transient features of the erosion of shales in the mackenzie basin canada evidences from boron isotopes abstract in order to refine our knowledge of the mechanisms that drive the weathering reactions and the rate at which elements are exported out of a shale basin we have analyzed the boron concentrations and isotopic compositions of 24 rivers contributing to the mackenzie basin canada boron has been chosen to conduct this study because of the relatively high sensitivity of its isotopic system to water rock interactions after examination of the chemical composition of the mackenzie river samples boron appears to be regulated in the largest part by reactions involving silicate rocks the other contributions of rainwaters and the dissolution of carbonate and evaporite rocks can locally control the b budget but they remain of second importance at the regional to continental scales it also appears that dissolved b in rivers is regulated by input of groundwaters the comparison between the isotopic composition of the b being exported by rivers soluble and particulates and of its bulk source indicates that it is behaving out of steady state in most of the mackenzie tributaries and particularly in rivers draining the plain a model of transport reaction is proposed in this study which demonstrates that b is controlled by rapid ion exchanges at the mineral water interface and by long term dissolution of shales the responses of the model to tested conditions reveal that the b isotopic ratio of river waters is highly sensitive to hydrological conditions and to changes of the weathering rate of shales of its partition coefficient with adsorbing surface and of the water velocity the departure of the b geochemical cycle from a steady state is interpreted as the record of changes in the weathering regime in the mackenzie basin the temporal evolution of the b cycle modeled here implies an increase of the weathering rate of shales in the mackenzie basin and or an increase of the partition coefficient between soluble b and adsorbing surfaces it also appears that these changes are consistent with timescales of the recent deglaciation of the basin this study demonstrates that the present b fluxes are actually responding to past changes of the water rock interactions and that the weathering history is a key parameter to interpret the modern geochemical fluxes this conclusion is valid for any other element that has similar chemical properties with solid surfaces

origin and petrogenetic implications of tourmaline rich rocks in the sierra nevada betic cordillera southeastern spain tourmaline rich rocks up to 60 tourmaline associated with low medium grade metamorphic assemblages occur in the sierra nevada area betic cordillera southeastern spain tourmaline appears in a variety of forms 1 stratiform tourmalinites 2 quartz tourmaline nodules 3 porphyroclasts in felsic orthogneisses and 4 disseminations in psammopelitic metasediments and gneisses tourmaline within these lithologic groups exhibits textural and chemical variations that reflect complex premetamorphic growth under open system conditions and subsequent changes due to alpine regional metamorphism microprobe analyses of the tourmalines reveal a wide compositional variation between schorl and dravite end members with variable contents of x site vacancies av 0 084 0 225 apfu ca av 0 095 0 269 apfu and excess of al up to 6 588 apfu compared with the theoretical value of 6 in ideal schorl and dravite the amount of ca may be significant in porphyroclasts from the gneisses fe fe mg ratios for tourmalines in tourmalinites metasediments and gneisses range from 0 34 to 0 95 0 16 to 0 92 and 0 28 to 0 97 respectively na na ca ratios are also variable mostly ranging from 0 5 to 0 9 many of the tourmalines have complex chemical and colour zoning patterns including significant fluctuations in al fe mg na ca ti and f based on petrographic and chemical data three generations of tourmaline have been established the first generation corresponds to magmatic postmagmatic tourmaline that is represented by tourmaline porphyroclasts within the orthogneisses the second generation of tourmaline formed during tourmalinization of psammopelitic rocks giving rise to tourmalinites the third generation of tourmaline is represented by cellular textures pale reaction rims and overgrowths developed during the alpine regional metamorphic overprint d 2002 elsevier science b v all rights reserved

a sequence of partial melting reactions at mt stafford central australia metasedimentary gneisses show a rapid change in grade in a 10 km wide low p high t regional aureole at mt stafford in the arunta block central australia migmatite occurs in all but the lowermost of five metamorphic zones which grade from greenschist zone 1 through amphibolite zones 2 3 to granulite facies zones 4 5 the sequence of partial melting reactions inferred for metapelitic rocks is dependant upon protolith temperature and fluid conditions the metapelite solidus in zone 2 reflects vapour present melting at p 3 kbar and t 640 c melting having initially been controlled by the congruent breakdown of the assemblage crd kfs bt qtz at slightly higher temperature andalusite in leucosome formed via the reaction kfs qtz bt h2oand melt and melt having been stabilized by the presence of boron sillimanite coaxially replaces andalusite in the high grade portion of zone 2 in zone 3 large aluminosilicate aggregates in leucosome are armoured by spl crd grt symplectites garnet partially pseudomorphs biotite cordierite or spinel in high grade portions of zone 3 zone 4 grt crd opx bearing metapsammite assemblages and garnet bearing leucosome reflect t 800 c and p 2 2 0 9 kbar in the model kfmash system the principal vapour absent melting step reflected significant modal changes related to the breakdown of the as bt tie line and the establishment of the spl crd tie line the bulk rock geochemistry of migmatite samples straddle the spl crd tie line the aluminous bulk rock composition of the common bedded migmatite restricted its potential to witness garnet forming and orthopyroxene forming reactions minor textural and modal changes in and above zone 3 reflecting biotite destablization in biotite poor assemblages

