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1.
The lanthanide tetrad effect was investigated in a 5.4 m thick terra rossa profile overlying dolomite on the Yunnan-Guizhou Plateau, China. The results demonstrate that the chondrite-normalized rare earth element pattern of dolomite bedrock displays a W-type tetrad effect. The insoluble residue from the dolomite bedrock does not exhibit any significant tetrad effect. In contrast, some ferromanganese concretions and the terra rossa show tetrad effect. It is worth noting that the conjugate M- and W-types of the tetrad effect are observed in some terra rossa samples. The tetrad effect in the ferromanganese concretions and the terra rossa possibly originates from redistribution of dissolved rare earth elements during their downwards movement in the profile and not only from water/rock interaction. Within the dolomite weathering system, the ferromanganese concretions and surrounding terra rossa present similar correlations of Eu/Eu*, Y/Ho, Sm/Nd, Ce/Ce*, with the size of the tetrad effect. The ferromanganese concretions and the terra rossa with tetrad effect are characterized by a reduced, non-chondritic Y/Ho ratio. Also the Y/Ho ratio exhibits a clear negative correlation with the size of the tetrad effect in the ferromanganese concretions and the terra rossa. In addition, the Eu/Eu* tends to increase with increasing size of the tetrad effect in the ferromanganese concretions and the terra rossa, as does the Sm/Nd ratio. The regular variation for Eu/Eu*, Y/Ho and Sm/Nd is likely a result of the fractionation of rare earth elements and yttrium with the tetrad effect. On the other hand, the correlation of the Ce/Ce* with the size of the tetrad effect in the ferromanganese concretions and the terra rossa is random. This likely indicates that the Ce behavior within weathering system is mainly controlled by redox condition, rather than tetrad effect. Comparative study indicates that the correlations of Eu/Eu*, Y/Ho, Ce/Ce*, with the size of the tetrad effect in the ferromanganese concretions and the terra rossa, are not similar to those found in a highly evolved igneous system. Nevertheless, the correlation of Sm/Nd with the size of tetrad effect in weathering system is similar to that in igneous system. In general, it appears to indicate that the tetrad effect occurrence in granitic rocks is not associated with weathering. 相似文献
2.
The mobilization, redistribution and fractionation of trace elements during chemical weathering processes have been investigated on a 4.05 m thick terra rossa profile overlying dolomite on the Yunnan-Guizhou Plateau, in Southwest China. In this in situ weathering profile, the ferromanganese concretions and the gibbsite spots coexist in the terra rossa saprolite. The mass-balance evaluation reveals that titanium, Nb and Hf in the terra rossa matrix are conservative elements during chemical weathering compared to Zr. The elements of Li, Sc, V, Cr, Fe, Ga, As, Mo, Cs, Ce, Ta, Tl, Pb and Th in the terra rossa matrix include additions from external sources. Beryllium, Mn, Co, Ni, Cu, Rb, Ba and La are depleted in the shallow parts of the terra rossa profile and enriched in the deep parts. The elements of Zn, Sr, Y, Cd, Sn and U in the terra rossa profile are lost during weathering. Compared to the terra rossa matrix, the ferromanganese concretions are significantly enriched in most trace elements, especially Mn, Co, Cd, Ce, Tl and Pb. In contrast, the gibbsite spots are depleted in all trace elements, except for U. The results regarding specific inter-element relationships indicate that most trace elements have different inter-element relationships in the ferromanganese concretions, the gibbsite spots and the terra rossa matrix. This suggests that the behavior of many trace elements during mobilization and redistribution differs from their behavior during incorporation into secondary mineral phases, especially the Mn and Fe oxides and/or oxyhydroxides in the ferromanganese concretions. It is worthy to note that the fractionation between Ce and Mn occurs under intensive chemical weathering conditions. Correspondingly, beryllium exhibits a similar geochemical behavior as that of rare earth elements (except for Ce) and Y during surface weathering. 相似文献
3.
