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

gold in the oceans through time during sedimentation and diagenesis of carbonaceous shales in marine continental margin settings au is adsorbed from seawater and organic matter and becomes incorporated into sedimentary pyrite la icpms analysis of over 4000 sedimentary pyrite grains in 308 samples from 33 locations around the world grouped over 123 determined ages has enabled us to track in a first order sense the au content of the ocean over the last 3 5 billion years gold was enriched in the meso and neoarchean oceans several times above present values then dropped by an order of magnitude from the first great oxidation event goe1 through the paleoproterozoic to reach a minimum value around 1600 ma gold content of the oceans then rose with perturbations through the meso and neoproterozoic showing a steady rise at the end of the proterozoic 800 to 520 ma which most likely represents the effects of the second great oxidation event goe2 gold in the oceans was at a maximum at 520 ma when oxygen in the oceans rose to match current maximum values in the archean and proterozoic the au content of seawater correlates with the time distribution of high mg greenstone belts black shales and banded iron formations suggesting that increases in atmospheric oxygen and marine bio productivity combined with the higher background of au in komatiitic and mg rich basalts were the first order causes of the pattern of au enrichment in seawater we suggest the lack of major au deposits from 1800 to 800 ma is explained by the low levels of au in the oceans during this period

petrogenetic relationships between diogenites and olivine diogenites implications for magmatism on the hed parent body abstract diogenites are orthopyroxenites and harzburgites that are petrogenetically associated with basaltic magmatism linked to the earliest stages of asteroidal melting on the parent body for the howardite eucrite diogenite hed meteorites there are several models proposed for their origin 1 accumulation of orthopyroxene opx chromite chr olivine ol during the crystallization of a magma ocean during the initial stages of asteroidal differentiation 2 accumulation of opx chr ol during the crystallization of compositionally distinct basaltic magmas emplaced into the crust of the hed parent body and 3 the orthopyroxenites formed by the crystallization of basaltic magmas within the hed parent body crust whereas the harzburgites represent the mantle of the hed parent body although ol and opx experienced varying degrees of subsolidus reequilibration 1100 700 c their minor and trace element characteristics appear to partially preserve magmatic signatures that provide insights into distinguishing among different models for the origin of diogenites the opx exhibits a continuous and very systematic variation in incompatible elements such as al ti zr y and yb polymict diogenites i e roda eet 79002 can contain distinct lithologies with both different incompatible element characteristics and different model abundances of ol there appears to be no relationship between the appearance and abundance of ol and the incompatible element characteristics of the opx the ol exhibits a range in mg and systematic variations ni co ni co and mn for examples low ni co appears to be closely associated with the harzburgites and ni and mn exhibit a negative correlation surprisingly incompatible element concentrations in opx are not negatively correlated to ni concentrations in ol the continuous nature of the minor and trace element characteristics of the opx and ol is consistent with the all the diogenite lithologies forming through a single process such as crystallization within a magma ocean or a series of layered intrusions further the range in incompatible element variability in the opx the ni and co systematics in the ol and the association of distinctly different lithologies within polymict diogenites are most consistent with the diogenites representing lithologies from diverse layered intrusions alternatively they may represent crystallization products of a magma ocean much more complex than has been thus far proposed i e multiple mos there are some distinct differences between diogenites and the ol rich achondrite que 93148 that was also analyzed during this study these differences such as ni co in ol estimated conditions of fo2 suggest that que 93148 is closely related to main group pallasites rather than the parent bodies for the hed meteorites

observational evidence for the mechanism of the poleward propagation of zonal wind anomalies over the north atlantic this study examines the physical mechanisms that drive the poleward propagation of zonal mean flow anomalies over the north atlantic during the boreal winter with ecmwf era40 reanalysis data that spans the years 1958 2001 an empirical orthogonal function eof analysis is performed on the zonal wind anomalies for the north atlantic domain based on time lag correlations between the first two eofs 14 poleward propagation events are identified a series of lagged composite calculations of the poleward propagation events reveals the following processes midlatitude synoptic scale rossby waves propagate equatorward and break when they encounter their critical latitudes in the tropics and subtropics a new critical latitude is generated slightly poleward of the previous critical latitude and the subsequent wave breaking occurs at this new critical latitude this interaction between the wave breaking and the critical latitude drives the poleward propagation of zonal mean zonal wind anomaly a comparison between the poleward propagation events and zonal index events indicates that the poleward propagation is associated with a relatively weak potential vorticity gradient over the subtropics these north atlantic poleward propagation events are found to be preceded by anomalously strong transient eddy activity over the subtropical north pacific and by anomalously weak tropical convection over the tropical atlantic ocean and the amazon copyright c 2012 royal meteorological society

olivine rich exposures at bellicia and arruntia craters on 4 vesta from dawn fc we present an analysis of olivine rich exposures at bellicia and arruntia craters using dawn framing camera fc color data our results confirm the existence of olivine rich materials at these localities as described by ammannito et al 2013a using visual infrared spectrometer vir data analyzing laboratory spectra of various howardite eucrite diogenite meteorites high ca pyroxenes olivines and olivine orthopyroxene mixtures we derive three fc spectral band parameters that are indicators of olivine rich materials combining the three band parameters allows us for the first time to reliably identify sites showing modal olivine contents 40 the olivine rich exposures at bellicia and arruntia are mapped using higher spatial resolution fc data the exposures are located on the slopes of outer inner crater walls on the floor of arruntia in the ejecta as well as in nearby fresh small impact craters the spatial extent of the exposures ranges from a few hundred meters to few kilometers the olivine rich exposures are in accordance with both the magma ocean and the serial magmatism model e g righter and drake 1997 yamaguchi et al 1997 however it remains unsolved why the olivine rich materials are mainly concentrated in the northern hemisphere approximately 36 42 n 46 74 e and are almost absent in the rheasilvia basin

three dimensional spectral analysis of compositional heterogeneity at arruntia crater on 4 vesta using dawn fc abstract we introduce an innovative three dimensional spectral approach three band parameter space with polyhedrons that can be used for both qualitative and quantitative analyzes improving the characterization of surface compositional heterogeneity of 4 vesta it is an advanced and more robust methodology compared to the standard two dimensional spectral approach two band parameter space the dawn framing camera fc color data obtained during high altitude mapping orbit resolution 60 m pixel is used the main focus is on the howardite eucrite diogenite hed lithologies containing carbonaceous chondritic material olivine and impact melt the archived spectra of heds and their mixtures from relab hoserlab and usgs databases as well as our laboratory measured spectra are used for this study three dimensional convex polyhedrons are defined using computed band parameter values of laboratory spectra polyhedrons based on the parameters of band tilt r0 92 m r0 96 m mid ratio r0 75 m r0 83 m r0 83 m r0 92 m and reflectance at 0 55 m r0 55 m are chosen for the present analysis an algorithm in idl programming language is employed to assign fc data points to the respective polyhedrons the arruntia region in the northern hemisphere of vesta is selected for a case study because of its geological and mineralogical importance we observe that this region is eucrite dominated howarditic in composition the extent of olivine rich exposures within an area of 2 5 crater radii is 12 larger than the previous finding thangjam g et al 2014 meteorit planet sci 49 1831 1850 lithologies of nearly pure cm2 chondrite olivine glass and diogenite are not found in this region although there are no unambiguous spectral features of impact melt the investigation of morphological features using fc clear filter data from low altitude mapping orbit resolution 18 m pixel suggests potential impact melt features inside and outside of the crater our spectral approach can be extended to the entire vestan surface to study the heterogeneous surface composition and its geology

