rock varnish on petroglyphs from the hima region southwestern saudi arabia chemical composition growth rates and tentative ages we investigated rock varnish formed on sandstone and petroglyphs in the hima area southwestern saudi arabia to characterize the rock varnish we made in situ measurements by portable x ray fluore

marine shell dates and surface lithic assemblages on the west coast of south africa archaeological surface finds are difficult to date there are several useful methods but each requires special circumstances and has one drawback or another on the west coast of south africa marine shell are abundant on surface sites but they are rarely dated because they are perceived to be in disturbed context and in questionable association with artefacts this paper attempts to rectify this misconception and shows that although far from perfect a large suite of surface dates can shed as much light as excavated data on the vredenburg peninsula they help refute the hypothesis that two economically and culturally distinct populations shared this pre colonial landscape since 2000 bp

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

baking black opal in the desert sun the importance of silica in desert varnish desert varnish a widespread black manganese rich rock coating contains labile organic compounds but a mechanism for its formation and for their preservation remains unproven using raman spectroscopy x ray diffraction and scanning transmission electron microscopy we analyzed varnish and found amorphous hydrated silica opal and the silica mineral moganite similar to findings we have reported from siliceous hot spring deposits we suggest that the slow dissolution of silica from anhydrous and hydrous minerals and its subsequent gelling condensation and hardening provides a simple explanation of a formation mechanism for desert varnish and silica glazes and the incorporation of organic material from local environments these chemical signatures sequestered in silica provide valuable information about terrestrial and extraterrestrial paleoenvironments

models of rock varnish formation constrained by high resolution transmission electron microscopy nanometre scale transmission electron microscope imagery of manganiferous rock varnishes from death valley california peru antarctica and hawaii confirms prior infrared mineralogy studies the building blocks of rock varnish are clay minerals that are cemented to the rock by oxyhydroxides of manganese and iron rock varnish is layered on the scale of nanometres with the basic structure defined by the subparallel alignment of detrital clay minerals although only a few examples of bacteria were found possible cell wall encrustations are ubiquitous and aligned with the clay minerals mn fe oxides appear to be mobilized from bacterial casts and then reprecipitate on clay minerals that weather into monolayers these observations have implications for varnish dating and palaeoenvironmental techniques k ar and uranium series dating of rock varnish oxides can only yield minimum ages however this small spatial scale of mobilization would not alter the signal from micron scale microchemical laminations

fe mn nodules in a southern indiana loess with a fragipan and their soil forming significance abstract little is known about how fe mn nodules vary in relation to pedogenetic horizons in soils derived from loess in this investigation nodules were collected according to soil genetic horizons from a fragiudalf in loess at southeast purdue agricultural center sepac in indiana and physical chemical micro and macromorphological features of nodules and their soil matrix were determined as a function of soil depth the quantity chemical composition and micromorphology of the nodules varied with genetic horizons the ap horizon was found to contain the largest amount by weight of nodules 25 43 g kg and this was likely due to soil erosion after the ap horizon the 2btx1 and 2btx2 horizons had the greatest content of fe mn nodules by weight nodules had lower concentrations of sio2 al2o3 k2o tio2 mgo na2o and cao in contrast fe2o3 mno and p2o5 in nodules showed clearly greater concentrations than that in the corresponding soil material the sio2 content decreased with nodule size whereas fe2o3 and mno increased the least depletion of sio2 in nodules of 1 2 mm n2 and 0 5 1 mm n1 was in the bt2 horizon and was greatest in the 2btx2 the al2o3 had accumulated in the n2 and n1 nodules within the ap horizon and in the n2 within the 2btx2 while other horizons were depleted of al2o3 brown nodules had a small mn fe ratio 1 the internal morphology of the nodules also varied with mn fe ratios the fungal hyphae or bacteria resulted in honeycomb cell cone or dendritic structures the cell and cone morphology required large mn fe ratios low ph and high content of ald the scanning electron microscopy sem analysis illustrated an elemental distribution trend such that the mn was centralized in the nodule internal structure whereas fe was concentrated towards the exterior the band structure of nodules likely formed in response to seasonal wetting and drying as an accretionary process three basic formation stages for a well developed nodule can be inferred which correspond to different soil forming environments 1 fe enrichment for nucleus formation in wet soil 2 mn enrichment in an intense dry soil and 3 fe banding enrichment in a slightly dry soil nodule formation occurred synchronously with soil pedogenesis and can therefore be used as a proxy for understanding soil pedogenesis and the environment under which it occurred

terminal pleistocene wet event recorded in rock varnish from las vegas valley southern nevada analyses of rock varnish samples from latest pleistocene alluvial fan surfaces in las vegas valley southern nevada reveal replicable lamination patterns that are characterized by low mn orange surface layers and high mn dark basal layers radiocarbon dating from beneath the sampled alluvial fan surfaces suggests that the mn rich basal layers accumulated during a short wet phase 10 11 14c ka when extensive black mats were deposited throughout the region and paleolake records in the great basin also indicate wet conditions during this time period in contrast the mn poor orange surface layers formed under relatively dry conditions in the holocene thus these varnish microlaminations are connected with environmental fluctuations that appear to be related to climate change evidence from las vegas valley together with that from death valley and the mojave desert suggests that the deposition of these mn rich dark basal layers in rock varnish likely corresponded in time to the terminal pleistocene younger dryas aged wet event in the great basin 2000 elsevier science b v all rights reserved

trace element evidence for the origin of desert varnish by direct aqueous atmospheric deposition abstract smooth rock surfaces in arid environments are often covered with a thin coating of fe mn oxyhydroxides known as desert varnish it is debated whether such varnish is formed a by slow diagenesis of dust particles deposited on rock surfaces b by leaching from the underlying rock substrate or c by direct deposition of dissolved constituents in the atmosphere varnishes collected from smooth rock surfaces in the mojave desert and death valley california are shown here to have highly enriched and fractionated trace element abundances relative to upper continental crust ucc they are highly enriched in co ni pb and the rare earth elements rees in particular they have anomalously high ce la and low y ho ratios these features can only be explained by preferential scavenging of co ni pb and the rees by fe mn oxyhydroxides in an aqueous environment high field strength elements hfses zr hf ta nb th however show only small enrichments despite the fact that these elements should also be strongly scavenged by fe mn oxyhydroxides this suggests that their lack of enrichment is a feature inherited from a solution initially poor in hfses the first two scenarios for varnish formation can be ruled out as follows the high enrichment factors of fe mn and many trace elements cannot be generated by mass loss associated with post depositional diagenesis of dust particles because such a process predicts only a small increase in concentration in addition the highly fractionated abundance patterns of particle reactive element pairs e g ce la and y ho rules out leaching of the rock substrate this is because if leaching were to occur varnishes would grow from the inside to the outside and thus any particle reactive trace element leached from the substrate would be quantitatively sequestered in the fe mn oxyhydroxide layers prohibiting any significant elemental fractionations one remaining possibility is that the fe mn and trace metals in varnish are derived from leaching of dust particles entrained in rain or fog droplets either in the atmosphere or during wet atmospheric deposition the high trace metal enrichment factors require that most of the dust was physically removed before or during varnish formation the remaining aqueous counterpart would be depleted in hfses and th relative to the rees co ni and pb because the former are more insoluble and hence largely retained in the removed dust fraction the high ce la ratios suggest that precipitation of trace metals may have been governed by equilibrium partitioning in an excess of wet atmospheric deposition if varnishes are indeed derived from wet atmospheric deposition they may provide a record of the aqueous component of atmospheric dust inputs to various environments

nanometer scale complexity growth and diagenesis in desert varnish nanometer scale element mapping and spectroscopy of desert varnish from the northern sonoran desert in southwestern arizona reveal a dynamic disequilibrium system characterized by postdepositional mineralogical chemical and structural changes activated by liquid water lack of equilibrium is suggested by the large variety of coexisting mn phases sparse secondary ba and sr sulfates also occur as do carbonaceous particles individual mn oxide particles contain variable concentrations of ba and ce reflecting their role as repositories of trace elements presumably derived from atmospheric aerosols desert varnish is analogous to more familiar sediments in displaying authigenic and diagenetic structures but with total sediment thicknesses 1 mm and structures at the nanometer scale as such it is neither a weathering rind nor patina but a unique subaerial sediment that is in dynamic disequilibrium our results suggest continuing adjustment of varnish to changing environmental conditions

how fast does rock varnish grow rates of rock varnish accumulation have never been systematically documented owing to the difficulty in accurately determining both varnish thickness and age in this study we quantitatively assess varnish accumulation rates through thin sectioning and microscopic examination of rock varnish from radiometrically dated geomorphic features of late quaternary age in the western united states drylands our data indicate that rock varnish grows at rates ranging from 1 to 40 m k y on subaerially exposed rock surfaces and rarely reaches a thickness exceeding 200 m regardless of age our data also indicate that varnish accumulation rates vary greatly from sample to sample at a given site suggesting that varnish thickness does not correlate with the age of the associated geomorphic feature invalidating the potential use of varnish thickness as a relative age indicator in geomorphology and archaeology nevertheless being the slowest known accumulating terrestrial sedimentary deposit rock varnish constitutes a unique long term microscale sedimentary archive of past environmental changes in deserts

