multiple sulfur isotopes monitor fluid evolution of an archean orogenic gold deposit abstract the evolution of a gold bearing hydrothermal fluid from its source to the locus of gold deposition is complex as it experiences rapid changes in thermochemical conditions during ascent through the crust although it is well established that orogenic gold deposits are generated during time periods of abundant crustal growth and or reworking the source of fluid and the thermochemical processes that control gold precipitation remain poorly understood in situ analyses of multiple sulfur isotopes offer a new window into the relationship between source reservoirs of au bearing fluids and the thermochemical processes that occur along their pathway to the final site of mineralisation whereas 34s is able to track changes in the evolution of the thermodynamic conditions of ore forming fluids 33s is virtually indelible and can uniquely fingerprint an archean sedimentary reservoir that has undergone mass independent fractionation of sulfur mif s we combine these two tracers 34s and 33s to characterise a gold bearing laminated quartz breccia ore zone and its sulfide bearing alteration halo in the 6 moz au structurally controlled archean waroonga deposit located in the eastern goldfields superterrane of the yilgarn craton western australia over 250 analyses of gold associated sulfides yield a 34s shift from what is interpreted as an early pre mineralisation phase with chalcopyrite pyrrhotite 34s 0 7 to 2 9 and arsenopyrite cores 34s 0 5 to a syn mineralisation stage reflected in au bearing arsenopyrite rims 34s 7 6 to 1 5 this shift coincides with an unchanging 33s value 33s 0 3 both temporally throughout the au hosting hydrothermal sulfide paragenesis and spatially across the au ore zone these results indicate that sulfur is at least partially recycled from mif s bearing archean sediments further the invariant nature of the observed mif s signature demonstrates that sulfur is derived from a homogeneous mif s bearing fluid reservoir at depth rather than being locally sourced at the site of au precipitation finally by constraining the mif s bearing sulfur source to a fixed reservoir we are able to display the thermochemical evolution of the ore fluid in 34s space and capture the abrupt change in oxidation state that causes au precipitation our results highlight the importance of constraining multiple sulfur isotopes in space and time in order to elucidate the source and evolution of any given au bearing fluid

oxidized and reduced mineral assemblages in greenstone belt rocks of the st ives gold camp western australia vectors to high grade ore bodies in archaean gold deposits hydrothermal sulfide oxide gold mineral assemblages in gold deposits in the archaean st ives gold camp in western australia indicate extremely variable redox conditions during hydrothermal alteration and gold mineralization in space and time reduced alteration assemblages pyrrhotite pyrite occur in deposits in the southwest of the camp e g argo junction deposits and moderately to strongly oxidized assemblages magnetite pyrite hematite pyrite occur in deposits in the central corridor in the northeast e g north orchin revenge deposits reduced mineral assemblages flank the central corridor of oxidized deposits and locally cut across it along e w trending faults oxidized mineral assemblages in the central corridor are focused on gravity lows which are interpreted to reflect abundant felsic porphyritic intrusions at about 1 000 m below present surface hydrothermal magnetite predates and is synchronous with early phases of gold associated albite carbonate pyrite biotite chlorite hydrothermal alteration later stage gold associated pyrite is in equilibrium with hematite the spatial distribution and temporal sequence of iron sulfides and oxides with gold indicate the presence of at least two spatially restricted but broadly synchronous hydrothermal fluids with contrasting redox states sulfur isotope constraints support the argument that the different mineral assemblages reflect differences in redox conditions the 34s values for pyrite for the st ives gold camp range between 8 4 and 5 1 with the negative values occurring in oxidized magnetite rich domains and slightly negative or positive values occurring in reduced pyrrhotitic domains preliminary spatial and paragenetic analysis of the distribution of iron sulfides and oxides in the st ives camp suggests that gold grades are highest where the redox state of the hydrothermal alteration assemblages switches from relatively reduced pyrrhotite pyrite to relatively oxidized magnetite pyrite and hematite pyrite both in space and time gold deposition is inferred to have occurred where fluids of contrasting redox state mixed

laser ablation icp ms trace element systematics of hydrothermal pyrite in gold deposits of the kalgoorlie district western australia the kalgoorlie district in the archean yilgarn craton of western australia contains two world class gold deposits the giant golden mile shear zone system and the mt charlotte quartz vein stockworks mineralization occurs in three styles a fimiston style is characterized by ankerite pyrite hematite magnetite gold replacement b oroya style overprints fimiston ore in the shear zones and is characterized by silica ankerite v muscovite pyrite pyrrhotite gold telluride replacement and c mt charlotte style is characterized by veins with ankerite sericite albite pyrite pyrrhotite gold selvages hydrothermal pyrite is ubiquitous in all styles and occurs in several stages laser ablation inductively coupled plasma mass spectrometry la icp ms spot analyses n 652 were collected on 54 representative samples of pyrite from three deposits smooth sections in the ablation spectra were selected for quantitative analysis excluding peaks caused by micron sized inclusions linear mixed effects lme modeling of the analytical results indicates no systematic differences between the fimiston oroya and mt charlotte styles the variance introduced to the dataset by geological variability reflected in random differences between samples and deposits is large this may be a major reason for difficulties in distinguishing the differences due to mineralization style however there are clear differences between pyrites co existing with different mineral assemblages these indicate a strong control on pyrite chemistry by the composition of the hydrothermal fluids finally au te as systematics show that a substantial proportion of the analyzed pyrites in all deposits fall into the field of gold saturation consistent with the known metallurgical character of the ores mineralogical studies ultra fine grinding and recovery by cyanide leach show that 82 of all gold is present in native grains or in au ag tellurides the refractory nature of the fimiston pyrite concentrates is due to clusters of micron to nano sized inclusions rather than due to abundant lattice bound gold

terrane amalgamation in the eastern goldfields superterrane yilgarn craton evidence from tectonostratigraphic studies of the laverton greenstone belt abstract tectonostratigraphic evolution of the laverton greenstone belt involves amalgamation of structural relics of sedimentary basins and continental fragments in the burtville terrane to the east prior to their accretion to the kurnalpi terrane to the west the burtville terrane records sedimentation and volcanism in a continental setting between 2758 ma and 2715 ma the kurnalpi terrane is dominated by 2715 2700 ma andesitic volcaniclastic rocks with erosional remnants of uplift of the margaret dome a granite gneiss cored batholith north of the laverton domain is interpreted to have been the main driving force for rapid deposition and burial of conglomeratic and turbiditic siliciclastic sequences in the lake carey basin a switch from submarine canyon deposits to deep water turbiditic rocks with time suggests extension and basin formation was initially driven by the uplift of the dome however basin development switched to a flexural phase with increasing sediment load and ongoing uplift to the north the 2663 ma maximum depositional age for the granny smith sequence indicates that active sedimentation may have been occurring contemporaneous with collisional orogeny the collisional orogeny comprises four main episodes of compressive deformation starting after either 2675 ma or 2665 ma and ending at 2650 ma d 1 involved development of n s upright to inclined km scale folds and axial planar foliation and inversion of pre collision extensional faults as reverse faults during east west directed compression d 2 involved reactivation of d 1 reverse faults as transcurrent faults and development of nw se directed dm scale folds with associated axial planar foliation that overprints the early n s foliation d 2 occurred under a ne sw directed compressive stress field to the west the celia fault records d 2 as its first deformation suggesting a westward migrating deformation front the celia fault zone records its second deformation episode d 3 as sinistral reactivation of the fault zone and locally influenced lode gold development d 3 occurred during wnw ese directed maximum compression the final compressive deformation event d 4 involved overprinting of the d 3 shear fabric by conjugate arrays of kink bands in the celia fault zone during a clockwise rotation of the compressive stress field into a nnw sse orientation the tectonic process responsible for such a rapid uplift and deposition of thick synorogenic sediments lateral to the deformation front and penecontemporaneous with collisional orogeny invites comparisons with modern arc related settings the present suture zone between the indo australian plate and the pacific plate in new guinea records active deposition of fluvial sediments laterally along the accretion zone and in thick deep water fans onto the bismarck sea floor

origin of the wangpingxigou pb zn deposit in east qinling orogenic belt china distal response to the giant donggou porphyry mo system abstract the southern margin of the north china craton ncc hosts many world class porphyry mo and vein type pb zn ag deposits forming an important polymetallic metallogenic belt in china even over the world although the mo and pb zn ag mineralization are temporarily and spatially associated with each other their possible genetic links are still unclear to delineate the relationships between the two types of ore mineralization we carried out in situ geochemical and s pb isotopic analyses on sulfides from the two spatially associated deposits i e the wangpingxigou pb zn and donggou porphyry mo deposits in the ore district based on field and microscopic observations on the crosscutting relationships of various veins and paragenetic relationships of various hydrothermal minerals three i iii and four i iv stages of hydrothermal veins have been identified in the wangpingxigou and donggou deposits respectively pyrite grains from stage ii of the wangpingxigou deposit have high co ni ratios mostly 1 and au and as contents similar to those of typical epithermal systems moreover sulfides from this deposit have in situ 206pb 204pb 17 345 17 417 207pb 204pb 15 454 15 514 and 208pb 204pb 38 138 38 364 ratios similar to those of sulfides from the donggou deposit indicating that the two deposits were relevant to a common source the concentrations of many elements i e pb ag sn zn sb mn au and as in pyrite decrease gradually from the stage ii of the wangpingxigou deposit to the stage ii of the donggou deposit consistent with metal zonation typically observed in porphyry related metallogenic systems further considering similar ages of the two deposits we propose that the wangpingxigou pb zn deposit is likely distal to the donggou porphyry mo system the range of 34s values of pyrites 7 63 8 76 from the stage ii in the donggou deposit is similar to those of the ancient strata xiong er group 7 31 8 17 in the ore district indicating that the sulfur in ore forming fluids may be mainly derived from the ancient strata however the 34s values 9 20 9 70 of stage iii sulfides in the donggou deposit are higher than those of stage ii sulfides in the donggou deposit and stage ii sulfides in the wangpingxigou deposit 7 34 9 29 the different sulfur isotopic compositions may be related to varied physicochemical conditions of the ore forming fluids confirmation of a mo pb zn metallogenic system in the region provides important clues on further prospecting of mo and pb zn resources in the southern margin of the north china craton

