mobility and fractionation of rees during deep weathering of geochemically contrasting granites in a tropical setting malaysia in this study we describe the mobility and fractionation of rees in two deep up to 30 m tropical weathering profiles developed on two granites from the kuala lumpur pluton malaysia sampled at cheras and rawang on the basis of na2o and k2o both are s type granites but rawang has higher cao mgo and feo than cheras and lower sio2 with respect to al saturation rawang is i type and cheras is s type we compared the two profiles in terms of total rees magnitude and changes in ce and eu anomalies ree mobility and lree hree fractionation rawang profiles have higher ree contents display lower mobility for most except the heaviest rees and show higher lree hree fractionation than those from cheras these differences can be linked to differences in primary mineralogy and degree of weathering the latter controlling the type and volume of secondary minerals specifically bowl shaped parent rock normalised patterns in the cheras saprolites appear to be a result of apatite dissolution moreover moderate weathering evident in lower mineralogical indices of alteration mia at cheras has conserved parent rock ree patterns and fractionation factors in the saprolites by contrast more intense weathering observed in rawang profiles has produced abundant kaolinite group minerals that have preferentially retained lree which consequently display high lree hree fractionation this study provides important insights into the factors controlling ree mobility during tropical weathering and its potential as an indicator of weathering intensity

the composition and evolution of the continental crust rare earth element evidence from sedimentary rocks the composition of the present day upper crust inferred from the uniformity of sedimentary rock r e e rare earth element patterns is close to that of granodiorite a revised andesite model is used to obtain total crustal composition the lower crust is the composition remaining assuming that the upper crust one third of the total is derived from intracrustal partial melting the upper crustal r e e pattern has pronounced eu depletion eu eu 0 64 the lower crustal pattern has eu enrichment eu eu 1 17 and the total crust has no eu anomaly relative to chondritic abundances the eu depletion in the upper crust is attributed to retention of eu in plagioclase in the lower crust because plagioclase is not stable below 40 km 10 kbar the anomaly is intracrustal in origin the archaean upper crust has a different r e e pattern to that of the present day upper crust being lower in total r e e and la yb ratios and lacking an eu anomaly these data are used to infer the archaean upper crustal composition which resembles that of the present day total crust except that ni and cr contents are higher the archaean crustal composition can be modelled by a mixture of tholeiites and tonalite trondhjemites the latter have steep light r e e enriched heavy r e e depleted patterns consistent with equilibration with garnet and hence probable mantle derivation there is little reason to suppose that the archaean lower crust was different in composition from the upper crust except locally where partial melting episodes occurred the r e e evidence is consistent with isotopic and geological evidence for a low continental growth rate in the early archaean a massive increase to about 70 of the total crust between about 3000 and 2500 ma b p and a slow increase until the present day the change from archaean to post archaean r e e patterns in the upper crust is not isochronous but is reflected in the sedimentary rock r e e patterns at differing times in different continents on the basis of a model composition for the mantle 36 of the potassium 30 of uranium 15 of lanthanum and 3 of ytterbium are concentrated in the present continental crust this enrichment is related to ionic size and valency differences from common mantle cations e g mg fe pre 3 9 ga b p crusts were obliterated by meteorite bombardment no geochemical evidence exists for primordial anorthositic sialic or mafic crusts

the impact of redox conditions on the rare earth element signature of redoximorphic features in a soil sequence developed from limestone abstract redox processes which are widespread in soils need to be quantified for an improved comprehension of the dynamics of fe and mn oxides and their associated trace elements the classical methodology used to study these redox processes generally relies on the quantification of all mineral species in the various pedological features that can be related to different redox stages however this approach usually encounters the difficulty of precisely quantifying the different forms of poorly crystallised fe and mn oxides in this study we use the signature of rare earth elements rees to visualise and eventually quantify the importance of redox processes in soils our approach relies on that developed by laveuf et al 2008 and the idea that the relative contribution to the mobilisation of rees that is made by the primary minerals reactive to redox conditions depends on the following factors i their initial proportion in the different pedological features that can be related to various redox processes ii their relative mobilisation during the redox process in question and iii their initial ree signatures the catena studied is characterised by two stages of redox conditions the first is related to the formation and subsequent dissolution of fe mn concretions and the second is related to the bleaching of the soil matrix due to morphological degradation in this soil the main minerals reactive to redox conditions are mn oxides ferrihydrite goethite and fluor apatite the results indicate that the primary redox conditions can be characterised by a positive ce anomaly on the ree pattern which has been attributed to a preferential immobilisation of this element due to its association with mn oxides the results also indicate that the secondary redox conditions can be characterised by depletion in medium rees mrees in the ree pattern which has been attributed to a preferential release of these elements during the dissolution of fluor apatite and to a lesser extent of ferrihydrite these results emphasise the potential of ree signatures of the visualisation of the various redox processes that have been active in a soil additionally ree signatures are a proxy of the frequency and intensity of the redox conditions

