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1.
A mass transfer model of bauxite formation   总被引：1，自引：0，他引：1  
The formation of bauxite due to weathering of a granitic protolith has been simulated by means of a one-dimensional flow and reaction model based on the mass transfer principle. The model couples mineral dissolution and precipitation reactions, speciation in solution, and advective solute transport in a porous medium. A very important aspect of the modeling study is the use of mineral reaction rates determined experimentally in the laboratory. The important effects of solution saturation state and pH have been incorporated into the kinetic rate laws governing the heterogeneous reactions. The values of these parameters have been obtained from the scientific literature to guarantee that realistic reaction rates are used in the simulations. Albite and quartz are the minerals that make up the parent rock in the model. Gibbsite, kaolinite, and a Na-mica (as a surrogate for smectite) are the secondary minerals that have been taken into account. Long-term simulations (>1 Ma) have been run, and the formation of a bauxitic profile, with an upper gibbsite-rich and a lower kaolinite-rich zone, is predicted. In early stages of the process (up to a few hundreds of thousands of years), both gibbsite and kaolinite precipitate directly from solution as a consequence of albite dissolution. In later stages, the bulk of gibbsite precipitation derives from the incongruent dissolution of kaolinite, while kaolinite precipitation is still caused by the dissolution of albite. This is also reflected by the formation of two reaction fronts in the profile. These results are compared with weathering sequences from the Los Pijiguaos bauxite deposit, Venezuela. The overlap between the gibbsite and kaolinite zones and the replacement of kaolinite by gibbsite are consistent with model calculations. Mechanical denudation has to be called upon to explain the limited thicknesses of the weathering profiles in the field. The role of mechanical erosion is supported by the presence of microsedimentary structures in the bauxite and the balance between dissolved and suspended loads in the streams draining the area.  相似文献   

2.
Bauxite deposits of Mainpat Plateau Surguja District, India, are composed of kaolinite, gibbsite, goethite, anatase, and bohemite. Quartz and micas are absent in the samples. The presence of boehmite and goethite are evidences of intense weathering during the formation of the bauxite deposits. The Mainpat Plateau is a mesa landform, at an elevation of around 1,060 m from msl in comparison to the general elevation of 580, consisting of Archaeans (granite?gneisses, phyllite, etc.) at the base, Gondwanas and Deccan basalt, and at the top having a cover of laterite and bauxite. The extremely high values of the chemical index of alteration, and the low values of the alkali metals and alkali earth metals, support an intense weathering origin for the bauxite deposit. There is evidence of deposition in the deposits based on the presence of pisoids in the bauxite samples and the composition of the parent rock. Kaolin minerals were first produced by the hydrolytic weathering of aluminous sediments and then gibbsite was formed as early kaolin was desilicated. The bauxite is having high TiO2 up to 17 %. The Mainpat laterite/bauxite deposits are characterized by having 50?58 % average Al2O3 and 10?30 % Fe2O3.  相似文献   

3.
《Geochimica et cosmochimica acta》1999,63(23-24):3939-3957
A simple geochemical balance of lateritization processes governing the development of several tens of meters of weathering profiles overlain by ferricretes is estimated on the basis of detailed mineralogical and geochemical data. The lateritic weathering mantle of the “Haut–Mbomou” area in Central Africa is composed of different weathering layers described from the base to the top of vertical profiles as a saprolite, a mottled clay layer, a soft nodular layer, a soft ferricrete, and a ferricrete in which kaolinite, gibbsite, goethite, and hematite occur in various quantities. Incongruent dissolution of kaolinite leads to the formation of gibbsite in the upper saprolite, whereas the hematite does not clearly replace the kaolinite according to an epigene process in the upper ferruginous layers of the profiles. Instead, that kaolinite is also transformed into gibbsite according to an incongruent dissolution under hydrated and reducing conditions induced by a relatively humid climatic pattern. The respective relations of the silica, iron, and aluminum balances and the Al substitution rate of the hematite on the one hand, and of RHG [RHG = 100 (hematite/hematite + goethite)] and the kaolinite on the other hand, to the consumption or the release of protons H+ permit differentiation of aggrading ferruginization and degradation processes operating in the different lateritic weathering profiles. The Al substitution rate of the Fe–oxyhydroxides varies according to the nature of lateritization processes, e.g., saprolitic weathering and aggrading ferruginization vs. degradation. The observations and results indicate that the ferruginization process of the weathering materials of parent rocks is not a simple ongoing process as often thought. This suggests that the actual lateritic weathering mantle of the Haut–Mbomou area may result from different stages of weathering and erosion during climatic changes.  相似文献   

