the impact of hydrothermal mineral replacement reactions on the formation and alteration of carbonate hosted polymetallic sulfide deposits a case study of the artemis prospect queensland australia abstract hydrothermal sulfidation of carbonate rocks and the reverse replacement of sulfides by carbonates are important processes responsible for the formation and subsequent alteration of ore deposits these processes have been recognized in the case study of the artemis zn cu au prospect which is located in the cloncurry district within the eastern succession of the mount isa inlier nw queensland australia the high grade polymetallic mineralization displays a complex association of massive sulfides and carbonates hosted in a vertical marble lens adjacent to garnet bearing schist staurolite muscovite schist and quartzo feldspathic psammite petrographic analyses of drill core specimen by optical and electron microscopy micro x ray florescence elemental maps electron probe microanalyses cathodoluminescence and bulk geochemistry suggested three major stages of mineralization i pre ore stage marble calcite 0 ii ore stage involving sulfidation of the marble and precipitation of calcite 1 and spherical sulfide inclusions in the first episode and the formation of calcite 2 and massive sulfide in the second episode and iii post ore stage involving replacement of sulfides by calcite 3 and garnet mineral replacement reactions are dominant processes in rocks of ore stage and post ore stage the ore stage involved the dissolution of coarse and pristine calcite 0 ca0 95mn0 3fe0 2co3 and the precipitation of sulfides and calcite 1 ca0 96mn0 3fe0 1co3 and calcite 2 ca0 96mn0 3fe0 1co3 the sulfide assemblage consists of pyrrhotite sphalerite chalcopyrite galena arsenopyrite cobaltite costibite bi cubanite ag sulfides and au in decreasing order of abundance in episode 1 calcite 1 contains spherical sulfide inclusions while in episode 2 calcite 2 envelopes calcite 1 the replacement of co rich arsenopyrite fe0 75co0 26as1 13s0 83 by relatively co poor arsenopyrite fe0 86co0 15as0 99s0 99 via a coupled dissolution precipitation reaction occurred in episode 2 based on arsenopyrite geothermometry the temperatures for the first and second episode are 650 50 and 450 70 c respectively micro xrf elemental maps of the garnet bearing schist adjacent to the sulfidized marble revealed the sulfidation front where pre ore garnet and amphibole were replaced by pyrrhotite chalcopyrite au biotite and muscovite in the post ore stage calcite 2 was partially replaced by siderite and calcite 3 ca0 94mn0 4fe0 2mg0 1co3 which shows sectoral and oscillatory zoning galena was replaced by calcite 3 as documented by embayed lobate grain boundaries between these minerals and pyrrhotite fe 1 x s x 0 091 0 119 was pervasively replaced by garnet mn1 2fe1 2ca0 6 al2si3o12 the microscale investigations of the mineralization processes in the artemis orebody document the impact of hydrothermal mineral replacement reactions on metal sequestration mineral replacement reactions facilitate the formation of ore deposits and subsequent alteration processes which may lead to the loss of economic value of the deposit

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

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

ice and debris in the fretted terrain mars viking moderate and high resolution images along the northern highland margin were studied monoscopically and stereoscopically to contribute to an understanding of the development of fretted terrain results suport the hypothesis that the fretting process involved flow facilitated by interstitial ice the process apparently continued for a long period of time and debris apron formation shaped the fretted terrain in the past as well as the present interstitial ice in debris aprons is most likely derived from ground ice obtained by sapping or scarp collapse debris aprons could have been removed by sublimation if they consisted mostly of ice or by deflation if they consisted mostly of debris to remove the debris wind erosion was either very intense early in martian history or was intermittent perhaps owing to climatic cycles the location of debris aprons in two midlatitudinal belts can be attributed to atmospheric conditions that permit ice to remain in the ground at moderate depth in those latitudes and climatic factors that permit temperatures to be warm enough for ice to flow channels have minimum gradients of 5 8 m km which permits flowing ice to deform by dislocation creep at exceedingly low strain rates alternately ice charged debris may have been buoyed by brines by analogy with the fretted channels ice could have flowed through the outflow channels if the atmospheric pressure was somewhat higher in the past and permitted ice to exist in the equatorial area

gold bearing arsenian pyrite and marcasite and arsenopyrite from carlin trend gold deposits and laboratory synthesis invisible gold in natural and synthetic arsenian pyrite and marcasite correlates with anomalous as content and fe deficiency and high contents of invisible gold in most natural and all synthetic arsenopyrite correlate with excess as and fe deficiency as rich fe deficient arsenopyrite synthesized hydrothermally contains up to 3 0 wt au uniformly distributed in growth zones of light backscattered electron contrast at the deep star gold deposit carlin trend nevada the sulfide compositions apparently span the full range of metastability from fesz to near feass 40 at s arsenian pyrite contains up to 0 37 wt au but arsenopyrite has excess s and is relatively au poor observed minimum fe contents are 29 1 at in arsenian pyrite and marcasite from the deep star deposit and 31 3 at in synthetic arsenopyrite we suggest that invisible gold in arsenian pyrite and marcasite and arsenopyrite from sediment hosted gold deposits represents au removed from ore fluids by chemisorption at as rich fe deficient surface sites and incorporated into the solids in metastable solid solution however the oxidation state of invisible gold aua au1 remains uncertain because the chemisorption process is intrinsically nonsystematic in terms of crystal chemical parameters and does not result in definitive atomic substitution trends

gold remobilisation and formation of high grade ore shoots driven by dissolution reprecipitation replacement and ni substitution into auriferous arsenopyrite abstract both gold rich sulphides and ultra high grade native gold oreshoots are common but poorly understood phenomenon in orogenic type mineral systems partly because fluids in these systems are considered to have relatively low gold solubilities and are unlikely to generate high gold concentrations the world class obuasi gold deposit ghana has gold rich arsenopyrite spatially associated with quartz veins which have extremely high localised concentrations of native gold contained in microcrack networks within the quartz veins where they are folded here we examine selected samples from obuasi using a novel combination of quantitative electron backscatter diffraction analysis ion microprobe imaging synchrotron xfm mapping and geochemical modelling to investigate the origin of the unusually high gold concentrations the auriferous arsenopyrites are shown to have undergone partial replacement 15 by au poor nickeliferous arsenopyrite during localised crystal plastic deformation intragranular microfracture and metamorphism 340 460 c 2 kbars our results show the dominant replacement mechanism was pseudomorphic dissolution reprecipitation driven by small volumes of an infiltrating fluid that had relatively low s 2 and carried aqueous nicl 2 we find that arsenopyrite replacement produced strong chemical gradients at crystal fluid interfaces due to an increase in s 2 during reaction which enabled efficient removal of gold to the fluid phase and development of anomalously gold rich fluid potentially 10 ppm or more depending on sulphur concentration this process was facilitated by precipitation of ankerite which removed co 2 from the fluid increasing the relative proportion of sulphur for gold complexation and inhibited additional quartz precipitation gold re precipitation occurred over distances of 10 m to several tens of metres and was likely a result of sulphur activity reduction through precipitation of pyrite and other sulphides we suggest this late remobilisation process may be relatively common in orogenic belts containing abundant mafic ultramafic rocks which act as a source of ni and co scavenged by chloride bearing fluids both the preference of the arsenopyrite crystal structure for ni and co rather than gold and the release of sulphur during reaction can drive gold remobilisation in many deposits across broad regions

volcanism on mars more than 15 years of planetary exploration of mars have given insight into the geologic processes that have shaped its surface the newly acquired viking data have shown that volcanism is one of the most important geologic processes operating on mars throughout its history in situ chemical analyses of martian soil by the viking lander spacecraft indicate mafic to ultramafic source rocks this is consistent both with available remote sensing data which indicate the presence of mafic minerals such as pyroxene and olivine and with petrologic modeling based on available geophysical data which suggest that martian lavas are probably iron rich and ultramafic these data strongly suggest that basaltic volcanism is widespread on mars and much of the photogeological data may be studied in this context photogeological analysis of the martian surface has shown two main types of volcanic morphologies the first type is central volcanoes which are volcanic landforms developed by continued and prolonged eruption from a point source vent this category includes 1 shields the classic low profile volcanic mountains of which olympus mons is the most spectacular example 2 domes steep sided constructs such as tharsis tholus that may represent lower rates of eruption than the shields or possibly more silicic lava compositions 3 highland patera radially textured low profile volcanoes that occur in the cratered terrain and are interpreted as ash shields 4 alba patera an apparently unique volcanic landform consisting of a vast volcanic center over 1500 km across with flank slopes of less than a tenth of a degree and 5 various small features such as cinder cones the second major category is volcanic plains which are units recognized by several criteria of which the presence of mare ridges and flow lobes are the most useful volcanic plains are subdivided into four main groups 1 simple flows broad smooth to rolling plains that contain numerous mare type ridges but no flow lobes interpreted as being composed of thick single cooling units 2 complex flows displaying multiple overlapping flow lobes interpreted to be indicative of thin multiple cooling units 3 undifierentiated flows plains that typically lack any morphologic identifying feature but are considered to be volcanic partly on the basis of their association with large volcanic centers and 4 questionable plains volcanic units heavily modified by other processes erosion tectonism etc so that their origins are uncertain when these categories of volcanic morphologies are combined with relative age data provided by crater statistics a volcanic history for mars can be derived as follows early heavy bombardment of mars was accompanied and followed by small scale fluvial channeling extensive flood volcanism the plateau plains and ash shield volcanism in the cratered terrain shortly after this time less extensive flood volcanism continued to resurface the planet during formation of the northern southern hemisphere dichotomy central volcanism became more prominent with the development of the alba patera center as well as the older shields and domes of the northern hemisphere early tharsis and elysium regions the development of the tharsis and elysium uplifts may have triggered the release of large scale catastrophic floods producing large channels continued uplift and lithospheric thinning concentrated volcanic activity in the tharsis region producing large shield volcanoes and extensive lava plains both central vent and plains volcanism have been active throughout martian history but the volumes of extrusion have gradually decreased with time this is consistent with a moonlike thermal history involving a lithosphere of increasing thickness with time gradually turning off the volcanism although many questions remain regarding martian volcanism the viking data have provided a remarkable detailed overview of the probable nature of the volcanic history of mars

