Simulating experiment on the enrichment of precious metals in Lower Cambrian black shale series of Hunan and Guizhou provinces

Adsorption experiments were made at room temperature and neutral pH value on different types of min-erals associated with the Lower Cambrian black shale series polymetallic layers in Hunan and Guizhou provinces on nanometer-sized Pt colloids and PtCl42--bearing ionic solutions with an attempt to constrain the relationship between the different types of minerals in the polymetallic layers and the enrichment of platinum group elements (PGEs). Experimental results showed that the different types of minerals show strong selectivity to the adsorption of nano-meter-sized Pt colloids and PtCl42--bearing ionic solutions. Metallic sulfides, organic matter and clay minerals are the strong adsorbents of PGEs, while quartz, albite, muscovite and other silicate minerals show a week adsorbility to both of them. This phenomenon is well consistent with the geological fact that metallic sulfides, organic matter and clay minerals in the polymetallic layers of the black shale series are the major carrier minerals of PGEs, giving a thorough explanation to the mechanism of enrichment of previous metal elements. Adsorption may be a principal mechanism of enrichment of precious metal elements under lower temperature conditions. The presence of the aforementioned strong adsorbents is the good geochemical barriers for the enrichment of PGEs.     

我国南海北部湾第三系粘土岩中有机物的赋存状态及其与生油关系的探讨

The chemistry of organo-clay in somc Tertiary clay-stones from the northern part of the South China Sea was studied. The preliminary results are summarized as follows : (1) Three basic types of organic matter are distinguished in the claystones after treated with different chemical agents: spluble, combined and insoluble (kerogen). It is suggested that the distribution of organic matter and its conversion to petroleum are closely related with the composition and structure of expansive clay minerals in the claystones. Therefore, more detailed studies of these expansive clay minerals may provide new indices for oil-generating potentiality. (2) It is considered from the study of the state of existence of organic matter and. of organo-clay complexes in tile clay-stones that the accumulation and preservation of organic substances may substantially take the form of organo-clay complexes in the process of sedimentation and burial and that the organo-clay complexes may make considerable contributions to the formation of petroleum hydrocarbons during diagenesis. Studies in this aspect are of great significance in developing new theories conccrning petroleum generation and in localizing oil-generating occurrences.     

Geochemical Signatures of Early Paleogene Source Rocks in the Sanshui Basin, South China

The Honggang member of the early Paleogene Buxin Formation is the main source rock in the Sanshui Basin, characterized by organic-rich black shales with the cyclic recurrence of organic- poor sediments. The geochemical characteristics of the Honggang member have been documented to determine the organic matter types and depositional environments in this paper. The organic matter of the black shales mainly consists of a mixture of land plant-derived and phytoplankton-derived organic matter. Total organic carbon content (TOC)–sulfur–iron (Fe) relationships suggest that the organic- rich black shales were deposited under dysoxic-to-euxinic water conditions. The time that iron minerals remained in contact with H2S in anoxic waters possibly influenced the formation of syngenetic pyrite, and organic carbon controlled the formation of diagenetic pyrite. Organic-poor intervals usually show pyrite sulfur enrichment and higher degree of pyritization values relative to low organic carbon contents. This resulted from HS– diffusing downward from overlying organic-rich sediments and formed Fe sulfides through reactions with sufficient Fe. Trace elements generally exhibit low concentrations and little TOC dependence, suggesting some degree of depletion in these elements in the early Paleogene sediments of the Sanshui Basin. This probably resulted from cyclic recurrences of oxic benthic conditions, which promoted the remobilization of trace elements and caused the low concentration of trace elements.     

