首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Zusammenfassung Die kohlige Substanz von Uranvererzungen im Bereich des Mitterberger Kupferbergbaues wurde genauer untersucht. Das Uran ist an pflanzliches Material gebunden. Metamorphose führte zur Umwandlung bis zum Meta-Anthrazit-Stadium. Das Uran ist feindispers verteilt und erreicht durchschnittliche Gehalte von über 1%; Thorium fehlt gänzlich. Elektronen-Mikrosonden-Scanningbilder veranschaulichen die Verteilung der Elemente U, C, N und S. Die chemischen Beziehungen zwischen organischer Substanz und Urananreicherung werden erläutert.
On uranium concentrations in carbonaceous matter in rocks of the copper deposit mitterberg, (Salzburg, Austria)
Summary The carbonaceous matter of an uranium mineralization in the Mitterberg copper deposit has been investigated in detail. The uranium is associated with plant material. Metamorphism of the latter has reached the meta-anthracite stage. The uranium is finely dispersed, with an average concentration of more than 1%. Thorium is lacking. Electron-microprobe scanning figures show the distribution of the elements U, C, N and S. The chemical relationship between the organic matter and the uranium enrichment is being discussed.

Mit 3 Abbildungen  相似文献   

2.
The problems involved with the interpretation of carbon isotopes as indicators for early life in highly metamorphosed early Archean rocks have prompted the search for additional chemical and isotopic biomarkers. Here we report an attempt to identify the origin of carbonaceous matter in the 3.8 Ga old Isua Supracrustal Belt in southern West Greenland by measuring the concentration and isotopic composition of a trapped nitrogen component. Stepped-combustion/pyrolysis-mass spectrometry of carbonaceous matter in several rock samples revealed three different reservoirs of trapped nitrogen: (1) nitrogen associated with a very small amount of reactive carbonaceous material, (2) nitrogen intercalated in graphite, correlated with intercalated radiogenic argon, (3) nitrogen strongly retained at defects or chemically bound in the graphite structure. The δ15N of nitrogen associated with reactive carbonaceous matter (ca. +6‰) overlaps with that of average Phanerozoic sedimentary organic matter, and is believed to be part of nonindigenous postmetamorphic biologic material. In situ Raman spectroscopy confirmed the high degree of crystallinity of the metamorphosed indigenous carbonaceous material, and this material is further referred to as graphite. Graphite interpreted as epigenetic (associated with Mg,Mn-siderite in metacarbonates) contains a very small strongly retained nitrogen component with a low δ15N ratio (−3 to −1‰). This range overlaps with values that are typically found in Archean kerogens, but also those of a metamorphically emplaced inorganic basaltic source. Geological constraints suggest that this graphite incorporated nitrogen from surrounding metabasaltic rocks. Graphite interpreted as syngenetic and biogenic found in a turbidite deposit is relatively similar to this Mg,Mn-siderite-derived graphite, based on degree of graphite crystallinity, amount of trapped radiogenic argon, low nitrogen concentration and δ15N signature. We conclude that nitrogen concentration and its isotope ratio in graphite cannot be used conclusively as a biomarker in these rocks from the highly metamorphosed Isua Supracrustal Belt.  相似文献   

