geology and metallogenic evolution of the polymetallic deposits of the alcudia valley mineral field eastern sierra morena spain the alcudia valley is intensely mineralized with a large number of pb zn ag cu deposits hosted by neoproterozoic and paleozoic sedimentary rocks five distinct types of deposits have been recognized the most significant mineralizing events were related to the two major phases of deformation hd1 hd2 and granite emplacement during the hercynian orogeny stable isotope and lithogeochemical data demonstrate that the metals as well as sulfur and carbon were sourced from the local sedimentary rocks type a deposits are minor occurrences of strata bound mineralization with zn pb occurring as disseminations and small veins in late ordovician limestone a syndiagenetic origin is suggested by the limited stratigraphic distribution of the mineralization and anomalous base metal contents of late ordovician early silurian black shales overlying the mineralized limestone minor remobilization of disseminated sulfides into joints took place during late diagenesis or early hercynian deformation types b c and d are syntectonic deposits with zn pb type b deposits are strongly deformed veins in hd1 fractures in ordovician rocks a process involving local mobilization of metals by a surface derived fluid is indicated by depleted metal contents of host rocks adjacent to the veins the similarity of 34s values of ore sulfides with disseminated pyrite in the host rocks and the 18oh2o values type c deposits exhibit a greater variation in morphology and degree of deformation compared to other types and are found in both hd1 and hd2 fractures in late ordovician and silurian rocks the stratigraphic distribution and 34s values of sulfides are similar to type a deposits suggesting that localized hydrothermal systems either remobilized type a mineralization or derived metals and sulfur from the same source type d deposits occur in hd2 shear fractures in neoproterozoic rocks the 13c values of carbonate gangue and the similarity of 34s values of ore sulfides and disseminated pyrite in the host rocks indicate that black shales of the neoproterozoic sequence are the major source of sulfur and carbon mixing of a metamorphic fluid with a surface derived fluid is suggested by fluid inclusion and oxygen isotope data type e deposits the most abundant and economically most important type are post tectonic pb zn veins occupying hd2 fractures and are widely distributed through the district in rocks ranging from neoproterozoic to late ordovician mineral assemblages and ag contents of the veins show a zonal relationship with respect to monzogranite outcrops indicating that late hercynian magmatism was the source of heat driving fluid migration through the fracture system fluid inclusion and oxygen isotope data are typical of basinal brines reaction of the fluid with black shales of the neoproterozoic sequence is suggested by 34s values of sulfides and 13c values of carbonates of the main stages of the paragenetic sequence the final paragenetic stage consists of barite calcite and pyrite which may have been deposited during a later hydrothermal event probably in the early triassic

mixing of metamorphic and surficial fluids during the uplift of the hercynian upper crust consequences for gold deposition a detailed geochemical study of fluids from representative quartz sealed faults hosting late hercynian gold concentrations shows that fluids percolating the mineralised faults had two main distinct reservoirs one was a quite shallow and the other rather deep seated both fluids have lost a great part of their original geochemical signature through interactions with host metamorphic formations early fluids present during the primary sealing of the faults by quartz are considered to have effectively equilibrated with the metamorphic pile and then predominantly flowed upwards along the faults they are characterised by ch4 co2 h2o ratios rather typical of fluids equilibrated with graphite and moderate to medium chlorinities with a high br cl ratio the striking feature of the gold bearing quartz is that gold is not synchronous within any quartz deposition and appears located in late microfractures and associated with pb bi sb sulphosalts and sulphides these late stages are characterised by fluids whose salinities decrease to very low values indicating their progressive dilution by waters of more surficial origin in the fault system the long lived activity of the fault favoured the connection between two distinct fluid reservoirs at a critical time during the basement uplift the fluids evolved through two main driving mechanisms which were responsible for the au deposition i decrease in temperature accompanying decompression from supra lithostatic to hydrostatic conditions which yielded in some instances volatile unmixing in the faulted systems ii mixing of the resulting fluids with waters entering the hydrological systems from shallower reservoirs in addition to dilution and fluid mixing which are favourable factors for decreasing the gold solubility the presence of microfractured sulphides could have enhanced gold precipitation through electrochemical processes d 2002 elsevier science b v all rights reserved

magnetic fabrics and fluid flow directions in hydrothermal systems a case study in the chaillac ba f fe deposits france this study presents a possible use of anisotropy of magnetic susceptibility ams to describe the mineralizing process in hydrothermal systems ba f fe rich deposits within the chaillac basin are on the southern border of the paris basin in these deposits hydrothermal textures and tectonic structures have been described in veins sinters and sandstone cemented by hydrothermal goethite 278 oriented cores from 24 sites have been collected in these formations in addition a lateritic duricrust superimposed on the hydrothermal formation has been sampled rock magnetic investigations show that the principal magnetic carrier is goethite for the hydrothermal mineralization and for the laterite level the ams measurements show distinguishable behaviors in the different mineralogical and geological contexts the k1 magnetic lineation maximum axis is strongly inclined for the vertical veins for the horizontally mineralized sinters the magnetic lineation is almost horizontal with an azimuth similar to the sedimentary flow direction the ams of goethite rich sandstone close to the veins shows strongly inclined k1 as they are probably influenced by the vertical veins however when the distance from the vein is larger than 1 m the ams presents rather horizontal k1 directions parallel to the sedimentary flow the laterite has a foliation dominance of ams with vertically well grouped k3 axes and scattered k1 and k2 axes field structural observations suggest that the ore deposit is mainly controlled by ew extension tectonics associated with ns trending normal faults combining the ams results on the deposit with vein textures and field data a model is proposed in which ams results are interpreted in terms of hydrothermal fluid flow this work opens a new investigation field to constrain hydrodynamic models using the ams method textural study combined with efficient ams fabric measurements should be used for systematic investigation to trace flow direction in fissures and in sand porosity

