A polymetallic layer is usually developed at the bottom of the early Cambrian black shale in Guizhou Province.The mineral that makes up the polymetallic layer is related to the sedimentary facies.To analyze the differ...A polymetallic layer is usually developed at the bottom of the early Cambrian black shale in Guizhou Province.The mineral that makes up the polymetallic layer is related to the sedimentary facies.To analyze the differentiation mechanism between polymetallic deposits(Ni-Mo and V),the Zhijin Gezhongwu profile located in the outer shelf and the Sansui Haishan V deposit located in the lower slope are selected to study the in situ sulfur isotopes and trace elements of pyrite.The results show that δ^(34)S values of pyrite vary widely from−7.8‰to 28‰in the Gezhongwu profile,while the δ^(34)S values are relatively uniform(from 27.8‰to 38.4‰)in the Haishan profile.The isotopic S composition is consistent with the transition that occurs in the sedimentary phase from the shelf to the deep sea on the transgressive Yangtze platform;this indicates that the δ^(34)SO_(4)^(2−)values in seawater must be differently distributed in depositional environments.The sulfur in the Ni-Mo layer is produced after the mixing of seawater and hydrothermal fluid,while the V layer mainly originates from seawater.Overall,the Ni-Mo and V deposits have been differentiated primarily on the basis of the combined effect of continental weathering and hydrothermal fluid.展开更多
The recovery of vanadium from a black shale from Guizhou Province of China was performed using a three-step process, which consists of a leaching step in the H2SO4-HF-NaClO system under atmospheric pressure,the vanadi...The recovery of vanadium from a black shale from Guizhou Province of China was performed using a three-step process, which consists of a leaching step in the H2SO4-HF-NaClO system under atmospheric pressure,the vanadium separation from leachate by solvent extraction and stripping,followed by precipitation of ammonium vanadate and thermal decomposition.Under the optimum leaching conditions of 100 g/L sulfuric,15 g/L hydrofluoric acid,1.5 g/L NaClO,6 h leaching at 90℃and oxygen partial pressure of 1 200 kPa,and the liquid-to-solid ratio of 2,about 91%vanadium extraction is achieved.The vanadium extraction yields of solvent and stripping are 99.83%and 97.66%when using 10%(volume fraction)P204,5%TBP and 85%sulfonated berosene as organic phase and 15%(mass fraction)sulphuric acid as stripping agent.After thermal decomposition the purity of powder vanadium pentoxide products is 99.18%and the overall vanadium recovery is over 81%in the whole process.展开更多
Extraction of vanadium from black shale was attempted in pressure acid leaching.The chemical components of the sample obtained from Guizhou Province of China show that it contains 3.258%V2O5,52.880%SiO2 and 16.140%Al2...Extraction of vanadium from black shale was attempted in pressure acid leaching.The chemical components of the sample obtained from Guizhou Province of China show that it contains 3.258%V2O5,52.880%SiO2 and 16.140%Al2O3.Phase analyses of vanadium indicates vanadium mainly exists in the free oxide and mica.Vanadium contents in the two phases are 18%and 53%, respectively.The contents of V3 +,V 4+and V 5+are almost equal.Under the optimum parameters of one-step leaching(reaction time of 3 h,sulfuric addition of 25%,temperature of 150℃,liquid to solid ratio of 1.2 mL/g,catalyst(FeSO4)addition of 5%and size of 85%particle 0.074 mm),about 77%of vanadium is recovered.After two-step countercurrent leaching,the leach recovery of vanadium can reach above 90%.Air replacing oxygen is completely feasible.The impurity metals can dissolve into solution in different degrees.展开更多
: Black shales are marine sediments with argillaceous, silty and siliceous compositions and high contents of organic materials, disseminated pyrite and uranium. Uraniferous black shale has uranium content of more than...: Black shales are marine sediments with argillaceous, silty and siliceous compositions and high contents of organic materials, disseminated pyrite and uranium. Uraniferous black shale has uranium content of more than 20 ppm.Black shales are widely distributed in 17 provinces or autonomous regions in northwestern and southern-central China. Their sedimentary ages are from the Sinian to the Tertiary and uraniferous black shales are mainly exposed in Yunnan, Guizhou, Sichuan, Hunan, Hubei, Jiangxi, and Zhejiang provinces and Guangxi Zhuang Autonomous Region and the economically significant uranium deposits associated with black shale occur in Hunan and Jiangxi provinces and Guangxi Zhuang Autonomous Region.Uranium mineralization associated with black shale has the following main features: (1) forming stratabound deposits; (2) controlled by structures such as interlayer and intersected faults and fractures; (3) associated with different ore-forming processes such as leaching and hydrothermal reworking; (4)展开更多
To improve the understanding of the relationship between silica source and organic matter accumulation,the origin of silica and its implications for organic matter enrichment in the Upper OrdovicianLower Silurian(O_(3...To improve the understanding of the relationship between silica source and organic matter accumulation,the origin of silica and its implications for organic matter enrichment in the Upper OrdovicianLower Silurian(O_(3)w-S_(1)l)black shale in western Hubei Province in the middle Yangtze area,were investigated through geochemical and petrological analyses.The results show that the O_(3)w-S_(1)l black shale is mainly composed of five lithofacies with varying graptolite abundance,total organic carbon(TOC),and silica contents.Biogenic silica and terrigenous siliciclastic input constitute the main silica sources in O_(3)w-S_(1)l black shale and they exhibit an upward inverse variation trend interpreted to be related to sea-level changes.Moreover,with the increase in biogenic silica content or decrease in terrigenous siliciclastic input,TOC values in black shale initially rise and then fall,which is different from originally expected simple linear relationship.We infer that organic matter enrichment and the distribution of silica from different origins are controlled by sea-level changes and variations in terrigenous input in a continental shelf with little hydrothermal influence.An environment with appropriate sea level and terrigenous input should be most favorable for organic matter accumulation,rather than one with excessive high sea level and less terrigenous input.展开更多