3.
When using 36Cl to date very old groundwater in regional aquifer systems, knowledge of the subsurface 36Cl input into the aquifer system is essential. Although 36Cl can be produced through nuclear reactions in the subsurface, in many situations, the input of 36Cl into sedimentary aquifer systems by this avenue of production can be neglected. This is a valid assumption when investigating long-flowpath groundwater systems composed of sandstones, limestones, and shales of typical composition. These rock types are not sufficiently enriched in radioactive elements to produce significant 36Cl in the deep subsurface. Carbonaceous shales, on the other hand, can concentrate the radioactive elements necessary to produce significant 36Cl in the deep subsurface. Chlorine-36 ratios (36Cl/Cl) for a suite of Late Devonian and Pennsylvanian carbonaceous shales were calculated from bulk-rock chemistry as well as measured using accelerator mass spectrometry. The poor agreement between calculated and measured ratios is the result of the assumption of chemical homogeneity used by the calculation algorithm, an assumption that was not satisfied by the carbonaceous shales. In these shales, organic matter, clay minerals, and accessory minerals are heterogeneously distributed and are physically distinct on a micron-order scale. Although organic matter and clay minerals constitute the overwhelming bulk of the shales, it is the phosphate minerals that are most important in enhancing, and suppressing, 36Cl production. Minerals such as apatite and carbonate-apatite (francolite)—by including uranium, rare earth elements (REEs), and halogens—have an important impact on both neutron production and thermal neutron absorption. By incorporating both uranium and fluorine, phosphate minerals act as neutron production centers in the shale, increasing the probability of 36Cl production. By incorporating REEs and chlorine, phosphate minerals also act to shield 35Cl from the thermal neutron flux, effectively suppressing the production of 36Cl. To reconcile the measured 36Cl ratios with the ratios calculated assuming chemical homogeneity, the shales were artificially split into three fractions: organic, clay mineral, and phosphate mineral. Neutron production was calculated separately for each fraction, and the calculation results demonstrated that the phosphate fraction exerted much more control on the 36Cl ratio than the organic or clay mineral fractions. By varying the uranium and chlorine contents in the phosphate fraction, a new, heterogeneous 36Cl ratio was calculated that agreed with the measured ratio for the overwhelming majority of the carbonaceous shales. When using rock chemistry to calculate the 36Cl ratio, rock types that show mineralogical heterogeneity on a micron scale can be divided into bulk fractions and accessory fractions for separate calculations of neutron production and neutron absorption. In this manner, a more accurate, heterogeneous 36Cl ratio can be calculated for the rock as a whole.  相似文献   

4.
Carbonaceous units commonly host or are closely related to lode-gold mineralization in the mesothermal Fazenda Maria Preta (FMP) and Fazenda Canto (FC) deposits of the Paleoproterozoic Rio Itapicuru greenstone belt of northeastern Brazil. In these deposits, the carbonaceous matter occurs mainly as: (1) straight to anastomosing seams (Type I) along or transecting the rock fabric, or as stylolitic structures in quartz veins; (2) single grains composed of an agglomerate of highly anisotropic subgrains (Type II); or (3) single grains with a homogeneous internal texture (Type III), which are either enclosed in Type-I carbonaceous seams or disseminated in the rock matrix. Type-I carbonaceous matter commonly hosts or is overgrown by the gold-related sulfide paragenesis, particularly arsenopyrite, whereas both Type I and Type II enclose crystals of arsenopyrite or occur as inclusions and in sharp contact with the sulfide phases.

The three morphological types of carbonaceous matter exhibit similar Raman spectral characteristics, with distinct D and O peaks at wave numbers between 1351 cm?1 and 1357 cm?1, and 1585 cm?1 and 1598 cm?1, respectively. In contrast to the FMP deposit, the carbonaceous matter of the FC deposit shows D peaks of higher intensities than the O peaks. The O peaks are accompanied by an additional disorder-induced band on the high wave number side (≈ 1622 cm?1), and the O/D peak intensity ratios are higher and the half-height O-peak widths smaller. These spectral parameters indicate that the carbonaceous matter in both deposits corresponds to some form of microcrystalline disordered graphitic material and defines a graphitization trend from the FMP to the FC deposit.

The carbonaceous matter of the FMP deposit is isotopically lighter (δ13C = ?23.3‰ to ?30.8‰; x = ?27.4 ± 1.8‰ relative to PDB) than the carbonaceous material of the FC (δ13C = ?18.5‰ to ?21.0‰, x = ?19.7 ± 0.9‰). These δ13C values, together with the geologic evidence, point toward a primarily biogenic organic origin for the carbonaceous matter. The marked differences in the Raman spectral parameters and the δ13C values are interpreted as resulting from different degrees of thermal maturation of carbonaceous matter attained during the regional greenschist metamorphism and granite intrusions of the Rio Itapicuru greenstone belt.

