a sulfate control on marine mid depth euxinia on the early cambrian ca 529 521 ma yangtze platform south china abstract given the high oxygen demands of complex metazoans a sound understanding of marine redox conditions is essential to reconstruct the factors that lead to the dramatic increases in ecosystem complexity and biological diversity in the early cambrian in this study we report new fe mo c s geochemical data from black shale rich strata of the early cambrian continental margin yangjiaping section in the yangtze platform south china integrated fe speciation and mo abundance data from the yangjiaping section in combination with previously reported data from shatan inner shelf songtao slope and longbizui basinal sections suggest mid depth euxinic waters coexisting with ferruginous deep waters and oxic surface waters this redox structure is similar to conditions previously suggested for the ediacaran yangtze platform and other proterozoic marine basins indicating that proterozoic layered ocean redox structure in some basins persisted into the early cambrian furthermore the fe mo data demonstrate that the mid depth euxinia was widespread during a marine transgression but shrank gradually along with widespread shelf oxygenation when the basin evolved into subsequent regression excess highly reactive iron fe hr in deep water with a hydrothermal origin may have had a control on the mid depth euxinia given geochemical and geological evidence for basinal hydrothermal activities on the other hand a sulfate limitation on bacterial sulfate reduction bsr and sulfide generation was suggested by a weak correlation r 2 0 22 between pyrite iron versus fe hr and total organic carbon toc form anoxic deep water sections and high toc averagely 6 in the deepest ferruginous water longbizui section furthermore a spatial gradient was observed in sulfur isotopic composition of pyrite averagely from 0 2 to 21 0 consistent with a lateral gradient of sulfate in concentration or and in isotope from shore to distal waters on the transgressive yangtze platform we accordingly proposed that two distinct sources riverine input and ocean reservoir provided sulfate for bsr dominantly in near shore and distal areas respectively and the euxinic retreat observed for the regression can be explained as a response to the progressive sulfate consumption of the ocean reservoir by intensive bsr and pyrite formation during preceding transgression therefore our results support a sulfate control on the spatiotemporal distribution of mid depth marine euxinia on the yangtze platform in early cambrian when complex metazoans rapidly evolved

monsoon related variations in zaire congo sediment load and influence of fluvial silicate supply on marine productivity in the east equatorial atlantic during the last 200 000 years two sediment cores from the zaire fan and the angola margin have been investigated for their composition of terrigenous and biogenic constituents respectively for the late quaternary kaolinite feldspar ratios and variations of terrigenous element ratios of zr ti k rb and al reveal that the composition of zaire river sediment load has fluctuated in tune with precessional variations of boreal summer insolation in particular the correspondence of high kaolinite feldspar and al k ratios with low latitude insolation maxima strongly corroborates the assumption that west african monsoonal precipitation and chemical weathering was enhanced during periods of increased central african heating the most striking feauture observed is that opal accumulation has been 2 to 10 times higher in zaire fan sediments than outside in continental margin sediments off angola although biogenic ba and corg fluctuations from both areas indicate that changes of total paleoproductivity were of the same magnitude in the zaire river plume and off angola from this we infer that the contribution of biogenic opal production to total paleoproductivity has been significantly higher within the zaire river plume than in the oceanic upwelling regime farther to the south off angola over the last 200 000 years the pattern of opal accumulation rates with respect to that of marine organic carbon implies that enhanced opal production off the zaire river to a great extent was the result of additional fluvial supply of dissolved silica during humid climates characterized by more intense chemical weathering on the continent while total paleoproductivity created by oceanic upwelling was high in periods of increased zonal trade wind intensity at precessional insolation minima and during cold more arid glacial climate conditions we presume that paleoproductivity off the zaire was controlled by the following two sources of nutrients 1 marine nutrients including nitrate and phosphate as well as the uptake of ba on particulate corg caused by upwelling and 2 silica mainly delivered by the zaire river dissolved silicate hence our results underline the importance of dissolved silicate in large rivers for marine silicate cycling in the tropical to subtropical atlantic at a millenial timescale

collapse of the thickened variscan crust in the french massif central mont pilat extensional shear zone and st etienne late carboniferous basin abstract a large scale extensional shear zone is described from the mont pilat area in the northeastern part of the french massif central this shear zone is about 2 km thick and is characterized by well developed n dipping foliation and stretching lineations deformation occurred under conditions of retrograde metamorphism from high temperature conditions to greenschist facies it is superimposed on a composite foliation related to the earlier variscan 380 350 ma compressional events associated with southward emplacement of nappes and hp mt metamorphism regional n s lineations and shear criteria observed at a regional scale indicate a northward displacement of the hanging wall during extension large strains locally recorded in thick mylonitic zones suggest that displacement was substantial some tens of kilometres late superimposed extensional brittle deformation and pseudotachylites show that northward displacement on normal faults continued at a shallower depth a large granitic pluton granite du velay intruded late in the the variscan orogeny was associated with extension some small leucogranitic syntectonic melts were emplaced within the shear zone and are strongly deformed geochronological rb sr data on these leucogranite bodies give an age of 320 ma and 40 ar 39 ar dating of synkinematic biotites from gneissose rocks in the shear zone yields a plateau age of 313 ma these data show that extensional ductile deformation and magmatism were still active during the latest late carboniferous thus extension occurred immediately after the well known late palaeozoic collision type compressional tectonics which had significantly thickened the crust we propose that the extensional tectonism described here is due to the gravitational collapse of the initially thick variscan crust the stephanian intracontinental sedimentary basin of st etienne was formed along the hanging wall of the normal shear zone during the late stages of this post orogenic crustal extension

the emergence of life from iron monosulphide bubbles at a submarine hydrothermal redox and ph front here we argue that life emerged on earth from a redox and ph front at c 4 2 ga this front occurred where hot c 150 c extremely reduced alkaline bisulphide bearing submarine seepage waters interfaced with the acid warm c 90 c iron bearing hadean ocean the low ph of the ocean was imparted by the ten bars of co 2 considered to dominate the hadean atmosphere hydrosphere disequilibrium between the two solutions was maintained by the spontaneous precipitation of a colloidal fes membrane iron monosulphide bubbles comprising this membrane were inflated by the hydrothermal solution upon sulphide mounds at the seepage sites our hypothesis is that the fes membrane laced with nickel acted as a semipermeable catalytic boundary between the two fluids encouraging synthesis of organic anions by hydrogenation and carboxylation of hydrothermal organic primers the ocean provided carbonate phosphate iron nickel and protons the hydrothermal solution was the source of ammonia acetate hs h 2 and tungsten as well as minor concentrations of organic sulphides and perhaps cyanide and acetaldehyde the mean redox potential eh across the membrane with the energy to drive synthesis would have approximated to 300 millivolts the generation of organic anions would have led to an increase in osmotic pressure within the fes bubbles thus osmotic pressure could take over from hydraulic pressure as the driving force for distension budding and reproduction of the bubbles condensation of the organic molecules to polymers particularly organic sulphides was driven by pyrophosphate hydrolysis regeneration of pyrophosphate from the monophosphate in the membrane was facilitated by protons contributed from the hadean ocean this was the first use by a metabolizing system of protonmotive force driven by natural aph which also would have amounted to c 300 millivolts protonmotive force is the universal energy transduction mechanism of life taken together with the redox potential across the membrane the total electrochemical and chemical energy available for protometabolism amounted to a continuous supply at more than half a volt the role of the iron sulphide membrane in keeping the two solutions separated was appropriated by the newly synthesized organic sulphide polymers this organic take over of the membrane material led to the miniaturization of the metabolizing system information systems to govern replication could have developed penecontemporaneously in this same milieu but iron sulphur and phosphate inorganic components of earliest life continued to be involved in metabolism

hydrothermal alteration and fluid circulation related to w au and sb vein mineralization haut allier massif central france w as au and as sb vein mineralizations in the haut allier french massif central are associated with ortho and parametamorphic rocks containing biotite or sillimanite which have been locally intruded by small granitoid bodies hydrothermal alteration is well developed around these veins and has been studied here from a petrographic and a chemical point of view the results are compared with those which were obtained by microthermometric study of fluid inclusions in both mineralized types three superimposed hydrothermal stages are distinguished showing good agreement with the results obtained by other methods in the early stage fluids enriched with co 2 or ch 4 developed a quartz 2m1 muscovite assemblage with 8 paragonitic substitution at temperatures of about 400 degrees c minor chlorite appears replacing biotite near the transition of altered to fresh rocks this early stage is predominant in veins with w as au mineralization in the intermediate stage low salinity aqueous fluids dilute the earlier fluids and control a new alteration with quartz 2m1 phengite or carbonate assemblages at slightly lower temperatures this alteration stage is particularly important in the environment of veins with as sb mineralization in the late stage the last hydrothermal event occurs at a low temperature 200 degrees c and forms a 1m illite kaolinite or quartz assemblage in small alteration veinlets chemically the different phyllosilicates that successively occur in w as au and as sb veins are very similar the differences between these mineralization types can be explained by the proximity of the granitoid bodies to w as au veins and by a greater fluid rock ratio involved in the alteration processes for as sb vein deposition

gold deposits and hydrothermal eruption breccias associated with a maar volcano at wau papua new guinea emplacement of endogenous domes and eruption of pyroclastic flows in the morobe goldfield took place in the interval from 4 to 2 4 m y ago during the later part of this time interval following tilting of the ignimbrite pile a maar was generated at wau the subjacent diatreme is believed to extend downward for about 1 km to a regional dip slip fault zone which hosts deeper level gold mineralization at the nearby ribroaster mine following initial maar formation hydrothermal brecciation and gold deposition were controlled by low angle extensional faults which developed during incipient subsidence of a wedge of poorly supported rock between the regional fault zone and the ring fault delimiting the maar epiclastic sedimentation was widespread in the maar volatile depleted magma reached the surface around the perimeter of the maar during active sedimentation and constructed two principal endogenous domes one dacitic and the other andesitic the dacitic dome dated previously at 2 4 m y gave rise to an apron of crumble breccia along the northwestern edge of the maar accumulation of the intramaar sequence was accompanied and followed by widespread subsidence and slumping which resulted in steep dips and locally overturned beds the regional drainage system eventually breached the crater rim and resulted in deposition of channel conglomerates and fluviolacustrine beds all carrying alluvial gold radiocarbon dating of wood from this unit showed that it accumulated 42 000 years ago the most recent events at wau are believed to be a series of hydrothermal eruptions which constructed a composite breccia apron at koranga crater on the southeastern edge of the maar the most recent eruption is tentatively inferred to have taken place in 1967 modified journal abstract

evolution mineralogique et isotopique pb du filon sulfure complexe des borderies massif central francais implications metallogeniques le filon polymetallique sb pb zn ag cu des borderies puy de dome france resulte de la succession de quatre stades de mineralisations possedant chacun ses propres caracteristiques mineralogiques geochimiques et isotopiques pb le premier stade est represente par la berthierite dont l habitus et la composition isotopique du plomb 206pb 204pb 17 76 revele un episode metallogenique ancien malgre une nette evolution geochimique du depot le second stade a mispickel jamesonite i andorite stibine zinkenite etc presente des compositions isotopiques du plomb homogenes 206pb 204pb 17 96 qui demontrent son appartenance a un meme episode metallogenique cet episode est date a 313 5 ma par la methode k ar la source du plomb present dans ces deux stades est a rechercher dans un socle metamorphique de type limousin inconnu a l affleurement dans le district enfin la nature des mineraux du troisieme stade zinkenite ii fuloppite semseyite et les compositions isotopiques du plomb 206pb 204pb 18 21 attestent d une remobilisation des sulfures deja presents dans le filon sous l action d un fluide tardif plombifere ce fluide est a rattacher aux distensions liasiques et emprunte le plomb aux roches du district granite et metamorphites le dernier stade plagionite jamesonite ii zinkenite iii est un simple prolongement du troisieme comme le demontrent la nature des sulfures et les similitudes isotopiques 206pb 204pb 18 21 l etude de filon illustre la complementarite des observations mineralogiques et des analyses isotopiques du plomb sur phases minerales bien identifiees cette double approche est necessaire pour apprehender la source des metaux et les conditions de genese de gites polyphases a parageneses complexes

electron microprobe and la icp ms study of monazite hydrothermal alteration implications for u th pb geochronology and nuclear ceramics this paper presents new data that quantify the response of magmatic monazite to three main types of hydrothermal alteration namely sericitization chloritization and greisenization the samples were taken from three paleozoic granites the st nectaire granite massif central france the carnmenellis granite cornwall england and the skiddaw granite lake district england fluid inclusion thermometry and hydrothermal parageneses indicate that alteration took place at temperatures ranging from 260 to 340 c and salinities from 3 to 18 wt nacl equivalent possible monazite alteration mechanisms found in the course of this study using backscattered scanning electron microscopy bse sem electron microprobe laser raman spectroscopy and laser ablation inductively coupled plasma mass spectrometry la icp ms include cationic substitutions monoclinic to hexagonal structure transition accompanied by chemical exchanges selective th removal dissolution reprecipitation and dissolution with replacement by a different mineral these results show that despite the compositional and crystallographic simplicity of monazite it exhibits varied chemical responses to different mineral fluid interactions elemental and isotopic measurements by la icp ms for the unaltered monazites yield statistically significant 232th 208pb and 238u 206pb magmatic crystallization ages in some cases it was possible to give a reasonable estimate of the age of mineral fluid interaction using the altered parts of the monazites or newly precipitated crystals for other minerals 232th 208pb and 238u 206pb systematics were strongly disturbed by variable inputs and or depletions of u th and pb the data suggest that monazite like nuclear waste forms would be good hosts for tetravalent actinides but may release the lanthanides and actinides with lower and higher valencies especially if the fluids are oxidizing or tend to dissolve monazite

