ree th and u behaviour during hydrothermal and supergene processes in a granitic environment the two mica granites which host the two main uranium deposits from the northwestern massif central france margnac fanay and le bernardan deposits were hydrothermally altered both before and during the deposition of the primary u mineralization both altered rocks and mineralizations were then subjected to supergene processes we have analyzed the rare earth elements ree th and u in fresh and altered mineralized and barren whole rocks and in the pitchblendes to study the behaviour of these elements during hydrothermal and supergene processes in a granitic environment when fluids are aqueous with a low salt content mainly chloride then irrespective of temperature 400 450 c for feldspar episyenitization 350 c for mica episyenitization and 100 150 c for the quartz coffinite montmorillonite adularia stage the ree patterns and parameters the hree lree fractionation the th concentration and the th ce ratio are not modified this indicates that monazite which controls these elements in the two mica granites remains stable under such conditions in contrast when ligands are present in the solutions co2 3 or hco 3 with the pitchblende stage at 350 c hpo2 4 or other phosphorous anions during supergene events at low temperatures ree are either leached or concentrated depending on the prevailing redox conditions and there is hree lree fractionation the ree content of the newly formed minerals pitchblende appears to be mainly controlled in such deposits by the fluid composition

episyenitisation dans le gisement d uranium du bernardan marche comparaison avec des gisements similaires du nord ouest du massif central francais le gisement d uranium du bernardan exploite dans le granite a deux micas de la marche occidentale appartient au groupe des gisements d impregnation la mineralisation uranifere pechblende coffinite produits noirs autunite est disseminee dans une roche vacuolaire appelee episyenite cette derniere resulte d une alteration hydrothermale du granite par des solutions chaudes 370 260 c 2 5 7 poids equiv nacl le quartz est dissout les feldspaths principalement les plagioclases et les biotites sont partiellement transformes en phengites les muscovites et orthoses granitiques se reequilibrent avec perte de sodium cette alteration est guidee par un reseau de fractures a differentes echelles une alteration comparable a ete observee dans d autres gisements du nord ouest du massif central francais comme margnac et fanay dans le massif de st sylvestre et hyverneresse dans celui du millevaches les transformations mineralogiques a l exception de la quantite de phengites secondaires les changements chimiques lessivage de silice et metasomatisme potassique les conditions p t et le controle tectonique sont les memes dans tous ces gisements

uranium migration and retention during weathering of a granitic waste rock pile abstract this study investigates the post mining evolution of s type granitic waste rocks around a former uranium mine vieilles sagnes haute vienne nw massif central france this mine was operated between 1957 and 1965 in the la crouzille former world class uranium mining district and is representative of intra granitic vein type deposits 50 years after mine closure and the construction and subsequent re vegetation of the granitic waste rock pile we evaluate the environmental evolution of the rock pile including rock alteration neo formation of u bearing phases during weathering and u migration vertical trenches have been excavated through the rock pile down to an underlying paleo soil allowing the investigation of the vertical differentiation of the rock pile and its influence on water pathways weathering processes and u migration and retention arenization dominantly drives liberation of u by dissolution of uraninite inclusions in the most alterable granitic minerals i e k feldspar and biotite retention of u in the matrix at the base of the waste rock pile and in the underlying paleo soil most likely occurs by precipitation of nano uranyl phosphates or a combination of co precipitation and adsorption reactions of u onto fe oxy hydroxides and or clay minerals even though u migration was observed u is retained in stable secondary mineral phases provided the current conditions will not be modified