The δ13C compositions of CO2 resulting from the oxidation or hydrolysis of the carbonaceous matter, calculated by applying the equilibrium CO2-graphite fractionation, fall within the range ?9.7‰ to ?18.8‰ at 360 to 420°C (FMP deposit) and ?6.0° to ?10.0° at 390 to 455°C (FC deposit). These calculated δ13C values are lower than those obtained from primary fluid-inclusion CO2 in gold-bearing veins (?6.0° to ?10.2° for the FMP deposit; ?2.8° to ?4.9° for the FC deposit) and imply that the thermal maturation process of the carbonaceous matter contributed little to changes in the chemistry and isotopic composition of the ore fluid. The presence of the carbonaceous matter may have been an important factor in gold deposition during fluid-carbon interaction, acting: (1) as a chemical trap, by reducing the f(O2) of the ore fluids or enhancing fluid immiscibility by adding small quantities of CH4 and N2 to the fluid phase; and/or (2) as a physical barrier, by adsorbing gold on its surface as activated carbon.  相似文献   

5.
三穗铀矿床位于黔中—湘西北铀成矿带内,产于震旦—寒武系老堡组炭质泥岩中,是贵州省近年勘查发现的第一个大型铀矿床。[研究目的]鉴于黔东地区铀矿成矿规律、富集机理及矿石矿物学等研究程度低,查明典型铀矿床矿石矿物组合及化学组分,探讨成矿环境,揭示成矿过程,深化成矿理论认识,将为促进区域成矿预测、扩大找矿勘查成果及丰富该类型铀矿成矿理论提供科学依据。[研究方法]基于三穗铀矿床地质、地球化学特征,通过电子探针、扫描电镜等测试,分析了铀成矿机理及成岩成矿的环境演化。[研究结果]本区含铀岩系老堡组形成于震旦纪/寒武纪转折期的陆缘裂谷和陆缘裂陷缺氧还原环境,铀成矿初始物源与海底火山活动有关;铀矿石主要由铀矿物、铁矿物、黏土矿物、有机质及白云石、石英（或玉髓）、重晶石、方解石等组成,呈微晶—隐晶结构、微晶—粉晶晶粒状结构,层状、纹层状构造;铀矿物丰富,主要有沥青铀矿、硅钙铀矿、硒铅铀矿、钛铀矿、磷铀矿及水碳铀等,以纳米—微米级粒状、柱状（粒径多<10 μm）、细脉状、或隐晶质形式赋存于有机质、铁质、黏土矿物等聚铀矿物中。[结论]三穗铀矿床形成物源具有多源性,与雪峰期海底火山作用带来部分成矿物质、燕山—喜马拉雅期成矿流体在运移的途中不断浸取地层内的成矿物质密切相关,经历了铀初始富集、氧化淋滤及热液叠加再富集过程,成因属典型的碳硅泥岩型。三穗铀矿床中发现大量铀矿物显示,铀富集程度高、成矿作用强,找矿远景好、潜力大。创新点：基于三穗铀矿床地质地球化学特征,通过电子探针、扫描电镜等矿物学研究,揭示本区铀成岩成矿的环境演化及成矿机理,探讨了找矿远景。  相似文献   

