zircon u pb geochronology geochemistry and s pb isotopic compositions of the lietinggang iron polymetallic deposit tibet china abstract the lietinggang deposit is a representative skarn iron polymetallic deposit in the nyainqentanglha skarn polymetallic zone nsp in lhasa terrane tibet the mineralization is hosted in skarn of the early and middle triassic chaqupu formation plutons in the deposit include gabbro diorites divided into the d1 and d2 diorites granodiorite syenogranite and porphyritic granite and the d2 diorite and syenogranite are the mineralization associated plutons in this study we present la icp ms zircon u pb dating zircon hf isotopic and whole rock geochemical data of the diorites and porphyritic granite and s pb isotopic compositions of the ore sulfides in the lietinggang deposit zircon u pb dating results for these intrusions yield paleocene ages of 62 2 59 0 ma all the intermediate and felsic intrusions are i type and characterized by arc magma geochemical features enriched in lree and lile well developed negative eu anomalies and depletion in hfse with most having positive ehf t values these geochemical characteristics are similar with the coeval intrusions of the gangdese batholith and linzizong group volcanic rocks indicating they share a similar magma source this magma source is proposed to be partial melting of the young metasomatized asthenospheric mantle wedge derived basaltic rocks during the magma evolution the fractionated crystallization has also play an important role 34s values for sulfides have features of magma source the 206pb 204pb 18 043 18 711 207pb 204pb 15 520 15 776 and 208pb 204pb 38 288 39 215 values of sulfides show that ore forming metals were derived from mixing sources of mantle with upper crust materials geochemical characteristics of the intermediate and felsic intrusions combined with the dating results indicate that the lietinggang magmatism and mineralization were formed within the india asia continental collision tectonic setting

radial variations of melt viscosity around growing bubbles and gas overpressure in vesiculating magmas abstract the viscosity of silicic melts depends strongly on their water content as bubbles grow in a supersaturated melt water evaporates from the bubble melt interface a diffusive profile develops and leads to steep viscosity gradients across the melt shell here we investigate the effects of radial viscosity profiles on the dynamics of bubble growth we find that the effective melt viscosity resisting gas overpressure in the bubbles is close to the viscosity at the dehydrated rind and may be higher than that of the surrounding melt by more than an order of magnitude as a result bubbles may retain pressures that are higher than ambient pressure for longer times magma degassing is delayed to shallower depth and fragmentation of magma due to gas overpressure may occur over a wider range of conditions measured water content in eruption products yields information on the average melt viscosity however additional information about the concentration profiles is needed for estimating the effective viscosity that controlled the evolution of bubble growth in the ejecta

epithermal mineralization and ore controls of the shasta au ag deposit toodoggone district british columbia canada the shasta gold silver deposit british columbia canada is an adularia sericite type epithermal deposit in which deposition of precious metals coincided with the transition of quartz to calcite dominant gangue mineralization is associated with stockwork breccia zones in potassically altered dacitic lapilli tuffs and flows and consists of pyrite sphalerite chalcopyrite galena acanthite electrum and native silver pre and post ore veins consist solely of quartz and calcite respectively fluid inclusion microthermometry indicates that ore minerals were deposited between 280 and 225 c from a relatively dilute hydrothermal fluid 1 5 wt nacl equivalent abundant vapor rich inclusions in ore stage calcite are consistent with boiling oxygen and hydrogen isotopic data 18ofluid 1 5 to 4 1 dfluid 148 to 171 suggest that the fluid had a meteoric origin but was 18o enriched by interaction with volcanic wallrocks initial 280 c fluid ph and log f o2 conditions are estimated at 5 3 to 6 0 and 32 5 to 33 bar respectively during ore deposition the fluid became more alkaline and oxidizing ore deposition at shasta is attributed to localization of meteoric hydrothermal fluids by extensional faults mineralization was controlled by boiling in response to hydraulic brecciation calcite and base metal sulfides precipitated due to the increase in ph that accompanied boiling and the associated decrease in h2s concentration led to precipitation of gold and silver

microgranular enclaves in island arc andesites a possible link between known epithermal au and potential porphyry cu au deposits in the tulasu ore cluster western tianshan xinjiang china abstract the successful exploration for porphyry copper deposit in western tianshan xinjiang faces great challenge tulasu basin is an important epithermal gold ore cluster in western tianshan which was formed in a southwest pacific type island arc setting during the late paleozoic by the southward subduction of the north tianshan ocean beneath the yili plate porphyry cu au deposits are possibly to be found at depth or adjacent to these epithermal gold deposits some sulfide mineralized microgranular enclaves of monzonite porphyry and microdiorite were found in andesites of the tawuerbieke gold district tulasu basin the enclaves are randomly distributed with generally round or subangular shape and commonly clearly defined within their host andesite and have a chilled surrounding margin of andesite the monzonite porphyry enclaves mpe exhibit porphyritic texture with the phenocrysts of plagioclase and k feldspar the microdiorite enclaves mde are mainly composed of plagioclase and hornblende with an aplitic texture and massive structure the host andesites show porphyritic texture with the phenocrysts major of plagioclase minor of hornblende and clinopyroxene the groundmass consists of short column plagioclase and minor clinopyroxene with a hyalopilitic texture zircon grains from a mpe sample yield a weighted 206pb 238u age of 356 2 4 3 ma n 13 mswd 1 11 which is effectively coincident with the 360 5 3 4 ma n 20 mswd 0 61 of an andesite sample within analytical error indicating that they were coeval in addition the mpe mde and the andesite samples share similar normalized incompatible element and rare earth element patterns that are characterized by a pronounced enrichment of large ion lithophile elements and a deficit of high field strength elements moreover the samples show similar nd isotope compositions to the contemporary andesites and basaltic andesites detailed petrology geochronology and geochemistry studies suggest that these enclaves were captured from an underlying body during the eruption of island arc magma thus unmapped cognate porphyry intrusions associated with cu au mineralization may exist under the andesite strata this evidence in combination with the low and high sulfidation epithermal gold deposits acidic hydrothermal alterations and copper mineralization evidence suggests that a porphyry epithermal cu au metallogenic system might occur in the tulasu basin of western tianshan and that the tawuerbieke district should be an important target for porphyry cu au exploration

