cation ratios of fluid inclusions in a gold quartz vein at brusson val d ayas northwestern italian alps comparison of bulk crush leach results with sims analyses of individual inclusions abstract this study tests the widely made assumption that with favourable fluid inclusion samples bulk crush leach analyses accurately reflect the electrolyte compositions of individual fluid inclusions secondary ion mass spectrometric sims analyses of individual inclusions calibrated by synthetic fluid inclusion standards are compared to crush leach analyses of the same natural quartz sample quartz from the bechaz mesothermal au vein at brusson northwestern italian alps is dominated by fluid inclusions of uniform low salinity low x co 2 composition these inclusions represent the liquid phase of an originally immiscible hydrothermal system whereas much rarer high x co 2 inclusions of even lower salinity represent the conjugate vapour phase sims analyses of the low x co 2 inclusions yield mean molar k n 0 050 and ca na 0 016 these results are identical well within experimental uncertainty to replicate crush leach analyses made in two different laboratories the excellent agreement between the sims and crush leach results confirms the accuracy of both analytical methods despite the low salinity of the bechaz fluid inclusions and the rare muscovite and dolomite impurities in the host quartz the crush leach analyses are both highly precise and accurate furthermore the agreement between methods demonstrates that sims analyses of natural multi component fluid inclusions may be reliably calibrated by synthetic inclusions with simple compositions a sims analysis of a high x co 2 vapour inclusion yields k na and ca na ratios that are not significantly different from those of the coexisting low x co 2 inclusions this suggests that under the p t conditions of immiscibility in the bechaz vein 230 c and 600 bar liquid vapour fractionation of k and ca relative to na was only very slight

gold bearing mesothermal veins from the gubong mine cheongyang gold district republic of korea fluid inclusion and stable isotope studies the gubong deposit consists of five massive gold bearing mesothermal quartz veins that fill fractures oriented northeast and northwest along fault shear zones over an area of 14 km2 in precambrian metasedimentary rocks of the gyeonggi massif the veins are divided into three groups based on their orientation and location they have a ribbon texture that is interpreted to result from repeated hydraulic fracturing events mineral deposition was associated with hydrothermal fluid overpressuring within and below the active fault shear zones the vein mineralogy and paragenesis of the veins allow two separate discrete mineralization episodes to be recognized separated by a major faulting event the ore minerals are contained within quartz and calcite associated with fracturing and healing of veins that occurred during both mineralization episodes wall rock alteration minerals during stage i the main ore stage include sericite chlorite and minor pyrite and carbonates sulfide minerals deposited along with electrum during this stage include arsenopyrite pyrite pyrrhotite sphalerite marcasite chalcopyrite galena and argentite electrum also was deposited during stage ii mineralization in the one group of veins along with pyrite sphalerite chalcopyrite and galena but the second stage of deposition in other veins was barren petrographic examination of textural relationships among sulfides fluid inclusions microfracturing and quartz shows chronological and genetic relationships between gold deposition and fluid entrapment systematic studies of fluid inclusions in stage i vein indicate two contrasting events a relatively high temperature 203 432 c and pressure 943 2 098 bars event related to early sulfide deposition and associated with h2o co2 ch4 nacl n2 fluids less than about 13 4 wt nacl and a lower temperature 202 399 c and pressure 670 850 bars late sulfide depositional event involving h2o nacl fluids 3 9 17 3 wt nacl the h2o nacl fluid involved in ore related stage ii mineralization had a salinity of 0 4 to 4 2 wt percent nacl and a homogenization temperature of 201 to 378 c the calculated sulfur isotope compositions of hydrothermal fluids from the stage i veins 34sh2s 3 5 10 5 indicate that ore sulfur was derived mainly from a magmatic source but also in part from sulfur contained in the host rocks the calculated and measured oxygen and hydrogen isotope compositions of the ore forming fluids stage i 18oh2o 1 1 9 0 d 92 to 21 stage ii 18oh2o 0 1 to 0 3 d 95 to 93 indicate that the fluids were derived from magmatic and or deep seated metasedimentary rocks stage i and evolved by mixing with local meteoric water stage ii by limited water rock exchange and by degassing during mineralization in uplift zones the h2o nacl fluids involved in the stage i development of these veins represent fluids that evolved either through unmixing of h2o co2 ch4 nacl n2 fluids following a decrease in fluid pressure or through mixing with deeply circulating meteoric waters possibly as a result of uplift and or unloading during mineralization the h2o nacl fluid involved in stage ii was derived from meteoric water early deposition of gold in stage i was caused by a decrease in sulfur fugacity h2s loss that accompanied the immiscible separation of carbonic vapor from h2o co2 ch4 nacl n2 fluids gold in late stage i and stage ii veins was precipitated from h2o nacl fluids by cooling and by dilution caused by mixing with meteoric water

evolution of a metamorphic fluid and its role in lode gold mineralisation in the central lberian zone the central iberian zone of spain and portugal contains numerous gold deposits of varying size age and host lithology previous work concentrated on single deposits leading to a need to apply a range of techniques to the region as a whole to form a model for metallogenesis throughout the region with this aim a number of occurrences of gold mineralisation in the south western central iberian zone were studied the central iberian zone consists essentially of greenschist facies metasedimentary units intruded by hercynian granitoids hercynian deformation occurred in three main stages the earliest d1 being the most intense quartz veining is common throughout the region and a vein chronology was established relative to these deformation events v1 veins are pre hercynian and may predate the precambrian sardic deformation v2 veins are syndeformational d1 and associated with peak greenschist metamorphism v3 veins are late kinematic syn to post d2 v4 veins are syn to post d3 occurring in the final stages of the hercynian and often associated with or post dating granites reactivation of vein sets by later fluids was common fluid chemistry studies of samples of known chronology indicate three main sources of fluid the dominant fluid throughout the region from v2 to v4 is a dilute aqueo carbonic fluid of varying composition the combination of fluid inclusion analyses and geochemical studies of wallrock alteration indicates that the fluid was the result of devolatilisation and dehydration during prograde metamorphism at varying depths the resulting aqueo carbonic fluids flowed upwards mixing with each other and with meteoric waters contact metamorphism associated with granite intrusions during the d3 deformation released further aqueo carbonic fluids which in some cases unmixed to form separate carbonic and aqueous inclusions circulation of meteoric waters was important during later stages d3 prolonged low temperature fluid rock interaction produced highly saline aqueous fluids which post date all major quartz veining no single set of characteristics exists for gold mineralisation in the central iberian zone deposits cover a wide spectrum but three main types have been identified 1 early d1 v2 syn peak metamorphic gold quartz veins associated with an aqueo carbonic fluid with high n2 and ch4 2 late kinematic d2 v3 veins often associated with late brittle faults again the fluid present at the time of formation was aqueo carbonic but with lower n2 and ch4 3 late v4 low temperature veins formed by a mainly meteoric fluid which was also responsible for remobilisation and concentration of gold in earlier deposits the gold mineralisation in the central iberian zone supports the continuum model for lode gold deposits gold was leached from metasediments during prograde metamorphism transported to shallower crustal levels and deposited wherever suitable traps occurred channelling of fluid from deeper levels resulted in the localisation of deposits close to major shear zones depositional sites were usually dilational zones in faults and more rarely folds but locally lithological controls were important h2o co2 unmixing was common but was not necessarily related to gold deposition

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

recent developments in element concentration and isotope ratio analysis of individual fluid inclusions by laser ablation single and multiple collector icp ms abstract laser ablation inductively coupled plasma mass spectrometry la icp ms has become a most powerful technique for the elemental analysis of individual polyphase inclusions completely enclosed in minerals be they solid or a solid liquid gas mixture at the time of measurement simultaneous accurate quantification of major to ultra trace element concentrations from li to u by well controlled ablation of the entire fluid or melt inclusion content and successful use of largely matrix independent external calibration protocols are unique features of this method this contribution reviews fluid inclusion fundamentals relevant for their bulk analysis by la icp ms and discusses key aspects of the analytical protocol emphasis is on figures of merit precision accuracy obtained from the analysis of individual inclusions and fluid inclusion assemblages and procedures and technical developments to improving data quality are elaborated a new equation for the calculation of detection limits for la icp ms analysis is presented which closely follows iupac conventions applications are reviewed with emphasis on the use of synthetic fluid inclusions in constraining metal solubility and distribution between co existing phases new data for natural bismuth fluid inclusions document the seamless transition to melt inclusion analysis by la icp ms thus highlighting the fact that the procedures presented here are generally applicable to the analysis of inclusions in complex host minerals isotope ratio analysis of individual fluid inclusions by multicollector icp ms mc icp ms is a recent development that requires fast transient signals to be accurately recorded by instrumentation designed for high precision static measurements of long lasting stable ion beams we address the general principles based on pb isotopes and review a first application to the bingham canyon porphyry cu au mo deposit a pilot study using about 50 synthetic fluid inclusions containing srm 987 sr and variable nacl ca and rb concentrations demonstrates that accurate 87 sr 86 sr isotope ratios can be obtained on an individual rb poor fluid inclusion at absolute 2 precisions of 0 0003 to 0 002 a residual trend in 87 sr 86 sr as a function of the rb sr abundance ratio in the fluid inclusions suggests that interference correction of 87 rb on mass 87 assuming identical mass bias coefficients for the two elements may be inaccurate however the offset can be accurately corrected for by regressing the data to zero 87 rb the versatility and detection power of la icp ms makes this technique the method of choice for solute abundance and isotope ratio analysis of individual fluid inclusions significant future progress can be achieved by improvements in ion production transmission and data recording efficiency and by further improving control on inclusion ablation by pulsed laser beams data quantification strategies may also have to be further refined to keep pace with instrumental progress and innovation