6.
The Baxingtu deposit is a typical redox front tabular-shaped uranium deposit hosted in sandstones of the Late Cretaceous Yaojia Formation deposited within a braided river environment during the post-rift stage of the Songliao Basin, in northeast China. This study proposes the first metallogenic model for the Baxingtu deposit and provides new data on genetic processes involved in the uranium mineralisation of sandstone-type deposits that were characterised through petrographic observations, whole-rock geochemistry, and geochemical and/or mineralogical study of iron disulphide, uranium minerals, Fe-Ti oxides (EPMA, LA-ICP-MS), and organic matter (REP). The δ34S value has been measured in situ by SIMS on the different generations of iron disulphide.Within regional primary reduced sandstones, pre-ore uranium enrichment (Umean = 7.6 ppm in whole rock) was identified on altered Fe-Ti oxides along with minor concentrations on organic matter (respectively 26.3% and 1.3% of the whole-rock U content), which together represent a significant source of uranium for the mineralisation. Additional pre-ore uranium concentrations may also be associated with clay minerals. Petrographic observations and REP data indicate that organic matter occurring in the host-sandstone is mainly inherited from land plants and corresponds to type III or type IV kerogens. Ore-stage iron disulphides largely occur as framboids and in replacement of organic matter or also as sub-idiomorphic to idiomorphic cement and crystal. Trace element signatures detected within framboids are likely indicative of formation mainly from a single event. Framboids and iron disulphide in replacement of organic matter have a light sulphur isotope signature characterised by δ34S values from −72.0 to −6.2‰, suggesting that sulphur originated from bacterial sulphate reduction, which was mainly responsible for (1) the liberation of U from Fe-Ti oxides and organic matter, (2) the generation of ore-stage iron disulphides, (3) the bioreduction of uranium and (4) the production of a secondary H2S-rich reducing barrier also involved in uranium reduction. Uranyl and sulphate ions were transported through the host sandstone by low-temperature oxygenated groundwater and U(IV) was precipitated at the redox interface as nano to microcrystals of pitchblende and coffinite, dominantly associated with bacterial substrate and as intergrowth with biogenic iron disulphide or directly associated with organic matter and residual Ti-Fe oxides. The uranium mineralisation does not replace ore-stage iron disulphides. Therefore, the combined mineralogical, geochemical, and isotopic characteristics of the Baxingtu tabular uranium deposit characterise dominantly biogenic processes for the genesis of the uranium mineralisation.  相似文献   

7.
In the westernmost part of the Bundelkhand Granitoid Complex (BGC), a mesa structure represents a unique outlier, surrounded by brecciated granite and filled with Vindhyan sedimentary rocks locally known as the Dhala Formation near Mohar village of Shivpuri district, Madhya Pradesh. Uranium mineralisation located in the area is mostly associated with rhyolite of peralkaline to peraluminous in nature, that has a high average uranium concentration (30 ppm). The mineralization is in or adjacent to caldera and is hydrothermal vein-type. Radioactivity is mainly due to coffinite with limited radioactivity due to U-Ti complex, uranium adsorbed in clay and labile uranium along fracture. Coffinite occurs in association with pyrite and chalcopyrite or chlorite with presence of fluorite. Features such as chloritisation, clay formation and sulfide mineralisation manifest hydrothermal alteration. Chemical analysis indicates the aluminous nature of the rock and their high K2O/Na2O (3.81–12.84) ratios are suggestive of predominance of potash feldspar over sodic. The alteration index varies from 49.88–92.40, which, reflects high intensity of hydrothermal alteration. Chlorite-carbonatepyrite index (CCPI), a measure of the intensity of replacement of sodic feldspars and glass by sericite, chlorite, carbonate, and pyrite associated with hydrothermal alteration proximal to the ore bodies varies from 3.84–49.66. On the basis of core study, geochemistry and mineralogy, it is envisaged that epigenetic hydrothermal solutions were responsible for concentration of uranium as coffinite, radioactive carbonaceous matter and adsorbed uranium phases in rhyolite with sulfide confined to weak planes.  相似文献   

