North American Shale Composite Research Articles

Rare Earth Elements in Sediments from the Laptev Sea Shelf: Insight into Sources and Distribution Factors

The study of rare earth elements (REEs) in marine sediments is a powerful geochemical tool for determining depositional processes and sediment provenance, as well as for understanding paleoenvironmental changes. In this context, we present REE, some major and trace elements, grain size, and mineralogy data on surface and core sediments, which were collected in different areas of the eastern Laptev Sea Shelf (LSS; Arctic Ocean). The primary objective of this paper was to assess the principal controlling factors influencing REE concentration and their vertical to lateral distribution. The total REE content (ΣREE) ranged from 139 ppm to 239 ppm within the studied sediment samples, predominantly consisting of silt. The normalized REE distribution patterns, based on North American Shale Composite (NASC) standard, exhibited an enrichment in light REE (LREE) when compared to heavy REE (HREE), which is similar to that in Lena River suspended particulate matter. The primary sources of REEs in the eastern LSS were both the suspended particulate matter from the Lena River and sediments originating from the coastal ice complex. The spatial distribution of REEs was primarily contingent upon the distance from sediment sources and prevailing hydrological conditions and was generally characterized by a decrease in REE concentration seaward. There was a moderate positive correlation between ΣREE and mean grain size in the studied surface sediment. However, this relationship was specific only for surface samples and was not found in the sediment cores, indicating that sediment grain size does not play a significant role in the REE vertical distribution. The strong positive correlation between ΣREE and Al, K, Ti, V, Cr, Zr, Hf, and Th suggests that REEs are hosted by not only heavy but also clay minerals. The vertical fluctuations of LREE/HREE, Eu/Eu*, (La/Lu)N can point at variable dominance of one or another REE source for during sediment accumulation.

Rare Earth Element Characteristics of Shales from Wufeng-Longmaxi Formations in Deep-Buried Areas of the Northern Sichuan Basin, Southern China: Implications for Provenance, Depositional Conditions, and Paleoclimate.

To explore the sedimentary environment and the background of the source area of organic-rich shales in the Wufeng-Longmaxi Formations in the northern Sichuan Basin, samples from Well XX1 in the area were subjected to geochemical testing and analysis of organic carbon content, trace elements, and rare earth elements (REEs). The results show that the total content of REE (ΣREE) of the shale in the Wufeng-Longmaxi Formations varied from 183.08 to 234.66 μg/g with an average of 212.59 μg/g, which is significantly higher than the content of the North American shale composite. The fluctuations in the total amount of REEs in the shale of the Wufeng-Longmaxi Formations reflect certain differences in the geochemical conditions of the Upper Ordovician-Lower Silurian shale. The ratios of LREE/HREE, LaN/YbN, LaN/SmN, and GdN/YbN and the distribution of normalized REE patterns indicate that the source supply or sedimentary structural background may have changed during the shale deposition period of the Wufeng Formation, while the shale deposition period of the Longmaxi Formation may be in a relatively stable source supply and sedimentary structural background. There is no significant correlation between δCe and ΣREE, and the obviously negative Eu abnormity and the weak Ce abnormity indicated that the diagenesis had a limited impact on REEs. Geochemical parameters such as values of ∑REE, δEu, δCe, Ceanom, and LaN/YbN indicate that the climate during the Wufeng-Longmaxi Formation shale deposition period was warm and humid, and the shale was deposited mainly in the suboxic-anoxic water environment. The deposition rate was stable and slow, providing good conditions for the production and preservation of organic matter. At the same time, this shows that the water environment of Wufeng Formation is more anoxic and reductive than that of Longmaxi Formation, which is more conducive to the preservation of organic matter. The correlation between ΣREE and the content of Sc, Ti, Cr, Co, Zr, Nb, Th, Hf, Ta, and other elements indicates that the sources of REEs in the shale of Wufeng and Longmaxi Formations in the study area are similar, mainly terrestrial clasts, and some may come from the sea. The REE distribution pattern shows that the shale provenance of the Wufeng-Longmaxi Formations mainly comes from the upper crust. The La/Yb-∑REE diagram shows that the sediment-parent rocks are mainly early sedimentary rocks and these sediment-parent rocks have granite provenance characteristics. Compared to La/Yb, LREE/HREE, LaN/YbN, and other REE characteristic parameters, it is inferred that the tectonic background of the study area is dominated by passive continental margin.

