the giant dexing porphyry cu mo au deposit in east china product of melting of juvenile lower crust in an intracontinental setting the dexing porphyry cu mo au deposit in east china 1 168 mt at 0 45 cu is located in the interior of the south china craton scc made up of two lithospheric blocks the yangtze and cathaysia blocks the cu mo au mineralization is associated with mid jurassic granodioritic porphyries with three high level intrusive centers controlled by a series of lineaments at the southeastern edge of the yangtze block available age data define a short duration 172 170 ma of the felsic magmatism and the mineralization 171 1 ma the deposit shows broad similarities with deposits in volcanoplutonic arcs although it was formed in an intracontinental setting porphyries associated with mineralization are mainly granodiorites which contain abundant phenocrysts 40 60 and carry contemporaneous microgranular mafic enclaves mmes they are mainly high k calc alkaline and show geochemical affinities with adakite characterized by relatively high mgo cr ni th and th ce ratios the least altered porphyries yielded relatively uniform end t values from 0 9 to 0 6 and wide 87sr 86sr i range between 0 7046 and 0 7058 partially overlapping with the sr nd isotopic compositions of the mmes and mid jurassic mafic rocks in the scc zircons from the porphyries have positive ehf t values 3 4 to 6 9 and low 18o values 4 7 to 6 3 generally close to those of depleted mantle all data suggest an origin by partial melting of a thickened juvenile lower crust involving mantle components e g neoproterozoic mafic arc magmas triggered by invasion of contemporaneous mafic melts at dexing the mmes show textural mineralogical and chemical evidence for an origin as xenoliths formed by injection of mafic melts into the felsic magmas these mmes usually contain magmatic chalcopyrite and have original variable contents of cu up to 500 ppm their geochemical characteristics suggest that they were derived from an enriched mantle source metasomatized by proterozoic slab derived fluids and supplied a part of cu au and s for the dexing porphyry system during their injection into the felsic magmas the 171 1 ma magmatic hydrothermal event at dexing is contemporaneous with the mid jurassic extension in the scc followed by 160 90 ma arc like magmatism in southeastern china with respect to the tectono magmatic evolution of the scc the emplacement of cu bearing porphyries and the associated cu mineralization occurred in response to the transformation from a tensional regime related to mid jurassic extension to a transpressional regime related to the subduction of the paleo pacific oceanic lithosphere

microbial method for construction of an aquaculture pond in sand a method to construct an aquaculture pond in sand using microbial biocementation is presented in this paper the microbially induced calcium carbonate precipitation process was used to form a low permeability layer in sand for the construction of a water pond model in the laboratory the test results indicated that the permeability of sand was reduced from the order of 10 4 m s to 10 7 m s when an average 2 1 kg of calcium ca per m2 of sand surface was precipitated the bending strengths of the walls and the base of the model pond were in the range of 90 256 kpa the unconfined compressive strengths for the samples taken from the walls and the base of the pond were in the range of 215 932 kpa

gold speciation and transport in geological fluids insights from experiments and physical chemical modelling this contribution provides an overview of available experimental thermodynamic and molecular data on au aqueous speciation solubility and partitioning in major types of geological fluids in the earth s crust from low temperature aqueous solution to supercritical hydrothermal magmatic fluids vapours and silicate melts critical revisions of these data allow generation of a set of thermodynamic properties of the auoh aucl 2 auhs and au hs 2 complexes dominant in aqueous hydrothermal solutions however other complexes involving different sulphur forms chloride and alkali metals may operate in high temperature sulphur rich fluids vapours and melts the large affinity of au for reduced sulphur is responsible for au enrichment in s rich vapours and sulphide melts which are important gold sources for hydrothermal deposits thermo dynamic speciation and partitioning data and their comparison with au and s contents in natural fluid inclusions from magmatic hydrothermal gold deposits provide new constraints on the major physical chemical parameters temperature pressure salinity acidity redox and ubiquitous fluid components sulphur carbon dioxide arsenic affecting au concentration transport precipitation and fractionation from other metals in the crust the availability and speciation of sulphur and their changes with the fluid and melt evolution are the key factors controlling gold behaviour in most geological situations

an experimental study of the partitioning of copper between pyrrhotite and a high silica rhyolitic melt the partitioning of copper has been investigated experimentally between a natural pyrrhotite and a natural high silica rhyolitic melt under water saturated conditions at 800 degrees c 1 kbar and two oxygen fugacities the partition coefficients d super po melt cu defined as the ratio of the concentrations of copper in pyrrhotite to copper in melt are 910 or 436 1sigma at the c ch 4 buffer and 554 or 220 1sigma at one half of a log unit above nno the mean value for all determinations is 773 or 400 1sigma although the experimental results show wide scatter at test indicates that the partition coefficients at the two oxygen fugacities may be considered significantly different at the 88 percent confidence level the results are consistent with hypothetical chemical potential equilibria and with previous field and experimental data estimates obtained through mathematical modeling suggest that such partition coefficients may result in sequestration of 98 percent of the copper by pyrrhotite in a relatively s rich and h 2 o poor magma whereas 24 percent of the copper may be sequestered by pyrrhotite in a relatively low sulfur magma in which water saturation and evolution of an aqueous fluid occur early the results may provide significant constraints in interpretation of the behavior of cu in felsic magmatic systems and in application of the orthomagmatic hydrothermal hypothesis to geologic processes associated with porphyry type copper deposits

darcy scale modeling of microbially induced carbonate mineral precipitation in sand columns 1 this investigation focuses on the use of microbially induced calcium carbonate precipitation micp to set up subsurface hydraulic barriers to potentially increase storage security near wellbores of co2 storage sites a numerical model is developed capable of accounting for carbonate precipitation due to ureolytic bacterial activity as well as the flow of two fluid phases in the subsurface the model is compared to experiments involving saturated flow through sand packed columns to understand and optimize the processes involved as well as to validate the numerical model it is then used to predict the effect of dense phase co2 and co2 saturated water on carbonate precipitates in a porous medium