4.
The intra- and epicontinental basins in north-east Africa (Egypt, Sudan) bear ample evidence of weathering processes repeatedly having contributed to the formation of mineral deposits throughout the Phanerozoic.The relict primary weathering mantle of Pan-African basement rocks consists of kaolinitic saprolite, laterite (in places bauxitic) and iron oxide crust. On the continent, the reaccumulation of eroded weathering-derived clay minerals (mainly kaolinite) occurred predominantly in fluvio-lacustrine environments, and floodplain and coastal plain deposits. Iron oxides, delivered from ferricretes, accumulated as oolitic ironstones in continental and marine sediments. Elements leached from weathering profiles accumulated in continental basins forming silcrete and alunite or in the marine environment contributing to the formation of attapulgite/saprolite and phosphorites.The Early Paleozoic Tawiga bauxitic laterite of northern Sudan gives a unique testimony of high latitude lateritic weathering under global greenhouse conditions. It formed in close spatial and temporal vicinity to the Late Ordovician glaciation in north Africa. The record of weathering products is essentially complete for the Late Cretaceous/Early Tertiary. From the continental sources in the south to the marine sinks in the north, an almost complete line of lateritic and laterite-derived deposits of bauxitic kaolin, kaolin, iron oxides and phosphates is well documented.  相似文献   

5.
Bauxite is the ultimate fine-grained products of chemical weathering,and thus it is closely linked with the intense chemical weathering. Based on variations of parent rock and weathering processes,the weathering products can be subdivided into laterite and terra rossa,of which the former is formed by weathering of aluminosilicates and the latter is produced by the weathering of carbonates. During the intense chemical weathering,minerals in original subaerial sediments(parent rocks)would suffer a series of processes(dissolution,hydrolyzation,hydration,carbonation,and oxidation)and be destroyed or transformed,leading to formation of new minerals. In the favorable environment,continuously intense chemical weathering would cause the loss of most mobile elements(e.g., K,Na,Ca,Mg,Si)and the enrichment of Al,resulting in the formation of bauxite. Although sedimentary bauxites are closely linked with the weathering curst,they show obvious differences in formation processes. Sedimentary bauxites are composed of intense chemical weathering products that are transported from outside of the basin and re-deposited in the basin,while most weathering crusts are transformed from saprolite and/or deluvium in-situ,and they can only form low-grade bauxites. Sedimentary environments also differ in bauxite ore layers and bauxitic claystone layers. Bauxite ore layers are formed in the subaerial environment and controlled by the leaching process of groundwater in the vadose zone. Based on the analysis of bauxitization,this study proposes to use multiple parameters,such as provenance,sedimentation and mineralization,to build the new classification of Chinese bauxite deposits. In this classification,lateritic and karstic types of bauxite deposits are autochthonous or parautochthonous saprolite and/or deluvium,while sedimentary type is dominated by heterochthonous provenance.  相似文献   

6.
Los Pijiguaos bauxite deposit is located in Southern Venezuela, in a tropical rain forest environment. Among the various impurities during the bauxite processing (Bayer process), organic matter compounds present in Bayer liquor can slow the rate of alumina precipitation, and reduce product yield and quality. Soil samples were taken from a 37-m-deep core and the distribution of organic carbon (OC) was investigated as well as its relationship with major oxides Al2O3, Fe2O3, SiO2 and with the mineral phases gibbsite, hematite, kaolinite and quartz. Each sample was subjected to an adsorption process of humic acids by interaction with solutions of known concentrations. Maximum adsorption capacity was also studied in each mineral separately, which allowed calculation of the theoretical adsorption capacity of each soil sample. Even if concentrations of OC were higher in the first 5 m of the profile (0.2–0.5%), samples exhibited a low adsorption capacity (0.02%), while at depth between 10 and 37 m, samples showed lower OC concentrations (0.03–0.05%), and a larger OC adsorption capacity (0.08%). The model for the adsorption capacity only works between 10 and 30 m of depth, since in the first 10 m the bauxitic profile seems to be saturated in OC, because the concentration of OC is higher than the maximum predicted by adsorption experiments.  相似文献   