new understandings of ni mo mineralization in early cambrian black shales of south china constraints from variations in organic matter in metallic and non metallic intervals abstract the well known ni mo ores hosted in early cambrian black shales of south china are one of the research highlights in economic geology for the past few decades however their origin is complex and still debated here based on a case study in the huangjiawan ore of zunyi city guizhou province we generate several new understandings regarding ni mo mineralization through a comparative investigation of organic matter in metallic and non metallic stratigraphic intervals including abundance type maturity and relationship to mineralization we find new direct evidence for biotic impacts on mineralization organic matter and rhodophyte cystocarps red algae in particular may be significantly correlated to mineralization as it accumulates mineralized ni and mo however this organic material as well as disseminated and amorphous organic matters is not the sole and predominant factor controlling mineralization as implied from the nonlinear correlation between organic matter abundance maturation and mineralization other fluid sources e g hydrothermal and or seawater also contribute to mineralization which may be influenced by hydrothermal activity ni and mo may have mineralized independently as suggested by their differential accumulation in different structures of the cystocarps different relationships between organic matter abundance and thermal maturation and mineralized element concentration as well as the large variation in element accumulation coefficients the history of mineralization is complex as ni and mo may be or not be deposited together during the same stage of mineralization these results might also have broader implications for understanding the origin of sediment hosted ores worldwide

spatial and temporal distribution of the orogenic gold deposits in the late palaeozoic variscides and southern tianshan how orogenic are they abstract a principal uncertainty in models of orogenic ore deposits concerns their ages relative to orogenic processes the yardstick of the relation has resided loosely in the peak of metamorphism age estimates in the variscides and tianshan indicate that most orogenic ore deposits were formed in the course of the late carboniferous to middle triassic with a peak between 305 and 280 ma their locations settings and ages suggest an association with coeval lithosphere scale strike slip deformation which played a role in the destruction of the orogenic system following crustal shortening this destruction tends to invalidate the orogenic association of the orogenic ore deposits observation of a mantle signature in some of these ore deposits and in coeval magmatic rocks suggests that the strike slip belts tapped into sub crustal levels here lithological composition had been modified by subduction during the stage of construction consequently any orogenic element in the ore deposit models is apart from location only an element of inheritance of subduction modified lithosphere features acquired during construction of the orogen these features may however well have been crucial for the formation of the ore deposits in view of the translithospheric extent of the strike slip belts fluids which contributed to the ore deposits may have come from at least the entire in part metasomatized lithosphere column the ore deposits could probably not have been formed without these deep reaching strike slip systems a model is proposed for the geological setting of the orogenic gold deposits in the variscides and the southern tianshan it consists of plutono metamorphic elements in the mantle in the lower and in the middle crust within a transpressional to transtensional tectonic framework of translithospheric faults and associated domes and pull apart basins with shallow marine to terrestrial sediments and interlayered felsic and mafic volcanics the thermal engines of these systems were probably in localized upwellings of the asthenosphere prompted and controlled by the lithosphere scale deformation at the time at an even larger scale oroclinal bending of the old orogenic backbone may have played yet another role in the localization of the ore deposits the thesis of specific localized tectono thermal engines is at odds with the original proposals of a relation between orogenic ore deposits and regional metamorphism it suggests that the late palaeozoic gold antimony mercury ore deposits in the variscides and the southern tianshan are more akin to the intrusion related ore systems

early palaeozoic palaeobiogeography of the variscan regions abstract the palaeobiogeographic method appears to be an attractive alternative for reconstruction of the palaeogeography of the variscan regions during the palaeozoic the evolution of faunal assemblages and climatic characteristics from the cambrian up to the end of the devonian demonstrates that baltica and north gondwana represent two major and independent palaeogeographic entities separated by a mid european rheic ocean which opened as early as the cambrian and closed progressively from the devonian the south armorican ocean whose closure generated the so called ligerian orogen is regarded as a branch of the rheic ocean both a tornquist s sea separating baltica from its western extension avalonia during the ordovician and a proto tethys ocean extending between southwestern europe and north africa during the devonian are excluded from our reconstructions

fluid rock interaction processes related to hydrothermal vein type mineralization in the siegerland district germany implications from inorganic and organic alteration patterns altered wallrocks of vein type pb zn sb mineralization siegerland district rheinisches schiefergebirge have been investigated by a combination of inorganic and organic geochemical methods including major and trace element analysis vitrinite reflectance measurements c isotope and elemental analysis of kerogen alteration features of the siliciclastic pelitic psammitic lower devonian wallrocks are increased k na ratios significant desilicification and relative immobility of a number of elements notably al ti zr cr v wallrock kerogens display elevated vitrinite reflectance values decrease in h c atomic ratios coupled with increase in s c atomic ratios and heavier c isotope compositions compared to the unaltered precursor sedimentary rocks interaction processes between the hydrothermal fluids and the respective wallrocks related to injection of high temperature silica undersaturated solutions are dominated by quartz dissolution coupled with sericitization reactions heat transfer due to fluid infiltration convection and wallrock reactions caused fluid cooling which promoted the sequential deposition of quartz and stibnite sulphosalts within the vein systems hydrocarbons detected in ore assemblages of pb zn and sb mineralization were most probably derived from the lower devonian very low grade meta sedimentary rocks high maturity levels and pronounced typical organic alteration patterns indicate that thermochemical so2 4 reduction tsr played an important role in precipitation of metal sulphides the present study demonstrates that a combination of inorganic and organic investigations on fluid rock interaction processes is particularly useful for deciphering precipitation mechanisms of base metal sulphides

life in extreme environments hydrothermal vents eruption of volcanic rocks at the midocean ridges is the major mechanism by which heat is lost from the interior of the earth approximately one third of the heat is removed from the spreading centers by convective circulation of seawater 1 the magnitude of this heat loss requires that the entire volume of the oceans circulates through the midocean ridges in approximately 10 million years seawater interaction with volcanic rocks at near 400 c results in substantial chemical flux and makes an important contribution to buffering the composition of some elements in seawater cations from seawater mg 2 ca 2 and na form hydroxyl bearing alteration minerals in the volcanic rocks releasing hydrogen ion to solution the hot acidic altered seawater releases metals fe mn zn and cu and reduced sulfur h2s from the volcanic rock these are transported by hydrothermal solutions to the seafloor and form metallic mineral deposits

early cambrian ocean anoxia in south china the cause of the most marked changes in the evolution of life which define the first order stratigraphic boundary between the precambrian and the phanerozoic eon remains enigmatic and a highly topical subject of debate a global ocean anoxic event triggered by large scale hydrogen sulphide h 2 s release to surface waters has been suggested by wille et al on the basis of two data sets from south china and oman to explain the fundamental biological changes across the precambrian cambrian pc c boundary here we report a new precise shrimp u pb zircon age of 532 3 0 7 million years myr ago fig 1 for a volcanic ash bed in the critical unit that reflects the ocean anoxic event the lowermost black shale sequence of the niutitang formation in the guizhou province south china this age is significantly younger than the precise pc c boundary age of 542 0 0 3 myr ago approximately 10 myr younger than the extinction of the ediacaran fauna and thus challenging the view of a major ocean anoxic event having been responsible for the major changes in the direction of evolution at the pc c boundary

palaeoceanographic redox environments for the lower cambrian hetang formation in south china evidence from pyrite framboids redox sensitive trace elements and sponge biota occurrence abstract the lower cambrian hetang formation a black shale sequence contains a stone coal a flammable organic rich mudstone unit abundant pyrite framboids occur in this unit with the average mean sizes falling in a narrow range from 4 6 to 5 4 m and the maximum diameters being around 10 m the size distribution pattern of the pyrite framboids indicates a euxinic depositional environment the redox sensitive trace metals of the stone coal samples reveal a large enrichment of mo 10 180 times v 4 40 times u 10 60 times and ni 2 20 times compared to the average upper continental crust value consistent with an anoxic environment for their deposition the redox sensitive element ratios th u v v ni v cr indicate that the depositional environment for the lower part of the stone coal unit was the most anoxic and euxinic in contrast a sponge biota including eleven species of demosponges and hexactinellids and two undetermined forms indicate an oxic or dysoxic environment to reconcile these two facts we propose that although an anoxic euxinic environment predominated during the deposition of the lower cambrian hetang formation black shales occasional currents may also have brought free oxygen to the bottom water column to allow the growth of the sponges on the sea floor

rare earth element and srnd isotope geochemistry of phosphate nodules from the lower cambrian niutitang formation nw hunan province south china abstract phosphate nodules are widely distributed in the early cambrian black shale sequence in yangtze platform south china in this study we carried out x ray diffraction major element rare earth element and sr nd isotopic studies on phosphate nodules from two pc c sections in hunan province south china two different types of phosphate nodules can be recognized based on ree and nd isotopic characteristics type 1 with seawater like ree patterns higher end t values and type 2 with hat shaped ree patterns and more negative end t values we suggest that the difference in ree patterns and nd isotopic compositions between the two types reflects changes in pore water geochemistry from seawater dominated towards diagenetic fluid dominated conditions during early diagenesis positive eu anomalies are displayed in most samples and are likely to record not only the anoxic environments but also the involvement of submarine exhalative hydrothermal fluids which prevailed in south china during early cambrian

the oldest early ediacaran sr isotope record of mid ocean surface seawater chemostratigraphic correlation of a paleo atoll limestone in southern siberia abstract by examining sr isotope stratigraphy of the ediacaran paleo atoll limestone in southern siberia we first demonstrated the surface seawater information from the lost ediacaran late neoproterozoic oceans the ediacaran baratal limestone in the gorny altai mountain in siberia is a remnant of a mid oceanic paleo atoll complex developed on a paleo seamount sr isotope ratios 87 sr 86 sr from the basal 20 m thick interval of the baratal limestone vary mostly by 0 7069 0 7079 and these show a generally increasing trend upsection the relatively low sr ratios indicate that mid oceanic seawater i e global seawater was more influenced by hydrothermal activities along mid oceanic ridges rather than continental erosion during the ediacaran a chemostratigraphical correlation with the hitherto known secular change in sr isotope suggests that the basal baratal limestone was deposited particularly in the early ediacaran this timing corresponds to the immediate aftermath of the neoproterozoic marinoan snowball earth event the relatively low sr isotope ratios and the increasing trend upsection are concordant with the onset of continental erosion during the deglaciation during the early ediacaran

geochemical implications of rare earth element patterns in hydrothermal fluids from mid ocean ridges abstract rare earth element data are reported for vent fluids collected from eight deep sea hydrothermal areas including samples from sediment hosted and bare rock hydrothermal systems the morb normalized ree patterns from these diverse settings are remarkably similar to each other but distinctly different than seawater or basalt being lree enriched and possessing a strikingly positive eu anomaly the ree concentrations making up these patterns vary widely however both on a spatial and temporal basis when plotted against ionic radii these fluid trends are remarkably linear and show the same fractionation patterns exhibited by plagioclase during magma segregation this analysis suggests that the partitioning of the ree between fluid and rock during high temperature hydrothermal alteration of morb is dominated by crystochemical exchange during dissolution and recrystallization reactions at the exposed surfaces of plagioclase phenocrysts a comparison of ree ionic radii in eight coordination indicate that the partitioning of 3ree and 2eu are dominated by chemical substitution for ca 2 and sr 2 respectively these considerations predict that the total 3ree content of vent fluid varies in a systematic way during the transition from an rich morb plagioclase to ab rich hydrothermal plagioclase and that these parameters can be used as indicators of the average extent of alteration inside active hydrothermal systems

the evolution of pleistocene climate a time series approach abstract in the later part of the pleistocene variations in global ice volume have been dominated by an approximate 100 000 year cycle analysis of 2 myr long oxygen isotope record from an equatorial pacific core indicates that this is true only for the last 900 000 years prior to this time the amplitude of the 100 000 year cycle is much reduced as is the variance of all oscillations with periods greater than 60 000 years based on results of time series analysis of this 2 myr long record the pleistocene glacial cycles can be divided into three sections 1 the late pleistocene 0 900 kyr b p where the variations in the isotope record are dominated by the 100 000 year cycle 2 the middle pleistocene 900 1450 kyr b p in which low frequency components are not as important as in the later period of the pleistocene and 3 the early pleistocene late pliocene 1450 2000 kyr b p where general reductions of importance at all frequencies is seen as compared to the later intervals recent modeling efforts which describe variations in global ice volume show that the dominant low frequency component observed in the late pleistocene can result from different time constants for the rate of glacial growth and decay in response to variations in the earth s orbital parameters it is hypothesized that during the early pleistocene the rate of growth and decay of glaciers were more similar and that continental erosion by successive glacial advances lowered the land surface in areas of ice cap formation to below sea level when the ice caps became marine based more rapid decay of the ice became possible

