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 265 毫秒
1.
Authigenic iron and titanium oxides occur in three main textural varieties in the St. Bees Sandstone, a Triassic red bed succession in Cumbria. These are: (a) overgrowths of haematite, titaniferous haematite, anatase, and rutile which generally occur on detrital host grains of similar compositions. The overgrowths may occur as syntaxial rim cements or rhombohedral and prismatic projections and are always in optical continuity, (b) discrete crystals of anatase (including octahedrite) and haematite 10-40 μm in size occur in pore spaces, and (c) fine grained ( < 1 μm) pigmentary haematite occurs as grain coatings around detrital grains and in the interstitial matrix. The euhedral nature and pore-filling habit clearly indicate the authigenic origin of these iron- and titanium oxides. All three textural varieties are believed to have been precipitated from ground waters containing dissolved ferrous and titanium ions. These ions were derived from the intrastratal solution of detrital iron and titanium bearing grains including ferromagnesian silicates and iron-titanium oxides. The precipitation of iron oxides from migrating ground waters in the manner described here goes some way to explaining how thick, uniformly red successions can be formed.  相似文献   

2.
The Ringerike Group is a meandering fluviatile succession which is about 60% red. Most of the red zones are formed of mudrocks and siltstones and correspond to the fine members of fining-upwards cyclothems. The majority of coarse members are drab coloured.Textural studies of thin and polished sections show that the red colour is caused by finely crystalline hematite as matrix and grain-coatings. This hematite apparently crystallized post-depositionally. Hematite also occurs in other textural sites: within altered phyllosilicates, as detrital grains and as totally pseudomorphed phyllosilicates. This, and the lack of consistency between colour and clay mineralogy, suggests that the red beds have had a long and complex diagenetic history.Iron analyses indicate that the red beds are enriched in Fe3+ and total iron (FeO) by about 1%. This is thought to have been derived from the pre-depositional weathering of iron minerals and introduced into the sediments as amorphous iron hydroxide or iron-bearing clays. Crystallization of iron hydroxide under oxidizing conditions and the post-depositional alteration of iron-silicates and oxides is thought to be responsible for the formation of the red beds.  相似文献   

3.
Diagenetic overgrowths on detrital quartz sand grains in sandstones can be isolated for direct measurement of their oxygen isotope ratios. Interfacial materials between detrital cores and diagenetic overgrowths are dissolved by etching with dilute HF. The weakened interface breaks when grains are agitated ultrasonically. Subsequent particle size separation is an effective means of concentrating the diagenetic component.  相似文献   

4.
The fluvial Triassic reservoir subarkoses and arkoses (2409·5–2519·45 m) of the El Borma oilfield, southern Tunisia, were subjected to cementation by haematite, anatase, infiltrated clays, kaolinite and K-feldspar at shallow burial depths from meteoric waters. Subsequently, basinal brines controlled the diagenetic evolution of the sandstones and resulted initially in the precipitation of quartz overgrowths, magnesian siderite, minor ferroan magnesite and anhydrite. The enrichment of siderite in 12C isotope (δ13CPDB= - 14·5 to - 9‰) results from derivation of carbon from the thermal decarboxylation of organic matter. During further burial, the precipitation of dickite and pervasive transformation of kaolinite into dickite occurred, followed by the formation of microcrystalline K-feldspar and quartz, chlorite and illite, prior to the emplacement of oil. Present day formation waters are Na-Ca-Cl brines evolved by the evaporation of seawater and water/mineral interaction and are in equilibrium with the deep burial (≤ 3·1 km) minerals. These waters are suggested to be derived from the underlying Silurian and Devonian dolomitic mudstones.  相似文献   