behaviour of rare earth elements and yttrium in ferromanganese concretions gibbsite spots and the surrounding terra rossa over dolomite during chemical weathering abstract the behaviour of rare earth elements rees and yttrium y during chemical weathering processes has been investigated on a 4 05 m thick terra rossa profile over dolomite on the yunnan guizhou plateau china in this profile ferromanganese concretions and gibbsite spots coexist in the terra rossa solum analyses of rees y zr f s and toc as well as mineralogical studies were conducted on a suite of ferromanganese concretions gibbsite spots terra rossas dolomites and insoluble residues from the underlying dolomite these analyses helped us to understand the mobilization redistribution and fractionation of rees and y during chemical weathering the rees and y are mobilized and redistributed during the terra rossa formation rees except for ce are removed from the upper and middle profiles transferred downwards and then precipitated in the base profile resulting in remarkable enrichment in the terra rossa near the weathering front the significant increase of ph near the weathering front was responsible for ree excluding ce and y enrichment in the base profile y is quite mobile during extreme chemical weathering and most of it was carried away from the profile because of very efficient oxidative fractionation of ce a significant positive ce anomaly in terra rossa was found in the middle of the profile whereas the terra rossa near the weathering front exhibited notably negative ce anomalies moreover the presence of cerianite and its content in the ferromanganese concretions can explain the markedly positive ce anomaly and the variation of ce ce values with depth in profile these ce anomalies are characteristic of the geochemical environment especially the redox condition studies of ree distribution in the ferromanganese concretions gibbsite spots and surrounding terra rossa revealed that significant ree fractionation occurred rees and y were preferentially concentrated in the ferromanganese concretions rather than in the gibbsite spots the water rock interaction resulted in m type tetrad effects in some of the ferromanganese concretions gibbsite spots and terra rossa samples in addition the tetrad effect in terrestrial weathering processes likely played an important role in the fractionation of rees and y such as y ho sm nd and the eu anomaly change

rare earth elements ree and yttrium in stream waters stream sediments and fe mn oxyhydroxides fractionation speciation and controls over ree y patterns in the surface environment we have collected 500 stream waters and associated bed load sediments over an 400 km 2 region of eastern canada and analyzed these samples for fe mn and the rare earth elements ree y in addition to analyzing the stream sediments by total digestion multi acid dissolution with metaborate fusion we also leached the sediments with 0 25 m hydroxylamine hydrochloride in 0 05 m hcl to determine the ree y associated with amorphous fe and mn oxyhydroxide phases we are thus able to partition the ree into dissolved 0 45 lm labile hydroxylamine and detrital sediment fractions to investigate ree fractionation and in particular with respect to the development of ce and eu anomalies in oxygenated surface environments surface waters are typically lree depleted la sm nasc ranges from 0 16 to 5 84 average 0 604 n 410 where the ree are normalized to the north america shale composite have strongly negative ce anomalies ce ce nasc ranges from 0 02 to 1 25 average 0 277 n 354 and commonly have positive eu anomalies eu eu nasc ranges from 0 295 to 1 77 average 0 764 n 84 in contrast the total sediment have flatter ree y patterns relative to nasc la sm nasc ranges from 0 352 to 1 12 average 0 778 n 451 and are slightly middle ree enriched gd yb nasc ranges from 0 55 to 3 75 average 1 42 most total sediments have negative ce and eu anomalies ce ce nasc ranges from 0 097 to 2 12 average 0 799 and eu eu nasc ranges from 0 39 to 1 43 average 0 802 the partial extraction sediments are commonly less lree depleted than the total sediments la sm nasc ranges from 0 24 to 3 31 average 0 901 n 4537 more mree enriched gd yb nasc ranges from 0 765 to 6 28 average 1 97 and ce and eu anomalies negative and positive are more pronounced the partial extraction recovered on average 20 of the fe in the total sediment 80 of the mn and 21 29 of the rees ce 19 and y 32 comparison between rees in water partial extraction and total sediment analyses indicates that rees y in the stream sediments have two primary sources the host lithologies i e mechanical dispersion and hydromorphically transported the labile fraction furthermore eu appears to be more mobile than the other ree whereas ce is preferentially removed from solution and accumulates in the stream sediments in a less labile form than the other rees y despite poor statistical correlations between the rees y and mn in either the total sediment or partial extractions based on apparent distribution coefficients and the ph of the stream waters we suggest that either sediment organic matter and or possibly d mno2 feooh are likely the predominant sinks for ce and to a lesser extent the other ree in the stream sediments

behaviors of rees during pedogenetic processes in the karst areas of southwest china abstract to understand the behavior of rare earth elements rees during pedogenetic processes in karst area sw china we investigated the leaching characteristics in order to better understand the mobility and fractionation of rees in two soil profiles developed on dolomite the two soil profiles namely qingzhen qz and pingba pb were sampled from guizhou province hydrochloric acid leaching method was used and the soil samples from the profiles were compared ree contents decreased from the bottom of the profiles 1360 39 ppm of qz and 2236 61 ppm of pb to the topsoil 247 32 ppm of qz and 168 ppm of pb from the soil samples to leachates la yb n n means chondrite normalized values increased from 3 8 92 to 2 36 25 02 in qz and 6 34 9 06 to 5 28 14 83 in pb and gd yb n increased from 1 01 1 80 to 1 40 2 71 in qz and 1 16 2 03 to 2 07 3 29 in pb these results indicate that the degree of ree fractionation increases with continuous weathering obvious differences in lree hree and ree th ratios between the soil samples and leachates indicated strong weathering and pedogenesis under a simulated acid leaching environment negative and positive cerium ce anomalies were observed in the lower and upper parts respectively of the profiles ce anomalies in the soil samples and leachates may be due to the sensitivity of ce to redox conditions given that the decrease of y ho ratio and the negative correlation with soil ph incipient pedogenetic processes likely play an important role in y ho fractionation on the basis of the characteristics of ree behavior the studied profiles have the characteristics of in situ weathering

