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1.
Summary The Lower Lias Clay at Blockley, 20 km due south of Stratford-upon-Avon, UK, is thought to be representative of this clay formation over much of the Severn Basin. As far as the mineralogy of the clay is concerned, illite is the dominant clay mineral, kaolinite being subsidiary, with quartz, calcite, pyrite and chlorite/vermiculite present in subsidiary or accessory amounts. Weathering changes the mineralogy, with illite being degraded and calcite and pyrite being removed. Furthermore free iron oxide coatings become important as a result of weathering, with the maximum concentrations being present in the highly weathered material.The unweathered clay possesses a preferred orientation associated with turbostratic structures. At certain horizons microfolding and remoulding occurs in the unweathered clay and silty layers are displaced. Weathering has progressively destroyed the micro-structures present in the weathered clay horizons.The fissures in the Lower Lias Clay occur in five uniplanar sets. In the unweathered clay the intensity is fairly constant but it increases in a narrow zone just below the weathered horizons. The number of curved fissures also increases at this depth. This intense fissuring continues into the lowest zone of weathered clay where weathering is confined to the fissure surfaces. Fissures become less apparent in the more weathered horizons as more and more degradation has taken place. However, new smaller fissure systems are developed in the weathered clay, as are desiccation cracks.Engineering index properties and values of shear strength are given. Relationships between moisture content and strength, liquid limit and iron (Fe) content were observed, and a relationship between weathering zones and the shear strength-depth curve was established. 相似文献
2.
Amar Deep Regmi Kohki Yoshida Megh Raj Dhital Biswajeet Pradhan 《Environmental Earth Sciences》2014,71(6):2711-2727
Sangrumba landslide is one of the largest and the most active landslides in Nepal Himalaya. Geologically the landslide belongs to the Higher Himalaya and consists of Pre-Cambrian biotite–garnet and sillimanite gneiss with some quartzite. The present paper aims at describing various degrees of rock weathering and their effect in Sangrumba landslide. Field study followed by mineralogical, geochemical and geotechnical analyses of the collected rock and soil samples from the landslide zone were used in characterizing weathering degree. The gneisses are intensely weathered while quartzite is unweathered. Petrographical and X-ray diffraction analyses showed that the rocks in the landslide zone had undergone weathering process with the formation of different types of clay minerals as kaolinite, vermiculite, smectite and chlorite. This was further confirmed by the Scan Electron Microscope and Energy Dispersive X-ray analyses. These clay minerals drastically reduced the rock strength facilitating the extensive failure of the Sangrumba landslide. The major and trace element composition of the rock and soil samples was calculated from the XRF analyses. The geochemical analyses and weathering indexes of rocks showed that they are significantly weathered and had a major influence in the formation of the Sangrumba landslide. In addition, mechanical strength measurement of rock/soil showed that the strength drastically decreases as the weathering intensity increases. Rainfall followed by the rock type are the most dominant parameters influencing the weathering process which leads to the formation of large landslide as the present one. These findings can be used in other areas with similar geological and topographical conditions. 相似文献
3.
《Organic Geochemistry》2011,42(9):1076-1088
Bulk geochemical, petrographical, mineralogical and molecular compositions of unweathered, weathered and transitional zones of a Middle Jurassic fossil wood were analyzed to trace changes caused by oxidative weathering of the immature terrestrial organic matter (OM). The occurrence of such zones was confirmed by the mineral composition, showing replacement of siderite and pyrite by goethite. Vitrinite reflectance analysis of weathered and unweathered fossil wood samples revealed that weathering elevated the vitrinite reflectance values by ca. 0.1%, which should be taken into account during modeling of low maturity terrestrial OM. In the weathered part of the wood, most of the biomarkers and biomolecules were totally removed or the concentration decreased significantly. The concentration of most of the polynuclear aromatic hydrocarbons (PAHs) decreased by 50–80%, being >90% for the more reactive and less stable benzo[a]pyrene and perylene. On the other hand, several aromatic compounds, like phenanthrene and its methyl derivatives, phenyl naphthalenes, fluoranthene and oxygen-containing aromatic compounds increased in concentration in the weathered zone. This results from processes such as formation of phenyl derivatives of PAHs and their cyclization, as well as aromatization of diterpenoids and incorporation of oxygen into aromatic structures. Weathering should always be considered in studies of fossilized terrestrial OM, especially in the case of thermal maturation modeling, because it significantly decreases the OM content and total sulfur content, changes vitrinite reflectance values and alters the extract composition as a result of organic compound degradation. 相似文献
4.
