Mineralogical characteristics of polymetallic sulfides from the Deyin-1 hydrothermal field near 15°S,southern Mid-Atlantic Ridge

A seafloor hydrothermal field, named Deyin-1 later, near 15°S southern Mid-Atlantic Ridge(SMAR) was newly found during the 22 nd cruise carried out by the China Ocean Mineral Resources Research Development Association(COMRA). Sulfide samples were collected at three stations from the hydrothermal field during the26 th cruise in 2012. In this paper, mineralogical characteristics of the sulfides were analyzed with optical microscope, X-ray diffractometer, scanning electron microscope and electron microprobe to study the crystallization sequence of minerals and the process of hydrothermal mineralization. According to the difference of the ore-forming metal elements, the sulfide samples can be divided into three types:(1) the Ferich sulfide, which contains mainly pyrite and chalcopyrite;(2) the Fe-Cu-rich sulfide consisting predominantly of pyrite, chalcopyrite and isocubanite, with lesser amount of sphalerite, marmatite and pyrrhotine; and(3) the Fe-Zn-rich sulfide dominated by pyrite, sphalerite and marmatite, with variable amounts of chalcopyrite, isocubanite, pyrrhotine, marcasite, galena and gratonite. Mineral precipitations in these sulfides are in the sequence of chalcopyrite(isocubanite and possible coarse pyrite), fine pyrite,sphalerite(marmatite), galena, gratonite and then the minerals out of the dissolution. Two morphologically distinct generations(Py-I and Py-II) of pyrite are identified in each of the samples; inclusions of marmatite tend to exist in the coarse pyrite crystals(Py-I). Sphalerite in the Fe-Zn-rich sulfide is characterized by a"chalcopyrite disease" phenomenon. Mineral paragenetic relationships and a wide range of chemical compositions suggest that the environment of hydrothermal mineralization was largely changing. By comparison, the Fe-rich sulfide was formed in a relatively stable environment with a high temperature, but the conditions for the formation of the Fe-Cu-rich sulfide were variable. The Fe-Zn-rich sulfide was precipitated during the hydrothermal venting at relatively low temperature.     

Sulphide mineralisation in the deep sea hydrothermal vent polychaete, Alvinella pompejana: implications for fossil preservation

Hydrothermal vent fauna, particularly vestimentiferan and polychaete worm tubes, are occasionally preserved in the geological record. The early stages of mineralisation are particularly important in defining whether or not preservation will occur, and they are poorly understood. Tube samples of the polychaete worm Alvinella pompejana collected from 13°N on the East Pacific Rise have been studied to identify the processes occurring during early pyrite/marcasite mineralisation. Iron sulphide mineralisation is present within the walls of the organic dwelling tube, and is induced by microbial fauna preserved within the tube micro-layers. Various microorganisms were observed coating the inner tube surfaces, together with 10-100 μm-sized Fe- and Zn-sulphide particles precipitated from vent fluids. The microbes and particulate sulphides become entombed within the tube wall as further layers of organic material are secreted by the worm, during tube-building episodes. This results in a laminated tube structure being formed, composed of alternating layers of tube material and microbial/sulphide-rich interlayers. The microbial/sulphide layers provide a template for further mineralisation and replacement of the microbes with pyrite while degradation of the organic components occurs. The iron monosulphides mackinawite and greigite have been identified as intermediatory phases that occur as precursor minerals during the formation of pyrite. Later marcasite mineralisation is observed to form over some of the pyritised organic layers. Once mineralisation has replaced most of the organic tube material, the structure will then be preserved along with the host sulphide body. These observations enhance our understanding of the mechanisms of fossil pyritisation in fine-scaled organic structures throughout the geological record.     

