A 2400-year record of trace metal loading in lake sediments of Lagoa Vermelha, southeastern Brazil

Sediments of the Lagoa Vermelha (Red Lake), situated in the Ribeira Valley, southeastern Brazil, are made of a homogeneous, organic-rich, black clay with no visible sedimentary structures. The inorganic geochemical record (Al, As, Ba, Br, Co,Cs, Cr, Fe, Mn, Ni, Rb, Sc, Sb, V, Zn, Hg and Pb) of the lake sediments was analyzed in a core spanning 2430 years. The largest temporal changes in trace metal contents occurred approximately within the last 180 years. Recent sediments were found to be enriched in Pb, Zn, Hg, Ni, Mn, Br and Sb (more than 2-fold increase with respect to the “natural background level”). The enhanced accumulation of Br, Sb, and Mn was attributed to biogeochemical processes and diagenesis. On the other hand, the anomalous concentrations of Pb, Zn, Hg and Ni were attributed to pollution. As Lagoa Vermelha is located in a relatively pristine area, far removed from direct contamination sources, the increased metal contents of surface sediments most likely resulted from atmospheric fallout. Stable Pb isotopes provided additional evidence for anthropogenic contamination. The shift of ²⁰⁶Pb/²⁰⁷Pb ratios toward decreasing values in the increasingly younger sediments is consistent with an increasing contribution of airborne anthropogenic lead. In the uppermost sediments (0-10 cm), the lowest values of the ²⁰⁶Pb/²⁰⁷Pb ratios may reflect the influence of the less radiogenic Pb from the Ribeira Valley District ores (²⁰⁶Pb/²⁰⁷Pb between 1.04 and 1.10), emitted during the last 50 years.     

Geochemistry of rare earth elements in bottom sediments of the Brazil Basin, Atlantic Ocean

The sedimentation and ore formation were studied in sediments from nine stations located in the 24°W profile in the Brazil Basin of the Atlantic Ocean. The sediments are represented by mio- and hemipelagic muds, which are variably enriched in hydrothermal iron and manganese oxyhydroxides. As compared to the sediments from other basins of the Atlantic Ocean, these rocks are marked by extremely high manganese contents (up to 1.33%) and maximal enrichment in Ce. It was shown that the positive Ce anomaly is related to the REE accumulation on iron oxyhydroxides. Influence of hydrothermal source leads to the decrease of Ce anomaly and LREE/HREE ratio. In the reduced sediments, preservation of positive Ce anomaly and/or its disappearance was observed after iron and manganese reduction. The REE contents were determined for the first time in the Ethmodiscus oozes of the Brazil Basin. Ore deposits of the Brazil Basin are represented by ferromanganese crust and ferromanganese nodules. Judging from the contents of iron, manganese, rare, and trace elements, these formations are ascribed to the sedimentation (hydrogenic) deposits. They are characterized by a notable positive Ce anomaly in the REE pattern. The extremely high Ce content (up to 96% of total REE) was discovered for the first time in the buried nodules (Mn/Fe = 0.88).     

Fertiliser characterisation: Major,trace and rare earth elements

In recent years, there has been increasing concern regarding the chemical impact of agricultural activities on the environment so it is necessary to identify contaminants, and/or characterise the sources of contamination. In this study, a comprehensive chemical characterisation of 27 fertilisers of different types used in Spain has been conducted; major, minor and trace elements were determined, including rare earth elements. Results show that compound fertilisers used for fertigation or foliar application have low content of heavy metals, whereas fertilisers used for basal and top dressing have the highest content of both REE and other heavy metals. REE patterns of fertilisers have been determined in order for them to be used as tracers of fertilisers in future environmental studies. Furthermore in this work REE patterns of fertilisers are used as tracers of the source of phosphate in compound fertilisers, distinguishing between phosphorite and carbonatite derived fertilisers. Fertilisers from carbonatites have higher contents of REE, Sr, Ba and Th whereas fertilisers from phosphorites have higher contents of metals of environmental concern, such as Cd, U and As; and the sum of the heavy metals is higher. Some of the analysed fertilisers have Cd concentrations that exceed maximum values established in some countries and can be expected to produce long-term soil accumulation. Furthermore, other elements such as U, As and Cr are 10–50 times higher in concentration than those of Cd, but there is no legislation regarding them, therefore it is necessary to regulate fertiliser compositions in order to achieve environmental protection of soils and waters.     