magmatic and structural controls on porphyry style cu au mo mineralization at kemess south toodoggone district of british columbia canada kemess south is the only cu au mo mine in the toodoggone district and a major cu and au producer in british columbia porphyry style cu au mo mineralization is mainly hosted by the tabular sw plunging 199 6 0 6 ma maple leaf granodiorite which intrudes tightly folded sw dipping permian asitka group siltstone and limestone and homogeneous triassic takla group basalt southwest dipping 194 0 0 4 ma toodoggone formation conglomerate volcaniclastic and epiclastic rocks overlie the granodiorite and asitka group rocks minor cu au mo mineralization is hosted by the immediate takla group basalt country rock whereas low tonnage high grade cu zones occur beneath a 30 m thick leached capping in supergene altered granodiorite and in exotic positions in overlying toodoggone formation conglomerate granodiorite has an intrusive contact with mineralized and altered takla group basalt but displays a sheared contact with unmineralized and less altered asitka group siltstone the north block fault is a deposit scale e striking steeply s dipping normal fault that juxtaposes the granodiorite basalt ore body against unmineralized asitka group rocks younger nw and ne striking normal dextral faults cut all rock types orebodies and the north block fault with displacements of up to 100 m and result in the graben and horst style block faulting of the stratigraphy and ore body both basalt and granodiorite host comparable vein sequence and alteration histories with minor variations in hydrothermal mineral assemblages caused by differing protolith chemistry early potassic alteration and associated early stage cu au mo mineralization is partly replaced by phyllic and intermediate argillic alteration associated with main stage cu au mo mineralization two main stage veins have re os molybdenite ages of 201 3 1 2 and 201 1 1 2 ma these mineralization ages overlap the 199 6 0 6 ma u pb zircon crystallization age for the maple leaf granodiorite late stage pyrite rich stringer veins and related phyllic alteration assemblages are cut by anhydrite rich carbonate rich and chlorite veins fluids and metals associated with early main and late stage veins were probably derived principally from the same deep magma chamber as the maple leaf granodiorite these magmatic derived fluids interacted with asitka and takla group country rocks and possibly with meteoric and metamorphic fluids prior to mineralization

cenozoic high k alkaline magmatism and associated cu mo au mineralization in the jinping fan si pan region southeastern ailao shan red river shear zone southwestern china northwestern vietnam abstract the jinping fan si pan jfp cenozoic magmatic and cu mo au metallogenic belt in the southeastern part of the ailao shan shear zone host the tongchang chang an habo and chinh sang cu mo au deposits these deposits form an integrated epithermal porphyry regional mineralization system associated with 40 32 ma high k alkaline magmatism the magmatic rocks in the belt have relatively low tio2

transitions between explosive and effusive eruptions of silicic magmas water rich silicic magmas may erupt explosively giving rise to massive columns of fragmented ash1 5 or effusively as viscous bubbly lavas to form lava domes6 8 complex cycles of explosive and effusive eruptions are often observed8 12 although these two eruption mechanisms have been modelled independently1 8 the conditions under which a volcano exhibits a particular style of eruption are not known and the transitions between eruption styles are poorly understood by modelling the ascent of magma along a permeable conduit we show here that for small magma chamber overpressures the style of eruption explosive or effusive is dependent on the magma flow rate we also identify a critical overpressure above which only explosive eruptions occur complex eruption sequences follow naturally for example if a shallow magmatic system is supplied with magma at an intermediate flow rate the eruption will be slow and effusive until the chamber over pressure becomes too large an explosive eruption then relieves the overpressure and an effusive eruption style resumes we suggest that monitoring of temporal variations in chamber overpressure for example by measuring ground deformation can be used to assess whether a passively effusing volcano has the potential to erupt explosively

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

three fragmentation mechanisms for highly viscous magma under rapid decompression abstract analysis of the behavior of viscous magma under short term tensile stresses demonstrates that the strain rates anticipated in the eruptive stages of collapse related events may be high enough under certain circumstances to provide fragmentation of the melt by brittle failure mechanisms of fragmentation of a highly viscous vesicular magma by the propagation of an unloading wave by layer by layer vesicle bursting fragmentation wave propagation and by rapid filtration gas flow are outlined fragmentation scenarios involving possible combinations of the three fragmentation mechanisms are evaluated for two models of magma with isolated and with connected pores experimental results for magma fragmentation under high decompression rates appear to support such mechanisms these mechanisms of highly viscous magma fragmentation by rapid decompression probably have their greatest application in cases of explosive disintegration of lava domes and cryptodomes caused by collapse events

examining potential genetic links between jurassic porphyry cu au mo and epithermal au ag mineralization in the toodoggone district of north central british columbia canada the toodoggone district comprises upper triassic to lower jurassic hazelton group toodoggone formation volcanic and sedimentary rocks which unconformably overlie submarine island arc volcanic and sedimentary rocks of the lower permian asitka group and middle triassic takla group some of which are intruded by upper triassic to lower jurassic plutons and dikes of the black lake suite although plutonism occurred episodically from ca 218 to 191 ma the largest porphyry cu au mo systems formed from ca 202 to 197 ma with minor mineralization occurring from ca 197 to 194 ma porphyry style mineralization is hosted by small volume 468 c saline and deposited metals at deep crustal depths 2 km sulfur c o and pb isotope data confirm the involvement of a magmatic fluid but also suggest that the ore fluid interacted with asitka and takla group country rocks prior to metal deposition in contrast in the shasta lawyers and griz sickle low sulfidation epithermal systems there is no clear association with magmatic fluids instead their fluid inclusion data indicate the involvement of low temperature 175 to 335 c low salinity 1 to 11 equiv wt nacl fluids that deposited metals at shallow depths 850 m their isotope i e o h pb data suggest interaction between meteoric and or metamorphic ore fluids with basement country rocks

contemporaneous formation of adjacent porphyry and epithermal cu au deposits over 300 ka in northern luzon philippines there is commonly a close spatial relation between porphyry cu au and high sulfidation epithermal cu au deposits throughout the world although a genetic association has not been proven nowhere is this spatial association better seen than in northern luzon philippines where the lepanto epithermal cu au deposit overlies the far southeast fse porphyry cu au deposit both world class orebodies fresh rock and hydrothermal mineral separates yield k ar ages indicating that premineralization and postmineralization volcanism occurred at 2 2 1 8 ma and 1 2 0 9 ma respectively and that the hydrothermal system was active from 1 5 to 1 2 ma k ar ages of alunite from lepanto have the same range as those of hydrothermal biotite and illite from the fse deposit indicating that both epithermal and porphyry mineralization formed from an evolving magmatic hydrothermal system that was active for about 300 ka this temporal relation strengthens the argument for a genetic link between these two styles of ore deposit and has implications for exploration where one style of mineralization is found there is potential for the other nearby

