a compositional tipping point governing the mobilization and eruption style of rhyolitic magma measurements of the composition dependent viscosity of rhyolitic magma reveal a tipping point that changes the physical properties of the melt and controls the transition between effusive and explosive eruptions calcalkaline rhyolites produce the largest explosive volcanic eruptions but these eruptions can switch repeatedly between being effusive and explosive this is difficult to attribute to the rheological effects of magma water content or crystallinity danilo di genova and co authors report the viscosity of a series of melts spanning the compositional range of the yellowstone rhyolitic volcanic system they find that within a narrow compositional zone melt viscosity increases by up to two orders of magnitude which they propose to be the consequence of melt structure reorganization the authors confirm that such a compositional tipping point exists in the global geochemical record of rhyolites which separates effusive from explosive deposits they conclude that the anhydrous water free composition of calcalkaline rhyolites is decisive in determining mobilization and eruption dynamics of the earth s largest volcanic systems the most viscous volcanic melts and the largest explosive eruptions1 on our planet consist of calcalkaline rhyolites2 3 these eruptions have the potential to influence global climate4 the eruptive products are commonly very crystal poor and highly degassed yet the magma is mostly stored as crystal mushes containing small amounts of interstitial melt with elevated water content5 it is unclear how magma mushes are mobilized to create large batches of eruptible crystal free magma further rhyolitic eruptions6 7 8 can switch repeatedly between effusive and explosive eruption styles and this transition is difficult to attribute to the rheological effects of water content or crystallinity9 10 here we measure the viscosity of a series of melts spanning the compositional range of the yellowstone volcanic system and find that in a narrow compositional zone melt viscosity increases by up to two orders of magnitude these viscosity variations are not predicted by current viscosity models11 12 and result from melt structure reorganization as confirmed by raman spectroscopy we identify a critical compositional tipping point independently documented in the global geochemical record of rhyolites at which rhyolitic melts fluidize or stiffen and that clearly separates effusive from explosive deposits worldwide this correlation between melt structure viscosity and eruptive behaviour holds despite the variable water content and other parameters such as temperature that are inherent in natural eruptions thermodynamic modelling demonstrates how the observed subtle compositional changes that result in fluidization or stiffening of the melt can be induced by crystal growth from the melt or variation in oxygen fugacity however the rheological effects of water and crystal content alone cannot explain the correlation between composition and eruptive style we conclude that the composition of calcalkaline rhyolites is decisive in determining the mobilization and eruption dynamics of earth s largest volcanic systems resulting in a better understanding of how the melt structure controls volcanic processes

the ad 1362 oraefajokull eruption s e iceland physical volcanology and volatile release abstract the explosive rhyolitic eruption of oraefajokull volcano iceland in ad 1362 is described and interpreted based on the sequence of pyroclastic fall and flow deposits at 10 proximal locations around the south side of the volcano oraefajokull is an ice clad stratovolcano in south central iceland which has an ice filled caldera 4 5 km diameter of uncertain origin the main phase of the eruption took place over a few days in june and proceeded in three main phases that produced widely dispersed fallout deposits and a pyroclastic flow deposit an initial phase of phreatomagmatic eruptive activity produced a volumetrically minor coarse ash fall deposit unit a with a bi lobate dispersal this was followed by a second phreatomagmatic possibly phreatoplinian phase that deposited more fine ash beds unit b dispersed to the sse phases a and b were followed by an intense climactic plinian phase that lasted 8 12 h and produced unit c a coarse lapilli pumice clast dominated fall deposit in the proximal region at the end of plinian activity pyroclastic flows formed a poorly sorted deposit unit d presently of very limited thickness and exposed distribution much of eastern iceland is covered with a very fine distal ash layer dispersed to the ne this was probably deposited from an umbrella cloud and is the distal representation of the plinian fallout a total bulk fall deposit volume of 2 3 km3 is calculated 1 2 km3 dre pyroclastic flow deposit volumes have been crudely estimated to be

combining in situ isotopic trace element and textural analyses of quartz from four magmatic hydrothermal ore deposits this study couples in situ 16o 17o and 18o isotope and in situ trace element analyses to investigate and characterize the geochemical and textural complexity of magmatic hydrothermal quartz crystals euhedral quartz crystals contemporaneous with mineralization were obtained from four magmatic hydrothermal ore deposits el indio au ag cu deposit summitville au ag cu deposit north parkes cu au deposit and kingsgate quartz mo bi w deposit the internal features of the crystals were imaged using cathodoluminescence and qualitative electron microprobe maps quantitative isotopic data were collected in situ using 157 nm laser ablation inductively coupled plasma mass spectrometry for 40 trace elements in quartz and sensitive high resolution ion microprobe for 3 isotopes in quartz imaging revealed fine oscillatory zoning sector zoning complex macromosaic textures and hidden xenocrystic cores in situ oxygen isotope analyses revealed a 18o range of up to 12 4 0 3 in a single crystal the largest isotopic range ever ascribed to oscillatory zonation in quartz some of these crystals contain a heavier 18o signature than expected by existing models while sector zoned crystals exhibited strong trace element variations between faces no evidence for anisotropic isotope fractionation was found we found 1 isotopic heterogeneity in hydrothermal quartz crystals is common and precludes provenance analysis e g d 18o using bulk analytical techniques 2 the trace element signature of quartz is not an effective pathfinder toward noble metal mineralization and 3 in three of the four samples both textural and isotopic data indicate non equilibrium deposition of quartz

in situ oxygen isotope trace element and fluid inclusion evidence for a primary magmatic fluid origin for the shell shaped pegmatoid zone within the giant dahutang tungsten deposit jiangxi province south china abstract the world class dahutang tungsten deposit is located within the jiuling mining district of the central jiangnan orogenic belt jiangxi province china the deposit consists of a massive and gently dipping scheelite orebody that contains disseminated and veinlet hosted mineralization located within a medium to coarse grained biotite granodiorite the no 1 ore block of the deposit also contains a 1 50 1 75 m thick shell shaped pegmatoid zone that defines an inner contact zone between the mineralization related porphyritic like biotite granite and strongly mineralized biotite granodiorite that hosts the tungsten deposit this pegmatoid zone contains very low concentrations of tungsten but records the processes involved in the migration and enrichment of this element within the deposit the pegmatoid contrasts with typical hydrothermal pegmatite type ore in that it often contains megacrystic to giant alkali feldspar quartz and muscovite and is spatially zoned in terms of unique texture and composition the pegmatoid is zoned from a felsic aplite zone with a layered texture proximal to the intrusion through quartz feldspar pegmatoid and feldspar quartz pegmatoid zones to a final distal quartz dominated zone the quartz feldspar pegmatoid is striped and contains megacrystic feldspars that have grown nearly perpendicular to the edge of the pegmatoid indicating the direction of movement of early exsolved magmatic fluids cathodoluminescence imaging indicates that there are five types of quartz within the feldspar quartz pegmatoid megacrystic large phenocrystic small phenocrystic matrix and vein hosted quartz each of these generations of quartz crystallized early with the disseminated metasomatic quartz that crystallized during the middle stages of pegmatoid generation being followed by the uniform crystallization of late stage space filling quartz in situ oxygen isotopic and trace element analysis indicates that all of the quartz within the pegmatoid records accelerated growth with the middle stage disseminated metasomatic quartz associated with an increase in 18oquartz values and the late stage space filling quartz associated with a decrease in 18oquartz values all of this quartz contains elevated concentrations of alkali metals and has low li al ratios generally 10 reflecting the fact that the fluids that formed these minerals were of the peraluminous granite water pgw the trace element compositions of the samples analyzed during this study also indicate a drop in the ph of the pegmatoid forming fluids over time the quartz within the feldspar quartz pegmatoid also contains melt and gas liquid fluid inclusions with the latter containing significant amounts of gas phase ch4 indicating that the pegmatoid formed from low oxygen fugacity fluids our data indicate that the shell shaped pegmatoid zone within the dahutang no 1 ore block formed from primary pgw exsolved from the hosting intrusion with the pegmatoid recording the transition from magmatic to hydrothermal processes during the continuous but multi stage evolution of the dahutang deposit the late stage high temperature water rich high 18o alkali metal rich low oxygen fugacity and acidic nature of the hydrothermal fluids that formed the deposit promoted the transportation and further deposition of tungsten

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

a melt inclusion study of the toba tuffs sumatra indonesia the toba caldera in northern sumatra indonesia is the site of earth s largest quaternary volcanic eruption this eruption dated at 74 ka produced the 2800 km3 youngest toba tuff ytt and ash fall quartz bearing silicic pumices ranging from 68 to 77 wt sio2 indicate that the ytt magma was zoned compositionally and mineralogically prior to the ytt eruption two other silicic quartz bearing tuffs known as the middle toba tuff mtt and the oldest toba tuff ott were erupted from toba at 0 501 ma and 0 840 ma respectively although the volatile contents of the toba magmas are poorly constrained aerosols generated by the ytt eruption are generally thought to have caused a global volcanic winter an evaluation of the pre eruptive dissolved gas contents of the ytt magma is fundamental to understanding the global effects of this eruption we used melt inclusions in quartz crystals to determine the dissolved h2o co2 s cl and f contents of the ytt mtt and ott magmas quartz crystals selected from pumice blocks and welded tuffs that spanned the compositional ranges of the three units were chosen for study major and trace element analyses of melt inclusions were also conducted to characterize melt evolution and provide context to the volatile data melt inclusions from the ytt mtt and ott are rhyolitic in composition 73 77 wt sio2 and have overlapping indistinguishable major element trends inclusions from the large eruptions ytt and ott have similar geochemical relationships where the most evolved melt inclusions occur in the least silicic bulk rock samples and are more evolved than their matrix glasses in contrast the least evolved melt inclusions occur in the most silicic samples and either overlap with or are less evolved than their matrix glasses these patterns can be explained if quartz crystals in the least silicic magmas were inherited from more evolved melt while those in the most silicic melt formed in situ several lines of evidence suggest that crystal settling of early formed quartz crystals in long lived magma bodies was an important process in the ytt and ott magmas trace element data from the ytt melt inclusions have wide ranges rb 250 830 ppm ba 10 485 ppm and mostly support these models however incompatible trace elements are enriched 2 3 over their matrix glass compositions in all samples in the smaller mtt melt inclusions overlapped with the compositional range of the bulk rock samples and are consistent with in situ crystallization ftir analyses indicate that the ytt mtt and ott melts contained about 4 0 5 5 2 0 5 5 and 2 0 5 5 wt h2o respectively co2 contents in all units are generally 100 ppm and cl is 2000 ppm water gradients occur in all 3 tuffs cl gradients are evident only in the ytt and the least silicic samples from all units had no detectable co2 sulfur contents in melt inclusions are low in all samples 32 ppm and overlap with matrix glass s contents applying broad degassing constraints about 1014 g of h2so4 aerosols were likely loaded into the atmosphere during the ytt eruption 2 orders of magnitude less than previous petrologic estimates considerably more cl and f about 1015 g of each may have been part of the ytt aerosol cloud

explosive subglacial rhyolitic eruptions in iceland are fuelled by high magmatic h2o and closed system degassing rhyolitic eruptions beneath icelandic glaciers can be highly explosive as demonstrated by quaternary tephra layers dispersed throughout northern europe however they can also be small and effusive a subglacial rhyolitic eruption has never been observed so behavioral controls remain poorly understood and the influence of pre eruptive volatile contents is unknown we have therefore used secondary ion mass spectrometry to characterize pre eruptive volatile contents and degassing paths for five subglacial rhyolitic edifices within the torfajokull central volcano formed in contrasting styles of eruption under ice 400 m thick this includes the products of the largest known eruption of icelandic subglacial rhyolite of 16 km 3 at ca 70 ka we find pre eruptive water contents in melt inclusions h 2 o mi of up to 4 8 wt which indicates that icelandic rhyolite can be significantly more volatile rich than previously thought our results indicate that explosive subglacial rhyolite eruptions correspond with high h 2 o mi closed system degassing and rapid magma ascent whereas their effusive equivalents have lower h 2 o mi and show open system degassing and more sluggish ascent rates volatile controls on eruption style thus appear similar to those for subaerial eruptions suggesting that ice plays a subsidiary role in influencing the behavior of subglacial rhyolitic eruptions

ti distribution in quartz across a heterogeneous shear zone within a granodiorite the effect of deformation mechanism and strain on ti resetting abstract the study of a heterogeneous ductile shear zone that developed at 500 c and 0 2 gpa during post magmatic cooling of a granodiorite has allowed the effect of strain and recrystallization on ti re equilibration of quartz to be assessed understanding this effect is critical for applying ti in quartz thermobarometry to mylonites differently strained quartz across the shear zone shows a heterogeneous distribution of ti concentrations ti measured by secondary ion mass spectrometry sims ranging between 2 and 45 ppm quartz cathodoluminescence cl is proven by spectral analysis to be correlated with ti allowing cl images to be calibrated as ti maps using sims measurements coarse grained weakly deformed domains consist of magmatic quartz extensively recrystallized by grain boundary migration gbm and mostly 65 75 area contain 20 38 ppm ti resetting to lower ti occurred locally i in haloes surrounding titanite and biotite inclusions ti as low as 6 ppm ii along grain boundaries and iii towards the interface of quartz domains with other mineral domains with increasing strain quartz underwent progressive grain size reduction and developed a bimodal microstructure with elongate grains 100 s m long surrounded by mantles of new grains 10 30 m in size recrystallized by subgrain rotation sgr dynamic recrystallization by sgr associated with prism slip became increasingly dominant over gbm as strain increased towards the shear zone core significant resetting of ti in quartz only occurred in high strain domains at shear strain probably 10 in the shear zone core where fine recrystallization amounts to 50 60 by area and coarser cores are strongly sub structured these domains are not compositionally homogeneous and still show a range of ti mostly between 2 and 10 ppm in all strain facies of the shear zone quartz filled pressure shadows associated with feldspar show an almost constant ti of 2 ppm the pristine ti content of the magmatic quartz mylonitized in the shear zone core is therefore significantly reset and converges asymptotically towards the equilibrium 2 ppm ti shown by new quartz precipitated in pressure shadows it is inferred that extensive recrystallization by sgr and repeated cycles of dislocation creep and rearrangement provided fluid access to quartz grain interiors promoting chemical buffering and leading to partial re equilibration to low ti these observations imply limitations on the use of the ti in quartz thermobarometry to constrain ambient conditions of ductile deformation

late quaternary icelandic tephras in ireland and great britain detection characterization and usefulness microscopic studies of late quaternary tephras from iceland yield a detailed tephrochronology in deposits of the british isles where the quantities of volcanic glass employed are much less than those used to construct almost any other late quatemary tephrochronology we summarize improved methods of isolating extremely sparse glass shards for light microscope and electron microprobe analysis and provide major element geochemistry for 20 volcanic glass layers detected in ireland including those which comprise an outline historic tephrochronology for ireland the paper highlights possible limitations of chronology construction when attempting to separate dated tephras whose major element geochemistries are almost identical tephras in other parts of the british isles and europe are used with those in ireland to demonstrate further applications of tephrochronology especially for dating deposits where other dating methods e g radiocarbon have proved difficult

