late archaean synorogenic basins of the eastern goldfields superterrane yilgarn craton western australia part ii kurnalpi terrane abstract the penny dam belches yilgangi white hills granny royal lucky brock and wallaby supersequences of the kurnalpi terrane crop out in synclines that are the erosional remnants of basins that developed as linear zones of subsidence between approximately north trending compartment bounding faults dominant sedimentary facies range from gravel rich and sand rich concentrated density flow deposits to thickly and thinly bedded bouma type turbidites background deposits are black shales or laminated green mudstones and banded iron formation is preserved in some condensed sections periods of non deposition are recorded by bedded chert which is the product of early diagenetic sea floor silicification the basins were separate deep marine canyon to linear fan systems that were linked laterally and distally by mud rich deposits there is only minor evidence for fault anchored canyon margin slope aprons basin development occurred during two stages separated by a period of deformation uplift and erosion sparse palaeocurrents establish sediment dispersal was to the south or southeast indicating that uplift to the north or northwest controlled palaeoslopes stacking of lithofacies is aggradational and consistent with deposition in fault bound basins tectonostratigraphic equivalence with siliciclastic supersequences of the kalgoorlie and gindalbie terranes is established by common depositional systems stratigraphic styles and stratigraphic responses to tectonic forcing consequently the siliciclastic supersequences represent overlap or late stage basins that tied together arc related terranes following terrane amalgamation similar depositional facies aggradational styles of facies stacking and two stage development characterise the syncollisional plio pleistocene coastal range basin of taiwan modern analogues are the deep marine southern longitudinal and taitung troughs off southeastern taiwan that are being filled by synorogenic sediments derived from the taiwan orogen

results of la icp ms sulfide mapping from algoma type bif gold systems with implications for the nature of mineralizing fluids metal sources and deposit models quantitative laser ablation inductively coupled plasma mass spectrometry la icp ms element distribution maps combined with traverse mode analyses have been acquired on various sulfides pyrite pyrrhotite arsenopyrite from three canadian algoma type bif hosted gold deposits 4 moz au meadowbank 2 8 moz au meliadine district 6 moz au musselwhite these data in conjunction with detailed petrographic and sem eds observations provide insight into the nature and relative timing of gold events the presence and implication of trace element zoning regarding crystallization processes and elemental associations that fingerprint gold events furthermore the use of an innovative method of processing the la icp ms data in map and traverse modes whereby the results are fragmented into time slice data to generate various binary plots ag versus ni provides a means to identify elemental associations te bi not otherwise apparent this integrated means of treating geochemical data along with petrography allows multiple gold events and remobilization processes to be recognized and their elemental associations determined the main gold event in each of these deposits is characterized by the coupling of an as se te ag element association coincident with intense stratabound sulfide replacement of the fe rich host rock additionally the data indicate presence of a later remobilization event which upgraded the au tenor as either non refractory or refractory type along fracture networks due to the ingress of subsequent base metal bearing metamorphic fluids mainly a pb bi association furthermore the data reveal a stratigraphic influence as reflected in the elemental associations and the elemental enrichments observed and the nature of the sulfide phase hosting the gold mineralization arsenopyrite versus pyrite

on the effective thermal and hydraulic conductivity of binary heterogeneous sediments abstract heterogeneity is present in geological sedimentary structures at all scales from pore to basin and its distribution has an impact on transport processes such as heat and fluid flow the rock masses at any scale need to be characterized by their effective properties at that scale based on the individual characteristics of the heterogeneous porous medium the effective thermal and hydraulic conductivity of sediments characterized by a stochastic distribution of heterogeneity is studied using an inverse approach based on numerical experiments the simulations covering a large range of conductivity contrasts are carried out for actual core scale cases of shale clasts in a sand matrix and on a diagrammatic cross section through a clastic sedimentary group at the basin scale the effective conductivity depends primarily on the heterogeneity fraction and on the conductivity contrast between heterogeneities and the embedding matrix a dependency which can be described by a generalized weighted mean model this model is better suited to estimate the effective conductivity at any scale than other models like the self consistent or any of the arithmetic geometric or harmonic averages the effective conductivity has an anisotropic character although the individual components are homogeneous and isotropic the variation in effective conductivity is significant even for small conductivity contrasts like in heat flow processes and exhibits an asymptotic behaviour for large conductivity contrasts characteristic of fluid flow processes the effective conductivity has a second order dependence on such heterogeneity characteristics as shape aspect ratio orientation and distribution depending on these characteristics the bounds of effective conductivity values can be narrowed further from the extreme bounds expressed by the arithmetic and harmonic averages

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

late archaean deep marine volcaniclastic sedimentation in an arc related basin the kalgoorlie sequence of the eastern goldfields superterrane yilgarn craton western australia abstract the kalgoorlie sequence 2658 ma is a 3000 m thick succession of volcaniclastic sedimentary rocks and subordinate rhyolite dacite andesite and basalt spatially and temporally associated with subvolcanic sills and dykes of rhyolite and dacite gabbro sills and i type granitoids although basalts are tholeiitic the felsic rocks have ttd affinity the sequence comprises mostly deep marine channel levee turbidite complexes and hemipelagites resedimented syneruptive volcaniclastic deposits are associated with coherent lavas but almost all of the sedimentary fill was recycled from prior cycle volcanic and volcaniclastic sources provenance was mainly dacitic rhyolitic with minor andesitic basaltic and polymictic compositions volcano bound and fault bound architectures and two styles of basin filling are identified progradational or aggradational transverse fans and slope aprons and retrogradational longitudinal fans of a linear trough retrogradation in longitudinal systems is consistent with basin lengthening and deepening six depositional sequences are grouped in four unconformity bounded tectonic stages that record uplift subsidence cycles coeval mafic and felsic magmatism indicate that the tectonic stages represent extensional tectonic settings whereas volcanogenic provenance spatially linked volcanism and plutonic magmatism and deep marine environments support an intra arc site cyclic uplift subsidence and basin lengthening are more consistent with strike slip controls on basin formation than with orthogonal extension the tectonic setting is interpreted to have been a pull apart basin associated with strike slip faulting and amalgamating arc related terranes similar to the modern philippines archipelago the strong similarity between archaean volcaniclastic and modern arc related volcaniclastic environments implies comparable tectonic settings and therefore comparable controlling tectonic factors

experiment on estimating thermal conductivity of sedimentary rocks from oil well logging geologic note oil well are an important source of geothermal data for studying regional tectonics reconstructing the evolution of sedimentary basins and theorizing petroleum generation migration and accumulation a more satisfactory less laborious method of estimating the thermal conductivity of sedimentary rocks is badly needed the thermal conductivity of cores from two gas wells in france was measured and correlated with neutron porosity index sonic interval travel time bulk density and gamma ray logs to obtain reasonable predictions of conductivity data were segregated into lithologic groups such as sand shale carbonate shale and carbonate sand a set of regression coefficients in the equation that predicts the conductivity from the logs was calculated for each group t e correlation coefficients between the measured and predicted conductivities of the core samples were 0 81 0 75 and 0 61 respectively for the three lithologic groups the average percent difference between the measured and the calculated conductivities for the lithologies likely to be encountered in practice is 13 4 we expect this figure can be reduced to 10 by enlarging the data base for calculating the regression coefficients in the same basin or oil field the relative errors from well to well probably will be 6 or smaller because the lithology will be nearly homogeneous

geochemical characteristics of gold bearing boninites and banded iron formations from shimoga greenstone belt india implications for gold genesis and hydrothermal processes in diverse tectonic settings abstract this paper is the first documentation of boninites from the kudrekonda formation of shimoga greenstone belt sgb in western dharwar craton wdc india and the occurrence of native gold in the associated quartz veins we also investigate the gold mineralization hosted in the banded iron formations bifs of ganajur karajgi and palavanahalli areas of the sbg the kudrekonda metavolcanic rocks are composed of clinopyroxene orthopyroxene and plagioclase with secondary amphibole the geochemical attributes of these rocks based on mgo tio 2 ni cr and co contents al 2 o 3 tio 2 gd yb n and la sm n ratios classify them as boninites and their relative lile hfse abundance suggests magma generation in an intraoceanic arc setting the gd yb and dy yb ratios suggest parent magma origin through partial melting of a spinel lherzolite mantle source geochemical signatures of the boninites suggest high temperature shallow level melting of refractory mantle wedge metasomatized by fluids derived through dehydration of oceanic slab during subduction initiation quartz veins present in the kudrekonda boninites contain gold grains showing affinity towards quartz carbonate vein type greenstone hosted occurrences epma data record 88 5 90 3 wt au content with 7 7 8 4 wt fe 0 05 2 1 wt s and negligible ag the au is hosted in fe oxides bulk chemical analyses show 4 1 684 4 ppb au and 139 4 2186 4 ppb ag in the studied samples the gold mineralization of kudrekonda boninites is syngenetic mesothermal convergent margin orogenic type decarbonation desulphidization and metamorphism of subducted oceanic lithosphere and devolatilization of metasomatized enriched mantle wedge in intraoceanic arc setting are the viable processes that contributed to gold genesis in the kudrekonda boninites devolatilization during prograde metamorphism hydrothermal fluid generation syntectonic gold remobilization and migration of gold enriched fluids through shear zones account for au transportation and precipitation in quartz veins emplaced within the boninites the bifs of ganajur karajgi and palavanahalli areas of shimoga greenstone belt dominantly comprise alternating si rich layers of quartz and fe rich hematite and magnetite layers geochemical characteristics of the bif samples including their depleted ree positive eu anomalies negative to negligible ce anomalies and superchondritic y ho ratios suggest that the bifs were i derived by chemical sedimentation from paleo ocean enriched in dissolved iron and silica with marked contributions from hydrothermal fluids of volcanic origin and ii deposited in an off shelf marine environment proximal to a mid oceanic spreading centre where hydrothermal activity induced release of eu and y enriched hydrothermal solutions under low oxygen fugacity conditions native gold occurs in banded strata bound disseminated sulphide lenses compositionally characterized as pyrite arsenopyrite chalcopyrite and galena mineral chemical analyses reveal 73 100 au content with variable concentrations of ag 0 02 15 2 wt geochemical compositions of bifs are characterized by pronounced enrichment in au 706 15 831 ppb and ag 630 2435 ppb gold mineralization in shimoga bifs is epigenetic epithermal type akin to homestake type iron formation hosted vein and disseminated lode gold deposit gold genesis in these bifs is attributed to migration of oxygen depleted reducing sulphidic auriferous fluids of hydrothermal origin to the site of bif deposition that served as chemical traps for the auriferous fluids the kudrekonda boninites represent accretion and preservation of a slice of older oceanic crust onto a relatively younger active continental margin through arc continent collision during neoarchean time