magma fragmentation by rapid decompression the processes leading to magma fragmentation and the generation of pyroclastic debris during explosive volcanic eruptions are of fundamental importance in volcanology observations of explosive eruptions1 3 as well as theoretical analyses of the underlying processes4 have raised the question of whether the rapid decompression of highly viscous vesicular magma that results from the collapse of a lava dome or volcanic edifice can in itself produce explosive magma fragmentation and pyroclast formation here we report the results of a laboratory investigation of pyroclast formation following rapid decompression samples of magma from the 1980 eruption of mount st helens when rapidly depressurized from initial pressures of up to 12 mpa and at temperatures in the range 750 825 c fragmented to form pyroclastic products that are in many respects similar to those formed in real eruptions moreover we observe explosive fragmentation at temperatures well below those normally associated with magmatic processes suggesting that even relatively cool magma bodies can be very hazardous when subjected to rapid unloading events

depressurization of fine powders in a shock tube and dynamics of fragmented magma in volcanic conduits abstract samples of fine glass beads mean grain size equal to 38 and 95 m have been depressurized within a vertical shock tube these short lived rapid decompressions resemble discrete cannon like vulcanian explosions and produce two phase flows that are inhomogeneous in density in both vertical and horizontal directions because of the presence of bubble like heterogeneities we suggest that also volcanic flows may present similar inhomogeneities in density in the experimental apparatus the flow velocities increase from approximately 1 to 13 m s when the pressure drop increases from approximately 200 to 900 mbar a physical model of the initial velocities of expansions in the shock tube has been applied to a range of volcanic overpressures between 0 1 and 20 mpa suggesting initial velocities of volcanic flows caused by the removal of a rock plug in volcanic conduits between 25 and 400 m s during the experiments at large pressure drops as the mixture expands and moves up the tube the flow front becomes highly irregular and bubble like heterogeneities form the shape of these bubbles becomes distorted and stretched in the turbulent flow during the experiments at relatively small pressure drops the sample oscillates when the particles after the expansion flow back and bounce upward again jets with diameter smaller than that of the tube are ejected from the oscillating samples generating independent pulses large bubble like heterogeneities whose diameter is a significant fraction of the tube diameter can also discretize the flows similar mechanisms in real volcanoes may produce pulse like ejections of gas particle mixtures out of the vent

two mineralization events in the baiyinnuoer zn pb deposit in inner mongolia china evidence from field observations s pb isotopic compositions and u pb zircon ages abstract the xing mong orogenic belt xmob is located in the eastern part of the central asian orogenic belt caob and has experienced multiple tectonic events the baiyinnuoer pb zn deposit may be a rare case that documents two periods of mineralization in the tectonically complex xmob there are two types of pb zn mineralization in the deposit 1 skarn type ore hosted by the skarn in the contact zone between marble and granodiorite and within the marble and 2 vein type ore hosted by crystal tuff and feldspar porphyry this study revealed that the host rocks mineral assemblages mineralization occurrences s pb isotopes and ages between the two types of ore are notably different zircon u pb dating indicates that the granodiorite was emplaced in the early triassic 244 1 to 242 1 ma the crystal tuff was deposited in the early cretaceous 140 1 to 136 1 ma and the feldspar porphyry was intruded in the early cretaceous 138 2 to 136 2 ma the first skarn mineralization occurred at 240 ma and the second vein type pb zn mineralization took place between 136 and 129 ma thus the triassic orebodies were overprinted by early cretaceous mineralization the sphalerite and galena from the skarn mineralization have higher 34s values 4 7 to 0 3 than the sphalerite galena and aresenopyrite from the vein type mineralization 7 5 to 4 2 indicating different sulfur sources or ore forming processes for the two types of mineralization the pb isotopic compositions of the two types of ore are very similar suggesting similar lead sources geochemistry and nd pb hf isotopic systematics of the igneous rocks in the region show that the triassic granodiorite was generated from hybridization of mafic and felsic magmas due to strong crust mantle interaction under the collisional setting that resulted following the closure of the paleo asian ocean and the collision of north china and siberian cratons at the end of the permian while the cretaceous igneous rocks at baiyinnuoer originated from the partial melting of a juvenile lower crust with minor input from the crust caused by the underplating of mafic magma in an extensional setting

fragmentation of magma during plinian volcanic eruptions the ratio of the volume of vesicles gas to that of glass liquid in pumice clasts v g v l reflects the degassing and dynamic history experienced by a magma during an explosive eruption v g v l in pumices from a large number of plinian eruption deposits is shown here to vary by two orders of magnitude even between pumices at a given level in a deposit these variations in v g v l do not correlate with crystallinity or initial water content of the magmas or their eruptive intensities despite large ranges in these variables gas volume ratios of pumices do however vary systematically with magma viscosity estimated at the point of fragmentation and we infer that pumices do not quench at the level of fragmentation but undergo some post fragmentary evolution on the timescale of plinian eruptions pumices with viscosities 109 pa s can expand after fragmentation as long as their bubbles retain gas at a rate inversely proportional to their viscosity once the bubbles connect to form a permeable network and lose their gas expansion halts and pumices with viscosities 105 pa s can collapse under the action of surface tension textural evidence from bubble sizes and shapes in pumices indicates that both expansion and collapse have taken place the magnitudes of expansion and collapse therefore depend critically on the timing of bubble connectivity relative to the final moment of quenching we propose that bubbles in different pumices become connected at different times throughout the time span between fragmentation and quenching after accounting for these effects we derive new information on the fragmentation process from two characteristics of pumices the most important is a relatively constant minimum value of v g v l of 1 78 64 vol vesicularity in all samples with viscosities 105 pa s this value is independent of magma composition and thus reflects a property of the eruptive mechanism the other characteristic is that highly expanded pumices 85 vol vesicularities are common which argues against overpressure in bubbles as a mechanism for fragmenting magma we suggest that magma fragments when it reaches a vesicularity of 64 vol but only if sheared sufficiently strongly the intensity of shear varies as a function of velocity in the conduit which is related to overpressure in the chamber so that changes in overpressure with time are important in controlling the common progression from explosive to effusive activity at volcanoes

stratigraphy of the upper hazelton group and the jurassic evolution of the stikine terrane british columbia11ess contribution 20120051 the lower to middle jurassic hazelton group represents the final stage of magmatic arc activity in the intraoceanic stikine terrane which was followed by accretion within the cordilleran terrane c

