the effect of fluorine boron and excess sodium on the critical curve in the albite h 2 o system experiments to define the critical curve for a series of silicate melts in equilibrium with a hydrous fluid were carried out in a hydrothermal diamond anvil cell silicate compositions studied were albite with several wt excess na2o b2o3 and f2o 1 complete miscibility between melt and water was observed at lower pressure and temperature conditions compared to pure albite for all compositions for albite excess na2o the critical curve had been lowered by 143 and 247 c at 10 kbar for 5 and 10 wt excess na for albite 5 and 10 wt f the difference at 10 kbar was 147 and 246 c respectively and for albite 5 and 10 wt b differences of 168 and 262 c were found these results are likely to be additive with the presence of more than one of the components depressing the critical curve to even lower temperatures and pressures the results suggest that in complex pegmatitic systems complete miscibility between melt and fluid may be important in the final stages of crystallisation the unusual properties of fluid phases under conditions close to the critical curve in a silicate melt water system may be essential for the enrichment of trace elements in pegmatites as well as for the formation of typical pegmatite textures

magmatic hydrothermal processes recorded by muscovite andcolumbite group minerals from the bailongshan rare element pegmatites in the west kunlun karakorum orogenic belt nw china abstract the mineralization of rare element pegmatites is attributed to complex magmatic hydrothermal processes such as magma fractionation fluid exsolution and fluid melt metasomatism however it is still unclear how these processes affect the evolution of pegmatites and the fractionation of rare elements here we use the textures and major and trace element compositions of muscovite and columbite group minerals cgm from the newly discovered bailongshan li cs ta lct type pegmatites in the west kunlun karakorum orogenic belt nw china to decipher the magmatic hydrothermal processes related to enrichment of rare elements four major regional zones are recognized in the bailongshan area quartz albite tourmaline qat zone quartz muscovite qm zone quartz albite spodumene qas zone and quartz spodumene qs zone the qat and qm zones are barren whereas the qas and qs zones host six major li rb ore segments i to vi along the nww see strike from the qm zone through the qas to the qs zone the k rb ratios of muscovite decrease gradually from 26 0 to 7 8 and cgm has mn s increasing from 0 28 to 0 56 consistent with the trend of progressive evolution of the pegmatites the ta profiles across individual cgm grains reveal a three stage growth process i e from a nb rich cgm magmatic stage to a ta rich cgm magmatic stage to a nb rich cgm hydrothermal stage high resolution elemental mapping of primary muscovite from the qas and qs zones shows that melt metasomatism induced local enrichment of f li cs and ta and the precipitation of secondary lepidolite along the rims or cleavages of primary muscovite in addition late stage f poor fluid metasomatism caused the release of fe mn b rb and cs from primary muscovite and induced complex zoning patterns and crystallization of hydroxylapatite in cleavage planes of primary muscovite secondary muscovite has higher li be b rb and cs and lower nb than primary muscovite indicating that these elements may have been partially dissolved and remobilized from primary spodumene muscovite and cgm into late stage hydrothermal fluids from which the secondary muscovite and nb rich cgm crystallized therefore the complex zoning patterns and compositional variations of both muscovite and cgm from the bailongshan pegmatites record a progressive magmatic hydrothermal process related to the rare metal mineralization

evidence for aqueous liquid liquid immiscibility in highly evolved tin bearing granites mount pleasant new brunswick canada abstract three distinct types of fluid inclusions i e liquid vapor lv liquid vapor solid lvs and v only co exist within a single primary fluid inclusion assemblage in fluorite crystals that formed prior to and in close association with cassiterite mineralization in an assemblage comprising fluorite arsenopyrite topaz cassiterite in the sn w mo deposit of the north zone mount pleasant new brunswick the mineral assemblage occurs in vugs with late quartz and chlorite filling the remainder of the open space solid bearing inclusions contain up to eight optically different solids which are estimated to occupy up to approximately 70 vol of the fluid inclusions in a given fluid inclusion assemblage each type of fluid inclusion shows consistent l v or l v s phase ratios the results of microthermometric analyses show that lv inclusions have low salinities that vary from 0 to 10 wt nacl eq and homogenization temperatures that vary from 91 to 250 c within a given assemblage the ranges of salinity and homogenization temperatures of lv inclusions are even less in contrast co existing lvs inclusions are highly saline with salinities ranging from 36 to 40 wt nacl eq and have much higher homogenization temperatures that vary from 425 c to 600 c the upper limit of the microthermometric stage the salinity and homogenization temperature ranges of lvs inclusions show a limited range for a given assemblage the solids in lvs inclusions are interpreted as daughter phases due to consistent phase ratios in lvs fluid inclusions and because during heating experiments all solid phases melted prior to liquid vapor homogenization the consistency of phase ratios and the results of microthermometric analysis among lv or among lvs inclusions show that these inclusions were not formed through necking down of larger inclusions in addition the absence of sweat halos and re entrants rules out water loss as a possible mechanism for producing these coexisting fluid inclusions fluid inclusions of highly contrasting salinities and homogenization temperatures are therefore interpreted to be the result of trapping from two immiscible aqueous liquids it is unknown whether the two liquids exsolved from one single aqueous fluid or have different origins but consideration of the nature of inclusion assemblages in samples from other parts of the system suggest the latter topaz and cassiterite within the same mineral assemblage as well as late quartz contain lv fluid inclusion assemblages with microthermometric behaviors that are similar to the lv type inclusions in coexisting fluorite hosted lv and lvs inclusions suggesting that cassiterite deposited from the low salinity and temperature fluid

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

melt inclusions in pegmatite quartz complete miscibility between silicate melts and hydrous fluids at low pressure fluorine boron and phosphorus rich pegmatites of the variscan ehrenfriedersdorf complex crystallized over a temperature range from about 700 to 500 c at a pressure of about 1 kbar pegmatite quartz crystals continuously trapped two different types of melt inclusions during cooling and growth a silicate rich h2o poor melt and a silicate poor h2o rich melt both melts were simultaneously trapped on the solvus boundaries of the silicate fluorine boron phosphorus water system the partially crystallized melt inclusions were rehomogenized at 1 kbar between 500 and 712 c in steps of 50 c by conventional rapid quench hydrothermal experiments glasses of completely rehomogenized inclusions were analyzed for h2o by raman spectroscopy and for major and some trace elements by emp electron microprobe both types of melt inclusions define a solvus boundary in an xh2o t pseudobinary system at 500 c the silicate rich melt contains about 2 5 wt h2o and the conjugate water rich melt about 47 wt h2o the solvus closes rapidly with increasing temperature at 650 c the water contents are about 10 and 32 wt respectively complete miscibility is attained at the critical point 712 c and 21 5 wt h2o many pegmatites show high concentrations of f b and p this is particularly true for those pegmatites associated with highly evolved peraluminous granites the presence of these elements dramatically reduces the critical pressure for fluid melt systems at shallow intrusion levels at t 720 c water is infinitely soluble in a f b and p rich melt simple cooling induces a separation into two coexisting melts accompanied with strong element fractionation on the water rich side of the solvus very volatile rich melts are produced that have vastly different physical properties as compared to normal silicate melts the density viscosity diffusivity and mobility of such hyper aqueous melts under these conditions are more comparable to an aqueous fluid

phase equilibria of a fluorine rich leucogranite from the st austell pluton cornwall highly evolved leucogranitic rocks in the st austell pluton cornwall of hercynian age contain accessory muscovite topaz and fluorite the authors have studied the h sub 2 o saturated melting behavior of one representative sample its solidus and liquidus pass through the points 663 and 725 sup 0 c respectively at 1 kbar 640 and 665 sup 0 c at 2 kbar 610 and 717 sup 0 c at 4 kbar and 608 and 700 sup 0 c at 8 kbar plagioclase is on the liquidus at low pressure and topaz is on the liquidus at 4 kbar the fluorite is consumed in the formation of the first formed liquid calcium can partition into an evolved granitic melt if complexed by fluorine the fluorite appears to be largely primary in fresh fluorite granite at st austell and not to reflect the albitization of oligoclase in the surrounding biotite granite such fluorine rich leucogranites can be expected to be of subsolvus character

magmatic evolution of li f rare metal granites a case study of melt inclusions in the khangilay complex eastern transbaikalia russia abstract we report compositions of homogenized quartz hosted melt inclusions from a layered sequence of li f rich granites in the khangilay complex that document the range of melt evolution from barren biotite granites to ta rich lepidolite amazonite albite granites the melt inclusions are crystalline at room temperature and were homogenized in a rapid quench hydrothermal apparatus at 200 mpa before analysis homogenization runs determined solidus temperatures near 550 c and full homogenization between 650 and 750 c the compositions of inclusions determined by electron microprobe and raman spectroscopy for h 2 o show regular overall trends of increasing differentiation from the least evolved khangilay units to apical units in the orlovka intrusion total volatile contents in the most evolved melts reach over 11 wt h 2 o 8 6 wt f 1 6 wt b 2 o 3 1 5 wt concentrations of rb range from about 1000 to 3600 ppm but other trace elements could not be measured reliably by electron microprobe the resulting trends of melt evolution are similar to those described by the whole rock samples despite petrographic evidence for albite and mica rich segregations previously taken as evidence for post magmatic metasomatism melt variation trends in most samples are consistent with fractional crystallization as the main process of magma evolution and residual melt compositions plot at the granite minimum in the normative qz ab or system however melts trapped in the highly evolved pegmatitic samples from orlovka deviate from the minimum melt composition and show compositional variations in al na and k that requires a different explanation we suggest that unmixing of the late stage residual melt into an aluminosilicate melt and a salt rich dense aqueous fluid hydrosaline melt occurred experimental data show the effectiveness of this process to separate k aluminosilicate melt from na hydrosaline melt and high mobility of the latter due to its low viscosity and relatively low density may explain local zones of albitization in the upper parts of the granite

