Tungsten accumulation in Pacific ferromanganese deposits

Tungsten has often been reported in marine ferromanganese deposits and the question arises as to how the large oxyanionic species (WO ₄ ^2- ) enters the appropriate phases. Very low W concentrations in seawater (less than 0.0002 g/kg) suggest that it is not directly related to precipitation processes. Of all the comparable marine samples, manganese micronodules have the highest W contents, in the range 1.4 to 3.6 times, 3 higher than in the associated macronodules. A depositional record for more than 60 million years obtained for a thick manganese crust shows that the tungsten distribution with depth correlates best with As and to a lesser extent with Fe. The mechanism favoured for enrichment of W is precipitation onto fine hydrothermal manganese-rich particles supplied by ridge volcanic activity. Such particle plumes are usually released in cycles, stay for comparatively long periods in the water column, and are then transported from the hydrothermal centres to the deep basins where they settle and probably contribute to the growth of ferromanganese oxide phases on the ocean floor which is mainly by diagenetic and hydrogenetic processes.     

Helium isotopes in ferromanganese crusts from the central Pacific Ocean

Helium isotopes have been measured in samples of two ferromanganese crusts (VA13/2 and CD29-2) from the central Pacific Ocean. With the exception of the deepest part of crust CD29-2 the data can be explained by a mixture of implanted solar- and galactic cosmic ray-produced (GCR) He, in extraterrestrial grains, and radiogenic He in wind-borne continental dust grains. ⁴He concentrations are invariant and require retention of less than 12% of the in situ He produced since crust formation. Loss has occurred by recoil and diffusion. High ⁴He in CD29-2 samples older than 42 Ma are correlated with phosphatization and can be explained by retention of up to 12% of the in situ-produced ⁴He. ³He/⁴He of VA13/2 samples varies from 18.5 to 1852 R_a due almost entirely to variation in the extraterrestrial He contribution. The highest ³He/⁴He is comparable to the highest values measured in interplanetary dust particles (IDPs) and micrometeorites (MMs). Helium concentrations are orders of magnitude lower than in oceanic sediments reflecting the low trapping efficiency for in-falling terrestrial and extraterrestrial grains of Fe-Mn crusts. The extraterrestrial ³He concentration of the crusts rules out whole, undegassed 4-40 μm diameter IDPs as the host. Instead it requires that the extraterrestrial He inventory is carried by numerous particles with significantly lower He concentrations, and occasional high concentration GCR-He-bearing particles.     

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.     

Interelement relationship in abyssal Pacific ferromanganese nodules and associated pelagic sediments

By R-mode factor analysis and enrichment factor calculations, most of the elements in abyssal ferromanganese nodules and associated pelagic sediments (excluding common authigenic minerals like apatite, barite, opal and carbonates) are found to be preferentially concentrated in one of the following three major phases: aluminosilicates (e.g., Al, Si, Sc, Ga, Cr, Be, Na, K, Rb and Cs), Fe-oxides (e.g., Fe, P, S, V, Se, Te, As, B, Sn, U, Hg, Pb, Ti, Ge, Y, Zr, Nb, Pd, In, rare-earths, Hf, Th, Pa, Pu, Am, Ru and Bi), and Mn-oxides (e.g., Mn, Tl, Ag, Cd, Mg, Ca, Ba, Ra, Co, Ni, Cu, Zn, Mo, Sb and probably W). The specific association of elements with these three phases can be explained by the difference in chemical forms of elements in seawater and by fundamental differences in physicochemical properties (e.g., the pH of zero point of charge and dieletric constant) of these three phases.     

