an analysis of the microstructures developed in experimentally deformed polycrystalline pyrite and minor sulphide phases using electron backscatter diffraction abstract samples of polycrystalline pyrite previously deformed in tri axial compression tests at a confining pressure of 300 mpa and a strain rate of 2 10 4 s 1 but varying temperature were analysed in this study five samples including the original starting material have undergone analysis using forescatter orientation contrast oc imaging coupled with electron back scatter diffraction ebsd to determine how the micro structures in pyrite and to an extent the surrounding minor phases have changed with increasing temperature between 550 c and 650 c the dominant deformation mechanism in pyrite is that of dislocation creep above 650 c this mechanism becomes less apparent and few if any dislocation walls are present within pyrite grains by 700 c this is a result of either increased dynamic recrystallisation with temperature or a change in the dominant deformation mechanism dislocation creep occurs via lattice rotation principally about a single 100 axis but also about two separate 100 axes and more rarely about a single 110 axis deformation has not resulted in a crystallographic preferred orientation cpo within any of the samples shape change of pyrite grains has occurred and this can account for most if not all of the shortening applied but dynamic recrystallisation of pyrite and grain boundary sliding accommodated along the minor phases are also likely to be important mechanisms in all of the samples

effects of magmatic processes serpentinization and talc carbonate alteration on sulfide mineralogy and ore textures in the black swan disseminated nickel sulfide deposit yilgarn craton the black swan disseminated orebody occurs predominantly within the partially carbonated serpentinite core of a zoned serpentinite talc carbonate ultramafic cumulate body of komatiitic parentage the black swan disseminated sulfides depart significantly from the characteristic pattern observed in otherwise similar deposits in western australia and canada which display magnetite bearing pentlandite rich sulfide aggregates blebs in serpentinites and s rich millerite bearing assemblages in talc carbonates the black swan disseminated ores in contrast are dominated by millerite pyrite polydymite assemblages in both serpentinites and talc carbonates with no evident relationship to the progression of carbonation sulfides show three types of intergrowth with gangue minerals which can occur separately or all together intergrowth with magnetite at least some of which appear to be primary magmatic in origin fine intergrowth with interlocking lath textured antigorite and intergrowth with carbonate minerals carbonate commonly replaces the core of sulfide blebs while retaining the primary magmatic outline carbonate replacement of sulfide roughly parallels the overall progression of carbonation of the whole rock but no systematic relationship of the other intergrowth types to carbonate content is observed in the serpentinites serpentine mineralogy determined by microbeam raman spectroscopy comprises lizardite which occurs in pseudomorphic mesh textures after olivine and antigorite formed by variable degrees of overprinting of original lizardite mesh textures ranging to a completely overprinting interlocking texture with no relic igneous texture this progression is interpreted as the result of mild thermal metamorphism of original lizardite serpentinite this progression is completely independent of carbonate content and is also apparently independent of extent of sulfide antigorite intergrowth which is interpreted as being early and related to volume expansion during initial sea floor serpentinization talc is almost completely absent from serpentinites while carbonate content varies widely whole rock ni and s data are very strongly correlated in millerite poor pentlandite rich samples and poorly correlated in samples where millerite is the dominant ni bearing sulfide on this basis we conclude that the pentlandite assemblages are slightly modified survivors of the original magmatic event while the millerite pyrite assemblages formed during the earliest stages of serpentinization overprinting of the early serpentinization event by talc carbonate had essentially no effect on sulfide mineralogy other than inducing intergrowth with carbonate a number of distinctive features such as magnetite rich bleb cores the association of sulfides with segregation vesicles and chromite shells the subspherical morphology of the blebs and preferential replacement of bleb cores are considered to be inherited from the magmatic phase and are attributed to an original high but variable oxygen and halogen content of the sulfide melt component exsolution of this component during solidification of the blebs in some cases produced sulfide centered bubbles now preserved as segregation vesicles while in other cases oxygen was retained within the bleb forming magnetite sulfide intergrowths chromite shells formed as a result of exsolved oxygen interacting with komatiite magma volatile rich blebs solidified in some cases with hollow or porous cores which were subsequently exploited by carbonate replacement

chalcophile and platinum group element pge concentrations in the sulfide minerals from the mccreedy east deposit sudbury canada and the origin of pge in pyrite magmatic sulfide deposits consist of pyrrhotite pentlandite chalcopyrite pyrite and platinum group minerals pgm understanding the distribution of the chalcophile and platinum group element pge concentrations among the base metal sulfide phases and pgm is important both for the petrogenetic models of the ores and for the efficient extraction of the pge typically pyrrhotite and pentlandite host much of the pge except pt which forms pt minerals chalcopyrite does not host pge and the role of pyrite has not been closely investigated the ni cu pge ores from the south range of sudbury are unusual in that sulfarsenide pgm rather than pyrrhotite and pentlandite are the main carrier of pge probably as the result of arsenic contribution to the sulfide liquid by the as bearing metasedimentary footwall rocks in comparison the north range deposits of sudbury such as the mccreedy east deposit have as poor granites in the footwall and the ores commonly contain pyrite our results show that in the pyrrhotite rich ores of the mccreedy east deposit os ir ru rh ipge and re are concentrated in pyrrhotite pentlandite and surprisingly in pyrite this indicates that sulfarsenides which are not present in the ores were not important in concentrating pge in the north range of sudbury palladium is present in pentlandite and together with pt form pgm such as ptpd tebi 2 platinum is also found in pyrite two generations of pyrite are present one pyrite is primary and locally exsolved from monosulfide solid solution mss in small amounts 2 wt together with pyrrhotite and pentlandite this pyrite is unexpectedly enriched in ipge as pt and the concentrations of these elements are oscillatory zoned the other pyrite is secondary and formed by alteration of the mss cumulates by late magmatic hydrothermal fluids this pyrite is unzoned and has inherited the low concentrations of ipge and re from the pyrrhotite and pentlandite that it has replaced

geochemistry and textures of gold bearing arsenian pyrite twin creeks nevada implications for deposition of gold in carlin type deposits this study relates morphology size texture and chemistry of arsenian pyrite in the twin creeks carlin type gold deposits to the chemical position and amount of gold that it contains arsenian pyrite is confirmed as the most important gold hosting mineral and four types of gold bearing arsenian pyrite are recognized among these four types the lowest amount of gold and arsenic 1 wt as 17 60 ppm au is contained in arsenian pyrite with relatively large grain sizes 10 30 mu m it formed at relatively high temperatures 250 degrees c and k super h super ratios adularia stable probably relatively slowly the largest amount of gold and arsenic 1 05 2 43 wt as 595 1 465 ppm au is contained in arsenian pyrite with small grain sizes up to 2 mu m that formed at low temperatures 120 degrees 200 degrees c and moderate k super h super ratios illite stable probably by relatively rapid deposition xanes exafs and sims analyses show that gold in arsenian pyrite is both structurally bound au i and in submicroscopic inclusions of free gold au highest amounts of structurally bound gold were observed in the relatively coarse grained arsenian pyrite noted above whereas most inclusions of free gold were observed in fine grained arsenian pyrite in general there is a good correlation between gold and arsenic in arsenian pyrite although au as ratios vary from one pyrite to another it is suggested that gold in arsenian pyrite was deposited by direct deposition of native gold and by adsorption of au i from hydrothermal solutions adsorption of gold by arsenian pyrite can take place from solutions that are not saturated with respect to native gold relative volumes of gold bearing pyrite from different paragenetic stages at twin creeks suggest that as much as 50 percent of the total gold in the deposit could have formed from solutions that were not saturated with respect to native gold because both au and au i are found together in arsenian pyrite it is likely that they were deposited by the same process consideration of possible depositional reactions suggests that a decrease in the activity of reduced sulfur is most likely to cause gold deposition