fluid inclusion examination of the transition from magmatic to hydrothermal conditions in pegmatites from san diego county california thermometric properties and compositions of fluid inclusions in quartz are used to constrain the roles that fluid soluble elements principally li b cl and f have in controlling the transition from magmatic to hydrothermal mineral paragenesis in pegmatites and to ultimately understand why some pegmatites in the san diego county pegmatite district contain abundant gem quality li bearing minerals in pockets whereas others do not in this district lithium cesium tantalum type pegmatites occur in the mesozoic peninsular ranges batholith emplacement of the dikes occurred at low pressures 200 300 mpa that resulted in the formation of large miarolitic cavities pockets some of which contain gem quality li bearing minerals two pegmatite suites were studied the gem bearing himalaya and the more barren la posta the inclusions measured in this study further underscore highly undercooled crystallization of pegmatites pressure corrected homogenization temperatures t h of 400 to 515 and 70 to 425 c were obtained for primary inclusions in the intermediate zone and the core respectively of a la posta dike primary inclusions in the intermediate zone and the massive quartz core of the himalaya pegmatite have t h ranges of 350 to 420 and 150 to 300 c respectively the high portion of the latter temperature range is interpreted to represent the conditions that existed during the initial crystallization of minerals that line pegmatite pockets the most important cations in fluid inclusions in both pegmatites are na b3 and li lithium concentrations are much higher in inclusions in the himalaya pegmatite up to 51 at of all cations within the massive quartz in the core zone in the la posta pegmatite few primary inclusions contain appreciable li the b content of inclusions in both pegmatites is high up to 65 at of cations the dominant anions in the inclusions are cl f and formula 1 the data suggest that hydrothermal fluids that collected in pockets were acidic and promoted the growth of tourmaline and other minerals that are stable in acidic solutions in both pegmatites na and b dominate secondary inclusions these inclusions reveal fluids stripped of li and k by crystallization of lepidolite within fractures of primary minerals throughout the pegmatites and sometimes as an alteration product in pockets the lowering of alkali h ratios in the fluid stabilized clays including kaolinite that line the walls of pockets coeval crystallization of terminated quartz crystals with clays is consistent with its precipitation from the fluids 1 embed mml math 1 gif

experimental evidence for a relationship between liquid immiscibility and ore formation in felsic magmas abstract geological studies demonstrate that liquid immiscibility in felsic magma closely associates with the ore forming process in order to obtain experimental evidence demonstrating the relationship between the ore forming process and liquid immiscibility in felsic magma we carried out a series of experiments at high temperature and atmospheric pressure the experimental results show that the granite kbf 4 na 2 moo 4 system is a homogeneous melt at high temperature with decrease in temperature however the melt decomposes into two immiscible melts silicate melt and ore forming melt the ore forming melt exists as globules in the silicate phase molybdenm ca na mg p mn f b and oh are concentrated in these globules the ore forming melt is characterized with very low sio 2 and al 2 o 3 concentrations but the concentration of moo 3 and cao is very high in contrast the silicate melts are significantly enriched in sio 2 and al 2 o 3 and depleted in moo 3 and cao in the silicate melt the concentrations of network modifying elements e g mo ca na p mg and volatiles f oh are very low the differences between the two immiscible melts exist not only in chemical composition but also in structure the ore forming melt structurally consists of moo 4 moof 4 b oh 4 and oh while the silicate melt is si0 4 because of the difference in composition and structure the two immiscible melts possess different physical properties compared to silicate melt the ore forming melt has a lower density and viscosity which permits the globules to behave as bubbles in granite magma and to move and concentrate in the upper part of magma chamber this process is probably responsible for the concentration of ore forming elements in the upper part of granite bodies and their immediate aureoles the present experimental results suggest that liquation in felsic magma can be the first step in the ore forming process during granitoid evolution

tungsten solubility in evolved granitic melts an evaluation of magmatic wolframite abstract a variety of parameters that potentially control the solubilities of synthetic hubnerite mnwo4 and ferberite fewo4 in haplogranitic melts rich in fluxing compounds have been determined at 200 mpa in order to test the hypothesis that wolframite can occur as a magmatic mineral the melts considered representative of highly evolved pegmatites contain 1 1 1 7 and 2 02 wt of li2o p2o5 and b2o3 respectively although the molar al na k ratio is one if li is considered to be an alkali element the molar al na k li asili of the melt is 0 88 and the melt is peralkaline hubnerite and ferberite solubilities at 800 c are strongly controlled by melt composition they are much lower in subaluminous melt asili 1 05 than in peralkaline melt by contrast hubnerite and ferberite solubilities are nearly independent of the fluorine content of the melt for up to 8 wt f hubnerite and ferberite solubilities at 800 c are also nearly independent of oxygen fugacity over a log f o 2 range of approximately ni nio 3 to ni nio 2 which implies that the predominant oxidation state of tungsten in the melts is 6 even at moderately reduced conditions a series of experiments on haplogranitic melt rich in fluxing compounds with 0 and 6 wt f at 850 650 c shows that temperature strongly influences hubnerite solubility e g the solubility product of hubnerite k sp hub in the melts with 6 wt f decreases from 71 0 7 9 10 4 mol2 kg2 at 850 c to 4 4 2 3 10 4 mol2 kg2 at 650 c our experimental results show that ferberite solubilities are much higher than those of hubnerite with the same composition of melt but the mn fe and w concentrations in natural melt inclusions indicate that these melts were undersaturated with wolframite at 800 c however flux rich melts crystallize at lower temperatures in nature and the occurrence of natural magmatic wolframite was evaluated by comparing experimental solubility product values extrapolated to 500 c with wolframite activities at these temperatures magmatic wolframite is unlikely in flux rich peralkaline melts but by contrast flux rich subaluminous to peraluminous melt inclusions appear to have been saturated with wolframite at approximately 500 c because of the strong temperature dependence of wolframite solubility the dominant effect of fluxing compounds is to lower the solidus temperature of the melt

liquid immiscibility and its role at the magmatic hydrothermal transition a summary of experimental studies several types of fluid immiscibility may affect the evolution of volatile rich magmatic systems at the magmatic hydrothermal transition the topology of silicate salt h2o systems implies that three fluid immiscibility silicate melt hydrosaline melt vapour should be stable in a broad range of compositions and p t conditions the most important factor controlling the immiscibility appears to be the coulombic properties electric charges z and ionic radii r of the main network modifying cations and the capacity for immiscibility appears to decrease in the following sequence mg ca sr ba li na k liquid immiscibility is enhanced in peralkaline compositions and in the presence of nonsilicate anions such as f cl co32 and bo33 in volatile rich magmatic systems the h2o is likely to react with the chloride fluoride borate and carbonate species and the chemical effects of high temperature hydrolysis may be greatly enhanced by phase separation in systems with multiple immiscible fluid phases natural granitic magmas can thus exsolve a range of chemically and physically diverse hydrosaline liquids and the role of these fluid phases is likely to be especially significant in pegmatites and li f rare metal granites

formation of extremely f rich hydrous melt fractions and hydrothermal fluids during differentiation of highly evolved tin granite magmas a melt fluid inclusion study quartz crystals from topaz zinnwaldite albite granites from zinnwald erzgebirge germany contain in addition to primary and secondary fluid inclusions fis abundant crystalline silicate melt inclusions mis with diameters up to 200 m these mis represent various stages of evolution of a highly evolved melt system that finally gave rise to granite related sn w mineralization the combination of special experimental techniques with confocal laser raman microprobe spectroscopy and empa permits precise measurement of elevated contents of h2o f and b in re homogenized mis the contents of h2o and f were observed to increase from 3 to 30 and 1 9 to 6 4 wt respectively during magma differentiation however there is a second mi group very rich in h2o with values up to 55 wt h2o and an f concentration of approximately 3 wt ongoing enrichment of volatiles h2o f b and cl and of cs and rb can be explained in terms of magma differentiation triggered by fractional crystallization and thus is suggested to reflect elemental abundances in natural magmas and not boundary layer melts partitioning between melt and cogenetic fluids has further modified the magmatic concentrations of some elements particularly sn the coexistence of two types of mis with primary fis indicates fluid saturation early in the history of magma crystallization connected with a continuous sequestration of sn f and b the results of this study provide additional evidence for the extraordinary importance of the interplay of h2o f and b in the enrichment of sn during magma differentiation by decreasing the viscosity of and increasing the diffusivity in the melts as well as by the formation of various stable fluoride complexes in the melt and coexisting fluid

