dolomite compositions as a guide to epigenetic copper mineralization mount isa inlier nw queensland dolomites associated with copper mineralization have higher fe contents and lower mn fe ratios than their unmineralized equivalents over a wide stratigraphic interval and range of original depositional environments copper associated dolomite in the proterozoic mount isa inlier of nw queensland has mn fe 0 11 vein dolomite has a higher fe content than its corresponding matrix nevertheless the mn fe ratio of the matrix is a good guide to the maximum mn fe ratio for a dolomitic vein thus the simple determination of the fe and mn component in the dolomite of a rock gives information about the possible association with copper mineralization even when the rock itself is completely barren

magma evolution and the formation of porphyry cu au ore fluids evidence from silicate and sulfide melt inclusions silicate and sulfide melt inclusions from the andesitic farallon negro volcanic complex in nw argentina were analyzed by laser ablation icpms to track the behavior of cu and au during magma evolution and to identify the processes in the source of fluids responsible for porphyry cu au mineralization at the 600 mt bajo de la alumbrera deposit the combination of silicate and sulfide melt inclusion data with previously published geological and geochemical information indicates that the source of ore metals and water was a mantle derived mafic magma that contained approximately 6 wt h2o and 200 ppm cu this magma and a rhyodacitic magma mixed in an upper crustal magma chamber feeding the volcanic systems and associated subvolcanic intrusions over 2 6 million years generation of the ore fluid from this magma occurred towards the end of this protracted evolution and probably involved six important steps 1 generation of a sulfide melt upon magma mixing in some parts of the magma chamber 2 partitioning of cu and au into the sulfide melt enrichment factor of 10 000 for cu leading to cu and au concentrations of several wt or ppm respectively 3 a change in the tectonic regime from local extension to compression at the end of protracted volcanism 4 intrusion of a dacitic magma stock from the upper part of the layered magma chamber 5 volatile exsolution and resorption of the sulfide melt from the lower and more mafic parts of the magma chamber generating a fluid with a cu au ratio equal to that of the precursor sulfide 6 focused fluid transport and precipitation of the two metals in the porphyry yielding an ore body containing au and cu in the proportions dictated by the magmatic fluid source the cu s ratio in the sulfide melt inclusions requires that approximately 4 000 ppm sulfur is extracted from the andesitic magma upon mixing this exceeds the solubility of sulfide or sulfate in either of the silicate melts and implies an additional source for s the extra sulfur could be added in the form of anhydrite phenocrysts present in the rhyodacitic magma it appears thus that unusually sulfur rich not cu rich magmas are the key to the formation of porphyry type ore deposits our observations imply that dacitic intrusions hosting the porphyry cu au mineralization are not representative of the magma from which the ore fluid exsolved the source of the ore fluid is the underlying more mafic magma and unaltered andesitic dikes emplaced immediately after ore formation are more likely to represent the magma from which the fluids were generated at alumbrera these andesitic dikes carry relicts of the sulfide melt as inclusions in amphibole sulfide inclusions in similar dykes of other less explored magmatic complexes may be used to predict the au cu ratio of potential ore forming fluids and the expected metal ratio in any undiscovered porphyry deposit

behavior of halogens during the degassing of felsic magmas 1 residual concentrations of halogens f cl br i and h2o in glass matrix glass and melt inclusions have been determined in a series of volcanic clasts pumice and lava dome fragments of plinian vulcanian and lava dome forming eruptions felsic magmas from calc alkaline trachytic and phonolitic systems have been investigated montagne pelee and soufriere hills of montserrat lesser antilles santa maria santiaguito guatemala fogo azores and vesuvius italy the behavior of halogens during shallow h2o degassing primarily depends on their incompatible character and their partitioning between melt and exsolved h2o vapor however variations in pre eruptive conditions degassing kinetics and syn eruptive melt crystallization induce large variations in the efficiency of halogen extraction in all systems studied cl br and i are not fractionated from each other by differentiation or by degassing processes cl br i ratios in melt remain almost constant from the magma reservoir to the surface the ratios measured in erupted clasts are thus characteristic of pre eruptive magma compositions and may be used to trace deep magmatic processes f behaves as an incompatible element and unlike the other halogens is never significantly extracted by degassing cl br and i are efficiently extracted from melts at high pressure by h2o rich fluids exsolved from magmas or during slow effusive magma degassing but not during rapid explosive degassing because h2o and halogen mobility depends on their speciation which strongly varies with pressure in both silicate melts and exsolved fluids we suggest that the rapid pressure decrease during highly explosive eruptions prevents complete equilibrium between the diverse species of the volatiles and consequently limits their degassing conversely degassing in effusive eruptions is an equilibrium process and leads to significant halogen output in volcanic plumes

exsolution of magmatic volatile phases from cl enriched mineralizing granitic magmas and implications for ore metal transport abstract to understand cl dissolution in aluminosilicate liquids and the exsolution of cl rich magmatic volatile phases experiments were conducted to determine the solubility of nacl kcl and h2o in felsic liquids at 0 5 and 2 kbar the cl content of h2o poor nacl saturated and kcl saturated silicate liquids is low i e 1 3 wt to very low i e 0 2 wt and varies with changes in pressure and composition the cl concentration increases with the f concentration and the molar al na ca mg si ratio of the liquid and decreases with increasing activity of h2o in the system exsolution of a volatile phase depends on the partial pressures of all dissolved volatiles and low cl solubilities in nacl saturated and kcl saturated silicate liquids imply that exsolution of a cl bearing volatile phase will occur early in cl bearing granitic magmas i e prior to extensive melt crystallization and or at comparatively low water fugacities the solubility behavior of h2o and cl is very similar to that of co2 and h2o in felsic liquids small quantities of co2 are known to facilitate volatile phase exsolution holloway 1976 and in a similar manner volatile phases may exsolve early in cl enriched granite magmas whereas 5 to 6 wt dissolved h2o is necessary for volatile phase exsolution from a co2 free and cl free haplogranite liquid at 2 kbar and 800 c a cl rich brine will exsolve if the liquid contains only 1 wt h2o and 0 26 wt cl at the same conditions these new solubility data are interpreted in light of h2o f and cl concentrations in felsic liquids determined from silicate melt inclusions to constrain the exsolution of cl bearing magmatic volatile phases from mineralizing granitic magmas felsic magmas genetically associated with cu porphyry and mo porphyry mineralization contain sufficient h2o and cl to become saturated with respect to a hypersaline brine without strong pressure reduction boiling of the volatile phase i e exsolution of immiscible vapor and brine or strong volatile enrichment resulting from extensive crystal fractionation experiments were also conducted to investigate the solubility of mo in highly saline volatile phases coexisting with granitic liquids at 2 and 0 5 kbar the apparent partition coefficient for mo in the volatile phase s relative to silicate liquid d mo is defined as the computed concentration of mo in a volatile phase or phases the measured concentration of mo in granite glass d mo ranges from 8 to 80 as the nacl and kcl content of the volatile phase s increases from 15 to 90 wt because mo does not complex with cl in aqueous fluids it appears that mo solubility may be a strong function of the activity of na and k in alkali chloride rich volatile phases

tungsten solubility in evolved granitic melts an evaluation of magmatic wolframite abstract a variety of parameters that potentially control the solubilities of synthetic hubnerite mnwo4 and ferberite fewo4 in haplogranitic melts rich in fluxing compounds have been determined at 200 mpa in order to test the hypothesis that wolframite can occur as a magmatic mineral the melts considered representative of highly evolved pegmatites contain 1 1 1 7 and 2 02 wt of li2o p2o5 and b2o3 respectively although the molar al na k ratio is one if li is considered to be an alkali element the molar al na k li asili of the melt is 0 88 and the melt is peralkaline hubnerite and ferberite solubilities at 800 c are strongly controlled by melt composition they are much lower in subaluminous melt asili 1 05 than in peralkaline melt by contrast hubnerite and ferberite solubilities are nearly independent of the fluorine content of the melt for up to 8 wt f hubnerite and ferberite solubilities at 800 c are also nearly independent of oxygen fugacity over a log f o 2 range of approximately ni nio 3 to ni nio 2 which implies that the predominant oxidation state of tungsten in the melts is 6 even at moderately reduced conditions a series of experiments on haplogranitic melt rich in fluxing compounds with 0 and 6 wt f at 850 650 c shows that temperature strongly influences hubnerite solubility e g the solubility product of hubnerite k sp hub in the melts with 6 wt f decreases from 71 0 7 9 10 4 mol2 kg2 at 850 c to 4 4 2 3 10 4 mol2 kg2 at 650 c our experimental results show that ferberite solubilities are much higher than those of hubnerite with the same composition of melt but the mn fe and w concentrations in natural melt inclusions indicate that these melts were undersaturated with wolframite at 800 c however flux rich melts crystallize at lower temperatures in nature and the occurrence of natural magmatic wolframite was evaluated by comparing experimental solubility product values extrapolated to 500 c with wolframite activities at these temperatures magmatic wolframite is unlikely in flux rich peralkaline melts but by contrast flux rich subaluminous to peraluminous melt inclusions appear to have been saturated with wolframite at approximately 500 c because of the strong temperature dependence of wolframite solubility the dominant effect of fluxing compounds is to lower the solidus temperature of the melt

