Absolute Rare Earth Element Research Articles

Rare earth elements in gneiss regoliths in southern Minas Gerais, Brazil

ABSTRACT: Regolith characterization in its entirety is particularly difficult in gneissic regoliths due to the heterogeneity of their rock structure. Rare earth elements (REE) are a useful tool in helping understand the evolution of regoliths. This study relates the mineralogy and weathering indexes of three gneisses regoliths (P1-leucocratic, P2-mesocratic and P3-melanocratic gneisses) to the distribution of REE at depth. In soil, clay activity, iron and manganese oxides, CaO, SiO2, P2O5, TiO2, Fe2O3, and MgO showed high positive correlation with REE. The absolute content of REE was enriched in mafic minerals. At the interface between the soil and saprolite, the sum of absolute REE content was greater in soil than in saprolite in P1, while the opposite pattern was found in P2 and P3. The sums of absolute REE in the whole profiles did not overlap between P1, P2 and P3, and the absolute concentration of Gadolinium (Gd) differentiated the three gneisses in all and every horizon/layer of their regoliths without overlapping values. Normalized REE content was greater in the subsurface of P1 due to Eu content in plagioclase, and fractionation had less variation when estimated by Light REE / Heavy REE (LREE/HREE) than by La/Yb, since the variation in REE is great in gneisses (due to the segregation of minerals into bands), and had low levels of association with the Chemical Index of Alteration (CIA) and the Weathering Index of Parker (WIP).

Carbonate–silicate melt immiscibility, REE mineralising fluids, and the evolution of the Lofdal Intrusive Suite, Namibia

The Lofdal Intrusive Suite, Namibia, consists of calcio-carbonatite and silica-undersaturated alkaline intrusive rocks ranging in composition from phono-tephrite to phonolite (and nepheline syenite). The most primitive of these rocks is the phono-tephrite, which, on the basis of its Y/Ho and Nb/Ta ratios, is interpreted to have formed by partial melting of the mantle. Roughly linear trends in major and trace element contents from phono-tephrite to phonolite and nepheline syenite indicate that the latter two rock types evolved from the phono-tephrite by fractional crystallisation. The nepheline syenite, however, has a lower rare earth element (REE) content than the phonolite. The carbonatite has a primitive mantle-normalised REE profile roughly parallel to that of the silica-undersaturated alkaline igneous rocks, although the absolute REE concentrations are higher. Like the phono-tephrite, it also has a mantle Y/Ho ratio. However, the Nb/Ta and Zr/Hf ratios are significantly higher. Moreover, the carbonatite displays strong negative Ta, Zr and Hf anomalies on spidergrams, whereas the silicate rocks display positive anomalies for these elements. Significantly, this behaviour is predicted by the corresponding carbonatite-silicate melt partition coefficients, as is the behaviour of the REE. Based on these observations, we interpret the carbonatite to represent an immiscible liquid that exsolved from the phono-tephrite or possibly the phonolite melt. The result was a calcio-carbonatite that is enriched in the heavy REE (HREE) relative to most other carbonatites. Fluids released from the corresponding magma are interpreted to have been the source of the REE mineralisation that is currently the target of exploration.

Geochemistry of Kolmani-1 Well Sediments from the Upper Benue Trough, Gongola Basin, Northeastern Nigeria

Aims: To assess the source rock characteristics and the depositional environment through Geochemical studies of sediment samples from the Upper Benue Trough. Place and Duration of Study: Department of Geology, Obafemi Awolowo University, Nigeria and The Activation Laboratory Ltd, Ontario, Canada between February 2011 and March 2012. Methodology: Eighteen samples made up of sand, shale, coaly shale, shaly sand and sandy shale, occurring between the depths of 18.3 m and 2725 m were analysed for thirty-four elements, comprising eight major, twelve trace, and fourteen rare earth elements (REE) using the Inductively Coupled PlasmaMass Spectrometry technique. Results: The results show that the sediments are compositionally rich in Al2O3 and Fe2O3. The low TiO2 values of compared to those of Post-Archean Australian average shale (PAAS) suggest that they were derived from more evolved felsic source rock. The relatively low average Rb/Sr and high Th/U ratios indicate that moderate to more intense weathering occurred in the source rock area. The absolute rare earth elements (REE) concentrations were in the order of coaly shale > shale > sandy shale > shaly sand > sand. Original Research Article British Journal of Applied Science & Technology, 4(20): 2931-2945, 2014 2932 Conclusion: The Al2O3/TiO2, Eu/Eu*, Th/Sc, La/Sc, Th/Co, La/Co, and Th/Cr ratios indicate that the sediments were probably derived from felsic source rocks. In addition, the high LREE/HREE ratios and the negative Eu anomaly also support felsic source rocks for the sediments whilst the very low V/Cr ratios indicate that these sediments were deposited under anoxic environment, consistent with the series of horst and graben structural framework model of the Benue Trough.

