the mokrsko west gold deposit bohemian massif czech republic mineralogy deposit setting and classification abstract the mokrsko west deposit is unique among european variscan gold deposits from the points of view of both the structure an approx 200 m thick complex of sheeted several mm thick densely spaced quartz veins and the economic viability gold reserves of about 100 t the deposit is hosted mainly by tonalite of the calc alkaline sazava tonalite suite ca 354 ma of the central bohemian plutonic complex mineralization is characterized by quartz dominated gangue no visible hydrothermal alteration low sulfide content high fineness native gold accompanied by maldonite aurostibite native bismuth and numerous bi te s phases five mineralogical stages are described in great detail arsenopyrite and chlorite thermometers mineral phase stabilities and published isotope and fluid inclusion data are used to reconstruct the temperature and compositional evolution of the system the role of liquid bismuth in the sequestration of gold is also discussed the deposit shares the features of both orogenic gold org and intrusion related gold irg deposits the irg model is advocated by close spatial association between the ore zone and the tonalite host intrusion by the absence scarcity of hydrothermal alteration by the au bi te as elemental association and by marked thermal gradients from the early to late mineralization stages the org model is advocated by an approx 15 10 ma gap between the intrusion of the tonalite host and the ore formation by isotope and geochemical evidence for a key role of metamorphic fluids in the mobilization and transfer of many elements species inclusive s and au the apparently ambiguous classification of the deposit can most probably be attributed to deposit formation at a depth of 9 km and to setting of the deposit at inside a large scale plutonic complex with multiple and prolonged tectonic and intrusive activity

dynamics of shallow late variscan gold mineralization the le châtelet au arsenopyrite quartz veins massif central france the le ch telet gold deposit is unique among the mined deposits of the french variscan basement in that the gold is not free but caught up in the arsenopyrite crystal lattice microstructural analysis shows that the au arsenopyrite quartz veins are hosted by north trending dextral strike slip faults resulting from nne ssw compression during the early stephanian around 300 ma textural study indicates that vein emplacement was due to sequential dynamics related to spasmodic strike slip movements along these brittle structures seismic regime the classic sequence begins with the slow crystallization of sulphide free comb quartz followed by a co deposition of microcrystalline quartz and needles of au arsenopyrite the rapid crystallization of the au arsenopyrite bearing microcrystalline quartz was due to a sudden drop in fluid pressure the veins correspond to dilational jogs formed by a suction pump mechanism during a late phase of the variscan orogeny they were trapped in migmatite about 1 km below surface

seismically induced changes of the fluid signature detected by a multi isotope approach he co2 ch4 n2 at the wettinquelle bad brambach central europe 1 we present a study considering the systematics of gas and isotope compositions 3 he 4 he 13 c co2 13 c ch4 15 n of a permanent magmatic co 2 flux in the hydrothermal system of the spring wettinquelle in bad brambach and their relation to the seismic activity beneath the western eger rift the gas and isotope compositions were monitored for more than 3 years the time series includes periods before during and after a 4 month long seismically active period from the end of august to the end of december 2000 shifts due to admixture of crustal components were found for all monitored isotope ratios during and after the seismically active period in case of helium and nitrogen isotopic anomalies occurred already about 6 weeks before the beginning of the seismically active period contemporaneous with a water level anomaly of the well vl4 near the wettinquelle on the one hand preseismic deformations may be responsible for the observed isotope anomalies on the other hand coseismic fracturing processes in the surroundings of the hypocenters may play a role both effects produce greater permeability and result in the release of crustal fluids the migration and admixture of these crustal components to the permanent upper mantle derived fluid flux result in geochemical anomalies that persist for more than 2 years the results of the detailed isotope monitoring have proven to be an important contribution to understand the geodynamic processes that may presently be going on in the region vogtland nw bohemia

the krasna hora milesov and přicovy sb au ore deposits bohemian massif mineralogy fluid inclusions and stable isotope constraints on the deposit formation the krasna hora milesov and p icovy districts czech republic are the unique examples of sb au subtype orogenic gold deposits in the bohemian massif they are represented by quartz stibnite veins and massive stibnite lenses grading into low grade disseminated ores in altered host rocks gold postdates the stibnite and is often replaced by aurostibite the ore zones are hosted by hydrothermally altered dikes of lamprophyres krasna hora milesov or are associated with local strike slip faults p icovy formation of sb au deposits probably occurred shortly after the main gold bearing event 348 338 ma au only deposits in the central part of the bohemian massif fluid inclusion analyses suggest that stibnite precipitated at 250 to 130 c and gold at 200 to 130 c from low salinity aqueous fluids the main quartz gangue hosting the ore precipitated from the same type of fluid at about 300 c early quartz arsenopyrite veins are not associated with the sb au deposition and formed from low salinity aqueous carbonic fluid at higher pressure and temperature 250 mpa 400 c the estimated oxygen isotope composition of the ore bearing fluid 4 1 smow based on post ore calcite suggests its metamorphic or mixed magmatic metamorphic origin and excludes the involvement of meteoric water rapid cooling of warm hydrothermal fluids reacting with cold host rock was probably the most important factor in the formation of both stibnite and gold

