Submarine groundwater discharge is an important net source of light and middle REEs to coastal waters of the Indian River Lagoon, Florida, USA

Porewater (i.e., groundwater) samples were collected from multi-level piezometers across the freshwater-saltwater seepage face within the Indian River Lagoon subterranean estuary along Florida’s (USA) Atlantic coast for analysis of the rare earth elements (REE). Surface water samples for REE analysis were also collected from the water column of the Indian River Lagoon as well as two local rivers (Eau Gallie River, Crane Creek) that flow into the lagoon within the study area. Concentrations of REEs in porewaters from the subterranean estuary are 10-100 times higher than typical seawater values (e.g., Nd ranges from 217 to 2409 pmol kg⁻¹), with submarine groundwater discharge (SGD) at the freshwater-saltwater seepage face exhibiting the highest REE concentrations. The elevated REE concentrations for SGD at the seepage face are too high to be the result of simple, binary mixing between a seawater end-member and local terrestrial SGD. Instead, the high REE concentrations indicate that geochemical reactions occurring within the subterranean estuary contribute substantially to the REE cycle. A simple mass balance model is used to investigate the cycling of REEs in the Indian River Lagoon and its underlying subterranean estuary. Mass balance modeling reveals that the Indian River Lagoon is approximately at steady-state with respect to the REE fluxes into and out of the lagoon. However, the subterranean estuary is not at steady-state with respect to the REE fluxes. Specifically, the model suggests that the SGD Nd flux, for example, exported from the subterranean estuary to the overlying lagoon waters exceeds the combined input to the subterranean estuary from terrestrial SGD and recirculating marine SGD by, on average, ∼100 mmol day⁻¹. The mass balance model also reveals that the subterranean estuary is a net source of light REEs (LREE) and middle REEs (MREE) to the overlying lagoon waters, but acts as a sink for the heavy REEs (HREE). Geochemical modeling and statistical analysis further suggests that this fractionation occurs, in part, due to the coupling between REE cycling and iron redox cycling within the Indian River Lagoon subterranean estuary. The net SGD flux of Nd to the Indian River Lagoon is ∼7-fold larger than the local effective river flux to these coastal waters. This previously unrecognized source of Nd to the coastal ocean could conceivably be important to the global oceanic Nd budget, and help to resolve the oceanic “Nd paradox” by accounting for a substantial fraction of the hypothesized missing Nd flux to the ocean.     

Environmental biogeochemical characteristics of rare earth elements in soil and soil-grown plants of the Hetai goldfield,Guangdong Province,China

Very few studies deal with the biogeochemical behaviors of rare earth elements (REEs) in goldfields. This paper presents the geochemical and biogeochemical characteristics of REEs within the soil–plant system in the Hetai goldfield, Guangdong, China. The samples from the goldfield region show anomalies in distribution patterns and behavioral characteristics of REES as compared with those from the background areas. The REEs in rocks, soils, and plants prove to be much higher than those in the surrounding regions. The distribution patterns of REEs are characterized by LREE-enrichment and HREE-depletion, with the REE concentrations in Layer A being the highest. Differentiations between LREEs and HREEs may lead to some extent of negative Eu anomaly in the soils. Research results demonstrate that the REEs in a soil profile can be transferred and accumulated during the mineral formation and supergenic geochemical processes, and the anomalies are obviously related to the geological settings for the REE-bearing ore-forming processes and to the geochemical characteristics of the habitats for the REE-bearing plants. For Dicranopteris dichotoma, the total amount of REEs in the tissues shows an order of leaf > root > stem, while for Pinus massoniana the order becomes root > leaf > stem. The distribution patterns of REEs in Pinus massoniana leaves are similar to those in soils where the plants grow up in the mineralization area. However, in the background areas the REE distribution patterns for Pinus massoniana stems are similar to those for soils where the plants grow up. Parameters such as biological absorption coefficients and biological transfer coefficients show the differences in REE absorption features among plants and indicate that REEs can be transferred among plant organs. The two coefficients can reveal the different survival mechanisms for the two plant species, which are subject to long-term REE-affected stress conditions in the gold mineralization zone.     

