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

discrete element modeling of progressive failure in a wide coal roadway from water rich roofs abstract progressive failure of roadway roofs is a common failure mechanism in underground coal mines especially when water rich roofs are in close proximity to the roadway in this case study at a chinese coal mine the udec voronoi method was used to investigate the process of progressive roof failure in a wide coal roadway from water rich roofs in the numerical scheme the studied domain was partitioned into polygonal blocks bonded through contacts with pre defined dimensions the parameters of polygons and contacts in the voronoi program were calibrated to rock mass properties obtained through laboratory tests based upon laboratory tests and previous research findings a time dependent strength degradation process from water absorption was assumed and implemented in the numerical modeling next the progressive failure of a roadway from water rich roofs was analyzed in detail the numerical results agreed well with field measurements and observations this method was demonstrated to reproduce the real phenomenon of roof failure in all of its complexity the numerical results revealed that the progressive failure mechanism was characterized by an initial fracturing of the roof due to strength degradation which was followed by significant dilation as fractures grew the large span of the roadway further contributed to the roof failure process the results also clearly showed that shear cracks were predominant in the roof and played a major role in the behavior of the roadway roof additionally support and excavation schemes that affect roof stability were observed

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

modeling the role of sodic alteration in the genesis of iron oxide copper gold deposits eastern mount isa block australia liberation of iron and potassium by widespread postmetamorphic albitization of country rocks was one of the likely contributing processes in the formation of both barren and mineralized magnetite chalcopyrite biotite gold hematite clinopyroxene actinolite apatite ironstones in the cloncurry district of the proterozoic mount isa block whole rock geochemical data indicate nearly immobile al ga ti zr during transformation of a variety of least altered rocks toward albitite the data indicate that the addition of na from a brine to the rock accompanied the loss of fe k ba rb ca sr co v mn pb and zn from those altered rocks and enrichment in the brine but that cu was not systematically stripped from a variety of wall rocks during albitization conversely the formation of metasomatic ironstones the immediate hosts to some cu au ores involves addition of most of the same elements that were lost during albitization the correlation between intensity of alteration its distribution and timing e g in breccias cored by ca 1530 1500 ma granitoids and convergence of all rock types toward magmatic stable isotope values provides strong evidence for a substantial component of igneous derived fluid simulations of the albitization process were carried out isothermally at 550 c and 350 mpa and polythermally from these conditions down to 400 c and 200 mpa using the gibbs minimization method with hch software and the unitherm database both simple fluid rock mixing models and more complicated reactor style algorithms used a range of input fluids from fluids equilibrated fluid with two feldspar granite through to na k ratios consistent with fluid inclusion results and geochemical data for initially unaltered wall rocks the apparent paradox of widespread albitization resulting from fluid released by two feldspar granites can be explained by relatively small shifts away from the k feldspar albite equilibrium curve and even isothermal model fluids derived from two feldspar granites produce albitites in calc silicate rocks outboard of granite proximal k feldspar clinopyroxene skarns matching field patterns those models with fluid na k ratios similar to those of fluid inclusions produced the most realistic alteration assemblages dominated by albite for both isothermal conditions and decreasing temperature which approximate those observed in the field pixe and microthermometric data on fluid inclusions from quartz in two feldspar quartz monzonite and pegmatite at the top of the mount angelay pluton indicate bulk na k molar ratios in the fluid of between 10 and 20 considerably higher than our thermodynamically calculated values for fluid in equilibrium with two feldspar granite of around 3 at 550 c 350 mpa such shifts may have been attained by admixture of magmatic hydrothermal fluid with small amounts of nacl brines trapped along grain boundaries in scapolite bearing calc silicate wall rocks by fluid immiscibility due to high initial co2 contents in the felsic intrusions by contributions from mafic magmas or from dissolution of salt rich layers into the intrusions prior to crystallization and fluid release with increasing amounts of fluid rock interaction in the models the fluids were enriched in k fe and ca approaching compositions observed in fluid inclusions in the ore deposits these fluids reacted with pelitic rocks which are common ore hosts would produce magnetite clinopyroxene biotite actinolite alteration at high temperature similar to the proximal alteration around ore deposits we infer that precipitation of sulfides in the cu au deposits was the result of mixing of cu bearing brine of ultimately magmatic origin but modified extensively via albitization with sulfur bearing fluids or reaction of the brine with sulfur bearing rocks when cu was absent from the initial magmatic fluid barren ironstones may have been the result

continuum discontinuum analysis of failure mechanisms around unsupported circular excavations in anisotropic clay shales abstract the stability of circular excavations in clay shales is a key issue in the drilling and tunnelling industries as well as in the field of deep geological waste storage a large body of experimental evidence indicates that the damaged zone around these cavities is influenced by strong mechanical anisotropy induced by the layered material structure the vast majority of numerical models adopted to date to analyse the stability of openings in layered rocks have been based on continuum mechanics principles using classic shear failure theory for elasto plastic materials however a number of experimental observations demonstrate that clay shales may fail in a brittle manner under low confinement conditions such as those characterizing the near field of the excavation therefore an alternative numerical approach based on non linear fracture mechanics principles and the discrete element method is adopted to gain new insight into the failure process of this class of geomaterials in order to account for the influence of clay shale microstructure on its mechanical behaviour a newly developed approach to capture the anisotropy of strength is proposed with this numerical approach the cohesive strength parameters of the fracture model are assumed to be a function of the relative orientation between the element bonds and the layering orientation the effectiveness of the numerical technique is quantitatively demonstrated by simulating standard rock mechanics tests on an indurated claystone namely opalinus clay emergent strength and deformation properties together with the simulated fracture mechanisms are shown to be in good agreement with experimental observations the modelling technique is then applied to the simulation of the excavation damaged zone edz around a circular tunnel in horizontally bedded opalinus clay the simulated fracturing process is mainly discussed in the context of the damage mechanisms observed at the mont terri url furthermore the influence of in situ stress on resulting edz geometry is analysed together with possible implications for ground support and tunnel constructability modelling results highlight the importance of shear strength mobilization along bedding planes in controlling the edz formation process in particular slippage of bedding planes is shown to cause rock mass deconfinement which in turn promotes brittle failure processes in the form of spalling the numerical technique is currently limited to two dimensional analyses without any thermo hydro mechanical coupling

the stable isotope signature of kilometre scale fracturedominated metamorphic fluid pathways mary kathleen australia abstract large calcite veins and pods in the proterozoic corella formation of the mount isa inlier provide evidence for kilometre scale fluid transport during amphibolite facies metamorphism these 10 to 100 m scale podiform veins and their surrounding alteration zones have similar oxygen and carbon isotopic ratios throughout the 200 10 km mary kathleen fold belt despite the isotopic heterogeneity of the surrounding wallrocks the fluids that formed the pods and veins were not in isotopic equilibrium with the immediately adjacent rocks the pods have 13ccalcite values of 2 to 7 and 18ocalcite values of 10 5 to 12 5 away from the pods metadolerite wallrocks have 18owhole rock values of 3 5 to 7 and unaltered banded calc silicate and marble wallrocks have 13ccalcite of 1 6 to 0 6 and 18ocalcite of 18 to 21 in the alteration zones adjacent to the pods the 18o values of both metadolerite and calc silicate rocks approach those of the pods large calcite pods hosted entirely in calc silicates show little difference in isotopic composition from pods hosted entirely in metadolerite thus 100 to 500 m scale isotopic exchange with the surrounding metadolerites and calc silicates does not explain the observation that the 18o values of the pods are intermediate between these two rock types pods hosted in felsic metavolcanics and metasiltstones are also isotopically indistinguishable from those hosted in the dominant metadolerites and calc silicates these data suggest the veins are the product of infiltration of isotopically homogeneous fluids that were not derived from within the corella formation at the presently exposed crustal level although some of the spread in the data may be due to a relatively small contribution from devolatilization reactions in the calc silicates or thermal fluctuations attending deformation and metamorphism the overall l shaped trend of the data on plots of 13c vs 18o is most consistent with mixing of large volumes of externally derived fluids with small volumes of locally derived fluid produced by devolatilization of calc silicate rocks localization of the vein systems in dilatant sites around metadolerite calc silicate boundaries indicates a strong structural control on fluid flow and the stable isotope data suggest fluid migration must have occurred at scales greater than at least 1 km the ultimate source for the external fluid is uncertain but is probably fluid released from crystallizing melts derived from the lower crust or upper mantle intrusion of magmas below the exposed crustal level would also explain the high geothermal gradient calculated for the regional metamorphism

the candelaria punta del cobre iron oxide cu au zn ag deposits chile several iron oxide rich cu au zn ag deposits define an approximately 5 km wide and at least 20 km long belt along the eastern margin of the coastal batholith near copiapo chile this belt includes the large candelaria mine and a group of middle and small sized mines in the punta del cobre district which is located about 3 km northeast of the candelaria deposit estimated geologic resources of the belt are on the order of 700 to 800 million metric tons mt at 1 0 percent cu the ore occurs in veins breccia and stringer bodies and in replacement bodies that are roughly concordant to bedding the orebodies are hosted mainly by volcanic and volcaniclastic rocks of the punta del cobre formation and in places also occur in volcaniclastic intercalations in the lower part of the overlying early cretaceous chanarcillo group most of the larger orebodies in the belt are located where northwest trending brittle faults intersect the contact between massive volcanic and volcaniclastic rocks these northwest faults and a major northeast trending ductile shear zone control portions of the ore of the candelaria deposit chalcopyrite is the only hypogene cu mineral the cu au ore is characterized by abundant magnetite and or hematite and by locally elevated concentrations of ag zn mo and light rare earth elements the ore is hosted mainly in zones with biotite potassium feldspar calcic amphibole epidote alteration at candelaria in the punta del cobre district ore in the deeper parts of the deposits is similarly associated whereas at shallow levels it occurs in zones of biotite potassium feldspar or albite chlorite calcite alteration mineralization at candelaria punta del cobre took place under relatively oxidized conditions manifested by the formation of specular hematite in parts of the district the pseudomorphic replacement of early specular hematite by magnetite during the main iron oxide formation marks a shift toward more reduced conditions or higher temperatures the bulk of the magnetite probably formed at temperatures of about 500 to 600 c the main sulfide stage followed with formation of pyrite and chalcopyrite at temperatures of 470 to 328 c subsequent martitization of the magnetite points to a temperature decrease cooling of the hydrothermal system is also indicated by the homogenization temperatures of 236 c of saline fluid inclusions in late stage calcite oxygen isotope combined with microthermometric data suggest that magmatic fluids or nonmagmatic fluids equilibrated with magmatic silicates were dominant during the main copper mineralization relatively light oxygen isotope signatures of fluids in equilibrium with late calcite suggest mixing with a nonmagmatic fluid e g basinal brines or meteoric waters during the late stages of hydrothermal activity sulfur isotope ratios of chalcopyrite pyrite pyrrhotite and sphalerite from the bronce candelaria las pintadas santos and socavon rampa deposits range from 34scdt values of 0 7 to 3 1 per mil this narrow range of sulfur isotope ratios near 0 per mil is consistent with sulfur of magmatic origin anhydrite from the candelaria mine paragenetically overlaps with chalcopyrite fluid inclusions in this anhydrite homogenize between 340 and 470 c and it has 34scdt values between 14 5 and 17 5 per mil a sulfate sulfide value of 13 4 per mil for a sample with coexisting anhydrite and chalcopyrite is consistent with sulfide sulfate fractionation at temperatures on the order of 400 c ore lead isotope signatures are homogeneous and similar to those of least altered volcanic host rocks and nearby intrusive rocks radiometric ages including new 40ar 39ar ages for hydrothermal alteration at candelaria point to a main cu au mineralization event at candelaria punta del cobre at around 115 ma the ages indicate that ore formation was broadly coeval with batholithic granitoid intrusions and with regional uplift they further imply that the cu au zn ag deposits formed at shallow crustal levels 3 km the stable isotope data the presence of previously reported hypersaline co2 rich fluid inclusions in the main cu ore stage and saline fluid inclusions in late stage calcite the oxidized character of the first ore fluid pulses and the mineralization age coeval with nearby intrusive activity are consistent with but not unequivocally evidence of magmatic fluid contribution into the hydrothermal system

