Structure, chemistry and origins of gypsum crusts in southern Tunisia and the central Namib Desert

Gypsum crusts are broadly defined as accumulations at or within about 10 m of the land surface from 0.10m to 5.0 m thick containing more than 15% by weight gypsum (CaSO₄·2H₂O) and at least 5.0% by weight more gypsum than the underlying bedrock. The deposits are often, but not invariably, consolidated owing to cementation by gypsum. The crusts are found in many of the world's deserts where mean monthly potential evaporation exceeds mean monthly precipitation throughout the year. Using structural, fabric and textural criteria, three main types of crust may be distinguished:(1) bedded crusts, found either at or beneath the land surface, which are made up of discrete horizontal strata up to 0.10 m thick, each showing a gradation in gypsum crystal size from less than 50 μm at the top to more than 0.50 mm at the base; (2) subsurface crusts, of which there are two forms, one made up of large, lenticular crystals (up to 0.50 m in diameter)—the desert rose crusts—and the other, a mesocrystalline form, with gypsum crystals up to about 1.0 mm in diameter; and (3) surface crusts, which are subdivided into columnar, powdery and cobble forms, all of which are made up of predominantly alabastrine gypsum (crystallites less than 50 μm in diameter). In southern Tunisia and the central Namib Desert, bedded crusts are found around ephemeral lakes and lagoons. They are characterized by size-graded beds, gypsum contents of 50–80% by weight and comparatively high concentrations of sodium, potassium, magnesium and iron. They are interpreted as shallow-water evaporites which accumulate when saline pools evaporate to dryness. Desert rose crusts or croûtes de nappe generally contain 50–70% by weight gypsum, and have higher sodium concentrations than the second subsurface form. Texturally they are characterized by poikilitic inclusion of clastic material within large lenticular crystals. They are interpreted as hydromorphic accretions, which precipitate in host sediments at near-surface water tables through the evaporation of groundwater. The second form of subsurface crust—the mesocrystalline—often occurs in close association with the various surface forms. Unlike the hydromorphic crusts, they are not restricted to low-lying terrain. They are characterized by gypsum contents reaching 90% by weight, and have a close chemical and textural similarity to columnar surface crusts. This mesocrystalline form represents an illuvial accumulation; the surface forms—excluding the bedded crusts—are exhumed examples at various stages of solutional degradation. Subsurface precipitation of gypsum from meteoric waters containing salts leached from the surface, results in displacive gypsum accumulation in the soil zone. In southern Tunisia, the gypsum is derived from sand and dust deflated from evaporitic basins; in the central Namib, salts dissolved in fog water are the most likely source. Where other salts are present, differential leaching may form two-tiered crusts, calcrete—gypsum or gypsum—halite, if rainfall is sufficient to mobilize the less soluble salt yet insufficient to flush the more soluble. Gypsum crust genesis is restricted to arid environments, and if their susceptibility to post-depositional alteration is acknowledged, they can provide valuable palaeoclimatic indicators.     

Rare earth elements in phosphate-ferromanganese crusts on Pacific seamounts

Based on publications devoted to the composition of P-rich ferromanganese crusts on Pacific seamounts, relationships between the REE distribution in the crusts and the contents of phosphates and Fe-Mn hydroxides therein are considered. It is shown that REEs in the crusts are related to all three mineral phases and their contents are variable. In general, the REEs show weak correlations with P, Mn, and Fe in different varieties of ore crust. Average REE contents are comparable in samples with the maximal and minimal phosphorus contents, suggesting irregularity of REE distribution in the phosphates and ferromanganese phases. This fact is consistent with data on the presence of natural REE minerals in the phosphates.     

Abnormally high mercury contents in hydrogenic ferromanganese crusts from Seth Guyot (Northwestern Pacific)

Variations in mercury contents in marine sediments have implications for hydrothermal activity, paleoclimate, depositional environments, and primary bioproduction. Mercury contents reach 148 ppb in hydrogenic ferromanganese crusts on flat-topped seamounts. Such crusts, with up to 4120 ppb Hg, were dredged from the slopes of Seth Guyot in the western Marcus-Wake Seamounts in 1982, during the 13th cruise of RV Vulkanolog. The Seth Fe-Mn crusts are of the same origin as hydrogenic Co-rich ferromanganese deposits from seamounts in other oceanic regions. Mercury accumulated in the Cenozoic as Fe-Mn oxyhydroxides in the crusts adsorbed Hg from bottom water. The process was especially rapid during the Pliocene volcano-tectonic rejuvenated stage.     