vapor transfer prior to the october 2004 eruption of mount st helens washington dome lavas from the 2004 eruption of mount st helens show elevated li contents in plagioclase phenocrysts at the onset of dome growth in october 2004 these cannot be explained by variations in plagioclase melt partitioning but require elevated li contents in coexisting melt a fact confirmed by measurements of li contents as high as 207 g g in coexisting melt inclusions similar li enrichment has been observed in material erupted prior to and during the climactic may 1980 eruption and is likewise best explained via pre eruptive transfer of an exsolved alkali rich vapor phase derived from deeper within the magma transport system unlike 1980 however high li samples from 2004 show no evidence of excess 210pb 226ra implying that measurable li enrichments may occur despite significant differences in the timing and or extent of magmatic degassing diffusion modeling shows that li enrichment occurred within 1 yr before eruption and that magma remained li enriched until immediately before eruption and cooling this short flux time and the very high li contents in ash produced by phreatomagmatic activity prior to the onset of dome extrusion suggest that vapor transfer and accumulation were associated with initiation of the current eruption overall observation of a high li signature in both 1980 and 2004 dacites indicates that li enrichment may be a relatively common phenomenon and may prove useful for petrologic monitoring of mount st helens and other silicic volcanoes lithium diffusion is also sufficiently rapid to constrain vapor transfer on similar time scales to short lived radionuclides

liquid immiscibility and its role at the magmatic hydrothermal transition a summary of experimental studies several types of fluid immiscibility may affect the evolution of volatile rich magmatic systems at the magmatic hydrothermal transition the topology of silicate salt h2o systems implies that three fluid immiscibility silicate melt hydrosaline melt vapour should be stable in a broad range of compositions and p t conditions the most important factor controlling the immiscibility appears to be the coulombic properties electric charges z and ionic radii r of the main network modifying cations and the capacity for immiscibility appears to decrease in the following sequence mg ca sr ba li na k liquid immiscibility is enhanced in peralkaline compositions and in the presence of nonsilicate anions such as f cl co32 and bo33 in volatile rich magmatic systems the h2o is likely to react with the chloride fluoride borate and carbonate species and the chemical effects of high temperature hydrolysis may be greatly enhanced by phase separation in systems with multiple immiscible fluid phases natural granitic magmas can thus exsolve a range of chemically and physically diverse hydrosaline liquids and the role of these fluid phases is likely to be especially significant in pegmatites and li f rare metal granites

silicate melt inclusion evidence for extreme pre eruptive enrichment and post eruptive depletion of lithium in silicic volcanic rocks of the western united states implications for the origin of lithium rich brines to evaluate whether anatectic and or highly fractionated lithophile element enriched rhyolite tuffs deposited in arid lacustrine basins lose enough lithium during eruption lithification and weathering to generate significant li brine resources pre eruptive melt compositions preserved in inclusions and the magnitude of post eruptive li depletions evident in host rhyolites were documented at six sites in the western united states each rhyolite is a member of the bimodal basalt rhyolite assemblage associated with extensional tectonics that produced the basin and range province and rio grande rift an evolving pattern of closed drainage basins and geothermal energy or mineral resources results from the 0 8 ma bishop tuff geothermal in california 1 3 to 1 6 ma cerro toledo and upper bandelier tephra geothermal and 27 9 ma taylor creek rhyolite sn in new mexico 21 7 ma spor mountain tuff be u f and 24 6 ma pine grove tuff mo in utah and 27 6 ma hideaway park tuff mo in colorado support the following conclusions melt inclusions in quartz phenocrysts from rhyolite tuffs associated with hydrothermal deposits of sn mo and be are extremely enriched in li 1 000s of ppm those from spor mountain have the highest li abundance yet recorded max 5 200 ppm median 3 750 ppm forty five to 98 of the li present in pre eruptive magma was lost to the environment from these rhyolite tuffs the amount of li lost from the small volumes 1 10 km3 of li enriched rhyolite deposited in closed basins is sufficient to produce world class li brine resources after each eruption meteoric water leaches li from tuff which drains into playas where it is concentrated by evaporation the localized occurrence of li enriched rhyolites may explain why brines in arid lacustrine basins seldom have economic concentrations of li considering that hydrothermal deposits of sn mo be u and f may indicate potential for li brines in nearby basins we surmise that the world s largest li brine resource in the salar de uyuni 10 mt received li from nearby rhyolite tuffs in the bolivian tin belt

lead isotope studies bearing on the genesis of copper orebodies at mount isa queensland significant differences between the lead zinc silver and copper ore bodies unlike the lead zinc silver deposits the copper orebodies appear epigenetic two texturally distinct generations of iron sulfides later relative to the lead zinc mineralization origin of the main copper ore bodies from the basement metamorphic and granitic complexes direct relationship between the regional metamorphism generation of hypersaline fluids and metal extraction modified journal abstract

fluid fractionation of tungsten during granite pegmatite differentiation and the metal source of peribatholitic w quartz veins evidence from the karagwe ankole belt rwanda abstract the identification of a magmatic source for granite associated rare metal w nb ta and sn mineralisation in metasediment hosted quartz veins is often obscured by intense fluid rock interactions which metamorphically overprinted most source signatures in the vein system in order to address this recurrent metal sourcing problem we have studied the metasediment hosted tungsten bearing quartz veins of the nyakabingo deposit of the karagwe ankole belt in central rwanda the vein system 992 2 ma is spatiotemporal related to the well characterised b rich f poor g4 leucogranite pegmatite suite 986 10 ma to 975 8 ma of the gatumba gitarama area which culminated in nb ta sn mineralisation muscovite in the nyakabingo veins is significantly enriched in granitophile elements rb cs w and sn and show alkali metal signatures equivalent to muscovite of less differentiated pegmatite zones of the gatumba gitarama area pegmatitic muscovite records a decrease in w content with increasing differentiation proxies rb and cs in contrast to the continuous enrichment of other high field strength elements nb and ta and sn this is an indication of a selective redistribution for w by fluid exsolution and fluid fractionation primary fluid inclusions in tourmaline of these less differentiated pegmatites demonstrate the presence of medium to low saline h 2 o nacl kcl mgcl 2 complex salt e g rb cs fluids which started to exsolve at the g4 granite pegmatite transition stage laser ablation inductively coupled plasma mass spectrometry shows significant tungsten enrichment in these fluid phases 5 500 ppm fractional crystallisation has been identified previously as the driving mechanism for the transition from g4 granites less differentiated biotite biotite muscovite towards muscovite pegmatites and eventually columbite tantalite mineralised pegmatites the general absence of tungsten mineralisation in this magmatic suite including the most differentiated columbite tantalite mineralised pegmatites of the gatumba gitarama area emphasises the efficiency of fluid saturation to extract crystal melt incompatible tungsten from the differentiating melt phase fluid melt crystal partitioning calculations support the concept of a magmatic hydrothermal fluid source for tungsten and constrain the range of permissible crystal melt and fluid melt partition coefficients together with realistic values for water solubility in the parental g4 granitic melt consequently we propose that for highly differentiated b rich f poor granite systems fluid saturation started prior to or at the granite pegmatite transition stage resulting in apical to peribatholitic tungsten veins systems that are paragenetically older than the final pegmatite stage

experimental and modeled chlorine solubilities in aluminosilicate melts at 1 to 7000 bars and 700 to 1250 c applications to magmas of augustine volcano alaska hydrothermal experiments were conducted at ca 1 to 7000 bars and 700 to 1250 c in 121 rhyolitic to basaltic systems to determine cl solubility in silicate melts i e the maximum cl concentration in melts that are saturated in a hydrosaline liquid with or without an aqueous or aqueous carbonic vapor the cl concentration of melts increases with the cl contents of the fluid unless the melt coexists with vapor plus hydrosaline liquid at fixed pressure and temperature this phase assemblage buffers the cl content of each phase with increasing cl in the system the cl content of fluid s saturated melts is independent of the co 2 concentration of the saline liquid vapor with up to 21 wt co 2 in the fluid s the experiments show that cl dissolution in aluminosilicate melts increases with temperature and pressure chlorine solubility is also a function of melt composition it increases with the molar al 1 2 ca 1 2 mg 1 2 na si of the melt these experimental data have been integrated with results involving 41 other experiments webster and de vivo 2002 to develop a broadly expanded model that supports calculation of cl solubility in 163 aluminosilicate melts this empirical model applies to cl dissolution in melts of most silicate magmas at depths as great as 25 km it determines the exsolution of hydrosaline liquid with or without a coexisting vapor as magmas ascend from depth cool crystallize and differentiate from mafic to felsic compositions in combination with h 2 o solubility models our model supports determination of h 2 o cl solubility relations for most aluminosilicate magmas and is useful for barometric estimations based on silicate melt inclusions containing low co 2 and moderate to high cl concentrations the model is applied to the phase relations of fluids in volatile enriched magmas of augustine volcano alaska the cl and h 2 o concentrations of melt inclusions from 14 basaltic to dacitic eruptive units are compared with modeled solubilities of cl and h 2 o in augustine melts the majority of these eruptions involved magmas that first exsolved aqueous to aqueous carbonic vapors when the melts were dacitic in composition i e before the residual melts in these magmas had evolved to felsic compositions and well prior to the eruptions hydrosaline liquid with or without a vapor phase exsolved from other more felsic fractions of augustine melts at low near surface pressures of several tens of bars

