advances in fourier transform infrared spectroscopy of natural glasses from sample preparation to data analysis fourier transform infrared spectroscopy ftir is an analytical technique utilized to measure the concentrations of h and c species in volcanic glasses water and co2 are the most abundant volatile species in volcanic systems water is present in magmas in higher concentrations than co2 and is also more soluble at lower pressures and therefore it is the dominant volatile forming bubbles during volcanic eruptions dissolved water affects both phase equilibria and melt physical properties such as density and viscosity therefore water is important for understanding magmatic processes additionally quantitative measurements of different volatile species using ftir can be achieved at high spatial resolution recent developments in analytical equipment such as synchrotron light sources and the development of focal plane array fpa detectors allow higher resolution measurements and the acquisition of concentration maps these new capabilities are being used to characterize spatial gradients or lack thereof around bubbles and other textural features which in turn lead to new insights into the behavior of volcanic feeder systems here practical insights about sample preparation and analysis of the distribution and speciation of volatiles in volcanic glasses using ftir spectroscopy are discussed new advances in the field of ftir analysis produce reliable data at high spatial resolution that can be used to produce datasets on the distribution dissolution and diffusion of volatiles in volcanic materials

iron oxide copper gold iocg deposits through earth history implications for origin lithospheric setting and distinction from other epigenetic iron oxide deposits the iron oxide copper gold iocg group of deposits initially defined following discovery of the giant olympic dam cu u au deposit has progressively become too embracing when associated deposits and potential end members or analogs are included the broader group includes several low ti iron oxide associated deposits that include iron oxide p rich iron oxide f and ree rich fe or cu au skarn high grade iron oxide hosted au cu carbonatite hosted cu ree and f rich and iocg sensu stricto deposits consideration of this broad group as a whole obscures the critical features of the iocg sensu stricto deposits such as their temporal distribution and tectonic environment thus leading to difficulties in developing a robust exploration model the iocg sensu stricto deposits are magmatic hydrothermal deposits that contain economic cu and au grades are structurally controlled commonly contain significant volumes of breccia are commonly associated with presulfide sodic or sodic calcic alteration have alteration and or brecciation zones on a large commonly regional scale relative to economic mineralization have abundant low ti iron oxides and or iron silicates intimately associated with but generally paragenetically older than fe cu sulfides have lree enrichment and low s sulfides lack of abundant pyrite lack widespread quartz veins or silicification and show a clear temporal but not close spatial relationship to major magmatic intrusions these intrusions where identified are commonly alkaline to subalkaline mixed mafic even ultramafic to felsic in composition with evidence for mantle derivation of at least the mafic end members of the suite the giant size of many of the deposits and surrounding alteration zones the highly saline ore fluids and the available stable and radiogenic isotope data indicate release of deep volatile rich magmatic fluids through devolatization of causative mantle derived magmas and variable degrees of mixing of these magmatic fluids with other crustal fluids along regional scale fluid flow paths precambrian deposits are the dominant members of the iocg group in terms of both copper and gold resources the 12 iocg deposits with 100 tonnes t resources are located in intracratonic settings within about 100 km of the margins of archean or paleoproterozoic cratons or other lithospheric boundaries and formed 100 to 200 m y after supercontinent assembly their tectonic setting at formation was most likely anorogenic with magmatism and associated hydrothermal activity driven by mantle underplating and or plumes limited amounts of partial melting of volatile rich and possibly metal enriched metasomatized early precambrian subcontinental lithospheric mantle sclm fertilized during earlier subduction probably produced basic to ultrabasic magmas that melted overlying continental crust and mixed with resultant felsic melts with devolatilization and some penecontemporaneous incorporation of other lower to middle crustal fluids to produce the iocg deposits preservation of near surface deposits such as olympic dam is probably due to their formation above buoyant and refractory sclm which resisted delamination and associated uplift most precambrian iron oxide p rich or magnetite apatite kiruna type deposits have a different temporal distribution apparently forming in convergent margin settings prior to or following supercontinent assembly it is only in the phanerozoic that iocg and magnetite apatite deposits are roughly penecontemporaneous in convergent margin settings the phanerozoic iocg deposits such as candelaria chile occur in anomalous extensional to transtensional zones in the coastal cordillera which are also the sites of mantle derived mafic to felsic intrusions that are anomalous in an andean context this implies that special conditions possibly detached slabs of metasomatized sclm may be required in convergent margin settings to generate world class iocg deposits it is likely that formation of giant iocg deposits was mainly a precambrian phenomenon related to the extensive mantle underplating that impacted on buoyant metasomatized sclm generally smaller and rarer phanerozoic iocg deposits formed in tectonic settings where conditions similar to those in the precambrian were replicated

conditions and timescales for welding block and ash flow deposits welding of pyroclastic deposits to reform a coherent rock mass is a common phenomenon especially for pumiceous pyroclastic density current deposits i e ignimbrites however and despite the pervasive abundance of block and ash flow baf deposits in the geological and modern record instances of strongly welded baf deposits are few here we present a series of high temperature 800 900 c compaction experiments designed to map the conditions deposit thickness stress and temperature viscosity and timescales that permit or inhibit the welding of baf deposits our experiments were performed on unconsolidated aggregates containing an ash and lapilli component derived from crushed and sieved lava blocks containing 25 crystals taken from the well documented welded baf deposit at mount meager volcano british columbia canada the experiments demonstrate that welding efficiency increases with increasing time and temperature progressive welding is expressed by increasing axial strain porosity loss and bulk density the rate of change of each of these physical properties reduces as welding progresses microstructural analysis of the experimental products shows that the loss of interclast porosity during welding results from the progressive sintering and amalgamation of vitric fragments and that the pore shape changes from sub equant pores to stretched lenses sandwiched between vitric and crystal fragments the coincidence between the microstructure and rock physical properties of the natural and experimental samples highlight that we have successfully reproduced welded baf in the laboratory furthermore our permeability measurements highlight a hysteresis in the return journey of the there and back again volcanic permeability cycle expressed by an increase in permeability due to vesiculation and fragmentation followed by a decrease due to welding this hysteresis cannot be described by a single porosity permeability power law relationship and reflects the change in pore shape and connectivity during welding finally we show that a simple model for welding can accurately forecast the welding timescales of the baf deposit at mount meager as reconstructed from the collapse of the lillooet river valley dam using our experimental data we use this validation as a platform to provide a universal window for the welding of baf deposits also applicable for comparable welded deposits e g welded autobreccias in block lavas and lava domes for a broad range of deposit thickness or stress and effective viscosity

repeated fracture and healing of silicic magma generate flow banding and earthquakes textures in an exceptionally preserved effusive rhyolite conduit at torfajokull iceland indicate that rising magma repeatedly fractured and healed at shallow levels in the conduit rfh process anastomosing tuffisite veins filled by fine grained juvenile clasts were generated by shear fracture of highly viscous magma in the glass transition interval welding of the particulate material during subsequent deformation led to thorough healing of veins allowing repeated fracture of the same body of magma we propose that the rfh process is a rechargeable trigger mechanism for hybrid seismicity and show that the time scale of the process and the fractures formed by it are consistent with the repeat time and magnitude of hybrid earthquakes during silicic eruptions the rfh process may also form the flow banding that is nearly ubiquitous in obsidian

shallow vent architecture during hybrid explosive effusive activity at cordon caulle chile 2011 12 evidence from direct observations and pyroclast textures in june 2011 an eruption of rhyolite magma began at the puyehue cordon caulle volcanic complex southern chile by january 2012 explosive activity had declined from sustained pyroclastic plinian to sub plinian fountaining to mixed gas and ash jetting punctuated by vulcanian blasts this explosive activity was accompanied by synchronous effusion of obsidian lava in a hybrid explosive effusive eruption fortuitous climatic conditions permitted ground based observation and video recording of transient vent dynamics as well as real time collection of proximal juvenile ash as it sedimented from the active plume the main eruptive vent complex and site of lava effusion was represented by two loci of vulcanian blasts within a single tephra cone containing a pancake shaped proto lava dome these blast loci each consisted of clusters of sub vents that expressed correlated shifts in eruption intensity indicating the presence of partially connected and or branching zones of high permeability within the upper conduit pyroclast textures were examined by x ray computed microtomography and their permeability was modeled by lattice boltzmann simulations the porosity 39 to 67 and darcian permeability 3 1x10 15 m2 perpendicular to fabric to 3 8x10 11 m2 parallel to fabric of fine ash emitted during ash jetting indicates that the permeable zones comprised highly sheared tube like bubbly magma and contrast with the low porosity 17 and nul permeability of bombs ejected to hundreds of metres from the vent in vulcanian blasts residual h2o content of ash 0 14 wt and two bombs 0 2 0 25 wt determined by karl fischer titration indicate degassing of this pyroclastic material to near atmospheric pressures ash textures and simple degassing vesiculation models indicate the onset of permeability by ductile processes of shear enhanced bubble coalescence in the upper 1 to 1 5 km of the conduit repeated ash jetting and vulcanian blasts indicate that such ductile processes were not sufficiently effective to accommodate all degassing requirements and additional brittle e g fragmentation events transiently assisted in maintaining an open system degassing regime that permitted long lived hybrid explosive effusive activity the eruption at cordon caulle has provided an excellent opportunity to closely observe key processes of silicic volcanism

gold metallogeny and the copper gold association of the australian proterozoic australian proterozoic gold producing deposits emplaced mainly at 1 55 2 00 ga are divided into the following categories 1 iron oxide dominated brecciahosted cu u au replacement deposits spatially associated with felsic intrusions 273t au 2 stratabound au cu bearing iron formations 152 4t au 3 unconformity style u cu pgm au deposits 53t au 4 iron oxide dominated au cu mineralisation hosted within elements of ductile deformation 146 7t au 5 broken hill and volcanic hosted massive sulphides 150t au 6 iron sulphide dominated veins and replacement zones spatially related to felsic intrusions 150 7t au and 7 iron sulphide dominated veins and replacement zones spatially related to elements of regional deformation 159 9t au categories 1 to 4 are mainly confined to proterozoic rocks constituting an association in which au and cu are commonly present together with variable amounts of u bi co w se te and ree most examples in categories 1 4 fall into either of two groups cu aumagnetite hematite types formed at relatively high temperature 300 450 c and cu u au hematite types formed at 150 300 c we postulate that these ores formed from a common high salinity 15 35 wt nacl equiv low total sulphur a s 10 3 to 10 2 high fo2 fluid type in which metal transport was dominated by chloride complexing the most effective method of metal deposition was fluid mixing achieving a synchronous decrease in fo2 and temperature this unusual oxidised fluid association was favoured in high heat flow extensional settings containing oxidised and or oxidised evaporitic sedimentary sequences the intrusion of oxidised fractionated granites which are commonly temporally associated with metal emplacement acted in some places to heat and focus basinal fluids and in others was the ultimate source of metals

magma degassing buffered by vapor flow through brecciated conduit margins obsidian pyroclasts a common component of rhyolitic tephra preserve a range of volatile contents which has been used to infer syneruptive conditions of magmatic degassing here we show that the textures of obsidian pyroclasts provide information on physical mechanisms of magma flow and degassing along conduit margins obsidian clasts often contain xenoliths sheared bands of lithic powder and textures consistent with magma autobrecciation these features suggest that pyroclastic obsidian primarily forms near conduit walls where magma fragments and reanneals during ascent we use these observations to develop a degassing model for pyroclastic obsidian from the a d 1340 mono craters california eruptions we suggest that degassing was buffered by continual flux of vapor through highly permeable brecciated magma along conduit walls continuous reequilibration of magma with vapor of relatively constant composition not only explains the co 2 h 2 o and d h 2 o data from mono craters pyroclastic obsidian but also requires much lower magmatic co 2 values than the commonly accepted model of closed system degassing taken together the chemical and physical evidence suggests that magma brecciation along conduit walls aids the degassing of ascending rhyolite