the lightning creek sill complex cloncurry district northwest queensland a source of fluids for fe oxide cu au mineralization and sodic calcic alteration the lightning creek cu au prospect is hosted by a cogenetic suite of plutonic i type granitoids the dominant rock type is a porphyritic quartz monzodiorite that is intruded by more fractionated rocks including monzogranite and alkali feldspar granite a series of flat lying sills are interpreted to be late stage differentiates based on their timing mineralogy and chemistry in parts of the prospect there is pervasive sodic calcic alteration pyroxene after amphibole albite after k feldspar and oligoclase of the plutonic rocks this alteration predates sill emplacement and is unrelated to veining or fracturing of any kind the presence of small amounts of carbonate in the altered rocks suggests that the fluids were co2 bearing quartz and feldspar separates from these altered rocks have oxygen isotope compositions similar to those from fresh quartz monzodiorite suggesting that the fluids were hot and of magmatic composition sodium and ca were added and k fe cl and cu were stripped during what is interpreted as an autometasomatic event the sills display considerable textural and mineralogical complexity and evolved from equigranular quartzofeldspathic rocks aplites with magmatic chemistry to unusual fe rich rocks albite magnetite quartz that exhibit a range of bizarre spherulitic textures some of the albite and magnetite in the sills is secondary albite forms pseudomorphs after k feldspar na fe ca alteration along sill margins and within sills at the contacts between different textural zones halos of disseminated magnetite clinopyroxene fe ca na alteration are developed adjacent to early magnetite veins fluid inclusion studies indicate that these rocks crystallized at temperatures in excess of 500 c and at pressures in excess of 1 5 kbar the range of spherulitic textures is taken to indicate crystallization under hydrous conditions with the episodic release of a fluid phase this magmatic fluid phase was dominated by h2o co2 and chlorine and underwent phase separation into a co2 rich vapor and a hypersaline brine 33 55 wt nacl equiv the hypersaline fluid was enriched in fe 10 wt and cu 1 wt pixe analysis in addition to na k and ca where this fluid was retained within fe rich portions of the sills it caused ca fe na alteration pyroxene albite magnetite growth at the expense of quartz where the fluid was expelled from the sills it produced quartz magnetite clinopyroxene albite veins broadly coeval with the early magnetite veins although rich in cu these granitoid derived magmatic fluids did not generate significant cu au mineralization perhaps because of the high temperatures involved and or a lack of reduced sulfur in the fluids or host rock however the amount of iron present is estimated from the aeromagnetic anomaly to be in excess of 2 000 million tonnes mt a later generation of calcite chlorite pyrite chalcopyrite veins contain traces of cu au mineralization fluid inclusion and stable isotope work indicate that these veins probably crystallized from cooler 200 c more dilute 15 28 wt nacl equiv fluids perhaps generated by the admixture of a meteoric component the conclusions reached in this study have implications for understanding the genesis of fe oxide cu au deposits and related sodic calcic alteration the study indicates the potential for co2 rich granitoid magmas to evolve hypersaline fe and cu rich fluids capable of causing intense magnetite veining and cu au mineralization autometasomatic sodic calcic alteration of the granitoids may be an important precursor to mineralization contributing fe k cu and cl to the magmatic fluids

geomechanical behaviour of laminated weak coal mine roof strata and the implications for a ground reinforcement strategy this paper describes a component of the results from an arc spirt funded collaborative research project between unsw powercoal pty ltd and springvale coal pty ltd the research project was aimed at identifying strategies for appropriate ground control in particularly weak and soft roof strata in underground coal mining a field investigation was undertaken at angus place colliery in the western coalfield of new south wales the investigation incorporated a range of geotechnical instrumentation and was conducted over a period of time from the development face until the site was lost into the goaf of a retreating longwall panel this paper describes the outcomes from the field investigation together with a selection of supporting laboratory studies the paper also presents a number of alternative presentation modes for extensometry data the results clearly demonstrate the time and face proximity related influences on roof integrity and particularly demonstrated the distribution of deformation bed separation and strata failure into the roof and across the full span of the roadway together with reflection of this behaviour within the fully encapsulated roof bolt reinforcement system installed

numerical modelling of the effects of weak immediate roof lithology on coal mine roadway stability abstract the stability and associated design of roof reinforcement requirements of tunnels driven in united kingdom coal measures strata is directly related to the engineering characteristics of the immediate roof lithology and the effects of redistribution of the in situ stress numerical modelling carried out by the authors has been used to simulate the widely observed detrimental effects of both high horizontal stress and weak immediate roof lithology on tunnel roof stability different numerical modelling techniques such as continuum discontinuum and hybrid finite element discrete element codes have been used to model the deformational behaviour of coal measures strata and are discussed in the context of specific case examples to highlight their application and suitability for modelling of weak rock the modelled results demonstrate that the thickness of the relatively weak mudstone in the roof of the tunnel has a significant influence on the extent of failure and ultimately the need for additional reinforcement

geochemistry of hypersaline fluid inclusions from the starra fe oxide au cu deposit cloncurry district queensland studies of liquid vapor multisolid l v ns and liquid vapor halite fluid inclusions suggest that at least three fundamentally different brines were involved in the genesis of the proterozoic ironstone hosted starra au cu deposit element concentrations determined from proton induced x ray emission pixe analysis of groups of l v ns inclusions from the early barren magnetite ironstone stage 400 550 c and the younger mineralization stage 220 360 c covary over concentration ranges greater than the deduced analytical errors the l v ns inclusions in the two stages are very different with higher ratios of fe and k to ca mn cu zn sr ba and pb in the ironstone stage quite distinct pseudosecondary nacl cacl h o inclusions are abundant in mineralization stage quartz calcite and anhydrite high concentrations of cu ca 1 000 ppm are present in some l v ns inclusions of both stages and the data suggest that large amounts of cu mn zn as ba and pb passed through the starra system as it evolved cl br ratios in the inclusions are mostly less than 0 002 and clearly different from those of ore fluids of the giant sedimentary hosted copper orebody at mount isa this could reflect a major magmatic contribution to the salinity at starra that is consistent with the preferred origin of the water in published stable isotope studies ba concentrations of at least several wt percent in some mineralization stage l v ns inclusions are associated with oxidized sulfur bearing mineral parageneses given the low solubility of barite this suggests that a s2 f o2 relationships varied during mineralization

radiogenic and stable isotope constraints on the genesis of the eloise cu au deposit cloncurry district northwest queensland new radiogenic 40ar 39ar and stable oxygen hydrogen and sulfur isotope analyses of metamorphic and metasomatic minerals constrain the age metasomatic evolution and genesis of the eloise cu au deposit 3 1 mt 5 5 cu 1 4 g t au and 16 g t ag biotite from a pre to syn d2 stage vein has an 40ar 39ar age of 1555 4 ma which is interpreted to coincide with a regional metamorphic event synchronous with d2 six later stages of alteration and mineralization are recognized all of which postdate peak metamorphism and d2 stages i to iii are volumetrically the most significant and comprise early albitization stage i quartz hornblende biotite veins and alteration stage ii and cu au mineralization stage iii stages iv v and vi are localized vein events and postdate the main cu au mineralization stage ii vein and alteration hornblendes have 40ar 39ar ages of 1530 3 ma biotite from the same stage has an 40ar 39ar age of 1521 3 ma muscovite from a postore shear zone has an 40ar 39ar age of 1514 3 ma these results provide a maximum ca 1530 ma and minimum ca 1514 ma age for the mineralizing event however the intimate relationship between stage ii mafic silicate veins and alteration and the stage iii cu au event combined with fluid inclusion results which indicate that a cooling evolving high salinity fluid was responsible for both stages suggests that the older age is likely to be closer to the age of mineralization the stage ii biotite age of ca 1521 ma is interpreted to record thermal resetting during postore ductile deformation the results suggest that micas in the cloncurry district are more susceptible to later thermal resetting than amphiboles which may have significant implications for deposits which have only been dated by micas quartz from stages ii iii and iv have 18oquartz values ranging between 10 1 and 11 9 per mil stage ii biotite has a lower 18o composition 5 6 than biotite from a pre d2vein 6 9 but both have identical d compositions 84 stage ii hornblende has lower 18o 6 8 and 7 4 and d 88 and 90 values than does stage iii actinolite 8 0 and 84 respectively the 34s values for chalcopyrite pyrrhotite and pyrite fall in a narrow range between 0 0 and 2 3 per mil a distinct trend can be recognized with 34s values becoming progressively greater from south to north thus reflecting the zoned alteration system magnetite pyrite rich in the south through to pyrrhotite rich in the north the change in mineralogy and sulfur isotope values may be due to cooling and sulfidation processes which resulted in changes in oxygen and sulfur fugacities the oxygen hydrogen and sulfur isotope data combined with high temperature and high salinity fluid inclusion data indicate a predominantly magmatic origin for the ore forming fluids the deposit is interpreted to have formed from magmatic hydrothermal fluids which were tapped by deep seated crustal structures

the nature of sulfidic metasediments at kambalda and their broad relationships with associated ultramafic rocks and nickel ores sedimentary horizons at kambalda occur at the base of and at interflow boundaries within the same lower one third of the ultramafic sequence as do the major ni cu orebodies although sediments occur on all the same stratigraphic horizons as the ores they are almost entirely absent from within the volume containing the ores being separated by zones free of both sediments and ni cu sulfides generally they are broadly lenticular are not very extensive in area and correlate poorly laterally mineralogically and chemically the sediments are very variable but much of this is attributable simply to a variable iron sulfide content geographic and stratigraphic location and lithology are other significant causes of these variations proximity to the ni cu ores has at best an exceedingly subtle control on chemistry or mineralogy the kambalda sediments are not compositionally very different from other archean sediments in broadly similar environments however their sulfur and chalcophile element levels are high and au is especially enriched sulfur isotopes have a narrow spread near zero range 1 5 5 and the s se is around 15 000 to 20 000 indicating a little modified magmatic source for the sulfur apart from transfer of sulfur due to pyrite breakdown at peak metamorphism to the ultramafics there was negligible chemical exchange across sediment ultramafic interfaces virtually no ni was extracted from the ultramafic silicates during this sulfurization and migration of ni into the sediments was negligible nickel sulfide ore formation by sulfurization or sedimentary replacement is rejected ores intimately involved with sediments make up only 3 to 5 percent of the total ni reserve there is a strong inverse relationship between the quality of ore environments and the amount of their ore which is in contact with sediments the four largest ore locations accounting for about 70 of the reserve each has considerably less than 1 percent of ore with sediments extensive ore sediment contact occurs locally and can result from either 1 physical injection of preexisting ni cu ore into previously barren sediments 2 a synsedimentary intermixing of ores and sediments or 3 a passive and largely coincidental relationship the volcanic exhalative model of lusk 1976 for the ni ores is rejected the sediments are interpreted to be a mixture of local mafic ultramafic and distant felsic granitic detritus s pb zn fe and cu from ultramafic exhalations s co ni and cu from local sea floor leaching of ultramafics a biological carbonaceous component and probably minor chemical silica sea floor alteration affecting na k and mn diagenesis and metasomatic k rb ba sr and co 2 introductions are evident

characteristics of the displacement of a landslide with shallow sliding surface in a heavy snow district of japan the displacement of a landslide with shallow sliding surface in a heavy snow district was automatically monitored for over 4 years by a newly developed displacement gauge meteorological properties meltwater and or rainfall mr water equivalent of snow and other factors were simultaneously observed pore water pressure was monitored but only for a limited period of time since the displacement of the landslide was too large statistical analyses showed that maximum daily displacements of each year were observed not in snow melting periods but immediately before or at the beginning of a snow cover period there are three types of annual variation pattern with peaks in mid november to mid december mid april and mid july the variation pattern of displacement from the beginning of march to the beginning of june showed the least total displacement of those three types therefore snow cover is likely to affect the displacement of a landslide detailed investigation of the landslide displacement during snow cover periods showed that the rate of displacement slowed as the snow cover deepened meaning a decrease in mr and increase in water equivalent of snow the displacement ratio for the unit antecedent mr effect during snow cover periods dropped when the snow started to accumulate on the ground in all 4 years the reduction was likely attributable to snow load since it was found to have a negative logarithmic relation with the water equivalent of snow changes in pore water pressure and the relationship between pore water pressure and displacement during the snow cover periods differed from those in the other periods therefore the displacement of a landslide that has a shallow sliding surface in a snowy region was considered to be affected by snow accumulation conditions especially water equivalent of snow

numerical observations of the failure of a laminated and jointed roof and the effective of different support schemes a case study roof failure related to laminated and jointed rock masses has been recognized as a major cause of fatalities in underground coal mines this paper presents numerical simulations of the failure of a laminated and jointed roof using the discrete element method while focusing on the initiation and propagation of and the interactions between microcracks and macroscopic fractures and the development of the associated damage stress and deformation in the laminated and jointed roof numerical modeling shows that the behaviors of bedding planes and vertical joints governed the progressive failure of the laminated and jointed roof microseismic activity corresponding to the development of microcracks in the roof intensified before major roof displacements and subsided in the later stages such activity could serve as a precursor of roof fall events the effectiveness of various support elements rock bolts metal meshes and anchor cables on the roof stability was numerically evaluated rock bolts and or anchor cables produced a banded compressive stress in the laminated roof restricting the separation of bedding planes rock bridges in the bolted roof suppressed the formation of macroscopic fractures and significantly reduced the interactions between fractures the roof skin support with a metal mesh provided confinement to the fractured roof thereby preventing fragmented rocks from falling and restricting progressive spalling between bolts the numerical simulations presented in this paper can be helpful for understanding the likely failure mechanisms of laminated and jointed roofs and for finding potential solutions

