the mokrsko west gold deposit bohemian massif czech republic mineralogy deposit setting and classification abstract the mokrsko west deposit is unique among european variscan gold deposits from the points of view of both the structure an approx 200 m thick complex of sheeted several mm thick densely spaced quartz veins and the economic viability gold reserves of about 100 t the deposit is hosted mainly by tonalite of the calc alkaline sazava tonalite suite ca 354 ma of the central bohemian plutonic complex mineralization is characterized by quartz dominated gangue no visible hydrothermal alteration low sulfide content high fineness native gold accompanied by maldonite aurostibite native bismuth and numerous bi te s phases five mineralogical stages are described in great detail arsenopyrite and chlorite thermometers mineral phase stabilities and published isotope and fluid inclusion data are used to reconstruct the temperature and compositional evolution of the system the role of liquid bismuth in the sequestration of gold is also discussed the deposit shares the features of both orogenic gold org and intrusion related gold irg deposits the irg model is advocated by close spatial association between the ore zone and the tonalite host intrusion by the absence scarcity of hydrothermal alteration by the au bi te as elemental association and by marked thermal gradients from the early to late mineralization stages the org model is advocated by an approx 15 10 ma gap between the intrusion of the tonalite host and the ore formation by isotope and geochemical evidence for a key role of metamorphic fluids in the mobilization and transfer of many elements species inclusive s and au the apparently ambiguous classification of the deposit can most probably be attributed to deposit formation at a depth of 9 km and to setting of the deposit at inside a large scale plutonic complex with multiple and prolonged tectonic and intrusive activity

fluid evolution of the hub stock horni slavkov krasno sn w ore district bohemian massif czech republic the horni slavkov krasno sn w ore district is hosted by strongly altered variscan topaz albite granite krudum granite body on the northwestern margin of the bohemian massif we studied the fluid inclusions on greisens ore pockets and ore veins from the hub stock an apical expression of the krudum granite fluid inclusions record almost continuously the post magmatic cooling history of the granite body from 500 to 50 c rarely observed highest temperature 500 c highest salinity 30 wt nacl eq fluid inclusions are probably the result of secondary boiling of fluids exsolved from the crystallizing magma during pressure release which followed hydraulic brecciation of the gneissic mantle above the granite cupola the greisenization was related to near critical low salinity 0 7 wt nacl eq aqueous fluids with low amount of co2 ch4 and n2 10 mol in total at temperatures of 350 400 c and pressures of 300 530 bar crush leach data display highly variable and negatively correlated i cl and br cl values which are incompatible with both orthomagmatic and or metamorphic origin of the fluid phase but can be explained by infiltration of surficial and or sedimentary fluids low fluid salinity indicates a substantial portion of meteoric waters in the fluid mixture that is in accordance with previous stable isotope data the post greisenization fluid activity associated with vein formation and argillitization is characterized by decreasing temperature 350 to 50 c decreasing pressure down to 50 100 bar and mostly also decreasing salinity

calcic amphibole equilibria and a new amphibole plagioclase geothermometer there is currently a dearth of reliable thermobarometers for many hornblende and plagioclase bearing rocks such as granitoids and amphibolites a semi empirical thermodynamic evaluation of the available experimental data on amphibole plagioclase assemblages leads to a new thermometer based on the aliv content of amphibole coexisting with plagioclase in silica saturated rocks the principal exchange vector in amphiboles as a function of temperature in both the natural and experimental studies is left na square 1 right a left alsi 1 right t1 we have analysed the data using 3 different amphibole activity models to calibrate the thermometer reactions 1 edenite 4 quartz tremolite albite 1 2 pargasite 4 quartz hornblende albite 2 the equilibrium relation for both 1 and 2 leads to the proposed new thermometer t frac 0 677p 48 98 y 0 0429 0 008314 ln k and k left frac si 4 8 si right x ab plag where si is the number of atoms per formula unit in amphiboles with p in kbar and t in k the term y represents plagioclase non ideality rtln ab from darken s quadratic formalism dqf with y 0 for xab 0 5 and y 8 06 25 5 1 xab 2 for xab 0 5 the best fits to the data were obtained by assuming complete coupling between al on the t1 site and na in the a site of amphibole and the standard deviation of residuals in the fit is 38 c the thermometer is robust to ferric iron recalculation procedures from electron probe data and should yield temperatures of equilibration for hornblende plagioclase assemblages with uncertainties of around 75 c for rocks equilibrated at temperatures in the range 500 1100 c the thermometer should only be used in this temperature range and for assemblages with plagioclase less calcic than an92 and with amphiboles containing less than 7 8 si atoms pfu good results have been attained on natural examples from greenschist to granulite facies metamorphic rocks as well as from a variety of mafic to acid intrusive and extrusive igneous rocks our analysis shows that the pressure dependence is poorly constrained and the equilibria are not suitable for barometry

amphibole as an archivist of magmatic crystallization conditions problems potential and implications for inferring magma storage prior to the paroxysmal 2010 eruption of mount merapi indonesia amphibole is widely employed to calculate crystallization temperature and pressure although its potential as a geobarometer has always been debated recently ridolfi et al contrib mineral petrol 160 45 66 2010 and ridolfi and renzulli contrib mineral petrol 163 877 895 2012 have presented calibrations for calculating temperature pressure fo2 melt h2o and melt major and minor oxide composition from amphibole with a large compositional range using their calibrations we have i calculated crystallization conditions for amphibole from eleven published experimental studies to examine the problems and the potential of the new calibrations and ii calculated crystallization conditions for amphibole from basaltic andesitic pyroclasts erupted during the paroxysmal 2010 eruption of mount merapi in java indonesia to infer pre eruptive conditions our comparison of experimental and calculated values shows that calculated crystallization temperatures are reasonable estimates calculated fo2 and melt sio2 content yields potentially useful estimates at moderately reduced to moderately oxidized conditions and intermediate to felsic melt compositions however calculated crystallization pressure and melt h2o content are untenable estimates that largely reflect compositional variation in the crystallizing magmas and crystallization temperature and not the calculated parameters amphibole from merapi s pyroclasts yields calculated conditions of 200 800 mpa 900 1 050 c nno 0 3 nno 1 1 3 7 7 2 wt melt h2o and 58 71 wt melt sio2 we interpret the variations in calculated temperature fo2 and melt sio2 content as reasonable estimates but conclude that the large calculated pressure variation for amphibole from merapi and many other arc volcanoes is evidence for thorough mixing of mafic to felsic magmas and not necessarily evidence for crystallization over a large depth range in contrast bimodal pressure estimates obtained for other arc magmas reflect amphibole crystallization from mafic and more evolved magmas respectively and should not necessarily be taken as evidence for crystallization in two reservoirs at variable depth

experimental calibration of the aluminum in hornblende geobarometer with application to long valley caldera california volcanic rocks a new geobarometer based on the al content of igneous hornblendes in equilibrium with melt fluid biotite quartz sanidine plagioclase sphene and magnetite or ilmenite has been calibrated experimentally the calibration was performed by equilibrating the required phase assemblage over the pressure range 2 8 kbar at 740 780c and then analyzing euhedral hornblendes in equilibrium with glass melt experiments were performed on natural samples of both volcanic and plutonic rocks earlier empirical calibrations of this geobarometer relied on analyzing natural hornblendes from plutons with the required phase assemblage and inferring pressure from nearby metamorphic country rocks the experimental calibration differs from the empirical calibrations especially above 5 kbar and shows that the al content of hornblendes in equilibrium with the required phase assemblage is greater for a given total pressure than previously thought the geobarometers uncertainty is dramatically reduced the derived equation is p plus minus 0 5 kbar 3 minus 3 46 plus minus 0 24 4 23 plus minus 0 13 al sup t the geobarometer is applied to post bishop tuff volcanic rocks from long valley caldera california and reveals that most rhyodacites in this complex erupted from depths of about 6 km these eruptions occurred over 500 000 yr suggesting that the rhyodacitic magma reservoir beneath longmore valley had reached a steady p depth t state less

dating multiply overprinted granites the effect of protracted magmatism and fluid flow on dating systems zircon u pb shrimp sims la icp ms ca id tims and rb sr ar ar granites from the western erzgebirge bohemian massif germany abstract the variscan granites from the western erzgebirge were repeatedly dated by various methods but no consensus has been reached about their exact intrusion ages this study presents a multi dating approach for the four largest intrusions from the western erzgebirge aue schwarzenberg bergen eibenstock kirchberg we analysed several samples from each pluton suite with zircon u pb ca id tims chemical abrasion isotope dilution thermal ionization mass spectrometry to obtain robust temporal information on their age and tempo of intrusion these data enable us for the first time to define three intrusive episodes of 1 2 ma each separated by quiet periods of several ma the aue schwarzenberg suite represents the oldest granites that intruded at 323 322 ma followed by the granites from bergen and kirchberg 2 4 ma later the highly evolved ore bearing granites from the eibenstock pluton intruded after a time lag of 5 ma at 315 314 ma the new data show that there is a resolvable age difference between the two known granite groups granite group 2 also assigned as younger igneous complex represented by the eibenstock pluton is 5 ma younger than granite group 1 assigned as older igneous complex represented by granites from aue schwarzenberg bergen and kirchberg protracted magmatism and late post magmatic fluid flow partly reset the u pb system of these granites to variable degrees making a precise and accurate dating of their intrusion ages challenging pb loss in zircons is often combined with high common pb pbc shrimp sims sensitive high mass resolution ion microprobe secondary ion mass spectrometry and la icp ms laser ablation inductively coupled plasma mass spectrometry on non ca zircons document that pb loss and high pbc is quite variable within zircon grains and may be located in micro fractures we demonstrate that chemical abrasion ca clearly minimizes or removes both pb loss and pbc results from prior la icp ms and shrimp dating on non ca zircons from the same samples considerably helped the interpretation of the ca id tims data when pb loss was not completely erased by ca in such cases we often had to choose the oldest analyses for mean age calculation in contrast to the common practice of the ca id tims community to choose the youngest dates rb sr and ar ar dating systems revealed age differences between the older group and the younger ore bearing granites albeit with diverging absolute ages most ar ar ages are identical with ca id tims ages and would imply rapid cooling however samples from the older group have excess ar that could have led to too old ages in contrast rb sr ages for the older granites are 0 7 ma younger than their intrusions fluid induced alteration led to the formation of li mica fluorite and cassiterite greisenization for the youngest granite eibenstock li mica was used to date the first greisenization samples without visible hydrothermal overprint yielded identical ar ar and rb sr ages as severely greisenized samples this implies re equilibration due to the hydrothermal overprint for all ar ar and rb sr ages from the eibenstock pluton according to ar ar dating the first ore formation 315 ma is coeval with the ca id tims intrusion age of the eibenstock granite while it is delayed by 6 3 ma according to rb sr dating 308 3 ma

chemical signature of quartz from s and a type rare metal granites a summary abstract about 800 new and 1200 already published laser ablation inductively coupled plasma mass spectrometry analyses of quartz from rare metal granites and related greisens quartz tourmaline rocks and quartz veins were evaluated in order to define typical trace element signatures of quartz of different origin the studied dataset comprises typical examples of sub aluminous to slightly peraluminous plutons a type granites of the kimi stock finland eastern erzgebirge czech republic orlovka russia and ongon chairchan mongolia and strongly peraluminous plutons s type granites of beauvoir france cornwall england panasqueira and argemela portugal western erzgebirge czech republic additional 700 mostly already published analyses of quartz from barren granites of all geochemical types i s a type rhyolites and barren and rare element pegmatites were evaluated for comparison compiled data reveal high diversity in the contents of trace elements in quartz even among rocks of similar geochemical composition the most common trace elements in magmatic quartz are al li and ti with medians of 447 39 6 and 17 4 ppm in s type rare metal granites and 160 15 and 6 6 ppm in a type rare metal granites the contents of all these elements in greisens and quartz veins are significantly lower than in their parental granites al contents above 450 ppm should serve as a reliable indicator of s affinity of the analyzed granite while contents

