Cyprus umbers: Chemical precipitates on a Tethyan ocean ridge

Iron-rich mudstones (umbers), directly overlying pillow lavas of the Troodos Massif, Cyprus, are interpreted as precipitates connected with late stages of volcanism on a Cretaceous ocean ridge. Chemical composition of the basal sediments allies them with the basal iron-rich sediments of the East Pacific Rise. Overlying radiolarites and chalks are more comparable to normal pelagic sediments. Sedimentary features and stratigraphic relations suggest rapid deposition of umbers, relative to the overlying sediments.     

Metallogenesis on a Mesozoic passive continental margin,Antalya Complex,southwest Turkey

A variety of Fe, Mn and trace-metal-enriched Mesozoic pelagic sediments are associated with the tectonically emplaced Antalya Complex in southwestern Turkey. Palaeotectonic settings represented within the complex comprise a continental platform, passing laterally through a Mesozoic passive margin into a zone of marginal oceanic crust, formed during the early stages of continental separation. The origins of the metalliferous sediments are elucidated using mineralogical, major, trace element and REE data, and comparisons with oceanic and ophiolite-related sediments.Late Triassic deposition during the initial continental separation was mostly terrigenous, including detrital carbonate derived from adjacent reef complexes. During the Jurassic and Early Cretaceous the passive margin underwent accumulation of fine-grained terrigenous matter and biogenic silica in deep water below the carbonate compensation depth. Argillaceous mudstones deposited during a regional hiatus at the end of the Upper Triassic show unusual Fe and trace metal enrichment, together with a marked positive Ce anomaly, indicative of slow hydrogenous accumulation.The marginal oceanic crustal zone also shows dominantly terrigenous and siliceous biogenic deposition but with the addition of an important hydrothermal component represented by Fe-Mn deposits. These occur within and immediately above the Upper Triassic lavas of the oceanic crust and as intercalations in the overlying Lower Cretaceous radiolarian chert sequence. Most of these sediments show strong Fe-Mn fractionation; several show a negative Ce anomaly implying rapid incorporation of the REEs from seawater.The Upper Triassic Fe-Mn deposits associated with the lavas are relatively trace-element-depleted and record rapid localised precipitation from relatively high-temperature hydrothermal solutions. By contrast, the more manganiferous and trace-element-enriched metalliferous horizons in the Jurassic to Lower Cretaceous chert sequences represent more dilute low-temperature hydrothermal discharge. Regional comparisons suggest that dominantly manganiferous deposits free of sulphides are characteristic of the early formed Mesozoic ocean crust compared with well established spreading axes like the Troodos Massif, Cyprus.     

Metallogenesis along a fossil oceanic fracture zone: Arakapas fault belt,Troodos Massif,Cyprus

The Arakapas fault belt, southern Troodos Massif, which is interpreted as a fossil oceanic fracture zone, contains a sedimentary and volcanic “fill” including basaltic lava breccias, volcaniclastic sandstones, intercalated Fe-rich mudstones, and minor Cu sulphide mineralisation. The volcaniclastic sedimentary rocks were produced by submarine weathering and gravity redeposition of basalt within the transform zone. In contrast, the Fe-mudstones predominantly originated as chemical precipitates from hydrothermal solutions generated by hydrothermal leaching of basalt by seawater. The rare earth elements, and some trace metals, including Co, Ni, Pb, V and Zr, are thought to have been incorporated from seawater into the ferruginous precipitates. Unusually high Fe/Mn ratios of the Fe-mudstones relative to most modern ocean-ridge sediments may reflect deposition in relatively oxygen-depleted waters on the floor of a major bathymetric depression created by the transform faulting; release of acidic thermal waters would have further suppressed Mn precipitation. Contrary to recent suggestions of metallogenesis along oceanic fracture zones, none of the major Cyprus cupriferous sulphide bodies lie along the fossil Arakapas transform zone.     

