Geochemical Constraints on Leucogranite Magmatism in the Langtang Valley, Nepal Himalaya

A complex of crustally derived leucogranitic sills emplacedinto sillimanite-grade psammites in the upper Langtang Valleyof northern Nepal forms part of the Miocene High Himalayan graniteassociation. A series of post-tectonic, subvertical leucograniticdykes intrude the underlying migmatites, providing possiblefeeders to the main granite sills. The leucogranite is peraluminous and alkali-rich, and can besubdivided into a muscovite–biotite and a tourmaline–muscovitefacies. Phase relations suggest that the tourmaline leucogranitescrystallized from a water-undersaturated magma of minimum-meltcomposition at pressures around 3–4 kbar. Potential metasedimentaryprotoliths include a substantial anatectic migmatite complexand a lower-grade mica schist sequence. Isotopic constraintspreclude the migmatites as a source of the granitic melts, whereastrace-element modelling of LILEs (Rb, Sr, and Ba), togetherwith the Nd and Sr isotopic signatures of potential protoliths,strongly suggest that the tourmaline-bearing leucogranites havebeen generated by fluid-absent partial melting of the muscovite-richschists. However, REE and HFSE distributions cannot be reconciledwith equilibrium melting from such a source. Systematic covariationsbetween Rb, Sr, and Ba can be explained by variations in protolithmineralogy and P–T–a_H2O. Tourmaline leucogranites with high Rb/Sr ratios represent low-fraction-melts(F{small tilde} 12%) efficiently extracted from their protolithsunder conditions of low water activity, whereas the heterogeneoustwo-mica granites may result from melting under somewhat highera_H2O conditions. The segregation of low-degree melts from sourcewas probably by deformation-enhanced intergranular flow andmagma fracturing, with the mechanisms of migration and emplacementcontrolled by variations in the uppercrustal stress regime duringlate–orogenic extensional collapse of the thickened crust.     

Environmental quality assessment and spatial pattern of potentially toxic elements in soils of Guangdong Province, China

The spatial distributions of Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, and Zn concentrations in surface soils of Guangdong Province, China, were investigated to evaluate the environmental quality of these potentially toxic elements using 261 samples. The following average concentrations were obtained: Cu, 17.4 mg/kg; Ni, 17.7 mg/kg; Cr, 56.7 mg/kg; Co, 6.8 mg/kg; Mn, 223.2 mg/kg; Pb, 36.6 mg/kg; Hg, 0.10 mg/kg; Cd, 0.09 mg/kg; Zn, 49.8 mg/kg. Correlation analysis was applied to the data matrix to evaluate the results and identify the possible sources of metals. Distribution maps of the elements were created using the inverse distance weighted interpolation method. The nine metals exhibited generally distinct geographical patterns. Results showed that 5,173 km² of the study area presented higher pollution indices and was slightly polluted.     

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.     

An evaluation of the inverted metamorphic gradient at Langtang National Park, Central Nepal Himalaya

Abstract The crystalline core of the Himalayan orogen in the Langtang area of Nepal, located between the Annapurna-Manaslu region and the Everest region, contains middle to upper amphibolite grade pelitic gneisses and schists. These rocks are intimately associated with the Main Central Thrust (MCT), one of the major compressional structures in the northern Indian plate, which forms a 3.7-km-wide zone containing rocks of both footwall and hangingwall affinity. An inverted metamorphic gradient is noticeable from upper footwall through hangingwall rocks, where metamorphic conditions increase from garnet grade near the MCT zone to sillimanite + K-feldspar grade in the upper hangingwall. Petrographic data distinguish two metamorphic episodes that have affected the area: a high-pressure, moderate-temperature episode (M1) and a moderate-pressure, high-temperature episode (M2). Comparison with appropriate reaction boundaries suggests that conditions for M1 in the hangingwall were approximately 900–1200 MPa and 425–525°C. Thermobarometric results for 24 samples from the footwall, MCT zone and hangingwall reflect P-T conditions during the M2 phase of 400–1200 MPa and 490–660° C. The decrease in estimated palaeopressures from footwall to hangingwall approximate a lithostatic gradient of 27 MPa km^-1, with slight fluctuations in the MCT zone reflecting structural discontinuities. In contrast to the palaeopressures, palaeotemperatures are indistinguishable across the entire area sampled. Although field evidence suggests the presence of the inverted palaeothermal gradient well known in the Himalaya, quantitative thermobarometry indicates that temperatures of final equilibration were all within error of each other across 17 km of section. At Langtang, change in pressure is responsible for the presence of the sequence of index minerals through the section. I interpret these data to reflect diachronous attainment of equilibrium temperature conditions in a lithostatic palaeopressure profile after ductile faulting of the sequence.     