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

siderophile and other geochemical constraints on mixing relationships among hed meteoritic breccias we have used neutron activation and electron probe fused bead techniques to analyze the bulk major and trace element compositions of 104 named hed meteorites about 100 102 distinct meteorites depending upon pairings including 32 polymict eucrites 30 howardites and six diogenites most were not previously analyzed for siderophile trace elements many not even for major elements our typical sample was 350 mg and in some cases two separate chips were analyzed as a test of meteorite heterogeneity meteorites with extraordinary compositions include bluewing 001 an unequilibrated eucrite that is rich in ti sm and other incompatible elements y 791192 a cumulate dominated polymict eucrite and lew 87002 an oddly sm rich howardite dominated by a ferroan variety of diogenite the eucrite diogenite mixing ratio is the single most important factor determining the compositions of polymict heds but wide ranges in eucrite incompatible element contents in diogenite cr and v contents and in sc contents of both eucrites and diogenites make for diversity among the polymict heds as our new siderophile data help to show the common practice of describing the entire class of howardites as regolith breccias is erroneous most howardites are fragmental breccias showing no sign of origin from true in the lunar sense i e soil like near surface regolith howardites are highly diverse in ni content often remarkably ni poor compared to lunar regolith breccias however the few 8 howardites with between 300 and 1200 lg g ni consistently show some combination of other traits suggestive of regolith origin most importantly all four cases or five if we include malvern which appears to have been altered by annealing of howardites known to have enrichments in solar wind noble gases belong to the 300 lg g ni group in many cases an abundance of glasses particularly in spheroidal or turbid brown form provides additional evidence for regolith origin we propose that the important subset of howardites that are regolith breccias be formally distinguished by the designation regolithic howardite apart from high siderophile levels the regolithic howardites are compositionally distinctive in having al2o3 consistently near 8 9 wt corresponding to a eucrite diogenite mixing ratio of precisely 2 1 assuming the heds are reasonably representative of the ancient i e pre vestoid launch surface of vesta this clustering of regolith composition is difficult to explain unless most of the ancient diogenite component was brought to the surface in a single early episode i e probably a single great impact after which smaller scale cratering with no further major excavations of diogenite until the vestoid forming event efficiently homogenized the surface such a single excavation model may also help to explain why diogenites in marked contrast with eucrites are seldom polymict and why al2o3 poor diogenite dominated howardites consistently lack major siderophile enrichments the low siderophile contents of polymict eucrites are most enigmatic possibly in the hedasteroidal context low collision velocities etc only materials blended by multiple impacts consistently acquire major enrichments in siderophile elements 2009 elsevier ltd all rights reserved

the genesis of diogenites and hed parent body petrogenesis abstract samples of clasts and whole rocks from eighteen of the twenty four known diogenites orthopyroxenite breccia meteorites have been studied by combined inaa empa in order to elucidate their petrogenetic history the incompatible elements a12o3 and tio2 are positively correlated in diogenite orthopyroxenes these elements determined by empa are also positively correlated with incompatible trace elements such as yb determined by inaa on bulk samples these correlations indicate that most diogenites may form a single igneous fractionation sequence the incompatible minor and trace elements are decoupled from the major elements for essentially constant mg tio2 varies by about 4 times and yb by about 8 times hence there is no strong evidence for igneous fractionation preserved in the major element composition of orthopyroxenes geothermometry calculations using two pyroxene and spinelorthopyroxene thermometers show that these phases in diogenites maintained equilibrium to temperatures in the range 650 880 c far below likely magmatic temperatures in some diogenites orthopyroxenes of differing composition are in breccia contact therefore the low equilibration temperatures were achieved in the diogenites prior to brecciation decoupling of major and trace elements was most likely caused by slow subsolidus cooling in the diogenite pluton which allowed ca fe and mg to reach diffusive equilibration incompatible trace elements likely have much lower diffusivities in orthopyroxene and therefore may have largely preserved their magmatic distributions the extensive variation in incompatible trace elements indicates that either the diogenites were formed through an extensive crystallization interval or that partition coefficients greatly increased during crystallization if the former were true one would expect to find substantial amounts of plagioclase in the diogenites if they are comagmatic with eucrites this is contrary to observations a model in which diogenites crystallized from one or more melts of approximately orthopyroxenitic composition can satisfy both the mineralogie and trace element constraints

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

petrology of the unbrecciated eucrites abstract twenty nine unbrecciated eucrites have been thoroughly characterized in terms of the petrologic factors that affect their spectra such as mineral chemistry modal adundances grain sizes and textures we have conducted a combined petrologic and spectral study designed to provide insight into the petrogenesis of the basaltic crust of vesta and the variety of rock types that exist within it as well as aid in the petrologic interpretation of spectra to be collected by the dawn orbiting spacecraft this paper details the petrology part of the study unbrecciated eucrite samples were selected to avoid the complications of lithologic mixing in the accompanying spectral study a wide variety of textural types are seen within the basaltic eucrites encompassing quenched coarse grained and granoblastic samples zoned pyroxenes in eucrites and those that preserve a history of initial rapid cooling are rare nearly all eucrite samples have been thermally metamorphosed and would commonly be classified as equilibrated however this term reflects only the quadrilateral mg fe and ca compositions of pyroxenes and considerable variations are seen within the minor elements al ti and cr in pyroxenes as well as plagioclase compositions determination of both pyroxene and plagioclase compositions together with pyroxene geothermometry provides a better estimate for the relative degree of thermal metamorphism a eucrite has experienced the petrologic differences observed here might allow different eucrites to be distinguished spectrally this is especially true for the varying pyroxene compositions as the spectra of eucrites are dominated by absorption features attributed to pyroxene

an olivine fabric database an overview of upper mantle fabrics and seismic anisotropy we present a unique database of 110 olivine petrofabrics and their calculated seismic properties the samples come from a variety of the upper mantle geodynamic environments ophiolites subduction zones and kimberlites with a wide range of micro structures a phenomenological relationship is established between p and s wave seismic anisotropy and the degree of crystal alignment fabric strength seismic anisotropy increases rapidly at low fabric strength before reaching a near saturation level of 15 to 20 for p waves and 10 to 15 for s waves despite a large variation in the symmetry of fabric patterns the average seismic properties of the different fabric micro structural and geodynamic settings have similar anisotropies in both magnitude and symmetry hence it would seem possible to determine some measure of fabric strength from seismic anisotropy if the dimensions of the anisotropic region are known but not geodynamic environment or details of the petrofabric pattern a simple pattern of seismic anisotropy characterises the average sample of the database which has the following features the polarisation plane of the fastest s wave is parallel or sub parallel to the foliation plane the maximum shear wave splitting is parallel to the y structural direction in foliation plane and normal to the lineation the maximum of the p wave velocity is parallel to the high concentration of 100 axes which is sub parallel to the lineation the 100 orientation distribution has the greatest influence on the p wave seismic anisotropy the 100 and 001 orientation distributions have the greatest influence on the symmetry of s wave anisotropy although the magnitude of anisotropy is influenced by the distribution of all three principal axes although the database only contains olivine petrofabrics this statistical study clearly shows that seismic anisotropy can be used to deduce the orientation of the structural frame in the upper mantle 1998 elsevier science b v all rights reserved

olivine diogenites the mantle of the eucrite parent body abstract two olivine rich antarctic diogenites alh a77256 and alh 84001 of the howardite eucritediogenite hed meteorite association have olivine pyroxene ratios similar to normative ratios in devolatilized ordinary chondrites based on chemical data and petrological analysis these meteorites represent the residuum of partial melting of the mantle in the eucrite parent body epb mineral assemblages in these olivine rich diogenites record a continuum in thermal histories from initial partial melting 1150 1200 c to subsolidus re equilibration 795 55 c the small number of olivine rich diogenites known hints that only the outer portion of the epb has been sampled

olivine xenocrysts in picritic magmas experimental partial melting of plagioclase lherzolite at 0 7 mpa confining pressure has produced euhedral olivine crystals by corrosion and overgrowth during cooling the particular conditions of this experiment allow observation of both processes recorded in the crystal shape corrosion boundaries are rounded or straight when parallel to 001 intersection of 110 planes 010 and 110 facets are developed by fast overgrowth during quenching these observations support the contention that phenocrysts in basaltic or picritic magmas are in part xenocrysts the possible mantle origin of olivine crystals in two natural occurrences of ultramafic magmas the picritic pillow lavas of the troodos and a wehrlitic intrusion of the oman ophiolite is investigated in both cases discriminant characteristics are deduced from detailed microstructural study the mantle origin of olivine megacrysts in the investigated picrites raises the question about the existence of picritic magmas in the mantle

