behavior of rare earth elements in a paleoweathering profile on granodiorite in the front range colorado usa abstract a paleoweathering profile on the boulder granodiorite in northern colorado provides an opportunity to trace the behavior of rees from parent rock through a weathering profile into unconformably overlying permian sediments with progressive upward weathering of the granodiorite na2o cao sio2 ta hf co th cr sc cr th zr hf la sc zr y and la th decrease al2o3 and fe2o3t increase and tio2 mgo k2o p2o5 rb zr sc cr co hf nb ta y th u ree ti nb and zr nb increase to maximum values and then either level off or decrease lree enrichment is less in the weathering profile than in the parent granodiorite and although the parent does not have an eu anomaly or only a slight positive anomaly all samples from the weathering profile and overlying sediments have significant negative eu anomalies this observation is especially important in that it shows conclusively that a negative eu anomaly can be produced during chemical weathering of granitoids we suggest these eu anomalies are due to relative enrichment of the other rees and partial loss of eu during the breakdown of plagioclase the boulder weathering profile also has a very minor negative ce anomaly that is within error of a ce anomaly in the parent in the unweathered parent 50 of the ree are contained in sphene and in the case of la also in allanite from 10 20 of the ree are contained in apatite and biotite hornblende and from 7 10 of the hrees are in zircon with exception of eu for which feldspars contribute about 8 negligible amounts of rees occur in the feldspars in weathered samples 75 of the rees are contained in clay minerals the crossover between sphene and clay control of rees occurs over a distance of 1 m near the contact with fresh rock except for their small negative eu anomalies the clay minerals have ree patterns very similar to those of the parent rock isocon plots suggest apparent enrichments of many elements in the boulder weathering profile result from losses of na ca and si during plagioclase weathering in addition variable amounts of sr eu ta nb p and ba were lost during weathering although th u zr y th sc zr hf lu hf and ti zr may have been transferred relatively unchanged from granodiorite parent to the bulk weathering profile most other element ratios and ree distributions were significantly changed during weathering this observation implies that caution needs to be exercised when using ree patterns and element ratios to trace sediment provenance the fact that most element ratios and ree distributions also differ between fountain sediments and the bulk weathering profile may be related to one or a combination of four factors listed in order of probable decreasing importance contribution of other sources to the fountain sediments sorting of minerals during sediment deposition remobilization of elements during diagenesis and leaching of elements by water flow through the upper meter of the weathering profile

vertical distribution of trace elements in laterite soil suriname abstract the vertical distribution of 20 elements in a 12 5 m thick laterite profile from suriname south america has been investigated using neutron activation analysis atomic absorption spectrometry and x ray fluorescence the mineralogical composition was quantitatively determined from calculations based on results from x ray diffraction thermal gravimetric methods and from the data obtained for major elements using x ray fluorescence the most characteristic change observed in the mineralogy with depth is the increase in kaolinite relative to gibbsite a considerable fractionation with depth is found for different trace elements the enrichment of the lanthanoids la and ce at 3 4 m below surface and of sm and eu at 10 12 5 m depth demonstrates that the distribution of elements despite the similarity in chemical properties is seriously affected by weathering processes the laterite soil samples were also separated in al and fe rich fractions using naoh these separation experiments demonstrated that the trace elements are mainly associated with the fe rich red mud fraction of the laterite soil

effect of mechanical interaction on the development of strike slip faults with echelon patterns abstract the overlapping geometry of echelon strike slip faults is well known we have quantified this observation by measuring the amount of overlap and separation and plotting them against each other for over 120 examples although there is large scatter the data show a linear trend suggesting that the overlap increases proportionally with separation up to a limiting value we have analyzed this conspicuous relationship in terms of fault interaction by using a numerical model based on displacement discontinuity the results show that fault interaction is in fact an important factor in contributing to the overlapping geometry of echelon strike slip faults

chemical processes affecting the mobility of major minor and trace elements during weathering of granitic rocks abstract the behaviour of 38 major and trace elements as well as changes in the mineralogy have been examined in 10 weathering profiles developing on some portuguese granitic rocks element mobilities are calculated from geochemical data normalized with respect to ti in the fresh parent rock chemical elements are divided into two groups immobile and mobile on the basis of their geochemical distribution during weathering elements that are immobile during weathering are zr hf fe al th nb sc and the ree very mobile are ca na p k sr ba rb mg and si mobile elements are derived mainly from leachable minerals such as feldspars micas and apatites whereas immobile elements are either concentrated in resistate phases or strongly adsorbed by secondary minerals the geochemical behaviour of mn cr v fe and ce is very dependent on redox conditions redox transformations of these elements can be used to set limits on the oxidation state of a weathering suite the ree are mobilized or fractionated during late stages of weathering but not during moderate stages of weathering this fractionation is caused by selective leaching of rocks composed of both stable and unstable minerals containing ree

