mobilization of gold as a polymetallic melt during pelite anatexis at the challenger deposit south australia a metamorphosed archean gold deposit the challenger gold deposit in south australia is hosted by pelitic migmatites that underwent peak metamorphism at 7 5 1 5 kbars and at least 800 c nd model ages suggest a protolith age of 2900 ma zircon u pb and garnet sm nd dating indicates that peak metamorphism occurred at 2440 ma and that garnet was present during this event at this time in situ vapor absent melting affected the pelitic host rock indicating that peak metamorphism occurred without introduction of a foreign fluid or melt thus evidence indicating the presence of ore minerals during peak metamorphism implies a prepeak mineralization event this evidence includes the occurrence of invisible gold in lollingite but not in adjacent arsenopyrite and the presence of spherical gold sulfide inclusions in peak metamorphic garnet and other silicates textures developed between pyrrhotite lollingite arsenopyrite and gold the lack of silicate alteration minerals supports this conclusion experimental evidence is presented to support our interpretation that a gold rich polymetallic melt was mobilized into leucosomes synchronously with silicate melt during peak metamorphism visible gold is restricted to migmatitic leucosomes and to a lesser extent melanosomes large inclusions of gold with coexisting arsenopyrite pyrrhotite and bismuth are hosted within peak metamorphic silicate minerals and at grain boundaries trails of micrometric spherical inclusions of predominantly gold and bismuth propagate along annealed fractures from these larger inclusions we show that these gold sulfide inclusions represent the crystallized products of an immiscible polymetallic melt metamorphism of the challenger deposit resulted in partial melting of the pelitic host rock and formation of this gold rich melt these two melts were synchronously redistributed to accumulate as leucosomes during development of a stromatic migmatite formation of a polymetallic melt thereby enabled extensive mobilization of gold producing leucosomes enriched in gold this occurred because the immiscible metallic melt was physically entrained rather than chemically dissolved within the silicate melt gold rich shoots at challenger parallel the plunge of ptygmatically folded leucosomes that are shown to be parasitic to a larger scale fold geometry which appears to be structurally related to the ore shoots it is interpreted that concurrent migration of polymetallic and silicate melt allowed concentration of gold into a series of dilational structures which developed within the larger scale fold geometry challenger represents a new deposit type other deposits around the world such as renco and griffins find are hosted in granulite facies rocks but challenger is the first reported example of leucosome hosted gold in migmatites

evidence for two stages of mineralization in west africa s largest gold deposit obuasi ghana the supergiant obuasi gold deposit is the largest deposit in the paleoproterozoic birimian terranes of west africa with 62 moz of gold past production resources the deposit is hosted in the paleoproterozoic kumasi group sedimentary rocks composed of carbonaceous phyllites slates psammites and volcaniclastic rocks intruded by different generations of felsic dikes and granites a three stage deformation history is defined for the district the d1 ob stage is weakly recorded in the sedimentary rocks as a layer parallel fabric and indicates that bedding parallel shearing occurred during the early stage of deformation at obuasi the d2 ob is the main deformation stage affecting the obuasi district and corresponds to a nw se shortening tight to isoclinal folding as well as intense subhorizontal stretching occurred during d2 ob parallel with the plane of a pervasive ne striking subvertical foliation s2 ob finally a n s shortening event d3 ob refolded previously formed structures and formed a distinct ene striking variably dipping s3 ob cleavage that is domainal in nature throughout the deposit two economic styles of mineralization occur at obuasi and contribute equally to the gold budget these are 1 gold bearing sulfides dominantly arsenopyrite mainly disseminated in metasedimentary rocks and 2 native gold hosted in quartz veins that are as much as 25 m wide microstructural evidence such as strain shadows surrounding gold bearing arsenopyrite parallel with s2 ob but folded by s3 ob indicates that the sulfides were formed during d2 ob concentrations of as much as 700 ppm au are present in the epitaxial growth zones of the arsenopyrite grains although the large mineralized quartz veins are boudinaged and refolded indicating their formation during d2 ob field and microanalytical observations demonstrate that the gold in the veins is hosted in microcracks controlled by d3 ob where the s3 ob cleavage crosscuts the quartz veins in the main ore zones thus these observations constitute the first evidence for multiple stages of gold deposition at the obuasi deposit futhermore three dimensional modeling of stratigraphy structure and gold orebodies highlights three major controls on oreshoot location which are 1 contacts between volcaniclastic units and pre d 1 felsic dikes 2 fault intersections and 3 f3 ob fold hinges the maximum age for the older disseminated gold event is given by the age of the granites at 2105 2 ma which is within error of hydrothermal rutile in the granites of 2098 7 ma the absolute age of the younger gold event is not known

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

geochronological constrains on the timing of magmatism deformation and mineralization at the karouni orogenic gold deposit guyana south america abstract the karouni deposit is located in central guyana 35 km to the w of the former producing 5 moz omai mine and is interpreted to be an orogenic gold deposit it is hosted in rhyacian aged 2 2 to 2 1 ga volcano sedimentary and intrusive rocks metamorphosed to greenschist facies detailed structural and crosscutting relationships coupled with robust new u pb geochronology on intermediate to felsic intrusive rocks and hydrothermal minerals from the karouni camp have constrained the structural evolution of the deposit and provided a new age for gold mineralization with important implications for the structural framework and timing of gold mineralization throughout the region magmatism within the 200 km2 of the karouni camp progressed from early synvolcanic intermediate composition dikes at 2147 ma to a major voluminous pulse of felsic magmatism coeval with regional deformation during the trans amazonian orogeny between 2120 and 2088 ma a late pulse of granitic magmatism at 1950 ma may be related to a post orogenic event inherited zircons within the felsic intrusive rocks indicate assimilation of crust as old as 2223 32 ma gold mineralization associated with camp scale d2 deformation has been dated to 2084 15 ma on the basis of u pb geochronology of hydrothermal titanite these results show gold mineralization is coeval with felsic magmatism and contemporaneous with a major pulse of orogenic gold mineralization in the birimian province of west africa

the improve 1 storm of 1 2 february 2001 part i development of a forward tilted cold front and a warm occlusion abstract analysis of observations and the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 are used to study the development of a forward tilted cold front off the coast of washington state the vertical velocity associated with the cold front produced a wide cold frontal rainband in the early stage of development the midtropospheric baroclinic zone or upper cold front moved forward with time over the warm sector to produce a structure similar to a split front the movement of the upper cold front was due to horizontal transport and frontogenetical propagation the frontogenetical propagation was produced by a combination of tilting and diabatic frontogenesis which resulted in a negative positive couplet of frontogenesis straddling the baroclinic zone the lower tropospheric cold front eventually caught up with the warm front to form a classical warm occlusion in the initial occluding process the converging frontal zones tilted i

textural control on gold distribution in as free pyrite from the dongping huangtuliang and hougou gold deposits north china craton hebei province china article i nfo pyrite from the dongping huangtuliang and hougou gold deposits hebei province china was investigated using a combination of ore microscopy including back scattered imaging and in situ laser ablation inductively coupled plasma mass spectroscopy la icp ms a range of elements including au te ag pb bi cu co ni and as was analyzed with the aim to constrain the textural controls and influence of superimposed deformation on the distribution of invisible gold in as free pyrite thedatasetshowsexcellentcorrespondence betweenmeasuredhighgoldvaluesandthreekeytexturalcriteria i areasofclusteredtellurideinclusions especiallyindongping ii microshearingandfracturing brecciation dongping and huangtuliang and iii pyrite recrystallization huangtuliang invisible gold is only at trace levels in the hougou and gold bearing telluride minerals are not observed this is considered to result from larger scale remobilization of gold during advanced brecciation and recrystallization of pyrite pyrite grains containing clustered inclusions have by far the highest gold concentrations up to 1 wt with consistent values of thousands of ppm au interpretation of textures and la icp ms data infers that in these areas the distribution of telluride inclusions extends pervasively from micron to nanoscale i e as fields of nanoparticles local employment of coupled dissolution reprecipitation reaction between pyrite and fluids driving the k metasomatic alteration dated at 150 ma is invoked to explain such patterns syn deformational grain scale mobilization of gold and other elements took place leading to a portion of the gold being recrystallized within fractures and microshears the deformational event leads to gold enrichment in the huangtuliang pyrite where brittle fracturing brecciation has been followed by a resorption and recrystallization in the latter case foam textured pyrites again without as can contain up to hundreds of ppm gold theinterpreted sequenceof pyritepost depositional eventsis inaccordancewith the protracted magmaticevolution of the area starting with variscan alkaline intrusions 390 ma and reactivated during the yanshanian orogeny 150 ma thestudyshows i thatas freepyritecanreadilycontainsignificantamountsofinvisiblegold bothasnanoparticles

influence of strong gradients of wind and humidity on frontal ageostrophic circulations the impact is studied of strong gradients of wind and humidity on the ageostrophic circulation developed around a conceptual cold frontal system the simulated basic wind and temperature fields are chosen to best represent the frontal observations made during the fronts 87 field experiment and in particular to take account of the presence of strong low level jets the numerical solution of the diagnostic sawyer eliassen equation in both its adiabatic and diabatic forms permitted us to test the impact of the wind and humidity structure on the corresponding ageostrophic circulation in particular strong negative shear above the low level jet core enhanced subsiding motions on the warm side of the front which restricted the horizontal extent of the cloud cover on the other hand the presence of well marked horizontal humidity gradients aloft at the rear edge of the cloud cover enhanced the ascending motions ahead of the frontal surface creating locally a secondary maximum of upward motions the degree of stability within the prefrontal boundary layer was found to be of major importance with regard to the intensification of the upright convection near the leading edge of the front moreover the incorporation of a parametrization scheme representing the ekman pumping at the top of the boundary layer enhanced the diagnosed circulation ahead of the front a comparison with observations made during two case studies of fronts 87 seems to confirm these results