muscovite recrystallization and saddle shaped 40 ar 39 ar age spectra example from the blond granite massif central france muscovites from the blond granite west french massif central were dated by the 40ar 39ar single grain method the 40ar 39ar ages obtained vary from 305 5 0 3 ma to 311 3 0 5 ma and most of the age spectra are slightly saddle shaped the analyzed muscovites show phengitic recrystallization under optical microscope observations sem images and electron microprobe chemical analyses it is proposed that the saddle shaped age spectra result from a partial recrystallization which produced three different isotopic reservoirs in the analyzed white mica single grains domains of early muscovite domains of neocrystallized muscovite formed by phengitic and al fe substitutions and low activation energy sites

triple junctions of bay of biscay and north atlantic new constraints on the kinematic evolution recently surveyed triple junction trajectories in the bay of biscay and newly available magnetic maps constrain the early oceanic evolution of the north atlantic and bay of biscay from chrons m0 to a33o 118 to 80 ma the opening of the bay of biscay is of the scissors opening type with a pole of rotation located near bordeaux lat 44 6 n long 0 3 w and predicted simultaneous compression in the central and eastern pyrenees structural directions west of iberia do not fit the north america iberia motion therefore a second triple junction of the ridge ridge fault type is postulated just south of the first one which propagated north ward from a more southerly position

fluid fractionation of tungsten during granite pegmatite differentiation and the metal source of peribatholitic w quartz veins evidence from the karagwe ankole belt rwanda abstract the identification of a magmatic source for granite associated rare metal w nb ta and sn mineralisation in metasediment hosted quartz veins is often obscured by intense fluid rock interactions which metamorphically overprinted most source signatures in the vein system in order to address this recurrent metal sourcing problem we have studied the metasediment hosted tungsten bearing quartz veins of the nyakabingo deposit of the karagwe ankole belt in central rwanda the vein system 992 2 ma is spatiotemporal related to the well characterised b rich f poor g4 leucogranite pegmatite suite 986 10 ma to 975 8 ma of the gatumba gitarama area which culminated in nb ta sn mineralisation muscovite in the nyakabingo veins is significantly enriched in granitophile elements rb cs w and sn and show alkali metal signatures equivalent to muscovite of less differentiated pegmatite zones of the gatumba gitarama area pegmatitic muscovite records a decrease in w content with increasing differentiation proxies rb and cs in contrast to the continuous enrichment of other high field strength elements nb and ta and sn this is an indication of a selective redistribution for w by fluid exsolution and fluid fractionation primary fluid inclusions in tourmaline of these less differentiated pegmatites demonstrate the presence of medium to low saline h 2 o nacl kcl mgcl 2 complex salt e g rb cs fluids which started to exsolve at the g4 granite pegmatite transition stage laser ablation inductively coupled plasma mass spectrometry shows significant tungsten enrichment in these fluid phases 5 500 ppm fractional crystallisation has been identified previously as the driving mechanism for the transition from g4 granites less differentiated biotite biotite muscovite towards muscovite pegmatites and eventually columbite tantalite mineralised pegmatites the general absence of tungsten mineralisation in this magmatic suite including the most differentiated columbite tantalite mineralised pegmatites of the gatumba gitarama area emphasises the efficiency of fluid saturation to extract crystal melt incompatible tungsten from the differentiating melt phase fluid melt crystal partitioning calculations support the concept of a magmatic hydrothermal fluid source for tungsten and constrain the range of permissible crystal melt and fluid melt partition coefficients together with realistic values for water solubility in the parental g4 granitic melt consequently we propose that for highly differentiated b rich f poor granite systems fluid saturation started prior to or at the granite pegmatite transition stage resulting in apical to peribatholitic tungsten veins systems that are paragenetically older than the final pegmatite stage

low pressure facies series metamorphism in an accretionary sedimentary prism southern alaska the low pressure high temperature metamorphism of the chugach metamorphic complex alaska occurred in an ocean continent convergence zone to achieve the high temperatures at a relatively shallow depth in an accretionary prism we propose the large scale transport of heat by fluids which preheated the metamorphic belt by tectonic focusing of fluids followed by injection of melts both of which were generated downdip in a shallow subduction zone