Natural analogues are an important source of long-term data and may be viewed as naturally occurring experiments that often include processes, phenomena, and scenarios that are important to nuclear waste disposal safety assessment studies. The Koongarra uranium deposit in the Alligator Rivers region of Australia is one of the best-studied natural analogue sites. The deposit has been subjected to chemical weathering over several million years, during which many climatological, hydrological, and geological changes have taken place, resulting in the mobilization and spreading of uranium. Secondary uranium mineralization and dispersed uranium are present from the surface down to the base of the weathering zone, some 25 m deep. In this work, a simple uranium transport model is presented and sensitivity analyses are conducted for key model parameters. Analyses of field and laboratory data show that three layers can be distinguished in the Koongarra area: (1) a top layer that is fully weathered, (2) an intermediate layer that is partially weathered (the weathering zone), and (3) a lower layer that is unweathered. The weathering zone has been moving downward as the weathering process proceeds. Groundwater velocities are found to be largest in the weathering zone. Transport of uranium is believed to take place primarily in this zone. It appears that changes in the direction of groundwater flow have not had a significant effect on the uranium dispersion pattern. The solid-phase uranium data show that the uranium concentration does not significantly change with depth within the fully weathered zone. This implies that uranium transport has stopped in these layers. A two-dimensional vertically integrated model for transport of uranium in the weathering zone has been developed. Simulations with a velocity field constant in time and space have been carried out, taking into account the downward movement of this zone and the dissolution of uranium in the orebody. The latter has been modelled by a nonequilibrium relationship. In these simulations, pseudo-steady state uranium distributions are computed. The main conclusion drawn from this study is that the movement of the weathering zone and the nonequilibrium dissolution of uranium in the orebody play an important role in the transport of uranium. Despite the fact that the model is a gross simplification of what has actually happened in the past two million years, a reasonable fit of calculated and observed uranium distributions was obtained with acceptable values for the model parameters. 相似文献
5.
准噶尔盆地滴西地区石炭系火山岩储集性能分布规律研究 总被引：1，自引：0，他引：1
火山岩储集性能分布的非均质性非常强,探索其分布规律成为火山岩油气勘探的难点和重要任务。本文以实际岩心及其分析化验等资料为基础,从滴西地区取心最佳储集性能段、最差储集性能段、风化壳储集性能分布模式、薄层熔岩储集性能分布模式、厚层熔岩储集性能分布模式等方面总结了石炭系火山岩储集性能的垂向分布规律,同时分析了储集性能的平面分布情况。火山熔岩储集性能在垂向上的分布差异,成岩阶段主要受岩相的影响,后期主要受构造作用及风化溶蚀作用等的影响。受成岩阶段岩相的影响,溢流相上部亚相和下部亚相均有可能形成较好的储集性能。与碎屑岩互层的薄层熔岩常具有较好的储集性能。与碎屑岩互层的厚层熔岩段的底部储集性能可能较好,其次是顶部,而中部常沦落为储集性能相对较差的位置。风化壳的风化粘土层、强风化带、中等风化带、弱风化带、未风化带5个垂向分带结构中,中等风化带往往具备相对最佳的储集条件。应用W风化指数新型工具对火山岩进行风化程度评估显示,准噶尔盆地火山岩具有多期风化的特征,并残留有大量未风化、轻微风化及中等风化的火山岩,这其中不乏储集性能优良的岩性段。从平面分布来看,研究区域火山岩储集性能具有强烈的各向异性特征,常表现为局部富集,快速变迁,随机分布。 相似文献
6.