ignimbrites of amazonis planitia region of mars a series of postulated ignimbrite units is mapped in the amazonis memnonia and aeolis quadrangles of mars the units cover about 2 2 106 km2 within a broad but discontinuous and irregular belt trending east west along the highland lowland boundary the ignimbrites overlie parts of the western and southern aureole materials of olympus mons but are embayed in places by the lava plains of the lowlands stratigraphic relations between the basalt flows from the tharsis montes region and the ignimbrites are not clearly defined crater counts suggest that the younger ignimbrites postdate the lava flows crater counts per square kilometer for the ignimbrites range from 7 29 1 95 10 4 to 6 36 2 01 10 5 for craters larger than 1 km in diameter the ignimbrite materials form thick 100 m extensive relatively flat sheets that are smooth to grooved or gently undulating grooved surfaces appear to be yardangs and in most places are not alined with prevailing wind directions the seven mapped ignimbrite units are characterized by morphologic expression stratigraphic position and crater counts similarities to ignimbrites in the pancake range of central nevada include 1 rounded patches of smooth high albedo nonwelded material superposed on jointed low albedo welded material 2 local complementary joint sets in welded materials and 3 thick flow sheets of great areal extent that follow but subdue underlying topography four major eruptive centers occur in areas where units are thickest and where a dominant nnw sse structural trend is expressed locally by unit margins elongate collapse features and normal faulting a minimum volume of 3 85 106 km3 for the deposits has been calculated from thickness estimates based on shadow measurements and crater rim height relations

the nature and partitioning of invisible gold in the pyrite fluid system the most characteristic feature of hydrothermal deposits of gold is its intimate association with pyrite microscopically visible gold occurs in pyrite ore as metal particles of 0 1 m in size together with so called invisible gold undetectable by conventional microscopic methods the chemical redox and structural state of this invisible gold and the mechanisms of its incorporation into pyrite remain both inconsistent and controversial since the dawn of economic geology to clarify these issues we performed laboratory experiments to simulate interactions of gold bearing sulfur rich hydrothermal fluids with arsenic free pyrite at temperatures from 350 to 450 c and pressures from 400 to 700 bar typical of the formation conditions of many types of gold deposits gold solubility was measured in these fluids as a function of sulfur speciation and acidity gold redox and structural state in pyrite was characterized by high energy resolution fluorescence detected x ray absorption spectroscopy herfd xas together with more traditional analytical techniques such as scanning electron microscopy sem x ray diffraction xrd electron probe micro analysis epma laser ablation inductively coupled plasma mass spectrometry la icpms and inductively coupled plasma atomic emission spectrometry icp aes results show that dissolved au in sulfide sulfate solutions forms complexes with hydrogen sulfide and tri and di sulfur radical ions whose amounts depend mostly on the fluid ph and total sulfur concentration invisible gold in pyrite occurs as au metal submicron to nano sized particles and chemically bound au i in the form of poly sulfide clusters composed on s au s linear units similar to those in aqueous complexes our findings contest the common belief that au i substitutes for fe and or s in the structure of as poor pyrite the partition coefficient of au i between pyrite and the fluid dpy fl is determined to be 0 15 0 07 at 450 c in a wide range of au fluid phase concentrations 10 1000 ppm but much higher dpy fl values between 10 and 50 are found at 350 c these au partitioning trends coupled with the new data on au molecular environment in pyrite suggest a control of au i incorporation in the mineral by a chemisorption step extrapolated to au contents of hydrothermal fluids of the earth s crust which are typically below 1 ppm our dpy fl values reproduce fairly well the natural au tenors in as poor pyrites 0 1 1 ppm au which are 100 1000 times lower than those typically observed in arsenian pyrites and arsenopyrites 10 1000 ppm au at as tenors of 0 01 10 wt our results thus indirectly highlight a key role played by arsenic in gold enrichment in as bearing iron sulfide ore a role that yet remains to be fully understood and quantified

tectonic and stratigraphic controls of hydrocarbon systems in the ordos basin a multicycle cratonic basin in central china the ordos basin is the oldest and still an important hydrocarbon province in central china it is a typical cratonic basin developed on the archean granulites and lower proterozoic greenschists of the north china block the development of the ordos basin during the paleozoic mesozoic can be divided into three evolutionary stages cambrian early ordovician cratonic basin with divergent margins middle ordovician middle triassic cratonic basin with convergent margins and late triassic early cretaceous intraplate remnant cratonic basin two hydrocarbon systems are present in the basin the paleozoic gas and mesozoic oil systems in the paleozoic gas system the lower ordovician marine carbonates and pennsylvanian lower permian coal measures serve as source rocks the lower ordovician karst modified dolomites and pennsylvanian bauxitic mudstones form a significant reservoir seal association and the pennsylvanian lower permian deltaic sandstones and upper permian lacustrine mudstones form another effective reservoir seal association in the mesozoic oil system the upper triassic lacustrine mudstones are mature source rocks the upper triassic deltaic sandstones and overlying shallow lacustrine and swamp mudstones form a reservoir seal association and the lower jurassic fluvial sandstones and overlying shallow lacustrine and swamp mudstones form another reservoir seal association in both hydrocarbon systems the stratigraphic variations provide the principal traps the ordos basin is characterized by a stable tectonic setting that controlled the distribution of depositional systems and the development of erosional surfaces and ultimately governed the distribution of oil and gas fields and trap types

gold and sulfur sources of the taipingdong carlin type gold deposit constraints from simultaneous determination of sulfur isotopes and trace elements in pyrite using nanoscale secondary ion mass spectroscopy abstract the youjiang basin in southwestern china is known for the occurrence of abundant carlin type gold deposits similar to those of northern nevada in the u s among them taipingdong is a representative deposit nearby the super large shuiyindong mine in the huijiabao ore field though some data of in situ sulfur isotopes and trace element geochemistry of pyrite have been collected recently the ore forming fluid source and genesis model of the deposits remain under debate the mineral chemistry and isotopic compositions of au carrying pyrite in the taipingdong gold deposit were studied in detail using nanoscale secondary ion mass spectroscopy nanosims in this study to further understand the aforementioned issues petrographic observations identified two types of pyrite syn sedimentary framboidal pyrites and hydrothermal pyrites back scattered electron observations and electron microprobe analysis elemental mapping showed that the latter have three generations termed as as poor py1 the core as rich py2 the middle overgrowth and as weak py3 the outmost overgrowth zone respectively nanosims high resolution multiple elemental maps showed the following 1 py1 is poor in as and other trace elements py2 is rich in as and cu and relatively rich in se and py3 is rich in au and relatively rich in as cu and se 2 gold is heterogeneously distributed as solid solution and nanoparticle focusing on the outermost rim of the zoned pyrite py3 other metal nanoparticles of cu se and pb were identified in py2 or py3 3 arsenic elemental mapping showed dense mineral growth of pyrite in the subzones 4 line profile analyses of trace elements showed high cu contents in py2 and py3 and that as is positively correlated with cu but not with au in situ sulfur isotopic analyses showed that the 34s values range from 15 4 to 6 1 with a median of 2 0 for py1 from 1 8 to 7 1 with a median of 1 4 for py2 and from 3 0 to 6 2 with a median of 3 9 for py3 intensive spot analyses showed a slight fluctuation in s isotopic values within a short distance in pyrite subzones the 34s values of py2 and py3 dropped into a narrow range from 3 to 6 with a median of 3 3 considering the composition and isotopic characteristics py1 is classified as pre ore pyrite and py2 and py3 as ore pyrites with py3 representing the au climax event the au state and distribution in the pyrite of the taipingdong deposit imply that the ore forming fluid was unsaturated for au but occasionally hosted metal nanoparticles the au climax event occurred towards the end of the fluid evolution the decoupling of as and au in the ore pyrites indicate that the au carrying capacity of the pyrite was limited by the higher concentration of cu ions in the ore forming fluids the s isotopic data of the taipingdong deposit is similar to the available in situ s isotopic range of 5 to 5 of the representative au deposits in the basin except for the lannigou zhenfeng mine the s isotopic deviation of pyrite in the huijiabao ore field to the typical magmatic fluid 0 may be the result of a mixture of hydrothermal and basin fluid to a certain extent this feature combined with the intensive fluctuation of trace elements and isotopic compositions over a short duration accord with the characteristics of magmatic hydrothermal fluid combined with the strong silicification characteristic of the host rock and the previous geophysical works in the ore district a magmatic hydrothermal model might be suitable for the taipingdong gold deposit and even other carlin type gold deposits in the youjiang basin