tectonics and plate tectonics model for the variscan belt of europe abstract a plate tectonics model is presented to explain the tectonometamorphic characteristics of the european variscides after the closing of two oceanic domains by two sided subduction 500 420 ma and obduction 420 380 ma collision of the european and african continental plates occurred we propose that the subsequent complex intracontinental deformation 380 290 ma is the result of a double subduction of the continental lithosphere accompanied by crust mantle decollement this mechanism explains the progressive crustal thickening and migration of the deformation through time from the sutures toward the external parts of the variscan belt accounting for this model and for the relationships between the european variscides and the other paleozoic peri atlantic belts caledonides appalachian mauritanides and morocco we infer the relative positions of africa america and europe between the silurian and the permian

metal sources for the polymetallic ni mo pge mineralization in the black shales of the lower cambrian niutitang formation south china abstract total organic carbon content toc trace element and platinum group element pge concentrations were determined in the black shales of the lower cambrian niutitang formation in the nayong area guizhou province south china in order to study the polymetallic ni mo pge mineralization the results demonstrate that numerous elements are enriched in the polymetallic ores compared to those of the nearby black shale particularly ni mo zn toc and total pge which can reach up to 7 03 wt 8 49 wt 11 7 wt 11 5 wt and 943 ppb respectively the elemental enrichment distribution patterns are similar to those in the zunyi and zhangjiajie areas except that the nayong location is exceptionally enriched in zn whereas positive correlations are observed between the ore elements of the polymetallic ores no such correlations are observed in the black shale these positively correlated metallic elements are classified into three groups co ni cu pge zn cd pb and mo tl toc the geological and geochemical features of these elements suggest that proterozoic and early palaeozoic mafic and ultramafic rocks dolomites and or pb zn deposits of the neoproterozoic dengying formation and seawater could be the principal sources for co ni cu pge zn cd pb and mo tl toc respectively furthermore the chondrite normalized patterns of pges with pd pt pd ir and pt ir indicate that pge enrichment of the polymetallic ores is most likely related to hydrothermal processes associated with the mafic rocks in contrast pge enrichment in the black shale resembles that of the marine oil shale with terrigenous and seawater contributions our investigations of toc trace elements and pge geochemistry suggest that multiple sources along with submarine hydrothermal and biological contributions might be responsible for the formation of the polymetallic ni mo pge mineralization in the black shales of the lower cambrian niutitang formation across southern china

biogenic origin of intergrown mo sulphide and carbonaceous matter in lower cambrian black shales zunyi formation southern china abstract the lower cambrian zunyi formation in southern china hosts complex intergrown phases of mo sulphides and anthracite like carbonaceous matter and graphite mosc pyrite and ni sulphides these sulphides occur in a few centimeters thick polymetallic stratiform layer in black shales above phosphorites cherts dolomites and barite the ore horizon contains 7 wt mo 2 wt ni 19 wt s and 13 wt c org and c tot co 2 58 wt 14 wt cao 1 2 wt as 2000 ppm se 5400 ppm zn 450 ppm u and v and up to 1 ppm platinum group elements three types of mosc phases always including framboidal pyrite are distinguished 1 rounded structures few hundred microns large 2 relict inclusions in diagenetic pyrite 3 grains interstitial to sulphurised and phosphatised organic matter at the nanoscale mosc is represented by nanometric porous rounded structures of mos 2 finely intergrown with carbonaceous matter of typical nano onion structures mosc also contains nanocrysts of quartz clays ca sulphate carbonate and ni sulphides micro raman spectroscopy shows that the carbon phase has a maturation grade of anthracite indicating temperatures below 300 c mosc is mainly composed of 25 wt mo 23 wt s 5 6 wt fe 2 5 wt ni 33 wt c 1 5 wt o 0 6 wt n and several hundreds of ppm of cu as se sb pd zn co and sn electron energy loss spectra show that n is related to nanosized carbonaceous matter the mean c n ratio 57 of mosc is similar to those observed in marine organic matter and those reported from zooplankton at hydrothermal vents the mineralized shales are crosscut by hydrothermal veins composed of carbonate or barite always associated with quartz apatite and fe and zn sulphides a paragenesis also observed as nanocrysts in mosc although mo originated from seawater its extreme concentration is due to an enhanced growth of bacterial consortia in a diffuse hydrothermal vent system these consortia may be dominated by nitrogen fixing and mo dependant hyperthermophilic or mesophilic species containing nitrogenase composed also of mo s fe organic matter decay led thus to the formation of mosc and the included framboidal pyrite

the la belliere gold and antimony district french armorican massif a two stage evolution model controlled by variscan strike slip tectonic the la belliere gold district in the ligerian domain of the armorican massif is the third one of france in term of production it shows gold bearing quartz veins neighboring with a complex network of sb veins hosted in the neoproterozoic metasedimentary basement of the mauges nappe new structural data mineralogical textural and geochemical assays have been carried out to clarify the gold and sb veins relationships our results favor of two step hydrothermal event with an early deep seated gold event followed by a late shallower sb event the gold bearing quartz veins are hosted by n60 e to n90 e sinistral strike slip faults these veins exhibit a four stage paragenesis 1 early barren quartz filling 2 arsenopyrite pyrite with minor scheelite assemblage 3 gold and base metal sulfides crystallized after a ductile brittle deformation stage and 4 pyrite carbonate coeval with a late brittle stage these results support a continuous evolution model from a deep emplacement level 12 to 9 km to a shallow one 7 to 5 km with a brutal change in the p t conditions that triggered the deposition of gold stage 2 controlled by a seismic valve mechanism on the contrary sb veins correspond to open space vein types hosted in a n20 w to n20 e conjugated strike slip fault network arranged in a riedel shear model controlled by n130 140 e regional dextral strike slip shear zone associated to the south armorican shear zone system a two stage evolution is recognized the first one consists of early pyrite arsenopyrite with microcrystalline quartz followed by a late stibnite stage formed after geodic quartz deposition quartz texture argues for a shallow emplacement 5 km of veins controlled by a suction pump mechanism chronologically the gold vein opening complies with a ne sw maximum shortening direction different from the late variscan stress field responsible for the dextral armorican shear zone during late carboniferous and constrains an indirect dating thus a visean age is proposed for the formation of gold veins the overall features of gold deposits are close to those of mesozonal orogenic gold deposits in europe conversely sb bearing veins are generated by a n s shortening during the late carboniferous the sb event distinct in time from the earlier gold one might correspond to a different expression of the so called epizonal type in the orogenic gold model it is proposed that the late carboniferous or 300 event is not the unique metallogenic period for gold deposition in the french variscan domain our study highlights the role of the sinistral strike slip shearing of possible visean age in the gold metallogenesis of the ligerian domain

carbonate hosted zinc lead deposits in the lower cambrian of hunan south china a radiogenic pb sr isotope study zinc lead deposits hosted by lower cambrian carbonate rocks near huayuan in the hunan guizhou orogenic belt southern china have been studied by means of pb and sr isotopes the deposits are characterized by two mineralization stages 1 a main economic stage comprising cockade style sphalerite galena pyrite marcasite fluorite barite and calcite and 2 a subsequent noneconomic stage with nodular rosette sphalerite saddle dolomite and bitumen both ore stages are postdated by a generation of late calcite main stage sulfides 206pb 204pb 18 162 18 225 display a steep linear trend on conventional pb pb diagrams which indicates binary mixing of lead components bearing the imprint of ancient 207pb dominated crustal rocks and reservoirs with elevated th u ratios possibly located in the lower crust nodular rosette sphalerites fall outside this line but reflect a second mixing trend between mineralizing fluids characterized by 206pb 204pb 18 3 and lead isotopically similar to specific main stage cockade sphalerites suggesting either remobilization of pb from main stage ores or contemporaneous mixing of three distinct lead components in the course of an evolving hydrothermal event the 87sr 86sr ratios of diagenetic and hydrothermal carbonate cements and barites range from 0 70905 to 0 71006 and increase systematically with the paragenetic sequence indicating progressive mixing of marine sr derived from the lower cambrian carbonate host rocks with radiogenic sr supplied by external mineralizing fluids in order to identify possible local metal sources u pb and rb sr analyses were performed on six whole rock samples from the lower cambrian sequence and their time integrated pb and sr isotope evolution was compared to the isotopic signature of the mineralization whereas shales and black shales of the cambrian balang and niutitang formations underlying the ore bearing qingxudong carbonate unit appear to be possible external sources for the radiogenic sr found in hydrothermal carbonates the u pb data do not permit these shales to be considered as primary source rocks for the ore lead both the pb and the sr isotopes indicate mineralizing fluids that had interacted with various external metal sources some of them most probably being located in sedimentary or crystalline basement rocks this refutes prevailing genetic models favoring the hydrocarbon and metal rich lower cambrian niutitang black shales as the most likely source reservoir for the zn and pb in the deposits of the huayuan district the pb and sr isotope mixing trends observed for the ore and gangue preciptates reflect small scale heterogeneous fluid systems that were not capable of producing large deposits this may indicate that the huayuan district is not a favorable target for future exploration of economic ore deposits it also limits the prospects of successful radiometric dating of the mineralization since conventional geochronologic models require initial isotopic homogeneity

extensional tectonics in the central iberian peninsula during the variscan to alpine transition abstract the passage from the variscan cycle to the early alpine framework in the central part of the iberian peninsula can be explained in terms of a transitional process involving four clearly differentiated tectonic episodes 1 1 a first variscan compressional stage vi middle devonian to early carboniferous dominated by compressional conditions leading to the building up of the orogenic edifice the stress regime was relevant to what might be called variscan type compression e w oriented this stage was characterized by major himalayan type tectonics with frontal nappes thrusts overturned folds lateral transcurrent ramps and localized anatectic magmatism minor synorogenic extension and plutonism was also recorded during this stage in the tormes granitic dome 2 2 a second variscan stage v2 early to middle carboniferous was characterized by increasing extensional conditions leading to widespread plutonism adamellites granodiorites wanning compressional conditions were restricted to the eastern and southern realms of central iberia the eastern part of the spanish central system and the toledo mountains 3 3 a third stage here defined as late variscan lv developed from middle carboniferous to early permian as a result of n s late orogenic extension this episode is relevant to detachment tectonics and the gravitational collapse of the variscan orogenic edifice under combined simple pure shear conditions plutonism granites and leucogranites was still of major importance early permian andesitic to dacitic volcanism and sedimentary basins developed within the eastern part of the spanish central system 4 4 a fourth stage here defined as early alpine ea early permian to triassic marks the onset of the alpine framework this stage was characterized by what might be called an early alpine type regional stress regime i e e w extension and n s compression within a simple shear model and resulted in the configuration of the iberian peninsula into two contrasted realms a western inherited variscan block and an eastern alpine block subjected to post orogenic extension elements developed during this event include n s high angle normal faults nw se and ne sw conjugate strike slip faulting and asymmetric rifting involving listric low angle detachments

gas bearing property of the lower cambrian niutitang formation shale and its influencing factors a case study from the cengong block northern guizhou province south china abstract to gain a better understanding of the gas bearing property of lower cambrian niutitang formation shale and its influencing factors the shale gas bearing conditions gas content and composition in the cengong block were investigated in this work based on wells cy1 tx1 and tm1 the niutitang shale reservoir is characterized by large thickness abundant organic matter with an average total organic carbon content of 4 74 and high quartz content averaging 53 9 therefore it has good shale gas bearing potential the results of water immersion and ignition tests intuitively revealed the existence of shale gas based on the occurrence of continuous dense clusters of bubbles and long flames of 1 2 m the langmuir volumes of shale samples from well tm1 which ranged from 1 70 to 5 53 m3 t were positively associated with toc content and brunauer emmett teller surface area indicating a strong adsorption capacity and significant adsorbed gas potential however large differences were observed among the three wells with regard to gas bearing properties wells cy1 and tx1 had average total gas contents of 1 25 and 0 33 m3 t respectively the gas composition of well tm1 was dominated by nitrogen n2 with contents generally exceeding 95 furthermore the gas from well tx1 was mainly composed of methane with an average content exceeding 80 burial depth and toc and quartz contents had significant control on the vertical distribution of gas content and local tectonic preservation conditions resulted in differences of gas bearing properties among various wells the measured lost and total gas contents all presented positive correlations with toc quartz contents and porosity and were negatively related to clay content the shale formed in deep water shelf environments had better gas bearing properties than that formed in shallow water shelf environments the broad axis of the box syncline in the cengong block is a favorable location for shale gas accumulation and fault development affects the shale gas plane distribution because of the influence of faults the shale of well tm1 had low hydrocarbon content furthermore based on the combined patterns of folds and faults as well as other special specific factors a classification scheme of shale gas accumulation patterns in south china was developed