modulation of magmatic processes by co2 flushing abstract magmatic systems are the engines driving volcanic eruptions and the source of fluids responsible for the formation of porphyry type ore deposits sudden variations of pressure temperature and volume in magmatic systems can produce unrest which may culminate in a volcanic eruption and or the abrupt release of ore forming fluids such variations of the conditions within magmatic systems are commonly ascribed to the injection of new magma from depth however as magmas fractionating at depth or rising to the upper crust release co2 rich fluids the interaction between carbonic fluids and h2o rich magmas stored in the upper crust co2 flushing must also be a common process affecting the evolution of subvolcanic magma reservoirs here we investigate the effect of gas injection on the stability and chemical evolution of magmatic systems we calculate the chemical and physical evolution of magmas subjected to co2 flushing using rhyolite melts we compare the calculations with a set of melt inclusion data for mt st helens merapi etna and stromboli volcanoes we provide an approach that can be used to distinguish between melt inclusions trapped during co2 flushing magma ascent and decompression or those affected by post entrapment h2o loss our results show that co2 flushing is a widespread process in both felsic and mafic magmatic systems depending upon initial magma crystallinity and duration of co2 input flushing can either lead to volcanic eruption or fluid release we suggest that co2 flushing is a fundamental process modulating the behaviour and chemical evolution of crustal magmatic systems

fluid fluid interactions in magmatic hydrothermal ore formation hydrothermal ore deposits have provided some of the first geological evidence for the interaction of multiple fluids in the earth s interior including fluid mixing as well as fluid phase separation physical evidence comes from veins and breccias documenting the impact of fluids in breaking rocks and creating fracture permeability for ore formation as a result of the fluid expansion that is commonly associated with phase separation between melts and multiple fluids chemical evidence of fluid fluid interaction includes the precipitation of minerals in veins as a result of fluid boiling or mixing between chemically contrasting fluids fluid inclusions record interactions of multiple fluids especially in magmatic hydrothermal ore deposits and associated igneous rocks fig 1 in recent years fluid inclusions have contributed to a more quantitative understanding of the role of fluid fluid interactions since new microanalytical techniques allow determination of element concentrations in all types of fluids from low density vapor through aqueous and hypersaline liquids to hydrous salt melts roedder 1984 samson et al 2003 figure 1 geological evidence for fluid phase separation in ore forming magmatic hydrothermal systems a bonanza grade gold 1 wt that was precipitated together with fine grained pyrite in a fluidized breccia resulting from instantaneous boiling and expansion of magmatic fluids ascending from an underlying andesite porphyry intrusion the breccia consists of adularia sericite altered clasts of sedimentary wall rock s and nodules of originally colloidal pyrite with bright specks of gold p g both cemented by roscoelite r vanadium rich muscovite and late calcite c zone vii ore body porgera papua new guinea ronacher et al 2004 b bladed manganocalcite the characteristic habit of calcite precipitated from aqueous epithermal fluids as a result of the ph change following loss of co2 to a separating vapor phase madan bulgaria kostova et al 2004 c growth band in a euhedral quartz

proterozoic copper deposits in nw queensland australia sulfur isotopic data sulfur isotopic disequilibrium is commonly observed between associated pyrite and copper sulfides in nw queensland a sulfur isotopic study of copper mineralization in dolomites at paradise valley and arenites at mammoth has allowed the significance of such disequilibrium to be evaluated copper mineralization at paradise valley is characterized by a greater enrichment in 34s with 34s values often greater than 30 for both copper sulfides and associated syngenetic diagneetic pyrite at mammoth copper sulfides have isotopic compositions 34s 15 9 to 0 3 transitional between disseminated syngenetic diagenetic pyrite 34s 5 7 to 1 7 and epigenetic vein pyrite 34s 17 9 to 7 1 suggesting progressive reaction and replacement of syngenetic diagenetic pyrite by a copper bearing mineralizing fluid under oxidizing conditions the isotopic data within the constraints imposed by geological and geochemical factors support a model of reaction between copper bearing mineralizing fluids and pre existing syngenetic diagenetic pyrite for both the carbonate and arenite hosted deposits

using amphibole phenocrysts to track vapor transfer during magma crystallization and transport an example from mount st helens washington abstract in order to evaluate and further constrain models for volatile movement and vapor enrichment of magma stored at shallow levels amphibole phenocrysts from 2004 2005 mount st helens dacite were analyzed for major and selected trace elements li cu zn mn and ree and li isotopes several recent studies have examined fluid mobile trace element abundances in phencryst phases and melt inclusions as a means of tracking volatile movement within subvolcanic magmatic systems and high li contents in plagioclase phenocrysts from 1980 and 2004 mount st helens dacites have been interpreted as evidence that shallow magma was fluxed by a li bearing vapor phase prior to eruption in amphibole phenocrysts zn and mn behave compatibly correlating to feo and al 2 o 3 and show no systematic change with time in contrast li and cu abundances in amphibole vary by up to 3 orders of magnitude 7 6 1140 g g and 1 7 to 94 g g respectively and do not generally correlate with either major or trace elements however they do correlate moderately well r 2 0 54 95 confidence with each other and show systematic temporal variations that are opposite to those observed for plagioclase precluding a simple 1 step diffusion model for li enrichment we propose a diffusion crystallization multi stage dcms model to explain the temporal variations and co variations of li and cu in early erupted dacite october december 2004 profiles of li isotopes in conjunction with measured 7 li intensities and core to rim increases in li concentration are characteristic of li diffusion into the amphiboles consistent with prior models of plagioclase enrichment in amphiboles from 2005 dacite average li and cu concentrations are high 260 660 g g and 29 45 g g respectively and in contrast to amphiboles from earlier erupted dacite correlate weakly with al 2 o 3 wt amphibole al 2 o 3 concentrations are an indicator of pressure with high al amphiboles crystallizing at higher pressures and we suggest that li and cu are partitioned into a fluid phase during ascent and crystallization of the magma so that amphiboles crystallizing at lower pressure have correspondingly lower li and cu concentrations however low li and cu in amphiboles from the dacite at the start of the eruption also require crystallization from a low li cu bearing melt or residence times long enough for amphiboles to re equilibrate with a li cu depleted melt estimated residence times suggest that amphiboles in early dacite could have been present since the end of the 1980 1986 eruptive episode at mount st helens

2000 ma sulphide concretions from the productive formation of the pechenga greenstone belt nw russia genetic history based on morphological and isotopic evidence abstract two hundred and fifty nine sulphide samples from black shales of the productive formation belonging to the palaeoproterozoic 2000 ma petsamo supergroup in the kola region nw russia have been analysed for their sulphur isotope ratio the sulphide bearing black shales were formed in a non euxinic basin within an oceanic rift environment the rocks have undergone greenschist facies metamorphism the black shales are marked by very high s corg ratios and a strong positive correlation between corg and s r 0 70 with zero intercept on the sulphur axis different generations of sulphide concretions have been distinguished by means of concretional analysis individual isotope study of synsedimentary sulphide layers and sulphides from early middle and late diagenetic catagenetic sulphide concretions yields trends which suggest bacterial sulphate reduction as the concretion forming process the overall spread of 34 s from 8 3 to 24 9 indicates 34 s sulphate sulphide between 29 and 4 given a seawater sulphate at around 21 the first order trend is a progressive enrichment in 34 s with increase of burial two major populations of sulphides have been distinguished the first concretions and perhaps thin layers formed in an open system with respect to seawater sulphate and has a limited 34 s range of 2 7 to 3 8 this is coupled with extensive formation of diagenetic carbonate beds marked by 13 c of 8 7 to 12 5 the second population lenses thin layers concretions and microconcretions in carbonate nodules formed in a closed system and is characterized by a high fe2 s2 ratio and progressive development of a rayleigh distillation process which drove 34 s from 8 3 up to 24 9 the high fe2 s2 and possibly change in ph parameter resulted in pyrrhotite rather than in pyrite associated abundant carbonate nodules have 13 c in the range 8 2 to 14 1 overall low 34 s sulphate sulphide and the high s corg ratio are consistent with one stage bacterial sulphate reduction in a non euxinic basin the observed 34 s sulphate sulphide of 29 as maximum is within the pure sulphate reducing bacteria range of 4 46 advanced isotopic modification involving the oxidative part of the sulphur cycle has not been detected based on the data available one can not exclude the presence of a third population of sulphides thin massive layers with 34 s from 2 5 to 0 3 which might have inorganic origin and formed from an exhalative source

