Phase associations and potential selective extraction methods for selected high-tech metals from ferromanganese nodules and crusts with siderophores

Deep-sea ferromanganese deposits contain a wide range of economically important metals. Ferromanganese crusts and nodules represent an important future resource, since they not only contain base metals such as Mn, Ni, Co, Cu and Zn, but are also enriched in critical or rare high-technology elements such as Li, Mo, Nb, W, the rare earth elements and yttrium (REY). These metals could be extracted from nodules and crusts as a by-product to the base metal production. However, there are no proper separation techniques available that selectively extract certain metals out of the carrier phases. By sequential leaching, we demonstrated that, except for Li, which is present in an easily soluble form, all other high-tech metals enriched in ferromanganese nodules and crusts are largely associated with the Fe-oxyhydroxide phases and only to subordinate extents with Mn-oxide phases. Based on this fact, we conducted selective leaching experiments with the Fe-specific organic ligand desferrioxamine-B, a naturally occurring and ubiquitous siderophore. We showed by leaching of ferromanganese nodules and crusts with desferrioxamine-B that a significant and selective extraction of high-tech metals such as Li, Mo, Zr, Hf and Ta is possible, while other elements like Fe and the base metals Mn, Ni, Cu, Co and Zn are not extracted to large extents. The set of selectively extracted elements can be extended to Nb and W if Mn and carbonate phases are stripped from the bulk nodule or crust prior to the siderophore leach by e.g. a sequential leaching technique. This combination of sequential leaches with a siderophore leach enhanced the extraction to 30–50% of each Mo, Nb, W and Ta from a mixed type Clarion-Clipperton Zone (CCZ) nodule and 40–80% from a diagenetic Peru Basin nodule, whilst only 5–10% Fe and even less Mn are extracted from the nodules. Li is extracted to about 60% from the CCZ nodule and a maximum of 80% Li is extracted from the Peru Basin nodule.Our pilot work on selective extraction of high-tech metals from marine ferromanganese nodules and crusts showed that specific metal-binding organic ligands may have promising potential in future processing technologies of these oxide deposits.     

Composition of manganese nodules and manganese carbonates from Loch Fyne,Scotland

Manganese nodules and manganese carbonate concretions occur in the upper 10–15 cm of the Recent sediments of Loch Fyne, Argyllshire in water depths of 180–200 m. The nodules are spherical, a few mm to 3 cm in diameter, and consist of a black, Mn-rich core and a thin, red, Fe-rich rim. The carbonate occurs as irregular concretions, 0.5–8 cm in size, and as a cement in irregular nodule and shell fragment aggregates. It partially replaces some nodule material and clastic silicate inclusions, but does not affect aragonitic and calcitic shell fragments.The nodules are approximately 75% pure oxides and contain 30% Mn and 4% Fe. In the cores, the principal mineral phase is todorokite, with a Mn/Fe ratio of 17. The rim consists of X-ray amorphous Fe and Mn oxides with a Mn/Fe ratio of 0.66. The cores are enriched, relative to Al, in K, Ba, Co, Mo, Ni and Sr while the rims contain more P, Ti, As, Pb, Y and Zn.The manganese carbonate has the composition (Mn_47.7 Ca_45.1 Mg_7.2) CO₃. Apart from Cu, all minor elements are excluded from significant substitution in the carbonate lattice.Manganese nodules and carbonates form diagenetically within the Recent sediments of Loch Fyne. This accounts for the high Mn/Fe ratios in the oxide phases and the abundance of manganese carbonate concretions. Mn concentrations in the interstitial waters of sediment cores are high (ca. 10 ppm) as also, by inference, are the dissolved carbonate concentrations.     

Mn-oxide: a major source of easily mobilisable Co and Ni under reducing conditions in New Caledonia FerralsolsLes oxydes de Mn : une source majeure de Co et Ni facilement mobilisables en conditions réductrices dans les Ferralsols de Nouvelle-Calédonie

Chemical and bacterial reduction and dissolution of Fe and Mn-oxide and the concomitant solubilisation of Co and Ni were studied in a surface horizon of a New-Caledonia Ferralsol. Chemical extractions showed that Mn and Co were in a large part associated in Mn-oxides. The main part of Ni was associated with goethite, but a very small fraction was also associated with Mn-oxides. Anaerobic reducing bacterial activity was responsible for Fe solubilisation at a smaller extent than for Mn solubilisation and consequently for associated metal release. Submicroscopic investigations revealed the presence of a Mn-oxide containing Co, Ni and Al, close to a lithiophorite–asbolane mixed-layers Mn-oxide, which can be considered as a main source of easily available metals in this soil. To cite this article: C. Quantin et al., C. R. Geoscience 334 (2002) 273–278.     