source and partitioning of b and sn in the cornubian batholith of southwest england abstract emplacement of the variscan s type cornubian batholith initiated the formation of the historical world class sn and cu deposits and extensive tourmalinisation of southwest england the hypothesis is tested that the sn and tourmaline mineralisation were wholly formed by magmatically derived hydrothermal fluids with no requirement for a contribution from the stripping of country rocks by circulating hydrothermal fluids from simple geochemical modelling sufficient sn concentrations to match those in the main 90 of granite outcrop biotite granites average of 23 mg kg and to produce the large sn deposits can be derived by partial melting of pre granite southwest england crust at geologically realistic levels of partial melting 30 fractionation 10 to 50 and melt aqueous fluid partitioning assumed to be 6 wt of the mass of the granite batholith in contrast insufficient b 700 mg kg or b concentrations found in many of the granites we conclude that tourmaline in the biotite granites was formed from magmatically derived hydrothermal fluids which emanated as a result of first and possibly second boiling an additional source of b for the hydrothermal fluids may have been the devolatilisation of stoped blocks of country rock mudstones these findings provide fundamental constraints on the evolution of the cornubian batholith which is used as a model for a large number of sn provinces worldwide

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

the metamorphic aureole of the nisa alburquerque batholith sw iberia implications for deep structure and emplacement mode the nisa alburquerque granitic batholith southern variscan belt iberian peninsula has been studied by petrological structural and geophysical approaches obtaining contrasting models for its deep structure and emplacement sequence in order to test these models and gain knowledge on the thermal increase induced by the intrusion we have studied its contact aureole which was developed in similar country rock lithologies mica schists alternating with metasandstones and feldespatic schists all along the northern external contact of the batholith our results indicate no change in metamorphic grade and some variations in aureole width which narrows toward the western sectors of the batholith cordierite is the only contact metamorphic mineral developed together with a high temperature biotite probably related to the granite thermal input by considering these new data together with zircon saturation temperatures within the granite and previous petrological and geophysical studies we propose a model in which the feeder zones of the granitic magmas were an eastern main one and a western secondary one we have also made comparisons of the metamorphic grade in the country rocks and the xenoliths within the granite most of the xenoliths have the same metamorphic facies as the country rocks crd zone though some of them contain slightly different assemblages and crd which could be explained in different ways 1 differences in the primary schist compositions 2 increased time span of xenoliths in contact with the melt and 3 xenolith incorporation at slightly higher depths during final granite ascent

contrasting behaviour of boron during crustal anatexis the study of volatile elements in crustal anatectic terranes may provide information about the role of fluid flow and fluid pathways during high temperature metamorphism we have studied the distribution of li and b in two migmatitic areas the pena negra anatectic complex central spain and the migmatites and leucogranites associated with the ronda peridotites southern spain they represent two contrasting cases in the behaviour of volatiles particularly b during anatexis the pena negra migmatites are dominated by diatexites where it is possible to distinguish granitic leucosomes melanosomes metric to decimetric leucogranitic segregates and decimetric to metric sillimanite rich restitic enclaves all lithologies are characterized by low b concentrations mean values 30 ppm and b is enriched in melanosomesrrestites with respect to leucosomesrleucogranites this may be due to the fact that a notable proportion of b can reside in restitic sillimanite b concentrations in leucosomes and leucogranites can be explained by closed system anatexis at ronda metatexitic and diatexitic migmatites underlie the ronda peridotites and diatexite and leucogranite dikes intrude the peridotites diatexites underlying the peridotites are characterized by cordierite q biotite garnet as ferromagne sian phases with rare or absent tourmaline low b contents 10 ppm and cordierite garnet leucosomes leucogranite dikes have high b concentrations mean valuef 400 ppm with tourmaline being a common and sometimes the most abundant ferromagnesian phase a genetic relationship between diatexites and leucogranites is strongly suggested by the presence of dikes of diatexites intruding the bottom of the peridotites we conclude that b in the leucogranites may stem from the dissolution of tourmaline originally present in the metasediments or infiltration of b rich aqueous fluids into the anatectic zone according to recent experimental work textures in some tourmaline rich ronda leucogranites suggest initial b o 23 contents in the melt higher than the present measured concentrations preliminary experimental results presented in this paper propose that this difference is not due to water activities in the melt rapid crystallization of the melts following undercooling may explain the existence of abundant euhedral tourmaline in leucogranites with low aluminium saturation index asis molar al o r caoq na oq k o and relatively low b contents q 2001 elsevier science b v all rights 23 2 2 reserved

boron in granitic magmas stability of tourmaline in equilibrium with biotite and cordierite experiments at 750 c 200 mpa h2o a h2o 1 and fo2 ni nio established that the equilibrium among tourmaline biotite cordierite and melt spinel aluminosilicate or corundum occurs with 2 wt b2o3 in strongly peraluminous melt with an aluminosity measured by the parameter asi of 1 2 the experiments demonstrate the relationship of tourmaline stability to the activity product of the tourmaline components boron and aluminum which are inversely related to one another tourmaline is unstable in metaluminous to mildly peraluminous melts asi 2 wt b2o3 in their bulk magmas