quantitative mineralogy from infrared spectroscopic data ii three dimensional mineralogical characterization of the rocklea channel iron deposit western australia this study demonstrates how mineralogy generated from spectroscopic visible near and shortwave infrared reflectance data collected using rapid drill core logging systems can be used to build one two and three dimensional models of the architecture of ore systems with applications toward exploration and mining in particular this study examines both spectroscopic and traditional mining data laboratory geochemistry and field geologist logging from 180 drill holes through the rocklea channel iron deposit in the hamersley region of western australia valuable infrared reflectance spectroscopy based mineralogy includes the types and abundances of iron oxyhydr oxides hematite vitreous goethite and ochreous goethite clays well and poorly ordered kaolin al and fe smectite and carbonates calcite and dolomite algorithms to determine the abundance and composition of these minerals from infrared reflectance spectra were validated in an associated study by haest et al 2012 and were found to be accurate e g root mean square error rmse for fe oxyhydr oxide abundance prediction of 9 1 wt fe petrographic analysis and validated infrared reflectance spectroscopy based mineralogy constrained the stratigraphy in the paleochannel and the paragenetic history of each horizon the rocklea channel iron deposit developed over weathered basalt and metasedimentary rocks with an internal channel stratigraphy dominated from bottom to top by the following 1 well ordered in situ kaolinite and a partially denaturated channel iron deposit 2 poorly ordered transported kaolinite 3 ochreous goethite with scarce ooidal textures no clays and late stage vitreous goethite silica replacement 4 mostly poorly ordered kaolinite and 5 calcrete with associated fe smectite the mineral paragenesis of the rocklea deposit was compared against current models for channel iron deposit formation a key finding is the relationship between parent rock composition superimposed regolith cover and channel iron deposit ore quality which are linked through ground water interactions and the physicochemistries of both the parent rock and the deposit this has implications for both exploration and ore deposit characterization 1 ore grade channel iron deposits can develop several kilometers downstream 50 km in this case from the proposed source rock areas above mafic volcanics and metasediments 2 vitreous goethite calcrete al and fe smectite cover the rocklea deposit and are proposed as potential vectors to channel iron deposit mineralization at depth 3 improved mineralogy from hyperspectral data in terms of iron oxyhydr oxide and clay content composition can improve iron ore resource delineation iron ore processing separation of vitreous and ochreous goethite and pit design differentiating swelling smectite requiring pit walls with lower slopes from kaolin or white mica

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

chromite in komatiites 3d morphologies with implications for crystallization mechanisms high resolution x ray computed tomography has been carried out on a suite of komatiite samples representing a range of volcanic facies chromite contents and degrees of alteration and metamorphism to reveal the wide range of sizes shapes and degrees of clustering that chromite grains display as a function of cooling history dendrites are spectacularly skeletal chromite grains formed during very rapid crystallization of supercooled melt in spinifex zones close to flow tops at slower cooling rates in the interiors of thick flows chromite forms predominantly euhedral grains large clusters up to a dozen of grains are characteristic of liquidus chromite whereas fine dustings of mostly individual 20 m grains form by in situ crystallization from trapped intercumulus liquid chromite in coarse grained olivine cumulates from komatiitic dunite bodies occurs in two forms as clusters or chains of euhedral crystals developing into chicken wire texture where chromite is present in supra cotectic proportions and as strongly dendritic semi poikilitic grains these dendritic grains are likely to have formed by rapid crescumulate growth from magma that was close to its liquidus temperature but supersaturated with chromite in some cases this process seems to have been favoured by nucleation of chromite on the margins of sulphide liquid blebs this texture is a good evidence for the predominantly cumulus origin of oikocrysts and in situ origin of heteradcumulate textures our 3d textural analysis confirms that the morphology of chromite crystals is a distinctive indicator of crystallization environment even in highly altered rocks

the significance of intergranular diffusion to the mechanisms and kinetics of porphyroblast crystallization the spatial disposition compositional zoning profiles and size distributions of garnet crystals in 11 specimens of pelitic schist from the picuris range of new mexico usa demonstrate that the kinetics of intergranular diffusion controlled the nucleation and growth mechanisms of porphyroblasts in these rocks an ordered disposition of garnet centers and a significant correlation between crystal radius and near neighbor distances manifest suppressed nucleation of new crystals in diffusionally depleted zones surrounding pre existing crystals compositional zoning profiles require diffusionally controlled growth the rate of which increases exponentially as temperature increases with time an acceleration factor for growth rate can be estimated from a comparison of compositional profiles for crystals of different sizes in each specimen crystal size distributions are interpreted as the result of nucleation rates that accelerate exponentially with increasing temperature early in the crystallization process but decline in the later stages because of suppression effects in the vicinity of earlier formed nuclei simulations of porphyroblast crystallization based upon thermally accelerated diffusionally influenced nucleation kinetics and diffusionally controlled growth kinetics quantitatively replicate textural relations in the rocks the simulations employ only two variable parameters which are evaluated by fitting of crystal size distributions both have physical significance the first is an acceleration factor for nucleation with a magnitude reflecting the prograde increase during the nucleation interval of the chemical affinity for the reaction in undepleted regions of the rock the second is a measure of the relative sizes of the porphyroblast and the diffusionally depleted zone surrounding it crystal size distributions for the picuris range garnets correspond very closely to those in the literature from a variety of other localities for garnet and other minerals the same kinetic model accounts quantitatively for crystal size distributions of porphyroblastic garnet phlogopite sphene and pyroxene in rocks from both regional and contact metamorphic occurrences these commonalities indicate that intergranular diffusion may be the dominant kinetic factor in the crystallization of porphyroblasts in a wide variety of metamorphic environments

quantified multi scale x ray fluorescence element mapping using the maia detector array application to mineral deposit studies the maia large solid angle detector array and imaging system is capable of collecting high resolution images of up to 100 m pixels in size with dwell times of less than 0 2 ms per pixel and thus it is possible to document variation in textures associated with trace element chemistry by collecting quantified elemental maps of geological samples on the scale of entire thin sections in a short time frame 6 8 hr the analysis is nondestructive and allows variation to be recognised on a centimetre scale while also recognising zonations at the micron scale

deformation mechanisms and phase distribution in mafic high temperature mylonites from the jotun nappe southern norway abstract shear zones and mylonites in anorthositic to gabbroic rocks from the jotun nappe in southern norway have been studied as an example of high temperature deformation in polyphase rocks the deformation has taken place at approximately 700 c and maximum confining pressures of 900 mpa the constituent phases amphibole pyroxene and plagioclase have recrystallized synkinematically reducing the grain size of the rock to about 20 to 70 m two different microstructures develop depending on the recrystallization mechanism dynamic recrystallization of plagioclase hornblende and pyroxenes produces monophase layers which extend from porphyroclasts heterogeneous nucleation of phases due to chemical disequilibrium produces phase mixtures of hornblende and plagioclase or clinopyroxene and plagioclase these phase mixtures extend from hornblende or clinopyroxene porphyroclasts the product of the deformation and simultaneous recrystallization is a well laminated microstructure of some monophase hornblende pyroxene and plagioclase layers which alternate with abundant layers of phase mixtures different deformation mechanisms operate in the different types of microstructures dislocation substructures dynamic recrystallization microstructures and a crystallographic preferred orientation measured by ji and mainprice 1988 on samples of the same shear zone indicate crystal plastic deformation in monophase plagioclase layers dynamic recrystallization in monophase hornblende layers indicates also crystal plastic deformation the phase distribution of plagioclase and hornblende grain shapes and lower dislocation densities in the phase mixtures suggest that the deformation mechanism is not crystal plasticity but rather a granular flow grain boundary sliding probably accommodated by diffusional mass transfer in the plagioclase hornblende mixtures the phases show an anticlustered non random distribution grain boundary sliding may contribute to phase mixing but cannot be the main reason for the anticlustering of phases and the complete phase mixing directly at the boundaries of the porphyroclasts the reason for the anticlustered distribution is not clear but could be explained by preferential heterogeneous nucleation of hornblende at plagioclase grain boundaries