Modes of sapropel formation in the eastern Mediterranean: some constraints based on pyrite properties

Pyrite formation within and directly below sapropels in the eastern Mediterranean was governed by the relative rates of sulphide production and Fe liberation and supply to the organic-rich layers. At times of relatively high SO²⁻₄ reduction, sulphide could diffuse downward from the sapropel and formed pyrite in underlying sediments. The sources of Fe for pyrite formation comprised detrital Fe and diagenetically liberated Fe(II) from sapropel-underlying sediments. In organic-rich sapropels, input of Fe from the water column via Fe sulphide formation in the water may have been important as well. Rapid pyrite formation at high saturation levels resulted in the formation of framboidal pyrite within the sapropels, whereas below the sapropels slow euhedral pyrite formation at low saturation levels occurred. δ³⁴S values of pyrite are −33‰ to −50‰. Below the sapropels δ³⁴S is lower than within the sapropels, as a result of increased sulphide re-oxidation at times of relatively high sulphide production and concentration when sulphide could escape from the sediment. The percentage of initially formed sulphide that was re-oxidized was estimated from organic carbon fluxes and burial efficiencies in the sediment. It ranges from 34% to 80%, varying significantly between sapropels. Increased palaeoproductivity as well as enhanced preservation contributed to magnified accumulation of organic matter in sapropels.     

Significance of gabbronorite occurrence in the crustal section of the Semail ophiolite

The eastern end of the Haylayn massif exposes a complex paleoridge structure interpreted as the tip of a northwestward propagating segment (Nicolas et al., this issue). The area, revisited from a petrostructural and geochemical viewpoint, offers the most documented exposures of the association of olivine gabbros and gabbronorites in Oman (Juteau et al., 1988). Gabbronorites were injected while the main gabbro unit was deforming in the magmatic state. Both units do not differ chemically, except for the SiO₂ enrichment of the orthopyroxene-rich gabbros relative to olivine-gabbro. In addition, they display the same trace element signature, which implies the same parent magma for both units. The extension of the stability field of orthopyroxene is assigned to increase of oxygen fugacity due to hydration. The source of hydration is the ridge axis hydrothermal circulation, suggesting hydrothermal/magma interaction at temperatures above the gabbro solidus. The distribution of gabbronorites at the scale of the entire ophiolite suggests a relation with ridge tectonics where high-T conditions of hydrothermal-magmatic interaction are met. Such conditions are met when propagating segments rotate the structures of the dying magma chamber.     

西南印度洋脊龙旂热液场金属硫化物的矿物学组成及指示意义

西南印度洋脊(SWIR)是当前洋底超慢速扩张洋脊的典型代表, 具有独特的热液硫化物矿床形成机理, 对位于该洋脊的龙旂热液场硫化物样品进行了系统的矿物学分析, 结果表明:该区硫化物为高温热液喷溢活动所形成的富Fe型硫化物, 目前已经历了一定程度的氧化蚀变; 硫化物矿物组合以磁黄铁矿、黄铁矿为主, 其次是少量黄铜矿、白铁矿和(铁)闪锌矿; 黄铜矿出溶等轴古巴矿现象普遍, 部分样品中可见自然金颗粒。经综合分析, 该区热液成矿作用可划分为3个成矿阶段和1个后期海底风化阶段: (1)高温的黄铁矿+黄铜矿(等轴古巴矿) +磁黄铁矿阶段, (2)中高温的黄铁矿+闪锌矿阶段, (3)低温的胶状或莓球状黄铁矿+白铁矿+自然金阶段, (4)后期硫化物海底氧化性蚀变阶段主要是形成Fe的氧/羟化物。在整个成矿期间, 流体温度有不同程度的波动, 主要硫化物矿物形成时端元流体的温度应在335℃以上, 瞬间(短时)或局部热液的最高温度推测超过400℃。本区的磁黄铁矿属于富钴型磁黄铁矿亚类, 经历了六方磁黄铁矿+黄铁矿→单斜磁黄铁矿+黄铁矿的变化, 表明该区热液流体发生了快速降温的演化过程。     

Resistivity measurements of an ocean floor sulphide mineral deposit from the submersible Cyana

Electrical resistivity measurements of the sea bed have been made from the submersible Cyana at four locations on a seamount close to the axis of the East Pacific Rise. Two of the sites were on a major sulpide deposit close to the top of the seamount, and the other two on pillow basalts near its base. The resistivity of the pillow-lava terrain was found to be about forty times greater than that of the sea water, in good agreement with downhole logging measurements in DSDP drill holes. The resistivity of the sulphide bottom was one to two orders of magnitude less than that of the pillow basalts. At one site the sea bed was almost twice as conductive as the overlying sea water and the deposit at this location is estimated to be about 9 m thick.Self-potentials of up to 10 mV, measured between a pair of electrodes 10 m apart, were associated with the sulphide deposit but were undetectable (i.e.0.1 mV) on the pillow basalts. The largest SP was associated with the most conductive sea bed, i.e. with the greatest concentration of sulphides.     