permeability generation and resetting of tracers during metamorphic fluid flow implications for advection dispersion models advection dispersion fluid flow models implicitly assume that the infiltrating fluid flows through an already fluid saturated medium however whether rocks contain a fluid depends on their reaction history and whether any initial fluid escapes the behaviour of different rocks may be illustrated using hypothetical marble compositions marbles with diverse chemistries e g calcite dolomite quartz are relatively reactive and will generally produce a fluid during heating by contrast marbles with more restricted chemistries e g calcite quartz or calcite only may not if the rock is not fluid bearing when fluid infiltration commences mineralogical reactions may produce a reaction enhanced permeability in calcite dolomite quartz or calcite quartz but not in calcite only marbles the permeability production controls the pattern of mineralogical isotopic and geochemical resetting during fluid flow tracers retarded behind the mineralogical fronts will probably be reset as predicted by the advection dispersion models however tracers that are expected to be reset ahead of the mineralogical fronts cannot progress beyond the permeability generating reaction in the case of very unreactive lithologies e g pure calcite marbles cherts and quartzites the first reaction to affect the rocks may be a metasomatic one ahead of which there is little pervasive resetting of any tracer centimetre scale layering may lead to the formation of self perpetuating fluid channels in rocks that are not fluid saturated due to the juxtaposition of reactants such layered rocks may show patterns of mineralogical resetting that are not predicted by advection dispersion models patterns of mineralogical and isotopic resetting in marbles from a number of terrains for example chillagoe marulan south reynolds range australia adirondack mountains old woman mountains notch peak usa and stephen cross quarry canada vary as predicted by these models

fluid flow mineral reactions and metasomatism a general model that relates fluid flow along a temperature gradient to chemical reaction in rocks can be used to quantitatively interpret petrologic and geochemical data on metasomatism from ancient flow systems in terms of flow direction and time integrated fluid flux the model is applied to regional metamorphism quartz veins and a metasomatized ductile fault zone

geology and alteration geochemistry of the porphyry cu au deposit at bajo de la alumbrera argentina this paper describes the igneous geology alteration mineralogy and geochemistry as well as the ore mineralization history of bajo de la alumbrera a world class porphyry copper gold deposit in northwestern argentina the deposit occurs in the k rich calc alkaline farallon negro volcanic complex located 200 km east of the main andean porphyry copper belt of chile the deposit consists of a composite stock of dacitic porphyry intrusions and extends into the surrounding andesitic volcanic rocks two of the earliest intrusions now occupying the center of the intrusive complex show intense hydrothermal alteration and mineralization these two porphyries host the highest ore grades and were subsequently intruded by several weakly mineralized or barren porphyries intense quartz magnetite k feldspar alteration pervades the first mineralized porphyry whereas similar but lower intensity alteration affected the second laterally this alteration grades into potassic alteration secondary k feldspar and biotite which affects all porphyries except the latest dikes andesitic wall rocks within a hundred meters of the intrusions are dominated by dark hydrothermal biotite an outer halo of propylitic alteration epidote chlorite albite calcite extends up to 1 km into the andesites feldspar destructive alteration sericite pyrite clay minerals gypsum overprints the potassic and propylitic alteration in the volcanic rocks and all porphyries the alteration is locally controlled by faults and late fractures and developed most pervasively upon the outer part of the potassic zone and toward the transition to propylitic alteration in the upper part of the deposit mass balance calculations show small positive changes in net volume for the potassic alteration and minor volume decreases for the chlorite epidote and feldspar destructive alteration the intensely quartz magnetite veined sample of quartz magnetite alteration indicates a total volume increase of 350 percent copper and gold are intimately associated at all scales they occur as composite gold sulfide grains chalcopyrite rarely bornite show a close correlation of ore grades in sample assays and have a closely overlapping distribution on the mine scale a well developed ore shell coincides with potassic alteration and partly with the distribution of intense quartz magnetite veins even though the bulk of the ore minerals now occupy texturally late positions in vugs and fractures a barren zone with intense quartz magnetite potassic alteration and veins but little or no sulfides is interpreted as the focus of upflow of high temperature ore fluids prior to ore mineral saturation and coprecipitation of copper sulfides and gold in the ore shell

the effect of heterogeneous stress and strain on metamorphic fluid flow mary kathleen australia and a model for large scale fluid circulation in the proterozoic mary kathleen fold belt northern australia infiltration of large volumes of externally derived fluid occurred synchronously with regional amphibolite facies metamorphism and deformation this paper develops a model of structurally controlled fluid migration by comparing the distribution of fossil fluid pathways with the inferred stress and strain patterns during the deformation intense fluid flow was localized within strong relatively brittle meta intrusive bodies and in discrete veined brecciated and altered zones around their margins in metasediments folded in a ductile manner outside these areas fluid infiltration was negligible the direct correlation between structural styles and the magnitude of veining and metasomatism suggests control of permeability enhancement and hence fluid flow by deformation finite difference modelling of a strong body in a weaker matrix has been used to evaluate the variation of stresses during the deformation from which it is clear that stress and strain heterogeneities have systematically influenced the development and maintenance of metamorphic fluid pathways particular regions in which mean stress may be significantly lower than the average lithostatic pressures include the strain shadow zones adjacent to the strong bodies other dilatant zones around the bodies and the bodies themselves this geometry is favourable not only for localized brittle deformation under amphilobite facies conditions but also for focused fluid flow in the low mean stress regions as evidenced by the abundance of veins fluid access through these metamorphic aquifers occurred during tensile failure episodes with particularly large dilations and decimetre scale veining in areas of strain incompatibility it appears likely that fluid circulated many times through the fold belt with flow concentrated in the metamorphic aquifers a model is developed that explains both the structurally focused fluid flow and the postulated multi pass recirculation by dilatancy pumping the pump engines comprising the low mean stress zones

quantified spatial relationships between gold mineralisation and key ore genesis controlling factors and predictive mineralisation mapping st ives goldfield western australia abstract determining the spatial relationships between various geological features and mineralisation is not only important for understanding the ore genesis of mineral deposits but can also help to guide mineral exploration by providing predictive mineral maps in this gis based study we quantify the spatial relationships between gold mineralisation and plausible controlling factors in the central part of the st ives area western australia we weigh plausible control factors including rock types lithological boundaries and faults using gold occurrences in drill cores and then apply the weights to the geological data to generate a predictive map for the entire st ives area the three major findings of this study are 1 all major gold deposits are controlled by faults and small scale fault systems have a stronger correlation with gold mineralisation than large faults 2 felsic to intermediate intrusive rocks show strong correlations with gold mineralisation whereas metamorphic mafic rocks greenstones possibly acted as part of the broad regional environment for the mineral province rather than as a factor controlling the exact locations of the deposits and 3 our predictive mapping indicates that the southeast part of the st ives goldfield has a high potential for discovering new gold mineralisation

multi approach back analysis of a roof bed collapse in a mining room excavated in stratified rock roof bed deformation mechanics is a complex topic in mining practice there are a number of empirical analytical and numerical techniques that can be used to analyze and design underground excavations in stratified rock masses each has particular drawbacks however so the use of just one approach in order to obtain consistent and economic designs is not practical to deepen understanding of this topic it is useful to study real failure in mines in this paper we describe how a roof bed failure in an underground mine excavated in a stratified rock mass was back analyzed using different approaches namely the empirical stability graph method the analytical voussoir techniques and the numerical discrete element method the study enabled us to better understand the conditions of failure and to define the most significant parameters affecting the failure it has also been shown how relaxation or loss of confinement stress can play an important role in roof bed deformation

fluid wall rock interaction in an archean hydrothermal gold deposit a thermodynamic model for the hunt mine kambalda gold mineralization at the hunt mine kambalda is situated in a 20 m thick steeply dipping shear zone within a sequence of rather uniform metabasalts zonal alteration of the host rocks occurred around fractures which acted as conduits during gold mineralization limited major element mobility ensured assemblages of low variance over most of the alteration zone providing a suitable environment for the application of thermodynamics in conjunction with detailed petrographic geochemical electron microprobe analysis of mineral compositions and fluid inclusion studies microthermometry equilibrium equations involving fluid components and alteration minerals are used to determine conditions during the alteration event and in particular activity gradients of components profiles across the schist zone show increasing f sub h 2 s around auriferous quartz veins log f sub h 2 s 0 6 but constant f sub o 2 log f sub o 2 29 7 these results are near the magnetite pyrrhotite pyrite triple point for the inferred temperature of 350 degrees c and explain the pyrite pyrrhotite magnetite zonation sequence outward from veins the profile of x sub co 2 is very close to the value of 0 25 determined independently from fluid inclusions the k super h super profile shows increases adjacent to auriferous veins corresponding to the zone of biotite stability using a value for fluid salinity of 2 equiv wt percent nacl ph was calculated to be around 6 9 the solubility of gold in solution was estimated for the calculated conditions for the complex au hs super 2 the maximum solubility is around 0 5 mg kg super 1 i e 0 5 ppm for au cl super 2 it is close to 10 super 6 mg kg super 1 indicating the efficacy of sulfide transport of gold compared to chloride transport under these conditions the calculated decrease in f sub h 2 s away from the auriferous quartz veins results in an 80 percent or greater decrease in gold solubility suggesting hat the sulfidation of fe rich wall rocks is a geologically reasonable and very efficient mechanism for precipitating gold from solution at elevated temperatures

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

fluid inclusion and stable isotope o h c constraints on the genesis of the pedra branca gold deposit troia massif borborema province ne brazil an example of hypozonal orogenic gold mineralization abstract at the archean paleoproterozoic troia massif ne brazil two major paleoproterozoic greenstone belts are documented algodoes and serra das pipocas they share similar lithostratigraphic characteristics with other 2 2 2 1 ga greenstone belts of the surrounding cratonic domains e g guiana shield and west africa craton gold mineralization in the serra das pipocas greenstone belt is associated with a regional ne trending shear zone in the mineralized area the pedra branca gold deposit the main gold mineralization is found in association with quartz veins calc silicate alteration e g diopside k feldspar amphibole titanite biotite pyrite albite magnetite carbonates and albitization pyrrhotite is commonly found as inclusions in pyrite and late magnetite replaces pyrite suggesting progressive oxidation of the ore forming fluid free milling gold commonly precipitates at the late stages of alteration in close association with magnetite and tellurides the main tellurides found are hessite altaite sylvanite calaverite and tellurobismuthite two fluid inclusion assemblages were identified from mineralized quartz veins assemblage 1 is characterized by pseudo secondary trails that show the coexistence of co2 rich and low salinity 0 8 wt nacl equiv co2 h2o nacl and h2o nacl inclusions suggesting formation during phase separation fluid immiscibility assemblage 2 is represented by late secondary low temperature th

implications of pb isotope signatures of rocks and iron oxide cu au ores in the candelaria punta del cobre district chile lead isotope ratios of ores of the candelaria punta del cobre iron oxide cu au deposits and associated early cretaceous volcanic and batholithic rocks have been determined for the igneous rocks a whole rock acid attack technique based on the separate analyses of a leachate and the residual fraction of a sample was used the lead isotope systematics of leachate residue pairs are significantly different for unaltered and altered igneous rocks of the candelaria punta del cobre district residues of unaltered igneous rocks likely represent the common lead in contrast residues of all the altered igneous rocks except two samples have higher pb isotope ratios than those of unaltered magmatic rocks and cannot represent common lead we suggest that this is a result of the hydrothermal alteration suffered by these rocks and that the common lead composition of the altered igneous volcanic and plutonic rocks must have been similar to that of the unaltered batholith rocks the conclusion that the altered volcanic rocks originally had a similar common lead isotope composition as the batholith is consistent with geological and geochemical arguments e g setting regional geologic evolution ages and relative distribution of volcanic and intrusive rocks magmatic affinities which indicate that these rocks were derived from similar early cretaceous parent magmas the modification of the leachate residue pair lead isotope systematics of most altered igneous rocks is consistent with a selective removal of lead and uranium from these rocks by an oxidized hydrothermal fluid the result of the hydrothermal leaching has been to alter magmatic rocks in a way that 1 their leachable fraction is presently a mix of common lead similar to that of the ore event and of radiogenic lead evolved from a source with a consistently high th u and that 2 their residual fraction has less common lead than unaltered rocks the outcrop area with altered volcanic rocks displaying anomalously high lead isotope ratios extends over 25 km along the eastern margin of the batholith since lead of the ores in the candelaria punta del cobre district has the same isotopic composition as the common lead of unaltered magmatic rocks of the area the lead isotope data are consistent with a derivation of the ore lead and by inference of other metals like cu both directly from a magmatic fluid exsolved during crystallization of the batholith and or from hydrothermal leaching of the volcanic rocks originally having similar isotopic compositions as the batholith

