Rare earth elements in garnets and clinopyroxenes from garnet lherzolite nodules in kimberlites

Six pairs of coexisting garnets and clinopyroxenes were separated from the sheared and granular garnet lherzolite nodules in kimberlites and analyzed for rare earth elements (REE). The sheared and granular nodules can be distinguished in terms of REE pattern of both clinopyroxene and garnet. However, there are no significant differences in REE partitioning between clinopyroxene and garnet, indicating that the partitioning may be insensitive toP, T and composition. REE partition coefficients between garnet and liquid were estimated by using clinopyroxene-liquid partition coefficients found in the literature and clinopyroxene-garnet partitioning reported here. The estimated values agree with those reported by Philpotts et al. (1972). The estimated whole-rock REE pattern for the sheared nodules is similar to a chondritic pattern suggesting that the sheared nodules appear to be close to the primary mantle material. The REE data suggest that the granular nodules were originally garnet-free assemblages equilibrated with kimberlitic or nepheline-melilite basalt-like liquid, and later recrystallized as a garnet lherzolite assemblage.     

Effects of topography and vegetation on distribution of rare earth elements in calcareous soils

This study investigated the impact of topography and vegetation on distribution of rare earth elements(REEs)in calcareous soils using methods of single extraction and mass balance calculation. The purposes of the study were to set a basis for further research on the biogeochemical REE cycle and to provide references for soil–water conservation and REE-containing fertilizer amendments. The results show a generally flat Post-Archean Average Australian Shale—normalized REE pattern for the studied calcareous soils. REE enrichment varied widely. The proportion of acidsoluble phases of heavy REEs was higher than that of light REEs. From top to bottom of the studied hills, dominant REE sources transitioned from limestone in-situ weathering to input from REE-containing phases(e.g., clay minerals,amorphous iron, REE-containing fluids). Our results indicate that the REE content of calcareous soils is mainly controlled by slope aspect, while the enrichment degree of REEs is related to geomorphological position and vegetation type.Furthermore, the proportion of acid-soluble phases of REEs is mainly controlled by geomorphological position.     

Geochemical fractionation of rare earth elements in lacustrine deposits from Qaidam Basin

Based on the concentration and distribution pattern analysis of the rare earth elements (REEs) at the Shell Bar section from Qaidam Basin, we studied the geochemical fractionations of REE in paleolake deposits and their paleo-environmental significance. Our results show that the REE concentration in AS (acid soluble) and AR (acid residual) fractions are 20.9 μg/g and 95.4 μg/g (except element Y) individually, showing a strong REE differentiation between AS and AR fractions. However, the two types of fractions (AS & AR) have similar REE distribution patterns, which are slightly rich in light earth rare elements (LREEs), with slightly right-tilting and negative Eu anomaly. The LREE of AR is richer than that of AS. There were no significant correlations between the REE in AS, AR and other proxies. It indicated that the lacustrine deposition had different material sources and experienced varying geochemical procedures. Correlation analysis between the REE and the content of fine grain-size (<4 μm) of the sediments, Rb/Sr ratio and Mn concentration showed high correlation coefficients. Our results demonstrated that the REE in acid soluble and residual fractions bear different environmental significances, which are strongly dependent on local environment. The REE of acid soluble fraction is closely related to the paleoclimatic changes in the lake catchment and the evolutionary processes of lake itself. Our results suggest that δCe and (La/Yb)_n could be used as proxies of the reduction-oxidation conditions and furthermore the temperature change and the lake level fluctuations. Using these proxies, we reconstructed the paleoclimate and water level fluctuation history during the high lake level period lasting between 43.5 and 22.4 cal. ka BP.     

Geochemistry of rare earth elements in basalts from the Walvis Ridge: implications for its origin and evolution