Manganese ore deposits in Koira-Noamundi province of Iron Ore Group, north Orissa, India: In the light of geochemical signature

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).     

Geochemistry and specific features of manganese ore formation in sediments of oceanic bioproductive zones

Processes of authigenic manganese ore formation in sediments of the northern equatorial Pacific are considered on the basis of study of the surface layer (<2 mm) of ferromanganese nodule and four micronodule size fractions from the associated surface sediment (0–7 cm). Inhomogeneity of the nodule composition is shown. The Mn/Fe ratio is maximal in samples taken from the lateral sectors of nodule at the water-sediment interface. Compositional differences of nodules are related to the preferential accumulation of microelements in iron oxyhydroxides (P, Sr, Pb, U, Bi, Th, Y, and REE), manganese hydroxides (Co, Ni, Cu, Zn, Cd, Mo, Tl, W), and lithogenous component trapped during nodule growth (Ga, Rb, Ba, and Cs). The Ce accumulation in the REE composition is maximal in the upper and lower parts of the nodule characterized by the minimal Mn/Fe values. The compositional comparison of manganese micronodules and surface layers of the nodule demonstrated that the micronodule material was subjected to a more intense reworking during the diagenesis of sediments. The micronodules are characterized by higher Mn/Fe and P/Fe ratios but lower Ni/Cu and Co/Ni ratios. The micronodules and nodules do not differ in terms of contents of Ce and Th that are least mobile elements during the diagenesis of elements. Differences in the chemical composition of micronodules and nodules are related not only to the additional input of Mn in the process of diagenesis, but also to the transformation of iron oxyhydroxides after the removal of Mn from the close association with Fe formed in the suspended matter at the stage of sedimentation.     

Deep-ocean mineral deposits as a source of critical metals for high- and green-technology applications: Comparison with land-based resources

Ferromanganese (Fe–Mn) crusts are strongly enriched relative to the Earth's lithosphere in many rare and critical metals, including Co, Te, Mo, Bi, Pt, W, Zr, Nb, Y, and rare-earth elements (REEs). Fe–Mn nodules are strongly enriched in Ni, Cu, Co, Mo, Zr, Li, Y, and REEs. Compared to Fe–Mn crusts, nodules are more enriched in Ni, Cu, and Li, with subequal amounts of Mo and crusts are more enriched in the other metals. The metal ions and complexes in seawater are sorbed onto the two major host phases, FeO(OH) with a positively charged surface and MnO₂ with a negatively charged surface. Metals are also derived from diagenetically modified sediment pore fluids and incorporated into most nodules. Seafloor massive sulfides (SMS), especially those in arc and back-arc settings, can also be enriched in rare metals and metalloids, such as Cd, Ga, Ge, In, As, Sb, and Se. Metal grades for the elements of economic interest in SMS (Cu, Zn, Au, Ag) are much greater than those in land-based volcanogenic massive sulfides. However, their tonnage throughout the global ocean is poorly known and grade/tonnage comparisons with land-based deposits would be premature.The Clarion–Clipperton Fe–Mn Nodule Zone (CCZ) in the NE Pacific and the prime Fe–Mn crust zone (PCZ) in the central Pacific are the areas of greatest economic interest for nodules and crusts and grades and tonnages for those areas are moderately well known. We compare the grades and tonnages of nodules and crusts in those two areas with the global terrestrial reserves and resources. Nodules in the CCZ have more Tl (6000 times), Mn, Te, Ni, Co, and Y than the entire global terrestrial reserve base for those metals. The CCZ nodules also contain significant amounts of Cu, Mo, W, Li, Nb, and rare earth oxides (REO) compared to the global land-based reserves. Fe–Mn crusts in the PCZ have significantly more Tl (1700 times), Te (10 times more), Co, and Y than the entire terrestrial reserve base. Other metals of significance in the PCZ crusts relative to the total global land-based reserves are Bi, REO, Nb, and W. CCZ nodules and PCZ crusts are also compared with the two largest existing land-based REE mines, Bayan Obo in China and Mountain Pass in the USA. The land-based deposits are higher grade but lower tonnage deposits. Notably, both land-based deposits have < 1% heavy REEs (HREEs), whereas the CCZ has 26% HREEs and the PCZ, 18% HREEs; the HREEs have a much greater economic value. Radioactive Th concentrations are appreciably higher in the land-based deposits than in either type of marine deposit. A discussion of the differences between terrestrial and marine impacts and mine characteristics is also presented, including the potential for rare metals and REEs in marine deposits to be recovered as byproducts of mining the main metals of economic interest in nodules and crusts.     

