waveform classification of volcanic low frequency earthquake swarms and its implication at soufriere hills volcano montserrat low frequency volcanic earthquakes are indicators of magma transport and activity within shallow conduit systems at a number of volcanoes these events exhibit a high degree of waveform similarity providing a criterion for classification using cross correlation techniques to quantify the degree of similarity we develop a method to sort events into families containing comparable waveforms events within a family have been triggered within one small source volume from which the seismic wave has then travelled along an identical path to the receiver this method was applied to a series of 16 low frequency earthquake swarms well correlated with cyclic deformation recorded by tiltmeters at soufriere hills volcano montserrat in june 1997 nine waveform groups were identified containing more than 45 events each the families are repeated across swarms with only small changes in waveform indicating that the seismic source location is stable with time the low frequency seismic swarms begin prior to the point at which inflation starts to decelerate suggesting that the seismicity indicates or even initiates a depressurisation process a major dome collapse occurred within the time window considered removing the top 100 m of the dome this event caused activity within some families to pause for several cycles before reappearing this shows that the collapse did not permanently disrupt the source mechanism or the path of the seismic waves

petrology of the 1991 1995 eruption at unzen effusion pulsation and groundmass crystallization abstract effusive eruption of dacite magma 2 1 108 m3 during 1991 1995 formed a lava dome at the summit of unzen volcano japan the effusion rate was highest at the beginning 4 0 105 m3 day 4 6 m3 s and decreased roughly with time to almost zero before this pattern was repeated with a second pulse of magma supply the whole rock chemistry of lavas shows significant variation attributable to variations in phenocryst abundance the more mafic the more abundant the phenocrysts the pattern of chemical variation with time shows some difference from that of the effusion rate all phenocrysts in dacite plagioclase hornblende biotite quartz and magnetite show evidence of disequilibrium with melt although a glomerophyric aggregation of phenocrysts suggests coexistence with each other phenocrysts are isotopically heterogeneous from species to species the calculated initial melt composition was rhyodacite and was nearly constant throughout the activity in contrast the bulk phenocryst population is andesite a model explaining the textures and the isotopic heterogeneity is the capture of diorite fragments or xenocrysts by parental rhyodacite magma it is suggested that when effusion rate was high less viscous crystal poor magma exited from the reservoir groundmass glass and plagioclase microlite rims show temporal chemical variations correlating with the effusion rate the higher the effusion rate the more evolved the compositions groundmass crystallinity increased with decreasing effusion rate from 33 to 50 textures in dome lavas suggest that groundmass crystallization had been mostly completed when magma reached the conduit top the fe ti oxide temperature 880 780 c was low when the crystallinity was high micropumice erupted before dome growth provided a sample recording magmatic foam in the conduit porosity of dome lavas was lower at lower effusion rates collapse of foam magma and simultaneous escape of volatiles through the conduit top were probably responsible for the accompanying low frequency earthquakes phenocrysts were broken and the breakdown rims on hornblende phenocrysts were torn off during collapse and successive compaction when effusion waned degassing and the resultant crystallization proceeded more completely so that the magma became too viscous to flow in the conduit top and behaved as a plug resulting in a temporary halt of effusion in turn groundmass crystallization in magma below the plug increased excess pressure in the upper parts of conduit due to slow cooling the plug was scavenged when rising excess pressure overcame its effective strength then the second pulse of magma supply began strong endogenous growth and extrusion of a lava spine in the later stage probably occurred for the same reason

instability of magma flow from volatile dependent viscosity volatiles dissolved in silicic magma at depth exsolve as the magma nears the surface and cause an increase in viscosity of the magma a model of a volcanic conduit within an elastic medium and a viscosity dependent on the volatile content of the magma produces oscillatory magma flow for a critical range of steady input flow rates oscillatory flow is recognized as a fundamental mode of behavior at silicic volcanoes and understanding it allows improved short term forecasting of timing and eruption style

imaging surface contacts power law contact distributions and contact stresses in quartz calcite glass and acrylic plastic a procedure has been developed to obtain microscope images of regions of contact between roughened surfaces of transparent materials while the surfaces are subjected to static loads or undergoing frictional slip static loading experiments with quartz calcite soda lime glass and acrylic plastic at normal stresses to 30 mpa yield power law distributions of contact areas from the smallest contacts that can be resolved 3 5 m2 up to a limiting size that correlates with the grain size of the abrasive grit used to roughen the surfaces in each material increasing normal stress results in a roughly linear increase of the real area of contact mechanisms of contact area increase are by growth of existing contacts coalescence of contacts and appearance of new contacts mean contacts stresses are consistent with the indentation strength of each material contact size distributions are insensitive to normal stress indicating that the increase of contact area is approximately self similar the contact images and contact distributions are modeled using simulations of surfaces with random fractal topographies the contact process for model fractal surfaces is represented by the simple expedient of removing material at regions where surface irregularities overlap synthetic contact images created by this approach reproduce observed characteristics of the contacts and demonstrate that the exponent in the power law distributions depends on the scaling exponent used to generate the surface topography

remarkable cyclic ground deformation monitored in real time on montserrat and its use in eruption forecasting telemetered high resolution tiltmeters were installed in montserrat in summer of 1995 in december 1996 and in may 1997 the 1995 installations several km from the soufriere hills vent were too distant to yield useful data however the 1996 and 1997 installations on the crater rim revealed 6 14 h inflation cycles caused by magma pressurization at shallow depths 0 6 km below the base of dome the tilt data correlated with seismicity explosions and pyroclastic flow activity and were used to forecast times of increased volcanic hazard to protect scientific field workers and the general public