the partitioning behavior of silver in a vapor brine rhyolite melt assemblage abstract the partitioning of silver in a sulfur free rhyolite melt vapor brine assemblage has been quantified at 800 c pressures of 100 and 140 mpa and f o 2 nno nickel nickel oxide silver solubility 2 in rhyolite increases 5 fold from 105 21 to 675 98 g g as pressure increases from 100 to 140 mpa nernst type partition coefficients d ag i j 2 describing the mass transfer of silver at 100 mpa between vapor and melt brine and melt and vapor and brine are 32 30 1151 238 and 0 026 0 004 respectively at 140 mpa values for d ag i j 2 for vapor and melt brine and melt and vapor and brine are 32 10 413 172 and 0 06 0 03 respectively apparent equilibrium constant values 2 describing the exchange of silver and sodium between vapor and melt k ag na v m at 100 and 140 mpa are 105 68 and 14 6 the average values 2 for silver and sodium exchange between brine and melt k ag na b m at 100 and 140 mpa are 313 288 and 65 12 these data indicate that the mass transfer of silver from rhyolite melt to an exsolved volatile phase s is enhanced at 100 mpa relative to 140 mpa suggesting that decompression increases the silver ore generative potential of an evolving silicate magma model calculations using the new data suggest that the evolution of low density aqueous fluid i e vapor may be responsible for the the silver tonnage of many porphyry type and perhaps epithermal type ore deposits for example halter et al halter w e pettke t and heinrich c a 2002 the origin of cu au ratios in porphyry type ore deposits science 296 1842 1844 used detailed silicate and sulfide melt inclusion and vapor and brine fluid inclusions analyses to estimate a melt volume on the order of 15 km3 to satisfy the copper budget at the bajo de la alumbrera copper gold silver ore deposit using their melt volume estimate with the data presented here model calculations for a 15 km3 felsic melt saturated with pyrrhotite and magnetite suggest that a low salinity magmatic vapor may scavenge on the order of 7 1012 g of silver from the melt this quantity of silver exceeds the discovered 2 109 g of ag at alumbrera calculated tonnages for numerous other deposits yield similar results the excess silver in the vapor remaining after porphyry formation is then available to precipitate at lower ptconditions in the stratigraphically higher epithermal environment these data suggest that silver and perhaps other ore metals in the porphyry epithermal continuum may be derived solely from the time integrated flux of dominantly low salinity vapor exsolved from a series of sequential magma batches

the role of magmatic sulfides and mafic alkaline magmas in the bingham and tintic mining districts utah this paper reports the existence of abundant magmatic sulfides in introduction latite lava vitrophyres and vent facies dikes from the bingham and the eruption of sulfur rich magmas from el chichon tintic districts in central utah these dikes and flows appear to luhr et al 1984 and mt pinatubo westrich gerlach be comagmatic with the ore related monzonite intrusions in addition 1992 in recent years has attracted attention to the limited analytical data suggest that the magmatic sulfides contain most of solubility of sulfur in intermediate magmas and the factors the cu and ag present in the latites magmatic sulfides are preserved potentially responsible for the formation of magmatic only in the least oxidized and least degassed lavas and vitrophyres sulfides and anhydrite however the occurrence of magpetrography of comagmatic dikes and intrusions suggests that matic sulfides in intermediate magmas is not universal resorption and oxidation s degassing of the globules may make many volcanic suites appear to be sulfide unsaturated the metal content available to a magmatic ore fluid minette and inasmuch as magmatic sulfides may sequester chalcophile shoshonite lavas occur in subordinate amounts in the latitic volcanic metals what would their presence signify in magmatic fields associated with latite monzonite intrusions and hydrothermal systems that formed porphyry cu and mesothermal vein ore deposits of the tintic ag pb zn cu au and bingham deposits do they sequester a significant portion of the porphyry cu au mo districts utah the ages chemical and magmatic cu pb zn ag and au thereby restricting modal compositions and field relations of the mafic alkaline lavas metal availability of subsequent ore forming fluids suggest that such magmas mixed and fractionated at shallow crustal we have examined the volcanic rocks from the tintic levels to form the ore related latites and monzonites the unaltered and bingham mining districts fig 1 utah and found mafic alkaline lavas in these districts are some of the most cu rich that almost all of the volcanic units contain magmatic lavas in the great basin province sulfides some quenched dikes and intrusion margins also have preserved magmatic sulfides comparable with those in the volcanic rocks several lines of evidence indicate that the volcanic and intrusive rocks are comagmatic keith et al 1989 1991 waite 1996 the tintic district and east tintic sub district in utah have recorded over

the influence of oxygen fugacity on tungsten and molybdenum partitioning between silicate melts and ilmenite the partitioning of molybdenum and tungsten between ilmenite ilm and silicic melts has been determined at 800 degrees c 1 kbar of pressure and at two oxygen fugacities at the oxygen fugacity of the graphite methane water buffer d super ilm melt mo 0 42 and d super ilm melt w 0 39 near the nickel nickel oxide buffer d super ilm melt mo 0 22 and d super ilm melt w 0 5 the variations in the partition coefficients with f sub o 2 are significant at the 0 06 and 0 33 levels for molybdenum and tungsten respectively the observed variation with oxygen fugacity is tentatively extrapolated to more complex systems and implies that the oxygen fugacity which prevails during magmatic crystallization may play a role in determining the mo w ratio in porphyry skarn or other hydrothermal mineral deposits examination of the literature on molybdenum and tungsten bearing mineral deposits indicates that systems with high w mo ratios are rather reduced and exhibit high ch 4 co 2 ratios in fluid inclusions low fe super 3 fe super 2 ratios in iron bearing minerals and low oxygen fugacities in associated igneous rocks on the other hand deposits with high mo w ratios are associated with rather oxidized magmatic systems we suggest that f sub o 2 dependent sequestration of molybdenum and tungsten in ferromagnesian phases during plutonic consolidation exerts a control on the relative efficiencies of removal of these metals from magmas into ore forming fluids

unusually cu rich magmas associated with giant porphyry copper deposits evidence from bingham utah mass balance constraints indicate that formation of giant porphyry copper deposits pcds requires either highly efficient collection of cu from large volumes of magma or unusually cu rich parent magmas support for the second of these possibilities has been discovered in the form of mafic enclaves with abundant bornite and chalcopyrite in the last chance stock one of the parent intrusions of the giant bingham pcd utah united states mineral assemblages and compositions indicate that the last chance enclaves are autoliths consisting of phases that crystallized from the intrusion and that the intrusion was unusually enriched in cu one possible mechanism for generating cu rich magmas is fractional crystallization during pyrrhotite undersaturated conditions the high fo 2 conditions observed for the last chance stock may have allowed such an evolution alternatively if the magma has not undergone significant fractionation early crystallization of chalcopyrite and bornite from the magma would indicate that the lower crustal source region for the magma probably contained cu fe sulfides possible cu rich source regions are a subcrustal mafic intrusion with sulfide cumulates or a deeply buried metamorphic terrane containing cu deposits such as those in the curaca valley brazil or okiep south africa heterogeneous distribution of cu fe sulfides in an okiep type source terrane would produce local pcds such as bingham or large accumulations of cu fe sulfides possibly in the form of cumulates in subcrustal intrusions at convergent margins could produce giant pcd provinces such as those in indonesia papua new guinea and central chile

