Physical and chemical steady-state compaction in deep-sea sediments: Role of mineral reactions

Marine sediments typically exhibit steep porosity gradients in their uppermost centimeters. Although the decrease in porosity with depth below the sediment-water interface is primarily due to compression arising from the accumulation of overlying sediment, early diagenetic mineral dissolution and precipitation reactions may potentially also affect the porosity gradient. Here, we present a steady state compaction model, based on the mass and momentum conservation of total fluid and solid phases, in order to quantify the relative contributions of mineral reactions and physical compaction on porosity changes. The compaction model is applied to estimate hydraulic conductivity and compressive response coefficients of deep-sea sediments from measured porosity depth profiles. The results suggest an inverse relation between the compressive response coefficient and the lithogenic content of marine sediments. For deep-sea sediments exhibiting high rates of dissolution of siliceous shell fragments, the compaction model ignoring mineral reactions overestimates the hydraulic conductivity and compressive response coefficients. In contrast to non-compacting porous media, mineral dissolution in surficial sediments can lead to lower porosity. However, as illustrated for a deep-sea sediment in the equatorial Atlantic characterized by extensive dissolution of calcareous shell fragments, the effect of mineral dissolution and precipitation reactions on porosity gradients is, in most cases, negligible.     

青藏高原典型地区沉积物地球化学特征与矿物组成的粒度效应

地表松散沉积物中不同粒级的颗粒蕴含着不同的信息,这种差异与其物质来源、搬运和沉积过程中的分选作用以及沉积后的风化作用等有关。因此,可根据沉积物中不同粒级颗粒地球化学特征与矿物组成的差异,进行沉积物物源追踪或沉积环境重建。选择青藏高原在气候和地貌方面具有典型意义的柴达木盆地、错那湖、雅鲁藏布江流域作为研究区,分别采集了这几个地区的沙丘沙、黄土、湖积物、冲积物、洪积物、残坡积物等地表松散沉积物样品,用干筛法将沉积物样品分为两个部分,粗颗粒部分粒径范围为≥75~500 μm,细颗粒部分粒径<75 μm。对上述粗、细颗粒分别进行稀土与微量元素、Sr-Nd同位素、轻矿物组成的实验室分析测试,并对沉积物中粗、细颗粒的测试结果采用古典多维尺度方法进行相似性分析。结果表明：青藏高原松散沉积物中粗、细颗粒在轻矿物组成、微量和稀土元素含量、稀土特征、元素参数等方面存在差异;细颗粒部分蕴含了更多的环境信息,富含容易受化学风化影响的黏土矿物以及硬度较小、容易被磨蚀的方解石等矿物。在物源示踪中不同气候区的沉积物细颗粒不宜进行直接比较,应根据样品的粒度分布情况优先选择合适的粗颗粒组分进行物源示踪。     

深海沉积物中的稀土矿产资源研究进展

近年发现,太平洋和印度洋的深海盆地中存在大量富含稀土的深海沉积物。主要类型为多金属软泥、沸石黏土和远洋黏土,其中的全稀土含量(∑REY,∑REE+Y)为400×10-6~2000×10-6,最高可达6600×10-6,重稀土含量(HREE)已达到或超过中国南方离子吸附型矿床的重稀土品位两倍以上,是潜在的新型稀土资源,具有重要的经济价值。目前不少学者对富稀土的深海沉积物进行了大量地球化学及部分矿物学的工作,认为多金属软泥中的稀土元素多赋存于与海底热液作用有关的铁锰氧化物和氢氧化物中,而沸石黏土和远洋黏土中稀土元素的富集则与磷酸盐的混入密切相关,其稀土元素主要存在于与磷灰石成分相当的生物鱼骨屑中。深海黏土的北美页岩标准化稀土配分模式与海水相似,表明其中的稀土元素主要来自于海水,REY富集成矿可能主要受控于磷灰石早期成岩阶段,期间稀土元素未发生分异。尽管近些年对深海沉积物中的稀土元素研究取得了不少成果,但是,对于沉积物中的稀土富集机制及影响因素等问题仍然需要更加深入的研究。作为稀土资源大国,为了争取我国在国际海底稀土资源竞争中的话语权,维护中国的稀土利益,中国应加紧开展相关的稀土资源勘查和潜力评价。     

