experimental reactions of amphibolite with boron bearing aqueous fluids at 200 mpa implications for tourmaline stability and partial melting in mafic rocks reactions between hornblende plagioclase amphibolite and acidic and alkaline b bearing aqueous fluids have been investigated by experiments at 475 600 c and 200 mpa at 600 c hornblende calcic plagioclase react to form tourmaline danburite clinopyroxene quartz in acidic fluids containing 0 5 1 0 wt b2o3 tourmaline is precipitated directly from acidic fluids and the reaction is driven by neutralization of fluids by na ca derived from the breakdown of reactant solids the concentration of b2o3 in fluids needed to stabilize tourmaline increases as ph increases above approximately 6 0 and tourmaline is unstable in alkaline fluids ph approximately 6 5 7 0 regardless of b concentration in addition to acid base relations tourmaline stability is favored by comparatively higher activity coefficients for al species in acidic fluids the concentrations of al and si in fluid increase with alkalinity with the eventual production of felsic borosilicate melts through partial melting of the plagioclase component of the amphibolite in seeded experiments tourmaline also contributes components to melt partial melting is evident in the range 500 525 c at 200 mpa in experiments with 8wt b2o3 in fluid as na2b4o7 the experimental results are applied primarily to metasomatic reactions between mafic rocks and borate fluids derived from granitic magmas but tourmaline stability and partial melting in mafic regional metamorphic systems are also discussed briefly

chemical and boron isotopic compositions of tourmaline from the paleoproterozoic houxianyu borate deposit ne china implications for the origin of borate deposit abstract the houxianyu borate deposit in northeastern china is one of the largest boron sources of china hosted mainly in the paleoproterozoic meta volcanic and sedimentary rocks known as the liaohe group that are characterized by high boron concentrations the borate ore body has intimate spatial relationship with the mg rich carbonates silicates of the group with fine grained gneisses meta felsic volcanic rocks as main country rocks the presence of abundant tourmalinites and tourmaline rich quartz veins in the borate orebody provides an opportunity to study the origin of boron the nature of ore forming fluids and possible mineralization mechanism we report the chemical and boron isotopic compositions of tourmalines from the tourmaline rich rocks in the borate deposit and from the tourmaline bearing fine grained gneisses tourmalines from the fine grained gneisses are chemically homogeneous showing relatively high fe and na and low mg with 11b values in a narrow range from 1 22 to 2 63 tourmalines from the tourmaline rich rocks however commonly show compositional zoning with an irregular detrital core and a euhedral overgrowth and have significantly higher mg ree and more pronounced positive eu anomalies v 229 1852 ppm and sr 208 1191 ppm than those from the fine grained gneisses they show varied b isotope values ranging from 4 51 to 12 43 which plot intermediate between those of the terrigenous sediments and arc rocks with low boron isotope values as represented by the 11b 1 22 to 2 63 of the fine grained gneisses of this study and those of marine carbonates and evaporates with high boron isotope values in addition the rim of the zoned tourmaline shows notably higher mg ti v sn and pb and ree particularly lrees but lower fe co cr ni zn mn and lower 11b values than the core these data suggest that 1 the sources of boron of the borate ore body are mainly the paleoproterozoic meta volcanic and sedimentary rocks and 2 the ore forming fluids should be the high temperature metamorphic fluids related to the amphibolite facies metamorphism of the paleoproterozoic foldbelt which leach boron from the boron rich meta volcanic and sedimentary rocks of the liaohe group and the boron rich metamorphic fluids subsequently interacted with the marine mg rich carbonates and evaporates forming borate deposit the tourmaline overgrowth in the rim and the tourmaline rich rocks

discriminating fluid source regions in orogenic gold deposits using b isotopes abstract the genesis of orogenic gold deposits is commonly linked to hydrothermal ore fluids derived from metamorphic devolatilization reactions however there is considerable debate as to the ultimate source of these fluids and the metals they transport tourmaline is a common gangue mineral in orogenic gold deposits it is stable over a very wide p t range demonstrates limited volume diffusion of major and trace elements and is the main host of b in most rock types we have used texturally resolved b isotope analysis by secondary ion mass spectrometry sims to identify multiple fluid sources within a single orogenic gold ore district the loulo mining district in mali west africa hosts several large orogenic gold ore bodies with complex fluid chemistry associated with widespread pre ore na and multi stage b metasomatism the gara deposit as well as several smaller satellites formed through partial mixing between a dilute aqueous carbonic fluid and a hypersaline brine hydrothermal tourmaline occurs as a pre ore phase in the matrix of tourmalinite units which host mineralization in several ore bodies clasts of these tourmalinites occur in mineralized breccias disseminated hydrothermal and vein hosted tourmaline occur in textural sites which suggest growth during and after ore formation tourmalines show a large range in 11 b values from 3 5 to 19 8 which record a change in fluid source between paragenetic stages of tourmaline growth pre mineralization tourmaline crystals show heavy 11 b values 8 19 8 and high x site occupancy na ca 0 69 1 apfu suggesting a marine evaporite source for hydrothermal fluids syn mineralization and replacement phases show lighter 11 b values 3 5 to 15 1 and lower x site occupancy 0 62 0 88 apfu suggesting a subsequent influx of more dilute fluids derived from devolatilization of marine carbonates and clastic metasediments the large overlapping range in isotopic compositions and a skew toward the opposing population in the 11 b data for both tourmaline groups reflects continual tourmaline growth throughout mineralization which records the process of fluid mixing a peak in 11 b values at 8 largely controlled by tourmalines of syn to post ore timing represents a mixture of the two isotopically distinct fluids this paper demonstrates that b isotopes in tourmaline can be instrumental in interpreting complex and dynamic hydrothermal systems the importance of b as an integral constituent of orogenic ore forming fluids and as a gangue phase in orogenic gold deposits makes b isotope analysis a powerful tool for testing the level of source region variability in these fluids and by extension that of metal sources

fluid sources and metallogenesis in the baiganhu w sn deposit east kunlun nw china insights from chemical and boron isotopic compositions of tourmaline abstract tourmaline is widespread in the baiganhu w sn deposit xinjiang province nw china in this study electron microprobe analysis reveals that tourmaline in the baiganhu deposit belongs to the alkali and x site group with low ca and moderate x site vacancy all beyond the confines of schorl dravite series with na na ca and fe fe mg ratios ranging from 0 769 to 0 965 and 0 518 to 0 822 respectively in chemical discrimination diagrams the tourmaline samples plot in the fields of li poor granite associated with al saturated metapelites and metapsammites the tourmaline cores are depleted in mg ca ti but enriched in al and fe compared to the rims substitution mechanisms for the compositional variations are dominantly due to mgfe 1 al nafe 1 al namg 1 and alo fe 1 oh 1 exchange vectors the 11b values of the tourmalines range from 12 9 to 7 9 with a slight variation between cores and rims which reflect a common boron source and also indicate that the tourmaline crystallized during a single magmatic hydrothermal event related to monzogranite tourmaline is a valuable prospecting indicator of w sn mineralization

b rich melt immiscibility in late cretaceous nattaung granite myanmar implication by composition and b isotope in tourmaline abstract there is a strong controversy about the petrogenesis of tourmaline nodules and their relationship with coeval tourmaline bearing granites which are commonly associated with magmatic hydrothermal rare metal deposits e g sn nb and ta in this study tourmaline is extensively distributed in tourmaline bearing nodules nt type pegmatite pt type and fine grained granitic dyke gt type which are hosted by the late cretaceous nattaung biotite granite myanmar zircon u pb dating results 71 ma indicate that pt and gt types tourmaline bearing magmatic rocks formed synchronously with biotite granite all tourmalines have alkali group and schorl composition with mg mg fe ratios of 0 03 0 45 and na na ca ratios of 0 73 to 1 00 nt type tourmaline shows high nb ta ratios and v and sr contents indicating that they were likely crystallized from b rich melts early immiscible with less evolved granitic magmas pt and gt type tourmalines probably formed in aggregated b rich melts that continuously separated from more evolved granitic magma supported by their low nb ta ratios and v and sr contents in addition the studied tourmaline displays a slight variation of b isotopic compositions 11b values ranging from 12 2 0 7 to 14 9 0 4 likely resulted by rayleigh fractionation of tourmaline their light b isotopic values are consistent with those of average continental crust also revealing that the nattaung granite was mainly derived from partial melting of the ancient sibumasu crust importantly late stage pt and gt type tourmalines have higher sn zn nb and ta contents than early stage nt type tourmaline suggesting that the evolved b rich magma could be one precursor to produce sn nb ta zn deposits associated with extensive tourmaline in the world

boron isotope variations in nature a synthesis the large relative mass difference between the two stable isotopes of boron 10b and 11b and the high geochemical reactivity of boron lead to significant isotope fractionation by natural processes published 11b values relative to the nbs srm 951 standard span a wide range of 90 the lowest 11b values around 30 are reported for non marine evaporite minerals and certain tourmalines the most 11b enriched reservoir known to date are brines from australian salt lakes and the dead sea of israel with 11b values up to 59 dissolved boron in present day seawater has a constant world wide 11b value of 39 5 in this paper available 11b data of a variety of natural fluid and solid samples from different geological environments are compiled and some of the most relevant aspects including possible tracer applications of boron isotope geochemistry are summarized

source of boron in the palokas gold deposit northern finland evidence from boron isotopes and major element composition of tourmaline the recently discovered palokas gold deposit is part of the larger rompas rajapalot gold mineralized system located in the paleoproterozoic perapohja belt northern finland tourmaline is an important gangue mineral in the palokas gold mineralization it occurs as tourmalinite veins and as tourmaline crystals in sulfide rich metasomatized gold bearing rocks in order to understand the origin of tourmaline in the gold mineralized rocks we have investigated the major element chemistry and boron isotope composition of tourmaline from three areas 1 the palokas gold mineralization 2 a pegmatitic tourmaline granite and 3 the evaporitic petajaskoski formation based on textural evidence tourmaline in gold mineralization is divided into two different types type 1 is located within the host rock and is cut by rock forming anthophyllite crystals type 2 occurs in late veins and or breccia zones consisting of approximately 80 tourmaline and 20 sulfides commonly adjacent to quartz veins all the studied tourmaline samples belong to the alkali group tourmaline and can be classified as dravite and schorl the 11b values of the three localities lie in the same range from 0 to 4 tourmaline from the au mineralization and from the petajaskoski formation has similar compositional trends mg is the major substituent for al inferred low fe3 fe2 ratios and na values 0 8 atoms per formula unit apfu of all tourmaline samples suggest that they precipitated from reduced low salinity fluids based on the similar chemical and boron isotope composition and the re os age of molybdenite related to the tourmaline sulfide quartz veins we propose that the tourmaline forming process is a result of a single magmatic hydrothermal event related to the extensive granite magmatism at around 1 79 1 77 ga tourmaline was crystallized throughout the hydrothermal process which resulted in the paragenetic variation between type 1 and type 2 the close association of tourmaline and gold suggests that the gold precipitated from the same boron rich source as tourmaline