ore deposits of the french massif central insight into the metallogenesis of the variscan collision belt the french massif central fmc represents the whole west european variscan wev belt in terms of both the geodynamic evolution and the metallic content thus a study of the metallogenic evolution of the fmc may elucidate the conditions that allow the mineralisation of a collision belt since recent collision belts e g the himalayas or the alps show that mineralisation does not necessarily result from the collision process the palaeozoic history of the fmc is divided into three geodynamic stages unevenly involved from the metallogenic view point the eo variscan stage cambrian to silurian was not important the meso variscan stage devonian early carboniferous was of limited importance and most of the mineralisations formed during the neo variscan stage late carboniferous early permian in addition some more mineralisation was produced during the mesozoic because of the thermal reactivation linked with the alpine orogenies

shear zone hosted polymetallic sulfides in the south limousin area massif central france remobilized sulfide deposits related to variscan collisional tectonics and amphibolite facies metamorphism this paper investigates the relationship between deformation and mineralization developed in amphibolite facies shear zones in the south limousin area using structural microstructural and textural analyses the investigated shear zone is a ductile thrust fault that stacked low grade metamorphic rocks onto a highly metamorphosed basement with both being folded during a late orogenic tectonic phase the shear zone hosts sulfide bearing mylonitic quartzites composed of dynamically recrystallized quartz syntectonic pyrite pyrrhotite sphalerite chalcopyrite and late covellite mylonites display northwest southeast trending lineation and asymmetric microstructures including sigmoidal quartz aggregates and shear bands that indicate a northwestward movement along the shear zone sulfides occur mainly along shear bands and exhibit primary undeformed textures attesting to their syntectonic emplacement based on petrographic analyses of the metamorphic host rocks mineralization formed at p 5 0 to 5 5 kbars and t 300 to 600 c consistent with p t conditions for recrystallization of metapelites and metabasites involved in the shear zone all data indicate that ductile deformation and emplacement of mineralization were coeval the occurrence of similar pretectonic sulfide deposits in the hanging wall of the mineralized shear zone suggests that the sulfides in the thrust fault were remobilized from preexisting mineralization by fluid that migrated toward the thrust this is the first evidence for thrust zone hosted mineralization within the massif central and attests to the role of crustal scale thrust faults as occasional pathways for mineralized fluids during the upper paleozoic continental collision these results suggest that ductile thrust faults may be important sites of ore deposition in the variscan belt of western europe and in similar collisional belts elsewhere

hydrothermal fluids assisted crustal scale strike slip on the argentat fault zone abstract the role of hydrothermal fluids in assisting the activity of strike slip faults is investigated using a range of new geological geophysical and geochemical data obtained on the argentat fault massif central france this fault zone 180 km long and 6 to 8 km width has experienced coeval intense channeling of hydrothermal fluids and brittle deformation during a short time span 300 295 ma according to seismic data the fault core is a 4 km wide vertical zone of high fracture density that rooted in the middle crust 13 km and that involved fluids in its deeper parts 9 13 km depth if stress analyses in the fault core and strain analyses in the damage zone both support a left lateral movement along the fault zone it is inferred that hydrothermal fluids have strongly influenced fault development and the resulting fault has influenced fluid flow fluid pressure made easier fracturing and faulting in zones of competent rocks units and along rheological boundaries repeated cycles of increase of fault fracture permeability then overpressure of hydrothermal fluids at fault extremity favored strong and fast development of the crustal scale strike slip fault the high permeability obtained along the fault zone permitted a decrease of coupling across the weak fault core connections between shallower and lower crustal fluids reservoirs precipitate the decrease of fault activity by quartz precipitation and sulfides deposition the zones of intense hydrothermal alteration at shallows crustal levels and the zones of fluid overpressure at the base of the upper crust both controlled the final geometry of the crustal scale fault zone

in situ sims uraninite u pb dating and genesis of the xianshi granite hosted uranium deposit south china abstract the southeastern part of the nanling metallogenic province china is host to numerous granite hosted vein type hydrothermal uranium deposits the geology and geochemistry of these deposits have been extensively studied however accurate and precise ages for the uranium mineralization are scarce because the uranium minerals in these deposits are usually fine grained and may have formed in several stages therefore the ages previously obtained by the bulk dating techniques are possibly a mixed age the xianshi uranium deposit located in the southeastern part of the guidong granite complex is a major uranium deposit in south china the uranium mineralization from this deposit is mainly fine grained uraninite in quartz or calcite veins which are spatially associated with the cretaceous mantle derived mafic dykes micro raman spectroscopy and x ray diffraction analyses indicate that the dominant uranium mineral occurs as a rare form of uraninite u 3 o 7 three distinct generations of uranium minerals have been identified based on petrographic and field relations stage 1 uraninite has the lowest uo 2 and highest pbo contents whereas stage 3 uraninite has the highest uo 2 and lowest pbo contents uraninite from the xianshi deposit was dated using an in situ sims u pb dating technique the results show three distinct age groups 135 4 ma 113 2 ma and 104 2 ma which are in excellent agreement with the ages of three episodes of mantle derived mafic dykes therefore the xianshi uranium deposit has experienced at least three hydrothermal events that are responsible for the deposition of uranium ores which are genetically related to the emplacement of three sets of mafic dykes