广西岩溶区土壤铁锰结核重金属富集的地质特征

广西岩溶区农田土壤重金属污染形势严峻。该地区土壤含有大量铁锰结核,其主要成分为铁和锰的氧化物,对重金属有着较强的富集作用。铁锰结核伴随着土壤形成过程而产生,也是反映土壤形成过程及成土环境变化的良好载体。研究铁锰结核中重金属的富集特征有助于了解广西岩溶区土壤中重金属元素的富集过程和富集特征。文章对广西柳江和桂平的土壤与其中的铁锰结核进行了成分分析,通过微量元素分析得到铁锰结核对Ni、Cu、Cd、Zn、Pb、Co、Ba、As、Cr等重金属元素的富集特征,通过Ti/Al2O3的比值关系推断了铁锰结核与土壤的物质来源。此外,还对铁锰结核进行了激光共聚焦显微拉曼光谱仪（Laser Microscopic Confocal Raman Spectrometer）、扫描电镜和能谱仪（SEM-EDS）分析。通过铁锰结核内部同心环带状圈层结构及其内部的元素分布周期性变化的特征,推测结核形成机制。铁锰结核的形成固定了大量重金属元素,减轻了土壤重金属污染负担;但如果铁锰结核发生了溶解则会导致Mn及受其控制的部分重金属（Co、Cu、Ni、Ba）重新释放回到土壤,加重重金属污染。     

Ferromanganese oxide deposits from the Central Pacific Ocean,II. Nodules and associated sediments

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.     

Geochemistry of ferromanganese nodules from DOMES site a,Northern Equatorial Pacific: Multiple diagenetic metal sources in the deep sea

The major and minor element composition of ferromanganese nodules from DOMES Site A has been determined by X-ray fluorescence methods. Three phases appear to control the bulk compositions: Mn and Fe oxyhydroxides and aluminosilicates. Relatively wide compositional variations are evident throughout the area. Nodules with high Mn/Fe ratios, high Cu, Mg, Mo, Ni and Zn concentrations and high todorokite/δ-MnO₂ ratios have granular surface textures and are confined to an east-west trending depression with thin Quaternary sediment cover. Nodules with low Mn/Fe ratios, high concentrations of As, Ca, Ce, Co, La, P, Sr, Ti, V, Y and Zr and low todorokite/δ-MnO₂ ratios have smooth surfaces and are confined to shallower areas with relatively thick Quaternary sediment to the north and south of the depression.All nodules in the area have compositions which are influenced by diagenesis, but those with the most marked diagenetic signature (high Mn/Fe and Cu/Ni ratios, low Ce/La ratios and more todorokite) are found in areas of very slow or non-existent sedimentation; many of these nodules are actually in contact with outcropping Tertiary sediment. This paradox may be resolved by postulating, by analogy with some shallow-water occurrences, that the nodules accrete from bottom waters which have enhanced particulate and dissolved metal contents derived from diagenetic reaction in areas remote from the site of nodule formation. The metals are supplied in a bottom flow (probably Antarctic Bottom Water) which also erodes, or prevents modern sedimentation in, the depression. Nodules on the flanks of the depression are not evidently affected by this flow and derive at least pan of their constituent metals from diagenetic reaction in the underlying Quaternary sediment.Apparently, abyssal diagenetic nodules can have an immediate and a remote diagenetic metal source. Metal fluxes derived from pore water dissolved metal gradients may not be relevant to particular accreting nodules if a significant fraction of their metals is derived from outside the area in which they form.     

