共查询到20条相似文献，搜索用时 15 毫秒
1.
Tuffaceous sediments as source rocks for uranium: A case study of the White River Formation, Wyoming
Robert A. Zielinski 《Journal of Geochemical Exploration》1983,18(3):285-306
Fine-grained tuffaceous sediments of the White River Formation (Oligocene) are evaluated as a possible source of uranium for the sedimentary uranium deposits of Wyoming. The evaluation is based upon a model in which volcanic glass is considered to be a major host of uranium and thorium and in which uranium and silica are released during alteration of glass to montmorillonite. The evaluation scheme is applicable to other tuffaceous sediments in similar geologic settings. The average uranium and thorium contents of glass separates and glassy air-fall ashes of the White River Formation are 8 ppm and 22.4 ppm respectively, and these values approximate the average composition of glass deposited in Wyoming basins in Oligocene time. Comparison of these values with the uranium and thorium concentrations in montmorillonite separates indicates little change in thorium concentrations but reductions in uranium concentrations which average 3.3 ppm. In spite of the apparent major removal of uranium during alteration of glass to montmorillonite, whole-rock samples of tuffaceous siltstones show an average uranium loss of only 0.4 ± 0.4 ppm, because of generally small amounts of clay alteration. This conclusion is generated by comparisons between glassy ash and partially altered vitric siltstones, the latter corrected for dilution of glass and clay-altered glass with uranium- and thorium-poor primary and detrital materials. The original volume of the White River Formation is adequate to generate economically significant quantities of mobile uranium, even with such modest losses. Uranium and silica which are mobilized during glass alteration can coprecipitate as uraniferous secondary silica in areas where solutions become silica saturated. These precipitates indicate pathways of ancient, uranium-rich solutions in tuffaceous rocks. Exploration efforts in the White River Formation and underlying units should concentrate on areas where such pathways intercept reducing environments. Intercepts of this type are present at some uranium deposits in the study area and this lends support to a tuffaceous source rock model. 相似文献
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Uraniferous Holocene sediments occur in the Carson Range of Nevada and California, U.S.A., between Lake Tahoe and Carson Valley. The hosts for the uranium include peat and interbedded organic-rich sand, silt, and mud that underly valley floors, fens, and marshes along stream valleys between the crest of the range and the edge of Lake Tahoe. The known uranium accumulations extend along the Carson Range from the area just southeast of South Lake Tahoe northward to the area just east of Carson City; however, they almost certainly continue beyond the study area to the north, west, and south. Due to the young age of the accumulations, uranium in them is in gross disequilibrium with its highly radioactive daughter products. These accumulations have thus escaped discovery with radiation detection equipment in the past. The uranium content of these sediments approaches 0.6 percent; however, the average is in the range of 300–500 ppm. Waters associated with these sediments locally contain as much as 177 ppb uranium. Modest levels of helium and radon also occur in these waters.Uraniferous waters are clearly entering the private and public water supply systems in some parts of the study area; however, it is not known how much uranium is reaching users of these water supplies. Many of the waters sampled in the study area exceed the published health effects guidance level of the Environmental Protection Agency. Regulatory standards for uranium in waters have not been published, however.Much uranium is stored in the sediments along these stream valleys. Estimates for a marsh and a fen along one drainage are 24,000 and 15,000 kg, respectively. The potential effects of man-induced environmental changes on the uranium are uncertain. Laboratory studies of uraniferous sediment rich in organic matter may allow us to evaluate the potential of liberating uranium from such sediments and creating transient increases in the level of uranium moving in water in the natural environment. 相似文献
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ZHANG Qiuying Bureau of Geology China National Nuclear Corporation P.O. Box Beijing 《《地质学报》英文版》2000,74(3):602-604
