extensive continental-scale datasets on soil fungi and modelled the relative abundance of dominant fungal phyla and community diversity in Australian soils from forests, grasslands, shrublands, woodlands, and croplands. Across these diverse ecosystems, the Ascomycota and Basidiomycota dominate Australian soils, and fungal diversity declines as climates become more arid. Climate and the water balance exert dominant control on soil fungal abundance and diversity, mediated by interactions between ecosystem type, the ensuing vegetation and edaphic factors, such as organic matter, clay and iron-oxide mineralogy, pH and nutrients. Soil organic matter and mineralogy, represented by absorptions of visible–near-infrared (vis–NIR) radiation, helped to improve characterisation of the abiotic controls on soil fungi. This better representation of edaphic factors improved the predictability of the models by up to 40%. Our findings contribute to the understanding of fungal ecology at a macroecological scale. They help to appreciate better the links between fungi, soil and the environment, which underpin ecosystem stability and resilience and have implications for developing strategies for preservation, adaptation and mitigation of global change.

Precipitation thresholds for iron oxides dissolution and the enhanced Eurasian aridity across the Mid-Pleistocene Transition: Evidence from loess deposits in subtropical China

The extensive loess deposits in southern China (‘Xiashu’ loess) are a valuable paleoclimatic archive in the subtropical monsoon region. We carried out a combined study of iron oxide mineralogy, pedostratigraphy, and magnetostratigraphy of three new loess sections in subtropical China. A detailed comparison of the iron oxides content of the Xiashu loess and the loess of the Chinese Loess Plateau reveals that the iron oxides of paleosol units in the Xiashu loess are partially dissolved. The estimated minimum mean annual precipitation levels required for the dissolution of maghemite, hematite, and goethite and the 95% confidence bounds are ~793 mm (679–907 mm), 728 mm (683–772 mm), and 941 mm (834–1048 mm) respectively. A regional comparison of the stratigraphy and magnetic susceptibility of the loess deposits in subtropical China reveals a general lack of correlation. The relatively low continuity of dust deposition combined with iron oxide dissolution is the main cause of the spatial inconsistency of the stratigraphy and magnetic properties. Magnetostratigraphic analysis reveals a basal age of 1.1 Ma for the loess deposits in subtropical China, which demonstrates that the intensification of aridification of the subtropical regions and a strengthened East Asian winter monsoon began by at least 1.1 Ma. Thus, the loess deposits in subtropical China provide terrestrial evidence from mid−low latitudes for global cooling and enhanced aridity across the Mid-Pleistocene Transition.

Magnetic properties of surface sediments in Schirmacher Oasis, East Antarctica: spatial distribution and controlling factors

PurposeWe investigated the magnetic properties (abundance, grain size, and mineralogy) of iron oxides present in Lake L-55 sediments, Schirmacher Oasis, East Antarctica, with an aim to understand their spatial distribution and the underlying mechanisms that control their formation and distribution.MethodsTwenty-five surficial sediments retrieved from different parts of Lake L-55 were subjected to the entire range of environmental magnetic (magnetic susceptibility, anhysteretic remanent magnetization (ARM), isothermal remanent magnetization (IRM)) measurements (at different field strengths). Inter-parametric ratios (χARM/SIRM, χARM/χlf, χARM/χfd, IRM20 mT/SIRM, IRM20 mT/ARM, S-ratio, L-ratio) provided insights into the magnetic properties (abundance, grain size, and mineralogy of iron oxides). Scanning electron microscopic-energy dispersive X-ray spectroscopic (SEM-EDS) analysis was performed on magnetic extracts from a few sediments. Besides, organic matter (%) was also calculated for the sediment samples. Principal component analysis was performed to gain information on the presence of different components and their relative dominance.ResultsThe iron oxides are strongly magnetic (high values of concentration-dependent parameters). The principal iron oxide is magnetite (S-ratio > 0.90) which is coarse-grained (multi-domain (MD) and stable single-domain (SSD) grains), and there is no influence of authigenic greigite, bacterial magnetite, and anthropogenic magnetite. The mineralogy is confirmed by SEM-EDS data. The iron oxides are of different grain sizes, and their contribution is in the order of MD > SSD > SP as shown by the principal component analysis. Pedogenic iron oxide minerals seem to be present in the samples whose formation is due to the oxidation of magnetite into hematite. However, they are of SSD size and not SP, suggesting that the intensity of pedogenesis is not sufficient to form SP grains.ConclusionThe iron oxide minerals are mainly terrigenous, and the biogenic activity within the lake is not sufficient to modify the ferrimagnetic minerals. Spatial distribution patterns suggest the non-uniform distribution of magnetite/titanomagnetite of varying sizes in the lake basin which is transported by both melt water streams and winds.

