late precambrian u pb ages for the brookville gneiss southern new brunswick tonalitic orthogneiss from the brookville gneiss in southern new brunswick has an igneous protolith age of 605 pm 3 ma based on u pb dating of zircon metamorphic titanite from the same sample gives a minimum age of 564 pm 6 ma for upper amphibolite facies metamorphism of the unit based on u pb analyses of single detrital zircons a maximum sedimentary protolith age of about 641 ma is suggested for associated paragneiss these ages indicate that the igneous protolith of the orthogneiss was at most 35 ma younger than the sedimentary rocks it intruded and that the brookville gneiss is younger than the green head group to which it was previously considered basement both orthogneiss and paragneiss in the brookville gneiss contain proterozoic and archean detrital zircon grains suggesting an old heterogeneous continental source we conclude that the brookville gneiss does not represent the basement to the avalon terrane

40ar 39ar whole rock phyllite ages from late precambrian rocks of the avalon composite terrane new brunswick evidence of silurian devonian thermal rejuvenation several variably deformed and metamorphosed late precambrian volcanic sedimentary successions have been recognized within the avalon composite terrane exposed in the caledonian highlands of southern new brunswick whole rock samples of metasedimentary phyllite and phyllitic metatuff from the oldest ca 600 635 ma avalonian succession display similar internally discordant 40ar 39ar age and apparent k ca spectra intermediate temperature gas fractions were experimentally evolved solely from very fine grained cleavage aligned white micas these yield apparent ages between ca 430 and 410 ma and are interpreted to closely date a static late silurian early devonian thermal rejuvenation evidence for a silurian devonian thermal event has not been previously documented in avalonian rocks of the caledonian highlands caledonia assemblage however a thermal overprint of similar age ca 400 ma is recorded by metamorphic muscovite in high grade gneisses and platformal metasedimentary rocks brookville a

history of stage 5 sea level in bermuda review with new evidence of a brief rise to present sea level during substage 5a abstract oxygen isotope substage 5e is represented by the devonshire formation in bermuda the occurrence of these coastal marine deposits to about 5 m indicates pleistocene sea level data in bermuda do not need tectonic corrections a few published u series coral dates suggest that a conglomerate spencer s point formation may have formed during substage 5c geologic mapping however indicates that the eolianite beneath the conglomerate is pre rather than post devonshire formation in age as was previously thought and the aminostratigraphy of marine sheels also confirms the correlation of the spencer s point and devonshire formations substages 5c and 5a are represented by the southampton formation large eolianites comprise the bulk of this formation they are onlapped by a few small younger marine 1 m and eolian deposits aminostratigraphy confirms that these late southampton age deposits are significantly younger than the devonshire formation and u series dates indicate a substage 5a age the setting of some of these deposits along a protected shoreline precludes discounting their position as anomalous due to large storms this evidence that sea level in bermuda was at about present datum late in substage 5a agrees with interpretations of neotyrrhenian deposits of mediterranean shorelines but not with inferences from the deep sea oxygen isotope record or with data from uplifted coral reefs

the late devensian 22 000 bp irish sea basin the sedimentary record of a collapsed ice sheet margin the late devensian 20 ka bp glacial geology of the irish sea basin 4000 km2 is an event stratigraphy recording the entry of marine waters into a glacio isostatically depressed basin and the rapid retreat of the irish sea glacier as a tidewater ice margin marine limits occur up to 140 m o d across much of the central basin the ice margin was uncoupled from its bed exposing a subglacially scoured topography to glaciomarine processes the irish sea glacier was a major drainage conduit of the last british ice sheet calving of the marine ice margin resulted in fast flow surging of ice streams recorded by drumlin fields around the northern basin margin and tunnel valleys rapid evacuation of the basin may have stranded large areas of dead ice in peripheral zones e g cheshire shropshire lowlands and initiated the collapse of the ice sheet thick wedges of ice contact glaciomarine sediments were deposited during ice retreat as morainal bank complexes by successive tidewater ice margins stabilized at pinning points around the irish sea coast where morainal banks occur on the seaward side of drumlin swarms there is a clear sequential relationship between rapid ice loss from calving ice margins the development of fast flowing ice streams drumlinization and the pumping of subglacial sediment to tidewater raised delta complexes are locally associated with marine limits along the high relief coastal margins of wales east central ireland and the lake district associated valley infill complexes record downslope resedimentation of heterogenous sediments into the marine environment during ice retreat co eval offshore deposits are represented by well stratified glaciomarine complexes that infill a subglacially scoured topography that shows networks of tunnel valleys glaciomarine mud drapes occur well to the south of the maximum limit of grounded ice in the basin e g north devon scilly islands southern ireland the age of these distal sediments previously mapped as pre devensian tills is constrained by amino acid ratios basin rebound following deglaciation was rapid with over 100 m recovery in 3 ka and was followed by a low marine still stand peat accumulating in offshore areas now as much as 55 m below sea level has been drowned by the postglacial eustatic rise in sea level the glacio sedimentary model identified in this paper involving rapid ice retreat and related sedimentation triggered by rising relative sea level suggests that isotatic downwarping is an important mechanism for deglaciating continental shelves

silurian orogenesis in the western penobscot bay region maine new 40ar 39ar mineral ages from rocks collected west of penobscot bay maine indicate this region was regionally deformed metamorphosed to amphibolite facies conditions and intruded by plutons in silurian times rather than in the devonian as previously assumed disturbed hornblende age spectra along with the presence of some devonian felsic plutons and extensive retrograde metamorphic textures do suggest however that these rocks were subsequently affected by low grade devonian thermal events in sharp contrast rocks west of the sennebec pond thrust fault a major tectono stratigraphic boundary in this region lack a significant silurian tectono thermal signature and instead record the effects of intense devonian deformation and high grade regional metamorphism the data suggest the two regions experienced very different pre devonian histories and were most likely juxtaposed by the sennebec pond thrust fault in latest silurian to early devonian time rocks now exposed east of the sennebec pond faul

a uranium thorium dated late eemian or early midlandian organic deposit from near kilfenora between spa and fenit co kerry ireland this paper discusses the dating of stratigraphically important quaternary sequences from a site near fenit co kerry which have been the subject of debate since they were first described by mitchell in 1970 the overall stratigraphy of the quaternary deposits have been investigated and detailed analyses of the organic material carried out pollen from biogenic sediments have been analysed and samples of peat dated using the uranium thorium disequilibrium method the pollen assemblages match no others previously recorded in ireland and appear to represent a cool temperate phase following the last interglacial the uranium thorium dates of between 114000 and 123000 yr bp indicate that the deposit dates from oxygen isotope stage 5 possibly post dating the last temperate stage the eemian stage interglacial oxygen isotope substage 5e the dating of this deposit and the realisation that it is not penultimate temperate stage gortian in age invalidates much recent speculation on the age of the gortian interglacial

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr

age of amphibolitic metamorphism in the ophiolitic unit of the morais allochthon portugal implications for early hercynian orogenesis in the iberian massif structurally lower portions of the allochthonous morais complex are comprised of an ophiolitic unit exposed in two contrasting structural units separated by a ductile thrust fault the lower unit is dominated by variably foliated amphibolite whereas the upper unit is largely comprised of metaperidotite and metagabbro most of the ophiolitic unit has recrystallized synkinematically under amphibolite facies metamorphic conditions c 500 c and 5 kbar amphiboles formed during this metamorphism are typically magnesio hornblende an amphibole concentrate from the lower structural unit records a 39 ar 40 ar plateau age of 397 3 4 ma an amphibole concentrate from the upper structural unit displays an internally discordant 39 ar 40 ar age spectrum corresponding to a total gas age of 431 1 27 3 ma gas fractions evolved from each amphibole concentrate at intermediate and high experimental temperatures are characterized by similar apparent k ca ratios and yield well defined 36 ar 40 ar v 39 ar 40 ar isotope correlations which result in similar ages of 384 2 5 2 and 392 4 7 3 ma these are considered to be more reliable than the plateau ages and are interpreted as dating the last cooling through those temperatures required for intracrystalline retention of argon within constituent amphibole grains the associated tectonothermal event represented a first stage of hercynian orogenesis in the iberian massif it was probably related to oceanic closure and associated obduction of granulitic eclogitic massifs which at present structurally overlie the ophiolitic unit

variations in os isotope ratios of pyrrhotite as a result of water rock and magma rock interaction constraints from virginia formation duluth complex contact zones abstract os isotope ratios in pyrrhotite bearing pelitic rocks of the 1 85 ga virginia formation are variable with perturbations linked to the emplacement of the 1 1 ga duluth complex pyrrhotite in footwall rocks of the contact aureole show evidence for a mixing event at 1 1 ga involving a low 187 os 188 os fluid however because rocks with perturbed pyrrhotite os isotope ratios occur 1 km or more from the duluth complex the fluid is unlikely to have been of magmatic origin fluid inclusions in layer parallel quartz veins provide evidence of the involvement of a boiling fluid at temperatures between 300 and 400 c analyses of fluid inclusions via la icp ms show that the fluids contain up to 1 7 wt na 1 1 wt k 4330 ppm fe 2275 ppm zn and 415 ppm mg the veins also contain pyrite or pyrrhotite plus minor amounts of chalcopyrite bornite pentlandite and sphalerite the re os isotopic ratios of pyrite from the veins indicate that they crystallized from low 187 os 188 os fluids 18 o values of vein quartz range from 7 7 to 9 5 consistent with an origin involving fluid with a relatively low 18 o value between 2 and 5 meteoric water with such a low 18 o value could have interacted with the igneous rocks of the complex and would have acquired os with a low 187 os 188 os ratio strongly serpentinized olivine rich rocks of the complex are commonly characterized by such low 18 o values and we propose that the fluid involved in serpentinization was also responsible for the perturbation of the os isotopic system recorded by pyrrhotite in the virginia formation two important observations are that only pyrrhotite bearing assemblages in the contact aureole show isotopic perturbation and that intervals showing os exchange are spatially restricted and not uniformly distributed os exchange and mixing has occurred only where temperatures were sufficient to convert pyrite to pyrrhotite and where time integrated water rock ratios in the aureole were high enough to provide a supply of os troctolitic and gabbroic rocks of the partridge river intrusion duluth complex are characterized by os isotope ratios that are indicative of variable degrees of crustal contamination os values of 0 543 xenoliths of carbonaceous and sulfidic pelitic rocks of the virginia formation found in the igneous rocks provide evidence that os was released by organic matter and pyrite in the sedimentary rocks and assimilated by mantle derived magma however residual pyrrhotite produced as a result of pyrite breakdown in the xenoliths is characterized by 187 os 188 os ratios that are much lower than anticipated and similar to those of pyrrhotite in the contact aureole the os exchange and addition shown by pyrrhotite in the xenoliths highlight an unusual cycle of re os liberation during devolatilization kerogen maturation and pyrite to pyrrhotite conversion processes that contribute to magma contamination followed by os uptake by pyrrhotite during back reaction involving magma and or fluid characterized by a relatively low 187 os 188 os ratio the extreme os uptake recorded by pyrrhotite in the xenoliths as well as the lesser degree of uptake recorded by pyrrhotite in the contact aureole is in line with the high os diffusivity in pyrrhotite experimentally determined by brenan et al 2000 our data confirm that os isotope ratios in pyrrhotite bearing rocks may be readily perturbed for this reason caution should be exercised in the interpretation of os isotope ratios in rocks where pyrrhotite may be the primary host of os

recent developments in element concentration and isotope ratio analysis of individual fluid inclusions by laser ablation single and multiple collector icp ms abstract laser ablation inductively coupled plasma mass spectrometry la icp ms has become a most powerful technique for the elemental analysis of individual polyphase inclusions completely enclosed in minerals be they solid or a solid liquid gas mixture at the time of measurement simultaneous accurate quantification of major to ultra trace element concentrations from li to u by well controlled ablation of the entire fluid or melt inclusion content and successful use of largely matrix independent external calibration protocols are unique features of this method this contribution reviews fluid inclusion fundamentals relevant for their bulk analysis by la icp ms and discusses key aspects of the analytical protocol emphasis is on figures of merit precision accuracy obtained from the analysis of individual inclusions and fluid inclusion assemblages and procedures and technical developments to improving data quality are elaborated a new equation for the calculation of detection limits for la icp ms analysis is presented which closely follows iupac conventions applications are reviewed with emphasis on the use of synthetic fluid inclusions in constraining metal solubility and distribution between co existing phases new data for natural bismuth fluid inclusions document the seamless transition to melt inclusion analysis by la icp ms thus highlighting the fact that the procedures presented here are generally applicable to the analysis of inclusions in complex host minerals isotope ratio analysis of individual fluid inclusions by multicollector icp ms mc icp ms is a recent development that requires fast transient signals to be accurately recorded by instrumentation designed for high precision static measurements of long lasting stable ion beams we address the general principles based on pb isotopes and review a first application to the bingham canyon porphyry cu au mo deposit a pilot study using about 50 synthetic fluid inclusions containing srm 987 sr and variable nacl ca and rb concentrations demonstrates that accurate 87 sr 86 sr isotope ratios can be obtained on an individual rb poor fluid inclusion at absolute 2 precisions of 0 0003 to 0 002 a residual trend in 87 sr 86 sr as a function of the rb sr abundance ratio in the fluid inclusions suggests that interference correction of 87 rb on mass 87 assuming identical mass bias coefficients for the two elements may be inaccurate however the offset can be accurately corrected for by regressing the data to zero 87 rb the versatility and detection power of la icp ms makes this technique the method of choice for solute abundance and isotope ratio analysis of individual fluid inclusions significant future progress can be achieved by improvements in ion production transmission and data recording efficiency and by further improving control on inclusion ablation by pulsed laser beams data quantification strategies may also have to be further refined to keep pace with instrumental progress and innovation