物源—河流过程—化学风化对松花江水系沉积物重矿物组成的影响

松花江水系作为我国七大水系之一,对其沉积物组成的深入探究对揭示源区控制因素和沉积物的搬运—沉积过程具有重要意义。重矿物蕴含着源岩母岩的重要信息,是解开由源到汇过程和物源示踪的重要工具。为了评估物源、河流过程和化学风化对重矿物组成的影响,我们从松花江水系干流和支流的边滩以及阶地共取32个样品,进行分粒级（<63 μm、63～125 μm和125～250 μm）的重矿物分析。结果表明,松花江水系源区母岩信息在嫩江各支流（诺敏河最为典型）的重矿物组成中得到很好的反映,但在嫩江干流中没有得到反映,这表明物源对重矿物组成的控制受到河流过程的影响。松花江水系的重矿物组成以角闪石、绿帘石、钛铁矿和榍石为主。河流沉积物的重矿物组成主要富集在63～125 μm组分,同一河流的不同河段的重矿物组成存在显著差异（巴兰河尤为典型）,表明了河流搬运—沉积过程对重矿物组成起到重要控制。哈尔滨松花江T2阶地沉积物（弱风化）的重矿物组成基本保留了现代河流砂特征,讷谟尔河T1阶地沉积物（中等风化）的重矿物受到一定程度的改造,而受到严重化学风化影响的通河松花江T3阶地的重矿物组成已遭受严重破坏,不稳定矿物（角闪石和辉石）以及蕴含的母岩信息已完全消失,表明了重矿物组成明显受到沉积物化学风化程度的影响。由于源—汇过程中重矿物的混合和由此导致的稀释作用,使得沉积物携带的物源信息经过长距离搬运之后逐渐变得模糊。因此,我们认为,在进行河流重矿物源—汇过程研究中,宽粒度分析窗口和足够多的样品数量需要考虑以充分获取源区完整的重矿物组成信息。同时,在利用河流阶地重矿物组成进行源—汇联系和古水系演化研究时,需要首先评估阶地沉积物的化学风化程度。     

Mössbauer spectroscopic studies on the iron forms of deep-sea sediments

Mössbauer spectroscopy was applied to characterize the valence states Fe(II) and Fe(III) in sedimentary minerals from a core of the Peru Basin. The procedure in unraveling this information includes temperature-dependent measurements from 275?K to very low temperature (300?mK) in zero–field and also at 4.2?K in an applied field (up to 6.2?T) and by mathematical procedures (least-squares fits and spectral simulations) in order to resolve individual spectral components. The depth distribution of the amount of Fe(II) is about 11% of the total Fe to a depth of 19?cm with a subsequent steep increase (within 3?cm) to about 37%, after which it remains constant to the lower end of the sediment core (at about 40?cm). The steep increase of the amount of Fe(II) defines a redox boundary which coincides with the position where the tan/green color transition of the sediment occurs. The isomer shifts and quadrupole splittings of Fe(II) and Fe(III) in the sediment are consistent with hexacoordination by oxygen or hydroxide ligands as in oxide and silicate minerals. Goethite and traces of hematite are observed only above the redox boundary, with a linear gradient extending from about 20% of the total Fe close to the sediment surface to about zero at the redox boundary. The superparamagnetic relaxation behavior allows to estimate the order of magnitude for the size of the largest goethite and hematite particles within the particle-site distribution, e.g. ～170?Å and ～50?Å, respectively. The composition of the sediment spectra recorded at 300?mK in zero-field, apart from the contributions due to goethite and hematite, resembles that of the sheet silicates smectite, illite and chlorite, which have been identified as major constituents of the sediment in the <2?μm fraction by X-ray diffraction. The specific “ferromagnetic” type of magnetic ordering in the sediment, as detected at 4.2?K in an applied field, also resembles that observed in sheet silicates and indicates that both Fe(II) and Fe(III) are involved in magnetic ordering. This “ferromagnetic” behavior is probably due to the double-exchange mechanism known from other mixed-valence Fe(II)–Fe(III) systems. A significant part of the clay-mineral iron is redox sensitive. It is proposed that the color change of the sediment at the redox boundary from tan to green is related to the increase of Fe(II)–Fe(III) pairs in the layer silicates, because of the intervalence electron transfer bands which are caused by such pairs.     