Selected basalts from a suite of dredged and drilled samples (IPOD sites 525, 527, 528 and 530) from the Walvis Ridge have been analysed to determine their rare earth element (REE) contents in order to investigate the origin and evolution of this major structural feature in the South Atlantic Ocean. All of the samples show a high degree of light rare earth element (LREE) enrichment, quite unlike the flat or depleted patterns normally observed for normal mid-ocean ridge basalts (MORBs). Basalts from Sites 527, 528 and 530 show REE patterns characterised by an arcuate shape and relatively low (Ce/Yb)_N ratios (1.46–5.22), and the ratios show a positive linear relationship to Nb content. A different trend is exhibited by the dredged basalts and the basalts from Site 525, and their REE patterns have a fairly constant slope, and higher (Ce/Yb)_N ratios (4.31–8.50).These differences are further reflected in the ratios of incompatible trace elements, which also indicate considerable variations within the groups. Mixing hyperbolae for these ratios suggest that simple magma mixing between a “hot spot” type of magma, similar to present-day volcanics of Tristan da Cunha, and a depleted source, possibly similar to that for magmas being erupted at the Mid-Atlantic Ridge, was an important process in the origin of parts of the Walvis Ridge, as exemplified by Sites 527, 528 and 530. Site 525 and dredged basalts cannot be explained by this mixing process, and their incompatible element ratios suggest either a mantle source of a different composition or some complexity to the mixing process. In addition, the occurrence of different types of basalt at the same location suggests there is vertical zonation within the volcanic pile, with the later erupted basalts becoming more alkaline and more enriched in incompatible elements.The model proposed for the origin and evolution of the Walvis Ridge involves an initial stage of eruption in which the magma was essentially a mixture of enriched and depleted end-member sources, with the N-MORB component being small. The dredged basalts and Site 525, which represent either later-stage eruptives or those close to the hot spot plume, probably result from mixing of the enriched mantle source with variable amounts and variable low degrees of partial melting of the depleted mantle source. As the volcano leaves the hot spot, these late-stage eruptives continue for some time. The change from tholeiitic to alkalic volcanism is probably related either to evolution in the plumbing system and magma chamber of the individual volcano, or to changes in the depth of origin of the enriched mantle source melt, similar to processes in Hawaiian volcanoes.     

An evaluation of the behavior of the rare earth elements during the weathering of sea-floor basalt

We present rare earth element (REE) data for fresh and altered tholeiitic basalts sampled during a dredging transect at 23°N in the Atlantic Ocean and covering a time span of 0 to 57 million years. These data have been used to evaluate the behavior of the REE during low-temperature weathering processes. Compositional trends from altered basalt interiors to palagonitized rinds in individual pillow samples indicate significant mobility of the light REE: some elements are enriched by four orders of magnitude in rinds relative to interiors. The heavy REE show no selective mobilization and can be used in a normalization procedure which indicates that the light REE are enriched in altered interiors relative to fresh interiors of the basalts. Cerium behaves anomalously and accords with either its abundance in seawater or its fractionation from seawater during the formation of ferromanganese deposits.These results indicate that REE data from fresh glassy or crystalline basalt samples only may be used with confidence in petrological models.     

Studying distribution of rare earth elements by classifiers,Se-Chahun iron ore,Central Iran

The increased production and price of rare earth elements(REEs) are indicative of their importance and of growing global attention. More accurate and practical exploration procedures are needed for REEs, and for other geochemical resources. One such procedure is a multivariate approach. In this study, five classifiers, including multilayer perceptron(MLP), Bayesian, k-Nearest Neighbors(KNN), Parzen, and support vector machine(SVM),were applied in supervised pattern classification of bulk geochemical samples based on REEs, P, and Fe in the Kiruna type magnetite-apatite deposit of Se-Chahun,Central Iran. This deposit is composed of four rock types:(1) High anomaly(phosphorus iron ore),(2) Low anomaly(metasomatized tuff),(3) Low anomaly(iron ore), and(4)Background(iron ore and others). The proposed methods help to predict the proper classes for new samples from the study area without the need for costly and time-consuming additional studies. In addition, this paper provides a performance comparison of the five models. Results show that all five classifiers have appropriate and acceptable performance. Therefore, pattern classification can be used for evaluation of REE distribution. However, MLP and KNN classifiers show the same results and have the highest CCRs in comparison to Bayesian, Parzen, and SVM classifiers. MLP is more generalizable than KNN and seems to be an applicable approach for classification and predictionof the classes. We hope the predictability of the proposed methods will encourage geochemists to expand the use of numerical models in future work.     