in situ sr isotope analysis of apatite by la mc icpms constraints on the evolution of ore fluids of the yinachang fe cu ree deposit southwest china apatite is a ubiquitous accessory mineral in a variety of rocks and hydrothermal ores strontium isotopes of apatite are well known to retain petrogenetic information and have been widely used to investigate the origin of igneous rocks but such attempts have rarely been made to constrain ore forming processes of hydrothermal systems we here report in situ la mc icpms sr isotope data of apatite from the 1660 ma yinachang fe cu ree deposit southwest china the formation of this deposit was coeval to the emplacement of regionally distributed doleritic intrusions within a continental rift setting the deposit has a paragenetic sequence consisting of sodic alteration stage i magnetite mineralization stage ii cu sulfide and ree mineralization stage iii and final barren calcite veining stage iv the stage ii and iii assemblages contain abundant apatite allowing to investigate the temporal evolution of the sr isotopic composition of the ore fluids apatite of stage ii apt ii is associated with fluorite magnetite and siderite whereas apatite from stage iii apt iii occurs intimately intergrown with ankerite and cu sulfides apt ii has 87sr 86sr ratios varying from 0 70377 to 0 71074 broadly compatible with the coeval doleritic intrusions 0 70592 to 0 70692 indicating that ore forming fluids responsible for stage ii magnetite mineralization were largely equilibrated with mantle derived mafic rocks in contrast apt iii has distinctly higher 87sr 86sr ratios from 0 71021 to 0 72114 which are interpreted to reflect external radiogenic sr likely derived from the paleoproterozoic strata some apt iii crystals have undergone extensive metasomatism indicated by abundant monazite inclusions the metasomatized apatite has much higher 87sr 86sr ratios up to 0 73721 which is consistent with bulk rock rb sr isotope analyses of cu ores with 87sr 86sri from 0 71906 to 0 74632 the elevated 87sr 86sr values of metasomatized apatite and bulk cu ores indicate that later fluids were dominated by highly radiogenic sr equilibrated with the paleoproterozoic country rocks results of this study highlight the utilization of in situ sr isotope analysis of apatite in unraveling the evolution of hydrothermal systems

extreme enrichment of polymetallic ni mo pge au in lower cambrian black shales of south china an os isotope and pge geochemical investigation extreme metal enrichments occur in the lower cambrian niutitang formation a thick black shale sequence deposited on the yangtze platform of south china and form a regionally distributed conformable polymetallic ni mo pge au sulfide horizon the origin for the extreme enrichment of metals in these black shales is discussed based on a comprehensive geochemical investigation of re os isotopes and platinum group elements the black shales of the lower cambrian niutitang formation in guizhou province yielded an re os isochron age of 535 11 ma with an initial 187 os 188 os ratio of 0 80 0 04 which is similar to the initial 187 os 188 os ratio 0 78 0 19 of the ni mo sulfide ores but slightly lower than the initial 187 os 188 os ratio 1 18 0 02 of lower cambrian black shales from the lesser himalaya india a comparison of os isotope data among the chinese ni mo sulfide ores the seafloor massive sulfide deposits and contemporaneous seawater suggests a possible similar hydrothermal forming mechanism for these deposits the pge concentrations pt anomaly pt pt pt pd ir pd au pd ratios of the chinese ni mo sulfide ores are similar to those metal rich black shales of submarine volcanogenic hydrothermal origin from czech republic namibia and canada but are different from those data of the ocean floor fe mn crusts that have scavenged their pge and other metals directly from seawater it is therefore suggested that the ni mo sulfide ores from the niutitang black shale sequence in south china had a submarine hydrothermal origin the anoxic environments and abundant organic matter in the ocean basin also played a key role for the extreme metal enrichments the discharge of hydrothermal fluids into the cambrian ocean may have had a great effect on life during the cambrian explosion 2007 elsevier b v all rights reserved

fluid inclusion study of the bournac polymetallic sb as pb zn fe cu vein deposit montagne noire france mineralogical studies demonstrate that the hercynian polymetallic antimony rich deposit of bournac can be described by four stages of ore deposition and one of partial ore remobilization fluid inclusion data permit calculation of the composition and temperature of the fluids associated with each stage of hydrothermal mineralization and concomitant wall rock alteration stages i and ii fe as and zn are represented by moderate salinity h2o co2 nacl inclusions which correlate closely with early carbonate deposition stage iii fluids which are responsible for the deposition of pb sb ores are characterized by low salinity h2o nacl inclusions during the final stage of mineralization iv corresponding to the main phase of stibnite deposition abundant aqueous inclusions confirm the continued involvement of low salinity fluids and the intense development of potassic clays and secondary silica in the wall rocks homogenization temperatures suggest that the whole cycle of mineralization took place during a gradual decrease in fluid temperature of 380 140 c stibnite deposition is restricted to the interval of 230 140 c thus confirming an essentially epithermal environment stage v partial remobilization is distinguished by the presence of high salinity cacl2 rich inclusions which are tentatively related to triassic barite mineralization in the region and therefore postdate the bournac antimony ores homogenization temperatures for this stage range 140 60 c

genesis of hydrothermal silver antimony sulfide veins of the braunsdorf sector as part of the classic freiberg silver mining district germany the peripheral regions of the freiberg vein type silver mining district comprise several sub districts of which braunsdorf was among the richest in terms of ag grade historically 114 t about 3 9 million ounces of ag were produced from the neue hoffnung gottes mine near braunsdorf the neuer segen gottes stehender is a sigmoidally shaped nne ssw trending vein which varies significantly in thickness 0 05 to 3 m and extends over about 2 6 km strike length at the surface the vein infill is marked by a pb zn cu fe sulfide quartz stage 1 and an abundant ag sb sulfide sulfosalt quartz carbonate assemblage stage 2 to develop a sound genetic understanding of the polymetallic mineralisation in the braunsdorf sub district we conducted detailed textural analyses of ore and gangue minerals fluid inclusion analyses electron microprobe analyses and thermodynamic computations in order to characterise the ore fluids and ore forming processes the early stage pb zn cu fe sulfide mineralisation stage 1 is related to fluids with low salinities 0 5 4 eq w nacl and formed at temperatures 300 c microthermometric data related to the ag sb sulfide sulfosalt assemblage stage 2 show similar salinites compared to ore stage 1 but have significantly lower homogenisation temperatures in the range of 180 280 c based on fluid inclusion data cooling can be regarded as the major ore forming process reaction path model calculations for cooling of fluids with different initial ph values 4 5 5 and 7 reproduce the observed mineral assemblages very well and predict spatial zonation of the ag sb and sb sulfide minerals that are in excellent agreement with field observations we conclude that ag rich zones may well occur below sb rich zones in hydrothermal vein type systems similar to those of the freiberg district this relationship may be of potential use for exploration targeting

from thickening to extension in the variscan belt kinematic evidence from sardinia italy the variscan nappe stack of se sardinia originated as a result of several stages of nappe imbrication during the lower carboniferous phases of the variscan orogeny the crustal shortening caused regional ssw and w directed thrusting greenschist facies metamorphism and open to isoclinal polyphase folding the final stage of shortening produced large scale antiforms and synforms post collisional deformation resulted in inversion of earlier thrusts as normal faults development of low angle normal faults and refolding of earlier foliation and thrust planes by asymmetric folds with subhorizontal axial planes facing directions of these latest folds are directed horizontally outward from the hinge zones of main antiforms suggesting that they cannot be regarded as parasitic folds of the latest thickening phase but instead are the consequence of vertical shortening during gravitational collapse of dome like km scale antiforms leading to denudation of antiformal culminations

constraints of sr isotopic compositions of apatite and carbonates on the origin of fe and cu mineralizing fluids in the lala fe cu mo lree deposit sw china abstract numerous fe cu deposits with mineralization styles similar to iron oxide copper gold iocg deposits form the kangdian fe cu metallogenic province southwestern sw china as one of the largest deposits in the region the 1 0 ga lala fe cu deposit is hosted in a paleoproterozoic volcanic sedimentary succession named the hekou group which is alternately intruded by 1 0 ga doleritic plutons this deposit has a paragenetic sequence evolving from stage i of na alteration to stage ii of fe mineralization and finally to stage iii of cu mo ree mineralization coeval with mafic felsic intra plate magmatism in the region this study conducted in situ sr isotopic analyses on apatite and carbonate aiming to resolve the long controversial issue regarding the origin of the fe and cu mineralizing fluids in the deposit apatite of stage ii has 87sr 86sr ratios varying from 0 71380 to 0 72733 much higher than those of synchronous igneous rocks in the region 0 7074 to 0 7091 but similar to the paleoproterozoic host rocks 0 71368 to 0 71837 at 1 0 ga this similarity indicates that radiogenic sr of the fe mineralizing fluid was dominantly sourced from the host rocks apatite and calcites of stage iii have 87sr 86sr ratios 0 75758 0 79293 much higher than apatite of stage ii and the host rocks but similar to the archean basement rocks as high as 0 80 at 1 0 ga beneath the cover of the yangtze block suggesting that the highly radiogenic sr isotopic composition of the cu mineralizing fluid was mainly inherited from the old basement rocks in combination with previous c o s isotopic data indicating a magma hydrothermal origin it was suggested that the fe mineralizing fluid was exsolved from a mafic magma that generated the 1 0 ga doleritic plutons and inherited radiogenic sr from the host rocks during fluid rock interaction by contrast the cu mineralizing fluid might have been sourced from another pulse of magmatic cu mo ree and co2 rich fluid which have once interacted with archean basement rocks prior to mineralization the source of such a cu mo ree rich fluid was not well constrained in current study but was inferred to be exsolved from a hidden felsic magma we propose that intrusions of the bimodal magmas in kangdian are responsible for regional hydrothermal circulation which led to fe cu mo ree mineralization in the kangdian province

selenium speciation in lower cambrian se enriched strata in south china and its geological implications abstract to understand the impact of selenium se into the biogeochemical cycle and implications for palaeo redox environment a sequential extraction method was utilized for samples including black shales cherts a ni mo se sulfide layer k bentonite and phosphorite from lower cambrian se enriched strata in southern china seven species water soluble phosphate exchangeable base soluble acetic acid soluble sulfide selenide associated residual se and different oxidation states selenate se vi selenite se iv organic se se 0 and mineral se ii were determinated in this study we found that the ni mo se sulfide layer contained a significantly greater amount of se ii associated with sulfides selenides than those in host black shales and cherts furthermore a positive correlation between the degree of sulfidation of iron dos and the percentage of the sulfide selenide associated se ii was observed for samples which suggests the proportion of sulfide selenide associated se ii could serve as a proxy for palaeo redox conditions in addition the higher percentage of se iv in k bentonite and phosphorite was found and possibly attributed to the adsorption of se by clay minerals iron hydroxide surfaces and organic particles based on the negative correlations between the percentage of se iv and that of se ii in samples we propose that the k bentonite has been altered under the acid oxic conditions and the most of black shale and cherts and the ni mo se sulfide layer formed under the anoxic and euxinic environments respectively concerning se accumulation in the ni mo se sulfide layer the major mechanism can be described by 1 biotic and abiotic adsorption and further dissimilatory reduction from oxidized se vi and se iv to se ii through elemental se 2 contribution of hydrothermal fluid with mineral se ii

sr isotope variations in vent fluids from 9 46 9 54 n east pacific rise evidence of a non zero mg fluid component abstract sr isotopic variations in vent fluids from six high temperature hydrothermal vents from between 9 46 n and 9 54 n on the east pacific rise are reported the mg sr 87sr 86sr systematics of one vent biovent require the presence of a fluid component that has experienced significant mg depletion 50 but has undergone very little sr exchange with local basalts this fluid component accounts for 3 to 10 of the biovent samples by volume similarities between the composition of the inferred fluid component and that of bore hole fluids sampled from hole 504b suggest that this fluid component is modified seawater partially reacted with basalt at temperatures less than 150 c and subsequently entrained by high temperature vent fluids previously reported vent fluid data from 12 50 n east pacific rise suggest that the presence of the additional lower temperature fluid component admixed in biovent samples may not be unique among seafloor hydrothermal systems if such a fluid component is common in seafloor hydrothermal systems it will need to be considered in estimates of axial hydrothermal fluxes if not accounted for properly the presence of an additional fluid component can bias calculated end member 87sr 86sr ratios after correction for the influence of the additional fluid component on the biovent samples the calculated end member 87sr 86sr ratio of this vent is 0 7041 other nearby vents p vent and bio9 are slightly more radiogenic 0 7042 a and l vents from the southern portion of the study area have end member 87sr 86sr ratios that are less radiogenic 0 7039 and 0 7037 respectively the reason for the greater influence of seawater derived sr in the more northern vents is not known but it may be related to entrainment of seawater in the upflow zone

paleo marine environments of the early cambrian yangtze platform abstract previous studies have generated conflicting interpretations of the nature of oceanographic conditions on the early cambrian yangtze platform we investigated paleo environmental conditions there through an analysis of major elements and redox sensitive trace elements in the lower cambrian niutitang formation from two new drillcores ry1 and ry2 in guizhou province high toc and excess ba concentrations record elevated productivity in the study area redox variation was documented based on enrichment factors efs for redox sensitive trace elements mo u v cr ni and co and c org p ratios these proxies indicate that the lower unit of the niutitang formation was deposited under fluctuating but mostly anoxic conditions whereas the upper unit was deposited under predominantly suboxic conditions mo toc ratios suggest persistently moderate to strong basinal restriction although mo u covariation patterns show no evidence for operation of a particulate shuttle despite the semi restricted anoxic nature of the deep watermass episodic deep water oxygenation events occurred within the yangtze platform sea and longer term secular variation may record eustatic influences additionally patterns of trace metal enrichment record evidence of submarine hydrothermal inputs we propose an integrated paleoenvironmental model to account for the observed productivity redox and hydrographic patterns in the early cambrian yangtze platform on the basis of paleo marine environmental analysis we ascribe the scarcity of trace fossils in the bottom to oxygen deficiency and deny considering the songlin biota as the onset of the intense biogenic evolution after global atmospheric and oceanic oxygenation