Mobility of some potentially toxic trace elements in the coal of Guizhou, China

 The mobility of 10 potentially toxic trace elements (PTTE), As, Cd, Cr, Cu, Hg, Ni, Pb, Se, Tl, and Zn from 32 coals of the Longtan Group formed in Permian Period in Guizhou Province, China was investigated using sequential extraction procedures. The results demonstrate that PTTEs such as Hg, As, Se, Cd, Cu, and Pb have the highest mobility at surface conditions, and the average extractable fractions of them are 86%, 95%, 79%, 76%, 69%, and 69% of the total amount in coal, respectively. The elements in coal with the lowest leachability include Tl, Cr, and Ni, and the average extractable fractions of them are 30%, 20%, and 29% of the total amount in coal respectively. Zinc has an intermediate behavior, and the average leachable fraction of it accounts for 46% of the total amount in coal. The results demonstrate that mobility of PTTE in coal depends on the speciation of these elements. The elements associated with sulfates, carbonates, sulfides and some organic matter in coal show the highest extraction rates during the weathering process, while elements with silicate affinities are inert at surface conditions. Received: 29 December 1998 · Accepted: 10 November 1998     

Environmental risk assessment of some potentially toxic elements in El-Tabbin region (Cairo, Egypt)

As much as 24 soil samples and 6 stream sediments from the River Nile were studied in El-Tabbin region (Great Cairo, Egypt). Twelve chemicals, potentially toxic elements posing potential environmental risk, were the object of concern in this study. Mean contents of analysed elements (in mg kg^?1) in soils and the River Nile stream sediments were the following: As_s 3.6/As_ss 1.5, Cd_s 0.33/Cd_ss 0.12, Cr_s 87.7/Cr_ss 141.5, Cu_s 40.3/Cu_ss 43.8, Hg_s 0.03/Hg_ss 0.13, Pb_s 33.3/Pb_ss 20.2, Zn_s 150/Zn_ss 109, Se_s 0.24/Se_ss 0.05, Ni_s 37.2/Ni_ss 48, Sb_s 1.25/Sb_ss 1, Ba_s 892/Ba_ss 431, V_s 103.3/V_ss 167.8. Furthermore, geochemical background values were derived for soil and stream sediment samples. The values are as follows (in mg kg^?1): As_s 1.33/As_ss 1, Cd_s 0.48/Cd_ss 0.05, Cr_s 54.7/Cr_ss 106.5, Cu_s 23.8/Cu_ss 23, Hg_s 0.025/Hg_ss 0.095, Pb_s 15.3/Pb_ss 13.5, Zn_s 70/Zn_ss 55, Se_s 0.13/Se_ss 0.05, Ni_s 19.5/Ni_ss 32.5, Sb_s 1/Sb_ss 1, Ba_s 266/Ba_ss 275, V_s 50.7/V_ss 119. More than two-thirds of soil and sediment samples exceeded established (based on literature data) risk limit values for non-polluted environment. Based on environmental risk assessment for potentially toxic elements in soils and sediments in more than 45% of total area disturbed environment (I _ER = 1–3) was documented and more than 13% of territory was characterised with highly disturbed environment (I _ER > 3).     

Available contents of potentially toxic elements in soils from the Eastern Amazon

Background Values of potentially toxic elements (PTEs) in soils are typically obtained from total or pseudo-total contents, but not represent the fraction of these elements available for plant uptake due to the predominance of the stable forms. Available contents to plants, in turn, tend to be positively correlated with the potential risk of contamination of PTEs. In this study, we determined the available contents, extracted with Mehlich-III solution, of Ba, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn in Oxisols and Ultisols in the state of Pará, Eastern Amazon, Brazil. Available contents ranged from low to very low when compared to soils from other Brazilian regions and from other countries. Contents of PTE were higher in Oxisols than in Ultisols, except for Cu and Ni. In the Oxisols, PTEs were positively correlated with clay content. However, PTEs were not correlated with soil pH, organic matter and cation exchange capacity. In the Ultisols, Ba, Cu, Pb, and Mn contents were significantly correlated with pH, while Ni contents were correlated with the contents of silt.     

