catalogue of palaeomagnetic directions and poles from fennoscandia archaean to tertiary abstract palaeomagnetic data from fennoscandia ranging from the archaean to the tertiary have been compiled into a catalogue the data are presented in table format listing precambrian data according to tectonomagmatic blocks and late precambrian phanerozoic data according to geological periods each pole is graded with the modified briden duff classification scheme the catalogue complete to the end of 1988 contains 350 entries from 31 tectonomagmatic blocks and or geological periods normal and reversed polarity data are listed separately to allow polarity asymmetries to be studied each entry also has an indexed abstract summarizing relevant information such as the age of the rock the age of the natural remanent magnetization and the basis for the assigned reliability grade all the data are stored in the palaeomagnetic data bank which will be updated annually with new data the catalogue is the basic source of data for the microcomputer based palaeomagnetic database for fennoscandia now being compiled

geochemistry of cassiterite and wolframite from tin and tungsten quartz veins in portugal cassiterite and wolframite compositions from snnw and wnsn bearing quartz veins in northern and central portugal are compared to provide evidence on fluid compositions in snnw bearing quartz veins euhedral cassiterite shows sequences of alternating parallel darker and lighter zones the darker zones are pleochroic oscillatory zoned exhibit exsolutions of columbite and ixiolite and are richer in nb ta and fe than the lighter zones which consist of nearly pure sno2 cassiterite from wnsn bearing quartz veins is usually zoned with homogeneous and slightly pleochroic darker zones which are chemically similar to lighter zones bothzoneshaveinclusionsofrutileandrareilmenite thedarkerzonesofcassiteritefrom theformer veins arericherin nb taandfe contents and poorer in ti than the darker and lighter zones of cassiterite from the latter veins this is attributed to differences in the composition of magmatic hydrothermal fluids wolframite compositions from snnw and wnsn bearing quartz veins do not show any significant distinction because they precipitate from relatively similar magmatic hydrothermal fluids in some deposits most wolframite crystals are homogeneous but others are heterogeneous inner patches rich in a hubnerite component rarely occur in crystals from the filharoso and panasqueira deposits zoned crystals showing an increase in fe and a decrease in mn from core to rim were found in the vale das gatas deposit complex oscillatoryzonedcrystals occur inthe carris deposit later wolframite contains inclusions ofscheelite partially replaces itand is richer in fe and poorer in mn than earlier wolframite wolframite from snnw bearing quartz veins in the argozelo deposit and wnsn bearing quartz veins from vale das gatas and panasqueira deposits has significant nb content this does not depend on the fe and mn content of the wolframite but w content is negatively correlated with nb content only very rare single crystals of wolframite show an increase in w and a decrease in nb from core to rim snnw bearing quartz veins contain wolframite poorer in nb than the darkerzones of cassiterite which exsolved columbite andixiolite inwnsn bearing quartz veins from panasqueira and vale das gatas the wolframite has a higher nb content than the cassiterite which contains rutile inclusions enriched in nb because cassiterite and wolframite are derived from two distinct magmatic hydrothermal fluids of different age the fluid responsible for wolframite precipitationwillhaveasimilarcompositiontothatresultingfromtheevolutionofthefluidresponsibleforcassiteriteprecipitationinthe

mantle derived noble gases in ore forming fluids of the granite related yaogangxian tungsten deposit southeastern china more than 90 of the tungsten resources of china are in the nanling region of south china and the yaogangxian vein deposit is the largest tungsten deposit in this region the tungsten deposits have ages of 150 160 ma and are spatially temporally and genetically related to granites which were previously believed to be produced by crustal anatexis this paper provides he and ar isotope data of fluid inclusions in pyrite and arsenopyrite from the yaogangxian w veins 3he 4he ratios range from 0 41 to 3 03 ra where ra is the 3he 4he ratio of air 1 39 10 6 and 40ar 36ar ratios from 328 to 1 191 moreover there are excellent correlations between he and ar isotopic compositions the results suggest that the ore forming fluids are a mixture between a crustal fluid containing atmospheric ar and crustal 4he and a fluid containing mantle components it is likely that the former is a low temperature meteoric fluid and the later is a fluid exsolved from the w associated granitic magma which formed by crustal melting induced by intrusion of a mantle derived magma

the tectonic implications of asymmetrically zoned plutons abstract asymmetrically zoned plutons have been mapped in many parts of the world and whereas many of these are asymmetrical for reasons unrelated to regional tectonic environment there are large areas in which the majority of asymmetric plutons are asymmetric in the same direction in these domains of asymmetry either the mechanisms of emplacement or post emplacement deformation have produced a systematic exposure orientation recognition of these domains may lead to discovery of the tectonic mechanisms responsible for systematic orientation ultimately domains of pluton asymmetry may serve to identify the manner of tectonic emplacement or post emplacement deformation

tectonics of the kola collision suture and adjacent archaean and early proterozoic terrains in the northeastern region of the baltic shield as preparation for the deep seismic and other geophysical experiments along the polar profile which transects the granulite belt and the kola collision suture structural field work has been performed in northernmost finland and norway and published geological information including data from the neighbouring soviet territory of the kola peninsula have been compiled and reinterpreted based on these studies and a classification according to crustal and structural ages the northeastern region of the baltic shield is divided into six major tectonic units these units are separated and outlined by important low angle ductile shear or thrust zones of late archaean to early proterozoic age the lateral extension of these units into soviet territory and their involvement in large scale crustal deformation structures are described using the view down the plunge method a generalised tectonic cross section that predicts the crustal structures along the polar profile is compiled and the structures around the kola deep drill hole are reinterpreted the kola suture belt through parts of which the kola deep bore hole has been drilled is considered to represent a ca 1900 ma old arc continent and continent continent collision suture it divides the northeastern shield region into two major crustal compartments a northern compartment comprising the murmansk and sorvaranger units and a southern compartment including the inari unit the granulite belt and the tanaelv belt as well as the more southernly situated south lapland karelia craton of the karelian province of the svecokarelian fold belt the kola suture belt is outlined by a 2 40 km wide and ca 500 km long crustal belt composed of 1 1 early proterozoic ca 2400 2000 ma old metavolcanic and metasedimentary sequences which originally formed part of the attenuated margin of the northern archaean compartment and 2 2 the remains of a ca 2000 1900 ma old predominantly andesitic island arc terrain this island arc terrain was built up above a sw plunging subduction zone initiated ca 2000 ma ago in the southern part of a newly formed oceanic domain the kola ocean due to continued subduction and complete consumption of this ocean the northern passive margin deposits and the island arc terrain were brought into tectonic juxtaposition and during the final arc continent and continent continent collision they were overthrusted onto the northern archaean continent along its southern boundary the kola suture belt is tectonically overlain by the archaean rocks of the inari unit this unit was derived from a microcontinent split from the southern compartment the depositional basin of the protoliths of the granulite belt being formed to the south of the microcontinent the inari microcontinent appears to have wedged out towards the southeast as the continuation of the granulite belt north of the white sea is in direct tectonic contact with the kola suture belt the granulite belt is composed of high grade paragneisses and minor amounts of meta igneous rocks the paragneisses formed from thick turbidite and mass flow deposits lain down in a back arc basin south of the inari microcontinent a thermal anomaly beneath the partly oceanic basement of the back arc basin is believed to have contributed to the ca 2000 1900 ma old granulite facies metamorphism of the granulite assemblages granulite facies conditions still prevailed when the inari microcontinent overrode the granulites and when the granulite belt as such was formed and was overthrusted for at least 100 km towards the southwest in conjunction with the latter event the rocks of the basement of the basin also became involved in thrust movements these now form the tanaelv belt which shows gradational tectonic contacts towards underlying cover and basement rocks of the south lapland karelia craton although not all parts of this craton were affected by the svecokarelian deformation it is considered to belong to the karelian province of the svecokarelian fold belt a ca 1900 1800 ma old episode of wrench faulting and the intrusion of 1790 1770 ma old post kinematic granites concluded the svecokarelian evolution of the northeastern shield region

how well do precambrian paleomagnetic data agree with the phanerozoic apparent polar wander path a baltica case study abstract precambrian paleomagnetic data are crucial for various tectonic and geophysical applications the reconstructions of fusion and fission of supercontinents in particular due to many objective reasons the variety of stability tests for these data are abridged in comparison to phanerozoic results and is further hindered by the rather common refusal to consider the resemblance between precambrian and younger poles in this paper we selected precambrian paleomagnetic data with ages of

metallogenesis at the carris w mo sn deposit geres portugal constraints from fluid inclusions mineral geochemistry re os and he ar isotopes abstract the carris orebody consists of two partially exploited w mo sn quartz veins formed during successive shear stages and multipulse fluid fillings they cut the variscan post d3 geres i type granite the most important ore minerals are wolframite scheelite molybdenite and cassiterite there are two generations of wolframite the earlier generation of wolframite is rare and has the highest wo4mn content 91 mol and the most common wolframite contains 26 57 mol wo4mn re os dating of molybdenite from the ore quartz veins and surrounding granite yields ages of 279 1 2 ma and 280 3 1 2 ma respectively which are in very good agreement with the previous id tims u pb zircon age for the carris granite 280 5 ma 3he 4he ratio of pyrite ranging between 0 73 and 2 71 ra 1 ra 1 39 10 6 and high 3he 36ar 0 8 5 10 3 indicate a mixture of a crustal radiogenic helium fluid with a mantle derived fluid the fluid inclusion studies on quartz intergrown with wolframite and scheelite beryl and fluorite reveal that two distinct fluid types were involved in the genesis of this deposit the first was a low to medium salinity aqueous carbonic fluid co2 between 4 and 14 mol with less than 1 95 mol n2 which was only found in quartz associated with wolframite the other was a low salinity aqueous fluid found in all the four minerals the homogenization temperatures indicate minimum entrapment temperatures of 226 310 c average 280 c for the h2o co2 n2 nacl fluid and average temperatures of 266 c for scheelite and 242 c 190 c and 160 c for the last generations of beryl fluorite and quartz respectively it was estimated that wolframite was deposited 7 km depth assuming a lithostatic pressure probably due to strong pressure fluctuation caused by seismic events triggered by brittle tectonics during the exhumation event precipitation of scheelite and sulphides took place later at the same depth but under a hydrostatic or suprahydrostatic pressure regime and probably caused by mixing between the magmatic hydrothermal fluid and meteoric waters that deeply penetrated the basement during post variscan decompression