The purpose of this study was to determine and evaluate the geochemical characteristics of the limestone of the Upper Cretaceous Mortas Formation and related terra rossa in a 50 km2 area which is located 20 km south of the city of Seydisehir, Central Anatolia, by using data obtained from the ICP-MS analysis of randomly collected 42 samples of limestone and 18 samples of the terra rossa.The limestone of the Mortas Formation is composed of fossilliferous, gray-cream colored, medium to thick bedded, partially dolomitic carbonate rocks, and generally has dismicrite, intrapelmicrite composition. It includes the largest bauxite reservior in Turkey and has many occurences of terra rossa formation on it. According to mean distance, the Ba, Be, Hg, Mo, Nb, Sb and Th concentrations in the limestones overlying and underlying the bauxite deposits are different, but the main oxides, REE and other trace elements are same. In factor analysis, the first component reflects relative enrichment of clay against to CaO contents of the limestone, the second component corresponds to the degree of dolomitization. The PAAS-normalized REEs pattern for the Mortas Formation limestone samples illustrate similar main features as seawater.The terra rossa soils in the study area are considered to be highly weathered and weakly mature soil with respect to their generally low Al2O3 (21%), but high CaO (2%) contents, and their alteration indices. The element ratios in the terra rossa and limestone show that in the process of the transformation from limestone to terra rossa, Ba, Si, Ti, Al and Fe were enriched together by staying in-situ. Except Ce, all lanthanides show similar behavior, but the HREE, which were richer in limestone, were consumed fast relative to the LREE during soil formation. The association and the enrichment of Co, Cu, Cr, Ni and Pb as well as Ba, Zr, Ga, Nb and Rb in soil relative to the limestone are interpreted as being resulted from eolian transportation. Ca, Au, Hg, Sr, Se, Sb, Mo, Ag, U, Cd and Na were found to be the most mobile elements during pedogenic transformation. According to main oxide composition ratios of the limestone and terra rossa, the soils were described as representing a well washed soil completing the leaching and accumulation phase, but not totally completing the silicate weathering phase. In the processes of soil formation, 97.76% of the limestone was washed away; only 2.24% of limestone was deposited as soil. Therefore, 61 times mass reduction was realized. 相似文献
4.
通过与粉尘堆积,以及玄武岩和片麻杂岩风化剖面磁组构的对比,探讨了以贵州平坝白云岩之上红色粘土剖面磁组构特征及其成因指示意义。红色粘土的各向异性较弱,并且不具有明显的沉积磁组构;母岩的组构特征对红色粘土磁化率各向异性没有明显的控制“痕迹” ;红色粘土与粉尘堆积物之间磁组构特征的明显差异,表明它们在物源和形成机制方面是不同的;红色粘土磁化率及磁组构特征反映出红色粘土中磁性矿物的物质来源和成因具有一定的特殊性。 相似文献
5.
The Jinshajiang–Red River alkaline igneous belt in the eastern Indian–Asian collision zone, of southwestern China, hosts abundant, economically important Cu–Mo–Au mineralization of Cenozoic age. Major- and trace-element compositions of titanites from representative Cu-mineralized intrusions determined by LA-ICP-MS show higher values for Fe2O3/Al2O3, ΣREE?+?Y, LREE/HREE, Ce/Ce*, (Ce/Ce*)/(Eu/Eu*), U, Th, Ta, Nb and Ga, and lower values for Al2O3, CaO, Eu/Eu*, Zr/Hf, Nb/Ta and Sr than those for titanites from barren intrusions. Different ΣREE?+?Y, LREE/HREE, U, Th, Ta and Nb values of titanites between Cu-mineralized and barren intrusions were controlled mainly by the coexisting melt compositions. However, different Sr concentrations and negative Eu anomalies of titanites between Cu-mineralized and barren intrusions were most probably caused by different degrees of crystallization of feldspar from melts. In addition, different Ga concentrations and positive Ce anomalies of titanites between Cu-mineralized and barren intrusions were most likely caused by different magmatic fO2 conditions. Pronounced compositional differences of titanites between Cu-mineralized and barren intrusions can provide a useful tool to help discriminate between ore-bearing and barren intrusions at an early stage of exploration, and, thus, have a potential application in exploration for porphyry Cu deposits in the Jinshajiang – Red River alkaline igneous belt, and to other areas. 相似文献
6.
