controls of multimodal wave conditions in a complex coastal setting coastal hazards emerge from the combined effect of wave conditions and sea level anomalies associated with storms or low frequency atmosphere ocean oscillations rigorous characterization of wave climate is limited by the availability of spectral wave observations the computational cost of dynamical simulations and the ability to link wave generating atmospheric patterns with coastal conditions we present a hybrid statistical dynamical approach to simulating nearshore wave climate in complex coastal settings demonstrated in the southern california bight where waves arriving from distant disparate locations are refracted over complex bathymetry and shadowed by offshore islands contributions of wave families and large scale atmospheric drivers to nearshore wave energy flux are analyzed results highlight the variability of influences controlling wave conditions along neighboring coastlines the universal method demonstrated here can be applied to complex coastal settings worldwide facilitating analysis of the effects of climate change on nearshore wave climate

archean turbidite hosted orogenic gold mineralization in the gadag greenstone belt western dharwar craton peninsular india abstract turbidite hosted orogenic gold mineralization in the archean gadag greenstone belt of the western dharwar craton forms a major auriferous zone central auriferous zone extending over a strike length of about 12 km in the gadag duplex the turbidite sequence comprises thick inter bedded medium to coarse grained lithic graywacke and thin laminated layers of fine grained carbonaceous phyllite gold bearing quartz veins impregnate preferentially along the en echelon shear planes fractures and schistosity planes auriferous quartz veins are enveloped by the altered wall rocks mineralogy of the auriferous zone is dominated by gangue minerals like quartz ankerite chlorite sericite and carbonaceous matter with subordinate plagioclase monazite and xenotime are the important accessory minerals arsenopyrite and pyrite are the major sulfide minerals but pyrrhotite chalcopyrite sphalerite galena and scheelite are also present gold in native state occurs within quartz silicates and arsenopyrite notable distinctions in mineral assemblage texture and in chemical compositions of altered wall rocks compared to the precursor host rock in the study area implies that the metasomatism and wall rock alterations are the results of pervasive infiltration and intense interaction between hydrothermal fluids and the surrounding host rocks over a prolonged period sulfides carbonates carbonaceous matter k2o mgo cao cr ni cu pb zn as and higher values of gold 0 98 4 72 ppm are added into the altered wall rocks immediately enveloping the auriferous quartz vein bodies the chondrite normalized ree pattern of altered wall rocks exhibits enriched lree lan ybn av 9 54 with prominent negative eu anomaly the observed variation in geochemical characteristics and mineral assemblages in the alteration zones indicates differential response of the host rock and intensity of alteration depending on the composition of host rocks and hydrothermal fluids the auriferous hydrothermal fluids were of low salinity 2 0 to 6 6 wt nacl dominated by co2 h2o about 30 mol co2 with moderate densities 0 7 to 1 04 g cm3 and gold deposition occurred over a wide temperature range between 175 c and 325 c gold deposition was influenced by fluid mixing phase separation and redox reactions mixing between co2 h2o fluids and more reduced fluids which evolved during fluid reaction with adjacent carbonaceous wall rocks was the key factor causing gold deposition the formation of the gadag duplex deformation folds and reverse strike slip faults discontinuities was caused by the compression associated with subduction related tectonic processes during the initial period of intrusive magmatism 2 555 6 ma regional metamorphism occurred in the entire greenstone belt while during later period hydrothermal fluids responsible for gold mineralization probably were derived from metamorphic processes as well as from intrusive granites such fluids channeled through the thrust in host turbidite sequence carrying dissolved gold associated metals and sulfur ultimately were precipitated in a reducing environment in the splays to the thrust in the gadag duplex at about 2 522 6 ma resulting in retrograde alteration assemblages