4d architecture and tectonic evolution of the laverton region eastern yilgarn craton western australia abstract the laverton region located in the eastern yilgarn craton eyc western australia is second only to the kalgoorlie region for gold endowment the integration of high density potential field data regional and camp scale seismic reflection data regional and mine scale structural analysis and geochronologically constrained stratigraphy provided new insights into the 4d architecture and tectonic evolution of laverton region at a regional scale the map patterns of laverton are dominated by the mt margaret dome in the northwest and the kirgella dome in the southeast these domes are flanked to the east and west by north northwest striking shear zones with the central zone between the two domes being dominated by north to north northeast striking sigmoidal shear zones these distinctly different strikes to the shear zones developed early in the tectonic evolution and resulted in a favourable architecture for late stage orogenic gold mineralisation a series of regional seismic reflection lines have imaged the sub surface architecture of the laverton region with a major crustal penetrating shear extending to the moho mapped as the laverton tectonic zone ltz the ltz consists of a basal fault the north northwest striking celia fault and a series of steeper faults for example the north to north northeast striking childe harold fault and far eastern fault which sole at depth into the celia fault beneath the laverton region lower angle faults imaged in the seismic reflection data develop parallel to granite gneiss domes that postdate the north northwest striking and north to northeast striking faults the construction and integration of the new 3d map with the structural stratigraphic and geochronological analysis has defined six main deformation events and their effects on the architectural evolution of the region this analysis suggests that early formed faults are genetically associated with late stage orogenic gold mineralisation regional and mine scale structural analysis at the wallaby and sunrise dam deposits indicate that gold deposition occurred synchronously during the d4b event in both deposits both mines are separated by the ltz which records sinistral and later d5 dextral movement the kinematic model which best describes the observed architecture is a restraining step over within a sinistral strike slip system a structural model consistent with analogue modelling of strike slip systems is proposed where two early extensional basement faults were reactivated during d4b northwest southeast contraction as low angle thrusts in a pop up zone this architecture has been mapped in 3d in the region between wallaby and sunrise dam where both deposits are located on the low angle thrusts on opposing sides of a sigmoidal structure developed during sinistral strike slip movement this strike slip step over architecture provided significant opportunity for dilation and fluid flow late dextral movement of the basement faults during northeast southwest contraction d5 reactivated the low angle thrusts at sunrise dam producing extensional movement and further dilation within the overall restraining step over this event is not significant at wallaby mine a detailed 3d stress analysis at sunrise dam revealed that the most favourable fault segments to reactivate during the d4b event were orientated at 30 towards 310 a comparison of the spatial distribution of gold defined from extensive production and resource estimation drilling with the favourably orientated segments of faults was confirmed the analysis also highlighted down dip extensions beyond the coverage of the drilling of favourably oriented segments which may provide additional targets during future near mine exploration the same approach was applied to the regional 3d map and new targets generated beneath the major salt lake between wallaby and sunrise dam

ore genesis of the late cretaceous larong porphyry w mo deposit eastern tibet evidence from in situ trace elemental and s pb isotopic compositions abstract the late cretaceous ca 92 ma larong porphyry w mo deposit 39 44 mt wo3 0 1541 a newly discovered deposit in the easternmost bangong nujiang metallogenic belt bnmb is located in eastern tibet the w mo mineralization occurs as veins and stock works hosted in monzogranite porphyry granodiorite porphyry and surrounding quartz schist and can be divided into two main paragenetic stages the w mineralization stage stage i consists of various k feldspar quartz scheelite veins and the quartz sulfide stage stage ii is dominated by molybdenite and pyrite of which the latter can be further subdivided into three sub stages here we present la icpms in situ trace elements and s pb isotopes of sulfides from the larong deposit in order to constrain the sources of ore forming elements and the processes of mineralization our study shows that pyrite is rich in co and as molybdenite is rich in w pb and bi and chalcopyrite has high sn contents these results are consistent with the mineralization characteristics of the larong deposit where the main metallogenic elements are w and mo accompanied by bi sn and cu overall sulfides from the larong deposit have calculated 34svcdt values ranging from 0 25 to 6 37 suggesting a predominantly magmatic origin for sulfur from stage ii 1 to stage ii 2 to stage ii 3 the average 34svcdt values of pyrite change from 0 33 to 1 88 to 5 34 showing a progressive and gradual change in redox and temperature conditions molybdenite has high pb isotopic ratios 208pb 204pb 39 356 39 908 207pb 204pb 15 747 15 928 206pb 204pb 18 843 20 120 but low re contents and pyrite has low ni contents implying that the ore forming materials were mainly derived from the crust we propose that the w mo mineralization is genetically related to the late cretaceous monzogranite porphyry with the mineralization of w and mo occurring as a result of decreases in temperature and oxygen fugacity of the ore forming fluid exsolved from the magma in combination with previous studies our study led to the identification of three w dominated polymetallic metallogenic events and mineralization potential of igneous rocks in the bnmb

pyrite textures and compositions in jiangshan gold deposit bengbu uplift southeastern north china craton implications for ore genesis abstract many phanerozoic gold deposits in east china e g those in the jiaodong peninsula hosted either in granitoids of the same age or precambrian basement rocks of the north china craton have been well documented the bengbu uplift along the southeastern margin of the north china craton is believed to be the western extension of the jiaodong gold province separated by the large scale sinistral tan lu fault zone however no deposits with more than 10 t gold resources have been discovered in the bengbu uplift and it is unclear whether the timing and genesis of gold deposits in the bengbu uplift are similar to those in the jiaodong gold province in this study laser ablation inductively coupled plasma mass spectrometry trace element analyses mapping and in situ sulfur isotope analyses were used to determine the source and process of gold mineralization in jiangshan gold deposit the largest in the region the wall rocks in the jiangshan gold deposit are metamorphic rocks of the neo archaean wuhe group and the ore bodies are controlled by the eastern part of the guangou xiajijia fault four stages were identified from cross cutting relationships and textural and mineralogical characteristics pre ore stage stage i quartz pyrite muscovite alteration stage ii pyrite quartz veins stage iii and quartz pyrite veinlets stage iv each of the four stages is characterized by a different type of pyrite here named py1 py2 py3 and py4 py1 formes the core of py2 has elliptical and irregular shapes contains low gold and arsenic concentrations and has 34s values of 0 86 2 86 py2 is hosted in quartz pyrite muscovite altered rocks with disseminated and aggregated euhedral to subhedral textures it has elevated arsenic content and the lowest gold content with some rhythmic zones and fractures stage ii was crosscut by stage iii py3 has anhedral textures with brittle deformation and occupies fractures in stage iii pyrite quartz veins the gold content of py3 is slightly higher than that of py1 and py2 but its arsenic content is extremely low py4 in the quartz pyrite veinlets has cataclastic textures with the highest gold and chalcophile element contents native gold and electrum also formed in stage iv which is the main gold stage in the jiangshan deposit the 34s values of py2 py4 are broadly similar 5 79 7 98 suggesting a common sulfur source based on previous studies and higher 34s values of hydrothermal pyrite the fluid sulfur isotopes are interpreted to relate to degassing of the mantle wedge metasomatized by slab fluids during the westward subduction of the palaeo pacific plate beneath the north china craton during the early cretaceous based on the geological characteristics of the deposit we classify the jiangshan gold deposit as a jiaodong fracture disseminated type gold deposit which occurs as disseminated veinlets and disseminated mineralization in wallrocks along fracture zones tectonic events may be the most important factor in gold mineralization in fracture disseminated type gold deposits

microstructural evolution and trace element mobility in witwatersrand pyrite microstructural analysis of pyrite from a single sample of witwatersrand conglomerate indicates a complex deformation history involving components of both plastic and brittle deformation internal deformation associated with dislocation creep is heterogeneously developed within grains shows no systematic relationship to bulk rock strain or the location of grain boundaries and is interpreted to represent an episode of pyrite deformation that predates the incorporation of detrital pyrite grains into the central rand conglomerates in contrast brittle deformation manifest by grain fragmentation that transects dislocation related microstructures is spatially related to grain contacts and is interpreted to represent post depositional deformation of the central rand conglomerates analysis of the low angle boundaries associated with the early dislocation creep phase of deformation indicates the operation of 100 slip systems however some orientation boundaries have geometrical characteristics that are not consistent with simple 100 deformation these boundaries may represent the combination of multiple slip systems or the operation of the previously unrecognized 120 slip system these boundaries are associated with order of magnitude enrichments in as ni and co that indicate a deformation control on the remobilization of trace elements within pyrite and a potential slip system control on the effectiveness of fast diffusion pathways the results confirm the importance of grain scale elemental remobilization within pyrite prior to their incorporation into the witwatersrand gold bearing conglomerates since the relationship between gold and pyrite is intimately related to the trace element geochemistry of pyrite the results have implications for the application of minor element geochemistry to ore deposit formation suggest a reason for heterogeneous conductivity and localized gold precipitation in natural pyrite and provide a framework for improving mineral processing