Rare earth element–SiO2 systematics of mid-ocean ridge plagiogranites and host gabbros from the Fournier oceanic fragment, New Brunswick, Canada: a field evaluation of some model predictions

The two most commonly invoked processes for generating plagiogranites in mid-ocean ridge environments are extended fractional crystallization of mid-ocean ridge basalt (MORB) magma and “hydration melting” of hot, dry MOR gabbro initiated by the influx of seawater-derived hydrothermal fluids within localized zones of shear. Brophy (Contrib Mineral Petrol 158:99–111, 2009) has proposed on theoretical grounds that, for liquids greater than ~62 wt. % SiO2, hydration melting should yield, among other features, a negative correlation between rare earth element (REE) abundances and increasing SiO2, while fractional crystallization should yield a positive correlation. If correct, the REE–SiO2 systematics of natural systems might be used to distinguish between the two processes. The Ordovician Fournier oceanic fragment, New Brunswick, Canada, contains MOR gabbro-hosted plagiogranite veins and dikes that are believed to have formed from hydration melting, thus forming an appropriate location for field verification of the proposed REE–SiO2 systematics for such a process. In addition to a negative correlation between liquid SiO2 and REE abundance for liquids in excess of ~62% SiO2, other important model features include the following: (1) relative to a gabbro source rock, the degree of enrichment at liquids of 62 and 75% SiO2 decreases from the LREE to the HREE; (2) the degree of enrichment at 75% SiO2 approaches 1 for the HREE; (3) the rate of change of the degree of enrichment with increasing liquid SiO2 (i.e., the slope) diminishes from the LREE to the HREE. All of these predicted features are observed in the Fournier plagiogranites. Assuming an initial source rock equivalent to the host gabbro, an additional strongly LREE-enriched component must be added prior to melting in order to make the absolute REE abundances agree with the model values. The most likely candidates are the very seawater-derived hydrothermal fluids that triggered hydration melting in the first place.

Rare earth element abundances in hydrothermal fluids from the Manus Basin, Papua New Guinea: Indicators of sub-seafloor hydrothermal processes in back-arc basins

Rare earth element (REE) concentrations are reported for a large suite of seafloor vent fluids from four hydrothermal systems in the Manus back-arc basin (Vienna Woods, PACMANUS, DESMOS and SuSu Knolls vent areas). Sampled vent fluids show a wide range of absolute REE concentrations and chondrite-normalized (REE N) distribution patterns (La N /Sm N ∼ 0.6–11; La N /Yb N ∼ 0.6 – 71; Eu N / Eu N ∗ ∼ 1 – 55 ). REE N distribution patterns in different vent fluids range from light-REE enriched, to mid- and heavy-REE enriched, to flat, and have a range of positive Eu-anomalies. This heterogeneity contrasts markedly with relatively uniform REE N distribution patterns of mid-ocean ridge hydrothermal fluids. In Manus Basin fluids, aqueous REE compositions do not inherit directly or show a clear relationship with the REE compositions of primary crustal rocks with which hydrothermal fluids interact. These results suggest that the REEs are less sensitive indicators of primary crustal rock composition despite crustal rocks being the dominant source of REEs in submarine hydrothermal fluids. In contrast, differences in aqueous REE compositions are consistently correlated with differences in fluid pH and ligand (chloride, fluoride and sulfate) concentrations. Our results suggest that the REEs can be used as an indicator of the type of magmatic acid volatile (i.e., presence of HF, SO 2) degassing in submarine hydrothermal systems. Additional fluid data suggest that near-seafloor mixing between high-temperature hydrothermal fluid and locally entrained seawater at many vent areas in the Manus Basin causes anhydrite precipitation. Anhydrite effectively incorporates REE and likely affects measured fluid REE concentrations, but does not affect their relative distributions.