control of magnetic rock fabrics by mica preferred orientation a quantitative approach magnetic anisotropy analysis represents a well established and frequently used method in structural geology several attempts were made to relate the anisotropy of magnetic susceptibility ams to rock fabrics and to discover the sources of the ams in gneissic rocks paramagnetic phyllosilicates with lattice dependent magnetic properties are assumed to control the whole rock ams i e it is dominated by mica lattice preferred orientation texture in this study ams was modelled on the basis of the mica texture the rock composition and compared to the experimentally determined ams the orientations of the modelled and experimental tensors agree quite well whereas all the other characteristic parameters shape anisotropy mean susceptibility display large differences it has been concluded that accessory high susceptible phases as well as the diamagnetic rock constituents may have significant influence on ams consequently mica pole figure measurements cannot be replaced by ams measurements without control of the sources of ams it was also concluded that the march model to evaluate strain from mica preferred orientations is not valid for highly strained rocks beside the fact that the obtained strains are too low the deformation is generally inhomogeneous which leads to an overprint of the mica texture since the microstructural fabric elements which originate in different strain regimes prolate or oblate may create similar modifications of the mica orientation patterns it is obvious that the relationship between ams and deformation is rather complex

melt inclusions in quartz from an evolved peraluminous pegmatite geochemical evidence for strong tin enrichment in fluorine rich and phosphorus rich residual liquids abstract we have investigated the magmatic evolution of a late stage f and p rich pegmatite forming aluminosilicate liquid and the geochemical controls on magmatic mineralizing processes by remelting totally crystallized melt inclusions in quartz and analyzing the quenched glass by epma and sims the quartz phenocrysts were sampled from a pegmatite that occurs in a variscan granite genetically associated with cassiterite and wolframite mineralized greisen veins at the ehrenfriedersdorf sn w deposit central erzgebirge se germany the melt inclusion compositions imply that the pegmatite forming liquid achieved extreme levels of chemical differentiation it contained high abundances of sn f p li rb cs nb ta and be and abnormally low concentrations of ca y sr and ree for a granite and it was strongly peraluminous the molar al 2 o 3 cao na 2 o k 2 o ranged from 1 3 to 2 0 fractions of the pegmatite forming liquid were extremely enriched in p 2 o 5 f al 2 o 3 and the molar abundances of f p in the glasses correlate strongly with moles of network modifying al ions implying that the bulk liquid included f p and al bearing complexes formation of these complexes reduced the activities of f p and al in bulk liquid suppressed the crystallization of magmatic topaz and p rich minerals and allowed the liquid to become enriched in these constituents some fractions of the ehrenfriedersdorf aluminosilicate liquid contained 1000 2000 ppm sn these levels of sn enrichment were up to 2 orders of magnitude greater than that ever reported for nonmineralized metaluminous and peraluminous igneous materials and are consistent with some experimentally derived sn solubilities in cassiterite saturated granitic liquids at geologically relevant pressures and temperatures this concordance implies that cassiterite could have crystallized directly from this highly evolved p and f rich peraluminous granitic liquid without the involvement of hydrothermal fluids

paleozoic evolution of continental crust in the beaujolais lyonnais area northeastern part of the massif central france in the beaujolais lyonnais area of the northeastern massif central accretion of continental and possibly oceanic crustal fragments occurred between cambrian and early carboniferous time three distinct lithotectonic units terranes have been recognized the southern lyonnais unit consists of medium to high grade metamorphics and includes eclogites it formed in the early paleozoic the brevenne unit to the north contains low to medium grade metamorphic mafic and felsic volcanics and subordinate sedimentary rocks which possibly originated during the early paleozoic until devonian time in a sialic back arc environment or along an active continental margin the beaujolais unit is represented by volcanics on the south and predominantly shallow marine clastics and carbonates on the north it developed in a late devonian or early carboniferous ensialic marginal basin the peak of metamorphism in the lyonnais unit hp ht was reached in silurian time subsequent nw se to e w oriented convergence produced mylonitic foliation structural imbrication of the lyonnais basement rocks with the brevenne unit and se vergent folds accompanied by low to medium grade metamorphism late visean to namurian n s to nw se directed n vergent thrusting produced tectonic imbrication of the metamorphic northern brevenne unit with the nonmetamorphic beaujolais unit in the southern brevenne unit and in the lyonnais unit updoming along right lateral high angle normal faults was followed by emplacement of voluminous granitic plutons of crustal origin late carboniferous to early permian crustal thinning in the beaujolais lyonnais area was associated with n s trending left lateral strike slip faults and e w to ne sw trending right lateral strike slip faults basins that developed along these faults contain continental red beds

neo tethyan magmatism and metallogeny in myanmar an andean analogue abstract plate margin tectonism magmatic and hydrothermal processes and the genesis of mineral deposits are intricately linked in myanmar two near parallel magmatic belts that together contain a significant proportion of that country s mineral wealth have contrasting metallogenic endowments the mogok mandalay mergui belt hosts crustal melt s type granites with significant tin tungsten mineralization while the wuntho popa arc comprises i type granites and granodiorites with copper gold mineralization the spatial juxtaposition of the two belts and their distinct but consistent metallogenic endowment bears strong similarities to the metallogenic belts of the south american cordillera recent u pb age dating has shown the potential for the two belts to be near contemporary from the late cretaceous to eocene here we investigate whether an andean type setting during subduction of neo tethys could explain the observed magmatism and mineralization within these two belts

