re os age of the pueblo viejo epithermal deposit dominican republic re os analyses of pyrite from the pueblo viejo high sulfidation epithermal deposit both monte negro and moore ore zones yield an isochron age of 111 9 3 7 ma and initial 187 os 188 os ratio of 0 22 0 18 mean square of weighted deviates 84 n 21 isochrons grouped by pyrite setting layered versus vein or locations yield ages within uncertainty of the overall isochron and with each other and as such do not yield temporally distinguishable ages sphalerite vein samples as well as shale source rocks show evidence of open system behavior and loss of re and therefore are not included in the above regression these results confirm that the pueblo viejo deposit is early cretaceous in age and coeval with the volcanic los ranchos formation which hosts the deposit recent paleontological age assignments for the hatillo formation which overlies the los ranchos formation show that it is only slightly younger opening the possibility that mineralization in the hatillo formation could also be related to late stages of los ranchos magmatism whether these revised los ranchos hatillo relations provide sufficient cover to account for the paragenetically late formation of pyrophyllite at pueblo viejo remains unclear recognition that pueblo viejo is coeval with the los ranchos formation shows that large scale high sulfidation epithermal mineralization can form from basal island arc tholeiitic magmatism a review of available experimental data confirms that these magmas can generate hydrothermal solutions of the necessary composition favorability of the los ranchos formation might have been enhanced by its bimodal composition these results suggest that exploration for epithermal precious metal deposits should include basal island arc tholeiite terranes

re os isotopic dating of molybdenite and pyrite in the baishan mo re deposit eastern tianshan nw china and its geological significance the baishan mo re deposit is located in the eastern section of the eastern tianshan orogenic belt nw china the deposit has a grade of 0 06 mo and a high content of rhenium of 1 4 g t rhenium and osmium isotopes in sulfide minerals from the baishan deposit are used to determine the age of mineralization rhenium concentrations in molybdenite samples are between 74 and 250 g g analysis of eight molybdenite samples yields an isochron age of 224 8 4 5 ma 2 pyrite samples have rhenium and osmium concentrations varying in the range 33 4 330 6 ng g and 0 08 0 81 ng g respectively isotope data on seven pyrite samples yield an isochron age of 225 12 ma 2 on the 187re 188os versus 187os 188os plot and an age of 233 14 ma 2 on the 187os versus 187re correlation diagram the ages of molybdenite and pyrite are consistent within the analytical errors combined with field observations the data indicate that mo re mineralization in the baishan deposit is produced by a magmatic hydrothermal event in an intracontinental extensional setting after late paleozoic orogeny the initial 187os 188os ratio of pyrite is 0 3 0 07 the 34s values of molybdenite vary from 0 5 to 3 6 both data indicate that mineralization is derived mainly from a mantle source

kinematic considerations for mantle mixing recent experimental and computational studies tal and computational mixing studies in highly controlled show that islands u mixedrcgions that donot interactwith flows show that even seemingly inconsequential errors in the surrounding regions are ubiquitous features in chaotically computed velocity field of 3 d or time dependent flows can advecting fluids such is ands uitenaturall account for the geochemically inferred coexistence of apparently distinct long lived geochemical heterogeneity with relatively homo geneous regions of an actively convecting mantle these results also indicate that mixing patterns the set of islands and folds characterizing the large scale material advection are sensitive to small variations in the rheology of the fluid therefore interpretation of numerical simulations of mantle transport and mixing is less straightforward than currently supposed computational studies of analytic flow solutions with systematically introduced and controlled errors indi cate that mantle simulations are unlikely to accurately com pute individual trajectories for even moderate time but that tmjectory ensembles can be accuntely computed for long time significantly computations also indicate that mixing and transport resultsmay not evolve smoothly with increased rheological realism

variations in os isotope ratios of pyrrhotite as a result of water rock and magma rock interaction constraints from virginia formation duluth complex contact zones abstract os isotope ratios in pyrrhotite bearing pelitic rocks of the 1 85 ga virginia formation are variable with perturbations linked to the emplacement of the 1 1 ga duluth complex pyrrhotite in footwall rocks of the contact aureole show evidence for a mixing event at 1 1 ga involving a low 187 os 188 os fluid however because rocks with perturbed pyrrhotite os isotope ratios occur 1 km or more from the duluth complex the fluid is unlikely to have been of magmatic origin fluid inclusions in layer parallel quartz veins provide evidence of the involvement of a boiling fluid at temperatures between 300 and 400 c analyses of fluid inclusions via la icp ms show that the fluids contain up to 1 7 wt na 1 1 wt k 4330 ppm fe 2275 ppm zn and 415 ppm mg the veins also contain pyrite or pyrrhotite plus minor amounts of chalcopyrite bornite pentlandite and sphalerite the re os isotopic ratios of pyrite from the veins indicate that they crystallized from low 187 os 188 os fluids 18 o values of vein quartz range from 7 7 to 9 5 consistent with an origin involving fluid with a relatively low 18 o value between 2 and 5 meteoric water with such a low 18 o value could have interacted with the igneous rocks of the complex and would have acquired os with a low 187 os 188 os ratio strongly serpentinized olivine rich rocks of the complex are commonly characterized by such low 18 o values and we propose that the fluid involved in serpentinization was also responsible for the perturbation of the os isotopic system recorded by pyrrhotite in the virginia formation two important observations are that only pyrrhotite bearing assemblages in the contact aureole show isotopic perturbation and that intervals showing os exchange are spatially restricted and not uniformly distributed os exchange and mixing has occurred only where temperatures were sufficient to convert pyrite to pyrrhotite and where time integrated water rock ratios in the aureole were high enough to provide a supply of os troctolitic and gabbroic rocks of the partridge river intrusion duluth complex are characterized by os isotope ratios that are indicative of variable degrees of crustal contamination os values of 0 543 xenoliths of carbonaceous and sulfidic pelitic rocks of the virginia formation found in the igneous rocks provide evidence that os was released by organic matter and pyrite in the sedimentary rocks and assimilated by mantle derived magma however residual pyrrhotite produced as a result of pyrite breakdown in the xenoliths is characterized by 187 os 188 os ratios that are much lower than anticipated and similar to those of pyrrhotite in the contact aureole the os exchange and addition shown by pyrrhotite in the xenoliths highlight an unusual cycle of re os liberation during devolatilization kerogen maturation and pyrite to pyrrhotite conversion processes that contribute to magma contamination followed by os uptake by pyrrhotite during back reaction involving magma and or fluid characterized by a relatively low 187 os 188 os ratio the extreme os uptake recorded by pyrrhotite in the xenoliths as well as the lesser degree of uptake recorded by pyrrhotite in the contact aureole is in line with the high os diffusivity in pyrrhotite experimentally determined by brenan et al 2000 our data confirm that os isotope ratios in pyrrhotite bearing rocks may be readily perturbed for this reason caution should be exercised in the interpretation of os isotope ratios in rocks where pyrrhotite may be the primary host of os

an overview of the platinum group element nanoparticles in mantle hosted chromite deposits abstract this paper reviews the occurrence of platinum group elements nanoparticles pge nps in mantle hosted chromite deposits showing that pge nps are more frequently found in these deposits than previously thought a comparison of published experimental data with observations in natural samples reveal that pge nps might form at the pressure 1 0 5 gpa temperature 1200 c and f o 2 fmq 1 conditions in which chromite deposits form in the upper mantle the crystallization of pge nps may take place earlier or simultaneously to the segregation of chromite and or sulfide liquids from silicate melts if the pges are dissolved in the silicate melt the segregation of pge nps could be linked to local changes in f o 2 and f s 2 during the early crystallization of chromite and or olivine mobile crystals of chromite and droplets of sulfide melts entrained in the basaltic parent melt may also play an additional role as physical collectors of pge nps providing a complementary or even an alternative mechanism for the fractionation of pges in high temperature silicate melts furthermore hydrothermal alteration of the chromite deposits during seafloor metamorphism or exhumation i e retrograde metamorphism of upper mantle rocks has also a significant effect on the internal structure of the oxides and sulfides that host the pge nps frequently pge nps are found along the replacement contacts between primary and secondary minerals suggesting that pge nps can also form during low temperature alteration events 200 600 c finally heating events overimposed on chromite deposits previously affected by hydrous metamorphism may enhance fluid infiltration subsequently triggering chemical mineralogical or textural responses in the oxide or sulfide matrices hosting the pge nps promoting coarsening of metal nanoparticles the interplay between these processes can explain the wide spectrum of particle sizes of pge inclusions that are observed in many altered chromite deposits which can vary from a few nanometers to larger than a micron these studies provide evidence that pge nps can eventually form under a wide spectrum of thermal and pressure conditions and show that aqueous fluids may play a relevant role in producing pge nps during metamorphism and metasomatism of mantle hosted chromite deposits

subgrain scale decoupling of re and 187os and assessment of laser ablation icp ms spot dating in molybdenite abstract reproducibility of re os molybdenite ages depends on sample size and homogeneity suggesting that re and os are decoupled within individual molybdenite crystals and do not remain spatially linked over time in order to investigate the re os systematics of molybdenite at the subgrain micron scale we report la icp ms re os ages for an archean molybdenite crystal from aittojarvi finland analyzed in situ in a white aplite matrix a related aittojarvi molybdenite a996d in the form of a very fine grained mineral separate is used as one of our in house ntims standards and thus its age of 2760 9 ma is well established measurements of 187 re 187 os 185 re on micron scale spots along 200 m traverses across the crystal yield a wide range of ages demonstrating that in this case microsampling of molybdenite does not produce geologically meaningful ages experimentation with mineral separations and sample size over a 7 yr period predicted that this would be the outcome we suggest that 187 os is more likely to be the mobile species based on its charge and ionic radius and that 187 os becomes decoupled from parent 187 re with time on the micron and larger scale incompatible charge and ionic radius for os ions formed during reduction of molybdenite forming fluids may explain the widely observed absence of common initial os in molybdenite geologically accurate ages for molybdenite can only be obtained for fully homogenized crystals or crystal aggregates so that any post crystallization 187 re 187 os decoupling is overcome a growing number of geologically accurate id ntims 187 re 187 os ages for homogenized molybdenite suggest that postcrystallization mobility of radiogenic 187 os must be limited to within the molybdenite mineral phase we suggest that radiogenic 187 os may be stored in micron scale dislocations kink bands and delamination cracks produced by deformation and that the unusual structure and deformation response of molybdenite results in an increased chemical stability in this mineral migration of 187 os into adjacent silicate phases is highly unlikely but other contacting sulfides may take in os in an example from a proterozoic skarn deposit at pitkaranta western russia we demonstrate minor loss of radiogenic 187 os from molybdenite and a corresponding gain in adjacent chalcopyrite such that the molybdenite age is not perceptibly disturbed whereas the resulting chalcopyrite ages are impossibly old therefore it is unadvisable to perform re os analytical work on any sulfide in contact or intimate association with molybdenite in addition to large errors in the age if the isochron method is employed initial 187 os 188 os ratios could be erroneously high leading to seriously errant genetic interpretations

a study of strontium diffusion in k feldspar na k feldspar and anorthite using rutherford backscattering spectroscopy abstract sr chemical diffusion has been measured in orthoclase anorthoclase and anorthite under dry 1 atm conditions a strontium oxide aluminosilicate powder mixture was used as the source material with rutherford backscattering spectroscopy rbs used to measure diffusion profiles over the temperature range 725 1075 c the following arrhenius relations were obtained orthoclase normal to 001 d 5 97 10 0 0060 0 0030exp 67900 1600rtcm 2 s 1 measurements of diffusion perpendicular to 010 and 100 indicate little diffusional anisotropy in orthoclase anorthoclase normal to 010 d 4 51 10 1 358 5 6exp 89100 4800rt cm 2 s 1 normal to 001 d 2 25 10 2 1615 31exp 89300 4600rt cm 2 s 1 anorthite normal to 010 d 3 85 10 2 0 380 0 0039 exp 78800 5400rt cm 2 s 1 the correlation of sr uptake with a reduction of k and ca in orthoclase and anorthite respectively indicates that sr is exchanging with these species nuclear reaction analysis nra measurements of al in orthoclase suggests that the coupled exchange sr 2 al 3 k 1 si 4 is taking place as expected sr closure temperatures for feldspars calculated with the above parameters are relatively high compared to those of some other minerals e g biotite muscovite apatite however closure temperatures of feldspars may be significantly depressed if they are exsolved or twinned leading to small effective diffusion lengths feldspar crystals of millimeter size should retain 87 sr 86 sr ratios except when subjected to thermal events of extreme temperature or duration