alongshore variation in foredune height in response to transport potential and sediment supply south padre island texas abstract the height and extent of coastal dune development can exhibit considerable variability over short distances leading to variable storm impact alongshore the source of this variation is not well understood in general and in many cases is not easily explained by models that ascribe dune height and development to regional variations in sediment availability and foreshore slope in this paper lidar data collected in 2000 and 2005 from south padre island texas are used to characterize the alongshore variation in dune morphology and to identify how the variation is related to foreshore morphology and nearshore state results of cross wavelet analysis suggest that foredune height exhibits a statistically significant coherence with the surf similarity parameter at length scales of 1300 of 2300 m the resulting variation in beach state alongshore from intermediate to dissipative is the consequence of wave refraction and focusing by transverse ridges on the inner shelf dune height reaches a local maximum approximately halfway between the more intermediate and dissipative sections of the coast where the volume of sediment in the backshore and in the foreshore bars are also at a maximum the greater elevation of the foreshore and backshore also provides a wider fetch and potential for aeolian transport during the storm surge that tends to accompany storm winds it is argued that the variation in dune morphology is not strictly the result of transport limitations as suggested by the fetch model but rather depends on the alongshore coincidence of transport potential with an available supply of sediment in the backshore and on the foreshore

an experimental study of b p and f rich synthetic granite pegmatite at 0 1 and 0 2 gpa extreme enrichment in h2o b p and f is characteristic of many evolved granites and pegmatites we report experimental phase relations of a synthetic peraluminous pegmatite spiked with p2o5 b 2o3 and f 5 wt of each rb2o cs2o 1 wt of each and li2o 0 5 wt experiments were carried out in h2o satu rated conditions in cold seal rapid quench pressure vessels at 0 1 0 2 gpa crystallisation starts at about 820 c with berlinite and topaz quartz appears at 700 750 c topaz is replaced by muscovite at about 600 c at near solidus temperatures 450 500 c amblygonite lacroixite and a cs bearing aluminosilicate crystallise in all charges aluminosilicate melt coexists with low density hydrous fluid and hydrosaline melt the latter is strongly enriched in na3alf6 and h3bo3 components experi mental evidence of the liquid immiscibility and mineral reactions documented in our study offers new explana tions of many enigmatic features of natural pegmatites

stable isotope b h o and mineral chemistry constraints on the magmatic to hydrothermal evolution of the varutrask rare element pegmatite northern sweden abstract the internal evolution of the varutrask rare element pegmatite skellefte district northern sweden has been investigated using stable isotope b h o geochemistry of tourmaline and coexisting micas feldspar and quartz varutrask is a classic and typical example of highly fractionated lct type pegmatites with a pronounced concentric zoning pattern composed of well developed border wall and intermediate zones and a quartz core the pegmatite displays considerable rare element enrichment culminating in the formation of albite lepidolite and pollucite units in the innermost zones major and trace element variations in tourmaline from the main pegmatite zones correlate well with the internal zoning pattern mineral compositions record an abrupt change in fractionation trends between the barren outer and intermediate zones and the inner late stage assemblages that carry rare element mineralization this change is also shown by the b isotope variations of tourmaline early and mid stage tourmalines record a systematic increase in 11 b from 14 6 to 6 2 which can be explained by closed system melt mineral isotope fractionation whereby crystallization of large amounts of muscovite preferentially removes 10 b from the residual melt in contrast tourmaline from late stage assemblages in the inner zones and cross cutting veinlets shows a reversal in the b isotope trend with a decrease in 11 b from 8 to 14 1 this reversal cannot be explained by mineral melt isotope fractionation but requires fluid melt partitioning and partial fluid loss hydrogen isotope variations in mica support this model the systematic increase in d from 75 in the outer zones muscovite to 63 and 53 in the inner zones li micas cannot be explained by closed system variations in temperature or melt mica fractionation but it is consistent with late fluid exsolution oxygen isotope compositions of tourmaline 18 o from 9 7 to 11 6 quartz 13 3 to 14 and mica 10 3 to 11 3 show good agreement with equilibrium partitioning and yield temperatures in the range 450 c to 600 c combining this with the stability fields of li aluminosilicates petalite and spodumene indicates crystallization pressures of 2 3 kbar taken together the stable isotope and mineral chemistry data demonstrate that rare element enrichment in the innermost fractionated assemblages in the varutrask pegmatite was associated with the transition from purely magmatic crystallization to conditions where a separate aqueous fluid phase became important

revisiting complete miscibility between silicate melts and hydrous fluids and the extreme enrichment of some elements in the supercritical state consequences for the formation of pegmatites and ore deposits abstract using water and major and trace element data obtained from melt inclusions primarily in pegmatite quartz we have shown in this and previous papers that melt melt fluid immiscibility is widespread and an important process during the generation of granitic pegmatites furthermore we have shown that the formation of pegmatites actually begins in the supercritical melt fluid stage in this study we extend previous work and in particular explore the behavior of 10 different elements be f p s cl as rb sn cs and ta in the supercritical range from preliminary studies we suggest that other elements such as b na k zn nb and sb will behave similarly near the solvus crest of a generalized pseudo binary melt water system this provides important evidence that pegmatite forming processes have already begun at high temperatures in the range of 850 750 c and that may require a re think on the partitioning behavior of metals in late stage residual melts exsolved from granitic magmas the existence of this parental supercritical silicate melt fluid although derived from granitic magmas imposes significant constraints of its own so drawing conclusions about pegmatite forming processes from data gained from slightly modified granite compositions becomes highly problematic we propose that the extremely high concentration of some elements over a small but well defined water concentration range symmetrically distributed around the critical point of the pseudo binary solvus must be derived from the unusual properties of the near critical or supercritical phases these unusual properties include extremely low density viscosity and surface tension and high diffusivity reactivity and mobility these are exactly the qualities that make such supercritical fluids an excellent medium for the formations of pegmatites by reactions with the existing matrix melt crystal mush and for the extreme enrichment of some ore forming elements highly soluble in alkali and water rich supercritical fluids a very important point in mineral crystallization is the non uniform local enrichment of rare and economically significant elements at specific locations in pegmatites granites and other rocks given the properties of the supercritical phase identified from melt inclusions the process of ostwald ripening can operate very effectively the driving force for ostwald ripening arises because the concentration of solute in the vicinity of small crystals or clusters is greater than and in the vicinity of larger crystals or clusters less than the average supersaturation the solute in the supercritical fluid therefore flows from the small crystals to the larger crystals and permits the growth of very large crystals at the expense of smaller ones this is favored by the extraordinary properties of supercritical fluids given the low surface tension the supercritical fluid can move also through grain boundaries and small channels or dislocation pipes aiding incompatible element transport additionally their consequences for the formation of some important granite related ore deposits are briefly outlined

trace element geochemistry by laser ablation icp ms of micas associated with ta mineralization in the tanco pegmatite manitoba canada in the tanco pegmatite one of the world s major ta deposits tantalum mineralization shows a complexity that reflects the complex petrogenesis of its host pegmatite micas are common in most of the pegmatite units and are intimately associated with the successive stages of ta mineralization from the wall zone to the central zones where micaceous replacement is pervasive different generations of micas both primary and secondary associated with ta oxides were selected for electron microprobe and laser ablation icp ms investigation their chemical trends are used to constrain the magmatic versus hydrothermal processes that played a role in their crystallization and their associated ta mineralization micas range from dioctahedral muscovite to trioctahedral lepidolite through al li substitution unexpectedly the most evolved compositions low k rb ratios and high li contents occur in the wall zone they are interpreted to reflect nonequilibrium crystallization from an undercooled melt with or without boundary layer effects in the central zones the fine grained mica quartz assemblage hosts some coarser grained li muscovite which has the highest ta contents up to 400 ppm these li f a rich micas are interpreted to originate from a magmatic metasomatic event which was also at the origin of the mqm style ta mineralization at tanco however the li ta poor muscovite end member compositions of fine grained alteration micas suggest crystallization from an aqueous fluid during a metasomatic hydrothermal event involving late pegmatitic fluids the low ta concentrations around 50 ppm of this fine grained muscovite suggest that this fluid transported at least small amounts of ta

internal differentiation of rare element pegmatites effects of boron phosphorus and fluorine lithium rich rare element pegmatites are characterized by high concentrations of b p and f the interactions of these components with h2o and rare alkalis lower liquidas and solidus temperatures enhance silicate liquid h2o miscibility and control partitioning and concentration of group i elements and higher field strength cations boron f and perhaps p may form peralkaline na and li species that promote early saturation in mica quartz activities of f p and especially b are largely unbuffered throughout crystallization concentration of these components through fractional crystallization involving muscovite generates a peralkaline na aluminosilicate rich melt or vapor from which albitites rich in tourmaline phosphates f rich micas beryl zircon and nb ta sn oxides crystallize phase equilibrium experiments with peraluminous b p f rich rhyolite obsidian macusanite simulate many features of rare element pegmatites especially at h2o undersaturated conditions