systematic variations in magmatic sulphide chemistry from mid ocean ridges back arc basins and island arcs abstract immiscible sulphide liquids preserved as magmatic sulphide globules are hosted in igneous rocks of highly variable composition formed during magmatic processes at different tectonic settings here we report on compositional in situ data of magmatic sulphides from mid ocean ridge back arc and island arc magmatic systems iron ni rich monosulphide solid solutions mss that mainly consist of pyrrhotite and pentlandite are the dominant phases in magmatic sulphide globules in subduction related magmas mss are most abundant in relatively evolved melts and characterised by low ni and high fe contents as well as low ni cu ratios 1 thus mss chemistry varies systematically in lavas from the different tectonic settings in terms of their fe ni distribution and ni cu ratio the observed mineralogical and chemical variations between mss from the different settings reflect early s saturation accompanied by olivine fractionation along mid ocean ridges compared to later stage s saturation in arc systems associated with fe ti oxide fractionation these systematics are probably related to the relatively oxidised character of subduction zone magmas opposed to more reduced mid ocean ridge melts large ni cu variations in mss from the same locality and in individual samples suggest that s saturation is a multistage or continuous process leading to inclusions of magmatic sulphides that represent different fractionation stages in the ascending magma

is gold solubility subject to pressure variations in ascending arc magmas magmas play a key role in the genesis of epithermal and porphyry ore deposits notably by providing the bulk of ore metals to the hydrothermal fluid phase it has been long shown that the formation of major deposits requires a multi stage process including the concentration of metals in silicate melts at depth and their transfer into the exsolved ore fluid in more superficial environments both aspects have been intensively studied for most of noble metals in subsurface conditions whereas the effect of pressure on the concentration i e solubility of those metals in magmas ascending from the sublithospheric mantle to the shallow arc crust has been quite neglected here we present new experimental data aiming to constrain the processes of gold au dissolution in subduction linked magmas along a range of depth we have conducted hydrous melting experiments on two dacitic adakitic magmas at 0 9 and 1 4 gpa and 1000 c in an end loaded piston cylinder apparatus under fo2 conditions close to nno as measured by solid co pd o sensors experimental charges were carried out in pure au containers the latter serving as the source of gold in presence of variable amounts of h2o and for half of the charges with elemental sulfur s so as to reach sulfide saturation au concentrations in melt quenched to glass were determined by la icpms when compared to previous data obtained at lower pressures and variable redox conditions our results show that in both s free and sulfide saturated systems pressure has no direct detectable effect on melt au solubility nevertheless pressure has a strong negative effect on sulfur solubility since gold dissolution is closely related to the behaviour of sulfur in reducing and moderately oxidizing conditions pressure has therefore a significant but indirect effect on au solubility the present study confirms that au dissolution is mainly controlled by fo2 in s free melts and by a complex interplay of fo2 and melt s2 concentration in sulfide saturated melts at given temperature in addition we propose that the transition from sulfide s2 to sulfate s6 species in melt is shifted towards more oxidizing conditions when pressure and the degree of melt polymerization increase if this is true this may have important consequences during mantle melting and magma ascent in particular if mantle melting occurred in moderately oxidizing conditions a small degree of partial melting would allow the primary melts to become au enriched but the relatively high pressure would move the sulfide sulfate transition to more oxidizing conditions making the primary melts saturated with sulfide phases that would sequester gold from the melt during magma ascent the decreasing pressure would favour the destabilization of sulfides and the release of gold to the silicate melt however at shallow levels decreasing pressure magma evolution and varying redox conditions would be continuously competing to concentrate or fractionate gold

oxygen fugacity of yanshanian granites in south china and implications for metallogeny abstract oxygen fugacity fo 2 of magmas exerts an important control on the speciation of multivalent elements in magmatic hydrothermal processes which has a great significance for mineralization this paper examines the relationships between oxygen fugacity and mineralization associated with yanshanian jurassic to cretaceous granites in south china which hosts many world class w sn cu mo au pb and zn deposits the oxygen fugacities of yanshanian granites were evaluated using published chemical compositions of biotite and the redox states were further constrained with whole rock fe 3 fe 2 as well as zircon ce 4 ce 3 ratios from the literature systematic differences in oxygen fugacity between granites related to cu au mo cu pb zn w sn and w sn mineralization and between ore bearing and barren granites were found log fo 2 values relative to nno buffer are 1 08 to 13 07 average 4 22 for cu au mo related granites 1 01 to 5 36 average 3 51 for cu pb zn related granites 1 51 to 5 68 average 3 78 for w related granites 1 70 to 3 22 average 1 71 for w sn related granites and 5 32 to 2 43 average 0 83 for sn related granites in the biotite fe 3 fe 2 mg 2 ternary and log fo 2 t diagrams the cu au mo related granites are located between the mh and nno buffers and above the mh buffer and sn and w sn related granites are centered around the nno buffer and spread toward the fmq and mh buffers whereas the cu pb zn and w related granites are plotted between the nno and mh buffers similar trends were also observed for whole rock fe 2 o 3 feo ratios and zircon ce 4 ce 3 ratios in areas of cu au mo mineralization ore bearing granites have higher oxygen fugacities than barren granites regional scale variations of oxygen fugacities coupled with changes in la sm and ba th ratios which are considered as proxies of subducted sediments and slab dehydration fluids support the distinction of two metallogenic systems in the yanshanian period in south china a jurassic system related to ne to sw subduction and a cretaceous one related to se to nw subduction of the paleo pacific plate each with a trend of decreasing oxygen fugacities in the direction of subduction