gis based evaluation of diagnostic areas in landslide susceptibility analysis of bahluieț river basin moldavian plateau ne romania are neolithic sites in danger abstract the aim of this study is to compare the predictive strenghtness of different diagnostic areas in determining landslide susceptibility using frequency ratio fr statistical index si and analytic hierarchy process ahp models in a catchment from the northeastern part of romania scarps point landslide areas polygon and middle of the landslide point have been tested and checked in regards to their performance the three statistical models have been employed to assess the landslide susceptibility using eleven conditioning factors slope angle elevation curvature lithology precipitations land use topographic wetness index twi landforms aspect plan curvature and distance to river the three models were validated using the receiver operating characteristic roc curves and the seed cell area index scai methods the predictive capability of each model was established from the area under the curve auc for fr si and ahp the values are 0 75 0 81 and 0 78 using polygon as diagnostic area respectively among the three methods used si had a better predictability when it comes to the predictability values regarding the diagnostic areas the landslide area polygon proves to have the highest values this results from the entire surface of the landslide being taken into account when validating the data approximately 70 of the neolithic sites are located in areas with high and very high susceptibility to landslides meaning that they are in danger of being destroyed in the future the final susceptibility maps are useful in hazard mitigation risk reduction a sustainable land use planning evaluation of cultural heritage integrity and to highlight the most endangered sites that are likely to be destroyed in the future

geochronology of the porgera gold deposit papua new guinea resolving the effects of excess argon on k ar and age estimates for magmatism and mineralization abstract mesothermal epithermal gold mineralization at porgera in the highlands of papua new guinea png occurs in structurally controlled veins and disseminations which overprint and cross cut a suite of shallow level comagmatic mafic alkaline stocks and dykes the porgera intrusive complex pic and their sedimentary host rocks conventional k ar apparent ages of twelve hornblende separates from eight different intrusions scatter between 7 and 14 ma but four biotite separates are concordant at 6 02 0 29 ma 2 40 ar 39 ar step heating experiments on six of the hornblende separates reveal saddleshaped age spectra which indicate the presence of excess 40ar one of these samples yields a well defined plateau with an apparent age of 5 96 0 25 ma 2 this age is identical to that of the biotites and suggests an age of 6 0 0 3 ma 2 for emplacement of the pic older apparent ages obtained from conventional k ar and 40 ar 39 ar analyses are explained by excess 40ar contamination conventional k ar analyses of six separates of hydrothermal illite and roscoelite associated with gold mineralization yield apparent ages of between 5 1 and 6 1 ma and indicate that ore deposition occurred within 1 ma of magmatism at porgera evidence for the evolution of a magmatic volatile phase and the presence of excess 40ar both in the intrusives and in hydrothermal fluids associated with the orebody suggest that magmatic fluids may have had some involvement in metallogenesis but the exact nature of this involvement is not yet clear late miocene magmatism and mineralization at porgera are thought to have occurred shortly prior to or during the initiation of continent arc collision and to pre date associated pliocene uplift and foreland deformation in the highlands

chemical and boron isotope composition of tourmaline from the kiaka orogenic gold deposit burkina faso west african craton as a proxy for ore forming processes the kiaka orogenic gold deposit burkina faso located in the paleoproterozoic domain of the west african craton is characterized by a two stage gold mineralization hosted in volcano sedimentary metamorphic rocks that was formed during the eoeburnean 2 20 2 13 ga and eburnean 2 13 2 05 ga orogenic cycles these two stages include an early disseminated low grade gold mineralization and a late vein hosted high grade gold mineralization paragenetic studies indicate that the first gold stage was coeval with the deposition of hydrothermal tourmaline the aim of this paper is twofold i to determine the processes responsible for deposition of the economic disseminated gold mineralization and ii to identify the source of the mineralizing fluids for this purpose we performed an in situ study on tourmaline by combining electron probe microanalysis and secondary ion mass spectrometry measurements of boron isotopes hydrothermal tourmaline hosted in metamafic volcanic rocks and metagreywackes has a dravite composition but shows different 11b values falling within the two intervals of 25 1 to 22 0 and 19 6 to 15 1 respectively our results suggest that tourmaline formed from a distal high temperature ca 400 c reduced and low salinity hydrothermal fluid that interacted with the local host rocks based on the modeling of tourmaline fluid boron isotope fractionation we propose a metamorphic fluid origin derived from devolatilization of deeply buried muscovite schists during the regional prograde to peak metamorphism prior ca 2 13 ga this metamorphic fluid rock interaction model may possibly extend to other orogenic gold deposits in the west african craton