Iron oxide mineralogy in Mollisols, Aridisols and Entisols from southwestern Pampean region (Argentina) by environmental magnetism approach

Ferromagnetic compounds of seven southwestern soils from Pampean region comprise iron oxides and oxyhydroxides that have an important role, because of their high surface reactivity, controlling soil adsorption and formation/conservation of soil structure among other properties. We detected minutes of iron oxides quantities by selective dissolution techniques: acid oxalate extraction (<12% of the total Fe) and dithionite-citrate-bicarbonate (<44% of the total Fe), moreover, we identified/quantified mixtures of magnetite, maghemite, goethite and hematite minerals by environmental magnetism approach. The magnetic particle size dependent parameters evidence a relationship with extractable Fe oxides, indicating that magnetic particle size distribution on these soils is a relevant property associated to poorly crystalline and free amorphous Fe oxides. In addition, the particle size and SP concentration of ferromagnetic iron oxides are associated with increments of cation exchange capacity and the specific surface area of soil samples. The estimated amounts of hematite are below 2.20 wt%, and lower contents of about 0.25 wt% correspond to magnetite components. Both magnetic iron oxides concentration, as well as the remanent coercivity, increase towards the western region, on the contrary, anhysteretic ratios decrease and hence relatively coarser magnetic particles are dominant in this western region. The present study provides valuable data to characterize Aridisols, Entisols and Mollisols in a region of high fertility that comprises ones of the world’s most productive agricultural soil region.

Electrochemical Analysis of Changes in Iron Oxide Reducibility during Abiotic Ferrihydrite Transformation into Goethite and Magnetite.

Electron transfer to ferric iron in (oxyhydr-)oxides (hereafter iron oxides) is a critical step in many processes that are central to the biogeochemical cycling of elements and to pollutant dynamics. Understanding these processes requires analytical approaches that allow for characterizing the reactivity of iron oxides toward reduction under controlled thermodynamic boundary conditions. Here, we used mediated electrochemical reduction (MER) to follow changes in iron oxide reduction extents and rates during abiotic ferrous iron-induced transformation of six-line ferrihydrite. Transformation experiments (10 mM ferrihydrite-FeIII) were conducted over a range of solution conditions (pHtrans = 6.50 to 7.50 at 5 mM Fe2+ and for pHtrans = 7.00 also at 1 mM Fe2+) that resulted in the transformation of ferrihydrite into thermodynamically more stable goethite or magnetite. The changes in iron oxide mineralogy during the transformations were quantified using X-ray diffraction analysis. MER measurements on iron oxide suspension aliquots collected during the transformations were performed over a range of pHMER at constant applied reduction potential. The extents and rates of iron oxide reduction in MER decreased with decreasing reaction driving force resulting from both increasing pHMER and increasing transformation of ferrihydrite into thermodynamically more stable iron oxides. We show that the decreases in iron oxide reduction extents and rates during ferrihydrite transformations can be linked to the concurrent changes in iron oxide mineralogy.