source and evolution of ore fluids in the zhenyuan orogenic gold deposit se tibet constraints from the s c o isotopes abstract orogenic gold deposits commonly have large variation of stable isotopic values of ore minerals induced by complicated ore fluids evolution which was considered to provide equivocal evidence for ore sources in contrast this study has revealed relatively narrow range of s and c o isotopes of pyrites and carbonate minerals in the zhenyuan gold deposit 100 t at 3 5 g t on ailaoshan shear zone southeastern margin of tibet the zhenyuan deposit is a disseminated orogenic gold deposit with mineralization and alteration occurring in various types of wall rocks including carbonaceous slate meta quartz sandstone lamprophyre quartz porphyry and meta basalt the pre ore pyrites include the diagenetic pyrites in carbonaceous slate and meta quartz sandstone and the barren hydrothermal pyrites in quartz porphyry diagenetic pyrites have much varied 34s values from 54 58 38 31 and barren hydrothermal pyrites have elevated positive 34s values 8 76 43 24 the ore related pyrites disseminated in all types of host rocks and commonly with repetitive gold rich zones are the most important gold bearing minerals they contain high concentration of au along with other trace elements including cu as sb tl pb and bi little difference of 34s values is observed for the pyrites in different types of host rocks and for the low au and high au zones in single pyrite grain all ore related pyrites display a relatively narrow range of 34s values 5 22 4 16 with a peak at 0 this narrow range implies that the deposition of gold from ore fluids at zhenyuan deposit was mainly controlled by sulfidation of iron bearing minerals in the wall rocks the 34s values of ore related pyrites are consistent with the explanation that the ore fluids were from the subcrustal source instead of the crustal source with much varied sulfide 34s values carbonate minerals from different types of host rocks also have consistent and relatively narrow range of 13cpdb 3 77 0 68 and 18osmow 14 85 20 77 values indicating that the composition of ore fluids were little affected by water rock reaction at deposit scale the 13cpdb and 18osmow values of carbonates minerals are between those of the mantle peridotite and marine carbonates which can be explained by that the ore fluids have experienced crustal carbonate contamination in the subcrustal level or and along the migration conduit of the ore fluids

magmatic evolution and related w mo mineralization in the larong deposit eastern tibet evidence from zircon u pb ages geochemistry and sr nd hf isotopes abstract the late cretaceous ca 92 ma larong porphyry w mo deposit 39 44 mt wo3 0 1541 is the first discovered giant w mo deposit in the leiwuqi zogang metallogenic belt sanjiang region multi stage granitoids including the dacite porphyry dp granodiorite porphyry gp biotite granite porphyry bgp monzogranite porphyry mp biotite granite bg and granite aplite ga have been identified in the larong deposit however the magmatic evolution and related w mo mineralization in this deposit are still poorly understood la icp ms zircon u pb dating of the dp gp bgp mp bg and ga yield weighted mean 206pb 238u ages of 214 0 0 7 ma 213 8 1 3 ma 104 4 0 9 ma 93 9 1 3 ma 91 7 0 5 ma and 36 2 0 6 ma respectively the late triassic dp and gp should be classified as peraluminous a cnk values of 0 95 1 57 s type granitoids they are characterized by pronounced negative end t values 10 01 to 13 92 and ehf t values 8 5 to 16 6 with old tdm2 nd and tdm2 hf ages 1 81 2 12 ga and 1 79 2 30 ga respectively indicating that the dp and gp were mainly derived from partial melting of ancient crustal materials after break off of the paleo tethyan oceanic slab the late cretaceous bgp mp and bg and late eocene ga have low a cnk ratios 0 92 1 06 but high sio2 70 57 77 34 and differentiation index di 87 55 98 06 similar to the characteristics of highly fractionated i type granite detailed elemental e g depletion in nb ta ti sr ba eu and p and isotopic data 87sr 86sr i 0 71192 0 72932 end t 11 81 to 9 11 ehf t 10 4 to 1 4 demonstrate that they were the result of magma mixing between ancient crust derived melts and mantle derived melts the bgp was produced during the final stage of bangong nujiang tethyan ocean bnto subduction the mp and bg were formed under a post collisional tectonic setting related to slab break off of the bnto and the ga was likely associated with delamination of the thickened eclogitic lower crust together with lithospheric mantle the w mo mineralization in the larong deposit is genetically associated with the mp with four favorable factors that can account for the formation of this deposit 1 high w background 2 multi stage magmatism 3 highly evolved relatively oxidized and f rich magmatic system and 4 sufficient calcium obtained by intense fluid rock interaction

fluid density control on vapor liquid partitioning of metals in hydrothermal systems hot aqueous fluids both vapor and saline liquid are primary transporting media for metals in hydrothermal magmatic systems despite the growing geological evidence that the vapor phase formed through boiling of magmatic ore bearing fluids can selectively concentrate and transport metals the physical chemical mechanisms that control the metal vapor liquid fractionation remain poorly understood we performed systematic experiments to investigate the metal vapor liquid partitioning in model water salt gas systems h2o nacl kcl hcl at hydrothermal conditions measurements show that equilibrium vapor liquid fractionation patterns of many metals are directly related to the densities of the coexisting vapor and liquid phases despite differences in the vapor phase chemistry of various metals that form hydroxide chloride or sulfide gaseous molecules of contrasting volatile properties water solute interaction is a key factor that controls the metal transfer by vapor like fluids in earth s crust these findings allow quantitative prediction of the vapor liquid distribution patterns and vapor phase metal transport in a wide range of conditions our density model accounts well for the vapor brine distribution patterns of na si fe zn as sb and ag observed in fluid inclusions from magmatic hydrothermal deposits for au and cu the partitioning in favor of the liquid phase predicted in a sulfur free system contrasts with the copper and gold enrichment observed in natural vapor like inclusions the formation of stable complexes of cu and au with reduced sulfur may allow for their enhanced transport by sulfur enriched magmatic hydrothermal vapors

trace element and sulfur isotopic evidence for redox changes during formation of the wallaby gold deposit western australia abstract wallaby is a major gold deposit of the st ives gold field of western australia with an estimated resource of 8 million ounces of gold it has a well established paragenesis across five vein sets that displays macroscopic evidence of changing redox through time from hematite to magnetite micro analysis of pyrite from each vein generation shows a progressive and gradual change in redox conditions the sulfur isotope composition has a 34 s range of 7 7 to 9 8 using 3 m spots on the sensitive high resolution iron micro probe stable isotope shrimp si negative values indicative of an oxidized sulfur signature are found in the earliest generation of pyrite which coexists with hematite that also contains high concentrations of as ni zn ag sb cu and pb conversely positive values representative of reduced sulfur are found in later generations of pyrite with lower concentrations of as ni sb cu zn and pb these later pyrite crystals display higher as ni as sb and as bi and lower cu te these geochemical trends are the result of redox controlled transport and partitioning into pyrite of minor and trace elements now within the pyrite structure previous studies suggested a single orogenic event formed the wallaby deposit this is not supported by the present study trace element ratios such as as ni clearly delineate the high au generations and could be used as an exploration tool it is suggested that pyrite from the wallaby gold deposit formed via desulfidation and a gradual change in redox conditions within an evolving fluid and did not result from mixing of two separate fluids as previously advocated utilizing pyrite to link the entire fluid history of wallaby demonstrates the general use of pyrite as a valuable mineral tracer in gold bearing fluid systems

tectono stratigraphy of late archaean greenstone terranes in the southern eastern goldfields western australia abstract late archaean greenstone terranes in the southern part of the eastern goldfields are regionally extensive faultbounded entities defined on the basis of small but distinct differences in stratigraphy and structure the greenstones comprise volcano sedimentary successions that were all deposited at the same time c 2720 2675 ma on sialic crust hence the terranes are interpreted to represent contemporaneous probably adjacent basins these basins were affected by the same history of granite plutonism and regional deformation c 2675 2620 ma early subhorizontal deformation is poorly understood but includes at least locally significant thrust stacking d1 with a south to north movement direction this was followed by regional east west extension affecting all supracrustal successions above a province wide detachment now lying at depths between 4 and 7 km this detachment may have evolved from the greenstone basement contact but only after extensive reworking clastic basins developed along or above major extensional faults but no volcanism is associated with this extension subsequent east west d2 shortening resulted in regional scale thrusting folding and associated late stage transcurrent fault movements the d2 event is contemporaneous with a major thermal event represented by voluminous granite emplacement c 2660 ma and associated peak regional metamorphism in the greenstone succession predominantly monzo granite derived from older sialic crust was emplaced throughout the period of basin formation and deformation early synvolcanic granite c 2719 2710 ma is a minor component late synvolcanic granite c 2685 2675 ma is widespread and syn d2 granite c 2660 ma is abundant there are a few small late tectonic intrusions c 2640 ma to 2600 ma the lateral lithostratigraphic persistence of the contemporaneous basins the syn d2 low pressure regional metamorphism and the province wide monzo granite magmatism suggest that the greenstone basins possibly developed in a tectonic setting similar to that of failed rifts above aborted spreading centres the basins closed in response to far field compressional stresses