Authigenic associations between selected rare earth elements and trace metals in lacustrine sediments

Surficial sediment samples were collected at 47 stations in Little Traverse Bay, Lake Michigan, to determine the geochemical associations between certain rare earth elements (REE's) and trace metals. Each sample was analyzed for carbonate carbon, organic carbon, grain size, and the elements Al, Ca, Ce, Co, Cr, Eu, Fe, Hf, La, and Mn. Two distinct Ce subpopulatins were identified by graphical analysis, and an R-mode factor analysis was applied to data from the “enriched” Ce subpopulation (18 samples). Results show that the REE's and trace metals are primarily enriched in the authigenic phase of these sediments. Partial correlation analyses indicate that the REE's are primarily associated with hydrous Fe oxides relative to organic matter in this phase. The ratio of Ce/La concentrations increased markedly from the bay margins to the central trough of the bay, indicating that Ce, similar to Fe, exhibits a variable oxidation state in the authigenic phase of nearshore fine-grained sediments. The results of the present study suggest that the REE's and trace metals behave coherently in the authigenic phase of recent lacustrine sediments, and the REE's may be useful as geochemical tracers to differentiate between trace metal enrichments in surface sediments as a result of diagenesis and pollution loadings.     

The behaviour of trace and rare earth elements (REE) during hydrothermal alteration in the Rangan area (Central Iran)

The rhyolitic dome in the Rangan area has been subjected to hydrothermal alterations by two different systems, (1) A fossil magmatic–hydrothermal system with a powerful thermal engine of a deep monzodioritic magma, (2) An active hydrothermal system dominated by meteoric water. Based on mineralogical and geochemical studies, three different alteration facies have been identified (phyllic, advanced argillic and silicic) with notable differences in REE and other trace elements behaviour. In the phyllic alteration zone with assemblage minerals such as sericite, pyrite, quartz, kaolinite, LREE are relatively depleted whereas HREE are enriched. The advanced argillic zone is identified by the presence of alunite–jarosite and pyrophyllite as well as immobility of LREE and depletion in HREE. In the silicic zone, most of LREE are depleted but HREE patterns are unchanged compared to their fresh rock equivalents. All the REE fractionation ratios (La/Yb)_cn, (La/Sm)_cn, (Tb/Yb)_cn, (Ce/Ce¹)_cn and (Eu/Eu¹)_cn are low in the phyllic altered facies. (Eu/Eu¹)_cn in both advanced and silicic facies is low too. In all alteration zones, high field strength elements (HFSE) (e.g. Ti, Zr, Nb) are depleted whereas transition elements (e.g. V, Cr, Co, Ni, Fe) are enriched. Geochemically speaking, trace and rare earth elements behave highly selective in different facies.     

长江三峡地区成冰纪-埃迪卡拉纪转换时期微量元素和稀土元素地球化学特征

通过微量元素和稀土元素地球化学分析,对长江三峡地区陡山沱组层型剖面--田家园子剖面成冰系南沱组顶部和埃迪卡拉系陡山沱组下部102个岩石样品进行了地球化学研究。重点分析了氧化还原敏感元素(Zn,Co,U,Mo,Ni,V)的富集特征,并探讨其可能成因机制以及三峡地区成冰纪-埃迪卡拉纪转换时期的水体特征。结果表明:在南沱组顶部仅Zn和Co富集;在盖帽白云岩下部,氧化还原敏感元素均富集,而在盖帽白云岩上部,除Zn和V外,其他氧化还原敏感元素均亏损;在陡山沱组Ⅱ段下部,氧化还原敏感元素由最初的亏损,逐渐变为较稳定的富集。在陡山沱组下部,出现2次明显的富集峰值,分别出现在剖面的0.4m处(盖帽白云岩中间)和6.5m处(陡山沱组Ⅱ段下部)。整个剖面大部分样品具有Eu的轻微正异常(Eu/Eu^*＜1.6), 而在剖面0.4m和6.5m处,Eu具有明显的正异常,结合稀土配分类型、Y/Ho值、La异常、Ce异常等指标,推测这2次异常均可能受到深海热液流的影响,而缺氧海水的上涌造成水体缺氧,导致这些元素出现富集峰值。U/Th、V/(V+Ni)以及稀土元素指标综合指示,三峡地区南沱组顶部冰碛岩应为氧化环境下的沉积物;随着冰川消融,冰融淡水注入古海洋,陡山沱组盖帽碳酸盐的沉积受冰融淡水的影响,深部缺氧海水的上涌使沉积水体经历氧化-缺氧-氧化的转变,海水的分层性较强;而陡山沱组Ⅱ段下部沉积环境以分层性较弱的弱氧化环境为主。     