microanalytical methods for in situ high resolution analysis of rock varnish at the micrometer to nanometer scale abstract a wide range of analytical techniques were used to investigate rock varnish from different locations negev israel knersvlakte south africa death valley and mojave desert california a 200 nm femtosecond laser ablation inductively coupled plasma mass spectrometer la icp ms an electron probe microanalyzer epma focused ion beam fib slicing and scanning transmission x ray microscopy near edge x ray absorption fine structure spectroscopy stxm nexafs this combination enables comprehensive high spatial resolution analysis of rock varnish femtosecond la icp ms and epma were used for quantitative determination of element concentrations in situ measurements were conducted on thick and thin sections with a resolution of 10 40 m and 2 m respectively the results demonstrate that some elements such as mn co pb ni and cu are highly enriched in varnish relative to the upper continental crust up to a factor of 100 the varnish composition is not influenced by the composition of the underlying rock which is witnessed by plots of mno 2 vs sio 2 contents furthermore the mn free end members fall in the range of average dust compositions the varnishes from the various locations show distinct differences in some elemental ratios in particular mn fe 0 3 25 1 mn ba 4 170 ni co 0 03 1 8 and pb ni 0 4 23 the rare earth element ree patterns vary with la n yb n 3 5 12 and different degrees of ce anomalies ce ce 1 5 5 3 to study the internal structure of the varnish 100 200 nm thick fib slices were prepared and mappings of fe mn n co 3 2 ca c and si at the nm scale performed banded internal structures of mn fe and organic c were observed in the israeli and californian samples however no fe rich layers are present in the south african rock varnish samples furthermore cavities were found that are partly filled by c fe and mn rich material internal structures are different for varnish from different locations which might reflect different types of genesis the results of the combined microanalytical techniques give important detailed insights towards unraveling the genesis of rock varnish

rare earth elements yttrium and h o c sr nd and pb isotope studies in mineral waters and corresponding rocks from nw bohemia czech republic the sparkling waters from the area of kyselka near karlovy vary at the western slope of the doupovske hory bohemia czech republic and co2 poor waters from two underground boreholes at jachymov krusne hory bohemia have been studied with the aim of characterizing the distribution of rare earth elements yttrium and h o c sr nd pb isotopes during the low temperature alteration processes of the host rocks additionally leaching experiments were performed at ph 3 on the granitic and basaltic host rocks from kyselka and the granite of jachymov all ree patterns of the granite and the basalt derived waters from the kyselka area are different from those of their source rocks and the leachates of the latter this elucidates the inhomogeneous distribution of ree and y among the solid phases in the altered magmatic rocks the eu and ce anomalies in granite derived waters are inherited the y anomaly is achieved by fluid migration yttrium is always preferentially leached by mineral waters whereas y ho ratios of rocks and their leachates are very similar the ree abundances in waters from the wells in jachymov are derived from rocks intensely leached and depleted in easily soluble ree bearing minerals whereas the granites and basalts from kyselka still contain soluble ree bearing minerals a comparison of ree ca patterns of the experimental leachates with those of the mineral waters elucidate the high retention of ree in rocks during water rock interaction in strongly altered rocks sr isotope ratios of mineral waters and rocks differ widely whereas the corresponding nd isotope ratios are very similar 207pb 208pb 206pb 208pb and 206pb 207pb ratios in mineral waters are independent from u th ratios in the rocks 206pb 208pb and 206pb 207pb are lower in mineral waters than in their source rocks and their leachates which indicates that pb is primarily derived from solid phases that do not contain significant contents of leachable u and th thus mineral waters although co2 rich only interact with surface films on minerals and not with the bulk of the minerals as in the leaching experiments calculation of mixing ratios of waters from the granitic and basaltic sources of the waters from the kyselka area yield about 40 of water from the underlying granite in water recovered from the basalt whereas the granite derived water is mixed with only about 5 of the water from the basalt

zn isotope compositions of the thermal spring waters of la soufriere volcano guadeloupe island abstract to trace the sources and pathways of zn in hydrothermal systems the zn isotope compositions of seventeen water samples from eight thermal springs and six gas samples from two fumaroles from la soufriere an active volcano on guadeloupe island french west indies fwi were analyzed using a method adapted for purifying zn from fe and so4 enriched thermal solutions the fumaroles are enriched in zn 100 to 8000 times compared to the local bedrock and have isotopic compositions 66zn values from 0 21 to 0 35 similar to or slightly higher than fresh andesite 0 21 the enrichment of zn in the thermal springs compared with the surface waters shows that zn behaves as a soluble element during hydrothermal alteration but is significantly less mobile than na the 66zn values of most of the spring waters are relatively constant approximately 0 70 indicating that the thermal springs from la soufriere are enriched in heavy isotopes i e 66zn compared to the host rocks from 0 14 to 0 42 only three thermal springs have lower 66zn values as low as 0 43 while the zn in the fumaroles is essentially derived from magma degassing which is consistent with a previous study on merapi volcano toutain et al 2008 we show that the zn in the thermal springs is mainly derived from water rock interactions the 66zn enriched isotopic signature in most of the spring waters can be explained qualitatively by the precipitation at depth of sulfide minerals that preferentially incorporate the light isotopes this agrees with the isotopic fractionation that was recently calculated for aqueous complexes of zn the few thermal springs with lower 66zn values also have low zn concentrations indicating the preferential scavenging of heavy zn isotopes in the hydrothermal conduits this study shows that unlike chemical weathering under surface conditions hydrothermal alteration at high temperatures significantly fractionates zn isotopes and enriches thermal waters in heavy zn isotopes e g 66zn continental hydrothermal systems therefore constitute a source of heavy zn isotopes to the oceans this should be taken into account in the global oceanic budget of zn

reactivity of neodymium carriers in deep sea sediments implications for boundary exchange and paleoceanography the dissolved neodymium nd isotopic distribution in the deep oceans is determined by continental weathering inputs water mass advection and boundary exchange between particulate and dissolved fractions reconstructions of past nd isotopic variability may therefore provide evidence on temporal changes in continental weathering inputs and or ocean circulation patterns over a range of timescales however such an approach is limited by uncertainty in the mechanisms and importance of the boundary exchange process and the challenge in reliably recovering past seawater nd isotopic composition end from deep sea sediments this study addresses these questions by investigating the processes involved in particulate solution interactions and their impact on nd isotopes a better understanding of boundary exchange also has wider implications for the oceanic cycling and budgets of other particle reactive elements sequential acid reductive leaching experiments at ph 2 5 on deep sea sediments from the western indian ocean enable us to investigate natural boundary exchange processes over a timescale appropriate to laboratory experiments we provide evidence that both the dissolution of solid phases and exchange processes influence the end of leachates which suggests that both processes may contribute to boundary exchange we use major element and rare earth element ree data to investigate the pools of nd that are accessed and demonstrate that sediment leachate end values cannot always be explained by admixture between an authigenic component and the bulk detrital component for example in core wind 24b acid reductive leaching generates end values between 11 and 6 as a function of solution solid ratios and leaching times whereas the authigenic components have end 11 and the bulk detrital component has end 15 we infer that leaching in the mascarene basin accesses authigenic components and a minor radiogenic volcanic component that is more reactive than madagascan derived clays the preferential mobilisation of such a minor component demonstrates that the nd released by boundary exchange could often have a significantly different end composition than the bulk detrital sediment these experiments further demonstrate certain limitations on the use of acid reductive leaching to extract the end composition of the authigenic fraction of bulk deep sea sediments for example the detrital component may contain a reactive fraction which is also acid extractible while the incongruent nature of this dissolution suggests that it is often inappropriate to use the bulk detrital sediment elemental chemistry and or end composition when assessing possible detrital contamination of leachates based on the highly systematic controls observed and evidence from ree patterns on the phases extracted we suggest two approaches that lead to the most reliable extraction of the authigenic end component and good agreement with foraminiferal based approaches either i leaching of sediments without a prior decarbonation step or ii the use of short leaching times and low solution solid ratios throughout