Bacterial sulphate reduction in sediments of a european salt marsh: Acid-volatile and tin-reducible products

The products of ³⁵S-sulphate reduction by sedimentary bacteria were measured at two sites in a salt marsh on the east coast of England. Non-acid-volatile products were measured, after acid-volatile sulphide was removed, by their reduction to sulphide by digestion with tin. The proportion of the sulphate reduced to tin-reducible products varied between 25% in a salt marsh pan and 61% in creek sediment, over a 0–25 cm depth profile. There were also variations with depth at each site in the proportions of sulphate reduced to tin-reducible products. Further examination revealed differences in the proportions of sulphate which were reduced to free sulphide, acid-volatile sulphide, sulphur or pyrite at the two sites. The data suggest that previous work which did not measure non-acid-volatile products underestimated sulphate reduction rates by three-fold in the creek site, but by only one third in the pan.     

西南印度洋中脊龙旂热液区中硫化物的结构和微量元素特征对金赋存形式和沉淀机制的启示

相比于快速和中速扩张洋中脊,慢速和超慢速扩张洋中脊热液区通常含有丰富的金属硫化物资源。近年来的研究表明大洋中脊的扩张速率与矿石中金的品位呈明显的负相关,即超慢速扩张洋中脊热液区矿石中金的含量高。前人对龙旂热液区的构造环境以及硫化物组合进行了详细研究,但是对龙旂热液区硫化物中贵金属金的赋存形式和沉淀机制研究较少。本文对西南印度洋龙旂热液区中的硫化物进行了精细的矿物结构和微量元素分析,并探讨了金的赋存形式和沉淀机制。龙旂热液区的硫化物主要以黄铁矿为主,其次是黄铜矿和闪锌矿,黄铜矿普遍出溶等轴古巴矿,此外还观察到了少量的针钠铁矾和自然金等矿物。根据矿物结构和形态,黄铁矿明显被划分为两期,一期黄铁矿（Py1）自形度低,呈细粒状或胶状,内部多孔洞;二期黄铁矿（Py2）自形度高,呈自形−半自形,且粒径较大。Py1往往存在于Py2内部或以包体的形式被Py2所包裹,Py2则与自形−半自形黄铜矿和闪锌矿等矿物共生。自然金主要存在于Py1的内部孔洞之中,少量存在于Py2以及Py2与其他硫化物之间。相比于Py2,Py1含有更高的Ni、Zn、Pb、Ba、Mn、V、Mg、U、Au、Ag、Cd元素含量,更低的Co、Se、As、Sb元素含量。在龙旂热液区的物理化学条件下,热液流体中金的主要存在形式为Au(HS),HS⁻浓度的降低和pH值升高均会促进金的沉淀。龙旂热液区早期热液流体与海水的混合造成热液流体pH值升高,而混合作用导致的热液流体温度降低会促使黄铁矿（Py1）的结晶,从而促使热液流体中HS⁻浓度的降低,热液流体pH值升高和黄铁矿结晶（Py1）引起的硫逸度降低是龙旂热液区自然金沉淀的主要机制。     

The characterization of iron sulfide minerals in anoxic marine sediments

The performance of extractants commonly used in the determination of acid volatile sulfide minerals (e.g., ‘amorphous-FeS’, mackinawite and greigite) and pyrite has been evaluated using pure mineral phases and anoxic sediments. ‘Amorphous-FeS’ and mackinawite are quantitatively recovered by most cold acid extractions, but greigite recovery is incomplete. Harsher extractants with reducing agents are necessary for the complete recovery of greigite, but dissolution of fine-grained synthetic pyrite occurs under such conditions. A quantitative separation between greigite and pyrite is not possible using these techniques, but the use of ‘acid volatile sulfide’ and ‘pyrite’ as operational categories is adequate for most field studies.     