quantified whole section trace element mapping of carbonaceous chondrites by synchrotron x ray fluorescence microscopy 1 cv meteorites abstract we present the application of a new synchrotron based technique for rapid mapping of trace element distributions across large areas of the cv3 meteorites allende and vigarano this technique utilizes the australian synchrotron x ray fluorescence microscopy xfm beam line with its custom designed and built x ray detector array called maia xfm with maia allows data to be collected using a 2 m spot size at very low dwell times 0 1 0 5 ms resulting in maps of entire thin sections in 5 h maia is an energy dispersive detector system with a large collection solid angle which allows full spectral acquisition and high sensitivity hence there is no need to constrain the elements of interest a priori we collected whole section maps 2 cm 1 cm from 3 thick sections of allende and a single map 2 cm 1 5 cm from a thick section of vigarano our experimental conditions provide data for elements with 20 z 40 k shell ca through zr and the l emissions of os ir pt au and pb we illustrate the unique capabilities of this technique by presenting observations across myriad length scales from the centimeter scale down to the detection of sub micrometer particles within these objects our initial results show the potential of this technique to help decipher spatial and textural variations in trace element chemistry between cais chondrules matrix and other chondritic components we also illustrate how these datasets can be applied to understanding both nebular and parent body processes within meteorites

trophic regions of a hydrothermal plume dispersing away from an ultramafic hosted vent system von damm vent site mid cayman rise 1 deep sea ultramafic hosted vent systems have the potential to provide large amounts of metabolic energy to both autotrophic and heterotrophic microorganisms in their dispersing hydrothermal plumes such vent systems release large quantities of hydrogen and methane to the water column both of which can be exploited by autotrophic microorganisms carbon cycling in these hydrothermal plumes may therefore have an important influence on open ocean biogeochemistry in this study we investigated an ultramafic hosted system on the mid cayman rise emitting metal poor and hydrogen sulfide methane and hydrogen rich hydrothermal fluids total organic carbon concentrations in the plume ranged between 42 1 and 51 1 m background 43 2 0 7 m n 5 and near field plume samples with elevated methane concentrations imply the presence of chemoautotrophic primary production and in particular methanotrophy in parts of the plume characterized by persistent potential temperature anomalies but lacking elevated methane concentrations we found elevated organic carbon concentrations of up to 51 1 m most likely resulting from the presence of heterotrophic communities their extracellular products and vent larvae elevated carbon concentrations up to 47 4 m were detected even in far field plume samples within the von damm hydrothermal plume we have used our data to hypothesize a microbial food web in which chemoautotrophy supports a heterotrophic community of microorganisms such an active microbial food web would provide a source of labile organic carbon to the deep ocean that should be considered in any future studies evaluating sources and sinks of carbon from hydrothermal venting to the deep ocean

high resolution x ray computed tomography and its application to ore deposits from data acquisition to quantitative three dimensional measurements with case studies from ni cu pge deposits high resolution x ray computed tomography hrxct is a nondestructive technique that allows exploration of the three dimensional distribution of minerals and pore space in natural and synthetic rock samples recent technological developments allow the characterization of samples up to few centimeters in diameter at a resolution down to 0 7 m this combined with the development of dedicated workflows algorithms and softwares is opening new doors for the quantitative three dimensional characterization of ores at the sample scale when combined with three dimensional image analysis hrxct provides quantitative three dimensional mineralogical and textural measurements volume shape three dimensional relationship that are impossible to assess accurately by any other method this manuscript describes the principles of hrxct and presents dedicated methodologies from data acquisition throught to quantitative three dimensional measurements these methodologies are applied to ni cu pge ore samples but are suitable for a range of geologic materials the combination of hrxct with quantitative three dimensional image analysis applied to geologic materials hosting ore deposits provides a better understanding of ore mineralogy ore forming processes and parameters required for mineral or metallurgical processing with benefit for both academic studies and mineral industry applications

natural gold nanoparticles abstract the nanoparticulate gold component in ore deposits and exploration samples is yet to be fully realised but new methods of characterisation and analysis access to high grade gold samples and a strong focus on au nanoparticles in the manufacturing sector provide a new impetus to quantify its significance in geology nanoparticles are increasingly recognised as a fundamental step in geochemical reactions a critical component in weathering processes in biomineralisation and metal migration in ore systems the nanoparticulate population of au is a significant factor in the formation of economic deposits as a refractory component locked up in sulphides in secondary supergene enrichments the formation of surface geochemical anomalies and in the formation of high grade accumulations a better understanding and characterisation of this nanoparticulate gold could unlock hidden resources in known deposits through easier beneficiation and processing but also assist in the discovery of new deposits through advanced exploration methods

mechanisms of dynamic recrystallization in naturally deformed dolomite inferred from ebsp analyses abstract in order to investigate the mechanisms of dynamic recrystallization in dolomite single grain orientation measurements on a mantled porphyroclast have been carried out by means of electron back scattered patterns ebsps the local orientations in the grain fabric were analysed to establish meaningful orientation families in addition to a twinned grain the porphyroclast consists of two domains each with a specific orientation pattern both domains are polygonized by subgrain rotation which gives great and small circle dispersion patterns of the crystal orientation data in the pole figures however even the simple and well defined dispersion patterns for which one can assume a single slip system are not consistent with any of the theoretical dispersion patterns of the known slip systems additional mechanisms like rigid body rotation nucleation and or combinations of different slip systems are the likely explanation no definitive orientation relationship has been found between the porphyroclast and the mantle the lack of such a relationship together with the shape of the grain boundary point to grain boundary migration the texture of the mantle agrees with the global texture of the sample indicating that mechanisms of crystal plasticity were active during flow around the clast the results demonstrate the potential of ebsp data for the deduction of active mechanisms but a proper interpretation requires a better theoretical foundation this could be achieved by modelling dispersion patterns for different mechanisms and different combinations and by including orientation correlations

geometallurgy of the pebble porphyry copper gold molybdenum deposit alaska implications for gold distribution and paragenesis the pebble cu au mo deposit in southwest alaska is one of the world s largest porphyry deposits the deposit contains over 80 billion pounds blbs cu 107 million ounces moz au and 5 6 blbs mo in all resource categories copper and gold grades vary across diverse hydrothermal alteration assemblages with higher grades associated with sericite and pyrophyllite rich assemblages in an advanced argillic alteration zone moderate grades are associated with the potassic and sodic potassic alteration assemblages that dominate the deposit and low grades are found in quartz illite pyrite assemblages these variations reflect fluctuations in both the temperature and composition of the magmatic hydrothermal fluids in time and space qemscan scanning electron microscope based mineral mapping and in situ laser ablation inductively coupled plasmamass spectrometry methods designed to document the spatial and temporal variations in metal deportment across alteration zones show that gold occurs as inclusions of electrum and high fineness gold in chalcopyrite and pyrite and as free grains hosted by silicate minerals with the proportion of each related to the principal host alteration assemblage gold associated with the earliest high temperature sodic potassic and potassic assemblages occurs as electrum inclusions in chalcopyrite and to a lesser extent pyrite and pyrite trace element signatures have high gold silver and copper concentrations pyrite 1 during cooling of the hydrothermal system lower temperature illite and illite kaolinite alteration overprinted the earlier assemblages with varying degrees of recrystallization and precipitation of more pyrite rich assemblages with pyrite having a gold poor trace element composition pyrite 2 gold released during recrystallization formed high fineness gold inclusions in newly formed pyrite and narrow gold rich pyrite rims pyrite 3 a second magmatic hydrothermal event resulted in a sericite and pyrophyllite rich advanced argillic overprint which introduced more copper and gold to the system and recrystallized preexisting sulfides into both high and low sulfidation assemblages with high fineness gold inclusions in pyrite and chalcopyrite and solid solution gold in bornite a second generation of pyrite 1 with elevated palladium concentrations is associated with this hydrothermal fluid pulse and also possibly high arsenic pyrite pyrite 4 understanding the controls on gold deportment provides genetic constraints on ore deposit genesis alteration and sulfide assemblages and gold compositions provide information on the hydrothermal fluid compositions ph and temperature evolution of the magmatic hydrothermal system the presence of electrum inclusions in chalcopyrite and pyrite in potassic and sodic potassic alteration is consistent with these zones forming from early high temperature magmatic fluids because both gold and silver are transported together in such fluids high fineness gold inclusions in younger pyrite related to low temperature clay alteration are evidence that the gold in early electrum was partially remobilized and reprecipitated the low temperature clay alteration most likely formed from a mixture of h2s rich vapor with meteoric waters conditions where gold is transported as a bisulfide complex and silver is not resulting in the separation of the two metals a second structurally controlled pulse of magmatic fluids formed a well mineralized advanced argillic alteration assemblage containing high fineness gold inclusions in chalcopyrite and pyrite the only part of the deposit where high fineness gold is hosted by chalcopyrite in the pyrophyllite stability field acidic fluid compositions transport gold and silver as different complexes and gold solubility is significantly lower than silver leading to the precipitation of highfineness gold inclusions palladium is transported by the same complex as gold under these conditions consistent with the elevated palladium content of pyrite in the advanced argillic alteration assemblage the temporal and spatial studies of variations in gold deportment across the pebble deposit provide critical inputs to optimization of mineral processing design the greatest influence on metallurgical gold recovery at pebble is the proportion of gold that is hosted by pyrite pyrite hosted gold may require different mineral processing methodologies compared with gold hosted by chalcopyrite therefore defining domains of consistent hydrothermal alteration and sulfide mineralogy and gold deportment is the key to the geometallurgical characterization of the deposit