cu and fe diffusion in rhyolitic melts during chalcocite dissolution implications for porphyry ore deposits and tektites copper diffusion plays an important role in natural processes such as metal transport during the formation of magmatic hydrothermal porphyry type ore deposits and cu isotope fractionation during tektite formation copper diffusion data in natural silicate melts however are limited in this study chalcocite cu 2 s dissolution experiments were carried out using chalcocite rhyolite diffusion couples to study cu and s diffusion in rhyolitic melts instead of chalcocite dissolution as initially expected our experiments show that cu is transferred from the chalcocite crystal to the rhyolitic melt and fe is transferred from the rhyolitic melt to chalcocite whereas the s concentration profile in the rhyolitic melt is essentially flat from the cu and fe exchange profiles in the rhyolitic melts cu diffusivities and fe diffusivities are obtained and reported copper diffusivity in rhyolitic melts containing 0 10 to 5 95 wt h 2 o at temperatures of 750 to 1391 c and pressures of 0 5 to 1 0 gpa can be described as d cu rhy exp 14 75 0 35 0 23 0 10 w 11647 491 698 117 w t which allows the estimation of an activation energy for diffusion in dry rhyolitic melts to be 96 8 4 1 kj mol in the above equation diffusivity d is in m 2 s t is the temperature in k w is the h 2 o concentration in the rhyolitic melts in wt and all errors reported are at 1 level combining cu diffusion data from this study and previous data in basaltic melt gives a general equation for cu diffusivity in natural silicate melts d cu exp 17 3 0 9 3 8 1 5 si al h 4403 1094 9700 1921 si al h t where si al h is the cation mole fraction of si plus al minus h in the silicate melt on a wet basis iron diffusivities obtained in this study in anhydrous to 6 wt h 2 o rhyolite are combined with previous data to get a general equation for fe diffusion in rhyolitic melts d fe rhy exp 16 1 1 7 19859 2541 1218 135 w t our data demonstrate that cu diffusion is faster than h 2 o or cl in rhyolitic melts containing 6 wt water which indicates that the scavenging and transport of cu by a magmatic volatile phase during formation of porphyry type ore deposits is not limited by diffusion of cu based on our experimental data cu diffusivity is almost four orders of magnitude higher than zn in anhydrous rhyolitic melts which supports the explanation of more diffusive loss of cu leading to more fractionated cu isotopes than zn isotopes in tektites

pge mineralization in andesite explosive breccias associated with the poperechny iron manganese deposit lesser khingan far east russia whole rock geochemical 190pt 4he isotopic and mineralogical evidence abstract we report in this paper an unusual occurrence of platinum group minerals in evolved explosive breccia associated with the poperechny iron manganese deposit lesser khingan range far east russia pgms in andesite breccia are represented by fe pt solid solutions 85 and pgm mostly os ir ru solid solutions sulfides and sulfarsenides 15 textural and compositional variations in pgm assemblages suggest that pt fe and os ir ru solid solutions as well as erlichmanite laurite series sulfides were formed during high temperature fractionation of mantle derived mafic parental melt similar to alaskan type complexes and were entrained in the evolved andesitic melt during its emplacement in the crust pd pt plumbostannide and copper gold solid solutions reflect late magmatic re crystallization and metasomatism early cretaceous 125 ma age of ferroplatinum in the explosive breccia suggests that pgm bearing ultramafic material could have been sampled during regional slab window tectonics related to the late mesozoic subduction of izanagi plate along southern margin of the north asian continent

genesis of late proterozoic copper mineralization copper claim south australia bedded disseminations no evidence for hydrothermal alteration the disseminated sulfides have a delta 34 s range of 17 3 to 15 8 per mil consistent with bacterial reduction of sulfate veinlet sulfides have a similar but smaller delta 34 s range in accord with formation by remobilization of the disseminated sulfides no significant delta 13 c differences between bedded and veinlet carbonates marked variations in delta 18 o values with magnesite values being generally higher than dolomite and the median value for bedded carbonates being around 23 per mil some 3 per mil higher than the median value for veinlet carbonates low temperature oxygen isotope equilibration during early diagenetic carbonate reactions low grade regional metamorphism caused minor recrystallization and formation of additional veinlets but did not extensively overprint the diagenetic isotopic trends isotopic similarities between the cupriferous and the unmineralized lithologies support introduction of the copper during sedimentation and or early diagenesis veinlet carbonates contain small nacl rich fluid inclusions formed at around 300 degrees c and 4 km depth during the metamorphism general trend of increasing mean delta 34 s values with decreasing age of the late proterozoic strata in the adelaide geosyncline and stuart shelf this trend may be the product of local environmental conditions which resulted in sulfate reduction outweighing sulfate replenishment alternatively it could be reflecting global processes which caused major 34 s enrichment of seawater sulfate modified journal abstract

mineralogical and isotopic characteristics of sodic calcic alteration in the highland valley copper district british columbia canada implications for fluid sources in porphyry cu systems

metamorphosed proterozoic zn pb ag mineralization in the foster river area northern saskatchewan canada metamorphosed zn pb occurrences fable lake george sito south sito southwest sito west sito east robyn lake and mackie lake with high zn pb ratios occur in the foster river area northern saskatchewan on the southeast margin of the paleoproterozoic wollaston domain the sito east prospect the largest of these occurrences contains 50 000 tonnes of 4 5 zn with one drill intercept containing 11 m of 4 2 zn and 0 6 pb most prospects are hosted in a thin areally extensive metaquartzite within a thick sequence of metasiltstones and metaquartzites in the middle of the paleoproterozoic wollaston group occurrences in metaquartzites and metaarkoses which locally contain gahnite spessartine and or graphite are spatially associated with metaexhalites iron formation and quartz garnetite and strata bound metamorphosed hydrothermal alteration zones nodular sillimanite rock post archean australian shale normalized rare earth element ree patterns of all three rock types are characterized by light ree enrichment positive ce anomalies neutral to strongly negative eu anomalies and heavy ree depletion consistent with an environment of deposition distinguished by a high 30 wt continental detrital component and formation from or interaction with low temperature 250 c near neutral ph and high fo2 fluids sulfur isotope compositions of sulfides at foster river are highly enriched in 34s 34s 26 2 38 1 n 20 and resulted from microbial reduction of partially reduced seawater sulfate in a restricted basin the spatial association of spessartine and gahnite bearing lithologies and silicate facies iron formation with paleoproterozoic base metal sulfides in a psammopelitic host sequence implies similarities between sulfide mineralization in the foster river area and broken hill type pb zn ag deposits however the markedly enriched 34ssulfide compositions low pb pb zn and ag pb zn ag ratios low ag contents and apparent absence of metavolcanic and metavolcaniclastic rocks in the dominantly clastic rock sequence hosting the sulfides in the foster river area suggest that these occurrences are part of a metamorphosed sedimentary exhalative system with broken hill type affinities similar to that associated with the formation of the gamsberg zn south africa kanmantoo group pb zn south australia and sullivan pb zn canada deposits

amphibole clinopyroxene and plagioclase melt partitioning of trace and economic metals in halogen bearing rhyodacitic melts

the geochemical differentiation of s type pegmatites constraints from major trace element and li b isotopic composition of muscovite and tourmaline pegmatites often exhibit regional as well as internal zonation in this study we use major and trace element and li b isotopic composition of muscovite and tourmaline from internally zoned and un zoned s type pegmatites and their host granites to characterize the geochemical and isotopic fractionation associated with their formation the internally zoned pegmatites comprise three distinct textural zones namely wall intermediate and core muscovite and tourmaline occur in all the zones of these pegmatites the trace element concentrations ratios of muscovite from the three zones form well defined differentiation trends marked by enrichment of incompatible elements such as rb cs sr b zn nb ta p and the depletion of ni co v sc ti ba from the wall zone through the intermediate zone to the core zone this is suggestive of a strong role of fractional crystallization in producing the compositional diversity in the internally zoned pegmatites alkali element ratios such k rb and k cs in muscovite exhibit near exponential decline from the wall to the core zone which is suggestive of rayleigh type fractional crystallization fractional crystallization modelling reveals that the formation of the wall zone requires 69 crystallization the intermediate zone 85 95 and the core zone ca 99 crystallization leading to extreme enrichment of rb and cs and other incompatible elements muscovites and tourmaline from the un zoned pegmatites display similar compositional trends as the internally zoned ones but with a significant compositional gap between the host granite and the pegmatite lithium isotopic composition of muscovites and b isotopic composition of tourmalines become progressively lighter from wall to core zone of the internally zoned pegmatite and from the granite to the pegmatite for the un zoned pegmatites this is suggestive of an important role of vapour exsolution in the formation of the pegmatites taken together the geochemical and isotopic trends in the pegmatites can be explained by rayleigh fractional crystallization operating in tandem with vapour exsolution