formation and deformation of pyrite and implications for gold mineralization in the el callao district venezuela the el callao mining district is the most important gold producing region in venezuela it is hosted in the paleoproterozoic guasipati el callao greenstone belt which forms part of the guayana craton the venezuelan extension of the guiana shield of south america it consists of volcanic and volcanosedimentary sequences that were affected by several deformation events particularly localized shear zones the colombia mine the largest active mine in the district produces 4 tonnes t 128 600 oz of gold annually with reserves estimated at 740 t 24 moz and grades of up to 60 g t gold mineralization is concentrated within a vein network in the colombia corridor a shear fracture hosted mesh of interconnected quartz ankerite albite veins enclosing fragments of altered metabasaltic host rocks gold occurs mostly in the metabasaltic fragments and is spatially associated with pyrite in which it occurs as invisible gold micron sized native gold inclusions and filling fractures based on optical and scanning electron microscopy backscattered electron observations two types of pyrite are recognized a simple zoned pyrite and a less common oscillatory zoned pyrite both types consist of a mineral inclusion rich core and a clearer rim however in oscillatory zoned pyrite the latter is composed of complex rhythmic overgrowths of alternating as rich and as poor bands laser ablation inductively coupled plasma mass spectrometry la icp ms analysis and elemental mapping reveal the presence of invisible gold in all generations of pyrite the highest concentrations 5 23 ppm au are found in oscillatory zoned pyrite rims which correlate with the highest as concentrations 16 000 23 000 ppm in as poor bands au up to 1 5 ppm and as 300 6 000 ppm concentrations decrease by about an order of magnitude copper bi te sb pb and ag always occur with invisible gold particularly in pyrite cores suggesting that at least part of the gold occurs in sulfosalt nanoparticles of these metals and metalloids visible native gold grains occur as small inclusions throughout core and rim of both pyrite types as well as in fractures within it in both occurrences chalcopyrite sphalerite tellurobismuthite ankerite albite and chlorite accompany native gold and gold fineness ranges between 900 and 930 at an early stage of vein mesh formation pyrite formed in the metabasaltic fragments at the expense of ankerite which in turn resulted from alteration of fe ti oxides gold together with other chalcophile elements was incorporated within the structure of pyrite most likely by destabilization of metal sulfide complexes during ankerite replacement subsequent cyclic reactivations of the shear zone caused development of pressure shadows around pyrite generating local and repeated decreases in pressure which triggered local boiling of the hydrothermal fluid as evidenced by the presence of primary fluid inclusions containing immiscible liquid rich and vapor rich aqueous carbonic fluids this process was responsible for a number of physical chemical changes in the liquid all of which contributed to the formation of the as and au rich overgrowths in pyrite 1 removal of h 2 o into the vapor phase inducing saturation of dissolved metals in the remaining liquid 2 an increase in ph due to partition of h 2 s and co 2 into the vapor thus decreasing the solubility of sulfide minerals and 3 an adiabatic decrease in temperature lowering the solubility of as and au in the liquid waning of this process restored precipitation of as poor pyrite until the onset of a new cycle because pressure drops are more significant adjacent to open spaces oscillatory zoned pyrite probably crystallized near newly formed veins whereas simple zoned pyrite formed away from them previously formed pyrite underwent fracturing during reactivation of the deformation especially through the brittle deformation events that postdated shearing resulting in local pulverization of pyrite this newly created porosity facilitated fluid circulation and remobilization of structurally bound gold as well as of other chalcophile elements ag cu bi te pb and sb which reprecipitated together with pyrite in the form of native gold sulfides and tellurides either as small inclusions or as larger grains within fractures this remobilization process facilitates the exceptionally high gold tenor found in the deposit where the colombia corridor is intersected by the santa maria fault

the tectonic history of drake passage and its possible impacts on global climate this study provides an integrated review of plate tectonic models of the evolution of the antarctica patagonia connection compared to geological records collected on land in patagonia and tierra del fuego and offshore along the northern edge of the scotia sea a temporal framework for the sedimentary and tectonic events of the north scotia ridge and tierra del fuego is constructed with additional data compiled from entire patagonia and the austral basin this review provides robust correlations of seaways and tectonic events along the scotia and south america plates and indicates that the opening of the drake passage was not steady state since ca 30 ma rather the regions forming the present day northern limit of this gateway experienced important paleogeographic changes from deep marine basins to shallow ridges and emerged regions during the late oligocene and early middle miocene time our compilation of geological data shows that emergence along the north scotia ridge and tierra del fuego was achieved at 23 22 ma and has been followed by elimination of the patagoniano sea in patagonia starting at 22 23 ma and achieved at 20 ma this transition towards more continental sedimentation in southern south america is correlated with more shallow marine conditions in the austral basin this succession of events had a strong influence on the general geometry of the drake passage corresponding to a constriction of its northern limit starting in the window 29 22 ma and achieved at 21 ma this period of active deformation in southern south america also corresponds to a period of the global climate having two anomalies well known from the isotopic records the late oligocene warming around 26 ma and the mid miocene climatic optimum which ended between 15 and 14 ma the possible effects of the post oligocene tectonic evolution of the drake passage region on general oceanic circulation are discussed causes for the synchronicity between tectonic events and these global warming events are examined

modification of fluid inclusions in quartz by deviatoric stress i experimentally induced changes in inclusion shapes and microstructures fluid inclusions in quartz are known to modify their shapes and microstructures textures during weak plastic deformation however such changes have not been experimentally demonstrated and criteria are not available to relate them to paleostress conditions to address these issues quartz crystals containing natural co2 h2o nacl fluid inclusions have been experimentally subjected to compressive deviatoric stresses of 90 250 mpa at 700 c and 600 mpa confining pressure strains of up to 1 cause the inclusions to develop irregular shapes and to generate microcracks in crystallographic planes oriented subperpendicular to the major compression axis 1 the uniform alignment of the microcracks imparts a planar fabric to the samples the microcracks heal and form swarms of tiny satellite inclusions these new inclusions lose h2o by diffusion thereby triggering plastic deformation of the surrounding quartz via h2o weakening consequently the quartz samples deform plastically only in domains originally rich in inclusions this study shows that fluid inclusions deformed by deviatoric stresses may indeed record information on paleostress orientations and that they play a key role in facilitating crystal plastic deformation of quartz

fluid record of rock exhumation across the brittle ductile transition during formation of a metamorphic core complex naxos island cyclades greece fluid inclusions trapped in quartz veins hosted by a leucogneiss from the southern part of the naxos metamorphic core complex attic cycladic massif greece were studied to determine the evolution of the fluid record of metamorphic rocks during their exhumation across the ductile brittle transition three sets of quartz veins v m2 v bd v b are distinguished the v m2 and v bd are totally or respectively partially transposed into the foliation of the leucogneiss they formed by hydrofracturing alternating with ductile deformation accommodated by crystal plastic deformation the v b is discordant to the foliation and formed by fracturing during exhumation without subsequent ductile transposition fluids trapped during crystalplastic deformation comprise two very distinct fluid types namely a co2 rich fluid and a high salinity brine that are interpreted to represent immiscible fluids generated from metamorphic reactions and the crystallization of magmas respectively they were initially trapped at approximate to 625 degrees c and 400mpa and then remobilized during subsequent ductile deformation resulting in various degrees of mixing of the two end members with later trapping conditions of approximate to 350 degrees c and 140mpa in contrast brittle microcracks contain aqueous fluids trapped at 250 degrees c and 80mpa all veins display a similar 13c pointing to carbon that was trapped at depth and then preserved in the fluid inclusions throughout the exhumation history in contrast the d signature is marked by a drastic difference between i v m2 and v bd veins that are dominated by carbonic aqueous carbonic and high salinity fluids of metamorphic and magmatic origin characterized by d between 56 parts per thousand and 66 parts per thousand and ii v b veins that are dominated by aqueous fluids of meteoric origin characterized by d between 40 parts per thousand and 46 parts per thousand the retrograde pt pathway implies that the brittle ductile transition separates two structurally chemically and thermally distinct fluid reservoirs namely i the ductile crust into which fluids originating from crystallizing magmas and fluids in equilibrium with metamorphic rocks circulate through a geothermal gradient of 30 degrees c km1 at lithostatic pressure and ii the brittle upper crust through which meteoric fluids percolate through a high geothermal gradient of 55 degrees c km1 at hydrostatic pressure

prograde evolution and geothermal affinities of a major porphyry copper deposit the cerro colorado hypogene protore i region northern chile the middle eocene 51 8 0 6 ma hypogene protore underlying the supergene orebody of the cerro colorado porphyry cu mo deposit i region chile exhibits features not commonly documented in such hydrothermal systems early stage alteration of upper cretaceous plagioclase phyric andesite generated a sub horizontal blanket of pervasive extremely fine grained but texture preserving biotite 35 modal albite 40 magnetite 3 alteration 8 km 2 in area but lacking sulfide minerals at least seventy percent of the chalcopyrite pyrite stockwork mineralization was emplaced during the subsequent main stage alteration which comprises with decreasing depth quartz albite sericite chlorite clay smectite quartz sericite clay and andalusite diaspore pyrophyllite assemblages the deposit is apparently unique among documented central andean porphyry systems in the association of the highest grade copper mineralization with intermediate argillic alteration the subsequent transitional stage phyllic i e quartz sericite pyrite tourmaline alteration was associated with the emplacement of molybdenite rich breccia bodies the occurrence of undumortieri tized tourmaline veinlets cutting andalusite diaspore assemblages confirms that much of the advanced argillic alteration took place during the main stage early stage alteration was the product of nonboiling cool trapping temperature ca 380 c low salinity 8 wt nacl equiv fluids which added substantial k na mg fe 2 cl f and water to the host andesite the initial main stage fluids boiling at a paleodepth of ca 2 5 to 3 0 km were up to 160 c hotter 544 c and highly saline 52 wt nacl equiv as these fluids rose they cooled to 320 c were diluted to 37 wt nacl equiv deposited sulfides and leached k na ca mg fe 2 and cl from the host rocks yielding diverse broadly contemporaneous intermediate and advanced argillic alteration facies pressure estimates require that low density 0 3 g cm 3 and thus more acidic fluids were primarily responsible for the formation of the quartz sericite clay and shallow advanced argillic alteration subsequent phyllic alteration was similarly caused by boiling fluids which were hot 486 c and saline 47 wt at depth but cooler 334 c dilute 8 wt and vapor dominated at shallower levels even terminal stage pyrite veins formed at temperatures as high as 450 c albeit from low salinity 8 wt fluids following a major prograde thermal transition from the early to the main stage each sulfide depositing alteration episode at cerro colorado was generated by a pulse of high temperature fluid which cooled and diluted as it rose such changes in fluid characteristics temperature and alteration relationships are well documented in numerous geothermal fields where potassic alteration generally develops at ca 270 to 350 c and are likely to occur at an early stage in any hydrothermal system in which magmatic fluids exsolving at relatively high pressures ascend into the near surface environment the initial alteration at cerro colorado plausibly developed under conditions similar to those in nonexplosive geothermal systems in which hydrothermal fluids cool and disperse laterally at shallow depths extensive zones of biotite rich alteration generally barren and with a hornfelsic appearance occur in many andesite hosted porphyry copper deposits but few data are available elsewhere for mineralogical pressure temperature or metasomatic exchange relationships in such systems cerro colorado may however be representative of a subclass of porphyry copper deposits exhibiting unusually close analogies with geothermal systems

fluid inclusion evidence for p v t x evolution of hydrothermal solutions in late alpine gold quartz veins at brusson val d ayas northwest italian alps