ree and other trace elements in a granitic weathering profile from serre southern italy abstract ree v cr ni rb sr y zr and nb behaviour in a granitic weathering profile in southern italy is studied in the saprolites of the considered profile depletion of v cr ni rb sr zr and nb is observed this is quite remarkable for sr and cr whereas ree and y are enriched in the more altered portion of the profile and especially in its m fraction such enrichment is associated with the lree hree fractionation and the positive ce anomaly the former results from an increased solubility of hree in a non acid environment as well as from the removal of the hree rich phases from the residual component the latter is related to the redox chemistry of ce which as ceo 2 is less soluble than the other ree no analogy is observed between the behaviour of ce and fe mn and cr saprolites also exhibit a negative eu anomaly which is mostly inherited from the parental material finally the influence of accessory minerals in the ree distribution of weathering products and in sediments calls for a careful evaluation of preferential settling phenomena of heavy minerals during transportation and deposition processes this is especially true in the parent material sediment relationships

mobilization and redistribution of rees and thorium in a syenitic lateritic profile a mass balance study abstract ree th geochemistry and mineralogy have been studied in a lateritic profile derived from a syenite at akongo in sw cameroon ree and th mass balance calculations for the host rock minerals show that at least 70 of the lree s and 50 of the hrees are contained in allanite apatite titanite and epidote and at least 50 of the th is controlled by the same accessory minerals which represent about 2 wt of the unaltered syenite these accessory phases are destroyed during the first stages of weathering causing most of the rees and th to be rapidly released into the soil comparison of the variation in the zr ti and th content as a function of the apparent density of the different zones of the saprolite shows that th is the least mobile element the presence of secondary thorianite tho2 the etched surface on zircon grains and the presence of ti in secondary cerianite support this geochemical interpretation the concentration of thorium was therefore chosen as invariant relative to the concentration of the other elements especially the rees in mass balance calculations most of the rees are leached in the iron rich upper horizons loose nodular horizon iron crust and top of mottled clay horizon where the groundwater table moves saprolite and bottom of the mottled clay horizon the rees are fractionated and redistributed there is a juxtaposition of leached and accumulation zones with precipitation of lree aluminous hydrated phosphates this study supports the existence of two different cycles for the redistribution of elements in the soil 1 1 as dissolved ions in the saprolite horizon and 2 2 as individual particles in the upper part of the profile

mobility of rare earth elements during weathering of till in northern sweden abstract continuous volume controlled sampling from the surface down to a depth of 130 cm was conducted at two stations on weathered till typic haplocryods all the samples were analysed for major and trace elements including the rare earth elements ree eight thousand seven hundred years of weathering since the glacial ice left the area has resulted in a strong depletion of ree in the e horizon this loss decreases as atomic number increases so that 80 85 of the la and 54 60 of the yb have been lost europium has been lost to a greater degree than have the neighbouring elements possible explanations for the release of ree are weathering of common silicates such as hornblende and epidote and plagioclase in the case of eu weathering of apatite weathering of rare but ree rich minerals such as allanite and monazite and release of ree adsorbed on clay minerals further studies on various size fractions and minerals are needed to quantify the importance of the various possible mechanisms of ree release the release of ree continues within and below the bs1 horizon but the results from one station show that light ree can be enriched in the bs1 horizon this secondary enrichment could be caused by adsorption on secondary oxy hydroxides on clay minerals or on organic material however the net result of the weathering is that all ree have been released to the groundwater

constitutive mass balance relations between chemical composition volume density porosity and strain in metasomatic hydrochemical systems results on weathering and pedogenesis relations characterizing the chemical physical and mechanical changes resulting from metasomatic hydrochemical processes are developed using mass balance models which formally link chemical composition to bulk density mineral density volumetric properties porosity and amount of deformation strain rigorous analysis of aqueous solute transport effects is then made possible in a variety of porous media flow environments including chemical weathering pedogenesis soil formation diagenesis ore deposition and enrichment and metamorphism application of these linear constitutive relations to chemical weathering profiles shows that immobile and locally mobile chemical elements with masses conserved on the scale of soil profiles can be accurately identified from analysis of appropriate data arrays and then used as natural geochemical tracers to infer the nature and extent of hydrochemical weathering processes and volume changes during pedogenesis assumptions commonly made in the past about the supposed immobility of certain elements e g ti and zr become unnecessary quantitative differentiation between the effects of residual and supergene fractionation is then easily made these methods are applied to ni rich laterites developed by weathering of ultramafic rocks showing that during ordinary residual enrichment ni is concentrated by as much as 4 protolith peridotite concentrations this occurs simply by silicate mineral dissolution and removal of chemical elements other than ni e g mg with a corresponding reduction in saprolite density and increase in bulk porosity without significant deformation in contrast laterites with mineable concentrations of ni which are similarly undeformed such as the nickel mountain mine in riddle oregon have experienced in addition to residual enrichment strong supergene enrichment by fractionation of ore elements between a leached zone from which ni is extracted and a complementary enriched zone positioned farther along the direction of ground water flow soil forming processes in podzol chronosequences developed on sandy beach terraces of the mendocino coast of california involved soil column collapse of 60 percent by dissolution of silicate minerals in the albic horizon of al and fe leaching and 70 percent dilation expansion in the overlying organic rich layer by root growth the amount of erosion based upon paleosurface reconstructions using the excess mass of fe al pb ga and cu in the zone of supergene enrichment spodic horizon below the ground water table indicates that subsurface erosion by dissolutional collapse is three times that of surficial erosion finally using published chemical data for ti zr and cr on major bauxite deposits in australia where erosion rates are thought to be low we infer that there may have been major amounts of dissolutional collapse to explain the upwards increase of detrital zircon and rutile in weathering profiles