boron isotope fractionation between tourmaline and fluid an experimental re investigation the fractionation of boron isotopes between synthetic dravitic tourmaline and fluid was determined by hydrothermal experiments between 400 and 700 c at 200 mpa and at 500 c 500 mpa tourmaline was crystallized from an oxide mix in presence of water that contained boron in excess in one series of experiments b fluid b tour was 9 after the run in another series it was 0 1 all experiments produced tourmaline as the sole boron bearing solid along with traces of quartz and talc powder xrd and rietveld refinements revealed no significant amounts of tetrahedrally coordinated boron in tourmaline 11b always preferentially fractionated into the fluid for experiments where b fluid b tour was 9 a consistent temperature dependent boron isotope fractionation curve resulted approximated by 11b tour fluid 4 20 1 000 t k 3 52 r2 0 77 and valid from 400 to 700 c no pressure dependence was observed the fractionation 2 7 0 5 at 400 c and 0 8 0 5 at 700 c is much lower than that previously presented by palmer et al 1992 experiments where b fluid b tour was 0 1 showed a significant larger apparent fractionation of up to 4 7 in one of these runs the isotopic composition of handpicked tourmaline crystals of different size varied by 1 3 this is interpreted as resulting from fractional crystallization of boron isotopes during tourmaline growth due to the small boron reservoir of the fluid relative to tourmaline thus indicating larger fractionation than observed at equilibrium the effect is eliminated or minimized in experiments with very high boron excess in the fluid we therefore suggest that values given by the above relation represent the true equilibrium fractionations

archean magmatic hydrothermal fluid evolution in the quadrilatero ferrifero se brazil documented by b isotopes la mc icpms in tourmaline abstract in the archean quadrilatero ferrifero district se brazil tourmaline occurs as a major constituent in a leucogranitic intrusion and numerous pegmatitic aplitic veins within magmatic basement complexes as well as in quartzo feldspathic veins in quartz tourmaline rocks tourmalinites and as disseminated grains in the surrounding greenstone belt metasediments the chemical and boron isotope composition of these tourmalines was analysed by electron microprobe and la mc icp ms to determine the origin of the fluids involved and to shed light on the hydrothermal evolution of the region the tourmalines exhibit an overall decrease in fe fe mg ratio and a net increase in cr up to 0 75 wt from tourmaline hosted in the leucogranite the quartzo feldspathic veins the tourmalinites to the disseminated grains in the schists these variations mirror the bulk composition of the host schists and illustrate a strong protolith control on tourmaline major element composition the full range of tourmaline 11b is from 27 1 to 9 2 with a major cluster between 12 and 19 which includes the magmatic tourmaline in the leucogranite 15 2 to 12 5 most of these isotope compositions can be reconciled with a model involving tourmaline growth from late stage exsolved magmatic fluids percolating through the magmatic basement and into the nearby metasediments this model agrees well with the trends of major element compositions as well as with the critical observation that tourmaline occurrence is restricted to the vicinity of the basement complexes 11b values lower than 19 in our dataset are beyond the reach of isotope fractionation during magmatic fluid exsolution and temperature decrease and suggest the presence of a distinct fluid component we propose that an isotopically light fluid was released from mica breakdown in the country rocks during local upper amphibolite facies metamorphism in the dome border shear zone

the boron isotopic evolution of the little three pegmatites ramona ca abstract tourmaline mica hambergite danburite and axinite from three pegmatite dikes named main swamp and spessartine at the little three mine near ramona california have been analyzed by secondary ion mass spectrometry sims for their boron isotopic compositions 11b tourmaline is the sole host of b in the massive footwall and hanging wall sections of the dikes and the principal sink for b in the miarolitic cavities in the thinner spessartine and swamp dikes the pocket mineralogy includes foitite spessartine muscovite axinite danburite and rare beryl the thicker main dike culminates in cavities containing topaz elbaite lepidolite boromuscovite hambergite and rare stibiotantalite values of 11btur from the little three pegmatites are strikingly heavy 0 1 to 13 8 compared to other pegmatitic tourmaline 27 to 9 which is best explained by inheritance from an 11b enriched source material such as altered oceanic crust flat patterns of 11btur from margin to core of each pegmatite attest to a negligible fractionation of boron isotopes between tourmaline granitic melt and granitic melt aqueous fluid tourmaline samples from intermediate zones and miarolitic cavities have identical boron isotopic compositions except for miarolitic cavities that contain axinite and danburite whose b is in 4 fold structural coordination in these cavities the 11b of tourmaline increases relative to tourmaline from the intermediate zone interpretations of 11btur from margin to core in these and other pegmatites are hampered by uncertainties in the boron isotopic fractionation factors for melt aqueous fluid and for tourmaline granitic melt based on modeled cooling and crystallization of these dikes the growth of tourmaline should have been fast relative to the diffusivity of b through granitic melt hence an equilibrium distribution of 11b and 10b between tourmaline bulk melt and an aqueous solution i e rayleigh fractionation process is unlikely the negligible isotopic fractionation of boron in tourmaline from margins to center therefore probably records only the bulk isotopic composition of the pegmatite forming melts

chemical and boron isotope composition of tourmaline from the kiaka orogenic gold deposit burkina faso west african craton as a proxy for ore forming processes the kiaka orogenic gold deposit burkina faso located in the paleoproterozoic domain of the west african craton is characterized by a two stage gold mineralization hosted in volcano sedimentary metamorphic rocks that was formed during the eoeburnean 2 20 2 13 ga and eburnean 2 13 2 05 ga orogenic cycles these two stages include an early disseminated low grade gold mineralization and a late vein hosted high grade gold mineralization paragenetic studies indicate that the first gold stage was coeval with the deposition of hydrothermal tourmaline the aim of this paper is twofold i to determine the processes responsible for deposition of the economic disseminated gold mineralization and ii to identify the source of the mineralizing fluids for this purpose we performed an in situ study on tourmaline by combining electron probe microanalysis and secondary ion mass spectrometry measurements of boron isotopes hydrothermal tourmaline hosted in metamafic volcanic rocks and metagreywackes has a dravite composition but shows different 11b values falling within the two intervals of 25 1 to 22 0 and 19 6 to 15 1 respectively our results suggest that tourmaline formed from a distal high temperature ca 400 c reduced and low salinity hydrothermal fluid that interacted with the local host rocks based on the modeling of tourmaline fluid boron isotope fractionation we propose a metamorphic fluid origin derived from devolatilization of deeply buried muscovite schists during the regional prograde to peak metamorphism prior ca 2 13 ga this metamorphic fluid rock interaction model may possibly extend to other orogenic gold deposits in the west african craton

geological relationships and u pb zircon and 40 ar 39ar tourmaline geochronology of gneisses and tourmalinites from the nevado filabride complex western sierra nevada spain tectonic implications abstract the nevado filabride complex the lowest complex in the betic hinterland forms a stack of alpine nappes the tectonic units consist of metasedimentary sequences whose ages are not well constrained gneiss bodies included in the sequences have been one of the few sources of geochronological data in this metamorphic complex new radiometric data from u pb zircon dating on gneisses from the western sierra nevada confirm the presence of late carboniferous intrusive rocks in the betic hinterland these results combined with available data from the literature and a detailed structural analysis suggest that the gneisses represent a single late variscan magmatic event evidence for a close genetic relation between gneisses and tourmalinites is provided by field and petrographic observations in conjunction with geochemical data u pb zircon 314 7 304 23 ma and 40 ar 39 ar tourmaline 319 85 5 81 317 85 3 67 ma geochronology a pre late carboniferous age for the basal formation of the nevado filabride sequence can be inferred the gneiss protolith and the graphite schist are considered to be the boron source and the precursor of the tourmalinites respectively superposed tectonic units rather than a continuous palaeozoic sequence is supported by the occurrence of palaeozoic rocks at the top of the nevado filabride complex the nappe tectonics as evidenced from the contractional character of the unit boundaries and the superposition of higher grade on lower grade metamorphic rocks is additionally supported by the superposition of older on younger rocks as revealed from radiometric data

exploration of driving mechanisms of equilibrium boron isotope fractionation in tourmaline group minerals and fluid a density functional theory study abstract the equilibrium boron isotope fractionations 3 4 11b tur fluid between tourmaline mineral groups and fluids at 0 5 gpa 600 1000 k are investigated using density functional theory calculations the first solvent shell controls boron isotope fractionation in solution where the values of both h3bo3 and b oh 4 decrease with increasing numbers of hydrogen bonds in supercritical fluids the weakening of hydrogen bonds and the diversity in configurations of hydrated boron species both contribute to variations in the vibrational frequencies the 1000ln tur fluid value increases with increasing mg fe mg ratios in the dravite schorl solid solution series this effect together with the crystallization sequence predicted from the gibbs free energies of tourmaline formation accounts well for the association of boron isotope and chemical zonation observed in zoned tourmaline grains the dependence of boron isotope fractionation on the b o bond length in tourmaline group minerals reflects the changes in relevant molar volumes caused by differences in the mass and charge of the atoms occupying the x y and z sites of tourmalines this study suggests that the chemical composition of the tourmaline plays an important role in controlling the boron isotope composition in tourmalines crystallized from hydrothermal systems

chemical and boron isotope compositions of tourmaline in the hadamiao porphyry gold deposit inner mongolia china abstract the hadamiao porphyry gold deposit in inner mongolia china is located in the northern margin of the north china craton ncc tourmaline is a common mineral in hydrothermal veins and granitic rocks contemporaneous with the mineralized granite porphyry in this deposit the tourmaline can be divided into six types including magmatic tourmaline tur m1 in granite porphyry dikes magmatic hydrothermal transitional tourmaline tur m2 in nodular granitic rocks and hydrothermal tourmalines in early tourmaline veins tur v1 gold bearing quartz tourmaline chalcopyrite veins tur v2 breccia cements tur v3 and late carbonate quartz veins tur v4 the gold mineralization is closely related to the occurrence of tur v2 almost all the tourmalines from the hadamiao deposit belong to the alkali group and show a schorlitic dravitic composition except for some tur m1 belonging to uvite the concentrations of most elements in different tourmaline types overlap tur m1 has higher ca w th u pb mn and zr contents than other types and the hydrothermal tourmalines v1 v4 show slightly higher ba cu and y contents than tur m1 and tur m2 the concentration of au in tur m1 and tur m2 can reach up to 80 ppb and is higher than that in tur v1 the au content in tur v2 is an order of magnitude higher than that in other stages of tourmaline systematic contrasts in major and trace element compositions between magmatic and hydrothermal tourmalines are attributed to the assimilation of the country rock by the magmatic hydrothermal system the six types of tourmaline exhibit variable 11b values ranging from 8 7 to 21 2 tur m1 shows the highest 11b values of 15 1 to 21 2 and tur v2 yields the lowest values ranging from 8 7 to 5 4 the boron probably came from two sources with different isotopic compositions one with high positive 11b values and the other with negative 11b values magmatic hydrothermal fluids could have provided isotopically light boron for hydrothermal tourmalines whereas the heavy boron in magmatic tourmaline was probably derived from marine carbonates that are widespread in the study area the magma related to the mineralization and the one containing magmatic tourmaline may have experienced different degrees of interaction with wall rocks resulting in the diversity of 11b values in hadamiao tourmaline