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

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

lead isotope and pb pb model age determinations of ores from central europe and their metallogenetic interpretation the paper presents lead isotope data from 211 samples from phanerozoic lead bearing ore occurrences in central europe particularly from the southern part of the former german democratic republic the data are interpreted in terms of amov s dynamic model of continuous lead isotope evolution the relationships between thoro genic and urano genic model ages and the source of lead in different regional units are discussed we observed differences in lead isotope evolution in the hercynian internides and externides within the moldanubian and saxothuringian zones we distinguish five main lead bearing ore associations 1 cambrian stratiform base metal hermsdorf waldsassen 206pb 204pb 17 50 17 70 2 devonian vein type sb bearing metamorphogene neumuhle hartmannsdorf 17 80 18 00 3 upper carboniferous permian polymetallic including tin vein type kutna hora freiberg altenberg 18 00 18 20 4 triassic jurassic pb ba vein type st ibro halsbrucke 18 20 18 60 5 cenozoic polymetallic vein type riftogene roztoky banska stiavnica 18 80 19 10 pb isotope characteristics from ores of the montagne noire and the brioude massiac district correspond to this subdivision ore associations from the rheno hercynian zone display higher 207pb 204pb ratios which can be explained by more evolved and less metamorphosed source rocks mineralizations of the eastern harz strasberg neudorf belong to the permian association those from the western harz clausthal bad grund to the triassic jurassic because of pb isotope agreement the stratabound rammelsberg and the vein bound ramsbeck i mineralization are presumed to be isogenetic pb isotope identity of distinct mineralizations in the basement zone halsbrucke bad grund and in the triassic sediments gorny slask mechernich bleiglanzbanke suggests a strong genetic coherence pb isotope conformity between the upper carboniferous permian triassic ore associations and hercynian postkinematic granitoids and lamprophyric rocks also favours a close relationship pb isotope and other data indicate crustal sources as the age of the ore associations decreases crustal influences generally increase apart from the roztoky mineralization

fluid fractionation of tungsten during granite pegmatite differentiation and the metal source of peribatholitic w quartz veins evidence from the karagwe ankole belt rwanda abstract the identification of a magmatic source for granite associated rare metal w nb ta and sn mineralisation in metasediment hosted quartz veins is often obscured by intense fluid rock interactions which metamorphically overprinted most source signatures in the vein system in order to address this recurrent metal sourcing problem we have studied the metasediment hosted tungsten bearing quartz veins of the nyakabingo deposit of the karagwe ankole belt in central rwanda the vein system 992 2 ma is spatiotemporal related to the well characterised b rich f poor g4 leucogranite pegmatite suite 986 10 ma to 975 8 ma of the gatumba gitarama area which culminated in nb ta sn mineralisation muscovite in the nyakabingo veins is significantly enriched in granitophile elements rb cs w and sn and show alkali metal signatures equivalent to muscovite of less differentiated pegmatite zones of the gatumba gitarama area pegmatitic muscovite records a decrease in w content with increasing differentiation proxies rb and cs in contrast to the continuous enrichment of other high field strength elements nb and ta and sn this is an indication of a selective redistribution for w by fluid exsolution and fluid fractionation primary fluid inclusions in tourmaline of these less differentiated pegmatites demonstrate the presence of medium to low saline h 2 o nacl kcl mgcl 2 complex salt e g rb cs fluids which started to exsolve at the g4 granite pegmatite transition stage laser ablation inductively coupled plasma mass spectrometry shows significant tungsten enrichment in these fluid phases 5 500 ppm fractional crystallisation has been identified previously as the driving mechanism for the transition from g4 granites less differentiated biotite biotite muscovite towards muscovite pegmatites and eventually columbite tantalite mineralised pegmatites the general absence of tungsten mineralisation in this magmatic suite including the most differentiated columbite tantalite mineralised pegmatites of the gatumba gitarama area emphasises the efficiency of fluid saturation to extract crystal melt incompatible tungsten from the differentiating melt phase fluid melt crystal partitioning calculations support the concept of a magmatic hydrothermal fluid source for tungsten and constrain the range of permissible crystal melt and fluid melt partition coefficients together with realistic values for water solubility in the parental g4 granitic melt consequently we propose that for highly differentiated b rich f poor granite systems fluid saturation started prior to or at the granite pegmatite transition stage resulting in apical to peribatholitic tungsten veins systems that are paragenetically older than the final pegmatite stage

package fluids 1 computer programs for analysis of fluid inclusion data and for modelling bulk fluid properties the computer package fluids contains five sets of computer programs written in c for the calculation of fluid properties both model fluids and data from fluid inclusions can be analysed in the programs bulk density molar volume and composition of fluid inclusions are calculated with the program bulk which uses microthermometric data micro raman spectroscopic data cation ratios and volume fraction estimations as input the program offers a broad variety of equations of state which are selected according to the fluid system or the temperature and pressure conditions of interest the isochores that correspond to the output or test v x properties of fluid inclusions are calculated by the program isoc in calculating the isochores this program takes account of the compressibility and expansion of selected host minerals the program test allows different equations of state to be compared directly with experimental data thereby facilitating selection of the most adequate model in the programs bulk and isoc loner is a group of programs that handle individual equations of state eos for all fluid systems presented in the programs bulk and isoc aqso is a group of programs that allows purely empirical modelling of electrolyte bearing aqueous solutions henry s law for dilute gas bearing aqueous solutions and osmotic coefficients for dilute electrolyte bearing aqueous solutions the programs are available on the university of leoben web site at http www unileoben ac at buero62 minpet ronald

pechenga ferropicrites and other early proterozoic picrites in the eastern part of the baltic shield ti poor komatiites and ti rich picrites exist among the widely occurring primitive mgo rich volcanics in the early proterozoic successions of the kola peninsula both have been encountered in the imandra varzuga belt but only picrites are found in the pechenga complex the picritic rocks are divided into two types the first type restricted to the kolasjoki and pilgujarvi suites and the tominga series is called ferropicrite due to its exceptionally high total iron content which usually exceeds 14 feotot the second type found in the south pechenga series and in the umba and panarechka suites has more typical iron content and geochemically resembles suisaarian picrites from southern karelia ferropicrites occur as pillow lavas lava breccias tuffs massive lavas and up to 50 m thick differentiated spinifex textured flows in addition to high feotot contents these rocks are characterized by low al2o3 contents and by high concentrations of tio2 zr and other incompatible elements they are strongly lree enriched and have immobile trace element characteristics similar to within plate transitional or alkali basalts it is shown that with regard to both the major and trace element compositions the parental magma of the ni bearing intrusions of the pilgujarvi suite is similar to ferropicrite suggesting that the emplacement of the intrusions took place contemporaneously with ferropicritic volcanism the high incompatible element contents of the ferropicritic rocks rule out a genetic relationship with associated tholeiitic basalts proposed geotectonic settings for the pechenga area including an intracratonic rift zone a passive continental margin an oceanic island arc a mature continental volcanic arc and a collisional suture zone are discussed the presence of ti rich picritic rocks does not support a subduction related environment

isotopic data upb rbsr pbpb and smnd on mafic granulites from finnish lapland abstract a combined approach using several methods pb pb u pb rb sr sm nd on granulitic rocks selected from classic areas in northern finland is presented the results show that the emplacement of igneous rocks and the granulitic metamorphism occurred nearly coevally 1 9 2 0 ga this result which is supported by field observations means that these rocks are not ideal for comparing the response of the various parent daughter pairs to the high grade metamorphism or for checking the special geochronological possibilities of each method nevertheless because of the coherence of results from rocks of different origins a discussion is possible the bulk of the mafic granulite was certainly derived from upper mantle sources or short lived crustal mafic materials granulites of the granulitic belt and anorthosites are thought to have originated from two distinct mantle sources reflecting mantle heterogeneities at that time

ore deposits of the french massif central insight into the metallogenesis of the variscan collision belt the french massif central fmc represents the whole west european variscan wev belt in terms of both the geodynamic evolution and the metallic content thus a study of the metallogenic evolution of the fmc may elucidate the conditions that allow the mineralisation of a collision belt since recent collision belts e g the himalayas or the alps show that mineralisation does not necessarily result from the collision process the palaeozoic history of the fmc is divided into three geodynamic stages unevenly involved from the metallogenic view point the eo variscan stage cambrian to silurian was not important the meso variscan stage devonian early carboniferous was of limited importance and most of the mineralisations formed during the neo variscan stage late carboniferous early permian in addition some more mineralisation was produced during the mesozoic because of the thermal reactivation linked with the alpine orogenies

helium and argon isotope geochemistry of alkaline intrusion associated gold and copper deposits along the red river jinshajiang fault belt sw china abstract the red river jinshajiang strike slip fault zone on the eastern margin of the tibetan plateau was originally produced by the india eurasia collision 60 70 myr ago numerous post collisional mantle derived alkaline igneous rocks with ages of 40 30 ma have been intruded along this fault zone in recent years several copper and gold deposits associated with the alkaline intrusions of this region were discovered such as the yao an and beiya gold deposits and the yulong and machangqing copper deposits studied in this paper the mineralised intrusions are felsic with sio 2 ranging from 61 4 to 67 7 wt k 2 o na 2 o from 8 1 to 11 5 wt and k 2 o na 2 o 1 the deposits are located at both the exo and endo contact zones of the intrusions the mineral deposits are of hydrothermal origin with the ore forming temperatures mainly in the range 150 450 c this paper presents he and ar isotope analyses of these four deposits the concentrations of 4 he trapped in fluid inclusions of pyrites from the ores are 0 7 54 1 10 6 cm 3 stp g 1 and those of 40 ar are 0 6 7 3 10 6 cm 3 stp g 1 3 he 4 he ratios are 0 3 2 5 ra ra represents the 3 he 4 he ratio of air 1 39 10 6 40 ar 36 ar ratios are 316 1736 and 3 he 36 ar ratios are 0 2 11 2 10 3 generally the 3 he 4 he 40 ar 36 ar and 3 he 36 ar ratios for the gold deposits are higher than those for the copper deposits we suggest that the ore forming fluids of both gold and copper deposits were differentiated from the mantle derived alkaline magmas but were diluted by modified air saturated water masw that experienced intensive interaction with crustal rocks however the magmatic fluids responsible for the gold deposits were less extensively diluted by masw resulting in higher 3 he 4 he 40 ar 36 ar and 3 he 36 ar ratios than the copper deposits