Geochemical characteristics and provenance implication of rare earth elements in surface sediments from bays along Guangdong Coast, Southeast China

A systematic study of the granulometric properties and the occurrence and distribution of rare earth elements (REE) within surface sediments from ten bays situated along the coast of Southeast China has facilitated a more rigorous understanding of constraints on sediment provenance in the area. The results show that REE concentrations are similar within a single bay, but vary considerably (133.58–251.77 mg/kg) among the bays. The chondrite-normalized distribution patterns show the typical enrichment of light REEs (LREEs: La–Eu) relative to heavy REEs (HREEs: Gd–Lu), and an apparent depletion of Eu, which is diagnostic of a terrigenous sediment source. Obvious enrichments of the middle REEs (MREEs: Sm–Ho) in the PAAS-normalized (Post-Archean Australian Shale) distribution patterns of these bay sediments are similar to results reported from large rivers in China. Comparing the REE composition of the bay sediments with those of adjoining fluvial sediments and with the bedrock of the surrounding drainage basins, the latter are indicated as the dominant sediment source. The uniform REE distribution patterns, and MREE enrichments, prove that the sediments are derived from the material transported by the streams and rivers that discharge into the bays.     

A rare earth element-rich carbonatite dyke at Bayan Obo, Inner Mongolia, North China

Summary ?A carbonatite dyke, extremely enriched in rare earth elements (REE), is reported from Bayan Obo, Inner Mongolia, North China. The REE content in the dyke varies from 1 wt% to up to 20 wt%. The light REEs are enriched and highly fractionated relative to the heavy REEs, and there is no Eu anomaly. Although carbon isotope δ¹³C (PDB) values of the carbonatites (−7.3 to −4.7‰) are within the range of normal mantle (−5±2‰), oxygen isotope δ¹⁸O (SMOW) (11.9 to 17.7‰) ratios apparently are higher than those of the mantle (5.7±1.0‰), indicating varying degrees of exchange with hydrothermal fluids during or after magmatic crystallization. The carbonatite is the result of partial melting followed by fractional crystallization. Primary carbonatite melt was formed by less than 1% partial melting of enriched mantle, leaving a garnet-bearing residue. The melt then rose to a crustal magma chamber and underwent fractional crystallization, producing further REE enrichment. The REE and trace element distribution patterns of the carbonatites are similar to those of fine-grained dolomite marble, the ore-host rock of the Bayan Obo REE–Nb–Fe giant mineral deposit. This fact may indicate a petrogenetic link between the dykes described here and the Bayan Obo mineral deposit. Received November 1, 2001; revised version accepted June 16, 2002     

Geochemistry and biogeochemistry of rare earth elements in a surface environment (soil and plant) in South China

Plants and soils derived from different kinds of parent materials in South China were collected for analyses of rare earth elements (REEs) by inductively coupled plasma-mass spectrometry (ICP-MS). The distribution patterns and transportation characteristics of REEs in the soil–plant system were studied. The results show that geochemical characteristics of REEs depend on the types of soils, soils derived from granite being the highest in REE concentration. In a soil profile, REE concentrations are higher in B and C horizons than those in A horizon, with Eu negative anomaly and Ce positive anomaly. Plants of different genera growing in the same sampling site have quite similar REE distribution pattern, but plants of the same genera growing in different soils show considerable variation in characteristics of REEs. The patterns of the different parts of plant resemble each other, but the slope of the patterns becomes different. REEs have fractionated when they were transported and migrated from soil to plant root, stem and leaf, revealing that heavy REEs are relatively less available. REEs distributions in plants are influenced by the soil they grow in and also characterized by their individual biogeochemical characteristics. Biological absorption coefficients indicate difference of REE absorption capacity of plants. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Retention of Sm–Nd isotopic ages in garnets subjected to high-grade thermal reworking: implications for diffusion rates of major and rare earth elements and the Sm–Nd closure temperature in garnet