sulfur isotope and metal variations in sulfides in the bif hosted orogenic cuiaba gold deposit brazil implications for the hydrothermal fluid evolution abstract textural chemical and multiple sulfur isotope analyses of sulfides from the archean world class cuiaba orogenic au deposit quadrilatero ferrifero district brazil were conducted to track distinct trace element signatures from syngenetic to epigenetic hydrothermal pyrite types in different host units and to deduce the nature and source of the mineralizing fluids gold mineralization in cuiaba is hosted in greenschist facies volcanic and sedimentary host rocks belonging to the archean rio das velhas supergroup especially in association with quartz veins and sulfide minerals the bif hosted fonte grande sul orebody is controlled by quartz veins and disseminated gold bearing pyrite pyrrhotite and arsenopyrite in the wall rocks five pyrite types are classified based on textural relations as spongy syngenetic py1 porous early py2 smooth main py3 and smooth isolated and overgrown late stage py4 and py5 types variably present in metamorphosed carbonaceous pelites bif and andesite besides pyrite pyrrhotite and arsenopyrite are also defined according to textural and paragenetic differences and they display significant trace element contents trace element abundance maps and la icp ms analyses display trace element incorporations in py1 present only in carbonaceous pelite py2 and py3 in all host rocks and py4 and py5 only in bif py1 yields high as co ni pb and ag concentrations whereas py2 formed by agglomeration of py1 maintains high trace element concentrations with slightly less of those elements trace element incorporation in py3 is similar to py1 in carbonaceous pelite early stage py2 and main stage py3 in bif and andesite have increased co and ni but have less au and as late stage py4 is characterized by lower trace element concentrations whereas py5 is further enriched in as bi co ni and pb the hydrothermal alteration is divided into early main and late stage which correlate to the sulfide hydrothermal evolution the study shows that carbonaceous pelite is pre enriched in co ni and pb whereas certain elements like ag au bi and as are only hydrothermally concentrated either during the early main or late stage in bif and andesite this geochemical pattern supports a syngenetic versus hydrothermal origin of distinct elements including some trace elements now in the ore zones multiple sulfur isotope data suggest that mineralizing fluids at the cuiaba gold deposit reflect a complex mixing of sulfur evolved from three possible sources seawater mantle and reduced elemental sulfur spongy syngenetic py1 yields 33s values ranging from 2 28 to 0 25 separated into two ranges the first from 2 28 to 1 97 and the second from 0 96 to 0 25 the first range suggests py1 in the carbonaceous pelite was deposited in a seawater environment these pyrites probably mixed with later mantle sulfur carrying a near zero 33s signature which is indicated by the second 33s range or could have mixed with fluids sourced from sedimentary rocks at depth carrying a positive 33s signature the second scenario is more common in sedimentary and diagenetic pyrites an unequivocal contrast is shown by early main and late stage pyrite types py2 py3 py4 and py5 in carbonaceous pelite bif and andesite which present a continuous process of crustal assimilation values towards increasingly positive 34s and 33s values this confirms evidence for a sedimentary derived sulfur source as also indicated by fluid inclusion data of the andesite hosted orebody at the cuiaba deposit

detection and prediction of warm season midtropospheric vortices by the rapid update cycle the authors perform a statistical and dynamical analysis of midtropospheric mesoscale vortices captured by analyses from the rapid update cycle version 2 ruc 2 during the period 1 may to 31 august 1999 a total of 203 vortices meeting conditions of an automated algorithm were found of these 86 were observed to form within organized convection and were termed mesoscale convective vortices mcvs mcvs were favored over a broad area from eastern colorado and western nebraska to the mississippi river valley essentially collocated with the loci of organized convection the remaining 117 vortices termed dry vortices clustered in the immediate lee of the rocky mountains and over the southeastern united states vortices arising from convection had considerably greater intensity and longevity than dry vortices they were roughly five times more likely to be involved with the triggering of new convection a relationship was found between intensity and longevity such that there appears to be a maximum vortex lifetime that can be estimated from its maximum intensity vortices arising from convection had markedly greater humidity and water vapor mixing ratio underneath their centers compared to dry vortices consistent with many dry vortices having a topographic origin and mcvs arising from organized convection parameters such as horizontal scale background vertical wind shear and horizontal deformation were not systematically related to intensity or longevity prediction of mesoscale vortices by the ruc 2 was examined for a subsample of all cases in general the ruc 2 was able to predict the evolution of vortices once analyzed but had virtually no skill at predicting 12 h in advance the formation of the vortices however forecasts of organized convection should still benefit from accurate predictions of long lived vortex tracks

reduced and oxidized au cu bi iron oxide deposits of the tennant creek inlier australia an integrated geologic and chemical model iron oxide associated au cu bi deposits of the tennant creek gold field range from magnetite pyrrhotite pyrite reduced cu rich deposits through sulfide poor magnetite rich high grade au bi intermediate f o2 deposits to hematite rich high grade au oxidized deposits discordant magnetite hematite chlorite quartz ironstone bodies that host the ore formed hydrothermally during the 1840 to 1860 ma barramundi orogeny at temperatures up to 350 to 400 c and 2 5 to 5 kbars deposition of ironstone minerals was localized by dilatency that was generated during d1 reverse shearing and folding a separate au cu bi hydrothermal stage overprinted selected ironstones during d2 at or before 1825 to 1830 ma where favorable d1 structures and fluid pathways were reactivated the extremes of the reduced to oxidized deposit spectrum represent divergent chemical conditions that cannot be reconciled by the action of a single fluid we have identified both reducing and oxidizing fluids that helped to form the au cu bi deposits at the west peko deposit which represents the reduced end member subtype constraints from oxide silicate sulfide mineral stabilities fluid inclusions and chlorite thermochemistry indicate that au cu bi ore was introduced into ironstone at 300 to 340 c by a reducing pyrrhotite stable weakly acidic sulfur rich and n2 ch4 rich aqueous fluid containing 3 to 10 wt percent nacl equiv an ore fluid source outside the relatively oxidized metasedimentary host sequence warramunga formation is implied we suggest similar ore fluids for other reduced cu and sulfide rich deposits in the district chemical mass transfer modeling of reactions between reducing fluid and ironstone incorporating estimated thermodynamic properties for aqueous bismuth complexes indicates that highly efficient gold and native bi deposition was predominantly in response to desulfidation and oxidation of the fluid chalcopyrite precipitated mainly in response to increased ph gold bismuth ore in the eldorado deposit an oxidized and hematitic end member is interpreted to have involved mixing of an oxidizing hematite stable ca na cl brine with an intermediate f o2 low to moderate salinity ore fluid as well as reaction of both fluids with ironstone furthermore the mass transfer modeling suggests that mixing of reducing and oxidizing fluids in the absence of ironstones could have resulted in high grade au deposits lacking fe oxides a subtype that has received comparatively little exploration attention in the tennant creek district

archean high mg monzodiorite syenite epidote skarn and biotite sericite gold lodes in the granny smith wallaby district australia u pb and re os chronometry of two intrusion related hydrothermal systems the granny smith 37 t au production and wallaby deposits 38 t out of a 180 t au resource are located northeast of kalgoorlie in 2 7 ga greenstones of the eastern goldfields province the youngest orogenic belt of the yilgarn craton western australia at granny smith a zoned monzodiorite granodiorite stock dated by a concordant titanite zircon u pb age of 2 665 3 ma cuts across east dipping thrust faults the stock is fractured but not displaced and sets a minimum age for large scale 1 km thrust faulting d2 regional folding d1 and dynamothermal metamorphism in the mining district the local gold pyrite mineralization controlled by fractured fault zones is younger than 2 665 3 ma in augite hornblende monzodiorite alteration progressed from a hematite stained alkali feldspar quartz calcite assemblage and quartz molybdenite pyrite veins to a late reduced sericite dolomite albite assemblage gold related monazite and xenotime define a u pb age of 2 660 5 ma and molybdenite from veins a re os isochron age of 2 661 6 ma indicating that mineralization took place shortly after the emplacement of the main stock perhaps coincident with the intrusion of late alkali granite dikes at wallaby a ne trending swarm of porphyry dikes comprising augite monzonite monzodiorite and minor kersantite intrudes folded and thrust faulted molasse the conglomerate and the dikes are overprinted by barren 1 600 m long replacement pipe which is intruded by a younger ring dike of syenite porphyry pervasively altered to muscovite calcite pyrite skarn and syenite are cut by pink biotite calcite veins containing magnetite pyrite and subeconomic gold silver mineralization au ag 0 2 the veins are associated with red biotite sericite calcite albite alteration in adjacent monzonite dikes structural relations and the concordant titanite u pb age of the skarn constrain intrusion related mineralization to 2 662 3 ma the main stage gold pyrite ore au ag 10 forms hematite stained sericite dolomite albite lodes in stacked d2 reverse faults which offset skarn syenite and the biotite calcite veins by up to 25 m the molybdenite re os age 2 661 10 ma of the ore suggests a genetic link to intrusive activity but is in apparent conflict with a monazite xenotime u pb age 2 651 6 ma which differs from that of the skarn at the 95 confidence level the time relationships at both gold deposits are inconsistent with orogenic models invoking a principal role for metamorphic fluids released during the main phase of compression in the fold belt instead mineralization is related in space and time to late orogenic magnetite series high mg monzodiorite syenite intrusions of mantle origin characterized by mg mg fetotal 0 31 0 57 high cr 34 96 ppm ni 22 63 ppm ba 1 056 2 321 ppm sr 1 268 2 457 ppm th 15 36 ppm and rare earth elements total ree 343 523 ppm at wallaby shared ca k co2 metasomatism and th ree enrichment in allanite link au ag mineralization in biotite calcite veins to the formation of the giant epidote skarn implicating a th ree rich syenite pluton at depth as the source of the oxidized hydrothermal fluid at granny smith lead isotope data and the rb th u signature of early hematite bearing wall rock alteration point to fluid released by the source pluton of the differentiated alkali granite dikes

