砂金矿的化学-机械成因新观点

本文在分析前人提出的砂金矿成因的不同观点及存在的问题的基础上,根据新取得的资料,首次提出砂金矿的化学—机械成因新认识。即砂金矿的形成全过程中,既存在着化学作用,又存在着机械作用,前者主要存在于含金岩体的风化过程中,其作用使金产生次生加大及胶结作用;后者是含金岩体风化剥蚀后砂金搬运、沉积及富集成矿的主要形式。文中还据新的成因观点,提出了砂金矿的找矿方向。     

Solubility and speciation of rhenium in anoxic environments at ambient temperature and applications to the Black Sea

The aqueous speciation of rhenium at the temperatures on or near the Earth's surface, especially in anoxic environments, is not well known. For the first time, the relative importance of ReO₄⁻ and the neutral rhenium species, Re(OH)₄⁰, is thermodynamically modeled in anoxic environments at ambient temperature where ReS₂ or its solid solution(s) is likely to control the solubility. This thermodynamic model suggests that ReO₄⁻ is an insignificant species in anoxic environments. In comparison to observed total rhenium concentrations in anoxic waters (from ∼3 to ∼30 pmol/kg), the contribution from ReO₄⁻ would be less than 10⁻⁸ ppb (∼4×10⁻⁵ pmol/kg). In contrast, the neutral rhenium species is an important species in anoxic environments. At ΣH₂S=10⁻⁴ molal, 10⁻² ppb (∼40 pmol/kg) of Re(OH)₄⁰ can exist in equilibrium with ReS₂ in the HS⁻ field at a pH of about 9 or under the oxygen fugacity conditions imposed by the HS⁻/SO₄²⁻ redox couple, demonstrating its importance in anoxic environments. Applications of the present study to the Black Sea indicate that rhenium concentrations in the anoxic water column at depths ranging from 105 to ∼390 m can be successfully modeled as Re(OH)₄⁰, implying that the dominant species in solution may be Re(OH)₄⁰.     

The distributions of particulate atmospheric trace metals and mineral aerosols over the Indian Ocean

Data are presented for the concentrations of Al, Fe, Mn, Ni, Co, Cr, V, Cu, Zn, Pb and Cd in aerosols collected over two contrasting regions of the Indian Ocean. These are: (1) the northern Arabian Sea (AS), from which samples were collected in the northeast monsoon, during which the region receives an input of crustal material from the surrounding arid land masses; and (2) the Tropical Southern Indian Ocean (TSIO), a remote region from which samples were collected from air masses for which there were no large-scale up-wind continental aerosol sources. The TSIO samples can be divided into two populations: Population I aerosols, collected from air masses which have probably impinged on Madagascar, and Population II aerosols, which have been confined to open-ocean regions to the south of the area.The data indicate that there are strong latitudinal variations in the chemical signatures of aerosols over the Indian Ocean. The input of crustal material to the Arabian Sea gives rise to an average Al concentration of about 1000 ng m⁻³ of air in the northeast monsoon regime. As a result, the concentrations of all trace metals are relatively high, and the values of crustal enrichment factors are less than 10 for most metals, in the AS aerosols. In contrast, TSIO Population II ‘open-ocean southern air’ sampled during the southwest monsoon season, has an average Al concentration of only about 10 ng m⁻³ of air. Trace metal concentrations in the TSIO ‘open-ocean southern air’ during the southwest monsoon season are representative of ‘clean’ remote marine air and are generally similar to those reported over the central North Pacific.Mineral dust concentrations over the Indian Ocean decrease in a north to south direction, from about 15–20 μg m⁻³ of air in the extreme north to about 0.01–0.25 μg m⁻³ of air in the far south. The deposition of mineral dust over the northern Arabian Sea can account for approximately 75% of the non-carbonate material incorporated into the underlying sediments.In the Arabian Sea the dissolved atmospheric inputs of all the trace metals, with the exception of Cu and Co, exceed those from fluvial run-off by factors which range from 9.6 for Pb to 1.6 for Cr.     

