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1.
The partitioning and incorporation mechanism of Ni and Ba in a ferromanganese nodule from Lake Baikal were characterized by X-ray microfluorescence, microdiffraction, and absorption spectroscopy. Fe is speciated as goethite, and Mn as romanechite (psilomelane) and 10 Å-vernadite (turbostratic buserite) with minor 7 Å-vernadite (turbostratic birnessite). Barium is associated with romanechite and Ni with vernadite in distinct and irregularly distributed layers, and each type of Mn oxide is separated from the other type by goethite. The binary Mn oxide banding pattern is interpreted by a two-mode accretionary model, in which the variation in Ba flux induced by hydrothermal water pulses determines whether a tectomanganate (romanechite) or phyllomanganate (vernadite) is formed during the ferromanganese nodule accretion. Consistent with the dependence of Ni sorption on pH and the circumneutral pH of the lake water, nickel is mainly substituted isomorphically for Mn in the manganese layer, and is not sorbed at vacant Mn layer sites in the interlayer.  相似文献   

2.
The mineralogy of natural ferromanganese coatings on quartz grains and the crystal chemistry of associated trace elements Ni, Zn, Ba, and As were characterized by X-ray microfluorescence, X-ray diffraction, and EXAFS spectroscopy. Fe is speciated as ferrihydrite and Mn as vernadite. The two oxides form alternating Fe- and Mn-rich layers that are irregularly distributed and not always continuous. Unlike naturally abundant Fe-vernadite, in which Fe and Mn are mixed at the nanoscale, the ferrihydrite and vernadite are physically segregated and the trace elements clearly partitioned at the microscopic scale. Vernadite consists of two populations of interstratified one-water layer (7 Å phyllomanganate) and two-water layer (10 Å phyllomanganate) crystallites. In one population, 7 Å layers dominate, and in the other 10 Å layers dominate. The three trace metals Ni, Zn, and Ba are associated with vernadite and the metalloid As with ferrihydrite. In vernadite, nickel is both substituted isomorphically for Mn in the manganese layer and sorbed at vacant Mn layer sites in the interlayer. The partitioning of Ni is pH-dependent, with a strong preference for the first site at circumneutral pH and for the second at acidic pH. Thus, the site occupancy of Ni in vernadite may be an indicator of marine vs. continental origin, and in the latter, of the acidity of streams, lakes, or soil pore waters in which the vernadite formed. Zinc is sorbed only in the interlayer at vacant Mn layer sites. It is fully tetrahedral at a Zn/Mn molar ratio of 0.0138, and partly octahedral at a Zn/Mn ratio of 0.1036 consistent with experimental studies showing that the VIZn/IVZn ratio increases with Zn loading. Barium is sorbed in a slightly offset position above empty tetrahedral cavities in the interlayer. Arsenic tetrahedra are retained at the ferrihydrite surface by a bidentate-binuclear attachment to two adjacent iron octahedra, as commonly observed. Trace elements in ferromanganese precipitates are partitioned at a few, well-defined, crystallographic sites that have some elemental specificity, and thus selectivity. The relative diversity of sorption sites contrasts with the simplicity of the layer structure of vernadite, in which charge deficit arises only from Mn4+ vacancies (i.e., no Mn3+ for Mn4+ substitution). Therefore, sorption mechanisms primarily depend on physical and chemical properties of the sorbate and competition with other ions in solution, such as protons at low pH for Ni sorption.  相似文献   

3.
多金属结核微层原位微区分析能够更好地揭示结核生长过程中元素的赋存和迁移过程,为认识多金属结核元素富集机制和成因提供新的证据.通过使用电子探针(EPMA)和激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)等手段对采集自东太平洋克拉里昂?克利珀顿断裂区(CCFZ区)的多金属结核进行了分析研究.研究结果表明,结核矿物主要为...  相似文献   