water in granite and pegmatite forming melts article i nfo in this paper we have compiled water concentration data obtained from melt inclusion in minerals mostly quartz and topaz from granites and pegmatites a small number of data come from analysis of natural glasses about 4600 melt inclusions are from granites and about 2100 melt inclusions are from pegmatites another 4159 values are from melt inclusions and glasses of rocks with more than 66 g g sio2 are added belonging to a recent compilation the total of 10 859 melt inclusions provides a statistically significant basis from which to derive some conclusions generally the water concentration in granite melt inclusion is b10 g g with three maxima at 4 0 1 3 5 9 1 2 and 8 1 1 1 g g water for pegmatites a larger range of water contents was found from 2 to more than 50 g g water with two distinct maxima at 10 5 8 1 and 26 2 14 3 g g we show that the great spread and the generally high water content of the pegmatite forming melts as sampled by melt inclusions are the result of melt melt immiscibility pro cesses connected with the formation of conjugate melt fraction with contrasting physical and chemical char acteristics which have also a major influence on the element partitioning between such fractions in this paper we also discuss viscosity as an important transport property of natural silicate melts and we show that due to high primary water concentration in the pegmatite forming melts their viscosity is very low over a wide range of temperatures in the case of water rich peralkaline melt fractions the viscosity can decrease still further together these suggest that liquidus undercooling as the major cause of pegmatite textures is redundant furthermore we demonstrate that the effect of boron carbonates and bicarbonates on pegmatite melts these two last mostly ignored in the past have a large influence on the melt structure and they enable pegmatite formation in the absence of the usual discussed fluxing elements such as f and p

transpressional folding and associated cross fold jointing controlling the geometry of post orogenic vein type w sn mineralization examples from minas da panasqueira portugal the world class w sn panasqueira deposit consists of an extensive subhorizontal vein swarm peripheral to a late orogenic greisen cupola the vein swarm consists of hundreds of co planar quartz veins that are overlapping and connected laterally over large distances various segmentation structures a local zigzag geometry and the occurrence of straight propagation paths indicate that they exploited a regional joint system a detailed orientation analysis of the systematic joints reveals a geometrical relationship with the subvertical f2 fold generation reflecting late variscan transpression the joints are consistently orthogonal to the steeply plunging s0 s2 intersection lineation both on the regional and the outcrop scale and are thus defined as cross fold or ac joints the joint system developed during the waning stages of the variscan orogeny when already uplifted to an upper crustal level veining reactivated these cross fold joints under the conditions of hydraulic overpressures and low differential stress the consistent subperpendicular orientation of the veins relative to the non cylindrical f2 hinge lines also when having an inclined attitude demonstrates that veining did not occur during far field horizontal compression vein orientation is determined by local stress states variable on a meter scale but with the minimum principal stress consistently subparallel to fold hinge lines the conspicuous subhorizontal attitude of the panasqueira vein swarm is thus dictated by the geometry of late orogenic folds which developed synchronous with oroclinal buckling of the ibero armorican arc

the ibero armorican arc a collision effect against an irregular continent the ibero armorican arc is the main variscan macrostructure in western europe although it was recognized in the 1920s its genesis is still debatable and the proposed models for its generation questionable however even if some doubts persist it seems that most agree on the general geodynamic evolution of this virgation in both branches in the middle to late devonian iberia was deformed by a sinistral transpressive regime while in the northern branch thrusting events were predominant in the carboniferous a dextral transpression begins to predominate in the armorican branch while the southern branch was deformed by southward thrusting in an attempt to correlate these events we propose that during the late devonian a cantabrian indentor moved northward producing the oblique closure of the southern part of the rheic ocean and an almost orthogonal closure in central europe in the carboniferous the collision with the irregular margin of laurasia induced a rotation of the indentor the intracontinental deformation was then achieved by dextral transpression in the northern branch and thrusting in the southern one

role de la deformation du granite dans la genese des episyenites feldspathiques des massifs de lovios geres galice et des zaer maroc central l etude de la deformation du granite dans les zones encaissant les bandes d episyenites feldspathiques de deux massifs hercyniens a permis de degager un modele tectonique rendant compte des caracteristiques structurales de celles ci les bandes d episyenites feldspathiques se forment lors des phases ultimes de la mise en place des intrusions granitiques sous l effet d un champ de contrainte local susceptible d engendrer des surpressions fluides aboutissant a une fracturation de type hydraulique la genese des mineralisations filoniennes intragranitiques a tungstene etain associees spatialement a ces episyenites doit etre rapportee a des evenements tectoniques et a des circulations fluides posterieures

paleomagnetism of 2 44 ga mafic dykes in russian karelia eastern fennoscandian shield implications for continental reconstructions abstract results of a paleomagnetic study of paleoproterozoic dykes and archean host rocks in the eastern fennoscandian shield are reported here most of the dykes are related to ca 2440 ma layered intrusions and have isotopic ages between 2349 and 2476 ma the dykes form an extensive nw se and e w trending swarm the majority are unaltered gabbronorites which carry stable remanent magnetizations with multicomponent nature the high temperature remanence component d which is thought to represent the primary 2 44 ga magnetization of the dykes has a paleomagnetic pole at 20 s 278 8 e a95 6 0 n 11 sites another d like component d with shallower inclination vgp 9 6 n 256 2 e eight samples at one site from baked archean host rock may also represent the primary remanence of the dykes the commonest remanence component a records an extensive svecofennian partial overprint and is interpreted to be ca 1 84 ga old it yields a paleomagnetic pole at 52 6 n 226 8 e a95 2 7 n 23 the fourth component b has a paleopole at 53 9 n 169 6 e a95 6 3 n 16 and is inferred to be ca 1 75 ga on the basis of isotopic dating although ages of 2 1 1 3 and 0 3 ga are also possible baked contact tests for the 2 44 ga dykes are negative as shown by the occurrence of component d in archean host rocks beyond one dyke width it is proposed that the negative baked contact test indicates regional reheating and remagnetization of the archean basement at ca 2 44 ga ago due to the spatially vast occurrence of coeval 2 44 ga mafic dykes layered intrusions volcanics and granites in the area based on this hypothesis it is suggested that component d in the dykes may be primary and acquired at ca 2 44 ga ago the similarity of pole d with poles from coeval dykes and layered intrusions elsewhere in the karelian province and kola peninsula suggest that within the archean domain of the fennoscandian shield no large scale block movements have taken place since 2 44 ga at 2 44 ga the fennoscandian shield was located at the latitude of ca 30 s which is different to that at 1 84 and 1 75 ga when fennoscandia was located at the latitudes of ca 30 n a continental reconstruction based on pole d and the pole from the 2 45 ga matachewan dykes of the superior craton in laurentia places the kola peninsula adjacent to southern greenland reconstructions based on recent geological interpretations and a reconstruction yielding pole d are also discussed

a petrological and rbsr isotopic study of an early archean fertile granite pegmatite system the sinceni pluton in swaziland abstract the sinceni pluton in the eastern kaapvaal craton of swaziland is one of the world s earliest examples of a fertile granite with associated rare metal pegmatites the rb sr isochron age of the pluton is 2990 43 ma 87 sr 86 sr i 0 711 7 95 confidence limit errors cogenetic rare metal lct type pegmatites yield k feldspar and muscovite rb sr ages of 3000 100 ma the sinceni pluton is asymetrically zoned in chemical and mineralogical composition and the sinceni pegmatite field occurs at the most differentiated southern end of the pluton geochemical modelling shows that the internal differentiation of the pluton is consistent with 25 35 fractional crystallization and that over 90 99 fractional crystallization would produce the observed rb sr ba and cs contents of the pegmatites the geochemically primitive pre 3000 ma archean crust in swaziland is unlikely to constitute a direct source of the sinceni pluton according to the sr isotopic and age data the origin of the pluton can best be explained as a late differentiate from a large volume of granitic magma which formed penecontemporaneous batholiths

dating multiply overprinted sn mineralized granites examples from the erzgebirge germany granites and primary tin mineralization in the erzgebirge were dated using 1 conventional u pb dating of uraninite inclusions in mica 2 rb sr dating of inclusions in quartz that represent highly evolved melts 3 re os dating of magmatic hydrothermal molybdenite and 4 chemical th u pb dating of uraninite conventional isotope dilution and thermal ion mass spectrometry and chemical th u pb dating of uraninite in granites from the ehrenfriedersdorf mining district provide ages of 323 9 3 5 ma 2 greifenstein granite and 320 6 1 9 and 319 7 3 4 ma 2 both sauberg mine in agreement with u pb apatite ages of 323 9 2 9 and 317 3 1 6 ms 2 both sauberg mine rb sr analysis of melt inclusions from zinnwald gives highly radiogenic sr isotopic compositions that with an assumed initial sr isotopic composition permit calculation of precise ages from single inclusions the scatter of the data indicates that some quartz hosted melt inclusions have been affected by partial loss of fluid exsolved from the melt inclusion re os dating of two molybdenite samples from altenberg provides ages of 323 9 2 5 and 317 9 2 4 ma 2 together with age data from the literature our new ages demonstrate that primary tin mineralization and the emplacement of the large sn specialized granites in the erzgebirge fall in a narrow range between 318 and 323 ma primary sn mineralization occurred within a short interval during post collisional collapse of the variscan orogen and was essentially synchronous over the entire erzgebirge in contrast to earlier claims no systematic age difference between granites of the eastern and western erzgebirge was established furthermore our data do not support a large age range for late variscan granites of the erzgebirge 330 290 ma as has been previously suggested

preliminary results of a palaeomagnetic and rock magnetic study of the proterozoic tsuomasvarri intrusions northern fennoscandia abstract preliminary palaeomagnetic results are presented for the proterozoic tsuomasvarri central ultramafic intrusion and surrounding older gabbro diorite intrusion in the northeastern fennoscandian shield in the ultramafic intrusion five remanence components reflecting different geological processes were isolated in the alternating field af and thermal demagnetization of 55 samples from ten sites a reversed polarity remanence component c pole plat 26 n plon 245 e dp 5 dm 9 n 32 samples dominates in the ultramafic intrusion the normal polarity pole a plat 44 n plon 232 e dp 4 dm 6 n 9 samples corresponds to an age of 1 88 ga on the apparent polar wander path apwp and is probably a thermochemical remanence acquired during the svecokarelian orogeny or in the late stages of magma cooling pole b plat 35 n plon 158 e dp 9 dm 15 n 5 samples normal polarity corresponds to the 1 75 ga old post orogenic activity in the area and is also seen in results of k ar whole rock isotopic age determinations from the vicinity the normal polarity pole d pole plat 25 s plon 285 e dp 12 dm 19 n 11 samples has a palaeomagnetic age of 2 44 ga which is in contrast with the isotopic age determination of 1 93 ga u pb age on zircon of the gabbro diorite intrusion pole f plat 3 n plon 212 e dp 10 dm 18 n 5 samples indicates an age of 0 5 0 4 ga on the palaeozoic apwp segment of fennoscandia and probably reflects a weak caledonian overprint in northeastern finland in the gabbro diorite intrusion two remanence components were isolated in 46 samples from eight sites the palaeomagnetic age 1 93 ga of the dominant normal polarity component a pole plat 40 n plon 247 e dp 5 dm 8 n 28 samples is consistent with the isotopic age of 1 93 ga u pb determination on zircon the normal polarity component d pole plat 20 s plon 285 e dp 14 dm 23 n 5 samples which was also isolated in the ultramafic intrusion contradicts the u pb isotopic age determination