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

late magmatic controls on the origin of schorlitic and foititic tourmalines from late variscan peraluminous granites of the arbus pluton sw sardinia italy crystal chemical study and petrological constraints abstract tourmalines from the late variscan arbus pluton sw sardinia and its metamorphic aureole were structurally and chemically characterized by single crystal x ray diffraction electron and nuclear microprobe analysis mossbauer infrared and optical absorption spectroscopy to elucidate their origin and relationships with the magmatic evolution during the pluton cooling stages the arbus pluton represents a peculiar shallow magmatic system characterized by sekaninaite fe cordierite bearing peraluminous granitoids linked via afc processes to gabbroic mantle derived magmas the fe2 al dominant tourmalines occur in a pegmatitic layers and pods as prismatic crystals b greisenized rocks and spotted granophyric dikes as clots or nests of fine grained crystals in small miaroles locally forming orbicules c pegmatitic veins and pods close to the contacts within the metamorphic aureole structural formulae indicate that tourmaline in pegmatitic layers is schorl whereas in greisenized rocks it ranges from schorl to fluor schorl tourmalines in thermometamorphosed contact aureole are schorl foitite and mg rich oxy schorl the main substitution is na fe2 al which relates schorl to foitite the homovalent substitution oh f at the o1 crystallographic site relates schorl to fluor schorl while the heterovalent substitution fe2 oh f al o relates schorl fluor schorl to oxy schorl tourmaline crystallization in the arbus pluton was promoted by volatile b f and h2o enrichment low oxygen fugacity and fe2 activity the mineralogical evolutive trend is driven by decreasing temperature as follows sekaninaite quartz schorl quartz fluor schorl quartz foitite quartz the schorl foitite evolution represents a distinct trend towards al increase and unit cell volume decrease these trends are typical of granitic magmas and consistent with li poor granitic melts as supported by the absence of elbaite and other li minerals in the arbus pluton tourmaline bearing rocks reflect the petrogenetic significance of contribution from a metapelitic crustal component during the evolution of magmas in the middle upper crust

sooty sweat stains or tourmaline spots the argonauts on the island of elba tuscany and the spread of greek trading in the mediterranean sea in various ancient authors e g the argonautika of apollonios rhodios curious news about the island elba can be found concerning the existence somewhere on the shore near portoferraio of pebbles that are dirty from the argonauts sweat the argonauts are said to have stopped on the island during their journey back from the looting of the golden fleece these pebbles are found to be typical of the gravelly beaches below the capo bianco cliffs such walls are made up of a bony white aplitic rock dotted with blue black tourmaline spots capo bianco aplite is the uncommon result of the solidification of a boron rich magma in a subvolcanic setting here the separation of a boron rich fluid phase gave way to the crystallization of peculiar spherical dark tourmaline spots in a very fine grained white groundmass this rock was noted by argonauts i e the ancient travellers they represent and used as a lighthouse to the harbour of argoos limen now portoferraio also in the myth the unique mottled pebbles were recorded as stained by the argonauts sweat the occurrence within the same complex myth of data concerning navigation the white cliffs and geology description of the spotted aplite identify the argonauts as a blending of mineral prospectors explorers and early eighteenth century like naturalists legitimatizing the commercial political presence of greeks in the region fanciful tales or myths have arisen during the course of each culture s history most often from either religious or social motivations in some cases a pre scientific view of the natural world generated observations that became a relevant element of the structure of the myth only with progress in the scientific analysis of nature perhaps first truly introduced by herodotus have we gradually developed a distinction between natural and mythical explanations one aspect of myths is that they often recall specific places in which special or peculiar natural features are present and for this reason the island of elba could not be absent in the ancient mythology in fact this island has a privileged position for navigation in the central mediterranean sea being located between corsica and the tuscan shoreline and it was also famous in the classical world for its iron deposits noted by ps aristoteles de mirabilibus auscultationibus 93 vergilius aeneis x 143 144 and strabo geography v see also corretti 2004a and references therein in particular elba occurs in the myth of jason and the argonauts that was codified by apollonios rhodios who describes the exceptional character of some unique rocks perhaps the capo bianco aplite as having both a special petrographical and mineralogical nature as well as an extraordinarily bright white colour of outcrop in this paper we describe the geology and petrology of the tourmaline rich capo bianco aplite cropping out as a dismembered laccolith along the northern coast of central elba and we highlight the strict similarity between the petrographic features of the capo bianco rocks and the descriptions contained in the argonauts myth reported by apollonios rhodios finally we discuss how accurate observations on this oddity of nature were metamorphosed in the structure of a mythic narration the tuscan magmatic province and the island of elba granitic rocks

