geochemical characteristics of biotite from felsic intrusive rocks around the sisson brook w mo cu deposit west central new brunswick an indicator of halogen and oxygen fugacity of magmatic systems abstract the sisson brook w mo cu deposit was formed by hydrothermal fluids likely related to the nashwaak granites muscovite biotite granite group i and biotite granite group ii and related dykes biotite granitic dykes group iii and a feldspar biotite quartz porphyry dyke group iv chemical data obtained using epma and la icp ms data of primary magmatic biotites were used to investigate magmatic processes and associated hydrothermal fluids trace element features of biotite in the group i two mica granite suggest other magmatic processes along with a simple fractional crystallization the k rb ratios and compatible elements cr ti co v and ba in biotite from groups ii iii and iv decrease whereas incompatible elements including ta tl ga cs li and sn increase with magma fractionation no correlation of cu w and mo with k rb ratios is evident suggesting that partitioning of cu w and mo into biotite may not be entirely controlled by magma fractionation halogen fugacity of the parental magma of the nashwaak granites and related dykes calculated from zircon saturation temperature shows that group i has high f hf f cl ratios broadly higher than 0 similar to the plutons at the henderson porphyry mo deposit the f hf f cl ratios of the other groups are generally lower than 0 comparable to the santa rita porphyry cu deposit the f h 2 o f hcl and f h 2 o f hf ratios inferred from biotite in the nashwaak granites and related dykes range from 3 to 5 and from 4 to 5 respectively the inferred oxygen fugacity shows that the dyke phases groups iii and iv have the oxygen fugacity around the nickel nickel oxide buffer the plutonic phases groups i and ii have the oxygen fugacity around the quartz fayalite magnetite qfm buffer at high temperatures and oxidized to nickel nickel oxide buffer at lower temperatures this oxidation process in the plutonic phases groups i and ii could be caused by h 2 release at or near h 2 o vapor saturation at high h 2 o fe 2 the magma associated with the biotite dykes group iii is more likely the source of the hydrothermal fluids at the sisson brook deposit since it has the highest differentiation degree and seems to have formed in an oxidized setting necessary for mo to concentrate in the late stage fluids

volatile induced magma differentiation in the plumbing system of mt etna volcano italy evidence from glass in tephra of the 2001 eruption mount etna volcano was shaken during the summer 2001 by one of the most singular eruptive episodes of the last centuries for about 3 weeks several eruptive fractures developed emitting lava flows and tephra that significantly modified the landscape of the southern flank of the volcano this event stimulated the attention of the scientific community especially for the simultaneous emission of petrologically distinct magmas recognized as coming from different segments of the plumbing system a stratigraphically controlled sampling of tephra layers was performed at the most active vents of the eruption in particular at the 2 100 m cal and at the 2 550 m lag scoria cones detailed scanning electron microscope and energy dispersive x ray spectrometer sem eds analyses performed on glasses found in tephra and comparison with lava whole rock compositions indicate an anomalous increase in ti fe p and particularly of k and cl in the upper layers of the lag sequence mass balance and thermodynamic calculations have shown that this enrichment cannot be accounted for by classical differentiation processes such as crystal fractionation and magma mixing the analysis of petrological features of the magmas involved in the event integrated with the volcanological evolution has evidenced the role played by volatiles in controlling the magmatic evolution within the crustal portion of the plumbing system volatiles constituted of h2o co2 and cl complexes originated from a deeply seated magma body dbm their upward migration occurred through a fracture network possibly developed by the seismic swarms during the period preceding the event in the upper portion of the plumbing system a shallower residing magma body abt had chemical and physical conditions to receive migrating volatiles which hence dissolved the mobilized elements producing the observed selective enrichment this volatile induced differentiation involved exclusively the lowest erupted portion of the abt magma due to the low velocity of volatiles diffusion within a crystallizing magma body and or to the short time between volatiles migration and the onset of the eruption furthermore the increased amount of volatiles in this level of the chamber strongly affected the eruptive behavior in fact the emission of these products at the lag vent towards the end of the eruption modified the eruptive style from classical strombolian to strongly explosive

the sarcheshmeh porphyry copper deposit kerman iran a mineralogical analysis of the igneous rocks and alteration zones including halogen element systematics related to cu mineralization processes abstract the giant sarcheshmeh porphyry copper deposit is located 65 km southwest of kerman city southeastern iran numerous miocene porphyry stocks and dykes intruded thick sequences of upper cretaceous sedimentary and eocene volcanic rocks hypogene and supergene porphyry cu mineralization occurs within the granodioritic porphyry and host rock sequence which was extensively altered to a dominantly potassic phyllic and argillic assemblage with interstitial to distal propylitic types biotite bearing assemblages occur as both primary phenocrysts and secondary replacements showing variable size colour and shape fluorine contents 0 22 to 1 33 wt and x mg 0 54 to 0 71 in biotites from the potassic and phyllic zones are higher than those of non mineralized granitoids f 0 09 to 0 56 wt x mg 0 43 to 0 54 whereas their cl contents cl 0 05 to 0 24 wt are lower than those of the non mineralized granitoids cl 0 11 to 0 45 the biotites from the phyllic zone have higher log f h 2 o f hf and log f h 2 o f hcl values than those of the potassic zone as well as the granitoid and andesitic dykes the log f hf f hcl values determined for the granitoid potassic and phyllic zones are similar though more negative than those of the andesitic dykes the log f hf f hcl values have a similar range for biotite from the granitoid and potassic and phyllic zones the halogen fugacity ratios established for fluids associated with the sarcheshmeh deposit from their f and cl contents in biotite show that the granitoid potassic zone and phyllic zone are increasingly affected by meteoric waters the fluids that circulated in the phyllic zone are predominantly of meteoric origin possibly overprinting original phyllic zone halogen contents the cl intercept values of biotite in the granitoid and phyllic and potassic are similar to other ore forming systems and tend to be more cl rich than cl intercept values of biotites in common igneous rocks calculated f cl intercept values for biotite in the granitoid and potassic zone are also consistent with many other porphyry copper forming systems

maskelynite hosted apatite in the chassigny meteorite insights into late stage magmatic volatile evolution in martian magmas apatite hosting maskelynite and alkali maskelynite within regions interstitial to cumulus olivine differ compositionally from that found within melt inclusions in the chassigny martian meteorite feldspar glass compositions within the interstitial regions evolve along a high temperature crystallization path within the melt inclusions feldspar glass shows evolution to low temperatures extending into the subsolidus regime coupled with these differences in maskelynite compositions are differences in volatile abundance in apatite included within the maskelynite apatite found within the large olivine hosted polyphase melt inclusions is uniformly fluorapatite whereas that interstitial to cumulus olivine is chlor fluorapatite we propose that the differences in maskelynite and apatite compositions within the melt inclusion and interstitial regions arose primarily from different crystallization conditions melt inclusion maskelynite and apatite are consistent with nearly closed system buildup of magmatic volatiles during crystallization within the melt inclusions exsolution of a cl bearing fluid phase and retention of this fluid phase within the melt inclusions into the hydrothermal regime for the interstitial regions however the higher solidus temperatures of the interstitial melts the early crystallization of feldspar with significant ternary component and the cl rich nature of the apatite all suggest open system fluid migration through the cumulus pile ingress of cl rich h2o poor brine from a hotter less evolved portion of the magma plumbing system and interaction of this cl rich fluid with melt prior to the crystallization of feldspar such processes of fluid migration through a cumulus pile have been suggested on earth in layered intrusions and apatite is the primary recorder of this process

a model for granite evolution based on non equilibrium magma separation evidence from the gharib and qattar fluorite bearing granites eastern desert egypt we present 77 new granite whole rock analyses from the qattar and gharib areas eastern desert egypt both areas include a normal granite and either a hypersolvus gharib or an almost plagioclase free granite qattar enriched in fluorite according to earlier results f influences element distribution in granitic melts forming complexes with specific elements as nb ta ga hf th zn sn whereas f excludes ba and sr we use principal component analyses to split the granite into chemical groups allowing an unbiased study of the inter group element distribution this adds the heavy rees and y to the earlier lists of elements with an affinity for f the light rees show a decreasing affinity with decreasing atomic mass fluorine separates sm from nd whereas zr follows la opposite to some but in accordance with other earlier results the ratio nb ta is higher in the fluorite enriched than in the other granite weak tetrad effects are present zircon in the hypersolvus granite is high in common lead we suggest f to be instrumental for separating pb 2 from pb 4 two hypotheses may explain the occurrence of the two contrasting granites they have either different sources or they are co magmatic but the magma was split into two discrete types we apply the second hypothesis as our working hypothesis the liquidus has a gentler slope with pressure than the diapir requiring crystallisation to be most important in the lower part of the magma chamber our hypothesis suggests that globules of magma enriched in volatile components form during crystallisation due to slow diffusion rates in the crystallizing magma elements accompanying f are distributed into this magma batch which has a lowered density and viscosity than the rest of the magma due to its increased contents of volatile components a mushroom formed diapir rises forming the hypersolvus or almost plagioclase free granite due to an edge effect it is concentrated close to the wall of the magma chamber the size and form of the outcropping granite depend on the intersection of the diapir with the erosion surface fluorine only makes it possible to follow the process the model may be generalised to explain the diversification of non f enriched granite since the buoyancy of a magma batch several thousand m 3 in size has a much larger impact on the system than the small negative buoyancy of crystals or small crystal aggregates a type granite classified merely from its trace element content may form from separated f enriched magma batches this may be the reason for their high frequency in the eastern desert

synthetic fluid inclusions in natural quartz iii determination of phase equilibrium properties in the system h2o nacl to 1000 c and 1500 bars phase equilibria in the system h2o nacl have been determined to 1000 c and 1500 bars using synthetic fluid inclusions formed by healing fractures in inclusion free brazilian quartz in the presence of the two coexisting immiscible h2o nacl fluids at various temperatures and pressures petrographic and microthermometric analyses indicate that the inclusions trapped one or the other of the two fluids present or mixtures of the two salinities of the two coexisting phases were obtained from heating and freezing studies on those inclusions which trapped only a single homogeneous fluid phase results of the present study are consistent with previously published data on the h2o nacl system at lower temperatures and pressures and indicate that the two phase field extends well into the p t range of most shallow magmatic hydrothermal activity as a consequence chloride brines exsolved from many epizonal plutons during the process of second boiling should immediately separate into a high salinity liquid phase and a lower salinity vapor phase and produce coexisting halite bearing and vapor rich fluid inclusions this observation is consistent with results of numerous fluid inclusion studies of ore deposits associated with shallow intrusions particularly the porphyry copper deposits in which halite bearing and coexisting vapor rich inclusions are commonly associated with the earliest stages of magmatic hydrothermal activity