potential vorticity anomalies associated with squall lines abstract this study involves observations and model simulations of potential vorticity anomalies in the wake of midlatitude squall lines using data from the oklahoma kansas pre storm experiment we analyze potential vorticity fields near two squall lines one with and one without a trailing stratiform region from this observational analysis we suggest that squall lines with trailing stratiform regions can leave large positive midtropospheric potential vorticity anomalies in their wake to further interpret these observations we consider a two dimensional version of semigeostrophic theory formulated in isentropic and geostrophic coordinates which results in a simple potential pseudodensity inverse potential vorticity equation using apparent heat source fields that model those computed diagnostically from pre storm data we find that theory does indeed predict large midtropospheric potential vorticity anomalies for model squall lines with a trailing stratiform region but not for model squall lines t

flash vaporization during earthquakes evidenced by gold deposits fluids flowing through cavities in earth s crust can deposit gold thermo mechanical modelling of a fluid filled cavity that expands suddenly during an earthquake shows that the drop in pressure would cause the fluid to vaporize and deposit the gold almost instantaneously

fragmentation of stratospheric intrusions evidence is presented pointing to the existence of rich and coherent subsynoptic and mesoscale flow features at tropopause levels these features are related to and evolve from the classical v shaped intrusions of stratospheric air down to tropospheric elevations it is shown that intrusions can develop into elongated 2000 3000 km and slender 200 km streamers and that thereafter such a streamer can roll up to form a train of stalactite shaped vortex subentities with an accompanying substantial thinning of the intervening filament in addition there are indications that the vortices themselves can develop a spirallike interior structure of interleaved stratospheric and tropospheric air these inferences are based upon two independent but complementary sources analysis of the potential vorticity distribution on tropopause transcending isentropic surfaces derived from the analysis fields of the european centre for medium range weather forecasts either directly or indirectly using a contour advection technique and imagery from the water vapor channel of the european space agency meteosat 4 satellite streamers were observed to occur with a frequency of approximately one per week over central and southern europe during the winter of 1991 1992 the fragmentation is linked to the instability or self development of a filament of enhanced potential vorticity and it can modify or instigate surface weather systems moreover by inducing a substantial and rapid enlargement of the intrusion s surface area it greatly enhances the potential for local irreversible mixing of stratospheric and tropospheric air

the crustal continuum model for late archaean lode gold deposits of the yilgarn block western australia most archaean gold ores belong to a coherent genetic group of structurally controlled lode deposits that are characteristically enriched in au with variable enrichments in ag as w sb bi te b and pb but rarely cu or zn and are surrounded by wallrock alteration haloes enriched in k lile and co2 with variable na and or ca addition evidence from the yilgarn block of western australia combined with similar evidence from canada and elsewhere indicates that such deposits represent a crustal continuum that formed under a variety of crustal regimes over at least a 15 km crustal profile at pt conditions ranging from 180 c at 1 kb to 700 c at 5 kb individual deposits separated by tens to hundreds of kilometres collectively show transitional variations in structural style of mineralisation vein textures and mineralogy of wallrock alteration that relate to the pt conditions of their formation at varying crustal depths specific transitions within the total spectrum may be shown also by deposits within gold camps although nowhere is the entire continuum of deposits recorded from a single gold camp or even greenstone belt

the world class wallaby gold deposit laverton western australia an orogenic style overprint on a magmatic hydrothermal magnetite calcite alteration pipe gold mineralisation at the wallaby gold deposit is hosted by a 1 200 m thick mafic conglomerate the conglomerate is intruded by an apparently comagmatic alkaline dyke suite displaying increasing fractionation through mafic monzonite monzonite syenite syenite porphyry to late stage carbonatite in the mine area a pipe shaped zone of actinolite magnetite epidote calcite amec alteration overprints the conglomerate gold mineralisation associated with dolomite albite quartz pyrite alteration is hosted in a series of sub horizontal structurally controlled zones that are largely confined within the magnetite rich pipe the deposit has a current ore reserve of 2 0 moz au and a total resource of 7 1 moz au

a mesoscale convective complex generated inertially stable warm core vortex abstract a long lived mesoscale convectively generated vortex mcv associated with a mesoscale convective complex mcc is documented the mcv with a rossby number of approximately 0 5 is investigated as a feature intrinsic to the organization of the mcc on 6 7 july 1982 a particularly large and intense mcc developed in a region of high convective available potential energy cape but weak vertical wind shear bulk richardson number 150 and weak advection of temperature and vorticity convection initially was organized in a narrow line with elements propagating relative to the mean environmental flow these elements subsequently developed a large semicircular area of stratiform precipitation and a surface mesolow to the rear heavy rain fell over a broad area amounts as great as 10 9 cm accompanied by flooding were reported in central oklahoma as the large semicircular rain area dissipated a three layered structure became evident a large upper tropospheric anticyclone a rain cooled mesoscale h

syenitic group intrusions of the archean kurnalpi terrane yilgarn craton hosts to ancient alkali porphyry gold deposits abstract archean alkali rich syenitic group intrusions in the eastern goldfields superterrane yilgarn craton are chemically similar to intrusions associated with phanerozoic alkali porphyry systems high temperature potassic and ferruginous alteration associated with the yilgarn intrusions are also similar to those in phanerozoic counterparts but these are generally not well mineralized disseminated and fracture controlled gold mineralization associated with syenitic group intrusions is commonly hosted by mesothermal albite carbonate pyrite assemblages the origin of which is ambiguous this communication aims to stimulate discussion on the origin of gold in and around syenitic group intrusions and the apparent absence of significant gold or copper mineralization in associated high temperature alteration gold associated with syenitic group intrusions in the yilgarn craton has many similar characteristics to disseminated gold deposits associated with syenitic intrusions in the abitibi greenstone belt canada and may be present in other archean greenstone belts

mantle dynamics and cretaceous magmatism in east central china insight from teleseismic tomograms abstract both the rich mineralization in the lower yangtze block lyb and the post collisional mafic rocks in the dabie orogen dbo are closely related to the cretaceous magmatism in east central china various geodynamic models have been proposed for explaining the mechanism of the cretaceous magmatism but these models are controversial and even contradictory with each other especially on the mechanism of adakites a unified geodynamic model is required for explaining the magmatism in east central china in particular the spatial and temporal correlations of magmatic activity in the dbo and that in the lyb for this purpose we apply teleseismic tomography to study p wave velocity structure down to 800 km depth beneath east central china a modified multiple channel cross correlation method is used to collect 28 805 high quality p wave arrival time data from seismograms of distant earthquakes recorded by permanent seismic stations and our temporary stations in the study region to remove the influence of crustal heterogeneity on the mantle tomography we used the crust1 0 model to correct the teleseismic relative residuals our tomography revealed distinct high velocity high v anomalies beneath the dbo and two flanks of the lyb and low velocity low v anomalies above the high v zones combining our tomographic images with previous geological geochemical and geophysical results we infer that these high v and low v anomalies reflect the detached lithosphere and upwelling asthenospheric materials respectively which are associated with the late mesozoic dynamic process and the cretaceous magmatism we propose a double slab subduction model that a ridge subduction yielded the adakitic rocks in the lyb during 150 135 ma and the subsequent pacific plate subduction played a crucial role in not only the formation of igneous rocks in the lyb but also remelting of the subducted south china block beneath the dbo during 135 101 ma

remobilization of metasomatized mantle lithosphere a new model for the jiaodong gold province eastern china the 120 ma jiaodong province in the north china craton composed of abundant mesozoic granites that intrude precambrian metamorphic basement is bordered by the sulu orogenic belt which formed through the collision between the north china and yangtze cratons in the triassic insights on the geodynamic setting and source of gold and fluids in the jiaodong gold province are based on a detailed study of the sanshandao deposit the 13cpdb and 18o values of hydrothermal calcite from this deposit range from 4 3 to 6 5 and 11 4 to 15 1 respectively which are compatible with a mantle source pre ore mafic dykes in the deposit show typical arc like geochemical features suggesting that the mantle source was metasomatized prior to the basic magmatism the 34s values of gold related pyrite from sanshandao and other large deposits in the province range from 10 9 to 11 5 and are higher than those of the country rocks but consistent with the signature of orogenic gold deposits sourced from a neoproterozoic sedimentary reservoir these high positive 34s values are interpreted to be inherited from auriferous neoproterozoic sedimentary rocks of the northern yangtze craton which were subducted into the mantle lithosphere beneath the north china craton during the formation of eclogite in the adjacent sulu orogenic belt in the triassic the syn ore lower cretaceous mafic dykes display oceanic island basalt like geochemical features suggesting that asthenosphere upwelling triggered the release of gold and sulfur from an enriched and fertilized mantle lithosphere contributing to the auriferous fluid which formed the widespread gold mineralization in the jiaodong province at ca 120 ma