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

mineralogy chemistry and fluid aided evolution of the pea ridge fe oxide y ree deposit southeast missouri usa the kiruna type pea ridge iron oxide apatite ioa deposit is hosted by a sequence of 1 47 ga rhyolite tuffs of the st francois mountains southeast missouri usa it consists of a series of altered zones composed mainly of amphibole magnetite hematite and quartz together with the presence of several rare earth element y ree rich breccia pipes in many cases the fluorapatite within these zones is rich in inclusions of monazite iron oxide and quartz inclusions plus minor xenotime monazite and minor xenotime are also found intergrown as inclusions in the fluorapatite as well as in surrounding recrystallized magnetite and hematite in the magnetite ore monazite and xenotime typically occur as inclusions within both oxides monazite ce and xenotime y are both relatively poor 2 wt in tho2 and uo2 no significant compositional differences exist in the y ree chemistry between monazite and xenotime inclusions in fluorapatite compared to grains intergrown with magnetite and hematite suggesting that these two ree rich minerals are cogenetic monazite xenotime geothermometry and geochronology of monazite inclusions in fluorapatite provide evidence that formation remobilization of the y ree phosphates took place at ca 50 to 400 c approximately 5 to 10 m y after emplacement of the main iron oxide phosphate orebody evidence from field relationships and fluid inclusion chemistry together with the massive recrystallization and remobilization of fluorapatite monazite xenotime and iron oxides at pea ridge suggest a subvolcanic origin coupled with a strong metasomatic reworking of the ioa deposit

fragmentation efficiency of explosive volcanic eruptions a study of experimentally generated pyroclasts abstract products of magma fragmentation can pose a severe threat to health infrastructure environment and aviation systematic evaluation of the mechanisms and the consequences of volcanic fragmentation is very difficult as the adjacent processes cannot be observed directly and their deposits undergo transport related sorting however enhanced knowledge is required for hazard assessment and risk mitigation laboratory experiments on natural samples allow the precise characterization of the generated pyroclasts and open the possibility for substantial advances in the quantification of fragmentation processes they hold the promise of precise characterization and quantification of fragmentation efficiency and its dependence on changing material properties and the physical conditions at fragmentation we performed a series of rapid decompression experiments on three sets of natural samples from unzen volcano japan the analysis comprised grain size analysis and surface area measurements the grain size analysis is performed by dry sieving for particles larger than 250 m and wet laser refraction for smaller particles for all three sets of samples the grain size of the most abundant fraction decreases and the weight fraction of newly generated ash particles up to 40 wt increases with experimental pressure potential energy for fragmentation this energy can be estimated from the volume of the gas fraction and the applied pressure the surface area was determined through argon adsorption the fragmentation efficiency is described by the degree of fine particle generation results show that the fragmentation efficiency and the generated surface correlate positively with the applied energy

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

apatite at olympic dam south australia a petrogenetic tool abstract the 10 000 million tonne olympic dam cu au u ag deposit eastern gawler craton south australia is one of the largest orebodies in the world the deposit is hosted within the olympic dam breccia complex placed at the centre of and resulting from multiple brecciation and fe metasomatism of the roxby downs granite rdg the latter is part of a larger batholith emplaced at 1 6 ga apatite petrography and chemistry were studied in non mineralised rdg and coeval granitoids and dolerites as well as in mineralised rdg from deep 2 km and distal 2 7 km to ne locations in both latter cases although the mineralisation corresponds to the same early chalcopyrite pyrite magnetite hematite stage identified in the outer and deeper zones of the deposit itself the character of granite alteration differs sericite chlorite alteration with all feldspar replaced in the deep location and red stained k feldspar on top of prevailing albitization in the distal location close to end member fluorapatite is a key accessory mineral in all igneous rocks and a common product of early hydrothermal alteration within mineralised granite variations in habit morphology and textures correlate with chemical trends expressed as evolving cl f ratios and concentrations of ree y hereafter rey sr mn s si and na magmatic apatite is unzoned in the dolerite but features core to rey enriched rim zonation in the granitoids increases in cl and sr contents correlate with rock basicity calculation of cl in the vapour phase relative to melt at the apatite saturation temperature for zoned apatite in the rdg shows higher values for grains with inclusion rich cores associated with mafic enclaves concordant with assimilation of exotic material during magma crystallisation hydrothermal alteration of magmatic apatite is most varied in the dolerite where interaction with fluids is expressed as subtle changes in cl versus f and rey enrichment and most importantly s enrichment in grains adjacent to crosscutting carbonate sulphide bearing veins highly acidic fluids which not only corroded apatite but also quartz led to recycling of rey via subsequent crystallisation of discrete rey bearing species notably monazite hydrothermal apatite often occurs as interstitial aggregates and displays a wider range of textures indicating variability in local growth conditions and or sustained interaction with evolving hydrothermal fluids apatite from the deep mineralisation is richer in cl whereas increases in rey and s correlate with higher si in both deep and distal cases the co correlation between na and s in apatite from distal mineralisation ties apatite crystallisation to replacement of albite by sericite chlorite the textural and chemical variation of apatite relative to magmatic to hydrothermal transition suggests that the mineral represents a petrogenetic tool to gain insights into mineralising processes at olympic dam apatite evolution clearly played a key contributing role in the elevated rey concentrations seen at olympic dam the marked differences in apatite chemistry between mineralised and non mineralised lithologies show promise for potential application as a tool in mineral exploration in which apatite chemistry represents a means for outlining spatial position within an alteration envelope or identifying if a particular alteration system is barren or fertile with respect to cu au mineralisation

iron rich melts magmatic magnetite and superheated hydrothermal systems the el laco deposit chile we propose an integrated model that explains the magmatic and hydrothermal features of the unique el laco iron deposit that is located in a pliocene pleistocene volcano of the chilean andes sub volcanic crystallization of an iron rich melt as massive magnetite promoted the exsolution of a small volume of a hydrosaline melt and of large amounts of vapor that led to the formation of an alkali calcic hydrothermal assemblage replacing the host andesite this assemblage is capped and overprinted by a large zone of acid sulfate steam heated alteration forming as a whole a protracted shallow level magmatic hydrothermal system oxygen isotopic data for the massive magnetite 18o 4 3 5 0 and the alkali calcic altered rock diopside 18o 7 2 8 7 magnetite 18o 4 4 6 7 suggest that these rocks are genetically related to the host andesite 18o 7 4 9 6 the estimated temperature of the mineral assemblage 900 c may be the highest recorded in hydrothermal systems is attributed to exsolution of fluids from the crystallizing iron rich melts and is considered unlikely to reflect the convection of surficial fluids

long period earthquakes and co eruptive dome inflation seen with particle image velocimetry dome growth and explosive degassing are fundamental processes in the cycle of continental arc volcanism johnson et al present novel optical geodetic observations to constrain the sources responsible for long period volcanic earthquakes which are coincident with frequent explosive eruptions at santiaguito volcano guatemala they find that acceleration in deformation of the volcanic dome extracted from high resolution optical image processing is coincident with recorded long period seismic sources based on these observations abrupt mass shift of solidified domes conduit magma or magma pads seem to be part of the mechanism responsible for generating long period earthquakes at silicic volcanic systems this study presents optical geodetic observations to constrain the sources responsible for long period volcanic earthquakes which are coincident with frequent explosive eruptions at santiaguito volcano guatemala it is found that acceleration in deformation of the volcanic dome extracted from the high resolution optical image processing is coincident with recorded long period seismic sources on the basis of these observations abrupt mass shift of solidified domes conduit magma or magma pads seem to be part of the mechanism responsible for generating long period earthquakes at silicic volcanic systems dome growth and explosive degassing are fundamental processes in the cycle of continental arc volcanism1 2 because both processes generate seismic energy geophysical field studies of volcanic processes are often grounded in the interpretation of volcanic earthquakes3 although previous seismic studies have provided important constraints on volcano dynamics4 5 6 such inversion results do not uniquely constrain magma source dimension and material properties here we report combined optical geodetic and seismic observations that robustly constrain the sources of long period volcanic earthquakes coincident with frequent explosive eruptions at the volcano santiaguito in guatemala the acceleration of dome deformation extracted from high resolution optical image processing is shown to be associated with recorded long period seismic sources and the frequency content of seismic signals measured across a broadband network these earthquake sources are observed as abrupt subvertical surface displacements of the dome in which 20 50 cm uplift originates at the central vent and propagates at 50 m s 1 towards the 200 m diameter periphery episodic shifts of the 20 80 m thick dome induce peak forces greater than 109 n and reflect surface manifestations of the volcanic long period earthquakes a broad class of volcano seismic activity that is poorly understood and observed at many volcanic centres worldwide7 on the basis of these observations the abrupt mass shift of solidified domes conduit magma or magma pads may play a part in generating long period earthquakes at silicic volcanic systems

