high precision u pb ages for granulite metamorphism and deformation in the archean kapuskasing structural zone ontario implications for structure and development of the lower crust abstract precise u pb isotopic ages for two subhorizontal granulite gneisses in the kapuskasing structural zone indicate that formation and emplacement occurred more than 50 m y after cessation of volcanism in the steeply folded nearby greenstone belts by successive stages of ductile underplating across a zone of crust mantle delamination volcanism and batholith formation had ceased by 2700 and 2680 ma respectively while granulite formation occurred between 2660 and 2640 ma and ductile deformation continued until 2585 ma emplacement of the oldest granulite caused the development of shear planes and melting in the older overlying tonalite while emplacement of the younger granulite caused rupturing and rehydration of the overlying older granulite widespread tectonic underplating is implied since all superior province granulites have similar young ages anomalous ar ages that post date accretion by about 150 m y and scrambled pb pb and rb sr whole rock systems also suggest that late low temperature alteration accompanied this event temporal relationships and the presence of post volcanic 2670 ma conglomerate cobbles at granulite grade support a model of ductile underplating of a post accretion thermally softened back arc fore arc complex with components welded onto an overlying volcanic plutonic complex at successively deeper levels multistage deformation in active fault zones and hydrothermal emplacement of major gold deposits in greenstone belts are coeval with ductile underplating with ages between 2670 and 2585 ma anomalously abundant gold production from archean rocks may indicate that shallow underplating granulitization and devolatization was a widespread phenomenon at this time post accretion ductile underplating must be considered as a primary cause of seismic reflectors in archean terrains

crustal outgassing and lile enrichment in major lithosphere structures archean abitibi greenstone belt evidence on the source reservoir from strontium and carbon isotope tracers major structural discontinuities in the abitibi greenstone belt acted as conduits for outgassing of the archean crust as reflected in fixation of a select group of lithophile elements including si c k rb ba li cs b and pb in metasomatized faults for two of the largest structures the destor porcupine dp and kirkland lake cadillac kc fault zones 6 1015 g si 3 1015 g co2 and 1015 g k were introduced into the faults during expulsion of an estimated 6 1018 g aqueous fluids strontium isotope ratios of tourmaline piemontite actinolite and scheelite mineral separates characterized by rb sr 0 02 are concordant with respect to 87sr 86sr initial ratios over local sectors of the faults the sr isotope data record geographic variations which from east to west on the kc fault is 0 7031 0 7041 val d or 0 7008 0 7022 bourlemaque 0 7017 0 7019 bousquet 0 7029 0 7031 noranda and 0 7013 to 0 7015 kirkland lake at timmins on the pd fault 87sr 86sr initial ratios cluster at 0 7010 to 0 7020 metasomatised fault zones are systematically more radiogenic than contiguous host lithologies and imply a source reservoir 0 7010 to 0 7041 generally more radiogenic than the upper mantle at 2690 ma 0 700 0 001 or contemporaneous volcanic rocks of mafic to ultramafic composition 0 700 to 0 7012 whereas certain minerals are concordant and retentive rb sr isochrons based on suites of rocks at progressive intensities of metasomatism have been systematically reset over an elpased time of 200 ma after termination of outgassing due to disturbance accompanying incremental displacements on structures

integrated model for meguma group lode gold deposits nova scotia canada meguma group lode gold deposits represent concentrations of a variety of auriferous quartz veins in lower paleozoic metaturbidites of the meguma terrane of southern nova scotia our studies incorporating extensive field regional and detailed mapping and laboratory petrography fluid inclusions geochemistry isotopes studies of 30 of these deposits in the eastern meguma terrane suggest that mineralization occurred at ca 370 ma 40 ar 39 ar dating of hydrothermal vein minerals during widespread incursion of mafic and felsic magmatism into the crust concurrent with subvertical shear zone development thus postdating regional acadian deformation by some 30 40 m y isotopic data s c o sr indicate that vein forming fluids were not solely magmatic and were in part exotic to the meguma group thus earlier magmatic and metamorphogenic lateral secretion models that considered either late stage magmatic fluids or the enveloping meguma group metasedimentary rocks as the sole source of vein components are invalidated

testate amoebae record from the laptev sea coast and its implication for the reconstruction of late pleistocene and holocene environments in the arctic siberia abstract our study aims to look for testate amobae ta in the surface and fossil sediments from the cape mamontov klyk 73 60 73 63 n 116 88 117 18 e southern coast of the laptev sea ca 150 km west of the lena delta and to discuss the potential of ta analysis for glacial interglacial environmental reconstructions in arctic siberia the radiocarbon age determination suggests that the studied sediments accumulated between ca 45 000 14c yr bp and present a total of 98 ta taxa were identified in the 10 recent surface and 59 fossil samples results of taxonomical identification and ecological analysis of ta in the modern and fossil samples suggest that major changes in the soil moisture conditions took place our results show that soil living taxa dominated the ta assemblages at the study sites during the past 45 000 years the environmental conditions of the study area were most favourable relatively warm and humid during the kargin interstadial ca 45 000 25 000 14c yr bp an opposite situation is reconstructed for the sartan stadial ca 25 000 15 000 14c yr bp during the kargin interstadial optimum conditions occurred between ca 44 000 and 40 000 14c yr bp characterised by highest ta abundances and taxa diversity this initial optimal phase was followed by the interval with drier and colder conditions about 40 000 30 000 14c yr bp the sediments dated between ca 24 000 and 18 000 14c yr bp show low ta abundances and diversity in agreement with the much colder and drier environments during the maximum phase of the last glacial the onset of the holocene is indicated by a broad representation of obligate hydrophilic taxa especially from genus difflugia suggesting wet and relatively warm conditions by comparison with other environmental proxies used in the studied sections as well as from the neighbouring arctic regions our results suggest that ta analysis can provide valuable information contributing to the better understanding of the late quaternary climate and environments in arctic siberia

multiproxy approach for holocene paleoenvironmental reconstructions from microorganisms testate amoebae and foraminifera and sediment analyses the infilling of the loire valley in nantes france foraminifera and testate amoebae are jointly used with sediment characteristics sediment size calcium carbonate c h n and s proportions and clay mineralogy to reconstruct the holocene sediment infilling of the loire estuary nantes france the results reveal the infilling of the loire valley during the holocene deposited on the hercynian substratum the first deposits are made of gravels with rare associated fauna this corresponds to the gravel lag usually present as basal deposits in the river course the clay mineralogy indicates an erosion of the substratum then from 8850 to 5850 cal yr bp estuarine fauna settled in a laminated sediment that alternates between clay and sand the smectite associated with kaolinite and illite suggests increased input from the sevre nantaise river the fauna progressively shifts from estuarine to marine indicating a rise in the sea level from 5850 cal yr bp the pace of the sea level rise slowed and channels migrated implying intense erosion after 2100 cal yr bp the fauna was dominated by testate amoebae indicating a continentalization of the environment the top samples reflect recent human activity and urbanization