new martian paradigms several interrelated paradigms concerning the nature and the evolution of mars are discussed these include an impact origin of the northern lowland mars as a water rich planet former oceans in the northern lowlands a warm wet climate on early mars and the possibility of ancient life on mars locations on mars suggested for the search of possible ancient life include the heavily cratered terrain dissected by valley networks possible lacustrine deposits in valles marineris the oxidizing layer below the surface sites along the fringes of the hypothetical northern circumpolar ocean and in evaporite deposits

ore characteristics of the sandstone type daying uranium deposit in the ordos basin northwestern china the ordos basin is one of the top oil gas and coal producing basins in china and is increasingly recognized as an important uranium mineralization province uranium deposits occur near the margin of the basin and are mainly hosted in the sandstones of the jurassic zhiluo formation the daying uranium deposit in the ordos basin is one of the most important large sandstone type uranium deposits in china based on thin section analysis and electron microprobe measurements we used analytical chemical data to study the characteristics of the daying uranium deposit including the type structure particle size material composition chemical composition form and valence state of the uranium the uranium mainly exists in three forms an absorbed form independent minerals and uranium bearing minerals most of the uranium in the ore is u4 and the proportion of u6 ranges from 18 to 55 with an average of 33 the proportion of u6 is relatively high in the cores containing low grade ore this study pr

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

multiple element mapping and in situ s isotopes of au carrying pyrite of shuiyindong gold deposit southwestern china using nanosims constraints on au sources ore fluids and mineralization processes abstract this study employed high sensitivity and high resolution secondary ionizing mass spectrometry nanosims to determine the distribution of au as cu se and s isotopes of pyrite from the shuiyindong au deposit southwestern china nanosims maps show that au occurs as solid solution and heterogeneously distributes at micron scale in the ore pyrite which is the overgrowth of the preexisting synsedimentary or hydrothermal pyrite core commonly rimmed again by the as and au poor outermost zone there is no detectable au in the synsedimentary pyrite invisible au was observed to fill in the submicron scale cracks of the ore pyrite meanwhile element line profile analysis shows that au occurs in three discrete climaxes in the ore pyrite in situ s isotopic analyses identified two types of s sources the synsedimentary pyrites have large negative 34s values ranging from 38 3 to 18 8 which is a typical biogenetic s generated by bacterial reduction of sea water sulfate the hydrothermal pyrites with zoned texture have a narrow 34s range of 3 5 7 4 with a median of 2 3 similar to the recently published sulfur isotope data of the southwest china s carlin type gold deposits except for the lannigou mine combining the distribution of au and s isotopes in pyrite indicates that the au carrying zones have lower 34s values than that of the ore unrelated zones these nanosims observations indicate that the au mineralization was closely associated with strong deformation of the host rock the au forming the deposit was exotic instead of the reactivated au in the preexisting pyrite formed in the synsedimentary basin the mineralization progress was multistage the distribution of au and s isotopes is hard to interpret by the viewpoint of metamorphic fluid or fluid pressure fluctuation instead it is more consistent with magmatic fluid likely contaminated by sedimentary sulfur during its ascending to the surface in addition the multistage ore formation pattern discovered in this study poses new challenges to determine the mineralization age of the au deposits in southwestern china

source of gold in neoarchean orogenic type deposits in the north atlantic craton greenland insights for a proto source of gold in sub seafloor hydrothermal arsenopyrite in the mesoarchean abstract given that gold au mostly remained in the incipient earth mantle until ca 3 9 3 8 ga a proto source of gold may have been present in the dominantly mafic crust precursor born through first stage melting of the early earth mantle in south westernmost greenland a fragment of the north atlantic craton is characterised by greenstone belts comprising mafic volcanic and magmatic rocks and harzburgite cumulates that were emplaced at ca 3 0 ga prograde amphibolite facies metamorphic assemblages and caused local dissolution of arsenopyrite during this retrograde tectono metamorphic stage in gold rich shear zones the re os geochronometer in arsenopyrite was reset to a neoarchean age while invisible gold was liberated and deposited as free gold with 2 66 ga pyrite re os isochron ages the initial os isotope ratios of neoarchean arsenopyrite 187os 188osi 0 13 0 02 and gold bearing pyrite 0 12 0 02 overlap with the estimated 187os 188os ratio of the mesoarchean mantle 0 11 0 01 and preclude contribution of radiogenic crustal os from evolved lithologies in the accretionary arc complex but instead favour a local contribution in os from basaltic rocks and serpentinised harzburgite protoliths by metamorphic fluids thus the ca 2 66 ga lode gold mineralisation identified in the north atlantic craton may illustrate a gold endowment in shear zones in earth s stabilizing continental crust at the time of the 2 75 2 55 ga global gold event through metamorphic upgrading of bulk gold which had originally been extracted from the mesoarchean mantle and concentrated in hydrothermal arsenopyrite deposits in oceanic crust beneath the overall reduced mesoarchean ocean

detecting magmatic derived fluids using pyrite chemistry example of the chibougamau area abitibi subprovince quebec abstract magmatic fluids are an important carrier of precious and base metals in many mineralized systems porphyry deposits intrusion related gold systems irgs volcanogenic massive sulfides vms recognizing magmatic inputs is essential for understanding metallogenic processes and for developing accurate exploration models and the importance of fluids exsolved from magmas remains a source of much debate for some contexts such as irgs and orogenic gold deposits this study aims to identify magmatic fluids in the chibougamau area northeastern corner of the neoarchean abitibi subprovince canada using pyrite chemistry this is achieved by comparing the chemistry of pyrites recovered from the cu au magmatic hydrothermal porphyry systems of the chibougamau area to background compositions i e the chemistry of pyrites from weakly mineralized rocks from the same area analyses of quantitative laser ablation inductively coupled plasma mass spectrometry la icp ms are processed in three distinct manners to better evaluate the trace elements controlled by silicates oxides sulfides and sulfosalt inclusions and the trace elements that are structurally bound to pyrite detailed investigation of the trace element content of pyrite indicates that most elements are controlled by silicate inclusions some reflect the composition of the host rock others correlate with the mineralizing style and only te and bi are discriminant of the porphyry systems of the chibougamau area tellurium is structurally bound to pyrite or forms telluride nanoparticles in the study area while the distribution of bi is controlled by galena and chalcopyrite inclusions and pyrite chemistry is interpreted using absolute te values and bi ratios bi pb and bi cu this study provides insight into the cu au magmatic hydrothermal systems of the chibougamau area it also has implications for the way pyrite chemistry can be used to probe for magmatic fluids in other mineralized contexts

multi stage enrichment processes for large gold bearing ore deposits abstract a review of previous studies of the world s large hydrothermal gold deposits indicates that the largest deposits tend to show complicated parageneses where multiple gold enrichment events and processes have been involved in the deposit generation these observations suggest that multistage processes may even be a requirement for the formation of large deposits in some deposits e g witwatersrand boddington cadia sukhoi log or carlin the different enrichment processes occur millions of years apart in others such as many large porphyry deposits the different stages are much closer in time in many deposits particularly sedimentary hosted deposits early diffuse enrichment occurs within a particular province that is then upgraded by more focused processes e g sukhoi log kalgoorlie the presence of this early diffuse enrichment could explain the tendency for gold deposits to cluster into camps this model has important implications as the presence or absence of multiple gold events could be used to discriminate at the exploration and feasibility stages between small deposits with single stage ore genesis and more complicated deposits with multistage enrichment and the potential for larger gold endowment