magmatic fluids in the breccia hosted epithermal au ag deposit of rosia montana romania the breccia hosted epithermal au ag deposit of rosia montan is located 7 km northeast of abrud in the northern part of the south apuseni mountains romania estimated total reserves of 214 91 million metric tons mt of ore at 1 46 g t au and 6 9 g t ag 10 1 moz of au and 47 6 moz of ag make rosia montan one of the largest gold deposits in europe at this location miocene calc alkaline magmatic and hydrothermal activity was associated with local extensional tectonics within a strike slip regime related to the indentation of the adriatic microplate into the european plate during the carpathian orogenesis the host rocks of the magmatic complex consist of pre mesozoic metamorphosed continental crust covered by cretaceous turbiditic sediment flysch magmatic activity at rosia montan and its surroundings occurred in several pulses and lasted about 7 m y rosia montan is a breccia hosted epithermal system related to strong phreatomagmatic activity due to the shallow emplacement of the montana dacite the montana dacite intruded miocene volcaniclastic material volcaniclastic breccias and crops out at cetate and c rnic hills current mining is focused primarily on the cetate open pit which was mapped in detail leading to the recognition of three distinct breccia bodies the dacite breccia with a dominantly hydrothermal matrix the gray polymict breccia with a greater proportion of sand sized matrix support and the black polymict breccia which reached to the surface contains carbonized tree trunks and has a dominantly barren clastic matrix the hydrothermal alteration is pervasive adularia alteration with a phyllic overprint is ubiquitous silicification and argillic alteration occur locally mineralization consists of quartz adularia carbonates commonly mn rich pyrite fe poor sphalerite galena chalcopyrite tetrahedrite and native gold and occurs as disseminations as well as in veins and filling vugs within the montana dacite and the different breccias the age of mineralization 12 85 0 07 ma was determined by 40 ar 39 ar dating on hydrothermal adularia crystals from vugs in the dacite breccia in the cetate open pit microthermometric measurements of fluid inclusions in quartz phenocrysts from the montana dacite revealed two fluid types that are absent from the hydrothermal breccia and must have been trapped at depth prior to dacite dome emplacement brine inclusions 32 55 wt nacl equiv homogenizing at t h 460 c and intermediate density fluids 4 9 15 6 wt nacl equiv t h between 345 430 c secondary aqueous fluid inclusion assemblages in the phenocrysts have salinities of 0 2 to 2 2 wt percent nacl equiv and t h of 200 to 280 c fluid inclusion assemblages in hydrothermal quartz from breccias and veins have salinities of 0 2 to 3 4 wt percent nacl equiv and t h from 200 to 270 c the oxygen isotope composition of several zones of an ore related epithermal quartz crystal indicate a very constant 18 o of 4 5 to 5 0 per mil for the mineralizing fluid despite significant salinity and temperature variation over time following microthermometry selected fluid inclusion assemblages were analyzed by laser ablation inductively coupled plasma mass spectrometry la icpms despite systematic differences in salinity between phenocryst hosted fluids trapped at depth and fluids from quartz in the epithermal breccias all fluids have overlapping major and trace cation ratios including identical na k rb sr cs ba consistent with the constant near magmatic oxygen isotope composition of the hydrothermal fluids these data strongly indicate a common magmatic component of these chemically conservative solutes in all fluids cu pb zn and mn show variations in concentration relative to the relatively non reactive alkalis reflecting the precipitation of sulfide minerals together with au in the epithermal breccia and possibly of cu in an inferred subjacent porphyry environment the magmatic hydrothermal processes responsible for epithermal au ag mineralization at rosia montan are however not directly related to the formation of the spatially associated porphyry cu au deposit of rosia poieni which occurred about 3 m y later

seismicity associated with dome growth and collapse at the soufriere hills volcano montserrat varied seismicity has accompanied growth and collapse of the lava dome of the soufriere hills volcano montserrat earthquakes have been classified as either volcano tectonic long period or hybrid and daily variations in the numbers of events have mapped changes in the style of eruption repetitive hybrid earthquakes were common during the first months of dome growth in july 1996 the style of seismicity changed and regular short lived hybrid earthquake swarms became common this change was probably caused by an increase in the magma flux earthquake swarms have preceded almost all major dome collapses and have accompanied cyclical deformation thought to be due to a build up of pressure in the upper conduit which is later released by magma moving into the dome

an extension of the insar based probability integral method and its application for predicting 3 d mining induced displacements under different extraction conditions underground extraction can be roughly classified into three types i e subcritical critical and supercritical extraction in accordance with the geological conditions in the overburden and the geometry of mined out areas in 2016 we proposed an approach based on the interferometric synthetic aperture radar insar technique and the probability integral method pim for the cost effective prediction of 3 d mining induced displacements abbreviated as insar pim due to the inherent assumption of critical extraction in the pim the insar pim method performs well in predicting the 3 d displacements caused by critical and or supercritical extraction but poorly for subcritical extraction in this paper we first propose a generalized pim gpim by modifying the traditional pim with a simplified boltzmann function we then replace the pim of the insar pim with the proposed gpim to develop an extension of insar pim referred as to insar gpim the insar gpim was tested in the qianyingzi coal mining area china the results show that the insar gpim predicted horizontal and vertical displacements caused by subcritical critical and supercritical extraction agree well with the in situ observations with average root mean square errors of about 0 032 and 0 050 m respectively these accuracies represent improvements of 60 9 and 59 when compared with the accuracies predicted by the insar pim in the horizontal and vertical directions the results indicate that the insar gpim is capable of accurately predicting 3 d mining induced displacements under different extraction conditions i e subcritical critical and supercritical extraction and it performs much better than the insar pim in the case of subcritical extraction it is therefore believed that insar gpim will have a wider scope of applications than the previous insar pim

factors predictive of roof instability in addition to the existing cmrr criteria at two case study coal mines abstract this work uses two underground longwall coal mines located in the western us mines a and b as case studies to investigate which parameters are indicative of roof fall potential and whether the coal mine roof rating cmrr is predictive of stability at these mines data were collected at 30 sites in each mine these data sets included the cmrr a record of the roof stability and a series of non cmrr parameters thought to also be potentially indicative of roof stability but which are not included in the cmrr these data were then statistically analyzed for correlation between cmrr and roof stability the cmrr was found to be moderately effective at mine a but not effective at mine b at mine a faulting was found to be the primary control on roof stability topographic curvature slope angle and depth of cover were found to have reasonable predictive capability for assessment of roof stability category at mine b based on a logistic regression analysis these differences in roof stability controls are likely due at least in part to the unusual topography above mine b with differential erosion resulting in a landscape of flat plateaus and sharp river valleys it is likely that these sudden changes in slope and topography lead to in situ stress rotation and the development of shear stresses near the excavation at mine b this combined with a lack of major discontinuities such as slickensides which are central to the cmrr system explains why the cmrr is much less effective at predicting roof stability at mine b compared to mine a

recent remobilisation of shallow level intrusions on montserrat revealed by hydrogen isotope composition of amphiboles abstract ion probe measurements of hydrogen isotopes were made on amphiboles representing different stages of the ongoing eruption of the soufriere hills volcano montserrat the majority 80 of the andesitic amphiboles show relative intra and inter crystal d homogeneity with a mean of 38 12 consistent with known primary magmatic values the remainder 20 of amphiboles show marked d heterogeneity with a mean of 6 30 the heterogeneous amphiboles have 100 m rims with d values similar to the homogeneous crystals but core values which are significantly heavier than primary magmatic values early in the eruption 50 of amphiboles are isotopically heterogeneous but post spring 1996 all amphiboles are homogeneous we interpret these ion probe data in terms of development of a shallow andesitic magma chamber by repeated emplacement of andesitic magma in the shallow crust over at least the last 100 yr we suggest such shallow intrusions emplaced during the volcano seismic crises preceding the ongoing eruption solidified some regions interacted with hydrothermal fluids and isotopic exchange took place generating the heavy hydrogen isotope signatures in the heterogeneous amphiboles on onset of the ongoing eruption such old igneous material was remobilised with intimate mixing between the new magma batch and the old intrusions indicated by the close proximity of homogeneous and heterogeneous crystals the isotopically primary magmatic rims on the heterogeneous crystals indicate hydrogen isotope exchange over a period of a few weeks consistent with timescales of magma ascent at the soufriere hills volcano once the old igneous material was flushed out by spring 1996 the eruption proceeded by extruding material dominated by the new batch of magma this resulted in a marked increase in extrusion rate