Statistical empirical index of chemical weathering in igneous rocks: A new tool for evaluating the degree of weathering 总被引：6，自引：0，他引：6
Chemical weathering indices are useful tools in characterizing weathering profiles and determining the extent of weathering. However, the predictive performance of the conventional indices is critically dependent on the composition of the unweathered parent rock. To overcome this limitation, the present paper introduces an alternative statistical empirical index of chemical weathering that is extracted by the principal component analysis (PCA) of a large dataset derived from unweathered igneous rocks and their weathering profiles. The PCA analysis yields two principal components (PC1 and PC2), which capture 39.23% and 35.17% of total variability, respectively. The extent of weathering is reflected by variation along PC1, primarily due to the loss of Na2O and CaO during weathering. In contrast, PC2 is the direction along which the projections of unweathered felsic, intermediate and mafic igneous rocks appear to be best discriminated; therefore, PC1 and PC2 represent independent latent variables that correspond to the extent of weathering and the chemistry of the unweathered parent rock. Subsequently, PC1 and PC2 were then mapped onto a ternary diagram (MFW diagram). The M and F vertices characterize mafic and felsic rock source, respectively, while the W vertex identifies the degree of weathering of these sources, independent of the chemistry of the unweathered parent rock.
The W index has a number of significant properties that are not found in conventional weathering indices. First, the W index is sensitive to chemical changes that occur during weathering because it is based on eight major oxides, whereas most conventional indices are defined by between two and four oxides. Second, the W index provides robust results even for highly weathered sesquioxide-rich samples. Third, the W index is applicable to a wide range of felsic, intermediate and mafic igneous rock types. Finally, the MFW diagram is expected to facilitate provenance analysis of sedimentary rocks by identifying their weathering trends and thereby enabling a backward estimate of the composition of the unweathered source rock. 相似文献
7.
东营凹陷永北地区T1不整合面之下风化壳发育带的的预测是地层油藏勘探的重点与难点。综合利用高精度三维地震解释、岩心观察、薄片鉴定、测录井分析及物性分析等方法,结合构造发育史、埋藏史等研究成果,对东营凹陷永北地区T1不整合面下沙三上亚段地层中特殊的地震反射特征进行研究,并对其地质意义进行了探讨。研究表明:T1不整合面下发育典型埋藏风化壳,包括风化粘土层和半风化淋滤带2层结构;在大气淡水风化、淋滤作用下,半风化淋滤带内部地震同相轴消失,表现为空白反射特征;半风化淋滤带物性得到改善,与未风化岩石之间形成一个物性差异界面,表现为不连续的角度不整合面;未受明显风化、淋滤作用的地层,则表现为典型的角度不整合;地震反射特征的演化过程可划分4个阶段:沙三上沉积后阶段、沙三上抬升后阶段、风化壳形成早期阶段、风化壳形成阶段。地震空白反射带的发育范围是风化壳发育带的保守范围或最小范围,向湖盆方向逐渐过渡为正常地层。风化壳的发育大大改善了原岩的储集性能,可作为良好的油气储集空间和运移通道,是下步地层油气藏勘探的重点目标。 相似文献
8.