magma evolution and the formation of porphyry cu au ore fluids evidence from silicate and sulfide melt inclusions silicate and sulfide melt inclusions from the andesitic farallon negro volcanic complex in nw argentina were analyzed by laser ablation icpms to track the behavior of cu and au during magma evolution and to identify the processes in the source of fluids responsible for porphyry cu au mineralization at the 600 mt bajo de la alumbrera deposit the combination of silicate and sulfide melt inclusion data with previously published geological and geochemical information indicates that the source of ore metals and water was a mantle derived mafic magma that contained approximately 6 wt h2o and 200 ppm cu this magma and a rhyodacitic magma mixed in an upper crustal magma chamber feeding the volcanic systems and associated subvolcanic intrusions over 2 6 million years generation of the ore fluid from this magma occurred towards the end of this protracted evolution and probably involved six important steps 1 generation of a sulfide melt upon magma mixing in some parts of the magma chamber 2 partitioning of cu and au into the sulfide melt enrichment factor of 10 000 for cu leading to cu and au concentrations of several wt or ppm respectively 3 a change in the tectonic regime from local extension to compression at the end of protracted volcanism 4 intrusion of a dacitic magma stock from the upper part of the layered magma chamber 5 volatile exsolution and resorption of the sulfide melt from the lower and more mafic parts of the magma chamber generating a fluid with a cu au ratio equal to that of the precursor sulfide 6 focused fluid transport and precipitation of the two metals in the porphyry yielding an ore body containing au and cu in the proportions dictated by the magmatic fluid source the cu s ratio in the sulfide melt inclusions requires that approximately 4 000 ppm sulfur is extracted from the andesitic magma upon mixing this exceeds the solubility of sulfide or sulfate in either of the silicate melts and implies an additional source for s the extra sulfur could be added in the form of anhydrite phenocrysts present in the rhyodacitic magma it appears thus that unusually sulfur rich not cu rich magmas are the key to the formation of porphyry type ore deposits our observations imply that dacitic intrusions hosting the porphyry cu au mineralization are not representative of the magma from which the ore fluid exsolved the source of the ore fluid is the underlying more mafic magma and unaltered andesitic dikes emplaced immediately after ore formation are more likely to represent the magma from which the fluids were generated at alumbrera these andesitic dikes carry relicts of the sulfide melt as inclusions in amphibole sulfide inclusions in similar dykes of other less explored magmatic complexes may be used to predict the au cu ratio of potential ore forming fluids and the expected metal ratio in any undiscovered porphyry deposit

biostratigraphy of the last glacial period in europe the european early weichselian early wurmian is characterized by two long and relatively warm interstadials brorup and odderade which can be traced and correlated with certainty across large parts of europe the amersfoort interstadial described earlier from the netherlands has been included in the brorup and represents the older part of it both great interstadials were forested in north west central and southern europe in the north conifer forests prevailed giving way towards the south to deciduous forests the climatic gradient was distinctly steeper mainly due to southward displacement of the gulf stream the two great interstadials are synchronous with the isotopic stages 5a and 5c in the deep sea cores subsequent to eemian brorup and odderade and from within the context of a continuous series two additional and clearly delimited interstadials have been recorded in a new standard profile from oerel nw germany these are now described as the oerel and glinde interstadials they were not forested and belong to the early pleni weichselian the lower one oerel can probably be correlated with the 3rd weichselian wurmian interstadial in southern central europe ognon ii durnten samerberg 3 while the upper one glinde has so far no known counterpart for the younger pleni glacial it is assumed that there was a long phase during which it was not too cold the formation of humic layers during this phase took place at different times partly due to local edaphic factors so that the relevant 14c dates show a wide scatter the hengelo and denekamp interstadials represent only slight ameliorations which facilitated the formation of shrub tundra and can be recorded in certain regions only

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

the partitioning behavior of silver in a vapor brine rhyolite melt assemblage abstract the partitioning of silver in a sulfur free rhyolite melt vapor brine assemblage has been quantified at 800 c pressures of 100 and 140 mpa and f o 2 nno nickel nickel oxide silver solubility 2 in rhyolite increases 5 fold from 105 21 to 675 98 g g as pressure increases from 100 to 140 mpa nernst type partition coefficients d ag i j 2 describing the mass transfer of silver at 100 mpa between vapor and melt brine and melt and vapor and brine are 32 30 1151 238 and 0 026 0 004 respectively at 140 mpa values for d ag i j 2 for vapor and melt brine and melt and vapor and brine are 32 10 413 172 and 0 06 0 03 respectively apparent equilibrium constant values 2 describing the exchange of silver and sodium between vapor and melt k ag na v m at 100 and 140 mpa are 105 68 and 14 6 the average values 2 for silver and sodium exchange between brine and melt k ag na b m at 100 and 140 mpa are 313 288 and 65 12 these data indicate that the mass transfer of silver from rhyolite melt to an exsolved volatile phase s is enhanced at 100 mpa relative to 140 mpa suggesting that decompression increases the silver ore generative potential of an evolving silicate magma model calculations using the new data suggest that the evolution of low density aqueous fluid i e vapor may be responsible for the the silver tonnage of many porphyry type and perhaps epithermal type ore deposits for example halter et al halter w e pettke t and heinrich c a 2002 the origin of cu au ratios in porphyry type ore deposits science 296 1842 1844 used detailed silicate and sulfide melt inclusion and vapor and brine fluid inclusions analyses to estimate a melt volume on the order of 15 km3 to satisfy the copper budget at the bajo de la alumbrera copper gold silver ore deposit using their melt volume estimate with the data presented here model calculations for a 15 km3 felsic melt saturated with pyrrhotite and magnetite suggest that a low salinity magmatic vapor may scavenge on the order of 7 1012 g of silver from the melt this quantity of silver exceeds the discovered 2 109 g of ag at alumbrera calculated tonnages for numerous other deposits yield similar results the excess silver in the vapor remaining after porphyry formation is then available to precipitate at lower ptconditions in the stratigraphically higher epithermal environment these data suggest that silver and perhaps other ore metals in the porphyry epithermal continuum may be derived solely from the time integrated flux of dominantly low salinity vapor exsolved from a series of sequential magma batches

triassic 40ar 39ar ages from the sakaigawa unit kii peninsula japan implications for possible merger of the central asian orogenic belt with large scale tectonic systems of the east asian margin the 218 4 0 4 228 8 0 9 and 231 9 0 7 ma 40ar 39ar laser probe pseudo plateau ages 2 49 63 39ar release of very low grade meta pelitic whole rocks from the sakaigawa unit date high p t metamorphism we argue that this event occurred in a subduction accretion complex not along the east asian continental margin but on the pacific side of the proto japan superterrane proto japan was a permian magmatic arc presently dispersed in the japanese islands which also contained older subduction accretion complexes the arc system was fringing but not yet part of the eurasian continent the middle to late triassic high p t tectono metamorphic event was partly coeval with proto japan s collision with proto eurasia along the southward extension of the central asian orogenic belt causing the main metamorphism in the hida oki terrane it is possible that this system continued via the cathaysia block china to indochina the late permian to middle triassic indosinian event might stem from docking of pacific derived terranes with southeast asia s continental margin the concept of the proto japan superterrane implies that the qinling dabie sulu suture zone joined the central asian orogenic belt to the east of the north china craton and did not continue to japan as commonly assumed

investigations of the stillwater complex part v apatites as indicators of evolving fluid composition variations in the f cl and oh contents of apatite are not constrained by crystal chemical factors in contrast to micas and amphiboles and thus changes in the abundance of these components provide an indicator of halogen fugacity variations and insights into the degassing history of igneous rocks microprobe analysis of intercumulus apatites from the stillwater complex reveal that cl rich apatites typically containing 6 0 wt cl occur throughout the lower 1 3 of the complex excluding the basal series a change from cl rich to more f rich apatite occurs within olivine bearing zone i ob i of the banded series the host zone of the platiniferous j m reef although apatite compositions are somewhat variable above the j m reef more f rich apatites predominante and typically contain 1 2 wt f and 3 0 wt cl the most f rich apatites occur in the uppermost exposed cumulates pristine apatites from coeval sills and dikes from below the complex and from the basal series are similarly f rich in all apatites the cl and f contents are lower in rocks affected by later metamorphic fluids rare earth element ree concentrations in chlorapatites show a marked peak in the olivine rich rocks of the j m reef and contain up to 2 wt ce2o3 la2o3 the trend of first increasing then decreasing cl f ratios with stratigraphic height is modeled by a vapor driven zone refining process occurring within the cumulate pile causing cl enrichment in the interstitial melt accompanied by degassing at the top of the magma chamber causing overall loss of cl from the magma as crystallization proceeded the abrupt change from cl rich to more f rich apatites within ob i is interpreted as the result of a breakdown of the cl rich zone refining front and mixing with cl poor supernatant melt any high temperature fluids that exsolved and circulated through the lower 1 3 of the complex must have been enriched in cl and could have transported ree and trace metals

sources of metals in the porgera gold deposit papua new guinea evidence from alteration isotope and noble metal geochemistry the porgera gold deposit is spatially and temporally associated with the late miocene mafic alkalic epizonal porgera intrusive complex pic located in the highlands of papua new guinea png the highlands region marks the site of a tertiary age continent island arc collision zone located on the northeastern edge of the australasian craton the pic was emplaced within continental crust near the lagaip fault zone which represents an oligocene suture between the craton and volcano sedimentary rocks of the sepik terrane magmatism at porgera probably occurred in response to the late miocene elimination of an oceanic microplate and subsequent early pliocene collision between the craton margin and an arc system located on the bismarck sea plate gold mineralization occurred within 1 ma of the time of magmatism metasomatism accompanying early disseminated au mineralization in igneous host rocks resulted in additions of k rb mn s and co2 and depletions of fe mg ca na ba and sr rare earth and high field strength elements remained largely immobile pervasive development of illite k feldspar quartz carbonate alteration assemblages suggests alteration by mildly acidic 200 to 350 c fluids at high water rock ratios strontium and lead isotopic compositions of minerals from early base metal sulphide veins associated with k metasomatism and later quartz roscoelite veins carrying abundant free gold and tellurides are remarkably uniform e g 87sr86sr 0 70745 0 00044 n 10 207pb204pb 15 603 0 004 n 15 these compositions fall between those of unaltered igneous and sedimentary host rocks and specifically sedimentary rocks from the jurassic om formation which underlies the deposit igneous rocks 87sr86sr 0 7035 207pb204pb 15 560 om formation 87sr86sr t 0 7153 207pb204pb 15 636 it is therefore suggested that the hydrothermal fluids acquired their sr and pb isotopic signatures by interaction with or direct derivation from a plutonic root of the pic and host sedimentary rocks of the om formation it is likely that au was also derived from one or both of these two sources concentrations of au in unaltered igneous and sedimentary rocks from porgera 10 ppb au do not indicate that either lithology represents a significantly enriched protore although au and platinum group element pge abundances in the igneous rocks suggest a mild primary magmatic enrichment of au relative to the pge average au pt pd mantlenormalized 14 0 6 5 n 8 evidence that the porgera magmas were rich in volatiles permits speculation that au may have been concentrated in a magmatic fluid phase but alternative possibilities such as derivation of au by hydrothermal leaching of solidified igneous materials or sedimentary rocks cannot be excluded at this time

age estimates for the late quaternary high sea stands abstract a database of more than 300 published alpha counted uranium series ages has been compiled for coral reef terraces formed by late pleistocene high sea stands the database was screened to eliminate unreliable age estimates 230 th 232 th 5 and those without quoted without quoted errors and a distributed error frequency curve was produced this curve can be considered as a finite mixture model comprising k component normal distributions each with a weighting by using an expectation maximising algorithm the mean and standard deviation of the component distributions each corresponding to a high sea level event were estimated eight high sea stands with mean and standard deviations of 129 0 33 0 123 0 13 0 102 5 2 0 81 5 5 0 61 5 6 0 50 0 1 0 40 5 5 0 and 33 0 2 5 ka were resolved the standard deviations are generally larger than the values quoted for individual age estimates whilst this may be due to diagenetic effects especially for the older corals it is argued that in many cases geological evidence clearly indicates that the high stands are multiple events often not resolvable at sites with low rates of uplift the uranium series dated coral reef terrace chronology shows good agreement with independent chronologies derived for antarctic ice cores although the resolution for the latter is better agreement with orbitally tuned deep sea core records is also good but it is argued that isotope stage 5e is not a single event as recorded in the cores but a multiple event spanning some 12 ka the much earlier age for isotope stage 5e given by winograd et al 1988 is not supported by the coral reef data but further mass spectrometric uranium series dating is needed to permit better chronological resolution