8.
Incorporation of uranium in modern corals   总被引：1，自引：0，他引：1  
Uranium occurs in corals at three sites: 1, in organic matter; 2, adsorbed on the surfaces of skeletal aragonite; and 3, in the aragonite lattice. Organic matter incorporates from sea water by chelation 40–70 ppm uranium; skeletal aragonite incorporates only 3 ppm. However, as the organic fraction is low (0·1%), its high concentration of uranium does not significantly affect the total concentration of uranium in the coral. A negligible concentration of uranium, 40–60 ppb, is adsorbed on skeletal aragonite from which it is readily leached or exchanged. This low concentration of adsorbed uranium (<2% of the total uranium in skeletal aragonite) is related to the very small specific surface area (1·5–1·8 m2/g of the corals.  相似文献   

9.
This work presents geochemical characterization of isolated kerogen out of clay fraction using petrography studies, infrared absorption and solid state 13C nuclear magnetic resonance (NMR) spectroscopy, with N‐alkane distributions of saturated hydrocarbon. Mineralogical study of clay mineral associations was carried out using X‐ray diffraction (XRD), on Ypresian phosphatic series from Gafsa‐Metlaoui basin, Tunisia. The XRD data indicate that smectite, palygorskite and sepiolite are the prevalent clay minerals in the selected samples. In this clay mineral association, the N‐alkane (m/z = 57) distribution indicates that the marine organic matter is plankton and bacterial in origin. The kerogens observed on transmitted light microscopy, however, appear to be totally amorphous organic matter, without any appearance of biological form. The orange gel‐like amorphous organic matter with distinct edges and homogenous texture is consistent with a high degree of aliphaticity. This material has relatively intense CH2 and CH3 infrared bands in 13C NMR peaks. This aliphatic character is related to bacterial origin. Brown amorphous organic matter with diffuse edges has a lower aliphatic character than the previous kerogen, deduced from relatively low CH2 and CH3 infrared and 13C NMR band intensities.  相似文献   

10.
The Tono sandstone-type uranium mine area, middle Honsyu, Japan is composed of Miocene lacustrine sedimentary rocks in the lower part (18–22 Ma) and marine facies in the upper part (15–16 Ma). Calcite and pyrite occur as dominant diagenetic alteration products in these Neogene sedimentary rocks. The characteristics of calcite and pyrite differ significantly between lacustrine and marine facies. Abundant pyrite, calcite, organic matter, and small amounts of marcasite or pyrrhotite occur in the lacustrine facies, whereas small amounts of calcite and framboidal pyrite, organic matter and no marcasite or pyrrhotite are found within the marine units. The δ13C values of calcite in the lacustrine deposits are low (−19 to −6‰ PDB) but those in marine formation are high (−11 to +3‰). This implies that the contribution of marine carbonate is larger in upper marine sedimentary rocks, and carbon in calcite in the lower lacustrine formation was derived both from oxidation of organic matter and from dissolved marine inorganic carbon. The δ34S values of framboidal pyrite in the upper marine formation are low (−14 to −8‰ CDT), indicating a small extent of bacterial seawater sulfate reduction, whereas those of euhedral-subhedral pyrite in the lower lignite-bearing arkose sandstone are high (+10 to +43‰), implying a large extent of closed-system bacterial seawater sulfate reduction. The δ34S and δ13C data which deviate from a negative correlation line toward higher δ13C values suggest methanogenic CO2 production. During diagenesis of the lacustrine unit, large amounts of euhedral-subhedral pyrite were formed, facilitated by extensive bacterial reduction of seawater sulfate with concomitant oxidation of organic matter, and by hydrolysis reactions of organic matter, producing CH4 and CO2. Uranium minerals (coffinite and uraninite) were also formed at this stage by the reduction of U6+ to U4+. The conditions of diagenetic alteration within the lacustrine deposits and uranium mineralization is characterized by low Eh in which nearly equal concentrations of CH4 and HCO3 − existed and reduced sulfur species (H2S, HS−) are predominant among aqueous sulfur species, whereas diagenetic alteration of the marine formations was characterized by a predominance of SO4 2− among dissolved sulfur species. Modern groundwater in the lacustrine formation has a low Eh value (−335 mV). Estimated and measured low Eh values of modern and ancient interstitial waters in lacustrine environments indicate that a reducing environment in which U4+ is stable has been maintained since precipitation of uranium minerals. Received: 9 February 1996 / Accepted: 11 April 1997  相似文献   