icp ms a powerful tool for high precision trace element analysis in earth sciences evidence from analysis of selected u s g s reference samples abstract inductively coupled plasma mass spectrometry icp ms is a powerful analytical technique with considerable application to geochemistry in this paper we demonstrate the power of icp ms as a tool in petrogenetic studies data for 28 elements in seven u s g s basalt and andesite reference samples agv 1 bcr 1 bhvo 1 bir 1 dnc 1 w 1 and w 2 are presented accuracy and precision standard deviation for 26 of these elements is either excellent a detailed description of the icp ms technique we have developed is given a simple hf hno 3 dissolution in screwtop teflon bombs was used for sample preparation icp ms instrumental sensitivity was measured by external solutions with surrogate calibration for 4 elements matrix correction was made by use of standard addition naturally occurring internal standards rb y ce and pb were used to correct for instrumental drift between sample and spiked sample measurements we report data for the elements li cs rb sr ba zr hf nb ta y sc u th pb and all 14 of the ree in addition the procedure acquired data for be mo w tl and bi many elements in this array are crucial for the evaluation of petrogenetic models and source tracing herein lies the real power of icp ms one technique one dissolution small sample size good limits of detection good to excellent accuracy and good precision for many geochemically important elements

lahars in the elysium region of mars photogeological studies of the elysium volcanic province mars show that its sinuous channels are part of a large deposit that was probably emplaced as a series of huge lahars some flows extend 1000 km from their sources the deposits are thought to be lahars on the basis of evidence that they were 1 gravity driven mass flow deposits lobate outlines steep snouts smooth medial channels and rough lateral deposits deposits narrow and widen in accord with topography and extend downslope 2 wet channeled surfaces draining features and 3 associated with volcanism the deposits and channels extend from a system of fractures which also fed lava flows heat associated with magmatism probably melted ground ice below the elysium volcanoes and formed a muddy slurry that issued out of regional fractures and spread over the adjoining plain the identification of these lahars adds to the evidence that mars has a substantial volatile element endowment

ore forming fluid source of the orogenic gold deposit implications from a combined pyrite texture and geochemistry study abstract interpretation of bulk sulfur isotope data of the orogenic gold deposit is frequently hampered by complex zoning in pyrite which calls for in situ determination of sulfur isotope composition of sulfide minerals the qiuling gold deposit located in qinling orogen is representative of orogenic type and selected here to further constrain the source of sulfur and au and test the current popular ore genesis models for deposits of this type detailed backscattered electron imaging bse study is applied to characterize intragrain texture and subsequently in situ sulfur isotope and trace element determination using secondary ion mass spectrometry sims and laser ablation inductively coupled plasma mass spectrometry la icp ms are used to reveal sulfur and metal source and evolution of the ore forming fluid two generations of pyrite i e pre ore stage py1 and ore stage pyrite py2 were investigated in this study in most cases py1 occurs as pyrite framboids while py2 as euhedral grains in which py2a as anhedral core py2b and py2c as euhedral inner and outer rim respectively the 34s values of both py1 and py2 have unusual wide ranges i e a 34s variation from 31 1 to 106 7 for py1 average 0 8 and from 2 7 to 24 1 for py2 average 13 2 the distribution pattern of 34s values in py1 is accommodated with rayleigh fractionation in sulfate restricted pore water modeling results show that neither temperature nor oxygen fugacity change could result the variations in 34s values of py2 and contribution of both preexisting pyrite and a pulse of ore forming fluid with 34s about 14 2 may be responsible for the observed variation in py2 such fluid may have been sourced from metamorphism of old strata such as the neoproterozoic basement furthermore py2a shows an intimate relationship with py1 in its 34s values indicating py1 may have acted as part of sulfur source in the formation of py2a py1 is rich in a suit of element such as bi co mn ni tl and has the lowest as and au py2a is similar with py1 but with elevated as and au py2b contains more abundant as and au compared to py2a py2c is rich in as and especially au but depleted in other elements compared to py2a the distribution pattern coupled with sulfur isotope composition indicates that py2a was likely formed with a contribution of trace elements and sulfur from py1 at the start of hydrothermal process py2b was formed with elevated proportion of contribution from the ore forming hydrothermal fluid while py2c was formed solely by the ore forming fluid without a contribution from previous pyrite consequently the ore forming fluid in the qiuling gold deposit was rich in as au cu and sb while depleted in other metals such as bi co mn ni and tl indicating that the pre ore framboid pyrite may have not contributed any au and as during mineralization this study highlights the importance of detailed texture characterization coupled with relatively large data set of in situ sulfur isotope and trace elements for orogenic gold deposit research and further proves that metamorphic fluids may have significant contribution for au mineralization in orogenic gold deposits

geomorphic evidence for the distribution of ground ice on mars high resolution viking orbiter images show evidence for quasi viscous relaxation of topography the relaxation is believed to be due to creep deformation of ice in near surface materials the global distribution of the inferred ground ice shows a pronounced latitudinal dependence the equatorial regions of mars appear to be ice poor while the heavily cratered terrain poleward of 30 latitude appears to be ice rich the style of creep poleward of 30 varies with latitude possibly due to variations in ice rheology with temperature the distribution suggests that ice at low latitudes which is not in equilibrium with the present atmosphere has been lost via sublimation and diffusion through the regolith thereby causing a net poleward transport of ice over martian history

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

ice in the northern lowlands and southern highlands of mars and its enrichment beneath the elysium lavas a comprehensive study of the elysium region has revealed evidence of widespread ground ice whose concentration and depth has varied considerably ejecta mobility and crater morphology analyses of a database of 7289 craters which range in diameter from 1 875 to over 160 km have been used to investigate the distribution of ice between longitudes 245 155 and latitudes 20 s 45 n an area incorporating all of the elysium quadrangle and large portions of amenthes amazonis mare tyrrhenum aeolis memnonia cebrenia and diacria quadrangles assuming that the observed variations in the crater characteristics are the result of the incorporation of varying concentrations of subsurface volatiles the ice distribution is shown to be strongly dependent upon latitude though its concentration varies with depth and is strongly influenced by geological setting important differences have been detected in the distribution of southern and northern lowland ground ice while there is substantial evidence of near surface ice in the northern lowlands where near surface limits are strongly influenced by latitude the greatest concentrations of subsurface ice occur at much greater depths in the southern highlands in addition the ice appears to be enriched at depth in the elysium lavas and nearer to the surface in deposits located to the northwest of elysium mons and in the vastitas borealis formation this distribution suggests that several ice emplacement mechanisms have operated on mars including the enrichment of the deeper ice by juvenile water from beneath the elysium volcanic province and the redistribution to the lowlands of a highly concentrated ice reservoir from a great depth within the highlands

protracted fluid rock interaction in the mesoarchaean and implication for gold mineralization example from the warrawoona syncline pilbara western australia abstract oxygen isotopic and geochemical analyses on whole rock and quartz veins are combined with structural observations in order to constrain the fluid circulation history within the mesoarchaean warrawoona syncline of the north pilbara craton western australia the plumbing system which is the focus of this study is localized in the so called fielding s find shear zone ffsz a km scale shear zone formed during the burial of greenstones and coeval exhumation of granitic complexes this shear zone runs parallel or close to the axial plane of the syncline it involves a prominent quartz vein network and is lined with strongly hydrothermally altered mafic felsic and sedimentary rocks towards the ffsz felsic and mafic volcanic rocks become intensely silicified with an increase in bulk rock 18 o values from 10 8 to 25 1 for altered felsic volcanics and from 7 1 to 18 3 for altered mafic volcanics geochemical modelling ascribes the silicification to a dissolution precipitation process ree and most other trace elements are strongly depleted in the silicified units with the exceptions of elements such as v cr ni and co which are enriched throughout the warrawoona syncline vein quartz 18 o data are within a small range of 13 2 2 significantly lower than their silicified host rocks these data are interpreted as the result of two main paleo fluid circulation stages intense silicification and 18 o enrichment represent alteration driven by low temperature hydrothermal convection probably involving archaean seawater in contrast the quartz veins network is related to the infiltration of metamorphic and or magmatic fluids during a later deformation episode these quartz veins represent the event responsible for the bulk of economic lode gold formation in the area the protracted fluid rock interaction history in the warrawoona syncline may have played a major role in setting the stage for the late mineralizing event the early hydrothermal circulation could have formed an efficient plumbing system characterized by high permeability low reactivity and possibly au enrichment upgrading the au endowment to the late hydrothermal fluids

volcano ground ice interactions in elysium planitia mars abstract the occurence within elysium planitia of meltwater deposits possible pseudocraters collapse features within troughs and outflow channels indicates that a layer of subsurface volatiles existed at the time of volcanic activity within this area the pseudocraters are interpreted to be indicators of near surface volatiles while meltwater deposits and the degree of preservation of trough walls and floors are thought to signify greater volatile depths a latitudinal variation in the distribution of these features indicates either that the depth to the volatile layer increased from less than about 50 m at 35 n to greater than 600 m at 24 n or that an ice wedge that existed at 35 n thinned to nonexistence at 24 n braided distributary channel systems within the chaotic terrain north of elysium planitia show that ephemeral lakes were repeatedly created and drained at this locality the existence of volatiles contemporaneous with volcanic activity permits a search to be made for explosively generated landforms predicted to exist by previous theoretical models morphological evidence for strombolian vulcanian and plinian eruptions is lacking within western elysium planitia there are no identifiable cinder cones pyroclastic flow deposits or mantled areas indicative of large airfall deposits at an image resolution of 50 150 m pixel however the pseudocraters indicate that small scale phreatomagmatic activity may have taken place