pleistocene paleosol development and paleoenvironmental dynamics in east africa a multiproxy record from the homo bearing aalat pedostratigraphic succession dandiero basin eritrea abstract the climatic changes during the early middle pleistocene transition are a key to understand the ecosystem dynamics that involved the homo erectus ergaster distribution the aalat pedostratigraphic succession represents a continental archive in the african rift valley eritrea where remains of homo around 1 ma were identified high resolution magnetostratigraphy dated this succession between the base of the jaramillo subchron and the lower brunhes chron despite the present arid desert climate the aalat section records a persistence of water driven fluvio lacustrine environments which suggests a major tectonic control on sedimentation although climate changes are clearly overprinted macro and micromorphological physico chemical mineralogical and geochemical features up to now poorly available for pleistocene paleosols in east africa depict a poor to moderate degree of development although calcic and petrocalcic petrogypsic horizons at different stratigraphic heights indicate phases of geomorphic stability the concurrent alternation of these horizons with iron stained layers suggests cyclical changes from dry to wet conditions which fit well with aeolian dust fluxes and marine isotope stages of glacials and interglacials at higher latitudes stable isotope data are consistent with these climatic cycles and suggest a succession of monsoonal and non monsoonal conditions the homo erectus settlement lasted apparently for a short time span because a long high discharge fluvial sedimentation and or an aridity phase at the base of the fluvial facies could have made the area less suitable for human settling and could have hindered preservation of fossils and artifacts

rare earth element and mineralogic changes in holocene soil and stream sediment a case study in the wet mountains colorado u s a size fractions of soil and stream sediment developed on plutonic metamorphic or mixed plutonic metamorphic sources in the wet mountains colorado have been analyzed for ree rare earth elements and mineralogy the clay sized fractions 0 5 m and 0 5 2 m or 2 m have ree contents that are similar to more enriched than the source eu sm ratios that are similar to the source and la lu ratios that are higher than their corresponding source the 0 5 m fractions have lower ree contents than the corresponding 0 5 2 m fraction in every stream sediment for example unweathered san isabel batholith near the sampled stream sediment contains ree 511 712 ppm and eusmratio 0 17 0 19 and lalu cn 9 8 10 3 the corresponding 0 5 and 0 5 2 m fractions of sediment formed from san isabel batholith are enriched in the ree ree 1135 and 2225 ppm respec are slightly lower in eu sm ratios 0 16 and 0 14 respec and are higher in la lu ratios 12 2 and 16 3 respec than the unweathered rocks the silts have lree light ree contents and eu sm ratios very similar to the source due to similar mineralogy but silts have hree heavy ree contents higher than the source due to high zircon for example silt sized fractions in stream sediment draining the san isabel batholith contain ree 808 ppm eusmratio 0 18 and lalu cn 7 4 in contrast the sands contain lower ree contents similar to higher eu sm ratios and lower la lu ratios than the corresponding source due to depletion in heavy minerals concentrated in the ree and containing lower eu sm ratios relative to quartz and feldspar depleted in the ree and containing higher eu sm ratios for example the sand fraction from stream sediment from the san isabel batholith has ree 206 ppm eusmratio 0 17 and lalu cn 5 6 small variations of accessory minerals concentrated in the ree like allanite or sphene may cause drastic variation in ree content in the sand fraction clays and silts derived only from the plutonic rocks have higher ree and similar to lower eu sm ratios than corresponding fractions derived only from migmatites e g ree of silt fractions from migmatites 224 ppm and from plutons 375 808 ppm eu sm ratios from migmatites 0 17 and from plutons 0 11 0 18 the ree content and the eu sm ratio of clays and silts derived from migmatites are much more similar to the average of mcps mid continent platform sediment than corresponding fractions derived from the plutons mcps has ree 192 ppm eusm 0 19 lalu 8 0 the eusm ratio of sands derived from plutons and migmatite are lower to mostly higher than the mcps the ree content of sands from plutons are not necessarily higher than the mcps due to variation in heavy minerals like allanite or sphene concentrated in the ree sediments derived from mixed sources have ree contents in fine fractions that may not necessarily reflect the ree content of the nearest source for example 0 5 2 m and silt fractions developed on the san isabel batholith with a migmatite upstream have the high ree content of the batholith ree in 0 5 2 m fraction 1100 ppm silt 573 ppm while the corresponding 0 5 m fraction has the very low ree content of the migmatites ree 110 ppm these results suggest fine grained material near the source may sample a much larger area than coarser material near the source thus analysis of fine grained sediment associated with coarse grained material near the source may give a much different impression of the source than would determination of the source using classic petrographic examination of the sand or gravels