hydrothermal transport and depositional processes in archean lode gold systems a review abstract compelling evidence now exists for the formation of archean lode gold deposits over a substantial range in metamorphic conditions and crustal depth the commonality of ore fluid isotopic and geochemical characteristics the extreme fluid rock ratios within actual ore zones and the observed depth continuity within individual orebodies all suggest that these deposits formed within vertically extensive crustal scale hydrothermal systems calculations based on new thermodynamic data and estimated ore fluid conditions suggest that gold would have been transported as au hs 2 over most of this range gold transport in the ore fluids that formed some diopside and diopside k feldspar class deposits t 550 c would have been as aucl2 whereas the au hs complex may have been significant in some of the lower temperature 270 c less alkaline ore fluids the high solubility of gold in lode gold ore fluids at amphibolite facies conditions 10 s to 1000 s ppb suggests that fluids may have been undersaturated in gold within their source regions promoting the ore fluid s capacity to retain gold in solution over the large transport distances involved ore depositional mechanisms were also likely to vary between crustal levels fluid rock interactions and wallrock sulphidation in particular appear to be the most important type of precipitation mechanism however with decreasing depth of formation the scope of other depositional mechanisms notably phase separation and fluid mixing becomes greater

effect of water and stress on the lattice preferred orientation of olivine the influence of water and stress on the lattice preferred orientation lpo of olivine aggregates was investigated through large strain shear deformation experiments at high pressures and temperatures p 0 5 2 1 gpa t 1470 1570 k under both waterpoor and water rich conditions the specimens are hot pressed synthetic olivine aggregates or single crystals of olivine water was supplied to the sample by decomposition of a mixture of talc and brucite deformation experiments were conducted up to shear strain 6 using the griggs apparatus where water fugacity was up to 13 gpa at the pressure of 2 gpa the water content in olivine saturated with water increases with increasing pressure and the solubility of water in olivine at p 0 5 2 gpa was 400 1200 ppm h si several new types of lpo in olivine are found depending on water content and stress samples deformed in waterpoor conditions show a conventional lpo of olivine where the olivine 100 axis is subparallel to the shear direction the 010 plane subparallel to the shear plane type a however we identified three new types type b c and e of lpo of olivine depending on the water content and stress the type b lpo of olivine which was found at relatively high stress and or under moderate to high water content conditions is characterized by the olivine 001 axis subparallel to the shear direction the 010 plane subparallel to the shear plane the type c lpo which was found at low stress and under water rich conditions is characterized by the olivine 001 axis subparallel to the shear direction the 100 plane subparallel to the shear plane the type e lpo which was found under low stress and moderate water content is characterized by the olivine 100 axis subparallel to the shear direction the 001 plane subparallel to the shear plane observations by transmission electron microscopy tem and scanning electron microscopy sem show that the dislocations in water poor samples type a are curved and both b 100 and b 001 dislocations have a similar population numerous subgrains are seen in water poor samples in backscattered electron images in contrast water rich samples both type b and type c contain mostly b 001 dislocations and dislocations are straight and sub grain boundaries are rare compared to those in water poor samples these observations suggest that 1 dominant slip systems in olivine change with water fugacity and stress and 2 grain boundary migration is enhanced in the presence of water seismic anisotropy corresponding to the fabrics under water rich condition is significantly different from that under water poor condition consequently the relationship between seismic anisotropy and flow geometry in water rich regions is expected to be

olivine 100 normal to foliation lattice preferred orientation in prograde garnet peridotite formed at high h2o activity cima di gagnone central alps automated electron backscattered diffraction ebsd was applied using a scanning electron microscope to obtain lattice preferred orientation lpo data for olivine in garnet peridotites of the central alps as a reference frame the lpos of enstatite were also investigated in the garnet peridotite at cima di gagnone cdg a weak foliation carrying a distinct lineation is present the lineation is characterized by elongated enstatite olivine and poikiloblastic garnet olivine shows a very unusual lpo with 100 normal to foliation and 001 parallel to lineation achsenverteilungsanalyse ava maps demonstrate that 001 of olivine grains corresponds quite well to their maximum length axes which are preferentially parallel to the lineation numerous planar hydrous defects within 001 planes of olivine are marked by palisades of ilmenite rods and show a preferred orientation normal to lineation calculated p wave velocities for cdg are fastest 8 32 km s 1 normal to foliation with a relatively low anisotropy 2 9 compared to mantle peridotites with the usual 010 100 lpo where the fastest vp direction is towards the lineation the relationship between flow geometry and seismic anisotropy is significantly different at cdg several mechanisms for the formation of the lpo type at cdg are considered with glide possible on 100 001 of olivine on the basis of field data as well as petrographic and petrologic evidence it has been demonstrated that the cdg garnet peridotite formed by prograde metamorphism from a hydrous protolith at pressures and temperatures of about 3 0 gpa and 750 c respectively the cdg lpo is interpreted to have formed during hydrous subduction zone metamorphism the same interpretation may hold for the previously investigated olivine lpo at alpe arami which is similar to that at the nearby cdg the observed anomalous lpo is no proof for ultradeep 3 0 gpa conditions

petrology and geochemistry of northwest africa 5480 diogenite and evidence for a basin forming event on vesta we performed a petrological and geochemical study of an olivine diogenite northwest africa nwa 5480 nwa 5480 is a crystalline stone but shows a heterogeneous texture olivine aggregates and grains of olivine and chromite display resorption textures set in a crystalline pyroxene matrix large olivine aggregates are penetrated by pyroxene matrix flow textures are observed near olivine aggregates olivine chromite and pyroxene show minor chemical zoning implying relatively rapid cooling nwa 5480 contains a significant amount of platinum group elements with chondritic relative proportions all this evidence supports that nwa 5480 is an impact melt breccia from a target composed of olivine and pyroxene rich lithologies such impact melt would have formed by melting crustal materials possibly during one of the impacts that formed the south pole basins on vesta

structural analysis and vein episode of the penjom gold deposit malaysia implications for gold mineralisation and tectonic history in the central belt of malaysia abstract gold mineralisation at the penjom gold deposit in the central belt of peninsular malaysia is dominantly hosted in structurally controlled quartz carbonate veins that display a variable degree of overprinting events under a ductile brittle regime mineralised veins are categorised into two main episodes fold and thrust related veins mainly comprised of bedding and penjom thrust parallel shear veins and associated extension veins developed during a d2 event in addition ne to nne trending splays and penjom thrust parallel reverse dextral and locally nnw to ns reverse sinistral faults overprint earlier vein events forming a new episode of extensional veins during d3 event mostly at the fault contacts of intrusives either as shallow dipping or vertical sheeted stockwork or brecciated veins at least two episodes of faulting d4 d5 are evident which postdates the main episodes of veining and mineralisation this is indicated by a series of late episodes ns trending sinistral and oblique to normal faults which transect and displace the penjom thrust and the folded footwall sequence at low angles and responsible for intensive vein deformation along the penjom thrust and displacement of ore body structural interpretations of mineralised veins suggest that the veins were formed under a compressional to transpressional regime with later post vein displacement in a transtensional to extensional regime vein formation in response to deformation observed at penjom reflects regional structural deformation within the central belt of peninsular malaysia and specifically along the bentong raub suture zone

late accretion as a natural consequence of planetary growth the mantles of the terrestrial planets contain elemental abundances that suggest accretion continued at a late stage after core formation geochemical data of meteorites from differentiated asteroids are consistent with such a late accretion event suggesting that the phenomenon occurred throughout the solar system and was related to planet formation