multiphase formation of the obři důl polymetallic skarn deposit west sudetes bohemian massif geochemistry and re os dating of sulfide mineralization the ob i d l fe cu as polymetallic sulfide skarn deposit is developed in a metamorphic series in the west sudetes bohemian massif it consists of lenses of marble calc silicate rocks and skarns we studied the gustav orebody which is located few hundred meters away from the contact with a large late orogenic variscan krkonose jizera plutonic complex kjpc emplaced into shallow crust mineralogical and fluid inclusion study evidence indicates that the main sulfide stage dominated by pyrrhotite arsenopyrite and chalcopyrite originated from aqueous hydrothermal fluids with salinity up to 8 wt nacl eq with minimum homogenization temperatures ranging from 324 to 358 c these fluids mainly replaced carbonate rich lithologies carbon oxygen and strontium isotope data in ca rich rocks imply total overprinting by channelized metasomatic fluid flow which is most probably related to the intrusion of the kjpc whereas 34s values of sulfides argue for a magmatic source of sulfur the re os age of arsenopyrite overlaps published age data for the kjpc and suggests synchronous formation of the main sulfide mineralization and pluton emplacement

origin ore forming fluid evolution and timing of the logrosan sn w ore deposits central iberian zone spain the logrosan sn w ore deposits in the metallogenic sn w province of the european variscan belt consist of endo and exogranitic greisen type and quartz cassiterite veins associated with a s type granite mineral characterization fluid inclusion study isotope geochemistry and ar ar geochronology have been combined in order to reconstruct the conditions for sn w mineralization the endo and exogranitic mineralization must have been developed in a relatively long lived system 308 303 ma during or soon after the emplacement of the logrosan related granite at ca 308 ma the mineralizing fluids are characterized by complex aqueous and volatile h2o n2 co2 ch4 nacl fluid inclusions microthermometry and raman analyses indicate that fluid composition evolved from n2 ch4 to n2 rich followed by co2 rich fluids with varying amounts of h2o the presence of n2 and ch4 suggests the interaction with fluids derived from the nearby metasedimentary host rocks a model of host rock interaction assimilation and mixing of metamorphic and magmatic fluids resulting in change of the redox conditions is proposed for tin deposition later sulfide minerals were precipitated as a result of pressure and temperature release

rhyolite melts vs derp newer does not make it better a comment on the effect of anorthite content and water on quartz feldspar cotectic compositions in the rhyolitic system and implications for geobarometry by wilke et al 2017 journal of petrology 58 789 818

experimental evidence for a protracted enrichment of tungsten in evolving granitic melts implications for scheelite mineralization the solubility of scheelite in evolved granitic magmas qz ab or an system with minor feototal tio2 and cao added was studied experimentally at 200 mpa 750 850 c and relatively oxidizing condition logfo2 nno 2 3 where nno is ni nio oxygen buffer water saturated granitic melts have been equilibrated with seeds of scheelite crystals the resulted wo3 contents in the melts vary only slightly from 0 21 to 0 32 wt wo3 over the investigated temperature and compositional range 0 7 to 1 4 wt cao but tends to increase with increasing temperature and decreasing cao concentration one important message conveyed from the study is that wo3 concentrations at scheelite saturation are more dependent on temperature in evolved ca poor melts than in ca rich melts natural granitic rocks associated with scheelite mineralization and associated melt inclusions hosted in quartz have much lower w contents than the experimental melts equilibrated with scheelite this implies that enrichment of tungsten w at magmatic stages is not sufficient to produce significant scheelite mineralization and confirms the important role of w mobilization by magmatic hydrothermal fluids in the formation of scheelite deposits

quartz and feldspar zoning in the eastern erzgebirge volcano plutonic complex germany czech republic evidence of multiple magma mixing abstract zoned quartz and feldspar phenocrysts of the upper carboniferous eastern erzgebirge volcano plutonic complex were studied by cathodoluminescence and minor and trace element profiling the results verify the suitability of quartz and feldspar phenocrysts as recorders of differentiation trends magma mixing and recharge events and suggest that much heterogeneity in plutonic systems may be overlooked on a whole rock scale multiple resorption surfaces and zones element concentration steps in zoned quartz ti and feldspar phenocrysts anorthite content ba sr and plagioclase mantled k feldspars etc indicate mixing of silicic magma with a more mafic magma for several magmatic phases of the eastern erzgebirge volcano plutonic complex generally feldspar appears to be sensitive to the physicochemical changes of the melt whereas quartz phenocrysts are more stable and can survive a longer period of evolution and final effusion of silicic magmas the regional distribution of mixing compatible textures suggests that magma mingling and mixing was a major process in the evolution of these late variscan granites and associated volcanic rocks quartz phenocrysts from 14 magmatic phases of the eastern erzgebirge volcano plutonic complex provide information on the relative timing of different mixing processes storage and recharge allowing a model for the distribution of magma reservoirs in space and time at least two levels of magma storage are envisioned deep reservoirs between 24 and 17 km the crystallisation level of quartz phenocrysts and subvolcanic reservoirs between 13 and 6 km deflation of the shallow reservoirs during the extrusion of the teplice rhyolites triggered the formation of the altenberg teplice caldera above the eastern erzgebirge volcano plutonic complex the deep magma reservoir of the teplice rhyolite also has a genetic relationship to the younger mineralised a type granites as indicated by quartz phenocryst populations the pre caldera biotite granites and the rhyodacitic schonfeld volcanic rocks represent temporally and spatially separate magma sources however the deep magma reservoir of both is assumed to have been at a depth of 24 17 km the drastic chemical contrast between the pre caldera schonfeld westfalian b c and the syn caldera teplice westfalian c d volcanic rocks is related to the change from late orogenic geotectonic environment to post orogenic faulting and is considered an important chronostratigraphic marker

geochemical specialization of the tin bearing granitoid massifs of nw bohemia the geochemistry of hercynian tin bearing granitoid massifs of the krusne hory mts erzgebirge slavkovsk les forest kaiserwald and smrciny eastern fichtelgebirge is compared by statistical processing of 270 analyses including a wide spectrum of major and trace elements seven different types of granites are distinguished out of these five types represent the successive differentiation of the largest massif of nw bohemia the karlovy vary karlsbad massif this comprises strongly differentiated peraluminous granites evolving towards extreme li rb cs f and sn enrichment in the youngest members which are albite topaz zinwaldite lithium granites the sixth and seventh types are different from the former by their location in the eastern krusne hory and tectonic setting and they display geochemical features of anorogenic granites they are metaluminous albite zinwaldite granites with marked enrichment of nb y and hree in addition to li rb cs f and sn indicating contamination by sub crustal material sn w mineralizations including flat peri contact greisen bodies steep greisen veins and tourmalinized phyllites are all intimately associated with the most strongly differentiated granites the li granite and the cinovec granite respectively

degassing of the h2o rich rhyolites of the okataina volcanic center taupo volcanic zone new zealand the taupo volcanic zone tvz new zealand is the most active region of rhyolitic volcanism on earth with 50 rhyolitic eruptions and 780 km3 of magma erupted in the past 60 k y here we use analyses of quartz hosted melt inclusions from eight eruptions in the okataina volcanic center ovc of the tvz to constrain magmatic volatile contents pressures and temperatures of quartz crystallization and degassing of h2o cl and minor co2 from the rhyolitic magmas the ovc melt inclusions trapped volatile rich melts with 6 wt h2o and 0 27 wt cl our data indicate that vapor saturated crystallization of quartz occurred at low temperatures 760 805 c over a wide range of pressures 50 200 mpa for some eruptions variations in volatiles and major and trace elements provide evidence for simultaneous crystallization and partial loss of h2o cl and co2 into a vapor phase using the combination of melt inclusion and pumice glass volatile contents we calculate minimum volatile emissions of 3 1011 to 8 1012 kg h2o and 7 109 to 4 1010 kg cl during the ovc eruptions we estimate that emissions from the smaller volume 100 of the global arc h2o flux and as much as 90 of the global arc cl flux these results underscore the importance of individual magmatic provinces in creating large temporal variations in global arc volatile fluxes to earth s hydrosphere

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

temporal evolution of mineralization events in the bohemian massif inferred from the re os geochronology of molybdenite molybdenite is a common mineral accompanying sn w au and base metal mineralizations located in different geotectonic units of the bohemian massif but it is also widespread in granitoids and or related quartz veins pegmatites forming disseminated mo mineralization thirty re os ages were obtained for molybdenite samples from the bohemian massif to provide constraints on the timing and duration of mineralization event s within the framework of previously published geochronological data for the host and or associated rocks the obtained data for sn w li deposits in the erzgebirge metallogenetic province indicate the predominance of one and or multiple short time mineralization events taking place between 319 and 323 ma with the exception of the krupka deposit associated with the altenberg teplice caldera where the data may suggest prolonged activity until 315 ma the ages of the pb zn au mo h rky u rakovnika and fe cu as ob i d l mineralizations from the exocontacts of the cista pluton and krkonose jizera plutonic complex respectively provide evidence for synchronous emplacement of the ore and the associated granitic rocks in contrast the padr fe as mo mineralization postdates the age of the associated padr granite disseminated mo mineralization in cadomian and variscan granitoids and or related to quartz veins pegmatites provides re os ages that overlap with the previously published geochronological data for the host rocks suggesting coeval evolution molybdenite samples from the sazava suite granites of the central bohemian plutonic complex cbpc have resolvable younger ages than their host granites but similar to the age of spatially related au mineralization which is associated with the latest evolution of the cbpc

phase equilibrium geobarometers for silicic rocks based on rhyolite melts part 3 application to the peach spring tuff arizona california nevada usa establishing the depths of magma accumulation is critical to understanding how magmas evolve and erupt but developing methods to constrain these pressures is challenging we apply the new rhyolite melts phase equilibria geobarometer based on the equilibrium between melt quartz and two feldspars to matrix glass compositions from peach spring tuff arizona california nevada usa high silica rhyolite we compare the results to those from amphibole geothermobarometry projection of glass compositions onto the haplogranitic ternary and glass sio2 geobarometry quartz 2 feldspar rhyolite melts pressures span a relatively small range 185 230 mpa consistent with nearly homogeneous crystal compositions and are similar to estimates based on projection onto the haplogranitic ternary 250 50 mpa and on glass sio2 255 275 mpa amphibole geothermobarometry gives much wider pressure ranges temperature independent 65 300 mpa temperature dependent 75 295 mpa amphibole only 80 950 mpa average anderson and smith am mineral 80 549 559 1995 blundy and holland contrib miner petrol 104 208 224 1990 or holland and blundy contrib miner petrol 116 433 447 1994 thermometer a b pressures are most similar to phase equilibria results 220 210 190 mpa respectively crystallization temperatures determined previously with rhyolite melts 742 c zr in sphene 769 20 c and zircon saturation 770 780 c geothermometry are similar but temperatures from amphibole geothermometry 450 955 c are notably different the average anderson and smith holland and blundy 1994 thermometer b 710 c temperature is most consistent with previous estimates the rhyolite melts geobarometer effectively culls glass compositions affected by alteration or analytical issues peach spring glass compositions that yield pressure estimates reveal a tight range of plausible na2o and k2o contents suggesting that low na2o and high k2o contents of many peach spring samples are due to alteration use of altered whole pumice compositions in rhyolite melts simulations is likely the cause of the incorrect crystallization sequence reported previously for peach spring compositions using the rhyolite melts geobarometer we estimate a more realistic composition for peach spring tuff high silica rhyolite and the calculated composition finds close matches with some analyzed rocks and results in the expected sequence of crystallization