4.
Sequential digestions of Fe-Mn oxide coated boulders collected upstream and downstream from the Magruder mine, Lincoln Co., Georgia, indicate probable partitioning relationships for Zn, Cu, Pb, Co, and Ni with respect to Mn and Fe. Initial digestion with 0.1M hydroxylamine hydrochloride (Hxl) in 0.01M HNO3 selectively dissolyes Mn oxides, whereas subsequent digestion with 1:4 HCl dissolves remaining Fe oxides.The results indicate that partitioning is not constant, but varies systematically with respect to the location of metal-rich waters derived from sulfide mineralization. Upstream from the mineralized zone Zn and Ni are distinctly partitioned to the Fe oxide component and Co and Cu are partitioned to the Mn oxide component. Immediately downstream from the mineralized zone, Mn oxides become relatively more enriched in Zn, whereas Fe oxides are relatively more enriched in Cu, Co, and Ni. Analytical precision for Pb is poor, but available data suggests it is more closely associated with Fe oxides.For routine geochemical surveys utilizing coated surfaces, a one-step digestion method is probably adequate. Parameters useful for detecting sulfide mineralization are metal concentrations normalized to surface area or various ratios (e.g. Zn/(Mn + Fe), Cu/Mn, Pb/Fe). Ratios can be obtained much faster, and at lower analytical costs than conventional analysis of stream sediment.  相似文献   

5.
The Ni geochemistry of limonite and saprolite laterite ores from Pujada in the Philippines has been investigated using a mixture of laboratory and synchrotron techniques. Nickel laterite profiles are typically composed of complicated mineral assemblages, with Ni being distributed heterogeneously at the micron scale, and thus a high degree of spatial resolution is required for analysis. This study represents the first such analysis of Philippine laterite ores. Synchrotron bulk and microprobe X-ray absorption spectroscopy (XAS), comprising both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies, together with synchrotron microprobe X-ray fluorescence microscopy (XFM) and diffraction (XRD) have been applied to provide quantitative analysis of the mineral components and Ni speciation.Synchrotron microprobe EXAFS spectroscopy suggests that the limonite Ni is associated with phyllomanganate via adsorption onto the Mn oxide layers and substitution for Mn within these layers. Laboratory scanning electron microscopy, coupled to electron dispersive spectroscopy analyses, indicates that Ni is also associated with concentrated Fe containing particles and this is further confirmed by synchrotron bulk and microprobe investigation. Linear combination fitting of the bulk EXAFS limonite data suggests 60 ± 15% of the Ni is associated with phyllomanganate, with the predominant fraction adsorbed above vacancies in the MnO6 layers with the remainder being substituted for Mn within these layers. The remaining 40 ± 10% of the Ni in the limonite ore is incorporated into goethite through replacement of the Fe. In the saprolite ore, 90 ± 23% of the Ni is associated with a serpentine mineral, most likely lizardite, as a replacement for Mg. The remaining Ni is found within phyllomanganate adsorbed above vacancies in the MnO6 layers.  相似文献   

6.
The Montaña de Manganeso is a manganese vein-type deposit spatially associated with back-arc basin remnants of the Guerrero tectonostratigraphic terrane. The study of major- and trace-element geochemical characteristics of the deposit provides insight into the controls on ore-forming processes within the area. The deposit is characterized by low Co, Cu and Ni abundances, and high Ba (>10,000 ppm) contents and Mn/Fe ratios (<500), typical of hydrothermal Mn deposits. In addition, the low ∑REE abundances (18.7 to 103 ppm), negative Ce anomalies (0.2 to 0.6), and positive Y (1.00 to 2.34) and Eu anomalies (0.6 to 4.4) also suggest a hydrothermal source for the deposit. Discrimination plots involving ∑REE and Zr vs. (Cu + Ni + Co) and Ce/Ce* vs. Nd and Y/Ho further indicate a hydrothermal source in an oxidizing depositional environment. The Mn-Fe-(Ni + Cu + Co), MnO2-MgO-Fe2O3, (Cu/Zn)/Fe2O3 vs. (Zn/Ni)/MnO2 and Na/Mg diagrams display intermediate signatures between marine and terrestrial environments. This suggest that the Montaña de Manganeso deposit is the result of two metallogenic stages: (I) the earliest stage, which involved the formation of Mn oxides by hydrothermal/diagenetic processes in the Arperos back-arc basin during the Cretaceous; and (II) the latest stage took place subsequent to accretion the Guerrero tectonostratigraphic terrane onto the continent and involved the remobilization of the Cretaceous submarine Mn oxides (and associated trace elements) and subsequent redepositation by Tertiary continental hydrothermal activity.  相似文献   