detrital zircon age spectra for late archaean synorogenic basins of the eastern goldfields superterrane western australia abstract the kalgoorlie gindalbie kurnalpi duketon and burtville terranes were amalgamated by 2658 ma into the eastern goldfields superterrane which was later accreted cordilleran style onto the foreland of a pre existing continent late stage synorogenic basins developed within the eastern goldfields superterrane during the early stage of accretion the basins are similar to all late stage basins of archaean provinces developing late in the tectonic cycle in a strike slip regime they developed in two stages during the gap in granite emplacement between 2658 ma and 2648 ma basin analysis suggests that the bulk of sediments was derived from rocks readily identifiable today within the superterrane consistent with the provenance style of all late stage basins sediment derivation from the foreland occurred only during stage ii and is recorded only from basins proximal to the suture detrital zircon geochronology has corroborated those interpretations eleven new shrimp u pb detrital zircon datasets and 14 previously published datasets indicate that the bulk of zircon bearing sediment was derived from the 2715 ma to 2658 ma high ca ttg granites and volcanic rocks that define the terranes moreover primary modes in the detrital zircon age spectra of 2680 3 ma 2673 ma 2666 3 ma and 2660 3 ma coincide with the peaks of emplacement of high ca granites provenance from across the suture has also been corroborated with detrital zircon age spectra of the kurrawang basin a stage ii basin close to the suture having no match to rocks of the eastern goldfields superterrane defining modes of 2730 ma and 3000 ma some as old as 3750 ma and 3540 ma can be matched to an 2735 ma calc alkaline volcanic province and quartzites with 4350 3130 ma detrital zircon in the foreland the study shows that detrital zircon age spectra can be powerful supporters of tectonic analysis but for the study presented here their interpretation has been greatly assisted by prior basin analysis and a considerable geochronological database of source rock equivalents

laser microprobe sulphur isotope analysis of arsenopyrite experimental calibration and application to the boliden au cu as massive sulphide deposit abstract metamorphic remobilization of arsenopyrite rich ores is a globally important process which can lead to significant concentrations of gold in order to understand this and related processes relations of sulphur isotopes can give a number of important clues to resolve such relations in detail we have successfully calibrated and applied a laser combustion system for in situ analysis of sulphur isotopic compositions of arsenopyrite experimental calibration of the laser fractionation factor 0 4 was obtained by using compositionally and isotopically homogeneous natural samples from ore deposits at boliden sweden and freiberg germany subsequent to detailed microscopic study the s isotope ratios of these samples were measured by conventional and laser combustion techniques the present application to different types of arsenopyrite in the palaeoproterozoic metamorphosed vhms ores of the boliden au cu as deposit skellefte district northern sweden shows that the sulphur isotope composition of arsenopyrite is essentially unmodified during medium grade metamorphic recrystallization and remobilization here massive arsenopyrite ore is crosscut by later veins that carry a complex quartz sulphosalt sulphide assemblage the latter ore type is markedly au rich compared to the host ore and thus of significant economic interest we find that both ore types exhibit very similar sulphur isotope compositions ca 2 to 3 v cdt which is similar to most massive sulphide deposits in the skellefte district thus the crosscutting au rich vein ore has inherited the sulphur isotope composition from sulphur liberated by metamorphic reactions affecting the massive ore and most likely also inherited the au through this mechanism the latter finding clearly has important implications both for the general discussion on and the prospecting for similar high grade au ores in this world class mining region

estimating thermal conductivity in sedimentary basins using lithologic data and geophysical well logs a method for estimating in situ thermal conductivity profiles in oil and gas wells is advanced to rectify a major shortcoming in thermal analyses of sedimentary basins thermal conductivity estimates are made in a two stage procedure and are based on a model for the conductivity of mixtures and input data from lithological and geophysical logs first rock matrix conductivity for an arbitrary depth interval i e drill cuttings sample interval which is about 3 m is determined from the laboratory calibrated conductivities and volumetric representation of its individual lithologic components using a geometric mean model in situ conductivity is then estimated by a second application of the model correcting for temperature and porosity determined from geophysical logs the method is illustrated for three uinta basin utah wells that penetrate a series of tertiary sandstones shales and muddy carbonates detailed lithologic descriptions together with sonic and neutron logs were digitized and used for estimating in situ conductivity the validity of the method was tested by comparing the prediction against laboratory measurements on 565 samples from the same wells rock matrix thermal conductivity ranges from 1 6 to 6 8 w m k and is predicted within 20 of the actual measurement for 90 of the samples both in situ conductivity values and variations for a given lithologic unit are reduced at increased porosity and increased temperature thermal conductivity nomograms are presented as useful tools to predict directly the in situ thermal conductivit of a formation from a well log signal

thermal conductivity and well logs a case study in the paris basin summary the estimation of thermal conductivity from well logs is of great importance for all studies on thermal evolution of sedimentary basins the approach proposed here is to first interpret the well logs in terms of mineralogic composition and porosity and then to estimate the in silu conductivity from a mixing formula the geometric average of individual conductivities weighted by the volumetric proportion of each component the validity of the model has been widely verified by laboratory measurements on isotropic samples however there is a need for validation of such an approach for in situ conditions temperature data recorded at equilibrium in two wells of the paris basin offer a unique possibility of testing this approach in the case of a steady state conductive thermal rcgime fourier s law the conductivity must be proportional to the inverse of the temperature gradient the well logs are quantitatively interpreted in terms of mineralogic composition porosity and then thermal conductivity using a conductivity law calibrated on cuttings and cores laboratory measurements for three examples of well sections the computed thermal conductivity compares reasonably well with the inverse of the gradient for each of the three examples it is possible to define a depth range where the apparent heat flow is almost constant with depth and where the conductive regime seems to prevail this allows a refinement of the conductivity model with emphasis on the contribution of clays assuming that the conductivities of non clay end terms are known it is possible to obtain the conductivity of clay giving the best fit to the temperature measurements in the three cases the conductivity of clay 1 21 4 w m k is found to be lower than the assumed one 1 8 w m k i which probably indicates an anisotropy effect finally an empirical model where the bulk conductivity is expressed directly as a function of well logs is tested in one case the results obtained are quite compatible with the previous one but in the other two sections the stability and the physical meaning of this model are found to be questionable this could be due to the lack of constraints in the underlying implicit mineralogy model

a biogeochemical influence on the secular distribution of orogenic gold orogenic gold deposits are unevenly distributed in geologic time the richest period of orogenic gold deposit formation was the phanerozoic which followed a 1 b y period of relatively meager deposit generation during the proterozoic this proterozoic low gold period developed despite continent building episodes which should have been appropriate for orogenic gold genesis here a brief review of the changes in global geochemistry brought on by evolving interactions between plate tectonics and the biosphere is conducted before the consequences for gold uptake into sedimentary pyrite are discussed it is suggested that the extensive oxygenation of the deep oceans during the second great oxidation event over the period 635 to 510 ma produced conditions where gold was soluble in the deep oceans from that point on regions where bacterial sulfate reduction drove formation of sedimentary pyrite also destabilized this soluble gold promoting its uptake into pyrite and allowing formation of metallogenically enhanced sedimentary sequences these sediments would have become ideal source rocks for gold deposits during subsequent collisional tectonics and metamorphism this biogenic influence on source region enhancement may explain the association during the phanerozoic eon between some of the world s most gold productive regions and sedimentary sequences that contain pyritic carbonaceous rocks

potential salinity driven free convection in a shale rich sedimentary basin example from the gulf of mexico basin in south texas we investigate the plausibility of salinity driven free thermohaline convection in sedimentary rocks of the south texas part of the gulf of mexico basin using salinity data rayleigh number calculations and numerical models previous studies speculated that free convection could account for high fluxes evidently required for diagenesis in the basin but low permeability shales are calculated to be a barrier to free convection in the study area salinity inversions occur either above or within the transition zone from hydropressures to overpressures the positioning of brines over less saline fluids provides a significant buoyancy force rayleigh number calculations and numerical simulations suggest that homogeneous shaly systems are unstable near the high end of the expected ranges of shale permeability 10 15 10 16 m2 numerical simulations show that the influx of brine into the permeable layers and permeability heterogeneity in the shales are both conducive to free convection simulations indicate that salinity driven free convection can occur at lower permeabilities 10 16 10 18 m2 that may approximate the permeabilities of shales in the zone of extreme overpressures over geologic time simple rayleigh numbers are inadequate to predict the occurrence of free convection in heterogeneous systems salinity driven free convection at depths in some large sedimentary basins such as the gulf of mexico may be more common than expected

characteristics of heat flow through diapiric salt structures on the texas continental slope abstract we characterize heat flux through two diapiric salt features in deep 1080 m water on the texas continental slope sediment stratigraphy and salt top morphology delineated by a previous single channel seismic reflection survey beckley and behrens this volume provide inferences on the two salt structures one is a cylindrical stock about 5 km in diameter and the other is a sub circular salt tongue about 10 km in diameter 74 heat flow measurements show large scaled positive anomalies factor of two to three relative to the values off salt of 32 mw m2 over the two features variation of the heat flow coincides with the thickness variation of the salt that is inferred from the seismic records we believe that these anomalies mainly reflect the high thermal conductivity of the salt and give major constraints on geometry of the salt bodies our three dimensional steady state thermal model provides estimates on the feeder depths of the two salt features analyses are also made on the secondary thermal effects such as 1 differential sedimentation 2 salt movement and 3 unknown fluid migration 1 and 2 based on the seismic stratigraphy suggest that these effects alone can produce a significant positive anomaly probably 20 and should be reflected in thermal modeling the episodic nature of 3 does not seem to produce persistent large scaled thermal anomalies

age constraints on recycled crustal and supracrustal sources of archaean metasedimentary sequences eastern goldfields province western australia evidence from shrimp zircon dating abstract shrimp u pb zircon dating of sedimentary volcanic and subvolcanic intrusive rocks from unconformity bounded sequences in the eastern goldfields province defines maximum depositional ages for those sequences the kambalda sequence which records a backarc basin was deposited prior to 2700 ma and from at least 2715 ma the spargoville sequence which records an arc adjacent volcano bound basin was deposited between 2700 and 2683 ma the kalgoorlie sequence which records an intra arc rift basin comprises two tectonic stages with depositional ages of 2681 2670 and 2661 2655 ma deposition of the spargoville and kalgoorlie sequences overlapped with the intrusion of granitoids and subvolcanic porphyries thereby indicating that those granitoids were emplaced during crustal extension younger submarine fan kurrawang sequence and braided fluvial merougil and jones creek sequences deposits of a remnant ocean basin were deposited at when coupled to palaeocurrent data provenance dating of detrital zircon suites fingerprints southeast oriented amalgamation of felsic detritus from multiple sources within longitudinal depositional systems and longitudinal reworking of felsic detritus from single sourced transverse systems most felsic detritus was recycled from coeval volcanoplutonic arcs and the orogen to the remnant ocean basin sequences with zircon ages ranging from 2730 to 2660 ma older felsic sources with age ranges of 3570 3130 3030 2900 2870 2770 and 2760 ma could have been structural enclaves within the volcanoplutonic arcs or orogen but were more likely within a distant cratonic basement when coupled with stratigraphic data it is concluded that detrital zircon age distributions preserve evidence for the sedimentary recycling of coeval volcanoplutonic arc or orogenic sources uplifted basin floor and dissected arc successions and cratonic basement virtually all source terrains have apparently vanished presumably through the combination of tectonic and sedimentary recycling and tectonic severance increased use of detrital zircon suites from archaean sedimentary sequences is advocated in order to quantify the balance between sedimentary recycling of felsic rocks from contemporaneous volcanoplutonic sources which themselves document crustal growth in arc environments and from relict volcanoplutonic and crustal basement sources which document the degree of crustal recycling

