Article

The release of Pb and REE from granitoids by the dissolution of accessory phases

March 2002
Geochimica et Cosmochimica Acta 66(5):837-848

March 2002
66(5):837-848

Authors:

Hebrew University of Jerusalem

The release of Pb and rare earth elements (REE) during granitoid weathering was investigated through dissolution experiments of fresh granite and soil samples. Two aliquots of a granite sample from the El-Capitan Granite, Sierra Nevada, California, were leached several times using a dilute acid at pH = 1. The results of the experiment were compared with Pb and REE data from soils developed on the same rock. During the early stages of granitoid dissolution, Pb and REE were preferentially released from some of the accessory phases (i.e., allanite, sphene, and apatite). This caused higher 206Pb/207Pb and 208Pb/207Pb values and different REE patterns in solution compared with the rock values. Based on Pb isotopes and REE patterns, three stages of rock dissolution can be identified. In the first stage the dissolution of allanite dominates the release of Pb and REE from accessory phases, as 208Pb/207Pb, Ce/Pb, and chondrite-normalized Ce/Yb ratios in solution increase and approach the values of allanite. In the second stage, the dissolution of apatite and sphene become more significant. In the third stage, the isotopic ratios of Pb and the normalized-REE patterns reflect the depletion of accessory phases and the increase in the rate of feldspar dissolution. According to our estimate (based on Si release from the rock) all three stages account for the first 500 kyr of granitoid weathering.Using the isotopic ratios of Pb, major elemental compositions, and REE concentrations both in the experimental solutions and in the soil we were able to establish the following order of the weathering rates of accessory phases: allanite > apatite > sphene. In addition, we have demonstrated that biotite is significantly less resistant to weathering than hornblende under acidic conditions, and is probably dissolved completely after approximately 500 kyr of rock weathering. We also suggest that within 500 kyr of granitoid weathering K-feldspar accounts for 15% of the released K.

Grain Size Distribution and Clay Mineral Distinction of Rare Earth Ore through Different Methods

Article

Full-text available

Apr 2020

Although clay mineral content in ion-absorbed rare earth ores is crucial for migrating and releasing rare earth elements, the formation, distribution, and migration of clay minerals in supergene rare earth ores have not been fully understood. Therefore, this study analyzes the characteristics of clay mineral type and content, soil particle size, pH value, leaching solution concentration, and leaching rate. This analysis was performed using different methods, such as regional rare earth mine soil surveys, in situ leaching profile monitoring, and indoor simulated leaching. The results showed that the grain size and volume curve of rare earth ore have unimodal and bimodal shapes, respectively. X-ray diffraction showed the differences in clay mineral types formed by different weathered bedrocks. The principal clay minerals were kaolinite, illite, chlorite, and vermiculite, with their relative abundance varying with parent rock lithology (granite and low-grade metamorphic rocks). In the Ganxian granite weathering profile, the kaolinite content increased from top to bottom. The decomposition of feldspar minerals to kaolinite was enhanced with an increase in the SiO2 content during weathering. The in situ leaching profile analysis showed that the kaolinite content increased initially and then decreased, whereas the illite/mica content exhibited the opposite trend. Under stable leaching solution concentration and leaching rate, clay mineral formation is favored by lower pH. Low pH, low leaching rate, and highly-concentrated leaching solution (12 wt%) resulted in a slow increase in kaolinite content in the upper part of the profile (30 cm). A lower concentration of the leaching solution (4 wt%) resulted in rapid enrichment of kaolinite after 15 days. Low pH, leaching solution concentration, and leaching rate promoted the formation of distinct kaolinite horizons. We suggest that by disregarding other control factors, rare earth recovery of over 90% can be achieved through leach mining with solutions of 8 wt% and a pH of 5 at a leaching rate of 5 mL/min.

Tracing biogeochemical processes and anthropogenic impacts in granitic catchments : temporal and spatial patterns and implications for material turnover and solute export

Thesis

Jan 2019

Christina Weyer

From a biogeochemical perspective, catchments can be regarded as reactors that transform the input of various substances via precipitation, deposition, or human activities as they pass through soils and aquifers towards receiving streams. Understanding and modeling the variability of solute concentration in catchment waters require the identification of prevailing processes, determining their respective contributions to the observed transformation of substances, their interplay with hydrological processes, and the determination of anthropogenic impacts. However, numerous biogeochemical processes often interact in a highly non-linear way and vary on temporal and spatial scales, resulting in temporally and spatially varying water chemistry in catchments. This is particularly true for riparian wetlands. Processes in this catchment area often superimpose the influence of the hill slope (and largest) area of the catchment on surface water quality. Accordingly, the first part of this thesis (Study 1 and 2), focuses on the temporal and spatial variability of biogeochemical processes at the catchment scale. Therefore, the first aim was to identify the prevailing biogeochemical processes which affect the quality of catchment waters in two forested granitic catchments. Based on these results, (i) the long-term behavior of these processes was determined (Study 1) and (ii) hot spots of these processes at the catchment scale along different flow paths were identified (Study 2). The second part (Study 3) focuses on the interplay between hydrological and biogeochemical processes in a riparian wetland, with the aim of systematically tracing back the temporal patterns of stream water chemistry to different biogeochemical processes and antecedent hydrological boundary conditions in the wetland. The third part (Study 4 and 5) focuses on weathering processes with the goal (i) of identifying the mineralogical sources of the groundwater’s buffer capacity against acid atmospheric deposition in a forested granitic catchment and (ii) determining the mineralogical sources of the high cation loads in surface water, induced by intensive agricultural activities in two agricultural granitic catchments. To reach these aims, multivariate statistical methods of dimensionality reduction (linear Principal Component Analysis, non-linear Isometric Feature Mapping), a low-pass filtering of time-series, a Cluster analysis, and major and trace element ratios and strontium isotopes were used. A small number of biogeochemical process bundles explained 94% and 89% of the variance of the data set in Study 1 and 2, respectively. In Study 1, redox and topsoil processes, road salt and sulfate contamination were identified as predominating processes influencing water chemistry in the respective catchments. Low-pass filtered time series of component scores revealed a different long-term behavior at different sampling sites in both catchments, which could be traced back to the fraction of wetland area in the respective subcatchments as well as by the varying thickness of the regolith. Study 2 revealed that the upper 1 m topsoil layer could be considered as a biogeochemical hot spot for redox processes, acid-induced podsolization, and weathering processes along different flow paths. Up to 97% of the biogeochemical transformation of the chemical composition of soil solution, groundwater and stream water in the Lehstenbach catchment was restricted to this soil layer representing less than 2% of the catchment’s regolith. Wetland stream water, mobilized in the topsoil layer being considered a biogeochemical hot spot, showed a highly dynamic temporal pattern of component scores. Study 3 revealed four different types of wetland stream water chemical status, depending on the interplay between discharge dynamics, biological activity, and the water table position in the wetland. The sequence of different stream water types roughly followed a seasonal pattern, albeit being heavily modified by the respective hydrological boundary conditions for different years. Extended periods of low groundwater level in the second half of the growing season drastically changed the chemical boundary conditions, becoming evident in a drastic reoxidation of reduced species like sulfides and corresponding effects. Weathering processes are one of the predominating biogeochemical process bundles influencing water chemistry in forested catchments. Study 4 showed that the mineralogical sources of the groundwater’s buffer capacity against acid atmospheric deposition were dominated by the release of base cations from apatite dissolution, preferential cation release from feldspars and biotite, and feldspars weathering. In Study 5, determining the mineralogical sources of the high cation loads in surface water induced by intensive agricultural activities revealed a dominant manure contribution in the topsoil, and enhanced mineral dissolution (plagioclase and biotite) by fertilizer application in subsoils, becoming the unique source of base cations in the saprolite. Stream water chemistry differed from that of soil water, suggesting that stream water chemistry was dominated by elements issued from enhanced mineral and rock weathering. Soil acidification induced by agriculture allows the mobilization of cations stored in soil layers, enhances the rock weathering and accelerates plagioclase dissolution, which can highly influence stream water quality. Numerous biogeochemical, hydrological, and anthropogenic processes were found to interact with each other, mostly with non-linear patterns, influencing catchment water chemistry. The integral approach used in this thesis would be a useful prerequisite to develop accurate and parsimonious models commonly used for water management purposes by distinguishing between short- term and long-term shifts, reducing the number of processes to the predominating ones ultimately to be included in the model, focusing on hot spots and including spatial patterns where necessary and appropriate.

Experimental evidence for mineral-controlled release of radiogenic Nd, Hf and Pb isotopes from granitic rocks during progressive chemical weathering

Article

Mar 2019
CHEM GEOL

The role of accessory minerals in the incongruent release of Hf and Pb during continental weathering and its implications for the generation of distinct seawater isotope compositions is subject of debate. While it has been suggested that radiogenic Hf and Pb isotope signatures released during the dissolution of rocks are controlled by the relative abundances of minerals with distinct isotope compositions and differences in their resistance to dissolution there has not been a comprehensive experimental investigation of these processes to date. We carried out systematic sequential leaching experiments on fresh and partly weathered granitic rock samples as well as separated zircons from the Central Aar Granite in Switzerland. Combined with major and rare earth element concentrations our new quantitative experimental data reveal systematic preferential release of radiogenic Nd, Hf and Pb isotopes primarily controlled by dissolution characteristics of the host rock's easily dissolvable accessory and major minerals, in particular apatite and sphene, during weak chemical weathering. Moreover, Pb isotope signatures of incipient weathering conditions, contrary to expectations, indicate initial congruent release of Pb from freshly exposed mineral surfaces that becomes subsequently incongruent. During more advanced chemical weathering stages, as well as enhanced physical weathering conditions, the dissolution of major minerals (i.e. feldspars) becomes dominant for Nd and Pb isotope signatures, whereas Hf isotopes are still dominated by contributions from highly radiogenic accessories. Additional leaching experiments of zircon separates were performed to test the specific role of zircons for Hf isotope compositions of riverine runoff. It is demonstrated that zircon is more efficiently dissolved when physical weathering is enhanced. This increased Hf release originating from partial dissolution of zircons, however, is quantitatively not sufficient to explain less radiogenic Hf isotope signatures in seawater during episodes of enhanced mechanical erosion alone. Moreover, the observed addition of Hf from the more congruent dissolution of the zircon-free fractions of the parent rock due to enhanced physical weathering indicates that these minerals also play an important role in controlling Hf isotope signatures released under deglacial conditions.

Pb speciation in rare earth minerals and use of entropy and fuzzy clustering methods to assess the migration capacity of Pb during mining activities

Article

Full-text available

Sep 2018
ECOTOX ENVIRON SAFE

Ionic rare earth mining is of strategic importance in China; however, the heavy metal pollution it causes is of great concern, both at home and abroad. Data on Pb speciation at a rare earth mine were used to analyse the migration capacity of Pb during the process of ore leaching. The major factors thought to influence the migration capacity of Pb, including the clay mineral content, soil pH, oxidation-reduction potential, organic matter content, and cation exchange capacity (CEC), were quantified. Entropy and fuzzy clustering methods were used to identify the most predictive factors. The results showed that the clay mineral content of the soil exerts the strongest influence on the migration capacity of Pb in rare earth mines; the other factors demonstrated relatively weak influences on the transport processes. The results obtained from the classification of Pb per the potential migration index (PMI) approximated those obtained from fuzzy clustering, and the results of entropy analyses were consistent with those of fuzzy clustering. Thus, the methods upon which the proposed model is based are suitable for predicting the migration capacity of Pb in ore during the mining of ionic rare earth minerals.

Spatial Heterogeneity of Rare Earth Elements: Implications for the Topsoil of Regional Ion-Adsorption Type Rare Earth Deposit Areas in Southern China

Article

Full-text available

Jun 2023

The migration and spatial distribution characteristics of topsoil rare earth elements (REEs) are significant for the risk assessment of the external environment. However, the spatial distribution of REEs in the topsoil of ion-adsorption type rare earth element (REE) mining areas is poorly studied. We aimed to determine the differences and control factors of the spatial distribution of REEs in the topsoil of typical rare earth mines in South Jiangxi, South China. Sixty-five topsoil samples and eighteen profile samples were collected and analyzed for their rare earth content to elucidate spatial autocorrelation and heterogeneity using statistical analysis software (IBM SPSS Statistics 26.0.0.0, GS+9.0, and Arcgis10.2.0.3348). Moran index analysis showed that the positive correlation between sampling points was significant within the range of 0–500 m. The best fitting models of the semi-variance variogram were the exponential model, Gaussian model, and spherical model. The sequence of the spatial structure (C0 + C) was Ho > Tb > La > Pr > Nd > Sm > Gd > Tm > Lu > Dy > Er > Yb > Ce > Eu. The spatial fractal distribution pattern was Ho > Tb > Lu > Er > Dy > Yb > Tm > Gd > Ce > La > Eu > Sm > Pr > Nd. This indicated that the light rare earth elements (LREEs) and heavy rare earth elements (HREEs) in the topsoil were significantly different from the other sediments. This study provides new evidence for the environmental quality assessment of the in situ leaching of ionic rare earth ores into the topsoil layer.

REE fractionation controlled by REE speciation during formation of the Renju regolith-hosted REE deposits in Guangdong Province, South China

Article

Apr 2021
ORE GEOL REV

Regolith-hosted rare earth element (REE) resources in South China are the dominant global source of heavy REEs (HREEs), which are critical for high technology and military industries. Most previous studies focused on the proportion of ion exchangeable REE fractions, but other speciations thereof and their effects on REE fractionation are still poorly understood. Therefore, to address this issue, this study focused on a systematic analysis of the geochemistry and mineralogy of a complete weathering 78 m profile in the Renju regolith-hosted REE deposit in northeast Guangdong Province, China. In the quartz diorite bedrock, the main REE minerals were titanite, allanite, and REE fluorocarbonates abundant in REEs (332-338 ppm). During the breakdown of rocks during weathering, the light REE (LREE)-rich minerals, e.g., titanite and allanite, were dissolved preferentially, resulting in the release of the REEs. Thus, the HREE-rich minerals, including xenotime and zircon, are preserved with progressive weathering. The results of sequential extraction show that the activated REEs are immobilised, occurring mainly as ion exchangeable and Fe-Mn (hydr)oxide fractions, with a few amounts of the organic and carbonate binding fractions. Fe (hydr)oxides, as seen via transmission electron microscopy, usually occur in the form of goethite and hematite in the lower and upper parts of regoliths, respectively, while Mn is present as a trace element in Fe (hydr)oxides. The lower La/Yb ratios in the Fe-Mn (hydr)oxide fraction indicate that HREEs are preferably bonded on Fe-Mn (hydr)oxides, causing LREEs to exist mainly as ion exchangeable fractions. In addition, positive Ce anomalies exist in both the lateritic horizon with strong oxidation of weak acid and in the Fe-Mn (hydr)oxide fraction as a co-precipitate with Fe oxides. The results obtained advance our understanding of the mechanisms of REE fractionation and the mutual effect of REE speciation on the formation of regolith-hosted REE deposits in South China.

Advances in geochemical footprint, iron speciation, and Pb isotopes in the tropical regolith of north-northwestern Amazonia, Brazil

Article

Mar 2021
J S AM EARTH SCI

A dataset with information on samples of gabbro, charnockite, gneiss, granite, basalt, and sandstone-derived iron lateritic duricrusts, concretions, nodules, and soils was analyzed to address the multi-element chemical composition, background values, scavenger trace elements in Fe oxyhydroxides, parent rock inheritance, and weathering effect on Pb isotopes. Tropical weathering causes high mass loss of SiO2, Ba, Rb, and Sr assigned to the mineral rock framework (quartz, feldspar, and mica). The aqua regia leaching indicates that part of these elements was probably accumulated in authigenic Al-phosphates minerals affecting their mobility in the lateritic terrains. There is a generally Sc and V high accumulation in the lateritic duricrusts with Fe oxyhydroxide mineral framework (goethite, hematite, and amorphous). Th, U, and Pb are also accumulated on the gabbro and granite-derived lateritic duricrusts, Cr on the basalt-derived ones, REE on the gabbro-derived ones, as well as Th and U low to high loss on gneiss-derived ones, thus allowing to track inheritance of parent rocks. The more refined geochemical information obtained from the Pb isotopes related to the Fe oxyhydroxides of the lateritic duricrusts, concretions and soils indicated changes according to the parent rocks since the gabbro-derived lateritic duricrust samples are more radiogenic while the gneiss and granite-derived ones are less radiogenic. The basalt and sandstone-derived lateritic duricrust samples maintain the radiogenic signature of the respective parent rocks. Although homogenization was expected, the mineral, the main and trace elements, and Pb isotope compositions produced by leaching and accumulation in the tropical regolith highlight the parent rock signature and a complex weathering process.