synthetic fluid inclusions viii vapor saturated halite solubility in part of the system nacl cacl2 h2o with application to fluid inclusions from oceanic hydrothermal systems abstract halite solubility along part of the vapor saturated liquidus in the system nacl cacl 2 h 2 o has been determined using the synthetic fluid inclusion technique data allow the construction of liquidus isotherms for temperatures up to 500 c and bulk compositions containing 60 wt total salt and as much as 25 wt cacl 2 combined with previous data for the binary system nacl h 2 o and for the ternary system nacl cacl 2 h 2 o in the low salinity low temperature region a preliminary ternary phase diagram can be constructed that remains incomplete only in the cacl 2 rich region results are applied to the interpretation of saline fluid inclusions from quartz veins in oceanic metagabbros and can be applied to many other natural inclusions containing aqueous solutions with nacl and cacl 2 the dominant solutes microthermometric measurements at equilibrium of the melting temperature of ice tm ice and of the dissolution temperature of halite tm halite are sufficient to determine the bulk composition of the nacl cacl 2 h 2 o fluid

u pb geochronological constraints on the evolution of the aspy terrane cape breton island implications for relationships between aspy and bras d or terranes and ganderia in the canadian appalachians new u pb zircon ages from nine samples of igneous and sedimentary rocks in the aspy terrane cape breton island show that neoproterozoic rocks form a major part of the terrane and confirm that the terrane was affected by a major silurian devonian tectonothermal event a rhyolitic crystal tuff a leucotonalite pluton and a felsic sheet yield ages of 618 8 0 6 ma 619 7 0 9 ma and 573 5 2 7 ma respectively a metasedimentary unit contains zircon ranging in age from ca 546 to ca 1520 ma a diorite has an age of 428 6 1 9 ma and another diorite unit and a quartz porphyry also have probable late silurian ages a third diorite yields an age of 373 0 0 5 ma part of a widespread bimodal igneous event represented by both volcanic and plutonic rocks throughout the aspy region geochronological results and field relationships indicate that the neoproterozoic rocks are similar to those in the bras d9or terrane and form the basement to the ordovician silurian rocks in the aspy terrane and that the aspy terrane is probably correlative with rocks in the hermitage flexure of southern newfoundland where silurian metasedimentary and metavolcanic rocks lie unconformably on similar neoproterozoic rocks likely correlative rocks also occur in the kingston terrane of southern new brunswick the results of this study support the idea that the aspy kingston terrane is part of ganderia and that neoproterozoic rocks in the bras d9or terrane and correlative rocks in southwestern newfoundland and elsewhere represent exposed basement to ganderia in the canadian appalachians

a long late quaternary record from lake poukawa hawke s bay new zealand abstract the lake poukawa basin is a large co seismic depression located at 20 m above mean sea level in hawke s bay in eastern north island new zealand we present a detailed environmental history of the basin for the last c 60 ka based on analyses of the top 105 m of a 200 m core record dating control is provided by radiocarbon optically stimulated luminescence osl and u th disequilibrium ages the chronology is supported by nine tephras of inferred age including marker tephras kawakawa 22 590 230 yr bp at 18 25 m core datum tahuna c 35 43 ka at 33 1 m core datum and rotoehu 45 50 ka at 39 1 m core datum disagreements between some of the older tephra ages and the numerical ages from the osl and u th dating mean that more than one age model can be applied three major lithostratigraphic units are identified a basal calcareous silt with lignitic peats between 105 28 and 98 58 m of marine oxygen isotope stage mis 3 age an extended sequence of detrital shelly sands and silts between 98 58 and 8 m of mis 3 and 2 age and a holocene peat unit mis 1 from 8 to 0 m alternatively but less likely the basal unit may represent stage mis 5a and the detrital shelly sands would then contain an amalgam of mis 4 3 and 2 deposits we propose a notably moist phase represented by the peat which our numerical dating model places near the start of isotope stage 3 this suggests the existence of mild conditions during an interstadial in central new zealand at c 55 50 ka when a podocarp beech broadleaf forest of near interglacial affinity surrounded the basin the interstadial is marked by both lake and peat formation in the basin after 50 ka a thermal decline set in though the climate remained moist initially under these conditions the poukawa basin was rapidly infilled by alluvial fan deposits from the surrounding hills the floor of the basin was occupied by grasses and sedges responding to both the highly disturbed environment and swampy conditions in the basin after the deposition of the rotoehu ash effective precipitation declined markedly and woody shrubs expanded across the previously swampy basin floor the data suggest an apparent thermal decline of c 6 7 c for much of mis 2 and the latter half of mis 3 the holocene was marked by the establishment of fen and lake environments on the basin floor prior to human disturbance podocarp broadleaf forest surrounded the basin

subepithermal au pd mineralization associated with an alkalic porphyry cu au deposit mount milligan quesnel terrane british columbia canada at the mount milligan cu au porphyry deposit quesnel terrane british columbia canada barren and weakly mineralized late stage hydrothermal veins occur in volcanic rocks adjacent to zones of cu au porphyry mineralization and have overprinted the porphyry stage veins the earliest of the late stage hydrothermal veins are barren and consist of quartz pyrite carbonate chlorite tourmaline these veins are similar to transitional to late stage hydrothermal veins in other alkaline porphyry cu au deposits and we consider these to be the equivalent of transitional post porphyry pre epithermal quartz sericite pyrite veins in calc alkaline porphyry environments a later generation of volumetrically minor mineralized veins are composed of pyrite hg and as bearing quartz carbonate chlorite and contain early electrum arsenopyrite tetra hedrite tennantite platinum group element pge tellurides galena sphalerite barite and chalcopyrite as inclusions in pyrite and a later assemblage of electrum pge tellurides arsenides and antimonides galena sphalerite chalcopyrite and various au ag te bi minerals in annealed fractures and open space infillings in quartz and pyrite metal precipitation in these veins was temporally and spatially associated with the deposition and later recrystallization of pyrite primary fluid inclusions in quartz in the barren and weakly mineralized veins are two phase l v homogenize to liquid over a narrow range in t 170 270 c n 96 12 veins and show a wide range in salinity 4 2 wt nacl equiv to 28 7 wt cacl2 equiv when all samples are considered however individual veins show narrow ranges in salinity and homogenization temperature la icp ms analyses indicate that the fluids were highly enriched in as to 2 260 ppm sb to 230 ppm b to 5 400 ppm au 1 2 ppm and pd 0 5 1 ppm but depleted in cu 80 ppm compared to typical porphyry stage fluids metal ratios in the fluids overlap with bulk rock metal ratios in the mineralized veins the inclusions are interpreted to contain a contracted magmatic vapor produced by boiling that lost cu during the formation of porphyry stage veins at depth fluids show decreasing b as sb and increasing sr ca and salinity with time stable c o and h isotope analyses of vein minerals indicate that mixing of this magmatic fluid with meteoric water was not responsible for metal deposition rather metal precipitation was possibly the result of mixing of the magmatic derived fluid with a heated saline groundwater the precious and accessory metal mineralogy of the hydrothermal veins is similar to that found in low to intermediate sulfidation epithermal systems fluid inclusion microthermometry and chlorite thermometry constrain the approximate formation conditions of the veins between 200 and 1 500 bars and 240 and 280 c after the formation of the mineralized veins circulation of low salinity metal depleted fluids occurred these latest stage fluids may have formed by mixing of the saline magmatic fluid groundwater hybrid with meteoric water the results of this study suggest a genetic link between porphyry stage events and the deposition of au and pge in late stage veins in an alkalic igneous environment recognition of hydrothermal processes involving the transport of au pge as sb bi te b rich fluids in the subepithermal regimes implies that low sulfidation epithermal au deposits may have been present in the shallower parts of the magmatic hydrothermal complex and that there is potential for the discovery of pge rich epithermal veins in less deeply exhumed terranes on the other hand the formation of high grade low sulfidation epithermal au pge deposits may be prohibited if porphyry epithermal transitional fluids precipitate ore metals through mixing with groundwater prior to reaching the level where meteoric water mixing and epithermal boiling normally occur

contemporaneous formation of adjacent porphyry and epithermal cu au deposits over 300 ka in northern luzon philippines there is commonly a close spatial relation between porphyry cu au and high sulfidation epithermal cu au deposits throughout the world although a genetic association has not been proven nowhere is this spatial association better seen than in northern luzon philippines where the lepanto epithermal cu au deposit overlies the far southeast fse porphyry cu au deposit both world class orebodies fresh rock and hydrothermal mineral separates yield k ar ages indicating that premineralization and postmineralization volcanism occurred at 2 2 1 8 ma and 1 2 0 9 ma respectively and that the hydrothermal system was active from 1 5 to 1 2 ma k ar ages of alunite from lepanto have the same range as those of hydrothermal biotite and illite from the fse deposit indicating that both epithermal and porphyry mineralization formed from an evolving magmatic hydrothermal system that was active for about 300 ka this temporal relation strengthens the argument for a genetic link between these two styles of ore deposit and has implications for exploration where one style of mineralization is found there is potential for the other nearby

the glass transition in hydrous granitic melts abstract the influence of water on the glass transition temperature of hydrous granitic melts is estimated on the basis of a variety of available sources of data that provide phenomenological data for the liquid glass transition and for which the relaxation timescale can be accurately estimated these sources include a dilatometric micropenetration viscosity determinations b temperature dependent spectroscopic investigations of hydrous melts and c densities of synthetic fluid inclusions in glasses all available evidence on the glass transition temperature of hydrous granitic melts when corrected for equivalent timescales yields a single consistent trend of decreasing tg with increasing water content that has powerful applications in the rheology and kinetics of processes involving late stage silicic intrusives and eruptive products the brittle ductile transition in hydrous silicic liquids can be accurately predicted using this trend combination of the presently derived relationship for the influence of water on the glass transition of granitic melts with presently available data for the high temperature viscosities of such systems permits the estimation of the temperature dependence of the viscosity of hydrous melts over the entire range of temperature relevant to granite petrogenesis such a comparison reveals that the viscosity temperature relationships of hydrous granitic melts are not arrhenian as is assumed by most existing calculational schemes for the prediction of hydrous melt viscosities the increasing deviation of viscosity temperature relationships of hydrous granitic melts from arrhenian with increasing water content is broadly consistent with similar trends accompanying the addition of excess alkalies to metaluminous granitic melt base compositions in detail however the influence of water on the deviation of viscosity temperature relationships of hydrous granitic melts from arrhenian is not as strong as would be predicted from a molar comparison of the effects of h2o vs alkali oxide or alkaline earth oxide added to these melts the answer to this apparent discrepancy may lie in the incomplete dissociation of water in the melt structure

compaction of density stratified cumulates effect on trapped liquid distribution igneous rocks formed by the accumulation of crystals from a cooling magma body compose a significant fraction of both the terrestrial oceanic crust and the lunar crust and mantle here we report the results of numerical simulations of compaction of accumulating crystals for which the bulk density is not constant the simulations are designed to provide insight into the behavior of interstitial liquid during compaction when a sharp drop in the density of the cumulus minerals is encountered e g at the ultramafic mafic boundary in a layered intrusion the simulations provide an explanation for trapped liquid distributions associated with sharp mineral density transitions density transition in the mineral assemblage is a feature common to many layered intrusions and the oceanic crust this process does not require external mechanisms such as injections of new and different magmas and has important implications for the formation of pt ores found at ultramafic mafic transitions the model also has implic

metal redistribution during fluid exsolution and migration in the middle banded series of the stillwater complex montana abstract olivine bearing zones iii and iv ob iii and iv of the stillwater complex mt preserve evidence of fluid migration particularly in the variation of apatite compositions this feature coupled with the lack of evidence of the addition of substantial amounts of primitive magma allows these zones to be used to test the importance of volatile fluids in redistributing metals the concentrations of cu au ag and as all show marked increases at and or below the levels inferred to represent the top of the fluid migration front in the crystal pile however no significant sulfide enrichment is associated with the maximum metal enrichments the au concentration peak is much sharper and offset stratigraphically above that of cu and corresponds with the maximum cl content of interstitial apatite these concentration profiles are modeled numerically assuming fluid transport and chromatographic concentration of the metals mass balance calculations indicate that cumulates significantly below the level of the inferred fluid saturation front lost cu while those at or immediately below gained cu we conclude that cl rich fluids redistributed the background metal concentrations although no dramatic enrichments are observed enrichment factors range from two to three the results demonstrate the potential importance of fluids in redistributing and concentrating metals in layered intrusions

