implementation and evaluation of concurrent gradient search method for reprojection of modis level 1b imagery this paper presents details regarding implementation of a novel algorithm for reprojection of moderate resolution imaging spectroradiometer modis level 1b imagery the method is based on a simultaneous 2 d search in latitude and longitude geolocation fields by using their local gradients due to the segmented structure of modis imagery caused by the instrument whiskbroom electrooptical design the gradient search is realized in the following two steps intersegment and intrasegment search this approach resolves the discontinuity of the latitude longitude geolocation fields caused by overlap between consecutively scanned modis multidetector image segments the structure of the algorithm allows equal efficiency with nearest neighbor and bilinear interpolation a special procedure that combines analytical and numerical schemes is designed for reprojecting imagery near the polar region where the standard gradient search may become unstable the performance of the method was validated by comparison of reprojected modis terra and modis aqua images with georectified landsat 7 enhanced thematic mapper plus imagery over canada it was found that the proposed method preserves the absolute geolocation accuracy of modis pixels determined by the modis geolocation team the method was implemented to reproject modis level 1b imagery over canada north america and arctic circumpolar zone in the following four popular geographic projections plate care cylindrical equidistant lambert conic conformal universal transverse mercator and lambert azimuthal equal area it was also found to be efficient for reprojection of advanced very high resolution radiometer and medium resolution imaging spectrometer satellite images and general type meteorological fields such as the north american regional reanalysis data sets

optical algorithm for cloud shadow detection over water the application of ocean color product retrieval algorithms for pixels containing cloud shadows leads to erroneous results thus shadows are an important scene type that should be identified and excluded from the set of clear sky pixels in this paper we present an optical cloud shadow detection technique called the cloud shadow detection index csdi this approach is for homogeneous water bodies such as deep waters where shadow detection is very challenging due to the relatively small differences in the brightness values of the shadows and neighboring sunlit or some other regions the csdi technique is developed based on the small differences between the total radiances reaching the sensor from the shadowed and neighboring sunlit regions of similar optical properties by amplifying the differences through integrating the spectra of the two regions the integrated value iv is then normalized by the mean of the ivs within a spatial adaptive sliding box where atmospheric and marine optical properties are assumed homogeneous assuming that the true color and the iv images represent accurate shadow locations the results were visually compared the csdi images agree reasonably well with the corresponding true color and the iv images over open ocean also the shape of the cloud shadow particularly for the isolated cloud closely follows that of the cloud as expected reconfirming the potential of the csdi technique

deciphering the hydrothermal evolution of a vms system by la icp ms using trace elements in pyrite an example from the bracemac mcleod deposits abitibi canada and implications for exploration textural and chemical characterization of pyrite was used to reconstruct the hydrothermal evolution of the bracemac mcleod archean volcanogenic massive sulfide vms deposits 6 mt in the matagami district abitibi canada the mineralization hosted in a bimodal volcanic sequence is divided into a 1 zn rich zone concordant to the key tuffite a marker horizon at the district scale 2 a cu rich zone which locally crosscuts the stratigraphic pile and 3 some localized magnetite rich zones replacing sphalerite and pyrite detailed petrographic and laser ablation inductively coupled plasma mass spectrometry la icp ms studies of whole pyrite grains including inclusions and zonation from the key tuffite and from the different ore zones of the deposits has revealed five pyrite types nodular pyrites i in the key tuffite and subidiomorphic pyrites from the low temperature 250 c zn rich zone ii have the same chemical signature suggesting that both precipitated under similar physicochemical conditions a wide range of trace elements cu zn ag sn sb te au pb bi tl are present in both but compared to the other types of pyrite they are significantly enriched in sb and tl subidiomorphic pyrites from the copper rich zone iii have a different signature enriched only in se co in pb and bi these pyrites commonly overgrow the nodular pyrites and are related to later higher temperature fluids 300 c pyrite preserved during a later magnetite replacement 350 c stage iv also are enriched in se but are depleted in all other elements a similar signature is found in idiomorphic metamorphic pyrite v which occurs at the district scale during high temperature recrystallization of pyrite iv and v only the contents of ni co as and se are mostly preserved whereas other base metals are expelled from the pyrite structure consequently only ni co as se sb and tl were useful to reconstruct the hydrothermal evolution of the vms system and used to build a suite of discrimination diagrams specifically the ratio se tl can discriminate pyrites from mineralized zn rich zone se tl 10 000 the innovative approach of this study based on la icp ms acquisition of the chemistry of entire pyrite grains makes our results directly applicable for exploration consequently pyrite concentrate samples analyzed for as tl and se by more classical mass spectrometric techniques have the potential to be used for vectoring to ore by using the proposed discrimination diagrams

mineralization at the golden grove cu zn deposit western australia i premetamorphic textures of the opaque minerals the competent opaque minerals in the archaean golden grove deposit pyrite and magnetite retain pre regional metamorphic textures despite the lower greenschist facies grade of metamorphism the pre regional metamorphic textures and structures recognized include the development of pyrite and magnetite overgrowths the replacement of pyrrhotite by pyrite the conversion of a primary hematite goethite mineralogy to magnetite and as a result of thermal metamorphism further local replacement of pyrrhotite and sphalerite by magnetite comparisons between pyrite from the cu rich mineralization at the base of the deposit and that from the zn rich mineralization in the hanging wall indicate that postdepositional modification and recrystallization were more extreme at the base of the deposit the pre regional metamorphic textures and structures indicate that pyrite and magnetite overgrowths developed almost immediately after primary precipitation ceased and that overgrowths continued to develop into the late h

the archean cu zn magnetite rich gossan hill volcanic hosted massive sulfide deposit western australia genesis of a multistage hydrothermal system the gossan hill volcanic hosted massive sulfide vhms deposit is an archean cu zn magnetite rich deposit located in the warriedar fold belt of the yilgarn craton western australia the deposit is hosted by redeposited rhyodacitic tuffaceous volcaniclastics of the golden grove formation and is overlain by felsic volcanic rocks of the scuddles formation the deposit consists of two separate subvertical ore zones the stratigraphically lower cu rich ore zone 7 0 mt 3 4 cu is strata bound and varies from podiform massive pyrite chalcopyrite pyrrhotite magnetite to sheetlike massive magnetite carbonate chlorite talc the upper zn cu ore zone 2 2 mt 11 3 zn 0 3 cu 1 5 g t au and 102 g t ag contains strata bound massive sphalerite pyrite chalcopyrite that overlies discordant moundlike massive pyrite pyrrhotite chalcopyrite magnetite sulfide stockwork connects the upper and lower ore zones metal zonation varies from cu au in the lower ore zone to zn cu at the base of the upper ore zone which grades upward and laterally to zn ag au cu pb multiphase deformation and greenschist facies metamorphism overprint the deposit the relationship between host rocks and sulfide indicates that mineralization was broadly codepositional with sedimentation of the golden grove formation however gradational and interdigitating contacts between these volcaniclastic rocks and magnetite support the formation of massive magnetite by subsea floor replacement sulfides replace and vein the massive magnetite with inferred synchronous formation of the upper and lower sulfide ore zones although these sulfide ore zones formed mainly by subsea floor replacement stratiform hydrothermal chert sulfide sediment layers within and adjacent to the upper zn rich ore zone attest to some local exhalation the thickest development of massive magnetite massive sulfide and stringer stockwork occurs in the north of the deposit and supports a common feeder during massive magnetite and sulfide formation furthermore local chlorite quartz hydrothermal alteration massive magnetite massive sulfide and stockwork all form asymmetric zones that thin southward these attributes indicate strong synvolcanic structural control during mineralization the relict synvolcanic growth structure is obscured and probably occupied and by a dacite dome of the hanging wall scuddles formation thermodynamic considerations suggest that massive magnetite and sulfide formed from similar high temperature 300 degrees celsius slightly acidic low fo2 hydrothermal fluids massive magnetite formed from h2s poor fluids whereas massive sulfide formed from relatively rich h2s fluids physicochemical changes associated with interaction between upwelling h2s bearing fluids and preexisting massive magnetite may have resulted in the subsea floor precipitation of sulfide in the lower cu rich ore zone the gossan hill vhms deposit represents a multistage hydrothermal system within an environment characterized by rapid volcaniclastic sedimentation and changing structural and magmatic processes the six main stages were as follows 1 initiation of the hydrothermal system 2 sedimentation metasomatism and progressive heating of convecting fluids 3 deposition of massive magnetite from h2s poor fluids by subsea floor replacement above a buried synvolcanic conduit 4 structural reactivation tapping deeper h2s and metalbearing fluids 5 subsea floor replacement and minor exhalative sulfide mineralization with 6 burial and preservation of the deposit resulting from proximal felsic volcanism