three stage formation of greenstone hosted orogenic gold deposits in the val d or mining district abitibi canada evidence from pyrite and tourmaline abstract orogenic gold deposits are the most widespread type of gold deposit worldwide defining important exploration targets in precambrian greenstone belts here we refine the model for orogenic gold formation in the world class val d or mining district quebec canada using geochemical isotopic and mineralogical data from quartz tourmaline carbonate qtc veins from several deposits across the district multi element ag as au b ba co mg mo ni and pb pyrite mapping as well as major trace and rare earth element variations in tourmaline define a three stage paragenesis across several deposits the first reduced phase crystallized the quartz carbonate gold association in the veins the second oxidized phase favored tourmaline and barite crystallization barite was not previously reported from this district the third phase involved a reduced fluid and the crystallization of non auriferous as co ni rich cubic pyrite and tourmaline boron isotope ratios of tourmaline vary from 15 6 to 7 7 which is attributed to the mixing of at least two fluids one related to a deep metamorphic source and the other to shallower possibly relict formation water a systematic regional pattern in b isotope variation is found with lighter values in the volcanic rocks and heavier ones in or close to intrusions which suggests different mixing proportions in the vein field from ne to sw

boron and magnesium rich marine brines at the origin of giant unconformity related uranium deposits δ11b evidence from mg tourmalines in giant unconformity related u deposits from the athabasca basin canada the origin of the ore fluids and the source of elements typically associated with u ore such as mg and b are highly controversial this paper presents a petrographic and boron isotopic study of mg tourmalines dravites coeval with u oxides and of primary tourmalines from basement rocks the heavy b isotopic compositions of dravites 11 b 19 6 36 5 contrast with the light composition of basement tourmalines 11 b 8 1 3 3 and clearly show that most of the b was brought to the ore system by basinal brines of marine origin because the latter are also typically mg rich a similar origin for mg is proposed these results support the idea that marine derived brines were the only fluids involved in the formation of the deposits and therefore challenge the previous models in which the b and mg were leached from sedimentary and or basement rocks or carried by a basement derived fluid

boron isotope record of peak metamorphic ultrahigh pressure and retrograde fluid rock interaction in white mica lago di cignana western alps this study presents boron b concentration and isotope data for white mica from ultra high pressure uhp subduction related metamorphic rocks from lago di cignana western alps italy these rocks are of specific geological interest because they comprise the most deeply subducted rocks of oceanic origin worldwide boron geochemistry can track fluid rock interaction during their metamorphic evolution and provide important insights into mass transfer processes in subduction zones the highest b contents up to 345 g g b occur in peak metamorphic phengite from a garnet phengite quartzite the b isotopic composition is variable 11b 10 3 to 3 6 and correlates positively with b concentrations based on similar textures and major element mica composition neither textural differences prograde growth zoning diffusion nor a retrograde overprint can explain this correlation modelling shows that b devolatilization during metamorphism can explain the general trend but fails to account for the wide compositional and isotopic variability in a single well equilibrated sample we therefore argue that this trend represents fluid rock interaction during peak metamorphic conditions this interpretation is supported by fluid rock interaction modelling of boron leaching and boron addition that can successfully reproduce the observed spread in 11b and b taking into account the local availability of serpentinites as potential source rocks of the fluids the temperatures reached during peak metamorphism that allow for serpentine dehydration and the high positive 11b values 11b 20 5 modelled for the fluids an influx of serpentinite derived fluid appears likely paragonite in lawsonite pseudomorphs in an eclogite and phengite from a retrogressed metabasite have b contents between 12 and 68 g g and 11b values that cluster around 0 11b 5 0 to 3 5 white mica in both samples is related to distinct stages of retrograde metamorphism during exhumation of the rocks the variable b geochemistry can be successfully modelled as fluid rock interaction with low to moderate 3 fluid rock ratios where mica equilibrates with a fluid into which b preferentially partitions causing leaching of b from the rock the metamorphic rocks from lago di cignana show variable retention of b in white mica during subduction related metamorphism and exhumation the variability in the b geochemical signature in white mica is significant and enhances our understanding of metamorphic processes and their role in element transfer in subduction zones

synthesis of tourmaline solid solutions in the system na 2 o mgo al 2 o 3 sio 2 b 2 o 3 h 2 o hcl and the distribution of na between tourmaline and fluid at 300 to 700 c and 200 mpa tourmaline has been synthesized hydrothermally at 200 mpa between 300 and 700 c from oxide mixtures with mg al ratios for the end members dravite namg3al6 si6o18 bo3 3 oh 3 oh and mg foitite mg2al al6 si6o18 bo3 3 oh 3 oh six different na concentrations were investigated to determine the distribution of na between tourmaline and fluid in the sio2 saturated system na2o mgo al2o3 sio2 b2o3 h2o hcl synthetic tourmaline ranges from x site vacant tourmaline mg foitite to nearly ideal dravite with na 0 95 apfu there are small but significant amounts of proton deficiency and negligible tetrahedral al chemical variation is primarily caused by the substitutions al mg 1na 1 and minor almg 1h 1 varying amounts of na and determine the mg al ratios besides tourmaline and quartz additional mg al phases are chlorite and at 700 c cordierite albite is also present at high na concentrations in the bulk composition the c dimension of the tourmaline crystals increases with na in tourmaline the amount of na in the x site depends strongly on the bulk concentration of na in the system as well as on the temperature these factors in turn control the phase assemblage and the composition of the fluid phase for the assemblage tourmaline quartz chlorite cordierite fluid a linear relationship exists between na concentration in the fluid quenched after the run and tourmaline with temperature t c 25 c nafluid natur 558 878 14 692 r2 0 96

boron isotopic constraints on the petrogenesis of hematitic phyllite in the southern serra do espinhaco minas gerais brazil abstract metasiliciclastic rocks predominate in the lower units of the palaeo mesoproterozoic espinhaco supergroup in the southern serra do espinhaco minas gerais brazil the lower units also comprise rocks with locally preserved igneous fabrics but which have very unusual chemistries these rocks collectively known as hematitic phyllite are characterised by abundant fine grained muscovite i e sericite and variable amounts of titaniferous hematite rutile and tourmaline currently the hematitic phyllite has been interpreted as a metamorphosed palaeosol after basaltic rocks and as such has been used as a palaeoclimatic indicator however the lateritic nature of the hematitic phyllite cannot unambiguously be determined because of the k metasomatism hematitisation and tourmalinisation recorded in the hematitic phyllite and in the arenaceous country rocks here we report the b isotopic and chemical compositions of tourmaline from the hematitic phyllite our 11b data are in the range between 15 and 4 the tourmaline compositions fall along the povondraite oxy dravite join which defines a meta evaporitic tourmaline trend a meta evaporitic b source is constrained by the b isotopic data as non marine our model for the hematitic phyllite suggests that b and k rich brines were derived from the metamorphic dewatering of non marine evaporites such brines extensively altered volcanic rocks of basaltic and rhyolitic compositions leading to tourmaline bearing hematite sericite assemblages of the hematitic phyllite

boron isotopes in tourmaline as a tracer of metasomatic processes in the bamble sector of southern norway the bamble sector of southern norway comprises metagabbros and metasediments that were metasomatically altered to various extents during a late stage of the sveconorwegian orogeny 1 06 ga the infiltration of highly saline brines along veins led to penetrative scapolitization and albitization on a regional scale and the local deposition of fe ti oxides typical secondary mineral assemblages include either scapolite apatite amphibole phlogopite tourmaline or albite epidote calcite chlorite white mica indicating that the fluids introduced large amounts of na cl mg ca k p and b to the system metasomatic tourmalines associated with different alteration stages as identified by variations in major element composition and initial 87sr 86sr were analyzed for b isotopic compositions to constrain possible sources and the evolution of the hydrothermal fluid s measured 11b values range from 5 to 27 relative to srm 951 suggesting marine evaporites interlayered with various amounts of continental detritus and pelagic clay as a possible b source reservoir the influence of a seawater derived component is clearly indicated by the heavy b isotope signature of tourmaline related to al mg rich metapelites in contrast negative 11b values can be explained by the influence of pneumatolytic fluids associated with granitic pegmatites on a regional scale i e several km 11b values in tourmaline vary widely whereas variations within a single outcrop tens of m are typically small and can be ascribed to different generations of tourmaline related to several fluid pulses

tourmaline occurrences within the penamacor monsanto granitic pluton and host rocks central portugal genetic implications of crystal chemical and isotopic features tourmalinization associated with peraluminous granitic intrusions in metapelitic host rocks has been widely recorded in the iberian peninsula given the importance of tourmaline as a tracer of granite magma evolution and potential indicator of sn w mineralizations in the penamacor monsanto granite pluton central eastern portugal central iberian zone tourmaline occurs 1 as accessory phase in two mica granitic rocks muscovite granites and aplites 2 in quartz mica tourmaline rocks tourmalinites in several exocontact locations and 3 as a rare detrital phase in contact zone hornfels and metapelitic host rocks electron microprobe and stable isotope 18o d 11b data provide clear distinctions between tourmaline populations from these different settings a schorl oxyschorl tourmalines from granitic rocks have variable foititic component x 17 57 and mg mg fe ratios 0 19 0 50 in two mica granitic rocks and 0 05 0 19 in the more differentiated muscovite granite and aplites granitic tourmalines have constant 18o values 12 1 0 1 with wider ranging d 78 2 4 7 and 11b 10 7 to 9 0 values b vein breccia oxyschorl mg mg fe 0 31 0 44 results from late b and fe enriched magma derived fluids and is characterized by 18o 12 4 d 29 5 and 11b 9 3 while replacement tourmalines have more dravitic compositions mg mg fe 0 26 0 64 close to that of detrital tourmaline in the surrounding metapelitic rocks and yield relatively constant 18o values 13 1 13 3 though wider ranging d 58 5 to 36 5 and 11b 10 2 to 8 8 values and c detrital tourmaline in contact rocks and regional host metasediments is mainly dravite mg mg fe 0 35 0 78 and oxydravite mg mg fe 0 51 0 58 respectively boron contents of the granitic rocks are low 650 ppm compared to the minimum b contents normally required for tourmaline saturation in granitic melts implying loss of b and other volatiles to the surrounding host rocks during the late magmatic stages this process was responsible for tourmalinization at the exocontact of the penamacor monsanto pluton either as direct tourmaline precipitation in cavities and fractures crossing the pluton margin vein breccia tourmalinites or as replacement of mafic minerals chlorite or biotite in the host rocks replacement tourmalinites along the exocontact of the granite thermometry based on 18o equilibrium fractionation between tourmaline and fluid indicates that a late b enriched magmatic aqueous fluid av 18o 12 1 at 600 c precipitated the vein breccia tourmaline 18o 12 4 at 500 550 c and later interacted with the cooler surrounding host rocks to produce tourmaline at lower temperatures 400 450 c and an average 18o 13 2 closer to the values for the host rock although b metasomatism associated with some granitic plutons in the iberian peninsula seems to be relatively confined in space extending integrated studies such as this to a larger number of granitic plutons may afford us a better understanding of variscan magmatism and related mineralizations