The Indian Ocean Nodule Field: petrotectonic evolution and ferromanganese deposits

The Indian Ocean Nodule Field (IONF) is significant from several points of view. Roughly bordered by 10°S to 16°30′S and 72°E to 80°E and located within the Central Indian Ocean Basin (CIOB), the field hosts the world's second largest and second high grade manganese nodule deposit, after the equatorial nodule belt in the north Pacific Ocean. Moreover, the crust underlying this field is characterised by unique morphotectonic signatures owing to its formation between 60 and 49 Ma under three variable spreading conditions, fast, intermediate and slow, from the Indian Ocean Ridge System (IORS).The nodule field has been surveyed both extensively (more than 0.4 million km² area) and intensively (comprising of a large geophysical data set and geological sample inventory) during the last two decades. Several morphotectonic features, such as seamounts, hills, ridge-normal lineaments and ridge-parallel lineations, have disturbed the apparently smooth topographic gradient (1:7000) of the seafloor here.Variations in the rate of spreading and formation of new oceanic crust along the ridge crest, during more than one episode of India–Eurasia collision, are imprinted in the IONF. Based on the nature of the ridge-parallel lineations, which are related to the rate of crustal accretion, the field is divided in to four sectors: A, B, C, and D, from north to south. Sectors A and C were formed at a fast rate of spreading (90–95 mm/year, half-rate) and sectors B and D were formed at an intermediate (55 mm/year) and slow (26 mm/year) rates, respectively. The predominance of tensional stress in sectors A and C caused asymmetrical flexuring of the seafloor, resulting in widely spaced faults and folds with low amplitude and large wavelength. In contrast, the seafloor flexuring in sector D are closely spaced, long, symmetrical and of high amplitude. The timing and intensity of the collision of India with Eurasia is constrained by the variable intensity of these flexures, suggesting probably a ‘soft’ touch at ∼58 Ma and the hard collision at about 51 Ma.The nodule field hosts several seamounts, both as isolated entities and in linear chains, which are arranged parallel to the flow lines along the direction of absolute motion of the Indian plate. The distribution, morphology and growth patterns of a majority of these seamounts are related to spreading rate, suggesting their formation at the ridge crest. However, many of the seamounts show more than one stage of growth with local intraplate volcanism contributing to the enlargement of the larger ancient seamounts. Varieties of volcanics, such as tholeiitic basalts, spilites, ferrobasalts and pumice, occur within the IONF. The alteration of some of these volcanics has resulted in palagonitisation of the glass and formation of zeolites.Subsequently, during its journey away from the ridge crest to the abyssal areas, the crust underlying the nodule field witnessed intraplate volcanism. This is evident from the addition of younger rocks at the base of the ancient seamounts, inconsistent growth of volcanoes, eruption of ferrobasalt corresponding to the areas of high amplitude magnetic zones and presence of volcanogenic–hydrothermal materials (vhm) of 10 ka age. These findings collectively hint that the IONF is geodynamically unstable and may have been volcanically active in the recent past.During the last 8 Ma, growth of authigenic ferromanganese deposits in the form of manganese nodules and crusts has occurred in the nodule field. The deposits occur at an average water depth of 5000 m. The basinal geomorphology, intraplate tectonic deformations and volcanic eruptions considerably influence the formation, development, morphology, mineralogy and composition of these deposits. The data show that the large seamounts, reverse faults and fracture zones (FZs) supply rock fragments as ‘seeds’ for the nodule formation. The hydrogenous precipitation from the overlying water column is the primary source of metal accumulation in the nodules. The secondary (relatively weak) intraplate eruptions along the base of ancient seamounts or lineaments, subsurface igneous activity and diagenetic remobilisation of metals have also played significant role in the growth and enrichment of the deposit.Based on a large data set, we estimate the contribution of various physico-chemical parameters and model the probable conditions of formation of the ferromanganese deposits in the IONF. The model also hints at the location where the resource exploitation should be rewarding.     

Role of organic matter in the accumulation of platinum in oceanic ferromanganese deposits

In order to elucidate possible processes leading to platinum accumulation in ferromanganese deposits, we analyzed published data on the interaction of dissolved platinum species in different valence states with iron and manganese oxyhydroxides under oceanic conditions and experimentally studied the kinetics of sorption of inorganic and organic complexes of platinum (II) and platinum (IV) on synthetic iron and manganese oxyhydroxides and natural materials (marine colloids, and ferromanganese crust samples). The role of dissolved and suspended particulate aquatic organic matter in the sorption accumulation of platinum was evaluated. Possible reasons for the preferential (compared with other noble metals) accumulation of platinum in oceanic ferromanganese deposits were discussed.     