extreme p bi nb sc u and f rich zircon from fractionated perphosphorous granites the peraluminous podlesi granite system czech republic abstract the strongly peraluminous and p rich protolithionite and zinnwaldite leucogranites from podlesi western krusne hory mts czech republic contain accessory zircon with extraordinary enrichment of several elements which constitute trace elements in common zircon elements showing a not yet reported anomalous enrichment include p up to 20 2 wt p2o5 equivalent to 0 60 apfu formula calculated on the basis of 4 oxygen atoms bi up to 9 0 wt bi2o3 0 086 apfu nb up to 6 7 wt nb2o5 0 12 apfu sc up to 3 45 wt sc2o3 0 10 apfu u up to 14 8 wt uo2 0 12 apfu and f up to 3 81 wt f 0 42 apfu strong enrichment of p preferentially involved the berlinite type substitution 2 si4 p5 al3 implying that significant al may enter the si position in zircon incorporation of other exotic elements is primarily governed by the xenotime si4 zr4 p5 y3 pretulite sc3 p5 zr4 si4 brabantite type ca2 u th 4 2p5 2zr4 2si4 and ximengite type bi3 p5 zr4 si4 substitution reactions one part of the anomalous zircons formed late magmatically from a strongly peraluminous p f u rich hydrous residual melt that gave rise to the zinnwaldite granite interaction with aggressive residual fluids and metamictization have further aided in element enrichment or depletion particularly in altered parts of zircon contained in the protolithionite granite most of the zircon from f rich greisens have a composition close to endmember zrsio4 and are chemically distinct from zircon in its granite parent this discrepancy implies that at podlesi granitic zircon became unstable and completely dissolved during greisenization part of the mobilized elements was reprecipitated in newly grown hydrothermal zircon

insights into silicic melt generation using plagioclase quartz and melt inclusions from the caldera forming rotoiti eruption taupo volcanic zone new zealand the rotoiti 120 km3 and earthquake flat 10 km3 eruptions occurred in close succession from the okataina volcanic centre at 50 ka while accessory mineral geochronology points to long periods of crystallization prior to eruption 104 105 years and separate thermal histories for the magmas little was known about the rates and processes of the final melt production and eruption crystal zoning patterns in plagioclase and quartz reveal the thermal and compositional history of the magmatic system leading up to the eruption the dominant modal phase plagioclase displays considerable within crystal zonation an37 74 40 227 ppm mgo 45 227 ppm tio2 416 910 ppm sr and 168 1164 ppm ba resorption horizons in the crystals are marked by sharp increases 10 30 in sr mgo and xan that reflect changes in melt composition and are consistent with open system processes melt inclusions display further evidence for open system behaviour some are depleted in sr and ba relative to accompanying matrix glass not consistent with crystallization of modal assemblage mi also display a wide range in xh2o that is consistent with volatile fluxing quartz cl images reveal zoning that is truncated by resorption and accompanied by abrupt increases in ti concentration 30 80 ppm that reflect temperature increases 50 110 c diffusion across these resorption horizons is restricted to zones of 20 m suggesting most crystallization within the magma occurred in 2000 years these episodes are brief compared to the longevity 104 105 year of the crystal mush zones all textural and compositional features observed within the quartz and plagioclase crystals are best explained by periodic mafic intrusions repeatedly melting parts of a crystal rich zone and recharging the system with silicic melt these periodic influxes of silicic melt would have accumulated to form the large volume of magma that fed the caldera forming rotoiti eruption

phase equilibrium geobarometers for silicic rocks based on rhyolite melts part 1 principles procedures and evaluation of the method constraining the pressure of crystallization of magmas is an important but elusive task in this work we present a method to derive crystallization pressures for rocks that preserve glass compositions either glass inclusions or matrix glass representative of equilibration between melt quartz and 1 or 2 feldspars the method relies on the well known shift of the quartz feldspar saturation surface toward higher normative quartz melt compositions with decreasing pressure the critical realization for development of the method is the fact that melt quartz and feldspars need to be in equilibrium at the liquidus for the melt composition the method thus consists of calculating the saturation surfaces for quartz and feldspars using rhyolite melts over a range of pressures and searching for the pressure at which the expected assemblage quartz 1 feldspar or quartz 2 feldspars is found at the liquidus we evaluate errors resulting from uncertainties in glass composition using a series of monte carlo simulations for a quartz hosted glass inclusion composition from the bishop tuff which reveal errors on the order of 20 45 mpa for the quartz 2 feldspars constraint and on the order of 25 100 mpa for the quartz 1 feldspar constraint we suggest actual errors are closer to the lower bounds of these ranges we investigate the effect of fluid saturation in two ways 1 by applying our procedure over a range of water contents for three glass compositions we show that the effect of fluid saturation is more important at higher pressures 300 mpa than at lower pressures 100 mpa but reasonable pressure estimates can be derived irrespective of fluid saturation for geologically relevant h2o concentrations 3 wt and 2 by performing the same type of pressure determinations with a preliminary version of rhyolite melts that includes a h2o co2 mixed fluid phase we use a range of h2o and co2 concentrations for two compositions characteristic of early erupted and late erupted bishop tuff glass inclusions and demonstrate that calculated pressures are largely independent of co2 concentration for co2 1 000 ppm at least for relatively high h2o contents as expected in most natural magmas such that co2 concentration can be effectively neglected for application of our method finally we demonstrate that pressures calculated using the rhyolite melts geobarometer compare well with those resulting from h2o co2 glass inclusion barometry and al in hornblende barometry for an array of natural systems for which data have been compiled from the literature the agreement is best for quartz hosted glass inclusions while matrix glass yields systematically lower rhyolite melts pressures suggestive of melt evolution during eruptive decompression

a jurassic cretaceous island arc in the ladakh himalayas abstract the ladakh mesozoic ophiolite belt western himalaya contains a pile of volcanic thrust sheets dras unit which differ significantly in structure and composition from the ophiolitic melange zones the dras unit is composed of pillow lavas doleritic sills very irregular basaltic basaltic andesites and dacitic flows intercalated with pyroclastics volcanoclastic sediments and radiolarian cherts according to fossil evidence this volcanism must have been active between upper jurassic and upper cretaceous the presence of relict primary minerals such as magnesiochromite clinopyroxene hastingsitic hornblende and ti magnetite as well as distinctive bulk chemistries suggests that the volcanics belong to island arc tholeiite and to calc alkaline rock series typical of present island arcs in the caribbean and pacific model calculations incorporating probed phenocryst phases indicate that in addition to olivine clinopyroxene and plagioclase amphibole and titanomagnetite are crucial fractionating phases in the development of the dacites from a primitive tholeiitic melt the latter process must have taken place at about 1000 c and at moderate depth of 5 15 km within or underneath the island arc today hornblende bearing mafic cumulates appear in the vicinity of kargil within and close to the dras volcanics in a sr evolution diagram the dras volcanics have yielded a pseudo isochron with a low initial 87 sr 86 sr ratio of 0 7035 0 0003 which is in the same range as the mean of modern island arc volcanics however a geologically unrealistic age of 263 m y is obtained from the slope of this isochron the upper mantle is regarded as the source material for the island arc tholeiitic magmas enrichment in k ba sr and lree supports the involvement of components derived from dehydration or incipient melting of subducted tethyan oceanic crust in the mantle

compositional evolution and substitutions in disseminated and nodular tourmaline from leucocratic granites examples from the bohemian massif czech republic two distinct textural types of tourmaline were distinguished in leucocratic granites of the bohemian massif moldanubicum saxothuringicum i commonly euhedral disseminated tourmaline dt crystallized in relatively early stage of the granite consolidation and ii typically interstitial nodular tourmaline nt formed during the stage transitional from late solidus to early subsolidus crystallization very similar chemical composition and similar fractionation trends in both dt and nt tourmaline types indicate crystallization in a quasi closed system from early solidus to early subsolidus stage of granite consolidation the substitutions in tourmaline from nt granites in the moldanubicum are more similar to the substitutions in tourmaline from li poor granitic pegmatites in the same region relative to tourmaline from dt granites plotting of emp analyses of tourmaline in diverse diagrams strongly suggests using combination of ternary diagrams al fe mg and na ca xsite vacancy and simple plots involving single cations elements such as na al f na fe mg rather then more complicated diagrams e g r1 r2 r3 to characterize chemical composition and to derive substitution mechanisms in ca poor tourmaline from granitic rocks the complex diagrams e g r1 r2 versus r3 do not enable to investigate compositional evolution in the xsite and wsite properly and oversimplifies the real substitutions we recommend using specific diagrams for specific tourmaline compositions e g carich lirich

are strongly peraluminous magmas derived from pelitic sedimentary sources igneous compositions that require the presence of a phase more aluminous than biotite are here designated as strongly peraluminous ps such compositions are common but subordinate in felsic rocks and exceedingly rare in more mafic rocks the term s type has been applied to many igneous rocks based largely or even solely upon their ps compositions neglecting or placing less emphasis on other criteria for sedimentary parentage in chappell and white s i and s type classification system the s type designation was in fact initially restricted to granites which were thought to have been derived from a chemically mature strongly weathered pelitic shaly source application of chappell s and white s criteria together with others based upon isotopic and phase equilibria considerations leads to the following conclusions about ps igneous rocks worldwide 1 very few ps rocks are derived entirely from pelitic sources 2 a majority are derived largely from intermediate to felsic crustal sources including

nearly contemporaneous evolution of the a and s type fractionated granites in the krusne hory erzgebirge mts central europe abstract the krusne hory erzgebirge mountains is one of the best known provinces of granite magmatism and associated metallogenesis in europe variscan magmatic activity in the krusne hory erzgebirge area spanned the period from 330 to 295 ma for much of this time two types of magma were generated and emplaced in close proximity in this province strongly peraluminous p rich s type melts were formed alongside slightly peraluminous p poor melts a type two suites of strongly peraluminous p f li rb cs u sn rich and zr th y hree poor magmas were intruded in rapid succession over a period of about 10 ma about 330 320 ma over the entire region of the krusne hory several peraluminous rhyolitic dykes near gottesberg mark an isolated event at about 295 ma slightly peraluminous f li rb cs sn zr y hree rich and p poor magmas were intruded in several events separated in space and time 325 295 ma both magmatic episodes culminated with strongly fractionated subvolcanic granite intrusions accompanied by explosive brecciation and followed by sn w mineralization of greisen type successive volcanic eruption of rhyolites and dacites of s type and rhyolites of a type form the fill of the altenberg teplice caldera atc thus demonstrating the close temporal and spatial relationship between these two types of magma when these two geochemically distinct types of rock are in direct contact then the rocks of a type are always younger the absolute time difference between the two types can range from less than 1 ma the first eruption of the teplice rhyolite versus the schonfeld dacite in the atc to about 15 ma eruption of rhyolites at gottesberg versus emplacement of the eibenstock granite the assumed protolith of all late variscan granites in the area of krusne hory erzgebirge is a mixture of fertile quartzo feldspathic rocks with micaceous metapelites enriched in lile and sn w the differences in chemical composition of s and a type melts originated from local changes in the proportion of quartzo feldspathic and pelitic lithologies different pt conditions of melting the degree of melting and the degree of metamorphic dehydratation of the protolith prior to the melting

