basal platinum group element mineralization in the federov pansky layered mafic intrusion kola peninsula russia the 2501 to 2446 ma federov pansky layered mafic intrusion in the central part of the kola peninsula russia is situated along the northern contact of the early proterozoic imandra varzuga rift and archean granite gneiss the federov pansky intrusion has eight major zones from bottom to top 1 marginal zone mafic schists 50 to 100 m 2 taxitic gabbronorite zone bpca 150 to 300 m 3 norite zone bcpa pbc 200 m 4 main gabbronorite zone pacb 1 000 m 5 lower layered horizon zone bc pc pbac 100 m 6 gabbro zone pacb pbac 1 500 m 7 upper layered horizon zone pocab 250 m 8 upper gabbro zone pacb 400 m the taxitic gabbronorite zone is restricted to the federov and east lastjavr blocks this zone is distinctive due to its pegmatitic taxitic textures and abundant norite xenoliths concentrated near its upper contact with the norite zone chemically the taxitic gabbronorite is more feldspathic and iron enriched than the overlying mgo and cr 2 o 3 rich norite zone and norite xenoliths the zone hosts cu ni pge mineralization with disseminated sulfides which is continuous for over 2 5 km along strike and 150 to 200 m downdip 98 percent of the sulfides consist of varying amounts of pyrrhotite chalcopyrite and pentlandite the mineralization is divided into an upper mineralized section with two higher grade lenses a and b and the restricted lower mineralized section with six narrower lenses the lower mineralized section is less continuous and less uniform in terms of cu ni pge distribution the norite xenoliths and blocks occurring within the taxitic gabbronorite zone are practically barren of sulfide and can dilute higher pge and base metal grades in the gabbronorite matrix average total pge grades in rocks do not exceed a few grams per tonne the mineralization is palladium rich with a pd pt ratio from 4 22 to 4 34 rh and au grades are 0 1 to 0 5 g t os and ir grades are the most common pge bearing minerals are merenskyite moncheite kotulskite sobolevskite and michenerite less common are sperrylite and vysotskite braggite the cu ni pge sulfides are primarily magmatic in origin this is supported by s isotope compositions with a narrow range of 34 s of 0 2 to 1 4 percent and s se ratios of 1 050 to 3 300 a three stage process is postulated for the genesis of the federov mineralization this involves the intrusion of a more fractionated and sulfur saturated gabbronorite magma and its brecciation and mixing with a residual primitive magma forming immiscible sulfides that scavenged cu ni pge the federov resembles other contact type mineralization such as in the portimo intrusion in finland and the lac des iles and east bull lake intrusions in ontario canada

glacial thermohaline circulation states of the northern atlantic the compatibility of modelling and observations observational evidence from deep sea cores suggests that the ocean circulation during the last glacial cycle was highly variable at times occupying states very different from those found today modelling can be used to dynamically constrain the possible circulation states compatible with observations thus guiding both understanding of past climate but also the geographical and scientific thrust of future palaeoceanographic research the last glacial maximum has been extensively studied and here using carbon isotopes among other variables the most likely thermohaline state consistent with palaeoclimatic data is constructed past and new modelling efforts for the last glacial maximum are then examined to contrast questions resolvable by the modelling data comparison with those that remain unanswered this shows modelling evidence to confirm the prevailing view of intermediate depth north atlantic deep water being produced at the last glacial maximum in combination with deep water production around antarctica the potential sites for this deep and intermediate water production are defined by the basic state of the thermohaline circulation however their relative importance is a function of small perturbations in the surface temperature and salinity fields brought about by active coupling between the ocean and atmosphere regions where these water masses may have been produced at the last glacial maximum are suggested

nutrient irrigation of the north atlantic abstract the north atlantic as all major oceans has a remarkable duality in primary production manifested by the existence of well defined high and low mean primary production regions the largest region is the north atlantic subtropical gyre nastg an anticyclone characterized by bowl shaped isopycnals and low production the nastg is surrounded at its margins by smaller cyclonic high production regions where these isopycnals approach the sea surface the most extensive cyclonic regions are those at the latitudinal extremes i e the subpolar and tropical oceans though smaller ones do occur at the zonal boundaries in this article we review historical data and present new analyses of climatological data and a selected number of hydrographic cruises in the western northwestern and eastern southeastern boundaries of the nastg with the objective of investigating the importance of upward epipycnal advection of nutrient rich subsurface layers irrigation in maintaining high primary production in the euphotic layers in the north atlantic subpolar gyre naspg irrigation implies intergyre exchange caused by the outcropping extension of the gulf stream gs following the formation of the deep winter mixed layer in the eastern boundary of the nastg irrigation is attained through a permanent upwelling cell which feeds the canary upwelling current cuc in the southeastern corner irrigation occurs in fall when the guinea dome gd is reinforced and in winter when the cuc reaches its southernmost extension other characteristics of the north south extension of the gs cuc are the seasonal nutrient replenishing of subsurface layers spring restratification of naspg and winter relaxation of the gd and the maintenance of high levels of diapycnal mixing during the last phase of nutrient transfer to the euphotic layers off the mid atlantic bight the gs transports a total of about 700 kmol s 1 of nitrate with almost 100 kmol s 1 carried in the surface

platinum in earth surface environments platinum pt is a rare precious metal that is a strategic commodity for industries in many countries the demand for pt has more than doubled in the last 30years due to its role in the catalytic conversion of co hydrocarbons and nox in modern automobiles to explore for new pt deposits process ores and deal with ecotoxicological effects of pt mining and usage the fundamental processes and pathways of pt dispersion and re concentration in surface environments need to be understood hence the aim of this review is to develop a synergistic model for the cycling of pt in earth surface environments this is achieved by integrating the geological biogeo chemical literature which focuses on naturally occurring pt mobility around ore deposits with the environmental ecotoxicological literature dealing with anthropogenic pt dispersion in pt deposits pt occurs as sulfide telluride and arsenide native metal and alloyed to other pges and iron fe increased mining and utilization of pt combined with the burning of fossil fuels have led to the dispersion of pt containing nano and micro particles hence soils and sediments in industrialized areas urban environments and along major roads are now commonly pt enriched platinum minerals nuggets and anthropogenic particles are transformed by physical and bio geochemical processes complexation of pt ions with chloride thiosulfate ammonium cyanide low and high molecular weight organic acids lmwoas and hmwoas and siderophores can facilitate pt mobilization iron oxides clays organic matter and micro biota are known to sequester pt complexes and particles microbes and plants are capable of bioaccumulating and reductively precipitating mobile pt complexes bioaccumulation can lead to toxic effects on plants and animals including humans bio mineralization in organic matter rich sediments can lead to the formation of secondary pt particles and grains ultimately pt is enriched in oceanic sediments where pt is commonly concentrated in manganese mn oxides when these sediments are subducted pt re enters the magmatic cycle in conclusion this review demonstrates that geological geochemical as well as biological and most recently anthropological processes are strongly interlinked in driving the cycling of pt in surface environments

the j m platinum palladium reef of the stillwater complex montana ii origin by double diffusive convective magma mixing and implications for the bushveld complex sequences of cumulates form concurrently by downdip accretion from a column of liquid layers that are primarily separated by diffusive interfaces the low cumulates grow in advance of the upper cumulates in accord with their higher crystallization temperatures an important observation is that mixing of the two parent liquids lowers their crystallization temperatures and consequently should produce unsaturated hybrids that could dissolve earlier cumulates the repetition of cyclic units above the j m reef is explained by having periodic additional injections of dense magma beneath the subsiding column of crystallizing liquid layers neither the j m reef nor the bushveld ore zones should ever have been continuous across the floor of their respective magma chambers and for bushveld the circumstances resulted in zones that are actually minable modified journal abstract

changes in sulfides and platinum group minerals with the degree of alteration in the roby twilight and high grade zones of the lac des iles complex ontario canada the lac des iles complex hosts pd deposits with unusually high pd pt and pd ir ratios these high ratios have been attributed to the introduction of pd by late magmatic hydrothermal fluids the presence of hydrous silicates and low temperature sulfide mineral assemblages has been advanced as evidence for fluid overprint this idea has been investigated by documenting the change in silicate sulfide and platinum group mineralogy and texture in samples from the deposit ranging from fresh gabbronorite to extensively altered chlorite actinolite schist in addition whole rock analysis combined with laser ablation analysis of the sulfides was used to determine which phase controlled each of the pge in fresh gabbronorite the sulfide assemblage is igneous pyrrhotite pentlandite chalcopyrite and pd is present mainly in pentlandite and kotulskite pdte inclusions associated with the sulfide minerals all other pge except pt are present in solid solution in pyrrhotite and pentlandite platinum is present as sperrylite ptas2 and montcheite ptte2 inclusions associated with the sulfide minerals these observations suggest that the pge in the fresh gabbronorite were all collected by magmatic sulfide liquid in the chlorite actinolite schist the sulfide assemblage is a low temperature assemblage consisting of chalcopyrite pyrite millerite a minor amount of palladium is present in millerite but most is present as bismuth rich kotulskite and pd arsenides both of which are associated with hydrous silicate all other pge except pt are hosted by pyrite a minor amount of pt is present in pyrite but most is found as sperrylite and montcheite associated with hydrous silicate minerals the pyrite could have formed by fe loss from pyrrhotite resulting in the pyrite inheriting os ir ru and rh and fe loss from pentlandite to form millerite resulting in the millerite inheriting some pd the pge concentrations of the whole rock show there is no direct correlation between the sulfide assemblage the degree of alteration of the silicate minerals and ore grade thus although fluids have clearly altered the sulfide silicate and platinum group mineralogy and their textures it is not clear that these fluids have changed the pge content of the rocks

increased aridity during the early holocene in west greenland inferred from stable isotopes in laminated lake sediments abstract palaeoclimatic inferences from the greenland ice cores suggest that holocene climate was relatively uniform the ice core records primarily reflect hemispheric temperature related climate processes whereas lakes tend to reflect regional scale climatic variability stable isotopes in closed basin lakes are sensitive to changes in effective precipitation here we report stable isotope evidence 18 o and 13 c records from authigenic calcite in laminated lake sediments from two oligosaline closed basin lakes in southern west greenland sondre stromfjord the stable isotope profiles indicate a dynamic early to mid holocene climate as a strongly negative precipitation evaporation balance from 7000 to 5600 cal yr bp lowered lake levels throughout the region this interpretation of the stable isotope data is supported by a survey of modern lake water isotopic composition and fossil shorelines around many closed basin saline lakes which indicate higher lake levels in the past the increased aridity during the early holocene resulted from a shift in regional circulation patterns in the davis straits baffin bay area enhanced stability of the west greenland depression and the situation of a regional trough over the sondre stromfjord area caused weakened westerly airflow and strengthened outflow i e winds blowing off the ice sheet resulting in reduced precipitation in the region decreased precipitation coupled with higher insolation probably caused the negative precipitation evaporation balance

precious and volatile metals in the perseverance nickel deposit gossan implications for exploration in weathered terrains lateritization of the perseverance nickel sulfide deposit near agnew western australia has produced mineralogical and chemical changes in the sulfides and serpentinized dunite host rocks culminating in a thick goethite quartz magnesite gossan the trace and minor elements au ag pd pt ir as sb tl se co and cr were analyzed in 30 samples to assess their mobility under conditions of extreme chemical weathering gold pd pt se as sb and tl are retained or enriched in samples from the oxidized zone while ag is lost the additional metal must have been derived from the overlying gossan since removed by erosion because the metal abundances in the surrounding barren host rocks are too low to act as a potential source the different sampling techniques employed in the study allow an assessment to be made of geochemical sampling procedures in weathered terrain grab samples generally yield the same trends as do channel samples however the grab samples display greater variability reflecting small scale heterogeneity in the fresh parent rocks the observed absolute enrichments and depletions of the trace elements investigated in this study in the oxide zone at perseverance indicate that their retention or loss is a complex process not simply controlled by the eh and ph fluctuations during lateritization the enrichment of as and sb in all the strongly oxidized weathered material and the retention of tl in the lower parts of the oxide zone indicates that primary dispersion halos of these elements should persist in intensely weathered terrain the use of ir and pd and pt to discriminate barren gossans from those developed above nickel sulfides has been confirmed