dating the onset of variscan crustal exhumation in the core of the bohemian massif new u pb single zircon ages from the high k calc alkaline granodiorites of the blatna suite central bohemian plutonic complex abstract the variscan central bohemian plutonic complex crops out between the upper crustal tepla barrandian and the high grade moldanubian units bohemian massif much of the complex is made up of calc alkaline plutonic rocks 1 the geochemically more primitive na rich 354 4 ma sazava suite which was emplaced syntectonically during regional shortening 2 the younger more evolved potassic blatna suite which records both the shortening along its nw contact and the onset of normal shearing related to exhumation of the moldanubian unit to the se new ion microprobe u pb zircon ages for the high k calc alkaline blatna suite pinpoint this major switch in the tectonic regime both blatna and kozarovice granodiorites 346 2 ma and 347 2 ma 2 were generated by melting of heterogeneous crust and were emplaced contemporaneously to form the blatna composite pluton from age spectra preserved in inherited zircons and whole rock sr nd isotope signatures the likely crustal sources for the magmas were immature greywackes rich in neoproterozoic 615 10 ma kozarovice or late cambrian early ordovician 492 4 ma blatna volcanogenic detritus an additional important petrogenetic process was variable mixing with enriched mantle derived monzonitic magmas which may also have supplied the extra heat for crustal anatexis supplementary material analytical techniques selected whole rock major and trace element geochemical analyses and u th pb data are available at http www geolsoc org uk sup18391

source complexity of small earthquakes near matsushiro japan abstract broad band seismograms from a suite of small strike slip earthquakes which occurred in the matsushiro region of honshu japan during the period august 1971 september 1974 and recorded on carnegie seismograph mat are used to study source properties for events ranging in size from 10 11 10 15 nm in an earlier study dysart et al modelled frequency spectra of these events with a single brune pulse and made estimates of moment corner frequency and stress drop they employed cepstral filtering to suppress the effects of structure and to increase the stability of parameter estimates the same 32 waveforms considered here display a notable variation in complexity which cannot be explained by size local structure or stopping phases in order to understand better the time history of the complex events within the suite the sh waveforms were divided into successive time segments and the same modelling procedure was applied to the segments as was applied to the initial sh arrivals cepstral filtering was particularly helpful in reducing the interference effects of the s coda the results indicate that corner frequency changes little from subevent to subevent this suggests that small earthquakes proceed by incremental slippage on the same fault in a sequence of partial stress releases

carbon oxygen isotopic covariation in hydrothermal calcite during degassing of co 2 the effect of the outgassing of co2 from a hydrothermal fluid on the c and o isotopic compositions of calcite which is precipitated from this fluid is quantitatively modelled in terms of batch and rayleigh distillation equations both co2 degassing and calcite precipitation are considered to be the removal mechanisms for dissolved carbon species from the fluid combined degassing precipitation models are then developed by taking h2co3 and hco 3 respectively as the dominant dissolved carbon species a positive correlation array between 13c and 13o values of calcite can be yielded by the precipitation of calcite from a h2co 3 dominant fluid accompanied by a progressive decrease in temperature during co2 degassing whereas calcite precipitated from a hco 3 dominant fluid under the same conditions tends to display much smaller variation in 13c values than in 18o values the combined processes of co2 degassing and calcite precipitation result in lowering the 13c value of calcites with respect to those precipitated in a closed system simply due to temperature effect carbon and oxygen isotopic data for calcite from the kushikino gold mining area in japan illustrate the application of quantitative modelling and degassing of co2 is suggested as a more likely cause for the precipitation of the calcite and quartz in this mining area

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

structure and stratigraphy of the tepla barrandian neoproterozoic bohemian massif a new plate tectonic reinterpretation abstract the tepla barrandian unit tbu of the bohemian massif exposes a section across the once extensive avalonian cadomian belt which bordered the northern active margin of gondwana during late neoproterozoic this paper synthesizes the state of the art knowledge on the cadomian basement of the tbu to redefine its principal component units to revise an outdated stratigraphic scheme and to interpret this scheme in terms of a recent plate tectonic model for the cadomian orogeny in the bohemian massif the main emphasis of this paper is on an area between two newly defined fronts of the variscan pervasive deformation to the nw and se of the barrandian lower paleozoic overlap successions this area has escaped the pervasive variscan late devonian to early carboniferous ductile reworking and a section through the cadomian orogen is here superbly preserved the nw segment of the tbu consists of three juxtaposed allochthonous belts of unknown stratigraphic relation the kralovice rakovnik radnice kralupy and zbiroh sarka belts differing in lithology complex internal strain patterns and containing sedimentary and tectonic melanges with blocks of diverse ocean floor meta basalts we summarize these three belts under a new term the blovice complex which we believe represents a part of an accretionary wedge of the cadomian orogen the se segment of the tbu exposes the narrow picin belt which is probably a continuation of the blovice complex from beneath the barrandian lower paleozoic and a volcanic arc sequence the davle group their stratigraphic relation is unknown flysch units the st chovice group and svrchnice formation overlay the arc volcanics and both units contain material derived from volcanic arc the former was also sourced from the nw segment whereas the latter contains an increased amount of passive margin continental material in contrast to the blovice complex the flysch experienced only weak cadomian deformation the new lithotectonic zonation fits the following tectonic scenario for the cadomian evolution of the tbu well the s to se directed cadomian subduction beneath the tbu led to the involvement of turbidites chaotic deposits and 605 39 ma ocean floor in the accretionary wedge represented by the blovice complex the accretionary wedge formation mostly overlapped temporally with the growth of the volcanic arc the davle group at 620 560 ma upon cessation of the arc igneous activity the rear of the wedge and some elevated portions of the arc were eroded to supply the deep water flysch sequences of the st chovice group whereas the comparable svrchnice formation 560 to