multistage processes linked to tectonic transition in the genesis of orogenic gold deposit a case study from the shanggong lode deposit east qinling china abstract the shanggong lode deposit represents one of the largest mesozoic orogenic gold deposits in the east qinling metallogenic belt of central china here we investigate the texture trace element and sulfur isotopic composition of pyrite from this deposit to gain insights in the ore genesis three types of pyrite are recognized by its texture py1 is represented by coarse grained cubic and pentagonal dodecahedron belonging to the stage i quartz pyrite vein py2 comprises fine grained disseminated pentagonal dodecahedron belonging to stage ii quartz sulfides vein py2 can be further divided into core and rim porous cores py2c carrying abundant visible mineral inclusions and significantly higher arsenic concentration and clean rims py2r with low arsenic systematic la icpms trace elements and sims sulfur isotopic analyses reveal two distinct stages of mineralization with diverse source materials 1 the early stage is represented by py1 which contains 0 65 70 ppm au average 11 6 ppm with relatively low and variable concentrations of cu ag te pb zn and bi the 34 s values of py1 range from 2 7 to 7 2 suggesting that the sulfur source for the early stage fluid was mainly derived from the taihua and xiong er groups and that the depleted 34 s values reflect changes of ph f o2 and fluid rock interaction 2 the main stage is represented by py2 which contains au in the range of 0 14 189 ppm average 39 7 ppm the py2 carries significantly higher contents of compatible elements ni co v and cr and ore metals e g au ag pb zn as te than those in py1 with the ore metals occurring as invisible lattice bound or nanosized particles and visible micron sized inclusions the 34 s values of py2 show marked depletion with a range of 16 3 to 11 7 attributing to the fractionation between barite and sulfide minerals together with previous studies and trace element characters in py2 we identify a contribution of au from mantle source into the ore forming fluid system during the main stage we propose that the two stages of gold mineralization in the shanggong deposit in response to the collisional assembly of qinling orogenic belt preserve evidence for diverse metal sources with the early stage derived from partial melting of the lower crust taihua and xiong er groups in the compressional stage and the main stage characterized by mantle contribution in a post collisional extensional setting our findings may have important implications for the exploration of regional triassic gold and molybdenum deposits

linking high grade gold mineralization to earthquake induced fault valve processes in the porgera gold deposit papua new guinea processes responsible for high grade gold enrichment are of significant economic interest and have long been elusive structural and geophysical models postulate that earthquake induced fault valve processes are frequently responsible for gold mineralization in structurally controlled hydrothermal systems although a comprehensive geochemical record of these processes has been lacking the porgera gold deposit papua new guinea provides an opportunity to examine the complex processes surrounding high grade au mineralization in structurally controlled hydrothermal systems new high resolution trace element and sulfur isotope data obtained in situ by laser ablation inductively coupled plasma mass spectrometry and sensitive high resolution ion microprobe stable isotope analysis of pyrite across a well constrained paragenetic sequence reveal a temporal evolution in fluid chemistry the data uncover a stratigraphy of repeated high au negative 34 s and low au positive 34 s zones within individual pyrite crystals present in the highest grade gold event stage ii results provide the first clear geochemical documentation of rapid complete switching in ore forming processes preserved in individual pyrite crystals throughout an evolving hydrothermal system it is postulated that geochemical variations are attributable to rapid au deposition during pressure release due to fault failure followed by switching to more reduced rock buffered metal poor fluids from adjacent sediments as the rupture seals the cyclicity of this process is reflected in the pyrite zonation seen at the porgera deposit this study demonstrates the usefulness of applying contemporary analytical techniques to pyrite in hydrothermal systems to gain new insights into ore genesis and fluid pathways revealing that deposition of exceptionally high grade ore at the porgera deposit was the result of multiple events in a fluctuating ore forming environment

influence of structural setting on sulphur isotopes in archean orogenic gold deposits eastern goldfields province yilgarn western australia the published mean 34s values of ore related pyrites from orogenic gold deposits of the eastern goldfields province yilgarn craton lie between 4 and 4 as for orogenic gold deposits worldwide most deposits have positive means and a restricted range of 34s values but some have negative means and wider ranges of 34s values wall rock carbonation and back mixing of similar source fluids with different fluid pathways can explain some of the more negative 34s signatures however structural setting appears to be the most important factor controlling ore fluid oxidation state and hence the distribution of 34s values in gold related pyrites shear hosted deposits appear to have experienced fluid dominated processes such as phase separation whereas stockwork vein hosted or disseminated deposits formed under conditions of greater rock buffering at victory defiance in particular negative 34s values are more common in gently dipping dilational structures compared to more compressional steeply dipping structures it appears most likely that fluid pressure fluctuations during fault valve cycles establish different fluid flow regimes in structures with different orientations rapid fluid pressure fluctuations in dilational structures during seismic activity can cause partitioning of reduced gas phases from the ore fluid during extreme phase separation and hence are an effective method of ore fluid oxidation leading to large local fluctuations in oxidation state it is thus not necessary to invoke mixing with oxidised magmatic fluids to explain 34s signatures indicative of oxidation in any case available robust geochronology in the eastern goldfields province does not support the direct involvement of oxidised magmatic fluids from adjacent granitic intrusions in orogenic gold genesis thus negative mean 34s values and large variations in 34s values of ore related pyrites in world class orogenic gold deposits are interpreted to result from multiple mechanisms of gold precipitation from a single ubiquitous ore fluid in varying structural settings rather than from the involvement of oxidised ore fluids from a different source such signatures are indicative but not diagnostic of anomalously large orogenic gold systems

midlevel cyclonic vortices generated by mesoseale convective systems abstract despite the large number of convective systems that occur over the central united states every year there are typically only a few well defined midlevel vortices apparent in satellite imagery after the overlying anvil debris from some convective complexes has dissipated or advected away a climatology of mesoscale convectively generated vortex mcv events for 1981 1988 is presented and the synoptic setting in which the circulation becomes apparent is discussed proximity sounding data from numerous cases are used to examine features of the kinematic and thermodynamic setting of mcvs at various lifelycle stages defined by satellite imagery features ofthe large scale environment that appear conducive to the formation and longevity of mcvs include weak flow weak vertical shear weak background relative vorticity and intense horizontal and vertical moisture gradients the rapid mesovortex generation observed can be explained by the stretching term of the vorticity equation most mcvs emerge fro

geology mineralogy and stable isotope geochemistry of the dzuunmod area in northern mongolia constraints for gold ore genesis and sources abstract the dzuunmod area located in the north khentii gold belt nkgb of northern mongolia includes lode gold deposits such as gatsuurt sujigtei and boroo with several minor gold deposits and occurrences they show similar hydrothermal alteration assemblages sericitic siliceous and potassic and ore mineral assemblages pyrite and arsenopyrite with minor amount of galena sphalerite and chalcopyrite gold occurs as native form and invisible gold in pyrite and arsenopyrite the major sulfide minerals are separated into earlier non auriferous stage and later auriferous grains containing invisible gold native gold postdates the major sulfide mineralization gold and arsenic content of pyrite grains indicates that gold exists mainly as solid solution form au 1 in the gatsuurt and boroo deposit whereas gold nanoparticle au0 is present in the sujigtei deposit high co ni and mo ni ratios of pyrite grain suggest a post sedimentary or hydrothermal origin and the ore forming fluid was significantly affected by fluid host rock interactions during mineralization processes large variation of 34s values of pyrite and arsenopyrite from 2 6 to 17 2 indicates that sulfur seems to be mainly derived from a source with heterogeneous sulfur isotope composition even though the role of magmatic sulfur as one of possible sulfur sources cannot be ruled out consistent with geological evidence relatively positive 34s values suggest that sulfidation plays an important role for gold and sulfide precipitation the calculated 18o values of hydrothermal fluid from the measured 18o values of quartz samples from 14 7 to 17 7 indicate a metamorphic derivation of ore forming fluid gold mineralization processes in the dzuunmod area seem to occur several times by multiple input of hydrothermal fluid and fluid host rock interactions the gold deposits in the dzuunmod area are considered to be orogenic gold type influenced by fluid host rock interactions in the deposit area