230th 234u dating of holocene tufas possibilities and problems high resolution chronologies in continental carbonate deposits such as tufas are required for detailed palaeoclimatic and environmental studies this work set out to establish if high resolution u series dating of detritus rich holocene tufas is routinely possible the study centres on a paludal holocene tufa from southern england that already has an existing holocene chronology based on 14c and supported by biostratigraphy against which to compare u series dates the results show that significant detrital contamination combined with low initial u concentrations and short time for ingrowth of radiogenic 230th make high resolution u series dating of holocene tufa very difficult moreover a single 230th 232th initial value to correct for the presence of detrital 230th is not appropriate at the study site a finding that may apply to most holocene tufas total sample dissolution of coeval samples demonstrates considerable variability in the isotopic composition of the detritus the total sample dissolution data are too scattered to constrain chronologies at the required resolution and may indicate the incorporation of a 230th rich component in the detritus

can biological toxicity drive the contrasting behavior of platinum and gold in surface environments abstract in spite of the similar chemical properties of gold au and platinum pt au is highly mobile in surface environments whereas pt appears to be far less so in this study we assess if geomicrobial processes are likely to cause these differences as the mobility of pt and au should differ little based on thermodynamic solubility alone to achieve an accurate comparison it is important that both metals occur in the same environment mineral and groundwater samples were obtained from the fifield pt au field in new south wales australia where pt and au nuggets occur in a series of tertiary eluvial and alluvial paleo placers in particular we studied the m scale dispersion of au and pt within an extraordinary 10 mm sized fragment of ferruginous paleochannel material which contained abundant native au and isoferroplatinum grains gold grains displayed complex secondary morphologies indicative of biogeochemical transformations whereas isoferroplatinum grains appeared smooth and well rounded and showed no signs of supergene transformation gold grains were surrounded by a dusting of highly pure metallic au particles 10 m in diameter whereas no metallic pt particles were detected a search for ionic pt was also unsuccessful a series of biotic and abiotic incubation experiments was conducted to investigate the hypothesis that these differences in mobility are driven by interactions with microbiota biofilms consisting of metallophilic bacteria formed on ultraflat au surfaces and caused significant surface transformations in contrast only subtle changes were observed on pt surfaces incubated under similar conditions minimal inhibitory concentrations for au complexes are more than an order of magnitude lower than those measured for pt complexes in cupriavidus metallidurans cells this higher cell toxicity of mobile au compared to pt complexes can lead to toxic levels of mobile au in the vicinity of au grain surfaces the elevated toxicity drives the formation of au detoxifying biofilms that catalyze the biomineralization of spheroidal nano particulate and bacteriomorphic au in contrast this does not occur on isoferroplatinum grains due to the lower toxicity of pt in conclusion these results are consistent with microbial adaptation to element toxicity driving the cycling of precious metals in surface environments

introduction to special issue of canadian journal of earth sciences the lake nipigon region geoscience initiative the lake nipigon region geoscience initiative lnrgi was a 3 year collaborative geoscience data acquisition and compilation project that focussed on lake nipigon in ontario and involved partnerships between mineral industry university and provincial and federal government geoscientists a major objective of the initiative was to collect new geoscience information to better understand the geological history of the nipigon region to inform land use planning identify areas of high mineral potential and attract mineral exploration the special issue on the lnrgi highlights the scientific successes of the initiative in the fields of geology petrology geochemistry geochronology stratigraphy and basin analysis mineral deposits and surficial geology and geochemistry

geology u pb zircon geochronology and geochemistry of pge bearing neoarchean and paleoproterozoic gabbroic rocks of the peter lake domain southern hearne craton canada the peter lake domain a component of the hearne craton in saskatchewan includes several intrusive complexes ranging in age from 2 70 to 1 83 ga two gabbroic complexes swan river and porter bay together represent one of the largest accumulations of precambrian mafic intrusion both metamorphosed at amphibolite facies sulfide poor pge occurrences are found in both complexes and share many textural and lithological characteristics with magmatic contact type pge ni cu deposits such as the chaotic lac des iles pluton and with layered stratiform deposits of large layered intrusions such as bushveld or stillwater lithologically both complexes are dominated by leucocratic gabbronorite and gabbro locally characterized by cumulate layering cross bedding brecciated and pegmatitic textures u pb zircon crystallization ages between 2562 and 2560 ma were obtained for the swan river complex sulfide formation is interpreted to be of magmatic origin rather than remobilized as had been speculated by explora

crustal evolution of archean rocks in the kakagi lake area wabigoon subprovince ontario as interpreted from high precision u pb geochronology the evolution of the archean volcanic plutonic complex in the kakagi lake area occurred during a time interval of ca 32 ma the earliest age is from analysis of zircon and baddeleyite in a gabbro intruding the lowermost katimiagamak volcanic group an age of 2723 2 1 8 ma on a tonalite gneiss from the interior of the underlying sabaskong batholith is indistinguishable from a previously dated massive border phase of the batholith and shows no evidence for inheritance from an older sialic component an early tonalite phase from the adjacent aulneau batholith is dated at and the latest granodiorite phase is dated at this defines a time span of about 7 ma for intrusion of the bulk of the batholith and indicates that previously dated felsic volcanism from the uppermost sequence above the kakagi lake volcanic group is coeval with late plutonic activity in the aulneau batholith the end of regional deformation in the area is given by the ages of two late tectonic intrusions the heronry lake pluton and

circulation characteristics in three eddy permitting models of the north atlantic a systematic intercomparison of three realistic eddy permitting models of the north atlantic circulation has been performed the models use different concepts for the discretization of the vertical coordinate namely geopotential levels isopycnal layers terrain following sigma coordinates respectively although these models were integrated under nearly identical conditions the resulting large scale model circulations show substantial differences the results demonstrate that the large scale thermohaline circulation is very sensitive to the model representation of certain localised processes in particular to the amount and water mass properties of the overflow across the greenland scotland region to the amount of mixing within a few hundred kilometers south of the sills and to several other processes at small or sub grid scales the different behaviour of the three models can to a large extent be explained as a consequence of the different model representation of these processes

could a pile of slippery sacks behave like an ocean abstract a method for simulating fluid motions that shows promise for application to the oceans is explored incompressible inviscid fluids with free surfaces are represented as piles of slippery sacks a system of ordinary differential equations governs the motions of the sacks and this system is solved numerically in order to simulate a nonlinear deformation internal and external gravity waves and rossby waves the simulations are compared to analytic and finite difference solutions and the former converge to the latter as the sizes of the sacks are decreased the slippery sack method appears to be well suited to ocean modeling for the following reasons 1 it perfectly conserves a fluid s distributions of density and tracers 2 unlike existing isopycnic models the slippery sack method is capable of representing a continuum of fluid densities and vertically resolving neutral regions 3 the inclusion of continuous topography adds no numerical complexity to the slippery sack method 4 the slippery

isotopes in quaternary palaeoenvironmental reconstruction isopal this special issue of quaternary science reviews comprises a selection of papers mostly deriving from a meeting on isotopes in quaternary palaeoenvironmental reconstruction isopal held at the british geological survey nottingham uk in april 2002 the object of the meeting was to discuss recent research on isotopes in palaeoenvironmental change with particular emphasis to the uk and northern europe the meeting is one of a series of workshops dealing with isotope research sponsored by igbp pages international geosphere biosphere program past global changes programme and contributes specifically to the pole equator pole pepiii transect professor tom edwards university of waterloo presented the pages isomap initiative a programme which is dedicated to fuller characterisation of earth s isotope climate and palaeoclimate based on the framework provided by both direct observational data of the past four decades and reconstruction of the isotopic composition of palaeo precipitation from various natural archives extending into the past professor edwards outlined other isomap activities which are focussed on improved mapping of the present day global isotope climate exploiting observational data mainly provided by the iaea wmo gnip programme as well as on the development of time slices and time series for several key periods in the past this issue aims to contribute to the pages programme by presenting a series of isotope systematics review papers and the application to quaternary records the opening paper by darling 2004 is concerned with the interpretation of isotopes in precipitation in the uk and northern europe and is followed by a series of papers on stable isotope records from tree rings mccarroll and loader 2004 lake sediments both inorganic leng and marshall 2004 and organic street perrott et al 2004 speleothems mcdermott 2004 including a series of shorter case study papers as well as a shorter review of stable isotopes from bone hedges et al 2004 we attempt to demonstrate that the isotope composition of terrestrial sedimentary materials can yield a wide range of useful palaeoclimate information however the overwhelming message from the keynote papers is that to fully interpret isotope data from the various components requires a detailed knowledge of the processes that control and modify the signal and these must be determined it is particularly important to carry out a calibration exercise investigating the basic systematics of isotopic variation in the modern environment to establish the relationship between the measured signal and the isotopic composition of the host waters a robust calibration may not be easy the materials may not occur in the contemporary environment for example or the region of study may be geographically isolated making a rigorous contemporary study impossible where such calibrations are not possible assumptions have to be made but should be based on evidence from both a multi proxy approach using isotope signals from different materials as well as using other techniques

mineral chemistry and stable isotope constraints on the magmatism hydrothermal alteration and related pge base metal sulphide mineralisation of the mesoarchaean baula nuasahi complex india the baula nuasahi complex on the southern flank of the singhbhum archaean nucleus in north eastern india exposes a series of mesoarchaean igneous suites these are 1 a gabbro anorthosite unit which is petrographically homogeneous although mineral chemistry data hint at a subtle eastward differentiation 2 a peridotite unit with three chromitite layers together with 3 a pyroxenite unit which display cumulate textures modal layering and for the peridotite unit differentiation trends in both mineralogy and mineral chemistry and 4 the bangur gabbro 3 1 ga which defines an oblong intrusion crosscutting the older igneous suites in the southern part of the complex with a curvilinear nw trending apophysis 2 km long and up to 40 m wide magmatic breccia comprising ultramafic and chromitite wall rock clasts in a gabbro matrix is exposed at the contact of the main bangur gabbro body and also forms the entire bangur gabbro apophysis concentrations of platinum group minerals pgms are found where the breccia contains abundant chromitite clasts and two types of platinum group element pge mineralisation are recognised type 1 pt 1 1 14 2 pd 0 1 2 1 ppm with an average pt pd 8 9 is a contact type mineralisation which occurs in the breccia at the contact between the bangur intrusion and its ultramafic host the pgms pt alloys isoferroplatinum and sulphides braggite malanite are enclosed by pyroxene and plagioclase reflecting a magmatic origin significant wall rock assimilation by the magma giving rise to the bangur gabbro is indicated by changes in pyroxene composition and by the presence of relicts of chromite from the host now altered to secondary ferritchromite in the contact zone type 2 pge mineralisation pt 0 3 1 6 pd 1 8 6 0 ppm with pt pd 0 5 3 0 is restricted to the breccia apophysis of the bangur gabbro where it occurs in the breccia matrix associated with an intense hydrothermal alteration which does not exist in the contact zone pgms pge arsenides tellurides bismuthides and antimonides and where present base metal sulphides bmss form intergrowths with hydrous silicates reflecting a hydrothermal origin oxygen isotope geothermometry documents the main stages of hydrothermal alteration within a decreasing temperature range between 700 1 000 and 500 600 c and oxygen hydrogen and sulphur isotopes show that the hydrothermal fluids were derived from the magma rather than an external source pervasive hydrothermal alteration in the breccia apophysis likely represents upward channelling of late magmatic fluids along a narrow near vertical subplanar conduit which led away from the main magma chamber we suggest that type 2 mineralisation was produced by late magmatic hydrothermal remobilisation and reconcentration of type 1 pge mineralisation and that the composition of the hydrothermal fluids controlled whether bmss were enriched along with the pgms