porphyry epithermal transition maricunga belt northern chile the refugio aldebaran and la pepa districts in the maricunga belt of northern chile contain advanced argillic alteration zones that locally host high sulfidation epithermal gold deposits in proximity to porphyry gold copper deposits the spatial association suggests a genetic link mineralized zones are characterized by four main vein types that formed at different times and have specific zonal relationships a veinlets are the earliest and deepest vein type they are restricted to potassic alteration zones in intrusive rocks a veinlets contain variable amounts of quartz magnetite biotite and chalcopyrite and locally have k feldspar halos they have nonmatching irregular vein walls and lack internal symmetry hypersaline liquid rich inclusions coexisting with vapor rich inclusions in a veinlets indicate temperatures as high as nearly 700 c and pressures between 200 and 400 bars assuming a lithostatic load depths of 0 8 to 1 6 km are inferred zones of abundant a veinlets contain mostly 1 ppm gold and 0 1 to 0 4 percent hypogene copper banded quartz veinlets occur mostly above a veinlets and cut a veinlets where they overlap dark gray bands the color resulting from a high density of vapor rich fluid inclusions and micron sized grains of magnetite commonly occur as symmetric pairs near the vein walls vein walls are parallel and slightly wavy vuggy vein centers are common and alteration envelopes are absent data from rare liquid rich inclusions in banded quartz veinlets indicate temperatures 350 c at pressures between 20 and 150 bars assuming a hydrostatic load depths of 0 2 to 1 5 km are inferred zones of abundant banded quartz veinlets generally contain 0 5 to 2 ppm gold and 0 1 percent hypogene copper d veins are pyrite veins with quartz sericite pyrite halos they are widespread and crosscut a veinlets and banded quartz veinlets the brittle nature of d veins and limited fluid inclusion data suggest temperatures 400 c d veins serve as important time lines they are nowhere truncated or crosscut by intrusions a veinlets or banded quartz veinlets quartz alunite replacement veins referred to as ledges in this paper are typical of the high sulfidation epithermal environment they are mostly limited to overlying volcanic rocks they contain local core zones of vuggy residual quartz that can contain enargite or at higher elevations barite of the three districts studied only la pepa has mineable quartz alunite ledges which contain an average gold grade of about 20 ppm a spectrum of porphyry style deposits exists cerro casale at aldebaran shares many characteristics of porphyry copper deposits worldwide whereas verde at refugio is a true porphyry gold deposit potassic alteration zones and a veinlets are strongly developed at cerro casale whereas they are absent at verde banded quartz veinlets predominate at verde whereas they occur only at the upper levels of cerro casale the pancho deposit at refugio and the cavancha deposit at la pepa are telescoped systems in which banded quartz veinlets overprint potassic alteration zones and a veinlets a veinlets and banded quartz veinlets cut and are cut by intrusions indicating multiple cycles of intrusion potassic alteration a veinlets banded quartz veinlets during formation of porphyry style mineralization banded quartz veinlets are thought to have formed by flashing of magmatic fluids during episodic transitions from lithostatic to hydrostatic pressure loss of sulfur to the vapor phase during flashing inhibited formation of copper sulfides in banded quartz veinlets and therefore resulted in high gold copper ratios where rising magmatic vapors condensed into overlying meteoric water along faults barren quartz alunite ledges formed this conclusion is supported by equivalent 40ar 39ar dates on hydrothermal biotite associated with porphyry style ore and alunite from barren ledges at aldebaran 40ar 39ar dates at la pepa indicate alunite formed at least 140 000 years to as long as 900 000 years after hydrothermal biotite within the high sulfidation epithermal environment the development of ore depends on the ability of late moderate salinity magmatic fluids to reach the surface without condensing a brine upon ascent cooling and boiling of the moderate salinity fluid below its critical temperature results in the formation of sericite at depth and alunite near the surface that is essentially synchronous with high sulfidation ore formation the timing of the switch from lithostatic pressures to brittle hydrostatic conditions relative to the life of the hydrothermal system might determine how much porphyry style ore forms relative to high sulfidation epithermal ore

synthetic fluid inclusions in natural quartz i compositional types synthesized and applications to experimental geochemistry synthetic fluid inclusions having a wide range of geologically applicable compositions in the c o h s na k ca cl cu fe system have been formed by healing fractures in inclusion free natural quartz and by precipitating new quartz overgrowths on an original seed crystal inclusion types synthesized include 1 1 liquid rich pure h2o inclusions of primary and secondary origin 2 2 pure h2o inclusions with the critical density 3 3 liquid rich inclusions containing undersaturated aqueous solutions of nacl or kcl or cacl2 or mixtures of the three salts 4 4 h2o nacl inclusions containing halite daughter minerals 5 5 h2o nacl kcl inclusions containing halite and sylvite daughter minerals 6 6 h2o co2 inclusions of various compositions containing liquid h2o and either co2 vapor or co2 liquid or both at 25 c 7 7 h2o co2 nacl inclusions containing an aqueous phase liquid and vapor co2 and halite at 25 c 8 8 c o h inclusions containing liquid h2o a co2 ch4 liquid phase and graphite daughter minerals at 25 c 9 9 h2o nacl inclusions that contain a chalcopyrite daughter mineral and 10 10 inclusions representing trapping of the coexisting immiscible fluids in the h2o nacl h2o co2 nacl and na c o h systems the inclusions exhibit uniform phase ratios at room temperature and the temperatures of various phase changes within individual inclusions agree with those predicted from experimental and theoretical data indicating that the inclusion fluid has the same composition and density as the parent solution these miniature autoclaves thus may be used to study various problems related to fluid inclusion research to calibrate analytical equipment used to study natural inclusions and to study phase equilibria solubility and pvt relations of a variety of chemical systems

the last interglacial glacial period on spitsbergen svalbard the glaciation history of svalbard 78 n and the nw barents sea is reconstructed for the last 130 ka based on studies of sediments exposed in coastal cliffs at the head of isfjorden four different till beds separated by marine sediments are recognized the lowest marine formation containing mytilus edulis reflects warmer conditions than at present and is correlated with the last interglacial the eemian of europe and oxygen isotope substage 5e in the deep sea the post eemian tills are inferred to represent major glaciations around 110 ka bp 75 50 ka bp and 25 10 ka bp during the intervening intervals the glaciers on svalbard were not significantly larger than at present and the nw barents sea was probably ice free the ice free periods named phantomodden and kapp ekholm interstadials lasted from about 110 to 75 and from 50 to 25 ka bp respectively the marine fauna from both these interstadials indicate seasonally ice free conditions the ages of the recorded glaciations coincide with or are slightly younger than periods with insolation minima which at this latitude is determined by a low tilt of the earth s axis thus we postulate that the quaternary glaciations of svalbard were driven by orbital variations with the 41 ka tilt period in contrast to the lower latitude glaciations of scandinavia that were partly driven by the precession cycle with a periodicity of around 23 ka

concentration of platinum group elements by magmatic fluids in layered intrusions evidence leading to a model which supports the formation of pt pd reefs in a layered intrusion by the action of magmatic fluids is presented as well as some of the constraints imposed on such a model the stillwater complex is used as an example of this model within the stillwater complex no laterally continuous sulfide enriched cumulates occur above the lowermost parts of the ultramafic series until one reaches the platiniferous j m reef this sulfide poor stratigraphic interval beneath the j m reef is characterized by unusually cl rich apatite although reported sulfide modes and whole rock sulfur contents in the cumulates below the j m reef are approximately an order of magnitude lower than that expected for a sulfide saturated magma sulfide saturation prior to the formation of the j m reef is suggested by relatively high pd and pt concentrations reported in the cumulates below the j m reef as well as by the presence of sulfide as inclusions in silicate and oxide cumulus minerals hence it is suggested that the footwall cumulates to the j m reef were originally sulfide saturated but later lost sulfur to a fluid phase exsolving from inter cumulus liquid sporadic sulfide bearing pegmatoids in some of these rocks are additional evidence for late loss of sulfur these observations as well as the association of the j m reef at the first significant stratigraphic break in the cl cl f ratio of apatite and the relatively high solubility of pt and pd as aqueous cl complexes are consistent with the formation of the j m reef by exsolution of cl and volatile rich fluids from footwall intercumulus liquids which leached and transported ore components both the pge and s upward to the level of the reef using published whole rock platinum group element pge concentrations for the ultramafic and lower banded series the cumulates below the j m reef must have been enriched by a factor of at most 1 24 for pt and 1 75 for pd if these rocks were to be the source for the metals in the j m reef model raleigh fractionation calculations suggest that the cumulates beneath the j m reef could have had the required metal concentrations if during the crystallization of a parent magma containing no more than 15 ppb of either metal the average bulk solid liquid distribution coefficients for pt and pd were no more than 5 these values are consistent with assumption of sulfide saturation prior to the formation of the j m reef during solidification of intercumulus liquid the separation and loss of a cl rich fluid will deplete the residual assemblage of s and pge if 0 1 to 0 5 wt percent fluid containing 5 percent s evolved during solidification of the footwall cumulates the amount of fluid expected to be exsolved by the crystallization of approximately 2 to 10 percent fluid saturated intercumulus liquid the fluid liquid distribution coefficients for pt and pd would need to be almost as large as the sulfide liquid silicate liquid distribution coefficients to remove significant amounts of pt and pd much smaller distribution coefficients are needed if sulfide is completely lost to fluid during degassing the latter possibility is consistent with the low s contents of the footwall cumulates beneath the j m reef numerical models of the degassing of intercumulus liquids suggest that thick cumulus sequences can act as chromatographic columns to separate the pge and s during the degassing of intercumulus silicate liquids the pge being enriched at a sulfide dissolution front as upward migrating sulfide undersaturated fluids resorb cumulus sulfides zones of pge and s enrichment can occur where degassing fronts encounter stratigraphic physical chemical discontinuities such as changes in the fluid saturation temperature of the intercumulus silicate liquids

amino acid geochronology of raised beaches in south west britain abstract based on 1 the epimerization of l isoleucine to d alloisoleucine d l ratios in patella vulgata littorina littorea l littoralis l saxatilis littorina species and nucella lapillus from raised beaches in south west britain 2 statistical analysis of the d l ratios and 3 lithostratigraphic and geomorphic evaluation three d l stages are proposed the d l ratios for all the species measured are converted to a patella vulgata standard the three d l stages are 1 1 the minchin hole d l stage d l ratios 0 175 0 014 defined at a stratotype in minchin hole cave gower wales 2 2 a provisionally defined but as yet unamed d l stage because of the current unavailability of a suitable stratotype with d l ratios of 0 135 0 014 3 3 the pennard d l stage d l ratios 0 105 0 016 defined at a stratotype in minchin hole cave gower wales two geochronological models of the three high sea level events representing the d l stages are constrained by uranium series age determinations on stalagmite interbedded with marine beds in minchin hole and bacon hole caves gower wales a potential fixed point in model evaluation is an age determination which is equivalent to oxygen isotope sub stage 5e 122 ka the two models are oxygen isotope stage and age ka bp d l stage d l ratio model 1a model 1b model 2 pennard 0 105 0 016 5a ca 80 5e 122 5e 122 5c ca 100 unnamed 0 135 0 014 5e 122 7 194 minchin hole 0 175 0 014 7 186 245 7 186 245 7 216 the ages of the raised beaches are used to constrain the timing and extent of glaciation in the area the extent of the late devensian glaciation is fixed by reference to localities where raised beaches of the pennard d l stage outcrop as well as by using unpublished data on molluscs incorporated into glacial deposits two pre devensian glaciations antedate the minchin hole d l stage the irish sea glaciation of the bristol channel irish sea older drift of south wales fremington till of north devon is ascribed to oxygen isotope 10 or earlier while the paviland welsh glaciation is ascribed to oxygen isotope stage 8 or earlier an earlier glaciation berwyn glaciation is inferred from erratics of known welsh provenance in essex

