吉林东部花岗岩区地下水化学成分及其对岩石风化作用的制约

在吉林东部花岗岩区地下水化学成分和化学类型研究的基础上,以Na作为参比元素,确定了花岗岩风化过程中22种主量元素和微量元素的相对活动顺序。花岗岩区地下水的地球化学类型属低矿化度(变化范围为69.51×10-6~386.49×10-6,平均值为199.48×10-6)的HCO3-Ca和HCO3-Na-Ca型。花岗岩风化过程中元素的活动性顺序(RM)从大到小依次为:B、Ca、Mo、Zn、Sr、Na、Mg、Cr、Cu、Ni、K、Co、Li、V、As、Ba、Si、Y、Fe、Ti、Al、Mn。风化产物中的粘土矿物主要为高岭土、蒙脱石,反映出本区花岗岩的风化淋滤程度较弱的特点。     

Geochemistry of mineralization with exchangeable REY in the weathering crusts of granitic rocks in South China

Mineralization with exchangeable rare earth element (REE) and yttrium (MEX-REY) has been recognized in the weathering profiles in South China since the early 1970's. This type of REY mineralization occurs in weathering profiles of parent rocks ranging in composition from granite to acidic volcanic rocks and lamprophyre. The majority of the known resources occurring in the weathering profiles of granitic rocks. Total resources of this type of REY amount to millions tons of rare earth oxides, and therefore represent one of the most important types of rare earth resources in China, particularly for heavy rare earth elements (HREE) and yttrium.Accumulation of REY in the weathering profiles of granitic rocks is strongly controlled by the resistance to weathering of the principal REY-bearing accessory minerals in the parent rocks; only a limited proportion of total REY (< 30%) is incorporated in the rock-forming minerals. MEX-REY more commonly occur in weathering profiles developed on granitic rocks within which most of the REY are incorporated in accessory minerals weakly resistant to weathering (doverite, parisite, etc.). For the well-developed weathering profiles, three horizons can be distinguished from surface downwards: the lateritic horizon (A), the weathered horizon (B), and the weathering front (C). Continuous leaching, coupled with low rate of denudation, results in the accumulation of REY in the subsurface horizons (the B and C horizons), and thus results in REE differentiation within the well-developed, layered, and mature weathering profiles. Exchangeable REY, which can be replaced by cations like NH⁴⁺ and Na⁺ etc. in electrolyte solutions and can be removed by complexing agents such as EDTA, are commonly the major form of REE occurrence in the B horizon. Cerium is enriched in the top layer (A horizon) and depleted in the subsurface horizons of the weathering profiles, most likely due to the oxidation of Ce(III) to Ce(IV) followed by cerianite formation or absorption onto clays and/or Fe and Al oxyhydroxides.     

The role of trace minerals in chemical weathering in a high-elevation granitic watershed (Estibère, France): chemical and mineralogical evidence

We investigated chemical weathering in a high elevation granitic environment in three selected watersheds located in the Pyrenees (France). The sites were located on glacial deposits derived from similar Hercynian (∼300 Ma) granites characterized by the occurrence of zoned plagioclases and trace calcic phases (epidote, prehnite, sphene, apatite). The surface waters at those sites show high Ca/Na molar ratios (>1) which could not be explained by the dissolution of the major plagioclase (oligoclase) present in the rocks. The coupled approach of investigating stream water chemistry and the mineralogy and chemistry of rocks and soils allowed us to explore the role of the weathering of trace calcic minerals in calcium export at the watershed scale. The weathering of the trace calcic minerals which represent ∼ 1% of the total rock volume are responsible for more than 90% of the calcium export at the sites. Annual cationic fluxes (∼ 23.10⁴ eq/km²/yr) calculated for the Estibère watershed are among the highest reported for high elevation systems draining granitic rocks and ∼ 80% of this annual cationic flux can be attributed to the weathering of trace calcic phases. Calculations based on isotopic values (⁸⁷Sr/⁸⁶Sr) go in the same direction. Except apatite, the trace calcic phases appear to be mainly silicates, thus the type of chemical weathering observed in the Estibère watershed may have an influence on atmospheric CO₂ consumption by granite weathering. However, comparison with other watersheds draining granitic environments worldwide, and with the two other sites in the Pyrenees, indicate that the role of trace calcic phases is important in most young environments exposed to chemical weathering (e.g., high elevation catchments on glacial deposits). Other factors such as the date of glacial retreat, the physical denudation rate, the hydrological functioning of the watershed and the nature and structure of the soil cover are also important.     