formation of gold deposits a metamorphic devolatilization model a metamorphic devolatilization model can explain the enrichment segregation timing distribution and character of many goldfields such as those found in archean greenstone belts slate belts and other gold only provinces in this genetic model hydrated and carbonated greenschist facies rocks particularly metabasic rocks are devolatilized primarily across the greenschist amphibolite facies boundary in an orogenic setting devolatilization operates on the scale of individual mineral grains extracting not just h2o and co2 but also s and in turn au elevated gold in solution is achieved by complexing with reduced s and by h2co3 weak acid buffering near the optimal fluid ph for gold solubility the buffering is more important than being at the point of maximum gold solubility low salinity ensures low base metal concentrations in the auriferous metamorphic fluid migration of this fluid upwards is via shear zones and or into hydraulic fracture zones in rocks of low tensile strength the geometry of the shear zones dictates the kilometre scale fluid migration paths and the degree of fluid focusing into small enough volumes to form economic accumulations of gold deposition of gold from solution necessitates breakdown of the gold thiosulphide complex and is especially facilitated by fluid reduction in contact with reduced carbon bearing host rocks and or by sulphidation of wallrocks to generate iron bearing sulphide and precipitated gold as such black slate carbon seams banded iron formation tholeiitic basalt magnetite bearing diorite and differentiated tholeiitic dolerite sills are some of the important hosts to major goldfields gold deposition is accompanied by carbonation sulphidation and muscovite biotite alteration where the host rock is of suitable bulk composition the correlation of major gold deposits with rock type even when the gold is primarily in veins argues for rock dominated depositional systems not fluid dominated ones as a consequence a general role in gold deposition for fluid mixing temperature decrease and or fluid pressure decrease and boiling is unlikely although such effects may be involved locally several geological features that are recorded at gold only deposits today reflect subsequent modifications superimposed upon the products of this generic metamorphic devolatilization process overprinting by higher grade metamorphism and deformation and or palaeo weathering may provide many of the most obvious features of goldfields including their mineralogy geochemistry geometry small scale timing features geophysical response and even mesoscopic gold distribution

early proterozoic cu au and fe ore deposits associated with regional nacl metasomatism in northern fennoscandia scapolite is widely distributed in 1 9 2 5 ga volcano sedimentary rocks and 1 77 2 2 ga igneous rocks over several hundred square kilometres in northern fennoscandia comprising northern sweden no

geochemistry of post 1540 ma granites in the cloncurry district northwest queensland proterozoic fe oxide cu au co mineralization in the cloncuriy district is spatially and temporally related to intrusion of voluminous postpeak metamorphic granites that form most of the williams and naraku batholiths detailed mapping and geochemical study of these granites in the southern part of the district have identified two groups of intrusions that are referred to here as the cloncurry supersuite and eureka supersuite the cloncurry supersuite is composed mainly of monzogranite and syenogranite which consist of quartz plagioclase alkali feldspar hornblende biotite with accessory magnetite titanite apatite and zircon the timing of intrusion of the wiley igneous complex is interpreted to be pre or syn d 3 based on overprinting relationships while hornblende geobarometry suggests an emplacement depth of approximately 14 km the granites are subalkaline high k metaluminous rocks and range from 59 to 74 wt percent sio 2 increasing sio 2 is accompanied by increasing k 2 o rb and th and decreasing mgo fe 2 o 3 feo tio 2 cao p 2 o 5 sr eu zr cu zn ni v and sc this is consistent with fractionation of observed phases including plagioclase amphibole biotite magnetite titanite and apatite the eureka supersuite ranges from diorite to syenogranite in composition more mafic varieties contain pyroxene and hornblende while more felsic varieties contain biotite as the only ferromagnesian silicate sodiccalcic alteration events are closely linked in space and time to intrusion of eureka supersuite magmas the timing of intrusion is interpreted to be pre and post d 3 based on overprinting relationships between different plutons and mylonitic fabrics hornblende geobarometry suggests an emplacement depth of approximately 10 km for the mount angelay igneous complex eureka supersuite granites in the mount angelay igneous complex range from 51 to 76 wt percent sio 2 the granites are alkaline and k 2 o rich leading to their classification as a shoshonite series with increasing sio 2 content tio 2 al 2 o 3 fe 2 o 3 t mno mgo cao p 2 o 5 sr eu cu zn ni v and sc decrease indicating fractionation of observed minerals including apatite magnetite pyroxene hornblende plagioclase and biotite some samples are characterized by very high abundances of k 2 o p 2 o 5 sr ba and light rare earth elements lree compared to other eureka supersuite samples this may reflect their derivation from a source that was variably enriched in incompatible elements compared with many other shoshonitic rocks high k eureka supersuite samples are strongly depleted in sr and to a lesser extent eu and enriched in y and heavy rare earth elements hree this suggests that garnet was not a stable phase in the source region that the source contained plagioclase as a stable phase and or the granites evolved by extensive plagioclase fractionation partial melting in the lower crust to generate post 1540 ma granites was most likely caused by intrusion of basic magma into the crust eureka supersuite magmas were probably derived from partial melting of variably incompatible element enriched gabbroic rocks while cloncurry supersuite magmas were most likely derived from partial melting of more felsic material of dioritic to tonalitic composition

biotite and apatite as tools for tracking pathways of oxidized fluids in the archean east repulse gold deposit australia fluid pathways in hydrothermal ore deposits can potentially be traced through alteration zoning patterns and the chemistry of mineral phases i e major trace elements and isotopic composition which provide insight into the physico chemical gradients within and adjacent to pathways world class neoarchean gold deposits of the eastern yilgarn can be zoned with respect to alteration assemblages but in many cases fluid pathways are poorly understood which makes it difficult to identify the nature and source of fluids this study conducted detailed core logging sem mineral mapping of alteration assemblages and microprobe analysis of biotite and apatite in order to identify chemical gradients across the east repulse gold deposit of the st ives gold camp eastern yilgarn western australia results show that the east repulse deposit is vertically zoned with relatively oxidized sulfate rich alteration in the footwall of the deposit anhydrite celestine and or barite sulfide rich alteration in the core of the deposit pyrite magnetite with minor barite and celestine and relatively reduced sulfide only assemblages pyrite pyrrhotite with minor pentlandite millerite and cobaltite in the hanging wall of the deposit gold was identified as inclusions in pyrite and associated biotite implying a link between biotite pyrite alteration and gold mineralization the abundance of f in biotite and apatite progressively decreases from the footwall of the deposit into the mineralized core this trend of decreasing f in biotite and apatite with decreasing depth is consistent with an hypothesis that oxidized f and k bearing fluids were focused along subvertical pathways beneath the deposit within or subjacent to granitoid dikes the biotite apatite geothermometer shows that these fluids were relatively hot 480 60 c at the time of alteration these relatively high temperature oxidized f and k bearing fluids may have been derived from a proximal magmatic source

field and numerical investigations of gateroad system failure induced by hard roofs in a longwall top coal caving face abstract in longwall mining hard roofs located immediately above the coal seam should not cave and cause ground control problems around the working longwall face in this paper comprehensive field observations and numerical simulations were used to investigate the chain pillar and adjoining gateroad failure during a longwall top coal caving ltcc face retreat at the majialiang coalmine located in shanxi china the results show that hard roof strata did not cave behind the longwall face but overhung to form a cantilever beam above the chain pillar the roof beam concentrated high stress in the chain pillar and caused the pillar failure the concentrated stress moved close to the headgate and the solid side of the next panel causing gateroad damage and rib collapse numerical simulations found that hard roof treatment could fill the space near the goaf edge and deliver support pressure to the roof as well as alleviate the stress concentration in the pillar and the solid side of the next longwall panel simulations suggested that a pillar size of 50 m or larger was feasible without consideration of hard roof treatment a 40 m chain pillar with hard roof treatment could also satisfy the demand on the pillar and supply gateroad safety during the service period field practices verified the numerical results and suggested that hard roof treatment by hydraulic fracturing is a feasible method for overcoming ground control problems in a situation such as that presented in this paper

occurrence and origin of marialitic scapolite in the humboldt lopolith n w nevada the occurrence and origin of marialitic scapolite in the humboldt lopolith was investigated in the field and in the laboratory using petrographic and experimental techniques scapolite occurs in three modes as a pervasive replacement of plagioclase and other minerals in gabbro diorite and extrusive rocks as a poikiloblastic mineral in scapolitite dikes and as a fracture filling mineral with analcime albite and sphene in scapolite veins additional secondary minerals associated with scapolite include epidote prehnite hornblende and diopside salite clinopyroxene relations with these minerals suggest that most marialitic scapolite grew at temperatures around 400 c scapolite composition varies from eqan12 to eqan37 containing from 72 to 96 atomic cl in the r position experiments on systems of similar compositions indicate that nacl h2o fluid having more than 40 mol nacl is needed to stabilize the scapolite

stable isotope evidence for the origin of the mesoproterozoic starra au cu deposit cloncurry district northwest queensland new stable isotope data are consistent with a metasomatic origin for the controversial mesoproterozoic ironstone hosted au cu deposit at starra in the cloncurry district of northwest queensland this supports textural and mineralogical evidence that the ore bearing ironstones formed after the peak of metamorphism and were strongly controlled by brittle ductile deformation three dominant paragenetic stages are recognized these are 1 early widespread na ca metasomatism quartz albite scapolite actinolite 2 localized k fe metasomatism biotite magnetite hematite quartz pyrite and 3 mineralization quartz anhydrite barite hematite calcite gold pyrite chalcopyrite bornite chalcocite chlorite muscovite crosscutting anhydrite veins associated with carbonate or hematite are rare in the upper parts of the system but more common at depths greater than 700 m stage 3 minerals demonstrate that the ore fluid was highly oxidized a restricted range of fe oxide delta 18 o implies isotopically similar fluids were responsible for the magnetite ironstones and later hematite alteration associated with gold and sulfides between 0 2 to 3 3ppm except for one magnetite at 5 4ppm sulfur isotope compositions suggest that pyrite 0 2 to 3 9ppm chalcopyrite 5 8 to 0 7 and 14 6ppm bornite 4 7ppm chalcocite 0 1ppm and anhydrite 1 1 2 4ppm all formed from the same sulfur source anhydrite delta 34 s falls within the sulfide range suggesting that the sulfate inherited its delta 34 s through hydrolytic processes similar to those of some porphyry environments delta 13 c of ore stage carbonates range from 7 3 to 2 2 per mil temperatures based on stage 2 quartz magnetite pairs imply 400 degrees to 500 degrees c for ironstone formation and stage 3 calcite hematite pairs indicate 180 degrees to 330 degrees c for mineralization stage 2 fluid inclusions have homogenization temperatures between 345 degrees and 615 degrees c and salinities of 34 to 52 wt percent nacl equiv stage 3 fluid inclusions homogenized between 225 degrees and 360 degrees c and have salinities of 30 to 42 wt percent nacl equiv calculated delta 18 o fluid compositions for magnetite quartz and hematite calcite average 7 8 per mil and 9 5 per mil respectively fluid compositions for stages 2 and 3 fall within the range for a magmatic or metamorphic fluid however combined stable isotope and fluid inclusion data and thermodynamic considerations suggest a magmatic metasomatic origin for both the magnetite ironstones and the highly oxidized mineral assemblage associated with high grade gold deposition

high radiogenic heat producing granites and metamorphism an example from the western mount isa inlier australia the origins of metamorphism 600 c and 3 4 kbar in the western mount isa inlier australia remain controversial for a number of reasons 1 no synmetamorphic intrusive bodies can be recognized 2 high temperatures appear to be sustained for periods 100 m y and 3 metamorphism follows an extended phase of thermal subsidence we show that the burial of granite batholiths enriched in radiogenic elements beneath the thick insulating sedimentary succession of the mount isa group deposited in response to repeated rift sag cycles was capable of generating steep upper crustal thermal gradients immediately prior to the isan orogeny these gradients are appropriate to peak metamorphic conditions such that the ensuing isan orogeny required no significant additional heat input this result is significant in that it may provide a mechanism for understanding the origins of high temperature metamorphism in other terranes where the involvement of transient heating is not obvious

metasomatic albitites and related biotite rich schists from a low pressure polymetamorphic terrane snake creek anticline mount isa inlier north eastern australia microstructures and p t d paths rocks of the snake creek anticline are mainly pelitic schists psammitic schists and quartzites that were metamorphosed during multiple high t low p events extending from d1 to d5 with the metamorphic peak occurring late to post d3 albitites are widespread but are concentrated in five areas they are typically fine to medium grained and consist of albite with or without combinations of quartz biotite staurolite cordierite garnet andalusite sillimanite kyanite gedrite and tourmaline from the presence or absence of albite inclusions in porphyroblasts the albitites are interpreted as forming early in the d3 event as a result of infiltration of external fluids psammitic schists and quartzites were preferentially altered but pelitic schists were also albitized in localities where the alteration was more extreme with the replacement of muscovite total and the replacement of quartz and biotite variable structural controls on albitization include fracturing and syn d3 shear zones in fold hinges biotite schists with abundant porphyroblasts combinations of staurolite garnet andalusite and cordierite occur adjacent to albitites and it is argued that they formed by the addition of fe and mg sourced from the albitites in several albitite rich areas cordierite grew early in d3 and was partly or entirely replaced during or after d3 by combinations of biotite andalusite tourmaline staurolite and sillimanite a postulated p t d path involved an increase in pressure with or without a decrease in temperature subsequent to early d3 albitization followed by an increase in temperature up to the metamorphic peak late d3 to early d4 the metamorphism was contemporary in part with the emplacement of the williams batholith c 1550 1500 ma which probably supplied the na rich fluids

a test of the viability of fluid wall rock interaction mechanisms for changes in opaque phase assemblage in metasedimentary rocks in the kambalda st ives goldfield western australia transitions from pyrrhotite magnetite to pyrite magnetite and pyrite hematite bearing assemblages in metasedimentary rocks in the kambalda st ives goldfield have been shown to be spatially associated with economic gold grades fluid mixing fluid rock interaction and phase separation have been proposed previously as causes for this association textural mineralogical and isotopic evidence is reviewed and thermodynamic calculations are used to investigate the mineralogical consequences of progressive fluid rock interaction in interflow metasediments fluid rock interactions in response to fluid infiltration and or bulk composition variation are plausible mechanisms for production of the observed features