A global survey of radiogenic strontium isotopes in river sediments

Article

Jan 2021
CHEM GEOL

Radiogenic strontium isotopes are routinely used in provenance studies, but their application to sediments is often complicated by various grain size and weathering effects, which can influence measured ⁸⁷Sr/⁸⁶Sr ratios. Here, we report Sr isotopic data for a large number of sediment samples (n = 61) from the world's largest rivers and other river catchments draining particular geological and climatic settings; using both clay-rich (<4 μm) and silt-size (4-63 μm) detrital fractions to re-examine the factors controlling their distribution in sediments. In agreement with previous studies, the detrital material transported by world rivers defines general inverse Nd-Sr isotope relationships, which provide further empirical evidence for the utility of radiogenic Sr isotopes in sediment provenance studies. In a novel departure, however, we show that the ⁸⁷Sr/⁸⁶Sr difference between paired clay- and silt-size fractions (Δ⁸⁷Sr/⁸⁶Sr Clay-Silt) relates to the degree of chemical alteration of river sediments, as inferred from various relationships with weathering indices, such as the CIA, WIP and Na2O/Al2O3. The weathering dependence of Δ⁸⁷Sr/⁸⁶Sr Clay-Silt appears to be mainly controlled by temperature. In sub-Arctic and temperate regions, river sediments systematically display positive Δ⁸⁷Sr/⁸⁶Sr Clay-Silt indicative of preferential alteration of biotite in soils. In contrast, in sub-tropical watersheds characterized by mean annual temperatures >20 °C, intense feldspar weathering leads to the preferential incorporation of unradiogenic Sr into secondary clay minerals; a process which results in negative Δ⁸⁷Sr/⁸⁶Sr Clay-Silt values. In addition to climate forcing, the degree of size-dependent Sr isotope decoupling is also shown to be dependent on the type of weathering regime in watersheds, being more pronounced in low-elevation environments (< 2000 m), where transport-limited conditions and the presence of thick soil sequences can be associated with intense silicate weathering, than in high mountain regions (> 4000 m) dominated by kinetically-limited weathering regimes. While further studies will be required to test the validity of these conclusions at the local scale of weathering profiles, these findings suggest that combined Sr isotopic analyses of separate size fractions could be used as a new weathering proxy in sediment records, ideally complementing the conventional use of radiogenic Sr isotopes as provenance tracers. Finally, our results are also used to re-assess the mean Sr flux and ⁸⁷Sr/⁸⁶Sr composition of the suspended sediment exported to the ocean yearly, yielding a global flux-weighted average of 0.7160, identical to that proposed earlier in the seminal study of Goldstein and Jacobsen (1988).

Development of a Correlated Fe‐Mn Crust Stratigraphy Using Pb and Nd Isotopes and Its Application to Paleoceanographic Reconstruction in the Atlantic

Article

Full-text available

Oct 2020

Eight ferromanganese crust samples spanning the complete depth range of Tropic Seamount in the northeast Atlantic were analyzed for Pb and Nd isotopes to reconstruct water mass origin and mixing over the last 75 Ma. Pb isotopes were determined by laser ablation multicollector inductively coupled plasma mass spectrometer (LA‐MC‐ICP‐MS), which enables the rapid production of large, high spatial resolution data sets. This makes it possible to precisely correlate stratigraphy between different samples, compare contemporaneous layers, and create a composite record given the abundance of hiatuses in crusts. Pb and Nd isotope data show the influence of various oceanic and continental end‐members in the northeast Atlantic Ocean. This reflects its evolution from a restricted, isolated basins in the Late Cretaceous with influxes from the Tethys Ocean, to an increasingly well‐mixed, large‐scale basin, with a dominant Southern Ocean signature until the Miocene. Less radiogenic Nd isotope signatures suggest Labrador Sea Water influenced the northeast Atlantic basin as early as 17–15 Ma, flowing through a northern route such as the Charlie‐Gibbs Fracture Zone. Pb and Nd isotopes highlight the increasing influence of Saharan eolian dust input about 7 Ma, imparting a less radiogenic excursion to the binary mixing between North Atlantic water masses and riverine discharge from West and Central Africa. This highlights the influence of eolian dust input on the open ocean Pb and Nd budget and supports an early stage of North African aridification in the Late Miocene. This signature is overprinted about 3 Ma to the present by a strong North Atlantic Deep Water signature following the onset of Northern Hemisphere glaciation.

Characteristics and Genesis of Ion Adsorption-Type Rare Earth Element Deposits

Chapter

Jan 2016

Distribution of REE-bearing minerals in felsic magmatic rocks and paleosols from Gran Canaria, Spain: Intraplate oceanic islands as a new example of potential, non-conventional sources of rare-earth elements

Article

Jun 2019
J GEOCHEM EXPLOR

Early stage weathering systematics of Pb and Nd isotopes derived from a high-Alpine Holocene lake sediment record

Article

Mar 2019
CHEM GEOL

Radiogenic Pb and Nd isotopes are well established tools in paleoceanographic science tracing ambient climate and continental runoff to the oceans down to sub-millennial timescales. Particularly in case of Pb isotopes, a clear climate dependency of continental isotopic runoff on glacial-interglacial transitions has been observed. Pb isotopes were reported to be released incongruently during initial chemical weathering. This incongruent release implies that Pb isotopic runoff compositions differ from the bulk catchment Pb isotopic signal. Yet only little is known about the processes leading to the incongruent release and the timescales of weathering on the continents. In this study we targeted the adsorbed trace metal signature in sediments from a Swiss high-Alpine lake that have accumulated since the retreat of the large Alpine ice domes during the last deglaciation to investigate initial Pb and Nd isotope weathering processes in a granitic environment. Additionally, selected adsorbed element concentrations and ratios were analysed to complement the isotopic physico-chemical weathering information. The integrity of the presented isotope records is supported by further investigation into the lake environment (e.g. oxic/anoxic conditions) and its potential influence on the isotopic record. The Pb isotope records during the early lake phase witnessed high-amplitude isotopic fluctuations linked to the initial chemical weathering of fine glacial substrate. This finding is also supported by the lithology of the core and rapidly decreasing adsorbed Th and U concentrations. Following this early lake phase, the majority of the Holocene traced congruent release of ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁶Pb/²⁰⁴Pb and a significant depletion of ²⁰⁸Pb/²⁰⁴Pb in the adsorbed phase. These findings corroborate earlier suggestions of more effective weathering of uranogenic minerals yet also call for the presence of more weathering-resistant thorogenic minerals in the lake catchment. The latest 2.2 ka of the record are significantly overprinted by anthropogenic Pb deposition coinciding with the rise and fall of the Roman Empire. Finally, our data suggest that Nd isotopes are equally affected by incongruent weathering during the initial deglacial weathering processes, albeit at smaller magnitude than seen for Pb isotopes.

Origine de l'eau et des éléments dissous par traçage isotopique (H, O, S, Mg, Sr) sur le bassin amont de la Moselle :

Thesis

Jan 2006

Agnès Brenot

Ce travail propose d'identifier et de quantifier dans le temps et dans l'espace l'origine de l'eau et de certains éléments dissous sur le bassin versant amont de la Moselle en utilisant trois familles de traceurs isotopiques. La singularité du bassin étudié réside dans la diversité des lithologies drainées et une occupation des sols variée. Un fort contraste réside entre les Vosges cristallines avec des sols principalement forestiers en amont et le plateau lorrain carbonaté dominé par les activités agricoles en aval. Un premier volet de ce travail a permis d'apporter des éléments à la compréhension du fonctionnement hydrologique du bassin versant de la Moselle. L'analyse de la composition isotopique de l'H et de l'O de l'eau a permis de décrire une dynamique des eaux et un temps de réponse au signal des eaux météoriques variable suivant le compartiment hydrologique étudié et la période de l'année. Les temps de réponse estimés sont de quelques jours pour les eaux de sols collectées par drainage en période de haut régime hydrique, à plusieurs semaines pour les eaux de rivières, jusqu'à plusieurs mois pour les eaux de sols collectées par bougies poreuses et les eaux de sources. Un deuxième volet de ce travail a permis d'identifier l'origine spatiale et temporelles des sulfates dissous dans les eaux de rivières. Trois sources principales de sulfates ont été identifiées: les apports atmosphériques, le lessivage d'évaporites et le lessivage d'engrais soufrés. L'apport de sulfates provenant d'engrais soufrés est saisonnier et n'apparaît qu'en période de haut régime hydrique (octobre 2003 à mars 2004), lorsque le lessivage des sols agricoles est le plus intense et peut représenter jusqu'à 13% des sulfates exportés annuellement par le Madon à Mirecourt. La composition isotopique du Sr de la phase dissoute des rivières indique que le Sr des eaux de la Moselle provient d'un mélange simple entre le pôle silicate et le pôle carbonate/évaporite définis localement, témoignant d'une relative simplicité du système étudié. Nous avons donc abordé l'utilisation du Mg comme traceur isotopique en hydrochimie. Les compositions isotopiques en Mg sur le bassin de la Moselle sont parmi les premières valeurs mesurées pour le Mg dissous dans des eaux de rivières et de sols. Les eaux de rivières drainant uniquement des silicates ( 26Mg=-1,2 à -0,7 ) présentent un appauvrissement systématique en isotopes lourds par rapport aux roches silicatées ( 26Mg=0,22 à 0,94 ) et à leurs sols associés ( 26Mg=0,36 à 1,68 ). Ce résultat suggère un fractionnement isotopique du Mg lors de l'altération. Les eaux de rivières drainant le plateau lorrain à dominante carbonatée ont une gamme de valeurs ( 26Mg=-1,6 à -1,2 ) significativement plus basse que celle du bassin silicaté. En plus d'être contrastées selon la lithologie drainée, les valeurs de 26Mg du Mg dissous sont bien corrélées avec les rapports 87Sr/86Sr et Sr/Mg témoignant clairement de la capacité des isotopes du Mg à tracer la source de Mg dissous dans ces rivières. Enfin un important excès de Mg et de Sr par rapport au Ca a été mis en évidence pour les rivières drainant les roches sédimentaires du plateau lorrain et seule la perte de Ca dissous par précipitation de calcite permet de rendre de cet excès

Weathering co-mineralization of placer type ilmenite and ion-adsorption type rare earth elements in Guangxi, China: Nature, origin and exploration implications

Article

Full-text available

Dec 2023
ORE GEOL REV

Composition of Rare Earth Elements in Fluvial Sediments of the Lesser Zab River Basin, Northeastern Iraq: Implications for Tectonic Setting and Provenance

Article

Full-text available

Dec 2023

During the past few decades, rare earth elements (REEs) have gained enormous attention in geochemical studies worldwide as a result of their important role in the manufacturing of high-tech equipment. REEs in river sediment have been widely used for provenance determination and in geochemical studies of continental crust, rock and sediment environments, and anthropogenic pollution. This study aims to elucidate the origin and tectonic setting of Little Zab River Basin (LZRB) sediments by examining 23 fluvial sediment samples of rare earth elements (REEs) collected from both the primary river and the inter-sub-basin regions during the rainy or high-flow season. The ICP-MS method was employed to analyze all samples to identify and assess the compositions of REEs. A fraction of the river sediments, smaller than 2 mm, which is more representative and more homogeneous, was used to carry out geochemical analysis. REE concentrations in the Little Zab River (LZR) and the upper parts of the LZRB were generally higher than those in the lower parts. The concentration of REEs in nearly all samples was lower than that of the North American Shale Composite (NASC), and the Upper Continental Crust (UCC), except for the sub-basin sediment Sbs2, which was higher than these references; also, the sediment sample Zrs4 was slightly higher than NASC. Light rare earth elements (LREEs) display enrichment relative to heavy rare earth elements (HREEs) with a range between 7.15 µg/g and 12.37 µg/g for LZR samples and between 5.95 µg/g and 13.03 µg/g for the sub-basin samples. The REE discrimination diagrams, along with the chondrodite-normalized pattern of the studied sediments, confirm that the sediment is predominantly sourced from the alkaline basaltic unit of the late Cretaceous Walsh group of an arc tectonic affinity.

Redistribution of REE in granitic bedrocks during incipient weathering: insights into the role of groundwater in the formation of regolith‑hosted REE deposit

Article

Full-text available

Sep 2023
CONTRIB MINERAL PETR

The regolith-hosted rare earth element (REE) deposits in the Nanling Mountain Range, South China, are the most important source of heavy REE (HREE) in the world. A perplexing thing is that only a few of these deposits are relatively enriched in HREE and most of them are actually light REE (LREE)-enriched, although they are all originated from the granitic bedrocks with similar HREE concentrations. This is supposed to be related to the redistribution of REE in the weathered bedrocks due to groundwater-rock interaction, however, it remains enigmatic how REEs are mobilized and fractionated in the interaction. Titanite is an important REE contributor to the regolith-hosted REE deposit. Here, we investigate textural and compositional variations of the titanite from the granitic bedrocks to weathered profiles in the Zuokeng regolith-hosted REE deposit, the largest one that is newly discovered in this region. Together with thermodynamic modelling, we deduce the nature of the fluids, temperature range for titanite alteration, and the mechanism of REE fractionation. Primary titanite is of magmatic in origin and shows relatively high REE contents and negative Eu anomaly on the chondrite-normalized REE pattern. Secondary titanite is commonly associated with chloritized biotite and is characterized by extremely low REE, high Al2O3, F and significant positive Eu anomaly, typical of authigenic origin due to chloritization of biotite under oxidized conditions in supergene environment. From the bedrocks upward to the surface, primary titanite is gradually replaced by calcite, synchysite- (Ce) and TiO2 in the weathered bedrocks. This is interpreted as the result of infiltration of the F, carbonate-rich, alkaline fluids derived from local groundwater through the bedrocks. The irregular dark patches in primary titanite display typical alteration texture and may have formed through fluid leaching of primary titanite. The patches in primary titanite have lower REE concentrations and higher LREE/HREE ratios than magmatic domains, indicating that the groundwater preferentially scavenges HREE from primary titanite, leaving behind LREE in weatherable secondary minerals, such as synchysite-(Ce) and allanite. Mass balance calculation results also confirm that more HREE are lost from weathered bedrocks than LREE. Therefore, the interaction of groundwater and granitic bedrocks may be favorable to enrich LREE rather than HREE in the regolith. This may explain why most regolith-hosted REE deposits like Zuokeng in South China are of predominant in LREE. This study highlights the role of groundwater in mobilizing, fractionating and enriching REE from the granitic bedrocks to resultant regolith-hosted REE deposits.

Lead Components of Bulk Sediments from Dahu Swamp in Nanling Mountains (South China): Implications for the Climatic and Environmental Changes Since the Last Deglaciation

Article

Jun 2023

We show, from a 16.6 ka record of lead isotopes from a core sediments in Dahu Swamp in eastern Nanling Mountains, that the chemical weathering responds to changes in climatic conditions. Pb isotopic signals reveal that the local weathered granitoid was the dominant source of Pb deposition. However, two isotopic excursions appeared from 15.5–15.2 and 5.2–4.8 ka BP, which coincide with the dry/cold H1 event and the mid- and late-Holocene respectively, likely suggesting an additional contribution of aeolian dust from North China. Even more, more radiogenic Pb signal of E2 exhibits a mixed contribution of enhanced anthropogenic mining. We expect strong enough EAWM would dominate these two intervals. Supported by multiproxy records, we conclude that variations Pb isotopic signals (e.g., 06Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios) are closely related to climate-induced chemical weathering. Synchronous variations of 208Pb/204Pb,206Pb/204Pb and 207Pb/204Pb ratios in the core display a congruent Pb isotope signals released from both Uand Th-rich accessory minerals. During intensive chemical weathering under wetter/warmer conditions (e.g., the Bølling and Allerød events, and the Holocene Optimum period), more preferential release of radiogenic 206Pb, 207Pb and 208Pb can be absorbed by fine detritus and then eroded to the lake thus resulting in increased 208Pb/204Pb, 206Pb/204Pb and 207Pb/204 ratios in sediments, and vice versa if a drier/colder climate dominates (e.g., the H1, the Older and Younger Dryas events, and the mid- & late-Holocene). The inferred changes in chemical weathering from Dahu sediments have varied in tandem with multi-regional monsoonal proxies in China, and exhibited a sensitive response of chemical weathering to global climate change.