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

pyrite textures and compositions in jiangshan gold deposit bengbu uplift southeastern north china craton implications for ore genesis abstract many phanerozoic gold deposits in east china e g those in the jiaodong peninsula hosted either in granitoids of the same age or precambrian basement rocks of the north china craton have been well documented the bengbu uplift along the southeastern margin of the north china craton is believed to be the western extension of the jiaodong gold province separated by the large scale sinistral tan lu fault zone however no deposits with more than 10 t gold resources have been discovered in the bengbu uplift and it is unclear whether the timing and genesis of gold deposits in the bengbu uplift are similar to those in the jiaodong gold province in this study laser ablation inductively coupled plasma mass spectrometry trace element analyses mapping and in situ sulfur isotope analyses were used to determine the source and process of gold mineralization in jiangshan gold deposit the largest in the region the wall rocks in the jiangshan gold deposit are metamorphic rocks of the neo archaean wuhe group and the ore bodies are controlled by the eastern part of the guangou xiajijia fault four stages were identified from cross cutting relationships and textural and mineralogical characteristics pre ore stage stage i quartz pyrite muscovite alteration stage ii pyrite quartz veins stage iii and quartz pyrite veinlets stage iv each of the four stages is characterized by a different type of pyrite here named py1 py2 py3 and py4 py1 formes the core of py2 has elliptical and irregular shapes contains low gold and arsenic concentrations and has 34s values of 0 86 2 86 py2 is hosted in quartz pyrite muscovite altered rocks with disseminated and aggregated euhedral to subhedral textures it has elevated arsenic content and the lowest gold content with some rhythmic zones and fractures stage ii was crosscut by stage iii py3 has anhedral textures with brittle deformation and occupies fractures in stage iii pyrite quartz veins the gold content of py3 is slightly higher than that of py1 and py2 but its arsenic content is extremely low py4 in the quartz pyrite veinlets has cataclastic textures with the highest gold and chalcophile element contents native gold and electrum also formed in stage iv which is the main gold stage in the jiangshan deposit the 34s values of py2 py4 are broadly similar 5 79 7 98 suggesting a common sulfur source based on previous studies and higher 34s values of hydrothermal pyrite the fluid sulfur isotopes are interpreted to relate to degassing of the mantle wedge metasomatized by slab fluids during the westward subduction of the palaeo pacific plate beneath the north china craton during the early cretaceous based on the geological characteristics of the deposit we classify the jiangshan gold deposit as a jiaodong fracture disseminated type gold deposit which occurs as disseminated veinlets and disseminated mineralization in wallrocks along fracture zones tectonic events may be the most important factor in gold mineralization in fracture disseminated type gold deposits

airborne doppler radar and sounding analysis of an oceanic cold front abstract an analysis of a cold front over the eastern atlantic ocean based on airborne doppler wind syntheses and dropsonde data is presented the focus and unique aspect of this study is a segment of the front that was near the center of the cyclone the dual doppler wind synthesis of the frontal zone combined with an average dropsonde spacing of 30 km covers a total distance of 450 km in the cross frontal direction the finescale resolution and areal coverage of the dataset are believed to be unprecedented the cold front was characterized by a distinct wind shift and a strong horizontal temperature gradient the latter was most intense aloft and not at the surface in contrast to the classical paradigm of surface cold fronts the shear of the alongfront component of the wind was relatively uniform as a function of height within the frontal zone this observation is contrary to studies suggesting that frontal zones decrease in intensity above the surface the surface convergence within the frontal zon

re examination of the split cold front in the british isles cyclone of 17 july 1980 an analysis of an mm5 model simulation of a cyclone that passed over the british isles on 17 july 1980 indicates that the cyclone had some characteristics of both the split cold front model of browning and monk 1982 and of a schematic by browning and roberts 1996 most importantly the cyclone had the characteristic upper level baroclinic zone and its associated vertical velocity in advance of the surface front this is an integral part of both the split cold front model of browning and monk and browning and roberts s schematic and confirms the analysis of browning and monk simultaneously at different locations the cyclone also had the characteristics of a warm occlusion in the lower levels with the portion of the cold front that was above the warm front tipped forward with height the lower and upper portions of the cold front were not only fronts in equivalent potential temperature as proposed by browning and monk but true baroclinic zones with significant associated vertical velocity the complex structure of this cyclone in the british isles was similar to that of some storms in the pacific northwest of the united states locatelli et al 2005 copyright 2005 royal meteorological society

the mesoscale dynamics of freezing rain storms over eastern canada abstract a severe ice storm affected the east coast of canada during the canadian atlantic storms project ii a hierarchy of cloud resolving model simulations of this storm was performed with the objective of enhancing understanding of the cloud and mesoscale processes that affected the development of freezing rain events the observed features of the system were reasonably well replicated in the high resolution simulation diagnosis of the model results suggests that the change of surface characteristics from ocean to land when the surface warm front approaches newfoundland disturbs the quasi thermal wind balance near the frontal region the cross frontal circulation intensifies in response to the thermal wind imbalance which in turn leads to the development of an extensive above freezing inversion layer in the model storm depending on the depth of the subfreezing layer below the inversion the melted snow may refreeze within the subfreezing layer to form ice pellets or they may refreeze at the surf

partial melting of the broken hill galena sphalerite ore experimental studies in the system pbs fes zns ag2s for many years the genesis of the broken hill pb zn ag deposit has been and continues to be hotly debated mostly because many of the original characteristics of the deposit have been obscured by high grade metamorphism and deformation metamorphism not only overprinted the deposit but fundamentally modified the sulfides through metamorphic remobilization based on experimental studies it had also been speculated that partial melting of the sulfides may have occurred the lack of experimental data at elevated pressures in the pbs fes zns system has limited this suggestion to mere speculation we present the results of an experimental study of the melting behavior of sulfides which show that broken hill ores must have been partially molten under peak metamorphic conditions

slip partitioning along major convergent plate boundaries along plate boundaries characterized by oblique convergence earthquake slip vectors are commonly rotated toward the normal of the trench with respect to predicted plate motion vectors consequently relative plate motion along such convergent margins must be partitioned between displacements along the thrust plate interface and deformation within the forearc and back arc regions the deformation behind the trench may take the form of strike slip motion back arc extension or some combination of both we observe from our analysis of the harvard moment tensor catalog that convergent arcs characterized by back arc spreading specifically the marianas and new hebrides are characterized by a large degree of slip partitioning however the observed rates directions and location of back arc spreading are not sufficient to account for degree of partitioning observed along the respective arcs implying that the oblique component of subduction is also accommodated in part by shearing of the overriding plate in the case of the sumatran arc where partitioning is accommodated by strike slip faulting in the overriding plate the degree of partitioning is similar to that observed along the marianas but the result is viewed with caution because it is based on a predicted plate motion vector that is based on locally derived earthquake slip vectors in the case of the alaskan aleutian arc where back arc spreading is also absent the degree of partitioning is less and rotation of slip vectors toward the trench normal appears to increase linearly as a function of the obliquity of convergence if partitioning in the alaskan aleutian arc is accommodated by strike slip faulting within the upper plate the positive relationship between obliquity of convergence and the rotation of earthquake slip vectors to the trench normal may reflect that either 1 the ratio of the depth extent of strike slip faults behind the trench z s to the subduction thrust z t increases westward along the arc 2 the dip of the subduction thrust increases westward along the arc or 3 the strength of the subduction thrust decreases westward along the arc

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

complex mineral zoning patterns caused by ultra local equilibrium at reaction interfaces chemically zoned minerals are useful records of temporal variations in ambient conditions and bulk chemical composition of the fl uid from which the minerals precipitate in fl buffered systems zoning of mineral compositions is expected to refl ect directly the evolution of fl composition here we show that during rapid fl uid rock reactions ultra local equilibrium can form complex mineral zoning patterns even when the overall system is highly fl uid buffered we reacted cleaved calcite single crystals with aqueous arsenate phosphate solutions with molar ratios of as as p between 0 01 and 0 15 at 250 c and water saturated pressure we fithat complex zoning patterns and solid solution between hydroxylapatiteand arsenate bearing hydroxylapatite that pseudomorphically replaced calcite formed within hours and these zoning patterns were destroyed within days during secondary reactions we propose a two stage reaction process in the formation of the fi nal reaction product 1 on an hour time scale calcite is dissolved and replaced by compositionally heterogeneous apatite the thin reaction interface fllayer becomes extremely enriched in arsenic at an ultra local scale as the reaction removes phosphate faster than the interface fl uid can re equilibrate with the bulk fl uid 2 the heterogeneous apatite is replaced by homogeneous apatite that refl ects the bulk fl uid composition over a longer days time scale through interface coupled dissolution precipitation this paper highlights the complexity that can arise from ultra local fl uid composition variations due to rapid fl uid rock interaction in a short lived fl uid fl ow event for example during a seismic cycle subsequent interpretation of complex zoning patterns as refl ecting the evolution of bulk fl uid would be erroneous