co variability of s6 s4 and s2 in apatite as a function of oxidation state implications for a new oxybarometer in this study we use micro x ray absorption near edge structures xanes spectroscopy at the s k edge to investigate the oxidation state of s in natural magmatic hydrothermal apatite durango mexico and mina carmen chile and experimental apatites crystallized from volatile saturated lamproitic melts at 1000 c and 300 mpa over a broad range of oxygen fugacities formula 1 fmq 1 2 fmq 3 fmq fayalite magnetite quartz solid buffer the data are used to test the hypothesis that s oxidation states other than s6 may substitute into the apatite structure peak energies corresponding to sulfate s6 2482 ev sulfite s4 2478 ev and sulfide s2 2470 ev were observed in apatite and the integrated areas of the different sulfur peaks correspond to changes in formula 2 and bulk s content here multiple tests confirmed that the s oxidation state in apatite remains constant when exposed to the synchrotron beam at least for up to 1 h exposure i e no irradiation damages to our knowledge this observation makes apatite the first mineral to incorporate reduced s2 intermediate s4 and oxidized s6 s in variable proportions as a function of the prevailing formula 3 of the system apatites crystallized under oxidizing conditions fmq 1 2 and fmq 3 where the s6 stotal peak area ratio in the coexisting glass i e quenched melt is 1 are dominated by s6 with a small contribution of s4 whereas apatites crystallizing at reduced conditions fmq contain predominantly s2 lesser amounts of s6 and possibly traces of s4 a sulfur oxidation state vs s concentration analytical line transect across hydrothermally altered apatite from the mina carmen iron oxide apatite ioa deposit chile demonstrates that apatite can become enriched in s4 relative to s6 indicating metasomatic overprinting via a so2 bearing fluid or vapor phase this xanes study demonstrates that as the formula 4 increases from fqm to fmq 1 2 to fmq 3 the oxidation state of s in igneous apatite changes from s2 dominant to s6 s4 to s6 s4 furthermore these results suggest that spectroscopic studies of igneous apatite have potential to trace the oxidation state of s in magmas the presence of three s oxidations states in apatite may in part explain the non henrian partitioning of s between apatite and melt our study reveals the potential to use the s signature of apatite to elucidate both oxygen and sulfur fugacity in magmatic and hydrothermal systems 1 embed mml math 1 gif 2 embed mml math 2 gif 3 embed mml math 3 gif 4 embed mml math 4 gif

depth shifting cores incompletely recovered from the upper oceanic crust iodp hole 1256d seafloor drilling operations especially those in crustal rocks yield incomplete recovery of drilled sections and depths of the recovered core pieces are assigned with some uncertainty here we present a new depth shifting method that is simple and rapid requires little subjective input and is applicable to any core log integration problem where sufficient comparable data have been collected in both the open hole and from the recovered core over the depth range for which both core and log data have been collected an automatic algorithm selected the best new depth for each piece the criteria for determining the best depth were as follows 1 find new depths for as many pieces as possible and 2 minimize the difference between core density and log density in this study depth shifting is applied at integrated ocean drilling program iodp hole 1256d which is our first opportunity to study a section of intact in situ upper ocean crust drilled down to gabbro the new depths significantly improve the agreement between an independent data set and the logging record

phosphorus and the rare earth elements in felsic magmas an assessment of the role of apatite abstract the solubility of fluorapatite in 17 silica rich melts in the system na 2 o k 2 o al 2 o 3 sio 2 with and without cao or caf 2 was determined at 1 kbar water pressure and 750 900 c apatite saturation occurs at levels of dissolved p 2 o 5 ranging between 0 04 0 02 and 0 28 0 13 wt with only 4 values outside the 0 09 0 20 wt range the results demonstrate not only that apatite is a common liquidus phase in felsic melts but also that under most circumstances it remains in the residue during episodes of partial fusion of the crust given a solubility limit of 0 14 wt dissolved p 2 o 5 the mean of the experimental values a source containing as little as 0 05 p 2 o 5 must be 35 melted before apatite is lost from the residue and no longer buffers the melt p 2 o 5 concentration at the saturation value higher abundances of p 2 o 5 in the source postpone the loss of residual apatite to still higher degrees of melting and if the source p 2 o 5 content exceeds 0 14 wt apatite must be residual for all degrees of melting increasing in abundance as melting proceeds the generally secondary influence of apatite on the rare earth element ree patterns of melt and residue is most apparent when garnet and or amphibole is minor or lacking in the residue fractional crystallization of intermediate e g andesitic magmas toward felsic compositions invariably results in saturation in apatite and some consequent depletion of ree in the melt

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

strain field analysis on montserrat w i as tool for assessing permeable flow paths in the magmatic system of soufriere hills volcano strain dilatometers have been operated on the volcanic island of montserrat west indies for more than a decade and have proven to be a powerful technique to approach short term dynamics in the deformational field in response to pressure changes in the magmatic system of the andesitic dome building soufriere hills volcano shv we here demonstrate that magmatic activity in each of the different segments of the shv magmatic system shallow dyke conduit upper and lower magma chambers generates a characteristic strain pattern that allows the identification of operating sources in the plumbing system based on a simple scheme of amplitude ratios we use this method to evaluate strain data from selected vulcanian explosions and gas emission events that occurred at shv between 2003 and 2012 our results show that the events were initiated by a short phase of contraction of either one or both magma chambers and a simultaneous inflation of the shallow feeder system the initial phase of the events usually lasted only tens to hundreds of seconds before the explosion gas emission started and the system recovered the short duration of this process points at rapid transport of fluids rather than magma ascent to generate the pressure changes we suggest the propagation of tensile hydraulic fractures as viable mechanism to provide a pathway for fluid migration in the magmatic system at the observed time scale fluid mobilization was initiated by a sudden destabilization of large pockets of already segregated fluid in the magma chambers our study demonstrates that geodetic observables can provide unprecedented insights into complex dynamic processes within a magmatic system commonly assessed by theoretical modeling and petrologic observations

sulfur bearing magmatic accessory minerals almost all magmas contain sulfide or sulfate bearing phases in most natural samples the sulfur bearing phase is a sulfide which typically is pyrrhotite fe1 x s or pyrite fes2 although chalcopyrite cufes2 pentlandite fe ni 9s8 sphalerite zns or molybdenite mos2 may be present as well sulfate minerals are rare at magmatic conditions and anhydrite caso4 is the most common other magmatic so4 bearing minerals include the sodalite group minerals hauyne simplified formula na ca 4 8 al6si6 o s 24 so4 cl 1 2 scapolite minerals silvialite ca na 4al6si6o24 so4 co3 and s bearing apatite ca5 po4 3 f cl oh barite baso4 has been mentioned in rare cases marchev 1991 sulfur bearing minerals usually constitute a negligible fraction of the mineral assemblage in magmatic rocks and thus can be classified as accessory minerals the crystallization of sulfide sulfate and s bearing minerals strongly depends on melt composition temperature and pressure and the s speciation in melt which in turn is strongly dependent on the prevailing oxygen fugacity baker and moretti 2011 this volume wilke et al 2011 this volume irrespectively of the low abundance of s bearing minerals the evolution of sulfur in magmas may be evaluated from the occurrence of sulfides and sulfates these minerals are critical for estimating the activity of various sulfur bearing species in magmas and can be used to constrain the oxygen fugacity and the s concentration in the melt e g pre eruptive sulfur concentration in melts the presence of either sulfide or sulfate in silicate melt indicates that the predominant dissolved sulfur species in the melt are s2 or s6 respectively typically one of these species is dominant but there are conditions where s2

the permeability evolution of tuffisites and implications for outgassing through dense rhyolitic magma there is growing evidence that outgassing through transient fracture networks exerts an important control on conduit processes and explosive effusive activity during silicic eruptions indeed the first modern observations of rhyolitic eruptions have revealed that degassed lava effusion may depend upon outgassing during simultaneous pyroclastic venting the outgassing is thought to occur as gas and pyroclastic debris are discharged through shallow fracture networks within otherwise low permeability conduit plugging lava domes however this discharge is only transient as these fractures become clogged and eventually blocked by the accumulation and sintering of hot melt rich pyroclastic debris drastically reducing their permeability and creating particle filled tuffisites in this study we present the first published permeability measurements for rhyolitic tuffisites using samples from the recent rhyolitic eruptions at chaiten 2008 2009 and cordon caulle 2011 2012 in chile to place constraints on tuffisite permeability evolution we combine 1 laboratory measurements of the porosity and permeability of tuffisites that preserve different degrees of sintering 2 theoretical estimates on grainsize and temperature dependent sintering timescales and 3 h2o diffusion constraints on pressure time paths the inferred timescales of sintering driven tuffisite compaction and permeability loss spanning seconds in the case of compaction driven sintering to hours surface tension driven sintering coincide with timescales of diffusive degassing into tuffisites observed vent pulsations during hybrid rhyolitic activity extrusive behaviour coincident with intermittent explosions and more broadly timescales of pressurisation accompanying silicic lava dome extrusion we discuss herein the complex feedbacks between fracture opening closing and sintering and their role in outgassing rhyolite lavas and mediating hybrid explosive effusive activity

mineral thermometry and fluid inclusion studies of the pea ridge iron oxide apatite rare earth element deposit mesoproterozoic st francois mountains terrane southeast missouri usa mineral thermometry and fluid inclusion studies were conducted on variably altered and mineralized samples from the mesoproterozoic pea ridge iron oxide apatite ioa rare earth element ree deposit in order to constrain p t conditions fluid chemistry and the source of salt and volatiles during early magnetite and later ree mineralization scanning electron microscopy sem cathodoluminescence and sem backscatter electron images show that quartz and rutile precipitated before during and after magnetite and ree mineral growth ti in quartz and zr in rutile equilibration temperatures range from 350 to 750 c in the amphibole magnetite hematite and silicified zones where t increased during magnetite and quartz growth and dropped precipitously after fracturing and brecciation late drusy quartz cements within a ree rich breccia pipe record the lowest t 315 400 c liquid vapor rich and hypersaline hematite calcite fluid inclusions are common and liquid co 2 is present locally salinities define three populations saline 10 27 wt nacl equiv hypersaline 34 60 wt nacl equiv and dilute 0 10 wt nacl equiv the wide range of eutectic melting temperatures 67 to 19 c suggests that saline inclusions trapped variable proportions of a cacl mgcl fecl bearing fluid end member and an nacl kcl fluid end member homogenization temperatures and pressures of these saline inclusions suggest they were trapped when fluids unmixed into brine and vapor at t the na cl na k and cl br ratios of fluid inclusion extracts provide evidence for mixtures of magmatic hydrothermal fluids and evaporated seawater extracts from magnetite hematite and pyrite plot in the magmatic hydrothermal field indicating that fe was derived from a magmatic source their enrichments in mg and ca are consistent with a mafic magmatic source the positive correlation between na mg and na ca ratios may be due to halite saturation or albitization of igneous rocks extracts from barite in the ree rich breccia pipes are enriched in na and br and plot near the seawater evaporation trend he is highly enriched relative to ne and ar in fluid inclusion extracts which precludes air as a source of he although the he is mostly of crustal origin pyrite with a 3 he 4 he r r a of 0 1 contains up to 12 mantle he many extracts have low 20 ne 22 ne ratios due to nucleogenic production of 22 ne in high f o minerals such as fluorapatite or f biotite the arrays of data for 3 he 4 he r r a and 22 ne 20 ne suggest that volatiles were derived from two sources a moderate f mafic magma containing mantle he and a high f silicic magma with crustal he together with other evidence cited in this report these data 1 support a magmatic hydrothermal origin for the mesoproterozoic magnetite apatite deposit with ore fluids derived from a concealed mafic to intermediate composition intrusion 2 suggest that the ree minerals in breccia pipes were either derived from apatite or precipitated in response to decompression and cooling during breccia pipe formation 3 provide evidence for the influx of basinal brine magmatic fluids from granitic intrusions and meteoric water after breccia pipe formation and 4 show that pea ridge was relatively unaffected by the late paleozoic mississippi valley type mvt pb zn system in overlying cambrian sedimentary rocks