fluid and mass transfer during metabasalt alteration and copper mineralization at mount isa australia metabasalts surrounding the metasediment hosted base metal deposit at mount isa have been modified by metamorphism polyphase deformation and several stages of hydrothermal alteration this study aims to understand the large scale hydrothermal processes that determined the chemical composition of syn to postmetamorphic ore brines prior to being focused into chemicaly anomalous metasediments that acted as a chemical trap for localized copper precipitation field mapping of the metabasalts provided the framework to determine the relative timing of district scale alteration events which were then studied by mineralogic observations and bulk mass balance measurements microthermometry raman microspeetrometry and br cl analyses of fluid inclusions and h o c and s stable isotope measurements on vein minerals were used to characterize the hydrothermal fluids associated with the alteration events all fluids are moderately to highly saline variably ca enriched with high br cl compared to modern seawater and isotopiealy most akin to modern evolved basin or low grade metamorphic brines the timing and fluid tracer observations in conjunction with thermodynamic mass transfer modeling permit the following correlation between district scale alteration processes and the mine scale hydrothermal events associated with copper deposition at mount isa district scale epidote sphene alteration of metabasalts temporally overlapped with the peak of greenschist facies metamorphism and deformation and is widely distributed in flow top breccias and as halos around synmetamorphic quartz calcite veins it is associated with calcic brines with 12 to 38 wt percent cacl 2 nacl equiv and thermodynamic modeling suggests that the observed mineralogy and bulk mass changes can be explained by focusing of metabasalt equilibrated fluids and by reaction with similar rocks at somewhat higher temperature similar timing and fluid characteristics are associated with dolomitic alteration at the mount isa mine where mixing of metabasalt derived calcic brine with metamorphic co 2 from the metasediments led to massive dolomite precipitation kilometer scale fracture zones associated with carbonate fe oxide alteration calcite albite magnetite or hematite or biotite or chlorite cut all penetrative foliations in the metabasalts east of mount isa they are locally associated with uranium mineralization and are characterized by medium salinity nacl rich fluid inclusions 8 93 wt nacl equiv carbonate fe oxide alteration is interpreted to mark channelways of infiltration by oxidized sulfate bearing brines from outside the metabasalt sequence possibly from an overlying evaporitic cover sequence fluid characteristics evidence for extreme copper mobility and timing criteria of alteration relative to deformation suggest a temporal and possibly genetic correlation with the main copper and silica deposition stage at the mount isa mine mg chlorite rutile alteration is restricted to metabasalts immediately below the copper deposit and the vicinity of the mount isa fault zone where higher grade amphibolite facies metabasalts were upthrust against the greenschist facies metabasalts and metasediments now hosting the copper ore bodies mg chlorite rutile alteration of metabasalts and copper mineralization in the adjacent reduced sediments can both be explained by fluid focusing along an actively extending contact zone between the oxidized metabasalts and the reducedmetasediments the brines focused into this contact zone were initially oxidized as a result of infiltration through the carbonate fe oxide fracture zones and less altered metabasalts and became reduced by reaction with the metasediments the unusual geochemical and isotopic low 13 c and high 34 s composition of mg chlorite rutile alteration can be explained as a result of back flow of reduced fluids from the metasediments into the metabasalts although mg chlorite rutile alteration of metabasalts probably liberated some of the copper now present in the orebodies this alteration may be a relatively localized effect associated with the site of ore deposition rather than an essential sourcing mechanism for the copper the regional feature of greatest significance to ore formation at mount isa and to exploration for similar high grade copper deposits elsewhere is not the somewhat elevated initial copper content of the metabasalts nor their locally significant copper depletions but their moderately high oxidation state evident from the ubiquitous occurrence of fe rich epidote and the large scale fe oxide altered fracture zones oxidation of the basalts or any other silicate rocks favored high copper solubility along extensive transport paths and provided the essential chemical contrast to the depositional environment which was anomalously reduced and sulfide rich as a result of an earlier process of sedimentary to diagenetic pb zn fe s mineralization

two sulphur isotope provinces deduced from ores in the mount isa eastern succession australia the sulphur isotopic characteristics of ore deposits in the australian mount isa eastern succession are not well known unlike those of the western succession in this study new detailed analyses are provided for recently discovered eastern succession mineralisation such as the starra and osborne bif hosted cu au ores the dugald river sediment hosted pb zn prospect and four vein hosted cloncurry style cu au deposits hampden mt elliot swan mt cobalt and the answer mine all of the deposits of the eastern succession have 34ssulphide between 8 and 9 regardless of their genesis empirically a moderate 34s range averaging close to 0 characterises starra style cu au and pegmont pb zn bif ores whereas shear and vein style cu mineralisation populations are tighter and do not average close to 0 this is a particularly surprising result for dugald river where a larger isotopic variation more typical of stratiform sediment hosted pb zn ores in the region might have been expected by comparison western succession stratiform pb zn and vein style cu deposits span a huge range of 15 to 51 large sulphur isotope ranges typify sulphate evaporite or organic sulphur rich sedimentary successions the lack of such variation in the eastern succession in turn suggests that primary evaporite sequences there were halite dominated but sulphate poor and or contained only limited volumes of organic sulphur rich sediment eastern succession sequences were therefore less likely hosts for giant stratiform pb zn deposits because of their paucity of sulphur although local sulphur sources permitted small deposits such as dugald river to develop sedimentary conditions were more favourable for the development of sulphur poor synsedimentary hydrothermal systems such as starra osborne and pegmont although sulphur isotope evidence is equivocal about the origin of these epigenetic deposits close to the williams batholith mt dore hampden owe their clustering around 0 to their granitic fluid source

iron oxide copper gold deposits an andean view iron oxide copper gold iocg deposits defined primarily by their elevated magnetite and or hematite contents constitute a broad ill defined clan related to a variety of tectono magmatic settings the youngest and therefore most readily understandable iocg belt is located in the coastal cordillera of northern chile and southern peru where it is part of a volcano plutonic arc of jurassic through early cretaceous age the arc is characterised by voluminous tholeiitic to calc alkaline plutonic complexes of gabbro through granodiorite composition and primitive mantle derived parentage major arc parallel fault systems developed in response to extension and transtension induced by subduction roll back at the retreating convergent margin the arc crust was attenuated and subjected to high heat flow iocg deposits share the arc with massive magnetite deposits the copper deficient end members of the iocg clan as well as with manto type copper and small porphyry copper deposits to create a distinctive metallogenic signature

calc silicate mineralization in active geothermal systems detailed study of the calc silicate mineralogy in the cerro prieto geothermal system was used to demonstrate examples for thermodynamic evaluation of phase relations among minerals of variable composition and to calculate the chemical characteristics of hydrothermal solutions compatible with the observed calc silicate assemblages in general there is a close correlation between calculated and observed fluid compositions calculated fugacities of o 2 at about 320 degrees c in the cerro prieto geothermal system are about five orders of magnitude less than those at the nearby salton sea geothermal system this observation is consistent with the occurrence of fe super 3 rich epidotes and andradite garnets in the latter system and the presence of prehnite at cerro prieto modified journal abstract

high radiogenic heat producing granites and metamorphism an example from the western mount isa inlier australia comment and reply extract we welcome the paper of mclaren et al 1999 because it makes an important contribution to our understanding of the source of thermal anomalies in low pressure metamorphic belts however we argue that high radiogenic heat producing granites such as the sybella batholith although locally important in the overall thermal budget were not the primary cause of low pressure metamorphism in the mount isa inlier and that synmetamorphic intrusions were a significant additional factor

influences of the snow cover on landslide displacement in winter period a case study in a heavy snowfall area of japan the displacement of a relatively small reactivated landslide in a snowy area in japan was monitored over a long period the displacement rate of the landslide which was approximately of 20 mm d 1 before the formation of snow cover decelerated drastically during the continuous snow cover period every winter period possible causes included reduction in the amount of water that reached the ground surface mr meltwater and or rainwater and increase in snow load given that the actual displacement of the landslide was far below the predicted value based on the relationship between landslide displacement and mr immediately before the continuous snow cover period the deceleration of landslide displacement was more likely attributable to the increase in snow load than to the reduction in mr an investigation of the link between snow load and landslide displacement showed a negative logarithmic relationship a dynamic analysis based on the limit equilibrium method showed that snow load increases the effective normal stress and the stability of a landslide in which the mean inclination angle of the slip surface is smaller than the internal friction angle the stability of the actual slope was also analyzed by conducting soil tests on samples collected at the site and using the resultant parameters the analysis also showed that the increase in snow load increases the safety factor and reduces the landslide displacement the displacement of a relatively small landslide that has a shallow slip surface was found to be greatly influenced by snow cover

contrasting fluid chemistries alteration characteristics and metamorphic timing relationships recorded in hybridized orebodies of the missanabie renabie gold district archean wawa subprovince ontario canada

chronology of magmatism skarn formation and uranium mineralization mary kathleen queensland australia uranium mineralization is hosted in a metasedimentary sequence intruded by felsic and mafic bodies in which the zircon u pb systems are 1 730 to 1 740 m y old felsic dikes characterized by exceptionally high uranium contents crystallized at essentially the same time 1 737 or 15 m y primary rb sr systematics in these igneous rocks are profoundly disturbed u pb discordia establish age of uranium mineralization as 1 550 or 15 m y derivation of uranium protore in the host rocks prior to regional metamorphism and 1 550 m y uraninite formation was probably by ca 1 740 m y hydrothermal activity modified journal abstract

inherited zircon and titanite upb systems in an archaean syenite from southwestern australia implications for upb stability of titanite abstract inherited zircon and titanite have been identified in a syenite from the archaean of southwestern australia conventional and shrimp analyses on euhedral zoned zircon and zoned rims on complex grains define a crystallisation age of 2654 5 ma for the syenite in addition shrimp analyses on zircon cores and unzoned subhedral zircons show that zircon has a ca 3250 ma inherited component conventional u pb ages on titanite also fall between ca 3250 ma and ca 2650 ma demonstrating that inherited titanite as well as zircon is present in the syenite the syenite has been affected by regional upper amphibolite facies metamorphism at an estimated temperature of 625 650 c retention of the inherited radiogenic pb in the titanite is evidence that the closure temperature for titanite is greater than 650 c the presence of inherited titanite and zircon also demonstrates a crustal source component for the syenite and indicates it originated by partial assimilation of crustal rocks by a potassic magma at

magmatic hydrothermal albite actinolite apatite rich rocks from the cloncurry district nw queensland australia abstract albite quartz actinolite apatite rich rocks with accessory titanite form a carapace that caps a small dome like intrusion of roxmere pluton and provide evidence of the accumulation and release of magmatic fluids that may have contributed to regionally extensive na ca alteration in the proterozoic cloncurry district australia the roxmere pluton was emplaced after the peak amphibolite facies metamorphism and into psammitic metasedimentary rocks that are stratigraphically younger and overlie the calc silicate rich mary kathleen group na ca hydrothermal assemblages closely spatially related to the roxmere pluton suggest that na ca alteration in this case is inconsistent with excepted up temperature metamorphic fluid circulation models the carapace rocks comprise two variants aplite and pegmatite both of which were affected by alteration and brecciation aplitic material predominates and the carapace has a brecciated top and a distinct textural zonation from an aplite rich pegmatite poor base to a relatively aplite poor pegmatite rich top this zonation is interpreted to represent the progressive accumulation of volatile phases toward the top of the carapace which culminated in fluid overpressuring and brecciation of the granitoid stock the convoluted and ptygmatic habit of the aplitic and pegmatitic material within the carapace is similar in nature to the comb quartz unidirectional solidification textures that are developed in the roof zones of some porphyry stocks these complex textures are interpreted to have formed from a single phase of fluid saturation the roxmere pluton or a deeper equivalent has a na mg and ca rich composition and a clinopyroxene amphibole rich mineralogy that is consistent with the formation of the contained albite actinolite apatite rich phases however the source of the rocks within the carapace is equivocal given that their contact relationships are obscured the 18 o composition of minerals within the carapace has the following ranges albite 7 1 8 7 actinolite 8 0 8 5 and quartz 8 9 11 4 albite and quartz 18 o equilibria suggest that these minerals in the pegmatitic and aplitic components formed at temperatures of 510 c to 540 c the calculated 18 o composition of a fluid in equilibrium with these minerals 6 0 to 8 0 at temperatures between 450 c and 550 c is consistent with a magmatic origin these estimated temperatures and 18 o fluid composition are comparable to estimates for regional na ca alteration in contrast d analysis of actinolite 136 to 150 within the carapace demonstrates that these fluids have a significantly lower d signature compared to na ca alteration assemblages associated with regional alteration 70 to 90 the low values in the carapace could either be interpreted as being produced from meteoric fluids or from degassed magmatic fluids although a meteoric fluid model is deemed improbable as meteoric fluids in the district have a documented d composition of ca 0 0 as a consequence an open system degassed magmatic hydrothermal fluid origin is considered to be the most plausible explanation for the low isotopic signatures and is also consistent with the complex textural relationships described within the carapace