the miarolitic pegmatites from the konigshain a contribution to understanding the genesis of pegmatites in this paper we show that the crystallization of miarolitic pegmatites at konigshain started at about 700 c in melts containing up to 30 mass water such high water concentration at low pressures 1 3 kbar is only possible if the melts are peralkaline such peralkaline melts are highly corrosive and reacted with the wall rock here the granite host forming the graphic granite zone in part via a magmatic metasomatic reaction with cooling the water concentration in some melt fractions increased up to 50 mass h2o the melt dominated system ends below 600 c and passes into a fluid dominated system the beginning of which is characterized by strong pressure fluctuations caused by the change of oh and co32 in the melt to molecular water and co2 we note two generations of smoky quartz one crystallized above the transition of quartz 573 c and one below both of which contain melt inclusions this indicates that some melt fraction remains during at least the higher temperature portion of the growth of minerals into the miarolitic cavity contradicting the view that minerals growing into a pegmatite chamber only do so from aqueous fluids we show that the konigshain miarolitic pegmatites are part of the broad spectrum of pegmatite types and the processes active at konigshain are representative of processes found in most granitic pegmatites and are thus instructive in the understanding of pegmatite formation in general and constraining the composition and characteristics of pegmatite forming melts

a sulphide bearing orthopyroxenite layer in the bjerkreim sokndal intrusion norway implications for processes during magma chamber replenishment the bjerkreim sokndal layered intrusion contains an up to 3 m thick layer of sulphide bearing orthopyroxenite or melanorite that can be followed for about 30 km along the boundary between megacyclic units ii and iii the layer of orthopyroxenite is developed within a sequence of ilmenite leuconorites and defines the base of zone iiia the leuconorites are generally succeeded by ilmenite magnetite leucotroctolite which defines the base of zone iiib the orthopyroxenite layer has an initial sr isotopic ratio similar to the leucotroctolites ca 0 7051 and lower than the enveloping ilmenite leuconorites of zones iic and iiia ca 0 7054 variations of tetrahedrally coordinated al in orthopyroxene and elevated cr tio2 in the orthopyroxenite layer and the leucotroctolite imply that the orthopyroxenite is genetically more related to the leucotroctolite than the enveloping leuconorites on the basis of field observations and analytical results we conclude that the orthopyroxenite crystallised as a result of mixing between relatively primitive magma and differentiated resident magma both of which were sulphide saturated during chamber replenishment the injected magma formed a buoyant plume that spread out laterally at its level of neutral buoyancy within the compositionally zoned resident magma some distance above the magma chamber floor mixing in the plume resulted in a hybrid saturated in orthopyroxene ilmenite and sulphide melt batches of relatively dense magma containing crystals of orthopyroxene and ilmenite and droplets of sulphide melt sank to the floor of the chamber from the hybrid magma layer and formed a layer of orthopyroxenite on the magma chamber floor removal of orthopyroxene from the hybrid melt resulted in the sporadic crystallisation of plagioclase at the orthopyroxene plagioclase cotectic plagioclase joined orthopyroxene and sulphide droplets in the dense melt batches which sank to the floor resulting in the local development of melanorite instead of orthopyroxenite crystallisation of ilmenite leuconorite from the resident magma below the hybrid magma layer resumed after formation of the orthopyroxenite layer this continued as the hybrid layer thickened and eventually came into contact with the chamber floor when leucotroctolites of zone iiib started to crystallise on the deeper parts of the floor elsewhere lower temperature cumulates formed on elevated portions of the floor from magma higher in the stratified column the sulphide bearing orthopyroxenite layer is not associated with pge mineralisation because both the replenishing and differentiated resident magmas had lost pge through earlier sulphide saturation zone iiib is followed by a sequence of lithologies that reflect progressive fractional crystallisation with the appearance of cumulus orthopyroxene at the expense of olivine zone iiic and the successive entries of magnetite zone iiid and clinopyroxene plus apatite zone iiie a new major influx of magma took place at this time to produce megacyclic unit iv

melt inclusions in quartz from an evolved peraluminous pegmatite geochemical evidence for strong tin enrichment in fluorine rich and phosphorus rich residual liquids abstract we have investigated the magmatic evolution of a late stage f and p rich pegmatite forming aluminosilicate liquid and the geochemical controls on magmatic mineralizing processes by remelting totally crystallized melt inclusions in quartz and analyzing the quenched glass by epma and sims the quartz phenocrysts were sampled from a pegmatite that occurs in a variscan granite genetically associated with cassiterite and wolframite mineralized greisen veins at the ehrenfriedersdorf sn w deposit central erzgebirge se germany the melt inclusion compositions imply that the pegmatite forming liquid achieved extreme levels of chemical differentiation it contained high abundances of sn f p li rb cs nb ta and be and abnormally low concentrations of ca y sr and ree for a granite and it was strongly peraluminous the molar al 2 o 3 cao na 2 o k 2 o ranged from 1 3 to 2 0 fractions of the pegmatite forming liquid were extremely enriched in p 2 o 5 f al 2 o 3 and the molar abundances of f p in the glasses correlate strongly with moles of network modifying al ions implying that the bulk liquid included f p and al bearing complexes formation of these complexes reduced the activities of f p and al in bulk liquid suppressed the crystallization of magmatic topaz and p rich minerals and allowed the liquid to become enriched in these constituents some fractions of the ehrenfriedersdorf aluminosilicate liquid contained 1000 2000 ppm sn these levels of sn enrichment were up to 2 orders of magnitude greater than that ever reported for nonmineralized metaluminous and peraluminous igneous materials and are consistent with some experimentally derived sn solubilities in cassiterite saturated granitic liquids at geologically relevant pressures and temperatures this concordance implies that cassiterite could have crystallized directly from this highly evolved p and f rich peraluminous granitic liquid without the involvement of hydrothermal fluids

zircon textures and composition refractory recorders of magmatic volatile evolution zircon textures and composition have been used to infer magmatic processes including closed system fractional crystallization magma mixing or replenishment and country rock assimilation here we propose that zircon textures and composition may also be refractory recorders of magmatic volatile evolution we present field whole rock chemical textural mineral chemical and u pb age data from evolved fine to coarse grained granite intrusions on melville peninsula nunavut canada zircon forms two main populations in these granites type 1 and type 2 zircon type 1 zircon is present in all samples but predominant in fine grained granite crystals are euhedral and inclusion rich and show periodic fine scale oscillatory zoning comparatively low concentrations of u 2 200 ppm and hf 1 6 wt high zr hf 40 62 and pervasive alteration type 2 zircon is predominant in coarse grained granite crystals form overgrowths on type 1 zircon and individual crystals they are subhedral and inclusion poor and show weak irregular large scale oscillatory zoning high u up to 7 250 ppm and hf 1 5 2 0 wt low zr hf 37 44 and only local alteration compatible trace element concentrations and zr hf change sharply across the boundary of type 1 to type 2 zircon 207pb 206pb ages preclude a significant hiatus between crystallization of the two types we argue against magmatic versus hydrothermal crystallization country rock assimilation or magma mixing as causes for the crystallization of type 1 and type 2 zircon we propose instead that type 1 zircon formed from volatile undersaturated magmas and that type 2 zircon formed from volatile saturated magmas magmas fractionated by volatile driven filter pressing into crystal rich mush and crystal poor magma crystal rich mush with abundant type 1 zircon crystallized to fine grained granite volatile rich magma crystallized to type 2 zircon and coarse grained granite while type 1 zircon was pervasively altered by exsolving magmatic volatiles type 2 zircon was only locally affected by subsolidus hydrothermal alteration

monitoring the crystallization of water saturated granitic melts in real time using the hydrothermal diamond anvil cell critical aspects of the crystallization dynamics of h2o saturated melts of a typical granitic composition as well as granitic melts enriched in lithium 8800 ppm were investigated in real time experiments using the hydrothermal diamond anvil cell at 480 700 c and 220 960 mpa complete crystallization of the charges was achieved within 5 118 h with average crystal growth rates ranging from 3 to 41 cm year for quartz and from 18 to 58 cm year for alkali feldspars demonstrating that crystals formed from a silicate melt in the presence of a coexisting aqueous phase crystallize rapidly the combination of substantial nucleation delays low nucleation densities and rapid growth rates for quartz and alkali feldspars led to the formation of euhedral megacrysts of these minerals in the vicinity of clusters comprised of much smaller muscovite or spodumene crystals subsolidus replacement processes initiated during crystal fluid interactions after the silicate melt was consumed were directly observed in the experiments the experimental results underscore the important role of water as a medium for the transport of essential elements such as si al na and k from the silicate melt to the newly formed crystals and provide important insights into the crystallization of miarolitic pegmatites

granite related ore deposits an introduction a symposium on mineralization associated with granitic magmatism was held within the framework of the 33rd igc in oslo norway in august 2008 while our initial idea was to bring together field experimental and theoretical studies in order to review and summarize the current ideas and recent progress on granite related mineralization systems we were caught by surprise realizing that participants were inclined to focus more on ore deposits related to granitic magmatism this spontaneous shift from granites the major intended focus of the symposium to mineralization associated with them spawned the idea for a special issue on this theme and ultimately to the nine papers assembled here chosen from about 60 scientific contributions at the symposium around twenty oral presentations were given and forty posters were presented at the meeting the 60 papers were grouped according to the current main granite related ore systems as follows granite pegmatite skarn and greisen veins porphyry orogenic gold intrusion related epithermal and porphyry related gold and base metal iron oxide copper gold iocg and special case studies importance of granite related mineralization systems diversity of mineralization styles and related