late quaternary climate and sea level changes recorded in sediment composition off the buyuk menderes river delta eastern aegean sea turkey abstract influences of holocene climatic and sea level changes on sedimentation on the continental shelf off the buyuk menderes river delta sw turkey were investigated using grain size and x ray clay mineralogical data on surficial and 14c dated core sediments collected at 19 81 m water depths modern fine grained siliciclastic sediments cover most of the seafloor of inner to mid shelf areas a narrow relict belt extends from northwest to south at 66 81 m water depths where sediments are characterized by abundant sand and gravel 27 52 and biogenic carbonate 16 44 contents and microscopic examination suggests an older origin the radiocarbon ages of mid and lower sections in cores 3670 10 380 yr bp reflect sedimentation under depositional conditions from early to late holocene in the study area additionally downcore changes of grain size toward coarser grained sediments most probably record global climatic effects with sea level changes specifically the transition from lowstand in early holocene to highstand at mid late holocene the presence of this relict belt in offshore waters can be attributed largely to active uplift tectonics the coarser grained relict belt compared with available seismic profiles corresponds to an lowstand unconformity of bottomset beds of the prograding buyuk menderes delta reconstruction from nautical charts clearly showed the presence of an e w trending submarine canyon paleo buyuk menderes river valley in the course of buyuk menderes graben this is interpreted as product of combination of sea level lowstands and subsidence tectonics throughout the late quaternary smectite 35 62 illite 28 51 and kaolinite 12 19 constitute the dominant clay minerals in the

contrasted monazite hydrothermal alteration mechanisms and their geochemical implications in spite of the major importance of monazite as a repository for the rare earths and th in the continental crust for u th pb geochronology and as a possible form for high level nuclear waste very little work has been carried out so far on the behaviour of this mineral during fluid rock events this contribution describes two contrasting examples of the hydrothermal alteration of monazite the first case comes from a sample of the carnmenellis granite cornwall southwest england chloritized at 284 16 c whereas the other occurs in the skiddaw granite lake district northwest england which underwent greisenization at 200 30 c an integrated study involving backscattered scanning electron microscopy electron microprobe analyses and laser ablation inductively coupled plasma mass spectrometry la icp ms reveals that the chloritization event was characterized by the coupled substitution 2ree3 th4 ca2 in the altered parts of the monazite thus leaving the p o framework of the crystal untouched in contrast greisenization led to the coupled substitution ree3 p5 th4 si4 and therefore involved a partial destruction of the phosphate framework the resulting rare earth element patterns are quite different for these two examples with a maximum depletion for dy and er in the altered parts of the carnmenellis monazite whereas the skiddaw monazite shows a light rare earth depletion but an yb and er enrichment during alteration this latter enrichment accompanied by an increase in u but roughly unchanged pb concentrations probably resulted from a decrease in the size of the 9 coordinated site in monazite thereby favouring the smaller rare earths these contrasted styles of monazite alteration show that the conditions of fluid rock interaction will not only affect the aqueous geochemistry of the lanthanides actinides and lead and the relative stability of the different minerals holding these elements variations in these conditions will also lead to various possible chemical exchanges between the crystalline phases and the hydrothermal fluids the occurrence of common lead along penetrative cracks in the carnmenellis monazite shows that only a leaching prior to the u pb analyses of the whole grain will permit an accurate determination of the magmatic crystallization age in contrast for the skiddaw case it may be possible to date the fluid rock event by in situ 207pb 206pb geochronology the observation that the altered parts of both monazite examples display nd leaching and no significant sm nd fractionation indicates that they should not affect the host whole rock nd isotopic signatures finally it appears that monazite like ceramics designed for the containment of high level nuclear wastes will retain th and the geochemically equivalent transuranic elements during fluid rock events similar to those documented in this study but may release nd u and the corresponding radionuclides to the environment

volcanism and uranium mineralizations the concept of source rock and concentration mechanism abstract comparative mineralogical petrographical and geochemical studies were undertaken in several places in the world sierra pena blanca mexico macusani field peru meseta los frailes bolivia and puna argentina in order to understand the behaviour of uranium in volcanic environment and to define the characteristics of a volcanic source rock and the main concentration mechanisms our results indicate 1 1 a fertile volcanic rock is alumina and alkali rich alumino potassic in the granite terminology alkaline subalkaline and calc alkaline volcanics are much less favorable 2 2 because of the stability of the accessory minerals during all the events which occur during and or after the cooling of the volcanic formations uranium is only leached from the matrix thus the leachable metal stock is directly related to the proportionate volume of the matrix and to its u content 3 3 the early post magmatic stages such as the high temperature devitrification and the vapor phase crystallization concentrate the previously disseminated uranium at the mineral scale and increase the efficiency of the subsequent leaching stages the glass hydration does not mobilize uranium 4 4 the uranium deposits spatially related to volcanism may result from different processes either hydrothermal and related to the volcanic activity or supergene the host rocks may be the volcanic rocks themselves or the surrounding country rocks