Patterns of rare earth and other trace elements in Paleogene and Miocene clayey sediments from the Mondego platform (Central Portugal)

In the present study the origin of clay deposits occurring in an inland platform, in central Portugal, was investigated by their mineralogical and chemical composition. The clay deposits, exploited for ceramic industry are composed of silt-clay facies, the Monteira Member and the Arroça Member, which are assigned to the Coja Formation (Paleogene) and the Campelo Formation (Miocene), respectively. These clayey facies show almost compositional homogeneity, especially concerning texture. The mineralogical composition of the Monteira Member displays slightly higher content in smectite and interstratified clay minerals, which is supported by the chemical composition of samples analyzed. Both members present similar REE patterns, displaying an intense weathering record and little variation in the source area composition. Minor element geochemistry suggests low content in heavy minerals and transition metals. REE patterns and ratios of geochemical parameters support the dominant metasedimentary provenance, with a granite source contribution and also mature recycled sediments of continental origin. The study results’ suggest that the clays of these two members have the same source in terms of lithology and recycled sediments from the Hesperian massif. During the deposition of the Arroça Member, a major remobilization of the Monteira Member is suggested, explaining the geochemical similarity of both facies.     

贵州碳酸盐岩风化壳主元素、微量元素及稀土元素的地球化学特征

选取贵州高原喀斯特地区的典型碳酸盐岩原生风化剖面为研究对象,研究主元素、微量元素及稀土元素在风化壳的迁移转化及其分布规律特征,为解释碳酸盐岩风化壳元素的地球化学变化提供依据。结果显示,从上陆壳标准化蛛网图可知,Pb、Co在剖面富集,而Na、K、Cr、Rb、Sr和Ba则亏损。风化壳∑REE的变化范围为167.4~1814.2μg/g,稀土元素从剖面下部往上逐渐减少,剖面中上部LREE比HREE淋滤程度大。稀土元素球粒陨石标准化后Ce正负异常,Eu轻微负异常。以风化前缘为分界,在风化前缘以下的土层,Ce负异常,风化前缘以上的土层,Ce正异常。此外,在风化壳岩土界面附近存在一个明显且突变的碱性障,岩土界面土样的元素含量较岩粉平均增加了21倍。我们的研究显示,风化剖面主元素和微量元素的变化波动特征较为一致,说明主元素和微量元素在风化过程中的地球化学行为较为一致。铁壳层中稀土元素的含量最低,与上陆壳稀土元素十分相近,为研究上陆壳与碳酸盐岩铁壳层之间的相互联系起到了一定的借鉴作用。     

新疆金矿火山岩微量及稀土元素地球化学特征

金矿火山岩微量元素以Th和Zr的明显正异常及Nb和Ti的明显负异常为特征。微量元素比值蛛网图模式曲线均呈微向左倾斜的多峰多谷曲线。过渡元素以Cr和Ni的明显负异常及Sc,Co,Cu明显正常为特征。过渡元素球粒陨石标准化曲线，也均呈微向右倾斜的W形曲线。稀土元素以稀土总量偏低，轻稀土富集，重稀土亏损，Eu具微弱异常至微弱正常为特征。稀土元素配分模式均呈微向右倾斜和近于水平的平滑曲线，陆相火山作用两类成矿岩浆建造－陆相火山岩与潜火山杂岩具有基本一致的微量元素和稀土元素地球化学特征。     

龙感湖稀土元素的地球化学特征

采用液-液萃取法,连续提取法和ICP-MS测试技术,对龙感湖不同季节水和颗粒物中稀土元素进行研究.结果表明,龙感湖的溶解态稀土含量极低,稀土总含量(ΣREE)在3.14～129.81ng/kg之间,且季节性变化明显.龙感湖溶解态稀土元素表现出平坦型的页岩配分模式,这是由于在草型湖泊中溶解态稀土主要以吸附在微细胶体上的形式存在,水粒相互作用在这个过程中起主要控制作用.悬浮物中的稀土含量顺序为:残渣态>>Fe-Mn结合态>>有机态和AEC态,颗粒物中稀土元素主要以残渣态形式存在.Fe-Mn结合态、有机态和AEC态的页岩配分模式为中稀土富集,残渣态的页岩配分模式为平坦型.这说明中稀土与轻重稀土相比具有更强的潜在地球化学活性,但在龙感湖的环境中的迁移能力相对轻重稀土来说较弱.     