Early Paleozoic black organic sediments and bentonites occur widely in the craton basin within the Yangtze block and are generally believed to be genetically related to a specific tectonic setting on the cratonic boun...Early Paleozoic black organic sediments and bentonites occur widely in the craton basin within the Yangtze block and are generally believed to be genetically related to a specific tectonic setting on the cratonic boundary.However,the intimate relationship between their origins and the dynamic mechanisms are unclear,as exemplified by the genesis of the black shale series and bentonites from the Wufeng Formation during the Ordovician–Silurian transition(OST).In order to reveal the relationship between the Wufeng Formation and the convergence of the Yangtze and Cathaysia blocks(i.e.,the intracontinental Kwangsian Orogeny),two stratigraphic sections respectively in Zhaotong area(Northeast Yunnan)and Puyi area(Northwestern Guizhou)that were located in the semi-restricted inner Yangtze Sea during the OST were systematically studied,on the basis of whole-rock geochemical composition,pyriteδ^(34)S(δ^(34)Spy),total organic carbon(TOC),stable Sr isotope,pyrite framboid size distribution and zircon U-Pb age,trace elements.The evidence shows that the paleo-oceanic environment changed significantly at the turn of the early–late Katian and formed the black shale series in the Wufeng Formation.These acritarch assemblages were formed in the transition process of the Upper Yangtze Basin from passive continental margin basin to foreland basin during this interval.Based on previous research on the genetic relationship between black shale series and plate tectonic movement,a basin-mountain evolution model suitable for South China in the Late Ordovician is presented.The two bentonites in the Wufeng Formation with U-Pb ages of 445.5±0.8 Ma and 441.9±2.4 Ma primarily originated from the intermediate–acid volcanic eruption during the collision and convergence between the Yangtze and Cathaysia blocks in the Late Ordovician,the provenance region probably being located in the Jiangnan orogenic belt.Thus,we believe that the appearance of the black shale series and bentonite in the Wufeng Formation at the turn of the early–late Katian may represent the initiation of basin-mountain transformation and the Kwangsian Orogeny in South China,which provides important evidence for the collision and convergence of the Yangtze and Cathaysia blocks in the Late Ordovician.展开更多
Based on geochemical analysis results of core samples from the Triassic Chang 7 Member of Well Feng 75 drilled in the northwest margin of Ordos Basin,combined with geological characteristics of this region,the formati...Based on geochemical analysis results of core samples from the Triassic Chang 7 Member of Well Feng 75 drilled in the northwest margin of Ordos Basin,combined with geological characteristics of this region,the formation environment of the black shale and its control on shale oil enrichment are comprehensively studied.From the Chang 73 to Chang 71 Sub-members,the black shale have organic carbon contents decreasing from 5.70%to 3.55%,hydrogen indexes decreasing from 345 mg/g to 269 mg/g,while the oxygen indexes increasing gradually from 6 mg/g to 29 mg/g,indicating that the sedimentary environment during the depositional period of Chang 72 and Chang 73 Sub-members was anoxic.Biomarkers in the black shale change regu-larly,and have an obvious“inflection point”at the depth of 2753–2777 m in the Chang 73 Sub-member,indicating that the input of terrigenous organic matter increased.However,there is a negative drift about 2%of organic carbon isotopic composition near the“inflection point”,which is in conflict with the results of biomarker compounds.This is because the extreme thermal and anoxic events caused by continental volcanic activity in the ancient Qinling region caused negative drift of carbon isotopic composition of the black shale in the Ordos Basin.The volcanic activity caused rise of temperature,polluted air,extreme weathers,more floods and thus more input of terrigenous organic matter,and gave rise to extremely anoxic environment con-ducive to the preservation of organic matter.Terrigenous organic matter is more conducive to the formation of light oil than aquatic organic matter,so these sections in Yanchang Formation are major“sweet spots”for shale oil enrichment.展开更多
This work aimed for pyrite separation from Abu Tartur black shale as a source of sulfur to be an added economic value of Abu Tartur area. The considered samples in the present work were collected from a core drilled i...This work aimed for pyrite separation from Abu Tartur black shale as a source of sulfur to be an added economic value of Abu Tartur area. The considered samples in the present work were collected from a core drilled in Abu Tartur plateau representing the pyrite-rich black shale of the U. Cretaceous age.Sample characterization was carried out using petrographic microscope, XRD, DTA/DTG, C/S and XRF techniques. Clay minerals, silt-sized quartz, calcite, and hematite were the main minerals associating pyrite(5.34%). Liberation behavior of the sample was about 80% below 5 lm.Sample processing was achieved through one-day soaking followed by classification using 1 inch Mozley hydro-cyclone where about 35.5% by weight went to underflow and 64.5% went to overflow.The underflow product was subjected to an advanced gravity separation process using SB-40 Falcon Concentrator through a CCD statistical design prepared by Design-Expert 6.0 software proposed to optimize the separation process through a study for the effects of frequency(Hz) and water pressure(Psi) on both assay and recovery of the sulfur-rich heavy fraction.A heavy concentrate weighed 10.90% with inorganic sulfur content reached 11.37%(21.24% pyrite) with overall recovery(50.01%) was obtained after two cleaning at the optimum conditions.展开更多
The lower Cambrian Niutitang Formation, a widespread black shale deposition, is of geological interest because of its polymetallic beds, Cambrian explosion, depositional ages, dramatic environmental changes and so on....The lower Cambrian Niutitang Formation, a widespread black shale deposition, is of geological interest because of its polymetallic beds, Cambrian explosion, depositional ages, dramatic environmental changes and so on. Previous study focused mainly on inorganic geochemistry and few studies have investigated the organic fractions of upper Neoproterozoic-lower Cambrian strata in South China. Here we report a study of biomarkers plus organic carbon isotopes for black shales from Ganziping, Hunan Province (China). All the saturated hydrocarbon fractions have a unimodal distribution of n-alkanes, a high content of short-chain alkanes and maximize at C 19 or C 20 (C 23 for sample Gzh00-1). The C 27 /C 29 sterane ratio ranges from 0.77 to 1.20 and 4-methylsteranes are in low abundance. These parameters indicate that algae and bacteria are the important primary producers. Furthermore, biomarker maturity proxies show the samples to be higher maturity. The low Pr/Ph values (<0.7) suggest that the samples were deposited under anoxic conditions and, likely, under stratified water columns. In addition, 25-norhopanes and gammacerane are present as diagnostic indicators of normal marine salinity and dysoxic to anoxic conditions. During the Early Tommotian, known to coincide with a transgression event, small shelly fossils increased in abundance and diversity. Moreover, positive δ 13 C org excursions close to 1.4‰ occur at the base of the Tommotian stage. In summary, the Early Cambrian black shales were deposited under dramatic paleoenvironmental changes, including oceanic anoxia, higher primary productivity and sea-level rise.展开更多