Constrained 3D modelling and geochemical analyses of the Horseshoe Range BIF: tools for evaluating magnetic signatures under cover

The Horseshoe Range is a banded iron formation (BIF) in the Southern Capricorn Orogen, WA and is associated with a large horseshoe-shaped positive magnetic anomaly. Electron microscope mineralogy identified ubiquitous goethite and magnetite/hematite. This study focussed on measuring the magnetic properties of the rocks at Horseshoe Range in order to accurately predict their geophysical responses when buried beneath cover. Remanent magnetisation intensities of the rocks were high (up to 1300 A/m) and vectors measured in the rocks were oriented predominately downward which typically result in negative anomalies which is inconsistent with the observed anomaly. Due to the positive nature of the magnetic anomaly and the ability to accurately model the response without remanent magnetisation it appears that the high intensity remanent magnetisations may be volumetrically insignificant and likely limited to the near surface. The remanence may be caused by near surface formation of maghemite during bushfires and/or induced by lightning strikes. The BIF can be modelled using a single homogenous layer with a susceptibility of 0.8 SI. However, this is not geologically consistent with BIFs which typically display variable iron-oxide mineralogy and associated petrophysical properties. One way to more accurately model BIFs is to use the first vertical derivative as the model input. Using this approach, a 4 layer model was generated which matched the anomaly to an RMS of ~1%. Modelled susceptibilities ranged from 0.01 – 0.55 SI which are consistent with the measured properties. However, this model did not take into account the measured high intensity downward magnetisation vectors.

Ore\u2013Waste Discrimination in Epithermal Deposits Using Near-Infrared to Short-Wavelength Infrared (NIR-SWIR) Hyperspectral Imagery

Near-infrared (NIR) and short-wavelength infrared (SWIR) hyperspectral imagery can be used to detect certain alteration minerals. At epithermal deposits, the formation of alteration minerals is, in theory, related to the mineralisation of gold and silver. In order to provide foundations for developing sensor-based sorting applications at a mine that exploits such a deposit, it was investigated if NIR-SWIR hyperspectral imagery can be used to distinguish between ore and waste particles by characterising the alteration mineralogy. Maps were produced from the NIR-SWIR hyperspectral images of 827 drill core samples that show mineral occurrences, mineral absorption feature intensities and characteristics of the iron oxide mineralogy. Partial least squares discriminant analysis (PLS-DA) was applied to the information contained in these maps to investigate if this information can be used to discriminate between ore and waste. The results showed that NIR-SWIR hyperspectral imagery could be used to segment a population of waste samples by detecting occurrences of pyrophyllite, dickite and/or illite. This result can be explained by the fact that these minerals are commonly deposited further away from the ore-bearing epithermal veins, while the absence of SWIR-active minerals or detected occurrences of alunite are more closely associated with these structures. The ability to identify waste with NIR-SWIR spectral sensors means there is potential that sensor-based sorting can be used to remove this waste from mineral processing operations. Additional research is still required to assess the economic feasibility of such a sensor-based sorting application.

Pentachlorophenol dechlorination with zerovalent iron: a Raman and GCMS study of the complex role of surficial iron oxides.