transmission electron microscopy of muscovite alteration of tourmaline partially sericitized tourmaline from a pegmatite was investigated using high resolution transmission electron microscopy hrtem fine grained muscovite crystals form extensive narrow veinlets preferentially developed along the 110 and 100 cleavages of tourmaline indicating that a cleavage controlled alteration mechanism was dominant hrtem images show that tourmaline muscovite interfaces parallel well defined 110 and 100 of tourmaline in general 001 of muscovite parallels the c axis of tourmaline but otherwise tourmaline and replacing muscovite lack crystallographically oriented relation

boron isotope variations in tourmaline from hydrothermal ore deposits a review of controlling factors and insights for mineralizing systems abstract tourmaline group minerals are typically the predominant host of boron in hydrothermal mineral deposits boron is a fluid mobile element whose isotopic composition reflects many factors that are relevant to understanding mineralizing processes including fluid source s fluid rock interaction and formational temperature a new compilation of 2622 published 11b values for tourmaline from diverse types of hydrothermal ore deposits is presented here with the focus 2215 analyses on seven main types porphyry cu mo au deposits granite related sn w deposits iocg deposits orogenic au deposits stratabound vms and sedex deposits and sediment hosted u deposits the total range of 11b values for the seven types is 26 8 to 35 0 four granite sn w orogenic au stratabound vms and sedex have median 11b values close to the continental crustal average of about 10 the median values for iocg and porphyry cu mo au deposits are higher 3 9 and 2 1 respectively whereas sediment hosted u deposits have distinctly high 11b median 25 3 importantly a considerable range of 11b values exists for tourmaline within each deposit type the smallest 17 8 for granite sn w deposits and the largest 48 0 for iocg deposits the boron isotope variations in tourmaline from different deposits are suggested reflect three levels of controlling factors and how these factors operated is illustrated with selected number of case studies the primary factor is the composition of the boron source secondary effects relate to fluid tourmaline fractionation equilibrium or rayleigh there are commonly also tertiary factors that depend on evolution of the specific deposit these include fluid mixing changing water rock ratio and or depositional temperature influences of other boron bearing minerals and where relevant post ore metamorphism separating the effects of these factors is rarely possible from boron isotopes alone however the growth of multi isotope studies of tourmaline and coexisting phases such as mica as well as developments in modelling experimentation of boron isotopes and element partitioning suggest that this limitation will be overcome

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

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

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

chemical and stable isotopic characteristics of syn tectonic tourmaline from the western fold belt mount isa inlier queensland australia abstract understanding hydrothermal fluid flow events related to orogenic events is important because they provide large scale redistribution of metals which may become concentrated in ore deposits in this study we determine the origin of tourmaline bearing quartz veins and pegmatites in the western fold belt of the proterozoic mount isa inlier a region which host numerous syn orogenic cu deposits this paper uses tourmaline mineral chemistry and isotopic analyses in situ b and bulk o and h isotopes to fingerprint the fluid reservoirs that contributed to the fluid budget during the isan orogeny all the tourmaline samples have schorl dravite solid solution compositions quartz tourmaline 18 o 11 0 12 6 and 7 7 9 4 v smow respectively pairs yield equilibrium formation temperatures of 305 to 575 c with the higher temperatures related to pegmatitic tourmaline tourmaline d values have a relatively narrow range from 68 to 56 v smow in most cases calculated 18 o fluid and d fluid values are compatible with primary magmatic water with a small component of metamorphic 18 o enriched formation waters however there are large variations in tourmaline 11 b values which range from 10 7 to 17 0 with the majority of values between 10 and 15 variations in 11 b tur in the pegmatites suggest that boron degassing generated relative 11 b depletion during crystallization similar 11 b tur values in quartz tourmaline veins spatially associated with the pegmatites in cordierite and sillimanite bearing metamorphic rocks west of the mount isa fault demonstrate a similar origin for b in this tourmaline in contrast quartz tourmaline veins of similar timing hosted by greenschist grade metamorphic rocks east of the mount isa fault have much higher 11 b tur values 6 2 to 10 7 which reflect the involvement of a distinct b isotopic reservoir mostly likely a near surface derived evaporitic brine thus the b isotopic data reveal important differences in fluid origin that are not reflected in the 18 o values therefore at least two isotopically distinct fluids one sourced from fractionating anatectic pegmatites and the other from external basinal brines circulated contemporaneously in separate areas during the isan orogeny there is no evidence based on the tourmaline isotopic data to suggest that these fluids mixed which demonstrates that the hydrothermal plumbing system in the western fold belt during the isan orogeny was disconnected probably due to differences in thermal structure metamorphic grade across the western fold belt during orogenesis