Control of various factors, including mineral components, primary productivity and redox level, on the total organic carbon(TOC) in the lower Cambrian black shale from southeastern margin of Upper Yangtze(Taozichong, ...Control of various factors, including mineral components, primary productivity and redox level, on the total organic carbon(TOC) in the lower Cambrian black shale from southeastern margin of Upper Yangtze(Taozichong, Longbizui and Yanbei areas) is discussed in detail in this article. Mineral components in the study strata are dominated by quartz and clay minerals. Quartz in the Niutitang Formation is mainly of biogenic origin, and the content is in positive correlation with TOC, while the content of clay minerals is negatively correlated with TOC. Primary productivity, represented by the content of Mobio(biogenic molybdenum), Babio(biogenic barium) and phosphorus, is positively correlated with TOC. The main alkanes in studied samples are nC_(18–n)C_(25), and odd–even priority values are closed to 1(0.73–1.13), which suggest the organic matter source was marine plankton. Element content ratios of U/Th and Ni/Co and compound ratio Pr/Ph indicate dysoxic–anoxic bottom water, with weak positive relative with TOC. In total, three main points can be drawn to explain the relationship between data and the factors affecting organic accumulation:(1) quartz-rich and clay-mineral-poor deep shelf–slope–basin environment was favorable for living organisms;(2) high productivity provided the material foundation for organic generation;(3) the redox conditions impact slightly on the content of organic matter under high productivity and dysoxic–anoxic condition.展开更多
The Biluo Co and Amdo 114 station, northern Tibet, cropping out the Early Toarcian and Middle-Late Tithonian (Jurassic) organic-rich black shales, have been a focus to petroleum geologists in discussing their oil-prod...The Biluo Co and Amdo 114 station, northern Tibet, cropping out the Early Toarcian and Middle-Late Tithonian (Jurassic) organic-rich black shales, have been a focus to petroleum geologists in discussing their oil-producing potential. This paper first reports the trace elements and rare earth elements to discuss the paleoenvironments, redox conditions and sedimentary mechanisms of those black shales. Both sections exhibit variation in trace element abundances with concentrations <0.1 ppm to 760 ppm, mostly enriched in V, Cr, Ni, Cu, Zn, Mo, Ba and U. Element ratios of Ni/Co, V/Cr, U/Th and V/(V+Ni) plus U were used to identify redox conditions. The shale-normalized rare earth element (REE) patterns are characterized by the flat-shale type with instable Ce anomalies and very weekly positive Eu anomalies. Positive Ceanom values are significant with values varying between - 0.064 and 0.029 in Biluo Co, which may be interpreted as release of REE and input of riverine terrestrial matter with rich Ce (resulting in pH change) during the anoxic conditions. In the middle parts of Amdo 114 station, distinct negative Ceanom values are observed (-0.238 to -0.111) and associated surface water warming were interpreted as being related to a major sea level rise. In contrast, the formation of the black shales in the lower and upper part of the studied succession took place during a cooler (Ceanom values >-0.10), lower surface water productivity, and lower sea-level stage. Thus, we emphasize the role of different factors that control the formation of local and regional black shales. The most important factors are sea-level fluctuations and increasing productivity.展开更多
The recovery of nickel from molybdenum leach residue by the process of segregation roasting-sulfuric acid leaching-solvent extraction was investigated. The residue was characterized by microscopic investigations, usin...The recovery of nickel from molybdenum leach residue by the process of segregation roasting-sulfuric acid leaching-solvent extraction was investigated. The residue was characterized by microscopic investigations, using X-ray fluorescence spectrometry (XRF) and X-ray diffractometry (XRD) techniques and the residue after segregation roasting was characterized by chemical phase analysis method. A series of experiments were conducted to examine the mass ratio of activated carbon (AC) to the residue, segregation roasting time and temperature, sulfuric acid concentration, liquid-to-solid ratio, leaching time, leaching temperature, addition amount of 30% H2O2, stirring speed (a constant) on the leaching efficiency of nickel. A maximum nickel leaching efficiency of 90.5% is achieved with the mass ratio of AC to the residue of 1:2.5, segregation roasting time of 2 h, segregation roasting temperature of 850 °C, sulfuric acid concentration of 4.5 mol/L, liquid-to-solid ratio of 6:1, leaching time of 5 h, leaching temperature of 80 °C, addition of 30% H2O2 of 0.6 mL for 1 g dry residue. Under these optimized conditions, the average leaching efficiency of nickel is 89.3%. The nickel extraction efficiency in the examined conditions is about 99.6%, and the nickel stripping efficiency in the examined conditions is about 99.2%.展开更多
Black shale samples were collected from Chimiari Khyber Pakthunkhawa region of Pakistan and were analyzed for elemental compositions. Atomic Absorption Spectrophotometry (AAS) was utilized for the determination of ele...Black shale samples were collected from Chimiari Khyber Pakthunkhawa region of Pakistan and were analyzed for elemental compositions. Atomic Absorption Spectrophotometry (AAS) was utilized for the determination of elements in the digested solutions. The analysis of black shale was performed precisely with relative standard deviation (RSD) lower than 2%. Results showed that the samples contained high concentrations of Ca (11.98 %), Al (7.09%), Fe (3.03%), Mg (0.59%) and Ti (0.58%).展开更多
More and more evidence indicates that organic matter (OM) in immature organic-rich sediments and sedimentary rocks is chemically adsorbed onto the outer surfaces of minerals and into interlayer (inner) surfaces of sme...More and more evidence indicates that organic matter (OM) in immature organic-rich sediments and sedimentary rocks is chemically adsorbed onto the outer surfaces of minerals and into interlayer (inner) surfaces of smectitic clay minerals in the form of amorphous molecular-scale carbon. But there have been few reports about the occurrence of highly mature OM in marine black shales (petroleum source rocks). The occurrence of highly mature OM in the black shales of basal Cambrian from northern Tarim Basin is studied in this paper. Based on the comprehensive analyses of total organic carbon contents (TOC), maximum thermolysis temperatures (T-max) of OM, mineral surface areas (MSA), and scanning electronic microscopic (SEM) and transmission electronic microscopic (TEM) observations of the black shales, it is concluded that the highly mature OM in the marine black shales of the basal Cambrian from northern Tarim Basin occurs in particulates ranging in size from 1 to 5 μm in diameter. Through the contrast of the occurrence of the highly mature OM in the black shales with that of the immature ones in modern marine continental margin sediments, some scientific problems are proposed, which are worth to study further in detail.展开更多