Geochemical and mineralogical evidence of tectonic and sedimentary factors controlling the origin of ferromanganese crusts associated to stratigraphic discontinuities (Betic Cordilleras, SE of Spain)

Ferromanganese crusts were found in carbonates of tectonostratigraphic units located in the northern and southern areas of the eastern External Subbetic of the Betic Cordilleras (SE Spain). The crusts are associated with four stratigraphic discontinuities of the Jurassic pelagic swells sequences: D1 (Late Carixian-Early Domerian), D2 (Middle Toarcian-Early Bajocian), D3 (Middle Bathonian-Middle Oxfordian), D4 (Early Tithonian-Late Albian). Two main textural types of crusts are distinguished. Type I crusts are thin and characterized by the presence of goethite, quartz, albite and phyllosilicates. Moreover, they show Si, Al, Mg, Na, Ti and K contents close to the European Shale Composite contents and Fe/Mn ratios (>350) higher than type II crusts. Type II crusts occur as thicker banded laminae and/or macrooncoids. They consist mainly of goethite and Mn-oxyhydroxides, which are enriched in REE, Co, Ni and Cu and show a strong Ce positive anomaly. After stratigraphical, mineralogical and geochemical data, the crust formation would be produced by the exposition of bottom sediments during long periods to a thin layer of oxidizing sea and porewater enriched in metallic elements. The textural and compositional variations between crusts can be explained by taking into account the bathymetric conditions. In shallower swells, the precipitation of a thick layer of banded type II crusts and in deeper areas, thin type I crusts were formed. Organic influence was only important in crusts from D3 of the northern area where textural evidence indicates the existence of seasonal periodically alternation between organism accretion and fine sedimentation. These were preceded and followed by phases in which the inorganic precipitation of oxides prevailed together with the fine sedimentation.     

Comparison of elemental accumulation rates between ferromanganese deposits and sediments in the South Pacific Ocean

Rates of accumulation of Fe and Mn, as well as Cu, Ni, Co, Pb, Zn, Hg, U and Th have been determined for five ferromanganese deposits from four localities in the South Pacific Ocean.Manganese is accumulating in nodules and crusts at a rate roughly equivalent to that found to be accumulating in sediments in the same area. Iron shows a deficiency in accumulation in nodules and crusts with respect to sediments, especially near the continents, but also in the central and south-central Pacific. Copper is accumulating in nodules and crusts at a rate one order of magnitude less than the surrounding sediments.This is interpreted as meaning that most of the Mn is supplied as an authigenic phase to both sediments and nodules while Fe is supplied mostly by ferromanganese micro-nodules and by detrital and adsorbed components of sediments; and Cu is enriched in sediments relative to nodules and crusts most probably through biological activity.     

太平洋海山钴结壳资源量估算

为合理地估算出太平洋海山钴结壳资源量, 基于我国西太平洋海山钴结壳拖网采样调查资料以及对太平洋海山钴结壳资源分布规律和钴结壳矿区圈定参数指标的深入研究, 创造性地按海山不同高度、不同洋壳年龄赋予不同结壳厚度, 进而首次计算出太平洋海山干结壳资源量为(507.06~1 014.11)×108 t, 锰为(111.15~222.29)×108 t, 钴为(3.04~6.08)×108 t, 镍为(2.23~4.46)×108 t, 铜为(0.66~1.32)×108 t, 结壳分布面积为2 062 862 km2.通过Co通量与结壳Co沉积量、结壳厚度的相关分析表明, 赋予不同洋壳年龄段的结壳厚度是理论厚度的6.10%~12.20%, 这与Ku et al.得出"结壳生长时间只占其整个生命史4%"的认识非常相近, 说明所赋结壳厚度基本合理, 得出的结壳资源量基本正确.为整个大洋海盆内海山钴结壳资源量的估算提供了新方法.      

Distribution and Genesis of Platinum Group Minerals in Nickel Ores of the Sakhara and Elizavet Deposits in the Urals

Nickel and iron–cobalt ores from weathering crusts on ultramafic massifs in the Urals contain elevated PGE concentrations. Platinum group minerals first found in weathering crusts in Russia are primarily represented by Pt-palladium, native platinum, and compounds of Pd and Pt with Bi, Sb, and Te. Platinum group elements are characterized by a high differentiated mobility in the weathering profile. This is manifested by a difference in values of the PGE accumulation coefficient and a spatial separation of local accumulation zones of different PGE. This is also experimentally confirmed by different values of the PGE solubility in natural waters. An important factor of the formation of PGE-rich zones in weathering crusts at the Sakhara and Elizavet ore deposits is their substrate represented by the Sakhara and Uktus massifs of the Ural Platinum Belt. It is supposed that geochemical barriers for the PGE concentration in these weathering crusts were provided by the iron oxide zone and horizons enriched in manganese minerals.     