Effects of fine grain size on distribution of Mn in shallow and deep water Black Sea sediments: A comparison between oxic and anoxic depositional environments

The uppermost 5–6 cm of the sediments (between 8 and 2248 m water depths) were studied to understand the effects of varying redox conditions on the Mn distribution in the recent sediments of the Black Sea. It was found that most Mn concentrations are consistent with the average abundance in crustal and/or sedimentary rocks. There exist no important differences between Mn concentrations in oxic (shallower water; <70 m) and anoxic (deeper water; 120 m) sediments. Previously reported Mn-enrichment above the Black Sea oxic/anoxic interface, due to the peculiar redox cycling, shows no significant contribution of Mn to the bottom sediments. A marked relationship between total Mn concentrations and clay/mud contents at shelf depth along the southern Black Sea margin indicates increased accumulation of Mn in association with the fine-grained particles and eastward water circulation.     

Detectability analysis of interplate fault slips in the Nankai subduction thrust using seafloor observation instruments

To help the decision making regarding where to locate new observation instruments on the seafloor, we examined the detectability of interplate earthquakes and slow slips in the Nankai subduction thrust in Japan using seafloor observation instruments. Here, the detectability is defined as the smallest magnitude of the interplate fault slip detected by the assumed observation points based on crustal deformation simulation. In the detectability analyses, we considered the effect of sensor drifts that are particularly associated with seafloor observations. In addition, we introduced high-resolution three-dimensional (3D) finite element modeling of crustal deformation to consider the effect of the topography and 3D heterogeneous crustal structure around the Nankai Trough. The results of the detectability analyses show that introducing new seafloor stations for tilt observation in the Nankai region should increase the detectability of small- or medium-sized interplate earthquakes and slow slips significantly. Based on the obtained results, we also discuss the advantage of both the existing and the new observation instruments in detecting interplate fault slips.

     

中国近海大气气溶胶的时间和地理分布特征

通过对中国近海10个航次气溶胶观测资料的统计分析得出:(1)从黄海、东海至日本以南海域气溶胶中地壳元素年平均浓度明显减小,在春季尘暴多发期间地壳元素浓度离到岸距离接指数规律递减.污染元素气溶胶浓度分布与陆源排放量和离岸距离有一定关系.(2)海上陆源气溶胶浓度的季节分布为:春季最大,秋冬次之,夏季最小.受日本排放源的影响,日本以南海域污染元素浓度最大值出现在冬季.(3)Se元素浓度与海洋源密切相关.海盐元素从黄海、东海至日本以南海域浓度逐渐增加,主要受周围海况影响,与风速呈现一定程度的正相关.影响近海气溶胶浓度的主要因素有陆源气溶胶排放量、降水分布和大尺度天气形势.     

南海北部地球物理特征及地壳结构

为了研究南海地壳结构，中国和日本合作在南海北部首次进行了以炸药为震源的综合地球物理调查。经初步分析其地壳结构主要特征为：南海北部地壳分为沉积层、上地壳层、中地壳层及下地壳层。大陆架及上陆坡地壳厚度大、稳定。下陆坡地壳厚度除中地壳外，其他壳层厚度减薄且不稳定。深海盆地壳分３层，厚度虽薄但相对稳定，其底部缺失７．３ｋｍ·ｓ－１的高速层。测区内地壳总厚度：陆壳２６—３０ｋｍ，过渡壳１３—２２ｋｍ，洋壳为８ｋｍ。     

Cadmium,copper and lead in the western Mediterranean Sea

The results of determinations of cadmium, copper and lead in western Mediterranean waters collected during the PHYCEMED 81 cruise are discussed in this paper. The analyses were carried out according to two different methods: flameless atomic absorption and anodic stripping voltammetry. Very strict conditions of sampling and treatment were maintained in order to reduce the chance of contamination. The concentrations found are considerably lower than those usually reported for Mediterranean waters. The distributions are homogeneous, both vertically and from one station to another. The average concentrations are 8 ng 1^?1 for Cd, 90 ng 1^?1 for Cu and 30–40 ng^?1 for Pb. This homogeneity, as well as the concentrations of cadmium and lead, may be explained by the hydrological conditions of the Mediterranean Sea.     