postdepositional sm nd fractionation in sandstones implications for neodymium isotope stratigraphy abstract sandstone reservoirs from the norwegian continental shelf commonly show varying degrees of postdepositional fractionation of sm nd ratio apparently due to preferential incorporation of sm in the crystal lattice of diagenetic apatite based on data from leaching experiments an apatite mineral separate and petrography it is proposed that fractionation occurred mainly during closed system burial diagenesis as phosphate deposited on the sea floor recrystallized to apatite and incorporated rare earth elements ree from the surrounding rock matrix as a result the sm nd model age parameter in general contains two components of information a the true crustal age of the sediment and b a secondary component of sm nd fractionation which can be either negligible or dominant it is difficult to separate these components and thus correct for component b even in data showing no obvious signs of postdepositional fractionation model ages may be variably disturbed by subordinate amounts of diagenetic alteration however the isotope ratio 143nd 144nd is expected to be relatively resistant to alteration by secondary sm nd fractionation and should therefore be used rather than model age as the principal correlation parameter in stratigraphic studies in this way nd isotope stratigraphy can still be used as a valuable and unique tool for studies of provenance and correlation even in strata showing strong sm nd fractionation effects strongly sm nd fractionated horizons recognized by bulk rock sm nd ratios 0 23 may also be useful for stratigraphic correlation but it is clear that their occurrence reflects special depositional conditions rather than shifts in sediment provenance

ree distribution in the clay fraction of pelites from the southern apennines italy abstract in order to evaluate whether clay minerals or accessory phases control the ree pattern of the only illite is correlated with ree while a smectite rich sample is characterized by the lowest content in ree strong correlations exist between ree and tio2 nb zr and a less significant one with sr no correlations exist between these elements and y r mode factor analysis indicated that three factors account for 87 of the total variance the first factor var 43 2 seems to express mainly the tendency of some resistate minerals to concentrate ree in the fine fraction the second factor var 30 0 may be related to the effect of circulating fluids responsible for dickite genesis the third factor may be linked to the weathering of micaceous phases the ree do not have a significant weight in the second and third factors resistate minerals appear dominant in controlling at least the lree and nb it is proposed that in the studied samples illite likely conveyed ree via the included minerals

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

hydrothermal remobilization of rare earth elements and its effect on nd isotopes in rhyolite and granite abstract although several studies have shown that the sm nd radiometric system is not remobilized during the hydrothermal alteration of felsic rocks it is doubtful that the rare earth element ree mobility noticed under certain hydrothermal conditions always leaves the sm nd systematics unperturbed this contribution describes two cases of such isotopic disturbances of hydrothermalised felsic rocks from two different geological contexts in rhyolites from the esterel southeastern france and in the red granite of porto northwest corsica southeastern france although these two igneous bodies were initially very homogeneous as regards their nd isotopes some samples display very contrasting nd isotopic signatures i e comparatively low initial143nd 144nd ratios that are anomalous from a magmatic point of view moreover these isotopically perturbed rocks are invariably associated with peculiar ree patterns that are also difficult to explain in terms of differentiation or contamination at the magmatic stage it is thus inferred that the sm nd system in these samples was perturbed by hydrothermal alteration in the two examples studied the perturbation of the sm nd radiometric system cannot be solely explained by a modification of thesm nd ratio significantly after the emplacement of the igneous bodies although the net result of the hydrothermal alteration is leaching of the rees from the rocks i e mainly the middle and heavy ree for the granite and the light ree for the rhyolites the isotopic compositions of the samples were modified by a component introduced from a fluid having contrasting143nd 144nd ratios this inference together with structural observations indicates that rees were transported over distances exceeding several tens to hundreds of metres even in the case of the granite studied in this work where mineralised fractures are absent this is far greater than previous estimates and this conclusion is of great importance for environmental and nuclear waste disposal site studies where light ree are often taken as natural analogues for artificial radionuclides

concentration of rare earth elements in the faixa placha tin deposit pedra branca a type granitic massif central brazil and its potential for ion adsorption type ree y mineralization abstract the goias tin province gtp in brazil has great potential for rare earth elements ree deposits associated with a type granites such as the pedra branca massif which contains several sn deposits and ree anomalies hosted in its cupola and fracture greisens the faixa placha is the most important tin deposit in the pedra branca massif and has high ree y concentrations both in the sn ore and parent biotite granite as well as greisenized granites and greisens with the potential to be economically used as a byproduct of tin the values exceed 1000 ppm in light rare earth elements lrees and 500 ppm in heavy rare earth elements hrees y in the parent granite ree concentrations in greisenized granites and greisens are similar to that of the parent granite indicating that the enrichment in ree is due to the presence of ree bearing primary minerals and that greisenization did not affect the original magmatic primary ree content the ree bearing minerals in the parent granite are allanite monazite xenotime thorite apatite and zircon these minerals except zircon are altered to secondary monazite silicates fluorcarbonates and oxyfluorides which are responsible for the concentration of ree in greisenized granites and greisens and the availability of these metals for the clay fraction of saprolites and soils ion exchange analyses in the saprolites and soils of a faixa placha profile show that the extractions in the clay fraction are more enriched in ree y compared to the whole soil extractions with values between 3425 and 36 762 ppm and between 2804 and 21 689 ppm respectively the rees are more enriched in the basal part of the profile especially the lrees these exchangeable ree y concentrations indicate the potential of the faixa placha and nearby areas to constitute an important ree y deposit of the ion adsorption type