mineralogy chalcopyrite reos geochronology and sulfur isotope of the hujiayu cu deposit in the zhongtiao mountains north china craton implications for a paleoproterozoic metamorphogenic copper mineralization abstract the hujiayu cu deposit located in the zhongtiao mountains district of southern north china craton is hosted by graphite schist and dolomitic marble with disseminated to veinlet stage i and thick vein stage ii mineralization stage i mineralization characterized by stratabound disseminated pyrite and chalcopyrite within the graphite schist host rock formed at the syn metamorphic stage graphite geothermometry showed that the host rock was subjected to an upper greenschist to lower amphibolite metamorphism at a temperature range of 486 to 596 c averaging of 546 35 c 1 n 19 stage ii mineralization consisting of brecciated dolomitic thick veins cemented by quartz sulfide assemblages was a product of metamorphic hydrothermal activity this thick vein was subdivided into an early hydrothermal dolomitic alteration composing of dolomitic breccia with some cobaltiferous pyrite stage iia and a late siliceous copper mineralization consisting of quartz sulfide assemblages stage iib a clausthalite siegenite sphalerite chalcopyrite mineral assemblage was observed in stage iib constraining the sulfur fugacity and selenium fugacity within 18 7 to 11 7 and 21 7 to 14 7 respectively it was inferred stage iib was marked by a drop in sulfur fugacity and a substantial increase in selenium fugacity after the major chalcopyrite precipitation calculations based on the compositions of cobaliterous pyrite and sphalerite reveal that the mineral assemblage at stage iia formed at an approximately temperature range of 400 to 300 c whereas the minerals in stage iib occurred at temperature of 256 9 c 1 n 7 sulfides from stage i have 34s value ranging from 10 1 to 22 2 with an average value of 16 9 3 4 1 n 27 supporting the model that sulfides precipitated through thermochemical reduction of sulfate at sedimentary stage followed by metamorphic homogenization of 34s isotopic signatures sulfides from the stage ii have 34s values in highly variable ranging from 3 4 to 19 2 indicating a rather complex source four chalcopyrite samples yielded a weighted model age of 1952 39 ma 1 mswd 1 5 suggesting that the copper mineralization formed synchronously with regional metamorphism 1970 1850 ma and hence a paleoproterozoic metamorphogenic copper mineralization is implicated therefore we envisaged disseminated veinlet mineralization formed during a metamorphic peak and the major hydrothermal copper mineralization occurred during the retrograde cooling

a characteristics based method for solving the transport equation and its application to the process of mantle differentiation and continental root growth summary purely advective transport of composition is of major importance in the geosciences and efficient and accurate solution methods are needed a characteristics based method is used to solve the transport equation we employ a new hybrid interpolation scheme which allows for the tuning of stability and accuracy through a threshold parameter eth stability is established by bilinear interpolations and bicubic splines are used to maintain accuracy with this scheme numerical instabilities can be suppressed by allowing numerical diffusion to work in time and locally in space the scheme can be applied efficiently for preliminary modelling purposes this can be followed by detailed high resolution experiments first the principal effects of this hybrid interpolation method are illustrated and some tests are presented for numerical solutions of the transport equation second we illustrate that this approach works successfully for a previously developed continental evolution model for the convecting upper mantle in this model the transport equation contains a source term which describes the melt production in pressure released partial melting in this model a characteristic phenomenon of small scale melting diapirs is observed de smet et al 1998 de smet et al 1999 high resolution experiments with grid cells down to 700 m horizontally and 515 m vertically result in highly detailed observations of the diapiric melting phenomenon

diffusion of osmium in pyrrhotite and pyrite implications for closure of the re os isotopic system abstract in order to better constrain the extent to which common sulfide minerals will retain their osmium isotopic composition subsequent to crystallization we have conducted experiments to quantify the diffusion behavior of osmium in pyrite and pyrrhotite experiments consisted of either 1 isothermal soaking of diffusion couples consisting of natural pyrite or pyrrhotite crystals packed against powdered os bearing fe sulfide or 2 relaxation of initially high near surface osmium concentrations produced in the latter experiments pyrite only osmium penetration into samples was characterized by depth profiling using rutherford backscattering spectroscopy rbs pyrite or electron microprobe analyses across sectioned run products pyrrhotite results of the first type of diffusion experiment involving pyrite show only limited osmium penetration into sample surfaces with the extent of penetration uncorrelated with run duration images of pyrite samples using atomic force microscopy show roughening of initially smooth surfaces as a consequence of step formation and suggest that osmium incorporation into the near surface occurred by solute uptake during step growth and not by volume diffusion prolonged 1000 h relaxation experiments revealed no additional osmium penetration into pyrite surfaces and based on the depth resolution for rbs a maximum diffusion coefficient of 2 5 10 23 m2 s at 500 c was calculated experiments involving pyrrhotite over the temperature range of 950 1100 c showed extensive osmium uptake and osmium concentration gradients that conform with fickian diffusion behavior we found that pyrrhotite fe s could be varied by changes in the composition of the starting material and osmium source and over the range of fe s produced in experiments molar fe s 0 83 0 90 we observed no systematic variation in the osmium diffusion coefficient diffusion coefficients measured parallel to the a crystallographic axis were on average 1 4 higher than values measured parallel to c and regression of the c axis data yielded the arrhenius relation d t 1 31 0 16 10 5 m 2 s exp 211 5 14 7 kj mol rt the application of these diffusion data to simple models of diffusive exchange during static or polythermal time temperature histories is used to assess the conditions under which radiogenic osmium will be retained during isothermal annealing calculations indicate that the cores of millimeter sized spherical pyrrhotite crystals undergoing diffusive exchange with an external osmium reservoir will have their initial compositions perturbed in 0 5 ma at temperatures exceeding 400 c pyrite undergoing the same process at 500 c requires in excess of 10 ma before crystal cores are affected the relatively short core retention time scales for pyrrhotite indicates that this mineral may be prone to isotopic resetting following relatively brief crustal thermal events thus possibly accounting for the scatter that commonly occurs in re os isochrons generated from massive sulfide samples calculated closure temperatures tc for osmium exchange in pyrrhotite yielded values of 300 400 c for grain sizes ranging from 10 to 1000 m these values of tc are similar to those calculated for ar retention in biotite and considerably lower than for sr in apatite and plagioclase for example such low closure temperatures for pyrrhotite suggest this mineral will date the final stage in the cooling of a magmatic system and possibly be susceptible to open system osmium exchange in the presence of late stage hydrothermal fluids this latter result infers that caution be applied when interpreting elevated initial osmium isotopic ratios as a product of crustal assimilation at the magmatic stage

anhydrite solubility in differentiated arc magmas abstract the solubility of anhydrite in differentiated arc magmas was experimentally studied at 200 mpa and 800 1000 c over a range of oxygen fugacities from 0 5 log units above the ni nio buffer to the hematite magnetite buffer anhydrite is stable only at oxidizing conditions fo2 re reo2 whereas sulfides only form under reducing conditions the solubility of anhydrite in the melt ultimately regulates the amount of sulfur available to partition between melt and fluid phase during the eruption at oxidizing conditions the solubility product of anhydrite increases with temperature nbo t and melt water content we provide a new calibration of the anhydrite solubility product ksp xcao xso3 which reproduces all available experimental data with greatly improved accuracy ln k sp anhydrite 8 95 146 5 nbo t 2 696 10 4 t k 19 72 nbo t 10 4 t k 0 409 h 2 o wt in this equation the molar fractions xcao and xso3 in the melt as well as the number of non bridging oxygen atoms per tetrahedron nbo t are calculated on an anhydrous basis h2o refers to the melt water content t is temperature in kelvin we apply our model to estimate the sulfur yield of some recent volcanic eruptions and we show that the sulfur yield of the 1991 mt pinatubo dacite eruption was unusually large because only a small fraction of the sulfur was locked up in anhydrite in general high sulfur yields are expected when anhydrite solubility in the melt is high i e for somewhat depolymerized melts for rhyolitic systems most of the available sulfur will be locked up in anhydrite so that even very large eruptions may only have a small effect on global surface temperatures our model therefore allows improved predictions of the environmental impact of explosive volcanic eruptions

two stage gold mineralization of the axi epithermal au deposit western tianshan nw china evidence from re os dating s isotope and trace elements of pyrite the axi gold deposit is one of the largest epithermal deposits in northwestern china and is characterized by multistage generations of pyrite associated with gold mineralization genetic models for superjacent epithermal au and porphyry cu systems involve either contemporaneous or episodic mineralization implying different metal sources and ore forming events nine pyrite separates from disseminated ores associated with pyrite sericite quartz alteration in the axi deposit yield a re os isochron age of 350 10 ma mswd 5 1 initial 187os 188os ios 0 20 0 11 this age likely reflects a mixed contribution of two subtypes of disseminated pyrite py1 based on zoned pyrite crystals the isochron age of 353 6 ma mswd 1 6 ios 0 107 0 021 n 6 excluding samples with pyrite cores overlaps previous ages for andesite from the dahalajunshan formation ca 356 ma indicating that the early mineralization event occurred shortly after the formation of host rocks ca 353 ma pyrite from disseminated ores shows little variation of sulfur isotopic compositions 2 9 to 4 0 and has high cu co ni and v contents which favors a magmatic hydrothermal origin pyrite grains from gray quartz veins yield a younger re os isochron age of 332 8 ma mswd 0 22 n 4 vein hosted pyrite shows characteristics of a mantle derived magma source ios 0 171 0 024 34s 0 10 3 10 which result from the intrusion driven convective hydrothermal circulation accompanying fluid exsolution and metal remobilization from basement and wallrocks our data demonstrate that the axi gold deposit was formed during two temporally separated hydrothermal events this model of ore formation may apply to other epithermal porphyry deposits within the axi tawuerbieke district disseminated au and porphyry style au cu mineralization occurred shortly after magmatic activity 356 353 ma whereas epithermal style au mineralization occurred at ca 332 ma

re os dating of chalcopyrite from selected mineral deposits in the kalatag district in the eastern tianshan orogen china the kalatag cu zn au district contains a number of economically important cu deposits in eastern tianshan in xinjiang nw china due to the lack of precise mineralization ages the metallogenesis of this area has long been a matter of debate in this study chalcopyrite re os isotope methods are used to date the south meiling cu zn and hongshi cu deposits in the eastern part of kalatag area the south meiling cu zn deposit is hosted in volcanic sedimentary rocks of the late ordovician to early silurian daliugou formation the deposit consists of two parts a concordant massive sulfide ores and discordant vein type ores located in the footwall strata the principal ore minerals are pyrite chalcopyrite sphalerite minor tetrahedrite galena and pyrrhotite gangue minerals include quartz sericite and barite and minor chlorite plagioclase and carbonate minerals the hongshi cu deposit represents a hydrothermal vein system hosted in the mafic volcanic rocks of daliugou formation the orebodies are associated with quartz veins and controlled by subsidiary faults of the kalatag fault the ore forming process can be divided into the early middle and late stages and is characterized by quartz pyrite quartz chalcopyrite pyrite and quartz carbonate gypsum veins respectively re os analyses of chalcopyrite from the south meiling cu zn deposit yield an isochron age of 434 2 3 9 ma and initial 187os 188os ratio of 0 647 0 098 mswd 0 59 re os analyses of chalcopyrite from the hongshi cu deposit yield an isochron age of 431 8 2 7 ma and initial 187os 188os ratio of 0 165 0 075 mswd 0 77 since chalcopyrite is the primary copper mineral we interpret these isochron ages as the timing of cu mineralization based on field geology and petrographic evidence these results suggest that the re os ages presented here provide for the first time a direct constraint on an early paleozoic cu mineralization event of the eastern tianshan orogen the high initial 187os 188os ratios 0 647 0 098 ratio of 434 ma chalcopyrite from the south meiling deposit suggest that the metal was sourced from a two end member mixing of crust and mantle materials moreover we propose that the vms mineral system and hydrothermal vein system of the kalatag district were related to the south dipping subduction of the kalamaili oceanic plate during the late ordovician silurian

rhenium osmium systematics of the mount isa copper orebody and the eastern creek volcanics queensland australia implications for ore genesis the syn tectonic breccia hosted mount isa cu deposit in northwest queensland is the largest sediment hosted cu deposit in australia whole rock samples of chalcopyrite rich cu ore form an isochron with a re os age of 1 372 41 ma this age is more than 100 ma younger than the previously accepted age of cu ore formation an ar ar mineral age for biotite separated from the host rocks within the alteration envelope to the cu orebody this discrepancy cannot be unequivocally resolved due to a lack of other absolute geochronological constraints for cu mineralisation or the deformation event associated with cu emplacement the 1 372 41 ma date may reflect a the time of cu deposition b the time of a hydrothermal event that reset the re os signature of the cu ore or c mixing of the re os isotope systematics between the host rocks and cu bearing fluids however a range of published ar ar and rb sr dates for potassic alteration associated with cu mineralisation also records an event between 1 350 and 1 400 ma and these are consistent with the 1 372 ma re os age the 1 8 ga eastern creek volcanics are a series of tholeiitic basalts with a primary magmatic cu enrichment which occur adjacent to the mount isa cu deposit the whole rock os isotopic signature of the eastern creek volcanics ranges from mantle like values for the upper pickwick member to more radiogenic crustal values for the lower cromwell member the re os isotope signature of the cu ores overlaps with those calculated for the two volcanic members at 1 372 ma hence the os isotope data are supportive of the concept that the os in the cu ores was sourced from the eastern creek volcanics by inference it is therefore postulated that the eastern creek volcanics are the source of cu in the mount isa deposit as both os and cu are readily transported by oxidised hydrothermal fluids such as those that are thought to have formed the cu orebody the pickwick member yields a re os isochron age of 1 833 51 ma which is within error of previously reported age constraints the initial 187os 188os isotopic ratio of 0 114 0 067 os 0 7 is slightly subchondritic and together with other trace element geochemical constraints is consistent with a subcontinental lithospheric mantle source the pickwick member records a minimum age of ca 1 95 ga for melt depletion in the subcontinental lithospheric mantle beneath the mount isa inlier prior to the extraction of the magmas which formed the eastern creek volcanics this corresponds with the end of subduction related magmatism along the eastern margin of the northern australian craton which included the mount isa inlier