Melt viscosity, temperature and transport processes, Troodos ophiolite, Cyprus

The lava section in the Troodos ophiolite, Cyprus, is chemically stratified and divided into a shallow lava sequence with low TiO₂ content and a deeper lava sequence with high TiO₂ content. We calculate the viscosity at magmatic temperature based on major element chemistry of lavas in Cyprus Crustal Study Project (CCSP) Holes CY-1 and 1A. We find that typical shallow low-Ti lavas have a magmatic viscosity that is two to three orders of magnitude lower than that of the deeper high-Ti lavas. This implies that, after eruption on-axis, Troodos low-Ti lavas would have been able to flow down the same slope faster and farther than high-Ti lavas. The calculated lava viscosity increases systematically from the lava-sediment interface to the bottom of the composite Hole CY-1/1A. This suggests that an efficient process of lava segregation by viscosity on the upper flanks of the paleo Troodos rise may have been responsible for the chemical stratification in the Troodos lava pile. Calculated magmatic temperature and molar Mg/(Mg+Fe), or Mg#, decrease systematically down-section, while SiO₂ content increases. Correlation of Mg# in the lavas with Mg# in the underlying, lower crustal plutonic rocks sampled by CCSP Hole CY-4 shows that the shallow lavas came from a high-temperature, lower crustal magma reservoir which is now represented by high-Mg# pyroxenite cumulates, while the deeper lavas were erupted from a lower-temperature, mid-crustal reservoir which is now represented by gabbroic cumulates with lower Mg#.     

Ce anomalies in Gough Island lavas — Trace element characteristics of a recycled sediment component

High precision trace element data obtained by inductively coupled plasma mass spectrometry and Sr–Nd isotope analyses are presented for mafic volcanic rocks from Gough Island, South Atlantic. The new data reveal negative Ce anomalies, with Ce/Ce^? values in Gough lavas extending down to ～ 0.92. Ce is only fractionated from other rare earth elements (REE) due to formation of Ce⁴⁺ under oxidizing conditions of near-surface environments while other REE remain trivalent. Ce anomalies in convergent margin magmas have been shown to indicate a contribution of a subducted sediment component. In contrast, Ce anomalies in intra-plate basalts have been attributed to weathering processes, but can be excluded here based on element–element systematics indicating magmatic trends rather than weathering-induced element mobility. Shallow-level contamination by local marine sediments with negative Ce anomaly inherited from seawater can be excluded because Gough lavas with increasingly negative Ce anomalies do not trend towards low Ce/Pb ratios characterizing such sediments. Rather, it is argued that the negative Ce anomalies in Gough Island lavas are consistent with variable amounts of a sediment component in the mantle plume source. Mixtures between estimates of subducting sediment columns with negative Ce anomaly and mantle capable of giving rise to Gough Island magmas without Ce anomalies reproduce the Gough compositional array with the exception of highly fluid-mobile elements. The calculated trace element composition of the deeply recycled sediment in the Gough plume source is depleted in fluid-mobile elements such as Ba and Pb relative to the composition of some present-day subducting sediments. This loss is attributed to the dehydration or flushing of sediment in the subduction factory, consistent with constraints from arc magmas.     

Bay of Islands ophiolite suite,Newfoundland: Petrologic and geochemical characteristics with emphasis on rare earth element geochemistry

Characteristic geochemical features of the ophiolite suite from the Bay of Islands Complex have been determined by major and trace element analyses of 13 rocks. Based on elements, such as rare earth elements (REE), whose abundances are relatively immobile during alteration and metamorphism, we find that (1) the pillow lavas and diabases are relatively depleted in light REE similar to most tholeiites occurring along spreading oceanic ridges, in back-arc basins and comprising the early phases of volcanism in island arcs; (2) the gabbros, composed of cumulate plagioclase and olivine with poikilitic clinopyroxene, have REE contents consistent with formation as cumulates precipitated from magmas represented by the overlying pillow lavas and diabases; (3) as in most harzburgites from ophiolites, the Bay of Islands harzburgite and dunite have relative REE abundances inconsistent with a genetic relationship to the overlying basic rocks — this inconsistency may be primary or it may result from late-stage alteration, contamination and/or metamorphism; (4) some Bay of Islands lherzolites have major and trace element abundances expected in the mantle source of the overlying basic rocks. Overall, the geochemical features of this Bay of Islands ophiolite suite are similar to those from Troodos and Vourinos, but these data are not sufficient to distinguish between different tectonic environments such as deep ocean ridge, small ocean basin or young island arc.     