evolution from magmatic to hydrothermal activity beneath the cerro escorial volcano nw argentina as sampled by erupted quartz and brines abstract large quartz pebbles erupted with the escorial ignimbrite provide insight into the late magmatic evolution of the shallow cooling magmatic hydrothermal system below the cerro escorial volcano of the southern central volcanic zone in the argentine andes the ignimbrite is of relatively small volume crystal rich dacitic in composition and not particularly water rich as amphibole is absent eruption temperature was estimated to be close to 850 c the quartz pebbles provide insight into the magmatic hydrothermal transition beneath the volcano based on textures trace element composition analyzed by laser ablation inductively coupled plasma mass spectrometry and inclusion content the pebbles can be separated into pegmatite like megacrysts and lower temperature epithermal microcrystalline quartz both types are distinct from magmatic phenocrysts present in porphyritic clasts ejected by the ignimbrite the megacrysts show a wide range of trace element concentrations with elevated al concentrations and al ti and ge ti ratios compared to quartz phenocrysts although some contamination by submicroscopic inclusions and cooling to near solidus temperatures may perturb the signal in some cases the range of trace element concentrations in quartz crystals from this system may reflect a change in crystallization conditions from initial precipitation from typical evolved silicate melt to fast growth from residual melt and or fluid in pegmatitic pockets or coarse grained hydrothermal veins at locally variable precipitation conditions abundant primary and secondary silicate melt inclusions and a variety of secondary fluid inclusions are present within the megacrysts in particular brine inclusions are densely packed with salt crystals sometimes anhydrite and or a silicate crystal but no visible liquid at room temperature and co existing vapor inclusions are of very low density heating experiments of brine inclusions reveal last salt and vapor bubble dissolution temperatures around 600 700 c but an immiscible silicate melt surrounding the homogenized salt globule remains even at unreasonably high temperature the co existence of silicate melt and fluid inclusions reinforces the magmatic nature of the fluids while boiling trails of brine with cu concentrations of several percent and vapor point to relatively low pressures

texture and geochemistry of multi stage hydrothermal scheelite in the tongshankou porphyry skarn cu mo w deposit eastern china implications for ore forming process and fluid metasomatism

p t d histories from quartz a case study of the application of the titaniq thermobarometer to progressive fabric development in metapelites 1 this study investigates the ability of quartz to record segments of the pressure temperature deformation p t d path in poly deformed metamorphic terranes and the associated application of the ti in quartz thermobarometer titaniq metapelites from the strafford dome eastern vermont were selected for this study because they record progressive fabric development during prograde metamorphism and have well constrained p t d histories from previous work results of this investigation are in agreement with previous studies and demonstrate that quartz in these samples records additional distinct intervals of the p t d path six preserved quartz equilibration events include 1 early prograde growth during burial 2 kyanite in quartz producing reactions 3 prenappe emplacement equilibration during isobaric heating 4 precipitation of quartz in quartz feldspar domains during crenulation cleavage development due to solution transfer 5 quartz producing chlorite out reactions during heating postnappe emplacement and 6 retrograde quartz overgrowths from an influx of siliceous fluids modeling quartz volume allows for the identification of quartz producing reactions in p t space the same may be done for ti phases to better constrain activities during reequilibration events an integration of cathodoluminescence imaging microstructural and petrographic investigation isochemical forward stability modeling and thermobarometry allows identification and interpretation of zoning patterns in quartz to unravel histories that would otherwise not be obtainable

geochemical compositions of ore related pyrite quartz and fluid inclusions of bangbu gold deposit in the indus yurlung zangbo suture zone tibet abstract the bangbu gold deposit is the largest au deposit and the only deposit in production within an orogenic au belt hosted by the indus yurlung zangbo suture zone in tibet strontium isotopes and in situ trace element data from ore related pyrite quartz and fluid inclusions were used to determine the composition of ore forming fluids the sources of ore components and ore forming processes arsenic se and ge are incorporated into au bearing pyrite by isomorphic substitution for s while co and ni replace fe in the pyrite lattice and au occurs either as lattice bound or in the form of nanoparticles in pyrite the individual fluid inclusions have au contents of 0 59 4 41 ppm with an average of 1 43 ppm single fluid inclusion analyses show a negative correlation between au and cl contents indicating that au did not complex with cl ions and was probably transported as au hs 2 aluminum is positively correlated with li and ge in ore related quartz consistent with a contribution from magmatic hydrothermal fluids the average 87sr 86sr ratio of fluid inclusions in quartz is 0 71577 which indicates a contribution from mantle derived material gold is likely to have been sourced from fluids evolved from mantle derived magma rather than the surrounding rocks

using titanium in quartz geothermometry and geospeedometry to recover temperatures in the aureole of the ballachulish igneous complex nw scotland titanium in quartz geothermometry suggests quartzites could yield reliable temperature estimates we here apply four calibrations of the titanium in quartz geothermometer to contact metamorphosed quartzites surrounding the ballachulish igneous complex scotland two agree broadly with thermal modelling and pre existing geothermometry two give temperatures consistently too low as reported in earlier studies the technique suffers from difficulties in analysing low titanium ti levels with high spatial and analytical precision however this study finds that the critical problem is one of ti heterogeneity which poses difficulties in constraining the chemical activity of ti during quartz growth under metamorphic conditions scanning electron microscope cathodoluminescence sem cl textures support an interpretation of extensive ti disequilibrium despite the presence of rutile indicating dynamic interplay between grain boundary diffusion fluid melt percolation and grain growth the strong zonation suggests a possible geothermometer based on apparent volume diffusion of ti in quartz to derive grain growth histories analysis of rutile quartz interaction implies peak contact temperatures of 645 12 c precise but reliant on external estimates of cooling rate from thermal models our conclusions support caution in applying ti in quartz geothermometry in aureole settings however rutile quartz juxtaposition prior to heating to 600 c defines a ti diffusion couple employable as a thermometer if cooling rates are constrained by other means

the chemistry of quartz in granitic pegmatites of southern norway petrogenetic and economic implications trace element concentrations in quartz from 188 granitic pegmatites in the froland and evje iveland pegmatite fields southern norway have been determined to establish exploration targets for high purity quartz and to gain a better understanding of the genesis of pegmatites hosting these deposits both pegmatite fields were formed during the sveconorwegian grenvillian orogeny 1145 900 ma at the western margin of the fennoscandian shield in situ raster analyses within single quartz crystals were undertaken by laser ablation inductively coupled plasma mass spectrometry la icp ms spot size 75 m to assess levels of lattice bound impurities rather than mineral and fluid inclusions that are relatively easily removed during high purity quartz processing quartz in the froland pegmatites has relatively pure and homogeneous compositions containing 46 24 gg 1 al 8 3 gg 1 ti 1 4 0 8 gg 1 ge and 11 7 gg 1 li the ti in quartz geothermobarometer gives an average pegmatite crystallization temperature of 537 39 c temperature estimates are highest along the northwestern margin of the pegmatite field 550 c whereas the most differentiated pegmatites occur toward the northeast the area of greatest economic potential for high purity quartz lies just north of the central part of the field where individual pegmatites contain 1 million metric tons mt quartz with low average trace element contents of 67 11 gg 1 from mineral chemical criteria and a range of other geologic factors we propose that pegmatite melts in the froland field were generated by fluid present crustal melting at about 1060 ma in zones of localized high strain deformation during progressive thrusting along the porsgrunn kristiansand fault zone quartz in the evje iveland pegmatites has more variable compositions with 69 57 gg 1 al 19 11 gg 1 ti 2 3 1 8 gg 1 ge and 7 5 gg 1 li from its ti content it crystallized at temperatures of 613 70 c the regional spatial distribution of ti in quartz temperatures appears irregular mainly due to the scattered distributions of chemical evolved pegmatites with amazonite cleavelandite replacement zones which show crystallization temperatures down to 442 c quartz from the evje iveland pegmatites is unlikely to be of current economic interest due to its moderate to high trace element contents heterogeneous chemistry and low volume the evje iveland pegmatites show no apparent genetic link to a granite intrusion instead they probably formed as a result of partial melting at the depth of their amphibolite country rocks at around 910 ma this is related to a regional low pressure high temperature metamorphic event at about 930 to 920 ma

chemical interactions between a sedimentary diapir and surrounding magma evidence from the phepane dome and bushveld complex south africa the phepane dome is a circular outcrop of metasedimentary rock within the eastern lobe of the bushveld complex hypothesized to have formed as a diapir when underlying wallrock rose into the overlying magma body interactions between the metasedimentary rock of the phepane dome and the magma of the bushveld complex were investigated through measurements of oxygen and lithium isotopic compositions determination of mineral modes and major element mineral compositions cathodoluminescence imaging and dihedral angle analysis evidence from cathodoluminescence imaging and dihedral angle analysis suggest that heat transfer during diapirism caused partial melting and complete recrystallization of the phepane dome metasedimentary rock oxygen isotope analysis of samples from traverses spanning the contact between metasedimentary and igneous rocks demonstrates that relatively minimal exchange of oxygen over distance 4 m occurred across the contact between the phepane dome and the surrounding bushveld magma the lithium concentrations and isotopic compositions of metasedimentary rock are significantly different from the associated igneous rocks lithium isotope analysis of samples from traverses across the contact demonstrates exchange of li over somewhat greater distances 60 m than oxygen consistent with evidence that suggests a higher diffusivity of li than most major elements models of oxygen diffusion through intergranular melt and aqueous fluid are used to place maximum constraints on the duration of diffusive exchange across the contact resulting in estimates ranging from 5 kyr to 5 myr these values are consistent with previous estimates of the duration of crystallization of the bushveld complex and phepane diapir development

scanning electron microscopy cathodoluminescence of quartz principles techniques and applications in ore geology abstract scanning electron microscopy cathodoluminescence sem cl of quartz has been a prevalent research technique in porphyry and epithermal systems for the past two decades quartz from specific geological environments reveals unique textures in sem cl which can be used to constrain the evolution of these ore bearing systems when complemented by fluid inclusion hyperspectral mapping and trace element studies we review sem cl principles and instrumentation sample preparation and handling and experimental conditions of quartz sem cl imaging that result in the high quality cl images the effects of sample polishing accelerating voltage beam spot size working distance vacuum conditions image acquisition and post processing were examined through experimental trial for the xl 30 esem and the attached gatan panacl detector used the optimum experimental conditions to obtain high quality panochromatic sem cl images of quartz at high vacuum mode for carbon coated conductive samples are as follows 15 kv accelerating voltage relative beam spot size 6 approximately 500 nm in diameter ht 570 v to 580 v photomultiplier tube pmt voltage low vacuum mode with chamber h 2 o vapor pressure from 0 1 to 1 0 torr working conditions are similar to the conditions at high vacuum mode except the pmt voltage should be reduced to 550 v to 560 v working distances vary based on the position of user s retractable cl detector the sample surface should be as close as possible to the cl detector but a 1 mm clearance between the detector and the sample surface is recommended to prevent detector from possible damage by the sample several minutes of beam exposure prior to image acquisition at 320 second scan speeds at 50 1500 magnifications is recommended to generate the greatest cl emission monochromatic cl imaging requires three scans over the same area using red green and blue optical filters that can be merged to produce a true color image the red and green filters require stronger pmt voltages to produce sufficient cl emissions by an increase of 200 v to 300 v and 150 v to 200 v respectively from the pmt voltage used for panochromatic imaging special attention is given to the challenges associated with imaging hydrothermal quartz veining in ore deposits and the value of cl data as a foundation for geochemical studies sem cl imaging of vein quartz is explored through case studies of the red hills porphyry cu mo deposit texas usa and the ertsberg grasberg cu au district papua indonesia to aid in vein paragenesis the most common application of quartz sem cl in ore geology is to reveal the relative timing of mineral precipitation mineral dissolution and inherited structural features understanding of temporal relations among these events makes it possible to select specific generations of quartz within a vein for further studies such as the titaniq thermometry and fluid inclusion microthermometry in order to establish t p x fluctuations throughout the development of a hydrothermal system

extreme fractionation in a granite pegmatite system documented by quartz chemistry the case study of tres arroyos central iberian zone spain abstract the tres arroyos granite pegmatite system is located in the sw margin of the nisa alburquerque variscan batholith two granitic facies monzogranite and marginal leucogranite and three types of aplite pegmatite dykes barren intermediate and highly evolved li rich have been distinguished in the area with a zoned distribution from the granite southwards trace elements in quartz from the five facies have been analysed by la icp ms in order to obtain information about the petrogenetic links among the different lithologies of this system as well as to better understand the regional and individual fractionation processes that led to the distinct rocks aluminium ti li and ge show continuous trends from the monzogranite through the marginal granitic facies the barren and intermediate aplite pegmatites up to the most evolved li rich dykes titanium and ge contents respectively decrease and increase gradually with fractionation in contrast al and li show a more complex trend with an initial descending trend to the marginal granitic facies and then showing the highest al and li contents in the quartz from the most fractionated li rich aplite pegmatites this suggests the influence of different competing factors controlling the incorporation of these trace elements in quartz such as the chemical composition of the melt the p and t conditions and the rate of crystallization based on the good correlation between al and li the substitution si4 al3 li seems to be the dominant mechanism of li incorporation into quartz the negligible amount of other trace elements suggests that the remaining al was mainly compensated with h ions via the si4 al3 h substitution a continuous fractionation trend from the monzogranite up to the most fractionated aplite pegmatites is inferred from geochemical modelling by applying the rayleigh equation for fractional crystallization fractionation rates over 50 are needed to obtain the marginal granite and the barren aplite pegmatites compositions and over 99 for the most evolved dykes no pattern in the chemical variation of the trace elements in quartz from different layers in the layered aplite pegmatites has been found suggesting the lack of internal fractionation processes most probably due to the rapid crystallization of the pegmatitic melt intruded into a colder country rock

the effect of deformation on the titaniq geothermobarometer an experimental study we performed high strain up to 47 axial compression experiments on natural quartz single crystals with added rutile powder tio2 and 0 2 wt h2o to investigate the effects of deformation on the titanium in quartz titaniq geothermobarometer one of the objectives was to study the relationships between different deformation mechanisms and incorporation of ti into recrystallized quartz grains experiments were performed in a griggs type solid medium deformation apparatus at confining pressures of 1 0 1 5 gpa and temperatures of 800 1 000 c at constant strain rates of 1 10 6 or 1 10 7 s 1 mobility of ti in the fluid phase and saturation of rutile at grain boundaries during the deformation experiments are indicated by precipitation of secondary rutile in cracks and along the grain boundaries of newly recrystallized quartz grains microstructural analysis by light and scanning electron microscopy the latter including electron backscatter diffraction mapping of grain misorientations shows that the strongly deformed quartz single crystals contain a wide variety of deformation microstructures and shows evidence for subgrain rotation sgr and grain boundary migration recrystallization gbmr in addition substantial grain growth occurred in annealing experiments after deformation the gbmr and grain growth are evidence of moving grain boundaries a microstructure favored by high temperatures electron microprobe analysis shows no significant increase in ti content in recrystallized quartz grains formed by sgr or by gbmr nor in grains grown by annealing this result indicates that neither sgr nor moving grain boundaries during gbmr and grain growth are adequate processes to facilitate re equilibration of the ti content in experimentally deformed quartz crystals at the investigated conditions more generally our results suggest that exchange of ti in quartz at low h2o contents which may be realistic for natural deformation conditions is still not fully understood thus the application of the titaniq geothermobarometer to deformed metamorphic rocks at low fluid contents may not be as straightforward as previously thought and requires further research