heterogeneous os isotope compositions in the kalatongke sulfide deposit nw china the role of crustal contamination re os isotope compositions of mantle derived magmas are highly sensitive to crustal contamination because the crust and mantle have very different os isotope compositions crustal contamination may trigger s saturation and thus the formation of magmatic ni cu pge sulfide deposits the 287 ma kalatongke norite intrusion of nw china are hosted in carboniferous tuffaceous rocks and contain both disseminated and massive sulfide mineralization the re os isotope compositions in the intrusion are highly variable norite and massive sulfide ores have os values ranging from 59 to 160 and a re os isochron age of 239 51 ma whereas disseminated sulfide ores have os values from 117 to 198 and a re os isochron age of 349 34 ma the variability of os isotope compositions can be explained as the emplacement of two distinct magma pulses massive sulfide ores and barren norite in the intrusion formed from the same magma pulse whereas the disseminated sulfide ores with more radiogenic os isotopes formed from another magma pulse which underwent different degrees of crustal contamination re os isotopes may not be suitable for dating sulfide bearing intrusions that underwent variable degrees of crustal contamination to form magmatic sulfide deposits

origin of the inconsistent apparent re os ages of the jinchuan ni cu sulfide ore deposit china post segregation diffusion of os abstract apparent re os ages of some magmatic sulfide ore deposits are older than the zircon and baddeleyite u pb ages which are interpreted as the formation age of the host intrusions the jinchuan ni cu pge deposit of china the world s third largest is such a case we report apparent re os isochron ages of 1117 67 ma 1074 120 ma and 867 75 ma with initial 187os 188os ratios of 0 120 0 012 0 162 0 017 and 0 235 0 027 for disseminated ores sulfides from the disseminated ores and massive ores from jinchuan respectively using these data and re os ages from the literature we find that the oldest apparent re os age and lowest initial os isotope ratio are from disseminated ores which contain small amounts of sulfide minerals the highest initial os isotope ratios and youngest apparent re os ages consistent with the zircon and baddeleyite u pb ages are from massive ores containing 90 100 modal sulfide and net textured ores with about 25 modal sulfides yield apparent re os ages and initial os ratios intermediate between those of the disseminated and massive ores because os diffusion between sulfides is inhibited by the intervening silicates even at high temperatures re equilibration did not occur in the disseminated ore and the samples retained the os ratios of the contaminated magma leading to geologically meaningless ages that are older than the formation age of the rocks while os bearing sulfide minerals and magnetite show low closure temperatures of os diffusion and the sulfide minerals in the massive ore are closely connected with each other facilitating fast diffusion of os re equilibration of os was achieved during cooling of the ore from about 850 c after the segregation to about 400 c thus an age corresponding to the formation time and an elevated initial os ratio were yielded by the massive ore os isotopes in the net textured ore behave in the way intermediate between the disseminated and massive ores pb isotope data support the os results disseminated ores have heterogeneous pb isotope ratios whereas pb in the massive ores is more uniform consistent with pb isotopic equilibration in the massive ores but not in the disseminated ores

re os isotope and pge constraints on the timing and origin of gold mineralisation in the witwatersrand basin abstract analyses of the re os isotope system and pge abundances have been used to investigate the timing and origin of mineralisation in the vaal reefs section of the witwatersrand basin the world s largest gold deposit consistent interelement pge fractionation in both organic and sulphide phases intimately associated with gold mineralisation suggests that the re os isotope system was fractionated during gold mobilisation the re os isotope data on organic separates intimately associated with the gold in this part of the basin indicate open system behaviour until 2 26 0 19 ga 2 of the order of 450 myr younger than the minimum age of sedimentation the overlying ventersdorp volcanics preserve a re os isochron age of 2 43 0 21 ga 250 ma younger than their u pb zircon emplacement age these data indicate substantial post sedimentary noble metal mobility within portions of the witwatersrand basin re os model age calculations on os rich fractions suggest that noble metals were derived from a 3 0 3 1 ga terrain of granite greenstone affinities significantly younger than the barberton greenstone belt these data support a hybrid model involving post depositional mobilisation of ancient probably detrital noble metals for the origin of mineralisation in this part of the witwatersrand basin such a model is applicable to other areas of gold mineralisation in the basin that display similar textural characteristics and geochemistry

oxygen and sulfur isotopic composition of volcanic sulfate aerosol at the point of emission volcanic sulfate aerosol is emitted from the vents of many active volcanoes but its origin has not yet been explained we report the first measurements of the isotopic compositions of near vent volcanic aerosol sulfate and use the combined sulfur and oxygen isotope systematics of the aerosol and magma at masaya volcano nicaragua to draw preliminary conclusions about the production mechanism of near source volcanic sulfate the sulfate aerosol does not display a significant mass independent oxygen or sulfur isotopic signature which suggests that primary volcanic aerosol does not contribute to the larger mass independent anomalies found in some ambient atmospheric aerosols and as preserved in ice cores the oxygen isotope composition of the sulfate appeared to become heavier on the particle filters with increasing amount of sample collected and suggests that the 18o value of the sulfate aerosol is 8 the sulfur isotopic composition of the sulfate did not vary with sample loading on the filters and had a mean 34s value of 7 7 0 8 similar to that of the magma 6 6 0 2 the low 17o value the 18o value of the magma 6 6 0 3 and the high 18o value of atmospheric oxygen 23 5 suggest that known atmospheric oxidation pathways at ambient temperatures are not the major routes of production for this sulfate instead the isotopic systematics of aerosol and magma are consistent with sulfate production either by high temperature equilibration of the magmatic gas mixture with small amounts of atmospheric oxygen or by direct emission of so4 2 from the magma

effects of frictional viscous oscillations and fluid flow events on the structural evolution and re os pyrite chalcopyrite systematics of cu rich carbonate veins in northern norway abstract mesothermal chalcopyrite pyrite magnetite bearing calcite dominated vein deposits in the repparfjord tectonic window northern norway have been studied to constrain the mechanics of their emplacement and the timing of initial vein formation and reactivation the veins cut across paleoproterozoic tholeiitic metabasalts and present textural contrast between their hydrofractured coarse grained margins and the fine grained mylonitic cores they formed under overall viscous conditions although cyclically increased fluid pressures caused transient embrittlement as mineral precipitation sealed the fractures deformation was accommodated again viscously leading to mylonitization of the vein s core local brecciation of the calc mylonite demonstrates the cyclicity of this process re os chalcopyrite pyrite and k ar fault gouge dates define an almost continuous age range from 2540 ma to 460 ma regression of three re os analyses yields a 2069 14 ma age 187os 188os 0 18 0 04 interpreted as the age of vein emplacement sulfide precipitation and initial frictional viscous deformation k ar ages are mixed ages that constrain a maximum age of faulting in association with the veins at approximately 460 ma hence indicating structural reactivation connected with silurian caledonian orogenic compression the spread in re os model ages reflects this reactivation wherein renewed strain accommodation and circulating oxidizing fluids caused fracturing dynamic recrystallization and isotopic disturbance of the sulfides the study provides evidence for fluid flow during viscous deformation and demonstrates that strain and flow of oxidizing fluids can have a significant yet localized control on the integrity of the re os systematic in pyrite and chalcopyrite

re os isotopic ages of pyrite and chemical composition of magnetite from the cihai magmatic hydrothermal fe deposit nw china the eastern tianshan orogenic belt of the central asian orogenic belt and the beishan terrane of the tarim block nw china host numerous fe deposits the cihai fe deposit 90 mt at 45 6 fe in the beishan terrane is diabase hosted and consists of the cihai cinan and cixi ore clusters ore minerals are dominantly magnetite pyrite and pyrrhotite with minor chalcopyrite galena and sphalerite gangue minerals include pyroxene garnet hornblende and minor plagioclase biotite chlorite epidotite quartz and calcite pyrite from the cihai and cixi ore clusters has similar re os isotope compositions with 14 to 62 ppb re and 10 ppt common os pyrrhotite has 5 to 39 ppb re and 0 6 ppb common os pyrite has a mean re os model age of 262 3 5 6 ma n 13 in agreement with the isochron regression of 187os vs 187re the re os age 262 ma for the cihai fe deposit is within uncertainty in agreement with a previously reported rb sr age 268 25 ma of the hosting diabase indicating a genetic relationship between magmatism and mineralization magnetite from the cihai deposit has mg al ti v cr co ni mn zn ga and sn more elevated than that of typical skarn deposits but both v and ti contents lower than that of magmatic fe ti v deposits magnetite from these two ore clusters at cihai has slightly different trace element concentrations magnetite from the cihai ore cluster has relatively constant trace element compositions some magnetite grains from the cixi ore cluster have higher v ti and cr than those from the cihai ore cluster the compositional variations of magnetite between the ore clusters are possibly due to different formation temperatures combined with regional tectonic evolution of the beishan terrane the re os age of pyrite and the composition of magnetite indicate that the cihai fe deposit may have derived from magmatic hydrothermal fluids related to mafic magmatism probably in an extensional rift environment

metal saturated sulfide assemblages in nwa 2737 evidence for impact related sulfur devolatilization in martian meteorites nwa 2737 a martian meteorite from the chassignite subclass contains minute amounts 0 010 0 005 vol of metal saturated fe ni sulfides these latter bear evidence of the strong shock effects documented by abundant fe nanoparticles and planar defects in northwest africa nwa 2737 olivine a ni poor troilite fe s 1 0 0 01 sometimes cr bearing up to 1 wt coexists with micrometer sized taenite tetrataenite type native ni fe alloys ni fe 1 and fe os ir ru alloys a few hundreds of nanometers across the troilite has exsolved flame like pentlandite fe fe ni 0 5 0 6 chalcopyrite is almost lacking and no pyrite has been found as a hot desert find nwa 2737 shows astonishingly fresh sulfides the composition of troilite coexisting with ni fe alloys is completely at odds with chassigny and nahkla sulfides pyrite metal deficient monoclinic type pyrrhotite it indicates strongly reducing crystallization conditions close to iw several log units below the fo2 conditions inferred from chromites compositions and accepted for chassignites fmq 1 log unit it is proposed that reduction in sulfides into base and precious metal alloys is operated via sulfur degassing which is supported by the highly resorbed and denticulated shape of sulfide blebs and their spongy textures shock related s degassing may be responsible for considerable damages in magmatic sulfide structures and sulfide assemblages with concomitant loss of magnetic properties as documented in some other martian meteorites

late paleozoic sedex deposits in south china formed in a carbonate platform at the northern margin of gondwana abstract sedex sulfide deposits hosted in black shale and carbonate are common in the south china block the dajiangping pyrite deposit is the largest of these deposits and is made up of stratiform orebodies hosted in black shales sandstone interlayered with stratiform orebodies contains detrital zircon grains with the youngest ages of 429 ma pyrite from the orebodies has a re os isochron age of 389 62 ma indicative of formation of the hosting strata and syngenetic pyrite ores in the mid late devonian the hosting strata is a transgression sequence in a passive margin and composed of carbonaceous limestone in the lower part and black shales in the upper part the ore hosting black shales have high toc total organic carbon mo as pb zn and cd indicating an anoxic euxinic deep basin origin the high redox proxies v v ni 0 6 and v cr 1 and the positive correlations of toc with mo and v in black shales are also consistent with an anoxic depositional environment the dajiangping deposit is located close to the ne trending wuchuan sihui fault which was active during the devonian the mid late devonian mineralization age and the anoxic euxinic deep basinal condition of this deposit thus imply that the formation of this deposit was causally linked to hydrothermal fluid exhalation in an anoxic fault bounded basin that developed in a carbonate platform of the south china block the regional distribution of many devonian stratiform carbonaceous sediment hosted sulfide deposits along the ne trending fault bounded basins in south china similar to the dajiangping deposit indicates that these deposits formed at a basin developed in the passive margin setting of the south china block during the devonian this environment was caused by the break up and northward migration of the south china block from gandwana

rhenium osmium isotope systematics of an early mesoproterozoic sedex polymetallic pyrite deposit in the north china craton implications for geological significance and the marine osmium isotopic record abstract the rhenium osmium re os isotopic system preserved in ancient seafloor hydrothermal sulfide deposits can be used to gain insight into the os composition of ancient seawater in particular the age of sedimentary exhalative sedex deposits can be determined by measuring re os isotopes in syn depositional pyrite a common constituent of sedex deposits here we report on the gaobanhe sediment hosted polymetallic pyrite deposit which is hosted within the gaoyuzhuang formation in the central part of the northern margin of the north china craton ncc re os isotopic data from syn depositional pyrite yield an isochron age of 1505 55 ma constraining the timing of primary mineralization as well as the minimum age of the host sediments to the mesoproterozoic analyzed pyrite grains indicate an initial 187os 188os osi value of 0 181 0 066 suggesting that the mineralizing fluids were an admixture of seawater and submarine hydrothermal fluids with the os being primarily derived from seawater the osi value is slightly higher than that of paleoproterozoic seawater 0 13 suggesting that there was a radiogenic riverine flux to the oceans and that atmospheric oxygen must have been sufficiently high at that time to drive this increased continental radiogenic os input to the oceans we propose that the re os isotopic system as recorded by these sedex deposits may provide key insights when examining changes in the os isotopic composition of seawater throughout the precambrian