The role of zircon in hydrothermal heavy REE mineralisation: The case for unconformity-related ore deposits of north-west Australia

Article

Apr 2023
CHEM GEOL

Rare Earth Occurrence States of Weathered Crust Elution-Deposited Rare Earth Ores in Southern Yunnan

Article

Full-text available

Apr 2023

To reveal the regularity of variation in the rare earth occurrence states of weathered crust elution-deposited rare earth ores, ore samples from different weathering crust layers were obtained by performing the sequential extraction procedure. The order of rare earth contents firmly obeyed the following sequence: the weathered layer > humic layer > partly weathered layer. The occurrence states of rare earth elements were mainly the ion exchange state, carbonate bound state, iron–manganese oxide state, organic binding state and residual state. The proportions of rare earth elements found in the rare earth ion exchange state of the weathered layer, humic layer and partly weathered layer were 78.55%, 73.53% and 53.88%, respectively. The light rare earth elements (LREEs) found in the rare earth ion exchange state were enriched in the upper part of the weathering crust, while the heavy rare earth elements (HREEs) were enriched in the lower part. There were also obvious negative anomalies in the content of cerium in the ion exchange state. The content of rare earth elements found in the carbonate bound state was small, and the rare earth partition pattern was basically consistent with that of the ion exchange state, which had little effect on the differentiation of the rare earth elements. The iron–manganese oxide state was mainly enriched with cerium, and the content of cerium increased with the depth of the weathering crust. The iron–manganese oxide state was the main factor causing the phenomenon of the anomaly in the cerium content. Meanwhile, the iron oxides in the iron–manganese oxide state were mainly hematite and goethite. The organic binding state mainly beneficiated yttrium and cerium by complexation and certain adsorption. The content of elements found in the rare earth residual state was related to the degree of weathering and reflected the release sequence of rare earth elements in the mineralization process. Clarifying the rare earth occurrence states is conducive to better revealing the metallogenic regularity of weathered crust elution-deposited rare earth ores. In addition, the results can provide a valuable reference for expanding the available rare earth resources and the efficient comprehensive utilization of rare earth ore.

Nitrogen isotope geochemistry of ion adsorption-type REE mineralization: Insights from the weathered granitoid rocks in the Sancheong district, South Korea

Article

Full-text available

Apr 2023
ORE GEOL REV

Reconstructions paléocéanographiques et paléogéographiques du Canal du Mozambique (Océan Indien) : apport de l'étude isotopique des encroûtements Fe-Mn

Thesis

Apr 2022

Claire Charles

Le canal du Mozambique, localisé à l’est du craton africain et à l’ouest de la marge continentale de Madagascar, abrite d’intenses mélanges de masses d’eau des océans Atlantique et Indien qui soulèvent des interrogations, à savoir si et comment elles ont circulé au cours du temps, en s’adaptant à la géodynamique du canal. L’analyse géochimique (éléments majeurs, traces ; isotopie Nd, Pb) et la datation absolue (isotopie Be) de 33 encroûtements Fe-Mn, répartis depuis le Plateau des Aiguilles au sud jusqu’au bassin des Comores au nord, permet ici d’établir des séries temporelles afin d’étudier l’évolution des courants régionaux jusqu’à 30.7Ma. Depuis 80 000ans, le NADW circule jusqu’à la ride de Jeffrey alors que dans l’archipel des Comores, le NIDW est majoritaire. Cependant, ce modèle océanographique n’a pas toujours fonctionné ainsi. Dès sa mise en place, le NADW a eu une forte influence jusqu’aux Îles Glorieuses. Entre 11.7 et 3.4Ma, un soulèvement bouleversa la géodynamique du canal, entrainant une élévation de la ride de Davie. Le NADW diminua au nord, jusqu’à se retirer du bassin des Comores, au profit de l’augmentation du NIDW. Entre 5.1 et 1.6 Ma, une subsidence, enregistrée au centre du canal, modifia à son tour la bathymétrie et l’océanographie du secteur. La géochimie révèle également des apports élémentaires téthysiens et himalayens dans les courants profonds. Ainsi, grâce à une étude haute résolution des courants profonds du canal du Mozambique ce doctorat complète les modèles océanographiques de l’océan Indien et innove dans les reconstructions géodynamiques grâce à l’utilisation des encroutements Fe-Mn dans la caractérisation de mouvements verticaux.

Characterization of Saharan and Sahelian dust sources based on geochemical and radiogenic isotope signatures

Article

Full-text available

Sep 2022
QUATERNARY SCI REV

Mineral dust can significantly impact climate and biogeochemical cycles on Earth. To understand dust provenance, an accurate characterization of dust sources and emission regions is required. In this study, we combine rare-earth element patterns, elemental ratios, and radiogenic Sr-Nd-Pb isotopes to discriminate dust sources from key regions in North Africa responsible for ∼55% of the total dust load emitted annually on Earth. This new dataset, based on fifty-nine analyses of deflatable fine soil material, improves our current knowledge about North African dust sources, especially those underrepresented in Saharan-Sahelian regions. Six potential source areas (PSA) – Libya-Algeria-Mali (PSALAM), Libya-Egypt (PSALE), Bodélé Depression (PSABD), Mali Center (PSAMC), West African Coast (PSAWAC) and Mauritania (PSAMa) – are defined based on several lithogenic tracers as well as on the geological subdivision of North African geological provinces, providing a unique chemical and isotope fingerprint for each PSA. For example, the PSABD – the main dust activation area in North Africa – is clearly distinguished from western African sources using Pb isotopes. Major elements show a large variability within each PSA and are not alone diagnostically useful. Comparison of the newly defined PSA with aerosols collected in remote locations over the North Atlantic shows that their sources are predominantly from western African regions (PSALAM and PSAWAC). Bodélé-derived dust has a limited impact on the bulk dust transported over the tropical North Atlantic, regardless of the season and altitude of dust transport. The low impact of the Bodélé Depression can be explained by a high deposition rate (wet and dry) of aerosols along its southwestward trajectory. A detailed analysis of dust collected over South America during winter will be essential to confirm this observation at a global scale. The present dataset can be efficiently used to track modern dust emissions as well as their changes at the scale of glacial/interglacial cycles or during the development of African Humid Periods as stored in sedimentary archives.

Arctic drainage of Laurentide Ice Sheet meltwater throughout the past 14,700 years

Article

Full-text available

Apr 2022

During the last deglaciation substantial volumes of meltwater from the decaying Laurentide Ice Sheet were supplied to the Arctic, Gulf of Mexico and North Atlantic along different drainage routes, sometimes as catastrophic flood events. These events are suggested to have impacted global climate, for example initiating the Younger Dryas cold period. Here we analyze the authigenic Pb isotopic composition of sediments in front of the Arctic Mackenzie Delta, a sensitive tracer for elevated freshwater runoff of the retreating Laurentide Ice Sheet. Our data reveal continuous meltwater supply to the Arctic along the Mackenzie River since the onset of the Bølling–Allerød. The strongest Lake Agassiz outflow event is observed at the end of the Bølling–Allerød close to the onset of the Younger Dryas. In context of deglacial North American runoff records from the southern and eastern outlets, our findings provide a detailed reconstruction of the deglacial drainage chronology of the disintegrating Laurentide Ice Sheet.

-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). XRD and TEM analyses of a simulated leached rare earth ore deposit: Implications for clay mineral contents and structural evolution

Article

Sep 2021

Chen Ling-kang

Apatite Texture, Composition, and O-Sr-Nd Isotope Signatures Record Magmatic and Hydrothermal Fluid Characteristics at the Black Mountain Porphyry Deposit, Philippines

Article

Aug 2021

The trace elemental and isotopic signatures in apatite can be modified during hydrothermal alteration. This study investigates the suitability of apatite as an indicator of the source, chemistry, and evolution of magma and hydrothermal fluids. In situ textural, elemental, and O-Sr-Nd isotope analyses were performed on apatite in thin sections, from fresh and propylitically altered pre- and synmineralized dioritic porphyries from the Black Mountain porphyry Cu deposit in the Philippines. All studied apatite crystals have similar subhedral to euhedral shapes and are homogeneous in the grayscale in backscattered electron images. In cathodoluminescence images, the apatite in fresh and altered rocks displays yellow to yellow-green and green to brown luminescence, respectively. Apatite in fresh rocks has a higher Cl and Mn content, and lower Fe, Mg, Sr, Pb, and calculated XOH-apatite, compared to apatite in altered rocks. The content of F, rare earth elements (REEs), Y, U, Th, and Zr, and the Sr-Nd isotope signatures of apatite from fresh and altered rocks are similar in all apatite grains (87Sr/86Sr = 0.7034–0.7042 vs. 0.7032–0.7043, εNd(t) = 5.3–8.0 vs. 5.1–8.4). The X-ray maps and elemental and oxygen isotope signatures across individual apatite crystals are typically homogeneous in apatite from both fresh and altered rocks. The distinct luminescence colors, coupled with distinct mobile element compositions (Cl, OH, Mn, Mg, Fe, Sr, Pb), indicate modification of primary magmatic apatite during interaction with hydrothermal fluids. The similarities in Sr isotope ratios (87Sr/86Sr = 0.7032–0.7043) but slight differences in O isotope signatures (δ18O = 6.0 ± 0.3‰ vs. 6.6 ± 0.3‰) in apatite from fresh and altered rocks are consistent with the magma and hydrothermal fluids having the same source and suggest significant phase separation in the hydrothermal fluids given that 18O preferentially fractionates into the residual liquid relative to 16O during phase separation. The similarity of immobile element (REE, Y, U, Th, and Zr) contents in both populations of apatite, consistency of textures and Nd isotope compositions, and absence of obvious dissolution-reprecipitation features all suggest that altered apatite retains some magmatic characteristics. The apatite in fresh rocks has oxygen isotope compositions similar to that of zircons from the same sample (δ18O = 5.9 ± 0.3‰), indicating little to no oxygen isotope fractionation between zircon and apatite and that apatite can be a good proxy for the oxygen isotope composition of the magma. Based on the Cl contents of the magmatic and replacement apatite, and assuming their equilibrium with high-temperature magma fluid and replacement hydrothermal fluid, respectively, the calculated Cl content of the early magmatic fluid and the later replacement fluid can be estimated to be 6.4 to 15.1 wt % and ~0.25 ± 0.03 wt %, respectively. This indicates a depletion of Cl from the early high-temperature fluid to the replacement fluid, consistent with phase separation. This study demonstrates that cathodoluminescence, elemental compositions (such as Cl, Mn, Mg, Fe, Sr, Pb) and Sr-O isotope signatures in apatite can be modified during hydrothermal alteration, whereas other components (REE, Y, U, Th, and Zr) and the Nd isotope composition are preserved. These features can be used to constrain the origin, chemistry, and evolution of the primary magma and ore-forming hydrothermal fluids.

Nature of the ore-mineralizing fluids in the Balda and Motiya W-prospects, western India: Constraints from chemical and B-isotope composition of tourmaline

Article

Jul 2021
CHEM GEOL

In the Proterozoic tungsten belts of Balda and Motiya in western India, tungsten mineralization is hosted in tourmaline-bearing quartz veins intrusive into pelitic schists and granites. Tourmaline is a ubiquitous phase in all rock types, and in this study, we use its major, trace element and B-isotope composition to constrain the nature of the tungsten (W)-bearing hydrothermal fluid and the processes involved in the precipitation of wolframite. We have also reconstructed the compositions of the W-precipitating fluids from mineral-fluid trace element partition coefficients that were extrapolated using the Lattice Strain Model. The tourmalines from both belts are of schorl composition and have high alkali, low Ca content, and moderate X-site vacancies. High Li, Mn, Zn, and Sn in the fluid in Motiya is suggestive of relatively saline fluid possibly derived from a granitic source. The high V/Sc ratios of tourmalines in the mineralized veins and wall-rock tourmalinites indicate an important role of biotite dissolution and fluid-rock interaction that contributed FeMn for the precipitation of tourmaline and wolframite. The tourmalines in the mineralized veins at Balda (δ¹¹Btur = −10.9 ± 0.7‰, 2σ; n = 10) and those in the associated granites (δ¹¹Btur = −11.5 ± 0.7‰, 2σ; n = 6) have similar B-isotope composition, while those of the associated topaz granites and pegmatites (−13.9 ± 0.7‰, 2σ; n = 19) are isotopically lighter than the granites. The B-isotopic variation in the granite-pegmatite-vein system can be explained by fluid exsolution with the mineralized vein forming from exsolved fluid and the topaz-bearing granites and the pegmatites crystallizing from the residual melts. The δ¹¹B of the mineralizing fluid is estimated to be ca. -7.4‰ at Balda and ca. −7.6‰ at Motiya, and were possibly derived from granites, consistent with extensive tourmalinization and muscovitization of the adjacent wall rocks, and high concentration of elements such as F, Li, B, Sn, Mn in the tourmalines and the reconstructed fluid. The chemistry and B-isotope composition of tourmalines in both the belts support the hypothesis that W-bearing hydrothermal fluid was primarily derived from a fractionated granitic source, and that precipitation of wolframite and tourmaline involved interaction of the granitic fluid with surrounding pelitic rocks.

Source-to-sink and evolutionary processes of the East China Sea inner-shelf mud belt and its response to environmental changes since the Holocene: New evidence from the distal mud belt

Article

Full-text available

Apr 2021

During the past decades, the elongated mud belt, 1000 km length, in the inner shelf of the East China Sea (ECS), has been extensively studied. Previous studies mainly focused on the northern part of the mud belt. There are still many arguments on various issues of the mud belt, including the provenance discrimination, the formation mechanism, and its evolution response to climate and environmental changes. In this paper, a borehole acquired from the distal southern mud belt which penetrated the Holocene strata with the collected data was analyzed. According to the parameters of (La/Sm) UCC versus (Gd/Yb) UCC and the ternary diagram of smectite-illite-(kaolinite + chlorite), sediments from the top section of Core ECS1601 originated from the Yangtze River since 13.7 ka. Sediments from upper and lower reaches of the Yangtze River can be clearly distinguished by (Gd/Yb) UCC value. The provenance of the distal mud belt shifted from upper reaches to lower valley since 5 ka and returned to the upper reaches again since 2.5 ka, which was related to the asynchronous evolution of Asian monsoon system and anthropogenic activities. The high sedimentation rates occurring in the distal mud belt between 5 and 2.5 ka were related to the decreased sediment supply of the upper reaches and the strengthened Zhejiang-Fujian Coastal Current (ZFCC) caused by the intensified East Asian Winter Monsoon (EAWM).

Provenance and Weathering of Clays Delivered to the Bay of Bengal During the Middle Miocene: Linkages to Tectonics and Monsoonal Climate

Article

Full-text available

Feb 2021

Tectonics and regional monsoon strength control weathering and erosion regimes of the watersheds feeding into the Bay of Bengal, which are important contributors to global climate evolution via carbon cycle feedbacks. The detailed mechanisms controlling the input of terrigenous clay to the Bay of Bengal on tectonic to orbital timescales are, however, not yet well understood. We produced orbital‐scale resolution geochemical records for International Ocean Discovery Program Site U1443 (southern Bay of Bengal) across five key climatic intervals of the middle to late Miocene (15.8–9.5 Ma). Our new radiogenic Sr, Nd, and Pb isotope time series of clays transported to the Ninetyeast Ridge suggest that the individual contributions from different erosional sources overall remained remarkably consistent during the Miocene despite major tectonic reorganizations in the Himalayas. On orbital timescales, however, high‐resolution data from the five investigated intervals show marked fluctuations of all three isotope systems. Interestingly, the variability was much higher within the Miocene Climatic Optimum (around 16–15 Ma) and across the major global cooling (~13.9–13.8 Ma) until ~13.5 Ma, than during younger time intervals. This change is attributed to a major restriction on the supply of High Himalayan erosion products due to migration of the peak precipitation area toward the frontal domains of the Himalayas and the Indo‐Burman Ranges. The transient excursions of the radiogenic isotope signals on orbital timescales most likely reflect climatically driven shifts in monsoon strength.