global distribution and migration of subsurface ice on mars a thermal diffusive model of h2o kinetics and equilibrium was developed to investigate the long term evolution and depth distribution of subsurface ice on mars the model quantitatively takes into account 1 obliquity variations 2 eccentricity variations 3 long term changes in the solar luminosity 4 variations in the argument of subsolar meridian in planetocentric equatorial coordinates 5 albedo changes at higher latitudes due to seasonal phase changes of co2 and the varying extent of co2 ice cover 6 planetary internal heat flow 7 temperature variations in the regolith as a function of depth time and latitude due to the above factors 8 atmospheric pressure variations over a 104 year time scale 9 the effects of factors 1 through 5 on seasonal polar cap temperatures and 10 knudsen and molecular diffusion of h2o through the regolith the migration of h2o into or out of the regolith is determined by two boundary conditions the h2o vapor pressure at the subsurface ice boundary and the annual average h2o concentration at the base of the atmosphere these are controlled respectively by the annual average regolith temperature at the given depth and seasonal temperatures at the polar cap starting from an arbitrary initial uniform depth distribution of subsurface ice h2o fluxes into or out of the regolith are calculated for 100 selected obliquity cycles each representing a different epoch in mars history the h2o fluxes are translated into ice thicknesses and extrapolated over time to give the subsurface ice depth as a function of latitude and time the results show that obliquity variations influence annual average regolith temperatures in varying degrees depending on latitude with the greatest effect at the poles and almost no effect at 40 lat insolation changes at the pole due to obliquity argument of subsolar meridian and eccentricity variations can produce enormous atmospheric h2o concentration variations of 6 orders of magnitude over an obliquity cycle superimposed on these cyclic variations is a slow monotonic change due to the increasing solar luminosity albedo changes at the polar cap due to seasonal phase changes of co2 and the varying thickness of the co2 ice cover are critically important in determining annual average atmospheric h2o concentrations despite the strongly oscillating character of the boundary conditions only small amounts of h2o are exchanged between the regolith and the atmosphere per obliquity cycle 10 g cm2 the net result of h2o migration is that the regolith below 30 40 lat is depleted of subsurface ice while the regolith above 30 40 lat contains permanent ice due to the depth of penetration of the annual thermal wave this result is supported by recent morphological studies the rate of migration of h2o is strongly dependent on average pore capillary radius for which we have assumed values of 1 and 10 m we estimate that the h2o ice removed from the regolith would produce a permanent ice cap with a volume between 2 106 and 6 106 km3 this generally agrees with estimates deduced from deflationary features at lower latitudes depositional features at higher latitudes and the mass of the polar caps

insights into the liquid bismuth collector model through analysis of the bi au stormont skarn prospect northwest tasmania the liquid bismuth collector model has previously been proposed to explain the common association between gold and bismuth seen in many ore deposits and involves the scavenging of gold from hydrothermal fluid by liquid bismuth here textural relationships and temperature and chemical conditions of mineralization at the stormont bi au skarn prospect in northwestern tasmania are analyzed to investigate whether the liquid bismuth collector model can explain gold accumulation at this prospect the calc silicate skarn assemblage containing grandite hedenbergite actinolite magnetite epidote quartz and calcite suggests that initial metasomatism involved temperatures 400 to 500 c visible gold is associated with native bismuth bismuthinite maldonite galena and an unknown bi te s mineral native bismuth is directly associated with grandite which formed during initial stages of metasomatism this implies that bismuth would have precipitated from a hydrothermal fluid as a liquid heating experiments showed that bismuth alloy inclusions in garnet melt between temperatures of 250 and 288 c the mineralization setting at stormont and textural relationships suggest that gold was scavenged from hydrothermal fluids by liquid bismuth rhythmically zoned grandite crystals provide evidence for fluctuating hydrothermal fluid conditions which may have contributed to dissolution and reprecipitation of gold thus facilitating an ore zone refining process within the prospect this refining process is made possible by the tendency of liquid bismuth to scavenge gold from significantly under saturated fluids infiltrating gold undersaturated fluids can dissolve gold not in contact with bismuth which can then be preferentially redeposited upon encountering a bismuth droplet enhancing the correlation between the two elements a long lived and focused fluid flow system would maximize the efficiency of this ore zone refining process which is likely to be relevant to gold deposition at a range of deposit types

sedimentary record of triassic intraplate extension in north china evidence from the nonmarine nw ordos basin helan shan and zhuozi shan abstract the helan shan and zhuozi shan of the nw ordos basin china contain thick up to 4 km sequences of nonmarine triassic strata these rocks represent a major intraplate sedimentary basin the paleogeography tectonic setting and provenance of which are poorly understood and controversial studies of the sedimentary geology of the basin supported by new palinspastic reconstruction of younger deformation demonstrate that the basin filled from three sides by fluvial lacustrine deltaic and alluvial fan depositional systems the basin forms a westward thickening wedge that reaches its maximum thickness along the western margin of the helan shan and thins to a relatively constant 600 800 m east of the zhuozi shan the stratigraphy of the basin is strongly asymmetric alluvial fan strata are restricted to the extreme western margin of the basin and interfinger with axial fluvial deposits low in the section and deep lacustrine facies high in the section much of the eastern part of the basin is dominated by west flowing meandering river and deltaic systems large structures of triassic age have not been identified in the helan shan or zhuozi shan but small triassic normal faults have been documented in the western and central helan shan these characteristics most strongly support an extensional origin for the triassic basin in nw ordos the basin is interpreted to have been a north trending half graben bound along its western margin by an east dipping normal fault presently concealed beneath quaternary cover west of the helan shan the eastern margin now found in the zhuozi shan has simple ramp margin geometry driving mechanisms for this extension are not obvious due to limited documentation of triassic structure throughout the region but probably relate to far field stresses from the qinling or jinsha active margins interacting with the stable ordos block

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

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

the mechanism and kinetics of the transformation from marcasite to pyrite in situ and ex situ experiments and geological implications despite the natural abundance of pyrite and marcasite and their intergrowth and a wealth of information they can provide on the physical chemical conditions of mineral deposits a complete mechanistic and kinetic study on the phase transformation from the thermodynamically metastable polymorph marcasite to the stable polymorph pyrite is yet to be made this limits the application of marcasite as an indicator mineral for low temperature geological environments here we report results from in situ synchrotron powder x ray diffraction and ex situ anneal quench experiments at 400 540 c demonstrating that the mechanism and kinetics of this transformation depend not only on temperature but also on particle size the presence of water vapor and the presence of pyrite inclusions in marcasite under dry conditions the transformation is limited by surface nucleation and occurs via epitaxial nucleation of pyrite on marcasite with 100 pyrite 101 marcasite and 001 pyrite 010 marcasite in contrast in the presence of water vapor there is little crystallographic orientation relationship between the two phases the transformation is still limited by surface nucleation but modification of the surface properties by water vapor results in a different nucleation mechanism and consequently different kinetics kinetic analysis estimates a half life of 1 5 ma at 300 c for the transformation under dry conditions with small and pyrite free marcasite grains but this estimation should be used with extreme caution due to the complexity of the transformation from synchrotron x ray fluorescence elemental mapping trace elements as and pb play an insignificant role in the transformation however the presence of a fluid phase changes the behavior of pb under dry conditions randomly oriented particles of galena formed in pyrite while under water vapor conditions arrays of nano to microparticles of galena precipitated in pores this study highlights that although the natural occurrence of marcasite can indicate low temperature environments precise estimation of temperature should not be made without considering the influences from various reaction parameters

ore forming processes in the wang ershan gold deposit jiaodong china insight from microtexture mineral chemistry and sulfur isotope compositions abstract the microtexture trace element characteristics and sulfur isotopic features of ore related minerals provide important clues to trace physico chemical conditions and source characteristics of ore formation in this study we investigate the wang ershan gold deposit in the jiaodong gold province of eastern north china craton where three hydrothermal stages were distinguished stage i is characterized by k feldspar sericite quartz with minor pyrite precipitation py i sericite quartz qtz a and pyrite py ii with minor gold precipitated during stage ii and stage iii involved quartz qtz b gold and polymetallic sulfides with minor pyrite py iii in situ 34s results show a decreasing trend from 21 7 to 14 6 py i to 9 2 8 3 py ii and 8 9 8 6 py iii the py ii and py iii are poor in mineral inclusions and porous microtextures and have no oscillatory composition zoning the co content is 1 2 order of magnitudes higher in py i 371 2 823 2 ppm av 597 2 ppm than late stage pyrites 0 4 524 2 ppm av 95 4 ppm qtz a show cataclastic breccia cemented by qtz b with little dissolution during the injection of stage iii ore forming fluids the al contents decrease from qtz a 49 0 426 6 ppm to qtz b 18 2 46 8 ppm based on the sulfur isotope trace element and microtextural characteristics in py ii and py iii combined with previous fluid inclusion studies we infer that the ore forming fluids of stage ii and iii experienced gentle immiscibility and were suggested to be of different evolutionary stages of a single ore forming fluid sharing common sources with similar and near equilibrium physicochemical conditions the trace element characteristics with lack of oscillatory compositional zoning in the two stages of quartz suggest gentle cooling with lack of any abrupt change of physicochemical conditions during fluid immiscibility the decoupling of au and as contents in py ii and py iii was likely controlled by chemisorption of gold in pyrite structure complex variation in geochemical features of ore forming fluids from early alteration to main mineralization period is indicated by the large range of 34s and co contents in py i and late stage pyrites and the differences in alteration processes based on a comparison of the co ni ni and as among pyrites from the wang ershan gold deposit typical porphyry deposits and orogenic gold deposits together with the large positive deviation of 34s relative to mantle values we propose that ore forming materials of the wang ershan gold deposit were derived from mixed sources involving magmatic hydrothermal related and sedimentary strata related components

