rapid thermal rejuvenation of high crystallinity magma linked to porphyry copper deposit formation evidence from the koloula porphyry prospect solomon islands magmas containing the components needed to form porphyry copper deposits are relatively common within arcs yet mineralising events are uncommon within the long lived magmatic systems that host them understanding what causes the transition from barren to productive intrusions is critical to the development of conceptual deposit models we have constrained the tempo of pre and syn mineralisation magmatic events in relationship to the thermal evolution of the plutonic body that underlies one of the world s youngest exposed plutonic porphyry systems the inamumu zoned pluton koloula porphyry prospect solomon islands high precision id tims u pb dates of texturally and chemically characterised zircons indicate pluton emplacement over 50 crystals state past the point of rheological lock up we estimate that thermal rejuvenation of the deeper high crystallinity magma and generation of a mobile melt fraction may have occurred 10 kyr before its transport and emplacement within the porphyry environment the underlying pluton likely cooled and returned to high crystallinity states prior to subsequent remobilisation emplacement events titanium in zircon geothermometry and whole rock geochemistry suggest pre mineralisation intrusions were remobilised by mixing of a silicic magma with a high temperature less evolved melt in contrast syn mineralisation melts were most likely remobilised by the percolation of hot volatiles exsolved from contemporaneous less evolved intrusions cooling beneath the crystalline silicic magma the evidence for the rapid thermal rejuvenation and long term storage of highly crystalline silicic magmas is consistent with previous studies that indicate two components of exsolved volatiles contribute to ore forming fluids we conclude that the liberation of crystal rich porphyry copper deposit forming magmas and the addition of the chemical components required for ore formation are intrinsically linked to the volatiles released during the recharge of less evolved melt into a highly crystalline silicic magma

controls on the disseminated ni cu pge sulfide mineralization at the tubane section northern molopo farms complex botswana implications for the formation of conduit style magmatic sulfide ores abstract the molopo farms complex mfc is located near the western margin of the archean kaapvaal craton in southern botswana the complex hosts low grade disseminated ni cu and platinum group elements pge mineralization restricted to the lower ultramafic cumulates notably in the feldspathic orthopyroxenites the mineralized feldspathic orthopyroxenites contain up to 0 47 ppm pt pd au manifested in the form of platinum group mineral pgm assemblages dominated by pge bismuthotellurides asernides and minor au and ag alloys the pgm encountered are froodite pdbi2 moncheite ptte2 michenerite pdbite sperrylite ptas2 largely associated with altered silicates and sulfide minerals the association of pgm with sulfides suggests that they were originally concentrated by sulfide melt while late stage reaction of sulfides with hydrothermal fluids resulted in the observed spatial proximity of pgm with altered silicates the cu pd ratios of most of the rocks fall within the primitive mantle range however the cu pd ratios of the feldspathic orthopyroxenites are more variable with few samples falling above and below the primitive mantle range suggesting the prior sulfide extraction from the magmas and the presence of cumulus sulfides this is supported by the cu zr ratios of these rocks which are also variable above and below unity trace element ratios on the th yb pm versus nb th pm plot indicate strong crustal contamination across all units including those not in proximity to the country rocks the 34s of the magmatic rocks are variable between 6 3 and 11 4 in contrast the 34s of dolomitic siltstones of the transvaal supergroup which constitute the immediate country rocks vary from 4 1 to 0 6 these data indicate that crustal contamination largely occurred prior to magma emplacement it is inferred that the most important contaminant and source of crustal s were the ramotswa and ditlhojana formations that include sulfidic shales at depth we consider that magnesian basaltic magmas of b1 bushveld magma composition underwent crustal contamination assimilation of crustal s and segregation of sulfide melt in the feeder conduit or staging chamber prior to final magma emplacement the feeder conduit or staging chamber was subsequently invaded by further b1 magma this magma entrained some of the sulfides lodged in the plumbing system and flushed them to the final mfc chamber studied here after the staging chamber had already partially solidified it was invaded by yet another influx of magma possibly even more primitive than the b1 bushveld magma being a crystal mush this magma assimilated and entrained some of the previously formed orthopyroxenites manifested by fragments of orthopyroxenite in the harzburgites of the final mfc chamber the presence of centimeter sized globular sulfides and fragments of orthopyroxenite within harzburgites suggests that the complex was emplaced as separate pulses of magmas therefore it is considered that sulfide accumulations may remain undiscovered in the feeder zones or the staging chamber

determination of rapid deccan eruptions across the cretaceous tertiary boundary using paleomagnetic secular variation 2 constraints from analysis of eight new sections and synthesis for a 3500 m thick composite section 1 the present paper completes a restudy of the main lava pile in the deccan flood basalt province trap of india chenet et al 2008 reported results from the upper third and this paper reports the lower two thirds of the 3500 m thick composite section the methods employed are the same i e combined use of petrology volcanology chemostratigraphy morphology k ar absolute dating study of sedimentary alteration horizons and as the main correlation tool analysis of detailed paleomagnetic remanence directions the thickness and volume of the flood basalt province studied in this way are therefore tripled a total of 169 sites from eight new sections are reported in this paper together with the results of chenet et al 2008 these data represent in total 70 of the 3500 m combined section of the main deccan traps province this lava pile was erupted in some 30 major eruptive periods or single eruptive events see each with volumes ranging from 1000 to 20 000 km3 and 41 individual lava units with a typical volume of 1300 km3 paleomagnetic analysis shows that some sees with thicknesses attaining 200 m were emplaced over distances in excess of 100 km both likely underestimates due to outcrop conditions and up to 800 km the total time of emission of all combined sees could have been much less than 10 ka with most of the time recorded in a very small number of intervening alteration levels marking periods of volcanic quiescence so called big red boles the number of boles thickness of the pulses and morphology of the traps suggest that eruptive fluxes and volumes were larger in the older formations and slowed down with more and longer quiescence periods in the end on the basis of geochronologic results published by chenet et al 2007 and paleontological results from keller et al 2008 we propose that volcanism occurred in three rather short discrete phases or megapulses an early one at 67 5 1 ma near the c30r c30n transition and the two largest around 65 1 ma one entirely within c29r just before the k t boundary the other shortly afterward spanning the c29r c29n reversal we next estimate sulfur dioxide likely a major agent of environmental stress amounts and fluxes released by sees they would have ranged from 5 to 100 gt and 0 1 to 1 gt a respectively over durations possibly as short as 100 years for each see the chemical input of the chicxulub impact would have been on the same order as that of a very large single pulse the impact therefore appears as important but incremental neither the sole nor main cause of the cretaceous tertiary mass extinctions

atmospheric oxygenation caused by a change in volcanic degassing pressure around two and a half billion years ago following the end of the archaean eon the atmosphere turned from anoxic to weakly oxic in what is known as the great oxidation event using a model of volcanic degassing gaillard et al demonstrate that a preceding period of continental crust formation may have been the trigger they propose that as continents emerged and volcanoes became increasingly subaerial rather than submarine magmatic volatiles were degassed at lower pressures leading to a progressive oxidation of the gases released this shift to a release of sulphur as sulphur dioxide rather than as hydrogen sulphide could then have fed marine sulphate reduction and the eventual oxygenation of earth s atmosphere the precambrian history of our planet is marked by two major events a pulse of continental crust formation at the end of the archaean eon and a weak oxygenation of the atmosphere the great oxidation event that followed at 2 45 billion years ago this oxygenation has been linked to the emergence of oxygenic cyanobacteria1 2 and to changes in the compositions of volcanic gases3 4 but not to the composition of erupting lavas geochemical constraints indicate that the oxidation state of basalts and their mantle sources has remained constant since 3 5 billion years ago5 6 here we propose that a decrease in the average pressure of volcanic degassing changed the oxidation state of sulphur in volcanic gases initiating the modern biogeochemical sulphur cycle and triggering atmospheric oxygenation using thermodynamic calculations simulating gas melt equilibria in erupting magmas we suggest that mostly submarine archaean volcanoes produced gases with so2 h2s 1 and low sulphur content emergence of the continents due to a global decrease in sea level and growth of the continental crust in the late archaean then led to widespread subaerial volcanism which in turn yielded gases much richer in sulphur and dominated by so2 dissolution of sulphur in sea water and the onset of sulphate reduction processes could then oxidize the atmosphere

flotation mechanism of sulphide melt on vapour bubbles in partially molten magmatic systems abstract the motion of dense fe rich immiscible sulphide liquids is generally supposed to be dominated by gravitational settling in crustal magma chambers however they may become buoyant by attachment to low density vapour bubbles to form compound drops possibly contributing to the upward transfer of sulphur and transition metals in degassing magma bodies here using numerical models we consider constraints on the flotation of compound drops and find a wide range of morphologies that would be expected to be capable of migrating through magmatic systems including both melt and mush dominated domains but also some situations where the compound drops will spontaneously separate to allow the vapour to rise while the sulphide phase is sequestered in the mush the stability of compound drops is empirically related to a function f b o m v m s m s 1 b o s v s m s m s 1 b o v where m v and s denote silicate melt vapour and sulphide liquid is surface tension n m 1 and bo is the bond number over a range of plausible conditions in magmas f bo must exceed values of 3 to 4 for capillary forces to overcome buoyancy forces tending to pull them apart using published thermodynamic models for vapour and sulphide solubility in silicate melts we show that in many magmas the second boiling of vapour occurs synchronously with the saturation of sulphide liquid increasing the potential for coupling of vapour and sulphide droplets diffusive coarsening produces mm sized bubbles within 100 500 years generating enough buoyancy to trigger the migration of compound drops during compaction driven expulsion of interstitial melt compound drops can pass through constrictions between crystals in mush the flotation of sulphide vapour aggregates is likely to occur in crustal magma reservoirs and provides a feasible mechanism for the removal of sulphide liquid from crystal mushes promoting its ability to participate in the generation of magmatic sulphide and porphyry copper deposits emissions of the metals during volcanic eruptions and even the remobilization of chalcophile metals sequestered in deep arc cumulates to generate porphyry cu au deposits

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

a global view of martian surface compositions from mgs tes thermal emission spectrometer tes data from the mars global surveyor mgs are used to determine compositions and distributions of martian low albedo regions two surface spectral signatures are identified from low albedo regions comparisons with spectra of terrestrial rock samples and deconvolution results indicate that the two compositions are a basaltic composition dominated by plagioclase feldspar and clinopyroxene and an andesitic composition dominated by plagioclase feldspar and volcanic glass the distribution of the two compositions is split roughly along the planetary dichotomy the basaltic composition is confined to older surfaces and the more silicic composition is concentrated in the younger northern plains

trace elements in magnetite from massive iron oxide apatite deposits indicate a combined formation by igneous and magmatic hydrothermal processes iron oxide apatite ioa deposits are an important source of iron and other elements e g ree p u ag and co vital to modern society however their formation including the namesake kiruna type ioa deposit sweden remains controversial working hypotheses include a purely magmatic origin involving separation of an fe p rich volatile rich oxide melt from a si rich silicate melt and precipitation of magnetite from an aqueous ore fluid which is either of magmatic hydrothermal or non magmatic surface or metamorphic origin in this study we focus on the geochemistry of magnetite from the cretaceous kiruna type los colorados ioa deposit 350 mt fe located in the northern chilean iron belt los colorados has experienced minimal hydrothermal alteration that commonly obscures primary features in ioa deposits laser ablation inductively coupled plasma mass spectroscopy la icp ms transects and electron probe micro analyzer epma wavelength dispersive x ray wdx spectrometry mapping demonstrate distinct chemical zoning in magnetite grains wherein cores are enriched in ti al mn and mg the concentrations of these trace elements in magnetite cores are consistent with igneous magnetite crystallized from a silicate melt whereas magnetite rims show a pronounced depletion in these elements consistent with magnetite grown from an fe rich magmatic hydrothermal aqueous fluid further magnetite grains contain polycrystalline inclusions that re homogenize at magmatic temperatures 850 c smaller inclusions 500 ppm concentrations

low temperature aqueous alteration of basalt mineral assemblages of deccan basalts and implications for mars spectra of basalt samples were dominated by fe 2 crystal field transitions with weak alteration bands near 1 4 and or 1 9 mm reststrahlen bands in mid infrared showed the convolution of plagioclase and pyroxene features typical of basalts saprolite samples were incompletely leached and their spectra were dominated by complex al and fe mg bearing smectite clays and retained no original mafic signatures xrd and mossbauer detected pyroxene and plagioclase not visible by reflectance spectroscopy in some saprolite samples zeolites were present throughout the saprolite the laterite was the most leached horizon and all analyses showed kaolinite and iron oxide assemblages this kaolinite and hematite association would be expected if kaolinite on mars formed through leaching under conditions similar to those on earth and has implications for abundant freshwater on the martian surface