7.
The upper 25 m of Bandelier Tuff at Pajarito Mesa, New Mexico, include soils, shallow fractures, deeper fractures, and tuff matrices in which clays provide a record of transport and alteration. The principal pathways within this system are fractures that penetrate the tuff. Large fractures that host deep root penetration provide a setting in which clay deposits accumulate through particulate or colloidal migration from the soil zone. Clays throughout the system are predominantly expandable interstratified illite/smectites (I/S), but clays of the tuff matrix at depth are distinctly Fe-rich and are not mixed with clays transported from the surface into fractures. Chemical alteration superimposed on clay particles transported into fractures results in clays with lower Al : Si ratios, higher Na, and higher lanthanide content with increasingly negative Eu anomalies with depth. These changes are accompanied by invasion and precipitation of Mn oxides, principally birnessite, within clay bodies. Investigation of the Mn oxides by synchrotron X-ray fluorescence (SXRF) shows that Mn is associated with Ba, Ce, Ni, and Pb. In addition, synchrotron X-ray absorption near-edge structure (XANES) spectra show that Ce in Mn oxides occurs as Ce3+ and Ce4+, with average Ce oxidation state of ∼3.75. The Mn oxides intergrown with clays actively participate in removal of Ce from solution, accompanied by oxidation of Ce3+ to Ce4+. Other lanthanides are accumulated by the clays but are not concentrated along with Ce in the Mn oxides. Extraction of Ce from solution by Mn oxides is more effective than lanthanide accumulation in clay, a process that is variable and likely influenced by defects, extent of recrystallization, and particle sizes. This dichotomy in lanthanide interaction results in locally constant Ce content but either negative or positive Ce anomalies in the clay-Mn oxide system as a consequence of variability in the abundance of the other lanthanides. Nevertheless, the net lanthanide pattern for the sum of all clay-Mn oxide samples in either shallow or deep fractures has no Ce anomaly, indicating that other lanthanides segregated from Ce are not transported beyond the range of either the shallow or deep fracture systems. Evidence from Eu anomalies indicates that lanthanides accumulated in the fracture clays are acquired from the local tuff. The clay-Mn oxide assemblage is more effective than clay alone in accumulating of a wide variety of heavy metals.  相似文献   

8.
A series of samples from the Hine Hina hydrothermal field (HHF) and the Mariner hydrothermal field (MHF) in the Central and Southern Valu Fa Ridge (VFR), Lau Basin were examined to explain the source origin and formation of the hydrothermal Fe-Si-Mn oxide deposits. The mineralogy was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), Mössbauer spectroscopy, and energy-dispersive spectroscopy (EDS). For the Fe-Mn oxide crusts in the HHF, varying amounts of volcanic fragments and some seawater contributions were recognized, along with higher concentrations of Mn, Al, Co, Ni, Zn, Sr, Mo, elevated ∑REE and negative Ce anomalies. In contrast, the Si-rich oxide samples of the MHF were enriched in Cu, Pb and Ba, indicative of proximity to a hydrothermal jet. Moreover, conductive cooling of hydrothermal fluid evoked the Si-rich deposit formation in the MHF. The Sr, Nd and Pb isotope data provided further constraints regarding the source and formation of the Fe-Si-Mn deposits in the VFR by showing that the samples of the HHF are a mixture of three components, namely, hydrothermal fluid, seawater and volcanic materials, whereas the samples of the MHF were dominated by hydrothermal fluids. The seawater had a minor influence on the Nd isotope data, and the Pb isotope data exhibited a close association with the substrate rock and preformed volcaniclastic layers in this area. The occurrence of relatively high Mn/Fe ratios in the hydrothermal deposits of this area may be a good indicator of the propagating activities of the VFR over geological time.  相似文献   

9.
Bulk chemical, mineralogical and selective leach analyses have been made on a suite of abyssal ferromanganese nodules and associated sediments from the S.W. equatorial Pacific Ocean. Compositional relations between nodules, sediment oxyhydroxides and nearby ferromanganese encrustations are drawn assuming that the crusts represent purely hydrogenetic ferromanganese material. Crusts, δMnO2-rich nodules and sediment oxyhydroxides are compositionally similar and distinct from diagenetic todorokitebearing nodules. Compared to Fe-Mn crusts, sediment oxyhydroxides are however slightly enriched, relative to Mn and Ni, in Fe, Cu, Zn, Ti and Al, and depleted in Co and Pb, reflecting processes of non-hydrogenous element supply and diagenesis. δMnO2 nodules exhibit compositions intermediate between Fe-Mn crusts and sediment oxyhydroxides and thus are considered to accrete oxides from both the water column and associated sediments.Deep ocean vertical element fluxes associated with large organic aggregates, biogenic calcite, silica and soft parts have been calculated for the study area. Fluxes associated with organic aggregates are one to three orders of magnitude greater than those associated with the other phases considered, are in good agreement with element accumulation rates in sediments, and are up to four orders of magnitude greater than element accumulation rates in nodules. Metal release from labile biogenic material in surface sediments can qualitatively explain the differences between the composition of Fe-Mn crusts and sediment oxyhydroxides.Todorokite-rich diagenetic nodules are confined to an eastwards widening equatorial wedge. It is proposed that todorokite precipitates directly from interstitial waters. Since the transition metal chemistry of interstitial waters is controlled dominantly by reactions involving the breakdown of organic carbon, the supply and degradation rate of organic material is a critical factor in the formation of diagenetic nodules. The wide range of (trace metal/Mn) ratios observed in marine todorokite reflects a balance between the release of trace metals from labile biogenic phases and the reductive remobilisation of Mn oxide, both of which are related to the breakdown of organic carbon.  相似文献   