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

mars a water rich planet abstract mars had outgassed at least 0 5 to 1 km of water 10 to 20 bar of co2 and 0 1 to 0 3 bar of n2 the volatiles that have been retained are mostly in the cratered uplands terrain softening fretted channels debris flows and closed depressions indicate that at least the upper 2 km of the cratered uplands at high latitudes 30 contain ice in amounts that exceed the porosity estimated to be 10 20 theoretical studies and lack of these features in the cratered uplands at low latitudes suggest that the upper 1 km of the uplands at low latitudes is ice poor however valley networks indicate that water was present near the surface early in the planet s history although in amounts smaller than at high latitudes the entire upper 1 km planetwide is estimated to have contained 75 125 m of water at the end of heavy bombardment the largest sink for water is the megaregolith below 1 km episodic eruption of water from the deep megaregolith cut many of the large outflow channels from the volume of water needed to cut the circum chryse channels and assuming uniform planetwide distribution of water the deep megaregolith is estimated to have contained at least 350 m of water at the end of heavy bombardment thereby giving a total minimum inventory of 424 475 m planetwide most of the water lost from the low latitude uplands by diffusion and in cutting the valley networks is now believed to be in the polar layered terrains most of the water involved in cutting the outflow channels is in the low lying northern plains where a variety of features that have been attributed to ground ice is present a large fraction of the planet s surface has been overplated with water poor volcanics of which we have samples in the snc meteorites the younger volcanics have reacted extensively with the old volatile rich basement some of the co2 and n2 outgassed was lost during heavy bombardment by impact erosion of the atmosphere and other processes the remaining was fixed carbonates and folded deep into the megaregolith during heavy bombardment

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

martian impact craters correlations of ejecta and interior morphologies with diameter latitude and terrain abstract the premise of this study is that global analysis of crater morphologies can discriminate between the effects of impact energy atmosphere and subsurface volatiles based on the correlation between morphology and latitude diameter and terrain this study focuses on seven ejecta and nine interior morphologies associated with 3819 craters 8 km in diameter distributed across the entire martian surface this data set is sufficiently large to provide statistically viable results on a global scale the results of the analyses indicate that changes in ejecta and interior morphology correlate with increases in crater diameter excavation depths corresponding to these diameters are calculated from depth diameter relationships and are compared to the theoretical distribution of subsurface volatiles the different ejecta morphologies can be described by impact into material with varying proportions of volatiles and the latidudinal variations seen for rampart crater morphologies correlate well with the proposed latitude depth relationship for ice and brines across the planet many of the interior structres show distributions indicative of terrain dependent influences for example the concentrations of central pit craters around ancient impact basins and on alba patera suggest that volatiles preferentially collect in these areas however central peak and peak ring interior morphologies show little relationship to planetary properties and probably result from changes in impact energy thus many of the unique morphologies associated with martian impact craters result from the presence of subsurface volatiles

explosive volcanism on hecates tholus mars investigation of eruption conditions evidence is presented supporting the identification of a discrete well preserved air fall deposit generated by explosive volcanism on mars the deposit is located immediately to the west of the summit caldera of hecates tholus 32on 209ow the northernmost of the three volcanic constructs in the elysium planitia region the absence of superposed impact craters larger than the resolution limit of the viking images 40 m per pixel indicates a very young age for this eruption which evidently postdates even the most recent collapse episode of the olympus mons caldera 300 m y b p neukum and hiller 1981 from the distribution of craters smaller than 2 km in diameter it appears that the air fall material mantles an area about 50 x 75 km in extent to an estimated thickness of about 100 m by adapting numerical models for terrestrial volcanic eruptions to the martian environment these dimensions imply an eruption cloud height of about 70 km in order to attain such an altitude the mass eruption rate must have been 107 kg s and the volatile content either 1 wt for h20 or 2 wt for co2 although it is not possible to distinguish between silicic and basaltic volcanism on hecates were the volatile species co2 the depth of most recent storage prior to eruption of the magma would have to be 50 100 km due to the solubility of co2 in the melt if h20 were the driving volatile a minimum depth of storage would be 0 2 4 km thereby permitting the possibility of ground water assimilation by the magma

hydrothermal mineralization in the sandstone hosted hangjinqi uranium deposit north ordos basin china abstract tabular type uranium ore deposits the hangjinqi and daying deposits have recently been found in the middle jurassic zhiluo formation north of the ordos basin china petrographic observations the chemical composition of u minerals determined by empa and fs la icp ms whole rock geochemistry and the microthermometric study of fluid inclusions have been integrated to characterize the genetic conditions of the u mineralization in the hangjinqi sandstone hosted deposit two different groups of u minerals have been identified one group includes coffinite i associated with vanadium rich micas coffinite i is enriched in vanadium v and devoid of iron fe and yttrium y and has a lree enriched chondrite normalized ree pattern the u minerals of this group are similar to meteoric fluid infiltration related deposits the second group has coeval coffinite ii and coarsely crystalline calcite cement coffinite ii is enriched in y and fe and depleted in v and is marked by a flat chondrite normalized ree pattern which is compatible with typical hydrothermal genetic deposits with high salinity mineralizing fluids the temperature and salinity of the primary aqueous inclusions in the ore stage calcite are 120 180 c and 8 00 16 34 eq wt nacl respectively these mineral assemblages temperatures and salinities indicate that the hangjinqi deposit was affected by two distinct types of ore bearing fluids low salinity meteoric waters and high salinity hydrothermal fluids the meteoric fluids event began at 97 5 ma with the titling of the northern ordos basin and the uplift of the hetao region to the north hydrothermal u mineralization occurred since 39 2 ma with the rifting of the hetao graben thus the previous biogenic model for the u mineralization should be modified in the uraniferous region of the north ordos basin

timing of gold and arsenic sulfide mineral deposition at the getchell carlin type gold deposit north central nevada pregold mineralization at the getchell carlin type gold deposit includes quartz and base metal vein mineralization associated with intrusion of a cretaceous granodiorite stock the veins contain minor pyrite and trace chalcopyrite arsenopyrite galena and sphalerite the pyrite is moderately coarse and in thin section has high relief is well polished and is fractured and locally cemented by the gold ore assemblage white micas are associated with veins near the granodiorite intrusion gold was not observed or detected by fire assay analyses of samples or electron microprobe analyses of pyrites microprobe analyses show that pregold pyrites have near stoichiometric compositions variable low arsenic is present in pyrite in samples overprinted by gold mineralization secondary ion mass spectrometry sims analyses detected trace gold in the coarse near stoichiometric pyrite in overprinted samples the pregold vein assemblage was fractured and cemented by gold ore stage mineralization the gold ore stage assemblage consists of gold and arsenic enriched pyrite and marcasite encompassed by jasperoid and drusy quartz and local late fluorite orpiment and galkhaite the consistent spatial association of jasperoid and ore pyrite reflects their near contemporaneous formation the ore pyrite occurs as either fine irregularly shaped grains or rims on earlier gold free pyrite in thin section the pyrite is visibly distinct and has a low polishing relief and a poor polish sims and electron microprobe analyses show that ore pyrites commonly contain 8 to 11 wt percent arsenic and as much as 2 400 ppm gold near the end of the ore stage fluorite orpiment and galkhaite precipitated locally in open space created by faulting or limestone dissolution late ore stage mineralization consists dominantly of open space filling realgar and calcite with minor quartz stibnite and framboidal pyrite realgar conforms to euhedral crystal faces of ore stage quartz fluorite and galkhaite calcite filled most remaining open space and conforms to euhedral crystal faces of quartz fluorite and realgar significant textural observations argue against an earlier interpretation that the gold mineralization and arsenic minerals formed as two discrete events separated by 40 m y in a few areas where calcite and realgar are in contact with ore stage quartz containing gold bearing pyrite realgar and calcite enclose gold bearing pyrite grains massive realgar and calcite distal from these contacts do not contain the gold bearing pyrite the presence of ore pyrite in realgar calcite and jasperoid requires close timing of these minerals and shows that there is no major time break separating ore stage and late ore stage mineral deposition textures indicate instead that the ore stage and late ore stage formed as part of a single evolving hydrothermal system the consistent successive overgrowth of younger minerals on perfectly preserved euhedral faces of older minerals supports the continuous evolution of the gold ore stage into the late ore stage these results are consistent with fluid inclusions that indicate that paragenetically successive minerals precipitated from an aqueous ore fluid with consistent salinity and gas contents but at declining temperatures results show that within error the 34 39 and 42 ma ages determined for fluorite and galkhaite at getchell and adularia at the nearby twin creeks mine respectively most closely approximate the timing of gold deposition at getchell