assimilation of sulfate and carbonaceous rocks experimental study thermodynamic modeling and application to the noril sk talnakh region russia most of the intrusions in the noril sk talnakh region siberia are hosted in thick sedimentary sequences including abundant evaporitic and terrigenous sedimentary rocks three mafic ultramafic intrusions in this region contain unusually thick massive sulfide deposits which represent one of the world s largest economic concentrations of ni cu and pge the interaction of siberian magmas with sulfate and organic matter rich sedimentary rocks has been proposed as a possible mechanism for the origin of these exceptional sulfide deposits but the interaction process and the reaction paths have never been fully investigated here we clarify by both experimental petrology and thermodynamic modeling how sulfate and organic matter assimilation occur in mafic ultramafic magmas affecting magma composition crystallization and sulfide saturation interaction experiments were conducted at conditions relevant to the emplacement of noril sk type intrusions 1200 c 80 mpa to simulate the assimilation of sulfate and or organic compounds by ultramafic magmas we used a picrite from noril sk1 intrusion and coal and anhydrite from the area as starting materials the experimental results show that the incorporation of anhydrite into the magma occurs by chemical dissolution in the melt which increases the magma s sulfur content but suppresses sulfide saturation and reduces olivine crystallization extreme assimilation leads to sulfate saturation in the magma and high dissolved sulfur contents of 0 9 0 1 wt s conversely coal assimilation promotes sulfide segregation and magma crystallization while decreasing the dissolved h2o content of the melt and increasing the amount of coexisting fluid phase we also employed gas melt thermodynamic calculations to quantify the effect of these assimilations on the redox conditions and the s content of the magma and investigate the role of temperature pressure and initial gas content of the magma in the assimilation process we quantify how sulfate assimilation strongly oxidizes the magma and increases its s content both effects are intensified by increasing pressure from 50 to 100 mpa in this study decreasing temperature from 1350 to 1200 c in this study and decreasing amounts of fluid phase initially coexisting with the magma from 2 to 0 wt the interaction with organic matter ch in this study induces a strong reduction of the magma even for extremely low degrees of assimilation few tenths of wt and the dehydration of the melt we therefore suggest that in the noril sk talnakh district 1 additional s was supplied to mantle derived magmas by the assimilation of evaporitic rocks and was transported during magma ascent in the form of dissolved oxidized s 2 a substantial reduction of the magma inducing sulfide segregation and important crystallization then occurred due to the interaction with carbonaceous sediments this mechanism can potentially produce massive sulfide deposits by important sulfate assimilation locally higher than 3 wt caso4 and minor organic matter assimilation few tenths of wt ch however if one of the two steps does not occur or the assimilation in 1 is not large enough disseminated sub economic or no sulfide deposits are produced we conclude that exceptional conditions favoring substantial assimilation of sediments are needed to generate exceptional ore deposits like those of the noril sk talnakh district

metal fluxes during magmatic degassing in the oceanic crust sulfide mineralisation at odp site 786b izu bonin forearc volcanogenic massive sulfide deposits are enriched in metals that are either derived from hydrothermal alteration of the basement rocks or supplied by exsolution of metal rich volatiles during magmatic differentiation the extent to which each process contributes to metal enrichment in these deposits varies between different tectonic settings ocean drilling program hole 786b recovered 800 m of upper oceanic crust from a supra subduction zone setting and includes a 30 m thick mineralised zone in situ s isotopic compositions of pyrite decrease from 5 9 2 9 in the upper mineralised zone down to 3 3 2 1 in the extensively altered central mineralisation zone potentially indicating strong magmatic fluid input in this area whole rock data and in situ trace element analyses in sulfide minerals show enrichment of ag as au bi mo s se sb and te in the mineralised zone evaluation of metal behaviour during magmatic differentiation and primary metal fertility of basement rocks suggests that degassing melt is the main source for the high au se and s enrichment observed in the mineralised zone magmatic volatile exsolution occurred late during the magmatic differentiation 2 wt mgo concomitant with oxide crystallisation and metal depletion in the melt comparison of ocean drilling program hole 786b with volcanogenic massive sulfide deposits hosted by boninitic volcanic successions such as in the semail ophiolite the newfoundland appalachians and the flin flon belt suggests that magmatic fluid exsolution could be a common mechanism for au enrichment in bimodal mafic volcanogenic massive sulfide deposits

role of degassing of the noril sk nickel deposits in the permian triassic mass extinction event the largest mass extinction event in earth9s history marks the boundary between the permian and triassic periods at circa 252 ma and has been linked with the eruption of the basaltic siberian traps large igneous province slip one of the kill mechanisms that has been suggested is a biogenic methane burst triggered by the release of vast amounts of nickel into the atmosphere a proposed ni source lies within the huge noril sk nickel ore deposits which formed in magmatic conduits widely believed to have fed the eruption of the slip basalts however nickel is a nonvolatile element assumed to be largely sequestered at depth in dense sulfide liquids that formed the orebodies preventing its release into the atmosphere and oceans flotation of sulfide liquid droplets by surface attachment to gas bubbles has been suggested as a mechanism to overcome this problem and allow introduction of ni into the atmosphere during eruption of the slip lavas here we use 2d and 3d x ray imagery on noril sk nickel sulfide combined with simple thermodynamic models to show that the noril sk ores were degassing while they were forming consequent bubble riding by sulfide droplets followed by degassing of the shallow sulfide saturated and exceptionally volatile and cl rich slip lavas permitted a massive release of nickel rich volcanic gas and subsequent global dispersal of nickel released from this gas as aerosol particles

mineral magnetic and diffuse reflectance spectroscopy characteristics of the deccan volcanic bole beds implications to genesis and transformations of iron oxides abstract deccan volcanic bole beds are important indicators of paleoenvironmental conditions during cretaceous tertiary volcanism however little attention has been paid to iron oxide characteristics of these lava flow hosted sediments therefore in order to understand the genesis and transformation of various iron oxides in different colored bole beds we studied the mineral magnetism and diffuse reflectance spectroscopy drs characteristics of red brown and green boles that are extensively exposed in the deccan volcanic province dvp of western india mineral magnetism and drs characteristics indicate hematite fe 2 o 3 as the major iron oxide in all the bole beds with traces of goethite feooh in many maghemite fe 2 o 3 was also present in red boles as well as in few brown and green boles the higher concentration of magnetic minerals in red boles is due to the neo formation of fine magnetic minerals produced from heating of the weathered sediments by the overlying lava flow the increasing concentration of superparamagnetic sp fraction indicated by frequency dependent susceptibility fd with increased reddening of the bole beds mean fd for green brown and red boles 2 5 11 1 and 19 3 10 8 m 3 kg 1 respectively facilitates the use of fd as first order estimate for degree of heating in red boles the paragenesis of ferrimagnetic and antiferromagnetic minerals in green and brown boles is indicated by good correlation r 2 0 78 between hard isothermal remanent magnetization hirm and fd suggests that green and brown boles have undergone some pedogenesis the overall distribution of iron oxides in these bole beds indicate their genesis from incipient weathering of fe mg minerals e g olivine and pyroxenes under humid conditions leading to the formation of ferrihydrite and goethite as precursors partial to complete heating resulted into oxidation of precursors and titanomagnetite to maghemite as the intermediate transformation phase and hematite as end product the green brown and red boles thus represent the transitional baking environments under various hydrous anhydrous conditions and pedogenic processes the genesis and transformation of various iron oxides in dvp bole beds may have significant implications for the characterization of such interflow sediments paleosols from other igneous provinces e g israel karoo flood basalt south africa and columbia river basalt usa further complex genesis of the iron oxides in the dvp bole beds also envisages a great scope to study them as martian analogues apart from their significance to paleoenvironment and demands more advanced rock magnetic and spectroscopic approaches

an attempt to constrain the age duration and eruptive history of the karoo flood basalt naude s nek section south africa we have carried out paleomagnetic sampling of a similar to 750 m sequence of the karoo large igneous province naude s nek pass south africa k ar dating cassignol gillot has been performed on four samples from the 650 m upper unit mean age 179 2 1 8 ma and a sample from the lower unit 184 8 2 6 ma a succession of two phases of volcanism is suggested the lower 25 flows 115 m thick have recorded a reversed polarity the next 23 flows 135 m thick are transitional and contribute a detailed record of the van zijl 1962 jurassic reversal the upper 38 flows 500 m thick have normal polarity directional groups dgs of lava flows with quasi identical remanence directions indicate eruption durations too short to have recorded geomagnetic secular variation and hence are interpreted as single eruptive events altogether 19 dgs and 10 sheet lobes yield a sequence of 29 distinct directions this could correspond to a total eruptive activity shorter than 3000 years less than one per mil of the total duration over which the section was emplaced we obtain a new paleomagnetic pole for south africa at similar to 180 ma lambda 75 2 degrees n phi 276 4 degrees e a 95 5 8 degrees n 19 which is consistent with earlier reports

textural morphological and compositional varieties of modern arc sulfides a case study of the tolbachik volcano kamchatka abstract magma unmixing into separate sulfide and silicate melts is a key process in the formation of magmatic sulfide ore deposits sulfide inclusions in olivine preserve the original chemical composition of the segregated sulfide melt whereas the phase compositions of the solidified sulfide droplets and their textures record the final stages of sulfide evolution sulfide globules hosted in olivine phenocrysts of magnesian basalts from the tolbachik volcano kamchatka display a variety of textures ranging from homogeneous to fine grained to coarse grained and lamellar porous textures and textures associated with the oxidation and dissolution of sulfides were identified as separate categories the outer surfaces of sulfides vary significantly in shape which includes normal spherical or elliptical globules gravitationally layered inclusions thin sulfide foils and concave deformed sulfides in contact with fluid bubbles the estimated cooling rate of olivine phenocrysts responsible for observed crystallization textures varies by five orders of magnitude the fe ni cu ratio also exerts an influence on the resulting texture whereas the size of the globules does not have any significant effect the morphology and textural patterns of individual grains indicates that fine grained textures resulted from the rapid breakdown of a homogeneous solid phase which the sulfide melt solidified into during extremely rapid quenching the presence of large or abundant small pores in sulfides along with channels at the globule periphery indicates the separation of an appreciable amount of dissolved fluid from the sulfide melt during crystallization sulfides in the form of thin foils and planar swarms in healed cracks indicate cyclic pressure changes in the olivine environment which resulted in phenocrysts rupturing and healing the sulfide mineralogy is represented by high temperature sulfides mss monosulfide solid solution and iss intermediate solid solution as well as pyrrhotite pentlandite chalcopyrite cubanite bornite magnetite assemblages which formed at lower temperatures

microchemical and sulfur isotope constraints on the magmatic and hydrothermal evolution of the black swan succession western australia the black swan succession consists of an archean bimodal dacite komatiite association largely dominated by ultramafic cumulates hosting a number of massive and disseminated magmatic sulfide orebodies although it was affected by multiple alteration events the low degree of penetrative deformation allowed the preservation of magmatic textures and stratigraphic relationships in this context we apply a combined multiple sulfur isotope and microchemical approach to unravel the potential of sulfides to simultaneously retain information about their magmatic and hydrothermal history negative 33s signatures in both massive 0 56 and disseminated 0 66 sulfide orebodies reflect the assimilation of photochemically derived sulfur into the komatiite magma which attained sulfide liquid supersaturation through the assimilation of crustal material analogous to the intercalated breccia dacite hosting colloform sulfides 33s 0 91 the slightly different 33s signatures between disseminated and massive orebodies reflect the assimilation of different proportions of crustally derived sulfur and imply that the respective sulfide liquids segregated from distinct komatiite magma pulses subsequent alteration episodes imparted to the black swan succession a concentric zonation consisting of a serpentinite core and talc carbonate margins the black swan disseminated orebody extends through both alteration styles without major variations in the dominant millerite pyrite sulfide assemblage pyrite in both serpentinite and talc carbonate samples exhibits a consistent trace element signature suggesting a relative immobile behavior of ni and co during the percolation of the talc carbonate fluids conversely variable 34s signatures between the two alteration styles reflect mobilization of sulfur during talc carbonate alteration whereas the 2 range of 34s values in serpentinites can be attributed to moderate equilibrium fractionation processes the 10 range of 34s values in talc carbonate rocks suggests that highly oxidizing fluids promoted the mobilization of sulfur as so42 which decreased the 34s of the disseminated sulfides furthermore sulfur isotope and microchemical signatures of euhedral pyrite from intercalated dacitic breccia indicate that this pyrite generation was deposited from a late hydrothermal event which is characterized by variable and least negative 33s signatures between 0 20 and 0 48 relative to all sulfide orebodies these features suggest that the late fluids developed in a heterogeneous hydrothermal system with a minor component of sulfur recycled from the sulfide orebodies