geochemistry of footwall alteration associated with the early proterozoic united verde massive sulfide deposit arizona three zones of progressively increasing alteration occur in the deception rhyolite associated with the united verde massive sulfide deposit of early proterozoic age near jerome arizona zone 1 most intense alteration is comprised chiefly of chlorite and exhibits apparent losses of sio 2 na 2 o cao and k 2 o enrichments in mgo fe 2 o sub 3 total 1 al 2 o 3 volatile constituents chiefly h 2 o and relatively unchanged tio 2 which is used to monitor changes in other major elements sio 2 and k 2 o losses are most prominent in zone 1 quartz chlorite and sericite are the dominant secondary minerals in zones 2 and 3 these zones also show major losses of na 2 o and cao and variable but small enrichments in mgo fe 2 o sub 3 total 1 sio 2 and locally in k 2 o zone 1 is characterized by major decreases in k rb sr and ba and increases in cs u th mn sc co rare earth elements and high field strength elements zr nb y ta hf increases in cu zn and pb occur in all zones but are greatest in zone 1 with the exception of light rare earth elements nb and y in zone 1 ratios of high field strength elements viz ti zr ta hf hf th and rare earth element distribution patterns are relatively unchanged during alteration and provide a means of identifying protoliths alteration at jerome is complex involving both submarine diagenetic hydrothermal and possibly metamorphic processes zone 1 formed at the highest temperatures and at high water rock ratios the geochemical character and lithologic association of the volcanic host rocks are consistent with a back are basin tectonic setting for the united verde deposit 1 fe 2 o sub 3 total total fe expressed as fe 2 o 3

the hydrothermal fluid of archaean lode gold deposits at different metamorphic grades compositional constraints from ore and wallrock alteration assemblages a low salinity mixed aqueous carbonic fluid is common to all archaean lode gold deposits throughout the range of mineralising conditions from sub greenschist to lower granulite facies temperatures alteration assemblages and fluid inclusion data give constraints on the fluid composition fluid xco2 is 0 1 0 3 in typical greenschist facies mesothermal deposits at higher temperatures the assemblages are consistent with formation from a fluid of similar composition but slightly higher or lower xco2 cannot be ruled out and fluid inclusion data indicate that ch4 may be an important component in ore fluids at these temperatures fluid ph is neutral or weakly alkaline at all conditions a range of relative oxidation states of four orders of magnitude fo2 is indicated at any temperature with deposits more oxidising relative to qfm at lower temperature sulphur contents of the fluids vary from 10 to 10 3 5m s with a trend towards lower sulphur contents at lower temperatures the relative concentrations of major cations in solution are similar at all conditions with na k ca although ca may be less abundant at low temperatures the broad similarities in ore fluid composition at all temperatures give support to crustal continuum models in which archaean lode gold mineralisation involved either a single fluid moving through the middle and upper crust or derivation of ore fluids by similar processes at different crustal levels many of the compositional differences between high and lowtemperature ore fluids may be attributed to evolution of deep sourced hydrothermal solutions as they rise along structurally controlled conduits the constancy of major ore fluid component concentration e g co2 cl k suggests fluid buffering and high fluid rock ratios along fluid pathways fluid buffered conditions can also explain the ore fluid fo2 temperature relations with equilibria between oxidised and reduced aqueous carbon or sulphur species controlling the oxidation state in contrast the concentrations of components present in lesser abundance in archaean gold ore fluids e g s ca h were probably controlled either by saturation of one or more mineral phases brought on by decreasing temperature or were rock buffered through fluid rock reactions extrapolation to high temperatures of the k na and ca contents of the gold bearing fluids indicates that their composition is consistent with derivation from or final equilibration with rocks of intermediate granitic composition thus giving support to isotopic and geological arguments for ore fluid source regions external to the greenstone belts the fluid oxidation states are characteristic of a wide range of potential source rocks including mantle derived igneous rocks calc alkaline granitoids and magmas and seaflooraltered metabasalts strongly oxidised magmatic sources or unusually oxidising source processes e g co2 streaming during granulitisation of the lower crust are therefore not required in the genesis of arch an lode gold deposits

rb sr k ar and stable isotope evidence for the ages and sources of fluid components of gold bearing quartz veins in the northern sierra nevada foothills metamorphic belt california gold bearing quartz veins occur in and near major fault zones in deformed oceanic and island arc rocks west of the main outcrop of the sierra nevada composite batholith veins typically occupy minor reverse faults that crosscut blueschist to amphibolite grade metamorphic rocks whose metamorphic ages range from early paleozoic to jurassic vein micas and carbonate quartz mica assemblages that formed by hydrothermal metasomatism of ultramafic wall rocks in the alleghany grass valley washington and mother lode districts yield concordant k ar and rb sr ages the dated veins are significantly younger than prograde metamorphism penetrative deformation and accretion of their host rocks to the continental margin new and previously published mineralization ages from 13 localities in the sierra foothills range from about 140 to 110 m y ago with mean and median between 120 and 115 m y the age relations suggest that mineralizing fluids were set in motion by deep magmatic activity related to the resumption of east dipping subduction along the western margin of north america following the late jurassic nevadan collision event co 2 bearing fluids responsible for metasomatism and much of the vein mica carbonate albite and quartz deposition in several northern mines were isotopically heavy delta 18 o asymp 8 14ppm delta d between about 10 and 50ppm and do not resemble seawater magmatic or meteoric waters metasomatic and vein filling mica dolomite magnesite and quartz in altered ultramafic rocks generally formed from fluids with similar sr and o isotope ratios at a given locality consistent quartz mica delta 18 o fractionations delta 18 o sub q m 4 5 4 9ppm from various localities imply uniform equilibration temperatures probably between 300 degrees and 350 degrees c on a local mine scale fluids responsible for both carbonate alteration of mafic and ultramafic wall rocks and albitic alteration of felsic and pelitic rocks had similar sr isotope ratios samples from three veins in the central alleghany district fit a 115 7 or 3 m y rb sr isochron with a 87 sr 86 sr i value of approximately 0 7119 inferred 87 sr 86 sr ratios of metasomatic fluids from mines in different parts of the foothills region vary considerably 0 704 0 718 suggesting that sr was derived from sources ranging from western assemblage mesozoic ophiolitic or arc volcanic rocks to early paleozoic continent derived clastic rocks of the shoo fly complex systematic geographic variations in both sr and o isotopes can be rationalized by assuming extensive fluid interaction with rocks similar to the ones that are exposed within a few kilometers of the veins but the ultimate sources of the fluids and of au and other constituents may be independent of these isotopically lighter meteoric fluids deposited some late quartz overgrowths and occupied secondary fluid inclusions in earlier vein quartz

composition and origin of fluids associated with lode gold deposits in a mesoarchean greenstone belt warrawoona syncline pilbara craton western australia using synchrotron radiation x ray fluorescence microthermometry and raman spectroscopy techniques are routinely use to constrain ore fluids 18o and molar proportions of anhydrous gas species co2 ch4 n2 however these methods remain imprecise concerning the ore fluids composition and source synchrotron radiation x ray fluorescence allows access to major and trace element concentrations cl br and k ca fe cu zn as rb sr of single fluid inclusion in this paper we present the results of the combination of these routine and newly developed techniques in order to document the fluids composition and source associated with a mesoarchaean lode gold deposit warrawoona syncline western australia fluid inclusion analyses show that quartz veins preserved records of three fluid inclusion populations early fluids inclusions related to quartz veins precipitation are characterized by a moderate to high br cl ratio relative to modern seawater co2 ch4 n2 low to moderate salinities and significant base metal fe cu zn and metalloid as concentrations late fluid inclusions trapped in secondary aqueous fluid inclusions are divided into two populations with distinct compositions the first population consists of moderately saline aqueous brines with a br cl ratio close to modern seawater and a low concentration of base metals and metalloids the second population is a fluid of low to moderate salinity with a low br cl ratio relative to modern seawater and significant enrichment in fe zn sr and rb these three fluid inclusion populations point to three contrasting sources 1 a carbonic fluid of mixed metamorphic and magmatic origin associated with the gold bearing quartz precipitation 2 a secondary aqueous fluid with seawater affinity and 3 a surface derived secondary aqueous fluid modified through interaction with felsic lithologies before being flushed into the syncline primary carbonic fluids present similar characteristics than those ascribed to mesoarchaean lode gold deposits this suggests similar mineralization processes for mid and mesoarchaean lode gold deposits despite contrasting fluid rock interaction histories however in regard to the protracted history documented in the warrawoona syncline we question the robustness of the epigenetic crustal continuum model as ore fluid characteristics equally support an epigenetic or a polyphased mineralization process