evidence for hydrothermal alteration and source regions for the kiruna iron oxide apatite ore northern sweden from zircon hf and o isotopes zircon grains from the kiruna iron oxide apatite ioa ore bodies in northern sweden are distinct in their hafnium and oxygen isotopic ratios compared to zircon grains from adjacent metavolcanic host rocks and related intrusions here we combine these two isotopic systems on previously dated zircon grains to improve our understanding of these ore deposits with a long debated origin contrasting theories for the formation of the kiruna iron ores suggest either 1 emplacement through immiscible silicate iron oxide melts or 2 transportation and deposition of iron by hydrothermal fluids zircon from the metavolcanic host rocks and intrusions have oxygen isotopic ratios 18 o 3 that lie below typical magmatic compositions which is evidence that roof rocks altered by meteoric water were digested into the magma in contrast the ores show an influence of a fluid that is higher in 18 o 7 based on these findings we propose the involvement of episodic magmatic hydrothermal fluids in the ore genesis of the kiruna iron ore deposits 1 the first episode related to a deep seated magmatism and to regional scale metasomatic alteration and 2 a later fluid event related to shallow intrusions and responsible for the ore formation distinct differences in the hf isotopic ratios for host rocks and intrusions e hfi 6 to 10 archean crust and ore e hfi 5 to 3 depleted mantle further allow us to screen possible fluid sources for their involvement in the ore process

tracing the fluid evolution of the kiruna iron oxide apatite deposits using zircon monazite and whole rock trace elements and isotopic studies the ore genesis of the paleoproterozoic iron oxide apatite deposits in the vicinity of kiruna in northern sweden is poorly understood despite a century long mining history and 2500 mt of iron ore with grades of 30 to 70 wt fe produced in the region to date zircon grains from the ore recently dated at ca 1874 ma show very different appearances compared to zircon from surrounding host rocks ca 1880 ma and related intrusions ca 1880 and ca 1874 ma particularly an inclusion rich rim in contrast zircon from the host rocks and a proximal granite intrusion exhibit typical igneous growth zoning electron microprobe results show near stoichiometric composition for zr si and hf in the host rock zircon grains the ore zircon crystals have low analytical totals with significant concentrations of ca fe y and p and infrared spectroscopy showed several weight percent of water these ore zircon grains further show fe rich inclusions zones and or veins in elemental x ray maps and light rare earth elements lree enrichment transmission electron microscopy tem shows that the lree are not due to micro or nano inclusions in the zircon but are likely hosted as lree oxides in amorphous regions of the grains based on these characteristics the rims on ore zircon grains are interpreted to be of hydrothermal origin uranium pb in monazite from the ore measured by sims suggests a secondary event influencing the area at ca 1624 ma a period of known geologic activity in fennoscandia electron microprobe x ray mapping of these monazite grains shows no zoning and relatively low u and th concentrations stark contrasts are visible between the ore depleted mantle influence and host rocks crustal influence in the whole rock lu hf and sm nd data the depleted mantle signature of the ore could be related to the kiruna greenstone group as a potential source region for the iron the sm nd isotopic composition of monazite from the ore shows a crustal influence and indicates that the younger event has not disturbed the whole rock sm nd signature of the ore the hydrothermal nature of the ore zircon grains and the isotopic signatures point to a hydrothermal influence on the ore formation with a high temperature magmatic fluid related to the intrusions as most likely heat and fluid source

trace element signature of pyrite from the los colorados iron oxide apatite ioa deposit chile a missing link between andean ioa and iron oxide copper gold systems although studies have proposed that iron oxide apatite ioa deposits may represent the deeper roots of some andean iron oxide copper gold iocg systems their genetic links remain obscure and controversial a key question when considering an integrated genetic model is whether a magmatic hydrothermal fluid that precipitates massive magnetite will continue transporting significant amounts of dissolved fe cu and au after ioa precipitation here we provide new geochemical data for accessory pyrite from the los colorados ioa deposit in the chilean iron belt that confirm the role of this sulfide as a relevant repository for economic metals in ioa deposits pyrite occurs at los colorados as disseminated grains and as veinlets associated with magnetite and actinolite that postdate the main igneous magnetite stage electron probe microanalysis epma data for pyrite show anomalously high co and ni concentrations up 3 9 and 1 5 wt respectively and relatively high as contents 100s of ppm to a maximum of 2 000 ppm when combined with results from secondary ion mass spectrometry sims spot analyses pyrite data show significant amounts of cu that range from sub ppm values 100 ppb up to 1 000s of ppm plus nonnegligible concentrations of zn pb cd sb se and te up to 100 ppm the highest contents of cu measured wt level most likely record the presence of cu bearing submicron sized mineral inclusions contents of au and ag are up to 1 and 10 ppm respectively with maximum concentrations that can rise up to 800 ppm au and 300 ppm ag due to the presence of submicron sized inclusions the high co ni ratios of pyrite from los colorados are consistent with a magmatic hydrothermal origin associated with a greater mafic affinity compared to pyrite from porphyry cu deposits furthermore the geochemical signature of los colorados pyrite shares important similarities of composition and microtexture with the few published data for pyrite from iocg deposits e g ernest henry australia and manto verde chile these findings combined with recent geochemical and isotopic studies that support an igneous origin for the dike shaped magnetite orebodies at los colorados point to a magmatic source of mafic to intermediate composition for the contained metals and support the hypothesis that ioa systems can source fe cu au rich fluids based on experimental studies these ioa derived fluids may continue transporting significant amounts of metals to form iocg mineralization at shallower levels in the crust

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

cryptic metasomatism during late stage lunar magmatism implicated by sulfur in apatite the use of volatile bearing h 2 o cl f c s minerals as proxies for constraining the volatile content of lunar magmas remains controversial in this study we apply published f cl s signature trends in apatite from lunar mare basalts new experimentally determined apatitemelt partition coefficients for s and thermodynamic modeling to demonstrate unequivocally that fractional crystallization of lunar silicate melt could not have produced the observed s signatures of lunar apatite instead metasomatic cryptic alteration by a s cl bearing f poor volatile phase plausibly explains the volatile element zoning in lunar apatite consistent with some lunar magmas being more volatile rich than previously suggested

fe o stable isotope pairs elucidate a high temperature origin of chilean iron oxide apatite deposits abstract iron oxide apatite ioa ore deposits occur globally and can host millions to billions of tons of fe in addition to economic reserves of other metals such as rare earth elements which are critical for the expected growth of technology and renewable energy resources in this study we pair the stable fe and o isotope compositions of magnetite samples from several ioa deposits to constrain the source reservoir of these elements in ioas since magnetite constitutes up to 90 modal of many ioas identifying the source of fe and o within the magnetite may elucidate high temperature and or lower temperature processes responsible for their formation here we focus on the world class los colorados ioa in the chilean iron belt cib and present data for magnetite from other fe oxide deposits in the cib el laco mariela we also report fe and o isotopic values for other ioa deposits including mineville new york usa and the type locale kiruna sweden the ranges of fe isotopic composition 56fe 56fe 54fe relative to irmm 14 of magnetite from the chilean deposits are los colorados 56fe 2 0 08 0 03 to 0 24 0 08 el laco 56fe 0 20 0 03 to 0 53 0 03 mariela 56fe 0 13 0 03 the o isotopic composition 18o 18o 16o relative to vsmow of the same chilean magnetite samples are los colorados 18o 2 1 92 0 08 to 3 17 0 03 el laco 18o 4 00 0 10 to 4 34 0 10 mariela 18o 1 48 0 04 the 18o and 56fe values for kiruna magnetite yield an average of 1 76 0 25 and 0 16 0 07 respectively the fe and o isotope data from the chilean ioas fit unequivocally within the range of magnetite formed by high temperature magmatic or magmatic hydrothermal processes i e 56fe 0 06 0 49 and 18o 1 0 4 5 consistent with a high temperature origin for chilean ioa deposits additionally minimum formation temperatures calculated by using the measured 18o values of coexisting los colorados magnetite and actinolite separates 630 c as well as fe numbers of actinolite grains 610 820 c are consistent with this interpretation we also present fe isotope data from magmatic magnetite of the bushveld complex south africa where 56fe ranges from 0 28 0 04 to 0 86 0 07 based on these data and comparison to published fe and o stable isotope values of igneous magnetite we propose extending the magmatic high temperature 56fe range to 0 86 considering that the chilean ioas and kiruna deposit are representative of ioa deposits worldwide the fe and o stable isotope data indicate that ioas are formed by high temperature magmatic processes

element variations in rhyolitic magma resulting from gas transport abstract tuffisite veins are glass filled fractures formed when magma fragments during degassing within the conduit these veins form transient channels through which exsolved gases can escape from magma the purpose of this study is to determine the extent to which chemical heterogeneity within the melt results from gas transport and assess how this can be used to study magma degassing two tuffisite veins from contrasting rhyolitic eruptions at torfajokull iceland and chaiten chile were studied in detail the tuffisite vein from torfajokull is from a shallow dissected conduit 70 ka that fed a degassed lava flow while the sample from chaiten was a bomb ejected during the waning phases of plinian activity in may 2008 the results of detailed in situ chemical analyses synchrotron xrf ftir la icp ms show that in both veins larger vesiculated fragments are enriched in volatile elements torfajokull h li cl chaiten li cl cu zn as sn sb compared to the host while the surrounding smaller particles are depleted in the torfajokull vein li cl zn br rb pb but enriched in the chaiten vein k cu zn as mo sb pb the lifespans of both veins and the fluxes of gas and particles through them can be estimated using diffusion profiles and enrichment factors the torfajokull vein had a longer lifespan a day and low particle velocities cm s while the chaiten vein was shorter lived

nanogeochemistry of hydrothermal magnetite magnetite from hydrothermal ore deposits can contain up to tens of thousands of parts per million ppm of elements such as ti si v al ca mg na which tend to either structurally incorporate into growth and sector zones or form mineral micro to nano sized particles here we report micro to nano structural and chemical data of hydrothermal magnetite from the los colorados iron oxide apatite deposit in chile where magnetite displays both types of trace element incorporation three generations of magnetites x z were identified with concentrations of minor and trace elements that vary significantly sio2 from below detection limit bdl to 3 1 wt al2o3 0 3 2 3 wt cao bdl 0 9 wt mgo 0 02 2 5 wt tio2 0 1 0 4 wt mno 0 04 0 2 wt na2o bdl 0 4 wt and k2o bdl 0 4 wt an exception is v2o3 which is remarkably constant ranging from 0 3 to 0 4 wt six types of crystalline nanoparticles nps were identified by means of transmission electron microscopy in the trace element rich zones which are each a few micrometres wide 1 diopside 2 clinoenstatite 3 amphibole 4 mica 5 ulvospinel and 6 ti rich magnetite in addition al rich nanodomains which contain 2 3 wt of al occur within a single crystal of magnetite the accumulation of nps in the trace element rich zones suggest that they form owing to supersaturation from a hydrothermal fluid followed by entrapment during continuous growth of the magnetite surface it is also concluded that mineral nps promote exsolution of new phases from the mineral host otherwise preserved as structurally bound trace elements the presence of abundant mineral nps in magnetite points to a complex incorporation of trace elements during growth and provides a cautionary note on the interpretation of micron scale chemical data of magnetite