partitioning of molybdenum between magnetite and melt a preliminary experimental study of partitioning of ore metals between silicic magmas and crystalline phases the partitioning of molybdenum between magnetite mt and two rhyolitic melts has been determined at 800 degrees c 1 kb of pressure and at two oxygen fugacities at an oxygen fugacity one half a log unit above nickel nickel oxide d super mt melt mo 0 21 or 0 08 a decrease in the oxygen fugacity to the graphite methane buffer is accompanied by an increase in d super mt melt mo to 0 52 or 0 13 the differences in melt composition have no discernible effect these data are interpreted by writing balanced chemical potential relationships involving independently variable phase components the nernst partition coefficients given above are then formulated as a function of these equilibria given the observed variation in d super mt melt mo with oxygen fugacity and assuming that fe 2 moo 4 is the molybdenum bearing phase component in magnetite our data suggest that mo iii may be present in naturally occurring silicic magmas further we suggest the establishment of critical bulk partition coefficients for ore forming systems defined in terms of critical values of the efficiency of removal function defined by candela and holland 1986 these preliminary results indicate that the crystallization of ferromagnesian or titanium bearing phases may be important in reducing the amount of molybdenum available for orthomagmatic hydrothermal ore formation oxygen fugacity may play a large role in the melt crystal vapor equilibria ofmolybdenum under magmatic conditions

exsolution of magmatic volatile phases from cl enriched mineralizing granitic magmas and implications for ore metal transport abstract to understand cl dissolution in aluminosilicate liquids and the exsolution of cl rich magmatic volatile phases experiments were conducted to determine the solubility of nacl kcl and h2o in felsic liquids at 0 5 and 2 kbar the cl content of h2o poor nacl saturated and kcl saturated silicate liquids is low i e 1 3 wt to very low i e 0 2 wt and varies with changes in pressure and composition the cl concentration increases with the f concentration and the molar al na ca mg si ratio of the liquid and decreases with increasing activity of h2o in the system exsolution of a volatile phase depends on the partial pressures of all dissolved volatiles and low cl solubilities in nacl saturated and kcl saturated silicate liquids imply that exsolution of a cl bearing volatile phase will occur early in cl bearing granitic magmas i e prior to extensive melt crystallization and or at comparatively low water fugacities the solubility behavior of h2o and cl is very similar to that of co2 and h2o in felsic liquids small quantities of co2 are known to facilitate volatile phase exsolution holloway 1976 and in a similar manner volatile phases may exsolve early in cl enriched granite magmas whereas 5 to 6 wt dissolved h2o is necessary for volatile phase exsolution from a co2 free and cl free haplogranite liquid at 2 kbar and 800 c a cl rich brine will exsolve if the liquid contains only 1 wt h2o and 0 26 wt cl at the same conditions these new solubility data are interpreted in light of h2o f and cl concentrations in felsic liquids determined from silicate melt inclusions to constrain the exsolution of cl bearing magmatic volatile phases from mineralizing granitic magmas felsic magmas genetically associated with cu porphyry and mo porphyry mineralization contain sufficient h2o and cl to become saturated with respect to a hypersaline brine without strong pressure reduction boiling of the volatile phase i e exsolution of immiscible vapor and brine or strong volatile enrichment resulting from extensive crystal fractionation experiments were also conducted to investigate the solubility of mo in highly saline volatile phases coexisting with granitic liquids at 2 and 0 5 kbar the apparent partition coefficient for mo in the volatile phase s relative to silicate liquid d mo is defined as the computed concentration of mo in a volatile phase or phases the measured concentration of mo in granite glass d mo ranges from 8 to 80 as the nacl and kcl content of the volatile phase s increases from 15 to 90 wt because mo does not complex with cl in aqueous fluids it appears that mo solubility may be a strong function of the activity of na and k in alkali chloride rich volatile phases

the influence of oxygen fugacity on tungsten and molybdenum partitioning between silicate melts and ilmenite the partitioning of molybdenum and tungsten between ilmenite ilm and silicic melts has been determined at 800 degrees c 1 kbar of pressure and at two oxygen fugacities at the oxygen fugacity of the graphite methane water buffer d super ilm melt mo 0 42 and d super ilm melt w 0 39 near the nickel nickel oxide buffer d super ilm melt mo 0 22 and d super ilm melt w 0 5 the variations in the partition coefficients with f sub o 2 are significant at the 0 06 and 0 33 levels for molybdenum and tungsten respectively the observed variation with oxygen fugacity is tentatively extrapolated to more complex systems and implies that the oxygen fugacity which prevails during magmatic crystallization may play a role in determining the mo w ratio in porphyry skarn or other hydrothermal mineral deposits examination of the literature on molybdenum and tungsten bearing mineral deposits indicates that systems with high w mo ratios are rather reduced and exhibit high ch 4 co 2 ratios in fluid inclusions low fe super 3 fe super 2 ratios in iron bearing minerals and low oxygen fugacities in associated igneous rocks on the other hand deposits with high mo w ratios are associated with rather oxidized magmatic systems we suggest that f sub o 2 dependent sequestration of molybdenum and tungsten in ferromagnesian phases during plutonic consolidation exerts a control on the relative efficiencies of removal of these metals from magmas into ore forming fluids

hydrothermal jarosite and hematite in a pyroxene hosted melt inclusion in martian meteorite miller range mil 03346 implications for magmatic hydrothermal fluids on mars low temperature aqueous processes have been implicated in the generation of jarosite and hematite on the martian surface but little is known regarding the role that high temperature magmatic fluids may have played in producing similar assemblages on mars we have identified jarosite and hematite in a clinopyroxene hosted melt inclusion in martian meteorite mil 03346 that shows evidence of having been hydrothermally precipitated in addition to jarosite and hematite the melt inclusion contains titanomagnetite pyrrhotite potassic chlorohastingsite an iron rich silicate glass and possibly goethite these phases were identified and characterized using scanning electron microscopy sem con focal raman spectroscopy and electron probe microanalysis epma based on observed textural relationships and the compositions of the hosted phases we report that the jarosite bearing melt inclusion in mil 03346 has recorded a fluid rich history that began in the magmatic stage and continued to low temperatures this history begins at entrapment of a volatile rich silicate melt that likely reached fluid saturation after only minor crystallization within the melt inclusion this fluid rich in chlorine reacted with surrounding silicate material to produce the potassicchlorohastingsite as cooling proceeded the liquid phase eventually became more oxidized and reacted with the pyrrhotite sulfide oxidation resulted in so4 2 formation and concomitant acid production setting the stage for jarosite formation once the fluid cooled beyond the upper thermal stability of jarosite 200 c as the fluid cooled below 200 c jarosite continued to precipitate with hematite and or goethite until equilibrium was established or reactions became kinetically unfavorable this work suggests an additional jarosite hematite formation pathway on mars one that may be important wherever magmatic hydrothermal fluids come into contact with primary sulfide grains at the martian surface or subsurface moreover hydrothermal fluids rich in chlorine sulfur and iron are important for ore forming processes on earth and their indirect identification on mars may have important implications for ore formation on mars

340 000 year centennial scale marine record of southern hemisphere climatic oscillation in order to investigate rapid climatic changes at mid southern latitudes we have developed centennial scale paleoceanographic records from the southwest pacific that enable detailed comparison with antarctic ice core records these records suggest close coupling of mid southern latitudes with antarctic climate during deglacial and interglacial periods glacial sections display higher variability than is seen in antarctic ice cores which implies climatic decoupling between mid and high southern latitudes due to enhanced circum antarctic circulation structural and temporal similarity with the greenland ice core record is evident in glacial sections and suggests a degree of interhemispheric synchroneity not predicted from bipolar ice core correlations

magmatic petrogenesis and the evolution of f cl oh fluid composition in barren and tungsten skarn associated plutons using apatite and biotite compositions case studies from the northern canadian cordillera abstract a detailed study of apatite and biotite compositions in multiple intrusive phases from five composite plutons in the northern canadian cordillera was undertaken with the aim of determining the composition of magmatic fluids relative to f cl oh for several plutons both barren and mineralizing and for specific intrusive phases from each pluton that may be related to nearby tungsten skarns magmatic apatite and biotite compositions are consistent with a crustal source of magma either derived from predominantly supracrustal rocks and or derived from predominantly infracrustal rocks and fractionated to felsic compositions increasing mno feo and xf xcl with decreasing cao in apatite broadly correlates with an increasing degree of magmatic differentiation although fe vs total aluminum in biotite is a better indicator of inter and intra plutonic differentiation anomalously iron rich biotites occur in highly fractionated and or wallrock contaminated phases of plutons associated with tungsten skarns estimates of magmatic fluid composition calculated as the activity ratios log a hcl a hf and log a hoh a hf from apatite and biotite compositions show several trends with respect to magmatic differentiation two barren plutons demonstrate that fluids in silicic magmas become hf enriched relative to hcl with increasing differentiation although re equilibration with late stage sub solidus or hydrothermal fluids may obscure this trend the three intrusions with associated tungsten skarn mineralization including the world class cantung deposit also become hf enriched with magmatic evolution however magmatic apatite and biotite in individual intrusive phases that are the most closely associated with mineralization have equilibrated with compositionally distinct fluids in these particular intrusive phases apatite appears to have equilibrated with an earlier hcl and h 2 o rich magmatic fluid and biotite appears to have equilibrated with a later hcl and a particularly h 2 o rich magmatic fluid the fluid in these magmas apparently evolved to a h 2 o rich or less saline composition as the temperature of the magma decreased none of the other intrusive phases from either the barren or tungsten associated plutons have apatite and biotite activity ratios that are suggestive of equilibration with such an hcl hf and h 2 o hf rich fluid instead the activity ratios calculated from apatite and biotite in intrusive phases that are not as closely associated with mineralization are well coupled and unremarkable although small variations are common which would suggest that both minerals equilibrated with similar fluids these intrusive phases do not appear to have produced a large quantity of saline hydrous fluid capable of seggregating and transporting tungsten the identification of intrusive phases that did produce magmatic fluids that were anomalously enriched in hcl and h 2 o could therefore be a predictor of nearby tungsten skarn mineralization