integrated pan arctic melt onset detection from satellite active and passive microwave measurements 2000 2009 1 an integrated pan arctic melt onset data set is generated for the first time by combining estimates derived from active and passive microwave satellite data using algorithms developed for the northern high latitude land surface ice caps large lakes and sea ice the data set yields new insights into the spatial and temporal patterns of mean melt onset date mmod and the associated geographic and topographic controls for example in the terrestrial arctic tree fraction and latitude explain more than 60 of the variance in mmod with the former exerting a stronger influence on mmod than the latter elevation is also found to be an important factor controlling mmod with most of the arctic exhibiting significant positive relationships between mmod and elevation with a mean value of 24 5 m d 1 melt onset progresses fastest over land areas of uniform cover or elevation 40 80 km d 1 or both and slows down in mountainous areas on ice caps and in the forest tundra ecotones over sea ice melt onset advances very slowly in the marginal seas while in the central arctic the rate of advance can exceed 100 km d 1 comparison of the observed mmod with simulated values from the third version of the canadian coupled global climate model showed good agreement over land areas but weaker agreement over sea ice particularly in the central arctic where simulated mmod is about 2 3 weeks later than observed because of a cold bias in simulated surface air temperatures over sea ice

alteration characteristics of the archean golden grove formation at the gossan hill deposit western australia induration as a focusing mechanism for mineralizing hydrothermal fluids the archean golden grove formation is a 550 m thick rhyodacitic tuffaceous volcaniclastic succession that hosts the cu zn rich gossan hill volcanic hosted massive sulfide vhms deposit in the yilgarn craton western australia the golden grove formation consists of volcanic quartz and altered pumice and shards which were deposited during successive episodes of subaqueous mass flow coherent volcanics are absent from the golden grove formation at gossan hill but form the main rock type in the hanging wall scuddles formation a massive dacite dome that overlies its volcanic feeder dike is inferred to occupy a synvolcanic structure that focused mineralizing fluids during the formation of the gossan hill deposit the gossan hill deposit consists of two stratigraphically separate ore zones interconnected by stockwork the cu rich lower ore zone and the zn rich upper ore zone occur in the middle and upper parts of the golden grove formation respectively podiform zones of massive magnetite occur in the cu rich ore zone where the formation of magnetite predates massive sulfide the asymmetry of massive sulfide massive magnetite and alteration zones at the gossan hill deposit attest to synvolcanic structural control during mineralization the principal lithofacies of the golden grove formation are sandstone and pebble breccia which have a regionally extensive quartz fe rich chlorite and lesser muscovite alteration at gossan hill this alteration has resulted in near complete replacement of tuffaceous components causing substantial chemical modification of the primary lithologies quartz chlorite muscovite alteration is characterized by severe k2o na2o and cao depletion with rocks consisting principally of sio2 feo al2o3 and mgo along a quartz chlorite mixing trend widespread preservation of pumice and shard volcanic textures within the golden grove formation indicates that quartz chlorite muscovite alteration occurred soon after or possibly during sedimentation the absence of diagenetic compaction textures further suggests induration of the succession during this early alteration stage with the tuffaceous succession largely sealed from the texturally destructive effects of subsequent hydrothermal alteration except where mineralizing fluids were locally channeled along synvolcanic feeder conduits local intense hydrothermal alteration zones surround the gossan hill deposit and overprint earlier quartz chlorite muscovite alteration these local alteration zones have the same extent as the sulfide vein envelope and represent hydrothermal alteration formed during sulfide magnetite mineralization intense fe rich chlorite ankerite siderite alteration occurs as a strata bound envelope around massive magnetite cu rich veins and massive sulfide in the lower ore zone this chlorite rich alteration has strong feo and mgo enrichment with minor chloritoid and andalusite that reflect intense acid leaching during hydrothermal alteration iron chlorite ankerite siderite alteration grades upward into discordant to strata bound intense quartz alteration intense quartz alteration forms an envelope around zn rich veins and massive sulfide in the stockwork and upper ore zone the trend from fe chlorite ankerite siderite to quartz alteration toward the top of the deposit is consistent with the cooling of hydrothermal mineralizing fluids nearing the sea floor rhyodacite and dacite volcanics of the hanging wall scuddles formation have a pervasive muscovite calcite alteration muscovite calcite alteration led to na2o depletion and cao and k2o enrichment associated with burial of the gossan hill mineralizing system we propose that the gossan hill sulfide magnetite vhms deposit formed during an evolving archean hydrothermal system that began as part of a regional scale low temperature seawater convection alteration system initially this system caused extensive replacement of the golden grove formation by quartz and fe chlorite muscovite a process that sealed and indurated the volcaniclastic rocks by infilling of primary porosity and permeability structures due to subsequent impermeability of the host rock succession later and hotter mineralizing fluids that generated alteration and massive magnetite and sulfide at the gossan hill deposit were constrained to and focused upward along a synvolcanic feeder structure

precambrian tectonic evolution of part of gondwana southwestern australia southwestern australia has a long dynamic precambrian history of crustal fragmentation and aggregation by continental collision and accretion this interpretation contrasts with the widely held belief that most of australia was part of a proterozoic supercontinent in which all tectonic magmatic and metamorphic activity was intracontinental the pilbara and yilgarn cratons are two quite different fragments of archean continental crust that collided to form the capricorn orogen between 2000 and 1600 ma the albany fraser orogen formed along the southern margin of the yilgarn craton during another major continental collision at 1300 to 1100 ma rifting removed the northeastern part of these combined cratons and orogens between 1100 and 700 ma subsequent continental collision along this rifted margin formed the paterson orogen at 700 to 600 ma therefore the assembly of this considerable part of gondwana may not have been completed until about 600 ma

the precious metal rich south hercules mineralization western tasmania a possible subsea floor replacement volcanic hosted massive sulfide deposit south hercules is a newly delineated disseminated to semimassive base metal sulfide deposit with significant gold and silver grades the deposit lies a kilometer along strike south from the hercules mine a 2 0 mt polymetallic massive sulfide deposit in the mount read volcanics belt western tasmania the mineralization and alteration at the south hercules deposit has been divided into two major facies the mineralized sulfide facies and the carbonate facies the carbonate facies interfingers with and surrounds the upper part of the sulfide facies the mineralized sulfide facies includes three zones a massive pyrite or barite zone a siliceous or stringer sulfide zone and a sphalerite galena or pyrite zone the carbonate facies also consists of three zones a blebby carbonate chlorite zone a massive carbonate zone and a cherty carbonate zone the massive pyrite or barite zone contains significant gold grades and occurs mostly at the top of the sulfide facies this zone is characterized by colloform aggregates of pyrite and compact massive pyrite in chert the siliceous or stringer sulfide zone is a silicified and sericitized tuffaceous shale with disseminated to stringer pb zn mineralization the massive sphalerite galena or pyrite zone contains subordinate gold and silver and occurs as thin lenses toward the base of the sulfide facies significant zinc and lead values occur throughout the mineralized sulfide facies with the highest values occurring along stratigraphically controlled layers copper values are conspicuously low throughout the south hercules deposit rarely exceeding 0 5 percent the carbonate facies is conspicuous by its lack of significant precious metal and base metal grades mineragraphic investigations indicate that electrum occurs in two general associations with pyrite and with other sulfides such as sphalerite galena and tetrahedrite the electrum locked in the pyrite euhedra is generally fine grained 5 40 mu m whereas the electrum associated with other sulfides displays a range between 5 and 200 mu m microprobe analysis indicates that the fineness 1 000 au au ag wt for gold in the deposit ranges from 427 to 965 the delta 18 o isotope composition of the carbonate varies from 9 8 to 16 7 per mil and the delta 13 c values range from 3 5 to 0 6 per mil the calculated isotopic composition of the ore fluid at 150 degrees and 250 degrees c is consistent with derivation from evolved seawater sulfur isotope analyses of selected samples from the mineralized facies give delta 34 s values of 8 2 to 14 1 per mil which is in the same range as values from the rosebery deposit and consistent with values of sulfur derived from cambrian seawater the form texture mineralogy stable isotopes and fluid inclusion data for the south hercules deposit suggest that it was formed largely by a subsea floor replacement process from relatively low temperature 150 degrees 250 degrees c near neutral fluids the very low copper content and relatively high au ag pb zn ratio of the ores support a low temperature environment in which gold was transported as the au hs 2 super complex and pb and zn were transported as chloride complexes