application of geochemical discrimination diagrams for the tectonic interpretation of igneous rocks hosting gold mineralisation in the canadian shield abstract application of the high field strength elements zr y ti nb and ta to the tectonic interpretation of mafic rocks hosting gold mineralisation is illustrated by example of the joburke mine property near timmins ontario canada discrimination diagrams using these analytical data suggest that the mafic rocks are predominantly high fe tholeiitic basalts distinguishable from average archean basalts the derived geochemical signatures of the host rocks for the joburke mine will be of assistance for gold exploration in the timmins camp or in greenstone belts generally

cyanobacteria and testate amoeba as potential proxies for holocene hydrological changes and climate variability evidence from tropical coastal lowlands of sw india cyanobacteria and thecamoebians are the two major constituents of non pollen palynomorphs npp found in the palynological preparations the former is well represented in the sediment archives while the latter has restricted occurrence in the holocene sequence apart from the conventional organic matter of pollen and spores well preserved morphotypes of gleotrichia and rivularia are the best forms of cyanobacteria found in almost all the studied profiles and their abundance towards early to middle holocene coincides with the heavy rainfall and wet climate conditions during the holocene climate optimum hco contrary to cyanobacterial diversity thecamoebians are restricted to late holocene in most of the studied profiles and their occurrence is correlated with the prevailing dry and stressful environmental conditions the major elements of thecamoebians identified belong to arcellaceans centropyxids and cucurbitella types abundance of centropyxids and arcellaceans in varapuzha west kadungallur koonamavu pachcha and ernakulam indicates low humidity and low precipitation however the relative abundance of centropyxids in mid holocene at ernakulam and koonamavu reflects the early colonization of this type competing with the cyanobacteria whereas arcellaceans are essentially confined to late holocene dominance of cyanobacteria and its proliferation is directly related to freshwater influx of the rainfall as well as the local hydrological regimes associated with the active aquifers controlled by the geomorphological features of the region in which the wetland system sustained considering the signatures of cyanobacteria and thecamoebians observed in the sediment archives their occurrence in the wetlands during the holocene corresponds to the hydrodynamic regimes brought in by the freshwater influx as a result of monsoon variability the well preserved cyanobacterial signatures in sediment archives of kerala coast and their scarcity or even absence elsewhere along the west coast of india indicates that they are exclusively adapted to the wetland habitats where the hydrodynamic regimes are regularly controlled by fresh water influx in the form of extended rainy days of the monsoon system

a 3500 ma plutonic and volcanic calc alkaline province in the archaean east pilbara block variably foliated predominantly granodioritic plutonic rocks from the northern part of the shaw batholith in the east pilbara archaean craton are dated at 3 499 22 ma 2 errors by a whole rock pb pb isochron these rocks intrude the surrounding greenstone sequence and their age is indistinguishable from that sequence high strain grey gneisses which occupy much of the western and southern shaw batholith are chemically and isotopically similar to the north shaw suite and are inferred to have been derived from this suite by tectonic processes felsic volcanics within the greenstones together with a major portion of the granitic batholiths apparently formed in a calc alkaline volcanic and plutonic province at 3 500 ma this volcanic and plutonic suite is similar to modern calc alkaline suites on the basis of major element rare earh element and most other trace element contents the archaean suite contrasts with modern equivalents only in having lower concentrations of hree and higher concentrations of ni and cr

k rb sr ba u and th geochemistry of the lapland granulites fennoscandia lile fractionation controlling factors the lile geochemical patterns of the three main lithological units graywacke shale metasedimentary sequence tholeiitic metaigneous rocks and migmatitic rocks of the lapland granulite belt are described k ba sr and th concentrations in metasediments are nearly similar to average continental crust whereas rb and u are unevenly impoverished in particular graphitic metashales and calcsilicate rocks are not significantly depleted in uranium tholeiitic metaigneous rocks comprises metavolcanics which present k rb ratios similar to metasediments and metaplutonics with lile abundances close to those of the low k tholeiites migmatites show wide range in lile content metatexites and diatexites have higher k rb th and u concentrations and similar k rb ratios with respect to equivalent unmobilized rocks potassic pegmatoids are strongly enriched k rb ba and th but moderately in sr and u plagioclasic pegmatoids and ferromagnesian restites are rich in sr and poor in other lil elements

response of testate amoeba assemblages to environmental and climatic changes during the lateglacial holocene transition at lake lautrey jura mountains eastern france we tested the response of lacustrine testate amoebae thecamoebians to climate and environmental changes for the lateglacial holocene transition the palaeoenvironmental history of the study site lake lautrey jura mountains eastern france was previously established based on high resolution multi proxy studies of the same core the present study is characterised by a high taxonomic resolution 54 taxa inclusion of small species clown to 25 mu m and high total counts 500 individuals per sample on average changes in the composition of testate amoeba assemblages dominant species and assemblage structure as well as in the accumulation rate tests cm 2 a 1 corresponded to major climatic phases i e oldest dryas bolling allerod interstadial younger dryas preboreal as well as changes in organic matter inputs furthermore decreases in the accumulation rate characterised minor short lived cooling events such as older dryas event or gerzensee oscillation however the preboreal oscillation which was well registered by other proxies at lake lautrey could not be recognised in the testate amoeba record this work demonstrates that lacustrine testate amoebae can be used for palaeoclimatic and palaeoecological reconstructions nevertheless a better understanding of the relation between climate organic matter and lacustrine testate amoebae requires further high resolution studies based on multi proxy approaches and the development of appropriate modern analogues copyright c 2010 john wiley sons ltd