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

elemental mobility during the weathering of exposed lower crust the kinzigitic paragneisses from the serre calabria southern italy weathering and transportation studies of the chemical composition of sediments have determined how surface fractionation processes modify the elemental signature due to provenance and tectonic setting of siliciclastic rocks although the bulk of the exposed upper continental crust comprises granitoids metamorphic rocks from the intermediate to lower crust may be in some geological contexts the provenance of siliciclastic sediments a preferential enrichment of the lree relative to the hree is observed in weathered garnet rich kinzigitic paragneisses from the calabrian arc southern italy this fractionation is due mostly to the mineralogical control exerted by monazite which is concentrated in the silt size fraction of the soil however a significant part of hree released during garnet alteration is trapped by secondary minerals in the clay sized fraction of the soil in a manner similar to pb2 and cs cations of some concern in environmental geochemistry in the weathered material monazite is also important in controlling the eu anomaly the negative size of which increases with increasing th addition the eu anomaly in the clay sized fraction of the soil is very similar to that of the fresh rock suggesting that the eu eu index in pelitic sediments deriving from the intermediate to lower crust may be regarded as a reliable indicator of parental affinity other provenance indicators include la th which share the same mineralogical control indicators of contrasting mafic and felsic provenance e g sc th should be used with care

genesis of the guangou karstic bauxite deposit in western henan china abstract the guangou bauxite deposit in western henan china is located in the north china block and to the north of the north qinling orogenic belt the orebody is hosted within the lower member of the carboniferous benxi formation which overlies unconformably upon the ordovician majiagou formation in the lower member of the benxi formation the bauxite orebody with a diaspore illite anatase mineral assemblage is sandwiched between underlying ferric clay illite hematite goethite and overlying top clay kaolinite quartz goethite according to field observations and geochemical evidence including trace and rare earth element ree compositions especially zr hf ratios the ferric clays were weathered from the underlying argillaceous limestones in the majiagou formation during this weathering process trace elements s zn ni cr v sc f ba and be are depleted li rb and b are enriched and zr hf bi ta ga nb and th are relatively immobile rees exhibit evident differentiation with enrichment of la ce pr and nd and depletion of gd tb dy ho er tm yb and lu the bauxite formed in weak reducing slightly basic water conditions according to the geneses of coexisting diaspore and anatase and it was altered during the epigenetic and second exposure periods forming kaolinite and goethite respectively interelemental relationship analyses of the ores suggest that the elemental behaviors of trace elements and rees in the bauxitization process are mainly controlled by the mineral compositions in bauxite ore and chemical properties of the elements for instance zircon rutile and anatase contain zr hf nb ta w and u based on geochemical evidence together with age data and chemical compositions of the detrital minerals both distant igneous rocks in the plate margin and paleozoic carbonates and precambrian rocks inside north china block provide the miscellaneous material for the bauxite ore and the top clay

the coupled release of ree and pb to the soil labile pool with time by weathering of accessory phases wind river mountains wy abstract rare earth element ree distributions and pb isotope compositions were explored in soils varying in age from ca 0 4 to 300 ka developed on moraines in the wind river mountains wyoming soil extracts 0 6 m hcl were used to examine the soil labile pool while the major element distribution in soil profiles was used to determine the extent of weathering at different soil depths the results show that the chondrite normalized ree patterns of the deepest bulk soil within each profile reflects the composition of the moraine till except for the oldest soil up to ca 12 ka the soil extract fraction is enriched in light ree indicating early release of light ree to the soil labile pool while that of the two oldest soils are relatively enriched in heavy ree in the soil extracts the la sm ratio normalized to the deepest soil la d sm d decreases systematically with soil age similarly the eu anomaly in the deepest soil from each profile eu d eu d decreases slightly with soil age in the three young soils however eu d eu d increases with soil age in the older soils the systematic trends of these two ratios indicate the depletion of light ree in young soils and the enrichment of eu and heavy ree in the older soils based on the pb isotope ratios the relative contribution of pb to the soil labile pool via mineral weathering of u or th rich phases was assessed for the different stages of weathering the whole soil profile 208 pb 204 pb ratio was found to decrease with soil age and with la d sm d whereas it increased with the eu d eu d ratio in each horizon pb isotope ratios 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratio generally decrease with soil age in order to overcome possible effects from parent material heterogeneity the amount of radiogenic pb as compared to the whole soil composition was calculated and this was found to decrease systematically with soil age