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

meta evaporite sequence exhalative chemical sediments and associated rocks in the proterozoic willyama supergroup south australia implications for metallogenesis abstract the willyama supergroup comprises proterozoic meta sedimentary and meta igneous rocks in western new south wales and eastern south australia and contains the giant broken hill pb zn ag deposit in addition to numerous small stratiform stratabound and vein mineral deposits new lithological geochemical and fluid inclusion data from the olary block west of broken hill suggest the presence of former evaporite rocks now metamorphosed to a variety of chemically and mineralogically unusual lithologies these evaporite rocks overlie relatively oxidised strata and are in turn overlain by reduced graphite bearing pelites rocks of sodic composition abound represented by albite quartz rich rocks calcite actinolite epidote garnet clinopyroxene inferred to represent metamorphosed analcime rich strata of felsic volcaniclastic provenance with variable proportions of carbonates for example calcite dolomite trona and shortite these rocks are interspersed with potassic rocks possibly also with an evaporitic origin in addition to normal clastic meta sediments the presence of halogen rich minerals in a distinctive mineral assemblage hypersaline fluid inclusions pseudomorphic voids and minerals after gypsum and carbonate in addition to tourmalines with isotopically light boron isotopes is interpreted as evidence for a non marine evaporite parent rock for portions of the olary block types of mineral occurrences in the olary block form a continuum between chemical sediments formed by the exhalations of hydrothermal fluids to intrasediment deposits inferred to have been formed due to the chemical changes imposed on these and or diagenetic fluids during their passage through the sedimentary pile disseminated stratabound pyrite including cobaltian types and chalcopyrite extend along strike for many kilometres and are interpreted to have formed by a diagenetic mechanism the presence of massive sulphide bearing strata iron formations barite tourmalinite and manganiferous rocks are typical of chemical sediments derived from hot spring sources the olary block meta evaporites have similar whole rock compositions to tertiary analcime rich rocks of the green river formation wyoming these new data imply that portions of the adjacent broken hill block may also comprise meta evaporites for example the quartz albite rich strata of the thackaringa group and the calcsilicates of the lower broken hill group and that the disseminated cobaltian pyrite mineralisation in the thackaringa group may not be of exhalative origin

trace element content of pyrite from the kapai slate st ives gold district western australia the kapai slate is a continuous pyrite rich carbonaceous shale horizon within the st ives au district that is spatially related to high grade au mineralization in situ laser ablation inductively coupled mass spectrometry la icpms trace element analyses in situ sensitive high resolution ion microprobe stable isotope shrimp si s isotope analyses and optical microscopy pyrite texture analyses were used to examine the different pyrite types in the kapai slate and au deposits these data were also used to confirm that the trace element signature of sedimentary pyrite can be preserved in rocks that underwent upper to mid greenschist facies metamorphism and significant hydrothermal overprint the data were further utilized to gain a more detailed understanding of the ocean conditions during deposition of the kapai slate and determine whether some of the au and s in the st ives district could have been sourced from the kapai slate seven different types of pyrite were identified fine grained sedimentary pyrite py 1 nodular sedimentary pyrite py 2 remobilized sedimentary pyrite py 3 coarse grained inclusions poor late pyrite py 4 inclusion rich magnetite series pyrite py 5 ore stage pyrite py 6 and pyrite associated with the mafic units py 7 each type of pyrite was found to have distinctive trace element compositions and s isotope signatures the results of the la icpms analyses provide evidence for early trace element enrichment in the kapai slate sedimentary pyrite median values of 158 ppm ni 387 ppm co 82 ppm cu 727 ppm as 1 91 ppm mo 13 ppm se 0 25 ppm au 7 72 ppm te and 3 36 ppm ag for py 1 and 223 ppm ni 158 ppm co 99 ppm cu 856 ppm as 1 27 ppm mo 10 2 ppm se 0 57 ppm au 10 09 ppm te and 6 62 ppm ag for py 2 concentrations of ni and co are low relative to other late archean sedimentary pyrite median of 813 and 465 ppm respectively and mo levels are near that of the euxinic shales of the similar aged jeerinah formation in the hamersley basin western australia these data suggest that the kapai slate was deposited in an anoxic to euxinic basin with relatively low biological productivity the 33 s and 34 s signatures of the sedimentary pyrite suggest two different sources of s positive 34 s and negative 33 s signatures indicate bacterial reduction of so 4 2 from seawater whereas positive 34 s and positive 33 s signatures indicate an elemental s 8 source indicating the pyrite formed later during diagenesis this s isotope signature is consistent with a transition between a near sediment environment to a more distal environment source analyses of the ore phase pyrite yield weakly positive 33 s values this suggests there was a minor contribution of sedimentary s to the more significant oxidized ore forming fluids which is consistent with a small contribution of au from a sedimentary source approximations of the degree of sedimentary pyrite destruction in the pyrrhotite pyrite dominated zones and pyrrhotite magnetite pyrite zones of the northern part of the st ives district were used to calculate the amount of au released from the early sedimentary pyrite the calculation suggests that a minor though possibly locally significant amount of au could have been sourced from the kapai slate

origin of hydrothermal fluids at olympic dam preliminary results from fluid inclusions and stable isotopes fluid inclusions and stable isotope data provide evidence of the temperature composition and sources of hydrothermal fluids associated with formation of the fe rich breccias that host cu u au ag ore at olympic dam early magnetite associated with pyrite and siderite precipitated from fluids of high delta 18 o content approx 10ppm at temperatures near 400 degrees c and magnetite in k feldspar apatite veins at the nearby acropolis deposit probably formed from similar fluids in contrast hematite associated with ore bearing breccias formed at lower temperatures 200 degrees 400 degrees c from fluids of lower delta 18 o content 9ppm fluid inclusion homogenization temperatures in quartz fragments within hematite breccias overlap with and are lower than those indicated by isotope geothermometry two phase liquid plus vapor inclusions mainly homogenize at temperatures between 130 degrees and 280 degrees c with a mode at 170 degrees to 190 degrees c quartz fragments within rare laminated barite clasts display a larger range of homogenization temperatures from 110 degrees to 420 degrees c and may have preserved evidence of early high temperature hydrothermal events measurement of freezing point depressions in fluid inclusions provides evidence of widely varying salinities and complex solute chemistry indicated salinities vary from a minimum of 7 3 wt percent nacl equiv 1 3 m to a maximum of 23 7 wt percent nacl equiv 4 2 m in two phase fluid inclusions and up to 42 wt percent nacl equiv in halite saturated three phase inclusions all the fluid inclusions studied displayed evidence of additional solutes in addition to nacl all required a high degree of supercooling to induce freezing and displayed initial ice melting at temperatures below 23 degrees c and many formed distinctive brown granular ice in addition several inclusions also formed co 2 clathrates and other metastable solids qualitative assessment of these characteristics indicates fluids carrying multiple solutes probably including nacl kcl cacl 2 fecl 2 caf and co 2 these preliminary results suggest that at least two sources of fluids of contrasting temperature composition and oxygen isotope characteristics were involved in the formation of olympic dam early magnetite was deposited from hydrothermal fluids of deep seated possibly magmatic origin but magnetite bearing rocks are not significant hosts for copper uranium mineralization later hematite associated with ore bearing breccias was deposited by fluids of significantly lower temperature and lower delta 18 o values the geologic setting of the deposit a fault bounded depression at or near the palcosurface implies that waters of surficial origin seawater closed basin water or ground water may have been involved in the later stages of hydrothermal activity that formed the hematite breccias although our preliminary isotopic data do not require such waters they are consistent with this conclusion

discrete element modelling of cutter roof failure in coal mine roadways abstract cutter roof failure is a common failure mechanism in coal mine roadways due to the oblique orientation of the major horizontal stress with respect to roadway advance direction in the present study two 3d numerical models based on the discrete element method have been developed to simulate cutter roof failure in the first model created using pfc3d the rock surrounding a roadway is represented by an assembly of spheres glued together at their boundaries high horizontal stress at varying orientations to the roadway advance direction is applied to the model to investigate the mechanism of fracturing around the roadway the numerical results indicate that a roadway driven at a large angle 75 90 with respect to the maximum horizontal stress suffers significantly more fracturing than that driven at a small angle 0 15 the second model created using the distinct element code 3dec adopts a newly developed trigon logic in which the roadway roof is represented by an assembly of tetrahedral blocks bonded together at their contacts both the pfc3d and 3dec models successfully simulate the cutter roof failure process which is characterized by a fracture zone initiating at the corner where the major horizontal stress and the roadway roof intersect this fracture zone propagates across the roof span with continued roadway advance the influence of pre existing fractures is evaluated in the pfc3d model and the results show that incorporating bedding planes and cross joints in the roadway roof promotes the development of distinct cutter roof failure immediately behind the advancing face the numerical results presented provide additional insight into cutter roof failure mechanisms and important insight for guiding design and layout of roadway support

albite rich silica depleted metasomatic rocks at emuford northeast queensland mineralogical geochemical and fluid inclusion constraints on hydrothermal evolution and tin mineralization late paleozoic fluorine rich granites and their host metasediments in the emuford district of the herberton tin field contain small zones of intense albitization that host cassiterite mineralization sodium metasomatism was accompanied by hydrothermal leaching of granite quartz to form vuggy albite rocks episyenites vugs created by quartz dissolution were filled in by hydrothermal minerals including albite k feldspar and or muscovite and cassiterite late phases are dominated by quartz and fluorite swarms of parallel veinlets crosscut the albitized zones these veinlets were formed by repeated fracturing in response to local fluid over pressures they contain infill mineralogy similar to the vugs and probably formed at least partly contemporaneously with vug infill due to the overprinting at various scales of alteration vug infill and vein formation stages chemical changes associated with episyenite formation are only qualitatively constrained however the mineralogical and textural features of the alteration zones suggest that most major and trace elements had substantial mobility during their formation major chemical changes associated with episyenite formation include leaching of sio 2 k 2 o rb and ba with introduction of na 2 o and minor sr during vug and vein filling stages there was an introduction of sio 2 al 2 o 3 na 2 o k 2 o cao f and sn the erratic behavior of ree is probably related to the growth of fluorite and minor accessory phases zircon monazite xenotime with preferential enrichment of heavy ree in rocks with the highest fluorine concentrations fluid inclusion study indicates that vug and vein filling stages of the hydrothermal evolution involved two types of fluids a high salinity fluid 30 50 equiv wt nacl of probable magmatic origin and homogenization temperatures up to 428 degrees c was associated with vug filling in the granite hosted deposits a lower salinity fluid 5 15 equiv wt nacl containing variable amounts of co 2 and having homogenization temperatures between 160 degrees and 420 degrees c was associated with veinlet formation in the granite hosted deposits and with vein and cavity filling in the metasediment hosted deposit this lower salinity fluid may represent a condensed vapor phase derived from boiling of the magmatic fluid or may be a mixture of magmatic and meteoric components the close association of albitization and quartz dissolution suggests a genetic link between the two processes it is proposed that exchange of na for k in the fluorine rich hydrothermal fluids caused a substantial increase in quartz solubility and led to quartz dissolution in the albitized rocks

alteration mineralization and fluid evolution at the eloise cu au deposit cloncurry district northwest queensland australia the eloise deposit 3 1 million metric tons mt 5 5 cu 1 4 g t au and 16 g t ag is hosted by proterozoic rocks of the soldiers cap group in the eastern fold belt of the mount isa inlier the deposit is characterized by very high grade chalcopyrite pyrrhotite rich mineralization hosted by mafic silicate alteration alteration and mineralization lie within and adjacent to a major shear zone the main metasomatism comprised three stages early pervasive albite alteration stage i was overprinted by stage ii hornblende biotite quartz veins and alteration stage iii chalcopyrite pyrrhotite magnetite pyrite calcite quartz chlorite and actinolite replaced and brecciated the earlier mafic silicates the lodes occupy a narrow portion of a zoned mineralized system that is at least 2 km in length magnetite pyrite rich mineralization occurs in the south with chalcopyrite pyrrhotite rich mineralization in the central lode zone and pyrrhotite rich mineralization in the north the system has a distinct chemistry with enriched cu au ag co ni and zn fluid inclusions in pre syn and late to postmineralization veins indicate an evolving fluid history primary inclusions and associated hornblende biotite assemblages in premineralization veins indicate a high temperature fluid 450 degrees 600 degrees c and salinity estimates suggest it was an ultrasaline brine 32 68 wt total salts fluid inclusions in stage iii quartz in mineralized veins display a wide range of homogenization temperatures approximately 100 degrees 500 degrees c and gangue assemblages actinolite chlorite muscovite suggest mineralization was a cooler event 200 degrees 450 degrees c inclusions associated with the mineralization have a lower salinity 30 47 wt total salts than do premineralization inclusions and variable fluid inclusion types occur within the same clusters which may reflect fluid mixing the ultrasaline nature of the fluids and preliminary sulfur isotope results 0 4 2 0ppm suggest the ore fluid was predominantly magmatic metals were carried as chlorocomplexes and h 2 s was the dominant sulfur species important factors in ore deposition were a decrease in temperature and salinity and sulfidation of fe silicates eloise is interpreted to be a structurally controlled distal magmatic hydrothermal vein deposit