The Ediacaran and early Cambrian black shales are widespread across the South China Craton(Yangtze and Cathaysia blocks). However, the trace element distribution patterns of the Ediacaran and early Cambrian black shal...The Ediacaran and early Cambrian black shales are widespread across the South China Craton(Yangtze and Cathaysia blocks). However, the trace element distribution patterns of the Ediacaran and early Cambrian black shales in the Cathaysia Block are still unclear. In this study, thirtyfour black shale samples in the Lechangxia Group(Ediacaran) and thirteen black shale samples in the lower Bacun Group(early Cambrian) from Guangning area, western Guangdong Province, South China, were analyzed for major and trace elements concentrations. Compared to the upper continental crust, the Ediacaran black shales exhibit strongly enriched Se, Ga, and As with enrichment factor values(EF) higher than 10, significantly enriched Bi and Rb(10>EF>5), weakly enriched Mo, Ba, Cs, V, In, Be, Tl, and Th(5>EF>2), normal U, Cr, Cd, Sc, Pb, Cu, and Li(2>EF>0.5), and depleted Ni, Zn, Sr, and Co. Early Cambrian black shales display strongly enriched Se, Ga, and As, significantly enriched Ba, Bi, and Rb, weakly enriched Mo, Cs, Cd, V, U, Be, In, and Tl, normal Sc, Th, Cr, Li, Cu, Ni, and Pb and depleted Co, Zn, and Sr. Moreover, Se is the most enriched trace element in the Ediacaran and early Cambrian black shales: concentrations vary from 0.25 to 30.09 ppm and 0.54 to 5.01 ppm, and averaging 4.84 and 1.72 ppm, with average EF values of 96.87 and 34.32, for the Ediacaran and early Cambrian shales respectively. The average concentration of Se in the Ediacaran black shales is 2.8 times higher than that of early Cambrian black shales. Se contents in the Ediacaran and early Cambrian black shales exhibit significant variation(P = 0.03). Provenance analysis showed that Se contents of both the Ediacaran and early Cambrian black shales were without detrital provenance and volcanoclastic sources, but of hydrothermal origin. The deep sources of Se and the presence of pyrite may explain the higher Se contents in the Ediacaran black shales. Similar with the Se-rich characteristics of the contemporaneous black shales in the south Qingling Mountain and Yangtze block, the Ediacaran and early Cambrian black shales in Guangning area, Cathaysia, are also enriched in Se, which may provide a clue for looking for the selenium-rich resources in western Guangdong Province.展开更多
Analyses of organic carbon, nitrogen, sulfur and iron have been performed in order to understand sources and preservation of organic matter in black shale of the Buxin Formation (Early Paleogene) from the Sanshui Basi...Analyses of organic carbon, nitrogen, sulfur and iron have been performed in order to understand sources and preservation of organic matter in black shale of the Buxin Formation (Early Paleogene) from the Sanshui Basin. The C/N ratios show that the organic matter is characterized by a mixture of terrestrial and phytoplanktonic contributions. The relative importance of different sources depend on climate conditions and most of organic matter is of terrestrial origin.The relationships between C, S and Fe indicate that the brackish environment with alternation of anoxia and low-O2 developed in the bottom waters during the deposition of these organic-rich sediments as a result of a mixed setting of thermal stratification and salinity stratification, the latter being the consequence of intermittent sea water incursion.Bacterial sulfate reduction is the most effective early diagenesis affecting the preservation of organic matter. The intensity of sulfate reduction is related to the relative proportion of metabolizable organic matter supplied to sediments.展开更多
The late Aptian(118-115 Ma) continental flood basalts of the Rajmahal Volcanic Province(RVP) are part of the Kerguelen Large Igneous Province,and constitute the uppermost part of the Gondwana Supergroup on the eastern...The late Aptian(118-115 Ma) continental flood basalts of the Rajmahal Volcanic Province(RVP) are part of the Kerguelen Large Igneous Province,and constitute the uppermost part of the Gondwana Supergroup on the eastern Indian shield margin.The lower one-third of the Rajmahal volcanic succession contains thin layers of plant fossil-rich inter-trappean sedimentary rocks with pyroclasts,bentonite,grey and black shale/mudstone and oolite,whereas the upper two-thirds consist of sub-aerial fine-grained aphyric basalts with no inter-trappean material.At the eastern margin and the north-central sector of the RVP,the volcanics in the lower part include rhyolites and dacites overlain by enstatite-bearing basalts and enstatite-andesites.The pyroclastic rocks are largely felsic in composition,and comprise ignimbrite as well as coarse-grained tuff with lithic clasts,and tuff breccia with bombs,lapilli and ash that indicate explosive eruption of viscous rhyolitic magma.The rhyolites/dacites(>68 wt.%) are separated from the andesites(< 60 wt.%) by a gap in silica content indicating their formation through upper crustal anatexis with only heat supplied by the basaltic magma.On the other hand,partially melted siltstone xenoliths in enstatite-bearing basalts suggest that the enstatite-andesites originated through mixing of the upper crust with basaltic magma,crystallizing orthopyroxene at a pressure-temperature of ~3 kb/1150℃.In contrast,the northwestern sector of the RVP is devoid of felsic-intermediate rocks,and the volcaniclastic rocks are predominantly mafic(basaltic) in composition.Here,the presence of fine-grained tuffs,tuff breccia containing sideromelane shards and quenched texture,welded tuff breccia,peperite,shale/mudstone and oolite substantiates a subaqueous environment.Based on these observations,we conclude that the early phase of Rajmahal volcanism occurred under predominantly subaqueous conditions.The presence of grey and black shale/mudstone in the lower one-third of the succession across the entire Rajmahal basin provides unequivocal evidence of a shallow-marine continental shelf-type environment.Alignment of the Rajmahal eruptive centers with a major N—S mid-Neoproterozoic lineament and the presence of a gravity high on the RVP suggest a tectonic control for the eruption of melts associated with the Kerguelen plume that was active in a post-Gondwana rift between India and Australia-Antarctica.展开更多
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 nan...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.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.42272103,92062221,42063009,U1812402)the Guizhou Provincial Science and Technology Projects(Grant No.Qiankehejichu–ZK[2022]common 213)the Higher Education Scientific Research Projects of the Education Department of Guizhou Province(Grant No.Qianjiaoji[2022]157).
