formation of the fanshan lithocap and implications for exploration in the luzong basin anhui province china abstract lithocaps in island arc settings are genetically related to porphyry epithermal systems and can be used to guide exploration for porphyry deposits the fanshan area of the luzong basin in the eastern china hosts a large lithocap but no porphyry or epithermal deposits have been found the fanshan lithocap in the luzong basin is centred on the dafanshan alunite mining district with vuggy quartz alunite pyrite quartz dickite kaolinite alunite quartz kaolinite and kaolinite illite smectite from northeast to southeast the alteration zoning reflects the gradual decrease in the temperatures and acidities of the fluids four types of alunite including bladed alunite needle alunite granular alunite and powdery alunite suggest that the fanshan lithocap formed in the magmatic hydrothermal and supergene environment from the southwest to the northeast of the dafanshan district pb and 106pb na k in the alunite samples gradually decrease au content gradually increases but the cu content does not change significantly the peak positions at 1480 nm and the na content of the magmatic hydrothermal alunite gradually increase whereas pb and 106pb na k in the alunite minerals gradually decrease this suggests that the source of the hydrothermal fluids and a potential zone of precious metal mineralization area may be in the northeast of the dafanshan district and the potential area of copper mineralization may be in the huangtun area northeast of the luzong basin

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

magmatic hydrothermal activity in the shuteen area south mongolia the shuteen area is located in the gurvansaikhan island arc terrane of south mongolia it contains a large domain of intensely developed silicic and advanced argillic alteration that has strongly affected the adakitic volcanoplutonic shuteen complex the local occurrence of low grade copper mineralization within porphyritic intrusive rocks is indicative of porphyry style mineralization hydrothermal quartz veins host gold mineralization locally the results of scanning electron microscope cathodoluminescence imaging and fluid inclusion microthermometry indicate that the veins and altered rocks at shuteen were produced by multiple hydrothermal events the occurrence of co2 inclusions in quartz from granitoids and the 34s values obtained for sulfide and sulfate within the hydrothermal breccias provide evidence of the involvement of magmatically derived fluids in the early stages of the shuteen magmatic hydrothermal system inferred to be sourced from a porphyry style intrusive center late stage fluids produced abundant barren quartz veins and clay alteration assemblages the weak mineralization and widespread alteration in the shuteen complex are typical of lithocaps found in high level porphyry copper gold molybdenum and high sulfidation epithermal districts the presentday erosion level at shuteen is relatively shallow implying that economic porphyry style mineralization may exist at depth within or beneath the shuteen lithocap

emplacement temperature determinations of proximal pyroclastic deposits on santorini greece and their implications this paper presents the results of a study undertaken to determine emplacement temperatures of volcanic deposits on the volcano of santorini greece using palaeomagnetic methods two types of breccia have been identified on santorini lithic lag breccias and ground breccias they have been interpreted as deposits from pyroclastic flows however where the breccia deposits are not intimately associated with ignimbrite their origin is ambiguous emplacement temperature determinations were carried out on lithic clasts within these deposits to assess the origin and to place constraints on their emplacement mechanisms the results of thermal demagnetization show that all the clasts display at present earth s field component of magnetization the earth s field component indicates that these clasts have cooled from elevated temperatures within the deposits therefore these breccia deposits were emplaced hot verifying their origin as primary products of pyroclastic eruption many of the deposits display a wide range of emplacement temperatures and the lowest temperature at any one location probably represents the equilibrium temperature of the deposit an emplacement temperature determination records the highest temperature experienced by the clast before cooling in situ these clasts may have been heated before during or after the eruption in estimating the emplacement temperature it is important to understand at what stage the clasts were heated thermal modelling was carried out to assess the effects of heating of the clasts a during the eruption and subsequent transport by hot gases and juvenile pyroclasts within pyroclastic flows and b by an overlying hot deposit such as a pyroclastic deposit or lava flow results from this study indicate that many of the clasts were hot before incorporation took place this indicates that clasts were either derived from depth within the volcano or that there were abundant rocks at elevated temperature near or at the surface

evolution of magmatic vapor to gold rich epithermal liquid the porphyry to epithermal transition at nevados de famatina northwest argentina fluid inclusions in the subeconomic porphyry cu mo au system at nevados de famatina and closely associated high sulfidation epithermal cu au ag as sb te veins at la mejicana northwest argentina were studied to reconstruct the evolution of hydrothermal fluids from their deep magmatic source to the shallow epithermal environment field geology vein petrography fluid inclusion microthermometry and single inclusion microanalysis by laser ablation inductively coupled plasma mass spectrometry la icp ms were combined to determine the evolution of pressure temperature and ore metal concentrations in the fluids cathodoluminescence imaging complements transmitted light petrography to constrain the successive stages of quartz formation and the entrapment sequence of the fluid inclusion populations aqueous liquid inclusions of 5 wt percent nacl equiv salinity trapped in quartz sericite pyrite qsp veins between 360 and 325 c contain unusually high concentrations of cu 400 5 000 ppm as 200 ppm sb and te both up to 100 ppm and au several ppm along with other ore forming elements these veins are paragenetically transitional between subeconomic porphyry copper mineralization exposed in the valley floor and high sulfidation epithermal veins with high au grades which are preserved along a high ridge adjacent to the porphyry stock low density vapor and hypersaline liquid i e brine inclusions were trapped in early formed quartz of the porphyry stockwork veins between 450 and 600 c the brine contains lower cu and au concentrations than coexisting vapor inclusions and texturally even earlier inclusions of intermediate density that are trapped in phenocrysts and some stockwork veins the latter may be equivalent to a parental fluid the low and intermediate density fluids compositionally overlap in salinity with the aqueous liquids recorded by the later transitional quartz sericite pyrite veins fluid inclusions and geologic time relations indicate that the transitional quartz sericite pyrite veins were the channelways for metal rich aqueous liquids that generated the high sulfidation epithermal cu au deposit these mineralizing liquids are interpreted to have evolved by continuous density increase contraction from a low salinity s rich magmatic fluid of low to intermediate density this vaporlike fluid was produced by exsolution from a magma that existed at greater depth during the late stages of cooling of the magmatic hydrothermal complex and probably underwent minor brine separation prior to reaching the present level of exposure epithermal mineral precipitation occurred upon dilution of the low salinity magmatic fluid with meteoric water which entered the hydrothermal system as it was cooled and successively eroded during continued magmatic fluid ascent

discolored seawater detection using aster reflectance products a case study of satsuma iwojima japan discolored seawater caused by volcanic activity can be detected with satellite remote sensing at some submarine volcanoes and volcanoes near coastlines we demonstrate that two kinds of discolored seawaters can be discriminated by their reflectance patterns using aster reflectance products at satsuma iwojima japan white to green seawater that is due to hydrous oxides formed when al and fe rich acidic waters mix with seawater shows high medium and low reflectances at band 1 central wavelength 0 56 m band 2 central wavelength 0 66 m and band 3 central wavelength 0 81 m respectively on the other hand reddish brown seawater that is due to the outflow of neutral ph iron bicarbonate water shows high reflectance at band 2 medium reflectance at band 1 and low reflectance at band 3 the chemical composition of discolored seawater which is one of the characteristics of volcanic activity can be estimated from remote sensing data the aster reflectance product is a standard validated product generated by the aster ground data system using an atmospheric correction