partitioning of sn and w between granitic melt and aqueous fluid abstract hydrothermal granite related sn and w deposits typically show predominance of one metal over the other at the intrusion and deposit scale this separation may reflect contrasting behavior of these elements during late stage magmatic processes in our experimental study we determined fluid melt partition coefficients of sn and w at 750 c 200 mpa as function of the alumina saturation index asi of the melt for nacl kcl hcl fluids two sets of data were obtained one from analysis of fluid inclusions trapped in glass and the other based on analysis of the quenched fluid our data indicate slight partitioning of sn into the melt and at asi of 0 99 1 16 strong partitioning of w into the aqueous fluid the effect of quenching was evident for tungsten which indicates that fluid melt partition coefficients of w reported in the literature are underestimated the contrasting fluid melt partitioning of sn and w implies that hydrothermal sn and w mineralization is rarely cogenetic furthermore contrasting fluid melt partitioning accounts for the separation and zonation of these metals on the deposit scale and the different style of predominant mineralization tin precipitates from the granitic melt as cassiterite or is incorporated in biotite and other minerals later exsolution of hcl bearing magmatic fluids can efficiently mobilize sn from the granite or the wall rock of the intrusion but can transport sn only over relatively short distances due to reaction of the fluid with feldspar greisenization which results in precipitation of cassiterite and formation of tin greisens tungsten is partitioned into the magmatic fluid and will be lost from the intrusion along with this fluid because greisenization reactions do usually not result in tungsten mineralization w can be transported farther away from the intrusion than sn and is deposited in scheelite bearing skarns or upon cooling in quartz wolframite veins

two sulphur isotope provinces deduced from ores in the mount isa eastern succession australia the sulphur isotopic characteristics of ore deposits in the australian mount isa eastern succession are not well known unlike those of the western succession in this study new detailed analyses are provided for recently discovered eastern succession mineralisation such as the starra and osborne bif hosted cu au ores the dugald river sediment hosted pb zn prospect and four vein hosted cloncurry style cu au deposits hampden mt elliot swan mt cobalt and the answer mine all of the deposits of the eastern succession have 34ssulphide between 8 and 9 regardless of their genesis empirically a moderate 34s range averaging close to 0 characterises starra style cu au and pegmont pb zn bif ores whereas shear and vein style cu mineralisation populations are tighter and do not average close to 0 this is a particularly surprising result for dugald river where a larger isotopic variation more typical of stratiform sediment hosted pb zn ores in the region might have been expected by comparison western succession stratiform pb zn and vein style cu deposits span a huge range of 15 to 51 large sulphur isotope ranges typify sulphate evaporite or organic sulphur rich sedimentary successions the lack of such variation in the eastern succession in turn suggests that primary evaporite sequences there were halite dominated but sulphate poor and or contained only limited volumes of organic sulphur rich sediment eastern succession sequences were therefore less likely hosts for giant stratiform pb zn deposits because of their paucity of sulphur although local sulphur sources permitted small deposits such as dugald river to develop sedimentary conditions were more favourable for the development of sulphur poor synsedimentary hydrothermal systems such as starra osborne and pegmont although sulphur isotope evidence is equivocal about the origin of these epigenetic deposits close to the williams batholith mt dore hampden owe their clustering around 0 to their granitic fluid source

geochemical precursors to volcanic activity at mount st helens usa the importance of the interplay between degassing and crystallization before and after the eruption of mount st helens washington usa in 1980 is well established here we show that degassing occurred over a period of decades to days before eruptions and that the manner of degassing as deduced from geochemical signatures within the magma was characteristic of the eruptive style trace element lithium and short lived radioactive isotope lead 210 and radium 226 data show that ascending magma stalled within the conduit leading to the accumulation of volatiles and the formation of lead 210 excesses which signals the presence of degassing magma at depth

explosive rhyolitic volcanism in the jemez mountains vent locations caldera development and relation to regional structure the jemez volcanic field straddles the western margin of the rio grande rift where the rift is intersected by the jemez lineament in north central new mexico the field has a record of volcanism extending back to before 13 ma initial basaltic activity was related to active rifting with minor rhyolitic eruptions occurring along n s rift bounding faults between 10 and 7 ma voluminous andesitic volcanism took place in the central jemez mountains area overwhelming contemporaneous basaltic and rhyolitic magmatism an apparent tectonic lull took place from 7 to 4 ma accompanied by lower eruption rates during this interval dacitic magmas were erupted to form the tschicoma volcanic center but mafic and rhyolitic volcanism virtually ceased since 4 ma accompanying resumption of rifting a growing silicic magma system has been present under the central part of the jemez mountains ultimately evolving to the magma body that produced the voluminous rhyolitic bandelier tuffs explosive rhyolitic eruptions from this large magma body have occurred many times since 3 to 4 ma early eruptions 3 6 2 8 ma produced high silica rhyolite ignimbrites restricted to the southwest part of the jemez mountains formation of these units may have been accompanied by caldera collapse these events were followed by the two caldera forming bandelier tuff ignimbrite eruptions 1 45 and 1 12 ma post caldera explosive and effusive rhyolite eruptions have also tapped the magma body from vents generally located along ring fractures after both bandelier events vent and caldera locations for the rhyolitic eruptions during 3 4 ma have been inferred from grain size characteristics dispersal patterns and facies variations in the plinian deposits and ignimbrites lithic breccia zones of the pre bandelier ignimbrites indicate possible caldera sources in the southwest part of the present valles caldera during the eruption of both bandelier tuffs initial plinian falls and early pyroclastic flows emanated from vents centrally located in the jemez mountains in the lower bandelier tuff eruption a transition to ring fracture vents occurred before the emission of later pyroclastic flows but there is no strong evidence to suggest such a transition occurred during the upper bandelier eruption calderas associated with the lower and upper bandelier tuffs toledo and valles respectively are almost identical in location as are the plinian vent sites for these two large eruptions the toledo embayment northeast of the valles caldera contains lava domes from up to 3 6 ma and may be a caldera or crater associated with early explosive dacitic volcanism in the tschicoma volcanic center post 1 4 ma lava domes also fill this depression the main volcanic features of the jemez mountains field including the valles caldera complex eruption vents and the apical graben of the post valles redondo resurgent block appear to be aligned along the ne sw trending jemez fault zone this zone the local expression of a precambrian basement feature the jemez lineament has exerted strong control on the location and style of eruptions from the bandelier rhyolitic magma system

tracing fluid saturation during pegmatite differentiation by studying the fluid inclusion evolution and multiphase cassiterite mineralisation of the gatumba pegmatite dyke system nw rwanda abstract aqueous fluid saturation during the internal evolution of phosphorus and boron rich pegmatites in nw rwanda has been investigated using petrography fluid inclusion microthermometry and microanalysis of minerals and fluid inclusions raman microspectroscopy and la icp ms the gatumba dyke system gds in rwanda has been selected for this study because it hosts a multiphase cassiterite mineralisation in wall core and internal replacement zones suggesting an advancing influence of magmatic hydrothermal conditions during dyke solidification as such multiphase cassiterite precipitation is applied as a tracer for magmatic to hydrothermal crystallisation processes in granitic pegmatites the gds consists of a group of six major lct lithium caesium tantalum family dykes which all belong to the most differentiated rare element pegmatites in the gatumba gitarama field petrography identified a well developed internal anatomy consisting of a border wall intermediate and a quartz core zone in addition replacement zones developed as cleavelandite after perthitic microcline units in the intermediate zone and as muscovite quartz pockets in the intermediate and wall zones the latter replacement zone display muscovitisation reactions with the formation of greisens texturally the greisen pockets replace the secondary cleavelandite units during internal differentiation multiphase cassiterite mineralisation formed in 1 large microcline crystals of the wall zone cst1 2 assemblage with quartz f poor montebrasite and carbonate and boron enriched mn fluorapatite in the core zone cst2 and 3 the greisen replacement units in the wall and intermediate zones cst3 fluid inclusion micro analyses demonstrate that a saline aqueous h2o nacl kcl co2 n2 l1 type fluid 20 wt nacl and 3 wt kcl was saturated during onset of crystallisation of the wall and intermediate zones and precipitation of the disseminated magmatic hydrothermal cst1 mineralisation in and around large perthitic k feldspars isochore reconstructions of this l1 fluid indicate crystallisation conditions of 535 560 c and 5 1 5 6 kbar for the gds extensive microcline fractionation and subsequent replacement reactions of cleavelandite after microcline in the intermediate zone were induced by a li enriched and more na depleted h2o nacl licl co2 n2 l2 type fluid which was present during solidification of the core zone and present during precipitation of cst2 phase mineralisation 6 12 wt nacl 1 10 wt licl late stage hydrothermal cst3 mineralisation in the greisen pockets precipitated from a cs enriched h2o nacl kcl co2 n2 l3 type fluid 15 wt nacl distinctly after the formation of the cleavelandite replacement units subsolidus cst3 precipitation is dominantly driven by metasomatic hydrolytic fluid rock reactions combining textural microthermometric and fluid compositional data with reported sn melt fluid partitioning and solubility data demonstrate that primary cassiterite i e cst1 and cst2 in the wall and core zone of the gds precipitated from the exsolved saline aqueous l1 and l2 fluid present at the interface of the highly fractionated melt phase fast disequilibrium growth of near anhydrous mineral assemblages likely caused the formation of flux rich and at least locally water saturated melt compositions at the crystallisation front of the large crystals this study emphasises the importance of local magmatic hydrothermal conditions and the presence of an immiscible aqueous fluid phase during the internal crystallisation and cassiterite mineralisation of rare element pegmatites