A preliminary study on fingerprinting approach in marine sediment dynamics with the rare earth elements

Locating the quantitized natural sediment fingerprints is an important work for marine sediment dynamics study. The total of 146 sediment samples were collected from the Shelf of the East China Sea and five rivers, including Huanghe (Yellow), Changjiang (Yangtze), Qiantang, Ou and Min River. The sediment grain size and the contents of rare earth elements (REEs) were measured with laser particle size analyzer and ICP-MS technology. The results show that absolute REE content (Sigma REE) and the concentration ratio of light REEs to heavy REEs (L/HREE) are different in the sediments among those rivers. There are higher REE contents in being less than 2 m and 2-31 mu m fractions in the Changjiang Estuary surface sediments. The REE contents of bulk sediment are dominated by the corresponding values of those leading size-fractions. Sigma REE of sediment is higher close to the estuaries and declines seaward on the inner shelf of the East China Sea (ECS). The L/HREE ratio has a tendency of increase southward from 28 degrees N. Hydrodynamic conditions plays a predominate role on spacial distributions of the surficial sediment's REE parameters. In some situations, the currents tend to remove the coarser light grains from initial populations, as well as the deposit of the finer heavy mineral grains. In other situations, the currents will change the ratio of sediment constituents, such as ratio between silts and clays in the sediments. As a result, the various values of Sigma REE or L/HREE ratio in different bulk sediments are more affected by the change of size-fractions than source location. Under the long-term stable hydrodynamic environment, i.e., the East China Sea Shelf, new sediment transport model based on the size and density gradation concept may help to understand the spatial distribution patterns of REE parameters.

Rare-earth elements as source indicators of Pan-African granites from Obudu Plateau, Southeastern Nigeria

The rare-earth element (REE) concentrations of representative granite samples from the southeast of the Obudu Plateau, Nigeria, were analyzed with an attempt to determine the signatures of their source, evolutionary history and tectonic setting. Results indicated that the granites have high absolute REE concentrations (190×10−6−1191×10−6; av.=549×10−6) with the chondrite-normalized REE patterns characterized by steep negative slopes and prominent to slight or no negative Eu anomalies. All the samples are also characterized by high and variable concentrations of the LREE (151×10−6−1169×10−6; av. = 466×10−6), while the HREE show low abundance (4×10−6−107×10−6; av.=28×10−6). These are consistent with the variable levels of REE fractionation, and differentiation of the granites. This is further supported by the range of REE contents, the chondrite-normalized patterns and the ratios of LaN/YbN (2.30–343.37), CeN/YbN (5.94–716.87), LaN/SmN (3.14–11.68) and TbN/YbN (0.58–1.65). The general parallelism of the REE patterns, suggest that all the granites were comagmatic in origin, while the high Eu/Eu* ratios (0.085–2.807; av.=0.9398) indicate high f O2 at the source. Similarly, irregular variations in LaN/YbN, CeN/YbN and Eu/Eu* ratios and REE abundances among the samples suggest behaviors that are related to mantle and crustal sources.

A fast method for apatite selective leaching from granitic rocks followed through rare earth elements and phosphorus determination by inductively coupled plasma optical emission spectrometry

Rare earth elements (REE) and phosphorus (P) in apatite were determined using inductively coupled plasma optical emission spectrometry (ICP-OES) after partial dissolution of the granitic rocks and pure apatite. The dissolution was performed with nitric acid in an open system and the matrix elements were separated by a cation exchange procedure. Samples of pure apatite from granitic rocks were dissolved with, 0.14 mol L −1 nitric acid. The results showed that the release of REE is due to apatite leaching because it could be assessed by comparing the chondrite-normalised pattern corresponding to the rocks and the pure apatite. Similar results were found for absolute REE abundance from the partial dissolution of the rocks and pure apatite. This simple and rapid method can be applied for the determination of REE in apatite as an indicator for mineral exploration, although its use in petrology could be possible.