trace element composition of quartz from porphyry systems a tracer of the mineralizing fluid evolution trace element composition of hydrothermal quartz reflects the p t x conditions of the mineralizing fluids and can be a potential tracer of the fluid evolution to explore this potential quartz trace element data from 21 porphyry cu au mo and epithermal polymetallic deposits were compiled in addition quartz trace element data from six granite related systems granite pegmatite greisen sn w mo veins and from a subset of calc alkaline arc related volcanic rocks were also compiled for comparison for porphyry cu au mo deposits quartz compositions are from publications in which the sequence of quartz bearing veins and their potential reopening were documented as well as their precipitation temperatures and pressures the compiled dataset shows that trace element composition of quartz continuously evolved between the different porphyry veins and quartz generations a b c d and e the observed evolution reflects the cooling and or compositional variations of the hydrothermal fluids the quartz al ti sb ti ge ti and sb ge ti ratios allow for the discrimination of quartz from different vein generations of porphyry cu au mo deposits this study shows that quartz composition preferentially combined with cathodoluminescence images is an efficient proxy for tracing the evolution of the hydrothermal fluids in porphyry systems and can be used as a vectoring tool to target the centers of porphyry systems

genesis of the xiaolonghe quartz vein type sn deposit sw china insights from cathodoluminescence textures and trace elements of quartz fluid inclusions and oxygen isotopes abstract quartz textures revealed by scanning electron microscope cathodoluminescence sem cl images suggest that quartz in the xiaolonghe sn deposit formed in at least three fluid episodes quartz q1 in the pre ore silicification zone has homogeneous texture high cl intensity and high ti content 19 53 ppm fluid inclusions hosted in q1 are vapor rich v1 type and homogenized as supercritical fluid at 570 c quartz q2 in the syn ore topaz cassiterite quartz veins has lower cl intensity and is characterized by euhedral growth zones with lower ti content 1 3 12 ppm fluid inclusions hosted in q2 topaz and cassiterite are liquid rich fluid inclusions of moderate salinity 15 wt nacl equiv l1 type which homogenized at 423 c the post ore quartz q3 closely associated with sericitization of topaz generally crosscuts q2 and has dark cl intensity and much lower ti concentration the upper limits of t p conditions of pre ore and syn ore stage are constrained by the intersection of nacl h2o fluid inclusion isochores and ti in quartz isopleths and the lower limits are based on microthermometry results of fluid inclusions combined with the 18ofluid value 8 3 of q1 it indicates that the pre ore supercritical fluid was directly exsolved from a granitic magma at t 570 600 c and p 0 70 0 77 kbars corresponding to a maximum depth of 2 8 km under lithostatic pressure the syn ore subcritical fluid 8 0 18ofluid 6 3 mixed with some meteoric water was under 423 450 c 0 32 0 45 kbars the transition from the pre ore supercritical fluid to the syn ore subcritical fluid indicates boiling condition probably at 512 c 0 62 kbars which was likely caused by hydraulic fracturing under high pressure both the fluid boiling and fluid mixing contribute to the cassiterite precipitation in xiaolonghe sn deposit in the post ore stage the coexisting s type and v2 type fluid inclusions in q3 indicates a second fluid boiling at 269 c 0 05 kbars which was probably caused by decompression due to rapid denudation of the overlain strata the low salinity 5 5 wt nacl equiv l2 type fluid inclusions hosted in fluorite homogenized at 199 c and

fluid inclusion systematics in porphyry copper deposits the super giant grasberg deposit indonesia as a case study abstract fluid inclusion data provide a unique insight into the behaviour of magmatic fluids as they expand from source to surface to form porphyry copper deposits for example saline liquid phase inclusions in combination with vapor phase inclusions help to define the environment of mineralization in terms of large scale two phase fluid flow within a magmatic vapor plume however the pressure at which ore formation occurs within the plume is controversial because inclusion based estimates are commonly much higher than those based on geological estimates uniquely the grasberg supergiant porphyry copper deposit occupies the breccia filled diatreme underlying the crater of a maar volcano and preserved a lacustrine volcaniclastic sequence that marks the paleo surface to within a few hundred meters interpreting fluid inclusion data with respect to this paleo surface shows that porphyry mineralization extended from a paleo depth of about 500 m to over 1500 m depth as defined by drilling the grasberg deposit has three distinct populations of fluid inclusions low salinity hypersaline liquid and multi solid inclusions that are strongly clustered with respect to salinity and trapping temperature similar clusters of co existing liquid and vapor rich inclusions are also common to porphyry copper deposits worldwide applying the principles of energy and mass conservation a simple model of isenthalpic phase separation by condensation may be derived to account for these data clusters and how they are related vapor and liquid rich hypersaline inclusions may be shown quantitatively to be the consequence of expansion of a continuum low salinity low density magmatic vapor phase to a two phase fluid where the liquid fraction is minor the application of mass and energy conservation principles also shows that even though metal partitioning to the liquid phase may be favored the proportion of total metal fractionated to the small mass of liquid is low relative to that remaining in the vapor phase therefore while partitioning of metals between liquid and vapor phases may be a contributing process for metal deposition in porphyry copper deposits other vapor phase processes are required to efficiently deposit these major metal resources

diversity of primary cl textures in quartz from porphyry environments implication for origin of quartz eyes porphyry style mineralization is related to the intrusion and crystallization of small stocks which can be of different compositions from intermediate to felsic and can intrude into different host rocks from magmatic to sedimentary we used cathodoluminescence and electron probe microanalysis to study the internal textures of more than 300 quartz eyes from six porphyry deposits panguna papua new guinea far southeast porphyry philippines batu hijau indonesia antapaccay peru rio blanco chile and climax usa significant diversity of the internal textures in quartz eyes was revealed sometimes even within a single sample quartz grains with ti rich cores surrounded by ti poor mantles were found next to the grains showing the opposite ti distribution or only slight ti fluctuations we propose that diversity of the internal patterns in quartz eyes can actually reflect in situ crystallization history and that prolonged crystallization after magma emplacement under conditions of continuous cooling can account for the observed features of internal textures formation of quartz eyes begins at high temperatures with crystallization of high titanium quartz 1 which as the melt becomes more and more evolved and cooler is overgrown by low ti quartz 2 subsequent fluid exsolution brings about dramatic change in the melt composition oh alkalis and other cl complexed elements partition into the fluid phase whereas ti stays in the melt contributing to a rapid increase in ti activity separation of the fluid and its further cooling causes disequilibrium in the system and the quartz 2 becomes partially resorbed exsolution of the fluid gradually builds up the pressure until it exceeds the yield strength of the host rocks and they then fracture this pressure release most likely triggers crystallization of quartz 3 which is higher in ti than quartz 2 because ti activity in the melt is higher and pressure of crystallization is lower as a result of the reaction between the exsolved fluid and quartz a new phase a so called heavy fluid forms from this phase quartz 4 crystallizes this phase has extremely high metal carrying capacity and may give a rise to mineralizing fluids finally on the brink of the subsolidus stage groundmass quartz crystallizes prolonged crystallization under conditions of continuous cooling accounts better for the diversity of cl textures than crystallization in different parts of a deep magma chamber it is also in a better agreement with the existing model for formation of porphyry style deposits

new insights into the hydrothermal evolution of skarn deposits a case study of the dongzhongla pb zn deposit in tibet sw china abstract revealing hydrothermal evolution from the early quartz sulfide to the late fluorite carbonate sulfide stages of skarn sulfide deposits is significant for understanding their ore formation processes but the detailed studies are rare in this study we choose the dongzhongla skarn pb zn deposit 0 38 mt pb zn located in central lhasa tibet as a case study and present detailed ore deposit geology and dataset of in situ chemical compositions of quartz in situ pb isotopic ratios of galena sulfur isotopic compositions of sulfides and c o isotopic compositions of hydrothermal calcite and wall rocks to address this issue there are two types of hydrothermal quartz in the early stage 1 the early phase euhedral quartz qz1 crosscut by quartz sulfide veins and 2 the late phase subhedral quartz qz2 coexisting with sulfides titaniq thermometer of qz1 and qz2 limits the two phases with a temperature range of 336 427 c mean 373 c and 357 461 c mean 386 c respectively the decreasing al concentrations of qz1 from core to rim suggest that magmatic fluids mixed with acidic meteoric water prevented the precipitation of sulfides during the early phase the increasing al and decreasing sulfur concentrations of qz2 indicate that the increasing ph values of hydrothermal fluids made principal sulfides precipitate during the late phase in addition fluid inclusions and c o isotopic studies reveal that the late stage minerals were deposited from low salinity

fluid and metal sources of the wenquan porphyry molybdenum deposit western qinling nw china the wenquan porphyry moybdenium deposit western qinling nw china with a resource of 247 million tonnes at 0 048 mo formed during triassic collision between south china and north china blocks ore fluids at wenquan vary widely in composition from single phase low salinity aqueous to low salinity vapor and hypersaline inclusions fluid inclusion assemblages in a quartz molybdenite vein contain 60 vol vapor are equant to negative crystal shaped and form clusters or distinct inclusion trails they yield homogenization temperatures of 285 295 c with an estimated trapping temperature of 425 c suggesting a paleodepth of about 5 km calculated at a pressure correction of 100 150 mpa hydrothermal k feldspar from early stockwork veins related to potassic alteration have calculated 18ofluid values of 1 9 to 1 9 hydrothermal sericite from an overprinting phyllic alteration associated with late quartz pyrite veins has calculated dfluid values between 68 and 60 and 18ofluid values from 3 7 to 1 4 these isotopic data suggest that both early and late stage fluids are dominated by magmatic fluids with influx of meteoric water during the late stage exsolution of volatiles from magma in a late stage open system results in more variable d values than an earlier closed system molybdenite and pyrite have 34s values ranging from 1 1 to 6 6 indicating that sulfur at wenquan had a magmatic source a linear relationship between 34s values of sulfides separated from early potassic alteration and late phyllic alteration could reflect incorporation of isotopically heavy evaporate sulfate into source magmas from underlying devonian sedimentary rocks during late alteration the 56fe whole rock values of altered porphyries range from 0 08 to 0 26 similar to 56fe values of 0 15 0 32 for pyrite from quartz veins related to both the potassic and phyllic alteration assemblages the 56fe values of pyrite are positively correlated to but in general slightly lighter than those of altered porphyries indicating similar metal sources moreover both altered porphyries and the pyrite are progressively enriched in heavy fe isotopes from biotite through potassic to late phyllic alteration consistent with isotopic evolution from an early lithostatic load to a late hydrostatic load the triassic intrusive rocks and fluids responsible for mineralization were derived from a deeply sourced hybrid mantle crustal magma crystallizing at a paleodepth of 5 km under lithostatic load external late triassic meteoric or devonian formational fluids became a part of the hydrothermal system during the post fracturing final stage of ore formation under a hydrostatic regime the formation of the wenquan magmatic hydrothermal systems spans the ductile brittle transition based on a normal thermal gradient as constrained by the temperature range of 550 300 c the early high temperature potassic alteration developed under a ductile regime whereas the later low temperature phyllic alteration correlates to a brittle environment where hydraulic rock fracturing enhances permeability and fluid circulation most sulfur and metals were precipitated from vapor rich fluids resulting from cooling and expansion of a single phase fluid exsolved from a hybrid magma

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

subglacial and ice contact volcanism at the oraefajokull stratovolcano iceland eruptions of oraefajokull have produced mafic and silicic magmas and have taken place in both glacial and interglacial periods the geology of the volcano records the differing response of magmas of contrasting composition to interaction with ice of variable thickness and gives insight into the development of a long lived ice covered stratovolcano vatnafjall a ridge on the southeast flank of oraefajokull is the first area of the volcano to have been mapped in detail and the geological map is presented here alongside descriptions of each erupted unit the oldest units comprise pillow lavas hyaloclastite and jointed lava flows that were formed during subglacial basaltic eruptions involving abundant meltwater the products of a subsequent explosive initially phreatomagmatic subglacial rhyolite eruption were confined by ice to form a tephra pile over 200 m thick that was intruded by dense rhyolite magma towards the end of the eruption confinement by ice caused a later trachydacite lava flow to form buttresses and a steep pillar whilst some of the meltwater produced infiltrated the lava to generate red and black glassy breccias and cause localised steam explosions it is likely that much of it drained down the steep topography the most recently erupted units are subaerial basaltic lava flows the oldest of which were erupted during an interglacial period and have subsequently been partially eroded and scoured by advancing ice ice has been important in shaping the edifice by confining eruptive products to form constructional features and by later eroding parts of them to form deep valleys reconstructions of volcano ice interaction allowed the local thickness of the glacier at the time of each eruption to be estimated and demonstrates that the upper surface of the ice has varied in elevation by over 700 m

tracking meteoric infiltration into a magmatic hydrothermal system a cathodoluminescence oxygen isotope and trace element study of quartz from mt leyshon australia the oxygen isotope and trace element composition of hydrothermal quartz has been integrated with scanning electron microscope cathodoluminescence sem cl images and fluid inclusion properties to track fluid sources and hydrothermal processes in the mt leyshon an deposit australia oxygen isotope and trace element data were collected on parallel traverses across the same quartz sections using secondary isotope mass spectrometry sims and laser ablation inductively coupled plasma mass spectrometry la icp ms respectively with sem cl images obtained before analysis for petrographic context over the 280 to 650 degrees c quartz precipitation range suggested by fluid inclusion microthermometry delta o 18 quartz varies from 0 0 to 14 4 o corresponding to a wide range of equilibrium delta o 18 fluid values from 6 1 to 10 2 o vs v smow the delta o 18 quartz signature varies systematically among distinct sem cl quartz generations both within and between samples and can be correlated with variations in temperature and fluid composition but is independent of intra generational oscillatory zoning in contrast al and li concentrations correlate broadly with cl intensity in oscillatory quartz whereas their concentration is unpredictable in sealed fractures and overgrowths concentrations of b mg na p cl k ti mn fe ge and sn are independent of al li and oscillatory cl features but ti correlates with quartz precipitation temperature although no systematic correlation between delta o 18 quartz and trace element concentrations was found complementary patterns exist in narrow overgrowths of low delta o 18 quartz similar to 0 o and high al g 10 000 ppma these quartz zones likely formed during the incursion of o 18 depleted meteoric water into the magmatically dominated mt leyshon hydrothermal system we interpret the highest al concentrations as the result of high quartz precipitation rates triggered by depressurisation of the hydrothermal cell the decoupling of oxygen isotope and trace element patterns in quartz leads to the suggestion that 1 under most circumstances temperature and fluid chemistry dominate delta o 18 quartz and 2 the trace element record and in particular al and li is influenced by the superimposed effects of quartz precipitation rate c 2007 elsevier b v all rights reserved

scanning electron microscope cathodoluminescence analysis of quartz reveals complex growth histories in veins from the butte porphyry copper deposit montana scanning electron microscope cathodoluminescence sem cl analysis of quartz reveals textures that cannot be observed using optical microscopy or backscattered electrons these cryptic textures yield insight into timing and physical conditions of quartz growth especially in environments with multiple quartz precipitation events hydrothermal quartz from quartz sulfide veins in the porphyry copper deposit in butte montana was analyzed by sem cl revealing the following textures euhedral growth zones wide nonluminescing bands that cut across multiple quartz grains rounded luminescent quartz grain cores with euhedral overgrowths nonluminescing splatters of quartz connected by networks of cobweb like nonluminescing quartz in otherwise luminescent quartz concentric growth zones and wide nonluminescent grain boundaries these textures indicate that many veins have undergone fracturing dilation growth of quartz into fluid filled space quartz dissolution and recrystallization of quartz precipitation and dissolution textures indicate that early quartz molybdenite veins formed as a result of pressure fluctuations between lithostatic and hydrostatic at high temperatures and later pyrite quartz veins formed near hydrostatic pressure in response to temperature decrease through and beyond the field of retrograde quartz solubility