geochemistry of red residua underlying dolomites in karst terrains of yunnan guizhou plateau ii the mobility of rare earth elements during weathering the aim of this study is to characterize the evolution of the rare earth elements ree in the pingba red residua on karst terrain of yunnan guizhou plateau the in situ weathering and the two stage development of the profile had been inferred from ree criterions the ree were significantly fractionated and ce was less mobilized and separated from the other rees at the highly enriched top of the profile this is consistent with the increase of oxidation degree in the regolith and it is also suggested that the wet dry climate change during chemical weathering caused ce alternative change between enrichment and invariance in the upper regolith chondrite normalized ree distribution patterns for samples from dolomites and the lower regolith are characteristic of mree enrichment and remarkable negative ce anomalies patterns similar to the convex up ree patterns the following processes are interpreted for the patterns in this study 1 the accumulation of mrre rich minerals in dolomite dissolution 2 water rock interaction in the weathering front and 3 more leaching mree from the upper part of the profile the latter two explanations are considered as the dominant process for the formation of the ree patterns samples from the soil horizon exhibit typical ree distribution patterns of the upper crust i e la n yb n 10 and eu eu 0 65 all data indicate that the leaching process is very important for pedogenesis in this region the experiments demonstrating that abnormal enrichment of ree at the upper regolith bedrock interface is caused by a combination of volume change accumulation of ree bearing minerals leaching of ree from the upper regolith and water rock interaction during rock soil alteration processes our results support the conclusion that the weathering profile represents a large continental elemental storage reservoir whereas ree enrichment occurs under favorable conditions in terms of stable tectonics low erosion and rapid weathering over sufficiently long time c 2003 elsevier b v all rights reserved

ree fractionation and ce anomalies in weathered karoo dolerite abstract analyses of samples from a weathering profile on karoo dolerite allow elements to be divided into three groups depending on their behaviour si k na mg ca sr ba and v are mobilized and removed from weathered products fe al ti zr hf zn cu sc co and ni are immobile ree y and to a lesser extent cr are mobile and redistributed within the profile without a net loss of these elements from the profile large positive ce anomalies are developed in oxidized weathered products by preferential leaching of the other ree s negative ce anomalies and ree enrichment is a feature of less altered dolerite

weathering of gneiss in calabria southern italy abstract the effects of weathering in a mediterranean climate on the mineralogy and microfabric of paleozoic gneiss of the sila massif calabria southern italy have been studied field observations show highly weathered rock forms a residual soil micromorphological and mineralogical properties of bedrock and saprolite show that the weathering process is characterized by at least two major stages having two distinct rock microfabrics in the first stage the morphological features of the original rock are preserved and weathering is manifested mainly by microfracturing and large portions of the rock remain unaltered the second stage of weathering involves further development of microcracks and progressive chemical attack on the minerals this latter stage occurs along both compositional and microstructural discontinuities with etch pitting of feldspar and neoformation of clay minerals and ferruginous products replacing feldspar biotite and iron bearing garnet the determination of quantitative petrographic indices provides a measure of the various stages of weathering

rare earth elements in marine sediments and geochemical standards abstract a comparison was made of sediment dissolution methods used for analysis of rare earth elements ree and major elements fe al ti zr p dissolution by hf and lithium metaborate fusion were compared in seven geochemical standards and twenty marine sediments using hf dissolution of shelf and slope sediments this author previously observed that these marine sediments were significantly depleted in heavy ree hree relative to the crustal abundance i e shale this observation plus published ree compositions of river particles lead to the conclusion that the riverine input of particles to the oceans cannot be assumed to have the crustal abundance for ree comparisons of fusion total to hf dissolutions for marine sediments show that the latter method misses between 20 and 100 of the hree i e dy er yb lu and large percentages of zr in contrast fusion and hf dissolution yield similar concentrations for the light la ce nd and middle eu gd ree and other major elements the fusion data show that the marine sediments are more similar in ree composition to shales than previously reported by this author who underestimated the contribution of hf insoluble residues to the concentration of hree the heavy mineral zircon is the most likely cause of this observation zircons known to be enriched in hree were identified by x ray diffraction as a major component of the hf insoluble residues geochemical standards also have a significant but usually smaller fraction of their hree associated with hf insoluble phases these compositional differences have significance with respect to interpreting river inputs oceanic abundances and diagenesis of ree