Apatite/liquid partition coefficients for the rare earth elements and strontium

Sixteen sets of apatite/liquid partition coefficients (D^ap/liq) for the rare earth elements (REE; La, Sm, Dy, Lu) and six values for Sr were experimentally determined in natural systems ranging from basanite to granite. The apatite + melt (glass) assemblages were obtained from starting glasses artificially enriched in REE, Sr and fluorapatite components; these were run under dry and hydrous conditions of 7.5–20 kbar and 950–1120°C in a solid-media, piston-cylinder apparatus. An SEM-equipped electron microprobe was used for subsequent measurement of REE and Sr concentrations in coexisting apatites and quenched glasses. The resulting partition coefficient patterns resemble previously determined apatite phenocryst/groundmass concentration ratios in the following respects: (1) the rare earth patterns are uniformly concave downward (i.e., the middle REE are more compatible in apatite than the light and heavy REE); (2) D_REE^ap/liq is much higher for silicic melts than for basic ones; and (3) strontium (and therefore Eu²⁺) is less concentrated by apatite than are the trivalent REE. The effects of both temperature and melt composition on D_REE^ap/liq are systematic and pronounced. At 950°C, for example, a change in melt SiO₂ content from 50 to 68 wt.% causes the average REE partition coefficient to increase from ～7 to ～30. A 130°C increase in temperature, on the other hand, results in a two-fold decrease in D_REE^ap/liq. Partitioning of Sr is insenstitive to changes in melt composition and temperature, and neither the Sr nor the REE partition coefficients appear to be affected by variations in pressure or H₂O content of the melt.The experimentally determined partition coefficients can be used not only in trace element modelling, but also to distinguish apatite phenocrysts from xenocrysts in rocks. Reported apatite megacryst/host basalt REE concentration ratios [12], for example, are considerably higher than the equilibrium partition coefficients, which suggest that in this particular case the apatite is actually xenocrystic.A reversal experiment incorporated in our study yielded diffusion profiles of REE in apatite, from which we extracted a REEαCa interdiffusion coefficient of 2–4×10^?14 cm²/s at 1120°C. Extrapolated downward to crustal temperatures, this low value suggests that complete REE equilibrium between felsic partial melts and residual apatite is rarely established.     

Naturally occurring radionuclides and rare earth elements in weathered Japanese soil samples

The activity concentrations of ²²⁶Ra and ²²⁸Ac in weathered Japanese soils from two selected prefectures have been measured using a γ-ray spectroscopy system with high purity germanium detector. The uranium, thorium, and rare earth elements (REEs) concentrations were determined from the same soil samples using inductively coupled plasma mass spectrometry (ICP-MS). For example, granitic rocks contain higher amounts of U, Th, and light REEs compared to other igneous rocks such as basalt and andesites. Therefore, it is necessary to understand the interaction between REEs and nature of soils since soils are complex heterogeneous mixture of organic and inorganic solids, water, and gases. In this paper, we will discuss about distribution pattern of ²³⁸U and ²³²Th along with REEs in soil samples of weathered acid rock (granite) collected from two prefectures of Japan: Hiroshima and Miyagi.     

Vapour transport of rare earth elements (REE) in volcanic gas: Evidence from encrustations at Oldoinyo Lengai

Fumarolic encrustations and natrocarbonatite lava from the active crater of Oldoinyo Lengai volcano, Tanzania, were sampled and analysed. Two types of encrustation were distinguished on the basis of their REE content, enriched (~ 2800–5600 × [REE_chondrite]) and depleted (~ 100–200 × [REE_chondrite]) relative to natrocarbonatite (1700–1900 × [REE_chondrite]. REE-enriched encrustations line the walls of actively degassing fumaroles, whereas REE-depleted encrustations occur mainly along cracks in and as crusts on cooling natrocarbonatite lava flows; one of the low REE encrustation samples was a stalactite from the wall of a possible fumarole. The encrustations are interpreted to have different origins, the former precipitating from volcanic gas and the latter from meteoric/ground water converted to steam by the heat of the overlying lava flow(s). REE-profiles of encrustations and natrocarbonatite are parallel, suggesting that there was no preferential mobilization of specific REE by either volcanic vapour or meteoric water vapour. The elevated REE-content of the first group of encrustations suggests that direct REE-transport from natrocarbonatite to volcanic vapour is possible. The REE trends observed in samples precipitating directly from the volcanic vapour cannot be explained by dry volatility based on the available data as there is no evidence in the encrustation compositions of the greatly enhanced volatility predicted for Yb and Eu. The observed extreme REE-fractionation with steep La/Sm slopes parallel to those of the natrocarbonatite reflects solvation and complexation reactions in the vapour phase that did not discriminate amongst the different REE or similar transport of REE in both the natrocarbonatite magma and its exsolving vapour. The low concentrations of REE in the encrustations produced by meteoric vapour suggest that the temperature was too low or that this vapour did not contain the ligands necessary to permit significant mobilization of the REE.     