the berezovsk giant intrusion related gold quartz deposit urals russia evidence for multiple magmatic and metamorphic fluid reservoirs abstract the berezovsk gold deposit in the middle urals has been mined for 270 years its endowment past production and gold reserves is estimated to be 490 t of gold the deposit is located in the greenschist metamorphosed silurian volcanogenic sedimentary rocks intruded by granitoid dykes to the north east of late carboniferous shartash granite massif mineralisation is represented by sulphide quartz veins in the granitoid dykes ladder veins and in the host rocks krassyk veins formed in the following four stages ankerite quartz quartz pyrite gold polymetallic and carbonate ore veins are accompanied by halos of gumbeite quartz orthoclase carbonate beresite quartz sericite ankerite pyrite and listvenite quartz fe mg carbonate fuchsite pyrite the veins mainly consist of quartz with sulphide minerals commonly 3 5 vol about 180 minerals have been identified in ores but the most abundant minerals are quartz calcite ankerite pyrite galena tennantite chalcopyrite aikinite native gold and sphalerite native gold was deposited during quartz pyrite au i and gold polymetallic au ii stages fineness of gold ranges from 863 to 984 and from 723 to 848 for au i and au ii respectively the mineral and metal zoning was identified relative to the roof of the shartash granite massif the fluid inclusion study revealed that the gold mineralisation at the berezovsk deposit was formed at 300 230 c and 0 3 2 3 kbar mostly 0 5 1 2 kbar from a h2o co2 nacl fluid with salinity of 7 3 18 2 wt nacl equiv the fluid was separated into h2o co2 nacl and co2 rich fluids due to temperature and or pressure drop at the deposition site calculated 18o and d values are 5 2 8 1 and 39 to 63 respectively for the fluid in equilibrium with alteration assemblages the average 13c value for the fluid equilibrated with carbonates from the inner zones of metasomatic halos is 5 3 the calculated 18o and 13c values are 3 0 9 6 and 3 to 9 respectively for ore forming fluids the 34s values are 1 4 12 9 and 1 6 to 11 7 for the fluid in equilibrium with early and late sulphides respectively in addition to the isotopic data the geological mineralogical and fluid inclusion data confirmed the predominant contribution of the magmatic fluid to formation of the berezovsk hydrothermal system the light c o and s isotope enrichment of the fluid was mainly caused by fluid phase separation fluids generated by decarbonation and dehydration reactions due to the contact metamorphism of the host rocks during the shartash massif emplacement were responsible for additional 34s input the ore forming fluid was enriched in the light 16o isotope on the deposit flanks indicating the mixing with heated meteoric water

behaviour of tl relative to k rb sr and ba in mineralized and unmineralized metavolcanics from the dir area northern pakistan copper mineralization in the dir area of northern pakistan is confined to the quartz veins and associated with hydrothermally altered metavolcanics chalcopyrite is the main copper bearing phase with subordinate amounts of bornite chalcocite covellite malachite and azurite both mineralized quartz veins and associated unmineralized least altered and mineralized strongly altered metavolcanics have been analyzed for cu au ag tl k rb ba and sr an increase of cu au ag rb sr and tl sr and a decrease of sr and k rb is observed in both mineralized metavolcanics and mineralized quartz veins thallium shows lithophile behaviour in the dir metavolcanics and no chalcophile behaviour was observed the tl sr ratio might be an indirect guide for the exploration of volcanic hosted hydrothermal copper deposits

multi proxy lake sediment record of prehistoric paleoindian archaic archaeological paleoenvironments at rice lake ontario canada abstract the arrival of paleoindian peoples in the lower great lakes ca 11 5 ka cal bp coincided with a phase of lowstand lakes and rapid environmental change in southern ontario at rice lake an archaeologically rich area north of lake ontario rising early holocene water levels inundated wetland areas exploited by paleoindian and archaic peoples in order to better understand the distribution of submerged archaeological sites and the water level history of rice lake a detailed multi proxy study was conducted on two vibracores extracted from the open lake and a shallow the basin stratigraphy consisted of holocene organic rich muds gyttja laminated marls and peats overlying glacial lake iroquois sands and clay deposits two erosional hiatuses indicating lowstand phases eh 1 ca 12 5 11 ka cal bp eh 2 ca 6 3 ka cal bp were identified by rapid shifts in particle size and thecamoebian abundance and assemblages the dominant thecamoebian species in the open lake basin were arcella vulgaris and centropyxis constricta aerophila indicating the trophic status of the lake has remained stable throughout the holocene in the mcintyre lagoon the eh 1 lowstand was associated with a unique bog and wetland species bullinularia and phryganella sp along with the recovery of microdebitage indicating that paleoindian peoples were likely exploiting wetland resources such as plants fish and waterfowl we show that the study of lacustrine paleoenvironments using a multi proxy approach provides additional information for identifying areas of archaeological potential and gaining additional understanding of settlement patterns and resource procurement strategies of paleoindian and archaic peoples in southern ontario

ree geochemistry and isotopic data of archean silicic volcanics and granitoids from the pilbara block western australia implications for the early crustal evolution eighteen silicic volcanic rocks of the warrawoona group and ten associated plutonic rocks from the pilbara block western australia have been chosen for geochemical and isotopic studies silicic volcanics of the unsb upper member of north star basalt are dated at 3 56 3 57 by both the rb sr and the sm nd methods the respective 1 initial isotopic composition values are 0 7005 5 sr and 0 50810 39 nd this age is consistent with the stratigraphic interpretation that the talgatalga subgroup in which the north star basalt occupies the lowermost position is overlain by the duffer formation whose age was earlier established at 3 45 by the zircon u pb method the new rb sr data on six silicic lava samples from the duffer formation yield an isochron of 3 23 0 28 2v though imprecise this age agrees with the zircon age within error limits rb sr ages of 2 3 2 4 obtained for the panorama rocks and the wyman formation do not correspond to their initial eruption ages chemical arguments suggest that these ages represent the time of metasomatism associated with the widespread thermal event in this region about 2 3 2 4 ago geochemically most of these analyzed rocks volcanic and plutonic are of tonalite trondhjemitegranodiorite ttg composition a typical feature found in many other archean terrains they generally show fractionated ree patterns except the panorama formation rocks furthermore the wyman formation rhyolites and the post tectonic adamellites show significant negative eu anomalies suggesting a similar mode of magma generation and a probable genetic link theoretical considerations suggest that most of these ttg rocks could have been generated by partial melting of amphibolitic or basaltic sources followed by fractional crystallization although the archean granitic gneisses often possess mantle like isr values the trace element data indicate that they could not have been derived by direct melting of upper mantle materials the immediate tectonic implication is that in any archean terrain the formation of na rich continental crust of ttg suite must be preceded by the presence of basaltic crust the occurrence of this basaltic crust is a matter of controversy such crust might have been totally destroyed by repeated melting processes or its remnants are now represented by some of the mafic ultramafic enclaves within the tonalite trondhjemite batholiths

the macassa mine archean lode gold deposit kirkland lake ontario geology patterns of alteration and hydrothermal regimes the only remaining gold producer of seven interconnected mines the district has produced over 710 000 kg au since 1913 the area is underlain by part of the timiskaming group three types of gold ore 1 native au in chloritic fault gouge or small quartz lenses within a thrust fault system called break ore 2 gold bearing quartz veins in both hanging and footwalls of this fault system termed vein ore 3 several relatively wide zones of intensely fractured bleached silicified and pyritized rock containing lenses and pods of quartz with native au and telluride minerals called breccia ore the delta 18 o and delta d of rocks and mineral separates in these three ore types suggest that the ore was precipitated from hydrothermal fluids of delta 18 o 7 to 9 6 per mil and delta d 35 to 85 per mil at 350 degrees to 460 degrees c initial hydrothermal regime was followed by downward penetration of oxidizing sulfate bearing fluids delta 18 o 0 to 2 per mil delta d 20 to 70 per mil and of probable marine and or meteoric water origin initially at temperatures of 200 degrees c waning to 50 degrees c or less a third fluid regime is indicated for quartz magnetite chlorite veins which have mineral pair fractionations corresponding to fluids of delta 18 o 4 0 to 0 5 per mil and 210 degrees to 260 degrees c these three hydrothermal fluid regimes are interpreted to reflect a sequence of crustal compression relaxation and finally uplift above sea level probably all during the archean incremental 39 ar 40 ar upper plateau age of 2 575 m y for vein actinolite the deposit is interpreted to have formed during a period of major fracturing ductile deformation and thermal perturbation accompanying the episode of batholith emplacement modified journal abstract