trace element concentrations in porphyry copper deposits from metaliferi mountains romania a reconnaissance study there are fifteen miocene intrusions with porphyry copper mineralization in the metaliferi mountains romania most are associated with epithermal au ag te bi se ge vein systems the investigation of fifty samples from six deposits rosia poieni bucium tarni a colnic rovina valea morii and bolcana indicated bulk rock mean values of 0 16 0 88 ppm au 1000 ppm in bornite in the porphyry type mineralization galena forms microinclusions in pyrite chalcopyrite and bornite and contains up to 3750 ppm ag 17 380 ppm se 1570 ppm ge and 780 ppm te galena and pyrite from the epithermal mineralization in the m gura bolcana troi a system contain concentrations of ag and se ten times lower than in the same minerals from the porphyry copper mineralization the present data show that te is a significant trace element in the potassic zone of the investigated porphyry systems the data also shows that this does not correlate with the presence or absence of ophiolitic basement or with variation in the chemistry of the host intrusions tellurium enrichment in porphyry type deposits of the metaliferi mountains supports their genetic relationship with the spatially associated epithermal systems

pb isotope evidence for contaminant metal dispersal in an international river system the lower danube catchment eastern europe abstract lead isotope signatures 207pb 206pb 208pb 206pb 208pb 204pb 206pb 204pb determined by magnetic sector icp ms in river channel sediment metal ores and mine waste have been used as geochemical tracers to quantify the delivery and dispersal of sediment associated metals in the lower danube river catchment due to a diverse geology and range of ore body ages pb isotope signatures in ore bodies within the lower danube river catchment show considerable variation even within individual metallogenic zones it is also possible to discriminate between the pb isotopic signatures in mine waste and river sediment within river systems draining individual ore bodies lead isotopic data along with multi element data were used to establish the provenance of river sediments and quantify sedimentary contributions to mining affected tributaries and to the danube river data indicate that mining affected tributaries in serbia and bulgaria contribute up to 30 of the river channel sediment load of the lower danube river quantifying relative sediment contributions from mining affected tributaries enables spatial patterns in sediment associated metal and as concentrations to be interpreted in terms of key contaminant sources combining geochemical survey data with that regarding the provenance of contaminated sediments can therefore be used to identify foci for remediation and environmental management strategies

genesis of acid sulfate alteration and au cu ag mineralization at summitville colorado the summitville au cu ag deposit occurs within a porphyritic quartz latite primarily in a zone of vuggy silica alteration characterized by leaching of all major elements except silica and iron vuggy silica is best developed between an elevation of 3 700 and 3 500 m where it occurs in irregular pipes and lenticular pods up to 70 m wide and is enclosed by up to 30 m of intense quartz alunite alteration the vuggy silica zones diminish in size with decreasing elevation and rarely exceed a width of 2 m below an elevation of 3 400 m these deep vuggy silica zones are enclosed by quartz kaolinite alteration with little or no alunite sulfide mineralization occurs primarily within the vuggy silica the sulfide assemblage changes with decreasing elevation from covellite luzonite or native gold to chalcopyrite tennantite sulfides occur lining voids or in microveinlets and are accompanied by minor kaolinitc but not by alunite gold also occurs in a near surface barite goethite jarosite assemblage that crosscuts the vuggy silica consideration of alunite kaolinitc and pyrite stability relations and of aluminum speciation at 250 degrees c indicates that a ph of 2 or below and a log f sub o 2 of 31 or 1 at 250 degrees c were necessary to produce vuggy silica alteration the chalcopyrite tennantite mineralization occurring at depth in the vuggy silica zone is indicative of less oxidizing and less acidic conditions the covellite luzonite or gold assemblage requires conditions intermediate between those necessary for vuggy silica alteration and for deep sulfide mineralization barite gold mineralization is interpreted as a near surface assemblage produced under highly acidic oxidizing conditions these textural and geochemical relationships indicate that sulfide and gold mineralization postdate the formation of vuggy silica alteration in the deposit and are not directly related to the highly acidic solutions necessary for this early acid leaching event the change from extreme acid leaching to copper sulfide and precious metal deposition may represent a transition from a magmatic vapor dominated to a liquid dominated system leading to more reducing and less acidic conditions during sulfide deposition

1 subduction slab detachment and mineralization the neogene in the apuseni mountains and carpathians abstract the inner carpathians comprise several distinct neogene late stage orogenic pb zn cu ag au ore districts the mineral deposits in these districts are closely related to volcanic and subvolcanic rocks and represent mainly porphyry and epithermal vein deposits which formed within short periods of time in each district here we discuss possible geodynamic and structural controls that suggest why some of the neogene volcanic districts within the carpathians comprise abundant mineralization while others are barren the neogene period has been characterized by an overall geodynamic regime of subduction where primary roll back of the subducted slab and secondary phenomena like slab break off and the development of slab windows could have contributed to the evolution location and type of volcanic activity structural features developing in the overlying lithosphere and visible in the carpathian crust such as transtensional wrench corridors block rotation and relay structures due to extrusion tectonics have probably acted in focusing hydrothermal activity as a result of particular events in the geodynamic evolution and the development of specific structural features mineralization formed during fluid channelling within transtensional wrench settings and during periods of extension related to block rotation in the slovakian ore district of the western carpathians neogene volcanism and associated mineralization were localized by sinistral ne trending wrench corridors which formed part of the extruding alcapa block the baia mare ore district in the eastern carpathians reflects a transtensional wrench setting on distributed oversteps close to the termination of the dragos voda fault there mineralization was spatially controlled by the transtensional dragos voda master fault and associated cross fault systems the golden quadrangle cu au ore district of the southern apuseni mountains reflects an unusual rotated transtensional extensional setting close to the termination of a graben system there fluid flow was probably localized by fault propagation at the inner tip of the graben system the spatial and temporal evolution of the magmatism and its changing geochemical signature from n w to s e strongly suggests a link with the contemporaneous northeastward roll back of the subducted slab and a progressive southeastward detachment during accelerating roll back this geodynamic evolution is further supported by the present day overall and detailed mantle lithospheric density images the present day heat flow patterns the crustal architecture and its interpreted evolution and the spatial and temporal evolution of depocentres around the carpathian arc in contrast to all these features the mineral deposits in the west carpathians east carpathians and apuseni mountains are too synchronous with respect to their individual volcanic history and contrast too much with younger volcanics of similar style but barren in southeastern parts of the carpathians to simply link them directly to the slab evolution in all three districts the presence of magmatic fluids released from shallow plutons and their mixing with meteoric water were critical for mineralization requiring transtensional or extensional local regimes at the time of mineralization possibly following initial compressional regimes these three systems show that mineralization was probably controlled by the superposition of favourable mantle lithospheric conditions and partly independent evolving upper crustal deformation conditions in the 13 to 11 ma period the dominant mineralization formed all across the carpathians and was superimposed on structurally favourable crustal areas with at that time volcanic hydrothermal activity the period may reflect the moment when the upper part of the crust failed under lithospheric extension imposed by the slab evolution this crustal failure would have fragmented the overriding plate possibly breaking up the thermal lid to provoke intensive fluid flow in specific areas and allowed subsequent accelerated tectonic development block rotation and extrusion of a family of sub blocks that are arbitrarily regarded as the tisia dacia or alcapa blocks even though they have lost their internal entity