Mineralogical,geochemical and microfabric evidences of gypsum crusts: a case study from Budapest

High levels of SO₂ and particulate pollution enable the rapid development of gypsum-rich weathering crusts in Budapest. Two types of white crusts, thin and thick ones, and two forms of black crusts, laminar and framboidal ones, were studied in limestone buildings of the parliament and Citadella. The percentage of crust cover and damage categories were documented on selected walls. Petrographic, XRD, XRF and sulphur isotope analyses were performed under laboratory conditions to understand the mechanism of crust formation. White crusts found both on exposed and sheltered walls display a calcite-rich layer with gypsum, while black crusts are enriched with gypsum. The sulphur isotopic composition of white and black crusts overlaps, but the crusts are slightly enriched in heavy isotopes compared to rainwater. S content, Si/Al ratios and particulates in black crusts suggest that air pollution (SO₂, dust) contributes to black crust formation. The accumulation of sulphur and Zn enrichment of white crusts were also documented indicating that under high pollution levels, even these compound can accumulate on exposed facades.     

Composition and distribution of REE in ferromanganese crusts of the Belyaevsky and Medvedev seamounts in the Sea of Japan

This paper presents the results of the integrated study of ferromanganese crusts from the Belyaevsky (Central Basin) and Medvedev (Honshu Basin) seamounts from the Sea of Japan. The study of the mineral composition using powder diffraction and optical and electron microscopy showed that the crusts are made up of todorokite, birnessite, and pyrolusite minerals typical of hydrothermal ferromanganese deposits of the World Ocean. The composition of the ferromanganese crusts from the Sea of Japan was determined by ICP-MS and ICP-OES. The contents of Mn, Fe, Co, Cu, Ni, and other major and trace elements indicate the hydrothermal genesis of the crusts. The obtained data on the composition of ferromanganese crusts of the Sea of Japan, as well as their comparison with different types of deposits of the World Ocean, suggest the endogenic genesis of the studied crusts. However, the REE and Y distribution patterns testify to a significant admixture of hydrogenic matter, which participated in the growth of ferromanganese crusts from the Belyaevsky and Medvedev seamounts.     

中太平洋海山富钴结壳主要成壳元素特征

通过大洋一号船DY105--12 /14 航次采集的结壳样品,对中太平洋CL、CM2、CM3、CX、CQ、 CA、CB 海山结壳的主要成壳元素Mn、Fe、Co、Ni、Cu 的含量进行了测试统计,并与邻区的麦哲伦海山、马绍尔群岛、夏威夷群岛和莱恩群岛进行了对比,中太平洋各海山以及不同区域海山结壳的主成分之间存在一些差异,这主要与各海山结壳的物质来源、成壳环境和成壳时代的差异有关。不同形态类型的结壳主成分具有一定的差别,其主要原因可能是生长机制和形成环境不同造成的。     

Global occurrence of tellurium-rich ferromanganese crusts and a model for the enrichment of tellurium