long chain unsaturated ketones and esters in living algae and marine sediments abstract series of c37 c39 di and triunsaturated ketones and methyl and ethyl esters of hexatriacontadienoic acid c36 2 have been previously identified in marine sediments and the coccolithophorid emiliania huxleyi these compounds have now been found in four further species of the isochrysidales prymnesiophyta which are not known to bear coccoliths suggesting that they are more widely distributed in living algae than previously thought in addition the ketones have been recognised in sediments of eocene age ca 45 ma which greatly extends their known geological time range and increases their potential as molecular markers for algal input heptatriacontatetraen 2 one c37 4 octatriacontatetraen 3 one c38 4 methyl and ethyl esters of hexatriacontatrienoic acid c36 3 and the ethyl ester of hexatriacontatetraenoic acid c36 4 have also been identified in varying amounts in these algae by gas chromatography and computerised gas chromatography mass spectrometry

marine redox variations and nitrogen cycle of the early cambrian southern margin of the yangtze platform south china evidence from nitrogen and organic carbon isotopes the early cambrian is a crucial interval during which the marine environment encountered significant perturbations alongside key biological innovations the nitrogen isotopic composition of ancient sediments has the potential to record co variation between the marine ecosystem and environmental conditions here we report bulk nitrogen and organic carbon isotopic compositions accompanied by mo concentration data a proxy for redox conditions for a shelf marginal drill core section sancha and a deep basinal outcrop section yuanjia in hunan province south china for the cambrian fortunian stage variable delta n 15 bulk values 4 to 2 parts per thousand and low delta c 13 org values 35 parts per thousand to 33 from the yuanjia section indicate that anoxic waters shoaled into the photic zone with ammonia assimilation competing with anammox in the basinal area in the late cambrian stage 2 low delta n 15 bulk and delta c 13 org values together with high mo bulk concentrations delta n 15 bulk 5 to 0 parts per thousand delta c 13 org 33 5 to 31 0 parts per thousand 100 ppm mo bulk in sancha section and delta n 15 bulk 0 parts per thousand delta c 13 org similar to 33 parts per thousand 100 ppm mo bulk in yuanjia section reflect intense n 2 fixation accompanied by intermittent ammonia assimilation under expanded euxinic condition with shoaling chemocline possibly into the photic zone in the early cambrian stage 3 relatively high delta n 15 bulk values alongside positive delta c 13 org excursions at both sections indicate an increasing contribution from n 15 enriched nitrate assimilation and hence more oxic conditions shelf margin sediments from the middle and late parts of cambrian stage 3 are characterized bylaw delta n 15 bulk values similar to 0 parts per thousand being lowest in the basinal area 3 to 0 parts per thousand in combination with high mo bulk concentration 100 ppm and high mo tocbulk ratios averaging similar to 18 in deep basinal sediments these data suggest that the photic zone became anoxic again but that sulfidic conditions occurred in the basinal area only compared with stage 2 euxinia was less extensive during this interval with photosynthetic biomass dominating over chemoautotrophic biomass at both localities based on a combination of delta n 15 data from this study and published data from studies on contemporaneous sections in yunnan province and the three gorges area it is possible to reconstruct the spatial variability and temporal evolution of redox conditions in the various marine environments along the southern margin of the yangtze platform the basinal area appears to have been dominated by anoxia and intermittent euxinia in the photic zone during most of the early cambrian fortunian stage to stage 3 with the exception of more oxic conditions during early stage 3 on the platform oxygenated shallow water prevailed with the exception of the notable cambrian stage 2 anoxic event the outer shelf area experienced anoxia from stage 2 to stage 3 of the early cambrian although of possibly limited areal extent the high mo bulk concentrations and mo tocbulk ratios suggest that the south china basin was well connected with the considerably oxygenated open ocean and that the mean low delta n 15 bulk values similar to 1 6 parts per thousand from the basin may reflect generally lower delta n 15 composition for seawater nitrate in the early cambrian compared with modern value c 2015 elsevier b v all rights reserved

reconstruction of early cambrian ocean chemistry from mo isotopes the neoproterozoic cambrian transition was a key time interval in the history of the earth especially for variations in oceanic and atmospheric chemical composition however two conflicting views exist concerning the nature of ocean chemistry across the precambrian cambrian boundary abundant geochemical evidence suggests that oceanic basins were fully oxygenated by the late ediacaran while other studies provide seemingly conflicting evidence for anoxic deep waters with ferruginous conditions fe ii enriched persisting into the cambrian here two early cambrian sedimentary platform and shelf slope sections in south china were investigated to trace early cambrian ocean chemistry from mo isotopes the results reveal that early cambrian sediments deposited under oxic to anoxic euxinic conditions have 98 95mo values ranging from 0 28 to 2 29 which suggests that early cambrian seawater may have had 98 95mo values of at least 2 29 similar to modern oceans the heaviest and relatively homogeneous 98 95mo values were recorded in siltstone samples formed under completely oxic conditions which is considered that mn oxide free shuttling was responsible for such heavy 98 95mo value further combined with fe species data and the accumulation extent of mo and u the variation of 98 95mo values in the two studied sections demonstrate a redox stratified ocean with completely oxic shallow water and predominantly anoxic even euxinic deeper water having developed early on which eventually became completely oxygenated this suggests that oceanic circulation at the time became reorganized and such changes in oceanic chemistry may have been responsible for triggering the cambrian explosion of biological diversity

collapse of a hercynian tibetan plateau into a late palaeozoic european basin and range province the large width the importance of crustal shortening and the likelihood of thick crust in the late palaeozoic hercynian or variscan belt of southern europe suggest a tectonic evolution analogous to the evolution of the tibetan plateau and its neighbouring himalaya1 and of the altiplano and other high plateaux of the andes here we extend dewey and burke s analogy1 of the hercynian chain with tibet to include the subsequent stage of pervasive normal faulting and crustal extension and thinning which characterize the active tectonics of tibet parts of the high andes and the basin and range province of western north america it appears that normal faulting and rifting also characterize the late palaeozoic tectonic activity of the hercynian chain

environmental impact of mineralised black shales abstract black shales are sedimentary rocks containing 0 5 of organic carbon they host polymetallic deposits which have been mined for cu ni zn mn p mo v u au and pge platinum group elements even sub economic occurrences provide potential risk of acid rock drainage when exposed to oxic surface environment the natural acid neutralisation potential varies depending on the adjacent rock units especially on the presence of calcareous rocks the chemical and mineralogical composition of black shale is reflected in the quality of the surface waters and groundwater cu ni pb u and zn are recognised as major pollutants though the environmental impact is characteristically polymetallic just like the black shale occurrences hence the environmental impacts have to be evaluated in each occurrence the proterozoic ni zn cu co deposit at talvivaara finland is reviewed in more detail as an example of a large low grade deposit that is currently exploited with open pit mining and a bioleaching process together with the proterozoic central african copperbelt the cambrian u mo deposits in sweden the cambrian ni mo pge deposits in china and the cambrian ordovician u deposits in south korea the devonian ni zn pge occurrences in yukon canada and kentucky usa and the permian cu ag deposits in poland and germany the mineralised horizons may be merely few centimetres thick like in yukon or hundreds of metres thick like at talvivaara both natural and anthropogenic environmental impacts of black shales are reviewed world wide and based on the overview of the state of the art an integrated research approach is suggested for the comprehensive assessment of the risk black shales are natural sources of soil and water contamination at talvivaara the geochemical background includes higher than average concentrations of ni cu zn and mn in glacial till peat surface waters and groundwater as well as in stream and lake sediments bioaccumulation by plants has been reported in china and korea even endemic diseases have been proposed to be linked with the contamination derived from the weathering and leaching of harmful elements from black shale anthropogenic actions exposing the black shale bedrock and associated soils to oxic conditions further intensifies acid rock drainage regional or nation wide mapping of the black shales is recommended to detect potential risk areas finland has recently completed the country wide mapping program of black shales with airborne geophysics integrated with geological petrophysical and geochemical studies the black shale database is actively used in regional planning and by environmental authorities research institutes and consulting companies in the case of the historical black shale mining areas like in the kupferschiefer in germany restoration measures have been applied to prevent further acid mine drainage in active and future mining projects a comprehensive environmental impact assessment with effective monitoring programmes and closure plans play a crucial role in the prevention of acid mine drainage from the black shale associated deposits

antimony deposits in the variscan armorican belt a link with mafic intrusives the variscan armorican belt was the world leading producer of antimony at the beginning of the twentieth century however geological controls on the deposits remain unconstrained here we illustrate the field setting of mineralisations and perform a statistical analysis using geographical information system software geophysical and geological data the analysis shows that sb deposits are spatially correlated with high density and magnetic zones this may reflect the presence of mafic ultramafic bodies at depth a suggestion that is further supported by numerous occurrences of doleritic dykes throughout the region future antimony prospecting should focus on the high density and high magnetic zones which comprise about 18 of the armorican massif links between sb deposits and mafic intrusions are recognised elsewhere in the west european variscan belt emphasising that these may be key for antimony prospecting in deformation belts

the influence of oxic degradation on the sedimentary biomarker record i evidence from madeira abyssal plain turbidites free and ester bound lipid biomarkers were analysed in oxidised and unoxidised parts of four distinct turbidites from the madeira abyssal plain map which contained 1 to 2 organic carbon homogeneously distributed throughout the turbidites at the time they were deposited these turbidites are well suited to study the effects of oxic degradation on lipid biomarkers without the complicating influence of varying organic matter sources sedimentation rates or bioturbation one sample from the oxidised turbidite was compared with two samples from the unoxidised part of each turbidite postdepositional oxic degradation decreased concentrations of biomarkers by several orders of magnitude the ester bound lipids were degraded to a far lesser extent than their free counterparts were the extent of degradation of different compounds differed substantially within a specific class of biomarkers degradation also took place to a different extent altering their distributions this study shows that oxic degradation of the organic matter may have a profound effect on the biomarker fingerprint and may result in a severe bias in for example the interpretation of organic matter sources and the estimation of the palaeoproductivity of specific groups of phytoplankton

evaluating episodic hydrothermal activity in south china during the early cambrian implications for biotic evolution abstract the early cambrian 541 514 ma was a crucial interval for the evolution of life on earth popularly known as the cambrian explosion here we report the timing of changes in hydrothermal and depositional inputs as well as paleo redox state which may have influenced biogeochemical changes according to high resolution petrology fossil distributions isotopic records and inorganic geochemistry the lower cambrian of the south china can be subdivided into four intervals the lowermost cambrian zhujiaqing formation cam i the cambrian stage 2 shiyantou formation cam ii the lower part of the cambrian stage 3 yu anshan formation cam iii and the mid upper cambrian stage 3 and the middle upper part of the yu anshan formation continuing into the canglangpu formation cam iv hydrothermal events are detected during the early cam i cam ii and cam iii intervals during the early cam i and cam ii intervals these events coincided with extensive bottom water euxinia which in turn may have restricted the spread or proliferation of ediacaran fauna and small shelly fauna through the whole cam iii interval further hydrothermal events occurred concurrently with euxinic and ferruginous conditions probably within a single spatially stratified water column again plausibly restricting the spread of aerobic organisms in conjunction with the cessation of hydrothermal events and the gradual lowering of sea level during the late cam iii oxic water environments gradually spread into relatively deep water regions concurrent with the emergence of the chengjiang and qingjiang faunas these data suggest that periodic hydrothermal events may have had a significant impact on the spread radiation and extinction of macroscopic fauna during the early cambrian in south china

the variscan post collisional volcanism in late carboniferous permian sequences of ligurian alps southern alps and sardinia italy a synthesis abstract in the considered wide sector of the west mediterranean southern europe the collisional phase of the variscan orogeny during late carboniferous and permian times was followed by magmatic intrusive and effusive activity and sedimentation into intracontinental alluvial to lacustrine basins originated by wrench to normal fault systems the first volcanic cycle generally late carboniferous early permian in age is represented by early calc alkaline andesites and rhyolites in variable amounts and by following large volume of rhyolites and by dacites both andesites and rhyolites show k normal and high k calc alkaline character the origin of the liquids of the first cycle is ascribed to partial melting processes at the mantle crust interface telescoped within a thickened crust the melting is considered as the consequence of thermal re equilibration following isostatic disequilibrium and the subsequent collapse of the orogenic belt the ascent of liquids occurred in a trans tensional regime the second magmatic cycle is represented by alkaline magmatism and exhibits typical anorogenic features consistent with a rifting regime this event was no more related with the collapse of the variscan belt but rather to the post variscan global re organization of plates that evolved during late triassic times to the neo tethyan rifting in both cycles important differences in timing areal distribution and outpoured volumes arise