Settings of the formation of mineral composition of bottom sediments in the barrier zone of the Angara River

The paper considers conditions of the accumulation of bottom sediments and the formation of their mineral composition in a specific type of barrier zones that was formed due to the overregulation of natural runoff of the Angara River and construction of the Angara reservoir cascade. It was established that the bottom sediments accumulated in the barrier zone were supplied by the runoff of the Angara River and its tributaries. The mineral composition of solid runoff of the rivers is determined by the petrographic composition of their water drainage basins. Boundaries of the distinguished mineralogical subprovinces of the bottom sediments coincide with a sharp change in the dynamic parameters of water flow. The revealed compositional variations of the heavy fraction depending on the water flow velocity can be used to solve an inverse problem: deciphering the hydrodynamic conditions of the formation of river bed sediments.     

A geochemical study of some lithified carbonate sediments from the deep-sea

Unconsolidated oozes, partially lithified oozes, recrystallized limestones, dolostones and crystalline aragonite are some of the varieties of carbonate sediment that have been found in the deep-sea; chemical and isotopic analyses of these varieties are presented here. The consolidated oozes and recrystallized limestones are low-Mg calcites and are often associated with basement rock (generally serpentinized peridotite or basalt) detritus. Lithification is suggested to arise from changes in the carbonate-equilibria system of the interstitial waters resulting from chemical degradation of the igneous rocks. When compared to unconsolidated oozes, lithification is seen to be accompanied by loss of Sr and a slight increase in B, Ba, Co, Cr, Ni and Y in most instances. The tuffaceous limestones are also low-Mg calcites, but are characterized by low Sr and relatively high B, Ba, Co, Cr, Cu, Ni, V, Y and Zn concentrations compared to the oozes. Three dolostones are described of very different isotopic and chemical composition, possibly indicating three different pathways of dolomitization. One with much depleted ¹³C and high Ba concentrations is probably derived from waters containing carbon from a fractionated organic source. Another is not greatly different from the consolidated limestones in minor and trace element composition and may be derived from them. The third variety is characterized by low concentrations of Sr, B, Ba, Cu and Y and relatively high concentrations of Pb: Crystalline aragonite is commonly found in many areas associated with serpentinized peridotite. This aragonite is characterized by relatively high concentrations of Sr and Ni; petrographic and isotopic analyses indicate precipitation from cold, carbonate-rich solutions percolating through the peridotite.     

Implications of precise 10Be measurements in deep-sea sediments

Precise ¹⁰Be measurements in a vertical profile of a large-diameter gravity core with uniform chemical composition from the central equatorial Pacific have not shown the expected decrease with depth. The decay-corrected ¹⁰Be activities ranged from 5.79 ± 0.21 d.p.m. kg^?1 at the top of the core to 9.88 ± 0.46 d.p.m. kg^?1 at the bottom, with a mean of 7.24 ± 1.18 d.p.m. kg^?1. This variation is attributable to the combined variations in the intensity of cosmic rays and that of the earth's magnetic field during the past ～ 1 Ma.     