Occurrence modes of silver in the Ni-Mo-PGE polymetallic layer of the Lower Cambrian black shales in Zunyi,Guizhou Province,South China

The Ni-Mo-PGE polymetallic mineralization of the Lower Cambrian black shales locate in Zunyi, South China and contain abundant noble metals such as Ag, Au and PGE, and especially Ag with average concentration of 64×10-6. The occurrence modes of Ag have been investigated using methods of selective chemical dissolution and transmission electron microscopy. The results demonstrate that the occurrence modes of Ag are complex and diversiform. It might be associated with clay minerals, organic matter, sulfides and also occurred as native silver and sulfides with nanometer in size. Combined with results of previous studies, we suggest that the sulfides, clay minerals and organic matter which hosted in the Ni-Mo-PGE polymetallic ores of black shales can play the roles of important reduction and adsorption geochemical barriers for the enrichment and distribution of silver. This study further implies that the selective chemical dissolution and transmission electron microscopy may pave the way to study the occurrence modes of other noble metals in black shales.     

Relationship between the geochemistry of organic matter and the generation of palygorskite in Jiangsu-Anhui border and Gansu Province, China

Soluble organic matter had been separated from several palygorskite and bentonite samples in the Ji-angsu-Anhui border area(across Jiangsu Province and Anhui Province) and Linze County in Gansu Province of China and was analyzed with the techniques and methods of organic geochemistry.The composition and distribution of hydrocarbons were analyzed by gas chromatography(GC).Organic stable carbon isotopic ratios(δ13C) in typical samples were determined.The abundance of soluble organic matter in all clay samples analyzed was low.In Ji-angsu-Anhui samples,the preservation states of organic matter are different;hydrocarbons in organic matter have some features of aquatic plankton but are short of the input of terrigenous higher plants;organic δ13C in a palygor-skite of Yongxiaoshan in Xuyi County,Jiangsu Province,is-6.72‰.These features may be typical of a sedimentary environment of closed or semi-closed and relatively isolated different waters near coast or seashore.On the contrary,in samples from Gansu,the preservation states of organic matter are good;the GC graphs of hydrocarbons show that the precursors of the organic matter are from a mixed source of aquatic organisms and land-sourced higher plants;organic δ13C of a palygorskite from Yangtai of Gansu is-15.62‰.It indicated that the sedimentary environment may be an inland salty lake.Preliminary results suggest that palygorskite minerals in the Jiangsu-Anhui area may be evolved from rapidly accumulated fine material or volcanic ash,but clays in Gansu Province may be transformed from terrigenous inorganic clastic components carried to the lake through river and then deposited.The generation process of the samples studied in the paper seems to be related to salty water.     

碳酸盐矿物的包裹有机质及其生油意义

Fluorescent slice observations have revealed a considerable amount of organic matter enclosed in carbonate minerals, most of it giving off yellow-brown fluorescence and being zonally distributed in calcite and dolomite. The amount of enclosed organic matter released from the enclosure when treated with HCl is two times higher than that of extractable organic mattes in the same rock sample. In comparison to the extractable organic matter, the enclosed organic matter is possessed of some compositional characters of its own. In terms of the distribution of biological markess, it is suggested that the enclosed organic matter may be low in maturity relative to the extractable organic matter in the same source rock.Results of the simulating experiments under high temperatures and pressures show that this kind of organic matter enclosed in carbonate minerals can be converted into oil-generating substances. Therefore, detailed studies of the enclosed organic matter are of much help to the evaluation of oil-generating potentiality of carbonate source rocks.     

Separation of Clay Minerals from Host Sediments Using Cation Exchange Resins

Classic physical and chemical treatments applied to separating clay minerals from the host sediments are often difficult or aggressive for clay minerals. A technique using cation exchange resins (amberlite IRC-50H and amberlite IR-120) is used to separate clay minerals from the host sediments. The technique is based on the exchange of cations in the minerals that may be associated clay minerals in sediments, such as Ca and Mg from dolomite; Ca from calcite, gypsum and francolite with cations carried by resin radicals. The associated minerals such as gypsum, calcite, dolomite and francolite are removed in descending order. Separation of clay minerals using cation exchange resins is less aggressive than that by other classic treatments. The efficiency of amberlite IRC-50H in the removal of associated minerals is greater than that of amberlite IR-120.     