mineralogical and isotopic characteristics of sodic calcic alteration in the highland valley copper district british columbia canada implications for fluid sources in porphyry cu systems

chemical and stable isotopic b h and o compositions of tourmaline in the maocaoping vein type cu deposit western yunnan china constraints on fluid source and evolution abstract this study determined the chemical and stable isotopic b h and o compositions of three stages of ore related hydrothermal tourmaline in the newly discovered maocaoping vein type cu deposit western yunnan china as well as the chemical and b isotopic compositions of magmatic tourmaline tourmaline g from a neighboring peraluminous granitic intrusion that is contemporaneous with the cu mineralization the objective was to constrain the source and evolution of the co 2 rich ore forming fluid the maocaoping cupriferous veins types v1 and v2 are hosted in mylonitized and metamorphosed jurassic sedimentary rocks early to late stage hydrothermal tourmaline occurs as vein related alteration halos tourmaline a in altered marble or schist as tourmaline v1 in type v1 veins and as tourmaline v2 in type v2 veins tourmaline a v1 and v2 belong to the alkalic group and consist mostly of dravite with 11 b values of 3 9 to 1 1 2 8 to 0 5 and 6 3 to 3 9 respectively tourmaline g belongs to the alkalic group and consists of schorl with 11 b values of 14 7 to 12 2 the similarities in chemical composition between marble and schist hosted tourmalines and between tourmalines in veins and alteration halos indicating their formation at different water rock ratios suggest that the compositions of the hydrothermal tourmaline at maocaoping were controlled mainly by the chemistry of ore fluid rather than that of the host rocks the similarities together with the lack of systematic variations in 11 b values in individual tourmaline grains imply that mixing of multiple fluids cannot be important during the mineralization the positive shift in 11 b values from tourmaline a to tourmaline v1 is interpreted to result from continuous precipitation of tourmaline in a closed fluid system relative to tourmaline a and v1 tourmaline v2 is fe rich al poor and 11 b depleted these differences may be explained by fluid phase separation and subsequent escape of the co 2 rich vapor phase during the formation of type v2 veins consistent with the observations that these veins are extensional contain large amounts of carbonate minerals and include fluid inclusions trapped in the vapor liquid two phase field the earliest tourmaline a records the initial ore fluid chemistry the calculated 11 b 18 o and d values of the initial ore fluid in equilibrium with tourmaline a at mineralization temperatures of 280 to 320 c are 0 3 to 3 0 10 7 to 11 8 and 110 to 84 respectively the 11 b values as well as the chemical compositions of tourmaline a are much different from those of tourmaline g suggesting that the ore fluid at maocaoping was not derived directly from the peraluminous granitic magma the b h o isotopic features as well as enrichment of co 2 in fluid inclusions also suggest the ore fluid cannot solely be derived from basinal fluid or meteoric water the simplest explanation is that the fluid was derived from a metamorphic fluid that had obtained isotopically lighter hydrogen via reaction with organic compounds e g ch 4 h 2 s alternatively the ore fluid sourced from the mixed metamorphic fluid and basinal brine meteoric water or degassed magmatic fluid it implies that the vein cu ore formation in the lanping basin is unlikely as a result of a sole magmatic or basinal fluid activity and it needs the involvement of metamorphic fluid process

ionospheric flows relating to transpolar arc formation 1 transpolar arcs are large scale auroral features which are observed within the polar cap when the imf has a northward component one leading candidate formation mechanism proposes that they are formed by reconnection in the magnetotail some time after a period of dayside reconnection with a non zero imf by component which introduces a twist into the magnetotail as a result of the twist the mechanism predicts that the return flows of the newly closed magnetic field lines are asymmetric about midnight their direction should depend upon the imf by component in the hours beforehand and should be opposite in the northern and southern hemispheres in this paper we use data from the superdarn network of high latitude ionospheric radars to examine whether such ionospheric flows are present before the formation of 33 transpolar arcs we find that the flows are present and in a manner that is consistent with the reconnection mechanism for 76 of the events in the remaining few the discrepancy can be attributed either to an uncertainty in the formation time determined for the arc due to previous polar cap activity in the same local time sector or due to the geometry of the radars which observe the backscatter

the diversity of b isotope variations in tourmaline from rare element pegmatites in the borborema province of brazil abstract tourmaline chemical and b isotope compositions have been determined from 4 rare element pegmatites and 1 barren pegmatite in the borborema pegmatite province of ne brazil and also from a leucogranite considered to be parental to the pegmatites the rare element pegmatites are of the lct lithium cesium tantalum class and they display a classic zoning structure with tourmaline present in all units but the quartz core tourmaline major element composition varies systematically from schorl dravite in the border and wall zones to varicolored elbaite in the inner zones consistent with increasing differentiation of a pegmatite magma previous studies supposed a continuous variation in li contents from schorl dravite to elbaite but the sims data instead show a major gap between 0 07 wt and 0 72 wt li 2 o followed by a continuous variation to the maximum value of 1 8 wt the barren pegmatite and leucogranite contain schorl dravite only the full range of 11 b values in tourmaline from the borborema pegmatites is from 20 2 to 1 6 n 62 which comes close to the total known diversity of pegmatite tourmalines worldwide and is much broader than the range of the associated leucogranite 15 1 to 13 4 n 3 however more than 80 of the pegmatite tourmalines define a main range between 17 and 9 11 b the average value of the latter 13 5 s d 2 3 n 50 is identical within error with the leucogranite supporting suggestions of a genetic relationship the b isotope compositions of barren and mineralized pegmatites overlap within the main range we find no correlation between chemical composition and b isotope ratios famous for the borboreman province are gem quality crystals of blue paraiba type elbaite the 11 b values of blue tourmaline from the capoeira pegmatite also fall within the main range 16 4 to 11 9 n 5 four of the 5 pegmatites studied are heterogeneous in 11 b with typical variations of 6 however there are no consistent trends in these examples from outer to inner units or from core to rim of zoned crystals that would fit any one scenario of melt evolution instead the factors controlling b isotope evolution e g crystallization fluid exsolution or mixing with external b reservoirs appear to vary locally and can be specific to the individual pegmatite or internal zone within it for example the carrascao pegmatite shows a shift from higher to lower 11 b values in tourmaline from the outer to inner zone 14 9 to 9 1 vs 20 2 to 13 9 resp and there is a parallel trend of lighter rims in zoned elbaite from the inner intemediate zone these trends are consistent with 11 b removal by tourmaline crystallization and or fluid exsolution an opposite trend in isotopic variation was found in zoned tourmaline from the wall zone of the boqueirao pegmatite whose core compositions are in the main range 15 1 to 14 9 and whose rims are much heavier 5 5 to 1 7 similarly high 11 b values about 10 beyond the main range were found in wall zone tourmaline in the barren fazenda turmalina pegmatite 6 0 to 1 6 the patchy distribution of heavy b isotopic compositions found only in outer zones of pegmatites and the strong isotopic contrast with the main range suggest the possibility of mixing with heavy b from the country rocks a potential source being layers of marble and calc silicate rocks

tourmaline boron and strontium isotope systematics reveal magmatic fluid pulses and external fluid influx in a giant iron oxide apatite ioa deposit abstract tourmaline is a common boron bearing mineral in hydrothermal system and has been widely used as a mineral probe to reconstruct geological processes because of its broad range in composition and resistance to metasomatic alteration the origin of kiruna type iron oxide apatite ioa deposits commonly linked to andesitic subvolcanic or volcanic rocks is highly controversial constraints on the evolution of these mineralizing systems are needed to advance understanding of the ore forming process in this study we apply in situ elemental and combined b sr isotopic analyses of tourmaline to elucidate the nature and evolution of the subsurface hydrothermal system associated with ioa mineralization in the giant taocun deposit eastern china taocun is hosted at the top of a diorite intrusion and exhibits three stages of hydrothermal alteration that contain tourmaline pre ore na alteration tur i syn ore magnetite formation and associated ca fe alteration tur ii and post ore ca mg alteration with sulfide veins tur iii compositional data for each stage of tourmaline plot along the oxy dravite povondraite join which is indicative of precipitation from relatively oxidizing fluids ranges of sr isotopic compositions in tur i 0 7065 0 7078 and tur ii 0 7068 0 7076 are identical to those of the igneous host rocks indicating precipitation from magmatic hydrothermal fluids the range of b isotopic compositions in tur i 11b values of 6 3 to 1 2 is also consistent with a magmatic source higher 11b values 2 4 to 5 4 obtained from tur ii are mainly ascribed to rayleigh fractionation in the magmatic hydrothermal system as tourmaline precipitated post ore tur iii has a wide range of mostly lower b isotopic compositions 8 5 to 0 8 that record another pulse of magmatic fluid input this interpretation is supported by the enrichment of na li be w sn v and ti in tur iii relative to tur i and ii however the higher sr isotope composition 0 7076 0 7086 of tur iii and available o isotope composition 7 to 3 5 of fluids of this stage record the infiltration of meteoric ground water from adjacent sedimentary country rocks the results suggest that the taocun ioa deposit formed in a magmatic hydrothermal system characterized by two or more pulses of magmatic fluid discharge from subvolcanic diorite intrusions followed by the influx of external ground water as the system waned this study highlights the utility of tourmaline as a robust geochemical and isotopic monitor of ore forming processes in such systems

fluid sources in the twangiza namoya gold belt democratic republic of congo evidence from tourmaline and fluid compositions and from boron and rb sr isotope systematics abstract the twangiza namoya gold belt tngb developed in a proterozoic variably composed sedimentary sequence that is associated with felsic and mafic igneous rocks during polyphase tectono metamorphic episodes the basement was exposed to repeated periods of heat influx that mobilised hydrothermal fluids and at the meso to neoproterozoic boundary led to the formation of g4 granites and pegmatites the evolution of the tngb hydrothermal system and its associated gold mineralisation are poorly understood here we investigate the tourmaline major elemental and the boron isotopic composition from one pegmatite and seven tourmaline bearing hydrothermal veins sampled from the kamituga and the lugushwa gold deposits tourmalines from the hydrothermal veins are essentially dravitic with variable ca contents in contrast the pegmatitic tourmaline is schorl elbaite dominated and largely ca free the boron isotopic signature of hydrothermal tourmaline from the kamituga deposit 11b 18 4 to 15 3 is distinctly lighter than that from lugushwa 11b 13 0 to 8 9 pegmatitic tourmaline from kamituga shows intermediate 11b values between 14 2 and 13 1 with an average of 13 9 the pegmatitic fluid most likely had a 11b composition in the range of 12 8 the isotopically significantly lighter boron in tourmaline from hydrothermal veins from kamituga cannot have formed by fractionation from this pegmatitic source using the rb sr mineral isochron method we have dated the kamituga pegmatite as 981 16 ma which correlates in time with the regional late kibaran g4 granites tourmaline bearing veins from lugushwa are significantly younger and formed during the early stages of the pan african orogenic period 677 17 ma rb sr mineral data fluid inclusions in quartz that are texturally associated with hydrothermal tourmaline contain abundant saline brines and co2 rich fluids that are commonly associated with ch4 and in places with amorphous carbon and n2 we interpret these fluids as having been derived from the hosting sedimentary sequence this model is in agreement with the observed tourmaline composition which are most readily affiliated with a variably ca and al rich pelitic source our model based on the isotopic age and mineral compositional evidence indicates a sedimentary source of fluids forming the tourmaline bearing hydrothermal veins in kamituga and lugushwa