5.
ABSTRACT Detrital alkali feldspars currently at burial depths of 3·2–3·5 km in the Upper Jurassic Humber Group of the Fulmar oilfield, UK North Sea, are overgrown and have been partially replaced by authigenic Or‐rich feldspar. Intracrystal microtextures suggest several different provenances for the detrital grains. The overgrowths are uniformly non‐cathodoluminescent and have occasional celsian‐rich zones. Transmission electron microscopy shows that they are composed of a microporous mosaic of subµm‐ to µm‐sized sub‐grains associated with barite, illite and pyrite. The subgrains are somewhat rounded but have an approximate {110} Adularia habit and display a faint modulated microtexture on the nanometre scale. They have triclinic symmetry, but the lattice angles depart only slightly from monoclinic symmetry. These features are characteristic of K‐feldspar precipitated relatively rapidly and at low temperature. Authigenic Or‐rich feldspar has also partially replaced microcline and perthitic albite within the detrital grains, often at a suboptical scale. Although, like diagenetic albitization, replacement by K‐feldspar is probably a very common diagenetic reaction, it has rarely been reported owing to difficulties in imaging the diagnostic textures with the scanning electron microscopy techniques used by most workers. The permeability of the subgrain microtexture may significantly hinder the use of feldspar overgrowths for K/Ar and 40Ar/39Ar dating of diagenesis, and the existence of suboptical, replacive authigenic K‐feldspar within detrital grains may significantly modify the apparent Ar ages of detrital grains. Similar subgrain microtextures in optically featureless quartz overgrowths are also illustrated.  相似文献   

6.
Detrital zircon U–Pb ages and heavy mineral assemblages provide conflicting evidence of the provenance of the Ordovician–lower Silurian Tumblagooda Sandstone, a fluvial to shallow marine, red-bed succession over 2000 m thick, within the northern Perth and Southern Carnarvon basins in Western Australia. Tourmaline composition indicates a main provenance from interior continental terranes dominated by ‘Li-poor granitoids, pegmatites and aplites’ and ‘Ca-poor metapelites, metapsammites and quartz-tourmaline rocks,’ akin to the Yilgarn Craton to the east of outcrop of the Tumblagooda Sandstone. Other possible source areas include orogens mostly to the south but lack tourmaline analyses for comparison. Taking into account the lack of garnets—a conspicuous component of the adjacent Proterozoic Northampton Inlier—the limited zircon data are compatible with the Albany–Fraser and Pinjarra orogens along the southern and western margins of Australia and/or terranes in or adjacent to East Africa and/or Antarctica, as ultimate source regions with a minor contribution from the Yilgarn Craton, as with other Phanerozoic strata in Western Australia. Whereas the textural and mineralogical maturity of the sandstone could be explained by derivation from such regions, it is more likely that the source was relatively local and that the sediment passed through several phases of reworking. The main source of ilmenite and hematite, by comparison, may have been mafic–ultramafic rocks and/or banded iron formations within the Archean Yilgarn Craton to the east or the Pilbara Craton to the northeast, mobilised by acidic meteoric waters. Iron oxides forming the earliest cements may have been derived from the oxidation of detrital hematite and ilmenite grains concentrated along some bedding laminae or transported in solution from beyond the zone of deposition. Whereas the detrital iron oxides most likely come from the craton to the east of outcrop of the Tumblagooda Sandstone, the sand grains appear to have originally come from a relatively local orogenic source.  相似文献   

7.
The Gercus Formation (Eocene) in northeastern Iraq consists of a fluvial sequence of associated red and drab beds deposited under an arid to semi-arid climate. Occurrence of pigment on grain contacts in the sandstones and the uniform distribution of pigment in the marls and siltstones indicate that part of the pigment is of predepositional or syndepositional origin, most probably detrital ferric hydroxides that coated the grains. Alteration and corrosion of iron oxides and ferromagnesian minerals, intensified pigment around some opaque grains, and decreased heavy-mineral content (compared to the recent river sediments in the area) point to intrastratal alteration and the diagenetic origin of part of the pigment. Iron contents indicate that leaching of ferric iron with an average of 1.41% Fe from the drab marl and siltstone beds and 0.74% Fe from the drab sandstone beds washed out the pigment (or its precursor) from these beds.  相似文献   

8.
Xenotime overgrowths on detrital zircon in siliciclastic sediments have been reported in numerous studies. However, in natural samples, solid solution of zircon and xenotime is limited to near-end-member compositions. In order to characterize the interface region between both minerals and to draw inferences on the growth mechanisms of authigenic xenotime, we studied xenotime overgrowths on detrital zircon grains from two Phanerozoic sandstone samples with contrasting post-depositional histories. In one sample, the small (≤10 μm), pyramidal xenotime overgrowths are of diagenetic origin and grew without major discontinuity on the detrital zircon grain. The second sample shows up to >50-μm-wide, porous and inclusion-rich, hydrothermal xenotime overgrowths on detrital zircon, whereas the transition zone between both minerals is accompanied by large pore volume. Chemical compositions of the xenotime precipitates from the two samples differ particularly in Y, REE, Th and Sc concentrations, whereas high MREE availability in the diagenetic sample and the presence of Sc in the hydrothermal sample, respectively, appear to have promoted xenotime growth. Transmission electron microscopy on electron-transparent foils cut from the interface region shows that both the diagenetic xenotime and the hydrothermal xenotime are crystalline and grew in optical and crystallographic continuity to their detrital zircon substrata. Only a narrow transition zone (≤90 nm—diagenetic sample, 200–300 nm—hydrothermal sample) between zircon and xenotime is in part made up of nanometre-scale crystalline domains that are slightly distorted and may have formed from dissolution–re-precipitation processes at the zircon rim along with precipitation from the respective fluid.  相似文献   