Geochemistry and palaeo-oceanography of metalliferous and pelagic sediments from the Late Cretaceous Oman ophiolite

Metalliferous and pelagic sediments are exposed within and above the extrusive successions of the Upper Cretaceous Oman ophiolite which, on the basis of mostly geochemical evidence, is believed to have formed in an incipient marginal basin setting located above a NE-dipping subduction zone. The ophiolitic extrusives document various volcano-tectonic settings which include the axial zones of a spreading ridge, fault-controlled seamounts and off-axis volcanic edifices. Most of the Fe, Mn and trace metal-enriched sediments studied are interpreted as precipitates formed by oxidation of solutions derived from high-temperature sulphide-precipitating vents. The trace element content (e.g. REE and Sr) was largely scavenged from seawater. The sediments are similar to the dispersed metalliferous sediments on the flanks of modern spreading ridges, and the ‘basal’ sediments of DSDP wells and of other ophiolite complexes (e.g. Troodos, Cyprus).Distinctive mound structures located low in the lavas are attributed to percolation of sulphide-rich solutions into already deposited metalliferous oxide sediments. The resulting iron-silica rock was probably originally precipitated as ferruginous silicates.Major massive sulphides formed off-axis at the base of intermediate-basic edifices of volcanic arc affinities. Fe, Mn and trace metal enrichment in the sediment cover of a flat-topped seamount of axial lavas is interpreted as a dispersion halo around the largest massive sulphide orebody which is situated 5 km away (Lasail). Small massive sulphide bodies are common in the axial lavas particularly along major seafloor fault zones. The metalliferous sediments, locally precipitated near these vents, are ferromanganiferous, but trace metal-depleted.The metalliferous and pelagic sediment cover of the extrusive successions, generally, documents waning hydrothermal input after volcanism ended in the area.A model is discussed in which the ophiolite was created at a spreading axis above a subduction zone dipping away from the Arabian continental margin. With progressive subduction this crust approached the margin. Initially, calcareous sediment accumulated above the calcite compensation depth (CCD), but then non-calcareous radiolarites were deposited as the ophiolitic crust approached the continental margin where the CCD was higher and marginal upwelling possibly enhanced productivity. As the edge of the Arabian continental margin entered the trench, the over-riding ophiolite was regionally uplifted allowing short-lived chalk accumulation above the CCD. This was followed by volcaniclastic deposition related to the tectonic emplacement.     

Barite chimneys on the Gulf of Mexico slope: Initial report on their petrography and geochemistry

Barite chimneys associated with hydrocarbonrich fluid venting were recently documented and sampled on the Gulf of Mexico slope offshore Louisiana at 510–520 m water depth. The chimneys are dominated by barite associated with minor amounts of pyrite, iron oxide, Mg calcite, and detrital silicates. The barite displays distinct string-like and dendritic-like morphologies assembled from rosette-shaped crystals that are typically 20–40 µm in diameter. The chimneys exhibit macroscopic growth layers 1–5 mm thick, which alternate between dark gray and light yellow colors. The dark layers are dominated by string barites associated with disseminated pyrite, while the light layers are dominated by dendritic barites with little or no pyrite. The barites are anomalously enriched in Sr (average 15.5 mol% and maximum 30 mol%) and Ca (average 2.8 mol% and maximum 4.6 mol%), and exhibit rhythmic, paired, microscopic light and dark bands. The exact origin of the barites and their mode of deposition has not yet been elucidated, but they are likely to be related to the hydrocarbon-rich fluids venting on the seabed.     