gold transporting hydrothermal fluids in the earth s crust an introduction hydrothermal ore deposits that are exploited for gold include both gold only deposits such as orogenic deposits and gold bearing examples of the common hydrothermal deposit types that are formed around upper crustal magmatic centres in particular porphyry and epithermal deposits fluid inclusion data have shown that ore fluids of gold only deposits are compositionally distinct compared to fluids of other deposit types fluids of the latter deposit types are in contrast not distinctive and recent research has been focussed on relating gold content to geochemical and petrological aspects of related magmatic systems and to fluid evolution on migration through the crust this special publication includes an up to date summary of thermodynamic parameters of aqueous au species at high temperatures and pressures a dataset of fluid inclusion properties and compositions from orogenic deposits of different parts of the world several comprehensive case studies of different types of gold deposits and their fluids from the usa brazil egypt slovakia and bulgaria and numerical modelling aimed to define key parameters that affect fluid flow and gold deposition at a range of scales historical and disciplinary context the majority of gold deposits of the earth s crust are generated by fluxes of hot aqueous hydrothermal fluids that are efficiently focussed within relatively small volumes of rock a proportion of this gold is extracted from hydrothermal deposit types such as iron oxide copper gold iocg deposits porphyry deposits and lowand high sulphidation epithermal deposits as a co product with other metals most commonly with copper or silver the other group 12 elements a similar proportion is however a product of gold only hydrothermal deposits including orogenic gold intrusion related gold irgd and carlin type gold deposits in these gold only deposit types au is in most cases not only the only commodity of economic interest in the ore but we can infer from the available multi element compositional data on fluid inclusions that it is the only commodity of interest transported in the hydrothermal fluids of these deposits e g yardley et al 1993 su et al 2009 gold only hydrothermal deposits are thus environments in which gold is very effectively fractionated from other metals presumably as a consequence of gold s unique chemical properties such as high electronegativity and the tendency to form bonds with strong covalent character e g crerar et al 1985 and the strength of relativistic effects on bonding behaviour e g pyykko 2012 the affinity of gold with reduced sulphur in hydrothermal fluids was first experimentally demonstrated by seward 1973 and has been confirmed in all subsequent experimental studies see pokrovski et al 2014 gold only deposits including orogenic gold deposits do appear to be products of hydrothermal fluids that are chemically distinct compared to fluids of other higher temperature hydrothermal ore deposit types including porphyry deposits epithermal deposits and greisens hypersaline fluids are absent at almost all deposits the dominant fluid contains sufficient co2 to form a carbonic phase in fluid inclusions and has relatively low salinity in contrast the fluids of gold rich epithermal and porphyry deposits are not distinct from those of typical deposits of these types at least with respect to compositional fluid parameters that can be constrained through routine microthermometry it is difficult to pinpoint who first recognized that co2 bearing and relatively low salinity ore fluids are characteristic and almost ubiquitous in orogenic gold deposits roedder 1973 in his early comprehensive summary of knowledge of fluid inclusion compositions reported that kravtsov fridman 1965 recorded high co2 in fluid inclusions in gold quartz veins and suggested that its abundance might be an effective exploration tool for gold boyer et al 1967 recognized co2bearing fluid inclusions in quartz veins and summarized the results of other similar studies to suggest a clear relation direct or indirect between gold and co2 in another early work coveney kelly from garofalo p s ridley j r eds gold transporting hydrothermal fluids in the earth s crust geological society london special publications 402 http dx doi org 10 1144 sp402 9 the geological society of london 2014 publishing disclaimer www geolsoc org uk pub ethics at universita di bologna on june 30 2014 http sp lyellcollection org downloaded from

microthermometric laser raman spectroscopic and volatile ion chromatographic analysis of hydrothermal fluids in the paleozoic muruntau au bearing quartz vein ore field uzbekistan fluid inclusions in quartz and scheelite from flat steeply dipping central and stockwork type quartz veins within the muruntau au bearing quartz vein ore field have been investigated in a reconnaissance study using fluid inclusion mapping microthermometry laser raman spectroscopy and integrated gas and ion chromatography for bulk volatile and cation anion analysis muruntau central veins are dominated by inferred early co2 bearing fluid inclusions in contrast flat quartz veins contain considerable numbers of low density pure aqueous inclusions on deformation and recrystallization related microstructures fluid phase separation is indicated for samples from the muruntau central ore veins by fluid inclusion observational work as well as by microthermometry and bulk fluid geochemistry co2 ch4 co2 n2 and co2 c2 and c3 hydrocarbon ratios salinity data however in flat veins and all samples from the myutenbai deposit no evidence for fluid immiscibility could be found quartz microstructural results and fluid inclusion data suggest formation of the low grade mineralized flat veins before the main stage of hydrothermal activity and considerable variation in the geochemical conditions during fluid evolution in the muruntau and myutenbai deposits mixing of fluids from different sources in variable proportions may be inferred from halide geochemistry furthermore fluid inclusion br cl ratios differ significantly for samples from different vein types fluid phase separation is suggested as a mechanism for the precipitation of au from the hydrothermal fluid in the muruntau high grade au mineralized central veins

polynostratigraphy and palaeoenvironments across the oligocene miocene boundary within the centinela formation southwestern argentina abstract palynological analysis of the centinela formation exposed in the foothills of the patagonian andes has revealed the presence of pollen dinoflagellate cysts and chlorococcalean and prasinophycean algae these groups are here reported from the centinela formation for the first time sporomorph and dinoflagellate cyst assemblages suggest a late oligocene and early miocene age these results coincide with a 87 sr 86 sr age close to the age of the oligocene miocene boundary obtained from the lower part of the section palynological information from the centinela formation permits correlation with upper oligocene and lower miocene units cropping out along the atlantic patagonian coast assemblages from the lower part of the section suggest that the beds were deposited under marine near shore palaeoenvironmental conditions with a strong continental influence in the middle part of the section high dinoflagellate cyst ratios coincide with a maximum flooding surface recorded in the centinela formation towards the top of the centinela formation the sporomorph assemblages reflect the development of vegetation adapted to coastal environments which agrees with the sparse occurrence of marine palynomorphs a new dinoflagellate species hystrichostrogylon sulcatum is proposed this species appears to range across the oligocene miocene boundary and is particularly abundant in the lowest miocene

fluid inclusion evidence for the physicochemical conditions of sulfide deposition in the olympias carbonate hosted pb zn au ag sulfide ore deposit e chalkidiki peninsula n greece the olympias pb zn au ag sulfide ore deposit e chalkidiki n greece is hosted by marbles of the polymetamorphic kerdilia formation of paleozoic or older age the geologic environment of the ore also comprises biotite hornblende gneisses and amphibolites intruded by tertiary pegmatite aplite dikes lamprophyre dikes the 30 ma stratoni granodiorite and porphyritic stocks only limited parts of the deposit display shear folding and brecciation most of it is undeformed microthermometry of fluid inclusions in gangue syn ore quartz indicates three types of primary and pseudosecondary inclusions 1 h2o rich 1 18 wt nacl equivalent 3 6 mol co2 2 h2o co2 inclusions 4wt nacl equivalent with variable co2 contents coexisting in both undeformed and deformed ore 3 aqueous highsalinity 28 32 wt nacl equivalent inclusions found only in undeformed ore type 2 inclusions are differentiated into two sub types 2a relatively constant co2 content in the narrow range of 8 15 mol and homogenization to the liquid phase 2b variable co2 content between 18 and 50 mol and homogenization to the vapor phase type 1 and 2b inclusions are consistent with trapping of two fluids by unmixing of a high temperature saline aqueous co2 bearing fluid of possible magmatic origin probably trapped in type 2a inclusions fluid unmixing and concomitant ore mineralization took place at temperatures of 350 30 c and fluctuating pressures of less than 500 bar for both undeformed and deformed ores the wide salinity range of type 1 inclusions probably represents a complex effect of salinity increase due to fluid unmixing and volatile loss and dilution due to mixing with low salinity meteoric waters high solute enrichment of the residual liquid due to extreme volatile loss during unmixing may account for high salinity type 3 inclusions the olympias fluid inclusion salinity temperature gradients bear similarities to analogous gradients related to pb zn ores formed in granite hosted low t distalskarn skarn free carbonate replacement and epithermal environments

sediment hosted gold deposits in guizhou china products of wall rock sulfidation by deep crustal fluids sediment hosted gold deposits in guizhou china are hosted in late paleozoic and early mesozoic sedimentary rocks along the southwest margin of the precambrian yangtze craton they have characteristics similar to carlin type gold deposits in nevada and are notably enriched in as sb hg and tl the shuiyindong and yata deposits consist of disseminated strata bound sulfides in permian bioclastic limestone and fault controlled mineralization in middle triassic calcareous clastic rocks respectively mineralization in both deposits consists of barren milky quartz veins disseminated gold bearing arsenian pyrite and arsenopyrite stibnite realgar and orpiment the barren milky quartz veins occur in the ore controlling structures with an envelope of gold mineralization in the host rock consisting of disseminated gold bearing arsenian pyrite and arsenopyrite and replacement style quartz veinlets later drusy quartz stibnite realgar and orpiment fill fractures and vugs on the periphery of gold mineralization petrography microthermometry laser raman spectroscopy and laser ablation inductively coupled plasma mass spectrometric la icp ms analyses of fluid inclusions are used to characterize the chemical evolution of ore fluids at shuiyindong and yata early barren milky quartz veins trapped aqueous fluid with moderate salinity 6 0 wt nacl equiv and minor co2 2 4 mol at a temperature of 230 30 c this fluid contains measurable b na k cs sr as sb and au 3 8 0 5 5 7 2 3 g g determined by la icp ms and is interpreted to approximate the mineralizing fluid responsible for precipitation of early barren quartz veins low salinity 0 9 2 3 wt nacl equiv co2 bearing 6 3 8 4 mol aqueous fluids are recorded in replacement style quartz veinlets they formed gold bearing arsenian pyrite and arsenopyrite and quartz veinlets at a temperature of 210 20 c and pressures of 450 to 1 150 bars corresponding to depths between 1 7 and 4 3 km under lithostatic conditions fluid inclusions in late stibnite orpiment realgar quartz veins contain high co2 58 64 mol and n2 19 2 23 7 mol with trace ch4 up to 1 6 mol the increasing content of co2 and decrease in the concentrations of au and as in aqueous carbonic inclusions are interpreted to result from carbonate dissolution at the level of the deposits during gold mineralization covariance of au as sb and sr concentrations in the fluids is interpreted to reflect deposition of as and sb sulfides and gold concurrent with carbonate crystallization iron is below detection limit 400 g g in all fluid inclusion types suggesting that the ore fluids were fe poor but possibly sulfur rich possibly explaining their exceptionally high gold contents iron in sulfide minerals was probably derived from dissolution of ferroan minerals in the host rocks sulfidized by h2s rich fluids to precipitate arsenian pyrite arsenopyrite and gold pressure fluctuation induced by faulting resulted in local fluid immiscibility and led to late deposition of realgar orpiment stibnite and calcite hydrogen and oxygen isotope compositions of ore fluids d h2o 35 to 68 18o h2o 4 16 5 indicate a metamorphic origin possibly related to crustal thickening and prograde metamorphism during the late yanshanian orogeny