10.
富钴结壳生长过程中铁锰氧化物矿物组合的变化   总被引：3，自引：0，他引：3  
富钴结壳的矿物学研究是一个难点，本文运用电子探针微区分析结合X射线衍射和矿相显微镜观察的综合方法对富钴结壳中的铁锰氧化物矿物组合及其组分变化进行了研究，研究发现，富钴结壳是从与胶状粘土类混合共沉积开始生长的，结壳内部的韵律层和柱状构造也是始于粘土层终于粘土层的；铁锰团粒的核心一般是较纯的水羟凶国矿小核心，可能是在生物媒介作用下在水体中形成后沉降叠积的，FM、FPE海山结壳的中层存在一较纯水羟锰矿层，但该层中Co含量FM15比FPE06低得多，可能反映了FM15在该层形成时Co通量较低，而该层在FN12中不存在，反映了区域环境的较大差异，在FN12火焰状构造亚带存在Mn氧化物和Fe氧化物的极度分异现象，可能反映了结壳形成环境的重大变化。  相似文献   

11.
Microorganisms play important roles in mediating biogeochemical reactions in deep-sea hydrothermal plumes, but little is known regarding the mechanisms that underpin these transformations. At Guaymas Basin (GB) in the Gulf of California, hydrothermal vents inject fluids laden with dissolved Mn(II) (dMn) into the deep waters of the basin where it is oxidized and precipitated as particulate Mn(III/IV) oxides, forming turbid hydrothermal “clouds”. Previous studies have predicted extremely short residence times for dMn at GB and suggested they are the result of microbially-mediated Mn(II) oxidation and precipitation. Here we present biogeochemical results that support a central role for microorganisms in driving Mn(II) oxidation in the GB hydrothermal plume, with enzymes being the primary catalytic agent. dMn removal rates at GB are remarkably fast for a deep-sea hydrothermal plume (up to 2 nM/h). These rapid rates were only observed within the plume, not in background deep-sea water above the GB plume or at GB plume depths (∼1750-2000 m) in the neighboring Carmen Basin, where there is no known venting. dMn removal is dramatically inhibited under anoxic conditions and by the presence of the biological poison, sodium azide. A conspicuous temperature optimum of dMn removal rates (∼40 °C) and a saturation-like (i.e. Michaelis-Menten) response to O2 concentration were observed, indicating an enzymatic mechanism. dMn removal was resistant to heat treatment used to select for spore-forming organisms, but very sensitive to low concentrations of added Cu, a cofactor required by the putative Mn(II)-oxidizing enzyme. Extended X-ray absorption fine structure spectroscopy (EXAFS) and synchrotron radiation-based X-ray diffraction (SR-XRD) revealed the Mn oxides to have a hexagonal birnessite or δ-MnO2-like mineral structure, indicating that these freshly formed deep-sea Mn oxides are strikingly similar to primary biogenic Mn oxides produced by laboratory cultures of bacteria. Overall, these results reveal a vigorous Mn biogeochemical cycle in the GB hydrothermal plume, where a distinct microbial community enzymatically catalyzes rapid Mn(II) oxidation and the production of Mn biooxides.  相似文献   