the cadomian orogeny in saxo thuringia germany geochemical and nd sr pb isotopic characterization of marginal basins with constraints to geotectonic setting and provenance abstract the cadomian basement and the cambro ordovician overstep sequence in saxo thuringia is characterized by clastic sedimentation from the late neoproterozoic to the ordovician magmatism in the avalonian cadomian arc preserved in saxo thuringia occurred between ca 570 and 540 ma peri gondwanan basin remnants with cadomian to early palaeozoic rocks are exposed as very low grade metamorphosed rocks in six areas schwarzburg anticline berga anticline doberlug syncline north saxon anticline lausitz anticline and elbe zone a hiatus in sedimentation between 540 and 530 ma cadomian unconformity is related to the cadomian orogeny a second gap in sedimentation occurred during the upper cambrian 500 to 490 ma and is documented by a disconformity between lower to middle cambrian rocks and overlying tremadocian sediments major and trace element signatures of the cadomian sediments reflect an active margin continental arc those of the ordovician sediments a passive margin the cambrian sediments have inherited the arc signature through the input of relatively unaltered cadomian detritus initial nd and pb isotope data from the six saxo thuringian areas demonstrate that there is no change in source area with time for each location but that there are minor contrasts among the locations 1 cadomian sediments from the lausitz anticline the doberlug syncline and the elbe zone have lower 207pb 204pb than all other areas 2 the core of the schwarzburg anticline which is overprinted by greenschist facies conditions and detached is isotopically heterogeneous one part of its metasedimentary units has less radiogenic nd than sediments from other low grade units of similar age in the same area 3 cadomian sediments from the schwarzburg anticline show an input of younger felsic crust 4 the rothstein group shows distinct input of young volcanic material also 5 cadomian sediments from the lausitz anticline the elbe zone and parts of the north saxon anticline are characterized by input from an old mafic crust nd isotope data of the remaining areas yield average crustal residence ages of the sediment source of 1 5 1 9 ga which suggests derivation from an old craton as found for other parts of the iberian armorican terrane collage similarly the pb isotope data of all areas indicate sediment provenance from an old craton the rapid change of lithologies from greywacke to quartzite from the late neoproterozoic cadomian basement to the ordovician does not reflect changes in sediment provenance but is essentially due to increased reworking of older sediments and old weathering crusts that formed during various hiatus of sedimentation this change in sediment maturity takes its chemical expression in lower overall trace element contents in the quartzite dilution effect by quartz and relative enrichment of some trace elements zr mree hree due to detrital zircon and garnet the rb sr systematics of the quartzites and one ordovician tuffite was disturbed most likely during the variscan orogeny which suggests a lithology controlled mobility of alkali and calc alkali elements by comparison with available data it seems unlikely that only nd tdm model ages are useful to distinguish between west african and amazonian provenance nd tdm model ages of 1 5 to 1 9 ga in combination with paleobiogeographic aspects age data from detrital zircon and palaeogeographic constraints especially through tillites of the saharan glaciation in the hirnantian strongly indicate a provenance of saxo thuringia from the west african craton