physical chemical properties and metal budget of au transporting hydrothermal fluids in orogenic deposits we use a set of analytical techniques for fluid inclusion analysis to determine the bulk properties of the ore fluids from five orogenic gold deposits the most common ore fluid is a low salinity 0 4 6 5 wt nacl twoto three phase aqueous carbonic fluid its th total range is 200 400 8c and total homogenization occurs by bubble or liquid disappearance a less common aqueous fluid of similar bulk salinity and t h total is also documented microchemical data show that the ore fluid in the five deposits is chemically uniform and made of na subordinate k and b and minor to trace amounts of cu as li sr rb ba cs sb and au range 0 5 5 mg g thermodynamic modelling carried out for one of the studied deposits indicates that the ore fluid was in equilibrium with vein minerals at the time of gold deposition and that its vapour phase was distinctly enriched in au b as and sb the proposed mechanism of gold precipitation is a combination of fluid decompression and boiling combining these results with 3d geometrical reconstructions of one of the studied deposits sigma we estimate that a minimum ore fluid volume of c 0 1 1 0 km is sufficient to generate a world class orogenic deposit orogenic deposits provide about a third of the global gold production goldfarb et al 2001 frimmel 2008 these deposits are formed within active continental margins in orogenic belts where major tectonic boundaries juxtapose metamorphosed volcanic plutonic and sedimentary terranes the ore bodies consist of au mineralized vein networks filled with quartz carbonates and other silicates that in places crosscut the stacked terranes of the continental margins the veins are dilated portions of vertically extensive brittle ductile to ductile fracture networks that form due to the advection of aqueous hydrothermal fluids within the continental crust ridley et al 1996 groves et al 2003 these ore fluids are generated in still undefined source regions deep in the crust and transported to shallower levels 3 15 km depth through the vein networks along which they deposit gold a number of studies kerrich et al 2000 ridley diamond 2000 groves et al 2003 showed that although these networks do not occur systematically in all orogens they have a set of important geological features in common which include 1 formation during accretionary orogenic events 2 occurrence relatively close to regional tectonic lineaments especially along lower order splays of these structures 3 spatial association with granitoid intrusions 4 occurrence within some metamorphic belts with gold precipitation being synto postmetamorphic in age 5 relatively low sulphide abundance within the veins 6 carbonate sericitealbite sulphide hydrothermal alteration of host rocks postdating metamorphism 7 poorly developed mineral and metal zoning within the ore bodies and 8 genesis from low to moderate salinity ore fluids over a large temperature range 250 700 8c but mostly within 300 350 8c these common traits occur systematically in deposits from different terrains having distinct ages suggesting that a common geological process and au transporting fluid are responsible for their formation here we present a database of fluid inclusion properties from five typical orogenic deposits which show most of the geological characteristics listed above the database was constructed with the aim of determining as accurately as possible the properties of the au transporting fluid in this geological environment in particular laser ablation inductively coupled plasma mass spectrometry la icp ms of single fluid inclusions paragenetically coeval with vein gold provides the concentration of a suite of metals including au in this fluid this dataset when combined with 3d geometrical reconstructions of one of these deposits offers new constraints on the volume of the ore from garofalo p s ridley j r eds gold transporting hydrothermal fluids in the earth s crust geological society london special publications 402 http dx doi org 10 1144 sp402 8 the geological society of london 2014 publishing disclaimer www geolsoc org uk pub ethics by guest on april 3 2014 http sp lyellcollection org downloaded from

a magneto and chemostratigraphically calibrated dinoflagellate cyst zonation of the early palaeogene south pacific ocean abstract investigation of the early palaeogene palaeoecological and palaeoclimatological evolution of the polar regions is hindered by the absence of calcite microfossils in sedimentary archives which are conventionally the main dating tool to overcome this problem we have generated large datasets of organic dinoflagellate cyst dinocyst assemblages from southern ocean shelf sediments over the past decade and we here calibrate these to the geomagnetic polarity time scale gpts using magnetostratigraphy and stable isotope stratigraphy this now for the first time allows a high resolution southern pacific ocean dinocyst zonation for the late palaeocene to late eocene 58 36 million years ago ma we compile published dinocyst chronologies from ocean drilling program odp hole 1171d on the south tasman rise hole 1172a d on the east tasman plateau and integrated ocean drilling program iodp hole u1356a on the wilkes land margin correlation to dinocyst zonations from new zealand lead to revisions of the magnetostratigraphic age model at holes 1171d and 1172a d stable carbon and oxygen isotope records reveal the stratigraphic location of the palaeocene eocene thermal maximum 56 ma and the middle eocene climatic optimum 40 ma respectively the resulting zonation consists of thirteen dinocyst zones calibrated to the geomagnetic polarity time scale gpts of vandenberghe et al 2012 which can likely be applied to the entire southern ocean finally we apply the revised stratigraphy to all published tex86 data a biomarker based proxy for sea surface temperature sst from odp site 1172 to assess long term climate evolution this shows that southwest pacific sst trends mimic the global compilation of benthic foraminiferal oxygen isotopes even better than previously appreciated

fluid inclusion characteristics of hematite bearing quartz vein from the daenam mine republic of korea abstract the daenam mine which produced over 9250 tons of iron oxide ore from 1958 to 1962 is situated in the early cretaceous yeongyang subbasin of the gyeongsang basin it consists of two lens shaped hematite bearing quartz veins that occur along faults in cretaceous leucocratic granite the hematite bearing quartz veins are mainly composed of massive and euhedral quartz and hematite with minor amounts of pyrite pyrrhotite mica feldspar and chlorite fluid inclusions in quartz can be divided into three main types co2 rich co2 h2o and h2o rich hydrothermal fluids related to the formation of hematite are composed of either h2o co2 nacl ch4 homogenization temperature 262 455 c salinity

modification of fluid inclusions in quartz by deviatoric stress ii experimentally induced changes in inclusion volume and composition fluid inclusions in quartz are known to modify their densities during shear deformation modifications of chemical composition are also suspected however such changes have not been experimentally demonstrated their mechanisms remain unexplained and no criteria are available to assess whether deformed inclusions preserve information on paleofluid properties to address these issues quartz crystals containing natural co2 h2o nacl fluid inclusions have been experimentally subjected to compressive deviatoric stresses of 90 250 mpa at 700 c and 600 mpa confining pressure the resulting microcracking of the inclusions leads to expansion by up to 20 producing low fluid densities that bear no relation to physical conditions outside the sample nevertheless the chemical composition of the precursor inclusions is preserved with time the microcracks heal and form swarms of tiny satellite inclusions with a wide range of densities the highest reflecting the value of the maximum principle stress 1 these new inclusions lose h2o via diffusion thereby passively increasing their salt and gas contents and triggering plastic deformation of the surrounding quartz via h2o weakening using microstructural criteria to identify the characteristic types of modified inclusions both the pre deformation fluid composition and syn deformation maximum stress on the host mineral can be derived from microthermometric analysis and thermodynamic modelling

crystallization conditions and evolution of magmatic fluids in the harney peak granite and associated pegmatites black hills south dakota evidence from fluid inclusions abstract a microthermometric study of inclusions in granites and pegmatites in the proterozoic harney peak granite system identified four types of inclusions type 1 inclusions are mixtures of co2 and h2o and have low salinities on average 3 5 wt nacleq type 2 inclusions are aqueous solutions of variable salinities from 0 to 40 wt nacleq type 3 inclusions are carbonic dominated by co2 with no detectable water and type 4 inclusions consist of 20 to 100 solids with the remaining volume occupied by a co2 h2o fluid many inclusions have a secondary character however a primary character can be unambiguously established in several occurrences of the type 1 inclusions these inclusions were trapped above the solidus and represent the exsolved magmatic fluid the secondary populations of types 1 2 and 3 probably formed as a result of reequilibration and unmixing of the type 1 fluid that progressively changed composition and density with decreasing temperature and pressure and was finally trapped along healed microfractures under subsolidus conditions type 4 inclusions are primary and are interpreted to be trapped fluid bearing complex silicate melts that subsequently solidified or underwent other posttrapping changes it is demonstrated that primary type 1 fluid inclusions that coexist with crystallized melt inclusions in the complex li bearing tin mountain pegmatite were trapped along the two fluid phase boundary in the system co2 h2o nacleq consequently the temperature and pressure conditions of trapping are identical to the bulk homogenization conditions on average 340 c and 2 7 kbar these conditions indicate that this li cs rb p and b rich pegmatite crystallized at some of the lowest known temperatures for a silicate melt in the crust an internally consistent empirical solvus surface in p t xco2 coordinates was generated for the pseudobinary co2 h2o 4 3 wt nacleq pegmatite fluid system distribution coefficients for the major species co2 h2o nacl and ch4 between the immiscible co2 rich and h2o rich fluid phases as a function of pressure and temperature were extracted from data for the two cogenetic fluid inclusions types

hypersaline fluids generated by high grade metamorphism of evaporites fluid inclusion study of uranium occurrences in the western zambian copperbelt in the pan african lufilian belt western zambian copperbelt uranium mineralizations preferentially scattered in kyanite talc micaschists metamorphosed evaporitic sediments or concentrated along transposed quartz veins provide an opportunity to 1 understand the time space relationship between the ore minerals and the deformation of the host rocks 2 identify the different fluid events associated with specific stages of quartz deformation and 3 characterize the ore fluid geochemistry in terms of fluid origin and fluid rock interactions in the u occurrences studied in lolwa and mitukuluku domes region western zambian copperbelt two mineralizing stages are described the first generation of ore fluids 53 59 wt cacl2 13 15 wt nacl n2 h2 in the gas phase of fluid inclusions circulated during the high temperature quartz recrystallization at 500 700 c this temperature is in agreement with the p t conditions recorded during the crustal thickening related to continental collision at ca 530 ma la icpms analyses show the presence of uranium within this fluid with a concentration mode around 20 ppm the second generation of ore fluid 21 32 wt nacl 19 21 wt cacl2 co2 co in the gas phase of fluid inclusions percolated at lower temperature conditions at the brittle ductile transition between 200 and 300 c this temperature could be related to the exhumation of the high grade metamorphic rocks at ca 500 ma the formation of h2 and co is interpreted as the result of radiolysis in the presence of dissolved uranium in the aqueous phase of these fluid inclusions finally a late fluid 14 16 wt naclequiv circulated in the brittle domain but seems unrelated to u re mobilization event