petrography mineral chemistry fluid inclusion microthermometry and re os geochronology of the kure volcanogenic massive sulfide deposit central pontides northern turkey the re os isotopic system is applied for the first time to the sulfide ores and the overlying black shales at the kure volcanogenic massive sulfide deposit of the central pontides northern turkey the ore samples collected include predominantly pyrite accompanied by chalcopyrite sphalerite and other species massive ore is almost free of gangues whereas the stockwork ore includes quartz and calcite gangue the composition of sphalerite is similar to ancient and modern massive sulfide mineralizations globally microthermometric studies from quartz from the stockwork ore has shown two populations of two phase fluid inclusions with vapor liquid ratios between 4 to 28 low to intermediate th 161 5 317 0 c and low salinities 0 9 5 wt nacl equiv which are mostly in good agreement with the ranges for volcanogenic massive sulfide mineralizations these studies also suggest a h2o cacl2 kcl mgcl2 ore forming fluid system in a shallower subsurface near the seafloor vents the re os dating of the llhr sulfides yield a nominal depositional age of upper toarcian for the massive sulfide mineralization two largely different model ages obtained are attributed to other pyrite crystallization events prior to and postdating the main sulfide deposition some lower homogenization temperatures 200 c from the quartz of the stockwork may also similarly be related to the post vms events it is concluded that a submarine volcanic extrusion episode has continued until upper toarcian in the kure basin when it has entered a stagnation period that allowed the discharge of hydrothermally circulated sulfide laden fluids from the seafloor vents this age data promotes the palaeotectonic models interpreting the kure basin as a permian early jurassic marginal back arc basin of the devonian triassic karakaya ocean the re os data from the overlying black shale provide a glimpse to the initial os isotope ratio of the water column at the time of the sedimentation 0 45 0 46 for 180 ma the lack of common os from the sulfides does not let us to infer a source of os and initial 187os 188os ratios from the black shale are not statistically robust to make a significant deduction a further detailed study on the isotopic composition of the black shale strata may help us to make an apporach to the os source s in the deposition environment of the kure vms deposit

re os isotope systematics of ni cu sulfide ores sudbury igneous complex ontario evidence for a major crustal component sudbury igneous complex sublayer ores from the levack west falconbridge and strathcona mines were analyzed for their re and os concentrations and os isotopic compositions the re os isotope systematics of three ores from the different mines give isochron ages of1 840 60 ma 1770 60 ma and 1780 110 ma suggesting that the re os system became closed at the time of or soon after the 1850 1 ma crystallization age of the complex the os isotopic compositions of different portions of the complex at the time of crystallization varied considerably with initial187os 186os1850 ranging from 4 64 at levack west to 7 55 at strathcona these heterogeneities require that the os and probably also the other platinum group elements contained in the ores were derived from at least two sources in addition the high initial187os 186os ratios indicate that the os was derived predominantly from ancient crust previous studies have suggested that the complex either crystallized from a mixture of mantle derived basaltic melt and ancient continental crust or was derived exclusively from the fusion of ancient continental crust resulting from a meteorite impact results of modelling suggest that if a contemporaneous mantle derived basaltic melt was involved in the origin of the sic it likely contributed 50 of the os to all three ores the large percentage of ancient crust involved in the production of the ores is most consistent with an interpretation of substantial crustal fusion resulting from meteorite impact

dynamical consequences on fast subducting slabs from a self regulating mechanism due to viscous heating in variable viscosity convection the authors have studied 2 d time dependent convection for a rheology which is both non newtonian and temperature dependent strong effects associated with viscous heating are found in the downwelling sheets which are heated on both sides with an intensity around o 10 sup 2 times the chondritic value the magnitude of viscous heating increases strongly with the subduction speed the slab interior is weakened by viscous heating and slab breakoff then takes place this process provides a self regulating mechanism for governing the speed of intact slabs able to reach the deep mantle timescales associated with viscous heating are quite short a few million years internal heating by radioactivity decreases the amount of shear heating 13 refs 5 figs

diffusion in carbonates fluorite sulfide minerals and diamond this chapter focuses on diffusion in non silicate minerals that do not fall under any of the other chapter categories this includes minerals that are not oxides fluorite sulfide minerals diamond and those like the carbonates that are not among the oxide minerals discussed in chapter 17 of this volume van orman and crispin 2010 although there are numerous minerals in these categories limited diffusion data exist for many of them so the primary phases that will be considered are carbonates fluorite diamond and sulfide minerals carbonate minerals are major constituents of sediments and many sedimentary rocks fractionation of o and c isotopes between carbonate rocks and fluids can provide insight into paleoclimates and sedimentary histories the behavior of the isotopes of major elements in calcite and aragonite has become of increasing interest due to the important role of co2 and carbonate dissolution precipitation in the oceans and the connections to global climate e g arita and wada 1990 chacko et al 1991 dickson 1991 beck et al 1992 cole 1992 graham et al 1998 cole and chakraborty 2001 ca mg diffusion rates affect the process of dolomitization hardie 1987 fisler and cygan 1999 and characterization of diffusion of these species is important for refinements in application of the calcite dolomite geothermometer e g essene 1982 farver and yund 1996 and better understanding of deformation mechanisms for example calcium isotopic fractionation between seawater and calcite and aragonite has been observed in marine samples zhu and macdougall 1998 de la rocha and depaolo 2000 schmitt et al 2003 with possible applications as a thermometer ca isotopic fractionation also occurs in biologic systems as in the growth of foraminifera skulan et al 1997 zhu and macdougall 1998 diffusion of major elemental species plays an important rate limiting

an overview of chalcophile element contents of pyrrhotite pentlandite chalcopyrite and pyrite from magmatic ni cu pge sulfide deposits we have compiled the trace element concentrations in pyrrhotite pentlandite chalcopyrite and pyrite from magmatic ni cu pge ore deposits with the aim of understanding their petrogenesis and whether these minerals can be used as indicator minerals among the samples there are some of the most studied world class ni cu aguablanca duluth jinchuan noril sk talnakh kharaelakh sudbury voisey s bay and others and pge dominated bushveld lac des iles stillwater great dyke and penikat deposits crustal assimilation may be constrained using as se and sb se ratios in pentlandite the degree of interaction between the silicate and sulfide liquids r factor can be estimated by the content of highly chalcophile elements dsulf liq sil liq above 1000 in sulfide minerals the fractional crystallization of the sulfide liquid can be traced using se te ratios of pentlandite pyrite formed by exsolution from mss has higher rh ru ir and os than co existing pyrrhotite whereas pyrite formed by hydrothermal alteration of pyrrhotite inherits the rh ru ir and os contents of the pyrrhotite it replaced sulfide minerals are preserved in transported glacial cover and their trace element chemistry can be used to discriminate their source pentlandite from ni cu deposits has much lower rh and pd concentrations than those from pge dominated deposits pyrite from magmatic deposits has higher co sb and se as ratios relative to pyrite from hydrothermal deposits and chalcopyrite from magmatic deposits has much higher ni and lower cd concentrations than those from hydrothermal deposits

variable initial pb isotopic compositions of rocks associated with the ug2 chromitite eastern bushveld complex abstract an investigation of the pb isotopic compositions of plagioclase and sulfide in a stratigraphic interval including the ug2 chromitite of the eastern bushveld complex has been conducted to determine the pb isotopic composition s of the magma s that crystallized to form this part of the intrusion gain a better understanding of why coexisting plagioclase and sulfide commonly exhibit widely different pb isotopic compositions and explore the use of pb isotopes in deducing post accumulation history analyses were obtained in situ with a nuplasma multicollector icp ms coupled with 193 nm excimer or 213 nm lasers most plagioclase compositions fall on the 207pb 204pb vs 206pb 204pb geochron of 2 06 ga which is the solidification age of the intrusion the measured ratios have not been affected by radiogenic ingrowth and plagioclase generally remained closed to pb exchange after initial cooling the array of plagioclase compositions on the geochron is significantly larger than that defined by analytical error this indicates that in terms of pb at least two different magma compositions were present the composition of the least radiogenic magma was approximated by that of the contemporaneous bse with 238u 204pb and 232th 204pb values of 9 0 and 35 respectively suggesting a mantle derivation with little or no involvement of the continental crust while the second magma possessed a pb isotopic composition similar to the upper crust with 9 6 compared to plagioclase sulfides generally possess slightly higher 206pb 204pb ratios for equivalent 207pb 204pb ratios such that their compositions fall between the 2 06 and 1 86 ga geochrons the latter age is much younger than the cooling age the data are interpreted to mean that the bushveld complex remained buried in the crust at temperatures of several hundred c for about 200 ma after solidification and that any sulfides accessible to fluid continued to re equilibrated during this time with more radiogenic pb the sulfide pb may have been transported into the bushveld complex by fluids from an external reservoir when the rocks were still partially molten and thus permeable alternatively the sulfide pb may have originated mainly from radiogenic decay of u and th present in minerals other than the sulfides in the immediately surrounding bushveld rocks followed by local redistribution of pb by whatever fluid was present indeed some sulfides are characterized by 208pb 204pb ratios sufficiently high that an external source is unlikely this observation and the fact that the sulfides display small scale heterogeneity suggest that most if not all of the radiogenic sulfide pb was locally derived it also implies that during the post solidification re equilibration period there was no large scale fluid flow through the microfracture network because otherwise the isotopic heterogeneities would not have been preserved the minerals in 2 of the 19 samples studied contain young pb presumably introduced by meteoric waters that permeated the macrofracture network

on the relation between seismic anisotropy and finite strain because seismic anisotropy in the upper mantle is due primarily to lattice preferred orientation lpo of olivine crystals induced by deformation observations of anisotropy can provide constraints on mantle deformation and flow in this paper we use a previously published theory for deformation induced lpo ribe and yu 1991 to quantify the relation between seismic anisotropy and deformation for two model compositions a pure olivine dunite aggregate and a harzburgite comprising 70 olivine and 30 enstatite analytical and numerical solutions of the governing equations show that the predicted lpo and hence also the seismic anisotropy depends only on the finite strain and not on the deformation path by which that strain is produced the magnitude of the anisotropy depends only on the ratios c1 c2 and c2 c3 where c1 c2 c3 are the lengths of the principle axes of the finite strain ellipsoid and the directions of maximum and minimum compressional wave velocity vp coincide with the axes c1 and c3 respectively we calculate the percent anisotropies for compresional and shear waves propagating along the three principle axes of the finite strain ellipsoid as functions of the axial ratios c1 c2 and c2 c3 for our two model compositions however inferences of the magnitude of finite strain obtained using these results are likely to be minimum estimates because our theory neglects the effects of dynamic recrystallization finally we present as a byproduct of this study a new direct method for calculating the finite strain produced by an arbitiary deformation history

constraints on the timing of late eburnean metamorphism gold mineralisation and regional exhumation at damang mine ghana the damang gold deposit in southwest ghana is unique among known deposits in ghana comprising gold mineralisation in two distinct styles early gold hosted in a stratigraphically controlled auriferous quartz pebble conglomerate horizon is overprinted by later gold mineralisation contained in a sub horizontal fault fracture quartz vein array a multi system geochronological study is used to constrain the timing of igneous activity regional metamorphism gold mineralisation and the thermal history at damang u pb analysis of zircons from birimian volcaniclastic and intrusive rocks constrain volcanism and associated intrusive activity at 2178 0 9 3 ma and 2164 6 8 0 ma respectively which is consistent with previous studies the age of formation of staurolite grade amphibolite facies peak metamorphic mineral assemblages at 2005 26 ma is provided by u th total pb epma analysis of metamorphic monazite grains in the tarkwa phyllite measured 40ar 39ar biotite ages range between 1980 9 ma and 1898 11 ma argon diffusion modelling with the programme diffarg suggests that this age range could be achieved by a period of rapid cooling at a rate of approximately 17 c ma followed by a prolonged period of much slower cooling at a rate of 0 15 c ma the period of rapid cooling is interpreted to represent localised exhumation of the damang host rocks during the latest stage of the eburnean orogeny at the time of hydrothermal gold mineralisation given these age constraints hydrothermal gold mineralisation is inferred to have occurred between approximately 2030 ma and 1980 ma these ages constrain metamorphism fluid flow and gold mineralisation at damang and are the youngest currently recognised in the birimian of sw ghana