thermomechanical erosion of ore hosting embayments beneath komatiite lava channels textural evidence from kambalda western australia abstract archean komatiite hosted nickel deposits at kambalda western australia are located in embayments within channelized lava flows the origin of these embayments is controversial the currently favoured model invokes pre existing topographic features filled in by the komatiite and sulfide melt and subsequently modified by thermomechanical erosion new evidence from sulfide deposits on the eastern limb of the kambalda dome includes well preserved magmatic textural relationships of the sulfides with the surrounding rocks suggesting the entire embayment was formed by thermomechanical erosion these textures are particularly well preserved within the moran deposit of the long victor complex which lacks the younger intense structural deformation that other kambalda deposits have undergone the vestiges of an older broad concave embayment are represented by sediment sulfide textures present on the flanks up to 150 m away from the younger steep sided embayment sediment sulfide contacts are marked here by a globular silicate sulfide intergrowth interpreted as emulsion and cumulate like mono sulfide solid solution mss grains surrounded by interstitial silicate melt textures preserved from the formation of a steep sided embayment are frozen into the basalt sulfide contact and include an undulating contact with sulfide filled microfractures and a ferrichromite layer basalt sulfide breccia and interpreted crystallized silicate sulfide liquid emulsions and basalt plumes rising into the sulfides textures from the last step of embayment formation are found in the pinchouts i e where the massive sulfide ore is bounded top and bottom by basalt they include the same textures that were formed during the excavation of the steep sided embayment but they also feature interpreted basalt sulfide emulsions on the upper contact cm scale silicate sulfide ferrichromite layering on the upper contact and a vesicular basalt scum layer floating on the sulfides beneath the solid older basalt all these textures represent frozen examples of different stages during the excavation and formation of the embayment and reflect physical processes responsible for thermomechanical erosion the initial disposition and orientation of ore hosting channels was controlled by paleo topography probably defined by syn volcanic faults but the textures we describe show that within the channel the geometry of the entire embayment was the product of erosion the sulfide melt itself played a major role in the process owing to its high density high heat content and very low viscosity but the hydrated nature of the underlying altered basalt was also critical fluids were released from the basalt due to the high temperature in the 1 2 cm immediately beneath the sulfide melt with instant flash boiling creating a network of microfractures pre existing fracture networks and breccia in the basalt allowed the sulfide melt to locally infiltrate the substrate to a greater depth increasing the hydraulic head at the tip of the fracture thus accelerating the erosion process once a critical sulfide melt thickness is reached partly aided by a growing pile of matrix net textured sulfides the pressure difference on the embayment floor compared to the basalt at the bottom edges of the embayment becomes high enough to allow the liquid sulfides to melt sideways to form a pinchout

zircon u pb dating reveals late jurassic gold mineralization in the jidong district of the northern north china craton abstract the north china craton ncc hosts numerous gold deposits clustering in several districts which combined have proven reserves of 7000 t au geochronological studies have shown that the craton wide gold mineralization occurred mostly in the 140 120 ma interval coincident with the peak of thinning and destruction of the lithospheric keel beneath the ncc here we integrate geological relations with la icp ms zircon u pb dating to reveal a new gold mineralization event in the jidong district northern ncc the xiajinbao yu erya and jinchangyu gold deposits in this district are characterized by crosscutting relationships between gold veins and various dikes this relation suggests that zircon u pb dating of the pre ore and post ore dikes can provide tight constraints on the time of gold veining la icp ms zircon u pb dating of pre and post ore dikes from the three gold deposits yields concordant u pb dates of 165 163 ma 165 164 ma and 165 164 ma respectively these indistinguishable u pb dates within analytical uncertainty are interpreted as the timing of gold deposition 165 163 ma and thus reveal a previously unrecognized late jurassic gold mineralization event in the jidong district a large variety of mafic to intermediate dikes in the jidong district have zircon u pb dates of 166 1 to 164 2 ma consistent with ages of the three gold deposits investigated the temporal consistency and abundant sulfide inclusions hosted in the mafic intermediate intrusions along with the close spatial relations between gold veins and various dikes within and surrounding the mines indicate a possible magmatic source for ore fluids synthesis of regional geological geochemical and isotopic data led us to conclude that the late jurassic gold mineralization in the northern ncc is genetically related to lithosphere destruction of the ncc an additional implication from this study is that the mesozoic decratonization of the ncc and associated gold mineralization are spatially and temporally heterogeneous and much more prolonged than commonly thought

the variability of ruthenium in chromite from chassignite and olivine phyric shergottite meteorites new insights into the behavior of pge and sulfur in martian magmatic systems the martian meteorites comprise mantle derived mafic to ultramafic rocks that formed in shallow intrusions and or lava flows this study reports the first in situ platinum group element data on chromite and ulvospinel from a series of dunitic chassignites and olivine phyric shergottites determined using laser ablation icp ms as recent studies have shown that ru has strongly contrasting affinities for coexisting sulfide and spinel phases the precise in situ analysis of this element in spinel can provide important insights into the sulfide saturation history of martian mantle derived melts the new data reveal distinctive differences between the two meteorite groups chromite from the chassignites northwest africa 2737 nwa 2737 and chassigny contained detectable concentrations of ru up to 160 ppb ru in solid solution whereas chromite and ulvospinel from the olivine phyric shergottites yamato 980459 y 980459 tissint and dhofar 019 displayed ru concentrations consistently below detection limit 42 ppb the relatively elevated ru signatures of chromite from the chassignites suggest a ru rich 1 4 ppb parental melt for this meteorite group which presumably did not experience segregation of immiscible sulfide liquids over the interval of mantle melting melt ascent and chromite crystallization the relatively ru depleted signature of chromite and ulvospinel from the olivine phyric shergottites may be the consequence of relatively lower ru contents 1 ppb in the parental melts and or the presence of sulfides during the crystallization of the spinel phases the results of this study illustrate the significance of platinum group element in situ analysis on spinel phases to decipher the sulfide saturation history of magmatic systems

high resolution x ray computed tomography and its application to ore deposits from data acquisition to quantitative three dimensional measurements with case studies from ni cu pge deposits high resolution x ray computed tomography hrxct is a nondestructive technique that allows exploration of the three dimensional distribution of minerals and pore space in natural and synthetic rock samples recent technological developments allow the characterization of samples up to few centimeters in diameter at a resolution down to 0 7 m this combined with the development of dedicated workflows algorithms and softwares is opening new doors for the quantitative three dimensional characterization of ores at the sample scale when combined with three dimensional image analysis hrxct provides quantitative three dimensional mineralogical and textural measurements volume shape three dimensional relationship that are impossible to assess accurately by any other method this manuscript describes the principles of hrxct and presents dedicated methodologies from data acquisition throught to quantitative three dimensional measurements these methodologies are applied to ni cu pge ore samples but are suitable for a range of geologic materials the combination of hrxct with quantitative three dimensional image analysis applied to geologic materials hosting ore deposits provides a better understanding of ore mineralogy ore forming processes and parameters required for mineral or metallurgical processing with benefit for both academic studies and mineral industry applications

giant kiruna type deposits form by efficient flotation of magmatic magnetite suspensions kiruna type iron oxide apatite ioa deposits are an important source of fe ore and two radically different processes are being actively investigated for their origin one hypothesis invokes direct crystallization of immiscible fe rich melt that separated from a parent silicate magma while the other hypothesis invokes deposition of fe oxides from hydrothermal fluids of either magmatic or crustal origin here we present a new model based on fe and o stable isotopes and trace and major element geochemistry data of magnetite from the 350 mt fe los colorados ioa deposit in the chilean iron belt that merges these divergent processes into a single sequence of events that explains all characteristic features of these curious deposits we propose that concentration of magnetite takes place by the preferred wetting of magnetite followed by buoyant segregation of these earlyformed magmatic magnetite bubble pairs which become a rising magnetite suspension that deposits massive magnetite in regionalscale transcurrent faults our data demonstrate an unambiguous magmatic origin consistent with the namesake ioa analogue in the kiruna district sweden further our model explains the observed coexisting purely magmatic and hydrothermal magmatic features and allows a genetic connection between kiruna type ioa and iron oxide copper gold deposits contributing to a global understanding valuable to exploration efforts

high resolution nitrogen stable isotope sclerochronology of bivalve shell carbonate bound organics nitrogen stable isotope ratios 15n of organic material have successfully been used to track food web dynamics nitrogen baselines pollution and nitrogen cycling extending the 15n record back in time has not been straightforward due to a lack of suitable substrates in which 15n records are faithfully preserved thus sparking interest in utilizing skeletal carbonate bound organic matter cbom in mollusks corals and foraminifera here we test if calcite pecten maximus shells from the bay of brest and the french continental shelf can be used as an archive of 15n values over a large environmental gradient and at a high temporal resolution approximately weekly bulk cbom 15n values from the growing tip of shells collected over a large nitrogen isotope gradient were strongly correlated with adductor muscle tissue 15n values r2 0 99 n 6 p 0 0001 we were able to achieve weekly resolution on average over the growing season from sclerochronological profiles of three shells which showed large seasonal variations up to 3 4 however there were also large inter specimen differences up to 2 5 between shells growing at the same time and location generally high resolution shell 15n data follow soft tissue 15n values but soft tissues integrate more time hence soft tissue data are more time averaged and smoothed museum archived shells from the 1950s 1965 and 1970s do not show a large difference in 15n values through time despite expected increasing n loading to the bay over this time which could be due to anthropogenic n sources with contrasting values compiling shell cbom 15n data from several studies suggests that the offset between soft tissue and shell 15n values tissue shell differs between calcite and aragonite shells we hypothesize that this difference is caused by differences in amino acids used in constructing the different minerals which should be specific to the caco3 polymorph being constructed future work should use compound specific isotope analyses csia to test this hypothesis and to determine whether certain amino acids could specifically track n sources or possibly identify amino acids that are more resistant to diagenesis in fossil shells in conclusion bivalve shell cbom 15n values can be used in a similar manner to soft tissue 15n values and can track various biogeochemical events at a very high resolution

paleoclimate deduced from some early jurassic basalt derived paleosols from northern israel abstract earthy red layers intercalated amid basalt flows from an early jurassic 2500 m thick volcanic sequence in northern israel were examined mineralogically micromorphologically and chemically distinct pedological features such as wavy illuviation argillans and iron oxide nodules observed by micromorphological examinations identified the clayrich layers as basalt derived paleosols the clay by comparison with the mineralogy and micromorphology of modern basalt derived vertisols a moderately wet mediterranean type climate with pronounced seasonality was inferred for the formation time of the paleosols a similar lower jurassic paleoclimate had previously been inferred from a paleosol in the negev

the role of early sulfide saturation in the formation of the yulong porphyry cu mo deposit evidence from mineralogy of sulfide melt inclusions and platinum group element geochemistry abstract sulfide melt inclusions enclosed in silicate minerals have been observed in many oxidized cu bearing porphyries the origin of such sulfide melt inclusions could bear critical information of metal enrichment or depletion during magma evolution of porphyry systems the giant yulong porphyry cu mo deposit in eastern tibetan plateau consists of a series of felsic intrusions among which the mineralized yulong intrusion emplaced at a late stage of the magmatic activity this study reports detailed texture and composition of sulfide melt inclusions from barren and mineralized intrusions as well as platinum group elements of these intrusions to evaluate potential role of early sulfide saturation in the porphyry mineralization system these sulfide melt inclusions occurring as globules or droplets are preserved in zircon amphibole and quartz grains most of them are composed of a major phase of pyrrhotite and minor pyrite chalcopyrite and pentlandite smooth boundaries between these phases suggest the origin of fractionation from sulfide melt upon cooling small amounts of cu and ni are heterogeneously distributed in the pyrrhotite the sulfide melt inclusions could be observed in both the pre and syn mineralization intrusions at yulong indicating that sulfide saturation had commonly occurred during magma evolution magnetite mineral inclusions could be observed in zircon and amphibole grains as well the mineral assemblage of magnetite pyrrhotite pyrite of the mineral inclusions constrains the yulong magmatic system to redox conditions near the magnetite pyrite pyrrhotite buffer and above the fayalite magnetite quartz buffer fmq high eu eu values 0 56 0 78 of the hosting zircons and high calculated nno values 0 5 of the hosting amphibole indicate highly oxidized nature of the parental magma both pre and syn mineralization intrusions have low pge contents pt 0 04 to 0 17 ppb pd 0 19 0 60 ppb with compositions plotting in the au poor porphyry cu fields in discriminating diagrams early sulfide saturation may have been reached and small amounts of sulfides have been segregated from magma most pges and au but little cu have been removed from the evolved magma because the partition coefficient of cu between sulfide and silicate melt is about two orders of magnitude lower than pge or au as a consequence the evolved magma would have high cu but very low pge and au resulting in the au poor porphyry cu mineralization at yulong