the variscan kasperske hory orogenic gold deposit bohemian massif czech republic kasperske hory one of the largest gold deposits in the bohemian massif is characterised by shear zone related gold bearing quartz veins at the tectonic boundary of the two metamorphic terranes of the moldanubian unit studies of the geology mineral paragenesis fluid inclusions and oxygen geothermometry have been carried out to determine the mineralisation events and alternative p t t model of this deposit the pre mineralisation stage is characterised by geochemical evidence of pegmatites 700 c and 1 1 0 45 gpa and metamorphic structures resulting from deformation dx 1 at the regional metamorphic peak 650 c and 0 5 gpa the mineralisation in dx 2 began to develop from the formation of the q1 and q2 quartz veins stage i under brittle ductile conditions with the n s extension these quartz veins were filled mainly by apatite plagioclase 1 muscovite and arsenopyrite 1 revised and reinterpreted gechronological data indicate that the earliest quartz veins can be dated at 344 ma the q3 veins were formed later under brittle to brittle ductile conditions with crystallisation of plagioclase 2 arsenopyrite 2 scheelite chlorite pyrite and calcite stage ii the corresponding fluids of stages i and ii belong to the c h o n system the p t conditions correspond to 590 520 c and to 0 44 0 25 gpa for stage i and 480 390 c and 0 2 gpa for stage ii stage iii is characterised by the precipitation of younger quartz chlorite molybdenite calcite pyrrhotite 1 galena 1 native gold bismuth and other bi te minerals the associated aqueous fluids salinity 1 5 8 wt nacl equiv follow fluid inclusion trails and were trapped at relatively low pressures and temperatures 290 180 c and 0 1 gpa stage iv is mainly dominated by carbonate and fluorite fillings of the open fractures and cracks arsenopyrite 1 and 2 and molybdenite are the main gold bearing and gold carrying ore phases at this deposit the means of microanalysis indicate the presence of both micron sized and probably submicron sized particles of gold 920 1000 in the fractures and fissures of the arsenopyrite 1 and structurally bound invisible gold in the arsenopyrite 2 crystal lattice e g gold as au i economic gold mineralisation native free gold flakes 930 1000 is linked to stage iii

anomalous au silicifications in the upper carboniferous of the french massif central timing and temperature constraints by combined geochemical and organic matter studies hydrothermal silicification in some of the carboniferous rocks at lugeac and saint etienne french massif central is noteworthy for its significant au and ag anomalies two types are distinguished according to the hydrothermal mode of formation one associated with geyser deposits st etienne and the other associated with fluid circulation through the rocks following diagenesis st etienne and lugeac in the absence of analysable fluid inclusions we determined the temperatures of the fluids involved in the hydrothermal events from parameters used in ranking organic matter i e 100 c at lugeac and 150 165 c at st etienne silicification at lugeac was accompanied by barite and adularia and so it can be associated to the barite fluorite vein complex of the paulhaguet district where the lugeac carboniferous deposits are located thus the age of 209 8 ma hettangien assigned to the paulhaguet mineralization is taken as the age of silicification in the lugeac carboniferous the circulation of au ag mineralization fluids occurred several times starting at around 330 ma and apparently continued at least up to the lias

40 ma of hydrothermal w mineralization during the variscan orogenic evolution of the french massif central revealed by u pb dating of wolframite we present u pb thermal ionization mass spectrometer tims ages of wolframite from several granite related hydrothermal w sn deposits in the french massif central fmc located in the internal zone of the variscan belt the studied wolframite samples are characterized by variable u and pb contents typically 10 ppm and show significant variations in their radiogenic pb isotopic compositions the obtained u pb ages define three distinct geochronological groups related to three contrasting geodynamic settings i visean to namurian mineralization 333 327 ma coeval with syn orogenic compression and emplacement of large peraluminous leucogranites ca 335 325 ma ii namurian to westphalian mineralization 317 315 ma synchronous with the onset of late orogenic extension and emplacement of syn tectonic granites ca 315 310 ma and iii stephanian to permian mineralization 298 274 ma formed during post orogenic extension contemporaneous with the permian volcanism in the entire variscan belt the youngest ages 276 274 ma likely reflect the reopening of the u pb isotopic system after wolframite crystallization and may correspond to late hydrothermal alteration e g ferberitization our results demonstrate that w sn mineralization in the fmc formed during at least three distinct hydrothermal events in different tectono metamorphic settings over a time range of 40 ma

comment on formation and evolution processes of the salanfe w au as skarns aiguilles rouges massif western swiss alps by chiaradia m mineralium deposita 38 154 168