Mineralogy and BCR sequential leaching of ion-adsorption type REE: A novelty study at Johor, Malaysia

Article

Oct 2020
PHYS CHEM EARTH

Since year 2010, advance research in resource investigation, mineralogy and geochemistry, environmental impact as well as processing technique of ion-adsorption type rare earth elements (REE) deposit particularly in mining industry has been conducted worldwide. Ion-adsorption type REEs are formed by weathering process of igneous rocks (typically granites) that contain certain REE-bearing minerals. Effect of the rapidly weathering, REE minerals are decomposed, and ionized REEs are absorbed on clay minerals such as kaolinite and halloysite. A research study has been made in discovery the ion-adsorption type REE prospecting in Johor, Southern Peninsular Malaysia with three vertical weathering profiles (up to 11 m) sampled on Besar island, Tengah island and Hujung island. Parent granite is A-type consist of quartz, K-feldspar, plagioclase, biotite and 0.6–1.4 wt% accessory minerals (zircon, apatite, monazite-(Ce) and chlorite). The main REE-bearing minerals are monazite-(Ce), apatite, zircon, titanite, allanite-(Ce) and bastnaesite-(Ce). Total REE concentrations in raw saprolite (potential REE horizon in weathering profiles) is ranging between 1167 and 2339 ppm. The laboratory leach ability of the REE in different parts of the A-type granite weathering profiles was determined by carrying out a three step BCR sequential extraction procedures. The evidence from the three-step BCR-701 (certified freshwater sediment standard) sequential extraction procedure for ion-adsorption was consistent with a near instant process (≤1 h) with 70–80% recovery rate. This is due to the re-precipitation of REE³⁺ ions in solution and due to hydrolysis of ions on the clay surface. The ion-adsorption (leached) fraction was enriched in light rare earth elements (LREE) compared with the raw sample compositions of the saprolites and saprocks (Ce/Ce* ratio range largely from 0.17 to 0.82). The LREE accounted for 80–90% of the total REE content in the investigated saprolite and saprock; allowed in agreement with the trend that was observed in Thailand and South China ores.

Geochemical evidence of Milankovitch cycles in Atlantic Ocean ferromanganese crusts

Article

Full-text available

Nov 2020
EARTH PLANET SC LETT

Hydrogenetic ferromanganese crusts are considered a faithful record of the isotopic composition of seawater influenced by weathering processes of continental masses. Given their ubiquitous presence in all oceans of the planet at depths of 400-7000 meters, they form one of the most well-distributed and accessible records of water-mass mixing and climate. However, their slow accumulation rate and poor age constraints have to date limited their use to explore 100 ka paleoclimatic phenomena. Here it is shown how the Pb isotope signature and major element content of a Fe-Mn crust from the northeast Atlantic responded to changes in the intensity and geographic extent of monsoonal rainfall over West Africa, as controlled by climatic precession during the Paleocene. The studied high-spatial resolution (4 μm) laser-ablation multi-collector inductively coupled plasma mass spectrometer (LA-MC-ICP-MS) Pb isotope data is a nearly 2 order of magnitude improvement in spatial and temporal resolution compared to micro-drill subsamples. The record demonstrates cyclicity of the 206 Pb/ 204 Pb and 208, 207 Pb/ 206 Pb ratios at the scale of single Fe-Mn oxide laminae, in conjunction with variations in the Fe/Mn ratio, Al, Si and Ti content. Time-frequency analysis and astronomical tuning of the Pb isotope data demonstrates the imprint of climatic precession (∼20 ka) modulated by eccentricity (∼100 and 405 ka), yielding growth rates of 1.5-3.5 mm/Ma consistent with previous chemostratigraphic age models. In this context, boreal summer at the perihelion causes stronger insolation over West Africa, resulting in more intense and geographically extended monsoonal rainfalls compared to aphelion boreal summer conditions. This, in turn, influences the balance between the weathering endmembers feeding the northeast Atlantic basin. These results provide a new approach for calibrating Fe-Mn crust records to astronomical solutions, and allow their isotopic and chemical archive to be exploited with an improved temporal resolution of 1000-5000 years.

Ultra-trace Element Characterization of the Central Ottawa River Basin using a Rapid, Flexible, and Low-volume ICP-MS Method

Article

Full-text available

Dec 2020
AQUAT GEOCHEM

Ultra-trace (< 1 ng g−1) rare earth elements and yttrium (REE + Y) and high field strength element (HFSE) geochemistry of freshwater can constrain element sources, aqueous processes in hydrologic catchments, and the signature of dissolved terrestrial fluxes to the oceans. This study details an adapted method capable of quantifying ≥ 38 elements (including all REE + Y, Nb, Ta, Zr, Hf, Mo, W, Th, U) with minimal sample preparation in natural water aliquots as low as ≤ 2 mL. The method precision and accuracy are demonstrated using measurement of the National Research Council – Conseil national de recherches Canada (NRC-CNRC) river water certified reference material (CRM) SLRS-6 sampled from the Ottawa River (OR). Data from SLRS CRM are compared to those of new, filtered (< 0.45 µm) stream water samples from the central Ottawa River basin (ORB), and discussed in terms of processes and geochemical signatures inherited from the highly evolved igneous/metamorphic Archean and Proterozoic bedrock in the catchment. The ORB waters have significantly LREE > HREE-enriched REE + Y patterns, small natural positive Y and Gd anomalies, and negative Eu and Ce anomalies. These REE + Y features are coherent downstream in the OR apart from amplification of Eu and Ce anomalies during REE removal/dilution. The OR samples capture a downstream decrease in sparingly soluble HFSE (Th, Nb, Ta, Zr, Hf), presumably related to their colloid-particulate removal from the dissolved load, accompanied by crustal Zr/Hf (32.5 ± 5.1) and supercrustal Nb/Ta (25.1 ± 7.7) ratios. Subcrustal Th/U (0.17–0.96) and supercrustal Mo/W (12.0–74.5) ratios in all ORB waters indicate preferential release and aqueous solubility of U > Th and Mo > W, with the latter attributed primarily to preferential W adsorption on soil or upstream aquatic (oxy)(hydr)oxide surfaces.

Geological overview of clay nanoparticles

Chapter

Jan 2020

Cristina Villanova-de-Benavent

Behavior of beryllium in the weathering environment and its delivery to the ocean

Article

Aug 2019
GEOCHIM COSMOCHIM AC

Chemical weathering of silicate rock is one of the major long-term sinks of atmospheric CO 2. While several radiogenic isotope systems (e.g. Nd, Pb, Os) in the authigenic component of marine sediments show temporal patterns that could be interpreted in terms of fluctuations in chemical weathering rate over glacial cycles, recent work using beryllium isotopes suggests little such variation. However, our knowledge of the sources of 9 Be to the oceans is incomplete. Here, we address some of the gaps in knowledge with new data on Be in Croatian and Scottish rivers and estuaries, as well as with mixing experiments between Amazon tributaries and ocean water. The new data, combined with data from the literature, confirm that riverine Be is only marginally affected by carbonate weathering, which only accounts for 0.4-1.5% of dissolved riverine Be fluxes. The behavior of Be in estuaries is highly variable, with some estuaries showing removal and others addition. Based on the available data, about 55% of dissolved riverine Be is removed in estuaries, with complexation by both organic vs. inorganic ligands appearing to exert a strong control on the specific behavior in a given estuary. Beryllium complexation with organic material facilitates transport across estuaries, whereas the presence of inorganic complexants results in loss. Presence of both ligand types may lead to stronger non-conservative behavior than the presence of only one. Combining different approaches for estimating the dissolved riverine Be flux and estuarine removal, we calculate that 13-30% (4-48% error range) of the marine 9 Be input is derived from riverine dissolved loads, and 70-87% (53-96% error range) from other sources like desorption from particulate matter and release from shelf sediments. It seems likely that this 13-30% of the marine Be input would respond quickly to changes in continental weathering rates, instantaneously impacting marine Be isotopes. However, the exact response of marine Be isotopes to changes in continental weathering rates also depends on the timescale of Be release from the riverine particulate pool stored in sediments on continental margins.

Enrichment of ion-exchangeable rare earth elements by felsic volcanic rock weathering in South China: genetic mechanism, formation preference

Article

Sep 2019
ORE GEOL REV

Sources of bias in detrital zircon geochronology: Discordance, concealed lead loss and common lead correction

Article

Full-text available

Jul 2019
EARTH-SCI REV

The distribution pattern of U-Pb ages of detrital zircon in a sedimentary rock is commonly assumed to reflect the ages of igneous or metamorphic processes in rocks that have contributed material to the sedimentary basin (i.e. the protosources), directly or through recycling of older sedimentary rocks. If the Pb isotopic composition of detrital zircon is modified by processes after crystallization, or influenced by unintended effects of data treatment such as discordance filters and common lead correction, the value of detrital zircon as geological indicator is compromised. Discordance filters will identify zircons having suffered recent lead loss, but significant amounts of ancient lead loss may pass undetected. Lead loss events after the zircon's primary crystallization can be induced by regional or contact metamorphism, but also by low temperature processes during diagenesis and weathering, and can be coupled to uptake of a mixture of common lead and unsupported radiogenic lead, which cannot be properly corrected by common‑lead correction routines. Concealed ancient lead loss and overcorrection for common ²⁰⁷Pb may cause bias towards lower ages, while remaining within acceptable discordance limits. This creates spurious age fractions that may give false indications of sedimentary provenance, invalidate estimates of maximum limits for the age of deposition, and cause problems for comparison and correlation studies based on detrital zircon age data. Careful scrutiny of all U-Pb analyses in combination with Hf isotope analysis may help identifying these effects in detrital zircon data, but will not provide a universal guarantee against biased age spectra.

Chemical weathering across the western foreland of the Greenland Ice Sheet

Article

Nov 2018
GEOCHIM COSMOCHIM AC

Proglacial streams deliver melt water and chemical weathering products, including nutrients and radiogenic isotopes, from continental ice sheets to the ocean. Weathering products are also delivered to the ocean in non-glacial streams that form following ice sheet retreat and are disconnected from ice sheet meltwater by hydrologic divides. If weathering reactions differ in non-glacial and proglacial stream catchments, the streams could deliver different types and magnitudes of solutes to the ocean, depending on relative discharge volumes. Unlike proglacial streams, however, little is known of non-glacial stream solute compositions or discharge. Here we show specific discharges are similar from a proglacial stream draining the Greenland Ice Sheet (GrIS) with several streams disconnected from the ice sheet. We also evaluate weathering reactions across a 170-km transect in western Greenland that contains one proglacial stream draining the GrIS, and two coastal (ice distal) and three inland (ice proximal) areas with non-glacial streams. Non-glacial streams exhibit solute compositions and offsets between dissolved and bedload Sr isotope ratios that indicate weathering increases toward the coast with exposure age and precipitation. Major element mass balance calculations show weathering reactions shift from predominately carbonic acid weathering of carbonate minerals inland near the ice sheet to predominately sulfuric acid weathering of carbonate minerals near the coast. Strontium concentrations and isotopic ratios of the proglacial stream reflect mixing of at least two subglacial sources and minor in-stream weathering that consumes CO2. About 5 times less CO2 is consumed per liter in the proglacial than inland non-glacial streams; however, arid conditions inland suggest limited discharge from the ungauged inland streams leads to less total CO2 weathering than proglacial stream. One coastal area consumes less CO2 per liter than the proglacial stream and another coastal area exhibits net CO2 production. These results indicate estimates for glacial foreland solute fluxes and CO2 weathering consumption and production should include estimates from both non-glacial and proglacial streams. Understanding weathering fluxes from these two types of streams will be important for evaluations of past ice sheet retreat and predictions of future solute and CO2 fluxes associated with continued ice sheet retreat.

Provenance of the great Cambrian sandstone succession of northern Gondwana unravelled by strontium, neodymium and lead isotopes of feldspars and clays

Article

Mar 2018
SEDIMENTOLOGY

The great Cambro-Ordovician sandstone succession of northern Gondwana is one of the most voluminous siliciclastic deposits on Earth. Its deposition took place following the Neoproterozoic Pan-African Orogeny and the consolidation of Gondwana, a crucial episode in Earth history. Its provenance is of great importance for reconstructing palaeogeographic and tectonic settings and determining sediment dispersal patterns. In Israel and its environs, Palaeozoic sandstones overlie the juvenile Neoproterozoic basement of the Arabian-Nubian Shield. These basement rocks were considered as an important sediment source to the Cambro-Ordovician succession. However, recent studies established that a dominant portion of detrital zircons in the succession was derived from Archean-Proterozoic remobilized terranes, suggesting transportation distances of thousands of kilometres beyond the Arabian-Nubian Shield, and thus question the provenance of other, less weathering-resistant constituents, which were not necessarily derived from the same localities. Feldspars and clays were separated from 13 samples and analyzed for mineralogical and geochemical compositions, strontium, neodymium and lead isotopes, in order to further constrain the provenance of the Cambro-Ordovician succession of northern Gondwana. Detrital feldspars have εNd values significantly different from feldspars of the Arabian-Nubian Shield, ranging from -8 to -14, with model ages of 950 to 1750 Ma, more radiogenic lead compositions, and μ (²³⁸U/²⁰⁴Pb) values ranging from 9·8 to 10·26. Clays are dominated by illite, smectite and kaolinite, with εNd values ranging between -14 and -9, with ⁸⁷Sr/⁸⁶Sr ratios up to 0·757. These findings point to a significant contribution of remote ancient terranes from outside the Arabian-Nubian Shield to the Cambro-Ordovician sandstone of northern Gondwana. The possible sources for these sediments are the Saharan Metacraton and the southern regions of the East African Orogen.

Les manteaux d'altération développés sur les schistes de la série de Lom à Bétaré-Oya (Est-Cameroun): pétrologie, métallogénie et dynamique du paysage

Thesis

Jan 2022

Idriss Franklin Tiomo

The Lom series is a wide geological complex unit with an overall NE-SW trend. Its location in the geomorphological map of Cameroon evidences an upper landsurface related to the Meïganga surface of the Adamaoua plateau and a lower landsurface linked to the African I surface of the South-Cameroonian plateau. Petrological (XRD, XRF and ICP-MS), metallogenic and geodynamic (landscape analysis) issues have been carried out on the lateritic weathering mantles over schist basement in the Bétaré-Oya Gold District, with the aim to assess the implication of supergene processes on the fractionation and redistribution of chemical elements and on lateritic landscape evolution. Thus, five (05) soil profiles digged in five (05) elevation levels were studied. Their spatial distribution provides evidence of three morpho-pedologic area: ferricretes upper of the study area, less-developed soils at the center and carapaces in the lower landscape. Mineralogical data show the abundance of newly formed minerals such as kaolinite (18-45 %), gibbsite (15-39 %), goethite (9-20 %) and hematite (2-35 %) in the upper landsurface, whereas residual mineral phases known as quartz (22-55 %), muscovite (1-11 %) and felspars (1-9 %) are more abundant in the lower landsurface. Geochemical indices and correlative ternary diagrams reveal a strong weathering intensity and moderate to low rate of lateritization, controlled more significantly by lithology and variation of altitude. Silica (28 - 64 %), alumina (14 - 39 %), iron (7 - 49 %) and titanium (0.8 - 2 %) are the most abundant major oxides in the weathering products. Trace elements highlight a preferential enrichment in the matured soil horizons and involve mineralization made up by Sb (28-208), U (5-21), Mo (11-18), Sn (2-6), Th (3), Pb (2) and Zn (2) in the upper landscape; Sb (2-5), Mo (2-4), U (2- 4), Th (2-3), Pb (2-3) and Sn (2) in the lower landscape. REEs (155.7 – 691.1 ppm) and Au (0.034 – 3.632 ppm) are more enriched in the lowermost part of soil profiles. Based on spearman’s correlation function, trace elements and REEs are linked to less mobile major elements (Al, Fe and Ti) and suggest their strong redistribution into the crystalline structure of newly formed minerals. Meanwhile, residual zircon, apatite, rutile, titanite, muscovite and feldspars also play prominent role on trace and REEs elements behaviour. Geodynamic studies show that, the distribution and layering of lateritic landsurfaces in the Lom series at Bétaré-Oya were significantly influenced by ancient local and regional tectonic activity and erosive action of water. However, two stages of planation - induration (Cretaceous and Eocene) separated by a stripping stage explain the genesis of the Meïganga surface and African I surface in the Lom series at Bétaré-Oya.