7.
The Dajia Salento-type bauxite deposit in western Guangxi is hosted within the Quaternary ferrallitic soil profile, and it formed via breaking up, weathering and oxidizing of Permian bauxite orebodies occurring as a semi-continuous layer in the upper Permian. Mineralogical analyses reveal that diaspore, hematite and kaolinite are the major minerals in bauxite ores with small amounts of anatase, chamosite, gibbsite, goethite, illite, zircon, quartz and pyrite. The ore texture and mineral assemblage reveal that the depositional/diagenetic environment of the Dajia bauxite was much close to phreatic environment. Both the ore texture and the morphology of zircon grains also indicate that most of the bauxitic soils were transported a short distance. Diaspore is suggested to be non-metamorphic in origin and mainly formed in a reducing condition of diagenetic environment, while kaolinite is the product of the in situ epigenetic replacement of alumina in diaspore by dissolved silica. Geochemical analyses indicate that Al2O3, Fe2O3, SiO2 and TiO2 are the main components of the bauxite ores and trace elements such as Zr, Hf, Nb, Ta, Th and U were enriched during the bauxitization process. Simultaneously, Zr vs. Hf and Nb vs. Ta show a high correlation. Geochemical indices such as Zr/Hf, Nb/Ta and Eu/Eu* (among others) denote that the magmatic rocks related to the Emeishan plume in western Guangxi and the carbonates in the underlying Maokou Formation provided the main sources of material for the bauxite ores.  相似文献   

8.
Bauxite deposits of the Fria district, Guinea, have been exploited since 1960. These lateritic bauxites, located on the upper parts of plateaus, result from weathering of paleozoic schists. The ores are composed of gibbsite associated with pyrophyllite, Al-substituted gœthite, and kaolinite. Pyrophyllite and Al-substituted gœthite may contain up to 9% of the total Al2O3 content of the bauxite; this cannot be recovered through the Bayer process because these phases are insoluble in the leaching solutions. Kaolinite is soluble under Bayer leaching but this dissolution induces precipitation of sodium aluminosilicates, which apart from loss of further alumina results in decreasing efficiency of the process through scale formation. Detailed knowledge of the distribution of the different ore types and their mineralogical composition is necessary for efficient processing.  相似文献   

9.
The present study examines a fossil saprock–saprolite–laterite-profile beneath the sub-Cambrian peneplain in the Pan-African Roded Granite, Israel, with regard to structure and magnetic fabrics (anisotropy of magnetic susceptibility, AMS), and image analysis of compaction. The deformed granite shows two pre-weathering foliations, S1m (magmatic) and S2g (gneissic). Pre-Early Cambrian weathering comprised weathering-brecciation in saprock and saprolite, and chemical weathering with clay-formation in saprolite and laterite. During subsequent Phanerozoic burial the laterite was vertically compacted to 73% of its original thickness. In the laterite, compaction produced an unconformity-parallel cleavage (S3d) with increasing intensity towards the unconformity. Bulk susceptibility (κbulk) and anisotropy (P′) decrease from the unweathered granite into the saprolite, as a result of progressive magnetite breakdown, martitization and weathering-brecciation. In the laterite, an enrichment of haematite and relic Fe–Mg–mica lead to increased κbulk. Here, magnetic fabrics trace the compaction fabrics. The subhorizontal, compactional clay–/mica-fabric S3d defines a structurally weak and impermeable layer. The mechanical weakness of a clay-enriched weathering horizon with an unconformity-parallel, planar shape-preferred orientation, combined with the potentially overpressured state due to the sealing character of such a zone provides a viable explanation for the abundant localization of decollement horizons at or beneath basement-cover interfaces.  相似文献   