Garnet is a vital mineral for determining constrained P–T–t paths as it can give both the P–T and t information directly. However, estimates of the closure temperature of the Sm–Nd system in garnet vary considerably leading to significant uncertainties in the timing of peak conditions. In this study, five igneous garnets from an early Proterozoic 2414 ± 6 Ma garnet—cordierite bearing s-type granite—which was subjected to high-T reworking have been dated to examine their diffusional behaviour in the Sm–Nd system. Garnets 8, 7, 6 and 2.5 mm in diameter were compositionally profiled and then dated, producing two-point Sm–Nd isochron ages of 2412 ± 10, 2377 ± 5, 2370 ± 5 and 2365 ± 8 and 2313 ± 11 Ma, respectively. A direct correlation exists between grain size and amount of resetting highlighting the effect of grain size on closure temperature. Major element EMPA and LA-ICPMS REE traverses reveal homogenous major element profiles and relict igneous REE profiles. The retention of REE zoning and homogenisation of major element zoning suggest that diffusion rates of REEs are considerably slower than that of the major cations. The retention of REE zoning and the lack of resetting in the largest grains suggest that Sm–Nd closure temperature in garnet is a function of grain size, thermal history and REE zoning in garnet.     

Petrological and geochemical characteristics of Zhaibei granites in Nanling region,Southeast China: Implications for REE mineralization

Mineralization with ion adsorption rare earth elements (REEs) in the weathering profile of granitoid rocks from Nanling region of Southeast China is an important REE resource, especially for heavy REE (HREE) and Y. However, the Jurassic granites in Zhaibei which host the ion adsorption light REE (LREE) ores are rare. It is of peraluminous and high K calc-alkaline composition, which has similar geochemical features of high K₂O + Na₂O and Zr + Nb + Ce + Y contents and Ga/Al ratio to A-type granite. Based on the chemical discrimination criteria of Eby [Geology 20 (1992) 641], the Zhaibei granite belongs to A1-type and has similar source to ocean island basalts. The rock is enriched in LREE and contains abundant REE minerals including LREE-phosphates and halides. Minor LREE was also determined in the feldspar and biotite, which shows negligible and negative Eu anomalies, respectively. This indicates that the Zhaibei granite was generated by extreme differentiation of basaltic parent magmas. In contrast, granites associated with ion adsorption HREE ores contain amounts of HREE minerals, and show similar geochemical characteristics with fractionated felsic granites. Note that most Jurassic granitoids in the Nanling region contain no REE minerals and cannot produce REE mineralization. They belong to unfractionated M-, I- and S-type granites. Therefore, accumulation of REE in the weathering profile is controlled by primary REE mineral compositions in the granitoids. Intense fractional crystallization plays a role on REE enrichment in the Nanling granitoid rocks.     

Groundwater quality,nitrate pollution and irrigation environmental management in the Neogene sediments of an agricultural region in central Thessaly (Greece)

The degradation of groundwater quality, which has been noted in the recent years, is closely connected to the intensification of agriculture, the unreasonable use of chemical fertilizers and the excess consumption of large volumes of irrigation water. In the hilly region of central Thessaly in Greece, which suffers the consequences of intense agricultural use, a hydrogeological study is carried out, taking groundwater samples from springs and boreholes in the Neogene aquifers. The aim of this study is the investigation of irrigation management, water quality and suitability for various uses (water supply, irrigation), the degradation degree and the spatial distribution of pollutants using GIS. The following hydrochemical types prevail in the groundwater of the study area: Ca–Mg–HCO₃, Mg–Ca–Na–HCO₃ and Na–HCO₃. In the above shallow aquifers, especially high values of NO₃ ⁻ (31.7–299.0), NH₄ ⁺ (0.12–1.11), NO₂ ⁻ (0.018–0.109), PO₄ ³⁻ (0.07–0.55), SO₄ ²⁻ (47.5–146.5) and Cl⁻ (24.8–146.5) are found, particularly near inhabited areas (values are in mg L⁻¹). The water of shallow aquifers is considered unsuitable for human use due to their high polluting load, while the water of the deeper aquifers is suitable for human consumption. Regarding water suitability for irrigation, the evaluation of SAR (0.153–7.397) and EC (481–1,680 μS cm⁻¹) resulted in classification category ‘C3S1’, indicating high salinity and low sodium water which can be used for irrigation in most soils and crops with little to medium danger of development of exchangeable sodium and salinity. The statistical data analysis, the factor analysis and the GIS application have brought out the vulnerable-problematic zones in chemical compounds of nitrogen and phosphates. The groundwater quality degradation is localized and related exclusively to human activities. Based on 2005 and 2008 estimates, the annual safe yield of the region’s aquifers were nearly 41.95 MCM. However, the existing situation is that 6.37 MCM of water is over extracted from these aquifers.     