re os geochronology of the iimori besshi type massive sulfide deposit in the sanbagawa metamorphic belt japan abstract besshi type cu deposits are strata bound volcanogenic massive sulfide deposits usually associated with mafic volcanic rocks or their metamorphic equivalents although there are numerous besshi type deposits in the sanbagawa metamorphic belt japan their tectonic settings and depositional environments remain controversial because of a lack of depositional age constraints we report re os data for the iimori deposit one of the largest besshi type deposits in western kii peninsula in order to examine the robustness of the re os isotope system for dating sulfide minerals in the high p t metamorphic belt and to elucidate the primary depositional environment of the iimori sulfide ores an 11 point re os isochron plot yields an age of 156 8 3 6 ma as this re os isochron age is significantly older than the timing of the sanbagawa peak metamorphism 110 120 or 90 ma and a well defined isochron was obtained the re os age determined here is most likely the primary depositional age despite high grade metamorphism at up to 520 25 c and 8 9 5 kbar the re os isotope system of the iimori sulfides was not disturbed hence we consider that the whole rock re os closure temperature for the iimori sulfide ores was probably higher than 500 c as the accretion age of the sanbagawa metamorphic belt is considered to be 120 130 or 65 90 ma on the basis of radiolarian and radiometric ages we estimated the time from the iimori sulfide deposition on the paleo seafloor to its accretion at the convergent plate boundary to be greater than 25 myr consequently the depositional environment of the iimori sulfide ores was not in the marginal sea but was truly pelagic

jarosite and hematite at meridiani planum from opportunity s mossbauer spectrometer mossbauer spectra measured by the opportunity rover revealed four mineralogical components in meridiani planum at eagle crater jarosite and hematite rich outcrop hematite rich soil olivine bearing basaltic soil and a pyroxene bearing basaltic rock bounce rock spherules interpreted to be concretions are hematite rich and dispersed throughout the outcrop hematitic soils both within and outside eagle crater are dominated by spherules and their fragments olivine bearing basaltic soil is present throughout the region bounce rock is probably an impact erratic because jarosite is a hydroxide sulfate mineral its presence at meridiani planum is mineralogical evidence for aqueous processes on mars probably under acid sulfate conditions

chalcophile siderophile element systematics of hydrothermal pyrite from martian regolith breccia nwa 7533 unlike other martian meteorites studied so far martian regolith breccia nwa 7533 and 56 paired meteorites that have sampled 4 4 ga old impact lithologies show only sulfides of 57 hydrothermal origin mostly pyrite 1 the reasonably good positive correlation r 2 0 72 between se and 65 ni reflects a temperature control on the solubility of both elements apart from the chalcogens s se 66 and te pyrite appears to be a minor contributor 400 c temperature crystallization for nwa 7533 pyrite as deduced from 69 its se and ni contents ii magmatic sulfide depletion of brecciated early martian crust iii 70 precipitation from near neutral h 2 s hs h 2 o rich hydrothermal fluids that did not provide halogen 71 ligands for extensive transport of chalcophile siderophile metals it is suggested that the 1 4 ga 72 lithification event that precipitated hydrothermal pyrite left the chalcophile siderophile element 73 budget of the early martian crust nearly unmodified except for s se and te 74 75 76

pyrite re os isotope systematics at the zijinshan deposit of sw fujian china constraints on the timing and source of cu au mineralization abstract zijinshan is the largest high sulfidation epithermal cu au deposit on mainland china the primary mineralization at the deposit is characterized by pyrite digenite and covellite although some rb sr isochron ages of the fluid inclusions in quartz and the apparent k ar age of the cu bearing alunite alteration zone have been previously interpreted as the ore forming age the rb sr and k ar dating systems are usually readily reset due to their closure temperature and thus document the latest thermal event in order to precisely determine the age of the cu mineralization eight pyrite separates were re os dated and seven yielded an isochron age of 103 4 ma with an initial 187 os 188 os ratio of 0 45 0 14 this date is interpreted as the age of cu mineralization which is in agreement with geochronological data from molybdenite and the porphyritic granodiorite that hosts cu mo mineralization at luoboling located 2 km ne of zijinshan suggesting that these two deposits were formed during the same metallogenic event the relatively low initial 187 os 188 os ratio indicates that the source of the cu at zijinshan is predominantly the crust with input from the mantle

significance of late devonian lower carboniferous ages of hydrothermal sulphides and sericites from the urals volcanic hosted massive sulphide deposits abstract formation of the urals volcanic hosted massive sulphide vhms deposits is considered to be related with the intra oceanic stage of the island arc s development in late ordovician middle devonian time ca 460 385 ma based on the biostratigraphic record of ore hosting sedimentary rocks however the known radiometric ages of ore hosting volcanics are very limited here we present direct dating results of sulphide mineralisation from the yaman kasy and kul yurt tau vhms deposits using re os isotope systematics showing similar mineralisation ages of 362 9 ma and 363 1 ma these ages coincide with the previous re os dating of the alexandrinskoe 355 15 ma and dergamysh 366 2 ma vhms deposits this late devonian famennian age corresponds to the late stage of the magnitogorsk arc laurussia continent collision event and coincides with a beginning of large scale subduction related granitoid magmatism the younger mineralisation age relative to the biostratigraphic ages of host rocks is interpreted as one of the latest episodes of the multi stage history of vhms deposits development ar ar ages of sericites from metasomatic rocks of barsuchi log and babaryk deposits show even younger ages clustering around 345 ma and testify another late hydrothermal event in the history of the urals vhms deposits

metamorphism disturbs the re os signatures of platinum group minerals in ophiolite chromitites the os isotope compositions of platinum group minerals pgms in ophiolite chromitites are commonly regarded as resistant to fluid related processes and have been used to track the evolution of earth s convecting mantle however we have found significant differences in 187os 188os between primary and secondary pgms from metamorphosed ophiolite chromitites of the dobromirtsi ultramafic massif in the central rhodope metamorphic core complex of southeastern bulgaria primary magmatic pgms hosted in unaltered chromite cores have 187os 188os from 0 1231 to 0 1270 and 187re 188os 0 002 t ma and t rd model ages calculated relative to the enstatite chondrite reservoir cluster around three main peaks ca 0 3 0 4 and 0 6 ga secondary pgms produced by alteration of magmatic pgms have a wider range of variation 187os 188os 0 1124 0 1398 187re 188os 0 024 these grains yield t ma and t rd model ages from 1 7 ga up to 2 2 ga the larger range in 187os 188os in the secondary pgms is interpreted as due to reactions between the primary pgms and infiltrating metamorphic hydrothermal fluids with a range of os isotope compositions this redistribution of os in pgms during metamorphism has significant implications for the interpretation of both whole rock and in situ os isotope data in mantle derived rocks

s process os isotope enrichment in ureilites by planetary processing abstract ubiquitous nucleosynthetic isotope anomalies relative to the terrestrial isotopic composition in mo ru and other elements are known from both bulk chondrites and differentiated meteorites but os isotope ratios reported from such meteorites have been found to be indistinguishable from the terrestrial value the carriers of s and r process os must thus have been homogeneously distributed in the solar nebula as large os isotope anomalies are known from acid leachates and residues of primitive chondrites the constant relative proportions of presolar s and r process carriers in such chondrites must have been maintained during nebular processes it has long been assumed that partial melting of primitive chondrites would homogenize the isotopic heterogeneity carried by presolar grains here ureilites carbon rich ultramafic achondrites dominantly composed of olivine and low ca pyroxene are shown to be the first differentiated bulk solar system materials for which nucleosynthetic os isotope anomalies have been identified these anomalies consist of enrichment in s process os heterogeneously distributed in different ureilites given the observed homogeneity of os isotopes in all types of primitive chondrites this os isotope variability among ureilites must have been caused by selective removal of s process poor os host phases probably metal during rapid localized melting on the ureilite parent body while mo and ru isotope anomalies for all meteorites measured so far exhibit s process deficits relative to the earth the opposite holds for the os isotope anomalies in ureilites reported here this might indicate that the earth preferentially accreted olivine rich restites and inherited a s process excess relative to smaller meteorite bodies consistent with earth s high mg si ratio and enrichment of s process nuclides in mo ru and nd isotopes our new os isotope results imply that caution must be used when applying nucleosynthetic isotope anomalies as provenance indicators between different classes of meteorites

constraints on the genesis of gold mineralization at the homestake gold deposit black hills south dakota from rhenium osmium sulfide geochronology the homestake gold deposit located in the black hills south dakota usa is one of the largest known hydrothermal gold deposits globally with total mining production exceeding 40 moz au rhenium osmium geochronology of ore associated arsenopyrite and pyrrhotite was performed in an effort to delineate the timing of gold mineralization in relation to known tectonothermal events in the northern black hills arsenopyrite yields a rhenium osmium re os age of 1 736 8 ma mean squared weighted deviation 1 6 consistent with existing age constraints for gold mineralization whereas re os pyrrhotite data are highly scattered and do not yield a meaningful mineralization age this is taken to indicate that the re os arsenopyrite chronometer is robust to at least 400 c whereas the re os pyrrhotite chronometer is likely disturbed by temperatures of 300 350 c the re os arsenopyrite age and initial os ratio 0 28 0 15 are interpreted to indicate that gold was introduced at ca 1 730 ma coincident with the onset of exhumation of crustal blocks and possibly the earliest intrusive phases of harney peak granite magmatism new in situ u pb monazite analyses from an aplite dike in the east central black hills indicate that granite magmatism was a protracted event persisting until at least ca 1 690 ma

the early formation of the iva iron meteorite parent body the iva iron meteorites are magmatic cumulates from the core of a small asteroid which broke apart similar to 400 ma ago as the depletion of this planetary body in volatile elements is expected to be reflected in high u pb ratios of its minerals we embarked on analyzing the isotope composition of pb in the cm sized troilite inclusions of muonionalusta and gibeon both iron meteorites belonging to the iva family the bulk of the data for nine troilite subsamples of muonionalusta scatter with an apparent age of 4 57 ga which is shown to reflect the presence of both primordial and common terrestrial pb components in addition to radiogenic pb the most radiogenic subsample however has fractions with pb 206 pb 204 ratios as high as over 1000 and gives a statistically significant 207 pb pb 206 age of 4565 3 0 1 ma mswd 0 08 consistent with the hf 182 w 182 metal silicate segregation age of 2 4 2 0 ma these data make the age of muonionalusta the oldest documented yet for all differentiated bodies in the solar system and constitute the first high precision pb pb age determined for crystallization of a phase contained within an iron meteorite group hence advancing our understanding of early solar system chronology using literature values for the cooling rate and assuming a closure temperature for pb of 300 degrees c it is further estimated that the iva parent body accreted within 1 ma of cai formation and had cooled to the pb closure temperature within an additional 1 2 ma the overlap between the high precision pb pb and hf w ages points to a small or rapidly fragmented planetary body the isotopic composition of pb in gibeon troilite yields a significantly younger age of 4544 7 ma mswd 1 5 consistent with evidence from the pd 107 ag 107 chronometer but we believe this age has been reset by melting upon shock one puzzling observation is that the apparent th 232 u 238 of muonionalusta troilite is particularly low similar to 0 32 requiring a mechanism capable of efficiently fractionating th from u presumably the reduction of u to its trivalent form or the crystallization of phosphate average pb concentrations of the order of 5 10 ppb and high u 238 pb 204 ratios of 1000 require u concentrations in troilite in the sub ppb to one ppb range this may indicate that troilite inclusions in iva meteorites do not represent metal sulfide unmixing but rather correspond to late stage s rich liquid residues from extreme crystallization of the interstitial melts

re os and u pb constraints on gold mineralisation events in the meso to neoarchaean storo greenstone belt storo southern west greenland the storo greenstone belt in godthabsfjord southern west greenland consists of juxtaposed rock units of different age and origin and hosts gold mineralisation that is associated with arsenopyrite along a contact between lithological units and along the axial plane of a large fold core the age and origin of the gold is debatable but in this paper we present new arsenopyrite re os and zircon u pb data to constrain the age of the storo gold deposit a 2 71 0 05 ga arsenopyrite isochron and 2 707 0 008 ga highly radiogenic arsenopyrite from a mineralisation along a rock contact together with a 2 64 0 02 ga arsenopyrite isochron along the axial plane of the fold core indicate a two stage mineralisation process while the 2 707 0 008 ga highly radiogenic arsenopyrite provides firm support for an early mineralisation event a mixing origin cannot yet be excluded for the 2 71 0 05 ga isochron the 2 64 0 02 ga isochron is in perfect agreement with recent u pb zircon data nutman et al 2007 precambrian research 159 19 32 and these data are best explained by orogenic mineralisation during amphibolite facies metamorphism along structural weak planes the initial os 187 os 188 value of 0 56 0 16 for the 2 64 0 02 ga isochron indicates a crustal source for the metals whereas the initial os 187 os 188 0 1 0 6 for the 2 71 0 05 ga isochron remains unconstrained re os data are best explained by relatively short crustal residence times of less than 0 1 ga wherein the os and associated metals were extracted from the mantle at a time younger than 2 8 ga and in which the 2 64 0 02 ga stage formed by mobilisation of an earlier mineralisation detrital zircon constraints imply volcanism and sediment deposition for parts of the belt at 2 84 ga and that these units were tectonically juxtaposed to similar to 3 05 ga rocks within the belt the units that were deposited 2 84 ga record metamorphic zircon u pb ages of similar to 2 63 ga but evidence for 2 72 ga metamorphism which is ubiquitous in adjacent terranes is lacking c 2012 elsevier b v all rights reserved