p t x conditions of hydrothermal fluids and precipitation mechanism of stibnite gold mineralization at the wiluna lode gold deposits western australia conventional and infrared microthermometric constraints the wiluna lode gold deposits are located in the archean wiluna greenstone belt in the northern sector of the norseman wiluna belt in the yilgarn craton of western australia they are hosted in subgreenschist facies meta basalts and controlled by the wiluna strike slip fault system and associated shear veins and breccias the 13 individual lode gold deposits have produced around 115 t au from 1901 to 1946 and 1986 to today historically they also produced 38 3 t as and 3 5 t sb gold formed in two stages stage 1 gold pyrite arsenopyrite is finely disseminated in the wallrock and breccia fragments whereas stage 2 gold stibnite is located in massive shear veins and breccia matrix as fracture fill and in banded colloform textured veins stibnite gold orebodies only occur in some of the deposits e g moonlight and northern part of the west lode and also display a restricted vertical extent being preserved only in the uppermost 200 m of stibnite bearing lodes petrographic conventional and infrared microthermometric and laser raman analysis on stibnite bearing quartz veins and breccias reveal that the antimony and gold rich hydrothermal fluid was of mixed h2o nacl co2 ch4 type microthermometric measurements reveal maximum homogenization temperatures of 340 c average 290 25 c and a wide range of salinities between 0 2 and 23 eq wt nacl aqueous carbonic fluid inclusions contain variable xco2 ch4 0 03 to 0 82 with the carbonic phase containing a maximum xch4 of 0 21 combined petrographic and microthermometric evidence suggests that the fluid inclusion properties reflect fluid immiscibility of a low salinity medium xco2 ch4 homogeneous parent fluid at about 290 c and pressures between 700 and 1 700 bar fluid immiscibility was triggered by cyclic pressure release during fault zone movement the decompression adiabatic cooling of the hydrothermal fluids shifted the ore fluid to lower temperatures significantly reduced the degree of stibnite undersaturation and caused stibnite to precipitate the deposition of stibnite reduced the ore fluid h2s concentration thereby destabilized gold bisulfide complexes in solution and caused gold precipitation locally this mechanism explains the intimate spatial association of stibnite and gold in quartz veins and breccias in the stibnite gold orebodies at wiluna

structural controls on hydrothermal alteration and gold antimony mineralisation in the hillgrove area nsw australia the hillgrove gold antimony deposit is hosted in late palaeozoic biotite grade metasedimentary rocks and permo carboniferous granitoid intrusions of the new england orogen mineralisation occurred at a range of structural levels during rapid uplift in the orogen at 255 245 ma hydrothermal fluids were controlled by extensional faults in a regional scale sinistral strike slip fault system principal faults in this system were developed in and possibly evolved from mylonite zones which were active during late permian tectonics earliest mineralisation formed scheelite bearing quartz veins and these were followed by auriferous arsenopyrite pyrite quartz carbonate veins with minor base metal sulphides this latter type was accompanied by sericitisation and carbonation of the host rock with addition of sulphur arsenic and gold in zones up to 20 m from veins quartz stibnite veins with electrum gold aurostibite and arsenopyrite form a prominent and economically important hydrothermal type with little wall rock alteration but extensive hydrothermal breccia formation and local open space filling textures below a mining depth of 300 500 m this type passes over a short distance downwards into stibnite poor gold bearing veins late stage carbonate stibnite veins with gold and silver sulphosalts cut all earlier veins and have open space filling textures aspects of the hillgrove deposit have similarities to many other orogenic gold deposits in the sw pacific which have been formed at different structural levels hillgrove is distinctive in having evidence for mineralisation at this wide range of structural levels in the one deposit formed progressively during syn orogenic uplift