in situ elemental and boron isotopic variations of tourmaline from the maogongdong deposit in the dahutang w cu ore field of northern jiangxi province south china insights into magmatic hydrothermal evolution abstract in this paper we present a systematic investigation of in situ major trace elements and boron isotopic variations of tourmaline from the maogongdong deposit in the dahutang w cu ore field of northern jiangxi province south china which demonstrates both the magmatic and hydrothermal origin for the formation of the tourmalines the tourmaline occurs mainly in granites pegmatites and quartz veins five types of tourmaline are identified 1 disseminated tourmaline in the pegmatites tur p type 2 isolated and disseminated tourmaline clots in the granites tur r1 type 3 typical anhedral quartz tourmaline nodulars in the granites tur r2 type 4 tourmaline clots in quartz tungsten sulfide veins tur q1 type 5 euhedral needle columnar tourmaline crystals in quartz or quartz sulfide veins tur q2 type these tourmalines mostly fall into the alkali group representing schorl dravite solid solution series petrography and chemical discrimination diagrams suggest that the tur p tur r1 and tur r2 are of magmatic origin and the tur q1 and tur q2 are of hydrothermal origin hydrothermal tourmalines have higher mg mg fe ratios higher li be sn rb co sr v pb zn ni contents and lower na na ca ratios lower nb ta contents than the magmatic tourmalines the tur p show negative eu anomalies and their ree patterns are equivalent to the muscovite granite the eu anomalies in tur r1 and tur r2 change from negative to positive compared with magmatic tourmalines tur q1 and tur q2 exhibit more pronounced positive eu anomalies and a majority of the tur q1 and tur q2 have higher ree contents tourmalines from the maogongdong deposit have a b isotopic composition range from 17 9 to 12 3 the average 11b values of the tur p tur r1 and tur r2 are 13 8 14 8 and 14 5 respectively tourmalines in early hydrothermal veins have similar 11b values average 14 6 while the tourmalines in later hydrothermal veins have slightly lower 11b values average 16 5 boron isotopic variations of tourmaline are controlled by temperature rayleigh fractionation and external fluid

an experimental study on k and na incorporation in dravitic tourmaline and insight into the origin of diamondiferous tourmaline from the kokchetav massif kazakhstan tourmaline was synthesized in the system mgo al2o3 b2o3 sio2 kcl nacl h2o from an oxide mixture and excess fluid at 500 700 c and 0 2 4 0 gpa to investigate the effect of pressure temperature and fluid composition on the relative incorporation of na and k in dravitic tourmaline incorporation of k at the x site increases with pressure temperature and kcl concentration a maximum of 0 71 k pfu leaving 0 29 x vacant sites pfu was incorporated into k dravite synthesized at 4 0 gpa 700 c from a 4 78 m kcl na free fluid in contrast na incorporation depends predominately on fluid composition rather than pressure or temperature dravite with the highest na content of 1 00 na pfu was synthesized at 0 4 gpa and 700 c from a 3 87 m nacl and 1 08 m kcl fluid all synthesized crystals are zoned and the dominant solid solution in the na and k bearing system is between magnesio foitite mg2al al6si6o18 bo3 3 oh 3oh and dravite namg3al6si6o18 bo3 3 oh 3 oh with the dravitic component increasing with the concentration of na in the fluid in the k bearing na free system the dominant solid solution is between magnesio foitite and k dravite kmg3al6si6o18 bo3 3 oh 3 oh with the k dravitic component increasing with pressure temperature and the concentration of k in the fluid the unit cell volume of tourmaline increases with k incorporation from 1555 1 3 to 1588 1 2 a3 reflecting the incorporation of the relatively large k ion comparison of our results to the compositional data for maruyamaite k dominant tourmaline from the ultrahigh pressure rocks of the kokchetav massif in kazakhstan suggests that the latter was formed in a k rich na poor environment at ultrahigh pressure conditions near the diamond stability field

tourmaline b isotopes as tracers of fluid sources in silicified palaeoarchaean oceanic crust of the mendon formation barberton greenstone belt south africa pervasive silicification is a common phenomenon in early archaean volcano sedimentary sequences reflecting the interaction between si rich fluids and the archaean oceanic crust in the palaeoarchaean barberton greenstone belt south africa the silicified zones locally contain abundant tourmaline in order to constrain the source of fluids responsible for the alteration six tourmaline bearing samples from the 3 3 ga mendon formation were investigated by in situ analyses of mineral chemistry and boron isotopes the samples comprise a silicified finely laminated sedimentary chert and five highly altered and silicified komatiites electron microprobe analysis empa indicates that tourmaline is mostly dravitic with one sample between dravite and mg foitite tourmaline has a weakly developed patchy colour and chemical zonation with variations in al fe and mg composition some samples show strong zoning in cr concentration with cr enrichment in the core and locally the high cr domains are at contacts with other cr rich phases such as magnesiochromite and chromian muscovite fuchsite overall the boron isotope composition 11b ranges from 20 7 to 10 2 two groups of tourmaline are distinguished based on the variation in 11b ratios within single samples 1 those with small 4 range in 11b values spinifex textured komatiites and silicified sediment and 2 those with a large range in 11b values of up to 18 brecciated and foliated samples positive boron isotope values 6 to 10 are found in one spinifex textured komatiite and are interpreted as being derived from seawater interacting with archaean oceanic crust in shallow hydrothermal systems the intermediate boron isotope values 5 to 8 found in all other samples are similar to morb and may represent boron derived from the archaean oceanic crust the rare and exceptionally light boron isotope values 10 to 21 were found in rims of group 2 tourmaline these values cannot be produced by fractionation alone and point to the presence of another fluid source the source of the light boron has yet to be identified but possible candidates are remobilized boron either derived from granitic crust or from marine evaporites that precipitated from seawater enriched in 10b in any case the isotopically light boron appears to have been present during seafloor hydrothermal alteration and deposition of the mendon formation at ca 3 3 ga

the boron isotopic composition of tourmaline as a guide to fluid processes in the southwestern england orefield an ion microprobe study the boron isotopic composition 11b and chemistry of tourmalines from a series of sites in the western southwest england orefield has been determined using ion microprobe and electron microprobe techniques respectively the range of 11b values determined is relatively wide 0 6 to 12 7 and falls at the lighter end of the range for typical continental crust within this range granite tourmalines show a depletion in 11b from coarse grained early magmatic examples to fine grained late magmatic tourmaline we attribute this to fractionation of boron isotopes between aqueous and melt species during the exsolution of an aqueous fluid phase from the magma the aqueous phase formed by degassing of the magma is considered to have crystallised to form the tourmalinites and quartz topaztourmaline rocks common throughout the area decreases in the 11b values occur within certain zones of individual tourmaline crystals from these rocks this is ascribed to loss of 11b in the vapour phase during boiling caused by decompression of the aqueous fluid on fracturing the calculated boron isotope composition of fluids in equilibrium with tourmalines from the cligga head greisen bordered vein system agrees closely with that calculated for the tourmalinite fluid and suggests a constant granite derived source of boron during the early hydrothermal evolution of the stock the lack of isotopic zoning within the tourmalines from the cligga head hydrothermal veins suggests that phase separation did not occur or was very limited during hydrothermal circulation in the vein system

chemical and boron isotopic composition of hydrothermal tourmaline from the panasqueira w sn cu deposit portugal abstract tourmaline is a locally abundant hydrothermal mineral in the wallrocks surrounding the w sn cu mineralized veins in the panasqueira deposit portugal and a minor phase within the veins themselves tourmaline chemical and boron isotope compositions have been determined from three settings 1 pervasive fine grained tourmalinization zones in wallrocks within 10 cm of the veins 2 coarser tourmaline in wallrock hosted fault zones and 3 needle shaped tourmaline from late stage vugs in the quartz veins all tourmalines from panasqueira have ferromagnesian compositions with significant octahedral aluminum contents and variable x site vacancies tourmaline compositions show significant chemical variations at the grain and sample scale but are homogeneous on the deposit scale tourmaline is typically optically and chemically zoned showing significant increases in fe and f and decrease in mg ca and al from core to rim moreover as a general trend al increases and mg decreases with proximity to the vein contact the observed chemical variation seems to have been controlled mainly by the vectors femg 1 x alna 1 r2 1 x al oh na 1 r2 1f 1 r2 oh f al 1o 1 and x al2o na 1 r2 2 oh f 1 the total range in tourmaline 11b values from the panasqueira w sn cu deposit is from 3 7 to 12 7 including tourmaline from the three settings the calculated b isotope composition of the hydrothermal fluid based on the average tourmaline composition of 9 and an estimated alteration temperature in the wallrocks based on ti in quartz thermometry of 500 c is 7 1 this isotopic composition is permissive of a boron source from local metasediments or an s type granite but the high boron concentration in the wallrocks with 50 vol tourmaline along with the typical element association of panasqueira w sn f nb ta rb makes a granitic source more likely late stage tourmaline needles in vugs within the mineralized veins show the same patterns and ranges in both chemical and boron isotope composition suggesting that exsolved magmatic fluids were injected in at least two pulses the variations in chemical and boron isotopic compositions of tourmaline combined with estimates from ti in quartz thermometry suggest that hydrothermal ore formation is associated with fluid cooling and geochemical fluid rock interactions