开展热带岩溶地区红色风化壳元素地球化学演化规律研究,有助于丰富碳酸盐岩风化成土理论的认识。在越南北部选取典型的碳酸盐岩风化剖面,分析热带气候条件下碳酸盐岩上覆红色风化壳中主量元素的物质来源和演化特征。结果表明:无论Ti/Zr的元素比值分析,Hf-Zr、Nb-Ta及Sm-Nd的元素对协变分析,还是上地壳元素平均值(UCC)标准化分析,两个剖面的上覆风化壳均显示原地残积的特征,即两个剖面是碳酸盐岩的原位风化产物。碳酸盐岩风化成土过程中,CaO、MgO淋失明显,Al_2O_3和Fe_2O_3发生富集,显示两个剖面均经历较强的风化过程,但是白云岩和灰岩剖面有一定的分异特征。越南北部白云岩风化剖面从基岩到上部土层显示出稳定的Ti-Fe元素共富集特征,而灰岩剖面中Fe的增长速率明显超过Ti。白云岩上覆风化壳经历了强烈的风化作用,其脱硅作用弱于灰岩风化剖面,而富集铝的作用强于灰岩。迁移系数的演化规律说明两个剖面中长石成分(钾长石、钠长石等)或次生矿物(伊利石等)在风化成土过程中逐渐分解,同时Al、Fe、Si等稳定元素的在风化剖面中不断富集。 相似文献
7.
H. M. Zakir Hossain Quazi Hasna Hossain Atsushi Kamei Daisuke Araoka 《Arabian Journal of Geosciences》2018,11(23):749
The modal and chemical composition of sands from Cox’s Bazar beach (CBB) and Kuakata beach (KB) areas of Bangladesh has been investigated to infer their maturity, chemical weathering, and provenance signatures. The CBB and KB sands are typically high quartz, low feldspar, and lithic fragments, representing a recycled orogen source. Major element compositions of CBB sands are characterized by high SiO2 (83.52–89.84 wt%) and low Al2O3 (4.39–6.39 wt%), whereas KB sands contained relatively low SiO2 (63.28–79.14 wt%) and high Al2O3 (9.00–11.33 wt%) contents. The major, trace and rare earth element (REE) compositions of beach sands display comparable distribution patterns with enriched Th and SiO2 for both sands relative to upper continental crust (UCC). Pb, Rb, Y, and Fe for KB sands are little higher than UCC and the rest of the elements are marked depleted for both suites reflecting destruction of plagioclase and K-feldspar during fluvial transportation. The CBB and KB sands are compositionally low mature to immature in nature subsequently classified as subarkose and litharenite, respectively. Chondrite-normalized REE patterns for CBB and KB sands show LREE enrichment and nearly flat HREE (LaN/YbN, 7.64–9.38 and 5.48–8.82, respectively) coupled with prominent Eu anomalies (Eu/Eu*, 0.51–0.72 and 0.52–0.76, respectively), suggesting felsic source provenance. The provenance discrimination diagrams, immobile trace element ratios (Th/Sc, Zr/Sc, Ce/Sc, and Ti/Zr), and REE (∑LREE/HREE, Eu/Eu* and GdN/YbN) parameters indicate that CBB and KB sands were largely derived from felsic source rocks, with compositions close to average rhyolite, granodiorite, granite, and UCC. 相似文献
8.