origin of red clay layers interbedded with basalts of the golan heights abstract red clay layers interbedded with basalt flows of pleistocene age in the golan heights have been described and sampled for analyses data for these layers have been compared with those for modern soils of the locality because the layers have pedogenic features and most also contain quartz of assumed aeolian origin they are considered to by paleosols even though they are low in organic matter smectite is the dominant clay mineral in the paleosols as it is in modern soils of the area at the same time minerals characteristic of hydrothermal activities are absent low proportions of kaolinite as compared to those of modern soils are attributed to weathering under a drier climate in the middle pleistocene approximately 0 7 1 6 m y b p than that of the present the paleosols are dense have strong columnar structure and have well expressed mangans these features as well as the dehydration of iron oxides are attributed to contacts with molten rock that become the basalt flows

magnetic enhancement is linked to and precedes hematite formation in aerobic soil 1 soil formation usually increases magnetic susceptibility most often by increasing the concentrations of magnetite and maghemite which are two ferrimagnetic iron oxides here we provide evidence that magnetic enhancement in aerobic soils not affected by detrital magnetic inputs or thermal transformation of other iron oxides is mostly due to the formation of maghemite which is later transformed into hematite the iron oxide that gives red color to soil we show that the maghemite hematite ratio is influenced by the particular environment and the degree of soil development so it constitutes an effective tool for paleoenvironmental and planetary studies

ingress of magmatic ni cu sulphide liquid into surrounding brittle rocks physical structural controls abstract field observations and theoretical considerations suggest that dense magmatic sulphide liquids are injected into and or passively infiltrate surrounding wall rocks late in the emplacement history of intrusion hosted magmatic ore systems using analogies with other engineering and mineral systems we evaluate the structural and physical controls on the ingress of sulphide liquid into brittle host rocks gravity driven infiltration of sulphide liquid out of the host igneous intrusion into country rock may be analogous to the behaviour of dense immiscible fluids in groundwater systems dense non aqueous phase liquids dnapl which is controlled by the body force of the liquid itself downward penetration of sulphide liquid into micro fractures may occur once a sufficient thickness of sulphide known as the critical accumulation height is reached in the overlying intrusion upward and lateral injection of sulphide liquid is a similar process to the behaviour of crustal hydrothermal fluids where active deformation fluid pressure and host rock anisotropy play critical roles such physical controls must be considered and integrated with well established petro geochemical concepts in order to better understand the genesis of magmatic ni cu pge sulphide deposits

new geochemical insights into volcanic degassing magma degassing plays a fundamental role in controlling the style of volcanic eruptions whether a volcanic eruption is explosive or effusive is of crucial importance to approximately 500 million people living in the shadow of hazardous volcanoes worldwide studies of how gases exsolve and separate from magma prior to and during eruptions have been given new impetus by the emergence of more accurate and automated methods to measure volatile species both as volcanic gases and dissolved in the glasses of erupted products the composition of volcanic gases is dependent on a number of factors the most important being magma composition and the depth of gas melt segregation prior to eruption this latter parameter has proved difficult to constrain in the past yet is arguably the most critical for controlling eruptive style spectroscopic techniques operating in the infrared have proved to be of great value in measuring the composition of gases at high temporal resolution such methods when used in tandem with microanalytical geochemical investigations of erupted products are leading to better constraints on the depth at which gases are generated and separated from magma a number of recent studies have focused on transitions between explosive and effusive activity and have led to a better understanding of gas melt segregation at basaltic volcanoes other studies have focused on degassing during intermediate and silicic eruptions important new results include the recognition of fluxing by deep derived gases which buffer the amount of dissolved volatiles in the melt at shallow depths and the observation of gas flow up permeable conduit wall shear zones which may be the primary mechanism for gas loss at the cusp of the most explosive and unpredictable volcanic eruptions in this paper i review current and future directions in the field of geochemical studies of volcanic degassing processes and illustrate how the new insights are beginning to change the way in which we understand and classify volcanic eruptions

a comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials some results from lake sediments abstract a new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility arm i e specific arm obtained in a 1 oe steady field which is particularly sensitive to the single domain sd and small pseudo single domain psd grains of the finer magnetite fraction a second parameter low field susceptibility is relatively more sensitive to the coarser magnetite fraction larger psd and smaller multidomain md grains we can then obtain a measure of the ratio of coarse to fine grain magnetite for large numbers of samples by plotting arversus a simple idealized model based on sized magnetite samples is proposed to explain the use of the armversus plot for detecting relative grain size changes in the magnetic content of natural materials the sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of arm and are used to test the model the model is used to interpret the magnetic variations observed and the interpretations are supported by high field hysteresis measurements of the same sediments the combination of the high field hysteresis method of day et al 1 and the arm vs method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite the armvs method should be used as an intial means of identifying distinct groups of samples the high field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation

magnetic minerals in calcic luvisols chromic developed in a warm mediterranean region of spain origin and paleoenvironmental significance abstract soil formation under aerobic conditions usually enhances magnetic signals mainly through neoformation of sub micron magnetite and or maghemite in order to better understand the nature and magnitude of the enhancement in this work we characterized the iron fe oxides and magnetic properties of two calcic luvisols chromic developed on calcareous orthoquartzites in a spanish region with a warm mediterranean climate weathering of the fe bearing minerals in the parent material mostly fe rich smectite had resulted in the neoformation of hematite and maghemite rather than goethite thus causing a substantial increase in magnetic susceptibility saturation magnetization m s and other magnetic signals the absolute frequency dependent magnetic susceptibility fd which is a typical proxy for the concentration of sub micron superparamagnetic pedogenic maghemite was strongly correlated with the concentration of hematite hm the estimated percent frequency dependent magnetic susceptibility fd was 15 7 this and various other magnetic indicators indicate that the grain size distribution gsd of the pedogenic maghemite is narrower around the superparamagnetic single domain threshold than is that of maghemite in soils and paleosols developed under other temperate climates e g the chinese loesss plateau where fd fd ratio fd the hematite goethite ratio and several indicators of the degree of weathering provides a better tool for paleoclimatic reconstructions than does the current use of alone

identifying goethite and hematite from rock magnetic measurements of soils and sediments we describe a sequence of experiments involving the acquisition of isothermal remanent magnetization irm in high 2 t fields followed by orthogonal demagnetization and the cooling and heating of remanent magnetization mr over the temperature range 196 c to 680 c the main aim of these experiments is to improve the basis for identifying the imperfect antiferromagnetic minerals contributing to the magnetic properties of natural soil and sediment samples which often contain complex mineral mixtures the procedures developed are first applied to a series of ore and synthetic samples of hematite and goethite each characterized by x ray diffraction xrd spectra and second to controlled mixtures of the two minerals the results confirm the mineral diagnostic nature of the experiments used they are subsequently used to identify goethite and hematite contributions to the rock magnetic properties of a variety of soils and recent sediments goethite can be unambiguously identified often accompanied by hematite in the majority of the samples studied despite indications from the synthetic mixtures that the ratio of goethite to hematite may have to exceed an order of magnitude before the goethite signatures are readily recognizable the rock magnetic tests are a much more sensitive basis for recognizing the presence of goethite in natural samples than are xrd analyses the results suggest that goethite s contribution to the rock magnetic properties of soil and sediment samples may often have been underestimated

silica coatings in the ka u desert hawaii a mars analog terrain a micromorphological spectral chemical and isotopic study high silica materials have been observed on mars both from orbit by the crism spectrometer and in situ by the spirit rover at gusev crater these observations potentially imply a wet geologically active martian surface to understand silica formation on mars it is useful to study analogous terrestrial silica deposits we studied silica coatings that occur on the 1974 kilauea flow in the ka u desert hawaii these coatings are typically composed of two layers a 10 m layer of amorphous silica capped by a 1 m layer of fe ti oxide the oxide coating is composed of 100 nm spherules suggesting formation by chemical deposition raman spectroscopy indicates altered silica glass as the dominant phase in the silica coating and anatase and rutile as dominant phases in the fe ti coating jarosite also occurs within the coatings oxygen isotopic contents of the coatings were determined by secondary ion mass spectrometry cameca 7f and nanosims the measured values 18 o fe ti 14 6 2 1 and 18 o silica 12 1 2 2 relative to smow are enriched in 18 o relative to the basalt substrate the observations presented are consistent with a residual formation mechanism for the silica coating acid sulfate solutions leached away divalent and trivalent cations leaving a silica enriched layer behind micrometer scale dissolution and reprecipitation may have also occurred within the coatings chemical similarities between the hawaiian samples and the high silica deposits at gusev suggest that the martian deposits are the product of extended periods of similar acid sulfate leaching

redox controlled generation of the giant porphyry cu au deposit at pulang southwest china some porphyry cu au deposits with relatively reduced ore assemblages characterized by high hydrothermal pyrrhotite contents and a lack of primary hematite and magnetite are generally considered to be associated with reduced i type granitoids however the role of magmatic oxygen fugacity fo2 in controlling cu au mineralization in such reduced porphyry deposits is poorly understood the giant late triassic ca 216 ma pulang porphyry cu au deposit of southwest china shows typical reduced ore assemblages this study reported the systematical variation of upper crustal magmatic fo2 of pulang deposit based on detailed investigations of mineral crystallization sequences and compositional features of the mineralization related porphyries early p1 and late p2 porphyry results indicate that magma of the mineralization related porphyries experienced complex fo2 fluctuations during its upper crustal evolution the early primary magma had very high initial fo2 with fmq 3 0 at depths of 12 km fmq is the deviation of logfo2 from the fayalite magnetite quartz fmq buffer the fo2 of evolved parental magma subsequently decreased with fmq 1 9 due to injection of relatively reduced dioritic magmas fmq 1 4 to 2 3 from a deeper chamber 17 21 km depth into the primary magma chamber at 10 12 km depth magma mixing had largely ceased at 6 10 km depth the parental magma then ponded within the reduced tumugou formation at a depth of 3 7 km where magmatic fo2 decreased to a moderately oxidized state fmq 1 6 and finally to a moderately reduced state reflected by log fe2o3 feo ratios of 0 5 for p2 porphyry results of this study of magmatic fo2 indicate that porphyry magmas associated with reduced pulang ore assemblages were initially generated as highly oxidized magma which was subsequently reduced through magma mixing and contamination by reduced sedimentary rocks of the tumugou formation the sharp fo2 decrease at very shallow depth prevented the early loss of cu and au because the magma remained oxidized until it was emplaced at 3 7 km depth moderately reduced magmas may thus have a genetic association with porphyry cu au mineralization

roles of xenomelts xenoliths xenocrysts xenovolatiles residues and skarns in the genesis transport and localization of magmatic fe ni cu pge sulfides and chromite abstract most sulfide rich magmatic ni cu pge deposits form in dynamic magmatic systems by partial melting s bearing wall rocks with variable degrees of assimilation of miscible silicate and volatile components and generation of barren to weakly mineralized immiscible fe sulfide xenomelts into which ni cu co pge partition from the magma some exceptionally thick magmatic cr deposits may form by partial melting oxide bearing wall rocks with variable degrees of assimilation of the miscible silicate and volatile components and generation of barren fe ti oxide xenocrysts into which cr mg v ti partition from the magma the products of these processes are variably preserved as skarns residues xenoliths xenocrysts xenomelts and xenovolatiles which play important to critical roles in ore genesis transport localization and or modification incorporation of barren xenoliths autoliths may induce small amounts of sulfide chromite to segregate but incorporation of sulfide xenomelts or oxide xenocrysts with dynamic upgrading of metal tenors pge cu ni co and cr v ti respectively is required to make significant ore deposits silicate xenomelts are only rarely preserved but will be variably depleted in chalcophile and ferrous metals less dense felsic xenoliths may aid upward sulfide transport by increasing the effective viscosity and decreasing the bulk density of the magma denser mafic or metamorphosed xenoliths may also increase the effective viscosity of the magma but may aid downward sulfide transport by increasing the bulk density of the magma sulfide wets olivine so olivine xenocrysts may act as filter beds to collect advected finely dispersed sulfide droplets but other silicates and xenoliths may not be wetted by sulfides xenovolatiles may retard settling of or in some cases float dense sulfide droplets reactions of sulfide melts with felsic country rocks may generate fe rich skarns that may allow sulfide melts to fractionate to more extreme cu ni rich compositions xenoliths xenocrysts xenomelts and xenovolatiles are more likely to be preserved in cooler basaltic magmas than in hotter komatiitic magmas and are more likely to be preserved in less dynamic less turbulent systems domain phases than in more dynamic more turbulent systems domains phases massive to semi massive ni cu pge and cr mineralization and xenoliths are often localized within footwall embayments dilations jogs in dikes throats of magma conduits and the horizontal segments of dike chonolith and dike sill complexes which represent fluid dynamic traps for both ascending and descending sulfides oxides if skarns residues xenoliths xenocrysts xenomelts and or xenovolatiles are present they provide important constraints on ore genesis and they are valuable exploration indicators but they must be included in elemental and isotopic mass balance calculations

