origin of co2 and carbonate veins in mantle derived xenoliths in the pannonian basin the origin and evolution of co2 inclusions and calcite veins in peridotite xenoliths of the pannonian basin hungary were investigated by means of petrographic investigation and stable isotope analyses the fluid inclusions recovered in paragenetic olivine and clinopyroxene belong to distinct populations type a texturally early inclusions with regular shapes often with negative crystal forms forming intragranular trails type b texturally late inclusions defining randomly oriented trails that reach grain boundaries type b inclusions are often associated with silicate melt type c inclusions stable carbon isotope compositions in inclusion hosted co2 were obtained by vacuum crushing followed by conventional dual inlet as well as continuous flow mass spectrometry in order to eliminate possible lab artifacts olivines clino and orthopyroxenes of the host peridotite have oxygen isotope compositions from 5 3 to 6 0 relative to v smow without any relationship with xenolith texture some of the xenoliths contained calcite in various forms veins and infillings in silicate globules in veins secondary carbonate veins filling cracks and metasomatic veins with diffuse margins the former two carbonate types have 13c values around 13 relative to v pdb and low sr contents 0 5 wt whereas the third type veins with high temperature metasomatic features have a 13c value of 5 0 and high sr contents up to 3 4 wt in spite of the mantle like 13c value and the unusually high sr content typical for mantle derived carbonate trace element compositions have proven a crustal origin this observation supports the conclusions of earlier studies that the carbonate melt droplets found on peridotite xenoliths in the alkaline basalts represent mobilized sedimentary carbonate the large 13c range and the 12c enrichment in the carbonates can be attributed to devolatilization of the migrating carbonate or infiltration of surficial fluids containing 12c rich dissolved carbon carbon isotope compositions of inclusion hosted co2 range from 17 8 to 4 8 relative to v pdb with no relation to the amount of co2 released by vacuum crushing low 13c values measured by stepwise heating under vacuum suggest that the carbon component is pristine and not related to surficial contamination and that primary mantle fluids with 13c values around 5 were at least partly preserved in the xenoliths tectonic reworking and heating by the basaltic magma resulted in partial co2 release and local 13c depletion

post collisional tertiary quaternary mafic alkalic magmatism in the carpathian pannonian region a review mafic alkalic volcanism was widespread in the carpathian pannonian region cpr between 11 and 0 2 ma it followed the miocene continental collision of the alcapa and tisia blocks with the european plate as subduction related calc alkaline magmatism was waning several groups of mafic alkalic rocks from different regions within the cpr have been distinguished on the basis of ages and or trace element compositions their trace element and sr nd pb isotope systematics are consistent with derivation from complex mantle source regions which included both depleted asthenosphere and metasomatized lithosphere the mixing of dmm himu emii mantle components within asthenosphere derived magmas indicates variable contamination of the shallow asthenosphere and or thermal boundary layer of the lithosphere by a himu like component prior to and following the introduction of subduction components various mantle sources have been identified lower lithospheric mantle modified by several ancient asthenospheric enrichments source a young asthenospheric plumes with oib like trace element signatures that are either isotopically enriched source b or variably depleted source c old upper asthenosphere heterogeneously contaminated by dm himuemii emi components and slightly influenced by miocene subduction related enrichment source d old upper asthenosphere heterogeneously contaminated by dm himu emii components and significantly influenced by miocene subduction related enrichment source e melt generation was initiated either by i finger like young asthenospheric plumes rising to and heating up the base of the lithosphere below the alcapa block or ii decompressional melting of old asthenosphere upwelling to replace any lower lithosphere or heating and melting former subducted slabs the tisia block d 2004 published by elsevier b v