The distribution of Mn,Fe, Cu,Ni, Co,Ga, Cr,V, Ba,Sr, Sn,Zn, and Pb,in some soil-sized particulates from the lower troposphere over the world ocean

Soil-sized particulates have been collected on board ship by a mesh technique from the lower troposphere of the North, Equatorial and South Atlantic Ocean, northern and southern Indian Ocean, South and East China Sea and various coastal localities.Spectrographic analysis reveals that, on average, the particulates have concentrations of Mn, Ni, Co, Ga, Cr, V, Ba, and Sr which are of the same order of magnitude as those in average crustal material. In contrast, the average concentrations of Pb, Sn, and Zn are one order of magnitude higher than those in average crustal material.Within this “world-wide” average there are significant geographical variations in the distributions of Pb, Sn, and Zn which may be related to anthropogenic sources.On the basis of trace-element distributions lower tropospheric soil-sized marine particulates have been divided into four genetic components; local, zonal, inter-zonal, and global. The proportions of these components vary geographically, and each component may have both a natural and an anthropogenic fraction.     

Geophysical interpretation of features in the marine geoid of fennoscandia

An interpretation of the geoid in and around Scandinavia in terms of crustal depth structure has been made. Correlations as high as 0.92 were found between current models of crustal depth and the geoid for marine areas of Scandinavia. The Fennoscandian land uplift together with its corresponding resultant change of geoid were also found to be highly correlated with crustal depth structure. Results of these correlations compare favorably with theoretical models based upon large scale isostatic behavior of the lithosphere. These models indicate that the crustal thickness variations of Scandinavia are compensated generally at depths greater than 100 km. The results indicate that previous attempts to correlate the geoid with the causes of present land uplift have overestimated the remaining isostatic geoid anomaly in Fennoscandia. The application of these results would reduce the isostatic geoid anomaly by as much as 80% for marine areas of Fennoscandia. This may be interpreted as placing the estimated upper mantle viscosities for Fennoscandia closer to 10²¹ Pa s.     

The occurrence of gold in hydrothermal sulfide at Southwest Indian Ridge 49.6°E

Massive sulfide precipitates found in the Southwest Indian Ridge(SWIR) 49.6°E hydrothermal field are enriched in gold.Here,the mineralogy and mineral chemistry of these massive sulfides to constrain the process of gold precipitation were studied.Sulfide samples in this field include lowertemperature Zn-rich sulfides and relative higher-temperature Fe-rich sulfides.Zn-rich sulfides are dominated by sphalerite-pyrite-chalcopyrite assemblages,with concentrations of gold ranging from 9.08 to 17.0 μg/g.Fe-rich sulfides consist mainly of pyrite-marcasite-isocubanite assemblages,with gold concentrations from 2.17 to 3.79 μg/g.The significant enrichment in gold within the lowertemperature Zn-rich sulfides and the effective separation of Zn and Fe in hydrothermal precipitates at the surface of this field are here interpreted to reflect the strong temperature dependence of gold transportation and deposition within the sulfides.In Zn-rich samples,large amounts of isolated native gold grains were identified.They were found mainly as inclusions up to 8 μm in diameter,occupying porous cavities in sphalerite or in the elevated iron content rim of sphalerite.The fineness of the gold ranged from 810 to 830.Unlike previously published results on other hydrothermal fields,these data show a low gold fineness values in SWIR 49.6°E.The FeS content of sphalerite associated with gold grains ranged from 3.2 mole % to 18.9 mole %.This was higher than in other fields,indicating that the sulfur activity is relatively low during the gold precipitation process and that sulfur activity may be one of the main factors affecting gold fineness in the SWIR 49.6°E hydrothermal field.Evidence regarding gold fineness and sulfur activity suggests that gold was quite likely transported as AuHS0 rather than as a Au(HS)-2 complex.     

HOLOCENE SEA LEVEL CHANGES AND CRUSTAL MOVEMENTS ALONG THE NORTHERN COASTS OF THE SOUTH CHINA SEA

This paper discusses level changes of the sea in the last 6000 years and the recent crustal movements of the coasts of the South China Sea. There was one transgression in the middle Holocene (about 6000-3000 years ago); the sea level might not be higher than the actual one. Many terraces and coral reef platforms above the sea level can be explained by recent crustal movements.As far as the intensity of the crustal movements are concerned, the NE faults are the strongest, the NW next, and the WE are the weakest. They intersect ia block-faulting, differing in seismic activity, crustal movement rate and amplitude. On the whole, they gradually become stronger from west to east in accordance with the increasing tendency of stress field.The land is tilting toward the sea, especially ia western Guangxi Province.     