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

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.

On the Geochemistry of the Danube River Sediments (Serbian Sector).

To determine the nature and origin of the unconsolidated bottom sediments, as well as to demonstrate and quantify the presence of Presumably Contaminating Elements (PCE) in the Serbian Danube River, as a novelty, the mass fractions on nine major elements as oxides—SiO2, TiO2, Al2O3, FeO, MnO, MgO, CaO, Na2O, and K2O, as well as Sc, V, Cr, Co, Ni, Cu, Zn, As, Rb, Sr, Zr, Sb, Cs, Ba, La, Hf, Ta, W, Th, and U were determined by Instrumental Neutron Activation Analysis (INAA) in 13 sediment samples collected between Belgrade and Iron Gate 2 dam. INAA was chosen for its ability to perform elemental analysis without any preliminary sample treatment that could introduce systematic errors. The distribution of major elements was relatively uniform, with the sampling locations having less influence. Concerning the trace elements, excepting the PCE Cr, Ni, Cu, Zn, As, and Sb, their distributions presented the same remarkable similarity to the Upper Continental Crust (UCC), North American Shale Composite (NASC), Average Bottom Load (ABL), and Average Dobrogea Loess (AVL), and were in good concordance with the location of the Serbian Danube River in the Pannonian Plain. In the case of considered PCE, both Enrichment Factor and Pollution Load Index showed values higher than the pollution threshold, which pointed towards a significant anthropogenic contamination, and rising concern to what extent the water quality and biota could be affected.

On the Geochemistry of Major and Trace Elements Distribution in Sediments and Soils of Zarafshon River Valley, Western Tajikistan

To assess the geochemical features of sedimentary material of Zarafshon river, (Western Tajikistan) catchment basin, the mass fractions of 38 major and trace elements were determined by Instrumental Neutron Activation Analysis (INAA) in 2 × 116 paired samples of sediments and soils collected along the Zarafshon River and its main tributaries from the sources to Tajik—Uzbek border. At each collecting location, the distance between sediments and soils’ sampling was no greater than 10 m allowing the studying of the interrelation between sediments and soils. This evidenced a significant similarity between paired soils and sediments’ samples, including the potentially contaminating elements As, Sb and Hg, whose mass fractions in some places were significantly higher than for the Upper Continental Crust (UCC) and North American Shale Composite (NASC), suggesting a common provenience. At the same time, the distribution of major, as well as of incompatible trace elements, Sc, Zr, REE, Th, and U, in spite of geological diversity of the Zarafshon river catchment basin, suggest a possible felsic origin of investigated material.

Nodular sillimanite rocks as field indicators to metamorphosed massive sulfide deposits

Nodular sillimanite rocks (NSR), some of which are spatially associated with massive sulfide deposits, consist of intergrowths of quartz, sillimanite (mainly fibrolite), and muscovite (up to 30 cm in length) that occur predominantly in Archean-Proterozoic metapelites, ortho- and para-gneisses, and metavolcanic rocks metamorphosed to the amphibolite/granulite facies. Such rocks are particularly abundant in central Colorado where they either enclose or occur stratigraphically above or below at least 10 metamorphosed Proterozoic Cu-Zn-(Pb-Au-Ag) deposits. A plot of NSR compositions in terms of SiO2/Al2O3 vs Na2O/K2O and a K2O-MgO-Na2O ternary diagram suggest that the protoliths of NSR spatially associated with sulfide occurrences in Colorado were predominantly shale, arenite, lithic arenite or greywacke. North American shale composite (NASC)-normalized rare earth element (REE) patterns of NSR associated with these deposits show compositions close to NASC values with flat patterns and slightly negative Eu anomalies, which also supports the concept of a sedimentary protolith. Such a protolith contrasts with NSR spatially associated with massive sulfide deposits elsewhere in the world that more commonly have volcanoclastic/igneous precursors. Mass-balance calculations of NSR from the Cotopaxi deposit (Colorado) show major and trace element mobility with mostly mass gains in K2O, MgO, Ba, Cu, Pb, and Zn, and depletions in CaO, and Na2O relative to their protolith (lithic arenite), an unaltered biotite-muscovite-feldspar gneiss. Although Al2O3 and SiO2 show both gains and losses, the mass gains are considerably larger for Al2O3. The gains in base metals (Cu, Pb and Zn), the enrichment of Cu and Zn (rather than Pb) that mimics the ore concentrations, the presence of gahnite (ZnAl2O4) in sillimanite nodules in some metallic deposits in Colorado, and the existence of chalcopyrite and pyrrhotite in NSR suggest the sedimentary protoliths were hydrothermally altered and that NSR, where spatially associated with sulfide deposits, represent zones of metamorphosed stratabound alteration zones. Nodular sillimanite rocks are easy to recognize in the field and constitute an exploration guide for massive sulfide deposits that were subjected to regional metamorphism at the amphibolite to granulite facies.