new constraints on the timing of host rock emplacement hydrothermal alteration and iron oxide apatite mineralization in the kiruna district norrbotten sweden high spatial resolution zircon u pb geochronological data obtained directly on the kiirunavaara iron oxide apatite ioa deposit related orebodies and host rocks provide new constraints on the timing of mineralization in these deposits these data raise new arguments in the debate of a magmatic versus hydrothermal metasomatic genesis of these major 2 500 mt 30 70 wt fe paleoproterozoic deposits the main orebody at kiirunavaara contains ti poor magnetite and minor 0 05 5 wt p apatite located between a trachyandesite footwall and a rhyodacite hanging wall which also hosts smaller orebodies nukutus rektorn and tuolluvaara the pervasive na and k metasomatism in the host rock is documented by whole rock geochemical data and cathodoluminescence cl microscopy zircon u pb data for the metavolcanic rocks in the footwall and hanging wall cluster between 1884 4 and 1880 3 ma in the footwall a syenite aplite system yields ages of 1880 7 and 1881 4 ma a granite pluton exposed underground has an age of 1874 4 ma zircons in two ore samples never directly dated before this study yield ages of 1877 4 and 1874 7 ma brecciation at the contacts between the ore and host rocks the tight age at ca 1880 ma for most volcanic and plutonic rocks in the footwall and hanging wall and the marginally younger age for ore at ca 1877 to 74 ma matching the age of the spatially related granite pluton suggest a magmatic hydrothermal emplacement model for the kiruna area ioa ores

crystallization and degassing in the basement sill mcmurdo dry valleys antarctica the basement sill is part of the ferrar large igneous province exposed in the mcmurdo dry valleys antarctica the sill is 330 m thick in the bull pass area and 450 m thick in the dais area 12 km to the west and is characterized by phenocryst free lower and upper margins and an orthopyroxene rich central tongue opx 1 5 mm in size halogen variations in apatite from a suite of samples collected along vertical transects through the sill were examined to evaluate the process of crystallization induced degassing i e second boiling and its effects on magma chemistry apatite grains from any given sample are generally unzoned with respect to cl and f concentrations but may vary by 20 30 mol in the halogen site between grains overall average cl f mass ratios increase with height from the lower margin to the center of the sill and then decrease to near zero towards the top margin where the rocks are relatively oxide rich the cl f trend parallels those of bulk mgo and grain size the upper margin contains abundant mafic pegmatoids and the apatite in these segregations has lower cl f ratios compared with that in the host rocks although ree show no measurable difference numerical modeling illustrates that a cooling and crystallizing sill initially develops two separate vapor saturated zones at the lower and upper margins owing to the irreversible heat loss to the cooler country rock vapor separating from the lower zone migrates upward into hotter silicate liquid where it is resorbed thus increasing the cl f mass ratio of the liquid this process leads to saturation and precipitation of apatite from the liquid with a higher cl f ratio than would otherwise occur volatile enrichment can also aid compaction and grain growth in the central part of the sill in contrast the relatively fe rich cl poor nature of the upper zone rocks suggests that these rocks may have crystallized from more evolved degassed silicate liquid possibly compacted out of the underlying crystal mush in addition as vapor sourced from the lower and central parts of the sill ascends into the cooler upper zone of the sill the vapor may be localized along with late interstitial silicate liquid to form pegmatoids at temperatures at which cl is less favored in apatite and can be leached from existing apatite by the ascending vapor the latter causing the observed decrease in the cl f mass ratio of apatite in the evolved pegmatoids

iron oxide copper gold deposits an andean view iron oxide copper gold iocg deposits defined primarily by their elevated magnetite and or hematite contents constitute a broad ill defined clan related to a variety of tectono magmatic settings the youngest and therefore most readily understandable iocg belt is located in the coastal cordillera of northern chile and southern peru where it is part of a volcano plutonic arc of jurassic through early cretaceous age the arc is characterised by voluminous tholeiitic to calc alkaline plutonic complexes of gabbro through granodiorite composition and primitive mantle derived parentage major arc parallel fault systems developed in response to extension and transtension induced by subduction roll back at the retreating convergent margin the arc crust was attenuated and subjected to high heat flow iocg deposits share the arc with massive magnetite deposits the copper deficient end members of the iocg clan as well as with manto type copper and small porphyry copper deposits to create a distinctive metallogenic signature

bubble nucleation in rhyolite and dacite melts temperature dependence of surface tension surface tension profoundly influences the ability of gas bubbles to nucleate in silicate melts to determine how temperature impacts experiments were carried out in which high silica rhyolite melts with 5 wt dissolved water were decompressed at temperatures that ranged from 775 to 1 085 c decompressions were also carried out using dacite melts with 4 3 wt dissolved water at 1 150 c water bubbles nucleated in rhyolite only when decompressions exceeded 95 mpa at all temperatures bubbles nucleated in number densities that increased as decompression increased and at hotter temperatures at a given amount of decompression after correcting decompression amounts for temperature differences values for were estimated from nucleation rates and found to vary between 0 081 and 0 093 n m 1 surface tension decreases as temperature increases from 775 to 875 c but then increases as temperature increases to 1 085 c those values overlap previous results but only when melt viscosity is less than 104 pa s for low viscosity rhyolite there is a strong correlation of with temperature in which increases by 6 9 10 5 n m 1 c 1 that variation is robust for 5 9 wt dissolved water as long as melt viscosity is 104 pa s more viscous rhyolite deviates from that correlation probably because nucleation is retarded in stiffer melts bubbles nucleated in dacite when decompressions exceeded 87 mpa and occured in one or more events as decompression increased surface tension is estimated to be 0 083 0 001 n m 1 and when adjusted for temperature agrees well with previous results for colder and wetter dacite melts at a given water content dacite melts have lower surface tensions than rhyolite melts when corrected to a fixed temperature

fluorapatite monazite allanite relations in the grangesberg apatite iron oxide ore district bergslagen sweden fluorapatite monazite xenotime allanite mineralogy petrology and textures are described for a suite of kiruna type apatite iron oxide ore bodies from the grangesberg mining district in the bergslagen ore province south central sweden fluorapatite occurs in three main lithological assemblages these include 1 the apatite iron oxide ore bodies 2 breccias associated with the ore bodies which contain fragmented fluorapatite crystals and 3 the variably altered host rocks which contain sporadic isolated fluorapatite grains or aggregates that are occasionally associated with magnetite in the silicate mineral matrix fluorapatite associated with the ore bodies is often zoned with the outer rim enriched in y ree compared to the inner core it contains sparse monazite inclusions in the breccia fluorapatite is rich in monazite ce xenotime y inclusions especially in its cores along with reworked larger monazite grains along fluorapatite and other mineral grain rims in the host rocks a small subset of the fluorapatite grains contain monazite xenotime inclusions while the large majority are devoid of inclusions overall these monazites are relatively poor in th and u allanite ce is found as inclusions and crack fillings in the fluorapatite from all three assemblage types as well as in the form of independent grains in the surrounding silicate mineral matrix in the host rocks the apatite iron oxide ore bodies are proposed to have an igneous subvolcanic origin potentially accompanied by explosive eruptions which were responsible for the accompanying fluorapatite rich breccias metasomatic alteration of the ore bodies probably began during the later stages of crystallization from residual magmatically derived hcl and h2so4 bearing fluids present along grain boundaries this was most likely followed by fluid exchange between the ore and its host rocks both immediately after emplacement of the apatite iron oxide body and during subsequent phases of regional metamorphism and deformation

compaction and crystallization in magma chambers towards a model of the skaergaard intrusion the geochemical variations within the skaergaard intrusion provide an opportunity to discover what features of the intrusion can be understood using the simplest form of the equations governing the two phase flow of melt and matrix the equations governing the conservation of mass momentum and energy are first simplified by using the extended boussinesq approximation and then solved numerically to study the time dependent behaviour of a compacting solidifying layer at the base of a magma chamber when variations in the horizontal plane can be neglected the most important result is that the concept of a trapped liquid fraction which has been widely used to model the bulk composition of layered intrusions is a useful concept to describe the steady state behaviour of compacting layers this result is at first sight surprising because there is relative movement between the melt and crystals during compaction and the system is therefore open the reason why it is useful is because both the melt and the crystals are moving downwards in a frame fixed to the upper surface of the compacting layer because the mass of all elements must be conserved what goes into the top of the layer as melt and solid must come out of its bottom as a solid when the behaviour is not time dependent however when time dependent behaviour occurs the concept of a trapped liquid fraction ceases to be useful the governing equations are used to model the concentration of phosphorus uranium and rubidium in the lower part of the skaergaard intrusion where they behave incompatibly the observed behaviour requires the viscosity of the solid part of the compacting layer to have a value of 10 pa s

influence of macro fractures and micro fractures on permeability and elastic wave velocities in basalt at elevated pressure fractures are ubiquitous on all scales in crustal rocks the investigation of fractures and their influence on physical and transport properties of rocks is therefore essential for understanding of many key problems in seismology volcanology and rock engineering in crystalline rocks pore water is primarily stored in and migrates through networks of cracks and fractures at all scales it is therefore essential to know how fluid flow in such fracture networks responds to the elevated pressures found at depth here we report results from an investigation of changes in fluid permeability and associated changes in p wave and s wave velocities at elevated effective pressure for intact macro fractured and micro fractured samples of seljadur basalt in all cases permeability decreases and both wave velocities increase with increasing effective pressure permeability decreases were smallest in the intact material from approximately 10 19 m 2 to 3 x 10 20 m 2 intermediate in the micro fractured material from approximately 5 x 10 17 m 2 to 1 x 10 17 m 2 and largest in the macro fractured material from approximately 3 x 10 15 m 2 to 9 x 10 19 m 2 for a material containing both micro fractures and macro fractures the closure of macro fractures dominated the permeability reduction at low pressure with the closure of micro fractures exerting an increasing influence at higher pressure c 2010 elsevier b v all rights reserved