the explosive eruption of soufriere hills volcano montserrat west indies 17 september 1996 on 17 september 1996 the soufriere hills volcano started a 9 hour period of dome collapse involving 11 7 106 m dre of lava after 2 5 hours of quiescence a sustained explosive eruption began estimated eruption parameters are plume height at least 11 3 km and a maximum of 15 km 180 m s for launch velocities of ballistic clasts peak explosion pressure of 27 5 mpa magma water contents of 2 5 5 magma discharge rates from 2300 to 4300 m s ejecta volume of 3 2 0 9 106 m dre ejecta consists of pumice 1160 kg m higher density vesiculated ejecta 1300 to 2000 kg m dense glassy clasts 2600 kg m breccias cut by tuffisite veins and hydrothermally altered lithics the ejecta are interpreted as a conduit assemblage with evacuation of the conduit down to depths of about 3 to 5 km the eruption was triggered by unloading of a gas pressurised conduit due to dome collapse

determination of actual limit angles to the surface and their comparison with the empirical values in the upper silesian basin czech republic abstract this study deals with the determination of the actual limit angles in the long term formed subsidence basin in the czech part of the upper silesian basin the remaining part lays in poland here there was the most extensive underground exploitation of black coal in the north east of the czech republic a limit angle is absolutely decisive in the determination of deep mining influences in relation to the current and future utilisation of this territory the two csm and paskov mine localities on the edge of the subsidence basin were selected for this study since they could not have been affected by mining in neighbouring mines on the grounds of the long term levelling monitoring of points on the surface which started prior to mining the horizontal distance between the mined out area and the undisturbed ground surface was identified the impact of limit angle on the surface was calculated by means of the horizontal distance and the established mining depth such identified actual limit angles reached the values of 36 at the csm mine and 25 for the paskov mine the calculated values are significantly lower when compared with the currently applied empirical values of 57 for the csm mine and 56 for the paskov mine this means that the extent of the undermining effects is unambiguously wider by 611 m at the csm mine and by 883 m at the paskov mine this study thus establishes the existence of a significantly vaster area influenced by coal deep mining than previously expected the identified facts lead to the conclusion that regular revisions and follow up updates of the empirically determined parameters are recommended

upshot of strata movement during underground mining of a thick coal seam below hilly terrain underpinning based simultaneous extraction was successfully used to extract more than 90 of thick and contiguous sections of a coal seam at chirimiri mine lying below a hill cap with a rapid change in depth of cover and is placed above the surrounding ground level the last few panels of the mine encountered strata control problems during the depillaring underground instrumentation and observations showed that the last phase depillaring of the property near the free surface of the hill slope experienced shearing of overlying strata along two incompetent layers field investigations revealed that large amount of lateral movement due to the hilly nature of the overlying strata is the main source of the problem a simple two dimensional study on a simulated model also demonstrated the occurrence of the problem during working below an unconfined rock mass of hilly nature different evidences were collected from the site to identify the main horizons and the direction of lateral movement and accordingly two different strata management plans one for each section were successfully executed to overcome the encountered strata control problems field investigations in the rest of the panels of the site showed favourable impact of the adopted strata management plan

controls on conduit magma flow dynamics during lava dome building eruptions 1 lava dome eruptions commonly display fairly regular alternations between periods of high and low or no activity with timescales typically of weeks to years and sudden transitions between effusive and explosive activity we develop a transient model of the magma flow in a volcanic conduit from an open system magma chamber with continuous replenishment the model incorporates gas exsolution bubble growth gas escape through the magma and decompression induced crystallization and considers variations in magma temperature water content conduit diameter phenocryst size chamber volume and magma rheology calculations show the presence of periodic variations in discharge rate due to the transition from a stable regime when discharge rate is low and crystals grow efficiently leading to high magma viscosity to another stable state when discharge rate is high and crystallization is negligible the difference in discharge rates between these regimes can be several orders of magnitude periods are similar to the observed timescales and mainly depend on the chamber volume the system shows strongly nonlinear responses to the variation of governing parameters if magma has a bingham rheology pauses in discharge rate occur between peaks of discharge and the peaks are much higher than for the case of newtonian rheology large changes in discharge rate and eruptive behavior can occur as the consequence of small changes in magma temperature water content phenocryst size distribution or conduit diameter the system can fluctuate between low and high discharge rates with transitions to explosive activity

the hydrothermal system at soufriere hills volcano montserrat west indies characterization and role in the on going eruption mineralogical microtextural and geochemical studies have been performed on altered volcanic products from active hydrothermal areas on phreatic tephra from the 1995 activity and on fragments from older castle peak dome and the present 1995 97 dome the mineral assemblages of the hydrothermal system primarily silica polymorphs are typical of the upper alteration zone of a high sulfidation system volatile and mobile elements chemistry show no evidence of interaction between the hydrothermal system and erupting magmas these results suggest that the on going eruption conduits are isolated from the hydrothermal system due to precipitation of vapor transported silica which drastically reduces the magma degassing through country rocks

the relationship between degassing and ground deformation at soufriere hills volcano montserrat we examine the correlations between so2 emission rate seismicity and ground deformation in the month prior to the 25 june 1997 dome collapse of the soufriere hills volcano montserrat during this period the volcano exhibited a pattern of cyclic inflation and deflation with an 8 14 h period we find that so 2 emission rates measured by cospec correlate with the amplitude of these tilt cycles and that higher rates of so 2 emission were associated with stronger ground deformation and enhanced hybrid seismicity within tilt cycles degassing peaks coincide with maximum deformation gradients increases in the amount of gas in the magma conduit feeding the dome probably due to increases in volatile content of ascending magma volume can account for the observed increases in tilt amplitude hybrid seismicity and so2 emission rate q 2000 elsevier science b v all rights reserved

mineral chemistry of hydrothermal biotite from the kahang porphyry copper deposit ne isfahan central province of iran abstract the kahang porphyry cu deposit located northeast of isfahan city in central of iran is associated with a composite miocene stock and ranges in composition from diorite through granodiorite to quartz monzonite field observations and petrographic studies show that the emplacement of the kahang stock occurred in several pulses each associated with its related hydrothermal activity early hydrothermal alteration started with a potassic style in the central part of the system and produced a secondary biotite k feldspar magnetite assemblage accompanied by chalcopyrite and pyrite mineralization propylitic alteration that took place at the same time as the potassic alteration occurred in the peripheral portions of the stock subsequent phyllic alteration overprinted earlier potassic and propylitic alterations biotite grains from the potassic and phyllic zones show distinct chemical compositions the feo tio2 mno k2o and na2o concentrations in biotite from the phyllic alteration zone are lower than those from the potassic alteration zone the f and cl contents of biotite from the potassic alteration zone display relatively high positive correlation with the xmg the fluorine intercept values iv f from the potassic and phyllic alteration zones are strongly correlated with the fluorine chlorine intercept values iv f cl biotite geothermometry for the potassic and phyllic alteration zones based on the biotite geothermometer of beane 1974 yields a temperature range of 422 to 437 c mean 430 c and 329 to 336 c mean 333 c respectively the position of data in log xf xoh ratio vs xmg and xfe diagram suggests that biotite formed under dissimilar composition and temperature conditions in the potassic and phyllic alteration zones calculated log fugacity ratios of fh2o fhf fh2o fhcl and fhf fhcl show that hydrothermal fluids associated with the potassic alteration were distinctively different from those fluids associated with the phyllic alteration zone at kahang porphyry cu deposit the results of this research indicate that the chemistry of biotite is related to the chemical composition of the magma and the prevailing physical conditions during crystallization