traveling ionospheric disturbances propagating ahead of the tohoku oki tsunami a case study we document two kinds of traveling ionospheric disturbances namely ctids co tsunami traveling ionospheric disturbances and atids ahead of tsunami traveling ionospheric disturbances related to the tohoku oki tsunami of 2011 march 11 they are referred to the disturbances that remain behind and ahead of the principal tsunami wave front respectively we first note their presence in a numerical experiment performed using a simulation code coupling the tsunami atmosphere and ionosphere this code uses the tsunami wavefield as an input and simulates acoustic gravity waves agws in the atmosphere and tids in the form of total electron content tec disturbance in the ionosphere the simulated tec reveals the excitation of ctids at about 2 tecu and atids at about 1 tecu representing up to 5 per cent disturbance over the ambient electron density and they arise from the dissipation of agws in the thermosphere a novel outcome is that during the tsunami passage between 6 and 12 of epicentral distance strong atids arrive 20 60 min ahead of the tsunami wave front covering 3 10 of distance from the tsunami location simulation results are compared with the far field observations using gnss satellites and confirm that atids are the first detected tec maximum occurring 20 60 min ahead of the tsunami arrival our simulation also confirms the presence of largest tec maximum representing ctids 10 20 min after the first tsunami wave atids reported in this study have characteristics that can be potentially used for the early warning of the tsunami

geology fluid inclusion and h o s isotopes of the kuruer cu au deposit in western tianshan xinjiang china abstract western tianshan along the southwestern margin of the central asian orogenic belt is well endowed with epithermal and porphyry au deposits the kuruer cu au deposit recently discovered in the eastern part of western tianshan was considered as a high sulfidation epithermal deposit however our geological fluid inclusion and stable isotopic studies indicate that it actually formed in transition from high sulfidation to porphyry the host rocks include the dahalajunshan formation volcanic and volcano sedimentary rocks such as andesite rhyolite ignimbrite and tuff cu au mineralization mainly occurs as quartz dominated stockworks or disseminations with abundant pyrite and chalcopyrite and minor galena and sphalerite gold occurs as invisible phase in sulfides hydrothermal alteration includes a silicic core surrounded by phyllic alteration and peripheral propylitic alteration based on field observations paragenetic and crosscutting relationship the mineralization process can be roughly divided into three stages the early stage is characterized by the assemblage of quartz pyrite chalcopyrite while the middle stage contains quartz and chalcopyrite at absence of pyrite the late stage is characterized by calcite quartz chlorite chalcopyrite veins fluid inclusions at the early stage are mainly liquid rich aqueous and co2 rich inclusions and minor vapor rich aqueous and solid bearing inclusions their homogenization temperatures and salinities can be up to 420 c and 39 wt nacl eq respectively indicating that the initial ore forming fluids are high temperature high salinity h2o co2 nacl systems in the middle stage there are only liquid rich aqueous inclusions with homogenization temperatures and salinities of 130 190 c and 0 18 to 10 7 wt nacl eq respectively liquid rich aqueous inclusions in the late stage display much lower temperatures and salinities ranging from 110 to 130 c and 0 18 2 7 wt nacl eq respectively obtained dh2o and 18oh2o values of quartz from the middle stage are 98 to 107 and 2 1 to 0 74 respectively the 34s values of 9 chalcopyrite samples range from 10 2 to 2 4 with an average of 4 1 we conclude that the initial ore forming fluids are magmatic in origin and further cooled and diluted by mixing with meteoric water intensive fluid boiling and mixing facilitated hydrothermal alteration and mineralization

permeability control on magma fragmentation fragmentation of porous magma that is subject to gas overpressure is considered to be a crucial process in the generation of explosive volcanic eruptions a decompressive event e g rapid magma ascent landslide dome collapse disrupts the stress equilibrium between the gas phase and the surrounding melt when the gas in the pores is exposed to a pressure gradient it may either fragment the surrounding magma or escape from the magma along an existing pathway of cracks and interconnected bubbles therefore magma permeability can be a decisive parameter in determining if an eruption experiences fragmentation i e whether it is explosive or effusive or exhibits a temporal transition between the two eruptive styles despite the central role that gas permeability may play in the fragmentation of volcanic rocks previous studies have not experimentally verified or quantified this influence based on a comprehensive database of combined permeability and fragmentation experiments we show that high permeability substantially increases the overpressure required to fragment porous volcanic rocks our results allow us to deduce a fragmentation criterion that incorporates gas permeability as well as porosity and internal overpressure this criterion implies that the energy required for fragmentation is less dependent on the actual pore geometry than on the way the void space is interconnected and thus on the contribution of permeable gas flow to decompression

dynamics of explosive volcanism at unzen volcano an experimental contribution knowledge of the dynamics of magma fragmentation is necessary for a better understanding of the explosive behaviour of silicic volcanoes here we have measured the fragmentation speed and the fragmentation threshold of five dacitic samples 6 7 53 5 vol open porosity from unzen volcano kyushu japan the measurements were carried out using a shock tube based fragmentation apparatus modified after alidibirov and dingwell 1996a b the results of the experimental work confirm the dominant influence of porosity on fragmentation dynamics the velocity of the fragmentation front increases and the value of the fragmentation threshold decreases with increasing porosity further we observe that the fragmentation speed is strongly influenced by the initial pressure difference and the texture of the dacite at an initial pressure difference of 30 mpa the fragmentation speed varies from 34 m s for the least porous sample to 100 m s for the most porous sample these results are evaluated by applying them to the 1990 1995 eruptive activity of unzen volcano emplacements of layered lava dome lobes merapi type pyroclastic flows and minor explosive events dominated this eruption the influence of the fragmentation dynamics on dome collapse and vulcanian events is discussed

genesis of the changlingzi zn pb deposit in the southern great xing an range northeastern china constraints from fluid inclusions and h o s pb isotope systematics the changlingzi pb zn deposit is located in the southern great xing an range metallogenic belt of northeast china this deposit experienced two types of mineralization including skarn ore block i

a model for viscous magma fragmentation during volcanic blasts fragmentation of magma containing gas bubbles is of great interest in connection with developing models for the formation of pyroclastics and for volcanic blasts explosions this paper considers the problem of fragmentation of highly viscous 108 pa s or solidified magma containing bubbles with excess gas pressure it is suggested that the fragmentation of magma be considered on the basis of the fragmentation wave theory proposed by nikolsky and khristianovich which is generally applicable to gas dynamic phenomena occurring in mines then it becomes possible to derive the equations of conservation for the fragmentation wave front which moves into a body of magma from its free surface as a result the velocity n of magma fragmentation and the velocity u of the movement of the gas pyroclastic mixture behind the fragmentation wave front are determined calculations show that n can reach 5 m s therefore the duration of the fragmentation of the magma body blast duration proves to be long the suggested model explains the possibility of several explosions during the blast as a result of the fragmentation wave stopping and accounts for the angular shape of pyroclasts by the brittle disruption of interbubble partitions during fragmentation wave propagation through the porous magma body the initiation and cessation of fragmentation are defined by magma porosity magma tensile strength and the pressure differential between gas pressure in pores and the atmospheric pressure the physical model of magma fragmentation developed explains the mechanism of energy release during volcanic blasts of the vulcanian or pelean types