multiple fluid sources pathways and severe thermal gradients during formation of the jilove orogenic gold deposit bohemian massif czech republic abstract the jilove deposit in the central part of the bohemian massif represents a vein to stockwork type of orogenic type gold deposit it is hosted by neoproterozoic rocks of the jilove belt and by various magmatic dikes related to the 355 to 335 ma central bohemian plutonic complex the deposit is situated along the terrane boundary of the tepla barrandian and moldanubian units the deposit offered an exceptional opportunity to trace o c s and sr stable isotope evolution of parent fluids based on combined mineralogical and geochemical study of carbonate quartz scheelite and sulfide minerals which represent six stages of mineralization including the gold bearing event stable isotope data and mineral and isotope thermometry indicate gangue and ore mineral formation between 350 c and 18 o smow 4 2 0 5 and 13 c pdb 11 1 gold precipitation stage 5 probably started at about 300 c but the major event probably occurred at 230 30 c from a fluid with more variable isotope values 18 o smow 2 5 to 5 and 13 c pdb 9 to 13 5 the carbon speciation was characterized by predomination of dissolved co 2 h 2 co 3ap in the fluids some gold however undoubtedly precipitated from bicarbonate dominated fluids even at extreme variations in the 18 o values of carbonate minerals obtained from sampling profiles across individual veins with macroscopic gold revealed severe thermal gradients during vein formation 50 to 100 c difference of crystallization temperatures between the vein margin and core the sulfur stable isotope composition of sulfide minerals indicates the dominant role of sulfur remobilization from neoproterozoic rocks and stratiform mineralizations of the jilove belt by variscan hydrothermal fluids similarly the sr isotope composition of carbonates indicates both relatively primitive 87 sr 86 sr 0 7055 and more evolved 87 sr 86 sr 0 7090 fluid compositions probably indicating fluid exchange with the jilove belt and the central bohemian plutonic complex rocks respectively age determination of hydrothermal muscovite related to stage 2 via 40 ar 39 ar indicated an age of 339 0 1 5 ma for the quartz veins the mineralization is essentially coeval with the late intrusive phases of the central bohemian plutonic complex i e the ultrapotassic suite and with late orogenic large scale tectonic movements at the boundary between the two crustal terranes tepla barrandian and moldanubian based on evaluation of the available age data on the hydrothermal and magmatic activity within the broader area of the central bohemian plutonic complex we suggest two intervals of gold mineralization 347 to 341 ma and 340 to 337 ma the former interval overlaps with the intrusive activity of the blatna high k suite granodiorite the associated gold deposits mokrsko and petrackova hora exhibit strong affiliation to the intrusion related gold type deposit the later interval overlaps with the ultrapotassic magmatism and is associated with more or less classical orogenic gold type deposits jilove b lcice libcice deposits

origin of the fluids associated with granodiorite hosted sb as au w mineralisation at dubrava nizke tatry mts western carpathians mineral parageneses of the polymetallic sbrich deposit at dubrava has been formed during five separated stages a fluid inclusion study demonstrates that the earliest stages with scheelite molybdenite and arsenopyrite have been associated with immiscible co2 ch4 rich low saline fluids at temperatures between 300 and 400 c and pressures as much as 2 kbar deposition of the main superimposed ores stibnite and zinckenite has been intimately connected with circulation of aqeuous moderately saline fluids 15 5 23 5 wt nacl equiv upon epithermal conditions salinity of the aqueous fluids associated with tetrahedrite is clustered around 10 wt nacl equiv quartz from the latest barite stage has precipitated from aqueous fluids enriched in divalent cations these fluids are believed to be genetically linked with triassic evaporite formations preserved in the region temperature salinity diagrams constructed from microthermometry data indicate influx of diluted meteorite water in the stibnite tetrahedrite and barite stages isotopic data are in accordance with model the 18o values between 9 3 and 1 5 have been derived for water in equilibrium with quartz coexisting with sphalerite tetrahedrite and barite thus confirming the participation of isotopically lighter meteoric waters in the mineral forming solutions the 18o values between 3 3 and 8 5 estimated for the water associated with the scheelite and arsenopyrite stages are suggestive for the majority of metamorphic and or magmatic water in the mineral forming co2 rich solutions

sequence stratigraphy of coastal alluvial plain westphalian b coal measures in northumberland and the southern north sea abstract westphalian b coastal alluvial plain coal measures of northumberland and the southern north sea are susceptible to stratigraphic base level fluctuations of various magnitudes which create a hierarchy of flooding surfaces 1 high magnitude third order maximum flooding surfaces corresponding to the anthracoceratites vanderbeckei and anthracoceras aegiranum marine bands defining the top and bottom of the succession when vast areas of the westphalian foreland basin were flooded by marine incursions 2 high frequency fluctuations promoting small scale fourth order flooding of the entire or large areas 100 s km 2 of the alluvial plain resulting in deposition of non marine bivalve beds or marine bands depending on their position on the third order base level curve and 3 small scale localised base level rises due to differential compaction and autocyclic switching of minor crevasse splays and distributary channels a regionally extensive third order tectonically induced sequence boundary is also recognised in the southern north sea slightly above the maximum stand in stratigraphic base level recorded by the vanderbeckei marine band this sequence boundary which represents the lowest point on the background eustatic base level curve between the two maximum flooding surfaces is overlain by the multilateral multistorey caister sandstone the lack of significant erosional relief beneath this channel sandstone suggests that accommodation space at this time was being created at a very low rate the succession above the caister sandstone sequence boundary up to the aegiranum marine band maximum flooding surface records an increasing rate of stratigraphic base level rise this equates to a third order transgressive systems tract or sequence set comprising a number of fourth order sequences which change upwards in response to the background low frequency rise the increasing rate of base level rise and increased accommodation space is accompanied by a change in fluvial style to more isolated channels enclosed within floodplain deposits