geochemistry and evolution of ore forming fluids of the yueshan cu au skarn and vein type deposits anhui province south china abstract the yueshan mineral belt is geotectonically located at the centre of the changjiang deep fracture zone or depression of the lower yangtze platform two main types of ore deposits occur in the yueshan orefield cu au fe skarn deposits and cu mo au pb zn hydrothermal vein type deposits almost all deposits of economic interest are concentrated within and around the eastern and northern branches of the yueshan dioritic intrusion in the vicinity of the zongpu and wuhen intrusions there are many cu pb zn au s vein type and a few cu fe au skarn type occurrences fluid inclusion studies show that the ore forming fluids are characterised by a cl s na k chemical association hydrothermal activity associated with the above two deposit types was related to the yueshan intrusion the fluid salinity was high during the mineralisation processes and the fluid also underwent boiling and mixed with meteoric water in comparison the hydrothermal activity related to the zongpu and wuhen intrusions was characterised by low salinity fluids chlorine and sulphur species played an important role in the transport of ore forming components hydrogen and oxygen isotope data also suggest that the ore forming fluids in the yueshan mineral belt consisted of magmatic water mixed in various proportions with meteoric water the enrichment of ore forming components in the magmatic waters resulted from fluid melt partitioning the ore fluids of magmatic origin formed large cu au deposits whereas ore fluids of mixed magmatic meteoric origin formed small to medium sized deposits the sulphur isotopic composition of the skarn and vein type deposits varies from 11 3 to 19 2 and from 4 2 to 10 0 respectively these variations do not appear to have been resulted from changes of physicochemical conditions rather due to compositional variation of sulphur at the source s and by water rock interaction complex water rock interaction between the ore bearing magmatic fluids and sedimentary wall rocks was responsible for sulphur mixing lead and silicon isotopic compositions of the two deposit types and host rocks provide similar indications for the sources and evolution of the ore forming fluids hydrodynamic calculations show that magmatic ore forming fluids were channelled upwards into faults fractures and porous media with velocities of 1 4 m s 9 8 10 1 to 9 8 10 7 m s and 3 6 10 7 to 4 6 10 7 m s respectively a decrease of fluid migration velocity in porous media or tiny fractures in the contact zones between the intrusive rocks and the triassic sedimentary rocks led to the deposition of the ore forming components the major species responsible for cu transport are deduced to have been cucl cucl2 cucl32 and cucloh whereas au was transported as au2 hs 2s2 au hs 2 auhs and auh3sio4 complexes cooling and a decrease in chloride ion concentration caused by fluid boiling and mixing were the principal causes of cu deposition gold deposition was related to decrease of ph total sulphur concentration and fo2 which resulted from fluid boiling and mixing geological and geochemical characteristics of the two deposit types in the yueshan mineral belt suggest that there is a close genetic relationship with the dioritic magmatism geochronological data show that the magmatic activity and the mineralisation took place between 130 and 136 ma and represent a continuous process during the yanshanian time the cooling of the intrusions and the mineralisation event might have lasted about 6 ma the cooling rate of the magmatic intrusions was 80 to 120 c my 1 which permitted sufficient heat supply by magma to the ore forming system

depth of emplacement fluid provenance and metallogeny in granitic terranes a comparison of western thailand with other tin belts the most important tin mineralization in thailand is associated with the late cretaceous to middle tertiary western thai granite belt a variety of deposit types are present in particular pegmatite vein and greisen styles of mineralization a feature common to most of the deposits is that they are associated with granites that were emplaced into the khang krachan group which consists of poorly sorted carbonaceous pelitic metasediments most of the deposits contain low to moderately saline aqueous fluid inclusions and aqueous carbonic inclusions with variable ch4 co2 ratios low salinity aqueous inclusions represent trapped magmatic fluid in at least one case the nong sua pegmatite based on their occurrence as primary inclusions in magmatic garnet aqueous carbonic inclusions are commonly secondary and neither the co2 nor nacl contents of these inclusions decrease in progressively younger inclusions implying that they are not magmatic in origin reduced carbon is depleted in the metasediments adjacent to granites and the d values greisen muscovites are variable but are as low as 134 per mil indicative of fluid interaction with organic graphitic material this suggests that the aqueous carbonic fluid inclusions represent fluids that were produced at least in part during contact metamorphism metasomatism by comparing the western thai belt with other sn w provinces it is evident that there is a strong correlation between fluid composition and pressure in general low to moderately saline aqueous inclusions and aqueous carbonic inclusions are characteristic of mineralization associated with relatively deep plutonic belts mineralized pegmatites are also typically of deeper plutonic belts and pegmatite hosted deposits may contain cassiterite that is magmatic crystallized from granitic melt or is orthomagmatic hydrothermal crystallized from aqueous or aqueous carbonic fluids in origin the magmatic aqueous fluids those that were exsolved from granitic melts are interpreted to have had low salinities as a consequence of the low salinities tin is partitioned in favour of the melt on vapour saturation thus with a high enough degree of fractionation the crystallization of a magmatic cassiterite or different sn phase such as wodginite is inevitable because tin is not partitioned in favour of the vapour phase upon water saturation of the granitic melts it is proposed that relatively deep vein and greisen systems tend to form by remobilization processes in addition many deeper greisen systems are hosted in part by carbonaceous pelitic metasediments and the reduced nature of the metasediments may play a key role in remobilizing tin sub volcanic systems by contrast are characterized by high temperature high salinity fluids owing to the high chlorinity tin is strongly partitioned in favour of the vapour and cassiterite mineralization can form by of orthomagmatic hydrothermal processes similar relationships between the depth of emplacement and fluid composition also appear to apply to other types of granite hosted deposits such as different types of molybdenum deposits

geochemical evidence for relict degassing pathways preserved in andesite andesitic arc volcanoes degas large quantities of volatiles evidence for vapour transport in the erupted lavas is rarely preserved and poorly understood but is crucial for understanding eruption style we present geochemical evidence for the transport of metal bearing vapour in shear zones preserved in lavas erupted from soufriere hills volcano montserrat textural evidence suggests that shear induced brittle failure occurred in a narrow zone at the conduit wall or in the lava dome elevated metal concentrations cu au ag pb zn within the zones indicate that the fractures acted as a transient pathway for metal bearing magmatic gases during slip frictional heating to temperatures of 1000 c caused partial melting at the slip surface resorption of volatiles and metals into the partial melt preserved the geochemical signature of magmatic vapour in the shear zone cordierite which is highly unusual in volcanic rocks crystallised from the peraluminous partial melt with metal bearing sulphides and oxides the shear zones provide the first geochemical evidence for vapour segregation and transport through viscous andesite magmas and provide an insight into controls on eruption style

the probable occurrence of interstitial al in hydrous f bearing and f free aluminosilicate melts experiments carried out on the system sio2 naalsi3o8 kalsi3o8 qz ab or at 1 kbar in the presence of h2o and f show that the quartz alkali feldspar field boundary is progressively displaced towards the feldspar join as f contents increase from 0 to 4 wt f increasing p h 2 o in the absence of f has already been shown to have a similar effect tuttle and bowen 1958 luth jahns and tuttle 1964 the increased size of the quartz field in the f bearing system compared to the hydrous system is believed to be caused by progressive removal of al from the tetrahedral network of the melt by complexing with f the residual network in the melt is thus enriched in si and this stabilizes precipitation of quartz rather than feldspar for certain bulk compositions the common presence of quench cryolite na3alf6 in certain experiments carried out with 4 wt f supports this interpretation and indicates that some al in the melt may be present in six fold coordination with f the effect of h2o in the absence of f may be similar with al being progressively removed from four fold coordination as more h2o is dissolved in the melt although a proportion of al in hydrous melts may occur in six fold coordination dry melts predominantly contain al in four fold coordination this major difference in al complexing may be one of the main causes for differences in the high pressure phase relations of wet and dry albearing silicate systems

experimental and model constraints on degassing of magma during ascent and eruption surface volcanic gases may reflect volatile budgets of magma and forecast impending eruptions and their release to the atmosphere may affect climate the dynamics of magma degassing is complicated however by differences in the solubility partitioning and diffusion of the various volatiles all of which can vary with pressure temperature and melt composition to constrain possible gas outputs we carried out experiments to determine how cl partitions between water bubbles and silicate melt and decompression experiments to examine how cl behaves during closed and open system degassing we incorporate our findings and those from the literature for co2 and s into a steady isothermal and homogeneous flow model to estimate fluxes of gases at the vent from ascending water rich magma assuming different scenarios for the onset and development of permeability in bubbly magma we find that for given permeability scenarios total gas fluxes vary with magma flux but ratios of gas species do not change the s cl and so2 co2 ratios do change however depending on whether the magma is oxidized or reduced after magma fragments into a plinian eruption column gases continue to escape from cooling pumice in the plume but here the rate of gas release is controlled by diffusion which varies with temperature degassing of pumice and ash was modeled by linking a steady state plume model which gives the vertical variation of mean temperature and velocity of particles inside the plume to a conductive cooling model of pumices which controls diffusion of cl co2 and s in pumice we find that gas loss increases with column height mass flux and initial temperature because in both cases pumices cool over a longer time period allowing more gas to diffuse out of the matrix glass the amount of gas released also depends on the size distribution of particles in the erupting mixture with less being released for a finely skewed distribution

genesis and evolution of the leimengou porphyry mo deposit in west henan province east qinling dabie belt china constraints from hydrothermal alteration fluid inclusions and stable isotope data abstract the leimengou mo deposit is located in the east qinling dabie metallogenic mo belt located at the southern margin of the north china craton the deposit is hosted within the mesozoic leimengou granite porphyry pluton and at the contact between the granite and late archean gneisses in light of mineral assemblage and crosscutting relationships among veinlets the mineralization and alteration can be classified in four distinct stages 1 a mo barren pre mineralization stage of alteration characterized by massive k feldspar alteration of the granite porphyry 2 a k feldspar quartz vein stage that formed veinlets with minor molybdenite 3 a quartz sulfide veinlet stage which is the main stage of mineralization and 4 post mineralization quartz calcite vein stage stage 1 alteration is associated with fluid inclusions of low medium salinity 2 4 13 1 wt naclequiv that homogenized at medium to high temperatures 238 476 c stage 2 mineralization is associated with fluid inclusions that homogenized at 201 389 c and that have salinities of 2 0 13 6 wt naclequiv fluid inclusions that formed during stage 3 have homogenization temperatures of 205 370 c and corresponding salinities of 1 0 17 6 wt naclequiv to 31 4 40 6 wt naclequiv indicative of fluid immiscibility and mixing of hydrothermal fluids with meteoric water stage 4 h2o nacl fluids were trapped at lower temperatures 148 246 c and have salinities of 1 7 7 9 wt naclequiv stages 1 to 4 have calculated 18ofluid values of 3 6 4 3 2 7 2 8 0 6 2 3 and 3 2 to 3 8 respectively with dfluid values of 72 to 80 83 to 90 68 to 82 and 81 to 90 respectively these results are consistent with the fluid inclusion data outlined above and suggest that early fluids were exsolved from the granitic magma and underwent progressive mixing with meteoric water molybdenum was initially transported from the crystallizing magma in a hot alkaline and oxidized fluid while decreasing temperatures and ph water rock interaction and fluid immiscibility during fluid ascent resulted in its precipitation and deposition