Dispersed iron and manganese in Pacific Ocean sediments

The article considers the areal distribution of dispersed iron and manganese on the bottom of the Pacific Ocean. -Author.     

Geochemistry of the authigenic ferromanganese ore formation in sediments of the Northeast Pacific Basin

Authigenic ferromanganese formations in sediments from two horizons (0–10 and 240–250 cm) located in the low/high bioproductive transitional zone of the Pacific Ocean were studied. In addition to the compositionally different two types of micronodules, crusts and ferromanganese nodules were detected in the surface horizon (0–1 cm). Three size fractions (50–100, 100–250, and 250–500 μm) of manganese micronodules were investigated. In terms of surface morphology, color, and shape, the micronodules are divided into the dull round (MN1) and angular lustrous (MN2) varieties with different mineral and chemical compositions. The dull MN1 are enriched in Mn and depleted in Fe as compared with the lustrous MN2. The Mn/Fe value in the dull MN1 varies from 13 to 14. Asbolane-buserite and birnessite are the major manganese minerals in them. The lustrous MN2 is mainly composed of vernadite with Mn/Fe = 4.3–4.8. Relative to the dull MN1, fraction 50–100 μm of the lustrous MN2 is enriched in Fe (2.6 times), W (1.8), Mo (3.2), Th (2.3), Ce (5.8), and REE (1.2–1.8). Relative to counterparts from the dull MN1, separate fractions of the lustrous MN2 are characterized by a greater compositional difference. For example, increase in the size of micronodules leads to decrease in contents of the following elements: Fe (by 10 rel %), Ce (2 times), W (2.1 times), Mo (2.2 times), and Co (1.5 times). At the same time, one can see increase in contents of other elements: Th and Cu (2.1 times), Ni (1.9 times), and REE (1.2–1.6 times). Differences in the chemical and mineral compositions of MN1 and MN2 fractions can be related to alternation of oxidative and suboxidative conditions in the sediments owing to the input of a labile organic matter, which serves as the major reducer, and the allochthonous genesis of MN2.     

基于高斯混合模型的太平洋深海盆地多金属结核成因分类

多金属结核类型成因分类是海底矿产资源关注的重要地质问题,诸多学者一直探索利用多金属结核地球化学特征进行多金属结核成因判别。近年来,随着大数据分析方法的应用,为探索利用机器学习技术进行多金属结核地球化学特征进行成因分类提供了很好的思路和方法。本文基于多年调查研究获取的太平洋多金属结核地球化学数据,利用高斯混合模型聚类分析技术,实现了太平洋深海盆地多金属结核成因分类,并对水成型结核进行了进一步判别分析,共划分出成岩型、混合型、水成Ⅰ型和水成Ⅱ型四类成因多金属结核,为太平洋深海找矿突破和资源评价提供重要依据。同时,不同成因类型结核空间预测结果显示,西北太平洋海域是水成Ⅰ型富钴多金属结核的主要分布区域之一,主要分布在马尔库斯—威克海山群、麦哲伦海山群北部、马绍尔海山群和中太平洋海山群西南部的山间盆地,以及附近的皮嘉费他海盆和中太平洋海盆西北部,是未来西太平洋富钴多金属结核资源找矿突破需要关注的关键海域。     

Diatoms and silicoflagellates in suspension and floor sediments of the Pacific Ocean

In the eight climatic zones of the Pacific, a direct spatial-geographical correspondence is proved between density of diatom populations (together with the quantitatively unimportant associated silicoflagellates) and the relative abundance of their siliceous relics in sediments on the oceanic floor. This correspondence is almost ideal in the Subantarctic zone, demonstrable in the Subarctic zone and the equatorial belt, but is complicated (beyond recognition, in places) by terrigenic and other diluent materials and/or by the high solubility of the shells of certain species which never reach the ocean floor. There is no evidence of any significant drift of diatom relics during their sedimentation; the practical absence of diatoms, as in the Southern Subtropical zone, has its clear expression in the absence of their relics in the zonal sediments. — IGR Staff.     