multiple rhyolite magmas and basalt injection in the 17 7 ka rerewhakaaitu eruption episode from tarawera volcanic complex new zealand abstract the 17 7 ka rerewhakaaitu eruption episode volume 5 km3 dre rhyolite magma was the second of five major episodes that have built the tarawera volcanic complex in the okataina volcanic centre over the past 22 kyr the rerewhakaaitu episode produced a widespread tephra fall deposit associated proximal pyroclastic flow deposits and voluminous rhyolite lava extrusions two different rhyolite magmas t1 and t2 were simultaneously erupted from the main vent area throughout much of the eruption episode t1 magma was a crystal poor orthopyroxene hornblende rhyolite that is highly evolved whole rock sio2 77 wt with a moderate temperature 760 c based on fe ti oxides t2 is a crystal rich biotite hornblende rhyolite that is less evolved sio2 75 wt with a fe ti oxide temperature of 700 c ejecta from the simultaneous and sequential eruption of these two magmas include some pumice clasts with mixed hybrid and mingled glass compositions and crystal populations a third rhyolite magma t3 was extruded from another vent 3 km distant to form an apparently contemporaneous lava dome t3 was the least evolved sio2 74 wt and hottest 820 c of the three magmas saturation pressures calculated using dissolved h2o and co2 contents of melt inclusions in quartz crystals indicate that t2 magma stagnated and crystallised at about 12 km depth while small quartz crystals in t1 magma grew during ascent through 8 km depths some t1 and t2 rhyolite clasts contain vesicular brown blebs with widely variable andesite to rhyolite glass compositions accompanied by olivine clinopyroxene and calcic plagioclase crystals that are interpreted as xenocrysts derived from injected basalt temperatures over 1000 c estimated from pyroxene phase equilibria in these clasts reflect intrusion of the more mafic magma which is now identified as the priming and triggering mechanism for three of the four post 22 ka tarawera rhyolite eruption episodes however the rhyolite magma bodies and conduits modelled for each episode have considerable differences in characteristics and geometry our preferred model for the rerewhakaaitu episode is that eruptions occurred from three laterally and vertically isolated rhyolite magma bodies that were initially primed and triggered by basalt intrusion during a regional rifting event the ascending hotter and less viscous t1 rhyolite magma intersected and further invigorated a stagnant pond of cooler denser and more viscous t2 magma and lubricated its transport to the surface

phase equilibrium geobarometers for silicic rocks based on rhyolite melts part 2 application to taupo volcanic zone rhyolites constraining the pressure of crystallisation of large silicic magma bodies gives important insight into the depth and vertical extent of magmatic plumbing systems however it is notably difficult to constrain pressure at the level of detail necessary to understand shallow magmatic systems in this study we use the recently developed rhyolite melts geobarometer to constrain the crystallisation pressures of rhyolites from the taupo volcanic zone tvz as sanidine is absent from the studied deposits we calculate the pressures at which quartz and feldspar are found to be in equilibrium with melt now preserved as glass the quartz 1 feldspar constraint of gualda and ghiorso contrib mineral petrol 168 1033 doi 10 1007 s00410 014 1033 3 2014 we use glass compositions matrix glass and melt inclusions from seven eruptive deposits dated between 320 and 0 7 ka from four distinct calderas in the central tvz and we discuss advantages and limitations of the rhyolite melts geobarometer in comparison with other geobarometers applied to the same eruptive deposits overall there is good agreement with other pressure estimates from the literature amphibole geobarometry and h2o co2 solubility models one of the main advantages of this new geobarometer is that it can be applied to both matrix glass and melt inclusions regardless of volatile saturation the examples presented also emphasise the utility of this method to filter out spurious glass compositions pressure estimates obtained with the new rhyolite melts geobarometer range between 250 to 50 mpa with a large majority at 100 mpa these results confirm that the tvz hosts some of the shallowest rhyolitic magma bodies on the planet resulting from the extensional tectonic regime and thinning of the crust distinct populations with different equilibration pressures are also recognised which is consistent with the idea that multiple batches of eruptible magma can be present in the crust at the same time and can be tapped simultaneously by large eruptive events

how do metals escape from magmas to form porphyry type ore deposits abstract many precious and base metals cu au ag mo w sn in porphyry type deposits are extracted from a granitic to granodioritic silicate melt and transported by magmatic hydrothermal fluids to the site of ore deposition metals abundance increases from some ppb in the melt to in ore bodies assuming a unique magmatic source for metals it implies an exceptional combination of enrichment process acting over up to 4 orders of magnitude previous models of magma differentiation and hydrothermal circulations omitted to consider the role of metal segregation during magma chamber evolution models for the formation and evolution of intrusions have recently shifted from the so called melting storage assimilation homogenization mash paradigm basically steady state to the mantle melting segregation ascent emplacement m m sae paradigm dynamic and discontinuous in time successive magma injections of variable compositions progressively build the magma chamber this is supported by field relations e g cross cutting dykes and stocks textures e g partially resorbed enclaves or mineral fabrics geochemistry e g hybridization signatures and age dating aswell as istopic studies as melt crystallizes and forms a mush 50 crystals volatiles also exsolve forming a magmatic volatile phase mvp while melt motion slows down metals partition between the three phases melt crystals and mvp they generally prefer the mvp owing to more favorable partition coefficients this is indicated by metal content in coeval melt and fluid inclusions with homogenization temperatures above 600 c or in volcanic fumaroles here by simulating the physical interactions between the three phases we suggest a model of fluid sparging during which metals segregate towards the mvp by diffusion and are further transported by advection as metal complexes the model also provides estimates of metal enrichment an undimensional peclet number rules the competition between diffusion and advection basically scaling with respect to the inverse of the product of melt viscosity by metal diffusivity d the threshold value of the peclet number between diffusion and advection is roughly 10 9 fast diffusive metals au cu ag w readily diffuse from silicate melt and towards bubbles of the mvp to escape the mush through tubular structures the mvp must overcome a critical gas saturation level about 20 vol usually reached after several magma injections advection then takes over and transports the metal enriched mvp towards the top of the magma chamber this leads to nearly coeval 1 separation between a high salinity liquid phase and a low salinity vapor phase 2 fluid rock interactions resulting in potassic advanced argillic and phyllic alterations and 3 metal deposition the metal enrichment scales as the ratio between partition coefficient i e related to the gradient in chemical potential diffusivity i e related to the gradient of concentration and melt viscosity i e related to the gradient of momentum the rates at which all such gradients relax determe metals enrichment inducing chemical and physical instabilities leading to a cyclic process the whole cycle also encompasses the case of a partial non completed full enrichment yielding to barren intrusions a tentative model generalizes the sparging fluid model to other metal deposits linked to an intrusion such generalization should be interpreted as predicting metal enrichment by 3 4 orders of magnitude rather than predicting an exact value

wolframite solubility and precipitation in hydrothermal fluids insight from thermodynamic modeling abstract wolframite a solid solution series between hubnerite mnwo4 and ferberite fewo4 is the main tungsten bearing ore mineral in vein type tungsten deposits much progress has been made on characterizing the mineralizing fluids precipitating wolframite but it remains poorly understood what are the mechanisms depositing wolframite effectively and the variables controlling mn fe ratios in wolframite this study examines chemical controls on wolframite solubility in hydrothermal fluids and mn fe ratios in wolframite using thermodynamic models for fluids in the systems of w mn cl na o h and w fe cl na o h the fluid buffered models are established based on the characteristics of vein type tungsten deposits the modeling results indicate that solubilities of hubnerite and ferberite in hydrothermal fluids at typical w mineralizing conditions 300 400 c 500 1500 bars 5 15 wt nacl equivalent ph 4 6 reach up to hundreds of ppm the predominant tungsten manganese and iron species in fluids are h w o 4 m n c l 2 0 and f e c l 4 2 respectively an increase in ph and a decrease in fluid temperature and salinity are efficient mechanisms precipitating hubnerite and ferberite from acidic hydrothermal fluids hubnerite and ferberite are also significantly dissolved in alkaline hydrothermal fluids but their solubilities in alkaline fluids are insensitive to fluid temperature and salinity this may affect w mineralization at stages with different ph levels e g the greisen stage and the alkaline stage the mn fe ratio of mineralizing fluids is the principal variable controlling mn fe ratios in wolframite more supply of fe than mn from the fertile magma tends to produce fe rich mineralizing fluids this may be one of reasons why ferberite is more common than hubnerite in tungsten deposits and why hubnerite is more likely to precipitate at an early stage

a comment on titaniq under pressure the effect of pressure and temperature on the solubility of ti in quartz by jay b thomas e bruce watson frank s spear philip t shemella saroj k nayak and antonio lanzirotti trace concentrations of ti in quartz are used to indicate the pressure and temperature conditions of crystallization in the titaniq geothermobarometer of thomas et al contrib miner petrol 160 743 759 2010 it utilises the partitioning of ti into quartz as an indicator of the pressures and or temperatures of crystal growth for a given value of tio2 activity in the system if temperatures are inferred to 20 c pressure is constrained to 1 kbar and vice versa there are significant contrasts however between the conclusions from titaniq and those for natural quartz as well as other mineral phases in volcanic rocks application of the titaniq model to quartz from the 27 ka oruanui and 760 ka bishop high silica rhyolites where the values of t p and tio2 activity are constrained by other means fe ti oxide equilibria melt inclusion entrapment pressures in gas saturated melts melt and amphibole compositions yields inconsistent results if realistic values are given to any two of these three parameters then the value of the third is wholly unrealistic the model yields growth temperatures at or below the granite solidus pressures in the lower crust or upper mantle or tio2 activities inconsistent with the mineralogical and chemical compositions of the magmas cl imagery and measurements of ti and other elements in quartz are of great value in showing the growth histories and changes in conditions experienced by crystals but direct linkages to p t conditions during crystal growth cannot be achieved

low pressure origin of high silica rhyolites and granites abstracthigh silica rhyolites and granites 75 wt sio2 anhydrous basis are common features of the crust as part of both the volcanic and the plutonic records while low crystallization pressure 500 mpa we use glass compositions derived from the earthchem portal selected natural examples from the literature and rhyolite melts calculations to show that the phase relations in the quartz albite orthoclase ternary dictate the silica content of silicic melts in particular we show that silica content of melts increases with decreasing pressure as a result of the displacement of the quartz sanidine cotectic toward the qz apex with decreasing pressure it follows from our analysis that 1 the crust is expected to be stratified in terms of the silica content of residing melts 2 high silica glasses form at low pressure requiring shallow level cryst

the transhimalaya gangdese plutonism in the ladakh region a upb and rbsr study abstract the age and origin of the transhimalaya gangdese plutonic belt in the ladakh area has been studied by high resolution u pb analyses of accessory minerals zircon and monazite allanite and rb sr measurements on whole rock samples the ages determined of 101 2m y for a granodiorite and of 60 7 0 4m y for a granite substantiate that the transhimalaya plutonism was active at least in mid cretaceous albian and earliest tertiary palaeocene times a rb sr isochron of 73 4 2 4m y might be fortuitous because the rb sr systematics shows important heterogeneities on the whole rock scale the inherited radiogenic lead in zircon demonstrates that anatexis of continental crust was involved in magma genesis the thus recycled continental material was heterogeneous with respect to its primary ages and or metamorphic history the approximate minimum ages of the continental sources range from 350 to 590 m y the 101 2m y old transhimalaya granodiorite which intrudes a series of mainly basaltic island arc rocks dras series shows that this island arc was attached to the continental margin at that time this is consistent with the hypothesis that the ladakh tethys closed through two subduction regimes 1 an early cretaceous subduction which formed the dras island arc and 2 a late cretaceous to palaeocene subduction at the continental margin which caused the emplacement of the transhimalaya plutonic belt