first results on the lpo derived seismic properties of iron ores from the quadrilatero ferrifero region southeastern brazil abstract determinations of the lpo derived seismic properties of iron ores were carried out in five samples with contrasting mineralogy hematite magnetite and quartz and deformed in different conditions all the samples are seismically quasi isotropic or weakly anisotropic which reflect i an absent or weak crystallographic preferred orientation cpo in some samples ii the high modal content of magnetite iii the relatively weak anisotropy of elastic stiffness of hematite single crystal such variables induce a low anisotropic seismic behavior even in high strained iron ores with strong preferred orientation of hematite a plane of seismic transversal isotropy parallel to the foliation of the aggregates is developed in hematite magnetite aggregates and in itabirites with strong cpo of hematites in these high strained aggregates some relationships between the crystallographic axes of hematite and the propagation velocities can be observed the magnitudes of p and s wave velocities derived of hematite cpo are lower than the values experimentally determined in iron ores such a difference probably reflects other microstructural variable which were not taken into account in the present contribution e g shape preferred orientation

surface transformations of platinum grains from fifield new south wales australia a growing literature is demonstrating that platinum pt is transformed under surface conditions yet bio geochemical processes at the nugget soil solution interface are incompletely understood the reactivity of pt exposed to earth surface weathering conditions highlighted by this study may improve our ability to track its movement in natural systems e g focusing on nanoparticles as a strategy for searching for new undiscovered sources of this precious metal to study dissolution re precipitation processes of pt and associated elements grains of pt fe alloy were collected from a soil placer deposit at the fifield pt field australia optical and electron microscopy revealed morphologies indicative of physical transport as well as chemical weathering dissolution pits cavities striations colloidal nano particles and aggregates of secondary pt platelets as well as acicular iron fe hydroxide coatings were observed fib sem ebsd combined with s m xrf of a sectioned grain showed a fine layer of up to 5 mm thick composed of refined aggregates of 0 2 to 2 mm sized crystalline secondary pt overlying more coarsely crystalline pt fe alloy of primary magmatic origin these results confirm that pt is affected by geochemical transformations in supergene environments structural and chemical signatures of grains surfaces rims and cores are linked to the grains primary and secondary trans formational histories and pt mobility can occur under earth surface conditions intuitively this nanophase pt can disperse much further from primary sources of ore than previously thought this considerable mineral reactivity demonstrates that the formation and or release of pt nanoparticles needs to be measured and incorporated into exploration geochemistry programs

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

platinum group element gold silver and base metal distribution in compositionally zoned sulfide droplets from the medvezky creek mine noril sk russia concentrations of ag au cd co re zn and platinum group elements pge have been determined in sulfide minerals from zoned sulfide droplets of the noril sk 1 medvezky creek mine the aims of the study were to establish whether these elements are located in the major sulfide minerals pentlandite pyrrhotite chalcopyrite and cubanite to establish whether the elements show a preference for a particular sulfide mineral and to investigate the model which suggests that the zonation in the droplets is caused by the crystal fractionation of monosulfide solid solution mss nickel cu ag re os ir ru rh and pd were found to be largely located in the major sulfide minerals in contrast less than 25 of the au cd pt and zn in the rock was found to be present in these sulfides osmium ir ru rh and re were found to be concentrated in pyrrhotite and pentlandite palladium and co was found to be concentrated in pentlandite silver cd and zn concentrations are highest in chalcopyrite and cubanite gold and platinum showed no preference for any of the major sulfide minerals the enrichment of os ir ru rh and re in pyrrhotite and pentlandite exsolution products of mss and the low levels of these elements in the cubanite and chalcopyrite exsolution products of intermediate solid solution iss support the mss crystal fractionation model because os ir ru rh and re are compatible with mss the enrichment of ag cd and zn in chalcopyrite and cubanite also supports the mss fractionation model these minerals are derived from the fractionated liquid and these elements are incompatible with mss and thus should be enriched in the fractionated liquid gold and pt do not partition into either iss or mss and become sufficiently enriched in the final fractionated liquid to crystallize among the iss and mss grains as tellurides bismithides and alloys during pentlandite exsolution pd appears to have diffused from the cu rich portion of the droplet into pentlandite

hydrodynamic and geomorphological controls on surface sedimentation at the subtropical shelf front brazil malvinas confluence transition off uruguay southwestern atlantic continental margin abstract the hydrology of the southwestern atlantic margin is dominated by the confluence of water masses with contrasting thermohaline properties generating a frontal zone that extends from the brazil malvinas confluence zone bmc in the open ocean to the subtropical shelf front stsf on the continental shelf however the hydrodynamics of the transition between these hydrographic features is still not fully understood high resolution morphological multibeam and hydrological ctd data were integrated with sedimentological data textural and productivity proxies in order to develop a sound framework to understand surface sedimentation of the slope extension of the stsf subsurface outer shelf and upper slope and of the bmc intermediate level middle slope on the uruguayan continental margin 34 to 36 s since the detailed morphology of the study area is presented for the first time related geological processes are briefly discussed on the outer shelf and upper slope and north of the stsf the current direction of erosive mound scarps indicates the dominance of the southward flowing brazil current bc this suggests a northernmost boundary for the distribution of the stsf a strong flux of the bc favored by a steeper slope as well as by the occurrence of canyons incised on the upper slope is evidenced by the occurrence of coarser sediments and low values of productivity proxies but also by the presence of deep sea coral reefs southwards the effect of a less energetic malvinas current mc and the highly productive stsf is indicated by the deposition of fine sediments with high organic matter content as well as by the absence of deep sea coral reefs this depositional scenario is enhanced by a smooth slope and the occurrence of canyons incised deeper in the middle slope off shelf sediment transport along the stsf is inferred by the similar texture registered between the outer shelf and shallow upper slope the occurrence of biogenic shelly reworked sands and gravel and by the observed decrease in grain size with depth glacial iceberg transport northwards and or gravity processes are suggested by the occurrence of igneous metamorphic gravel in lag deposits on the upper slope on the middle slope the northernmost influence of the erosive antarctic intermediate water is evidenced by the vanishing of morphologic contouritic structures this is also imprinted in a pronounced northward fining in grain size this contribution increase our understanding of this highly dynamic and complex area providing the first detailed analysis of the regional sediment patterns and oceanographic and morphological controls on surface sedimentation

characterisation and 3d modelling of a nuggety vein hosted gold ore body sunrise dam western australia abstract in high nugget gold ore bodies samples taken from drill core for gold assay are typically too small to allow for the extreme spatial variability in grade and are a poor representation of the underlying distribution of mineralisation the gq north lode at the sunrise dam gold mine in western australia is a good example of an orebody which has a very strong nugget effect coefficient of variation 20 and that has proved very problematic to model gold is hosted in vein stockworks and shear zones and although there is a clear spatial relationship between mineralisation and alteration high vein density and well developed foliations the relationship is best defined statistically because the association between high gold grades and various combinations of these features is non trivial we present a method for automating the inclusion of geological data proxies for gold mineralisation into the prediction of mineralised rocks using conditional probability the method uses the gold assays and the logged geological data to calculate the probability that rocks with particular geological features will be mineralised the ore body can then be modelled automatically using interpolation software with isosurfaces indicating the regions with highest probability of gold mineralisation a good understanding of the geological features associated with mineralisation and consistent geological logging are important prerequisites for successful conditional probability modelling of drill hole data