rock fracture grouting with microbially induced carbonate precipitation microbially induced carbonate precipitation has been proposed for soil stabilization soil strengthening and permeability reduction as an alternative to traditional cement and chemical grouts in this paper we evaluate the grouting of fine aperture rock fractures with calcium carbonate precipitated through urea hydrolysis by the bacteria sporosarcina pasteurii calcium carbonate was precipitated within a small scale and a near field scale 3 1 m2 artificial fracture consisting of a rough rock lower surfaces and clear polycarbonate upper surfaces the spatial distribution of the calcium carbonate precipitation was imaged using time lapse photography and the influence on flow pathways revealed from tracer transport imaging in the large scale experiment hydraulic aperture was reduced from 276 m to 22 m corresponding to a transmissivity reduction of 1 71x10 5 m2 s to 8 75x10 9 m2 s over a period of 12 days under constantly flowing conditions with a modified injection strategy a similar three orders of magnitude reduction in transmissivity was achieved over a period of three days calcium carbonate precipitated over the entire artificial fracture with strong adhesion to both upper and lower surfaces and precipitation was controlled to prevent clogging of the injection well by manipulating the injection fluid velocity these experiments demonstrate that microbially induced carbonate precipitation can successfully be used to grout a fracture under constantly flowing conditions and may be a viable alternative to cement based grouts when a high level of hydraulic sealing is required and chemical grouts when a more durable grout is required

redox controlled generation of the giant porphyry cu au deposit at pulang southwest china some porphyry cu au deposits with relatively reduced ore assemblages characterized by high hydrothermal pyrrhotite contents and a lack of primary hematite and magnetite are generally considered to be associated with reduced i type granitoids however the role of magmatic oxygen fugacity fo2 in controlling cu au mineralization in such reduced porphyry deposits is poorly understood the giant late triassic ca 216 ma pulang porphyry cu au deposit of southwest china shows typical reduced ore assemblages this study reported the systematical variation of upper crustal magmatic fo2 of pulang deposit based on detailed investigations of mineral crystallization sequences and compositional features of the mineralization related porphyries early p1 and late p2 porphyry results indicate that magma of the mineralization related porphyries experienced complex fo2 fluctuations during its upper crustal evolution the early primary magma had very high initial fo2 with fmq 3 0 at depths of 12 km fmq is the deviation of logfo2 from the fayalite magnetite quartz fmq buffer the fo2 of evolved parental magma subsequently decreased with fmq 1 9 due to injection of relatively reduced dioritic magmas fmq 1 4 to 2 3 from a deeper chamber 17 21 km depth into the primary magma chamber at 10 12 km depth magma mixing had largely ceased at 6 10 km depth the parental magma then ponded within the reduced tumugou formation at a depth of 3 7 km where magmatic fo2 decreased to a moderately oxidized state fmq 1 6 and finally to a moderately reduced state reflected by log fe2o3 feo ratios of 0 5 for p2 porphyry results of this study of magmatic fo2 indicate that porphyry magmas associated with reduced pulang ore assemblages were initially generated as highly oxidized magma which was subsequently reduced through magma mixing and contamination by reduced sedimentary rocks of the tumugou formation the sharp fo2 decrease at very shallow depth prevented the early loss of cu and au because the magma remained oxidized until it was emplaced at 3 7 km depth moderately reduced magmas may thus have a genetic association with porphyry cu au mineralization

application of microbially induced calcite precipitation in erosion mitigation and stabilization of sandy soil foreshore slopes a preliminary investigation eroding foreshores endanger the floodplains of many estuaries as such effective and environmentally friendly interventions are sought to stabilise slopes and mitigate erosion as a step in forestalling these losses we developed laboratory microcosms to simulate tidal cycles and examined the mechanisms of erosion and failure on sandy foreshore slopes as an experimental aim we applied microbially induced calcite precipitation micp to selected slopes and compared the effectiveness of this microbial geo technological strategy to mitigate erosion and stabilise slopes to assess shoreline stability thirty cycles of slowly simulated tidal currents were applied to a sandy slope significant sediment detachment occurred as tides moved up the slope surface for steeper slopes one tidal event was sufficient to cause collapse of the slopes to the soil s angle of repose 35 subsequent tidal cycles gradually eroded surface sediments further reducing slope angle on an average 0 2 per tidal event these mechanisms were similar for all slopes irrespective of initial slope inclination micp was evaluated as a remedial measure by treating a steep slope of 53 and an erosion prone slope angle of 35 with sporosarcina pasteurii and cementation solution 0 7 m cacl2 and urea before tidal simulations micp produced 120 kg calcite per m3 of soil filling 9 9 of pore space cemented sand withstood up to 470 kpa unconfined compressive stress and showed significantly improved slope stability both slopes showed negligible sediment erosion with efforts towards optimisation for upscaling and further environmental considerations including effect of slope saturation on micp treatment saline water and estuarine coastal ecology amongst others the micp process demonstrates promise to protect foreshore slope sites

seasonal cycle of orographic gravity wave occurrence above small islands in the southern hemisphere implications for effects on the general circulation 1 orographic gravity waves generated by flow over the topography of small islands in the southern oceans have been observed from orbit with the atmospheric infrared sounder on the aqua satellite we examine the occurrence frequencies of these waves in the stratosphere at 40km above 14 islands and examine geographical and seasonal changes our results show that these small island mountain waves occur commonly in the stratosphere in the may september season though not every day differing seasonal variations are evident at different islands and the seasonal variations are closely related to latitude and prevailing wind patterns we also examine interannual variability in 2years of data and the relationships between occurrence frequencies momentum fluxes and stratospheric and surface winds the results suggest that stratospheric winds have a first order limiting effect on the observations of these island mountain waves in atmospheric infrared sounder airs data surface wind direction and island orographic relief have an additional but secondary influence on the island mountain wave occurrence frequencies in airs data the implications are that these wave events are extremely common and that on many days when the waves are not observed in airs data they have likely dissipated and induced a drag force on the atmosphere below the 40km observation level observations of momentum flux during these wave events also permit a first estimate of their importance to the general circulation of the southern hemisphere

experimental determination of au solubility in rhyolite melt and magnetite constraints on magmatic au budgets the solubility of au metal in rhyolite melt and coexisting magnetite has been determined at 800 c 140 mpa and f 0 2 nno in a au metal saturated sulfur free vapor brine silicate melt system whole crystals of magnetite suspended within quenched rhyolite glass were analyzed by la icp ms these data yield a solubility of au in magnetite on the order of 2 g g the solubility of au metal in rhyolite melt hosting the magnetite crystals is on the order of 500 ng g these data indicate a partition coefficient for au between magnetite and melt d m t m e l l au 4 using reasonable estimates of the mass fraction of magnetite that crystallizes in crustal magmatic systems we modeled the proportion of au sequestered by magnetite during fractional crystallization we considered fractionation in two steps the idealized derivation of a rhyolite by fractionation of basalt at depth and the closed system crystallization of the rhyolite in a magma chamber below the site of ore deposition magnetite sequesters 14 54 au from basaltic parent melt that produces a rhyolite melt via crystal fractionation at modal abundances of 1 5 less then 4 au is sequestered from a crystallizing rhyolite melt because of low modal abundances of magnetite 2 our experimental and model results suggest that early crystallization of magnetite can play a mitigating role in the ability of a calc alkaline magmatic system to yield a au rich ore fluid