geology geochemistry and metallogenesis of the selinsing gold deposit central malaysia malaysia is endowed with a number of major sediment hosted orogenic gold deposits that lie parallel to but east of the bentong raub suture zone which runs approximately n s in central malaysia the selinsing gold deposit is one of the major economic deposits in central malaysia and is hosted by meta sedimentary units the deposit is affected by later deformation and metamorphism during the triassic due to the collision of the sibumasu terrane with the sukhothai arc laser ablation icp ms u pb zircon dating of the host rocks indicates a carboniferous ca 331 300 ma maximum depositional age ore minerals include pyrite arsenopyrite galena sphalerite chalcopyrite pyrrhotite and gold detailed textural and geochemical studies revealed five distinctive pyrite types sub rounded framboidal pyrite pyrite 1 rounded recrystallized pyrite pyrite 2 anhedral inclusion rich pyrite pyrite 3 anhedral to subhedral clean pyrite pyrite 4 and coarse euhedral clean pyrite pyrite 5 laser ablation icp ms trace element analysis of the framboidal pyrite indicates enrichment in v as mo ni se te ag and zn relative to the other pyrite types pyrite sulfur isotope composition 1 2 9 2 suggests a likely mixture of magmatic and local sedimentary source for the sulfur pyrite pb isotope results pb206 pb204 18 94 19 10 pb207 pb204 15 72 15 73 suggest a high u source rock for the lead fluid inclusions are co2 rich 95 100 mol and yielded homogenization temperatures from 194 to 348 c and salinities between 1 23 and 9 98 wt nacl equiv suggesting involvement of metamorphic fluids during ore formation based on these results we suggest a two stage model for the formation of the gold deposit at selinsing stage 1 consists of early enrichment of the elements au v as mo se te ni ag and zn in framboidal pyrite in the sediments whereas stage 2 is characterized by multiple post diagenetic deformation and metamorphic processes favoring the development of fluid pathways and au remobilization into later pyrites regionally the selinsing gold deposit shares geological similarities in term of host rocks ore mineralogy and geochemistry with many other sediment hosted orogenic gold deposits in mainland se asia such as the sepon gold deposit laos langu gold deposit thailand modi taung and meyon gold deposits myanmar and phuoc son gold deposit central vietnam we suggest that our two stage model may have important implications to mineral exploration for future research on sediment hosted orogenic gold deposits in se asia

vesta as the howardite eucrite and diogenite parent body implications for the size of a core and for large scale differentiation if vesta is the parent body of the howardite eucrite and diogenite hed meteorites then geo chemical and petrologic constraints for the meteorites may be used in conjunction with astronomical constraints for the size and mass of vesta to 1 determine the size of a possible metal core in vesta and 2 model the igneous differentiation and internal structure of vesta the density of vesta and petrologic models for hed meteorites together suggest that the amount of metal in the parent body is 25 mass with a best estimate of 5 assuming no porosity for a porosity of up to 5 in the silicate fraction of the asteroid the permissible metal content is 30 these results suggest that any metal core in the hed parent body and vesta is not unusually large a variety of geochemical and other data for hed meteorites are consistent with the idea that they originated in a magma ocean it appears that diogenites formed by crystal accumulation in a magma ocean cumulate pile and that most noncumulate eucrites excepting such eucrites as bouvante and statinem formed by subsequent crystallization of the residual melts modelling results suggest that the hed parent body is enriched in rare earth elements by a factor of 2 5 3 5 relative to ci chondrites and that it has approximately chondritic mg si and al sc ratios stokes settling calculations for a vesta wide nonturbulent magma ocean suggest that early crystallizing magnesian olivine orthopyroxene and pigeonite would have settled relatively quickly permitting fractional crystallization to occur but that later crystallizing phases would have settled or floated an order of magnitude more slowly allowing instead a closer approach to equilibrium crystallization for the more evolved eucritic melts this would have inhibited the formation of a plagioclase flotation crust on vesta plausible models for the interior of vesta which are consistent with the data for hed meteorites and vesta include a metal core 130 km radius an olivine rich mantle 65 220 km thick a lower crustal unit 12 43 km thick composed of pyroxenite from which diogenites were derived and an upper crustal unit 23 42 km thick from which eucrites originated the present shape of vesta with 60 km difference in the maximum and minimum radius suggests that all of the crustal materials and possibly some of the underlying olivine from the mantle could have been locally excavated or exposed by impact cratering

the phuket terrane a late palaeozoic rift at the margin of sibumasu abstract it is widely accepted that sibumasu rifted from gondwana in the late palaeozoic but the rifts themselves have not previously been documented in southeast asia this paper identifies the pre middle permian kaeng krachan group of upper peninsular thailand as the infill of one such rift which is given the name phuket terrane indirect evidence suggests the rift infill is several kilometres thick and glacially influenced diamictites are conspicuous in the succession there are significant similarities with the 3 km thick pre middle permian rift infill of the carnarvon basin of western australia east of the khlong marui fault belt the succession is thinner and diamictites are a minor component a tectono stratigraphic model is proposed involving gondwana glaciers dropping their load at the present western margin of the phuket terrane from where it was re sedimented in the rapidly subsiding marine rift basin it is suggested that the khlong marui fault formed part of the eastern boundary of the rift system the three pagodas fault belt similarly juxtaposes different pre middle permian successions rifting ceased in the early permian and a passive margin formed as the mesotethys ocean widened the upper part of the kaeng krachan group and the overlying ratburi limestone representing the post rift sequence

the polymict eucrites the polymict eucrites are a suite of about 14 polymict achondritic meteorites that contain at least 90 vol of eucritic material and are found both in antarctica and elsewhere they are part of a continuum of polymict breccias that includes howardites and polymict diogenites rare gas data suggest that some are gas rich regolith breccias the clasts contained in polymict eucrites sample a variety of lithologies from their parent body and include eucritic clasts alkali enriched eucrites pyroxene cumulate eucrites two pyroxene mafic rocks possibly feldspar cumulate eucrites diogenites fayalitic lithologies and a variety of other mineral clasts the eucritic clasts are probably samples of near surface lithologies on the parent body but the presence of two pyroxene mafic rocks is considered to be evidence of magmatic activity at pressures in excess of 1 kbar in the parent body partial melt models may explain some of the diversity among the clasts but cumulus processes are believed to have been important if pressures greater than 1 kbar are confirmed then the basaltic achondrite parent body bap must have a diameter in excess of 200 km the variety of lithologies suggests that not all basaltic achondrites are samples of igneous rocks formed by single stage melting of a chondritic asteroid but are instead samples of an evolved and diverse crust produced by serial magmatism

the magnitude symmetry and origin of upper mantle anisotropy based on fabric analyses of ultramafic tectonites summary seismic anisotropy within the upper mantle originates from the preferred orientation of highly anisotropic single crystals the symmetry and magnitude of anisotropy depend upon 1 the volume percentages of the minerals constituting the upper mantle 2 the degree and symmetry of preferred orientation of each mineral and 3 the alignment of the minerals crystallographic axes relative to one another the nature of upper mantle anisotropy can be examined by studying mineral orientations within ultramafic rocks which were once part of the mantle petrofabric data for olivine and pyroxene have been used to obtain velocity anisotropy patterns over large regions of ultramafic rocks from the samail ophiolite oman the troodos ophiolite cyprus the bay of islands ophiolife newfoundland the twin sisters ultramafic washington usa the dun mountain ophiolite new zealand the red hills ophiolite new zealand and the red mountain ophiolite new zealand the compressional wave anisotropy calculated for these massifs ranges from 3 to 8 per cent in excellent agreement with observed seismic anisotropy in the upper continental and oceanic mantle the symmetry varies from orthorhombic to axial with the axial symmetry axis corresponding to the olivine a axes maxima and subparallel to spreading directions in oceanic upper mantle pyroxene a b and c axes maxima generally parallel olivine b c and a axes respectively and anisotropy decreases with increasing pyroxene content shear wave splitting is predicted for all propagation directions within the upper mantle symmetry is also orthorhombic or axial with the minimum difference in velocity between the two shear waves parallel to the maximum compressional wave velocity