The dechlorination of chlorinated organic pollutants by zero valent iron (ZVI) is an important water treatment process with a complex dependence on many variables. This complexity means that there are reported inconsistencies in terms of dechlorination with ZVI and the effect of ZVI acid treatment, which are significant and are as yet unexplained. This study aims to decipher some of this complexity by combining Raman spectroscopy with gas chromatography-mass spectrometry (GC-MS) to investigate the influence of the mineralogy of the iron oxide phases on the surface of ZVI on the reductive dechlorination of pentachlorophenol (PCP). Two electrolytic iron samples (ZVI-T and ZVI-H) were found to have quite different PCP dechlorination reactivity in batch reactors under anoxic conditions. Raman analysis of the "as-received" ZVI-T indicated the iron was mainly covered with the ferrous oxide (FeO) wustite, which is non-conducting and led to a low rate of PCP dechlorination. In contrast, the dominant oxide on the "as-received" ZVI-H was magnetite which is conducting and, compared to ZVI-T, the ZVI-H rate of PCP dechlorination was four times faster. Treating the ZVI-H sample with 1N H2SO4 made small change to the composition of the oxide layers and also minute change to the rate of PCP dechlorination. However, treating the ZVI-T sample with H2SO4 led to the loss of wustite so that magnetite became the dominant oxide and the rate of PCP dechlorination increased to that of the ZVI-H material. In conclusion, this study clearly shows that iron oxide mineralogy can be a contributing factor to apparent inconsistencies in the literature related to ZVI performance towards dechlorination and the effect of acid treatment on ZVI reactivity.

Iron Oxide Mineralization at the Contact Zone Between Phyllite and Itabirite of the Pau Branco Deposit, Quadrilátero Ferrífero, Brazil—Implications for Fluid-Rock Interaction During Iron Ore Formation

This study examines the whole-rock geochemistry and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) iron oxide chemistry of itabirite and related iron ore, as well as underlying phyllitic wall rock, of the Pau Branco iron ore deposit, Quadrilatero Ferrifero, Brazil. The phyllite and iron ore of Pau Branco extend from hypogene deep-seated into supergene weathered zones. The phyllitic sequence that underlies the itabirite-hosted iron ore along a sheared contact includes (from the bottom to top) carbonaceous and carbonate-, chlorite-, and Fe-rich zones, which likely reflect distal to proximal alteration halos. The Fe-rich phyllite and iron ore comprise a complex iron oxide mineralogy: (1) magnetite-martite is hosted in itabirite and related medium-grade iron ore and present as disseminated minerals in phyllite; (2) microplaty hematite replaces chlorite and carbonate in the phyllite; (3) granoblastic hematite is a recrystallization/precipitation product and the dominant iron oxide of the hard iron ore; (4) schistose specular hematite overgrows earlier iron oxides; and (5) goethite replaces earlier hematite and amphibole within the weathering horizon. Whole-rock geochemistry and related mass balance calculations reveal that, unlike the itabirite-hosted iron ore, interpreted to be the result of a solely residual iron enrichment via depletion of most major oxides and trace elements, the iron enrichment of the phyllite is caused by addition of Fe 2 O 3 . The Fe 2 O 3 is likely sourced from the overlying itabirite/iron ore and is mineralogically reflected in the replacement of carbonate and chlorite by hematite. The rare earth elements (REE) abundances of the different ore and phyllite zones reveal seawater-like REE signatures and Y/Ho ratios of the itabirite, hypogene and supergene iron ore, shale-atypical REE patterns in the unaltered phyllite, and Eu fractionation trends. This suggests a distinct input of hydrothermal fluids during the Fe enrichment of the phyllite. Locally, restricted Ce fractionation is attributed to distinct (e.g., Mn-rich) lithostratigraphic intercalations within the itabirite. Laser ablation-ICP-MS mineral chemistry of phyllite-hosted martite and microplaty hematite suggests a strong chemical inheritance by the host rock and precursor mineral. Positive Ce anomalies are restricted to phyllite- and itabirite-hosted martite only and, therefore, may reflect the highly oxidative conditions during martitization. At Pau Branco, the fluid-rock interaction affected not only the itabirite, but also the underlying phyllite, resulting in distinct alteration halos that extend beyond the itabirite toward the footwall. The significant chemical influence and importance of country-rock lithologies as a possible elemental source, for example, must be taken into account when interpreting whole-rock geochemical data and investigating an itabirite-/banded iron formation-hosted iron ore system.

