Composition and properties of the iron hydroxides-cemented lenses in Estonian sandstone of Middle Devonian age

The formation of hematite and goethite concretions in different sedimentary rocks including sandstones is an important diagenetic process in the geologic history of the Earth. Its interpretation can also contribute to understanding the diagenetic history of Martian iron hydroxide concretions. A case study of iron-rich concretions from Estonian Middle Devonian sandstones exposed in ancient river valleys in southeastern Estonia was carried out based on the results of mineralogical, petrographical, geochemical, petrophysical and magnetic analyses. It was found that the high Fe₂O₃(total) content (25.0–39.5%), high magnetic susceptibility, bulk and grain density, very low porosity, corrosion and fracturing of the quartz grains of the platy iron concretions are in contrast with properties of the Devonian host sandstones. However the ferrous iron content (measured as FeO) of iron-rich concretions was as low as in the other Devonian rocks, suggesting an oxidizing environment and arid climate during the cementation by iron-hydroxides. The fracturing of quartz grains cemented by iron hydroxides could take place at near-surface conditions including vadose and phreatic zones in arid climate with high evaporation rates. Such climatic conditions have been reported for the Baltic region during Devonian, Upper Permian and Triassic times. We have found that goethite is prevalent in the cement, replacing clay and carbonate minerals. We assume that this iron-rich cement is originated from the mobilization of iron in host sandstones by groundwater, associated with tectonic activity at the end of the Middle Devonian, evidenced by fracturing in Devonian outcrops and caves. Although this mobilization could occur under reducing conditions, precipitation of goethite and hematite for the cementation could take place in oxidizing environment along bedding planes close to the surface during short sedimentation breaks. Another possible time for the formation of iron concretions could be Permian, under the condition of both arid climate and tectonic activity.     

Extraterrestrial iron in the Cretaceous-Danian sediments

The composition and distribution of particles of native iron in eight sections of the Cretaceous-Danian sediments in the Caucasus, Crimea and Kopet Dagh were studied using thermomagnetic analysis up to 800°C. Iron particles are found in 330 of 571 tested samples, their percentage varies from 10⁻⁵ to 0.05%, and their distribution is bimodal. It was established that the Santonian sediments of the Caucasus and Kara-Kala are enriched with the iron particles; the upper boundary of these sediments is marked by a sharp drop in the iron content at approximately 84 Ma, which coincides with the upper boundary of the Dzhalal hyperchron. The variations in the Curie point of iron from 680°C up to 780°C reflect the fluctuations of the nickel admixture. A peak of the elevated iron content with nearly constant nickel of 5% was found in all studied sections, i.e., this is a global effect. The global pattern of the distribution and composition of the iron particles clearly indicates that their origin is associated with cosmic dust. At the same time, the particles of Ni-Fe alloy and pure nickel are very rare, and their concentration does not correlate with the content of iron particles. Apparently, there are very few Ni-Fe and pure nickel particles in cosmic dust, and, most likely, the particles of Ni-Fe alloy are mainly due to impact events.     

A preliminary study on ore-forming environments of Xianglushan-type iron deposit and the weathering mineralization of Emeishan basalt in Guizhou Province,China

Xianglushan-type iron deposits are one of the new types of iron deposits found in the Weining Area of Western Guizhou. The iron-bearing rock system is a paleo-weathered crustal sedimentary(or accumulating) stratum between the top of the Middle-Late Permian Emeishan basalt formation and the Late Permian Xuanwei formation. Iron ore is hosted in the Lower-Middle part of the rock system. In terms of the genesis of mineral deposit, this type of deposit should be a basalt paleo-weathering crustal redeposit type, very different from marine sedimentary iron deposits or continental weathering crust iron deposits. Based on field work and the analytical results of XRD Powder Diffraction, Electron Probe, Scanner Electron Microscope, etc., the geological setting of the ore-forming processes and the deposit features are illustrated in this paper. The ore-forming environment of the deposit and the Emeishan basalt weathering mineralization are also discussed in order to enhance the knowledge of the universality and diversity of mineralization of the Emeishan Large Igneous Province(ELIP), which may be a considerable reference to further research for ELIP metallogenic theories, and geological research for iron deposits in the paleo-weathering crust areas of the Emeishan basalt,Southwestern, China.     