the granite hosted gold deposit of moulin de cheni saint yrieix district massif central france petrographic structural fluid inclusion and oxygen isotope constraints the moulin de cheni orogenic gold deposit is the only granite hosted deposit of the saint yrieix district french massif central it occurs in 338 1 5 ma old peraluminous leucogranites and is characterized by intense microfracturing and bleaching of the granite in relation to pervasive sulfide crystallization formation of quartz veins and gold deposition occurred in two successive stages an early mesozonal stage of quartz sulfide fe as s deposition usually devoid of gold and a late epizonal stage of base metal and gold deposition both stages postdate peak metamorphism and granite intrusion the genesis of the deposit is the result of four successive fluid events 1 percolation of aqueous carbonic metamorphic fluids under an assumed lithostatic regime of 400 450 c at a maximum depth of 13 km 2 formation of the main quartz lodes with coeval k alteration and introduction of as and s from aqueous carbonic fluids percolating along regional faults arsenopyrite and pyrite deposition was linked to the alteration of fe silicates into k feldspar and phengite at near constant iron content in the bulk granite temperature was similar to that of the preceding stage but pressure decreased to 100 50 mpa suggesting rapid uplift of the basement up to 7 5 km depth 3 the resulting extensional tectonic leads to the deposition of gold boulangerite galena and sphalerite in brecciated arsenopyrite and pyrite from aqueous fluids during a mixing process temperature and salinity decrease from 280 to 140 c and 8 1 wt eq nacl to 1 6 wt eq nacl respectively 4 sealing of the late fault system by barren comb quartz which precipitated from dilute meteoric aqueous fluids 1 6 wt eq nacl to 0 9 wt eq nacl under hydrostatic conditions at 200 150 c

field and petrological evidence for the development of an ensialic marginal basin related to the hercynian orogeny in the massif central france six lithologic units in tectonic contact with each other have been defined during mapping of the devonian in the beaujolais area of the northeastern massif central five main igneous suites have been recognized 1 a transitional basaltic suite restricted to a single unit 2 an acid volcanic plutonic suite the members of which are related by fractional crystallization and magma mixing 3 low tio2 volcanic rocks with calc alkaline affinities 4 a tio2 rich tholeiitic suite related to an ophiolitic complex 5 a plutonic suite with close resemblances to alaskantype intrusions

tracing metal sources in peribatholitic hydrothermal w deposits based on the chemical composition of wolframite the example of the variscan french massif central abstract we present a complete dataset for major minor and trace elements in wolframite fe mn wo4 based on the example of several peribatholitic hydrothermal w deposits located in the variscan french massif central fmc the wolframite samples were characterized down to the micrometer scale by combining scanning electron microscopy observations and in situ chemical analysis by electron probe microanalyzer and laser ablation inductively coupled plasma mass spectrometry most samples are fe dominated wolframites and are characterized by variable fe fe mn values for the studied deposits from 0 36 to 0 86 without significant alteration features wolframites present intracrystalline variations for concentrations of several minor and trace elements principally for nb ta and sn which reflect growth zoning the minor and trace element compositions of the different wolframite samples show at first order similar enrichments in ta nb sn zn and in as well as depletions in lree li th ti zr hf pb v co and mg compared to the upper continental crust second order compositional variations are observed between the studied deposits which can be separated in four main regional geochemical groups this work highlights that the chemical composition of wolframite is controlled by both the crystallochemical parameters and the composition of the primary hydrothermal fluid the regional variations observed in the geochemical signatures of wolframite reflect local variations in the composition of the hydrothermal fluid i e variable metal sources therefore this suggests that the minor and trace element contents in wolframite likely represent direct markers of the source of the hydrothermal fluid and ultimately of the metals the comparison between the trace element compositions of wolframite with the compositions of regional granitic rocks and worldwide shales suggests that evolved peraluminous granites represent the main source of metals in peribatholitic hydrothermal w deposits from the fmc whereas metasedimentary rocks have a limited to no influence on the metal budget

origin of the carbonaceous debris and its implication for mineralization within the qianjiadian uranium deposit southern songliao basin abstract appearance and coal petrology of the carbonaceous debris cd from the qianjiadian uranium deposit southern songliao basin are illustrated in order to reveal the relationship between the cd and uranium mineralization response of the cd and uranium mineralization to diabase dikes and origin of the cd three types of cd have been identified in the yaojia formation cd serving as trapped sediments cd serving as laminae of cross bedding and cd occurring in lumpy sandstones with an average content of 91 2 in the cd organic macerals are primarily composed of homoeollinite desmocollinite and inertinite inorganic macerals of the cd mainly include pyrite with an average content of 8 8 average contents of the desmocollinite inertinite and pyrite from the cd in the ore bearing section are higher than that in the non ore bearing section respectively the study demonstrates that the cd rich in inertinite and desmocollinite facilitates uranium mineralization uranium is frequently adsorbed in the desmocollinite and inertinite and coffinite is embedded in the inertinite inferring that roles of the cd in uranium mineralization are both adsorption and reduction vitrinite reflectance vr of the cd ranges from 0 24 to 0 513 with an average value of 0 335 the vr of the cd in the ore bearing section is generally larger than that in the non ore bearing section uranium mineralization and enlargement of the vr are both attributed to the diabase dikes the cd originated from the late cretaceous wildfire related woody plants and it has been transported into fluvial channels and preserved in sandstones