infrared microthermometric and noble gas isotope study of fluid inclusions in ore minerals at the woxi orogenic au sb w deposit western hunan south china abstract the woxi au sb w deposit hosted by the neoproterozoic low grade metamorphic clastic rocks is located in a brittle ductile shear zone within the xuefengshan range south china orebodies are predominantly banded quartz veins which are strictly controlled by bedding faults and display significant vertical extents up to 2 km without obvious vertical metal zoning fluid inclusions hosted in quartz scheelite and stibnite from quartz scheelite and quartz sulfide gold veins have been studied using conventional and infrared microscopy respectively four types of fluid inclusions were identified based on petrography including type i two phase liquid rich aqueous inclusions type ii two or three phase co 2 rich inclusions type iii two phase vapour rich aqueous inclusions and type iv single phase aqueous inclusions the fluid inclusions in ore minerals scheelite and stibnite and their coexisting quartz largely share similar characteristics in terms of their types homogenization temperatures and salinities this is consistent with the fact that these ore minerals are always intergrown with quartz microthermometric and laser raman data indicate a low to moderate temperature 140 240 c low salinity 2 rich n 2 bearing aqueous ore forming fluid such fluid is further identified as a deeply non magmatic crustal fluid rather than a mantle source fluid by the significantly low 3 he 4 he ratios 0 002 0 281 ra and a small amount of meteoric water or host rock buffered fluid could be involved w ore precipitation was probably associated with mixing between a deeply originated crustal fluid and host rock buffered fluid based on the fluid inclusion features in scheelite and quartz i however au and sb ore deposition probably resulted from boiling which was caused by the marked pressure drop geological features such as banded structure and crack sealing structure also indicate that fluid pressure fluctuation induced by fault valve mechanism occurred during ore precipitation these characteristics of the ore forming fluids in the woxi deposit are in good agreement with the definition of orogenic gold deposits and the woxi au sb w deposit is probably an atypical orogenic gold deposit for its unique ore forming element association

magma mixing in the genesis of hercynian calc alkaline granitoids an integrated petrographic and geochemical study of the sazava intrusion central bohemian pluton czech republic the devonian early carboniferous 354 1 3 5 ma conventional zircon u pb age sazava intrusion biotite amphibole quartz diorite tonalite and granodiorite of the central bohemian pluton cbp associated with bodies of olivine pyroxene amphibole gabbro gabbrodiorite quartz diorite and rare hornblendite gives an opportunity for a comparative study of a rather shallow calc alkaline magma mixing zone at two levels separated by a vertical difference of approximately 1 km the deeper section p ibram displays the direct evidence for the existence of a long lived periodically tapped and replenished floored magma chamber masli the contacts between the subhorizontal sheet like basic bodies and the surrounding commonly cumulus rich sazava granitoid are arcuate and cut by a series of veins and ascending pipes shallow dipping swarms of strongly elongated and flow aligned mafic microgranular enclaves mme concordant with the contacts of the basic bodies are commonplace the higher level teletin section shows relatively independent basic intrusions some of them distinctly hybrid in character and mainly of quartz dioritic composition surrounded by relatively homogeneous nearly cumulus free sazava tonalite rich in texturally variable mme larger quartz microdiorite bodies and the mme both interpreted as hybrids contain varying proportions of highly heterogeneous plagioclase megacrysts with complex zoning particularly well shown by cathodoluminescence cl most often the megacrysts have cores of labradorite anorthite partly resorbed and overgrown by andesine rims but some are strongly brecciated and fragments have been annealed by rim growth also characteristic are long prisms of apatite oikocrysts of quartz and k feldspar and zoned amphibole the latter has brown pargasite and magnesiohastingsite cores resorbed and overgrown by magnesiohornblende compositionally similar to the amphibole in the sazava tonalite the brown cores are probably relics of a higher p t stage with temperature exceeding 900 c plots of major element analyses of the teletin quartz microdiorite and the mme fall close to the line joining the compositions of the evolved sazava granodiorite tonalite and the associated gabbros the estimated minimal proportions of the acidic end member range from ca 15 to 20 for the quartz microdiorite and ca 40 to 60 for the enclaves field relationships macroscopic and mineralogical features and whole rock geochemistry are consistent with a hybrid origin of the quartz microdiorite masses and enclaves unzoned calcic plagioclase cores are interpreted as having crystallized from a basic magma prior to its injection into a high level acidic magma chamber the sudden decrease in ca activity and introduction of water due to magma mixing with tonalitic melt led to their resorption and brecciation quartz ocelli that are abundant locally in some basic bodies are most likely xenocrysts introduced from the felsic magma in the basic melt they were resorbed and became a substrate for heterogeneous nucleation of the amphibole or pyroxene coronas strong undercooling of the basic magma resulted in the growth of long prismatic apatite together with dendritic boxy cellular plagioclase both types of plagioclase cores were subsequently overgrown by more sodic mantles at the same time small unzoned plagioclase crystals nucleated in the groundmass following thermal re adjustment crystallization of the hybrid magma ended with considerably slower growth of quartz and k feldspar oikocrysts