a model of vulcanian eruptions at galeras volcano colombia abstract a series of six vulcanian eruptions at galeras volcano colombia occurred during 1992 1993 these eruptions followed the emplacement of a lava dome in late 1991 which was accompanied by cooling crystallizing and partial solidification of the column of magma plugging the conduit five of the eruptions were preceded by episodes of monochromatic long period seismicity suggesting cyclic pressurization of the magma the quiescent intervals between eruptions generally decreased with each successive eruption we propose a model of gas release from magma into confined stationary pore spaces by 5 10 crystallization of anhydrous minerals causing repeated overpressurization of the magmatic system using initial lithostatic pressures of 20 100 mpa 800 3900 m depth gas buildup by crystallization indicates overpressures of 3 17 mpa which is the approximate fracture criterion for a magma chamber our galeras data suggest two models of pressurization 1 gas exsolution may have occurred at similar depths but with progressively smaller overpressures being developed before each successive eruption according to this model the comparatively long quiescent periods between the first eruptions resulted in relatively large amounts of gas exsolution from the magma and accumulation in pore spaces whereas the shorter quiescent periods for the later eruptions exsolved less gas the decrease in overpressure with time may have resulted from progressive fracturing of partly solidified magma during the eruptions which progressively decreased the tensile strength and increased the permeability of the magma 2 since overpressures are smaller at shallower depths for a given amount of crystallization the first eruptions of 1992 1993 were caused by gas exsolution at shallow depths while the last eruptions having shorter quiescent intervals resulted from a greater amount of gas exsolution at greater depths in this case the rate of gas exsolution varied as a function of depth the two scenarios for pressurization may be combined into a more general model involving edifice weakening and the development of a shallow hydrothermal system from continued degassing of the magma plug as weakening of the edifice formed an extensive system of fractures the shallow hydrothermal system deepened due to meteoric water input and magmatic degassing with time a greater number of fractures were filled and partly sealed by hydrothermal minerals at progressively deeper levels as a result the source of the overpressure also deepened with time

a chlorite solid solution geothermometer the los azufres mexico geothermal system chlorite constitutes a major hydrothermal alteration product of metamorphism of andesites in the active geothermal system of los azufres mexico electron microprobe analyses performed on a set of crystals from each sample show wide variations in composition correlation coefficients among chemical constituents were calculated it is shown that the tetrahedral charge is positively correlated with the octahedral vacancy and negatively with the iron content and there is almost no correlation with the octahedral aluminium and magnesium content a procedure is proposed to select end members and substitution vectors and to give a general formula for these chlorites

on prevention and mechanism of bed separation water inrush for thick coal seams a case study in china bed separation can occur in overlying strata especially in hard and soft interbedded roof strata if these strata prone to form bed separation are rich aquifers water can accumulate into bed separation and maybe cause a serious water hazard under the condition of water inflow passages existence therefore studying these types of roof water inrush mechanisms forecasting roof water inrush and formulating preventive and control measures in advance are extremely important to a mine in this paper we takes the typical case of water inrush in the workface number 1121 at hongliu coal mine as an example and study the mechanism of water inrush in detail primarily field drilling with water leakage and color tv observations showed that the maximum height of the water conducting fractured zone was 12 50 times the thickness of the coal seams which spread to the overlying coarse grained sandstone aquifer secondly the numerical simulation indicated that bed separation storage space was prone to form under the combination of coarse grained sandstone and mudstone geological structure the detection using uwtem revealed that the groundwater accumulated in this bed separation and formed a water bag bed separation water when the water bag reached a certain degree water bursting happened with the main roof collapsing finally prevention effective drainage methods and successful experiences with bed separation water have been summarized and it will have a major significance to coal mines suffering from bed separation water inrush

fault stability inferred from granite sliding experiments at hydrothermal conditions seismicity on crustal faults is concentrated in the depth interval 1 3 to 12 15km tse and rice 1986 suggested that the lower bound on seismicity is due to a switch with increasing temperature from velocity weakening destabilizing to velocity strengthening stabilizing friction they inferred this transition from friction data for dry granite however pore fluids exist at elevated temperatures throughout the crust and may strongly influence strength and sliding behavior we present new data from sliding experiments on granite at elevated t 23 to 600 plus elevated ph2o 100 mpa our results show velocity strengthening at room temperature but velocity weakening from 100 to 350 c except at 250 from 350 to 600 there are systematic trends from velocity weakening to strong velocity strengthening and from high to low friction neither trend was seen in tests on dry granite the velocity dependence data imply the potential for unstable slip in the interval 100 to 350 using a geotherm to map temperature to depth this interval closely matches the observed earthquake distribution

characterisation of the 1997 vulcanian explosions of soufriere hills volcano montserrat by video analysis the activity of convention at montserrat soufriere hills volcano montserrat during the period 1995 1999 included numerous violent explosions two major cycles of vulcanian explosions occurred in 1997 a first of 13 explosions between 4 and 12 august and a second of 75 between 22 september and 21 october the explosions were short lived events lasting a few tens of seconds during which partial fountain collapse generated pyroclastic surges and pyroclastic flows and buoyant plumes ascended 3 15 km into the atmosphere each explosion discharged on average 3 105 m3 dense rock equivalent dre of magma draining the conduit to depths of 1 2 km the paper focuses on the first few seconds of three explosions of the 75 that occurred in september october 1997 6 october 1997 at 17 50 7 october 1997 at 16 02 and 9 october 1997 at 12 32 physical parameters such as exit velocities magmatic water contents and magma pressures at fragmentation are estimated by following and modelling the ascent of individual momentum dominated finger jets visible on videos during the initial stages of each explosion the model treats each finger jet as an incompressible flow sustained by a steady flux of gas and particles during the few seconds of ascent and produces results that compare favourably with those using a multiphase compressible code run using similar eruptive parameters each explosion reveals a progressive increase in eruptive intensity with time jet exit velocities increasing from 40 m s 1 at the beginning of the explosion up to 140 m s 1 after a few seconds modelling suggests that the first magma to exit was largely degassed whereas that discharged after a few seconds contained up to 2 wt water magma overpressures up to 10 mpa are estimated to have existed in the conduit immediately prior to each explosion progressive increases in jet exit velocity with time over the first few seconds of each explosion provide direct evidence for strong pre eruptive gradients in water content and magma pressure in the upper reaches probably 100 500 m of the conduit fountain collapse occurred during the first 10 20 s of each explosion because the discharging jets had bulk densities up to 100 times that of the atmosphere and were unable to entrain enough air to become buoyant such high eruptive densities were due to the presence of partially degassed magma in the conduit