fine grained volcanic hydrothermal sedimentary rocks in permian lucaogou formation santanghu basin nw china implications on hydrocarbon source rocks and accumulation in lacustrine rift basins abstract subaqueous volcanic hydrothermal field is a complex hybrid geological system where sediments originated from volcanic hydrothermal lacustrine terrestrial and biotic sources are mixed recent petrological studies on such sediments have indicated a potential relationship between volcanic hydrothermal activities and oil generation and accumulation here we explore the mechanisms of sedimentation and oil accumulation in well laminated organic rich fine grained sedimentary rocks in permian lucaogou formation deposited in the lacustrine santanghu rift basin nw china we conducted petrographic carbon and oxygen isotopic and organic geochemical analyses of fifty four core samples from three wells forty eight samples from well w1 two from w2 four from w3 designed for tight oil exploration four main observations and interpretations are 1 the fine grained sediments are a mixture of volcanic hydrothermal detrital feldspar grains authigenic quartz crystals and primary lacustrine dolomite forming interbedded tuffaceous shale and dolostone 2 authigenic quartz crystals were precipitated from acidic hydrothermal fluids whereas fine grained angular alkaline feldspars were derived from subaqueous volcanic eruption 3 the toc content and oil generation potential increase with increased mixing of feldspars and carbonate minerals hence the dolomite bearing tuffaceous shale and tuffaceous dolostone are the best source rocks and 4 the fine grained sedimentary rocks are interpreted as a subaqueous volcanic hydrothermal deposit that controls the source potential the sedimentary processes of an ancient sediment hosted geothermal system and its implications on hydrocarbon source rocks and accumulation were first identified algal bloom induced by subaqueous eruptions is the main cause for episodic deposition of organic matter and extreme heterogeneity in both lithofacies and source rock distribution the results suggest that cone shaped buildups on seismic sections which were formed by volcanic hydrothermal deposits and contain highly mixed feldspar and carbonate sediments are the best hydrocarbon reservoirs and demonstrate a strong relationship between volcanic hydrothermal activities and hydrocarbon accumulation in an extensional tectonic setting

heterogeneous melt and hypersaline liquid inclusions in shallow porphyry type mineralization as markers of the magmatic hydrothermal transition cerro de pasco district peru recently identified occurrences of porphyry style mineralization evidence the link of the world s second largest known epithermal base metal cerro de pasco deposit peru to a porphyry system emplaced at depth they consist of i quartz monzonite dykes and ii the south western part of the large diatreme dome complex adjacent to the main ore bodies of cerro de pasco and iii stockwork of banded quartz magnetite chalcopyrite pyrite porphyry type veinlets crosscutting trachyte porphyritic intrusion cropping out at surface in the central part of the diatreme dome complex the latter porphyry type mineralization observed at the same erosion level as the main epithermal base metal carbonate replacement ore bodies is the subject of this work geological constraints indicate a shallow emplacement level depth 1 km p 270 bar implying rather unusual low pressure and high temperature environment for the formation of porphyry style mineralization the banded porphyry type veinlets record a multiphase history of formation with two successive high temperature n600 c stages followed by a lower temperature b350 c stage more than 90 of the quartz in veinlets precipitates during the first two high temperature stages stage 1 is characterized by the entrapment in hydrothermal quartz of inclusions containing variable proportions of both silicate melt and metal rich hypersaline n90 wt nacl eq liquid hereafter referred to as heterogeneous silicate melt inclusions hsmis the latter are rarely described in porphyry type mineralization we suggest that during stage 1 the inclusions result from heterogeneous entrapment of an evolved hydrous rhyolitic melt mixed with a hypersaline fluid phase at low pressure 270 bar and high temperature n600 c the stage 2 is marked by the entrapment of metaland sulfur rich hypersaline liquid inclusions with salinity around 70 wt nacl eq originated from the adiabatic ascent of magmatic hypersaline fluids transferred fromdeeper parts of the system the lower temperature stage 3 is characterized by an important temperature drop from n600 c to b350 c as revealed bymicrothermometry of aqueous two phase liquid vapor l v inclusions quartz textures revealed by sem cl imaging allowascribing the sulfide precipitation to the low temperaturemineralization stage 3 in situ sims 18o 16o isotope analyses of quartz across the veinlets are indicative of a magmatic signature of the fluids during the first two stages while quartz from stage 3 has oxygen isotopic compositions suggestive of minor contribution of meteoric waters to a predominantly magmatic aqueous fluid 10 vol of meteoric input which probably triggered cu fe sulfide precipitation in the stockwork high metal and sulfur contents of hsmis and hypersaline liquid inclusions determined by la icp ms are interpreted to represent the fluid composition prior to the main sulfide precipitation event the similar pb zn ratio of the bulk ore extracted from the epithermal ore bodies at cerro de pasco and the hsmis and hypersaline liquid inclusions suggest a common source of the fluids associated with the different mineralization styles at cerro de pasco

intensity of quartz cathodoluminescence and trace element content in quartz from the porphyry copper deposit at butte montana textures of hydrothermal quartz revealed by cathodoluminescence using a scanning electron microscope sem cl refl ect the physical and chemical environment of quartz formation variations in intensity of sem cl can be used to distinguish among quartz from superimposed mineralization events in a single vein in this study we present a technique to quantify the cathodoluminescent intensity of quartz within individual and among multiple samples to relate luminescence intensity to specific mineralizing events this technique has been applied to plutonic quartz and three generations of hydrothermal veins at the porphyry copper deposit in butte montana analyzed veins include early quartz molybdenite veins with potassic alteration pyrite quartz veins with sericitic alteration and main stage veins with intense sericitic alteration cl intensity of quartz is diagnostic of each mineralizing event and can be used to fingerprint quartz and its fluid inclusions isotopes trace elements etc from specific mineralizing episodes furthermore cl intensity increases proportional to temperature of quartz formation such that plutonic quartz from the butte quartz monzonite bqm that crystallized at temperatures near 750 c luminesces with the highest intensity whereas quartz that precipitated at 250 c in main stage veins luminesces with the least intensity trace element analyses via electron microprobe and laser ablation icp ms indicate that plutonic quartz and each generation of hydrothermal quartz from butte is dominated by characteristic trace amounts of al p ti and fe thus in addition to cl intensity each generation of quartz can be distinguished based on its unique trace element content aluminum is generally the most abundant element in all generations of quartz typically between 50 and 200 ppm but low temperature main stage quartz containing 400 to 3600 ppm al is enriched by an order of magnitude relative to all other quartz generations phosphorous is present in abundances between 25 and 75 ppm and p concentrations in quartz show little variation among quartz generations iron is the least abundant of these elements in most quartz types and is slightly enriched in cl dark quartz in pyrite quartz veins with sericitic alteration titanium is directly correlated with both temperature of quartz precipitation and intensity of quartz luminescence such that bqm quartz contains hundreds of ppm ti whereas main stage quartz contains less than 10 ppm ti our results suggest that ti concentration in quartz is controlled by temperature of quartz precipitation and that increased ti concentrations in quartz may be responsible for increased cl intensities

geochemistry of historical age silicic tephras in iceland the major element chemistry of nine silicic tephras of historical age from iceland is assessed as a key step in the development of the recent tephrochronology of the north atlantic region the tephras include the largest such layers produced by each of the five central volcanoes hekla o raefajokull eyjafjallajokull torfajokull and askja since the ninth century ad h 1104 o1362 e 1821 landnam tephra c 870 a 1875 and four other tephras h 1158 h 1510 h 1947 o1727 the determination of grain discrete major element chemistry of the glass fraction is a fundamental stage in the identification and correlation of tephra and allows links to be made between icelandic source areas with precise dating evidence and distal deposits elsewhere in the north atlantic region although major element data can be used to discriminate between tephra layers produced by the different central volcanoes on its own it cannot be used to identify all the holocene layers produc

ti resetting in quartz during dynamic recrystallization mechanisms and significance the ubiquity of quartz in continental crust and the involvement of sio 2 in multiple metamorphic processes such as reactions fluid flux and solution transfer processes makes quartz an obvious choice for reconstructing prograde metamorphic conditions in various rock types recent studies have shown the usefulness of analyzing ti distribution in quartz to constrain pressure temperature relative time deformation p t t d in metamorphosed tectonites new high precision single crystal x ray diffraction volume constraints on ti doped and chemically pure quartz provide further evidence for substitution of ti 4 for si 4 in the tetrahedral site in quartz with resultant lattice strain on the structure recent applications of the ti in quartz thermobarometer to dynamically recrystallized quartz have identified recrystallized subgrains that contain lower ti concentrations ti than their host porphyroclasts in addition ti are lower than expected for the temperatures of recrystallization atomistic simulations that estimate energetic perturbations resulting from ti incorporation into the quartz lattice indicate that significant increases in strain energy occur only at very high ti the strain energy increase is negligible for ti typical of quartz grown under mid crustal conditions this suggests that lattice strain rarely provides an appreciable driving force for ti loss from quartz instead it appears that subgrain boundaries and dislocation arrays migrating through recrystallizing quartz crystals can promote localized re equilibration thermodynamically regulated by the composition of the intergranular medium typically undersaturated in ti it therefore appears that analyses from dynamically recrystallized quartz cannot be meaningfully interpreted until methods are developed that can account quantitatively for the reduction of ti resulting from crystal plastic flow

time scales of porphyry cu deposit formation insights from titanium diffusion in quartz porphyry dikes and hydrothermal veins from the porphyry cu mo deposit at butte montana contain multiple generations of quartz that are distinct in scanning electron microscope cathodoluminescence sem cl images and in ti concentrations a comparison of microprobe trace element profiles and maps to sem cl images shows that the concentration of ti in quartz correlates positively with cl brightness but al k and fe do not after calibrating cl brightness in relation to ti concentration we use the brightness gradient between different quartz generations as a proxy for ti gradients that we model to determine time scales of quartz formation and cooling model results indicate that time scales of porphyry magma residence are 1 000s of years and time scales from porphyry quartz phenocryst rim formation to porphyry dike injection and cooling are 10s of years time scales for the formation and cooling of various generations of hydrothermal vein quartz range from 10s to 10 000s of years these time scales are considerably shorter than the 0 6 m y overall time frame for each porphyry style mineralization pulse determined from isotopic studies at butte montana simple heat conduction models provide a temporal reference point to compare chemical diffusion time scales and we find that they support short dike and vein formation time scales we interpret these relatively short time scales to indicate that the butte porphyry deposit formed by short lived episodes of hydrofracturing dike injection and vein formation each with discrete thermal pulses which repeated over the 3 m y generation of the deposit

volcanic ash from the 1362 a d oraefajokull eruption iceland in the greenland ice sheet a continuous record of electrical conductivity measurements ecm was made on site during the drilling of a 200 m ice core at summit greenland and was used to identify horizons in the ice that might be linked to volcanic eruptions in one detailed section that we studied a large peak in the number of particles two orders of magnitude above the background was measured the particle peak was not associated with an ecm peak however the particles were identified as volcanic ash on the basis of both particle morphology and chemical composition the ash composition suggests an explosive rhyolitic eruption and is believed to have originatedfrom oraefajokull in iceland in 1362 a d

the plinian eruptions of 1912 at novarupta katmai national park alaska the three day eruption at novarupta in 1912 consisted of three discrete episodes episode i began with plinian dispersal of rhyolitic fallout layer a and contemporaneous emplacement of rhyolitic ignimbrites and associated proximal veneers the plinian column was sustained throughout most of the interval of ash flow generation in spite of progressive increases in the proportions of dacitic and andesitic ejecta at the expense of rhyolite accordingly plinian layer b which fell in unbroken continuity with purely rhyolitic layer a is zoned from 99 to 15 rhyolite and accumulated synchronously with emplacement of the correspondingly zoned ash flow sequence in mageik creek and the valley of ten thousand smokes vtts only the andesiterichest flow units that cap the flow sequence lack a widespread fallout equivalent indicating that ignimbrite emplacement barely outlasted the plinian phase on near vent ridges the passing ash flows left proximal ignimbrite veneers that share the compositional zonation of their valley filling equivalents but exhibit evidence for turbulent deposition and recurrent scour episode ii began after a break of a few hours and was dominated by plinian dispersal of dacitic layers c and d punctuated by minor proximal intraplinian flows and surges after another break dacitic layers f and g resulted from a third plinian episode iii intercalated with these proximally are thin intraplinian ignimbrites and several andesite rich fall flow layers both cd and fg were ejected from an inner vent 400 m wide nested within that of episode i into which the rhyolitic lava dome novarupta was still later extruded two finer grained ash layers settled from composite regional dust clouds layer e which accumulated during the d f hiatus includes a contribution from small contemporaneous ash flows and layer h settled after the main eruption was over both are distinct layers in and near the vtts but distally they merge with cd and fg respectively they are largely dacitic but include rhyolitic shards that erupted during episode i and were kept aloft by atmospheric turbulence published models yield column heights of 23 26 km for a 22 25 km for cd and 17 23 km for fg and peak mass eruption rates of 0 7 1x108 0 6 2x108 and 0 2 0 4x108 kg s 1 respectively fallout volumes adjusted to reflect calculated redistribution of rhyolitic glass shards are 8 8 km3 4 8 km3 and 3 4 km3 for episodes i ii and iii microprobe analyses of glass show that as much as 0 4 km3 of rhyolitic glass shards from eruptive episode i fell with cde and 1 1 km3 with fgh most of the rhyolitic ash in the dacitic fallout layers fell far downwind se of the vent near the rhyolite dominated ignimbrite however nearly all of layers e and h are dacitic showing that the downwind rhyolitic ash is of co plinian rather than co ignimbrite origin

sedimentological analysis of the tephra from the 12 15 august 1991 eruption of hudson volcano the tephra fallout from the 12 15 august 1991 explosive eruption of hudson volcano cordillera de los andes 45 54 s 72 58 w chile was dispersed on a narrow elongated ese sector of patagonia covering an area on land of more than 100 000 km2 the elongated shape of the deposit together with the relatively coarse mean and median values of the particles at a considerable distance from the vent were the result of strong winds blowing to the southeast during the eruption the thickness of the fall deposit decreases up to 250 km ese from hudson volcano where it begins to thicken again secondary maxima are well developed at approximately 500 km from the vent secondary maxima together with grainsize bimodality in individual layers and in the bulk deposit suggest that particle aggregation played an important role in tephra sedimentation the fallout deposit is well stratified with alternating fine grained and coarsegrained layers which is probably a result of strong eruptive pulses followed by relatively calm periods and or changes in the eruptive style from plinian to phreatoplinian the tephra is mostly composed of juvenile material the coarse mode mostly pumice shifts to finer sizes with distance from the volcano the fine mode mostly glass shards is always about 5 6 phi glass shards and pumice are mostly light gray to colorless however considerable amounts of dark poorly vesiculated blocky shards suggest a hydromagmatic component in the eruption a land based tephra volume of 4 35 km3 was estimated and a total volume of 7 6 km3 arose from an extrapolation which took into account the probable volume sedimented in the sea bulk density ranges from 0 9 to 1 10 gr cm3 beyond 110 km from the vent rather uniform density values measured in crushed samples 2 45 2 50 gr cm3 at all distances from the vent reveal a relatively homogeneous composition mean and median sizes decrease rapidly up to 270 km from the vent beyond that point they are more or less constant whereas the maximum size 1 phi shows a steady decrease up to 550 km a concomitant improvement in sorting is observed this is attributed to sorting due to wind transport combined with particle aggregation at different times and distances from the vent the hudson tephra fallout shares some strikingly similar features with the mount st helens 18 may 1980 and quizapu 1932 eruptions