new contributions to the understanding of kiruna type iron oxide apatite deposits revealed by magnetite ore and gangue mineral geochemistry at the el romeral deposit chile abstract iron oxide apatite ioa or kiruna type deposits are an important source of iron and other elements including ree u ag and co the genesis of these deposits remains controversial with models that range from a purely magmatic origin to others that involve variable degrees of hydrothermal fluid involvement to elucidate the formation processes of this deposit type we focused on the chilean iron belt of cretaceous age and performed geochemical analyses on samples from el romeral one of the largest ioa deposits in northern chile we present a comprehensive field emission electron microprobe analysis fe empa dataset of magnetite apatite actinolite pyroxene biotite pyrite and chalcopyrite obtained from representative drill core samples two different types of magnetite grains constitute the massive magnetite bodies an early inclusion rich magnetite type i and a pristine inclusion poor magnetite type ii that usually appears as an overgrowth around type i magnetite high v 2500 2800 ppm and ti concentrations 80 3000 ppm and the presence of high temperature silicate mineral inclusions e g pargasite 800 1020 c determined by micro raman analysis indicate a magmatic origin for type i magnetite on the other hand high v 2300 2700 ppm and lower ti 50 400 ppm concentrations of pristine inclusion poor type ii magnetite indicate a shift from magmatic to hydrothermal conditions for this mineralization event furthermore the composition of primary actinolite ca and mg rich cores within type ii magnetite and the presence at depth of fluorapatite and high co ni ratios 1 10 of pyrite mineralization are consistent with a high temperature up to 840 c genesis for the deposit at shallow depths of the deposit the presence of pyrite with low co ni ratios

permeability and melt flow in simulated and natural partially molten basaltic magmas abstract a lattice boltzmann method is used to calculate grain scale low reynolds number single phase interstitial porous melt flow in two independent igneous microstructures 1 a microstructure simulated using a stochastic algorithm for progressive crystallization and 2 a natural microstructure obtained through x ray computed tomography ct of a partially melted basalt in both cases the error in the calculated flow field due to finite discretization and domain size has been estimated or demonstrated to be insignificant visually the porous melt flow tends to localize into high flux channels especially with increasing crystallinity and this impression is quantitatively confirmed by increasing skewness of the velocity distribution in the direction parallel to the imposed pressure gradient driving the flow a change from uniform to localized melt flow in naturally occurring situations may have a profound effect on the distribution of trace elements and if the melt is reactive the chemical and structural evolution of the igneous microstructure through localized phase change permeabilities of both microstructures are determined from the calculated steady flow field the permeabilities are then fitted to two different correlation models which are based on the rumpf gupte and carman kozeny relations in these models we express permeability as functions of melt fraction and either the mean crystal length or specific surface area extrapolated permeability to higher melt fractions using both correlation models for the partially melted basalt is shown to be within a factor of four of experimentally determined permeability of a similar sample we determine permeability estimates in the relatively unexplored melt fraction range of 30 80 and find consistency with previous work for permeability estimates in the melt fraction range of 20 30

a review of magnetite geochemistry of chilean iron oxide apatite ioa deposits and its implications for ore forming processes abstract magnetite is the most important iron ore in iron oxide apatite ioa deposits which represent the cu poor end member of the iron oxide copper gold iocg clan magnetite chemistry has been used as a petrogenetic indicator to identify the geological environment of ore formation and as a fingerprint of the source reservoir of iron in this study we present new textural and microanalytical epma and la icp ms data of magnetite from carmen fresia mariela and el romeral ioa deposits located in the cretaceous coastal cordillera of northern chile we also provide a comprehensive summary and discussion of magnetite geochemistry from andean ioas including los colorados cerro negro norte el romeral chilean iron belt and the pliocene el laco ioa deposit located in the central volcanic zone of the chilean andes microtextures coupled with geochemical data were used to define and characterize the occurrence of different magnetite types magnetite exhibits a variety of textural features including oscillatory zoning colloform banding re equilibration textures exsolution lamellae and symplectites the magmatic vs hydrothermal origin of the different magnetite types and the evolution of ioa deposits can be assessed using diagrams based on compatible trace elements however magnetite is very susceptible to hydrothermal alteration and to both textural and compositional re equilibration during magmatic and superimposed hydrothermal events based on the data presented here we conclude that v and ga are possibly the most reliable compatible elements in magnetite to trace ore forming processes in the andean ioa deposits magnetite chemistry reveals different conditions events of formation for each ioa deposit ranging from high temperature low oxygen fugacity o2 purely magmatic 600 c conditions to lower temperature and higher o2 magmatic hydrothermal 300 600 c to low temperature hydrothermal

unraveling the origin of the andean iocg clan a re os isotope approach the andean iocg clan in the coastal cordillera of northern chile comprises the iron oxide cu au sensu stricto the iron oxide apatite ioa and the stratabound cu ag deposits also known as manto type cu ag deposits iocgs and manto type deposits constitute the second source of copper in chile after porphyry cu mo systems whereas ioas are an important source of iron regardless of their economic importance little is known about their formation and contrasting genetic models have been proposed i e an origin from magmatic hydrothermal fluids exsolved from a cooling intrusion or formation from non magmatic basinal brines heated by plutonic bodies here we report re os data for five iocg deposits candelaria mantoverde casualidad diego de almagro and barreal seco three ioas los colorados el romeral carmen and two manto type deposits altamira and franke calculated re os ages for some of these deposits are consistent with previously published geochronological data and indicate an early to late cretaceous age the calculated ages for the altamira manto type cu deposit yield a 90 ma age indicating that the cretaceous manto type cu belt of central chile extends further north than previously thought additionally the calculated initial os ratios using reported ages show that iocgs have a more radiogenic signature 2 0 2 4 than ioas 1 0 1 2 and manto type cu deposits 1 1 a comparison with previously published os initial ratios for the mantoverde 0 2 and candelaria 0 4 iocgs suggests that the mineralization in chilean iocgs is the result of different events with metals derived from diverse sources i e the magmatic hydrothermal system and basement host rocks rhenium and os concentrations for the various studied deposits vary over a wide range of values at the ppb and ppt level respectively with many sulfides and magnetite bearing appreciable no common os the re and os contents in sulfides pyrite chalcopyrite from iocgs are low ranging from 2 to 149 ppb re and up to 49 ppt os pyrite from ioa deposits show re and os concentrations ranging from 10 8 to 214 ppb re and os 156 ppt whereas magnetite has lower re and os contents 0 7 129 ppb re 0 2 3 6 ppt os however rhenium and os concentrations in magnetite might be attributed to small sulfide inclusions chalcocite from manto type cu deposits shows the widest range and highest re and os concentrations 15 to 253 ppb and 34 to 639 ppt respectively the os present in all these deposits is dominated by radiogenic 187os a comparison of re and os data from different deposit types show that andean iocg and ioa deposits have similar characteristics to chilean porphyry cu mo systems with low to moderate re content 90 osr and variable initial os ratios our data supports the idea that andean iocg and ioa deposits formed by magmatic hydrothermal processes with little involvement of basinal brines in contrast published re os information from iocgs in china and australia argue for the involvement of a much more radiogenic crustal source possibly related to non magmatic oxidized saline brines that leached basement rocks we conclude that andean iocg and ioa deposits in northern chile were formed mainly by magmatic hydrothermal processes related to the formation and emplacement of plutonic rocks with moderate contribution from leaching of basement and or volcanic host rocks surface or basin derived brines as well as sediments appear to play only a minor role in the formation of the chilean iocg clan

bubble nucleation in rhyolitic melts experiments at high pressure temperature and water content abstract we report the first measurement of bubble nucleation in hydrated rhyolitic melts in response to pressure release two rhyolitic obsidians one containing less than 1 of microlites of fe ti oxides and the other about 20 of various crystals were hydrated at 150 mpa and 780 850 c after saturation was reached 5 3 5 5 wt water pressure was lowered and the samples were allowed to nucleate and grow bubbles for various amounts of time before the final rapid quenching of the experiments the results demonstrate the importance of heterogeneous nucleation microlites of fe ti oxides are very efficient as sites for bubble nucleation in their presence modest nucleation was observed even after decompression by 6 10 8 bubbles cm 3 in the absence of microlites no nucleation occurred at p mpa at p 10 mpa bubbles also nucleated on crystals of biotite zircon and apatite modest nucleation 10 3 10 5 cm 3 took place even in crystal free samples but it was still heterogeneous when p exceeded 80 mpa nucleation in crystal free samples became extensive 10 5 10 7 cm 3 the lack of correlation of bubble density with either time or decompression suggests that nucleation was still heterogeneous nucleation rates were controlled mainly by the availability of sites rates were faster than 10 6 cm 3 s 1 when microlites were present and faster than 10 5 cm 3 s 1 in the absence of microlites at p 70 mpa narrow size distributions in most samples suggests that nucleation took place immediately after the pressure drop the experimental data we present here indicate that the presence or absence of efficient nucleation sites can lead to two distinct modes of bubble formation when a large number of efficient sites e g fe ti oxide are present bubble nucleation requires very little supersaturation and to a good approximation gas and magma are in equilibrium in magmas that are crystal free or contain crystals that are inefficient at nucleating bubbles very high degrees of supersaturation are required in order to initiate nucleation these two modes of exsolution may lead to contrasting styles of convection pressure build up and eruption

a model of degassing at galeras volcano colombia 1988 1993 galeras volcano reactivated in early 1988 as evidenced by increased seismicity gas emissions and fumarole temperatures and had a series of explosive eruptions in may 1989 during 1989 1990 the volcano was characterized by high so 2 flux reaching 5000 t metric tons day this period of strong degassing was followed by upward movement of magma july september 1991 and the emplacement of a lava dome october november 1991 since november 1991 long period seismicity and so 2 flux have decreased indicating that the conduit has partially sealed itself probably by crystallization and solidification of the magma on july 16 1992 the dome was destroyed by an explosion consistent with pressurization due to sealing and degassing in a nonporous medium continued pressurization beneath the volcano is indicated by eruptions on january 14 march 23 april 4 april 13 and june 7 1993 glass inclusion and matrix glass analyses support a hypothesis of significant magma degassing at depth in the magma chamber and in the conduit this degassing has reduced the h 2 o s and cl contents of the magma but the f content appears to have increased due to crystallization of anhydrous mineral phases and to the low fluid melt partition coefficient for f despite its degassed state galeras is currently a dangerous volcano because the sealing process forces gas saturated magma to release volatile components into confined spaces thereby causing pressurization and explosive eruptions

magnetite bubble aggregates at mixing interfaces in andesite magma bodies magnetite is a particularly favourable site for heterogeneous bubble nucleation in magma and yet only very rarely is evidence for this preserved due to the myriad of processes that act to overprint such an association the possibility of bubble magnetite aggregates in magmas carries with it interesting implications for the fluid mechanics of magma bodies and for the magma mixing process responsible for the formation of andesites we use image analysis and statistical methods to illustrate a spatial association between magnetite and bubbles in mafic enclaves there is a large range in magnetite contents in the enclaves up to 7 5 which is related to the porosity of the enclaves indicating a mechanism of enrichment of the mafic magma in magnetite in the andesite there is no spatial association between bubbles and magnetite and the magnetite content of the andesite is small we suggest a mechanism for enclave formation whereby in vapour saturated magma bubbles nucleate on magnetite upon intrusion into the base of an andesite magma body these bubble magnetite aggregates rise and sweep up other magnetites resulting in the accumulation of aggregates at the magma interface instabilities lead to the flotation of enclaves characterized by enrichment in magnetite and bubbles