on the origin and fluid content of some rare crustal xenoliths and their bearing on the structure and evolution of the crust beneath the bakony balaton highland volcanic field w hungary rarely occurring clinopyroxene plagioclase bearing felsic granulite and skarn xenoliths were studied from the mantle and crustal xenolith bearing alkaline basaltic and pyroclastic localities of the bakony balaton highland volcanic field w hungary geobarometry and geothermometry of the xenoliths made it possible to categorise them in three groups according to their depth of formation the first group formed in the lower crust together with mafic and metasedimentary granulites the second group represents magmatic intrusions of the middle crust and the third one comprises contact metamorphic rocks of relatively shallow origin the calculated pressure difference from the core and rim compositions of plagioclase and clinopyroxene as well as garnet breakdown reactions in some xenoliths show evidence for pressure decrease due to crustal thinning both in lower crustal and middle crustal xenoliths during formation of the pannonian basin fluid inclusion studies reveal the dominance of the co2 rich fluids in the whole crustal section in contrast with fluids found in mafic garnet bearing xenoliths crustal stratigraphy was constructed for the periods prior to the extension and after the extension on the basis of geobarometry and geophysical data on the basis of mineral stabilities and geothermo barometry we estimated that the pre extensional thickness of the lower and upper crust may have been 27 34 and 26 28 km respectively comparison of pre extensional and present day thickness of the lower and upper crust indicate that thinning affected both the lower and the upper portion of the crust but on a different scale the calculated thinning factors are between 2 25 and 3 4 for the lower crust and 1 3 1 56 for the upper crust

the multiple sulfur isotope architecture of the golden mile and mount charlotte deposits western australia the golden mile and mount charlotte deposits in the kalgoorlie terrane western australia display three main mineralization styles fimiston comprised of interconnected shear zones associated with ankerite pyrite hematite magnetite gold telluride alteration oroya made up of breccia bodies with v muscovite ankerite pyrite pyrrhotite gold telluride alteration and mount charlotte which consists of vein arrays with symmetrical ankerite sericite albite pyrite pyrrhotite gold alteration pyrite is in equilibrium with gold in all three mineralization styles and has been selected as a proxy to record the sulfur source of the mineralizing fluids as well as the nature of the hydrothermal processes the 34s 33s and 36s analyses on pyrite grains from the different mineralization styles including oxidized and reduced sulfide oxide assemblages reveal 1 a large variation in 34s from 12 6 to 23 5 and 2 a previously unrecognized occurrence of anomalous 33s and 36s signatures from 1 0 to 1 1 and from 2 3 to 0 9 respectively it is argued that the mineralizing fluids that formed the golden mile and mount charlotte deposits record mixing among three components mantle sulfur oxidized seawater sulfur e g so4 and reduced elemental sulfur e g s8 petrographic evidence in conjunction with 33s and 36s data suggest that mif s was acquired during the deposition of shales and basalts present in the kalgoorlie terrane and later mixed with mantle derived sulfur during the mineralization events the negative 34s values that predominate in fimiston style mineralization are consistent with a prevalence of oxidized fluids during the ore forming process as reflected by the presence of hematite pyrite magnetite gold assemblages conversely the positive 34s values that dominate in the mt charlotte and oroya mineralization styles reflect a reducing environment as reflected by the presence of pyrite pyrrhotite gold assemblages