11.
Stepwise pyrolysis-gas chromatography is used to examine and characterize the carbonaceous matter in sedimentary rocks. Low-temperature steps remove material normally volatile or extracted by benzene-methanol. Successively-higher temperature steps degrade the insoluble carbonaceous matter (kerogen) into smaller molecular pieces. The sequential pyrolysis steps have the advantage of breaking the kerogen at several temperatures which may be related to bond type or strength. The pyrolysis product chromatograms from each step can be compared. The molecular sizes (chain length) of kerogens fragments can be determined. The results presented here show the molecules in the range C11 to C23 because: (1) they can be compared to normal petroleum source rock extractables; and (2) these large molecules give a feeling for the molecular construction of the kerogen.Green River and Antrim shales show low-temperature material which is indigenous and not modified compared to the pyrolyzed kerogen fragments in the range C11C23. Kupferletten shows low-temperature material of a narrow molecular weight range of C15C19 which is probably derived from the kerogen. Monterey shale low-temperature material appears to be unrelated to the kerogen as represented by its pyrolysis products. The Pierre shale kerogen shows molecules over the range C11C23. Kerogen from the Romney shale has no molecules large than C8 in its pyrolysis products and no petroleum potential due to thermal and tectonic diagenesis.  相似文献   

12.
Dissolved organic matter (DOM) is a very important environmental constituent due to its role in controlling factors for soil formation, mineral weathering and pollutant transport in the environment. Prediction of DOM physical-chemical properties is achieved by studying its chemical structure and spatial conformation. In the present study, dissolved organic matter extracted from compost obtained from the organic fraction of urban wastes (DOM-P) has been analysed by FT-IR, CPMAS 13C NMR spectroscopy and 1H T1 NMR relaxometry with fast field cycling (FFC) setup. While the first two spectroscopic techniques revealed the chemical changes of dissolved organic matter after adsorption either on kaolinite (DOM-K) or montmorillonite (DOM-S), the latter permitted the evaluation of the conformational variations as assessed by longitudinal relaxation time (T1) distribution at the fixed magnetic field of 500 mT. Alterations of T1 distributions from DOM-P to DOM-K and DOM-S were attributed to a decreasing molecular complexity following DOM-P adsorption on the clay minerals. This study applied for the first time solid state 1H T1 NMR relaxometry to dissolved organic matter from compost obtained from the organic fraction of urban wastes and revealed that this technique is very promising for studying environmentally relevant natural organic systems.  相似文献   

13.
通过野外采样、化学分析、电子探针(EPMA)和X射线衍射(XRD)分析等手段,研究了贵州织金地区黑色页岩矿物成分、化学组分、微量元素、稀土元素特征。研究区矿样化学成分以SiO_2和Al_2O_3为主,且具有高K低Na的特征。电子探针和X射线衍射分析表明,研究区黑色页岩主要矿物组成有石英、粘土矿物、白云石及黄铁矿等。织金黑色页岩中Pb、Ni、U、V、Cr等金属元素存在不同程度的富集,稀土元素总量为153.2×10~(-6)~224.89×10~(-6),属轻稀土元素富集型。同时从多金属层、页岩气、页岩提钾及近底部含磷铀矿资源等方面讨论了织金黑色页岩资源化利用。织金黑色页岩多金属层含有Mo、V、Ni、Ag及U等多金属元素,具综合利用价值;其中有机碳含量达到页岩气开发大于2%的条件,可进一步开展研究;页岩中伊利石含量较多,可提取黑色页岩中的钾制备含钾复合肥;黑色页岩底部与磷矿层接触带产出磷铀矿,主要为胶状磷铀矿,接触带可作为铀矿找矿的标志层。  相似文献   