Magnetic characteristics and trace elements concentration in soils from Anthemountas River basin (North Greece): discrimination of different sources of magnetic enhancement

The magnetic minerals (e.g., iron oxides) that are present in soils can be easily identified by using rock-magnetic techniques. Increased magnetic susceptibility of soils may reflect particles rich in iron oxides of anthropogenic, lithogenic, and pedogenic origin. Therefore, reliable discrimination of these sources is required, especially in areas where neither of them is dominant. The aim of the present study is to assess the lithogenic and anthropogenic contributions to iron-oxide mineralogy of soils in the area of the Anthemountas River basin in the southeast part of Thessaloniki city. Previous investigations within the study area, based on spatial distribution of magnetic susceptibility, revealed the presence of two magnetically enhanced regions. Therefore, the present study is focused on these two areas, in order to characterize the origin of magnetic enhancement. Detailed magnetic analyses include properties reflecting the type, concentration, and relative grain-size distribution of magnetic particles. Moreover, trace element concentration is determined with an aim to establish the link between low-field mass-specific magnetic susceptibility and concentration of Fe, Cr, Ni, Mn, Pb, Zn, and Ti. These findings are supported by descriptions of the micromorphology performed by scanning electron microscopy and determination of elemental composition by energy-dispersive spectrometer analyses in selected points. Finally hierarchical cluster analysis is applied to classify the soil samples into appropriate groups according to their magnetic properties. The results reveal that magnetic measurements provide a useful tool for the discrimination between different magnetic sources responsible for the enhancement of magnetic susceptibility in soils. Low-field mass-specific magnetic susceptibility reflects increased concentration of trace elements, while its combination with other magnetic measurements clearly differentiates the origin of magnetic enhancement in both parts of the study area.

Constraints on iron sulfate and iron oxide mineralogy from ChemCam visible/near-infrared reflectance spectroscopy of Mt. Sharp basal units, Gale Crater, Mars

Relative reflectace point spectra (400–840 nm) were acquired by the Chemistry and Camera (ChemCam) instrument on the Mars Science Laboratory (MSL) rover Curiosity in passive mode (no laser) of drill tailings and broken rock fragments near the rover as it entered the lower reaches of Mt. Sharp and of landforms at distances of 2–8 km. Freshly disturbed surfaces are less subject to the spectral masking effects of dust, and revealed spectral features consistent with the presence of iron oxides and ferric sulfates. We present the first detection on Mars of a ~433 nm absorption band consistent with small abundances of ferric sulfates, corroborated by jarosite detections by the Chemistry and Mineralogy (CheMin) X-ray diffraction instrument in the Mojave, Telegraph Peak, and Confidence Hills drilled samples. Disturbed materials near the Bonanza King region also exhibited strong 433 nm bands and negative near-infrared spectral slopes consistent with jarosite. ChemCam passive spectra of the Confidence Hills and Mojave drill tailings showed features suggestive of the crystalline hematite identified by CheMin analyses. The Windjana drill sample tailings exhibited flat, low relative reflectance spectra, explained by the occurrence of magnetite detected by CheMin. Passive spectra of Bonanza King were similar, suggesting the presence of spectrally dark and neutral minerals such as magnetite. Long-distance spectra of the “Hematite Ridge” feature (3–5 km from the rover) exhibited features consistent with crystalline hematite. The Bagnold dune field north of the Hematite Ridge area exhibited low relative reflectance and near-infrared features indicative of basaltic materials (olivine, pyroxene). Light-toned layers south of Hematite Ridge lacked distinct spectral features in the 400–840 nm region, and may represent portions of nearby clay minerals and sulfates mapped with orbital near-infrared observations. The presence of ferric sulfates such as jarosite in the drill tailings suggests a relatively acidic environment, likely associated with flow of iron-bearing fluids, associated oxidation, and/or hydrothermal leaching of sedimentary rocks. Combined with other remote sensing data sets, mineralogical constraints from ChemCam passive spectra will continue to play an important role in interpreting the mineralogy and composition of materials encountered as Curiosity traverses further south within the basal layers of the Mt. Sharp complex.