la icpms and epma studies of pyrite arsenopyrite and loellingite from the bhukia jagpura gold prospect southern rajasthan india implications for ore genesis and gold remobilization abstract the bhukia jagpura gold prospect is hosted by a paleoproterozoic metasedimentary rock sequence that constitutes the lowermost part of the aravalli supergroup lying in close proximity to the basement cover contact a combined ore petrographic la icpms and epma studies of iron sulfides and sulfarsenides from the prospect has revealed four varieties of pyrite and two varieties of arsenopyrite with different trace element compositions the data indicates a sedimentary diagenetic origin for the earliest pyrites py i and ii which are devoid of any gold in contrast to hydrothermal py iii and iv with a minor but significant content of invisible gold 0 3 1 6 ppm associated loellingite 35 51 ppm and arsenopyrite aspy i 0 28 10 ppm contain the maximum concentration of invisible gold while it is substantially lower in aspy ii 0 06 1 5 ppm the compositions of the gold bearing pyrites low ni co ratios arsenopyrites and loellingite rich in co and the presence of au bi te mineral phases within arsenopyrite support a magmatic hydrothermal model for the origin of gold sulfide mineralization which appears to have taken place during the peak of regional metamorphism or at an earlier stage the different stages of deformation and metamorphism released and remobilized gold in invisible and discrete forms from the sulfarsenides during prograde metamorphism of aspy i gold was partially incorporated and relatively enriched within the structure of loellingite later during retrograde metamorphism gold was exsolved as visible grains at the interface of loellingite and aspy ii and or within loellingite

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

dam induced and natural channel changes in the saskatchewan river below the e b campbell dam canada abstract the e b campbell dam on the saskatchewan river east central saskatchewan was constructed in 1962 forming tobin lake 2 2 billion m3 capacity which today impounds most fluvial sediment and disrupts normal outflow patterns thirty five kilometers below the dam the river diverts into a 500 km2 belt of alluvial sediment initiated by an avulsion 140 years ago rejoining the parent channel 108 km from the dam effects of the dam on channel geomorphology including the historical channel reach i and the more recent avulsion affected channels were investigated by pre and post dam cross section surveys combined with grain size and bedload measurements twenty three sites were surveyed at least twice and 14 were resurveyed annually in 2003 2014 except 2007 during which significant floods occurred in 2005 2011 and 2013 all channel cross sections up to 81 km below the dam have coarsened and enlarged since closure resulting in excavation of 35 4 106 m3 of channel perimeter sediment since 1962 the most proximal segment is armored and has changed little in recent years since 2003 channel enlargement has been greatest in the 35 81 km segment between the avulsion site and the forks reaches ii iii manifested as widening and deepening enlargement rates were greatest during the three floods and the paucity of bedload has prevented degraded portions of the channel bed from replenishment following flooding budget calculations based on bedload measurements and channel cross section areas suggest that 30 years would be required to replace the sediment removed between 2003 and 2014 assuming all available bedload remains in the affected reach dam effects appear to be absent or uncertain beyond 81 km a multichanneled region of varied stages of activity reach iv recombining and eventually rejoining the parent saskatchewan river channel at km 108 reach v sediment evacuated from reaches i iii is sufficient to sustain modest aggradation in some distal portions of the avulsion belt including the mossy delta but little bedload is returned to the parent channel dam induced sediment starvation is speeding the rate at which a single dominant channel is evolving between the avulsion site and rejoined parent a process that will likely shift the patterns of flood inundation in the future

delta allometry growth laws for river deltas 1 under projected scenarios of sea level rise subsidence and sediment starvation many deltas around the world are expected to drown delta growth dynamics which determine the ability of a delta to adapt to these changes are poorly understood due to the difficulty of measuring change in slowly evolving landscapes we use time series imagery of experimental numerical and field scale deltas to derive four laws that govern the growth of river dominated deltas land area grows at a constant rate in the absence of relative sea level change while wetted area keeps pace maintaining a constant wetted fraction over the delta surface scaling of edge lengths versus areas suggests delta shorelines are nonfractal even though the channel network is fractal consequently channel edge length which provides critical habitat grows more rapidly than delta area these laws provide a blueprint for delta growth that will aid in delta restoration and help predict how existing deltas will evolve

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

unraveling the western churchill province paleoproterozoic gold metallotect constraints from re os arsenopyrite and u pb xenotime geochronology and la icp ms arsenopyrite trace element chemistry at the bif hosted meliadine gold district nunavut canada the gold endowment of the western churchill province is conventionally attributed to reworking and attendant metamorphism during the trans hudson orogeny 1 9 1 8 ga the meliadine gold district is regarded as a type example of this inferred paleoproterozoic gold metallotect and also represents one of canada s largest emerging orogenic greenstone and banded iron formation bif hosted gold districts 2 8 moz contained au in reserves and total resource of 5 8 moz au the largest gold deposits are cospatial with the pyke fault and associated quartz ankerite veining which cuts neoarchean ca 2 66 ga plutonic and supracrustal rocks comprising the rankin inlet greenstone belt meliadine gold occurs as inclusions within idioblastic arsenopyrite crystals at sulfide crystal boundaries and or as sulfide fracture fills in hydrothermally altered sulfidized and veined bif clusters of gold bi mo telluride chalcopyrite and galena inclusions characterize high grade ore zones and are spatially associated with sieve textured arsenopyrite domains these microtextural relationships suggest that incipient sulfide recrystallization liberated gold which along with other precious and base metals was redistributed during late fluid assisted and deformation metamorphic driven remobilization late precious and base metal enrichment is also demonstrated by in situ laser ablation inductively coupled plasma mass spectrometry la icp ms arsenopyrite mapping hydrothermal xenotime crystals occur with gold in low strain microtextural sites and yield u pb ages at ca 1 86 ga suggesting that remobilization was concomitant with trans hudson orogenesis new re os arsenopyrite model ages range from 2 3 to 1 8 ga and document a hitherto unrecognized pre 1 86 ga hydrothermal activity the range of re os model ages tends to support partial open system behavior and or mixing of disparate arsenopyrite generations that are evident from microtextural observations and in situ la icp ms element mapping replicate analyses of the two most rhenium rich arsenopyrite samples yield reproducible re os model ages at ca 2 27 and 1 90 ga these rhenium rich samples are also gold poor and likely yield ages that predate gold remobilization and subsequent enrichment along arsenopyrite crystal boundaries and fractures we suggest that pre 1 86 ga hydrothermal activity was likely critical to the gold endowment of the district but is obscured by reworking during the later stages of the trans hudson orogeny at 1 86 ga if correct these new ages imply that the paleoproterozoic gold metallotect which is recorded across the western churchill province in fact comprises multiple temporally distinct gold events differentiating between disparate paleoproterozoic gold events represents a critical step for effective mineral exploration in the western churchill province and at other reworked archean terranes

alteration paragenesis and the timing of mineralised quartz veins at the world class geita hill gold deposit geita greenstone belt tanzania abstract the world class geita hill deposit is one of the largest gold deposits located within the geita greenstone belt in nw tanzania the deposit is hosted within a complexly deformed sedimentary package dominated by ironstone and intruded by diorite dykes the gold mineralisation is spatially associated with the geita hill shear zone which is a ne trending moderately nw dipping deformation zone consisting of a network of discontinuous shear fractures that record early thrusting overprinted by later strike slip and normal events the regional metamorphic assemblage in the meta sediments is characterised by biotite chlorite actinolite k feldspar magnetite pyrrhotite pyrite indicating upper greenschist facies conditions the gold related alteration overprints the regional metamorphic assemblage and is characterised by silicification and sulfidation fronts that generally extend out from the mineralised zone by no more than one meter the alteration assemblage includes sub vertical mineralised quartz veins that trend approximately e w the mineralised quartz veins are accompanied by alteration halos of quartz biotite k feldspar pyrite which overprints the peak metamorphic assemblage gold is closely associated with secondary pyrite and occurs as free gold and gold tellurides sylvanite calaverite and nagyagite it occurs mainly as inclusions in pyrite and as invisible gold in pyrite but also as gold inclusions in biotite and along quartz grain boundaries two distinct textural styles of auriferous pyrite can be distinguished inclusion rich subhedral pyrite hosting invisible gold and inclusion free euhedral pyrite hosting visible gold grains it is common for the inclusions rich pyrite to have thick rims of inclusion free pyrite the mineralising alteration is overprinted by barren multiphase quartz carbonate and carbonate chlorite veins this alteration is characterised by the assemblage calcite siderite chlorite quartz pyrite barite palaeostress analysis of mineralised shear fractures along the geita hill shear zone are indicative of sigma 1 being vertical and sigma 3 trending n s indicating n s extension which is consistent with the orientation of the mineralised quartz veins

a new source of isotopically heavy sulphur in lode gold deposits of nw spain a batch volatilization process in the conversion of pyrite to pyrrhotite by contact metamorphism the conversion of pyrite to pyrrhotite is identified in this study as a new source of isotopically heavy sulphur in thermal domes contact metamorphism of a sequence of pyrite rich shales by the penedela blind intrusion nw spain causes the conversion of diagenetic pyrite to pyrrhotite at a temperature of 150 c this process occurred in a closed system with total consumption of the diagenetic pyrite and production of h2s rich fluids the h2s liberated in this unidirectional reaction shows a relatively heavy 34s in agreement with a batch volatilization process the mixture of this h2s rich fluids with derived sulphur from lower cambrian carbonates produced gold bearing pyrite at a temperature of 340 c the contribution from these two different sulphur sources was 86 and 14 respectively the metamorphic fluids migrated through permeable zones such as fractures and shear zones producing a lode gold deposit