in situ elemental and boron isotopic variations of tourmaline from the sanfang granite south china insights into magmatic hydrothermal evolution abstract tourmaline often occurs in boron rich granites and its genesis is still in dispute either formed from residual boron rich silicate melt or from magmatic hydrothermal fluids with or without external fluid involvement here we present a systematic investigation of in situ major trace elemental and boron isotopic variations of tourmaline from the sanfang granite in guangxi province of south china which demonstrate both the magmatic and hydrothermal origin for the formation of the tourmalines the tourmaline occurs mainly in quartz tourmaline nodules and tourmaline pegmatitic segregations within the sanfang granite four types of tourmaline are identified 1 isolated and disseminated tourmaline tur d type distributed in granite 2 euhedral and subhedral tourmaline in quartz tourmaline nodules tur n type 3 the earlier stage tourmaline tur pe type in pegmatitic segregations and 4 the later stage tourmaline tur pl type which replaced the tur pe type tourmaline in pegmatitic segregations all the tourmalines belong to the alkali group representing dravite schorl solid solution series with the former three types being schorl and the tur pl type being dravite petrography chemical discrimination diagrams and al occupations in the y site suggest that the tur d tur n and tur pe type tourmalines are of magmatic origin and the tur pl type tourmalines are of hydrothermal fluid origin elemental and boron isotopic composition variations of tourmalines reflect the compositional and environmental evolution from late boron rich magma to exsolved hydrothermal fluids chemical variations from the tur d to the tur n tourmalines are controlled by magma differentiation the increase of mg mg fe and ca ca na ratios from the tur n to the tur pe tourmalines suggests the contamination of surrounding strata e g the sibao group hydrothermal tourmalines have higher mg mg fe and lower na na ca ratios than the magmatic tourmalines there is clear correlation at least in some trace elements e g sr pb with major elements for all tourmalines indicating the potential crystal chemical effects on their incorporation other trace element incorporation in tourmaline is largely controlled by melt and fluid composition hydrothermal tourmalines have high and stable v co and ni contents indicating relatively constant partition coefficient between hydrothermal tourmalines and the fluid hydrothermal tourmalines exhibit lower total ree contents but more pronounced positive eu anomalies than the magmatic tourmalines the 11b values of all tourmalines from the sanfang granite vary from 14 4 to 9 3 which indicate the boron in the sanfang granite was mainly derived from partial melting of the metasedimentary source rocks boron isotopic variations of tourmaline are controlled by fractionation between melt fluid and rayleigh fractionation

campanian maastrichtian intermediate to deep water changes in the high latitudes benthic foraminiferal evidence 1 during the latest cretaceous cooling phase a positive shift in benthic foraminiferal 18o values lasting about 1 5 myr 71 5 70 ma can be observed at a global scale campanian maastrichtian boundary event cmbe this 18o excursion is interpreted as being influenced by a change in intermediate to deep water circulation or by temporal build up of antarctic ice sheets here we test whether benthic foraminiferal assemblages from a southern high latitudinal site near antarctica odp site 690 are influenced by the cmbe if the 18o transition reflects a change in intermediate to deep water circulation from low latitude to high latitude water masses then this change would result in cooler temperatures higher oxygen concentration and possibly lower organic matter flux at the seafloor resulting in a major benthic foraminiferal assemblage change if however the 18o transition was mainly triggered by ice formation no considerable compositional difference in benthic foraminiferal assemblages would be expected our data show a separation of the studied succession into two parts with distinctly different benthic foraminiferal assemblages species dominating the older part 73 0 70 5 ma tolerate less bottom water oxygenation and are typical components of low latitude assemblages in contrast the younger part 70 0 68 0 ma is characterized by species that indicate well oxygenated bottom waters and species common in high latitude assemblages we interpret the observed change in benthic foraminiferal assemblages toward a well oxygenated environment to reflect the onset of a shift from low latitude toward high latitude dominated intermediate to deep water sources this implies that a change in oceanic circulation was at least a major component of the cmbe

hydrothermal gold mineralization at the hira buddini gold mine india constraints on fluid evolution and fluid sources from boron isotopic compositions of tourmaline we determined the boron isotope and chemical compositions of tourmaline from the hira buddini gold deposit within the archean hutti maski greenstone belt in southern india to investigate the evolution of the hydrothermal system and to constrain its fluid sources tourmaline is a minor but widespread constituent in the inner and distal alteration zones of metabasaltic and metadacite host rocks associated with the hydrothermal gold mineralization the hira buddini tourmaline belongs to the dravite schorl series with variations in al fe fe mg ca ti and cr contents that can be related to their host lithology the total range of 11b values determined is extreme from 13 3 to 9 0 but 95 of the values are between 4 and 9 the boron isotope compositions of metabasalt hosted tourmaline show a bimodal distribution with peak 11b values at about 2 and 6 the wide range and bimodal distribution of boron isotope ratios in tourmaline require an origin from at least two isotopically distinct fluid sources which entered the hydrothermal system separately and were subsequently mixed the estimated 11b values of the hydrothermal fluids based on the peak tourmaline compositions and a mineralization temperature of 550 c are around 1 and 10 the isotopically lighter of the two fluids is consistent with boron released by metamorphic devolatilization reactions from the greenstone lithologies whereas the 11b rich fluid is attributed to degassing of i type granitic magmas that intruded the greenstone sequence providing heat and fluids to the hydrothermal system

boron isotope geochemistry of metasedimentary rocks and tourmalines in a subduction zone metamorphic suite abstract in order to understand the behavior of boron b and its isotope fractionation during subduction zone metamorphism b contents and isotopic compositions together with major element compositions were determined for metasedimentary rocks and tourmalines from the sambagawa metamorphic belt central shikoku japan no systematic changes in whole rock b content and isotope composition of the metasediments were observed among the different metamorphic grades indicating the lack of a bulk fluid rock b isotope fractionation as a result of devolatilization both modal abundance and grain size of tourmaline increase with increasing metamorphic grade in contrast b contents in muscovite and chlorite decrease with increasing metamorphic grade these observations combined with mass balance calculations of b suggest the formation of tourmaline during progressive metamorphism from metamorphic fluids containing b mainly derived from muscovite and subordinately from chlorite without allowing significant net removal of b from the metasedimentary rocks tourmalines in the higher grade metasedimentary rocks have zonal structure of b isotope and major element composition with decreasing 11 b and increasing mg mg fe from the inner rim core to the outer rim the change of mg mg fe in the tourmalines with increasing grade is paralleled by similar variation in chlorite these observations suggest that the growing tourmalines record the progressive evolution of the b isotopic composition of the metamorphic fluid in the outermost rims preserving the isotope signature of peak metamorphic p t fluid conditions based on the above observations the 11 b of the tourmaline is thought to have been nearly identical to that of the metamorphic fluid resulting in the apparent b isotopic fractionation factor between metamorphic fluid and whole rock 11 b 10 b fluid 11 b 10 b whole rock which decreases from 1 007 0 003 to 1 001 0 003 from chlorite to biotite zone metamorphism such results together with the formation of tourmaline from and sequestering of b in metamorphic fluids may lead to less b isotopic fractionation as a result of subduction zone devolatilization than noted in suites containing less tourmaline this therefore makes it possible to transport b isotopic signatures which ultimately reflect earth s surface materials to the deep mantle perhaps resulting in mantle b isotope anomalies near convergent margins

tourmaline in a mesoarchean pelagic hydrothermal system implications for the habitat of early life abstract the rna world hypothesis requires the synthesis of rna to allow the emergence of life on earth hydrothermal systems have been proposed as potential candidates for constructing complex biomolecules however in order to successfully form rna it is necessary to stabilize ribose a rna carbohydrate component borate has been found to stabilize ribose therefore boron rich hydrothermal systems are important environments concerning the origin of life on earth the 3 2 ga dixon island formation of the west pilbara superterrane western australia is a volcano sedimentary sequence the formation represents a mesoarchean pelagic hydrothermal system which formed adjacent to an immature island arc fine grained tourmaline in addition to biogenic carbonaceous matter and spherulitic and tubular bacteriomorphs are found in black chert a boron rich environment was responsible for the formation of these deposits to explore the implications of such a boron enriched environment on microbial activity modes of occurrence and chemical compositions of the tourmaline were examined the tourmaline is schorl or dravite of the alkali tourmaline group and the boron isotope compositions range in 11b from 7 3 to 2 6 the tourmaline occurs in microcrystalline quartz matrix of black chert veins that cross cut a volcanic unit and also in a bedded black chert which overlays the volcanic unit the volcanic unit contains highly altered zones with hydrothermal veins the associated lithologic and stratigraphic features suggest that the black chert veins were the conduits for upward moving hydrothermal fluids which reached the sea floor subsequently the volcanic unit was covered by organic matter rich cherty sediments that in part were fed and or altered by the hydrothermal fluids these results suggest that the origin of boron enrichment to form dixon island tourmaline is not the associated sedimentary mineral assemblage which includes diagenetic clay low grade metamorphic mica and organic matter instead the tourmaline was directly precipitated from hydrothermal fluid enriched in boron furthermore the hydrothermal fluids had already concentrated the boron in the mesoarchean pelagic system prior to the apex of organic matter production and microbial activity our findings support a hypothesis that the boron enriched hydrothermal environment aided the survival and evolution of early life

boron sulphur and copper isotope systematics in the orogenic gold deposits of the archaean hattu schist belt eastern finland abstract the hattu schist belt is located in the western part of the archaean karelian domain of the fennoscandian shield the orogenic gold deposits with au bi te geochemical signatures are hosted by ne sw n s and nw se oriented shear zones that deform 2 76 2 73 ga volcanic and sedimentary sequences as well as 2 75 2 72 ga tonalite granodiorite intrusions and diverse felsic porphyry dykes mo w mineralization is also present in some tonalite intrusions both separate from and associated with au mineralization somewhat younger unmineralized leucogranite intrusions 2 70 ga also intrude the belt lower amphibolite facies peak metamorphism at 3 5 kbar pressures and at 500 600 c temperatures affected the belt at around 2 70 ga and post date hydrothermal alteration and ore formation in this study we investigated the potential influence of magmatic hydrothermal processes on the formation of orogenic gold deposits on the basis of multiple stable isotope b s cu studies of tourmaline and sulphide minerals by application of in situ sims and la icp ms analytical techniques crystal chemistry of tourmaline from a mo w mineralization hosted by a tonalite intrusion in the hattu schist belt is characterized by fe3 al3 substitution indicating relatively oxidizing conditions of hydrothermal processes the range of 11b data for this kind of tourmaline is from 17 2 to 12 2 the hydrothermal tourmaline from felsic porphyry dyke swith gold mineralization has similar crystal chemistry e g dravite povondraite compositional trend with fe3 al3 substitution and 11b values between 19 0 and 9 6 the uvite foitite compositional trend and 11b values between 24 1 and 13 6 characterize metasomatic hydrothermal tourmaline from the metasediment hosted gold deposits composition of hydrothermal vein filling and disseminated tourmaline from the gold bearing shear zones in metavolcanic rocks is transitional between the felsic intrusion and metasedimentary rock hosted hydrothermal tourmaline but the range of average boron isotope data is essentially identical with that of the metasediment hosted tourmaline rock forming magmatic tourmaline from leucogranite has 11b values between 14 5 and 10 8 and the major element composition is similar to that of the metasediment hosted tourmaline the range of 34svcdt values measured in pyrite chalcopyrite and pyrrhotite is from 9 1 to 8 5 which falls within the typical range of sulphur isotope data for archaean orogenic gold deposits in the hattu schist belt positive 34svcdt values characterize metasediment hosted gold ores with sulphide parageneses dominated by pyrrhotite and arsenopyrite the 34svcdt values are both positive and negative in ore mineral parageneses within felsic intrusive rocks in which variable amounts of pyrrhotite are associated with pyrite purely negative values were only recorded from the pyrite dominated gold mineralization within metavolcanic units therefore the shift of 34svcdt values to the negative values reflects precipitation of sulphide minerals from relatively oxidizing fluids the range of measured 65cunbs978 values from chalcopyrite is from 1 11 to 1 19 positive values are common for mineralization in felsic intrusive rocks and negative values are more typical for deposits confined to metasedimentary rocks positive and negative 65cunbs978 values occur in the ores hosted by metavolcanic rocks there is no correlation between sulphur and copper isotope data obtained in the same chalcopyrite grains evaluation of sulphur and boron isotope data together and comparisons with other archaean orogenic gold provinces supports the hypothesis that the metasedimentary rocks were the major sources of sulphur and boron in the orogenic gold deposits in the hattu schist belt variations in major element and boron isotope compositions in tourmaline as well as in the 34svcdt values in sulphide minerals are attributed to localized involvement of magmatic fluids in the hydrothermal processes the results of copper isotope studies indicate that local sources of copper in orogenic gold deposits may potentially be recognized if the original distinct signatures of the sources have not been homogenized by widespread interaction of fluids with a large variety of rocks and provided that local chemical variations have been too small to trigger changes in the oxidation state of copper during hydrothermal processes