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

experimental silicate phosphate equilibria in peraluminous granitic magmas with a case study of the alburquerque batholith at tres arroyos badajoz spain with the actual mineralogy and whole rock p in the granite experimental results presented here establish the p2o5 content of aplite pegmatite facies at tres arroyos peraluminous silicic melt for three potential buffering reactions at 200 mpa h2o and t from 525 to 850 c 1 biotite sarcopside 2 spessartine sarcopside 3 petalite amblygonite montebrasite quartz the first two equilibria are moderately insensitive to t and buffer the p content of melt between 1 30 1 57 wt

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

petrologic and geochemical links between the post collisional proterozoic harney peak leucogranite south dakota usa and its source rocks abstract the proterozoic terrane of the black hills south dakota includes the composite harney peak leucogranite and associated pegmatites that were emplaced into metamorphosed pelites and graywackes available dates indicate that granite generation post dated regional metamorphism and deformation that have been attributed to collision of the wyoming and superior cratons at 1760 ma previous radiogenic and stable isotope work indicates that the exposed metasedimentary rocks are equivalent to sources of the leucogranites in this study whole rock and mineral compositions of the metasedimentary rocks were used to calculate the likely average residue mineralogies and melt fractions that would be generated by muscovite dehydration melting of the rocks these were then used to model observed trace element compositions of the granites using published mineral melt distribution coefficients model trace element melt compositions using pelitic and graywacke protoliths yield similar results the models reproduce well the observed depletion of transition metals and ba in the granites relative to metasedimentary protoliths the depletion is due mainly to high proportion of biotite with variable amounts of k feldspar in the model residue sr is also depleted in the granites compared to source rocks but to a lesser relative extent than ba this is because of the low biotite melt distribution coefficient for sr and because high proportion of plagioclase in the residue is compensated by high sr concentrations in protoliths rubidium cs and ta behaved as slightly compatible to incompatible elements and therefore were not strongly fractionated during melting of the considered elements only b appears to have been highly incompatible relative to residue during melting the protoliths had sufficient b to allow tourmaline crystallization in those parts of the harney peak granite in which ti concentration was sufficiently low not to enhance crystallization of biotite the reproducibility of observed trace element concentrations in the harney peak granite by the models supports the often made proposition that metapelites and metagraywackes are common sources for leucogranites this argues against mass input from the mantle into metagraywacke and metapelitic crustal sources or melting of amphibolites to generate the post collisional harney peak and other similar peraluminous granite suites

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

influence of orographically enhanced sw monsoon flux on coastal processes along the se arabian sea 1 the arabian sea has an excess evaporation over precipitation regime the southeast arabian sea is however anomalous because it has 2800 4800 mm rainfall during the southwest monsoon swm despite a high rainfall the fluvial influence on supply of total suspended matter tsm and marine productivity is deemed insignificant and remains unevaluated we evaluated the poorly resolved influence of fluvial influx on shelf processes we documented low salinity stratification high productivity and turbidity over the entire inner shelf chlorophyll a 2 4 mg m 3 po4 3 2 5 m no3 6 8 2 1 m tsm 88 182 mg l 1 salinity near shore region 26 offshore region 33 8 34 6 p s u the deeper regions 40 m however had greatly reduced tsm and nutrient levels no3 po4 3 1 0 m tsm 24 mg l 1 and patches of high chlorophyll a upon cessation of the swm nutrient levels and tsm reduced considerable we identify two processes that contribute to the marine productivity and turbidity during the swm over the deeper regions there is a poor influence of fluvial supply and upwelling regulates productivity over the shallow inner shelf the sequestering of fluvial influx due to the prevalence of strong winds upwelling and equatorward flow is dominant the later processes induced high marine productivity and eutrophication in the near shore region and may have implications for siltation of channels reduced turbidity nutrient and chlorophyll a levels and higher salinity of the coastal waters during rest of the year imply a substantial role of fluvial fluxes on coastal processes

evolved granitic systems as a source of rare element deposits the ponte segade case galicia nw spain abstract in the ponte segade area galicia nw spain strongly differentiated granites often associated with rare element mineralization sn ta nb li be cs that could be of economic interest have recently been discovered these granites appear in the northern sector of the ollo de sapo antiform central iberian zone variscan orogen three different muscovite rich synkinematic and peraluminous types of leucogranite leucogranites s s albite rich leucogranites i and albite rich leucogranites ii and two pegmatite types associated with the albite rich leucogranites zoned and banded have been identified in the studied area the geochemistry of whole rock leucogranites indicates an enrichment in incompatible elements lithium rubidium beryllium cesium and hafnium al2o3 and na2o and an impoverishment in barium strontium zirconium cerium yttrium and sio2 geochemical studies of zircon muscovite k feldspar and tourmaline in the different types of granites and pegmatites indicate the grade of evolution of the granitic system with differentiation of the system the zircon is enriched in hafnium and uranium and is impoverished in zirconium in muscovite and k feldspar there is an increase in cesium and rubidium the opposite behavior is observed with regards to the mg fe and ti contents in the case of tourmaline the increase in li is the best indicator of the grade of evolution by contrast fe and mg decrease the sequence of evolution of the granitic system obtained from the geochemical studies indicates that the leucogranites s s are the least differentiated evolving gradually in accordance with field relationships to albite rich leucogranites i the albite rich leucogranites ii are the most evolved but no direct relationship between them and leucogranites s s has been found the banded pegmatites associated with the albite rich leucogranites ii are more differentiated than the zoned pegmatites associated with the albite rich leucogranites i but are the poorest in sn ta and nb