hydrothermal geochemistry and ore genesis of sea floor volcanogenic copper bearing oxide ores the term volcanogenic copper bearing oxide mineralization is proposed to describe exhaled sea floor chemical sediments which are dominated by magnetite quartz and hematite with subordinate chalcopyrite pyrite and in some cases gold they occur within or close to volcanic piles three australian examples the starra osborne and big cadia deposits form the basis for a more general volcanogenic copper bearing oxide model the shapes of the deposits vary from massive mounds and pods cadia with no laterally developed sedimentary iron formation through to extensive well banded stratiform examples osborne the orebody style of the deposits correspondingly varies from small high grade cu au lenses such as area 251 at starra 2 6 mt at 6 7 g t au 3 4 cu to large lower grade deposits such as osborne 13 6 mt at 1 9 cu and 1 0 g t au including a higher grade pod in all cases intense footwall alteration is present a hallmark of vent proximal exhalative sediments varying from albite iron oxide chlorite to massive quartz iron oxide to muscovite epidote chlorite depending on the salinity and ph of the ore fluid and the presence or absence of boiling solutions at osborne three stratigraphic ore positions record three episodes of hydrothermal activity in a stacked system with evidence of overprinting in the earlier exhalites at starra and cadia there is evidence that the most proximal exhalites are dominated by magnetite quartz and chalcopyrite whereas the distal portions are hematite dominated and variably pyritic ore formation is attributed to precipitation from the oxidized and h 2 s deficient version of a volcanic hosted massive sulfide fluid in an oxidized water column such fluids must be buffered by hematite and or magnetite during deep footwall fluid rock reaction below vent complexes to provide a sink for h 2 s produced by the reduction of seawater sulfate thus the ore type is favored in intracontinental basins which are common hosts for the requisite oxidized fluvial and shallow marine sediments a second possible source of oxidized metal bearing fluids is highly fractionated magnetite series granites in the australian proterozoic these are particularly prevalent in rift settings to achieve cu au solubility as chloride complexes and to account for the ore mineral assemblages the ore fluids must have had a t 260 degrees to 380 degrees c a log f sub o 2 27 5 to 30 a ph 3 9 to 6 and an sigma s approximately 10 super 3 m high salinities are not an essential condition but serve to greatly enhance the efficiency of metal transport by increased chloride ion pair metal solubility higher salinities favor the transport of the elements au w sn mo and co which constitute a distinct secondary element association salinity is also the strongest control on ore deposit shape by determining the behavior of the fluid after it exits from the vent for instance modeling suggests that a high salinity fluid cooling at constant ph can explain the si fe ratio and thickness of some starra ore lenses an important geochemical feature of volcanic copper bearing oxide mineralization is a distinct depletion of pb and zn usually less than 10 ppm of each occurs in ore zones this is attributed to the very low h 2 s content of the ore fluid and water column which permits precipitation of cu and fe as chalcopyrite and pyrite at temperatures greater than approximately 280 degrees c removing all h 2 s prior to galena and sphalerite saturation a volcanic copper bearing oxide brine from which cu was removed at the vent could migrate across a sea floor and precipitate pb and zn distally in localized biogenic h 2 s bearing deeps by this means or by slightly increasing the exhaled h 2 s concentration pb zn rich iron oxide ores with greater pb zn contents could be produced mineralogically transitional between volcanic copper bearing oxide cu au banded iron formation and broken hill pegmont style pb zn banded iron formation ores

a comparison of the horne volcanogenic massive sulfide deposit and intracauldron deposits of the mine sequence noranda quebec most of the massive sulfide deposits of the rouyn noranda area are associated with rhyolite and andesite flows of the mine sequence and occur within the noranda cauldron a volcanic subsidence structure related to partial evacuation of an underlying magma chamber the flavrian pluton the horne massive sulfide orebodies lie within a sequence of rhyolitic breccias located just south of the inferred margin of the subsidence structure and are separated from the mine sequence by the horne creek fault traditionally the horne deposits and the intracauldron deposits have been interpreted to occur within the same stratigraphic interval even though they share some characteristics such as mineral zoning patterns alteration assemblages and an association with synvolcanic faults the two deposit groups are clearly distinguishable intracauldron massive sulfide deposits are small 5 mt cu zn rich concordant mounds associated with interflow horizons and are closely linked to vent zones where synvolcanic faulting provided hydrothermal fluids with cross stratal structural permeability the three major sulfide deposits at the horne mine are much larger 20 150 mt and formed in a fault bounded sediment filled graben on the flank of a rhyolitic vent complex the orebodies are au cu rich but zn poor and have bowl shaped morphologies which resulted from extensive subsea floor sulfide precipitation whereas the intracauldron sulfide deposits lie within a bimodal flow dominated succession consisting mainly of andesite basalt and high silica rhyolite with volumetrically insignificant pyroclastic rocks the horne orebodies occur in felsic fragmental rocks and rhyolite flows which are part of a stratigraphic sequence which contains virtually no mafic volcanic rocks also compared to all intracauldron rhyolites the horne rhyolites show a fundamental depletion in incompatible trace elements such as the high field strength and rare earth elements which implies that the horne rhyolites may have followed a different magmatic evolutionary path such differences in deposit characteristics their paleoenvironments of formation and the physical volcanology and geochemistry of their host volcanic successions suggest that contrary to previous interpretations the massive sulfide deposits of the intracauldron mine sequence and those of the horne sequence may have formed at different stages in the evolution of the noranda cauldron

a synvolcanic origin for magnetite rich orebodies hosted by bif in the weld range district western australia abstract iron ore deposits hosted by archean banded iron formation bif in the weld range greenstone belt are representative of most of the documented iron ore deposits in the yilgarn craton they include near surface supergene goethite hematite orebodies that overlie and partly modify deeper occurrences of hypogene magnetite and specular hematite ores the cenozoic goethite hematite rich orebodies in these deposits are unequivocally the product of meteoric fluid alteration affecting bif in the near surface supergene environment however the deeper and likely older magnetite and specular hematite rich orebodies have a more contentious origin this study is the first to present a fluid alteration model for hypogene iron mineralization in the yilgarn craton that uses fluid inclusion and mineral chemistry data to constrain the physical chemical characteristics and source of hypogene fluids responsible for mineralization high grade 57 wt fe magnetite rich iron ore at the beebyn deposit defines a discontinuous series of 440 c and co2 rich paired o and c stable isotope data for stage 1 ferroan dolomite suggest that these fluids had a magmatic source while stage 1 magnetite chemistry e g enrichments in mg mn ca and na indicates chemical exchange took place between the fluids and mafic igneous rocks prior to crystallization of magnetite the presence of monophase carbonic fluid inclusions in stage 1 ferroan dolomite suggest that phase separation of a bicarbonate rich aqueous fluid took place in deeper parts of the hydrothermal system which led to the separation of the resultant volatile rich and brine phases during transport of the stage 1 fluid to shallower crustal levels cooling of the hydrothermal system during the stage 2 fluid event involved i an early brine 275 327 c 36 40 equiv wt nacl with cl br and c and o isotopes values that overlap the ranges for magmatic fluids with minor involvement of archean seawater and extensive chemical exchange with country rocks followed by ii pulses of moderate and lower temperature stage 2 brines 125 260 c 2 24 equiv wt cacl2 with cl br o and c isotope na br and ca ca na signatures that suggest cooling of magmatic derived fluids that mixed with archean seawater and reacted with mafic igneous country rocks in areas more distal to fluid pathways the last stage of formation of magnetite rich ore at the beebyn deposit involved the flow of stage 3 fluids through the existing fault network that controlled earlier fluids stage 3 fluids are lower temperature 98 175 c low to high salinity brines with cl br values that overlap reported ranges for 3 2 ga vent fluids and seawater thus they are likely the product of heated archean seawater that was chemically modified through interaction with mafic country rocks magnetite talc veins at the madoonga deposit have fluid halogen ratios for fluid inclusions hosted by magnetite that are compatible with a range of possible sources including low grade metamorphic fluids geothermal brines or oil field formation waters although their common spatial association with semi massive sulfides suggests their likely precipitation from brines derived from heated archean seawater more locally developed specular hematite quartz veins that cut folded magnetite rich ores at the beebyn and madoonga deposits are the product of iron redistribution in bif by heated meteoric fluids or seawater with precipitation of specular hematite as a consequence of oxidation and cooling of the fluid