titaniq recrystallized experimental confirmation of the original ti in quartz calibrations several studies have reported the p t dependencies of ti in quartz solubility and there is close agreement among three of the four experimental calibrations new experiments were conducted in the present study to identify potential experimental disequilibrium and to determine which ti in quartz solubility calibration is most accurate crystals of quartz rutile and zircon were grown from sio2 tio2 and zrsio4 saturated aqueous fluids in an initial synthesis experiment at 925 c and 10 kbar in a piston cylinder apparatus a range of quartz crystal sizes was produced in this experiment both large and small examples were analyzed by electron microprobe to determine whether ti concentrations are correlated with crystal size cathodoluminescence images and epma measurements show that intercrystalline and intracrystalline variations in ti concentrations are remarkably small regardless of crystal size the average ti in quartz concentration from the synthesis experiment is 392 1 ppmw ti which is within 95 confidence interval of data from the 10 kbar isobar of wark and watson contrib mineral petrol 152 743 754 2006 and thomas et al contrib mineral petrol 160 743 759 2010 as a cross check on the ti in quartz calibration we also measured the concentration of zr in rutile from the synthesis experiment the average zr in rutile concentration is 4337 32 ppmw zr which is also within the 95 confidence interval of the zr in rutile solubility calibration of ferry and watson contrib mineral petrol 154 429 437 2007 the p t dependencies of ti solubility in quartz and zr solubility in rutile were applied as a thermobarometer to the experimental sample the average ti in quartz isopleth calculated from the calibration of thomas et al contrib mineral petrol 160 743 759 2010 and the average zr in rutile isopleth calculated from the calibration of tomkins et al j metamorph geol 25 703 713 2007 cross at 9 5 kbar and 920 c which is in excellent agreement with the p t conditions of the synthesis experiment separates of the high ti quartz from the initial synthesis experiment described above were used as starting material in subsequent experiments at 20 kbar at which pressure the solubility of ti in quartz is expected to be significantly lower in the recrystallized quartz these recrystallization experiments were conducted under wet and dry conditions at 925 c and under wet conditions at 850 c both wet and dry recrystallization experiments produced polycrystalline quartzites rutile occurs as inclusions in quartz and as individual crystals dispersed along quartz grain boundaries quartz that grew during the recrystallization experiments has dark cathodoluminescence indicating substantially lower ti concentrations the average ti concentrations in quartz from the recrystallization experiments are within the 95 confidence interval of a linear fit to the 20 kbar data of thomas et al contrib mineral petrol 160 743 759 2010 collectively the results from the synthesis and recrystallization experiments confirm that the ti in quartz concentrations used to calibrate the p t dependencies of ti in quartz solubility in thomas et al s contrib mineral petrol 160 743 759 2010 calibration represent the equilibrium concentrations of ti in quartz

modeling ore generation in a magmatic context abstract magmatic ore deposit models are constructed from a set of measurables e g ore grade fluid composition structure from which important parameters temperature pressure chemistry can be estimated and possible genetic processes can be constrained such models include direct inverse or iterative problems direct problems separately consider an eulerian and a lagrangian formulation in the first case an analytical approach describes the bulk system from an external frame whereas the lagrangian approach provides a description from a discrete element attached to the system conversely inverse problems mostly rely on a system of equations or differential equations their solution requires a matrix inversion using statistical criteria to bracket errors subsequently an iterative approach is adopted commencing with an initial bulk model that is successively refined to fit the observations the direct problem always results in a unique solution though the formulation is highly overdetermined such unique solution highly depends on the input parameters and multiple solutions vary with the initial imposed conditions conversely the inverse problem is underdetermined by construction atlan 2001 accordingly it provides a set of solutions generally identified and separated by statistical tests as exemplified bythe least squares approximation both methods intrinsically ignore feedback loops iterative methods are weak in quantifying the results based on the insights gained from this review we developed a new integrative model for porphyry deposits that relies on the magmatic segregation of metals through a fluid sparging process a formulation under the direct problem basically considers the enrichment factor for groups of metals e g cu mo au a lagrangian approach using a lattice boltzmann model examines metal diffusion from the melt toward an immiscible phase commonly a salty aqueous fluid metals first diffuse in the melt the motion of which slows down when the mush development reduces the porosity thus tapping the mobile fluid phase gas bubbles turn to tubes they offer more mobility and allow the progression of the fluid phase leading to metal advection followed by metal precipitation the quantitative results are poorly constrained owing to the large uncertainties on the input parameters but the metal enrichment factor fits observations from crustal abundance to ore grade levels nevertheless the results aid in designing an inverse approach linking metal enrichment to metal partitioning diffusion and viscous melt motion from this approach a simple diagram can be deduced using a logarithmic scale to smooth the parametric uncertainties the diagram serves to illustrate the link between the above parameters and metal enrichment also explaining differences in ore grade for different metals magma pairs

application of cathodoluminescence to magmatic quartz in a tin granite case study from the schellerhau granite complex eastern erzgebirge germany a model of the cooling history of tin bearing granitic magma forming the schellerhau granites eastern erzgebirge germany is shown on the basis of quartz textures similar grain size similar grain habit and correlatable growth textures of phenocrysts in different granite varieties give proof of a common crystallization history before the melts of the schellerhau granite varieties were intruded four nucleation events occurred during crystallization in different crustal levels between about 20 and 1 km depth the parental melt of the schellerhau granites is interpreted to have contained 2 5 wt h2o originally the water content of the melt during the subvolcanic intrusion stage amounted to more than 5 wt and characterizes highly evolved residual melts that enable the formation of tin deposits this study contributes to a better understanding of the development and behaviour of fractionated tin bearing granitic melts and links quartz cathodoluminescence cl with microanalytical studies

titaniq a titanium in quartz geothermometer titanium is one of many trace elements to substitute for silicon in the mineral quartz here we describe the temperature dependence of that substitution in the form of a new geothermometer to calibrate the titaniq thermometer we synthesized quartz in the presence of rutile and either aqueous fluid or hydrous silicate melt at temperatures ranging from 600 to 1 000 c at 1 0 gpa the ti contents of quartz in ppm by weight from 13 experiments increase exponentially with reciprocal t as described by text log left x text qtz text ti right 5 69 pm 0 02 frac 3765 pm 24 t k application of this thermometer is straightforward typically requiring analysis of only one phase quartz this can be accomplished either by epma for crystallization temperatures above 600 c or by sims for temperatures down to at least 400 resulting temperature estimates are very precise usually better than 5 c potentially allowing detailed characterization of thermal histories within individual quartz grains although calibrated for quartz crystallized in the presence of rutile the thermometer can also be applied to rutile absent systems if tio2 activity is constrained

variscan silicic magmatism and related tin tungsten mineralization in the erzgebirge slavkovský les metallogenic province integration of geochemical mineralogical isotopic and geochronological data with geodynamic considerations suggests that the variscan granites in the erzgebirge slavkovsk les domain originated from repeated melting events and were emplaced over a period of about 40 ma 330 290 ma several lines of evidence exist supporting the idea that erzgebirge granites assigned to different types biotite granites two mica granites strongly peraluminous p rich li mica granites and slightly peraluminous p poor granites are in most cases not genetically related via continuous fractional crystallization from a common magmatic reservoir the genesis of the slavkovsky les granites however might be discussed in terms of an uninterrupted fractionation series geological models of sn w deposits based upon geochemical and structural results imply that the main ore depositional events followed immediately the emplacement and solidification processes of melt via fluid melt immiscibility breccia pipe formation and or pervasive rock fluid interactions

volcanic plutonic connections and metal fertility of highly evolved magma systems a case study from the herberton sn w mo mineral field queensland australia abstract understanding the connection between the highly evolved intrusive and extrusive systems is essential to explore the evolution of high silicic magma systems which plays an important role in discussions of planetary differentiation the growth of continents crustal evolution and the formation of highly evolved magma associated sn w mo mineral systems to discern differences between fertile and non fertile igneous rocks associated with sn w mo mineralization and reveal the genetic links between coeval intrusive and extrusive rocks we integrate whole rock geochemistry geochronology and hf isotope signatures of igneous zircons from contemporaneous plutonic and volcanic rocks from the world class herberton mineral field of queensland australia the 310 300 ma intrusive rocks and associated intra plutonic w mo mineralization formed from relatively oxidized magmas after moderate degrees of crystal fractionation the geochemical and isotopic features of the coeval volcanic succession are best reconciled utilizing the widely accepted volcanic plutonic connection model whereby the volcanic rocks represent fractionated derivatives of the intrusive rocks older intrusions emplaced at 335 315 ma formed from relatively low fo2 magmas that fractionated extensively to produce highly evolved granites that host sn mineralization coeval volcanic rocks of this suite are compositionally less evolved than the intrusive rocks thereby requiring a different model to link these plutonic volcanic sequences in this case we propose that the most fractionated magmas were not lost to volcanism but instead were effectively retained at the plutonic level which allowed further localized build up of volatiles and lithophile metals in the plutonic environment this disconnection to the volcanism and degassing may be a crucial step for forming granite hosted sn mineralization the transition between these two igneous regimes in herberton region over a 30 m y period is attributed to a change from an early compressive tectonic environment with a thickened crust to conditions of crustal thinning and lithospheric extension due to progressive slab rollback such tectonic transitions may provide favorable conditions for intrusion related mineralization given the common occurrence of volcanic and plutonic rocks associated with sn w mo mineralization worldwide we suggest that a combined understanding of temporal tectonic evolution and plutonic volcanic connections can assist in assessment of regional scale mineralization potential which in turn can aid strategies for future ore deposit exploration

millennial timescale resolution of rhyolite magma recharge at tarawera volcano insights from quartz chemistry and melt inclusions most rhyolite eruption episodes of tarawera volcano have emitted several physiochemically distinct magma batches 1 10 km3 these episodes were separated on a millennial timescale the magma batches were relatively homogeneous in temperature and composition at pumice scale 4 cm but experienced isolated crystallisation histories at the sub cm scale matrix glasses have trace element compositions sr ba rb that vary by factors up to 2 5 indicating incomplete mixing of separate melts some quartz hosted melt inclusions are depleted in compatible trace elements sr ti ba compared to enclosing matrix glasses this could reflect re melting of felsic crystals deeper in the crystal pile individual quartz crystals display a variety of cathodoluminescence brightness and ti zoning patterns including rapid changes in melt chemistry and or temperature 50 100 c and point to multi cycle crystallisation histories the tarawera magma system consisted of a crystal rich mass containing waxing and waning melt pockets that were periodically recharged by silicic melts driven by basaltic intrusion

chemical characteristics of zircon from a type granites and comparison to zircon of s type granites abstract the trace element content in zircons from a type granites and rhyolites was investigated by using back scattered electron images and electron microprobe analyses the studied proterozoic wiborg batholith finland and para amazonas and goias states brazil and variscan krusne hory erzgebirge czech republic and germany plutons cover a wide range of rocks from large rapakivi textured geochemically primitive plutons to small intrusions of f li sn nb ta and u enriched rare metal granites while zircon is one of the first crystallized minerals in less fractionated metaluminous and peraluminous granites it is a late crystallized phase in peralkaline granites and in evolved granites that may crystallize during the whole process of magma solidification the early crystals are included in mica quartz and feldspar the late grains are included in fluorite or cryolite or are interstitial the zircon in hornblende biotite and biotite granites from the non mineralized plutons is poor in minor and trace elements the zircon in moderately fractionated granite varieties is slightly enriched in hf th u y and hrees whereas the zircon in highly fractionated ore bearing granites may be strongly enriched in hf up to 10 wt hfo 2 th up to 10 wt tho 2 u up to 10 wt uo 2 y up to 12 wt y 2 o 3 sc up to 3 wt sc 2 o 3 nb up to 5 wt nb 2 o 5 ta up to 1 wt ta 2 o 5 w up to 3 wt wo 3 f up to 2 5 wt f p up to 11 wt p 2 o 5 and as up to 1 wt as 2 o 5 metamictized zircons may also be enriched in bi ca fe and al the increase in the hf content coupled with the decrease in the zr hf value in zircon is one of the most reliable indicators of granitic magma evolution in the zircon of a type granites the zr hf value decreases from 41 67 porphyritic granite to 16 19 equigranular granite in the kymi stock finland and from 49 52 biotite granite to 18 36 leucogranite in the pedra branca pluton brazil in the in situ strongly fractionated cinovec cupola erzgebirge the zr hf value decreases from 33 51 in the protolithionite granite at a depth of 1255 m to 7 5 25 in the zinnwaldite granite at a depth of 40 m at the scale of individual crystals the zr hf value decreases from 86 to 68 from the cores to the rims of the zircons from the teplice rhyolite and from 64 to 33 in the zircons from the biotite granite at krupka erzgebirge the contents of hf and u in zircon are dependent mainly on the degree of granite fractionation and the nature and volume of the volatile phases and are independent of the a or s character of the parental melt the zircon zr hf ratios 55 and 25 are proposed to approximately distinguish common moderately evolved and highly evolved granites zircons from the moderately and highly evolved granites of a and s type can be discriminated on the basis of their hree content and the u th ratios nb ta and w are present in zircon from the highly evolved granites from all studied areas while high as bi and sc contents are typical only for the erzgebirge