can oxygen stable isotopes be used to track precipitation moisture source in vascular plant dominated peatlands a b s t r a c t variations in the isotopic composition of precipitation are determined by fractionation processes which occur during temperature and humidity dependent phase changes associated with evaporation and condensation oxygen stable isotope ratios have therefore been frequently used as a source of palaeoclimate data from a variety of proxy archives which integrate this signal over time applications from ombrotrophic peatlands where the source water used in cellulose synthesis is derived solely from precipitation have been mostly limited to northern hemisphere sphagnum dominated bogs with few in the southern hemisphere or in peatlands dominated by vascular plants new zealand nz provides an ideal location to undertake empirical research into oxygen isotope fractionation in vascular peatlands because single taxon analysis can be easily carried out in particular using the preserved root matrix of the restionaceous wire rush empodisma spp that forms deep holocene peat deposits throughout the country furthermore large gradients are observed in the mean isotopic composition of precipitation across nz caused primarily by the relative influence of different climate modes here we test whether 18o of empodisma cellulose from ombrotrophic restiad peatlands in nz can provide a methodology

quaternary science 2007 a 50 year retrospective this paper reviews 50 years of progress in understanding the recent history of the earth as contained within the stratigraphical record of the quaternary it describes some of the major technological and methodological advances that have occurred in quaternary geochronology examines the impressive range of palaeoenvironmental evidence that has been assembled from terrestrial marine and cryospheric archives assesses the progress that has been made towards an understanding of quaternary climatic variability discusses the development of numerical modelling as a basis for explaining and predicting climatic and environmental change and outlines the present status of the quaternary in relation to the geological time scale the review concludes with a consideration of the global quaternary community and the challenge for the future

weathering of pge sulfides and pt fe alloys in the freetown layered complex sierra leone fresh and weathered rocks and saprolite from horizon b of the freetown layered complex contain platinum group minerals pgm the pgm in the fresh rocks are 1 7 m across including cooperite pts isoferroplatinum pt3fe minor tetraferroplatinum ptfe tulameenite pt2fecu os bearing laurite rus2 and other base metal sulfide bms bearing pgm the weathered rocks contain fewer of those pgm but a high proportion of disordered cu pd bearing pt fe alloys the saprolite hosts scarce smaller 1 3 m ordered ptfe and disordered ptfe3 the pt fe alloys became increasingly fe rich as weathering proceeded pt fe oxides appeared during weathering copper sulfides associated with the primary pgm and cooperite with 3 pd were destroyed to provide the minor cu and pd found in some of the disordered pt fe alloys platinum and pd bearing saprolites have retained the original rock fabric and to a depth of about 2 m surround residual rocks that show progressive weathering corestones ground water passing through the saprolite has transported pt and pd and probably au in solution down slope into saprolite over unmineralized rocks transport is marked by changes in the pt pd ratio indicating that the metals have moved independently palladium is present in marginally higher concentrations in the deeper saprolite than in the corestones suggesting some retention of pd in the deeper saprolite platinum and pd are less concentrated in the upper saprolite than the deeper saprolite indicating surface leaching alteration occurred over a long period in an organic and microbial rich environment that may have contributed to the leaching and transport of pge

northern latitude chemical weathering rates clues from the mackenzie river basin canada abstract the main scope of this study is to investigate parameters controlling chemical weathering rates for a large river system submitted to subarctic climate more than 110 river water samples from the mackenzie river system northern canada have been sampled and analyzed for major and trace elements and sr isotopic ratios in the dissolved phase the three main morphological units are reflected in water chemistry rivers from the canadian shield are very dilute dominated by silicate weathering millot et al 2002 whereas the rivers of the rocky and mackenzie mountains as well as the rivers of the sedimentary interior platform are dominated by carbonate weathering and are so 4 rich compared to the rivers of the mackenzie and rocky mountains the rivers of the interior plains are organic silica and na rich and constitute the dominant input term to the mackenzie river mainstream rivers of the canadian shield area do not significantly contribute to the mackenzie river system using elemental ratios and sr isotopic ratios a mathematical inversion procedure is presented that distinguishes between solutes derived from silicate weathering and solutes derived from carbonate weathering carbonate weathering rates are mostly controlled by runoff which is higher in the mountainous part of the mackenzie basin these rates are comparable to the carbonate weathering rates of warmer areas of the world it is possible that part of the carbonate weathering is controlled by sulfide oxidative weathering but its extent remains difficult to assess conversely to what was stated by edmond and huh 1997 overall silicate weathering rates in the mackenzie basin are low ranging from 0 13 to 4 3 tons km 2 yr na k ca mg and confirm the negative action of temperature on silicate weathering rates for river basins in cold climates in contrast to what has been observed in other large river systems such as the amazon and ganges rivers silicate weathering rates appear 3 to 4 times more elevated in the plains than in the mountainous headwaters this contradicts the raymo hypothesis raymo and ruddiman 1992 isotopic characterization of suspended material clearly shows that the higher weathering rates reported for the plains are not due to the weathering of fine sediments produced in the mountains e g by glaciers and deposited in the plains rather the relatively high chemical denudation rates in the plains are attributed to lithology uncompacted shales high mechanical denudation and the abundance of soil organic matter derived from incomplete degradation and promoting crystal lattice degradation by element complexation the three to fourfold factor of chemical weathering enhancement between the plains and mountains is similar to the fourfold factor of enhancement found by moulton et al 2000 between unvegetated and vegetated watershed this study confirms the negative action of temperature on silicate weathering for cold climate but shows that additional factors such as organic matter associated with northern watersheds are able to counteract the effect of temperature this acceleration by a factor of 4 in the plains is equivalent to a 6 c increase in temperature

the platiniferous dunite pipes of the eastern bushveld the platinum group mineralogy of the platinum pipes has been well documented in recent years the same however cannot be said for their silicate and oxide constituents a microscopic study of mineralized and unmineralized dunites hortonolite dunites and dunite bronzitites from the onverwacht mooihoek and driekop pipes revealed the presence of one phase and polyphase spinels the results of more than 300 microprobe analyses show that pipe deposit type spinels do not plot within the field of stratiform deposit type spinels from the chromitite layers of the bushyeld complex because they are characterized by lower cr fe and mg and occasionally higher ti there are however certain similarities with spinels from the merensky reef polyphase spinels comprise up to four constituent phases with increasing reflectance and fe contents corresponding to decreasing cr al and mg they are interpreted as products of complex postmagmatic processes graphite occurs in dunties as globules as intergranular films between olivine grains and on fractures in cr ti spinel small amounts of sulfides and platinum group minerals are also found in these locations accelerator mass spectrometry of dunites and chromitite reveals extremely low pt 0 03 38 0 ppb values the results suggest that the actual platinum group element content of the silicates is low with the platinum group elements contained in sulfides or platinum group minerals microprobe data and the presence of graphite in the dunites support the concept of metasomatic pipe formation from fe rich late and postmagmatic solutions with some of the platinum group elements possibly transported as organometallic compounds pegmatoid features spinel compositions and graphite encountered in both the pipes and the merensky reef suggest a common genetic denominator

palaeoclimate interpretation of stable isotope data from lake sediment archives the isotope composition of authigenic and biogenic carbonates and diatom silica are commonly used as palaeoclimate proxies from lake sediments this article reviews the controls on the isotope composition of lacustrine skeletal and non skeletal deposits and illustrates how stable isotope studies contribute to an understanding of changes in temperature precipitation patterns evaporation and the carbon cycle it highlights the differences in the palaeoclimate potential of a wide range of lakes ranging from open to closed lake basins a large number of the case histories but not all are drawn from studies of temperate lakes from europe large closed lake systems in the tropics and elsewhere lose water predominantly through evaporation and contain sediments with variable and generally high 18o values fluctuations in the isotope composition of authigenic or biogenic minerals are mainly a function of long term changes in the precipitation evaporation ratio in contrast small open lakes which have a degree of through flow typically contain sediments with 18o values that vary by no more than a few these variations are generally ascribed to variations in temperature or the isotope composition of precipitation p from which either an annual or seasonally specific signal can be gained these types of lakes are common in northern europe and at high altitudes the interpretation of isotope data from a lacustrine succession requires a knowledge of the local processes that might control and modify the signal their effects need to be quantified and a robust calibration using the modern lake system is necessary to establish the relationship between the measured signal the isotopic composition of the host waters and climate

roots of an archean volcanic arc complex the lac des iles area in ontario canada abstract the lac des iles area is located in the wabigoon subprovince an archean granite greenstone terrain in the superior province in ontario canada the area consists of several unmetamorphosed plutons of biotite and hornblende tonalite and mafic and ultramafic intrusions which are emplaced into an older tonalitic gneiss the mafic ultramafic bodies are concentric in shape and consist of periodotite pyroxenite gabbro and hornblende gabbro cumulates and diorite the largest intrusion the lac des iles complex consists of several mafic and ultramafic centers an internal sm nd isochron from the southern ultramafic complex gives an intrusion age of 2736 28 ma mswd 1 5 nd t 1 2 this age is also assumed to be representative of the time of emplacement of the other mafic and ultramafic bodies as well as the unmetamorphosed tonalite plutons the tonalitic gneiss represents older continental crust and had an nd value of 1 at this time the nd t values of the felsic and mafic ultramafic suites are positive ranging from 0 to 2 this range can be explained if primary magmas derived from a depleted mantle reservoir assimilated continental crust such as the tonalite gneiss during their ascent this implies that the tonalite magmas in the lac des iles area represent mixtures of the tonalite country rock and mantle magmas which formed by partial melting of depleted mantle or of mafic rocks underplated beneath the continental lithosphere the morphology and the rock assemblages of the mafic and ultramafic intrusions in the lac des iles area resemble alaskan type intrusions which are common components of phanerozoic magmatic arcs associated with subduction zones in addition the crystallization sequence in the mafic ultramafic intrusions suggests that they are derived from a parental magma with high al basalt affinities the mafic ultramafic rocks are depleted in high field strength elements but enriched in large ion lithophile elements and the tonalites belong to calc alkaline rock series displaying fractionation trends towards trondhjemitic compositions thus the archean lac des iles area and the root zones of phanerozoic active continental margins share many geological geochemical and petrological features which would suggest that the lac des iles area formed in an andean type continental margin