《Chemical Geology》2004,203(1-2):29-50
The aim of this study is to characterize the evolution of the rare earth elements (REE) in the Pingba red residua on karst terrain of Yunnan-Guizhou Plateau. The in-situ weathering and the two-stage development of the profile had been inferred from REE criterions. The REE were significantly fractionated, and Ce was less mobilized and separated from the other REEs at the highly enriched top of the profile. This is consistent with the increase of oxidation degree in the regolith. And it is also suggested that the wet/dry climate change during chemical weathering caused Ce alternative change between enrichment and invariance in the upper regolith. Chondrite-normalized REE distribution patterns for samples from dolomites and the lower regolith are characteristic of MREE enrichment and remarkable negative Ce-anomalies patterns (similar to the convex-up REE patterns). The following processes are interpreted for the patterns in this study: (1) the accumulation of MRRE-rich minerals in dolomite dissolution, (2) water–rock interaction in the weathering front, and (3) more leaching MREE from the upper part of the profile. The latter two explanations are considered as the dominant process for the formation of the REE patterns. Samples from the soil horizon exhibit typical REE distribution patterns of the upper crust, i.e., LaN/YbN=10 and Eu/Eu*=0.65. All data indicate that the leaching process is very important for pedogenesis in this region. The experiments demonstrating that abnormal enrichment of REE at the upper regolith–bedrock interface is caused by a combination of volume change, accumulation of REE-bearing minerals, leaching of REE from the upper regolith, and water–rock interaction during rock–soil alteration processes. Our results support the conclusion that the weathering profile represents a large, continental elemental storage reservoir, whereas REE enrichment occurs under favorable conditions in terms of stable tectonics, low erosion and rapid weathering over sufficiently long time. 相似文献
9.
Lithogenic concentrations of trace metals in soils and saprolites over crystalline basement rocks: A case study from SW Nigeria 总被引：2，自引：0，他引：2
Moshood N. Tijani Olugbenga A. Okunlola Akinlolu F. Abimbola 《Journal of African Earth Sciences》2006,46(5):427-438
In this study, an assessment of the lithogenic concentrations of trace metals in soils and saprolite over basement rock units in Ibadan, SW-Nigeria is presented in respect of bedrock types and geochemical controls on the weathering-associated release of trace metals. Consequently, soil, weathered and fresh rock samples from the Precambrian Basement of SW Nigeria were collected from three different bedrock units within Ibadan metropolis and subjected to mineralogical and geochemical analyses. The analytical results revealed major proportions of oxides in the range of 18–20% Al2O3, 2–6% Na2O and 1–6% K2O for weathered profiles over granite-gneiss and pegmatite units, compared to 2–3% Al2O3, <0.5% Na2O and <1.0% K2O over schist-quartzite. For the trace elements, weathered profiles on granite-gneiss and schist-quartzite settings exhibit similar enrichment trends (enrichment factor, EF l) for most of the trace elements, unlike the pegmatite bedrock. However, enrichments are relatively greater in the top soil unit compared to the intermediate saprolite unit, especially for Pb, Ni, Zn, Cr, Co, Rb, Sr and Ba, a situation attributed to leaching and redistribution within the weathered profiles through pedogenetic process and percolating groundwater.Furthermore, the estimated weathering indices using Ruxton Ratio (RR = {SiO2/Al2O3}) and Chemical Index of Alteration (CIA = 100{Al2O3/[Al2O3 + CaO + Na2O + K2O]}) revealed RR of 2.9–3.7 and CIA of 54–73% for granite-gneiss and pegmatite units, implying medium levels of weathering, compared to RR of 30.8–35.5 and CIA of >60% for schist-quartzite units, which suggest weak chemical weathering. Also, the estimated high percentage loss, especially for Pb, Rb, Sr, Ba relative to the bedrocks, shows that the trace elements can be mobilized within the weathering profiles even at a low degree of chemical weathering. Such weathering-induced release of trace metals is of environmental significance as natural lithogenic input sources and as background reference for future monitoring of possible human/anthropogenic impacts. 相似文献
10.