Iron geochemistry under mussel rafts in the Galician ria system (Galicia-NW Spain)

The intensive mussel culture carried out in the past 40 years in the Rias of Vigo and Arousa (Galicia-NW Spain) has led to substantial changes in the ecology and geochemistry of the seabed in these areas. Organic C enrichment of the seabed has generated strongly reducing conditions that directly affect the geochemistry of Fe and S. In the present study a total of six sediment cores were collected from the seabed under mussel rafts, and two different layers were distinguished: the biodeposit generated by the mussels, and the sediment situated immediately below this. Samples of each were analyzed to determine the pH, redox potential, sulphate and chloride in the interstitial water, as well as total percentage of organic C (TOC), N and S. Sequential extraction of the samples differentiated six fractions of Fe: exchangeable, carbonate, ferrihydrite, lepidocrocite, goethite and pyrite. The contents of total Fe, Fe associated with silicates, Fe soluble in 1 M HCl and AVS-Fe were also determined. In general, both the biodeposit and the sediment were anoxic (Eh < 100 mV) and there were no significant differences between the two in the total Fe or in the Fe associated with silicates, which appears to indicate that the input of Fe to the system did not vary greatly. However, there were significant differences between the sediment and the biodeposit in terms of the forms of Fe in each layer. The concentrations of pyrite in the biodeposit (0.37 ± 0.25 μmol g⁻¹) were high but significantly lower than in the sediment (1.10 ± 0.20 μmol g⁻¹), and there remained large quantities of reactive-Fe that were susceptible to pyritisation. In contrast, in the sediment, the reactive-Fe was intensively pyritised, and judging from the ratio of TOC–DOP, it limited synthesis of pyrite. Furthermore, a plot of the concentration of pyrite-S against TOC revealed an excess of ∼15% of pyrite-S, which is explained by the partial decoupling of pyrite formation from organic matter accumulation, caused by the formation of pyrite from the H₂S generated by the anaerobic oxidation of methane. The latter process also appears to favour, although to a lesser extent, the precipitation of Ca carbonate, with incorporation of Fe.     

Petrofabric Investigation of Gabbros from the Oman Ophiolite: Comparison between AMS and Rock Fabric

The anisotropy of magnetic susceptibility was measured on 42 gabbros sampled across a complete plutonic sequence from the Oman ophiolite. The rock fabrics, investigated in the field and through plagioclase crystallographic fabric measurements, were compared to the magnetic fabrics. This comparative study reveals that from the paleo-Moho to the top of the foliated gabbros level, 73% of the rocks display a good correspondence in orientation, between the magnetic and rock fabric orientation. In these rocks, the AMS is controlled by secondary magnetites located in the fracture network of the olivines, and probably, but to a lesser extent, by secondary magnetites located in the exsolution lamellae of the clinopyroxenes. The high correlation between the AMS ellipsoid orientation and the rock fabric orientation is explained by the fact that the magnetic foliation is essentially constrained by the orientation of the olivine fracture planes, which is in turn constrained by the orientation of the overall magmatic rock fabric. In contrast to the primary mineral phases, the orientation of magnetite crystals in these gabbros is not due to their alignment in a flowing magma, so their preferred orientation, although usually mimicking that of the rock fabric, does have not the same origin. Furthermore, given that the preferred orientation of the anisometric secondary magnetites is much less perfect than the preferred orientation of the plagioclases, no correlation between the shape and magnitude of the AMS and plagioclase fabrics can be established. In the uppermost levels of the sequence there is no correspondence between the magnetic and rock fabric orientation. The magnetism of these rocks is mainly carried by primary magnetite and ilmenite grains. These minerals occur as small and scattered interstitial grains that exhibit neither alignment nor parallelism with the pre-existing rock fabric. Hence, the anisotropy, shape and orientation of the AMS ellipsoid are independent of the rock fabric ellipsoid. Although in the Wadi Al Abyad gabbros, just like in other magnetite bearing rocks (Rochette et al., 1992; Archanjo et al., 1995), the AMS cannot be used to evaluate the shape and strength of the finite strain ellipsoid, it can be reliably used to get the orientation of the rock fabric ellipsoid when the AMS is controlled by secondary magnetites.     

Effect of phenol on embryo development and expression of metallothionein in the sea urchin Hemicentrotus pulcherrimus

In this study, we identified and cloned the sea urchin Hemicentrotus pulcherrimus MT (Hp-MT) mRNA. We examined the gameto- and embryo-toxic effects and the expression of Hp-MT mRNA at various concentrations of phenol in H. pulcherrimus. We found that the normal embryogenesis rate was significantly inhibited when H. pulcherrimus was exposed to phenol (EC₅₀ = 1565.86 ppb, 95% Cl = 1183.47-2037.84 ppb). The no observed effective concentration (NOEC) and the lowest observed effective concentration (LOEC) of the normal embryogenesis rate were < 10 ppb and 100 ppb, respectively. Hp-MT cDNA is 651 bp in length and encodes a protein of 64 amino acids. We found that the expression of Hp-MT mRNA was significantly increased with phenol treatment in a concentrationdependent manner. These results suggest that phenol at greater than 100 ppb has a toxic effect during the early embryonic stages of H. pulcherrimus, and MT mRNA may be used as a biomarker for risk assessment of phenol contamination.     