10.
华北克拉通在中奥陶世至晚石炭世期间一直出露地表,经历了长期的风化作用,形成大规模的铁-铝黏土矿,其成矿物源一直是研究的热点,尤其是本溪组底部铁矿和铁质黏土矿与上部铝黏土矿是否为同一来源尚未查清。本研究选取克拉通南缘大安铝黏土矿床作为研究对象,展开微区矿物及元素地球化学组成分析,进一步探讨铁-铝黏土矿物质来源。大安矿床内含矿岩系自下而上包括铁质黏土岩、铝土矿、铝质黏土矿;局部喀斯特高地缺失铝土矿,铝质黏土矿直接覆盖于铁质黏土岩之上。铁质黏土岩在洼地以菱铁矿、黄铁矿和伊利石为主,在隆起区以赤铁矿、伊利石和高岭石为主。铝土矿以硬水铝石、伊利石和锐钛矿为主;铝质黏土矿主要矿物为伊利石。矿物微区分析在黏土矿底部发现大量的碳化硅和少量自然硅、硅铁矿、铬铁矿;区域对比揭示北秦岭造山带内商丹缝合带和二郎坪群中的蛇绿岩为铝黏土矿形成提供了成矿物质。本溪组底部铁质黏土与上部铝黏土矿稳定元素比率(例如Zr/TiO2、Hf/TiO2、Nb/TiO2、Ta/TiO2)存在明显差异,揭示二者为不同来源: 底部铁质黏土岩和铁矿层为底板碳酸盐岩原地风化的产物;而上部铝黏土矿是异地搬运物,北秦岭造山带在晚石炭世的整体抬升为华北铝黏土矿形成提供了重要的成矿物质。  相似文献   

11.
During the Middle Ordovician to Late Carboniferous period,the North China Craton(NCC)was exposed and experienced prolonged weathering that resulted in the formation of large-scale iron,clay and bauxite deposits. The source of ore-forming material has always been a research focus,in particular,whether the sources of the iron ore and the Fe-bearing clay at the bottom of Benxi Formation are the same as the upper bauxite and clay deposit is still unclear. In this study,the Da'an bauxite and clay deposit at the southern margin of the NCC was chosen to carry out a detailed analysis of the micro-region mineral composition and elemental geochemical characteristics for further exploring the sources of iron,bauxite and clay deposits. The composition of the ore-bearing rocks in the Da'an bauxite deposit from the bottom to top includes Fe-bearing clay(locally iron ore),bauxite,and bauxitic clay;locally,in karstic uplift,bauxitic clay layer is directly overlying on the Fe-bearing clay. The Fe-bearing clay is dominated by siderite,pyrite,and illite in the karstic depression,and hematite,illite,and kaolinite in the uplift. Bauxite is mainly composed of diaspore,illite,and anatase,while bauxitic clay is mainly composed of illite. Mineral microanalysis revealed the development of large amounts of moissanite and small amounts of natural silica,silicalite,and chromite at the bottom of bauxitic clay layer. Regional comparison and correlation reveal that the ophiolite in the Shangdan suture zone and Erlangping Group in the North Qinling orogenic belt(NQOB)likely provides source materials for bauxite and clay deposits. The obvious differences in immobile element ratios (e.g., Zr/TiO2,Hf/TiO2,Nb/TiO2,Ta/TiO2)between the bottom Fe-bearing clay layer and the upper bauxite and clay layer in Da'an deposit,revealing that they are from different sources. The bottom Fe-bearing clay and iron ore layers are the products of in-situ weathering of underlying carbonates,while the top bauxite and clay are allochthonous. The regional uplift of the NQOB during the Late Carboniferous period provided important ore-forming materials for the formation of the NCC bauxite and clay deposits.  相似文献   

12.
Abstract. The Dholkata bauxite deposit of Keonjhar district, Orissa, has developed on the metavolcanics of tholeiitic basalt composition. The weathered profile reveals five distinct altered zones, such as topsoil, laterite, bauxite, lithomarge and altered metavolcanics. The mineralogy of different zones studied in a representative pit shows the association of major mineral constituents like gibbsite, goethite, hematite, kaolinite, limonite and quartz. Gibbsite is the most dominant one followed by goethite and hematite in the bauxite zone. The geochemical study of all weathering zones indicates the geochemical affinity of the elements Ni, Th and U for laterites and Cr, Zr and Hf for bauxites to occur in high quantities. Trend surface maps predict the bauxite zones in the different levels of the deposit. If the zones having A12O3 35–40 % are blended with high grade ores, the deposit may prove to be a potential one.  相似文献   