craton scale distribution of archean greenstone gold deposits predictive capacity of the metamorphic model genetic models should not only attempt to explain features of archean gold mineralization on the scale of mines or districts but should also explain its marked spatial and temporal heterogeneity in greenstone belts the application of genetic models developed with such a philosophy can have predictive capacity in gold exploration the metamorphic model one of a number of current genetic models for archean gold deposits involves generation of auriferous h 2 o co 2 fluids by devolatilization of the stratigraphically lowermost greenstones during metamorphism and broadly synchronous synkinematic granitoid intrusion crustal scale fault shear systems are required to induce channeled fluid flow and to focus ore fluids toward suitable host rocks and structural sites declining temperature below the amphibolite greenschist transition combined with sulfidation of fe rich host rocks is a particularly efficient au depositing mechanism the model suggests that the major controlling factors in declining order of importance are 1 high temperature low pressure generally low strain metamorphic regimes 2 crustal scale fault systems 3 unaltered fe rich rocks tholeiites banded iron formation at a suitable stratigraphic metamorphic level and 4 abundant au enriched komatiites and s rich sediments in source regions the low pressure metamorphic conditions combined with the occurrence of elongate high strain zones in most if not all generally low strain greenstone belts may explain the ubiquitous occurrence of gold deposits in archean terranes all four favorable parameters appear to act in concert to produce the largest gold deposits and most abundant gold mineralization in 2 7 or 0 1 b y old rift phase greenstone belts interpreted to have formed under conditions of high crustal extension and extensive crustal thinning i e with predicted high geothermal gradients high fault density limited synvolcanic alteration and abundant komatiites and sulfidic sediment horizons more widespread commonly older platform phase greenstone belts which formed under conditions of lesser crustal extension and thinning are less mineralized as predicted by the metamorphic model the ability of the model to explain the regional distribution of known archean gold deposits lends credence to its predictive capacity for example 1 greenstone belts in any one craton can be broadly ranked in order of likely relative gold potential 2 the likelihood of discovery of large deposits in poorly exposed or poorly explored belts of known type can be estimated 3 areas with the highest potential can be defined in rift phase greenstone belts by the coincidence of critical parameters such as specific host rock sequences and metamorphic facies 4 prospective structural sites for gold mineralization can be postulated in platform phase greenstone belts affected by diapiric tectonics and 5 the possible spacing of large deposits can be estimated further the potential use of the model in exploration emphasizes serious gaps in our knowledge of parameters crucial to understanding greenstone belt metallogeny including alteration patterns metamorphic p t paths and regional scale structural regimes

la icp ms trace element analysis of arsenopyrite from the samgwang gold deposit south korea and its genetic implications abstract the samgwang deposit previously classified as an orogenic gold deposit consists of several structurally controlled auriferous quartz veins hosted by metasedimentary rocks of the precambrian gyeonggi massif south korea the gold at samgwang occurs as electrum commonly associated with arsenopyrite laser ablation inductively coupled plasma mass spectrometry la icp ms coupled with ore microscopy was conducted on au and trace elements distributed in arsenopyrite grains contained in quartz vein and wall rock samples resulting profiles for au co ni and sb were relatively flat and showed little variability indicating that the elements were relatively homogeneously distributed and exchanged via substitution in arsenopyrite while variability and noisy depth profiles inferred that pb was present as tiny inclusions or discrete particles furthermore measured gold concentrations were typically higher in arsenopyrite grains from laminated quartz veins avg 2 07 ppm than in grains from massive quartz veins avg 0 26 ppm and wall rock samples avg 0 33 ppm in the case of wall rock and massive quartz vein samples arsenopyrite grains of euhedral shape illustrate an element distribution pattern whereby au concentrations tend to decrease towards the rims of the analyzed grains in contrast the rims of arsenopyrite grains in laminated quartz vein samples recorded much higher au concentrations of up to 20 1 ppm with increasing pb bi and ag particularly within domains of fractured or recrystallized arsenopyrite grains the newly acquired la icp ms data along with textural evidence may be interpreted in terms of the release and remobilization of invisible gold that was originally locked up in the arsenopyrite this release is linked to late deformation and hydrothermal event during which the remobilized invisible gold was redeposited as electrum in addition there is evidence for the introduction of additional gold and other precious and base metals by the late stage hydrothermal fluids based on the above and in contrast to previous genetic models we propose a more complex metallogenic concept for samgwang in which the economically important gold enrichment process was genetically related to intrusive activity during the waning stages of jurassic to early cretaceous daebo orogenesis

multistage gold mineralization events in the archean tati greenstone belt northeast botswana constraints from integrative white mica ar ar garnet u pb and sulfides pb pb geochronology abstract the tati greenstone belt tgb in northeastern botswana hosts numerous au deposits shashe mupane and signal hill associated with sulfides garnet and white mica in this study integrative white mica ar ar garnet u pb and sulfides pb pb dating techniques were combined with whole rock and sulfide pb isotope characteristics to track the source s of gold and constrain the timeframes of gold mineralization events all sulfides and arsenopyrite samples from the tgb yielded overlapping pb pb errorchron ages of 2227 66 ma and 2220 73 ma respectively which coincide with the shashe sulfides pb pb errorchron age of 2250 110 ma these relatively imprecise pb pb dates suggest heterogeneity in the initial pb isotope ratios of sulfides at mupane whereas au mineralization associated hydrothermal almandine garnet yielded overlapping tera wasserburg lower intercept 206pb 238u age and a concordia age of 2119 18 ma mswd 1 03 and of 2105 24 ma mswd of concordance 1 10 respectively sulfides produced an errorchron pb pb age of 2873 140 ma which despite the large error remains geologically meaningful as it coincides within error with the first neoarchean limpopo liberian orogeny 2 70 2 65 ga granitoids intrusion emplacement 2 65 2 73 ga and deposition of banded iron formation 2 73 0 15 ga ore related white mica from signal hill yielded an overlapping ar ar plateau age of 1987 24 ma and a weighted mean ar ar age of 1987 13 ma n 15 mswd 4 3 which coincide within error with the 2 05 1 95 ga second limpopo liberian tectonic cycle herein considered to have possibly triggered the au mineralization in this area the obtained radiometric dates point to at least three well constrained gold mineralization events with two of them possibly triggered by two different regional tectonic events lead isotope compositions of most of the sulfides overlap with those of spatially associated schists and granitoids thus suggesting these units possibly represent pb and by inference au rock sources the genetic model of the tgb au deposits is consistent with many greenstone hosted gold deposits worldwide suggesting our results are not solely of local regional interest but can be used to characterize greenstone hosted gold deposits worldwide

analysis of fluid and heat regimes in sedimentary basins techniques for use with large data bases fluid and heat regimes as well as mass transport are an integral part of dynamic basin analysis all must be included to understand both the rocks and the processes affecting their contained fluids this paper is concerned with the interpretation and integration of fluid and heat data from point form into synthesized form within the geologic framework are obtained from well logs whereas that for evaluation of the fluid flow and geothermal regimes originates from formation water analyses drill stem tests cores and bottom hole temperature measurements a data base management system has been developed that allows integrating these various parameters into a form suitable for study by using maps cross sections graphs and statistical techniques the final product is synthesis of the fluid flow and geothermal regimes in terms of hydrostratigraphic units and an evaluation of the flow of both fluids and heat vertical and lateral fluxes of fluid flow can be determined using an integral mass balance approach fluid flow information is used to produce a virtual potentiometric surface for oil when looking for hydrodynamic entrapment of hydrocarbons examples of the application of the various techniques are taken from the swan hills and cold lake areas of alberta canada

heat flow in the gulf coastal plain forty four new heat flow values from panhandle florida southwestern georgia southern alabama mississippi and louisiana range from 13 mw m sup 2 0 3 hfu 1 hfu 1 mu cal cm sup 2 s sup 1 41 8 mw m sup 2 in florida and alabama to 88 mw m sup 2 2 1 hfu in northern louisiana in general the values depict the eastern gulf coastal plain as an area with low to normal continental heat flow that increases from east to west anomalously low heat flow 13 33 mw m sup 2 0 3 0 8 hfu characterizes northcentral florida southwestern georgia and southern alabama while in northern louisiana 13 measurement sites yield values ranging from 50 mw m sup 2 1 2 hfu to 88 mw m sup 2 2 1 hfu distinctive disruptions in the temperature depth profiles attributed to convective effects within aquifers are limited in magnitude and extent and do not alter the geothermal gradient computations the region of relatively high heat flux in northern louisiana is coincident with an area underlain by cenozoic alkalic igneous rocks of the monroe uplift and an abnormal concentration of radiogenic heat sources within that body is postulated as the cause of the thermal anomaly

multistage sedimentary and metamorphic origin of pyrite and gold in the giant sukhoi log deposit lena gold province russia gold mineralization at sukhoi log in eastern siberia is hosted in a deformed neoproterozoic organic bearing and pyritic black shale and siltstone sequence that is folded into a tight overturned anticline the deposit contains about 30 million ounces of gold at an average grade of 2 0 g t au and is one of the largest known undeveloped gold resources the high grade gold zone forms a gently dipping tabular body in the core of the anticline the best gold grades occur in narrow bedding parallel pyrite quartz veinlets that have been folded during the main deformation event lower grade gold is associated with disseminated pyrite developed in and around the high grade core of the deposit detailed paragenetic studies of the mineralization and host rocks have defined six stages of pyrite development in the carbonaceous sediments the two earliest forms of pyrite termed py1 and py2 are commonly developed in stratiform layers of micron sized crystals framboids and fine euhedra which are interpreted as synsedimentary to early diagenetic in origin coarser grained bedding parallel aggregates of inclusion rich pyrite termed py3 contain inclusions of arsenopyrite native gold and gold tellurides and are interpreted to form during late diagenesis and earliest deformation coarse euhedral pyrite py4 overgrows the earlier pyrite py1 py2 and py3 and the slaty cleavage developed in the host rocks indicating a syndeformation timing late stage inclusion free pyrite py5 overgrows and replaces earlier sulfides and is considered to be syn to late deformation laser ablation inductively coupled plasma mass spectrometry la icpms analyses of the various pyrite types indicate that the synsedimentary py1 contains the highest levels of invisible gold varying from 0 4 to 12 1 ppm with a mean of 3 22 ppm au and 1 900 ppm as py1 is also enriched in a suite of trace elements mo sb ni co se te ag cu pb zn mn ba cr u v which are similar to those concentrated by organic processes in euxinic sedimentary environments later generations of pyrite from py2 to py5 including pyrite in bedding parallel pyrite quartz veinlets contain progressively lower contents of invisible gold and most other trace elements however this metamorphic and postmetamorphic pyrite contains microinclusions of free gold arsenopyrite pyrrhotite sphalerite and chalcopyrite the paragenetic textural and chemical relationships at sukhoi log suggest that gold was clearly initially introduced prior to cleavage development accompanying sedimentation of the organic rich shales and fixed during diagenesis within the structure of diagenetic arsenian pyrite subsequently accompanying deformation gold was liberated from recrystallized diagenetic pyrite to become concentrated as free gold and gold tellurides within metamorphic pyrite and folded bedding parallel pyrite quartz veinlets two key processes are considered vital to the formation of the sukhoi log deposit original synsedimentary and early diagenetic concentration of gold dissolved within arsenian pyrite in organic rich black shales and metamorphic processes that liberated gold from the early forms of arsenian pyrite to be concentrated as free gold and gold tellurides within late diagenetic and metamorphic pyrite and associated pyrite quartz veinlets in the core of an overturned anticline these ore forming processes are unlikely to be unique to sukhoi log other black shale and turbidite hosted deposits that occur in rifted continental margin environments which have undergone collision and basin inversion may form by similar processes