the application of high resolution sequence stratigraphy to fluvial systems a case study from the upper carboniferous breathitt group eastern kentucky usa the pennsylvanian pikeville hyden and four corners formations of the breathitt group in eastern kentucky usa contain six major facies associations along with a number of subassociations these facies associations are offshore siltstone rhythmically bedded mouthbar heteroliths predominantly fine grained floodplain deposits minor channel fills major distributary channels and major stacked fluvial bodies the stacked fluvial bodies are incised into a variety of open marine and delta plain deposits have widths of several kilometres and exhibit a range of sandy fill types these fluvial complexes are interpreted as incised valley fills parasequences and parasequence sets are not identifiable nonetheless it is possible to identify systems tracts on the basis of sequential position facies associations and systematic changes in architectural style and sediment body geometries the studied portion of the breathitt group comprises stacked 4th order sequences which occur in lowstand transgressive and highstand sequence sets related to the development of a lower frequency base level cycle in the lowstand sequence set incision associated with successive 4th order sequence boundaries has commonly removed all the hst and tst of the underlying sequences such that succeeding 4th order incised valley fills are amalgamated within the transgressive sequence set incision is at a minimum and incised valley fills tend to stack discretely with the maximum amount of fine grained tst and hst between them the highstand sequence set is transitional between the lowstand and transgressive sequence sets in terms of the amount of transgressive and highstand deposits preserved incised valley fills tend to stack discretely

chronology of the kasperske hory orogenic gold deposit bohemian massif czech republic the kasperske hory deposit represents one of the economically most important hydrothermal gold deposits in the bohemian massif czech republic we present new re os age determinations for sulfides complemented by ar ar determinations on silicate minerals in order to provide temporal constraints on the deposit formation arsenopyrite and molybdenite formed during gold bearing stages i iii yielded similar re os ages between 341 and 333 ma overlapping with the ar ar cooling age of the metamorphic host rocks below 500 c continuous cooling of the ore system below 270 c during stage iii is reflected by ar ar muscovite ages spanning from 332 to 325 ma representing the long interval of formation of gold productive stage iii thus the kasperske hory gold deposit is younger than the gold deposits spatially associated with the central bohemian plutonic complex 349 339 ma belonging to the central bohemian metallogenetic zone e g mokrsko west jilove petrackova hora this may indicate a rather close relationship to the nearby moldanubian batholith while still suggesting an intimate link between mineralization and variscan orogenesis and associated magmatism

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

variscan sb au mineralization in central brittany france a new metallogenic model derived from the le semnon district numerous sb au deposits are known in the european variscan belt and are often associated with the latevariscan hydrothermal events linked to postorogenic extension and strike slip faults through the whole belt thecentral part of the armorican massif central brittany hosts several sb au deposits such as the le semnondeposit however little is known about its formation its structural control or hydrothermal history in order toprovide new constraints on the sb au mineralization framework of the variscan armorican massif structural geochronological and chemical analyses have been performed on the le semnon sb au deposit first wehighlight that sb au mineralization consists of fault fill and flat extensional vein systems resulting from smallscalefault valve mechanism controlled by fluid overpressure at shallow depth indeed this deposit is characterizedby the presence of dolerite dykes which acted as the plumbing system for fluids within impermeableslates the low permeability of the slates permitted the establishment of local supralithostatic fluid pressure in apredominantly hydrostatic regime coupled with new micro textural evidences a reappraisal of the parageneticevolution and new physico chemical data 40ar 39ar and u pb analyses show that the le semnon sb aumineralization was emplaced around 360 ma and therefore indicates an early hydrothermal event in thevariscan history of the armorican massif moreover absolute dating of mafic magmatism coupled with hydrothermalalteration associated with the deposition of sb au mineralization strongly suggest that the emplacementof the sb au mineralization was coeval with the emplacement of the host rock doleritic dyke furthermore the high temperature recorded in fluid inclusions and the paragenetic evolution suggests an elevatedthermal anomaly in central brittany thus we propose that the emplacement of the widespread maficmagmatism at ca 360 ma played a major role in the mobilization of fluid flows and the redistribution of metalsin the armorican crust

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

perspectives on the sequence stratigraphy of continental strata this report is the result of a working group on continental sequence stratigraphy that was set up at the 1991 nuna conference in banff canada to date sequence stratigraphic concepts have been applied mainly to the marine realm but unconformity bounded units have long been recognized in nonmarine strata successful application of sequence stratigraphic concepts to continental strata requires careful consideration of controls on base level and sediment supply as with shallow marine environments relative sea level can be considered as the stratigraphic as well as the geomorphic base level for coastal nonmarine settings farther inland stratigraphic base level which determines accommodation space is more complex and takes various forms such as the graded profile for fluvial strata groundwater tables for some eolian strata and lake level for some intermontane sediments sediment supply is also generally a more complex variable for nonmarine environments than in the marine realm because of the proximity to the source area the influence of climate and tectonism on sediment supply can clearly be seen in many continental sediments the fact that the major controls of climate tectonism and eustasy are somewhat interdependent and that a change in one parameter will most likely be reflected in others is also more readily apparent in continental strata although in its infancy sequence stratigraphic concepts have been applied to a wide variety of continental settings in attempts to explain variations in facies architecture of particular interest are studies that have linked fluvial architecture on coastal plains to variations in relative sea level as indicated by coeval marine strata and studies of lacustrine environments that show marked variation in facies between highstand and lowstand deposits the application of sequence stratigraphy to continental strata will likely result in the development of better correlation techniques and models that better predict the location and nature of fluvial and eolian reservoirs