Ultramafic-carbonate breccias from the equatorial Mid Atlantic Ridge

Breccias consisting of fragments of serpentinized peridotite in a carbonate cement were dredged abundantly from the slopes of transverse ridges existing at the offsets of the Mid Atlantic Ridge in the Romanche and Vema fracture zones. The carbonate cement consists of microcrystalline, low-magnesium calcite and occasionally also of aragonite. The results of chemical and of ¹⁸O/¹⁶O, ⁸⁷Sr/⁸⁶Sr, and ²³⁴U/²³⁸U isotopic analyses of these carbonates suggest that in part they were deposited at high pH from interstitial sea water circulating in the spaces between the serpentinized peridotite fragments. Several possibilities are discussed as to the mechanisms which caused the ultramafic rocks to become brecciated. It is concluded that the breccias are probably tectonic in origin, and were formed in shear zones resulting from one of several possible types of differential motions between crustal blocks in the tectonically active offset zones. The breccias from the Mid Atlantic Ridge are similar to serpentinite-carbonate breccias associated with serpentinite bodies in the Apennine (Italy) ophiolite complex, which represents uplifted fragments of Mesozoic oceanic crust. The origin of these ophiolitic breccias may be similar to that of the Mid Atlantic Ridge breccias.     

National distribution of chemical concentrations in mussels and oysters in the USA

Since 1986 the NOAA National Status and Trends (NS&T) Program Mussel Watch has monitored concentrations of trace chemicals in the coastal United States by sampling mussels, oysters, and sediment. The sediment data have been used to define the status or geographic distribution of chemical concentrations (Daskalakis, K. D., & O'Connor, T. P. (1995). Distribution of chemical contamination in coastal and estuarine sediments. Marine Environmental Research 40, 381-398) and the molluscan data have provided an estimate of temporal trends (O'Connor, T. P. (1996). Trends in chemical concentrations in mussels and oysters collected along the US coast from 1986 to 1993. Marine Environmental Research 41,183-200, O'Connor, T. P. (1998). Mussel Watch results from 1986 to 1996. Marine Pollution Bulletin 37, 14-19). This paper centers on chemical concentrations in mollusks at 263 sites around the United States. It provides perspective on concentration ranges and on geographic distributions. For most organic chemicals and lead, concentrations vary in proportion to numbers of people living near a site. For elements, other than lead, high concentrations in mollusks can be due more to natural factors than to human activity. Concentrations of PAHs in tissues of mussels from urban areas are in a range reported to exert biological responses.     

Organic sedimentation in the water column in the Arabian Sea: Relationship between the lipid composition of small and large-size,surface and deep particles

Small and large-size particulates (>50 μm) have been collected during the ORGON IV cruise in the Arabian Sea (North-western Indian Ocean), using conventional metallic bottles and vertical near-surface (200-0 m) and deep (below 1000 m) plankton nets. This area presents remarkable conditions for studying organic sedimentation: a high superficial productivity, low oxygen content of seawater and low terrigenous inputs.Lipids have been quantified and analysed by gas-liquid chromatography and gas-liquid chromatography/mass spectrometry for fatty acids, saturated hydrocarbons and sterols. The distribution of biological species, size range and biological nature have been determined through microscopic examination.Principal results are presented in a geochemical context: small and large-size particles belong to two different reservoirs both for concentrations and chemical compositions.The comparison between the size range of particles and chemical characteristics observed through analyses of net and bottle samples emphasizes the importance of large-size particles in the geochemical process of material transfer between surface and sediment. For various lipids, this transfer concerns freshly biosynthesized molecules such as long-chain polyunsaturated fatty acids, pristane and sterols, compounds which are of high metabolic value for abyssal and pelagic organisms.The lipid fluxes, determined from in situ concentrations, and settling velocity estimated from the size range of deep particulate material, are compared to those reported by different authors using other sampling procedures for deep settling matter.     