南太平洋东劳扩张中心表层沉积物氨基酸组成所揭示的生物地球化学意义

通过对南太平洋劳盆地东劳扩张中心(ELSC)表层沉积物进行水解氨基酸(THAA)分析、氨基酸对映异构体比值(D/L)分析及总有机碳(TOC)分析,对沉积物中氨基酸含量和来源、有机质降解程度和采样区域生物活动性及温度特征等问题进行了探讨。结果表明,ELSC区域样品中有机质含量较低,TOC含量为0.70～2.15 mg/g(干重),THAA含量为30～511μg/g(干重),热液活动区域原位化能合成作用对沉积物中氨基酸的相对富集有较大的贡献。沉积物中THAA含量和生物群落活动状况与分布范围有关,样品矿物组分对氨基酸的保存亦有一定的影响。由于各采样点热液活动、沉积物类型、生物群落的类型及分布均有所不同,样品中个体氨基酸的组成分布特征有较大差异。以TOC中氨基酸态碳所占百分比TAAC%作为指标对样品有机质活性进行了判别,热液喷口区域样品有机质新鲜程度要普遍高于非热液喷口区域样品,高温热液环境对氨基酸降解途径有一定的影响。样品中个体氨基酸D/L比值变化范围较大,天冬氨酸(Asp)为0.08～0.46,谷氨酸(Glu)为0.06～0.19,丝氨酸(Ser)为0.01～0.81,丙氨酸(Ala)为0.10～0.30。根据样品中THAA含量、TAAC%及个体氨基酸的D/L比值可以粗略判断生物活动性的大小及细菌对THAA的相对贡献,但并不能准确地区分热液活动活跃区域和非活跃区域在温度和生物活动性方面的差异。     

New constraints on the sources and behavior of neodymium and hafnium in seawater from Pacific Ocean ferromanganese crusts

The behavior of dissolved Hf in the marine environment is not well understood due to the lack of direct seawater measurements of Hf isotopes and the limited number of Hf isotope time-series obtained from ferromanganese crusts. In order to place better constraints on input sources and develop further applications, a combined Nd-Hf isotope time-series study of five Pacific ferromanganese crusts was carried out. The samples cover the past 38 Myr and their locations range from sites at the margin of the ocean to remote areas, sites from previously unstudied North and South Pacific areas, and water depths corresponding to deep and bottom waters.For most of the samples a broad coupling of Nd and Hf isotopes is observed. In the Equatorial Pacific ε_Nd and ε_Hf both decrease with water depth. Similarly, ε_Nd and ε_Hf both increase from the South to the North Pacific. These data indicate that the Hf isotopic composition is, in general terms, a suitable tracer for ocean circulation, since inflow and progressive admixture of bottom water is clearly identifiable.The time-series data indicate that inputs and outputs have been balanced throughout much of the late Cenozoic. A simple box model can constrain the relative importance of potential input sources to the North Pacific. Assuming steady state, the model implies significant contributions of radiogenic Nd and Hf from young circum-Pacific arcs and a subordinate role of dust inputs from the Asian continent for the dissolved Nd and Hf budget of the North Pacific.Some changes in ocean circulation that are clearly recognizable in Nd isotopes do not appear to be reflected by Hf isotopic compositions. At two locations within the Pacific Ocean a decoupling of Nd and Hf isotopes is found, indicating limited potential for Hf isotopes as a stand-alone oceanographic tracer and providing evidence of additional local processes that govern the Hf isotopic composition of deep water masses. In the case of the Southwest Pacific there is evidence that decoupling may have been the result of changes in weathering style related to the buildup of Antarctic glaciation.     