12.
The Sjögruvan deposit is one of the Långban-type Fe-Mn oxide deposits hosted by marble interbeds within Svecofennian metavolcanic rocks in the Bergslagen region, central Sweden. Mineralogical and geochemical studies have been carried out to clarify the premetamorphic origin of this type of deposit, which is set apart from most other Mn mineralizations by a significant enrichment in Ba, As, Sb, Pb, W and Be contained by various oxyminerals. The principal ore types at Sjögruvan are (1) hematite+quartz-magnetite, (2) hausmannite+calcite+tephroite and (3) braunite+celsian+phlogopite. The Mn ores are compositionally akin to modern Mn deposits formed by submarine hydrothermal processes (with a high Mn/Fe ratio and low contents of Co, Ni, Th, U and REE) and likely owe their existence to similar mechanisms of formation. Pb isotope data indicate that the metal source and timing of deposition is similar to the major stratabound base-metal and iron deposits in Bergslagen. All the key elements have been leached from the local felsic volcanic units and were deposited on the sea floor; the excellent Mn-Fe separation occurred in an Eh-pH gradient that essentially corresponded to the mixing zone of hydrothermal solutions and seawater. The braunite ore is chemically distinct from the hausmannite ore, with a high concentration of refractory elements (Al, Ti, Zr) and a positive Ce anomaly, which indicate a detrital/hydrogenetic contribution to its protolith. Carbon isotope ('13C) values around 0‰ (relative PDB) suggest that carbonates in the deposit formed directly from seawater.  相似文献   

13.
Thick ferromanganese (Fe-Mn) crusts from four Cretaceous seamounts (The Paps, Tropic, Echo and Drago) at the southern Canary Island Seamount Province (CISP) in the northeastern tropical Atlantic were recovered along the flanks and summits from 1700 to 3000 m water depths. CISP is composed of > 100 seamounts and submarine hills, is likely the oldest hotspot track in the Atlantic Ocean, and is the most long-lived of known hotspots globally. The Fe-Mn crusts grow on basalt-sedimentary rock substrates below the northeastern tropical Atlantic core of the oxygen minimum zone (OMZ) with a maximum thickness of 250 mm at a water depth of 2400 m. The mineralogical and chemical composition of these Fe-Mn crusts indicate a hydrogenetic origin. The main Mn minerals are vernadite with minor interlayered todorokite and asbolane-buserite. Fe oxides are essentially ferroxyhyte and goethite. The Fe-Mn crusts show high average contents in Fe (23.5 wt%), Mn (16.1 wt%), and trace elements like Co (4700 μg/g), Ni (2800 μg/g), V (2400 μg/g) and Pb (1600 μg/g). Rare earth elements plus yttrium (REY) averages 2800 μg/g with high proportions of Ce (1600 μg/g). Total platinum group elements (PGEs) average 230 ng/g, with average Pt of 182 ng/g. Two main types of growth layers form the crusts: 1) a dense laminae of oxides with high contents in Mn, Co and Ni associated with vernadite and Cu, Ni, and Zn associated with todorokite; 2) botryoidal layers with high contents in Fe, Ti, V and REY associated with goethite. The Fe-Mn crusts from the CISP region show higher contents in Fe, V, Pb and REY but lower Mn, Co, Ni and PGEs contents than Pacific or Indian ocean seamount crusts. The oldest maximum age of initiation of crust growth was at 76 Ma (Campanian, Late Cretaceous). Using a combination of high resolution Co-chronometer and geochemical data along an Electron Probe Micro Analysis (EPMA) transect, four stages in morphology, chemical contents and growth rates can be differentiated in the the Cenozoic crusts since 28 Ma, which we interpret as due to changes in the ventilation of the North Atlantic OMZ and to the increase of Saharian dust inputs. An earliest growth period, characterized by similar contents of Fe and Mn in the interval 27.8–24.45 Ma (late Oligocene-early Miocene) reflects slow precipitation related to a thick OMZ. An intermediate laminated zone with higher contents of Fe, Si and P, high growth rates reaching 4.5 mm/Ma, and precipitation of Fe-Mn oxides during the interval 24.5–16 Ma is related to periods of ventilation of the OMZ by intrusion of deep upwelling currents. Significant increase in Fe contents at ca. 16 Ma correlates with the onset of incursions of Northern Component Waters into the North Atlantic. Finally, since 12 Ma, the very low growth rates (< 0.5 mm/Ma) of the crust are related to a thick North Atlantic OMZ, an increase in Sahara dust input and a stable thermohaline circulation.  相似文献   