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

the effect of chrysotile nanotubes on the serpentine fluid li isotopic fractionation we determined the lithium isotope fractionation between synthetic li bearing serpentine phases lizardite chrysotile antigorite and aqueous fluid in the p t range 0 2 4 0 gpa 200 500 c for experiments in the systems lizardite fluid and antigorite fluid 7li preferentially partitioned into the fluid and 7li values followed the t dependent fractionation of li bearing mica fluid wunder et al 2007 by contrast for chrysotile fluid experiments 7li weakly partitioned into chrysotile this contrasting behavior might be due to different li environments in the three serpentine varieties in lizardite and antigorite lithium is sixfold coordinated whereas in chrysotile lithium is incorporated in two ways octahedrally and as li bearing water cluster filling the nanotube cores low temperature ir spectroscopic measurements of chrysotile showed significant amounts of water whose freezing point was suppressed due to the li contents and the confined geometry of the fluid within the tubes the small inverse li isotopic fractionation for chrysotile fluid results from intra crystalline li isotope fractionation of octahedral li 6 with preference to 6li and lithium within the channels li ch of chrysotile favoring 7li the nanotubes of chrysotile possibly serve as important carrier of li and perhaps also of other fluid mobile elements in serpentinized oceanic crust this might explain higher li abundances for low t chrysotile bearing serpentinites relative to high t serpentinites isotopically heavy li bearing fluids of chrysotile nanotubes could be released at relatively shallow depths during subduction prior to complete chrysotile reactions to form antigorite during further subduction fluids produced during breakdown of serpentine phases will be depleted in 7li this behavior might explain some of the li isotopic heterogeneities observed for serpentinized peridotites

tourmaline as a petrogenetic indicator in the pfitsch formation western tauern window eastern alps abstract tourmaline is a common accessory mineral in the metasedimentary pfitsch formation located in the pfitscher joch passo de vizze area in the tauern window of the eastern alps these post variscan metasedimentary units experienced peak metamorphic conditions of 550 c 1 0 gpa during the alpine orogeny tourmaline is most abundant in a 25 m thick unit of feldspathic gneiss 20 200 g g b where it occurs as idiomorphic crystals typically 10 mm in length the abundance and size of the tourmaline crystals increase near coarse grained quartzofeldspathic segregations 1200 g g b reflecting the mobilization and concentration of b by metamorphic fluids near segregations individual tourmaline crystals have up to three growth zones recording pro 350 500 c 0 7 1 0 gpa and retrograde 400 c 0 2 gpa growth as determined by combining textural information and sector zoning thermometry retrograde tourmaline occurs as individual crystals as well as overgrowths on prograde tourmaline crystals especially on the surface of extensional fractures formed by e w extension during regional decompression tourmaline in the pfitsch formation is dravitic with a variable fe content that correlates with the fe content of its respective host unit charge balance calculations suggest that a significant proportion of fe in tourmaline is ferric supporting the interpretation of a subaerial continental sedimentary protolith tourmaline near segregations has the highest inferred ferric iron content which decreases across growth zones potentially reflecting a reduction of the fluid during metamorphism the mg mg fe ratio increases with prograde tourmaline growth and decreases in retrograde overgrowths in contrast the ca ca na ratio increases gradually from 0 05 to 0 20 with prograde growth and continues to increase up to 0 25 in the retrograde overgrowths recording the maximum ca ca na ratio of the fluid during alpine metamorphism the metasediments of the pfitsch formation have very low and variable whole rock 11 b values 14 1 to 33 6 with the highest values 17 7 to 14 1 found in b rich samples 165 1200 g g b containing abundant tourmaline and the lowest values 24 2 to 33 6 in b depleted samples 21 40 g g which lack tourmaline this observation supports preferential loss of 11 b from the rocks during prograde metamorphism zoned tourmaline crystals in the pfitsch formation show successively decreasing b isotope ratios from 7 8 to 11 2 in their cores and 17 3 to 20 3 in their rims as supported by a rayleigh fractionation model the b isotope values of the host rocks and the tourmaline crystals are most easily explained by the internal redistribution of b from a b rich precursor mineral e g mica to the tourmaline during alpine metamorphism

isotopic and elemental partitioning of boron between hydrous fluid and silicate melt the fractionation of b and its isotopes between aqueous fluid and silicate melt has been studied from 550 to 1100 c and 100 500 mpa fluid melt partition coefficients are 1 for rhyolite melt this shows that b is not always strongly extracted from melts into hydrous fluids boron isotopic fractionation is large compared with the carbon and oxygen stable isotopic systems especially at high t and is most simply explained by differences in coordination trigonal vs tetrahedral among coexisting phases combined with earlier measurements on illite water 300 350 c b isotopic fractionation defines a temperature dependent trend from 300 to 1100 c because of the large magnitude and apparent low sensitivity to bulk composition b isotopic fractionation can be readily applied to studies of diagenesis hydrothermal alteration of planetary bodies subduction zone processing and arc magma generation and magma chamber evolution

the geochemical cycle of boron constraints from boron isotope partitioning experiments between mica and fluid abstract the fractionation of boron isotopes between synthetic boromuscovite and fluid was experimentally determined at 3 0 gpa 500 c and 3 0 gpa 700 c for near neutral fluids 11b mica fluid 11b mica 11b fluid is 10 9 1 3 at 500 c and 6 5 0 4 at 700 c this supports earlier assumptions that the main fractionation effect is due to the change from trigonal coordination of boron in neutral fluids to tetrahedrally coordinated boron in micas clays and melts the t dependence of this effect is approximated by the equation 11b mica clay melt neutral fluid 10 69 1000 t k 3 88 r2 0 992 valid from 25 c for fluid clay up to about 1000 c for fluid silicate melt experiments at 0 4 gpa that used strongly basic fluids produced significantly lower fractionations with 11b mica fluid of 7 4 1 0 at 400 c and 4 8 1 0 at 500 c showing the reduced fractionation effect when large amounts of boron in basic fluids are tetrahedrally coordinated field studies have shown that boron concentrations and 11b 10b ratios in volcanic arcs systematically decrease across the arc with increasing distance from the trench thus reflecting the thermal structure of the subducting slab our experiments show that the boron isotopic signature in volcanic arcs probably results from continuous dehydration of micas along a distinct p t range continuous slab dehydration and boron transport via fluid into the mantle wedge is responsible for the boron isotopic signature in volcanic arcs

boron isotope composition of coexisting tourmaline and hambergite in alkaline and granitic pegmatites abstract the boron isotopic composition of tourmaline and hambergite be2bo3 oh f from peraluminous n 12 peralkaline n 1 and peralkaline nepheline syenite n 16 pegmatites has been measured by secondary ion mass spectrometry for which a new hambergite reference material was developed the focus of this study is on nepheline syenite pegmatites from the larvik plutonic complex norway and one peralkaline pegmatite related to the nearby eikeren skrim complex norway where we investigate the source of boron as being from magmatic vs external fluids tourmaline hambergite mineral pairs were also analysed from peraluminous pegmatite localities russia tajikistan and pakistan to test for systematic b isotope fractionation between these two minerals tourmaline and hambergite from peraluminous granitic pegmatites have light boron ratios 11b 12 9to 1 0 associated with s type granites whereas peralkaline granitic and nepheline syenite pegmatites have boron ratios 11b 1 7 to 11 8 which we interpret is a result of heavy boron enrichment from external fluids our data show that hambergite tracks isotope variations of its geochemical setting and could therefore be used as a proxy mineral in place of tourmaline when geochemical stability favours hambergite the results suggest a slight but consistent partitioning of b isotopes between tourmaline and hambergite with 11b 11btourmaline 11bhambergite in the range of approximately 3 to 5 boron is in trigonal coordination with oxygen in both of these mineral phases as verified by nmr single crystal xrd analyses of tourmaline and hambergite reveal consistent longer distances of tourmaline relative to hambergite we attribute the boron isotopic fractionation to the longer bond lengths in tourmaline compared with hambergite

chemical and boron isotopic composition of tourmaline from the conadong leucogranite pegmatite system in south tibet abstract tourmalines occur widely within leucogranites and pegmatites that intrude the leucogranites in the south tibetan plateau morphological and geochemical elemental and boron isotopic studies on these tourmalines are very limited furthermore the tourmaline genetic correlation between the leucogranite and the pegmatite is also unknown in this contribution two types of tourmaline occurrences have been identified in the conadong area south tibet including randomly disseminated tourmaline in leucogranite gt type and radial dendritic or massive tourmaline aggregates in pegmatite dikes that intrude the leucogranite pt type we performed major element and boron isotopic analyses of tourmaline using electron microprobe empa and laser ablation multi collector inductively coupled plasma mass spectrometry respectively the two types of tourmalines are enriched in fe na and al but relatively depleted in ca and mg elements with compositions close to alkali group tourmaline and schorl all the tourmalines are likely the products of equilibrium crystallization and their dominance of na was controlled by the magmatic compositions of their host rocks the gt type tourmalines show a narrow range of 11b values between 9 78 0 81 and 8 53 0 68 with a mean of 8 91 0 18 whereas the pt type tourmalines have significantly lower 11b values than the gt type ranging from 14 02 0 85 to 11 83 0 57 with a mean of 13 31 0 49 these data together with their morphology and petrography indicate that the conadong granitic tourmalines were derived by the melts at the early magmatic stage whereas the pegmatitic tourmalines precipitated from magmatic hydrothermal fluids at the late magmatic stage the variation in boron isotopic compositions 11b 4 4 between the pt and the gt type tourmalines is most likely correlated with their different melt fluid source regions that had distinct sr nd b isotopic compositions