hydrothermal interaction between basaltic glass deionized water and seawater abstract this paper presents the results of a series of experiments on the interactions of a basaltic glass with deionized water and natural seawater at 200 c and autogenous pressure in a closed system investigations showed the different mineralogical and geochemical behavior of the basaltic glass in the two solutions the initial stage of interaction with deionized water was characterized by hydration and rapid hydrolysis of the basaltic glass variations in ion concentration showed a parabolic trend from the first hours of interaction indicating selective dissolution of the glass phillipsite mg smectite and analcime were the alteration products according to ph values reached in the solution our data also suggest that only the first reaction stages are affected by grain size and that this controls the times of appearance of the secondary phases experiments on seawater fall into the category of rock dominated but acid ph and quite high mg content persisted throughout this behavior may be correlated to the alteration layer that covers the granules reducing exchanges between glass and seawater and changing our system into the seawater dominated type the continuous acid ph throughout the experiments favoured 6 coordination of al ions in aqueous solution and prevented the crystallization of zeolitic phases mg smectite and anhydrite were the only alteration products in this set of experiments grain size played a minor role in the alteration process since it did not control the time of appearance of secondary phases

rare earths and yttrium hydrostratigraphy along the lake kinneret dead sea arava transform fault israel and adjoining territories rare earth elements and y rey have been analysed in 49 groundwaters from localities in the areas of lake kinneret and the jordan and arava valleys these waters originate from various aquifers and the rey abundances are expected to be controlled by the aquifer rocks the rey pattern allow one to distinguish interaction of waters with basalts basalt limestone interaction zones silicified limestones limestones from the judea and avdat groups upper cretaceous and eocene respectively and sandstones of the lower cretaceous kurnub group groundwater from the quaternary alluvial fill dead sea group are either controlled by judea group limestone or kurnub group sandstone the rey patterns show characteristic features for each group in hydrogeological systems the rocks of natural replenishment areas are usually not the same as rock units from which the waters are collected this becomes evident by comparing the lithostratigraphic groups from which the waters were collected and the hydrochemical grouping according to rey patterns with their characteristic trends and anomalies in many cases there is a correspondence between the lithostratigraphic and the hydrochemical grouping in other cases the 2 groupings disagree this disagreement proves inter aquifer flow of groundwater in some cases the geologically derived aquifers rocks of origin differ from those indicated by rey patterns thus applying the rey grouping new fundamental information for hydrological models can be given and sources of salinisation can be elucidated

loess is not just the accumulation of dust most regrettably there is much misuse of terminology in connection with the concept of loess and the interpretation of its origin people often speak and write incorrectly about loess accumulation even loess specialists who are aware of the fact that loess as a concept has to satisfy at least 10 criteria loess is not simply dust carried and deposited by wind dust only becomes loess after the passage of a certain amount of time in a given geographical zone i e only through diagenesis in certain ecological environments to state that loess is of aeolian origin is an oversimplification and an incorrect definition because an aeolian origin applies only to the dust from which the loess has been formed we are aware of the fact that airborne dust cannot be transformed into loess in every geographical environment but only under those conditions typical of semi arid grassland or steppe or forested steppe the process primarily occurs where the rate of dust accumulation exceeds sheet wash or weathering soil formation rates if the rate of dust accumulation is less than that of surface erosion or of soil biogenetic processes the dust then develops into soil or through intensive weathering and increased precipitation into loam or clay only part of the aeolian dust transported and deposited in a zone suitable for loess formation remains there permanently and is transformed in situ into loess dust not affected by diagenesis is usually further transported by snowmelt or rainwash and is only transformed into loess after it has been redeposited the loess itself however is easily erodible and its minerals are readily reworked and reaccumulated and given the appropriate conditions it readily undergoes diagenesis again we do not always have sufficient evidence to determine whether a given loess body is of primary or secondary origin traditionally the minerals making up primary loess have been regarded as originating in dust accumulated by aeolian processes secondary loess by contrast is different from typical loess in many ways and it is not unusual to find various loess series in which superimposed dust fractions have been transformed into loess by different processes recently we have observed that the origin of various types of loess is governed by differences in litho ecological conditions rather than by the way in which the mineral material from which the loess is derived dust has been primarily accumulated loessification is therefore determined by environmental conditions

mineralogy of fe mn nodules in albeluvisols in the carpathian foothills poland fe mn nodules are common components occurring in various soils and especially in soils exhibiting imperfect drainage the formation distribution chemical composition size and shape of fe mn nodules are the subject of many studies and the research literature contains a lot of information concerning these issues on the other hand data regarding the mineral composition of fe mn nodules in the soil environment are limited to only a few studies the main aim of the present study was to determine the mineral composition of the fe mn nodules found in albeluvisols in the carpathian foothills in poland using quantitative x ray diffraction qxrd fourier transform infrared spectroscopy ftir and mossbauer spectroscopy ms the obtained results show that fe mn nodules from albeluvisols in the carpathian foothills in poland are composed mainly of silicates quartz k feldspars plagioclases and phyllosilicates dioctahedral mica smectite chlorite and kaolinite which are impregnated with iron and manganese oxides iron minerals are represented by goethite and probably lepidocrocite both iron minerals are characterized by very small particles and poor crystallinity goethite occurring in all of the studied fe mn nodules clearly prevails over lepidocrocite which exhibits a higher concentration only in nodules from the lower part fragipan of the soil profile located on a footslope and showing the strongest stagnic color pattern manganite and todorokite represent manganese minerals however todorokite was observed only in nodules obtained from illuvial horizons btx btg of the studied albeluvisols the fe mn nodules obtained from eluvial horizons eg show higher amounts of silicates quartz k feldspars plagioclases than the nodules obtained from illuvial horizons on the other hand fe mn nodules obtained from illuvial horizons fragipan and argillic exhibit higher amounts of phyllosilicates i e clay minerals in comparison with the eluvial horizon the differences in the quantitative mineral composition of the fe mn nodules between eluvial and illuvial horizons are related to the translocation of clay minerals from upper soil horizons into the lower part of the soil profiles this indicates that the nodules from e horizons were formed after translocation of major portion of clay fraction down the soil profile the similar mineral composition of the fe mn nodules and bulk soil material indicates that the nodules were formed in situ because of cyclic reduction and oxidation of fe and mn oxides

weathering and global denudation a negative correlation between sediment yield and weathering history as measured by the chemical alteration cia of the suspended sediment is observed for many of the world s major rivers and other regions of denudation the weathering history is a first order control on the sediment yield of such areas termed equilibrium denudation regions for other areas data scatter with either apparent increases or decreases of sediment yield for given cia values these areas are termed nonequilibrium denudation regions low sediment yields can be attributed to moderated erosion either natural or human induced and or the incorporation of unweathered glacial debris accelerated erosion resulting in high sediment yield is primarily human induced and results from cultivation and other land use each of these effects has a profound influence on global sediment discharge from the continents pre human suspended sediment discharge from the continents is estimated to be 12 6 times 10 15 g yr or about 0 6 the

rare earth element mobility in the oceanic lower sheeted dyke complex evidence from geochemical data and leaching experiments hydrothermally altered rocks from the base metal depleted reaction zone in the lower sheeted dyke complex odp hole 504b show significant losses of rare earth elements ree in extensively altered domains alteration patches while very similar in major element composition and alteration mineralogy the alteration patches have up to 50 lower ree concentrations than the surrounding weakly altered diabases in order to test if there is a dependence of ree mobility on the alteration history we carried out leaching experiments on a weakly altered diabase and an adjacent alteration patch the leaching experiments are used as a probe to identify the hosting phases of major and trace elements before and after alteration they are not designed to simulate natural alteration processes major element compositions of the leaching solutions show that small amounts 9 to 14 of the rocks and similar proportions of plagioclase amphibole and chlorite were dissolved from both rock types in contrast to the major elements up to 100 of the ree could be leached from the strongly recrystallised alteration patch after 20 h all leaching solutions were light ree enriched and had negative eu anomalies compared to the host rock geochemical modelling suggests that mainly interstitial material formerly late stage magmatic liquids and probably some apatite are the main ree sources in the rocks affected during experimental leaching dissolution of plagioclase amphibole clinopyroxene and chlorite cannot explain the ree compositions of the leachates the higher ree leachability of the heavily altered rock suggests that the extensive hydrothermal alteration resulted in a complete redistribution of the ree from lattices of the magmatic minerals to the grain boundaries of secondary minerals this can explain the marked increase in ree accessibility during ongoing alteration which finally led to ree depletions in the highly altered rock we propose that late stage interstitial material provides the most important ree source of rocks in the oceanic crust this interpretation is in contrast to a model by klinkhammer et al klinkhammer g p elderfield h edmond j m mitra a 1994 geochemical implications of rare earth element patterns in hydrothermal fluids from mid ocean ridges geochim cosmochim acta vol 58 pp 5105 5113 who suggested that the similarity in the ree patterns of plagioclase and that of hydrothermal vent fluids is a result of chemical exchange between plagioclase and hot fluids in the ocean crust our leaching results indicate that although dramatic dissolution of plagioclase occurred it did not control the ree patterns of the leachates moreover ree patterns inferred for fluids that mobilised ree from the highly altered rock are different from those of vent fluids we therefore propose that the characteristic ree pattern of vent fluids may result from differences in aqueous chloride complex stabilities sorption controlled ree fractionation during fluid migration and mineral precipitation in the discharge zone