paragenesis and composition of ore minerals in the randalls bif hosted gold deposits yilgarn craton western australia implications for the timing of deposit formation and constraints on gold sources the randalls district comprises three individual gold deposits cock eyed bob maxwells and santa craze hosted in the same unit of banded iron formation bif in the southern eastern goldfields superterrane yilgarn craton western australia the iron formation is a silicate oxide facies unit with overprinting sulfides and has undergone metamorphism upper greenschist facies and deformation two generations of folds the gold deposits are hosted in two structural locations hinge zones of anticlinal folds e g santa craze and maxwells and overturned steeply dipping limbs of anticlinal folds e g cock eyed bob gold dominantly occurs as inclusions of native gold and or electrum within or around pyrrhotite magnetite and arsenopyrite the earliest mineral assemblage preserved in the banded iron formation at randalls is banded magnetite quartz magnetite in all forms has elevated mg al ti v mn cr zn and w but very low ni compared to other bifs globally pyrrhotite the most abundant sulfide is restricted to ore zones and occurs as laminae blebs and veinlets all of which have replaced magnetite some pyrrhotite in the hydrothermally altered bifs especially in near surface samples has been re sulfidized to pyrite trace elements associated with pyrrhotite include co ni ag sb and pb large coarse grained arsenopyrite overgrows the pyrrhotite defined foliation it is enriched in co ni sb and te but contains very little invisible gold 0 01 ppm au unlike arsenopyrite in many orogenic au systems globally commonly 0 1 ppm au petrographic studies of several mineralized bifs from randalls reveal that pyrrhotite and arsenopyrite are associated with fe ca amphibole which grew during contact metamorphism caused by granite plutons this spatial sulfide amphibole relationship indicates that gold mineralization likely occurred during granite intrusion consistent with prior studies on randalls the trace element characteristics of the sulfides show that they were not inherited from replaced magnetite further these characteristics suggest that the fluid from which sulfides crystallized was not indigenous to the bifs and that this s rich fluid either contained s in abundance originally or interacted with a lithology lithologies that were rich in s before reaching the bifs black shale containing diagenetic nodular pyrite occurs in the upper black flag group which unconformably underlies the belches supersequence at depth 3 km the trace element composition of nodular pyrite from this unit fits well with the trace element characteristics of the bif pyrrhotite and arsenopyrite and the nodular pyrite contains an average of 0 5 ppm au however the nodular pyrites have an average 34s value of 5 6 n 13 which contrasts markedly with the 34s average of pyrrhotite pyrite and arsenopyrite in mineralized bifs 0 8 n 17 thus a definitive source of gold arsenic silver and tellurium in the randalls system remains elusive although we would contend that the upper black flag group should be considered as a possible metal and s source in areas of the yilgarn where it forms a thick substrate to ore camps

geochemistry of banded sulphidic cherts of sandur greenstone belt dharwar craton india constraints on hydrothermal processes and gold mineralization abstract the banded iron formations which are hosted in the greenstone belts of dharwar craton are potential sources of iron and also major archives of gold mineralization at some places the gold bearing banded sulphidic cherts from the neoarchean sandur greenstone belt of western dharwar craton have been reported in this paper in order to understand their geochemical characteristics source of gold mineralization and depositional conditions these rocks are predominantly characterized as mixed oxide sulphide facies which are generally referred as sulphide facies iron formations consisting of alternate mesoscale bands of silica and iron with sulphides such as pyrite chalcopyrite galena arsenopyrite and sphalerite occurring as minor opaque phases mineral chemical analyses of pyrite having high fe s as co ni and pb as ratios suggests hydrothermal source native gold occurs as disseminations in these sulphides with its concentrations ranging from 0 05 to 1 48 ppm gold mineralization is sediment hosted variety epigenetic epithermal hydrothermal in origin where the sulphidic auriferous fluids generated at mid oceanic ridge mor hydrothermal system were transported and deposited in an oxygen deficient environment low cao mgo k2o and ree contents suggests minor detrital input while la th sc relationship indicate minor volcaniclastic source from metabasic rocks low k rb and th u illustrate negligible effects of weathering in these samples geochemical proxies such as superchondritic y ho ratios along with post archean australian shale paas and mud from queensland muq normalized ree y patterns with depleted lree and positive eu la and y anomalies suggest that these bifs were generated by the chemical precipitation of iron and silica in sea water at mor and continental margin setting which had suboxic to anoxic paleo redox conditions

bimodal distribution of gold in pyrite and arsenopyrite examples from the archean boorara and bardoc shear systems yilgarn craton western australia this study investigates the microstructures geochemistry and hydrothermal evolution of gold bearing pyrite and arsenopyrite from six orogenic gold deposits in the archean eastern goldfields province western australia scanning electron microscope sem electron microprobe emp and laser ablation inductively coupled plasma mass spectroscopy la icp ms analyses show that the gold bearing minerals possess a number of similar textural features including the occurrence of invisible gold within initial phases of growth and later stage visible gold associated with alteration rims the alteration rims are characterized by a higher than average atomic mass mainly owing to arsenic enrichment and are preferentially located along fractures and grain boundaries in the pyrite and arsenopyrite these observations suggest that visible gold formation is associated with hydrothermal alteration of preexisting pyrite and arsenopyrite textural observations and la icp ms data suggest that some invisible gold was remobilized from early formed pyrite and arsenopyrite to form visible gold during development of these alteration rims gold may also have been added by hydrothermal fluids during a later stage of mineralization in situ geochemistry and phase relationships of alteration rims are used to further constrain the hydrothermal process responsible for formation of alteration rims and visible gold in fractures based on sulfide stability relations our data indicate that development of arsenopyrite alteration rims associated with late stage visible gold formation was related to an increase in temperature maximum increase from 310 to 415 c and up to of sic orders of magnitude increase in sulfur fugacity whereas changes in oxygen fugacity were less important la icp ms analyses show that the relative and absolute variations in selected trace element au ag sb bi ba te pb co and mo concentrations can also be used to distinguish between unaltered and altered pyrite and arsenopyrite in general trace elements within pyrite and arsenopyrite have a relatively uniform distribution whereas later stage alteration rims have more variable trace element distributions although the observed textures are typical of prograde metamorphic coronae we suggest that they are the consequence of variations in fluid conditions and chemistry and that mineralization occurred in response to syn and or postpeak metamorphic fluid infiltration

thermal histories and hydrocarbon generation example from utah wyoming thrust belt the thermal history of the utah wyoming thrust belt in the vicinity of the pineview oil and gas field is studied with a detailed thermal model the model incorporates a heterogeneous thermal conductivity structure radioactive heat generation in the crust sediment compaction variable basal heat flow through time and thermal effects of sedimentation erosion and thrust faulting the analysis is constrained by 206 corrected bottom hole temperatures 660 thermal conductivity measurements and 10 new vitrinite reflectance measurements present surface heat flow in this part of the utah wyoming thrust belt is estimated to be 60 8 mw m2 surface heat flow in the late cretaceous about 70 ma is inferred to have been 38 8 mw m2 from an lysis of vitrinite reflectance data about half of the apparent difference between ancient and present surface heat flow may be attributed to transient thermal effects of sedimentation erosion and thrusting the hypothesis of a constant background thermal state in this part of the thrust belt for the last 70 m y may not be ruled out however thermal history simulations in which the background thermal state changes through time better match constraints imposed by estimated present surface heat flow and vitrinite reflectance data application of the thermal history analysis to hydrocarbon generation is illustrated with a kinetic model of organic maturation oil and gas at the pineview field may have been generated in two stages first stage just before and during thrusting and the second stage during cenozoic warming

u pb ages constraining batholith emplacement contact metamorphism and the formation of gold and w mo skarns in the southern cross area yilgarn craton western australia gold mines in the archean southern cross greenstone belt central yilgarn craton have produced more than 220 metric tons t of gold the deposits are characterized by a pyroxene rich gangue and have been interpreted as synmetamorphic amphibolite facies replacement deposits and as postmetamorphic intrusion related skarns we present ion microprobe u pb zircon data constraining the age of amphibolite facies contact metamorphism in the aureole of the ghooli dome the largest granitoid batholith intruding the southern cross belt drill cores from the copperhead gold mine provided zircons from an altered quartz porphyry sill located 300 m southwest of the ghooli dome and zircons from the monzogranite gneiss at the border of the batholith the porphyry sill contains embayed igneous zircons dated by a concordant u pb age of 2912 5 ma and euhedral zircons of metamorphic crystal habitus dated by a second concordant age of 2772 5 ma the igneous zircons are slightly younger than those recovered from another sill of quartz porphyry sampled at the southern star mine which define a single concordant u pb age of 2934 7 ma the metamorphic zircons in the porphyry at copperhead record the same age as the igneous zircons 2775 10 ma in the monzogranite gneiss of the ghooli dome this pluton extends more than 40 km to the southeast of copperhead and also forms the batholith border at the corinthian and fraser s mines these gold deposits too are hosted by amphibolite facies greenstones contact metamorphosed at 2772 5 ma the corinthian skarn 2620 6 ma formed 150 m y after high grade metamorphism and consequently cannot be classified as synmetamorphic or metamorphogenic a review of field relationships and of published geochronometric data suggests that the gold skarns in the southern cross area are related in space and time to a suite of magnetite series granite pegmatite complexes these granites dated regionally at 2 66 to 2 60 ga are also associated with gold bearing w mo skarn greisen or skarn systems of up to 6 km strike length the numerous skarns exposed in the deeply eroded 14 km paleodepth central yilgarn craton are members of a recently recognized group of intrusion related gold deposits which are part of continental margin tungsten tin provinces