deformation of popocatepetl volcano using gps regional geodynamic context and constraints on its magma chamber we have operated a gps network on popocatepetl volcano since 1994 consisting of a total of 7 continuous gps stations on its northern and southwestern flanks and one additional station in the vicinity of the volcano the overall characteristic behavior of popocatepetl volcano during this period can be described as a minimally deforming system in sharp contrast with its essentially continuous visible eruptive activity a north component motion analysis assuming a fixed north american plate shows a close correspondence of the popocatepetl sites to those of other regional gps sites most of the large deformation transients observed on the popocatepetl sites are therefore not of magmatic origin but instead reflect aseismic transients that have been recognized recently as part of the mid american trench subduction process the surface deformation record of popocatepetl volcano therefore suggests a magmatic system that lacks a well defined shallow magma chamber where most of the magma storage transport and ascent is carried out via a network of deep rooted conduits that eventually extend to the summit crater in most cases popocatepetl seems to operate as a semi open system thereby preventing any significant pressure build up

formation of volcanogenic massive sulfide deposits the kuroko perspective abstract the main objective of this paper is to identify the geochemical hydrological igneous and tectonic processes that led to the variations in the physical size geometry and chemical mineralogy metal ratios and zoning characteristics of volcanogenic massive sulfide deposits with respect to space from a scale of mining district size area to a global scale and time from a all volcanogenic massive sulfide deposits vmsds appear to have formed in extensional tectonic settings such as at mid ocean spreading centers backarc spreading centers and intracontinental rifts and failed rifts all vmsds appear to have formed in submarine depressions by seawater that became ore forming fluids through interactions with the heated upper crustal rocks submarine depressions especially those created by submarine caldera formation and or by large scale tectonic activities e g rifting become most favorable sites for the formation of large vmsds because of hydrological physical and chemical reasons the fundamental processes leading to the formation of vmsds include the following six processes 1 1 intrusion of a heat source typically a 10 3 km size pluton into an oceanic crust or a submarine continental crust causes deep convective circulation of seawater around the pluton the radius of a circulation cell is typically 5 km the temperature of fluids that discharge on the seafloor increases with time from the ambient temperature to a typical maximum of 350 c and then decreases gradually to the ambient temperatures in a time scale of 100 to 10 000 years the majority of sulfide and sulfate mineralization occurs during the waxing stage of hydrothermal activity 2 2 reactions between low temperature t 2 4 as disseminated gypsum and anhydrite in the country rocks 3 3 reactions of the modified seawater with higher temperature rocks at depths during the waxing stage cause the transformation of the seawater to metal and h 2 s rich ore forming fluids the metals and sulfide sulfur are leached from the county rocks the previously formed gypsum and anhydrite are reduced by fe 2 bearing minerals and organic matter providing additional h 2 s the mass of high temperature rocks that provide the metals and reduced sulfur is typically 10 11 tons 40 km 3 in volume the roles of magmatic fluids or gases are minor in most massive sulfide systems except for so 2 to produce acid type alteration in some systems 4 4 reactions between the ore forming fluids and cooler rocks in the discharge zone cause alteration of rocks and precipitation of some ore minerals in the stockwork ores 5 5 mixing of the ore forming fluids with local seawater within unconsolidated sediments and or on the seafloor causes precipitation of primitive ores with the black ore mineralogy sphalerite galena pyrite barite anhydrite 6 6 reactions between the primitive ores with later and hotter hydrothermal fluids cause transformation of primitive ores to matured ores that are enriched in chalcopyrite and pyrite variations in the mineralogical and elemental characteristics the geometry and the size of submarine hydrothermal deposits are controlled by the following four parameters 1 a the chemical and physical characteristics of seawater composition temperature density which depend largely on the geographical settings e g equatorial evaporating basins 2 b the chemical and physical characteristics of the plumbing system lithology fractures 3 c the thermal structure of the plumbing system which is determined largely by the ambient geothermal gradient and the size and temperature of the intrusive and 4 d the physical characteristics of the seafloor depth basin topography for example the submarine hydrothermal deposits developed in basaltic plumbing systems are generally poor in pb and ba compared to those developed in felsic plumbing systems the lower temperature systems are generally poorer in sulfides but richer in iron oxides and sulfates the higher temperature and larger hydrothermal systems tend to produce chalcopyrite and pyrite rich ores contrasts in the metal ratios between the noranda type archean vmsds and the younger vmsds reflect the differences in the geothermal gradient of the plumbing systems the submarine hydrothermal deposits developed in the near equatorial regions tend to form large continuous bedded type ores because of the likeliness of creating large stratified basins the basic processes of submarine hydrothermal mineralization have remained essentially the same throughout the geologic history from at least 3 5 billion year ago to the present

variability of biome reflectance directional signatures as seen by polder reflectance measurements acquired with the spaceborne polder instrument are used to analyze the variability of land surface directional signatures as a function of vegetation cover type the reflectance directional signatures are quantified by the three parameters of a modified version of the ross li reflectance model the variability of the estimated parameters with respect to the seven modis biome classes was found to be higher within the classes than between classes with the exception of the desert targets that show more isotropic reflectances a limited number of standard brdfs typically 5 in the red and near infrared capture most of the variability of the directional reflectance measurements supporting the idea that different land surfaces have similar directional signatures over vegetation targets they are characterized by a strong increase toward backscattering and much smaller variations in forward directions the results express the diversity in structural situations within a given biome class and indicate that at the resolution of the polder sensor i e a few kilometers the brdf contains little information on the dominant vegetation type we show that standard directional signatures may be used to correct the reflectance measurements for directional effects with an rms error on the order of 0 011 in the red and 0 015 in the near infrared

the distribution of 3 0 ga and 2 7 ga volcanic episodes in the yilgarn craton of western australia abstract the results of a conventional zircon u pb investigation of the ages of felsic volcanic rocks in a number of greenstone belts in the yilgarn craton of western australia indicate that volcanism took place during two distinct episodes at ca 3 0 and ca 2 7 ga each episode spans a time period of about 75 ma and the two ages of volcanism are spatially separated 3 0 ga volcanic rocks are found in greenstone belts in the northern part of the western gneiss terrain and in the murchison province whereas 2 7 ga volcanic rocks are present in the southern part of the western gneiss terrain and in the southern cross and eastern goldfields provinces there is no evidence of inheritance in the zircon u pb systems which would support an older crustal origin for these rocks present results together with previous studies of the ages of granites and gneisses suggest that the volcanic episodes were accompanied by broadly contemporaneous granite plutonism it is suggested that the evolution of the yilgarn craton took place in three main stages the first was the development of a stable 3 4 ga granitic nucleus which incorporated earlier generations of granitoid a 3 7 ga layered complex and possibly 4 2 ga primitive crust this was followed by the two separate granite greenstone episodes at ca 3 0 and ca 2 7 ga involving the addition of significant amounts of new crust each episode was characterised by the accretion of extensive granite greenstone terranes at the margins of the stable craton the intrusion of granite plutons into the evolving craton and the reworking of older cratonic rocks to form granites and gneisses with inherited isotopic systems

a multistage genetic model for the metamorphosed mesoproterozoic swartberg base metal deposit aggeneys gamsberg ore district south africa

sulfur isotope characteristics of the archean cu zn gossan hill vhms deposit western australia gossan hill is an archean 3 0 ga cu zn magnetite rich volcanic hosted massive sulfide vhms deposit in the yilgarn craton of western australia massive sulfide and magnetite occur within a layered succession of tuffaceous felsic volcaniclastic rocks of the golden grove formation the gossan hill deposit consists of two stratigraphically separate ore zones that are stratabound and interconnected by sulfide veins thickly developed massive sulfide and stockwork zones in the north of the deposit are interpreted to represent a feeder zone the deposit is broadly zoned from a cu fe rich lower ore zone upwards through cu zn to zn ag au pb enrichment in the upper ore zone new sulfur isotope studies at the gossan hill deposit indicate that the variation is wider than previously reported with sulfide 34s values varying between 1 6 and 7 8 with an average of 2 1 1 4 1 error sulfur isotope values have a broad systematic stratigraphic increase of approximately 1 2 from the base to the top of the deposit this variation in sulfur isotope values is significant in view of typical narrow ranges for archean vhms deposits copper rich sulfides in the lower ore zone have a narrower range 34s values of 1 6 to 3 4 average 1 6 0 9 than sulfides in the upper ore zone the lower ore zone is interpreted to have formed from a relatively uniform reduced sulfur source dominated by leached igneous rock sulfur and minor magmatic sulfur towards the upper zn rich ore zone an overall increase in 34s values is accompanied by a wider range of 34s values with the greatest variation occurring in massive pyrite at the southern margin of the upper ore zone 1 0 to 7 8 the higher average 34s values 2 8 2 1 and their wider range are explained by mixing of hydrothermal fluids containing leached igneous rock sulfur with archean seawater 34s values of 2 to 3 near the paleoseafloor the widest range of 34s values at the southern margin of the deposit occurs away from the feeder zone and is attributed to greater seawater mixing away from the central upflow zone