contribution of mafic melt to porphyry copper mineralization evidence from mount pinatubo philippines and bingham canyon utah usa mount pinatubo in the philippines known for its cataclysmic eruption in 1991 hosts several porphyry copper deposits and active geothermal systems an underlying mafic melt supplied much of the sulphur for the dacitic magma and its injection into the dacitic magma chamber triggered the eruption the eruption caused purging of the sulphur rich fluid from the dacite to the atmosphere and extensive fracturing similar events took place at bingham canyon utah site of the largest copper and gold deposit in north america at 38 ma the bingham canyon mineralization took place beneath an active stratovolcano and pyroclastic flows contemporaneous with the mineralization show evidence for magma mingling ascent of mafic melt supplied sulphur and chalcophile elements to the felsic magma which consolidated to form the bingham stock and its underlying magma chamber injections of the mafic melt caused periodic eruptions of felsic magma to form the stratovolcano and deposition of sulphide minerals in highly fractured rocks in and around the stock

discussion on au transportation mechanism in melt magma fluid in porphyry cu deposit a case study from jinchang porphyry au cu deposit heilongjiang province china abstract at present there are au in most porphyry type copper deposits and there are also many reserves of au resources there are 11 porphyry type cu deposits with au resources greater than 500 t as of 2010 previous studies on the source migration and mineralization of cu s and cl in porphyry type cu deposits were relatively thorough but au was rarely involved especially since geologists recognized the genetic relationship of hydrothermal gold deposits and porphyry copper deposits here we proposed the mechanism of the au source transport and storage in jinchang porphyry au cu deposit located in the easternmost portion of the central asian orogenic belt in china the gold bearing characteristics and au chemical properties of siegenite show that in the initial magmatic environment with high oxygen fugacity au enters the melt phase from the solid phase with au0 oxidized to au3 the ni3 and co3 ions have similar chemical properties thus migrate together in the melt phase the gold bearing siegenite provides strong evidence for the affinity and elemental replacement of au3 and ni3 the symbiosis and differentiation mechanisms of rare earth elements also provide evidence for the affinity and differentiation mechanism between au3 and ni3 after the au3 melt undergoes the initial magma evolution to the magma chamber the oxygen fugacity of the melt phase is reduced to a certain degree during the crystallization and separation of the magma which causes the au3 in the ore forming elements to be reduced to au1 and enter the fluid phase au1 is dissolved in the fluid phase and enriched gradually as the temperature pressure and oxygen fugacity further decrease then au1 is reduced to au0 and precipitates to form native gold in porphyry or quartz veins

the geochemistry of apatite from the los colorados iron oxide apatite deposit chile implications for ore genesis apatite grains from the los colorados iron oxide apatite ioa deposit the largest ioa deposit in the chilean iron belt cib exhibit significant intracrystalline spatial variability with respect to the concentrations of f cl and oh and trace elements statistical interrogation of the compositional data indicates that individual apatite grains contain spatially discrete f rich and cl rich domains the chemical composition of the f rich domains is consistent with apatite growth from silicate melts whereas the chemical composition of the cl rich domains is consistent with apatite growth from a magmatic hydrothermal fluid that cooled as it percolated outward from the los colorados fault the structural control for emplacement of the ore body into the surrounding brecciated diorite and andesite host rocks apatite in the deposit is intimately intergrown with magnetite and actinolite for which trace element fe h and o stable isotope data indicate a combined magmatic magmatic hydrothermal genesis for the deposit the compositional data for apatite are consistent with a genetic model wherein f rich apatite cores crystallized with magnetite from silicate melt followed by exsolution of a magmatic hydrothermal fluid during decompression of the parent magma experimental studies demonstrate that magmatic hydrothermal volatile phase bubbles preferentially nucleate and grow on the surfaces of apatite and magnetite microlites during decompression of a magma body continued degassing of the melt results in the volatile phase sweeping up apatite and magnetite microlites and forming a magnetite apatite fluid suspension that is buoyant in the magma chamber and ascends from the source magma along faults during regional extension halite saturated fluid inclusions in magnetite which is paragenetically equivalent to apatite at los colorados indicate that the magmatic hydrothermal fluid was a brine which allows this fluid to efficiently scavenge cl p rare earth elements and other fluid compatible elements from the silicate melt during ascent the xcl xf ratio of apatite increases as it grows from the evolving cl rich magmatic hydrothermal fluid during decompression and cooling

komatiites and nickel sulfide ores of the black swan area yilgarn craton western australia 2 geology and genesis of the orebodies the black swan ultramafic succession hosts a number of magmatic fe ni cu pge sulfide ore shoots ranging from high grade massive ore to low grade disseminated sulfides of these the most economically significant is the silver swan massive sulfide orebody associated with the basal contact of the succession the deposit varies in thickness between 5 and 20 m reaches a n s strike length of 75 m extends for at least 1 2 km of vertical plunge and is open at depth overlying matrix net textured ore is rare inclusions of dacite are abundant within the lower 5 m of the massive sulfide they range from angular fragments through smooth sinuous and plumose morphologies to fine lace like intergrowths with the sulfide matrix and comprise variable proportions of cores of porphyritic dacite and carapaces with skeletal plagioclase phenocrysts dynamic crystallisation and kinetic melting textures in the carapaces indicate that the inclusions have been heated to various temperatures some well above their liquidus temperature the composition of the inclusions ranges from a perfect match with the immediate footwall dacites to mixtures of dacite with up to 30 komatiite the consistent thickness of the inclusion bearing basal layer within the massive sulphide is interpreted as the extent of 3 d physical connectivity between the inclusions and a partially molten underlying hybrid layer primary contacts between the silver swan massive sulfide orebody and overlying ultramafic rocks are marked by thin rinds containing coarse grained chevron textured chromites with skeletal textures compositions of these chromites match those from kambalda perseverance and other localities and are inconsistent with a metamorphic origin they are interpreted as markers of primary magmatic contacts the combination of this feature with the general paucity of matrix ore implies that the massive ore accumulated and solidified before the accumulation of the overlying thick sequence of olivine cumulates taken together with observations on the internal fractionation of platinum group elements within the massive ores these observations are consistent with a model where the massive ore were emplaced at the floor of a small partially drained lava tube the floor of the tube had been previously heated by passage of large volumes of lava such that it had reached its melting range the felsic inclusions within the ore are the result of buoyant ascent of partially molten substrate into the ore magma this constitutes strong evidence for the operation of thermo mechanical erosion during ore emplacement the disseminated cygnet and black swan orebodies show a number of distinctive features cygnet contains a assemblage of clasts and inclusions which are interpreted as the result of rip up transport and redeposition of sulfides from a pre existing massive sulfide orebody of which black duck may be a remnant the black swan orebody by contrast does not show xenolithic features but is characterised by an association of sulfide blebs with segregation vesicles and by unusually coarse grained olivine the black swan orebody is interpreted as the result of transport of sulfide droplets within a lava charged with a suspended load of coarse olivine crystals

contrasting behavior of hematite and goethite within paleosol s5 of the luochuan profile chinese loess plateau 1 the chinese loess paleosol sequence provides an excellent record of long term variations in the east asian paleomonsoon for representative loess profiles paleosol units have enhanced magnetic properties compared to loess units however at some depth intervals with special paleoenvironmental conditions selective depletion of antiferromagnetic afm minerals hematite and goethite could occur resulting in complexities in accurately linking variations in magnetic properties to long term fluctuations in paleoclimate to resolve this problem we directly measured the mass concentrations of these afm minerals using second order diffuse reflectance spectroscopy drs and then correlated the drs results to high field isothermal remanent magnetization hirm from paleosol unit s5 at the luochuan profile central chinese loess plateau our results suggest that a low hirm anomaly just below the sub paleosol unit s5s1 is caused by fluctuations specifically in goethite content while the hematite concentration exhibits a maximum over the same depth interval this appears to rule out significant loss of hematite to reductive dissolution and further indicates that hematite and goethite may respond differently to changes in the paleoclimate conditions

hirm variations in the chinese red clay sequence insights into pedogenesis in the dust source area abstract although extensive rock magnetic studies have been performed on the chinese loess paleosol sediments few comparable studies have been applied to the underlying red clay sediments because of this paucity of data our understanding of the mineral magnetic properties of the red clay sequence and the paleoenvironmental information encoded in them is limited here we report hard isothermal remanent magnetization hirm variations from 8 1 to 1 2 ma in the lower part of the loess paleosol and the underlying red clay sequences of the chaona section on the chinese loess plateau the results indicate that there is a negative correlation between hirm and frequency dependence of magnetic susceptibility fd fd lf hf where lf and hf are magnetic susceptibility measured at 470 hz and 4700 hz respectively from 3 4 to 2 6 ma and a positive correlation between these two proxies from 8 1 to 3 4 ma and 2 6 to 1 2 ma we argue that the hirm variations from 8 1 to 3 4 ma and from 2 6 to 1 2 ma reflect hematite availability in the dust source region determined by the size of the area and climatic conditions of the dust source region the negative correlation between hirm and fd between 3 4 and 2 6 ma suggests that magnetic enhancement during this time interval may be related to the alteration of hematite goethite to magnetite maghemite we also find that hirm data between 8 1 and 3 4 ma show high coherence with the 100 kyr eccentricity signals suggesting eccentricity forcing of concentration variations of hematite in the dust source area higher resolution samples are needed to determine if concentration variations of hematite in the dust source area are coherent with the orbital obliquity and precession forcing signals

petrogenesis of the massive chromitite layer from the jacurici complex brazil evidence from inclusions in chromite the jacurici complex hosts the largest chromite deposit in brazil in an up to 8 m thick chromitite layer within a tectonically segmented 300 m thick intrusion the ore has been interpreted as the result of crustal contamination driven crystallization in a magma conduit this study addresses the stratigraphy mineralogical and textural relationships and mineral chemistry of the monte alegre sul segment focusing on chromite hosted inclusions from the main chromitite layer to understand the role of volatiles in the genesis of the massive chromitite silicate inclusions enstatite phlogopite magnesiohornblende diopside and olivine are commonly monomineralic and sub to euhedral and crystallized prior to or coeval with the chromite crystallization carbonate inclusions dolomite and magnesite are irregular or have negative crystal shapes suggesting entrapment as melt droplets sulfides pentlandite millerite heazlewoodite polydymite pyrite and chalcopyrite are often polymineralic irregular or hexagonal shaped indicating entrapment as sulfide melt and as monosulfide solid solution the inclusions indicate an h2o and s saturated resident magma with immiscible droplets of carbonate melt during chromite crystallization inclusion rich and inclusion free chromites that occur together have similar compositions and are considered to have formed from the same magma in response to variations in the degree of cr saturation hot primitive magma might have heated and mobilized co2 and probably water from devolatized and assimilated carbonate rich wall rocks increasing fo2 and triggering chromite crystallization we propose that the formation of the chromitite layer started as in situ crystallization with additional material added by slumping of locally remobilized chromite slurries facilitated by the presence of volatiles

preliminary comparison of ancient bole beds and modern soils developed upon the deccan volcanic basalts around pune india potential for palaeoenvironmental reconstruction abstract relict weathering mantles are frequently preserved in the form of paleosols which generally document the long term evolution of earth surface processes bole beds occur as prominent horizons composed of fine grained clayey or earthy material having colors in shades of red to chocolate brown green purple or gray often marking the flow contacts of deccan basalts which date to approximately 65 ma bole beds preserved between two successive lava flows can be studied relative to soils developed into the same basalts during the holocene the bole beds have slightly lower ph but significantly lower electrical conductivity values and organic matter contents compared to modern soils they also have higher sio 2 and lower al 2 o 3 and h 2 o crystal lattice water content than modern soils results indicate that the bole beds may not have been subjected to intense weathering and long term pedogenesis but nonetheless formed under uniform rainfall with surface runoff exceeding evaporation weathering chemistry suggests different types of protolith for red and green boles the high stratigraphic frequency of bole beds throughout the deccan volcanics makes them an important source of information about the frequency and environment of inter eruption intervals

influence of paleorelief on the mid miocene climate variation in southeastern washington northeastern oregon and western idaho usa abstract terrestrial climate proxy records repeatedly show spatial heterogeneity because regional climate condition is largely influenced by the relationship between large scale atmospheric circulation patterns and regional topographic features the paleosols developed on the top of columbia river basalt flows emplaced between 15 3 and 15 8 ma in the northwestern united states show significant spatial variations in the mid miocene soil forming processes the paleosol in the northwestern part of the study area has the least degree of chemical weathering fine scale and very shallow penetrating depth of root traces with the estimated paleoprecipitation and paleotemperature of about 550 mm and 16 c respectively the paleosols in the southeastern part of the study area indicate more intense chemical weathering with the estimated paleoprecipitation and paleotemperature of approximately 1400 to 1500 mm and 17 c respectively the spatial variations in paleo pedogenesis were predominantly affected by spatial heterogeneity in the mid miocene regional climate and regional paleotopographic features taking the other ancient soil forming factors including time parent rock materials and biological activities into account we suggest that intrusions of hot columbia river basalt magma into the crust were responsible for the regional surface uplift and the paleoclimate heterogeneity because the major vent systems of the columbia river basalt eruptions were located in the area where development of the mid miocene high topography existed within the blue mountains paleotopography of the earth s surface can be reconstructed by the paleoprecipitation and paleotemperature estimations from several spatially distributed chrono stratigraphic paleosols although it is difficult to estimate the magnitude of the paleorelief precisely