b and li in proterozoic metapelites from the black hills u s a implications for the origin of leucogranitic magmas the abundance and distribution of b and li in metasedimentary rocks and in the harney peak granite hpg in the black hills south dakota u s a elucidate the behavior of these two elements during 1 regional metamorphism that began at 1760 ma 2 subsequent contact metamorphism associated with emplacement of the hpg and associated pegmatites at 1715 ma and 3 anatexis leading to production of the granite there is no clear evidence for changes in b and li concentrations with progressive regional metamorphism of the metapelites from chlorite biotite grade up to staurolite grade rocks outside the pegmatite aureole that surround the hpg have average b contents of 80 ppm there is no correlation of b with other elements in the pelitic schists which indicates that none of the major phases is the dominant host for b boron content is mainly controlled by small amounts of randomly distributed tourmaline that was identified in alpha track maps of thin sections in the aureole of the granite b concentrations are depleted in many samples the depletion is attributed to consumption of tourmaline during interaction of the rocks with alkalic fluids the average li contents in metapelites far away from the hpg are also 80 ppm near the hpg li concentrations reach roughly 190 ppm indicating significant metasomatism by fluids that emanated from the granite and pegmatites the concentrations of b and li in the low grade metapelites are sufficient to explain their abundances in the hpg if the granite formed by partial melting of the metapelites and if there was total breakdown of tourmaline stabilization of tourmaline in leucogranites is not necessarily related to sources enriched in b but may be related to its competition for fe and mg with biotite

the geochemistry of aliphatic and polar organic tracers in sediments from lake bera malaysia abstract the molecular distributions of homologous aliphatic lipid compounds n alkanes n alkanoic acids n alkanols n alkanals and n alkan 2 ones were investigated in sediments of lake bera malaysia as well as in plant waxes from the vicinity using gas chromatography mass spectrometry in addition triterpenoids of the oleanane ursane lupane and friedelane series and their diagenetic products were also identified using the aquatic proxy p aq it was found that the n alkanes present in surface sediments s1 s5 and s6 correspond to an input from emergent macrophytes whereas in sediments collected from open water s2 s3 and s4 they correspond to input from submerged floating macrophytes the presence of n alkan 2 ols a commonly found homologous series in the sediments as well as in the plant wax is novel here in addition the presence of 24 methylcycloart 22 enol and 24 ethylcycloart 22 enol in sediments as well as the plant wax of pandanus helicopus a dominant reed around the lake also supports the input of plant biomarkers to the sediments the occurrence of 5 membered ring triterpenoid derivatives as major diagenetic products of the triterpenoids identified e g friedelan 2 3 dione shows that the degradation of the organic matter in the sediments occurs mainly under oxic conditions also the presence of ring a degraded triterpenoids dihydroputranjivic acid 3 nor 2 4 seco friedelane 4 and 4 3 norfriedelanes a norfriedel 10 one and a norfriedel 8 en 10 one and the aromatized triterpenoid hydrocarbons mono and triaromatic derivatives as minor diagenetic products indicates photochemical and microorganism mediated alteration reactions of natural products in the sediments additional novel polyfunctional friedelane derivatives namely friedelane 2 3 dione friedelane 1 3 diol 2 one and friedel 1 10 ene 1 3 diol 2 one were identified for the first time in this study these novel polyfunctional triterpenoids were inferred to derive from the oxidation of the triterpenoids from higher plants in this oxic tropical environment for future reference purposes the mass spectra of the identified polar triterpenoids are also presented here this study provides important data on the biogeochemistry of organic matter in a tropical lake of se asia