Behavior of REE Fractionation during Weathering of Dolomite Regolith Profile in Southwest China 总被引：3，自引：0，他引：3
<正>REE fractionation during the weathering of dolomite has been recognized for decades.A regolith profile on dolomite in southwest Yunnan of China was selected to investigate the behaviors of REE during weathering.The weathering of dolomite is divided into two stages:the pedogenesis stage and soil evolution stage,corresponding to the saprolites and soils respectively in the regolith profile. SiO_2,TiO_2,P_2O_5,Zr,Hf,Nb and Ta were immobile components during the weathering by and large, while Al_2O_3,K_2O and Fe_2O_3 were lost during the soil evolution stage in the physical form(clay minerals probably).REE were fractionated during the whole weathering of dolomite.The field weathering profile and the lab acid-leaching experiments on dolomite indicate that MREE were enriched clearly relative to other REE during the pedogenesis stage in a "capillary ascending-adsorption" mechanism, but they did not fractionate clearly in the soil evolution stage.REE were lost and accumulated in the weathering front of dolomite during the soil evolution stage in a "physical-chemical leaching" mechanism. 相似文献
11.
Jingzhe Xu Bo PENG Changxun Yu Guang Yang Xiaoyan Tang Changyin Tan Shurong Xie Xianglin Tu Zhicheng Bao Meijie Quan Min Xiao 《Environmental Earth Sciences》2013,70(1):175-190
The geochemistry of major and trace elements (including heavy metals and rare earth elements) of the fresh and weathered black shales, and the soils derived from black shales in the Ganziping mine area in western Hunan province (China) were studied using the following techniques: X-ray fluorescence (XRF), inductively coupled plasma mass spectrometer (ICP-MS) and X-ray diffraction (XRD). The results show that the black-shale soils are significantly enriched with Al2O3 and Fe2O3, and depleted of mobile elements CaO, Na2O and K2O. The soils are also highly enriched with heavy metals U, V, Ni, Ba, Cu, Zn and Pb, that may cause potential heavy-metal contamination of the soils. Composition of the soils is homogeneous compared to the weathered black shales, for which the concentrations of major elements except CaO and Na2O, and trace elements except heavy metals (U, V, Ni, Ba, Cu, Zn and Pb) as well as the mobile Sr, show lower variations than in the weathered black shales. Ratios of Zr/Hf, Ta/Nb, Y/Ho, Nd/Sm, and Ti/(Ti + Zr), of the soils are also less variable, with values constantly similar to that of the fresh and weathered black shales correspondingly. Thus, components of the soils are believed to be contributed from the parent black shales through weathering and pedogenesis. It is concluded that the soils were formed by at least two stages of geochemical processes: the early stage of chemical differentiation and the later stage of chemical homogenization. The chemical differentiation that was taken during black-shale weathering might have caused the depletion of CaO and Na2O, and the enrichment of Al2O3 and Fe2O3; while the chemical homogenization that was taken during pedogenesis led to the depletion of SiO2 and K2O, and to the further enrichment of Al2O3 and Fe2O3. The heavy-metal enrichment (contamination) of the soils was then genetically related to the enrichment of Al2O3 and Fe2O3 in the soils. 相似文献
12.