ground movement due to longwall mining in high relief areas in new south wales australia abstract the theoretical pattern of ground movement observed in flat terrains was modified by surface topography and geological structures in high relief areas e g creeks and gullies the observed pattern of movement was asymmetrical about the centre of the extraction panel the lateral movement of both sides of the valley caused large compressive strains and a hump at the creek bed the strains were three four times those normally observed in flat or fairly gentle topographies the hump was due to the rock mass in the creek bed being pushed up by the lateral forces from the valley sides a major geological fault caused both sides of the valley to move laterally away from the fault plane the magnitude of the maximum horizontal movement was as large as 40 of the observed vertical movement outside the goaf the horizontal movements were generally larger than the corresponding vertical movements however the horizontal movements outside the goaf appeared to be rigid body type movements with small deformations which may only have insignificant surface consequences

petrology of philippine geothermal systems and the application of alteration mineralogy to their assessment abstract philippine geothermal systems occur in the vicinity of large holocene calc alkaline volcanic complexes wells drilled in these areas encountered multiple intrusions the latest dikes are the subsurface manifestations of the youngest heat source commonly at least two hydrothermal regimes are juxtaposed in a single area with the latest being in equilibrium with the present temperature and chemical regime alteration by neutral ph water is pervasive and abundant a contact metamorphic aureole also occurs near intrusives alteration due to acid sulfate fluids is generally confined to permeable structures neutral ph alteration is divided into four zones on the basis of key clay minerals and two subzones are defined by calc silicates these are the smectite ambient to 180 c transition 180 230 c illite 230 320 c and biotite 270 340 c zones subzones are defined by epidote 250 340 c and amphibole 280 340 c the four main zones of acid alteration are kaolinite ambient to 120 c dickite kaolinite 120 200 c dickite pyrophyllite 200 250 c and pyrophyllite illite 230 320 c where relict high temperature alteration reaches the surface the area being drilled is usually the outflow zone of the present system these hydrothermal mineral assemblages are used 1 as geothermometers 2 to assist in determining the depth at which the production casing will be set during drilling 3 to estimate fluid ph and other chemical parameters 4 to predict possible corrosion and scaling tendencies of the fluids 5 as a measure of permeability and possible cold water influx into wells 6 as a guide to field hydrology and 7 to estimate roughly the thickness of the eroded overburden

bubble growth in rhyolitic melts experimental and numerical investigation bubble growth controlled by mass transfer of water from hydrated rhyolitic melts at high pressures and temperatures was studied experimentally and simulated numerically rhyolitic melts were hydrated at 150 mpa 780 850 c to uniform water content of 5 5 5 3 wt the pressure was then dropped and held constant at 15 145 mpa upon the drop bubbles nucleated and were allowed to grow for various periods of time before final rapid quenching of the samples the size and number density of bubbles in the quenched glasses were recorded where number densities were low and run duration short bubble sizes were in accord with the growth model of scriven 1959 for solitary bubbles however most results did not fit this simple model because of interaction between neighboring bubbles hence the growth model of proussevitch et al 1993 which accounts for finite separation between bubbles was further developed and used to simulate bubble growth

non newtonian rheological law for highly crystalline dome lavas volcanic eruption models are hampered by the lack of multiphase magmatic flow laws most rheological models estimate the viscosity of multiphase lavas via the einstein roscoe equation but this simplification cannot be used for high crystallinity and it does not consider the non newtonian strain rate dependence of viscosity we carried out parallel plate experiments on natural samples to simulate multiphase lava deformation under various stresses and strain rates multiphase lavas exhibit an important component of shear thinning and appear to invalidate the adequacy of einstein roscoe based formulations for highly crystalline lava rheology the remarkable singular dependence of viscosity on strain rate yields a novel universal rheology law at eruptive temperatures t i e log 0 993 8974 t 0 543 log our work reveals the importance of considering microcracking and viscous dissipation at very high strain rate 10 3 s 1 explaining the occurrence of seismic swarms along the conduit margins and consequently supporting plug like magma ascent models

estimation of limit angle using laminated displacement discontinuity analysis in the soma coal field western turkey determination of the limit angle at the manisa soma eynez coal field a major coal production area in turkey is difficult because of the presence of a landslide caused by the waste from a neighboring open pit site being dumped over the underground mine at the soma eynez basin in fact it is not possible to determine the effect of extraction on the surface from field studies thus in order to determine the limit angle in situ subsidence measurements geophysical measurements rock based tests in the laboratory and the data obtained from a physical model have supported numerical modeling studies the software lamodel used for the numerical modeling was developed by national institute for occupational safety and health niosh and is based on the boundary element method the results obtained from modeling have been found to be compatible with other studies and as a result the limit angle has been determined

evolution mechanism of water flowing zones and control technology for longwall mining in shallow coal seams beneath gully topography the height and evolution mechanism of fractured water flowing zones are of great importance for prevention of water inrush disasters and protection of immediate environments particularly in ecological vulnerable areas in this paper comparative approaches including empirical formula calculation physical simulation numerical simulation and protem transient electromagnetic analysis are employed to identify the development of the fracture zones caused by water flowing so as to ensure mining safety and protection of groundwater in shallow coal seams beneath gully topography an empirical formula was used to calculate the height of the water flowing fracture zone and an experimental study utilizing a model based on a similar material was adopted to analyze the movement and fracture development of the overlying strata results provide a reasonable basis from which a rational mining height may be determined the protem transient electromagnetic apparatus was employed to detect the water flowing structure conductivity of the overlying strata induced by mining beneath gully topography in the field the water flowing fracture of the overlying strata can be estimated according to comprehensive analysis of the apparent resistivity changes of the field gully surface crack development and aquifer water level accordingly the control technologies in the field were implemented and discussed regarding preventing gully water from rushing into underground mining spaces through water flowing fracture zones results indicate that safe and efficient mining of shallow seams beneath gully topography can be achieved by prevention of gully accidents and protecting the surface water resources of the ecological environment

shear stress along the conduit wall as a plausible source of tilt at soufriere hills volcano montserrat 1 surface deformations recorded in close proximity to the active lava dome at soufriere hills volcano montserrat can be used to infer stresses within the uppermost 1000 m of the conduit system most deformation source models consider only isotropic pressurisation of the conduit we show that tilt recorded during rapid magma extrusion in 1997 could have also been generated by shear stresses sustained along the conduit wall these stresses are a consequence of pressure gradients that develop along the conduit numerical modelling incorporating realistic topography can reproduce both the morphology and half the amplitude of the measured deformation field using a realistic shear stress amplitude equivalent to a pressure gradient of 3 5 104 pa m 1 along a 1000 m long conduit with a 15 m radius this shear stress model has advantages over the isotropic pressure models because it does not require either physically unattainable overpressures or source radii larger than 200 m to explain the same deformation