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

heavy rainfall associated with double low level jets over southern china part ii convection initiation abstractheavy rainfall that occurred at the south coast of china on 10 11 may 2014 was associated with a synoptic system related low level jet sllj and a boundary layer jet blj to clarify the

on the initiation of metamorphic sulfide anatexis mineral assemblages in common sulfide ore deposits are examined together with phase relations to 1 investigate the pressure temperature conditions required for the onset of metamorphically induced partial melting involving economic minerals and 2 place constraints on the amount of melt produced deposits that contain sulfosalt or telluride minerals may start to melt at conditions ranging from lowest greenschist facies to amphibolite facies deposits lacking sulfosalt and or telluride minerals may begin to melt once p t conditions reach the upper amphibolite facies if galena is present or well into the granulite facies if galena is absent the result is two broad melting domains a lowto medium temperature low melt volume domain involving melting of volumetrically minor sulfosalt and or telluride minerals and a high temperature potentially higher melt volume domain involving partial melting of the major sulfide minerals epithermal gold deposits which are especially rich in sulfosalt minerals are predicted to commence melting at the lowest temperatures of all sulfide deposit types massive pb zn cu deposits may start to melt in the lower to middle amphibolite facies if pyrite and arsenopyrite coexist at these conditions and in the upper amphibolite facies if they do not excepting sulfosalt bearing occurrences massive ni cu pge platinum group element deposits will show little to no melting under common crustal metamorphic conditions whereas disseminated cu deposits are typically incapable of generating melt until the granulite facies is reached when partial melting commences in bornite bearing rocks the volume of polymetallic melt that can be generated in most deposit types is therefore largely a function of the abundance of sulfosalt minerals even at granulite facies conditions this volume is usually less than 0 5 the exception is massive pb zn deposits where melt volumes significantly exceeding 0 5 vol may be segregated into sulfide magma dykes allowing mobilization over large distances

instability characteristics of radar derived mesoscale organization modes within cool season precipitation near portland oregon abstractthe instability characteristics associated with different radar derived mesoscale organization modes are examined using six cool seasons of operational scanning radar data near portland oregon and operational sounding data from salem oregon additionally several years of microwave rain radar ka band vertically pointing radar data from portland and merwin washington are used to characterize the nature and occurrence of generating cells and fall streaks the combination of a new metric convective stratiform intermittency with the classification of radar reflectivity maps into convective and stratiform precipitation types was applied to periods when the freezing level was 1 4 km altitude this method distinguishes periods with embedded convective within stratiform mesoscale organization from those that were mostly convective or mostly stratiform mesoscale organization occurs in a continuum of states with predominantly stratiform structure occurring most frequently generating cells in the s

fingerprinting multiple gold mineralization events at the dome mine in timmins ontario canada trace element and gold content of pyrite abstract the dome mine is host to over 16 moz of orogenic gold deposited during a period of up to 25 ma through multi stage enrichment the earliest economic stage of veining is an extensive set of ankerite veins which were historically considered barren except where overprinted by subsequent veining events gold in these veins is intimately associated with pyrite mineralization and three stages of pyrite growth have been identified py1 2 3 the trace element content of each stage of pyrite growth determined by dynamic secondary ion mass spectrometry and synchrotron radiation x ray fluorescence reveals that there were three auriferous fluid events each with a unique gold and trace element fingerprint which can be related to deposits wide mineralization events early ankerite vein forming fluids were auriferous lower temperature 200 250 c and deposited py1 enriched in gold metals and metalloids as cu ni zn py2 growth is related to deposit wide quartz tourmaline and quartz fuchsite veining based on trace element geochemistry au ag and associated mineral assemblages this deposited ni enriched pyrite tellurides galena and gold with anomalously high au ag ratios there is also evidence for remobilization of early gold and trace elements from py1 pyrite during the py2 forming event the final stage of gold endowment in the ankerite veins is related to a deposit and camp wide quartz veining event py3 growth is trace element as ni cu and au poor with respect to py1 and py2 however this veining event contributed the bulk of the ankerite vein gold endowment the remobilization of gold and trace elements from sieve textured py1 in addition to overprinting py2 and py3 and their associated gold endowments helps explain the difficulty in applying bulk rock trace element vectors to gold at the dome mine the work also provides conclusive evidence for the auriferous nature of early ankerite veining at the dome mine and reveals that the system was fertile for a period of over 7 to 25 ma a key component for the formation of a world class deposit

unusually long duration multiple doppler radar observations of a front in a convective boundary layer abstract dual doppler observations acquired by a network of mobile radars deployed in the oklahoma panhandle on 3 june 2002 are used to document the kinematic structure and evolution of a front the data were collected during the international h2o project on a mission to study the initiation of deep convection synchronized scanning allowed for the synthesis of three dimensional wind fields for nearly 5 5 h of the 1557 0000 utc period the front initially moved southward as a cold front stalled and later retreated northward as a warm front deep convection failed to be initiated along the front in situ thermodynamic measurements obtained by a mobile mesonet were used to document changes in the density gradient at the surface this paper examines the relationships among the changes in baroclinity the thermally direct frontal circulation updraft intensity alongfront updraft variability and the intensity of vortices along the front increases in the front normal density gradient tended to be associate

numerical study of horizontal shear instability waves along narrow cold frontal rainbands abstractthe effects of variations in low level ambient vertical shear and horizontal shear on the alongfront variability of narrow cold frontal rainbands ncfrs that propagate into neutral and slightly unstable environments are investigated through a series of idealized cloud resolving simulations in cases initialized with slightly unstable sounding and weak ambient cross frontal vertical shears core gap structures of precipitation along ncfrs occur that are associated with wavelike disturbances that derive their kinetic energy mainly from the mean local vertical shear and buoyancy however over a wide range of environmental conditions core gap structures of precipitation occur because of the development of a horizontal shear instability hsi wave along the ncfrs the growth rate and amplitude of the hsi wave decrease significantly as the vertical shear of the ambient cross front wind is reduced these decreases are a consequence of the enhancement of the low level local vertical shear immediately beh

gold mineralization in as rich mesothermal gold ores of the bogosu prestea mining district of the ashanti gold belt ghana remobilization of invisible gold the bogosu prestea mining district of southwestern ghana is a 33 km section of the early proterozoic ashanti gold belt greenschist facies carbonaceous and carbonate bearing turbidites and greywackes and mafic dikes host numerous economic mesothermal gold deposits structurally higher ores in the bogosu concession have brittle deformation and consist of disseminated sulphide lodes in tectonically disrupted sedimentary rocks and carbonate altered mafic dikes most gold occurs as micrometre size particles in arsenian pyrite and as invisible gold in arsenian pyrite and arsenopyrite the structurally deeper ores of the adjoining prestea concession are associated with brittle ductile deformation and consist of extensive crack seal quartz veins and graphitic shear zones only minor amounts of invisible gold were detected in these deeper lodes gold occurs dominantly as abundant microscopic and larger particles in sulphide arsenide minerals and in gangue the gold distribution patterns revealed by sims microprobe analysis and ion maps emp and colour staining suggest that most of the primary gold in the bogosu prestea system precipitated in solid solution with sulphide arsenide minerals however post depositional concentration and redistribution occurred in increasing degree with 1 increase in metamorphic hydrothermal gradients in the gold system depth 2 decrease in the refractory properties of the host mineral and 3 increase in the amount of post depositional host mineral recrystallization and deformation gold evolved from primary solid solution within sulphide arsenide minerals to colloidal and micrometre size particles concentrated in voids fractures and internal grain boundaries and finally to microscopic and larger particles at sulphide arsenide grain margins and in the gangue assemblage the general conclusions presented here are applicable to as rich gold deposits of all ages worldwide the presence of gold in late fractures is insufficient evidence for late stage introduction of gold in mesothermal gold systems

kinematic and moisture characteristics of a nonprecipitating cold front observed during ihop part i across front structures abstract a wide array of ground based and airborne instrumentation is used to examine the kinematic and moisture characteristics of a nonprecipitating cold front observed in west central kansas on 10 june 2002 during the international h2o project ihop this study the first of two parts is focused on describing structures in the across front dimension coarsely resolved observations from the operational network and dropsondes deployed over a 200 km distance centered on the front are combined with higher resolution observations from in situ sensors doppler radars a microwave radiometer and a differential absorption lidar that were collected across a 40 km swath that straddled a 100 km segment of the front the northeast southwest oriented cold front moved toward the southeast at 8 10 m s 1 during the morning hours but its motion slowed to less than 1 m s 1 in the afternoon in the early afternoon the cold front separated cool air with a northerly component flow of 2 4 m s 1 from a 10 km wide ban