anthropogenic lead as a tracer of rock varnish growth implications for rates of formation rock varnish is a thin dark coating best known from deserts and is believed to grow extremely slowly varnish samples from near socorro new mexico united states contain as much as 3 7 pbo derived from nearby smelters operating from a d 1870 to 1931 additional varnish measuring as much as 4 m beyond the pb rich layer indicates continued growth from 1931 to 2003 comparison with other varnish confirms that the pb is not an artifact based on pb layer thickness and the period of smelter operation these very young rock varnishes yield growth rates of 28 639 m k y substantially higher than previously documented fastest rates of 40 m k y these rates imply that the average 1 2 m k y rate for older varnish is not the active growth rate rather it is a long term value including periods of nondeposition erosion and active growth therefore models of rock varnish formation should be reevaluated with consideration of much faster maximum growth rates

determination of easily accessible metal fractions in rocks by batch leaching with acid cation exchange resin the easily accessible fraction of metals in rocks is derived from leaching experiments aliquots of rock powders are mixed with ion exchange resin and distilled water the ph self adjusts to a value of 3 after batch leaching times of 2 48 hr at 70 c the resin is quantitatively separated from the rock powder and eluted with 4 n hno3 the metal contents of the leachates are determined and related to the respective contents of the whole rock the leaching kinetics of each element is related to that of a reference element aluminium is most commonly chosen as a reference element because it is considered to represent the dissolution behaviour of the main rock forming minerals the easily accessible trace element fraction eat is given as the percentage of leached element at 1 al dissolution these eat values are reproducible and independent from grain size and sample resin ratio the procedure is tested on basaltic glass and variably altered gneisses the glass shows congruent release of all metals a slightly crystalline glass of the same chemical composition displays heterogeneous leaching behaviour the leaching kinetics of variably altered gneisses provide insight into the mineralogical siting of elements and their accessibility to fluids consequences for rb sr dating of rocks are discussed

sequential leaching of marine ferromanganese precipitates genetic implications abstract sequential leaching experiments were carried out on twenty one hydrogenetic crust samples from different locations in the central pacific and the results are compared with four crust and nodule samples of different genetic origin fe vernadite mno2 is the most important minor and trace metal bearing mineral phase and shows high concentrations of co ni cd ti ba zn and cu which are present in seawater mainly as hydrated and labile complexed cations elements forming carbonate and hydroxide complexes and oxyanions in seawater like pb mo v and minor proportions of cu and zn are bound in the fe00h fraction the ca carbonate phase and the residual fraction which consists of aluminosilicates and crystalline oxides show only minor heavy metal associations e g cu and zn only a small part of the high ti concentrations in hydrogenetic crusts is of detrital origin ti mainly forms a hydrogenetic phase probably consisting of ti02 2h20 intergrown with the amorphous fe00h phase analyses of different sample types and crust layers show that aging and diagenetic effects can change the phase associations of some elements the most notable change was observed for pb which during phosphatization of crusts is transferred from the mn fe oxide fraction to the apatite fraction a colloid chemical model for the hydrogenetic precipitation of ferromanganese crusts on seamounts is proposed in the first stage mn2 rich water from the oxygen minimum zone is mixed with oxygen rich deep water and oxidized mn iv and other metals like fe ti al and si form oxide and hydroxide colloids these form mixed colloidal phases and scavenge trace metals by sorptive processes which are dominated by coulombic and chemical interactions between colloid surfaces and dissolved metal species in stage two the colloidal phases precipitate on the substrate rocks of the seamounts as ferromanganese oxide encrustations incorporating the sorbed heavy metals into the mineral phases

ree systematics in hydrothermal fluorite abstract ree patterns of fluorite from 63 post variscan hydrothermal veins of the schwarzwald area germany can be divided into two major groups type a fluorite shows roof shaped paas normalized patterns with enriched mree the turning point of the curvature is at ho or er position all patterns of type a show a distinct positive eu anomaly type b fluorite shows roof shaped patterns with enriched mree and strongly depleted hree and a characteristic steep slope between nd and sm the turning point of the curvature is at gd to dy all patterns of type b show negative or no eu anomalies laser ablation icp ms traverses through single grains combined with cathodoluminescence imagery revealed either i identical ree patterns and total ree concentrations from core to rim ii identical ree patterns but concentration gradients or iii variable ree patterns and concentration gradients from core to rim these features are explained by different degrees of supersaturation or different fluid fluorite ratios during crystallization and by complexly controlled precipitation processes under closed system conditions petrographically late fluorites from several deposits show the characteristics of new fluid batches rather than the expected remobilization features lree enrichment close to the crystal faces in some grains may result from the copreciptiation of a submicrometer sized lree enriched phase or from lree clustering in late cool fluids by comparison with literature data on natural waters from gneissic and granitic aquifers and of leachates of granites and gneisses we show that the hydrothermal vein fluorite preserves the characteristic source related ree feature of the hydrothermal fluid that migrated through either gneissic type a or granitic type b host rocks the immediate host rocks of the veins however are not the source rocks of the ree which indicates large scale fluid convection in the basement gneiss related type a fluorite shows tb ca tb la trends of primary hydrothermal crystallization whereas granite related type b fluorite indicates remobilization of possibly pegmatitic or variscan fluorite

the new nb p aplite at reinhardsrieth a keystone in the lateral and depth zonations of the hagendorf pleystein pegmatite field se germany abstract the hagendorf pleystein pegmatite field hppf is the largest pegmatite concentration in central europe which has been intensively studied for its mineralogy mainly at hagendorf south pegmatite stock it was not until recently that the lateral and depth zonations of the hppf could be clarified when the newly discovered tabular aplite at reinhardsrieth aplite has been found at transition into the so called barren zone devoid of rare metals thereby the theory of the derivation of the hppf felsic mobilizates as a result of a successive differentiation of a pegmatitic melt from the flossenburg granite has to be discarded from the structural and lithological point of view stock like well zoned pegmatites e g hagendorf south developed in the hinge zone whereas tabular aplites such as reinhardsrieth evolved along the limb zone of strongly folded basement rocks in the latter case the accommodation space was smaller and the cooling of the felsic mobilizates much faster giving rise to fine grained aplitic rather than coarse grained felsic mobilizates chilled margin effect during the incipient stages of the evolution in the hppf at reinhardsrieth a stronger impact of granitization can be determined than at the neighboring aplites and pegmatites based upon the ree fractionation a tripartite subdivision may be established for the various pegmatites and aplites in the hppf 1 barren zone minor amounts of lree in a system otherwise dominated by feldspar and quartz 2 marginal zone mainly fe al phosphates plus columbite fe 3 central zone fe zn li phosphates plus columbite fe the afore mentioned zonation shows an e w trend and a bilateral symmetric arrangement of the various areas there are significant indications of an oxidizing facies to substitute for a more reducing facies at the transition from the central into the marginal zone of the hppf the key mineral for the primary pegmatite mineralization in the marginal and central zones is columbite fe its mn fe ratios plotted vs the ta nb ratios allow for an assessment to what extent metamorphic and magmatic processes have contributed to the built up of the pegmatites and aplites in the hppf even the most primitive nigrine hosted columbites fit well into this pattern forming a lithochemical halo in the roof rocks of the pegmatites the heavy mineral aggregated of rutile ilmenite nigrine giving host to the columbite as armored relicts got released from the basement rock on top of the pegmatites into the stream sediments where they are operative as an ore guide the morphology of zircon in the stream sediments has been utilized as an economic ore indicator the zr silicate is also indicative of the temperature of formation and closely supports the tripartite zonation established above manganiferous apatite is a good depth of emplacement indicator for each aplite and pegmatite respectively the higher the feo mno content of apatite the shallower the depth of emplacement of its host pegmatite or aplite vivianite in turn marks the onset of the hydrothermal alteration of the pegmatites and aplites and its mn contents relate to the depth where alteration has taken place or emplacement of the secondary phosphates the higher the mn content the shallower the depth of alteration peculiar element ratios were selected to design some key diagrams so as to corroborate the field based mineralogical and geological results in terms of zonation of genetic economic geology as well as to cater for applied economic geology as proximity indicators and ore guides when exploring for rare element pegmatite