The provenance and tectonic setting of sandstones from the Bombouaka Group of the Voltaian Supergroup, in the northeastern part of Ghana, have been constrained from their petrography and whole-rock geochemistry. Modal analysis carried out by point-counting sandstone samples indicates that they are quartz arenites. The index of compositional variability values and SiO2/Al2O3, Zr/Sc, and Th/Sc values indicates that the sediments are mature. The sandstones are depleted in CaO and Na2O. They are, however, enriched in K2O, Ba, and Rb relative to average Neoproterozoic upper crust. These characteristics reflect intense chemical weathering in the source region as proven by high weathering indices (i.e., CIA, PIA, and CIW). In comparison with average Neoproterozoic upper crust, the sandstones show depletion by transition metals and enrichment by high field strength elements. They generally show chondrite-normalized fractionated light rare-earth element (LREE) patterns (average LaN/SmN = 4.40), negative Eu anomalies (average Eu/Eu* = 0.61), and generally flat heavy rare-earth elements (HREE) (average GdN/YbN = 1.13). The sandstones have La/Sc, Th/Sc, La/Co, Th/Co, Th/Cr, and Eu/Eu* ratios similar to those of sandstones derived from felsic source. Mixing calculations using the rare-earth elements (REE) suggests 48% tonalite–trondhjemite–granodiorite and 52% granite as possible proportions for the source of the sandstones. Both the petrographic and whole-rock geochemical data point to a passive margin setting for the sandstones from the Bombouaka Group. 相似文献
13.
The radon-222 (222Rn) activity in groundwater of the Apulian karstic aquifer in southern Italy is as great as 500 Becquerel per liter (Bq/L)
locally. Normal radium-226 (226Ra) activity in the limestone and calcareous dolomites of the aquifer is not enough to explain such a high level. Laboratory
investigations identified high 226Ra activity in the "terra rossa," the residuum occupying fissures and cavities in the bedrock, and also the relation between
(1) 226Ra-bearing bedrock and "terra rossa" and (2) 222Rn in water. The "terra rossa" is the primary source of the radon in the groundwater. The experimental results show the need
to characterize the "terra rossa" of Apulia on the basis of 226Ra activity and also to study the distribution and variations in 222Rn activity over time in the aquifer.
Received, January 1996 · Revised, March 1997, September 1997, June 1998 · Accepted, July 1998 相似文献
14.
The Kouambo iron deposit contains banded iron formations (BIFs) and is located in the northwestern margin of the Congo craton. The BIFs are hosted in Palaeoproterozoic Nyong series, a dominantly metasedimentary formations, which were metamorphosed into greenschist to granulite facies. The Kouambo BIFs are medium- to coarse-grained banded rocks consisting of alternation of Si-rich and Fe-rich mesobands, and belong to oxide facies iron formations. Geochemistry analyses reveal that these iron formations are composed of > 96 wt% Fe2O3 and SiO2 and have low concentrations of Al2O3, TiO2 and trace HFSE, suggesting chemical precipitates of silica and iron. Moreover, these BIFs have low concentrations of Al2O3, TiO2 and trace HFSEs (high field strength elements, e.g., Zr, Hf, Ta, Pb and Th), suggesting that terrigenous detrital materials contributed insignificantly to the sedimentation. The Post-Archean Australian Shale (PAAS)-normalized REE-Y patterns display seawater-like profile: minor LREE depletion and HREE enrichment, positive Y anomalies. However, they display positive Eu and negative Ce anomalies, and low Y/Ho ratio (average 29), which suggest the influence of the hydrothermal fluids. The weak positive Eu/Eu*(PAAS) ratio (average 1.5), associated with the low V (17.5 ppm), Co (6.1 ppm) and Ni (27.5 ppm) contents similar to other Superior-type BIFs worldwide, are consistent with the deposition of the Kouambo BIFs in continental marginal sea or back-arc basin environment. In summary, the Kouambo BIFs show a seawater-like REE + Y signature, however, the positive Eu anomalies and reduced Y/Ho ratios relative to seawater indicates a possible mixing with hydrothermal fluids (∼ 0.5%). 相似文献
15.