Distribution of rare earth elements of granitic regolith under the influence of climate

The distribution and anomalies of rare earth elements(REEs) of granitic regolith were studied in Inner Mongolia and Hainan Island, China. One profile showed slight REE enrichment of an upper layer and no obvious light REE/heavy REE(LREE/HREE) fractionation(La_N/Yb_N of 0.9). The second profile was significantly enriched in REEs and enriched in LREEs in the upper portion(La_N/Yb_N1.8). Eu, Ce, and Gd anomalies of the two profiles are different. Slightly negative Eu, Ce, and Gd anomalies in NMG-3-1 indicate slow dissolution of primary minerals and little secondary products; in contrast, a positive Eu anomaly in HN-2 suggests the vegetation cycle may contribute to soil. The Ce anomaly of HN-2 reflects oxidation of Ce and coprecipitation by Fe-and Mn-oxides and organic matter. Correlation between Ce and Gd anomalies in HN-2 suggests Ce and Gd are both influenced by redoxreduction.     

Behavior of rare earth elements in granitic profiles,eastern Tibetan Plateau,China

Rare earth elements(REEs) can record geologic and geochemical processes. We studied two granitic regolith profiles from different climatic zones in eastern Tibetan Plateau and found that(1)∑ RREEs ranged from119.65 to 275.33 mg/kg in profile ND and5.11–474.55 mg/kg in profile GTC, with average values of205.79 and 161 mg/kg, respectively. ∑RREEs was higher in accumulation horizon and semi-regolith;(2) Influenced by climate, the fractionation of light and heavy REEs(LREEs and HREEs) varied during weathering. The ratio of LREEs/HREEs in pedosphere was higher than semi-regolith in tropical profile;(3) A negative Eu anomaly in both profiles was the result of bedrock weathering. A positive Ce anomaly was observed in all layers of profile ND, and only in the upper 100 cm of profile GTC. This indicates that redox conditions along the regolith profile varied considerably with climate.(4) Normalized by chondrite,LREEs accumulated much more than HREEs; REE distribution curves were right-leaning with a V-type Eu anomaly in both profiles.     

Distribution of rare earth elements in marine sediments from the Strait of Sicily (western Mediterranean Sea): evidence of phosphogypsum waste contamination

Concentrations of rare earth elements (REE), Y, Th and Sc were recently determined in marine sediments collected using a box corer along two onshore-offshore transects located in the Strait of Sicily (Mediterranean Sea). The REE + Y were enriched in offshore fine-grained sediments where clay minerals are abundant, whereas the REE + Y contents were lower in onshore coarse-grained sediments with high carbonate fractions. Considering this distribution trend, the onshore sediments in front of the southwestern Sicilian coast represent an anomaly with high REE + Y concentrations (mean value 163.4 μg g⁻¹) associated to high Th concentrations (mean value 7.9 μg g⁻¹). Plot of shale-normalized REE + Y data of these coastal sediments showed Middle REE enrichments relative to Light REE and Heavy REE, manifested by a convexity around Sm-Gd-Eu elements. These anomalies in the fractionation patterns of the coastal sediments were attributed to phosphogypsum-contaminated effluents from an industrial plant, located in the southern Sicilian coast.     

Geochemistry of rare earth elements in the mid-late Quaternary sediments of the western Philippine Sea and their paleoenvironmental significance

Based on a δ18O chronology,rare earth elements(REE) and other typical elements in sediments from core MD06-3047 in the western Philippine Sea were analyzed to constrain the provenances of the sediments and investigate quantitative changes in the Asian eolian input to the study area over the last 700 ka.Among the competing processes that might affect REE compositions,sediment provenance is the most important one.Provenance analysis suggests that the study sediments have two provenance end-members;local volcanic sources are dominant,and eolian dust from the Asian continent has a smaller contribution.During glacial periods,eolian input to the western Philippine Sea was enhanced.In contrast,material supply from local volcanics increased during interglacial periods.Changes in eolian input to the study area were probably related to the strength of the East Asian winter monsoon(EAWM) as well as aridity in the Asian continent on an orbital time scale,and were partly influenced by local control factors on shorter time scales.Therefore,we propose that the present study expands the application of the REE-based method for quantitatively estimating the eolian component from the mid-latitude northern Pacific to the low-latitude western Pacific.Additionally,the study preliminarily confirms the influence of EAWM-transported eolian material on sedimentation in the western Philippine Sea since 700 ka.     