three dimensional mesoscale circulation within a convective post frontal system possible role of conditional symmetric instability for triggering convective motion the role of the conditional symmetric instability csi in the formation of convective systems in the cold airmass located at the rear of a secondary cold frontal system is evaluated this study is based on observations made on 4 june 1984 during the french experiment landes fronts 84 in particular the mesoscale three dimensional circulation deduced from doppler radar data within one of these convective systems is studied in detail and compared with that predicted by the csi theory in spite of the fact that on the one hand notable convective scale motion masks the mesoscale circulation and that on the other hand the synoptic scale circulation is poorly described this comparison shows that among the various theories involved at the mesoscale only csi gives a proper account of the observed mesoscale circulation

a wide cold frontal rainband and its relationship to frontal topography a wide cold frontal rainband associated with a vigorous surface cold front was investigated using conventional meteorological data and the velocity and reflectivity data from high resolution doppler radar it was found that the movement of the rainband was closely related to the velocity of the frontal surface and that the substructural features of the rainband corresponded closely with the topographical features of that surface the evolution of the topography of the frontal surface is described and some processes that might affect frontal topography and therefore the structure and movement of rainbands are examined

quartz albite and diopside solubilities in h 2 o nacl and h 2 o co 2 fluids at 0 5 0 9 gpa the solubility of quartz and incongruent dissolution apparent solubility of albite and diopside in h2o nacl and h2o co2 fluids have been determined at pressures up to 0 9 gpa 9 kbar and temperatures of 500 900 c solubilities of quartz and albite decrease with increasing salt concentration x nacl salt out effect whereas the solubility of diopside increases with increasing x nacl salt in effect quartz solubilities in the systems h2o nacl and h2o co2 are very similar and are proportional to x h2o 2 quartz solubility in nacl rich brines does not change with pressure under the p t conditions of our experiments at 0 9 gpa and 800 c albite solubility in pure water is higher 100 g kg h2o than that of quartz 74 g kg h2o but at nacl concentrations 6 mol these solubilities are very similar albite dissolution is slightly incongruent formation and composition of secondary and quench phases paragonite na margarite amorphous quench spheres indicate that the solution is enriched in sio2 and na2sio3 as fluid composition changes from h2o towards more co2 rich fluids or nacl rich brines the solubilities of albite and quartz decrease by about one order of magnitude but are still measurable at x h2o 0 5 a thermodynamic analysis of new quartz solubility data for h2o co2 fluids at 0 9 gpa indicates that complexing is dominated by sio2 4h2o for water rich fluids but for x h2o 0 7 the mean solvation number decreases to 3 this speciation is similar to that reported previously for lower pressures and is in agreement with recent high p t spectroscopic data for the system h2o sio2 for dissolution of quartz in both h2o co2 and h2o nacl fluids the molecular proportions of silica to water are almost the same at any x h2o assuming similar non ideal water salt interactions irrespective of whether the water is in the fluid or is complexed with silica then the speciation of silica appears to be similar in both h2o co2 and h2o nacl fluids under the experimental conditions we conclude that the speciation of silica in both h2o co2 and h2o nacl fluids at 0 9 gpa and 800 c is comparable is dominated by si oh 4 2h2o and or hydrated species with lower hydration numbers and is also comparable to that proposed for lower p t conditions

mineralogy of the sulphide deposits at sulitjelma northern norway abstract the pyritic vms deposits at sulitjelma northern norway have been regionally metamorphosed at amphibolite facies during the caledonide orogen the deposits contain a wide diversity of sulphide sulphosalt and related minerals which are systematically discussed with reference to their occurrence paragenesis and mineral chemistry most of these minerals are however rare to absent within the massive deposits which are dominantly composed of pyrite with subordinate chalcopyrite sphalerite and pyrrhotite galena arsenopyrite cubanite molybdenite stannite and tetrahedrite occur in minor amounts syn metamorphic mobilisation has however resulted in the redistribution of a range of elements including cu pb sb as ni and au these elements have been reconcentrated into mobilised segregations where they have crystallised under retrograde conditions into a range of discrete phases ore mobilisation which took place along tectonically controlled pathways is however of a highly localised nature with a considerable range in mineral textures and parageneses observed in different samples typical associations within these mobilisates include a range of cu pb sb and cu pb as sulphosalts including bournonite meneghinite seligmannite and jordanite breithauptite nisbite costibite arsenopyrite and gudmundite co existing galena is characterised by elevated concentrations of ag bi and se argentian tetrahedrite 9 17 wt ag the chief ag carrier in the deposits as well as other ag bearing phases including pyrargyrite hessite and empressite are strongly enriched in the mobilisates gold as electrum 50 75 wt au and more rarely as aurostibite is also relatively enriched in the mobilisate samples over those from more massive parts of the deposits a further range of minerals including native antimony native arsenic allargentum dyscrasite argentite mckinstryite jalpaite and native silver occur as low temperature breakdown products of earlier formed minerals preserved textures do not contradict a model involving more than a one phase of mobilisation during the metamorphic evolution

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

precipitation type transition regions in winter storms over southern ontario two winter storms passed through the toronto area during november and december 1987 information from radar rawinsonde and surface observations was analyzed in order to determine the kinematic flow fields and thermodynamic environment in the vicinity of the transition at the surface between snow and rain this region was also linked to heavy precipitation and thunder updrafts preferentially occurred over the snow region and deep near 0 c layers occurred in the transition region observations are consistent with a mesoscale circulation initiated by melting snow and possibly with the occurrence of symmetric instability it is further suggested that large possibly wet snowflakes being formed within such deep near 0 c layers would contribute to the radar detection of precipitation bands near the precipitation transition region

a hydrothermal ni as pge geochemical halo around the miitel komatiite hosted nickel sulfide deposit yilgarn craton western australia the remobilization of metals during postdeposition hydrothermal alteration of magmatic sulfide ores has the potential to result in large haloes the recognition of which could potentially enlarge the detectable footprint of this ore type the miitel komatiite hosted nickel sulfide deposit in western australia was used as a case study to investigate the nature and 3 d geometry of the geochemical halo created by the remobilization of base metals gold and platinum group elements pge into the rocks surrounding the mineralization at miitel anomalous metal enrichment is found in the country rocks surrounding the massive sulfides up to 250 m away from the ore this enrichment detected using portable x ray fluorescence pxrf and backed up by laboratory analyses occurs in the mount edwards footwall basalt within decimeters of the contact with the overlying widgiemooltha komatiites it is associated with the presence of nickel arsenides gersdorffite and minor nickeline are concentrated within small quartz and carbonate veinlets and are interpreted to form during the circulation of arsenic rich hydrothermal fluids results of lead fire assay analyses and in situ laser ablation inductively coupled plasma mass spectrometer la icp ms analyses indicate high pge concentrations pd and pt and minor gold associated with the observed nickel and arsenic enrichment results from a larger regional scale study combined with this pge enrichment suggest that the massive nickel sulfides from the miitel ore are the source of the remobilized nickel in the country rocks the presence of pd and pt enriched trace arsenide phases in country rocks and shear zones may be a generally applicable proximity indicator for nickel sulfides in hydrothermally altered terranes

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones xi comparisons between observational and theoretical aspects of rainbands abstract comparisons are made between the characteristics of several types of rainbands observed in an extratropical cyclone and dynamical mechanisms relevant on the mesoscale the warm sector flow ahead of the cold front and above the cold frontal zone aloft was unstable to conditional symmetric instability and theoretical predictions for this mechanism am consistent with several aspects of the warm sector and wide cold frontal rainbands in the case of the warm sector rainbands other mechanisms e g wave cisk and mixed dynamic convective instabilities may have also played a role the core structure of the narrow cold frontal rainbands appeared to be affected by an instability that derived its energy from the horizontal shear across the surface front also many aspects of the narrow cold frontal rainband were similar to a density current shear induced gravity waves appeared to be responsible for the wavelike rainbands observed in the vicinity of the cold frontal zone aloft the orientation of the