the rare earth element geochemistry of acid sulphate and acid sulphate chloride geothermal systems from yellowstone national park wyoming usa rare earth element ree concentrations have been determined by inductively coupled plasma mass spectrometry icp ms in acid sulphate and acid sulphate chloride waters and the associated sinters and volcanic rocks from the yellowstone national park ynp wyoming usa geothermal system ree concentrations in the volcanic rocks range from 222 to 347 ppm their chondite normalised ree patterns are typical of upper continental crust with lree hree and negative eu anomalies total ree concentrations in the fluids range from 3 to 1133 nmol kg 1 162 ppm and ree concentrations in sinter are 181 ppm ree abundances and patterns in drill core material from ynp indicate some ree mobility normalisation of ree concentrations in altered lava creek tuff lct from y 12 drill core to ree concentrations in fresh lct indicate that the ree overall have been depleted with the exception of eu which has been decoupled from the ree series and concentrated in the altered rocks relative to the host rocks the ree patterns of the fluids are variably depleted in hrees and lrees and usually have a pronounced positive eu anomaly this decoupling of eu from the ree suite suggests that 1 eu has been preferentially removed either from the host rock glass or from the host rock minerals or 2 the waters are from a high temperature or reducing environment where eu2 is more soluble than the trivalent rees since the latter is inconsistent with production of acid sulphate springs in a low temperature oxidising near surface environment we suggest that the positive eu anomalies in the fluids result from preferential dissolution of a eu rich phase in the host rock spatial and temporal variations in major element chemistry and ph of the springs sampled from norris geyser basin and crater hills accompany variations in ree concentrations and patterns of individual geothermal springs these are possibly related to changes in subsurface plumbing which results in variations in mixing and dilution of the geothermal fluids and may have lead to changes in the extent and nature of ree complexing

dating multiply overprinted sn mineralized granites examples from the erzgebirge germany granites and primary tin mineralization in the erzgebirge were dated using 1 conventional u pb dating of uraninite inclusions in mica 2 rb sr dating of inclusions in quartz that represent highly evolved melts 3 re os dating of magmatic hydrothermal molybdenite and 4 chemical th u pb dating of uraninite conventional isotope dilution and thermal ion mass spectrometry and chemical th u pb dating of uraninite in granites from the ehrenfriedersdorf mining district provide ages of 323 9 3 5 ma 2 greifenstein granite and 320 6 1 9 and 319 7 3 4 ma 2 both sauberg mine in agreement with u pb apatite ages of 323 9 2 9 and 317 3 1 6 ms 2 both sauberg mine rb sr analysis of melt inclusions from zinnwald gives highly radiogenic sr isotopic compositions that with an assumed initial sr isotopic composition permit calculation of precise ages from single inclusions the scatter of the data indicates that some quartz hosted melt inclusions have been affected by partial loss of fluid exsolved from the melt inclusion re os dating of two molybdenite samples from altenberg provides ages of 323 9 2 5 and 317 9 2 4 ma 2 together with age data from the literature our new ages demonstrate that primary tin mineralization and the emplacement of the large sn specialized granites in the erzgebirge fall in a narrow range between 318 and 323 ma primary sn mineralization occurred within a short interval during post collisional collapse of the variscan orogen and was essentially synchronous over the entire erzgebirge in contrast to earlier claims no systematic age difference between granites of the eastern and western erzgebirge was established furthermore our data do not support a large age range for late variscan granites of the erzgebirge 330 290 ma as has been previously suggested

the pb isotopic systematics during crustal contamination of subcrustal magmas the hercynian magmatism in the serie dei laghi southern alps italy abstract the pb isotopic composition and pb u and th concentrations of a series of hercynian granite plutons and mafic intermediate stocks and dykes belonging to the serie dei laghi western southern alps have been analyzed the initial pb isotope ratios of both the granites and the dykes are typical of the lower crust and are spread over a significant range 206 pb 204 pb 280 17 883 18 530 207 pb 204 pb 280 15 597 15 710 and 208 pb 204 pb 280 38 077 38 708 four dykes all at the same locality display evidence of post emplacement fluid circulation with mobilization of u and pb in spite of the pb isotopic crustal signature of the studied rock series the 87 sr 86 sr ratios reach values as low as 0 704 in the dykes and as low as 0 707 in the granites suggesting a mantle contribution in the genesis of both lithologies indeed when compared with the metasediments from the same area the magmatic rocks have somewhat lower initial 207 pb 204 pb ratios which weakly trend towards the less radiogenic pb isotopic composition of the mantle the relationships between the pb isotopic composition and the pb content along with the pb and sr isotopic covariation suggest that the suite under examination was generated from a mantle derived primary magma that underwent extensive crustal contamination a primary magma similar to the neighbouring ivrea mafic complex has been inferred further assimilation of crustal material is particularly evident in the dykes while the granites appear to have been generated mainly by crystal fractionation processes from the intermediate magma already contaminated