9.
Using X-ray diffraction (XRD) analysis and an electron-probe microanalyser (EPMA), this research found that the main independent mineral of titanium (Ti) in the kaoline of Songyi is anatase. The granularity of anatase is from 0.5 um to 1.5 um, and some exceed 10 um. This research provides important scientific evidence for the exploitation of the coal-measure kaoline in the Sooth China.  相似文献   

10.
Cathodoluminescence is used in a new application to study extensional strains recorded by calcite overgrowths on detrital calcite grains. The geometry of the overgrowths yields an extension of +0.39 that is parallel to a pressure solution cleavage. A volume change of −0.21 was calculated from this geometry and an independently determined strain ratio.  相似文献   

11.
The Middle Muschelkalk (Middle Triassic) of the Catalan Coastal Range (north-east Spain) comprises sandstone, mudstone, anhydrite and minor carbonate layers. Interbedded sandstones and mudstones which are dominant in the north-eastern parts of the basin are terminal alluvial fan deposits. South-westward in the basin, the rocks become dominated by interbedded evaporites and mudstones deposited in sabkha/mudflat environments. The diagenetic and pore water evolution patterns of the Middle Muschelkalk suggest a strong facies control. During eodiagenesis, formation of microdolomite, anhydrite, baryte, magnesite, K-feldspar and mixed-layer chlorite/smectite was favoured within and adjacent to the sabkha/mudflat facies, whereas calcite, haematite, mixed-layer illite/smectite and quartz formed mainly in the alluvial facies. Low δ18OSMOW values for microdolomite (+23.7 to +28.4%) and K-feldspar overgrowths (+17.3 to +17.7%) suggest either low-temperature, isotopic disequilibrium or precipitation from low-18O porewaters. Low-18O waters might have developed, at least in part, during low-temperature alteration of volcanic rock fragments. During mesodiagenesis, precipitation of quartz overgrowths and coarse dolomite occurred in the alluvial sandstones, whereas recrystallization of microdolomite was dominant in the sabkha/mudflat facies. The isotopic compositions of these mesogenetic phases reflect increasing temperature during burial. Upon uplift and erosion, telogenetic calcite and trace haematite precipitated in fractures and replaced dolomite. The isotopic composition of the calcite (δ18OSMOW=+21.5 to +25.6%o; δ13C= 7.7 to - 5.6%o) and presence of haematite indicate infiltration of meteoric waters.  相似文献   

12.
Detrital tourmaline grains and their associated tourmaline overgrowths provide a means to unravel the provenance and petrogenetic history of low grade clastic metasedimentary rocks. Evidence derives from tourmaline grains found in a lithic wacke metamorphosed to chlorite zone conditions. The detrital tourmaline cores are diagnostic indicators of the source rocks of the sediment whereas the overgrowths record both diagenetic and metamorphic reactions in the rock. Tourmaline grains consist of a detrital core surrounded by asymmetric overgrowths comprised of inner and outer rims. Abrupt chemical discontinuities between each of these zones implies that volume diffusion within tourmaline was minor under the conditions of formation. Compositions of the detrital cores vary widely, yet can be correlated with source rock types that are consistent with lithic fragments recognizable in the metawacke. At either the analogous or antilogous pole, inner rim compositions proximal to the detrital cores converge, despite the substrate tourmaline composition, indicating an approach to chemical equilibrium. However, significant dufferences in Al and X-site vacancies at the expense of Mg, Na and Ti between the analogous and antilogous poles of the inner rims demonstrate the presence of significant amounts of compositional polarity. Outer rim compositions at either pole also converge but compositional polarity between the analogous and antilogous poles persists. The presence of the inner and outer rims separated by a compositional discontinuity suggests punctuated evolution of the overgrowth. This implies that boron was sporadically available during diagenesis and metamorphism. Based on boron contents of minerals, this may correspond to a mechanism such as boron release due to polytypic change of illite or consumption of illite and/or muscovite. As such, tourmaline growth stages may serve as a monitor of chemical reactions in low grade metamorphic rocks.  相似文献   