spatial temporal and geographic considerations of the problem of rock varnish diagenesis article i nfo the rock varnish literature hosts an abundance of prima facie contradictory empirical data past and perhaps future empirical contradictions however can be resolved by theoretical considerations of different spatial and temporal scales of varnish diagenesis as well as the geomorphic position of different types of varnishes for example twentieth century contamination by lead and other heavy metals has led to claims of accumulation rates in the last century far more rapid than prior published empirical studies a consideration of spatial scales resolves this contradiction nanoscale processes allow migration of lead into varnish deposited well before the twentieth century time of heavy metal pollution evidence of nanometer scale disequilibrium in three samples led to claims that varnish cannot be used in paleoclimatic research these data rest in contrast to replicable patterns in varnish deposition observed by dr tanzhuo liu and others in over ten thousand micro sedimentary basins this contraction can be resolved by understanding that the types of varnishes studied differ and that processes differ substantially between the nanoscale and the micron scale a lack of evidence of mn oxidizers in genetic analyses contrasts with culturing studies and in situ evidence of mn enhancement by bacteria this contradiction has a likely resolution in vastly different temporal scales dna material analyzed may be no older than 200 years but in situ fossilized remains of bacteria may be preserved for thousands of years recording palaeoecological conditions favoring growth of mn enhancing bacteria

diversity of rock varnish bacterial communities from black canyon new mexico 1 scientists vigorously debate the degree to which rock varnish is formed through the actions of microorganisms to investigate this enigma we utilized a three pronged approach that combined 1 culture independent molecular methods to characterize bacterial communities associated with varnish that coats the rhyolitic volcanic rocks of black canyon new mexico and rocks with no visible varnish 2 culturing of varnish in media supplemented with reduced forms of manganese and or iron and no or low amounts of carbon to isolate bacteria capable of precipitating iron and or manganese oxides and 3 scanning electron microscopy sem of varnish and nearby rock that lacks macroscopically visible varnish our culture independent studies revealed significant differences between varnish and nonvarnish communities chloroflexi and ktedobacteria dominated one varnish site while the other varnish site was dominated by cyanobacteria the nonvarnish sites were dominated by actinobacteria and to a lesser extent cyanobacteria and were the only samples to contain deinococcus thermus sequences approximately 65 of varnish cultures produced visible manganese precipitates most culture isolates were not closely related to known manganese oxidizers with the exception of bacillus spp sem revealed microbial morphologies and two types of varnish morphologies 1 relatively smooth layers and 2 patches of botryoidal pinnacles which were often associated with increased manganese concentrations bare rock showed evidence of incipient varnish these results have important implications for the detection of life on extraterrestrial planets such as mars where putative varnish coatings have been observed and represent some of the first culture independent characterizations of varnish communities

study of the weathering of albite at room temperature and pressure with a fluidized bed reactor reply to a comment by r a berner g r holdren jr and j schott

impacts of simulated acid solution on the disintegration and cation release of purple rock mudstone in southwest china abstract rock disintegration and cation release not only impact on terrestrial geomorphology but also provide nutrients for plants further fractal theory has been widely used to characterize the distribution of fragments in rocks for measuring the degree of disintegration yet the effects of an acidic environment on the trajectory of fractal dimensions of rock disintegration and cation release are not fully clear therefore to investigate the impacts of a solution s ph on disintegration and cation release from the purple rock in southwest china a series of laboratory experiments were performed by soaking the purple rocks in solutions with phs from 2 5 to 7 0 over 24 treatment cycles the results show that the lower the ph the fewer cycles required to obtain a stable fractal dimension the fractal dimension of purple rock under different ph values approached three after 24 treatment cycles until decay ratios the mass of decayed rock of 90 acidic treatment increased cation release especially when the ph value of the solution was below 3 5 compared with a deionised water soaking solution the amounts of k na ca2 and mg2 were increased by 4 92 1 27 1 12 and 1 08 times with ph values of 2 5 3 5 4 5 and 5 6 soaking solution respectively at the disintegration stage in addition the release of ca2 and mg2 were more sensitive to acid than that of k and na and ca2 weathering occupied the dominant position in the cation weathering rates moreover due to disintegration processes that transformed each rock sample into fragments fresh surfaces were exposed from which cations were liberated creating a significant p

rare earth elements yttrium and pb isotope ratios in thermal spring and well waters of west anatolia turkey a hydrochemical study of their origin abstract rare earth elements ree yttrium major elements and pb isotope ratios were determined in thermal well and spring waters and rocks of the buyuk menderes and gediz grabens turkey which includes the geothermal fields of kizildere salavatli germencik kula and salihli together with the results of short and long time leaching of local rocks ree and y and pb isotope ratios indicate that the palaeozoic mica schists dominantly control the ree and y signatures of the deep seated na hco 3 waters marbles may also be involved but their low ree contribution is overridden by the much higher ree and y abundances in the mica schists palaeozoic gneisses can be excluded as source rocks by both pb isotope ratios and ree leaching behaviour the deep seated waters either ascend rapidly in production wells and precipitate carbonate silica scales at temperatures of about 200 c or these waters ascend slowly to springs become enriched in ca 2 cl and so 4 2 and discharge with temperatures up to 100 c as fumaroles or hot springs some of these spring waters precipitate large amounts of travertine upon exsolution of co 2 in contrast the thermal ca hco 3 type of water from pamukkale has its source in the regional pliocene limestones

sources of lead in the san cristobal pulacayo and potosi mining districts bolivia and a reevaluation of regional ore lead isotope provinces new lead isotope data on ores crustal rocks and leachates of crustal rocks combined with data in the literature provide important new constraints on the sources of ore metals in southwest to south central bolivia including the very large recently discovered silver zinc deposit at san cristobal the pulacayo polymetallic district and the giant potosi silver tin base metal deposit lead isotope ratios of ores and igneous rocks from the san cristobal deposit and from paleozoic and cretaceous sedimentary rocks are compared with published data on high grade middle proterozoic metamorphic basement rocks these data constrain the major source of lead and by inference of other ore metals at san cristobal to be the metamorphic basement rocks leaching experiments on samples of paleozoic and cretaceous sedimentary rocks show that the easily leachable lead from these rocks is much less radiogenic than the whole rock compositions however lead isotope ratios of both whole rocks and leachates of these upper crustal rocks are too radiogenic for them to be major sources of ore lead at san cristobal lead isotope ratios of ores from pulacayo and potosi are similar to each other and lie within the range of paleozoic and cretaceous sedimentary whole rock compositions leaching of pb from the sedimentary rocks cannot explain the isotopic compositions of the pulacayo and potosi ores and the isotopic homogeneity of the potosi ores also argues against mixing of lead from diverse sources in the hydrothermal system lead from the sedimentary rocks may have been incorporated by magmatic assimilation followed by extraction of ore metals from the resulting magma lead isotope ratios of san cristobal ores are different from those of pulacayo potosi and other deposits to the east but resemble the compositions of ores and volcanic rocks in western bolivia on this basis we identify a new ore lead isotope province extending from san cristobal northward across the eastern altiplano and into southern peru this province is coincident with but smaller than the extent of the proposed arequipa antofalla metamorphic basement craton the degree of incorporation of ore metals from the metamorphic basement appears to depend on the timing and or location of the mineralizing event ore deposits in the northern part of province iv formed before the thickening of andean crust beginning around 20 ma and incorporated minor amounts of metals from the metamorphic basement younger deposits farther to the south contain major to dominant components of basement lead

alteration effects of volcanic ash in seawater anomalous y ho ratios in coastal waters of the central mediterranean sea this paper presents the results of a study based on data collected during the oceanographic cruise ansic 2001 carried out in the ionian sea during the explosive activity of mount etna in the summer of 2001 anomalous low values of y ho ratios in seawater suggest extensive scavenging processes on the surfaces of smectitic alteration products with y and ho fractionation controlled by the differences in their electronic configurations and behaviour during solution surface complexation equilibria these processes can also be traced through the presence of significant tetrad effects recorded in the chondrite normalised rare earth elements and yttrium yrees patterns of suspended particulate matter this suggests that the preferential y scavenging from seawater is due to the formation of inner sphere complexes with oh groups on montmorillonite crystal surfaces the preliminary results of kinetic experiments of yree released from volcanic ash to coexisting seawater and the related effects on y ho ratios and ce anomalies are consistent with the fractionation of light rare earth elements lrees with respect to heavy rare earth elements hrees observed in dissolved phase they suggest a behaviour of y similar to that reported for lrees particularly for ce and pr

parabolic dissolution kinetics of silicate minerals an artifact of nonequilibrium precipitation processes the rate limiting step for the dissolution of many primary silicate minerals is thought to be a surface controlled reaction this should result in dissolution rates that are linear functions of time however the observed dissolution rates for aluminosilicate minerals have commonly been characterized as parabolic that is the apparent rates of release of silicon and of the alkali ions are linear functions of the square root of time t here data are presented which suggest that this discrepancy may result in part from the precipitation of secondary aluminosilicates during the dissolution experiments in simulated dissolution studies the kinetics of formation and the stoichiometries of precipitates can be studied unambiguously as functions of time component concentrations and ph results of these studies indicate that significant amounts of silicon are incorporated into amorphous aluminum rich precipitates at dissolved silicon concentrations greater than 170 m at higher concentrations silicon precipitation rates increase these precipitation reactions result in apparent rates of addition of dissolved silicon to solution which are linear functions of t as a result of the type of precipitation reactions observed here estimates for the rates of dissolution obtained for aluminum rich silicate minerals may be low by as much as a factor of two