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

the weathering of volcanic tephra and how they impact histosol development an example from south east iceland abstract little is known about the impact of tephra deposits from explosive volcanic eruptions on soil formation and weathering processes in organic soils the weathering of tephra of basaltic and rhyolitic origin and their impact on icelandic histosols were studied through a combination of physical chemical and mineralogical analyses two sampling sites were selected according to the presence of the light coloured rhyolitic tephra from the oraefajokull eruption in 1362 ce and a dark coloured basaltic vei ivotn tephra from 1477 ce in the volcanically active area south of vatnajokull in south east iceland the determining factor of pedogenesis in the investigated histosols is the om but the influence of tephra and aeolian material from external sources must be taken into consideration the soils are the result of altered plant residues and volcanic material tephra and aeolian material plant remnants as well as the soil itself are protected from decomposition by the prevailing anaerobic conditions a low soil ph and the repeated addition of inorganic matter clay formation is low while metal humus complexes are predominant feo fed ratios indicated a generally low degree of weathering being higher close to the basaltic tephra the mineralogy was dominated by plagioclase and pyroxene with quartz and zeolite as minor components in contrast to previous research on icelandic soils our investigations revealed layer silicates at both sites while we found evidence of smectite in the soils at kalfafell hydroxy interlayered minerals were found at reynivellir in the basaltic tephra traces of layer silicates could be verified in contrast the rhyolitic tephra did not show any pedogenic minerals suggesting that it had hardly altered since its deposition in 1362 ce it is not the chemical composition of the inorganic parent material but the location that may be an influencing factor on the formation of clay minerals in the investigated histosols

the bishop tuff new insights from eruptive stratigraphy the 0 76 ma bishop tuff from long valley caldera in eastern california consists of a widespread fall deposit and voluminous partly welded ignimbrite the fall deposit f exposed over an easterly sector below and adjacent to the ignimbrite is divided into nine units f1 f9 with no significant time breaks except possibly between f8 and f9 maximum clast sizes are compared with other deposits where accumulation rates are known or inferred to estimate an accumulation time for f1 f8 as ca 90 hrs the ignimbrite ig is divided into chronologically and or geographically distinct packages of material earlier packages ig1 were emplaced mostly eastward are wholly intraplinian coeval with fall units f2 f8 lack phenocrystic pyroxenes and contain few or no glass mountain derived rhyolite lithic fragments earlier packages ig2 were erupted mostly to the north and east are at least partly intraplinian interbedded with fall unit f9 to the east contain pyroxenes and have lithic fractions rich in g

holocene tephras highlight complexity of volcanic signals in greenland ice cores 1 acidity peaks in greenland ice cores have been used as critical reference horizons for synchronizing ice core records aiding the construction of a single greenland ice core chronology gicc05 for the holocene guided by gicc05 we examined sub sections of three greenland cores in the search for tephra from specific eruptions that might facilitate the linkage of ice core records the dating of prehistoric tephras and the understanding of the eruptions here we report the identification of 14 horizons with tephra particles including 11 that have not previously been reported from the north atlantic region and that have the potential to be valuable isochrons the positions of tephras whose major element data are consistent with ash from the katmai ad 1912 and oraefajokull ad 1362 eruptions confirm the annually resolved ice core chronology for the last 700 years we provide a more refined date for the so called ad860b tephra a widespread isochron found across nw europe and present new evidence relating to the 17th century bc thera aniakchak debate that shows n american eruptions likely contributed to the acid signals at this time our results emphasize the variable spatial and temporal distributions of volcanic products in greenland ice that call for a more cautious approach in the attribution of acid signals to specific eruptive events

formation and evolution of multistage ore forming fluids in the miocene bangpu porphyry skarn deposit southern tibet insights from la icp ms trace elements of quartz and fluid inclusions abstract the large bangpu mo cu pb zn deposit is a mo rich 0 089 cu poor 0 32 porphyry skarn deposit located in the northeastern gangdese porphyry copper belt gpcb southern tibet in this study la icp ms data for fluid inclusions and quartz formed during different stages of the mineralization are used to 1 constrain changes in fluid composition during mineralization 2 infer the origin transport pathways and conditions of ore precipitation and 3 explore the influence of magma chamber on fluid exsolution and shallow mineralization the cu content of the vapor rich vl inclusions is higher than that of the halite bearing lvh inclusions while the mo pb and zn contents of the vl and lvh inclusions are similar indicating that mo cu pb and zn had a common source which is inferred to be the intermediate level magma chamber the metal contents of fluid inclusions in the early stage potassic alteration related vein a vein and later stage sericitic alteration related vein b vein are similar but variable implying the intermediate level magma chamber was too small to form a large stable fluid system the enrichment of mo pb and zn in the bangpu deposit relative to other porphyry deposits in the gpcb is related to the participation of ancient crustal material a comparison of our results with those from super large porphyry cu deposits elsewhere indicates that metal rich fluids are not the sole factor to form ore deposits and the variability of metal contents in the early exsolved fluids is a better predictor of mineralization potential than absolute metal concentrations

mixed biogenic and hydrothermal quartz in permian lacustrine shale of santanghu basin nw china implications for penecontemporaneous transformation of silica minerals the cycling of various isomorphs of authigenic silica minerals is a complex and long term process a special type of composite quartz qc grains in tuffaceous shale of permian lucaogou formation in the sediment starved volcanically and hydrothermally active intracontinental lacustrine santanghu rift basin nw china is studied in detail to demonstrate such processes samples from one well in the central basin were subject to petrographic elemental chemical and fluid inclusion analyses about 200 qc bearing laminae are 0 1 2 mm and mainly 1 mm thick and intercalated within tuffaceous shale laminae the qc grains occur as framework grains and are dispersed in igneous feldspar dominated matrix suggesting episodic accumulation the qc grains are bedding parallel uniform in size 100 s m elongate and radial in crystal pattern suggesting a biogenic origin qc grains are composed of a core of anhedral microcrystalline quartz and an outer part of subhedral mega quartz grains whose edges are composed of small euhedral quartz crystals indicating multiple episodic processes of recrystallization and overgrowth abundance of al and ti in quartz crystals and estimated temperature from fluid inclusions in qc grains indicate that processes are related to hydrothermal fluids finally the qc grains are interpreted as original silica precipitation in microorganism algae cysts which were reworked by bottom currents and altered by hydrothermal fluids to recrystalize and overgrow during penecontemporaneous shallow burial it is postulated that episodic volcanic and hydrothermal activities had changed lake water chemistry temperature and nutrient supply resulting in variations in microorganic productivities and silica cycling the transformation of authigenic silica from amorphous to well crystallized had occurred in a short time span during shallow burial

significance of trace elements in syntaxial quartz cement haushi group sandstones sultanate of oman abstract trace element contents and distributions in authigenic quartz cement in deeply buried 2500 4000 m haushi group sandstones from wells in oman have been investigated in order to determine the factors that control trace element uptake during precipitation scanning electron microscope cathodoluminescence images show well developed growth zones within the quartz cement which correlate with chemical zonations observed in electron microprobe al distribution maps the most abundant trace elements are al 50 3000 g g 1 li 1 100 g g 1 na 1 40 g g 1 and ge 0 3 5 g g 1 with a strong linear correlation between li and al and a weaker one between ge and al the molar concentration of li na accounts only for 15 of the charge compensation for al 3 substitution of si 4 though h was not measured in this study these data indicate a major role of h in charge balancing al 3 the samples belong to the same stratigraphic unit and have similar petrography but show considerable variability in absolute trace element concentrations between different wells this variability does not correlate with either sample depth or temperature and shows no regional pattern but seems to reflect petrophysical and tectonic differences within the sedimentary basin petrographic observations of the cogenetic mineral assemblages and hydrochemical modelling indicate that a change from the equilibrium assemblage quartz kaolinite dolomite to quartz illite dolomite reflects a decrease in the co 2 concentration and concurrent variations of the al concentration it is concluded that changes in the co 2 concentrations are responsible for fluctuations in fluid al concentrations and thus likely also in the investigated quartz cements

upper crustal fluids in a large fault system microstructural trace element and oxygen isotope study on multi phase vein quartz at the bavarian pfahl se germany fault systems are zones of crustal weakness and are used as pathways for ascending hydrothermal fluids one impressive example is the more than 150 km long bavarian pfahl system at the sw boundary of the bohemian massif dextral ductile shearing of moldanubian basement has shaped a several hundred meter wide zone of mylonites and ultramylonites this setting was reactivated under brittle conditions and infiltrated by fluids resulting in a multi phase quartz lode structural analysis using scanning electron microscopy cathodoluminescence sem cl images has been carried out in combination with trace element and oxygen isotope analysis on quartz along the system three successive quartz phases have been distinguished due to their structural details and trace element contents cryptocrystalline quartz fabric in the first quartz phase results from crystallization from a silica gel whereas in phases ii and iii quartz precipitation is characterized by repeated fragmentation and sealing visible due to strongly varying cl intensities the 18o of bavarian pfahl quartz decreases from 13 8 in the nw to 8 5 in the se whereas quartz from the close by situated wolsendorf fluorite deposit shows 18o between 15 9 and 18 5 vs smow flat shale normalized rare earth element patterns point towards an upper crustal origin of the hydrothermal fluids the southeastern part of the bavarian pfahl is interpreted to represent a deeper crustal level with higher mineralization temperatures about 350 c compared to the rest of the pfahl 250 c

trace elements in hydrothermal quartz relationships to cathodoluminescent textures and insights into vein formation high resolution electron microprobe maps show the distribution of ti al ca k and fe among quartz growth zones revealed by scanning electron microscope cathodoluminescence sem cl from 12 hydrothermal ore deposits formed between 100 and 750 c the maps clearly show the relationships between trace elements and cl intensity in quartz among all samples no single trace element consistently correlates with variations in cl intensity however in vein quartz from five porphyry cu mo au deposits cl intensity always correlates positively with ti concentrations suggesting that ti is a cl activator in quartz formed at 400 c ti concentrations in most rutile bearing vein quartz from porphyry copper deposits indicate reasonable formation temperatures of 750 c using the titaniq geothermometer titanium concentrations of 10 ppm in all veins that formed at temperatures 350 c suggest a broad correlation between ti concentrations and temperature of quartz precipitation in quartz from most deposits formed at 2000 ppm but in high temperature quartz al concentrations are consistently in the range of several hundred ppm aluminum concentrations in quartz reflect the al solubility in hydrothermal fluids which is strongly dependent on ph aluminum concentrations in quartz therefore reflect fluctuations in ph that may drive metal sulfide precipitation in hydrothermal systems

geology and ore genesis of the late paleozoic heijianshan fe oxide cu au deposit in the eastern tianshan nw china abstract the heijianshan fe cu au deposit located in the aqishan yamansu belt of the eastern tianshan nw china is hosted in the mafic intermediate volcanic and mafic felsic volcaniclastic rocks of the upper carboniferous matoutan formation based on the pervasive alteration mineral assemblages and crosscutting relationships of veins six magmatic hydrothermal stages have been established including epidote alteration stage i magnetite mineralization stage ii pyrite alteration stage iii cu au mineralization stage iv late veins stage v and supergene alteration stage vi the stage i epidote calcite tourmaline sericite alteration assemblage indicates a pre mineralization ca mg alteration event stage ii fe and stage iv cu au mineralization stages at heijianshan can be clearly distinguished from alteration mineral assemblages and nature and sources of ore forming fluids homogenization temperatures of primary fluid inclusions in quartz and calcite from stage i 189 370 c ii 301 536 c iii 119 262 c and v 46 198 c suggest that fluid incursion and mixing probably occurred during stage i to ii and stage v respectively the stage ii magmatic hydrothermal derived fe mineralization fluids were characterized by high temperature 300 c medium high salinity 21 2 56 0 wt nacl equiv and being na ca mg fe dominated these fluids were overprinted by the external low temperature in situ sulfur isotopes also indicate that the sulfur sources vary in different stages viz stage ii magmatic hydrothermal iii basinal brine related and iv magmatic hydrothermal stage ii disseminated pyrite has 34 s fluid values of 1 7 4 3 comparable with sulfur from magmatic reservoirs 34 s fluid values 24 3 29 3 of stage iii type a pyrite coexists with hematite probably indicate external basinal brine involvement consistent with the analytical results of fluid inclusions with the basinal brines further interacting with volcanic volcaniclastic rocks of the carboniferous matoutan formation stage iii type b pyrite chalcopyrite pyrrhotite assemblage with low 34 s fluid values of 4 6 10 0 may have formed at low f o 2 and temperature 119 262 c the continuous basinal brine volcanic volcaniclastic rock interactions during the basin inversion 325 300 ma may have leached sulfur and copper from the rocks yielding magmatic like 34 s fluid values 1 5 4 1 such fluids may have altered pyrite and precipitated chalcopyrite with minor au in stage iv eventually the stage v low temperature 160 c and low salinity meteoric water may have percolated into the ore forming fluid system and formed late hydrothermal veins the similar alteration and mineralization paragenetic sequences ore forming fluid sources and evolution and tectonic settings of the heijianshan deposit to the mesozoic central andean iocg deposits indicate that the former is probably the first identified paleozoic iocg like deposit in the central asian orogenic belt

pre eruptive volatile content degassing paths and depressurisation explaining the transition in style at the subglacial rhyolitic eruption of dalakvisl south iceland many volcanoes express a variety of contrasting eruptive styles with behavioural transitions between explosive and effusive activities understanding eruptive mechanisms is of key importance but we currently have little insight into the behavioural controls for rhyolitic eruptions beneath ice this paper addresses a subglacial rhyolitic eruption at dalakvisl in south iceland that involved both explosive and effusive activities we present measurements of pre and post eruptive magmatic volatile contents that we use to track magma degassing from the chamber to the surface and reconstruct pressure conditions during the eruption explosive and effusive phases involve significant differences in 1 pre eruptive volatile contents 2 the openness of magma degassing and 3 inferred confining pressure this final factor is potentially associated with a jokulhlaup induced decompression due to the combination of these factors dalakvisl experienced a change from effusive to explosive behaviour although we cannot currently resolve cause from effect our work points towards complex interactions between the dynamics of magma ascent and the response of overlying ice and meltwater during rhyolitic eruptions beneath ice