The distribution of elements between co-existing phases in some marine ferromanganese-oxide deposits

Analyses of ferromanganese oxides from the Indian and Atlantic Oceans for the elements Mn, Fe, Co, Ni, Cu, Zn, Pb, Ca, AI, Ti, Cr and Cd have helped to elucidate some of the controls on their geochemistry. In most samples virtually all of the Mn and much of the Fe are present as acid-reducible phyllomanganates and Fe oxyhydroxides respectively. By contrast, in samples in which goethite was identified, much of the Fe and significant amounts of the Mn. are not acid-reducible. The partition patterns of the minor elements reflect to varying extents the mineralogy of the hydrous Mn and Fe oxide phases. In δ-Mn-O₂-rich samples the ratio of adsorbed to crystallographically-bound Ni. Cu and Zn, is higher than in todorokite-rich samples, but in each case these metals are virtually entirely phyllomanganate-associated. In goethite-rich samples, however, significant amounts of Ni. Cu and Zn may be associated with the goethite itself rather than with phyllomanganate minerals. Cobalt shows very close association with the phyllomanganates irrespective of the specific mineralogy, but Pb behaves in a way which cannot yet be fully characterised. The non-reducible fractions of the samples contain most of the Ca, Al. Ti and Cr. Some Ca however is also present in the phyllomanganates.     

Partitioning of manganese,iron, copper,zinc, lead,cobalt, and nickel in black coatings on stream boulders in the vicinity of the Magruder mine,Lincoln Co., Georgia

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.     

Geochemistry of ferromanganese nodule–sediment pairs from Central Indian Ocean Basin

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.     

Geochemical fractionation of Ni,Cu and Pb in the deep sea sediments from the Central Indian Ocean Basin: An insight into the mechanism of metal enrichment in sediment

Metal speciation study in combination with major element chemistry of deep sea sediments provided possible metal enrichment pathways in sediments collected from environmentally different locations of Central Indian Ocean Basin (CIB). Metal speciation study suggests that Fe–Mn oxyhydroxide phase was the major binding phase for Ni, Cu and Pb in the sediments. The second highest concentrations of all these metals were present within the structure of the sediments. Easily reducible oxide phase (within the Fe–Mn oxyhydroxide binding phases) was the major host for all the three metals in the studied sediments. Major element chemistry of these sediments revealed that there was an increased tendency of Cu and Ni to get incorporated into the deep sea sediment via the non-terrigenous Mn-oxyhydroxide fraction, whereas, Pb gets incorporated mostly via amorphous Fe-hydroxides into the sediment from the CIB. This is the first attempt to provide an insight into the mechanism of metal enrichment in sediment that host vast manganese nodule.     

Processes controlling the heavy metal distribution in pacific ferromanganese nodules and crusts

The ferromanganese precipitates existing in deep-sea waters of the Pacific consist of two types of deposits: (1) nodules mainly are distributed in pelagic basins beneath the CCD (Calcite Compensation Depth) where the rate of sedimentation is low; (2) polymetallic encrustations are formed on exposed seamount rocks where currents prevent normal sediment accumulation. Nodules, being formed in areas bordering the equatorial zone of high biological productivity, grow by two different processes: (A) early diagenetic growth by supply of metals and metal compounds from pore water and (B) hydrogenetic growth by supply of colloidal particles from near-bottom seawater. These processes lead to different kinds of oxide and different metal contents. The diagenetic growth process takes place under oxidizing to suboxidizing conditions and is supplied by an ionic solution of Mn²⁺ and other divalent metal ions. The mobilization of Mn is caused by the decomposition of organic matter. The growth features of the early diagenetic nodules show alternating laminae of crystalline and amorphous material. These rhythmic sequences of different microlayers are explained by physico-chemical changes (variation of pH) in the microenvironment of the accreting nodule surface. The hydrogenetic crust growth on seamounts leads to ferromanganese precipitates which are in particular rich in Co. The Co concentration is inversely related to the water depth. Co is positively correlated to Mn which can be derived from the oxygen minimum zone. Contrary to the diagenetic nodule growth, the crust accretion is also a colloidal precipitation process. In the water column below the oxygen minimum zone, a mixture of particles of Mn-Fe-oxyhydroxide and silicate accrete together on the surface of substratum rocks. Surface chemical mechanisms control the enrichment of Ni, Co, Pb, and other metals from the seawater; for Pt, a coprecipitation with MnO₂ caused by a redox reaction is proposed. Distinct oceanographical and geological conditions enable or promote, respectively, the ferromanganese crust formation on seamounts.     