mineralogical and geochemical evolution of the bidgol bauxite deposit zagros mountain belt iran implications for ore genesis rare earth elements fractionation and parental affinity the present study focuses on the late cretaceous bidgol bauxite deposit in the zagros simply fold belt sw iran the orebody is located in the eroded major nw se trending koh e hosseyn anticline and hosted as discontinuous stratified layers and lenses within the upper member of the cenomanian turonian sarvak formation detailed mineralogical analysis reveals that diaspore hematite goethite anatase clinochlore chamosite and calcite are the major mineral components accompanied by minor amounts of detrital and ree bearing minerals such as rutile zircon and parisite the ore texture suggest that the bauxite material has an authigenic origin but in some parts it has been transported short distances from a primary in situ environment and redeposited in karstic depressions the spheroidal pisolites of the bidgol bauxite formed under conditions of low water activity favouring the formation of large diaspore cores and a single dry to wet climatic fluctuation the mass change calculations relative to the immobile element ti show that elements such as si fe mg k na and sr are leached out of the weathered system al ni zr ga cr and ba are concentrated in the residual system and hf ta co rb cs be and u are relatively immobile during the bauxitisation processes the nb th y v sc sn and ree are relatively immobile in the initial stage of bauxitisation processes in the bauxite ores but were slightly mobile at the later stage of bauxitisation geochemical data reveal progressive enrichment of the ree and intense lree hree fractionation toward the lower parts of the bauxite profile cerium behaves differently from the other rees especially lree and show positive anomalies in the upper horizons that gradually become negative in the deeper parts of the profile the distribution and fractionation of trace elements and rees during the bauxitisation process in the bidgol deposit are mainly controlled by the presence of ree bearing minerals fluctuations in soil solution ph ree ionization potential and the presence of bicarbonates or organic matter geochemical analyses confirm a protolith contribution from the bedrock argillaceous limestone and suggest that the source material for the bidgol bauxite was provided from a siliciclastic material derived from a continental margin the mid turonian uplift led to the formation of karstic topography rubbly breccia and a layer of ferruginous argillaceous debris that was affected by lateritic weathering under humid tropical climate subsequently mobile elements are removed from the profiles while al fe and ti are enriched resulting in the formation of the pristine bauxite materials when the platform subsided into the water again the pristine bauxitic materials were partly converted to bauxite during the exposure of bauxite orebodies on the limbs and crests of anticlines and subsequent eroding and accumulation in the karstic depressions during folding and faulting in oligocene miocene important factors such as intensity of the weathering drainage and floating flow may have improved the qualities of the bauxite ores

ce anomalies in the textural components of upper cretaceous karst bauxites from the apulian carbonate platform southern italy the chemical and mineralogical composition of upper cretaceous apulian karst bauxites southern italy and their textural components i e ooids and matrix has been studied the bulk samples are composed of boehmite hematite anatase and kaolinite the samples collected along a vertical profile show a downward enrichment for the elements rb sr ba ni and cr a similar distribution is observed in deposits bauxitized in situ at the expense of matrix like material collected in the karst zone the ooids consist mainly of hematite with minor boehmite and anatase whereas in the matrix boehmite prevails on hematite kaolinite and anatase in the void fillings in the matrix there is a ca fluorocarbonate having a ce ce of 5 8 the ooids with the exception of ce are enriched in ree and show a higher la yb ch ratio relative to the matrix the matrix exhibits a large positive ce anomaly whereas the ooids have negative ce anomaly the ce fractionation between the textural components can be explained assuming 1 ce oxidation and cerianite precipitation in the uppermost part of the deposits 2 scavenging of ree from ce depleted percolating solutions by the iron oxide inducing both ree enrichment and ce negative anomalies in ooids 3 remobilization of cerium as fluoride complex as a consequence of more acidic conditions in the uppermost part of the deposit and precipitation of ce3 as fluorocarbonate mineral toward the carbonate bedrock barrier at alkaline ph alternatively the cerium remobilization possibly as a carbonate fluoride complex could be due to an eh decrease favoured by a rise of the groundwater level

mobilization and re distribution of major and trace elements during extreme weathering of basalt in hainan island south china major trace and organic elements of a laterite profile developed on neogene basalts in northern hainan island south china were reported in this paper the aim of which was to investigate element mobilization and re distribution during extreme weathering the results indicate that most of the elements have been mobilized and transferred downwards along the profile by aqueous solution organic matter om can significantly improve the transport of insoluble elements among all the elements th is the least mobile as for the general conservative elements during incipient chemical weathering such as fe ti zr hf nb and ta the removals are up to 20 40 in the upper profile however these elements behave as conservatively as th in the lower profile in the middle profile oxic environment occurs accompanied with significant om decomposition the mn and ce transferred downward are readily oxidized into insoluble mn iv and ce iv and precipitate in the oxic front important om decomposition decreases the capacity of transfer of insoluble elements in aqueous solution consequently al significantly precipitates in the oxic front and rees with the exception of ce precipitate largely in the omdepleted layers co and u are also concentrated in the oxic front in association with mn and ce respectively however cr shows a negative correlation with mn because its response to redox condition changes is reversed from that of mn mn oxides hydroxides fe oxides hydroxides and secondary phosphate minerals other than clay minerals are potential hosts for rees except for ce in the profile rees with high concentrations in the profile seem closely associated with mn oxides hydroxides remarkable highly correlated ce and gd anomalies are observed in the profile ce anomalies are caused by ce precipitation in the oxic environment and successive decomposition of organic matter gd anomalies are likely to have resulted from lower stability constants of gd om complexes compared to those of neighboring rees the overall elemental behaviors in this profile suggest that organic matter plays a very important role in the mobilization and re distribution of the elements during extreme weathering