文摘A polymetallic layer is usually developed at the bottom of the early Cambrian black shale in Guizhou Province.The mineral that makes up the polymetallic layer is related to the sedimentary facies.To analyze the differentiation mechanism between polymetallic deposits(Ni-Mo and V),the Zhijin Gezhongwu profile located in the outer shelf and the Sansui Haishan V deposit located in the lower slope are selected to study the in situ sulfur isotopes and trace elements of pyrite.The results show that δ^(34)S values of pyrite vary widely from−7.8‰to 28‰in the Gezhongwu profile,while the δ^(34)S values are relatively uniform(from 27.8‰to 38.4‰)in the Haishan profile.The isotopic S composition is consistent with the transition that occurs in the sedimentary phase from the shelf to the deep sea on the transgressive Yangtze platform;this indicates that the δ^(34)SO_(4)^(2−)values in seawater must be differently distributed in depositional environments.The sulfur in the Ni-Mo layer is produced after the mixing of seawater and hydrothermal fluid,while the V layer mainly originates from seawater.Overall,the Ni-Mo and V deposits have been differentiated primarily on the basis of the combined effect of continental weathering and hydrothermal fluid.
基金Project(50874053)supported by the National Natural Science Foundation of ChinaProject(2007GA010)supported by the Science and Technology Bureau of Yunnan Province,China
文摘The recovery of vanadium from a black shale from Guizhou Province of China was performed using a three-step process, which consists of a leaching step in the H2SO4-HF-NaClO system under atmospheric pressure,the vanadium separation from leachate by solvent extraction and stripping,followed by precipitation of ammonium vanadate and thermal decomposition.Under the optimum leaching conditions of 100 g/L sulfuric,15 g/L hydrofluoric acid,1.5 g/L NaClO,6 h leaching at 90℃and oxygen partial pressure of 1 200 kPa,and the liquid-to-solid ratio of 2,about 91%vanadium extraction is achieved.The vanadium extraction yields of solvent and stripping are 99.83%and 97.66%when using 10%(volume fraction)P204,5%TBP and 85%sulfonated berosene as organic phase and 15%(mass fraction)sulphuric acid as stripping agent.After thermal decomposition the purity of powder vanadium pentoxide products is 99.18%and the overall vanadium recovery is over 81%in the whole process.
基金Project(2006AA06Z130)supported by the Hi-tech Research and Development Program of ChinaProject(2007GA010)supported by Yunnan Provincial Science and Technology Agency
文摘Extraction of vanadium from black shale was attempted in pressure acid leaching.The chemical components of the sample obtained from Guizhou Province of China show that it contains 3.258%V2O5,52.880%SiO2 and 16.140%Al2O3.Phase analyses of vanadium indicates vanadium mainly exists in the free oxide and mica.Vanadium contents in the two phases are 18%and 53%, respectively.The contents of V3 +,V 4+and V 5+are almost equal.Under the optimum parameters of one-step leaching(reaction time of 3 h,sulfuric addition of 25%,temperature of 150℃,liquid to solid ratio of 1.2 mL/g,catalyst(FeSO4)addition of 5%and size of 85%particle 0.074 mm),about 77%of vanadium is recovered.After two-step countercurrent leaching,the leach recovery of vanadium can reach above 90%.Air replacing oxygen is completely feasible.The impurity metals can dissolve into solution in different degrees.
文摘: Black shales are marine sediments with argillaceous, silty and siliceous compositions and high contents of organic materials, disseminated pyrite and uranium. Uraniferous black shale has uranium content of more than 20 ppm.Black shales are widely distributed in 17 provinces or autonomous regions in northwestern and southern-central China. Their sedimentary ages are from the Sinian to the Tertiary and uraniferous black shales are mainly exposed in Yunnan, Guizhou, Sichuan, Hunan, Hubei, Jiangxi, and Zhejiang provinces and Guangxi Zhuang Autonomous Region and the economically significant uranium deposits associated with black shale occur in Hunan and Jiangxi provinces and Guangxi Zhuang Autonomous Region.Uranium mineralization associated with black shale has the following main features: (1) forming stratabound deposits; (2) controlled by structures such as interlayer and intersected faults and fractures; (3) associated with different ore-forming processes such as leaching and hydrothermal reworking; (4)
基金financially supported by the Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education(China University of Geosciences)(Grant no.TPR-2021-13)the Science and technology research project of Hubei Provincial Department of Education(Grant no.Q20211304)+1 种基金the National Science and Technology Major Project of China(Grant no.2016ZX050340010022017ZX05035001-002)。
文摘To improve the understanding of the relationship between silica source and organic matter accumulation,the origin of silica and its implications for organic matter enrichment in the Upper OrdovicianLower Silurian(O_(3)w-S_(1)l)black shale in western Hubei Province in the middle Yangtze area,were investigated through geochemical and petrological analyses.The results show that the O_(3)w-S_(1)l black shale is mainly composed of five lithofacies with varying graptolite abundance,total organic carbon(TOC),and silica contents.Biogenic silica and terrigenous siliciclastic input constitute the main silica sources in O_(3)w-S_(1)l black shale and they exhibit an upward inverse variation trend interpreted to be related to sea-level changes.Moreover,with the increase in biogenic silica content or decrease in terrigenous siliciclastic input,TOC values in black shale initially rise and then fall,which is different from originally expected simple linear relationship.We infer that organic matter enrichment and the distribution of silica from different origins are controlled by sea-level changes and variations in terrigenous input in a continental shelf with little hydrothermal influence.An environment with appropriate sea level and terrigenous input should be most favorable for organic matter accumulation,rather than one with excessive high sea level and less terrigenous input.