13.
The oxygen isotopic compositions of authigenic quartz cements in sandstones provide a monitor of the temperatures, compositions, and origins of pore-occluding fluids during diagenesis, but quartz overgrowths are too fine-grained to be amenable to conventional isotopic analysis. We have used a Cameca ims-4f ion microprobe to determine oxygen isotopic variations in authigenic and detrital quartz in four samples of the Ordovician St. Peter Sandstone from the Michigan Basin and Wisconsin Arch, midwestern USA. Ion microprobe isotopic analyses have been successfully accomplished with an internal precision of ±1‰ (1 σ) and a spatial resolution of 20–30 μm at low mass resolution using a high voltage offset technique. Repeated analyses of the quartz standard demonstrate a reproducibility of close to ±1‰ (1 sd) in good agreement with that expected from counting statistics. The four ion probe samples were chosen as representative of thirteen samples that were mechanically and chemically disaggregated, sieved, and analysed as a function of sieve size by conventional bulk-mineral techniques. Conventional and ion microprobe analyses are mutually consistent, supporting the accuracy of the ion microprobe analyses. Within-sample isotopic variations of up to 13%. and micro-scale isotopic variations of at least 4‰ over a distance of 100 μm have been measured within quartz overgrowths in a sandstone from the Wisconsin Arch. Overgrowths are uniformly higher in δ18O than detrital grains, and gradients of up to 25% exist across a few microns.

18O-enriched quartz overgrowths in sandstones from the Wisconsin Arch show complex CL zonation and reflect one of two possible processes: (1) low-temperature quartz precipitation during mixing of meteoric waters with upwelling basinal fluids; (2) higher temperature quartz precipitation during episodic gravity-driven upwelling of warm basinal fluids (of comparable isotopic composition to Michigan Basin fluids) from the Illinois Basin, related to evolution of Mississippi Valley type Pb---Zn ore-forming fluids. Quartz overgrowths in Michigan Basin sandstones, which derived their silica locally by pressure solution, are thought to have precipitated continuously over a range of temperatures from hot basinal fluids of restricted isotopic composition and circulation. Detrital quartz shows significant intea-grain and intergrain isotopic variation (5–13‰) but no significant inter-sample variation, consistent with a uniform source of granitoid and metamorphic quartz in space and time.  相似文献   


14.
S. FLINT 《Sedimentology》1987,34(1):11-29
The Oligo-Miocene Pacencia Group of Antofagasta Province, northern Chile consists of over 2 km of molassic sediments deposited in a series of alluvial fan and playa sub-environments. Sandstones of the Artolla Member, exposed around San Bartolo, represent playa-marginal sandflat deposits and locally host stratiform copper mineralization. A detailed study of these sediments has revealed a complex sequence of diagenetic modifications to the arkosic detrital mineral assemblage. Early dissolution of unstable ferro-magnesian minerals and calcic feldspar resulted in the release of ions into intra-stratal solution and the subsequent formation of a suite of eogenetic authigenic minerals. These include early hematite coatings on framework grains, pore-lining zeolite and pore-filling calcite, gypsum and celestite cements. Syntaxial overgrowths of albite, quartz and less common K-feldspar are well developed. Following early oxidative intrastratal conditions, the influx of acidic fluids derived from mudrocks during mesogenesis resulted in an important secondary porosity generation and the establishment of an acidic, reducing intrastratal environment. This facilitated the subsequent introduction of low temperature mineralizing solutions and formation of the San Bartolo copper deposit. A return to oxidative diagenetic conditions is recorded by late stage overgrowths of K-feldspar and quartz and the oxidation of native copper/chalcopyrite cements to cuprite/tenorite and chalcocite/covellite assemblages. This final telogenetic modification to the mineral assemblage is related to flushing by meteoric waters and provides independent evidence for an important phase of Andean deformation and uplift in the middle to upper Miocene.  相似文献   