A comparison between manganese nodules and cobalt crust economics in a scenario of mutual exclusivity

The past 20 years have been characterised by limited interest in the economic viability of deep seabed mining with the exception of those mineral ores rich in precious metals such as polymetallic sulphides. This paper goes against the tide. After reviewing the most significant literature, it compares the economic feasibility of mining polymetallic manganese nodules and cobalt-rich ferromanganese crusts in a scenario of mutual exclusivity. It uses a new indicator, the cobalt-nickel price ratio, whose aim is to verify at what metal prices the net present value of the two mining projects equalises. Previous research has shown that the turning margin between manganese nodules and cobalt crusts is a cobalt price of $50/kg. The present paper revises this by showing that the choice between mining crust and nodules depends on fluctuations in the price of nickel. A Monte Carlo simulation proves that cobalt crust mining could be reasonably preferred to manganese nodules at cobalt prices of $40-60/kg if the price of nickel fell below $11/kg. Within this condition, investors would receive the minimum acceptable internal rate of return of 15%, which is at a level of risk closer to the land-based mining. However, when the price of nickel passes the $11/kg threshold, the equilibrium between the two ventures can be reached only at a cobalt price greater than $100/kg, causing cobalt crust to become uncompetitive. Finally, the paper, recognising that prices are not unique drivers, introduces legal, political, technological and environmental concerns to show that the final choice between the two mining ventures cannot be merely driven by economic issues.     

Glass inclusions in volcanic rocks in the Okinawa Trough back-arc basin:constraints on magma genesis and evolution

INTROOUcr1ONThe Okinawa Trough is a typical marginal back-arc basin, where its oPening began in rela-tively recent years* There is a great controversy about the origin of its initial magYna. haltand acid volcanic pumice make up the bimedal volcanism in the Okinawa Trough. MOSt of geol-ogists believed that the acid pumice was the preduct of extremely crystal fractionation of baseltInagTna, but the others argued that it should com from the melting of lower-crust. Som de-tailed petrolOgic…     

Determination of inorganic sulphur speciation with polarographic techniques: Some preliminary results for recent hypersaline anoxic sediments

Polarographic techniques have been used to determine reduced inorganic sulphur speciation in recent anoxic marine sediments from two hypersaline basins, the Tyro and the Bannock Basins, in the Eastern Mediterranean. The following phases were determined: acid volatile sulphur (AVS), pyritic sulphur and zerovalent sulphur. The determination of AVS and pyrite was based respectively on the acidification and Cr(II) reduction of these sulphur components to H₂S. H₂S was collected in base and the sulphide concentration was measured by polarography. Standard Na₂S and pyrite gave recoveries of 99.6% ± 3.9% and 97% ± 12% respectively. Total zerovalent sulphur in a sediment sample was measured by the reaction of sulphite with thiosulphate. Thiosulphate was measured directly by polarography.

Pyrite is the main phase of inorganic reduced sulphur in the sediments from the Tyro and the Bannock Basins, and it has about the same average level (125 υmoles per gramme dry weight) in the cores recovered from the two areas. However, the distribution of pyrite in the top 100 cm of the two cores differs significantly. In the Bannock Basin a sharp increase is observed with depth, whereas in the Tyro Basin there is a small decrease with depth.

The total amount of reduced inorganic sulphur is less than the total amount of sulphur in the sediments. This indicates that there must be additional sulphur-bearing phases. One of these phases may be gypsum, and indeed, gypsum crystals have been observed in the Bannock Basin.