Die Entstehung von Pyrit in rezenten Sedimenten des Piburger Sees

The occurrence of pyrite (FeS₂) and iron sulfide in surficial sediments of Piburger See was compared with thermodynamic calculations based on chemical analyses of iron and hydrogen sulfide in the interstitial water. The area below 17 m, where black spots were found in the sediments, showed ion products (log K_FeS=a_Fe2·a_HS/a_H+) between?3.11 and ?4.01. In areas with no visible FeS concretions logK_FeS values were in the range of ?4.74 to ?5.77, thus thermodynamic calculations seem to be in accordance with the appearance of iron sulfide. Nevertheless pyrite framboids, composed by more than 1,000 single crystals, coul be found even in shallow parts of the lake. Therefore the formation of pyrite is assumed to occur in microniches (diatom frustules, testacean shells). Inside these microcompartments high concentrations of hydrogen sulfide are reached due to the anaerobic decomposition of organic matter, whereas iron and additional sulfur are supplied by the diffusion of ferrous iron and sulfate from the anoxic environment.     

Preferential sputtering as a method of producing metallic iron,inducing major element fractionation and trace element enrichment

The mechanism responsible for the formation of finely divided metallic iron in lunar samples has been the subject of considerable debate. A review of the data currently available from laboratory simulation studies would appear to favour an origin involving preferential sputtering of oxygen atoms by the solar wind.Using a model presented here we find that it is thermodynamically predictable that preferential sputtering would lead to the formation of free iron. Likewise titanium should be enriched in particle surfaces due to the formation of Ti₂O₃ from TiO₂. Other major elements will be fractionated according to the ratio of their heat of sublimation to the heat of dissociation of their oxide. The changes induced in the surfaces of fine grains will be of considerable importance when these particles are incorporated into complex grains. Thus, we suggest that preferential sputtering may be implicated in the major element fractionations observed for glassy agglutinates. A 1% component of Fe∮ is able to account easily for the enrichment in the total iron observed.If sufficient exposure time is available preferential sputtering may be able to produce metallic iron-rich layers ca. 40Åthick on the surfaces of lunar grains. Most of this metal would derive from helium sputtering rather than hydrogen bombardment. Provided reduction takes place predominantly in fine particles with a mean grain size <10 μm diameter which are subsequently incorporated into glassy agglutinates, preferential sputtering could account for all the free iron in the lunar soil.For elements of atomic number ca. Z = 30 and above, thermodynamic effects become insignificant compared to momentum transfer considerations. Heavy (Pb, Hg) and medium heavy elements (Rb, Sr) could all be enriched by preferential sputtering. Monovalent elements (e.g. K, Rb) in silicates will have a lower binding energy and knock-on collisions with incoming solar wind atoms could cause their increased abundance in fine fractions of lunar soil.     

Native iron in the Earth and space

Thermomagnetic and microprobe studies of native iron in the terrestrial upper-mantle hyperbasites (xenoliths in basalts), Siberian traps, and oceanic basalts are carried out. The results are compared to the previous data on native iron in sediments and meteorites. It is established that in terms of the composition and grain size and shape, the particles of native iron in the terrestrial rocks are close to each other and to the extraterrestrial iron particles from sediments and meteorites. This suggests that the sources of the origin of these particles were similar; i.e., the formation conditions in the Earth were close to the conditions in the meteorites’ parent bodies. This similarity is likely to be due to the homogeneity of the gas and dust cloud at the early stage of the solar system. The predominance of pure native iron in the sediments can probably be accounted for by the fact that interstellar dust is mostly contributed by the upper-mantle material of the planets, whereas the lower-mantle and core material falls on the Earth mainly in the form of meteorites. A model describing the structure of the planets in the solar system from the standpoint of the distribution of native iron and FeNi alloys is proposed.     

Unique phenomenon of the accumulation of <Emphasis Type="Italic">terrestrial</Emphasis> metal iron particles in lacustrine deposits: Zhombolok volcanic region,East Sayan

The native iron particles that were previously detected by thermomagnetic and microprobe analyses in the sediments of different age in many regions of the world are of extraterrestrial origin. The similarity in the compositions, grain shapes, and sizes observed in the extraterrestrial and terrestrial particles of native iron testifies to the common production conditions of iron particles during the formation of planets. In this paper, the single finding of terrestrial iron in the lacustrine sediments of the Zhombolok volcanic region, East Sayan, is discussed. The uniqueness of the results indicates that the spatial distribution of the particles of native iron is limited to a fairly narrow area around their source—volcanic eruption or/and the fall of a large meteorite.     