magmatic hydrothermal evolution of highly fractionated granites evidence from the kuiqi miarolite in fujian province se china abstract the kuiqi miarolite a highly evolved alkaline granite pluton is situated in fujian province southeastern china quartz crystals from the kuiqi miarolite contain abundant inclusions which have preserved a complete record of the magmatic hydrothermal evolution five inclusion type were identified i e the melt m type melt fluid ml type daughter mineral bearing s type vapor rich v type and aqueous l type inclusions integrated petrographic microthermometric and laser raman spectroscopy studies demonstrate that the whole magmatic hydrothermal evolution at kuiqi comprises three stages i e the magmatic magmatic hydrothermal and hydrothermal stages the m type inclusions minimal trapping temperatures ca 710 800 c represent the melts entrapped at the magmatic stage of crystallization while the occurrence of euhedral prismatic arfvedsonites in these melt inclusions indicates that the granitic magma was probably volatile rich at the magmatic hydrothermal stage both the ml type inclusions t h ca 500 710 c and coexisting m and v type inclusions reflect the presence of late magmatic fluid circulation and melt volatile immiscibility exhibiting a transition toward the hydrothermal stage at the hydrothermal stage the pressure and temperature 700 485 c drop may have led to oversaturation of the primary saline fluids resulting in the phase separation a highly saline and a volatile rich fluid occurred accompanied by the widespread vapor brine immiscibility the l type inclusions in the miarolitic quartz display bimodal salinity distribution the t h and salinity of the inclusions at the bottom l 1 miarolitic quartz are ca 303 427 c and ca 6 6 17 9 wt nacl equiv respectively while that of the inclusions at the top l 2 are ca 165 232 c and ca 0 2 5 7 wt nacl equiv respectively this indicates a drop of fluid temperature and salinity during the miarolitic cavity formation moreover the low homogenization temperatures and salinities of the l type inclusions suggest an influx of meteoric water during the late hydrothermal evolution stage

the geochemical signature of fluid saturated magma determined from silicate melt inclusions in ascension island granite xenoliths abstract silicate glasses in crystal free to crystal poor melt inclusions from two coarse grained granite xenoliths in alkaline volcanic rocks of ascension island were analyzed for 29 major minor and trace elements for most constituents the glass compositions are similar to those of the volcanic whole rocks and the xenoliths we interpret the glasses to be chemically representative of granite melt the melt inclusions are silicic alkaline contain low s and p abundances and are enriched in h 2 o cl f and na relative to k inclusions from one xenolith contain 1 3 wt f on average whereas those from the other xenolith contain half that amount the melt inclusion compositions allow investigation of the means and extent of granite magma evolution the presence of magmatic fluid inclusions in close proximity to melt inclusions in the phenocrysts indicates that the granite melt was saturated in one or more volatile phases roedder and coombs 1967 the cl and h 2 o contents of the melt inclusions are consistent with the exsolution of volatile phase s at pressures of 3000 to 2000 bars the glasses also show trends involving the cl h 2 o ratio and the incompatible trace elements in melt that are indicative of melt evolution via crystal fractionation of volatile phase saturated melt these trends should be useful for recognizing volatile phase saturation in other cl enriched melts

mueilha rare metals granite eastern desert of egypt an example of a magmatic hydrothermal system in the arabian nubian shield abstract the mueilha granite pluton is one of the rare metals bearing peraluminous granitic plutons in the arabian nubian shield it represents the apical part of a highly evolved magma chamber emplaced at a shallow level subsequent to the post pan african orogeny the pluton can be seen as a highly leucocratic medium grained albite oligoclase framework infilled with quartz k feldspar and muscovite that are variably overgrown by k feldspar muscovite quartz and topaz megacrysts the increasing number and size of the k feldspar megacrysts at the expense of the whitened albite oligoclase framework imparts variably red color to the mueilha granite contacts between the milky white and red granites are usually gradational but may be locally sharp or may form narrow transition zones resulting from abrupt variations in texture and lithology textural relations indicate an initial stage of hydrothermal albitization of magmatic plagioclase and crystallization of topaz megacrysts resulting from infiltration of na rich fluorine bearing fluids a subsequent stage of metasomatic enrichment is characterized by extensive growth of large k feldspar quartz and muscovite megacrysts at the expense of the albite oligoclase crystals as a result of infiltration of k si rich hydrous fluids post magmatic infiltration of hydrous fluids along the fault planes is shown by the intense replacement of alkali feldspar megacrysts by quartz development of myrmekitic intergrowth pockets along the k feldspar megacrysts and sealing of the micro fractures by cryptocrystalline mixtures of clay minerals iron oxides sericite and chlorite compositionally the red granitic rocks have higher sio 2 fe 2 o 3total k 2 o na 2 o ree y th u zr and zn and lower al 2 o 3 ga ta nb and mo compared to the milky white granites lile and sn do not show clear variation trends throughout the mueilha granite pluton suggesting their immobility during hydrothermal alteration microthermometric measurements indicate that the interactions with the hydrothermal fluids started at a minimum temperature 400 c most likely during the late stage crystallization of the mueilha granite and continued after their complete solidification i e subsolidus conditions at a temperature as low as 120 c the high fertility of mueilha granite is most plausibly the result of partial melting within the undepleted juvenile crust of the arabian nubian shield that has formed during the pan african orogeny

the monte guardia eruption lipari aeolian islands an example of a reversely zoned magma mixing sequence the monte guardia rhyolitic eruption 22 ka lipari aeolian islands italy produced a sequence of pyroclastic deposits followed by the emplacement of lava domes the total volume of dense magma erupted was nearly 0 5 km3 the juvenile clasts in the pyroclastic deposits display a variety of magma mixing evidence mafic magmatic enclaves streaky pumices mineral disequilibria and heterogeneous glass composition petrographic mineralogical and geochemical investigations and melt inclusion studies were carried out on the juvenile clasts in order to reconstruct the mixing process and to assess the pre eruptive chemico physical magmatic conditions the results suggest that the different mingling and mixing textures were generated during a single mixing event between a latitic and a rhyolitic end member a denser mixed magma was first erupted followed by a larger volume of an unmixed lighter rhyolitic one this compositional sequence is the reverse of what would be expected from the tapping of a zoned magma chamber the monte guardia rhyolitic magma stored below 200 mpa was volatile rich and fluid saturated or very close to this despite its relatively low explosivity in contrast to previous interpretations there exists the possibility that the rhyolite could rise and erupt without the trigger of a mafic input the entire data collected are compatible with two possible mechanisms that would generate a reversely zoned sequence 1 the occurrence of thermal instabilities in a density stratified salic to mafic magma chamber and 2 the intrusion of rising rhyolite into a shallower mafic sill dike

biotite and apatite as tools for tracking pathways of oxidized fluids in the archean east repulse gold deposit australia fluid pathways in hydrothermal ore deposits can potentially be traced through alteration zoning patterns and the chemistry of mineral phases i e major trace elements and isotopic composition which provide insight into the physico chemical gradients within and adjacent to pathways world class neoarchean gold deposits of the eastern yilgarn can be zoned with respect to alteration assemblages but in many cases fluid pathways are poorly understood which makes it difficult to identify the nature and source of fluids this study conducted detailed core logging sem mineral mapping of alteration assemblages and microprobe analysis of biotite and apatite in order to identify chemical gradients across the east repulse gold deposit of the st ives gold camp eastern yilgarn western australia results show that the east repulse deposit is vertically zoned with relatively oxidized sulfate rich alteration in the footwall of the deposit anhydrite celestine and or barite sulfide rich alteration in the core of the deposit pyrite magnetite with minor barite and celestine and relatively reduced sulfide only assemblages pyrite pyrrhotite with minor pentlandite millerite and cobaltite in the hanging wall of the deposit gold was identified as inclusions in pyrite and associated biotite implying a link between biotite pyrite alteration and gold mineralization the abundance of f in biotite and apatite progressively decreases from the footwall of the deposit into the mineralized core this trend of decreasing f in biotite and apatite with decreasing depth is consistent with an hypothesis that oxidized f and k bearing fluids were focused along subvertical pathways beneath the deposit within or subjacent to granitoid dikes the biotite apatite geothermometer shows that these fluids were relatively hot 480 60 c at the time of alteration these relatively high temperature oxidized f and k bearing fluids may have been derived from a proximal magmatic source

partitioning of cl and f between fluid and hydrous phonolitic melt of mt vesuvius at 850 1000 c and 200 mpa abstract the solubilities of cl and or f bearing fluids in phonolitic melts of vesuvius volcano have been determined experimentally at temperatures of 845 865 c and 1000 c and pressure of 200 mpa at 845 865 c the maximum cl concentration in the melt m cl coexisting with cl rich 35 5 wt fl cl and f free fluid is about 0 5 wt an addition of f to the system increases the cl content of the melt up to 0 7 wt at 39 wt cl and 13 wt f in the fluid s the relationship between m cl and fl cl indicates that low density vapor and dense brine phases might have coexisted in some experiments the relationship between m cl and fl cl at 1000 c is similar to that determined at 845 865 c implying that variations of temperature in the range 850 1000 c have no significant effect on the partitioning of cl between fluid and phonolitic melt the concentration of f in phonolitic melt coexisting with f rich fluid s reaches at least 0 9 wt at 845 865 c and 1 3 wt at 1000 c the comparison of data from experiments conducted in au and pt capsules indicates that f may react with au which influences the quality of the experimental results the partition coefficients of f between bulk fluid and melt fl m d f are higher than 1 in all experiments indicating that fluorine is preferentially incorporated into the fluid phase in phonolitic systems in contrast to fl m d f values determined in rhyolitic systems the influence of cl on fl m d f is not detectable at the conditions of our experiments the experimental data imply that mt somma vesuvius phonolitic magmas from the eruptions between a d 79 and a d 1944 may have coexisted with cl rich and f rich fluid phase s prior to eruption

triple oxygen δ18o δ17o hydrogen δ2h and iron δ56fe stable isotope signatures indicate a silicate magma source and magmatic hydrothermal genesis for magnetite orebodies at el laco chile

fluid evolution and mineralization mechanism of the east kounrad porphyry mo w deposit in the balkhash metallogenic belt central kazakhstan abstract the east kounrad mo w deposit is located in the eastern part of the balkhash metallogenic belt central kazakhstan the intrusion in the east kounrad deposit is a permain complex that includes medium and fine grained granites both the primary magma and hydrothermal fluids of the east kounrad deposit are characterized by high fluorine and high oxygen fugacity which would be important for the formation of high grade large mo deposit four mineralization stages are identified in this study stage i quartz wolframite molybdenite fluorite veins which were associated with intensively greisen alteration were formed from fluids with high temperature 340 460 c high pressure 250 400 bars high low salinity 54 5 wt and 3 4 10 2 wt respectively and high oxygen fugacity with a fluid system of h2o nacl co2 stage ii quartz molybdenite pyrite veins which were accompanied by k feldspars muscovite fluorite alteration were formed from fluids with medium high temperature 260 400 c medium pressure 100 250 bars high low salinity 39 1 58 4 wt and 2 4 11 7 wt respectively and relatively low oxygen fugacity after the main stage of w and mo mineralization stage iii quartz pyrite molybdenite veins associated with quartz sericite alteration were formed from fluids with medium low temperature 160 340 c low pressure less than 100 bars various salinity 4 5 46 2 wt and high oxygen fugacity stage iv quartz polymetallic sulfide veins related to argillic alteration were formed under temperature of 120 220 c and salinity of 1 7 8 1 wt remarkably fluid boiling is the most important precipitation mechanism of molybdenite and wolframite in addition the decreasing oxygen fugacity and temperature also play a vital role in triggering deposition of molybdenite the pb isotopic composition of sulfides shows that the ore forming materials at east kounrad are dominantly derived from the lower crust