Structural point defects in “Iceland spar” calcite

Trace element concentrations by micro-PIXE, cathodoluminescence (CL) emission spectra and electron spin resonance (ESR) spectra of Mn 2+ in “Iceland spar” calcite have been measured. The average rare earth elements (REE) abundances of the Iceland spar calcite revealed a concave shape with positive Eu and Tb anomalies. All samples show comparable average REE abundances compared to average chondrites standard. The REE signal in hydrothermal solution seems to be similar for the different locations and age of formation although the absolute REE concentration in the solution was certainly different. The CL-properties of investigated Iceland spar varied from orange to green. The orange luminescence is based on Mn 2+ in Ca-position of calcite while this uncommon green luminescence is most likely attributed to UO 2 2+ complex ions associated with electron–hole centres.

Apatite chemical composition, determined by electron microprobe and laser-ablation inductively coupled plasma mass spectrometry, as a probe into granite petrogenesis

Major, minor, and trace element abundances in apatites from various I- and S-type (igneous and sedimentary) granites of the Lachlan Fold Belt have been determined using electron microprobe and laser ablation inductively coupled plasma mass spectrometer. The results show that apatite can accommodate many minor and trace elements, whose concentrations and ratios are relatively sensitive to factors controlling many of the fundamental differences between I- and S-type granites. Apatites from S-type granites generally have higher F but lower Cl contents than those from I-type granites, which is ascribed mainly to the loss of Cl during the weathering processes forming the source rocks of S-type granites, although fractional crystallisation can cause significant enrichment in F as well. High Mn and Fe contents in apatites from S-type granites, and high S and As abundances in apatites from mafic I-type granites, result from different oxygen fugacities and degrees of Al saturation (or aluminosity) between metaluminous mafic I-type magmas and peraluminous S-type and felsic I-type magmas. There are systematic and distinctive differences in absolute rare-earth element (REE) abundances, REE distribution patterns, and element ratios (e.g., La/Y, Sm/Nd, etc.) between apatites from different types of granite. The strong Eu depletion that characterises apatites from S- and felsic I-type granites is interpreted here to be a result of the uniqueness of crystal chemistry of apatite and high Eu 2+/Eu 3+ ratios in S-type and felsic I-type magmas, which are more reduced and peraluminous than mafic I-type magmas. Strong REE (La to Eu) and Th enrichment in apatites from mafic I-type granites and marked Nd depletion in apatites from most S-type and felsic I-type granites are caused by the precipitation and fractionation of monazite in the parental magmas of the latter rocks. Substitution mechanisms are responsible for high Na in apatites from S-type and felsic I-type granites, and for high Si in apatites from mafic I-type granites, and may also have important effects on REE partitioning between apatite and melt. Thus, apatite chemistry can be used as an excellent indicator of granite petrogenesis. The results have important implications for identifying different types of granite and are potentially significant for determining the provenance of sedimentary rocks.