thermochronology of economic mineral deposits dating the stages of mineralization at panasqueira portugal by high precision 40 39 ar age spectrum techniques on muscovite 40 ar 39 ar age spectrum dates for 13 muscovites have been used to reconstruct the thermal history thermochronology of the panasqueira portugal tin tungsten deposit a deposit spatially associated with a belt of hercynian plutons muscovite samples with an age difference as small as 2 2 m y 0 7 of the age are statistically distinct statistics are even better for comparison of multiple samples from separate events that is a difference of 0 9 m y 0 3 can be resolved in this approximately 300 m y old deposit the major tin and tungsten ore forming stages which are the oxide silicate stage the main sulfide stage and greisenization occurred between 296 3 or 0 8 1 sigma and 291 6 or 0 8 m y 1 sigma the first substage of the oxide silicate stage was a short lived thermal pulse at 296 3 or 0 6 m y the fluids responsible may have emanated from the known granite cupola the main sulfide stage was active at 294 5 or 0 9 m y as a slightly longer lived pulse with oldest evidence for this stage 295 8 or 0 6 m y coming from areas farthest away from the known cupola and youngest evidence 293 5 or 0 8 m y closest to the cupola a second substage of the oxide silicate stage occurred as a short lived thermal pulse at 292 9 or 0 7 m y synchronous with greisenization of the cupola and alteration of the silica cap at 292 1 or 0 4 m y the duration of activity of the oxide silicate stage the main sulfide stage greisenization and alteration of the silica cap based on the ages of all 13 muscovites was greater than 4 2 or 0 5 m y 1 sigma minor argon loss from all dated muscovites occurred during later reheating probably during the longer lived pyrrhotite alteration stage a single center the known cupola had a prolonged role and was the source for main sulfide stage oxide silicate stage ii greisenization and alteration of the silica cap and possibly oxide silicate stage i and the pyrrhotite alteration stage however a separate source for these latter two stages cannot be ruled out this study is an example of a new and powerful application of 40 ar 39 ar age spectrum dating of muscovite because of the high precision demonstrated in this study it is now possible to establish time constraints necessary for solving some of the long standing problems in economic geology beyond this the unique geologic situation of panasqueira has allowed us to quantify the thermal characteristics of muscovite published fluid inclusion data have been used to estimate a muscovite argon closure temperature of approximately 325 degrees c during rapid cooling or short reheating and a temperature of approximately 270 degrees c during slow cooling or extended reheating argon loss patterns displayed by all dated muscovites resulted from reheating after original closure the mechanism for this argon loss appears to have been argon transport by volume diffusion thus 40 ar 39 ar age spectrum dating of muscovite can be used to evaluate thermal conditions controlling argon diffusion as well as age duration and number of episodes of mineralization

geochemistry of white micas from portuguese tin and tungsten deposits abstract magmatic muscovite of hercynian s type granite muscovite of greisenized granite muscovite of selvages at quartz vein schist contacts and muscovite within the vein of the portuguese w sn deposit from panasqueira are distinguished mainly by trace element contents and there is a tendency for log f h 2 o f hf to increase in this sequence several correlations were found between major elements of these muscovites and of muscovites of hypothermal quartz veins of the sn deposit from montezinho the sn w deposit from argozelo and the w deposit from borralha northern portugal f content of muscovite depends on unit cell parameter b si mg fe2 fe3 alvi and oh sn content of muscovite seems to depend on its celadonite content and is carried by fluorine sn correlates positively with mg fe2 fe3 and f in muscovites from each deposit but a positive correlation between sn and cs was found in hydrothermal muscovites from all deposits the contents of both elements may be guides of sn and w mineralizations w is generally less abundant than sn in muscovite and was probably transported by water as tungstic acid or wo2 4 the muscovite of quartz veins from different deposits can be distinguished by major and trace element contents the muscovites of w quartz veins crystallized at greater log f h 2 o f hf than the muscovite of sn sn w and w sn quartz veins muscovite is also abundant in schists bordering quartz veins and has more distinct major and trace element contents than those of white mica of regional metamorphism and of hydrothermal muscovite of selvages along the vein schist contact it also crystallized at different log f h 2 o f hf

mantle like sr nd isotope composition of fe k subalkaline granites the peneda geres variscan massif nw iberian peninsula the peneda geres massif is one of the most representative nw iberian late to post orogenic variscan granitic plutons it resulted essentially from the subsynchronous emplacement at 290 296 ma of two granitic magmas of fe k subalkaline affinity with primitive isotopic composition sri 0 703 0 707 and endi 1 5 to 2 4 an origin by mantle input followed by mantle crust interactions is proposed implying the contribution of a less enriched mantle component than that involved in the genesis of synorogenic hybrid granitoids of mg k subalkaline affinity a less voluminous aluminopotassic and isotopically more evolved magma sri 0 708 0 709 and endi 3 5 to 3 9 with little or no mantle input was also generated suggesting the involvement of lower crust materi als therefore this study suggests an input of juvenile magmas in late variscan times the mantle like isotope signature of fe k granitic magmatism being clearly related to a geodynamic setting of extensional processes large scale uplift and thinning

u pb zircon and monazite geochronology of post collisional hercynian granitoids from the central iberian zone northern portugal abstract in the central iberian zone ciz of the iberian massif large volumes of granitoids were emplaced during the post collisional stage of the hercynian orogeny syn to post d3 the last ductile deformation phase twelve granitic units and a quartz monzodiorite were selected for a u pb zircon and monazite geochronological study they represent successive stages of the d3 event the ucanha vilar lamego sameiro and refoios do lima plutons are coeval 313 2 ma 319 4 ma 316 2 ma and 314 2 ma respectively and belong to the earliest stage later on the braga massif was emplaced its different units yielding the same age 309 3 ma for the braga granite 309 1 ma for the gonca granite and 311 5 ma for a related quartz monzodiorite the braga massif is subcontemporaneous with the agrela and celeiros plutons 307 3 5 ma and 306 2 ma respectively in agreement with field data the briteiros granite is younger 300 1 ma followed by the emplacement of the peneda geres massif geres paufito illa and carris granites the geres granite emplaced at 296 2 ma seems to represent a first magmatic pulse immediately followed by the intrusion of the paufito granite at 290 2 5 ma for the carris granite a minimum emplacement age of 280 5 ma was obtained based on these results the following chronology is proposed 1 syn d3 biotite granitoids 313 319 ma 2 late d3 biotite dominant granitoids 306 311 ma 3 late to post d3 granitoids ca 300 ma 4 post d3 granitoids 290 296 ma these chronological data indicate that successive granitic intrusions were emplaced in the ciz during a short time span of about 30 ma that corresponds to the latest stages of the hercynian orogeny a rapid and drastic change occurred at about 300 ma between a compressive ductile tectonic regime d3 ca 300 320 ma associated to calc alkaline monzonitic and aluminopotassic plutonism and a fragile phase of deformation d4 which controlled the emplacement of the subalkaline ferro potassic plutonism at 290 296 ma

rock magnetic and paleomagnetic study of the keurusselka impact structure central finland abstract there are 31 proven impact structures in fennoscandia one of the most densely crater populated areas of the earth the recently discovered keurusselka impact structure 62 08 n 24 37 e is located within the central finland granitoid complex which formed 1890 1860 ma ago during the svecofennian orogeny it is a deeply eroded complex crater that yields in situ shatter cones with evidence of shock metamorphism e g planar deformation features in quartz new petrophysical and rock magnetic results of shocked and unshocked target rocks of various lithologies combined with paleomagnetic studies are presented the suggested central uplift with shatter cones is characterized by increased magnetization and susceptibility the presence of magnetite and pyrrhotite was observed as carriers for the remanent magnetization four different remanent magnetization directions were isolated 1 a characteristic svecofennian target rock component a with a mean direction of d 334 8 i 45 6 95 14 9 yielding a pole plat 51 1 plon 241 9 a95 15 1 2 component b d 42 4 i 64 1 95 8 4 yielding a pole plat 61 0 plon 129 1 a95 10 6 3 component c d 159 5 i 65 4 95 10 7 yielding a pole plat 21 0 plon 39 3 a95 15 6 and 4 component e d 275 5 i 62 0 95 14 4 yielding a pole plat 39 7 plon 314 3 a95 19 7 components c and e are considered much younger possibly neoproterozoic overprints compared with the components a and b the pole of component b corresponds with the 1120 ma pole of salla diabase dyke and is in agreement with the 40ar 39ar age of 1140 ma from a pseudotachylitic breccia vein in a central part of the structure therefore component b could be related to the impact and thus represent the impact age

continental fault structure and the shallow earthquake source plate boundaries in continental crust are generally less sharply defined than in the oceans with seismicity spread over broad areas interplate displacements appear to be largely accommodated by networks of major fault zones a simple 2 level model for these important structures accounts for the depth distribution of most continental earthquakes and for the observed range of faulting styles and associated rock deformation textures the model consists of a seismogenic frictional slip regime overlying quasi plastic mylonite belts wherein shearing is largely accommodated aseismically due mainly to the changing response of quartz to deformation with increasing temperature shear resistance increases with depth to a peak value in the vicinity of the frictiona1 quasi plastic transition and then decreases rapidly the depth to which microseismic activity extends appears inversely related to regional heat flow and can be satisfactorily modelled as the frictional quasi plastic transition for different geotherms using laboratory determined flow laws for quartz bearing rocks larger earthquake ruptures m 5 5 tend to nucleate near the base of the seismogenic regime in the region inferred to have the highest shear resistance and concentration of distortional strain energy consideration is also given to the depression of isotherms and seismic activity in regions of thrusting and to the question of the downward continuation of major fault zones through the lithosphere decoupling of the upper crust on flat lying shear zones may accompany higher level dip slip and perhaps in some circumstances strike slip faulting being favoured by above average continental heat flow and a high quartz content in the middle or deep crust the average level of deviatoric stress within the seismogenic regime remains an outstanding problem

abundance and isotopic composition of helium in hydrothermal sulfides from the east pacific rise at 13 n abstract the helium isotopes composition of fluids trapped in hydrothermal sulfides from the east pacific rise 13 n were measured two extraction techniques i e crushing and heating were tested and sulfldes of different mineralogical types were studied the comparison between the two extraction methods suggests that both should give similar results provided the crushing efficiency is sufficiently high sulfides 3 he 4 he ratio for crushed samples are in the range 6 85 8 10 times the atmospheric ratio r a 1 38 10 6 and the measured helium concentration is of the order of 5 5 10 5 cm 3 stp per gram of trapped fluid comparison with the helium isotope composition of the hydrothermal vent fluids themselves shows that the mineral phases formed at the highest temperature i e with less dilution by the ambient seawater retain the helium information most effectively with values almost indistinguishable from the endmember vent fluid