basaltic rocks analyzed by the spirit rover in gusev crater the spirit landing site in gusev crater on mars contains dark fine grained vesicular rocks interpreted as lavas pancam and mini thermal emission spectrometer mini tes spectra suggest that all of these rocks are similar but have variable coatings and dust mantles magnified images of brushed and abraded rock surfaces show alteration rinds and veins rock interiors contain 25 megacrysts chemical analyses of rocks by the alpha particle x ray spectrometer are consistent with picritic basalts containing normative olivine pyroxenes plagioclase and accessory feti oxides mossbauer pancam and mini tes spectra confirm the presence of olivine magnetite and probably pyroxene these basalts extend the known range of rock compositions composing the martian crust

systematic mn fluctuations in laminated rock varnish developed on coeval early holocene flint artifacts along a climatic transect negev desert israel abstract this study presents an assessment of the potential application of mn content in rock varnish laminae as a paleoclimate indicator to investigate the environmental controls on varnish formation we determined mn composition in rock varnish formed on flint artifacts produced during the earliest holocene from eight coeval prehistoric sites in the negev desert israel these sites lie along a north south annual rainfall transect ranging between 120 and 30 mm yr 1 the varnish is 100 times enriched in mn relative to the content in the desert dust source material chemical profiles across the varnish display 4 6 distinct mn peaks in all sampled sites pointing to systematic fluctuations within the varnish along a wide range of environmental settings the mean mn contents in the various sites range between 10 7 and 15 6 at yet within this range the mn content in the negev varnish does not show a correlation with mean annual rainfall as moisture is needed for mn mobility wetting cycles by dew or light rain which are not adequately represented by the mean annual rainfall amounts but control the number of wetting drying cycles may explain the variance within the results from the arid and hyperarid negev varnish

assessing the effect of sequential extraction on the uranium series isotopic composition of a basaltic weathering profile abstract soil sustainability implies maintaining the balance between soil erosion and production while it is known how to assess soil erosion only recently we have been able to estimate rates of soil and saprolite namely regolith production using uranium series isotopes this method assesses the time elapsed since rock forming minerals start fractionating the u series isotopes in this study we assess a sample pre treatment protocol that has the potential to improve the method used to estimate regolith production rates we propose that removal or partial removal of secondary phases precipitated from solution during pedogenesis solution derived phases and organic matter from regolith may improve the accuracy of this method this is tested using sequential extraction followed by etching as sample pre treatment here we assess their effect on the u series isotopic composition of regolith and infer whether they minimize the presence of solution derived phases and organic matter we applied sequential extraction and etching to a basaltic weathering profile bedrock saprolite and soil and compared the u series isotopic composition before and after treatment we also measured major elements concentrations and assessed mineralogy the bedrock was in secular equilibrium and sequential extraction resulted in unchanged 234u 238u activity ratios while increased 230th 238u in contrast etching resulted in increased 234u 238u and 230th 238u activity ratios which is attributed to the removal of primary minerals relative to the untreated bedrock the untreated saprolite showed no changes in u and th concentrations and activity ratios we hypothesise that during the conversion of bedrock into saprolite u and th budgets are unaffected moreover major element and mineralogical analyses suggest that during this process rock forming minerals are converted into secondary phases clays we hypothesise that during this conversion the u series isotopes are not fractionated therefore the removal of these secondary phases is not necessary relative to the saprolite the soil showed gains of u and th 234u 238u 1 and 230th 238u 1 to minimize the presence of solution derived phases and organic matter in basaltic weathering profiles we suggest that only soil samples should undergo sequential extraction because only these are significantly affected by solution derived phases and organic matter additionally our experiments show the existence of fractionation processes that are often overlooked in u series isotopic studies i e implantation of 234u and 230th recoiled from u rich mineral i e glass into adjacent u poor phases e g pyroxene and feldspar

flux of volatiles and ore forming metals from the magmatic hydrothermal system of satsuma iwojima volcano the satsuma iwojima volcano southwest japan degasses 5 x 10 6 t yr h 2 o 9 x 10 4 t yr s and 6 x 10 4 t yr cl from high temperature 880 c fumaroles atop a now altered rhyolite dome that erupted 1200 yr ago acidic hot springs ph 1 1 1 8 discharge 20 x 10 6 t yr h 2 o to the sea this water is composed of 1 part magmatic vapor absorbed by 6 parts meteoric ground water the cl and so 4 in solution originate from the vapor whereas cation components are derived largely by dissolution of the rhyolite the flux of pb zn cu and mo in the vapor and acidic springs ranges from 0 1 to 10 t yr each whereas the au flux is 10 5 and 10 3 t yr respectively the low concentrations of nacl and metals in the vapor are due to the condensation of a hypersaline liquid from the vapor during ascent and depressurization meaning that the atmospheric pressure vapor does not reflect the composition of the fluid exsolving from the magma neither this low pressure vapor nor the acidic waters can account for high sulfidation cu au ore deposits deduced to have formed in this environment such mineralization requires the subsequent ascent of a metal rich fluid

ree mobility and fractionation during shale weathering along a climate gradient abstract we systematically investigated six soil profiles developed on a climosequence of gray shale to constrain the mobility and fractionation of rare earth elements ree during chemical weathering processes in addition one site developed on black shale marcellus formation was included to document ree behaviors in organic rich versus organic poor shale end members under the same environmental conditions our study shows that ree are mobilized intensively during shale weathering and the extent of depletion is larger under warm humid climates however the integrated release rates calculated from six soil profiles are not directly correlated to mean annual precipitation or temperature instead the primary control might be the ree concentrations in the most reactive minerals ree bearing phases in shale sulfides phosphates and organic matter probably react quickly at first mobilizing ree following that ree are then released more slowly during dissolution reactions of clay minerals consistent with this interpretation black shale weathers much faster and releases more ree than gray shale under the same climate conditions due to the higher organic matter and sulfide contents and lower soil ph ree are not 100 depleted in any of the investigated soil sites in northern sites depletion is minimal whereas in the southern warm and humid sites surface depletion is higher and re deposition is observed at depth retention of ree is likely caused by adsorption to mineral surfaces as ph increases and dissolved organic matter content decreases with depth this case study quantified loss redistribution and fractionation of ree during shale weathering improved our understanding of ree mobility in surficial environments and contributed to the exploration of ree as strategic mineral resources

rock varnish in the sonoran desert microbiologically mediated accumulation of manganiferous sediments rock varnish occurs in virtually all environments most commonly in arid and semi arid climates including antarctica rock varnish consists of thin layers of intimately mixed aeolian and chemical sediments often showing botryoidal and more rarely stromatolite like morphologies typical rock varnish samples collected at twin peak mountain park near phoenix arizona consist of abundant quartz with plagioclase illite and a mixed layer fe clay mineral probably corrensite eds sem bse and tem analyses revealed that the typical mn fe minerals occur as minute particles some of these particles and other mineral grains are attached to filaments xrd and electron diffraction showed that the mn fe bearing particles are poorly crystalline the filaments based on morphological criteria are virtually indistinguishable from fungal filaments most filaments are fragments probably broken by scraping during sample collection coccoid and rod shaped forms resembling cyanobacteria and other bacteria respectively are also present unlike definitive minerals these filaments disintegrated in the concentrated energy of the sem electron beam at the instrumental and experimental conditions used in addition no filamentous rod shaped or coccoid forms were observed in samples hydrolysed with 6 n hcl for 24 h at 100 c bacteria and fungi in powdered rock varnish were cultured on four media incubated aerobically in the dark at 25 c the culture media yielded dense growths of spore forming bacteria and filamentous fungi one fungus and two bacillus isolates oxidized and concentrated manganese control experiments revealed that fungi and bacteria are present on and below the surfaces of rock varnish free and hydrolysed peptide protein bound amino acids were identified in the rock varnish amino acids showed virtually no racemization with the exception of d l asp 0 1 relatively high molecular weight humic matter was also separated from the rock varnish high resolution mass spectrometry revealed non hydrocarbon moieties similar to a suwannee river fl humic acid standard micro organisms and their original biochemical compounds do not seem to be preserved for long in the accreting varnish layer the studies showed that the filaments helped to trap mineral particles of rock varnish and that bacteria and fungi abetted mn concentration some structures in the layers of rock varnish resemble stromatolites and present definitions would allow them to be termed as such