Lead isotopic fingerprinting as a tracer to identify the sources of heavy metals in sediments from the Four Rivers’ inlets to Dongting Lake, China

Article

Dec 2022
CATENA

In this study, Pb isotopic composition of bulk sediments and 1 M HCl leachates/residues of samples from the Four Rivers’ inlets to Dongting Lake (China) was determined to identify and differentiate the source of Pb inputs. Results highlighted that Xiangjiang river (XY-QS) sediments were highly enriched in Pb with less radiogenic Pb isotopes (e.g., ²⁰⁶Pb/²⁰⁷Pb ratios of 1.1830 ± 0.003), indicating the predominance of anthropogenic Pb inputs. In contrast, sediments of the Zijiang, Yuanjiang and Lishui rivers (ZD-LH) were moderately enriched in Pb and exhibited more radiogenic Pb (e.g., ²⁰⁶Pb/²⁰⁷Pb ratios of 1.1880 ± 0.008). Results from 1 M HCl extraction of XY-QS sediments illustrated that anthropogenic Pb was removed, which resulted in differentiation of ²⁰⁶Pb/²⁰⁷Pb isotope ratios between leachates (1.1740 ± 0.005) and residues (1.1846 ± 0.008), however, this difference was not observed in ZD-LH sediments (leachates: 1.1887 ± 0.009; residues: 1.1887 ± 0.008). Residual Pb isotope ratios suggested that Pb isotopic composition of lithologically inherited Pb in inlet sediments was similar, which was attributed to mixing, hydrological sorting, and averaging of different Pb sources from diverse geological settings. Pb isotopic tracing showed that Pb in XY-QS sediments resulted from the mixing of two end member sources, an anthropogenic source (less radiogenic Pb) from downstream ore smelting and upstream ore mining activities (53%) and a lithological source (37%) from granite through weathering. In contrast, Pb in ZD-LH sediments resulted from the mixing of multiple sources including Pb from upstream mining activities (20%), coal combustion (20%), and lithologically inherited Pb (60%) while surface sediments from the Yuanjiang river contained Pb from diesel oil usage (50%). Results from this study highlight the utility of a Pb isotope approach for identifying and differentiating Pb source inputs in diverse sediments from the Four River inlets to Dongting Lake (China).

Lead Isotopic Fingerprinting as a Tracer to Identify the Sources of Heavy Metals in Sediments from the Four River Inlets to Dongting Lake, China

Article

Jan 2021

Geochemical and REE mineralogical characteristics of the Zhaibei Granite in Jiangxi Province, southern China, and a model for the genesis of ion-adsorption REE deposits

Article

Nov 2021
ORE GEOL REV

The Zhaibei Granite in Jiangxi Province, southern China, hosts an ion-adsorption light rare earth element (LREE) deposit. Recently, heavy REE (HREE) ores have also been reported from weathered crusts of the granitic rocks. In this study, petrological, geochemical, and mineralogical characteristics of the Zhaibei pluton were analysed to establish the genesis of this REE deposit. The pluton contains coarse-grained biotite syenogranite and minor hornblende–biotite–quartz monzonite in its central zone, medium-grained biotite syenogranite in its transitional zone, and fine-grained muscovitic alkali-feldspar granite and porphyritic muscovitic biotite–alkali-feldspar granite together with monzogranite porphyry intrusions in its marginal zone. The REE minerals include titanite, allanite, monazite, bastnasite, and thorite-(Y) in the central zone, allanite, monazite, xenotime, bastnasite, and thorite-(Y) in the transitional zone, and synchysite-(Y), thorite-(Y), and xenotime in the marginal zone. The SiO2 content increases from 62 to 77 wt% from the centre to the margin, whereas the Al2O3, TiO2, MgO, FeO, and CaO contents decrease. In addition, the size of the negative Eu anomaly and HREE content increase, accompanied by decreases in Co, Zr, Hf, Sr, and Ba and increases in Rb, Cs, Nb, and Sn. These observations indicate that the Zhaibei Granite might have been formed by crystallisation differentiation of magma. The granitic pluton was also influenced by reactions with late-magmatic F-, CO2–, and REE-rich fluids that altered magmatic minerals and crystallised as REE-fluorocarbonates and thorite. The hydrothermal REE minerals constitute ∼ 40% of the total REEs in the bedrock and are the major supplier of ion-exchangeable REEs in the ores of the Zhaibei deposit. LREE-rich ores may have been derived from the LREE-rich granitic rocks, which contain bastnasite, titanite, and allanite, whereas HREE-rich ores were sourced mainly from the HREE-rich granites, which contain synchysite-(Y) and thorite-(Y). Furthermore, REE ores with enrichment in both HREEs and LREEs were probably sourced from the monzogranite porphyry bedrock, which contains bastnasite-(Y), bastnasite, allanite, and thorite-(Y).

XRD and TEM analyses of a simulated leached rare earth ore deposit: Implications for clay mineral contents and structural evolution

Article

Dec 2021
ECOTOX ENVIRON SAFE

The types, contents, and microstructures of clay minerals play important roles in controlling the adsorption and desorption of ion-absorbed type rare earth ores and heavy metals. By selecting a typical rare earth ore profile, we conducted a leaching experiment and used XRD (X-ray diffraction) and TEM (Transmission electron microscopy) analyses to determine the clay mineral types and microstructural changes after various leaching periods. The XRD phase analyses showed that the main minerals in the simulated rare earth ore were quartz, potassium feldspar, kaolinite, and illite. TEM images showed that the mineral aggregates were broken, disintegrated, and transformed by the leaching process, and a large number of moire fringes were visible. With continuous leaching, REEs (Rare Earth Elements) were gradually re-solved and leached. The results of the leaching experiment indicate that fine-grained minerals in rare earth ores, such as potassium feldspar and clay minerals, migrated downward with the leaching solution. Leaching also promoted the alteration of potassium feldspar to clay minerals, as well as mutual alteration of clay minerals. Under acidic or neutral conditions during the early stage, potassium feldspar was altered to kaolinite or illite, whereas during the middle and late stages of leaching it was altered as follows: illite → mixed-layer illite–kaolinite → kaolinite → mixed-layer kaolinite–illite → illite. This transformation has an important effect on the release of REEs and heavy metals and provides insights into improving the leaching process and explaining heavy metal pollution in rare earth mining areas.

Enhanced chemical weathering of albite under seawater conditions and its potential effect on the Sr ocean budget

Article

Jul 2019
GEOCHIM COSMOCHIM AC

Currently, knowledge about the dissolution kinetics of silicate minerals under seawater conditions in general and about feldspar minerals specifically is lacking, even though feldspars are the most common minerals in the earth’s crust. Consequently, global geochemical cycles of elements and isotopes overlook the potential effects of silicate dissolution in seawater and its contribution to mass balances. The aim of the present study is to quantify the effect of salinity on albite dissolution kinetics under seawater conditions and the possible impact of salinity on Sr concentrations and isotopic compositions in seawater. A series of albite dissolution experiments with synthetic NaCl solutions (0.0001–1 molal) at pH 5 and 25 °C were conducted using multi-point batch experiments (MPBEs). Above the Na concentration threshold (0.01 molal), the albite dissolution rate was found to increase with the NaCl concentration and with the ionic strength. Based on the present study and previous experimental studies, a combined model that describes the effects of pH, Na concentration and ionic strength on the albite dissolution rate was developed. The proposed model suggests that albite dissolution under natural seawater conditions is mainly controlled by the effect of ionic strength. Considering that seawater solutions are under far-from-equilibrium conditions, the dissolution rate of albite is more than order of magnitude faster in seawater than in the continental, abiotic environment. Hence, the potential of silicate dissolution in seawater to contribute elements to the oceans is significant. In addition, a MPBE was conducted with a Bancroft, Ontario, Canada albite sample using synthetic seawater (SSW). Based on the changes in Si, Al, Sr, Ca and ⁸⁷Sr/⁸⁶Sr with time in this experiment, it is suggested that the relative dissolution rates of albite and apatite inclusions in the albite sample control the Sr concentrations and isotopic compositions. The estimated contribution of Sr release due to feldspar dissolution in seawater under far-from-equilibrium conditions is 2.67∙10⁸ mol y⁻¹. This result is significant if considering other forms of Al-Si mineral dissolution on the ocean floor.

Behaviour of Li isotopes during regolith formation on granite (Massif Central, France): Controls on the dissolved load in water, saprolite, soil and sediment

Article

Jun 2019
CHEM GEOL

Lithium (Li) contents and isotopes were studied in all environments of a small river catchment draining granite in the Margeride mountains of the French Massif Central. This covered surface waters, primary and accessory minerals of the granites, the whole rock, and soil and sediment samples developed in the catchment, completed with regional data for mineral waters and rainwater. The integrated investigation aimed at evaluating the potential of Li isotopes as effective tracers of water/rock interaction processes within a granitic environment. The δ⁷Li values and Li concentrations were measured on sediment- and soil samples, following standard acid-dissolution procedures and chemical purification of Li using the cationic exchange resin protocol in a clean lab. Lithium-isotope compositions were measured with a Neptune MC-ICP-MS and Li concentrations by ICP-MS. The samples represented different stages of granite weathering, including fresh granite, weathered-rock, surface saprolite, and sediments in riverbanks and fields bordering the streams. The extent of Li mobility during granite weathering was first evaluated through determining the percentage change relative to Ti, with a range from −31 to −66% in the collected samples. The weathered-rock was depleted by −47% for Li with negative δ⁷Li values ranging from −1.9 to −3.4‰. Soil to riverbank sediment samples were characterized by less negative δ⁷Li values, indicating that Li is enriched in soil with fractionation of Li isotopes and changes of the mineral abundance in the samples. To complement this first view, we i) Modelled the theoretical Li isotope signature of water interacting with granite, using a weathering model based on dissolution; ii) Applied an atmospheric-input correction to surface waters; iii) Applied a Raleigh equation for modelling the Li isotope fractionation when compared with corrected surface water and mineral water; and iv) Compared Li isotopes with Sr-isotope data in a larger weathering framework.

Radium isotopes for groundwater age and sustainability in the highland of Antananarivo, Madagascar

Article

May 2019
J AFR EARTH SCI

Nowadays, the access to drinkable water becomes more and more difficult for many regions around the world and the highland of Antananarivo, Madagascar, does not escape this problem. The groundwater resources of Antananarivo region could be a solution to consider for water needs, especially during drought. Knowing the groundwater age permits to estimate the aquifer potentiality, to predict the sustainability if the water source is health safe, and then to help the decision maker for the best management of the groundwater resources. Radium isotopes in the groundwater of this area have been measured to estimate the residence time of the water in these shallow aquifers. The analyses were carried out by using high resolution gamma spectrometry on MnO2-impregnated fibers as radium collectors from groundwater. ²²⁶Ra activity ranges from 29.2 ± 10.2 to 241.7 ± 26.9 mBq/L⁻¹ and ²²⁸Ra activity ranges from 22.5 ± 4.9 to 684.9 ± 13.5 mBqL⁻¹ whereas ²²⁸Ra/²²⁶Ra activity ratio ranges between 0.20 ± 0.05 and 4.86 ± 0.88. Three variations of a same basic model depending on the variation of ²²⁸Ra/²²⁶Ra activity ratio in function of alpha-recoil, dissolution, adsorption and time were used to estimate the groundwater residence time. The most reliable ages of the highlands’ groundwater, calculated in this way, range from 0.2 to 10 years. According to these results, the groundwater of the E-NE sector of the area have the highest average residence time of 6.5 years and a total potential volume of available groundwater estimated to about 152· 10⁶ m³. These features, coupled with radium content below the WHO guidance levels for drinking water, show that the groundwater of this sector constitute a reliable resource to supply the region of its needs for human as well as for agricultural purposes.

Chemical weathering of S-type granite and formation of Rare Earth Element (REE)-rich regolith in South China: Critical control of lithology

Article

May 2019
CHEM GEOL

REE-rich granite regolith is a significant host for the ion-adsorption type Rare Earth Elements (REE) ore resources in South China. The issue of why and how such specific regolith was generated has attracted great attentions for both scientific and economic interests. To improve the understanding of critical factors that control the formation of REE-rich granite regolith, especially for those related to weathering of the S-type granite, an investigation of granite and its overlying regolith is conducted in South China's largest S-type granite terrain (Darongshan, Guangxi). The Hercynian and Indosinian granites outcrop as neighboring lithofaces, but their overlying regolith show significant differential chemical weathering. Examinations of their representative regolith profiles found that the profile from the Hercynian granite is thick and REE-rich, whereas that from the Indosinian granite is relative thin and REE-poor (12 m vs. 6 m in depth, 929 ppm vs. 226 ppm in REE concentration). Given similar climatic, topographic, and vegetative conditions, the difference between two profiles can be principally traced down to their parent granite lithology. Formation of the thick and REE-rich profile is closely associated with some specific lithological factors of its parent granite. Contrastingly, it has coarser grain size, wider microcracks, as well as higher biotite and plagioclase contents, which is expected to be more conductive to enhance water-rock interaction and drive deep weathering. Meanwhile, it contains higher initial REE concentration (342 ppm vs. 132 ppm) and, more importantly, richer REE-bearing accessory minerals (monazite, apatite and zircon), which offered dominant REE source to regolith. Especially, apatite (REE = 1549–4413 ppm) is an critical REE source mineral in supplying mobile REE to the regolith, through which REE have access to be fixed by clay minerals (mainly kaolinite and illite) and then developed ion-exchangeable form enrichment in the regolith. These evidences indicate that the granite lithology exerts a principal influence on the formation of thick and REE-rich regolith through fundamental control of chemical weathering and REE input. Moreover, this study find that, for the S-type granite particularly, the high P2O5 content (>0.08 wt%) granite seems more optimistic in generating ion-adsorption type REE ore (especially LREE) by weathering than previously thought.

Geochemical and mineralogical characteristics of REEY occurrences in the Mocambo Granitic Massif tin-bearing A-type granite, central Brazil, and its potential for ion-adsorption-type REEY mineralization

Article

Feb 2019
ORE GEOL REV

The Mocambo Granitic Massif is an A-type granite located in the northeastern part of Goiás State, near the city of Monte Alegre de Goiás. It belongs to the Pedra Branca Suite, which is itself part of the Goiás Tin Province, a group of stanniferous granites that exhibit similar geochemical features, including to a greater or lesser degree of rare earth elements enrichment. The parent rock in the Mocambo Granitic Massif is a coarse porphyritic pink biotite granite. Thin section observations coupled with electron microprobe analyses reveal the presence of several REE-bearing minerals: allanite, fergusonite (Ce), fergusonite-(Y), zircon and apatite as accessory minerals, and xenotime-(Y), bastnäsite-(Ce), thorite, monazite-(Ce) and hingganite-(Y) as secondary (hydrothermal) minerals. Fergusonite and hingganite are identified in this massif for the first time. This work investigates the forms of occurrence and enrichment of rare earth elements in the Mocambo Granitic Massif, in the parent rock, as well as in greisen, saprolite and soil, with emphasis placed on the rare earth elements adsorbed on clay minerals, and the entire process of transport and fractionation of these elements from the fresh rock until adsorption. The results show enrichment of rare earth elements (with the exception of Ce) in soils in comparison to rock, especially in the clay fraction. Moreover they suggest that these elements are mostly adsorbed on clay minerals, mostly kaolinite and illite, which are identified in the X-ray patterns. The surface oxidation of Ce³⁺ to Ce⁴⁺ on surfaces and the probable formation of Ce oxides cause this element to present a smaller quantity of exchangeable ions. The presence of cerianite grains in one superficial soil sample shows that Ce is mostly found in the Ce⁴⁺ state in the soil profile. The Mocambo Granitic Massif displays substantial enrichment in REEY, 555–1229 ppm for the parental granite and 569 ppm for the greisen, and the exchangeable REEY concentrations in the soils horizons, more than 600 ppm, in particular, representing a potential target for an ion-adsorption-type rare earth elements deposit.