Research on limestone decay in a polluting environment, I˙stanbul-Turkey

 I˙stanbul, the capital of the east Roman, Byzantine and Ottoman Empires embraces two continents, one arm reaching out to Asia, the other to Europe. It is therefore, a rich city in terms of monuments and historical cites. Shell limestones of Upper Miocene age are used as building stone in the majority of the monuments in I˙stanbul because of their attractiveness, availability and workability. The durability characteristics of the limestones are examined, and those factors that are responsible for atmospheric weathering are discussed, in a humid and marine environment with important problems of urban pollution, specifically due to traffic. In the present study weathering of the building stones were first examined in situ by macroscopic observations. The weathering that developed as a result of environmental effects since this limestone was first used in historical monuments has been affected 0.1–1.5 cm deep from the surface. The weathered facing stone of Şehzade Mehmed Mosque in I˙stanbul is undergoing a program of progressive replacement. During this study, samples were taken from this monument where the shell limestone was used. The stone surface was principally examined by means of Scanning Electron Microscopy (SEM). Petrographical and mineralogical analyses were made by using optical microscopy and X-ray diffraction method. The physico-chemical properties of these rocks control their weathering behaviour and reactivity. Major and trace element analyses and the effect of deterioration on the physical properties of the limestones (unit weight, porosity and water absorption) have also been investigated. Studies on the samples implies that weathering on the stone surface caused important variations on the physical characteristics of the rock. Received: 11 February 1998 · Accepted: 18 August 1998     

Mineralogical and geochemical constraints on environmental impacts from waste rock at Taojiang Mn-ore deposit,central Hunan,China

The mineralogy and geochemistry of the waste rocks distributed at Taojiang Mn-ore deposit, central Hunan province, China, were studied using X-ray powder diffraction (XRD), electron microprobe analysis (EMPA) fitted with energy dispersive spectrometer (EDS) and inductively coupled plasma mass spectrum (atomic emission spectra) ICP-MS (AES), with the aim of predicting the environmental impacts of weathering of the waste rocks. The mineralogical results from microscope observation and XRD and EMPA studies show that the waste rock is composed of black shale and minor Mn carbonates. The oxidation of sulfide minerals such as galena, pyrite and chalcopyrite is accompanied by decomposition of Mn carbonates and K-feldspar during exposure to atmospheric O₂. The geochemical characteristics of major, rare earth elements (REE) and trace elements of the waste rocks also show that the waste rock can be divided into black shale and Mn carbonate, and both of them are currently under chemical weathering. The major alkalies and alkaline elements (Ca, Mg, Na, K, Rb, Sr and Cs) and major elements (Fe, S and P) and heavy metals (Sc, V, Cr, Th, U, Sn, Co, Ni, Cu, Zn, Pb, Mo, Cd, Sb, an Tl) are being released during weathering. The mobility of alkalis and alkaline elements Ca, Mg, Na, K, Rb, Sr and Cs is controlled by decomposition of Mn carbonates. The dispersion of Cr, Sc and Th (U) might be related to weathering of K-feldspar, and the release of the heavy metals Co, Ni, Cu, Zn, Pb, Mo, Cd Sb and Tl is dominated by the breaking of sulfide minerals. The REE of the waste rocks and surrounding soils and the spidery distribution patterns of heavy metals in the waste rocks, the surrounding soils and the surface waters show that weathering of the waste rocks and bedrock might be the sources of heavy metal contamination for the surrounding soils and surface water system for the mining area. This is predicted by the mass-balance calculation by using Zr as an immobile element. Therefore, it is urgently necessary take measures to treat the waste rocks distributed throughout the area for the local environmental protection.     