geology fluid inclusions and isotope geochemistry of the herenping gold deposit in the southern margin of the yangtze craton china a sediment hosted reduced intrusion related gold deposit abstract the herenping gold deposit is a typical gold deposit in the xuefengshan arcuate tectonic zone in the southern margin of the yangtze craton and the major feature of the gold mineralisation in the zone is the varying degrees of tungsten and antimony mineralisation in the ore deposits the herenping gold deposit occurs in the reddish purple sandy slate in the middle section of the madiyi formation of the neoproterozic banxi group and is controlled by the fault fold zone associated with the liulincha anticlinorium and f8 fault zone however its sources of mineralisation and relationships between hydrothermal fluids and magmatic rocks are unclear which similar to those of many gold deposits in metasedimentary terranes in the worldwide the mineralisation can be divided into four stages an albite quartz stage i an albite quartz pyrite gold stage ii a quartz gold polymetallic sulphide stage iii and a quartz carbonate stage iv the gold mineralisation occurred in albite quartz veins in stage ii and in sulphide rich quartz veins in stage iii in the deposit a study of the fluid inclusions reveals that the homogenisation temperature and salinity were slightly higher in stage ii th 186 348 c w 5 2 17 43 wt nacl equiv than in stage iii th 145 249 c w 2 9 15 57 wt nacl equiv indicating that the temperature and salinity of the ore forming fluid are gradually decreasing the h o d 62 3 to 53 0 18o 4 2 11 8 isotope characteristics reveals that the ore forming fluid is a magmatic hydrothermal source the sulphur 34s 4 8 2 0 isotope characteristics and the alteration mineral assemblage sericite chlorite pyrite indicates that the ore forming fluids was reduced the lead 206pb 204pb 17 419 17 436 207pb 204pb 15 519 15 535 and 208pb 204pb 37 86 37 90 isotope characteristics reflect the ore forming materials were likely derived from a deep magmatic source in addition the geochemical characteristics of albitite veins show that they are silicon rich 64 02 66 26 wt and significantly reduced notably the herenping gold deposit is located in the western portion of the tungsten tin metallogenic provinces in south china is host in epimetamorphic detrital rocks and was formed at least two stages of mineralisation typical gold bearing albite quartz veins developed during the primary stage these characteristics are consistent with those of reduced intrusion related deposits such as the muruntau kumtor and telfer deposits thus the herenping gold deposit may be a sediment hosted intrusion related gold deposit based on the phase transition pattern from sulphide rich quartz veins to albite quartz veins to albitite veins with increasing depth in the deposit we propose that reduced intrusions deep in the herenping gold deposit could be discovered in the future which implies the possible existence of a reduced intrusion related gold system in the xuefengshan arcuate tectonic zone

salt sources and water rock interaction on the yilgarn block australia isotopic and major element tracers internal drainage in the south east of western australia are underlain by predominantly granitoid rocks the regional shallow ground water are nacl brines ratios of 87sr 86sr in the brines are 0 7155 0 0015 which are close to the ratio of modern marine sr 0 7092 a two component isotopic mixing model with end members of marine sr and sr from basement granitoid rocks implies strongly that 5 of the sr is derived from rock weathering and 95 is marine the isotropic composition of s in gypsum crystallised from the brines is 19 8 0 3 cdt this value is close to that of s in recent evaporites 21 5 1cdt and confirms that weathering of archaean sulphides with 34sof0 4 cdt has contributed insignificant amounts of s to the brines the isotopic data are compatible with a late tertiary to recent age for the sr and s and by implication for the salts as a whole the formation of alunite has been a major control on brine composition while gypsum and calcrete formation have been minor influences none of the ground waters is saturated with halite which suggests the brines are immature and have evolved their present chemistry within the past few tens of thousands rather than millions of years marine aerosols are the main source of salt water sequestered in internal drainage basins by a post middle miocene regression possibly provided a subordinate fraction

evidence from chromium abundances in mantle rocks for extraction of picrite and komatiite melts one of the more important aspects of understanding the geochemical differentiation of the earth is an accurate knowledge of the compositions of magmas produced by direct melting of the upper mantle which are called primary magmas1 it is clear that a variety of primary magma compositions can develop within the mantle depending on the source composition the presence of volatiles the extent of melting and the pressure of melt segregation1 4 proposed primary magma compositions span a wide composition range from basalts with 8 ll mgo through picrites with 11 20 mgo to komatiites with 20 28 mgo there is no agreement as to which is the dominant type of primary magma we suggest here that the abundances of chromium in samples of the earth s upper mantle indicate that of the wide variety of possible primary liquids produced in experimental studies of mantle melting the dominant type of primary liquid actually extracted from the mantle has been picritic to komatiitic with 15 mgo