fluid sources and the role of abiogenic ch4 in archean gold mineralization constraints from noble gases and halogens abstract the st ives goldfield of western australia hosts high grade gold mineralization in a variety of lithologies within 2 7 ga greenstone belts the low salinity co 2 bearing fluids responsible for gold mineralization could have been generated either by metamorphic processes within the greenstones or from external magmatic sources and independently sourced abiogenic ch 4 has been suggested as an important control on gold mineralization in order to better constrain possible fluid sources we applied a combination of he ne ar kr xe isotope and cl br i analyses to quartz and carbonate veins containing h 2 o co 2 fluid inclusions pyrite magnetite hematite and quartz veins containing ch 4 rich fluid inclusions pyrrhotite pyrite samples containing h 2 o co 2 fluid inclusions have higher br cl and i cl values and less radiogenic noble gas isotope signatures than suggested for ch 4 rich fluid inclusions the samples containing ch 4 fluid inclusions have maximum 40 ar 36 ar of 50 000 20 ne 22 ne of 9 8 and maximum 21 ne 22 ne of 0 56 in contrast h 2 o co 2 fluid inclusions have maximum 40 ar 36 ar of only 20 000 and maximum 21 ne 22 ne of 0 14 the use of 40 ar 39 ar methodology to measure k simultaneously with 40 ar 36 ar enables us to show the highest 40 ar 36 ar ratios are representative of the fluids trapped at 2 65 ga and have not been significantly modified by post entrapment 40 ar r production 40 ar r radiogenic 40 ar furthermore the 40 ar 36 ar ratio is correlated with the 21 ne 22 ne and 136 xe 130 xe ratios demonstrating that other heavy noble gas isotope ratios are also close to their original composition the highly radiogenic noble gas isotope signatures are unlikely to have been generated within the greenstone host rocks because seawater altered volcanic rocks have high abundances of non radiogenic atmospheric noble gas isotopes in contrast the strongly radiogenic noble gas isotope signatures are likely to have been generated in ancient basement rocks underlying the greenstones at 2 65 ga the combined noble gas and halogen data are consistent with models in which redox reactions triggered by interaction of independently and distally sourced h 2 o co 2 and ch 4 localized high grade gold mineralization we suggest that the fluids were intimately associated with crustal magmatism in the st ives goldfield and that abiogenic ch 4 could be an important moderator of redox processes in other crustal environments

evolution of fluid driving forces and composition within collisional orogens subaerial collisional mountain belts have a predictable asymmetric two sided wedge geometry the major driving forces for crustal fluid flow in this framework arc thermal and topographic gradients it is possible to predict both a time averaged fluid state and the evolution of the fluid regime during orogenesis with three distinct fluid flow regimes the outboard toe where material is incorporated into the orogen a transitional zone of concentrated deformation and a zone of rapid exhumation along the inboard slope adjacent to the indentor as rocks move into the outboard wedge relatively low temperature compaction and head driven fluid flow dominates mid crustal material undergoes disequilibrium dehydration as rock fluid packets move into the transition zone producing a dominantly aqueous metamorphic fluid in the inboard region rapid uplift produces geothermal gradients in excess of 80 c km which encourage vigorous free convection advecting fluids evolve through immiscibility towards increasing co2 content during uplift of the rock fluid packets mixing of thermally driven and head driven fluids occurs at depths of 5 10 km the southern alps of new zealand the european alps and the himalaya represent variants of this orogenic hydrothermal system

alteration of oceanic crust and geologic cycling of chlorine and water we report new estimates of transport rates for h2o and cl between the mantle and surface reservoirs our estimates take into consideration alteration of oceanic crust especially that of plutonic rocks and possible subduction of sediments the effect of hydrothermal alteration on the cl budget seems to be negligible but the effect on the h2o budget is significant altered oceanic crust excluding sediments contains about 10 times as much h2o as the unaltered crust and its subduction may result in a net transport of h2o to the upper mantle in subduction zones however the rate of expulsion of h2o from the mantle by subduction zone magmatism is comparable to the amount released by ridge magmatism and is only about 10 of the amount subducted therefore about 90 of the subducted h2o must be returned to the mantle or returned to the crust by other processes in addition subduction of oceanic sediments to mantle depths will result in 1 1 a further increase in the return rate of h2o to the mantle reservoir 2 2 possible net transfer of cl to the mantle depending on the rate of pore water expulsion

evaporitic source model for igneous related fe oxide ree cu au u mineralization we propose that many igneous related fe oxide rich ree cu au u bearing deposits form by hydrothermal processes involving evaporitic ligand sources either coeval salars or older evaporites these deposits are abundant in both phanerozoic and proterozoic extensional continental and continent margin settings they commonly form in global arid zones but they also occur where magmatism is superimposed upon older evaporites magmatic compositions exert only second order control mainly on alteration mineralogy and on element abundances hot s poor brines generated by interaction with evaporitic materials are consistent with geologic settings and help rationalize the distinctive element enrichments siderophile lithophile and hydrothermal alteration sodic locally alkaline found in these systems this model contrasts with immiscible oxide melt and magmatic hydrothermal origins commonly proposed for these deposits although all three mechanisms can occur 31 refs 3 figs 1 tab

fluctuation of the seasonal snowpack in a mountainous area of the heavy snow district in the warm temperate zone of japan the seasonal snowpack and meteorological factors associated with the accumulation and ablation of the snowpack were monitored for 11 years in a mountainous area in the warm temperate zone of japan no notable rise was observed in mean wintertime air temperature but an increase was seen in the difference between the maximum and minimum air temperatures precipitation exhibited annual variability but no notable reduction over the measurement period the length of the continuous snow cover period increased slightly over the 11 years but no trend in variability was observed the maximum snow depth and maximum water equivalent of snow varied greatly from year to year depending on the amount of snowfall in a heavy snow year about 1600 mm of water which is almost the mean annual precipitation for the whole of japan was found to be temporarily stored in the snowpack

modeling mechanical layering effects on stability of underground openings in jointed sedimentary rocks abstract this paper examines the significance of mechanical layering for blocky rock mass deformation around underground openings excavated through sedimentary rocks the analysis is based on an integration of geologically based discrete fracture models geodfn which incorporate mechanical layering with the numerical discrete element method the discontinuous deformation analysis dda we begin with addressing limitations of classical solutions for mine roof stability in layered and jointed rock masses via the analysis of the free standing unsupported 2000 year old underground quarry known as zedekiah s cave below the old city of jerusalem israel we show that both the clamped beam model and the voussoir beam analogue fail to predict the observed roof stability only application of discrete element modeling which allows for interactions between multiple blocks in the rock mass can capture correctly the arching mechanism which takes place in the roof and which properly explains the long term stability of this underground opening we continue with examining the effect of joint trace geometries on blocky rock mass deformation using the hybrid geodfn dda approach we show that with increasing joint length and decreasing bridge length vertical deformations in the rock mass are enhanced we explain this by the greater number of distinct blocks in the rock mass due to the greater joint intersection probability in such geometries we find that rock bridge length is particularly important when considering the stability of the immediate roof with increasing rock bridge length the number of blocks in immediate roof decreases and consequently individual block width is increased increased block width in immediate roof layers enhances stable arching development thus improving their load carrying capacity and overall stability of the underground structure

constraints on pb closure temperature in titanite based on rocks from the ungava orogen canada implications for u pb geochronology and p t t path determinations on the basis of multiequilibrium metamorphic pressure temperature p t estimates we have determined that 660 700 c is a reasonable minimum estimate of the closure t of pb diffusion in titanite a temperature significantly higher than previously suggested activity corrected reactions that produce titanite define narrow t stability fields 40 c that correspond closely to metamorphic p t determinations derived for coronitic garnet clinopyroxene hornblende samples growth of titanite occurring between 1789 and 1814 ma in the underthrust archean basement of the paleoproterozoic ungava orogen northern quebec is associated with retrograde metamorphism during underthrusting of the archean basement approx 1 b y after formation of the original granulitic assemblages

alteration patterns linked to high grade gold mineralization at the wattle dam deposit western australia abstract sharp physio chemical gradients occur in archean gold systems yet they are often poorly defined these physio chemical gradients can provide windows into fluids that deposit high grade gold mineralization recognizing different alteration styles and fluid types in mineral systems helps define processes that led to the deposition of high grade gold here we report on the architecture and chemical gradients across the komatiite hosted wattle dam gold deposit in the eastern yilgarn craton western australia which is one of australia s highest grade gold deposits the deposit notably contains millimeter to centimeter thick gold only veins with an absence of quartz whole rock geochemistry shows that high grade gold veins are hosted in komatiite flow margins facies with olivine orthocumulate komatiites in the footwall interbedded graphitic shale close to the lode and komatiite basalt in the hangingwall the komatiite flow margin facies that hosts high grade gold veins have been pervasively altered by stage 1 biotite actinolite stage 2 gold veins cross cut the biotite actinolite altered komatiite and these veins contain thin

nature of ore forming fluid and formation conditions of bif hosted gold mineralization in the archean amalia greenstone belt south africa constraints from fluid inclusion and stable isotope studies abstract orogenic gold mineralization in the amalia greenstone belt is hosted by oxide facies banded iron formation bif hydrothermal alteration of the bif layers is characterized by chloritization carbonatization hematization and pyritization and quartz carbonate veins that cut across the layers the alteration mineral assemblages consist of ankerite ferroan dolomite minerals siderite chlorite hematite pyrite and subordinate amounts of arsenopyrite and chalcopyrite information on the physico chemical properties of the ore forming fluids and ambient conditions that promoted gold mineralization at amalia were deduced from sulfur oxygen and carbon isotopic ratios and fluid inclusions from quartz carbonate samples associated with the gold mineralization microthermometric and laser raman analyses indicated that the ore forming fluid was composed of low salinity h 2 o co 2 composition 3 wt nacl equiv the combination of microthermometric data and arsenopyrite pyrite geothermometry suggest that quartz carbonate vein formation gold mineralization and associated alteration of the proximal bif wall rock occurred at temperature pressure conditions of 300 30 c and 2 kbar thermodynamic calculations at 300 c suggest an increase in f o 2 10 32 10 30 bars and corresponding decrease in total sulfur concentration 0 002 0 001 m that overlapped the pyrite hematite magnetite boundary during gold mineralization although hematite in the alteration assemblage indicate oxidizing conditions at the deposit site the calculated low f o 2 values are consistent with previously determined high fe fe mg ratios 0 7 in associated chlorite absence of sulfates and restricted positive 34 s values in associated pyrite based on the fluid composition metal association and physico chemical conditions reported in the current study it is confirmed that gold in the amalia fluid was transported as reduced bisulfide complexes e g au hs 2 at amalia gold deposition was most likely a combined effect of increase in f o 2 corresponding to the magnetite hematite buffer and reduction in total sulfur contents due to sulfide precipitation during progressive fluid rock interaction the epigenetic features coupled with the isotopic compositions of the ore forming fluid 34 s s 1 8 to 2 3 18 o h2o 6 6 to 7 9 and 13 c c 6 0 to 7 7 at 300 330 c are consistent with an externally deep sourced fluid of igneous signature or and prograde metamorphism of mantle derived rocks

chemical mass transfer modelling of ore forming hydrothermal systems current practise and problems abstract chemical mass transfer modelling is a numerical approach to predicting the progress of multicomponent fluid rock reactions in natural hydrothermal systems based on thermodynamic data for minerals and fluid species quantitative simulations of hydrothermal wall rock alteration and ore mineral deposition can be used to develop and test geological models for ore formation which are a basis for mineral exploration and resource assessment in practice the application of thermodynamic mass transfer modelling to specific ore forming systems faces two main problems even for the limiting assumption of local equilibration between fluids and minerals the first problem relates to the geometry of fluid rock interaction where the scheme of the model must be adjusted to the geological question of interest one dimensional reactor models defining reaction progress as a function of integrated fluid flux along a path through a chemically reactive rock do not necessarily provide a more realistic description of chemical mass transfer than simple titration models without temporal and spatial dimension because in most ore depositing systems the fluids are partially channelized by structures like veins or faults the efficiency of metal extraction at the ore deposition site is commonly determined by a sensitive balance between fluid focusing on one hand and wall rock reaction promoting ore mineral precipitation on the other an example of gold and scheelite mineralization associated with mesothermal quartz veins illustrates how ore deposition and alteration zoning parallel to the main fluid flow direction in partially channelized systems can be described by a two dimensional multibox model the second problem relates to the extent and quality of thermodynamic data explicit consideration of fe bearing silicate solid solutions is essential for predicting realistic mass balance in complex fluid silicate sulphide reactions associated with hydrothermal ore formation although a high level of internal consistency of multicomponent data sets has been achieved by simultaneous fitting of multiple thermodynamic and equilibrium measurements significant inconsistencies persist among the most comprehensive data compilations published for the three main groups of species relevant to hydrothermal ore deposits aqueous species in high temperature aqueous brines silicate oxide carbonate minerals including fe mg silicates and sulphur bearing minerals including sulphides and sulphates discrepancies between thermodynamic predictions and observed brine composition and mineral assemblages in the salton sea geothermal system suggest that the redox scale for rock forming silicates may be inconsistent with that of sulphides and aqueous s c o h species this analysis is preliminary but illustrates the importance of field testing of thermodynamic data particularly for hydrothermal conditions between 150 and 450 c which lie between the high temperatures of reliable equilibrium experiments among rock forming minerals 500 c and the low temperatures of many experiments defining the thermodynamics of aqueous species mostly