comparison of rates of ureolysis between sporosarcina pasteurii and an indigenous groundwater community under conditions required to precipitate large volumes of calcite ureolysis driven calcite precipitation has potential to seal porosity and fracture networks in rocks thus preventing groundwater flow and contaminant transport in this study urea hydrolysis and calcite precipitation rates for the model bacterium sporosarcina pasteurii were compared with those of indigenous groundwater communities under conditions required to precipitate large volumes of calcite up to 50 g l 1 we conducted microcosm experiments in oxic artificial and anoxic natural groundwaters collected from the permo triassic sandstone aquifer at birmingham uk that were inoculated with aerobically grown s pasteurii the rate constants for urea hydrolysis kurea ranged between 0 06 and 3 29 d 1 and were only affected by inoculum density higher ca2 concentration 50 500 mm ca2 as well as differences in fo2 did not inhibit the ureolytic activity of s pasteurii and did not significantly impact kurea these results demonstrate that s pasteurii has potential to improve calcite precipitation in both oxic and anoxic groundwaters especially if indigenous communities lack ureolytic activity urea hydrolysis by indigenous groundwater communities was investigated in anoxic natural groundwaters amended with urea and cacl2 a notable increase in ureolysis rates was measured only when these communities were stimulated with dilute nutrients with best results from blackstrap molasses furthermore there was a considerable lag time 12 20 days before ureolysis and calcite precipitation began calculated ureolysis rate constants kurea ranged between 0 03 and 0 05 d 1 and were similar to kurea values produced by s pasteurii at low inoculum densities overall this comparative study revealed that the growth of ureolytic microorganisms present within groundwaters can easily be stimulated to enhance rates of urea hydrolysis in the subsurface and thus can be used to induce calcite precipitation in these environments the time required for urea hydrolysis to begin is almost instantaneous if an inoculum of s pasteurii is included while it may take several weeks for ureolytic groundwater communities to grow and become ureolytically active

sulfur isotopic systematics of granitoids from southwestern new brunswick canada implications for magmatic hydrothermal processes redox conditions and gold mineralization bulk 34srock values sulfur contents and magnetic susceptibility were determined for 12 gold related granitoid intrusions in southwestern new brunswick the canadian appalachians the sulfur isotope compositions of sulfide minerals in some of the granitoid samples were also analyzed this new dataset was used to characterize two distinctive groups of granitoids 1 a late devonian granitic series gs and 2 a late silurian to early devonian granodioritic to monzogranitic series gms the gs rocks have a large range in 34s values of 7 1 to 13 with an average of 2 2 5 0 1 low bulk s contents 33 to 7 710 ppm and low magnetic susceptibility values 10 3 si indicative of oxidized magnetite series granites the exceptions for the gms rocks are the lake george granodiorite and tower hill granite that display reduced characteristics which may have resulted from interaction of the magmas forming these intrusions with graphite or organic carbon bearing sedimentary rocks the bulk 34s values and s contents of the gms rocks are interpreted in terms of selective assimilation fractional crystallization safc processes degassing processes may account for the 34s values and s contents of some gs rocks the characteristics of our sulfur isotope and abundance data suggest that mineralizing components s and au in intrusion related gold systems are dominantly derived from magmatic sources although minor contaminants derived from country rocks are evident in addition the molar sulfate to sulfide ratio in a granitic rock sample can be calculated from the 34srock value of the whole rock sample and the 34ssulfide or 34ssulfate value of sulfide and or sulfate mineral in the sample on the basis of s isotope fractionation and mass balance under the condition of magmatic equilibrium this may be used to predict the speciation of sulfur in granitic rocks which can be a potential exploration tool for intrusion related gold systems

origin and mode of copper enrichment in biotite from rocks associated with porphyry copper deposits a transmission electron microscopy investigation this paper presents results of a systematic transmission electron microscopy tem study of biotites from a suite of core samples from the cyprus casa grande porphyry copper deposit arizona the primary purpose of this study was to determine the mode and timing of copper enrichment in biotite and to compare the results to tem observations of biotites from other porphyry copper deposits the core samples represent both oxidized and unoxidized rock biotites and chlorites from unoxidized protore contain less than 200 ppm copper as measured by electron microprobe and are free of copper enriched expanded interlayers and the native copper inclusions described by ilton and veblen 1988 biotites and chlorites from oxidized ore are commonly copper enriched the mode of copper incorporation in biotites and chlorites in oxidized rock is complex and varies with depth biotites from the goethite zone contain submicroscopic native copper inclusions and both copper enriched expanded interlayers and submicroscopic iron oxide inclusions biotites and chlorites from the chrysocolla zone contain copper enriched expanded interlayers amorphous al si intergrowths with dense arrays of copper and iron rich inclusions and copper rich inclusions that rapidly evaporate under the electron beam and hence have yet to be identified it is possible that copper is incorporated into the brucite layer in chlorite biotites from the native copper zone contain native copper inclusions as expected but they also contain copper rich expanded interlayers biotites associated with atacamite mineralization contain high concentrations of copper that are associated with expanded interlayers in the chalcocite zone biotites appear relatively unweathered and contain minor concentrations of copper that are associated with infrequent expanded interlayers a comparison of observations from oxidized and unoxidized rock indicates that the occurrence of copper rich biotites and both copper enriched expanded interlayers and native copper inclusions in biotite are restricted to oxidized rock we conclude that the native copper inclusions and copper rich expanded interlayers in biotite from cyprus casa grande formed during weathering and not during the hydrothermal event native copper inclusions and copper rich expanded interlayers in biotites have been documented from a variety of porphyry copper deposits earlier studies of the same samples have suggested that copper in copper rich biotites was representative of magmatic hydrothermal events and that the difference between mineralizing and barren intrusions was recorded by differences in copper concentrations in biotite the present study together with previous experimental work suggests that the copper rich biotites became copper enriched during weathering and that copper concentrations in copper rich biotites do not reflect magmatic hydrothermal processes