ore forming processes of the daqiao epizonal orogenic gold deposit west qinling orogen china constraints from textures trace elements and sulfur isotopes of pyrite and marcasite and raman spectroscopy of carbonaceous material

eruptive and depositional history of a pliocene tuff ring that developed in a fluvio lacustrine basin kissomlyo volcano western hungary abstract kissomlyo volcano is a pliocene erosion remnant of an alkaline basaltic tuff ring belonging to the little hungarian plain volcanic field late miocene shallow subaqueous fluvio lacustrine sand and mud units underlie sub horizontally bedded lapilli tuff and tuff beds with an erosional contact the pyroclastic units a sequence up to 20 m thick constitute a semi circular mound with gentle

mass change during extreme acid sulphate hydrothermal alteration of a tertiary latite styria austria abstract the tertiary latitic rock from gossendorf in the gleichenberg volcanic area styria austria has in places been completely altered to various associations of the secondary minerals opal c ct alunite kaolinite and montmorillonite the associations occur in a zonal arrangement and correspond to the characteristics of the silicic advanced argillic and argillic alteration terminology all elements investigated were mobilized during the hydrothermal acid sulphate alteration process except ti which was selected as the immobile monitor element to calculate mass changes drastic differences in gains and losses of certain elements which refer to the different alteration conditions were found to exist not only between different alteration zones but also within such zones the gains depend on the newly formed minerals the losses however on the increase of the porosity in the altered rocks for one altered rock characterizing theoretically the alteration processes in gossendorf mass grains were calculated for so 3 h 2 o v and sr and mass losses for sio 2 al 2 o 3 fe 2 o 3 mno mg0 cao na 2 o k 2 o p 2 o 5 cr co ni cu zn rb y zr nb and ba with respect to an unaltered latite the net mass balance calculation i e the difference of elemental gains and losses shows a net mass loss of about 14 60 g the mass exchange was accompanied by a moderate average decrease in volume of 6 6 the chemical species added to the rock during alteration so 3 v 2 o 3 and sro probably originated from a volcanic source h 2 o could have been of exogenous and or endogenous origin the results of the mass change calculations of major minor and trace elements suggest that the secondary mineral associations and their zonal arrangement at gossendorf have been formed by a strongly acidic hydrothermal solution rich in so 4 2 which underwent chemical variations by reaction with the latite the calculations indicate that for the formation of the altered rocks and their zonal distribution the elements of the latitic precursor rock a volcanic source for s v and sr and probably exogenic water were necessarily involved based on these results a general chemical characteristic for alteration assemblages in epithermal acid sulphate districts is presented al 2 o 3 fe 2 o 3 mg0 cao so 3 and h 2 o by weight proves to be suitable to characterize silicic advanced argillic and argillic alteration

review of neogene and quaternary volcanism of the carpathian pannonian region abstract development of the pannonian basins as well as thrusting and folding of the carpathians was accompanied by widespread volcanic activity this volcanism can be divided into three main genetic types 1 1 early miocene mainly acidic volcanism tuffs and ignimbrites the recent spatial separation of these volcanics may be due to large right lateral displacement along the mid hungarian shear zone during the early miocene 2 2 middle miocene pliocene calc alkaline mainly intermediate stratovolcanic complexes in the inner western carpathians and in the east carpathians related to a subducted oceanic slab their geochemical compositions show a transitional character between active continental margin and island arc type magmatic rocks the thickness of the crust increased with time and from west to east beneath this volcanic arc 3 3 pliocene pleistocene alkali basaltic volcanism was related to an upwelling then cooling asthenospheric dome this is thought to have initiated the thermal regime from which these melts ascended the compositional difference in space and in time might reflect the existence of local individual small sized diapiric bodies as well as several processes e g fractional crystallization mixing which modified the original magma the eruption of these basaltic melts was temporally associated with the final phase of development of the pannonian basin this volcanism was associated with recent uplifts and tectonic rejuvenation of the area