Magnetic hysteresis in the F.M.R. spectra of fine-grained spherical iron: Possible evidence for a new carrier of hard remanence in lunar soils and rocks

Magnetic hysteresis effects have been observed in ferromagnetic resonance (FMR) spectra obtained at 9 and 16 GHz for certain simulated lunar glasses which were reduced by H₂ in the melt and rapidly quenched. Transmission electron microscopy has revealed that these samples contained spherical particles in the size range ～0.01–0.5 μm. FMR spectra obtained at 35 GHz (applied field ～ 12.5 kOe) exhibited a line shape characteristic of spherical, single-domain (SD) iron particles with no hysteresis. Computer simulations of the latter spectra confirmed that the average deviation from sphericity must be ?3% and that (2K₁/M_s) ≈ + 600 Oe for the precipitated magnetic phases. The principal features of the spectra obtained at all three frequencies have been explained on the basis of a simple theoretical treatment for spherical iron particles which have 2 domains in applied fields ?7 kOe, but become saturated at higher fields. Isothermal remanent magnetization (IRM) of these samples has been studied by both FMR and standard static techniques; the mean coercive force measured by the former (～4 kOe) contrasts with the mean value determined by the latter (～550 Oe). Apparently, FMR singles out and even amplifies the contributions of two-domain particles (which are magnetically hard), while the static measurement is more sensitive to the average of all particles present. The intensity of the FMR hysteresis of typical lunar soils is found to be ～1% of the total FMR intensity. In spite of this seemingly small value, two-domain iron particles may be important carriers of natural remanent magnetization (NMR) in certain lunar rocks.     

Thermomagnetic evidence of native iron in sediments

The paper summarizes the results of thermomagnetic analysis concerning the distribution of metallic iron in the sediments ranging in age from Miocene to Early Cretaceous sampled from the following sections: Gams (Austria); Verkhorech’e and Sel’bukhra (the Crimea); Kvirinaki and Tetritskaro (Georgia); Aimaki, Dzhengutai, Madzhalis, and Gergebil (Ciscaucasia, Russia); Klyuchi and Teplovka (Volga region, Russia); Koshak (Kazakhstan); and Khalats and Kara-Kala (Turkmenia). Small amounts of native iron (from 10⁻⁵% to 0.05%) are identified in 521 samples of 921 studied; i.e., iron particles are almost pervasive. This fact traces the origin of these particles to cosmic dust. Some established features point to the heterogeneous character of the cosmic dust: (a) the samples clearly fall into two groups. One group comprises the rocks that contain iron particles; the rocks of the other group are iron-free. In the first group, four intervals are distinguished where the sediments are globally enriched with iron with constant nickel content (5–6%); (b) in terms of composition, the iron particles are divided into three groups. The first group contains pure iron; the particles pertaining to the second group contain iron with a minor amount of nickel typical for kamacite; and the third group comprises the particles of Fe-Ni alloy with more than 20% nickel. The first and the second groups are ubiquitous; the particles of the third group are spread locally. They bear no relation to cosmic dust and are probably associated with the meteoritic impacts.     

New evidence of microbe origin for ferromanganese nodules from the East Pacific deep sea floor

Using a fluorescence microscope and EPMA, abundant microbe ”bodies“ and clear microbic fluorescent microstructure are determined in the ferromanganese nodules recently collected from the East Pacific deep sea floor. The microbic fluorescent structure shows a close relation to the formation of the ferromanganese nodules. According to their morphological features, the microbes are classified into two types: one is named clumpy microbe, which takes a bar-shaped manganese mineral as a pillar and grows like fasciculate coral, resulting in irregular cauliflorate nodules with rough surfaces; the other is called filamentous microbe, which grows in very thin arcuate and/or concentric circular laminae composed of a microbe layer and a metal (manganese and iron)-rich layer, leading to potato-shaped nodules with relatively smooth surfaces. It also can be seen that the two types of microbes are intergrown together, resulting in nodules complicated in compositions and shapes.     