spatial u pb age distribution in shock recrystallized zircon a case study from the rochechouart impact structure france abstract age determination of impact structures via the zircon u pb system remains challenging and often ambiguous due to highly variable effects of shock metamorphism on u pb geochronology it is therefore crucial to link the observed zircon microtextures including their temperature and pressure conditions associated with their formation directly to the u pb ages preserved here we analyzed three recrystallized zircon grains and one plastically deformed zircon crystal from the medium sized rochechouart impact structure in the northwestern massif central of france for the rochechouart impact structure the impact age 206 92 0 32 ma 40ar 39ar as well as the tectono themal history is well established making this study site ideal to test concepts about u pb systematics in shocked zircon and to differentiate between shock driven age resetting and pre impact crystallization and metamorphic overprinting zircon microstructures were studied using scanning electron imaging cathodoluminescence imaging and electron backscatter diffraction ebsd mapping further we conducted u pb laser ablation inductively coupled plasma mass spectrometry la icp ms depth profiling analysis allowing us to interpret the resultant age data in discrete steps with increasing ablation time depth the u pb depth profiling data demonstrate that plastically strained grains are incompletely reset and preserve rim and interior age domains reflecting typical pre impact pre variscan and variscan regional tectonic ages our results also reveal that the granular crystals encountered contain microstructural evidence for former reidite in granular neoblastic frign zircon reflecting both high pressure 30 gpa and high temperature 1200 c conditions this signifies that frign zircon is now known from an additional medium sized impact structure further supporting the hypothesis that this impact induced microstructure is commonly preserved in addition frign zircon has a high potential to preserve completely impact reset crystal domains 204 to 207 ma that can be identified by our combined analytical approach of u pb depth profiling and ebsd mapping and thus are suitable for determining reliable impact ages

the biards sb au bearing shear zone massif central france an indicator of crustal scale transcurrent tectonics guiding late variscan collapse structural textural mineralogic microthermometric and isotopic data obtained on the biards sb au district located in the south limousin area massif central france provide new evidence for the tectonic setting of stibnite and gold deposition during the late orogenic variscan collapse in western europe a variety of geologic and geophysical data define a major crustal scale left lateral strike slip shear zone that acted as a trap for sb au mineralization during these movements fault fill veins and then extensional veins of limited extent were created along rheologic heterogeneities that focused brittle deformation geometry and orientation of both vein sets indicate two main episodes of emplacement of ore related to a progressive wrench movement in response to an counterclockwise rotation of the regional stress axes both veins sets are filled by quartz and sulfides in three stages an early arsenopyrite pyrite stage with fine grained quartz a sphalerite pb sb sulfosalt native gold stage with comb quartz and a late stibnite berthierite stage with comb quartz combined fluid inclusion and stable isotope studies on quartz muscovite and sulfides reveal that the three stages result from the continuous evolution of a deep seated hydrothermal system in which the latest stages mixed with meteoric water these data argue for cooling and a pressure drop during ore deposition and indicate a shallow level of emplacement for sb au veins a comparison of the biards deposits with other upper paleozoic gold and antimony deposits in the massif central the western variscides and elsewhere in the world illustrates their common association with crustal scale strike slip shear zones the upper carboniferous age 305 300 ma of the sb au deposits indicates that they formed during the early stages of the postthickening extension of the variscan lithosphere sb au bearing strike slip shear zones resulted from the late variscan crustal collapse guided by the very large scale dextral shearing between central europe northern africa and the northern appalachians and associated with the opening of the paleo tethys and the closing of the theic ocean during the late paleozoic gondwana laurasia translation

the late eocene 187os 188os excursion chemostratigraphy cosmic dust flux and the early oligocene glaciation abstract high resolution records ca 100 kyr of os isotope composition 187os 188os in bulk sediments from two tropical pacific sites odp sites 1218 and 1219 capture the complete late eocene 187os 188os excursion and confirm that the late eocene 187os 188os minimum earlier reported by ravizza and peucker ehrenbrink earth planet sci lett 210 2003 151 165 is a global feature using the astronomically tuned age models available for these sites it is suggested that the late eocene 187os 188os minimum can be placed at 34 5 0 1 ma in the marine records in addition two other distinct features of the 187os 188os excursion that are correlatable among sections are proposed as chemostratigraphic markers which can serve as age control points with a precision of ca 0 1 myr we propose a speculative hypothesis that higher cosmic dust flux in the late eocene may have contributed to global cooling and early oligocene glaciation oi 1 by supplying bio essential trace elements to the oceans and thereby resulting in higher ocean productivity enhanced burial of organic carbon and draw down of atmospheric co2 to determine if the hypothesis that enhanced cosmic dust flux in the late eocene was a cause for the 187os 188os excursion can be tested by using the paired bulk sediment and leachate os isotope composition 187os 188os were also measured in sediment leachates results of analyses of leachates are inconsistent between the south atlantic and the pacific sites and therefore do not yield a robust test of this hypothesis comparison of 187os 188os records with high resolution benthic foraminiferal 18o records across the eocene oligocene transition suggests that 187os flux to the oceans decreased during cooling and ice growth leading to the oi 1 glaciation whereas subsequent decay of ice sheets and deglacial weathering drove seawater 187os 188os to higher values although the precise timing and magnitude of these changes in weathering fluxes and their effects on the marine 187os 188os records are obscured by recovery from the late eocene 187os 188os excursion evidence of the global influence of glaciation on supply of os to the ocean is robust as it has now been documented in both pacific and atlantic records