Some aspects of excellent marine source rock formation:implications on enrichment regularity of organic matter in continental margin basins

Through the analysis of ocean organisms, the distribution characteristics and enrichment of organic matters in modern marine sediments and ancient marine strata, this paper shows that the main factors influencing the formation of excellent marine source rocks are the paleoclimate, biologic productivity, terrestrial organic matter, oxidation–reduction environment, sedimentation rate, and the type of the basin. In addition to those factors,high biologic productivity or high content of terrestrial organic matter input is a requirement for the enrichment of the organic matter in a marine environment. Reducing environment was favorable for organic matter accumulation and preservation in depositing and early diagenesis stage, which is an important element for the formation of high-quality marine source rocks. Paleoclimate also influences the marine source rocks formation, as humid subtropical and tropical climates are the most favorable regimes for the formation of marine source rocks. Wind transports some vascular plant materials into the marine environment. Furthermore, upwellings driven by steady wind can cause high biologic productivity, thus formingorganic-C-rich mud. Suitable sedimentation rate is beneficial for marine organic matter accumulation. Moreover, the type of the basin also plays an important role in the development of marine source rocks. Silled basins with a positive water balance often act as nutrient traps, thus enhancing both productivity and organic matter preservations, while in open oceans, organic matter enrichment in sediments has just been found in the oxygen minimum layers.     

Comparison of components and distribution of heavy metals in sediments, suspended particulate matter and surface coatings in natural waters

Solid phases, such as surface coatings （SC）, suspended particulate matter （SPM） and deposited sediments （DS）, contribute to the pool of heavy metals in natural waters. Their existing and forming conditions lead to potential differences in enrichment capacity of pollutants, chemical compositions and crystals. In this study, the contents of heavy metals in SC, SPM and DS were determined by GF-AAS after digestion with a mixture of concentrated HNO3 and HClO4. The selective extraction method was employed to remove Fe, Mn oxides and organic matters and associated heavy metals （Cu, Pb, Zn）. X-ray diffraction analyses were performed to characterize the crystals in the samples. The results showed that no significant difference in the contents of Fe-oxides in DS, SPM and SC was found, but the contents of Mn-oxides and organic matter follow the order of SC〉SPM〉DS. The significant crystal characters were observed in DS, SPM and SC, and the kinds of minerals and crystallization degree follow the order of DS〉SC〉SPM. In addition, quartz was the most important matter of crystals in the solid phases. Enrichment capacity follows the order of SPM〉SC〉DS for Pb, Cu and Zn. Organic matter was the major sorbent for Cu, and Mn oxides and organic matter played an important role in the enrichment of Zn. However, Pb was absorbed mainly by Fe oxides. Moreover, compared with Fe oxides and organic matter, Mn oxides had a great enrichment capacity for these metals. Although DS, SPM and SC were formed in the same water system, contents of chemical components, crystals and enrichment capacities to heavy metals were obviously different.     

REE Geochemistry of Surficial Sediments from the Yellow Sea of China

REE geochemical studies of surficial sediment samples from the Yellow Sea of China have shown:(1)The average content of RE2O3 in the Yellow Sea sediments is 175 ppm,close to that in the East China Sea sediments.The REE distribution patterns in the Yellow Sea sediments are also similar to anomalies.These REE characteristics are typical of the continental crust.(2)The contents of REE are controlled mainly by the sediment grain size,i.e.,REE contents increase gradually with decreasing sediment grain size.REE are present mainly in clay minerals.In addition,REE contents are controlled obviously by heavy minerals.REE abundances in heavy minerals are much greater than those in light minerals.(3)Correlation analysis shows that REE have a close relationship with siderophile elements,especially Ti,which has the largest correlation coefficient relative to REE.Terrigenous clastic materials subjected to weathering and transport are suggested to be the main source of REE in the Yellow Sea sediments.     

Mechanism of Seasonal Deterioration of Water Quality in Lake Baihua,China

Water quality of Lake Baihua was found worsening in the autumn of 1994.Studies have shown that the decomposition of organic matter in the upper-level sediments resulted in seasonal anoxia with the release of P,Mn,and S^2- from the sediments to the overlying water column,and the increase of NO2^- concentration led to blackening of the water column,deat of fishes and secondary Mn pollution.     