pyrite as a record of hydrothermal fluid evolution in a porphyry copper system a sims empa trace element study porphyry copper deposits are currently the world s largest source of copper and molybdenum and are also among the largest reservoirs of gold in the upper crust despite the fact that pyrite is a ubiquitous mineral phase in these deposits and secondary cu enrichment processes are commonly controlled by the abundance of this sulfide the major and trace element chemistry of pyrite from porphyry systems remains unconstrained in this study we report the first comprehensive trace element database of pyrite from the dexing deposit china s largest porphyry cu deposit by combining high spatial resolution and x ray mapping capabilities of electron microprobe analysis empa with low detection limits and depth profiling capabilities of secondary ion mass spectrometry sims in a suite of samples from the dexing deposit we show that the concentrations of precious metals e g au ag metalloids e g as sb se te and heavy metals e g cu co ni zn hg in pyrite from porphyry systems are more significant than previously thought among the elements analyzed cu as au and ni are the most abundant with concentrations that vary from sub ppm levels to a few wt i e 6 wt cu 3 wt as 0 25 wt au and 0 2 wt ni detailed wavelength dispersive spectrometry wds x ray maps and sims depth vs isotope concentration profiles reveal that pyrite from the dexing deposit is characterized by complex chemical zoning where the studied elements occur in different mineralogical forms while as occurs as a structurally bound element in pyrite cu and au can occur as both solid solution and micro to nano sized particles of chalcopyrite and native au or au tellurides respectively indicating that pyrite can control metal speciation and partitioning during porphyry cu mineralization the well developed oscillatory zoning detected in pyrite where cu rich as depleted growth zones alternate with cu depleted as rich layers indicates that cu is geochemically decoupled from as suggesting that this selective partitioning of metals into pyrite is most likely the result of changes in hydrothermal fluid composition

gold and trace element zonation in pyrite using a laser imaging technique implications for the timing of gold in orogenic and carlin style sediment hosted deposits laser ablation icp ms imaging of gold and other trace elements in pyrite from four different sedimenthosted gold arsenic deposits has revealed two distinct episodes of gold enrichment in each deposit an early synsedimentary stage where invisible gold is concentrated in arsenian diagenetic pyrite along with other trace elements in particular as ni pb zn ag mo te v and se and a later hydrothermal stage where gold forms as either free gold grains in cracks in overgrowth metamorphic and or hydrothermal pyrite or as narrow goldarsenic rims on the outermost parts of the overgrowth hydrothermal pyrite compared to the diagenetic pyrites the hydrothermal pyrites are commonly depleted in ni v zn pb and ag with cyclic zones of co ni and as concentration the outermost hydrothermal pyrite rims are either as au rich as in moderate to highgrade deposits such as carlin and bendigo or co ni rich and as au poor as in moderate to low grade deposits such as sukhoi log and spanish mountain the early enrichment of gold in arsenic bearing syngenetic to diagenetic pyrite within black shale facies of sedimentary basins is proposed as a critical requirement for the later development of carlin style and orogenic gold deposits in sedimentary environments the best grade sediment hosted deposits appear to have the gold climax event toward the final stages of deformation related hydrothermal pyrite growth and fluid flow

trace element and fluid inclusion geochemistry constraint for genesis of gold polymetallic mineralization in the songhung deposit dpr korea abstract the songhung deposit is located in the southwestern part of the yangdok metamorphic core complex ymcc in the northern portion of the pyongnam basin the eastern part of the sino korean craton in this paper we present a detailed study on the magma sources of the granitoids yangdok and hoechang graintic intrusions genesis of pyrite and fluid inclusion characteristics for sufficient and additional understanding of tectonic events petrogenesis of the granitoids and mineralization in the study deposit the yangdok granite has lower al2o3 tio2 ratios mean value of 60 58 than the hoechang granite mean value of 994 46 indicating the higher temperature magma source of the former on the rb ba vs rb sr and cao tfeo mgo tio2 vs cao tfeo mgo tio2 discriminant diagrams the magma source of the yangdok granite belongs in the plagioclase rich and clay poor source rocks while those of the hoechang granite plots either in the plagioclase rich and clay poor source rocks for granite and fine grained granite or in the plagioclase poor and clay rich source rocks for granite porphyry and felsite on the nb vs y ta vs yb rb vs y nb and rb vs yb ta tectonomagmatic discrimination diagrams these two granites are connected with the volcanic arc related setting and plot in post collision setting moreover some data of the hoechang granite fall in wpg field suggesting that the volcanic arc setting may be changed to an intraplate setting from middle cretaceous the pyrite trace element geochemistry showing the high co ni ratio than one with an average of 8 2 and high co content and low ni content suggests that its formation was closely linked with i type granitic magma derived hydrothermal fluid mixed with meteoric water it could also be assumed by the co and as contents in pyrite indicating a certain degree of meteoric water in the ore forming fluid it is consonant to the pb s c and o isotope geochemistry in the previous study suggesting that ore forming fluids and metals could be derived from both the yangdok granite and the proterozoic and paleozoic meta sedimentary rocks exposed in the study area all of the pyrite grains have not compositional zoning and the similar distribution patterns of co and ni are appeared in single pyrite grain from core to rim suggesting the stable crystallization environment of pyrites and same ore forming fluid source in pyrite grains the positive correlation between gold and arsenic is appeared the au exists either as a micro and nano size inclusion in pyrite and other minerals or as a solid solution in pyrite lattice based on the petrological and microthermometric characteristics of the fluid inclusions in ore bearing quartz we suggest that the ore forming fluid is represented as nacl h2o or nacl kcl h2o systems with low salinity the absence of co2 enriched phase and vapor only or liquid only primary inclusions in quartz indicates the homogenous magma derived ore forming fluids and a lack of boiling during ore forming process the formation temperature and pressure of this deposit approximately vary from 317 to 326 c and from 105 46 to 111 69 105 pa respectively exhibiting the hydrothermal deposit origin in conclusion the songhung deposit is originated from i type granitic magma source derived hydrothermal fluid which was mixed with meteoric water

a fossil hydrothermal system or a source bed in the madiyi formation near the xiangxi au sb w deposit nw hunan pr china abstract in china a great number of au sb w deposits or mineralizations are located in nw hunan the xiangxi deposit is the largest and as 80 of such metal accumulations in this region occurs in the late proterozoic low grade metamorphic red slate madiyi formation ore bodies of the xiangxi mining district are strictly structurally controlled gold antimony tungsten and arsenic are strongly concentrated relative to bed rock lithologies sulfur hg mo and locally cu pb and zn are weakly enriched only the madiyi formation was deposited under oxidizing conditions in a shallow marine environment and is characterized by a high fe2o3 content with local accumulations of cao the stratigraphic horizon is probably not a source bed for the au sb and w mineralizations in this region high contents of these elements and as were likely introduced by hydrothermal fluids background values for au sb w and as in the madiyi formation are 1 4 ppb 0 42 ppm 1 9 ppm and 1 4 ppm respectively the stratigraphic sequence acts as a geochemical barrier controlling the distribution of au or and sb w

pyrite and pyrrhotite textures and composition in sediments laminated quartz veins and reefs at bendigo gold mine australia insights for ore genesis the various types textures and compositional zoning of pyrite in the gold bearing saddle reefs quartz veins and surrounding sedimentary rocks provide new information on the potential source and timing of gold and arsenic and related fluid processes responsible for mineralization at bendigo nodular diagenetic pyrite in the black shale tops to sandstone turbidites is enriched in invisible gold and arsenic with mean values of 0 61 ppm au 1 300 ppm as and au ag 1 based on la icpms analyses other elements enriched in the diagenetic pyrite within the organic rich shales are mn zn mo cu v ba ag cd tl co ni bi pb and te in contrast euhedral and growth zoned hydrothermal pyrite in the turbidites and bedding parallel laminated quartz veins contains lower contents of most trace elements but has higher contents of invisible au and as especially on the outermost rim of the pyrite the gold rich pyrite rims generally become thicker a few to hundreds of microns in proximity to the gold bearing saddle reefs pyrite in the reef commonly has the highest levels of invisible au and as and the lowest levels of other trace elements it is characterized by au ag 1 and au pb 0 01 in the deepest stratigraphic levels below known productive gold reefs diagenetic pyrite in the most carbonaceous shales has been replaced by pyrrhotite during metamorphism la icpms analyses reveal that the disseminated pyrrhotite contains similar levels of ni and co to the diagenetic pyrite but is strongly depleted in as and au the spatial relationships between organic rich shales folded bedding parallel laminated quartz veins and gold arsenic bearing saddle reefs combined with the consistent trends in the trace element composition of pyrite hosted by these three geological elements is interpreted to indicate that the black shales were an initial source of au and as and the laminated quartz veins acted as the initial pathways for hydrothermal fluid flow carrying au and as from the source shales to the saddle reefs maximum gold and arsenic input into the reefs principally as free gold plus arsenopyrite occurred late during deformation toward the end of the hydrothermal cycle and is expressed by the au as rich rims to hydrothermal pyrite in the sedimentary host rocks laminated quartz veins and reefs this corresponds with final fold lockup and the development of through going fault arrays linking adjacent anticlines the source of au and as for this final and most economically important fluid flow event is considered to be from carbonaceous shales deeper in the basin where original gold bearing diagenetic arsenian pyrite reacts with organic matter and is converted to pyrrhotite with release of au as and s to the metamorphic fluid