Hydrogenetic ferromanganese oxyhydroxide crusts (Fe-Mn crusts) precipitate out of cold ambient ocean water onto hard-rock surfaces (seamounts, plateaus, ridges) at water depths of about 400 to 4000 m throughout the ocean basins. The slow-growing (mm/Ma) Fe-Mn crusts concentrate most elements above their mean concentration in the Earth’s crust. Tellurium is enriched more than any other element (up to about 50,000 times) relative to its Earth’s crustal mean of about 1 ppb, compared with 250 times for the next most enriched element.We analyzed the Te contents for a suite of 105 bulk hydrogenetic crusts and 140 individual crust layers from the global ocean. For comparison, we analyzed 10 hydrothermal stratabound Mn-oxide samples collected from a variety of tectonic environments in the Pacific. In the Fe-Mn crust samples, Te varies from 3 to 205 ppm, with mean contents for Pacific and Atlantic samples of about 50 ppm and a mean of 39 ppm for Indian crust samples. Hydrothermal Mn samples have Te contents that range from 0.06 to 1 ppm. Continental margin Fe-Mn crusts have lower Te contents than open-ocean crusts, which is the result of dilution by detrital phases and differences in growth rates of the hydrogenetic phases.Correlation coefficient matrices show that for hydrothermal deposits, Te has positive correlations with elements characteristic of detrital minerals. In contrast, Te in open-ocean Fe-Mn crusts usually correlates with elements characteristic of the MnO₂, carbonate fluorapatite, and residual biogenic phases. In continental margin crusts, Te also correlates with FeOOH associated elements. In addition, Te is negatively correlated with water depth of occurrence and positively correlated with crust thickness. Q-mode factor analyses support these relationships. However, sequential leaching results show that most of the Te is associated with FeOOH in Fe-Mn crusts and ≤10% is leached with the MnO₂.Thermodynamic calculations indicate that Te occurs predominantly as H₅TeO₆⁻ in ocean water. The speciation of Te in ocean water and charge balance considerations indicate that Te should be scavenged by FeOOH, which is in agreement with our leaching results. The thermodynamically more stable Te(IV) is less abundant by factors of 2 to 3.5 than Te(VI) in ocean water. This can be explained by preferential (not exclusive) scavenging of Te(IV) by FeOOH at the Fe-Mn crust surface and by Fe-Mn colloids in the water column. We propose a model in which the extreme enrichment of Te in Fe-Mn crusts is likely the result of an oxidation reaction on the surface of FeOOH. A similar oxidation process has been confirmed for Co, Ce, and Tl at the surface of MnO₂ in crusts, but has not been suggested previously to occur in association with FeOOH in Fe-Mn crusts. Mass-balance considerations indicate that ocean floor Fe-Mn deposits are the major sink for Te in the oceans. The concentration and redox chemistry of Te in the global ocean are likely controlled by scavenging on Fe-Mn colloids in the water column and Fe-Mn deposits on the ocean floor, as is also the case for Ce.     

Role of Hydrology in the Formation of Co-rich Mn Crusts from the Equatorial N Pacific,Equatorial S Indian Ocean and the NE Atlantic Ocean

Co-rich Mn crusts from four different locations of the world ocean have been studied to understand the role of dissolved oxygen of the ambient seawater in the formation of Co-rich Mn crusts. WOCE (World Ocean Circulation Experiment) oxygen profiles of modern seawater in the Equatorial North Pacific Ocean, Equatorial South Indian Ocean and the North East Atlantic Ocean have been evaluated with respect to the occurrence of Co-rich Mn crusts at depths ranging from 1500 to 3200 m. The oxygen content at these depths varied from ∼90–240 µmol/kg. The oxygen minimum zone (OMZ), with oxygen contents in the range ∼45–100 µmol/kg, is located in the depth range 800–900 m in these regions. The age of the ocean crust on which seamounts formed is in the range 80.3–180 Ma. Profiles of the oxygen contents of seawater with depth in the oceans are shown to be extremely useful in establishing the optimum conditions for the formation of Co-rich Mn crusts. The use of WOCE oxygen profiles to study geochemical processes in the oceans is highly recommended.     

内蒙古二连盆地凝灰岩潜山多期风化壳形成及油气成藏效应

火山喷发的多期性是导致凝灰岩潜山纵向多期风化壳(带)发育的重要原因。从地球化学、测井响应特征和岩石学 证实了二连盆地凝灰岩潜山多期风化壳(带)的存在及其特征:(1)哈31井凝灰岩地层在1062~1080 m和1165~1179 m两 个井段表现为 K,Na,Ca 等元素淋滤,CIA 指数较大,而 Al,Fe,Mn,P 等元素相对富集,S/A 指数变小;(2)这两个层段 测井响应表现为风化壳的特征,而且其测井曲线在纵向上具旋回特征并有连井上的可对比性;(3)不同喷发期次形成的凝 灰岩结构、组分以及粒度不同。凝灰岩潜山多期风化壳(带)的存在对潜山油气藏的形成具有重要作用,成藏效应主要表 现在储集层垂向分带性、风化壳油藏(晚期风化壳中)和内幕油藏(早期风化壳中)纵向叠置和复式油气聚集成藏模式等 3 个方面。文中对多期凝灰岩古风化壳的认识扩展了火山岩潜山的勘探深度,为火山岩潜山内幕油气勘探提供了理论依据。     