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

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。     

Alteration of As-bearing phases in a small watershed located on a high grade arsenic-geochemical anomaly (French Massif Central)

At a watershed scale, sediments and soil weathering exerts a control on solid and dissolved transport of trace elements in surface waters and it can be considered as a source of pollution. The studied subwatershed (1.5 km²) was located on an As-geochemical anomaly. The studied soil profile showed a significant decrease of As content from 1500 mg kg⁻¹ in the 135–165 cm deepest soil layer to 385 mg kg⁻¹ in the upper 0–5 cm soil layer. Directly in the stream, suspended matter and the <63 μm fraction of bed sediments had As concentrations greater than 400 mg kg⁻¹. In all these solid fractions, the main representative As-bearing phases were determined at two different observation scales: bulk analyses using X-ray absorption structure spectroscopy (XAS) and microanalyses using scanning electron microscope (SEM) and associated electron probe microanalyses (EPMA), as well as micro-Raman spectroscopy and synchrotron-based micro-scanning X-ray diffraction (μSXRD) characterization. Three main As-bearing phases were identified: (i) arsenates (mostly pharmacosiderite), the most concentrated phases As in both the coherent weathered bedrock and the 135–165 cm soil layer but not observed in the river solid fraction, (ii) Fe-oxyhydroxides with in situ As content up to 15.4 wt.% in the deepest soil layer, and (iii) aluminosilicates, the least concentrated As carriers. The mineralogical evolution of As-bearing phases in the soil profile, coupled with the decrease of bulk As content, may be related to pedogenesis processes, suggesting an evolution of arsenates into As-rich Fe-oxyhydroxides. Therefore, weathering and mineralogical evolution of these As-rich phases may release As to surface waters.     

基于微量元素岩性地球化学基因的构建与检验

地球化学基因是近年来提出的新技术。在分析地球化学基因构建方法的基础上提出一种基于微量元素的岩性地球化学基因,并将其编号为LG03,其基因链元素序列为Nb→Ti→Zr→Cr→La→V→Pb→Co→U→Ni→Th。分别选择发育在广东连阳花岗岩与佛冈花岗岩的2个花岗岩风化剖面、海南文昌3个玄武岩风化剖面、北京房山1个花岗闪长岩风化剖面、胶东2个花岗岩风化剖面与1个玄武岩风化剖面及1个花岗闪长岩风化剖面共计10个风化剖面对新构建的LG03基因以及以前基于主量和微量元素混合构建的LG01岩性基因进行检验。采用基因相似度≥80%作为样品之间具有相似基因的判别标准来检验地球化学基因在风化过程中的稳定性时,发现基于微量元素的LG03岩性基因与基于主量和微量元素混合的LG01岩性基因在遗传性与继承性方面基本相似,但LG03基因相对于LG01基因更稳定。采用酸性相似度20%和80%作为划分类基性成分、类中性成分和类酸性成分的标准时,发现LG03和LG01岩性基因在成分分类与物源示踪等方面也基本相似。在物源示踪方面LG03基因相对于LG01基因更稳定;在成分分类方面当二者划分结果不一致时应以LG01基因的酸性相似度划分结果为准,可进一步以LG03基因的划分结果加以约束。在风化、搬运与沉积过程中,地质样品的主量成分可能会受到风成沙、生物体等介质的加入而发生明显改变,进而导致LG01基因发生改变。但这些较单一成分物质的加入并不影响相对不活动微量元素之间的相互关系,从而可使LG03基因保持较好的稳定性。因此相对于LG01基因而言,LG03基因由于消除了受风成沙、生物体等介质的影响而可能具有更广泛的应用领域。     

同步辐射X射线吸收光谱在环境矿物学中的应用

本文介绍了同步辐射X射线吸收光谱（XAS）在环境矿物学中的应用与进展,尤其是在矿物载体催化剂的环境催化活性研究、固-液界面的微观机制研究、毒性痕量元素在矿物中赋存状态的研究、核废料的矿物处置研究等方面的发展现状。最后指出,XAS对推动环境矿物学的发展、优化环境矿物材料和原料的工艺流程具有独特的优势,在我国还有待进一步加强其发展和应用。     

A Study on the Dissolution Kinetics of Basalt—Water Interaction under Different pH Conditions I：Release of Elements and pH Neutralization Effect

Experimental research on the chemical weathering of alkaline-olivine basalt from Huangyi Mountain,Kuandain County,Liaoning.Province and olivine basalt from Dayangke,Mingxi County,Fujian Province has shown that the acidity of the solution tends to become neutral regardless of what the acidity of the starting solution would be during basalt0-water interaction.We call this phenome-non“pH neutralized Effect”.The dissolved species in the solution were determined and unreacted and reacted sample-surface chemical components involved or uninvolved in reaction were analyzed using X-ray photoelectron spectroscopy(XPS).The results revealed two different mechanisms of dissolution of basalt in acidic and basic solutions.     