anorogenic gross spitzkoppe granite stock in central western namibia part i petrology and geochemistry the gross spitzkoppe is a small 30 km2 anorogenic granite stock that was emplaced into the damara orogenic belt of central western namibia in response to mantle plume activity and early cretaceous rifting of western gondwanaland the epizonal gross spitzkoppe stock gss penecontemporaneous mafic and felsic dikes in the country rocks and synplutonic mafic dikes and mafic magmatic inclusions within the gss indicate bimodal magmatism the gss consists of three zonally arranged granitic units medium grained biotite granite at the margins coarse grained biotite granite and porphyritic granite at the center of the stock late stage silicic dikes and pegmatites cut the granites of the stock all the granites are mildly peraluminous topaz bearing high silica monzogranites that contain extremely fe rich biotite siderophyllite annite as the only primary mafic silicate common accessory minerals include topaz fluorite magnetite zircon monazite thorite ilmenite columbite and niobian rutile miarolitic cavities and pegmatite pockets within the stock suggest that fluid saturation was attained rectilinear structures of biotite rich schlieren along the marginal parts of the stock suggest that magma flow was parallel to the walls of the chamber whereas turbulent or plume like flows are indicated by curved circular and ladder dike schlieren geochemical variation among the granites can be attributed to fractional crystallization of major and accessory minerals and by accumulation of halogen complexes with rare earth and high field strength elements the negative partially irregular correlation between whole rock contents of f and cl suggests that cl was partially lost to a vapor phase during magmatic degassing the granites of the gross spitzkoppe show clear a type and within plate granite characteristics corresponding to the actual tectonic setting the granites are interpreted to have formed by partial crustal remelting related to mafic underplating in a continental rift environment

immiscible phases of magmatic fluid and their relation to be and mo mineralization at the yermakovka f be deposit transbaikalia russia abstract melt and fluid inclusions in minerals from the peralkaline granite intrusion and associated mineralized country rocks from the yermakovka f be deposit were studied to characterize the behaviour of trace elements and exsolved fluids in the transition from magmatic to hydrothermal processes ore mineralization was mostly due to volatile release from a deep seated pluton for which crystallization history and fluid exsolution can be tracked by three batches of magma gr1 gr3 intruded at the level of the ore deposition to form the yermakovka stock each batch of the sequential granite group is found to intrude at decreasing temperature from 840 to 730 c and progressively increasing extent of crystallization of magma in the parental pluton this resulted in the enrichment of the ascending melts in h2o 3 9 to 6 1 wt f 2 6 to 4 1 wt and some incompatible elements zr nb th rb pb although the earliest evidence for the exsolution of homogeneous fluoride sulphate brine correlates with the final stage of the gr2 ascent the most intensive volatile s release from the emplaced magmas is shown to occur during their in situ crystallization which was associated with the separation of exsolved fluid into immiscible phases brine and low salinity solution compositions of these fluid phases are determined using atomic emission spectroscopy of the appropriate fluid inclusions opened by a laser microprobe and empa and sem eds analyses of daughter crystals the brine phase is enriched in mo mn be up to 17 8 and 0 3 g kg respectively and contains perceptible abundances of ce la pb zn whereas the low salinity phase is enriched only in be up to 0 6 g kg the selective mobilization of the metals from the melt into fluids is considered to result from the oxidized state of the melt and fluids peralkalinity of the melt during crystallization and high f content of the melt the immiscible fluid phases are shown to migrate together through the solidifying stock giving rise to the albitized granite that is enriched in molybdenite but devoid of be minerals in the country rocks solutions similar to the brine and low salinity phases of the magmatic fluid made up separate fluid flows which produced be and mo mineralization and were issued predominantly from the parental pluton both types of mineralization are nearly monometallic which suggests that of the metals jointly transported by the brine only mo and in part ce and la precipitated separately at the level where the low salinity solutions deposited be ores

combining quantitative textural and geochemical studies to understand the solidification processes of a granite porphyry shanggusi east qinling china igneous rock textures reflect the cooling history of the parental magma combined with chemical data they can provide physical and chemical information about the evolution of a magma body the petrographic textures and chemical compositions of 21 coarse and fine grained granite samples along an 250 m horizontal outcrop of the shanggusi granite porphyry are presented in this case study the coarse grained granite porphyry is an early intrusion and the fine grained granite dykes mostly intruded into the granite porphyry are later intrusions the studied samples have nearly homogeneous major element bulk rock and mineral compositions but show large variations in their trace element compositions and textural characteristics the trace element data suggest the influence of hydrous fluids possibly enriched in co2 f and cl in the evolution of the plutonic body textural analysis of the coarse grained granite porphyry indicates that the crystal size distribution csd slopes intercepts and total numbers of groundmass decrease from the center to the margin of the intrusion in contrast to the maximum diameter of the crystals lmax average length of the four largest quartz crystals for each sample however most fine grained samples and the groundmass of the coarse grained samples show concave down csds indicating textural coarsening quartz csds in the coarse grained samples are kinked with a steep sloped log linear section representing small crystals 5 1mm and a shallow sloped log linear section representing large crystals 4 1mm these two crystal populations are interpreted as resulting from a shift in cooling regime the straight csds of two fine grained samples may be due to a different cooling history in general the spatial variation of the csd patterns can be attributed to various degrees of overgrowth and mechanical compaction the quartz phenocrysts in several coarse grained samples exhibit a high degree of alignment which may be the result of magmatic flow by integrating the field geology geochemistry and quantitative textural data from the horizontal profile of the shanggusi granite porphyry it is suggested that hydrous fluids at the top of the intrusion not only controlled the fractionation of elements but also affected its cooling history fluid migration controlled undercooling can explain the solidification processes in the shanggusi intrusion and may also be prevalent in other fluid rich shallow intrusions quantitative integration of textural and geochemical data for igneous rocks can contribute to our understanding of the relationships between physical and chemical processes in a magma system and provide relatively comprehensive insights into the petrogenesis of granites

water solubility and chlorine partitioning in cl rich granitic systems effects of melt composition at 2 kbar and 800 c abstract experiments have been conducted in the system na2o k2o al2o3 sio2 h2o cl2o 1 at 2 kbar and 800 c to determine the effects of melt composition on the solubility of water in haplogranite melt and on the distribution of cl between aqueous fluid and haplogranite melt the melts studied include peraluminous subaluminous and peralkaline haplogranites and quartz albite and quartz orthoclase compositions the solubility of water at 2 kbar and 800 c in water saturated haplogranite melts varies strongly as a function of melt composition water solubility in melt decreases in the order strongly peralkaline haplogranite quartz albite composition moderately peralkaline haplogranite peraluminous haplogranite subaluminous haplogranite quartz orthoclase composition d cl wt cl in fluid wt cl in melt is a strong function of system composition d cl increases as the concentration of cl in the system increases a comparison of the distribution of cl between haplogranite melts of subaluminous peraluminous and peralkaline compositions and aqueous fluids shows that with similar concentrations of cl in the system d cl is largest for subaluminous melts a nk 1 having relatively high k2o concentrations as the a nk of melt increases or decreases from 1 or as the n nk of the melt increases both d cl and the concentration of cl in the fluid decrease the experimental data imply that complexes involving cl and na in hydrous subaluminous granite melts are dominant furthermore the data imply that in hydrous peraluminous granite melts cl complexes with network modifying a13 and in hydrous peralkaline granite melts cl complexes with network modifying na k on a molar basis cl apparently complexes with network modifying a13 in peraluminous melts as strongly as it does with na and k in peralkaline melts experimental studies of cl partitioning in granitic systems suggest that the strongest enrichment of magmatic hydrothermal fluids in cl and ore metals complexed with cl will most likely occur in fluids exsolved from subaluminous granite magmas that are relatively enriched in k2o sio2 and cl and relatively depleted in f co2 and na2o

fluid melt partitioning of re mo w tl and pb in the system haplobasalt h2o cl and the volcanic degassing of trace metals abstract the partition coefficients kd x f m of re mo w tl and pb between fluid h 2 o cl and a haplobasaltic melt in the cao mgo al 2 o 3 sio 2 system were measured between 1300 and 1400 c at 1 gpa and fluid chlorine molarities from 7 7 to 27 mol l dissociation of hydroxides added to a trace metal doped oxide powder produced a fluid phase in equilibrium with melt at the run conditions the kd x f m values were determined by mass balance of trace metals added with those determined in glass from the run products at 1300 c and fluid molarity of 7 7 mol l kd re f m 9 8 1 8 kd mo f m 11 8 1 6 kd w f m 3 7 1 6 kd tl f m 4 5 1 4 and kd pb f m 2 4 1 8 both mo and re were shown to partition most strongly into the fluid at all temperatures and fluid chlorinities at 1400 c kd pb f m and kd tl f m were the only elements showing any correlation with fluid chlorinities at 1400 c re and mo completely partitioned into the fluid and thus our calculated kd re mo f m are minima controls on fluid melt partitioning are explored in detail calculated values of kd re tl pb f m were combined with the diffusivity of these elements in a 1 d bubble growth model to evaluate the change in metal concentrations and metal ratios expected during the degassing of magma the model results were compared with emanation coefficients for trace metals from natural volcanoes the magnitudes of the modeled re tl and re pb in fluids using the diffusivity and partitioning values at 1300 c and the lowest fluid chlorinities were less than that observed from their emanation coefficients

what controls chemical variation in granitic magmas abstract consideration of the models that have been applied to explain the chemical variations within granitic rock suites shows that most are inadequate to account for the main variations this stems from a variety of model deficiencies ranging from physical or energetic inadequacies to incompatibility with the chemical data or internal inconsistency between models based on for example isotope or trace element data and major element data we contend that any model that fails any of these tests of internal consistency cannot be considered further thus although we can point to examples in which many of the traditionally accepted mechanisms have played secondary roles in producing variation there presently remains but one viable choice for the primary mechanism by which most granitic magmas acquire compositions beyond the range defined by the compositions of crustal melts that primary mechanism is peritectic assemblage entrainment pae we infer that once a partial melt has formed in a crustal protolith it may segregate from its complementary solid residue carrying small crystals of the peritectic phase assemblage formed in the melting reaction and that the ratios of individual peritectic minerals in the entrained assemblage remains fixed in the ratio decreed by the stoichiometry of the melting reaction for those elements with low solubilities in granitic melts pae in varying degrees accompanied by co entrainment of accessory minerals is responsible for most of the primary elemental variation in granitic magmas in contrast the concentrations of elements with high solubilities in silicic melts reflect the protolith compositions in a simple and direct way the source is the primary control on granite magma chemistry it dictates what is available to dissolve in the melt and what will be formed as the entrainable peritectic assemblage the apparent complexity in granitic rock suites is largely a consequence of these processes in the source all other mechanisms contribute only as a secondary overlay