a review of current testate rhizopod thecamoebian research in canada thecamoebians are a diverse group of testate rhizopods present in a variety of lacustrine and terrestrial habitats among this group certain agglutinating forms primarily arcellacea have tests that are highly resistant to decay and thus fossilize well although the canadian fossil record of thecamoebians extends back as far as the carboniferous the group is particularly common in quaternary lacustrine and peatland environments from temperate to arctic regions of the country research on thecamoebians during the past few years has resulted in great progress on realizing the potential of this group as an important new class of paleoenvironmental indicator applied research on thecamoebian faunas in canada has emphasized aspects of paleolimnology e g eutrophication ph temperature oxygen levels monitoring of land use changes monitoring effectiveness of remediation efforts in contaminated substrates paleo sea level reconstruction paleo water table assessment and paleoclimatic reconstruction 2002 elsevier science b v all rights reserved

structural development of angular volcanic belts in the archean slave province narrow belts of metavolcanics lying between metasediments and granitoid rocks in the southwestern part of the archean slave province display a distinctive angular map pattern steep homoclinal segm

archaean carbon reservoirs and their relevance to the fluid source for gold deposits it is commonly assumed1 2 that seawater derived carbon in altered volcanic rocks is the only major pre metamorphic carbon in carbonate reservoir in archaean greenstone belts thus carbonates from archaean gold deposits with stable isotope ratios too negative median 13c 3 to have been derived from such carbon 13c usually assumed to be near 0 have been interpreted as being derived from a local felsic magmatic source1 barley and groves3 however recognize two carbonate alteration styles that predate regional metamorphism and gold mineralization in the norseman wiluna greenstone belt of western australia evidence is summarized below these are seafloor alteration and fault controlled regional alteration which as shown below have completely different carbon isotope compositions the latter median 13c 4 8 implies a major juvenile carbon co2 flux from the mantle during greenstone belt evolution and is thus of fundamental importance in itself however here we show why the mere existence of two carbon in carbonate reservoirs and variation in carbon isotope ratios of carbonates between individual gold deposits in one area negate some of the fundamental assumptions used to support magmatic fluid models1

the mattagami lake mine archean zn cu sulfide deposit quebec hydrothermal coprecipitation of talc and sulfides in a sea floor brine pool evidence from geochemistry 18 o 16 o and mineral chemistry orebody 2 is 21 million metric tons grading 10 5 percent zn 0 17 percent cu and 0 014 oz au plus 1 15 oz ag per short ton quartz in the orebody has a delta 18 o of 10 to 11 9 per mil or approximately 2 per mil heavier than footwall quartz signifying precipitation temperatures 250 degrees to 280 degrees c this is corroborated by filling temperatures of primary fluid inclusions within gangue quartz t f 240 degrees 270 degrees c both isotopic and fluid inclusion temperatures signify a broad thermal zonation from approximately 270 degrees c at the base to approximately 240 degrees c at the top of the orebody minimum water depths of 300 m are indicated from nonboiling hydrothermal fluids of 3 to 5 weight percent nacl equivalent at approximately 250 degrees c a approximately 50 degrees c cooling of fluids during passage from the footwall to a suggested sea floor brine pool above the ore zone may have been induced by turbulent mixing of approximately 20 percent pristine archean marine bottom water at approximately 70 degrees c downward into the brine pool chert in the overlying key tuffite has delta 18 o of 10 to 12 per mil probably representing equilibrium precipitation from brine pool fluids at 200 degrees to 250 degrees c spreading laterally across the sea floor in a gravitationally stable boundary layer modified journal abstract

hydrothermal alteration zoning and gold concentration at the kerr addison archean lode gold deposit kirkland lake ontario kerr addison a major archcan lode gold deposit of the abitibi belt with a production of approximately 10 x 10 6 oz au approximately 320 metric tons up to 1983 is localized in a zone of talc carbonate and chlorite carbonate rocks immediately south of a regional structural break the kirkland lake larder lake fault zone relict volcanic textures taken in conjunction with the ratios of diag nostic relatively less mobile elements collectively indicate that most of the wall rocks of the mine were originally mafic and ultramafic rocks along with their clastic derivatives regional greenschist facies metamorphism is locally superposed by a distinct zonation of gold associated hydrothermal alteration characterized by massive introduction of co 2 coupled with variable enrichments of alkali metals and calcium which produced systematic trends of alteration mineral assemblages alteration types of the initial stage contain chlorite which is replaced by muscovite or albite in the advanced stage of alteration with a concomitant increase in the proportion of carbonate minerals numerous generations of crosscutting veins are enveloped by alteration borders in which the sequence of the al bearing minerals namely albite mus covite and chlorite develop from the vein to the wall rocks always in a systematic sequence the same sequence is observed at a larger scale from the ore zone to the periphery of the mine area the intensity of alteration can be monitored by saturation indices co 2 ca fe mg for carbonates and 3k na al 3k al and na al for muscovite albite muscovite and albite respectively molar ratios plots of the moving averages of these indices across the 3 850 ft level of the mine reveal a remarkable correspondence to variations of gold abundance suggesting a genetic relationship of gold enrichment to hydrothermal alteration on a broad scale gold is concentrated to the south of the kirkland lake larder lake fault zone and at a more detailed scale in the transition zone between carbonate muscovite and carbonate albite alteration types during advanced alteration fluid x sub co 2 was approximately 0 1 and na k asymp 10 volcanics of the kinojevis and larder lake groups are 18 o enriched relative to pristine tholeiites and possess distinct mineral delta 18 o values probably due to different conditions of marine water alteration during or shortly after extrusion in domains of advanced alteration these are all shifted down to a common narrow bracket here 18 o 16 o and d h data indicate fairly constant temperatures 270 degrees 300 degrees c and a common isotopic composition of hydro thermal fluids delta 18 o 5ppm delta d 30 to 50ppm across the alteration zoning these results are in common with many other archcan lode gold deposits fe dolomite has a uniform delta 13 c value of 2 8 or 0 42 per mil 1sigma throughout the footwall and ore zones but it is enriched by approximately 1 per mil in the graphite free hanging wall rocks fluid delta 13 c value was 4 or 1 per mil reflecting either a magmatic carbon reservoir or mixtures of marine carbonate carbonaceous and magmatic sources the enrichment of gold at one side of the kirkland lake fault zone is interpreted to be the result of development of a metasomatic zoning induced by gradients in oxidation state the precious metal being concentrated in the reducing side zonation of alteration types south of the kirkland lake larder lake fault zone represents various steps of a continuous process of incremental changes of the rocks to adapt to the composition of an externally generated fluid successive generations of fracture arrays and veins have the same alteration patterns and thus the composition of the incoming hydrothermal fluid seems to have remained essentially unchanged through time gold mineralization at the kerr addison mine and its contiguous alteration halo are interpreted to be the result of repeated cycles of hydraulic fracturing fluid penetration and local reaction with rocks fluid rock interaction produced lateral variations of fluid composition which led to gold concentration probably due to gradients in ph preferentially at the interface between the carbonate muscovite and carbonate albite alteration types which is also the site of pyrite concentration the alteration assemblages and specific site of gold pyrite concentration at kerr addison are common to several other described archcan lode gold deposits