thermal conductivity of wilcox and frio sandstones in south texas gulf of mexico basin thermal conductivity and petrographic data are presented for verifying mechanistic models of sandstone thermal conductivity we measured the thermal conductivity of 83 wilcox and frio sandstones from south texas in the gulf of mexico sedimentary basin and correlated conductivity to petrographic variables thermal conductivities of water saturated sandstones at 20 c 68 f and 3 mpa 435 psi were measured on core plugs using a divided bar apparatus thermal conductivity ranges from 2 06 to 5 73 w m k over a porosity range of 2 4 to 29 6 because of a higher quartz content wilcox sandstones at a given porosity are more conductive than frio sandstones a grain matrix conductivity of 5 9 w m k is estimated for wilcox sandstones matrix conductivity is adequately described with an arithmetic mixing model thermal conductivities of clean 35 of the solids sandstones the dependence on quartz content can be dropped and thermal conductivities can be predicted with a linear decrease in conductivity with increasing porosity these sandstones appear isotropic with respect to thermal conductivity

geodynamics of the eastern yilgarn craton abstract over the last decade there have been significant advances in our understanding of the stratigraphy magmatism deformation metamorphism and timing of mineralisation in the eastern yilgarn craton eyc of western australia the integration of these disciplines has enabled a holistic review of the tectonic history of the eyc which favours a paraautochthonous tectonic model a significant advance has been the recognition of a 2810 ma rifting event off the eastern margin of the youanmi terrane which set up the north northwest trending architecture of the eyc rifting was followed by a 100 myr long phase of tectonic activity initiated by the establishment of a convergent margin at 2715 ma characterised by a west dipping subduction zone to the east of the eyc subduction was associated with the deposition of 2715 2670 ma volcanic stratigraphy and the emplacement of voluminous tonalite trondhjemite granodiorite magmatism which resulted in magmatic thickening of the crust volcanism was terminated by a 5 myr pulse of east northeast contraction followed by mid orogenic extension possibly linked to lithospheric and lower crustal delamination the lack of ultra high pressure metamorphism and the presence of high geothermal gradients preclude this contractional event from recording continent continent collision mid orogenic extension at 2665 ma resulted in the introduction of metasomatised mantle melts mafic granites and syenites deposition of siliciclastic basins which record metamorphic anticlockwise ptt paths and the start of significant economic gold mineralisation in the eyc high stretching factors and or delamination associated with this extension event resulted in significant heat input into the base of the crust which eventually led to the emplacement of low ca crustal melt granites and cratonisation of the eyc major gold mineralisation postdates mid orogenic extension and was associated with renewed compression transpression 2650 ma and the development of steep predominantly north northwest striking sinistral and later north to north northeast striking dextral strike slip faults during low ca granite emplacement

a carbonaceous sedimentary source rock model for carlin type and orogenic gold deposits this paper presents evidence and arguments that carbonaceous sedimentary rocks were a source for au and as in sediment hosted orogenic and carlin type gold deposits and develops a corresponding genetic model in this two stage basin scale model gold and arsenic are introduced early into black shale and turbidite basins during sedimentation and diagenesis stage 1 and concentrated to ore grades by later hydrothermal structural or magmatic processes stage 2 in reduced continental margin basin settings organic matter sedimented under anoxic to euxinic conditions immobilizes and concentrates gold arsenic and a range of trace elements particularly v ni se ag zn mo cu u present in marine bottom waters into fine grained black mudstone and siltstone of slope and basin facies during early diagenesis gold and certain other trace elements ni se te ag mo cu pge are preferentially partitioned into arsenian pyrite that grows in the muds these processes produce regionally extensive black shale and turbidite sequences enriched in syngenetic gold and arsenic commonly from 5 to 100 ppb au and 10 to 200 ppm as rare organic and sulfide rich metalliferous black shales may contain up to 1 to 2 ppm au and over 1 000 ppm as present as refractory gold in arsenian pyrite and nanoparticles of free gold during late diagenesis and early metamorphism stage 2 the diagenetic arsenian pyrite is recrystallized to form coarser grained pyrite generations and the organic matter is cooked to bitumen under higher grade metamorphism lower greenschist facies and above arsenian pyrite in carbonaceous shales is converted to pyrrhotite these processes release gold arsenic sulfur and other elements sb te cu zn mo bi tl and pb from the source rocks to become concentrated by hydrothermal processes locally to produce gold ores in structural sites such as fold hinge zones shear or breccia zones within or above the black shale sequence la icp ms analyses of diagenetic pyrite in carbonaceous sediments both associated and not associated with gold deposits suggests that invisible gold contents of greater than 250 ppb in diagenetic pyrite are indicative of carbonaceous shale source rocks with the potential to produce economic gold deposits application of this sedimentary source rock model enables a systematic exploration approach for sediment hosted gold deposits based on the distribution composition and structure of carbonaceous shale sequences and their contained diagenetic pyrite

geothermal characteristics of the ries impact structure summary a new investigation of the thermal conductivity of the drill cores from the research drill hole nordlingen 1973 in the ries impact structure was conducted the 1206 m deep drill hole pen etrated 331 m of post impact lake formations then 275 m of suevitic impact formations with varying amounts of large crystalline basement blocks and then 600 m of fractured displaced basement blocks containing appreciable amounts of dyke breccias the main purpose of the measurements was to see the signature of the shock effects in the thermal properties of the impact formations the use of the new non contact optical scanning instrument allowed mea surements with a resolution of a few centimetres a complicated preparation of the samples was not required thermal conductivity values on dry and on water saturated drill cores and thermal inhomogeneity factors were obtained for samples with a spacing of about 2 m it could be shown that the thermal conductivity is extremely inhomogeneous on various scales and that there is a close relation with the degree of shock and thermal transformation of the target rocks an improved theoretical model for the thermal conductivity of rocks taking into account the form of grains pores and cracks and using measurements on dry and saturated cores yields information on the porous space of the rock samples correlations between the thermal con ductivity and other petrophysical properties determined from well logging data were found they allow other physical properties to be predicted from the conductivity values the new thermal conductivity data together with temperature logging data also gave the possibility of making new estimates of the undisturbed heat flow density in the crater area 90 95 mw m 2 with about 30 per cent higher values than previous estimates a significant increase of the heat flow density in the upper part of the structure indicates fluid migration from deeper parts the absence of thermal anisotropy in crystalline rocks increasing thermal conductivity with depth and increasing heat flow density may be characteristic features of impact structures

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

does gold in orogenic deposits come from pyrite in deeply buried carbon rich sediments insight from volatiles in fluid inclusions the origin of volatiles in fluid inclusions was reviewed for testing the involvement at depth of carbonaceous pyritic sedimentary rocks as the source for orogenic gold mineralization fluid inclusions from selected deposits were analyzed by solid probe mass spectrometry fluids are mostly aqueous carbonic with variable amounts of n 2 ch 4 c 2 h 6 ar h 2 s h 2 and he for fluids with ch 4 and c 2 h 6 their ratios c 1 c 2 range from 2 6 to 25 5 indicating that c 2 h 6 is sourced from thermally degraded organic matter proportions of co 2 ch 4 c 2 h 6 and h 2 are highly variable and can be explained by hydrothermal reactions where c 2 h 6 is degraded to co 2 by water consumption such reactions may account for the problematic co 2 rich h 2 o poor fluids associated with some of the richest gold districts conditions needed for c 2 h 6 degradation are also fundamental for forming gold deposits such as hs enriched fluids for carrying gold and local weakly oxidizing conditions for promoting gold precipitation the c 2 h 6 content is recorded in fluids from mesoarchean to cretaceous gold deposits providing support for a general model where fluids and gold were sourced from deeply buried carbon rich and pyrite gold bearing sedimentary rocks

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

an experimental study of the mechanism of the replacement of magnetite by pyrite up to 300 c abstract we present the results of an experimental study into the sulfidation of magnetite to form pyrite marcasite under hydrothermal conditions 90 300 c vapor saturated pressures a process associated with gold deposition in a number of ore deposits the formation of pyrite marcasite was studied as a function of reaction time temperature ph sulfide concentration solid weight to fluid volume ratio and geometric surface area of magnetite in polytetrafluoroethylene lined autoclaves ptfe and a titanium and stainless steel flow through cell marcasite was formed only at ph 21 c 21 c 1 11 while pyrite predominated at ph 21 c 2 and formed even under basic conditions up to ph 21 c 12 13 marcasite formation was favored at higher temperatures fine grained pyrrhotite formed in the initial stage of the reaction together with pyrite in some experiments with large surface area of magnetite grain size 120 c 0 96 4 42 and that rate of the transformation increased from 120 to 190 c scanning electron microscope sem imaging revealed that micro pores 0 1 5 m scale existed at the reaction front between the parent magnetite and the product pyrite and that the pyrite and or marcasite were euhedral at ph 21 c 155 c 4 42 the experimental results are in good agreement with sulfide phase assemblage and textures reported from sulfidized banded iron formations pyrite marcasite and pyrrhotite have been found to exist or co exist in different sulfidized banded iron formations and the microtextures show no evidence of sub m scale pseudomorphism of magnetite by pyrite

structural event framework for the eastern yilgarn craton western australia and its implications for orogenic gold abstract the nnw trending tectonic grain of the eastern yilgarn craton eyc was established as a result of predominantly ene wsw directed extension d1 and d3 and e ene w wsw d2 d4 to ne sw directed d5 contraction the result has been a succession of nnw striking temporally discrete fabric elements which can be difficult to interpret reliably at any single location despite this many past workers interpreted the nnw striking fabric as the result of only one regional contractional event and used it as a marker for correlating structural events across the region in order to unravel the complexity this paper presents a new sixfold d1 d6 deformation nomenclature based on 10 000 new mesoscale structural observations including their kinematic analysis and cross cutting relationships these mesoscale data were referenced with regional 3d map patterns stratigraphic magmatic metallogenic considerations and deep seismic reflection images this integrated geodynamic architectural approach is applicable to solving structural event histories in other polydeformed terrains gold mineralisation occurred during the first five events but was particularly concentrated from d3 onwards the d3 event marked the most profound change in the tectonic evolution of the eyc with changes in greenstones granites and tectonic mode lithospheric extension and core complexes with the first significant gold deposited within extensional shear zones that dissect the crust later contraction d4 was imposed at a high angle to the previously established anisotropic architecture the outcome was the creation of a new dynamic permeability framework which resulted in gold mineralisation during nnw striking sinistral strike slip faulting and associated thrusting a further stress switch d5 further modified the architecture resulting in n to nne striking dextral strike slip faulting and the final period of gold mineralisation before late stage extension d6