Origin of the troodos and other ophiolites: A reply to hynes

Geologic and tectonic evidence on the origin of the Troodos ophiolitic complex is ambiguous, being compatible with its creation in an island arc or a continent as well as in a mid-oceanic ridge. However, there is decisive petrologic and chemical evidence against its origin in a mid-oceanic ridge (and in a marginal sea). A large proportion (about half) of volcanic rocks in the sheeted complex and lower pillow lavas of Troodos have SiO₂ > 52.5% and FeO*/MgO > 2.0 in contrast to mid-oceanic ridge volcanics which are almost entirely basic (SiO₂ < 52.5%) with FeO*/MgO < 2.0. (FeO* means total iron as FeO.) A considerable proportion of volcanic rocks in Troodos belong to the calc-alkalic series. These facts indicate that the Troodos massif was formed probably in an island arc or a continental region.In order to rebut the above chemical evidence, Hynes resorts to an assumption of thorough compositional change of the Troodos volcanic rocks by metasomatism. However, this assumption is not plausible.     

Using <Emphasis Type="Italic">in situ</Emphasis> REE analysis to study the origin and diagenesis of dolomite of Lower Paleozoic,Tarim Basin

In situ REE concentrations of various dolomites from Tarim Basin were obtained by LA-ICP-MS analysis, and the data were normalized to standard seawater (Seawater Normalized=SWN). Most of the samples have a ΣREE range of less than 20 ppm. All samples show similar REE_SWN distributions with heavy REE depletion, and positive Ce anomaly, which indicates that they have the same dolomitization fluids (seawater). According to the origin and diagenetic process of dolomite, two types of dolomite are determined and described as follows: 1) syndepositional dolomite, with the highest REE concentrations (more than 20 ppm), the cores of which are more enriched in REE compared with their cortexes, indicating that they underwent the dolomitization of calcareous sediments by hypersaline and subsequent diagenesis decreased the REE content of the cortex because of the low REE concentration of the diagenetic fluids; 2) diagenetic dolomite, which can be subdivided into four groups. (1) burial dolomite which has higher REE concentrations than limestone, but lower than syndepositional dolomite. This shows that pore fluids with high salinity dolomitized the pre-existing limestone; (2) void filling dolomite which has the similar REE patterns with the matrix dolomite. In addition, the Eu anomaly is not obvious, suggesting that the dolomitization fluids originated from the diagenetic fluids; (3) recrystallized dolomite, whose REE concentration was obviously decreased, indicating that the REE concentration was decreased during the recrystallization processes; and (4) hydrothermal altered void-filling dolomite, which has the lowest REE concentration, but obvious positive Eu anomaly, reflecting its hydrothermal activity related origin. Thus, the diverse REE signatures, which were recorded in different dolomites, retain the information of their formation conditions and subsequent diagenetic processes. In situ REE analysis of dolomite is an effective probe into the origin and diagenetic process of dolomite. Supported by National Basic Research Program of China (Grant No. 2005CB422103)     

87Sr enrichment of ophiolitic sulphide deposits in Cyprus confirms ore formation by circulating seawater

The hypothesis that seawater was the source of the hydrothermal fluid which formed the Upper Cretaceous ophiolitic cupriferous pyrite ore desposits of the Troodos Massif (Cyprus) has been tested by analysing the strontium isotopic composition of thirteen mineralized samples from four mines. Initial⁸⁷Sr/⁸⁶Sr ratios range from 0.7052 ± 0.0001 to 0.7075 ± 0.0002, the latter value being indistinguishable from that of Upper Cretaceous seawater at 0.7076 ± 0.0006 (2σ). Hence, the mineralized metabasalt samples have been contaminated with⁸⁷Sr, relative to initial magmatic strontium isotope ratios of the Troodos ophiolitic complex (0.70338 ± 0.00010 to 0.70365 ± 0.00005).Since seawater was the only source of strontium available during formation of the Troodos Complex which was isotopically relatively enriched in⁸⁷Sr, the data confirm that seawater was the source of the hydrothermal oreforming fluid.     