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

bi melt formation and gold scavenging from hydrothermal fluids an experimental study abstract the role of polymetallic melts in scavenging ore components has recently been highlighted in the context of fluid poor metamorphosed ore deposits in contrast the role of polymetallic melts in systems dominated by hydrothermal fluids remains poorly understood using a simple au bi model system we explored experimentally whether such polymetallic melts can precipitate directly from a hydrothermal fluid and investigated the ability of these melts to scavenge au from the solution the experiments were conducted in custom built flow through reactors designed to reproduce a hydrothermal system where melt components are dissolved at one stage along the flow path e g bi was dissolved by placing bi minerals along the fluid path whereas melt precipitation was caused further along the flow path by fluid rock interaction bi rich melts were readily obtained by reaction with pyrrhotite graphite or amorphous fes when au was added to the system bi au melts with compositions consistent with the au bi phase diagram were obtained in the case of fluid reaction with pyrrhotite epitaxial replacement of pyrrhotite by magnetite was observed with textures consistent with an interface coupled dissolution reprecipitation reaction icdrr in this case the metallic melt precipitated as blebs that were localized at the replacement front or within the porous magnetite direct fractionation of bi au melts from a hydrothermal fluid or precipitation of a bi melt followed by partitioning of au from ambient fluid offer new pathways to the enrichment of minor ore components such as au without requiring fluid saturation with respect to a au mineral this mechanism can explain the strong geochemical affinity recognized between au and low melting point chalcophile elements such as bi in many gold deposits examples of deposits where such a model may be applicable include orogenic gold deposits and gold skarns contrary to models involving migration of polymetallic melts to explain element remobilization only small quantities ppm of polymetallic melts are required to affect the au endowment of a deposit via interaction with a hydrothermal fluid the experiments also show that micro environments can play a critical role in controlling melt occurrences for example reaction fronts developing via icdr reactions can promote melt formation as observed during the replacement of pyrrhotite by magnetite the associated transient porosity creates space for the melt and promotes melt fluid exchanges whereas the reaction front provides local geochemical conditions favorable to melt precipitation e g reduced low ah2s aq and catalytic surface

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

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

airborne doppler observations of a cold front in the vicinity of vancouver island abstract this study uses airborne doppler radar and flight level measurements from the coastal observations and simulations with topography experiment to examine the detailed mesoscale structure of an oceanic cold front upstream of vancouver island on 13 december 1993 these aircraft observations show that there were dramatic differences in frontal structure and movement between nearshore and offshore regions presumably due to the effects of blocking by the terrain the aircraft observations are considered in two parts since the behavior of the front evolved over the flight period during the early and middle portion of the flight the low level flow east of the front was out of the south southeast in the nearshore region rather than southerly as found farther offshore the nearshore segment of the front was oriented south north and appeared to be stationary the zone of orographic influence was found to extend to a region 20 km offshore and confined primarily to the lowest 1 5 km msl in distinct c

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

modeling of gold scavenging by bismuth melts coexisting with hydrothermal fluids the effect of gold scavenging by bismuth melts is investigated using equilibrium thermodynamic modeling of an aqueous solution mineral melt system the calculations for the au bi na cl s h o system performed at temperatures between 300 and 450 c demonstrate that au concentrations in the melt are several orders of magnitude higher than in the coexisting fluid indicating the possible formation of economic gold deposits from undersaturated aqueous fluids in which mineralization would not be expected in the absence of a bismuth melt the model applies to any deposit where a bi melt is stable and coexists with a hydrothermal fluid examples of such deposits are known from skarn intrusion related orogenic and volcanogenic massive sulfide vms gold systems in sulfur poor systems the partitioning curves presented here can be used directly to correlate the gold concentration in the fluid and the au grade in the ore e g escanaba trough vms deposit these results also illustrate important principles generally applicable to understanding magmatic hydrothermal and metamorphic deposits that may have contained significant volumes of more complex polymetallic melts

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

high grade iron ore at windarling yilgarn craton a product of syn orogenic deformation hypogene hydrothermal alteration and supergene modification in an archean bif basalt lithostratigraphy banded iron formation bif hosted iron ore deposits in the windarling range are located in the lower greenstone succession of the marda diemals greenstone belt southern cross domain yilgarn craton and constitute a total hematite martite goethite ore resource of minimum 52 mt at 60 wt fe 0 07 p banded iron formation is interlayered with high mg basalts at windarling and precipitated during episodes of volcanic quiescence trace element content and the rare earth element ree ratios y ho 42 to 45 sm yb 1 5 together with positive la and gd anomalies in least altered hematite magnetite metachert bif indicate the precipitation from archean seawater that was fertilised by hydrothermal vent fluids with a basaltic hree y signature hypogene iron ore in sub greenschist facies metamorphosed bif formed during three distinct stages ore stage 1 was a syn to post metamorphic syn d1 fe ca mg ni co p ree metasomatism that produced local ni ree rich fe dolomite magnetite alteration in bif hydrothermal alteration was induced by hot fluid flow controlled by brittle ductile reactivation of bif basalt margins and crosscutting d1 faults the ni co rich content of dolomite and a shift in ree ratios in carbonate altered bif towards archean mafic rock signature y ho to 31 to 40 sm yb to 1 to 2 and gd gd to 1 2 to 1 4 suggest that high mg basalts in the windarling range were the primary source of introduced metals during ore stage 2 a syn deformational and likely acidic and oxidised fluid flow along bif basalt margins and within d1 faults leached carbonate and precipitated lepidoblastic and anhedral granoblastic hematite high grade magnetite hematite ore is formed during this stage ore stage 3 hydrothermal specular hematite spch fe dolomite quartz alteration was controlled by a late orogenic brittle compressional transpressional stage d4 the regional scale shear zone related d3 is not preserved in windarling this minor event remobilised iron oxides carbonate and quartz to form veins and breccia but did not generate significant volumes of iron ore ore stage 4 involved mesozoic to recent supergene oxidation and hydration in a weathering environment reaching down to depths of 100 to maximum 200 m below surface supergene ore formation involved goethite replacement of dolomite and quartz as well as martitisation important ground preparation for supergene modification and upgrade were mainly the formation of steep d1 to d4 structures steep bif basalt margins and particularly the syn d1 to syn d2 carbonate alteration of bif that is most susceptible to supergene dissolution the windarling deposits are structurally controlled supergene modified hydrothermal iron ore systems that share comparable physical chemical and ore forming characteristics to other iron ore deposits in the yilgarn craton e g koolyanobbing beebyn in the weld range mt gibson however the remarkable variety in pre syn and post deformational ore textures relative to d1 and d2 has not been described elsewhere in the yilgarn and are similar to the ore deposits in high strain zones such as of brazil quadrilatero ferrifero or iron quadrangle and nigeria the overall similarity of alteration stages i e the sequence of hydrothermal carbonate introduction and hypogene leaching with other greenstone belt hosted iron ore deposits supports the interpretation that syn orogenic bif alteration and upgrade was crucial in the formation of hypogene supergene iron ore deposits in the yilgarn craton and possibly in other archean paleoproterozoic greenstone belt settings worldwide

numerical study of precipitation core gap structure along cold fronts abstract the mechanism responsible for the core gap structure of precipitation along narrow cold frontal rainbands ncfrs is investigated through analyses of idealized cloud resolving simulations of cold fronts the control simulation in which the prefrontal thermal stratification is characterized by a weak convective instability at low levels with convective available potential energy cape of 60 j kg 1 reproduces the typical alongfront variability of observed ncfrs the simulated ncfr is broken up into regularly spaced ellipsoidal cores oriented at a clockwise angle to the cold front while horizontal shear instability hsi has frequently been proposed as a mechanism leading to the alongfront variability of ncfrs no characteristic features of hsi are recognized in the simulated vertical vorticity field at the leading edge of the cold front the alongfront variability in precipitation is attributed to the formation of a wavelike disturbance just above the leading edge of the cold front the wave

mineralogical siting and distribution of gold in quartz veins and sulfide ores of the ashanti mine and other deposits in the ashanti belt of ghana genetic implications the ashanti belt of ghana constitutes a gold province which has produced a total of about 1500 t of gold historically gold mineralization is found in steep nne ssw to ne sw trending shear zones predominantly transecting metasediments of the palaeoproterozoic birimian supergroup 2 2 2 1 ga disseminated in ca 2 1 ga granitoids in paleo conglomerates of the tarkwaian group 2135 ma and in recent placers the distribution of gold its chemistry paragenesis and mineralogical siting in the mesothermal ores of the major mines in the ashanti belt namely konongo ashanti bogosu and prestea mine are the subject of this study at the localities studied gold is present in two main types of ores 1 quartz veins with free milling gold the gold is relatively silver rich true fineness values from 730 to 954 and is accompanied by a distinct suite of cu pb sb sulfides 2 sulfide ores consisting of arsenopyrite pyrite and rarer pyrrhotite and marcasite with refractory gold the ores have apparent fineness values larger than 910 arsenopyrite and locally at bogosu pyrite were identified as the hosts of submicroscopic gold mean concentrations of gold in arsenopyrite in various samples from the different mines obtained by secondary ion mass spectrometry sims range from 67 to 314 ppm au gold concentration mapping in individual arsenopyrite crystals from the different deposits revealed similar patterns of gold distribution the grains possess a gold poor core and elevated gold contents are present along distinct crystal growth zones towards their rims the outermost crystal layer is usually gold poor the well preserved distribution patterns also indicate that remobilization of gold from the sulfides played an insignificant role in the ores of the ashanti belt multiple quartz veining and growth zoning of the sulfides are interpreted as manifestations of multiple episodes of fluid infiltration fluid flow and mineral deposition the bimodal occurrence of gold in spatially closely associated quartz vein and sulfide ores indicates a genetic link between these ore types a model implying a grossly coeval formation of the ores from mesothermal fluids is proposed