14.
Fourteen ferromanganese nodule–sediment pairs from different sedimentary environments such as siliceous ooze (11), calcareous ooze (two) and red clay (one) from Central Indian Ocean Basin (CIOB) were analysed for major, trace and rare earth elements (REE) to understand the possible elemental relationship between them. Nodules from siliceous and calcareous ooze are diagenetic to early diagenetic whereas, nodule from red clay is of hydrogenetic origin. Si, Al and Ba are enriched in the sediments compared to associated nodules; K and Na are almost in the similar range in nodule–sediment pairs and Mn, Fe, Ti, Mg, P, Ni, Cu, Mo, Zn, Co, Pb, Sr, V, Y, Li and REEs are all enriched in nodules compared to associated sediments (siliceous and calcareous). Major portion of Si, Al and K in both nodules and sediments appear to be of terrigenous nature. The elements which are highly enriched in the nodules compared to associated sediments from both siliceous and calcareous ooze are Mo – (307, 273), Ni – (71, 125), Mn – (64, 87), Cu – (43, 80), Co – (23, 75), Pb – (15, 24), Zn – (9, 11) and V – (8, 19) respectively. These high enrichment ratios of elements could be due to effective diagenetic supply of metals from the underlying sediment to the nodule. Enrichment ratios of transition metals and REEs in the nodule to sediment are higher in CIOB compared to Pacific and Atlantic Ocean. Nodule from red clay, exhibit very small enrichment ratio of four with Mn and Ce while, Al, Fe, Ti, Ca, Na, K, Mg, P, Zn, Co, V, Y and REE are all enriched in red clay compared to associated nodule. This is probably due to presence of abundant smectite, fish teeth, micronodules and phillipsite in the red clay. The strong positive correlation (r ? 0.8) of Mn with Ni, Cu, Zn and Mo and a convex pattern of shale-normalized REE pattern with positive Ce-anomaly of siliceous ooze could be due to presence of abundant manganese micronodules. None of the major trace and REE exhibits any type of inter-elemental relationship between nodule and sediment pairs. Therefore, it may not be appropriate to correlate elemental behaviour between these pairs.  相似文献   

15.
Abstract. Rare earth, major and trace element geochemistry is reported for the Kunimiyama stratiform ferromanganese deposit in the Northern Chichibu Belt, central Shikoku, Japan. The deposit immediately overlies greenstones of mid-ocean ridge basalt (MORB) origin and underlies red chert. The ferromanganese ores exhibit remarkable enrichments in Fe, Mn, P, V, Co, Ni, Zn, Y and rare earth elements (excepting Ce) relative to continental crustal abundance. These enriched elements/ Fe ratios and Post-Archean Average Australian Shale-normalized REE patterns of the ferromanganese ores are generally analogous to those of modern hydrothermal ferromanganese plume fall-out precipitates deposited on MOR flanks. However in more detail, Mn and Ti enrichments in the ferromanganese ores are more striking than the modern counterpart, suggesting a significant contribution of hydrogenetic component in the Kunimiyama ores. Our results are consistent with the interpretation that the Kunimiyama ores were umber deposits that primarily formed by hydrothermal plume fall-out precipitation in the Panthalassa Ocean during the Early Permian and then accreted onto the proto-Japanese island arc during the Middle Jurassic. The presence of strong negative Ce anomaly in the Kunimiyama ores may indicate that the Early Permian Panthalassa seawater had a more striking negative Ce anomaly due to a more oxidizing oceanic condition than today.  相似文献   

16.
Cation exchange reactions with participation of heavy metals Mn, Co, Ni, Cu, Zn, Cd, Ba, and Pb were studed in oceanic low-temperature hydrothermal deposits of various mineral compositions and in hydrogenic Fe-Mn crusts. Individual minerals and their assemblages differ significantly in absorptive capacity, which increases in the following order: hematite ? Si-protoferrihydrite < protoferrihydrite < geothite < nontronite ? Fe-vernadite + Mn-feroxyhyte < Fe-free vernadite < bernessite + Fe-free vernadite < bernessite; i.e., it successively increases from the mineral with a coordination type of lattice to minerals with a layer-type structure. The exchange complex of all minerals includes Na+, K+, Ca2+, and Mg2+, i.e., the main cations of seawater. In Mn minerals, Mn2+ is the main exchange component. The contribution of all the mentioned cations to the exchange capacity of minerals is as high as 90–98%. The highest absorptive capacity among the examined low-temperature oceanic deposits is characteristic of hydrothermal Mn minerals. Their capacity exceeds substantially that of hydrothermal oxides, hydroxides, Fe-aluminosilicates, and hydrogenic Fe-Mn minerals. The absorptive capacity of all examined Mn minerals relative to heavy metals increases in the same order: Ni < Zn < Cd < Mn < Co < Pb < Cu.  相似文献   