陈家山矿煤中微量元素和稀土元素地球化学特征

通过对陈家山煤矿中下侏罗统延安组4^#主采煤层中微量元素和稀土元素的测试分析,发现煤中富集亲花岗岩的钨钼族元素W、Mo、Bi、Sn、Ba、Sr和Li,说明该区煤系形成期间的陆源碎屑主要来自花岗岩和花岗片麻岩等中、酸性岩石。4^#煤中ΣREE平均值为98.2×10^-6,稀土元素分布模式十分相似,呈左高右低的宽缓“V”型曲线,Eu负异常明显,反映出稀土元素与陆源碎屑岩关系密切,成煤期间稀土元素来源一致,陆源物质的供应相对稳定。     

Clinopyroxene-orthopyroxene major and rare earth elements partitioning in spinel peridotite xenoliths from Assab (Ethiopia)

Major element and rare earth element (REE) partitioning among coexisting clinopyroxene-orthopyroxene pairs from mantle xenoliths of the Assab Range (Ethiopia) are discussed in terms of crystal-chemistry.Major element partitioning indicates relatively uniform conditions of subsolidus equilibration over a narrow range of temperatures (mean value about 1100 C) in the spinel peridotite stability field. Major element distributions and correlations, moreover, seem to indicate that the mantle material studied underwent slightly different depletions prior to the metamorphic equilibration.In spite of the rather homogeneous major element compositions for both cpx and opx, clinopyroxenes show chondrite-normalized REE patterns which are widely variable both in shape and absolute values, whereas orthopyroxenes exhibit more restricted ranges and concordant profiles.REE activity ratios have been investigated by applying Iiyama's (Bull. Soc. fr. Minéral. Christallogr.97, 143–151) thermodynamic model: the estimated activity patterns exhibit a good coherence for the different pyroxene pairs, in spite of the contrasting features of their REE concentration ratios. The wide ranges in the measured partition values for the same rare earth element in different pyroxene pairs have been related to coupled substitutions involving A1 in the Z site and REE in the M₂ site of clinopyroxene.     

相山铀矿田成矿流体特征:来自微量、稀土元素地球化学证据

相山铀矿田的成矿流体性质和来源存在争议,为进一步探讨相山铀矿田成矿流体的性质和来源,本文对相山铀矿田西部的居隆庵铀矿床和北部的沙洲铀矿床中的新鲜围岩、蚀变围岩及矿石的微量、稀土元素含量及其变化进行了研究。结果显示:在含较多热液成因萤石的居隆庵铀矿床中,从新鲜围岩到蚀变围岩到矿石,Zr、Hf含量先降低再升高;而在含少量热液萤石的沙洲铀矿床中,新鲜围岩、蚀变围岩和矿石的Zr、Hf含量基本一致。鉴于富F流体易汲取岩石中的Zr、Hf,因此,这两个矿床中不同类型样品Zr、Hf含量的不同变化趋势,可能与居隆庵铀矿床的成矿流体富F、而沙洲铀矿床的成矿流体相对贫F有关。这两个铀矿床中矿石的稀土配分曲线与其各自的新鲜及蚀变围岩的稀土配分曲线形态相似但又存在差异,说明每个矿床的新鲜围岩、蚀变围岩和矿石之间的稀土元素既具有继承性、又受到不同性质的流体的影响。居隆庵铀矿床中矿石显示Eu负异常,可能主要是继承了围岩的Eu负异常;沙洲铀矿床中矿石Eu显示弱负异常至弱正异常的特征,可能与围岩中斜长石因热液蚀变作用而释放出的Eu的进入流体有关。基于新鲜围岩、蚀变围岩及矿石的U和REE研究,推断居隆庵铀矿床成矿流体中U和REE均以F的络合物形式迁移;但沙洲铀矿床中铀矿石品位较低,可能是与流体中相对贫F有关。     

淮南采煤沉陷区表层沉积物稀土元素地球化学特征

稀土元素由于其独特的化学特征被广泛应用于环境地球化学分析过程研究。以淮南采煤沉陷区表层沉积物中稀土元素(REEs)为研究对象,采集研究区潘一、顾桥、谢桥沉陷区的表层沉积物样品共12个,采用ICP-MS对样品的稀土元素含量进行测试分析,探讨了表层沉积物中稀土元素的含量分布特征、控制因素及其物质来源。结果表明:研究区表层沉积物中稀土元素含量为54.63~130.45 μg/g,平均102.60 μg/g;LREE/HREE比值为11.89~20.55,平均14.29,轻稀土呈现明显富集现象;相关性分析结果显示,REEs趋向于黏土组分中富集;研究区养殖和捕捞活动导致表层沉积物中稀土元素含量的降低;球粒陨石标准化结果表明,研究区稀土元素呈现不同程度的La和Gd正异常,其中,Gd正异常主要是受到燃煤的影响,而La正异常主要与燃煤和化肥有关。结合Pearson相关性、球粒陨石标准化和(La/Yb)_N-(La/Sm)_N-(Gd/Yb)_N三元图判别,认为研究区水体表层沉积物中稀土元素与人类活动(燃煤和化肥)有关,研究认识为污染物的源头控制和煤矿区环境的生态治理提供参考依据。      