mineralogy fluid inclusion and stable isotope constraints on the genesis of the roudný au ag deposit bohemian massif orogenic gold deposits with gold of low fineness are relatively rare in the bohemian massif but occur locally within the late variscan blanice graben structure in the moldanubian zone among them the roudn deposit has been the most important with total production of about 6 t of gold between 1895 and 1930 the ore is related to an irregular quartz stockwork and is represented by sulfide and electrum impregnations within the quartz gangue and the altered host rocks ore grade varies from 4 to 25 g t au the gold is present as macro and microscopic electrum fineness 658 665 and also as invisible gold in the crystal structure of early sulfides as rich pyrite and sb rich arsenopyrite three mineralization stages have been distinguished 1 the largely barren pre ore stage 2 the main ore stage with economic au ag mineralization 3 the late stage with subeconomic ag pb zn mineralization fluid inclusion and mineral thermometry indicate that the three stages were formed at about 400 to 330 350 to 250 and 250 to 70 c respectively early mineralization stages are related to complex h2o co2 ch4 n2 low salinity 3 9 wt nacl equiv fluids with isotopic signatures consistent with a metamorphic origin 18ofluid 4 7 2 9 smow most of the main ore stage minerals including the electrum precipitated from aqueous fluids 2 4 wt nacl equiv during the late mineralization stage the salinity of aqueous fluid was higher 7 9 wt nacl equiv the isotopic composition of the late fluid however also records gradually increasing proportions of meteoric water 18ofluid 2 to 1 smow elevated arsenic contents 120 210 ppm as were found in aqueous carbonic fluids by the la icp ms technique models of fluid mixing at the transition of the main to late mineralization stages are used to estimate the temperature and paleogeothermal gradient possible ages of electrum mineralization 300 to 275 ma and ag pb zn vein type mineralization 275 to 265 ma are discussed overall the roudn deposit shows striking similarities with 300 ma gold deposits of the french massif central

geology and genesis of variscan porphyry style gold mineralization petrackova hora deposit bohemian massif czech republic a large number of variscan mesothermal gold deposits are located in the central part of the bohemian massif close to the central bohemian plutonic complex the petrackova hora deposit has many features that distinguish it from other deposits in the region and suggest its mineralization is closely related to the late magmatic processes associated with the petrackova hora granodiorite the gold ores occur as sheeted arrays of quartz veins and veinlets hosted by the small petrackova hora granodiorite stock gold is found mainly as free grains of 900 fineness and is accompanied by abundant pyrrhotite and chalcopyrite and accessory pyrite arsenopyrite loellingite and molybdenite molybdenite from the petrackova hora deposit has been dated by the re os method at 344 4 2 8 ma hydrothermal alteration in the petrackova hora deposit exhibits a distinct temporal paragenesis selectively pervasive early k alteration and silicification are the oldest hydrothermal phases these were followed by early quartz veins q1 to q4 that contain most of the gold mineralization late quartz veins q5 and fracture controlled silicification are gold poor or barren barren calcite veins are the youngest hydrothermal product extensive low temperature meteoric water dominated alteration as is typical of classic porphyry deposits is absent however the lower 18o whole rock values for petrackova hora granodiorite and aplite 2 4 to 5 1 smow compared to other intrusions in the region reflect either interaction with isotopically light external fluids or magma assimilation of small volumes of hydrothermally altered country rock the 18o isotopic compositions for quartz scheelite and hornblende 7 7 to 13 4 smow and the 34s compositions for sulfide minerals 1 to 3 5 cdt from early gold rich quartz veins indicate formation at high temperatures 590 to 400 c from fluids with a magmatic isotopic signature 18ofluid of 5 7 to 7 2 fluids related to late quartz veins q5 suggest the presence of a significant component of non magmatic water 18ofluid 2 5 to 4 0 the 34s values of post q5 sulfide minerals 4 5 to 3 5 reflect at least partial derivation of late stage sulfur from a source external to the intrusions aqueous aqueous carbonic and nitrogen bearing fluid inclusions were identified in hydrothermal and igneous quartz with the aqueous inclusions being the most common in hydrothermal vein quartz the salinity of primary aqueous inclusions falls into ranges 6 to 23 and 33 to 41 equiv wt nacl in igneous quartz populations in salinity were observed between 5 to 16 35 to 40 and 62 to 70 equiv wt nacl the salt component of these fluids is best and minimally approximated by the nacl kcl cacl2 system low and high salinity aqueous carbonic inclusions are accessory in many of the analyzed samples three large successive pulses of fluids are recognized each pulse begins with a high salinity 30 equiv wt nacl magmatic fluid and evolves toward a lower salinity 5 equiv wt nacl fluid data suggest that external meteoric water s were significant for only the third fluid pulse which formed the late q5 quartz veins and the calcite veins polyphase fluid inclusions hosted by igneous quartz of the petrackova hora granodiorite indicate minimum trapping conditions of about 3 kbar and 550 c the gold rich q1 to q4 veins may have formed along a quasi isobaric cooling path at 2 5 to 1 5 kbar and 590 to 400 c this was followed by uplift and formation of late q5 quartz veins 0 5 to 1 5 kbar 300 c and post ore calcite veins 0 5 kbar 100 to 140 c the characteristics of the petrackova hora deposit suggest that it may represent a position intermediate between intrusion related gold systems e g fort knox deposit alaska and gold rich copper poor porphyry deposits e g maricunga belt in chile as such the petrackova hora deposit might be an example of the reduced gold sub type of porphyry deposit