isotopic systematics o h c sr nd of superimposed barren and u bearing hydrothermal systems in a hercynian granite massif central france abstract the hercynian 325 ma granitic complex of saint sylvestre experienced two hydrothermal episodes the first one leading to the formation of a typical alteration facies called episyenite mainly characterized by the dissolution of granitic quartz the second one leading to the deposition at 280 ma of a major u deposit the present study documents the isotopic characteristics of these hydrothermal events 18 o 16 o d h and 13 c 12 c systematics demonstrate that barren episyenites were generated during hydrothermal interaction of large amounts of mainly meteoric water with the granite the ore depositing fluid equilibrated in a sedimentary formation before entering the granite episyenitization was dated at 301 2 ma which is 25 ma later than the granite emplacement the rb sr isochron relationship implies isotopic equilibrium within the fluid phase and between the fluid and the host rocks which confirms the high water rock ratio inferred from o h isotope systematics a coupled nd and sr isotope investigation demonstrates that at least nd was reworked from the granite in the episyenite genesis but sr and possibly nd had an exotic origin consistent with the inferred sedimentary origin during the ore forming stage the present study emphasizes the fact that spatially superimposed hydrothermal events in a granitic environment can be 1 disconnected from the magmatic history of the granite itself and 2 mutually disconnected from chronological and chemical points of view

origin of negative ce anomalies in barberton sedimentary rocks deduced from la ce and sm nd isotope systematics abstract the origin of sedimentary rocks with negative ce anomalies among several samples derived from the barberton greenstone belt 3250 ma south africa was investigated using la ce and sm nd isotopic systematics together with light rare earth element lree abundances negative ce anomalies were recognized in two sedimentary rocks a banded ferruginous chert and a shale their ce ce values are 0 40 and 0 81 respectively initial ce isotopic ratio calculated for the ferruginous chert 138 ce 142 ce 3250 ma 0 0225059 is far lower than chur value at 3250 ma and even the value at earth formation 138 ce 142 ce chur 4560 ma 0 0225409 the calculated initial ce isotopic ratio for the shale with a ce anomaly is also lower than that of other rocks without ce anomalies these results indicate that the negative ce anomalies were not inherited from an archean redox change but occurred following later episodes of alteration two possible formation models were examined to estimate a plausible occurrence age for the negative ce anomalies one is characterized by ce extraction and the other is by an addition of la nd and sm both models indicate that negative ce anomalies arose before 1100 ma this study suggests that la ce isotopic systematics provides a unique tool to constrain the occurrence age of negative ce anomalies observed in archean sedimentary rocks and gives some hints about the redox condition in the archean ocean and the evolution of the earth

diapirism and sagduction as a mechanism for deposition and burial of timiskaming type sedimentary sequences superior province evidence from detrital zircon geochronology and implications for the borden lake conglomerate in the exposed middle to lower crust in the kapuskasing uplift abstract neoarchean timiskaming type sedimentary sequences are the youngest supracrustal rocks in many archean greenstone belts detrital zircon ages from such a sequence in the northwestern superior province match the known ages of volcanism and plutonism in the surrounding area they show a marked change in zircon provenance from the lower to upper part of the sequence in a clear pattern that can be best explained by a model involving basin formation by diapirism and sagduction in this model detritus were derived from down stratigraphy erosion above rising granitoid domes and deposited in a sinking synclinal keel between them these new data thus support the presence of vertical tectonism in the superior province at a time in which abundant evidence for horizontal tectonism has been documented diapirism and sagduction provides a mechanism to bring supracrustal rocks deep into the crust below the synclinal keel without involving crustal thickening and potentially during crustal extension this can readily explain the observation in the kapuskasing uplift that the borden lake conglomerate a timiskaming type sedimentary rock was buried up to 30 km deep in the crust and experienced upper amphibolite to granulite facies metamorphism very shortly after its deposition