基金funded by the China Geological Survey Basic Public Welfare Comprehensive Geological Survey Project(DD20191012,ZD20220504)the Chinese National Natural Science Foundation(42102065)。
文摘Early Paleozoic black organic sediments and bentonites occur widely in the craton basin within the Yangtze block and are generally believed to be genetically related to a specific tectonic setting on the cratonic boundary.However,the intimate relationship between their origins and the dynamic mechanisms are unclear,as exemplified by the genesis of the black shale series and bentonites from the Wufeng Formation during the Ordovician–Silurian transition(OST).In order to reveal the relationship between the Wufeng Formation and the convergence of the Yangtze and Cathaysia blocks(i.e.,the intracontinental Kwangsian Orogeny),two stratigraphic sections respectively in Zhaotong area(Northeast Yunnan)and Puyi area(Northwestern Guizhou)that were located in the semi-restricted inner Yangtze Sea during the OST were systematically studied,on the basis of whole-rock geochemical composition,pyriteδ^(34)S(δ^(34)Spy),total organic carbon(TOC),stable Sr isotope,pyrite framboid size distribution and zircon U-Pb age,trace elements.The evidence shows that the paleo-oceanic environment changed significantly at the turn of the early–late Katian and formed the black shale series in the Wufeng Formation.These acritarch assemblages were formed in the transition process of the Upper Yangtze Basin from passive continental margin basin to foreland basin during this interval.Based on previous research on the genetic relationship between black shale series and plate tectonic movement,a basin-mountain evolution model suitable for South China in the Late Ordovician is presented.The two bentonites in the Wufeng Formation with U-Pb ages of 445.5±0.8 Ma and 441.9±2.4 Ma primarily originated from the intermediate–acid volcanic eruption during the collision and convergence between the Yangtze and Cathaysia blocks in the Late Ordovician,the provenance region probably being located in the Jiangnan orogenic belt.Thus,we believe that the appearance of the black shale series and bentonite in the Wufeng Formation at the turn of the early–late Katian may represent the initiation of basin-mountain transformation and the Kwangsian Orogeny in South China,which provides important evidence for the collision and convergence of the Yangtze and Cathaysia blocks in the Late Ordovician.
基金Supported by the National Science and Technology Major Project(2016ZX05050)Scientific Research and Technology Development Program of the Research Institute of Petroleum Exploration and Development,Petrochina(No.2018YCQ02)。
文摘Based on geochemical analysis results of core samples from the Triassic Chang 7 Member of Well Feng 75 drilled in the northwest margin of Ordos Basin,combined with geological characteristics of this region,the formation environment of the black shale and its control on shale oil enrichment are comprehensively studied.From the Chang 73 to Chang 71 Sub-members,the black shale have organic carbon contents decreasing from 5.70%to 3.55%,hydrogen indexes decreasing from 345 mg/g to 269 mg/g,while the oxygen indexes increasing gradually from 6 mg/g to 29 mg/g,indicating that the sedimentary environment during the depositional period of Chang 72 and Chang 73 Sub-members was anoxic.Biomarkers in the black shale change regu-larly,and have an obvious“inflection point”at the depth of 2753–2777 m in the Chang 73 Sub-member,indicating that the input of terrigenous organic matter increased.However,there is a negative drift about 2%of organic carbon isotopic composition near the“inflection point”,which is in conflict with the results of biomarker compounds.This is because the extreme thermal and anoxic events caused by continental volcanic activity in the ancient Qinling region caused negative drift of carbon isotopic composition of the black shale in the Ordos Basin.The volcanic activity caused rise of temperature,polluted air,extreme weathers,more floods and thus more input of terrigenous organic matter,and gave rise to extremely anoxic environment con-ducive to the preservation of organic matter.Terrigenous organic matter is more conducive to the formation of light oil than aquatic organic matter,so these sections in Yanchang Formation are major“sweet spots”for shale oil enrichment.
基金the financial support of through the SNG program
文摘This work aimed for pyrite separation from Abu Tartur black shale as a source of sulfur to be an added economic value of Abu Tartur area. The considered samples in the present work were collected from a core drilled in Abu Tartur plateau representing the pyrite-rich black shale of the U. Cretaceous age.Sample characterization was carried out using petrographic microscope, XRD, DTA/DTG, C/S and XRF techniques. Clay minerals, silt-sized quartz, calcite, and hematite were the main minerals associating pyrite(5.34%). Liberation behavior of the sample was about 80% below 5 lm.Sample processing was achieved through one-day soaking followed by classification using 1 inch Mozley hydro-cyclone where about 35.5% by weight went to underflow and 64.5% went to overflow.The underflow product was subjected to an advanced gravity separation process using SB-40 Falcon Concentrator through a CCD statistical design prepared by Design-Expert 6.0 software proposed to optimize the separation process through a study for the effects of frequency(Hz) and water pressure(Psi) on both assay and recovery of the sulfur-rich heavy fraction.A heavy concentrate weighed 10.90% with inorganic sulfur content reached 11.37%(21.24% pyrite) with overall recovery(50.01%) was obtained after two cleaning at the optimum conditions.
基金This work is supported by the National Key Basic Research Program (2006CB701406);Natural Science Foundation of China for Youth (40403003) ;Key Project of the Natural Science Foundation of China (40332020), and is a contribution to IGCP 463.
基金supported by the "CAS Hundred Talents"Foundation of the Chinese Academy of Sciences to H.Z.,National Natural Science Foundation of China (Grant No.41102066, 40972084)Natural Science Foundation Project of CQ CSTC (Grant No. 2009BB7383)Opening Foundation of the State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences
文摘The lower Cambrian Niutitang Formation, a widespread black shale deposition, is of geological interest because of its polymetallic beds, Cambrian explosion, depositional ages, dramatic environmental changes and so on. Previous study focused mainly on inorganic geochemistry and few studies have investigated the organic fractions of upper Neoproterozoic-lower Cambrian strata in South China. Here we report a study of biomarkers plus organic carbon isotopes for black shales from Ganziping, Hunan Province (China). All the saturated hydrocarbon fractions have a unimodal distribution of n-alkanes, a high content of short-chain alkanes and maximize at C 19 or C 20 (C 23 for sample Gzh00-1). The C 27 /C 29 sterane ratio ranges from 0.77 to 1.20 and 4-methylsteranes are in low abundance. These parameters indicate that algae and bacteria are the important primary producers. Furthermore, biomarker maturity proxies show the samples to be higher maturity. The low Pr/Ph values (<0.7) suggest that the samples were deposited under anoxic conditions and, likely, under stratified water columns. In addition, 25-norhopanes and gammacerane are present as diagnostic indicators of normal marine salinity and dysoxic to anoxic conditions. During the Early Tommotian, known to coincide with a transgression event, small shelly fossils increased in abundance and diversity. Moreover, positive δ 13 C org excursions close to 1.4‰ occur at the base of the Tommotian stage. In summary, the Early Cambrian black shales were deposited under dramatic paleoenvironmental changes, including oceanic anoxia, higher primary productivity and sea-level rise.