cerium anomalies in lateritic profiles the ree geochemistry and mineralogy have been studied in four lateritic profiles one derived from a syenite akongo sw cameroon the others being developed on a gneissic basement and located along a soil toposequence goyoum e cameroon there is a fractionation between lree and hree in the lateritic samples during weathering the weathered residual products being enriched in lree from la to eu and depleted in hree from gd to lu sampled waters are enriched in hree in relation to the syenite host rock a positive ce anomaly has been found systematically at the top of the saprolite beneath a zone of iron oxide accumulation in the laterite up to 2000 ppm ce may be present in the akongo profile cerianite ceo2 is present as very fine coatings in non ferruginous clayey domains primary ree bearing accessory minerals are weathered at the bottom of the profile specifically allanite and apatite are transformed into florencite and rhabdophane but these phases have no ce anomaly all the data are interpreted as the result of the following processes 1 1 ree leaching in a reducing environment 2 2 oxidation of ce3 to ce4 in an oxidizing environment 3 3 deposition of cerium as cerianite whereas the other ree remain in solution

rare earth element mineralogy and geochemistry in a laterite profile from madagascar abstract in this study rare earth element ree distribution has been investigated in a weathering profile from central madagascar combination of bulk rock geochemical data elements and isotopes with mineral characterization reveals a remarkable evolution of the ree abundances and ree minerals in the vertical weathering profile in the fresh tonalite bedrock ree y concentrations are typical of granitoids 299 363 ppm and the main ree minerals are allanite and chevkinite in the c horizon saprolite primary ree minerals disappear and rees are transported via fluid to precipitate rhabdophane group minerals in cracks and pores the presence of sulfate ligands produced by sulfide oxidation may be responsible for the ree speciation as suggested by the composition of the secondary ree minerals rhabdophane group minerals contain up to 9 wt so 3 and 7 wt cao indicating a mixture between rhabdophane sensu stricto ree po 4 h 2 o and tristamite ca u fe iii po 4 so 4 2h 2 o due to intense ca leaching rhabdophane disappears and al phosphates alunite jarosite group are found in the soil cerianite ce iv o 2 also precipitates in the b horizon of the soil mass transfer calculations based on immobile ti indicate significant ree leaching in a horizon with preferential leaching of the heavy ree rees accumulate partly in the b horizon the uniform nd isotope compositions and the constant proportion of immobile elements do not reveal external input in the b horizon total ree y reach 2194 ppm with high ce concentrations 1638 ppm 9 ce bedrock compared to other ree 3 4 ree bedrock tetravalent ce state is dominant in the b horizon and requires oxidizing conditions that likely account for the accumulation of redox sensitive elements in b horizon e g mn fe co under oxidizing conditions cerianite precipitation causes a ce fractionation from other trivalent ree in comparison to the ion adsorption clay of southern china preferential heavy ree enrichment was not observed in the weathering profile another remarkable peculiarity of the studied profile is the occurrence of gd 2 so 6 grains the discovery of this new mineral demonstrates that a natural process exists that that can fractionate ree to such an extent to produce a pure gadolinium end member mineral an understanding of such a mechanisms is crucial for the ree geochemistry of low temperature alteration processes as well as for the formation of ree ore deposits or industrial processing

the behaviour of rees in thailand s mae klong estuary suggestions from the y ho ratios and lanthanide tetrad effects abstract the concentrations of rare earth elements and yttrium rey were measured in dissolved phase in suspended particulate matter spm and in sediments in seven sampling stations in the mae klong estuarine system inner thailand gulf in order to study their behaviour and distribution pattern the analysed samples generally show high rare earth element ree content in the dissolved phase with high medium rare earth elements mrees and y enrichments in the shale normalized pattern versus paas these chemical features are interpreted in terms of direct influences of weathering processes of ree rich minerals e g phosphates which abundantly out crop in the mae klong watershed these large mree enrichments also suggest that dissolved sulphate complexes play an important role in the dissolved ree fate close to the marine coastal system the shale normalized rees and y ho ratios additionally indicate a direct rey co precipitation with fe oxyhydroxides along the river path and consequent adsorption as coating onto feooh surfaces the rey behaviour in spm appears strongly influenced by al fe and mn content suggesting that the formation of an authigenic fe mn oxyhydroxides and aluminosilicate particulate leads to rey adsorption and or co precipitation the observed variations in the y ho ratios suggest that different y ho fractionation processes take place in the studied estuarine system strong similarities among chondrite normalized ree patterns in both sediments and granitic rocks out cropping in the surrounding regions suggest a generic relationship between the two groups of materials