40ar 39ar ages of detrital muscovite within early paleozoic overstep sequences avalon composite terrane southern new brunswick implications for extent of late paleozoic tectonothermal overprint concentrates of coarse grained detrital muscovite from the ratcliffe brook formation lowermost cambrian display internally discordant 40ar 39ar age spectra gas fractions evolved at intermediate and high experimental temperatures record apparent ages of ca 610 620 ma these are interpreted as dating initial cooling through temperatures appropriate for intracrystalline retention of 40ar and may indicate derivation from mylonite zones developed within proximal late precambrian granitic rocks gas fractions evolved at lower experimental temperatures record patterns of spectra discordance that suggest the constituent grains experienced partial intracrystalline diffusive loss of 40ar during a late paleozoic low grade thermal overprint a muscovite concentrate from pelitic schist beneath the allochthonous latest precambrian cranberry head granite records a 40ar 39ar plateau age of 318 1 ma this is interpreted as closely dating late carboniferous thrust emplacement of the allochthon

a marine isotope stage 4 age for pleistocene raised beach deposits near fethard southern ireland raised beach deposits around the irish coast have been interpreted as interglacial or last glacial in age on the south coast of ireland the courtmacsherry formation raised beach cfb near fethard county wexford was dated using optically stimulated luminescence osl this site was previously dated to marine isotope stage mis 6 5 but more recent dating of the cfb elsewhere along the south coast shows it is considerably younger mis 4 3 the osl analyses in this paper aimed to determine if new dating would support the greater age of the fethard raised beach or realign it with the cfb the new osl ages place the formation of the fethard raised beach between 57 6 and 45 6 ka with 53 5 ka the most likely age if a single depositional event is assumed this is consistent with osl dates of the cfb elsewhere an mis 4 3 age has important implications in understanding the palaeogeography and timing of glaciation in ireland and requires a reassessment of regional relative sea level history as the eustatic response to global ice volume resulted in lowered relative sea level during mis 4 2 a crustal response to glaciation is implied by the new dates

aluminous granite as a source magma of hydrothermal ore deposits an experimental study partition ratios of zinc and lead between synthetic granitic melts and aqueous phase were determined at 800 degrees c and under p sub h 2 o 3 5 or 0 25 kb two starting glasses in the system sio 2 al 2 o 3 cao na 2 o were prepared their bulk chemical compositions are similar i e sio 2 content of 75 65 percent in glass 1 and of 74 68 percent in glass 2 glass 1 is prepared to be slightly alkaline with 1 89 percent normative wollastonite and glass 2 is slightly aluminous with 2 42 percent normative corundum the partition ratio of sodium between aqueous fluid and melt k p na can be expressed by the following equation over the whole range of chloride concentrations in the aqueous solution m v cl mole kg regardless of the normative composition of the melt k p na 0 468 x m v cl however the partition ratio of zinc k p zn for the aluminous melt is more than two orders of magnitude larger than that for the alkaline melt k p zn varies with the square of the chloride concentration in the aqueous phase and is satisfied by the following two equations k p zn 9 40 x m v cl 2 aluminous melt 2 and k p zn 0 0833 x m v cl 2 alkaline melt 1 a similar contrast was also observed in the partition ratios of lead between aqueous phase and melts k p pb 2 26 x m v cl 2 aluminous melt 2 and k p pb 0 0474 x m v cl 2 alkaline melt 1 the log of the partition ratio shows an excellent inversely proportional relation with the ph at 25 degrees c of the aqueous solution which was equilibrated with granitic melts and quenched a slope of 2 is obtained for alkaline melt and is reasonably explained by the equation pbo melt 2h super vapor 2cl super vapor pbcl sub 2 vapor h 2 o the slope for the aluminous melt 1 2 may be explained only by complex reactions involving silicate ligands in the melt the results indicate that only aluminous granite is capable of producing hydrothermal fluids which would contain a significant amount of ore metals in other words aluminous granite can be ore bearing by postmagmatic processes this is likely to happen when a granitie magma which originally was slightly alkaline changed its composition to slightly aluminous during diapiric uplift by assimilation of pelitic sediments if this compositional evolution happened then granitic magma would tend to store up base metals during the early stages of its evolution and release them very efficiently in the later stages to form a hydrothermal ore solution

the lac des iles palladium deposit ontario canada part ii halogen variations in apatite analysis of apatite from the mine block intrusion mbi of the lac des iles igneous complex shows two pronounced trends in the halogens apatite from relatively fresh norite and melanorites from the pd sulfide zone contain up to 57 mol chlorapatite endmember with significant hydroxyapatite component in contrast in altered rock amphibolite and greenschist assemblages the chlorapatite component is typically less than 10 mol with wide variation in the f and oh endmember components the latter trend is attributed to cl loss to degassing and alteration whereas the former is attributed to cl enrichment in the ore bearing rocks it is suggested that the relatively h2o rich and intermediate cl content of the early igneous fluids degassed from the deeper levels of the mbi can explain the high pd pt and pd ir ratios of the deposit a model is presented in which disseminated pd rich sulfides are initially introduced by a high temperature magmatic fluid that also influenced crystallization to produce the gross modal variations of the igneous host rock this high temperature mineralization event was subsequently modified by the influx of late igneous and country fluids at amphibolite to greenschist conditions

quaternary deposits and glacial stratigraphy in ireland quaternary stratigraphic studies in ireland have been based largely on lithostratigraphy the division of complex sedimentary sequences into the traditional framework of munsterian and midlandian events has created a series of stratigraphic scenarios which cannot be fully substantiated either by biostratigraphy or by facies basin analysis many of the current problems of glacial stratigraphy in ireland therefore arise directly from the field procedures used and the frameworks used to subdivide sedimentary sequences these problems are centred on the selection of type sites the subdivision of sedimentary sequences into unnatural divisions the concepts of direct and indirect stratigraphy classical models of climatically determined ice advance retreat cycles and the genetic inferences of the term till the conceptual basis of various stratigraphic schemes has changed little since the work of farrington 1934 1966 it is argued that a more realistic approach to description and assessment of glacigenic sediments should be based on basinal facies analysis and must include a documentation of the composition and geometry of three dimensional facies variations palaeoenvironmental interpretations of complex glacigenic sequences especially in coastal locations should take account of the influences of marine ice sheets on the sedimentary record in the past most sequences were interpreted in terms of glacioterrestrial models a large body of sedimentary evidence now indicates that shallow glaciomarine environments occurred along the margins of the last ice sheet during its maximum and subsequent retreat phases the locations and patterns of associated icemarginal systems indicate that the magnitude of and patterns of crustal deformation were greater and more complex than formerly realised thus the primary control on sea level variation at successive ice sheet margins was largely a function of glacioisostatic disequilibrium although complex glacial and glacially related sequences are known it is argued here that most of the multiple glacigenic sequences in ireland can be accommodated within the midlandian cold stage the basal units from certain sequences and erratic fans have been attributed to events earlier than the midlandian however it is difficult to compare these traces of earlier events from different sectors of the island due to poor dating correlation and the fact that direct and indirect stratigraphy is not adequately defined or separated the age of the gortian style interglacial sequences the implications of their floristic composition and their relationships to drift stratigraphy remains a major problem in stratigraphic constructions of the irish quaternary the stratigraphic significance of many till units must remain largely unknown until these matters are resolved at present it is not clear if the gortian sequences represent more than one interglacial a series of exposures in ulster provide evidence for major environmental changes during the midlandian cold stage these include an early stadial an early forest biozone 48 1 ka bp an early herb biozone 41 5 ka bp a middle interstadial phase of cold but non glacial aspect 30 5 ka bp a late stadial max 24 22 ka bp and a late glacial climatic oscillation the late midlandian stadial comprises a major glaciation that almost covered the island and a later more restricted phase when drumlins formed in the northern and western parts of the island max 17 ka bp

polyphase late paleozoic tectonothermal evolution of the southwestern meguma terrane nova scotia evidence from 40ar 39ar mineral ages 40ar 39ar incremental release ages of hornblende muscovite and biotite from a variety of granitic stocks and host metamorphic rocks suggest a complex late paleozoic tectonothermal evolution for the southwestern meguma terrane regional d1 folding with cleavage formation under greenschist lower amphibolite facies m1 metamorphic conditions occurred at ca 400 410 ma and was followed by emplacement of a series of granitic stocks ranging in age between ca 375 and 315 ma these were emplaced at relatively shallow crustal levels and developed contact metamorphic aureoles of variable grade these are locally superposed on m1 regional metamorphic assemblages and result in a complex isograd pattern 40ar 39ar mineral ages suggest episodes of contact metamorphism occurred at 1 360 375 ma possibly related to emplacement of the south mountain batholith or temporal equivalents 2 350 356 ma around the port mouton pluton and northeastern shelburne pluton 3 ca 315 325 ma near the wedgeport pluton and in

metal fractionation between magmatic brine and vapor determined by microanalysis of fluid inclusions the major and trace element compositions of individual fluid inclusions from a range of magmatic hydrothermal ore deposits were analyzed by laser ablation inductively coupled plasma mass spectrometry to explore the behavior of ore forming components during fluid phase separation boiling in high temperature saline fluid systems data from 13 samples showing unambiguous evidence for coeval trapping of a liquid brine and a coexisting vapor phase identify two groups of elements with drastically different geochemical behavior na k fe mn zn rb cs ag sn pb and tl preferentially partition into the brine probably as cl complexes whereas cu as au probably as hs complexes and b selectively partition into the vapor fluid phase separation is probably a major previously underestimated process in the chemical differentiation that contributes to the extreme range of selective element enrichments in magmatic hydrothermal systems from deep plutons through porphyry style and greisen deposits to epithermal mineralization and volcanic fumaroles

the evolution of a porphyry cu au deposit based on la icp ms analysis of fluid inclusions bajo de la alumbrera argentina the chemical and physical evolution of magmatic to hydrothermal processes in the porphyry cu au deposit of bajo de la alumbrera northwestern argentina has been reconstructed with a quantitative fluid inclusion study fluid inclusion petrography microthermometry and single inclusion microanalysis by excimer laser ablation inductively coupled plasma mass spectrometry la icp ms are combined to determine the evolution of pressure temperature and ore metal concentrations including cu and au in the fluids complementary hydrogen and oxygen isotope analyses are used to further constrain the water sources in the evolving system the combined data provide a new level of insight into the mechanisms of metal sourcing and ore mineral precipitation in a porphyry style magmatic hydrothermal system based on previously reported observations of the igneous geology alteration geochemistry and veining history of the subvolcanic porphyries at alumbrera the distribution of fluid inclusion types in space and time is documented six major inclusion types are distinguished the highest temperature brine inclusions up to 750 c p 1 kbar are mainly recorded in barren quartz magnetite veins in the core of the alteration system these polyphase brine inclusions halite sylvite multiple opaque and transparent daughter crystals are interpreted as the most primitive magmatic fluid recorded at the level of the deposit they are of moderately high salinity 50 60 wt nacl equiv dominated by nacl kcl and fecl 2 and contain on average 0 33 wt percent cu and 0 55 ppm au upon cooling and decompression these saline liquids exsolve a vapor phase which is preferentially enriched in cu relative to its main salt components but probably plays a minor role in the formation of this particular deposit because of the inferred small mass fraction of vapor cooling and decompression from the highest initial p t conditions down to about 450 c causes magnetite k silicate alteration but no saturation in au or cu sulfides as recorded by continually high ore metal concentrations in the fluid inclusions coprecipitation of cu and au as chalcopyrite and native gold some early bornite occurs over a narrow range of decreasing fluid temperature with cooling from 400 to 305 c the cu concentration in the brine drops by about one order of magnitude to less than 0 07 wt percent without a proportional decrease in major salt components ore mineral precipitation extracts 85 percent of the cu and au from the fluid it is associated with potassic alteration as shown by a concomitant decrease in the k na ratio of the cooling magmatic brine and by an increase in its ba and sr concentrations elements which are probably liberated in the destruction of calcic igneous minerals the fluid chemical data demonstrate that the metal ratios in this and probably many other porphyry style ore deposits are primarily controlled by the magmatic source of the ore brines on the other hand the final hypogene ore grade of the deposit is controlled by the efficiency of ore mineral precipitation at alumbrera metal extraction is governed by the efficiency of cooling a high flux of magmatic fluid within a small rock volume dilution of residual magmatic fluids as recorded by aqueous fluid inclusions of decreasing salinities and temperatures below 295 c follows after the main stage of copper introduction and is associated with feldspar destructive phyllic alteration geometric relationships fluid analyses and stable isotope data together indicate that phyllic alteration results from postmineralization hydrothermal activity involving minor mixing between meteoric water residual brine and a waning input of magmatic vapor

on the diversity of the pge content in chromitites hosted in ophiolites and in porphyry cu systems controlling factors abstract the present study on the diversity of the platinum group elements pge content in chromitites and porphyry cu deposits from greece and everywhere literature data aims to define factors controlling precious metal enrichment in ophiolite complexes and the unknown pd and pt potential in porphyry cu systems through an integrated set of mineralogical and geochemical approaches the pge content in chromitites associated with ophiolite complexes is commonly low a few 100 s of ppb however a significant pge enrichment up to 10 s of ppm is a feature of relatively small chromite occurrences regardless their major element composition plots of the pd ir versus normalized pt pt ratios defined separate fields corresponding to various chromitite types large chromite deposits exhibit low pd ir values reflecting low degree of fractionation primitive magmas negative pt pt partial melting of already depleted mantle and increasing partial melting trend from high al towards to high cr deposits the association with hydrous silicates cr bearing hydrogrossular chlorite and serpentine and texture features of os ir ru rich compatible or ipge minerals coupled with very low pd ir and negative pt pt values were attributed to an origin by partial melting of already depleted mantle and increased partial melting degree during a subsequent crustal mantle recycling stage via fluid driven processes assuming that the increasing pd ir reflects a fractionation trend of parent magma a significant enrichment in pt and pd incompatible or ppge occurring in small occurrences either high cr or high al type may be a sensitive fingerprint for the orientation in the mantle sequence of the ophiolites and exploration for chromite commonly the pge content in porphyry cu mo au deposits is less than 10 ppb however elevated pd pt contents over 6 ppm in sulfide rich samples are a characteristic feature of certain porphyry cu au alkaline intrusions evidence of a favorable tectonic setting post collisional for the origin of porphyry cu au pd pt elevated porphyry deposits include elevated up to hundreds of ppm contents in cr co ni and re and elevated 187 os 188 os ratios reflecting mixing and contribution to the magma composition the oxidized nature of parent magmas abundant magnetite and the evolved mineralized fluid system in porphyry deposits are considered to be critical requirements for the transportation and deposition of sufficient au and pge elevated pd pt and au contents in porphyry deposits combined with the association of the major pd mineral merenskyite with bornite and chalcopyrite major cu minerals are encouraging economic factors for the contribution to the global pd pt production

current understanding of pleistocene temperate stages in ireland abstract research on irish pleistocene temperate stages has been dominated by investigation of deposits with very similar floristic records collectively termed the gortian and traditionally correlated with the continental holsteinian recently detailed investigation of interglacial material from cork harbour suggested the gortian group may contain floristically similar deposits of different ages the pollen record had gortian holsteinian characteristics and dating by measurement of uranium thorium disequilibrium and amino acid racemization suggested that the deposits were younger than stage 11 correlated with the holsteinian by reille and de beaulieu reille de beaulieu quat res 44 1995 205 the suggestion that there may have been more than one holsteinian style temperate stage in europe might explain the floristic similarity of gortian and holsteinian deposits and the apparent younger age of the cork deposits the lack of a last interglacial stratotype is the most outstanding problem in irish quaternary studies the pollen content of sediments at fenit co kerry dated to ca 118 ka bp suggested they may represent a cool temperate phase at the end of the last interglacial recently investigated sub drumlin organic rich deposits at knocknacran co monaghan are also possibly last interglacial in age and these are discussed in detail here