Rock-magnetic and geochemical characteristics of relict Vertisols—signs of past climate and recent pedogenic development

Rock-magnetic and geochemical characteristics of three Vertisol profiles with different degree of textural differentiation have been studied. Thermomagnetic analyses, thermal demagnetization of laboratory remanences and acquisition of isothermal remanence curves are applied for identification of iron oxide mineralogy. The main magnetic minerals in Vertisols are ferrihydrite, single-domain magnetite, maghemite and hematite. Variations in magnetic susceptibility, anhysteretic remanent magnetization, isothermal remanent magnetization, as well as different ratios (Xarm/X, ARM/SIRM, S-ratio) along depth are studied. Concentration of magnetic minerals in Vertisols is low, influenced by the intense reductomorphic processes. The lowest magnetic susceptibility is found in the most texturally differentiated soil. However, rock-magnetic data suggest the presence of small, but well defined fraction of single domain-like magnetite with relatively wide grain-size distribution found in those parts of the profiles, which are subjected to most intense and frequent seasonal changes in oxidation-reduction conditions. It is suggested that this fraction is formed as a result of transformations of ferrihydrite under repeated cycles of anaerobic/aerobic conditions. Based on geochemical data, CALMAG weathering index was calculated for the three Vertisols. Using the established relation between CALMAG and mean annual precipitation (MAP), palaeo-MAP was evaluated for the studied profiles. The obtained MAP estimations fall in the range 1000–1200 mm and are much higher compared to contemporary precipitation in the area (MAP in the interval 540–770 mm). This finding confirms the relict character of Vertisols on Bulgarian territory and gives more information about the palaeoclimate during the initial stages of Vertisol formation.

Enhanced detection of gossans using hyperspectral data: Example from the Cape Smith Belt of northern Quebec, Canada

Owing to the links between gossans and mineral deposits, detecting gossans by remote sensing means is essential for mineral exploration. In northern regions, gossans can develop as thin oxidized surfaces, named thin gossans, that can be covered with lichens. This study investigates the effects of spectral mixing between such gossans with lichens and their rock substrates using laboratory spectroscopic data obtained from samples collected in the Cape Smith Belt of Canada. These observations are then scaled up to the airborne hyperspectral data obtained from the same area. Our laboratory results indicate that the presence of lichens on gossans induces a general spectral shift towards shorter wavelengths of the iron absorption typical of gossan spectra. The opposite shift is observed due to the influence of the rock substrates. These effects can thus impede classification of gossans based on the interpretation of iron oxide mineralogy from spectra. Our airborne spectral results suggest that thin gossans can be detected and discriminated from thick gossans, and further broken down into several classes according to their host rock substrates. The ability to define distinct classes of thin gossans is significant since the association of these gossans with specific rock substrates can be exploited for exploration. The ability to distinguish thin and thick gossans alone can contribute to mineral exploration since it can be either the former or the latter group of gossans that acts as an ore deposit vector.

Iron Oxide Mineralogy of Asnawa Soils, Sulaimani Province, Kurdistan region

Forty soil samples from three different zones (A, B and C) in Asnawa area werestudied to identify and characterize the forms of Fe oxides in the &lt;2 mm soil fractionsusing chemical extractions and XRDA technique. Neither citrate dithionite nor aquaregia solution were not effective enough to extract free Fe oxides in the soil samples. Themaximum amounts of Fe oxides obtained were when five successive treatments withaqua regia solution had done. Soils of the quarry area (zone A) contained the highestamount of Fe oxides followed by soils from zone B and C. They were ranged from52.1%, 38.6% and 15.1% respectively. XRD traces of the studied soils showed peakscharacteristics of magnetite at 0.297, 0.256, 0.210, 0.161 and 0.147 nm. Other peaks ofhematite at 0.271 nm, and wustite (Fe(1-X)O at 0.88 were also present. Diffraction peaksof magnetite after a single treatment with citrate dithionite and aqua regia were stillevident on the X-ray chart whereas the diffraction peaks of hematite and wustite weredisappeared.