yttrium and rare earth elements in fluids from various deep sea hydrothermal systems rare earth element ree and yttrium y concentrations were measured in fluids collected from deep sea hydrothermal systems including the mid atlantic ridge mar i e menez gwen lucky strike tag and snakepit the east pacific rise epr i e 13 n and 17 19 s and the lau vai lili and manus vienna woods pacmanus desmos back arc basins bab in the south west pacific in most fluids y is trivalent and behaves like ho chondrite normalized y ree y reen concentrations of fluids from mar epr and two bab sites i e vai lili and vienna woods showed common patterns with lree enrichment and positive eu anomalies ree analysis of plagioclase collected at lucky strike strengthens the idea that fluid ree contents are controlled by plagioclase phenocrysts other processes however such as ree complexation by ligands cl f so42 secondary phase precipitation and phase separation modify ree distributions in deep sea hydrothermal fluids ree speciation calculations suggest that aqueous ree are mainly complexed by cl ions in hot acidic fluids from deep sea hydrothermal systems ree concentrations in the fluid phases are therefore influenced by temperature ph and duration of rock fluid interaction unusual y reen patterns found in the pacmanus fluids are characterized by depleted lree and a positive eu anomaly the demos fluid sample shows a flat y reen pattern which increases regularly from lree to hree with no eu anomaly these manus basin fluids also have an unusual major element chemistry with relatively high mg so4 h2s and f contents which may be due to the incorporation of magmatic fluids into heated seawater during hydrothermal circulation ree distribution in pacmanus fluids may stem from a subseafloor barite precipitation and the ree in demos fluids are likely influenced by the presence of sulfate ions

cerium anomaly variations in ediacaran earliest cambrian carbonates from the yangtze gorges area south china implications for oxygenation of coeval shallow seawater abstract the late neoproterozoic ocean witnessed the naissance of animals which is believed to have been stimulated by an increase in oxygen levels in the ocean however apart from the emergence of animal fossils little supporting evidence has been found for the rise of oxygen in shallow seawater here we present ce anomaly data a redox proxy with a higher reduction potential than many other redox proxies for carbonates from well preserved marine successions the doushantuo formation dengying formation and lower yanjiahe formation of the ediacaran period and the upper yanjiahe formation of early cambrian on the neoproterozoic yangtze platform in the yangtze gorges area in order to constrain the redox evolution of the shallow marine environment calculated ce anomalies were screened using the following criteria al 36 in acetic acid leached carbonate to target samples that preserve primary seawater ree features and ce anomalies the samples satisfying this screening show seawater like ree distribution patterns in leached carbonates and may have recorded ce anomalies of the seawater from which the carbonates precipitated these data show that the doushantuo formation has ce ce values between 0 92 and 0 71 the dengying formation between 0 90 and 0 40 and the yanjiahe formation between 0 52 and 0 72 the ce ce values of the doushantuo formation suggest that shallow waters during the doushantuo stage 635 551 ma were anoxic to suboxic from the bottom to the top of the dengying formation ce ce values decrease systematically which cannot be explained by a change in depositional depth of the carbonate but suggests that the shallow waters became more oxygenated during the dengying stages from 551 ma to ediacaran cambrian boundary these results may provide direct evidence for an increase in oxygen levels in the shallow marine environment during the ediacaran period

submarine hydrothermal contribution for the extreme element accumulation during the early cambrian south china throughout the geological history of the earth submarine hydrothermal activity has played an important role in seawater chemistry biological evolution and enrichment of metals in the earth crust however the prospect of hydrothermal activity for extreme element accumulation during the early cambrian a key geological period in south china has not been well constrained this study reports geochemical e g ree and sr isotope investigations of a coarse grained limestone layer and associated calcite veins in zunyi and nayong areas guizhou province to constrain the hydrothermal activity and evaluate the significance of hydrothermal contribution to extreme element accumulation during the early cambrian south china our results reveal positive eu anomalies and higher initial 87sr 86sr ratios 0 7083 0 7150 for carbonate samples than those of early cambrian seawater indicating the presence of hydrothermal processes combined with constraints from the spatial relationships and coincidence with adjacent mineralization these hydrothermal processes provide the most probable contribution for polymetallic ni mo pge mineralization furthermore there are abundant hydrothermal dolomite and barite calcite veins in the dolostone of the dengying formation indicating the occurrence of a variety of hydrothermal fluids overall multi stage hydrothermal pulses with different fluid compositions spanned the ediacaran cambrian transition in south china in particular these hydrothermal fluids with positive eu anomalies and enriched radiogenic sr originating from proterozoic mafic ultramafic rocks may have flowed through the underlying precambrian silicate clastic rocks e g xiajiang banxi and lengjiaxi groups and may have been crucial for the marine environment biological diversity and extreme element accumulation during the early cambrian south china

quartz veins with associated sb pb ag au mineralization in the schwarzwald sw germany a record of metamorphic cooling tectonic rifting and element remobilization processes in the variscan belt a combination of textural observations from 38 permian sb pb ag au bearing quartz veins in the schwarzwald sw germany with isotopic fluid inclusion and geochemical data allows to refine genetic models for this common type of mineralization to understand the origin of mineralogical diversity and the correlation with large scale tectonic events textures record four main mineralization stages i fe as sb au ii pb zn cu iii pb sb and iv ag sb stage i sulfides dominated by pyrite and arsenopyrite formed due to cooling of low salinity metamorphic fluids during the permian with maximum homogenization temperatures of 400 c invisible gold in arsenopyrite pyrite marcasite and stibnite was remobilized and locally precipitated as electrum at the end of stage i minerals of stages ii and iii comprise a rich diversity of sb bearing sulfosalts including e g bournonite zinkenite and jamesonite this assemblage formed during jurassic times due to mixing of high salinity mid and upper crustal fluids up to 27 wt nacl cacl2 with homogenization temperatures between 50 and 250 c stage iii is marked by a rich variety of pb sb sulfosalts its local abundance is directly related to the presence of stage i mineralization and its extent of remobilization during a significant influx of pb in the jurassic cretaceous the formation of the upper rhine graben during the tertiary reactivated especially ne sw oriented veins percolating ag rich fluids reacted with earlier stage iii pb sb sulfosalts forming ag rich minerals stage iv such as miargyrite pyrargyrite and stephanite the transition from metamorphic fluids to basinal saline e g pb bearing brines over hundreds of millions of years as is shown in this study and present in other variscan occurrences indicates a possibly typical poly stage characteristic of sb deposits worldwide which has however not been investigated in detail so far

sulphur isotope geochemistry of black shale hosted antimony mineralization arnsberg northern rhenish massif germany implications for late stage fluid flow during the variscan orogeny vein type and bedding concordant mesothermal 180 410 c stibnite sulphosalt mineralization at arnsberg ne rhenish massif germany is hosted by carboniferous pyrite rich black shales and siliceous limestones a detailed sulphur isotope study of the stibnite sulphosalt mineralization and pyrite from a variety of regional host rock lithologies has been carried out using an in situ laser combustion technique the 34 s values of stibnite of various textural types are distinctly negative and lie in a narrow range between 23 9 and 17 1 mean 20 1 in contrast regional sedimentary diagenetic pyrites display a large variation of their 34 s values between 45 4 and 9 3 there is little evidence for significant modification of the hydrothermal fluid during deposition and the s isotope signatures suggest that the sulphur of the stibnite mineralization was not locally derived the 34 s values of pyrite in givetian shales display a significantly narrower range of 28 2 to 7 5 and their mean composition 17 1 is close to the 34 s values of the arnsberg stibnite deposits considering the temperature dependent isotopic fractionation between stibnite and reduced sulfur species the 34 s values of the mineralizing fluid 16 8 200 c and the givetian rock source are essentially identical therefore we propose a model of leaching and isotopic homogenization of sulphur from the middle devonian shales and a subsequent northward migration of these fluids the fluids were trapped in permeability controlled positions within anticlinal zones where fluid cooling induced deposition of stibnite and sulphosalts

antimoniferous vein type mineralization of the berga antiform eastern thuringia germany a fluid inclusion study abstract the antimoniferous vein mineralization in the schleiz and greiz area eastern thuringia are bound to ne sw striking variscan fault zones along the margins of the berga antiform the sb pb zn ores form massive sulfide sulfosalt quartz carbonate veins breccias or stockworks within ordovician and silurian metasedimentary units devonian metabasalts and metagranitoids mineralogical investigations from several sb mines and hard rock quarries near schleiz and greiz germany show that the sb pb zn sulfides are texturally in close association with quartz and carbonates stibnite is the major sb bearing mineral minerals of the sb pb zn sulfide assemblage replace an earlier zn fe as sulfide quartz assemblage quartz i named the ore stage i mineralization stibnite and quartz ii overgrow these early sulfides accounting for the ore stage ii lead dominated sb sulfides e g zinkenite plagionite semseyite represent the ore stage iii phase followed by sphalerite ii galena and quartz iii accounting for ore stage iv fluid inclusion studies on ore and gangue minerals of the different ore stages give insights into the composition and temperature of the mineralizing fluid s primary fluid inclusion assemblages in ore stage ii stibnite and co genetic quartz ii show variable vapor fractions within fluid inclusion assemblages heterogeneous trapping of co2 at constant salinities of fluid inclusions of the same assemblage indicates the influx of a buoyant pure co2 fluid into an aqueous fluid phase the presented data demonstrates the first example of co2 influx into an aqueous fluid identified by fluid inclusion analyses during this ore stage ii a h2o co2 nacl fluid with eq w nacl of 1 to 2 7 at 220 226 c prevails in contrast fluid inclusions in ore stage iii minerals boulangerite contain a homogeneously trapped h2o nacl cacl2 fluid with eq w nacl up to 8 1 at temperatures 146 c ore stage iv minerals sphalerite ii quartz iii contain a homogeneously trapped h2o nacl cacl2 fluid with eq w nacl of 20 and homogenization into the liquid phase at around 120 c fluid inclusion data suggest p t conditions at the onset of mineralization at around 220 c at 0 70 to 0 75 kbar fluid pressure the mechanisms of sb ore precipitation were induced by the influx of co2 fluid cooling quartz ii stibnite boulangerite and late stage mixing with a high salinity fluid resulting in the precipitation of sphalerite ii galena and quartz iii the unique opportunity to analyze fluid inclusions in many different subsequently precipitating ore and gangue minerals enables the reconstruction of the temporal evolution of the sb veins the distinct change of the ore forming processes from the influx of co2 into an aqueous fluid and cooling ore stage i ii to mixing ore stage iii iv as the dominant precipitation mechanisms are also accompanied by a drastic change in the mineralogy from sb sulfides to pb zn sulfides late orogenic granitic intrusions served as a potential heat metal and sulfur source variscan wrench and thrust tectonics and associated metamorphism account for the ore stage i mineralization hydrothermal sb pb zn assemblages ore stages ii iii and iv precipitated during the latest part of the variscan orogeny most likely around the carboniferous permian boundary although fluid composition and formation temperatures of the greiz and schleiz mineralization are on the first view quite similar to those of other variscan sb mineralization the observation of co2 influx and fluid mixing with a high salinity fluid is unique for european sb occurrences

a c mos2 mixed layer phase mosc occurring in metalliferous black shales from southern china and new data on jordisite a new phase composed mainly of mo s and c and referred to herein as mosc occurs widely in organic rich metalliferous cambrian black shales in south china mosc which has previously been referred to as jordisite has been studied by scanning electron microscopy sem electron microprobe analysis empa transmission electron microscopy tem powder x ray diffraction xrd extended x ray absorption fine structure exafs and catalytic activity tem data show mosc to have a layered structure with packets resembling molybdenite and graphite like carbon that average five layers in thickness analytical data are consistent with an idealized formula of mo3s6c10 but it commonly contains 1 3 wt each of fe ni and as so that its composition may be better approximated by the formula mo fe ni 3 s as 6c10 selected area electron diffraction saed patterns show a small number of broad inhomogeneous rings corresponding to randomly oriented layers arranged in subspherical cells a single broad weak peak corresponds to a 10 11 a layer spacing in powder xrd diffraction patterns pseudomorphism after fossil bacteria implies an origin by replacement of sedimentary organic material in its chemical properties and structure mosc resembles synthetic compounds used as catalysts for hydrodesulfurization hds in the petrochemical industry the large surface to volume ratio for mosc may be an important factor in its relatively strong hds catalytic activity cotype samples of jordisite from germany previously thought to be amorphous mos2 were also studied by sem and tem jordisite occurs as sequences of a few curved layers that form sub spherical units with an appearance remarkably like that of mosc however the layer spacing is 6 a like that of molybdenite the ratio of mo s is 1 2 and no carbon was detected although it coexists with kerogen jordisite is thus confirmed to be a form of mos2 but because powder diffraction like saed patterns were obtained it is not amorphous