: 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) 相似文献
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Uranium Provinces in China 总被引：1，自引：0，他引：1
CHEN Zhaobo ZHAO Fengmin XIANG Weidong CHEN Yuehui China National Nuclear Corporation P.O. BOX: Beijing 《《地质学报》英文版》2000,74(3):587-594
Three uranium provinces are recognized in China, the Southeast China uranium province, the Northeast China-Inner Mongolia uranium province and the Northwest China (Xinjiang) uranium province. The latter two promise good potential for uranium resources and are major exploration target areas in recent years. There are two major types of uranium deposits: the Phanerozoic hydrothermal type (vein type) and the Meso-Cenozoic sandstone type in different proportions in the three uranium provinces. The most important reason or prerequisite for the formation of these uranium provinces is that Precambrian uranium-enriched old basement or its broken parts (median massifs) exists or once existed in these regions, and underwent strong tectonomagmatic activation during Phanerozoic time. Uranium was mobilized from the old basement and migrated upwards to the upper structural level together with the acidic magma originating from anatexis and the primary fluids, which were then mixed with meteoric water and resulted in t 相似文献
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中国东部中生代产铀火山岩的基本特征 总被引：1，自引：0，他引：1
产铀火山岩与非产铀火山岩存在岩石、岩石化学成分、微量元素及稀土元素的特征性差异;中国东部产铀火山洼地均形成于幔隆翼部重力高梯度带基底隆起构造环境,而火山洼地中铀的晚期主成矿作用,则以白垩纪拉张环境下贯入的中基性岩脉为先导,随后与之同步进行。 相似文献
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Pramod Kumar B. Panigrahi G. B. Joshi 《Journal of the Geological Society of India》2016,87(4):424-428
Sandstone–type uranium deposit hosted by reduced feldspathic sandstone sequence of lower part of Cretaceous Mahadek Formation occurs at Lostoin area of Mahadek basin and is confined within a prominent palaeochannel of NNE-SSW trend with flow towards SSW. The channel-fill comprises of about 10 m to 55 m grey to dark grey coloured, reduced, coarse to medium grained feldspathic sandstone along with abundant carbonaceous matter (5 to 15% by visual estimation) and is overlain by 5 m to 80 m of oxidized sub-feldspathic sandstone. Correlatable medium grade (～ 0.1% U3O8) uranium mineralization is intercepted in the boreholes aligned along the palaeochannel. Uraniferous solutions generated from the fertile provenance of south Khasi batholith flow through the channel and precipitated uranium at suitable reduction traps. Gentle slope of 2° to 3° of the basement channel facilitated prolonged interaction of uraniferous solution with reductants causing ore grade concentration. It has been envisaged that the control of palaeochannel and palaeobasement topography of the ore body would continue towards the SSW beyond Wahblei river. 相似文献
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Summary Skuppesavon represents a uranium mineralisation emplaced within a sequence of metavolcanics dominated by rocks of rhyolitic to trachytic composition. Uraniferous solutions have penetrated along zones previously opened by Na-Ca-rich mineralising fluids which caused albitisation of potassium feldspar, the partial to complete removal of quartz and the crystallisation of new mineral phases. Uranium, which has been transported mostly as uranyl carbonate complexes, has precipitated as uraninite which occurs as impregnations and only very rarely forms fracture infillings. The introduction of Ca-and Ti-bearing solutions, coeval and subsequent to uraninite precipitation, has resulted in the association of uraninite and sphene. The hydrothermal fluids responsible for the observed mineral parageneses have been activated during metamorphism. During the passage of these fluids through the volcano-sedimentary country rocks, elements such as Ca, Na, U and Ti were mobilised, concentrated and transported. Access through the rocks was facilitated by structural weaknesses and rock permeability variations. 相似文献
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通过对全国39个铀成矿带和29个预测区的重力数据处理、重力异常提取、地质构造推断,为全国铀矿资源潜力评价提供了构造单元、断裂构造、岩体范围及深度、盆地范围和地层结构等预测要素。总结了铀成矿环境的重力场特征,与热液成矿作用有关的铀矿（花岗岩型、火山岩型、及部分碳硅泥岩型）主要位于区域重力场从高场向低场过渡的部位或偏向低场区域,主要成矿要素花岗岩岩体、火山盆地均表现为重力低场;大型砂岩型铀矿成矿盆地位于区域重力场的高场区域,而蚀源区则为低场,盆地边缘或内部的隆起区一般位于剩余重力高场区;与上述各类型铀成矿有密切关系的断裂构造在重力场中显示为梯度带、不同性质重力异常的分界线、串珠状异常或条带状异常。 相似文献
11.
Mohamed F. Raslan 《Resource Geology》2009,59(1):99-105
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
12.