Determination of lead isotope ratios in Mn–Fe-rich nodules by laser ablation multi-collector inductively coupled plasma mass spectrometry

Article

Oct 2018

In this study, Pb isotopic ratios in ferromanganese nodules were determined with good repeatability and laboratory bias using laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). One certified ferromanganese nodule reference material, NOD-A-1, in the form of pressed powder pellet (PPP) produced upon ultrafine processing, was homogeneous enough to be used as an in-house matrix-matched standard or quality control sample for Pb isotopic microanalysis. The Tl normalization exponential law correction method with CTl-NIST SRM 997/CTl-sample ≥ 15 (method 1) and the standard-sample-bracketing (SSB) method (method 2) were utilized to determine Pb isotopic ratios with good repeatability and laboratory bias. In situ measurements of the Pb isotopes yielded good relative standard deviation (2RSD) of < 0.036% for 207,208Pb/206Pb and < 0.066% for 206,207,208Pb/204Pb. In addition, matrix effect was insignificant when silicate glass reference material was employed as the external standard in the ferromanganese nodules using these two methods, resulting in relative errors (RE) of < 0.064% for 206,207,208Pb/204Pb, and < 0.046% for 207,208Pb/206Pb. The in situ Pb isotopic compositions of the three Chinese ferromanganese nodules, GBW07249, GBW07295, and GBW07296, were in good agreement with those obtained by solution nebulization MC-ICP-MS (SN-MC-ICP-MS) within 2s (standard deviation) measurement uncertainties, demonstrating the reliability and robustness of our proposed analytical protocol.

The effects of lithology on trace element and REE behavior during tropical weathering

Article

Sep 2018
CHEM GEOL

The thick regolith developed in the humid tropics represents an endmember of critical zone evolution, where shallow and deep biogeochemical cycles can be decoupled in terms of the predominant source of trace elements (atmospheric input at the surface, weathering at depth) and of the processes that control their cycling. To investigate the influence of lithology on trace element behavior and in this potential decoupling, we studied two deep (9.3 and 7.5 m), highly-leached, ridgetop regolith profiles at the Luquillo Critical Zone Observatory, Puerto Rico. These profiles have comparable internal (degree of weathering, topography) and external (vegetation, climate) characteristics, but differ in their underlying bedrock (andesitic volcaniclastic and granitic). At these two sites, we analyzed a large suite of trace elements and used the rare earth elements and yttrium (REY) as tracers of critical zone processes because they are fractionated by the chemical reactions involved in weathering and pedogenesis (e.g., sorption, dissolution, colloidal transport) and by redox fluctuations. We found that both regolith profiles show atmospheric inputs of trace elements at the surface and evidence of bedrock dissolution at depth, as expected. We also found noticeable differences in the re-distribution of trace elements and REY within the profiles, indicative of different geochemical environments with depth and lithology. In the volcaniclastic profile, trace element and REY behavior is controlled mainly by redox-mediated, sorption/desorption reactions, whereas pH-controlled dissolution/precipitation and sorption reactions predominate in the granitic profile. The most noticeable difference between the two regolith profiles is in the long-term redox conditions, inferred from redox-sensitive elements and Ce anomaly variations, which are more variable and stratified in the volcaniclastic profile and change gradually with depth in the granitic profile. The contrasting redox conditions and the different sources of elements (dust vs. bedrock) produce a decoupling between the surface and deep geochemical environments of the volcaniclastic regolith. The difference in redox conditions between the two lithologies likely stems from the finer grain size and higher clay content of the volcaniclastic regolith.

Propriétés géochimiques et isotopiqes des sédiments du détroit de Fram, Océan Arctique. Implications paléocéanographiques et paléoclimatiques

Thesis

Apr 2012

Jenny Maccali

Les flux d'eau douce, glace de mer et courants océaniques, de l'Océan Arctique vers les mers nordiques jouent un rôle critique sur l'Atlantic Meridional Overturning Circulation et donc sur le système climatique. Les facteurs contrôlant ces flux sont encore partiellement méconnus. Un moyen indirect de retracer l'intensité et les schémas de circulation de la glace de mer est de retracer l'origine des sédiments qu'elle transporte, et qui sédimentent le long des grands courants de glace et d'eau douce vers l'Atlantique Nord. Il s'agit donc de tracer un flux particulaire direct, lié à la matrice des particules détritiques. Un second flux, indirect, provient des éléments dissous dans les masses d'eau, marqués par les processus d'adsorption/désorption le long des marges où les flux particulaires terrigènes sont les plus importants. L'extraction de la phase authigène d'un signal dissous par lessivage spécifique, a permis de documenter l'évolution des masses d'eau transitant par le détroit de Fram. Les données isotopiques de Pb, Nd et Sr nous ont permis d'identifier deux sources principales de sédiments depuis le dernier maximum glaciaire jusqu'au Dryas Récent : les marges canadiennes et russes alors recouvertes par des calottes de glace. Après le Dryas Récent, les sources sédimentaires sont plus diverses avec notamment une contribution des marges groenlandaises et des mers de Chukchi et Est Sibérienne. La fraction authigène montre un changement entre ~ 19.8 et 16.4 ka probablement liée à la déglaciation de la calotte Eurasienne. Plus récemment, les valeurs [Epsilon]Nd suggèrent une influence accrue des eaux Pacifiques sur les masses d'eaux sortantes par le détroit de Fram

Chapter 4. CHEMICAL WEATHERING RATES OF PYROXENES AND AMPHIBOLES

Chapter

Dec 1995

Chapter 3. PARTITIONING OF RARE EARTH ELEMENTS BETWEEN MAJOR SILICATE MINERALS AND BASALTIC MELTS

Chapter

Dec 1989

G. A. McKay

Dissolution and precipitation kinetics of sheet silicates

Article

Jan 1995

K.L. Nagy

Chemical weathering of feldspars

Article

Jan 1995

Rare earth elements and sedimentary rocks: influence of provenance and sedimentary processes

Article

Jan 1989

S.M. McLennan

Feldspar dissolution kinetics

Article

Jan 1995

The Kinetics of Base Metal Cation Release Due to Chemical Weathering

Article

Jan 1990

Harald Sverdrup

Aquatic chemical kinetics: reaction rates of processes in natural waters

Article

Jan 1990

Jerald L Schnoor

Dissolution and precipitation kinetics of sheet silicates

Article

K.L. Nagy

Lead isotope ratio measurements by ICP-MS: Accuracy, precision, and long-term drift

Article

Sep 1996

The application of inductively coupled plasma mass spectrometry (ICP-MS) for the direct, routine determination of Pb isotope ratios was investigated. Short-term precision of the measurements was 0.2 to 0.3% - Long-term precision, covering a period of four months, was nearly as good. The Pb isotope ratio measurements were corrected for the mass discrimination factor by using NIST SRM-981 (Common Pb Isotopic Standard). More than 30 soil samples were analyzed for 206Pb/207Pb using this method. The results were compared with those of thermal ionization mass spectrometry (TLMS). The ICP-MS results of all samples agree with the TIMS results within a relative standard deviation of 0.5%, and except for two samples, all agree even within a relative standard deviation of 0.3%.

Chemical weathering rates of a soil chronosequence on granitic alluvium: I. Quantification of mineralogical and surface area changes and calculation of primary silicate reaction rates

Article

Jan 1996
GEOCHIM COSMOCHIM AC

Uranium in granites from the Southwestern United States: actinide parent-daughter systems, sites and mobilization. First year report

Article

Oct 1980

Some of the principal findings of the study on the Lawler Peak Granite are: the granite is dated precisely by this work at 1411 +- 3 m.y., confirming its synchroneity with a great regional terrane of granites. Uranium is presently 8-10 times crustal abundance and thorium 2-3 times in this granite. Uranium is found to be enriched in at least eight, possibly ten, primary igneous mineral species over the whole-rock values. Individual mineral species show distinct levels in, and characteristics ranges of, uranium concentration. It appears that in a uraniferous granite such as this, conventional accuracy mineral suites probably cannot account for most of the uranium in the rock, and more rare, high U-concentration phases also are present and are significant uranium hosts. It appears that at least two different geological episodes have contributed to the disturbance of the U-Th-Pb isotope systems. Studies of various sites for transient dispersal of uranium, thorium, and radiogenic lead isotopes indicate a non-uniform dispersal of these components. It appears that the bulk rock has lost at least 24 percent of its original uranium endowment, accepting limited or no radiogenic lead or thorium migration from the sample.

Chemical Kinetics of Water-Rock Interaction

Article

Jun 1984

Antonio Lasaga

The recent literature on the kinetics of water-rock interactions is reviewed. The data are then extended to provide a quantitative framework for the description of weathering and alteration. The available experimental data on dissolution of silicates verifies quantitatively the usual mineral stability series in sedimentary petrology. The rate of hydration of carbonic acid is shown to be a possible limiting factor in water-rock interactions. The framework is developed to enable use of laboratory dissolution experimental results and thermodynamics to arrive at a rate law applicable up to equilibrium and therefore applicable to natural systems. The kinetic justification for the significance of a water-rock ratio is discussed. With a proper treatment of fluid flow, the equations are applied to the weathering profile leading to the development of bauxites from nepheline syenites.

Crystallization, fractionation, and solidification of the Tuolumne Intrusive Series, Yosemite National Park, California

Article

Jan 1979

Study of the Tuolumne Intrusive Series, a concentric texturally and compositionally zoned plutonic sequence in the eastern part of Yosemite National Park, was undertaken to develop and test a model for the origin of comagmatic plutonic sequences in the Sierra Nevada batholith. The granitoid units that make up the sequence are progressively younger and more felsic inward. The bulk of the rocks are granodiorite, but the outermost formation is quartz diorite, and the innermost one is granite porphyry. The compositional gradient changes both gradually within formations and abruptly between them. The change is greatest in the outer 1 km and lower toward the center of the sequence. Hornblende and biotite, abundant in the marginal rocks, decrease rapidly inward for 1 km as K-feldspar and quartz increase, but farther inward, they decrease slowly. The most conspicuous chemical changes are shown by the elements that are enriched in the mafic minerals. The compositional zoning indicates that with decreasing temperature, the sequence solidified from the margins inward. Solidification was interrupted repeatedly by surges of fluid core magma. The magma eroded the adjacent solidifying rock, and it expanded the area of the magma chamber at the exposed level by crowding the wall and roof rocks outward and upward and by breaking through the solidifying carapace into the wall rocks. The compositional zonation resulted from crystal fractionation that could have involved (1) preferential accretion of crystalline material present in the magma to the margins of the magma chamber, thus displacing the melt phase progressively inward, and/or (2) downward settling of crystals, probably accompanied by upward movement of melt and volatiles; the residual magma solidifying to form the granitoids. Although either mechanism can explain the observed relations, they lead to very different interpretations of the composition of the magma when the first exposed granitoids solidified at the margins of the magma chamber and as the sequence solidified inward.

Cycling of dissolved rare earth elements in Chesapeake Bay

Article

Jun 1988
GLOBAL BIOGEOCHEM CY

The measurement of dissolved rare earth elements (REE) in the surface waters, water column of anoxic basins, and pore waters in Chesapeake Bay has provided new insights to the biogeochemistry and estuarine chemistry of REE. All dissolved REE from the riverine source show large-scale removal in the lower salinity zone (0-10‰). The shale-normalized pattern of dissolved Susquehanna River water is opposite in form to that of surface sediments in the Bay. The former is enriched in heavy REE (HREE) while the latter are enriched in light REE (LREE). Neither component has a flat pattern normally assumed for river- transported REE to the ocean. The dissolved LREE (i.e., La, Ce, Nd, Sm, and Eu) are enriched 3 to 9 times) in the oxygen-depleted deep waters over their concentrations in the oxic surface waters. In contrast, HREE (Er, Yb, and Lu) are slightly depleted. All REE concentrations in the two surface (0-2 cm) pore waters are greatly enriched (8-17 times; 43 times for Ce) relative to oxygen-depleted bottom waters and have relative abundances opposite to those of their sediments. While Ce has a positive anomaly in the pore waters, negative anomalies exist in the oxygen-depleted bottom waters. The REE are participating in a set of complex biogeochemical cycles within the water column and surface sediments. Fractionation of REE during these cycles leads to the preferential enrichment of LREE in the seasonally oxygen-depleted bottom waters. It is proposed that this fractionation is coupled to redox cycles of Mn and Fe and the interaction of dissolved REE with suspended particles and surficial sediments.

Rare Earth Element Supply to the Ocean

Article

Jun 1976

More insight on rare earth element pathways from land to ocean comes from analyses of suspended matter in four major world rivers (Amazon, Congo, Ganges, Mekong), while their geochemical behavior at the river-ocean boundary has been studied in the Gironde estuary (France). The Gironde data indicate that soluble rare earth elements are removed from solution in the estuarine zone; this observation invalidates any rare earth element balance to the ocean which would not take into account the river-ocean boundary processes. Data on rare earth element concentrations in soluble and detrital river loads show that solid discharge represents the major part of rare earth elements supplied by rivers to the ocean. A rare earth material balance to the ocean is discussed on the basis of the results presented in this paper.

Kinetics of muscovite, phlogopite, and biotite dissolution and alteration at pH 1–4, room temperature

Article

Feb 1996
GEOCHIM COSMOCHIM AC

The reaction kinetics of dioctahedral muscovite and trioctahedral phlogopite and biotite were studied in aqueous solutions at pH 1–4 and room temperature. The experiments were performed in a reactor where mineral suspensions were separated from eluent solutions with dialysis membranes. Dissolution of muscovite was close to stoichiometric. In the experiments with trioctahedral micas, a solid residual of altered 2:1 layers was formed by preferential release of cations. A preferential release of K was found with phlogopite and biotite. Also, an excess release of octahedral cations compared to tetrahedral Si was obtained in biotite experiments. Describing the dissolution rates, R, by the equation R=kH+aHn+, apparent rate constants, kHstaggered+, of 1.7·10−2 for muscovite, 3.4·10−11 for phlogopite and 3.2·10−10 for biotite, in units of mol (O20(OH)4 formula units) m−2 s−1 were obtained. The corresponding exponents, n, were 0.14, 0.40, and 0.61. These values were calculated from rates that were normalized to the total mineral surface area at the start of experiments. Surface area changed during the experiments, partly due to delamination along basal surfaces, which affected the calculation of rate constants and the pH-dependence of rates. Rates that are normalized to total surface area may have little relevance for micas, since reactive sites probably are concentrated on edge surfaces which comprise a small fraction of total surface. Biotite Fe2+ was found to reduce dissolved Fe3+, confirming previous reports about the importance of Fe-rich silicates for the redox state of dissolved species. Possible effects of nonstoichiometric release of cations on the composition of altered products are discussed.

Fractionation of uranium, thorium and rare earth elements in a vertically zoned granodiorite: Implications for heat production distributions in the Sierra Nevada batholith, California, U.S.A

Article

May 1988
GEOCHIM COSMOCHIM AC

The abundances of heat-producing elements increase and of rare-earth elements decrease upward in a 1 km vertical section through a pluton in the eastern Sierra Nevada batholith, California. This distribution results mainly from magmatic processes and not from alteration. For samples containing between 47.7% and 65.5% SiO2, sphene is the predominant whole rock site for U, Th and REE. The variation in vertical heat production enables the characteristic depth scale (D) to be calculated from the linear heat flow-heat production relationship. The calculated value for the pluton, D = 2.2 km, is significantly lower than that of the batholith, D = 10.1 km, calculated from combined heat flow and heat generation. This result implies that plutons within a heat flow province may not follow the same distribution law for heat-producing elements. In the Sierra Nevada batholith two fundamentally different heat-producing element fractionation trends are evident. The western granitoids have inherently low heat production (0.2-1.5μW m−3) for compositions between 57% and 77% SiO2. The central-eastern granitoids have inherently high heat production (1.5–5.0 μW m−3) for compositions between 57% and 77% SiO2. We conclude that there is no geochemical evidence to support an exponential vertical HPE distribution of heat-producing elements as the cause of a linear heat flow-heat production relationship in the Sierra Nevada batholith.

Kinetics of alkali feldspar dissolution at low temperature

Article

Jan 1989

P Schweda

Geochemical Mass Balances and Weathering Rates in Forested Waters of the Southern Blue Ridge

Article

Dec 1985

M. A Velbel

Mass-balance equations expressing mineral weathering reactions have been derived on the basis of empirical determinations of mineral compositions and combination of compositional data with petrographic (micromorphological) data. Calculations of the rates of weathering for each of the three major rock-forming silicate minerals - as well as the rate of mineral nutrient uptake - in deeply weathered profiles of several small watersheds in the Nantahala Mountains, North Carolina, are presented. Published data on the elemental composition of forest biomass, elemental fluxes via rain and streams, and stoichiometries of mineralogical transformations serve as parameters for construction and constraint of the geochemical mass-balance calculations of the individual watersheds. They are quantitatively consistent with laboratory studies of mineral weathering and geomorphological studies of regional denudation rates. Possible sources of discrepancies are noted, and may be resolved by refinement of laboratory kinetic data and field surface area determinations. -M.S.