influence of balanced motions on heavy precipitation within a long lived convectively generated vortex abstract the forcing of heavy precipitation within a long lived convectively generated mesoscale vortex mcv is investigated with the aid of diagnoses from rapid update cycle gridded analyses organized convection within the mcv followed a distinct diurnal cycle which featured organized mesoscale convective systems mcss that matured overnight near the mcv center on successive days the mcv was typically most intense in the middle troposphere but intensified within the lower troposphere during the episodes of organized nocturnal convection the lower tropospheric vertical shear was an important organizing factor in mcs development and sustenance in the sense that its interaction with the cold temperature anomaly beneath the mcv center determined where balanced lower tropospheric ascent occurred from trajectory analyses we estimate that balanced ascent accounted for approximately half of the total vertical displacement of the thermodynamically unstable air that eventually composed elevated saturated

pyrite physical and chemical textures pyrite may crystallize initially in forms as diverse as framboids or cubes depending upon the temperatures and pressures fluid rich diagenesis or low grade metamorphism clearly results in thorough recrystallization and the common formation of cubes once these have formed the pyrite becomes much more refractory and retains many characteristics even in deposits which have undergone penetrative deformation this is in strong contrast to the behavior of most of the accompanying sulfides which often undergo ductile deformation solid state or chemical remobilization and annealing pyrite deforms sparingly until there is brittle failure however there may be significant pyrite corrosion and regrowth during metamorphism as the result of sulfur exchange with other minerals especially pyrrhotite pyrite fabrics may also be significantly modified by pressure solution or coble creep optical microscopic examination and electron microprobe chemical mapping of pyrites from a variety of mineral deposits including several high grade metamorphic ones reveals that the pyrites frequently contain both physical and chemical textures that may be interpreted in terms of the depositional and the post depositional history of the deposits inclusions of sulfides or other minerals reveal information on the timing of the crystallization or recrystallization of the pyrite chemical mapping of elements such as ni co and as reveals information on the relative time of transport of these elements in the ore fluids

orogenic gold common or evolving fluid and metal sources through time abstract orogenic gold deposits of all ages from paleoarchean to tertiary show consistency in chemical composition they are the products of aqueous carbonic fluids with typically 5 20 mol co 2 although unmixing during extreme pressure fluctuation can lead to entrapment of much more co 2 rich fluid inclusions in some cases ore fluids are typically characterized by significant concentrations of ch 4 and or n 2 common estimates of 0 01 0 36 mol h 2 s a near neutral ph of 5 5 and salinities of 3 7 wt nacl equiv with na k ca mg this fluid composition consistency favors an ore fluid produced from a single source area and rules out mixing of fluids from multiple sources as significant in orogenic gold formation nevertheless there are broad ranges in more robust fluid inclusion trapping temperatures and pressures between deposits that support a model where this specific fluid may deposit ore over a broad window of upper to middle crustal depths much of the reported isotopic and noble gas data is inconsistent between deposits leading to the common equivocal interpretations from studies that have attempted to define fluid and metal source areas for various orogenic gold provinces fluid stable isotope values are commonly characterized by the following ranges 1 18 o for precambrian ores of 6 to 11 and for phanerozoic ores of 7 to 13 2 d and 34 s values that are extremely variable 3 13 c values that range from 11 to 2 and 4 15 n of 10 to 24 for the neoarchean 6 5 to 12 for the paleoproterozoic and 1 5 to 10 for the phanerozoic secular variations in large scale earth processes appear to best explain some of the broad ranges in the o s and n data fluid rock interaction particularly in ore trap areas may cause important local shifts in the o s and c ratios the extreme variations in d mainly reflect measurements of hydrogen isotopes by bulk extraction of waters from numerous fluid inclusion generations many which are not related to ore formation radiogenic isotopes such as those of pb sr nd sm and os measured on hydrothermal minerals are even more difficult to interpret for defining metal source particularly as the low salinity ore fluids transport limited amounts of these elements and significant amounts of these may be locally added to the minerals during alteration reactions at the sites of gold deposition noble gas and halogen data are equally equivocal fluid exsolution from granitoids emplaced into the upper and middle crust metamorphism of the crust or fluids entering trans crustal fault zones from below the crust all remain as permissive scenarios associated with orogenic gold formation as the abundant geochemical data are equivocal however geological and geochronological data weigh heavily against a magmatic hydrothermal model in the upper to middle crust there is no universal temporal association between orogenic gold and magmatism and where there is an overlap in age there is no specific type of magmatism consistently associated with gold formation nor element zonation around any specific pluton a crustal metamorphic model for fluid and metal sources is very consistent with geological geochronological and geochemical data although metamorphism on a regional scale that releases these components into major fault zones can be associated with many processes along active continental margins these can include crustal thickening and radiogenic heating slab rollback and heating during crustal extension or subduction of a spreading ridge heating the base of an accretionary prism in rare examples where phanerozoic orogenic gold deposits are hosted in precambrian high grade metamorphic terranes fluids and metals must however enter a transcrustal fault system from a sub crustal source this could either be a devolatilized subducted relatively flat perhaps stalled slab and its overlying sediment or the corner of the fertilized mantle wedge that releases a fluid during a thermal event

ore genesis of the bake gold deposit southeastern guizhou province china constraints from mineralogy in situ trace element and sulfur isotope analysis of pyrite abstract the bake gold deposit is exceptional for its high native gold abundance relative to the other orogenic gold deposits in the southeastern guizhou district the grades of gold can be up to 2 to 3 wt in bonanza ore and native gold preferentially occurs within voids and fractures in pyrite arsenopyrite and quartz gold content can be up to 6 9 ppm in hydrothermal pyrite however the majority of the pyrite analyses have au contents less than 1 ppm mean 0 32 ppm based on la icpms analyses meanwhile empa reveals that arsenopyrite has a maximal au content of up to 0 14 wt but most analyses are below detection limit 0 01 wt moreover native gold grains in cataclastic pyrite and arsenopyrite are commonly high purity with fineness ranging from 949 to 977 given that paragenetically early hydrothermal pyrite and arsenopyrite contain variable but relatively high gold concentrations than later generations of sulfide it is suggested that early invisible gold may have been remobilized to form at least part of the microscopic visible gold post mineralization shear zones which cut the vein bearing anticline may have led to the deformation of the lode quartz vein system on the macro level and microscopically sulfide fragmentation and elemental remobilization although diagenetic pyrite from unaltered host rocks is enriched in invisible gold with mean values at 0 83 ppm evidence supporting the release of au from them is weak corresponding evidence comes from the distinct sulfur isotope signatures in different pyrite generations diagenetic pyrite has 34s values in the narrow range of 9 27 to 10 75 whereas hydrothermal pyrite shows a broad range 6 81 to 17 42 based on la mc icpms analyses the mesoproterozoic lengjiaxi group underlying the xiajiang group is most likely the source region on the basis of geological background and assuming the metamorphic devolatilization model

structural and geochemical controls on the development of turbidite hosted gold quartz vein deposits wattle gully mine central victoria australia gold quartz vein deposits in the wattle gully mine arefault related structures developed in a low grade metamorphosed ordovician quartz rich flysch sequence the major mineralization is associated with a high angle reverse fault wattle gully fault that has a maximum displacement of 40 m over 10 6 metric tons t of vein quartz averaging 10 5 g t au occur within a dilatant jog in this structure fold geometry has controlled fault geometry and resulted in the localization of the jog segment where the wattle gully fault traverses an east dipping fold limb to link two more steeply dipping bedding parallel fault sediments on adjacent west dipping fold limbs gold mineralization is also associated with several minor east clipping reverse faults and a bedding parallel fault whose development is related to flexural slip during fold tightening mineralization occurs within fault fill veins and extension veins adjacent to faults the geometry and internal structures of veins indicate that vein growth has been controlled by repeated fluctuations in fluid pressure and shear stress associated with fault valve behavior vein mineralogy is dominated by quartz with minor carbonates chlorite white mica albite and apatite arsenopyrite and pyrite are the major sulfide phases but sphalerite galena chalcopyrite and pyrrhotite are also present the highest au grades tend to be localised in vein systems that are in proximity to carbonaceous slates wall rock alteration is minor and restricted mainly to narrow zones adjacent to major vein systems sulfur isotope fractionation between galena and sphalerite indicates mineralization occurred at temperatures around 300 degrees c the delta 34 s compositions of pyrite and arsenopyrite are nearly uniform throughout the mine 1 5 2 8 but are generally not in equilibrium with the delta 34 s values of associated base metal sulfides 0 7 5 3 the delta 18 o values for vein quartz vary between 15 6 and 18 0 per mil and correspond to delta 18 o values

in situ trace element and sulfur isotope of pyrite constrain ore genesis in the shapoling molybdenum deposit east qinling orogen china abstract the early cretaceous ca 128 ma shapoling vein type molybdenum mo mineralization associated with the huashan intrusion is a newly discovered deposit in the xiong ershan district east qinling china where pyrite is a ubiquitous mineral phase here we present results from an integrated study on the texture in situ trace element chemistry from laser ablation inductively coupled plasma mass spectrometry la icp ms and sulfur isotopic composition using secondary ion mass spectrometry sims with a view to understand the geochemical variation genesis of mo mineralization and ore forming process the distinct textural patterns as revealed by petrographic observations suggest three types of pyrites py1 is composed of coarse grained euhedral pyrite in the wall rock and early barren quartz vein at stage i py2 is represented by subhedral anhedral grains coexisting with molybdenite in quartz veins at stage ii and py3 forms irregular interstitial grains in the quartz k feldspar molybdenite dominated veins at stage iii the mo enrichment mainly occurred in py3 with co ni ratios 1 and 34s values mainly