Factors affecting the distribution of potentially toxic elements in surface soils around an industrialized area of northwestern Greece

In order to investigate the factors influencing the distribution of 32 potentially toxic elements in the Ptolemais–Kozani basin, northwestern Greece, 38 soil samples were collected and analyzed. Concentrations of Al, Ca, Fe, K, Mg, Mn, Na, P, Ti, Ba, Co, Cr, Cu, La, Li, Ni, Pb, Sc, Sr, V, Y, and Zn were determined by ICP-AES and concentrations of As, Bi, Cd, Cs, Mo, Rb, Sb, Th, Tl, and U by ICP-MS. Bivariate analysis, principal component analysis, and geostatistical analysis were employed to investigate the factors influencing the distribution of the elements determined in the study area. The results indicate that the distribution of the majority of elements determined, especially for Cr, Ni, and associated elements, is greatly influenced by the geology and geomorphology of the study area. Principal component analysis has yielded four factors that explain over 77% of the total variance in the data. These factors are as follows: lithophilic elements that are associated with Al silicates minerals of K (factor I: 29.4%), ultramafic rocks (factor II: 20.5%), elements that are coprecipitated with Fe and Mn oxides (factor III: 18.0%), and anthropogenic activities (factor IV: 9.3%). The anthropogenic activities that influence the distribution of several potentially toxic elements (i.e., Cd, Cu, Pb, Zn) are agricultural practices and the deposition of fly ash in the vicinity of the local power stations.     

Mineralogical control of rare earth elements in acid sulfate soils

Major, trace and rare earth element concentrations were measured in porewater, surface water and sediments at an acid sulfate soil site. The concentrations of La and Ce in porewater are up to 1-3 ppm. There is a strong correlation between REE concentration and acidity, except that the maximum concentrations were consistently found below the horizon of maximum acidity, associated with an increase in pH (to ca. 4) and change in mineralogy from jarosite-dominated to goethite-dominated mottles. Jarosite replacement by goethite is as expected with the rise in pH, which in turn is due to the occurrence of a fossil shell bed just below. The rare earth element patterns in the porewaters are enriched in the MREE with respect to Post-Archaean Australian Shale (PAAS). Measurements and calculations show that this is in accord with experiments on low-degree partial dissolution of jarosite, even when the jarosite itself is highly enriched in LREE. There is a clear fractionation in the patterns between the clay-rich soil matrix, which is slightly depleted in the LREE when normalized to PAAS (La/Yb_PAAS ∼0.5), and the secondary mineral phase jarosite, which is enriched in the LREE (La/Yb_PAAS = 15-50). The REE pattern in the porewater changes with the transition from jarosite- to goethite-rich mottles, becoming relatively more enriched in the LREE compared to the HREE, which is consistent with the incongruent dissolution of jarosite to form goethite and the release of greater amounts of jarosite REE to solution, including proportionately more of the jarosite-compatible LREE.Maximum surface water REE concentrations in acidic water were 100-200 ppb La and Ce. REE patterns in surface water were very similar to the porewater transition zone, enriched in the MREE, but asymmetric, relatively enriched in the LREE compared to the HREE.     

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。     

Contamination risk assessment of fresh groundwater using the distribution and chemical speciation of some potentially toxic elements in Calabar (southern Nigeria)

The computer program PHREEQC was used to determined the distribution, chemical speciation and mineral saturation indices in a fresh groundwater environment with limited mining activities in the adjoining areas. The aim was mainly to determine the potential risk of a coastal plain aquifer contamination by some potentially toxic elements. The results show that the elements Ba, Cd, Cu, Fe, Mn, Ni, Rb, Sr, and Zn are distributed as free metal ions. Arsenic is in the neutral form of H₃AsO₃ ^o, while three species of aluminium [Al³⁺, AlOH₂, Al(OH)₂ ⁺] dominate. The major species of uranium include UO₂CO₃, UO₂²⁺+, UO₂⁺, and UO₂OH⁺, respectively, in order of abundance. The groundwater is saturated with respect to alunite [KAl₃ (SO₄)₂ (OH)₆], basaluminite [Al₄ (OH)₁₀ SO₄], boehmite [Al(OH)], Cu metal (Cu), cuprous ferrite (CuFeO₂), diaspore [AlO(OH)], gibbsite [Al(OH)₃], goethite (FeOOH), hematite (Fe₂O₃), magnetite (Fe₃O₄) and uraninite (UO₂). Most of the species are not mobile under the prevailing pH (3.3 to 5.9) and Eh (7 to 158 mV) conditions. The mobile ones are very low in concentration and will be immobilized by precipitation of mineral phases. The study concludes that presently these species do not pose any risk to the aquifer.     