14.
Uranium is so intimately associated with carbonaceous matter in marine black shales and some sands tone-type uranium deposits that it is said to be “fixed” by organic matter. But different kinds of organic matter are not of equal importance in the geochemistry of uranium. The nature and origin of organic matter in uranium deposits and its role in the transport and concentration of uranium are different from place to place. The reason why uranium is closely associated with certain types of organic matter (for example, humus or bitumen) is described in this paper from geochemical viewpoint. Many uranium deposits and uranium occurrences have been found both at home and abroad. The distribution and existing forms of uranium in these deposits, and the concentration of uranium and element association in the ore are directly or indirectly related to organic matter. This paper is intended to discuss the types of natural organic matter and the mechanism of uranium transport and enrichment by organic matter, on the basis of author’s research work in conjunction with previous data.  相似文献   

15.
The Tertiary sedimentary sequence of the Date Creek basin area of Arizona is composed principally of intertonguing alluvial-fan and lacustrine deposits. The lacustrine rocks contain large intermediate- to, locally, high-grade uranium deposits that form one of the largest uranium resources in the United States (an estimated 670,000 tons of U3O8 at an average grade of 0.023% is indicated by drilling to date). At the Anderson mine, about 50,000 tons of U3O8 occurs in lacustrine carbonaceous siltstones and mudstones (using a cutoff grade of 0.01%). The Anderson mine constitutes a new class of ore deposit, a lacustrine carbonaceous uranium deposit.Floral and faunal remains at the Anderson mine played a critical role in creating and documenting conditions necessary for uranium mineralization. Organic-rich, uraniferous rocks at the Anderson mine contain plant remains and ostracodes having remarkably detailed preservation of internal features because of infilling by opaline silica. This preservation suggests that the alkaline lake waters in the mine area contained high concentrations of dissolved silica and that silicification occurred rapidly, before compaction or cementation of the enclosing sediment. Uranium coprecipitated with the silica. Thinly laminated, dark-colored, siliceous beds contain centric diatoms preserved with carbonaceous material suggesting that lake waters at the mine were locally deep and anoxic. These alkaline, silica-charged waters and a stagnant, anoxic environment in parts of the lake were necessary conditions for the precipitation of large amounts of uranium in the lake-bottom sediments.Sediments at the Anderson mine contain plant remains and pollen that were derived from diverse vegetative zones suggesting about 1500 m of relief in the area at the time of deposition. The pollen suggests that the valley floor was semiarid and subtropical, whereas nearby mountains supported temperate deciduous forests.  相似文献   

16.
Poorly crystalline carbonaceous matter was observed in chlorite to sillimanite grade metasediments from the Trois Seigneurs Massif, in contrast to other studies of carbon crystallinity which observed well crystallised graphite under upper greenschist facies conditions. Using transmission electron microscopy four types of carbon particle were identified; globular carbon, composite flakes, homogeneous flakes and crystalline graphite. Globular carbon and composite flakes are poorly crystalline microporous carbon. Homogeneous flakes decompose in the electron beam and are probably composed of heavy volatile hydrocarbons. Graphite is confined to samples from retrograde shear zones and often occurs with globular carbon. The lack of graphitisation in metasediments is probably a consequence of the microporous structure of the carbonaceous matter combined with low f O 2. The preservation of carbonaceous matter in the Trois Seigneurs metasediments is not compatible with the metasediments having been externally buffered by a high X H2O fluid syn-metamorphism. An alternative hypothesis of internal buffering is preferred to explain the carbonaceous matter in the Trois Seigneurs metasediments.  相似文献   