modelling the spatial distribution of permafrost in labrador ungava using the temperature at the top of permafrost permafrost zonation in labrador ungava ranges from very isolated patches through to continuous permafrost here we present a new estimate of the distribution of permafrost at high resolution 250 m 250 m using spatial numerical modelling supported by station data from 29 air and ground climate monitoring stations permafrost presence was estimated using a modified version of the temperature at the top of permafrost ttop model mean ground surface temperatures were modelled using gridded air temperatures and a novel n factor parameterization scheme that compensates for regional differences in continentality snowfall and land cover and is transferable to other subarctic environments the thermal offset was modelled using land cover and surficial material datasets predicted ttop values for the average climate range regionally from 9 c for high elevations in northern quebec to 5 c for southeastern labrador quebec modelling for specific temporal windows 1948 1962 1982 1996 2000 2014 suggests that permafrost area increased from the middle of the 20th century to a potential peak extent 36 of the total land area in the 1990s subsequent warming is predicted to have caused a decrease in permafrost extent of one quarter 95 000 km2 even if air temperatures rise no further providing air and ground temperatures equilibrate zonal boundaries derived by upscaling the high resolution model are highly scale dependent precluding direct comparison with the permafrost map of canada that was generated without the use of geographic information system based analyses

reconstruction of landsat time series in the presence of irregular and sparse observations development and assessment in north eastern alberta canada abstract time series analysis of landsat is limited by sparse and irregular sampling of clear sky observations due to acquisition limitations clouds shadows atmosphere and sensor artifacts many remote sensing applications utilizing coarse spatial resolution time series methods are not suitable for landsat due to observation sparsity in this research we develop an imputation based approach to constrain the harmonic modeling method of zhu et al 2012 zhu et al 2015 and zhu and woodcock 2014b to reconstruct landsat time series at a regular temporal interval the approach was assessed for a boreal forest region in central canada for different sparsity conditions the imputed landsat estimates for a specific pixel were predicted from climate or avhrr data these estimates were given a small weight relative to available landsat observations in fitting the final harmonic model essentially constraining it to a more plausible range in addition we implemented the model in a piecewise manner to handle non linear temporal drift related to factors such as climate change drought or the allometric nature of vegetation regrowth results show that the inclusion of imputed estimates improved model predictions in the presence of observation sparsity where there were less than 3 observations within 20 days the imputation approach performed better with a reduction in average reflectance error of 0 001 to 2 5 error assessment with hold out observations comparison to modis time series and example predicted images are presented

the early development of an archean submarine caldera complex with emphasis on the mattabi ash flow tuff and its relationship to the mattabi massive sulfide deposit the south sturgeon lake area of northwestern ontario is underlain by an archean submarine caldera complex which is host to six massive sulfide deposits the complex is approximately 30 km in strike length and is partly filled by mesobreccias subaqueous debris flow deposits and other epiclastic rocks as well as five major ash flow tuff units the most voluminous of these the mattabi ash flow tuff is up to 800 m in thickness and can be traced for more than 15 km across the caldera complex based on flow morphology and composition the mattabi ash flow tuff is divisible into two distinct units a bedded quartz crystal and pumice rich unit 150 650 m thick and a massive to poorly bedded ash unit 20 150 m thick the bedded unit is host to the mattabi massive sulfide deposit as well as numerous other massive sulfide occurrences in addition this unit exhibits a pronounced stratigraphic and geochemical cyclicity individual beds flow units can be subdivided into basal quartz and pumice rich lower sections which are overlain by bedded ash tops thicknesses of individual beds vary from 14 to 155 m each bed also exhibits a pronounced zonation of trace elements with high concentrations of zr y and nb at and or near the base gradually decreasing upward into the ash tops the overlying massive ash unit contains no known massive sulfide mineralization and lacks any pronounced geochemical zoning the bedded nature and geochemical zonation of individual flow units can be explained by periodic eruptions from a zoned or layered recharged siliceous magma chamber the difference in flow morphology between the bedded unit and the overlying massive ash flow tuff most likely reflects the deeper submarine nature of the eruptive vents associated with the bedded deposits the periodic and subaqueous nature of the mattabi eruptions is indicated by the presence of exhalites and massive sulfide lenses between flow units the ore lenses which comprise the mattabi deposit formed between eruptive events from high temperature fluids whose origin may be related to processes within the magma chamber

australian volcanic hosted massive sulfide deposits features styles and genetic models the cambro ordovician period has yielded the major development of volcanic hosted massive sulfide vhms deposits in australia resulting in about 12 million metric tons of contained metal copper lead and zinc concentrated in the mount read volcanics tasmania and the mount windsor volcanics queensland the archean 4 million metric tons of metal and the silurian 3 5 million metric tons of metal constitute the next important episodes while the devonian and permian have produced isolated deposits the deposits range from cu type to zn cu type to zn pb cu type the zn cu type deposits are restricted to the archean and silurian whereas the cu type and zn pb cu type occur sporadically throughout the time span from early archean to permian in general terms the major vhms bearing districts are calc alkaline in character and display a thick basal pile of rhyolitic volcanics 1 3 km thick including lavas epiclastics and subvolcanic intrusions which is overlain by a polymodal sequence containing various proportions of rhyolite dacite andesite basalt and sediments the major deposits are commonly located at the top contact of the rhyolite pile or within the lower part of the overlying polymodal sequence there is a wide range in variability of styles of australian vhms deposits including mounds pipes sheets layered deposits stacked deposits stockwork and disseminated deposits distal reworked deposits and cyclic layered deposits although these various styles show a range of features there is a consistent theme across the spectrum of metal zonation alteration mineralogy alteration chemistry sulfur isotopes macrotextures microtextures and host volcanic relationships which strongly suggests that they all belong to the one genetic group of ore deposit the classic mound style deposits such as hellyer have a series of key features subsets of which are represented in the other deposit styles the mound deposits are considered to form from deposition of metal sulfides on the sea floor immediately around the hydrothermal vent growth of the mound occurs by upward replacement of sulfide assemblages stable at higher fluid temperatures leading to zone refining and lead zinc silver gold enrichment in the outer and upper parts of the mound departure from the classic mound style of deposit is related principally to three key factors the chemistry of the ore fluid salinity temperature f02 and ah2s the nature permeability and chemistry of the volcanic pile and the sea hoor environment sea hoor topography and seawater depth these factors control the aspect ratio of the deposit the extent of stringer zone development the degree of subsea floor replacement mineralization the nature and spatial development of footwall alteration and the development and style of related distal mineralization sulfur isotope studies of australian vhms deposits indicate that reduced seawater sulfate is a major source of sulfur in the deposit whereas lead and strontium isotope results are compatible with the metals being derived by seawater convection and leaching from the volcanic pile and basement rocks this conclusion is supported by the application of various leaching models which demonstrate the availability of an adequate source of both base and precious metals in the footwall volcanic sequences the input of metals directly from volcanic magma chambers is not precluded by the available data and one likely scenario involves the contribution of gold and copper from a magmatic vapor plume rising to mix with convective seawater fluids which contribute lead zinc silver and gold leached from the footwall volcanics and basement rocks the relative importance of the magmatic input compared with the seawater convective input may help to explain the spectrum of deposit styles arid their spatial relationship to volcanic centers or adjacent sedimentary basins

geology of the golden grove prospect western australia a volcanogenic massive sulfide magnetite deposit potentially economic deposit stratabound two phases of sulfide precipitation separated by a major phase of fe oxide development metamorphosed under lower greenschist facies hydrothermal alteration of host rocks fe oxide abundance is due to either sea floor weathering or to a change with time in the trend of the ore solution seawater mixing path modified journal abstract