immiscible iron and silica rich melts and magnetite geochemistry at the el laco volcano northern chile evidence for a magmatic origin for the magnetite deposits abstract the pliocene el laco volcano northern chile hosts a large iron oxide deposit that occurs as stratiform bodies with underlying feeder zones dykes hosted by hydrothermally altered andesite lava flows phenocrysts in the andesite hosting the mineralization have abundant melt inclusions displaying strong evidence for melt immiscibility most of the pyroxene and the plagioclase phenocrysts contain abundant fe rich melt inclusions with low ti magnetite pyroxene apatite and minor anhydrite the glassy groundmass of these melt inclusions is chemically similar to sub alkaline rhyolitic rocks e g 70 sio 2 si al k na rich large resorbed plagioclase phenocrysts also host another group of melt inclusions with a similar silica rich groundmass but hosting evenly distributed immiscible and complex fe rich spheroidal globules that are enriched in ti p mg ca and s these immiscible globules and the ti poor magnetite daughter crystals in the melt inclusions in pyroxene phenocrysts are thought to be the parental iron oxide melt liquid after which their coalescence leads to the formation of magnetite melts from which the magnetite that formed the el laco iron oxide deposits crystallized and were emplaced the mineralogy and chemistry of these melt inclusions tracks the chemical evolution of the fe ox melts and supports a magmatic origin for the el laco magnetite this is mainly recognized by the continuum of compositions between volcanic separate immiscible fe oxide melts and magnetite ores the trace element composition of the fe rich melt inclusions and of the magnetite in the host andesite and the ore bodies reveals a systematic depletion in most of the elements that are compatible in magnetite the ti content of the magnetite also records the separation and crystallization of the iron rich melt typically the magnetite in the orebodies and the melt inclusions is ti poor compared with titanomagnetite found in the andesite groundmass and that hosted by the hydrothermally altered andesite that is interpreted as being attributed to its crystallization under oxidizing and sulfur rich conditions the cause of this unusual chemical behaviour is probably due to the mechanism s governing the crystallization of the iron rich melt including the temperature changes in chemistry prior to eruption and an increase in the redox conditions of the silicate melt magma oxidation facilitates the prevalence of ferric iron and formation of ti poor magnetite preventing the incorporation of ti in the exsolving iron rich melt the likely reason for the formation of these large ti poor magnetite deposits is likely the contamination of the parental andesitic magma by oxidized crustal rocks and concomitant crystallization of magnetite under oxidizing conditions something that had a significant impact on the elemental distribution

the cretaceous iron belt of northern chile role of oceanic plates a superplume event and a major shear zone the cretaceous constitutes a turning point in the tectonic magmatic and metallogenic history of chile the geological evidence indicates that a major change occurred in late neocomian time when superplume emplacement mid pacific superplume and plate reorganization processes took place in the pacific the superplume event resulted in a major ridge push force resulting in increased coupling between the subducting and overriding plates this completely changed the tectonic setting of chile ending the early cretaceous extensional period aborted rifting in the back arc basin and increasing stress at a crustal scale as a consequence overpressurized dioritic magmas were pushed up mainly along the best possible structural path in northern chile i e the atacama fault zone eventually forming a 500 km long belt of kiruna type iron deposits with reserves of 2 000 mt 60 fe a unique case in chile s geological history

time scales of compaction in volcanic systems we used 12 high temperature deformation experiments on fabricated cores of rhyolite ash to explore the effect of porosity on the rheology of pyroclastic deposits during deformation the cores of ash accommodate strain mainly by shortening and reduction of porosity porosity loss creates a strain dependent rheology expressed by a marked and continuous increase in effective viscosity the effective viscosity graphic 1 of pyroclastic materials is predicted as a function of porosity graphic 2 and melt viscosity graphic 3 o by graphic 4 the optimal value for the parameter based on the experimental data is 0 78 0 15 these experiments provide constraints on the time scales of compaction and flow processes in volcanic systems under variable conditions i e temperature load stress our results indicate that welding and compaction processes in pyroclastic deposits e g ignimbrites conduits can occur on time scales of tens of minutes to hours at these time scales welding is fully decoupled from cooling of the deposits and may be coupled to depositional processes within volcanic conduits welding processes operate on fragmented magma rapidly enough to eliminate porosity in a matter of hours thereby sealing off permeability and supporting cyclical vulcanian style explosive eruptions 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif 3 embed inline graphic 3 gif 4 embed inline graphic 4 gif

gas storage transport and pressure changes in an evolving permeable volcanic edifice abstract the total volume of gas in a magma dissolved and subsequently exsolved greatly influences the degree of explosiveness of a volcanic system there is a marked contrast between the behaviour of a volcano in an open system compared to one which is closed it is therefore essential to understand the entire degassing process gas transport storage and loss a particular focus of this study is the effect different permeabilities and pressure gradients within a volcanic edifice have on the degree and pattern of the gas velocity gas loss is modelled numerically in two dimensions using a finite element approach which allows the specification of boundary conditions with respect to pressure and different permeability domains within the volcanic edifice by combining the time dependent continuity equation and darcy s law a partial differential equation is derived and solved for the pressure the associated pressure gradient is then used within darcy s law to determine the corresponding gas velocity distribution this method is used not only for stationary systems in equilibrium but also as a time dependent progression it permits the modelling of different situations to study how various volcanic characteristics affect the gas loss the model is used to investigate the change in pressure and gas in response to time dependent scenarios these are a dome collapse or sudden increase in permeability by magma rupture at the conduit margin the formation of cracks within the lava dome and sealing by crystallisation our results show that a combination of high and low permeability regions is required for effective gas storage high permeability allows the gas to enter the system but impermeable areas act to confine the gas thereby increasing its pressure and consequently increasing the amount of gas which may be dissolved in the melt furthermore our results show that permeability is an essential factor influencing the response time to system changes which could be linked in future to deformation and other geophysical observations our model is highly versatile and sheds new light on the understanding of gas storage and transport in a permeable volcanic edifice

evaporitic source model for igneous related fe oxide ree cu au u mineralization we propose that many igneous related fe oxide rich ree cu au u bearing deposits form by hydrothermal processes involving evaporitic ligand sources either coeval salars or older evaporites these deposits are abundant in both phanerozoic and proterozoic extensional continental and continent margin settings they commonly form in global arid zones but they also occur where magmatism is superimposed upon older evaporites magmatic compositions exert only second order control mainly on alteration mineralogy and on element abundances hot s poor brines generated by interaction with evaporitic materials are consistent with geologic settings and help rationalize the distinctive element enrichments siderophile lithophile and hydrothermal alteration sodic locally alkaline found in these systems this model contrasts with immiscible oxide melt and magmatic hydrothermal origins commonly proposed for these deposits although all three mechanisms can occur 31 refs 3 figs 1 tab

variation in the composition of apatite through the merensky cyclic unit in the western bushveld complex microprobe analysis of interstitial apatite from a 100 m section through the merensky reef of the bushveld complex reveals that this stratigraphic section marks a transition from cl rich to more f rich compositions in the critical and main zones respectively apatite compositions across the section vary by more than 80 mole percent in the chlorapatite component the trend of decreasing cl concentration with stratigraphic height is not regular and cl contents in apatites from some samples may vary as much as 50 mole percent la 2 o 3 and ce 2 o 3 tend to be enriched in the more melanocratic orthocumulate parts of the section sro concentrations of apatite show an increase with stratigraphic position a trend which is opposite that observed in coexisting cumulus plagioclase the data are consistent with mineralogic and textural evidence for an influx of cl rich vapor into the cumulus section which has affected the cl f variations through the lower portion of the bastard unit this influx occurred above the crystallization temperature of apatite 1 000 degrees 1 050 degrees c it is suggested that much of the modal variation seen in the section may be the result of shifts in liquidus field boundaries caused by gain or loss of volatile components from the melt

storage and eruption of near liquidus rhyolite magma at cordon caulle chile the last three eruptions at the cordon caulle volcanic complex chile have been strikingly similar in that they have started with relatively short pre eruptive warning and produced chemically homogeneous rhyolite to rhyodacite magma with glassy to aphyric texture these characteristics collectively call for an understanding of the storage conditions leading to the rise and extraction of crystal poor silicic magma from volcanoes we have analyzed and experimentally reproduced the mineral assemblage and glass chemistry in rhyolite magma produced in the most recent eruption of cordon caulle and we use these to infer magma storage and ascent conditions fe ti oxide mineral geothermometry suggests that the rhyolite was stored at 870 920 c at these temperatures the phenocryst assemblage plag an37 cpx opx mag ilm can be reproduced under h2o saturated conditions of between 100 and 50 mpa corresponding to crustal depths between about 2 5 and 5 0 km the shallow and relatively hot magma storage conditions have implications for the rapid onset degassing efficiency and progression from explosive to mixed pyroclastic effusive eruption style at cordon caulle

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

halogen geochemistry of the great dyke zimbabwe apatite from the great dyke of zimbabwe is relatively rich in the hydroxy fluorapatite end members the mole fraction of fluorapatite increases from approximately 40 in cumulates of the ultramafic sequence to over 60 in a sample near the top of the exposed mafic sequence the chlorapatite component decreases from a typical high of 10 20 mole in the ultramafic sequence to about 1 in the uppermost part of the mafic sequence however within sample variation may be as great as the entire stratigraphic variation halogen contents of marginal samples generally are similar to axial samples but tend not to have as high cl concentration and tend to oh enrichment biotite compositions approach hydroxyl end member compositions and apatite biotite oh f exchange geothermometers give an average closure temperature of 564 c apatite from the umvimeela dyke an unlayered dike that parallels the great dyke over much of its length contains less cl than is seen in the ultramafic sequence cumulates of the great dyke while the overall stratigraphic trend is characterized by a decrease in the cl f ratio with stratigraphic height within the p1 unit at the top of the ultramafic sequence there is a positive correlation between cl and other incompatible elements such as na and ce the apparent contradiction between the general stratigraphic trend of decreasing cl f ratio with fractionation and the apparent increase in cl and other incompatible elements seen in the p1 unit can be explained by assuming that the great dyke magma chamber was degassing near its top where confining pressure was lowest and cl was preferentially lost to a separating volatile rich fluid as cumulates formed on the floor they entrapped liquid that was increasingly depleted in cl at the higher stratigraphic levels however at any given stratigraphic interval either local fluid enrichment or the eventual crystallization of halogen bearing minerals that incorporate the smaller f ion in preference to the larger cl ion led to a local increase in the cl f ratio