深海沉积物与履带相互作用试验研究

深海沉积物与履带相互作用的力学特性是深海资源采运设备设计的重要依据。在国内外专家调查、研究的基础上,以膨润土与水的混合物代替深海沉积物,将履带分解为压陷板和剪切板,在特制的试验槽内开展了沉积物的压力沉陷试验与剪切变形试验,得到了沉积物与履带相互作用的压力-沉陷关系曲线和剪应力-剪切位移关系曲线。基于Bekker沉陷模型,得到了模拟沉积物压力-沉陷模型的各个参数值;同时,发现模拟沉积物剪切变形过程具有明显的阶段性,具体可分为线弹性阶段、应变强化阶段、应变软化阶段和残余应力阶段     

Analysis of the mineral composition of Phanerozoic sediments of the Voronezh anteclise cover: Implication for the primary diamond potential

Origin of diamond and its indicator-minerals found in the Cretaceous, Paleogene, and Quaternary sediments in the southern sector of the East European Platform has remained a debatable issue over the past period of approximately 40 years. It was assumed that the Cretaceous diamond in the Volch’e placer and Central deposit confined to the Voronezh anteclise was derived from the Uralian sources, whereas the Paleogene diamond was derived from the South Ukrainian sources. Analysis of paleogeographic maps of new generation (scales 1: 200000–1: 500000) and new data on samples (50 samples 0.5–20 t each) examined by scientists from the Geological Research Institute of Voronezh State University with the participation of authors of the present communication support the hypothesis of local origin of diamonds and localization of their provenance in the sedimentary cover of the Voronezh anteclise. This inference pertains to high-pressure minerals detected in pre-Quaternary sediments. Diamond grains and indicator-minerals hosted in the Quaternary postglacial sediments of the Voronezh anteclise were likely derived from the Don glacial apron in the early Pleistocene (gQ_I ds) from northern areas of the platform (southeastern Finland, Karelia, Kola Peninsula, and Zimnii Bereg area of the Arkhangel’sk region). Such grains are unsuitable for prospecting purposes. Lithofacies investigations made it possible to outline two areas in the Lipetsk and Voronezh regions that likely accommodate productive diatremes.     

On the relationship between silica and carbonate diagenesis in deep-sea sediments

Silica diagenesis and carbonate diagenesis are interrelated. This is confirmed by observations of DSDP Sites 462, 463, 465, 466, and 577. Carbonate sediments containing chert (1) tend to be more indurated and display more advanced diagenetic alterations, regardless of sub-bottom depth; and (2) microfossil components are more strongly affected (overgrown and/or dissolved), while the amount of micritic particles and larger, euhedral calcite crystals is greater. In addition, mass physical properties, porosity in particular, vary more widely in sediment sections containing chert. Furthermore, in the studied similarly composed sediments recrystallization of biogenic opal is indicated by a significant reduction of the specific surface area, reaching a minimum value when quartz is formed.One possible mechanism involved is the production of «surplus« dissolved carbonate created by the replacement of carbonate material by silica during the process of chert formation and silicification. The «extra« carbonate is then available for precipitation as overgrowths and cement outside the chert nodules and silicified zones. Hence silica diagenesis, if it occurs early enough in the sediment, bears some influence on carbonate diagenesis. It is therefore suggested that silica diagenesis be added to the list of factors included in the «diagenetic potential« equation ofSchlanger &Douglas (1974).

---

Zusammenfassung Die Diagenese von biogenem Silikat und Karbonat steht in engem Zusammenhang, wie Beobachtungen an Sedimenten der DSDP Sites 462, 463, 465, 466 und 577 zeigen. Karbonatische Sedimente, die biogenes SiO₂ enthalten, zeichnen sich aus durch (1) größere Verfestigung und stärkere diagenetische Veränderungen — unabhängig von der Tiefe im Sediment, (2) mehr Lösung und Überwuchs an Mikrofossil-Komponenten, (3) höheren Anteil mikritischer Partikel wie auch größerer idiomorpher Kalzitkristalle, (4) stärkere Variation der sedimentphysikalischen Eigenschaften, speziell der Porosität und damit zusammenhängender Parameter.Die Umkristallisation des biogenen SiO₂ führt in ähnlich Zusammengesetzen Sedimenten zu einer drastischen Abnahme der spezifischen Oberfläche. Minimalwerte werden erreicht, wenn sich Quarz bildet.Diagenetisch wichtig ist die Produktion von zusätzlichem Karbonat durch die Silizifizierung von Karbonatschalen. Dieses »Überschuß«-Karbonat wird dann als Überwuchs, Zement oder außen an den »Hornstein«-Aggregaten gefällt. Demzufolge beeinflußt die Diagenese von biogenem SiO₂ auch die Karbonatdiagenese. Daher ist es sinnvoll, die Diagenese von biogenem SiO₂ mit zu den Faktoren zu rechnen, die das »diagenetische Potential« — wie esSchlanger &Douglas (1974) definierten — ausmachen.