exsolution of immiscible vapor and liquid phases from a crystallizing silicate melt implications for chlorine and metal transport abstract the compositional variation of a cl bearing aqueous fluid exsolving from a crystallizing silicate melt is evaluated for the system haplogranitic melt na k c1 h 2 o with attention to the effect of vaporliquid immiscibility on the aqueous fluid above critical pressures for the aqueous fluid p 1 5 kb at 800 c where the fluid is single phase the cl concentration in the aqueous fluid c cl aq gradually decreases with crystallization of a silicate melt under rayleigh fractionation as demonstrated by previous studies however the variation of ca is quite different below critical pressures where vapor liquid immiscibility occurs in particular at low pressures p cl h 2 o ratio in a melt is small and ca will increase with crystallization a high cl h 2 o ratio at low pressure results in liquid exsolution and decreasing ca with crystallization eventually both vapor and liquid phases will exsolve simultaneously regardless of the initial exsolving phase during this simultaneous exsolution the composition of the exsolving vapor and liquid phases the mass ratio of these phases and the cl concentration of the silicate melt will all remain constant comparison of the model and published experimental data indicates that the simultaneous exsolution of vapor and liquid may occur from a normal rhyolite crystallized at pressures below the critical pressure for the aqueous fluid therefore simultaneous exsolution of the immiscible aqueous phases is likely to be a common phenomenon in magmatic hydrothermal systems at conditions for the vapor liquid immiscibility model calculations at 0 6 and 1 2 kb indicate that major amounts of cl in the system will be distributed to the liquid phase particularly at the lower pressure this suggests that the majority of chloridecomplexed metals exsolving from a magma may be transported in the liquid phase under shallow crustal conditions

magma storage conditions of large plinian eruptions of santorini volcano greece the intensive variables of dacitic rhyodacitic magmas prior to four large plinian eruptions of santorini volcano over the last 200 kyr minoan cape riva lower pumice 2 and lower pumice 1 were determined by combining crystallization experiments with study of the natural products including the volatile contents of melt inclusions trapped in phenocrysts phase equilibria of the silicic magmas were determined at pressures of 1 2 and 4 kbar temperatures of 850 900 c fluid h2o co2 saturation xh2o molar h2o h2o co2 between 0 6 and 1 melt h2o contents of 2 10 wt and redox conditions of fmq fayalite magnetite quartz buffer or nno 1 where nno is ni nio buffer experiments were generally successful in reproducing the phenocryst assemblage of the natural products the phase relationships vary significantly among the investigated compositions revealing a sensitivity to small variations in whole rock compositions our results show that the pre eruptive storage conditions of the four silicic magmas were all very similar the magmas were stored at t 850 900 c and p 2 kbar under moderately reduced conditions nno 0 9 to 0 1 and were poor in fluorine 500 800 ppm and sulphur 100 ppm but rich in water and chlorine 5 6 wt and 2500 3500 ppm respectively in all cases the melts were slightly undersaturated with respect to h2o but most probably saturated with respect to h2o cl co2 and a brine the santorini magma plumbing system appears to be dominated by a large long lived 200 kyr predominantly silicic magma storage region situated at 8 km depth from which crystal poor melt batches were extracted during the largest caldera forming eruptions of the volcanic system

tracing the evolution and distribution of f and cl in plutonic systems from volatile bearing minerals a case study from the liujiawa pluton dabie orogen china fluorine and chlorine play an important role in magmatic differentiation hydrothermal alteration and related mineralization processes but tracing their evolution in magmatic and especially plutonic systems is not an easy task the f and cl in melts can be estimated from f and cl concentrations in minerals provided that partitioning between minerals and melts are constrained based on available partitioning models between mineral melt mineral fluid and melt fluid a set of equations has been derived to determine f and cl concentrations in melts from the compositions of amphibole biotite and apatite the new calculation procedure has been applied to a plutonic system the liujiawa pluton eastern dabie orogen china cl and f concentrations in amphiboles biotites and apatites from different rock types gabbronorite two pyroxene diorite clinopyroxene diorite and hornblende gabbro have been determined by electron microprobe most amphiboles show a negative correlation between log cl oh and mg number and a positive correlation between log f oh and a site occupation biotites from the gabbronorite and two pyroxene diorite show a slight positive correlation between log cl oh and mg which is however not the case for the clinopyroxene diorite apatites from all the samples are rich in f and show negative correlations between cl and f concentrations in our case study we demonstrate that the cl concentration in melt remains approximately constant at 1 000 2 000 ppm over the major crystallization interval but decreases strongly at near solidus temperatures as a result of fluid exsolution the f concentration in melt remains nearly constant at ca 2 000 3 000 ppm at high temperatures as well as near solidus conditions indicating that it is not largely affected by fluid exsolution because of its strongly preferred incorporation into melt interestingly the evolution of cl and f concentrations in melt with magmatic differentiation is similar to that determined in volcanic systems suggesting that the evolution of cl and f in melts during crystallization and late magmatic stages at depth plutonic systems is similar to that observed in volcanic systems during decompression and degassing

comparative study of mineral chemistry of four biotite types as geochemical indicators of mineralized and barren intrusions in the sungun porphyry cu mo deposit northwestern iran abstract the sungun porphyry copper molybdenum deposit in the northwestern part of the post collisional urumieh dokhtar magmatic arc developed as a consequence of hydrothermal alteration related to the emplacement of the sungun quartz monzonite porphyry stock into eocene volcanic rocks based upon petrographic characteristics back scattered electron images and compositional attributes biotite from the sungun porphyry copper molybdenum deposit was grouped into least altered magmatic biotite la mbt least altered equilibrated magmatic biotite la eq mbt equilibrated magmatic biotite eq mbt and secondary hydrothermal biotite s hbt types the la mbt from the mineralized zone have high tio2 3 92 4 33 wt compared to la eq mbt 3 81 4 20 wt eq mbt 2 75 3 85 wt and s hbt 0 27 3 00 wt the la mbt of the barren dike is also characterized by high tio2 4 17 wt on average na2o sio2 and mno wt of biotite are systematically different between mineralized intrusions and barren ones the highest amounts of na2o 0 39 0 58 wt and mno 0 11 0 18 wt are found in the la mbt of the barren dike which contrast with la mbt of the mineralized zone having 0 08 0 15 wt na2o and 0 03 0 14 wt mno low sio2 values 36 wt on average are characteristic of la mbt from the barren dike in comparison with la mbt of the mineralized zone 37 wt on average the so3 contents in la mbt of the mineralized zone 0 03 0 12 wt are much higher than those for la mbt of the barren dike 0 01 0 04 wt the fluctuations in so3 content of s hbt reflect a complex history of formation of s hbt in two stages one group of s hbt has so3 0 04 wt and are principally related to the potassic medium high phyllic low assemblage forming with magnetite at high oxygen fugacity whereas the second group has so3 fmq 2 where fmq is the fayalite magnetite quartz oxygen buffer typical of oxygen fugacities associated with cu mo porphyry mineralization altered biotite types have higher cl contents than the least altered varieties indicating that cl may be used as an indicator of post magmatic hydrothermal processes the range of f contents 0 336 0 621 wt for the la mbt of the mineralized zone is higher than those of the la mbt types of the barren dike 0 219 0 347 wt fluorine in biotite may be used as an exploration vector to characterize mineralized versus subeconomic porphyry cu mo systems

experimental determination of liquidus h 2 o contents of haplogranite at deep crustal conditions the liquidus water content of a haplogranite melt at high pressure p and temperature t is important because it is a key parameter for constraining the volume of granite that could be produced by melting of the deep crust previous estimates based on melting experiments at low p 0 5 gpa show substantial scatter when extrapolated to deep crustal p and t 700 1000 c 0 6 1 5 gpa to improve the high p constraints on h2o concentration at the granite liquidus we performed experiments in a piston cylinder apparatus at 1 0 gpa using a range of haplogranite compositions in the albite ab naalsi3o8 orthoclase or kalsi3o8 quartz qz sio2 h2o system we used equal weight fractions of the feldspar components and varied the qz between 20 and 30 wt in each experiment synthetic granitic composition glass h2o was homogenized well above the liquidus t and t was lowered by increments until quartz and alkali feldspar crystalized from the liquid to establish reversed equilibrium we crystallized the homogenized melt at the lower t and then raised t until we found that the crystalline phases were completely resorbed into the liquid the reversed liquidus minimum temperatures at 3 0 4 1 5 8 8 0 and 12 0 wt h2o are 935 985 875 900 775 800 725 775 and 650 675 c respectively quenched charges were analyzed by petrographic microscope scanning electron microscope sem x ray diffraction xrd and electron microprobe analysis empa the equation for the reversed haplogranite liquidus minimum curve for ab36 25or36 25qz27 5 wt basis at 1 0 gpa is t 0 0995 w text h 2 text o 3 5 0242w text h 2 text o 2 88 183 w text h 2 text o 1171 0 for 0 le w text h 2 text o le 17 wt and t is in c we present a revised p t diagram of liquidus minimum h2o isopleths which integrates data from previous determinations of vapor saturated melting and the lower pressure vapor undersaturated melting studies conducted by other workers on the haplogranite system for lower h2o 5 8 wt and higher temperature our results plot on the high end of the extrapolated water contents at liquidus minima when compared to the previous estimates as a consequence amounts of metaluminous granites that can be produced from lower crustal biotite amphibole gneisses by dehydration melting are more restricted than previously thought

the role of discontinuous magma inputs in felsic magma and ore generation for a long time granites have been considered as passive bodies ascending under intrinsic negative density and viscosity contrasts with their host rocks chemical variations within a granitic body resulted from in situ differentiation and crystal fractionation since the mid 1980s this global view has been significantly modified by i shifting melting from water saturated conditions to fluid absent reactions ii increasing the role played by the mantle during granite generation iii reassessing the rheology of partially molten rocks iv demonstrating stepwise segregation and ascent of magmas by analogue and numerical models v combining structural geophysical and geochemical studies to reveal the internal structures in granitic plutons it results that a granitic body is built up by a discontinuous accumulation of successive magma intrusions the discontinuous nature of magma emplacement has also significant consequences for its ability to generate ore the processes that lead to ore deposits are examined with a brief review of the magmatic and fluid phases that concentrate ore forming elements examples are taken from crustal derived granites and porphyry type deposits those are considered as the two end members of magmatic and hydrothermal ore deposits the source characteristics of the magma the emplacement mechanisms and magma mixing processes are the frame that controls the potential to carry base metals with the magma the distribution of elements is controlled by diffusion partition between minerals and melt solubility and redox conditions variations of those parameters are examined by considering their activation energy which controls the exponential dependence with temperature a characteristic length depending on the activation energy temperature variation and time is estimated for a characteristic time lag of 30 ka the intrusion of a magma into a magma chamber of similar composition hence temperature has few effects on diffusion partition coefficient and redox conditions because of a too low temperature contrast the intrusion of a mafic magma into a felsic one induces a variation of 300 c in both magmas the characteristic length of diffusion may vary by up to two orders of magnitude whereas the variation of partition coefficients is only one order of magnitude the redox conditions are about 2 5 log unit in the mafic magma but they can vary by 7 log units in the felsic magma hence a strong decrease in d values is observed in porphyry type deposits the effect is a removal of the elements with higher activation energy w sn zr from the mafic to the felsic magma deformation during the late stages of emplacement also controls ore formation