geochemical signature of provenance in sand size material in soils and stream sediments near the tobacco root batholith montana u s a abstract trace element geochemistry of sandstones are being used to determine provenance we have conducted preliminary and limited experiments to determine to what extent daughter sands retain the geochemical signature of parent rocks six sets of first order stream sediments soils from adjacent slopes and a variety of parent rocks were collected from southwestern montana u s a sampling in a low relief area ensured that climate and residence time of soils on slopes could be eliminated as variables sand size fractions of stream sediments and soils and the corresponding parent rocks granodiorite quartz monzonite granite gneiss biotite tonalite gneiss and amphibolite were analyzed for most major elements and selected trace elements petrologic modal analysis of the parent rocks and the 0 25 0 50 mm fraction of each sand was done to monitor major mineralogic control if any on chemical compositions of the samples our data show that the abundances of the si and al in sediments do not discriminate provenance abundances of ca mg fe and ti may broadly distinguish between sands derived from metamorphic and igneous source rocks at least in the area studied differences in abundances of the ba and th and the ratio of la lu between granitic tonalitic and amphibolitic parent rocks are preserved in the daughter sediments that we studied however the size of the eu anomaly in the ree patterns of different daughter sediments is not diagnostic of parent rocks abundances of co and sc distinguish between sediments derived from felsic and mafic rocks a better provenance discrimination is obtained if the ratios la sc th sc la co ba sc and ba co are used petrologic modal data show that mineral contents and chemical compositions of parent rocks are compatible with each other the chemical composition of the sands may be roughly correlated to the petrological modal data but the abundances of some minor and trace elements of sediments cannot be inferred from modal mineralogy this is expected because these elements may concentrate in accessory minerals and or may weather out into aqueous or clay mineral fractions it is also compatible with conclusions of previous studies that some of these elements do not reside in sand size fractions of siliciclastic sediments

weathering profiles in granitoid rocks of the sila massif uplands calabria southern italy new insights into their formation processes and rates abstract in this paper we characterized several weathering profiles developed on granitoid rocks in the sila massif upland calabria southern italy integrating detailed macro and micromorphological observations with physico mechanical field tests and petrographic mineralogical and geochemical analyses we focused our attention on the main weathering and pedogenetic processes trying to understand apparent discrepancies between weathering grade classes based on field description and geomechanical properties and two common weathering indices such as the micropetrographic index ip and the chemical index of alteration cia our results showed that sericite on plagioclase and biotite chloritization that represent inherited features formed during late stage hydrothermal alteration of granitoid rocks may cause an overestimation of the real degree of weathering of primary mineral grains under meteoric conditions especially in lower weathering grade classes moreover the frequent identification of fe mn oxides and clay coatings of illuvial origin rather than or in addition to those formed in situ both at the macro and microscale may also explain an overestimation of the weathering degree with respect to field based classifications finally some apparent inconsistencies between field geomechanical responses and chemical weathering were interpreted as related to physical weathering processes cryoclastism and thermoclastism that lead to rock breakdown even when chemical weathering is not well developed hence our study showed that particular caution is needed for evaluating weathering grades because traditional field and geochemical petrographic tools may be biased by inherited hydrothermal alteration physical weathering and illuvial processes on the basis of chronological constraints to soil formation obtained from a 42 ka old volcanic input mixed to granite parent materials detected in the soil cover of the sila massif upland a first attempt to estimate soil formation rates was achieved for different depths of corresponding weathering profile zones soil formation rates ranged from 0 01 0 07 mm a 1 for a and bw horizons weathering class vi to 0 04 0 36 mm a 1 for the underlying saprolite c and cr layers class v by comparing these results with the corresponding erosion rates available in the literature for the study area that range from

the weathering of basalt and relative mobilities of the major elements at belbex france abstract a basalt and its weathered profile have been analysed for major elements graphical examination shows al fe and ti to have been essentially immobile determining mobility sequences for this deposit is complicated by the long pedogenetic history of the area three different sequences are presented two for different stages of weathering integrated over time and one that reflects the weathering regime of the present day