response to the discussion by b robins and f chiodoni of geochemistry of cumulates from the bjerkreim sokndal intrusion s norway part i constraints from major elements on the mechanism of cumulate formation and on the jotunite liquid line of descent abstract merging our data with those of robins and chiodoni robins b chiodoni f 2007 poles apart a discussion of the geochemistry of cumulates from the bjerkreim sokndal layered intrusion s norway part i constraints from major elements on the mechanism of cumulate formation and on the jotunite liquid line of descent lithos doi 10 1016 j lithos 2007 03 007 we examine the major element compositions of 135 samples of so called phi c cumulates of the bjerkreim sokndal layered intrusion we show the limits of the tio 2 mgo ratio vs al 2 o 3 diagram in order to ascertain the proportions of cumulus minerals ilmenite and orthopyroxene in the ilmenite leuconorite mafic pole we also discard anomalous samples as we did in the previous paper the rest of the samples 124 phi c i e 92 of the whole population are then used to confirm the existence of plagioclase and mafic poles it is shown that the mafic pole is indeed a mixture of ilmenite and orthopyroxene not induced by spurious correlation

halogens in volcanic systems the transport degassing and atmospheric release of halogens from active volcanism on earth have been the focus of increasing interest over the last few decades and have recently been the subject of the 1st workshop on halogens in volcanic systems and their environmental impacts that was held in december of 2007 at yosemite lodge in yosemite national park california as an introduction to this chemical geology special issue collecting contributions from many of the participants at the workshop we review here recent advances in this field including experimental and theoretical investigations of halogen behaviour in volcanic and related magmatic systems we discuss previous research on several aspects of halogen geochemistry including halogen abundances in the mantle and magmas on earth the effects of halogens on phase equilibria and melt viscosities their partitioning between melt and fluid phase s upon decompression cooling and crystallisation of magmas in the earth s crust and their final atmospheric release as volcanic gases the role of halogens in the genesis of hydrothermal systems and in the transport of ore forming metals is also reviewed and we discuss our current understanding of atmospheric processing of volcanic halogens in both the troposphere and stratosphere and their consequent impacts in spite of these recent advancements our current understanding of halogen geochemistry at active volcanoes is still far too fragmentary and the key questions that require answers from future research are summarised in our conclusions

origin of miarolitic pegmatites in the konigshain granite lusatia abstract in this study we examine an interesting occurrence of miarolitic pegmatites in the konigshain granite of the lusatia region of the bohemian massif this granite is characterized by the extensive development of micro sized miarolitic pegmatites typically with diameters of 5 to 15 mm irregularly distributed through its upper levels and larger miarolitic pegmatites up to 1 m in the uppermost levels this granite also shows evidence of varied forms of transport of extremely volatile rich residual melts fluids in the form of more or less discrete inter granular melt bodies and associated magmatic quartz veins formed in tectonic fissures together these provide evidence for the origin of miarolitic pegmatites both in the specific case of konigshain and more generally our evidence suggests that miarolitic pegmatites form from volatile and alkali rich residual melts ranging from 10 to 50 h 2 o far more than typical granitic melts but far more silicate components than aqueous fluids or vapor suggested by some authors using melt inclusions in quartz from the aplitic and graphic granite zones in miarolitic pegmatites in the konigshain granite we show that two different inclusion populations are present we provide evidence that the first inclusion population are those related to the primary granite at the level of intrusion and the second were trapped during the re crystallization of the granite wall rocks by silicate rich supercritical fluids moving through the solid crystal framework with a porosity 0 see clarke et al 2013 our results show that a significant volume fraction of the miarolitic pegmatites was not created by a pegmatite forming fluid but formed in situ by re crystallization of wall rocks triggered by highly reactive volatiles exsolved from the pegmatite forming melts evidence is also presented which suggests the nature and speed of emplacement of the konigshain granite this evidence may explain the unusual form and abundance of miarolitic pegmatites in the studied area and may have application to similar occurrences thus there is a mixture of features which are applicable to miarolitic pegmatites in general and others which help separate the overriding processes from the variations produced by local or regional chemical or tectonic characteristics

estimating abundances of volatile and other mobile components in evolved silicic melts through mineral melt equilibria to variable degrees of accuracy from source partitioning between and earths residual minerals and anatectic melts through melt fractionation partitioning between igneous minerals and residual melts to the end stages of magma solidification where higher concentrations of normally trace elements may promote saturation in their crystalline phases the magmatic abundance of rare alkalis and alkaline earths

textural features and chemical evolution in tantalum oxides magmatic versus hydrothermal origins for ta mineralization in the tanco lower pegmatite manitoba canada tantalum a key element in the electronics industry is produced mainly from rare element granitic pegmatites although their internal structure mineralogy and petrogenesis have been extensively investigated the processes that control tantalum mineralization remain poorly understood in particular the role of fluids in the crystallization of tantalum ore one of the major problems arises from the difficulty in distinguishing primary magmatic from secondary hydrothermal textures in such complex rocks in the tanco pegmatite manitoba canada tantalum mineralization shows a complexity that reflects the complex petrogenesis of its host pegmatite eight different families of tantalum oxides occur in various associations and compositions the tanco lower pegmatite is an isolated body beneath the main pegmatite body that contains abundant tantalum associated with mica alteration tantalum mineralization in the tanco lower pegmatite occurs as three different styles facies 1 is hosted by the wall zone and hosts primary magmatic ta oxides with simple textures progressive and oscillatory zoning facies 2 is hosted by the lower and upper intermediate zones where most mineralization occurs with dendritic amblygonite facies 3 is hosted by the central zone which is affected by mica alteration in this latter facies the oxides show particularly complex textures evident from x ray mapping by combining information obtained from textural observations and chemical analyses we are able to determine the paragenesis for each ta oxide bearing mineral assemblage and hence to evaluate the relative contributions of magmatic versus hydrothermal processes in complex associations we observe relics of primary ta phases that are replaced or overgrown by secondary ta phases we propose the paragenetic sequence columbite group minerals microlite early primary magmatic columbite wodginite group minerals microlite late primary magmatic wodginite group minerals microlite secondary magmatic ferrotapiolite secondary magmatic in addition chemical variations were identified in the columbite and wodginite group minerals both at the crystal scale and at the pegmatite scale columbite and wodginite group minerals show the typical ta ta ta nb and mn mn mn fe atomic ratios increase from earlier to later zones at the crystal scale the increase in ta and mn with fractionation in the columbite group is explained by the higher solubility of the ta end member relative to the nb end member and the crystallization of other minerals that shift the melt composition toward mn enrichment the fractionation trend in the wodginite group shows fe enrichment which is consistent with experimental results that show a higher solubility of the fe end member relative to the mn end member in columbite group minerals considering the available experimental data as well as the intimate association of ta oxides with zircon observed in this study we conclude that tantalum mineralization is a product of direct crystallization from the melt rather than hydrothermal in origin fluids are attributed an indirect role only as they could have brought minor elements fe mn or ca into the melt which resulted in the crystallization of secondary ta phases textural evidence shows that the late secondary phases were formed at the same time as mica alteration we suggest that mica alteration was due to a late melt rather than a hydrothermal fluid that reacted with the blocky k feldspar of the central zone during the alteration event tantalum was remobilized from primary phases and incorporated in new secondary ta oxide species

different melting conditions and petrogenesis of peraluminous granites in western qinling china and tectonic implications abstract the qinling orogen records the prolonged amalgamation history between the north china block ncb and the south china block scb accompanied by major granitoid intrusions during the triassic however the petrogenesis of these granitoids especially that of the peraluminous granites remains a matter of debate detailed study of these peraluminous granites which are the products of crustal melting will give insights into the melting process and petrogenesis of peraluminous magmas and will further constrain the regional geological evolution in this study xiahe xh tourmaline bearing two mica granite and baijiazhuang bjz two mica granite were selected for systematic analysis of their mineralogy petrology zircon u pb geochronology and geochemistry the zircon u pb dating showed that the xh and bjz granites were emplaced at approximately 242 ma and approximately 214 ma respectively the presence of muscovite and tourmaline high peraluminosity at 1 1 low oxygen fugacity o2 conditions below the fayalite magnetite quartz fmq buffer and low zircon saturation temperatures indicate sedimentary protolith s type granitic affinity the low cao na2o ratios

in situ analyses of micas in the yashan granite south china constraints on magmatic and hydrothermal evolutions of w and ta nb bearing granites article i nfo article history most rare metal granites in south china host major w deposits with few or without ta nb mineralization however the yashan graniticpluton located inthe yichun areaof western jiangxiprovince south china hosts a major nb ta deposit with minor w mineralization it is thus important for understanding the diversity of w and nb ta mineralization associated with rare metal granites the yashan pluton consists of multi stage intrusive units including the protolithionite muscovite granite li mica granite and topaz lepidolite granite from the early to late stages bulk rock ree contents and la yb ratios decrease from protolithionite granite to li mica granite to topaz lepidolite granite suggesting the dominant plagioclase fractionation this variation together with increasing li rb cs and ta but decreasing nb ta and zr hf ratios is consistent with the magmatic evolution in the yashan pluton micas are protolithionite muscovite li mica and lepidolite and zircons show wide concentration ranges of zro2 h fo2 u o2 t ho2 y 2o3 and p2o5 compositional variations of minerals such as increasing f rb and li in mica and increasing hf u and p in zircon are also in concert with the magmatic evolution from protolithionite granite to li mica granite to topaz lepidolite granite the most evolved topaz lepidolite granite has the highest bulk rock li rb cs f and p contents consistent with the highest contents of these elements and the lowest nb ta ratio in mica and the lowest zr hf ratio in zircon ta nb enrichment was closely related to the enrichment of volatile elements i e li f and p in the melt during magmatic evolution which raised the proportion of non bridging oxygens nbos in the melt the rims of zoned micas in the li mica and topaz lepidolite granites contain lower rb cs nb and ta and much lower f and w than the cores and or mantles indicating an exotic aqueous fluid during hydrothermal evolution some columbite group minerals may have formed from exotic aqueous fluids which were originally depleted in f rb cs nb ta and w but such fluids were not responsible for ta nb enrichment in the yashan granite the interaction of hydrothermal fluids with previously existing micas may have played an important role in leaching concentrating and transporting w fe and ti ta nb enrichment was associated with highly evolved magmas but w mineralization is closely related to hydrothermal fluid thus these magmatic and hydrothermal processes explain the diversity of w and ta nb mineralizations in the rare metal granites