challenges in detecting olivine on the surface of 4 vesta identifying and mapping olivine on asteroid 4 vesta are important components to understanding differentiation on that body which is one of the objectives of the dawn mission harzburgitic diogenites are the main olivine bearing lithology in the howardite eucrite diogenite hed meteorites a group of samples thought to originate from vesta here we examine all the antarctic harzburgites and estimate that on scales resolvable by dawn olivine abundances in putative harzburgite exposures on the surface of vesta are likely at best in the 10 30 range but probably lower due to impact mixing we examine the visible near infrared spectra of two harzburgitic diogenites representative of the 10 30 olivine range and demonstrate that they are spectrally indistinguishable from orthopyroxenitic diogenites the dominant diogenitic lithology in the hed group this suggests that the visible near infrared spectrometer onboard dawn vir will be unable to resolve harzburgites from orthopyroxenites on the surface of vesta which may explain the current lack of identification of harzburgitic diogenite on vesta

the volatile content of vesta clues from apatite in eucrites apatite was analyzed by electron microprobe in 3 cumulate and 10 basaltic eucrites eucritic apatite is fluorine rich with minor chlorine and hydroxyl calculated by difference we confirmed the hydroxyl content by measuring hydroxyl directly in apatites from three representative eucrites using secondary ionization mass spectroscopy overall most eucritic apatites resemble fluorine rich lunar mare apatites but intriguing oh and cl rich apatites suggest a role for water and or hydrothermal fluids in the vestan interior or on other related differentiated asteroids most late stage apatite found in mesostasis has little hydroxyl or chlorine and is thought to have crystallized from a degassed magma however several apatites exhibit atypical compositions and or textural characteristics for example the isotopically anomalous basaltic eucrite pasamonte has apatite in the mesostasis with significant oh apatites in juvinas also have significant oh and occur as veinlets crosscutting silicates euhedral apatites in the moore county cumulate eucrite occur as inclusions in pyroxene and are also hydroxyl rich 0 62 wt oh the oh was confirmed by sims analysis and this apatite clearly points to the presence of water at least locally in the vestan interior portions of elephant moraine eet 90020 have large and abundant apatites which may be the product of apatite accumulation in a zone of melt rock reaction relatively chlorine rich apatites occur in basaltic eucrite graves nunataks gra 98098 approximately 1 wt cl particularly striking is the compositional similarity between apatite in gra 98098 and apatites in lunar kreep which may indicate the presence of residual magmas from an asteroid wide magma ocean on vesta

constraints on geological strain rates arguments from finite strain states of naturally deformed rocks a summary of known finite strain states is presented longitudinal strains 1 e as measured in many rocks often range from 1 to 40 and 1 to 0 025 the time span available to produce such measureable strains in young orogenic zones seems to be less than 10 m y possibly less than 1 m y which constrains conventional strain rates into the range of 10 sup 13 s sup 1 to 10 sup 15 s sup 1 for both pure and simple shear the most efficient way and much less efficient way to accumulate incremental strains respectively the ellipticity of the finite strain ellipse increases in a nonlinear manner finite strain variations in adjacent layers which give rise to features such as cleavage refraction arise with only slight differences in the strain rates within these layers

viscoplastic self consistent and equilibrium based modeling of olivine lattice preferred orientations implications for the upper mantle seismic anisotropy anisotropy of upper mantle physical properties results from lattice preferred orientation lpo of upper mantle minerals in particular olivine we use an anisotropic viscoplastic self consistent vpsc and an equilibrium based model to simulate the development of olivine lpo and hence of seismic anisotropy during deformation comparison of model predictions with olivine lpo of naturally and experimentally deformed peridotites shows that the best fit is obtained for vpsc models with relaxed strain compatibility slight differences between modeled and measured lpo may be ascribed to activation of dynamic recrystallization during experimental and natural deformation in simple shear for instance experimental results suggest that dynamic re crystallization results in further reorientation of the lpo leading to parallelism between the main 010 100 slip system and the macroscopic shear thus modeled simple shear lpos are slightly misoriented relative to lpos measured in natural and experimentally sheared peridotites this misorientation is higher for equilibrium based models yet seismic properties calculated using lpo simulated using either anisotropic vpsc or equilibrium based models are similar to those of naturally deformed peridotites errors in the prediction of the polarization direction of the fast s wave and of the fast propagation direction for p waves are usually 15 moreover overestimation of lpo intensities in equilibrium based and vpsc simulations at high strains does not affect seismic anisotropy estimates because these latter are weakly dependent on the lpo intensity once a distinct lpo pattern has been developed thus both methods yield good predictions of development of upper mantle seismic anisotropy in response to plastic flow two notes of caution have nevertheless to be observed in using these results 1 the dilution effect of other upper mantle mineral phases in particular enstatite has to be taken into account in quantitative predictions of upper mantle seismic anisotropy and 2 lpo patterns from a few naturally deformed peridotites cannot be reproduced in simulations these abnormal lpos represent a small percent of the measured natural lpos but the present sampling may not be representative of their abundance in the earth s upper mantle

plastic deformation of olivine rich diogenites and implications for mantle processes on the diogenite parent body numerous petrologic and geochemical studies so far on the howardite eucrite and diogenite hed meteorites have produced various crystallization scenarios for their parent body believed to be the differentiated asteroid 4 vesta structural analyses of diogenites can reveal important insights into postcrystallization deformation on the parent body recently published results tkalcec et al 2013 of structural analysis on the olivine rich diogenite nwa 5480 reveal that it underwent solid state plastic deformation although not at the base of a magma chamber dynamic mantle downwelling has been proposed as a plausible deformation mechanism tkalcec et al 2013 the purpose of this study is to investigate whether the plastic deformation found in nwa 5480 is an isolated case we expand the structural analysis on nwa 5480 and extend it to nwa 5784 and mil 07001 6 two other samples of rare olivine rich diogenites using electron backscattered diffraction ebsd techniques our ebsd results show that the diogenites analyzed in this study underwent solid state plastic deformation confirming that the observed deformation of nwa 5480 was not an isolated case on the diogenite parent body the lattice preferred orientations lpos of olivine in nwa 5784 and nwa 5480 are clearly distinct from that typical for cumulate rocks at the base of magma chambers indicating a different stress environment and a different deformation mechanism the lpo of olivine in mil 07001 is less conclusive the structural results of this study suggest that plastic deformation occurred on the diogenite parent body at high temperatures 1273 t 1573 k in the solid state i e after crystallization of the diogenites themselves in a dynamic environment with active stress fields

structural deformation of the leoville chondrite foliations defined by alignment of elongated chondrules have been noted previously in chondrites but none displays this effect so well as leoville cv3 the shapes of leoville chondrules were produced by deformation in situ as indicated by inclusions and clasts with similar shapes and preferred orientations to those of chondrules similarities in the aspect ratios of apparent strain ellipses measured for chondrules alone 1 9 and 2 0 by several methods and for the whole meteorite 2 0 indicate either that leoville deformed homogeneously or that it deformed as a framework of touching chondrules this amount of strain corresponds to approximately 33 uniaxial shortening assuming constant volume because the strain ellipse was measured in only one orientation this strain value is a minimum estimate for the meteorite lack of correlation between foliation and either shock or thermal effects argues that impact or metamorphism are unlikely to have produced this deformation compaction due to overburden from progressive accretion on the chondrite parent body is suggested to have been its cause estimates of maximum deviatoric stresses in the interiors of asteroid sized bodies and constraints on maximum temperatures for cv3 chondrites are consistent with diffusional flow as the deformation mechanism for olivine in these chondrules diffusional flow is also suggested by the scarcity of observed lattice dislocations deformation of leoville olivines by this mechanism at geologically reasonable strain rates appears to require higher temperatures than those believed to have been experienced by this meteorite 600 c however differences in olivine grain size the presence of water or a more complex deformation history might explain this discrepancy

two dimensional numerical modeling of the rheasilvia impact formation 1 we numerically modeled the formation of rheasilvia crater an enormous impact basin centered on asteroid 4 vesta s south pole using a trial and error method our models were adjusted to produce the best possible fit to rheasilvia s size and shape as observed during the vesta orbital stage of the dawn mission the final model yields estimates of the shock wave decay escaped material volume depth of excavation and other relevant characteristics to the extent allowed by the two dimensional axially symmetric approximation of the simplified arbitrary lagrangian eulerian hydrocode our model results permit interpretation of the dawn data on vesta s shape topographic crater profiles and the origin of the vestoid asteroid family as escaped ejecta from the rheasilvia crater