chemical weathering in subtropical basalt derived laterites a mass balance interpretation misiones ne argentina abstract subtropical laterites are partially found in the argentinian province of misiones covering the jurassic cretaceous serra geral flood basalts known as posadas formation in argentina two hypotheses have been proposed to explain the origin of these laterites the autochthonous theory attributes the origin of these deposits to the chemical weathering of the underlying tholeiitic basalts however during the last decade an allochthonous tropical loess model was proposed several mineralogical geochemical characteristics of a lateritic profile 2 m thick 26 9 58 s 54 35 3 w are analyzed in this paper in order to constrain the nature of weathering processes in this region and the provenance of the lateritic layer the basaltic bedrock at the sampling site exhibits intergranular texture and is mainly composed of clinopyroxene plagioclase and opaque minerals likely titanomagnetite and ilmenite altered glass and apatite were also identified in lower proportions the x ray diffraction of the clay size fraction shows prevailing kaolinite and hematite in the most altered samples complemented by amorphous fe al hydr oxides serra geral basalts normalized spidergrams and mass balance calculations confirmed almost complete losses of all major oxides i e 50 g of material was removed by weathering from each 100 g of the original basalt and depletions of some trace elements e g sc v sr cr ni rb and u in the uppermost and intermediate layers of the lateritic profile reflecting the weathering of feldspars clinopyroxenes volcanic glass and apatite in contrast some elements are enriched in the topmost and intermediate layers due to intrinsic immobility during weathering e g zr hf ta th or adsorption onto clays e g cs rare earth elements rees are depleted in the top layers and enriched in the middle section of the profile the preferential leaching of rees from the uppermost levels during weathering and its accumulation in the middle section can be caused by a ph increase in this level the decomposition of organic matter and the consequent precipitation of rees which exhibit an affinity to form aqueous organic complexes or the presence of fe and mn hydr oxides in the intermediate level weathering intensity was appraised by means of different alteration indices which showed the extreme leaching endured by the basaltic bedrock the index of lateritization iol which ranges between 35 and 55 and the accompanying saf ternary plot sio2 al2o3 fe2o3 indicate an increasing weathering trend towards the profiles top reflecting the modest loss of sio2 relative to al2o3 and fe2o3 during kaolinitization the geochemical approach used to constrain the origin of the lateritic mantle that partially covers misiones province clearly relates the analyzed laterites to the underlying tholeiitic basalts supporting the autochthonous origin theory

influence of phosphate on mobility and adsorption of rees during weathering of granites in thailand abstract the permo jurassic north thai nt granites and the late cretaceous to paleogene western province wp granites in thailand are contrasting in terms of tectonic settings and chemical compositions the nt granites which are dominated by s type features are characterized by lower sio2 contents and higher p2o5 contents than the wp granites in this study in order to compare the mobility and adsorption of rare earth elements rees during weathering of the two granite suites geochemical analyses were conducted on the granite and weathered granites the weathered wp granites show wider ranges of rees y rey contents percentages of ion exchangeable rey and ce anomalies than the weathered nt granites these results indicate that rees were less mobile during weathering of the nt granites than those of the wp granites the low mobility of rees can be explained by the occurrences of residual monazite and secondary ree phosphates which immobilize rees during weathering therefore in the weathered nt granites rees are mostly contained in the phosphate minerals in contrast the weathered wp granites are dominated by ion exchangeable rees adsorbed rees which are likely to exist on the surface of clays previous studies and our study results suggest that the ion exchangeable rees in the weathered granites were probably sourced from weatherable allanite titanite apatite and or ree fluorocarbonate and rarely from monazite and zircon which are resistant to weathering the weathered granites of low phosphate contents potentially show high percentages of ion exchangeable rey although they can be influenced by the degree of hydrothermal alteration or weathering of granites

the antarctic palaeo record and its role in improving predictions of future antarctic ice sheet change this paper reviews the ways in which the palaeo record of antarctic ice sheet change can be used to improve understanding of contemporary ice sheet behaviour and thus enhance predictions of future sea level change the main areas where the palaeo ice sheet record can contribute are understanding long term ice sheet trajectory providing data against which ice sheet models can be tested to identify and understand the range and types of natural ice sheet behaviour to balance the global water budget to correct contemporary glaciological measurements of mass change and to understand the relationship between polar ecosystems and the ice sheet i review each in turn and argue that research priorities include understanding past west antarctic ice sheet collapse and its timing a focus on the palaeo record of rapid retreat events and how these unfolded in the geological past improving the number and range of ice sheet reconstructions particularly through the holocene continuing to investigate the potential for using sediments and landforms to parameterise basal conditions in ice sheet models and understanding past east antarctic ice sheet dynamics particularly the evidence for partial deglaciation copyright 2009 john wiley sons ltd