Chemical composition and origin of the Acapulco meteorite

New chemical data for both whole-rock and individual mineral samples from the Acapulco meteorite are reported. Results of instrumental neutron activation analysis (INAA) of bulk samples show large variation in La, Cr, Se, and Fe contents reflecting inhomogeneous distribution of the corresponding host phases: phosphate, chromite, sulfide, and FeNi metal. In contrast, Mn, Sc, and Na contents are uniformly distributed reflecting constant fractions of orthopyroxene, olivine, and plagioclase in bulk samples.INAA data were obtained on single olivine and orthopyroxene grains with numerous tiny metal inclusions. The siderophile elements in these inclusions, in particular the low Ir contents, suggest that the inclusions formed by partial melting of matrix metal. The composition of the metal inclusions and the absence of such inclusions in clinopyroxene suggests an upper limit of about 20% partial melting of Acapulco at around 1200°C. During melting and closed-system crystallization the inhomogeneous distribution of metal, chromite, sulfide, and phosphates was established. Acapulco phosphates are of igneous origin. Most of them were not formed by oxidation of metal. The uniform K contents of bulk Acapulco samples and the comparatively high contents of volatiles (including rare gases) in bulk samples demonstrate a closed-system behavior. Neither loss nor gain of volatile elements has occurred.Ion microprobe data of rare earth elements (REEs) in Acapulco minerals show an equilibrium distribution for heavy REEs and nonequilibrium for light REEs. Bulk Acapulco samples have large excesses of light REEs and U with phosphates being the major carrier. Absolute REE contents of phosphates are variable. The observed enrichments of REEs and U in bulk Acapulco samples cannot be explained by the addition of phosphates, since the approximately chondritic ratios of Ca/Mg and P/Mg exclude major gains of Ca and P through the addition of phosphates. It is suggested that a fluid phase rich in incompatible elements infiltrated Acapulco and that REEs and U were extracted by phosphates. The remaining fluid phase subsequently must have drained away. From temperatures determined by two-pyroxene equilibria, spinel-olivine and Ca zonation in olivine, a thermal history of Acapulco is constructed. Cooling rates at 900°C of about 100 K/Ma are estimated. The concentration profiles of Ca in olivine, showing constant Ca throughout grain interiors and sharp decreases at the rims, are difficult to explain. If the Ca zonation in olivine exclusively reflects cooling, slow cooling must have been followed by fast cooling at temperatures below 650°C. Alternatively, the low Ca contents of olivine rims may reflect other processes, such as, for example, formation of phosphates.A model for the evolution of Acapulco is presented: The parent body of Acapulco accreted earlier than that of the ordinary chondrites (OC), thus more 26Al was available for heating, leading to higher peak temperatures than in OC. Extensive solid state equilibration at 900°C completely erased the 26Mg signature in plagioclase. Acapulco is, despite the absence of chondrules, essentially a chondritic meteorite, attesting to the variety of planetesimals of chondritic composition in the asteroid belt.

Geochemistry of Upper Cambrian-Lower Ordovician black shale along a northeastern Appalachian transect

Samples of Upper Cambrian to Lower Ordovician black shale, collected in a transect extending across the Canadian Appalachians from the Humber Zone in Quebec, the Gander and Avalon Zones in New Brunswick, to the Meguma Zone in Nova Scotia, were analyzed for 40 elements, including rare earths. These geochemical data lend support to previously established plate-tectonic models of the region. They also provide information on provenance and depositional environments of sediments that are too fine grained for more traditional mineralogical and sedimentological studies. Generally high Al 2 O 3 contents, high Al/Ti values, and steep rare-earth-element (REE) distribution patterns are consistent with a continental-margin depositional setting for shale from the Humber and Meguma Zones on opposite sides of the Iapetus ocean. Generally higher K 2 O contents, lower La/Th values, and lower absolute REE abundances distinguish shale of the Humber Zone deposited on the Laurentian margin from that deposited in the Meguma Zone on the Gondwanan margin. High La/Th values indicate a similar Gondwanan source for shale from both the Meguma and Avalon Zones. Shale from the Gander Zone contains less Al 2 O 3 at increasing distances from its boundary with the Avalon Zone. Low Al/Ti and less fractionated REE distribution patterns suggest a greater component of volcanic detritus in shale of the Avalon and Gander Zones. The presence of distinctive Balto-Scandian signatures (high U, V, and Mo) in shale of the Avalon and northwestern Gander Zones is possibly related to deposition in isolated peri-Gondwanan back-arc basins during a highstand of sea level.