ore genesis and hydrothermal evolution of the baiyinnuo er zinc lead skarn deposit northeast china evidence from isotopes s pb and fluid inclusions the baiyinnuo er zinc lead deposit 32 74 mt at 5 44 zn 2 02 pb and 31 36 g t ag located in the south segment of the great xing an range is the largest zn pb deposit in northern china skarn and orebodies mainly occur between the different units of the huanggangliang formation or within the contact zone between the intrusions and permian marble several phases of igneous rocks exposed within the mining areas and among them the yanshanian plutonic rocks which intruded into limestone of the early permian huanggangliang formation are interpreted to be the source of ore since their pb isotope compositions 206pb 204pb 18 25 18 35 207pb 204pb 15 50 15 56 and 208pb 204pb 38 14 38 32 are highly consistent with the sulfides including sphalerite galena and chalcopyrite 206pb 204pb 18 23 18 37 207pb 204pb 15 47 15 62 and 208pb 204pb 37 93 38 44 sulfur isotope values of the sulfides give a narrow 34s interval of 6 1 to 4 6 mean 5 4 n 15 suggesting the ore forming fluid is of magmatic origin three main paragenetic stages of skarn formation and ore deposition have been recognized based on petrographic observation which are the preore stage garnet clinpyroxene wollastonite magnetite sulfides the synore stage sulfides epidote quartz calcite garnet and the postore stage calcite chlorite quartz fluorite several fluid evolution episodes can be inferred from microthermometric results at the baiyinnuo er zn pb deposit 1 immiscibility preore stage coexistence of halite bearing brine inclusions s1 type 44 wt nacl equiv and vapor rich fluid inclusions v type sharing the same homogenization temperatures 470 c confirms that fluid unmixing occurred under lithostatic pressures of 400 bars 1 5 km and the brine is considered to account for most prograde skarn minerals e g clinopyroxene 2 overpressure trapping preore stage brine inclusions homogenized by halite dissolution s2 type postdated the immiscible assemblages this type of inclusions is characterized by high but variable minimum trapping pressures 150 3 000 bars relative to s1 type inclusions and can be explained as a result of entrapment under overpressuring condition 3 boiling the presence of both vapor and liquid inclusions i e v and l type in the same assemblages within synore stage quartz calcite and sphalerite indicates the occurrence of fluid boiling 350 c at hydrostatic pressures of 150 bars and depth of 1 5 km which resulted in large scale mineralization in the baiyinnuo er zn pb deposit 4 mixing with external fluids fluid inclusions scattered within postore stage calcite or secondary trails in synore stage minerals show low homogenization temperatures 260 c and both decreasing for l type and increasing for cacl2 bearing inclusions i e lc type trends for salinities as homogenization temperatures decrease implying addition of both meteoric water low temperature low salinity and basinal brines low temperature ca rich respectively systematic fluid inclusion studies also indicate that the mineralization related fluid is of magmatic origin prograde minerals formed during the preore stage fluid immiscibility while sulfides deposition occurred during the synore stage fluid boiling mixing with external fluids began as the hydrothermal system cooled to 300 c when the main metal precipitation process had ended

the source and evolution of ore fluids in the heiniuwa gold deposit baoshan block sanjiang region constraints from sulfide trace element fluid inclusion and stable isotope studies abstract the heiniuwa gold deposit is located in the northwestern segment of the longyang au fe pb zn polymetallic ore cluster in the northern baoshan block sanjiang region sw china this ore cluster is characterized by skarn fe pb zn mineralization 120 ma in the central part and au mineralization in the distal part the genesis of the heiniuwa deposit and its relationship with the skarn deposits remain unclear all orebodies in heiniuwa are hosted in the upper cambrian calcareous slate and siltstone of the hetaoping formation and are controlled by the ns striking faults three main paragenetic stages of mineralization have been recognized based on petrographic observation including from early to late a pyrite arsenopyrite quartz stage stage i a pyrite pyrrhotite sphalerite galena chalcopyrite quartz calcite stage stage ii and a quartz calcite chlorite stage stage iii three types of fluid inclusions were identified in the quartz and calcite from the stage i to iii in heiniuwa including liquid rich l type vapor rich v type and solid bearing s type inclusions the s type inclusions only occur in stage i quartz the fluid inclusions from stage i homogenized at 185 326 c concentrating at 220 250 c with eutectic temperatures of 48 5 c to 36 7 c final ice melting temperatures of 11 34 c to 0 8 c and salinities ranging from 1 4 to 17 2 wt nacl equiv the inclusions from stage ii homogenized at 155 281 c concentrating at 190 230 c with eutectic temperatures of 51 6 c to 37 5 c final ice melting temperatures of 10 6 c to 0 5 c and corresponding salinities ranging from 0 9 to 14 6 wt nacl equiv the inclusions from stage iii homogenized at 116 202 c concentrating at 150 170 c with eutectic temperature of 45 5 c to 37 5 c final ice melting temperatures of 4 3 c to 0 6 c and salinities ranging from 1 3 to 7 2 wt nacl equiv the microthermometry reveals that the ore forming fluid of heiniuwa gold deposit is a typical h 2 o nacl cacl 2 fluid system the carbon and oxygen isotopes of calcite show that 13 c pdb and 18 o smow values respectively range from 13 4 to 6 8 and 9 1 to 9 6 in stage ii and from 8 1 to 1 5 and 6 4 to 8 2 in stage iii the bulk marble and calcareous slate samples have 13 c pdb and 18 o smow values from 3 0 to 0 7 and 7 8 to 11 9 respectively this suggests that the carbon in the ore forming fluid was probably from a magmatic source the 18 o fluid values of ore forming fluid vary from 1 6 to 2 5 in stage i from 6 2 to 0 6 in stage ii and from 10 8 to 2 5 in stage iii this indicates that the fluid in stage i is dominantly magmatic whereas the fluid in stage iii is close to meteoric water the decrease of na ca ratios of ore forming fluid from stage i to stage iii suggests that the interaction with carbonate wallrock is significant during fluid evolution the sulfide 34 s values range from 5 7 to 4 6 mean 0 3 n 19 agreeing with the explanation based on c o isotopes and fluid inclusions that the ore forming fluids are mainly magmatic in origin in addition la icp ms analysis of sulfides also supports this opinion the stage i pyrite has cu ni ratios greater than 1 and a high concentration of gold in contrast the stage ii pyrrhotite samples display a very low concentration of gold this suggests that gold mineralization mainly occurred in stage i the mixing between magmatic hydrothermal fluid and meteoric water is considered to be a key factor controlling the gold deposition