Comparison in Mineralization between Ferromanganese Nodules and Co-Rich Manganese Crusts in Pacific Ocean

The ferromanganese deposits in the deep- sea floor of thePacific Ocean are classified as two types:polymetallic nodule(hereafter shortened as nodule) and Co- rich crust(hereaftershortened as crust) . The comparative research between thenodule and the crust shows that several similarities and differ-ences are present geochemically between them.Both the nod-ule and the crust consisting of manganese and iron oxide andhydroxide that contain some of transitional and divalent metalelements such as …     

Metal accumulation rates in northwest Atlantic pelagic sediments

Measurements of ²³⁰Th, ${}^{87}\text{Sr}{}^{86}\text{Sr}$ and twenty-four metals were made on cores from the Nares Abyssal Plain. The sediment is characterized by slowly-accumulating (0.3–0.7 g/cm² 10³ yr) pelagic red clays and rapidly deposited grey clays transported by turbidity currents. Despite their colour differences and the enrichment of Mn, Fe, Cu, Co, Ni, Zn, V and, to a lesser degree, the rare earths in the red clays, Sr isotope evidence demonstrates that the clays have the same terrigenous origin. The excesses of metals in the red clays have been attributed to metal removal from the water column and a comparison with the grey clays has enabled the authigenic fluxes of metals to be estimated. The fluxes obtained are in the ranges 20–50 μmol/cm² 10³ yr for Mn and Fe, 0.1–0.4 μmol/cm² 10³ yr for Cu, Co, Ni, Zn, V, Sr and Ce, 10–20 nmol/cm² 10³ yr for La and Nd, and 0.5-3 nmol/cm² 10³ yr for Sm, Eu, Gd, Dy, Er and Yb. Authigenic fluxes of Y, Nb, Cr, Zr, Rb, U and Th were not resolvable. Fluxes appear to be near constant on the Plain but comparison with other areas shows that they are quite variable both between and within ocean basins. The chief factor controlling authigenic fluxes is the geochemical abundances of the elements but fractionation within both the transition element and rare earth series can be recognized from inter-element comparisons and from differences in fluxes between Atlantic and Pacific red clays corresponding to the oceanic reactivities of the elements.     

西太平洋海山富钴结壳稀土元素(REE)组成原位LA-ICPMS测定

利用激光剥蚀电感耦合等离子体质谱(LA-ICPMS)微区原位分析方法,对采自西太平洋海山具完整三层结构的富钴结壳样品进行了稀土元素(REE)含量测定,结果表明, 虽然均产于西太平洋海山且均具有明显的三层结构,富钴结壳化学组成受地理位置和沉积环境影响很大。绝大多数西太平洋富钴结壳具有高ΣREE、高LREE/HREE、δCe正异常和δEu基本无异常或微弱正异常的特点, 显示它们主要由正常海水沉积形成。结壳不同层圈之间REE组成有较大的区别, 其原因主要在于其形成环境和矿物组成不同。样品0327稀土元素总量(∑REE)由亮煤层到疏松层到外层逐渐升高,且亮煤层δCe和Y/Ho变化非常大,最大值分别为38.61和105.5,显示该层生长环境较为氧化且相对动荡,而样品0346中三层结构的∑REE都非常高,且变化趋势与0327正好相反,从亮煤层到致密层∑REE有降低的趋势。 亮煤层形成时海水相对较氧化的环境有利于铁锰氧化物的形成和Ce⁴⁺等稀土元素的吸附,导致其中ΣREE较疏松层和外层为高,而后期磷酸盐化导致REE元素的迁移和亏损。在结壳生长剖面上,由最外层到疏松层和亮煤层,δCe呈明显上升趋势,且变化范围趋大,说明该结壳所处的海水环境在由老至新的生长过程中由相对动荡和氧化变为相对平静和还原。     

Comparison of elemental composition of recent and ancient carbonaceous sediments

The concentrations of 13 macroelements and 36 microelements are determined in calcareous deposits from recent basins, namely, the Black Sea (coccolith and sapropel oozes), the Namibian shelf (diatomaceous oozes), and the Peruvian shelf (diatomaceous-terrigenous oozes). The essential similarity of the composition of the microelements is established for all three types of sediments, including calcareous, terrigenous, and siliceous sediments. The comparison of these data with the average composition of the world shales reveals similar trends of microelement distribution, which supports the former hypothesis about the comparable environment of formation of both ancient and some modern basins.