a chemical model for the concentration of gold in volcanogenic massive sulphide deposits abstract study and review of the gold distribution in selected volcanogenic massive sulphide deposits rosebery and hellyer in tasmania mt chalmers in queensland and millenbach in quebec indicates that gold has two distinct occurrences in these deposits 1 a gold zinc lead silver association which is commonly found in the upper part of zinc rich massive sulphide lenses e g rosebery and hellyer and 2 a gold copper association which is commonly present in the stringers and lower portions of copper rich deposits e g mt chalmers and millenbach in each deposit one of these occurrence dominates almost to the exclusion of the other thermodynamic modelling of the volcanogenic fluid which is based on previous work by large 1977 eldridge et al 1983 and pisutha arnond and ohmoto 1983 indicates that gold in the upper part of the zinc rich massive sulphide lenses was transported as au hs 2 while gold in the stringers and bases of copper rich massive sulphide deposits was transported as aucl 2 the ph and o 2 of the ore forming fluid have an important control on gold deposition and therefore gold grades high gold grades in zinc rich massive sulphide are promoted by near neutral oxidised and low temperature 150 c to 275 c fluids as indicated by the presence of barite carbonate feldspar gangue high gold grades in the copper rich stringers and base of the massive sulphide are promoted by higher temperatures 275 c to 350 c relatively oxidised fluids as indicated by bornite or by barite or hematite gangue and relatively acid fluids as indicated by kaolinite gangue in o 2 t space significant gold transport by au hs 2 occurs only in the pyrite stability field at relatively low temperatures 2 is not restricted by iron mineral equilibria but is greatest in the hematite magnetite and pyrite fields at high temperatures 300 c and high o 2 10 30 under conditions of au hs 2 transport bonanza type gold deposition may be found in areas where the hydrothermal fluids passed from the field of pyrite stability to that of hematite stability oxidation of hydrothermal fluids by seawater mixing and the rapid precipitation of sulphide minerals at the top of the massive sulphide lens may cause the precipitation of gold via the mechanisms of either h 2 s oxidation or sulphide gold coprecipitation other types of gold deposits may be classified into either the gold zinc or gold copper association the gold copper bismuth association is developed in higher temperature systems of moderate to high salinity where aucl 2 is the dominant complex e g porphyry cu au deposits and au rich skarns whereas the gold zinc lead silver association is developed in systems of low salinity and high h 2 s where au hs 2 is the dominant complex e g epithermal au ag and archean greenstone hosted au quartz

mineralogy bulk and rare earth element geochemistry of massive sulphide associated hydrothermal sediments of the brunswick horizon bathurst mining camp new brunswick massive sulphides are spatially and temporally associated with iron formation if and other hydrothermal sedimentary rocks in the vicinity of the brunswick no 12 brunswick no 6 and austin brook deposits bathurst mining camp sulphide carbonate oxide and silicate predominant if is present carbonate predominant if is best developed in and around the brunswick no 12 deposit whereas hematite bearing if is absent here but prominent in the austin brook brunswick no 6 area the if is composed dominantly of si co2 fe mn and ca minor constituents include mg p ti al and s statistically significant interelement correlations between eu fe mn pb zn cd au ca sr ba p co2 and s indicate that these elements were precipitated from hydrothermal fluids vented onto the seafloor positive interelement correlations between si ti al mg k zr rare earth elements ree s except eu se v y yb co ni and cr reflect the presence of detrital clastic mafic and aluminosilicate minerals and

generating synthetic landsat images based on all available landsat data predicting landsat surface reflectance at any given time abstract a new algorithm for generating synthetic landsat images is developed based on all available landsat data this algorithm is capable of predicting landsat surface reflectance for any desired date it first excludes cloud cloud shadow and snow observations and then uses the remaining clear observations to estimate time series models for each landsat pixel three time series models a simple model advanced model and full model are used for estimating surface reflectance for each pixel and the selection of a time series model is dependent on the number of clear observations available the more clear observations the more complex the model will be that is used for each time series model there are three components seasonality trend and breaks that are used for modeling intra annual and inter annual differences and abrupt surface change abrupt surface changes are detected by differencing predicted and observed landsat observations and if the difference is larger than twice the root mean square error rmse for six consecutive observations it will be detected as a break in the time series model the rmse values are temporally adjusted to provide better threshold range for each synthetic image a quality assessment qa band is provided that contains information on how the time series model was estimated and used for generating the synthetic data we have applied this approach to six landsat scenes within the united states we visually compared the synthetic images with real landsat images for different kinds of environments and they are similar for all image pairs we also quantitatively assessed the accuracy of the synthetic data by calculating the rmse value for all clear landsat observations the rmse values for the three visible bands are the lowest approximately 0 01 and the short wave infrared swir bands are slightly higher in magnitude between 0 01 and 0 02 the near infrared nir band has the highest rmse values between 0 02 and 0 03 the goal of this paper is to provide landsat images that are free of cloud cloud shadow snow and scan line corrector slc off gaps that can be used to derive land cover and bio physical products

initiation and collapse of active circulation in a hydrothermal system at the mid atlantic ridge 23 n gabbro and basalt collected from an area south of the kane fracture zone along the mid atlantic ridge have three stages of alteration which record the cooling of a hydrothermal system 1 stage 1 penetration of seawater began between 400 and 550 c altering pyroxene to fibrous green amphibole 2 stage 2 propylitic alteration formed along connected fractures between 250 and 300 c as fracture density increased the fe mg ratio of chlorite increased the final result being an fe chlorite quartz sulfide breccia 3 stage 3 late smectite veinlets formed at low temperatures 200 c after active circulation ceased the study focuses on stage 2 alteration by assuming local equilibrium between alteration minerals and the hydrothermal fluid constraints can be placed on the fluid composition responsible for stage 2 alteration the stage associated with deposition of sulfides the following activities of species in solution were determined for the system feo na2o cao mgo al2o3 sio2 h2o at 350 bars and 250 c log a ca a2 h 8 0 log a na a h 5 0 log a fe a2 h 1 7 log a mg a2 h 6 0 log a sio2 was set at quartz saturation 2 3 at 350 bars and 250 c fluid inclusions record the introduction of a low temperature seawater salinity fluid during formation of the latest quartz veins associated with stage 2 alteration mixing of this and the hydrothermal fluid caused a drop in temperature and increase in oxidation state resulting in increased precipitation of quartz pyrite and chalcopyrite the salinities of fluid inclusions trapped in quartz during stage 2 alteration are as much as 3 times that of seawater concentration of a fluid initially of seawater salinity may be the result of boiling at 350 c and 3000 m depth

the subsea floor formation of volcanic hosted massive sulfide evidence from the ansil deposit rouyn noranda canada the ansil cu zn volcanic hosted massive sulfide deposit is located approximately 14 km north northwest of rouyn noranda quebec within the blake river group of the archean southern abitibi greenstone belt the deposit is the second lowest within the central mine sequence a series of bimodal rhyolite andesite formations that fill in the noranda cauldron host to 17 volcanic hosted massive sulfide deposits the deposit consists of a single massive sulfide lens situated at the contact between rhyolite of the northwest formation and overlying andesite of the rusty ridge formation the rhyolite flow forms a ridge up to 500 m high which was inundated by the andesite flows the orebody is hosted within a unit of quartz porphyritic finely layered felsic volcaniclastite cranston tuff that fills in an east west trending graben formed on the upper surface of the rhyolite flow at the east end of the graben the cranston tuff is interlayered with a thin unit of dacite flows the deposit lies within an extensive discordant alteration zone characterized by feldspar destruction and na depletion the zone extends from 400 m below the deposit at the contact of the synvolcanic flavrian intrusive complex to over 400 m above the deposit this alteration zone is controlled by a fault system that served as a focus for hydrothermal fluid upflow from the beginning of cauldron formation until the end of the first cauldron cycle within the na depletion zone there are three distinct alteration facies associated with the orebody early hydrothermal activity is defined by hydrothermal explosion breccias that formed along the base of the east west trending graben walls they were filled with finely banded quartz albite sphalerite pyrite and the wall rock altered to sericite quartz with finely disseminated sphalerite and pyrite pyrrhotite the graben was then filled with the cranston tuff which was selectively altered and mineralized by the zn rich fluid subsequent development of northerly trending faults was accompanied by the upflow of cu rich fluid that selectively chloritized the footwall rhyolite below the graben floor and formed a