titaniq a titanium in quartz geothermometer titanium is one of many trace elements to substitute for silicon in the mineral quartz here we describe the temperature dependence of that substitution in the form of a new geothermometer to calibrate the titaniq thermometer we synthesized quartz in the presence of rutile and either aqueous fluid or hydrous silicate melt at temperatures ranging from 600 to 1 000 c at 1 0 gpa the ti contents of quartz in ppm by weight from 13 experiments increase exponentially with reciprocal t as described by text log left x text qtz text ti right 5 69 pm 0 02 frac 3765 pm 24 t k application of this thermometer is straightforward typically requiring analysis of only one phase quartz this can be accomplished either by epma for crystallization temperatures above 600 c or by sims for temperatures down to at least 400 resulting temperature estimates are very precise usually better than 5 c potentially allowing detailed characterization of thermal histories within individual quartz grains although calibrated for quartz crystallized in the presence of rutile the thermometer can also be applied to rutile absent systems if tio2 activity is constrained

pt and pd mobility in hydrothermal fluids evidence from komatiites and from thermodynamic modelling abstract komatiite host rocks and ores provide a natural laboratory for the study of pt and pd during hydration and carbonation of ultramafic rocks the degree of correlation between pt and pd and of those elements with lithophile elements such as ti in komatiitic rocks and ores is strongly dependent on the magmatic sulfide content of the rock pt and pd are typically very strongly correlated within s poor komatiites and in disseminated ores containing 5 volume or less magmatic sulfides in contrast they are almost completely decoupled in sulfide rich ore samples thermodynamic modelling based on the existing body of published experimental data on pt and pd solubilities suggests that pd and pt can be readily transported as bisulfide complexes in acidic neutral solutions under reduced and moderate oxidation condition at 300 c and chloride complexes are only important under extremely acidic oxidised conditions pd is much more soluble than pt in the case of fluids in sulfide rich environments in equilibrium with the characteristic assemblages found within altered and metamorphosed komatiites solubilities of both elements are much lower in sulfide poor environments especially where ph values are constrained to neutral values by the near ubiquitous presence of carbonate minerals in the alteration assemblage this accounts for the evident near immobility of pt and pd in even the most altered silicate host rocks as compared with their wide dispersion in sulfide rich ores

mixed messages in iron oxide copper gold systems of the cloncurry district australia insights from pixe analysis of halogens and copper in fluid inclusions proterozoic rocks of the cloncurry district in nw queensland australia are host to giant tens to hundreds of square kilometers hydrothermal systems that include 1 barren regional sodic calcic alteration 2 granite hosted hydrothermal complexes with magmatic hydrothermal transition features and 3 iron oxide copper gold iocg deposits fluid inclusion microthermometry and proton induced x ray emission pixe show that iocg deposits and the granite hosted hydrothermal complexes contain abundant high temperature ultrasaline complex multisolid type 1 inclusions that are less common in the regional sodic calcic alteration the latter is characterized by lower salinity three phase halite bearing type 2 and two phase type 3 aqueous inclusions copper contents of the type 1 inclusions 300 ppm is higher than in type 2 and 3 inclusions 1 000 ppm are found both in the granite hosted systems and in inclusions with br cl ratios that are consistent with a magmatic source the br cl ratios of the inclusions with lower cu contents are consistent with an evaporite related origin wide ranges in salinity and homogenization temperatures for fluid inclusions in iocg deposits and evidence for multiple fluid sources as suggested by halogen ratios indicate fluid mixing as an important process in iocg genesis the data support both leaching of cu by voluminous nonmagmatic fluids from crustal rocks as well as the direct exsolution of cu rich fluids from magmas however larger iocg deposits may form from magmatic derived fluids based on their higher cu content

reaction mechanism for the replacement of calcite by dolomite and siderite implications for geochemistry microstructure and porosity evolution during hydrothermal mineralisation carbonate reactions are common in mineral deposits due to co2 rich mineralising fluids this study presents the first in depth integrated analysis of microstructure and microchemistry of fluid mediated carbonate reaction textures at hydrothermal conditions in doing so we describe the mechanisms by which carbonate phases replace one another and the implications for the evolution of geochemistry rock microstructures and porosity the sample from the 1 95 moz junction gold deposit western australia contains calcite derived from carbonation of a metamorphic amphibole plagioclase assemblage that has further altered to siderite and dolomite the calcite is porous and contains iron rich calcite blebs interpreted to have resulted from fluid mediated replacement of compositionally heterogeneous amphiboles the siderite is polycrystalline but nucleates topotactically on the calcite as a result the boundaries between adjacent grains are low angle boundaries 10 which are geometrically similar to those formed by crystal plastic deformation and recovery growth zoning within individual siderite grains shows that the low angle boundaries are growth features and not due to deformation low angle boundaries develop due to the propagation of defects at grain faces and zone boundaries and by impingement of grains that nucleated with small misorientations relative to each other during grain growth the cores of siderite grains are aligned with the twin planes in the parent calcite crystal showing that the reactant fe entered the crystal along the twin boundaries dolomite grains many of which appear to in fill space generated by the siderite replacement also show alignment of cores along the calcite twin planes suggesting that they did not grow into space but replaced the calcite where dolomite is seen directly replacing calcite it nucleates on the fe rich calcite due to the increased compatibility of the fe bearing calcite lattice relative to the pure calcite both reactions are interpreted as fluid mediated replacement reactions which use the crystallography and elemental chemistry of the calcite experiments of fluid mediated replacement reactions show that they proceed much faster than diffusion based reactions this is important when considering the rates of reactions relative to fluid flow in mineralising systems

relationship between microstructures and grain scale trace element distribution in komatiite hosted magmatic sulphide ores komatiite hosted nickel sulphides from the yilgarn craton australia consist of two main sulphide phases pyrrhotite fe7s8 and pentlandite fe ni 9s8 two minor sulphide phases chalcopyrite cufes2 and pyrite fes2 and trace arsenides samples of massive sulphides from three deposits with diverse deformation and metamorphic histories the silver swan perseverance and flying fox deposits have been studied by electron backscatter diffraction and laser ablation inductively coupled plasma mass spectrometry and nano scale secondary ion mass spectrometry these ore bodies were selected to investigate the relationship between microstructures and mineral trace element chemistry in three dominant sulphide species in each deposit in all three samples pyrrhotite preserves a strong evidence of crystal plasticity relative to both pentlandite and pyrite the trace element composition of pyrrhotite shows significant variation in specific elements pb bi and ag this variation correlates spatially with intragrain pyrrhotite microstructures such as low angle and twin boundaries minor signatures of crystal plasticity in pyrite and pentlandite occur in the form of rare low angle boundaries pentlandite and mild lattice misorientation pyrite trace element compositions of pentlandite and pyrite show no correlation with microstructures variations in pyrrhotite are interpreted as a result of intragrain diffusion during the syn and post deformation history of the deposit intragrain diffusion can occur either due to bulk diffusion dislocation impurity pair diffusion or by pipe diffusion i e along fast diffusion pathways at high and low angle and twin boundaries this contribution examines three different diffusion models and suggests that dislocation impurity pair diffusion and pipe diffusion are the most likely processes behind increased trace element concentration along the microstructures in pyrrhotite the same phenomenon is observed in samples from three different deposits that experienced widely different metamorphic conditions implying that the final disposition of these elements reflects a post peak metamorphic stage of the geological history of all three deposits