dating granulite facies structures and the exhumation of lower crust in the moldanubian zone of the bohemian massif deformation of granulite facies rocks in the moldanubian zone of the southern bohemian massif is expressed in two intersecting planar fabrics steeply disposed s1 and flat laying s2 which correspond to two deformation stages d1 and d2 the existing sm nd garnet ages from banded granulite gneisses new u pb zircon data from deformed granite intrusions within the granulite gneisses and the p t and field structural relations constrain the ages and p t conditions of the two deformation phases the early deformation d1 was associated with a hp ht metamorphic stage with a minimum age of ca 354 ma which was followed by a near isothermal decompression a concordant u pb zircon age of 318 1 ma dates the emplacement of intrusions of deformed granite into the granulite gneisses and constrains deformation phase d2 this phase was associated with an lp ht metamorphism dated in the region at ca 340 330 ma the available structural and isotopic data indicate that granulites in the southern bohemian massif were exhumed from lower to middle crust during compression the structural relations and p t t data for the studied granulites are consistent with their exhumation by near vertical extrusion of the softened orogenic root

high pressure granulites formation recovery of peak conditions and implications for tectonics high pressure granulites are characterised by the key associations garnet clinopyroxene plagioclase quartz in basic rocks and kyanite k feldspar metapelites and felsic rocks and are typically orthopyroxene free in both basic and felsic bulk compositions in regional metamorphic areas two essential varieties exist a high to ultrahigh temperature group and a group representing overprinted eclogites the high to ultrahigh temperature type formerly contained high temperature ternary feldspar now mesoperthite coexisting with kyanite is associated with garnet peridotites and formed at conditions above 900 c and 1 5 gpa clinopyroxene in subordinate basic rocks is al rich and textural evidence points to a high pressure high temperature melting history the second variety contains symplectite like or poikilitic clinopyroxene plagioclase intergrowths indicating former plagioclase free i e eclogite facies assemblages this type of rock formed at conditions straddling the high pressure amphibolite high pressure granulite field at around 700 850 c 1 0 1 4 gpa importantly in the majority of high pressure granulites orthopyroxene is secondary and is a product of reactions at pressures lower than the peak recorded pressure in contrast to low and medium pressure granulites which form at conditions attainable in the mid to lower levels of normal continental crust high pressure granulites of nonxenolith origin mostly represent rocks formed as a result of short lived tectonic events that led to crustal thickening or subduction of the crust into the mantle short times at high temperature conditions are reflected in the preservation of prograde zoning in garnet and pyroxene high pressure granulites of both regional types although rare are known from both old and young metamorphic terranes e g c 45 ma namche barwa e himalaya 400 340 ma european variscides 1 8 ga hengshan china 1 9 ga snowbird saskatchewan and 2 5 ga jianping china this spread of ages supports proposals suggesting that thermal and tectonic processes in the lithosphere have not changed significantly since at least the end of the archean

5 late variscan mineralizing systems related to orogenic processes the french massif central abstract the french massif central constitutes an exceptional study area due to the diversity of its metallic deposits its internal position in the variscan belt and the abundance of available geological geophysical and metallogenic data obtained within the geofrance 3d programme the deposits formed towards the end of the orogenic evolution represent the economic products of two distinct mineralizing systems a au sb hydrothermal system and a w sn and rare metals magmatic hydrothermal system which were simultaneously active during a short time span between ca 310 and 300 ma two types of gold deposit can be distinguished on the basis of their depth of emplacement deep seated gold deposits developed under lithostatic to hydrostatic pressure during rapid exhumation and shallow gold deposits emplaced under hydrostatic pressure with no significant uplift deposits of w sn and rare metals were emplaced in the upper crust during final crystallization of specialized magmas after their rapid ascent perhaps enhanced by simultaneous regional uplift the gold bearing systems are associated with a complex network of re activated crustal scale faults initially active during the period between 335 and 315 ma normal motion along the faults coeval with 335 to 315 ma granite migmatite domes played a major role in the 3d distribution of the hydrothermal plumbing system gold and related metals were carried within huge hydrothermal cells which reached ca 100 km by 10 km in area and 30 km in depth in contrast granites rich in magmatophile elements w sn rare metals generated smaller hydrothermal cells 10 km by 10 km in area and