magmatic sulfides and au cu ratios in porphyry deposits an experimental study of copper and gold partitioning at 850 c 100 mpa in a haplogranitic melt pyrrhotite intermediate solid solution gold metal assemblage at gas saturation abstract the behavior of copper and gold in the phase assemblage pyrrhotite po intermediate solid solution iss haplogranitic melt gold metal capsule at 850 c 100 mpa and gas saturation ah2o 0 9 has been investigated the results are presented as nernst partition coefficients the partition coefficient dcupo melt 2 6 0 3 103 1 was determined for po and melt in equilibrium with an iss of composition cu 19 1 fe 30 1 s 51 1 2 for gold the partition coefficients are dauiss melt 5 7 2 2 103 1 between iss and melt and daupo melt 140 40 1 between po and melt these imply dauiss po 42 9 1 between iss and po the oxygen fugacity for the experiments log f o 2 13 2 0 3 1 was determined by using the hydrogen sensor technique the sulfur fugacity log f s 2 1 0 0 7 1 was calculated from the composition of po in our experiments melts at iss saturation have cu fe by weight of ca 1 100 the results indicate that crystallization of iss may deplete a melt in gold and crystallization of po may deplete a melt in copper however a melt saturated with iss at a given bulk composition temperature pressure oxygen and sulfur fugacity and feo concentration will have a fixed concentration of cu preventing strong depletion of the melt in cu until iss is fractionated from the melt or changes in environmental conditions destabilize iss a thermodynamic model for the partitioning of cu and au between po and melt in terms of oxygen and sulfur fugacity indicates that dcupo melt and daupo melt may increase greatly with increasing sulfur fugacity and decreasing oxygen fugacity within the po stability field the model also suggests that destabilization of both iss and po relative to magnetite due to changes in oxygen and sulfur fugacities can result in the release of cu and au from the sulfides to the melt

the magnetite crisis in the evolution of arc related magmas and the initial concentration of au ag and cu the association of large au cu ag ore deposits with convergent margins is commonly attributed to the higher content of chalcophile elements in the parental magmas generated at subduction zones compared with mid ocean ridges we present new geochemical data for arc like relatively oxidized mantle derived basalt to rhyolite magmas from the pual ridge and vicinity eastern manus basin which show that the initial abundances of base and precious metals in the parental basalts are similar to those of mid ocean ridge basalt morb the contents of au cu and ag are built up in the evolving pual ridge liquids to levels considerably in excess of those in morb because unlike morb they are not saturated in a sulfide phase which is a consequence of their being more oxidized than morb the behaviour of s during the evolution of the pual ridge magmas is obscured by late stage so2 loss during eruption but we show that it may be inferred by using se as a proxy because this element follows s closely during magmatic evolution except it is not lost during low pressure near sea floor degassing the onset of magnetite fractionation at 60 wt sio2 and an mg number of 40 is accompanied by an abrupt decrease in the contents of au cu and ag previously attributed to separation of cu au rich fluid which is also shown by se implying that magnetite fractionation triggers sulfide saturation petrological modelling reveals that the amount of magnetite fractionation involved is sufficient to convert most of the s originally dissolved in the magma as sulfate so42 to sulfide s2 triggering saturation in a cu rich sulfide phase tentatively identified as bornite cu5fes4 this sulfide phase sequesters au and ag elements with the same valence as cu in sulfides but not other potentially chalcophile elements such as ni re and pt which suggests that the phase is crystalline rather than an immiscible sulfide melt the relatively high contents of cu and au characteristic of evolved convergent margin magmas requires no enrichment from subducted material instead the association of major cu au deposits with convergent margin magmatism results specifically from the process of magmatic evolution under oxidizing conditions this same property also leads to early magnetite fractionation triggering the abrupt saturation in the cu rich sulfide hence the easily recognizable trend of magmatic evolution under oxidizing conditions i e the sharp drop in chalcophile element concentrations may be an exploration guide to economic au ag cu provinces or a crucial pre enrichment step in the formation of such deposits the decrease in p2o5 and sr at the same stage in the fractionation sequence 60 wt sio2 indicates that saturation in apatite is concomitant with magnetite sulfide saturation in the eastern manus basin

gold in porphyry copper deposits experimental determination of the distribution of gold in the cu fe s system at 400 to 700 c experiments in the system au cu fe s were carried out at temperatures of 400 to 700 c to determine how much gold could be accommodated by bornite and chalcopyrite the two most common ore minerals in porphyry copper gold deposits our results show that for all temperatures bornite contains one order of magnitude more gold than chalcopyrite or intermediate solid solution iss its high temperature equivalent the range of gold concentrations in bornite and chalcopyrite or iss decreases with decreasing temperature from 1 280 to 8 200 ppm au in bornite and 100 to 125 ppm au in iss at 600 c to 235 to 364 ppm au in bornite and 5 to 16 ppm au in chalcopyrite or iss at 500 c and to 13 to 80 ppm au in bornite and 2 to 4 ppm au in chalcopyrite or iss at 400 c the amount of gold in bornite is also strongly dependent on the composition of bornite being highest in stoichiometric bornite compositions cu5fes4 and decreasing toward cu rich and cu poor compositions phase equilibrium constraints for solutions with geologically reasonable reduced sulfur contents indicate that high temperature porphyry copper gold deposits will contain bornite and magnetite whereas lower temperature deposits whether primary or overprinted by phyllic alteration will contain chalcopyrite and pyrite if gold is present in the ore forming solutions more of it will be deposited in high temperature porphyry copper gold deposits where it will be closely associated with bornite coexisting magnetite in these deposits should generate magnetic anomalies lower temperature deposits will contain less gold which is hosted by pyrite as well as chalcopyrite and will lack magnetic anomalies comparison of the amount of gold hosted by natural porphyry copper gold ores to that hosted by bornite and chalcopyrite in our experiments suggests that significant amounts of gold can be lost from these deposits into surrounding hydrothermal systems