orogenic gold formation in an evolving decompressing hydrothermal system genesis of the samut gold deposit eastern desert egypt abstract samut is a vein type gold mineralization in the eastern desert of egypt which shares many geologic features with other orogenic deposits in this region the deposit has a long history of mining activity dating back to ancient times but so far has received little attention from the standpoint of geologic study here we present new field petrographic microthermometric and microanalytical data from the samut gold deposit to evaluate its genesis and fluid evolution vein quartz at samut shows abundant evidence of precipitation coinciding with early phases of ductile deformation that show transitions to increasing brittle fracturing and fragmentation through time in some samples brecciation of the vein quartz is intense and shows evidence of repeated episodes of fragmentation this brittle style of deformation culminates with latest stage brittle opening and loss of confining pressure resulting in open space filling textures backscattered electron images and electron microprobe analysis reveal three varieties of pyrite in the mineralized quartz veins py i py ii and py iii laser ablation icpms analysis of pyrites from mineralized quartz veins reveals that the earlier py i is low in arsenic and gold whereas py ii and py iii are enriched in both elements anhedral py ii is particularly gold rich and gives way to blocky euhedral py iii that is rich in arsenic but not as rich in gold compared to py ii fluid inclusions in the least brittle deformed vein quartz indicate that the veins formed at minimum temperatures of 300 c early in the hydrothermal system the calculated fluid pressures at homogenization of the aqueous carbonic inclusions furnish a wide range throughout the paragenesis perhaps on the order of 1 to 3 kbar the 34s values of pyrites imply sulfur isotopic composition of the mineralizing fluid on the order of 0 6 to 4 9 overlapping with the broad range of 34s values calculated for ore fluids in orogenic gold deposits worldwide together these results support a general model in which gold and sulfide deposition was coinciding with an ongoing syn deformational vein formation and tending towards the late stages of vein growth prior to loss of confinement free milling gold appears to be mostly related to the later stages of brittle fracturing and re sealing of the veins during repeated fluid release as the background fluid pressure evolved from earlier dominantly lithostatic to later fully hydrostatic conditions

fluid inclusion and stable isotope evidence for the genesis of quartz scheelite veins metaggitsi area central chalkidiki peninsula n greece scheelite mineralization accompanied by muscovite and albite and traces of mo stolzite and stolzite occurs in epigenetic quartz vein systems hosted by two mica gneissic schists and locally amphibolites of the paleozoic or older vertiskos formation in the metaggitsi area central chalkidiki n greece three types of primary fluid inclusions coexist in quartz and scheelite type 1 the most abundant consists of mixed h2o co2 inclusions with highly variable 20 90 vol co2 contents and salinities between 0 2 and 8 3 equivalent weight nacl densities range from 0 79 to 0 99 g cc type 1 inclusions contain also traces 2 mol of ch4 type 2 inclusions are nearly 100 vol liquid co2 with traces of ch4 and densities between 0 75 and 0 88 g cc type 3 inclusions the least abundant contain an aqueous liquid of low salinity 0 5 to 8 5 equivalent weight nacl with 10 30 vol h2o gas infrequently containing also small amounts of co2 2 mol densities range from 0 72 to 0 99 g cc the wide range of coexisting fluid inclusion compositions is interpreted as a result of fluid immiscibility during entrapment immiscibility is documented by the partitioning of ch4 and co2 into gas rich co2 rich type 1 inclusions and the conformity of end member compositions trapped in type 1 inclusions to chemical equilibrium fractionation at the minimum measured homogenization temperatures and calculated homogenization pressures minimum measured homogenization temperatures of aqueous and gas rich type 1 inclusions of 220 250 c either to the h2o or to the co2 phase is considered the best estimate of temperature of formation of the veins and temperature of scheelite deposition corresponding fluid pressures were between 1 2 and 2 6 kbar oxygen fugacities during mineralization varied from 10 35 to 10 31 bar and were slightly above the synthetic ni nio buffer values the fluid inclusion data combined with 18o water values of 3 to 6 per mil smow and 13c co2 fluid of 1 2 to 4 3 per mil pdb together with geologic data indicate generation of mineralizing fluids primarily by late to post metamorphic devolatilization reactions

the bronzewing lode gold deposit western australia p t x evidence for fluid immiscibility caused by cyclic decompression in gold bearing quartz veins abstract the bronzewing lode gold deposit is located in the yandal greenstone belt in the yilgarn craton of western australia gold mineralization is hosted in tholeiitic basalt that is metamorphosed to greenschist facies individual ore bodies are controlled by a complex gold bearing quartz vein system that comprises shear and extension veins formed during a progressive d2 deformation event gold is localized in quartz along fractures and deformed grain boundaries and is interpreted to have formed late in the formation of the veins detailed petrography and microthermometry on primary pseudosecondary and secondary fluid inclusions trapped in gold bearing shear and extension veins revealed five types of fluid inclusions 1 co2 ch4 h2o nacl inclusions of variable salinity 0 1 to 17 5 eq wt nacl containing between 10 and 99 mol co2 and molar volumes that range from 22 to 76 cm3 2 h2o nacl inclusions of variable salinity 0 4 to 22 1 eq wt nacl 3 co2 ch4 inclusions with up to 58 mol ch4 and molar volumes between 54 and 73 cm3 4 ch4 h2o inclusions with ch4 ranging from 80 to 90 mol and 5 ch4 inclusions with low molar volumes of 19 to 23 cm3 types 1 2 and 3 constitute a fluid inclusion assemblage that occurs consistently in primary pseudosecondary and secondary trails and clusters within the gold bearing quartz vein system these co existing fluids are interpreted to have formed by fluid immiscibility of a low salinity homogeneous parent fluid at about 300 c and 1500 bars locally type 2 fluid inclusions exhibit total homogenization temperatures that are on average 100 c less than the co genetically trapped type 1 aqueous carbonic inclusions this discrepancy is interpreted to have involved co2 effervescence in response to fluid pressure fluctuations types 4 and 5 fluid inclusions are rare and are only present locally in secondary trails and clusters in extension veins significant pressure fluctuations but relatively constant homogenization temperatures for types 1 2 and 3 fluid inclusions suggest that cyclic decompression of the hydrothermal fluids due to seismic activity along the shear zones that host the gold bearing veins triggered fluid immiscibility the process of fluid immiscibility and subsequent lowering of gold solubility is interpreted to be the most efficient precipitation mechanism for gold in the d2 shear zone hosted vein system at bronzewing

multiple hydrothermal processes in footwall units of the north range sudbury igneous complex canada and implications for the genesis of vein type cu ni pge deposits systematic regional sampling along the contact zone of the 1 85 ga age sudbury igneous complex with the archean levack gneiss footwall in the north range of the sudbury structure revealed textural mineralogical and fluid inclusion systematics of post sudbury igneous complex hydrothermal processes that affected the various lithologies at late stages of emplacement of the sudbury igneous complex and formation of magmatic fe ni cu sulfide deposits a partial melt from the levack gneiss invaded the contact zone this partial melt is revealed by small microdikes and irregular bodies of granophyric quartz plagioclase with megacrysts of hornblende clinopyroxene and titanite plagioclase hornblende equilibrium was established at 750 to 800 c and 1 10 to 1 55 kbars pressure corresponding to about a 4 to 6 km depth under lithostatic conditions f cl wt percent ratios around 15 for accessory apatite and hornblende indicate that a cl rich fluid phase separated during the crystallization of the footwall granophyre this is expressed as miarolites the cl rich fluid 50 wt nacl equiv salinity was trapped as primary fluid inclusions in quartz at around 480 c minimum temperature and around 1 1 kbars minimum pressure during supercooling these inclusions are rich in ca fe mn and k as well as na chloride this fluid may have interacted with earlier primary magmatic sulfide causing remobilization and reprecipitation of cu ni platinum group elements pge in veins and disseminations in the footwall these veins are parallel to the sudbury igneous complex footwall contact and are characterized by chalcopyrite pentlandite millerite magnetite stilpnomelane ferropyrosmalite epidote and chlorite michenerite moncheite merenskyite froodite insizwaite sobolevskite gold and bi ni sulfides are associated with sulfides epidote quartz actinolite and chlorite are common in the alteration selvages of the veins compositions and assemblages of platinum group minerals pgm indicate their precipitation below 575 to 485 c primary highly saline fluid inclusions about 40 wt nacl equiv in quartz indicate crystallization at 400 to 480 c and around 1 6 kbars minimum t and p respectively late carbonate epidote actinolite chlorite veins and alteration overprinted the earlier assemblages at about 300 to 400 c with some bornite millerite native silver and other bi sulfides the second stage of hydrothermal activity is characterized by regional carbonic aqueous nacl co 2 ch 4 h 2 o type immiscible fluids that were trapped as secondary inclusions in quartz from various lithologies no mineralization is related to this stage along the north range boiling of these fluids took place during a pressure drop from lithostatic to hydrostatic conditions during uplift from about a 5 to 6 to a 3 to 4 km depth at 300 to 350 c high 20 26 wt nacl equiv and low salinity 6 12 wt nacl equiv fluids coexisted with different carbonic species contents the predominant north south and northwest southeast orientations of fluid inclusion planes reveal that mobilization of carbonic aqueous solutions may be related to the northwesterly oriented thrusting in the sudbury structure during the late stages 1 8 1 7 ga of the penokean orogeny and to predominantly north south faulting in the north range the third stage of fluid mobilization also took place mostly along northerly and northwesterly oriented fractures aqueous fluids were ca rich brines 20 40 wt salinity with temperatures between 150 and 250 c some of these fluids also circulated in fractures parallel to the sudbury igneous complex footwall contact ne sw thus they locally may have interacted with the earlier sulfide assemblages and are also responsible for formation of late veinlets with chalcopyrite epidote quartz chlorite assemblages mobilization of these fluids took place under litho and hydrostatic conditions at about a 4 to 6 km depth this hydrothermal activity is related to a regional tectonothermal event during emplacement of northwesterly oriented sudbury dikes 1 24 ga regional scale fluid inclusion studies along the north range highlight the role of multiple hydrothermal processes in the metallogenic evolution of the sudbury igneous complex and especially in the distribution of copper and precious metals in the footwall units