This paper reports a geochemical study on the major and trace elements and Pb–Sr isotopes of a weathering profile developed in the Lower Cambrian black shales in central Hunan (China). Six weathering horizons were identified and sampled vertically throughout the profile. The chemical composition of the profile consists of variable concentrations of the major elements Fe2O3, FeO, MnO, MgO, CaO, Na2O, and P2O5 and of less variable concentrations of SiO2, TiO2, Al2O3, and K2O. The chemical change caused by weathering is estimated by mass-balance calculations, and the results show that the element mobility is characterised by substantial loss of SiO2, FeO, CaO, K2O, Na2O, LOI, Cr, V, Ba, Cs, Rb, Sr, U, and Th, and moderate loss of Al2O3, MgO, Fe2O3, Ni, Cu, Pb, Tl, Sn, Sc, Ge and REE (Y). The high field strength elements TiO2, Sn, Sc, U, Ga, Ge, Zr, Hf, Nb, and Ta were immobile during weathering. The chemical changes and the Pb–Sr isotopic data suggest that four types of chemical reactions occurred: the oxidation of sulphide minerals (e.g., pyrite) and organic carbon (OS), the dissolution of less resistant clinochlore-Ia, calcite, and P-bearing minerals (DL), the dissolution of detrital albite and microcline (DA), and the transformation of clay (TC) minerals (e.g., muscovite and illite–smectite). These chemical reactions then led to two stages of geochemical processes, an early stage of chemical differentiation and a later stage of chemical homogenisation. The chemical differentiation dominated by the OS, DL, and DA reactions, led to the leaching of mobile elements (e.g., MgO, Na2O, K2O, P2O5, Sr, and REE) and the redistribution of some less mobile elements (e.g., SiO2 and Al2O3). In contrast, the chemical homogenisation, which was caused by TC reactions, led to the leaching of both mobile and less mobile elements from the system and ultimately transformed the weathered black shales into soil. Soils derived from black shales in South China might result from the above two geochemical processes. 相似文献
16.
Al_2O_3和Ti在风化和热液蚀变等地球化学过程中通常被认为是不活动元素,两者的比值Al_2O_3/Ti常被用来指示地球化学作用过程。通过对中国157件火成岩样品元素含量平均值的统计发现,火成岩样品中Al_2O_3/Ti与SiO_2含量值之间存在着较好的幂函数关系:ln(Al_2O_3/Ti)=0.073×SiO_2-0.89,式中Al_2O_3和SiO_2和Ti含量单位均为%。本文基于得到的经验方程和TAS图解构建了一个新的判别岩石类型的图解——Al_2O_3-Ti图解。该图解可以区分酸性岩、中酸性岩、中性岩、中基性岩-基性岩四类岩性。通过对三个火成岩风化剖面的研究发现,花岗岩风化剖面从新鲜基岩到风化形成的土壤在Al_2O_3-Ti图解中均落在酸性岩区,花岗闪长岩风化剖面从新鲜基岩到风化形成的土壤样品均落在中酸性岩区,玄武质安山岩风化剖面从新鲜基岩到风化形成的土壤样品均落在中基性岩-基性岩区。不同风化程度的风化产物与其母岩在Al_2O_3-Ti图解中所在的区域一致,即Al_2O_3-Ti图解可以用来追溯火成岩风化产物的母岩岩性。通过对胶东焦家金矿和豫西牛头沟金矿两个矿区岩石的研究发现,黑云母花岗岩从新鲜岩石到其蚀变岩及其形成矿石的样品在Al_2O_3-Ti图解中均落在酸性岩区。玄武质安山岩从新鲜岩石到其蚀变岩及其形成矿石的样品在Al_2O_3-Ti图解中均落在中基性岩-基性岩区。即不同蚀变程度的蚀变产物与其原岩在Al_2O_3-Ti图解中所在的区域一致,这表明新构建的Al_2O_3-Ti图解可以用来示踪蚀变岩的原岩性质。 相似文献
17.