In neither basin is there a significant correlation between reduced sulphur and organic carbon. The pyrite that occurs in these basins may have been formed syngenetically at the interface of the anoxic brine and oxic seawater. Diagenetic pyrite may have been formed within the sediments of the basins. AVS and total zerovalent sulphur are still observed at depth. We therefore suggest that this may be due to the incomplete transformation of AVS and zerovalent sulphur into pyrite.     

Trace elements in suspended matter from the anoxic hypersaline Tyro and Bannock Basins (eastern Mediterranean)

In the anoxic hypersaline Tyro and Bannock Basins of the eastern Mediterranean, extremely high concentrations of Co (0.015%), Cu (1.35%) and Zn (0.28%) were found in suspended matter collected at the sharp interface between seawater and the anoxic brine. The high particulate Co, Cu and Zn concentrations can be explained by the sharp increase in dissolved sulphide at these interfaces, and the resultant precipitation of metal sulphides. The particulate As, Sb and Mo concentrations also showed a sharp maximum at or close to the interface. However, the contributions of As, Sb and Mo contents in suspended matter to the total concentrations in the water column are small. Scanning electron microscopy-energy-dispersive X-ray analysis (SEM-EDAX) of suspended particulate matter from the Tyro Basin revealed spherical particles strongly enriched in Fe, Cu and Zn at the seawater-brine interface.     

First insights into the structure and environmental setting of cold-seep communities in the Marmara Sea

A brackish-water cold seep on the North Anatolian Fault (NAF) in the Marmara Sea was investigated with the Nautile submersible during the MarNaut cruise in 2007. This active zone has already been surveyed and revealed evidence of active seeping on the seafloor, such as bubble emissions, patches of reduced sediments, microbial mats and authigenic carbonate crusts. MarNaut was the first opportunity to sample benthic communities in the three most common microhabitats (bioturbated and reduced sediments, carbonate crust) and to examine their relationships with environmental conditions. To do so, faunal communities were sampled and chemical measurements were taken close to the organisms. According to diversity indices, the bioturbated microhabitat exhibited the highest taxonomic diversity and evenness despite a lower number of samples. Conversely, the reduced sediment microhabitat exhibited the lowest taxonomic diversity and evenness. The carbonate crust microhabitat was intermediate although it had the highest biomass. Multivariate analyses showed that (1) fauna were relatively similar within a single microhabitat; (2) faunal community structure varied greatly between the different microhabitats; (3) there was a link between faunal distribution and the type of substratum; and (4) chemical gradients (i.e. methane, oxygen and probably sulphides) may influence faunal distribution. The estimated fluid flow velocity (0.4–0.8 m/yr) confirmed the presence of fluid emission and provided evidence of seawater convection in the two soft-sediment microhabitats. Our results suggest that the reduced sediments may represent a harsher environment with high upward fluid flow, which restrains seawater from penetrating the sediments and inhibits sulphide production, whereas bioturbated sediments can be viewed as a bio-irrigated system with sulphide production occurring at greater depths. Therefore, the environmental conditions in reduced sediments appear to prevent the colonization of symbiont-bearing fauna, such as vesicomyid bivalves, which are more often found in bioturbated sediments. Fluid flow appears to control sulphide availability, which in turn influences the horizontal and vertical distribution patterns of fauna at small spatial scales as observed at other seep sites.     

西南印度洋龙旂、断桥热液区沉积物中重矿物空间分布特征及其意义

以中国大洋第34航次在西南印度洋龙旂与断桥热液区采集的洋底表层沉积物样品为研究对象,为洋中脊热液硫化物勘查重砂找矿工作提供一定的理论与工作基础,开展了沉积物自然重砂矿物的相关研究。绘制了研究区重砂矿物分布图,并根据研究区已探明热液矿体(喷口)的位置,对沉积物重分散晕的形成与分布规律进行了分析;从研究区沉积物的34种矿物中,筛选出3种沉积物重砂找矿的指示性矿物(重砂总量、黄铜矿、黄铁矿)及5种参考性矿物指标(帘石类矿物、透闪石、磁铁矿、铬铁矿、钛铁矿);运用统计学方法,建立了沉积物中指标矿物含量与矿源距离之间的线性方程,提出了根据测站沉积物中指标矿物含量,初步推算矿源距离的方法。