基金supported by the National Natural Science Foundation Research (Grant 41672130, 41728004)the National Key S&T Special Projects (Grant 2016ZX05061-003-001)+1 种基金the National Postdoctoral Innovative Talent Support Program (Grant BX201700289)China Postdoctoral Science Foundation (Grant 2017M620296)
文摘Control of various factors, including mineral components, primary productivity and redox level, on the total organic carbon(TOC) in the lower Cambrian black shale from southeastern margin of Upper Yangtze(Taozichong, Longbizui and Yanbei areas) is discussed in detail in this article. Mineral components in the study strata are dominated by quartz and clay minerals. Quartz in the Niutitang Formation is mainly of biogenic origin, and the content is in positive correlation with TOC, while the content of clay minerals is negatively correlated with TOC. Primary productivity, represented by the content of Mobio(biogenic molybdenum), Babio(biogenic barium) and phosphorus, is positively correlated with TOC. The main alkanes in studied samples are nC_(18–n)C_(25), and odd–even priority values are closed to 1(0.73–1.13), which suggest the organic matter source was marine plankton. Element content ratios of U/Th and Ni/Co and compound ratio Pr/Ph indicate dysoxic–anoxic bottom water, with weak positive relative with TOC. In total, three main points can be drawn to explain the relationship between data and the factors affecting organic accumulation:(1) quartz-rich and clay-mineral-poor deep shelf–slope–basin environment was favorable for living organisms;(2) high productivity provided the material foundation for organic generation;(3) the redox conditions impact slightly on the content of organic matter under high productivity and dysoxic–anoxic condition.
基金supported by Natural Science Foundation Project of CQ CSTC (Grant No. 2009BB7383)National Natural Science Foundation of China (Grant No. 41102066, 40972084)Opening Foundation of the State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences
文摘The Biluo Co and Amdo 114 station, northern Tibet, cropping out the Early Toarcian and Middle-Late Tithonian (Jurassic) organic-rich black shales, have been a focus to petroleum geologists in discussing their oil-producing potential. This paper first reports the trace elements and rare earth elements to discuss the paleoenvironments, redox conditions and sedimentary mechanisms of those black shales. Both sections exhibit variation in trace element abundances with concentrations <0.1 ppm to 760 ppm, mostly enriched in V, Cr, Ni, Cu, Zn, Mo, Ba and U. Element ratios of Ni/Co, V/Cr, U/Th and V/(V+Ni) plus U were used to identify redox conditions. The shale-normalized rare earth element (REE) patterns are characterized by the flat-shale type with instable Ce anomalies and very weekly positive Eu anomalies. Positive Ceanom values are significant with values varying between - 0.064 and 0.029 in Biluo Co, which may be interpreted as release of REE and input of riverine terrestrial matter with rich Ce (resulting in pH change) during the anoxic conditions. In the middle parts of Amdo 114 station, distinct negative Ceanom values are observed (-0.238 to -0.111) and associated surface water warming were interpreted as being related to a major sea level rise. In contrast, the formation of the black shales in the lower and upper part of the studied succession took place during a cooler (Ceanom values >-0.10), lower surface water productivity, and lower sea-level stage. Thus, we emphasize the role of different factors that control the formation of local and regional black shales. The most important factors are sea-level fluctuations and increasing productivity.
基金Project(2007CB613604)supported by the National Basic Research Program of China
文摘The recovery of nickel from molybdenum leach residue by the process of segregation roasting-sulfuric acid leaching-solvent extraction was investigated. The residue was characterized by microscopic investigations, using X-ray fluorescence spectrometry (XRF) and X-ray diffractometry (XRD) techniques and the residue after segregation roasting was characterized by chemical phase analysis method. A series of experiments were conducted to examine the mass ratio of activated carbon (AC) to the residue, segregation roasting time and temperature, sulfuric acid concentration, liquid-to-solid ratio, leaching time, leaching temperature, addition amount of 30% H2O2, stirring speed (a constant) on the leaching efficiency of nickel. A maximum nickel leaching efficiency of 90.5% is achieved with the mass ratio of AC to the residue of 1:2.5, segregation roasting time of 2 h, segregation roasting temperature of 850 °C, sulfuric acid concentration of 4.5 mol/L, liquid-to-solid ratio of 6:1, leaching time of 5 h, leaching temperature of 80 °C, addition of 30% H2O2 of 0.6 mL for 1 g dry residue. Under these optimized conditions, the average leaching efficiency of nickel is 89.3%. The nickel extraction efficiency in the examined conditions is about 99.6%, and the nickel stripping efficiency in the examined conditions is about 99.2%.
文摘Black shale samples were collected from Chimiari Khyber Pakthunkhawa region of Pakistan and were analyzed for elemental compositions. Atomic Absorption Spectrophotometry (AAS) was utilized for the determination of elements in the digested solutions. The analysis of black shale was performed precisely with relative standard deviation (RSD) lower than 2%. Results showed that the samples contained high concentrations of Ca (11.98 %), Al (7.09%), Fe (3.03%), Mg (0.59%) and Ti (0.58%).
基金supported by the Natural Science Foundation of China for Youth(40403003)National Key Basic Research Program(2006CB701406)Key Project of Natural Science Foundation of China(40332020),and is a contribution to IGCP 463/555.
文摘More and more evidence indicates that organic matter (OM) in immature organic-rich sediments and sedimentary rocks is chemically adsorbed onto the outer surfaces of minerals and into interlayer (inner) surfaces of smectitic clay minerals in the form of amorphous molecular-scale carbon. But there have been few reports about the occurrence of highly mature OM in marine black shales (petroleum source rocks). The occurrence of highly mature OM in the black shales of basal Cambrian from northern Tarim Basin is studied in this paper. Based on the comprehensive analyses of total organic carbon contents (TOC), maximum thermolysis temperatures (T-max) of OM, mineral surface areas (MSA), and scanning electronic microscopic (SEM) and transmission electronic microscopic (TEM) observations of the black shales, it is concluded that the highly mature OM in the marine black shales of the basal Cambrian from northern Tarim Basin occurs in particulates ranging in size from 1 to 5 μm in diameter. Through the contrast of the occurrence of the highly mature OM in the black shales with that of the immature ones in modern marine continental margin sediments, some scientific problems are proposed, which are worth to study further in detail.