when does the lightning attachment process actually begin high speed video and electric field records of 43 first and 7 new ground termination subsequent strokes in negative lightning flashes obtained at the lightning observatory in gainesville florida were examined eighteen 36 of these strokes exhibited faintly luminous formations flfs below the downward leader tip just prior to the return stroke all the 18 flfs were connected to the strike object on the ground with 14 of them being also in contact with the downward leader tip for 11 located events showing flfs in contact with the downward leader tip the flf 2 d length ranged from 51 to 200 m and the time interval between the end of exposure of the flf frame and the return stroke onset ranged from 42 to 106 s we inferred that the flfs mostly consisted of relatively low conductivity streamers based on the following observations and estimates a the rates at which the 11 flfs were replaced by channels capable of guiding return stroke waves ranged from 0 7 106 m s to 2 2 106 m s which is comparable to leader speeds in virgin air in the same records b the overwhelming majority of downward leaders continued stepping while being connected to ground via flfs c the average electric field along flfs is 1 to 2 orders of magnitude higher than expected for hot leader like channels since in all cases the flf determined the strike point we conclude that its inferred initiation up to a few hundreds of microseconds before the return stroke onset signified the beginning of the lightning attachment process

asian monsoon modulation of nonsteady state diagenesis in hemipelagic marine sediments offshore of japan we have identifiedmillennial scale variations inmagneticmineral diagenesis from pacific ocean sediments offshore of japan that we correlate with changes in organic carbon burial that were likely driven by asian monsoon fluctuations the correlation was determined by identifying offsets between the positions of fossil diagenetic fronts and climatically induced variations in organic carbon burial inferred frommagnetic and geochemical analyses episodes of intense monsoon activity and attendant sedimentmagneticmineral diagenesis also appear to correlate with heinrich events which supports the existence of climatic telecommunications between asia and the north atlantic region several lines of evidence support our conclusions 1 fluctuations in down coremagnetic properties and diagenetic pyrite precipitation are approximately coeval 2 localized stratigraphic intervals with relatively strongermagneticmineral dissolution are linked to enhanced sedimentary organic carbon contents that gave rise to nonsteady state diagenesis 3 down core variations in elemental s content provide a proxy for nonsteady state diagenesis that correlate with key records of asianmonsoon variations and 4 relict titanomagnetite that is preserved as inclusions within silicate particles rather than secondary authigenic phases e g greigite dominates the strongly diagenetically altered sediment intervals and are protected against sulfidic dissolution we suggest that such millennial scale environmentalmodulation of nonsteady state diagenesis that creates a temporal diagenetic filter and relict magneticmineral signatures is likely to be common in organic rich hemipelagic sedimentary settingswith rapidly varying depositional conditions ourwork also demonstrates the usefulness of magnetic mineral inclusions for recording important environmentalmagnetic signals

assessing the impact of black shale processes on ree and the u pb isotope system in the southern appalachian basin abstract upper devonian java and huron shales from the southern appalachian basin exhibit evidence of ree redistribution and resetting of the u pb isotopic system at the time of deposition ca 365 ma this alteration to the primary detrital signature of these shales is indicative of black shale diagenetic depositional processes that in effect obscure paleoenvironmental and provenance information that may be recorded the most direct evidence of these black shale processes is the rotated nature of the whole rock ree patterns from this sequence of presumably source related shales the neo formation of ree bearing diagenetic phases such as apatite and possibly carbonate has led to an unusually large range in the whole rock 147 sm 144 nd and the ce ce for this sequence of shales changes to these whole rock ratios will effectively alter the nd model age and create a ce ce that records evidence of diagenetic processes rather than information about the paleooceanographic conditions of the basin simultaneously the sequestration of u at the time of deposition and subsequent fixation in diagenetic phases such as apatite has effectively reset the 238 u 206 pb isotopic system at 340 50 ma overprinting the pb isotopic signature of the source area the trace element and isotopic signatures recorded by the java and huron formation shales from the study area reveal a syn postdepositional history dominated by what can be referred to as black shale processes the diagenetic conditions that develop at and below the sediment water interface during the deposition of organic rich shale are unique and consequently leave behind a unique geochemical fingerprint that can potentially overprint paleoenvironmental and provenance information