geology and alteration in the golden mile kalgoorlie the giant kalgoorlie gold deposit 1 200 metric tons au recovered is surrounded by a wide wall rock alteration halo 1 x 3 km this alteration primarily represents the selectively pervasive formation of carbonate chlorite and localized intense pyrite and muscovite alteration which all formed synchronously with gold mineralization the carbonate alteration halo is interpreted as epigenetic because of evidence that carbonate chlorite assemblages overprint regional metamorphic fabrics furthermore the geometry of the alteration zone boundaries is controlled by ductile shear zones formed during regional deformation and the geochemistry of all the alteration zones suggests that one fluid was responsible for all assemblages there is no evidence of intense premetamorphic carbonation in the kalgoorlie area kalgoorlie is situated in the highly auriferous eastern goldfields province of the yilgarn block within a narrow corridor rift zone that contains several large gold deposits regional metamorphism has produced upper greenschist facies assemblages but has retained original rock textures at kalgoorlie the most important gold host is the golden mile dolerite 80 of gold produced a differentiated tholeiitic sill intruded between a lower mafic ultramafic pile including the paringa basalt the next most important gold host and overlying felsic rocks and metasediments the kalgoorlie syncline is the dominant tectonic structure in the main gold producing area of the golden mile adjacent to this infold of metasediments the golden mile dolerite and paringa basalt are the site of a number of ductile shear zones which formed synchronously with the syncline these zones and the many smaller shear zones between them have provided fluid channelways throughout the golden mile and are the site of most economic gold mineralization three alteration zones have been mapped in the golden mile dolerite on the basis of the mineralogic siting of fe i e the chlorite carbonate and pyrite zones the additional actinolite zone representing the unaltered regional metamorphic mafic assemblage has been converted to chlorite zone assemblages throughout the mined areas of the golden mile the carbonate zone bleached dolerite can be traced for 2 km through the main mineralized parts of the golden mile and to the full depth of lake view mine the boundary between the chlorite and carbonate alteration zones is locally sharp and controlled by ductile shear zones but is generally strata bound and preferentially developed in the more fe rich parts of the dolerite the pyrite zone which includes all economically gold mineralized areas is the site of the strongest muscovite alteration and is most intense and continuous in ductile shear zones the chlorite zone chlorite calcite or ankerite forms from mild carbonation of actinolite zone assemblages the carbonate zone ankerite siderite is a more local expression of this carbonation even after extensive carbonate alteration relative major element abundances are little changed and the main added components are limited to co 2 s k and rb the pyrite zone i e the gold lodes has ankerite muscovite quartz albite pyrite and minor siderite bearing assemblages it represents significant addition of sulfur the three alteration zones not only reflect differing degrees of alteration intensity but are also strongly influenced by host rock fe mg and this ratio largely determines the stability of chlorite favored by low fe mg and thus the distribution of the carbonate zone favored by high fe mg progressive deformation within the shear zones reworked existing mineralization kalgoorlie fits a metamorphic replacement model of gold formation by auriferous metamorphic fluids interacting with fe rich host rocks its great size is a function of a very well developed fluid channelway system via ductile shear zones and later fault zones and the favorable chemical nature of the host rocks especially the golden mile dolerite the full width of carbonation chlorite and carbonate zones reflects overlapping alteration envelopes around the closely spaced fluid pathways the processes responsible for the formation of most of the gold at kalgoorlie were essentially similar to those at several other archean gold deposits but on a larger scale

geochemistry and origin of the regan intrusive suite and other granitoids in the northeastern slave province northwest canadian shield the regan intrusive suite of about 100 plutons of tonalite granodiorite and quartz diorite intruded the yellowknife supergroup and migmatite terrain in the northwest slave structural province 2 59 ga ago rare earth element ree trace element and major element analyses from 39 representative whole rocks from the suite suggest it was derived by batch melting of the crust producing a parental magma of tonalitic or granodioritic composition by analysing ree from different parts of a zoned pluton it was concluded that ree distribution was controlled by early separation of quartz diorite from the parent magma by flow differentiation and that the bulk of the ree were contained in early cumulate accessory apatite and monazite the residual magma was further fractionated in pipelike magma chambers during ascent into more leucocratic rocks chondrite normalized ree patterns of single lithology plutons are similar to lithologies in zoned plutons and it is proposed they initially segregated during ascent

lacustrine thecamoebians mainly arcellaceans as potential tools for palaeolimnological interpretations abstract a number of thecamoebian genera of potential or demonstrated importance for palaeolimnological research mainly arcellacea are discussed what is known about their biology ecology spatial distribution mechanisms of dispersal and characteristic associations is briefly reviewed in the introductory part after a short discussion on the concept of species and the somewhat peculiar way in which it applies to this group of organisms a chapter on systematic taxonomy including an illustrated guide to the identification of the genera is presented the scarce fossil record of the group is then briefly discussed practical instructions on collection preparation and observation of thecamoebians for palaeolimnological research are supplied the paper closes with the presentation of a few studies performed by the authors as examples of how arcellacea can become tools for the solution of palaeolimnological problems

geochemical trends in the ackley granite southeast newfoundland their relevance to magmatic metallogenic processes in high silica granitoid systems the ackley granite occupying an area of approximately 2700 km2 was intruded at about 355 ma across the boundary between the avalon and gander tectonic terranes of southeast newfoundland it is dominated by k feldspar megacristic and equigranular biotite bearing granite with subordinate granodiorite but 10 separate phases have been recognized also including hornblende and muscovite bearing varieties small aplite pegmatite type molybdenite deposits occur in a southwest lobe and cassiterite wolframite bearing quartz topaz greisens are found as steeply dipping veins and pods within a south central lobe of the pluton a geochemical study of 357 rock samples randomly distributed on a grid of 2 km spacing shows systematic geographic variation in the concentrations of a range of elements the concentrations of silica and some other elements show a relatively abrupt change approximately 10 15 km west of the projected boundary between the avalon and gander terranes indicating that the different terranes ha