rb sr age and geochemical distinctions between the carboniferous tin bearing davis lake complex and the devonian south mountain batholith meguma terrane nova scotia the davis lake complex dlc composed of biotite monzogranite leucomonzogranite and cassiterite topaz greisen hosts the east kemptville tin mine in southwestern nova scotia the dlc monzogranite contains glomeroporphyritic biotite with ilmenite and many rare earth element ree bearing accessory minerals zircon bearing quartz phenocrysts and xenoliths of biotite granite primary muscovite is rare major and trace element geochemical trends indicate well defined but limited magmatic differentiation trends ree patterns of the least evolved granites are flat and show a ce yb ratio of 10 the dlc was previously considered cogenetic with the devonian south mountain batholith smb on the basis of its location lithologies and similarities in major and trace element geochemistry however new rb sr whole rock isotopic data indicate an rb sr date of 330 7 ma mean square of weighted deviates mswd 2 8 for the dlc implying that it is at least 35 ma younger than the smb the initial 87sr 86sr rat

anomalously high sc contents in ore minerals from sn w deposits possible economic significance and genetic implications abstract an investigation on sn w and w deposits and associated granites in the erzgebirge region central kazakhstan mongolian altai and central mongolia reveals anomalously high sc contents up to several thousands of parts per million in wolframite and cassiterite from sn w deposits in the eastern erzgebirge even though whole rock samples of granites from these localities have low sc contents typical of high silica granitic rocks it is possible to trace the distribution of sc in rocks and veins using data on accessory and ore minerals enriched in sc columbite rutile cassiterite wolframite zircon scheelite and mica there are no indications for an enrichment of sc during the magmatic evolution of the granite intrusions magmatic fractionation causes rather low sc contents in evolved granites on the other hand sc enrichment in zircon found in these rocks is clearly related to processes of secondary alteration leading to high u ca and fe besides sc enrichment in the mineral enhanced sc contents were also found in whole rock samples from the greisen the occurrence of sc rich wolframite and cassiterite is mainly restricted to endocontact orebodies greisen and veins outside the rare metal bearing granites the sc content in wolframite drops off if host rocks are formed by schist and gneiss correlation between sc and nb concentrations in wolframite found in endocontact orebodies also disappears in the exocontact veins except if the vein system provides a focused fluid flow sc enrichment in sn w mineralisation is accompanied by strong y sc y yb and th u fractionation in sc bearing minerals as indicated by trace element contents in wolframite and scheelite y sc ratios in wolframite below 0 1 are typical of sn deposits it is suggested that certain conditions of complexation ph and eh in f rich fluids are necessary prerequisites for sc enrichment and deposition our results hint for a sc input into the ore forming system by an external f rich fluid carrying also u and heavy ree and possibly derived from a mantle related source although whole rock samples of rare metal bearing topaz granite have low sc contents the related sn w ores may represent an interesting source for sc extraction because of their enrichment in sc

40 ma of hydrothermal w mineralization during the variscan orogenic evolution of the french massif central revealed by u pb dating of wolframite we present u pb thermal ionization mass spectrometer tims ages of wolframite from several granite related hydrothermal w sn deposits in the french massif central fmc located in the internal zone of the variscan belt the studied wolframite samples are characterized by variable u and pb contents typically 10 ppm and show significant variations in their radiogenic pb isotopic compositions the obtained u pb ages define three distinct geochronological groups related to three contrasting geodynamic settings i visean to namurian mineralization 333 327 ma coeval with syn orogenic compression and emplacement of large peraluminous leucogranites ca 335 325 ma ii namurian to westphalian mineralization 317 315 ma synchronous with the onset of late orogenic extension and emplacement of syn tectonic granites ca 315 310 ma and iii stephanian to permian mineralization 298 274 ma formed during post orogenic extension contemporaneous with the permian volcanism in the entire variscan belt the youngest ages 276 274 ma likely reflect the reopening of the u pb isotopic system after wolframite crystallization and may correspond to late hydrothermal alteration e g ferberitization our results demonstrate that w sn mineralization in the fmc formed during at least three distinct hydrothermal events in different tectono metamorphic settings over a time range of 40 ma

pb pb and u pb zircon dating of subvolcanic rhyolite as a time marker for hercynian granite magmatism and sn mineralisation in the eibenstock granite erzgebirge germany considering effects of zircon alteration tin mineralisation is closely related to rhyolite stocks and dykes which occur in the endo and exocontact of the eibenstock granite erzgebirge germany the same structures which cut the granite control the rhyolite emplacement and the location of ore bearing greisen bodies albitisation and greisenisation related to tin mineralisation as well as sericitisation and argillic alteration may be traced by changes in chemical and mineralogical composition of both rhyolite and granite wall rock comprehensive zircon studies by scanning electron microscopy secondary and backscattered electron as well as cathodoluminescence imaging edx measurements reveal that zircon from rhyolite and from the enclosing granite shows significant changes in chemical composition and crystallinity including distortion of the u pb isotope system when affected by greisenisation single evaporation analysis of zircon from rhyolite with little or no greisenisation gave a 207pb 206pb age of 290 5 ma whereas zircon from little altered granite gave a 207pb 206pb age of 320 8 ma the single evaporation age of zircon from rhyolite is confirmed by 238u 206pb shrimp ages of 297 8 ma the significant time gap of at least 20 ma between granite intrusion and rhyolite formation suggests that the late magmatic evolution of the eibenstock granite cannot be regarded as a source for tin ore forming fluids as previously assumed

skarn formation and tin enrichment during regional metamorphism the hammerlein polymetallic skarn deposit abstract the hammerlein sn rich polymetallic skarn deposit erzgebirge germany which is hosted by variscan schists and gneisses includes garnet amphibole pyroxene and magnetite skarns that formed during regional metamorphism at 340 ma the skarn deposit was overprinted during the intrusion of the ca 320 ma eibenstock granite tin was introduced into the system during regional metamorphism at 340 ma sn mostly hosted in silicate minerals and after the intrusion of the eibenstock granite at c 320 ma sn hosted in cassiterite the emplacement of late stage melts of the eibenstock granite also resulted in the formation of cassiterite quartz veins in the schists hosting the hammerlein skarns and at some distance in the formation of several cassiterite greisen major trace and rare earth element data of the skarn units and their hosts rocks demonstrate that skarns formed from impure carbonates with variable proportions of silicate minerals depending on the original modal compositions of the skarns and their host rocks the mineralizing fluid selectively added and removed elements which resulted for the skarns and the schist ore in a general enrichment in sn in cu and w and a noticeable depletion in al and sr the sr nd and pb isotopic composition of the skarns schists and gneisses resembles those of the metamorphic rocks of the erzgebirge rather than those of the granites possibly indicating that the geochemical signature of granite derived fluids had been severely altered during fluid rock interaction before these fluids reached the skarns schists and gneisses similarly the li and b isotopic composition of the skarn samples reflects the likely range of possible source rocks for metamorphic fluids rather than the composition of the granite derived fluid in contrast the li and b signature of greisen samples shows a variable mixture of material derived from the granite and the metasedimentary rocks respectively our data show that a first sn enrichment took place when the paleozoic sedimentary rocks were affected by regional metamorphism at ca 340 ma fluids derived from these siliciclastic sedimentary protoliths mobilized and transported sn and fe these fluids reacted with the impure carbonates resulting in decarbonation and the formation of calc silicate minerals and biotite in the various skarn types the changing fluid composition as well as the incorporation of fe in skarn silicates and formation of fe oxides resulted in the incorporation of sn into silicate minerals during or after the emplacement of the eibenstock granite the original skarn was to a variable extent retrogressed and sn was released from sn bearing calc silicates and biotite during this event additional sn was added to the skarn and the hosting schists released sn and newly added sn precipitated as cassiterite

magmatic and tectonic evolution of the ladakh block from field studies abstract the ladakh block is in an intermediate position between the indian plate in the south and the karakorum tibetan plate in the north to the west it is separated from the kohistan arc by the nanga parbat syntaxis to the east it is cut off from the lhasa block by the gartok nubra fault present data together with previously published results show that the ladakh block consists of an island arc in the south and a calc alkaline batholith in the north with remnants of a continental crust migmatitic gneisses and metasedimentary sequences such as quartzites and metapelites interbedded with basaltic volcanics and overlain by thick platform carbonates were found as evidence of a continental crust remnants of megafossils megalodon and lithiotis within the high grade metamorphic marbles indicate a probable age of late triassic to early jurassic these sediments were intruded by a faintly layered hornblende gabbro which preceded the calc alkaline magmatic episode gabbro and gabbronorites are found as roof pendants and large inclusions within diorites and granodiorites the major part of the batholith consists of granodiorite and biotite granite plutons ranging from late cretaceous to tertiary associated with the intrusives are volcanic rocks with trachyandesite to alkalibasalt and basalt andesite to rhyolite compositions garnet bearing leucogranites succeeded the emplacement of the major plutons the magmatic stage ended finally by intense fracturing and injections of ne sw striking andesitic dykes the southernmost unit of the ladakh block is formed by oceanic crust with serpentinized peridotite and hornblende gabbro and is covered by volcanics of an island arc type dras volcanics these units are intruded by gabbronorite as well as middle and upper cretaceous granodiorite and coarse grained biotite granite in a plate tectonic view the ladakh block represents a transitional sector between the pure island arc of kohistan in the west and the andean type margin of the lhasa block in the east

tracing metal sources in peribatholitic hydrothermal w deposits based on the chemical composition of wolframite the example of the variscan french massif central abstract we present a complete dataset for major minor and trace elements in wolframite fe mn wo4 based on the example of several peribatholitic hydrothermal w deposits located in the variscan french massif central fmc the wolframite samples were characterized down to the micrometer scale by combining scanning electron microscopy observations and in situ chemical analysis by electron probe microanalyzer and laser ablation inductively coupled plasma mass spectrometry most samples are fe dominated wolframites and are characterized by variable fe fe mn values for the studied deposits from 0 36 to 0 86 without significant alteration features wolframites present intracrystalline variations for concentrations of several minor and trace elements principally for nb ta and sn which reflect growth zoning the minor and trace element compositions of the different wolframite samples show at first order similar enrichments in ta nb sn zn and in as well as depletions in lree li th ti zr hf pb v co and mg compared to the upper continental crust second order compositional variations are observed between the studied deposits which can be separated in four main regional geochemical groups this work highlights that the chemical composition of wolframite is controlled by both the crystallochemical parameters and the composition of the primary hydrothermal fluid the regional variations observed in the geochemical signatures of wolframite reflect local variations in the composition of the hydrothermal fluid i e variable metal sources therefore this suggests that the minor and trace element contents in wolframite likely represent direct markers of the source of the hydrothermal fluid and ultimately of the metals the comparison between the trace element compositions of wolframite with the compositions of regional granitic rocks and worldwide shales suggests that evolved peraluminous granites represent the main source of metals in peribatholitic hydrothermal w deposits from the fmc whereas metasedimentary rocks have a limited to no influence on the metal budget

the invisible hand tectonic triggering and modulation of a rhyolitic supereruption identifying the processes that initiate and control large explosive eruptions on time scales of human interest is challenging we present evidence for syneruptive subsurface interactions between rhyolite magmas derived from distinctive sources that reflect tectonic processes starting then temporarily stopping the 27 ka oruanui supereruption 530 km 3 magma taupo new zealand subordinate 3 16 biotite bearing pumice lapilli occur in fall deposits from phases 1 and 2 of 10 among the biotite free normal pumices in the oruanui deposits the biotite bearing magma is sourced to an independent magmatic system 10 15 km northeast of taupo lateral migration of the biotite bearing magma was initiated during a rifting episode that also triggered the oruanui eruption limited physical mingling indicates that the biotite bearing and oruanui biotite free magmas interacted in the conduit simultaneously with eruption after phase 1 a time break of months elapsed before phase 2 explosive activity resumed from the same vent again with intermixed biotite bearing magma a rift related tectonic event with its accompanying stress change is inferred to have initiated diking from northeast to southwest transporting biotite bearing magma and triggering the oruanui eruption stress relaxation following the rifting event terminated phase 1 before a tectonic event caused renewed diking and activity in phase 2 tectonics may trigger large silicic eruptions through rupturing of shallow crustal magma chambers and lateral magma transport especially in extensional regimes without necessarily leaving any discernible geological imprint only the presence of a foreign magma in the oruanui deposits allows the tectonic control to be identified