15.
Porosity and permeability may be preserved in deep sandstone reservoirs by clay coating (mainly chlorite) which limits quartz overgrowths. Chloritization around quartz grains results mainly from mineralogical transformations of pre‐existing clays. It is fundamental to study those clay precursors to better understand and predict the location and distribution of clay coatings in subsurface sandstones for petroleum or geothermal prospecting. This paper reports a high‐resolution analysis of the composition, distribution and fabric of clays along a modern estuary, the Gironde (south‐west France). The scale of the study ranges from thin sections, through sand bar bodies, up to the entire estuary. Results show that clays are detrital and deposited at the same time as sand grains despite strong hydrodynamic conditions. Clays bind to medium‐grained sands forming detrital clay grain coats. On average, 26% of detrital sand grains are coated along the entire length of the estuary. Coat thickness varies from 1 μm to more than 200 μm, and coat coverage exceeds 30% in some samples. The turbidity maximum zone position (surface water turbidity from 1 to 10 g l?1) in the estuary, which is controlled by seasonal variations in hydrodynamic processes, significantly impacts the location of the maximum clay content and the abundance of coated grains in sandy facies along the estuary. Flocculation in the water column results in the accumulation of suspended matter and contributes to the high turbidity in the estuary. Exopolymeric substances produced by diatoms are observed both in the field and by cryo‐scanning electron microscopy, suggesting that they may play a major role in binding detrital clay around sand grains. Finally, tidal bars and heterolithic point bars in the estuary funnel and estuarine channels are prime sedimentological targets for finding clay coatings and potentially good reservoir quality in deeply buried sandstones.  相似文献   

16.
Petrographic analysis of hydrocarbon inclusions in reservoirs is the basis and prerequisite for study of hydrocarbon charge history using fluid inclusion analysis.Samples from Silurian reservoirs in the Kongquehe area were studied with microscopy,cathode luminescence and scanning electron microscopy,and the paragenetic sequence of diagenetic events was established.Aqueous and oil inclusions were found in four different occurrences,i.e.,① in healed cracks in detrital quartz grains,② in quartz overgrowths that were formed relatively early in diagenesis,③ in healed cracks crosscutting quartz overgrowths and detrital quartz,and ④ in paragenetically late calcite cements.Solid bitumens were found in intergranular pores and in late fractures,whereas gas inclusions occur in healed cracks crosscutting quartz overgrowths and detrital quartz.The homogenization temperatures of aqueous(Th_(aq)) and oil incluisons(Th_0) within individual fluid inclusion assemblages are very consistent,suggesting that the microthermometric data are reliable.The Th_(aq) values are generally larger than Th_0,indicating the oil charging events took place at significant depths.The results suggest that there were at least two episodes of hydrocarbon charging in the Kongquehe area:the early hydrocarbon charging occurred in late Caledonian,dominated by oil,and the late hydrocarbon charging occurred in the Yanshan-Himalayan,first by oil and then gases.In addition,two episodes of hydrocarbon reservoir adjustment and destruction occurred in the Hercynian and Himalayan,respectively,forming solid bitumen.  相似文献   

17.
The minerals and non-mineral inorganic constituents in Triassic and Tertiary low-rank coals from various coal deposits in South Australia were studied using selective chemical leaching and oxygen-plasma ashing techniques. Although gypsum may be present in some samples, most of the sodium, calcium and magnesium, as well as part of the sulphur, appears to occur as a combination of dissolved ions in pore water and exchangeable ions attached to carboxylate groups. Significant concentrations of iron and aluminium occur in acid-soluble form, probably as organometallic complexes within the hydrocarbon structure.Quartz is the dominant mineral in the Tertiary coal samples. It appears to be mainly detrital, but doubly terminated euhedral crystals suggest an authigenic origin in one of the deposits. Well crystallized kaolinite is common in the Triassic coals, while poorly crystallized kaolinite occurs in the Tertiary samples. Siderite, calcite and possibly collophane occur in the Triassic coals; sparse pyrite is present in both the Tertiary and the Triassic samples.The differences in minerals and other inorganic constituents between the Tertiary and Triassic deposits can be explained partly by variations in the composition of the pore waters permeating the strata, and partly by mobility of silica and alumina from different sources within the peat deposit. The relative mobility of the different inorganic constituents is also significant in beneficiation of the coal for use in combustion processes.  相似文献   