pyrite compositions from vhms and orogenic au deposits in the yilgarn craton western australia implications for gold and copper exploration abstract the archaean yilgarn craton western australia is a world class metallogenic province hosting considerable resources of au ag ni cu zn and fe here we present trace element compositions of pyrite from 30 orogenic au and 5 volcanic hosted massive sulphide vhms deposits across the yilgarn pyrites from vhms deposits tend to have higher sn se cu pb bi and lower ni relative to orogenic deposits vhms deposit pyrites commonly have co ni as 100au te au se te orogenic gold deposits could be subdivided based on association of au with as or te pyrites from au as ores generally have pb bi 5 se te 5 pb sb 100 and the majority of au is refractory in pyrite structure at the same time au te association pyrites are characterised by lower values of pb bi se te and tl te higher values of ag au pb sb and au generally resides in inclusions of different compositions our data can be used at the exploration stage to distinguish between vhms vs orogenic au signatures for all studied deposits inclusion populations are summarised with implications for au and ag deportment orogenic au deposits from the yilgarn mostly have multistage formation histories reflected in the presence of multiple generations of pyrites however only some deposits record multiple high au mineralisation events

the influence of salt domes on paleotemperature distributions a characteristic of salt domes is that an enhanced heat flux is associated with them due to the contrast in thermal conductivity between rock salt and typical sedimentary formations we present a simple analytical model of heat flow in the vicinity of an isolated salt dome with numerical evaluations for some sample cases in addition to an enhanced surface heat flow these models show that on the upper flanks of a salt dome a temperature higher than the regional trend is predicted thus enhancing hydrocarbon maturation at these depths on the lower flanks a temperature lower than the regional trend is predicted thus inhibiting overmaturation the magnitude of this temperature anomaly depends upon the position of the measurement point both vertical and radial relative to the salt dome roughly speaking it is confined to within one salt dome radius of the salt sediment interface the magnitude of the anomaly can be quite large for typical salt domes these basic ideas are corroborated by observing downhole measurements from a salt dome in the gulf of mexico the good agreement allows us to bracket the height of that particular dome at between 9 000 and 15 000 m and also permits us to determine that the total sediment thickness overlying the basal salt is between 13 200 and 19 200 m at the location of the salt dome these results indicate that the presence of a salt dome can have a significant impact on the subsurface temperature distribution and hence on the thermochemical maturation of any source rocks or hydrocarbon accumulations in close proximity to the salt dome in addition to providing trapping structures a salt dome also provides an enhanced environment for hydrocarbon maturation on its upper flanks and for inhibiting overmaturation on its lower flanks such effects should be included when evaluating the hydrocarbon potential of a salt dome province

silver rich telluride mineralization at mount charlotte and au ag zonation in the giant golden mile deposit kalgoorlie western australia the gold deposits at kalgoorlie in the 2 7 ga eastern goldfields province of the yilgarn craton western australia occur adjacent to the d2 golden mile fault over a strike of 8 km within a district scale zone marked by porphyry dykes and chloritic alteration the late golden pike fault separates the older d2 shear zone system of the golden mile 1 500 t au in the southeast from the younger d4 quartz vein stockworks at mt charlotte 126 t au in the northwest both deposits occur in the golden mile dolerite sill and display inner sericite ankerite alteration and early stage gold pyrite mineralization replacing the wall rocks late stage tellurides account for 20 of the total gold in the first but for 30 g t au is characterized by au ag 2 54 and as sb 2 6 30 the latter ratio caused by arsenical pyrite golden mile type d2 lodes occur northwest of the golden pike fault but the hidden secret orebody the only telluride bonanza mined 10 815 t at 44 g t au was unusually rich in silver au ag 0 12 0 35 due to abundant hessite we describe another array of silver rich d2 shear zones which are part of the golden mile fault exposed on the mt charlotte mine 22 level they are filled with crack seal and pinch and swell quartz carbonate veins and are surrounded by early stage pyrite pyrrhotite disseminated in a sericite ankerite zone more than 6 m wide gold grade 0 5 0 8 g t varies little across the zone but au ag 0 37 2 40 and as sb 1 54 13 9 increase away from the veins late stage telluride mineralization 23 g t au sampled in one vein has a much lower au ag 0 13 and as sb 0 48 and comprises scheelite pyrite native gold 830 854 fine hessite and minor pyrrhotite altaite bournonite and boulangerite assuming 250 300 c gold hessite compositions indicate a fluid log fte2 of 11 5 to 10 values well below the stability of calaverite the absence of calaverite and the dominance of hessite in the d2 lodes of the mt charlotte area point to a kilometer scale mineral and au ag zonation along the golden mile master fault which is attributed to a lateral decrease in peak tellurium fugacity of the late stage hydrothermal fluid the as sb ratio may be similarly zoned to lower values at the periphery the d4 gold quartz veins constituting the mt charlotte orebodies represent a younger hydrothermal system which did not contribute to metal zonation in the older one

mineralogy porosity and fluid control on thermal conductivity of sedimentary rocks summary estimates of thermal conductivity of the main non clay and clay sedimentary minerals are presented especially for the case of argillaceous ones these estimates are averaged estimates based on the interpretation of laboratory conductivity porosity and mineralogy measurements performed on small volumes of the order of 100cm3 of water saturated moist and air saturated samples the sampling is representative of the main sedimentary rocks sandstones carbonates evaporites and shales and it is composed of samples considered as structurally isotropic material first we experimentally verify the first order control of mineralogy porosity and fluid content on bulk conductivity and we demonstrate that such influences may be predicted accurately using a geometric mean model as long as isotropic samples are used then we interpret the data using an inverse method in order to estimate the average mineral conductivities of the main non clay and clay minerals which give the best fit to the individual laboratory measurements through the geometric mean model the analysis is based on measurements on 82 non clay samples and 29 clay samples taken on oil well cores or cuttings on outcrops and on artificially recompacted samples estimates of average mineral conductivities returned by the inversion process for the main non clay minerals are similar to generally admitted values 7 7 w m k for quartz 3 3 w m i k for calcite 5 3 w m l k for dolomite and 6 3 w m k for anhydrite values obtained for the clay minerals are systematically lower than those obtained for non clay ones they are of the order of 1 9 w m k for illite and smectite 2 6 w m k for kaolinite and 3 3 w m l k for chlorite these estimates combined with porosity and mineralogy data are used with the geometric mean model in order to verify its first order validity for predicting thermal conductivity of small volumes of porous isotropic sedimentary rocks the bulk conductivity is predicted with an accuracy of the order of f10 per cent for moist or water saturated samples and of the order of f20 per cent for air saturated samples

gold upgrading in metamorphosed massive sulfide ore deposits direct evidence from laser ablation inductively coupled plasma mass spectrometry analysis of invisible gold the metamorphosed boliden volcanic hosted massive sulfide vhms ore deposit northern sweden is characterized by an abundance of massive arsenopyrite ore and unusually high gold enrichments up to 300 600 g t in crosscutting veins and fracture zones the ore textures observed record progressive recrystallization and porphyroblast growth during meta morphism we conducted a systematic laser ablation inductively coupled plasma mass spectrom etry la icp ms study on the gold distribution in fine grained massive arseno pyrite and pyrite ore partially recrystallized arsenopyrite ore and both arsenopyrite and pyrite porphyroblasts found in gold rich veins the gold concentrations in massive arseno pyrite are highest 30 50 ppm on average and systematically decrease to 0 2 7 ppm with increasing degree of recrystallization by contrast gold concentrations in pyrite ore are much lower and do not exceed 0 2 ppm the la icp ms data coupled with textural data provide the first direct conclusive evidence that gold is progressively liberated from massive sulfide ores during metamorphism and reprecipitated in veins and other low strain sites we suggest that such upgrading is the principal mechanism responsible for significant gold enrichment observed in many metamorphosed vhms deposits worldwide

invisible gold in arsenian pyrite and arsenopyrite from a multistage archaean gold deposit sunrise dam eastern goldfields province western australia the sunrise dam gold mine 11 1 moz au is the largest deposit in the archaean laverton greenstone belt eastern goldfields province yilgarn craton western australia the deposit is characterized by multiple events of fluid flow leading to repeated alteration and mineralization next to a major crustal scale structure the au content of arsenian pyrite and arsenopyrite from four mineralizing stages d1 d3 d4a and d4b and from different structural and lithostratigraphic environments was measured using in situ laser ablation inductively coupled plasma mass spectrometry pyrite contains up to 3 067 ppm au n 224 whereas arsenopyrite contains up to 5 767 ppm n 19 gold in arsenopyrite d4a stage was coprecipitated and remained as invisible gold nanoparticles and or lattice bound during subsequent deformation events in contrast gold in pyrite is present not only as invisible gold but also as micrometer size inclusions of native gold electrum and au ag tellurides pristine d1 and d3 arsenian pyrite contains relatively low au concentrations 26 ppm the highest au concentrations occur in d4a arsenian rich pyrite that has recrystallized from d3 pyrite textures show that this recrystallization proceeded via a coupled dissolution reprecipitation process and this process may have contributed to upgrading au grades during d4a in contrast au in d4b pyrite shows grain scale redistribution of invisible gold resulting in the formation of micrometer scale inclusions of au minerals the speciation of au at sunrise dam and the exceptional size of the deposit at province scale result from multiple fluid flow and multiple au precipitating mechanisms within a single plumbing system

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

multi stage and multi sourced fluid and gold in the formation of orogenic gold deposits in the world class mana district of burkina faso revealed by la icp ms analysis of pyrites and arsenopyrites abstract mana is a world class paleoproterozoic orogenic gold district 8 0 moz that includes five gold deposits fofina nyafe siou wona kona and yaho hosted in various rocks in the northern part of the birimian hounde greenstone belt western burkina faso the gold deposits recorded different styles of mineralization associated with sulfides during polyphase deformation events detailed petrographic and la icp ms analyses of pyrites and arsenopyrites from the main mineralization of each deposit provide new information on the potential gold and arsenic sources and timing of fluids responsible for mineralization at mana four hydrothermal fluid events associated with two distinct source reservoirs and at least two hydrothermal systems were recognized the first hydrothermal fluid event was generated during the eoeburnean d1md md for mana district shortening event 2172 ma evidence of which is preserved in the fofina and siou deposits and occurred under greenschist metamorphic facies conditions economic gold deposits at fofina are associated with metamorphic disseminated pyrite py1f in black shale zoned pyrite py2f enriched in as ni cu ag sb w au and pb and arsenopyrite in folded v1f quartz carbonate veins in contrast the siou deposit exhibits au in porous pyrite cores py1s which are associated with ag bi te and w sb in v1s quartz veins hosted in the siou granodiorite these two trace element suites are interpreted as having been induced by a metamorphic source in the fofina deposit and by a local contribution of a magmatic source in the siou deposit the second hydrothermal fluid event occurred during the eburnean d3md transpressional event 2113 2090 ma in the nyafe deposit this event is defined by au as rich rims in hydrothermal pyrite py3n and by the co precipitation of au rich arsenopyrite in the v3n quartz veinlets v3n controlled by a second order dextral shear zone the third and main hydrothermal fluid event during the d4md transpressional event 2090 ma is characterized by the development of strong silicification and by zoned pyrites py3wk and py2y and au rich arsenopyrite in the wona kona and yaho deposits however the same late au as rich rims in hydrothermal pyrite are observed in both deposits and in the nyafe deposit and these rims are interpreted to be related to the same economic gold source related to the lower birimian metamorphic reservoir composed of black shale diagenetic framboidal pyrite and tholeiitic basalts the diagenetic framboidal py1wk in black shale lower birimian group is enriched in au median of 0 8 ppm low in as median of 70 ppm with other trace elements ni cu zn ag sb and pb the last hydrothermal event is associated with free gold remobilization in late microfractures in the wona kona and siou deposit during the reactivation of major transcurrent shear zones during the d4md event or the d5md shortening event as late as 2022 ma a binary diagram of as ag vs sb bi appears to be effective at separating the diagenetic magmatic and metamorphic pyrites and could be used in orogenic gold exploration to ascertain potential gold endowment at the district scale