An assessment of soil contamination due to heavy metals around a coal-fired thermal power plant in India

Combustion of coals in thermal power plants is one of the major sources of environmental pollution due to generation of huge amounts of ashes, which are disposed off in large ponds in the vicinity of the thermal power plants. This problem is of particular significance in India, which utilizes coals of very high ash content (∼55 wt%). Since the thermal power plants and the ash ponds are located in densely populated areas, there is potential chance for contamination of soil and groundwater of the surrounding areas from the toxic trace elements in the ash. An attempt has been made to study the extent of soil contamination around one of the largest thermal power plants of India located at Kolaghat, West Bengal India. Chemical analysis of the top soils and the soils collected from the different depth profiles surrounding the ash ponds, show that the top soils are enriched in the trace elements Mo, As, Cr, Mn, Cu, Ni, Co, Pb, Be, V, Zn, which show maximum enrichment (2–5) in the top soils collected from all the soil profiles. These elements are also enriched in the pond ash. Since there are no other sources of industrial effluents, it can be said that the enrichment of the trace elements (Mn, Co, Mo, Cr, Cu, Pb, Zn, As, Ni, Be, V) is attributed to their input from ash from the disposal pond. The study has been further strengthened by log-normal distribution pattern of the elements.     

Barium in Deccan Basalt Rivers: Its Abundance, Relative Mobility and Flux

The concentration of dissolved Ba in a number of rivers having their drainage almost entirely in Deccan Trap basalts has been measured. These results along with available data on the abundances of major elements in these waters, and on Ba and major elements in bed sediments of these rivers provide a measure of (i) the relative mobility of Ba during chemical weathering and erosion of basalts, particularly with respect to alkaline earths, Mg, Ca and Sr, and (ii) the flux of Ba out of the Deccan and its global significance. The concentration of dissolved Ba ranges from 8 to 105 nM. The average Ba/Mg*, Ba/Ca* and Ba/Sr (* is concentration corrected for atmospheric contribution) in waters is lower than the corresponding mean ratios in Deccan basalts, though they overlap within errors. Majority of the water samples, however, have ratios less than that in basalts. These findings can be interpreted as a cumulative effect of limited release/mobility of Ba during chemical weathering and erosion of basalts and its reactive behaviour in waters which promote its association with clays and oxy-hydroxides of Fe. These results also indicate that during chemical erosion of Deccan basalts, Ba is the least mobile among the alkaline earth elements. The abundance of Ba in sediments and their Ba/Al ratios relative to basalts are consistent with the above conclusion. Ba/Mg and Ba/Ca ratios in water and in sediments from the same location are strongly correlated; however, the mean ratios in waters are far less than those in sediments. This is a result of limited Ba mobility, effectively 5–6 times lower than that of Mg. The annual flux of dissolved Ba out of the Deccan Traps is ~1 × 10⁷ moles, ~ 0.2% of its global riverine transport to oceans. The contribution of dissolved Ba from Deccan Traps, seem lower than its aerial coverage, ~ 0.5% of the global drainage area; the potential causes for this could be the lower abundance of Ba in basalts relative to “average continental crust”, and its behaviour during chemical weathering and erosion.     