experimental evidence for a relationship between liquid immiscibility and ore formation in felsic magmas abstract geological studies demonstrate that liquid immiscibility in felsic magma closely associates with the ore forming process in order to obtain experimental evidence demonstrating the relationship between the ore forming process and liquid immiscibility in felsic magma we carried out a series of experiments at high temperature and atmospheric pressure the experimental results show that the granite kbf 4 na 2 moo 4 system is a homogeneous melt at high temperature with decrease in temperature however the melt decomposes into two immiscible melts silicate melt and ore forming melt the ore forming melt exists as globules in the silicate phase molybdenm ca na mg p mn f b and oh are concentrated in these globules the ore forming melt is characterized with very low sio 2 and al 2 o 3 concentrations but the concentration of moo 3 and cao is very high in contrast the silicate melts are significantly enriched in sio 2 and al 2 o 3 and depleted in moo 3 and cao in the silicate melt the concentrations of network modifying elements e g mo ca na p mg and volatiles f oh are very low the differences between the two immiscible melts exist not only in chemical composition but also in structure the ore forming melt structurally consists of moo 4 moof 4 b oh 4 and oh while the silicate melt is si0 4 because of the difference in composition and structure the two immiscible melts possess different physical properties compared to silicate melt the ore forming melt has a lower density and viscosity which permits the globules to behave as bubbles in granite magma and to move and concentrate in the upper part of magma chamber this process is probably responsible for the concentration of ore forming elements in the upper part of granite bodies and their immediate aureoles the present experimental results suggest that liquation in felsic magma can be the first step in the ore forming process during granitoid evolution

submarine venting of magmatic volatiles in the eastern manus basin papua new guinea abstract the susu knolls and desmos hydrothermal fields are located in the back arc extensional transform zone of the eastern manus basin in 2006 highly acidic and so4 rich vent fluids were collected at both sites and analyzed for the chemical and isotopic composition of major and trace species fluids exiting the seafloor have measured temperatures from 48 to 215 c and are milky white in appearance due to precipitation of elemental s0 vent fluid concentrations of na k and mg are depleted by as much as 30 relative to seawater but have the same relative abundance in contrast the fluids are highly enriched in dissolved co2 cl sio2 aq fe and al relative to seawater measured ph 25 c ranged from 0 95 to 1 87 and aqueous so4 ranged from 35 to 135 mmol kg the chemical and isotopic composition points to formation via subsurface mixing of seawater with a na k mg and ca free volatile rich magmatic fluid exsolved from subsurface magma bodies during a process analogous to subaerial fumarole discharge estimates of the magmatic end member composition indicate a fluid phase where h2o so2 co2 cl f the hydrogen and oxygen isotopic composition of h2o and carbon isotopic composition of co2 in the vent fluids strongly suggest a contribution of slab derived h2o and co2 to melts generated in the mantle beneath the eastern manus volcanic zone abundant magmatically derived so2 undergoes disproportionation during cooling in upflow zones and contributes abundant acidity so42 and s0 to the venting fluids interaction of these highly acidic fluids with highly altered mineral assemblages in the upflow zone are responsible for extensive aqueous mobilization of sio2 aq fe and al temporal variability in the speciation and abundance of aqueous s species between 1995 and 2006 at the desmos vent field suggests an increase in the relative abundance of so2 in the magmatic end member that has mixed with seawater in the subsurface results of this study constrain processes responsible for the formation of hot spring fluids in magmatically active back arc environments and the resulting chemical exchange between the lithosphere and water column

degassing of stratified magma by compositional convection abstract a new model is proposed for passive degassing from sub volcanic magma chambers the water content in stably stratified shallow magma chamber will be equated to its solubility at the upper boundary by convection water from a lower layer high in water content can enrich the contact zone of the upper layer and lead to further convective overturn of this boundary layer a complete set of equations describing convection with bubble formation and dissolution is reduced to a simplified form by assuming a small bubble content the development and pattern of flow driven by vesiculation is modeled numerically in a 2d magma chamber for relatively low raleigh numbers 5 105 bubbles rising from the magma will collect near the roof in a layer of 8 10 vol and then escape upward to fumaroles the stokes flux of bubbles escaping from an andesitic magma with viscosity 104 p and a top surface of about 500 500 m corresponds with observed total magmatic water fluxes of 35 kg s pressure within the chamber is buffered by elastic and local visco elastic deformations in the solid rocks bounding the chamber to the range between ambient and close to lithostatic values in a chamber closed to fresh magma inputs the decrease in volume due to such gentle volatile escape lowers the reference pressure bubbles flux from the lower layer induced by variation of the saturation level around stratification boundary may be efficient mechanism for the water transport between layers

the rosita hills epithermal ag base metal deposits colorado usa a stable isotope and fluid inclusion study the rosita hills volcanic centre is an alkalicalcic mid tertiary complex overlying orthoand paragneissic basement on the eastern margin of the rio grande rift in south central colorado usa the centre contains vein hosted adularia sericite type epithermal ag and base metal mineralisation with minor au stable isotope studies o and h of whole rock and mineral separate quartz and sericite samples from veins and hydrothermal eruption breccias show that the hydrothermal fluid had both magmatic and meteoric components the d and 18o values of the hydrothermal fluid calculated from mineral values range from 22 to 103 and 0 5 to 5 9 respectively fluid inclusion data from vein minerals quartz baryte and sphalerite and from an advanced argillic lithocap overlying the veins again show that the hydrothermal system had more than one component fluid fluid inclusions have salinities which range from 1 7 to 25 1 wt nacl equivalent and show evidence of boiling in the advanced argillic lithocap homogenisation temperatures range from 135 c to 298 c liquid co2 is present in some inclusions these data indicate that a saline isotopically heavy fluid mixed with a dilute isotopically light fluid to precipitate the ore we argue that the saline isotopically heavy fluid is magmatic and derived from a resurgent rhyolitic magma below the mineralisation

the behavior of metals pb zn as mo cu during crystallization and degassing of rhyolites from the okataina volcanic center taupo volcanic zone new zealand tthe taupo volcanic zone tvz new zealand is a region of voluminous and frequent rhyolitic volcanism and widespread geothermal activity additionally the hydrothermal systems of the tvz contain relatively high concentrations of base and precious metals here we present an extensive dataset of major element volatile and trace element including pb zn as mo cu abundances in melt inclusions pumice glasses and minerals from eight eruptions within the okataina volcanic center ovc of the tvz to investigate the behavior of metals during melt evolution the high sio2 rhyolites of the ovc contain high concentrations of volatiles 6 wt h2o 0 25 wt cl and underwent significant degassing prior to and during eruption the ovc melts contain moderate concentrations of metals 11 24 ppm pb 20 50 ppm zn 2 7 ppm as 2 5 ppm mo 5 ppm cu ferromagnesian minerals amphibole biotite and orthopyroxene in the ovc pumice have high concentrations of zn 1500 ppm and plagioclase and biotite contain moderate amounts of pb 11 ppm the melt inclusion and pumice glass trace element data reveal complex histories of magma mixing and mingling prior to eruption however discrete melt batches are easily identified based on trace element geochemistry variations in incompatible trace elements within these melt batches suggest that the ovc rhyolites underwent at least 20 25 fractional crystallization during quartz crystallization and melt inclusion entrapment at pressures of 100 200 mpa and little to no crystallization 5 during ascent and eruption comparison of melt inclusion metal and incompatible element e g u concentrations reveals that melt pb mo and as increase whereas melt zn decreases during fractional crystallization at depth 100 200 mpa these observations can be explained by minor partitioning of the metals pb mo and as into the fractionating minerals and stronger partitioning of zn into the ferromagnesian phases supported by calculated metal d values and analyzed metal concentrations in ovc minerals interestingly throughout both deep vapor saturated crystallization and during extensive degassing during magma ascent and eruption as recorded by pumice glasses the metals analyzed here do not appear to partition appreciably into the vapor we propose that the lack of volatility of the metals analyzed in this study can be attributed to a combination of several factors first vapor melt partitioning requires the presence of ligands commonly cl s and oh with which the metals may complex given the low cl h2o ratios in the ovc melts and the extensive degassing of h2o compared with cl it seems likely that the rhyolites would have exsolved h2o rich vapor with insufficient cl to transport metals in particular pb and zn into the vapor phase either at depth or during magma ascent second the overall small volumes of vapor present during crystallization at pressures of 100 200 mpa would have impeded significant vapor melt partitioning of the metals finally the estimated very rapid ascent of the ovc melts from depths of 4 8 km suggests that there was insufficient time at low pressure for diffusion of metals out of the melt these results imply that there may be an indirect connection between the rhyolites and the metals of the hydrothermal systems of the tvz as the metals and other species such as cl remain in the rhyolitic magmas upon eruption they are available in the large volumes of rhyolite emplaced in the upper crust of the tvz for leaching by heated meteoric waters