high cu concentrations in vapor type fluid inclusions an artifact abstract studies of natural fluid inclusions have shown that cu commonly occurs at higher concentrations in vapor type inclusions than in coexisting brine inclusions a phenomenon which has been interpreted to arise from copper partitioning into the vapor phase in the first part of this study we attempted to experimentally reproduce this behavior in hydrothermal experiments covering a range of p t conditions 600 800 c 70 130 mpa fluid compositions nacl kcl fecl 2 0 5 6 6 wt s fluid acidities quench fluid ph 0 3 10 and sulfur speciation h 2 s dominated to so 2 dominated however as in several other studies we did not succeed in reproducing conditions under which cu partitions into the vapor phase in view of recent observations that quartz hosted fluid inclusions can diffusively loose or gain cu after entrapment we set out to determine if the evidence from natural fluid inclusions could be compromised for this purpose we synthesized vapor and brine inclusions from cu h 2 o nacl s fluids at 800 c 130 mpa and re equilibrated them in slightly different fluids at 800 c 70 mpa measuring some inclusions by la icp ms after each step vapor inclusions indeed experienced a dramatic increase in cu from 0 3 0 03 to 5 7 3 3 wt while brine inclusions remained largely unmodified leading to a change in the partition coefficient d cu vap brine from a true value i e before re equilibration of 0 4 0 05 to an apparent value of 8 3 4 9 the requirements for substantial diffusional gain of cu in fluid inclusions are a change in the ph of the surrounding fluid from 1 to more neutral and the presence of s in the pre existing fluid inclusions these requirements are also fulfilled in nature cooling magmatic hydrothermal fluids experience a change from acidic to more neutral ph due to buffering along the feldspar mica join and natural vapor inclusions typically contain significant amounts of sulfur a reversal experiment performed on natural quartz hosted fluid inclusions from the erongo granite namibia showed that this process can be reversed with the measured d cu vap brine value of 11 9 3 being modified to 0 06 0 04 thus d cu vap brine values 1 measured on natural fluid inclusions in quartz are likely a secondary feature caused by post entrapment copper diffusion realistic d cu vap brine values in porphyry cu environments are between 0 11 and 0 15 and reconstructed vapor brine mass ratios are in the order of 4 9 this suggests that the main transporting agent of cu at the porphyry level are brines and that models based on copper into the vapor phase are incorrect

an early cretaceous carbonate replacement origin for the xinqiao stratabound massive sulfide deposit middle lower yangtze metallogenic belt china stratabound massive sulfide deposits are widespread along the middle lower yangtze metallogenic belt mlymb and serve as an important copper producer in china two contrasting genetic models have been proposed interpreting the stratabound massive sulfide deposits as a carboniferous sedex protore overprinted by cretaceous magmatic hydrothermal system or an early cretaceous carbonate replacement deposit these two contrasting models have been applied to the xinqiao stratabound cu au sulfide deposit which is dominated by massive sulfide ores hosted in marine carbonates of the carboniferous chuanshan and huanglong formations with minor cu au skarn ores localized in the contact zone between the cretaceous diorite jitou stock and the carboniferous carbonate rocks new sims zircon u pb dating suggests that the jitou stock formed at 138 5 1 1 ma 2 mswd 0 6 pyrite re os dating yields an imprecise date of 142 47 ma 2 mswd 7 8 the geochronological data thus constrain the mineralization of the xinqiao deposit at early cretaceous fluid inclusions in prograde skarn diopside have homogenization temperatures of 450 600 c and calculated salinities of 13 58 wt nacl equiv quartz from the stratabound ores and pyrite quartz vein networks beneath the stratabound ores have homogenization temperatures of 290 360 and 200 300 c with calculated salinities of 5 12 and 2 10 wt nacl equiv respectively quartz from the skarn ores and veins beneath the stratabound ores have 18o values of 12 32 0 55 2 sd n 22 and 15 57 1 92 2 sd n 60 respectively corresponding to calculated 18o values of 6 22 1 59 2 and 6 81 2 76 2 for the equilibrated ore forming fluids the fluid inclusion and oxygen isotope data thus support a magmatic hydrothermal origin rather than a sedex system for the stratabound ores with the hydrothermal fluids most likely being derived from the jitou stock or associated concealed intrusion results from this study have broad implications for the genesis and exploration of other stratabound massive sulfide deposits along the mlymb

late cretaceous metallogeny in the zhongdian area constraints from re os dating of molybdenite and pyrrhotite from the hongshan cu deposit yunnan china abstract the zhongdian area in yunnan southwestern china located at the southern end of the yidun volcano magmatic arc that was formed during the triassic westward subduction of the gaze litang ocean hosts numerous triassic large porphyry and skarn deposits the arc suffered jurassic to cretaceous arc continental orogenic collision and cenozoic intracontinental strike slip shearing the hongshan cu mo pb zn deposit is potentially a large deposit and contains two ore types 1 predominant layered skarn cu pb zn ores along marble hornfels contacts and 2 minor crosscutting vein type cu mo mineralization previous research forwards a two stage genetic model without sufficient dating evidence supposing the skarn mineralization is related to the triassic calc alkalic intrusions and the vein type mineralization related to cretaceous quartz monzonite porphyries re os dating of molybdenite from vein type ores and quartz monzonite porphyries and that of pyrrhotite from skarn ores are presented here to constrain the mineralization age and rebuild the genetic model analyses of eight molybdenite samples yield an isochron age of 79 7 3 1 ma mswd 9 2 for the vein type mineralization and a model age of 81 9 1 1 ma for the quartz monzonite porphyries isotope data on seven pyrrhotite samples from the skarn ores yield an isochron age of 79 16 ma z mswd 8 4 the re os ages for the two ore types are concordant within analytical errors indicating that the hongshan deposit was formed in the late cretaceous elevated re contents in molybdenite 13 65 to 63 91 g g and extremely radiogenic initial 187 os 188 os ratios in pyrrhotite 0 7673 to 0 8184 weighted average 0 796 0 038 together with elevated os values in pyrrhotite 507 to 547 average 528 imply a significant crustal component in the ore forming materials that was likely derived from a lower crustal reservoir combined with the tectonic evolution of the zhongdian area and geochemical characteristics of corresponding intrusions the ages of mineralization obtained in this study indicate that the hongshan deposit was formed in a post collision setting with a genetic relationship to the emplacement of the quartz monzonite porphyry these results provide significant new information for the study and exploration of the late cretaceous metallogeny in the zhongdian area

an experimental study on the geochemical behavior of highly siderophile elements hse and metalloids as se sb te bi in a mss iss pyrite system at 650 c a possible magmatic origin for co hse bearing pyrite and the role of metalloid rich phases in the fractionation of hse abstract pyrite the most abundant sulfide in the earth s crust is an accessory mineral in several magmatic sulfide deposits although most pyrite is hydrothermal previous experimental studies have shown that pyrite can also have a primary magmatic origin by exsolving from monosulfide solid solution mss during cooling of a sulfide melt if sulfur fugacity is sufficiently high pyrite from some localities has significant amounts of co and complex zonation in some low melting point chalcophile elements lmce such as as se sb te bi henceforth referred to as metalloids and some platinum group elements pge ru rh pd os ir pt however the origin of such pyrite and the causes of zonation are not clear because the distribution of some of these elements is heterogeneous and seems to be developed in concentric zones the zonation has been interpreted to represent growth stages some of them secondary and caused partly by hydrothermal fluids better constraints on the origin of co pge bearing pyrite could help unravel the geochemical processes affecting the sulfide assemblages in which it is found thus an experimental study was undertaken to characterize pyrite formation in magmatic sulfide environments and its relationship with metalloids and highly siderophile elements hse pge re au natural pyrrhotite chalcopyrite pentlandite and elemental s were mixed and doped with approximately 50 ppm of each hse a mixture of metalloids was added at 0 2 wt or 3 wt to aliquots of sulfide mixtures starting materials were sealed in evacuated silica tubes and fused at 1200 c the temperature was subsequently reduced to 750 c at 60 c h then to 650 c at 0 5 c h to produce relatively large euhedral pyrite crystals then quenched the experiments were analyzed using reflected light sem epma and la icp ms experimental products contained euhedral pyrite mss intermediate solid solution iss and metalloid rich phases interpreted as quench product of an immiscible metalloid rich liquid the results show that co ni hse bearing pyrite with complex zonation in ru rh os ir and pt can form by a subsolidus reaction involving both mss and iss and does not require secondary e g hydrothermal processes because such pyrite results from the cooling of a sulfide melt after mss and iss it can be described as magmatic among the hse ru rh os re and ir have identical zonation patterns in pyrite pt is also zoned but differently and au and pd are essentially excluded previously documented natural hse bearing pyrite also display identical zonation patterns in ru rh os and ir the complex zoning is likely preserved due to the extremely slow diffusion rates for those elements in pyrite thus the presence of pyrite with similar characteristic in natural sulfide assemblages is consistent with a magmatic origin and does not require hydrothermal processes the results also show that if a metalloid rich liquid is present it will significantly sequester au pd and pt but will not affect ru rh os re and ir in the absence of metalloid rich phases au partitions strongly into iss and pd partitions preferentially into mss

re os pyrite and u pb zircon geochronology from the taldybulak levoberezhny gold deposit insight for cambrian metallogeny of the kyrgyz northern tien shan abstract the taldybulak levoberezhny gold deposit located in the eastern part of the kyrgyz northern tien shan is hosted in highly deformed precambrian schist and gneisses that have undergone intense quartz carbonate fuchsite and tourmaline alterations gold mineralization is ultimately subdivided into two stages based on the observation of alteration assemblages orebody geometries and the occurrences of au bearing minerals negative thermal ionization mass spectrometry re os isotopic analyses of five au rich pyrite samples from the early stage yielded an isochron age of 511 18 ma zircon sensitive high resolution ion microprobe u pb dating of a diorite dike sample postdating the late stage mineralization yielded a wide range of ages from 3055 to 291 ma while a weighted mean 206 pb 238 u age of 414 6 6 8 ma is believed to represent the age of dike intrusion and the upper limit on the timing of the late stage quartz tourmaline gold formation the pyrite 187 os 188 os initial ratio of 0 132 0 011 together with os values varying from 0 to 14 indicate a major mantle component for the source of os and by inference ore metals which may be linked to the ophiolite suite of the kopurelisai complex in the taldybulak levoberezhny area considering the geodynamic setting of the kyrgyz northern tien shan during the early paleozoic we suggest that cambrian mineralization of the taldybulak levoberezhny deposit can be attributed to a subduction related setting probably associated with the earliest accretion of the northern tien shan

the oxidation state of sulfur in magmatic fluids abstract sulfur compounds in volcanic gases are responsible for the global cooling after explosive eruptions and they probably controlled the early evolution of the earth s atmosphere we have therefore studied the oxidation state of sulfur in aqueous fluids under the pressure and temperature conditions and oxygen fugacities typical for magma chambers 0 5 3 kbar 650 950 c ni nio to re reo 2 buffer conditions sulfur speciation was determined by raman spectroscopy of quenched fluids trapped as inclusions in quartz our results show that sulfur in hydrothermal fluids and volcanic gases is much more oxidized than previously thought and in particular some explosive eruptions may release a significant fraction of sulfur as so 3 or its hydrated forms in the pressure range from 500 to 2000 bar the equilibrium constant k 1 of the reaction 2h 2 s 3o 2 2so 2 2h 2 o in aqueous fluids can be described by lnk 1 57 1 7 1 173 480 7592 t 1 where t is temperature in kelvin the equilibrium constant k 2 for the reaction so 2 o 2 so 3 in aqueous fluids where so 3 may include hydrated forms such as h 2 so 4 was found to be strongly pressure dependent with lnk 2 5 2 5 7 19 243 5993 t 1 at 1500 bar lnk 2 11 1 1 3 25 383 1371 t 1 at 2000 bar and lnk 2 22 1 2 2 37 082 2248 t 1 at 2500 bar our data imply that volcanoes may directly inject hexavalent sulfur in the form of h 2 so 4 into the atmosphere not only on earth but possibly also on venus and on mars when it was still tectonically active remote measurements from satellites may have underestimated the sulfur yield of some recent eruptions moreover the mechanisms of the interaction of volcanic gases with the stratosphere need to be reconsidered

evidence for as contamination and the partitioning of pd into pentlandite and co platinum group elements into pyrite in the fazenda mirabela intrusion brazil the fazenda mirabela intrusion in brazil hosts two zones of mineralization the santa rita ni cu sulfide ore zone occurring predominantly in an orthopyroxenite layer and an underlying basal platinum group element pge anomaly hosted in s poor dunite we show that in the northern and southern marginal zones of the intrusion pt pd ni cu fe bi te 2 minerals are accompanied by as bearing platinum group minerals pgm sperrylite ptas2 and irarsite rhirpt ass these as bearing pgm are extremely rare in the central zone of the intrusion suggesting that as has been introduced into the margins of the intrusion from the country rocks via crustal assimilation or synmagmatic hydrothermal processes other pgm and precious metal minerals pmm including hessite ag2te pd ag tellurides electrum and native au are observed in the santa rita ore zone and do not show any lateral variation in the semimetal and s poor dunite hosting the basal pge anomaly pge are predominantly retained in the base metal sulfides and only minor pge alloys are present in this s poor dunite pt au and semimetals partitioned into a fractionated cu rich liquid which formed during the crystallization of monosulfide solid solution mss and was largely removed by high temperature magmatic fluids palladium was not affected by this process and significant concentrations of pd are identified in pentlandite suggesting that pd preferentially partitioned into mss as it crystallized and subsequently pentlandite as it exsolved pyrite in the santa rita ore zone is co rich and contains higher concentrations of ipge os ir ru and rh than pyrrhotite and pentlandite suggesting that pyrite has not replaced and inherited the pge concentrations of these sulfides the pd poor nature of pyrite also indicates that it has not replaced pd rich pentlandite it is proposed that the ipge and co preferentially partitioned into pyrite as it exsolved from mss