In-situ LA-ICP-MS trace elemental analyses of magnetite: The Bayan Obo Fe-REE-Nb deposit,North China

The Bayan Obo Fe-REE-Nb deposit in northern China is the world's largest light REE deposit, and also contains considerable amounts of iron and niobium metals. Although there are numerous studies on the REE mineralization, the origin of the Fe mineralization is not well known. Laser ablation (LA) ICP-MS is used to obtain trace elements of Fe oxides in order to better understand the process involved in the formation of magnetite and hematite associated with the formation of the giant REE deposit. There are banded, disseminated and massive Fe ores with variable amounts of magnetite and hematite at Bayan Obo. Magnetite and hematite from the same ores show similar REE patterns and have similar Mg, Ti, V, Mn, Co, Ni, Zn, Ga, Sn, and Ba contents, indicating a similar origin. Magnetite grains from the banded ores have Al + Mn and Ti + V contents similar to those of banded iron formations (BIF), whereas those from the disseminated and massive ores have Al + Mn and Ti + V contents similar to those of skarn deposits and other types of magmatic-hydrothermal deposits. Magnetite grains from the banded ores with a major gangue mineral of barite have the highest REE contents and show slight moderate REE enrichment, whereas those from other types of ores show light REE enrichment, indicating two stages of REE mineralization associated with Fe mineralization. The Bayan Obo deposit had multiple sources for Fe and REEs. It is likely that sedimentary carbonates provided original REEs and were metasomatized by REE-rich hydrothermal fluids to form the giant REE deposit.     

Dominants and accumulation of rare earth elements in sediments derived from riparian and depressional marshes

The rare earth elements (REEs) in the sediments of the Xianghai wetlands were measured by inductively coupled plasma spectrometry. The REEs accumulation rates in two sedimentation cores derived from the riparian and depressional marshes were determined by ²¹⁰Pb method. The results showed that REEs concentrations in the Xianghai wetland sediments (∑REEs, 116 mg kg⁻¹) were lower than the corresponding values in Chinese soils (181 mg kg⁻¹) and river sediments (∑REEs, 158–191 mg kg⁻¹). Under alkaline conditions (with pH, 8.2–10.3), the light REEs were more enriched than the heavy REEs. Cerium is the predominant element, and accounts for 30–33% of the total REEs. REEs in the depressional marsh sediments were relatively high (∑REEs, 127 vs. 104 mg kg⁻¹), especially light REEs contents. A significantly positive correlation was found between the neighboring elements except Pr and Dy. The different types of vertical distribution of REEs between the riparian and the depressional marsh can partly result from long-term differing hydrological regimes. Generally, depressional marsh had accumulated much more REEs than riparian marsh (the mean accumulation rates of ∑REEs, 102.98 vs. 48.89 μg cm⁻² year⁻¹).     