香花岭花岗岩稀土元素演化

香花岭地区花岗岩中的稀土元素呈逆向演化 ,其演化过程受花岗岩体系中的岩浆主成分、熔体结构相及流体组分变化等影响。花岗岩造岩矿物中稀土元素与各自岩石变化的一致性 ,可能暗示稀土元素的演化受岩浆的制约 ;稀土元素总量随岩浆演化而下降 ,与岩浆体系降温矿物的晶出、熔体相的相对减少、流体相的增加及射气分异作用的发生等有关 ,而轻稀土富集则是由于岩浆体系向碱性增强方向演化的结果。对于连续演化的花岗岩而言 ,稀土元素的分布样式或许可作为岩浆演化酸碱环境的指向 ;负铕异常的减小除与岩浆主成分的变化有关外 ,还与氧化 还原环境的变化有关     

Fractionation characteristics of rare earth elements (REEs) linked with secondary Fe,Mn, and Al minerals in soils

Soil secondary minerals are important scavengers of rare earth elements (REEs) in soils and thus affect geochemical behavior and occurrence of REEs. The fractionation of REEs is a common geochemical phenomenon in soils but has received little attention, especially fractionation induced by secondary minerals. In this study, REEs (La to Lu and Y) associated with soil-abundant secondary minerals Fe-, Al-, and Mn-oxides in 196 soil samples were investigated to explore the fractionation and anomalies of REEs related to the minerals. The results show right-inclined chondrite-normalized REE patterns for La–Lu in soils subjected to total soil digestion and partial soil extraction. Light REEs (LREEs) enrichment features were negatively correlated with a Eu anomaly and positively correlated with a Ce anomaly. The fractionation between LREEs and heavy REEs (HREEs) was attributed to the high adsorption affinity of LREEs to secondary minerals and the preferred activation/leaching of HREEs. The substantial fractions of REEs in soils extracted by oxalate and Dithionite-Citrate-Bicarbonate buffer solutions were labile (10 %–30 %), which were similar to the mass fraction of Fe (10 %–20 %). Furthermore, Eu was found to be more mobile than the other REEs in the soils, whereas Ce was less mobile. These results add to our understanding of the distribution and geochemical behavior of REEs in soils, and also help to deduce the conditions of soil formation from REE fractionation.     

Geochemistry of rare earth elements in the modern sediments of Amur Bay (the Japan/East Sea)

The distribution of REE in the bottom sediments of Amur Bay accumulated over the last 100 years was studied, and the REE contents were evaluated. The REE contents normalized to North American Shale Composite (NASC) show a negative Ce anomaly and a predominance of LREE and MREE. The inflow and accumulation of REE in the bottom sediments are influenced mainly by natural sources, whereas their dependence on anthropogenic factors is minimal.     

四川稀土精矿的稀土元素和微量元素地球化学特征及开发利用意义

产自广东省梅州市玉水铜矿的景文矿,属于含水、重稀土-矾-铝硅酸盐矿物(简写为HREE-V-铝硅酸盐矿物),其化学结构式为Y₂Al₂V₂⁴⁺(SiO₄)₂O₄(OH)₄,该矿物在全球属首次发现,暂未开展相关研究。相对于含轻稀土矿物,含重稀土矿物在电子探针分析过程中,当被高压电子束轰击时,被激发出来的特征X射线线系繁多,线系之间分布更加密集,彼此之间相互重叠的现象也更为严重,要获得理想数据的难度很大,是亟待解决和突破的技术难题。本文对该矿物进行了精细的电子探针定量分析,获得理想的化学成分数据,为新矿物命名提供了理论数据技术支撑。通过对实验方法的探索和总结获得以下结果：①利用15kV加速电压、100nA束流对试样进行全元素扫描,以此确定出17种元素;②在定量分析过程中,对重叠峰进行了剥离;③利用仪器软件中的Zoom-Peak ID程序,选择出17种元素的分析线系、精确的峰位及上下背景值;④选取合适的标样及测试时间等定量分析条件,最终获得理想的定量分析结果(平均总量97.41wt%)。上述四条也是确保获得理想定量分析数据的关键因素。