a review of the history of dating rock varnishes the history of rock varnish dating spans almost 20 years from the initial suggestion to use uranium series isotopes through the use of a geochemical ratio cation ratio dating to the current application of accelerator mass spectrometry radiocarbon dating ams 14c uranium isotopes were ignored while other dating methods were tested exhaustively on several continents evidence of the unreliable dating of the formation of varnishes using cation ratios was demonstrated by examples of environmental and textural observations reflecting localised leaching and by chemical analyses that contradicted the fundamental assumptions of the method the radiocarbon dating of substances embedded in varnishes is also problematic where carbon compounds and sources are not identified the incompatible coexistence of different carbonaceous components a recent controversial issue is explained with reference to different environments of formation the future of ams 14c dating of rock varnishes centres around overcoming the practical limitations of sampling and analysing extremely small quantities of carbon bearing substances future directions for dating varnished rock surfaces may include innovative refinements to the u series cosmogenic isotope and luminescence methods

evaluating effects of chemical weathering and surface contamination on the in situ provenance analysis of building stones in the cuzco region of peru with portable xrf as the only type of instrument capable of determining artifact geochemistry in a wide variety of settings portable x ray fluorescence pxrf may be frequently utilized as probably the best option for collecting data when removal of objects in part or in whole is unfeasible however using pxrf in circumstances where sample selection and preparation diverge from standards developed for lab based instrumentation requires assessing the impact of new and potentially limiting factors to establish the validity of the method in these new contexts here we examine the effects of surface contamination and chemical weathering on the ability to assess provenance of igneous building stones used in the cuzco region of peru surface contamination was assessed through comparing low impact cleaning methods on diorite and andesite blocks and weathering was examined by comparing weathered vs fresh surfaces of samples from two andesite quarries in general the lightest elements were most impacted by contamination and weathering while measurements of many of the heavier elements commonly used in provenance studies were relatively unaffected concentrations of pb and zn were problematic in the urban context of cuzco because of pollution ability to determine provenance of building stones within those limitations i e the validity of this application of pxrf was demonstrated in a preliminary study by comparing measurements from uncleaned exposed building stones in the region to fresh quarry samples

release of selected chemical elements from shale drill cuttings to aqueous solutions of different ph abstract the effect of ph changes on leachability of light and heavy metals from shale drill cuttings generated from unconventional shale gas production was investigated cuttings being the primary byproduct generated from drilling operations belong to the potentially hazardous type of wastes due to presence of heavy and radioactive elements and remains of drilling fluid in this regard assessment of potentially dangerous components pdcs from rock waste materials was performed by application of batch leaching tests which has provided information on the sensitivity of leaching under externally imposed changes in ph natural or caused by treatment in specific scenarios the description of shale rocks mineralogical and chemical properties was performed by means of x ray fluorescence spectroscopy diffractometry as well as scintillation spectrometry the concentrations of released constituents due to the leaching tests were measured by atomic absorption spectrophotometry results were compared and discussed accordingly with the waste acceptable criteria of elution limits analysis of the substrate revealed that the elemental composition was dominated by light elements whereas heavy metals were present in trace amounts however noticeable release of barium 2 0 4 6 was also recorded which has originated from not only rock material but also drill mud minor mobility was observed for transition elements such as cr co fe mn ni zn cu and pb results revealed that drill cuttings follow the requirements for other than hazardous and municipal type of deposition with exception for barium moreover content of radioactive isotopes fulfill the requirements range of acceptable concentrations

partitioning of rare earth elements yttrium and some major elements among source rocks liquid and vapor of larderello travale geothermal field tuscany central italy rare earth elements ree yttrium and some major element concentrations have been measured in the high enthalpy fluids hef of several geothermal wells and the fluid s source rocks in the larderello travale area tuscany central italy the ree and y abundances in the hef range from 0 1 to about 10 pmol kg and are slightly higher in the hef originating from evaporite carbonate sequences calcare cavernoso than in those from phyllites the resulting rey distribution factors between hef and source rocks appkdsource rockhef defined as the ratios of rey ca in both phases range from 0 01 to 0 03 and 0 03 to 0 1 for phyllites and evaporite limestone sequences calcare cavernoso respectively ree y are more retained by the source rocks than ca hef show no inherited and with exception of a small y anomaly no acquired anomalies this indicates a static equilibrium between hef and the source rocks the absence of any eu anomalies points to temperatures less than 250 c in the source region the small negative y anomalies are the result of y depletion in the rock fractions taking part in the water rock interaction due to depressurization of the hef to about 120 c and 2 bars a liquid and a vapor phase is produced which were sampled for the determination of the ree y partitioning between the two phases the apparent partition factors between vapor and liquid appdliquidvapor of ree y range between 0 05 to 0 2 and about 3 for hef originating from the phyllites and evaporites carbonates respectively among all ionic species determined only nh4 has an apparent partition factor appdliquidvapor above one in general rey partition more easily into the vapor phase than the earth alkaline and alkaline elements no significant correlation of ree y in the vapor phase with any of the determined ionic species could be detected this probably points to the dominant presence of ion pairing such as rey oh 3o or reyo oh o

the surface of labradorite feldspar after acid hydrolysis abstract after reaction with a ph both the surface area of the reacted feldspar and the porosity increase with acid hydrolysis modeling of nitrogen sorption onto the surface suggests that the pores have a nominal radius of 20 80 a or less this distribution of pore sizes resembles other acid reacted silicate materials such as glass chrysotile and kaolinite although the mineral surface clearly becomes more porous during acid hydrolysis the increase in powder area also does not coincide with an increase in the flux of dissolved si from the powder we thus attribute most of this increase in area to spallation of the silica rich surface from the feldspar upon drying

characteristics and origin of rock varnish from the hyperarid coastal deserts of northern peru abstract the characteristics of a new type of rock varnish from the hyperarid coastal deserts of northern peru combined with laboratory experiments on associated soil materials provide new insights into the formation of rock varnish the peruvian varnish consists of an fe rich mn poor component covering up to 95 of a varnished surface and a fe rich mn rich component found only in pits and along cracks and ridges the alkaline soils plus the catalytic fe oxyhydroxides that coat much of the varnish surfaces make the peruvian situation ideal for physicochemical precipitation of mn however the low mn content of the dominant fe rich mn poor component suggests that such precipitation is minor this plus the presence of abundant bacteria in the mn rich varnish and the recorded presence of mn precipitating bacteria in varnish elsewhere suggests that bacteria are almost solely responsible for mn precipitation in rock varnish a set of experiments involving peruvian soil samples in contact with water co2 solutions indicates that natural fogs or dews release mn but not fe when they come in contact with eolian materials on rock surfaces this mechanism may efficiently provide mn to bacteria on varnishing surfaces the lack of fe in solution suggests that a large but unknown proportion of fe in varnish may be in the form of insoluble fe oxyhydroxides sorbed onto the clay minerals that form the bulk of rock varnish the results of this study do not substantively change r i dorn s paleoenvironmental interpretations of varnish mn fe ratios but they do suggest areas for further inquiry

iron isotope fractionation during leaching of granite and basalt by hydrochloric and oxalic acids abstract transport of iron fe within hydrothermal and soil environments involves the transferral into aqueous solutions by leaching of complex polyminerallic rocks understanding the isotope fractionation mechanisms during this process is key for any application of the fe isotope system to biogeochemical studies here we reacted biotite granite and tholeiite basalt with 0 5 m hydrochloric acid and 5 mm oxalic acid solutions at ambient temperature solution aliquots were recovered over a seven day period and analysed for major and trace element concentrations and fe isotopic compositions in all experiments fe initially released into solution was isotopically lighter with 56fesolution rock as low as 1 80 in the granite hydrochloric acid system the oxalic acid experiments showed similar patterns but smaller fractionation in all experiments the 56fesolution rock reduced over time which would be in line with the formation of a leached layer as proposed before brantley s l liermann l j guynn r l anbar a icopini g a and barling j 2004 fe isotopic fractionation during mineral dissolution with and without bacteria geochim cosmochim acta 68 15 3189 3204 granite and basalts reacting with hydrochloric acid reached apparent steady state values of 0 60 0 15 and 0 40 0 20 respectively whilst experimental values with oxalic acid were 1 0 0 15 and 0 50 0 15 during the granite experiments alteration of biotite to chlorite followed by dissolution of chlorite were likely the dominant processes whilst in the basalt experiments dissolution of pigeonite was likely the principal source of fe variations in ph during the hydrochloric acid experiments were minimal remaining below 0 5 at all times in oxalic acid solutions the ph increased to over 4 leading likely to precipitation of secondary minerals and adsorption co precipitation of fe onto mineral surfaces these processes could contribute to the greater fractionation observed in the final stages of the oxalic acid experiments our results highlight the importance of mineralogy and fluid composition on the fe isotope systematics during weathering the fractionation processes identified for granites and basalts are in line with those inferred from field observations in soils sediments groundwater and hydrothermal deposits and from laboratory studies of single mineral leaching