Geochemical and Sm–Nd isotopic study of titanite from granitoid rocks of the eastern Dharwar craton,southern India

Titanite occurs as an accessory phase in a variety of igneous rocks, and is known to concentrate geologically important elements such as U, Th, rare earth element (REE), Y and Nb. The differences in the abundances of the REEs contained in titanite from granitoid rocks could reflect its response to changes in petrogenetic variables such as temperature of crystallization, pressure, composition, etc. Widespread migmatization in the granodiorite gneisses occurring to the east of Kolar and Ramagiri schist belts of the eastern Dharwar craton resulted in the enrichment of the REEs in titanite relative to their respective host rocks. A compositional influence on the partitioning of REEs between titanite and the host rock/magma is also noticed. The relative enrichment of REEs in titanite from quartz monzodiorite is lower than that found in the granodioritic gneiss. Depletion of REE and HFSE (high field-strength elements) abundances in granitic magmas that have equilibrated with titanite during fractional crystallization or partial melting has been modelled. As little as 1% of titanite present in residual phases during partial melting or in residual melts during fractional crystallization can significantly lower the abundances of trace elements such as Nb, Y, Zr and REE which implies the significance of this accessory mineral as a controlling factor in trace element distribution in granitoid rocks. Sm–Nd isotope studies on titanite, hornblende and whole rock yield isochron ages comparable to the precise U–Pb titanite ages, invoking the usefulness of Sm–Nd isochron ages involving minerals like titanite.     

Ligand extraction of rare earth elements from aquifer sediments: Implications for rare earth element complexation with organic matter in natural waters

The ability of organic matter as well as carbonate ions to extract rare earth elements (REEs) from sandy sediments of a Coastal Plain aquifer was investigated for unpurified organic matter from different sources (i.e., Mississippi River natural organic matter, Aldrich humic acid, Nordic aquatic fulvic acid, Suwannee River fulvic acid, and Suwannee River natural organic matter) and for extraction solutions containing weak (i.e., CH₃COO⁻) or strong (i.e., ) ligands. The experimental results indicate that, in the absence of strong REE complexing ligands in solution, the amount of REEs released from the sand is small and the fractionation pattern of the released REEs appears to be controlled by the surface stability constants for REE sorption with Fe(III) oxides/oxyhydroxides. In the presence of strong solution complexing ligands, however, the amount and the fractionation pattern of the released REEs reflect the strength and variation of the stability constants of the dominant aqueous REE species across the REE series. The varying amount of REEs extracted by the different organic matter employed in the experiments indicates that organic matter from different sources has different complexing capacity for REEs. However, the fractionation pattern of REEs extracted by the various organic matter used in our experiments is remarkable consistent, being independent of the source and the concentration of organic matter used, as well as solution pH. Because natural aquifer sand and unpurified organic matter were used in our experiments, our experimental conditions are more broadly similar to natural systems than many previous laboratory experiments of REE-humic complexation that employed purified humic substances. Our results suggest that the REE loading effect on REE-humic complexation is negligible in natural waters as more abundant metal cations (e.g., Fe, Al) out-compete REEs for strong binding sites on organic matter. More specifically, our results indicate that REE complexation with organic matter in natural waters is dominated by REE binding to weak sites on dissolved organic matter, which subsequently leads to a middle REE (MREE: Sm-Ho)-enriched fractionation pattern. The experiments also indicate that carbonate ions may effectively compete with fulvic acid in binding with dissolved REEs, but cannot out compete humic acids for REEs. Therefore, in natural waters where low molecular weight (LMW) dissolved organic carbon (DOC) is the predominant form of DOC (e.g., lower Mississippi River water), REEs occur as “truly” dissolved species by complexing with carbonate ions as well as FA, resulting in heavy REE (HREE: Er-Lu)-enriched shale-normalized fractionation patterns. Whereas, in natural terrestrial waters where REE speciation is dominated by organic complexes with high molecular weight DOC (e.g., “colloidal” HA), only MREE-enriched fractionation patterns will be observed because the more abundant, weak sites preferentially complex MREEs relative to HREEs and light REEs (LREEs: La-Nd).     