fluid pressure dominated orogenic gold mineralization under low differential stress case of the yaoure gold camp cote d ivoire west africa the 1 5 moz yaoure gold deposit which is located within the birimian greenstone belts of central cote d ivoire west africa is associated with two stages of economic gold mineralization both ore forming stages occurred during protracted e w directed shortening associated with the eburnean orogeny the first mineralization stage is hosted by fault fill veins along conjugate ene striking dextral and wnw striking sinistral strike slip fault arrays this ore stage is associated with a polymetallic assemblage including mo bi pb w te ag and au and cryptic alteration in wall rocks the second and main gold mineralization stage is associated with a low displacement fault fracture vein mesh formed during a reverse faulting episode this second gold phase is associated with a polymetallic assemblage including w and au pb and is characterized by pronounced albite ankerite pyrite hydrothermal alteration in wall rocks shear veins associated with this second mineralization episode formed during episodic fluid pressure variations under low differential stress within pre existing low angle reverse fault planes permeability destruction by albite ankerite pyrite hydrothermal sealing of these low angle reverse faults resulted in fluid pressure build up and ultimately in the development of extension veins under low differential stress in the late stages of the structural evolution of the deposit this study presents the structural evolution of a polyphase orogenic gold deposit and highlights that the interplay between fault zone activity hydrothermal alteration and fluid pressure fluctuations at low differential and deviatoric stresses were key in controlling fluid flow and the formation of ore within optimally oriented faults

archean polyphase deformation in the lake johnston greenstone belt area implications for the understanding of ore systems of the yilgarn craton abstract a structural and geochronology study on the 2900 ma lake johnston greenstone belt ljgb has defined multiple deformation events quantitative u pb age constraints have been obtained on the ductile deformation and peak metamorphic assemblages the d 1lj event is associated with the development of fold nappes during interpreted nne ssw shortening u pb shrimp dating on monazite from a dyke folded by the d 1lj event gives an age of 2634 1 ma providing an upper age limit on d 1lj this age could have been reset by the d 2lj metamorphic event a major metamorphic thermal event post dates the d 1lj event and is inferred to be the result of elevated temperatures coeval with the emplacement of granitoid intrusions the d 2lj event is associated with peak metamorphic temperatures and reflects nne ssw to ne sw shortening associated with dextral shearing a dyke that intrudes and crosscuts d 2lj fabrics yield a u pb shrimp age on monazite at 2629 1 ma and provides a lower age limit on the d 2lj event d 3lj is defined by crenulation cleavages developed during e w shortening the d 4lj episode is defined by brittle deformation and a series of n to ne trending steep dipping dextral faults formed during craton scale shortening under a ne sw directed far field stress the brittle d 5lj event is characterized by e w shortening with dip slip reverse n s faults the new d 2lj deformation age is younger than previously constrained ages for major deformation in the 2900 ma greenstone belts deformation within the ljgb was broadly coeval with the waning stage of formation of gold deposits in adjacent greenstone belts most peak magmatic and metamorphic events preserved in the greenstone belts have been constrained to ca 2640 2650 ma the presence of such a high temperature deformation event recorded at ca 2630 ma in the ljgb belt has implications for the thermal history fluid formation and geodynamic context of the development of these gold systems the 2630 ma age correlates with late stage and post gold emplacement of pegmatite dykes in surrounding terranes the ljgb is interpreted to have been a mobile belt associated with high grade metamorphism that was inboard west of and active during the formation of major world class gold systems in the eastern goldfields terranes the d 1lj to d 2lj changes in the kinematics of the system i e d 1lj to d 2lj may correlate with a stress switch linked to the influxes of gold bearing fluids in adjacent greenstone belts