chemical and boron isotope variations in tourmalines from an s type granite and its source rocks the erongo granite and tourmalinites in the damara belt namibia tourmaline is widespread in metapelites and pegmatites from the neoproterozoic damara belt which form the basement and potential source rocks of the cretaceous erongo granite this study traces the b isotope variations in tourmalines from the basement from the erongo granite and from its hydrothermal stage tourmalines from the basement are alkali deficient schorl dravites with b isotope ratios typical for continental crust 11b average 8 4 1 4 n 11 one sample at 13 n 2 virtually all tourmaline in the erongo granite occurs in distinctive tourmaline quartz orbicules this main stage tourmaline is alkali deficient schorl 20 30 x site vacancy fe fe mg 0 8 1 with uniform b isotope compositions 11b 8 7 1 5 n 49 that are indistinguishable from the basement average suggesting that boron was derived from anatexis of the local basement rocks with no significant shift in isotopic composition secondary hydrothermal tourmaline in the granite has a bimodal b isotope distribution with one peak at about 9 like the main stage tourmaline and a second at 2 we propose that the tourmaline rich orbicules formed late in the crystallization history from an immiscible na b fe rich hydrous melt the massive precipitation of orbicular tourmaline nearly exhausted the melt in boron and the shift of 11b to 2 in secondary tourmaline can be explained by rayleigh fractionation after about 90 b depletion in the residual fluid

elemental and b o h isotopic compositions of tourmaline and associated minerals in biotite muscovite granite of mashhad ne iran constraints on tourmaline genesis and element partitioning abstract abundant tourmaline occurs in late triassic biotite muscovite granites of mashhad ne iran with several distinct morphologies including tourmaline nodules in granite pegmatitic tourmalines aplitic tourmalines and vein related tourmalines quartz tourmaline vein tourmaline rich vein and radial tourmalines pegmatitic and aplitic tourmalines are compositionally fe rich schorl and the nodule radial and vein tourmalines are mg rich schorl the tourmalines have generally low abundances for most trace elements except for sr ga li be sn pb and some transition elements tourmalines have low ree abundances and are enriched in lree and depleted in hree mostly below detection limits with positive eu anomalies the concentration of several trace elements e g pb be sn ga sr pb and ree correlates well with the major element composition of the tourmalines e g mg mg mg fe vacancy x site vacancy na and na na ca trace element data of coexisting minerals with tourmaline indicate that the oligoclase and albite show the most preference in sr pb and eu and lrees biotite readily incorporates rb ba zn li cs and nb k feldspar has high contents of rb ba sr and pb and garnet incorporates hrees and y during magma differentiation the b o h isotopic compositions for all tourmalines are consistent with an s type granite source that was derived from partial melting of the continental crust the pegmatitic and aplitic tourmalines with fe rich schorl composition indicate magmatic conditions and the radial vein and nodule tourmalines with mg rich schorl composition formed during the transition from magmatic to hydrothermal conditions due to the internal evolution of the granitic magma

phase equilibria of a be u and f enriched vitrophyre from spor mountain utah abstract the equilibrium melting relations of a vitrophyre representative of topaz rhyolites have been experimentally determined in order to constrain the pre eruption temperature and h2o content of topaz rhyolite magmas the vitrophyre sample is strongly enriched in f and incompatible elements and consists of approximately 70 unaltered volcanic glass and 30 crystals of biotite quartz sanidine plagioclase magmatic fluorite and a variety of accessory phases biotite stability is strongly dependent on temperature pressure and ah2o in the melt and is apparently independent of the variations in o2 over the range investigated in this study the thermal stability of biotite increases relative to that of quartz sanidine and plagioclase in water saturated melts as pressure increases from 1 2 to 2 kbar fluorite is stable to temperatures below but within 50 to 75 c of the biotite stability curve and topaz is present in the products of runs at and near the solidus for all fluid conditions investigated the 1 2 wt f in the vitrophyre results in very low solidus temperatures of 525 c for all fluid conditions studied comparison of the experimentally determined crystallization sequence of the vitrophyre with the observed crystallization sequence of the vitrophyre and of the overlying topaz rhyolites indicates that the phenocrysts in the vitrophyre and in the topaz rhyolites crystallized at a pressure 1 kb that the magma contained at least 4 wt water during initial crystallization of biotite and that the magma contained a pre eruption water content of 5 wt

experimental evidence of three coexisting immiscible fluids in synthetic granitic pegmatite we present an experimental study of synthetic peraluminous granite doped with h2o b p and f which confirms that aluminosilicate melt hydrous fluid and hydrosaline melt high temperature brine can stably coexist at 450 900 c and 0 1 0 2 gpa in bulk compositions similar to those of natural granitic pegmatites hydrosaline melt is not quenchable unstable at room conditions and requires special techniques for synthesis and preservation raman spectroscopy and electron microprobe analyses of hydrosaline melt synthesized in our experiments show that it is composed of h3bo3 na3alf6 alpo4 h2o and aluminosilicate components aluminosilicate melt saturated in both hydrosaline liquid and hydrous fluid at 850 c and 0 2 gpa contains 3 6 wt f 4 2 wt p2o5 and 4 wt b2o3 natural hydrosaline melts have previously been found as inclusions trapped in rock forming minerals they are not restricted to granites and can be effective agents for enhanced crystal growth metasomatism and ore formation in addition hydrosaline melts may account for many characteristic features of rare element and miarolitic pegmatites such as giant size and perfect shapes of crystals in pegmatite cores diverse mineralogy and strong enrichment in rare elements

poles apart a discussion of geochemistry of cumulates from the bjerkreim sokndal intrusion s norway part i constraints from major elements on the mechanism of cumulate formation and on the jotunite liquid line of descent by j c duchesne and b charlier lithos 83 2005 229 254 abstract we dispute duchesne and charlier s duchesne j c charlier b 2005 geochemistry of cumulates from the bjerkreim sokndal intrusion s norway part i constraints from major elements on the mechanism of cumulate formation and on the jotunite liquid line of descent lithos 83 229 254 postulate that the major element compositions of cumulates in the bjerkreim sokndal intrusion vary linearly between plagioclase and mafic poles and their inference that this supports an origin by in situ crystallisation we use a larger set of major element data for plagioclase orthopyroxene ilmenite cumulates to show that some linear trends in harker diagrams simply reflect varying amounts of hemo ilmenite relative to plagioclase and orthopyroxene while others are probably spurious and induced by variations in modal plagioclase the most abundant cumulus mineral ratios of oxides that enter almost exclusively into orthopyroxene and hemo ilmenite are shown to be highly dispersed reflecting differential sorting of the mafic minerals

tourmaline rich features in the heemskirk and pieman heads granites from western tasmania australia characteristics origins and implications for tin mineralization distinctive magmatic hydrothermal tourmaline rich features have developed in the heemskirk and pieman heads granites from western tasmania australia they are categorized as tourmaline rich patches orbicules cavities and veins based on their distinctive morphologies sizes mineral assemblages and contact relationships with host granites these textural features occur in discrete layers in the roof zone of granitic sills within the heemskirk and pieman heads granites tourmaline patches commonly occur below a tourmaline orbicule rich granitic sill tourmaline filled cavities have typically developed above the tourmaline quartz orbicules in the upper layer of the white phase of the heemskirk granite tourmaline quartz veins penetrate all exposed levels of the granites locally cutting tourmaline orbicules and cavities the tourmalines are mostly schorl fe rich and foitite with an average end member component of schorl 45 dravite 6 tsilaisite 1 uvite 0 fe uvite 3 foitite 31 mg foitite 4 olenite 10 element substitutions of the tourmalines are controlled by femg 1 al y x square r2 na 1 and minor alo al y r2 oh 1 where r2 fe2 mg2 mn2 exchange vectors several trace elements in tourmaline have consistent chemical evolutions grouped from tourmaline patches through orbicules and cavities to veins there is a progressive decrease of most transition and large ion lithophile elements and a gradual increase of most high field strength elements these compositional variations in the different tourmaline rich features probably relate to element partitioning occurring in these phases due to volatile exsolution and fluxing of aqueous boron rich fluids that separated from the granitic melts during the emplacement of s type magmas into the shallow crust 4 to 5 5 km tourmalines from the heemskirk granite are enriched in fe na li be sn ta nb zr hf th and rare earth elements relative to the tourmalines from the pieman heads granite but depleted in mg mn sc v co ni pb sr and most transition elements these results imply that bulk compositions of the host granites exert a major control on the chemical variations of tourmalines the trace element compositions of tourmalines from the sn mineralized heemskirk granite are different from those of the barren pieman heads granite trace element ratios e g zn nb co nb sr ta and co la and sn concentrations in tourmaline can distinguish the productive heemskirk granite from the barren pieman heads granite