extensional failure and hydraulic valving at minas da panasqueira portugal evidence from vein spatial distributions displacements and geometries abstract at panasqueira portugal exceptional exposure and demonstrable vein connectivity allow robust characterisation of brittle elastic failure mechanisms in intrusive related environments extensional failure was driven by cycles of fluid injection hydraulic valving and vein growth under conditions with v 1 and differential stress

palaeomagnetism of the palaeoproterozoic ultramafic intrusion near lake konchozero southern karelia russia new palaeomagnetic results are presented from the recently dated palaeoproterozoic ultramafic konchozero sill and associated basalts three sites 38 oriented samples three stable components of remanence have been isolated during thermal and alternating field demagnetisation the component i with a mean direction of d 103 i 40 k 18 95 11 n 11 samples pole position of 14 s 282 e has been obtained from the unaltered deeper part of the sill and from baked schists the study of the baked contact confirms the conclusion that component i is supposed to be primary and corresponds to the sm nd age of the sill of 1974 27 ma the palaeopole of component i is not consistent with the accepted fennoscandian apparent polar wander path apwp for the period 2120 1880 ma and for that part the fennoscandian apwp should be revised two other components component ii d 349 i 39 k 35 95 6 n 19 samples pole position 49 n 231 e and component iii d 17 i 41 k 44 95 5 n 19 samples pole position 50 n 190 e fit the apwp well with palaeomagnetically estimated ages of ca 1860 and 1760 ma respectively

cryptic trace element variation as an indicator of reverse zoning in a granitic pluton the ricany granite czech republic cryptic variation recognized on the basis of trace element patterns shows the oieany granite in the northeastern part of the hercynian central bohemian pluton to be a reversely zoned high level intrusion unlike many other reversely zoned plutons there are no marked differences in modal composition between the margins and the centre of the intrusion the granite is generally peraluminous and geochemically evolved as demonstrated by its restricted and high sio 2 range and low k rb ratio coupled with a c two fold variation in ba and sr concentrations modelling shows that the geochemical variations can be most readily explained by k feldspar dominated fractionation in a magma chamber below the present level of exposure the reverse zoning is interpreted as the product of emplacement of an essentially single pulse of magma from a deeper level magma chamber in which fractionation has led to a vertical compositional gradient the least evolved magma was emplaced in the centre of the high level pluton with the more evolved magma around it recognition of cryptic reverse zoning in granites has major implications for granite petrogenesis in that the magmatic evolution of such bodies has to be established before assessing potential mechanisms of emplacement

pressure fluctuations phase separation and gold precipitation during seismic fracture propagation gold mineralization at croagh patrick western ireland occurs in quartz veins associated with three synchronous oblique tensile shear systems the veins evolved by progressive thickening of isolated en echelon lensoid tensile fractures that show a power law relation between their length and thickness a change in power law exponent marks the linking of the en echelon arrays by large oblique tensile veins fluid inclusion data show that gold was deposited due to unmixing of an h 2 o co 2 nacl fluid at 320 240 c and 160 30 mpa primarily due to decreases in fluid pressure evidence for phase separation is only observed in the large linking veins and is abundant close to intersections of the vein arrays these sites are where high gold grades occur the distribution of gold is believed to reflect both spatial and temporal variations in fluid pressure fluctuation during seismic fracture propagation controlled by the vein growth mechanism and zones of maximum dilation

infrared microthermometric and stable isotopic study of fluid inclusions in wolframite at the xihuashan tungsten deposit jiangxi province china the xihuashan tungsten deposit jiangxi province china is a world class vein type ore deposit hosted in cambrian strata and mesozoic granitic intrusions there are two major sets of subparallel ore bearing quartz veins the ore mineral assemblage includes wolframite and molybdenite with minor amounts of arsenopyrite chalcopyrite and pyrite there are only two phase aqueous rich inclusions in wolframite but at least three major types of inclusions in quartz two or three phase co2 rich inclusions two phase pure co2 inclusions and two phase aqueous inclusions indicating boiling fluid inclusions in wolframite have relatively higher homogenization temperatures and salinities 239 380 c 3 8 13 7 wt nacl equiv compared with those in quartz 177 329 c 0 9 8 1 wt nacl equiv these distinct differences suggest that those conventional microthermometric data from quartz are not adequate to explain the ore formation process enthalpy salinity plot shows a linear relationship implying mixing of different sources of fluids although boiling occurred during vein type mineralization it seems negligible for wolframite deposition mixing is the dominant mechanism of wolframite precipitation in xihuashan 34s values of the sulfides range from 1 6 to 0 1 indicative of a magmatic source of sulfur 18o values of wolframite are relatively homogeneous ranging from 4 8 to 6 3 oxygen isotope modeling of boiling and mixing processes also indicates that mixing of two different fluids was an important mechanism in the precipitation of wolframite

tracing metal sources in peribatholitic hydrothermal w deposits based on the chemical composition of wolframite the example of the variscan french massif central abstract we present a complete dataset for major minor and trace elements in wolframite fe mn wo4 based on the example of several peribatholitic hydrothermal w deposits located in the variscan french massif central fmc the wolframite samples were characterized down to the micrometer scale by combining scanning electron microscopy observations and in situ chemical analysis by electron probe microanalyzer and laser ablation inductively coupled plasma mass spectrometry most samples are fe dominated wolframites and are characterized by variable fe fe mn values for the studied deposits from 0 36 to 0 86 without significant alteration features wolframites present intracrystalline variations for concentrations of several minor and trace elements principally for nb ta and sn which reflect growth zoning the minor and trace element compositions of the different wolframite samples show at first order similar enrichments in ta nb sn zn and in as well as depletions in lree li th ti zr hf pb v co and mg compared to the upper continental crust second order compositional variations are observed between the studied deposits which can be separated in four main regional geochemical groups this work highlights that the chemical composition of wolframite is controlled by both the crystallochemical parameters and the composition of the primary hydrothermal fluid the regional variations observed in the geochemical signatures of wolframite reflect local variations in the composition of the hydrothermal fluid i e variable metal sources therefore this suggests that the minor and trace element contents in wolframite likely represent direct markers of the source of the hydrothermal fluid and ultimately of the metals the comparison between the trace element compositions of wolframite with the compositions of regional granitic rocks and worldwide shales suggests that evolved peraluminous granites represent the main source of metals in peribatholitic hydrothermal w deposits from the fmc whereas metasedimentary rocks have a limited to no influence on the metal budget

proterozoic basic dykes in the ukrainian shield a palaeomagnetic geochronologic and geochemical study the accretion of the ukrainian shield to fennoscandia a palaeomagnetic geochronologic and geochemical study of basic dykes in the ukrainian shield has been undertaken with the purpose of testing a hypothesis for timing of accretion of the ukrainian shield with fennoscandia on the basis of geological data it has been suggested that the two shields amalgamated at ca 1900 1800 ma with this study of 11 basic dykes the palaeomagnetic database for the ukrainian shield is extended the palaeomagnetic data indicate three generations of dykes this is supported by the age data and the difference in geochemical compositions ages of two ca 25 m wide dykes susly in the north western block of the shield have been determined one for which a positive palaeomagnetic field test is demonstrated the lower of the two ar 40 ar 39 hornblende ages of this dyke 2061 20 ma is similar to the u pb zircon age of the granitic host rock ca 2067 ma u pb zircon which suggests that the dyke intruded shortly after crystallization of the granite combined with the magnetization of the baked contact and that of another dyke a new ca 2060 ma pole is presented plat 15 7 degrees plon 182 9 degrees a 95 13 7 degrees which may be regarded as a vgp an u pb age of 1722 12 ma of baddeleyite from the khmelnik dyke which yields a well defined vgp is similar to the age of nearby anorthosite complexes a new 1740 1770 ma key pole for the ukranian shield is also presented plat 26 5 degrees plon 169 1 degrees a 95 3 9 degrees on the basis of palaeomagnetic and geochronological data a 2060 1720 ma apparent polar wander for the ukrainian shield is defined this apparent polar wander is significantly different from that of fennoscandia during the same time interval and indicates that the two shields were not in their present relative positions at ca 1770 ma a scenario is here proposed where the ukrainian shield and sarmatia collided with fennoscandia at ca 1900 1800 ma and after that event at ca 1720 1660 ma it rotated approximately 43 degrees into its present position c 2010 elsevier b v all rights reserved less

fluid regime and ore formation in the tungsten yttrium deposits of kyzyltau mongolian altai evidence for fluid variability in tungsten tin ore systems abstract the kyzyltau ore field is located in the northern part of the mongolian altai mountains w y be mo mineralization occurs in veins and stockworks in granites felsic volcanics basaltic flows and conglomerates the main ore minerals in the veins are wolframite fluorite beryl and minor molybdenite inclusions in hydrothermal quartz fluorite and beryl from veins as well as in magmatic quartz in vein hosting granites of the ulaan uul buraat uul and tsunkheg deposits were investigated using microthermometry and laser raman spectroscopy pseudosecondary primary inclusions in the kyzyltau ore veins are predominantly liquid rich aqueous inclusions containing variable amounts of co 2 as the main gas component and showing n 2 ch 4 ratios 1 secondary inclusions contain no or only trace concentrations of gases as indicated by clathrate melting the t h values of pseudosecondary primary inclusions in veins are between 180 and 433 c fluid inclusion data indicate that phase separation processes leading to fluid immiscibility occurred in vuggy quartz ii and green fluorite ii in the ulaan uul and buraat uul ore veins phase separation pressures of 100 350 bars were estimated fluorite i from the kyzyltau ore field shows a strong enrichment of hree and a strong negative eu anomaly common for rare metal bearing ore systems fluorite ii from buraat uul and tsunkheg is characterized by a change in the incorporation of rare earth elements ree with decreasing hree contents and a decreasing eu anomaly the ree distribution patterns in fluorite ii from ulaan uul remained unchanged compared with fluorite i despite a strong increase in the total ree content a review of the literature shows that from high temperature fe rich k dominated brines cassiterite ores can precipitate in quartz veins together with fe chlorite and fe tourmaline bolivian type if phase separation of a gas rich low salinity and fe rich fluid occurs cassiterite wolframite ores may be deposited cornwall devon type the deposits of kyzyltau are characterized by low fe alteration assemblages a predominance of sodium over potassium high contents of ree and y and a lack of extended tin mineralization despite the tin potential of the ore systems fluid inclusion data as well as geochemical and geological indications suggest formation of the tungsten deposits near the tops of li f rich sub volcanic intrusions we interpret the ph of the mineralizing fluid to be the main factor controlling wolframite precipitation in the kyzyltau ore field fluid wall rock interactions a lowering of the temperature and unmixing processes in the ore fluid generated contributions to neutralization and buffering of the acid co 2 bearing fluid into a ph range where tungstates were precipitated it can be inferred that formation of tungsten ores without precipitation of extended tin mineralization is possible in deposits characterized by high potential tin and tungsten according to this inference tin mineralization may be found in a more favourable setting in the vicinity of the kyzyltau deposits