quantifying uncertainty in model predictions for the pliocene plio qump initial results examination of the mid pliocene warm period mpwp 3 3 to 3 0 ma bp provides an excellent opportunity to test the ability of climate models to reproduce warm climate states thereby assessing our confidence in model predictions to do this it is necessary to relate the uncertainty in model simulations of mpwp climate to uncertainties in projections of future climate change the uncertainties introduced by the model can be estimated through the use of a perturbed physics ensemble ppe developing on the uk met office quantifying uncertainty in model predictions qump project this paper presents the results from an initial investigation using the end members of a ppe in a fully coupled atmosphere ocean model hadcm3 running with appropriate mpwp boundary conditions prior work has shown that the unperturbed version of hadcm3 may underestimate mpwp sea surface temperatures at higher latitudes initial results indicate that neither the low sensitivity nor the high sensitivity simulations produce unequivocally improved mpwp climatology relative to the standard whilst the high sensitivity simulation was able to reconcile up to 6 c of the data model mismatch in sea surface temperatures in the high latitudes of the northern hemisphere relative to the standard simulation it did not produce a better prediction of global vegetation than the standard simulation overall the low sensitivity simulation was degraded compared to the standard and high sensitivity simulations in all aspects of the data model comparison the results have shown that a ppe has the potential to explore weaknesses in mpwp modelling simulations which have been identified by geological proxies but that a best fit simulation will more likely come from a full ensemble in which simulations that contain the strengths of the two end member simulations shown here are combined

origin of proterozoic metal rich black shales from the bohemian massif czech republic proterozoic metal rich black shales metasiltstones in the bohemian massif are always closely associated with submarine mafic volcanic rocks and occur in semi isolated basins that formed most likely in connection with the evolution of an upper proterozoic intracontinental rift the black shales are characterized by an average of 3 5 wt percent c organic and 5 2 wt percent s and carry up to 0 42 wt percent zn 0 21 wt percent v 0 12 wt percent ni 0 12 wt percent cr 0 12 wt percent cu 0 06 wt percent as 0 03 wt percent mo 132 ppb au 102 ppb pd 25 ppb pt 1 7 ppb rh and 1 3 ppb ru their thickness varies from about 1 to 45 m sulfide minerals often include abundant framboidal pyrite which occurs widely in c organic rich layers grainy pyrite zn ni cu and mo sulfides appear to be restricted to late quartz and carbonate veinlets mo selenide mo telluride galena berthierite and gold are very rare sulfur isotope results suggest the dominant source of sulfur to have been seawater sulfate reduced by bacteria under different conditions the delta 13 c values of the organic matter 24 2 to 37 5ppm reflect the combination of the carbon isotope composition of dissolved hco 3 its high concentration and the type of organisms the results of rock eval pyrolysis as well as laser raman spectroscopy show a high maturity close to that of well crystallized graphite fluid inclusion and stable isotope data from quartz and carbonate veinlets of very low grade regionally metamorphosed metalrich black shales at kamenec and highly metamorphosed facies at hromnice indicate that they resulted from the interaction between 18 o rich fluids volcanics and metasediments the interaction could have occurred during subsea floor or later regional metamorphism

late quaternary changes in carbon cycling on mt kenya east africa an overview of the δ13c record in lacustrine organic matter abstract the 13 c signature of sedimentary organic matter acts as a tracer for past changes in the terrestrial and aquatic carbon cycles compound specific 13 c analysis enables these two signals to be disentangled we compare the molecular isotopic records from a transect of five lakes between 1820 and 4595 m a s l on mt kenya east africa spanning the last 100 000 years with multiproxy palaeoenvironmental data in order to determine the mechanisms underlying late quaternary variations in carbon cycling at different altitudes the amplitude of down core variations in the 13 c values of total organic carbon varied from 4 8 to 17 4 the 13 c signals in compounds of terrestrial aquatic macrophyte and algal origin were tightly coupled reflecting strong atmospheric control during the early glacial and the last glacial maximum the effects of sub ambient co 2 and enhanced moisture stress reinforced each other resulting in carbon starvation and very high 13 c values in contrast smaller millennial scale shifts in 13 c during the late glacial and holocene were driven primarily by fluctuations in monsoon precipitation however the impact of late quaternary atmospheric changes were complex involving variations in biomass burning vegetation cover soil erosion lake levels and water chemistry in addition to direct physiological responses by higher plants and algae

lead isotope study of the late archean lac des iles palladium deposit canada enrichment of platinum group elements by ponded sulfide melt lead isotopic compositions of mineral separates are presented from the mineralized zones roby twilight and high grade zones of the lac des iles palladium deposit approximately 2 69 ga and tonalitic country rocks approximately 2 727 to 2 775 ga in the wabigoon subprovince of the western superior province of canada plagioclase separates show pb isotope ratios similar to those of the late archean depleted mantle sulfide minerals coexisting with plagioclase have a more radiogenic pb isotope composition but very low concentrations of u 0 2 ppb u and th 0 01 ppb compared to pb 50 ppb the isotope data are consistent with a model involving the incorporation of radiogenic pb from country rocks to sulfide melt near the base of the magma chamber or along the conduit of the parental magmas the proposed interpretation is also supported by decreasing cu pd ratios from earlier barren to late fertile gabbro intrusions in the complex the ponding sulfide melt became enriched in platinum group elements as it was interacting with a large magma volume during the evolution of the lac des iles igneous complex

a synopsis of mineral deposits in the archean and proterozoic rocks of the lake nipigon region thunder bay district ontario a variety of metallic and non metallic mineral deposit types occur within archean and proterozoic rocks in the area encompassing the lake nipigon region geoscience initiative archean deposit types include algoma type banded iron formation hosted iron e g lake nipigon iron range volcanogenic massive sulphide copper zinc e g onaman tashota belt ultramafic intrusion hosted chromium e g puddy chrome lakes mafic to ultramafic intrusion hosted copper nickel platinum group element pge e g lac des iles and pegmatite hosted deposits of rare metals li ta be uranium and molybdenum e g georgia lake field black sturgeon lake and anderson lake respectively mesothermal lode gold deposits are prominent in the beardmore geraldton camp superior type iron formation occurs in paleoproterozoic gunflint formation red bed copper occurs in mesoproterozoic midcontinent rift related osler group volcanic and interflow sedimentary rocks native copper and copper sulphides occur in mesoprote

discovery of a palladium platinum gold mercury bitumen in the boss mine clark county nevada a bitumen containing high concentrations of sulfur palladium platinum gold and mercury has been found in the boss mine clark county nevada where rich ores of invisible palladium and platinum were mined from 1916 to 1919 the bitumen analyzed with x ray energy dispersive spectrometry on areas devoid of discrete particles down to a 40 aa limit contains 2 74 wt percent pd pt au pd 1 85 and 5 83 wt percent hg it is associated with particulate potarite pd au pt hg native gold plumbojarosite hydronium jarosite argentojarosite florencite and bismuth oxides the first four mineral species are also found included in the bitumen the paragenesis was derivation and formation of bitumen from the local limestone followed by interaction with the hydrothermal potarite and the supergene jarosite this type of organic material highly enriched in platinum group elements previously had been reported only in polish kupferschiefer thucholite

the geon 14 arc related mafic rocks from the central grenville province the late paleoproterozoic to mesoproterozoic ca 1 7 1 2 ga evolution of the active southeastern margin of laurentia terminated with the grenvillian continental collision and the development of a large hot long duration orogen at ca 1 09 0 98 ga as a result much of the hinterland of the grenville province consists of paleoproterozoic and mesoproterozoic rocks mostly preserved as an imbricate stack of high grade gneisses that represent a potential repository of active margin processes this study presents geochronologic geochemical and isotopic analyses of two granulite facies suites of ca 1 45 1 40 ga mafic tholeiites from the canyon domain manicouagan area central grenville province one suite consists of 1439 76 68 ma high feti mafic sills with end values of 0 4 tdm 2 57 2 72 ga indicate derivation from variably depleted to enriched morb type mantle sources probably in an extensional back arc setting before intrusion in a ca 1 5 ga supracrustal metasedimentary sequence the other

using the high mobility of palladium in surface media in exploration for platinum group element deposits evidence from the lac des iles region northwestern ontario platinium group element pge mineralization is commonly accompanied by large amounts of ni fe sulfides which are explored for using a variety of geophysical and geochemical methods appreciation of a new type of pge mineralization is emerging hosted by gabbroic rocks with low concentrations 5 vol of disseminated sulfides the host rocks commonly display textural complexity such as brecciation pods and veins of pegmatite and magma mingling of different lithological units examples include the lac des iles deposit in northwestern ontario the east bull lake suite in eastern ontario and several intrusions in the kola peninsula and northern finland such mineralization does not result in prominent geophysical and geochemical anomalies thus posing a challenge for exploration we initiated a project to develop new geochemical exploration approaches for such pge deposits with low sulfides and selected the lac des iles district northern ontario canada which contains one producing mine and many pd showings mineralization is hosted by gabbroic rocks with low concentrations 5 vol of sulfides enriched elements include pd pt au ni cu and co in separate sulfide rich mineralization base metals can be abundant up to 1 wt percent but pd is insignificant 200 ppb this reduces the relevance of ni cu and co as possible pathfinders for sulfide poor pge mineralization leaving pd pt and au a detailed study in the baker zone at the lac des iles mine and the legris lake property indicates the essentially immobile nature of pt in these surface environments by contrast pd is depleted in b horizon soil suggesting its removal during the conversion of c to b horizon soils the loss of pd in b horizon soil reflects the transport of pd as neutral and anionic complexes probably with oh and possibly with organic ligands which are not adsorbed by fe oxyhydroxides in the soils instead pd migrates in solution to accumulate in humus in swamps and organic rich lake sediments downslope from mineralization the distribution of pd in humus therefore provides a distal indicator of nearby mineralization total digestion of humus using fire assay or aqua regia yielded up to 160 ppb pd whereas a variety of commercially available leaching methods extracted few ppb pd the results indicate that pd is tightly held in organic matter this behavior of pd contrasts with many metallic elements such as cu and ni that are enriched in b horizon soil and may be extracted by a variety of leaching techniques palladium arsenides tellurides antimonides and sulfides are unstable in weathering environments and their dissolution releases pd to surface waters therefore pd can be used to indicate other pge mineralization as it is always abundant among pge where pge mineralization is associated with high concentrations of fe sulfides their oxidation produces acidic waters which further promotes pd dispersion thus the findings of this study are applicable to exploration for both sulfide rich and poor pge mineralization

north atlantic oceanic decadal variability in the hadley centre coupled model the hadley centre coupled model is used to investigate the relationship between the north atlantic oscillation nao labrador sea deep convection and sea surface temperature variability it is shown that the model is capable of simulating many features of the observed variability in particular the model reproduces the observed relationship between decadal variations in labrador sea convection and the nao it also has surface temperature anomalies that propagate along the path of the north atlantic current nac with a timescale close to that of observed anomalies a number of sensitivity experiments are performed with the coupled model to understand the underlying mechanisms simulations in which the labrador sea convection is artificially enhanced and surpressed illustrate a time lagged impact on the nac and therefore on sea surface temperature in that region further simulations with a sinusoidal forcing of convection confirm the role of labrador sea water lsw in determining the timescale for propagation of the surface temperature anomalies the timescale of surface anomalies moving along the path of the nac is determined by the movement of lsw at intermediate depths