inhomogeneous distribution of ree in scheelite and dynamics of archaean hydrothermal systems mt charlotte and drysdale gold deposits western australia scheelite is a widespread accessory mineral in hydrothermal gold deposits and its rare earth element ree patterns and nd and sr isotopic compositions can be used to constrain the path and origin of the mineralising fluids and the age of the hydrothermal activity micro analyses by laser ablation high resolution inductively coupled mass spectroscopy and cathodoluminescence imaging reveal a very inhomogeneous distribution of the ree in single scheelite grains from the mt charlotte and drysdale archaean gold deposits in western australia two end member ree patterns are distinguished type i is middle ree mree enriched with no or minor positive eu anomaly whereas type ii is flat or mree depleted with a strong positive eu anomaly the chemical inhomogeneity of these scheelites is related to oscillatory zoning involving type i and type ii patterns with zone widths varying from below 1 to 200 m intra sectorial growth discontinuities syn crystallisation brittle deformation and variations in the relative growth velocities of crystallographically equivalent faces suggest a complex crystallisation history under dynamic hydraulic conditions the co existence of mree enriched and mree depleted patterns within single scheelite crystals can be explained by the precipitation of a mineral which strongly partitions mree relative to light and heavy ree scheelite itself has such characteristics as does fluorapatite which is locally abundant and has ree contents similar to that of scheelite in this context the systematic increase of the eu anomaly between type i and type ii patterns is produced by the difference between the partition coefficients of eu2 and eu3 and not by fluid mixing or redox reactions consequently the high positive eu anomaly typical of scheelite from gold ores may not necessarily be inherited from the hydrothermal fluid but may reflect processes occurring during ore deposition this case study demonstrates that in hydrothermal systems characterised by low ree concentrations in the fluid and by the precipitation of a ree rich mineral which strongly fractionates the ree the ree patterns of such a mineral will be highly sensitive to the dynamics of the hydrothermal system

the coupled geochemistry of au and as in pyrite from hydrothermal ore deposits the ubiquity of au bearing arsenian pyrite in hydrothermal ore deposits suggests that the coupled geochemical behaviour of au and as in this sulfide occurs under a wide range of physico chemical conditions despite significant advances in the last 20years fundamental factors controlling au and as ratios in pyrite from ore deposits remain poorly known here we explore these constraints using new and previously published empa la icp ms sims and pixe analyses of as and au in pyrite from carlin type au epithermal au porphyry cu cu au and orogenic au deposits volcanogenic massive sulfide vhms witwatersrand au iron oxide copper gold iocg and coal deposits pyrite included in the data compilation formed under temperatures from 30 to 600 c and in a wide variety of geological environments the pyrite au as data form a wedge shaped zone in compositional space and the fact that most data points plot below the solid solubility limit defined by reich et al 2005 indicate that au1 is the dominant form of au in arsenian pyrite and that au bearing ore fluids that deposit this sulfide are mostly undersaturated with respect to native au the analytical data also show that the solid solubility limit of au in arsenian pyrite defined by an au as ratio of 0 02 is independent of the geochemical environment of pyrite formation and rather depends on the crystal chemical properties of pyrite and post depositional alteration compilation of au as concentrations and formation temperatures for pyrite indicates that au and as solubility in pyrite is retrograde au and as contents decrease as a function of increasing temperature from 200 to 500 c based on these results two major au as trends for au bearing arsenian pyrite from ore deposits are defined one trend is formed by pyrites from carlin type and orogenic au deposits where compositions are largely controlled by fluid rock interactions and or can be highly perturbed by changes in temperature and alteration by hydrothermal fluids the second trend consists of pyrites from porphyry cu and epithermal au deposits which are characterised by compositions that preserve the au as signature of mineralizing magmatic hydrothermal fluids confirming the role of this sulfide in controlling metal ratios in ore systems

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

constraints on early events in martian history as derived from the cratering record the shapes and densities of crater size frequency distribution curves are used to constrain two major events early in martian history termination of high obliteration rates and viability of the multiple impact origin of the crustal dichotomy distribution curves of fresh craters superposed on uplands intercrater plains and ridged plains display shapes and densities indicative of formation prior to the end of heavy bombardment this observation correlates with other geologic evidence suggesting a major change in the erosional regime following the last major basin size impact i e argrye in addition the multisloped nature of the curves supports the idea that the downturn in the crater size frequency distribution curves reflects the size frequency distribution of the impactors rather than being the result of erosion the crustal dichotomy formed prior to the heavy bombardment intermediate epoch based on distribution curves of knobby terrain if the dichotomy resulted from a single gigantic impact this observation places constraints on when this event happened an alternate theory for dichotomy formation the multiple impact basin idea is questioned since distribution curves of large basins as well as heavy bombardment era units are not represented by a 3 differential power law function this study finds fewer basins missing on mars compare to the moon and mercury than previously reported the area covered by these missing basins is less than that covered the northern plains

partitioning of arsenic between hydrothermal fluid and pyrite during experimental siderite replacement abstract arsenian pyrite is the major host mineral of gold in carlin type gold deposit ctgd and forms during the interaction of h2s bearing hydrothermal fluids with fe bearing carbonates e g siderite ankerite fe rich dolomite in the wall rock experimental replacement of siderite at hydrothermal conditions i e 200 c psat was used to study the parameters that control the formation of ctgd pyrite i e ph time ah2s and the partitioning of as between the hydrothermal fluid and newly formed pyrite hydrothermal pyrite formed via replacement of siderite in experiments mainly occurs as two types 1 porous massive pyrite at alkaline ph conditions or 2 clusters of dense euhedral to anhedral pyrite grains at slightly acidic conditions ph concentration of as in newly formed pyrite depends strongly on the as concentration of the hydrothermal fluid used in the experiment calculated partition coefficients vary between 300 and 1700 with lowest d values at high as concentrations of the fluid in the studied system as 1 substitutes for s 2 as indicated by the correlation of high as with low s concentrations experimental findings agree well with previous studies in natural ctgd on as substitution and the partitioning of as between ore stage pyrite and hydrothermal fluids trapped as fluid inclusions the newly constrained partition coefficients for as help to explain the large heterogeneity in natural ctgd pyrite compositions which is caused by changes in the fluid composition due to the strong partitioning of as into the forming pyrite

ground ice on mars inventory distribution and resulting landforms abstract most 90 of the estimated original volume of outgassed water on mars cannot be satisfactorily accounted for by exospheric escape or storage in the atmosphere as frost or in the permanent north polar ice cap the balance may be stored as ground ice in the martian cryosphere a zone of permanently frozen ground that is protected from the atmosphere by a debris cover ground ice can exist throughout the entire cryosphere but it need not fill it if the ground ice does fill the cryosphere then excess water can exist in a confined aquifer the theoretical distribution of ground ice can be tested by identification of forms on the martian surface that may be related to the presence of subsurface ice the observed features that are most likely to reflect ground ice are thermokarst like pits and debris flows landforms with ambivalent origins include polygonally patterned ground lobate ejecta blankets craters with central pits and curvilinear features the most persuasive morphologic evidence for ground ice is thermokarst pits and debris flows the thermokarst pits are primarily located in the volcanic regions of tharsis and elysium the association of ice related features with these volcanic areas suggests that these forms are not directly latitude dependent activation by orbital variations could produce periodic multiple episodes of melting that are dependent upon latitude the presence of ice related features in both hemispheres and the equatorial region of mars indicates that ground ice may be or have been present over the entire planet as predicted by the cryosphere model