modeling the formation of advanced argillic lithocaps volcanic vapor condensation above porphyry intrusions hypogene advanced argillic alteration typically quartz alunite with halos of kaolinite dickite and roots of pyrophyllite diaspore forms in the epithermal environment from condensates of magmatic vapor that contain so2 and hcl which exsolved from an underlying intrusive source the most aggressive nearly isochemical leaching of the host rock by the most acidic condensate commonly ph 1 leaves residual silica that recrystallizes to quartz within the flow channel at a high condensate rock ratio forming the core of alteration the alteration characteristically flares upward along feeder structures and if a permeable lithologic unit is intersected the alteration zones mushroom to form a subhorizontal blanket due to lateral flow where subsequently mineralized the residual quartz commonly with a vuggy texture that reflects the texture of the original lithology has higher au and cu grades than the quartz alunite halo tonnage in these high sulfidation systems may develop within the subhorizontal lithocap although the highest grades are typically confined to the structurally controlled feeders we modeled a typical volcanic vapor condensate starting with the measured composition of 877 c fumaroles from satsuma iwojima rhyolite dome japan as it cooled and reacted with a host rhyolite the predicted hydrothermal mineralogy reproduces the alteration pattern observed in lithocaps that host high sulfidation deposits the modeling confirms that aluminum rich minerals pyrophyllite diaspore locally andalusite are stable at higher temperature at depth whereas at lower temperature and shallower depth na and k alunite become stable at the lowest temperature 10 1 and where so2 h2s in the original volcanic vapor this so2 dominant composition is typical of andesitic to rhyolitic volcanoes the reason for this mineral transition and the upward flare widening of the alteration zone along structures is related to the dissociation and increased reactivity of h2so4 and hcl as the temperature decreases below 200 c only quartz pyrite native s and anhydrite are stable hence the formation of the dominant quartz from the silica residue a further check on our modeling is the observation that the calculated composition of the condensate after reaction with fresh satsuma iwojima rhyolite and alteration minerals and cooling to 100 c is similar within a factor of two to that of acidic springs with ph 1 that discharge around satsuma iwojima and other active volcanoes the most extensive lithocap alteration residual quartz and or quartz alunite is commonly offset from the surface projection of the causative intrusion this observation can be explained by a combination of two factors hydrology and temperature due to hydraulic gradients at shallow depths in a volcanic edifice the acidic condensate tends to flow along permeable lithologic units away from the locus of the high temperature vapor plume which rises directly over the intrusion where lateral flow occurs the most intense leaching and widespread advanced argillic alteration which develops largely at temperatures of 200 to 250 c based on our modeling will form away from the near surface projection of the intrusion which is the area of highest surface temperature due to ascent of the vapor plume this potential for lithocap alteration to form on the shoulder of the underlying causative intrusion must be assessed when exploring for high sulfidation ore the highest ore grades are commonly related to structures that are proximal to the parent intrusion but they are unlikely to lie directly over the intrusion in addition identifying the most likely location of the source intrusion will help the explorer to efficiently assess any potential for deeper porphyry style mineralization

porphyry epithermal transition maricunga belt northern chile the refugio aldebaran and la pepa districts in the maricunga belt of northern chile contain advanced argillic alteration zones that locally host high sulfidation epithermal gold deposits in proximity to porphyry gold copper deposits the spatial association suggests a genetic link mineralized zones are characterized by four main vein types that formed at different times and have specific zonal relationships a veinlets are the earliest and deepest vein type they are restricted to potassic alteration zones in intrusive rocks a veinlets contain variable amounts of quartz magnetite biotite and chalcopyrite and locally have k feldspar halos they have nonmatching irregular vein walls and lack internal symmetry hypersaline liquid rich inclusions coexisting with vapor rich inclusions in a veinlets indicate temperatures as high as nearly 700 c and pressures between 200 and 400 bars assuming a lithostatic load depths of 0 8 to 1 6 km are inferred zones of abundant a veinlets contain mostly 1 ppm gold and 0 1 to 0 4 percent hypogene copper banded quartz veinlets occur mostly above a veinlets and cut a veinlets where they overlap dark gray bands the color resulting from a high density of vapor rich fluid inclusions and micron sized grains of magnetite commonly occur as symmetric pairs near the vein walls vein walls are parallel and slightly wavy vuggy vein centers are common and alteration envelopes are absent data from rare liquid rich inclusions in banded quartz veinlets indicate temperatures 350 c at pressures between 20 and 150 bars assuming a hydrostatic load depths of 0 2 to 1 5 km are inferred zones of abundant banded quartz veinlets generally contain 0 5 to 2 ppm gold and 0 1 percent hypogene copper d veins are pyrite veins with quartz sericite pyrite halos they are widespread and crosscut a veinlets and banded quartz veinlets the brittle nature of d veins and limited fluid inclusion data suggest temperatures 400 c d veins serve as important time lines they are nowhere truncated or crosscut by intrusions a veinlets or banded quartz veinlets quartz alunite replacement veins referred to as ledges in this paper are typical of the high sulfidation epithermal environment they are mostly limited to overlying volcanic rocks they contain local core zones of vuggy residual quartz that can contain enargite or at higher elevations barite of the three districts studied only la pepa has mineable quartz alunite ledges which contain an average gold grade of about 20 ppm a spectrum of porphyry style deposits exists cerro casale at aldebaran shares many characteristics of porphyry copper deposits worldwide whereas verde at refugio is a true porphyry gold deposit potassic alteration zones and a veinlets are strongly developed at cerro casale whereas they are absent at verde banded quartz veinlets predominate at verde whereas they occur only at the upper levels of cerro casale the pancho deposit at refugio and the cavancha deposit at la pepa are telescoped systems in which banded quartz veinlets overprint potassic alteration zones and a veinlets a veinlets and banded quartz veinlets cut and are cut by intrusions indicating multiple cycles of intrusion potassic alteration a veinlets banded quartz veinlets during formation of porphyry style mineralization banded quartz veinlets are thought to have formed by flashing of magmatic fluids during episodic transitions from lithostatic to hydrostatic pressure loss of sulfur to the vapor phase during flashing inhibited formation of copper sulfides in banded quartz veinlets and therefore resulted in high gold copper ratios where rising magmatic vapors condensed into overlying meteoric water along faults barren quartz alunite ledges formed this conclusion is supported by equivalent 40ar 39ar dates on hydrothermal biotite associated with porphyry style ore and alunite from barren ledges at aldebaran 40ar 39ar dates at la pepa indicate alunite formed at least 140 000 years to as long as 900 000 years after hydrothermal biotite within the high sulfidation epithermal environment the development of ore depends on the ability of late moderate salinity magmatic fluids to reach the surface without condensing a brine upon ascent cooling and boiling of the moderate salinity fluid below its critical temperature results in the formation of sericite at depth and alunite near the surface that is essentially synchronous with high sulfidation ore formation the timing of the switch from lithostatic pressures to brittle hydrostatic conditions relative to the life of the hydrothermal system might determine how much porphyry style ore forms relative to high sulfidation epithermal ore

experimental constraints on metal transport in fumarolic gases abstract metals are efficiently transported in a gas phase and the gas composition strongly affects transport rates of these metals in the gas phase here we present a new approach to systematically investigate metal transport and deposition from volcanic gases of different compositions we test the effect of sulfur and chlorine on the volatilization of 30 metal oxides and the phases deposited along a temperature gradient of 1250 300 c in evacuated silica glass tubes in water free systems in total we observe 30 different deposited phases including oxides sulfides and chlorides the experimental results are compared with closed system and open system thermochemical equilibrium calculations the closed system calculations provide insights into the metal speciation in the gas phase and the open system calculations provide thermodynamic predictions of the temperature ranges over which metals deposited from the gas phase both approaches only partially reproduce the experimental observations of the deposited phases in the silica glass tubes however when we compare our experimental results with records from fumaroles on three different volcanoes kudriavy volcano russia la fossa crater on vulcano italy and momotombo nicaragua we find that our experiments agree very well with natural observations we suggest that similar experimental investigations are powerful tools in the study of metal transport in ore forming systems involving gas phases and results may be applied to various processes in terrestrial and planetary environments