18.
The Aztec Siltstone (Late Devonian) formed in a meandering fluviatile environment and is a variegated redbed sequence consisting of red or drab overbank mudstones and drab channel sandstones, commonly arranged in fining-upwards cycles. The pigmentation in the red mudstones is caused by euhedral cryptocrystalline haematite which is dispersed throughout the matrix, masking the green colour of the underlying illitic and chloritic clays. Textural, mineralogical and chemical analyses suggest that the pigment formed in situ by dehydration and crystallization of a detrital, amorphous or poorly crystalline, yellow-brown ferric oxide precursor. The hydrated precursor apparently was derived from the weathering of iron silicates in a source area regolith, and transported in suspension with the Aztec alluvium, commonly by attachment onto surfaces of clay platelets. The association of the precursor with the clays is a contributing reason for the absence of red sandstones in the formation.Dehydration and crystallization of the yellow-brown ferric oxide to form the red haematite pigment occurred prior to deep burial of the host sediment. At least part of it occurred before burial, in an oxidising environment in well-drained and well-aerated overbank soils which were exposed for prolonged periods of time (4,000–10,000 years) under a hot and at least seasonally arid climate. Crystallization of the red pigment may have been completed during early diagenesis.Reducing conditions, induced by the presence of organic debris in the sediment and a relatively high water table, affected much of the deposit by removing the “free” hydrated ferric oxide, either partially or completely, from the in-channel sands, the low-lying and poorly drained overbank sediments, and the lacustrine sediments. This reduction was both a syndepositional and an early post-depositional process.Iron analyses indicate that, on average, the red mudstones are enriched in total iron (Fe) and Fe3+ by 2%, all of which is attributable to the inherited “free” ferric oxide. There is no other significant difference in whole-rock mineralogy or major-element chemistry between the red and non-red mudstones.  相似文献   

19.
Reduction spheroids are small-scale, biogenic, redox-controlled, metal enrichments that occur within red beds globally. This study provides the first analysis of the compositionally unique reduction spheroids of the Tumblagooda Sandstone. The work aims to account for their composition and consequently improve existing models for reduction spheroids generally, which presently fail to account for the mineralogy of the Tumblagooda Sandstone reduction spheroids. Interstitial areas between detrital grains contained in the cores of these reduction spheroids are dominated by microplaty haematite, in addition to minor amounts of svanbergite, gorceixite, anatase, uraninite, monazite and illite. The haematite-rich composition, along with an absence of base metal phases and the vanadiferous mica roscoelite, makes these reduction spheroids notable in comparison to other global reduction spheroid occurrences. Analyses of illite crystallinity provide values for samples of the Tumblagooda Sandstone host rock corresponding to heating temperatures of ca 200°C. Consequently, while Tumblagooda Sandstone reduction spheroids formed via the typical metabolic processes of dissimilatory metal-reducing bacteria, the combination of a unique mineralogy and illite crystallinity analysis provides evidence of more complex late-stage heating and reoxidation. This has not previously been recognised in other reduction spheroids and therefore expands the existing model for reduction spheroid genesis by also considering the potential for late-stage alteration. As such, future reduction spheroid studies should consider the potential impact of post-formation modification, particularly where they are to be used as evidence of ancient microbial processes; such as in the search for early evidence of life in the geological record on Earth or other planets. Additionally, because of their potential for modification, reduction spheroids serve as a record of the redox history of red beds and their study could provide insights into the evolution of redox conditions within a given red bed during its diagenesis. Finally, this paper also provides insights into the relatively understudied diagenetic history of the Tumblagooda Sandstone; supplying the first reliable and narrow constraints on its thermal history. This has important implications for the thermal history of the Carnarvon Basin and its petroleum prospectivity more broadly.  相似文献   

20.
Uraniferous iron grains occur in some radioactive granite plutons in the Eastern Desert of Egypt. Modal analysis of these grains indicates that weight abundance of uraniferous grains amounts to 17.50%, 18.00% and 26.00% of the total accessory heavy minerals of the uranium-mineralized samples of Gabal Gattar, El Missikat and El Erediya, respectively. These grains are mainly restricted to shear zones associated with strong hematitization, and occur either as fracture fillings or as interstitial grains among the main rock-forming minerals. Uraniferous iron grains are mainly composed of uranophane and β-uranophane coated and stained with limonite. These grains represent the main radioactive minerals in addition to the bright canary yellow to yellow uranophane and β-uranophane mineral grains. The data obtained on scanning electron microscopy and electron microprobe analysis confirm the abundance of iron in the darker colored varieties with respect to the light colored varieties. This mode of occurrence of the uranium minerals requires special consideration during mineral processing by physical means.  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