Importance of the Spatial Distribution of Rare Earth Elements in the Bottom Sediments of Reservoirs as a Potential Proxy for Tracing Sediments Sources. A Case Study in the Dominican Republic

The geochemical composition of rare earth elements (REE) in the bottom sediments of two Dominican reservoirs and in soils from their catchments was studied to identify possible sources of the deposited materials. Knowledge of the origin of the sediments will serve to control the excessive rates of erosion and sedimentation that occur annually due to periodic extreme climatic events that promote excessive silting of the lakes, followed by loss of storage capacity and degradation of water quality. The REE contents of sediments and soils were normalized to the North American Shale Composite (NASC) and the ratio of light/heavy rare earths (LREE/HREE ratio), Ce and Eu anomalies, and some fractionation parameters were determined. The REE patterns are more homogeneous in the sediments, indicating uniform sedimentation in both deposits. The sediment data reflect depletion of REE from the sources, enrichment of light REE (LREE) and some middle REE (MREE), and positive Eu and Ce anomalies. All data were plotted in correlation diagrams between some fractionation parameters of light–middle–heavy REE and anomalies of Ce and Eu. The similarity of the ratios between these parameters in all samples and the overlap of data from soils and rocks on the sediment projection in the diagrams allowed a good discrimination of the main sources of the materials.

Environmental geochemical characteristics of rare-earth elements in surface waters in the Huainan coal mining area, Anhui Province, China.

This study investigated the environmental geochemical characteristics of rare-earth elements (REEs) in surface waters in the Huainan mining area, Anhui Province, China. The REEs concentrations were determined by ICP-MS, and the inorganic species of dissolved REEs in the river and coal mining subsidence area water samples were calculated by using the Visual MINTEQ (version 3.1) code. On this basis, the distribution and geochemical characteristics of REEs in the surface waters were systematically analyzed, and the main inorganic species of REEs were investigated. The results showed the following: (1) The REEs concentrations in the surface waters were relatively low, ranging from 0.1361 to 0.3536μg/L, and the average ∑REEs concentration was 0.2062μg/L. Compared with light rare-earth elements (LREEs), heavy rare-earth elements (HREEs) were significantly enriched, with an average enrichment factor of 1.4642. Due to the interaction of high pH values and high cation concentrations, the ∑REEs content in the subsidence area water was significantly lower than that in the river water. (2) The distribution pattern of REEs in the surface waters normalized against the North American Shale Composite (NASC) showed that the REEs in the study area had different degrees of cerium (Ce) and europium (Eu) anomalies. The negative Ce anomalies were probably closely related to the pH conditions, whereas the positive Eu anomalies were mainly attributed to preferential chemical weathering and the dissolution of feldspar minerals. (3) The simulation results obtained by using Visual MINTEQ code showed that the dominant and typically inorganic complex form of REEs in the surface waters was carbonate complexes, and this form was one of the reasons for the enrichment of HREEs in the surface water.