solid liquid ree fractionation in the lateritic system of goyoum east cameroon the implication for the present dynamics of the soil covers of the humid tropical regions the ree th weathering geochemistry and mineralogy has been investigated in a lateritic soil cover in relation to the close hydrographical system at goyoum east cameroon the stutied area composed of gneissic hills covered by humid tropical forest belongs to the sanaga river basin and corresponds to a transition vegetation zone between rainforest and savannah a representative soil catena was taken as a reference zone close to the sanaga river the gneissic parent rock soil and groundwater samples have been cut off in pits in the lower part of the catena waters were also sampled both in brooks rich in organic matter and in the sanaga river all the waters were sampled seasonally during the rainy and dry periods the water rock interactions and the exportation of ree and th have been discussed as a function of the evolution of specific ratios considering th as the less mobile element during laterization variation of parent rock pr normalized ratios ln th pr vs depth show that the upper ferruginous horizons are depleted in ree while the basal saprolite presents accumulation zones which are differently located for ce and the other lrees the hrees are also depleted the la accumulations are located near the saprolite gneiss weathering front associated with negative ce anomalies ce ce 0 4 the ce accumulations inducing strong positive ce anomalies ce ce 4 are located in the upper saprolite beneath the ferruginous horizons all along the soil catena the secondary lree bearing minerals which reflect lree fractionation during incipient weathering of the gneiss are hydrous phosphates rhabdophane lreepo4 nh2o and cerianite ceo2 whose precipitation depends on the eh ph changes in the soil profiles on the other hand hree depletion is controlled by the dissolution of xenotime the major hree bearer in the parent gneiss in the 0 45 m filtered acidic groundwater ph 5 5 which have flooded the saprolite for a long residence time th contents are extremely low 0 th 10 ppt while lree contents are high 90 la 450 ppt in these filtered waters th seems to be strongly controlled by minerals i e thorianite which lead to its immobilization in the soil while lree remain in the soluble and or colloidal pools moreover the groundwaters show significant negative ce anomalies throughout the year 0 1 ce ce 0 4 the mobilization of lree except redox active ce results from the dissolution and or the mobilization in colloidal form of the secondary phosphates which may present major negative ce anomalies as indicated by the bulk soil analyses at the saprolite gneiss weathering front therefore the groundwaters have the signature of saprolitic materials we propose that the strong positive ce anomalies of the upper saprolite result from ancient weathering processes these processes would have led to much stronger ce iii ce iv dissolution reprecipitation conditions than those occurring at the present time in the saprolite in the 0 45 m filtered brook acidic blackwaters lree and th contents are high 100 th 400 ppt 400 la 1700 ppt in this organic matter rich environment lree and th are highly mobilized the colloial pool controls half of the whole lree th load the geochemical signature of these waters is independent of the gneissic parent rock and soil lree contents there is no ce anomaly this signature is similar to those of other organic rich rivers draining humid tropical ecosystems in the world in the 0 45 m filtered sanaga waters lree and th contents are lower than in the brooks 15 th 40 ppt 40 la 300 ppt these concentrations are dependent on the time and on the colloidal composition however 90 of these elements are mainly controlled by the suspended pool

ree geochemistry of fine grained sediments from major rivers around the yellow sea abstract to investigate the distribution pattern and controlling factors of rare earth elements rees in riverine sediments river mouth sediments were collected at five geographically different rivers around the yellow sea two 1 m hcl leached and residual fractions and five step sequential extraction schemes the sedex method were applied to size separated sediments

the estuarine geochemistry of rare earth elements and indium in the chao phraya river thailand abstract a new filtration method using a 0 04 m hollow fiber filter was applied to the river estuarine and coastal waters in the chao phraya estuary for geochemical investigation the filtered waters were analyzed for all the lanthanides y and in by using inductively coupled plasma mass spectrometry icpms the dissolved concentrations of rare earth elements rees are significantly lower than those reported previously for other rivers presumably because of effective removal of river colloids by the ultra filtration the variation of dissolved rees in the estuary is dependent on the season the light rees vary considerably in the low salinity s 3 show almost conservative trends being consistent with some of the previous works europium is strongly enriched in the river and estuarine waters compared to the south china sea waters thus the ree source of the chao phraya river must be fractionated and modified in entering to the south china sea dissolved in and ce in the high salinity s 20 25 zone of the estuary are lower than those of the offshore waters and therefore the dissolved flux of the chao phraya river cannot account for the higher concentrations of dissolved in and ce in the surface waters of the south china sea the negative ce anomaly is progressively developed with increasing salinity being consistent with continued oxidation of ce iii to ce iv in the estuary fractionation of the light to heavy rees seems to take place whereas the y ho fractionation is unclear in the estuarine mixing zone

differentiated hydrothermal and meteoric alterations of the lueshe carbonatite complex democratic republic of congo identified by a ree study combined with a sequential acid leaching experiment the behavior of rare earth elements ree during hydrothermal alteration and progressive weathering has been studied by acid leaching experiments on minerals and whole rock samples of the lueshe carbonatite complex ne of democratic republic of congo the fresh and hydrothermally altered samples were successively leached with acetic acid hac 1 n and hydrochloric acid hcl 1 n an additional leaching step with nitric acid hno3 1 n was applied on meteoric weathered material after this sequential extraction procedure the residues were dissolved in a fluorhydric nitric solution hf hno3 the lueshe carbonatite complex contains a suite of ree carriers identified as ca bearing minerals including carbonates apatite and pyrochlore as primary minerals that are accompanied by hydrothermal ancylite ce parisite ce synchysite ce and monazite ce the hydrothermal alteration induces an enrichment in the light ree but the authigenic minerals except monazite do not in fact play an important part in the pre lateritic ree stock because of their low amounts during the early stage of weathering the residual minerals retain the bulk of the ree the distribution being only slightly modified during intense weathering the leaching experiments indicate that the ree are redistributed among secondary ree phosphate minerals and bonded to fe hydroxides in the lateritic profile