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

age origin and significance of nodular sulfides in 2680 ma carbonaceous black shale of the eastern goldfields superterrane yilgarn craton western australia abstract sulfide nodules composed of pyrite occur within black shales in the lucky bay area of the bulong domain eastern goldfields superterrane yilgarn craton western australia that correlate with the neoarchean black flag group detailed petrography reveals a variety of shapes and textures from spherical to ovoid and zoned to uniform some nodules have recrystallized resulting in a later generation of pyrite all have been affected by post depositional metamorphism as evidenced by pressure shadows containing quartz mica carbonate assemblages la icp ms analyses show that these nodules are enriched in a range of trace elements including co ni cu ag sb te au tl pb and bi gold and te concentrations range from 0 3 to 1 ppm and 10 to 50 ppm respectively the black flag group equivalents stratigraphically and structurally underlie a younger basin east of lucky bay that contains turbidites sandy debris flows and bif the latter of which hosts several gold deposits at randalls 60 km se of kalgoorlie it is likely that the lateral equivalents of the nodular sulfide bearing black shale originally occurred stratigraphically beneath what is now the ore horizon at randalls given its anomalous au and te content this lithology is a potential contributor of gold to the bif hosted gold deposits of the randalls goldfield as well as other similar gold resources elsewhere in the eastern goldfields superterrane

characterization of the sedimentary thermal regime along the corsair growth fault zone texas continental shelf using corrected bottomhole temperatures temperatures of deep 3 km 1 8 mi sediments along the corsair growth fault zone in the texas continental shelf are elevated relative to those off the fault zone this observation is based on a compilation of nearly 400 bottomhole temperatures bhts obtained from about 230 wells widely distributed across the continental shelf the bhts have been individually corrected for the thermal disturbance associated with drill fluid circulation the isotherm of 140 c 284 f derived from the corrected bhts shows more or less continuous peaks along the fault zone thermal gradients in the depth range of 3 to 5 km 1 8 to 3 1 mi shows higher values along the fault zone than off the fault zone these trends are similar to the previous observations made along the wilcox growth fault zone in the texas coastal plain previous studies suggest that the faults of the wilcox system serve as the conduits for hot fluids expelled from deep overpressured sediments a similar mechanism may explain the elevated temperatures along the corsair fault zone

constraining atmospheric oxygen and seawater sulfate concentrations during paleoproterozoic glaciation in situ sulfur three isotope microanalysis of pyrite from the turee creek group western australia abstract previous efforts to constrain the timing of paleoproterozoic atmospheric oxygenation have documented the disappearance of large mass independent sulfur isotope fractionation and an increase in mass dependent sulfur isotope fractionation associated with multiple glaciations at least one of these glacial events is preserved in diamictites of the 2 4 ga meteorite bore member of the kungarra formation turee creek group western australia outcrop exposures of this unit show the transition from the boolgeeda iron formation of the upper hamersley group into clastic glaciomarine sedimentary rocks of the turee creek group here we report in situ multiple sulfur isotope and elemental abundance measurements of sedimentary pyrite at high spatial resolution as well as the occurrence of detrital pyrite in the meteorite bore member the 15 3 range of 33 s in one sample containing detrital pyrite 3 6 to 11 7 is larger than previously reported worldwide and there is evidence for mass independent sulfur isotope fractionation in authigenic pyrite throughout the section 33 s from 0 8 to 1 0 the 90 range in 34 s observed 45 5 to 46 4 strongly suggests microbial sulfate reduction under non sulfate limiting conditions indicating significant oxidative weathering of sulfides on the continents multiple generations of pyrite are preserved typically represented by primary cores with low 34 s 34 s 4 7 and enrichments in as ni and co the preservation of extremely sharp sulfur isotope gradients 30 p o 2 first became sufficiently high to permit pervasive oxidative weathering of continental sulfides yet remained low enough to permit the production and preservation of mass independent sulfur isotope fractionation

three dimensional inverse modeling of the refractive heat flow anomaly associated with salt diapirism this article introduces a technique for three dimensional inverse modeling of geothermal heat conduction through heterogeneous media the technique is used to determine the basal geometry of a diapiric salt structure found on the continental slope offshore texas salt is two to four times more thermally conductive than other sedimentary rocks the geothermal field is perturbed by the presence of salt and results in an anomaly in the heat flow through the seafloor the spatial variation pattern of the anomalous heat flow reflects the geometry of the salt body the inverse modeling obtains a model for the thermal conductivity structure that causes the heat flow anomaly observed on the seafloor the inversion algorithm systematically searches for an optimal thermal conductivity model by iteratively minimizing the misfit between the model predicted and the observed heat flow to reduce the problem of nonuniqueness the inversion incorporates a priori information constrained independently such as the upper surface geometry of the salt and the lateral extent of the salt body which can be delineated by a limited coverage of two dimensional seismic data in addition it is assumed that the thermal conductivity of the sedimentary strata surrounding the salt body is well constrained this inversion method is applied to a heat flow data set obtained over a salt structure on the texas continental slope the salt structure was first surveyed with the single channel seismic reflection which yielded the a priori information necessary the base of the salt was not imaged seismically then three dozen heat flow measurements were obtained on the seafloor over and off the salt feature the inverse heat flow modeling performed here shows that this structure is a salt tongue which has a diapiric root on one side according to the most optimal thermal conductivity model obtained the root seems to extend to 6 km below the seafloor refinement in the model geometry and additional constraints on thermal conductivities of the surrounding strata should yield a model that is more detailed and would allow more thorough geological interpretation of the salt structure

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

inverse estimation of rock thermal conductivity based on numerical microscale modeling from sandstone thin sections abstract the effective thermal conductivity etc of porous rocks is primarily controlled by the matrix thermal conductivity mtc and the thermal conductivity of the pore fluid as a function of porosity rock etc has been investigated widely however information on mtc is rather sparse this study proposes a new approach using a numerical model to determine the mtc of porous rocks by parameter fitting to the measured etc the model represents realistic rock textures as detailed information on grain and pore geometries was obtained from microscopic images of thin sections mtc fitted from water saturated condition water as pore fluid showed plausible values between 4 9 and 7 6 w m k while mtc values from dry condition air as pore fluid were disproportionate except for one model with consistent mtc for both conditions this supports the idea that at constant temperature and pressure mtc is an intrinsic property independent of fluid saturation for this reason mtc from water saturated condition was used to calculate dry etc the model showed lower dry etc than the lab measurements but within a reasonable range for dry sandstones investigation of etc regarding saturation degree revealed that the samples may contain 12 45 residual moisture which explained the higher measured dry etc additionally the models allowed observation of textural influences showing that grain size distribution and connectivity affected the heat conduction of porous rocks

the geology of the giant nyankanga gold deposit geita greenstone belt tanzania nyankanga is the largest gold deposit in the geita greenstone belt of the northern tanzania craton the deposit is hosted within an archean volcano sedimentary package dominated by ironstones and intruded by a large diorite complex the nyankanga intrusive complex the supracrustal package is now included within the intrusive complex as roof pendants the ironstone fragments contain evidence of multiple folding events that occurred prior to intrusion the supracrustal package and nyankanga intrusive complex are cut by a series of ne sw trending moderately nw dipping fault zones with a dominant reverse component of movement but showing multiple reactivation events with both oblique and normal movement components the deposit is cut by a series of nw trending strike slip faults and e w trending late normal faults the nyankanga fault zone is a major nw dipping deformation zone developed mainly along the ironstone diorite contacts that is mineralised over its entire length the gold mineralization is hosted within the damage zone associated with nyankanga fault zone by both diorite and ironstone with higher grades typically occurring in ironstone ore shoots dip more steeply than the nyankanga fault zone the mineralization is associated with sulfidation fronts and replacement textures in ironstones and is mostly contained as disseminated sulphides in diorite the close spatial relationship between gold mineralization and the ironstone diorite contact suggests that the reaction between the mineralising fluid and iron rich lithotypes played an important role in precipitating gold intense brecciation and veining mainly in the footwall of nyankanga fault zone indicates that the fault zone increased permeability and allowed the access of mineralising fluids the steeper dip of the ore shoots is consistent with mineralization during normal reactivation of the nyankanga fault zone

the role of a transcrustal shear zone in orogenic gold mineralization at the ajjanahalli mine dharwar craton south india the ajjanahalli gold mine is spatially associated with a late archean craton scale shear zone in the eastern chitradurga greenstone belt of the dharwar craton india gold mineralization is hosted by an 100 m wide antiform in a banded iron formation original magnetite and siderite are replaced by a peak metamorphic alteration assemblage of chlorite stilpnomelane minnesotaite sericite ankerite arsenopyrite pyrite pyrrhotite and gold at ca 300 to 350 c elements enriched in the banded iron formation include ca mg c s au as bi cu sb zn pb se ag and te whereas in the wall rocks as cu zn bi ag and au are only slightly enriched strontium correlates with cao mgo co2 and as which indicates cogenetic formation of arsenopyrite and mg ca carbonates the greater extent of alteration in the fe rich banded iron formation layers than in the wall rock reflects the greater reactivity of the banded iron formation layers the ore fluids as interpreted from their isotopic composition 18o 6 5 8 5 initial 87sr 86sr 0 7068 0 7078 formed by metamorphic devolatilization of deeper levels of the chitradurga greenstone belt arsenopyrite chalcopyrite and pyrrhotite have 34s values within a narrow range between 2 1 and 2 7 per mil consistent with a sulfur source in chitradurga greenstone belt lithologies based on spatial and temporal relationships between mineralization local structure development and sinistral strike slip deformation in the shear zone at the eastern contact of the chitradurga greenstone belt we suggest that the ajjanahalli gold mineralization formed by fluid infiltration into a low strain area within the first order structure the ore fluids were transported along this shear zone into relatively shallow crustal levels during lateral terrane accretion and a change from thrust to transcurrent tectonics based on this model of fluid flow exploration should focus on similar low strain areas or potentially connected higher order splays of the first order shear zone