the physical volcanology of the 1600 eruption of huaynaputina southern peru volcan huaynaputina is a group of four vents located at 16 36 s 70 51 w in southern peru that produced one of the largest eruptions of historical times when 11 km3 of magma was erupted during the period 19 february to 6 march 1600 the main eruptive vents are located at 4200 m within an erosion modified amphitheater of a significantly older stratovolcano the eruption proceeded in three stages stage i was an 20 h sustained plinian eruption on 19 20 february that produced an extensive dacite pumice fall deposit magma volume 2 6 km3 throughout medial distal and distal parts of the dispersal area a fine grained plinian ashfall unit overlies the pumice fall deposit this very widespread ash magma volume 6 2 km3 has been recognized in antarctic ice cores a short period of quiescence allowed local erosion of the uppermost stage i deposits and was followed by renewed but intermittent explosive activity between 22 and 26 february stage ii this activity resulted in intercalated pyroclastic flow and pumice fall deposits 1 km3 the flow deposits are valley confined whereas associated co ignimbrite ash fall is found overlying the plinian ash deposit following another period of quiescence vulcanian type explosions of stage iii commenced on 28 february and produced crudely bedded ash lapilli and bombs of dense dacite 1 km3 activity ceased on 6 march compositions erupted are predominantly high k dacites with a phenocryst assemblage of plagioclase hornblende biotite fe ti oxides apatite major elements are broadly similar in all three stages but there are a few important differences stage i pumice has less evolved glass compositions 73 sio2 lower crystal contents 17 20 lower density 1 0 1 3 g cm3 and phase equilibria suggest higher temperature and volatile contents stage ii and stage iii juvenile clasts have more evolved glass 76 sio2 compositions higher crystal contents 25 35 higher densities up to 2 2 g cm3 and lower temperature and volatile contents all juvenile clasts show mineralogical evidence for thermal disequilibrium inflections on a plot of log thickness vs area1 2 for the fall deposits suggest that the pumice fall and the plinian ash fall were dispersed under different conditions and may have been derived from different parts of the eruption column system the ash appears to have been dispersed mainly from the uppermost parts of the umbrella cloud by upper level winds whereas the pumice fall may have been derived from the lower parts of the umbrella cloud and vertical part of the eruption column and transported by a lower altitude wind field thickness half distances and clast half distances for the pumice fall deposit suggests a column neutral buoyancy height of 24 32 km and a total column height of 34 46 km the estimated mass discharge rate for the 20 h long stage i eruption is 2 4 108 kg s and the volumetric discharge rate is 3 6 105 m3 s the pumice fall deposit has a dispersal index hildreth and drake 1992 of 4 4 and its index of fragmentation is at least 89 reflecting the dominant volume of fines produced of the 11 km3 total volume of dacite magma erupted in 1600 approximately 85 was evacuated during stage 1 the three main vents range in size from 70 to 400 m alignment of these vents and a late stage dyke parallel to the nnw sse trend defined by older volcanics suggest that the eruption initiated along a fissure that developed along pre existing weaknesses during stage i this fissure evolved into a large flared vent vent 2 with a diameter of approximately 400 m this vent was active throughout stage ii at the end of which a dome was emplaced within it during stage iii this dome was eviscerated forming the youngest vent in the group vent 3 a minor extra amphitheater vent was produced during the final event of the eruptive sequence recharge may have induced magma to rise away from a deep zone of magma generation and storage subsequently vesiculation in the rising magma batch possibly enhanced by interaction with an ancient hydrothermal system triggered and fueled the sustained plinian eruption of stage i a lower volatile content in the stage ii and stage iii magma led to transitional column behavior and pyroclastic flow generation in stage ii continued magma uprise led to emplacement of a dome which was subsequently destroyed during stage iii no caldera collapse occurred because no shallow magma chamber developed beneath this volcano

incursion of meteoric water triggers molybdenite precipitation in porphyry mo deposits a case study of the chalukou giant mo deposit there has been a long term debate about the timing of the incursion of meteoric water into porphyry systems and whether it plays an important role in ore precipitation to evaluate the role of meteoric water in the mineralization in porphyry mo deposits typical hydrothermal veins of different stages from the chalukou giant porphyry mo deposit are selected for combined scanning electron microscope cathodoluminescence sem cl fluid inclusion microthermometry and high resolution secondary ion mass spectroscopy sims oxygen isotope analyses multiple generations of quartz are identified in almost all of the veins the barren quartz veins and quartz magnetite veins of the early mo mineralization stage are dominated by granular cl bright quartz emq1 which usually shows dissolution and re deposition textures and are overprinted by cl dark quartz emq2 filled healed fractures the molybdenite precipitation in the quartz molybdenite veins of the main mo mineralization stage is synchronous with small volumes 85 of cl bright quartz mmq1 similar to the quartz molybdenite veins the precipitation of pyrite in the quartz pyrite veins during the transitional stage and sphalerite in the quartz sphalerite pyrite veins during the zn pb mineralization stage are also directly associated with cl dark quartz tsq2 zpq2 the sims oxygen isotopic values of emq1 and mmq1 fall into the range of 5 42 9 79 o with calculated equilibrium fluid compositions of 2 07 6 45 0 indicating a magma dominated fluid composition whereas mmq2 tsq2 and zpq2 have very low oxygen isotopic values from 4 68 to 4 29 parts per thousand with corresponding fluid compositions of 13 64 to 5 94 parts per thousand implying that the fluid formed by the mixing of magmatic water and a large proportion of meteoric water the contrasting sem cl features and oxygen isotopic compositions of the two generations of quartz in the quartz molybdenite veins demonstrate that the incursion of meteoric water into the hydrothermal system occurred earlier than the molybdenite precipitation based on these results and the crosscutting relationships and spatial distribution of the veins we reconstructed the quartz evolutionary sequence during the vein development process after the early precipitation of barren quartz the reduction in fluid pressure from lithostatic to hydrostatic conditions allowed the incursion of convecting cool meteoric water into the relatively hot hydrothermal system and the temperature of the evolved mo rich fluid decreased rapidly from 500 degrees c to 400 degrees c leading to concentrated molybdenite precipitation with small volumes of quartz fluid cooling resulting from the incursion of meteoric water may have played a greater role in the metal precipitation in the chalukou mo deposit than wallrock interactions and fluid boiling moreover this process may have also occurred in other porphyry mo deposits

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

mineral chemistry of rare earth element ree mineralization browns ranges western australia abstract green energy futures are driving unprecedented demand for rare earth elements ree underpinning significant exploration activity worldwide understanding how economic ree concentrations form is critical for development of exploration models ree mineralisation in the browns ranges gordon downs region western australia comprises xenotime dominant mineralisation hosted within archaean to palaeoproterozoic metasedimentary units browns range metamorphics mineralogical petrographic and mineral chemical investigation including trace element analysis by laser ablation inductively coupled plasma mass spectroscopy gives insights into the mineralogical distribution and partitioning of ree and also provides evidence for the genetic evolution of the browns range ree mineralisation via a succession of hydrothermal processes two main ree bearing minerals are identified xenotime y ree po4 which is hree selective and subordinate florencite reeal3 po4 2 oh 6 which is lree selective two morphological generations of xenotime are recognised compositions are however consistent xenotime contains dy up to 6 5 wt er up to 4 35 wt gd up to 7 56 wt yb up to 4 65 wt and y up to 43 3 wt laser ablation icp ms element mapping revealed a subtle compositional zoning in some xenotime grains lree appear concentrated in the grain cores or closest to the initial point of growth whereas hree particularly tm yb and lu are highest at the outer margins of the grains the hree enrichment at the outer margins is mimicked by as sc v sr u th and radiogenic pb florencite is commonly zoned and contains ce up to 11 54 wt nd up to 10 05 wt and la up to 5 40 wt and is also notably enriched in sr up to 11 63 wt and ca zircon which is not a significant contributor of rees overall due to its low abundance in the rocks is also enriched in ree up to 13 wt ree and is the principal host of sc up to 0 8 wt early coarse euhedral xenotime has undergone fracturing partial breakdown and replacement by florencite second generation xenotime occurs as abundant small blades commonly associated with acicular hematite mineralization is attributed to percolation of a volatile rich acidic fluid possibly granite derived through porous arkose units late hematite may suggest mixing with meteoric water and subsequent oxidation field observations suggest that faults acted as fluid conduits and that brecciation possibly associated with release of volatiles from the fluid occurred along these faults the data provide valuable constraints on chemical compositional trends in xenotime and coexisting minerals given the current surge in exploration for ree this information will assist in the development of exploration models for comparable terranes

complex proximal deposition during the plinian eruptions of 1912 at novarupta alaska proximal 3 km deposits from episodes ii and iii of the 60 h long novarupta 1912 eruption exhibit a very complex stratigraphy the result of at least four transport regimes and diverse depositional mechanisms they contrast with the relatively simple stratigraphy and inferred emplacement mechanisms for the previously documented better known medial distal fall deposits and the valley of ten thousand smokes ignimbrite the proximal products include alternations and mixtures of both locally and regionally dispersed fall ejecta and numerous thin complex deposits of pyroclastic density currents pdcs with no regional analogs the locally dispersed component of the fall deposits forms sector confined wedges of material whose thicknesses halve radially from and concentrically about the vent over distances of 100 300 m cf several kilometers for the medial distal fall deposits this locally dispersed fall material and many of the associated pdc deposits is rich in andesitic and banded pumices and richer in shallow derived wall rock lithics in comparison with the coeval medial fall units of almost entirely dacitic composition there are no marked contrasts in grain size in the near vent deposits however between locally and widely dispersed beds and all samples of the proximal fall deposits plot as a simple continuation of grain size trends for medial distal samples associated pdc deposits form a spectrum of facies from fines poor avalanched beds through thin bedded landscape mantling beds to channelized lobes of pumice block rich ignimbrite the origins of the novarupta near vent deposits are considered within a spectrum of four transport regimes 1 sustained buoyant plume 2 fountaining with co current flow 3 fountaining with counter current flow and 4 direct lateral ejection the novarupta deposits suggest a model where buoyant stable regime 1 plumes characterized most of episodes ii and iii but were accompanied by transient and variable partitioning of clasts into the other three regimes only one short period of vent blockage and cessation of the plinian plume occurred separating episodes ii and iii which was followed by a single pdc interpreted as an overpressured blast involving direct lateral ejection in contrast regimes 2 and 3 were reflected by spasmodic sedimentation from the margins of the jet and perhaps lower plume which were being strongly affected by short lived instabilities these instabilities in turn are inferred to be associated with heterogeneities in the mixture of gas and pyroclasts emerging from the vent of the parameters that control explosive eruptive behavior only such sudden and asymmetrical changes in the particle concentration could operate on time scales sufficiently short to explain the rapid changes in the proximal 1912 products

formation and evolution of snowball quartz phenocrysts in the dongping porphyritic granite hebei province china insights from fluid inclusions cathodoluminescence trace elements and crystal size distribution study abstract quartz phenocrysts are common in many granites volcanic rocks metamorphic rocks and hydrothermal deposits the dongping porphyritic granite contains large amounts of rounded to sub rounded quartz phenocrysts minerals in this porphyritic granite show weak but distinct orientation dense clusters of fluid inclusions and albite crystals exist in the quartz showing snowball texture two types of snowball quartz are recognized 1 large snowball quartz phenocrysts containing large albite grains distributed in the core and small albite grains distributed in the mantle and 2 small snowball quartz crystals containing small albite grains the granite is characterized by high sio2 7 15 73 44 wt k2o 4 70 5 10 wt and na2o 4 93 5 21 wt contents low cao 0 41 0 71 wt mgo 0 03 0 05 wt fe2o3 0 87 0 94 wt tio2 0 02 0 03 wt and ree 7 10 9 80 ppm contents the granite has similar mineral and chemical composition with the aplite in the area and they were derived from the residual melt of the shuiquangou magma that suffered assimilation fractional crystallization process fluid inclusions in the quartz phenocrysts have homogenization temperatures of 260 380 c and salinities of 1 4 12 4 wt nacl equiv for liquid vapor type inclusions and 34 1 44 3 wt nacl equiv for brine ones the quartz phenocrysts exhibit homogeneous cathodoluminescence without growth bands or zoning the trace element contents in the quartz phenocrysts are extremely low ti 3 4 5 1 ppm al 13 118 ppm li

cathodoluminescence properties of quartz eyes from porphyry type deposits implications for the origin of quartz hyperspectral cathodoluminescence cl mapping combined with electron probe microanalysis epma and fourier transform infrared spectroscopy was used for the reconstruction ofcrystallization conditions of quartz from porphyry environments quartz eyes from the two porphyry deposits rio blanco chile and climax u s a were studied three peaks are found to be responsible for the total cl emission 1 93 2 05 and 2 72 ev the first two peaks are assigned to o m with m being an alkali ion and oxygen vacancies respectively the 2 72 ev peak shows a linear correlation with the ti concentration determined by epma point measurements in addition a negative correlation between the 1 93 ev emission and the al concentration was observed quartz grains often form clusters in which adjacent grains show identical cl patterns indicating that they crystallized attached to each other and were not disturbed later quartz cores display sector zoning and enrichment in li oh and sometimes al which points to rapid crystallization from an extremely evolved melt quartz rims show high ti and low li and oh contents indicating crystallization from a less evolved melt either at higher temperatures or at higher titanium activities the al and ti distribution patterns are frequently not correlated and both show uneven distribution indicating fast growth from inhomogeneous melts only ti displays sharp transitions and fine oscillatory zoning which can be explained by the higher mobility of al in the quartz lattice the quartz eyes crystallized after magma emplacement under non equilibrium conditions it is likely that the crystallization occurred from the melt enriched in al li and oh and probably other metals and or volatiles on the brink of fluid exsolution subsequent fluid exsolution brought about disequilibrium to the system resulting in dissolution of quartz and redistribution of elements between the melt and the fluid the oh li and other alkali metals and volatiles partitioned into the fluid whereas ti and al remained in the melt resorption of quartz caused by the fluid exsolution continued until equilibrium was reached again after which crystallization of quartz rims began from the water alkali and volatile poor melt with higher ti activity furthermore accumulation of al and ti in the residual melt led to crystallization of extremely al and ti rich quartz

genesis of gold and antimony deposits in the youjiang metallogenic province sw china evidence from in situ oxygen isotopic and trace element compositions of quartz abstract abundant carlin type gold deposits and vein type antimony deposits were discovered in the youjiang basin of sw china constituting the youjiang metallogenic province ymp although they had been widely studied by geologists the genesis of these deposits remains debatable while both intrusion linked and non intrusion linked models have been proposed in this paper new data of in situ trace elements la icp ms and oxygen isotope sims analysis of hydrothermal quartz from the yata carlin type gold deposit and the qinglong vein type antimony deposit in the province were provided to better understand the origin of ore forming fluids as well as the genetic mechanism of au and sb mineralization four quartz generations were identified from the yata yti to ytiv and the qinglong qli to qliv deposits in the yata deposit the fluid inclusions in quartz have varied homogenization temperatures from 140 260 and salinities of 2 4 7 4 wt nacleq while in the qinglong deposit the temperatures and salinities ranged from 140 200 and 0 2 7 2 wt nacleq respectively both of the temperatures and salinities tend to decrease from early to late generations in the two deposits 18o values of initial fluids in the yata yti 7 70 10 56 and the qinglong qli 4 66 8 75 deposits are similar and suggest that they were mainly from magmatic or metamorphic fluids the covariability of oxygen isotope and al concentrations indicate that interaction between fluids and wall rocks is a significant factor in determining the compositions of fluids in au mineralization and the meteoric water is a key proxy in sb mineralization respectively from these observations we proposed that the carlin type au deposit and vein type sb deposit in ymp were sourced from an analogous ore fluid different lithologies of wall rocks and the dilution of meteoric water controlled the compositional evolution of fluids which might be the main reason for the diversity of au and sb mineralization