the genesis and tectonic control on archaean gold deposits of the western australian shield a metamorphic replacement model abstract gold deposits occur in greenstone belts world wide and contribute to anomalously high gold production from archaean terranes as in other cratons archaean gold mineralization of western australia represents a complex array of deposit styles despite this most deposits are clearly epigenetic and large deposits have a number of features in common including their strong structural controls distinctive wallrock alteration fe sulphide k mica albite ca mg fe carbonates consistent metal associations au ag as sb w b low base metals commonly fe rich host rocks great depth extension and lack of appreciable vertical zonation these shared characteristics combined with their ubiquitous occurrence indicate that archaean gold deposits had a common origin related to the tectonic evolution of greenstone belts auriferous hydrothermal systems were broadly synchronous with regional metamorphism and emplacement of synkinematic granitoids and felsic porphyry intrusions although these gold systems involved low salinity lowdensity reduced near neutral h 2 o co 2 fluids carrying gold as reduced sulphur complexes the origin of the fluids is equivocal most timing evidence and stable isotope data cannot distinguish metamorphic from magmatic granitoid or felsic porphyry orggins but the lack of consistent spatial relationships between specific volumetrically significant intrusive phases and large gold deposits in a number of cratons strongly favours metamorphic derivation of fluids the metamorphic replacement model for gold mineralization involves devolatilization of the lower portions of the greenstone pile with high geothermal gradients inhibiting significant melting co 2 possibly formed by the decarbonation of early alteration related to mantle degassing along crustal scale synbasinal fault zones auriferous fluids were channelled along greenstone scale faults in part developed during reactivation of crustal scale faults in a strike slip regime gold deposition occurred largely under greenschist facies conditions about 300 400 c 1 2 kb in response to decreasing gold solubility with declining temperature however a major control on gold deposition was fluid wallrock interaction many large deposits formed by sulphidation of fe rich host rocks with synchronous deposition of fe sulphides and gold however the variable nature of gold depositing reactions including lowering of fo 2 and ph allowed a multitude of small and some large deposits to form wherever that fluid circulation occurred in consequence several of the relatively small deposits currently worked from open pit are hosted by ultramafic and felsic rocks there are few constraints on the source of components au s k co 2 added to gold deposits but even giant deposits such as the golden mile kalgoorlie could have formed from a realistic greenstone source volume ca 8 8 5 km convective circulation of fluids could have contributed to the generation of high fluid rock ratios on the regional scale the markedly heterogeneous distribution of large gold deposits gold productivity and host rocks to deposits can be accommodated by the metamorphic replacement model the most favourable conditions for development of auriferous hydrothermal systems operated in younger ca 2 7 0 1 ga rift phase greenstones where greatest extension and crustal thinning produced high geothermal gradients crustal scale synbasinal faults and rapid extrusion and burial of volcanics including abundant komatiites iron rich tholeiitic basalts and dolerites were preferred host rocks for large gold deposits the least favourable conditions existed in older ca 3 5 3 4 ga platformphase greenstones where gentle sagging on submerged continental crust produced eruption of mainly mafic volcanics with few komatiites commonly in very shallow water environments this allowed intense synvolcanic alteration of both gold source rocks and potential host rocks the generally smaller gold deposits formed mainly in ultramafic or greywacke hosts younger ca 3 0 ga platform phase greenstones appear intermediate in nature but unlike other greenstones have significant epigenetic gold deposits in originally oxide facies bif which were deposited on relatively deep water platforms similar controls appear to exist on a world scale with gold mineralization peaking at ca 2 7 0 1 ga in response to development of major rift zones in thickened relatively mature continental crust interestingly the giant witwatersrand goldfield formed at about the same time

seismicity of south central coastal california october 1987 through january 1997 earthquakes recorded along south central coastal california from october 1987 through january 1997 by the pacific gas and electric company9s 20 station central coast seismic network and the u s geological survey9s northern and southern california networks are used to study their relation to previous seismicity mapped quaternary faults and regional tectonic features we developed p and s wave velocity models station corrections and duration magnitude calibrations to process 1184 reliable earthquake locations and 212 well constrained focal mechanisms seismicity generally coincides with mapped quaternary faults and areas of tectonic uplift including the southern offshore santa maria basin and areas to the west and the uplifted blocks within the los osos tectonic domain comparison of our data to previous microearthquake locations 1969 1987 and larger m 5 historical earthquakes shows that these patterns have been persistent seismically quiescent areas have few or no mapped quaternary faults and typically are structural lows the base of the seismogenic zone is about 12 km in depth above the relic oceanic crust microearthquake locations and strike slip focal mechanisms document the strike slip nature of the hosgri fault zone and its step over to the san simeon fault along the western boundary of the los osos domain uplifting blocks within the los osos domain are most seismically active toward their western ends along the hosgri fault zone and they exhibit reverse and oblique faulting consistent with block uplift and interaction with the hosgri fault zone the observed patterns and character of microseismicity and macroseismicity clearly show transpressional deformation associated with the hosgri fault zone overprinted by rotation and westward migration of the western transverse ranges within this tectonic setting clockwise rotation of the western transverse ranges causes internal deformation of the los osos domain and westward migration of the ranges appears to deflect the hosgri fault zone westward and causes east west directed crustal shortening in the southern offshore santa maria basin

chemistry of potassium feldspars from three zoned pegmatites black hills south dakota implications concerning pegmatite evolution abstract an initial phase of an extensive geochemical study of pegmatites from the black hills south dakota indicates potassium feldspar composition is useful in interpreting petrogenetic relationships among pegmatites and among pegmatite zones within a single pegmatite the k rb and rb sr ratios and li and cs contents of the feldspars within each zoned pegmatite to a first approximation are consistent with the simple fractional crystallization of the potassium feldspar from a silicate melt from the wall zone to the core of the pegmatites some trace element characteristics i e cs have been modified by subsolidus reequilibration of the feldspars with late stage residual fluid k rb ratios of the potassium feldspar appear to be diagnostic of the pegmatite mineral assemblage the relationship between k rb and mineralogy is as follows harney peak granite barren pegmatites 180 li fe mn phosphate bearing pegmatites 90 50 spodumene bearing pegmatites 60 40 pollucitebearing pegmatites k rb ratios suggest that the pegmatites studied are genetically related by fractional crystallization to each other and the harney peak granite overlapping rb sr ratios and the general increase in sr and ba with decreasing k rb indicate the genetic relationship is much more complex and may also be dependent upon slight variations in source chemistry and mineralogy material composition and degrees of partial melting

experimental determination of crystal melt partitioning of ga and ge in the system forsterite anorthite diopside the crystal liquid partitioning of ga and ge has been measured experimentally between forsterite diopside anorthite and spinel and melts in the pseudoternary system forsterite anorthite diopside at one atmosphere pressure and 1300 c gallium is incompatible with forsterite and diopside d ga 0 024 and 0 19 respectively is only slightly incompatible in anorthite d ga 0 86 and is highly compatible in spinel d ga 4 6 the partition coefficient for ge is within a factor of two of unity for forsterite diopside and anorthite d ge 0 62 1 4 and 0 51 respectively but ge is incompatible in spinel d ge 0 1 the coefficients for the exchange of ga and al and the exchange of ge and si between minerals and melts generally are within a factor of two of unity as is expected from the geochemical coherence of these element pairs in natural samples the application of our results to the interpretation of natural basaltic and mantle samples from the earth and basalts from the moon and the shergottite parent body demonstrates that it is possible to discriminate between different mantle source compositions using ga al and ge si ratios the ge variation among lunar mare basalts may be indicative of a heterogeneous lunar mantle the substantial depletion of ge in chassigny relative to the other snc meteorites may be evidence of either a heterogeneous shergottite parent body spb mantle or of different geochemical behavior for ge in the spb

mantle derived volatiles in continental crust the massif central of france co2 rich gases and groundwaters from springs and boreholes originating within the basement of the massif central have variable3he 4he ratios with correspondingr ra values ranging from 0 8 to 5 5 and 0 3 to 2 8 respectively indicating the presence of a significant component of mantle helium molar concentrations of rare gases in the co2 rich gases are approximately 5 orders of magnitude greater than in the waters and suggest that a near surface henry s law fractionation has occurred between exsolving co2 and water 13c values of the co2 rich gases are in the range 4 2 to 6 1 i e in that range normally attributed to mantle carbon but which could also represent an average crustal composition and therefore do not discriminate between mantle and crustal sources c 3he ratios show 4 orders of magnitude variation from 1 4 1012 to 5 108 and compared to a mantlec 3he ratio of 109 indicate that either a complex fractionation has occurred between mantle helium and mantle co2 or more likely that mantle rare gases have been diluted by large quantities of co2 with an average crustal carbon isotope composition the regional distribution of3he and c does not show any obvious relationship to age or proximity of volcanic centres or major faults suggesting that mantle derived c and he components decoupled from their silicate melt sources at some depth the results from this area of active fluid circulation suggest that c isotope data derived from metamorphic terrains should be interpreted with great caution but that input of some mantle derived carbon is expected to accompany crustal extension