40 ar 39 ar amphibole ages from the kingston complex new brunswick evidence for silurian devonian tectonothermal activity and implications for the accretion of the avalon composite terrane the kingston complex of southern new brunswick canada is a regional ne trending belt of mafic and felsic dikes bordered by dextral ductile shear zones the complex separates two contrasting late precambrian early paleozoic tectonostratigraphic assemblages near the nw margin of the avalon composite terrane rhyolitic dikes within the complex record an early silurian crystallization age dike orientations suggest that emplacement of the complex accompanied sinistral movement interpreted to reflect accretion of the avalon composite terrane to cratonic north america mafic dikes within the complex display greenschist to epidote amphibolite facies metamorphic assemblages that developed during dextral transpression amphibole concentrates from seven metamorphosed mafic dikes record late silurian to early devonian ca 416 390 ma 36 ar 40 ar vs 39 ar 40 ar isotope correlation ages interpreted to date closely the dextral transpressive deformation together with other recent age data the 40 a

palynology of organic beds below devensian glacigenic sediments at pen y bryn gwynedd north wales pollen diagrams from organic facies overlain by glacigenic sediments at pen y bryn north wales 53 7 n 4 16 w suggest that it is the first locality in the british isles to provide evidence for several devensian interstadials prior to devensian stadial glaciation s the evidence is not however unequivocal at least two main episodes of organic sedimentation are indicated separated by an interval of uncertain duration one eposide records a pinus picea betula forest a second possibly later event with tree pollen less than 10 of total land pollen tlp suggests a cool largely unforested environment a third episode with tree pollen up to 25 of tlp may be related to the latter or be of intermediate age whereas a fourth and later episode of organic accumulation may be of reworked material radiocarbon dating of organic deposits and of a wood macrofossil enclosed in basal till is inconclusive as is preliminary uranium series dating the principal biogenic episodes may correlate with oxygen isotope substages 5c and 5a but as the pollen records reflect facies floras the correlation remains tentative it is also possible that other temperate periods are recorded further resolution of the chronostratigraphy is required to help clarify the problematic correlation of interstadial and stadial events in northwest europe and to correlate more accurately the biogenic and glacigenic facies at pen y bryn with their pleistocene equivalents elsewhere

solubility of excess alumina in hydrous granitic melts in equilibrium with peraluminous minerals at 700 800 c and 200 mpa and applications of the aluminum saturation index we have studied the controls on the alumi num saturation index asi molec al2o3 cao na2o k2o and the concentration of normative corundum of granitic liquids saturated in alumina by equilibrating peraluminous minerals with initially meta luminous haplogranitic minimum composition liquids at 700 800 c and 200 mpa at and below h2o saturation the asi and normative corundum increase with increasing h2o concentration in the melt 0 04 to 0 10 moles excess al2o3 per mole of h2o temperature and with addition of the non haplogranitic components fe mg and b the asi parameter and concentration of normative corundum cannot be used to monitor aal2o3 between different mineral assemblages and melt because other components that affect the solubility of alumina including h2o fe mg and b do not appear in their formulations asi and normative corundum however provide petrogenetic information about magmas gener ated by partial melting of strongly peraluminous proto liths by virtue of their regular and predictable variation with melt composition e g h2o concentration and temperature for the application of these data to natural rocks it is necessary to choose as an analogue system the asi solubility or normative corundum solubility relations of the most chemically complex peraluminous mineral present in the rock comparison of asi values of anatectic leucosomes and allochthonous leucogranites with experimentally predicted values suggests low h2o concentrations in melt during crustal partial melting rapid melt segregation before equilibration with restitic peraluminous phases is also suggested in some cases

tectonic setting of avalonian volcanic and plutonic rocks in the caledonian highlands southern new brunswick canada the caledonian highlands of southern new brunswick consist of late proterozoic to cambrian rocks generally considered typical of the avalon terrane of the northern appalachian orogen mainly tuffaceous volcanic and sedimentary rocks of the broad river group and cogenetic dioritic to granitic plutons with ages ca 620 ma form most of the eastern caledonian highlands they have petrological features indicative of origin in a continental margin subduction zone significantly younger ca 560 550 ma dacitic to rhyolitic lapilli tuffs and flows laminated tuffaceous siltstone basaltic and rhyolitic flows and clastic sedimentary rocks of the coldbrook group form most of the western highlands and occur locally throughout the highlands the mainly tuffaceous lower part of the group has been intruded by gabbroic and syenogranitic plutons that are interpreted to be cogenetic with basaltic and rhyolitic flows in the upper part of the group this voluminous subaerial magmatism may have formed during postorogenic ex

freshwater organic deposits and stratified sediments between early and late midlandian devensian till sheets at aghnadarragh county antrim northern ireland the following events have been identified from a complex sequence of midlandian devensian sediments recently exposed at aghnadarragh county antrim 1 a lower till interpreted as early midlandian was deposited by a major lowland ice sheet which moved south eastwards from central ulster across the lough neagh depression 2 deglacial conditions were followed by a periglacial phase characterised by ice wedge growth and sedimentation by gravelly debris flows the latter contain the oldest known remains of mammuthus primigenius in ireland 3 an early midlandian interstadial is represented by a woody detritus peat with evidence of betula pinuos and picea woodlands and a rich beetle fauna wood from this horizon has been shown to be beyond the range of radiocarbon dating 48 180 bp 4 interstadial conditions were succeeded by a cold non glacial phase dominated by in channel gravelly flows and deposition of organic muds which contain plant and insect fossils these horizons are older than 46 850 bp 5 an upper non drumlinised till was deposited during the late midlandian by a major lowland ice sheet which moved generally eastwards across the lough neagh lowlands from central ulster this glaciation probably reached its maximum at ca 20 24 ka 6 drumlin formation occurred in the lough neagh lowlands towards the end of the late midlandian the limiting moraines are dated to 17 ka the lower till at aghnadarragh is the first positive record of a major lowland ice sheet in ireland during the early part of the last cold stage the early midlandian interstadial peats have not been documented elsewhere in ireland and correlate broadly with the chelford interstadial complex of the english midlands related exposures elsewhere in ulster confirm that the middle part of the last cold stage was free of major lowland ice masses but deposits of this period are absent from aghnadarragh

argon retentivity of hornblendes a field experiment in a slowly cooled metamorphic terrane hornblende from samples of amphibolite and granitic gneiss collected within a single outcrop in the central adirondacks yield significantly different sup 40 ar sup 39 ark sub k dates of 948 plus minus 5 and 907 plus minus 5 ma assuming that this terrane cooled slowly following high grade metamorphism and that the samples have experienced the same thermal history the difference in dates apparently reflects a corresponding difference in blocking temperature for diffusion of radiogenic argon in these hornblende samples the fe fe mg mn of the hornblende samples are 0 8 and 0 6 the higher ratio corresponding to the younger sup 40 ar sup 39 ar sub k date transmission electron microscopy observations indicate that both hornblende samples are homogeneous and devoid of any exsolution but contain zones of fibrous phyllosilicates approximately 0 1 to 2 mu m wide parallelling 100 and 110 these alteration zones probably formed during post metamorphic cooling as a result of the migration of fluids through the hornblendes and are obvious pathways for argon escape from hornblende as these features are more abundant in the hornblende sample with the younger sup 40 ar sup 39 ar date and higher fe fe mg mn they may influence the argon blocking temperature by effectively partitioning the hornblende grains intomore diffusion domains of varying size biotite from the granitic gneiss yields an sup 40 ar sup 39 ar sub k date of 853 plus minus 2 ma with a mildly discordant step heating spectrum that in part reflects the degassing of submicroscopic inclusions precipitated during alteration of the host biotite plagioclase from the amphibolite yields a sup 40 ar sup 39 ar sub k integrated date of 734 plus minus 3 ma less

allard stock la plata mountains colorado an alkaline rock hosted porphyry copper precious metal deposit the allard stock which hosts a porphyry cu ag au pt metals deposit is an epizonal laramide pluton at the southwest end of the colorado mineral belt the stock and associated mineralization evolved by a complex interaction of igneous and metasomatic processes as follows stage 1 forceful emplacement of syenite plutons stage 2 intense hydrothermal argillization of stage 1 syenites stage 3 intrusion of mafic syenite plutons some of which are layered along shear zones stage 4 violent escape of volatiles producing intrusive breccia pipes stage 5 intense k metasomatic alteration of the older stock units with production of a fenitelike alteration halo extending 1000 m beyond the stock and simultaneous intrusion of carbonate bearing alkali feldspar dikes stage 6 emplacement of trachyte syenite pegmatite and mafic pegmatite dikes stage 7 deposition of metallic minerals sanidine quartz calcite and fluorite as veinlets and disseminated replacement masses from hydrothermal solutions the stock

geology and geochemistry of the late precambrian coldbrook group near saint john new brunswick the late precambrian coldbrook group comprises basal basaltic flows and pyroclastic rocks fragmental andesitic to rhyolitic rocks and minor capping sedimentary strata all deformed and metamorpho

an evaluation of synthetic fluid inclusions for the purpose of trapping equilibrated coexisting immiscible fluid phases at magmatic conditions we report data that allow us to evaluate the method of trapping immiscible saline aqueous fluids i e vapor and brine in the nacl kcl hcl fecl2 auhcl2 h2o system as synthetic fluid inclusions in pre fractured quartz cores in order to quantify the concentrations of au fe k and na among coexisting three phase immiscible fluids i e haplogranite melt brine and vapor at magmatic conditions coexisting vapor and brine were trapped experimentally at 800 c and 100 110 mpa as synthetic fluid inclusions in both quartz microfractures and quenched silicate melt i e glass and also sampled indirectly using the recovered quenched aqueous fluid quartz hosted and glass hosted brine inclusions were analyzed by laser ablation inductively coupled plasma mass spectrometry la icpms and instrumental neutron activation analysis inaa respectively quenched aqueous fluid from each experiment containing a quartz core was recovered and analyzed by atomic absorption spectrophotometry aas the composition of aqueous fluids trapped as quartz hosted inclusions glass hosted inclusions and those recovered after quench yield consistent and precise data at the 2 uncertainty level for the elements of interest the overlapping au fe k and na concentrations in aqueous fluids trapped and analyzed via three entirely different instrumental techniques i e la icpms inaa and aas suggest strongly that quartz microfractures heal on a slow enough time scale to permit entrapment of fully equilibrated aqueous fluids at our experimental ptx conditions the data evince clearly that the chemical composition of fluids in quartz microfractures at the time of self healing represents equilibrium conditions hence synthetic fluid inclusions in experiments with low thermal gradients across the charge provide a reasonable estimate of fluid composition at least at the experimental conditions examined in this study