geological and shrimp ii u pb constraints on the age and origin of the breves cu au w bi sn deposit carajas brazil the breves deposit in the carajas copper gold belt brazil a member of the cu au w bi sn group of deposits contains about 50 mt of 1 22 cu 0 75 g t au 2 4 g t ag 1 200 g t w 70 g t sn 175 g t mo and 75 g t bi it is hosted by sandstones and siltstones of the aguas claras formation minimum age of 2 681 5 ma in the roof zone of a complex highly altered granite intrusion the mineralisation is disseminated in a greisenized zone resulting from alteration of probable monzogranites and syenogranites the ore bearing greisen contains abundant xenomorphic quartz in association with fe chlorite and muscovite the gangue assemblage also includes fluorite tourmaline and minor amounts of monazite xenotime chlorapatite thorite zircon calcite siderite and bastnaesite copper mineralisation is dominated by chalcopyrite associated with pyrite arsenopyrite pyrrhotite and molybdenite gold particles in equilibrium with native bismuth are common as inclusions in chalcopyrite the greisen contains sub economic concentrations of tungsten and niobium that are related to the presence of ferberite qitianlingite and nb rutile shrimp ii zircon dating of the host granites gives 207pb 206pb ages of 1 878 8 and 1 880 9 ma for two phases and a combined age of 1 879 6 ma shrimp ii dating of monazite and xenotime grains in late to post mineralisation veins gives a combined 207pb 206pb age of 1 872 7 ma indistinguishable from the ages of the granites this provides a genetic connection between the breves deposit and the ca 1 88 ga a type granite magmatism that typifies the carajas belt as part of a much larger intracratonic magmatic province that extends over much of the amazonian craton the recognition of this association has exploration implications not only for the geophysical signature of the granite roof zones but also for likely geochemical dispersion around the deposits of this type

lead mobilization during foreland metamorphism in orogenic belts examples from northern sweden the imbrication of the proterozoic basement during the caledonian orogeny was associated with fluid flow which caused locally low grade retrograde metamorphism of the basement and which introduced externally derived radiogenic lead 206pb 204pb 20 0 into permeable zones this radiogenic lead was leached from the proterozoic basement to the east of the present day caledonian front radiogenic lead is a pertinent geochemical tracer of the caledonian imbrication of the proterozoic basement since lithostratigraphic marker beds are absent and the distribution of the retrograde metamorphism also could reflect a proterozoic event

emplacement related microstructures in the margin of a deformed pluton the san jose tonalite baja california mexico abstract in the san jose tonalite pluton baja california mexico interior magmatic fabrics give way progressively to subparallel solid state fabrics with s c structures near the margins the outer rim marginal northern unit approximately 1 km thick is inferred to have been deformed during the emplacement of the inner parts of the magma chamber the rocks show a transition from strongly deformed at the outer edge to progressively less deformed towards the inner edge of the marginal northern unit a small amount of melt appears to have been present during the deformation as indicated by 1 apparent contact melting between some grains of plagioclase and 2 coarse grained aggregates and single grains of quartz k feldspar and or more sodic plagioclase in fracture controlled openings in primary plagioclase crystals the more sodic plagioclase typically grew as rims on the walls of the openings in twin continuity with the primary plagioclase the deformed rocks have a prominent foliation marked mainly by aggregates of biotite with contributions by hornblende and titanite grains as well as apparently recrystallized aggregates of quartz and or feldspar at least some of which may have originated as zones of fragmentation many primary grains of plagioclase hornblende biotite and titanite show evidence of brittle deformation and fragmentation the shapes of aggregates in the folia relationships between incipient folia and residual primary grains and occurrences of many folia in narrow zones transecting strong minerals plagioclase and hornblende suggest that brittle processes may have controlled at least some of the foliation development however evidence of strain induced grain boundary migration and bulge nucleation of new grains of quartz and plagioclase indicates that dislocation creep also played a part in the deformation recrystallization of plagioclase together with intrusion of the pluton at greenschist facies ambient temperatures confirms high temperature deformation with heat derived from the cooling magma

evolution and paragenetic context of low δd hydrothermal fluids from the panasqueira w sn deposit portugal new evidence from microthermometric stable isotope noble gas and halogen analyses of primary fluid inclusions abstract the evolution paragenetic context and origin of remarkably low d hydrothermal fluids from the hercynian panasqueira w sn cu ag deposit have been investigated through a combined microthermometric stable isotope halogen and noble gas fluid inclusion study large variations in d between 60 and 134 have been observed in primary fluid inclusions from growth zones in a quartz crystal pa66 paragenetically constrained to the main sulfide stage mss of ore formation the same fluids exhibited relatively constant fluid inclusion homogenisation temperatures 254 to 260 c salinities 7 4 to 8 7 wt nacl equivalent and calculated fluid 18o 3 8 to 4 4 all the fluids exhibited 40ar excesses mean molar br cl and i cl ratios varied from 2 3 10 3 4 2 10 3 and 8 10 4 10 10 4 respectively with the more br rich fluids being associated with the more deuterium depleted fluids the low palaeolatitude of panasqueira throughout the main stages of ore formation and the overwhelming predominance of meteoric fluids in the main late and post ore mineralising fluids with d of 40 to 65 lends little support for any models involving low d palaeometeoric water the limited range of 40ar cl ratios 1 1 10 5 1 6 10 5 also precludes boiling during the mss or mixing of meteoric water with highly fractionated deuterium depleted magmatic waters as viable mechanisms for producing the low d fluids the high br cl and i cl of the mss fluids indicate significant fluid interactions with organic rich sediments or metasediments in particular regionally abundant carboniferous coals or coaly sediments that are inferred to be depleted in deuterium by around 85 compared to palaeometeoric water the large range of d observed in the mss fluids may be explained by isotopic exchange of palaeometeoric water with these coals at varying water rock wt wt ratios between 0 02 and 0 002 with fluid oxygen isotopic compositions controlled by exchange with the beira schists such a model is consistent with the requirements that any satisfactory model must take into account viz i the relative constancy of temperature salinity 40ar and fluid 18o during excursions to low d ii the high i cl and br cl ratios observed and iii the coincidence of these low d fluids with the onset of precipitation of polymetallic sulfides and phosphates under reducing conditions the model indicates that meta sedimentary sources of ore forming components became increasingly important during the evolution of the panasqueira sn w deposit and accounts in part for the observed progression from oxide dominated to base metal sulfide dominated parageneses

origin and evolution of w mo producing fluids in a granitic hydrothermal system geochemical studies of quartz vein deposits around the susan granite hwanggangri district republic of korea the hwanggangri mineralized district is located approximately 130 km southeast of seoul within the paleozoic ogcheon belt of south korea the jungbo suri and deogman mines in the district occur around the late cretaceous whole rock k ar age 89 0 or 2 0 ma susan granite and are located on w mo bearing quartz veins these veins fill fractures in the granite and its host rocks which comprise early paleozoic limestone rich sedimentary rocks the k ar date of vein muscovite 88 58 or 1 95 ma is very similar to that of the susan granite 89 04 or 1 95 ma indicating that w mo mineralization was associated with intrusion of the granite molybdenite and wolframite rich deposits occur within or near 285 degrees c from h 2 o co 2 fluids with salinities of 0 4 to 9 7 wt percent nacl equiv probably in response to ph increase due to boiling including co 2 unmixing of the hydrothermal fluid at pressures between 150 and 220 bars following w mo deposition the high temperature fluids gave way to progressively cooler more dilute fluids associated with scheelite base metal sulfide deposition 200 degrees 320 degrees c 0 7 7 2 wt nacl equiv and carbonate fluorite deposition 105 degrees 225 degrees c 0 0 3 2 wt nacl equiv these trends are interpreted as the result of progressive mixing of magmatic fluids with cooler more dilute meteoric waters there is a systematic decrease in the measured and calculated isotopic compositions of hydrothermal waters with increasing paragenetic time and decreasing temperature stage i delta 18 o water 8 0 to 1 5 per mil and delta d water 56 to 74 per mil stage ii delta 18 o water 1 9 to 5 6 per mil and delta d water 88 to 95 per mil stage iii delta 18 o water 0 9 to 3 0 per mil and delta d water 93 to 97 per mil the trend reflects the progressive increase of meteoric water involvement in the mineralizing system during the cooling history of the susan granite stock molybdenum and tungsten were partitioned preferentially into a coexisting magmatic hydrothermal fluid delta 18 o 8ppm delta d 56 to 72ppm sulfur isotope analyses of hydrothermal sulfide minerals suggest an igneous source of sulfur with a delta 34 s sub sigma s value near 4 per mil following deposition of molybdenite and wolframite from magmatic fluids wolframite was dissolved or replaced by scheelite in the outer and or shallower portions of the hydrothermal system this remobilization of tungsten and later redeposition as scheelite at temperatures of 200 degrees 280 degrees c from fluids with delta 18 o 1 2ppm accompanied mixing with low temperature meteoric fluids increasing involvement of progressively larger volumes of meteoric water resulted in successive deposition of base metal sulfides fluorite and carbonates

antimony quartz and antimony gold quartz veins from northern portugal abstract antimony and pb sb quartz veins from the braganca district portugal are mainly hosted by silurian phyllites antimony au quartz veins from the durico beira region are mainly hosted by a cambrian schist metagraywacke complex as well as ordovician phyllites and quartzites the deposits were mostly exploited in the late 19th century mineralogical characteristics and chemical compositions of individual ore minerals are similar in the two areas first and second generations of arsenopyrite precipitated at 390 and 300 c respectively berthierite and stibnite are the most abundant sb bearing minerals and precipitated between 225 and 128 c native antimony at