hydrothermal evolution and ore genesis of the beiya giant au polymetallic deposit western yunnan china evidence from fluid inclusions and h o s pb isotopes abstract the beiya porphyry skarn gold polymetallic deposit is one of the largest gold deposits in china and also contains significant amounts of silver and base metals the estimated reserve at the end of 2015 was 130 million metric tonnes mt of ores grading 2 42 g t au 0 48 wt cu 25 5 wt fe 38 85 g t ag 1 24 wt pb and 0 53 wt zn the deposit is located in the jinshajiang ailaoshan porphyry skarn cu mo au metallogenic belt in western yunnan province southwest china skarn alteration and mineralization are spatially and temporally associated with eocene monzogranite porphyries which were emplaced into triassic carbonates field evidence and petrographic observations indicate there are four stages of hydrothermal activity i e prograde stage i iron oxide stage ii sulfide stage iii and carbonate stage stage iv stage i is characterized by the formation of garnet and pyroxene by high temperature 398 560 c hypersaline 48 81 67 24 wt nacl equiv hydrothermal fluids with h o isotopic compositions that are similar to typical magmatic fluids these fluids were most likely generated by the separation of brine from a silicate melt in stage ii garnet and pyroxene was replaced by epidote amphibole chlorite quartz and magnetite associated hydrothermal fluids are preserved in coexisting l type and v type fluid inclusions and are characterized by anomalously low d values approximately 80 and lower 18 o than stage i fluids the decrease in ore fluid 18 o h2o values with time coincided with marked decreases in fluid salinity and temperature based on the fluid inclusion and stable isotopic data we suggest that the ore fluid evolved by boiling of the magmatic brine stage iii is characterized by the development of pyrite chalcopyrite galena and sphalerite fluids inclusions associated with stage iii display and continuous range of salinities with the majority being low salinity inclusions 1 28 3 54 wt nacl equiv these fluids yield lower 18 o h2o values 0 85 to 5 52 and moderate d values 78 6 to 88 6 altogether these data indicate that stage iii fluids originated from the mixing of residual stage ii fluids with meteoric water the sulfur isotope 34 s values of stage iii sulfides cover a narrow range of 4 2 to 1 2 mean 1 1 and boiling also occurred at low temperatures 165 347 c during stage iii in stage iv only l type fluid inclusions are present which yielded the lowest homogenization temperatures 157 272 c and the lowest salinities 1 06 12 20 wt nacl equiv the h o isotope data indicate that the ore forming fluids were dominated by magmatic water in stage i and stage ii and that the magmatic water gradually mixed with circulating meteoric water during stage iii and stage iv this conclusion is further supported by the isotopic composition of lead of the ores which is similar to that of the monzogranite porphyries but differs significantly from permian basalts and triassic wall rocks

geochronological and geochemical constraints on the genesis of the huanren skarn cu zn deposit northeast china abstract the huanren skarn cu zn deposit is located in southeastern liaoning on the eastern edge of the north china craton ncc in this paper we present a study on the geochronologic geochemical and sr nd hf and s isotopic data for the magmatic rocks and sulfide minerals exposed in the deposit laser ablation inductively coupled plasma mass spectrometry la icp ms dating of zircon grains from two mining pits in the monzodiorite yields ages of 128 2 1 1 ma and 128 6 1 5 ma these results indicate that the magmatism in the huanren cu zn deposit might have occurred in the early cretaceous geochemically the huanren monzodiorite belongs to the high k calc alkaline and shoshonitic series is enriched in rb ba and k and is depleted in nb ta and ti the rocks also have relatively high 87sr 86sr i 0 7091 0 7099 and low end t 13 2 to 10 3 and ehf t values 14 3 to 7 8 the sr nd hf isotopic data for the monzodiorite indicate that the magma may be derived from mixed sources of the crust and mantle the 34s values of chalcopyrite galena and pyrite range from 4 4 to 5 8 with an average of 5 1 indicating that the sulfur in the deposit was mainly derived from a magmatic source the huanren cu zn deposit resulted from the magmatism and mineralization induced by the rollback of the paleo pacific plate

physico chemical controls on ore deposition in the arapucandere pb zn cu precious metal deposit biga peninsula nw turkey abstract arapucandere is one of a number of similar cu zn pb au ag epithermal deposits in the biga peninsula which are mineralogically and tectonically similar fluid inclusions have very low salinities between 1 7 and 0 wt nacl and a wide range of temperatures from 360 to 160 c there was extensive boiling and flashing of the hydrothermal fluids which initiated mineral deposition the range of temperatures is consistent with emplacement of the veins at 700 m depth with the pressure decreasing from near lithostatic to near hydrostatic and a decrease in temperature to 250 c due to adiabatic expansion of the fluids there is evidence of a limited amount of boiling but the temperature and pressure decrease was close to the liquid vapour curve flashing of the fluids was caused by sudden drops to sub hydrostatic pressures and even lower temperatures mineralization was caused by these pressure related temperature decreases as there is no evidence of cooling and dilution of the ore fluids 34 s values of sulphides indicate a magmatic source but the more negative than usual values also suggest boiling affected isotopes d and 18 o of the fluids indicate a mixing between meteoric waters and magmatic fluids with the large range of d due to boiling la icp ms analyses of fluid inclusions reveal high cu zn pb concentrations in the fluids despite their low salinity transported as chloride complexes exceptional pressure and temperature decrease causing the fluids to flash was likely to have been in response to earthquakes

fragmentation of a porous viscoelastic material implications to magma fragmentation fragmentation of vesicular magma by rapid decompression is one of the most likely triggers for explosive eruptions in this phenomenon the decompression rate and the viscoelastic nature of magma are considered to be key factors in order to obtain a clear idea on the effects of these two factors controlled fragmentation experiments have been conducted these experiments have three advantages first the specimen is made of a viscoelastic material with controlled porosity and geometry second the fragmentation process is directly monitored finally both the magnitude and rate of decompression are controlled brittle fragmentation and ductile expansion were both observed in the same porous material at different timescales the various mechanical responses of the specimen elastic flow and fragmentation were correlated with the pressure profile measured at the base of the specimen fragmentation was noted to occur when the decompression exceeded a critical value within a critical time two relevant timescales are discussed in terms of physical mechanisms of relaxation the first is the measured glass transition time the second is the estimated timescale for the onset of viscous bubble expansion the observed phenomena bear several similarities with natural magma fragmentation it is thus considered that the present results are a useful step toward constructing a model for magma fragmentation