Distribution of rare earth elements and stable isotopic constituents along the groundwater flow paths in the Quaternary deposits of Imphal valley in north‐east India

Groundwater samples collected from three flow paths (the western, central, and eastern flows) in the shallow aquifers of the Imphal valley of north‐east India were examined to study the variation in hydrochemical and rare earth element (REE) characteristics along these flow paths. Each flow path covers a length of around 45 km towards the down gradient. In the western flow, the hydrochemical facies evolved from Na‐Cl‐Ca to Ca‐Na‐Mg‐Cl‐HCO3; in the central flow, it varies from Ca‐Mg‐Na‐Cl to Na‐Ca‐Cl‐HCO3 and in the eastern flow, it changes from Na‐Cl to Ca‐Mg‐HCO3 indicating the evolution of saline water type in the piedmont zone to fresh water type towards the discharge zones around the Loktak Lake. The REE concentration varies along the flow path as the total light REE (LREE) is more enriched than total heavy REE (HREE) in the western and central flows, while LREE is less than HREE in the eastern flow. North American Shale Composite (NASC)‐normalized REE patterns in these flow types show significant convex‐up NASC‐normalized patterns with depleted LREEs. The redox condition in the flow paths is controlled by redox‐sensitive elements such as Eh, pH, Fe, Mn, U, Er, Gd, and Nd which vary relatively along with these flows. REE fractionation depicted by (Er/Nd)SN ratios are high around the upgradient and decrease along the down gradient towards Loktak Lake. The isotopic constituents (δ18O and δD) exhibit fluctuations in their ratios along the groundwater flow paths. The residual hill and piedmont zones are characterized by depleted isotopic composition while the alluvial and flood plains show enriched isotopic composition. Thus, the present study elucidates the behavioural change in major hydrochemical parameters including REE and isotopic constituents, along with the groundwater flow, which will provide a holistic view in understanding the evolution of groundwater in terms of its quality, quantity, and origin in the study area.

Distribution of rare earth elements in sediments of the North China Plain: A probe of sedimentation process

Rare earth elements (REE) are powerful tracers for our understanding of sedimentary provenance and depositional processes. This study investigated geochemical characteristics of REE in 226 sediment samples collected from the piedmont, central and littoral plains of the North China Plain. Results showed that total REE concentrations exhibited a decreasing trend as piedmont > central > littoral, and 82%, 70% and 67% samples had total REE concentrations higher than the value of upper continental crust. The REE concentrations were controlled by sedimentary provenance and sediment physicochemical properties. Ternary diagrams of sandstone classification and Al2O3–CaO + Na2O–K2O reflected that sediments originated from greywackes and they experienced an incipient to intermediate chemical weathering. Average chemical index of alteration (CIA) value was 68, 51 and 55 for sediments from piedmont, central and littoral plains, respectively. Sediment North American Shale Composite (NASC)-normalized patterns were characterized by light REE (LREE) enrichment over heavy REE (HREE) and coherent negative Eu anomaly (Eu/Eu* ranging between 0.57 and 1.00). Value of (La/Yb)NASC ranged from 0.86 to 1.15 (average 1.23), and from 1.03 to 1.49, and from 0.91 to 1.49 in three zones, respectively, indicating REE fractionation occurred from piedmont to littoral during sedimentation processes. A positive correlation between (La/Yb)NASC and total REE concentrations was observed in piedmont and central sediment samples, implying that LREE were preferentially enriched over HREE with an accumulation of REE. This positive correlation was not found in littoral sediment samples, where a general decreasing trend along depth for REE concentrations existed. The findings of this study have an implication for using REE as a tracer in provenance studies from a basin scale.

Rare earth element distributions in salt marsh sediment cores reveal evidence of environmental lability during bioturbation and diagenetic processes