Characterisation of early Archaean chemical sediments by trace element signatures

Rare earth element (REE) plus yttrium (Y) patterns of modern seawater have characteristic features that can be used as chemical fingerprints. Reliable proxies for marine REE+Y chemistry have been demonstrated from a large geological time span, including Archaean banded iron formation (BIF), stromatolitic limestone, Phanerozoic reef carbonate and Holocene microbialite.Here we present new REE+Y data for two distinct suites of early Archaean (ca. 3.7-3.8 Ga) metamorphosed rocks from southern West Greenland, whose interrelationships, if any, have been much debated in recent literature. The first suite comprises magnetite-quartz BIF, magnetite-carbonate BIF and banded magnetite-rich quartz rock, mostly from the Isua Greenstone Belt (IGB). The REE+Y patterns, particularly diagnostic anomalies (Ce/Ce*, Pr/Pr*), are closely related to those of published seawater proxies. The second suite includes banded quartz-pyroxene-amphibole±garnet rocks with minor magnetite from the so-called Akilia Association enclaves (in early Archaean granitoid gneisses) of the coastal region, some 150 km southwest of the IGB. Rocks of this type from one much publicised and highly debated locality (the island of Akilia) have been identified by some workers [Nature 384 (1996) 55; Geochim. Cosmochim. Acta 61 (1997) 2475] as BIF-facies, and their ¹³C-depleted signature in trace graphite interpreted as a proxy for earliest life on Earth. However, REE+Y patterns of the Akilia Association suite (except for one probably genuine magnetite-rich BIF from Ugpik) are inconsistent with a seawater origin. We agree with published geological and geochemical (including REE) work [Science 296 (2002) 1448] that most of the analysed Akilia rocks are not chemical sediments, and that C-isotopes in such rocks therefore cannot be used as biological proxies.Application of the REE+Y discriminant for the above two rock suites has been facilitated in this study by the use of MC-ICP technique which yields a more complete and precise REE+Y spectrum than was available in many previous studies.     

The Pb isotopic composition of Jurassic cherts overlying ophiolites in the North Apennines,Italy

In the Mesozoic eugeosynclinal sequences of the Italian North Apennines, ophiolitic rocks are commonly stratigraphically overlain by thick bedded chert sequences of Late Jurassic age. The isotopic composition of Pb contained in upper basalts, lower ferruginous (and in places manganiferous) cherts, middle cherts and upper cherts indicates that simple mixing occurred in the sediments between basalt-derived Pb, and more radiogenic Pb provided by fine-grained terrigenous detritus, radiolarian silica and possibly seawater.The most ferruginous cherts are those nearest the ophiolitic basement, which is interpreted as ocean crust formed early in the opening of the Apennine ocean. Hematite content, considered to represent original Fe hydroxy-oxide chemical precipitate in the sediment, decreases upwards in a general way to very low values in the upper cherts. The most ferruginous cherts also contain the highest volcanogenic Pb component and total Pb, whereas higher cherts contain mainly terrestrially-derived Pb. These relations indicate a volcanic-hydrothermal origin for a significant portion of the Pb in the basal to middle parts of the chert formation, and suggest a similar origin for the hematitic Fe. The vertical distribution of hematite and volcanogenic Pb suggests that some initial Fe precipitates, carrying such Pb, had a widespread lateral dispersal after formation at an active ridge.     

An “off-axis” alkali volcanic suite associated with the Bay of Islands ophiolites,Newfoundland

The Skinner Cove volcanic rocks, the lowermost of a sequence of thrust slices associated with the Bay of Islands ophiolites of western Newfoundland, make up a continuous alkaline differentiation sequence from pillowed ankaramites to trachytes. They are interpreted as having formed off the axis of the mid-ocean ridge on which the main ophiolitic rocks were formed, in a manner comparable to the Upper Pillow lavas of the Troodos Massif, Cyprus, and the alkaline rocks dredged near the flanks of modern mid-ocean ridges.     

Fe-rich deposits associated with Ordovician basalts in the Southern Uplands of Scotland: Possible lower Palaeozoic equivalents of modern active ridge sediments

Ferruginous mudstones and cherts occur in association with Ordovician basalts at the base of the pelagic sequence in the Southern Uplands of Scotland, an area which has recently been interpreted as a Lower Palaeozoic accretionary trench/fore-arc complex. Intimate contacts between the Fe-rich deposits and the basalts indicate contemporaneity between ocean-floor volcanism and metalliferous mud accumulation. This, together with a Ce-depleted REE analysis from a supra-basaltic sample, and impoverishment of the sediments in Al and Ti relative to normal pelagic clays, suggests a hydrothermal-exhalative origin for the deposits, analogous to that of metalliferous sediments from modern ocean basins and Mesozoic ophiolites.     