dynamic loading induced by the instability of voussoir beam structure during mining below the slope abstract dynamic loading events in the longwall faces under slopes in the shendong coalfield china seriously limit the safety and efficiency of mining the slope characteristics such as direction height and angle determine the load type and the stability of the voussoir beam structure vbs formed by fractured blocks of the primary key stratum pks whether or not dynamic loading events will occur can be directly determined based on the presence or absence of a stable vbs in the pks based on this relationship six structural mechanical vbs models for different load distributions were established and then the effects of the slope direction height and angle on the stability of vbs was analysed changes of load type intensified the compression force between the hinged blocks when the compression force between blocks exceeded the strength of the rock vbs instability and dynamic loading events occurred the compression force in the vbs increased with increasing slope angle and height when the slope directions were similar becoming more pronounced for mining under the uphill sections of the slopes therefore a method of determining the critical slope parameter values indicating a risk of dynamic loading was proposed enabling such slopes to be recognised in advance measures such as slope top cutting or backfilling can then be applied to prevent potential dynamic loading accidents this study can provide guidelines for safe mining under geological conditions involving widespread slopes and gullies

thickness and spatial distribution of veins in a porphyry copper deposit rosia poieni romania abstract a statistical analysis of the vein thickness distributions of veins in the rosia poieni porphyry copper deposit romania indicates that vein thickness data conform to a power law distribution whereas the spatial distribution of veins follows a negative exponential law a high clustering of the veins is indicated by both the spacing distribution and the cv values the similar vein densities observed at the open pit scale are representative of a saturation level of vein nucleation differences in the spacing distribution and in the mean vein thickness are explained by different initial nucleation rates in the deepest and the lowest parts of the porphyry copper the highly clustered organization of the system is explained by vein linkage processes during their growth and modification of the fluid pressure and local stress during the hydrofracturing

geology geochemistry and origin of high sulfidation cu au mineralization in the nansatsu district japan the nansatsu district of southern kyushu has been the site of calc alkaline volcanism for the last 10 m y shifting eastward with time associated hydrothermal activity followed deposition of the volcanic host rocks by about 0 5 m y and was characterized by interaction of magmatic fluids with meteoric water under epithermal conditions resulting in the formation of high sulfidation cu au deposits at kasuga iwato and akeshi the orebodies consist of 95 wt percent sio 2 and result from leaching of the original andesite lava and pyroclastic flows by acid chloride sulfate waters these are inferred to have formed when magmatic vapors containing hcl and so 2 condensed into meteoric water the residual silica now quartz orebodies are best developed where the host was initially permeable the margins of the quartz bodies are abrupt with narrow 1 2 m halos representing the reaction front of acid waters isochemically dissolving the host rock the halo comprises alunite strongly zoned in na and k with p rich cores dickite and or kaolinite or pyrophyllite grading out into illite and interlayered illite smectite clays and finally propylitic alteration this pattern is characteristic of deposits of this type throughout the world for example at summitville colorado and lepanto philippines mineralization occurred after initial leaching by the vapor condensates with metals transported by a dense magmatic fluid mixing with meteoric water and the subsequent temperature decrease caused the general decrease in grade toward the margin of the quartz bodies ore grades are restricted to the quartz bodies gold is most closely associated with enargite and pyrite later minerals include covellite and then sulfur the last stage of activity was steam heated with descending waters oxidizing sulfides to goethite and locally remobilizing au into fractures this varies in degree between deposits erosion exposed the orebodies to supergene weathering continuing the sulfide oxidation and au remobilization stable isotope results indicate that hypogene alunite formed from a mixture of magmatic fluid delta 18 o 7 or 2 per thousand delta d 25 or 5 per thousand similar to nearby active volcanic discharges with local meteoric water in contrast the clays in the marginal halo have isotopic compositions indicating a delta 18 o shift of 6 to 8 per mil from local meteoric water values probably due to water rock interaction and the delta 18 o values of residual silica quartz may also be due to meteoric water domination fluid inclusion study of postmineralization quartz crystals indicates that the fluids had a salinity of about 1 wt percent nacl equiv during late quartz growth though there is evidence in one sample for higher salinity fluid having been present up to 30 wt percent nacl equiv some inclusions contain daughter minerals of halite and sulfur the t h values of over 1 000 measurements on late quartz from the ore zones indicate that the mean temperature during that stage ranged from 200 degrees c at akeshi to about 200 degrees c at iwato and 230 degrees c at kasuga the presence of vapor rich inclusions some with t hv similar to t hl indicate the presence at times of a two phase fluid in the center of the ore zones with depths of about 150 to 300 m below the paleowater table the mineralizing fluid was relatively oxidized sulfide sulfate ratio about 3 1 close to pyrite alunite coexistence under these redox conditions a ph of 3 and over a temperature range of 200 degrees to 300 degrees c aucl 2 super complexing may dominate over hau sh 2 at salinities above about 2 wt percent nacl several conditions are conducive for high sulfidation mineralization to occur 1 a crystallizing magma exsolves a fluid with lower pressure conditions favoring metal fractionation from melt to fluid 2 the exsolved fluid separates into vapor and saline liquid phases due to immiscibility with the latter being metal rich 3 the gas rich hcl and so 2 h 2 s vapor ascends to the surface with at least a portion condensed into meteoric water forming an acid fluid which leaches the host rock to create permeable zones for later mixing and 4 the dense metal bearing fluid also ascends into this leached zoned and precipitates cu sulfosalts sulfides and au upon mixing with meteoric water if the saline liquid is not released from its source adjacent to the magma due to lack of fracturing or if there is a strong hydraulic gradient caused by high relief only the vapor related stage may occur this will leave leached barren rock which is characteristic of many eroded volcanic terranes

control of magma flow in dykes on cyclic lava dome extrusion 1 lava dome eruptions are commonly characterized by large fluctuations in discharge rate with cyclic behaviour on time scalesranging from hours to decades examples include bezymianny volcano russia merapi java santiaguito guatemala mt st helens usa mt unzen japan and soufriere hills volcano montserrat previous models have assumed simple cylindrical conduits for magma transport but extrusions are mainly fed by dykes with cylindrical geometries developing only at shallow levels the widths of dykes embedded in an elastic medium are influenced by local magma pressure affecting flow rates and system dynamics strongly we develop a model for magma flow in dykes which predicts intense pulsations of magma extrusion for the case of a constant source pressure the period time scale is determined by the elastic deformation of the dyke walls and the length to width ratio of the dyke the dyke acts like a volumetric capacitor storing magma as pressure increases and then releasing magma in a pulse of extrusion for the soufriere hills volcano cyclic extrusions with time scales of a few weeks are predicted for dykes 300 500 m long and 3 6 m wide matching observations the model explains the sharp onset of tilt pulsations and seismic swarms citation costa a o melnik r s j sparks and b voight 2007 control of magma flow in dykes on cyclic lava dome extrusion geophys res lett 34 l02303 doi 10 1029 2006gl027466

vesicle connectivity in pyroclasts and implications for the fluidisation of fountain collapse pyroclastic flows montserrat west indies abstract pyroclastic flows are noted for their highly mobile behaviour being able to flow on slopes as low as a few degrees and this has been attributed to fluidisation or partial fluidisation by escaping gases the three types of pyroclastic flows generated during the eruption of soufriere hills volcano on montserrat dome collapse fountain collapse and surge derived differ in their apparent mobility suggesting different degrees of fluidisation and friction reduction in the flowing granular materials several possible sources of fluidising gas operate in pyroclastic flows the purpose of this paper is to assess the feasibility of one mechanism the release during flow of pressurised gases trapped in the vesicles of juvenile clasts measurements with a helium pycnometer show that all vesicles in dense lava blocks from dome collapse pyroclastic flows are connected so that the mechanism is probably not viable for such flows on the other hand pumices from fountain collapse pyroclastic flows from soufriere hills and other volcanoes contain up to 10 vol of isolated vesicles this is confirmed by sem imagery which shows that soufriere hills pumices contain two vesicle populations with a bimodal size distribution the large vesicles are mostly interconnected whereas about two thirds of the smaller population