2 7 ga plume associated vhms mineralization in the eastern goldfields superterrane yilgarn craton insights from the low temperature and shallow water ag zn au nimbus deposit economic volcanic hosted massive sulfide vhms deposits of the archaean yilgarn craton of western australia are restricted to zones of juvenile crust as revealed through regional nd pb and hf isotopic variations and the geochemistry of felsic volcanic rocks interpreted as archaean paleo rift zones one of these runs n s through the eastern goldfields superterrane broadly coincident with the kurnalpi terrane and is associated with the high grade ca 2690 ma teutonic bore jaguar and bentley deposits plus sub economic vhms mineralization further south to date only small historic cu occurrences e g anaconda and barren pyritic lenses have been recognized in the older 2 7 ga plume dominated lower stratigraphy of the eastern goldfields superterrane the nimbus ag zn au deposit 12 1 mt at 52 g t ag 0 9 zn and 0 2 g t au is located approximately 10 km east of kalgoorlie near the margin of the kurnalpi terrane its origin has been contentious for a number of years with previous models favouring seafloor sub seafloor vhms mineralization or a high sulfidation fault hosted system we present a detailed account of the deposit its host stratigraphy and associated hydrothermal alteration plus two new shrimp u pb zircon ages pb isotope galena and o isotope zircon constraints compared to other vhms occurrences in the yilgarn craton the nimbus deposit is unusual in terms of its tectono stratigraphic position the geochemistry of its host sequence i e fi affinity felsic volcanic rocks ocean plateau like low th basalts mineralogy e g abundance of ag sb pb as bearing sulfosalts high hg low cu and quartz carbonate sericite dominated alteration assemblages classification of nimbus as a shallow water and low temperature vhms deposit with epithermal characteristics i e a hybrid bimodal felsic deposit is consistent with its position near the margin of the kurnalpi paleo rift zone and radiogenic 238u 204pb values the recognition that the nimbus deposit is associated with c 2705 ma plume magmatism opens new areas for vhms exploration in the eastern goldfields superterrane over a strike length exceeding 500 km

subsea floor replacement in volcanic hosted massive sulfide deposits abstract recent research on volcanic hosted massive sulfide vms deposits indicates that syngenetic subsea floor replacement ores form an important component of many deposits in the context of vms deposits subsea floor replacement can be defined as the syn volcanic formation of sulfide minerals within pre existing volcanic or sedimentary deposits by infiltration and precipitation in open spaces fractures inter and intra granular porosity as well as replacement of solid materials there are five criteria for distinguishing subsea floor replacement in massive sulfide deposits 1 mineralized intervals are enclosed within rapidly emplaced volcanic or sedimentary facies lavas intrusions subaqueous mass flow deposits pyroclastic fallout 2 relics of the host facies occur within the mineral deposit 3 replacement fronts occur between the mineral deposit and the host lithofacies 4 the mineral deposit is discordant to bedding and 5 strong hydrothermal alteration continues into the hanging wall without an abrupt break in intensity criteria 1 3 are diagnostic of replacement whereas criteria 4 and 5 may suggest replacement but are not alone diagnostic because clastic sulfide ores contain accessory rock fragments collected by the parent sediment gravity flow s during transport criteria 2 can only be applied to massive semi massive disseminated or vein style deposits and not clastic ores the spectrum of vms deposit types includes deposits that have accumulated largely subsea floor and others in which sedimentation and volcanism were synchronous with hydrothermal activity and precipitation of sulfides occurred at and below the sea floor over the life of the hydrothermal system deposits that formed largely subsea floor are mainly hosted by syn eruptive or post eruptive volcaniclastic facies gravity flow deposits water settled fall autoclastic breccia however some subsea floor replacement vms deposits are hosted by lavas and syn volcanic intrusions sills domes cryptodomes burial of sea floor massive sulfide by lavas or sediment gravity flow deposits can interrupt sea floor mineralization and promote subsea floor replacement and zone refining the distance below the sea floor at which infiltration and replacement took place is rarely well constrained with published estimates ranging from less than 1 to more than 500 m but mainly in the range 10 200 m the upper few tens to hundreds of metres in the volcano sedimentary pile are the favoured position for replacement as clastic facies are wet porous and poorly consolidated in this zone and at greater depths become progressively more compacted dewatered altered and less amenable to large scale infiltration and replacement by hydrothermal fluids furthermore sustained mixing between the upwelling hydrothermal fluid and cold seawater is regarded as a major cause of sulfide precipitation in vms systems and this mixing process generally becomes less effective with increasing depth in the volcanic pile the relative importance of subsea floor replacement in vms systems is related principally to four factors the permeability and porosity patterns of host lithofacies sedimentation rate the relative ease of replacement of host lithofacies especially glassy materials and early formed alteration minerals during hydrothermal attack and physiochemical characteristics of the hydrothermal fluid

the fluid evolution of the nimbus ag zn au deposit an interplay between mantle plume and microbial activity abstract the nimbus ag zn au volcanic hosted massive sulfide vhms deposit represents an exceptional orebody in the yilgarn craton of western australia it is located in a zone of juvenile crust running n s through the eastern goldfields superterrane however unlike most other vhms occurrences associated with the 2690 2680 ma rift sequence teutonic bore jaguar bentley erayinia it is hosted by the ca 2705 ma plume related stratigraphy which is more typically associated with komatiite hosted nickel sulfide mineralization the nimbus deposit displays hybrid vhms epithermal characteristics resulting from low temperature and shallow water conditions which developed a quartz carbonate sericite dominated alteration assemblage in the dacite host rocks sulfide mineralization comprises pyrite sphalerite galena arsenopyrite ag sb pb bi sulfosalts and rare chalcopyrite in this study we applied a combination of in situ analytical techniques to monitor the evolving sulfur isotope signature of the mineralizing fluids and propose that the nimbus vhms deposit developed as a result of a bimodal fluid history in the first stage the hydrothermal system powered by plume related magmatism deposited a series of barren pyrite lenses with colloform textures their variable but consistently negative mass independent sulfur isotope fractionation signature 33s 0 81 reflects the interaction between mantle derived magmatic fluids and archean seawater the ubiquitous presence of carbon rich porous textures and the remnants of carbonaceous nests in colloform pyrite also indicate a significant contribution of microbial sulfate reducers during the incipient stages of sulfide precipitation the gradual formation of colloform lenses eventually sealed the hydrothermal system establishing a physical barrier that limited the interaction with seawater this process promoted the onset of higher temperature and pressure conditions required to form the high grade zn ag mineralization sourcing sulfur and fluids largely from a magmatic reservoir 33s 0 09 whereas the identification of a predominantly magmatic sulfur source is supported by sulfur isotope signatures the recognition of a magmatic origin of the fluid may only be inferred indirectly it is consistent with the observed quartz sericite alteration style and the proposed mechanism of sulfide deposition via decompression which does not require any interaction with seawater the trace element distribution of the ore related sulfides also supports a closed hydrothermal system developed through multiple fluid pulses indeed this ore forming scenario is commonly favored by high confining pressures which at nimbus were established following the deposition of the colloform pyrite lenses that progressively sealed the hydrothermal system creating the favorable conditions for mineralization

subsurface deposition of cu rich massive sulphide underneath a palaeoproterozoic seafloor hydrothermal system the red bore prospect western australia the proterozoic bryah and yerrida basins of western australia contain important base and precious metal deposits here we present microtextural data trace element and s isotope analyses of massive sulphide mineralisation hosted in palaeoproterozoic subvolcanic rocks dolerite recently discovered at red bore the small scale high grade mineralisation which extends from the sub surface to at least 95 m down hole is dominated by massive chalcopyrite and contains minor pyrite and bi te se phases massive sulphide mineralisation is surrounded by discontinuous brecciated massive magnetite and a narrow 2 m alteration halo which suggests very focussed fluid flow laser ablation icp ms analyses indicate that chalcopyrite contains up to 10 ppm au and in excess of 100 ppm ag sulphur isotope analyses of pyrite and chalcopyrite indicate a narrow range of 34svcd 0 2 to 4 6 and no significant mass independent fractionation 0 1 33s 0 05 re os isotope analyses yield scattered values which suggests secondary remobilisation despite the geographical proximity and the common cu au ag association the mineralisation at red bore has significant differences with massive sulphide mineralisation at neighbouring degrussa as well as other massive sulphide deposits around the world these differences include the geometry sub volcanic host rocks extreme cu enrichment and narrow 34s ranges although a possible explanation for some of these characteristics is leaching of s and metals from the surrounding volcanic rocks we favour formation as a result of the release of a magmatic fluid phase along very focussed pathways and we propose that mixing of this fluid with circulating sea water contributed to sea floor mineralisation similar to neighbouring vhms deposits our data are permissive of a genetic association of red bore mineralisation with vhms deposits nearby thus suggesting a direct connection between magmatism and mineralising fluids responsible for vhms deposition at surface therefore the red bore mineralisation may represent the magmatic roots of a vhms system