tourmaline at diagenetic to low grade metamorphic conditions its petrologic applicability article i nfo tourmaline developed under low temperature conditions b 300 c typically has distinctive morphological and chemical characteristics that reveal significant information about the environments in which they crys tallize under diagenetic conditions tourmaline can develop as overgrowths on detrital tourmaline cores or as new authigenic crystals tourmaline as monopolar crystal overgrowths is found in sandstones shales conglomerates dolostones and limestones nucleating exclusively at the positive end of the c axis cpole on the detrital grain a feature related to the mineral s polar nature these overgrowths tend to have compo sitions dominated by x site vacant tourmaline species e g foitite and can be linked to growth in aqueous environments low in na with other chemical characteristics related to the host rocks as temperature in creases tourmaline overgrowths develop at both the cpole andc pole but continue to exhibit a signif icant degree of morphological and chemical asymmetries these differences at either pole diminish as a function of increasing temperature such that it can be used as an intramineral geothermometer authigenic tourmalines without detrital tourmaline nuclei are found in many sedimentary or weakly meta morphosed metasedimentary rocks as well as fluid dominated geothermal systems here tourmalines are commonly foititic but have mg fe contents influenced by the host rock composition low temperature tour malines developed in hypersaline environments e g salt domes have distinct chemical characteristics high na fe 3 and w o and follow a trend between oxy dravite and povondraite o p trend this composi tional trend can be used as a guide to indicate tourmaline development within low temperature hypersaline environments and appears to be diagnostic of an oxidizing environment with high na in the fluid and high sa linity with the resulting reduction of the activity of h2o the o p trend is retained in some meta evaporite de posits that are relatively high grade and is found in tourmaline from some types of economically important metal deposits although tourmalines in low temperature environments are largely overlooked they have po tential to be a useful indicator of the chemical and thermal environments in a regime largely absent of such indicators

the geology and mineralogy of the loulo mining district mali west africa evidence for two distinct styles of orogenic gold mineralization loulo is a world class orogenic gold mining district in the birimian terrane of western mali orebodies are located along second or higher order shears associated with the senegal mali shear zone with gold mineralization largely linked to a transtensional event the mine camp is divided into two distinct styles of gold deposit on the basis of differing geologic characteristics one group is typified by the gara deposit whereas the other by the yalea deposit both deposit styles are hosted by similar rock types calcareous graywackes and calciticdolomitic marbles gara style orebodies occur as sulfide disseminations or ankerite rich shear vein stockworks hosted in folded tourmalinized sandstones and breccias mainly within 2 km of the senegal mali shear zone these deposits are characterized by intense multi stage albitization and tourmalinization pre syn and postmineralization gold lodes are fe rich dominated by nickeloan pyrite contain cu ni co minor and trace sulfides e g chalcopyrite gersdorffite pentlandite cobaltite millerite and show consistently high levels of p ree w bearing phases apatite monazite xenotime and scheelite base metal concentrations show a marked increase in marble host rocks with the formation of nickeloan pyrite cobaltite clausthalite ores in contrast yalea style deposits are associated with quartz ankerite vein lodes and disseminated sulfide stringer zones mineralization occurs along highly altered tourmaline absent brittle ductile shears up to 8 km away from the senegal mali shear zone wall rock alteration is characterized by addition of k 2 o cao co 2 h 2 o and sio 2 with mineral assemblages consisting of chlorite sericite carbonate quartz albite ore paragenesis is enriched in as mainly as multistage growth of arsenopyrite and arsenian pyrite base metal sulfides scheelite and ree phosphates are extremely rare the diversity in the ore paragenesis is controlled by a dynamic hydrothermal system that sourced fluids and metals from different reservoirs within the region the as rich yalea style deposits have characteristics typical of birimian gold mineralization in ghana and auriferous fluids are likely derived from the dewatering of sedimentary rocks during regional metamorphism on the other hand the polymetallic fe b rich gara style orebodies show atypical features for birimian gold mineralization instead field relations and the mineralogy and geochemistry of the gara style lodes indicate a strong hydrothermal influence from surrounding intrusive stocks with possible links between gold mineralization and iron oxide skarn development in the region the data collected at loulo highlight the diverse nature of orogenic gold deposits especially in west africa this style of ore deposit can form from a variety of fluid sources both metamorphic and magmatic

boron metasomatism and behaviour of rare earth elements during formation of tourmaline rocks in the eastern arunta inlier central australia tourmaline rocks of previously unclear genesis and spatially associated with w cu bearing calc silicate rocks occur in palaeoproterozoic supracrustal and felsic intrusive rocks in the bonya hills in the eastern arunta inlier central australia tourmalinisation of metapelitic host rocks postdates the peak of regional low pressure metamorphism m1 d1 500 c 0 2 gpa and occurred synkinematically between the two main deformation events d1 and d2 coeval with emplacement of late strangways 1 73 ga tourmaline bearing leucogranites and pegmatites tourmaline is classified as schorl to dravite in tourmaline quartz rocks and surrounding tourmaline rich alteration zones and as fe rich schorl to foitite in the leucogranites boron metasomatism resulted in systematic depletion of k li rb cs mn and enrichment of b and in some samples of na and ca in the tourmaline rocks compared to unaltered metasedimentary host rocks whole rock ree concentrations and patterns of unaltered schist tourmalinised schist and tourmaline quartz veins the latter were the zones of influx of the boron rich hydrothermal fluid are comparable to those of post archaean shales thus the whole rock ree patterns of these rocks are mostly controlled by the metapelitic precursor in contrast ree concentrations of leucogranitic rocks are low 10 times chondritic and their flat ree patterns with pronounced negative eu anomalies are typical for fractionated granitic melts coexisting with a fluid phase ree patterns for tourmalines separated from metapelite hosted tourmaline quartz veins and tourmaline bearing granites are very different from one another but each tourmaline pattern mirrors the ree distribution of its immediate host rock tourmalines occurring in tourmaline quartz veins within tourmalinised metasediments have lree enriched lan ybn 6 3 55 shale like patterns with higher ree 54 108 ppm in contrast those formed in evolved leucogranites exhibit flat ree patterns lan ybn 1 0 5 6 with pronounced negative eu anomalies and are lower in ree 5 6 30 ppm we therefore conclude that ree concentrations and patterns of tourmaline from the different tourmaline rocks studied are controlled by the host rock and not by the hydrothermal fluid causing boron metasomatism from the similarity of the ree pattern of separated tourmaline with the host rock we further conclude that incorporation of rees in tourmaline is not intrinsically controlled i e by crystal chemical factors tourmaline does not preferentially fractionate specific rees or groups of rees during crystallisation from evolved boron and fluid rich granitic melts or during alteration of clastic metasediments by boron rich magmatic hydrothermal fluids