The distribution and accumulation of rare earth elements (REE) in the labile fraction of sediment cores collected from salt marshes in the Patos Lagoon estuary from southern Brazil were investigated. Sediment cores (ca. 40 cm) were obtained from three locations within the estuary to capture possible changes in REE content across the salinity gradient (i.e., where saline, brackish, and freshwater dominate). Salt marsh sediments from all three coring locations were enriched in the light REE (LREE) over the heavy REE (HREE) when normalized to the North American shale composite (NASC). Shale normalized values for the LREE of marsh sediments from sites M2 and M3 in the mid- and upper estuary commonly approximates unity indicating these sediments chiefly exhibit a terrigenous signature. In contrast, all 14 naturally occurring REE are depleted in the sediments from the M1 coring location in the lower estuary compared to shale. Sediments from the mid-estuary (M2 core location) where typical salinity values are ca. 10 practical salinity units, exhibit the greatest shale normalized LREE enrichments. The higher LREE contents of the M2 sediments likely reflect preferential removal of LREE from the water column owing to salt-induced coagulation of river-borne colloids that occurs during estuarine mixing processes. Sediments samples collected from the salt marsh in the lower estuary nearer the Atlantic Ocean (i.e., M1), have substantially lower REE contents than salt marsh sediments from sites M2 and M3 in the mid- and upper estuary, respectively. The more sand-rich lower estuary sediments are exposed to higher salinity water from the South Atlantic compared to the generally finer grained sediments from the mid- and upper estuary, which are dominated by brackish and freshwater conditions, respectively. Negative Ce-anomalies (i.e., Ce/Ce* < 1) in marsh sediments from depths generally greater than 27 cm support the occurrence of early diagenetic reactions consistent with suboxic to anoxic conditions whereby reductive dissolution of ferromanganese oxide/oxyhydroxide carrier phases, and/or Ce(IV) phases, release Ce(III) to the marsh pore waters. The negative Ce anomalies suggests that a suboxic or anoxic environment predominates to a depth of 9 cm, and then again below 27 cm depth in sediments from the M2 salt marsh core, and below a depth of 13 cm in the upper estuary marsh sediments (i.e., M3). In contrast, positive Ce anomalies (Ce/Ce* > 1) for much of the sediment from the M1 core, the mid depths of core M2 (i.e., 9 cm to 27 cm), and shallower than 13 cm in sediments from core M3 support oxic conditions where Ce is enriched in sediments from these depths by preferential scavenging from pore waters onto Fe/Mn oxides/oxyhydroxides. These trends in Ce/Ce* with depth in each sediment core are also consistent with known bioturbation that occurs within these marsh sediments. The relatively high REE contents of the sediments from location M3 are also related to the fact that these sediments are dominantly composed of clay-silt deposits that are enriched in organic matter. Finally, we find no conclusive evidence that the studied salt marsh sediments have been impacted by addition of REE from the local fertilizer manufacturing industry.

Geochemical Characterization of the Oil Source Rocks in the Ahwaz Oilfield, Southwestern Iran

The Ahwaz oilfield is located in the Dezful embayment of the Zagros fold-thrust belt in SW Iran. The oil source rocks predominantly with the argillaceous lithologies include the Kazhdumi, Gurpi, and Pabdeh formations as well as the basal part of the Asmari Formation. The concentrations of the major, trace, and rare earth elements (REEs) of these lithologies were determined using x-ray fluorescence spectroscopy (XRF) and inductively coupled plasma-emission/mass spectrometer (ICP-ES/MS), in order to infer the geochemical characteristics of the oil source rocks. The North American Shale Composite (NASC)-normalized major oxides displayed a positive anomaly in CaO, negative anomalies in other oxides and no anomaly in P2O5. According to the spider diagram of normalized trace element, there was enrichment in V, Ni, Cu, Cd, Pb, and Th values. In the NASC-normalized REEs pattern, the oil source rocks mostly display a smooth distribution shape, negative cerium anomaly, and slightly positive anomaly in the middle rare earth elements (MREES: Sm-Ho) values. The concentration of V, Ni, Co, and their ratios suggested a mixed marine and terrigenous source input. The ratios of redox-sensitive elements such as Ni/Co, V/Ni, V/V+Ni, Th/U, and Ce/Ce* suggested that the oil source rocks were mainly deposited under anoxic condition.

Heavy metal contamination and provenance of sediments recovered at the Grijalva River delta, southern Gulf of Mexico