13.
Karstic bauxite deposits are widespread in Central Guizhou Province, SW China, and high-grade ores are frequently sandwiched with overlying coal and underlying iron-rich layers and form a special “coal–bauxite–iron” structure. The Lindai deposit, which is one of the most representative karstic bauxite deposits in Central Guizhou Province, was selected as a case study. Based on textural features and iron abundances, bauxite ores in the Lindai deposit are divided into three types of ores, i.e., clastic, compact, and high-iron. The bauxite ores primarily comprise diaspore, boehmite, kaolinite, illite, and hematite with minor quartz, smectite, pyrite, zircon, rutile, anatase, and feldspar. The Al2O3 (53–76.8 wt.%) is the main chemical contents of the bauxite ore samples in the Lindai district, followed by SiO2, Fe2O3, TiO2, CaO, MgO, S, and P etc. Our geological data on the Lindai deposit indicated that the ore-bearing rock series and its underlying stratum have similar rare earth elements distribution pattern and similar Y/Ho, Zr/Hf, and Eu/Eu1 values; additionally, all ore-bearing rock samples are rich in MgO (range from 0.16 wt.% to 0.68 wt.%), and the plots of the dolomites and laterites lie almost on or close to the weathering line fit by the Al-bearing rocks in Zr vs. Hf and Nb vs. Ta diagrams; suggesting that the underlying Middle Cambrian Shilengshui Formation dolomite is the parent rock of bauxite resources in the Lindai district.Simulated weathering experiments on the modern laterite from the Shilengshui Formation dolomite in the Lindai bauxite deposit show that hydrogeological conditions are important for karstic bauxite formation: Si is most likely to migrate, its migration rate is several magnitudes higher than those of Al and Fe under natural conditions; the reducing inorganic acid condition is the most conducive to Al enrichment and Si removal; Fe does not migrate easily in groundwater, Al enrichment and Fe removal can occur only in acidic and reducing conditions with the presence of organic matter.The geological and experimental studies show that “coal–bauxite–iron” structure in Lindai deposit is formed under certain hydrogeological conditions, i.e., since lateritic bauxite or Al-rich laterite deposited upon the semi-closed karst depressions, Si can be continuously removed out under neutral/acidic groundwater conditions; the coal/carbonaceous rock overlying the bauxitic materials were easily oxidized to produce acidic (H2S, H2SO4, etc.) and reductant groundwater with organic materials that percolated downward, resulting in enrichment of Al in underlying bauxite; it also reduced Fe3+ to its easily migrating form Fe2+, moving downward to near the basal carbonate culminated in precipitating of ferruginous (FeS2, FeCO3, etc.) strata of the “coal–bauxite–iron” structure. Thus, the bauxitic materials experienced Al enrichment and Si and Fe removal under above certain hydrogeological conditions forming the high-quality bauxite.  相似文献   

14.
铝土矿是化学风化作用的细粒终极产物,与强烈的化学风化作用密切相关。根据母岩的类别及作用过程,风化作用进一步分为铝硅酸盐岩强化学风化形成的红土化作用和碳酸盐岩强化学风化形成的钙红土化作用。在强烈的化学风化过程中,地表的原始沉积物(母岩)的原生矿物发生溶蚀、水解、水化、碳酸化、氧化,破坏原始的矿物结构,形成新的细粒矿物(主要是黏土质矿物)。在适合的地质条件下,持续的强烈化学风化作用会造成大部分活动的元素(如K、Na、Ca、Mg、Si)的流失与Al的残留富集从而形成铝土矿。现在观察到的沉积型铝土矿,虽然与古风化壳具有密切联系,但沉积型铝土矿多数是由沉积过程搬运到沉积盆地中所形成的强化学风化产物的沉积层,与古风化壳的残坡积层具有显著差别,只有少数工业价值不大(品位低、品质差)的残坡积相铝土矿。铝土矿含矿岩系的沉积环境与铝土矿(尤其是高品位、高品质的铝土矿)的成矿环境不尽相同。铝土矿主要形成于暴露于大气中的陆表环境(而非水下环境),由地下水淋滤作用形成(在渗流带由活动元素流失、Al等稳定元素残留富集而成)。本研究在铝土矿成矿作用分析等基础上,提出了以铝土矿沉积物等物源和沉积、成矿作用为依据的中国铝土矿床分类方案,包括原地或准原地残坡积物成因的红土型和喀斯特型,和异地物源沉积成因的沉积型。  相似文献   