volatiles in glasses from mauna loa volcano hawai i implications for magma degassing and contamination and growth of hawaiian volcanoes glasses from mauna loa pillow basalts recent subaerial vents and inclusions in olivine were analyzed for s cl f and major elements by electron microprobe select submarine glasses were also analyzed for h2o and co2 by infrared spectroscopy the compositional variation of these tholeiitic glasses is dominantly controlled by crystal fractionation and they indicate quenching temperatures of 1 115 1 196 c submarine rift zone glasses have higher volatile abundances except f than nearly all other submarine and subaerial glasses with the maximum concentrations increasing with water depth the overwhelming dominance of degassed glasses on the submarine flanks of mauna loa implies that much of volcano s recent submarine growth involved subaerially erupted lava that reached great water depths up to 3 1 km via lava tubes anomalously high f and cl in some submarine glasses and glass inclusions indicate contamination possibly by fumarolic deposits in ephemeral rift zone magma chambers the relatively high co2 but variable h2o k2o and s k2o in some submarine rift zone glasses indicates pre eruptive mixing between degassed and undegassed magma within mauna loa s rift system volatile compositions for mauna loa magmas are similar to other active hawaiian volcanoes in s and f but are less cl rich than l ihi glasses however cl k2o ratios are similar mauna loa and l ihi magmas have comparable but lower h2o than those from kilauea thus kilauea s source may be more h2o rich the dissimilar volatile distribution in glasses from active hawaiian volcanoes is inconsistent with predictions for a simple concentrically zoned plume model

the recognition of multiple magmatic events and pre existing deformation zones in metamorphic rocks as illustrated by cl signatures and numerical modelling examples from the ballachulish contact aureole scotland the combination of cathodoluminescence cl analysis temperature and temperature time calculations and microstructural numerical modelling offers the possibility to derive the time resolved evolution of a metamorphic rock this combination of techniques is applied to a natural laboratory namely the ballachulish contact aureole scotland analysis of the appin quartzite reveals that the aureole was produced by two distinct magmatic events and infiltrated by associated fluids developing microstructures allow us to divide the aureole into three distinct regions region a 0 400 m 663 c t max 714 c exhibits a three stage grain boundary migration gbm evolution associated with heating fluid i and fluid ii gbm in region b 400 700 m 630 c t max 700 m of contact t max 630 c is characterised by healed intragranular cracks the combination of cl signature analysis and numerical modelling enables us to recognise whether grain size increase occurred mainly by surface energy driven grain growth gg or strain induced grain boundary migration sigbm gg and sigbm result in either straight bands strongly associated with present day boundaries or highly curved irregular bands that often fill entire grains respectively at a temperature of 620 c evidence for gbm is observed in the initially dry largely undeformed quartzite samples at this temperature evidence for gg is sparse whereas at 663 c cl signatures typical for gg are commonplace the grain boundary network approached energy equilibrium in samples that were at least 5 ka above 620 c

the geology and petrology of volcan san juan nayarit mexico and the compositionally zoned tepic pumice abstract volcan san juan is the westernmost quaternary composite volcano in the mexican volcanic belt its activity is divided into three stages of decreasing eruptive volume during stage 1 activity the main cone of san juan and the adjacent cerro alto grew to a combined volume of 60 km3 through eruption of hornblende bearing andesites dacites and rhyodacites stage 1 included explosive eruptions of hornblende dacite and an andesite dated at 33 750 a years ago and 23 010 a stage 2 activity involved a major plinian eruption 14 770 a that produced the hypersthene hornblende bearing compositionally zoned rhyodacitic andesitic tepic pumice and led to formation of an oval shaped caldera 4 1 km in diameter tepic the capital city of nayarit state with a population of 250 000 lies at the ne foot of volcan san juan this location was buried under 2 9 m of rhyodacitic pumice fall deposits from the tepic pumice eruption erosion has since removed virtually all exposures of tepic pumice 15 km from the caldera the estimated volume of erupted tephra is 5 6 km3 equivalent to 1 2 km3 of magma modeling of the eruption dynamics indicates that as the eruption evolved the column height increased from 15 km to 24 km and maximum mass discharge rate increased from 3 106 kg s to 6 107 kg s during stage 3 activity a hornblende andesitic lava dome partially filled the caldera and sent block lava flows down the north slope of the cone total erupted volume was 0 55 km3 compared to other composite volcanoes of the western mexican volcanic belt the products from san juan have the highest sr contents and the lowest rb y yb and lu contents resulting in high la yb and sr y with low rb sr these observations indicate a strong slab melt component at san juan consistent with its proximity to the middle america trench where young hot lithosphere is subducting the san juan andesites dacites and rhyodacites also have relatively high 87sr 86sr 206pb 204pb 207pb 204pb and 208pb 204pb and low end values compared to these other volcanoes which appear to reflect significant crustal contamination of san juan s magmas

trace elements and cathodoluminescence of quartz in stockwork veins of mongolian porphyry style deposits the combination of scanning electron microscope cathodoluminescence cl fluid inclusion analysis and high resolution electron probe microanalysis of al ti k and fe in vein quartz has yielded results permitting a greater understanding of the complex mineralisation of the central oyu tolgoi and zesen uul porphyry style deposits southern mongolia these data demonstrate the relationship between quartz precipitation dissolution and ore deposition as the mineralising fluid chemistry changed through time four major quartz generations are identified in the a type veins from the stockworks of both the central oyu tolgoi oti to otiv and zesen uul deposits zui to zuiv despite differences in the associated alteration and mineralisation style the observed cl textures and trace element signatures of the quartz generations are comparable between deposits the oti and zui stage formed both the primary network of a type veins and pervasive silicification of the host rock using the ti in quartz geothermometer crystallisation temperatures for oti and zui of between 598 c and 880 c are indicated the main stage of sulphide mineralisation was accompanied by the dissolution of pre existing quartz oti and zui and precipitation of a weakly luminescent generation of quartz otii and zuii with a low ti content reflected in a calculated temperature drop from approximately 700 c to 340 c in central oyu tolgoi and 445 c in zesen uul otii and zuii stage quartzes show high and variable al concentrations the next stage of quartz in both deposits otiii and zuiii forms a fine network of veins in cracks formed in pre existing quartz otiii and zuiii quartz contain measurable fluid inclusions of moderate salinity 3 17 1 wt nacl eq entrapped in the temperature range 256 c to 385 c otiii and zuiii are not related to any sulphide mineralisation the final otiv and zuiv stages are characterised by quartz calcite micro breccias that penetrate the a type veins based on the calculated entrapment temperatures the otiv zuiv stage crystallised between 212 c and 335 c and the quartz is characterised by elevated but variable al and fe contents the cl and trace element signatures of the oti to otiii and zui to zuiii stages of the two mongolian porphyries show similar features to those observed in porphyry style deposits from other regions this suggests that a common sequence of quartz crystallisation occurs during the formation of early veins in many porphyry copper systems

the eyjafjallajokull ad 2010 eruption and the preservation of medium sized eruptions in marine surface sediment offshore southern iceland the recent volcanic eruptions of eyjafjallajokull 2010 and grimsvotn 2011 demonstrated the risks that mediumsized explosive icelandic eruptions pose to the north atlantic region using the eyjafjallajokull 2010 eruption as a case study we assess how traceable such eruptions are in the marine sedimentary record at medial distances from the source and investigate which factors have affected the particle transport to the marine sedimentary archive during r v poseidon cruise 457 we recovered 13 box cores at 100 1600 m water depths and distances of 18 180 km southwest south and east of iceland volcanic glass shards from the uppermost surface sediment were analyzed for their major element composition by electron microprobe and assigned to their eruptive source by geochemical fingerprinting the predominantly basaltic particles are mostly derived from the katla grimsvotn lakagigar and bar arbunga vei ivotn volcanic systems we also identified rhyolitic particles from the askja 1875 and oraefajokull 1362 eruptions only three out of almost 900 analyzed glass shards are derived from the recent eyjafjallajokull 2010 eruption suggesting that medium sized eruptions are only poorly preserved in marine sediments located at medial distances southwest to east of iceland we conclude that the frequency of past medium sized eruptions is likely higher than detectable in this archive

morphological ripening of fluid inclusions and coupled zone refining in quartz crystals revealed by cathodoluminescence imaging implications for cl petrography fluid inclusion analysis and trace element geothermometry cathodoluminescence cl studies have previously shown that some secondary fluid inclusions in luminescent quartz are surrounded by dark non luminescent patches resulting from fracture sealing by late trace element poor quartz this finding has led to the tacit generalization that all dark cl patches indicate influx of low temperature late stage fluids in this study we have examined natural and synthetic hydrothermal quartz crystals using cl imaging supplemented by in situ elemental analysis the results lead us to propose that all natural liquid water bearing inclusions in quartz whether trapped on former crystal growth surfaces i e of primary origin or in healed fractures i e of pseudosecondary or secondary origin are surrounded by three dimensional non luminescent patches cross cutting relations show that the patches form after entrapment of the fluid inclusions and therefore they are not diagnostic of the timing of fluid entrapment instead the dark patches reveal the mechanism by which fluid inclusions spontaneously approach morphological equilibrium and purify their host quartz over geological time fluid inclusions that contain solvent water perpetually dissolve and reprecipitate their walls gradually adopting low energy euhedral and equant shapes defects in the host quartz constitute solubility gradients that drive physical migration of the inclusions over distances of tens of m commonly up to several mm rarely inclusions thus sequester from their walls any trace elements e g li al na ti present in excess of equilibrium concentrations thereby chemically purifying their host crystals in a process analogous to industrial zone refining non luminescent patches of quartz are left in their wake fluid inclusions that contain no liquid water as solvent e g inclusions of low density h2o vapor or other non aqueous volatiles do not undergo this process and therefore do not migrate do not modify their shapes with time and are not associated with dark cl zone refined patches this new understanding has implications for the interpretation of solids within fluid inclusions e g ti and al minerals and for the elemental analysis of hydrothermal and metamorphic quartz and its fluid inclusions by microbeam methods such as la icpms and sims as ti is a common trace element in quartz its sequestration by fluid inclusions and its depletion in zone refined patches impacts on applications of the ti in quartz geothermometer

quartz trace element composition by la icp ms as proxy for granite differentiation hydrothermal episodes and related mineralization the beauvoir granite echassieres district france despite quartz being a ubiquitous mineral in the earth s crust only little is known about its trace chemical composition and whether and how this is influenced by the medium from which it precipitated using in situla icp ms analysis we investigated the trace element composition of several types of quartz from a magmatic hydrothermal system in the echassieres district of the french massif central this system consists of the colettes granite the beauvoir rare element granite a w bearing stockwork and dispersed mineralized veins all of the elements tested li be b na al ti ge rb sr nb sn sb ta w were detected in quartz from at least one sample a rigorous multivariate statistical approach permitted to assign a specific chemical signature to each of the quartz groups that were recognized by petrographic observations differences among these groups were interpreted to reflect different sources or genetic evolutionary trends within magmatic and hydrothermally derived quartz groups for example the evolution of al rb ge li and ti could be related to genetic processes such as the degree of magma differentiation and crystallization temperatures quartz from the w stockwork anterior to the beauvoir leucogranite clearly stands out from that related to the beauvoir mineralization system i e the greisen facies and proximal ta nb sn w mineralized veins it was also possible to demonstrate a similarity in composition notably the sb contents between quartz from the greisen and from distal stibnite bearing veins in addition elevated values of sb sn as well as li and rb in quartz correspond to similarly high values of these elements in the rock indicating that quartz trace chemistry can provide useful information for the mineralization potential of its host at least for these elements on the other hand nb ta and w are less reliable as they occur mostly at very low levels in quartz the highest values corresponding to samples that were not particularly enriched in these metals a comparison of our quartz data with those from a similar granitic complex at cinovec czech republic breiter et al 2017a shows a similar trend for the ge ti ratio reflecting magmatic differentiation conversely the al ti ratio values differ in the two complexes the al content of quartz from the various cinovec granites being systematically lower than in quartz from echassieres nevertheless caution must be taken when analyzing quartz for its trace element chemistry as processes occurring during i e trapping of fluid inclusions and formation of zoning and after crystal growth i e diffusion and alteration can introduce heterogeneities thus affecting the original chemistry

mineralized breccia clasts a window into hidden porphyry type mineralization underlying the epithermal polymetallic deposit of cerro de pasco peru cerro de pasco peru is known for its large epithermal polymetallic zn pb ag cu bi mineralization emplaced at shallow level a few hundred meters below the paleo surface at the border of a large diatreme dome complex porphyry style veins crosscutting hornfels and magmatic rock clasts are found in the diatreme breccia and in quartz monzonite porphyry dikes such mineralized veins in clasts allow investigation of high temperature porphyry style mineralization developed in the deep portions of magmatic hydrothermal systems quartz in porphyry style veins contains silicate melt inclusions as well as fluid and solid mineral inclusions two types of high temperature 600 c quartz molybdenite chalcopyrite pyrite veins are found in the clasts early thin 1 2 mm and sinuous ht1 veins are crosscut by slightly thicker up to 2 cm and more regular ht2 veins the ht1 vein quartz hosts co2 and sulfur rich high density vapor inclusions two subtypes of the ht1 veins have been defined based on the nature of mineral inclusions hosted in quartz i ht1bt veins with inclusions of k feldspar biotite rutile and minor titanite and ii ht1px veins with inclusions of actinolite augite titanite apatite and minor rutile using an emplacement depth of the veins of between 2 and 3 km 500 to 800 bar derived from the diatreme breccia architecture and the supposed erosion preceding the diatreme formation multiple mineral thermobarometers are applied the data indicate that ht1 veins were formed at temperatures 700 c ht2 veins host assemblages of polyphase brine inclusions generally coexisting with low density vapor rich inclusions trapped at temperatures around 600 c rhyolitic silicate melt inclusions found in both ht1 and ht2 veins represent melt droplets transported by the ascending hydrothermal fluids la icp ms analyses reveal a chemical evolution coherent with the crystallization of an evolved rhyolitic melt quartz from both ht1 and ht2 veins also contains secondary low temperature 300 c brine and aqueous fluid inclusions that record the cooling of the system both vein types are locally crosscut and or reopened by a pre diatreme polymetallic event consisting of pyrite sphalerite with chalcopyrite disease galena chalcopyrite tetrahedrite tennantite and minor quartz la icp ms analyses of mineral and high temperature fluid inclusions hosted in ht1 and ht2 veins and in situ secondary ion mass spectrometry oxygen isotope analyses of vein quartz indicate a magmatic signature for the mineralizing fluids with no major meteoric water input and allow reconstruction of the source and chemical evolution of fluids that formed these porphyry style veins as snapshots of the early and deep mineralizations at cerro de pasco this detailed study of the porphyry type mineralization hosted in clasts offers a unique opportunity to reconstruct the late magmatic and early hydrothermal evolutions of porphyry mineralization underlying the world class cerro de pasco epithermal polymetallic zn pb ag cu bi deposit