influence of atmospheric deposits and secondary minerals on li isotopes budget in a highly weathered catchment guadeloupe lesser antilles abstract to better constrain li dynamics in the tropics we sampled critical zone compartments of a small forested andesitic catchment in guadeloupe soils parent rock atmospheric dust plants soil solutions stream and rain waters the aims of this study are to identify the origin of li in the different compartments and to better characterize the behavior of li and its isotopes during water rock interaction in a highly cation depleted soil the li isotope signature 7li of throughfall samples varies between 11 2 and 26 4 as this is lower than the seawater signature 31 and vegetation does not fractionate li isotopes our data indicate that saharan dust 0 7 significantly contributes to the throughfall signature li isotope composition measured in a 12 5 m deep soil profile varies from 3 9 near the surface to 13 5 at 11 m depth compared to unweathered andesite 5 the deep soil signature is in agreement with preferential incorporation of light li into secondary minerals in the top soil however our results also emphasized that atmospheric deposition wet and dry is a main source of li to the soil the decreasing 7li with increasing depth is consistent with a vertical gradient of incorporation of heavy atmospheric li this input being maximal near the surface at the catchment scale throughfall and total atmospheric inputs sea salts saharan dust provide 12 1 and 23 9 g li yr 1 respectively to the quiock creek catchment these fluxes represent 34 and 67 respectively of li exported at the outlet indicating that atmospheric deposition is one of the main li inputs to the critical zone li concentration and isotopic mass balance at the catchment scale indicate that in addition to atmospheric deposition secondary mineral phase dissolution is a major solute source and that andesite no longer participates in significant production of li

boron sulphur and copper isotope systematics in the orogenic gold deposits of the archaean hattu schist belt eastern finland abstract the hattu schist belt is located in the western part of the archaean karelian domain of the fennoscandian shield the orogenic gold deposits with au bi te geochemical signatures are hosted by ne sw n s and nw se oriented shear zones that deform 2 76 2 73 ga volcanic and sedimentary sequences as well as 2 75 2 72 ga tonalite granodiorite intrusions and diverse felsic porphyry dykes mo w mineralization is also present in some tonalite intrusions both separate from and associated with au mineralization somewhat younger unmineralized leucogranite intrusions 2 70 ga also intrude the belt lower amphibolite facies peak metamorphism at 3 5 kbar pressures and at 500 600 c temperatures affected the belt at around 2 70 ga and post date hydrothermal alteration and ore formation in this study we investigated the potential influence of magmatic hydrothermal processes on the formation of orogenic gold deposits on the basis of multiple stable isotope b s cu studies of tourmaline and sulphide minerals by application of in situ sims and la icp ms analytical techniques crystal chemistry of tourmaline from a mo w mineralization hosted by a tonalite intrusion in the hattu schist belt is characterized by fe3 al3 substitution indicating relatively oxidizing conditions of hydrothermal processes the range of 11b data for this kind of tourmaline is from 17 2 to 12 2 the hydrothermal tourmaline from felsic porphyry dyke swith gold mineralization has similar crystal chemistry e g dravite povondraite compositional trend with fe3 al3 substitution and 11b values between 19 0 and 9 6 the uvite foitite compositional trend and 11b values between 24 1 and 13 6 characterize metasomatic hydrothermal tourmaline from the metasediment hosted gold deposits composition of hydrothermal vein filling and disseminated tourmaline from the gold bearing shear zones in metavolcanic rocks is transitional between the felsic intrusion and metasedimentary rock hosted hydrothermal tourmaline but the range of average boron isotope data is essentially identical with that of the metasediment hosted tourmaline rock forming magmatic tourmaline from leucogranite has 11b values between 14 5 and 10 8 and the major element composition is similar to that of the metasediment hosted tourmaline the range of 34svcdt values measured in pyrite chalcopyrite and pyrrhotite is from 9 1 to 8 5 which falls within the typical range of sulphur isotope data for archaean orogenic gold deposits in the hattu schist belt positive 34svcdt values characterize metasediment hosted gold ores with sulphide parageneses dominated by pyrrhotite and arsenopyrite the 34svcdt values are both positive and negative in ore mineral parageneses within felsic intrusive rocks in which variable amounts of pyrrhotite are associated with pyrite purely negative values were only recorded from the pyrite dominated gold mineralization within metavolcanic units therefore the shift of 34svcdt values to the negative values reflects precipitation of sulphide minerals from relatively oxidizing fluids the range of measured 65cunbs978 values from chalcopyrite is from 1 11 to 1 19 positive values are common for mineralization in felsic intrusive rocks and negative values are more typical for deposits confined to metasedimentary rocks positive and negative 65cunbs978 values occur in the ores hosted by metavolcanic rocks there is no correlation between sulphur and copper isotope data obtained in the same chalcopyrite grains evaluation of sulphur and boron isotope data together and comparisons with other archaean orogenic gold provinces supports the hypothesis that the metasedimentary rocks were the major sources of sulphur and boron in the orogenic gold deposits in the hattu schist belt variations in major element and boron isotope compositions in tourmaline as well as in the 34svcdt values in sulphide minerals are attributed to localized involvement of magmatic fluids in the hydrothermal processes the results of copper isotope studies indicate that local sources of copper in orogenic gold deposits may potentially be recognized if the original distinct signatures of the sources have not been homogenized by widespread interaction of fluids with a large variety of rocks and provided that local chemical variations have been too small to trigger changes in the oxidation state of copper during hydrothermal processes