Modeling the buildup of iron oxide encrustations in wells

Ferric iron encrustations are a common problem that seriously affects the performance of wells and drains. Their formation is induced by the mixing of reduced ground water containing ferrous iron with oxic shallow ground water and exposure to air. The process of ferrous iron oxidation is a kinetically controlled reaction. The reaction rate has a quadratic dependency on pH. The precipitating oxides have an autocatalytic effect that further enhances reaction progress. This paper describes the application of kinetic models to the problem of encrustation formation. Influences of pH, residence time, and autocatalysis were modeled. The overall influence of the autocatalytic reaction path is particularly strong when initial amounts of iron oxides are present. Autocatalysis provides a good explanation on the development of well yield commonly measured in the field. Encrustation precipitation is slow at first, but speeds up after a sufficient amount of iron oxide has built up. An incomplete removal of iron oxide encrustations during rehabilitation leads to a renewed increase in catalytic efficiency and encrustation precipitation.     

腾冲台水平摆在中强以上地震前异常特征分析

以腾冲台水平摆资料分析了近年来滇西地区范围内发生的中强以上地震,发现震前资料出现了反映地震孕育过程的异常变化,重点对该地区中强震前短临异常的变化特征进行探讨,为使用腾冲台水平摆资料进行识别以及捕捉地震短临异常,预测地震提供参考依据。     

Native iron and other magnetic minerals in the sediments of the northwestern Atlantic: Thermomagnetic and microprobe evidence

The thermomagnetic and microprobe analyses of sedimentary samples from DSDP 386, 387, 391A, and 391C boreholes in the northwestern Atlantic reveal the ubiquitous occurrence of particles of native iron. The concentrations of native iron are bimodal everywhere with the zero mode necessarily present. The nickel admixture in native iron forms two groups, one represented by pure iron and the comprising native iron with 5–6% Ni. The redeposition of iron particles manifests itself in the correlation between the concentrations of these particles and terrestrial minerals (magnetite), as well as in the equalization and reduction of the concentration of the iron particles. Pyrite and pyrrhotite are widespread in the studied sediments, and the distribution of native iron does not depend on the presence of pyrite (i.e., on redox conditions) in them. At the same time, the distributions of pyrite and particles of magnetite + titanomagnetite are inversely correlated, which can probably be accounted for by the partial dissolution of magnetite and titanomagnetite in the reducing conditions. The increased concentration of particles of volcanogenic homogeneous titanomagnetite is revealed in the volcanoclastic turbidites of the Oligocene and early and middle Miocene age at the base of the Bermuda Rise (borehole 386). The titanomagnetite composition is characteristic of the basalts of plume magmatism; it corresponds to the depth of the magmatic source in the interval of 50–25 km.     

Dust production and the release of iron oxides resulting from the aeolian abrasion of natural dune sands

Global dust trajectories indicate that signi?cant quantities of aeolian‐transported iron oxides originate in contemporary dryland areas. One potential source is the iron‐rich clay coatings that characterize many sand‐sized particles in desert dune?elds. This paper uses laboratory experiments to determine the rate at which these coatings can be removed from dune sands by aeolian abrasion. The coatings impart a red colour to the grains to which previous researchers have assigned variable geomorphological signi?cance. The quantities of iron removed during a 120 hour abrasion experiment are small (99 mg kg^?1) and dif?cult to detect by eye; however, high resolution spectroscopy clearly indicates that ferric oxides are released during abrasion and the re?ectance of the particles alters. One of the products of aeolian abrasion is ?ne particles (<10 µm diameter) with the potential for long distance transport. Copyright © 2004 John Wiley & Sons, Ltd.     

Factors Controlling In Situ Biogeochemical Transformation of Trichloroethene: Field Survey