magma mixing in late archean tonalitic and mafic rocks of the lac des iles area western superior province abstract plutonic rocks in the lac des iles area of the western superior province provide a record of contemporaneous late archean mafic and tonalitic magmatism this suite of rocks consists of mafic to ultramafic intrusions mafic to intermediate dikes hornblendite and hornblende tonalite the tonalite contains net veined and disaggregated mafic to intermediate dikes mafic schlieren and zones of hornblendite to mela tonalite with skeletal hornblende these textures are interpreted to be the result of magma mixing the hornblende tonalite is geochemically characterized by high al 2 o 3 high na 2 o k 2 o low rb moderate sr and fractionated ree the hornblendite mafic to intermediate dikes and tonalite show whole rock trends of decreasing total ree increasing depletion of hree and increasing eu eu with increasing sio 2 amphiboles range in composition from edenitic and pargasitic hornblende to hornblende in dike rocks mela tonalite and hornblendite and from hornblende to actinolite in tonalite the development of skeletal amphiboles with strong normal zoning and resorbed hornblende with weak reverse zoning are attributed to conditions of supercooling and superheating respectively in zones of magma mixing the least fractionated dike rocks geochemically resemble lamprophyres derived from alkali basaltic magma variation of ree among the mafic to intermediate dikes suggests that they fractionated hornblende hornblendites and mela tonalites can be modeled as hornblende cumulates from the dike rocks the amphiboles probably crystallized rapidly during mixing leaving a feldspathic residue variation in hornblende tonalites is consistent with mixing of sio 2 rich tonalite melt with mafic to intermediate dike phases and associated hornblende cumulates and feldspathic residue open system magmatic processes at lac des iles result in a continuum of disequilibrium textures reflecting emplacement of mafic magma into a crystallizing felsic host the plutonic rocks probably formed from a zoned magma chamber with a mafic base and tonalitic top breccia zones in the tonalite suggest that explosive degassing of the chamber occurred structures similar to those reported here are common in other granitoids in the superior province and suggest that mafic magmatism and magma mixing played an important role in the development of late archean granitoid plutons

controls on the formation of contact type platinum group element mineralization in the east bull lake intrusion the east bull lake intrusion is the type example of a series of 2 48 to 2 49 ga layered mafic intrusions that developed within the rifted southern margin of the superior craton central ontario the east bull lake intrusion contains contact type pge mineralization e g strata bound pge rich disseminated sulfide mineralization occurring within 200 to 300 m of the contact with footwall and sidewall units although the mineralization locally occurs in massive plagioclase cumulates anorthosite zone most of the sulfides are concentrated within an underlying heterolithic inclusion rich unit inclusion bearing zone that grades into an intrusive breccia disseminated sulfides also occur in fine grained gabbroic veins within brecciated footwall rocks border zone geochemical characteristics of the contact type sulfide mineralization and its host rocks include 1 high average pd abundances throughout the east bull lake intrusion including an average of ca 200 ppb in the lower series 2 low average s contents typically contact type pge mineralization in the east bull lake intrusion reflects flow enhanced gravitational settling of a cu rich sulfide liquid followed by local fractionation of ni rich monosulfide solid solution to produce minor amounts of cu and pt rich residual sulfide liquid most of the observed compositional variation in the sulfides can be modeled using variable silicate liquid sulfide liquid mass ratios field and geochemical observations suggest that the parental magmas to the mineralized parts of the east bull lake intrusion were s saturated and pge rich at the time of their emplacement these fertile parent magmas most likely originated as buoyant feldspathic residual magmas that escaped from a deeper more primitive subchamber although first described from the east bull lake intrusion contact type pge mineralization is now recognized in all of the major east bull lake suite intrusions similar styles of magmatic sulfide mineralization are developed in the contact environments of the bushveld igneous complex platreef deposits and the duluth complex minnesota e g dunka road deposit these contact type deposits are part of the family of basal accumulation magmatic sulfide deposits the economics of low sulfide tenor contact type pge cu ni mineralization such as that developed in the east bull lake intrusion will be most favorable in systems in which 1 the parent magmas possessed high initial pge tenors and reached s saturation prior to emplacement 2 the parent magmas experienced vigorous convection in the early stages of chamber development and 3 segregated sulfide was not diluted by coprecipitating silicate minerals a scenario that is most likely to occur in feldspathic magmas in which plagioclase is the principal high temperature liquidus mineral

diatom oxygen isotopes in pro glacial lake sediments from northern sweden a 5000 year record of atmospheric circulation we use a pro glacial oxygen isotope record of diatom silica 18odiatom and a sedimentary proxy for glacier flutuations to determine centennial millennial scale climate change during the last 5000

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

proterozoic and archean geology of the nipigon embayment implications for emplacement of the mesoproterozoic nipigon diabase sills and mafic to ultramafic intrusions the nipigon embayment is underlain by archean rocks of the english river wabigoon and quetico subprovinces and intruded along the west side by late to post tectonic mafic to ultramafic intrusions the early mesoproterozoic ultramafic to felsic badwater intrusion and felsic english bay complex are located in the northwest corner of the nipigon embayment three mafic to ultramafic intrusions the disraeli seagull and hele intrusions are located south of lake nipigon and the kitto intrusion is located east of the lake a number of mafic to ultramafic bodies jackfish island shillabeer kama hill nipigon bay have only limited outcrops the gabbroic nipigon diabase sills intrude all other rocks in the nipigon embayment and generally have a consistent mineralogy and geochemistry except for the inspiration sill s and the mcintyre sill geological and geophysical data suggest emplacement of the ultramafic intrusions by mechanisms similar to those controlling emplacement of the saucer shaped diabase sills these mechanisms are partially dependent on a series of pre existing north northwest and northeast trending faults formed prior to keweenawan magmatism the presence of sills rather than dykes indicates that the nipigon embayment was not extensional during the keweenawan midcontinent rift suggesting that the nipigon embayment is not a classic failed arm

the petrogenesis of a platiniferous dunite pipe in the bushveld complex infiltration metasomatism by a chloride solution the driekop dunite pipe crosscuts part of the noritic layered sequence of the upper critical zone in the eastern bushveld complex the central orebody of the pipe contains platinum group minerals base metal sulfides magnetite and iron rich olivine the country rock forms a collapse structure around the pipe with the layered sequence becoming almost vertical near the contact with the pipe it is proposed that a high temperature chloride solution flowed through irregular channel ways along a structural weakness near the axis of the pipe and reacted with the noritic host rocks leading ultimately to the formation of dunite reaction fronts advanced at different rates outward from the channelways and produced a sequence of metasomatic zones characteristics of infiltration metasomatism that are evident in the pipe include the movement of material over large distances in predominantly one direction the formation of a monomineralic rock the occurrence of a marginal zone that is enriched by displaced components and plateaus in the compositions of mineral solid solutions the reactions responsible for the major changes in the bulk composition of the host rocks were desilication of orthopyroxene to produce olivine and dissolution of plagioclase the 67 percent volume loss accompanying these reactions can account for the structural collapse of the critical zone around the pipe some olivine in the pipe is too fayalitic to have been produced by simple desilication of host rock orthopyroxene the enrichment of olivine in iron can take place bymg 2 sio 4 2fecl sub 2 sub aq fe 2 sio 4 2mgcl sub 2 sub aq forsterite fayalite aqueous chloride complexes are also believed to have played an important role in the transport and precipitation of the platinum group elements the base metals and other cations interdependent chemical reactions involving a chloride solution olivine magnetite and the platinum group elements can account for the preferential association of the ore with iron rich olivine infiltration metasomatism by a high temperature chloride solution may have an important bearing on the interpretation of other features of the bushveld complex

holocene climate and vegetation change in the main ethiopian rift valley inferred from the composition c n and δ13c of lacustrine organic matter abstract in order to track changes in the relative abundance of c3 and c4 plants in savanna vegetation c n and 13c values were measured on bulk organic material in an 8840 14c year record from lake tilo ethiopia between 8840 and 2500 bp high c n ratios suggest that input to the lake was predominantly from terrestrial plants the corresponding 13c values thus provide a proxy for changes in catchment vegetation that are supported by pollen data 13c values in the early holocene are relatively low reflecting the dominance of c3 vegetation woody plants and a more humid climate 13c shows no response to a known regional arid interval at 7800 yr bp suggesting that woody vegetation was able to survive relatively prolonged dry periods a gradual rather than sharp 13c response to the end of the early holocene humid interval at 4500 yr bp further supports this higher 13c values at 2800 2300 and 1000 yr bp correspond to increases in sedge pollen thought to be growing in freshwater springs exposed as lake level fell the c n and 13c composition of bulk organic material complements the pollen evidence and may be useful in other lakes in savanna regions as indicators of terrestrial vegetation change

frictional sinking of the dense water overflow in a z coordinate ogcm of the mediterranean sea the overflow and subsequent spreading of dense water formed in the adriatic sea is studied in a high resolution z coordinate ocean general circulation model ogcm of the mediterranean sea via simulations of chlorofluorocarbons cfc12 frictional sinking is investigated using different parametrisations of the mean bottom stress in term of the mean currents a series of model integrations shows that increasing the strength of the bottom stress allows the dense overflow to descend the continental slope at a steeper angle as would be expected on the basis of theoretical streamtube models the use of a linear drag which can be thought of as parametrising unresolved time varying motions greatly improves the model s ability to capture a realistic dense water pathway and hence realistic cfc12 distributions

strontium isotope evidence for preserved density stratification in the main zone of the bushveld complex south africa the bushveld complex formed from two isotopically distinct magmas magma addition and mixing can be tracked by measuring initial strontium isotope ratios of cumulates rocks with ratios of 0 7065 lie below the lower 2 2 km of the main zone ratio 0 7085 whereas those with ratios of 0 7073 lie above it this unit represents a liquid layer intruded into the density stratified magma pile near the base of the chamber the merensky reef was produced by mixing of the pile with underlying trapped liquid enriched in precious metals

geochemistry of the mesoproterozoic intrusive rocks of the nipigon embayment northwestern ontario evaluating the earliest phases of rift development the intrusive rocks of the nipigon embayment comprise a series of four mafic to ultramafic intrusions and a number of laterally extensive diabase sills that are among the oldest expression of the

the lac des iles complex ontario petrology and platinum group elements mineralization in an archean mafic intrusion the lac des iles complex is a late archean mafic to ultramafic complex that is host to 20 4 106 t pt pd and au mineralization with an average grade of 6 34 g t platinum group elements pge the 30 km2 complex located in the wabigoon subprovince consists of several coalescing mafic to ultramafic intrusive centers the complex is emplaced into early gneissic tonalite and is contemporaneous with late granitoids the magmatic evolution of the complex reflects the emplacement of multiple pulses of previously fractionated magma some of which underwent subsequent in situ fractionation distinct magma sequences are recognized on the basis of intrusive relationships differences in the cumulus minerals crystallization order and trace element chemistry these sequences are 1 hornblende gabbro 2 gabbro and gabbronorite and 3 ultramafic where there is evidence of intrusive relations the most primitive sequences are emplaced late and occur toward the north end of the complex microprobe analyses in

decadal timescale changes of the atlantic overturning circulation and climate in a coupled climate model with a hybrid coordinate ocean component a wide range of statistical tools is used to investigate the decadal variability of the atlantic meridional overturning circulation amoc and associated key variables in a climate model chime coupled hadley isopycnic model experiment which features a novel ocean component chime is as similar as possible to the 3rd hadley centre coupled model hadcm3 with the important exception that its ocean component is based on a hybrid vertical coordinate power spectral analysis reveals enhanced amoc variability for periods in the range 15 30 years strong amoc conditions are associated with 1 a sea surface temperature sst anomaly pattern reminiscent of the atlantic multi decadal oscillation amo response but associated with variations in a northern tropical subtropical gradient 2 a surface air temperature anomaly pattern closely linked to sst 3 a positive north atlantic oscillation nao like pattern 4 a northward shift of the intertropical convergence zone the primary mode of amoc variability is associated with decadal changes in the labrador sea and the greenland iceland norwegian gin seas in both cases linked to the tropical activity about 15 years earlier these decadal changes are controlled by the low frequency nao that may be associated with a rapid atmospheric teleconnection from the tropics to the extratropics poleward advection of salinity anomalies in the mixed layer also leads to amoc changes that are linked to processes in the labrador sea a secondary mode of amoc variability is associated with interannual changes in the labrador and gin seas through the impact of the nao on local surface density