la icp ms trace element analysis of pyrite from the chang an gold deposit sanjiang region china implication for ore forming process abstract the chang an gold deposit yunnan province is one of five large gold deposits in the ailaoshan gold belt that is the most important ore belt of the sanjiang tethyan metallogenic domain geochemical study of pyrite in the deposit was conducted using laser ablation inductively coupled plasma mass spectroscopy three types of hydrothermal pyrite were identified in the ores and wall rocks i e the coarse euhedral crystals in syenite py1 the coarse grains disseminated in altered sandstones or sandstone ores py2 and the fine grained euhedral pyrite in sandstone ores py3 their trace elements exhibit different concentrations associations and rim core zoning implying different geneses and crystallization processes the cores of py1 were formed by magmatic fluids and have the lowest concentrations of au as cu and zn the cores of py2 were formed by metamorphic fluids and have relatively high au ag ni pb and cu concentrations the py3 grains and the growth rims of py1 and py2 show consistently high contents of au as pb and co suggesting that all of them were rapidly deposited from a mixing fluid system that was probably composed of fluids of metamorphic and magmatic origins this interpretation is supported by the observation that the high grade ores generally contain lots of py2 and py3 hence we consider that the deposit was formed during india asia collision slightly postdate the 33 35 ma tectono magmatism

arsenopyrite pyrite association in an orogenic gold ore tracing mineralization history from textures and trace elements laser ablation inductively coupled plasma mass spectrometry la icp ms spot analysis and element mapping coupled with high resolution focused ion beam scanning electron microscopy fib sem imaging has been performed on au hosting sulfides from a proterozoic orogenic gold deposit tanami gold province north central australia gold distribution patterns in the arsenopyrite pyrite assemblage which probably crystallized toward the end of the au forming event suggest a process of initial scavenging of au into arsenopyrite and subsequent remobilization of that au following brittle fracture gold expelled from the sulfide lattice during the remobilization event is reconcentrated around the margins of the same arsenopyrite grains and within swarms of crosscutting microfractures the distribution of pb bi and ag closely mimic au indicating that these elements were also reconcentrated preservation of oscillatory zonation patterns for co ni sb se and te in arsenopyrite imply however that no significant degree of sulfide recrystallization took place residual concentrations of invisible gold in grain centers are 5 ppm in arsenopyrite and 1 ppm in coexisting pyrite the presence of submicron sized pores is suggestive of a fluid driven process rather than solid state diffusion micron scale 2 10 m remobilized gold is accompanied by fine particles 200 nm 2 m and nanoparticles 200 nm of gold the extensive variation of au concentrations within single arsenopyrite grains underlines the significance of textures when using trace element data to understand how gold ores evolved

platinum ore in three dimensions insights from high resolution x ray computed tomography platinum group elements referred to as pge comprising pt pd rh ru ir and os are strategic metals with a wide variety of industrial applications most of the world s pge production is mined from large mafic ultramafic intrusions such as the bushveld complex in south africa which currently provides 75 of the world s pt production the pge mineralization is found within distinctive layers tens to hundred of centimeters thick but extending laterally for many tens of kilometers where the pge occur at low parts per million levels as platinum group minerals pgm and in solid solution within disseminated base metal sulfides there is still heated debate at the most fundamental level about the mode of formation of this class of deposit genetic models range from primary magmatic sulfide collection to concentration by migrating halogen rich fluids a crucial line of evidence is the spatial relationship between the pgm which are the most important pge bearing phases and the base metal sulfide aggregates or blebs so far all observations have been carried out using two dimensional mineralogical studies where textural relationships with other minerals are ambiguous and with statistical limitations owing to sampling of trace phases intersecting random surfaces we present the first detailed three dimensional in situ analysis of the pgm at the sample scale using high resolution x ray computed tomography coupled with conventional microscopic and mineralogical study we find a striking and highly consistent relationship of pgm grains with the edges of complex shaped magmatic sulfide blebs and the intersection of these blebs with chromite silicate grain boundaries these new three dimensional observations strongly support an orthomagmatic model coupled with nucleation and growth of pgm at the margins of sulfide liquid droplets

morphology and microstructure of chromite crystals in chromitites from the merensky reef bushveld complex south africa the merensky reef of the bushveld complex consists of two chromitite layers separated by coarse grained melanorite microstructural analysis of the chromitite layers using electron backscatter diffraction analysis ebsd high resolution x ray microtomography and crystal size distribution analyses distinguished two populations of chromite crystals fine grained idiomorphic and large silicate inclusion bearing crystals the lower chromitite layer contains both populations whereas the upper contains only fine idiomorphic grains most of the inclusion bearing chromites have characteristic amoeboidal shapes that have been previously explained as products of sintering of pre existing smaller idiomorphic crystals two possible mechanisms have been proposed for sintering of chromite crystals 1 amalgamation of a cluster of grains with the same original crystallographic orientation and 2 sintering of randomly orientated crystals followed by annealing into a single grain the ebsd data show no evidence for clusters of similarly oriented grains among the idiomorphic population nor for earlier presence of idiomorphic subgrains spatially related to inclusions and therefore are evidence against both of the proposed sintering mechanisms electron backscatter diffraction analysis maps show deformation related misorientations and curved subgrain boundaries within the large amoeboidal crystals and absence of such features in the fine grained population microstructures observed in the lower chromitite layer are interpreted as the result of deformation during compaction of the orthocumulate layers and constitute evidence for the formation of the amoeboid morphologies at an early stage of consolidation an alternative model is proposed whereby silicate inclusions are incorporated during maturation and recrystallisation of initially dendritic chromite crystals formed as a result of supercooling during emplacement of the lower chromite layer against cooler anorthosite during the magma influx that formed the merensky reef the upper chromite layer formed from a subsequent magma influx and hence lacked a mechanism to form dendritic chromite this accounts for the difference between the two layers

geological controls on refractory ore in an orogenic gold deposit macraes mine new zealand the macraes mine is hosted in an orogenic mesothermal gold deposit in metasedimentary rocks of the otago schist belt much gold occurs within altered schist with minimal silica addition and this study focuses on altered schist ore types the unmineralized host schists are chemically and mineralogically uniform in composition but include two end member rock types feldspathic schist and micaceous schist both rock types have undergone hydrothermal alteration along a shallow dipping foliation parallel shear zone but their different rheological properties have affected the style of mineralisation micaceous schist has been extensively recrystallized and hydrothermally altered during ductile deformation to form ores characterized by abundant disseminated millimetre scale pyrite cubes typically 1 2 wt s and minor silicification the earliest pyrite contained ni and or as in solid solution and no gold was imaged in these pyrites or later arsenopyrite grains the ore type is refractory and gold recovery by cyanide leaching is less than 50 with lowest recovery in rocks that have been less affected by later brittle deformation in contrast hydrothermally altered feldspathic schist is characterized by mineralised black microshears and veinlets formed during shear zone related brittle deformation microsheared ore has relatively low sulphur content 0 7 wt and muscovite has been illitised during hydrothermal alteration pyrite and arsenopyrite in microshears are fractured and deformed and contain 1 10 m blebs of gold later pyrite veinlets also contain micron to submicron scale inclusions of sphalerite chalcopyrite galena and gold 10 microns gold in microsheared ore is more readily recoverable than in the refractory ore although encapsulation of the fine gold grains inhibits cyanidation both microsheared ore and disseminated pyritic ore pass laterally into mineralised black shears which contain hydrothermal graphite and late stage cataclastic sulphides this black sheared ore releases gold readily but the gold is then adsorbed on to gangue minerals preg robbed and net cyanidation recovery can be less than 50 hence low gold recovery during cyanidation results from 1 poor liberation of gold encapsulated in microcrystalline quartz and unfractured sulphide grains and 2 preg robbing of liberated gold during cyanidation introduction of pressure oxidation of ore prior to cynidation has mitigated these issues

focussed ion beam transmission electron microscopy applications in ore mineralogy bridging micro and nanoscale observations abstract focussed ion beam scanning electron microscopy fib sem is a relatively new analytical tool that has been little applied to problems of ore genesis the technique enables high resolution cross section imaging and can be used to prepare thinned foils for study by transmission electron microscopy tem fib sem methods applied to sulphides and related compounds represent an in situ approach for sample characterisation and thus provides for crystal chemical data that can be placed into the geological context of a given ore deposit we present four study cases these deal with minor element incorporation and release in zns intergrowths and replacement among cu fe sulphides fabrics in au bearing as free pyrite and symplectites of bi sulphosalts within galena the data is discussed in the context of polytypism and planar defects for minor element incorporation and release superstructure ordering and formation of fine particles 100 2500 nm or nanoparticles