Geochemical and mineralogical investigation of domestic archaeological soil features at the Tiel-Passewaaij site,The Netherlands

Archaeological soil features can be defined as areas of staining in ancient cultural soil horizons and are frequently used in surveys to locate sites and activity areas. Visual observation of these features, however, provides only limited information on their origin and the processes leading to their formation and this limits site interpretation. This paper presents the results of geochemical and mineralogical analyses of domestic archaeological soil features in order to assess their composition, formation pathway and origin. The greenish soil features studied here belong to a house plan from a Roman farmhouse located at the Tiel-Passewaaij site in the Netherlands. The soils were investigated using a range of techniques, including X-ray Fluorescence (XRF) spectroscopy, sequential soil extractions, Fourier-transformed infrared (FT-IR) spectroscopy, X-ray Diffraction (XRD) and microprobe analysis. The results indicate that the studied soil features can chemically be distinguished from off-site soils e.g. based on their phosphate and carbonate content. Mineralogical analysis of aggregate samples from soil features further reveal that quartz and feldspar minerals are coated with Ca–Fe–P phases that closely resemble anapaite and mitridatite mineral forms. The formation of these mineral phases probably resulted from periodic reductive dissolution of Fe-oxide phases and subsequent precipitation of Fe–P phases, with inclusion of Ca from anthropogenic carbonates or groundwater. The combined presence of (Ca)-carbonates, P-phases and some anthropogenic trace elements (Cu, Zn) suggests that the greenish soil features stem from manure inputs.     

Geochemistry of trace and rare earth elements during weathering of black shale profiles in Northeast Chongqing,Southwestern China: Their mobilization,redistribution, and fractionation

In this study, the mobilization, redistribution, and fractionation of trace and rare earth elements (REE) during chemical weathering in mid-ridge (A), near mountaintop (B), and valley (C) profiles (weak, weak to moderate, and moderate to intense chemical weathering stage, respectively), are characterized. Among the trace elements, U and V were depleted in the regolith in all three profiles, Sr, Nb, Ta, Zr, and Hf displayed slight gains or losses, and Th, Rb, Cs, and Sc remained immobile. Mn, Ba, Zn, Cu, and Cr were enriched at the regolith in profiles A and B, but depleted in profile C. Mn, Pb, and Co were also depleted in the saprock and fractured shale zones in profiles A and B and enriched in profile C. REEs were enriched in the regolith and depleted at the saprock zone in profiles A and B and depleted along profile C. Mobility of trace and REEs increased with increasing weathering intensity. Normalized REE patterns based on the parent shale revealed light REE (LREE) enrichment, middle REE (MREE), and heavy REE (HREE) depletion patterns. LREEs were less mobile compared with MREEs and HREEs, and this differentiation increased with increasing weathering degree. Positive Ce anomalies were higher in profile C than in profiles A and B. The Ce fractionated from other REE showed that Ce changed from trivalent to tetravalent (as CeO₂) under oxidizing conditions. Minimal REE fractionation was observed in the saprock zone in profiles A and B. In contrast, more intense weathering in profile C resulted in preferential retention of LREE (especially Ce), leading to considerable LREE/MREE and LREE/HREE fractionation. (La/Yb)_N and (La/Sm)_N ratios displayed maximum values in the saprock zone within low pH values. Findings demonstrate that acidic solutions can mobilize REEs and result in leaching of REEs out of the highly acidic portions of the saprock material and transport downward into fractured shale. The overall behavior of elements in the three profiles suggests that solution pH, as well as the presence of primary and secondary minerals, play important roles in the mobilization and redistribution of trace elements and REEs during black shale chemical weathering.     

滇东地区碳酸盐岩上覆风化层的元素地球化学特征及其成因讨论

碳酸盐岩风化形成的红土保存着喀斯特发展演化历史证据,同时也是喀斯特地区土壤研究的重要对象。文章选取云 南石林地区的两处典型碳酸盐岩剖面为研究对象,对主量元素,微量元素及稀土元素在风化层的迁移特征及分布规律进行 研究,为探究风化层的成因提供依据。结果显示：（1） 以Ti为参比元素的剖面迁移特征表明,两剖面的主量元素在成土过 程中有相似的迁移规律,多数表现为淋失;微量元素略有差异,富集淋失程度不一。（2） UCC 标准化蜘蛛图显示,相对于 基岩,风化层中的Ca和Sr均出现亏损;与UCC相比,Fe、Ti等元素轻微富集,Mg、Ca、Na、K、P等元素显示了强烈的亏 损特征。（3） 基岩与风化层的REE分布模式相似,但风化层的稀土相对富集,轻稀土元素间的分异较大而重稀土元素间的 分异较小,且SJC剖面的轻、重稀土元素比值大于QST剖面;稀土元素球粒陨石标准化后,SJC剖面的Eu为负异常,剖面 上部和下部出现Ce负异常;QST剖面Ce负异常,Eu明显负异常。（4） 元素含量变化和元素对Al-Ti、Al-Fe及Zr-Hf相关性 说明剖面上覆红土是下伏基岩风化的结果。研究结果显示,两个剖面的元素地球化学特征与基岩存在很好的继承性,风化 层是基岩原位风化的产物。     