iib trioctahedral chlorite from the barberton greenstone belt crystal structure and rock composition constraints with implications to geothermometry iib trioctahedral chlorite in the barberton greenstone belt bgb metavolcanic rocks was formed during pervasive greenschist metamorphism the chem ical composition of the chlorite is highly variable with the fe fe mg ratio ranging from 0 12 to 0 8 among 53 samples the chemical variation of the chlorite results from the chemical diversity of the host rock especially the mgo content of the rock but major details of the variation pattern of the chlorite are due to the crystal structure of the chlorite all major cation abundances in the chlorite are strongly correlated with each other sil icon increases with mg and decreases with fe while aliv and alvi decrease with mg and increase with fe2 a complex exchange vector explains over 90 of the chlorite compositional variation mg4sife2 3alvi 1 aliv 1 which has 3 parts fe mg substitution coupled with one part tschermakite substitution this ratio is required to maintain the charge and site balances and the dimensional fit between the tetrahedral and octahedral sheets the subtle change in al substitution in chlorite implies that alvi is preferentially ordered in the m 4 site and about 84 of the alvi present is in the m 4 sites when they are nearly filled with alvi based on 47 analyzed chlorite bearing rock samples chlorite chl composition is strongly correlated with the mgo content of the host rock calculated correlation coefficients are 0 91 for sio2chl mgorock 0 87 for al2o3chl mgorock 0 89 for mgochl mgorock and 0 85 for feochl mgorock only weak correlations have been found between chlorite oxides and other oxides of rock between same oxides in chlorite and rock sio2 0 67 al2o3 0 59 feo 0 41 however mgochl is saturated at about 36 wt in rocks that have mgo above 22 wt the mgochl is about 5 wt when the host rock approaches 0 wt of mgo this implies that mg substituting into the chlorite is approximately limited to 1 5 9 2 mg atoms per formula unit and 1 0 3 2 aliv chlorite geothermometers can not be applied to all bgb samples however the empirical chlorite geothermometer based on aliv of chlorite may be applicable to chlorites formed under metamorphic conditions because it can predict the chemical composition of the chlorite from basaltic and dacitic samples in this study an estimated temperature of about 320 c for the greenschist metamorphism of the greenstone belt through this geothermometer is consistent with that obtained by other geothermometers

a magma ocean on vesta core formation and petrogenesis of eucrites and diogenites abstract available evidence strongly suggests that the hed howardite eucrite diogenite meteorites are samples of asteroid 4 vesta abundances of the moderately siderophile elements ni co mo w and p in the hed mantle indicate that the parent body may have been completely molten during its early history during cooling of a chondritic composition magma ocean equilibrium crystallization is fostered by the suspension of crystals in a convecting magma ocean until the crystal fraction reaches a critical value near 0 80 when the convective system freezes and melts segregate from crystals by gravitational forces the extruded liquids are similar in composition to main group and stannern trend eucrites and the last pyroxenes to precipitate out of this ocean before convective lockup span the compositional range of the diogenites subsequent fractional crystallization of a main group eucrite liquid which has been isolated as a body of magma produces the nuevo laredo trend and the cumulate eucrites the predicted cumulate mineral compositions are in close agreement with phase compositions analyzed in the cumulate eucrites thus eucrites and diogenites are shown to have formed as part of a simple and continuous crystallization sequence starting with a magma ocean environment on an asteroidal size parent body that is consistent with vesta

the origin of eucrites diogenites and olivine diogenites magma ocean crystallization and shallow magma chamber processes on vesta the asteroid 4 vesta is one of the very few heavenly bodies to have been linked to samples on earth the howardite eucrite diogenite hed meteorite suite this large and diverse suite of meteorites provides a detailed picture of vesta s igneous and postigneous history we have used the range of igneous rock types and compositions in the hed suite to test a series of chemical models for solidification processes following peak melting magma ocean conditions on vesta fractional crystallization cannot have been a dominant early process in the magma ocean because it leads to excessive fe enrichment in the melt models that are dominated by equilibrium crystallization cannot produce orthopyroxene cumulates diogenites our best models invoke 60 70 equilibrium crystallization of a magma ocean followed by continuous extraction of the residual melt into shallow magma chambers fractional crystallization in these magma chambers combined with continuous or periodic addition of more melt from the slowly compacting crystal mush magmatic recharge can produce all of the igneous hed lithologies noncumulate and cumulate eucrites diogenites dunites harzburgites and olivine diogenites magmatic recharge can also explain the narrow range in eucrite compositions and the variability of incompatible trace element concentrations in diogenites we predict an internal structure for vesta that permits excavation of the heds during the formation of the rheasilvia basin while remaining consistent with observations from the dawn mission and most impact models

petrogenesis of malaysian granitoids in the southeast asian tin belt part 2 u pb zircon geochronology and tectonic model in our complementary geochemical study part 1 the malaysian granitoids of the southeast asian tin belt were divided into a middle permian to late triassic i type dominated eastern province indochina terrane and a triassic to early jurassic transitional i s type main range province sibumasu terrane separated by the bentong raub suture zone which closed in the late triassic previous geochronology has relied on only a few u pb zircon ages together with k ar and whole rock rb sr ages that may not accurately record true magmatic ages we pre sent 39 new high precision u pb zircon ion microprobe ages from granitoids and vol canics across the malay peninsula our results show that ages from the eastern province granitoids span 289 220 ma with those from the main range province granitoids being entirely late triassic spanning 227 201 ma a general westerly younging magmatic trend across the malay peninsula is considered to refl ect steepening and roll back of the bentong raub subduction zone during progressive closure of paleo tethys the youngest ages of subduction related granites in the eastern province roughly coincide with the youngest ages of marine sedimentary rocks along the paleo tethyan suture zone our petrogenetic and u pb zircon age data support models that relate the eastern province granites to pre collisional andean type magmatism and the western main range province granites to syn and post collisional crustal melting of sibumasu crust during the late triassic tin mineralization was mainly associated with the latter phase of magmatism two alternative tectonic models are discussed to explain the triassic evolution of the malay peninsula the fi rst involves a second late triassic to jurassic or early cretaceous east dipping subduction zone west of sibumasu where subduction related hornblende and biotite bearing granites along sibumasu are paired with main range crustal melt tinbearing granites analogous to the bolivia cordilleran tin bearing granite belt the second model involves westward underthrusting of indochina beneath the west malaya main range province resulting in crustal thickening and formation of tin bearing granites of the main ranges cretaceous granitoids are also present locally in singapore ubin diorite on tioman island in the noring pluton of the stong complex eastern province and along the sibumasu terrane in southwest thailand and burma myanmar refl ecting localized crustal melting

solid state plastic deformation in the dynamic interior of a differentiated asteroid diogenite meteorites are thought to represent mantle rocks that formed as cumulates in magma chambers on 4 vesta or a similar differentiated asteroid microstructural analysis of olivine grains from a diogenite meteorite show that the preferred orientation of their crystal lattice was formed through plastic deformation indicating dynamic planet like processes in its parent body

ancient water on asteroid 4 vesta evidence from a quartz veinlet in the serra de mage eucrite meteorite abstract the meteorite serra de mage a eucrite inferred to be from the asteroid 4 vesta contains quartz veinlets they are identical to antitaxial or crack seal quartz veinlets in terrestrial rocks and are extraterrestrial and ancient because they pre date a 4 40 ga metamorphism the quartz was likely deposited from liquid water solutions as are terrestrial veins other potential solvents or transport mechanisms are inadequate or unlikely because there is no indication of internal magmatic water in the eucrite meteorites and thus in vesta the water from which the veinlet was deposited probably came from outside vesta by analogy with water ice deposits on the moon and mercury vesta and similar asteroids may have had or now have polar ice deposits possibly derived from comet impacts