We have previously defined in situ biogeochemical transformation as the biogenic formation of reactive minerals that are capable of abiotically degrading chlorinated solvents such as trichloroethene without accumulation of degradation products such as vinyl chloride (AFCEE et al. 2008 ). This process has been implemented in biowalls used to intercept contaminated groundwater. Abiotic patterns of contaminant degradation were observed at Altus Air Force Base (AFB) and in an associated column study, but not at other sites including Dover AFB. These abiotic patterns were associated with biogenic formation of reactive iron sulfide minerals. Iron sulfides in the form of small individual grains, coatings on magnetite, and sulfur‐deficient pyrite framboids were observed in samples collected from the Altus AFB biowalls and one of the EPA columns. Larger iron sulfide grains coated with oxide layers were observed in samples collected from Dover AFB. Altus AFB and the EPA column differed from Dover AFB in that groundwater flow at Dover AFB was relatively slow and potentially reversing. High volumetric sulfate consumption rates, an abiotic pattern of trichloroethene (TCE) degradation, and the formation of small, high surface area iron sulfide particles were associated with relatively high rates of TCE removal via an abiotic pattern. Geochemical modeling demonstrated that iron monosulfides such as mackinawite were near saturation, and iron disulfides such as pyrite were supersaturated at all sites. This environmental condition can be supportive of nucleation of small particles rather than crystal growth leading to larger particles. When nucleation is dominant, small, high surface area, and reactive particles result. When crystal growth dominates the crystals are larger and have lower specific surface area and reactivity. These results taken together suggest that creation of a dynamic environment can promote biogeochemical transformation based on generation of reactive iron sulfides.     

Early precambrian trondhjemitic suites in Western Australia and Northwestern Scotland,and the geochemical evolution of shields

Sodium-rich trondhjemites and quartz keratophyres, retained as pebbles in Archaean metaconglomerates, represent some of the oldest components (up to 3 by) of the Kalgoorlie System, Western Australia. New determinations indicate high Si, Na, Na/K, Ba/Rb, Ba/K, Sr/Ca+K, Ni, Ni/Mg, and Cr/Mg, and low K, Rb, Rb/Sr, and Y, in comparison to Taylor's (1965) [1] and other' average granites and to Nockolds and Allen's (1953) [2] acid calc-alkaline rocks. Syngeosynclinal quartz keratophyres (2.6 by) studied by O'Beirne (1968) [3] show similar comparisons. Similarly, high-grade acid and intermediate gneisses of the Lewisian, Scotland, have high Na/K, K/Rb, Ba/Rb, Ba/K, Sr/Ca+K, Ni, Ni/Mg, Cr, Cr/Mg, and low K, Rb, Rb/Sr, Y and Y/Ca. Secular decrease in Na/K, K/Rb and Sr/Rb is shown by granite series in Western Australia, Transvaal, Rhodesia and the Canadian Shield. The earliest members of these series compare with sodic acid plutons of island arcs, in particular Fiji, an archipelago showing a pattern of evolution analogous to that of the proposed model (Glikson, 1971) [4]. Evidence for an origin of Archaean sodic granites from below a basic crust is furnished by the abundance of basic xenoliths, by relationships in agmatite-gneiss terrains in Greenland, Scotland, and India, by K levels lower than those of Archaean metasediments, and by low initial⁸⁷Sr/⁸⁶Sr ratios. The abundance of euhedral quartz phenocrysts in the quartz keratophyres supports origin through partial melting of eclogite [5]. In high-grade belts, the originally low abundances of K and Rb were accentuated by synmetamorphic depletion, with which the formation of late-stage K-granites may have been associated. The correlation of chemical data enables an insight into spatial and temporal relationships between low- and high-grade early Precambrian terrains, and on the geochemical evolution of shields.     

Condensation and the composition of iron meteorites

The pressure-temperature conditions in the primordial nebula which could produce the observed Ni, Ga and Ge abundances in the major iron meteorite groups have been calculated assuming equilibrium condensation. Included in these calculations are the effect on the metal composition of Fe oxidation and sulphide formation during accretion, GeS and GaCl in the nebula gases and pressure variations in the nebula. It was found that the IIAB irons had their abundances of these elements fixed at the low-pressure extreme of the range which gives the IAB irons, but at 50 ± 10K higher temperatures. IIIAB and IVA formed over the same temperature range as IAB (600–670_?40⁺⁶⁰ K) in regions where the pressure was lower by a factor of 20 and 10⁴ respectively. Group IVB accreted soon after condensation of the metal and at pressures of less than 10^?3 atmosphere. The distribution of sulphur and carbon are consistent with this. The abundance of carbon in group IAB suggests that this and group IIAB accreted at about 10^?4 atmosphere, so that IIIAB and IVA accreted where the pressure was 5 × 10^?6 and 10^?8 atmosphere, respectively.     