structure and composition of the precambrian crust along the polar profile in the northern baltic shield abstract along the 500 km long polar profile the continental crust of the northern baltic shield consists of several archaean and early proterozoic crustal segments in the south in the karelian province the upper crust consists of a 3 1 2 6 ga old archaean substratum with a 0 6 km thick low to medium grade volcanosedimentary cover here shallow basin facies rocks of the central lapland complex have been thrust northwards onto the karasjok kittila greenstone belt the repeatedly folded cover rocks form linear troughs between domes and culminations of granitoids the 47 48 km thick crust of the karelian province is of a shield type it is characterised by a low velocity layer interpreted as a horizon of decollement below the supracrustal and granitoid rocks in the lapland granulite belt early proterozoic high grade metapelites and metapsammites with minor metaigneous intercalations have been thrust to the southwest they are separated from the underlying karelian province by the tectonic mixture zone of the tanaelv belt in the interpretations two alternative models are given for the shape of the lapland granulite belt it is either a synformal nappe or a ne dipping body pinching out at depth and overthrust from the north by the archaean inari terrain both the lapland granulite belt and the inari terrain have a 42 44 km thick crust with a relatively thin lower crust marked by lower seismic velocities the early proterozoic polmak pasvik pechenga belt separates the archaean inari terrain from the archaean sorvaranger terrain in the north this belt is interpreted as a suture zone which continues to depth it may either dip steeply towards irregularities in the moho or form a sw dipping low angle plane below the lapland granulite belt the northernmost part of the baltic shield is concealed beneath a 0 7 km thick very low grade metamorphic late proterozoic cover this cover is divided into two parts by the trollfjord komagelv strike slip fault here the crust is again of a normal shield type with a thickness of 42 46 km

petrology of nattanen type granite complexes northern finland abstract the nattanen type granites form a group of post tectonic and post metamorphic 1 77 ga old epizonal multiple granite intrusions in the granulite belt granitic gneiss surroundings in northern finland the granite complexes the tepasto pomovaara and nattanen stocks and the riestovaara batholith in finland and the juvoaivi stock in the u s s r are composed of various slightly peraluminous microcline plagioclasebiotite granites monzogranites that contain sphene and magnetite as typical minor constituents geochemical evolution within the complexes is demonstrated by the increase of sio2 and rb and decrease of tio2 feo mgo cao sr ba and zr from the oldest to the youngest granite varieties molybdenum mineralization is associated with the latest intrusive phases of the tepasto and juvoaivi stocks the isotope geochemical studies indicate a major archaean crustal component in the source of the nattanen stock that is situated within the early proterozoic granulite belt

palaeomagnetic study of palaeoproterozoic granitoids from the voronezh massif russia a palaeomagnetic investigation has been carried out of rocks from the eastern part of the voronezh massif which constitutes together with the ukrainian shield the sarmatian segment in the southern part of the east european craton the samples were collected in a quarry close to the town of pavlovsk 50 4 n 40 1 e where a syenitic granitic body intrudes archaean units u pb zircon dating has yielded an age of 2080 ma for the intrusion two characteristic magnetic components a and b were isolated by thermal and alternating field demagnetization component a was obtained from granites and quartz syenites 11 samples and has a mean direction of d 229 i 28 and a pole position at 12 n 172 e this pole is close to a contemporary mean pole 9 n 187 e for the ukrainian shield which implies that the voronezh massif and the shield constituted a single entity at 2 06 ga these poles differ from contemporaneous poles of the fennoscandian shield indicating that the relative positions of the two shields were different from their present configuration about 2100 myr ago a component b isolated only in quartz monzonites five samples has a mean direction d 144 i 49 and a pole position at 4 n 251 e which is close to late sveconorwegian approximately 900 ma poles for baltica this suggests that the east european craton was consolidated some time between 2080 and 900 ma comparison with other palaeomagnetic data permit us to narrow this time span to 1770 1340 ma

tin granites geochemical heritage magmatic differentiation metallogenic provinces are not self evident geochemical provinces a scheme to quantify the processes of geochemical heritage and magmatic differentiation in the evolution of tin granites is presented geochemical heritage can be limited to a maximum contribution in the 5 10 ppm sn range the crucial process in the formation of tin granites is magmatic differentiation a variable bulk sn distribution coefficient controls the tin ore potential of granites

pressure fluctuation during uplift of the northern apennines italy a fluid inclusions study abstract p t conditions existing after the main syn collision tectonic phase in the western part of the northern apenninic chain italy e g in the tuscan nappe outcropping in the la spezia area were estimated on the basis of a detailed microstructural structural petrographic and fluid inclusion study of quartz of syn tectonic d2 veins developed in the tertiary flysch at the top of the tuscan nappe macigno formation three main fluid events have been distinguished as follows during retrograde metamorphism d1 to d2 phase fluids in equilibrium with turbidites from the tuscan nappe were h2o ch4 mixtures issued from water organic matter interactions in temperatures conditions that may have reached at least 260 c or more 280 c depending on the considered depth estimates and maximum pressures around 210 250 mpa evidence of strong fluid pressure fluctuation between lithostatic and hydrostatic within the metamorphic formations up to 100 150 mpa possibly linked to fault valve activity at the beginning of the uplift triggered phase separation of the water methane fluids and production of methane rich and water rich fluids fluctuations in pressure during these events played a crucial role in quartz crystallization especially in extensional fissures formed perpendicular to the d2 folds axial foliation changes in the fluid regime and sources with time are evidenced by the input of brines which mix to distinct degrees and are trapped in healing microfissures during retrograde fluid evolution such mixing processes are an indication of the connection between separate fluid reservoirs with different temperature conditions consequently mass and heat transfer have to be taken into account as the downward percolation of cooler fluids probably accelerated the rate of cooling of the exhumed formations these processes are certainly common to most orogenic terrains and can be quantitatively studied through p v t x reconstruction using fluid inclusion data on the drainage zones where the mixing processes occurred this work confirms that fluid inclusion studies can provide accurate quantitative estimates of fluid pressure variations during the evolution of orogenic terrains and could therefore constitute a useful tool in tectonic interpretations at the light of the models developed for pressure variations in the upper crust

characterization and timing of the different types of fluids present in the barren and ore veins of the w sn deposit of panasqueira central portugal the panasqueira w sn deposit is the largest quartz vein type deposit of the iberian peninsula and the most important wolframite deposit in western europe the ore veins are almost exclusively sub horizontal besides ore bearing sub horizontal veins the panasqueira mine also contains barren quartz veins there are essentially two generations of barren quartz quartz contemporaneous with the earliest regional metamorphism qi and recrystallized quartz contemporaneous with the thermal metamorphism related to the granite intrusion qii fluid inclusion studies microthermometry and raman were undertaken in order to distinguish fluids contemporaneous with the barren quartz from those contemporaneous with the ore bearing quartz qiii fluid inclusion data indicate that the barren and ore bearing quartz fluids are dominantly aqueous 93 to 98 mol h2o with a nearly constant bulk salinity 8 to 12 wt eq nacl with the quantity of volatile component determined by raman spectrometry higher in qiii but never greater than 5 mol however the co2 ch4 n2 ratio is different for each type of quartz volatiles are dominated by ch4 10 to 96 mol zch4 and or n2 3 to 87 mol zn2 in the barren quartz and by co2 60 to 73 mol zco2 in ore bearing quartz the bulk chemical composition of the fluids in qiii is comparable to that found commonly in hydrothermal fluids associated with wolframite mineralization where na k ca and hco3 cl so4 a dispersion in th 226 to 350 c found in qiii together with a variation in the degree of filling 0 5 to 0 7 and with the consequent variation of fluid densities 0 70 to 0 79 may result from changes in the fluid pressure regime below lithostatic pressure suggesting vein filling related to tectonic events

crustal evolution of fennoscandia palaeomagnetic constraints abstract palaeomagnetic poles from fennoscandia ranging in age from archaean to tertiary are compiled and graded using a modified briden duff classification scale an new filtering technique is applied to select only the most reliable poles for analysis the filtering takes into account the following information 1 1 source block of rock unit 2 2 age of rock 3 3 age of magnetization component 4 4 scatter of palaeomagnetic directions 5 5 information from multicomponent analysis of natural remanent magnetization nrm 6 6 whether the pole considered belongs to a cluster or subcluster of poles 7 7 magnetic polarity and 8 8 the author s original assignment of results data are still insufficient for the drawing of separate apparent polar wander paths apwp for different blocks or cratons of fennoscandia treating fennoscandia as a single plate a new apwp from archaean to permian is constructed from the five previously drawn apwp loops or hairpins only one the jatulian loop 2200 2000 ma disappears in filtering the loops during 1925 1700 ma and during 1100 800 ma ago are linked to svecofennian and sveconorwegian orogenies respectively palaeomagnetic data support the concept that these orogenies took place episodically three distinct orogenic pulses early middle and late can be distinguished in the cluster plots of palaeopoles the drift history of fennoscandia from archaean to permian is presented during most of geological history fennoscandia has occupied low to moderate latitudes and undergone considerable latitudinal shifts and rotations the svecofennian and sveconorwegian orogenies have different kinematic characteristics during the svecofennian orogeny fennoscandia drifted slowly while rotating a large amount in an anticlockwise sense during the sveconorwegian orogeny it drifted rapidly and rotated first clockwise and then anticlockwise the most striking feature in the drift velocity curves is however the pronounced maxima in the latitudinal drift and rotation rates 9 cm yr and 0 8 ma respectively during the late subjotnian jotnian anorogenic magmatism and rifting phase 1450 1250 ma ago possibly reflecting the passage of fennoscandia across a thermal upwelling hotspot at equatorial latitudes the use of palaeomagnetism in delineating and dating movements between blocks is demonstrated with three examples from the polar profile area the northernmost section of the european geotraverse

arsenopyrite compositional variation over variable temperatures of mineralization otago schist new zealand compositions of arsenopyrite coexisting with pyrite from eight different mesothermal gold bearing systems in the otago schist fall mainly into a narrow band of 30 or 1 at percent as intragrain and intergrain compositional variations combined with analytical uncertainty preclude resolution of differences in arsenopyrite compositions between samples of less than 1 at percent as only one of the vein systems has an arsenopyrite compositional range that extends below 28 at percent as arsenopyrite from a pyrrhotite bearing assemblage has compositional range extending above 32 at percent as the vein systems have formed over a wide range of temperatures between about 200 degrees and 400 degrees c it is not possible to resolve the influence of temperature on arsenopyrite compositions for most samples sulfur and oxygen activity of the hydrothermal fluid may be responsible for the low degree of arsenopyrite compositional variation

mantle derived and crustal he and ar in the ore forming fluids of the xihuashan granite associated tungsten ore deposit south china abstract the xihuashan tungsten ore deposit in the central nanling region south china is a vein type hydrothermal deposit associated with the late jurassic granitoids that were previously thought to be the products of crustal anatexis alone in this study we use helium he and argon ar isotopes of fluid inclusions entrapped in pyrite and arsenopyrite to determine the origin of the ore forming fluids the 3he 4he ratios of the crushed fluid inclusions vary from 0 15 to 1 16 ra with a mean of 0 72 ra ra the atmospheric 3he 4he ratio of 1 4 10 6 indicating the presence of mantle derived noble gasses in the fluids the amounts of the mantle derived noble gasses are estimated to be between 2 and 17 the 40ar 36ar ratios of the fluid inclusions vary from 306 to 1023 with an average of 440 these ratios are significantly higher than the average crustal value indicating the presence of air saturated water in the volatiles released from the mineral separates the results from this study indicate that the associated coeval granitoids which is believed to provide the ore forming fluids during magma evolution are not the products of pure crustal melts mantle derived volatiles and heat was also involved in the genesis of the host granite pluton