Rare earth elements in pore waters of marine sediments

The rare earth elements (REEs) were measured in pore waters of the upper ∼25 cm of sediment from one site off Peru and three sites on the California margin. The pore water REE concentrations are higher than sea water and show systematic down core variations in both concentration and normalized pattern. From these analyses and from comparison to other chemical species measured (dissolved Fe, Mn, Ba, oxygen, nitrate, phosphate), it is suggested that pore water REEs can be grouped into three categories: those that are from an Fe-source, those that are from a POC-source, and cerium oxide. REEs from the Fe-source appear where anoxia is reached; they have a distinctive “middle-REE (MREE) enriched” pattern. The concentrations in this source are so elevated that they dominate REE trends in the Fe-oxide reduction zone. The net result of flux from the POC-source is relative enrichment of heavy-REEs (HREEs) over light-REEs (LREEs), reflecting remineralizing POC and complexation with DOC. A common “linear” REE pattern, seen in both oxic and anoxic sediments, is associated with this POC-source, as well as a “HREE enriched” pattern that is seen in surficial sediments at the Peru site. Overall, the pore water results indicate that Mn-oxides are not an important carrier of REEs in the oceans.A REE biogeochemical model is presented which attempts to reconcile REE behavior in the water and sediment columns of the oceans. The model proposes that POC, Fe-oxide and Ce-oxide sources can explain the REE concentration profiles and relative abundance patterns in environments ranging from oxic sea water to anoxic pore water. The model is also consistent with our observation that the “Ce-anomaly” of pore water does not exceed unity under any redox condition.     

Fluoride,nitrate and water hardness in groundwater supplied to the rural communities of Ensenada County,Baja California,Mexico

The hydrogeochemistry of 26 wells belonging to ten different aquifers in the county of Ensenada, Baja California, is studied. These wells are all used to supply the rural communities in the region, which comprise ~37,000 inhabitants, excluding the city of Ensenada. High total dissolved solids (TDS) concentrations (maximum 7.35 g l⁻¹) indicate that salt is a ubiquitous contaminant in the aquifers due to seawater intrusion. The aquifers that support extensive agriculture activities (Maneadero, San Quintín, San Simón and El Rosario) are characterized by higher N–NO₃ concentrations (maximum 20 mg l⁻¹) derived from fertilizers. Fluoride concentrations exceed the 1.5 mg l⁻¹ Mexican official limit in only four wells. The enrichments of F⁻ in the southern aquifers are thought to be associated to water–rock interactions controlled mainly by Na–Ca equilibrium reactions with fluorite, as suggested from high dissolved Na concentrations in these waters. In the northern aquifer of Maneadero, no enrichment of Na is found and a geothermal source for F⁻ is likely. Water is hard to moderately hard, with Ca/Mg ratios >1. Although drinking water directly from the tap is not a common practice in these localities, most sources have concentrations of major ions and TDS that exceed the Mexican official limits.     

广西某地花岗岩风化壳中稀土元素特征与iREE矿床成矿机制

为了解风化壳中离子交换相稀土元素的特征,对广西某地花岗岩风化壳剖面样品进行了X射线衍射及主量、稀土元素地球化学特征的研究.剖面自上而下可划分为腐殖土层(A₁)、亚粘土层(A₂)、网纹状风化层(B₁)和全风化层(B₂);自A₁至B₂,粘土矿物的含量和化学风化蚀变指数快速降低;与母岩相比A₁、A₂、B₁中全相Ce、Nd和HREE相对富集,B₂中全相稀土与母岩特征相似,所有样品的离子交换相HREE亏损,Y相对富集;离子交换相轻、重稀土一起富集在B₂中.据此推测,花岗岩中褐帘石、榍石等易风化的稀土矿物为离子交换相稀土提供了主要的物源,锆石、磷钇矿等难风化的稀土矿物的残留及表生稀土矿物的形成使全相HREE相对富集;离子交换相轻、重稀土元素的分馏程度随风化程度的增加而变化.      