外生铀矿床成矿铀质来源与资源评价若干问题 总被引：2，自引：0，他引：2
概述了外生铀矿床的基本特点,即近源、浅成、层控、有机萃取、多阶段成矿、多种成因类型。根据成矿作用和矿床成因,把外生成矿的铀质来源分为:1.同生铀源;2.再造铀源;3.后生铀源等三类。着重讨论了外生铀矿资源评价的若干问题,即铀源岩石的原始铀丰度及活化丢失情况;花岗岩类铀源岩的岩石化学标志;各种铀源地质体形成的大地构造背景;外生铀矿成矿省、成矿带的评价准则。 相似文献
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伊犁盆地砂岩型铀成矿同位素地质特征 总被引：12，自引：0，他引：12
本对伊犁盆地可地浸砂岩型铀矿及其蚀源区进行了同位素地质特征研究，结果表明：伊犁盆地砂岩型铀矿具有多时期成矿的特点，其成矿年龄分别为82.4,60,11.4,7.1,3.5Ma，而主要成矿期集中在第三纪的中、上新世。伊犁盆地南侧蚀源区发育有以海西期为主的花岗岩和火山岩，前为293－316Ma，后为235－259Ma，从含矿砂体精选出的锆石，其U－Pb同位素年龄为308Ma，与蚀源区花岗岩，火山岩的时代一致，从而肯定了含矿砂体的物质来源，此外，通过对含矿砂体和蚀源区岩石U-Pb同位素体系演化特征的研究，指伊犁盆地砂岩型铀矿具有多铀源富集的特点，这些铀源分别是：地层沉积时形成的富铀砂体（主要的）和富铀的蚀源区岩石的近代风化淋滤释出的铀。 相似文献
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KENNETH G. STEELE 《Boreas: An International Journal of Quaternary Research》1988,17(2):183-194
A field of uraniferous boulders was discovered in a drift-covered valley west of Dismal Lakes. Glacial geological information was combined with boulder location and trace element till geochemical data to model the dispersal of the boulders; and to predict their likely bedrock source. Uraniferous bedrock was eroded by the last, westward flowing glacial ice to cover the area. The debris was englacially transported and subsequently deposited during subglacial melt-out of ice block(s) stagnating below active ice. The distribution of the boulders forms acrude, westward-opening fan centred on the easternmost boulder and oriented with the last ice-flow direction. The largest uranium values from surface till samples (-2 μm fraction) occur 6.2 km east of the main boulder concentration or 1.5 km east of the first boulder occurrence. The likely bedrock source is 6.0 to 6.6 km east of the main boulder concentration. 相似文献
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Pradeep Pandey Jyotsana Chabbra G. B. Joshi P. S. Parihar 《Journal of the Geological Society of India》2014,83(1):5-12
Presence of Early Tertiary pyroclastic material (tephra) has been documented petrographically, for the first time, in the Mandi-Bilaspur Sector from Tileli area, Dharamsala basin of Himachal Pradesh. The tephra is reported from the red shale, identified as tuffaceous siltstone belonging to lower Dharamsala Formation that lies above the uraniferous sandstone body and occurs as thin layers of over 300m along the strike, close to the contact of lower and upper Dharamsala formations. The tuffaceous material shows crude but preferred orientation of minerals like biotite, muscovite, chlorite, clay, hematite and specularite. Various features indicating presence of tephra are, glass shards altered to clay but retaining ‘U’ shaped outline, spindle-shaped hematite with preferred orientation, spherical to sub-spherical clay and altered Feoxide rich balls, clay groundmass with flow pattern, flaky minerals in association with clast depicting asymmetrical ramp structure. A zone of approximately 300 m length containing tuffaceous material has been established at Tileli overlying the uraniferous sandstone body. Identification of tephra at Tileli has significant implications as it enabled in demarcating the boundary between the upper and lower Dharamsala formations in central part of the basin in Bilaspur-Mandi Sector of HP Himalaya and also in guiding the uranium exploration programme in the lower Dharamsala Formation. 相似文献
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中国非常规铀资源 总被引：8，自引：0，他引：8
中国非常规铀资源主要包含黑色岩系型和盐湖型。其中与黑色岩系有关的含铀黑色岩系型、含铀磷块岩型、铀多金属磷块岩型是对中远期保障我国铀资源可持续供给有重要意义的类型。陆缘裂谷、陆缘裂陷环境是中国黑色岩系非常规铀资源最重要、最有利的成矿环境,形成U-Cd型、U-V-Mo型、U-V-Re型、U-V-Ni-Mo型和U-V-Ni-Mo-Re-Tl型等地球化学组合。中国黑色岩系非常规铀资源铀成矿作用受控于陆缘裂谷、陆缘裂陷环境下伴随海底喷流作用和海底火山喷发而沉积的由热水沉积硅质岩、硅质磷块岩和碳硅泥岩组成的富铀海相黑色岩系,热水沉积作用或喷气-沉积是形成中国黑色岩系非常规铀资源或发生大规模铀成矿作用的成矿机制。 相似文献
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Jeong Hwang Sang-Ho Moon Edward M. Ripley Yang Ho Kim 《Environmental Earth Sciences》2014,72(10):4035-4046
Korea has suffered from high U concentrations in some groundwater, especially in Daejeon near the central Ogcheon metamorphic belt. However, clear explanation has not been yet reported for the uranium sources in groundwater. This study is focused on identifying the potential uraniferous host rocks and finding the exact U-minerals serving as uranium sources in groundwater near Daejeon, Korea. For this work, we performed an in situ gamma ray spectrometer survey and a laboratory microscopic study with electron micro-probe analysis. The measurements for radioactive element content did not show any prominent K- and Th-anomaly spots, but they did result in several observations of considerable U-anomalies in pegmatite and hydrothermally altered granite, in which uraninite, coffinite and uranophane were found by electron micro-probe analysis. The occurrences of U-minerals are the first such discovery except in the low-grade U deposits of the Ogcheon metamorphic belt in Korea. All observed U-minerals were intimately associated with hydrothermal alteration. The remarkably low Th/U ratios in the studied uraniferous rocks also suggest that the U enrichment was genetically related to a post-magmatic hydrothermal process. However, many of the uraniferous parts were controlled by a reducing environment and occurred near the border between graphite-rich mica-schist and Jurassic leucocratic granite. The findings on these uraniferous rocks can be used in elucidating the source of highly enriched U groundwater in granite aquifers as well as in understanding the occurrence of igneous U-minerals, which has not been previously reported in Korea. 相似文献
18.