15.
《Applied Geochemistry》2002,17(7):885-902
An ancient saprolite has developed on the Palaeoproterozoic granulite, granite gneiss and amphibolite bedrock of the Vuotso–Tankavaara area of central Finnish Lapland. The present day climatic regime in Finnish Lapland lies within the northern boreal zone and so the saprolite there can be regarded as fossil. Cores of saprolite were collected from 4 sections (42 samples) and analyzed chemically and mineralogically. In the study area, progressive weathering of the rocks has been marked by gradual enrichment in Al, Fe and Ti; and depletion of Na, K and Ca. The higher concentration of Fe(III) and water and reduced Na and Ca in weathered bedrock in the 4 sections are indicative of oxidation, hydration and leaching processes involved during weathering. The primary minerals in the saprolite are plagioclase feldspar, K-feldspar, quartz, garnet (almandine) and hornblende; the common secondary minerals are kaolinite, halloysite, and vermiculite in addition to minor amounts of sericite. Intense weathering is indicated by: (1) the presence of kaolinite and halloysite in 4 sections of different bedrock types, and (2) the comparatively lower SiO2/Al2O3 (wt.%) ratio (2.30) of weathered granulites (3 sections) as compared to fresh granulite (4.33) and that of weathered amphibolite (2.68) as compared to fresh amphibolite (3.56). In general, kaolinite and halloysite have formed through the weathering of feldspars, garnet, and biotite. Vermiculite is the most probable alteration product of biotite. The formation of kaolinite and halloysite in Finnish Lapland indicates wetter and warmer climatic conditions during the time of their formation than at present. The possible time for formation of the saprolite is early Cretaceous–early Tertiary into Middle Miocene.  相似文献   

16.
重庆南川-武隆铝土矿属于渝南-黔北铝土矿成矿带,为喀斯特型铝土矿床。经显微镜、X射线粉晶衍射、矿物自动分析仪（MLA）、扫面电子显微镜等方法对该矿床矿物学的研究,发现组成铝土矿的主要矿物为一水硬铝石、高岭石、绿泥石,次要矿物为伊利石、一水软铝石、三水铝石、鲕绿泥石、菱铁矿、赤铁矿、针铁矿、黄铁矿、锐钛矿、金红石、磷灰石、石英、锆石、方解石、长石及稀土矿物等。矿石组构及矿物组合表明形成铝土矿的沉积/成岩环境为接近于潜流的环境。矿石结构和锆石形态指示成矿物质经过了短距离的搬运。地球化学研究结果显示,组成铝土矿的主要化学成分为Al2O3、TFeO、SiO2和TiO2,铝土矿化过程中REE、Zr、Hf、Nb、Ta、Th、Sc、Li和Ga发生富集。形成铝土矿的母岩物质主要来自下伏页岩的风化作用,灰岩和酸性火山岩对铝土矿的形成也有一定的贡献。结合稳定同位素资料,认为铝土矿的形成可能与生物作用有关。  相似文献   

17.
Ge/Si and 87Sr/86Sr data from primary and secondary minerals, soil waters, and stream waters in a tropical granitoid catchment quantitatively reflect mineral alteration reactions that occur at different levels within the bedrock–saprolite–soil zone. Near the bedrock–saprolite interface, plagioclase to kaolinite reaction yields low Ge/Si and 87Sr/86Sr. Higher in the regolith column, biotite weathering and kaolinite dissolution drive Ge/Si and 87Sr/86Sr to high values. Data from streams at base flow sample the bedrock–saprolite interface zone, while at high discharge solutes are derived from upper saprolite–soil zone. Coupled Ge/Si and 87Sr/86Sr can be effective tools for quantifying the importance of specific weathering reactions, and for geochemical hydrograph separation.  相似文献   