Study of stable isotopes for highly deformed aquifers in the Hsinchu-Miaoli area, Taiwan

This study was based on the analysis of isotopic compositions of hydrogen and oxygen in samples from precipitation, groundwater and stream water. In addition, parts of groundwater samples were dated by carbon-14 and tritium. These data are integrated to provide other views of the hydrologic cycle in the Hsinchu-Miaoli groundwater district. The groundwater district is principally composed of Pleistocene and Holocene aquifers. The Pleistocene aquifers are highly deformed by folding and faults into small sub-districts with areas of only tens of square kilometers. These aquifers are exclusively recharged by local precipitation. The Holocene aquifers cover narrow creek valleys, only tens of meters in thickness. The local meteoric water line (LMWL), constructed from rainfall samples in the Hsinchu Science Park, is described by the equation δD=8.02δ¹⁸O+10.16, which agrees with the global meteoric water line. In addition, the precipitation isotopic compositions can be categorized into two distinct end members: typhoon type and monsoon type. The groundwater isotopic compositions are perfectly located on an LMWL and can be considered a mixture of precipitations. Based on the mass balance of isotopic compositions of oxygen and hydrogen, infiltration is more active in the rainy season with depleted isotopic compositions. The amount of infiltration during May–September is roughly estimated to comprise at least 55% of the whole year’s recharge. The isotopic compositions of stream water are expressed by a regression equation: δD=7.61δ¹⁸O+9.62, which is similar to the LMWL. Although precipitation isotopic compositions are depleted during summer time, the isotopic compositions contrarily show an enriched trend in the upstream area. This is explained by the opposite altitude effect on isotopic compositions for typhoon-related precipitations.     

Geochemistry of Lower Cretaceous limestones of the Alisitos Formation,Baja California,México: Implications for REE source and paleo-redox conditions

Measurement of the major and trace elements were carried out on the Lower Cretaceous limestones interbedded in the volcano-sedimentary Alisitos Formation, northwestern México to understand the source of rare earth elements (REEs) and paleo-redox conditions. The five limestone beds (from the base up, Unit 5 to Unit 9) of the Alisitos Formation show large variations in SiO₂ content (0.9–27.9%). A low concentration of CaO is observed in Unit 6 and Unit 8, and high content of CaO is observed in Unit 5, Unit 7 and Unit 9. The limestones are depleted in many trace elements with respect to Post-Archaean Australian Shale (PAAS), whereas Sr shows slight enrichment when compared to PAAS. The concentrations of ΣREE are higher in Unit 6 and Unit 8 (37.4 ± 7.5; 46.6 ± 19.4; respectively) than Unit5, Unit7, and Unit 9 (9.1 ± 3.2; 11.3 ± 9.4; 4.2 ± 2.5; respectively). The limestones of the Alisitos Formation show a non-seawater-like REE + Y pattern with positive Eu anomalies relative to PAAS (0.95–2.47). Variations in ΣREE, Al₂O₃, Zr, Sc, REE + Y patterns, and Y/Ho ratios are influenced mainly by the amount of terrigenous materials. The variations in the Eu/Eu*, La/Sc and La/Co suggest that the terrigenous materials included in the lower four limestone beds (from Unit 5, Unit 6, Unit 7 and Unit 8) were likely contributed by intermediate to felsic rocks whereas terrigenous materials from Unit 9 were derived from mafic to intermediate source rocks. The slightly negative to slightly positive Ce anomalies in the studied limestones resulted from variations in the bottom water oxygenation. This was also corroborated by V/Cr and Ni/Co ratios suggesting that the depositional environments experienced large fluctuations in oxygenation conditions ranging from oxic to anoxic conditions during the deposition of limestones of the Alisitos Formation.     

Rare earth elements,neodymium and strontium isotopic systematics in mineral waters: evidence from the Massif Central,France