native gold from volcanic gases at tolbachik 1975 76 and 2012 13 fissure eruptions kamchatka abstract aggregates and euhedral crystals of native gold were found in sublimates formed during new tolbachik fissure eruption in 2012 2013 ntfe gold bearing sublimate samples were taken from a red hot 690 c degassing fracture in the roof of an active lava tunnel 1 5 km from active naboko cinder cone in may 2013 the gas condensate collected at 690 c in this site contains 16 ppb au 190 ppb ag and 1180 ppm cu compared to 3 ppb au 39 ppb ag and 9 7 ppm cu in the condensate of pristine magmatic gas sampled at 1030 c the 690 c volcanic gas is most likely a mix of magmatic gas and local snow buried under the lava flows as indicated by oxygen and hydrogen isotope compositions of the condensate the lower temperature gas enrichment in gold copper and chlorine is resulted from evaporation of the 690 c condensate during forced gas pumping at sampling native gold was also found in fumarolic encrustations collected from caverns in basalt lava flows with temperature up to 600 c in june 2014 in a year after eruption finished the native gold precipitation in newly formed cu rich sublimates together with the well known gold occurrences in cinder cones of 1975 1976 large tolbachik fissure eruption manifest a transport capability of oxidized volcanic gas

rare earth element abundances in hydrothermal fluids from the manus basin papua new guinea indicators of sub seafloor hydrothermal processes in back arc basins abstract rare earth element ree concentrations are reported for a large suite of seafloor vent fluids from four hydrothermal systems in the manus back arc basin vienna woods pacmanus desmos and susu knolls vent areas sampled vent fluids show a wide range of absolute ree concentrations and chondrite normalized reen distribution patterns lan smn 0 6 11 lan ybn 0 6 71 eu n eu n 1 55 reen distribution patterns in different vent fluids range from light ree enriched to mid and heavy ree enriched to flat and have a range of positive eu anomalies this heterogeneity contrasts markedly with relatively uniform reen distribution patterns of mid ocean ridge hydrothermal fluids in manus basin fluids aqueous ree compositions do not inherit directly or show a clear relationship with the ree compositions of primary crustal rocks with which hydrothermal fluids interact these results suggest that the rees are less sensitive indicators of primary crustal rock composition despite crustal rocks being the dominant source of rees in submarine hydrothermal fluids in contrast differences in aqueous ree compositions are consistently correlated with differences in fluid ph and ligand chloride fluoride and sulfate concentrations our results suggest that the rees can be used as an indicator of the type of magmatic acid volatile i e presence of hf so2 degassing in submarine hydrothermal systems additional fluid data suggest that near seafloor mixing between high temperature hydrothermal fluid and locally entrained seawater at many vent areas in the manus basin causes anhydrite precipitation anhydrite effectively incorporates ree and likely affects measured fluid ree concentrations but does not affect their relative distributions

determination of easily accessible metal fractions in rocks by batch leaching with acid cation exchange resin the easily accessible fraction of metals in rocks is derived from leaching experiments aliquots of rock powders are mixed with ion exchange resin and distilled water the ph self adjusts to a value of 3 after batch leaching times of 2 48 hr at 70 c the resin is quantitatively separated from the rock powder and eluted with 4 n hno3 the metal contents of the leachates are determined and related to the respective contents of the whole rock the leaching kinetics of each element is related to that of a reference element aluminium is most commonly chosen as a reference element because it is considered to represent the dissolution behaviour of the main rock forming minerals the easily accessible trace element fraction eat is given as the percentage of leached element at 1 al dissolution these eat values are reproducible and independent from grain size and sample resin ratio the procedure is tested on basaltic glass and variably altered gneisses the glass shows congruent release of all metals a slightly crystalline glass of the same chemical composition displays heterogeneous leaching behaviour the leaching kinetics of variably altered gneisses provide insight into the mineralogical siting of elements and their accessibility to fluids consequences for rb sr dating of rocks are discussed

trace elements in the gas emissions from the erta ale volcano afar ethiopia high temperature 1084 c fumarolic emissions from a spatter cone at the erta ale north pit crater granted a rare opportunity to collect giggenbach bottles condensates and sublimates from the fumarolic gases of a rift plume volcano in the immediate proximity of degassing lava these results represent the highest temperature gases sampled directly for trace elements and the first high t fumarolic samples for a rift plume volcano sixty seven metals and metalloids were measured quantitatively by icp aes and icp ms in liquid gas condensates and solid sublimates the total amount of trace elements in the gas without si exceeded 170 ppm the ten most abundant elements transported in nonsilicate modes were na 61 ppm fe 41 ppm k 32 ppm br 12 4 ppm cd 3 0 ppm se 2 3 ppm cu 2 0 ppm zn 2 0 ppm te 1 7 ppm and as 1 2 ppm the gases contained 27 ppb re 1 5 ppb au 0 5 ppb pt and 0 27 ppb os rh and pd containing phases were observed in solid sublimates the only metal not detected by all analytical methods was ruthenium chalcophile elements cd cu zn se te as were transported primarily in the gaseous form alkali metals were emitted at least partially as liquid micron size sulfate droplets whereas alkali earths aluminum and ree had a high affinity to silicate aerosol in the form of basaltic microspheres the silicate aerosol content was evaluated at 59 ppm on average but varied within a 7 5 fold range during sampling because of the extremely high temperature refractory elements ca ba ta u and lree showed evidence of transport in the form of gaseous species the so2 flux in january 2011 was evaluated at 91 24 t d for the entire volcano including 31 t d from the north crater and 60 t d from the lava lake the daily output of trace elements from both erta ale craters without si was estimated at 53 kg d including 20 kg of na 13 5 kg of fe 10 5 kg of k 4 5 kg of chalcophile elements 9 g of re 0 5 g of au and 0 17 g of pt the trace element pattern of erta ale fumarolic gases do not possess any distinct geochemical specialization and resemble te patterns from fumarolic emissions of studied arc and plume volcanoes

venting of acid sulfate fluids in a high sulfidation setting at nw rota 1 submarine volcano on the mariana arc a comprehensive survey of hydrothermal plumes and their geochemistry revealed 16 hydrothermally active volcanoes along 1 200 km of the mariana arc from 13 5 n to 22 5 n of these 16 one volcano nw rota 1 is discharging sulfuric acid rich fluids producing some of the largest chemical anomalies ever observed in non buoyant hydrothermal plumes two types of venting were observed one of focused flow rich in al s si co2 fe mn and 3he and a second of diffuse flow rich in fe mn co2 and 3he but without al s and si the plume waters from the acid rich focused flow showed decreases in ph up to 0 73 ph units compared to ambient seawater and an estimated 80 percent of this change was brought about by volcanic and or hydrothermal so2 and possibly hcl with the remaining 20 percent by co2 conservative estimates suggest that the ph of the venting fluids was 1 0 the chemistry of this plume was also greatly different from that observed in any other hydrothermal setting an acid sulfate or high sulfidation fluid source was indicated from plume water samples rich in sulfuric acid native s al sulfate phosphate minerals and weathered silicate and amorphous silica phases the alunite group minerals and acidic fluids indicate that the most important hydrothermal reactions taking place within the hydrothermal system were resulting in advanced argillic alteration of the host volcanic rocks gas chemistry of the fluids revealed an he isotope signature with r ra 8 35 and 3he co2 3 25 109 these values are similar to those found along the global midocean ridge mor suggesting that the source of the 3he and co2 found here is predominantly from the upper mantle consistent with the position of nw rota 1 closest to the back arc in a chain of cross arc volcanoes the chemical signatures of the plumes arising from the diffuse flow remain greatly enriched in fe mn 3he and co2 but compared to the focused flow are low in mineral acidity h al and s the source of this diffuse flow is likely a fluid similar to that producing the acid rich plume but with a lower water to rock ratio and a longer reaction time resulting in the consumption of the mineral acidity this results in an increase in ph and the deposition of the alunite phosphate sulfate and other minerals close to the seafloor by comparison it is likely that the low ph focused flow ejects the vast majority of its mineral load into the water column which is not conducive to the formation of a mineral deposit at the sea floor and potentially would produce a barren prospect