rare earth elements in suspended particulate material of north atlantic surface waters on a transect between the northwest and northeast atlantic ocean 30 n 60 w to 60 n 2 w june july 1996 suspended particulate material spm in 24 near surface water samples 4 to 22 m3 with spm concentrations between 32 and 447 mg m 3 has been collected using a large volume centrifuge system the samples have been analyzed for y the rare earth elements rees and major inorganic and biogenic carrier phases such as al clay fe mn poc opal and caco3 the concentration pattern of particulate rees roughly follows the spm distribution average values pmol l 1 are for y 2 36 la 0 84 ce 0 82 pr 0 17 nd 0 67 sm 0 14 eu 0 030 gd 0 15 tb 0 024 dy 0 16 ho 0 036 er 0 12 tm 0 018 yb 0 13 and lu 0 022 extensive variability in negative ce anomalies have been observed along our transect with the strongest anomalies in areas of high poc abundances significant fractionation between lrees and hrees has been found for all major particulate phases these data are characterized by 1 strong relationships p 0 001 exist between concentrations of nonlithogenic excess hrees tb lu and poc values indicating that complexation with organic ligands promotes temporary hree enrichment on solid surfaces 2 the behavior of particulate fe and mn fractions is decoupled while fe and al clay phases exhibit preferential uptake of lrees la gd with crust like signatures particulate excess mn is strongly coupled to the poc phase r2 0 82 and to excess hrees we therefore suggest that the enrichment of rees in mn particles occurs via the formation of biogenic material probably mediated by bacteria and is not caused by adsorption onto mn oxihydroxides another result is that y in all studied relationships with the major inorganic and biogenic phases is very similar to ho implying their chemistries in surface ocean particulates are dominated by similar valency and ionic radii the y ho ratios average of 69 7 mol mol 1 have been very constant along our transect and lie in between the ratios for seawater 100 and continental crust 50

trace element mobility during spheroidal weathering of basalts and andesites in hawaii and guatemala abstract trace element mobility has been studied in spheroidally weathered corestone shell complexes developed on late tertiary and quaternary volcanic rocks the parent materials are basalts and andesites related to 1 a subduction zone tecuamburro and moyuta volcanoes guatemala and 2 a hot spot hawaiian islands of oahu maui and hawai i the initial major element compositions are largely preserved in the corestones each corestone sample shows major element abundances characteristic of the different magmatic processes through which the lavas were generated however the changes in trace element compositions due to weathering show similar patterns in the corestone shell complexes independent of the tectonic setting and age element mobility within the different corestone shell complex was determined using an isovolumetric reference frame in this method bulk density is chosen as an independent measure of the extent of weathering based on volumetric concentrations the notion of element immobility cannot be applied to all the corestone shell complexes elements commonly assumed to be immobile e g zr ti and al vary in volumetric concentration for some corestone shell complex despite petrographic evidence of only minor weathering two corestones oahu and tecuamburro have become enriched in ree 3 relative to other lava flows from the same volcanoes and display negative ce anomalies the exfoliated shells from these complexes tend to have lower concentrations of ree 3 and have positive ce anomalies the fractionation of ce from the other rare earth elements ree is inferred to be a manifestation of changes in the valence state of ce from trivalent to tetravalent under oxidizing conditions in settings where the development of corestone shell complex is advanced an acidic solution can mobilize trivalent ree leach them out of more extensively weathered materials and transport them to less acidic portions of the regolith undergoing incipient weathering the precipitation of the ree 3 in the rinds and centers of the corestones are likely due to increases of the ph of the weathering solution systematic weathering induced ree behavior enrichment of most ree with lesser ce enrichment resulting in a negative ce anomaly can be discerned even in corestone samples that exhibit major element abundances and petrographic features otherwise similar to unweathered basalts and andesites

rare earth elements as reactive tracers of biogeochemical weathering in forested rhyolitic terrain article rareearthelements rees were evaluatedaspotentialtracers of biogeochemicalweathering atpedon hillslope and catchment scales in the jemez river basin critical zone observatory jrb czo valles caldera national pre serve nm usa we investigated time series of ree patterns in precipitation soil pore water groundwater and stream water and related these data to ree composition of soil rock and atmospheric dust ree signatures in stream waters are dynamic reflecting processes that occur along hydrologic flowpaths during transport to the stream including organic matter complexation primary and secondary mineral weathering water soil bedrock interaction and atmospheric deposition strong compositional similarities for the ree between soil waters and stream waters during the initial snowmelt are consistent with shallow subsurface flows to streams most bio

rare earth element mobility during conversion of nepheline syenite into lateritic bauxite at passa quatro minais gerais brazil abstract in a lateritic bauxite formed by weathering of nepheline syenite at passa quatro minas gerais state brazil bauxites on the hill tops directly develop from the syenite bed rock while downslope a kaolinitic layer occurs between bauxite and synetie a petrological investigation was performed on undisturbed weathered rock samples collected from a representative upslope pit the undisturbed weathered rocks were chemically analysed for major trace elements including ree and zr mass balance calculations were applied and the behaviour of the ree in the passa quatro weathering system was established compared to ree reference chondrite and to ree reference parent rock in the lateritic bauxite the results suggest that the first stages of weathering induce a volumetric change of 50 i e collapse with respect to the parent rock and remove ree with a slightly larger loss of the lree except ce compared to the hree in the upper layers where bauxite is more mature a net mass gain in ree is observed relative to the underlying layers this gain takes place during the reduction of the upper layer during the downward progression of the weathering front very significant ree losses occurs during the bauxitization processes throughout the upslope profile in addition the downslope kaolinitic system is demonstrated to be depleted in ree in the same proportions as the upslope bauxite we proposed that the ree exported in solution from the whole weathering mantle have enriched neighbouring watershed sediments