relationship of foraminifera and thecamoebian distributions to sediments contaminated by pulp mill effluent saguenay fiord quebec canada gravity cores and grab samples collected in the saguenay fiord between 1976 and 1988 contain the record of a 20th century benthic marine environment contaminated primarily by organic matter discharges from several local pulp and paper mills spiroplectammina biformis is the dominant arenaceous species its living percent abundance decreases between 1982 and 1988 as a consequence of the apparent recolonization of the upper reaches of the fiord by several arenaceous taxa the most important beingtextularia earlandi cassidulina reniforme the dominant living calcareous species shows about a three fold increase in relative abundance over the six year interval grab sample observations also suggest a recolonization of some formerly barren benthic environments near the head of the fiord by foraminiferal species between 1982 and 1988 this recolonization may reflect the combined effect of government regulations imposed on local industrial polluters in the early 1970 s and the capping of a large area of contaminated sediment by a layer of clay that was transported to the basin at the head of the fiord as the result of a catastrophic landslide in 1971 x radiographs of core sections from a basin at the head of the fiord show sharp laminations that reflect both the absence of bioturbators and the seasonal variation of fluvial depositional processes organic waste deposition from pulp and paper mill outfalls first increased around 1910 and shows a first order inverse relationship to benthonic foraminiferal assemblage diversity the presence of only allochthonous thecamoebian and reworked planktonic foraminifera tests in many benthonic foraminifera barren core intervals supports the idea that common indigenous estuarine species such asspiroplectammina biformis were excluded from these areas at certain times as a consequence of pollution stress rather than having been removed from the sediment record as a result of post depositional diagenetic effects however future studies of estuarine pollution history based on proxy foraminiferal data from cores must give greater emphasis to distinguishing ecological stress responses from diagenetic process i e test dissolution effects since both mechanisms can be reflected in the proxy pollution signal in a similar way

postglacial stratigraphy and sea level change in southwestern new brunswick cores from small basins in southwestern new brunswick above present sea level but below the former marine limit were examined for microfaunal changes indicating a transition from marine to freshwater conditions carbon 14 dates of those transition points add to and strengthen a previous sea level curve from the area the oldest date places sea level at about 75 m above present at 16 000 years bp dates from the lower lakes 10 m appear to be anomalously old and it is suggested that after 12 000 years bp erosion became a factor in marine areas this erosion may be related to the overall breakup of ice in the north atlantic and may explain why few dates younger than 12 000 years bp are found in raised marine deposits of new brunswick and maine

lithophile element systematics of archean greenstone belt au ag vein deposits implications for source processes reply potassic alteration domains of greenstone belt lode gold deposits are characterized by systematic partitioning between lithophile elements k rb and ba are generally co enriched and linearly correlated over almost three orders of magnitude in abundance where k rb 220 400 and k ba 30 85 k cs 104 and k tl 2 104 are also correlated though more weakly lithium abundances and rb sr ratios are erratic in altered rocks these interelement trends collectively are present in deposits variously hosted by ultramafic mafic or felsic volcanic rocks and sediments or granitoids magmatic processes involving crystal fractionation of biotite k feldspar and plagioclase generate trends to systematically diminished k rb 50 k li k cs and k tl but enhanced k ba 8 103 and rb sr in most late stage differentiates such late stage trends are the rule in magmatophile deposits including the archean cadillac molybdenite deposit phanerozoic cu and mo porphyry deposits sn w greisens and most

u pb zircon geochronology in the southwestern abitibi greenstone belt superior province the abitibi belt is the largest continuous greenstone belt in the superior province of the canadian shield it comprises several composite komatiitic tholeiitic calc alkalic and sedimentary sequences that are folded transected by major faults and intruded by various generations of plutonic rocks precise u pb geochronology has been carried out in the belt for the past decade to solve chronostratigraphic and metallogenetic problems this paper presents new zircon ages and reassesses previously published ones now refined by the addition of abraded and concordant zircon analyses volcanic and subvolcanic units of the timmins area yield the following ages 2727 1 5 ma for a tuff of the upper deloro formation 2703 1 5 ma for a tuff of the upper tisdale formation and 2698 4 ma for the krist fragmental assigned to the top of the tisdale formation the age of a dunite intrusive into the upper deloro formation is revised at 2707 3 ma whereas the aquarius diorite east of timmins yields a poorly define

the crustal continuum model for late archaean lode gold deposits of the yilgarn block western australia most archaean gold ores belong to a coherent genetic group of structurally controlled lode deposits that are characteristically enriched in au with variable enrichments in ag as w sb bi te b and pb but rarely cu or zn and are surrounded by wallrock alteration haloes enriched in k lile and co2 with variable na and or ca addition evidence from the yilgarn block of western australia combined with similar evidence from canada and elsewhere indicates that such deposits represent a crustal continuum that formed under a variety of crustal regimes over at least a 15 km crustal profile at pt conditions ranging from 180 c at 1 kb to 700 c at 5 kb individual deposits separated by tens to hundreds of kilometres collectively show transitional variations in structural style of mineralisation vein textures and mineralogy of wallrock alteration that relate to the pt conditions of their formation at varying crustal depths specific transitions within the total spectrum may be shown also by deposits within gold camps although nowhere is the entire continuum of deposits recorded from a single gold camp or even greenstone belt

the gold carbonate association source of co2 and co2 fixation reactions in archaean lode deposits abstract abundant carbonate is a ubiquitous feature of archaean lode gold deposits both in domains of alteration enveloping veins and in rocks enclosing auriferous sediments detailed studies of chemical mass balance in metabasalts progressively altered towards gold bearing quartz carbonate veins disposed within shear zones at yellowknife reveal massive additions of co2 k si and fe accompanying mineralisation with concomitant depletions of na coherent behaviour of al sc zr also v and nb provides a reference for constraining the volume relations during hydrothermal alteration in the peripheral regions of alteration depletions of ca and mg result in overall volume reduction but these elements are added to veins and their immediate alteration envelopes where there is a large positive volume change precious metals together with cr ni cu zn pb rb cd and ba have been added to the veins and altered wall rocks whereas quartz noble metals and other trace elements have been precipitated from hydrothermal fluids solution of ca mg and some fe indigenous to peripheral alteration regions combining with co2 from the mineralising reservoir appears to be the process for forming the abundant ferri dolomite gangue observations of many archaean au deposits reveals that carbonate chemistry reflects the nature of wall rocks with wall rocks donating the bivalent metal cations and hydrothermal fluids the co2 alteration reactions at yellowknife involved hydrolysis of albite accompanied by fixation of kaqueous to produce muscovite with na loss and hydrolysis of chlorite epidote with co2 fixation to form ferri dolomite studies of oxygen isotopes fe 2 fe 2 fe 3 and structure reveal that au quartz and carbonate were precipitated in the presence of fluids of probable metamorphic origin 18 o 8 9 at low redox potential and at ambient temperatures of 400 450 c during episodes of hydrofracturing the abundant co2 and k required for extensive carbonate muscovite replacement alteration could be supplied by fluids released during prograde metamorphism under greenschist or greenschist amphibolite facies conditions where the relative proportion of co 2 h 2 o is in the order of 0 2 to 0 5 and k na 1 given high co2 co in the hydrothermal reservoir these molecules may act as complexing agents for transport of au and other rare elements e g w pd ni cr