epithermal deposits in north xinjiang nw china the north xinjiang region nw china is an important part of the central asia orogenic belt situated at the junction of siberia tarim and kazakhstan plates it is an area characterized by multiple stages of phanerozoic continental growth during which several porphyry and epithermal systems were formed the relationship of these mineral systems to the geodynamic evolution of the region has not yet been well understood in this paper we list the main geological characteristics of 21 significant epithermal precious and base metal deposits in north xinjiang and classify them into high sulfidation and low sulfidation styles with the latter being predominant we have selected seven epithermal deposits representing different styles formed under different tectonic regimes and discuss their geology and geochemistry in some detail the deposit scale geology and geochemistry of epithermal systems in north xinjiang are essentially similar to those in other parts of the world all epithermal deposits in north xinjiang are hosted in volcanic rocks with ages ranging from devonian to triassic with the early carboniferous volcanic sequences being the most important followed by the permian and triassic the devonian early carboniferous host rocks belong to the calc alkaline series that developed in pre collisional arc back arc basin systems whereas the permian triassic host volcanic rocks of shoshonite series formed in post subduction regimes available isotopic ages of these epithermal systems cluster in two periods early carboniferous 320 ma and late carboniferous triassic 320 220 ma reflecting two metallogenic episodes that occurred during subduction related accretion and post subduction collision regimes respectively accordingly three groups of epithermal deposits in north xinjiang can be recognized as 1 pre collisional deposits without or with negligible collisional related modification 2 deposits formed in collision regime and 3 ore systems strongly overprinted by fluid flow in post subduction collision regime

the pan african quartz syenite of guider north cameroon magnetic fabric and u pb dating of a late orogenic emplacement the small guider pluton 70 km2 in between the cities of maroua and garoua north cameroon is one of the quartz syenite bodies that intrude pan african orthogneisses and that are aligned along the western side of the nne directed poli lere volcano sedimentary corridor the guider syenite is here studied for its internal structures using field and anisotropy of magnetic susceptibility measurements and for its emplacement age of 593 4 ma u pb zircon 20 ma younger than the beginning of gneissification of the country rocks mainly made of deformed granodiorites and diorites in these orthogneisses constantly nne trending vertical foliations variously plunging stretching lineations and fold axes as well as kinematic markers attest to a transpressive and possibly dextral regime the guider syenite rich in k feldspar and magnetite displays typical magmatic microstructures with incipent solid state features such as chess board subgrains in quartz its magnetic fabric displays a well defined feeding zone in its centre and western side attesting to its unrooted nature however n to ne trending lineations at its northern and southern ends parallel to the overall linear structure of the country rocks point to its late orogenic emplacement our results reveal that the ne trending and dextral transpressive shear zone that acted in the guider area ended after the emplacement of the syenite body they specify the age of collage of the nw cameroon domain with the mayo kebbi domain they also show that the tectonic evolution of guider area is closer to the e nigerian domain to the west than to its eastern neighbouring mayo kebbi and adamawa yade domains the connection of our sector with e brazil is briefly discussed

geochemistry of the acid kawah putih lake patuha volcano west java indonesia abstract kawah putih is a summit crater of patuha volcano west java indonesia which contains a shallow 300 m wide lake with strongly mineralized acid sulfate chloride water the lake water has a temperature of 26 34 c ph s tot 2500 4600 ppm and cl 5300 12 600 ppm and floating sulfur globules with sulfide inclusions are common sulfur oxyanion concentrations are unusually high with s 4 o 6 2 s 5 o 6 2 s 6 o 6 2 2400 4200 ppm subaerial fumaroles thermodynamic modeling of the lake fluids indicates that the lake water is saturated with silica phases barite pyrite and various pb sb cu as bi bearing sulfides when sulfur saturation is assumed precipitating phases predicted by the model calculations are consistent with the bulk chemistry of the sulfur rich bottom sediments and their identified mineral phases much of the lake water chemistry can be explained by congruent rock dissolution in combination with preferential enrichments from entering fumarolic gases or brines and element removal by precipitating mineral phases as indicated by a comparison of the fluids volcanic rocks and lake bed sediment flank springs on the mountain at different elevations vary in composition and are consistent with local rock dissolution as a dominant factor and ph dependent element mobility discharges of warm sulfate and chloride rich water at the highest elevation and a near neutral spring at lower level may contain a small contribution of crater lake water the acid fluid induced processes at patuha have led to the accumulation of elements that are commonly associated with volcano hosted epithermal ore deposits the dispersal of heavy metals and other potentially toxic elements from the volcano via the local drainage system is a matter of serious environmental concern

evolution of high level magmatic hydrothermal systems new insights from ore paragenesis of the veladero high sulfidation epithermal au ag deposit el indio pascua belt argentina

generation and evolution of hydrothermal fluids at yellowstone insights from the heart lake geyser basin 1 we sampled fumaroles and hot springs from the heart lake geyser basin hlgb measured water and gas discharge and estimated heat and mass flux from this geothermal area in 2009 the combined data set reveals that diverse fluids share an origin by mixing of deep solute rich parent water with dilute heated meteoric water accompanied by subsequent boiling a variety of chemical and isotopic geothermometers are consistent with a parent water that equilibrates with rocks at 205 c 10 c and then undergoes 21 2 adiabatic boiling measured diffuse co2 flux and fumarole compositions are consistent with an initial dissolved co2 concentration of 21 7 mmol upon arrival at the caldera boundary and prior to southeast flow boiling and discharge along the witch creek drainage the calculated advective flow from the basin is 78 16 l s 1of parent thermal water corresponding to 68 14 mw or 1 of the estimated thermal flux from yellowstone helium and carbon isotopes reveal minor addition of locally derived crustal biogenic and meteoric gases as this fluid boils and degasses reducing the he isotope ratio rc ra from 2 91 to 1 09 the hlgb is one of the few thermal areas at yellowstone that approaches a closed system where a series of progressively boiled waters can be sampled along with related steam and noncondensable gas at other yellowstone locations steam and gas are found without associated neutral cl waters e g hot spring basin or cl rich waters emerge without significant associated steam and gas upper geyser basin

cosmic ray muon imaging of magma in a conduit degassing process of satsuma iwojima volcano japan 1 muon radiography can provide essentially a cross section through the object parallel to the plane of the detector on which the average density along all the muon paths is projected somewhat like x ray radiography very recently the use of emulsion films has given us a clue for visualization of the interior of volcanoes to image a larger volcano in shorter time we need a larger detector to collect more muon events however the time required for imaging will be proportional to the detection area in order to overcome this problem we developed a portable assembly type cosmic ray muon telescope module to image the density distribution of magma in the conduit of mt iwodake volcano japan a muon detector with an area of 1 m2 was set up at the foot of the volcano we mapped differentially absorbed cosmic ray muons which depend on the varying thickness and density beneath the crater floor we successfully imaged density distribution in the conduit as well as the conduit shape assuming the density anomaly is localized in the vent area the observed location of the magma head is consistent with the degassing model of rhyolitic systems proposed by k kazahaya et al in 2002