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

diogenites as polymict breccias composed of orthopyroxenite and harzburgite abstract a few relatively unbrecciated olivine rich diogenites consist of an equilibrium assemblage of olivine and magnesian orthopyroxene harzburgite more common diogenites with smaller amounts of olivine are breccias containing two distinct orthopyroxenes one magnesian and one ferroan these diogenites are mixtures of a harzburgite lithology that is more magnesian with the normal orthopyroxenite lithology that is ferroan and may contain small amounts of plagioclase both lithologies likely formed by fractional crystallization in multiple plutons emplaced within the crust of asteroid 4 vesta minor element trends in orthopyroxenes indicate that these plutons exhibited a range of compositions we propose a revised taxonomy for the hed howardites eucrites and diogenites suite where all ultramafic samples are referred to as diogenites within this group the prefixes dunitic harzburgitic and orthopyroxenitic are used to distinguish diogenites consisting of more than or equal to 90 olivine olivine orthopyroxene and more than or equal to 90 orthopyroxene respectively the prefix polymict is used to describe brecciated mixtures of any of these rock types the recognition that olivine is a significant phase in some diogenites is consistent with spectral interpretations of olivine in a deeply excavated crater on vesta and has important implications for the bulk composition and petrogenesis of that body

magnesium oxide iron oxide mass balance constraints and a more detailed model for the relationship between eucrites and diogenites according to a currently popular model for petrogenesis on the howardite eucrite and diogenite hed parent asteroid the diogenites are not comagmatic with most eucrites but instead formed in separate orthopyroxenite dominated plutons this model can be tested for consistency with mass balance for mgo and feo assuming the overall diogenite diogenite eucrite ratio d of the parent asteroid is at least comparable to the average d for the eucrite diogenite dominated howardite regolith breccias average mg mgo mgo feo is much lower for eucrites especially noncumulate eucrites than for diogenites unless the diogenite parent magmas eventually produced a large proportion of low mg residual basalt and gabbro rbg the implied initial magma s mg is vastly higher than that of any noncumulate eucrite starting from a source previously depleted by putative primary eucrite genesis melt mg can be estimated as a function of the exchange reaction kd and degree of melting using several very conservative assumptions e g assuming that the total mgo feo concentration is nearly the same in the nascent melt as in the residual solids the degree of melting required to yield a melt with mg high enough to satisfy mass balance without implying an rbg component that accounts for 50 of all eucrites is an implausibly high 60 80 wt the separate orthopyroxenitic plutons sop model also seems inconsistent with the uniform density of melts across the diogenite eucrite compositional spectrum 2 77 2 82 g cm3 which implies that diogenitic magmas should have been as capable as eucrites of extruding to form lavas this difficulty cannot be reduced by simply assuming that later formed magmas were systematically both more plutonic and more mgo rich than earlier ones because the plutonic cumulate eucrites equilibrated with melts systematically lower in mg than noncumulate eucrites conceivably the bulk mg of the asteroid s silicate system was increased between primary melt eucrite genesis and sop diogenite genesis by graphite fueled reduction of feo however the graphite oxidation process generates a huge proportion of gas which would have enhanced the buoyancy of the nascent diogenite parent magmas thus exacerbating the difficulty of achieving the implied high degrees of partial melting to avoid these difficulties but still form most eucrites as rapidly cooled extrusives i propose the nerd noncumulate eucrites as extruded residua of diogenites model in this model the diogenites form as early cumulates from a large magma system probably a global magma ocean that yields a large proportion of eucritic melt as residuum this residual melt zone undergoes relatively little crystallization during a period when it is episodically tapped to produce extrusions dikes and sills of rapidly cooled noncumulate eucrites slight 5 10 porosity in the nascent eucritic crust keeps it marginally buoyant over the residual melt zone the common thermal metamorphism of noncumulate eucrites results from baking by superjacent flows during the episodic venting of the melt zone the nerd model s greatest advantage is that it does not require implausibly high degrees of localized melting in the mature stages of igneous evolution of the hed asteroid

genesis of the selinsing gold deposit peninsular malaysia constraints from mineralogy geochemistry and in situ sulfur isotope compositions of sulfides abstract as a renowned orogenic lode gold deposit the selinsing gold deposit is located in the central belt of peninsular malaysia geologically the gold deposit is characterized by auriferous quartz veins and fine grained gold minerals coexisted with sulfides and the ore body is hosted by low grade metamorphic sedimentary rocks and volcanic rocks furthermore gold mineralization is closely related to tectonic deformation four main stages of vein formation have been identified namely 1 quartz pyrite arsenopyrite vein 2 quartz pyrite gold vein 3 quartz stibnite pyrite vein and 4 quartz chlorite vein the occurrence of gold includes two types i e visible gold and invisible gold the former is featured by coarse grained gold millimeter scale such as auriferous quartz veins and fine grained gold micron scale such as native gold calaverite and electrum the latter is contained in pyrite and arsenopyrite in the form of nano scale native gold particles au0 and lattice gold au1 the geothermometer of arsenopyrite and chlorite as well as temperature sulfur fugacity diagram indicate that the temperature and sulfur fugacity of hydrothermal fluid decrease gradually considering that the sulfur fugacity drops gradually and aqueous inclusions coexist with carbonic inclusions it is inferred that sulfuration reaction in which sulfur is consumed to produce sulfides and fluid immiscibility or phase separation may be responsible for gold precipitation tested by la mc icp ms the in situ sulfur isotope compositions of sulfides formed in different stages are homogenous about 1 to 1 and the calculated h2s dominated hydrothermal fluid is also consistent about 2 to 0 in sulfur isotope compositions which reflect the mantle or ultrabasic rock and basic rock or magmatic rocks may be a potential source of sulfur combined with possible source and tectonic evolution of peninsular malaysia possible metallogenic processes are proposed to explain genesis of the selinsing gold deposit and other gold deposits in the central belt i e ore forming fluid was differentiated from oceanic crust and or fertilized mantle wedge or ore forming fluid may be sourced from concealed magmatic rocks that formed by subduction of the palaeo tethys toward the east malaysia block

the leoville cv3 accretionary breccia leoville is a cv3 chondrite that contains a large variety of inclusions besides refractory inclusions resembling those in allende fine grained dark inclusions are especially prominent same of these are xenoliths of material very similar to cm chondrites in texture bulk composition and oxygen isotopes however they show an unusually large range in the degree of hydrous alteration other dark inclusions are similar to host matrix the cv3 host of this breccia is similar to other cv chondrites although less metamorphosed than allende we suggest that leoville is a typical accretionary breccia whose parent body accreted after the cm like material represented by the xenoliths had formed and undergone alteration after accretion leoville suffered severe deformation leading to foliation stronger than in any other chondrite but the nature of the event that caused this remains unclear

the misorientation index development of a new method for calculating the strength of lattice preferred orientation abstract using orientation data from experimentally deformed olivine we explore some practical problems with the j index a commonly applied measure of fabric strength we show that the j index is highly dependent on several factors including the number of discrete data in the orientation distribution function odf and arbitrary numerical parameters specified for its calculation because of this non uniqueness we conclude that the j index is difficult to interpret and should only be applied with caution as an alternative to the j index we propose a new measure of fabric strength that is based on the distribution of uncorrelated misorientation angles this m index is shown to be insensitive to the parameters specified for its calculation for typical deformed olivine samples we show that 150 discrete data are adequate to quantify fabric strength using the m index technique the m index correlates well with seismic anisotropy particularly for materials of the same fabric type therefore we conclude that the m index technique is well suited for the quantification of fabric strength and the comparison of like materials

u pb zircon geochronology of early permian to late triassic rocks from singapore and johor a plate tectonic reinterpretation article i nfo the results of u pb zircon geochronology of permian to middle triassic granitoids from singapore and neighbouring johor are presented rhyolite from pulau sibu is 276 5 ma gabbros from singapore give ages of 260 2 to 249 2 ma granites from singapore give ages from 249 2 to 230 6 ma and rhyolite from telkuma gives an age of 238 2 ma u pb detrital zircon age spectra from a late triassic conglomerate from singapore show carboniferous mid dle triassic and late triassic spikes at 350 245 and 217 ma respectively these new data when combined with published u pb zircon ages allow a revision of the plate tectonic evolution of the malaysian peninsula region a tin bearing magmatic arc evolved in the eastern malaysian peninsula part of indochina from the early permian to the middle triassic when the palaeo tethys ocean was subducted and sibumasu continental lithosphere was rifted from pangea this opened up the neo tethys ocean that the granitoid ages show a progressive decrease in age from pulau sibu 276 5 ma to singapore 230 6 ma suggests that during this andean type orogenic phase the subduction zone rolled back and steepened causing the locus of mainly i type magmatism to migrate from east to west in present day coordinates across the eastern and central belts and stretch the lithosphere as it did so in the late triassic sibumasu collided with indochina causing the western belt sibumasu to over thrust the central belt indochina along the bentong raub suture the lower half of the thickened crust formally the tin bearing indochina plate was partially melted and pre dominantly s type tin bearing granites were intruded into the upper crust formally sibumasu this late triassic collisional phase is the indosinian orogeny in peninsular malaysia