mineralogical and geochemical characteristics of hydrothermal alteration and episyenitization in the konigshain granites northern bohemian massif germany the late hercynian granites of konigshain underwent multistage hydrothermal processes extensive high temperature late magmatic alteration is for example indicated by low zr hf and an ree pattern displaying the tetrad effect intensive post magmatic alteration of the granite occurred along brittle structures at least two main stages of post magmatic hydrothermal alteration are involved the first high temperature stage which is characterized by albitization and or quartz leaching episyenitization resulted from fluid rock interaction with late magmatic fluids that very probably mixed with external low salinity fluids quartz dissolution was triggered by vapour condensation and or the cooling of these fluids below 450 c along brittle structures the high porosity resulting from quartz leaching during stage 1 assisted subsequent circulation of low temperature fluids at stage 2 the latter is characterized by the chloritization and illitization of episyenites almost all major and trace elements were enriched or depleted during one of the main alteration stages however zr hf th and ti were immobile during post magmatic alteration the significant depletion of lree and the enrichment of hree in albitized samples is controlled by the dissolution of monazite and the new formation of hree rich polycrase y or aeschynite y during post magmatic stage 1 negative ce anomalies of episyenites are associated with illitization and suggest oxidizing conditions during stage 2

hydrothermal metasomatic and tectono metamorphic processes in the isua supracrustal belt west greenland a multi isotopic investigation of their effects on the earth s oldest oceanic crustal sequence abstract despite superimposed metamorphic overprinting and metasomatic alterations primary volcanic features remain preserved in low strain domains of mafic volcanic sequences in the western isua supracrustal belt isb west greenland these basaltic successions represent the hitherto oldest known fragments of oceanic crust on earth early archean metasomatic fluids rich in light rare earth elements lree th u pb ba and alkalies invaded the supracrustal package and distinctively altered the basaltic sequences field relationships source characteristics traced by pb isotopes and geochronological results provide indications that these fluids were genetically related to the emplacement of tonalite sheets into the isb between 3 81 and 3 74 ga ago subsequent early archean metamorphism homogenized the mixed primary and metasomatic mineral parageneses of these metavolcanic rocks allanite occurs as the most characteristic and critical secondary metasomatic metamorphic phase and is developed in macroscopically discernible zones of increased metsomatic alteration even in domains of low strain because of its high concentration of lree th and u this secondary mineral accounts for much of the disturbances recorded by the sm nd and th u pb isotope systematics of the pillowed metabasalts the supracrustal sequences were tectono metamorphically affected to varying degrees during a late archean 2 6 to 2 8 ga old event also recognized in the adjacent gneiss terranes of the isuakasia area the degree to which bulk rocks were isotopically reequilibrated is directly dependent on the different relative contributions of allanite hosted parent daughter elements to the overall whole rock mass budget of the respective isotope systems although low strained initially only weakly metasomatized pillow basalts remained more or less closed with respect to the u pb and rb sr systems since 3 74 ga the sm nd system appears to have been partially opened on a whole rock scale during the late archean event this diversified behavior of the whole rock isotope systems with respect to late archean overprinting is explained by the combination of mass budget contributions of the respective elements added during metasomatism and the partial opening of metasomatic macroenvironments during late archean recrystallization processes with associated renewed fluid flow in reactivated zones of high strain where primary metasomatic alteration is most prominently developed late archean partial resetting also of the u pb isotope system on a whole rock scale occurred this is consistent with an apparent late archean age of kyanite which initially crystallized during the early archean metamorphism its age is controlled by the u pb systematics of allanite inclusions which have exchanged their isotopic properties during the tectono metamorphic event that overprinted the oceanic crustal sequence at isua more than 1000 myr later these results underline the need for care in the interpretation of whole rock geochemical data from polymetamorphic rocks in general and from the isua oceanic crustal sequences in particular to constrain isotopic models of early earth s evolution likewise this study cautions against the indiscriminate use of geochemical data of metavolcanic rocks from isua to infer models for geotectonic settings relevant for their formation