flux of volatiles and ore forming metals from the magmatic hydrothermal system of satsuma iwojima volcano the satsuma iwojima volcano southwest japan degasses 5 x 10 6 t yr h 2 o 9 x 10 4 t yr s and 6 x 10 4 t yr cl from high temperature 880 c fumaroles atop a now altered rhyolite dome that erupted 1200 yr ago acidic hot springs ph 1 1 1 8 discharge 20 x 10 6 t yr h 2 o to the sea this water is composed of 1 part magmatic vapor absorbed by 6 parts meteoric ground water the cl and so 4 in solution originate from the vapor whereas cation components are derived largely by dissolution of the rhyolite the flux of pb zn cu and mo in the vapor and acidic springs ranges from 0 1 to 10 t yr each whereas the au flux is 10 5 and 10 3 t yr respectively the low concentrations of nacl and metals in the vapor are due to the condensation of a hypersaline liquid from the vapor during ascent and depressurization meaning that the atmospheric pressure vapor does not reflect the composition of the fluid exsolving from the magma neither this low pressure vapor nor the acidic waters can account for high sulfidation cu au ore deposits deduced to have formed in this environment such mineralization requires the subsequent ascent of a metal rich fluid

exploration tools for linked porphyry and epithermal deposits example from the mankayan intrusion centered cu au district luzon philippines the mankayan mineral district of northern luzon philippines hosts several significant ore deposits and prospects of various types within an area of similar to 25 km 2 including the far southeast porphyry cu au deposit the lepanto high sulfidation epithermal cu au deposit the victoria intermediate sulfidation epithermal au ag vein deposit the teresa epithermal au ag vein deposit the guinaoang porphyry cu au deposit and the buaki old palidan porphyry cu au prospects all having formed in a period of about 2 m y from similar to 3 ma the geologic units include 1 a basement composed of late cretaceous to middle miocene metavolcanic rocks volcaniclastic rocks 2 the miocene 12 to 13 ma tonalitic bagon intrusive complex 3 the pliocene similar to 2 2 to 1 8 ma imbanguila dacite porphyry and pyroclastic rocks and 4 postmineralization cover rocks including die similar to 1 2 to 1 0 ma bato dacite porphyry and pyroclastic rocks and the similar to 0 02 ma lapangan tuff extensive advanced argillic alteration crops out for similar to 7 kin along the inconformity between the basement rocks and the imbanguila dacite formation consists of quartz alunite pyrophyllite or diaspore with local zones of silicic alteration and a halo of dickite kaolinite the alteration and its subhorizontal geometry indicate that it is a lithocap or coalesced lithocaps the northwest striking portion is similar to 4 km long and hosts the lepanto enargite au ore deposit also controlled by the lepanto fault the lepanto epithermal deposit is related to the underlying far southeast porphyry the quartz alunite alteration halo of lepanto is contemporaneous with the similar to 1 4 ma potassic alteration of the porphyry there are also silicic advanced argillic alteration patches similar to 600 m above the far southeast orebody at the present surface these are interpreted to be perched alteration there is no systematic mineralogical or textural zoning in the lepanto lithocap that indicates direction to the intrusive source most surface samples of the lithocap contain less than 50 ppb au despite many being less than a few hundred meters from underground cu au ore this study found that several characteristics of the lepanto lithocap change systematically with distance from the causative intrusion the alunite absorption peak at similar to 1 480 nm in the short wavelength infrared swir spectrum shifts to higher wavelengths where the sample is closer to the intrusive center due to higher na and lower k content in the alunite published experimental studies indicate that high na na k is related to higher formation temperature high ca alunite including huangite also occurs at locations proximal to the intrusive center alunite mineral composition analyzed by laser ablation inductively coupled plasma mass spectrometry la icp ms indicates that the pb content decreases toward the intrusive center whereas sr la sr ph and la pb increase markedly whole rock compositions using only nonmineralized taken as cu similar to 350 m above the upper extent of the veins an airborne geophysics survey indicates that the far southeast orebody is associated with a wide zone of demagnetization due to extensive magnetite destructive phyllic alteration such low magnetic anomalies on the margin of a large lithocap elsewhere may deserve attention the directional indicators and mineralization signatures found in this study have the potential to indicate direction to the intrusive center during exploration of similar porphyry epithermal districts

characteristics and source modeling of broadband seismic signals associated with the hydrothermal system at satsuma iwojima volcano japan abstract the broadband seismic data observed at satsuma iwojima volcanic island in southwestern japan show a wide variety of interesting features one of them is the periodic and frequency dependent amplitude modulation of volcanic tremors another interesting feature is the occurrence of very long period vlp seismic pulses synchronized with the tremor amplitude modulation both the tremor amplitude modulation and the vlp pulses have fairly regular intervals of 46 50 min suggesting a spatially fixed non destructive repetitive source we performed waveform inversions to reveal the source mechanism of the vlp pulses assuming a point source embedded in a medium that realistically represented the topography of the island numerical tests showed that the green s functions used in the inversion were significantly affected by the topography the observed vlp pulses were well explained by the rapid expansion of an inclined crack 100 m beneath the floor of the summit crater which had a seismic moment of 3 10 10 nm both the characteristic amplitude modulation and the vlp pulses are explained systematically by a model consisting of a water filled crack and a network of gas paths the water filled crack was heated above the boiling temperature of the water in it a sudden break of the unstable superheated state caused sudden vaporization and a pressure increase which was observed as the vlp pulse the network of gas paths consisted of swollen portions and constricted portions which worked as tremor generators when vapor from the water filled crack passed through

microthermometry of enargite hosted fluid inclusions from the lepanto philippines high sulfidation cuau deposit abstract the spatial relation between porphyry and high sulfidation epithermal deposits is particularly well revealed in the mankayan mineral district of northern luzon philippines where the lepanto high sulfidation cu au deposit lies over and adjacent to the far southeast fse porphyry cu au deposit consequently a study was undertaken to characterize the fluids responsible for epithermal mineralization in this environment the ore stage at lepanto consists of enargite luzonite cu 3 ass 4 pyrite tennantite tetrahedrite and chalcopyrite infrared petrography of the enargite reveals variable transparency with growth banding and twinning visible in euhedral specimens two phase liquid vapor fluid inclusions occur as primary and secondary types ranging from t h of fluid inclusions in enargite were measured from within the lateral 3 0 km and vertical 0 5 km extent of the enargite mineralization these values show a cooling trend toward the northwest away from the area over the porphyry deposit with average t h ranging from 285 c proximal to 166 c distal ice melting temperatures t m were measured using a cycling technique as ice was usually not visible in frozen inclusions apparent salinities range from 4 5 to 0 2 eq wt nacl with samples from the margins of the deposit showing a general decrease in apparent salinity with lower t h secondary fluid inclusions in quartz phenocrysts tend to have a higher average t h and lower apparent salinities compared to enargite hosted inclusion fluids from the same locations several samples of pyrite are also transparent to ir radiation and show internal features such as growth banding and in one instance a two phase liquid vapor fluid inclusion this inclusion yielded a salinity of 1 2 eq wt nacl there is a large discrepancy in t h and apparent salinities between the enargite mineralization and the subjacent porphyry deposit despite contemporaneous formation suggesting that the hot 500 c hypersaline magmatic brines associated with porphyry mineralization did not directly ascend to the elevation of the enargite deposit however absorbtion of magmatic vapors into overlying meteoric water may have created the mineralizing fluid of the lepanto deposit as this liquid moved to the northwest along the lepanto fault it was cooled and diluted by mixing with groundwater resulting in enargite deposition

acid sulfate chloride volcanic waters formation and potential for monitoring of volcanic activity abstract this paper deals mainly with acidic sulphate chloride asc waters that are discharged at volcanic edifices generally not associated with crater lakes geographically the largest number of such manifestations were found on japanese and kuril islands these waters are formed by 1 condensation of magmatic vapor under shallow conditions and or 2 dissolution of magmatic gases in underground waters 3 near surface mixing of steam heated sulphate waters with sodium chloride waters of deeper formation 4 interaction of sodium chloride waters with the rocks undergone by argillic and advanced argillic alteration including hydrolysis of elemental sulfur 5 a combination of several of the listed processes criteria to assess the nature of such waters using their chemical and isotopic composition are based on the relative abundances of major species and trends in isotopic compositions generally controlling by mixing of magmatic host rock meteoric endmembers an overview of available data on temporal chemical variations of such waters shows that usually volcanic activity is marked by an increase in the so4 cl ratio during or after the eruptive event the response on the volcanic activity depends on hydrogeological conditions that control the appearance of the asc springs