---

Résumé L'étude de sédiments provenant des sites DSDP 462, 463, 465, 466 et 577 montre qu'il existe une relation entre la diagenèse de la silice et celle du carbonate biogéniques. Les sédiments carbonatés qui renferment de la silice biogémque présentent: 1) une induration plus marquée et des modifications diagénétiques plus poussées — et ce indépendamment de la profondeur sous la surface du fond; 2) une dissolution et/ou un accroissement plus développés des micro-fossiles; 3) une plus grande teneur en particules micritiques et une plus grande taille des calcites idiomorphes; 4) un éventail plus large de leurs propriétés physiques, particulièrement de la porosité et des paramètres qui en dépendent.La cristallisation de l'opale biogénique, dans des sédiments de compositions semblables, se traduit par une réduction drastique de la surface spécifique, qui atteint une valeur minimale lorsque du quartz est formé.Un rôle diagénétique important est joué par l'excès de carbonate dissous engendré par la silicification de coquilles carbonatées; cet excès de carbonate est dès lors disponible pour la précipitation des auréoles d'accroissement et du ciment hors des nodules de chert et des zones silicifiées. Il s'ensuit que la diagenèse du SiO₂ biogénique influence la diagenèse du carbonate. Il conviendrait dès lors d'ajouter la diagenèse de la silice à la liste des facteurs qui interviennent dans l'équation du «potentiel diagénétique» deSchlanger etDouglas (1974).

---

462, 463, 465, 466 577, . , , : 1) , ; 2) ; 3) , 4) , . SiO₂ . . . »« , , « ». , .. «, 1974 Schlanger & Douglas.

     

Position of zone of reverse magnetic polarity in deep-sea sediments

We consider the tectonic structure of the eastern part of the Chukotka fold belt, classify the magmatic formations by types of intrusions, and record the basic patterns in distribution of gold and tin-tungsten mineralization. Three structures have been recognized: the Chaun-Iul'tin and Vankarem anticlinal zones and the Amgueroa synclinal zone, complicated by block and linear-folded structures of higher orders.

The magmatic formations consist of Early Triassic gabbros, pre-batholithic dikes, and small bodies of diorites, granodiorites, and lamprophyres. Late Jurassic-Early Cretaceous granitoid batholith-like massifs of the Metegyn- Veshkap type. Early Cretaceous granitoid bodies of the Iul'tin, and Late Cretaceous jointed granitoid massifs of the Telekay type

Gold within the anticlinal zones displays an association with the batholith-like massifs of the Metegyn-Veshkap type and with the pre-batholithic dikes of intermediate composition. In the Amguema zone, the sources of the gold were apparently intrusive bodies of intermediate composition, associated with the formation of the Ohkotsk-Chukotka volcanic belt. Tin and tin-tungsten deposits of the cassiterite-quartz association, distributed within the anticlinal zones, display an association with granites of the Iul'tin type; tin deposits of the cassiterite-silicate association concentrate mainly toward the Amguema synclinal zone and are associated with granites of the Telekay type. —Authors.     

Diffusion of ions in sea water and in deep-sea sediments

The tracer-diffusion coefficient of ions in water, D_j⁰, and in sea water, $\text{D}{}_{\mathrm{j}}{}^1$, differ by no more than zero to 8 per cent. When sea water diffuses into a dilute solution of water, in order to maintain the electro-neutrality, the average diffusion coefficients of major cations become greater but of major anions smaller than their respective $\text{D}{}_{\mathrm{j}}{}^1$ or D_j⁰ values. The tracer diffusion coefficients of ions in deep-sea sediments, D_j,sed., can be related to $\text{D}{}_{\mathrm{j}}{}^1$ by $\text{D}{}_{\mathrm{j,sed.}}\text{= D}{}_{\mathrm{j}}{}^1\text{·}\text{α}\text{θ}{}^2$, where θ is the tortuosity of the bulk sediment and a a constant close to one.     