a model analysis of the behavior of the mediterranean water in the north atlantic abstract the behavior of the mediterranean water in the north atlantic ocean sector of a global ocean general circulation model is explored starting from its entry point at the strait of gibraltar the analysis focuses primarily on one experiment in which explicit watermass exchange between the mediterranean sea and the atlantic at the strait of gibraltar is permitted the model produces an exchange rate of approximately 1 sv sv 106 m3 s 1 this is comparable to estimates derived from field measurements the density of the mediterranean outflow however is lower than observed mainly because of its high temperature more than 2 c higher than in reality the lower density of the outflow and the model s inadequate representation of the entrainment mixing in the outflow region cause the mediterranean water to settle in a depth range 800 1000 m in the north atlantic about 200 m shallower than observed here an interesting current system forms in response to the intrusion of the mediterranean water i

palaeoclimatic interpretation of high resolution oxygen isotope profiles derived from annually laminated speleothems from southern oman high resolution stable isotope profiles of three contemporaneously deposited stalagmites from a shallow cave in southern oman provide an annually resolved record of indian ocean monsoon rainfall variability for the past 780 years uranium series age dating and counts of annual growth bands enable an excellent age calibration although modern speleothems do not grow in perfect isotopic equilibrium oxygen isotope ratios 18o are a proxy for the amount of monsoon rainfall this is supported by the statistically significant correlation between 18o and the thickness of annual bands whereas 18o is inversely correlated with annual band thickness additionally overlapping 18o profiles are very similar in pattern and range indicating that sample specific noise did not blur the climatic signal the longest oxygen isotope profile derived from stalagmite s3 clearly shows the transition at 1320 ad from a generally wetter medieval warm period to a drier little ice age that lasted from approximately ad 1320 1660 in southern oman the decrease in monsoon rainfall since the 1960s is also obvious in meteorological records from northern africa and india indicating that our speleothem based rainfall records do not only reflect local monsoon rainfall variability

source and tectono metamorphic evolution of mafic and pelitic metasedimentary rocks from the central quetico metasedimentary belt archean superior province of canada abstract a study of the sedimentary rocks in the jean lake area of the quetico metasedimentary belt superior province canada was conducted in order to evaluate the origin source and evolution of rocks including mafic rocks previously mapped as ultramafics rocks bulk compositions of these sedimentary rocks show a mixing between two end members quartzo feldspathic sedimentary rock and komatiitic basalt high cao and mgo contents of the rocks suggest a proximal source of the komatiitic basalt the rocks in the study area record a pressure temperature p t path with three tectono metamorphic stages the first stage formed staurolite 500 700 c under medium p t mp mt metamorphic conditions shortly after the sedimentation the second stage yielded the biotite sillimanite garnet assemblage under the peak conditions of 0 6 0 1 gpa and 700 70 c during transpressional deformation the third stage low p medium t lp mt 0 25 0 11 gpa 540 80 c metamorphism was associated with regional south southeast compression and its timing is constrained by a new u th pb monazite age of 2667 20 ma combining the regional deformation events we suggest the burial metamorphism of sediments up to mp mt conditions during the d1 deformation at 2698 2689 ma they attained the peak metamorphic conditions during the regional transpressive d2 d3 deformation 2689 2671 ma and retrograded to lp mt condition during the south southeast compression regional d4 at 2671 2667 ma a short time span between the sedimentation and mp mt metamorphism accompanied by d1 deformation suggest that the quetico sedimentary rocks formed in an acretionary prism the studied rocks in the jean lake area deposited close to the wabigoon subprovince transported towards the south and buried up to 20 km by rapid underthrusting to amphibolite facies conditions subsequent dextral transpressive deformation d2 d3 during the oblique docking of the quetico belt to the wabigoon subprovince to the north and wawa greenstone belt from the south resulted in the displacement of the sedimentary rocks to the west from the original depositional site the p t time path of the quetico sedimentary rocks is similar to that in modern arc accretion prisms except for a high geothermal gradient of 30 c km recorded in the former compared to 10 c km in modern counterparts the high temperature gradient in the archean accretionary prism explains the lack of high pressure metamorphic rocks such as blueschist that are common in modern accretionary prisms

archean tectonic and metallogenic evolution of the superior province of the canadian shield abstract the superior province of the canadian shield has mainly experienced an archean tectonic history comprising several cycles of volcanism plutonism and tectonism although the rocks of the superior province span more than 500 million years of archean time most mineral deposits formed in an interval of 100 million years or less corresponding to a period of accretion of oceanic and pre existing continental fragments in the late archean at 2 7 ga in accord with recent tectonic syntheses which argue for the accretionary origin of the superior province the metallogenic history of the superior province can also be interpreted in the same context provided secular anomalies in the early history of the earth are acknowledged for relatively unique deposit types such as komatiitic nickel deposits and voluminous iron formations volcanogenic massive sulphide iode gold and granitoid associated deposits as well as ni cu pge cr and ti deposits associated with mafic ultramafic intrusions are readily interpreted in terms of the construction and accretion of late archean island arcs

stratigraphy and petrology of the lower part of the mulcahy gabbro northwestern ontario origin of reverse and normal fractionation trends and implications for tectonic setting of late archean mafic magmatism the mulcahy gabbro 2 73 ga is an exceptionally well preserved tholeiitic layered intrusion located in the wabigoon subprovince of the superior province the intrusion has a 900 m thick marginal z

transfer and deposition of gold in the congo watershed abstract gold has been measured in water and suspended particulate matter samples coming from the oubangui congo system gold anomalies up to 800 pico m l were measured at two different locations these are interpreted as the result of gold transport by dissolved organic complexes everywhere else the gold content is in the range of 10 11 m l and gold is present as an aurous hydroxichloride complex the knowledge of both discharge rates and gold content allows a quantification of the gold input into the atlantic ocean respective values for dissolved and particulate gold input are equal to 2 86 t a and 2 95 t a both chemical denudation and physical weathering rates were computed from this new set of data

mantle derivation of archean amphibole bearing granitoid and associated mafic rocks evidence from the southern superior province canada amphibole bearing late archean 2 73 2 68 ga granitoids of the southern superior province are examined to constrain processes of crustal development the investigated plutons which range from tonalite and diorite to monzodiorite monzonite and syenite share textural mineralogical and geochemical attributes suggesting a common origin as juvenile magmas despite variation in modal mineralogy the plutons are geochemically characterized by normative quartz high al2o3 15 wt na rich fractionation trends mol na2o k2o 2 low to moderate rb generally 150 ppm are comagmatic with the evolved granitoids and indicate that the suites are mantle derived isotopic studies of archean monzodioritic rocks have shown lree enrichment and initial 143nd 144nd ratios indicating derivation from mantle sources enriched in large ion lithophile elements lile shortly before melting mineral assemblages record lower ph2o with increased alkali contents of the suites this evidence in conjunction with experimental studies suggests that increased alkali contents may reflect decreased ph2o during mantle melting these features indicate that 2 73 ga tonalitic rocks are derived from more hydrous mantle sources than 2 68 ga syenitic rocks and that the spectrum of late archean juvenile granitoid rocks is broader than previously recognized comparison with phanerozoic and recent plutonic suites suggests that these archean suites are subduction related

the impact of a bottom boundary layer scheme on the north atlantic ocean in a global coupled climate model abstract although the overflow and descent of cold dense water across the greenland iceland scotland ridge is the principal means for the maintenance of the thermohaline circulation in the north atlantic ocean this feature is not adequately treated in global ocean numerical models in this paper a bottom boundary layer scheme is introduced into the hadcm3 coupled atmosphere ocean sea ice general circulation climate model in order to give an improved representation of cold water formation in the north atlantic ocean the scheme uses a simple terrain following bottom boundary layer incorporated into the ocean general circulation model only the tracer tendencies are evaluated in the bottom boundary layer with the velocities taken from the near bottom interior values it is found that with the bottom boundary layer scheme there are several significant effects on the deep water formation and flow the overflow of dense water from the nordic seas into the north atlantic seas is improved with the introduc

platinum group element mineralization in a hydrothermal cu ni sulfide occurrence rathbun lake northeastern ontario pt pd and au are concentrated in a hydrothermal cu ni sulfide occurrence near rathbun lake northeastern ontario the mineralization is associated with a sheared zone of the wanapitei intrusion where hydrothermal fluids have altered relatively pristine gabbronorite to chlorite sericite quartz epidote and biotite chalcopyrite and pyrite the principal sulfide minerals occur as massive and disseminated mineralization bismuthian merenskyite and to a lesser extent kotulskite michenerite and temagamite are the pd bearing minerals whereas pt occurs primarily in sperrylite 64 percent of the pd mineral grains are associated with altered silicates rather than sulfides although grains within sulfides may have been exsolved the size and number associated with silicates suggest many were precipitated independently grab samples average 9 percent cu 0 2 percent ni 20 829 ppb pd 9 736 ppb pt and 3 053 ppb au values for the other platinum group elements are near background levels no correlation is evident between cu and the platinum group elements or au the ratio of pt pd os ir ru is much larger than for tholeiitic hosted deposits of magmatic origin and probably reflects the relative solubilities of the platinum group elements

the difference between oceanic and continental tholeiites a fluid dynamic explanation continental tholeiites have higher sio2 k2o and light rare earth element contents and more evolved isotopic characteristics than their oceanic counterparts these differences can be explained if the compositions of the parent magmas to both types of tholeiites are similar but if continental magmas assimilate significant amounts of continental crust en route to the surface although there is little doubt that most continental tholeiites have assimilated crustal material the lcoation and mechanism of assimilation remain uncertain longhi 1981 has argued that magmas derived directly from the mantle should crystallize little orthopyroxene the abundance of orthopyroxene in most continental layered intrusions suggests that they have crystallized from magmas which have assimilated continental crust since orthopyroxene is an early crystallizing phase in layered intrusions this assimilation must occur early before the magma enters the chamber assimilation can occur at the margins of the dykes which feed magma chambers depending on the nature of the flow if the flow is turbulent the high temperatures at the centre of the dyke will extend to the margins and the magma will erode the dyke walls if the flow is laminar a conductive profile develops at the margin and the flowing magma chills against the walls protecting them from thermal erosion the nature of flow in a dyke can be predicted from the reynolds number the criteria for turbulence reynolds number calculations suggest that the flow of primitive magmas in continental dykes will be fully turbulent and if this is the case assimilation of low melting point components in the walls of the dyke is inevitable it is therefore suggested that many of the geochemical characteristics of continental tholeiites result from melting at the walls of dykes as primitive magmas ascend through the crust