碳酸岩分散有机质的基本存在形式、演化特征与碳酸岩地层油气评价

Two major characters are recognized with respect to the evolution of organic matter during diagenesis of carbonate rocks; (1) expellation of organic matter from carbonate minerals through crystallization, which could reduce the amount of organic matter significantly in the early stage of diagenesis; (2) protection of organic matter by the minerals, especially in the late stage of diagenesis. According to their nature and relations to the protection during diagenesis, three majer forms of disseminated organic matter in carbonate rocks can be distinguished: adsorbed, ctystallization-trapped organic matter and organic inclusions. Owing to the protection by minerals the maturation process of disseminated organic matter proceeds very slowly, and the matority of crystallization-trapped organic matter may play an important role in carbonate source rocks. Most of the organic inclusions are migrated organic matter, such as hydrocarb ons; so organic inclusions may be a good indicator which can be used to study the primary,secondary migration and the concentration of oil and gas in carbonate source rocks and carbonate reservoir strata,     

Distribution and controlling factors of selenium in weathered soil in Kaiyang County,Southwest China

Selenium is one of the life-related elements. Survey reveals that selenium enrichment in the studied strata from Kaiyang County is considered to be closely related to the following factors： regional black shale series in Ni- utitang Formation of Early Cambrian, strong adsorption of organic matter （OM）, magmatic hydrothermal migrate along the deep fault, mixing and migration of hydrothermal brine, regional uranium mineralization and presence of a great deal sulfides. For selenium enrichment in its weathered soil and crops, the reason responsible is sele- nium-enriched bedrock, which provides material sources for weathering profile and is considered as the main con- trolling factor of selenium content in the soil profile. After leaching and migrates downwards, organic carbon （OC） adsorption, iron-manganese layer adsorption, geochemical barrier role, selenium content in different profiles, there are mainly three types of distribution features： bottom enrichment type, top enrichment type and no significant en- richment type. Comprehensive analyses find that selenium enrichment area is mainly distributed in the Machang, Gaoyun-Fengsan-Guanpo, Baimadong, Chuandong-Hefeng-Shaoshang and Longgang-Gaozhai region, etc. Besides, around the east part of the county, in Huali and Yongxing selenium are relatively scarce.     

Geochemical records of the sediments and their significance in Dongping Lake Area,the lower reach of Yellow River,North China

Dongping Lake area, located in the lower reaches of Yellow River, is an ideal place to study the changes of modern river and lake sedimentary environment. The sediment samples of Dawen River, Yellow River, and Dongping Lake were collected, and the major elements, trace elements and organic matter geochemical composition of the samples were analyzed. Cluster analysis, characteristic element ratio method and graphic method were used to explore the geochemical characteristics of sediments and their environmental implication. The results show that the contents of SiO_2, Na_2O, TiO_2 and Zr in sediments of Dawen River and Yellow River are relatively high, and the contents of iron and manganese oxides, organic matter, CaO, P_2O_5 and Sr in lake sediments are relatively high. That reveals the differences of sedimentary environments between the rivers and the lake. The contents of Sr and Zr in Dawen River are affected by the rapid migration of clastic materials in the upstream carbonate source area during the flood season; the δCe,ΣREE and REE's ratios in the sediments of the Yellow River reflect the influence of the Loess source; and the distribution of elements changes along the flow direction during the flood season. The characteristics of p H, element composition and LREE HREE fractionation of the lake sediments indicate that the sediment source is complex, and the lake environment is affected by the flood season. The study shows that the geochemical content and its variation characteristics of sediments effectively reveal the sedimentary environment, material composition and characteristics of flood season of rivers and the lake in the study area.     