Weathering of the New Albany Shale, Kentucky, USA: I. Weathering zones defined by mineralogy and major-element composition 总被引：1，自引：1，他引：0
Comprehensive understanding of chemical and mineralogical changes induced by weathering is valuable information when considering the supply of nutrients and toxic elements from rocks. Here minerals that release and fix major elements during progressive weathering of a bed of Devonian New Albany Shale in eastern Kentucky are documented. Samples were collected from unweathered core (parent shale) and across an outcrop excavated into a hillside 40 year prior to sampling. Quantitative X-ray diffraction mineralogical data record progressive shale alteration across the outcrop. Mineral compositional changes reflect subtle alteration processes such as incongruent dissolution and cation exchange. Altered primary minerals include K-feldspars, plagioclase, calcite, pyrite, and chlorite. Secondary minerals include jarosite, gypsum, goethite, amorphous Fe(III) oxides and Fe(II)-Al sulfate salt (efflorescence). The mineralogy in weathered shale defines four weathered intervals on the outcrop—Zones A–C and soil. Alteration of the weakly weathered shale (Zone A) is attributed to the 40-a exposure of the shale. In this zone, pyrite oxidization produces acid that dissolves calcite and attacks chlorite, forming gypsum, jarosite, and minor efflorescent salt. The pre-excavation, active weathering front (Zone B) is where complete pyrite oxidation and alteration of feldspar and organic matter result in increased permeability. Acidic weathering solutions seep through the permeable shale and evaporate on the surface forming abundant efflorescent salt, jarosite and minor goethite. Intensely weathered shale (Zone C) is depleted in feldspars, chlorite, gypsum, jarosite and efflorescent salts, but has retained much of its primary quartz, illite and illite–smectite. Goethite and amorphous FE(III) oxides increase due to hydrolysis of jarosite. Enhanced permeability in this zone is due to a 14% loss of the original mass in parent shale. Denudation rates suggest that characteristics of Zone C were acquired over 1 Ma. Compositional differences between soil and Zone C are largely attributed to illuvial processes, formation of additional Fe(III) oxides and incorporation of modern organic matter. 相似文献
9.
Review of a new shear-strength criterion for rock joints 总被引：44，自引：0，他引：44
Nicholas Barton 《Engineering Geology》1973,7(4):287-332
Barton, N., 1973. Review of a new shear-strength criterion for rock joints. Eng. Geol., 7: 287–332.
The surface roughness of rock joints depends on their mode of origin, and on the mineralogy of the rock. Amongst the roughest joints will be those that formed in intrusive rocks in a tensile brittle manner, and amongst the smoothest the planar cleavage surface in slates. The range of friction angles exhibited by this spectrum will vary from about 75° or 80° down to 20° or 25°, the maximum values being very dependent on the normal stress, due to the strongly curved nature of the peak strength envelopes for rough unfilled joints.
Direct shear tests performed on model tension fractures have provided a very realistic picture of the behaviour of unfilled joints at the roughest end of the joint spectrum. The peak shear strength of rough—undulating joints such as tension surfaces can now be predicted with acceptable accuracy from a knowledge of only one parameter, namely the effective joint wall compressive strength or JCS value. For an unweathered joint this will be simply the unconfined compression strength of the unweathered rock. However in most cases joint walls will be weathered to some degree. Methods of estimating the strength of the weathered rock are discussed. The predicted values of shear strength compare favourably with experimental results reported in the literature, both for weathered and unweathered rough joints.
The shear strength of unfilled joints of intermediate roughness presents a problem since at present there is insufficient detailed reporting of test results. In an effort to remedy this situation, a simple roughness classification method has been devised which has a sliding scale of roughness. The curvature of the proposed strength envelopes reduces as the roughness coefficient reduces, and also varies with the strength of the weathered joint wall or unweathered rock, whichever is relevant. Values of the Coulomb parameters c and Φ fitted to the curves between the commonly used normal stress range of 5–20 kg/cm2 appear to agree quite closely with experimental results.
The presence of water is found in practice to reduce the shear strength of rough unfilled joints but hardly to affect the strength of planar surfaces. This surprising experimental result is also predicted by the proposed criterion for peak strength. The shear strength depends on the compressive strength which is itself reduced by the presence of water. The sliding scale of roughness incorporates a reduced contribution from the compressive strength as the joint roughness reduces. Based on the same model, it is possible to draw an interesting analogy between the effects of weathering, saturation, time to failure, and scale, on the shear strength of non-planar joints. Increasing these parameters causes a reduction in the compressive strength of the rock, and hence a reduction in the peak shear strength. Rough—undulating joints are most affected and smooth—nearly planar joints least of all. 相似文献
10.