Rare earth elements in the phosphatic-enriched sediment of the Peru shelf

Apatite-enriched materials from the Peru shelf have been analyzed for their major oxide and rare earth element (REE) concentrations. The samples consist of (1) the fine fraction of sediment, mostly clay material, (2) phosphatic pellets and fish debris, which are dispersed throughout the fine-grained sediment, (3) tabular-shaped phosphatic crusts, which occur within the uppermost few centimeters of sediment, and (4) phosphatic nodules, which occur on the seafloor. The bulk REE concentrations of the concretions suggest that these elements are partitioned between the enclosed detrital material and the apatite fraction. Analysis of the fine-grained sediment with which the samples are associated suggested that this detrital fraction in the concretions should have shale REE values; the analysis of the fish debris suggested that the apatite fraction might have seawater values. The seawater contribution of REE's is negligible in the nodules and crust, in which the apatite occurs as a fine-grained interstitial cement. That is, the concentration of REE's and the REE patterns are predominantly a function of the amount of enclosed fine-grained sediment. By contrast, the REE pattern of the pelletal apatite suggests a seawater source and the absolute REE concentrations are relatively high. The REE P 2 O 5 ratios of the apatite fraction of these samples thus vary from approximately zero (in the case of the crust and nodules) to as much as approximately 1.2 × 10 −3 (in the case of the pellets). The range of this ratio suggests that rather subtle variations in the depositional environment might cause a significant variation in the REE content of this authigenic fraction of the sediment. Pelletal glauconite was also recovered from one sediment core. Its REE concentrations closely resemble those of the fish debris.

The distribution of rare earth and minor elements in manganese nodules and sediments from the equatorial and S.W. Pacific

62 manganese nodules and 17 associated sediments from the equatorial and S.W. Pacific have been analyzed for a number of elements, including the rare earth elements (REE), by instrumental neutron activation. Sc, Co, As, Hf, Th and REE occur in higher concentrations in S.W. Pacific than in equatorial Pacific nodules, reflecting the higher iron content of the S.W. Pacific nodules. These elements are probably incorporated nondiscriminantly into the iron oxyhydroxide structure by direct sorption from seawater because they are too large to be incorporated into the manganese oxide structure. The highest Ce La ratios are also found in the S.W. Pacific nodules. This may result from the fact that these nodules lie beneath the path of the fast flowing, well-oxygenated Antarctic Bottom Water (AABW) which facilitates oxidation of Ce to the tetravalent state. If so, this supports the idea that the Ce La ratio of manganese nodules is an important redox indicator. Negative cerium anomalies were noted for nodules from Areas F and G can be interpreted on the same model. The REE contents in equatorial Pacific siliceous oozes and S.W. Pacific red clays are similar on a carbonate-free basis. The Ce La ratio of the S.W. Pacific red clays is, however, much higher than that of the equatorial Pacific sediments, possibly reflecting the preferential oxidation of Ce to the tetravalent state beneath the AABW. There appears to be no systematic relationship between the REE abundance in the nodules and their associated sediments, although absolute REE abundances are higher in nodules than in their associated sediments. Nodules with the highest Ce La ratios are, however, found on sediments with the highest Ce La ratios. The principal difference in the REE distribution pattern of the nodules and sediments lies in the well-known cerium anomaly which is positive to slightly negative for nodules and always negative for sediments.

The distribution of rare-earth elements in deeply buried Gulf Coast sediments

Analyses of rare-earth elements (REE) in Gulf Coast sediments indicate that the absolute REE content of the bulk sample is nearly constant between 174 and 165 ppm at depths of 1.81 and 3.67 km, respectively; but it increases perceptibly to 212 ppm at a depth of 4.77 km. Similarly, the absolute REE contents in the clay-sized fractions range between 175 and 205 ppm at depths of 1.81 and 4.42 km but they increase moderately to 272 ppm at a depth of 4.77 km. The ratios of the light to heavy rare-earths (LREE/HREE) of the bulk samples and their clay-sized fractions are nearly constant between 7.2 to 8.4 for depths between 1.81 and 4.42 km, whereas the ratio decreases to about 5.5 and 6.6 for sediments at 4.77 km. Both the absolute REE content and the LREE/HREE ratio of the sediments most likely reflect the character of the provenance(s) of the sediments, and they are influenced only to a minor extent by diagenesis. The Eu/Sm ratios of all samples cluster very tightly around the value of 0.21, similarly to that of the North American Shale composite. A nearly constant Eu/Sm ratio among samples at all depths may have been inherited primarily at the provenance(s) of these Gulf Coast sediments.