Controls on the distribution of rare earth elements in deep-sea sediments in the North Atlantic Ocean

Deep-sea sediments can contain relatively high concentrations of rare earth elements and yttrium (REY), with a growing interest in their exploitation as an alternative to land-based REY resources. To understand the processes that lead to enrichment of the REY in deep-sea sediments, we have undertaken a detailed geochemical study of sediments recovered from the Atlantic Ocean, on a transect along ~ 24°N that includes the deep Nares Abyssal Plain and the Canary and North America Basins.Total REY concentrations (ΣREY) range from 7.99 to 513 ppm, and total concentrations of the heavy REY (Eu - Lu) range from 0.993 to 56.3 ppm. REY concentrations are highest in slowly accumulating pelagic red clays, especially in samples that contain ferromanganese micronodules. Factor analysis reveals that hydrogenous Fe- and Mn-(oxyhydr)oxides are the primary REY carrier phase in the red clays. In situ analysis of individual micronodules confirms that they have high ΣREY (up to 3620 ppm). REY concentrations are higher in micronodules that have a hydrogenous source, characterised by higher Fe/Mn, compared to micronodules that have a diagenetic source.The ΣREY content of North Atlantic deep-sea sediments is ~ 4 times lower than in Pacific deep-sea sediments. We calculate that the area of seafloor required to extract ~ 10% of the global annual REY demand is ~ 100 km², assuming removal of the upper 1 m of sediment.     

Significance and origin of surface textures on broken sand grains in deep-sea sediments

The surface textures of fine sand particles from the Deep Sea Drilling Project Leg 39 have been studied via scanning electron microscopy. A large portion of the coarsest fraction of these grains from deep sea cores were formerly fragments of larger sand-sized grains that had been mechanically broken. Surface textures characteristic of previous aeolian and subaqueous environments were preserved in fragments broken from the original larger grain surfaces, thus making palaeo-environmental reconstruction possible. Previously, characteristic mechanical markings had not been observed on deep sea sands; the momentum of grain to grain collisions with respect to fine sands is generally insufficient to initiate mechanical breakage.     

Straightchain geolipids of deep-sea sediments: Comparison of two extraction procedures

The effects of carbonate demineralization with acid upon geolipid extraction yields were assessed in samples of Pleistocene and Miocene deep-sea sediments. Distributions of free and bound geolipids were similar in extracts from demineralized and intact sediment. Although amounts of n-alkanes were not affected, n-alkanoic acids and n-alkanols experienced losses as a result of demineralization. The biogenic carbonates in these old but nonlithified sediments evidently harbor low concentrations of lipid material, and demineralization of sediments is not recommended for routine use without prior testing.     

大气颗粒物矿物相组成与微观形貌研究进展

矿物颗粒是大气颗粒物的重要组成部分,其物相组成和微观形貌等特征既对人体危害的机理研究具有重要意义,同时蕴藏着颗粒物来源及变化等有用信息。自上个世纪80年代至今,大气颗粒物中矿物颗粒物相组成及微观形貌的研究大致经历了3个阶段,主要体现在研究方法和手段的不断探索与进步,研究对象由总悬浮颗粒向PM_2.5甚至更细颗粒物以及由全颗粒分析向单颗粒分析转移,不断重视原生矿物变化及次生矿物生成机理研究。本文提出发生硫化现象的原生矿物及二次成因硫酸盐颗粒是未来研究的重要方向之一。     

Influence of surface geology and mineral deposits on the spatial distributions of elemental concentrations in the stream sediments of Hokkaido,Japan