crystallization of alpo4 sio2 solid solutions from granitic melt and implications for p rich melt inclusions in pegmatitic quartz aluminum orthoposphate alpo 4 has polymorphs isostructural with tridymite cristobalite and quartz berlinite is the low temperature form that corresponds to quartz we report berlinite quartz solid solutions to crystallize from a synthetic p rich peraluminous granitic melt similar in composition to the most volatile rich silicate melt inclusions found in pegmatites the crystallization took place in experiments performed in cold seal pressure vessels at 450 700 c and 0 1 0 2 gpa h 2 o pressure at these conditions the berlinite quartz mutual solubility is limited to 5 7 mol sio 2 on the phosphate side of the solvus and to the maximum of 1 mol alpo 4 on the silica rich side the mutual solubility appears to decrease with falling temperature at low t the crystals of berlinite quartz solid solutions are strongly zoned and show complex intergrowths between the p rich and silica rich phases they were studied by electron microprobe transmission electron microscopy and raman spectroscopy in the light of our new experimental results the extreme p enrichment reported earlier for some natural quartz hosted melt inclusions may be explained as a post entrapment contamination by the berlinite bearing host

magma influx and mixing in the bjerkreim sokndal layered intrusion south norway evidence from the boundary between two megacyclic units at storeknuten abstract the bjerkreim sokndal layered intrusion belongs to the proterozoic anorthositic province in the rogaland area of southern norway the northwestern part of the intrusion comprises a ca 6 km thick layered series made up of megacyclic units mcu arranged in a syncline each megacyclic unit reflects the influx of fresh magma into the chamber the boundary between megacyclic units iii and iv has been studied in detail at storeknuten on the southern flank of the syncline the megacyclic units can be subdivided into a series of cumulate stratigraphic zones the interval from the top of zone iiie to the base of zone ivd is exposed in the storeknuten area modally layered plagioclase hypersthene ilmenite magnetite augite apatite cumulates belonging to zone iiie are overlain by 30 m of massive plagioclase rich rocks commonly containing ilmenite and or hypersthene constituting zone iva the entry of cumulus olivine defines the base of zone ivb dominantly plagioclase olivine ilmenite cumulates which is about 100 m thick many of the olivines are partly or completely replaced by ca poor pyroxene fe ti oxide symplectites this massive leucotroctolitic zone is overlain by modally layered laminated plagioclase hypersthene ilmenite cumulates of zone ivc the successive entry of magnetite apatite accompanied by ca rich pyroxene and inverted pigeonite defines zones ivd e and f respectively the entry of k feldspar accompanied by fe rich olivine defines the base of a jotunitic transition zone which passes upwards into mangerites and quartz mangerites there is a compositional regression through zone iva the upper part of zone iiie has ca poor pyroxene with about en68 plagioclase with an44 48 and a sr isotope ratio of about 0 7062 while the base of zone ivb has olivine with fo75 together with en78 an53 and 0 7050 respectively similar reversals are shown by the minor element compositions of plagioclase and fe ti oxides sr isotope ratios increase systematically up through zone ivb reaching 0 7058 in zone ivd while an and sr in plagioclase and ni and cr in fe ti oxides decrease olivine compositions vary unsystematically and are believed to have changed their fe mg ratios as a result of trapped liquid shift the magma residing in the chamber when the influx at the base of megacyclic unit iv took place was compositionally zoned and assimilation of gneissic country rock at the roof had resulted in the sr isotope ratio increasing up through the magma column the new magma had a sr isotope ratio of about 0 7050 while the resident magma had a ratio of 0 7062 at the floor increasing upwards the new magma mixed with the basal layer s of the compositionally zoned resident magma and crystallization of this hybrid magma during influx and mixing produced the compositional regression in zone iva when magma influx ceased olivine bearing rocks began to crystallize at the base of zone ivb the leucotroctolites at the base of this zone are the most primitive rocks in the entire intrusion the systematic increase in sr isotope ratios up through zone ivb resulted from progressive mixing between new and resident magma this mixing either took place during magma influx or by the progressive mixing of overlying resident magma layers during crystallization calculations based on geochemical modelling the thickness of cumulate stratigraphy repeated and sr isotope ratios indicate that the new magma influx had a thickness of 350 500 m in the storeknuten section and that the leucotroctolites of zone ivb represent about 20 30 crystallization of this influx

magmatic vs hydrothermal origins for zircon associated with tantalum mineralization in the tanco pegmatite manitoba canada complex textures in zircon associated with ta oxides have been used to assess the processes at the origin of zircon crystallization and associated ta mineralization in pegmatites in particular the role of magmatic vs hydrothermal processes the tanco pegmatite is used as an example because its zircon is devoid of post magmatic alteration and its petrogenesis is well constrained zircon in primary units is metamict with high u pb th contents by contrast in secondary assemblages affected by late magmatic micaceous alteration zircon is devoid of radiogenic elements but it may contain abundant ta2o5 up to 4 7 wt the incorporation of ta into zircon may occur through coupled substitution mechanisms involving other minor elements such as p al mn or li the presence of ta accounts for the distorted structures in the ta rich zircon as revealed in high resolution tem images four zircon types occur sequentially in single zircon crystals which permits a new model for zircon growth and evolution in rare element pegmatites to be advanced 1 zircon z1 is ta rich and crystallized possibly before discrete ta phases 2 z1 was overgrown by regularly zoned zircon z2 and z3 which show lower ta and extreme zr hf fractionation hfo2 up to 38 9 wt suggesting crystallization from a highly fractionated melt possibly at the onset of ta mineralization and 3 close to the solidus the aqueous fluid at the origin of micaceous alteration corroded the distorted structure of z1 and a low ta zircon z4 replaced z1 by dissolution reprecipitation whereas z2 and z3 resisted this alteration tantalum was no longer stable in the zircon structure and crystallized as ta oxide inclusions in the reequilibrated zircon z4

rapid crystallization of the animikie red ace pegmatite florence county northeastern wisconsin inclusion microthermometry and conductive cooling modeling we evaluated the crystallization regime of a zoned pegmatite dike and the degree of magma undercooling at the onset of crystallization by analyzing coeval fluid and melt inclusion assemblages the liquidus temperature of the pegmatite magma was 720 c based on re melting of crystallized melt inclusions in heating experiments the magma crystallized sequentially starting with a thin border zone which formed in less than one day at an average temperature of 480 c based on primary fluid inclusions meaning 240 c undercooling the primary inclusions from the outer zones were postdated by secondary inclusions trapped between 580 and 720 c representing fluid exsolved from hotter still crystallizing inner pegmatite units the huge temperature contrast between the pegmatite s inner and outer zones was simulated by conductive heat numerical modeling a 2 5 m wide dike emplaced in 220 c rocks cools entirely to 400 c in less than 50 days unidirectional and skeletal textures also indicate rapid disequilibrium crystallization

differentiated rare element mineralization in an ongonite topazite composite dike at the xianghualing tin district southern china an electron microprobe study on the evolution from niobium tantalum oxides to cassiterite our study characterizes in detail the mineralogical textural and compositional features of a highly evolved composite ongonite topazite dike and its magmatic differentiation history we present compositional data collected by established techniques i e by electron microprobe and wet chemical analysis which provide a detailed framework for future studies that employ state of the art analytical techniques the studied dike referred to as the no 431 dike crops out within the xianghualing area in the nanling range of southern china in close spatial association with jurassic sn nb ta granite plutons the rock samples in the no 431 dike were collected from a structurally lower drill hole and a trench at higher level the ongonite is encountered throughout the dike but the topazite is only revealed along the margin of the upper near surface dike the results of whole rock major and trace element analyses show that the rocks of the no 431 dike are strongly peraluminous with an average acnk value of 1 5 for ongonite and 3 9 for topazite they are enriched in f 1 7 wt and 5 4 wt on average for ongonite and topazite respectively the rocks have low zr hf and nb ta ratios and high levels of ore forming elements including nb ta sn and w silicate and oxide mineral assemblages textures and compositions are also distinct for the two rock types studied in the lower ongonite of the dike there are abundant phenocrysts of k feldspar quartz and albite and microphenocrysts of topaz and zinnwaldite in a matrix dominated by quartz k feldspar and albite characteristic oxides are columbite tantalite tapiolite and microlite but cassiterite is absent the upper ongonite of the dike has a silicate assemblage similar to the lower ongonite columbite mn uranomicrolite and limited amounts of cassiterite are the dominant accessory minerals the topazite is characterized by large amounts of topaz and zinnwaldite intergrown with quartz while k feldspar albite and quartz phenocrysts have rounded shapes and are relatively rare cassiterite is the most abundant ore mineral while nb ta oxide minerals are less abundant we interpret the whole rock compositional trends mineral textures assemblages and compositions to reflect the differentiation of an evolved initially homogeneous magma that separated into aluminosilicate and hydrosaline melts corresponding to crystallization of ongonite and topazite respectively the crystallization of nb ta and sn bearing ore minerals was strongly controlled by the separation of the two melt phases we hypothesize that dike propagation widening subsequent to the initial dike emplacement may have driven the separation of the aluminosilicate and hydrosaline melt phases that crystallized to ongonite in the core and topazite along the margins of the structurally higher part of the dike