Carbon and Oxygen Isotopic Compositions: How Lacustrine Environmental Factors Respond in Northwestern and Northeastern China

Surface lake sediments,28 from Hoh Xil,24 from northeastern China,99 from Lake Bosten,31 from Ulungur and 26 from Heihai were collected to determine δ13C and δ18O values.Considering the impact factors,conductivity,alkalinity,pH,TOC,C/N and carbonate-content in the sediments,Cl,P,S,and metal element ratios of Mg/Ca,Sr/Ca,Fe/Mn of bulk sediments as environmental variables enable evaluation of their influences on δ13C and δ18O using principal component analysis(PCA) method.The closure and residence time of lakes can influence the correlation between δ13C and δ18O.Lake water will change from fresh to brackish with increasing reduction and eutrophication effects.Mg/Ca in the bulk sediment indicates the characteristic of residence time,Sr/Ca and Fe/Mn infer the salinity of lakes.Carbonate formation processes and types can influence the δ13C–δ18O correlation.δ18O will be heavier from Mg-calcite and aragonite formed in a high-salinity water body than calcite formed in freshwater conditions.When carbonate content is less than 30%,there is no relationship with either δ13C or δ18O,and also none between δ13C and δ18O.More than 30%,carbonate content,however,co-varies highly to δ13C and δ18O,and there is also a high correlation between δ13C and δ18O.Vegetation conditions and primary productivity of lakes can influence the characteristics of δ13C and δ18O,and their co-variance.Total organic matter content(TOC) in the sediments is higher with more terrestrial and submerged plants infilling.In northeastern and northwestern China,when organic matter in the lake sediments comes from endogenous floating organisms and algae,the δ13C value is high.δ13C is in the range of 4‰ to 0‰ when organic matter comes mainly from floating organisms(C/N<6);in the range of 4‰ to 8‰ when organic matter comes from diatoms(C/N=6 to 8);and 8‰ to 4‰ when organic matter comes from aquatic and terrestrial plants(C/N>8).     

Sequential extraction of heavy metals during composting of urban waste

In urban waste （the first matter of compost）, elements such as copper, nickel and lead may be found in metallic state （wire, pile, accumulator, etc.）, which is considered as non-dependent state. The work undertaken at the laboratory of composting of the INRST in Henchir Lihoudia （Tunis） showed that the produced compost does not contain any mobile metallic element and the portion related to organic fraction （bioavailable） is tiny in size. We supposed that many reactions involving decomposition and complexation from elements related to the matrix components occurred during composting. The existence and importance of this phenomenon can be evaluated by studying the evolution of metal contents in the different fractions extracted sequentially during composting process.     

碳酸盐岩生油岩的有机地球化学、岩石学特征

Features of oil-generating carbonate rocks are studied in terms of petrology and organic geochemistry of fluorescent materials in rocks. It is postulated by the authors that the organic carbon content in oil-generatlng carbonate rocks is necessarily lower than that in shales, and the possible cause of this observation is discussed. The quality of oil-ganerating carbonate rocks may be judged by aromatic structure index,amino acid, pigment index, and DTA data on organic matter. However, the application of presently available organic geochemical criteria to non-oil-generating reservoir rocks may always give misleading results. To circumvent this difficulty, it is necessary first to make distinction between primary and secondary organic matter by cxamining the fluorescent materials under a fluorescence microscope. Measurementof radical content of the organic substances and DTA are useful techniques to determine the degree of maturation. The maturation of organic substances proceeds at a lower rate in carbonate rocks than in shales. It is likely, therefore, that some older carbonate strata can also be promising areas for petroleum exploration. Oil-generating carbonate rocks consist mainly of mierite limestones rich in organic matter and are thought to be formed under low-encrgy environment. Consequently, petrological(especially mierolithofacies) studies are very important in evaluating carbonate source rocks.     

Characterization of a Lacustrine Shale Reservoir and the Evolution of its Nanopores: A Case Study of the Upper Cretaceous Qingshankou Formation in the Songliao Basin,Northeastern China