Physical and chemical environments of abnormal vitrinite reflectance evolution in the sedimentary basins

Based on the tested data of pressure and vitrinite reflectance of some wells in sedimentary basins, abnormal high pressure is regarded as not the only factor to retard the increase of vitrinite reflectance (R _o). Apart from the types of the organic matter, the physical environment (temperature and pressure) and chemical environment (fluid composition and inorganic elements) will result in the abnormal vitrinite reflectance values in the sedimentary basins. This paper tested trace elements and vitrinite reflectance data from the the abnormal high pressure and normal pressure strata profiles, respectively, and found that the acidic and lower salinity starta are favorable for the increase of R _o. By discussing the corresponding relationship between the contents of some trace elements in the mudstone and the vitrinite reflectance values, the typical trace elements were found to suppress and/or catalyze the vitrinite reflectance of organic matter, while the elements of Ca, Mn, Sr, B, Ba and P may result in the retardation of R _o. However, elements of Fe, Co, Zn, Ni and Rb may catalyze the organic matter maturation. This study is conductive to the organic maturation correction, oil and gas assessment and thermal history reconstruction by the paleothermometry. Translated from Acta Geologica Sinica, 2006, 80(11): 1760–1769 [译自: 地质学报]     

渝东北黑色页岩元素迁移特征及化学风化程度

黑色页岩是富含有机质和硫化矿物的特殊沉积岩,但人们对其风化过程的元素活动性及矿物风化机制关注较少.为探讨不同地形位置的黑色页岩化学风化过程,采集了渝东北城口某山脊 (A)、近山顶 (B) 和沟谷 (C) 的下寒武统水井沱组黑色页岩风化剖面岩样,利用XRD、XRF和化学分析手段对采集样品的矿物成分、主量元素进行测定分析.元素和矿物的质量迁移系数 (τ) 和质量迁移通量 (M_{j, flux}) 的计算结果表明,黑色页岩风化过程中Ca、Mg和Na元素具有明显的贫化现象,近地表处存在Al元素的富集现象;矿物成分方面,黄铁矿和有机质氧化后形成的酸性水环境,造成方解石、白云石、斜长石等不稳定矿物溶解,并生成含水石膏、铁质氧化物、黏土矿物等次生矿物.不同赋存位置的黑色页岩风化程度有所差异,Na/K-CIA、K/Ca*-Al/Na、A-CN-K和A-CNK-FM图解显示:A剖面处于脱Ca过程的初级风化阶段,B剖面处于脱Ca、Na初期的初等-中等风化阶段,C剖面已发生脱Ca、Na过程,并伴随脱Si作用的中等-强烈风化阶段,结合不同风化指数 (如:CIA、CIW、PIA、MWPI等),得出各剖面的化学风化强弱程度依次为C＞B＞A.      

Chemical weathering in the drainage basin of a tropical watershed (Nsimi-Zoetele site, Cameroon) : comparison between organic-poor and organic-rich waters