Ship-borne geochemical investigations of deep-sea manganese-nodule deposits in the Pacific using a radioisotope energy-dispersive X-ray system

A radioisotope energy-dispersive X-ray (EDX) system has been used on board the German research vessel “Valdivia” during an exploration expedition in the northern equatorial Pacific in 1973. The instrumentation used consisted of an X-ray detection system incorporating a 30 mm² effective-area Si (Li) detector with a measured energy resolution of 195 eV for Mn Kα X-rays, standard nuclear electronics, a 1024-channel analyser and a data read-out unit. The X-ray spectra in the manganese-nodule samples were excited by a 30-mCi ²³⁸Pu source.The six elements Mn, Fe, Co, Ni, Cu and Zn were analysed on board. Precision values for the analyses were less than 3% for Mn, Fe, Ni, Cu and Zn and about 5% for Co. A total amount of 350 analyses was carried out during a one-month cruise.Average contents of 190 analysed whole manganese-nodule samples from all the sampling sites of the covered area were 23.3% Mn, 6.7% Fe, 0.23% Co, 1.16% Ni, 0.94% Cu and 0.10% Zn. The average content of the base metals expressed as the sum of the Co, Ni, Cu and Zn contents was 2.48%. A linear relationship between Mn and Ni in all analysed samples, including whole manganese-nodule samples, zones of manganese nodules and manganese crusts, was observed. The Mn/Ni ratio calculated by regression analysis was 23.0. Zonal variations of the chemical contents of the six elements in the manganese nodules were found. A size classification of the manganese nodules has been suggested. Geochemical correlations of Cu and Ni versus Mn/Fe in the investigated samples are given.     

太平洋调查区多金属结核的地球化学特征和成因

东太结核主要为半埋藏和埋藏型,发育于以黏土和硅质组分为主的沉积环境。东太结核的锰相矿物主要有水羟锰矿和钡镁锰矿,具有较高的REY、Cu、Ni含量和Mn/Fe比值,显示遭受间隙水的影响,落入水成成因和成岩成因两个区间范围。西太结核主体暴露在海水中,周围沉积物主要由深海黏土组成。西太结核的锰相矿物几乎只有水羟锰矿,具有较高的REY、Co含量和低Mn/Fe比值,属于典型的水成成因型。两个区域的多金属结核的稀土北美页岩标准化模式均显示Ce正异常、Y负异常和无或弱Eu异常,与海水稀土特征构成良好的耦合关系,是多金属结核对海水稀土选择性富集的结果。西太结核相对东太结核具有更高的Ce含量和δCe,Co、Ti与Ce具有良好的正相关关系。研究认为海水中溶解氧并不一定是控制结核Ce正异常程度的关键因素,Co、Ti等元素及其相关组分能够引起Ce与其他稀土元素的强烈分馏,也可能是影响多金属结核Ce正异常程度的控制因素。研究区多金属结核和富钴结壳表层样的ε_Nd范围为-6.6~-2.5,是全球最富放射性成因Nd的海洋铁锰壳层。结合稀土模式以及Eu异常特征,本研究认为多金属结核的稀土主要来自ε_Nd相对较高的周围陆壳,可以通过河流或者大气沉降等方式输送到大洋,而研究区广泛分布的海山玄武岩释放的放射性成因Nd同位素对海水的影响微弱。     

The Association of Cobalt with Iron and Manganese (Oxyhydr)oxides in Marine Sediment