uranium metallogenesis of the peraluminous leucogranite from the pontivy rostrenen magmatic complex french armorican variscan belt the result of long term oxidized hydrothermal alteration during strike slip deformation in the french armorican variscan belt most of the economically significant hydrothermal u deposits are spatially associated with peraluminous leucogranites emplaced along the south armorican shear zone sasz a dextral lithospheric scale wrench fault that recorded ductile deformation from ca 315 to 300 ma in the pontivy rostrenen complex a composite intrusion the u mineralization is spatially associated with brittle structures related to deformation along the sasz in contrast to monzogranite and quartz monzodiorite 3 3 the leucogranite samples are characterized by highly variable u contents 3 to 27 ppm and th u ratios 0 1 to 5 suggesting that the crystallization of magmatic uranium oxide in the more evolved facies was followed by uranium oxide leaching during hydrothermal alteration and or surface weathering u pb dating of uranium oxides from the deposits reveals that they mostly formed between ca 300 and 270 ma in monzogranite and quartz monzodiorite apatite grains display magmatic textures and provide u pb ages of ca 315 ma reflecting the time of emplacement of the intrusions in contrast apatite grains from the leucogranite display textural geochemical and geochronological evidences for interaction with u rich oxidized hydrothermal fluids contemporaneously with u mineralizing events from 300 to 270 ma infiltration of surface derived oxidized fluids leached magmatic uranium oxide from fertile leucogranite and formed u deposits this phenomenon was sustained by brittle deformation and by the persistence of thermal anomalies associated with u rich granitic bodies

stibnite microstructures as imprints of fault movement the natural deformation of stibnite in relation to the kinematic history of a regional fault is resolved using microstructural analysis of massive stibnite along the biards fault in the massif central france stibnite underwent intra crystalline deformation associated with a strong linear and planar anisotropy lepidoblastic textures undulatory extinction of oriented grains growth of antimony between these grains and a colour change of stibnite from white to black result from dynamic recrystallisation a range of asymmetric microstructures indicate non coaxial deformation and a left lateral sense of shear related to the movement of the fault zone the computed displacement corresponds to the geological offsets measured along the fault we conclude that stibnite has microstructurally recorded the bulk kinematics of its host fault zone

the quartz diorites of limousin elemental and isotopic evidence for devono carboniferous subduction in the hercynian belt of the french massif central a chain of late devonian early carboniferous intrusions on the western margin of the french massif central the limousin tonalite belt consists of quartz diorites which are unusual among french hercynian granitoids in their low silica contents 53 68 wt sio2 and abundant hornblende they represent the earliest and most primitive plutonism post dating the main phase of hercynian metamorphism and have chemical characteristics strongly resembling andesitic lavas of calc alkaline affinity they differ from other massif central hercynian granitoids in their low 87sr86sr360 0 7047 0 7059 and high nd360 0 7 to 1 8 their initial pb composition was rather homogeneous 206pb204pb360 18 15 18 38 207pb204pb360 15 57 15 62 208pb204pb360 38 06 38 26 and their 207pb204pbi values are significantly lower than those of other hercynian granitoids the limousin quartz diorites are considered to have originated from an enriched mantle with characteristics modified by subduction of oceanic crust and terrigenous sediments the primitive quartz dioritic magmas were then contaminated in the lower continental crust by an afc process involving acid metaigneous or metasedimentary lithologies the occurrence of such plutons in the earliest phase of hercynian plutonism in the massif central is probably related to minor subduction at an active continental margin

reply to discussion on formation and evolution processes of the salanfe w au as skarns aiguilles rouges massif western swiss alps by chiaradia m mineralium deposita 38 154 168

the roc blanc orogenic pb zn ag au deposit morocco a product of metamorphic dehydration and co 2 devolatilization during exhumation of the variscan jebilet massif the roc blanc pb zn ag au vein system in the variscan central jebilet massif morocco is confined within the contact metamorphic aureole of s and i type calc alkaline granitic stocks 327 4 to 295 15 ma along the marrakech shear zone host rocks consist of a succession of greenschist to amphibolite facies metasedimentary and metavolcaniclastic rocks of carboniferous age the ore mineralogy is predominantly base metal and ag bearing sulfides and sulfosalts intergrown with quartz and carbonates late stage gold mineralization is commonly present as electrum in intimate association with all major generations of sulfide and sulfosalt minerals ore related hydrothermal alteration includes silicification sericitization chloritization and carbonatization chlorite and arsenopyrite geothermometry suggest mean temperatures of 364 and 350 c respectively calculated 18ofluid values of 15 to 18 are consistent with metamorphic fluid sources by which the mineralizing fluids were produced during the emplacement of granitic intrusions and subsequent devolatilization of graphitic black shale and interlayered carbonate beds lead and strontium isotope data constrain the source of the ore forming components i e metals and sulfur to the enclosing host rocks a decrease in temperature during fluid ascent and subsequent alteration associated fluid rock interaction resulted in the deposition of the pb zn ag au mineralization in a post collisional extensional setting