transfer of sulfur in subduction settings an example from batan island luzon volcanic arc philippines sulfur abundances have been determined in silicic and basaltic melt inclusions in olivines from harzburgitic xenoliths and a basaltic lava sample all from batan island in mantle xenoliths olivines fo80 91 are present as neoblasts or in finely recrystallized patches the most magnesian olivines fo89 7 91 cao 85 cao 0 25 wt and their melt inclusions cao al2o3 from 0 8 to 1 15 have recorded early stages of crystallization the sulfur concentrations for these calc alkaline basaltic melts are estimated between 1720 and 3200 ppm with a mean value at 2550 ppm 1 390 and s cl ratio at nearly 1 this is in agreement with the idea that arc basaltic melts may contain high concentrations of sulfur s 2000 ppm at 1200 c however the heterogeneous distribution of s and its partitioning between silicate melts h2o rich vapor and s bearing solid phases as illustrated by the batan mantle xenoliths would result in highly variable sulfur concentrations in island arc basaltic magmas mostly controlled by fo2 and fs2

a new model for porphyry w mineralization in a world class tungsten metallogenic belt abstract the dongyuan deposit in the recently identified world class porphyry skarn w metallogenic belt east jiangnan orogen china is characterized by a set of nearly parallel and horizontal multi cycle orebodies within cupolas of porphyritic granodiorite almost every orebody from the top to the bottom shows similar vertical changes in vein morphology and mineral assemblage from 1 cm quartz feldspar scheelite calcite veins to 1 2 cm quartz feldspar muscovite scheelite veins to 2 5 cm quartz feldspar muscovite scheelite veins to 5 cm quartz veins from the bottom to the top of each orebody in every cycle the mole number of aliv in k feldspar decreases the concentrations of mn2 in calcite increases and the mole number of oh in muscovite decreases these changes reflect repetitive fluctuations in the concentrations of major elements that were involved in the precipitation of minerals as well as the physicochemical conditions of fluids during vein formation in the multi cycle orebodies the concentrations of mo are obviously lower in pyrite from the middle orebodies than in the top and bottom orebodies our data indicate that the ore forming fluids were sourced from multi batch fluids that were exsolved from magma the lree hree ratios in the scheelite decrease from the upper to lower orebodies similar trends are found within a single orebody from the top to the bottom of veins these trends were due to feldspar fractionation in the magmas and ore forming fluids respectively because the crystallization of feldspar tends to capture lrees therefore the following model is proposed for the formation of the dongyuan porphyry w deposit the magma crystallized first at the roof of the intrusion causing the underlying magmas to become oversaturated in h2o the exsolved h2o then accumulated at the boundary between the crystallized upper part and the underlying magmas as fluid pressures increased cracks formed in the overlying crystallized granodiorite and as a consequence the first cycle of vein networks was formed this process was repeated as the interface between magma and crystallized rock moved downwards thus forming the multi cycle w orebodies that are embedded in the pluton

excess volatiles supplied by mingling of mafic magma at an andesite arc volcano we present the results of a study of volcanic gases at soufriere hills volcano montserrat which includes the first spectroscopic measurements of the major gas species co2 and h2s at this volcano using a multisensor gas analyzer system multigas sensor the fluxes of co2 and h2s were 640 2750 t d and 84 266 t d respectively during july 2008 during a prolonged eruptive pause the flux of co2 is similar to estimates for the entire arc from previous geochemical studies while the measured h2s flux significantly alters our interpretation of the sulphur budget for this volcano the fluxes of both sulphur and carbon show considerable excesses over that which can be supplied by degassing of erupted magma we demonstrate using thermodynamic models and published constraints on preeruptive volatile concentrations that the gas composition and fluxes are best modeled by mixing between 1 gases derived from isobaric quenching of mafic magma against cooler andesite magma at depth and 2 gases derived from shallower rhyolitic interstitial melt within the porpyritic andesite the escape of deep derived gases requires pervasive permeability or vapor advection extending to several kilometers depth in the conduit and magma storage system these results provide more compelling evidence for both the contribution of unerupted mafic magma to the volatile budget of this andesitic arc volcano and the importance of the intruding mafic magma in sustaining the eruption from a broader perspective this study illustrates the importance and role of underplating mafic magmas in arc settings these magmas play an important role in triggering and sustaining eruptions and contribute in a highly significant way to the volatile budget of arc volcanoes copyright 2010 by the american geophysical union

droplets and bubbles solidification of sulphide rich vapour saturated orthocumulates in the norilsk talnakh ni cu pge ore bearing intrusions

comparative geochemical study of scheelite from the shizhuyuan and xianglushan tungsten skarn deposits south china implications for scheelite mineralization abstract scheelite has been analyzed from the shizhuyuan and the xianglushan world class w deposits from the nanling w sn region and jiangnan w belt respectively the shizhuyuan deposit consists of proximal skarn and greisen w sn mo bi and distal pb zn ag veins the xianglushan deposit contains layer like sulfide scheelite and skarn w orebodies on granite cupolas overprinted by w greisen veins scheelite in skarn ores from the shizhuyuan contains higher concentrations of mo than those in the sulfide scheelite and skarn ores from the xianglushan deposit reflecting differences between oxidizing and reducing magmatic hydrothermal fluids under oxidizing conditions w is accompanied by mo partitions into exsolved fluids to form w mo garnet skarns whereas under reducing conditions little mo is carried by exsolved fluids to form w pyroxene skarns trace element patterns of scheelite from both deposits show negative ba sr zr and ti and positive ta anomalies rare earth element ree patterns of scheelite within skarns from the shizhuyuan deposit have negatively inclined and flat m type tetrad patterns and scheelite from the greisens displays flat and positively inclined m type tetrad patterns we infer that the fluids formed scheelite within the w skarns and greisens inherited parental magma trace element and ree characteristics depleted ba sr zr and ti enriched ta negative eu anomalies and tetrad effects whereas scheelite from sulfide scheelite veins and skarns of the xianglushan deposit also has w and mw type tetrad ree patterns the w type tetrad ree patterns are complementary to ree patterns from the renjiashan granite and the mw type tetrad ree patterns occur during a single evolutionary stage within a complex hydrothermal environment sulfide mineralization can form after or before w skarns the former like shizhuyuan deposit and the latter like xianglushan deposit the formation conditions of the latter included reducing conditions and sulfide firstly supersaturated in the melt resulting in sulfide drops which carried w aggregated on the cupolas w skarns and greisens in both deposits underwent generally successive processes related to water supersaturation in the melt following a temperature decrease and crystallization bubbles carried material changing from si and metal to si oxide complexes

textural relationship of sulfide ores pge and sr nd os isotope compositions of the triassic piaohechuan ni cu sulfide deposit in ne china the 216 ma piaohechuan no 4 intrusion in northeastern china situated in the easternmost part of the central asian orogenic belt is composed of hornblende olivine gabbro overlain by hornblende gabbro the intrusion is about 630 m long 40 to 250 m wide and 50 to 150 m thick nickel sulfide mineralization is restricted to the lower part of the intrusion and contains 10 000 metric tons t of ni with average pge concentrations of 40 ppb os 30 ppb ir 36 ppb ru 26 ppb rh 255 ppb pt and 161 ppb pd in 100 sulfide

establishing fire incidence in temperate soils using magnetic measurements abstract natural unburnt topsoil samples from the cotswolds region of england and samples from archaeological contexts in the uk and hungary some of which are known to have been affected by burning have been used to identify a distinctive magnetic signature linked to the effects of fire on magnetic properties a combination of bulk low field lf and frequency dependent fd magnetic susceptibility and normalized anhysteretic remanent magnetization arm measurements have been used on both unburnt and experimentally burnt samples from the cotswolds and on the archaeological samples complementary determinations were made for both sets of samples of the maximum potential susceptibility max and hence percentage fractional conversion conv which provides independent evidence of burning the results show that the ferrimagnetic mineral assemblages produced as a result of fire have a significantly finer grain size than those arising from weathering and soil formation alone burning thus gives rise to a distinctive envelope of values on a bilogarithmic plot of arm fd versus arm lf such a diagram provides a convenient basis for identifying magnetic signatures in soils archaeological materials and palaeosols that have arisen mainly through burning

sulfur evolution of the 1991 pinatubo magmas based on apatite abstract using electron microprobe emp and laser ablation inductively coupled plasma mass spectrometry la icp ms to collect major and rare earth elements ree respectively from apatites from the 1991 mt pinatubo juvenile eruption products we have determined that two statistically distinct populations of apatite exist one population crystallized from the juvenile basaltic melt basalt apatites and the other population crystallized from the main dacitic magma body silicic apatites both populations contain high s apatites 0 7 wt so3 apatite has previously been shown to be a potential monitor for magmatic sulfur contents via numerous proposed coupled substitutions of p5 for s6 however simple apatite melt partitioning cannot account for high s silicic apatites which grew from a silicic melt with an apparent maximum s concentration of 80 ppm disparate apatite morphology i e skeletal and acicular for basalt apatites and euhedral for silicic apatites as well as compositional evidence reveal that high s silicic apatites were not inherited from the juvenile basalt during mingling mixing prior to eruption sulfur gain from neighboring anhydrite phenocrysts can also be ruled out as a source of high sulfur emp sulfur mapping of silicic apatites shows highly irregular patterns of sulfur enrichment that do not correspond with adjacent anhydrite and can be found within apatites hosted by other minerals e g hornblende and fe ti oxides with these data in mind we propose high s silicic apatites from pinatubo and other sulfur rich systems achieved elevated sulfur concentrations during high sulfur fluxing events that originated from underplated basalt during degassing of a so2 rich fluid phase that basalts were indeed sulfur rich and oxidized is here indicated by high s contents of apatites growing in basalt the predominant location of s rich areas of silicic apatite is crystal interiors of apatite inclusions in other mineral phases while large apatite microphenocrysts surrounded by groundmass glass have low sulfur contents this is evidence for placing sulfur fluxing periods long before events that ultimately led to the 1991 eruption

polymetallic droplets within trapped globules in a quartz diorite porphyry from gangcha kemo gold deposit west qinling orogen china implications for petrogenesis and prospecting abstract as immiscibility in magmas appears most significant in magmatic hydrothermal processes studies of magmatic fluid immiscibility should focus on the precipitation of metals a metallogenic belt along the northern margin of the western qinling belt china hosts several porphyry type cu au deposits detailed field investigations reveal that abundant ellipsoidal and sub spheroidal polymetallic globules exist in a quartz diorite porphyry associated with the gangcha kemo gold deposit which occurs at the eastern contact of the dewulu intrusion to reveal the characteristics and composition of these globules we present mineralogical and whole rock major and trace element data the globule formation temperature which was determined using by chlorite and two feldspar geothermometers is estimated at 297 429 c this temperature is much lower than the host quartz diorite porphyry which is estimated to be 860 979 c using an amphibole geothermometer based on the geochemistry of the globules their polymetallic droplets and the host quartz diorite porphyry we infer immiscible separation from the volatile rich quartz diorite porphyry and precipitation of the polymetallic droplets within the globules rapid migration and condensation of the fluids with limited escape of a fluid phase are inferred with the globules representing trapped ore forming elements we propose that the fluid globules were exsolved from a rising magma carrying abundant ore forming metals and that the globules with sulfide droplets can be used as an exploration tool for interpreting the genesis of mineralized rocks and related ore deposits

magnetic stratigraphy of chinese loess as a record of natural fires magnetic susceptibility records of paleosols and loess show high correlation with oxygen isotope stratigraphy of ocean sediments kukla 1987 providing a global paleoclimatic record different models have been put forth to explain the nature and cause of susceptibility variations but consensus has not yet been achieved our low temperature studies reveal a secondary magnetite component in paleosols that is characterized by a higher verwey transition 115k than that for the magnetite 100 k in unaltered loess the same shift in the verwey transition can be achieved by heating and cooling loess samples this is consistent with a new hypothesis that the magnetic signal from paleosols may be produced by natural fires in the past natural fire intensity is sensitive to the amount of annual precipitation so that increased fire induced susceptibilities should reflect an increase in the humidity of regional climate