geochronology of the lumby lake greenstone belt a 3 ga complex within the wabigoon subprovince northwest ontario the lumby lake greenstone belt lies within the central predominantly metaplutonic terrane of the western wabigoon subprovince it is conformable with gneiss of the marmion lake tonalite batholith u pb analyses of zircons from two felsic tuffs and a quartz porphyry within the greenstone belt give a scattered lead loss pattern indicative of early disturbance the ages of the oldest concordant fractions agree however and define an age of 2999 1 m y for emplacement of these felsic units zircons from a tonalite gneiss within the marmion lake batholith are also somewhat disturbed the oldest abraded fraction is concordant and has an age of 3003 5 m y indicating that the gneiss is probably close in age to the supracrustal rocks u pb analyses of rutile from one of the felsic units give an age of 2690 5 m y and record the effect of late archean metamorphism three titanite fractions from the tonalite gneiss agree within error and have an age of 2809 1 m y the age and consistency of the titanite fractions indicate that titanite in this rock was formed as a result of a metamorphic event and was never subsequently disturbed this age is therefore a minimum estimate for high grade metamorphism of the gneiss the presence of a pre 2809 ma fabric in a gneiss of regional extent suggests that an early metamorphic deformational event affected this area these data constitute the first firm evidence for extensive 3 0 ga crust in the southern superior province and give the first evidence of a regional deformational event which predates cratonization of the superior province

constraints on hydrological and paleotemperature variations in the eastern mediterranean region in the last 140 ka given by the δd values of speleothem fluid inclusions abstract speleothem fluid inclusions potentially provide vital data on the paleohydrological conditions in glacial and interglacial periods we show here that d analyses of fluid inclusions from speleothems in three caves in the eastern mediterranean region israel provide a basis for understanding hydrological and temperature variations in the last 140 ka using measured d fluid inclusion values and temperature ranges constrained by the present day mediterranean meteoric water line mmwl and the global mwl we show a strong compatibility between the land and marine temperature records with the highest land temperatures occurring at 120 130 ka 17 22 c and the present 18 c and the lowest temperatures during the lgm about 10 c lower than present interglacial waters are constrained to follow the mmwl and most glacial waters also plot close to the mmwl with a slight shift towards the mwl however during two remarkable brief periods at the termination of the lgm the waters plot on the mwl suggesting that both sharp cooling and an increase in relative humidity above the em sea reduced d excess values to those of the global system

geochemistry of peat over kimberlites in the attawapiskat area james bay lowlands northern canada abstract the james bay lowlands which is the se part of the hudson bay lowlands canada and within the paleozoic limestone terrane is covered mostly by peatlands peat samples were examined in the attawapiskat area a region of discontinuous permafrost where more than 19 kimberlite pipes have been found beneath a cover of peat 2 4 m thick and quaternary sediments up to 20 m thick of tyrell sea clay beds and glacial tills pore water at a depth of 40 cm in the peat has a consistently low ph the compositions of peat show spatial variation with the distribution of kimberlites suggesting that they are influenced by the underlying rocks even through there are thick layers of tills and sediments between the bedrocks and peat however elevated concentrations of pathfinder elements of kimberlites in bulk peat samples and aa5 leach are not necessarily directly above kimberlites the diffused metal anomalies around kimberlites are attributed to the dissolution precipitation of secondary phases carbonates and fe o oh in acidic and reduced waters in peat and the movement of waters through peat this pilot study suggests that peat compositions do reflect the underlying bedrock compositions for kimberlite exploration a geochemical survey of peat is useful to discriminate concealed kimberlites from other anomalies defined by geophysical and other techniques however such a geochemical survey is not suitable for delineating the shapes of the concealed kimberlites due to broad dispersed anomalies

platinum group element and gold enrichment in soils monitored by chromium stable isotopes during weathering of ultramafic rocks abstract weathering of ultramafic rocks can lead to the formation of soil profiles with high contents of fe ni co platinum group elements pge and gold traditionally these metal rich soils are known as laterites and are formed under tropical climates and stable tectonic conditions however little is known about their possible development in cold humid regions and the factors governing pge and gold mobility and enrichment under these weathering conditions are poorly constrained in this study five soil profiles developed on serpentinized chromite bearing ultramafic rocks at la cabana located in the coastal range of south central chile 38 s were studied by combining major and trace element geochemistry with chromium stable isotope data the results show that the soils developed at la cabana have higher pge and au contents than the parent serpentinite rock with pge and au reaching up to 160 ppb and 29 ppb in a limonitic soil horizon and clay saprolite respectively most soil samples have slightly negative 53 52crsrm979 values within a range of 0 089 0 012 to 0 320 0 013 average of 0 178 and are in agreement with previous data reported for modern soils a noteworthy relation between 53 52cr data and pge au contents is observed in the studied soil horizons where isotopically lighter values of 53 52cr match the higher contents of pge and gold these results show that pedogenetic processes operating at the cold and humid la cabana area are capable of increasing the total pge and au contents of certain soil horizons such processes are complex and multivariate but are primarily modulated by chromite dissolution and the formation of secondary phases such as clay minerals and oxy hydroxide phases in the soil these findings provide evidence that important weathering and pge au supergene accumulation are not only restricted to tropical latitudes and that the chromium isotope system is a useful proxy to track surface redox process and noble metal enrichment during pedogenesis

the geochemistry geochronology and paleomagnetism of dikes and sills associated with the mesoproterozoic midcontinent rift near thunder bay ontario canada abstract the midcontinent rift mcr of north america comprises a series of basaltic sheets flows and intrusive rocks emplaced in the lake superior region during the mesoproterozoic the mafic rocks preserved on the northern flank of lake superior represent the older portions of the rift sequence and offer insights into the early development of the rift new geochronological geochemical and paleomagnetic data are presented for the dikes and sills located in and south of thunder bay ontario three sill suites are recognized within the study area an earlier spatially restricted ultramafic unit termed the riverdale sill the predominant logan sills and nipigon sills in the north of the study area in addition three dike sets are recognized the north east trending pigeon river swarm the north west trending cloud river dikes and the mt mollie dike the geochemical data demonstrate that the majority of sills south of thunder bay are of logan affinity and distinct from those of broadly similar age in the nipigon embayment to the north the pigeon river dikes that intrude the sills are geochemically coherent but distinct from the logan sills and could not be feeders to the sills the new age of 1109 2 4 2 ma for the cloud river dike and its r polarity are consistent with published magnetostratigraphy the mt mollie dike age 1109 3 6 3 ma indicates that it is not coeval with the spatially associated crystal lake gabbro as previously thought the complexity of the dike and sill suites on the northern flank of suggests that the early phases of rifting occurred in distinct and changing stress fields prior to the main extensional rifting preserved in younger rocks to the south the geochemistry and geochronology of the intrusions suggest a long lived and complex magmatic history for the midcontinent rift

multimedia exploration strategies for pges insights from the surficial geochemistry case studies project lake nipigon region geoscience initiative northwestern ontario the surficial geochemistry case studies project in the lake nipigon region involved detailed quaternary mapping and multimedia geochemical sampling within five case study areas two of these areas lac des iles and tib lake contain known platinum group element pge mineralization the other three case study areas feature drainage catchments with lakes that contain anomalous levels of pges in bottom sediment surficial media sampled included till soils stream sediment lake sediment peat surface water and groundwater over archean terrain such as at lac des iles and tib lake there is excellent geochemical contrast between the pge prospective rock type mafic to ultramafic intrusive and the surrounding rock type e g granitoid rocks this geochemical contrast is mirrored in the geochemistry of most surficial media sampled during this project over the nipigon embayment the geochemical contrast between mafic and ultramafic rocks e g seagull type intrusions and the surrounding diabase sill rocks is inherently weaker due to the relatively high background levels for copper palladium and gold in the nipigon diabase sills however the results of stream water geochemistry over the seagull and disraeli ultramafic intrusions highlight their unique geochemical footprint on the surficial landscape in particular with respect to cr mg and ni compared with the surrounding nipigon diabase in addition lake sediments underlain by the seagull disraeli and hele intrusions have distinctly elevated cr concentrations and gd yb ratios compared with the surrounding areas underlain by nipigon diabase sills or sibley group rocks therefore exploration value can be maximized over the nipigon embayment by exploiting these geochemical contrasts in surficial media to discriminate between ultramafic rocks and the surrounding nipigon diabase sills the results of this study highlight the importance of chromium concentrations in surficial media as a diagnostic feature for the presence of ultramafic rocks regardless of their age or location in general a cost effective exploration strategy for pge mineralization includes targeting the associated metals cr ni within drift deposits c horizon till and drainage media stream sediment lake sediment to vector to prospective mafic ultramafic intrusive rocks prior to detailed property scale follow up involving the determination of base metals and pges within soil till stream sediment and peat samples relative to the metals copper nickel and chromium ppm levels the pges have significantly lower initial concentrations ppb levels are less mobile in the surficial environment have significantly shorter glacial dispersion trains and are less reliably determined at the laboratory

geology petrography geochemistry and genesis of sulfide rich pods in the lac des iles palladium deposits western ontario canada the lac des iles pd deposits are known for their pd rich sulfide poor mineralization however previously undocumented sulfide rich pods also occur within the intrusion that hosts the deposits given the complex magmatic and hydrothermal history of the mineralization at lac des iles the sulfide rich pods could have crystallized from magmatic sulfide liquids or precipitated from hydrothermal fluids sulfide rich pods occur throughout the stratigraphy in all rock types and along comagmatic shear zones and contain net textured to massive sulfides they can be divided into four main groups based on the variation in mineral assemblages 1 pyrrhotite pentlandite pyrite chalcopyrite magnetite ilmenite 2 chalcopyrite pyrrhotite pentlandite pyrite magnetite ilmenite 3 pyrite pentlandite chalcopyrite pyrrhotite magnetite ilmenite and 4 magnetite ilmenite pyrrhotite pentlandite pyrite chalcopyrite whole rock metal contents and s isotopic compositions do not change with the amount of pyrite present except for slight enrichments in as and bi the presence of an essentially magmatic sulfide mineral assemblage pyrrhotite pentlandite chalcopyrite with pentlandite exsolution flames in pyrrhotite in some pods suggests that the pods crystallized from magmatic sulfide liquids the very low cu contents of the pods suggests that they are mainly cumulates of monosulfide solid solution mss we propose a model whereby sulfide liquids were concentrated into dilation zones prior to crystallizing cumulus mss intermediate solid solution crystallized from the fractionated liquids at the edges of some pods leaving residual liquids enriched in pt pd au as bi sb and te these residual liquids are no longer associated with the pods during subsequent alteration pyrite replaced mss pyrrhotite but this did not affect the platinum group element contents of the pods

overburden geochemical signature of the lac des iles platinum group element deposit northwestern ontario canada many previously published studies of the behaviour of pt and pd in till and soils have been done in areas of complex stratigraphy or very thin overburden cover making the interpretation of soil results difficult because of the many variables associated with these settings at the lac des iles mine site in northwestern ontario there are excellent exposures of the overburden in a series of exploration trenches glacial dispersal trains can be observed in till c horizon geochemistry e g ni cr cu and co regional geochemical dispersal trains of elements such as ni cr mg and co associated with the north lac des iles intrusion can be detected for about 4 km beyond the western margin of the mine block intrusion entire dispersal trains range from 5 to 7 km in length and about 1 to 2 km in width the dispersal of north lac des iles intrusion rock fragments tends to mask the response of the mine block intrusion dispersal trains of pt and pd are not well defined and tend to be very short 1 km in