柴达木盆地阿尔金山前斜坡带发现了规模分布的东坪基岩气田,其基岩风化壳的作用成为关注的问题。依据元素分析、X-射线衍射分析、岩心薄片观察,常规测井响应和成像测井响应特征,识别出东坪地区基岩风化壳发育不同结构层,且不同结构层的储集特征有很大差异。研究表明,基岩风化壳结构可划分为土壤层、完全风化层和半风化层,而半风化层又可进一步分为溶蚀带和崩解带;其中土壤层厚度0~2 m,完全风化层厚度4~15 m,溶蚀带厚度365~164 m,崩解带厚度300~1 000 m。基岩半风化层是储层发育带,其中溶蚀带储集物性好于崩解带,溶蚀带发育较多的溶蚀孔洞和溶蚀加宽的网状裂缝,孔隙度范围2%~16%;而崩解带发育弱溶蚀构造缝和节理缝,孔隙度范围2%~8%。东坪地区大规模发育基岩风化壳为柴达木盆地远离烃源岩灶的斜坡地区寻找油气提供了借鉴依据。 相似文献
11.
二长花岗岩风化壳自下而上划分为原生带、微风化带、弱风化带和强风化带。风化壳中粘土矿物主要为埃洛石,其次为高岭石及少量伊利石。微风化带下部以高岭石为主,往上埃洛石逐渐占优势,并于弱风化带中、上部和强风化带中局部富集,这与当时地下水活动状态有关。高岭石结晶程度随风化程度的增强而提高。在弱酸性介质条件下及水分丰富、溶出条件强烈时,从长石解理面上和长石的“溶蚀”空隙中可以直接形成高岭石或埃洛石,而过渡阶段的伊利石很不发育或不存在。 相似文献
12.
M. M. Habteselassie C. I. Mathison R. J. Gilkes 《Australian Journal of Earth Sciences》2013,60(5):555-566
Shephards Discordant Zone is a 500–600 m thick interlayered sequence of deformed, altered and metamorphosed magnetite metagabbro and about 50 layers or lenses of magnetitite (> 80–90% magnetite). The sequence shows progressive magmatic fractionation upwards: Ti and Ti/Fe increase, and V, V/Ti and Cr decrease upwards in magnetite and in whole‐rock compositions. The main magnetite‐rich sequence (about 400 m thick) is deeply weathered, with 40 m of saprolite showing vertical zonation of weathering minerals due to progressive weathering. Magnetitites (average 1% V2O3) are resistant to weathering and show little chemical change, but magnetite gabbros (average 0.27% V2O3) are extensively weathered and show progressive loss of Ca, Na, Mg and S. Plagioclase, magnetite (1.37% V2O3), chlorite (up to 0.35% V2O3), actinolite, epidote and minor sulfides in unweathered rocks weather to kaolinite, hematite, goethite and minor vermiculite, ilmenite remaining largely unaffected. Vanadium is essentially immobile during weathering and is unaffected during weathering of magnetitites (1% V2O3), but is slightly depleted during weathering of magnetite gabbros (0.23% V2O3). 相似文献
13.
中国黄土中的风化壳研究 总被引：8，自引：2，他引：8
据野外调查和室内鉴定,在布容期 0.78～ 0MaBP形成的黄土剖面中确定了三个时期的风化壳,它们主要发育在黄土高原东南部。黄土中的风化壳是红褐色古土壤在特定的气候条件下转变而成的,厚度在 3～ 6m之间,风化壳剖面常由 3个层次构成,发育时间为 5～ 10万年不等。风化壳上部是发育好的红色古土壤,中部是褐黄色强风化破碎黄土,下部是棕黄色弱风化黄土。粘土矿物分析表明,黄土中的风化壳为伊利石-蒙脱石型。黄土中风化壳发育时的年均降水量在 90 0～ 10 0 0mm之间,是黄土高原降水丰富的气候事件的显示。黄土高原东南部和中部风化壳的发育证明黄土中有些古土壤确属淋溶型森林土壤,当时亚热带气候至少迁移到了黄土高原中部. 相似文献
14.