Minor and trace element distribution in melilite and pyroxene from the Allende meteorite

Melilite and pyroxene were separated from a coarsely crystalline chondrule in the Allende meteorite and analysed by microprobe and spark source mass spectrometer techniques. Elemental abundances in the bulk chondrule are consistent with a mixture of equal amounts of the two minerals, as observed microscopically. The lanthanide distributions are markedly different in the two minerals; relative to chondrite abundances, melilite shows progressive depletion of the lanthanides La-Sm, a positive Eu anomaly, and relatively constant abundances of the heavier lanthanides (Gd-Yb, and Y), whereas pyroxene shows progressive enrichment towards the heavier lanthanides, on which is superimposed a negative Eu anomaly. Both minerals, and the bulk chondrule, show unusual concentrations of the platinum metals, but the crystallographic site or sites of these metals remains to be determined.     

Adsorption experiment of water-soluble rare earth elements in atmospheric depositions and implications for source tracing in South China

The distribution patterns of rare earth elements(REEs) in fine-grained materials in various depositions were often found to be similar to those of the aeolian sediments deposited in the Loess Plateau in North China and the fine-grained materials were suggested to be derived from wind-blown dust.However,increasing evidence indicated that the REEs in the water-soluble portion of atmospheric depositions also displayed similar patterns to those of aeolian sediments.In this study,water-soluble REEs in three atmospheric depositions collected from different climatic zones in China were adsorbed with two adsorbents with distinct adsorption capacity,glass powder,and co-precipitated iron hydroxide.The results showed that the REEs adsorbed by the two adsorbents displayed patterns similar to those of the original atmospheric depositions.The typical characteristics of the REE patterns of atmospheric deposition can be well reproduced in the adsorbed REEs.The higher the REE concentrations in the atmospheric depositions,or the higher adsorption efficiency of the adsorbents,the better reproducibility of the REEs patterns.The results suggest that the REEs of the fine-grained materials in various sediments,which have a high adsorption capacity,especially those deposited in South China,may come from the water-soluble REEs in atmospheric deposition,and may not be appropriate tracers of wind-blown dust from North China.     

Importance of vertical geochemical processes in controlling the oceanic profiles of dissolved rare earth elements in the northeastern Indian Ocean

Vertical profiles of dissolved rare earth elements (REEs) were obtained in the Bay of Bengal and the Andaman Sea. The REE concentrations at various depths in the Bay of Bengal are the highest in the Indian Ocean. This is attributable ultimately to the large outflow of the Ganges–Brahmaputra and Irrawaddy rivers, but the dissolved REE flux to surface waters alone cannot explain the large and near-constant REE enrichment throughout the entire water column. The underlying fan sediments serve as not a source but a sink for dissolved REE(III)s. Absence of excess ²²⁸Ra in the deep waters suggests that lateral input of dissolved REEs from slope sediments is also small in these regions. Partial (<0.3%) dissolution of detrital particles, which are carried by the rivers and lateral surface currents and subsequently settle through the water column, appears to be a predominant source for the dissolved REEs. Vertical profiles showing an almost linear increase with depth are common features for the light and middle REEs everywhere, but their concentration levels are variable from basin to basin and from element to element. This suggests that their oceanic distributions respond quickly to the variation of particle flux and its REE composition through reversible exchange equilibrium with suspended and sinking particles much like the case for Th. The relative importance of the vertical geochemical processes of reversible scavenging over the horizontal basin-scale ocean circulation with passive regeneration like nutrients decreases systematically from the light to the heavy REEs. Using a model, the mean oceanic residence times of REEs in the Bay of Bengal are estimated to range from 37 years for Ce to 140–1510 years for the strictly trivalent REEs. In the deep water of the Andaman Sea, isolated from the Bay of Bengal by the Andaman–Nicobar Ridge (maximum sill depth of ∼1800 m), the REE concentrations are almost uniform presumably due to rapid vertical mixing. The REE(III) concentrations are similar to that of ∼1250 m depth water in the Bay of Bengal, consistent with other oceanographic properties. However, the REE composition of the deep water appears to be altered slightly by preferential scavenging of the light REE(III) at the bottom boundary of the basin.     