hydrothermal evolution of the el teniente deposit chile porphyry cu mo ore deposition from low salinity magmatic fluids the magmatic hydrothermal evolution of the el teniente porphyry cu mo deposit in the central andes in chile is reconstructed based on field relationships scanning electron microscopy cathodoluminescence petrography and fluid inclusion analysis by microthermometry and laser ablation inductively coupled plasma mass spectrometry la icpms three major stages of cu mo mineralization are observed following the barren hydrothermal stage 1 the stage 2 mineralization is characterized by quartz anhydrite stockwork veins and breccias with chalcopyrite bornite and molybdenite both stages 1 and 2 are associated with pervasive potassic alteration quartz anhydrite veins with chalcopyrite bornite and molybdenite associated with phyllic alteration represent stage 3 mineralization stage 4 mineralization linked to the formation of the large braden diatreme is characterized by breccias and rare veins containing a lower temperature assemblage with tourmaline sericite and lesser tennantite bornite and chalcopyrite with late gypsum in local vugs ten fluid types are distinguished in this study based on petrographic and microthermometric criteria such as phase proportions daughter minerals homogenization behavior and salinity the hydrothermal evolution across the stages of cu deposition is characterized by the contraction of a vapor phase originating by phase separation during stage 2 overall cooling of the system at pressures fluctuating around the two phase fluid surface led to a transition from a two phase fluid state dominated by vapor at 410 c and 300 bars in stage 2 to a single phase low salinity fluid derived from cooling and contraction of magmatic vapor to a liquid which dominates during stage 3 mineralization at 350 c and 200 bars copper mineralization mainly formed from the vapor phase and its low salinity liquid derivatives representing a large volume of fluid with an initially high cu content 1 2 0 4 wt cu copper sulfides precipitated upon cooling between 410 and 320 c indicated by a drop of cu na k mn fe ratios of over four orders of magnitude through the evolution of the deposit from stage 2 to stage 4 the highest mo concentrations occur in residual brines resulting from extreme boiling as indicated by concurrent halite saturation recent geochronology cannell 2005 maksaev et al 2004 suggests a relatively long lived magmatic hydrothermal system at el teniente our fluid chemical data show no evidence for major crystal fractionation in a large fluid generating upper crustal magma chamber because cs na k mn fe is constant from pre ore to all syn ore fluids however the initiation of copper mineralization was associated with a 4 to 10 fold increase in the concentration of cu mo li and fe in the inferred main ore forming input fluid compared with pre ore fluids of intermediate salinity and otherwise very similar major and trace element ratios these data indicate that injection from depth of an exceptionally cu mo li and probably also s rich volatile phase into an already actively evolving upper crustal magmatic hydrothermal system triggered the formation of this unusually large and rich copper deposit

biotite geochemistry deciphers magma evolution of sn bearing granite southern myanmar abstract hydrothermal sn w deposits are commonly formed by ore forming fluids that exsolved from water saturated granitic magmas however the timing of fluid exsolution and its influence on volatiles and ore forming elements still remain confused for this purpose geochemical and o h isotopic compositions of biotite from late cretaceous eocene granitic intrusions in the sibumasu terrane southern myanmar are presented mno content of biotite is a well negative correlation with the amount of biotite and whole rock la yb n ratio indicating that it could be a good index of granitic magma differentiation cl content of biotite from paleocene granite shows an increased first and subsequently decreased trend with increasing mno content 0 71 2 36 wt suggesting cl enrichment by magma evolution and depletion by late stage fluid exsolution fluid exsolution is also supported reduced li contents of biotite and o h isotopic compositions of residual magmatic water equilibrated with high mno biotite 18o 7 0 to 8 8 and d 114 to 93 5 all studied biotite grains from late cretaceous granite have low cl contents 0 01 0 11 wt decreased li with increasing mno contents and residual magmatic water like o h isotopic values 18o 6 9 and d 105 indicating that their host granitic melts had undergone fluid exsolution importantly a positive correlation between sn and mno contents in biotite suggests that magma differentiation is a dominant process for sn enrichment no depletion of sn by fluid exsolution likely caused by low salinity fluids exsolved from cl poor granitic melts which were estimated by low cl contents of biotite h isotopic compositions 18o 6 8 7 0 and d 61 9 to 90 2 with magmatic water suggesting that ore forming fluids probably exsolved from more evolved granitic melts with strong sn and f enrichment

generation of porphyry copper deposits by gas brine reaction in volcanic arcs we acknowledge research funding from bhp billiton a benjamin meaker visiting professorship to j m and a royal society wolfson research merit award and erc advanced grant critmag to j b

copper partitioning between silicate melts and amphibole experimental insight into magma evolution leading to porphyry copper ore formation abstract a series of piston cylinder experiments were conducted to determine the partition coefficient of cu between amphibole and andesitic to rhyolitic silicate melts the experiments were run at t 740 990 c p 0 7 gpa oxygen fugacity f o 2 ranging from that of the ni nio buffer nno to 2 3 log units higher nno 2 3 and dissolved water in variable concentrations under saturated to saturated conditions fixed metal activities were imposed by using au 97 cu 3 and au 92 cu 8 alloy capsules which allowed simultaneously determination of cu solubility our data demonstrate that cu solubilities in both the silicate melt and amphibole decrease with decreasing temperature the solubility of cu decreases by a factor of 6 from 990 to 740 c in equilibrium with andesitic to rhyolitic melt compositions the average amphibole silicate melt partition coefficient of cu d cu amph melt is 0 066 0 006 and is essentially constant without showing any correlation with silicate melt composition dissolved water concentration temperature or f o 2 the low d cu amph melt value suggests that amphibole crystallizing at any stage of calc alkaline magma evolution is unable to scavenge a significant fraction of the initially available cu from the melt however d cu amph melt is high enough to yield precisely measurable cu concentrations in natural amphiboles as d cu amph melt remains constant along the liquid line of descent of calc alkaline magmas amphibole compositions may thus be used as a proxy to monitor the evolution of the cu concentration in the silicate melt not the bulk magma if sulfide is present this may be useful for understanding the metallogenic evolution of intrusive rocks in which silicate melt inclusions in minerals are generally absent as most porphyry type cu ore deposits are associated with upper crustal intrusions in situ microanalysis of inclusion free amphiboles in such rocks may help understand ore genesis and might also be used in mineral exploration to assess the fertility of prospective magmatic systems

exsolution of immiscible vapor and liquid phases from a crystallizing silicate melt implications for chlorine and metal transport abstract the compositional variation of a cl bearing aqueous fluid exsolving from a crystallizing silicate melt is evaluated for the system haplogranitic melt na k c1 h 2 o with attention to the effect of vaporliquid immiscibility on the aqueous fluid above critical pressures for the aqueous fluid p 1 5 kb at 800 c where the fluid is single phase the cl concentration in the aqueous fluid c cl aq gradually decreases with crystallization of a silicate melt under rayleigh fractionation as demonstrated by previous studies however the variation of ca is quite different below critical pressures where vapor liquid immiscibility occurs in particular at low pressures p cl h 2 o ratio in a melt is small and ca will increase with crystallization a high cl h 2 o ratio at low pressure results in liquid exsolution and decreasing ca with crystallization eventually both vapor and liquid phases will exsolve simultaneously regardless of the initial exsolving phase during this simultaneous exsolution the composition of the exsolving vapor and liquid phases the mass ratio of these phases and the cl concentration of the silicate melt will all remain constant comparison of the model and published experimental data indicates that the simultaneous exsolution of vapor and liquid may occur from a normal rhyolite crystallized at pressures below the critical pressure for the aqueous fluid therefore simultaneous exsolution of the immiscible aqueous phases is likely to be a common phenomenon in magmatic hydrothermal systems at conditions for the vapor liquid immiscibility model calculations at 0 6 and 1 2 kb indicate that major amounts of cl in the system will be distributed to the liquid phase particularly at the lower pressure this suggests that the majority of chloridecomplexed metals exsolving from a magma may be transported in the liquid phase under shallow crustal conditions