fluid inclusions and ore precipitation mechanism in the giant xikuangshan mesothermal antimony deposit south china conventional and infrared microthermometric constraints abstract the giant xikuangshan antimony deposit located in the xiangzhong central hunan basin south china is the largest antimony deposit in the world stibnite is the predominant ore mineral and gangue minerals consist of quartz calcite fluorite and barite the ore mineral assemblages include early stage quartz stibnite fluorite quartz stibnite and barite quartz stibnite and late stage calcite stibnite in spite of numerous research works on the xikuangshan deposit during the past several decades the signatures of the ore forming fluids and the ore precipitation mechanisms are poorly constrained in order to characterize the fluids responsible for antimony mineralization and ascertain the genetic processes in the xikuangshan ore district conventional and infrared microthermometric measurements have been performed in this study on fluid inclusions hosted in transparent minerals quartz fluorite and barite and opaque stibnite respectively four types of fluid inclusions were identified for the early stage mineralization based on their phase assemblages including type i pure liquid inclusions type ii two phase liquid rich aqueous inclusions type iii two phase vapor rich aqueous inclusions and type iv pure vapor inclusions stibnite only contains type i and type ii inclusions while all types of fluid inclusions are common in the gangue minerals the homogenization temperatures and salinities of fluid inclusions in stibnite and associated gangue minerals in this ore district display significant differences fluid inclusions in stibnite exhibit relatively low homogenization temperatures 112 323 c and higher salinities 0 2 15 4 wt nacl equiv than inclusions in coexisting gangue minerals 119 366 c 0 2 4 2 wt nacl equiv usually about 50 c less than the intergrown gangue minerals according to the petrography of fluid inclusions and the relationship between their homogenization temperature and salinity it was concluded that stibnite and gangue minerals in the xikuangshan ore district are not co genetic instead they were deposited from two distinctly different hydrothermal solutions fluid mixing was responsible for stibnite precipitation but the precipitation of gangue minerals resulted from fluid boiling due to an abrupt drop in pressure the xikuangshan deposit is a typical example of mesothermal deposits rather than an epithermal deposit as previously considered

new u pb zircon ages of the ediacaran cambrian boundary strata in south china the ediacaran cambrian transition is a critical interval marking drastic biological oceanic and geochemical co evolutions in geological history but it is poorly constrained geochronologically in south china we here present two new sets of sims u pb zircon ages from ediacaran cambrian boundary strata dengying liuchapo and niutitang formations deposited in the slope basin environments of carbonate platforms two weighted mean u pb ages of 542 1 5 0 ma and 542 6 3 7 ma in the basal and mid upper liuchapo formation respectively in slope and basinal settings provide the first direct age set for the ediacaran cambrian boundary in south china another two u pb ages of 524 2 5 1 ma and 522 3 3 7 ma from the base of the overlying niutitang formation indicate that this widespread unit in south china was deposited about 20 ma after the onset of the cambrian

quartz trace element composition by la icp ms as proxy for granite differentiation hydrothermal episodes and related mineralization the beauvoir granite echassieres district france despite quartz being a ubiquitous mineral in the earth s crust only little is known about its trace chemical composition and whether and how this is influenced by the medium from which it precipitated using in situla icp ms analysis we investigated the trace element composition of several types of quartz from a magmatic hydrothermal system in the echassieres district of the french massif central this system consists of the colettes granite the beauvoir rare element granite a w bearing stockwork and dispersed mineralized veins all of the elements tested li be b na al ti ge rb sr nb sn sb ta w were detected in quartz from at least one sample a rigorous multivariate statistical approach permitted to assign a specific chemical signature to each of the quartz groups that were recognized by petrographic observations differences among these groups were interpreted to reflect different sources or genetic evolutionary trends within magmatic and hydrothermally derived quartz groups for example the evolution of al rb ge li and ti could be related to genetic processes such as the degree of magma differentiation and crystallization temperatures quartz from the w stockwork anterior to the beauvoir leucogranite clearly stands out from that related to the beauvoir mineralization system i e the greisen facies and proximal ta nb sn w mineralized veins it was also possible to demonstrate a similarity in composition notably the sb contents between quartz from the greisen and from distal stibnite bearing veins in addition elevated values of sb sn as well as li and rb in quartz correspond to similarly high values of these elements in the rock indicating that quartz trace chemistry can provide useful information for the mineralization potential of its host at least for these elements on the other hand nb ta and w are less reliable as they occur mostly at very low levels in quartz the highest values corresponding to samples that were not particularly enriched in these metals a comparison of our quartz data with those from a similar granitic complex at cinovec czech republic breiter et al 2017a shows a similar trend for the ge ti ratio reflecting magmatic differentiation conversely the al ti ratio values differ in the two complexes the al content of quartz from the various cinovec granites being systematically lower than in quartz from echassieres nevertheless caution must be taken when analyzing quartz for its trace element chemistry as processes occurring during i e trapping of fluid inclusions and formation of zoning and after crystal growth i e diffusion and alteration can introduce heterogeneities thus affecting the original chemistry

antimony quartz and antimony gold quartz veins from northern portugal abstract antimony and pb sb quartz veins from the braganca district portugal are mainly hosted by silurian phyllites antimony au quartz veins from the durico beira region are mainly hosted by a cambrian schist metagraywacke complex as well as ordovician phyllites and quartzites the deposits were mostly exploited in the late 19th century mineralogical characteristics and chemical compositions of individual ore minerals are similar in the two areas first and second generations of arsenopyrite precipitated at 390 and 300 c respectively berthierite and stibnite are the most abundant sb bearing minerals and precipitated between 225 and 128 c native antimony at

reply to the comment by f tornos et al we welcome the discussion of our paper by tornos et al the epithermal character of the hiendelaencina veins might have been an assumption in the early to mid 1980s however this early idea has been reaffirmed after many years of research involving fieldwork and mineralogical sulphur isotopes and fluid inclusions studies the same applies to the alleged extensional frame a tectonic episode now well documented not only in central spain spanish central system doblas 1987 doblas et al 1988 doblas 1991 but in france french central massif menard and molnar 1988 malavieille et al 1990 munoz et al 1992 the deposits are hosted by metamorphic rocks and the nearest volcanic outcrops to hiendelaencina are those of atienza andesites some 12 km northward this is the reason why the relationships between the atienza volcanics and the hiendelaencina veins were initially regarded as obscure these stephanian permian volcanic outcrops are only local evidence of the late variscan magmatism which in the case of hiendelaencina remained concealed it is evident that the geologic environments of hiendelaencina and atienza are very different see discussion p 88 of the paper as a direct consequence of this the local structural conditions led to contrasted expressions of the late variscan magmatism i e subaereal at atienza and hypabyssal at hiendelaencina

eclogites in the french palaeozoic orogen geodynamic significance abstract eclogites are widespread in the devonian internal zone of the french palaeozoic orogen they occur in different tectonic settings either in high pressure low temperature or in high pressure high temperature environments they are tectonically incorporated into several major allochthonous units as demonstrated either by their blastomylonitic texture or by their being in evident disequilibrium with their country rocks the protoliths of the presently well identified eclogite bearing series present different typical associations depending on their present location the igneous series include within plate basalts normal and transitional morbs and even calc alkaline rocks they were erupted mostly during the palaeozoic although they sometimes contain inherited precambrian zircons further some of them may be remnants of old precambrian oceanic crust most of the eclogitic parageneses were generated during the earliest silurian tectonometamorphic climax either in low temperature or in high temperature conditions later they followed various retrograde courses in still geographically distinct low temperature or high temperature associations the basic rocks in the leptynolitic amphibolitic complex and particularly the eclogites thus provide sufficiently clear evidence to support a new geodynamic scenario implying one or several subordinate narrow tensional zones in a thinned but well developed continental crust rather than in a true oceanic domain

ree and trace element patterns from organic rich rocks of the ediacaran cambrian transitional interval abstract it has been established that important changes in the marine environment and the biosphere occurred during the cambrian however the relationships between the so called cambrian explosion and the concomitant environmental changes are not yet fully understood this study presents new geochemical data from the black shale successions from different facies belts of the yangtze platform in south china variations in the concentrations of ree and trace elements varying ce ce th u v sc and v cr ratios in kerogen as well as in bulk rocks from different depositional environments along a transect from platform to basin indicate two oxidation events which led to the oxygenation of the water column in shallow marine environments and euxinic conditions weak correlation between toc v u and mo in the deeper sea during the first oxidation event in the late terreneuvian anoxic conditions in bottom waters rapidly changed to euxinic conditions subsequently the second oxidation event during the early epoch 2 of the cambrian led to oxic suboxic conditions in deeper seawater

the variscan belt in central europe main structures geodynamic implications open questions abstract the variscan belt of europe originated from the confrontation of northern europe and gondwana with intervening pre variscan blocks cadomian and older armorica tepla barrandean moravo silesian though a strike slip component cannot be excluded geological evidence suggests a subduction collision process newly discovered features include basaltic rocks with morb affinities high pressure metamorphic rocks trench deposits and large scale allochthonism which also affects the pre variscan basement and has often led to an inversion of the metamorphic isogrades large scale thrusting is evident at all crustal levels and is also observable by geophysical methods the structure of the variscan crust is best described as horizontal tectonic layering late ordovician through carboniferous convergence closed one rhenohercynian and one saxo thuringian basin to the north and at least one mediterranean basin to the south of the pre variscan blocks subduction occurred from the north as well as from the south down under the dorsal core region the exact timing and the driving mechanism of this bilateral activity remains a problem likewise uncertain are the exact limination of the pre variscan blocks and the existence and width of oceanic areas in the saxothuringian zone and in the south facing part of the moldanubian zone there is good evidence of early palaeozoic rifting and of late ordovician through carboniferous plate convergence palaeomagnetic and palaeoclimatic constraints however suggest only a limited extent of oceanic basins in these areas while they appear to allow a wider ocean at the rhenohercynian saxothuringian boundary which is relatively unobtrusive from the geological point of view research during the past decade has produced a wealth of information on the variscan fold belt in europe the resulting geodynamic models however are extremely diverging evidently it is not the time yet for definitive statements the present paper intends to review the state of knowledge to deduce such basic items of a geodynamic model as appear reasonably well documented and to point out the most urgent open questions stress will be laid on central europe which offers a complete cross section through the northern flank of the variscan belt and where we have carried out most of our studies during the last years

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

terrestrial vegetation change inferred from n alkane σ13c analysis in the marine environment abstract we report gas chromatography isotope ratio monitoring mass spectrometry gc irm ms measurements of the 13c values of individual biomarker compounds n alkanes extracted from a 3 m marine sediment core taken near the mouth of the johnstone river north queensland australia the technique allows a purely terrestrial isotope signal to be discerned despite mixing of terrestrial and marine derived carbon the results indicate that there has been a 2 increase in the 13c values of terrestrially derived n alkanes c29 c33 since clearing of the forested johnstone river drainage basin for sugarcane and pasture began in the late 19th century a much slower 1 increase in 13c values after 6 000 years bp and prior to european settlement may be related to a decrease in rainfall in the basin or to an increase in the abundance of c4 plants as a result of increased aboriginal burning the results from the sediment core are consistent with data obtained for modern river sediments from forested and cleared subcatchments within the basin and demonstrate that the 13c values of terrestrially derived n alkanes in the marine environment can be used to assess basin wide vegetation changes in adjacent river catchments on geological timescales

late hercynian polymetallic vein type base metal mineralization in the iberian pyrite belt fluid inclusion and stable isotope geochemistry s o h cl late variscan vein type mineralization in the iberian pyrite belt related to the rejuvenation of pre existing fractures during late variscan extensional tectonism comprises pyrite chalcopyrite quartz galena sphalerite quartz stibnite arsenopyrite quartz pyrite quartz cassiterite scheelite fluorite galena sphalerite chalcopyrite and quartz manganese oxide mineral assemblages studies of fluid inclusions in quartz stibnite and barite as well as the sulfur isotopic compositions of stibnite galena and barite from three occurrences in the central part of the iberian pyrite belt reveal compelling evidence for there having been different sources of sulfur and depositional conditions quartz stibnite mineralization formed at temperatures of about 200 c from fluids which had undergone two phase separation during ascent antimony and sulfide are most probably derived by alteration of a deeper lying volcanic hosted massive sulfide mineralization as indicated by 34s signatures from 1 45 to 2 74 sub critical phase separation of the fluid caused extreme fractionation of chlorine isotopes 37cl between 1 8 and 3 2 which correlates with a fractionation of the cl br ratios the source of another high salinity fluid trapped in inclusions in late stage quartz from quartz stibnite veins remains unclear by contrast quartz galena veins derived sulfide and metals by alteration of a sedimentary source most likely shale hosted massive sulfides the 34s values in galena from the two study sites vary between 15 42 and 19 04 barite which is associated with galena has significantly different 34s values 0 2 to 6 44 and is assumed to have formed by mixing of the ascending fluids with meteoric water