relationships between sem cathodoluminescence response and trace element composition of hydrothermal vein quartz laser ablation icp ms data of hydrothermal vein quartz with zonation in scanning electron microscope cathodoluminescence reveal two groups of trace elements one that co varies in concentration with luminosity and another that remains uniform throughout bright luminosity correlates with a high total abundance of trace elements in early quartz including al up to 410 g g ti up to 240 g g k up to 330 g g li up to 8 g g na up to 36 g g and fe up to 20 g g up to 20 times lower concentrations of these elements are associated with dark luminosity in late quartz concentrations of p 21 g g ga 0 3 g g ge 1 3 g g sn 1 5 g g cu 0 3 g g and ag 0 1 g g demonstrate no relationship with luminosity charge balance cannot be achieved for bright luminescent quartz unless the presence of up to 6 g g h not analyzed by la icpms or interstitial al3 is invoked interestingly the inferred 6 g g h remains constant for quartz containing more than 10 mol total trace elements and might represent the solubility of h in hydrothermal quartz at temperatures between 450 and 700 c la icpms results indicate that the fluid chemistry determines the quartz trace element pattern which may serve as a monitor for the chemical environment from which quartz crystallized ratios of na al and ti al are uniform whereas k al evolves toward lower values with decreasing luminosity combined evidence including quartz vein textures silica solubility data and estimates of the temperature of quartz growth suggest that early quartz crystallized fast but late quartz grew more slowly at 350 to 425 c it is speculated that the higher the quartz growth rate is the more trace elements are incorporated into quartz besides the temperature dependence known from the literature clearly growth rate temperature and fluid chemistry are important parameters affecting luminosity however their relative importance may vary from case to case

complex circular subsidence structures in tephra deposited on large blocks of ice varða tuff cone oraefajokull iceland several broadly circular structures up to 16 m in diameter into which higher strata have sagged and locally collapsed are present in a tephra outcrop on southwest oraefajokull southern iceland the tephra was sourced in a nearby basaltic tuff cone at var a the structures have not previously been described in tuff cones and they probably formed by the melting out of large buried blocks of ice emplaced during a preceding jokulhlaup that may have been triggered by a subglacial eruption within the oraefajokull ice cap they are named ice melt subsidence structures and they are analogous to kettle holes that are commonly found in proglacial sandurs and some lahars sourced in ice clad volcanoes the internal structure is better exposed in the var a examples because of an absence of fluvial infilling and reworking and erosion of the outcrop to reveal the deeper geometry the ice melt subsidence structures at var a are a proxy for buried ice they are the only known evidence for a subglacial eruption and associated jokulhlaup that created the ice blocks the recognition of such structures elsewhere will be useful in reconstructing more complete regional volcanic histories as well as for identifying ice proximal settings during palaeoenvironmental investigations

a numerical study of turbulent mixing in eruption clouds using a three dimensional fluid dynamics model 1 the dynamics of eruption clouds in explosive volcanic eruptions are governed by entrainment of ambient air into eruption clouds by turbulent mixing we develop a new numerical pseudo gas model of an eruption cloud by employing three dimensional coordinates a third order accuracy scheme and a fine grid size in order to investigate the behavior of entrainment due to turbulent mixing the quantitative features of entrainment are measured by a proportionality constant relating the inflow velocity at the edge of the flow to the average vertical velocity i e the entrainment coefficient our model has successfully reproduced the quantitative features of entrainment observed in the laboratory experiments as well as fundamental features of the dynamics of eruption clouds such as the generation of eruption columns and or pyroclastic flows the value of the entrainment coefficient for eruption clouds is estimated from the column height and critical condition for column collapse by comparing results of our model with those of previous one dimensional models it is suggested that the value of the entrainment coefficient for an eruption cloud is approximately constant although the value estimated from the critical condition for column collapse k 0 07 is slightly smaller than that based on the column height k 0 1 this difference reflects the vertical change of flow structure in the eruption cloud the eruption cloud in the upper region exhibits a meandering instability which leads to efficient mixing whereas the cloud near the vent maintains a concentric structure with an inner dense core surrounded by an outer shear region our model is consistent with previous one dimensional models for steady eruption clouds supported by the laboratory experiments and it is also applicable to unsteady and transient features of actual eruption clouds

distribution and composition of gold in porphyry gold systems example from the biely vrch deposit slovakia the biely vrch deposit in the western carpathians is assigned to the shallow sulfide poor porphyry gold deposit type and has an exceptionally low cu au ratio according to 3 d geochemical models there is a limited spatial correlation between au and cu due to the primary introduction of gold by a salt melt and cu by low density vapor despite a rough spatial correlation of gold grades with quartz stockwork intensity gold is hosted mostly by altered rock exclusively in native form three main gold mineral assemblages were recognized here in the deepest parts of the system the k and ca na silicate gold assemblage is associated with minerals of high temperature alteration plagioclase k feldspar actinolite with gold grades and fineness depending on depth and potassium content of the host rock k silicate alteration hosts the lowest fineness gold 914 whereas ca na silicate alteration has the highest 983 the intermediate argillic gold assemblage is the most widespread with gold hosted mainly by chlorite illite smectite and interstratified illite chlorite smectite minerals the gold fineness is mostly variable 875 990 and inherited from the former gold mineral assemblages the latest advanced argillic gold assemblage has its gold mostly in kaolinite the extremely high fineness 994 results from gold remobilization by late stage aqueous magmatic hydrothermal fluids uncommon bonanza grade appears where the earlier gold mineral assemblages were further enriched by this remobilized gold primary precipitation of gold occurred during ascent and cooling of salt melts at 450 to 309 c mostly during retrograde quartz solubility

geologic and geochemical insights into the formation of the taiyangshan porphyry copper molybdenum deposit western qinling orogenic belt china abstract taiyangshan is a poorly studied copper molybdenum deposit located in the triassic western qinling collisional belt of northwest china the intrusions exposed in the vicinity of the taiyangshan deposit record episodic magmatism over 20 30 million years pre mineralization quartz diorite porphyries which host some of the deposit were emplaced at 226 6 6 2 ma syn collisional monzonite and quartz monzonite porphyries which also host mineralization were emplaced at 218 0 6 1 ma and 215 0 5 8 ma respectively mineralization occurred during the transition from a syn collisional to a post collisional setting at ca 208 ma a barren post mineralization granite porphyry marked the end of post collisional magmatism at 200 7 5 1 ma the ore bearing monzonite and quartz monzonite porphyries have a e hf t range from 2 0 to 12 5 which is much more variable than that of the slightly older quartz diorite porphyries with t dm2 of 1 15 1 23 ga corresponding to the positive e hf t values and t dm1 of 0 62 0 90 ga corresponding to the negative e hf t values molybdenite in the taiyangshan deposit with 27 70 to 38 43 ppm re suggests metal sourced from a mantle crust mixture or from mafic and ultramafic rocks in the lower crust the 34 s values obtained for pyrite chalcopyrite and molybdenite from the deposit range from 1 3 to 4 0 0 2 to 1 1 and 5 3 to 5 9 respectively suggesting a magmatic source for the sulfur calculated 18 o fluid values for magmatic k feldspar from porphyries 13 3 hydrothermal k feldspar from stockwork veins related to potassic alteration 11 6 and hydrothermal sericite from quartz pyrite veins 8 6 to 10 6 indicate the taiyangshan deposit formed dominantly from magmatic water hydrogen isotope values for hydrothermal sericite ranging from 85 to 50 may indicate that magma degassing progressively depleted residual liquid in deuterium during the life of the magmatic hydrothermal system alternatively d variability may have been caused by a minor amount of mixing with meteoric waters we propose that the ore related magma was derived from partial melting of the ancient mesoproterozoic to neoproterozoic middle to lower continental crust this crust was likely metasomatized during earlier subduction and the crustal magmas may have been contaminated with lithospheric mantle derived magma triggered by mash e g melting assimilation storage and homogenization processes during collisional orogeny in addition a significant proportion of the metals and sulfur supplied from mafic magma were simultaneously incorporated into the resultant hybrid magmas

the transition from granite to banded aplite pegmatite sheet complexes an example from megiliggar rocks tregonning topaz granite cornwall abstract the genetic relationship between a granite pluton and adjacent complex of rare metal pegmatite aplite banded sheets megiliggar sheet complex msc has been studied at the border of the tregonning topaz granite at megiliggar rocks cornwall sw england similarities in whole rock chemical and mineralogical compositions together with a gradual change in textures away from the granite margin provide strong evidence for a genetic link between the tregonning granite and msc the sheets are likely to represent apophyses of residual melt which escaped from the largely crystallized roof of the granite pluton the escaping melt was peraluminous had a composition near the f b li slightly enriched granite minimum and in comparison with other cornish granites was enriched in f li rb cs sn w nb ta and u and depleted in fe mg ca sr th zr and ree with increasing distance from the tregonning granite the silicate melt crystallized as homogeneous leucogranite sheets and banded complex sheets i e combinations of bands with granitic aplitic and pegmatitic textures then layered aplite pegmatites this sequence becoming progressively more depleted in the fluxing and volatile elements f li rb and cs but showing no change in zr hf ratios the fixed zr hf ratio is interpreted as indicating a direct genetic link parental melt between all rock types however the melt progressively lost fluxing and volatile elements with distance from the granite pluton probably due to wall rock reaction or fluid exsolution and migration via fractures differentiation of the primary melt into na li f rich and separate k b rich domains was the dominant chemical process responsible for the textural and mineral diversity of the msc on a large cliff section scale the proximal na li f rich leucogranite passes through complex sheets into k b rich aplite pegmatites whilst at a smaller

porphyry cu mo stockwork formation by dynamic transient hydrothermal pulses mineralogic insights from the deposit at butte montana the systematic distribution of vein and alteration mineral assemblages in porphyry cu deposits largely arises from changes in the temperature and pressure of fluids that traversed fractures throughout the hydrothermal system magmatic and hydrothermal minerals record the complex history of the fluctuating temperature and pressure regime as hydrothermal fluids transfer heat from their magmatic source to cold wall rock in response to lithostatic to hydrostatic pressure variations we examine the thermal profile of the porphyry cu mo deposit in butte montana by determining formation temperatures for magmatic and hydrothermal samples representing different time frames and depths within the deposit in context with sample pressure estimates we use three independent mineral thermobarometers ti in quartz zr in rutile and x mg ti in biotite from which we estimate that final dike injection temperature and hence the initial magmatic hydrothermal fluid temperature was 700 c while the ambient host rock temperature was 450 to 500 c we find a magmatic hydrothermal continuum represented in hydrothermal veins ranging from 710 to

trace element diffusion and incorporation in quartz during heating experiments heating of quartz crystals in order to study melt and high temperature fluid inclusions is a common practice to constrain major physical and chemical parameters of magmatic and hydrothermal processes diffusion and modification of trace element content in quartz and its hosted melt inclusions have been investigated through step heating experiments of both matrix free quartz crystals and quartz crystals associated with sulfides and other minerals using a linkam ts1500 stage magmatic and hydrothermal quartz were successively analyzed after each heating step for cu al and ti using electron probe micro analyzer after the last heating step quartz crystals and their hosted melt inclusions were analyzed by laser ablation inductively coupled plasma mass spectrometry and compared to unheated samples heated samples reveal modification of cu li na and b contents in quartz and modification of cu li ag and k concentrations in melt inclusions our results show that different mechanisms of cu li and na incorporation occur in magmatic and hydrothermal quartz heated magmatic quartz records only small up to a few ppm enrichment in cu and na mostly substituting for li by contrast heated hydrothermal quartz shows enrichment up to several hundreds of ppm in cu li and na which substitute for originally present h this study reveals that the composition of both quartz and its hosted melt inclusions may be significantly modified upon heating experiments leading to erroneous quantification of elemental concentrations in addition each quartz crystal also becomes significantly enriched in cu in the sub surface layer during heating we propose that sub surface cu enrichment is a direct indication of cu diffusion in quartz externally sourced from both the surrounding sulfides as well as the copper pins belonging to the heating device our study shows that the chemical compositions of both heated quartz and its hosted inclusions must be interpreted with great caution to avoid misleading geological interpretations

trace element zoning of sulfides and quartz at sheba and fairview gold mines clues to mesoarchean mineralisation in the barberton greenstone belt south africa abstract the fairview and sheba mines are two of the major gold mines in the paleoarchean barberton greenstone belt of southern africa at these mines gold is associated with quartz carbonate rutile veins and occurs both as invisible gold finely dispersed in sulfides primarily pyrite and arsenopyrite and as visible electrum grains hosted in pyrite up to approximately 1000 ppm au are contained in pyrite and up to approximately 1700 ppm in arsenopyrite mapping of trace element distribution in sulfide minerals using electron microprobe and proton probe techniques revealed multiple events of ore formation and au mineralisation at fairview mine three stages of pyrite formation were identified the last of which is associated with arsenopyrite electrum and other sulfide minerals sphalerite chalcopyrite galena gersdorffite and sb sulfides at sheba mine pyrite was deposited in two stages and electrum is associated with the second stage at both mines the last stage of sulfide formation is the main stage of au deposition and is associated with mobilisation of au as sb cu zn and ni the host rock composition seems to have affected the composition of pyrite since higher ni and co concentrations up to 1 4 and 1 6 wt respectively have been measured in meta ultra mafic host rocks in comparison with chert and metagreywacke arsenopyrite is chemically zoned and has sb and s rich cores and as and ni rich rims this zoning indicates variations in fluid compositions decreasing sb and increasing ni and crystallisation conditions increasing as content for increasing temperature geothermometric estimates based on the as content of arsenopyrite as 32 at indicate temperatures up to 420 c for the crystal rims petrographic and cathodoluminescence observations of quartz associated with gold mineralisation show only local brittle deformation and no plastic deformation this supports the notion that the ore transporting veins were emplaced late in the deformation history variations of cathodoluminescence of quartz are correlated with changing al contents al 0 16 wt and can be related to fluctuations in the ph of the mineralising fluids

genetic significance of the trace element content in metamorphic and hydrothermal quartz a reconnaissance study abstract a reconnaissance study on trace elements in metamorphic and hydrothermal quartz was carried out using quartz samples from the tin district erzgebirge germany the gold mineralization at kasperske hory czech republic and the gold quartz vein deposits muruntau and myutenbai uzbekistan a new method of sample preparation has been developed to prepare pure quartz samples by combining conventional hand picking with microscopic and spectroscopic studies as well as acid wash etch procedures preparation of monomineralic samples was followed by sample dissolution and measurement by icp ms the metamorphic quartz has very low concentrations of li 0 4 ppm al 30 ppm k 35 ppm rb 50 ppb sr 0 3 ppm and y 15 ppb moreover it is characterized by light rare earth element enriched lanthanide distribution patterns lacking eu anomalies the low element concentrations in metamorphic quartz are interpreted to result from recrystallization metamorphic quartz from alteration halos enveloping tin and gold deposits has distinctly different trace element signatures these differences are related to the hydrothermal overprint of the pre existing metamorphic quartz by the mineralizing fluids hydrothermally altered metamorphic quartz from tin deposits has elevated concentrations of li 0 9 ppm al 50 ppm k 45 ppm rb 250 ppb and y 40 ppb whereas altered metamorphic quartz from gold deposits is characterized by elevated concentrations of sr 0 5 ppm the rare earth element distribution patterns of altered metamorphic quartz show variable enrichments of the heavy rare earth elements and frequently display positive eu anomalies hydrothermal vein quartz from the gold deposits usually has elevated al 50 ppm and sr 0 6 ppm contents the lanthanide distribution patterns exhibit variable enrichments of the heavy rare earth elements and commonly show positive eu anomalies the elevated sr concentrations in the quartz from gold deposits are best explained by sr release during feldspar alteration in the wall rocks this mechanism may also account for the relative enrichment of eu in the mineralizing fluids although other processes may not be unambiguously ruled out