a review of shallow ore related granites textures volatiles and ore metals shallow texturally complex granites can be associated spatially introduction and temporally with hydrothermal alteration and mineralization granite related ore deposits include porphyry and skarn the formation of a granite related ore deposit represents the confluence type ores and other hydrothermal deposits that are of many chemical and physical geological factors including magma spatially and temporally associated with granitic sensu composition e g concentrations of ore metals chlorine and water lato rocks in this paper i emphasize characteristics magma oxidation state the relative timing of crystallization magma found in porphyry style cu mo au deposits and some ascent magmatic volatile phase exsolution and the depth of em related systems however my treatment here is not meant placement early magmatic crystallization of ore metal rich minerals to cover the full range of granitic rocks and mineralization coupled with late exsolution of the magmatic volatile phase is that make up the granite related ore systems the forpromoted by deeper emplacement levels and lower magmatic water mation of granite related ore deposits by orthomagmatic concentrations and leads to low eyciencies of removal of compatible hydrothermal processes is dependent upon many physical elements from melts into the magmatic volatile phase s water and chemical magmatic factors including but not limited concentrations in the melt and pressures of crystallization can be to the composition and evolution of the associated estimated from phase equilibria and textural relationships of horn magmas the rate of magma ascent the depth and blende in some felsic systems physical factors avect the dynamics geometry of magma emplacement and the local temof fluid magma melt and volatile phase movement which in turn perature and stress fields at the site of magma emavect the size of zones of alteration and mineralization granite placement detailed studies of the igneous rocks textures can record the partial history of some dynamic processes associated with ore deposits can therefore yield critical miarolitic cavities are good evidence for magmatic volatile phase information regarding the source of metals and ligands exsolution both miarolitic cavities and pegmatitic texture exhibit in the ore generative hydrothermal solutions that are evidence for external nucleation of crystals nucleation controlled operative in the formation of granite related ores in this phenomena expressed as variations in granite textures can result review i will present a series of narratives consistent in from a multiplicity of causes including undercooling of the melt my view with prevailing field and experimental data on textural elements such as pegmatite aplite skeletal crystals and the orthomagmatic hydrothermal theory for the genesis graphic textures can form as a result of undercooling interconnected of some granite related deposits volumes of the magmatic volatile phase allow for advection of some high level granites i e those that are emplaced hydrothermal ore fluids through the magma in shallow granitic at depths of 8 km or less represent the crystallized systems miarolitic cavities can be interconnected consistent with remains of magmas that were associated with subvolcanic this hypothesis ore generative hydrothermal systems therefore studies of shallow granites aimed at understanding magmatic evolution and volatile phase exsolution at shallow levels are necessary if we are to understand ore genesis and the deep inputs to present day geothermal systems as well as evaluate hazards associated with the volcanic

transport of sporosarcina pasteurii in sandstone and its significance for subsurface engineering technologies the development of microbially mediated technologies for subsurface remediation and rock engineering is steadily increasing however we are lacking experimental data and models to predict bacterial movement through rock matrices here breakthrough curves btcs were obtained to quantify the transport of the ureolytic bacterium sporosarcina pasteurii through sandstone cores as a function of core length 1 8 7 5 cm bacterial density 4 10 6 to 9 10 7 cells ml and flow rate 5 8 17 5 m s s pasteurii was easily immobilised within the homogeneous sandstone matrix 80 in comparison to a packed sand column 20 under similar experimental conditions and percentage recovery decreased almost linearly with increasing rock core length moreover a decrease in bacterial density or flow rate enhanced bacterial retention a numerical model based on 1d advection dispersion models used for unconsolidated sand was fitted to the btc data obtained here for sandstone good agreement between data and model was obtained at shorter rock core lengths 4 cm suggesting that physicochemical filtration processes are similar in homogeneous packed sand and sandstones at these lengths discrepancies were however observed at longer core lengths and with varying flow rates indicating that the attributes of consolidated rock might impact bacterial transport progressively more with increasing core length implications of these results on microbial mineralisation technologies currently being developed for sealing fluid paths in subsurface environment is discussed

primary magmatic biotite in granitoid intrusions associated with late mesozoic jinchanggouliang erdaogou lode gold deposits north china craton linkage to gold mineralization abstract the late mesozoic jinchanggouliang and erdaogou lode gold deposits in the central segment of the northern north china craton are mainly hosted in late archaean metamorphic rocks of the jianping formation and jurassic volcanic sedimentary rocks these deposits are spatially and temporally associated with a series of i type granitoid intrusions i e the 128 136 ma duimiangou granodiorite complex with a massive margin and a porphyritic center at jinchanggouliang the 161 4 1 1 ma loushang quartz diorite intrusion and numerous syenite porphyry dykes 160 9 1 0 ma at erdaogou and the 227 217 ma xitaizi monzogranite batholith compositions of primary magmatic biotite in these granitoid intrusions have been used to investigate the nature of granitoid magmas and the evolution of magmatic processes and to identify possible linkages between gold mineralization and granitoid magmatism all primary magmatic biotite grains are mg rich in composition xmg mg mg fe 0 41 0 69 the cl contents of biotite 0 09 0 42 wt in the loushang quartz diorite and the duimiangou massive granodiorite correlate negatively with xmg and are consistent with the mg cl avoidance rule the cl contents of biotite 0 01 0 14 wt in the duimiangou porphyritic granodiorite syenite porphyry and xitaizi monzogranite on the other hand remain relatively constant and may be affected by multiple variables such as cl rich fluids and subtle changes in temperature halogen fugacity of the parental magma calculated from biotite shows that the duimiangou granodiorite complex at jinchanggouliang and syenite porphyry dykes at erdaogou have the log fhf fhcl ranges of 0 71 to 0 27 and 2 16 to 1 08 respectively and have similar log fh2o fhcl values from 3 53 to 4 23 oxygen fugacities logfo2 calculated from biotite equilibria for the duimiangou granodiorite complex and syenite porphyry dykes are 13 7 to 7 2 straddling on the nickel nickel oxide and hematite magnetite buffers the xitaizi monzogranite and the loushang quartz diorite have lower log fo2 values from 14 9 to 12 4 between the nickel nickel oxide and hematite magnetite buffers the duimiangou granodiorite complex and syenite porphyry dykes with high oxygen fugacities are similar to oxidized magmas associated with porphyry cu mo au deposits these results suggest that multiple episodes of i type granitoid magmas in the study area were rich in cl and high in oxygen fugacity especially those associated with the duimiangou granodiorite complex and syenite porphyry dykes the i type melts represented by the duimiangou granodiorite complex and syenite porphyry dykes as well as their related cl rich oxidizing fluids were likely efficient in dissolving transporting and precipitating gold for the formation of the jinchanggouliang and erdaogou lode gold deposits