partitioning behavior of chlorine and fluorine in the system apatite silicate melt fluid the partitioning behavior of cl among apatite mafic silicate melt and aqueous fluid and of f between apatite and melt have been determined in experiments conducted at 1066 to 1150 c and 199 205 mpa the value of dclapatite melt wt fraction of cl in apatite cl in melt 0 8 for silicate melt containing less than 3 8 wt cl at higher melt cl contents small increases in melt cl concentration are accompanied by large increases in apatite cl concentration forcing dclapatite melt to increase as well melt containing less than 3 8 cl coexists with water rich vapor that containing more cl coexists with saline fluid the salinity of which increases rapidly with small increases in melt cl content analogous to the dependency of apatite composition on melt cl content this behavior is due to the fact that the solubility of cl in silicate melt depends strongly on the composition of the melt particularly its mg ca fe and si contents once the melt becomes saturated in cl additional cl must be accommodated by coexisting fluid apatite or other phases rather than the melt itself because cl solubility depends on composition the cl concentration at which dclapatite melt and dclfluid melt begin to increase also depends on composition the experiments reveal that dfapatite melt 3 4 in contrast to cl the concentration of f in silicate melt is only weakly dependent on composition mainly on melt ca contents so dfapatite melt is constant for a wide range of composition the experimental data demonstrate that the fluids present in the waning stages of the solidification of the stillwater and bushveld complexes were highly saline the cl rich apatite in these bodies crystallized from interstitial melt with high cl f oh ratio the latter was generated by the combined processes of fractional crystallization and dehydration by its reaction with the relatively large mass of initially anhydrous pyroxene through which it percolated

extreme halogen abundances in tin rich magma of the taylor creek rhyolite new mexico crystal bearing glass inclusions are hosted by quartz phenocrysts in eruptive units of the tin mineralized taylor creek rhyolite new mexico inclusions from four units were refused at 2 to 4 kbars and temperatures or 890 degrees c and analyzed for major and minor elements by electron microprobe and for h li be b rb st y nb mo sn cs ce th and u by ion microprobe average glass inclusion compositions are chemically representative of taylor creek melt and comparison of inclusion compositions with their whole rock equivalents suggests that li f cl ca and h 2 o degassed from cooling lava and or magma after inclusion entrapment taylor creek magma was strongly and variably enriched in f and cl prior to eruption average f concentrations of melt apparently ranged from 0 15 to 3 9 wt percent eruptive units containing the most f enriched glass inclusions are characterized by comparatively high average molar na 2 o na 2 o k 2 o ratios low li concentrations and relatively low phenocryst contents which are compatible with high preeruptive concentrations of f in magma average c1 concentrations were more uniform ranging from 0 23 to 0 37 wt percent high concentrations of f and cl are in accord with the style and extent of alteration in vapor phase altered parts of taylor creek rhyolite and are consistent with alkali chloride rich fluid inclusions in vapor phase minerals of altered rhyolites preeruptive enrichments in other volatiles were not as significant b in melt was 100 ppm and the apparent h 2 o content of melt was 2 wt percent geochemical studies of other tin topaz rhyolites and molybdenite bearing climax type porphyritic granites imply that their magmatic f concentrations were highly variable and that some fractions of magma were strongly enriched in halogens we suggest that such high levels of halogen enrichment may be generally representative of other highly evolved granitic magmas genetically associated with lithophile mineralization

primary magmatic biotite in granitoid intrusions associated with late mesozoic jinchanggouliang erdaogou lode gold deposits north china craton linkage to gold mineralization abstract the late mesozoic jinchanggouliang and erdaogou lode gold deposits in the central segment of the northern north china craton are mainly hosted in late archaean metamorphic rocks of the jianping formation and jurassic volcanic sedimentary rocks these deposits are spatially and temporally associated with a series of i type granitoid intrusions i e the 128 136 ma duimiangou granodiorite complex with a massive margin and a porphyritic center at jinchanggouliang the 161 4 1 1 ma loushang quartz diorite intrusion and numerous syenite porphyry dykes 160 9 1 0 ma at erdaogou and the 227 217 ma xitaizi monzogranite batholith compositions of primary magmatic biotite in these granitoid intrusions have been used to investigate the nature of granitoid magmas and the evolution of magmatic processes and to identify possible linkages between gold mineralization and granitoid magmatism all primary magmatic biotite grains are mg rich in composition xmg mg mg fe 0 41 0 69 the cl contents of biotite 0 09 0 42 wt in the loushang quartz diorite and the duimiangou massive granodiorite correlate negatively with xmg and are consistent with the mg cl avoidance rule the cl contents of biotite 0 01 0 14 wt in the duimiangou porphyritic granodiorite syenite porphyry and xitaizi monzogranite on the other hand remain relatively constant and may be affected by multiple variables such as cl rich fluids and subtle changes in temperature halogen fugacity of the parental magma calculated from biotite shows that the duimiangou granodiorite complex at jinchanggouliang and syenite porphyry dykes at erdaogou have the log fhf fhcl ranges of 0 71 to 0 27 and 2 16 to 1 08 respectively and have similar log fh2o fhcl values from 3 53 to 4 23 oxygen fugacities logfo2 calculated from biotite equilibria for the duimiangou granodiorite complex and syenite porphyry dykes are 13 7 to 7 2 straddling on the nickel nickel oxide and hematite magnetite buffers the xitaizi monzogranite and the loushang quartz diorite have lower log fo2 values from 14 9 to 12 4 between the nickel nickel oxide and hematite magnetite buffers the duimiangou granodiorite complex and syenite porphyry dykes with high oxygen fugacities are similar to oxidized magmas associated with porphyry cu mo au deposits these results suggest that multiple episodes of i type granitoid magmas in the study area were rich in cl and high in oxygen fugacity especially those associated with the duimiangou granodiorite complex and syenite porphyry dykes the i type melts represented by the duimiangou granodiorite complex and syenite porphyry dykes as well as their related cl rich oxidizing fluids were likely efficient in dissolving transporting and precipitating gold for the formation of the jinchanggouliang and erdaogou lode gold deposits

timing of multiple magma events and duration of the hydrothermal system at the yu erya gold deposit eastern hebei province china constraints from u pb and ar ar dating abstract the yu erya deposit is a large granite hosted gold deposit in the eastern hebei province classified as an intrusion related gold system the yu erya complex contains the causative intrusion which was the source of hydrothermal metal bearing fluids this composite granite complex contains miarolitic pegmatite like cavities and pegmatite veins a combination of detailed field observations and u pb dating by shrimp and la icp ms is used to document multiple magmatic events which occurred at 210 220 175 173 171 170 167 166 and 161 ma formed the yu erya granite complex the initiation of the hydrothermal system as determined via ar ar dating is closely related to the exsolution of a magmatic volatile phase from the g1 granite at ca 176 ma the hydrothermal system operated for 16 my 176 160 ma and produced multiple mineralising events 176 172 168 and 162 160 ma linked to emplacement of repeated magma pulses from 175 ma to 161 ma our results suggest that multiple magmatic hydrothermal events over a time period of several million years may be a fundamental factor responsible for the enrichment process during formation of intrusion related gold deposits and thus may be a requirement for forming economic orebodies

fluid melt trace element partitioning behaviour between evolved melts and aqueous fluids experimental constraints on the magmatic hydrothermal transport of metals abstract the fluid melt partition coefficients of ten trace metals li mn cu zn rb sr mo w and pb along with k between hydrous evolved melts and coexisting cl bearing fluid s have been experimentally determined at 850 1050 c 0 6 2 2 kbar and o2 nno 0 5 to nno 2 log units the measured compositions of the quenched fluid phases vary from low salinity 2 wt cl to 19 wt cl with maximum starting fluid concentrations of 21 wt cl the results of 15 partitioning experiments confirm that dmetalfluid melt values depend strongly on the melt and fluid composition with the greatest metal affinities for the fluid phase shown in the experiments with high cl fluids and the most fractionated melts five experiments conducted in au96cu4 capsule alloy show dcufluid melt values ranging from 40 to 80 and a strong correlation with melt feo wt contents at equivalent fluid cl contents in contrast li shows only weak partitioning in favour of coexisting fluids across all melt compositions with dlifluid melt ranging from 0 16 in low salinity fluids to 1 17 in the highest cl fluid 19 15 wt cl a procedure was employed to redissolve and analyse the aluminosilicate precipitates that form during quenching of the experiments this procedure allows for metal contents of the final quench fluids to be constrained by both mass balance and direct measurement by solution icp ms analysis a comparison of the mass balance calculated vs directly measured fluid melt partition coefficients generally gives good agreement within an order of magnitude for most trace elements however discrepancies between these methods arise due to errors inherent in the mass balance calculations for metals with low abundances in the fluids e g sr and especially those showing affinities to alloy with the experiment capsule material e g mo these discrepancies in constraining experimental fluid trace element budgets also suggest that the precious metal capsule alloys cannot always be considered completely inert containers in experimental investigations and semi quantitative la icp ms analysis of the raw capsule alloys confirms the detectable presence of several of the trace elements investigated here integrating these new partitioning data with previous experimental and natural studies confirms that aqueous cl bearing fluids exsolved by hydrous calc alkaline melts stored at mid to upper crustal conditions are capable of efficiently sequestering and transporting some economically important trace metals e g mn cu zn however the new fluid melt li partitioning data in conjunction with evidence of very late post eruptive li modification suggests that li is moderately strongly fluid immobile at depth and suffers from significant post eruptive re equilibration this has implications for deciphering the signatures of volatile fluxing in arc magmas that are preserved in mineral and melt inclusion trace element concentrations and the development of mineralised stockwork regions in porphyry style metal deposits