radiogenic isotope characteristics of the mesoproterozoic intrusive rocks of the nipigon embayment northwestern ontario the ca 1110 1120 ma diabase sills of the nipigon embayment represent the oldest phase of the midcontinent rift recognized to date the sills can be subdivided into five geochemically distinct suites nipigon mcintyre inspiration shillabeer and jackfish sm nd rb sr and pb pb isotope data for the sills can be used to evaluate the source regions and emplacement histories of these sills the endt values for all the sill suites are consis tently negative 0 5 to 6 6 but show coherent variations both within and between suites the negative endt values can be interpreted as the result of contamination of a plume related mantle source by older crustal material the initial strontium sri values 0 7032 0 7068 for the sills indicate that at least two distinct contaminants are required 1 a source with strongly negative endt and lower sri likely archean metasediment or granite and 2 one with elevated sri likely sedimentary rocks of the proterozoic sibley group the pb data for the nipigon and inspiration sills form distinct linear arrays consistent with variable contamination of a source comparable to that of other igneous suites of the midcontinent rift the radiogenic isotopes preserve a complex contamination history best interpreted as the result of 5 contamination by a variety of archean and proterozoic sources the ultramafic jackfish sill shows the least ev idence of contamination and is interpreted to have been emplaced along a crustal scale fault with little interaction with crustal material in contrast the other sill suites have undergone complex contamination histories requiring variable crustal residence times and assimilation of material both at depth in large magma chambers and during emplacement

further refinement to the timing of mesoproterozoic magmatism lake nipigon region ontario the midcontinent rift in the lake superior region of north america is one of the best preserved examples of an aborted precambrian intercontinental rift one that hosts a diverse suite of rock types in addition to the well studied and voluminous rift fill flood basalts although there is a growing database of high precision age information for the main volcanic packages and the largest mafic intrusions there is relatively little information available on the absolute timing of mafic ultramafic intrusions dyke swarms and alkaline complexes especially in the ontario portion of the rift we report new high precision u pb ages for 29 samples primarily collected in the lake nipigon area ontario from these new age results it is now possible to expand the known distribution of geon 15 magmatism in the region confirm an early stage of midcontinent rift mafic magmatism between 1150 and 1130 ma provide evidence that significant mafic ultramafic magmatism occurred in the lake nipigon region slightly earlier

carbon and nitrogen stable isotope analysis of northwest european horse bone and tooth collagen 40 000 bp present palaeoclimatic interpretations abstract carbon and nitrogen stable isotope ratios of bone and tooth dentine collagen from 142 horses were analysed to consider the potential of isotopic analysis of faunal remains as a palaeoenvironmental and palaeoclimatic proxy a general trend through time towards lighter 13 c values was observed but with an obvious depletion at the late glacial holocene transition horse 13 c values appear to track plant 13 c although phenomenon such as the canopy effect may influence faunal 13 c values we believe that the influence on plants of increasing atmospheric co 2 is the primary factor in the change in faunal 13 c values at the late glacial holocene transition a post glacial depletion in horse 15 n values is observed in areas proximal to glacial retreat although no data is available in these areas during the last glacial maximum horse 15 n values are presumed to reflect plant 15 n values depleted plant nitrogen may be attributed to a number of factors e g water availability temperature cycling of nitrogen in the soil soil nutrient availability especially phosphorus in the post glacial period and the type of mycorrhizal associations formed with plant these effects may be interrelated and be linked such that a positive feedback can give a non linear response to a single parameter

differences between observed and a coupled simulation of north atlantic sea surface currents and temperature 1 north atlantic sea surface temperature sst distributions derived from observations and a coupled model from noaa s geophysical fluid dynamics laboratory cm2 1 are compared to evaluate the model s ability to simulate recent 1900 to the present oceanic surface characteristics the north atlantic focus will limit our analyses to spatial scales less than gyre scales usually not addressed in previous model observation comparisons identifying model differences from observations at these scales will assist modelers in identifying problems to be considered and remedies to be applied the properties compared are the mean annual sst standard deviation amplitude of the annual and semiannual harmonic decadal meridional movements of the axis of the gulf stream propagation of sst anomalies along the axis of the gulf stream and 100 year trends in sst records because of the dependence of sst on surface currents observed flow from surface drifters and simulated flow from 15 m fields are also compared the model simulates the large scale properties of all the variables compared however there are areas of differences in some variables that can be related to inadequacies in the simulated current fields for example the model gulf stream gs axis after separation from the western boundary is located some 100 km north of the observed axis which contributes to an area of warmer simulated ssts the absence of a slope current in the same region that advects colder water from the labrador sea in the observations also contributes to this area of higher model ssts the model north atlantic current nac is located to the east of the observed nac contributing to a large area of sst discrepancy the patterns of the amplitude of the annual harmonic are similar with maximum amplitude off the east coast of northern north america the semiannual harmonic exhibits relatively large amplitudes 1 c north of about 55 n a signal not found in the observations in both the model and observations a region of increased standard deviations encompasses the gs and nac the model simulates north south migrations of the gs core but at a longer period 20 years than observed the model does not simulate the sst anomalies that propagate along the observed gs and nac the model captures both the spatial and temporal characteristics of the atlantic multidecadal oscillation both model and observations exhibit a dipole in trends with positive trends in the subtropical atlantic and negative trends in the subpolar gyre the modeled region of negative trends is limited to the western subpolar atlantic the observed trends extend farther to the east

age of the mulcahy lake intrusion northwest ontario and implications for the evolution of greenstone granite terrains abstract zircon data from a 63 km 2 layered mafic intrusion in the wabigoon subprovince the mulcahy lake gabbro show that the gabbro crystallized at 2733 2 0 9 1 0 ma the largely unaltered and unmetamorphosed gabbro intrudes tholeiites of the crow lake savant lake greenstone belt which were generated over at least a 10 ma time span rb sr and sm nd data were obtained for pristine whole rock and mineral separates from the intrusion the rb sr data show disturbances in the system particularly in the case of pyroxenes samples with low rb sr ratios indicate an initial sr ratio of 0 7007 for an age of 2733 ma the sm nd age is 2744 55ma and an epsilon nd value of 2 6 1 2 indicates a light rare earth element depleted source the sm nd data show less disturbance than the rb sr data granitic and mafic intrusives with similar initial ratios occur 80 km to the south in the quetico subprovince primary hornblende was analyzed for 40 ar 39 ar the age obtained is 2703 20ma clearly younger than the zircon age indicating some argon loss the mulcahy lake gabbro is one of four layered mafic plutons of similar petrographic character and stratigraphic age which are arrayed in an arc in the crow lake savant lake greenstone belt the plutons appear to represent subvolcanic chambers which developed simultaneously and which crystallized at the end of the volcanic cycle all intrude basalts and are intruded in turn by the atikwa batholith a massive granitic intrusion of over 1000 km 2 in area previously published zircon ages for several sample sites within the batholith indicate crystallization at 2731 8 1 3 1 6 ma to 2732 2 2 9ma these data show that the batholith overlaps the age of the gabbros or is at most 5 ma younger this virtual contemporaneity is hidden in the rb sr and sm nd data the cessation of mafic magma production and the immediate if not parallel voluminous production of calc alkaline liquid may represent a process important in the development of greenstone granite belts a process not apparent when ages are not so precisely determined

the sensitivity of a coupled climate model to its ocean component abstract the control climates of two coupled climate models are intercompared the first is the third climate configuration of the met office unified model hadcm3 while the second the coupled hadley isopycnic model experiment chime is identical to the first except for the replacement of its ocean component by the hybrid coordinate ocean model hycom both models possess realistic and similar ocean heat transports and overturning circulation however substantial differences in the vertical structure of the two ocean components are observed some of which are directly attributed to their different vertical coordinate systems in particular the sea surface temperature sst in chime is biased warm almost everywhere particularly in the north atlantic subpolar gyre in contrast to hadcm3 which is biased cold except in the southern ocean whereas the hadcm3 ocean warms from just below the surface down to 1000 m depth a similar warming in chime is more pronounced but shallower and confined to the up

contrasting types of late archean plutonic rocks in northwestern ontario implications for crustal evolution in the superior province abstract the late archean aulneau and lount lake batholiths have contrasting geochemical characteristics that are interpreted to be a consequence of derivation from different sources the aulneau batholith which was intruded into low grade metavolcanic rocks of the wabigoon subprovince is characterized by high na2o and low k2o rb and y together with enriched light rare earth elements lree near chondritic heavy rare earth elements hree negligible eu anomalies and mantle type initial sr and nd isotopic compositions these geochemical characteristics are consistent with derivation from the partial melting of metamorphosed tholeiitic basalt in contrast the lount lake batholith which was intruded into older 2 83 3 17 ga tonalitic plutonic rocks of the winnipeg river subprovince has relatively high k2o rb y and ree low na2o and prominent eu anomalies the initial sr and nd isotopic compositions of the lount lake batholith are consistent with a crustal source at least 200 400 ma older than the crystallization age of the batholith these geochemical characteristics indicate that the lount lake batholith originated from the partial melting of deeper level equivalents of the tonalitic metaplutonic rocks 2 83 3 17 ga which they intrude these results suggest that reworked 3 0 ga crust may be extensive in the winnipeg river subprovince and that the geochemical and isotopic signature of late archean plutonic rocks may be a useful reconnaissance tool in the identification of areas of extensive older crust the results can be interpreted within a uniformitarian model diachronous ensimatic magmatic arcs represented by the winnipeg river and western wabigoon subprovinces developed independently collision of these arcs at 2707 8 ma marks the cessation of subduction and related magmatic activity and the initiation of high grade metamorphism and melting in tectonically thickened portions of the crust

an intercomparison of a bryan cox type ocean model and an isopycnic ocean model part i the subpolar gyre and high latitude processes abstract this paper describes a model intercomparison between a bryan cox type ocean model and an isopycnic coordinate ocean model the two models are integrated for 30 years on a domain of the north atlantic stretching from 20 s to 82 n the main purpose of this work is to illuminate aspects of the respective models that give a realistic representation of the north atlantic circulation and the physical processes that occur therein and to identify those which need to be improved to this end the same forcing fields and as many of the same parameter settings as possible were chosen so that differences between the models would be due to distinct model features rather than choice of parameters where we felt that using the same setup between the models was inappropriate or impossible we examined the possible difference this could make to the simulators in the isopycnic model the path of the north atlantic current after separation is simulated quite realistically whereas in the bryan cox model it become

mafic ultramafic intrusives and their gravity field lac des iles area northern ontario the bouguer anomaly map of the lac des iles area constitutes a number of distinct gravity highs and lows that are associated respectively with the mafic ultramafic and granitic components of a late archean plutonic terrane the apparent density and vertical derivative maps were computed to assist in the identification and the delineation of lithologies from the apparent density map several distinct density zones are recognized within the mafic ultramafic intrusions the identification of the density zones and their apparent densities are in good agreement with the mapped lithological groups and measured densities gravity models in 2 d were computed along six selected profiles the mafic ultramafic lac des iles complex with a mean density of 3 13 g cm 3 is characterized by a 30 mgal gravity high the complex is modeled as a flattened funnel shaped steeply inward dipping intrusive body part of which extends to a depth of about 4 5 km the tib gabbro represented by a 16 mgal gravity high is modeled as a tilted steeply inward dipping basin like intrusive body extending to a depth of 3 km gravity maxima for most of the mafic intrusions are located in proximity to faults in tonalite gneiss country rocks these faults may have acted as conduits allowing the emplacement of discrete pulses of mantle derived magma gravity models show that mafic magma locally underplated granitic plutons and that mafic plutons typically have limited depth extents relative to their horizontal dimensions these models indicate that intraplating by mafic magmas contributed to crustal thickening in the late archean