behavior of critical metals in metamorphosed pb zn ore deposits example from the pyrenean axial zone rare metals ge ga in cd are key resources for the development of green technologies and are commonly found as trace elements in base metal mineral deposits many of these deposits are in orogenic belts and the impact of recrystallization on rare metal content and distribution in sphalerite needs to be evaluated based on laser ablation inductively coupled plasma mass spectrometry la icp ms analyses and micro imaging techniques such as laser induced breakdown spectroscopy libs and electron backscattered diffraction ebsd we investigate the minor and trace element composition related to sphalerite texture for three types of mineralization from the pyrenean axial zone paz vein mineralization type 2b appears significantly enriched in ge and ga compared to disseminated and stratabound mineralizations type 1 and type 2a respectively in vein mineralization the partial recrystallization induced by deformation led to the remobilization of ge ga and cu from the sphalerite crystal lattice into accessory minerals we propose that the association of intragranular diffusion and fluid rock reaction were likely responsible for the formation of patchy oscillatory zoning in sphalerite and the crystallization of ge rich accessory minerals chemical and textural heterogeneity is common in sphalerite from various world class deposits and a full understanding of these heterogeneities is now crucial to assess the rare metal potential and associated extraction processes of deformed base metal ores

mobilization of tl hg as sb ag cu pb sulfosalt melts during low grade metamorphism in the alpi apuane tuscany italy we report the discovery of an exceptional assemblage of tl hg as sb ag cu pb sulfosalts showing textural evidence for their mobilization as melts in the barite pyrite iron oxide orebodies of the monte arsiccio mine alpi apuane tuscany italy the relative abundance of rare thallium sulfosalts including three new mineral species their peculiar textural features within the orebodies e g migration along matrix grain boundaries drop like internal textures low interfacial angles between sulfosalts and matrix minerals and the overall high thallium content in pyrite from the entire mining district to 900 ppm make the barite pyrite iron oxide deposits of the alpi apuane a reference locality for studying low temperature sulfosalt melts in low grade metamorphic complexes greenschist facies our study reveals how sulfosalt melting during low grade regional metamorphism controls the redistribution of economically valuable and environmentally critical elements such as thallium in sulfide orebodies containing significant amounts of low melting point chalcophile elements

timing of gold mineralization at red lake northwestern ontario canada new constraints from u pb geochronology at the goldcorp high grade zone red lake mine and the madsen mine the goldcorp high grade zone at the red lake mine has reserves proven and probable established at 1 775 million tons mt at an average grade of 80 6 g t au new u pb geochronologic data combined with detailed mapping and crosscutting relationships provide timing constraints and new insights into the formation of the exceptionally rich goldcorp high grade zone the results show that the main stage of the high grade mineralization in the high grade zone formed before 2712 ma and that a second stage of gold mineralization much smaller in terms of total gold content but spectacular in terms of grade formed after 2702 ma this second stage is attributed to gold remobilization caused by the enhanced thermal gradient and deformation associated with the emplacement of the cat island pluton 2699 ma approximately 7 km east of the deposit or by the ca 2 63 to 2 66 ga postorogenic regional thermal event indicated by hornblende muscovite and biotite ar ar cooling ages from the uchi subprovince it is proposed that the main stage of high grade mineralization formed between ca 2723 to 2712 ma possibly synchronous with emplacement of the dome and mckenzie island stocks the abino granodiorite and hammell lake batholith as well as with penetrative d2 main stage regional deformation lamprophyre dikes spatially associated with the deposit postdate main stage mineralization by at least 10 m y a postore granodiorite dike from the madsen mine the second largest deposit in the district was dated at 2698 1 ma this age is similar to a postalteration and late deformation diorite dike at the creek zone showing near the former starratt olsen mine which was dated at 2696 2 ma the crosscutting relationships confirm that the main stage of mineralization at the madsen mine is pre 2698 ma a folded and metamorphosed polymictic conglomerate located stratigraphically above the campbell red lake deposit and deposited after ca 2747 but before 2712 ma is correlated with the newly recognized huston assemblage crosscutting and overprinting relationships between the conglomerate and the alteration indicate protracted multistage aluminous and iron carbonate quartz veining and or alteration event s before and after deposition of the conglomerate the age of the conglomerate confirms that the campbell red lake deposit is proximal to a folded regional unconformity consistent with the empirical relationship between large gold deposits and unconformities elsewhere in archean greenstone belts this paleosurface represents a key first order exploration target and it is proposed that areas of high potential for gold exploration in red lake occur in the balmer assemblage rocks within 500 m to 1 km of the unconformity

mineralogy and textural relationships among sulphosalts and related minerals in the bleikvassli zn pb cu deposit nordland norway several distinct assemblages of pb sb pb as cu pb sb and cu fe zn sn sulphosalts are identified in sulphide samples from bleikvassli mine norway detailed optical microscopy and electron probe microanalysis have permitted investigation of textural relationships between minerals and compositional variations between different ore types tetrahedrite typically containing 10 16 wt ag rare freibergite containing 25 30 wt ag has also been identified in two samples stannite cu2 fe zn sns4 and meneghinite cupb13sb7s24 are widely distributed as trace constituents throughout massive pyritic and galena rich ores native antimony and pyrargyrite occur in trace amounts in all ore types as the breakdown products of earlier sulphosalts several distinct types of wall rock mineralisation are present at bleikvassli of considerable mineralogical interest are the coarse grained sulphide mobilisates within the wall rock which contain a distinct and characteristic suite of pb as sulphosalts tennantite jordanite pb14as6s23 seligmannite cupbass3 dufrenoysite pb2as2s5 bournonite cupbsbs3 is the only sb bearing sulphosalt recognised in significant amounts within the mobilisates meneghinite and tetrahedrite being conspicuously absent these mobilisates display considerable au enrichment electrum can be confirmed intimately associated with jordanite and tennantite appreciable sb up to 3 wt is contained within galena in the mobilisates in contrast to galena from massive ores which contains only negligible sb contents of ag and bi in galena vary considerably in all ore types but confirm earlier suggestions that galena is a major ag carrier at bleikvassli boulangerite pb5sb4s11 jamesonite fepb4sb6s14 and gudmundite fesbs occur in trace amounts sn sulphosalts are represented by kesterite cu2 zn fe sns4 but commonly zoned with respect to zn fe ratio in the mobilisates rather than by stannite a rare type of mobilisate also in the wall rock in which chalcocite and bornite are the main minerals contains native ag stromeyerite agcus mckinstryite ag cu 2 s ag free tetrahedrite an unnamed cu ag fe sulphide cu3ag2fes4 and native bi myrmekitically intergrown with chalcocite although a comprehensive genetic model for the wall rock mineralisation at bleikvassli is largely impossible given the limitations in the present state of knowledge regarding mechanisms involved in remobilisation processes a multi stage model of remobilisation during regional metamorphism is considered to best explain the observations an interplay of different solid and liquid state remobilisation mechanisms in various combinations is required to account for the macro and microscopic observations remobilisation probably began during the earlier stages of metamorphism with crystallisation and further remobilisation taking place during the entire metamorphic cycle giving rise to the extensive chemical and mineralogical diversity observed today preserved mineral assemblages and their textural relationships reflect a complex sequence of replacement and decomposition reactions taking place during the latest phase of late metamorphic crystallisation and subsequent cooling

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

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

relevance of conditional symmetric instability in the interpretation of wide cold frontal rainbands a case study 20 may 1976 comparisons are made between the characteristics of rainbands observed in a frontal system using a c band doppler radar and dynamical mechanisms relevant on the mesoscale 100 km the orientation of these rainbands nearly aligned with the thermal wind suggests that symmetric instability may play a role in their formation this possible explanation of the precipitation is discussed

uncloaking invisible gold use of nanosims to evaluate gold trace elements and sulfur isotopes in pyrite from carlin type gold deposits one hundred nm resolution secondary ionizing mass spectrometry nanosims was used to determine the distribution of au cu as sb and s and stable isotopes of s 34s 32s in gold bearing pyrite from two refractory carlin type gold deposits west banshee northern carlin trend and turquoise ridge getchell trend located in northern nevada nanosims maps reveal that gold occurs in two discrete episodes in each deposit elevated gold concentrations correlate with elevated concentrations of as sb cu te and lower 34s 32s ratios compared to periods when gold was not deposited precipitation of elevated gold and trace elements at west banshee was followed by precipitation of pyrite with lower gold concentrations whereas at turquoise ridge precipitation of trace element rich pyrite was followed by precipitation of late ore stage minerals these nanosims results are consistent with formation of the deposits by the episodic incursion of gold rich fluids into hydrothermal systems otherwise dominated by gold poor fluids such gold rich fluid pulses may be related to incursions of magmatic fluid which have been shown to have high concentrations of gold arsenic and copper in porphyry and high sulfidation epithermal systems