17.
The Changjiang and the Jiulong Estuaries, located in eastern and southeastern China, respectively, have different geomorphologic and tidal processes as well as anthropogenic development in their associated watersheds. Sediments in the Changjiang estuary mostly consist of SiO2, CaO and MgO (mean percentages of 63.9, 4.34 and 2.35%), whereas sediments from the Jiulong estuary mostly consist of Al2O3, Fe2O3 and organic matter (mean percentages 19.2, 6.82 and 4.14%). The Jiulong estuarine sediments contain more than twice the concentrations of Pb, Zn, Cu, than those from the Changjiang estuary. In the Jiulong estuary, these heavy metals are associated with carbonates and organic matter, whereas in the Changjiang estuary, they are associated with residual fractions or clay. Sediments from the Changjiang estuary, mostly sediments with little organic matter, do not efficiently sequester anthropogenic-derived trace metals. In contrast, sediments from the Jiulong estuary consist of a mixture of fluvial and marine matter which can sequester heavy metals contributed by larger landscapes with industrial and municipal wastewater.  相似文献   

18.
贵州铜仁坝黄磷矿中铀赋存状态的逐级化学提取研究   总被引：1，自引：1，他引：0  
王志罡  谢宏  杨旭  周忠容 《岩矿测试》2018,37(3):256-265
贵州铜仁坝黄磷块岩矿床富集放射性元素铀,利用逐级化学提取分析方法对该地区黄磷矿中铀的赋存状态进行探究,有助于进一步探讨磷块岩型铀矿的分布规律、成矿机理及铀资源的综合开发。本文采用经修改的Tessier法流程,提取了水溶态、可交换离子态、碳酸盐结合态、铁锰氧化物结合态、有机质黄铁矿态、强酸提取态和残渣态等七种不同形态的铀。研究发现:黄磷矿中的铀主要以独立铀矿物和类质同象置换的形式存在,分别占37.83%、37.21%,少量铀(占24.96%)以分散吸附形式存在。分析表明:独立铀矿物在富磷、黄铁矿脉和镜面擦痕发育的岩层中含量较高,说明热液活动有利于独立矿物形式铀的富集;类质同象铀与黄磷矿中的磷含量呈正相关关系,铀元素可能是以离子置换的方式赋存于胶磷矿的晶格缺陷中;吸附形态铀的含量受到岩石中黏土矿物含量和黄铁矿脉的影响,有机质黄铁矿态是吸附形态铀存在的主要方式,少量铀通过扩散作用吸附于黏土矿物表面。除类质同象铀因其存在形式不易被提取利用外,独立铀矿物及吸附形态铀对于未来优化资源配置具有现实意义。  相似文献   

19.
Dolostone of Vempalle Formation near Tummalapalle hosts large uranium deposit (>100,000 tonnes with an average grade of 0.045%U3O8). It is a unique type of uranium deposit because carbonate formations have been considered to be among the least uraniferous of all the rocks of the Earth’s crust due to mobility of uranium in aqueous fluid in the presence of carbonate and bicarbonate ions. Vempalle dolostone hosts syn-sedimentary uranium mineralization in the form of discrete uranium phases (pitchblende and coffinite) associated with collophane, and adsorbed uranium in organic matter. The organic matter has played dual role of concentrating uranium from solution and also chemically reducing it to pitchhblende and coffinite.  相似文献   

20.
We separated and analyzed several organic and inorganic phases of the carbonaceous chondrite matrix to determine whether they contained any inherent asymmetry. Our intent was to determine any possible foci of asymmetry besides the one determined for meteoritic amino acids. As a probe, we employed a very sensitive asymmetric autocatalytic reaction. We were able to determine that asymmetry still resides in powders after extraction with water and solvents as well as in the insoluble organic material (IOM) obtained after demineralization. Asymmetry is not found any longer in the IOM after hydrothermal treatment and in meteorite powders from which all organics had been removed by O2 plasma at low temperature. The data are interpreted to indicate a diverse molecular asymmetry residing in yet unknown meteorite organics; these organics might have had an inductive effect on organic molecular evolution upon exogenous delivery to the early Earth.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号