nd isotopes demonstrate the role of contamination in the formation of coexisting quartz and nepheline syenites at the abu khruq complex egypt the petrogenesis of abu khruq an 89 ma alkaline ring complex of eastern egypt which is composed of alkali gabbros and both silica over and undersaturated syenites has been investigated major and trace element relationships and nd and sr isotope data are consistent with formation of the gabbros from an alkaline mafic magma that experienced extensive fractionation and all syenites from a felsic derivative of this melt the parental magma had an 87sr 86sr of 0 7030 and an 143nd 144nd of 0 512750 nd 4 4 indicating derivation from a depeleted mantle source the initial 143nd 144nd ratios are 0 512721 to 0 512748 for the gabbros 0 512739 to 0 512750 for the alkali syenites and trachytes 0 512717 to 0 512755 for the nepheline syenites and 0 512706 to 0 512732 for the quartz syenites in contrast analyzed precambrian granites from eastern egypt have generally lower 143nd 144nd ratios ranging from 0 51247 to 0 51261 or nd 0 8 to 1 7 for 89ma their nd model ages range from 775 to 935 ma and suggest there was no significant input of pre pan african crust in their formation among abu khruq rocks 143nd 144nd ratios indicate that the quartz syenites formed by open system crustal contamination processes whereas the nepheline syenites experienced little or no contamination modeling shows that contamination occurred at various stages affecting both mafic and more evolved compositions with input of about 20 crustal nd for the most contaminated samples the degree of contamination is related to the silica saturation of the quartz syenites simplified modeling of magma evolution within petrogeny s residua system demonstrates the ability of afc processes to cause a critically undersaturated magma to evolve across the feldspar join and produce oversaturated rocks the oversaturated syenites at abu khruq were produced in this manner whereas the nepheline syenites formed by fractionation without similarly large degrees of contamination the results have broad implications for the formation of subvolcanic complexes in continental settings beyond the important production of silica oversaturated compositions from crustal interaction they underscore the importance of crustal interactions in the formation of the various lithologies such interactions occur at various stages in the evolution of the magmas and as such are not strictly coupled with fractional crystallization while previous study of abu khruq has demonstrated extensive hydrothermal alteration of o and sr isotopes the present work shows that the nd isotope ratios were not significantly affected and thus reflect magmatic signatures this feature combined with relatively small corrections for initial ratios emphasizes the utility of nd isotopes for petrogenetic studies

relationships between intermediate and acidic rocks in orogenic granitoid suites petrological geochemical and isotopic sr nd pb data from capo vaticano southern calabria italy abstract major trace element and isotopic data are reported for hercynian granodiorites and tonalites from capo vaticano calabria with the aim of clarifying the relationships between acidic and intermediate lithologies in orogenic intrusive suites these granodiorites sio 2 70 5 73 5 are peraluminous relatively depleted in rb u th and pb and display a large variation in many geochemical and isotopic parameters ree show fractionated cross cutting chondrite normalized patterns with small but significant negative eu anomalies initial 290 ma sr and nd and present day pb isotope ratios are 87 sr 86 sr 290 0 7105 0 7110 143 nd 144 nd 290 0 51175 0 51221 206 pb 204 pb 18 35 18 50 207 pb 204 pb 15 64 15 76 208 pb 204 pb 38 51 39 03 pb isotope ratios determined for separated feldspars show similar 207 pb 204 pb and 208 pb 204 pb and higher 207 pb 204 pb ratios compared to the present day values for the whole rock the tonalites sio 2 57 6 67 3 are typically calc alkaline in composition and most of them are weakly peraluminous they display large heterogeneities in trace element abundances ree patterns and nd and pb isotope ratios both between and within individual intrusive units sr nd and pb isotopic compositions display a range of values close to that of the associated granodiorites 87 sr 86 sr 290 0 7099 0 7111 143 nd 144 nd 290 0 51185 0 51224 206 pb 204 pb 18 31 18 56 207 pb 204 pb 15 65 15 72 208 pb 204 pb 38 41 39 59 the obtained data indicate that the tonalites and granodiorites share many compositional features which point to a genetic linkage likewise many petrological geochemical and field data exclude the possibility that all the granodiorites derive from intermediate magmas by any common evolutionary process such as crystal liquid fractionation or assimilation fractional crystallization afc and point to a different genesis for the two rock types an origin of the granodiorites by the mixing of two separate acidic melts one of crustal anatectic origin and one probably derived from an intermediate magma by crystal liquid fractionation or afc is suggested by the data presented the tonalites appear to have been generated by interaction of a mafic magma with crustal end member s with isotopic and geochemical signatures similar to those of the granodiorites the large involvement of crustal material in the genesis of the capo vaticano granitoids is responsible for the many common compositional characteristics observed in the intermediate and acidic rocks however a contribution from mantle components is also indicated by petrological and geochemical data as well as by the occurrence of mafic enclaves commonly present in the tonalites nevertheless the geochemical and isotopic features of such a mantle component appear to be greatly diluted by a large quantity of crustal material involved in the genesis of the studied granitoids