Removal of Selenium Species from Waters Using Various Surface‐Modified Natural Particles and Waste Materials

Waste red mud and natural pumice/volcanic slag particles were surface modified and their selenium adsorption from waters was investigated. Acid activation/heat treatment of original red mud (ORM) particles significantly increased their micropore and external surface area and cumulative volume of pores. Iron oxide coating of pumice/slags and acid activation of ORM decreased their pH_pzc values and increased surface acidity. Selenite/selenate adsorption on iron oxide surfaces and acid activated red mud (AARM) was very fast with approximately first‐order adsorption kinetics. Iron oxide coating of pumice/slag and acid activation of ORM particles significantly enhanced their selenite and selenate uptakes. Maximum Se adsorption capacities as high as 6.3 (mg Se/g adsorbent) were obtained by AARM. The extent of selenate uptakes by the surface modified particles was generally lower than those of selenite. Due to competition among Se species and other background water matrix for iron oxide adsorption sites, reduced selenite/selenate uptakes were found in natural water compared to single solute tests. Higher Se uptakes by iron oxide surfaces were found at pH 7.5 compared to pH 8.9, due to increased electrostatic repulsion among iron oxides and Se species at higher pH. The most effective adsorbents among the tested 17 different particles for Se uptake were AARM and iron oxide coated pumice. Se concentrations less than drinking water standards (5–10 µg/L) can be achieved by these particles. These low‐cost, natural, or recyclable waste particles appear to be promising adsorbents for Se removal after their surface modification.     

Optical dating and lithic microwaste—Archaeological applications

Lithic microwaste (<1 mm in maximum dimensions) is produced during lithic tools and rock engraving manufacture. For tools or rocks containing quartz, small particles persist as microwaste initially on the ground surface but later at least some particles are incorporated into sedimentary deposits associated with the occupation site. If microwaste is distinguished from naturally occurring sediments, then optical dating of microwaste or its surrounding sediment would provide a mechanism for establishing a terminus-ante-et-post-quem for archaeological deposits. Identification of microwaste is undertaken by comparing the shape of microwaste particles with those from surface sediments, taking particular note of angularity and irregular shapes; and by analysing quartz grain surface morphologies. On the basis of surface features identified on experimental microwaste, particles identified as microwaste are separated from the sedimentary grains. Scanning electron microscopy and light microscopy are used to determine surface differences between pedogenic grains and anthropogenic material from archaeological deposits. Single-grain OSL dating technique is then employed for age determinations for particles identified as microwaste. It has been noted in previous research that microwaste particles may lie within or close to the age boundaries of the surrounding sediments but not necessarily where larger lithic material is found. Microwaste is incorporated into sediment and is not subjected to the same degree of movement as larger lithic waste and stone tools within the deposit. The advantage of dating microwaste directly by OSL is that it removes ambiguity about archaeological association. Archaeological events can be dated directly and correlated with sediment ages from surrounding environments, regardless of post-depositional processes. Sand grains surrounding artefacts are dated, usually leaving open the question of the association of the artefact to the sedimentary level, as the artefact may have been displaced from its original depositional level.     

Eolian Transport of Geogenic Hexavalent Chromium to Ground Water

A conceptual model of eolian transport is proposed to address the widely distributed, high concentrations of hexavalent chromium (Cr⁺⁶) observed in ground water in the Emirate of Abu Dhabi, United Arab Emirates. Concentrations (30 to more than 1000 μg/L Cr⁺⁶) extend over thousands of square kilometers of ground water systems. It is hypothesized that the Cr is derived from weathering of chromium-rich pyroxenes and olivines present in ophiolite sequence of the adjacent Oman (Hajar) Mountains. Cr⁺³ in the minerals is oxidized to Cr⁺⁶ by reduction of manganese and is subsequently sorbed on iron and manganese oxide coatings of particles. When the surfaces of these particles are abraded in this arid environment, they release fine, micrometer-sized, coated particles that are easily transported over large distances by wind and subsequently deposited on the surface. During ground water recharge events, the readily soluble Cr⁺⁶ is mobilized by rain water and transported by advective flow into the underlying aquifer. Chromium analyses of ground water, rain, dust, and surface (soil) deposits are consistent with this model, as are electron probe analyses of clasts derived from the eroding Oman ophiolite sequence. Ground water recharge flux is proposed to exercise some control over Cr⁺⁶ concentration in the aquifer.