comparison of mixing properties in convection with the particle line method spatial resolution in mixing processes is an acute problem we propose a line method akin to the contour dynamics technique which is an extension of the particle method but with the particles redistributed on the line with time we have used up to 10 5 particles per line and ten lines to investigate the dynamical and structural properties of mixing for both newtonian and non newtonian temper ature dependent viscosity convection in 2d geometry the spatial structures and the time history of the lines formed in newtonian convection are dierent from those produced in non newtonian convection which has the tendency for producing long living horizontal structures ecient mixing in the upper mantle would be inhibited by non newtonian rheology

dynamical consequences of depth dependent thermal expansivity and viscosity on mantle circulations and thermal structure the effects of both depth dependent thermal expansivity and depth dependent viscosity on mantle convection have been examined with two dimensional finite element simulations in aspect ratio ten boxes surface rayleigh numbers between 107 and 6 107 have been considered the effects of depth dependent properties acting singly or in concert are to produce large scale circulations with a few major upwellings the interior of the mantle is cooled by the many cold instabilities which are slowed down and eventually swept about by the large scale circulation the interior temperature of the mantle can be influenced by the trade off between depth dependent properties and internal heating for chondritic abundance of internal heating and depth dependent thermal expansivity the viscosity increase across the mantle can be no greater than a factor of around ten in order to keep the lower mantle adiabatic the thermal contrasts between the cold blobs and the surrounding mantle are strongly reduced by depth dependent properties whereas the lateral differences between the hot upwelling and the ambient lower mantle can be significant over several hundred degrees depth dependent properties also encourage the formation of a stronger mean flow in the upper mantle which may be important for promoting long term polar motions

geology geochronology and s pb os geochemistry of the alastuo gold deposit west tianshan nw china the alastuo gold deposit located in the narati region of the chinese west tianshan is a newly discovered gold deposit within the world class tianshan gold belt the gold mineralization is hosted by an early carboniferous granodiorite intrusion and controlled structurally by subsidiary faults of the transcrustal north narati fault the deposit consists of auriferous alteration assemblages and minor vein ores field relations and petrographic data suggest four stages of mineralization with gold precipitated coevally with quartz chlorite epidote pyrite and galena during the second and third stages that are characterized by tectonic transformation from ductile shearing to brittle deformation the temperature range of gold precipitation is estimated to be 280 330 c using chlorite geothermometry ten auriferous pyrite samples yielded a well defined re os isochron age of 325 3 ma and two sericite samples yielded plateau like 40ar 39ar ages of 321 7 3 0 ma and 321 2 2 8 ma these consistent ages suggest that the gold mineralization in the narati region was emplaced in a transitional regime from subduction to continental collision between the tarim block and middle tianshan terrane 325 310 ma rather than during the post collisional stage as in most part of the tianshan gold belt gold bearing pyrite has an initial osi value of 0 7 0 1 and lead isotopes ratios of 17 897 to 18 723 for 206pb 204pb 15 474 to 15 643 for 207pb 204pb and 37 522 to 38 299 for 208pb 204pb while samples of pyrite galena and sphalerite have 34sv cdt of 1 9 to 7 8 the isotope data suggest that the sulfur and metals are most likely derived from mixed mantle and crustal sources including metamorphic devolatilization of subducted oceanic slab and overlying sedimentary rocks the mineralization styles structural controls metal and sulfur sources and the timing of gold mineralization with respect to the orogenic event all suggest that the alastuo gold deposit represents an orogenic type deposit this newly recognized carboniferous orogenic gold mineralization event calls for a re evaluation of the gold metallogeny in the middle tianshan

evidence for mixing of re os isotopes at 2 7 ga and support of a remobilized placer model in witwatersrand sulfides and native au abstract this study analyzes re and os contents of au rich sulfides from the carbon leader tau lekoa and mponeng the vcr mponeng and tau lekoa and the black reef modder east as well as native au in the carbon leader to further investigate the detrital placer modified detrital placer and hydrothermal models for the source of au in mines from the witwatersrand an isochron plot of the results from the four locations yields an imprecise isochron age of 2381 140 ma mswd 17 and initial 187 os 188 os 0 24 0 21 isochron plots for the individual reefs also yielded ages that are younger than the deposition of the basin witwatersrand sediments samples that possess higher concentrations of os 100 ppb and low 187 re 188 os ratios to unify all of the data providing a large variation of chronologic information os mixing diagrams for both gold and sulfide minerals produce realistic mixing trends when solving os initial ratios for 2050 ma the two most probable end members for the mixing relationships are a high os concentration non radiogenic source and a low os concentration highly radiogenic source the high concentration non radiogenic os source has been measured in multiple studies and has been clearly derived from the subcontinental lithospheric mantle sclm the low concentration highly radiogenic source is debatable the measured concentrations of os in the witwatersrand ores are much greater than published os concentrations in other hydrothermal ores the data could indicate a redistribution of the detrital os signatures at 2050 ma thus a modified detrital model best explains the previously published data and this data

sulfur sources of sedimentary buckshot pyrite in the auriferous conglomerates of the mesoarchean witwatersrand and ventersdorp supergroups kaapvaal craton south africa large rounded pyrite grains 1 mm commonly referred to as buckshot pyrite grains are a characteristic feature of the auriferous conglomerates reefs in the witwatersrand and ventersdorp supergroups kaapvaal craton south africa detailed petrographic analyses of the reefs indicated that the vast majority of the buckshot pyrite grains are of reworked sedimentary origin i e that the pyrite grains originally formed in the sedimentary environment during sedimentation and diagenesis forty one of these reworked sedimentary pyrite grains from the main vaal basal kalkoenkrans beatrix and ventersdorp contact reefs were analyzed for their multiple sulfur isotope compositions 34s 33s and 36s to determine the source of the pyrite sulfur in addition five epigenetic pyrite samples pyrite formed after sedimentation and lithification from the middelvlei and the ventersdorp contact reefs were measured for comparison the 34s 33s and 36s values of all 41 reworked sedimentary pyrite grains indicate clear signatures of mass dependent and mass independent fractionation and range from 6 8 to 13 8 1 7 to 1 7 and 3 9 to 0 9 respectively in contrast the five epigenetic pyrite samples display a very limited range of 34s 33s and 36s values 0 7 to 4 0 0 3 to 0 0 and 0 3 to 0 1 respectively despite the clear signatures of mass independent sulfur isotope fractionation very few data points plot along the primary archean photochemical array suggesting a weak photolytic control over the data set instead other factors command a greater degree of influence such as pyrite paragenesis the prevailing depositional environment and non photolytic sulfur sources in relation to pyrite paragenesis reworked syngenetic sedimentary pyrite grains pyrite originally precipitated along the sediment water interface are characterized by negative 34s and 33s values suggesting open system conditions with respect to sulfate supply and the presence of microbial sulfate reducers on the contrary most reworked diagenetic sedimentary pyrite grains pyrite originally precipitated below the sediment water interface show positive 34s and negative 33s values suggesting closed system conditions negligible 33s anomalies from epigenetic pyrite suggest that the sulfur was sourced from a mass dependent or isotopically homogenous metamorphic hydrothermal fluid contrasting sulfur isotope compositions were also observed from different depositional environments namely fluvial conglomerates and marine modified fluvial conglomerates the bulk of the pyrite grains from fluvial conglomerates are characterized by a wide range of 34s values 6 2 to 4 8 and small 33s values 0 3 this signature likely represents a crustal sulfate reservoir derived from either volcanic degassing or from weathering of sulfide minerals in the hinterland reworked sedimentary pyrite grains from marine modified fluvial conglomerates share similar isotope compositions but also produce a positive 33s 34s array that overlaps with the composition of archean barite suggesting the introduction of marine sulfur these results demonstrate the presence of multiple sources of sulfur which include atmospheric crustal and marine reservoirs the prevalence of the mass dependent crustal sulfur isotope signature in fluvial conglomerates suggests that sulfate concentrations were probably much higher in terrestrial settings in comparison to marine environments which were sulfate deficient however the optimum conditions for forming terrestrial sedimentary pyrite were probably not during fluvial progradation but rather during the early phases of flooding of low angle unconformities i e during retrogradational fluvial deposition coupled in some cases with marine transgressions immediately following inflection points of maximum rate of relative sea level fall

the evolution of material surfaces in convection with variable viscosity as monitored by a characteristics based method we have studied the evolution of material surfaces in strongly time dependent convection for both newtonian and non newtonian temperature and depth dependent rheologies a spline characteristic method has been employed the method of characteristics is second order in time and fourth order in space our strategy is to employ a very dense grid for the material surface field with about 50 to 100 times more points than for the temperature field grid we have detected sharp entrainment of the surrounding material into both the ascending and descending flow structures we have observed the breakoff process involving the descending plume mixing takes place very differently for the two rheologies with time small vortical features are developed inside the newtonian plumes while unmixed islands still persist in the non newtonian flow

structurally bound s2 s1 s4 s6 in terrestrial apatite the redox evolution of hydrothermal fluids at the phillips mine new york usa abstract the oxidation state of sulfur s plays a critical role in the formation of igneous and hydrothermal mineral systems constraining the oxidation state of s during mineralization and alteration is a valuable tool for understanding primary versus secondary processes that affect mineral systems recent experimental studies demonstrate that apatite which is a ubiquitous accessory mineral in igneous and hydrothermal ore forming systems structurally incorporates multiple oxidation states of s i e s6 s4 s2 and that the abundance of reduced versus oxidized s in apatite is systematically related to oxygen fugacity in this study we used micro x ray absorption near edge structure xanes spectroscopy at the s k edge to measure the oxidation states of s in natural apatite from the phillips mine magnetite sulfide mineral deposit putnam county new york micro xanes transects were collected within two apatite grains starting near the edge of 1 a pyrrhotite inclusion and 2 an inclusion assemblage consisting of pyrite ferroan carbonate pyroxene and magnetite significant compositional and textural variations within the apatite were observed by electron probe micro analysis epma wavelength dispersive wds spectroscopy element mapping and cathodoluminescence cl imaging and used in combination with the xanes data to discuss the formation of the phillips mine apatite the xanes analyses reveal that apatite contains variable proportions of s6 s4 s1 and s2 with corresponding peak absorption energies of 2481 7 0 3 ev 2477 9 0 4 ev 2471 8 0 1 ev and 2469 8 0 04 ev respectively notably this marks the first observation of reduced s species s2 s1 in terrestrial apatite peak areas ratios s6 s demonstrate systematic variations in the oxidation state of s within the apatite grains elevated s6 s peak area ratios typically coincide with higher concentrations of s and rare earth elements within the apatite grains several observations including the presence of multiple oxidation states of s in apatite and monazite inclusions that record secondary fluid mediated dissolution reprecipitation of apatite indicate differences in the oxidation of s thus oxygen fugacity during primary mineralization and secondary alteration i e metasomatism we propose a model for the formation of the phillips mine apatite wherein the primary apatite grains crystallized from a reduced s bearing hydrothermal fluid characterized by a low so2 h2s ratio subsequently metasomatism of apatite in the presence of an oxidized fluid which contained an elevated so2 h2s ratio resulted in the exsolution of rare earth elements from apatite and concomitant growth of monazite and the structural incorporation of oxidized s s6 and s4 in apatite this study demonstrates that the oxidation states of s in apatite provide valuable geochemical information regarding the redox evolution of mineralized systems

preservation of re os isotope signatures in pyrite throughout low t high p eclogite facies metamorphism pyrite in lt hp eclogites from the western tianshan orogenic belt yields a re os age of 378 1 8 9 ma which is 30 70 ma older than ages previously obtained for the same rocks using the rb sr sm nd ar ar u pb and lu hf isotope systems the tianshan lt hp eclogite experienced temperatures of up to 570 c combined with pressures of up to 2 1 gpa during metamorphism these conditions are below the transition of pyrite to pyrrhotite which defines both pyrite stability and possibly its closure temperature for re os pyrite can preserve re os signatures through eclogite facies peak metamorphic conditions and thus allow determination of the formation age of pyrite in the protolith