fluid inclusion and stable isotope o h c and s constraints on the genesis of the serrinha gold deposit gurupi belt northern brazil the serrinha gold deposit of the gurupi belt northern brazil belongs to the class of orogenic gold deposits the deposit is hosted in highly strained graphitic schist belonging to a paleoproterozoic 2 160 ma metavolcano sedimentary sequence the ore zones are up to 11 m thick parallel to the regional nw se schistosity and characterized by quartz carbonate sulfide veinlets and minor disseminations textural and structural data indicate that mineralization was syn to late tectonic and post metamorphic fluid inclusion studies identified early co2 ch4 n2 and co2 ch4 n2 h2o nacl inclusions that show highly variable phase ratios co2 homogenization and total homogenization temperatures both to liquid and vapor interpreted as the product of fluid immiscibility under fluctuating pressure conditions more or less asso ciated with postentrapment modifications the ore bearing fluid typically has 18 33mol of co2 up to 4mol of n2 and less than 2mol of ch4 and displays moderate to high densities with salinity around 4 5wt nacl equiv mineralization occurred around 310 to 335 c and 1 3 to 3 0 kbar based on fluid inclusion homogenization temperatures and oxygen isotope thermometry with estimated oxygen fugacity indicating relatively reduced conditions stable isotope data on quartz carbonate and fluid inclusions suggest that veins formed from fluids with 18 oh2o and dh2o 310 335 c values of 6 2 to 8 4

magmatism related localized deformation in the mantle a case study a deformed composite peridotite pyroxenite xenolith in pliocene alkali basalts from the pannonian basin szentbekkalla bakony balaton highland volcanic field has been studied in detail a narrow shear zone of intense deformation marked by porphyroclast elongation and recrystallization runs along the peridotite pyroxenite contact the xenolith contains a large volume of euhedral olivine neoblasts and tablet grains of olivine away from the shear zone interpreted as products of annealing and recrystallization in the presence of grain boundary fluid estimates of the time required for growth of recrystallized olivine grains suggest that the annealing took place in situ in the mantle and not during transport of the xenolith in the basalt magma the grain boundary fluid present during recrystallization was a vapor rich silicate melt different from the host basaltic melt that entrained the xenolith this study demonstrates that high stress deformation zones and associated fluid assisted recrystallization which are common features in kimberlite mantle xenoliths also occur in some mantle xenoliths from alkali basalts the suggested high stress deformation zones in the mantle beneath the pannonian basin may be produced by paleoseismic events in the lithosphere associated with faulting related to the ascent of basalt magma