fluid mediated partial alteration in monazite the role of coupled dissolution reprecipitation in element redistribution and mass transfer monazite ce lree th u ca p si o4 with complex zoning in th and other elements is commonly observed in metamorphic and igneous rocks the hypothesis that this alteration is a product of fluid mediated element mass transfer has been tested in the piston cylinder press caf2 assembly cylindrical graphite oven at 1 000 mpa and 900 c and in cold seal autoclaves on a hydrothermal line at 500 mpa and 600 c experiments included a relatively homogeneous monazite ce 7 8 wt tho2 from a heavy mineral sand plus a series of alkali bearing fluids including 2n naoh 2n koh and na2si2o5 h2o experiments were conducted using bse imaging emp analysis and both tem and hrtem a subset of monazite grains from each experiment show evidence of partial alteration in the form of areas enriched in th si with sharp curvilinear compositional boundaries extending from the grain rim into the monazite interior these thsio4 enriched textures are similar to those commonly seen in natural examples of metasomatised monazite in both magmatic and metamorphic rocks in the na2si2o5 h2o experiments scarce inclusions of britholite formed in the altered monazite the altered monazite is also characterised by strong depletion in pb ca and y thorium and si mobility coupled with the formation of britholite inclusions during partial alteration in the monazite grain is considered to be the product of fluid aided coupled dissolution reprecipitation as opposed to solid state diffusion since other fluids including nacl and kcl brines do not result in the formation of these textures the experimental replication of thsio4 enriched areas in the monazite strongly suggests that similar textures in monazite observed in nature are fluid induced specifically by alkali bearing fluids if true complex metasomatically induced textures in monazite could yield information concerning the nature of the fluid responsible for their formation as well as allow for the dating of the metasomatic event presuming that all the original radiogenic pb has been removed

age constraints on gold mineralization and paleoproterozoic crustal evolution in the ashanti belt of southern ghana abstract u pb isotopic dating in the region of the ashanti belt in ghana has been carried out to improve understanding of crustal evolution and gold mineralization in this paleoproterozoic terrane a u pb zircon age of ca 2174 2 ma for a belt type granitoid from sekondi accords with previous ages on belt type plutons in ghana but metamorphic titanite within this granitoid gives an age of 2092 3 ma coeval with intrusion of the late basin type granitoids the within belt granitoid at banso village has an age close to 2097 3 ma which falls into the age range typical for basin type granitoids 2116 2088 ma these results indicate that widespread plutonism in the birimian sedimentary basins also produced magmatic and metamorphic effects within the volcanic belts most dated detrital zircons from birimian metasediment samples at the ashanti gold mine agree in age at 2155 2 ma with others that are slightly older this gives a maximum estimate for the depositional age of the sediments and for gold mineralization at the ashanti gold mine hydrothermally altered and auriferous granitoid plutons along the western flank of the ashanti belt at anyankyerim nhyiaso yaomensakrom and esuajah ayanfuri all have intrusion ages within error of 2105 2 ma this is also the age of metamorphic titanite in an unmineralized basin type granitoid at kwapia rutiles from the hydrothermally altered yaomensakrom and the mineralized esuajah ayanfuri granitoid were dated at 2098 7 and 2086 4 ma respectively and probably provide minimum ages on gold mineralization these data indicate a close temporal association among auriferous granitoid plutons near the western margin of the ashanti belt at 2105 ma gold mineralization may be only slightly younger than magmatic emplacement of the plutons granitic plutonism in the sedimentary basins metamorphism and hydrothermal gold mineralization in southern ghana are all part of a major crust formation event the eburnean orogeny that can be constrained to the time range 2120 2080 ma

dynamics of a low level jet observed during the fronts 87 experiment a study of the internal dynamics of a low level jet its role on the frontal discontinuity evolution and its relevance to the organization of convection at mesoscale and small scale is presented the low level jet studied is associated with an active cold front that was observed during the french british co operative field experiment fronts 87 the originality of the present low level jet description lies in the fact that it is observed not only by means of soundings but also by means of a new tool for mesoscale meteorology observations a wind profiler stratospheric tropospheric uhf radar the high resolution of the wind profiler data in both time and height allows one to assess in precipitating as well as in clear sky areas a detailed image of the low level jet and the associated mesoscale and convective scale circulations the comparison between observations and predictions of various theories provides information on the physical mechanisms responsible for the initiation and maintenance of the observed mesoscale features the flow resulting from the presence of the low level jet produces inertial acceleration and baroclinic symmetric instability which lead to a narrow mesoscale line of sloping motions moreover the interaction of the cold surface outflow with the low level vertical shear below the jet maximum is found to be crucial in the intensification and maintenance of the observed narrow cold frontal rainband

convective snowbands downstream of the rocky mountains in an environment with conditional dry symmetric and inertial instabilities abstract convective snowbands moved slowly over wyoming and northern colorado on 16 17 february 2007 and produced up to 71 mm 2 8 in of snow that was unpredicted by operational numerical weather prediction models and human forecasters the northwest southeast oriented bands lasted for over 6 h comprising both a single major band more than 30 km wide and multiple minor bands about 10 km wide the convective bands initiated within the ascending branch of a secondary circulation associated with both near surface and elevated frontogenesis but the bands remained nearly stationary while the near surface frontogenesis moved quickly equatorward the bands occurred downstream of complex terrain on the anticyclonic shear side of a midlevel jet streak where conditional dry symmetric negative potential vorticity and inertial negative absolute vorticity instabilities were present to determine the mechanisms responsible for the development and organization of these bands simulations using a convectio

sulfide melt inclusions as evidence for the existence of a sulfide partial melt at broken hill australia polyphase sulfide melt inclusions are hosted within garnetite rocks and quartz veins in garnetite surrounding droppers and large masses of the orebody at broken hill australia and record the presence of a former sulfide melt sulfide melt inclusions are either primary or occur along healed fractures in both garnets and quartz veins common daughter minerals in the inclusions are galena sphalerite arsenopyrite chalcopyrite tetrahedrite tennantite and minor amounts of argentite bornite dyscrasite ag3sb and gudmundite fesbs the inclusions exhibit a strong enrichment in low melting point chalcophile elements compared to the main orebody experimental reequilibration of sulfide melt inclusions shows homogenous melt at temperatures as low as 720 10 c and 5 kbars well below that of peak metamorphism at broken hill 800 10 c and 5 kbars thus these inclusions are interpreted to represent a trapped sulfide melt formed during peak metamorphism at broken hill australia

the flux of gold and related metals through a volcanic arc taupo volcanic zone new zealand we determined the concentrations of gold silver arsenic antimony and mercury in deep hydrothermal solutions 1 km depth 200 to 300 c from six geothermal systems and calculated their fluxes for a 250 km long segment of volcanic arc in the taupo volcanic zone new zealand the three orders of variation in the concentrations

mobility of trace elements and oxygen in zircon during metamorphism consequences for geochemical tracing this study addresses the mobility of the rare earth elements ree o u and pb during the formation of metamorphic zircon by overgrowth and coupled dissolution reprecipitation for this purpose the texture and ree 18o and u pb compositions of zircon crystals from a metabasite an anatectic granite and a metapelite sampled on naxos island greece have been characterised the behaviour of o and ree during the formation of the zircon metamorphic domains shows that two end members can be distinguished i closed or partially closed system behaviour for oxygen and trace elements in zircon formed by coupled dissolution reprecipitation metamorphic domains partially preserve the textural and geochemical characteristics of the precursor zircon chemical or isotopic equilibrium between the metamorphic zircon and the matrix is not completely reached for all the elements such zircons have to be used with caution for geochemical tracing when re equilibration is not complete the u pb system is also not completely reset and the metamorphic domains yield old scattered ages ii open system behaviour for oxygen and trace elements in zircon formed by overgrowth these metamorphic zircons do not show an inherited shape and are devoid of relic magmatic zoning their composition reflects growth in an open system at the scale of the zircon grain with the fluid phase and the surrounding minerals because equilibrium between the metamorphic zircon and the matrix was thus favoured zircon crystallisation can be more confidently related to the p t history and fluid circulation events by geochemical tracing

evolution of a cold front encountering steep quasi 2d terrain coordinated aircraft observations on 8 9 december 2001 during improve 2 abstract research aircraft observations from the 8 9 december 2001 case of the second phase of the improvement of microphysical parameterization through operational verification experiment improve 2 describe the evolution of a wide cold frontal rainband wcfr during its eastward advance from the pacific coastline to a point 200 km inland over the cascade mountains of oregon this analysis has two objectives first to illustrate the rapid weakening of the circulation associated with a landfalling wcfr and the relationship of these changes to terrain induced airflow modifications and second to quantify the degree to which this weakening impacted cloud microphysical properties such as liquid water content ice particle concentrations and precipitation rate the kinematic structure of the wcfr is detailed using doppler radar observations from a noaa p 3 aircraft while some concomitant cloud microphysical properties are documented using flight level measurements from the university of washington convai

analysis of a dryline during ihop implications for convection initiation abstract a detailed analysis of a dryline that formed on 22 may 2002 during the international h2o project ihop is presented the dryline was classified as a null case since air parcels lifted over the convergence boundary were unable to reach the level of free convection preventing thunderstorms from forming a secondary dryline associated with a distinct moisture discontinuity developed to the west of the primary dryline the primary dryline exhibited substantial along frontal variability owing to the presence of misocyclones this nonlinear pattern resembled the precipitation core gap structure associated with cold fronts during one of the analysis times although the misocyclones were positioned within the gap regions radar refractivity has been recently shown to accurately retrieve the low level moisture fields within the convective boundary layer however its use in forecasting the initiation of convection has been restricted to qualitative interpretations this study introduces the total derivati