geochemistry of precambrian carbonates vi aphebian albanel formations quebec canada abstract the 1 85 0 15 ga old albanel formations of northern quebec canada an example of paleoproterozoic carbonate buildups are lithologically composed of cherty dolostones subordinate limestones are encountered only near the base of the sequence coincident with maximal transgression the chemistry of the bulk rocks is almost entirely controlled by noncarbonate phases such as chert quartz plagioclase illite k spar pyrite and fe mn oxides all abundant particularly in the basal part of the section the chemistry of the carbonate portion of limestones is strongly reset by post depositional phenomena but the relict high sr contents suggest that aragonite may have been an original precursor phase geochemically the carbonate portion of dolostones can be subdivided into two populations reflecting the stratigraphie bottom and top of the sequence trace element and oxygen isotope criteria suggest that the entire sequence was subjected to meteoric and subsequent burial diagenesis with the less deeply buried top portion of the sequence having recrystallized and stabilized at lower temperatures but in a more open system the latter reflects the greater lithological variability and permeability of the younger strata the 13c varies up section from about 3 to 1 perhaps a reflection of progressively more open marine circulation the associated four generations of post depositional pyrites have overlapping 34s from 7 1 to 54 with a mean of 24 a reflection of dissimilatory bacterial sulfate reduction in a relatively closed diagenetic system with perhaps a limited sulfate availability and or replenishment the best measured 87 sr 86 sr of 0 70600 although possibly not a direct reflection of the coeval seawater may still be a near original value as indicated by its coherency with the roughly co stratigraphic paleo proterozoic sequences evaluation of the existing data indicates that strontium isotopic composition of the precambrian seawater was characterized by oscillations similar to those of the phanerozoic the interval of 0 8 1 5 ga ago being dominated by relatively nonradiogenic values followed by a radiogenic period at 1 6 2 2 ga ago near mantle values during the late archean and possibly another radiogenic peak at 3 5 ga ago

massive siliciclastic discharge to slopes of the great barrier reef platform during sea level transgression constraints from sediment cores between 15 s and 16 s latitude and possible explanations abstract the northeast australian continental margin including the great barrier reef gbr platform provides an outstanding modern analogue for understanding sedimentation in tropical mixed siliciclastic carbonate depositional systems previous studies of cores from this margin have suggested that in contrast to widely accepted models maximum siliciclastic fluxes to slopes over the last 30 ky occurred when sea level transgressed the shelf ca 11 7 ka rather than when sea level was at a lowstand before 18 ka however climate and bathymetry can affect regional sediment deposition significantly and the cores examined to date have come from the southern queensland trough where the margin has a wet tropical climate and a broad shelf 50 km with gradual slopes in this study we examine the abundance and accumulation of siliciclastic material in four cores from lower slopes of the northern queensland trough where rivers drain a drier region and debouche onto a narrow shelf with steep incised slopes similar to previously examined cores all cores contain a dark greyish brown horizon within the upper few meters this horizon represents a low in carbonate content and corresponding high in siliciclastic material primarily clay and oxygen isotope stratigraphy shows that it was deposited during late transgression nominally between 11 and 7 ka moreover mass accumulation rate calculations demonstrate that this horizon reflects a significant rise in siliciclastic fluxes when combined with the previous work to the south it appears that slopes all along a large portion of the northeast australian continental margin received greatly enhanced inputs of siliciclastic material during late transgression independent of proximal climate and bathymetry two general explanations are offered for this observation 1 climate change induced highly variable riverine discharge over the past 30 ky with a prominent maximum coincident with late transgression or 2 the shelf stores large quantities of siliciclastic sediment during lowstand and releases this material to the slope during late transgression in either case siliciclastic accumulation on the northeast australia continental margin behaves completely opposite to predictions from conventional models

partitioning of f between h2o and co2 fluids and topaz rhyolite melt implications for mineralizing magmatic hydrothermal fluids in f rich granitic systems fluid melt distribution coefficients for f have been determined in experiments conducted with peraluminous topaz rhyolite melts and fluids consisting of h2o and h2o co2 at pressures of 0 5 to 5 kbar temperatures of 775 1000 c and concentrations of f in the melt ranging from 0 5 to 6 9 wt the major element f and cl concentrations of the starting material and run product glasses were determined by electron microprobe and the concentration of f in the fluid was calculated by mass balance the h2o concentrations of some run product glasses were determined by ion microprobe sims the solubility of melt in the fluid phase increases with increasing f in the system the solubility of h2o in the melt is independent of the f concentration of the system with up to 6 3 wt f in the melt no evidence of immiscible silica and fluoriderich liquids was detected in the hydrous but water undersaturated starting material glasses 8 5 wt f in melt or in the water saturated run product glasses f concentrates in topaz rhyolite melts relative to coexisting fluids at most conditions studied however df wt f in fluid wt f in melt increases strongly with increasing f in the system maximum values of df in this study are significantly larger than those previously reported in the literature linear extrapolation of the data suggests that df is greater than one for water saturated peraluminous granitic melts containing 8 wt f at 800 c and 2 kbar df increases as temperature and as h2o h2o co2 of the fluid increase for topaz rhyolite melts containing 1 wt f and with h2o rich fluids df is independent of changes in pressure from 2 to 5 kbar at 800 c for melts containing 1 wt f and in equilibrium with co2 bearing fluids the concentrations of f in fluid increases with increasing pressure f and lithophile element enriched granites may evolve to compositions containing extreme concentrations of f during the final stages of crystallization if f in the melt exceeds 8 wt df is greater than one and the associated magmatic hydrothermal fluid contains 4 molal f such f enriched fluids may be important in the mass transport of ore constituents i e f mo w sn li be rb cs u th nb ta and b from the magma

a physical model for metal extraction and transport in shallow magmatic systems 1 the highest concentrations of metals e g cu au ag mo in the earth s crust are found in porphyry type deposits the metals are ultimately sourced from magmas and appear to be concentrated hundred to thousand fold from typical magmatic contents ppm ppb in the exsolved volatile phase to better quantify the purging and transport of metals we develop a physical model of volatile evolution in an incrementally built upper crustal magma reservoirs that considers 1 partitioning of metals from the melt to an exsolved volatile phase and 2 advection of the buoyant volatile phase using a single dimensionless parameter the peclet number pe ratio of advection rate over diffusion rate we propose that metal extraction and segregation from magmas can occur in 3 stages with different pe 1 during exsolution of the magmatic volatile phase in shallow crystal poor magma bodies slow volatile advection pe 1 2 during the growth of volatile channels that develop in the reservoir as crystallinity increases pe 1 and 3 during advection in connected channels rapid volatile advection high pe 1 for each stage a metal enrichment factor can be calculated allowing insight into the optimal conditions to maximize metal mass flux into the overlying hydrothermal system the model predicts that the most efficient purging of metals occurs for magmas with intermediate volatile contents and is enhanced during late stage magmatic activity as the reservoirs reach high crystallinity and are not disturbed by volcanic venting in agreement with natural observations suggesting that ore formation post dates volcanic activity

fluid melt trace element partitioning behaviour between evolved melts and aqueous fluids experimental constraints on the magmatic hydrothermal transport of metals abstract the fluid melt partition coefficients of ten trace metals li mn cu zn rb sr mo w and pb along with k between hydrous evolved melts and coexisting cl bearing fluid s have been experimentally determined at 850 1050 c 0 6 2 2 kbar and o2 nno 0 5 to nno 2 log units the measured compositions of the quenched fluid phases vary from low salinity 2 wt cl to 19 wt cl with maximum starting fluid concentrations of 21 wt cl the results of 15 partitioning experiments confirm that dmetalfluid melt values depend strongly on the melt and fluid composition with the greatest metal affinities for the fluid phase shown in the experiments with high cl fluids and the most fractionated melts five experiments conducted in au96cu4 capsule alloy show dcufluid melt values ranging from 40 to 80 and a strong correlation with melt feo wt contents at equivalent fluid cl contents in contrast li shows only weak partitioning in favour of coexisting fluids across all melt compositions with dlifluid melt ranging from 0 16 in low salinity fluids to 1 17 in the highest cl fluid 19 15 wt cl a procedure was employed to redissolve and analyse the aluminosilicate precipitates that form during quenching of the experiments this procedure allows for metal contents of the final quench fluids to be constrained by both mass balance and direct measurement by solution icp ms analysis a comparison of the mass balance calculated vs directly measured fluid melt partition coefficients generally gives good agreement within an order of magnitude for most trace elements however discrepancies between these methods arise due to errors inherent in the mass balance calculations for metals with low abundances in the fluids e g sr and especially those showing affinities to alloy with the experiment capsule material e g mo these discrepancies in constraining experimental fluid trace element budgets also suggest that the precious metal capsule alloys cannot always be considered completely inert containers in experimental investigations and semi quantitative la icp ms analysis of the raw capsule alloys confirms the detectable presence of several of the trace elements investigated here integrating these new partitioning data with previous experimental and natural studies confirms that aqueous cl bearing fluids exsolved by hydrous calc alkaline melts stored at mid to upper crustal conditions are capable of efficiently sequestering and transporting some economically important trace metals e g mn cu zn however the new fluid melt li partitioning data in conjunction with evidence of very late post eruptive li modification suggests that li is moderately strongly fluid immobile at depth and suffers from significant post eruptive re equilibration this has implications for deciphering the signatures of volatile fluxing in arc magmas that are preserved in mineral and melt inclusion trace element concentrations and the development of mineralised stockwork regions in porphyry style metal deposits