salts in southern yakutian kimberlites and the problem of primary alkali kimberlite melts abstract alkali carbonates sodalite gypsum anhydrite halite and sylvite are present in the groundmass and matrix of many kimberlites in the southern part of the yakutian kimberlite province the kimberlites were emplaced through 2 km thick evaporite bearing carbonate sediments saturated with brines in the global context southern yakutian kimberlites are unprecedented in the amount of the crustal carbonate and evaporite material included in the pipes as evidenced by the bulk major element chemistry and isotopic compositions of sr c o cl and s we present geological and hydrogeological data on country rocks and kimberlites of the udachnaya mir and international naya pipes the secondary crustal origin of na k cl and s rich minerals is supported by the following 1 a regional correlation between the geology and hydrogeology of the local country rocks and the kimberlite mineralogy in particular the difference between southern and northern yakutian kimberlites 2 a restriction of halite or gypsum mineralization in the mir and international naya pipes to depths where pipes intersect country rock strata with similar mineralogy 3 the localization of the highest abundances of na k cl s bearing minerals in the udachnaya east kimberlite at a depth interval that correlates across three magmatic phases of kimberlites and coincides with the roof of the halite bearing country rock and an aquifer carrying anomalously na rich brines 4 the presence of evaporite xenoliths and veins of halite gypsum and carbonate cutting through the kimberlite and xenoliths 5 a secondary origin of halite and alkali carbonates as observed in their textural relationships to serpentine and other groundmass minerals 6 the geochemical and isotopic evidence for crustal contamination addition of crustal salts to kimberlite melt began prior to the volcanic fragmentation as a result of preferential melting and assimilation of evaporite xenoliths and may have continued in situ after the pipe emplacement via reactions with external saline fluids the hybrid alkali s and cl rich compositions of residual melts and fluids were trapped in secondary inclusions in olivine the crustal origin of salts in the udachnaya east kimberlite demonstrated here is incompatible with a model of alkali rich primary kimberlite melt it is significantly more ca na b and s rich than the deep seated mantle k and ba rich fluid inclusions in fibrous diamonds our analysis suggests that the udachnaya east kimberlite is not exceptional and uniquely fresh but rather typical of the other crust contaminated southern yakutian kimberlites

deformation controlled cation diffusion in tourmaline a microanalytical study on trace elements and boron isotopes abs tract plastic deformation of variable intensity has modified primary textures composition and element distribution in tourmaline from a mylonitic pegmatite from the nw argentinean sierras pampeanas the primary concentric tourmaline zonation has been overprinted and partly destroyed by synkinematic cation diffusion that occurred under amphibolite facies p t conditions textural changes include bending of crystals formation of subgrains and subgrain rotation leading locally to recrystallization of tourmaline some parts of deformed crystals were less affected or unaffected by plastic deformation and secondary cation diffusion two principal processes intracrystal trace element diffusion and matrix exchange of trace elements caused the compositional variations in deformed tourmaline domains intracrystal diffusion partly or completely destroyed the primary trace element zonation by cation diffusion from zones of high to low concentration small cations occupying the y position are readily mobilized even by weak deformation whereas large cations on the x site require higher deformation intensity to be mobilized and show less pronounced or no homogenization of the primary zonation matrix exchange between tourmaline and co existing solid or fluid phases generally leads to trace element loss from deformed tourmaline domains the extent of the matrix exchange is primarily controlled by the compatibility of mobilized cation species with matrix phases during mylonitization in contrast the b isotopic compositions in deformed and undeformed crystal domains are uniform indicating absence of significant b diffusion and isotope fractionation during crystal growth and plastic deformation i e the activation energy to move b in tourmaline must be too high even for intense plastic deformation to overcome

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