Compositional variations and abundances of selected elements in granitoid rocks and constituent mine

Article

Chemical Weathering Rates of Silicate Minerals

Article

Jan 1995

Applications of lead and strontium isotopic relationships to the petrogenesis of granitoid rocks, central Sierra Nevada batholith, California

Article

Apr 1991

Pb isotope data are given on 80 whole-rock and/or feldspar samples from 51 dated samples covering a traverse across the central Sierra Nevada batholith, largely between latitudes 36° and 37°N. In addition, Sr isotope data were measured on 30 whole-rock samples. No correlation is observed between age and isotope ratios. Pb and Sr isotopic data from the western-margin plutons plot within or close to the field of primitive island-arc magmas, indicating predominantly mantle sources. High 206Pb/204Pb ratios in the central batholith suggest assimilation of sediments derived from Precambrian basement rocks. Decrease in 206Pb/204Pb ratios in the eastern segment of the batholith without corresponding reduction in 208Pb/204Pb ratios is attributed to assimilation of lower crustal granulitic/amphibolitic rocks by mafic magmas. Initial Pb ratios for samples with 87Sr/86Sr > 0.706 from the central and eastern segments of the batholith indicate components from recycled crustal rocks with a mean 207Pb/206Pb age of ca. 1.8 Ga. Very similar isotope patterns to the present model are reported across the Salinian block. -from Authors

Uranium-lead isotopic ages from the Sierra Nevada Batholith, California

Article

Jun 1982

This study provides new information on the timing and distribution of Mesozoic magmatic events in the Sierra Nevada batholithic complex chiefly between 36° and 37°N. latitude. U-Pb ages have been determined for 133 zircon and 7 sphene separates from 82 samples of granitoid rocks. Granitoid rocks in this area range in age from 217 to 80 m.y. Triassic intrusions are restricted to the east side of the batholith; Jurassic plutons occur south of the Triassic plutons east of the Sierra Nevada, as isolated masses within the Cretaceous batholith, and in the western foothills of the range; Cretaceous plutons form a continuous belt along the axis of the batholith and occur as isolated masses east of the Sierra Nevada. No granitic intrusions were emplaced for 37 m.y. east of the Sierra Nevada following the end of Jurassic plutonism. However, following emplacement of the eastern Jurassic granitoids, regional extension produced a fracture system at least 350 km long into which the dominantly mafic, calc-alkalic Independence dike swarm was intruded 148 m.y. ago. The dike fractures probably represents a period of regional crustal extension caused by a redistribution of the regional stress pattern accompanying the Nevadan orogeny. Intrusion of Cretaceous granitic plutons began in large volume about 120 m.y. ago in the western Sierra Nevada and migrated steadily eastward for 40 m.y. at a rate of 2.7 mm/y. This slow and constant migration indicates remarkably uniform conditions of subduction with perhaps downward migration of parent magma generation or a slight flattening of the subduction zone. Such steady conditions could be necessary for the production of large batholithic complexes such as the Sierra Nevada. The abrupt termination of plutonism 80 m.y. ago may have resulted from an increased rate of convergence of the American and eastern Pacific plates and dramatic flattening of the subduction zone. U-Pb ages of the Giant Forest-alaskite sequence in Sequoia National Park are all in the range 99±3 m.y., indicating a relatively short period of emplacement and cooling for this nested group of plutons. U-Pb ages of a mafic inclusion and its host granodiorite indicate that both were derived from a common source or that the mafic inclusion was totally equilibrated with the granodioritic magma. Comparison of isotopic ages determined by different methods such as zircon U-Pb, sphene U-Pb, hornblende K-Ar, and biotite K-Ar suggests that zircon U-Pb ages generally approximate the emplacement age of a pluton. However, some plutons probably contain inherited or entrained old zircons, and the zircons of some samples are disturbed by younger thermal and metamorphic events. The ages reported here are consistent with U-Pb age determinations previously made on granitic rocks to the north [Stern et al., 1981], The age distribution of granitic belts determined here is in general agreement with those established by K-Ar dating [Evernden and Kistler, 1970] but does not differentiate the five epochs of plutonism determined in their study.

Fractionation of rare-earth elements in allanite and monazite as related to geology of the Mt. Wheeler mine area, Nevada

Article

Mar 1967
GEOCHIM COSMOCHIM AC

Rare-earth contents of 20 allanites and 13 monazites, accessory minerals from a restricted outcrop area of intrusive granitic rocks, are reported. A quantity called sigma ( ), which is the sum of the atomic percentages of La, Ce and Pr, is used as an index of composition with respect to the rare-earth elements. Values of sigma vary from 61.3 to 80.9 at.% for these allanites and monazites, representing an appreciable range of composition in terms of the rare-earth elements. Degree of fractionation of rare earths varies directly with CaO content of the granitic rocks, which in turn depends largely on proximity of limestone. Four xenoliths included in the study suggest that spotty mosaic equilibria are superimposed on the regional gradients and that locally the degree of fractionation of rare earths responds to whole rock composition over distances of a few yards or less. The chemistry of the granitic rocks under study appears to be similar in some respects to that of alkalio rocks and carbonatites. Allanites from the most calcium-rich rocks show a pronounced concentration of the most basic rare earths, and whole-rock concentrations of such rare constituents as total cerium earths, Zr, F, Ti, Ba and Sr increase sympathetically with whole-rock calcium. The explanation for the concentration gradients observed in this chemical system must involve assimilation more than magmatic differentiation.

Weathering rates in catchments

Article

Jan 1995

Kinetics of chemical waethering: A comparison of laboratory and field weathering rates

Article

Jan 1990

Jerald L Schnoor

The Continental Crust: Its Composition and Evolution

Book

Jan 1985

This book describes the composition of the present upper crust, and deals with possible compositions for the total crust and the inferred composition of the lower crust. The question of the uniformity of crustal composition throughout geological time is discussed. It describes the Archean crust and models for crustal evolution in Archean and Post-Archean time. The rate of growth of the crust through time is assessed, and the effects of the extraction of the crust on mantle compositions. The question of early pre-geological crusts on the Earth is discussed and comparisons are given with crusts on the Moon, Mercury, Mars, Venus and the Galilean Satellites.

Cretaceous metamorphism and plutonism in the Santa Cruz Mountains, Salinian Block, California, and correlation with the southernmost Sierra Nevada

Article

Oct 1992

Eric James

New data on the ages of plutonism and metamorphism in the northern Santa Cruz Mountains, clarify the area's geologic history. Uranium/lead dates on zircon, monazite, sphene, and apatite and initial Pb and Sr isotopic ratios provide a "fingerprint' for comparison to the rest of the Salinian block and to other terranes. Isotopic data and geologic histories of basement rocks in the northern Santa Cruz Mountains, fit the geographic patterns documented in the rest of the Salinian block. More intriguingly, the Santa Cruz Mountains plutons are strikingly similar to parts of the southern Sierra Nevada batholith. Ages of plutonism and metamorphism, U/Pb zircon discordance systematics, petrography, and initial Sr isotopes match closely between the Santa Cruz Mountains crystalline rocks and units in the southernmost Sierra Nevada batholith. These data reinforce the long-standing view that the Salinian block and Sierra Nevada batholiths were adjacent during their formation. -from Author

Chronology and correlation of glacial deposits in the Sierra Nevada, California

Article

Dec 1986
QUATERNARY SCI REV

David S. Fullerton

Mobility and Fractionation of Rare Earth Elements During Weathering of a Granodiorite

Article

May 1979

H.W. Nesbitt

The rare earth elements (REE) have been mobilised and fractionated during supracrustal alteration of the Torrongo granodiorite. Compared with the parent granodiorite, incipiently and moderately altered rocks are particularly enriched in the heavy REE, while the extremely altered residual products are especially depleted in the heavy REE. Mobilisation of the REE probably results from pH changes of soil and ground waters as they encounter different chemical environments while fractionation may largely result from mineralogical controls. Submarine and subaerial weathering processes may affect REE similarly, producing intensively weathered materials appreciably depleted in the REE. Spilitisation and hydrothermal alteration processes may affect basaltic rocks in much the same way as do weathering processes.

Determination of easily accessible metal fractions in rocks by batch leaching with acid cation-exchange resin

Article

May 1997
CHEM GEOL

The easily accessible fraction of metals in “rocks” is derived from leaching experiments. Aliquots of rock powders are mixed with ion-exchange resin and distilled water. The pH self adjusts to a value of ∼ 3. After batch leaching times of 2–48 hr at 70°C the resin is quantitatively separated from the rock powder, and eluted with 4 N HNO3. The metal contents of the leachates are determined and related to the respective contents of the whole rock. The leaching kinetics of each element is related to that of a reference element. Aluminium is most commonly chosen as a reference element because it is considered to represent the dissolution behaviour of the main rock-forming minerals. The easily accessible trace-element fraction (EAT) is given as the “percentage of leached element at 1% Al dissolution”. These EAT values are reproducible and independent from grain size and sample/resin ratio.The procedure is tested on basaltic glass and variably altered gneisses. The glass shows congruent release of all metals. A slightly crystalline glass of the same chemical composition displays heterogeneous leaching behaviour. The leaching kinetics of variably altered gneisses provide insight into the mineralogical siting of elements and their accessibility to fluids. Consequences for RbSr dating of rocks are discussed.

Systematic Changes in Lead Isotopic Composition with Soil Age in Glacial Granitic Terrains

Article

Jan 1998
GEOCHIM COSMOCHIM AC

Variations in the isotopic composition of Pb in soils developed on glacial moraines in granitoid terrains were investigated. Samples were collected from the Mesozoic Sierra Nevada batholith, California and the Archean Wind River Mountains, Wyoming, both in USA. Lead isotopes were measured in whole soil samples and in weak-acid leaches of both soils and fresh bedrock (granitoid) samples. In the Sierra Nevada, ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁶Pb/²⁰⁷Pb ratios of the acid-leached fraction of three soils of varying ages (approximately 20, 120, and ≥330 kyr) decreases systematically with moraine age from 20.73 ± .03 to 20.14 ± .02, and from 1.314 ± .001 to 1.279 ± .003, respectively. In contrast, ²⁰⁸Pb/²⁰⁴Pb ratios do not change systematically with soil age. In the Wind River Mountains, lead isotopes were measured in soils developed on six moraines of varying ages (∼0.4, ∼2, ∼12, ∼22, ∼140, and ≥300 kyr). ²⁰⁸Pb/²⁰⁴Pb ratios of the acid-leached fraction of soils decrease systematically with moraine age from 61.0 ± 7.8 to 38.7 ± .4 in soils ranging in age from ∼12kyr to ≥300 kyr. On the other hand, ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁷Pb/²⁰⁴Pb ratios of the acid-leached fraction do not change systematically with soil age, nor do the ²⁰⁸Pb/²⁰⁴Pb ratios of the acid-leached fractions of the three younger soils (∼0.4, ∼2, and ∼12 kyr). The isotopic composition of the acid-leached Pb in soils developed on the oldest moraines (≥300 kyr) in both the Sierra Nevada and the Wind River Mountains is very close to the isotopic composition of the whole soil. The fraction of radiogenic Pb in the weatherable pool is approximately 2% in the Sierra Nevada and 40% in the Wind River Mountains. This explains why changes in the isotopic composition of total Pb can be detected in the Wind River Mountains soils (ages 2 to ≥300 kyr ) but not in the Sierra Nevada soils.

The Aquatic Chemistry of Rare Earth Elements in Rivers and Estuaries

Article

Mar 1995

Edward R. Sholkovitz

Laboratory experiments were carried out to determine how pH, colloids and salinity control the fractionation of rare earth elements (REEs) in river and estuarine waters. By using natural waters as the reaction media (river water from the Connecticut, Hudson and Mississippi Rivers) geochemical reactions can be studied in isolation from the large temporal and spatial variability inherent in river and estuarine chemistry. Experiments, field studies and chemical models form a consistent picture whereby REE fractionation is controlled by surface/solution reactions. The concentration and fractionation of REEs dissolved in river waters are highly pH dependent. Higher pH results in lower concentrations and more fractionated composition relative to the crustal abundance. With increasing pH the order of REE adsorption onto river particle surfaces is LREEs > MREEs > HREEs. With decreasing pH, REEs are released from surfaces in the same order. Within the dissolved ( MREEs > LREEs, is most pronounced in the solution pool, defined here as MREEs > HREEs. While the large scale removal of dissolved river REEs in estuaries is well established, the release of dissolved REEs off river particles is a less studied process. Laboratory experiments show that there is both release and fractionation of REEs when river particles are leached with seawater. The order of sea water-induced release of dissolved REE(III) (LREEs > MREEs > HREEs) from Connecticut River particles is the same as that associated with lowering the pH and the same as that associated with colloidal particles. River waters, stripped of their colloidal particles by coagulation in estuaries, have highly evolved REE composition. That is, the solution pool of REEs in river waters are strongly HREE-enriched and are fractionated to the same extent as that of Atlantic surface seawater. This strengthens the conclusions of previous studies that the evolved REE composition of sea water is coupled to chemical weathering on the continents and reactions in estuaries. Moreover, the release of dissolved Nd from river particles to sea water may help to reconcile the incompatibility between the long oceanic residence times of Nd (7100 yr) and the inter-ocean variations of the Nd isotopic composition of sea water. Using new data on dissolved and particle phases of the Amazon and Mississippi Rivers, a comparison of field and laboratory experiments highlights key features of REE fractionation in major river systems. The dissolved pool of both rivers is highly fractionated (HREE enriched) with respect to the REE composition of their suspended particles. In addition, the dissolved pool of the Mississippi River has a large negative Ce-anomaly suggesting in-situ oxidation of Ce(III). One intriguing feature is the well developed maximum in the middle REE sector of the shale normalized patterns for the dissolved pool of Amazon River water. This feature might reflect competition between surface adsorption and solution complexation with carbonate and phosphate anions.

Age, origin, and thermal histories of some plutonic rocks from the Salinian block of California

Article

Oct 1978

James M. Mattinson

U-Pb isotopic measurements on zircons from some granitic rocks of the Salinian block indicate emplacement and crystallization of these rocks about 104 m.y. ago (mid-Cretaceous). The relatively radiogenic nature of initial Sr and common Pb in these rocks, and the presence of an inherited component of zircon in some of them strongly suggest the involvement of continental crust in the genesis of the magmas. Possibly the magmas were generated in a zone of melting that overlapped the boundary between the mantle and the continental crust. U-Pb measurements on sphene, apatite, and feldspar from the plutons, along with previously published K-Ar and fission-track ages shed light on the post-emplacement thermal histories of the plutons. Most of the samples from the northern part of the Salinian block (Bodega Head, Point Reyes) show relatively simple thermal histories. Evidently these plutons were emplaced at moderate levels in the crust, crystallized, and cooled to moderate temperatures over an interval of about 10–15 m.y. Plutons from the central Salinian block (Santa Lucia Range) show more complex and prolonged thermal histories. These plutons evidently were emplaced at greater depths in the crust than were the plutons from the northern Salinian block. They remained at elevated temperatures for ca. 25 m.y., then cooled fairly rapidly, probably as a result of rapid uplift and erosion. One sample from the northern Salinian block shows an even longer span of time between emplacement and cooling. The thermal evolution of the Salinian plutonic rocks predates major offset along the San Andreas fault zone and thus reflects the thermal evolution of the undisrupted source terrane of the Salinian block. Isotopic measurements of the type reported here might therefore prove valuable in correlations across the San Andreas fault zone. Moreover, detailed study of thermal evolution within the Salinian block could shed light on major offsets within the block.