boron isotope and light element sector zoning in tourmaline implications for the formation of b isotopic signatures hourglass sector zoning in metamorphic tourmaline is known to effectively fractionate the major and trace elements between different sectors producing three distinct compositions at the growth surface here we show that the light elements li be h and b as well as the 11 b signature are also affected by sector zoning the sector enrichment in elements is controlled by a dual process of initial preference due to growth surface charge and morphology followed by consecutive charge balance controlled enrichment the light elements especially b and h appear to act as charge balance cations in this mechanism with a preferred b 3 for si 4 and o 2 for oh substitution in the c sector a lighter 11 b signature d c c 1 8f0 6x accompanies this increase in b iv in the c sector in line with the lighter signatures for b iv compared to b iii in minerals however it exceeds this theoretical fractionation by a factor of 10 although we have not identified a definite process that is responsible for this fractionation it may be related to local variations in host medium along the growth surface resulting from preferred uptake of elements these observations show that 11 b signatures in tourmaline are not an independent measure of its host environment but also a function of mineral composition and the 3 dimensional zoning variations herein 2007 elsevier b v all rights reserved

lithium and boron in late orogenic granites isotopic fingerprints for the source of crustal melts abstract geochemically diverse late and post variscan granites of the erzgebirge vogtland the saxon granulite massif and thuringia germany formed by anatectic melting of palaeozoic sedimentary successions and associated mafic to felsic volcanic rocks the compositional diversity of the least evolved of these granites is largely inherited from the protoliths we present li and b isotopic data of these granites and compare them with the isotopic composition of their protoliths to investigate whether i there exist systematic differences in the li and b isotopic composition among different granite types and ii li and b isotopic compositions provide information on the granite sources complementary to information from the isotopic composition of sr nd and pb and the trace element signatures low f biotite and two mica granite types have flat upper continental crust ucc normalized trace element pattern with variable enrichments in li rb cs sn and w and depletions in sr ba and eu these signatures are least pronounced for the niederbobritzsch biotite granite which has the largest contribution of mafic material and most pronounced for the two mica granites the granites show a relatively narrow range of 7li values 3 0 to 0 5 and a broad range of 11b values 13 4 to 20 1 the 11b values are lower in rocks with distinctly higher contents of li rb cs and sn the high 11b of the niederbobritzsch granite may be explained by the melting of former altered oceanic crust in its source relative to ucc intermediate f to high f low p granites show strong depletions in sr ba eu as well as zr and hf strong enrichments in li rb and cs as well as nb sn ta and w and ree pattern with stronger enrichments for hree than for lree these granites show narrow ranges of 7li 2 0 to 1 6 and 11b values 14 7 to 9 1 reflecting the smaller variability of the li and b isotopic composition in their source lithologies the anomalously high 7li value 14 7 of one granite sample burgberg which is similar to 7li values of its wall rocks up to 14 5 may indicate late magmatic fluid rock interaction with external wall rock derived fluids because of the small compositional range of most source lithologies the li and b isotopic variation in the granites is also small indicating that the isotopic composition of li and b does not represent a particularly sensitive source tracer with the exception of source lithologies characterized by extreme 7li or 11b values

tourmaline as a recorder of contrasting boron source and potential tin mineralization in the mopanshan pluton from inner mongolia northeastern china abstract abundant tourmaline occurs in the mopanshan pluton in inner mongolia of ne china and can be classified by its occurrence into four types nodular tourmalines nd type pegmatite pocket tourmalines pp type stockwork tourmalines sw type and vein tourmalines vt type all these tourmalines belong to the alkali group and are dravite schorl petrography and major elements data suggest that the nd and pp type tourmalines crystallized during the transition from late magmatic to early hydrothermal evolution of granite with all the components derived from the magma petrography and trace elements especially sr v cr ni ti data suggest that the sw and vt type tourmalines may form by the mixing of magmatic and country rocks components in the post magmatic hydrothermal environment due to the similar 11b of the sw type with the nd and pp type tourmalines variation

neoproterozoic tourmaline bearing peraluminous granitoids in the western jiangnan orogen south china geochemistry petrogenesis and tectonic implications abstract neoproterozoic granitoids are widespread in the jiangnan orogen in south china that was formed by assemblage between the yangtze and cathaysia blocks the peraluminous s type granitoids from the guibei region in the western jiangnan orogen are composed of quartz alkali feldspar and plagioclase with subordinate biotite and muscovite they show large variable feo mgo 1 9 12 8 and k2o na2o cao 2 84 ratios indicating the rocks experienced fractional crystallization their end values 9 31 to 5 45 and two stage nd model ages 1 83 2 34 ga suggest that the guibei granitoids were derived from a mature source that was mainly composed of recycled supracrustal materials the tourmalines occurring as disseminated and nodular grains show high na k 0 56 0 77 apfu low ca 0 01 0 08 apfu and x site vacancy 0 18 0 51 apfu and belong to the alkali group their high fe 1 64 2 28 apfu low mg 0 14 0 80 apfu and mg mg fe 0 016 0 325 suggest that the minerals are dominated by schorl end member in the schorl dravite solid solution series the tourmalines have constant and strong negative 11b values 13 4 to 9 5 and the nodular tourmalines are isotopically lighter 11b 10 0 to 13 4 than the disseminated tourmalines 11b 9 5 to 12 5 the disseminated tourmalines are suggested to have been crystallized in melts at the early magmatic stage whereas the nodular tourmalines formed in fluid rich immiscible melts at the late magmatic stage the boron isotopic variations within or among the tourmaline generations are mainly controlled by rayleigh fractionation in combined with the regional geology the peraluminous granitoids in this study are considered to be partial melts of the supracrustal rocks in the post orogenic setting

talc mineralisation associated with soft hematite ore gongo soco deposit minas gerais brazil petrography mineral chemistry and boron isotope composition of tourmaline talc mineralisation occurs as hematite talc schist between soft hematite ore and dolomitic itabirite at gongo soco quadrilatero ferrifero of minas gerais brazil the hematite talc schist and soft hematite have a prominent tectonic foliation of tabular hematite tabular hematite without preferential orientation is superimposed on the tectonic foliation the talcose schist is enriched in f and has a constant fe s ratio electron microprobe analyses indicate trace amounts of s in different generations of hematite the whole rock fe s ratio possibly represents sulfate s from hematite hosted fluid inclusions fluid inclusions in foliation overprinting hematite and chlorite geothermometry from talcose rocks suggest respectively temperatures from 200 c to 300 c tourmaline a rarely observed mineral in the hematite talc schist belongs to the alkali group and falls in the dravite compositional field boron isotope determinations of tourmaline crystals using secondary ion mass spectrometry vary from 20 to 12 11b this compositional isotopic range and the tourmaline chemical composition suggest a meta evaporitic origin a non marine evaporitic setting is the most likely source of acidic highly oxidising fluids which resulted in the abundant f bearing talc and the presence of otherwise immobile ti in hematite oxidising brines were channelled along shear zones and converted dolomitic itabirite into the gongo soco soft hematite and the talc mineralisation the latter is envisaged as the hydrothermal wall rock alteration of dolomitic itabirite which gave rise to the soft hematite ore

diverse magma sources for the himalayan leucogranites evidence from b sr nd isotopes abstract the himalayan orogen is featured by widespread s type leucogranites ca 45 to 9 ma formed primarily from the partial melting of metapelites 800 480 ma and minor from the partial melting of amphibolite with subordinate metapelites the ama drime gneiss and mabja leucogranite pluton are both located at the footwall of the ns trending xainza dinggye normal fault in the central part of the himalayan orogen with published end t values of 21 0 to 19 6 and 19 3 to 18 3 and 87sr 86sr t values of 0 90954 0 92574 and 0 84853 0 85474 respectively in this study we presented new shrimp zircon u pb ages and laser ablation multi collector inductively coupled plasma mass spectrometry la mc icp ms tourmaline boron isotope data on the metamorphic rocks and leucogranites of the himalayan orogen the weighted mean 207pb 206pb age of the zircon cores of the ama drime gneiss t0446 2 3 is 1854 4 ma the tourmaline 11b values of the ama drime gneiss t0446 1 6 are 17 6 to 14 3 similar to those of the mabja leucogranite t0436 4 18 9 to 17 4 in contrast the tourmaline 11b values of the quedang metapelite t0389 18 and its partial melting product malashan leucogranite t0659 12a 3 are substantially higher i e 15 3 to 12 5 and 16 2 to 8 0 respectively the tourmaline 11b values of the yadoi leucogranite t0321 4 derived from partial melting of amphibolite range from 8 4 to 5 4 therefore the tourmaline b isotopes and sr nd isotopes results are consistent and may have reflected an e w extension along the southern tibetan rift system indicating a late miocene anatexis in the north himalaya region the melts derived from the partial melting of metapelites and mature crustal materials e g paleoproterozoic ama drime gneiss ascended along the n s trending xainza dinggye normal fault and were subsequently emplaced in the tethyan himalaya sequence

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

boron isotope fractionation in subducted serpentinites a modelling attempt abstract boron b and its isotopes are powerful geochemical tracers of subduction processes enabling to understand the role played by fluids in large scale mass transfer at convergent margins in such settings oceanic and forearc serpentinites are the most important reservoirs for b and heavy b isotopes contributing to the genesis of arc lavas literature data support the release of significant amount of b during the chrysotile lizardite to antigorite atg phase transition and during the partial to complete antigorite dehydration to form secondary peridotites however the information concerning the b isotope fractionation associated to these reactions is limited in this letter i attempt to model the b isotope fractionation affecting subducted serpentinites through the ab initio b isotope fractionation calculations provided for trigonal and tetrahedral coordinated b in both minerals and fluids the obtained results mainly confirm serpentinites as the main vector of positive 11b to depth as shown by natural high pressure serpentinites analysed so far however a lack of information on ph conditions hampers the proper estimate of the fractionation of b in serpentinites during their prograde evolution in subduction zones this may represent a limit in the approach proposed here since poor alkaline close to neutral ph conditions can result in low potentially negative 11batg signatures finally the letter try to address new research trends and major topics worth investigating to better unravel the b cycle in serpentinites and their dehydration products

boron isotopic composition of subduction zone metamorphic rocks abstract many arc lavas contain material derived from subducted oceanic crust and sediments but it remains unresolved whether this distinctive geochemical signature is transferred from the subducting slab by aqueous fluids silicate melts or both boron isotopic measurements have the potential to distinguish between slab transfer mechanisms because 11 b fractionates preferentially into aqueous fluids whereas little fractionation may occur during partial melting previous studies have shown that 11 b values of island arc lavas 6 to 7 overlap the range of 11 b values for altered oceanic crust 5 to 25 and pelagic sediments and turbidites 7 to 11 secondary ion mass spectrometry sims analyses of minerals in subduction zone metamorphic rocks yield 11 b 11 to 3 suggesting that slab dehydration reactions significantly lower the 11 b values of subducted oceanic crust and sediments in order to explain the higher 11 b values reported for arc lavas as compared to subduction zone metamorphic rocks the b bearing component derived from the metamorphosed slab must be enriched in 11 b relative to the slab favoring an aqueous fluid as the slab transfer mechanism