The loess of north-central China: Geotechnical properties and their relation to slope stability 总被引：2，自引：0，他引：2
T.A. Dijkstra C.D.F. Rogers I.J. Smalley E. Derbyshire Yong Jin Li Xing Min Meng 《Engineering Geology》1994,36(3-4):153-171
Loess is an aeolian deposit consisting of predominantly silt-sized quartz particles, and containing variable amounts of clay-sized minerals. Loess is generally classified as a water-softening material, because upon wetting the loess fabric rapidly weakens or collapses. The strain hardening of Malan loess and the brittle failure of Lishi and Wucheng loess are in strong contrast to the failure behaviour of these loess deposits in a remoulded state. From tests carried out on samples with varying moisture contents, using a modified Bromhead ring shear apparatus, it was found that the effective apparent cohesion gradually increases and the effective internal friction angle decreases with an increase in moisture content. When the moisture content reaches a material-specific threshold, the effective cohesion decreases rapidly and the effective internal friction angle stabilises at a residual value.
The frequent failure of loess slopes in the western part of the Chinese Loess Plateau is closely related to progressive weathering along zones in these slopes, which causes a dramatic decrease in strength from the peak strength condition. Progressive weathering is common in the loess slopes in the western part of the Chinese Loess Plateau. During the process shear strength reduction along potential slip surfaces may be achieved by leaching of readily soluble salts, destruction of cementation bonds, and redistribution of particles. Localized collapse of the loess fabric causes internal deformation and consequently peak strength conditions are concentrated on a progressively smaller area of the failure plane. Therefore, the mode of failure of loess slopes is generally determined by brittle failure of the undisturbed, and unweathered, central parts of the slopes. It is important that both the weathered and unweathered strength of the loessmaterials in this area be established in order to analyze the stability of existing loessslopes, many of which are steepand lie directly above domestic and industrial urban areas. 相似文献
15.
Within the Daly River basin, Northern Territory, three erosion surfaces are described and their relationships to deep weathering are discussed. The Bradshaw surface is the highest and oldest surface recognized. It is of considerable perfection and forms main divides; it is associated with a deep lateritic profile with a strongly silicified horizon forming the lower part of the pallid zone and extending into rocks immediately beneath. The Maranboy surface now forms secondary divides, with related rock‐cut terraces, below the level of the Bradshaw surface. In most areas it was produced by the stripping of the upper, less silicified parts of the Bradshaw pallid zone. The Maranboy surface is associated with a lateritic weathering profile less deep than the Bradshaw profile and mainly developed in the Bradshaw weathering mantle. A younger erosion surface, the Tipperary surface, advanced by the removal of the Maranboy re‐weathered layer exposing the resistant Bradshaw silicified rock which commonly forms a base‐level of denudation. The Tipperary surface consists of broad plains, gently undulating terrain, and dissected headwater valley floors. It is relatively unweathered and carries depositional mantles which are attributed to climatically induced slope instability. The ages of the erosion surfaces and the possibility of climatic changes in the area are also briefly discussed. 相似文献
16.
Joan Anne Walsh 《Environmental Geology》2008,56(3-4):561-569
This research identifies the changes which takes place in roofing slate due to natural exposure and tries to replicate these changes experimentally. Traditional methods of testing, used by the British and other national standards, concentrate on the properties of unweathered samples and give no information on the relative durability of the different slates. Instead of concentrating on the initial properties, this research focuses on changes in the properties in order to assess durability. The effects of natural weathering were assessed by comparing old, used slates with new slates from the same or a similar source. The new slates were then weathered experimentally by repeated cycles of wetting and drying, and the increase in water absorbency compared with that observed in naturally weathering. Mineralogical differences due to both natural and experimental weathering were also measured using X-ray diffraction analysis. It was found that the effects of experimental weathering, using repeated cycles of wetting and drying, are similar to those observed in natural weathering. These include increased water absorbency and loss of crystallinity of the principal minerals. The greatest changes are found in those slates which are the most vulnerable to weathering, making it possible to identify poor quality slates. 相似文献
17.