rock varnish in new york an accelerated snapshot of accretionary processes abstract samples of manganiferous rock varnish collected from fluvial bedrock outcrop and erie barge canal settings in new york state host a variety of diatom fungal and bacterial microbial forms that are enhanced in manganese and iron use of a dual beam focused ion beam scanning electron microscope to manipulate the varnish in situ reveals microbial forms that would not have otherwise been identified the relative abundance of mn fe enriched biotic forms in new york samples is far greater than varnishes collected from warm deserts moisture availability has long been noted as a possible control on varnish growth rates a hypothesis consistent with the greater abundance of mn enhancing bioforms sub micron images of incipient varnish formation reveal that varnishing in new york probably starts with the mortality of microorganisms that enhanced mn on bare mineral surfaces microbial death results in the adsorption of the mn rich sheath onto the rock in the form of filamentous networks clay minerals are then cemented by remobilization of the mn rich material thus the previously unanswered question of what comes first clay mineral deposition or enhancement of mn can be answered in new york because of the faster rate of varnish growth in contrast very slow rates of varnishing seen in warm deserts of microns per thousand years make it less likely that collected samples will reveal varnish accretionary processes than samples collected from fast accreting moist settings

insights into the formation of rock varnish in prevailing dusty regions financial support was provided by the ash and queca projects mineco cgl2008 00099 and cgl2011 23307 and by fundacio bosch i gimpera project fbg 307466

blind testing of rock varnish microstratigraphy as a chronometric indicator results on late quaternary lava flows in the mojave desert california rock varnish is a manganiferous dark coating ubiquitous in desert landscapes to test the validity of varnish microstratigraphy as a chronometric indicator varnish samples were collected from radiometrically dated and undated late quaternary lava flows in amboy cima and pisgah volcanic fields avf cvf pvf in the mojave desert of california western united states varnish microstratigraphies show a replicable layering sequence that appears to record regional climate changes that likely correspond in time to the younger dryas and heinrich events in the north atlantic region microstratigraphic patterns on these volcanic fields match patterns found in varnishes from other western us sites with available radiometric age constraints based on this regional chronology varnishes from the a flow h flow and a stone pavement surface in the cima volcanic field were estimated to be 16 5 24 74 85 and 74 85 ka respectively these ages are consistent with previously published cosmogenic 3 he ages of 18 20 72 74 and 80 85 ka for these geomorphic surfaces varnishes from the i flow at cima yielded a puzzling age estimate of 39 ka which is consistent with an older 3 he age of 37f6 ka reported for the i flow but inconsistent with a younger 3 he age of 31f7 ka and a cosmogenic 36 cl age of 27f1 3 ka for the same flow reinterpretation of the original varnish age data with knowledge of then available field mapping results of the i flow suggests that the i cone is polycyclic and different flow units were probably unintentionally sampled in the field the revised varnish ages of 30 and 39 ka for the i flow thus may be in good agreement with their corresponding 3 he and 36 cl ages in a blind test of the method varnishes from the phase 1 flow at pisgah an unnamed flow called here the ivflow at cima and the amboy flow were estimated to be 24 30 46 60 and 74 85 ka respectively these ages agree well with 36 cl ages of 22 5f1 3 46f2 and 79f5 ka reported for the same flows by phillips geomorphology 2002 these test results provide convincing evidence that varnish microstratigraphy once radiometrically calibrated can be used as a valid dating tool to estimate surface exposure ages of desert landforms in the western us drylands d 2002 elsevier science b v all rights reserved

from dust to varnish geochemical constraints on rock varnish formation in the negev desert israel abstract chemical compositions of rock varnish from the negev desert of israel and local settled dust were used to constrain the mechanisms of varnish formation and patterns of mn enrichment and accumulation in the varnish rock varnish was sampled from coeval undisturbed prehistoric flint artifacts along a south north climatic transect 30 120 mm yr of rain our analyses indicate that mn ba and pb in the varnish are significantly enriched 100 in respect to the local settling dust and that mn content systematically fluctuates with depth in the varnish the varnish and settled dust data combined with basic thermodynamic and kinetic reasoning are used to constrain the following geochemical model of rock varnish formation dust accumulates in micro basins on exposed rock surfaces under ph 8 common negev value and during wetting by dew and rain mn in the dust is mobilized and leached to a depth of 5 m under the varnish surface where hollandite mn oxides precipitate and are adsorbed onto and between the porous clay minerals that comprise most of the varnish during its mobile phase mn oxide is negatively charged and adsorbs rare earth elements once the solution dries abrasion removes the upper weakly cemented dust sediment which contains mainly si al and fe which are not mobile at ph 8 ca is also removed in large quantities mn ba pb and the ree are deposited at a depth and thus protected from erosion reoccurrences of these processes result in a noticeable accumulation of these elements but not of si al or fe the alternating mn rich and mn poor laminas form as a result of a competition between the leaching rate of mn and the adhesion rate of the clay minerals when moisture is high low lamina with high low mn clay mineral ratio forms

behaviour of rare earth elements during high pressure metamorphism abstract the behaviour of rare earth elements ree during high pressure metamorphism has been studied to estimate their possible use in determining the geodynamic settings of eclogite procoliths eclogites exhibiting various degrees of amphibolitization have been studied in a number lf metamorphic complexes in the urals mongolian fold belt the kokchetav massif in northern kazakhstan and the atbashi range in the central tien shan all in the u s s r in addition an eclogitized metagabbro from the koralpe austrian alps and gabbroids transformed into garnet amphibolites from the kokhchetav massif have been investigated the analytical data suggest that about 30 60 of the light rare earth elements lree in eclogites is present in the intergranular space the results of the investigation demonstrate that the ree were virtually immobile during eclogite formation their low mobility can be explained either by absence of complex formers in the fluid phase or by low fluid rock ratio

characteristics of desert varnish from nanometer to micrometer scale a photo oxidation model on its formation abstract rock varnish is a widespread mn rich rock coating commonly developed in arid environments but the mechanism for its formation is still under debate in this study rock varnish and adjacent soil dust collected from gobi desert were analyzed for exploring the possible abiotic oxidation mechanism of mn oxides the occurrence of rock varnish shows a direct and close relationship with strong irradiation of sunlight giving the first evidence of photochemical genesis abundant caves and tunnels with average diameter of 1 5 m are observed on varnish surface regions which facilitate the penetration of sunlight and water metal oxyhydr oxides including birnessite hematite goethite rutile and anatase account for the major components of rock varnish which are all solar light responsive semiconducting minerals the trace elements enrichment patterns revealed by la icp ms provide the indication of an aqueous origin the positive ce anomalies in varnish in contrast to the rock substrate as well as the positive correlation between ce and mn suggest a strong oxidizing environment in the genesis of rock varnish therefore the photo generated holes and reactive oxygen species ross on metal oxides in varnish can promote mn ii oxidation which are further demonstrated from thermodynamic and kinetic considerations ross including 1o2 and oh with strong oxidizing capability are detected by epr in varnish suspension providing the direct evidence for mn ii oxidation laboratory experimental simulations show the photocatalysis of metal oxides in rock varnish greatly promote mn ii oxidation by 2 10 7 97 times in comparison with homogenous solution oxidation all these lines of evidence suggest that light induced abiotic process may play important roles in the formation of rock varnish together with other abiotic and biotic pathways which can even provide implications for the evolution of mn oxides on surface of terrestrial planets

geochemistry of mineralization with exchangeable rey in the weathering crusts of granitic rocks in south china abstract mineralization with exchangeable rare earth element ree and yttrium mex rey has been recognized in the weathering profiles in south china since the early 1970 s this type of rey mineralization occurs in weathering profiles of parent rocks ranging in composition from granite to acidic volcanic rocks and lamprophyre the majority of the known resources occurring in the weathering profiles of granitic rocks total resources of this type of rey amount to millions tons of rare earth oxides and therefore represent one of the most important types of rare earth resources in china particularly for heavy rare earth elements hree and yttrium accumulation of rey in the weathering profiles of granitic rocks is strongly controlled by the resistance to weathering of the principal rey bearing accessory minerals in the parent rocks only a limited proportion of total rey 4 and na etc in electrolyte solutions and can be removed by complexing agents such as edta are commonly the major form of ree occurrence in the b horizon cerium is enriched in the top layer a horizon and depleted in the subsurface horizons of the weathering profiles most likely due to the oxidation of ce iii to ce iv followed by cerianite formation or absorption onto clays and or fe and al oxyhydroxides

rare earth elements ree minerals in the silius fluorite vein system sardinia italy publisher elsevier articletitle rare earth elements ree minerals in the silius fluorite vein system sardinia italy journaltitle ore geology reviews articlelink http dx doi org 10 1016 j oregeorev 2015 11 016 content type article copyright copyright 2015 elsevier b v all rights reserved