This study examines textural characteristics, carbonate, organic carbon and chemical composition of sediment samples recovered in the nearshore region (~3–19 m water depth) at the Grijalva River mouth, southern Gulf of Mexico. The aim of this study is to assess the heavy metal contamination and provenance variations in sediments between the dry and northers (rainy) seasons. The proportion of sand, carbonate, and organic carbon contents were abundant at sites located near to the Grijalva River mouth, principally in northers season. Silt content is dominant in the dry season, especially in the sites located away from the Grijalva River mouth. The Chemical Index (CIX) values obtained for the dry (~76–84) and northers (~75–87) seasons indicated a moderate to high intensity of weathering and a humid climate in the source area. The low K2O/Al2O3 ratio values (<0.5) in the dry and northers seasons indicated a higher proportion of aluminosilicates than detrital minerals, due to moderate-to-high intensity of weathering. The correlation among elemental concentrations revealed the association of Cr, Nb, Zr, Hf, Y, and rare earth elements (REE) with detrital minerals rather than aluminosilicates. The major element concentrations, Th/Sc, La/Sc, Co/Th, and Cr/Ni elemental ratios indicated the derivation of sediments from intermediate and mafic igneous rocks. A similarity in the North American Shale Composite (NASC) normalized rare earth element (REE) patterns and Eu anomaly between the dry and northers seasons suggested that the variations in sediment input played a less significant role and the provenance of sediments remained constant. The enrichment factor (EF) showed moderate to severe enrichment for Cr, Ni, and Sb (EF = ~2.63–7.57), highest in the northers season, especially at the Grijalva River mouth, although the index of geo-accumulation (Igeo) for these elements suggested as moderately polluted (Igeo = 0.34–2.0). The slightly elevated EF values for Cr, Ni, and Sb during northers season were probably due to an increase in sediment discharge into the sea during the northers season. We inferred that the enrichment of Cr, Ni, and Sb in sediments was due to both lithogenic and anthropogenic origins. The sediments were influenced by the intermediate and basic igneous rocks of the Chiapas Massif Complex, and the waste generated by the urban areas located within the Grijalva River drainage basin.

Rare earth elements as tracers of sediment contamination by fertilizer industries in Southern Brazil, Patos Lagoon Estuary

The content of rare earth elements (REE) and their distribution in sediment cores collected from the Patos Lagoon estuary from southern Brazil were investigated. Sediment cores (ca. 44 cm) were obtained from two locations within the estuary, including a relatively unimpacted site (PI) that has not been strongly affected by human activities and a well-known polluted area within Coroa do Boi Bay (CB), located in the industrialized central part of the estuary, to capture possible features that may help to identify contamination by the local fertilizer manufacturing industry. Sediments from both coring locations are enriched in the light REEs (LREE) over the heavy REEs (HREE) when normalized to the North American Shale Composite (NASC). The PI core was collected in the mid-estuary, an area where salinity values were lower than 10 practical salinity units and where river water and seawater mixing occurs. The features observed in PI sediments likely reflect preferential removal of LREEs from the water column owing to salt-induced coagulation of river-borne colloids. Sediments samples collected from the impacted CB location have substantially higher REE contents than PI sediments. Furthermore the relatively constant REE content and measures of REE fractionation (i.e., ΣLREE/ΣHREE ratios, NASC normalized patterns, NASC normalized La/Yb ratios) with depth in sediments from the CB site suggests that the impact of fertilizer manufacturing on these sediments is a long-term phenomenon. Using sedimentation rates determined for Coroa do Boi Bay, we show that anthropogenic contamination of the CB core sediments by total urban, industrial, and port emissions of REEs can be traced to the early 1900's and was largely continuous throughout the 20th century.

Rare earth elements and yttrium (REY) in coal mine drainage from Southwest China: Geochemical distribution and resource evaluation

The ever-intensifying global demand and supply shortage of rare earth elements (lanthanides and yttrium, REY) have led to investigations into alternative sources of REY. Coal mine drainage (CMD) has been suggested as an attractive supplementary source of REY primarily due to its high content of dissolved REY, and some CMD is considered critical-REY resource. Guizhou has the fifth largest coal reserve in China and a long history of coal mining activities with the continuous discharge of CMD, which is a long-overlooked likely source of REY. In the present study, 120 CMD samples were collected from the Guizhou coal mine areas of Southwest China to investigate REY concentrations, enrichment trends and potential resources for REY reclamation. The obtained concentrations of REY across all the CMDs vary from less than 0.02 μg/L to more than 8765.66 μg/L, with an average of 684.12 μg/L. The average ΣREY concentrations of CMD from different coal-bearing strata decrease in the following order: Liangshan Formation (LS Fm.; 2337.14 μg/L) > Xiangbai Formation (XB Fm.; 1591.82 μg/L) > Heshan Formation (HS Fm.; 1249.22 μg/L) > Longtan Formation (LT Fm.; 1243.48 μg/L) > Banan Formation (BN Fm.; 534.66 μg/L). When normalized to the North American Shale composite (NASC), most CMD samples generally display middle rare earth element (MREE) enrichment, but some are also enriched in light rare earth element (LREE) and heavy rare earth element (HREE). The REY distribution patterns, Mantel test and geochemical modelling results demonstrate that the geochemical compositions of CMD and the geological conditions are significantly correlated with the behaviours of REY in CMD. CMD with pH ≤ 5.5 contains elevated concentrations of dissolved ΣREY and is also enriched in critical-REY (Nd, Eu, Tb, Dy, Er and Y). Critical-REY in CMD with pH ≤ 5.5 accounts for 19.07%–68.21% of the total REY, and the outlook coefficients (Coutl) of REY reclamation in acidic CMD are in the range of 0.48–4.14. The data of high proportions of critical-REY and the Coutl values presented in this study suggest that CMDs with pH ≤ 5.5 from coal-bearing strata of the LS Fm., LT Fm. and XB Fm. could be a promising alternative source of REY, especially critical-REY.