lower crustal granulite xenoliths from the pannonian basin hungary part 1 mineral chemistry thermobarometry and petrology lower crustal granulite xenoliths have been found in pliocene basaltic tuffs at two newly discovered localities in the western pannonian basin most of them are mafic meta igneous rocks among which garnet rich lithologies are common in general clinopyroxene garnet and plagioclase with minor ilmenite and scapolite dominate their mineralogy several are amphibole bearing which is interpreted as evidence for a recent metasomatic event in the lower crust beneath the pannonian basin meta sedimentary granulite xenoliths have also been identified in the region for the first time their mineralogy is characterised by the absence of clinopyroxene combined with a high proportion of al rich phases especially plagioclase and garnet together with subordinate spinel sphene rutile orthopyroxene and quartz one sample contains biotite and several contain graphite thermobarometric results indicate temperatures and pressures of 800 950 c and 8 15 kbar for all xenolith types considerably higher than for most granulite xenoliths from other regions of phanerozoic europe given that the pannonian basin is currently underlain by thin crust 25 30 km thick the pressure estimates indicate that the crust must have been considerably thicker 40 50 km prior to the tertiary collapse in the region the higher pressures recorded for the meta igneous xenoliths thus suggest that they formed at or before a time when the crust was thicker i e pre tertiary a composite meta igneous meta sedimentary xenolith provides direct evidence for interaction between sediments or metasediments and the magmas that gave rise to the meta igneous granulites indicating that the metasediments are at least as old as the meta igneous granulites the protoliths of the meta igneous xenoliths had primitive mafic to slightly evolved tholeiitic liquid compositions they are dominated by lree depleted compositions that resemble those of mid ocean ridge basalts such compositions are rare in lower crustal xenolith suites they are also very low in large ion lithophile elements such as k and rb but relatively enriched in ba and pb a few slightly lree enriched meta igneous xenoliths are also k and rb depleted in contrast the meta sedimentary granulites are strongly lree enriched but have very variable lile contents one possible explanation for the unusual compositions is a process of subduction accretion of oceanic crust beneath the continental crust rather than basaltic underplating

geology and pyrite sulfur isotopes of the suoluogou gold deposit implication for crustal continuum model of orogenic gold deposit in northwestern margin of yangtze craton sw china abstract since the crustal continuum model was proposed mainly based on the variation of mineralization and alteration features of hypozonal mesozonal to epizonal deposits genetic relationship between the different types in one ore belt still requires research this issue was addressed by the research on the suoluogou mesozonal orogenic gold deposit and its comparison with the hypozonal orogenic gold deposit in northwestern margin of yangtze craton gold mineralization in suoluogou is controlled by the bends of roughly ew trending brittle fault developed in the late triassic strata and it is associated with quartz sericite chlorite carbonate and sulfide alteration pyrite and arsenopyrite are the predominant sulfide mineral with minor amounts of chalcopyrite sphalerite and galena four paragenetic stages are divided based on crosscutting relationship and mineral assemblage including the pre mineralization stage stage the hydrothermal quartz sulfide stage stage and carbonate quartz sulfide stage stage iii and the post mineralization carbonate pyrite stage stage the 34s values for pyrite in stage vary from 6 01 to 8 59 and those in stage iii are from 0 96 to 4 62 the decrease of 34s value from stage to iii is explained to the result of the isotope fractionation during separation of oxidised sulfur species in the brecciated space the sulfide 34s values in the initial gold mineralization stage of the suoluogou deposit are similar to those of regional hypozonal orogenic deposit with derivation from metasomatized mantle in the craton margin this similarity suggests that the mesozonal and hypozonal gold deposits formed in different depths of a crustal continuum model for the deposits sharing similar subcrustal source