sulfur evolution of oxidized arc magmas as recorded in apatite from a porphyry copper batholith uniformly sulfur rich cores abruptly zoned to sulfur poor rims 1 to 0 2 wt so3 in apatite from the yerington batholith nevada indicate that early magma that is crystal poor oxidizing and sulfate rich evolved to sulfate poor magma via crystallization of anhydrite a mineral observed in magmas from pinatubo and el chichon we predict that the characteristic zonation to sulfur poor rims of apatite in the yerington batholith is common in other oxidized hydrous calc alkaline magmas and can be used to track cryptic anhydrite saturation as well as to monitor sulfur evolution sulfate rich arc magmas such as yerington magmas may crystallize to produce hydrothermal fluids rich in chlorine copper and sulfur and porphyry copper ores

nonisothermal viscous sintering of volcanic ash volcanic ash is often deposited in a hot state volcanic ash containing glass deposited above the glass transition interval has the potential to sinter viscously both to itself particle particle and to exposed surfaces here we constrain the kinetics of this process experimentally under nonisothermal conditions using standard glasses in the absence of external load this process is dominantly driven by surface relaxation in such cases the sintering process is rate limited by the melt viscosity the size of the particles and the melt vapor interfacial tension we propose a polydisperse continuum model that describes the transition from a packing of particles to a dense pore free melt and evaluate its efficacy in describing the kinetics of volcanic viscous sintering we apply our model to viscous sintering scenarios for cooling crystal poor rhyolitic ash using the 2008 eruption of chaiten volcano as a case example we predict that moderate linear cooling rates of 0 1 c min 1 can result in the common observation of incomplete sintering and the preservation of pore networks

iron mobility during synmetamorphic alteration in the selwyn range area nw queensland implications for the origin of ironstone hosted au cu deposits the proterozoic metamorphic rocks of the selwyn range area in western queensland contain a variety of styles of au cu deposit including some e g selwyn mine and osborne prospect that are spatially associated with magnetite rich ironstones the area is characterized by extensive alkali chloride metasomatism that occurred during the later stages of regional metamorphism existing experimental data indicate that hot saline fluids will dissolve and transport iron as they move through temperature pressure gradients in the vicinity of the amphibolite greenschist facies transition and predict that circulation cells will move iron and concentrate it in relatively cool dilute and or oxidized parts of such systems new geological mapping coupled with geochemical data from the amphibolite facies zone of the selwyn range area suggest such processes occurred on a large scale and that large masses of fe were mobilized particularly in association with na metasomatism of biotite bearing metasediments and high fe tholeiitic dolerites field and textural features of ironstones and other fe rich lithologies demonstrate that some of them at least formed by replacement of other rocks during metamorphism and deformation mineralization localized within such iron stones must itself be epigenetic

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

the role of melt fracture degassing in defusing explosive rhyolite eruptions at volcan chaiten explosive volcanic eruptions of silicic magma often evolve towards non explosive emissions of lava the mechanisms underlying this transition remain unclear however a widely cited idea holds that shear induced magma fragmentation plays a critical role by fostering volatile loss from fragmentary magma and through ash filled cracks termed tuffisite we test this hypothesis by measuring h2o concentrations within glassy tuffisite from the 2008 2011 rhyolitic eruption at volcan chaiten chile we show that while h2o concentrations decrease next to tuffisite veins and at the margins of obsidian fragments the depletions cannot account for the disparity in h2o between explosively and effusively erupted rhyolite tuffisite vein lifetimes derived from diffusion modeling min to h imply degassing rates that are too slow to effectively degas magma unless the magma was entirely fragmented to mm or smaller particles this level of brecciation may locally develop near conduit margins but is unrealistic for entire conduits the primary role of melt fracturing may therefore be to provide gas escape pathways for more efficient degassing of permeable vesicular magma in the conduit interior

apatite in igneous systems apatite is a minor but ubiquitous mineral in most igneous rocks although the modal proportion of apatite in common rocks is generally low it can reach high concentrations in enclaves cumulates and other rocks of low abundance i e rocks that constitute a small volume of the crust and mantle e g nelsonites the presence of apatite in most rocks is due not only to its low solubility in naturally occurring melts and aqueous solutions but also to the limited ability of common rock forming minerals to accept the amount of phosphorus that occurs in most rocks into their structure in this paper we will discuss some aspects of the occurrence texture composition physical chemistry and petrogenetic significance of apatite in felsic rocks i e andesite to rhyolite and their plutonic analogs in mafic i e basalts and related rocks and plutonic analogs and ultramafic rocks of the earth s crust and mantle fluorapatite is by far the most common member of apatite family found in igneous rocks however most natural fluorapatite contains some chlorine and hydroxyl as well and these constituents can attain high concentrations in some cases the other halogens bromine and iodine also occur in apatite but their concentrations are much lower than chlorine and fluorine many cations commonly substitute for calcium and phosphorus in apatite however they rarely reach concentrations that warrant the definition of a separate mineral species apatite can be described by the general formula a5 xo4 3z following sommerauer and katz lehnert 1985 the a site accommodates large cations e g ca2 sr2 pb2 ba2 mg2 mn2 fe2 ree3 eu2 cd2 na pan and fleet ch 2 in this volume and comprises two sites that exhibit vii fold

apatite monazite relations in the kiirunavaara magnetite apatite ore northern sweden the magnetite apatite ores in the kiruna area northern sweden are generally considered to be of magmatic origin formed in a subvolcanic volcanic environment during the early proterozoic they are thought to have crystallised from volatile rich iron oxide magmas derived by immiscibility in calc alkaline to slightly alkaline parental magmas three major morphological types of the magnetite apatite ore primary brecciated and banded have been investigated for textural relations and mineral chemistry using transmitted light back scattered electron imaging bse electron microprobe analysis empa and laser ablation inductively coupled plasma mass spectrometry la icpms in all three types th and u poor monazite is present as small inclusions in the apatite larger up to 150 m recrystallised monazite grains both along apatite grain boundaries and intergrown with magnetite and silicate minerals are present in the brecciated and banded samples primary apatite grains without monazite inclusions are generally enriched in light rare earth elements lrees together with na and si petrological and mineralogical evidence suggest that the kiruna magnetite apatite ore experienced successive stages of fluid rock interaction the first stage occurred under high temperature conditions 700 800 c shortly after emplacement and crystallisation of the ore magmas and involved concentrated probably cl dominated brines expelled from the magma this fluid is held to be responsible for the nucleation of the numerous small monazite inclusions within the apatite due to high temperature leaching of na and si while the lrees were concentrated in the monazite the large monazite grains in the brecciated and banded samples are proposed to be the product of recrystallisation from the much smaller monazite inclusions during greenschist facies metamorphism t 300 400 c fluids from the surrounding country rock caused strong lree na si depletion along apatite grain boundaries and cracks in the apatite lrees were either redeposited as monazite grains along apatite grain boundaries or were flushed out of the ore this fluid interaction also introduced the silicate components responsible for the interstitial formation of allanite talc tremolite chlorite serpentine muscovite quartz and carbonates along apatite grain boundaries

fluid induced nucleation of y ree phosphate minerals within apatite nature and experiment part i chlorapatite this study investigates chlorapatite ideally ca10 po4 6cl2 from two spatially separated locations in the odegardens verk apatite mine bamble sector se norway which was partially metasomatized under amphibolite facies conditions relative to the original chlorapatite metasomatized areas in sample dl136 are enriched in oh and f depleted in na si and y ree and contain numerous inclusions 1 15 m of monazite and xenotime in contrast metasomatized areas in sample tn174 are enriched in f and si depleted in na show y ree abundances similar to the original chlorapatite and host only a few monazite and xenotime grains in order to define the role of fluids in the formation of y ree phosphate minerals associated with apatite a series of experiments covering wide ranges of temperature 900 300 c and pressure 1000 500 mpa for a series of fluid compositions pure h2o a 50 50 molar mix of h2o and caf2 and co2 with 1 2 wt h2o were conducted on unaltered chlorapatite from the odegardens verk in the h2o experiments features due to metasomatic alteration depletion in na si and y ree as well as numerous monazite and xenotime inclusions as observed in the natural sample dl136 were fully reproduced monazite and xenotime grains were also observed growing on the surface of the apatite in dissolution embayments in metasomatized areas in the 50 50 caf2 h2o experiments metasomatized regions are strongly enriched in f and si depleted in na show unchanged y ree abundances and contain only a very few small monazite and xenotime grains similar to what was observed in sample tn174 natural and experimental observation imply the presence of two coupled substitutions na y ree 3 2 ca2 and si4 y ree 3 p5 ca2 in the case of dl136 and h2o fluid experiments na and si4 went into solution whereas the released y ree contributed to the growth of monazite and xenotime within the metasomatized apatite structure for sample tn174 and the 50 50 caf2 h2o fluid experiments na in apatite became depleted but si was enriched thereby stabilizing the y ree in the now recrystallized fluor hydroxylapatite structure which retarded the growth of monazite or xenotime inclusions the basic conclusion of this study is that nucleation of monazite and xenotime in the metasomatized chlorapatite is principally a function of the composition of the infiltrating fluid and to a much lesser extent temperature and pressure

hydrothermal fluid characteristics and implications of the makou ioa deposit in luzong basin eastern china abstract a large number of iron oxide apatite ioa deposits occur in the middle and lower yangtze river metallogenic belt mlyb eastern china proterozoic phosphorus rich strata are also widely exposed in this belt providing a good opportunity to research the relationship between phosphorus rich layers and ioa deposits the makou ioa deposit is located in the central part of the volcanic luzong basin the ore body is developed in the contact zone between gabbro diorite and cretaceous trachyandesite and it is the only ioa deposit in the basin that spatially associated with a dioritic intrusion the main hydrothermal alteration minerals are albite diopside apatite chlorite and carbonate in this study we employed shrimp si to analyse in situ o isotope ratios of magmatic and hydrothermal apatite and in situ s isotope ratios of pyrite from the makou deposit additionally la icp ms was used for trace element analysis the results show that the sulfur in the pyrite of the makou deposit comes from different sulfur phases e g h2s and so2 in the hydrothermal fluid and s34total is similar to that of magmatic sulfur indicating that the hydrothermal fluid was weakly affected by evaporite which is substantially different from other ioa skarn iron deposits in the mlyb both analysed apatite samples are classified as fluorapatite in which the 18oap of the makou magmatic hydrothermal apatite is similar to that of the initial mantle 3 7 5 5 and much lower than that of the susong sedimentary metasomatic apatite 13 7 14 2 the lree hree ratio increase from magmatic to hydrothermal apatite whereas the sr y decreases indicating that the hydrothermal fluid metasomatised the dioritic intrusive rock resulting in a large amount of albite crystallisation and release fe from pyroxene and biotite to hydrothermal fluid indicates that fe rich fluid in ioa deposit could be formed by albitization of the consolidated intrusive rock by combining this finding with the oxygen isotope data we propose that the mineralization of the makou deposit was mainly controlled by a magmatic hydrothermal process the low co2 and so42 contents in the volcanic rock are a key factor leading to apatite precipitation the addition of a phosphorus rich layer or evaporites is not necessary for the formation of ioa type deposits in the mlyb