白云岩风化剖面元素地球化学特征:对黔中九架炉组“三稀金属”富集机制的启示 总被引：2，自引：1，他引：1
黔中早石炭世九架炉组铝土矿含矿岩系富集Ti、Li、Sc、V、Ga、Nb、Ta、Zr、Hf、Th和稀土(REEs)等"三稀金属",具有成为独立矿床或伴生资源的潜力。这些元素大部分与九架炉组共有同一母岩,且富集程度受母岩的成分和风化作用控制。本研究选取九架炉组母岩乌当娄山关群白云岩和纳雍牛蹄塘组泥质白云岩的现代风化剖面为研究对象,研究元素在风化作用过程中的迁移特征及分布规律,进而为九架炉组微量元素的富集机制提供启示。研究获得以下认识:1)依据剖面结构、ZrHf、Nb-Ta、Y-Ho二元图特征及REE配分曲线和Eu/Eu*值的相似性表明研究区土层主要来源于基底或母岩的风化; 2)白云岩风化成土过程中Si、Fe、Cr、As、Sb、Ti、Nb、Ta、Zr、Hf、Th、REEs等元素化学性质相对稳定,富集程度较高,而Ca、Mg、Na、K、Sr、P、Mo、Cd等元素化学性质活泼,容易淋失亏损; 3)纳雍剖面REEs~(3+)和Ca~(2+)半径差与REEs富集系数相关性良好,表明碳酸盐岩风化过程中,含钙矿物磷灰石是稀土元素分配的重要控制因素; 4)九架炉组的母岩也是Ti、Li、Sc、V、Ga、Nb、Ta、Zr、Hf、Th等微量元素的主要物质来源,母岩风化过程中,这些微量元素首先在副矿物、黏土矿物、铝矿物及磷灰石等矿物相中初步富集,之后随风化碎屑物一起沉积形成微量元素超常富集地层; 5)纳雍剖面地表和地下水提供了部分P、Be、Zn、Sb、Pb、Y及REEs来源,指示水体迁入作用也是九架炉组REEs富集的重要原因。研究表明黔中九架炉组微量元素的来源较复杂,风化-沉积过程中,化学性质稳定的元素残留在风化碎屑物中并被搬运-沉积在负地形中,而化学性质活泼的元素首先被带入水体,在沉积-成岩过程中特定条件下发生二次富集作用(例如次生矿物的形成及吸附)形成微量元素富集的地层。 相似文献
18.
Xuefei Liu Qingfei Wang Jun Deng Qizuan Zhang Silei Sun Jianyin Meng 《Journal of Geochemical Exploration》2010
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
19.
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
20.
Wenxiang Zhang Zhengtao Shi Guangjie Chen Yong Liu Jie Niu Qingzhong Ming Huai Su 《Environmental Earth Sciences》2013,70(5):2191-2202
The loess–paleosol deposit in Central Asia is a sensitive indicator of the evolution of the quaternary paleoclimate in the Westerlies, providing insight into the quaternary climate history and its relationship with global climatic changes. Based on the geochemical analysis of elemental composition of densely sampled strata from Talede loess–paleosol sequence in the Ili Basin, the results showed that SiO2 had the highest major elements content, followed by Al2O3. The order of compositional abundance of major elements was generally as follows: SiO2 > Al2O3 > CaO > Fe2O3 > MgO > Na2O > K2O. Trace elements (i.e. Rb, Sr, Sc, Ni, Cu, Ga, Mo, Y, Pb, Th) in the paleosol layers (i.e. S 0, S m, S 1) and the loess layer of L 1 were enriched relative to underlain loess (L 2) horizons, except for the contents of Zr, Cs, Nd, and La in paleosol layers. All of geochemical proxies, such as enrichment factor, Rb/Sr ratio, eluvial coefficient (K i ) and chemical weathering index, display no obvious differentiation in the Talede loess–paleosol deposit. The results indicate that the weak chemical weathering, greater evaporation and low effective moisture in Ili Basin, are to a degree weaker than those in the China Loess Plateau and the climate was warm–dry during the interglacial period. In addition, the loess of Ili area is rich in schistose minerals and implies that the loess may come from the deserts of Central Asia and it may be closely related to the widespread aridification of Central Asia. 相似文献