Rare Earth Elements (REEs), and Sr and Nd isotope distributions, have been studied in mineralized waters from the Massif Central (France). The CO₂-rich springs are characterized by a neutral pH (6–7) associated with total dissolved solids (TDS) from 1 to 7 g l⁻¹. The waters result from the mixing of very mineralized water pools, thought to have equilibrated at a temperature of around 200°C with superficial waters. These two mineral water pools evidenced by Sr isotopes and dissolved REEs could reflect 2 different stages of water–rock interaction and an equilibrium with different mineral assemblages.The concentrations of individual dissolved REEs and total dissolved REEs (ΣREE), in the mineral waters examined, vary over several orders of magnitude but are not dependent on the main parameters of the waters (TDS, T°C, pH, Total Organic C). The dissolved REE concentrations presented as upper continental crust normalized patterns show HREE enrichment in most of the samples. The time evolution of REE patterns does not show significant fluctuations except in 1 borehole, located in the Limagne d’Allier area, which was sampled on 16 occasions over an 18 month period. Ten samples are HREE-enriched, whereas 6 samples show flat patterns.The aqueous speciation of REEs shows that CO²⁻₃ complexes dominate (>80%) over the free metal, F⁻, SO²⁻₄ and HCO⁻₃ complexes. The detailed speciation demonstrates that the fractionation of REEs (i.e. the HREE enrichment) in CO₂-rich and pH neutral fluids is due essentially to the predominance of the CO²⁻₃ complexes.The Sr isotopic composition of the mineral waters in the Massif Central shows different mixing processes; in the Cézallier area at least 3 end-member water types exist. The most dilute end-member is likely to originate as poorly mineralized waters with minimal groundwater circulation. Two other mineralized end-members are identified, although the link between the geographical location of spring outflow and the mixing proportion between the 2 end-members is not systematic. The range in ϵ_Nd(0) for mineralized waters in the Massif Central correlates well with that of the known parent rocks except for 4 springs. One way to explain the ϵ_Nd(0) in these instances is a contribution from drainage of volcanic rocks. The isotopic systematics help to constrain the hydrogeological models for this area.     

Water quality analysis of groundwater in crystalline basement rocks,Northern Ghana

Hydrochemical data are presented for groundwater samples, collected from fractured aquifers in parts of northern Ghana. The data was collected to assess the groundwater suitability for domestic and agricultural use. Results of the study reveal that the pH of the groundwater in the area is slightly acidic to slightly alkaline. The electrical conductivity values, total dissolved solids (TDS) values and calcium, magnesium and sodium concentrations in the groundwater are generally below the limit set by the WHO for potable water supply. On the basis of activity diagrams, groundwater from the fractured aquifers appears to be stable within the montmorillonite field, suggesting weathering of silicate minerals. An inverse distance weighting interpolator with a power of 2 was applied to the data points to produce prediction maps for nitrate and fluoride. The distribution maps show the presence of high nitrate concentrations (50–194 mg/l) in some of the boreholes in the western part of the study area indicating anthropogenic impact on the groundwater. Elevated fluoride level (1.5–4 mg/l), higher than the WHO allowable fluoride concentration of 1.5, is recorded in the groundwater underlying the northeastern part of the study area, more specifically Bongo and its surrounding communities of the Upper East region. Results of this study suggest that groundwater from the fractured aquifers in the area exhibit low sodicity–low salinity (S1–C1), low sodicity–medium salinity (S1–C2) characteristics [United States Salinity Laboratory (USSL) classification scheme]. All data points from this study plot within the ‘Excellent to good’ category on a Wilcox diagram. Groundwater in this area thus appears to provide irrigation water of excellent quality. The hydrochemical results indicate that, although nitrate and fluoride concentrations in some boreholes are high, the groundwater in the study area, based on the parameters analyzed, is chemically potable and suitable for domestic and agricultural purposes.     

REE Geochemical Characteristics of Tungsten Minerals as a Discriminant Indicator of Genetic Types of Ore Deposits

Tungsten minerals (scheelite and wolframite) from two genetic types of granitoids show significant differences in REE distribution, probably due to different material sources and origins. Tungsten minerals in granite porphyry of the crust-mantle source are relatively high in ΣREE(1884ppm on average). Σ Ce is rich relative to Σ Y and Σ Ce/ΣY is relatively high (>1). The chondrite-normalized REE distribution patterns are characterized by a group of rightward-inclined curves. Tungsten minerals in quartz veins intruding the granites of crust origin have lower ΣREE (335 ppm on average). ΣY is rich relative to ΣCe and ΣCe/ΣY is relatively low (<1). The chondrite-normalized REE distribution patterns are characterized by a group of leftward-inclined curves. So the REE distribution patterns can be used to discriminate the sources of rock-and ore-forming materials and the genetic types of W deposits so as to provide clues to ore prospecting.