isotope systematics in vein gold from brusson val d ayas nw italy 1 pb pb evidence for a piemonte metaophiolite au source the monte rosa gold district nw italian alps comprises hundreds of late alpine epigenetic gold bearing quartz veins we report a lead isotope study on an important one of these veins fenilia brusson val d ayas which reveals a complex isotope geochemistry of petrographically cogenetic vein minerals petrographic observations allow to distinguish a quartz dominated main stage and a quartz poor final stage mineral assemblage most of the free gold crystallized in the beginning of the final stage whereas sulphides were deposited during its waning three distinct lead isotope fields result for the paragenetic sequence of vein minerals the variable lead isotope signature 15 517 15 706 as well as from the uniform radiogenic lead 15 649 207pb 204pb 15 691 characteristic of the waning final stage we favour a model where the deeply circulating final stage fluid the ultimate source of which remains obscure acquired lead and thus possibly its gold in piemonte metaophiolitic rocks beneath the monte rosa nappe during ascent the primitive gold bearing fluid was variably contaminated by an evolved crustal lead 15 706 207pb 204pb 15 743 compatible with derivation from monte rosa nappe rocks during deposition of final stage minerals the pb isotope composition of the fluid changed to a constant signature becoming again dominated by a radiogenic lead source thus within an assemblage defined as cogenetic on petrographic grounds the pb isotopic signature is not necessarily uniform and source modelling based on lead isotopes of associated minerals may be inappropriate it remains open at present whether the inferred piemonte metaophiolite gold source is confined to the fenilia vein in val d ayas only or whether it might be more widespread in the monte rosa gold district

contrasting fluid chemistries alteration characteristics and metamorphic timing relationships recorded in hybridized orebodies of the missanabie renabie gold district archean wawa subprovince ontario canada

past and present circulation of co 2 bearing fluids in the crystalline gran paradiso massif orco valley north western italian alps tectonic and geochemical constraints abstract in the orco valley inside the gran paradiso massif 3 main fault systems are present a e w striking faults dipping at 45 60 to the n b high angle nw se striking faults and c high angle ne sw to nne ssw striking faults the e w striking faults and the interposed nw se faults appear to represent a cogenetic structural association related to a larger scale transtensional shear zone while the ne sw faults are probably inherited by an older discontinuous deformation stage breccia bodies or veins mostly consisting of carbonate siderite ankerite calcite quartz with sulphide au mineralisation recording a multistage mesothermal evolution occur along both e w and nw se fault systems three water types are recognised type i ca 2 hco 3 waters with minor so 4 2 type ii ca 2 na hco 3 waters varying towards na hco 3 cl waters and type iii mg 2 hco 3 waters type i and type iii groundwaters are freshly recharged waters only slightly exchanged with rocks type ii includes waters which come into contact with carbonate fracture fillings and geochemical modelling indicates that dissolution of carbonates along fractures is the main process controlling the groundwater chemistry these waters evolve in a system open to uprising co 2 and their strongly negative 13 c co 2 suggests a substantial organic component in the co 2 discharge in the past co 2 bearing fluids were likely responsible for the formation of fe bearing carbonate fracture fillings the persistence through time of the co 2 flux in the region has important implications for the reconstruction of the alpine tectonic evolution and deep structure

fluid inclusion microthermometry and the p t evolution of gold bearing hydrothermal fluids in the niuxinshan gold deposit eastern hebei province ne china niuxinshan is a typical example of the numerous mesothermal gold deposits formed during mesozoic tectono magmatic reactivation of the archean north china craton in eastern hebei province gold occurs in quartz sulfide lodes in archean amphibolites and also in greisen zones in the mesozoic niuxinshan granite stock four mineralization stages can be recognized from early to late 1 quartz k feldspar 2 quartz pyrite 3 quartz polysulfide and 4 quartz carbonate gold mineralization mainly occurs in stages 2 and 3 fluid inclusions in quartz and fluorite from greisen zones in the niuxinshan granite and inclusions in vein quartz and sphalerite from stages 1 to 3 in the amphibolites have been studied by microthermometry three compositional types of inclusions are recognized type 1 tp1 are h2o co2 bearing inclusions and include primary tp1 p and secondary tp1 s inclusions these are found in quartz and fluorite from the greisen zones as well as in vein quartz and sphalerite from stages 1 to 3 the tp1 p inclusions are considered to represent the gold bearing hydrothermal fluids type 2 tp2 s are secondary h2o co2 solid phase inclusions in fluorite from the greisen zones type 3 tp3 s are secondary aqueous inclusions with a solid phase which coexist with the tp2 s in fluorite from the greisen zones the tp1 p inclusions show variable vco2 commonly 0 3 to 0 6 and xco2 values mainly 0 1 to 0 4 the salinities of inclusions cluster around 3 to 11 wt nacl equivalent and their homogenization temperatures to the liquid phase th l fall dominantly in the range of 260 to 360 c the compositional variations of inclusions in stage 1 probably result from exsolution of magmatic fluids at various stages immiscibility or boiling of the fluids can be ruled out the compositional variations of inclusions in the greisen zones and in vein stages 2 and 3 are attributed to cooling mixing dilution and necking down of the fluids the tp1 s and tp2 s inclusions show salinities of 3 to 6 wt nacl equivalent and xco2 values of 0 04 to 0 17 th l clusters at 240 to 260 c the tp3 s inclusions have salinities of 3 to 6 wt nacl equivalent and th l of 170 to 240 c isochoric reconstructions combined with oxygen and sulfur isotope geothermometry of mineral pairs give trapping p t conditions for the gold bearing fluids the greisen zones formed at 310 to 460 c and 1 3 to 3 7 kbar stage 1 veins at 300 to 430 c and 1 2 to 3 7 kbar stage 2 veins at 290 to 380 c and 1 to 3 kbar stage 3 veins at 250 to 350 c and 1 to 3 kbar h2o co2 fluids with low to moderate salinities and moderate to high densities 0 66 to 1 01 g cm3 dominated at early mineralization stages and evolved towards h2o richer and co2 and less saline fluids through time the retrograde p t evolution probably resulted from regional uplift and cooling of gold bearing hydrothermal fluids the gold bisulfide complex was dominant in the fluids during mineralization and gold deposition was mainly induced by decreases of temperature and pressure as well as destabilization of the bisulfide complex during sulfidization of wall rocks

fluid regimes fault valve behavior and formation of gold quartz veins the morro do ouro mine ribeira belt brazil abstract fluid inclusion studies petrographic analyses and structural analyses for neoproterozoic auriferous veins from the morro do ouro mine ribeira belt southeastern brazil are presented the deposit is classified as an orogenic gold deposit the vein type au mineralization at the mine is restricted to structurally controlled domains in a low grade calymmian ca 1500 1450 ma metasedimentary sequence that also hosts syngenetic au mineralization two main auriferous quartz vein systems are present i nw trending subvertical extensional veins and ii ne trending subvertical veins parallel to the axial surface of tight folds the mineralized veins are adjacent to a major dextral transcurrent fault zone and their structural relationships indicate that this fault is severely misoriented for frictional reactivation the nw trending veins present a fluid inclusion assemblage dominated by co 2 n 2 ch 4 inclusions h 2 o co 2 n 2 ch 4 nacl cacl 2 inclusions and h 2 o nacl cacl 2 inclusions both with highly variable salinities 0 5 to 52 wt nacl equivalent while the ne trending veins are dominated by h 2 o co 2 n 2 ch 4 nacl cacl 2 and h 2 o nacl cacl 2 inclusions also of highly variable salinities 1 to 45 wt nacl equivalent the entrapment of fluids occurred at temperatures between 225 and 240 c in the nw trending veins and at approximately 208 c in the ne trending veins involving processes of fluid immiscibility and mixing between fluids of contrasting compositions the nw trending extensional veins were formed predominantly under pressure fluctuating between near lithostatic and strongly supralithostatic conditions 100 250 mpa during pre seismic failure stages the ne trending veins precipitated predominantly under subhydrostatic to lithostatic pressure conditions 10 150 mpa following the discharge of fluids from different reservoirs along the ruptured zone after earthquake rupture stages the hydrothermal fluids were probably enriched with gold through interactions with the host rocks and its precipitation is attributed to changes in physicochemical properties due to fluid immiscibility and mixing between fluids of highly contrasting salinities as a consequence of cyclic fluctuations in the values of fluid pressure and tectonic stresses accompanying episodes of seismogenic fault activity

the role of vapor in the transportation of tin in hydrothermal systems experimental and case study of the dachang deposit china abstract in order to understand metal transportation by vapor which was found by detecting volcanic gases authors performed vapor liquid separation experiments at sub critical states the experiments indicate that the metal transportation by vapor of hydrothermal systems is derived from the liquid and vapor separation occurred in the transitions from a supercritical state to liquid vapor immiscibility field at a sub critical state of metal bearing hydrothermal fluids of nacl h 2 o the data of the fluid inclusions in minerals suggest that major ores were deposited in the temperature range from 300 to 500 c in hydrothermal systems the study on fluid inclusions in minerals of hydrothermal deposits provides evidence that the principal ore minerals of the deposits precipitated in the period from a supercritical state to a sub critical state of the nacl h 2 o a case study of fluid inclusions in minerals of the dachang tin deposit china indicates the evolution of ore forming fluids occurred in the l v immiscibility field of nacl h 2 o the experiments of liquid and vapor two phase immiscibility field of a tin bearing fluid show that sn was redistributed in vapor phase and liquid phase when the tin bearing supercritical fluid nahco 3 hcl h 2 o separates into liquid and vapor phases for a decreasing in temperature or pressure the experiments prove that tin could be transported by vapor phase in hydrothermal systems

geochemical and isotopic properties of fluids from gold bearing and barren quartz veins of the sovetskoye gold deposit siberia russia this paper reports on the comparative study of fluids trapped in inclusions in gold bearing and barren quartz veins at the sovetskoye gold deposit yeniseisky ridge siberia russia the host rocks are greenschist facies metasedimentary rocks of upper proterozoic age within the deposit some veins contain 10 to 25 ppm of au gold bearing veins others contain less than 1 ppm of au barren veins fluid inclusions trapped in barren veins are predominantly low salinity h2o 4 0 8 0 mass nacl equiv with variable contents of dissolved co2 12 5 mol ch4 1 3 mol and n2 1 7 mol homogenization temperatures vary from 200 to 410 c and the calculated pressures of entrapment are 1 5 kbars inclusion fluids trapped in the host schists are predominantly aqueous 97 6 99 3 mol h2o with co2 contents below 2 4 mol percent the fluids trapped in ore bearing quartz inclusions are different inclusions show higher homogenization temperatures up to 630 c and salinity up to 20 25 mass nacl equiv calculated pressures range from 0 7 to 2 0 kbars bulk gas chromatographic data of fluids extracted from native gold have contents of co2 that range from 29 3 to 62 0 mol percent n2 from 2 7 to 13 2 mol percent and ch4 from 0 0 to 2 8 mol percent in gold bearing quartz the contents of co2 range from 18 0 to 41 0 mol percent n2 from 0 1 to 0 2 mol percent and ch4 from 0 3 to 3 0 mol percent raman spectroscopic data of fluid from gold bearing quartz revealed co2 contents of individual inclusions as high as 98 2 mol percent n2 up to 66 4 mol percent and ch4 up to 88 7 mol percent fluids of the country rock schists which host gold bearing quartz veins are also enriched in co2 up to 49 5 mol the host rocks for both barren and gold bearing quartz veins show consistent ree patterns characterized by a negative eu anomaly fluids from barren quartz veins show similar ree patterns although with a less conspicuous negative eu anomaly whereas fluids from gold bearing quartz show a marked positive eu anomaly similar isotopic values of sulfur in pyrite pyrrhotite and arsenopyrite disseminated in country rocks 34s 14 7 21 6 and in barren 34s 12 9 19 9 and gold bearing quartz veins 34s 13 3 17 9 suggest that sulfur in sulfides was derived from the same source most likely being the adjacent country rocks co2 trapped in fluid inclusions of barren and gold bearing quartz has distinct isotopic compositions 13c 8 1 to 10 2 and 4 9 to 5 2 respectively and the 13c values are positively correlated with au contents in veins helium isotope composition of both types of quartz veins 3he 4he 0 04 0 05 ra for gold bearing veins and 3he 4he 0 02 ra for barren veins indicates a crustal provenance of mineral forming fluids the 40ar 39ar dating of sericite demonstrates that the barren veins 890 850 ma are significantly older than the gold bearing veins 830 730 ma on the basis of their ages barren veins are interpreted as synmetamorphic the age of the gold bearing veins corresponds to the age of the local granitoids 850 720 ma suggesting that the origin of the sovetskoye deposit is related to the tectonic activity syntetctonic magmatism