基金the National Natural Science Foundation of China (Grant No.41172310, 41472322 and 40872210)the National Basic Research Program of China (Grant No.2014CB238906)the Local Science and Technology Tasks "Distribution Patterns and Prospect of Exploitation and Utilization of Selenium in Foshan area, Guangdong" and "Construction for Laboratory of Selenium Resources Comprehensive Utilization"
文摘The Ediacaran and early Cambrian black shales are widespread across the South China Craton(Yangtze and Cathaysia blocks). However, the trace element distribution patterns of the Ediacaran and early Cambrian black shales in the Cathaysia Block are still unclear. In this study, thirtyfour black shale samples in the Lechangxia Group(Ediacaran) and thirteen black shale samples in the lower Bacun Group(early Cambrian) from Guangning area, western Guangdong Province, South China, were analyzed for major and trace elements concentrations. Compared to the upper continental crust, the Ediacaran black shales exhibit strongly enriched Se, Ga, and As with enrichment factor values(EF) higher than 10, significantly enriched Bi and Rb(10>EF>5), weakly enriched Mo, Ba, Cs, V, In, Be, Tl, and Th(5>EF>2), normal U, Cr, Cd, Sc, Pb, Cu, and Li(2>EF>0.5), and depleted Ni, Zn, Sr, and Co. Early Cambrian black shales display strongly enriched Se, Ga, and As, significantly enriched Ba, Bi, and Rb, weakly enriched Mo, Cs, Cd, V, U, Be, In, and Tl, normal Sc, Th, Cr, Li, Cu, Ni, and Pb and depleted Co, Zn, and Sr. Moreover, Se is the most enriched trace element in the Ediacaran and early Cambrian black shales: concentrations vary from 0.25 to 30.09 ppm and 0.54 to 5.01 ppm, and averaging 4.84 and 1.72 ppm, with average EF values of 96.87 and 34.32, for the Ediacaran and early Cambrian shales respectively. The average concentration of Se in the Ediacaran black shales is 2.8 times higher than that of early Cambrian black shales. Se contents in the Ediacaran and early Cambrian black shales exhibit significant variation(P = 0.03). Provenance analysis showed that Se contents of both the Ediacaran and early Cambrian black shales were without detrital provenance and volcanoclastic sources, but of hydrothermal origin. The deep sources of Se and the presence of pyrite may explain the higher Se contents in the Ediacaran black shales. Similar with the Se-rich characteristics of the contemporaneous black shales in the south Qingling Mountain and Yangtze block, the Ediacaran and early Cambrian black shales in Guangning area, Cathaysia, are also enriched in Se, which may provide a clue for looking for the selenium-rich resources in western Guangdong Province.
基金A financial support for this research was provided by the Natural Science Foundation of China under Grant No.4027201 1the Natural Science Foundation of Guangdong Province under Grant No.001203.
文摘Analyses of organic carbon, nitrogen, sulfur and iron have been performed in order to understand sources and preservation of organic matter in black shale of the Buxin Formation (Early Paleogene) from the Sanshui Basin. The C/N ratios show that the organic matter is characterized by a mixture of terrestrial and phytoplanktonic contributions. The relative importance of different sources depend on climate conditions and most of organic matter is of terrestrial origin.The relationships between C, S and Fe indicate that the brackish environment with alternation of anoxia and low-O2 developed in the bottom waters during the deposition of these organic-rich sediments as a result of a mixed setting of thermal stratification and salinity stratification, the latter being the consequence of intermittent sea water incursion.Bacterial sulfate reduction is the most effective early diagenesis affecting the preservation of organic matter. The intensity of sulfate reduction is related to the relative proportion of metabolizable organic matter supplied to sediments.
文摘The late Aptian(118-115 Ma) continental flood basalts of the Rajmahal Volcanic Province(RVP) are part of the Kerguelen Large Igneous Province,and constitute the uppermost part of the Gondwana Supergroup on the eastern Indian shield margin.The lower one-third of the Rajmahal volcanic succession contains thin layers of plant fossil-rich inter-trappean sedimentary rocks with pyroclasts,bentonite,grey and black shale/mudstone and oolite,whereas the upper two-thirds consist of sub-aerial fine-grained aphyric basalts with no inter-trappean material.At the eastern margin and the north-central sector of the RVP,the volcanics in the lower part include rhyolites and dacites overlain by enstatite-bearing basalts and enstatite-andesites.The pyroclastic rocks are largely felsic in composition,and comprise ignimbrite as well as coarse-grained tuff with lithic clasts,and tuff breccia with bombs,lapilli and ash that indicate explosive eruption of viscous rhyolitic magma.The rhyolites/dacites(>68 wt.%) are separated from the andesites(< 60 wt.%) by a gap in silica content indicating their formation through upper crustal anatexis with only heat supplied by the basaltic magma.On the other hand,partially melted siltstone xenoliths in enstatite-bearing basalts suggest that the enstatite-andesites originated through mixing of the upper crust with basaltic magma,crystallizing orthopyroxene at a pressure-temperature of ~3 kb/1150℃.In contrast,the northwestern sector of the RVP is devoid of felsic-intermediate rocks,and the volcaniclastic rocks are predominantly mafic(basaltic) in composition.Here,the presence of fine-grained tuffs,tuff breccia containing sideromelane shards and quenched texture,welded tuff breccia,peperite,shale/mudstone and oolite substantiates a subaqueous environment.Based on these observations,we conclude that the early phase of Rajmahal volcanism occurred under predominantly subaqueous conditions.The presence of grey and black shale/mudstone in the lower one-third of the succession across the entire Rajmahal basin provides unequivocal evidence of a shallow-marine continental shelf-type environment.Alignment of the Rajmahal eruptive centers with a major N—S mid-Neoproterozoic lineament and the presence of a gravity high on the RVP suggest a tectonic control for the eruption of melts associated with the Kerguelen plume that was active in a post-Gondwana rift between India and Australia-Antarctica.
基金supported jointly by the National Natural Science Foundation of China(Grant No.40773035)special Research Fund of State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry of Chinese Academa of Sciences
文摘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.