Geochemistry of Sedimentary Rocks from the Nkapa Formation, North Western Part of the Douala Basin, Cameroon: Implications for Provenance, Tectonic Setting and Paleoenvironmental Conditions

The Douala sedimentary basin in Cameroon is the main gas prospective basin in the country and has witnessed a number of investigations in this regard. The Nkapa Formation is one of the basin’s principal rock units and here we analyzed samples from sediments comprising this formation in order to constrain their provenance, tectonic setting and depositional environment using geochemical traits. Major and trace elements were analyzed by inductively coupled plasma mass spectrometry. Elemental ratios provide information on geochemical signatures of Eu/Eu ratios of the sandstones and shales, suggesting the provenance of the sediments was felsic from continental rock protoliths. Calculated K2O/Na2O ratios > 1 is reminiscent of quartz-rich sediments deposited in passive margin (PM) environments with significant terrigenous input. The elemental ratios La/Sc, La/Ca, Th/Sc, and Th/Co suggest that the sediment sources are felsic and mafic in nature. The clastic sediments were normalized using North American Shale Composite (NASC). The Ni/Co and V/(V + Ni) ratios reveal that the sediments were deposited under variable conditions including euxinic, dysoxic and anoxic. Overall, the evidence from discrimination diagrams using major and trace elements suggest that the sediments were derived from mostly Passive margins (PM) and continental island arc (CIA) with minor Oceanic island arch (OIA) sources. Limestones from the studied area at Kompina, rich in calcium carbonate above 98.5% make them suitable for use in the chemical industries. In addition the felsic and mafic source rocks can lead to formation of light and dark colored minerals which can be of economic value.

Accumulation of Organic Matter, Heavy Metals, and Rare-Earth Elements in Marine Sediment at Different Distance from the Indigirka River Delta

Abstract—Studies have shown that the concentration of heavy carbon isotope in the organic matter (OM) in the surface layer of the marine sediment increases and the amount of terrigenous OM decreases by about 1.4 times with increasing distance from the Indigirka River delta from 50 km to 600 km. This is accompanied by 1.3–2.1 times decrease of heavy metals and 1.3–1.4 times decrease of rare-earth elements (REE). A strong correlation is observed between the contents of OM, heavy metals, and REE in marine sediments, with the exception of the Cd and W contents. At a distance of 50 km from the river delta, the heavy metals contents exceed their Earth’s crust clarke values, while REE contents are higher than those of the North American Shale Composite (NASC). The opposite pattern is observed at a distance of 600 km from the river delta.

Accumulation of natural radionuclides (7Be, 210Pb) and micro-elements in mosses, lichens and cedar and larch needles in the Arctic Western Siberia.