An elucidation of the background levels of heavy metals, including certain toxic elements, is very essential to accomplish an important environmental assessment. A regional geochemical mapping in Hokkaido, Japan was undertaken by the Geological Survey of Japan, AIST as part of a nationwide geochemical mapping for this purpose. There were 692 stream sediments collected from the active channel (1 sample) / (100 km²) in Hokkaido and the fine fraction sieved through a 180 μm screen was analyzed using the AAS, ICP-AES, and ICP-MS techniques. The regional geochemical maps for 51 elements were created as a 2000 m mesh map using the geographic information system software. Spatial distribution patterns of elemental concentrations in stream sediments, particularly Neogene–Quaternary volcanic and pyroclastic rocks, are primarily determined by surface geology. The correspondence of elemental concentrations in stream sediments to parent lithology is clearly indicated by ANOVA and a multiple comparison. Sediment samples supplied from mafic volcanic and felsic–mafic pyroclastic rocks are significantly rich in MgO, Al₂O₃, P₂O₅, CaO, Sc, TiO₂, V, MnO, Total (T)-Fe₂O₃, Co, Zn, Sr, and heavy rare earth elements (REEs) (Y and Eu–Lu), but significantly lacking in alkali elements, Be, Nb, light REEs (La–Nd), Ta, Tl, Th, and U. Accretionary complexes with sedimentary rocks derived from sediments are in stark contrast to volcanic and pyroclastic rocks. Accretionary complexes with mafic–ultramafic rock have significantly elevated Nb, Ta, and Th abundances in sediments besides MgO, Cr, Ni, Co, and Cu. This inexplicable result is caused by the mixed distributions of granite and ultramafic–mafic rocks.The watersheds with mineral deposits relate to the high concentrations of certain elements such as Zn, As, and Hg. The geochemically anomalous pattern, which is a map of the regional anomalies, and a scatter diagram were applied to examine the contribution of mineral deposits to MnO, T-Fe₂O₃, Cr, Cu, Zn, As, Cd, Sb, Hg, Pb, and Bi concentrations. Consequently, they were grouped into four types: 1) Mineral deposits with no outliers resulting from mineralization (MnO, T-Fe₂O₃, and Cr), 2) sediments supplied from watersheds without metal deposits conceal high metal inputs from known mineral deposits (Cu), 3) deposits from a geochemically anomalous area that closely relates to the presence of mineral deposits (As, Sb, and Hg), and 4) deposits from the widely altered zone associated with the Kuroko as well as hydrothermal deposits corresponding to geochemically anomalous patterns (Zn, Cd, and Pb). This study provides an important regional geochemical database for a young island-arc setting and interpretational problems, such as complicated geology and active erosion, that are unique to Japan.     

太平洋富稀土深海沉积物中稀土元素赋存载体研究

太平洋深海沉积物中富含稀土(含Y,简称REY),尤其是(含)沸石粘土,其主要由粘土组分、沸石、鱼牙骨、微结核及生物残渣等组成,目前对于该类稀土矿床中REY的赋存载体存在争议。本文在中、西太平洋选取两个富REY的沸石粘土样品利用地球化学和矿物学对稀土赋存状态进行定量研究。矿物微区成分表明,鱼牙骨主要成分为磷灰石,含有最高的REY含量,为2497×10~(- 6)~18623×10~(- 6),微结核和沸石颗粒含有较低的REY含量,分别为246×10~(- 6)~333×10~(- 6)和29.36×10~(- 6)~256×10~(- 6)。通过三种矿物相在沉积物63~250μm粒级组分中各自所占质量比例,计算得出磷灰石对REY的贡献率可达90%以上,说明此粒级中磷灰石为主要REY赋存载体,然而相对全岩总的REY含量,该粒级中磷灰石的贡献仍较小。通过对全岩和粉砂级组分(小于63μm)主微量地球化学分析和XRD矿物相分析表明,2个样品中REY主要存在于粉砂级组分中,其中的磷灰石对全岩REY的贡献最高均可达70%左右。另外通过对粘土组分(2μm)研究发现2个样品粘土组分的REY含量相似,分别为530×10~(- 6)和631×10~(- 6),粘土组分对全岩沉积物的REY贡献意义不大,对整个沉积物REY而言其贡献率仅为2%~5%左右。因此认为磷灰石为整个沸石粘土中REY主要赋存载体。