Nuclide analyses of rare earth elements of the Oklo uranium ore samples: a new method to estimate the neutron fluence

Isotopic ratios and abundances of all REE in two Oklo ore samples have been measured. We have succeeded in developing a new method to estimate the neutron fluence, the conversion factor of uranium and the average neutron energy (or temperature) based on Gd and U isotopic ratios. This new calculation is found to be useful in evaluating those parameters for the natural nuclear reactors at Oklo. Comparison is made between the neutron fluence values evaluated by our new method employing Gd isotopes and a previous one [11] employing Sm and Nd isotopes. The relative agreement becomes better with the increase of fluence. A relationship between the abundances of fissiongenic nuclides of La, Ce, Nd, Sm, and Gd and their mass numbers is also presented.     

Behaviour of rare earth elements during hydrothermal alteration at the Buena Esperanza copper-silver deposit, northern Chile

A study of the REE behaviour in alteration zones of the Buena Esperanza subvolcanic CuAg deposit, located in the Coastal Range of northern Chile, reveals that the elements are mobile in the rocks during alteration. The ore-forming process developed in three different stages of alteration-mineralization.

The hydrothermal alteration of the early and middle stages affected basaltic fragments of a breccia pipe. La and Ce were leached from the rock fragments located at the bottom and at the middle part of the breccia pipe and partly redeposited at the top during alteration. Sm, Eu and Tb were released selectively and the heavy REE behaved as relatively immobile elements. Sericite is the most important alteration mineral for fixing the REE during this stage. The incoming fluids had low REE contents.

The late stage of hydrothermal alteration happened simultaneously with the intrusion of a gabbroic volcanic neck, affecting mainly these subvolcanic rocks. REE patterns of samples from the top and bottom of the alteration zone exhibit roughly parallel trends, but are systematically enriched in REE in comparison to unaltered samples. This enrichment seems to be more intensive at the top of the altered area coinciding with the enrichment of Rb, K and Cu in these rocks. Epidote plays the most important role for fixing this hydrothermal input of REE during the latest stage of alteration.     

Multi‐year tracking of sediment sources in a small agricultural watershed using rare earth elements

Rare earth elements (REEs) have been successfully used as a sediment tracer, but the REE technique has never been used for studying sediment sources for a multi‐year period. A nearly four‐year field experiment was conducted on a small agricultural watershed near Coshocton, OH, USA, to assess the applicability of the REE technique for a multi‐year period and to evaluate the relative contributions of sediment sources in the watershed. Tracer depletion and tracer enrichment ratio (ratio of the tracer concentrations in sediment to the concentrations in the soil in the areas of application) were evaluated to examine the applicability and accuracy of the technique. A minimum of 91 per cent of the mass of the applied elements was still available on any individual morphological element at the end of the experimental period. The tracer enrichment ratio varied from 0·4 to 2·3, and it was not significantly related to time. The relative contributions of six morphological elements within the watershed were evaluated as proportions to total sediment yield. The relative contribution of the lower channel was significantly increased as a function of the amount of sediment yield, while that of the lower backslope was significantly decreased. The relative contribution of the lower channel significantly decreased as a function of cumulative sediment yield, while the contributions of the shoulder and the upper backslope significantly increased. Our results showed that the REE technique can be used to track sediment sources for a relatively long period with two limitations or potential sources of error associated with a selective depletion of tracers and a contamination of downslope areas with tagged sediments from upslope areas. Copyright © 2006 John Wiley & Sons, Ltd.     

Bearing of rare earth patterns of apatites from igneous and metamorphic rocks

Twelve apatite samples from igneous and metamorphic rocks from the Black Forest and igneous rocks from the Kaiserstuhl were analysed for their REE content. The ΣREE range from 0.116 to 1.69 wt.%; the lowest values were found in the metamorphic rocks. All apatites from the various parent rocks show a general enrichment of the lighter rare earths over the heavier and their chondrite-normalized rare earth patterns exhibit a more or less pronounced negative Ce anomaly. This Ce depletion is accompanied by relatively low La and Pr values. In addition, the apatites from igneous rocks from the Black Forest show a marked negative Eu anomaly. An explanation is offered for the simultaneous occurrence of a negative Ce and a negative Eu anomaly in one investigated rock system. The negative Ce anomaly is attributed to the occurrence of phases enriched in Ce (e.g., monazite, allanite) which crystallized prior to or simultaneously with apatite. The negative Eu anomaly in these magmatic apatites most probably is caused by discrimination of Eu²⁺ from the apatite lattice. The result of this discrimination is a selective Eu enrichment in the later crystallizing feldspars, plagioclase and orthoclase. At least in this case, the positive Eu anomaly in feldspars is not a reliable indicator of low oxygen fugacity during their crystallization; the Eu depletion of the earlier crystallized apatites is preferable for this purpose.