the legacy of crystal plastic deformation in olivine high diffusivity pathways during serpentinization crystal plastic olivine deformation to produce subgrain boundaries composed of edge dislocations is an inevitable consequence of asthenospheric mantle flow although crystal plastic deformation and serpentinization are spatio temporally decoupled we identified compositional readjustments expressed on the micrometric level as a striped fe enriched bar x text fe 0 24 0 02 zones 0 12 0 02 bulk or fe depleted bar x text fe 0 10 0 01 zones 0 13 0 01 bulk zoning in partly serpentinized olivine grains from two upper mantle sections in norway focused ion beam sample preparation combined with transmission electron microscopy tem and aberration corrected scanning tem enabling atomic level resolved electron energy loss spectroscopic line profiling reveals that every zone is immediately associated with a subgrain boundary we infer that the zonings are a result of the environmental fe2 mg 1 exchange potential during antigorite serpentinization of olivine and the drive toward element exchange equilibrium this is facilitated by enhanced solid state diffusion along subgrain boundaries in a system which otherwise re equilibrates via dissolution reprecipitation fe enrichment or depletion is controlled by the silica activity imposed on the system by the local olivine orthopyroxene mass ratio temperature and the effect of magnetite stability the fe mg exchange coefficients k text d text atg text ol between both types of zoning and antigorite display coalescence toward exchange equilibrium with both types of zoning mn is enriched and ni depleted compared with the unaffected bulk composition nanometer sized heterogeneously distributed antigorite precipitates along olivine subgrain boundaries suggest that water was able to ingress along them crystallographic orientation relationships gained via electron backscatter diffraction between olivine grain domains and different serpentine vein generations support the hypothesis that serpentinization was initiated along olivine subgrain boundaries

climatology of banded precipitation over the contiguous united states abstracta climatology of banded precipitation features over the contiguous united states from 2003 to 2014 is constructed a band is defined as a precipitation feature with a major axis of 100 km or greater and a ratio of major axis length to minor axis length hereafter aspect ratio of 3 1 or greater by applying an automated feature based detection algorithm to composite radar imagery a database of 48 916 844 precipitation features is created of which 7 213 505 14 8 are bands this algorithm produces the first climatology of precipitation bands over the contiguous united states banded precipitation occurrence is broadly similar to total precipitation occurrence with a maximum of 175 h of banded precipitation annually over the ohio river valley in the warm season there is a strong diurnal signature associated with convective storm development for both the precipitation feature area and total area covered by precipitation but little diurnal signature in aspect ratio strong west east gradients

the hemlo gold deposit ontario an example of melting and mobilization of a precious metal sulfosalt assemblage during amphibolite facies metamorphism and deformation the timing of mineralization at the hemlo gold deposit has long been a controversial issue we present arguments that use partial melting of the ore assemblage to explain the mechanism of ore mobilization and resolve problems with the model of premetamorphic mineralization the results have implications for mine exploitation and exploration strategies we show that the ore mineral assemblage underwent partial melting during middle amphibolite facies metamorphism 600 650 c 6 7 kbars primarily through breakdown of stibnite and arsenopyrite in a high s2 environment concurrent deformation led to segregation of the resulting sb and as rich sulfosalt melt interaction between this melt and a range of unmelted sulfides led to further melting and incorporation of other elements into the melt the gold bearing melt was mobilized from compressional high strain sites into dilational domains such as boudin necks and extensional fractures developed in competent lithologies ore minerals that did not melt significantly pyrite molybdenite pyrrhotite and sphalerite were not extensively mobilized and largely remained within high strain compressional domains this segregation of melt from residue thus resulted in the observed heterogeneous distribution of ore minerals within the deposit crystallization of the sulfosalt melt produced a diverse suite of ore minerals dominated by stibnite and realgar and containing an array of rare sulfosalts native elements intermetallic compounds and tellurides some sulfosalt melt persisted to low temperature 300 c allowing continued small scale localized mobilization during late deformation although gold occurs at moderate concentrations within the compressional high strain domains it is particularly concentrated in the dilational domains a consequence of its mobilization within a sulfosalt melt our model of partial melting of the ore mineral assemblage with consequent mobilization explains how ore minerals that are unstable even at greenschist facies conditions came to be hosted in structures that formed at or near the peak of amphibolite facies metamorphism

hadean age for a post magma ocean zircon confirmed by atom probe tomography the only physical evidence from the earliest phases of earth s evolution comes from zircons ancient mineral grains that can be dated using the u th pb geochronometer 1 oxygen isotope ratios from such zircons have been used to infer when the hydrosphere and conditions habitable to life were established 2 3 chemical homogenization of earth s crust and the existence of a magma ocean have not been dated directly but must have occurred earlier 4 however the accuracy of the u pbzirconagescanplausiblybebiasedbypoorlyunderstood processes of intracrystalline pb mobility 5 7 here we use atomprobe tomography 8 to identify and map individual atoms in the oldest concordant grain from earth a 4 4 gyr old hadean zircon with a high temperature overgrowth that formed about 1gyrafterthemineral score isolatednanoclusters measuring about 10nm and spaced 10 50nm apart are enriched in incompatible elements including radiogenic pb with unusually high 207 pb 206 pbratios wedemonstratethatthelengthscales of these clusters make u pb age biasing impossible and that they formed during the later reheating event our tomography data thereby confirm that any mixing event of the silicate earth must have occurred before 4 4gyr ago consistent with

the role of vertically propagating gravity waves forced by melting induced cooling in the formation and evolution of wide cold frontal rainbands abstractrealistic mesoscale model simulations using the weather research and forecasting wrf model and idealized dry simulations were used to study the mechanisms responsible for the formation and evolution of wide cold frontal rainbands wcfrs associated with a wintertime cyclone that moved onto the washington coast the wrf simulation reproduced observed characteristics of three successively formed wcfrs including their spacing and movement as well as the timing of the formation of two wcfrs behind the first sensitivity experiments showed that melting induced cooling in the stratiform precipitation area behind the surface cold front was essential for the formation of the first and second wcfrs whereas the third wcfr was formed by the release of potential instability within an ascent forced by upper level frontogenesis enhanced frontal updrafts responsible for the first and second wcfrs were created by a superposition of a broad updraft caused by frontal dynamics and upward propagating gravity wav

a reexamination of the mechanisms responsible for banded precipitation abstract the processes responsible for a banded snowfall region during a december 1997 east coast storm are examined conventional data plus a numerical simulation with the fifth generation pennsylvania state university ncar mesoscale model mm5 are used calculations of slantwise potential area near the bands suggest that the release of conditional symmetric instability played a role in their formation the location and timing for the appearance of negative moist potential vorticity mpv cannot however be reconciled with band formation a balanced mpv model based on the geostrophic momentum approximation is developed it provided new insights into the mechanisms of mpv generation a swath of negative balanced mpv now coincides with the snowbands mpv sources are proposed that are linked to a vigorous mesoscale updraft near the bands the updraft occurred on the warm moist side of a zone of midtroposphere frontogenesis negative mpv develops through differential ageostrophic transports of geostrophic

multistage deformation of au quartz veins laurieras french massif central evidence for late gold introduction from microstructural isotopic and fluid inclusion studies abstract the relative chronology of fluid migration quartz and au deposition in a silicified fault from the main au district laurieras st yrieix district from northern french massif central has been determined from microstructural fluid inclusion isotopic and ore mineral evidences three main stages of fluid circulation microfracturing and quartz crystallization and ore deposition were distinguished on the basis of textural relationships and the pressure temperature and composition of the palaeo fluids 1 a series of early fluid events was responsible for the localized drainage of retrograde metamorphic fluids along the main fault and the subsequent sealing by milky and microcrystalline quartz preceeded the main au ore stages early fluids were aqueous carbonic trapped under lithostatic to sublithostatic pressures at temperatures in the range 350 500 c subsequently several types of microstructures were developed in the early quartz matrix 2 ns microfractures filled by clear quartz arsenopyrite and boulangerite i contain significant refractory gold concentrations clear quartz formed from aqueous carbonic fluids of lower densities than those of the earlier fluids significant pressure drops down to pressures around 55 mpa were responsible for a local immiscibility of the aqueous carbonic fluids at temperatures of 340 20 c 3 the main ore stage is characterized by the formation of dense sets of sub vertical ew microfractures healed fluid inclusion planes in quartz and filled by ore minerals native gold galena and boulangerite ii when they crosscut earlier sulfides the fluids are aqueous with low and decreasing salinity and probable trapping temperatures around 230 c isotopic data obtained on microfissured quartz indicate these dilute aqueous fluids may be considered as meteoric waters that deeply infiltrated the crust late microfissuring of a mesothermal quartz vein originally barren only with pyrite and arsenopyrite appears to be the main factor controlling gold enrichment it can be related to late hercynian deformational stages disconnected from the early fault formation and silicification these late stages which affected the hercynian basement during its uplift are of critical importance for the formation of au ores we concluded that this type of au ore formed under rather shallow conditions is distinct from those generally described in most mesothermal au veins