multi stage fluid incursion in the palaeozoic basement hosted saint salvy ore deposit nw montagne noire southern france abstract the saint salvy vein hosted zn ge deposit occurs in an e w fault system which flanks the southern margin of the late variscan sidobre granite and cross cuts cambrian black shales of the palaeozoic basement comprehensive mineralogical and geochemical studies of vein samples have revealed four mineralizing events m1 m4 related to late and post variscan tectonic events a further late stage event may be related to weathering m1 skarn deposits and m2 patchily mineralized quartz veinlets are associated with granite emplacement quartz contains low salinity h2o co2 nacl dominated fluids 6wt nacl equiv of relatively high temperature 300 580 c trapped under moderate to high pressure estimated m1 fluid d and calculated fluid 18o plot within the metamorphic water field there appears to be no involvement of magmatic fluids by contrast m3 barren quartz and m4 zinciferous economic mineralization stages have h2o co2 nacl cacl2 fluid inclusions with high salinities 23 25 wt nacl equiv and low temperatures 80 140 c which were trapped under low pressure conditions the high salinity and nacl cacl2 content of both m3 and m4 indicates that their parent fluids leached evaporitic salts m3 fluids are meteoric water dominated falling close to the meteoric water line d and 18o averaging 64 and 8 respectively m4 fluids have highly distinctive d averaging 101 and calculated fluid 18o varying from 1 2to 7 1 the unusually low d composition of m4 suggests the involvement of organic fluids in which h is derived directly or indirectly from organic matter the relatively high 18o of m4 fluids indicates that considerable isotopic exchange with sedimentary material took place displacing the 18o from the meteoric water line the data imply interaction of meteoric waters with evaporite and hydrocarbon bearing sedimentary sequences most probably the adjacent aquitain basin the main economic mineralization m4 stage took place during a tensional event probably coincident with the lias dogger transition calculated 34sh2s of m4 sulphide 5 4to 8 2 is almost identical to 34s of local cambrian sulphides 4 7to 9 4 suggesting a genetic link abundant siderite associated with m4 sphalerite has 13c ranging from 2 6to 4 4 indicating that carbon was sourced from sedimentary carbonate mobilized by or equilibrated with the hydrothermal fluid late stage sulphides exhibit extraordinary and highly distinctive 34s sphalerite has extremely low 34s 42 5to 50 5 whereas pyrite has an extraordinary large range from 33 2 to 74 3 closed system sulphate reduction is held to be responsible for the extremely high 34s whereas more open system reduction produces the very low values the coincidence of isotopically low 13c 7 6to 11 9 for co genetic calcite suggests the involvement of organic matter in the reduction process

petrology and geochemistry of chert on the marginal zone of yangtze platform western hunan south china during the ediacaran cambrian transition the ediacaran cambrian transition was one of the most critical intervals in earth history during this interval widespread chert was precipitated commonly as a stratal wedge in carbonates along the southern margin of the yangtze platform south china the chert wedge passes into a full chert succession further basinward to the south east four lithotypes of chert are identified across the marginal zone in western hunan mounded vein brecciated and bedded chert the mounded chert is characterized by irregular to digitiform internal fabrics generally with abundant original vesicles and or channels that mostly are lined by botryoidal chalcedony cements with minor quartz and barite crystals the host chert or matrix of these mounds is dominated by amorphous cryptocrystalline silica commonly disseminated with pyrite the vein chert with minor quartz locally generally cross cuts the overlying dolostone and chert horizons and terminates under the mounded and or bedded chert bodies the brecciated chert commonly occurs as splayed intrusions or funnel shaped wedges and cross cuts the topmost dolostones the bedded chert the most common type generally is thin to medium bedded and laminated locally it is composed of amorphous silica with minor amounts of black lumps microthermometry of fluid inclusions from vein and void lining minerals mainly quartz and barite revealed homogenization temperatures from 120 to 180 c for the trapped primary fluids compositionally these chert deposits generally are pure with sio2 92 wt and only minor fe2o3 and al2o3 contents most of which show positive europium anomalies in rare earth element patterns especially for the mounded chert all these data suggest that the marginal zone chert deposits resulted from a low temperature silica rich hydrothermal system in which the mounded chert was precipitated around the releasing vents i e as silica chimneys the vein and splayed brecciated chert however was formed along the syndepositional fault fracture conduits that linked downward while the bedded chert was precipitated in the quieter water column from the fallout of hydrothermal plumes onto the sea floor these petrological and geochemical data provide compelling evidence and a new clue to the understanding of the extensive silica precipitation rapid tectonodepositional and oceanic changes during the ediacaran cambrian transition in south china

correction to forcing of tropical atlantic sea surface temperatures during the mid pleistocene transition late quaternary versus minimum ice geob 1016 sst angola margin 0 76 0 64 28 20 3 2 2 3 e45 29 e49 18 sst south indian fronts 0 86 0 65 27 15 3 1 1 7 ps2082 1 sst south atlantic fronts 0 92 0 73 18 12 2 1 1 4 ps2489 2 ssst south atlantic fronts 0 82 0 80 13 15 1 5 1 7 etp describes summed orbital variance following the convention by imbrie et al 1989 using the data of berger and loutre 1991 odp 1090 ssst data are from becquey and gersonde 2002 data of odp 677 do are from shackleton et al 1990 data of dsdp 607 dc are from ruddiman et al 1989 with the stratigraphy of raymo et al 1997 results for the late quaternary are taken from the literature data of geob 1016 11 460s 11 410e are from schneider et al 1995 data for e45 29 44 530s 106 310e and e49 18 46 030s 90 100e are from howard and prell 1992 ps2082 1 43 130s 11 440e data are from brathauer and abelmann 1999 and ps2489 2 42 520s 8 580e data are from becquey and gersonde 2003 all late quaternary records are crossed with the inverse specmap record imbrie et al 1984 except for ps2489 2 ssst which is crossed with benthic foraminiferal do of that core becquey and gersonde 2003 a negative phase lag represents a lead paleoceanography vol 20 pa1019 doi 10 1029 2005pa001134 2005

the massive stibnite veins of the french palaeozoic basement a metallogenic marker of late variscan brittle extension the stibnite ore deposits of the french palaeozoic basement are spatially related to major late variscan strike slip faults they occur as small discontinuous veins mostly hosted in epizonal or catazonal siliciclastics stibnite crystallizes in the final stage of a polymetallic paragenesis from an antimony bearing solution which deposits a first discrete fe as assemblage at 300 400 c and 0 5 0 8 kbar experimental data have shown that antimony solubility drastically decreases on cooling characterization of the late variscan antimony bearing fluids enables us to predict the temperature range 270 150 c under which stibnite was precipitated since the latter coincides with the fluid inclusion homogenization temperature range the pressure at which stibnite crystallized can be estimated from vapour pressure data to have been around 0 1 kbar extensional brittle shear zones developed at the end of the late variscan orogeny probably at the westphalian stephanian boundary drained the hydrothermal fluids near to the surface c 1000 m reaching the critical p t conditions for stibnite crystallization

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

lead isotope systematics of vein type antimony mineralization rheinisches schiefergebirge germany a case history of complex reaction and remobilization processes mesothermal vein type sb mineralization in the rheinisches schiefergebirge germany is characterized by two different mineralization styles which are 1 extensional quartz stibnite vein systems and 2 cu pb sb sulphosalt assemblages in overprinted pre existing pb zn veins a detailed pb isotope study of 52 representative samples from both mineralization types indicates distinct compositional patterns cu pb sb sulphosalts meneghinite boulangerite bournonite formed by reaction remobilization are characterized by pb isotope compositions 206pb 204pb 18 179 18 223 which are identical to the precursor galena 206pb 204pb 18 168 18 223 the pb isotope composition of sulphosalt minerals in these vein systems was controlled by lead inherited from pre existing galena stibnite and pb sulphosalts zinkenite semseyite plagionite formed in quartz stibnite vein systems display pb isotope ratios 206pb 204pb 18 250 18 354 which are more radiogenic than galenas from variscan pb zn ore veins 206pb 204pb 18 162 18 303 detailed small scale investigation of thrust zones hosting pb zn ores and crosscutting quartz ankerite fissure veins ramsbeck deposit indicates that the pb isotope compositions of recrystallized galena and remobilized phases boulangerite semseyite bournonite are arranged along a linear trend this is interpreted as mixing between primary galena with 206pb 204pb 18 206 and overprinting hydrothermal fluids with a more radiogenic composition 206pb 204pb 18 354 expressed by intermediate compositions 206pb 204pb 18 256 18 334 of newly formed sulphosalts the pb isotope systematics of the vein type sb mineralization is in accordance with a model of pb extraction from similar crustal sources palaeozoic sedimentary sequences at different times

calcium isotope δ 44 40 ca fractionation along hydrothermal pathways logatchev field mid atlantic ridge 14 45 n we investigate the logatchev hydrothermal field at the mid atlantic ridge 14 degrees 45 n to constrain the calcium isotope hydrothermal flux into the ocean during the transformation of seawater to a hydrothermal solution the ca concentration of pristine seawater ca sw increases from about 10 mm to about 32 mm in the hydrothermal fluid endmember ca hydend and thereby adopts a delta ca 44 40 hydend of 0 95 0 07 parts per thousand relative to seawater sw and a sr 87 sr 86 isotope ratio of 0 7034 4 we demonstrate that delta ca 44 40 hydend is higher than that of the bedrock at the logatchev field from mass balance calculations we deduce a delta ca 44 40 of 1 17 0 04 parts per thousand sw for the host rocks in the reaction zone and 1 45 0 057 parts per thousand sw for the isotopic composition of the entire hydrothermal cell of the logatchev field the values are isotopically lighter than the currently assumed delta ca 44 40 for bulk earth of 0 92 0 187 parts per thousand sw skulan j depaolo d j and owens t l 1997 biological control of calcium isotopic abundances in the global calcium cycle geochim cosmochim acta 61 12 2505 2510 and challenge previous assumptions of no ca isotope fractionation between hydrothermal fluid and the oceanic crust zhu p and macdougall j d 1998 calcium isotopes in the marine environment and the oceanic calcium cycle geochim cosmochim acta 62 10 1691 1698 schmitt a d chabeaux f and stille p 2003 the calcium riverine and hydrothermal isotopic fluxes and the oceanic calcium mass balance earth planet sci lett 6731 1 16 here we propose that ca isotope fractionation along the fluid flow pathway of the logatchev field occurs during the precipitation of anhydrite two anhydrite samples from the logatchev hydrothermal field show an average fractionation of about delta 44 4c ca 0 57 parts per thousand relative to their assumed parental solutions ca isotope ratios in aragonites from carbonate veins from odp drill cores indicate aragonite precipitation directly from seawater at low temperatures with an average delta ca 44 40 of 1 54 0 08 parts per thousand sw the relatively large fractionation between the aragonite precipitates and seawater in combination with their frequent abundance in weathered mafic and ultramafic rocks suggest a reconsideration of the marine ca isotope budget in particular with regard to ocean crust alteration c 2008 elsevier ltd all rights reserved

trace and rare earth element geochemistry of black shale and kerogen in the early cambrian niutitang formation in guizhou province south china constraints for redox environments and origin of metal enrichments abstract early cambrian black shales of south china not only host important sponge arthropod and other soft bodied fossils that have helped to trace early metazoan diversification but also show extreme enrichments of a number of trace metals in particular ni mo and v in this study we use a new approach by analyzing rare earth elements in kerogen extracted from the black shales together with a number of redox sensitive trace element compositions and total organic carbon toc concentrations in an early cambrian black shale sequence in zunyi guizhou province south china to place better constraints on the oceanic redox conditions and the origin of the extreme metal enrichment our data show significant negative ce anomalies ce ce as low as 0 4 occurring in kerogen which indicate an oxygenated surface environment of primary productivity in consistent with the concept that the organic matter is mainly derived from organisms in the euphotic zone mass balance calculation suggests that the kerogen associated ree can dominate the measured black shale ree budget while similarity between our measured ree patterns and those of similarly aged phosphorites indicates that the ree content of ancient phosphorites may have also derived initially from organic matter the redox sensitive trace elements such as u v mo and their ratios of u al v al and mo al in black shales show different correlation patterns with toc contents the upper black shales show a good metal toc correlation but such a correlation is absent in the lower part the lower black shales exhibit much higher metal enrichments compared to black sea sulphidic euxinic sediment this is taken to indicate the presence of sulphidic bottom waters during the deposition of the lower black shales including the ni mo ore layer in contrast anoxic non sulphidic conditions occurred during the deposition of the upper black shales taking all these geochemical data together we suggest that the early cambrian south china seaway was strongly stratified and stagnant and that euxinic bottom water conditions may have led to enrichment of the redox sensitive metals such as u v and mo in the lower black shales and in one case the occurrence of a polymetallic ni mo sulphide ore bed bearing an extraordinarily extreme metal enrichment which according to the mo toc and ni toc ratios and much other geochemical evidence may have been additionally influenced by hydrothermal input of metals within the rift basin as suggested by a number of previous studies

organic clots and their differential accumulation of ni and mo within early cambrian black shale hosted polymetallic ni mo deposits zunyi south china abstract the celebrated early cambrian ni mo deposits that occur near zunyi city of guizhou province south china are hosted in shales the ore formation has been widely accepted to be related to biotic impact but direct evidence is still lacking in the present study of the huangjiawan ore deposit organic clots are found to occur widely in the ni mo ore beds but not in the barren layers the clots are generally elliptic with sizes ranging from 200 to 600 m the clot morphology is similar to that of modern rhodophyta as reported in the literature we tentatively interpret the clots as rhodophyte cystocarps electron microprobe analysis revealed that the clots have a differential accumulation of ni and mo with ni in the inner part and mo in the outer part of the cystocarp our study seems to have provided direct evidence for the biotic impact on the ore mineralization