re os isotopic systematics of the voisey s bay ni cu co magmatic ore system labrador canada abstract re and os concentrations and os isotopic compositions have been obtained for massive matrix and disseminated sulphide ores from three environments within the voisey s bay intrusion the ovoid eastern deeps and discovery hill zone in order to assess the role of crustal contamination in the genesis of this large cu ni co deposit these samples have high re concentrations 148 to 288 ppb in 100 sulphide for their common os concentrations 4 8 to 24 ppb in 100 sulphide yielding high re os ratios 12 to 33 these data confirm that the magma parental to the voisey s bay ore system was broadly basaltic in major element chemistry rather than picritic consistent with the low ni cu ratio of the ores 1 5 re os isotopic data exhibit a limited spread in 187 re 188 os 57 to 157 and define an imprecise 1323 135 ma model 3 isochron likely the result of small r factor variations within the ore system the re os isochron age is within error of 1334 ma u pb ages obtained for baddeleyite from the ore bearing troctolites demonstrating that whole rock re os isotopic systematics have remained closed since crystallisation the initial os isotopic composition of the isochron os 1040 200 implies significant magma interactions with radiogenic os that most likely resides in the nain churchill province crust these data are therefore consistent with the parental magma achieving sulphide saturation as a result of contamination by radiogenic crustal components with further addition of base and precious metals as a function of r factor analyses of sulphide separates from the proterozoic tasiuyak churchill and archaean nain gneisses confirm that both units contained significant os 8 6 ppb and 0 38 ppb respectively that was very radiogenic at 1334 ma os 1908 and 5202 respectively yielding crustal residence tchur model ages of 2200 to 2400 ma however these model ages may have been affected by re and or os mobility during the 1 85 ga torngat and 1 1 ga grenville orogeny re os isotopic modelling suggests that a reasonable fit to the ore data may be obtained via bulk crustal contamination of magmas parental to the nain plutonic suite nps with either tasiuyak 2 contamination or nain 16 contamination gneiss followed by an r factor process 200 to 1000 which improved the tenor of the sulphide liquid during transport in active magma conduits or after deposition in an active replenished voisey s bay intrusion magma chamber however the dominance of plagioclase rich high al2o3 magmas in the mafic members of the nps troctolites and anorthosites may indicate that other deeper forms of lithospheric interaction potentially involving mafic lower crust may be crucial to understanding this style of magmatic sulphide ore system

re os isotopic variations in carbonaceous pelites hosting the duluth complex implications for metamorphic and metasomatic processes associated with mafic magma chambers abstract previous mineralogic and isotopic studies of sulfide mineralization in the 1 1 ga duluth complex have suggested that sulfur and possibly metals have been derived from proterozoic sedimentary country rocks the re os isotopic system offers great potential in the evaluation of crustally derived metals in magmatic ore forming processes but an understanding of the mechanisms that could cause isotopic variations in country rock contaminants is a prerequisite a suite of sulfidic and carbonaceous pelitic rocks of the virginia formation country rock to the duluth complex ranging from unmetamorphosed through strongly recrystallized and partially melted xenoliths have been analyzed for their os isotopic composition sulfide mineral separates mainly pyrrhotite kerogen graphite isolates and whole rocks were analyzed whole rocks kerogen and graphite from metamorphosed samples plot between 1 85 ga and 1 1 ga chondritic reference isochrons sulfide separates from all metamorphosed samples plot nearer the chondritic 1 1 ga reference isochron and require exchange with a fluid or melt characterized by a chondritic os isotopic composition potentially derived from the duluth complex devolatilization and partial melting may perturb isotopic systematics when accompanied by the loss of re and os bearing fluids these processes could in part explain the scatter in isotopic values found in kerogen and metamorphosed whole rocks however metasomatic addition of os via interaction with a fluid or melt is required to explain the sulfide isotopic ratios and is consistent with sulfide minerals being more susceptible to os exchange with a fluid than kerogen the relative ease with which pyrrhotite may be reset during fluid interaction as well as the variable degrees of exchange shown by kerogen graphite suggest that a knowledge of the petrologic and isotopic evaluation of country rocks is necessary before a meaningful assessment of the isotopic variations found in igneous rocks or associated ore deposits can be undertaken

re os isotopic composition and pge contents of proterozoic carbonaceous argillites virginia formation northeastern minnesota abstract carbonaceous sulfidic argillites from the proterozoic virginia formation in minnesota have been investigated in terms of platinum group elements pge distribution and re os isotopic signatures kerogen from protoliths and slightly metamorphosed equivalents is characterized by re and os enrichment factors relative to whole rock concentrations that range from 4 to 272 re os isotopic values of kerogen in samples that show no evidence of extensive recrystallization fall near a 1 85 ga reference isochron this age is consistent with that estimated for the virginia formation and suggests that dating of organic rich precambrian sedimentary rocks and the retrieval of data pertinent to the os isotopic evolution of seawater may be possible using the re os isotopic system

re os geochronological evidence for multiple paleoproterozoic gold events at the scale of the west african craton the archean proterozoic craton of west africa hosts numerous gold deposits which are spatially and temporally related to the eburnean orogeny that took place between 2250 and 1980 ma and included multiple deformation events the majority of these gold deposits are located along shear zones the structural history is relatively well established for most gold deposits but absolute timing of the mineralization is commonly lacking five deposits hosted in the baoule mossi domain located in the southwestern part of the west african craton were studied to better constrain timing of gold events nassara and kiaka in burkina faso and wassa damang and obuasi in southern ghana gold mineralization was structurally characterized at each deposit and dated by the re os method on pyrite arsenopyrite and pyrrhotite grains that were coeval with the gold deposition combined structural and re os geochronological constraints allow two groups of gold deposits to be distinguished early orogenic gold formed during the eoeburnean orogeny i e between 2190 and 2125 ma as represented by kiaka1 at 2157 24 ma and wassa1 at 2164 14 ma these early gold occurrences are expressed as early disseminated gold enrichment 1 3 g t au at kiaka and gold hosted in folded and boudinaged quartz veins that are transposed along the primary s foliation at wassa these re os ages on the early sulfides at wassa and kiaka are significant because they definitively provide the first direct age constraints on gold only eoeburnean mineralization in the birimian of west africa late orogenic gold hosted by brittle structures and with higher gold grades up to 60g t at kiaka formed during late eburnean deformation d d events between 2120 and 2000 ma as represented by the re os dating of these ores at wassa at 2055 18 ma and obuasi at 2045 40 ma similar style ores dated at nassara at 2131 99 ma and damang at 2080 135 ma but both with large uncertainties and an undated younger event at kiaka are also suggested to be part of this later mineralizing episode the high uncertainties on the nassara and damang ages may be directly linked to the low rhenium and osmium contents of the studied samples these results highlight the polyphase character of the widespread gold mineralization in the west african craton although the late stages of the eburnean orogeny constitute a prolific period for the formation of high grade gold mineralization identification of less well studied early stage gold deposits which can also contain large quantities of gold is critical for mineral exploration in the west african craton

contemporaneous east west extension and north south compression at 43 ma in the himalayan orogen abstract it was previously proposed that the onset of east west extension in the himalayan orogen occurred after ca 19 ma here we present a re os isochron age of ca 43 ma for sulfides from the zhaxikang zn pb sb ag polymetallic deposits which occur within n s striking normal faults that reflect e w extension in the tethyan himalayan orogen this age is consistent with previously reported ages for regional metamorphism ca 48 42 ma granitoids ca 47 40 ma and gabbros ca 45 ma occurring along the indus yarlung suture in addition this type of structure also broadly occurs in the lhasa terrane and plays a critical role in the eocene porphyry skarn copper polymetallic mineralization there by ca 45 43 ma the north south directed horizontal deviatoric stresses had peaked and subducted neo tethyan slab breakoff had occurred at great depth leading to abrupt slowdown of indo asia convergence ca 45 ma e w extension initially developed at shallow depths resulting in formation of the north south trending normal faults in the plateau this type of extension would lead to collapse of the tibetan plateau and decrease in altitude subsequently resulted in central asian and the global climate changes our study places new constraints on the timing and nature of early cenozoic tectonics and metallogenesis in the himalayan orogen and climate changes in central asia

anhydrite stability and the effect of ca on the behavior of sulfur in felsic magmas the distribution of sulfur in the system na2o k2o cao al2o3 sio2 h2o s was investigated at 2 kbar 750 950 c and oxygen fugacities ranging from the co coo to the re reo2 buffer anhydrite caso4 crystallized in all the experiments conducted at oxidizing conditions ni nio 0 5 to 1 and above under otherwise equal conditions an inverse relationship between sulfur and cao concentration was observed in melts coexisting with anhydrite with the solubility product k cao so3 being constant where cao and so3 are the molar fraction of cao and so3 in the quenched glasses this suggests that anhydrite dissociates upon dissolution in the melt according to caso4 anhydrite ca2 melt so42 melt the solubility product strongly depends on temperature with lnk 28 573 917 t 11 26 0 80 this corresponds to an enthalpy of dissolution of h r 237 5 7 6 kj mol under reducing conditions co coo and ni nio buffer cao has no effect on the fluid melt partition coefficient of sulfur d sfluid melt at 850 c 2 kbar partition coefficients were 519 30 at the ni nio buffer and 516 11 at the co coo buffer for cao contents in the melt up to 1 wt these data are virtually identical to those measured in the cao free haplogranite system under reducing conditions however under more oxidizing conditions the fluid melt partition coefficient of sulfur appeared to have increased somewhat in the presence of cao this increase may however also be related to the fact that the final melt compositions in these runs were distinctly peraluminous our data show that calcium has no effect on the degassing of sulfur at reducing conditions but it greatly reduces the amount of sulfur available for rapid degassing under oxidizing conditions by stabilizing anhydrite

re os isotopic constraints on the genesis and evolution of the dergamish and ivanovka cu co au massive sulphide deposits south urals russia abstract rhenium and osmium elemental and isotopic data have been obtained for the two mafic ultramafic hosted volcanogenic massive sulphide vms deposits of dergamish and ivanovka from the south urals the associated ophiolitic blocks belong to the main uralian fault muf melange zone considered to represent obducted early palaeozoic oceanic crust despite their close geographical proximity the two ore bodies are morphologically mineralogically and isotopically quite different sulphides from ivanovka possess higher ni and os and lower re and cu relative to those from dergamish the re and os isotope data for dergamish define a best fit line corresponding to a late devonian age of 366 2 ma 2 with an mswd of 4 6 this age is some 40 my younger than the inferred silurian crystallisation age of the associated mafic ultramafic rocks but in good agreement with the previously published rb sr and ar ar ages of 360 380 ma corresponding to the high pressure metamorphic age of the adjacent maksyutov metamorphic complex these data suggest that re os systematics of the dergamish sulphide deposit were reset either by diffusion or recrystallisation during high pressure metamorphism or subsequent cooling the preservation of unradiogenic os isotopic ratios in some of the ivanovka samples and the near chondritic initial os isotopic composition obtained for the dergamish samples indicates that most of the os in the massive sulphides was ultimately derived from the mantle the corresponding tectonic setting equates to an area with submarine high level mantle rocks in contrast sulphides from ivanovka have experienced continued re equilibration and have been modified by post depositional processes at least some of which occurred relatively recently

photochemical and climate consequences of sulfur outgassing on early mars abstract ancient mars might have been warm and wet compared to today but climate models have trouble reproducing this warmth partly because of the faintness of the young sun and partly because of inherent limitations to co2 h2o greenhouse warming in particular rayleigh scattering of incoming sunlight by a dense co2 rich atmosphere leads to a high planetary albedo thereby reducing the amount of sunlight absorbed by the planet it has been recently suggested that the presence of 1 100 ppmv so2 in mars early atmosphere might have provided enough additional greenhouse warming to maintain a warm wet early mars we show however that this warming should have been more than offset by cooling from sulfate and sulfur aerosols in early martian atmosphere hence the paradox of mars early climate remains unresolved

volatile sulphur and chlorine major and trace element geochemistry of mafic to intermediate tephras from the chilean southern volcanic zone 33 43 s here we present the first systematic investigation of volatile geochemistry along the southern volcanic zone svz of chile holocene olivine hosted melt inclusions in the most mafic tephras sampled from 16 volcanoes along the volcanic front of the svz between 33 s and 43 s were analysed for pre eruptive sulphur chlorine and major element contents these results are combined with trace element compositions of the host whole rocks the highest fractionation corrected gas contents occur in the least degassed melt inclusions from small monogenetic cones of los hornitos cabeza de vaca and apagado from both the transitional and the southern central svz reaching 3 000 g g s and 1 400 g g cl while the lowest abundances of 1 100 g g s and 600 g g cl were found in the central svz at volcan lonquimay volcan llaima and volcan villarrica chlorine co varies with trace element indicators for the degree of melting and or source enrichment such that the lowest cl contents are found in high degree melts from the most depleted mantle sources the size of the volcanic edifices correlates inversely with cl abundances in the melt this could reflect more extensive degassing during ascent through the complex magma plumbing systems beneath the stratovolcanoes or greater dilution during larger degrees of melting of more depleted sources or a combination of these factors compared to other subduction zones the svz melt inclusions exhibit cl and s abundances in the same range as most of those from the central american and those from the marianas arcs

diagenetic origin of the stratiform cu co deposit at kamoto in the central african copperbelt sediment hosted stratiform ore deposits that underwent metamorphism and orogenesis are interpreted either to have a multiphase origin that might in part predate these events or to be exclusively related to fluid migration during the orogeny this controversy concerns the formation of many world class sediment hosted ore deposits such as in the central african copperbelt here we present re os dating results for disseminated and stratiform cu co sulfide pseudomorphs after anhydrite in nodules and layers from the copperbelt results demonstrate that at least some of the ores formed at around 800 ma during rifting and basin development and thus predate the pan african lufilian orogeny younger re os ages i e between 682 28 and 230 36 ma may be due to the replacement of the early cu co sulfides by younger sulfide phases alternatively these younger ages may result from the disturbance or resetting of the re os system during recrystallization metamorphism or the transition of chalcocite from its high to its low temperature polymorph