noble gases k u th and pb in native gold we present determinations of the noble gas and pb isotopic abundances and of k th and u concentrations of native gold our results demonstrate that gold is an excellent carrier for crustal volatiles but direct dating of gold using the u th 4he 40k 40ar and u fission xe methods was not successful for various reasons the main significance of this work is the great sensitivity of gold for trapped gases as well as for gases that were produced in situ which gives the prospects of using gold and its fluid and solid inclusions for the study of paleogas composition numerous nuclear effects characterize the noble gas inventory of placer gold from switzerland and italy vein gold from italy south africa and venezuela and lode gold from south africa the degassing patterns obtained by mass spectrometry show a low temperature release of volatiles around 500 c from fluid inclusions mainly in vein gold and a high temperature release from solid inclusions and the gold itself the low temperature volatiles represent species that were trapped when the gold crystallized we investigated the following trapped species the isotopes of he ne ar kr xe and pb and the abundances of k u th h2o and co2 the crustal gases trapped by gold comprise 3he from 6li n 3h 3he 4he and 40ar from the u th and k decay and xe from 238u fission we observe 4he 40ar 3 9 for the radiogenic trapped gases of tertiary gold and a ratio of 1 4 for archean gold these ratios are consistent with the production ratios from u and k at the respective times and demonstrate that gold can be used as a sampler of ancient atmospheric gases the concentrations of u and th range from a few parts per billion to a few parts per million and those of k and pb range up to some tens of parts per million the antiquity of trapped pb is indicated by the pb pb model age of about 3000 ma for the lead extracted from vein gold and quartz of the lily gold mine south africa gold also contains noble gases produced in situ by u th and k decay we obtained 4he up to the extremely high concentration of 6 8 10 2 cm3 stp g stp atmospheric pressure and 0 c for gold separated from a specimen of the witwatersrand west rand gold fields indicating that this gold has a large u content

fluid regime and ore formation in the tungsten yttrium deposits of kyzyltau mongolian altai evidence for fluid variability in tungsten tin ore systems abstract the kyzyltau ore field is located in the northern part of the mongolian altai mountains w y be mo mineralization occurs in veins and stockworks in granites felsic volcanics basaltic flows and conglomerates the main ore minerals in the veins are wolframite fluorite beryl and minor molybdenite inclusions in hydrothermal quartz fluorite and beryl from veins as well as in magmatic quartz in vein hosting granites of the ulaan uul buraat uul and tsunkheg deposits were investigated using microthermometry and laser raman spectroscopy pseudosecondary primary inclusions in the kyzyltau ore veins are predominantly liquid rich aqueous inclusions containing variable amounts of co 2 as the main gas component and showing n 2 ch 4 ratios 1 secondary inclusions contain no or only trace concentrations of gases as indicated by clathrate melting the t h values of pseudosecondary primary inclusions in veins are between 180 and 433 c fluid inclusion data indicate that phase separation processes leading to fluid immiscibility occurred in vuggy quartz ii and green fluorite ii in the ulaan uul and buraat uul ore veins phase separation pressures of 100 350 bars were estimated fluorite i from the kyzyltau ore field shows a strong enrichment of hree and a strong negative eu anomaly common for rare metal bearing ore systems fluorite ii from buraat uul and tsunkheg is characterized by a change in the incorporation of rare earth elements ree with decreasing hree contents and a decreasing eu anomaly the ree distribution patterns in fluorite ii from ulaan uul remained unchanged compared with fluorite i despite a strong increase in the total ree content a review of the literature shows that from high temperature fe rich k dominated brines cassiterite ores can precipitate in quartz veins together with fe chlorite and fe tourmaline bolivian type if phase separation of a gas rich low salinity and fe rich fluid occurs cassiterite wolframite ores may be deposited cornwall devon type the deposits of kyzyltau are characterized by low fe alteration assemblages a predominance of sodium over potassium high contents of ree and y and a lack of extended tin mineralization despite the tin potential of the ore systems fluid inclusion data as well as geochemical and geological indications suggest formation of the tungsten deposits near the tops of li f rich sub volcanic intrusions we interpret the ph of the mineralizing fluid to be the main factor controlling wolframite precipitation in the kyzyltau ore field fluid wall rock interactions a lowering of the temperature and unmixing processes in the ore fluid generated contributions to neutralization and buffering of the acid co 2 bearing fluid into a ph range where tungstates were precipitated it can be inferred that formation of tungsten ores without precipitation of extended tin mineralization is possible in deposits characterized by high potential tin and tungsten according to this inference tin mineralization may be found in a more favourable setting in the vicinity of the kyzyltau deposits

tectonically driven fluid flow and gold mineralisation in active collisional orogenic belts comparison between new zealand and western himalaya abstract hydrothermal activity and mesothermal styled gold mineralisation occurs near the main topographic divide of most active or young collisional mountain belts the southern alps of new zealand is used in this study as a model for the mineralising processes the collisional tectonics results in a two sided wedge shaped orogen into which rock is transported horizontally upper crustal rocks pass through the orogen and leave the orogen by erosion whereas lower crustal rocks are deformed into the mountain roots high relief drives meteoric water flow to near the brittle ductile transition lower to upper greenschist facies metamorphic reactions driven by deformation at the crustal decollement and in the root release water rich fluids that rise through the orogen intimate chemical interaction between fluid and rock results in dissolution and later precipitation of gold arsenic and sulphur fluid flow and mineralisation in the topographic divide region is facilitated by a network of steeply dipping faults and associated rock damage zones where oblique strike slip faults intersect the thrust faults that strike subparallel to the main mountain range the nanga parbat massif of the western himalaya is an example of an active collisional zone which hosts hydrothermal activity but no gold mineralisation the lack of gold mineralisation is due to the following factors co 2 dominated rising metamorphic fluid in dehydrated amphibolite granulite facies metamorphic rocks does not dissolve gold and arsenic hot up to 400 c meteoric water confined to fractures in the gneiss limits dissolution of gold and arsenic low density of hot water dry steam and low reduced sulphur content of fluid restrict solubility of gold and arsenic absence of fracture networks in the core of the massif and the small volumes of circulating fluid limit metal concentration and lack of reactive rock compositions limits chemically mediated metal deposition

morphological ripening of fluid inclusions and coupled zone refining in quartz crystals revealed by cathodoluminescence imaging implications for cl petrography fluid inclusion analysis and trace element geothermometry cathodoluminescence cl studies have previously shown that some secondary fluid inclusions in luminescent quartz are surrounded by dark non luminescent patches resulting from fracture sealing by late trace element poor quartz this finding has led to the tacit generalization that all dark cl patches indicate influx of low temperature late stage fluids in this study we have examined natural and synthetic hydrothermal quartz crystals using cl imaging supplemented by in situ elemental analysis the results lead us to propose that all natural liquid water bearing inclusions in quartz whether trapped on former crystal growth surfaces i e of primary origin or in healed fractures i e of pseudosecondary or secondary origin are surrounded by three dimensional non luminescent patches cross cutting relations show that the patches form after entrapment of the fluid inclusions and therefore they are not diagnostic of the timing of fluid entrapment instead the dark patches reveal the mechanism by which fluid inclusions spontaneously approach morphological equilibrium and purify their host quartz over geological time fluid inclusions that contain solvent water perpetually dissolve and reprecipitate their walls gradually adopting low energy euhedral and equant shapes defects in the host quartz constitute solubility gradients that drive physical migration of the inclusions over distances of tens of m commonly up to several mm rarely inclusions thus sequester from their walls any trace elements e g li al na ti present in excess of equilibrium concentrations thereby chemically purifying their host crystals in a process analogous to industrial zone refining non luminescent patches of quartz are left in their wake fluid inclusions that contain no liquid water as solvent e g inclusions of low density h2o vapor or other non aqueous volatiles do not undergo this process and therefore do not migrate do not modify their shapes with time and are not associated with dark cl zone refined patches this new understanding has implications for the interpretation of solids within fluid inclusions e g ti and al minerals and for the elemental analysis of hydrothermal and metamorphic quartz and its fluid inclusions by microbeam methods such as la icpms and sims as ti is a common trace element in quartz its sequestration by fluid inclusions and its depletion in zone refined patches impacts on applications of the ti in quartz geothermometer

multi fluid flow record during episodic mode i opening a microstructural and sims study cotiella thrust fault pyrenees abstract syntectonic veins commonly have been used to assess the composition and source of fluids involved in fault zone activity such veins also provide information on the ambient stress conditions during deformation and mineralization based on bulk sampling and bulk o and c isotope analysis combined with fluid inclusion microthermometry many studies have demonstrated that syntectonic veins provide snapshots of fluid composition and stress conditions over the course of fault history this is widely acknowledged for mode i extension veins that develop in the damage zones of faults however an important and unanswered question is the extent to which such veins record a more detailed fault history at the micron scale in this study we present new detailed in situ micron scale 18 o data measured using secondary ion mass spectrometry sims combined with detailed fluid inclusion microthermometry and 47 clumped isotope thermometry to document the fluid and temperature conditions during mode i vein growth related to deformation along the cotiella thrust fault pyrenees all the studied veins show three distinct episodes of vein opening recording a complex history of varying fluid composition and temperature results show that the studied fault portion passed from a hydrological rock buffered system in which formation waters were in isotopic equilibrium with the host sediments to a fluid buffered system involving meteoric water however such information is only achievable at the micron scale using secondary ion mass spectrometry this study demonstrates the potential of these new micro beam techniques for investigating fault behavior in more detail than previously available particularly with respect to the nature of the fluids involved and the p t conditions extant during fault activity