The Songliao Basin is one of the most important petroliferous basins in northern China. With a recent gradual decline in conventional oil production in the basin, the exploration and development of unconventional resources are becoming increasingly urgent. The Qingshankou Formation consists of typical Upper Cretaceous continental strata, and represents a promising and practical replacement resource for shale oil in the Songliao Basin. Previous studies have shown that low-mature to mature Qingshankou shale mainly preserves type Ⅰ and type Ⅱ1 organic matter, with relatively high total organic carbon(TOC) content. It is estimated that there is a great potential to explore for shale oil resources in the Qingshankou Formation in this basin. However, not enough systematic research has been conducted on pore characteristics and their main controlling factors in this lacustrine shale reservoir. In this study, 19 Qingshankou shales from two wells drilled in the study area were tested and analyzed for mineral composition, pore distribution and feature evolution using Xray diffraction(XRD), scanning electron microscopy(SEM), low-pressure nitrogen gas adsorption(N2-GA), and thermal simulation experiments. The XRD results show that clay, quartz, and feldspar are the dominant mineral constituents of Qingshankou shale. The clay minerals are mostly illite/smectite mixed layers with a mean content of 83.5%, followed by illite, chlorite, and kaolinite. There are abundant deposits of clay-rich shale in the Qingshankou Formation in the study area, within which many mineral and organic matter pores were observed using SEM. Mineral pores contribute the most to shale porosity;specifically, clay mineral pores and carbonate pores comprise most of the mineral pores in the shale. Among the three types of organic matter pores, type B is more dominant the other two. Pores with diameters greater than 10 nm supply the main pore volume;most are half-open slits and wedge-shaped pores. The total pore volume had no obvious linear relationship with TOC content, but had some degree of positive correlation with the content of quartz + feldspar and clay minerals respectively. However, it was negatively correlated with carbonate mineral content. The specific surface area of the pores is negatively related to TOC content, average pore diameter, and carbonate mineral content. Moreover, it had a somewhat positive correlation with clay mineral content and no clear linear relationship with the content of quartz + feldspar. With increases in maturity, there was also an increase in the number of carbonate mineral dissolution pores and organic matter pores, average pore diameter, and pore volume, whereas there was a decrease in specific surface area of the pores. Generally, the Qingshankou shale is at a low-mature to mature stage with a TOC content of more than 1.0%, and could be as thick as 250 m in the study area. Pores with diameters of more than 10 nm are well-developed in the shale. This research illustrates that there are favorable conditions for shale oil occurrence and enrichment in the Qingshankou shale in the study area.     

镉、铅在某些河流环境中迁移净化机理的研究

It has been found that Pb and Cd can be gradually purified during their transportation in rivers and that the rate of purification for Pb is much greater than that of Cd,Such process is not only closely related to the degree of water dilution and the properties of Pb and Cd themselves, but also to the existing ligands, oxidation-reduction conditions, colloids, pH and other factors in the aquatic environment. Suspended particles and river-bed sediments have a strong ability of adsorption and purification with respect to Pb and Cd. This ability shows a positive correlation with the composition of clay in sediments on the river bed, but a negative correlation with the grain-size of quartz particles. our results indicate that both the adsorption and possible desorption of Pb and Cd in river-bed sediments and suspended particles may be highly responsible for the variations in Pb and Cd concentrations in aquatic environments. The dynamic adsorptiondesorption balance of Pb and Cd between riverbed sedimeuts and water varies with pH.It may be favorable for the purification of Pb and Cd in aquatic environments if pH is adjusted to slightly alkaline within the tolerance of environmental capacity.     

Deep-penetrating geochemistry of the Tuwu copper deposit, northwestern China

Desert terrains in northern China are covered by widespread regolith sediments which mask geochemical signals from ore bodies and are major obstacles to mineral exploration. There is a critical need to study the vertical distribution of elements in this regolith and to establish optimum sampling and analytical methods. The aim of this study is to understand the dispersion and variation of elements throughout the cover in a vertical profile. The results demonstrate that the main elements show a distribution pattern of enrichment in clay layers in the vertical profile, i.e., most elements tend to be enriched in the most upper part of the profile above the orebodies except for some elements like Cu, Ca and Ag. Meanwhile, both fine (-160 mesh) and coarse (+20 mesh) fraction samples from clay-rich horizons are favorable samples and selective leaching of the elements absorbed on clays or oxide coatings is effective for localizing buried deposits. The distribution of active Cu and Mo is quite different because chalcopyrite is weathered into Cu sulfate and CuCO3, and is precipitated in alkaline environments in a layer below close to the surface. Mo is soluble in the alkaline environment so it can penetrate the caliche layer and be enriched on the surface of soil enriched with weakly cemented clay.