Rare earth elements in the pore waters of reducing nearshore sediments

The REE are mobile during early diagenesis in reducing nearshore sediments of Buzzards Bay leading to greatly enhanced concentrations in pore waters, e.g. 815 pmol kg⁻¹ Nd and 1910 pmol kg⁻¹ Ce within 30 cm of the sediment-seawater interface, about 10–50 times local seawater values. Two principal diagenetic reactions have been identified. Preferential Ce enrichment (positive Ce anomalies) and preferential heavy REE enrichment (light REE removal) in the pore waters is associated with redox cycling of Fe and Mn within the upper few centimeters of the sediment. Release of REE, without fractionation, from sediments and addition to pore waters occurs deeper within the sediment column. The impact on the bulk sediment chemistry is undetectable but the porewater gradients imply that there are significant dissolved REE fluxes, both internal to the sediment system and across the sediment-seawater interface.     

Lithium isotope variations in Tonga–Kermadec arc–Lau back‐arc lavas and Deep Sea Drilling Project (DSDP) Site 204 sediments

Lithium isotopes have been identified as a promising tracer of subducted materials in arc lavas due to the observable variations in related reservoirs such as subducting sediments and altered oceanic crust. The Tonga–Kermadec arc–Lau back‐arc provides an end‐member of subduction zones with the coldest thermal structure on Earth. Reported here are Li isotope data for 14 lavas from the arc front and 7 back‐arc lavas as well as 12 pelagic and volcaniclastic sediments along a profile through the sedimentary sequence at DSDP Site 204. The arc and back‐arc lavas range from basalts to dacites in composition with SiO₂ = 48.3–65.3 wt% over which Li concentrations increase from 2 ppm to 16 ppm. Li/Y ratios range from 0.08 to 0.77 and from 0.24 to 0.65 in the arc and back‐arc lavas, respectively. The majority of the lavas have δ⁷Li that ranges from 2.5 ‰ to 5.0 ‰ with an average of (3.6 ±0.7) ‰, similar to that reported from other arcs and there is no distinction between the arc front and back‐arc lavas. The pelagic sediments have variable Li concentrations (33–133 ppm) and δ⁷Li that ranges from 1.2 ‰ to 10.2 ‰ while the volcaniclastic sediments have an even greater range of Li concentrations (3.6–165 ppm) and generally higher δ⁷Li values (8–14 ‰). However, δ⁷Li in the lavas does not correlate with commonly used trace element ratio or isotope signatures indicative of slab‐derived fluids or the sediments. This is probably because the range of δ⁷Li in the lavas and sediments overlap. Calculated sediment mass‐balance models require significantly more sediment than previous estimates based on Th–Nd–Be isotopes. This may indicate that a sizeable proportion of the total Li budget in the lavas is provided by Li‐enriched fluids from the subducting sediments and/or altered oceanic crust.     

The rare earth element compositions of the Changjiang (Yangtze) and Huanghe (Yellow) river sediments

Thirty-four samples from the Changjiang and Huanghe were analyzed to characterize their rare earth element (REE) compositions. Although REE concentrations in the Changjiang sediments are higher than those of the Huanghe sediments, the former are less variable. Bulk samples and acid-leachable fractions have convex REE patterns and middle REE enrichments relative to upper continental crust, whereas flat patterns are present in the residual fractions. Source rock composition is the primary control on REE composition, and weathering processes play a minor role. Grain size exerts some influence on REE composition, as demonstrated by the higher REE contents of clay minerals in sediments from both rivers. Heavy minerals contribute about 10-20% of the total REE in the sediments. Apatite is rare in the river sediments, and contributes less than 2% of the REE content, but other heavy minerals such as sphene, allanite and zircon are important reservoirs of residual REE fractions. The Fe-Mn oxides phase accounts for about 14% of bulk REE content in the Changjiang sediments, which could be one of the more important factors controlling REE fractionation in the leachable fraction.     

Enrichment of rare earth elements as environmental tracers of contamination by acid mine drainage in salt marshes: A new perspective

Rare earth elements (REE) were analyzed in surface sediments from the Guadiana Estuary (SW Iberian Pyrite Belt). NASC (North American Shale Composite) normalized REE patterns show clearly convex curvatures in middle-REE (MREE) with respect to light- and heavy-REE, indicating acid-mixing processes between fluvial waters affected by acid mine drainage (AMD) and seawater. However, REE distributions in the mouth (closer to the coastal area) show slightly LREE-enriched and flat patterns, indicating saline-mixing processes typical of the coastal zone. NASC-normalized ratios (La/Gd and La/Yb) do not discriminate between both mixing processes in the estuary. Instead, a new parameter (E(MREE)) has been applied to measure the curvature in the MREE segment. The values of E(MREE)>0 are indicative of acid signatures and their spatial distribution reveal the existence of two decantation zones from flocculation processes related to drought periods and flood events. Studying REE fractionation through the E(MREE) may serve as a good proxy for AMD-pollution in estuarine environments in relation to the traditional methods.     