a rapid method for magnetic granulometry with applications to environmental studies we have developed a rapid method of characterizing the fine scale variation sub micron to hundreds of microns m in the grain size of magnetite in long sediment cores this method is a new rock magnetic tool and can be readily applied to the following disciplines 1 environmental studies 2 hydrology 3 petrology and 4 geomagnetism the method consists of a comparative plot of the depth variation of two magnetic parameters the first parameter low field less than 0 1 millitesla mt or 1 oe susceptibility in a steady field is plotted on the abscissa the second parameter anhysteretic remanent magnetization arm imparted by a smoothly decreasing af of peak value 100 mt 1 000 oe in the presence of a weak steady field 0 01 0 1 mt or 0 1 1 oe is plotted on the ordinate for a sediment column in which the magnetic mineral is magnetite a plot of the two magnetic parameters shows transitions in the average magnetic grain size with depth as clearly discernible changes in the slope of a regression line fit to the individual points arm

environmental magnetism past present and future environmental magnetism involves the application of rock and mineral magnetic techniques to situations in which the transport deposition or transformation of magnetic grains is influenced by environmental processes in the atmosphere hydrosphere and lithosphere the first explicit description of environmental magnetism as a distinct field was in 1980 since that time environmental magnetism has become a broad field that is finding application in an ever increasing array of scientific disciplines in this review of the present state of environmental magnetic studies we divide the field into three broad but arbitrary categories the first involves the use of mineral magnetic assemblages in the geological record to study physical processes in depositional environments this category includes the correlation of sediment cores using magnetic susceptibility measurements studies of geomagnetic field behavior the analysis of depositional and postdepositional mechanical processes that affect sediments and the examination of magnetic parameters that might represent proxies for paleoclimatic variation the second category encompasses studies of the processes responsible for variations in the magnetic minerals brought into a sedimentary environment these provenance investigations include studies of changes in catchment derived sediment in lakes fluctuations in contributions from terrigenous aeolian and glaciogenic components in deep sea sediments and the origin of atmospheric particulates the final category addresses in situ changes and transformations of magnetic minerals in sedimentary environments including pedogenesis authigenetic diagenetic formation of ferrimagnetic phases dissolution of magnetic minerals due to reductive diagenesis and contributions of biomagnetism to sedimentary magnetism because environmental magnetism can address problems in so many disciplines and because many of these problems may be inaccessible to other techniques it is likely that the scope of environmental magnetism will continue to expand rapidly environmental magnetism is capable of providing important data for studies of global environmental change climatic processes and the impact of humans on the environment all of which are major research initiatives in the international scientific community these factors suggest that environmental magnetism has a bright and diverse future

paleoclimatic significance of the temperature dependent susceptibility of holocene loess along a nw se transect in the chinese loess plateau we have conducted mineral magnetic investigations of samples of modern dune sand pristine loess and present day loess along a nw se transect from the northern to the central loess plateau in china the methods used include the temperature dependence of susceptibility tds before and after citrate bicarbonate dithionite cbd treatment as well as x ray diffraction xrd analysis the xrd analyses demonstrate that magnetite and hematite both exist in the chinese loess paleosol sequence and its modem source area but the tds measurements show that magnetite is the predominant contributor to magnetic susceptibility maghemite is present in the pristine loess and the present day loess due to pedogenesis the pedogenic processes that produce the maghemite are closely linked to paleoclimate and for this transect precipitation appears to be the most important climatic variable we suggest that tds can be used as a useful method for the analysis of pedogenesis and climatic change

sulphide melt and aqueous fluid saturation in the pge au mineralisation of the skaergaard intrusion evidence from melt inclusions the skaergaard intrusion in east greenland hosts mineralisation of platinum group elements and gold that is characterised by a remarkably low amount of sulphides about 0 02 wt sulphide and a very high metal sulphur ratio here we present the first quantitative analyses of sulphur s copper cu lithium li and other trace elements from melt inclusions in plagioclase to trace their evolution in the magma and to constrain the formation of the mineralisation the concentration of these elements in the melt inclusions varies considerably within each sample the s content in melt inclusions ranges from 165 to 320 ppm in the lower part of the intrusion but increases to 349 512 ppm immediately below the mineralisation interval in the same interval the li content increases from 22 43 to 40 69 ppm and cu ranges from 118 to 1586 ppm with no systematic variations across the mineralisation the li content drops an order of magnitude to 4 7 ppm and s drops to 250 326 ppm we explain these compositional changes as reflecting the magmatic evolution as the result of fractional crystallisation below and coinciding aqueous fluid exsolution and sulphide saturation across the mineralisation normally the s content of basaltic magmas is much higher at sulphide saturation we propose that sulphide saturation is possible nevertheless mostly due to the high cu content and high cu fe in the evolved ferrobasaltic melt resulting in a lowering of the s concentration required for sulphide saturation the relationship between exsolutions of aqueous fluids and sulphides remains unknown

characteristics of magnetite in submarine basaltic glass summary we have compared the rock magnetic characteristics of cretaceous submarine basaltic glass sbg from dsdp odp holes 417d 418a 807c and 543a to data from holocene glasses from the east pacific rise both groups are very similar in that they contain single domain low ti magnetite as the carrier of a strong and stable remanent magnetization the behaviour of magnetic hysteresis in sbg is however dominated by superparamagnetic grain size populations transmission electron microscopy revealed spherically shaped grains of 10 20 nm diameter with crystal lattice properties consistent with magnetite these grains could be responsible for the magnetic behaviour of sbg

mineralogical and geochemical evolution of a basalt hosted fossil soil late triassic ischigualasto formation northwest argentina potential for paleoenvironmental reconstruction reconstruction of paleoclimatic conditions in the ischigualasto basin northwestern argentina has been constrained by fi eld studies coupled with mineralogic whole rock and fi ne fraction chemical and stable isotope analysis of a triassic carnian basalt hosted fossil soil field evidence such as wedgeshaped aggregate structure and slickensides indicate this was likely a paleo vertisol whole rock analysis defi nes down profi le trends in clay mineralogy and chemical composition that are consistent with modern soils developed upon basalt parent material x ray diffraction analysis indicates that the basaltic parent material is dominated by plagioclase with trace amounts of weathered 2 1 phyllosilicate overlying weathered horizons show a progressive loss of plagioclase and an increase in phyllosilicates with minor amounts of kandite clays and detrital quartz x ray diffraction analysis of the 2 m fraction shows that the weathered layers are dominated by dioctahedral smectite montmorillonite with a minor fraction of kaolinite in the upper layers of the profi le there is a progressive loss of basic cations in conjunction with an increase in concentration on a wt basis of conservative elements from the basalt upward through the weathering profi le the combined data indicate that this soil likely formed on a stable landscape in a cool and humid climate in addition the presence of quartz in the paleosol profi le suggests an eolian contribution of sediment during pedogenesis despite these apparent morphologic and bulk chemical trends indicative of a pedogenic origin none of the authigenic minerals formed in isotopic equilibrium however based on measured oxygen and hydrogen isotope compositions these minerals apparently formed from meteoric waters with a narrow range of 18 o and d compositions at different temperatures if this is correct then amygdaloidal calcites formed at 60 100 c followed by precipitation of montmorillonites at 49 57 c during late stage hydrothermal alteration finally goethite formed at low temperatures of 6 3 c in a pedogenic environment this complex history of hydrothermal alteration and pedogenic overprinting brings to light the need for cautious interpretation of bulk chemical trends in paleosols as a means for paleoclimate reconstruction comparison of the calculated triassic oxygen isotopic compositions of meteoric water and soil temperature with modern environments suggests that this soil formed in a seasonal humid and cool climate

mineralogy and chemistry of altered icelandic basalts application to clay mineral detection and understanding aqueous environments on mars we used a suite of techniques including those emulating compositional data sets obtained from mars orbit and obtainable at the mars surface to examine aqueous alteration of basaltic rocks from iceland as a mineralogic and geochemical analog for noachian environments on mars a sample suite was collected for laboratory measurement of 1 whole rock visible near infrared vnir reflectance and thermal infrared tir emission spectra 2 vnir and tir reflectance spectra of particle size separates derived from the bulk rock and from materials extracted from fractures vesicles 3 x ray diffraction xrd patterns for determination of quantitative modal mineralogy 4 major element chemistry using flux fusion of whole rock powders and 5 electron microprobe analyses of minerals in thin sections conclusions about aqueous alteration can be influenced by technique for these basalts whole rock chemical data showed scant evidence for chemical fractionation but tir vnir and xrd measurements identified distinctive assemblages of hydrous silicate minerals differing by sample xrd provided the most complete and accurate quantitative determination of sample mineralogy however vnir spectroscopy was the technique most useful for determining composition of low abundance smectite clays and tir spectroscopy was the most useful for recognizing hydrated silicates in thin surface coatings high spatial resolution mineralogical and chemical data sets were useful for understanding the texture and distribution of alteration products and variations in fluid chemistry no single approach provides a complete assessment of the environment of alteration demonstrating the importance of employing multiple synergistic mineralogical and geochemical techniques and instruments in exploration of rock strata from aqueous paleoenvironments on mars

up down or sideways emplacement of magmatic fe ni cu pge sulfide melts in large igneous provinces the preferential localization of fe ni cu pge sulfides within the horizontal components of dike sill lava flow complexes in large igneous provinces lips indicates that they were fluid dynamic tra

hydrothermal mobilisation of au and other metals in supra subduction oceanic crust insights from the troodos ophiolite the troodos ophiolite is an ideal location to investigate the relationships between the mobilisation of metals by hydrothermal fluids from the lower oceanic crust and the formation of volcanogenic massive sulphide vms deposits the ophiolite hosts the classic cyprus type cu rich vms deposits as well as abundant zones of epidosite alteration in the lower sheeted dyke section that are significantly depleted in base metals including cu and zn and are considered to be the source of the metals enriched in the overlying deposits previous research indicates that the troodos vms deposits are irregularly enriched in au and related elements as sb and se but the behaviour of these elements during the hydrothermal alteration of the troodos ophiolite hitherto has been poorly investigated low detection limit whole rock analyses of fresh glass samples reveal that the troodos primitive crust has a similar metal content and distribution to modern day arc related environments such as the manus basin compared to mid oceanic ridge basalt morb the troodos primitive crust is enriched in as sb and pb most likely due to addition from a subducting slab during crustal formation during early stages of magmatic differentiation 9 3 5 wt mgo au as sb se cu zn and pb behave as incompatible elements due to the sulphide undersaturated nature of the melt the onset of magnetite crystallisation however at 3 5 wt mgo leads to sulphide segregation and depletion of strongly chalcophile elements au cu and se during continued differentiation 3 5 wt mgo whereas poorly chalcophile elements as sb zn and pb remain incompatible these differences in metal behaviour can account for the cu rich zn pb poor of the cyprus type vms deposits as the source area rocks show high cu fertility compared to zn and pb mobilisation of metals during hydrothermal alteration of the troodos ophiolite is more extensive than observed in hydrothermally altered morb mass balance calculations show that the epidosite zones are significantly depleted in au 88 16 as 89 23 sb 60 12 se 91 20 cu 84 18 zn 63 9 and pb 60 8 background altered diabase from outside epidosite zones shows similar metal depletions which suggests that the source areas of vms are not restricted to epidosite zones but are extended to the lower sheeted dyke section the masses of metals mobilised from a source area of 10 9 km3 composed of a 5 km3 epidosite zone and 5 9 km3 of background altered diabase in the solea graben are 47 t au 21 kt as 1200 t sb 3100 t se 2 4 mt cu 1 8 mt zn and 27 kt pb comparison of metal quantities mobilised from lower sheeted dike section in the solea graben with those hosted in vms deposits shows trapping efficiencies ranging from 4 to 37 indicating that most of the metals is lost by other processes

transport of metals and sulphur in magmas by flotation of sulphide melt on vapour bubbles emissions of sulphur 1 2 and transition metals 3 4 from magmas in the shallow crust have global impacts on human society by affecting climate after volcanic eruptions 5 6 and by forming giant copper and gold ore deposits which are massive anomalies of sulphur as well as of the ore metals themselves 3 4 7 8 these emissions vastly exceed the amounts that could have been derived from the associated magmas themselves 2 intrusion of denser hotter vapour and sulphide saturated magma beneath the cooler and more buoyant bodies that are finally erupted is the most probable source of the excess sulphur and metals in eruptive or hydrothermal systems 1 4 9 10 however the mechanism for the selective upward transfer of sulphur and metals remains poorly understood because their main carrier phase sulphide melt is dense and is generally assumed to settle to the bottoms of magma bodies here we show by experimental observation and by gas speciation and mass balance models that such transfers may be achieved by the flotation of compound drops 11 comprising droplets of sulphide melt attached to vapour bubbles by proposing and demonstrating the feasibility of a novel physical mechanism for upward mobility of sulphide liquids our work provides a mechanism for massive atmospheric releases of sulphur and contradicts widely held assumptions that dense sulphide liquids rich in sulphur copper and gold will remain sequestered in the crust