gold mineralisation and alteration of penakacherla schist belt india constraints on archaean subduction and fluid processes abstract in the dharwar craton southern india gold deposits are found mostly along the six arcuate shear zones passing through late archaean greenstone belts 2 7 ga one such shear zone complex extends for about 400 km within and along the ramagiri hungund schist belt the penakacherla sector of this shear zone is excellently exposed enabling a detailed investigation of synorogenic gold mineralisation and its relationship to associated hydrothermal alteration metamorphism and deformation under ne sw compression associated with archaean subduction processes converted mafic volcanic rocks into amphibolites and intermediate to felsic volcanic rocks into quartz mica schists continued compression generated a 50 100 m wide shear zone complex consisting of mafic phyllonites advection of hydrothermal fluids through this shear zone and reaction between fluids and the mafic phyllonites resulted in a silicified k metasomatic assemblage mainly consisting of chlorite amphibole k mica plagioclase ankerite quartz fe oxides pyrite chalcopyrite and arsenopyrite networks of quartz and carbonate veinlets a few millimeters to a few centimeters thick formed along the foliation planes giving rise to microscopic alteration envelope in which individual veinlet systems are merged into one another to form a composite alteration system gold is found within these quartz veinlets mafic phyllonites and at their mutual contacts hydrothermal fluids have modified the primary major minor trace and lree compositions of host rocks such that their mutual behaviour became non systematic some hfse and hree also show minor mobility but the overall ree pattern generally resembles that of the precursor mafic volcanic rocks mass and volume loss gain by si and ca has made significant impact on al ti and zr abundances which are generally immobile during hydrothermal alteration however element pairs such as zr hf v sc and nb ta maintain primary inter element ratios although their absolute abundances are drastically diluted similarly ree in highly silicified and carbonatised samples are reduced but patterns remain similar to those of relatively least altered mafic phyllonites with la n yb n between 1 and 3 in some samples lree enrichment is observed elevating in la n yb n from 3 to 11 pathfinder elements and base metals such as as cd cu pb zn and sb have been added along with the au and ag 13 c of carbon varies from 16 to 21 suggesting a biogenic origin whereas coexisting pyrite 34 s ranges from 1 to 3 pointing towards the involvement of magmatic or average crustal sulphur overall concentrations of k rb sr ba nb ta ti cs cr co v y and sc and many of the ratios such as k rb la sc la yb indicate that metamorphism devolatilisation and dehydration of an oceanic subducting slab might have partially contributed the mineralising fluids and generated the alteration assemblage observed in the host rocks fluid sources were mantle and greenstone belt dehydration and devolatilisation generating observed compositional and alteration diversity

lithostratigraphy and composition of 2 1 ga greenstone belts of the west african craton and their bearing on crustal evolution and the archean proterozoic boundary we have determined the lithostratigraphy of three early proterozoic 2 1 ga birimian greenstone belts in the west african craton and measured the concentrations of major and trace elements in samples of volcanic rocks from those belts the nangodi belt largely consists of tholeiitic basalt flows with mg numbers of 37 to 69 and flat to slightly lree depleted chondrite normalized ree patterns overlain by sodic na 2 o k 2 o 3 7 29 calc alkaline dacitic tuffs and lavas that are hree depleted la yb 4 5 8 9 times chondrites yb 3 9 8 7 times chondrites the volcanic sequence is capped by calc alkaline andesitic crystal tuffs with high mg numbers 66 75 and a high la yb ratio 10 5 times chondrites similar to archean and modern sanukitoids the dixcove belt largely consists of tholeiitic hyaloclastites and pillow lavas mg numbers 52 61 that grade upward into high mg mg numbers 59 calc alkaline andesitic tuffs and flows the winneba belt largely consists of massive tholeiitic h