the behavior of gold in unaltered island arc tholeiitic rocks from izu oshima fuji and osoreyama volcanic areas japan high au concentrations 4 25 ppb in titanomagnetite concentrates from basalts and basaltic andesites of the izu oshima and fuji volcanic areas in the east japan arc indicate that au is strongly partitioned into titanomagnetite relative to the bulk rock the concentration of an in volcanic rocks increases during the early stages of fractional crystallization dominated by olivine pyroxenes and plagioclase but decreases with subsequent fractional crystallization involving titanomagnetite a delay in titanomagnetite formation during fractional crystallization subsequently results in comparatively high concentrations of au in island arc tholeftes wide variations in the au concentration are observed in rocks derived from primary magmas across a single volcanic area and these can be positively correlated with the concentrations of incompatible elements such as rb and zr these features are inherited from a s depleted mantle source since variable degrees of partial melting do not significantly affect the au concentrations of the primary magmas

platinum solubility and partitioning in a felsic melt vapor brine assemblage abstract the solubility and partitioning of pt in a s free vapor brine rhyolite melt pt metal assemblage has been quantified at 800 c f o 2 nno and pressures of 100 and 140 mpa vapor and brine were sampled at run conditions by trapping these phases as glass hosted fluid inclusions as the melt cooled through the glass transition temperature the vapor and brine were in equilibrium with the melt at the time of trapping and thus represent fluids which were sampled at the termination of each experimental run the microthermometrically determined salinities of vapor and brine are 2 and 63 wt nacl eq and 9 and 43 wt nacl eq at 100 and 140 mpa respectively platinum solubilities in vapor brine and glass i e quenched melt were quantified by using laser ablation inductively coupled plasma mass spectrometry la icp ms equilibrium is discussed with reference to the major and trace element concentrations of glass hosted fluid inclusions as well as the silicate melt over run times that varied from 110 to 377 h at 140 mpa and 159 to 564 h at 100 mpa platinum solubility values 1 in h2o saturated felsic melt are 0 28 0 13 g g and 0 38 0 06 g g at 140 and 100 mpa respectively platinum solubility values 1 x at 140 and 100 mpa respectively in aqueous vapor are 0 91 0 29 g g and 0 37 0 17 g g and in are brine 16 10 g g and 3 3 1 0 g g the measured solubility data were used to calculate nernst type partition coefficients for pt between vapor melt brine melt and vapor brine the partition coefficient values 1 x for vapor melt brine melt and vapor brine at 140 mpa are 2 9 1 0 67 27 and 0 13 0 05 and at 100 mpa are 1 0 0 2 6 8 2 4 and 0 15 0 05 the partitioning data were used to model the pt scavenging capacity of vapor and brine during the crystallization driven degassing i e second boiling of a felsic silicate melt over a depth range i e 3 6 km consistent with the evolution of magmatic hydrothermal ore deposits model calculations suggest that aqueous vapor and brine can scavenge sufficient quantities of pt and by analogy other platinum group elements pge to produce economically important pge rich magmatic hydrothermal ore deposits in earth s upper continental crust

fluid immiscibility in volcanic environments volatile components enter the atmosphere oceans and other surface waters through pre syn and post eruptive volcanic processes that involve a variety of fluids aluminosilicate poor fluids include aqueous or carbonic to sulfide sulfate chloride fluoride carbonate and phosphate rich compositions in volcanic environments but other more complex combinations of these constituents may be involved giggenbach 1977 roedder 1984 1992 lowenstern 1995 other rare gases and dissolved constituents e g h2 n2 he ar h3bo3 hg ch4 and other hydrocarbon compounds metals and metalloids are also present but in general they are not sufficiently concentrated to form their own phases or control bulk fluid composition and volcanic processes as a result of their diverse compositions volcanic fluids ranging from vapor to liquid exhibit widely different densities and show strong distinctions in heat capacity dielectric behavior viscosity and other chemical and physical characteristics geiger et al 2006a the density of a saline liquid in the system nacl h2o at 50 mpa and 800 c for example is more than 7 times that of the coexisting aqueous vapor e g 0 2 gm cm3 henley and mcnabb 1978 multiple fluids move mix and or unmix in magma chambers and volcanic conduits in the root zone of fumaroles and in the convective hydrothermal systems that are ubiquitous to volcanic environments hydrothermal systems are typically centered on magmatic intrusions and may include crater lakes at the top of eruptive conduits hydrothermal processes involving two or more fluid phases operate through a variety of geologically relevant shallow crustal pressure temperature composition conditions volcanic fluids occur at supersolidus to subsolidus conditions meaning that the dense aluminosilicate melt that is common to volcanism may or may not be present this chapter addresses the evidence for and occurrence of two or more low density aluminosilicate poor fluids

gold mineralization in the guilaizhuang deposit southwestern shandong province china insights from phase relations among sulfides tellurides selenides and oxides abstract the guilaizhuang gold deposit is composed of limestone and breccia type ores in the limestone ores gold is hosted by pyrite as bearing pyrite and arsenopyrite whereas in the breccia ores tellurides are the main gold carriers selenium often isomorphously substitutes for sulfur in sulfides in the limestone ores but occurs as selenides in the breccia ores hematite is the only oxide in the breccia ores associated with barite and other tellurides in this paper the thermodynamic parameters especially the gibbs free energies of formation and reaction of related sulfides tellurides selenides and oxides are computed to explain the distinct mineral styles in the limestone and breccia type ores we construct the phase relations among minerals delineated by phase diagrams at 250 c the temperature for gold precipitation in the guilaizhuang deposit according to the phase relations between sulfides and selenides we propose that gold has been transported as au hs hse 2 and released during rapid formation of pyrite as pyrite and arsenopyrite at log f s 2 g between 12 8 and 11 4 250 c in the breccia ores log f te 2 g and log f se 2 g are constrained within 12 9 to 9 4 and 12 4 to 6 9 250 c respectively based on the mineral assemblages observed in the ores the phase relations between tellurides and selenides indicate that calaverite the only stable gold telluride mineral in nature was not stable in the breccia ores at 250 c during the gold precipitation based on empa analysis the so called calaverite revealed from microscopic observations is in fact au ag telluride probably derived from the decomposition of sylvanite auagte 4 and petzite auag 3 te 2 the only two stable au ag tellurides in nature at high temperature however we do not exclude the possibility that calaverite occurs in this deposit which may have precipitated in early relatively high tellurium concentration stage preceding gold mineralization selenium was not detected in gold bearing tellurides implying that selenide is unrelated with gold precipitation directly in the breccia ores but can buffer the tellurium fugacity and thus influence the gold precipitation indirectly furthermore in log f o 2 g range of 35 4 at 250 c the majority of the tellurides and selenides can be stable in the breccia ores but residual sulfides are proposed to be oxidized into sulfate minerals which could also free some gold into ores although less important relative to that formed from telluride decomposition