Formation and dissolution of authigenic Fe and Mn (oxyhydr)oxides influence cycling of trace metals in oxic/suboxic surface sediments. We used the diffusive gradients in thin films technique (DGT) to estimate the association of cobalt with iron and manganese oxides. We compared Co, Fe and Mn maxima measured by DGT in the pore waters of fresh and aged marine sediment cores and estimated the Co/Fe and Co/Mn ratios in the metal oxides. A Mn maximum was not visible in DGT concentration profiles of freshly collected sediment cores, but after ageing the sediment, we observed a distinct Mn peak, presumably due to broadening of the depth range over which the various electron acceptors occur. Estimated Co/Mn ratios from both experiments are within the range of literature values for marine sediments, but the value from the aged experiment is at the lower end of the range. This is attributed to stimulation of sulphate reduction and precipitation of cobalt sulphides. The good correlation between Co and Fe maxima in the fresh sediments is attributed to the similarity of their reactions with sulphide rather than Co being released during authigenic Fe oxide reduction.     

南海边缘海多金属结核与大洋多金属结核对比

本文通过系统对比分析前人研究成果,研究了南海边缘海多金属结核的成矿特征,结果表明：南海边缘海结核的矿物组成与大洋结核相似,均主要由锰相矿物和铁相矿物组成,其中锰相矿物主要为水羟锰矿和钡镁锰矿,铁相矿物主要以无定型铁氧化/氢氧化物形式存在,另外南海边缘海结核中含有大量硅酸盐矿物,表明在南海结核成矿过程中受到大量的陆源碎屑矿物混杂;相对于大洋主要经济成矿区的多金属结核,南海边缘海多金属结核中主要的经济元素如Mn、Cu、Co、Ni和Zn质量分数较低,而亲陆源性元素如Fe、Ti、P、Nb、Pb、Rb、Sc、Ta、Sr、Th和REY（REE和Y）等质量分数较高;南海边缘海多金属结核的元素地球化学特征和REE配分模式显示其为水成成因,并呈现更低的Mn/Fe值;同时南海边缘海结核也具有较快的平均生长速率及较高的δCe正异常,表明其生长在更为氧化的海水环境。虽然较快的沉积物沉积速率和动荡的海水环境影响了南海边缘海结核的成矿,但大量陆源物质进入海洋也为南海边缘海结核提供了丰富的成矿物质来源,便于南海边缘海结核的快速生长成矿。南海边缘海结核富集有Fe、Ti、Pb、Rb、Th和REY等金属元素,同样可以作为极具潜力的海洋矿产资源。南海边缘海多金属结核具有其独特的地球化学特征,与大洋多金属结核存在着明显差异。     

Importance of different types of marine particles for the scavenging of heavy metals in the deep-sea bottom water

In experiments of 7 days duration using voltammetric and radiotracer measurement techniques, the role of different particle types in the sorption of dissolved metal species in a disturbed deep-sea bottom seawater system were investigated. Resuspension of oxic to suboxic surface sediment into the bottom water in the deep sea (either by natural events or industrial activities like Mn nodule mining) has been shown to be followed quickly by scavenging of dissolved heavy metals, e.g. released from interstitial water, on the resuspended particles. Compared to other deep-sea particles (like clay minerals, calcite and apatite), Mn and Fe oxides and oxyhydroxides were found to be by far the most important phases in scavenging many dissolved heavy metals. Only Pb was sorbed strongly on all particles used, with highest affinity to carbonate fluorapatite. Caesium⁺ was significantly scavenged only by clay minerals like illite. The sorption experiments support a simple electrostatic model: Hydrated cations and labile cationic chloro-complexes in seawater like Mn²⁺, MnCl⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Ba²⁺, and PbCl⁺, are preferentially adsorbed or ion-exchanged on the negatively charged surfaces of Mn oxides. In contrast, oxyanions and neutrally or negatively charged complexes like HVO₄²⁻, MoO₄²⁻, HAsO₄²⁻, UO₂(CO₃)₂²⁻, and PbCO₃⁰ associate with neutral to slightly positive amphoteric Fe oxyhydroxide particles. Metals forming strong chloro-complexes in seawater like Cd (CdCl₂⁰), are less readily sorbed by oxides than others. A comparison of the results of voltammetric and radiotracer techniques revealed that after fast sorption within the first hour, isotopic exchange dominated reactions on MnO₂-rich particles in the following days. This was especially pronounced for Mn and Co which are bound to the Mn oxide surface via a redox transformation.