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

a new chlorite geothermometer for diagenetic to low grade metamorphic conditions the evolution of chlorite composition with temperature and pressure serves as basis to a number of chlorite chemical thermometers for which the oxidation state of iron has been recognised as a recurrent issue especially at low temperature t a new chlorite geothermometer that does not require prior fe3 knowledge is formulated calibrated on 161 analyses with well constrained t data covering a wide range of geological contexts and tested here for low t chlorites t 350 c and pressures below 4 kbar the new solid solution model used involves six end member components the mg and fe end members of al free chlorite s sudoite and amesite and so accounts for all low t chlorite compositions ideal mixing on site is assumed with an ordered cationic distribution in tetrahedral and octahedral sites applied to chlorite analyses from three distinct low t environments for which independent t data are available gulf coast texas saint martin lesser antilles toyoha hokkaido the new pure fe2 thermometer performs at least as well as the recent models which require an estimate of fe3 content this relief from the ferric iron issue combined with the simple formulation of the semi empirical approach makes the present thermometer a very practical tool well suited for for example the handling of large analytical datasets provided it is used in the calibration range t 350 c p 4 kbar

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

granitic magmatism basement ages and provenance indicators in the malay peninsula insights from detrital zircon u pb and hf isotope data abstract the malay peninsula lies on two continental blocks sibumasu and east malaya which are intruded by granitoids in two provinces the main range and eastern previous models propose that permian triassic granitoids are subduction related and syn to post collisional we present 752 u pb analyses that were carried out on zircons from river sands in the malay peninsula of these 243 grains were selected for hf isotope analyses our data suggest a more complex sibumasu east malaya collision history 176hf 177hfi ratios reveal that permian triassic zircons were sourced from three magmatic suites a permian crustally derived granitoids b early middle triassic granitoids with mixed mantle crust sources and c late triassic crustally derived granitoids this suggests three permian triassic episodes of magmatism in the malay peninsula two of which occurred in the eastern province although the exact timing of the sibumasu east malaya collision remains unresolved current data suggest that it occurred before the late triassic probably in late permian early triassic our data also indicate that sibumasu and east malaya basements are chronologically heterogeneous but predominantly of proterozoic age some basement may be neoarchaean but there is no evidence for basement older than 2 8 ga finally we show that hf isotope signatures of triassic zircons can be used as provenance indicators

asteroidal processes recorded by polyphase deformation in a harzburgitic diogenite nwa 5480 abstract expectations regarding structural deformation of asteroidal meteorites have typically revolved around impact induced shock metamorphism or the gravity driven axial compression of cumulates at the base of magma chambers recent structural analyses however of several olivine rich diogenites harzburgites reveal solid state plastic deformation not attributable to either scenario and propose dynamic mantle movements in the parent body assumed to be vesta in this study we examine the microstructures of pyroxene and olivine in the olivine rich diogenite nwa 5480 coarse grained poikilitic texture exsolution lamellae and plastic deformation attest to polyphase deformation and a re heating event followed by relatively slow cooling observations suggest that impact events alone are insufficient to generate and sustain the thermal and deformation conditions required to achieve all of the observed features the proposed dynamic mantle movements in the vestan interior may offer a means of heat transport to the system to provide a thermal environment inducive to slow cooling as well as generate the incremental stress fields required for the polyphase plastic deformation observed in the olivine

geology and fluid characteristics of the ulu sokor gold deposit kelantan malaysia implications for ore genesis and classification of the deposit abstract the ulu sokor gold deposit is one of the most famous and largest gold deposits in malaysia and is located in the central gold belt this deposit consists of three major orebodies that are related to ns and ne striking fractures within fault zones in permian triassic meta sedimentary and volcanic rocks of the east malaya block the faulting events represent different episodes that are related to each orebody and are correlated well with the mineralogy and paragenesis the gold mineralization consists of quartz dominant vein systems with sulfides and carbonates the hydrothermal alteration and mineralization occurred during three stages that were characterized by i silicification and brecciation ii carbonatization sericitization and chloritization and iii quartz carbonate veins fluid inclusions in the hydrothermal quartz and calcite of the three stages were studied the primary co 2 ch 4 h 2 o nacl fluid inclusions in stage i are mostly related to gold mineralization and display homogenization temperatures of 269 389 c salinities of 2 77 11 89 wt nacl equivalent variable co 2 contents typically 5 29 mol and up to 15 mol ch 4 in stage ii gold was deposited at 235 398 c from a co 2 ch 4 h 2 o nacl fluid with a salinity of 0 83 9 28 wt nacl equivalent variable co 2 contents typically 5 63 mol and up to 4 mol ch 4 the 18 o h 2 o and d values of the ore forming fluids from the stage ii quartz veins are 4 5 to 4 8 and 44 to 42 respectively and indicate a metamorphic hydrothermal origin oxygen fugacities calculated for the entire range of t p x co 2 conditions yielded log f o 2 values between 28 95 and 36 73 for stage i and between 28 32 and 39 18 for stage ii these values indicate reduced conditions for these fluids which are consistent with the mineral paragenesis fluid inclusion compositions and isotope values the presence of daughter mineral bearing aqueous inclusions is interpreted to be a magmatic signature of stage iiia combined with the oxygen and hydrogen isotopic compositions 18 o h 2 o 6 8 to 11 9 d 77 to 62 these inclusions indicate that the initial fluid was likely derived from a magmatic source in stage iiib the gold was deposited at 263 to 347 c from a co 2 ch 4 h 2 o nacl fluid with a salinity of 5 33 to 11 05 wt nacl equivalent variable co 2 contents typically 9 15 mol and little ch 4 the oxygen and hydrogen isotopic compositions of this fluid 18 o h 2 o 8 1 to 8 8 d 44 to 32 indicate that it was mainly derived from a metamorphic hydrothermal source the co 2 h 2 o ch 4 nacl fluids that were responsible for gold deposition in the stage iiic veins had a wide range of temperatures 214 483 c salinities of 1 02 to 21 34 wt nacl equivalent variable co 2 contents typically 4 53 mol and up to 7 mol ch 4 the oxygen and hydrogen isotopic compositions 18 o h 2 o 8 5 to 9 8 d 70 to 58 were probably acquired at the site of deposition by mixing of the metamorphic hydrothermal fluid with deep seated magmatic water and then evolved by degassing at the site of deposition during mineralization the log f o 2 values from 28 26 to 35 51 also indicate reduced conditions for this fluid in stage iiic moreover this fluid had a near neutral ph and 34 s values of h 2 s of 2 32 to 0 83 which may reflect the derivation of sulfur from the subducted oceanic lithospheric materials the three orebodies represent different gold transportation and precipitation models and the conditions of ore formation are related to distinct events of hydrothermal alteration and gold mineralization the gold mineralization of the ulu sokor deposit occurred in response to complex and concurrent processes involving fluid immiscibility fluid rock reactions and fluid mixing however fluid immiscibility was the most important mechanism for gold deposition and occurred in these orebodies which have corresponding fluid properties structural controls geologic characteristics tectonic settings and origins of the ore forming matter these characteristics of the ulu sokor deposit are consistent with its classification as an orogenic gold deposit while some of the veins are genetically related to intrusions