the gounkoto au deposit west africa constraints on ore genesis and volatile sources from petrological fluid inclusion and stable isotope data the loulo gounkoto complex in the kedougou kenieba inlier hosts three multi million ounce orogenic gold deposits situated along the senegal mali shear zone this west malian gold belt represents the largest west african orogenic gold district outside ghana the gounkoto deposit is hosted to the south of the gara and yalea gold mines in the kofi series metasedimentary rocks the ore body is structurally controlled and is characterised by sodic and phyllic alteration as and fe rich ore assemblages with abundant magnetite and overall enrichment in fe as cu au ag w ni co ree minor te pb se cd fluid inclusion analysis indicates that the deposit formed at p t conditions of approximately 1 4 kbar and 340 c and that two end member fluids were involved in mineralisation 1 a moderate temperature 315 340 c low salinity 10 wt nacl equiv low density 1 g cm 3 h2o co2 nacl h2s n2 ch4 fluid 2 a high temperature up to 445 c hypersaline 40 wt nacl equiv high density 1 3 g cm 3 h2o co2 nacl fecl2 fluid partial mixing of these fluids within the jog zone at gounkoto enhanced phase separation in the aqueo carbonic fluid and acted as a precipitation mechanism for au these findings demonstrate the widespread if heterogeneously distributed nature of fluid mixing as an ore forming process in the loulo gounkoto complex operating over at least a 30 km strike length of the shear zone stable isotope analyses of ore components at gounkoto indicate a dominant metamorphic source for h2o h2s and co2 and by extension au it thus can be reasoned that both the aqueo carbonic and the hypersaline fluid at gounkoto are of metamorphic origin and that the high levels of salinity in the brine are likely derived from evaporite dissolution

post nappe brittle tectonics and kinematic evolution of the north western alps an integrated approach abstract data from remote sensing structural geology and thermochronology provide the basis for this integrated reconstruction of the oligocene to present kinematic evolution of the north western alpine nappe stack two brittle tectonic phases post date the cretaceous eocene ductile deformation a nw se extension developed in the oligocene d1 along three main conjugate fault systems arranged in orthorhombic symmetry n nw and se dipping cooling rate contour maps from published apatite and zircon fission track ages and rb sr biotite ages highlight the differential exhumation of large fault bounded blocks during this phase whilst synkinematic hydrothermal veins and calc alkaline dykes 29 32 ma help to constrain its age from the miocene onwards a general rearrangement of the strain pattern led to sw directed lateral extrusion d2 of the pennine graian alps block bounded by a network of seismogenic shear zones the most important being the ospizio sottile simplon rhone and chamonix faults the internal deformation of the pennine graian alps block is characterised by an overall more or less homogeneous ne sw extension the approach undertaken integrating remote sensing structural analysis on different scales and thermochronology with the cooling rate map representation is therefore effective in reconstructing the late orogenic extensional tectonic evolution of metamorphic nappe stacks

late kinematic timing of orogenic gold deposits and significance for computer based exploration techniques with emphasis on the yilgarn block western australia abstract orogenic gold deposits are a widespread coherent group of epigenetic ore deposits that are sited in accretionary or collisional orogens they formed over a large crustal depth range from deep seated low salinity h2o co2 ch4 n2 ore fluids and with au transported as thio complexes regional structures provide the main control on deposit distribution in many terranes first order faults or shear zones appear to have controlled regional fluid flow with greatest ore fluid fluxes in and adjacent to lower order faults shear zones and or large folds highly competent and or chemically reactive rocks are the most common hosts to the larger deposits focusing of supralithostatic ore fluids into dilatant zones appears to occur late during the evolutionary history of the host terranes normally within d3 or d4 in a d1 d4 deformation sequence reactivation of suitably oriented pre existing structures during a change in far field stress orientation is a factor common to many deposits and repeated reactivation may account for multiple mineralization episodes in some larger deposits absolute robust ages of mineralization support their late kinematic timing and in general suggest that deposits formed diachronously towards the end of the 100 to 200 m y long evolutionary history of hosting orogens for example in the yilgarn block a region specifically emphasised in this study orogenic gold deposits formed in the time interval between 40 and 90 m y with most about 60 to 70 m y after the youngest widespread basic ultrabasic volcanism and towards the end of felsic magmatism the late timing of orogenic gold deposits is pivotal to geologically based exploration methodologies this is because the present structural geometries of i the deposits ii the hosting goldfields and iii the enclosing terranes are all essentially similar to those during gold mineralization at least in their relative position to each other thus interpretation of geological maps and cross sections and three dimensional models can be used to accurately simulate the physical conditions that existed at the time of ore deposition it is particularly significant that the deposits are commonly related to repetitive and predictable geometries such as structural heterogeneities within or adjacent to first order structures around rigid granitoid bodies or in specific locked up fold thrust structures importantly the two giant greenstone hosted goldfields kalgoorlie and timmins show a remarkably similar geometry at the regional scale computer based stress mapping and gis based prospectivity mapping are two computer based quantitative methodologies that can utilize and take advantage of the late timing aspect of this deposit type to provide important geological aids in exploration both in broad regions and more localized goldfields both require an accurate and consistent solid geology map stress mapping requires knowledge of the far field stresses during mineralization and the empirical prospectivity mapping requires data from a significant number of known deposits in the terrane the kalgoorlie terrane in the yilgarn block meets these criteria and illustrates the potential of these methodologies in the exploration for orogenic gold deposits low minimum stress anomalies interpreted to represent dilational zones during gold related deformation coincide well with the positions of known goldfields rather than individual gold deposits in the terrane and there are additional as yet unexplained anomalies the prospectivity analysis confirms that predictable and repetitive factors controlling the siting of deposits are i proximity to and orientation and curvature of granitoid greenstone contacts ii proximity to segments of crustal faults which strike in a preferred direction iii proximity to specific lithological contacts which have similar preferred strike iv proximity to anticlinal structures and v the presence of preferred reactive host rocks e g dolerite the prospectivity map defines a series of anomalous areas which broadly conform to those of the stress map 78 correspondence the most prospective category on this map covers less than 0 3 of the greenstone belts and yet hosts 16 of the known deposits which have produced 80 of known gold thus it discriminates in favour of the larger economically more attractive deposits in the terrane the successful application of stress mapping and prospectivity mapping to geology based exploration for orogenic gold deposits indicates that more quantitative analysis of geological map data is a profitable line of research the computer based nature of these methodologies is ideal for the production of an ultimate integrated deposit target map which can be compared to other more conventional targeting parameters such as geophysical and geochemical anomalies such an integrated strategy appears the way forward in the increasingly difficult task of cost effective global exploration for orogenic gold deposits in poorly exposed terranes

evolution of brines and co2 rich fluids and hydrothermal overprinting in the genesis of the borrachudo copper deposit carajas province abstract the carajas province is one of the world s major domains of iron oxide copper gold iocg deposits which formed during the neoarchean ca 2 70 2 68 ga and ca 2 57 ga the province also hosts other copper gold deposits of paleoproterozoic age ca 1 88 ga the borrachudo copper deposit is located about 6 km southwest of the world class cristalino iocg deposit porphyritic rhyolite and amygdaloidal andesite of the ca 2 76 2 74 ga grao para group formed in a volcano plutonic event during the neoarchean are the main host to the borrachudo deposit copper mineralization was related to two distinct hydrothermal events the first controlled by the development of ductile structures was likely linked to the carajas ca 2 70 ga iocg system it evolved from sodic alteration silicification and iron metasomatism through to calcic and potassic alteration chalcopyrite strings along foliation breccias and massive ore represent early copper mineralization during the early hydrothermal event aqueous 165 to 400 c 0 23 to 38 32 wt nacl equiv aqueous carbonic and carbonic fluid inclusions tmco2 60 1 to 59 4 c co2 density of 0 82 to 0 97 g cm3 were trapped in quartz formed during the silicification immiscibility of a magmatic fluid or heterogeneous trapping of brines and co2 bearing fluids followed by mixing with diluted colder fluids are suggested the late event controlled by brittle structures records recurrence of hydrothermal alteration stages such as silicification sodic alteration and potassic alteration as well as chlorite and carbonate alteration the copper mineralization is represented by chalcopyrite in branched breccia pipes and veins with minor magnetite pyrite siegenite cobaltite galena anglesite uraninite and thorite titanite in veins of albite chalcopyrite apatite yielded an la icp ms u pb titanite age of 2011 6 8 ma during the late hydrothermal event aqueous fluids 140 to 320 c 6 7 to 40 wt nacl equiv reflected a more advanced mixing process involving diluted external fluids the borrachudo deposit points to the recurrence of multiple hydrothermal events responsible for the copper metallogenesis which were intrinsically controlled by the magmatic and tectonic evolution of the carajas province

integrated stratigraphy and paleontology of the lower miocene monte leon formation southeastern patagonia argentina unraveling paleoenvironmental changes and factors controlling sedimentation abstract marine sedimentary rocks of the lower miocene monte leon formation of southeastern patagonia austral basin argentina are important geological archives for better understanding regional tectonics paleoenvironments oceanography and climate in this paper we describe assemblages of invertebrates palynomorphs foraminifera ostracods and calcareous nannofossils in a stratigraphical and sedimentological framework which suggest deposition during a transgressive regressive cycle from base to top the lowermost outcropping deposits of the punta entrada member represent an inner shelf environment formed during a transgressive phase the zone of maximum flooding is marked by a high diversity of protoperidiniaceans heterotrophic and offshore dinoflagellate cysts an increase in the percentage and size of planktonic foraminifera and a decrease in shallow water benthic foraminifera regressive deposits in the upper part of the punta entrada member exhibit a progradational stratal stacking pattern and are characterized by an upward decrease in bioturbation and in the content of marine invertebrates the dinoflagellate cyst assemblages point toward shallower and more restricted marine conditions than in underlying deposits the cycle ends with the monte observacion member which contains an impoverished and mostly reworked fauna of invertebrates the presence of monospecific reefs of crassostrea orbignyi the decrease in dinoflagellate cysts and calcareous microfossils diversity and the increase of continental palynomorphs suggest progressively shallower conditions and increasing influence of freshwater discharge although eustatic controls could have contributed to the sedimentary evolution of the monte leon formation the upward regressive trend is interpreted as the result of tectonism linked to the andean orogeny which led to the uplift exhumation and erosion of the highlands in the west this is supported by the abundance of pyroclastic material together with reworked specimens of upper cretaceous forams and upper cretaceous and middle eocene dinoflagellate cysts in the upper part of the punta entrada member and in the monte observacion member