fluids in early stage hydrothermal alteration of high sulfidation epithermal systems a view from the vulcano active hydrothermal system aeolian island italy abstract high sulfidation hs epithermal systems have elements in common with passively degassing volcanoes associated with high t acid fumarole fields or acid crater lakes they are considered to form in two stages the first of which involves advanced argillic alteration resulting from intense strongly acidic fluid rock interaction the la fossa hydrothermal system vulcano island represents a classic example of such an active hs system and can be considered as a modern analogue of this early stage of alteration resulting in a core of intense silicic 90 95 pure sio2 alteration surrounded by alunitic alteration zones this paper focuses on a geochemical and stable isotope study of the surficial alteration facies of vulcano particularly the horizon characterized by strong silicic alteration and on deep seated xenoliths ejected during the last eruption of la fossa volcano 1888 90 that can be considered as representative of fragments of the deep conduit system of la fossa volcano using directly measured temperatures at the sites of sampling we have calculated fluid composition in isotopic equilibrium with the alteration products the large range of measured silica 18o 12 3 to 29 reflects the wide range of formation temperatures 80 240 c the fluid compositions calculated for intense silicic alteration vary from 0 9 to 6 5 these are significantly heavier than local meteoric water 6 and are consistent with derivation from the condensation of high temperature fumarolic gases dominated by magmatic fluids and rich in acid gases so2 h2s hcl hf into shallow groundwaters of meteoric origin with dynamically variable ratios of fumarolic steam meteoric water the calculated 18o and d of water in equilibrium with alunite also suggest the mixing of magmatic and meteoric waters for the fluids involved in the genesis of advanced argillic alteration facies the calculated 18o of water in equilibrium with hedenbergitic clinopyroxene found in a veinlet in a metasomatized xenolith is 8 9 this value cannot reasonably result from water rock interaction between the host volcanic rocks and surface water instead it most likely represents a fluid brine exsolved from magma which was responsible for high temperature metasomatism in the deep conduit system

long term geochemical surveillance of fumaroles at showa shinzan dome usu volcano japan this study investigates 31 years of fumarole gas and condensate trace elements data from showa shinzan a dacitic dome cryptodome complex that formed during the 1943 1945 eruption of usu volcano forty two gas samples were collected from the highest temperature fumarole named a 1 from 1954 800 c to 1985 336 c and from lower temperature vents condensates were collected contemporaneously with the gas samples and we reanalyzed ten of these samples mostly from the a 1 vent for 32 cations and three anions modeling using the thermochemical equilibrium program solvgas shows that the gas samples are mild disequilibrium mixtures because they a contain unequilibrated sedimentary ch4 and nh3 b have unequilibrated meteoric water or c lost co either by air oxidation or by absorption by the sodium hydroxide sampling solution solvgas also enabled us to restore the samples by removing these disequilibrium effects and to estimate their equilibrium oxygen fugacities and amounts of s2 and ch4 the restored compositions contain 98 h2o with minor to trace amounts of co2 h2 hcl so2 hf h2s co s2 and ch4 we used the restored gas and condensate data to test the hypotheses that these time series compositional data from the dome s fumaroles provide 1 sufficient major gas data to analyze long term degassing trends of the dome s magma hydrothermal system without the influence of sampling or contamination effects 2 independent oxygen fugacity versus temperature estimates of the showa shinzan dacite 3 the order of release of trace elements especially metals from magma and 4 useful information for assessing volcanic hazards the 1954 1985 restored a 1 gas compositions confirm the first hypothesis because they are sufficient to reveal three long term degassing trends 1 they became increasingly h2o rich with time due to the progressive influx of meteoric water into the dome 2 their csandscl ratios decreased dramatically while their clf ratios stayed roughly constant indicating the progressive outgassing of less soluble components f cl s c from the magma reservoir and 3 their h2oh2 co2coandh2sso2 ratios increased significantly in concert with equilibrium changes expected for the 500 c temperature drop when plotted against reciprocal temperature the restored gas log oxygen fugacities follow a tight linear trend from 800 c to nno 2 5 at 400 c this trend largely disproves the second hypothesis because the oxygen fugacities for the 800 c restored gases can only be explained by mixing of hot magmatic gases with 350 c steam from superheated meteoric water but above 800 c this trend intersects the opposing linear trend for other usu eruptive products implying a log oxygen fugacity of 11 45 at 902 c for the showa shinzan magma the time series trace element data also disprove the third hypothesis because rock and incrustation particle contaminants in the condensates account for most of the trace element variation nonetheless highly volatile elements like b and as are relatively unaffected by this particle contamination and they show similar time series trends as cl and f finally except for infrequent sampling around the 1977 usu eruption the results generally confirm the fourth hypothesis since the time series trends for the major gases and selected trace elements indicate that with time the system cooled degassed and was infiltrated by meteoric water all of which are positive signs that volcanic activity declined over the 31 year history this study also suggests that second boiling of shallow magma within and possibly beneath the cryptodome sustained magmatic degassing for at least 20 years after emplacement

submarine hydrothermal activity and gold rich mineralization at brothers volcano kermadec arc new zealand brothers volcano of the kermadec intraoceanic arc is host to a hydrothermal system unique among seafloor hydrothermal systems known anywhere in the world it has two distinct vent fields known as the nw caldera and cone sites whose geology permeability vent fluid compositions mineralogy and ore forming conditions are in stark contrast to each other the nw caldera site strikes for 600 m in a sw ne direction with chimneys occurring over a 145 m depth interval between 1 690 and 1 545 m at least 100 dead and active sulfide chimney spires occur in this field and are typically 2 3 m in height with some reaching 6 7 m their ages at time of sampling fall broadly into three groups 4 23 and 35 years old the chimneys typically occur near the base of individual fault controlled benches on the caldera wall striking in lines orthogonal to the slopes rarer are massive sulfide crusts 2 3 m thick two main types of chimney predominate cu rich up to 28 5 wt cu and more commonly zn rich up to 43 8 wt zn geochemical results show that mo bi co se sn and au up to 91 ppm are correlated with the cu mineralization whereas cd hg sb ag and as are associated with the dominant zn rich mineralization the cone site comprises the upper cone site atop the summit of the recent main dacite cone and the lower cone site that straddles the summit of an older smaller more degraded dacite cone on the ne flank of the main cone huge volumes of diffuse venting are seen at the lower cone site in contrast to venting at both the upper cone and nw caldera sites individual vents are marked by low relief 0 5 m mounds comprising predominately native sulfur with bacterial mats vent fluids of the nw caldera field are focused hot 300 c acidic ph 2 8 metal rich and gas poor calculated end member fluids from nw caldera vents indicate that phase separation has occurred with cl values ranging from 93 to 137 of seawater values by contrast vent fluids at the cone site are diffuse noticeably cooler 122 c more acidic ph 1 9 metal poor and gas rich higher than seawater values of so4 and mg in the cone vent fluids show that these ions are being added to the hydrothermal fluid and are not being depleted via normal water rock interactions iron oxide crusts 3 years in age cover the main cone summit and appear to have formed from fe rich brines evidence for magmatic contributions to the hydrothermal system at brothers includes high concentrations of dissolved co2 e g 206 mm kg at the cone site high co2 3he negative d and 18oh2o for vent fluids negative 34s for sulfides to 4 6 sulfur to 10 2 and 15n2 to 3 5 vent fluid ph values to 1 9 and mineral assemblages common to high sulfidation systems changing physicochemical conditions at the brothers hydrothermal system and especially the cone site occur over periods of months to hundreds of years as shown by interlayered cu au and zn rich zones in chimneys variable fluid and isotopic compositions similar shifts in 3he 4he values for both cone and nw caldera sites and overprinting of magmatic mineral assemblages by water rock dominated assemblages metals especially cu and possibly au may be entering the hydrothermal system via the dissolution of metal rich glasses they are then transported rapidly up into the system via magmatic volatiles utilizing vertical 2 5 km long narrow 300 m diameter pipes consistent with evidence of vent fluids forming at relatively shallow depths the nw caldera and cone sites are considered to represent stages along a continuum between water rock and magmatic hydrothermal dominated end members