Rare earth distributions in clay minerals and in the clay-sized fraction of the Lower Permian Havensville and Eskridge shales of Kansas and Oklahoma

The REE (rare earth element) content of a wide variety of clay mineral groups have been analyzed using radiochemical neutron activation and have been found to be quite variable in absolute REE content (range of ∑ REE = 5.4–1732) and less variable in relative REE content (range of chondritenormalized La/ Lu = 0.9–16.5). The variable REE content of the clay mineral groups is probably determined by the REE content of the source rock from which the clay mineral was derived and not from the separate minerals in the rock. The clay-sized fractions of the Havensville and Eskridge shales of Kansas and Oklahoma have similar relative REE distributions and identical negative Eu anomaly size as the composite of NAS (N. American shales), but an absolute REE content (range of ∑ REE = 46–348) that may differ significantly from the composite of NAS. The clay-sized fraction of samples from any given outcrop did not vary much in absolute or relative REE content, but samples from northern Oklahoma, probably composed of continental to near-shore marine sediments, have higher absolute REE contents and higher La/Lu ratios than samples of marine deposits in Kansas (e.g. mean ∑REE in Oklahoma = 248; mean ∑REE in Kansas = 69–116). The differencess in the REE content between samples in Oklahoma and Kansas may be caused by chemical weathering processes in the source area, exchange reactions in the environment of deposition, or diagenesis and do not appear to be a result of the different clay minerals. Most samples have Eu anomalies relative to chondrites (range of Eu/Sm ratios of samples = 0.035–1.17; chondrites = 0.35). Some montmorillonites and kaolinites are anomalous in Eu relative to the NAS (range of Eu/Sm ratios of samples = 0.056–0.21; NAS = 0.22). These anomalies may be inherited from source rocks with Eu anomalies originally produced by igneous processes, or they may be produced by chemical weathering processes in the source area.

Abundances of the fourteen rare-earth elements, scandium, and yttrium in meteoritic and terrestrial matter

Abundances and isotopic ratios have been determined for the fourteen rare-earth elements (REE) (Pm excluded) plus Sc and Y by neutron-activation analysis in nineteen meteorites and in three terrestrial specimens. The meteorites investigated included eleven chondrites (1 carbonaceous, 2 pigeonitic, 2 hypersthenic, 3 bronzitic and 3 enstatitic), two calcium-rich and three calcium-poor achondrites, one mesosiderite and two iron meteorites; the terrestrial specimens included a fresh volcanic basalt, and a deep-seated peridotitic and an eclogitic specimen. The absolute abundance of a typical REE (La) in bronzitic and hypersthenic chondrites was found to be 0.34 p.p.m. Relative REE, Sc and Y distributions were identical in the five different chondrite categories. On an absolute basis, the REE, Sc, and Y per 10 6 Si atoms varied monotonically over the chondrite spectrum i.e. from carbonaceous through enstatitic meteorites. Meteoritic isotopic abundances of the sensitive Yb 168/Yb 174 ratio agreed to within ±5 per cent of the terrestrial abundance ratios. Absolute REE abundances in the two calcium-rich achondrites, Nuevo Laredo and Pasamonte, were from 10 to 12 times greater than the average chondritic values. No REE fractionation was found in these achondrites; however, Sc was fractionated by a factor of ~2 relative to the REE. Fractionation of the REE, Sc and Y was found in all three calcium-poor achondrites, Johnstown, Shalka and Norton County, relative to the chondritic meteorites. Absolute REE, Sc and Y abundances varied from ~0.05 to ~0.5 times the comparable values in chondrites. Eu has been depleted in Johnstown and Norton County by ~3—4 times. Th has been depleted in Johnstown to the same degree as La. No REE and Y fractionation was found in the mesosiderite, Estherville; however, Sc has been fractionated. Absolute REE abundances in the two Fe meteorites were ~10 −4 times the REE abundances in chondrites. In one iron, the REE may have been fractionated. Absolute REE. Sc and Y abundances in the uneroded Kilauea Iki-22 basalt, peridotitic and eclogitic specimens were from 30 to 10 times greater than the abundances in chondrites. Compared with chondrites, the light REE have been enriched by factors of up to 5, which agrees with the enrichments of the light REE in terrestrial sediments and igneous rocks, etc. Theoretical calculations of expected REE abundances by Clayton et al. agree well with the present chondritic REE values. For convenience, a description of the detailed procedure for the REE, Sc and Y determinations (now in current use at this Laboratory) has been relegated to the Appendix.