the stability of a laminated voussoir beam back analysis of a historic roof collapse using dda abstract the stability of a horizontally bedded and vertically jointed roof referred to here as a laminated voussoir beam is studied using careful documentation of a historic roof collapse which occurred in an ancient underground water storage reservoir dated back to ca 1000 b c the roof of the opening failed immediately after the excavation leaving a dome shaped loosened zone with a span of 7 m and height of 2 5 m consisting of horizontal beds and vertical joints with mean spacing of 50 and 25 cm respectively the ancient engineers erected a massive pillar at the center of the dome in order to passively support the failed roof and the opening remained in service for several hundred years following the failure analysis of the roof using iterative voussoir beam procedure beer g and meek j l design curves for roofs and hanging walls in bedded rock based on voussoir beam and plate solutions trans inst min metall 1982 91 a18 22 shows that the roof was more sensitive to failure by shear along the abutments rather than by crushing at hinge zones and that the required friction angle req for stability would have been 36 the available friction angle is estimated between 38 6 and 46 4 and therefore the result of the iterative solution is considered unconservatively wrong results of dda shi g h and goodman r e two dimensional discontinuous deformation analysis int j numer anal methods geomech 1989 13 359 380 shi g h block system modeling by discontinuous deformation analysis computational mechanics publications southampton 1993 pp 209 however indicate that req must have been greater than 60 a shear strength which was not available at the time of construction thus the immediate failure using dda we further demonstrate that req is related to joint spacing or block length in a parabolic function with increasing joint spacing req decreases to a minimum value and than increases with further increase in joint spacing this result is attributed to the interaction of two competing forces one is the stabilizing axial thrust which increases with increasing moment arm in individual blocks a function of joint spacing or block length the other is the destabilizing vertical load which increases with increasing weight of overlying blocks

simulation of cracking near a large underground cavern in a discontinuous rock mass using the expanded distinct element method abstract the rock masses in a construction site of underground cavern are generally not continuous due to the presence of discontinuities such as bedding joints faults and fractures the performance of an underground cavern is principally ruled by the mechanical behaviors of the discontinuities in the vicinity of the cavern a number of experimental and numerical investigations have demonstrated the significant influences of discontinuities on the mechanical thermal and hydraulic behaviors of discontinuous rock masses indicating that the deformation mechanism and stability of rock structures in the discontinuous rock masses depend not only on the existing discontinuities but also on the new cracks generated and thereafter keep propagating due mainly to the stress redistribution induced by excavation in this study an expanded distinct element method edem was developed for simulating the crack generation and propagation due to the shear and tension failures in the matrix rock blocks using this method excavation simulations of deep underground caverns have been carried out on the models with differing depths of cavern and differing geometrical distributions of the existing discontinuities model experiments by using the base friction test apparatus were conducted to verify the proposed numerical approach furthermore the support effects of rock bolts on controlling the deformations of the rock mass surrounding a cavern and movements of key blocks were evaluated by means of the edem approach

iron mobility during synmetamorphic alteration in the selwyn range area nw queensland implications for the origin of ironstone hosted au cu deposits the proterozoic metamorphic rocks of the selwyn range area in western queensland contain a variety of styles of au cu deposit including some e g selwyn mine and osborne prospect that are spatially associated with magnetite rich ironstones the area is characterized by extensive alkali chloride metasomatism that occurred during the later stages of regional metamorphism existing experimental data indicate that hot saline fluids will dissolve and transport iron as they move through temperature pressure gradients in the vicinity of the amphibolite greenschist facies transition and predict that circulation cells will move iron and concentrate it in relatively cool dilute and or oxidized parts of such systems new geological mapping coupled with geochemical data from the amphibolite facies zone of the selwyn range area suggest such processes occurred on a large scale and that large masses of fe were mobilized particularly in association with na metasomatism of biotite bearing metasediments and high fe tholeiitic dolerites field and textural features of ironstones and other fe rich lithologies demonstrate that some of them at least formed by replacement of other rocks during metamorphism and deformation mineralization localized within such iron stones must itself be epigenetic

internal control of fluid compositions in amphibolite facies scapolitic calc silicates mary kathleen australia unaltered metasediments of the mary kathleen fold belt are composed predominantly of layered amphibolite facies scapolitic calc silicate rocks in which minimal infiltration of externally derived fluids occurred during regional metamorphism there were substantial differences in volatile activities between different layers in the layered sequences in particular a co2 a h 2 o inferred from reaction progress estimates and analysis of biotite clinopyroxene fluid phase relations a nacl a h 2 o inferred from scapolite compositions and a hcl a h 2 o inferred from biotite compositions in one outcrop in which a clinopyroxene producing reaction dominated differences in approximate x co 2of up to 0 25 occurred between several samples collected over 50 metres variations in a h 2 o a hcl of up to one order of magnitude are inferred at 1 to 50 m scales from biotite cl contents and variations in nacl contents of scapolite from 0 0 to up to 0 6 cl atoms in the cl co3 so4 site reflect a large variation of a nacl in the coexisting fluid at similar scales most calcsilicate layers internally buffered fluid compositions in the h2o co2 nacl hcl system local occurrences of nacl rich scapolite suggest that some layers may have been in equilibrium with halite during early prograde metamorphism at peak metamorphic temperatures disolution of halite was complete but layers containing high nacl scapolite continued to buffer fluid at high values of a nacl fluid immiscibility does not appear to have affected the progress of the devolatilization reactions although fluid was predominantly internally buffered moderate quantities of fluid were released by prograde mineral reactions in many layers up to 30 cm3 fluid per 100 cm3 rock numerous episodes of fluid escape were required probably via microfractures such that the released fluid did not obviously influence reaction progress in the layers through which it passed the anomaly of beautifully preserved internal buffering signatures and the requirement for produced fluid locally to pass across layers in a deforming rock sequence suggest that the escaping fluid did not leave any readily observable tracks this is explained by rapid rates of fracture propogation and fluid migration therein this internally buffered system contrasts strongly with adjacent calc silicate rocks that show evidence for infiltration of externally derived fluids at high fluid rock ratios and highlights the broad range of fluid behaviour that can be expected in deforming heterogeneous rock sequences

sodic calcic alteration in fe oxide cu au districts an origin via unmixing of magmatic h 2 o co 2 nacl cacl 2 kcl fluids iron oxide cu au deposits particularly those formed in deeper level plutonic environments are commonly characterized by regional scale sodic calcic alteration which typically formed pre or syn cu au mineralization the sodic calcic assemblages include albite scapolite pyroxene actinolite apatite titanite epidote and calcite the consistent presence of coexisting hypersaline aqueous and co2 rich fluids in minerals from sodic calcic alteration and associated fe oxide cu au deposits is the result of unmixing of h2o co2 nacl cacl2 kcl magmatic fluids experimental evidence indicates that the na na k ratio of fluids in equilibrium with two alkali feldspars in co3 2 bearing parent fluids would be significantly higher than in unmixed chloride bearing aqueous fluids therefore fluid unmixing caused by decreases in temperature and or pressure will result in albitization of wall rocks as is observed in most deeper level fe oxide cu au deposits this alteration style may be succeeded by k feldspathization with decreasing temperature because of the increase in equilibrium na na k in chloride bearing fluids buffered by alkali feldspars

gilt by association origins of pyritic gold ores in the victory mesothermal gold deposit western australia sulfur isotope data and calculated fluid rock reaction paths constrain the origin of pyritic gold ores in the victory mesothermal gold deposit of western australia pyrite 34s values range from 4 4 to 5 1 and are negatively correlated with gold tenor in mafic host rocks indicating a significant increase in fluid oxidation state accompanied mineralization geologic evidence argues strongly that mineralization occurred with wall rock sulfidation but this process alone cannot produce the degree of fluid oxidation necessary to explain the sulfur isotope range in contrast either carbonation of ferric iron bearing minerals or separation of immiscible fluid phases both of which are consistent with the available geologic data can drive fluid oxidation to the point of aqueous sulfate dominance coupled decreases in gold solubility and sulfide sulfur isotope values that are predicted by such a scenario provide an explanation for the trend between 34s and gold tenor observed at victory because both wall rock carbonation and fluid phase separation involve loss of aqueous sulfide but do not require precipitation of iron sulfides these processes may explain the poor correlation between gold tenor and pyrite abundance in many mesothermal deposits and the occurrence of some gold ores in iron poor rocks

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

transport of stable isotopes kinetics dispersive advection and the isotopic fronts of baumgartner and rumble 1988 baumgartner and rumble 1988 apply a kinetic continuum theory for stable isotope transport to unidimensional infiltration of fluid into rock their numerical applications are restricted to the simplified case of rapid isotope exchange between phases where the sharp isotope fronts of pure advection are distended by dispersive mechanisms only however kinetic limitations of isotope exchange are potentially an equally important distending mechanism and it will only rarely be possible to ascribe front gradients to diffusion dispersion alone abrupt isotopic changes at vein boundaries are more often a secondary signal of lithologic change than the expression of a retarded advective front at such boundaries diffusion and dispersion play a role that is comparable to or greater than that of advection so that the detailed shapes of isotope fronts depend upon boundary conditions for the infiltration process zerodimensional box models have legitimate if limited uses in the modelling of fluid rock interaction and are reexamined

residual strength of clays in landslides folded strata and the laboratory the post peak drop in drained shear strength of an overconsolidated clay may be considered as taking place in two stages first at relatively small displacements the strength decreases to the fully softened or critical state value owing to an increase in water content dilatancy second after much larger displacements the strength falls to the residual value owing to reorientation of platy clay minerals parallel to the direction of shearing if the clay fraction is less than about 25 the second stage scarcely comes into operation the clay behaves much like a sand or silt with angles of residual shearing resistance typically greater than 20 degrees conversely when the clay fraction is about 50 residual strength is controlled almost entirely by sliding friction of the clay minerals and further increase in clay fraction has little effect the angles of residual shearing resistance of the three most commonly occurring clay minerals are approximately 15 degrees for kaolinite 10 degrees for illite or clay mica and 5 degrees for montmorillonite when the clay fraction lies between 25 and 50 there is a transitional type of behaviour residual strength being dependent on the percentage of clay particles as well as on their nature the post peak drop in strength of a normally consolidated clay is due only to particle reorientation measurements of strength on natural shear surfaces agree within practical limits of variation with values derived from back analysis of reactivated landslides this field residual strength can be recovered by multiple reversal shear box tests on cut plane samples but in high clay fraction materials it is typically somewhat higher than the strength measured in ring shear tests residual strength is little affected by variation in the slow rates of displacement encountered in reactivated landslides and in the usual laboratory tests but at rates faster than about 100 mm min qualitative changes take place in the pattern of behaviour a substantial gain in strength is followed with increasing displacement by a fall to a minimum value in clays and low clay fraction silts this minimum is not less than the slow or static residual but in clayey silts with clay fractions around 15 25 according to tests currently in progress the minimum can be as low as one half of the static value author trrl

can economic porphyry copper mineralization be generated by a typical calc alkaline melt numerical simulation of chlorine and copper partitioning between a crystallizing melt and exsolving aqueous fluids indicates that typical calc alkaline magmas contain sufficient copper chlorine and water to produce economic porphyry copper mineralization neither an elevated copper content in the magma nor an additional large volume of magma are required to provide metals or volatiles the most important variables that determine the volume of melt necessary to produce sufficient copper are the degree of compatible behavior displayed by copper the ratio of initial water in the melt to the water saturation level and the initial chlorine water ratio of the melt the absolute values for initial water in the melt and water content at saturation are relatively unimportant in determining the required melt volume the bulk salinity of the exsolved fluid may vary from 2 0 wt nacl to saturation levels 84 wt nacl at 700 c indicating that boiling is not necessary to produce high salinity brines at appropriate p t xnacl conditions the magmatic aqueous fluid separates into a saline liquid which transports most of the copper and a low salinity vapor the salinities of the two immiscible phases are governed by the p t conditions while the bulk fluid salinity determines the mass fractions of liquid and vapor formed pressure quenching causes rapid crystallization of the aplitic groundmass in porphyritic rocks associated with copper mineralization and significantly reduces the amount of chlorine and copper partitioning to the aqueous fluid this results in abrupt and possibly large reductions in fluid salinity and causes copper to become concentrated in the melt as copper is transported from the melt by the earliest exsolving fluids in deep 2 0 kbar systems and by late exsolving fluids in shallow 0 5 kbar systems the relative timing of pressure quenching aplite formation and fluid transport of copper from the melt can vary significantly in systems produced under different confining pressures model results incorporating petrologic constraints determined for yerington nevada are in good agreement with observed mineralization