17.
Hydrothermal manganese and ferromanganese deposits associated with Neyriz ophiolite colored mélange occurred as small ore deposits in the Abadeh-Tashk area, SE of Fars Province, SW Iran. The deposits are found in three types: a) banded syngenetic ores, b) massive boudin and lens shaped diagenetic ores and c) vein and veinlet epigenetic ores. Microtextural, geochemical and mineralogical data associated with petrographic Raman, FTIR and SEM studies indicated that the primary Fe compounds formed series of microbially mediated biomats and Mn compounds were precipitated as an amorphous oxide on an active oxide surface accompanying silica gels. Field relationships between ore and host rock, high Mn/Fe ratio (17.43 to 40.79), ΣLREE, positive Eu and negative Ce anomalies in syngenetic ore types reveal that the ores were formed by hydrothermal fluid in an oceanic floor environment. Manganese was fractionated from iron due to physicochemical changes as well as microbial activities in the sedimentary environment. Microbial remains as filamentous beads with regular circular shapes, vermiform structures, series of Fe-rich biomats, traces of embedded organic material besides trace metals and REE concentrations in Mn ores emphasize the role of microorganisms in Fe and Mn precipitation. Syngenetic mineralization took place under suboxic neutrophilic conditions, while diagenetic processes resulted in variably reduced Fe- and Mn-oxides via organic matter decomposition, forming rhodochrosite as the end product. Braunite formation occurred most probably as a biogeochemically mediated early diagenetic product. Diagenetic and epigenetic Mn ores were formed when primary Mn deposits underwent subsequent diagenetic and remobilization–redeposition events respectively.  相似文献   

18.
Biofilm-embedded Mn oxides exert important controls on trace metal cycling in aquatic and soil environments. The speciation and mobility of Zn in particular has been linked to Mn oxides found in streams, wetlands, soils, and aquifers. We investigated the mechanisms of Zn sorption to a biogenic Mn oxide within a biofilm produced by model soil and freshwater MnII-oxidizing bacteria Pseudomonas putida. The biogenic Mn oxide is a c-disordered birnessite with hexagonal layer symmetry. Zinc adsorption isotherm and Zn and Mn K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy experiments were conducted at pH 6.9 to characterize Zn sorption to this biogenic Mn oxide, and to determine whether the bioorganic components of the biofilm affect metal sorption properties. The EXAFS data were analyzed by spectral fitting, principal component analysis, and linear least-squares fitting with reference spectra. Zinc speciation was found to change as Zn loading to the biosorbent [bacterial cells, extracellular polymeric substances (EPS), and biogenic Mn oxide] increased. At low Zn loading (0.13 ± 0.04 mol Zn kg−1 biosorbent), Zn was sorbed to crystallographically well-defined sites on the biogenic oxide layers in tetrahedral coordination to structural O atoms. The fit to the EXAFS spectrum was consistent with Zn sorption above and below the MnIV vacancy sites of the oxide layers. As Zn loading increased to 0.72 ± 0.04 mol Zn kg−1 biosorbent, Zn was also detected in octahedral coordination to these sites. Overall, our results indicate that the biofilm did not intervene in Zn sorption by the Mn-oxide because sorption to the organic material was observed only after all Mn vacancy sites were capped by Zn. The organic functional groups present in the biofilm contributed significantly to Zn removal from solution when Zn concentrations exceeded the sorption capacity of the biooxide. At the highest Zn loading studied, 1.50 ± 0.36 mol Zn kg−1 biosorbent, the proportion of total Zn sorption attributed to bioorganic material was 38 mol%. The maximum Zn loading to the biogenic oxide that we observed was 4.1 mol Zn kg−1 biogenic Mn oxide, corresponding to 0.37 ± 0.02 mol Zn mol−1 Mn. This loading is in excellent agreement with previous estimates of the content of cation vacancies in the biogenic oxide. The results of this study improve our knowledge of Zn speciation in natural systems and are consistent with those of Zn speciation in mineral soil fractions and ferromanganese nodules where the Mn oxides present are possibly biogenic.  相似文献   