This is a study of the atmospheric-origin natural radionuclides (7Be and 210Pb) and a wide range of micro- and macro-element accumulation in mosses, lichens, cedar and larch needles in Arctic western Siberia (Yamal-Nenets Autonomous District). Based on the specific activities measurements of atmospheric precipitation markers (7Be and 210Pb), this study found that the concentration of dust particles in the studied objects incrementally increases in the following order, from lowest concentration to highest: cedar needles, larch needles, lichens and mosses. Concentrations of Zr, Hf, Ti, Th, Fe, V, Li, Na, Si, Be, Y, rare earth elements (REE) and Sc in this area also increase in the same ascending sequence. Enrichment factors of these elements (EF) relative to the North American Shale Composite (NASC) are close to unity, which proves their terrigenous origin. Also, the terrigenous origin of the elements in the studied biological objects is confirmed by their high correlation coefficients with Sc. This means that their concentration in the studied biological objects is the result of a background of solid atmospheric precipitation. Enrichment factors of biogenic elements and their analogues (P, Se, Mn, Mg, Ca, K, Zn, Sr, Ba, Rb, Cs) are significantly greater than unity, and this is associated with high concentrations of these elements in the biological part of the samples. A radially symmetric distribution of Pb content in biological objects is observed over the surface of the studied area (with a center located within the city of Novy Urengoy). This leads to the conclusion that there is a point source around which anthropogenic precipitation of Pb takes place. This distribution is most clearly manifested by the example of larch and cedar needles. Anthropogenic deposition of other elements has not been detected in this study area.

A User‐Friendly Workbook to Facilitate Rapid and Accurate Rare Earth Element Analyses by ICP‐MS for Multispiked Samples

AbstractThe rare earth elements (REEs) are widely used as geochemical tracers in the earth, planetary, and ocean sciences. Inductively coupled plasma‐mass spectrometry (ICP‐MS) has become the method of choice to analyze REE concentrations because it can rapidly measure the entire REE spectrum at the same time. This Technical Report presents a user‐friendly “REE Calculation Workbook” in Microsoft Excel to be used for calculating REE abundances in samples equilibrated with a multielement REE spike. This Workbook can be conveniently used to calculate REE concentrations in natural samples for spiked and unspiked elements measured by ICP‐MS. For the spiked elements, their concentrations are calculated using isotope dilution equations. Using these spiked elements as references, concentrations of the four mono‐isotopic REE elements, and other REE elements that are treated as mono‐isotopic elements (in our case, La and Lu), can be calculated. The REE Workbook can be easily set up for use with different REE spikes. Evaluation of our analytical quality using a quadrupole ICP‐MS on 10‐ml‐sized seawater samples shows that our analyses are comparable to high‐precision thermal ionization mass spectrometry (TIMS) studies, with much less time spent processing and analyzing, and with the added advantages of determining mono‐isotopic elements. An important result is the clear demonstration of enrichments in Gd and Er compared to neighboring elements in seawater samples. In addition, we compare and evaluate commonly used reference standards BCR‐1, Post‐Archean Australian Shale (PAAS), and North American Shale Composite (NASC).

Hydrogeochemical study of surface waters from Araxá city, Minas Gerais State, Brazil

Barreiro area at Araxá city, Minas Gerais State, Brazil, has been well-known since the 19th century when started the studies of the healing properties for the tuberculosis treatment of the natural mineral waters of the springs Dona Beja (DBS) and Andrade Júnior (AJS). In addition, extensive mining activities devoted to the niobum and phosphate fertilizer exploitation have been developed there since the 60's and 70's by different companies, favoring the release of contaminants into the hydric resources of that environment. This paper reports a hydrogeochemical study of surface waters occurring at Barreiro area, comparing their major hydrochemical characteristics with those of other surface waters and rainwater occurring there for identifying possible degradation of their quality due to the anthropogenic inputs associated to the mining activities. The systematic utilized in this approach consisted on the adoption of various experimental steps: hydrochemical analysis by different methods of the several samples collected; hydrochemical data treatment and plotting using traditional statistical tests and geochemical diagrams; use of geochemical data in various sections of six sediment core for calculating the Geoaccumulation Index (Igeo) taking into account sediments outside of Barreiro area for yielding background values, as well as the concentrations reported in the literature for shales and NASC (North American shale composite); leaching experiments of sediment aliquots at room temperature (~20 °C) during about 24 h and using distilled water equilibrated with the atmosphere as leachant for the analysis of the release of barium, chloride, sulfate, phosphate and nitrate. All these protocols allowed an integrated evaluation of the constituents transport at Barreiro area and nearby, improving the knowledge of the environmental impacts associated to the mining activities developed there, responsible by a production of about 20,000 tons/year of ground apatite for phosphate use in agriculture and circa 936 billion metric tons of Nb2O5 ore.