hydrothermal fluid evolution at the tiegelongnan porphyry epithermal cu au deposit tibet china constraints from h and o stable isotope and in situ s isotope abstract the tiegelongnan porphyry epithermal cu au deposit is located in the duolong porphyry district north of the bangong nujiang suture zone tibet china mineralization is hosted by jurassic sedimentary sandstone and several phases of diorite and granodiorite porphyry dikes intruded between 123 and 116 ma the hydrothermal alteration is characterized by alunite kaolinite dickite overprinting quartz muscovite pyrite and biotite alteration zones porphyry chalcopyrite pyrite molybdenite stage 1 mineralization is associated with biotite alteration porphyry chalcopyrite bornite stage 2 and covellite stage 3 mineralization is associated with quartz muscovite pyrite alteration formed at 121 ma epithermal mineralization consisting of pyrite alunite stage 4 chalcopyrite bornite digenite stage 5 and tennantite enargite stage 6 is hosted by two pulses of alunite kaolinite breccia and veins at 116 ma and 112 ma the fluid composition related to muscovite with average 18o of 8 9 and d of 56 indicates a magmatic water origin fluid 18o composition in equilibrium with quartz veins decreases from 6 7 to 2 3 which are likely the results of the water rock isotopic exchange quartz fluid inclusions d values between 50 to 84 are partly lower than that obtained from muscovite alteration fluids which may result from h fractionation during fluid inclusions decrepitation epithermal stage fluid composition equilibrium with alunite yield 18o from 1 2 to 2 7 and d from 71 to 51 n 11 which is comparable to the fluid composition equilibrium with type kaolinite hosting ores with 18o between 2 5 and 2 9 and d between 72 and 51 it suggests that alunite and type kaolinite formed with mixing between magmatic and high altitude cretaceous meteoric water late types and iii kaolinite filling alunite and quartz veins fluid 18o and d values plot along a mixing line between magmatic and low altitude cretaceous meteoric water probably following the erosion and plateau subsidence porphyry mineralization sulfide stage 1 chalcopyrite and pyrite yield 34s values between 5 8 and 0 9 with an average fluid 34sh2s 2 5 n 10 whereas stage 2 chalcopyrite returns 34s values from 8 7 to 3 with an average 34sh2s 5 6 n 5 the lower fluid 34sh2s values during sulfides stage 2 compared to that of stage 1 suggest that the chalcopyrite bornite mineralization formed under higher oxidation conditions than that of the chalcopyrite pyrite mineralization alunite yields 34s values from 11 to 18 3 n 8 and the associated sulfide stage 4 pyrite have varying 34s values from 32 2 to 5 4 disequilibrium s isotope in alunite pyrite pairs was likely because of rapid cooling and retrograde s isotope exchange during later sulfides emplacement epithermal mineralization sulfide stage 4 s equilibrated pyrite 14 9 to 9 5 stage 5 chalcopyrite 11 6 to 8 2 and stage 6 enargite 5 4 to 2 6 display increasing 34s values suggesting epithermal fluid compositions evolve towards more reducing conditions

tektite bearing deep water clastic unit at the cretaceous tertiary boundary in northeastern mexico the hypothesis of cretaceous tertiary k t boundary impact on yucatan mexico predicts that nearby sites should show evidence of proximal impact ejecta and disturbance by giant waves an outcrop along the arroyo el mimbral in northeastern mexico contains a layered clastic unit up to 3 m thick that interrupts a biostratigraphically complete pelagic marl sequence deposited at more than 400 m water depth the marls were found to be unsuitable for determining magnetostratigraphy but foraminiferal biostratigraphy places the clastic unit precisely at the k t boundary we interpret this clastic unit as the deposit of a megawave or tsunami produced by an extraterrestrial impact the elastic unit comprises three main subunits 1 the basal spherule bed contains glass in the form of tektites and microtektites glass spherules replaced by chlorite smectite and calcite and quartz grains showing probable shock features this bed is interpreted as a channelized deposit of proximal ejects 2 a set of lenticular massive graded laminated beds contains intraclasts and abundant plant debris and may be the result of megawave backwash that carried coarse debris from shallow parts of the continental margin into deeper water 3 at the top several thin ripple beds composed of fine sand are separated by clay drapes they are interpreted as deposits of oscillating currents perhaps a seiche an iridium anomaly 921 23 pg g is observed at the top of the ripple beds our observations at the mimbral locality support the hypothesis of a k t impact on nearby yucatan

silicate replacive high sulfidation massive sulfide orebodies in a porphyry cu au system bor serbia the cu au deposit of bor serbia represents a continuum of mineralization styles from porphyry style ore occurring in quartz magnetite chalcopyrite veins and chalcopyrite disseminations to high sulfidation epithermal cu au ores in pyrite chalcopyrite and anhydrite sulfide veins decisive for the great economic importance of bor is the presence of exceptionally rich high sulfidation massive sulfide orebodies composed of pyrite covellite chalcocite digenite and minor anhydrite and enargite they form irregular bodies measuring 0 5 10 million tons of ore grading up to 7 cu hosted by andesites and surrounded by intense argillic alteration this study focuses on a small but rich underground orebody mined out recently where limited drillcore is preserved for quantitative geochemical study this paper documents the vein relationships within the deep porphyry style orebody of borska reka the transitional porphyry epithermal veins and the overlying and laterally surrounding epithermal massive sulfides of the bor deposit geological observations indicate that the formation of massive sulfide orebodies concludes the ore formation mass balance calculations recast into geologically realistic bulk fluid rock reactions confirm textural evidence that near isovolumetric replacement of andesite host rocks is the dominant formation mechanism of massive sulfide orebodies at bor whereby all lithophile elements including si are dissolved and only ti stays relatively immobile while net volume changes for individual mineralization styles within the massive sulfide orebody vary from 16 volume loss to 127 volume gain overall volume change for the whole massive sulfide orebody was probably slightly negative brecciation is important only as means of creating channelways for reactive fluid that turns the andesite protolith into massive sulfide whereas net breccia infill occurred only locally

naturally acid waters from copahue volcano argentina volcanic acid sulfate chloride brines form through absorption of volcanic vapors in shallow reservoirs of meteoric water reaction with surrounding volcanic rocks leads to partial neutralization of the fluids and precipitation of secondary minerals chemical data of such acid waters from copahue volcano argentina covering 8 years of observations show evidence for changes in composition related to water rock interaction at depth prior to emergence of the fluids at the surface the chemical composition changed dramatically during the 2000 eruption of copahue with enhanced concentrations and fluxes of mg na fe and al followed in 2001 by rapidly declining concentrations and element fluxes the subsequent 5 years saw more variable element ratios and strong depletions in k and al most incompatible elements are released from the rock matrix stochiometrically whereas some elements are enriched through vapor input from the magma as pb zn most fluids have lree enrichments relative to the rock matrix but during periods of new magma intrusion the lree enrichment decreases as does the magnitude of the negative eu anomaly in the fluids these observations are interpreted assuming early dissolution of plagioclase olivine and volcanic glass that occurs during intrusion of new magma into the hydrothermal system the high field strength elements are virtually immobile even in these hot acid fluids with nb and ta more so than hf and zr the mobility of u and th in these fluids is comparable at variance with th behavior in neutral fluids the local rivers and lakes of copahue are fertilized by volcanic dissolved p and most surface waters with ph 3 have high levels of as the acid fluids from copahue may be surficial analogs for deep subduction fluids that evolve below zones of arc magma generation as well as for early mars environments that are thought to have had large acid lakes