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

a diatom maximum horizon in upper quaternary deposits diatom maxima have been observed in three sediment cores two from the skagerrak norwegian sea area and one from the fram strait the maxima occur between 11 000 b p and 9 000 b p in the skagerrak norwegian sea and between about 9 000 b p and 4 500 b p in the fram strait it is thus likely that high diatom productivity as reflected by the diatom maximum horizons are time transgressive and follow the movements of the oceanic polar front the occurrence of diatom maximum horizons can therefore be used as a signal indicating the presence of the polar front at the time of deposition in both the skagerrak and norwegian sea cores the maximum consist of two distinct peaks the oldest characterized by cold water species thalassiosira antarctica the youngest characterized by temperate species reflecting the present diatom flora

dissecting through the metallogenic potentials of precambrian granitoids case studies from the bastar and eastern dharwar cratons india

partitioning of lithophile trace elements between h 2 o and h 2 o co 2 fluids and topaz rhyolite melt experiments have been conducted with h 2 o and h 2 o co 2 bearing fluids and melts of a cl f and lithophile trace element enriched vitrophyre associated with topaz rhyolite from spor mountain utah the starting material is mildly peraluminous and contains 1 25 wt percent f and 1 500 ppm cl the experiments were conducted with f sub o 2 controlled near ni nio at pressures of 0 5 to 4 kbars and at temperatures of 770 degrees to 950 degrees c fluid melt trace element distribution coefficients d i were calculated for li be b rb sr y zr nb cs ba ce th and u after ion microprobe analysis of starting material and run product glasses the concentration of element i in the fluid was calculated by mass balance and the fluid melt distribution coefficient d i was calculated as ppm by weight of i in fluid ppm by weight of i in melt the partitioning of li rb sr y nb cs and ce between aqueous fluids and melts of topaz rhyolite composition depends strongly on temperature and pressure at 0 5 kbars li rb sr y nb cs and ce concentrate in the fluid at temperatures or 900 degrees c at 2 kbars this same group of lithophile elements except for sr concentrate in the fluid at t or 900 degrees c be b and ba partition in favor of the melt at 0 5 and 2 kbars and at all temperatures of this study in the presence of co 2 free aqueous fluids at 4 kbars and at temperatures of 770 degrees to 950 degrees c all lithophile elements partition in favor of the melt this behavior for lithophile elements mimics that of published data on the partitioning of pb and zn between rhyolitic melts and cl bearing fluids previous studies have demonstrated an equivalent effect of pressure on the distribution of chalcophile trace elements between granitic melts and cl bearing aqueous fluids fluid melt distribution coefficients for the lithophile trace elements are significantly smaller for topaz rhyolite melts in equilibrium with mixed co 2 h 2 o fluids than for topaz rhyolite melts plus co 2 free aqueous fluids there is no evidence for co 2 complexing with the lithophile trace elements at pressures 6 m the data imply that the alkali elements m dissolve into the fluid as mcl 0 complexes and that ce dissolves into the fluid as a cecl 0 3 complex water saturated magmas of topaz rhyolite composition may become differentiated with respect to li cs and rb or ce y and nb if an aqueous fluid phase is evolved and moves through the magma under the influence of a temperature gradient that has a maximum temperature of at least 850 degrees to 900 degrees c

immiscibility between silicate magmas and aqueous fluids a melt inclusion pursuit into the magmatic hydrothermal transition in the omsukchan granite ne russia abstract exsolution unmixing of the volatile element rich phases from cooling and crystallising silicate magmas is critical for element transport from the earth s interior into the atmosphere hydrosphere crustal hydrothermal systems and the formation of orthomagmatic ore deposits unmixing is an inherently fugitive phenomenon and melt inclusions droplets of melt trapped by minerals provide robust evidence of this process in this study melt inclusions in phenocrystic and miarolitic quartz were studied to better understand immiscibility in the final stages of cooling of and volatile exsolution from granitic magmas using the tin bearing omsukchan granite ne russia as an example primary magmatic inclusions in quartz phenocrysts demonstrate the coexistence of silicate melt and magma derived cl rich fluids brine and vapour and emulsions of these during crystallisation of the granite magma microthermometric experiments in conjunction with pixe and other analytical techniques disclose extreme heterogeneity in the composition of the non silicate phases even in fluid globules within the same silicate melt inclusion we suggest that the observed variability is a consequence of strong chemical heterogeneity in the residual silicate melt brine vapour system on a local scale owing to crystallisation immiscibility and failure of individual phases to re equilibrate the possible evolution of non silicate volatile magmatic phases into more typical hydrothermal chloride solutions was examined using inclusions in quartz from associated miarolitic cavities

magmatic hydrothermal evolution of the donggou porphyry mo deposit at the southern margin of the north china craton evidence from chemistry of biotite abstract late mesozoic granitoids are widespread in the southern margin of the north china craton ncc occurring commonly as both small porphyritic stocks and large batholiths most of the mo deposits are closely associated with small porphyritic bodies in order to determine the relationship between mo mineralization and the granitoids a systematic geochemical study of biotite from the taishanmiao batholith and the mo mineralization associated donggou porphyry was conducted trace element features of biotites indicate a differentiation trend from rocks of the taishanmiao batholith to those of the donggou porphyry as revealed by systematically decreasing k rb ratios co ba v and ti and increasing cs li ta and tl the contents of mo also increase with the degree of magmatic differentiation the compositions of biotite follow a trend towards more magnesium rich compositions and mostly plot above the nno buffer the fe3 fe2 values of biotite gradually increase from the taishanmiao batholith to the donggou porphyry indicating the progressive increasing fo2 during magmatic differentiation the halogen fugacities of magmatic fluids calculated from biotite compositions show a trend of magmatic differentiation the earlier fluids associated with the taishanmiao batholith are relatively f poor with log fhf fhcl 0 the high degree of melt fractionation and progressive increasing of oxygen fugacity is beneficial to concentrate mo in the residual melt in addition later relatively f rich fluid may be beneficial to extract mo from the melt and thus favorable for mo mineralization

fluid inclusion evidence for immiscibility in magmatic differentiation abstract after a brief review of recent work on melt inclusions in diamond and in normal magmatic environments the nature of the fluid inclusion evidence for various stages of magmatic immiscibility is summarized during magmatic differentiation by crystal fractionation from originally low volatile content silicate melts yielding normal plutonic rocks through hydrous silicate melts yielding pegmatites to late stage water rich fluids yielding quartz veins and ore deposits the composition of the residual liquid changes drastically in some geologic environments this change in composition of the residual liquid may be continuous with no phase change in the fluid part of the system under most natural conditions however it is far more likely to have one or more stages in the evolution during which globules of a separate new immiscible fluid phase exsolve the term immiscibility is used here in its more general sense to refer to the existence at equilibrium of two or more non crystalline polycomponent solutions fluids differing in properties and generally in composition i believe that the great bulk of the magmatic inclusions that are being studied today have come about through the intervention of one or more such stages of immiscible fluid separation i e magmatic differentiation by fluid immiscibility examples include silicate melt dense co2 fluid silicate melt sulfide melt silicate melt silicate melt silicate melt low density vapor i e vesiculation and as presented in more detail in this paper various stages of silicate melt hydrous saline melt aqueous fluid co2 fluid immiscibility generally only parts of these stages are recorded by the trapping of fluid inclusions and the interpretation of the inclusion record is commonly ambiguous and difficult particularly that stage between hydrous silicate melts and the hydrous saline melts and aqueous solutions responsible for many ore deposits the ambiguity results mainly from problems of inclusion origin and nonrepresentative trapping within any given individual inclusion thus the probability of trapping of only one vs various amounts of two immiscible fluids or of trapping solid phases along with the fluid present severe difficulties in addition there is the almost universal superposition of various stages of trapping of fluids within any given sample these problems can only be approached by very careful petrography and analysis of optimum material combined with field data and experimental p v t x studies of pertinent systems completely unequivocal statements of the course of evolution of the fluids in such natural systems may never be possible

the role of supercritical fluids in the potassium enrichment of magmas at mount etna volcano italy abstract the enrichment in potassium shown by the basic lavas erupted at mount etna volcano after 1971 k2o max 2 2 wt has been considered by previous researchers to be too high to be related to simple crystal fractionation and instead linked this high k2o content to either crustal assimilation or changes in the magma source unfortunately all existing models for the post 1971 k2o enrichment fail to explain the phenomenon satisfactorily leaving the question still open we present a critical re examination of published data for major elements 633 whole rock analyses trace elements 376 whole rock analyses and isotopic ratios 136 87sr 86sr analyses for historical and pre historical lavas potassium enrichment is not limited to the products of the last 35 years a comparable increase in potassium is noticed in lavas erupted during the pre historic phase of the recent mongibello k2o max 2 5 wt and in lavas related to the early phase of the ancient mongibello k2o max 3 wt moreover data from melt inclusions in olivines from the 2001 and 2002 eruptions reveal that potassium contents remain constant for melts with entrapment pressure between 490 to 100 mpa and increase significantly in melts entrapped at pressures below 100 mpa we propose that supercritical fluids coming from deeper magmas and carrying alkali cl complexes migrate through basic to intermediate magmas residing in the shallow feeding system as chlorine exsolves and leaves the system alkalis are released contributing to the observed potassium enrichment of the shallow magma fluctuations of the volatiles influx throughout time are likely related to the magma supply rate considering that the amount of magma entering a plumbing system is determined by the rate of regional extension the flux of alkali cl complexes entering the melt might be related to an extensional regime acting in the etnean area

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

can economic porphyry copper mineralization be generated by a typical calc alkaline melt numerical simulation of chlorine and copper partitioning between a crystallizing melt and exsolving aqueous fluids indicates that typical calc alkaline magmas contain sufficient copper chlorine and water to produce economic porphyry copper mineralization neither an elevated copper content in the magma nor an additional large volume of magma are required to provide metals or volatiles the most important variables that determine the volume of melt necessary to produce sufficient copper are the degree of compatible behavior displayed by copper the ratio of initial water in the melt to the water saturation level and the initial chlorine water ratio of the melt the absolute values for initial water in the melt and water content at saturation are relatively unimportant in determining the required melt volume the bulk salinity of the exsolved fluid may vary from 2 0 wt nacl to saturation levels 84 wt nacl at 700 c indicating that boiling is not necessary to produce high salinity brines at appropriate p t xnacl conditions the magmatic aqueous fluid separates into a saline liquid which transports most of the copper and a low salinity vapor the salinities of the two immiscible phases are governed by the p t conditions while the bulk fluid salinity determines the mass fractions of liquid and vapor formed pressure quenching causes rapid crystallization of the aplitic groundmass in porphyritic rocks associated with copper mineralization and significantly reduces the amount of chlorine and copper partitioning to the aqueous fluid this results in abrupt and possibly large reductions in fluid salinity and causes copper to become concentrated in the melt as copper is transported from the melt by the earliest exsolving fluids in deep 2 0 kbar systems and by late exsolving fluids in shallow 0 5 kbar systems the relative timing of pressure quenching aplite formation and fluid transport of copper from the melt can vary significantly in systems produced under different confining pressures model results incorporating petrologic constraints determined for yerington nevada are in good agreement with observed mineralization