the genesis and tectonic control on archaean gold deposits of the western australian shield a metamorphic replacement model abstract gold deposits occur in greenstone belts world wide and contribute to anomalously high gold production from archaean terranes as in other cratons archaean gold mineralization of western australia represents a complex array of deposit styles despite this most deposits are clearly epigenetic and large deposits have a number of features in common including their strong structural controls distinctive wallrock alteration fe sulphide k mica albite ca mg fe carbonates consistent metal associations au ag as sb w b low base metals commonly fe rich host rocks great depth extension and lack of appreciable vertical zonation these shared characteristics combined with their ubiquitous occurrence indicate that archaean gold deposits had a common origin related to the tectonic evolution of greenstone belts auriferous hydrothermal systems were broadly synchronous with regional metamorphism and emplacement of synkinematic granitoids and felsic porphyry intrusions although these gold systems involved low salinity lowdensity reduced near neutral h 2 o co 2 fluids carrying gold as reduced sulphur complexes the origin of the fluids is equivocal most timing evidence and stable isotope data cannot distinguish metamorphic from magmatic granitoid or felsic porphyry orggins but the lack of consistent spatial relationships between specific volumetrically significant intrusive phases and large gold deposits in a number of cratons strongly favours metamorphic derivation of fluids the metamorphic replacement model for gold mineralization involves devolatilization of the lower portions of the greenstone pile with high geothermal gradients inhibiting significant melting co 2 possibly formed by the decarbonation of early alteration related to mantle degassing along crustal scale synbasinal fault zones auriferous fluids were channelled along greenstone scale faults in part developed during reactivation of crustal scale faults in a strike slip regime gold deposition occurred largely under greenschist facies conditions about 300 400 c 1 2 kb in response to decreasing gold solubility with declining temperature however a major control on gold deposition was fluid wallrock interaction many large deposits formed by sulphidation of fe rich host rocks with synchronous deposition of fe sulphides and gold however the variable nature of gold depositing reactions including lowering of fo 2 and ph allowed a multitude of small and some large deposits to form wherever that fluid circulation occurred in consequence several of the relatively small deposits currently worked from open pit are hosted by ultramafic and felsic rocks there are few constraints on the source of components au s k co 2 added to gold deposits but even giant deposits such as the golden mile kalgoorlie could have formed from a realistic greenstone source volume ca 8 8 5 km convective circulation of fluids could have contributed to the generation of high fluid rock ratios on the regional scale the markedly heterogeneous distribution of large gold deposits gold productivity and host rocks to deposits can be accommodated by the metamorphic replacement model the most favourable conditions for development of auriferous hydrothermal systems operated in younger ca 2 7 0 1 ga rift phase greenstones where greatest extension and crustal thinning produced high geothermal gradients crustal scale synbasinal faults and rapid extrusion and burial of volcanics including abundant komatiites iron rich tholeiitic basalts and dolerites were preferred host rocks for large gold deposits the least favourable conditions existed in older ca 3 5 3 4 ga platformphase greenstones where gentle sagging on submerged continental crust produced eruption of mainly mafic volcanics with few komatiites commonly in very shallow water environments this allowed intense synvolcanic alteration of both gold source rocks and potential host rocks the generally smaller gold deposits formed mainly in ultramafic or greywacke hosts younger ca 3 0 ga platform phase greenstones appear intermediate in nature but unlike other greenstones have significant epigenetic gold deposits in originally oxide facies bif which were deposited on relatively deep water platforms similar controls appear to exist on a world scale with gold mineralization peaking at ca 2 7 0 1 ga in response to development of major rift zones in thickened relatively mature continental crust interestingly the giant witwatersrand goldfield formed at about the same time