cathodoluminescence properties of quartz eyes from porphyry type deposits implications for the origin of quartz hyperspectral cathodoluminescence cl mapping combined with electron probe microanalysis epma and fourier transform infrared spectroscopy was used for the reconstruction ofcrystallization conditions of quartz from porphyry environments quartz eyes from the two porphyry deposits rio blanco chile and climax u s a were studied three peaks are found to be responsible for the total cl emission 1 93 2 05 and 2 72 ev the first two peaks are assigned to o m with m being an alkali ion and oxygen vacancies respectively the 2 72 ev peak shows a linear correlation with the ti concentration determined by epma point measurements in addition a negative correlation between the 1 93 ev emission and the al concentration was observed quartz grains often form clusters in which adjacent grains show identical cl patterns indicating that they crystallized attached to each other and were not disturbed later quartz cores display sector zoning and enrichment in li oh and sometimes al which points to rapid crystallization from an extremely evolved melt quartz rims show high ti and low li and oh contents indicating crystallization from a less evolved melt either at higher temperatures or at higher titanium activities the al and ti distribution patterns are frequently not correlated and both show uneven distribution indicating fast growth from inhomogeneous melts only ti displays sharp transitions and fine oscillatory zoning which can be explained by the higher mobility of al in the quartz lattice the quartz eyes crystallized after magma emplacement under non equilibrium conditions it is likely that the crystallization occurred from the melt enriched in al li and oh and probably other metals and or volatiles on the brink of fluid exsolution subsequent fluid exsolution brought about disequilibrium to the system resulting in dissolution of quartz and redistribution of elements between the melt and the fluid the oh li and other alkali metals and volatiles partitioned into the fluid whereas ti and al remained in the melt resorption of quartz caused by the fluid exsolution continued until equilibrium was reached again after which crystallization of quartz rims began from the water alkali and volatile poor melt with higher ti activity furthermore accumulation of al and ti in the residual melt led to crystallization of extremely al and ti rich quartz

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

the distribution of platinum group elements pge and other chalcophile elements among sulfides from the creighton ni cu pge sulfide deposit sudbury canada and the origin of palladium in pentlandite concentrations of platinum group elements pge ag as au bi cd co mo pb re sb se sn te and zn have been determined in base metal sulfide bms minerals from the western branch 402 trough orebodies of the creighton ni cu pge sulfide deposit sudbury canada the sulfide assemblage is dominated by pyrrhotite with minor pentlandite chalcopyrite and pyrite and they represent monosulfide solid solution mss cumulates the aim of this study was to establish the distribution of the pge among the bms and platinum group minerals pgm in order to understand better the petrogenesis of the deposit mass balance calculations show that the bms host all of the co and se a significant proportion 40 90 of os pd ru cd sn and zn but very little 35 of the ag au bi ir mo pb pt rh re sb and te osmium and ru are concentrated in equal proportions in pyrrhotite pentlandite and pyrite cobalt and pd 1 ppm are concentrated in pentlandite silver cd sn zn and in rare cases au and te are concentrated in chalcopyrite selenium is present in equal proportions in all three bms iridium rh and pt are present in euhedrally zoned pge sulfarsenides which comprise irarsite irass hollingworthite rhass pge ni rich cobaltite coass and subordinate sperrylite ptas2 all of which are hosted predominantly in pyrrhotite and pentlandite silver au bi mo pb re sb and te are found predominantly in discrete accessory minerals such as electrum au ag alloy hessite ag2te michenerite pdbite and rhenium sulfides the enrichment of os ru ni and co in pyrrhotite pentlandite and pyrite and ag au cd sn te and zn in chalcopyrite can be explained by fractional crystallization of mss from a sulfide liquid followed by exsolution of the sulfides the early crystallization of the pge sulfarsenides from the sulfide melt depleted the mss in ir and rh the bulk of pd in pentlandite cannot be explained by sulfide fractionation alone because pd should have partitioned into the residual cu rich liquid and be in chalcopyrite or in pgm around chalcopyrite the variation of pd among different pentlandite textures provides evidence that pd diffuses into pentlandite during its exsolution from mss the source of pd was from the small quantity of pd that partitioned originally into the mss and a larger quantity of pd in the nearby cu rich portion intermediate solid solution and or pd bearing pgm the source of pd became depleted during the diffusion process thus later forming pentlandite rims of coarse granular veinlets and exsolution flames contains less pd than early forming pentlandite cores of coarse granular

new constraints on the origin of the skaergaard intrusion cu pd au mineralization insights from high resolution x ray computed tomography abstract this contribution presents the first detailed three dimensional 3d in situ analysis of samples from the platinova reef using high resolution x ray computed tomography hrxct and 3d image processing and quantification coupled with microscopic and mineralogical investigations our hrxct analyses reveal the complex textural relationships between cu rich sulfides bulk composition close to bornite skaergaardite pdcu au rich phases silicates and fe ti oxides and provide unequivocal textural evidences not observed previously the association in 3d between cu rich sulfide globules pdcu alloy and ilmenite is inconsistent with a hydrothermal origin of the cu pd mineralization in contrast our results combined with phase diagrams strongly support a primary magmatic origin for the cu pd mineralization where cu and pd rich fe poor sulfide liquid represents a cumulus phase that forms by in situ nucleation these sulfide droplets and attached skaergaardite grains were trapped during the formation and crystallization of the fe ti oxides subsequent post cumulus processes led to the partial to total dissolution of the sulfide not entirely enclosed by the fe ti oxides i e not protected from reaction leading to the observed variability in cu and pd composition at the aggregate sulfide pdcu scale and to the occurrence of free pdcu alloys in contrast to the pdcu alloy gold bearing minerals are never observed entirely enclosed within the fe ti oxide two hypotheses can be envisaged for the formation of the gold enriched layer in the upper part of the section gold may have either precipitated from high temperature late magmatic cl rich fluids alternatively gold may have been enriched during fractional crystallization after sulfide had been suppressed from the liquidus after the pd layer crystallized and then deposited along redox barriers

high resolution x ray computed tomography studies of grasberg porphyry cu au ores papua indonesia high resolution x ray computed tomography hrxct provides unique information of the geological and metallurgical significance for gold and related ore minerals in the supergiant grasberg porphyry cu au deposit digital radiographs have proved to be an effective means of screening samples for the presence of gold for hrxct studies digital radiograph effectiveness is limited by the thickness of samples typically to 2 cm as well as the associated minerals thus preselecting samples for gold studies using hrxct is most effective using digital radiographs combined with assay information differentiating between metallic mineral grains with relatively small differences in density e g bornite 5 1 g cm3 from chalcopyrite 4 2 g cm3 is relatively straightforward for isolated monominerallic grains or composites in a similar lower density matrix but difficulties are encountered with the interpretation of typical intergrown ore minerals x ray beam hardening artifacts lead to inconsistency in attenuation determination both within and among slice images complicating quantitative processing however differentiation of chalcopyrite and bornite has been successful in smaller diameter 22 mm cores of grasberg ores small diameter 10 mm cores of the grasberg stockwork cu au ore were analyzed using hrxct methods scanned at the minimum spacing currently available 7 5 m and data reduction protocols using the blob3d program were modified to improve the quantification of grain sizes and shapes grains as small as 6 5 m have been identified all of these grains are in direct contact with chalcopyrite providing support for gold distribution in porphyry copper systems being a result of exsolution from copper sulfides hrxct scanning digital radiography precisely defines the in situ location of mineral grains of interest within a sample which then can be studied in conventional petrographic sections and other types of analytical studies conducted e g gold trace element geochemistry