19.
The microbial catalysis of Mn(II) oxidation is believed to be a dominant source of abundant sorption- and redox-active Mn oxides in marine, freshwater, and subsurface aquatic environments. In spite of their importance, environmental oxides of known biogenic origin have generally not been characterized in detail from a structural perspective. Hyporheic zone Mn oxide grain coatings at Pinal Creek, Arizona, a metals-contaminated stream, have been identified as being dominantly microbial in origin and are well studied from bulk chemistry and contaminant hydrology perspectives. This site thus presents an excellent opportunity to study the structures of terrestrial microbial Mn oxides in detail. XRD and EXAFS measurements performed in this study indicate that the hydrated Pinal Creek Mn oxide grain coatings are layer-type Mn oxides with dominantly hexagonal or pseudo-hexagonal layer symmetry. XRD and TEM measurements suggest the oxides to be nanoparticulate plates with average dimensions on the order of 11 nm thick × 35 nm diameter, but with individual particles exhibiting thickness as small as a single layer and sheets as wide as 500 nm. The hydrated oxides exhibit a 10-Å basal-plane spacing and turbostratic disorder. EXAFS analyses suggest the oxides contain layer Mn(IV) site vacancy defects, and layer Mn(III) is inferred to be present, as deduced from Jahn-Teller distortion of the local structure. The physical geometry and structural details of the coatings suggest formation within microbial biofilms. The biogenic Mn oxides are stable with respect to transformation into thermodynamically more stable phases over a time scale of at least 5 months. The nanoparticulate layered structural motif, also observed in pure culture laboratory studies, appears to be characteristic of biogenic Mn oxides and may explain the common occurrence of this mineral habit in soils and sediments.  相似文献   

20.
Several small Mn–Fe oxide and Mn-oxide ore bodies associated with Precambrian Iron Ore Group of rocks are located within Koira-Noamundi province of north Orissa, India. These deposits are classified into in situ (stratiform), remobilized (stratabound) and reworked categories based on their field disposition. Volcaniclastic/terrigenous shale in large geographic extension is associated with these ore bodies.The in situ ore bodies are characterised by cryptomelane-, romanechite- and hematite-dominating minerals, low Mn/Fe ratio (1.1) and relatively lower abundance of trace (1500–2500 ppm) constituents. In such type of deposits the stratigraphic conformity of oxides with the tuffaceous shale suggests precipitation of Mn and Fe at a time of decreased volcaniclastic/terrigenous contribution. The minor and trace elements were removed from solution by adsorption rather than by precipitation. Both Mn and Fe oxides when precipitated adsorb trace elements strongly but the partitioning of elements takes place during diagenesis. The inter-elemental relationship reveals that Cu, Co, Ni, Pb and Zn were adsorbed on precipitating hydrous Mn oxides and form manganates. Some of these elements probably get desorbed from Fe oxide because of their inability to substitute for Fe3+ in the lattice of its oxide. However, P, V, As and Mo were less partitioned and retained in Fe-oxide phase. Positive correlation between Al2O3 and SiO2, MgO, Na2O, TiO2 and some traces like Li, Nb, Sc, Y, Zr, Th and U points to their contribution through volcaniclastic/terrigenous detritus of both mafic and acidic composition.The remobilized ore bodies are developed in a later stage through dissolution, remobilization and reprecipitation of Mn oxides in favorable structural weak planes under supergene environment. Increase in average Mn/Fe ratio (8) and trace content (5000–8500 ppm) by 5–2.5 orders of magnitude, respectively, or more above its abundance in adjoining/underlying protore is characteristic of these deposits. The newly formed Mn ores constituting lithiophorite, cryptomelane/romanechite and goethite get quantitatively enriched in traces like Cu, Co, Ni, Pb and Zn. Positive correlation between Mn, Li, Co and Zn is due to the formation of mineral of lithiophorite–chalcophanite group during redistribution and reconcentration of Mn oxide. P and V, which were present in Fe oxide, also get dissolved and reprecipitate with Fe oxyhydroxide in these ores. Some other elements like Y, Th and U show positive relation with Fe. This is probably due to leaching of these elements during chemical weathering of associated shale and getting re-adsorbed in Fe-oxyhydroxide phase.However, under oxidizing environment selective cations like Ba, K, etc. resorb from Mn-structure, resulting in the development of pyrolusite (Mn/Fe>20). In such transformation, trace metals from pyrolusitic structure expels out, resulting thereby in a considerable reduction in total trace value (<3000 ppm).The reworked ore bodies are allochthonous in nature and developed through a number of stages during terrain evolution and lateritisation. Secondary processes such as reworking of pre-existing crust; solution and remobilization; precipitation and cementation and transport, etc. are responsible for their development. Such deposits are usually very low in Mn/Fe ratio (3) and trace content (<2000 ppm).  相似文献   

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