alkali feldspars as a main phosphorus reservoirs in rare metal granites three examples from the bohemian massif czech republic phosphorus rich alkali feldspars were found in three peraluminous highly differentiated albite topaz li mica granites in the w and s parts of the bohemian massif the average contents of p2o5 in k feldspars k i ovy kamen 0 57 wt homolka 0 77 wt and podlesi 0 83 wt are higher than the average contents of p2o5 in albites k i ovy kamen 0 23 wt homolka 0 23 wt and podlesi 0 39 wt the analyses of feldspars indicate that partition coefficient of phosphorus between k feldspar and albite range from 1 5 to 2 5 measured data in k feldspars suggest a statistically significant difference from the al3 p5 2 si4 substitution mechanism for higher phosphorus concentration the p content in k feldspars from the podlesi granite represent the highest p content in natural feldspar known to date up to 2 5 wt of p2o5 it is suggested that all studied granites retained nearly all phosphorus of granitic melts and that their alkali feldspars represent major reservoirs of phosphorus

micro analytical perspectives on the bishop tuff and its magma chamber new in situ major and trace element analytical data are presented for crystals sanidine plagioclase biotite orthopyroxene clinopyroxene and matrix glasses from juvenile materials representing the full bishop tuff sequence from the earliest fall unit f1 to the latest ignimbrite package ig2nc these data are combined with published information to investigate the nature and zonation of the pre eruptive bishop magma chamber our data confirm that this magma chamber was a single unitary body that was thermally and compositionally zoned the zonation was largely established prior to the growth of crystals and also prior to mixing in the lower parts of the chamber induced by late stage intrusion of a magma of contrasting composition and slightly higher temperature the bright rim magma sparse mixed swirly and dacitic pumices show enrichments in ba sr and ti that identify these pumices as possible representatives of the bright rim magma a model revised from previously published work for the pre eruptive magma chamber comprises three main parts 1 an upper volumetrically dominant 2 3 relatively unzoned region that was the source of the earlier eastern erupted ignimbrite units and their coeval fall units 2 a volumetrically minor transition zone that shows evidence for minor degrees of mixing and was the dominant source for the latest eastern erupted part of ig1eb sherwin subunit and the earlier part of the northern erupted ignimbrite ig 2na 3 a lower volumetrically subordinate 1 3 region that was affected by mixing with the bright rim invasive magma in the lead up to the eruption and fed later northern erupted units ingress of the bright rim magma introduced orthopyroxene and bright rimmed zircon crystals and induced partial resorption then overgrowth of rims enriched in ti sr and ba on sanidine and quartz and development of zoning in clinopyroxene based on pumice proportions and associated crystal and glass chemistries through the eruptive sequence we infer that the roof and floor of the magma chamber were stepped down to the north such that the transition zone magma formed the floor of the southern part of the melt dominant chamber and the roof of the northern part our data reinforce the previous concept of a single compositionally and thermally zoned bishop magma chamber and additionally support a temporally constrained role for pre eruptive magma mixing and the introduction of melts and minerals with contrasting compositions to the resident bishop magma

geo tectonic framework of the himalaya of n pakistan in the karakorum range there is a structurally complicated cretaceous are comprising the kohistan sequence on its northern side the northern suture consists of a mega melange and is bounded to the s by tightly folded pillow bearing volcanics and sediments to the s the kohistan plutonic belt consists of southwards a early foliated and late post tectonic tonalites and diorites b aplites and pegmatites up to 30 of rock volume c basic dykes up to 10 m thick d the chilas complex a stratiform cumulate body over 300 km long and 8 km thick chromite layered dunites gabbros and norites with a low pressure granulite facies mineral fabric of tectonic origin e an amphibolite belt with a complex mixture of other rocks and f the jijal complex a 200 km 2 tectonic wedge of high pressure granulites and chromite layered dunites cumulate graded units in the chilas complex show that it is folded by an isoclinal anticline f 1 the mid upper crust of the are is folded by a 50 km half wavelength f 2 syncline the whole kohistan sequence with its two phases of isoclinal folds was tilted during himalayan collision so that the structures are now subvertical the southern suture main mantle thrust has a wedge of glaucophane schists the indian plate contains a basement of psammites and schists intruded by cambrian granites and overlain by isoclinally folded and metamorphosed carbonates and shales

the variation of cesium and 37 other elements in the sardinian granite batholith and the significance of cesium for granite petrogenesis a suite of granites from the hercynian batholith of sardinia italy was analysed for cesium and 37 other major and trace elements factor analysis was used to identify inter element associations in this set of data cesium is shown to be closely associated with tin lithium and rubidium and less closely with beryllium and thallium but it shows no correlation with any of the major elements the role of crystal fractionation magma mixing and the process of partial melting in the magmatic source region are examined as possible controls of cs distribution the pattern of element associations revealed by factor analysis eliminates crystal fractionation and magma mixing as the main cause of magmatic variation the variation in cs is considered to be primary in origin i e it originated in the magmatic source region the relationship between cs and other elements was mainly determined by the relative proportions of mica and feldspar entering the melt during anatexis

cassiterite u pb geochronology constrains magmatic hydrothermal evolution in complex evolved granite systems the classic erzgebirge tin province saxony and bohemia

isotopic study of the manaslu granite himalaya nepal inferences on the age and source of himalayan leucogranites a detailed isotopic study of the manaslu leucogranite was carried out a u pb age of 25 ma and a whole rock rb sr age isochron of 18 ma were obtained suggesting that the magmatic activity lasted at least 7 ma initial sr isotopic ratios are very high 0 740 to 0 760 and initial nd isotopic ratios are low nd in 13 to 16 and they show the existence of large isotopic variations even at the metre scale these are not the result of perturbations by fluids but rather they reflect the initial isotopic heterogeneity of the source material which has not been obliterated by magmatic processes e g fusion mixing by convection these results also support the crustal origin of this leucogranite the tibetan slab paragneisses whose sr and nd isotopic ratios are very similar to those of the granite at an age of 20 ma are the most probable parental material nd model ages for both the leucogranite and the gneisses are in the range 1 5 2 ga a model of formation of the manaslu granite by coalescence of different batches of magma is in agreement with the present data

the hammerlein skarn hosted polymetallic deposit and the eibenstock granite associated greisen western erzgebirge germany two phases of mineralization two sn sources the hammerlein polymetallic deposit is hosted in skarn schists and gneisses that reached their metamorphic peak at 340 ma during the variscan orogeny the deposit is spatially closely associated with one of the most voluminous granites of the erzgebirge the eibenstock granite which intruded the metamorphic units at 320 ma and locally also developed greisen mineralization cassiterite is the main ore mineral in the hammerlein skarn and in greisen mineralizations associated with the eibenstock granite the age of skarn formation is bracketed by multi mineral rb sr isochron ages of the gneisses 340 ma and the end of ductile deformation 330 ma the dated calc silicate minerals of the skarn have elevated sn contents which implies that some sn was present in the system during regional metamorphism i e well before the emplacement of the eibenstock granite tin in the 330 ma old skarn silicates possibly was mobilized from the metamorphic wall rocks retrogression of the skarn mineral assemblage may have released some sn that formed cassiterite in an assemblage with chlorite and fluorite the sr isotope signatures of fluorite indicate that this late assemblage is not related to cooling of the metamorphic rocks but to the emplacement of the eibenstock granite which introduced additional sn into the skarn thus mineralization in the hammerlein deposit includes sn that was introduced during two different events from different sources

magmatic hydrothermal transition of mo w mineralized granite pegmatite greisen system recorded by trace elements in quartz krupka district eastern krusne hory erzgebirge abstract magmatic hydrothermal transition of highly evolved granitic melts enriched in volatile and incompatible elements can involve disequilibrium intermediate products between aluminosilicate melt and hydrothermal fluid hydrosilicate liquids with high ore forming potential we investigate evolution from li f rich granites through pegmatites greisens and quartz veins in a composite stock at knottel in the krupka district eastern krusne hory erzgebirge mountain range by monitoring trace element variations in quartz interelemental correlations reveal si4 li al3 and likely si4 h al3 to be the most important substitution mechanisms variations in ti vs li be and al define distinct evolutionary trends i magmatic high li ti or al ti trend granites aplites k feldspar pegmatite ii transitional medium li ti trend quartz megacrysts and pegmatite lenses in granite quartz protolithionite pegmatite iii hydrothermal low li ti or al ti trend stockwork of coarse grained hydrothermal quartzites and quartz veins quartz replacement in greisens the medium li ti trend represents hydrosilicate liquid an h2o and sio2 rich medium with low density and effective viscosity that was probably formed during disequilibrium crystallization in front of rapidly propagating solidification front thermal evolution of the magmatic hydrothermal system was monitored by ti in quartz thermometry calculated rutile activity of the granites is very low 0 3 0 05 but it increases up to 1 that is saturation towards pegmatites and hydrothermal veins magmatic crystallization granites and aplites is constrained to 700 580 c pegmatite and bulk greisenization stage occurred at 600 500 c followed by a late hydrothermal stage associated with the formation of distal quartz veins at 500 390 c the granite pegmatite systems at knottel and in erzgebirge in general reach extremely high al li rb and ge and low ti concentrations in quartz in comparison with igneous rocks worldwide the knottel stock belongs to p poor a type granites in the erzgebirge and is linked with them by similar evolutionary trends in quartz trace elements furthermore the knottel system exhibits be enrichment in quartz probably related to high contents of f and this appears to be typical feature of mo w mineralized systems in general the hydrothermal phase with mo w mineralization at knottel is closely related to the magmatic phase of parental granite body which seems to be an important condition for mo w mineralization formation

precise electron microprobe age determination in altered uraninite consequences on the intrusion age and the metallogenic significance of the kirchberg granite erzgebirge germany an integral method of data evaluation for chemical dating of accessory uraninite by electron microprobe analysis and electron microscopy is proposed the internal structure of uraninite grains the contents of si ca and fe and tests for loss or gain of pb and u are suitable criteria to decide whether or not a given crystal area was affected by secondary alteration the method was applied to uraninite from the kirchberg granite erzgebirge germany and an age of 330 5 ma 2 was constrained this result supports earlier assumptions that there were at least two events of hercynian granite magmatism separated by a time gap of about 40 ma and that the magmatic evolution of the kirchberg granite is not related to the formation of the w mineralisation developed in the endocontact of this granite secondary alteration of uraninite is probably closely related to the formation of u deposits in the vicinity of the kirchberg massif which was extensively mined in the past