fluid immiscibility in volcanic environments volatile components enter the atmosphere oceans and other surface waters through pre syn and post eruptive volcanic processes that involve a variety of fluids aluminosilicate poor fluids include aqueous or carbonic to sulfide sulfate chloride fluoride carbonate and phosphate rich compositions in volcanic environments but other more complex combinations of these constituents may be involved giggenbach 1977 roedder 1984 1992 lowenstern 1995 other rare gases and dissolved constituents e g h2 n2 he ar h3bo3 hg ch4 and other hydrocarbon compounds metals and metalloids are also present but in general they are not sufficiently concentrated to form their own phases or control bulk fluid composition and volcanic processes as a result of their diverse compositions volcanic fluids ranging from vapor to liquid exhibit widely different densities and show strong distinctions in heat capacity dielectric behavior viscosity and other chemical and physical characteristics geiger et al 2006a the density of a saline liquid in the system nacl h2o at 50 mpa and 800 c for example is more than 7 times that of the coexisting aqueous vapor e g 0 2 gm cm3 henley and mcnabb 1978 multiple fluids move mix and or unmix in magma chambers and volcanic conduits in the root zone of fumaroles and in the convective hydrothermal systems that are ubiquitous to volcanic environments hydrothermal systems are typically centered on magmatic intrusions and may include crater lakes at the top of eruptive conduits hydrothermal processes involving two or more fluid phases operate through a variety of geologically relevant shallow crustal pressure temperature composition conditions volcanic fluids occur at supersolidus to subsolidus conditions meaning that the dense aluminosilicate melt that is common to volcanism may or may not be present this chapter addresses the evidence for and occurrence of two or more low density aluminosilicate poor fluids

phase relations of a f enriched peraluminous granite an experimental study of the kymi topaz granite stock southern finland phase relations of f rich kymi equigranular topaz granite have been investigated experimentally at 100 500 mpa as a function of water activity and f content fluorite and topaz can crystallize as liquidus phases in f rich peraluminous systems but the f content of the melt should exceed 2 5 3 0 wt for the crystallization of topaz in peraluminous f bearing melts containing more than 1 wt f topaz and muscovite are expected to be the first f bearing phases to crystallize at high pressure whereas fluorite and topaz should crystallize first at low pressure following reaction models the saturation of fluorite and topaz caal2si2o8 plagioclase 2 alf3 melt caf2 fluorite 2al2sio4f2 topaz the obtained partition coefficient for f between biotite and glass d f bt glass ranges from 1 89 to 0 80 average value 1 29 and can be used as an empirical fluormeter to determine the f content of coexisting melts combined petrological and experimental studies of the kymi equigranular topaz granite indicate that plagioclase was the liquidus phase at nearly water saturated fluid saturated conditions and that the f content of the melt was at least 2 wt the mean f content of natural biotite 3 92 wt suggests that the late stage crystallization of biotite occurred in melts containing about 3 wt f the early crystallization of biotite and the presence of muscovite in our experiments at 200 mpa contrasts with the late stage crystallization of biotite and the absence of muscovite in the natural assemblage indicating that crystallization pressure may have been lower than 200 mpa for the granite

magnetic fabric and deformation in charnockitic igneous rocks of the bjerkreim sokndal layered intrusion rogaland southwest norway abstract the bjerkreim sokndal intrusion bksk belongs to the proterozoic rogaland igneous complex of southwest norway the bksk displays an anorthosite to mangerite cumulate series folded into a syncline in the core of which crop out massive acidic rocks of quartz mangerite to charnockite composition we present a study which focuses on the acidic rocks in which we use the low field anisotropy of magnetic susceptibility ams technique systematic microscope examination of the samples collected at 148 ams stations and considerations based on mineral intrinsic magnetic susceptibilities reveal magnetic mineralogy and anisotropy controlled by magnetite macro to micro scale petrofabrics and magnetic fabrics indicate that the acidic rocks which intruded after deposition of the underlying cumulate series were also affected by the syn to post magmatic folding event which gave rise to the bksk syncline in absence of any recognized plate scale regional stress field it is suggested that this folding results from a gravity induced subsidence linked to the final stage of diapiric emplacement of huge neighbouring anorthosite plutons this model is mainly supported by the structural pattern in the bksk which reveals a convergent flow towards a central trough where lineations are sub vertical

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

formation mechanism of the lanthanide tetrad effect for a topaz and amazonite bearing leucogranite pluton in eastern xinjiang nw china abstract the baishitouquan bst pluton is a topaz and amazonite bearing leucogranite intrusion located in the middle tianshan orogen of xinjiang northwestern china this pluton exhibits five lithological zones gradational from the bottom upwards leucogranite zone a amazonite bearing granite zone b amazonite granite zone c topaz bearing amazonite granite zone d and topaz albite granite zone e contents of ree and other trace elements were analysed on major and accessory minerals including quartz plagioclase k feldspar white micas topaz fluorite garnet zircon and monazite separated from above five zones of the bst pluton chondrite normalized ree patterns of minerals from zone a to zone e display clear convex tetrad effect and the te1 3 quantification factor of tetrad effect values of these minerals increases from zone a to zone e except that a quartz sample from zone b and zircon from zone c exhibits w type tetrad effect therefore we conclude that ree tetrad features of the minerals such as quartz plagioclase zircon garnet and monazite are inherited directly from the melt and have not significantly affected by both fractional crystallization and surface weathering with progressing of magmatic differentiation total ree contents decrease eu anomaly becomes more negative whereas nb ta zr hf and y ho ratios decrease gradually from zone a to zone e with increasing te1 3 values therefore we suggest that f rich magmatic fluid melt interaction above its solidus may leave the residual silicate melt with the features of very low contents of all ree subchondritic y ho zr hf and nb ta values and with an m type tetrad pattern including minerals crystallizing from it such a pattern is manifested by both whole rock and separate minerals hydrothermal fluid rock interaction played only a minor role to the convex tetrad effect of the minerals and their host rocks

late magmatic immiscibility during batholith formation assessment of b isotopes and trace elements in tourmaline from the land s end granite sw england quartz tourmaline orbicules are unevenly distributed in the roof segment of the land s end granite sw england this study shows that the orbicules formed from an immiscible hydrous borosilicate melt produced during the late stages of crystallization and differentiates tourmaline formed by dominantly magmatic and dominantly hydrothermal processes trace elements and boron isotope fractionation can be tracked in tourmaline and create a timeline for crystallization tourmaline from the granite matrix has higher v cr and mg content and is isotopically heavier than the later crystallizing inner orbicule tourmaline overgrowths of blue tourmaline occurring together with quartz showing hydrothermal cathodoluminescence textures crystallized from an aqueous fluid during the very last crystallization and are significantly higher in sr and sn and isotopically heavier tourmaline associated with sn mineralization is also high in sr and sn but has boron isotopic compositions close to that of the magmatic tourmaline and is not formed by the same fluids responsible for the blue overgrowths the ore forming fluids precipitating tourmaline and cassiterite are likely derived from the same magma source as the granite but exsolved deeper in the magma chamber and at a later stage than orbicule formation tourmaline from massive quartz tourmaline rocks is concentrically zoned with major and trace element compositions indicating crystallization from a similar melt as for the orbicules but shows a more evolved signature

vapor undersaturated experiments with macusani glass h 2 o at 200 mpa and the internal differentiation of granitic pegmatites vapor undersaturated fractional crystallization experiments with macusani glass macusanite a peraluminous rhyolite obsidian at 200 mpa yield mineralogical fabrics and zonation and melt fractionation trends that closely resemble those found in zoned granitic pegmatites and other granitoids of comparable composition typically peraluminous li be ta rich deposits the zonation from the edge of charges inward is characterized by 1 fine grained sodic feldspar quartz border zones 2 a fringe of very coarse grained graphic quartz feldspar intergrowths that flair radially toward melt and terminate with nearly monophase k feldspar 3 cores of very coarse grained nearly monominerallic quartz or virgilite lialsi5o12 mica and 4 late stage fine grained albite mica intergrowths that are deposited from alkaline na rich interstitial melt at vapor saturation similar experimental products have been observed in compositionally simpler less evolved systems liquid lines of descent from initially h2o undersaturated runs are marked by a decrease in sio2 and increases in na k b p f h2o and a variety of trace lithophile cations these trends are believed to be governed by three factors 1 disequilibrium growth of feldspars quartz via metastable supersaturation 2 fractionation of melt toward sio2 depleted na rich compositions due to increases in b p and f and 3 changes in nucleation and growth rates mostly as a function of the h2o content of melt x w m in contrast experiments that are cooled below the liquidus from the field of melt aqueous vapor london et al 1988 fail to replicate pegmatitic characteristics in most respects on the basis of these and other experiments we suggest that the formation of pegmatite fabrics stems primarily from fractional crystallization in volatile rich melts and that enrichments in normally trace lithophile elements result from melt differentiation trends toward increasingly alkaline silica depleted compositions although vapor saturation at near solidus and subsolidus conditions may promote extensive recrystallization an aqueous vapor phase does not appear to be necessary for the generation of most of the salient characteristics of pegmatites