genetic and grade and tonnage models for sandstone hosted roll type uranium deposits texas coastal plain usa abstract the coincidence of a number of geologic and climatic factors combined to create conditions favorable for the development of mineable concentrations of uranium hosted by eocene through pliocene sandstones in the texas coastal plain here 254 uranium occurrences including 169 deposits 73 prospects 6 showings and 4 anomalies have been identified about 80 million pounds of u 3 o 8 have been produced and about 60 million pounds of identified producible u 3 o 8 remain in place the development of economic roll type uranium deposits requires a source large scale transport of uranium in groundwater and deposition in reducing zones within a sedimentary sequence the weight of the evidence supports a source from thick sequences of volcanic ash and volcaniclastic sediment derived mostly from the trans pecos volcanic field and sierra madre occidental that lie west of the region the thickest accumulations of source material were deposited and preserved south and west of the san marcos arch in the catahoula formation by the early oligocene a formerly uniformly subtropical climate along the gulf coast transitioned to a zoned climate in which the southwestern portion of texas coastal plain was dry and the eastern portion humid the more arid climate in the southwestern area supported weathering of volcanic ash source rocks during pedogenesis and early diagenesis concentration of uranium in groundwater and movement through host sediments during the middle tertiary era abundant clastic sediments were deposited in thick sequences by bed load dominated fluvial systems in long lived channel complexes that provided transmissive conduits favoring transport of uranium rich groundwater groundwater transported uranium through permeable sandstones that were hydrologically connected with source rocks commonly across formation boundaries driven by isostatic loading and eustatic sea level changes uranium roll fronts formed as a result of the interaction of uranium rich groundwater with either 1 organic rich debris adjacent to large long lived fluvial channels and barrier bar sequences or 2 extrinsic reductants entrained in formation water or discrete gas that migrated into host units via faults and along the flanks of salt domes and shale diapirs the southwestern portion of the region the rio grande embayment contains all the necessary factors required for roll type uranium deposits however the eastern portion of the region the houston embayment is challenged by a humid environment and a lack of source rock and transmissive units which may combine to preclude the deposition of economic deposits a grade and tonnage model for the texas coastal plain shows that the texas deposits represent a lower tonnage subset of roll type deposits that occur around the world and required aggregation of production centers into deposits based on geologic interpretation for the purpose of conducting a quantitative mineral resource assessment

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

gold mineralisation throughout about 45 ma of archaean orogenesis protracted flux of gold in the golden mile yilgarn craton western australia the golden mile deposit was discovered in 1893 and represents today the largest archaean orogenic lode gold system in the world 50 m oz produced gold the golden mile deposit comprises three major styles of gold mineralisation fimiston oroya and charlotte styles fimiston style lodes formed at 250 to 350 c and 100 to 200 mpa and are controlled by brittle ductile fault zones their subsidiary fault zone and vein networks including breccias and open cavity infill textures and hydrothermally altered wall rock fimiston lodes were formed late d1 prior to d2 regional upright folding hydrothermal alteration haloes comprise a progression toward the lode of diminishing chlorite an increase in sericite and in fe content of carbonates lodes contain siderite pyrite native gold 17 different telluride minerals au ag tellurides contain 25 of total gold tourmaline haematite sericite and v rich muscovite oroya style lodes formed at similar p t conditions as the fimiston lodes and are controlled by brittle ductile shear zones associated dilational jogs that are particularly well developed at the contact between paringa basalt and black shale interflow sedimentary rocks and altered wall rock the orebodies are characterised by micro breccias and zones of intense shear zone foliation very high gold grades up to 100 000 g t au and the common association of tellurides and vanadian mica green leader oroya lodes crosscut fimiston lodes and are interpreted to have formed slightly later than fimiston lodes as part of one evolving hydrothermal system spanning d1 and d2 deformation ca 2 675 2 660 ma charlotte style lodes exemplified by the mt charlotte deposit are controlled by a sheeted vein stockwork complex of north dipping quartz veins and hydrothermally altered wall rock the mt charlotte orebody formed at 120 to 440 c and 150 to 250 mpa during movement along closely spaced d4 2 625 ma and reactivated d2 faults with the quartz granophyre in the golden mile dolerite exerting a strong lithological control on gold mineralisation veins consist of quartz carbonate minor scheelite and wall rock alteration comprises chlorite destruction and growth of ferroan carbonate sericite pyrite native gold pyrite pyrrhotite is zoned on the scale of vein haloes and of the entire mine giving a vertical temperature gradient of 50 100 c over 1 000 vertical metres the structural hydrothermal model proposed consists of four major stages 1 d1 thrusting and formation of fimiston style lodes 2 d2 reverse faulting and formation of oroya style lodes 3 d3 faulting and dissecting of fimiston and oroya style lodes and 4 d4 faulting and formation of mt charlotte style sheeted quartz vein system the giant accumulation of gold in the golden mile deposit was formed due to protracted gold mineralisation throughout episodes of an archaean orogeny that spanned about 45 ma fluid conduits formed early in the tectonic history and persisted throughout orogenesis with the plumbing system showing a rare high degree of focussing efficiency and duration in addition to the long lasting fluid plumbing system the wide variety of transient structural and geochemical traps multiple fluid sources and precipitation mechanism contributed towards the richest golden mile in the world

occurrences and distributions of branched alkylbenzenes in the dongsheng sedimentary uranium ore deposits china abstract a series of branched alkylbenzene ranging from c15 to c19 with several isomers 2 5 at each carbon number were identified in sediments from the dongsheng sedimentary uranium ore deposits ordos basin china the distribution patterns of the branched alkylbenzenes show significant differences in the sample extracts the branched alkylbenzenes from organic rich argillites and coals range from c15 to c19 homologues in which the c17 or c18 dominated on the other hand the c19 branched alkylbenzenes dominated in the sandstone siltstone extracts the obvious differences of the branched alkylbenzene distributions between the uranium host sandstones siltstones and the interbedded barren organic rich mudstones coals probably indicate their potential use as biological markers associated with particular depositional environments and or maturity diagenetic processes possible origins for these branched alkylbenzenes include interaction of simple aromatic compounds with or cyclization and aromatization reactions of these linear lipid precursors such as fatty acids methyl alkanoates wax esters or alkanes alkenes that occur naturally in carbonaceous sediments the possible simple aromatic compounds may include substituted benzenes functionalized compounds such as phenols that are bound to kerogen at the benzyl position and phenols that are decomposition products derived from aquatic and terrestrial sources the distributions of methyl alkanoates and n alkanes were found to be different between organic rich mudstone coal and sandstone siltstone from this result it can be concluded that such differences of the alkylbenzene distributions were mainly resulting from the differences of organic precursors although maturity effect and radiolytic alteration cannot be completely excluded

invisible gold in arsenian pyrite from the high grade hishikari gold deposit japan significance of variation and distribution of au as ratios in pyrite abstract au and as concentrations in pyrite grains from the hishikari deposit were extensively determined by secondary ion mass spectrometry sims and electron probe microanalysis epma to investigate the microscale relationship between au and as the low sulfidation epithermal hishikari deposit which has produced more than 224 t of gold since 1985 as of march 2016 is world famous for its high grade ore accurate quantitative sims analyses of au in pyrite were possible by preparing an au implanted pyrite standard sample and by using a properly tuned sims analytical method an analysis size of 3 m was chosen since the pyrite grains from the hishikari deposit have heterogeneous as concentrations this paper presents the first comprehensive data set of au and as concentrations in a 3 m area of pyrite obtained from the widely distributed high grade au bearing hishikari veins microanalyses of arsenian pyrite from the hishikari gold deposit by sims and epma revealed that au concentrations of 0 1 2800 ppm are positively correlated with as concentrations of 0 to 7 wt in a 3 m area the formation of hishikari veins is divided into two stages that are further subdivided into the early and late sub stages the rim of a pyrite grain precipitates after formation of the core however the time scale of core and rim formation is far shorter than that of the entire mineralization sequence the specific value of the au as ratio in pyrite proves to be characteristic of the specific au bearing vein and its specific depth therefore it could be possible to infer the nature of unknown veins by the au as ratio obtained although the au as ratio varies from vein to vein a general tendency is observed for each ore zone of the hishikari deposit the au as ratio is high in the sanjin ore zone which consists of numerous high grade veins in or above the cretaceous accretionary sedimentary rocks of the shimanto group the au as ratio is moderate in the honko ore zone which consists of several high grade veins and also occurs in or above the basement sedimentary rocks on the other hand the yamada ore zone which consists of relatively low grade veins occurs in pleistocene andesitic pyroclastic rocks that overlie the basement sedimentary rocks unconformably the au as ratio in pyrite of the yamada ore zone is relatively low compared with that of other ore zones several previous papers have proposed that the as in pyrite may contribute to the reduction of au to au0 as au nanoparticles nps by as oxidation however au and as concentrations of arsenian pyrites fall on or below the au solubility limit in this study moreover the as and s concentrations in pyrite are inversely correlated which is consistent with the substitution of as for s as anionic as in the fe s1 xasx 2 solid solution of natural arsenian pyrite under reducing environments the present study suggests that the hishikari au exists as a solid solution in the hishikari arsenian pyrite although there remains a possibility that it exists partially in the form of nps even though the au and as concentrations of arsenian pyrites fall on or below the au solubility limit