The rare earth elements in rivers, estuaries, and coastal seas and their significance to the composition of ocean waters

Article

May 1990
GEOCHIM COSMOCHIM AC

The concentrations of the rare earth elements (REEs) in samples from 15 rivers, from 6 estuarine transects, and of 5 coastal seawaters are reported and have been used with literature data to examine the continuity in average REE pattern between average continental crust and the dissolved input of REE to the oceans via estuaries. Concentrations in river waters span a wide range (e.g., 120–3300 pmol kg−1 Nd). REE patterns, normalised to average shale, are of two main types: all show heavy REE enrichment between La and Gd but either heavy REE enrichment or depletion between Gd and Lu. Some patterns show negative cerium anomalies, and these can be related to pH in a small suite of carbonate rivers. Different patterns were found in rivers sampled at different times, and rivers draining different rock types had the same patterns, suggesting that the catchment rocks play a minor role in defining the REE chemistry of river waters. The results may be explained by the presence of two main pools for the REEs in rivers: a colloidal pool of REE-rich particles < 0.4 μm having a shale-like pattern, and a dissolved pool characterised by heavy REE enrichment. Significant REE removal during the mixing of river water and sea water was measured for the Connecticut, Delaware, Mullica, and, on two occasions, Tamar estuaries. This was confirmed by mixing experiments using radiotracers. Removal varied from about 30% to near-quantitative. In some cases, preferential removal of the light REE was observed, but this may be caused by coagulation of colloidally associated REEs, changing the proportions of the two REE pools. The REE concentrations and patterns of the coastal seawaters are intermediate between those for rivers and for ocean waters, reflecting the influence of continental drainage. The dissolved input of REEs to the oceans is characterised by REE patterns in which the evolution of the characteristic oceanic REE pattern has started to develop. The same fundamental processes that define the oceanic pattern appear to operate for continental waters also, but the REE patterns are not as “evolved,” i.e., fractionated relative to continental crust, because of lower pH and shorter water residence times.

Rare earth element distributions among minerals in a granodiorite and their petrogentic implications

Article

May 1983
GEOCHIM COSMOCHIM AC

A study of the distribution of lanthanide rare earths in a granodiorite from the eastern Peninsular Ranges batholith, southern California, reveals that a large fraction of the REE in this rock resides in the accessory phases sphene and allanite. The minerals plagioclase, alkali feldspar, biotite, epidote and apatite each contribute approximately 1% or less of each REE to the whole rock, with the exception of Eu for which plagioclase contributes 7%. Sphene and allanite together contain 80% to 95% of each REE. Each of these phases is zoned in REE concentration with substantial decreases from core to margin. Textural observations argue for relatively early saturation and precipitation of sphene and allanite in the magma. REE zoning trends in sphene and allanite, and unexpectedly low REE concentrations in largely later crystallizing minerals such as feldspar, indicate that the precipitation of sphene and allanite significantly reduced REE concentrations in residual melts. These results illustrate the potential that sphene and allanite have for controlling the behavior of REE in granitic magmas. Available information collectively suggest that the sampled granodiorite existed as a complete melt, that the REE contained in the assemblage of phases were derived by direct crystallization from the melt, and that the melt behaved essentially as a closed system once crystallization of the phases now present began. Close correspondences between the major and trace element chemistries of the granodiorite and phenocryst-poor lavas from similar tectonic settings support these conclusions. The REE pattern of the granodiorite melt appears to have originated at depth and is characteristic of its source regions and derivation mechanism. The high liquidus temperature of a granodiorite melt (~ 1000°C) indicates the importance of mantle-derived components within the sources of batholithic magmas in the Peninsular Ranges.

Dissolution kinetics of quartz in sodium chloride solutions: Analysis of existing data and a rate model for 25°C

Article

Dec 1992
GEOCHIM COSMOCHIM AC

A surface reaction model for the kinetics of quartz dissolution is derived from an analysis of low-temperature dissolution rate data published by seven experimenters. The model correlates seventynine quartz dissolution rate measurements with calculated surface species distributions to predict reaction kinetics. Using the triple layer electrostatic surface model, we compute the distributions of predominant acid-base surface species for the solution composition associated with each reported rate measurement. Reactivities of the modeled species are then obtained by fitting the calculated site distributions and the experimental rate data to a simple rate equation. This results in an expression valid for 25°C, pH 2–13 and 0-0.5 molal sodium chloride given by , where rate has units of mol m−2s−1,θ4;SiOH is the fraction of SiOH surface complexes and ∗ indicates that the reaction order dependence on this species is ill-determined. The θSiOsum term gives the sum of SiO-Na+ and SiO− fractions. This correlation removes much of the apparent scatter that is observed between experimenters and demonstrates that most measurements follow a consistent trend when a sodium complex, SiO-Na+, is included in the model. The model predicts that reaction rates are increased by a factor of 12 at pH 8 with the addition of 0.2 molal sodium to the reacting solutions.While this approach is an indirect measure of the reactivity of bonds at mineral surfaces, when compared to previous models, it offers a better understanding of rate-controlling processes because it specifically includes the calculated distributions of surface reactants. This analysis, in conjunction with evidence from the literature for cation-specific influences on silicon dioxide reactivity, supports a dissolution model incorporating cation interactions.

Chemical weathering rate laws and global geochemical cycles

Article

May 1994
GEOCHIM COSMOCHIM AC

In this paper, we discuss the recent kinetic work on water-rock interactions. Standard activity-activity diagrams are reinterpreted, using a mass transfer kinetic model and recent data on the relative rates of mineral reactions. The development of a fully integrated rate law is discussed, with special attention to the important effects of deviation from equilibrium on the rates of mineral-water reactions. The combined effects of temperature, pH, ionic strength, and saturation conditions on the overall dissolution and precipitation rates of minerals must be properly described before any seriously quantitative model of coupled fluid flow and chemical reaction can be undertaken. A rate law that integrates these effects is proposed.The functional dependence of the rate on ΔGr, the free energy change for the mineral reaction, is discussed, based on recent experimental work. An important result is the presence of a surface transition in the reaction mechanism leading to a very strong nonlinear dependence of the dissolution rates on ΔGr. The possible role of dislocation defects in this surface transition is discussed.The relation of global weathering rates and geochemical cycles to the recent experimental and theoretical water-rock kinetic work is explored. The temperature effect on the silica content of streams is reevaluated. The variation of silica concentration with runoff in the rivers of the world is quantified, using a coupled fluid flow and reaction model and the full rate law developed for a proto-granite system by the kinetic experiments. Implications of the water-rock kinetic data for the current geochemical cycles models are discussed with especial emphasis on the link between physical weathering and chemical weathering.

The geochemistry of rare earth elements in groundwater from the Carnmenellis area, southwest England

Article

Oct 1991
GEOCHIM COSMOCHIM AC

P.L. Smedley

Shallow groundwater samples from the Carnmenellis area of southwest England collected from wells, boreholes, springs, adits and stream baseflow represent recently recharged waters of low salinity. Their major ion concentrations closely reflect the lithology of their host rocks which comprise the Carnmenellis granite and Devonian metasediments (and metabasite) of greenschist grade. Groundwaters from the granite are predominantly Na-Cl or Na-Ca-Cl type whilst those from the metasediment are Na-Ca-Mg-Cl-HCO3 waters with a larger range of compositions. The major ion compositions are predominantly a function of water-rock interaction processes and the larger range of metasediment-water compositions probably reflects the greater lithological variation. The pH of groundwater samples circulating through granite is typically lower than that of groundwater in the metasediments, the range being 4.3 to 7.2 (median 5.7) and 4.7 to 8.0 (median 6.6) respectively.

Lead isotope systematics of granitoid weathering

Article

Dec 1994
GEOCHIM COSMOCHIM AC

The isotopic composition of lead released by chemical weathering of granitoids was investigated in order to evaluate the sensitivity of this natural tracer as a tool for monitoring mineral weathering and soil development. The isotopic composition of lead was found to change systematically with the relative degree (or maturity) of weathering in both Cretaceous granitoids from the Sierra Nevada batholith (SN) and Precambrian granitoids from the Wind River Range, Wyoming (WRR). In the SN, lead released from crushed bedrock by dilute acid leaching (to simulate the initial stages of weathering) has a composition more radiogenic than observed in soils (average ). Lead released by leaching from soils developed on a relatively young terrain (~10 kyr old) is less radiogenic (average ) than crushed bedrock and lead released by leaching from soil developed on older surfaces (~ 100 kyr) is even less radiogenic (average ). Lead released from the total digestion of the rock has the least radiogenic composition (average ). In the WRR, systematic changes in the isotopic composition of lead released by leaching were observed in soils developed on glacial moraines of variable ages. Lead released from soil developed on a 21 kyr old moraine was the most radiogenic (). Lead released from soil developed on a 130 kyr old moraine was less radiogenic () and lead released from soil developed on ≥350 kyr old moraine was the least radiogenic (). The observed systematic changes in the isotopic composition of lead with time in both field areas demonstrates the potential of lead isotopes to ascertain the degree (or maturity) of chemical weathering of granitoids and may have applications in determinations of the relative ages of some glacial deposits.

Chemical weathering rates of a soil chronosequence on granitic alluvium: I. Quantification of mineralogical and surface area changes and calculation of primary silicate reaction rates

Article

Jul 1996
GEOCHIM COSMOCHIM AC

Mineral weathering rates are determined for a series of soils ranging in age from 0.2–3000 Ky developed on alluvial terraces near Merced in the Central Valley of California. Mineralogical and elemental abundances exhibit time-dependent trends documenting the chemical evolution of granitic sand to residual kaolinite and quartz. Mineral losses with time occur in the order: hornblende > plagioclase > K-feldspar. Maximum volume decreases of >50% occur in the older soils. BET surface areas of the bulk soils increase with age, as do specific surface areas of aluminosilicate mineral fractions such as plagioclase, which increases from 0.4–1.5 m2 g−1 over 600 Ky. Quartz surface areas are lower and change less with time (0.11–0.23 m2 g−1). BET surface areas correspond to increasing external surface roughness (λ = 10–600) and relatively constant internal surface area (≈ 1.3 m2 g−1). SEM observations confirm both surface pitting and development of internal porosity.

Chemical evolution of rare earth elements: Fractionation between colloidal and solution phases of filtered river water

Article

Dec 1992
EARTH PLANET SC LETT

Edward R. Sholkovitz

Within the dissolved fraction of Connecticut River water, there is large scale fractionation of rare earth elements between colloidal and solution phases. Colloidal particles carry a large part of the dissolved REE pool. Filtration through filters with progressively smaller pore size (0.45, 0.22 and 0.025 μm) results in filtrates with lower absolute concentrations of REE and more fractionated compositions. With decreasing pore size, the filtrates have shale-normalized abundances which become systematically more depleted in the LREE relative to the HREE. Hence, both the solution and colloidal phases are significantly fractionated with respect to the dissolved fraction ( < 0.45 μm) of the river water. The solution and colloidal phases are HREE and LREE enriched, respectively, relative to the continental crust. In addition, river colloids are preferentially enriched in the redox-active REE Ce, leaving the solution phase with a more negative Ce anomaly than the filtered river water.These conclusions are consistent with previous studies of REE in rivers, estuaries and soils and with surface-solution speciation models. Colloids play an important role in the aquatic geochemistry of rare earth elements. They are responsible for the fractionation of REE during the estuarine removal of REE. The removal of suspended and colloidal particles from river water leaves the solution phase of river water with compositions of REE as evolved as those of surface seawater. Hence, the evolution of the composition of REE in river water and seawater is significantly influenced by colloid formation during chemical weathering on the continents.

Natural levels of lead and cadmium in a remote mountain stream

Article

Mar 1991
GEOCHIM COSMOCHIM AC

Lead and cadmium concentrations in marine and terrestrial ecosystems, on surfaces of soil particles, and in the atmosphere have been highly elevated on a global scale because of industrial pollution. In order to ascertain the natural (rock-derived) levels of lead and cadmium in streams, a pristine mountain watershed in the Sierra Nevada, California, was studied in respect to its lead and cadmium contents. The transport of lead and cadmium was compared to iron since it shares similar transport patterns with lead and cadmium, and is relatively uninfluenced by pollution. The concentrations of lead and cadmium in a late-summer mountain drainage water are shown to be close to natural levels that are controlled by the weathering of bedrock and soil. This is demonstrated by (1) measurements of lead isotopic composition, and Fe/Pb ratios in stream water, ground water, soil and bedrock, and (2) the rapid removal rate of excess atmospheric lead and cadmium from the water as it flows downstream. Lead is taken up by particles (mostly hydrous iron oxides) in the studied stream during the autumn at a relatively constant rate. On the other hand, cadmium behavior in the stream water is erratic and cannot be explained by the same adsorption mechanism as lead. The Fe/Pb ratio is constant within an order of magnitude in the bedrock, the soil, soil and rock leachates, unfiltered and filtered ground water, and in filtered and unfiltered stream water. Therefore, the Fe/Pb ratio may provide a first-order estimate for the concentration of natural lead in streams draining through granitoid bedrocks.

Rare Earth Elements in River Water

Article

Jun 1988
EARTH PLANET SC LETT

We measured rare earth element (REE) concentrations in river waters to characterize the suspended and dissolved river flux of the REE to the oceans. The REE pattern of river suspended materials is sensitive to drainage basin geology. A positive correlation is observed between La/Yb ratios and Nd model ages for the rivers studied. Major rivers have light REE enriched patterns relative to the North American Shale Composite (NASC), with (La/Yb)N = 1.6−2.7. River water dissolved material ( < 0.2 μm) is heavy REE enriched relative to suspended material, and the most pronounced negative Ce anomalies occur in rivers of high pH. Light REE concentrations vary by approximately 3 orders of magnitude and are inversely related to pH and major cation concentrations.From these data, we estimate that typical major river runoff has heavy REE depleted suspended material with (La/Yb)N ≈ 1.9. We conclude that the terrigenous input to the oceans from major rivers is heavy REE depleted relative to shales. From the available data, average river water dissolved material appears to be heavy REE enriched with (La/Yb)N ≈ 0.4. Estuarine removal processes lower the dissolved REE river flux by approximately 60% and result in a flux that is more heavy REE enriched with (La/Yb)N ≈ 0.2. Calculated oceanic residence times with respect to river input range from 2300 to 21,000 years, are shortest for Ce, and greatest for the heavy REE and La. Such long residence times may suggest the presence of additional sources of REE in seawater.

Oblique map showing maximum extent of 20,000-year-old (Tioga) glaciers, Yo-semite National Park, central Sierra Nevada, California, U.S. Geo-logical Survey Map I-1885,1 sheet Crystallization, fraction-ation, and solidification of the Tuolumne Intrusive Series

Jan 1979
465-482

T R Alpha
W Wahrhaftig
N K Huber

Alpha T. R., Wahrhaftig W., and Huber N. K. (1985) Oblique map showing maximum extent of 20,000-year-old (Tioga) glaciers, Yo-semite National Park, central Sierra Nevada, California, U.S. Geo-logical Survey Map I-1885,1 sheet. Bateman P. C., and Chappell B. W. (1979) Crystallization, fraction-ation, and solidification of the Tuolumne Intrusive Series, Yosemite National Park, California. Geol. Soc. Am. Bull. 90, 465– 482.

Mobile element contents related to alteration on the Harz-granites

Jan 1993
265-277

U Giese
P Moller
P Duliski

Giese U., Moller P., and Duliski P. (1993) Mobile element contents related to alteration on the Harz-granites. Monogr. Ser. Mineral Deposits. 30, 265-277.

Composi-tional variations and abundances of selected elements in granitoid rocks and constituents minerals, central Sierra Nevada batholith Dissolution kinetics of quartz in sodium chloride solutions: Analysis of existing data and rate model for 25°C

Jan 1982
4147-4156

F C W Dodge
H T Millard
H Elsheimer

Dodge F. C. W., Millard H. T., and Elsheimer H. N (1982) Composi-tional variations and abundances of selected elements in granitoid rocks and constituents minerals, central Sierra Nevada batholith, California. U. S. Geol. Surv. Profess. Paper. 1248. Dove P. M. and Elston S. F. (1992) Dissolution kinetics of quartz in sodium chloride solutions: Analysis of existing data and rate model for 25°C. Geochim. Cosmochim. Acta. 56, 4147– 4156.

The Kinetics of Base Cation Release due to Chemical Weathering The Continental Crust: Its Composition and Evolution

Jan 1985

H U Sverdrup
S R Taylor
S M Mclennan

Sverdrup H. U. (1990) The Kinetics of Base Cation Release due to Chemical Weathering. Lund Univ. Press. Taylor S. R., and McLennan S. M. (1985) The Continental Crust: Its Composition and Evolution. Blackwell Scientific Publications, Lon-don.

Transport of natural lead and cadmium in a remote mountain stream. Geochim. Cosmo-chim

Jan 1991
707-721

Y Erel
J J Morgan
C C Patterson

Erel Y., Morgan J. J., and Patterson C. C. (1991) Transport of natural lead and cadmium in a remote mountain stream. Geochim. Cosmo-chim. Acta. 55, 707–721.

The release of Pb and REE from granitoids by the dissolution of accessory phases

Abstract

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Rare earth element distributions among minerals in a granodiorite and their petrogentic implications