fractal analysis of sn w mineralization from central iberia insights into the role of fracture connectivity in the formation of an ore deposit sampling of late hercynian quartz veins from central iberia has demonstrated a power law distribution of vein thickness which changes systematically from unmineralized to mineralized sites these changes are related to the connectivity of the underlying vein networks and hence their potential role in sn w mineralizing processes simple percolation models are used to explain these changes thus the analysis of vein thickness distribution provides an additional guide to prospecting in vein systems

in situ raman spectroscopic investigation of the hydrothermal speciation of tungsten implications for the ore forming process abstract knowledge on hydrothermal tungsten w species is vital towards a better understanding of tungsten transport and mineralization mechanisms in this study in situ raman spectra of a 0 005 0 1 mol kg m k2wo4 solution containing co2 hcl and nahco3 were collected at 50 400 c and 20 60 mpa the spectra for the symmetric stretching vibration mode of the w o bond v1 w o were analyzed to investigate the hydrothermal tungstate species results showed that carbonate bicarbonate do not associate with tungstate to form carbonic tungstate species nevertheless the presence of co2 can increase the fluid acidity which favors the formation of polymeric tungstate species at o modes of these species are centered at 930 cm 1 and 950 cm 1 based on the above observations we simulated the mineralization process in the context of fluid rock interactions using tungstate and alkali tungstate ion pairs as the only aqueous w species the thermodynamic simulations showed that a the timing of mineralization mainly depends on the w concentration in the initial mineralizing fluid and the availability of ca2 fe2 and mn2 with higher w concentrations generally favoring higher temperature mineralization b highly w enriched fluid is not essential for w mineralization while extremely low contents of fe mn and ca in the magma are useful to maintain the mobility of aqueous w until favorable host rocks are encountered and c a hydrogen reservoir effect was identified for dissolved co2 the presence of co2 can promote the extraction of fe ii from the pelitic host rocks thereby facilitating a high grade vein type w mineralization at o modes are centered at 965 995 cm 1 are important hydrothermal w species along with monomeric tungstates therefore polymeric tungstate species should be considered in future thermodynamic modeling of w transport and mineralization at

geology geochronology and geochemistry of the miocene jiaoxi quartz vein type w deposit in the western part of the lhasa terrane tibet implications for ore genesis abstract the jiaoxi deposit is the first miocene quartz vein type w deposit discovered in the western part of the lhasa terrane comprising with 39 000 metric tons of wo3 the mineralization occurs in wolframite bearing hydrothermal tensional quartz veins and is associated with miocene granites the mineralization event can be divided into an early quartz oxide stage succeeded by a sulfide stage and a final fluorite carbonate stage magmatic intrusions at the deposit include biotite monzogranite porphyry biotite monzogranite granite porphyry and muscovite granite at depth and show crystallization ages ranging between 14 5 and 13 7 ma whole rock geochemistry shows that the intrusions are alkali rich peraluminous granites that experienced strong fractional crystallization the most evolved muscovite granite has high w nb and cs contents and is considered to be the source for mineralization during the late crystallization stage of the highly fractionated muscovite granite exsolved hydrothermal fluids interacted with the muscovite granite magma and migrated along extensional fractures forming the jiaoxi deposit zircon grains from the granites show uniform ehf t values with a wide range between 7 08 and 3 87 the granites have initial sr isotopic compositions ranging between 0 7094 and 0 7124 and negative end t values ranging between 4 9 and 9 4 the sr nd hf isotope data indicate that the granites were derived from partial melting of a crustal source with minor contributions from the lithospheric mantle the 3he 4he ratios for wolframite and pyrite vary between 0 30 and 0 74 ra ra 1 4 10 6 for air confirming that w was mainly sourced from the crust collectively the regional geology geochronology and geochemistry indicate that the miocene post collisional peraluminous granites and associated w mineralization were triggered by the roll back and gradual break off of the northward subducting indian continental lithosphere slab the less evolved biotite monzogranite porphyry which contains ore bearing veins and local greisen alteration appears to be unrelated to w mineralization

determination of domain structure in igneous rocks by alternating field and other methods abstract af alternating field demagnetization arm anhysteretic remanent magnetization and strong field hysteresis properties of a large collection of mostly continental igneous rocks are reported here the collection included rocks whose magnetic carriers were believed from previous work to be of one of three types md multidomain sd psd single domain pseudo single domain or a bimodal mixture of md grains e g discrete opaques and sd psd material e g silicate inclusions two series of subaerial basalts with a full range of deuteric oxidation classes included examples of all three classes of behaviour sd psd rocks have relatively hard inflected af decay curves decay rate initially increasing then decreasing md rocks have soft exponential like decay curves and bimodal rocks have a combination of these characteristics relative hardnesses of normalized decay curves of remanences acquired in weak intermediate and strong fields the lowrie fuller test are also distinctively different for the three classes and the results support the theory developed in an accompanying paper 1 that lowrie fuller characteristics are an expression of the shapes of decay curves the lowrie fuller test although its result can be expressed as a numerical parameter is not capable of fine scale classification of domain structure or grain size the shape of the arm induction curve does have a quasi continuous variation with grain size however the parameter ar j rs initial anhysteretic susceptibility normalized to saturation remanence which is easily measured with standard paleomagnetic instrumentation is potentially useful for magnetic granulometry although ar itself was not diagnostic of grain size

early paleoproterozoic archean dykes and gneisses in russian karelia of the fennoscandian shield new paleomagnetic isotope age and geochemical investigations abstract we present here new palaeomagnetic isotopic age and geochemical data from archean and early palaeoproterozoic rocks in the eastern fennoscandian shield we have studied ne sw trending gabbronorite dyke sets and their host archean basement rocks in the vodlozero block near the 2449 ma burakovka layered intrusion in southern russian karelia both dyke sets are genetically related to the burakovka intrusion the other ca 25 km long avdeev dyke locating a few kilometers south from the burakovka intrusion yields a stable single component remanence direction that is in agreement with the direction previously obtained from the burakovka intrusion another ne sw trending dyke 0 8 m wide shalskiy diabase dyke about 30 km south of the burakovka intrusion yields a similar remanence direction as the avdeev dyke the overall mean remanence direction has a palaeopole at plat 12 3 n plong 243 5 e a 95 15 4 4 sites 28 samples the thin shalskiy diabase dyke transects a similarly ne sw trending 500 m wide coarse grained gabbronorite dyke which has now been dated by sm nd method as 2608 56 ma geochemically all the dykes are quite similar showing slight calc alkaline affinity and low tio 2 and high sio 2 with moderate mgo and low cr and ni furthermore the dykes are geochemically identical to the 2 45 ga dyke swarm in the northern karelian province the remanence direction of the thin shalskiy diabase dyke differs significantly from the high temperature and high coercivity remanence component of the unbaked archean gabbronorite dyke which yields a palaeopole at plat 22 7 n plong 222 1 e dp 8 2 dm 16 2 five samples on the basis of different remanence directions of the diabase dyke and the unbaked archean gabbronorite dyke the baked contact test for the diabase dyke is positive in addition to the high temperature and high coercivity component of the baked and unbaked archean gabbronorite dyke in low temperatures and coercivities we isolated a similar component as in the diabase dyke a comparable remanence component was also obtained from the archean basement at ca 8 km from the dykes we propose that in the studied area the archean basement and the archaean dyke were partly remagnetized due to emplacement and subsequent uplift and cooling of the large burakovka layered intrusion and related dykes at about 2 40 ga ago this interpretation lends support from a new 40 ar 39 ar dating of hornblende from another area lake paajarvi area in northern karelia there a negative baked contact test was previously obtained for the remanence of the dated ca 2 45 ga dyke rocks related to the ca 2 45 ga oulanka layered intrusion the 40 ar 39 ar dating of the unbaked archean basement which yields the same remanence component as the dykes shows a plateau age of ca 2 6 ga but in addition it also shows resetting of the basement at ca 2 4 ga ago the dating thus supports reactivation and partial remagnetization of the archean basement at ca 2 4 ga ago our new palaeomagnetic results from the burakovka dykes and the new 40 ar 39 ar dating from the lake paajarvi area give support to our previous interpretation that at lake paajarvi area the remanence component suggested to be 2 4 ga despite to negative baked contact test is indeed of this age therefore it is implied that the results can be used for continental reconstructions

geochemistry of the adamello massif northern italy the tertiary adamello massif outcropping over an area of more than 550 km2 in the southern alps northern italy is composed mainly of granitoid rocks granodiorite tonalite quartz diorite with minor amounts of diorite and gabbro the major and trace element composition of these rocks is comparable to calc alkaline volcanic rocks of continental margins the granitoid rocks display spatial and temporal variations in their composition particularly in na p sr la nb and y contents and 87sr 86sr ratios the variations were probably produced by concurrent contamination wall rock assimilation and fractional crystallization of high alumina basaltic magma

extreme alkali bicarbonate and carbonate rich fluid inclusions in granite pegmatite from the precambrian ronne granite bornholm island denmark our study of fluid and melt inclusions in quartz and feldspar from granite pegmatite from the precambrian ronne granite bornholm island denmark revealed extremely alkali bicarbonate and carbonate rich inclusions the solid phases daughter crystals are mainly nahcolite nahco3 zabuyelite li2co3 and in rare cases potash k2co3 in addition to the volatile phases co2 and aqueous carbonate bicarbonate solution rare melt inclusions contain nahcolite dawsonite naal co3 oh 2 and muscovite in addition to fluid and melt inclusions there are primary co2 rich vapor inclusions which mostly contain small nahcolite crystals the identification of potash as a naturally occurring mineral would appear to be the first recorded instance from the appearance of high concentrations of these carbonates and bicarbonates we suggest that the mineral forming media were water and alkali carbonate rich silicate melts or highly concentrated fluids the coexistence of silicate melt inclusions with carbonate rich fluid and nahcolite rich vapor inclusions indicates a melt melt vapor equilibrium during the crystallization of the pegmatite these results are supported by the results of hydrothermal diamond anvil cell experiments in the pseudoternary system h2o nahco3 sio2 additionally we show that boundary layer effects were insignificant in the bornholm pegmatites and are not required for the origin of primary textures in compositionally simple pegmatites at least