the red chris porphyry copper gold deposit northern british columbia canada igneous phases alteration and controls of mineralization red chris is a late triassic porphyry cu au mo deposit in the stikinia island arc terrane in northern b c late triassic sedimentary and volcanic rocks of the stuhini group host a series of late triassic to early jurassic 204 198 ma diorite to quartz monzonite stocks and dikes the red chris deposit is hosted in the 204 ma red stock the largest 6 5 1 5 km and most altered intrusion in the area volcanic rocks approximately time equivalent with the stock are exposed 2 km to the southwest and west postmineral early and middle jurassic sedimentary rocks unconformably overlie the stuhini group and red stock to the south and southeast the composite red stock consists of multiple phases of crowded porphyries 30 65 plagioclase hornblende biotite phenocrysts including abundant premineral p1 leucodiorite multiple subphases of synmineral p2 quartz monzonite porphyries and volumetrically minor late mineral monzonite p3 and monzodiorite p4 porphyries the stock evolved from subalkaline to silica saturated alkalic composition with the mineral related p2 porphyries being high k calcalkalic and high sr y common septa of stuhini biotitic hornfels are entrapped within the stock minor postmineral weakly altered mafic dikes cut the stock the zone of 0 25 cu equiv cu au is 2 km long wsw ene and up to 650 m wide early a type quartz veins with disseminated bornite accompanied biotitic and k feldspar magnetite alteration which was coeval with p2 porphyries higher cu and au grades correlate in a general way with zones of more abundant a veins chlorite carbonate epidote actinolite replaced hornblende peripheral to biotitic alteration and chlorite overprinted much of the secondary biotite late alteration affected all porphyry phases and is subdivided into earlier sericite clay pyrite and later low sulfide carbonate clay hematite late sericite clay pyrite alteration sulfidized much of the primary bornite to chalcopyrite with or without pyrite and carbonate clay hematite alteration converted most magnetite to hematite highest cu au grades 2 cu equiv occur in and around the early and intermediate stage p2 porphyries zoning of cu au au cu ratios sulfides and quartz veins is centered and mostly symmetrical around a core of high grade cu au within and surrounding apices of p2 porphyry contact relationships confirm the close association of p2 porphyry phases with cu au zones of 50 ppm mo surround the highest grade cu au zone at depth west northwest and east northeast strike slip to oblique slip faults offset sulfide cu au and mo patterns several lines of evidence indicate 15 to 20 of southward tilt since the system formed due to glaciation oxidation is very thin and supergene enrichment negligible red chris was previously considered by most workers as an alkalic or hybrid alkalic deposit new chemical data on synmineral porphyry phases instead suggest high k calc alkalic composition similar to the monzonitic cu mo au class of porphyry deposits which includes bingham and bajo de la alumbrera red chris is also classified as an a vein type deposit due to strong control of higher grade cu au by a vein stockworks with abundant disseminated cu sulfides

data for s isotopic geochemistry zircon and cassiterite u pb geochronology of the haobugao sn polymetallic deposit southern great xing an range ne china abstract the southern great xing an range sgxr is the most important tin polymetallic metallogenic belt in north china the lack of previous research on the genesis of the tin mineralization especially its exact age prevents development of a deep understanding of tin deposits in this area haobugao sn polymetallic deposit is a large skarn type deposit in the huangang ganzhuermiao sn fe cu pb zn ag metallogenic belt in the sgxr the ore body occurs in the contact zone between a yanshanian intrusion and permian dashizhai formation marble 34 s v cdt values of sulfides from the haobugao sn polymetallic deposit range from 4 7 to 3 5 with an average of 0 65 and these values strongly indicate a deep magmatic source for the sulfur in the ore minerals of the deposit in this paper we also report the results of la icp ms u pb dating of tin mineralization in no i ore body and of the underlying granite cassiterite from no 1 ore body deposited at 139 0 6 ma and the closely associated granite has an age of 142 9 1 6 ma the similar ages indicate that the tin mineralization was produced by early cretaceous magmatic hydrothermal activity these results together with the ages of other tin deposits and related granites indicate extensive granitic magmatism and tin mineralization during the early cretaceous in the southern segment of the great xing an range

geological and isotopic evidence for magmatic hydrothermal origin of the ag pb zn deposits in the lengshuikeng district east central china the lengshuikeng ore district in east central china has an ore reserve of 43 mt with an average grade of 204 53 g t ag and 4 63 pb zn based on contrasting geological characteristics the mineralization in the lengshuikeng ore district can be divided into porphyry hosted and stratabound types the porphyry hosted mineralization is distributed in and around the lengshuikeng granite porphyry and shows a distinct alteration zoning including minor chloritization and sericitization in the proximal zone sericitization silicification and carbonatization in the peripheral zone and sericitization and carbonatization in the distal zone the stratabound mineralization occurs in volcano sedimentary rocks at 100 400 m depth without obvious zoning of alterations and ore minerals porphyry hosted and stratabound mineralization are both characterized by early stage pyrite chalcopyrite sphalerite middle stage acanthite native silver galena sphalerite and late stage pyrite quartz calcite the 34s values of pyrite sphalerite and galena in the ores range from 3 8 to 6 9 with an average of 2 0 the c o isotope values of siderite calcite and dolomite range from 7 2 to 1 5 with an average of 4 4 v pdb and from 10 9 to 19 5 with an average of 14 8 v smow respectively hydrogen oxygen and carbon isotopes indicate that the hydrothermal fluids were derived mainly from meteoric water with addition of minor amounts of magmatic water geochronology employing la icp ms analyses of zircons from a quartz syenite porphyry yielded a weighted mean 206pb 238u age of 136 3 0 8 ma considered as the emplacement age of the porphyry rb sr dating of sphalerite from the main ore stage yielded an age of 126 9 7 1 ma marking the time of mineralization the lengshuikeng mineralization classifies as an epithermal ag pb zn deposit

porphyry deposits of the northwestern cordillera of north america edited by t g schroeter special volume 46 canadian institute of mining metallurgy and petroleum montreal 1995 888 pp canadian 95 plus 15 handling isbn 0 919086 56 x