yttrium the immobility mobility transition during basaltic weathering trace elements have been used as provenance indicators of igneous rocks for many years even though the conditions under which they remain immobile during subaerial weathering have not been thoroughly defined we have used a novel geochemical and quantitative mineralogical data set of variably weathered basaltic rocks from northeast ireland to investigate the immobility of various elements titanium and niobium seem to be the most immobile of all elements relative to these elements zirconium is predominantly depleted but is also locally enriched yttrium displays a marked depletion from the early stages of weathering during the growth of clay minerals yttrium zirconium and their ratios with other elements should thus be used with caution as provenance indicators unless the rocks show no detectable signs of weathering

rare earth element patterns in archean high grade metasediments and their tectonic significance abstract metasediments from two contrasting types of archean high grade terrains are interpreted as being derived from distinct tectonic settings the kapuskasing structural zone canada represents the deep roots of a typical greenstone belt whereas the limpopo province southern africa and western gneiss terrain australia mainly consist of shelf sediments deposited on a granitic basement and then buried to the depths required for granulite fades metamorphism upper amphibolite to granulite fades paragneisses from the kapuskasing structural zone have ree patterns similar to those of greenstone belt sediments except where partial melting has occurred forming restites with eu enrichment and melts with eu depletion except in this latter instance metamorphism has not affected the primary ree patterns ree patterns in archean upper amphibolite to granulite facies metasediments from the central limpopo province and western gneiss terrain show wide differences ranging from patterns which resemble those in post archean terrigenous sediments to typical archean sedimentary rock patterns the diversity in ree patterns for these shallow shelf metasediments is interpreted as resulting from derivation from local provenances samples with post archean patterns displaying eu depletion are interpreted as being derived from k rich granitic plutons which were portions of small stable early archean terrains precursors of the widespread late archean proterozoic episode of major cratonic development

how mineralogy and slope aspect affect ree release and fractionation during shale weathering in the susquehanna shale hills critical zone observatory abstract to understand the factors that control rare earth elements ree release and fractionation during shale weathering we investigate the ree contents in solid bedrock regolith stream sediments and natural waters stream and pore waters from a first order catchment developed entirely on gray shales in central pennsylvania usa up to 65 of the ree relative to parent bedrock is depleted from the weathering profiles in the acidic and organic rich soils due to chemical leaching in addition newly formed fine particles were also lost along with the down slope movement of soil waters weathering profiles on the south facing slope show less depletion of ree than those on the north facing slope 33 vs 45 on average we hypothesize that the different degrees of ree depletion on the two transects reflect a history of different chemical weathering rates and possible different surface erosion rates controlled by contrasting slope aspect induced microclimate conditions in addition weathering profiles natural waters and sequential extractions all show a preferential removal of middle ree up to 22 more relative to light ree and heavy ree during shale weathering due to preferential release of mree from rhabdophane furthermore the long term phosphate mineral dissolution rates e g rhabdophane were estimated at 10 15 to 10 14 mol m 2 s 1 under field conditions based on ree depletion profiles strong positive ce anomalies average ce ce n value 1 79 observed in the regolith stream sediments and regolith extractions point to the fractionation and preferential precipitation of ce as compared to other ree due to the generally oxidizing conditions during release transport and redistribution of ree in the surface and subsurface environments positive eu anomalies average eu eu n value 1 30 observed in the natural waters of the catchment are attributed to weathering of plagioclases in the shale bedrock this study highlights the use of ree as natural tracers for low temperature geochemical processes

redistribution and mobilization of titanium zirconium and thorium in an intensely weathered lateritic profile in western australia abstract the mobility of titanium zirconium and thorium elements commonly considered insoluble during supergene weathering is still not well understood especially in intensely weathered regolith thus an intensely weathered lateritic profile jg developed on meta granitoids in jarrahdale western australia was investigated the mobility of ti zr and th has been assessed at both mineral assemblage and profile scales and the mode of occurrence has been investigated through the combined use of geochemical data from bulk regolith particle size fractions and sequential extractions with in situ data determined by electron probe micro analyzer and synchrotron x ray powder diffraction neoformed poorly crystalline phases containing trace to minor amounts of zr ce and th unassociated with silicates or phosphates were identified on the walls of al fe rich pores in the ferruginous duricrust this implies that some mobilization and redistribution of zr and th occurs within a sample scale breakdown of primary thorite and rare earth element rich fluorocarbonates is thought to be the source for zr and th in the neoformed phases rather than zircon thus the mineral hosts of zr ti and th in the parent rock and their relative susceptibility to weathering are the fundamental controls on subsequent mobility during initial weathering trace amounts of th in secondary phases such as rhabdophane and florencite show translocation of th at the mineral scale while strong partitioning of th into gravel rather than matrix reflects redistribution of th at the profile scale the absence of primary sphene from the regolith and the presence of partially dissolved ilmenite and rutile grains in the ferruginous mottled zone suggest mobilization and translocation of ti at a mineral assemblage scale furthermore the fluctuation of ti zr in the ferruginous zone is in contrast to the consistency of zr hf throughout the profile in general within the range of parent meta granitoid this suggests that ti and zr fractionate from each other and partition between gravel and matrix during extreme weathering and advanced lateritization this study demonstrates that ti zr and th are mobile at a variety of scales an important consideration that is often overlooked when calculating element mass flux in intensely weathered regolith