bubble growth during decompression of magma experimental and theoretical investigation a model of bubble growth during decompression of supersaturated melt was developed in order to explore the conditions for preservation of gas overpressure in bubbles or for maintaining supersaturation of the melt the model accounts for the interplay of three dynamic processes decompression rate of the magma deformation of the viscous melt around the growing bubble and diffusion of volatiles into the bubble generally these processes are coupled and the evolution of bubble radius and gas pressure is solved numerically for a better understanding of the physics of the processes we developed some analytical solutions under simplifying assumptions for cases where growth is controlled by viscous resistance diffusion or linear decompression rate we show that the solutions are a function of time and two dimensionless numbers which are the ratios of either the diffusive or viscous time scales over the decompression time scale the conditions for each growth regime are provided as a function of the two governing dimensionless parameters analytical calculations for some specific cases compare well with numerical simulations and experimental results on bubble growth during decompression of hydrated silicic melts the model solutions including the division to the growth regimes as function of the two parameters provide a fast tool for estimation of the state of erupting magma in terms of gas overpressure supersaturation and gas volume fraction the model results are in agreement with the conditions of plinian explosive eruption e g mount st helens 18 may 1980 where high gas overpressure is expected the conditions of effusion of lava domes with sudden onset of explosive activity are also in agreement with the model predictions mostly in equilibrium degassing and partly in overpressure conditions we show that in a situation of quasi static diffusion during decompression the diffusive influx depends on the diffusivity away from the bubble insensitive to the diffusivity profile

phyllosilicates and associated minerals in some paleozoic stratiform sulfide deposits of southeastern australia the pb zn ores of eight of the nine deposits are characterized by one or the other of the phyllosilicate assemblages chlorite talc phlogopite biotite or chlorite muscovite the other contains chlorite phlogopitic trioctahedral mica but no talc phyllosilicate mineral chemistry is highly systematic and is related to ore type and ore stratigraphy in all cases chemical equilibrium between the phyllosilicates has been approached on a small scale equilibria were established substantially at the sedimentary early diagenetic stage the phyllosilicates were deposited as chemical precipitates in the hydrothermal aprons at the time of sea floor exhalative activity subsequent metamorphism has done little more than perfect crystal structures and coarsen grain size modified journal abstract

rosia poieni copper deposit apuseni mountains romania advanced argillic overprint of a porphyry system the rosia poieni deposit is the largest porphyry copper deposit in the apuseni mountains romania hydrothermal alteration and mineralization are related to the middle miocene emplacement of a subvolcanic body the fundoaia microdiorite zonation of the alteration associated with the porphyry copper deposit is recognized from the deep and central part of the porphyritic intrusion towards shallower and outer portions four alteration types have been distinguished potassic phyllic advanced argillic and propylitic potassic alteration affects mainly the fundoaia subvolcanic body the andesitic host rocks are altered only in the immediate contact zone with the fundoaia intrusion mg biotite and k feldspar are the main alteration minerals of the potassic assemblage accompanied by ubiquitous quartz chlorite and anhydrite are also present magnetite pyrite chalcopyrite and minor bornite are associated with this alteration phyllic alteration has overprinted the margin of the potassic zone and formed peripheral to it it is characterized by the replacement of almost all early minerals by abundant quartz phengite illite variable amounts of illite smectite mixed layer minerals minor smectite and kaolinite pyrite is abundant and represents the main sulfide in this alteration zone advanced argillic alteration affects the upper part of the volcanic structure the mineral assemblage comprises alunite kaolinite dickite pyrophyllite diaspore aluminium phosphate sulphate minerals woodhouseite svanbergite series zunyite minamyite pyrite and enargite luzonite alunite forms well developed crystals veins with enargite luzonite and pyrite in a gangue of quartz pyrophyllite and diaspore are present within and around the subvolcanic intrusion this alteration type is partially controlled by fractures a zonal distribution of alteration minerals is observed from the centre of fractures outwards with 1 vuggy quartz 2 quartz alunite 3 quartz kaolinite alunite and in the deeper part of the argillic zone quartz pyrophyllite diaspore 4 illite illite smectite mixed layer minerals kaolinite alunite and e chlorite albite epidote propylitic alteration is present distal to all other alteration types and consists of chlorite epidote albite and carbonates mineral parageneses mineral stability fields and alteration mineral geothermometers indicate that the different alteration assemblages are the result of changes in both fluid composition and temperature of the system the alteration minerals reflect cooling of the hydrothermal system from 400 c biotite to 300 200 c chlorite and illite in veinlets and to lower temperatures of kaolinite illite smectite mixed layers and smectite crystallization hydrothermal alteration started with an extensive potassic zone in the central part of the system that passed laterally to the propylitic zone it was followed by phyllic overprint of the early altered rocks nearly barren advanced argillic alteration subsequently superimposed the upper levels of the porphyry copper alteration zones the close spatial association between porphyry mineralization and advanced argillic alteration suggests that they are genetically part of the same magmatic hydrothermal system that includes a porphyry intrusion at depth and an epithermal environment of the advanced argillic type near the surface

direct analysis of ore precipitating fluids combined ir microscopy and la icp ms study of fluid inclusions in opaque ore minerals laser ablation inductively coupled plasma mass spectrometry la icp ms in combination with near infrared microscopy of fluid inclusions hosted by ore minerals that are opaque to visible light can provide the composition of ore precipitating fluids we applied the two techniques to well constrained fluid inclusion assemblages hosted by pyrite enargite and quartz to trace the source and evolution of the fluids in high sulfidation epithermal veins overprinting a porphyry copper deposit at rosia poieni romania despite some analytical limitations caused by the sulfide host minerals the data demonstrate that fluids trapped in apparently cogenetic quartz and ore minerals are chemically different systematic changes in major and trace element ratios between liquid vapor vapor rich and brine fluid inclusion assemblages in the three minerals record an evolving fluid source at the porphyry to epithermal transition regarding their cs na k ratios most of epithermal quartz hosted fluid inclusion assemblages form a well defined cluster which coincides with the narrow range of the porphyry stage fluids trapped in early quartz of the porphyry stockwork veins their cu na k ratios are 10 to 100 times lower compared to the pyrite hosted inclusions and correspond to the lowest cu na k ratios recorded for the porphyry stage fluids by contrast pyrite hosted vapor rich fluid inclusions have the highest cu na k similar to the highest cu na k ratios measured in the porphyry stage fluid inclusions the results led to the conclusion that the gangue and ore minerals in the high sulfidation epithermal veins at rosia poieni formed by successive pulses of chemically distinct hydrothermal fluids that were successively exsolved from residual melt batches of a progressively crystallizing magma at greater depth these results are consistent with detailed textural observations but petrography alone could not have led to this unambiguous conclusion