This study deals with the weathering processes operating at the scale of a small catchment (Nsimi-Zoetele, Cameroon) and is focused on the role of organic colloids on mineral weathering and transport of elements in natural waters. Samples of river, spring and groundwaters from Nsimi-Zoetele were filtered through membranes of decreasing pore size (0.22 μm, 0.025 μm, or: 300,000 Da, 5000 Da) to separate colloidal fractions from the truly dissolved one. Major and trace elements and dissolved organic carbon (DOC) were analysed in each fraction. Two kinds of waters can be distinguished in the catchment: clear and coloured waters. Clear waters exhibit low concentrations of major and trace elements and DOC. Elements are carried in these solutions in a true dissolved form except Al and rare earth elements (REEs). By contrast, the higher abundances of Al, Fe and trace elements in coloured waters are controlled by the colloidal fraction. Thermodynamic equilibrium calculations show that clear waters are in equilibrium with kaolinite and iron oxi-hydroxide which are major minerals in the weathered soil. For coloured waters, the aqueous speciation of Ca, Mg, Cu, Fe, Al, La and Th was calculated taking into account the complexes with humic acids. Speciation calculations for Cu, Fe, Al, La, Th show a strong complexation with humic acids, in good agreement with the results of the filtration experiments. By contrast, although filtration experiments show a strong control of major cations by organic matter (for example 75% for Ca), speciation calculations reveal that their complexes with humic ligands do not exceed a few percent of total dissolved elements. This discrepancy is explained as an artefact induced by the organic colloids and occurring during the filtration procedure. Finally, both filtration experiments and speciation calculations show that organic matter plays an important role in natural DOC-rich waters. Organic acids increase significantly the dissolution rates of silicates and oxi-hydroxides and thus the amounts of solutes and of complexed elements leaving the catchment.     

Temporal transport of major and trace elements in the upper reaches of the Xijiang River,SW China

This study investigated the temporal variations of major and trace element contents and controlling factors in the upper reaches of the Xijiang River, SW China. The results showed the major ions principally derived from the weathering of carbonate and silicate rocks, with a seasonal variation impacted by the monsoonal climate. The contents of dissolved trace elements also varied seasonally in the two main tributaries: the Nanpan and Beipan rivers. Most dissolved trace elements such as Mn, Zn and Pb being affected by anthropogenic contributions displayed a large seasonal variability, from onefold to hundred-fold, while V, Rb and U show a relative stable trend uncorrelated with the different seasons, suggesting a natural origin by rock weathering. Suspended particle matter in the Nanpan and Beipan rivers was depleted in Ca, Mg, Na, K and Sr, but enriched in Al, Fe and Sb compared to the upper crust (UC) values. A binary mixture of silicate-rich and carbonate-rich sources dominates the behavior of elements such as Ca and Sr in riverine sediments, while a third end-member with an anthropogenic signature influenced the content of trace elements like Mn, Sb, Pb, Zn, Cd, Cr and Cu. The enrichments of Sb relative to the UC would be related to the mining activity in the studied area. The study highlights the importance of investigating temporal variations of major and trace element contents of rivers controlled by the monsoon climate and impacted by human activity.     

Discrimination between different water bodies from a multilayered aquifer (Kaluvelly watershed,India): Trace element signature

In the multilayered aquifer of Kaluvelly (India), comprising various sedimentary layers overlying a charnockitic basement, concentrations of trace elements were measured in aquifer formations and in groundwaters to identify geochemical tracers for water bodies. The two main sandstones (Cuddalore and Vanur) originate from the charnockites and the Cuddalore sandstone has experienced lateritization. In the studied area, two charnockite end-members were identified: a dioritic and a granitic one. Mineralogical composition and whole-rock Ti concentrations confirmed the charnockite which displayed the granitic composition as the parent rock of the two sandstones. Titanium distribution indicates that the Cuddalore sandstone originates from a more intense weathering of the parent material than the Vanur sandstone. Despite extensive differences in trace element contents recorded in aquifer formations, only a few trace elements were suitable to distinguish the water bodies. Among soluble elements, Li (in the Vanur aquifer) and Ba (in the charnockite and carbonaceous aquifers) can be used as tracers. As the input of these elements in solution is mainly regulated by the available stock, for a given mineralogical origin there is a direct link between the aquifer formation composition and water signature. With the exception of As, concentrations of redox-sensitive elements were not preserved during pumping because of oxidation, preventing their use as tracers. Low-mobility elements such as La, Ce, Th, Zr, Nb, Hf, or Ta were too insoluble to be detected in waters and/or to record the aquifer formation signature. Their input in solution was not regulated by the available stock but by the dissolution rate of rock-forming minerals. Only Ti can be used to distinguish between two out of the three aquifers (charnockite and Vanur). The specific behavior of Ti recorded in these waters may be linked to rutile inclusions within plagioclases and to the influence of climate on Ti solubility.