geology and mineralization of the uchkoshkon tin deposit associated with a breccia pipe eastern kyrgyzstan abstract the uchkoshkon tin deposit is one of the largest deposits in the sn w saryjaz ore district of eastern kyrgyzstan the district coincides spatially with the saryjaz syntaxis which is the narrowest portion of the south tien shan collisional belt the syntaxis is distinguished by collisional thrust tectonics and postcollisional a type granite magmatism of permian age the uchkoshkon deposit is in the exocontact zone of a 260 km 2 273 279 ma ilmenite series high heat production biotite granite pluton a satellite granite stock 400 250 m and an explosive breccia pipe 450 150 m crosscutting the stock are the central structural features of the deposit area the main stock accompanied by li f felsite dykes controlled early stage mo w and sn w greisen stockwork mineralization that surrounds the apical portion of the stock the breccia pipe postdates the emplacement of the li f felsite dykes and greisen stockwork mineralization the pipe is rooted in main pluton and has been traced by a borehole to a depth of 800 m the breccia was injected by a swarm of tree like branching dykes with diffuse contours consisting of k and b rich rhyolite porphyry cementing the breccia fragments the main breccia body has been intruded by a much smaller 150 100 m hydrothermal breccia pipe with quartz tourmaline matrix which immediately preceded main stage lode mineralization the majority of the lodes occur outside the breccia pipe within a zone of pervasive scapolitization that surrounds the main pluton the main stage lodes are represented by quartz tourmaline cassiterite veins with minor sulfides which occupy a series of steeply dipping near parallel north northeast trending shear fractures that are related to postcollisional strike slip tectonics where quartz tourmaline cassiterite veins crosscut moderately dipping skarn deposits the latter are commercially mineralized with cassiterite nordenskioldine and borosilicate minerals the formation of both explosive breccia and main stage lode mineralization was related to the evolution of b and h 2 o rich residual magma deep within the main pluton the suggested formation model of the uchkoshkon tin deposit is generally applicable to other major sn and sn w deposits in the saryjaz ore district

ascent driven crystallisation of dacite magmas at mount st helens 1980 1986 we introduce a novel scheme that enables natural silicic glasses to be projected into the synthetic system qz ab or h2o in order to relate variations in volcanic glass chemistry to changing pressure p and temperature t conditions in the sub volcanic magma system by this means an important distinction can be made between ascent driven and cooling driven crystallisation under water saturated or undersaturated conditions in samples containing feldspar and a silica phase quartz or tridymite quantitative p t estimates of the conditions of last equilibrium between crystals and melt can be made formation of highly silicic melts i e 77 wt sio2 is a simple consequence of the contraction of the silica phase volume with decreasing pressure such that high silica glasses can only form by crystallisation at low pressure resorption of quartz crystals appears to be a further diagnostic feature of decompression crystallisation groundmass and inclusion glasses in dacites from the 1980 1986 eruption of mount st helens volcano wa span a wide range in sio2 68 80 wt anhydrous the compositions of the least evolved sio2 poor inclusions in amphibole phenocrysts record entrapment of silicic liquids with 5 4 wt water corresponding to a water saturation pressure of 200 mpa at 900 c the compositions of more evolved higher sio2 plagioclase hosted inclusions and groundmass glasses are consistent with extensive ascent driven fractional crystallisation of plagioclase oxide and orthopyroxene phenocrysts and microlites to low pressures during this polybaric crystallisation plagioclase phenocrysts trapped melts with a wide range of dissolved water contents 3 5 5 7 wt magmas erupted during the plinian phase of the 18 may 1980 eruption were derived from a large reservoir at depths of 6 km subsequent magmas ascended to varying depths within the sub volcanic system prior to extraction from glass chemistry and groundmass texture two arrest levels have been identified at depths of 0 5 1 and 2 4 km a single dome sample from february 1983 contains groundmass plagioclase tridymite and quartz testifying to temperatures of at least 885 c at 11 mpa these shallow storage conditions are comparable to those in the cryptodome formed during spring 1980 the corresponding thermal gradient 0 2 c mpa 1 is consistent with near adiabatic magma ascent from 8 km we argue that the crystallisation history of mount st helens dacite magma was largely a consequence of decompression crystallisation of hot magma beyond the point of water saturation this challenges the conventional view that phenocryst crystallisation occurred by cooling in a large magma chamber prior to the 1980 1986 eruption because the crystallisation process is both polybaric and fractional it cannot be simulated directly using isobaric equilibrium crystallisation experiments however calculation of the phase proportions in water saturated 910 15 c experiments by rutherford et al 1985 over the pressure range 220 125 mpa reproduces the crystallisation sequence and phenocryst modes of mount st helens dacites from 18 may 1980 by allowing for the effects of fractional versus equilibrium crystallisation entrained residual source material and small temperature differences between nature and experiment phase compositions can also be matched to the natural samples we conclude that decompression of water saturated magma may be the dominant driving force for crystallisation at many other silicic volcanic centres

trace element composition of quartz from the variscan altenberg teplice caldera krusne hory erzgebirge mts czech republic germany insights into the volcano plutonic complex evolution abstract in this study the internal structures and appropriate trace element distributions within quartz grains were investigated using a laser ablation icp ms technique combined with a hot cathode and scanning cathodoluminescence analysis the studied variscan magmatic suite is located in the altenberg teplice caldera eastern krusne hory erzebirge along the czech republic germany border and composed of co magmatic volcanics peraluminous basal rhyolite and associated dacite overlying three units of subaluminous teplice rhyolite and granite porphyry and plutonic granites two intrusions of a type biotite and zinnwaldite granites the trace element distribution in the granite porphyry and rhyolite quartz demonstrates a distinct zoning in the cathodoluminescence images and chemical compositions the core is poor in ti the outer rim zones are enriched in ti and the trends recorded for al are opposite to those of ti the quartz from granites is either very weakly zoned or homogeneous based on the chemical composition of quartz and its zoning we assume that the quartz crystals began to crystallize gradually in the primary deep seated magma chamber with a p t condition of 10 kbar and 750 c and in an environment with an increasing concentration of al and decreasing concentration of ti the early stage was followed by the subsequent adiabatic ascent into a shallow magma chamber estimated by the ti in quartz thermobarometry at approximately 700 c 2 kbar during which crystal rims rich in ti formed and then extruded after the caldera collapse part of the magma intruded as granite and in the environment of the residual melt rich in water and flux agents late quartz grew in the form of snowball quartz with an increased al content and decreased ti content

variscan metagranitoids in the central tauern window eastern alps austria and their role in the formation of the felbertal scheelite deposit abstract the w mineralised early carboniferous orthogneisses k1 and k3 orthogneiss in the felbertal scheelite deposit represent a chemically evolved metagranitoid series some of its characteristics are high concentrations of f n ho n 1 93 2 81 the systematic chemical trends documented for a multitude of elements e g sio 2 tio 2 p 2 o 5 ba nb ta and their respective ratios e g 1 tio 2 nb ta zr hf indicate that crystal melt fractionation controlled the evolution of the granitic melts the higher differentiated peraluminous light coloured k1 k3 variety asi 0 99 1 08 nb ta 5 7 zr hf 13 18 evolved from the less differentiated metaluminous dark coloured variety asi 0 93 1 03 nb ta 6 10 zr hf 18 24 peraluminous holo leucocratic aplite gneiss represents the most evolved member of the series asi 1 11 1 12 nb ta 4 zr hf 9 10 modelling of magmatic differentiation assuming rayleigh fractionation shows that c 70 90 of the residual granitic magma had crystallised at the time of the emplacement of the aplites when compared to barren metagranitoids in the central tauern window zentralgneis the metaluminous dark coloured k1 k3 orthogneiss shows some geochemical similarities with the peraluminous felbertauern augengneiss one of the regional orthogneisses exposed near the w deposit elevated concentrations of nb

metamorphism of an obducted island arc example of the kohistan sequence pakistan in the himalayan collided range in northern pakistan the extraordinary 40 km thick kohistan sequence of metamorphosed mafic ultramafic and calc alkaline layered plutonic and volcanic mainly andesitic to rhyodacitic rocks has been recently reinterpreted as the only complete vertical section of an intra oceanic island arc presently exposed anywhere in the world plate scale models have been suggested to explain the origin and the tectonic evolution of this arc in the himalayan collision range despite some noticeable differences in the models there is general agreement that the kohistan sequence represents the crust of an arc obducted onto the northern edge of the indian plate before the oligocene collision of india against asia new data on the tectonometamorphic evolution of the kohistan sequence have led to the conclusion that a first major d 1 event developed with increasing metamorphic grades oriented downward the kohistan pile but also toward ensandwiched basic ultrabasic granulitic rocks rare geochronological data and petrological evidence indicate that the latter granulites pyriclasites and various plagiopyrigarnites pyrigarnites metatroctolites metawebsterites metadunites etc were parts of enormous lower to middle cretaceous layered calc alkaline plutons emplaced during the arc building stages as the d 1 metamorphic event is correlated with the upper cretaceous obduction process of the kohistan onto india it is proposed that the d 1 thermal structure was strongly controlled by remnant magmatic heat source s within the obducted arc this interpretation fits nicely with recent theoretical thermal models since the obduction of the arc was probably shortly after 10 20 ma the emplacement of the former plutonic arc rocks a blueschist tectonic melange underlying the obducted arc was possibly synchronous to the obduction and not clearly linked to the older subductive process the oligocene collision of india against asia was associated with a barrovian overprinting metamorphism in the kohistan arc during this second event the dynamo thermal structure was much more classical and not controlled by the occurrence of the cretaceous metaplutonic rocks a tentative model of the thermal structures during the major events which affected the kohistan arc is proposed

behavior of trace elements in quartz from plutons of different geochemical signature a case study from the bohemian massif czech republic article i nfo in this study the trace element content in igneous quartz from granitoids of different geochemical types was investigated using the laser ablation icp ms technique the variscan granitoids in the bohemian massif pro vide an excellent opportunity to study the chemical composition of magmatic quartz from the following granite types 1 geochemically primitive i type tonalites and granodiorites 2 peraluminous s type two mica granites 3 moderately fractionated a type volcano plutonic complexes of the teplice caldera and 4 highly fractionated s and a type rare metal granites this diversity of granitoids permitted the study of the chemical composition of magmatic quartz as the result of i different magma protoliths and ii variable degrees of differentiation there were only small differences in the quartz trace element con tents ranging from weakly to moderately differentiated plutons of all geochemical types al mostly in the range between 20 and 250 ppm ti mostly 20 110 ppm b b13 ppm be b0 7 ppm ge b1 ppm li b30 ppm and rb b2 ppm only the s type granites from western erzgebirge contain al enriched quartz mostly 200 400 ppm al since the beginning of its evolution however quartz from the highly fractionated granites group 4 differs significantly this quartz is generally poor in ti b20 ppm ti and enriched in al up to 600 ppm in a type and up to 1000 ppm in s type granites be up to 3 2 ppm ge up to 5 7 ppm li up to 132 ppm particularly in the s type granites and rb up to 15 ppm the contents of the analyzed lithophile elements in the quartz from the highly fractionated granites are similar to the contents reported to be present in evolved complex pegmatites although the input of ti into quartz is controlled mainly by the temperature and pressure of quartz crystallization the entry of al into quartz increases as a function of the water and fluorine content of the residual melt the contents of ge and li increase significantly with the fractionation of parental melt the concentrations of these elements in quartz from highly fractionated granites are controlled by the order of crystallization of the major minerals comb quartz crystallizing before li mica is strongly li enriched whereas groundmass and snowball quartz crystallizing after mica is relatively enriched in ge

magma residence and eruption at the taupo volcanic center taupo volcanic zone new zealand insights from rhyolite melts geobarometry diffusion chronometry and crystal textures the taupo volcanic center tvc taupo volcanic zone tvz new zealand is home to the two most recent silicic caldera forming eruptions in the tvz the giant 530 km3 dre oruanui supereruption and the large 35 km3 dre taupo eruption this offers a unique opportunity to investigate similarities and differences between large and supersized volumes of rhyolitic magma at the tvc and more generally we combine information from crystal textures crystal size distributions crystal compositions ti in quartz diffusion chronometry and glass compositions rhyolite melts geobarometry to investigate the crustal storage conditions longevity and eruption of these magmas results show differences between the storage depths of the oruanui and taupo magmas consistent with the differences in their glass silica contents but strikingly similar short crustal residence times for the final crystal poor eruptible magma bodies decades to centuries differences in groundmass textures between the two systems also likely reflect differences in ascent durations decompression paths and or amounts of undercooling experienced by these systems due to the differences in their storage depths finally comparing the evolution of storage depths and magma compositions at the tvc with those in a preceding central tvz ignimbrite flare up supports the idea that the modern tvc may be flaring up and highlights the evolution of magma storage depths with increasing system maturity in this volcanic region