Impact of adsorbed petroleum hydrocarbons on marine organisms

Adsorptions of south Louisiana crude oil from seawater by clays, non-clay minerals and sediments were conducted in the laboratory. Effect of sediment-adsorbed and water dispersed crude oil on adult oysters were investigated in aquaria. Hydrocarbons in oyster tissues and surrounding water were identified by gas chromatography. Field specimens from an area of a new oil spill and an area five months after an oil spill were also analysed. Evidence of secondary chemical effect of aged oil in sediments on oyster mortality is presented. Oil coated asbestos surfaces severely reduced recruitment of sedentary larval organisms.     

Geochemistry of the Middle to Late Permian limestones from the marginal zone of an isolated platform (Laibin, South China)

Major, trace and rare earth elements were measured in 27 samples of the Middle to Late Permian limestones from the Tieqiao section located on the marginal zone of an isolated platform (Laibin, South China). Shale-normalized REE+Y patterns of all samples show notably negative Ce anomalies (0.21–0.66, average 0.33), slightly positive Gd anomalies (1.08–1.30, average 1.20), and positive Y anomalies with superchondritic Y/Ho ratios (36–91, average 55), which are consistent with those of modern shallow seawater. Their relative LREEs enrichment with higher Nd_SN/Yb_SN ratios (0.58–1.80) than those of modern shallow seawater (0.21–0.50) suggests complicated sources of REEs for all samples. Compared with geochemical features of sediments influenced by terrigenous particles and hydrothermal fluids, it is concluded that ambient shallow seawater was the primary source of REEs in these limestones. Comparing the indicators of REE+Y elements (ΣREE, Nd_SN/Yb_SN, Ce/Ce*, Gd/Gd*, Eu/Eu* and Y/Ho) in limestones with those in bedded cherts from the Tieqiao section, we consider that limestone and bedded chert have similar sources of REE+Y elements: ambient shallow seawater with more or less hydrothermal fluids. In addition, there is a completely negative correlation between CaCO₃ and SiO₂ contents in limestones and bedded cherts. These results imply that precipitation of CaCO₃ was inhibited by that of SiO₂ which was derived mainly from hydrothermal fluid, especially in bedded cherts from the Tieqiao section.     

Origin of the anomalies in light and middle REE in sediments of an estuary affected by phosphogypsum wastes (south-western Spain)

Sc, Y, Th, Cu and rare earth elements (REE) concentrations have been analyzed in 14 samples of surface sediments and in two gravity cores by means of ICP-MS. Mean concentrations of Sc, Y and Th in surface sediments are 6.23, 4.76 and 16.30 ppm, respectively, lower than those present in the Upper Continental Crust (UCC). Cu concentration in these sediments is very high, 1466 ppm, and is caused by inputs from the Odiel and Tinto rivers, affected by acid mine drainage. SigmaREE mean concentration is 106.8 ppm, lower than that observed in other rivers and estuaries. In the cores, Sc, Y and Th concentrations show a significant increase in the intermediate levels, between 10 and 40 cm depth. The same pattern exists with Cu, where concentrations of 4440 ppm can be reached. Vertical evolution patterns for Sc, Y, Cu and heavy REE (HREE) are similar, and contrary to those shown by Th, light REE (LREE) and middle REE (MREE). Plots of North American Shale Composite (NASC)-normalized REE data of surface sediments show a slight depletion in REE concentrations. Most samples present with middle REE enrichment relative to light REE and heavy REE. Conversely, samples of the intermediate levels of the cores show significant enrichment of REE relative to NASC and high values in the (La/Gd)NASC and (La/Yb)NASC ratios. These anomalies in the fractionation patterns caused by enrichments in LREE and MREE concentrations is related to the presence of high concentrations of Th. They were generated by effluents from fertilizer factories between 1968 and 1998 which used phosphorite as source material.