magnetic proxy climate results from the duanjiapo loess section southernmost extremity of the chinese loess plateau we report mineral magnetic results from a 7 5 m loess sequence 150 samples from the southernmost extremity of the chinese loess plateau which includes the last two glacial cycles in this area the loess sediments experienced particularly intense weathering processes the magnetic assemblage is dominated by a mixture of pseudo single domain psd and multidomain md magnetite with associated superparamagnetic sp grains of either magnetite or maghemite in the paleosols and weathered loess horizons all the rock magnetic parameters fluctuate in parallel with marine sediment 18o data over the last 150 kyr thus reflecting changing global paleoclimatic conditions this relationship is also supported by the evidence of milankovitch cycles in the magnetic susceptibility record paleorainfall estimates when compared with other studies from the chinese loess plateau underline the more humid character of this region during the last 130 kyr

what do the hirm and s ratio really measure in environmental magnetism the hard isothermal remanent magnetization hirm and the s ratio are widely used in environmental magnetism to quantify the absolute and relative concentrations respectively of antiferromagnetic minerals hematite and goethite in mineral mixtures we demonstrate that synthetic al substituted hematite and goethite exhibit a wide range of coercivities which significantly influences the hirm and s ratio these parameters are therefore not necessarily straightforward indicators of the absolute and relative concentrations of hematite goethite to circumvent this problem we propose a new parameter the l ratio which is the ratio of two remanences after alternating field af demagnetization of an irm imparted in a 1 t field with a peak af of 100 mt and 300 mt irmaf 300mt irmaf 100mt these parameters are easily measured using modern vibrating sample or alternating gradient magnetometers changes in hirm only reflect changes in the absolute concentration of hematite and or goethite if the l ratio is relatively constant conversely l ratio fluctuations indicate variable coercivities that possibly reflect changes in the source of hematite goethite corresponding hirm and s ratio variations should be interpreted with caution in such cases the l ratio can be determined using equivalent terms depending on available instrumentation and measurement protocols for example the hirm is equivalent to irmaf 300mt likewise 0 5 sirm irm 100mt where irm 100mt represents the remanent magnetization obtained by first saturating the sample in a high field and then applying a back field of 100 mt is equivalent to irmaf 100mt the hirm 0 5 sirm irm 100mt ratio is therefore a suitable substitute for the l ratio when measurements are made with a long core magnetometer the newly proposed l ratio is straightforward to measure on a wide range of instruments and can provide significant new insights and reduce ambiguities associated with interpretation of two widely used parameters in environmental magnetism the hirm and s ratio

intra basaltic soil formation sedimentary reworking and eodiagenetic k enrichment in the middle to upper ordovician dunn point formation of eastern canada a rare window into early palaeozoic surface and near surface conditions mafic flows of the middle to upper ordovician dunn point formation of eastern canada were deeply weathered under warm and relatively humid conditions before being buried by subsequent flows in the absence of superior plants and in the context of relatively low atmospheric carbon levels the soils developed alkaline groundwater conditions through mineral water interactions which resulted in an enhanced mobility of al relative to si in most palaeosols of that formation although the vegetation cover was volumetrically insignificant compared with that of subsequent geological times it was apparently producing very efficient chelates which for most palaeosols of the succession generated a well defined cheluviation pattern for not only al and fe but also and mainly ti which is typically immobile in modern soils the resulting soils developed an al fe ti depleted upper horizon that was enriched in si probably through periodic ground saturation long term climatic variations related to orbital cycles are inferred to have accounted for a second type of soil in the succession which contrasts with the former by showing a si depleted and less al fe ti depleted upper horizon some soil material was substantially reworked by surface runoff but such occurrences can be easily differentiated from in situ soil material in terms of texture structure and composition a thick overlying rhyolite flow is thought to be responsible for providing abundant k in solution which was incorporated in the underlying basalt palaeosols as exchangeable cations within a probably montmorillonitic clay precursor to the fe mg rich phengite that later developed during deep burial and orogenic compression

the geochemistry of indian bole horizons palaeoenvironmental implications of deccan intravolcanic palaeosurfaces deccan intravolcanic bole horizons represent weathering products formed during major hiatuses of a major volcanic episode in these quiescent periods weathering processes pervasively altered the newly formed volcanic landscape and subsequent flows covered and effectively fossilized the resulting weathered palaeosurfaces the current work is a detailed geochemical study which examines patterns of element mobilization during these intravolcanic weathering events the bole horizons normally rest on top of altered basaltic lavas both boles and altered lavas represent a comparatively early stage in weathering because the content of chemically residual elements such as aluminium and iron are closer to fresh basalt than laterite nevertheless these is clear evidence for significant chemical alteration because the more mobile elements such as calcium and sodium have been substantially removed a chemically distinctive nature for some boles can be demonstrated from chondrite normalized ree plots and in these instances strontium and neodymium isotopic compositions demonstrate that the fine grained bole material is derived from a chemically distinct source in addition thin sections reveal that these fine grained portions commonly contains glass shards and occasionally fresh phenocrysts it is therefore suggested that many deccan boles are in fact weathered pyroclastic material and that the pyroclastic content of the basaltic succession may be greater than previously supposed a significant pyroclastic input during the deccan eruptions has important palaeoenvironmental implications for the fate of late cretaceous flora and fauna in peninsular india

the effects of weathering on the strength and chemistry of columbia river basalts and their implications for mars exploration rover rock abrasion tool rat results abstract basalt physical properties such as compressive strength and density are directly linked to their chemistry and constitution as weathering progresses basalts gradually become weaker and transition from intact rock to saprolite and ultimately to soil here we quantify the degree of weathering experienced by the adirondack class basalts at the mars exploration rover spirit site by performing comparative analyses on the strength and chemistry of a series of progressively weathered columbia river basalt crb from western idaho and eastern washington crb samples were subjected to compressive strength tests rock abrasion tool grinds neutron activation analysis and inductively coupled plasma optical emission spectroscopy analyses of terrestrial basalts indicate linked strength chemical changes as expected weathering sufficient to induce the loss of more than 50 of some cations including 50 of mgo and mno as well as 38 of fe 2 o 3 and 34 of cao was observed to weaken these samples by as much as 50 of their original strength in comparison with the terrestrial samples adirondack class basalts are most similar to the weakest basalt samples measured in terms of compressive strength yet they do not exhibit a commensurate amount of chemical alteration since fluvial and lacustrine activity in gusev crater appears to have been limited after the emplacement of flood basalt lavas the observed weakness is likely attributable to thin film weathering on exposed displaced rocks in the gusev plains in addition to some likely shock effects the results indicate that adirondack class basalts may possess a several mm thick weak outer rind encasing an interior that is more pristine than otherwise indicated and also suggest that long rock residence times may be the norm

interfacial tension between magmatic sulfide and silicate liquids constraints on kinetics of sulfide liquation and sulfide migration through silicate rocks we have measured the interfacial tension sf between sulfide and silicate melts over the temperature range from 1250 to 1325 c by in situ measurement of the shapes of sessile drops of sulfide immersed in silicate melt sitting upon level alumina substrates the silicate melt was an alkali free synthetic basaltic liquid the sulfide melts were synthetic mixtures of fe cu ni s or fe s o the interfacial tension ranges from about 500 mj m 2 for sulfide of fes composition to approximately 600 mj m 2 for sulfide containing 16 wt cu or 6 5 wt ni and up to 650 mj m 2 for fe s o liquid containing 4 wt o contact angles vary from 150 to 180 showing that sulfide liquid does not wet oxide minerals in silicate magmas the density of sulfide melt does not depend strongly on cu or ni content remaining between 4 0 and 4 5 g cm 3 over the range of cu and ni contents expected in sulfide magmas but increases substantially to about 5 5 g cm 3 in fe s o melts containing 4 wt o our results can be combined with conventional concepts of nucleation theory to indicate that when silicate magmas exist at small degrees of supersaturation sulfide drops may nucleate rarely and at widely spaced intervals leading to kinetic control of the compositions of the resulting droplets in light of our results we use simple scaling arguments to argue that sulfide magmas are not capable of migrating through partially molten silicate rocks by capillary forces alone but may be forced through narrow grain boundaries or grain edges only by the flow of the enclosing silicate melt during melt extraction by compaction of partially molten mantle peridotite it is highly unlikely that silicate flow rates could be sufficiently rapid to permit the entrainment of droplets of sulfide liquid at temperatures below the solidus of enclosing silicate rocks sulfide melt will be free to travel along fractures or grain boundaries the mobility of sulfide melts through completely solidified silicate rocks may account for the widespread observation that late stage highly fractionated sulfide liquids have escaped from cooling bodies of massive sulfide to form veins and disseminations of cu rich sulfide minerals in their silicate host rocks

sulphide magma as a source of metals in arc related magmatic hydrothermal ore fluids as magma ascends in subduction zones decreasing pressure and temperature cause it to separate into two or more phases in a process known as exsolution hydrothermal ore fluids and metal rich sulphide melts may be products of this exsolution conventionally the ore fluids are thought to acquire their metal content directly from the parent magma however it is probable that the ore fluids and sulphide melts interact after exsolution and therefore possible that the sulphide melts are an important source of metals for the ore fluids here we use petrographic analyses of erupted sulphide melts and compositional analyses of volcanic gases emitted immediately after an eruption at merapi volcano indonesia to show that magmatic hydrothermal fluids can derive their metals from dissolution of sulphide melts we find that the volcanic gases exhibit metal ratios that are comparable to those in the erupted sulphide melts furthermore we show that gases sampled immediately after the eruption have metal concentrations that are orders of magnitude higher than those of gases emitted during periods of quiescence we propose that the metal content of ores forming in volcanic arc environments is established by exsolution accompanying injections of primitive magma immediately before explosive eruptions the metal content of ore deposits formed during subduction zone volcanism was thought to be established when the ore fluid separates from the parent magma analyses of metal concentrations in erupted melts and the volcanic gases emitted after an eruption in indonesia reveal that metals can be added to the ore fluid later during mixing with separated melts

new insights for the formation of kiruna type iron deposits by immiscible hydrous fe p melt and high temperature hydrothermal processes evidence from el laco deposit

economic geology clues to hidden copper deposits economic grade deposits of copper are hard to find the aluminium content of magmatic rocks at the surface may provide an indicator of ore deposits buried deep below

origin and fate of sulfide liquids in hotspot volcanism la reunion pb isotope constraints from residual fe cu oxides immiscible sulfide liquids in basaltic magmas play an important role in trace metal transport and the sulfur budget of volcanic eruptions however sulfides are transient phases whose origin and fate are poorly constrained we address these issues by analyzing sulfide destabilization products preserved in lavas from la reunion island iron oxide globules and coatings typically 20 80 m in size were found to occur in vesicles of differentiated lavas from piton des neiges and recent pumice samples from piton de la fournaise field and mineralogical evidence indicates that the iron oxides are syn eruptive phases not resulting from hydrothermal processes samples were first studied by scanning electron microscopy the globules were separated whereas the smaller spherules and coatings were concentrated by magnetic sorting and acid leaching and samples were processed through wet chemistry the fe oxide phases comprise 49 74 wt fe 26 40 wt o and up to 6 wt cu 811 ppm ni 140 ppm bi and 8 5 ppm pb compared to the host lava cu ni and bi are enriched by a factor of 101 103 systematic pb isotope disequilibrium between 500 ppm and 2 9 for 206pb 204pb exists between fe oxides and host rocks with fe oxides generally displaying less radiogenic ratios unradiogenic pb is a typical signature of sulfide which tends to concentrate pb but not its parent elements u and th thus both the chemical and isotopic compositions of the vesicle hosted fe oxides suggest that they are more or less direct products of the destabilization of immiscible sulfide liquids although pb dominantly partitions into the gas phase during sulfide breakdown the original pb isotope signature of sulfide is preserved in the residual oxide the composition estimated for the parent sulfides 206pb 204pb 18 20 18 77 207pb 204pb 15 575 and 208pb 204pb 38 2 38 8 precludes a genetic link with the la reunion plume and suggests a lithospheric or crustal origin it is estimated that magma ascent velocities at piton de la fournaise are high enough to counterbalance the settling velocities of millimeter size sulfides despite their high density sulfide liquids are thus transferred upward during eruptions and their destabilization contributes to so2 emanations assimilation of foreign sulfides from the lithosphere can explain why so2 emissions sometimes e g during the april 2007 eruption exceed those predicted from the s content of melt inclusions

economic geology ore metals beneath volcanoes metals often accumulate in the crust beneath volcanoes laboratory experiments and observations reveal important roles for magmatic vapours and brines in transporting and concentrating the metals into deposits worth targeting for extraction