海州湾岩芯沉积物元素地球化学特征及其环境指示

使用X射线和ICP-MS方法对海州湾潮滩HZ02岩芯沉积物的常量与微量元素进行分析,探讨沉积物元素含量和地球化学特征,揭示沉积物来源。结果表明:常量元素平均含量大小为AlFeCaKNaMgTi,从底层到表层元素含量变化相似;微量元素从底层到表层的含量变化亦比较相似,且以1958年为时间节点,之前元素含量变化大,之后元素含量稳定。HZ02岩芯沉积物元素的多变量分析表明海州湾潮滩沉积环境变化主要受陆源影响。海州湾沉积物主要来源为从临洪河输入、其次为废黄河和黄海输入。1958年以前,主要从临洪河输入,其次为废黄河物质,之后主要从临洪河输入,其次为黄海沉积物。50年代的导沭工程和1958年的石梁河水库建设,临洪河沉积物物质输入明显减少,特别是粗颗粒物质输入减少。HZ02岩芯沉积物的化学元素含量及其变化特征清楚地揭示了海州湾潮滩沉积环境及其对人类活动的响应。     

Water—rock partition coefficients and the composition of natural waters — A reassessment

Recent data on world average river water composition and global mean composition of crustal rocks have allowed a reconsideration of earlier work on the concept of a chemical steady-state in the world ocean system. In the light of these new data, initial statistical analyses have been reinterpreted or modified. This paper reports improved correlations between mean oceanic residence times ($\text{t}{}_{\mathrm{<mtext>Y</mtext>}}$) and water—rock partition coefficients (K_Y), and between K_Y and the electronegativity function (Q_YO). Such correlations support the concept that the average composition of seawater can be estimated, based on a simple dynamic model, using the electronegativities of elements and the rate of input of dissolved components.     

Hydrothermal manganese oxide deposits from Baby Bare seamount in the Northeast Pacific Ocean

Manganese oxide crusts were recovered from Baby Bare seamount in order to investigate the history of off-axis hydrothermal venting. Baby Bare is a small basement high protruding from a regional sediment cover on the eastern flank of the Juan de Fuca Ridge that acts as a focus for discharging crustal fluids. Stratabound Mn-oxide crusts were collected where warm venting has been observed near the seamount summit. Mn-oxide crusts are composed primarily of 10 Å manganate ± pyrolusite, with minor nontronite, saponite, and/or barite. These assemblage and chemical characteristics such as high Mn/Fe ratios and low trace metal and REE concentrations are indicative of a hydrothermal origin. Minimum ages for these deposits, calculated using growth rates (324 to ∼ 1800 mm/Ma) and estimated thicknesses of manganese outcrops, show that Baby Bare has been hydrothermally active for at least 0.5 Myr, and possibly since its formation (1.7–2.7 Ma). Hydrothermal manganese oxide crusts such as these from Baby Bare record interactions between the hydrothermal fluids and seawater and are important tools for estimating the longevity of off-axis hydrothermal activity.     

Influence of the Moho surface distribution on the oil and gas basins in China seas and adjacent areas

Owing to the strategic significance of national oil and gas resources, their exploration and production must be prioritized in China. Oil and gas resources are closely related to deep crustal structures, and Moho characteristics influence oil and gas distribution. Therefore, it is important to study the relationship between the variation of the Moho surface depth undulation and hydrocarbon basins for the future prediction of their locations. The Moho depth in the study area can be inverted using the Moho depth control information, the Moho gravity anomaly, and the variable density distribution calculated by the infinite plate. Based on these results, the influences of Moho characteristics on petroleum basins were studied. We found that the Moho surface depth undulation deviation and crustal thickness undulation deviation in the hydrocarbon-rich basins are large, and the horizontal gradient deviation of the Moho surface shows a positive linear relationship with oil and gas resources in the basin. The oil-bearing mechanism of the Moho basin is further discussed herein. The Moho uplift area and the slope zone correspond to the distribution of oil and gas fields. The tensile stress produced by the Moho uplift can form tensile fractures or cause tensile fractures on the surface, further developing into a fault or depression basin that receives deposits. The organic matter can become oil and natural gas under suitable chemical and structural conditions. Under the action of groundwater or other dynamic forces, oil and natural gas are gradually transported to the uplift or the buried hill in the depression zone, and oil and gas fields are formed under the condition of good caprock. The research results can provide new insights into the relationship between deep structures and oil and gas basins as well as assist in the strategic planning of oil and gas exploration activities.