桂岭岩体稀土、微量元素地球化学特征研究

文章运用岩石地球化学方法,对桂岭岩体的构造环境和地球化学特征进行了研究,结果显示：桂岭岩体岩石平均LREE／HREE=7．68,（La／Yb）N-6．77,（La／Sm）N-4．65,（Gd／Yb）N-1．04,平均δEu=0．45〈1,表明轻重稀土轻度分异,轻稀土相对富集,轻稀土内部分馏明显,存在负铕异常;岩体明显亏损Nb、Sr、Ti,显示桂岭岩体的源区可能主要来自地壳,是地壳环境下壳源岩石发生部分熔融的产物;研究表明,桂岭岩体形成于挤压一伸展的大地构造环境。     

沈阳市土壤铅的空间分布及风险评价研究

经测定,沈阳市土壤铅含量范围为22～2910.600mg/kg,平均值是270.297mg/kg。铅污染比较严重且空间变化大,局地污染非常严重。利用地统计方法研究了沈阳市土壤铅的空间结构和分布特征。结果显示,沈阳市土壤铅具有较好的空间结构性,利用半方差函数的结果进行克里格插值得到土壤铅含量的分布图。沈阳市有6个土壤铅污染中心,其中以铁西区和太原街的污染比较突出。工业排放、汽车尾气和污灌是沈阳市铅污染的三大污染源。风险评价结果表明,铁西区属于极高风险区,儿童铅中毒的潜在风险非常大。     

中国南方红壤中稀土元素分布的研究

中国南方红壤中稀土元素总量主要集中在１５０￣２００μｇ／ｇ范围内,且土壤剖面层的底土层含量较高;稀土元素分布模式表明,红壤中轻稀土元素间略有分异,而轻,重稀土元素间以及重稀土元素间没有明显分异,稀土元素含量与红壤中有机质,粘粒含量及阳离子交换量间的相关性很弱,而与红壤中铁锰氧化物及磷酸岩呈显著的正相关关系。     

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。

     

Spatial distribution and geochemical baselines of major/trace elements in soils of Medak district,Andhra Pradesh,India

Regional-scale variations in soil geochemistry were investigated with special reference to differences among soil groups and lithology in an area of 9,699 km² in Medak district, Andhra Pradesh, India. The concentrations of 29 elements (major: Si, Al, Fe, Mn, Mg, Ca, Na, K, Ti, P and trace: As, Ba, Cd, Co, Cr, Cu, F, Mo, Ni, Pb, Rb, Se, Sr, Th, U, V, Y, Zn, Zr) in 878 soil samples collected (557-topsoil, 321-subsoil) at a sampling density of 1 site/17 km² from 557 sites representative of all the soil types present in studied area were determined, and their elemental composition are discussed. The baseline levels of these elements in soils are determined over different lithological units for the identification of anomalous values relative to these. For the first time, geochemical maps for Medak district are prepared on 1:50,000 scale and the lithogeochemical database generated provides information on the lateral and vertical distribution of elements in soil. The spatial variations in the distribution of elements reflect underlying geologic characteristics. Box-plots reveal that the concentration of most of the elements in soils were not strongly dependent on the soil group but the soil-geochemistry abruptly changes with the change in the soil parent materials indicating that the distribution of elements is mostly influenced by the bedrock lithology and other natural processes acting on them. For instance, the concentrations of Co, Cu, Fe, Mn, Ti, V and Zn are high in soils developed on basaltic terrain while the soils developed on granitic and gneissic terrain exhibit high elemental concentrations of K, Pb, Rb, Si, Th and Y. Alfisols had relatively high contents of elements while entisols had lower concentrations of most of the elements. The database can be used in the chemical characterisation of different geological units as well as applications in various environmental and agricultural fields. The results indicate that regional geology is an important determinant of soil geochemical baselines for soil pollution assessment and further emphasizes the importance of determining background levels locally. The defined baselines can be used to establish background values for future soil surveys.