18.
The Belterra Clay in Northern Brazil is a uniform, yellowish, unstratified kaolinitic clay with variable contents of gibbsite. It is generally 5–10 m thick and covers a lateritic weathering crust on remnants of a dissected table-land. Complete profiles with Belterra Clay, the underlying bauxite/laterite and saprolite/bed rock were sampled in three areas of the Amazon region. The chemical and mineralogical data show a distinct affinity between the Belterra Clay and the underlying layers above all with the saprolite. Variations in the composition of the underlaying layers are reflected by the Belterra Clay. Among the structural and textural features important for the discussion of the origin of the Belterra Clay are the sharp contact between the clay cover and the underlying laterite as well as conglomeritic/brecciate textures and occasional bedding structure in the upper part of the lateritic crust. The detailed analyses do not permit definite conclusions on the origin of the Belterra Clay. Three hypotheses ar discussed:
  1. In-situ formation of the clay cover by weathering processes.
  2. Clay deposition after lateral transport of saprolitic material coming from former elevations inside or outside the present laterite areas.
  3. Vertical transport of the saprolitic material to the surface by termites. However, thicknesses up to 20 m of the Belterra Clay cannot be explained solely by this process.
The compositional relations of the Belterra Clay with the underlying layers are of practical relevance for geological mapping and for mineral exploration.  相似文献   

19.
广西红土型高铁三水铝土矿资源潜力预测   总被引：1，自引：0，他引：1  
王瑞湖  李梅  陈定雄 《地质通报》2011,30(8):1303-1311
在对区域成矿特征与典型矿床研究的基础上,系统总结了广西红土型高铁三水铝土矿的成矿地质特征,深入分析了红土型高铁三水铝土矿成矿的控制因素。进而运用基于GIS的“矿床模型综合地质信息预测方法”对广西红土型高铁三水铝土矿进行了综合定位和定量预测,共圈定了42个最小预测区,估算未查明预测资源量7.67×108t。该成果对广西红土型高铁三水铝土矿进一步勘查开发具有重要的指导意义。  相似文献   

20.

Weathering profiles developed on granitic rocks, exposed in the breakaways of the Barr‐Smith Range in the N of the Yilgarn Block of Western Australia, consist of kaolinitic saprolites merging upwards into silcrete, sandstone and grit. The sandstones and silcretes may also form columns or dykes, penetrating downwards into the saprolite. The silcretes are cemented by quartz and anatase, with zircon (QAZ‐cement), and‐the sandstones are cemented by aluminosilicates, either apparently amorphous (as siliceous allophane) or partly crystalline, as kaolinite and opaline silica. Transitional zones between silcretes and sandstones have all cement types. The profiles are characterized by low concentrations of alkalis and alkaline earths and most metals. The QAZ‐silcrete horizons may contain over 3% TiO2 and 1000 p.p.m. Zr. The profiles evolved through at least four stages: (i) Formation of the deep saprolite‐sand weathering profile by kaolinization of feldspar and mica at depth, and the solution of kaolinite near the top of the profile, causing settling of resistant quartz grains, (ii) Precipitation of QAZ‐cement, the TiO2 and SiO2 being derived partly by lateral migration from upslope. (iii) Precipitation of aluminosilicates, in the sandstone and the saprolite. (iv) Erosion and exposure of the profiles by pedimentation. A similar profile occurs further S, at Gabbin, but no QAZ‐silcrete is present and the only exposures are in exploration pits. The kaolinitic saprolite‐quartz sand profiles probably formed under humid conditions, as the equivalents of ferruginous laterite developed on more basic rocks nearby and of lateritic bauxite in the Darling Range. However,’ the sand was a surface horizon and there is no evidence that there was ever a ferruginous zone at these sites. The sequential precipitation of QAZ‐ and aluminosilicate‐cements was probably, a response to increasing aridity and reduced groundwater flow. Aluminosilicate‐cemented materials tend to disaggregrate on exposure but they are probably more abundant than the more prominent QAZ‐silcretes.  相似文献   

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