翡翠的皮壳组成及其与内部玉石质量关系初步研究

在对广东南海平洲、广州花都国际翡翠展销会等翡翠原料集散地大量现场考察的基础上,选取了具有黄色色调、白色和灰黑色皮壳的翡翠原石样品,经肉眼和偏光显微镜观察、X射线粉末衍射和电子探针测试,研究了不同颜色系列翡翠原石皮壳的矿物组成和化学成分特征。结果表明,不同颜色翡翠皮壳的主要矿物均为硬玉,次要矿物则有所不同。黄色皮壳含高岭石、三水铝石、软锰矿和赤铁矿等,白色皮壳含高岭石和水钙铝榴石,黑色皮壳则含高岭石和绿泥石类矿物。与内部玉石成分相比,皮壳中的主要化学成分硼（Na2O）和w（SiO2）有所降低,而w（CaO）和w（MgO）及Fe的质量分数则相对增加;黄色皮壳翡翠中Fe的质量分数越高,则皮壳的黄色色调越深,但皮壳的化学成分受环境影响较大,难以用于判断其内部玉石质量。仅初步总结了翡翠皮壳矿物组成与其内部玉石质量的关系。     

Distribution and accumulation rate of Hg in the upper quaternary sediments of the Deryugin Basin,Sea of Okhotsk

The Hg distribution and some mineralogical-geochemical features of bottom sediments up to a depth of 10 m in the Deryugin Basin showed that the high and anomalous Hg contents in the Holocene deposits are confined to a spreading riftogenic structure and separate fluid vents within it. The accumulations of Hg in the the sediments were caused by its fluxes from gas and low-temperature hydrothermal vents under favorable oceanological conditions in the Holocene. The two mainly responsible for the high and anomalous Hg contents are infiltration (fluxes of hydrothermal or gas fluids from the sedimentary cover) and plume (Hg precipitation from water plumes with certain hydrochemical conditions forming above endogenous sources). The infiltration anomalies of Hg were revealed in the following environments: (1) near gas vents on the northeastern Sakhalin slope, where high Hg contents are associated only with Se and were caused by the accumulation of gases ascending from beneath the gas hydrate layer; (2) in the area of inferred occasionally operating low-temperature hydrothermal seeps in the central part of the Deryugin Basin, in which massive barite chimneys, hydrothermal Fe-Mn crusts, and anomalous contents of Mn, Ba, Zn, and Ni in sediments develop.     

微地域搬运——碳酸盐岩红色风化壳形成过程的一种方式

由于差异溶蚀作用,由碳酸盐岩强烈风化形成的红色风化壳通常表现出独特的剖面构型:风化壳发育深厚、下伏基岩面强烈起伏波动、溶沟和石牙相间展布。以黔中岩溶台地之上发育的红色风化壳——平坝剖面为例,通过宏观地质、地球化学、粒度分析以及矿物学等方法,并以邻近的两个石灰土剖面(罗吏剖面和龙洞堡剖面)作对比,对碳酸盐岩红色风化壳的形成过程进行了讨论,论证了微地域搬运是碳酸盐岩红色风化壳尤其是厚层红色风化壳形成过程的一种方式。溶沟部位的风化壳,从风化前锋向上的一定深度范围内,为原位残积风化的产物(残积层);在此深度以上的部分,为地势较高的相邻石牙部位不同风化程度的残积物的搬运堆积(堆积层),也是导致风化指标随深度呈锯齿状波动的直接原因。后者一般组成剖面的主体。风化壳的年代地层学表现为,在残积层,从风化前锋向上,风化年龄由新到老;在堆积层,从下到上,风化年龄由老到新。风化前锋是一个重要的地球化学作用场所,在这一狭窄的界面上,伴随碳酸盐矿物的快速淋失,残余酸不溶物开始了明显分解。而风化壳的后期演化是一个缓慢而长期的过程。达到重力平衡的剖面(即风化壳表面平缓、不发生微地域搬运的剖面),在由表及里的风化作用下,从地表向下的一定深度范...     