reconstruction of an extensive archaean dacitic submarine volcanic complex associated with the komatiite hosted mt keith nickel deposit agnew wiluna greenstone belt yilgarn craton western australia abstract felsic volcanic rock units characterise a large portion of the 2 7 ga agnew wiluna greenstone belt western australia stratigraphy and form the hangingwall and footwall sequences to several komatiite hosted nickel sulphide deposits in the region the mt keith region of the agnew wiluna greenstone belt awb comprises a sequence of felsic mafic and ultramafic extrusive and intrusive units the felsic volcanic dominated footwall and hangingwall sequences to the mt keith nickel deposit comprise cyclical packages of coherent dacite lavas with associated monomictic in situ to resedimented breccias clasts in the monomictic breccia facies are identical to the coherent dacite and the two facies are often in gradational contact the dacites are interpreted as submarine lavas and the breccias as associated autoclastic facies hyaloclastite autobreccia these dacite lavas are inferred to have been emplaced into a deep water environment which retarded volatile exsolution suppressing explosive fragmentation and increasing lava mobility resulting in large tabular flow units the awb sequence has undergone multiple periods of deformation and metamorphism subsequent to emplacement resulting in strain and alteration in large sections of the coherent lava facies a notable textural variant within the lavas is a set of pseudo textures structures resembling tuffaceous and brecciated dacitic units the process of pseudo clastic texture structure generation is related to a combination of polyphase alteration brecciation and development of a secondary structural metamorphic layering understanding the origin of these pseudo clastic textures structures has allowed recognition of the lateral and vertical facies variation of the felsic sequence and reconstruction of the original volcanic architecture

distribution of platinum group elements in the platreef at overysel northern bushveld complex a combined pgm and la icp ms study detailed mineralogical and laser ablation inductively coupled plasma mass spectrometry studies have revealed the physical manifestation of the platinum group elements pge within the platreef at overysel northern bushveld complex south africa the pge in the platreef were originally concentrated in an immiscible sulfide liquid along with semi metals such as bi and te as the sulfide liquid began to crystallize virtually all the os ir ru and rh partitioned into monosulfide solid solution mss which on further cooling exsolved to form pyrrhotite and pentlandite with os ir and ru remaining in solid solution in both phases with rh prefentially partitioning into pentlandite platinum some pd and au were concentrated in the residual sulfide liquid after mss crystallization and were then concentrated in an immiscible late stage melt along with semi metals which was expelled to the grain boundaries during crystallization of intermediate solid solution iss to form pt and pd tellurides and electrum around the margins of the sulfide grains tiny droplets of this melt trapped in the crystallizing mss and iss cooled to form pt bi te microinclusions in all sulfide phases whilst the excess pd was accommodated in solid solution in pentlandite minor redistribution and recrystallization by hydrothermal fluids occurred around xenoliths and at the very base of the mineralized zone within the footwall however the overall lack of secondary alteration coupled with the volatile poor nature of the gneissic footwall have allowed the preservation of what may be the most primary style of platreef mineralization the lack of pgm inclusions within early liquidus phases suggests very early sulfur saturation in the platreef lending support to theories involving s saturation occurring prior to intrusion of the platreef possibly within a staging chamber

minor and trace elements in bornite and associated cu fe sulfides a la icp ms studybornite mineral chemistry abstract in situ laser ablation inductively coupled mass spectroscopy la icp ms has been used to provide a baseline dataset on the minor element contents in hypogene bornite and accompanying cu sulfides from 12 deposits with emphasis on syn metamorphic cu vein systems in norway and skarn porphyry and epithermal systems in se europe bornite contains significant concentrations of both ag and bi especially in the vein and skarn deposits studied and has the potential to be a major ag carrier in such ores concentrations of up to 1 wt of both elements are documented measured concentrations appear to be independent of whether discrete ag and or bi minerals are present within the analyzed sulfide where bornite and chalcocite or mixtures of cu sulfides coexist ag is preferentially partitioned into chalcocite over co existing bornite and bi is partitioned into the bornite bornite is a relatively poor host for au which mimics ag by being typically richer in coexisting chalcocite most anomalous au concentrations in bornite can be readily tracked to micron and submicron scale inclusions but bornite and chalcocite containing up to 3 and 28 ppm au in solid solution can be documented selenium and te concentrations in bornite may be as high as several thousand ppm and correlate with the abundance of selenides and tellurides within the sample selenium distributions show some promise as a vector in exploration offering the possibility to track a fluid source bornite and chalcocite are poor hosts for a range of other elements such as co ni ga and ge etc which have been reported to be commonly substituted within sulfides hypogene bornite and chalcocite may have significantly different trace element geochemical signatures from secondary supergene bornite

domainal fabrics of hematite in schistose shear zone hosted high grade fe ores the product of the interplay between deformation and mineralization abstract schistose high grade hematite orebodies 64 wt fe in the iron quadrangle minas gerais were formed in shear zones by hydrothermal alteration of the paleoproterozoic caue bif during the transamazonian orogenesis the ore is comprised of platy hematite specularite grains that define the foliation and overprint a relict banded martite hematite fabric resembling at first sight a mylonite the ebsd analyses of a m scale schistose orebody from the pau branco mine show that specularite grew as elongated plates with the 00 1 plane parallel to the foliation the population of the measured grain aspect ratio gar is homogenous in different scales and the longest axes of the crystals align with the stretching lineation l x building continuous domains or anastomose around stretched iron oxide aggregates and rootless fold hinges the pole figure of the 00 1 plane shows usually a maximum centered on the pole of the foliation z often elongated on a girdle perpendicular to the lineation l the 10 4 pole figure has the configuration of a symmetric cleft girdle and the corresponding 11 0 and 10 0 pole figures present well developed girdles parallel to the foliation with an elongated maximum centered on x microstructures associated with crystal plastic behavior and dynamic recrystallization are missing and the fabric of the orebody probably results from precipitation of strain controlled oriented hematite plates and anisotropic syntaxial growth of favorably oriented grains with the intervention of hydrothermal fluids during fe enrichment the shear zone provided pathways for the percolation of mineralizing fluids under temperatures that varied from 140 to 350 c or higher under ductile or ductile brittle conditions the orthorhombic fabric and cpo crystallographic preferred orientation of the ore nevertheless contrast with the asymmetry of simple shear as observed in the torsion experiments by siemes et al 2010 siemes et al 2011 probably due to volume loss and possibly a flattening component of deformation in the ore zone

three dimensional morphology of magmatic sulfides sheds light on ore formation and sulfide melt migration the morphology of magmatic sulfides in igneous cumulates is controlled by the wetting properties of sulfide liquids against silicates the formation of nickel sulfide ores the behavior of sulfide liquids during mantle melting and potentially the segregation of the earth9s core are all controlled by the ability of sulfide liquids to migrate through the pore space of partially molten silicates three dimensional x ray tomographic images of sulfide aggregates in komatiitic olivine cumulates indicate that sulfide liquids have a limited tendency to wet olivine crystals forming interconnected networks only in the absence of silicate melt consequently the ability of sulfide liquids to migrate through the pore space of olivine cumulates is limited we conclude that disseminated sulfide ores in komatiites formed by accumulation of transported sulfide blebs a few millimeters in size and not by settling of sulfide olivine aggregates and that sulfides accumulated in the proportions in which they are now found rather than by percolation through cumulate pore space it is unlikely that sulfide droplets can be entrained and carried from the mantle at low degrees of partial melting our results also support the hypothesis that segregation of the earth9s core took place from a magma ocean rather than by percolation of sulfidic melt through partially molten mantle

microscale data to macroscale processes a review of microcharacterization applied to mineral systems microanalysis can provide rapid quantitative characterization of mineral systems that complements the field and core scale observations traditionally made in ore deposits we review recent innovations in microanalytical procedures and their application to studies of ore deposits case studies are presented examining how microanalysis can provide constraints on macroscopic processes within mineral systems synchrotron x ray fluorescence shows centimetre scale chemical variations associated with proximity to mineralization in samples from sunrise dam gold mine western australia pseudomorphs of igneous plagioclase and chemically driven recrystallization interpreted from electron backscatter diffraction suggest that the system was dominated by fluid driven brecciation with very little shearing both the fluid chemistry and fluid pressure evolved during a protracted sequence of vein formation and alteration accompanying gold mineralization a second case study of sulphide mineralogy at the mt keith nickel sulphide deposit western australia demonstrates how x ray computed tomography combined with trace element mapping can constrain the chemistry and dynamics of magmatic systems large scale interaction between silicate and sulphide melts shown by homogenous palladium enrichment in pentlandite leads to a large proportion of globular ores with a high nickel content increasing use of microanalysis in ore deposit geology is resulting in the constant reassessment of established models for ore genesis though a combination of micro and macroscale datasets