exsolution in hornblende and its consequences for 40ar39ar age spectra and closure temperature abstract step heating studies of hornblende and biotite which coexist in an amphibolite near north walpole vermont reveal dramatically different 40 ar 39 ar age spectra the biotite mg 59 is characterized by a plateau over 98 percent 39ar release at 343 5 ma in strong contrast to the amphibole which exhibits both a complex age spectrum and a k ar age significantly younger than the biotite the amphibole release pattern contains three complete age cycles which range between extremes of 199 ma and 408 ma interestingly the k ca ratio calculated from reactor produced isotopes also varies with ar release but follows a trend which is antipathetic to the 40 ar 39 ar age pattern detailed microstructural examination including transmission electron microscopy tem reveals a complex exsolution structure that is consistent with both the complexity of the release pattern as well as the low degree of radiogenic 40ar 40ar retentivity in the amphibole this result underscores the variability of closure temperature tc for 40ar in metamorphic amphiboles and should warn against accepting a single universal value of tc

precise timing of the last interglacial period from mass spectrometric determination of thorium 230 in corals the development of mass spectrometric techniques for determination of 230 th abundance has made it possible to reduce analytical errors in 238 u 234 u 230 th dating of corals even with very small samples samples of 6 x 10 8 atoms of 230 th can be measured to an accuracy of 3 percent 2 and 3 x 10 10 atoms of 230 th can be measured to an accuracy of 0 2 percent the time range over which useful age data on corals can be obtained now ranges from about 50 to about 500 000 years for young corals this approach may be preferable to 14 c dating the precision with which the age of a coral can now be determined should make it possible to critically test the milankovitch hypothesis concerning pleistocene climate fluctuations analyses of a number of corals that grew during the last interglacial period yield ages of 122 000 to 130 000 years the ages coincide with or slightly postdate the summer solar insolation high at 65 n latitude which occurred 128 000 years ago this supports the idea that changes in pleistocene climate can be the result of variations in the distribution of solar insolation caused by changes in the geometry of the earth s orbit and rotation axis

magmatic sulfides and au cu ratios in porphyry deposits an experimental study of copper and gold partitioning at 850 c 100 mpa in a haplogranitic melt pyrrhotite intermediate solid solution gold metal assemblage at gas saturation abstract the behavior of copper and gold in the phase assemblage pyrrhotite po intermediate solid solution iss haplogranitic melt gold metal capsule at 850 c 100 mpa and gas saturation ah2o 0 9 has been investigated the results are presented as nernst partition coefficients the partition coefficient dcupo melt 2 6 0 3 103 1 was determined for po and melt in equilibrium with an iss of composition cu 19 1 fe 30 1 s 51 1 2 for gold the partition coefficients are dauiss melt 5 7 2 2 103 1 between iss and melt and daupo melt 140 40 1 between po and melt these imply dauiss po 42 9 1 between iss and po the oxygen fugacity for the experiments log f o 2 13 2 0 3 1 was determined by using the hydrogen sensor technique the sulfur fugacity log f s 2 1 0 0 7 1 was calculated from the composition of po in our experiments melts at iss saturation have cu fe by weight of ca 1 100 the results indicate that crystallization of iss may deplete a melt in gold and crystallization of po may deplete a melt in copper however a melt saturated with iss at a given bulk composition temperature pressure oxygen and sulfur fugacity and feo concentration will have a fixed concentration of cu preventing strong depletion of the melt in cu until iss is fractionated from the melt or changes in environmental conditions destabilize iss a thermodynamic model for the partitioning of cu and au between po and melt in terms of oxygen and sulfur fugacity indicates that dcupo melt and daupo melt may increase greatly with increasing sulfur fugacity and decreasing oxygen fugacity within the po stability field the model also suggests that destabilization of both iss and po relative to magnetite due to changes in oxygen and sulfur fugacities can result in the release of cu and au from the sulfides to the melt

u pb age constraints on the stratigraphy and tectonic history of the avalon terrane new brunswick canada six new u pb ages for avalonian plutonic and volcanic rocks from the eastern caledonia highlands southern new brunswick indicate that magmatic activity occurred between 625 600 ma ago with another probably separate major episode at ca 550 ma this gap in igneous activity is consistent with differences in the metamorphic and deformational character of rocks from the two episodes the 625 600 ma activity was calc alkalic and probably occurred in an andean type magmatic arc it correlates with most volcanism and plutonism in the type avalon terrane of newfoundland the ca 550 ma activity formed bimodal volcanic rocks and high level plutons probably in an extensional setting u pb ages of xenocrystic zircons from avalonian igneous rocks indicate both archean and proterozoic components at depth in avalonian basement an observation consistent with pb isotopic signatures which suggest an old radiogenic crustal source the african craton for the magmatic products

stable isotope evidence for magmatic fluids in the pueblo viejo epithermal acid sulfate au ag deposit dominican republic stable isotope h c o and s systematics of the pueblo viejo acid sulfate system the world s largest bulk mineable acid sulfate gold deposit were investigated to determine the importance of magmatic fluids in hydrothermal systems of this type mineralization at pueblo viejo is hosted by a maar diatreme system that cuts sedimentary rocks and spilites of the late cretaceous los ranchos formation the deposit is characterized by two stages of advanced argillic alteration stage i fluids produced deep alunite quartz and shallower kaolinitc quartz both associated with disseminated pyrite stage ii fluids overprinted stage i and produced deep pyrophyllite diaspore and an overlying silica cap an increase in temperature from stage i 250oc to stage ii 250o 300oc is indicated by mineral stabilities and sulfur isotope thermometry of coexisting sulfide sulfate pairs stage i quartz alunite kaolinite pyrite alteration and associated disseminated au ag mineralization are interpreted to

the geordie lake intrusion coldwell complex ontario a palladium and tellurium rich disseminated sulfide occurrence derived from an evolved tholeiitic magma the geordie lake intrusion is a small body of sulfide bearing mafic rocks that has intruded contemporaneous syenites of the coldwell alkaline complex northwestern ontario the intrusion consists of alternating layers of troctolite containing dendritic olivines and ophitic gabbros cumulate rocks are absent and the rocks are interpreted to be a series of rapidly cooled intrusions of tholeiitic basaltic magma compositional data are presented for olivine plagioclase alkali feldspar clinopyroxene amphibole magnetite and ilmenite these data together with whole rock major and trace element analyses demonstrate that the geordie lake magma was relatively evolved at the time of emplacement the formation of secondary amphiboles and biotite together with low equilibration temperatures calculated for coexisting fe ti oxides demonstrates that extensive deuteric subsolidus reequilibration has occurred sulfides consist principally of disseminated chalcopyrite associated with minor bornite pyrite millerite cobaltite siegenite sphalerite and galena tellurides hessite melonite altaite and platinum group minerals are associated primarily with disseminated chalcopyrite and are rare in late stage massive chalcopyrite the platinum group minerals are dominantly palladium tellurides and arsenides rare sperrylite is the only platinum mineral present textural relationships suggest that rapid cooling of the magma and crystallization of olivine and magnetite induced the early separation of an immiscible sulfide melt this melt remained as a liquid until the silicate host rocks had cooled to subsolidus temperatures during the final stages of crystallization of the silicate magma the sulfide melt and residual water rich fluids were trapped together within pore spaces crystallization of ti poor magnetite tellurides and platinum group minerals from the sulfide melt occurred at low temperatures 550 degrees c the fugacities of sulfur and tellurium prevailing during crystallization of the sulfide melt are estimated from predominance diagrams pyrrhotite pentlandite and ir os and rh based minerals are absent from the sulfide assemblage the predominance of pd and cu tellurides and sulfides coupled with low pt pt pd and high cu cu ni ratios suggests that the geordie lake platinum group minerals sulfide assemblage crystallized from a relatively evolved sulfide melt associated with an evolved tholeiitic magma

the gortian temperate stage abstract interglacial sediments assigned to the gortian temperate stage are recorded at eleven sites throughout ireland but they remain undated by absolute means however the unique vegetational assemblages found within the gortian appear to belong to the middle pleistocene on biostratigraphic grounds the gortian vegetational records are reviewed and a summary of the possible age of the interglacial is presented along with recent work that has been carried out on stratigraphically important sites within ireland

40ar 39ar ages of detrital muscovite and whole rock slate phyllite narragansett basin ri ma usa implications for rejuvenation during very low grade metamorphism late pennsylvanian sedimentary rocks in the narragansett basin were metamorphosed lower anchizone to sillimanite grade during late paleozoic regional metamorphism at ca 275 280 ma twenty five variably sized concentrates of detrital muscovite were prepared from samples collected within contrasting low grade areas diagenesis lower greenschist facies microprobe analyses suggest that the constituent detrital grains are not chemically internally zoned however some grains within several concentrates display very narrow 25 m compositionally distinct low grade epitaxial peripheral overgrowths detrital muscovite concentrates from the lower anchizone are characterized by internally concordant 40ar 39ar age spectra which define plateau ages of ca 350 360 ma these are interpreted to date post devonian acadian cooling within proximal source areas concentrates from lower grade sectors of the middle anchizone display slightly discordant spectra in which apparent ages systematically increase from ca 250 275 ma to define intermediate and high temperature plateaus of ca 360 400 ma detrital muscovite within samples from higher grade sectors of the middle anchizone and the upper anchizone are characterized by systematic low age discordance throughout both low and intermediate temperature increments high temperature ages only range up to ca 330 ma six size fractions of detrital muscovite from a sample collected within the lower greenschist facies have similarly discordant spectra in which apparent ages increase slightly throughout the analyses from ca 250 ma to 275 ma the detrital muscovite results are interpreted to reflect variable affects of late paleozoic regional metamorphism however it is uncertain to what extent the systematic low age spectra discordance reflects intracrystalline gradients in the concentration of 40ar and or experimental evolution of gas from relatively non retentive epitaxial overgrowths however low age discordance occurs regardless of the extent of epitaxial overgrowth intermediate temperature increments evolved during 40ar 39ar whole rock analyses of five slate phyllite samples are characterized by internally consistent apparent k ca ratios these are attributed to gas evolved from constituent very fine grained white mica samples from lower grade portions of the middle anchizone are characterized by intermediate temperature apparent ages which systematically increase from ca 275 300 ma to ca 360 375 ma before evolution of a high temperature contribution from detrital plagioclase feldspar this age variation may reflect partial late paleozoic rejuvenation of very fine grained detrital material with a source age similar to that for the detrital muscovites slate phyllite samples from upper sectors of the middle anchizone and from the upper anchizone were completely rejuvenated during late paleozoic metamorphism and record intermediate and high temperature plateau ages of ca 270 290 ma these data document that metamorphic conditions of the lower to middle biotite zone ca 325 350 c are required to completely rejuvenate intracrystalline argon systems of detrital muscovite therefore the 40ar 39ar dating method may be useful in determination of detrital muscovite provenance and in resolution of the metamorphic evolution of low grade terranes

constraints on magma degassing beneath the far southeast porphyry cu au deposit philippines k silicate alteration in the far southeast fse porphyry cu au introduction deposit formed at 1 4 ma concentric to dikes of quartz diorite magmas become saturated with volatile components as porphyry at 2 km paleodepth the hydrothermal system consisted they ascend in the crust and either erupt or crystallize of magmatic hypersaline liquid and vapor at 550 c and 50 at depth saturated magmas that remain at depth exsolve mpa lithostatic pressure advanced argillic alteration formed at an aqueous fluid that forms a hydrothermal system on the same time over the deposit at 1 km paleodepth from acidic separation from the magma chamber burnham 1979 condensates of the vapor at 1 3 ma k silicate alteration was although part of the exsolved fluid a low density vapor overprinted by 350 c magmatic liquid 5 wt nacl equiv may discharge to the surface from passively degassing at hydrostatic pressure sericite alteration and much of the cu au volcanoes hedenquist 1995 part will remain at depth mineralization formed at this later stage evolution of the magmatic and this dense residual magmatic liquid may be asfluid composition was simulated with a magma chamber cryssociated with hydrothermal mineralization in the portallization model homogeneous crystallization during early stage phyry ore environment hedenquist lowenstern convection is assumed whereas at 50 vol crystals the chamber 1994 becomes stagnant and crystallizes from rim to core over a narrow in this paper we use evidence from a porphyry ore crystallization interval the model calculation based on a magma deposit in the philippines to determine the composition chamber with 2 km thickness at 6 km depth 150 mpa and of the fluid that exsolved from the deeper parent magma 800 c saturated melt composition at 30 vol crystals 5 the evolving composition of the magmatic fluid at the wt h2o 0 2 wt cl and dd of 40 can reproduce the depth of the ore body can then be used to place constraints chemical and isotopic compositions of the early and late magmatic on the nature of the evolved magma chamber far below fluids the most critical factor controlling the compositional evolution the porphyry ore body this approach differs from that of the model hydrothermal system is the transition from convective of other studies where a portion of the parent magma to stagnant magma chamber crystallization there is also a sharp chamber is available to study directly e g at yerington decrease in the rate of fluid exsolution associated with this transition nevada dilles 1987 which can account for the thermal collapse of the fse porphyry the far southeast fse porphyry cu au deposit system from k silicate to sericite alteration and overlying lepanto epithermal cu au ore body are