Hooked on Soils: A Day in the Life of Ed Landa

Hooked on Soils: A Day in the Life of Ed Landa

Dominance of goethite over hematite in iron oxides of mineral dust from Western Africa: Quantitative partitioning by X‐ray absorption spectroscopy

AbstractThis paper reports on the X‐ray absorption analysis of samples of mineral dust emitted from or transported to Western Africa. We found that iron oxides account, by mass, for 38% to 72% of the total elemental iron. They are composed of minerals in the Fe(III) oxidation state: goethite (FeO·OH) and hematite (Fe2O3). The apparent fraction of iron oxide attributed to goethite is higher than hematite regardless of the source region from which the dust originated. The goethite percent content of iron oxides is in the range 52–78% (by mass), the highest values being measured for dust originating in the Sahel. The limited number of samples analyzed and the sample‐to‐sample variability prevent us from concluding firmly on the regional variability of the goethite‐to‐hematite ratio. Based on the experimental data on mineralogical composition and on concurrent measurements of the number size distribution, the optical properties of mineral dust have been calculated in a Mie approximation for homogeneous spherical particles. At 550 nm, the single‐scattering albedo ω0 ranges between 0.89 and 0.93, the asymmetry factor g ranges between 0.76 and 0.8 and the mass extinction efficiency kext varies between 0.5 and 1.1 m2 g−1; these values are all in the range of those from independent direct measurements. Neglecting the partitioning between hematite and goethite and the assimilation of iron oxides by hematite, as it is often done with models, lowers the single‐scattering albedo and increases the asymmetry factor in the UV‐visible spectral region below 550 nm. The mass extinction efficiency is insensitive to the nature of the iron oxides but rather responds to variations in the number size distribution. The mineralogy of iron oxides should therefore be taken into account when assessing the effect of mineral dust on climate and atmospheric chemistry, in particular via interactions involving photolysis.

Rock magnetism, iron oxide mineralogy and geochemistry of Quaternary red earth in central China and their paleopedogenic implication

This paper presents a detailed investigation on the rock magnetism, iron oxide mineralogy and geochemistry of a Quaternary red earth (QRE) in central China. The magnetic profile of QRE showed a characteristic vertical variation pattern: the uniform red clay (URC) section (0.2–2m) of the profile had a higher magnetic susceptibility (χ) while vermiculated red clay (VRC) section (2–6m) had a very low χ (<30×10−8m3kg−1). Rock magnetism and differential XRD analysis revealed that magnetite/maghemite and hematite were the main magnetic carriers in the URC section. The major elements Fe2O3 and Al2O3 of QRE increased with depth while the SiO2 content decreased with depth, indicating a leaching of the mobile elements and an enrichment of the immobile elements. In comparison with the URC, the VRC has a greater depletion in the content of Na, Mg, K and Mg, indicating a stronger weathering intensity. The dithionite–citrate–bicarbonate (DCB) extracted iron (Fed), the ratio of Fed to total iron oxide (Fe/Fet), and the weathering indices of QRE confirmed that the VRC had experienced a stronger pedogenesis than the URC. Strong pedogenesis in the VRC resulted in a transformation of the highly magnetic maghemite to the weakly magnetic hematite, which was responsible for the weak magnetism and hard magnetic behavior of the VRC. Our studies suggest that the VRC had experienced a hot climate with a dry season following one that was warm and moister. Magnetic reduction of the VRC section resulting from the transformation of highly magnetic maghemite to weakly magnetic hematite appeared to be an important paleopedogenic process in the QRE. We concluded that the magnetic parameters, hard isothermal remanent magnetization (HIRM) and SIRM/χ of QRE, can be used for the analysis of paleopedogenic processes.