the ree content of some hydrothermal fluids ree concentrations were determined in solutions from submarine hydrothermal vents on the east pacific rise and for the first time from continental geothermal fields in tibet and bulgaria they indicate that in hydrothermal systems ree are immobile at temperatures below 350 c and for water rock ratios of 105 nd values of submarine solutions and anhydrites 4 7 to 6 2 suggests recharge on the sedimentcovered flanks of the ridge carbonate anions as measured by alkalinity appear to increase the solubility of heavy ree somewhat but not to the extent that substantial amounts of ree could be driven out from rocks by hydrothermal activity

rare earth elements and hydrothermal ore formation processes abstract the geochemical behaviour of ree is influenced by nearly all important hydrothermal ore formation processes including fluid rock interactions fluid precipitations adsorption and scavenging onto particles and changes in fluid temperature pressure ph eh alkalinity and ligand concentration destabilization of ree complexes in response to these physicochemical changes and possible chemical crystallographic controls determine the concentration and distribution of ree within hydrothermal minerals mineraloids and amorphous phases alteration assemblages of intrusive related mineralisations may exhibit a wide range of ree distributions and ree fractionation trends the ree distribution within these hydrothermally altered lithologies will depend on the ree concentration in the rock and the fluid the partitioning behaviour of the ree between the rock phases and the fluid and the types of alteration reactions which take place reactive rocks such as carbonate rich lithologies of skarn deposits may gain or loose significant amounts of ree during fluid rock interactions ree geochemical investigations combined with fluid inclusion and stable isotope studies may point to the origin of alteration products and the source s of ore fluids ancient massive sulphide ores commonly exhibit anomalous eu concentrations similar to many recent submarine hydrothermal precipitates the recognition of hydrothermal fluid seawater sedimentary or volcanically derived ree distributions within ores chemical sediments and hydrothermally altered lithologies may help to constrain genetic modelling of massive sulphide deposits care should be taken with the interpretation of ree distributions from metamorphosed hydrothermal ore deposits becase metamorphic and diagenetic alteration reactions may change the ree distributions mobility of ree may occur during diagenesis of carbonate rich rocks and during the development of shear zones and migmatites in contrast very large fluid rock ratios are necessary to cause significant changes in ree patterns of silicate rich rocks during diagenesis and regional metamorphism

mineralogical chemical and isotopic u pb method studies of hercynian uraniferous mineralizations margnac and fanay mines limousin france abstract mineralogical and chemical studies of pitchblendes pyrites and coffinites from the margnac and fanay mines limousin france indicate that chemical exchanges between uraniferous solutions and vein wall rocks are reflected in the chemical compositions of pitchblendes an age of 276 ma is given for the primary pitchblende pyrite association by the u pb method isotopic analysis of pb in galena crystallized during coffinitization of pitchblende gives an interval of 6 ma between pitchblende precipitation and its remobilization as coffinite analyses by electron microprobe indicate that this hydrothermal transformation affects more or less all the pitchblende spherulites even if the volume of coffinite is low this leads to si enriched pitchblende and explains the systematic age of 270 ma obtained by pb pb and concordia diagrams a mineralogically undetected remobilization stage is also found in some samples at 170 175 ma finally this work specifies the life time 20 30 ma of the geothermal system which is considered to be responsible for the episyenitization of the two mica granite the precipitation of pitchblende and its remobilization as coffinite