solubility of tin tungsten and molybdenum oxides in felsic magmas saturation versus undersaturation of granitic melts in tin tungsten and molybdenum oxides is discussed on the basis of experimental data results of dry and hydrothermal experiments are evaluated under the assumption of ideal solubility of sn w and mo oxides in granitic melts a conservative interpretation arrives at concentration levels of 1000 ppm sno2 wo3 and moo3 respectively considered as the maximum solubility of these components in granitic melts at 750 c 800 c such values are never reached in natural granites unaffected by hydrothermal alteration and therefore even highly evolved granites are expected to be undersaturated in these metals consequently cassiterite and scheelite are neither common liquidus minerals of ore bearing granites nor restite minerals from partial melting events

platinum solubility and partitioning in a felsic melt vapor brine assemblage abstract the solubility and partitioning of pt in a s free vapor brine rhyolite melt pt metal assemblage has been quantified at 800 c f o 2 nno and pressures of 100 and 140 mpa vapor and brine were sampled at run conditions by trapping these phases as glass hosted fluid inclusions as the melt cooled through the glass transition temperature the vapor and brine were in equilibrium with the melt at the time of trapping and thus represent fluids which were sampled at the termination of each experimental run the microthermometrically determined salinities of vapor and brine are 2 and 63 wt nacl eq and 9 and 43 wt nacl eq at 100 and 140 mpa respectively platinum solubilities in vapor brine and glass i e quenched melt were quantified by using laser ablation inductively coupled plasma mass spectrometry la icp ms equilibrium is discussed with reference to the major and trace element concentrations of glass hosted fluid inclusions as well as the silicate melt over run times that varied from 110 to 377 h at 140 mpa and 159 to 564 h at 100 mpa platinum solubility values 1 in h2o saturated felsic melt are 0 28 0 13 g g and 0 38 0 06 g g at 140 and 100 mpa respectively platinum solubility values 1 x at 140 and 100 mpa respectively in aqueous vapor are 0 91 0 29 g g and 0 37 0 17 g g and in are brine 16 10 g g and 3 3 1 0 g g the measured solubility data were used to calculate nernst type partition coefficients for pt between vapor melt brine melt and vapor brine the partition coefficient values 1 x for vapor melt brine melt and vapor brine at 140 mpa are 2 9 1 0 67 27 and 0 13 0 05 and at 100 mpa are 1 0 0 2 6 8 2 4 and 0 15 0 05 the partitioning data were used to model the pt scavenging capacity of vapor and brine during the crystallization driven degassing i e second boiling of a felsic silicate melt over a depth range i e 3 6 km consistent with the evolution of magmatic hydrothermal ore deposits model calculations suggest that aqueous vapor and brine can scavenge sufficient quantities of pt and by analogy other platinum group elements pge to produce economically important pge rich magmatic hydrothermal ore deposits in earth s upper continental crust

fluid immiscibility in volcanic environments volatile components enter the atmosphere oceans and other surface waters through pre syn and post eruptive volcanic processes that involve a variety of fluids aluminosilicate poor fluids include aqueous or carbonic to sulfide sulfate chloride fluoride carbonate and phosphate rich compositions in volcanic environments but other more complex combinations of these constituents may be involved giggenbach 1977 roedder 1984 1992 lowenstern 1995 other rare gases and dissolved constituents e g h2 n2 he ar h3bo3 hg ch4 and other hydrocarbon compounds metals and metalloids are also present but in general they are not sufficiently concentrated to form their own phases or control bulk fluid composition and volcanic processes as a result of their diverse compositions volcanic fluids ranging from vapor to liquid exhibit widely different densities and show strong distinctions in heat capacity dielectric behavior viscosity and other chemical and physical characteristics geiger et al 2006a the density of a saline liquid in the system nacl h2o at 50 mpa and 800 c for example is more than 7 times that of the coexisting aqueous vapor e g 0 2 gm cm3 henley and mcnabb 1978 multiple fluids move mix and or unmix in magma chambers and volcanic conduits in the root zone of fumaroles and in the convective hydrothermal systems that are ubiquitous to volcanic environments hydrothermal systems are typically centered on magmatic intrusions and may include crater lakes at the top of eruptive conduits hydrothermal processes involving two or more fluid phases operate through a variety of geologically relevant shallow crustal pressure temperature composition conditions volcanic fluids occur at supersolidus to subsolidus conditions meaning that the dense aluminosilicate melt that is common to volcanism may or may not be present this chapter addresses the evidence for and occurrence of two or more low density aluminosilicate poor fluids

partitioning of lithophile trace elements between h 2 o and h 2 o co 2 fluids and topaz rhyolite melt experiments have been conducted with h 2 o and h 2 o co 2 bearing fluids and melts of a cl f and lithophile trace element enriched vitrophyre associated with topaz rhyolite from spor mountain utah the starting material is mildly peraluminous and contains 1 25 wt percent f and 1 500 ppm cl the experiments were conducted with f sub o 2 controlled near ni nio at pressures of 0 5 to 4 kbars and at temperatures of 770 degrees to 950 degrees c fluid melt trace element distribution coefficients d i were calculated for li be b rb sr y zr nb cs ba ce th and u after ion microprobe analysis of starting material and run product glasses the concentration of element i in the fluid was calculated by mass balance and the fluid melt distribution coefficient d i was calculated as ppm by weight of i in fluid ppm by weight of i in melt the partitioning of li rb sr y nb cs and ce between aqueous fluids and melts of topaz rhyolite composition depends strongly on temperature and pressure at 0 5 kbars li rb sr y nb cs and ce concentrate in the fluid at temperatures or 900 degrees c at 2 kbars this same group of lithophile elements except for sr concentrate in the fluid at t or 900 degrees c be b and ba partition in favor of the melt at 0 5 and 2 kbars and at all temperatures of this study in the presence of co 2 free aqueous fluids at 4 kbars and at temperatures of 770 degrees to 950 degrees c all lithophile elements partition in favor of the melt this behavior for lithophile elements mimics that of published data on the partitioning of pb and zn between rhyolitic melts and cl bearing fluids previous studies have demonstrated an equivalent effect of pressure on the distribution of chalcophile trace elements between granitic melts and cl bearing aqueous fluids fluid melt distribution coefficients for the lithophile trace elements are significantly smaller for topaz rhyolite melts in equilibrium with mixed co 2 h 2 o fluids than for topaz rhyolite melts plus co 2 free aqueous fluids there is no evidence for co 2 complexing with the lithophile trace elements at pressures 6 m the data imply that the alkali elements m dissolve into the fluid as mcl 0 complexes and that ce dissolves into the fluid as a cecl 0 3 complex water saturated magmas of topaz rhyolite composition may become differentiated with respect to li cs and rb or ce y and nb if an aqueous fluid phase is evolved and moves through the magma under the influence of a temperature gradient that has a maximum temperature of at least 850 degrees to 900 degrees c

experimental evidence for the alteration of the fe3 σfe of silicate melt caused by the degassing of chlorine bearing aqueous volatiles the temporal evolution of the redox conditions undergone by degassing magmas has petrologic implications for magmatic phase equilibria we present new experimental data that demonstrate that a cl bearing magmatic volatile phase may affect the concentration and activity of ferrous iron in silicate liquid via the preferential mass transfer of fe 2 into the volatile phase the data are consistent with a model wherein the exsolution of a cl bearing volatile phase from the melt modifies the mgo feo ratio of the residual degassed melt increasing the fe 3 fe ratio of the melt degassing induced alteration of the melt may cryptically affect the phases that constitute the hypersolidus crystallizing assemblage the new results indicate that a low to moderate salinity magmatic volatile phase may contain several weight percent iron present as fecl 2 as such passive degassing over geologically plausible protracted periods has the potential to extract significant quantities of fe 2 resulting in a residual melt depleted in feo relative to fe 2 o 3 notably preferential mass transfer of fe 2 from the melt to the fluid results in self oxidation of the melt driving the oxygen fugacity of the melt across the phase boundary that demarcates the stability fields of sulfide and sulfate phases stabilizing sulfate at the expense of sulfide such a process has significant implications for the remobilization of chalcophile metals during the evolution of magmatic hydrothermal systems

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

triggers for the formation of porphyry ore deposits in magmatic arcs porphyry ore deposits supply much of the copper molybdenum gold and silver used by humans a review of the main processes that trigger porphyry ore formation suggests that sulphide saturation of the magmas that supply the metals could be the overriding mechanism that helps control the temporal and spatial distribution of the ore deposits