RICHARD J. BEHL 《Sedimentology》2011,58(2):325-351
Chert spheroids are distinctive, early‐diagenetic features that occur in bedded siliceous deposits spanning the Phanerozoic. These features are distinct in structure and genesis from similar, concentrically banded ‘wood‐grain’ or ‘onion‐skin’ chert nodules from carbonate successions. In the Miocene Monterey Formation of California (USA), chert spheroids are irregular, concentrically banded nodules, which formed by a unique version of brittle differential compaction that results from the contrasting physical properties of chert and diatomite. During shortening, there is brittle fracture of diatomite around, and horizontally away from, the convex surface of strain‐resistant chert nodules. Unlike most older siliceous deposits, the Monterey Formation still preserves all stages of silica diagenesis, thus retaining textural, mineralogical and geochemical features key to unravelling the origin of chert spheroids and other enigmatic chert structures. Chert spheroids found in opal‐A diatomite form individual nodules composed of alternating bands of impure opal‐CT chert and pure opal‐CT or chalcedony. With increased burial diagenesis, surrounding diatomite transforms to bedded porcelanite or chert, and spheroids no longer form discrete nodules, yet still display characteristic concentric bands of pure and impure microcrystalline quartz and chalcedony. Petrographic observations show that the purer silica bands are composed of void‐filling cement that precipitated in curved dilational fractures, and do not reflect geochemical growth‐banding in the manner of Liesegang phenomena invoked to explain concentrically banded chert nodules in limestone. Chertification of bedded siliceous sediment can occur more shallowly (< 100 m) and rapidly (< 1 Myr) than the bulk silica phase transitions forming porcelanite or siliceous shale in the Monterey Formation and other hemipelagic/pelagic siliceous deposits. Early diagenesis is indicated by physical properties, deformational style and oxygen‐isotopic composition of chert spheroids. Early‐formed cherts formed by pore‐filling impregnation of the purest primary diatomaceous beds, along permeable fractures and in calcareous–siliceous strata. 相似文献
19.
中非卢菲里安地区以铜钴资源闻名于世，同时也赋存一定的铀矿资源。铀成矿作用分别与大陆裂谷及盆地成岩期（876~823 Ma）、早期洋盆形成或大陆碰撞期（720~652 Ma）、卢菲里安变质高峰期（550~530 Ma）相对应。受区域构造活动影响形成的多期次热流体，从基底及加丹加超群富铀岩石萃取铀元素并在构造发育的区域富集成矿为其主要的成矿模式，其变质基底或班委乌卢基底可能提供了铀物质来源，热流体为载体，断裂及穹窿构造则提供通道与空间。含铀矿体多受地层及构造双重控制，围岩褐铁矿化及方柱石化对找矿具有指示意义。研究区内铀矿成矿条件较好，下罗安群受断裂及逆冲推覆构造影响强烈且蚀变较为发育的区域为有利的找矿前景区。 相似文献
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矿床产于中元古代地层中。矿区内酸性脉岩发育,常密集成带,矿床受穿过脉岩带的构造破碎带控制。矿化岩石主要为构造碎裂岩和角砾岩,其原岩为长英质脉岩、变石英砂岩、变安山岩、板岩及粉砂岩等。矿化以裂隙充填为主,对围岩化学成分的选择性不大。围岩蚀变有:绢云母化、硅化、钾长石化、黑云母化、黄铁矿化、赤铁矿化及水合多水高岭石化等。铀矿物主要为沥青铀矿、铀黑、铀石,其次有钛铀矿、水铀矾,含铀矿物有锐钛矿、金红石、赤铁矿、水合多水高岭石和褐铁矿等;其它金属矿物主要有辉钼矿、黄铁矿、方铅矿和黄铜矿。矿石具脉状、角砾状、块状和浸染状构造,沥青铀矿具胶状结构。矿床中钼的储量远大于铀,铀矿体产于钼矿体之中或其边部。通过室内、外研究,可以认为本矿床为与中酸性小侵入体有关的中-低温热液成因的钼-铀型复合矿床。 相似文献