The behaviour of the rare-earth elements(REE)during the weathering of granites was studied in southern Guangxi,China.Based on the study of the weathering profiles,the soil,weathered and sub-weatereb zones are identified with different REE geochemical behaviours throug the weathering profiles of granite.The Ce anomalies of the weathering profiles cover a large range of values with most falling between 1.02 and 1.43in the soil zone and 0.16and 0.40in the weathered and sub-weathered zones.Light rare-earth elements(LREE) and heavy rare-earth elements(HREE)are enriched to varying degree in the weathering profiles as compared to host granites.In the soil zone,more HREEs are leached than LREEs,and HREEs are more enriched than LREE in the weathered and sub-weathered zones.It is considered that infiltration and adsorption on clays are two processes controlling the enrichment and formation of REE deposits in the weathering profiles of granite. 相似文献
18.
19.
川西冕宁-德昌REE矿带中的风化型矿石研究相对缺乏.根据近几年的野外地质调查,采用电子探针、X光粉晶衍射、全岩分析等对大陆槽、牦牛坪和木落寨矿床中疑似风化矿的样品进行类型和成因分析.结果表明:大陆槽风化型矿石中大量粘土矿物（达40%）和矿石矿物（达60%）发育,风化程度高;相反,牦牛坪和木落寨疑似风化型矿石中几乎没有粘土矿物,风化程度低.通过对牦牛坪和木落寨疑似风化型矿石进行地球化学特征、矿物组成分析并与围岩、矿脉的组成和产状对比,表明疑似风化型矿石主要是由矿脉和围岩在强烈的构造作用下发生机械风化形成.频繁的角砾构造使大陆槽矿石发生强烈的机械风化作用,并加速了矿石发生一定的水岩反应,促进矿石发生中等强度的化学风化作用.目前整个矿带中未发现明显的生物风化作用.整个稀土矿带的风化型矿石比南岭离子吸附型稀土矿石的风化程度低,形成时间较晚（11 Ma）,氟碳铈矿大量保存,还没有形成离子吸附型矿床. 相似文献
20.
Concentration of Fe-oxides and alumina in weathering processes are main geological reactions for lateritization and bauxitization, respectively. In western Japan, red-coloured soil formed by weathering processes developed in many places. This soil is composed of hydrous Fe-oxide minerals, hydrous alumina minerals and other minerals. It was formed in the upper part of deep weathering crust by weathering processes under some kind of sub-tropical climate, probably in the Pliocene. One of these occurrences is observed in the upper part of Goshikidai and Konodai, west part of Takamatsu city, northeast Shikoku Island, west Japan. A deep weathering crust is distributed on wide hilly plains ranging from 250 to 400 m a.m.s.l. in the northwestern region of Takamatsu city. Original rock of the weathering crust is bronzite andesite and glassy bronzite andesite, so-called ‘sanukite’. The andesites had been weathered under some special climate, and the geological age of the weathering is the same as above. The mineral assemblage and formation mechanism are similar to those of laterite and bauxite. The weathering crust developing in this region are subdivided into the three following zones: (1) A zone, composed of hydrous Fe-oxides and metahalloysite with small amounts of gibbsite and it is associated with white veins of metahalloysite; (2) B zone, composed of hydrous Fe-oxides and metahalloysite (some material is associated with -cristobalite); and C zone, composed of metahalloysite or halloysite and -cristobalite with relict crystals of feldspar and quartz, and some material is associated with montmorillonite. Chemical analyses of the materials of the three zones show the formation mechanisms of the weathering crust. 相似文献