speciation and solubility of palladium in aqueous magmatic hydrothermal solutions combining thermodynamic data at 25c and 1 bar with correlation algorithms enables prediction of equilibrium dissociation constants for aqueous platinum group element pge complexes at high pressures and temperatures we used these data 1 to calculate the speciation of pd ii in nacl solutions at temperatures to 750c pressures to 2 kbar and values from 3 to 8 and 2 to predict the solubility of palladium at 2 kbar as a function of temperature oxygen fugacity f sub o2 ph and total chloride concentration m sub t cl sup minus calculations indicate that as ph increases there is a sharp transition from chloride to hydroxide complex dominance at all chloride concentrations this shift occurs at or below neutral ph in dilute solution but at m sub t cl sup minus ge 1 0 pd ii chloride complexes account for the majority of dissolved pd ii well into alkaline conditions solubility of palladium increases with increasing temperature m sub t cl sup minus and f sub o2 at 700c 2 kbar and the f sub o2 set by the fmq buffer palladium solubility in a 3 0 m nacl solution is approximately 0 3 ppm at a ph of 4 and one unit ph variation can change palladium solubility by two orders of magnitude these results suggest that pge can be transported as chloridemore complexes in cl rich magmatic hydrothermal solutions like those inferred from petrologic studies of the stillwater and bushveld complexes less

direct evolution of brine from a crystallizing silicic melt at the questa new mexico molybdenum deposit molybdenum mineralization in the southwest orebody at the questa deposit is associated with crystallization of aplite porphyry explosive brecciation and exsolution of magmatic hydrothermal fluids quartz k feldspar fluorophlogopite and molybdenite precipitated from exsolving aqueous fluids and cemented aplite porphyry and andesite wall rock clasts forming a magmatic hydrothermal breccia ore fluid inclusions in quartz in the breccia matrix trapped aqueous fluids that transported and precipitated molybdenum two fluid inclusion populations associated with molybdenite mineralization were identified the largest population commonly contains liquid vapor halite sylvite and one or more opaque daughter crystals these inclusions homogenize between 200 degrees and 500 degrees c and have a prominent mode at 360 degrees to 400 degrees c salinities vary from 31 to 57 wt percent nacl equiv low first ice melting temperatures suggest that additional fluid components possibly calcium or magnesium chlorides may be present approximately 80 percent of these inclusions homogenize by halite dissolution phase equilibria constraints require that these inclusions trapped fluids in the vapor absent field the remaining saline inclusions homogenize to liquid at temperatures above halite dissolution temperatures significantly the saline fluid did not coexist with a low density aqueous fluid a second population of inclusions contains fluids with salinities of 2 7 to 25 0 wt percent nacl equiv and homogenizes by vapor bubble disappearance vapor bubble expansion or critical behavior textural relationships and phase behavior during microthermometry indicate that these inclusions constitute a single population which formed as pressure and temperature fluctuated at near critical conditions pressure changes related to brecciation followed by crystallization and system resealing produced the observed fluids saline fluids were trapped as the system sealed following a major brecciation event these high salinity fluids were produced as the melt under pressure that increased from hydrostatic to lithostatic partitioned increasing amounts of chlorine into the exsolving aqueous fluid renewed fracturing and abrupt pressure decrease to hydrostatic conditions reduced the mass of chlorine partitioning to the exsolving fluid lower salinity fluids exsolved at near critical conditions and were trapped by inclusions that homogenize to liquid to vapor or by critical behavior the lack of cogenetic liquid and vapor rich fluid inclusions and phase equilibria constraints indicate that high salinity fluids or 57 wt nacl equiv were generated directly by the crystallizing magma and were not a product of aqueous fluid immiscibility

the last climatic cycle at la grande pile vosges france a new pollen profile a new pollen diagram has been made from an old unanalyzed core from la grande pile gp xx correlations with the previous work of woillard 1975 1978 leads to the following conclusions the end of the eemian was marked by a minor climatic change prior to the melisey i stadial the ognon ii and ognon iii interstadials are not consistent and correspond to the level of reworking of mesophilous taxa during the last pleniglacial the limitations of the botanical interpretation of pollen spectra from the last pleniglacial are underlined lastly bruckenthalia and larix are identified for the first time at la grande pile the respective roles of these taxa following the eemian are additional arguments for correlating the st germain i and ii with the early weichsel interstadials in the north of middle europe

experimental constraints on the partitioning of rhenium and some platinum group elements between olivine and silicate melt abstract we have performed partitioning experiments to assess the role of olivine in controlling the behavior of rhenium and the platinum group elements pges during basalt petrogenesis olivines were crystallized from an iron bearing basalt at 1 bar 105 pa and log fo2 of 2 6 4 9 and 7 4 fmq 4 3 2 and 0 5 respectively in situ analyses of olivine and glass by laser ablation inductively coupled plasma mass spectrometry la icp ms reveal a homogeneous distribution of ru rh pd re and pt but significant os heterogeneity at the m scale this latter behavior arises from the presence of undissolved os micronuggets suspended in the melt and included in olivine crystals olivine melt partition coefficients ds for re and the pges follow the order drh dru dpd dre dpt with decreasing fo2 rh and ru become more compatible with maximum partition coefficients of 2 6 and 2 respectively at log fo2 of 4 9 in contrast d values for pd become smaller with decreasing fo2 to a value of 0 006 at log fo2 of 7 4 olivine melt partitioning of rh ru pd re and pt derived from our experiments is confirmed by the behavior of these elements in lavas that have evolved by olivine fractionation an elastic strain model predicts the olivine melt partitioning of these elements excepting our measured value of dpt which is much lower the fo2 dependence on partitioning implies that at higher fo2 some portion of pges exist in higher valence states than predicted from their solubility

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

u pb geochronologic constraints on the volcanic evolution of the mira avalon terrane southeastern cape breton island nova scotia new u pb ages for late precambrian volcanic and associated plutonic units in the mira avalon terrane of southeastern cape breton island indicate that volcanic suites were erupted over a span of a

synthetic fluid inclusions in natural quartz ii application to pvt studies synthetic fluid inclusions have been used to determine volumetric properties of h2o and a 20 wt kcl solution from 300 700 c and 1 3 kb comparison of results obtained for h2o with previously published data indicates that the synthetic fluid inclusion technique provides pvt data that are within a few percent of those obtained from conventional pvt studies this technique thus provides a fast relatively simple means of determining pvt properties of many fluids of geologic interest

platinum solubility and partitioning in a felsic melt vapor brine assemblage abstract the solubility and partitioning of pt in a s free vapor brine rhyolite melt pt metal assemblage has been quantified at 800 c f o 2 nno and pressures of 100 and 140 mpa vapor and brine were sampled at run conditions by trapping these phases as glass hosted fluid inclusions as the melt cooled through the glass transition temperature the vapor and brine were in equilibrium with the melt at the time of trapping and thus represent fluids which were sampled at the termination of each experimental run the microthermometrically determined salinities of vapor and brine are 2 and 63 wt nacl eq and 9 and 43 wt nacl eq at 100 and 140 mpa respectively platinum solubilities in vapor brine and glass i e quenched melt were quantified by using laser ablation inductively coupled plasma mass spectrometry la icp ms equilibrium is discussed with reference to the major and trace element concentrations of glass hosted fluid inclusions as well as the silicate melt over run times that varied from 110 to 377 h at 140 mpa and 159 to 564 h at 100 mpa platinum solubility values 1 in h2o saturated felsic melt are 0 28 0 13 g g and 0 38 0 06 g g at 140 and 100 mpa respectively platinum solubility values 1 x at 140 and 100 mpa respectively in aqueous vapor are 0 91 0 29 g g and 0 37 0 17 g g and in are brine 16 10 g g and 3 3 1 0 g g the measured solubility data were used to calculate nernst type partition coefficients for pt between vapor melt brine melt and vapor brine the partition coefficient values 1 x for vapor melt brine melt and vapor brine at 140 mpa are 2 9 1 0 67 27 and 0 13 0 05 and at 100 mpa are 1 0 0 2 6 8 2 4 and 0 15 0 05 the partitioning data were used to model the pt scavenging capacity of vapor and brine during the crystallization driven degassing i e second boiling of a felsic silicate melt over a depth range i e 3 6 km consistent with the evolution of magmatic hydrothermal ore deposits model calculations suggest that aqueous vapor and brine can scavenge sufficient quantities of pt and by analogy other platinum group elements pge to produce economically important pge rich magmatic hydrothermal ore deposits in earth s upper continental crust

gold in magmatic hydrothermal solutions and the rapid formation of a giant ore deposit the ladolam hydrothermal system on lihir island papua new guinea hosts one of the youngest and largest gold deposits in the world several deep more than 1 kilometer geothermal wells were drilled beneath the ore bodies to extract water at 275 c and to facilitate open pit mining using a titanium down hole sampler we determined that the deep geothermal brine of magmatic origin contains 15 parts per billion gold at the current gold flux of 24 kilograms per year this deposit could have formed within 55 000 years the combination of sustained metal flux and efficient metal precipitation led to the formation of a giant hydrothermal gold deposit in a short period

geochemistry and radiometric dating of a middle pleistocene peat uranium lead and sulphur data for a middle pleistocene interglacial peat deposit from norfolk uk suggest that uptake of these elements was synchronous and confined to a single early diagenetic episode probably coeval with peat formation sulphur isotope data indicate that reducing conditions have been maintained within the deposit throughout its history both uranium and lead concentration profiles show a marked discontinuity near the middle of the bed probably indicating an environmental change possibly emergence the lead isotope data are compatible with a single lead component below the discontinuity and two components above groundwater is thought to be the dominant source of lead with an additional airfall component present in the upper peat the uranium and lead concentration profiles below the discontinuity and the sulfur isotope profile throughout the peat support the view that these elements were sequestered from upwelling groundwaters the organic material is particularly suitable for 230th238u dating because it contains a negligible allogenic mineral component and very low 232th activity a sequence of consistent ages through the peat profiel mean 317 14 ka over a wide range of uranium concentrations 7 65 mg g 1 strongly suggests that a discrete short lived uranium uptake event has been dated and that subsequent differential isotopic migration has not occurred one sample from immediately below the discontinuity has an infinite apparent age but there is strong evidence for sequestration of uranium from the peat into adjacent wood fragments found along the discontinuity calculated initial 234u238u values of 1 2 1 3 support a groundwater origin for the uranium rather than a marine origin resulting from a subsequent rapid transgression the very restricted range of u pb ratios in the lower part of the peat bed and the heterogeneity of the initial lead isotopic composition in the upper part preclude u pb isochron dating 210po measurements as a proxy for 210pb also indicate possible post depositional migration of 222rn which if active over a significant period would bias any u pb age estimate the 230th238u ages are consistent with deposition during oxygen isotope stage 9

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

climatic deterioration and the end of the gortian interglacial in sediments from derrynadivva and burren townland near castlebar county mayo ireland pollen and macrofossil analyses of two sequences of organic sediment in western ireland have allowed the recognition of the latter parts of the gortian interglacial a middle pleistocene temperate stage the palaeobotanical information from the two sites identifies the preservation of partial sequences from the gortian interglacial believed to be the equivalent of the hoxnian stage of britain and the holsteinian of europe the pollen and macrofossil data from one of the sites derrynadivva span the middle and latter parts of the temperate stage the results show that fire influenced the vegetation throughout the middle part of the temperate stage and the termination of the organic depositional sequence appears to have been due to environmental deterioration the former is identified through the abundant occurrence of charcoal in the sediments whereas the latter is apparent in the sediment sequence and in the reworking of thermophilous pollen types into the upper part of the deposit the second site burren townland records only part of the later zones of the interglacial but the ericaceous assemblages of the latter part of the gortian interglacial are well developed and well preserved macrofossil analyses and scanning electron microscopy work on the pollen at the latter site has allowed the recognition of rhododendron ponticum adding to previous records of this species which now has a very disjunct european distribution

petrology of the yerington batholith nevada evidence for evolution of porphyry copper ore fluids the jurassic yerington batholith western nevada is a composite pluton that contains several centers of porphyry copper mineralization and is exposed in structural cross section at paleodepths ranging from 0 to 8 km within these exposures the mcleod hill quartz monzodiorite bear quartz monzonite and luhr hill granite form successive intrusions that are in turn volumetrically smaller approximately 75 19 and 6 vol respectively more deeply emplaced tops at 65 km 3 luhr hill granite the low cu content approximately 10 ppm of the granite would allow extraction of approximately 50 ppm cu from it during crystallization these data suggest an orthomagmatic model in which both high and low density saline aqueous fluids formed during exsolution of water from the crystallizing luhr hill granite and from which salts cu fe and s strongly partitioned into the high density ore fluid low density fluids may have risen from the magma as a vapor plume mineralization occurred when fluid overpressures caused fracturing of wall rock and upward intrusion of granite porphyry dikes and high density saline ore fluids both the f sub o 2 path during subsolidus cooling and the deposition of most s as chalcopyrite pyrite in ore suggest that reduction of magmatic s to sulfide may have been a mechanism for oxidation of magmatic ferromagnesian silicate and fe ti oxide minerals

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