the scuddles cu zn prospect an archean volcanogenic massive sulfide deposit golden grove district western australia the scuddles volcanogenic massive sulfide prospect together with the nearby gossan hill golden grove prospect constitute the largest known potentially economic cu zn sulfide deposits in the archean yilgarn block of western australia enclosed in a submarine sequence of felsic to intermediate volcanics epiclastics and exhalative chemical sediments the scuddles deposit lies in a regionally extensive mineralized horizon this horizon is up to 80 m thick and is dominated by sulfidic and cherty exhalites and epiclastics a sequence of felsic to intermediate lavas pyroclastics and epiclastics lies above the mineralized horizon with felsic pyroclastics and epiclastics beneath pyroclastic rocks may have been resedimented by mass flow processes the entire sequence has sustained the effects of hydrothermal alteration and regional metamorphism and dips steeply to the west lying on the east limb of a major synclinal structure due to alteration major element values of the rocks are not an accurate guide to their primary composition however abundances of ti zr y nb and v are commonly unaffected and confirm an andesitic to rhyolitic spectrum zoning of ore metals in the scuddles mineralized horizon is typical of that in many precambrian felsic volcanic associated exhalative sulfide deposits the top is defined by a laminated magnetite bearing iron formation enriched in fe mn and base metals which conformably overlies several lenses of massive fe zn sulfides in places containing significant pb ag au and cu grading downward into pyritic sulfides in turn the massive sulfides overlie a zone of epigenetic stockwork stringer and disseminated cu fe sulfides in the middle and lower portions of the mineralized horizon massive to disseminated exhalative sulfides are in places accompanied by quartz chlorite talc and other silicates carbonates and magnetite also interpreted to be at least partly exhalative in origin the lower cu fe sulfide zone is considered to have formed immediately below the sea floor perhaps occupying an extensive feeder system for hot springs the upper zn fe sulfide zone may have formed by precipitation out of hydrothermal plumes as they vented into and mixed with seawater ore mineral deposition was attended by the development of a volumetrically large 10 km long several hundred meters thick strata bound zone of hydrothermal alteration well represented in the footwall and mineralized horizon upper hanging wall rocks are little altered but elsewhere the sequence displays moderate to intense feldspar destructive development of quartz chlorite sericite and locally abundant carbonate talc and sulfides these mineralogical changes are accompanied by pervasive depletion of na ca and sr and locally k the mineralized horizon and much of the footwall is enriched in fe mg mn base and precious metals as s co 2 and h 2 o interpreted to be the result of addition from exhalative sources the strata bound alteration zone represents a volume of hydrothermal flux in which major sites of sulfide deposition at scuddles and gossan hill were focused zones of fe mg base metal enrichment below and adjacent to positions of submarine metal bearing exhalations precipitation of exhalites occurred under relatively quiescent conditions in the mineralized horizon however the stratigraphic sequence indicates that at other times active mass flow deposition was taking place

interannual changes of the floating ice shelf of petermann gletscher north greenland from 2000 to 2012 petermann gletscher northwest greenland drains 4 of the greenland ice sheet into nares strait its floating ice shelf retreated from 81 to 48 km in length during two large calving events in 2010 and 2012 we document changes in the three dimensional ice shelf structure from 2000 to 2012 using repeated tracks of airborne laser altimetry and ice radio echo sounding icesat laser altimetry and modis visible imagery the recent ice shelf velocity measured by tracking surface features between flights in 2010 and 2011 is 1 25 km a 1 15 30 faster than estimates made before 2010 the steady state along flow ice divergence represents 6 3 gt a 1 mass loss through basal melting 5 gt a 1 and surface melting and sublimation 1 0 gt a 1 airborne laser altimeter data reveal thinning both along a thin central channel and on the thicker ambient ice shelf from 2007 to 2010 the ice shelf thinned by 5 m a 1 which represents a non steady mass loss of 4 1 gt a 1 we suggest that thinning in the basal channels structurally weakened the ice shelf and may have played a role in the recent calving events

mineralization at the golden grove cu zn deposit western australia ii deformation textures of the opaque minerals studies of the sulphide magnetite fabric at golden grove western australia metamorphosed under conditions of lower to middle greenschist facies indicate that pyrite and magnetite deformed in a b

the subsea floor replacement origin of the ordovician highway reward volcanic associated massive sulfide deposit mount windsor subprovince australia the highway reward massive sulfide deposit is hosted by a submarine below storm wave base silicic synsedimentary intrusion dominated volcanic succession the succession includes at least 13 porphyritic units in a volume of 1 x 1 x 0 5 km peperitic upper margins suggest that most of the rhyolites rhyodacites and dacites were emplaced as small 300 degrees c h 2 s dominant fluids by replacement of rhyolite rhyodacite and peperite lower temperature 300 degrees c fluids that diffused from the margins of the pipes deposited a halo of sphalerite rich ore

developing clear sky cloud and cloud shadow mask for producing clear sky composites at 250 meter spatial resolution for the seven modis land bands over canada and north america abstract a new technology was developed at the canada centre for remote sensing ccrs for generating canada wide and north america continental scale clear sky composites at 250 m spatial resolution for all seven modis land spectral bands b1 b7 the modis level 1b mod02 swath level data are used as input to circumvent the problems with image distortion in the mid latitude and polar regions inherent to the global sinusoidal sin projection utilized for the standard modis data products the modis 500 m land bands b3 to b7 are first downscaled to 250 m resolution using an adaptive regression and normalization scheme for compatibility with the 250 m bands b1 and b2 a new method has been developed to produce the mask of clear sky cloud and cloud shadow at 250 m resolution it shows substantial advantages in comparison with the modis 250 m standard cloud masks the testing of new cloud mask showed that it is in reasonable agreement with the modis 1 km standard product once it is aggregated to 1 km scale while the cloud shadow detection looks more reliable with the new methodology nevertheless more quantitative analyses of the presented scene identification technique are required to understand its performance over the range of input scenes in various seasons the new clear sky compositing scheme employs a scene dependent decision matrix it is demonstrated that this new scheme provides better results than any others based on a single compositing criterion such as maximum ndvi or minimum visible reflectance to account for surface bi directional properties two clear sky composites for the same time period are produced by separating backward scattering and forward scattering geometries which separate pixels with the sun satellite relative azimuth angles within 90 270 and outside of this range comparison with landsat imagery and with modis standard composite products demonstrated the advantage of the new technique for screening cloud and cloud shadow and generating high spatial resolution modis clear sky composites the new data products are mapped in the lambert conformal conic lcc projection for canada and the lambert azimuthal equal area laea projection for north america presently this activity is limited to modis terra due to known problems with band to band registration and noisy swir channels on modis aqua

a magnetite rich cyprus type vms deposit in ortaklar a unique vms style in the tethyan metallogenic belt gaziantep turkey abstract the ortaklar vms deposit is hosted in the kocali complex consisting of basalts and deep sea pelagic sediments which formed by rifting and continental break up of the southern neotethyan in late triassic the basalts are of nmorb type without notable crustal contamination from the surface to depth the ortaklar deposit consists of a gossan zone a thick massive ore zone and a poorly developed stockwork zone primary mineralisation is characterised by distinctive facies including sulphide breccias proximal graded beds distal stockworks and chimney fragments ore mineral abundances decrease in the order of pyrite magnetite chalcopyrite and sphalerite two distinct phases of mineralisation massive magnetite and massive sulphide are present in the ortaklar deposit textural evidence e g magnetite replacing sulphides and the spatial relationships with the host rocks indicate that magnetite and sulphide minerals were generated in different stages the transition from sulphide to magnetite mineralisation is interpreted to relate to variation in h2s content of ore fluids the 1st stage massive sulphide ore might have formed by early hydrothermal fluids rich in fe and h2s the 2nd stage massive magnetite might have formed by later neutral hydrothermal fluids rich in fe but poor in h2s replacing the pre existing sulphide ore the alteration patterns mineral paragenesis lithological features massive ore stockwork ore gossan of the ortaklar deposit together with its trace elements cu pb zn au ag and ree signatures are all consistent with a cyprus type vms system the 34s values in pyrite and chalcopyrite samples range from 2 6 to 5 7 indicating that the hydrothermal fluids were associated with sub seafloor igneous activity typical of cyprus type vms deposits however magnetite formed later than sulphide minerals in the ortaklar deposit contrasting with typical cyprus type vms deposits where magnetite generally occurs in lower sections consequently although the ortaklar deposit generally conforms to cyprus type deposits it is distinguished from them by its late stage and high magnetite concentration thus the ortaklar deposit is thought to be an exceptional and perhaps unique cyprus type vms deposit