长寿之乡如皋的生态地球化学特征研究

在前人研究如皋长寿成果的基础上,从生态地球化学入手,研究和分析了如皋地区土壤溶液、浅层地下水、大气干湿沉降物中的微量元素含量特点。结果表明,有益于人体健康的微量元素Se、I、Zn等丰富,而有害于健康的As、Hg、Cd、Pb等重金属在江苏为最低,表明良好的生态地球化学环境是如皋地区长寿的根本原因。     

Morphology and mineralogy of weathering crusts on highly porous oolitic limestones, a case study from Budapest

Black crusts are very common on limestones in polluted urban environments, but white crusts are less frequently developed. On the soft, porous and inherently weak oolitic limestone of Budapest both crusts are frequent, and indeed white ones are more common on the stone walls of the studied fortress. In this paper, black and white crusts and the host rock have been described using morphological criteria, mineralogical analyses (XRD, DTA), elements analyses (microprobe) and micro-morphological (SEM) tests. The analyses have shown that on white crusts the surface dissolution is combined with the precipitation of gypsum and calcite in the pores and accumulation of gypsum on the underside of the crust. Thin white crusts are removed by a combination of salt crystallisation (gypsum) and frost action while very thick stone layers scale off due to freeze-thaw cycles. Black crusts are enriched in gypsum relative to white crusts. Gypsum accumulates on the crust surface and signs of dissolution have not been observed. Airborne particulates (flyash, silt-sized quartz, and organic debris) adhere to the crust surface of sheltered black crusts. These particles are later incorporated into the expanding gypsum crystals, that are visible on the underside of the crust. The host rock also contains gypsum, but it is washed off the surface when the crust is removed. Further exposure of the host rock may lead to the dissolution of calcite crystals as it is observed by SEM. The micro-environment influences the crust formation and adherence of the crusts. On frequently wet and dry surfaces crust removal is more common. The crust serves as a protective layer on the stone surface, but this protection is temporary since trigger mechanisms such as salt crystallisation or frost action can cause rapid surface loss.Special Issue: Stone decay hazards     

Rare Earth Elements Composition and Constraint on the Genesis of the Polymetallic Crusts and Nodules in the South China Sea

The rare earth elements(REE) composition of the polymetallic crusts and nodules obtained from the South China Sea(SCS) were analyzed through inductively coupled plasma mass spectrometry.Results revealed great differences in the REE abundances(∑REE) of the SCS polymetallic crusts and nodules; the crusts show the highest ∑REE, whereas the nodules exhibit the lowest ∑REE. The similarity in their NASC-normalized patterns, the enriched light REE(LREE), the markedly positive Ce anomaly(δCe), and the non-or weakly positive Eu anomaly(δEu), suggest that the polymetallic crusts and nodules are of hydrogenetic origin. Moreover, the REE contents and their relevant parameters are quite different among the various layers of the crusts and nodules, which probably results from the different marginal sea environments and mineral assemblages of the samples. The growth profiles of the SCS polymetallic crusts and nodules reveal the tendency ∑REE and δCe to slightly increase from the outer to the inner layers, suggesting that the growth environments of these samples changed smoothly from an oxidizing to a relatively reducing environment; in addition, the crust ST1 may have experienced a regressive event(sea-level change) during its growth, although the REE composition of the seawater remained relatively stable. On the basis of the regional ∑REE distribution in the SCS crusts and nodules,the samples collected near the northern margin were influenced by terrigenous material more strongly compared with the other samples, and the REE contents are relatively low. Therefore, the special geotectonic environment is a significant factor influencing the abundance of elements, including REE and other trace elements. Compared with the oceanic seamount crusts and deep-sea nodules from other oceans,the SCS polymetallic crusts and nodules exhibit special REE compositions and shale-normalized patterns, implying that the samples are of marginal sea-type Fe-Mn sedimentary deposits, which are strongly affected by the epicontinental environment, and that they grew in a more oxidative seawater environment. This analysis indicates that the oxidized seawater environment and the special nano property of their Fe-Mn minerals enrich the REE adsorption.     

东菲律宾海新型铁锰结壳中元素的赋存状态

为了解东菲律宾海新型铁锰结壳中元素的赋存状态, 采用化学提取方法对3个结壳样品进行了物相分析.不同类型结壳中成矿和稀土元素的赋存状态总体一致, 表明它们形成于相近的地质和海洋环境中.成矿元素中的Fe和Cu绝大部分赋存在残渣态中, Mn、Co和Ni则主要赋存在锰氧化物结合态、有机结合态和残渣态中, 并且埋藏型结壳样品锰氧化物结合态中赋存了相对更高比例的成矿元素.三价稀土元素主要集中在锰氧化物结合态中.两个沉积物表层结壳样品中的Ce主要集中在残渣态中.而埋藏型结壳样品中的Ce则主要赋存在锰氧化物结合态中, 这可能与该样品此相态中赋存了相对较多的Mn有关.呈碳酸盐结合态和有机结合态的稀土元素含量仅各占稀土总量的1%左右, 表明两者对结壳中稀土元素的富集作用很小.