jurassic epithermal deposits in the toodoggone river area northern british columbia examples of well preserved volcanic hosted precious metal mineralization epithermal gold silver deposits in the toodoggone river area are hosted by early jurassic high k trachyandesite and trachydacite volcanic rocks that erupted during two major cycles spanning roughly 7 m y volcanism and related plutonic activity is intimately associated with the structural development of an elongate volcano tectonic depression in which extensional fracture zones confine the epithermal deposits younger sedimentary rocks overlay and protected the deposits from erosion gold and silver in the toodoggone district occur most commonly in quartz veins associated with adularia sericite and calcite locally gold barite veins cut volcanic rocks that are pervasively replaced by varying proportions of fine grained silica dickite and natroalunite fluid inclusions in quartz from most precious metal vein deposits are typical of epithermal environments they contain low temperature dilute hydrothermal fluids of predominantly meteoric origin t h 300 degrees c and 30 equiv wt nacl light stable isotope analyses show marked 18 o enrichment in the volcanic rocks hydrothermally altered host rocks and mineralized vein quartz with adularia or sericite of about 8 per mil the isotopic composition of the hydrothermal fluid is calculated to be about delta 18 o 0 per mil these hydrothermal fluids are isotopically evolved mixtures derived from meteoric and magmatic waters with possible metamorphic input whole rock analyses of mainly fine grained quartz dickite mineral mixtures document the largest 18 o shifts with values up to 15 7 per mil this is interpreted to be due to lower temperatures and or the presence of significant quantities of magmatic fluids in these altered zones k ar age determinations on alunite from several zones of intensely acid leached rocks suggest that an early mineralizing episode apparently occurred around 190 ma or earlier during a depositional hiatus between the two major volcanic cycles this coincides with the uplift and cooling of several plutons k ar dates on adularia and sericite from precious metal bearing quartz veins some of which are from volcanic rocks of the upper cycle suggest that there was also a younger mineralizing event recent argon step heating dates indicate that the major gold silver deposits with adularia sericite range from 189 7 or 2 6 to 186 7 or 1 7 ma clark and williams jones 1991 this closely follows the latest stages of toodoggone volcanism and fault block subsidence a depth zoning model for mineralization illustrates the two types of epithermal regimes adularia sericite and acid sulfate gold barite in the extensive advanced argillic and argillicly altered zones at the al deposit represent high level near surface acid sulfate alteration formed on the flanks of a stratovolcano the advanced argillic altered zone at silver pond next to the major lawyers adularia sericite deposit represents a downfaulted acid sulfate outflow i e the upper portion of the lawyers hydrothermal system the lawyers deposit and most of the other occurrences are adularia sericite type deposits formed at slight depth these deposits occur in grabens or half grabens in an extensional fault regime that created the central toodoggone depression nested within the broader volcanic belt

the fragmentation threshold of pyroclastic rocks in response to rapid decompression porous magma may fragment explosively this occurs when the melt can no longer withstand forces exerted upon it due to the overpressure in included bubbles this occurs at a critical pressure difference between the bubbles and the surrounding magma in this study we have investigated this pressure threshold necessary for the fragmentation of magma here we present the first comprehensive high temperature experimental quantification of the fragmentation threshold of volcanic rocks varying widely in porosity permeability crystallinity and chemical composition we exposed samples to increasing pressure differentials in a high temperature shock tube apparatus until fragmentation was initiated experimentally we define the fragmentation threshold as the minimum pressure differential that leads to complete fragmentation of the pressurized porous rock sample our results show that the fragmentation threshold is strongly dependent on porosity high porosity samples fragment at lower pressure differentials than low porosity samples the fragmentation threshold is inversely proportional to the porosity of the other factors permeability likely affects the fragmentation threshold at high porosity values whereas chemical composition crystallinity and bubble size distribution appear to have minor effects the relationship for fragmentation threshold presented here can be used to predict the minimum pressure differential necessary for the initiation or cessation of the explosive fragmentation of porous magma

ore genesis and hydrothermal evolution of the huanggang skarn iron tin polymetallic deposit southern great xing an range evidence from fluid inclusions and isotope analyses abstract the southern great xing an range is one of the most important metallogenic belts in northern china and contains numerous pb zn ag cu sn fe mo deposits the huanggang iron tin polymetallic skarn deposit is located in the sn polymetallic metallogenic sub belt skarns and iron orebodies occur as lenses along the contact between granite plutons and the lower permian huanggangliang formation marble or dashizhai formation andesite field evidence and petrographic observations indicate that the three stages of hydrothermal activity i e skarn oxide and sulfide stages all contributed to the formation of the huanggang deposit the skarn stage is characterized by the formation of garnet and pyroxene and high temperature hypersaline hydrothermal fluids with isotopic compositions that are similar to those of typical magmatic fluids these fluids most likely were generated by the separation of brine from a silicate melt instead of being a product of aqueous fluid immiscibility the iron oxide stage coincides with the replacement of garnet and pyroxene by amphibole chlorite quartz and magnetite the hydrothermal fluids of this stage are represented by l type fluid inclusions that coexist with v type inclusions with anomalously low d values approximately 100 to 116 the decrease in ore fluid 18oh2o values with time coincides with marked decreases in the fluid salinity and temperature based on the fluid inclusion and stable isotopic data the ore fluid evolved by boiling of the magmatic brine the sulfide stage is characterized by the development of sphalerite chalcopyrite fluorite and calcite veins and these veins cut across the skarns and orebodies the fluids during this stage are represented by inclusions with a variable but continuous sequence of salinities mainly low salinity inclusions these fluids yield the lowest 18oh2o values and moderate d values 1 6 to 2 8 and 101 to 104 respectively the data indicate that the sulfide stage fluids originated from the mixing of residual oxide stage fluids with various amounts of meteoric water boiling occurred during this stage at low temperatures the sulfur isotope 34s values of the sulfides are in a narrow range of 6 70 to 4 50 mean 1 01 and the oxygen isotope 18o values of the magnetite are in a narrow range of 0 1 to 3 4 both of these sets of values suggest that the ore forming fluid is of magmatic origin the lead isotope compositions of the ore 206pb 204pb 18 252 18 345 207pb 204pb 15 511 15 607 and 208pb 204pb 38 071 38 388 are consistent with those of k feldspar granites 206pb 204pb 18 183 18 495 207pb 204pb 15 448 15 602 208pb 204pb 37 877 38 325 but significantly differ from those of permian marble 206pb 204pb 18 367 18 449 207pb 204pb 15 676 15 695 208pb 204pb 38 469 38 465 which also suggests that the ore forming fluid is of magmatic origin

volcanic dilemma flow or blow volcanic eruptions can be either slow outpourings of lava or explosive ejections of fragmented rock in his perspective dingwell discusses the physical and chemical properties of magma that lead to these two styles of eruption new experiments and computer simulations are pointing to the involvement of solidlike behavior of liquid magma when it makes a transition to a glass