geochemical oxygen and neodymium isotope compositions of metasediments from the abitibi greenstone belt and pontiac subprovince canada evidence for ancient crust and archean terrane juxtaposition abstract the abitibi greenstone belt agb and pontiac subprovince ps in the southwestern superior province are adjacent greenstone plutonic and metasedimentary dominated terranes respectively separated by a major fault zone metasediments from these two contrasting terranes are compared in terms of major and trace element and o and nd isotope compositions and detrital zircon ages the following two compositional populations of metasediments are present in the low grade abitibi southern volcanic zone 1 1 a mafic element enriched population mep characterized by flat depleted ree patterns enhanced mg cr co ni and sc low incompatible element contents and minor or absent normalized negative troughs at nb ta and ti and 2 2 a low mafic element population lmep featuring lree enriched patterns enhanced rb cs ba th and u contents and pronounced normalized negative troughs at nb ta and ti these geochemical features are interpreted to indicate that the mep sediments were derived from an ultramafic and mafic dominated oceanic provenance whereas the lmep sediments represent mixtures of mafic and felsic arc source rocks the ps metasediments are essentially indistinguishable from abitibi lmep on the basis of majorelement and transition metal abundances suggesting comparable types of source rocks and degrees of maturity but are distinct in terms of some trace elements and o isotope compositions the pontiac metasediments are depleted in 18o and enriched in cs ba pb th u nb ta hf zr and total ree and also have higher ratios of rb k cs rb ba rb ta nb th la and ba la relative to the abitibi lmep two subtypes of ree patterns have been identified in ps metasediments both have moderately fractionated distributions with la yb n 3 9 17 and 7 8 13 6 respectively but the first has minor eu anomalies eu eu 0 89 1 16 whereas the second features pronounced negative anomalies eu eu 0 52 0 81 coupled with high concentrations of incompatible elements such as k rb th u nb and ta the first subtype is interpreted to be derived from provenances of mixed mafic and felsic volcanic rocks whereas the eu depleted type has geochemical features that are typical of post archean sediments or archean k rich granites and volcanic equivalents abitibi metasediments have nd 2 7 ga values of 0 71 to 1 83 corresponding to model tchur 2 82 2 55 ga with the majority around 2 65 ga close to the depositional age of 2 7 ga in contrast ps metasediments are characterized by nd 2 7 ga 0 95 to 3 51 corresponding to t dhur 2 7 to 3 1 ga consistent with a detrital zircon age spectrum of 2 69 ga to 3 1 ga pontiac subprovince and abitibi metasediments have contrasting provenances suggesting their separate initial geodynamic settings and later tectonic juxtaposition major and trace elements o and nd isotopic compositions and detrital zircon ages collectively suggest that some of the ps metasediments were derived mainly from juvenile rocks whereas others require various degrees of contribution from older 3 0 3 5 ga evolved crust mixed with juvenile 2 7 ga rocks older components were derived either directly from erosion of an ancient continental arc or from contemporaneous volcanic rocks which may contain recycled older components if the ps represents in part an accretionary prism to the abitibi southern volcanic zone then oblique subduction may have been involved which allowed the pontiac subprovince to juxtapose or sample exotic source rocks

hydrothermal gold mineralization at the hira buddini gold mine india constraints on fluid evolution and fluid sources from boron isotopic compositions of tourmaline we determined the boron isotope and chemical compositions of tourmaline from the hira buddini gold deposit within the archean hutti maski greenstone belt in southern india to investigate the evolution of the hydrothermal system and to constrain its fluid sources tourmaline is a minor but widespread constituent in the inner and distal alteration zones of metabasaltic and metadacite host rocks associated with the hydrothermal gold mineralization the hira buddini tourmaline belongs to the dravite schorl series with variations in al fe fe mg ca ti and cr contents that can be related to their host lithology the total range of 11b values determined is extreme from 13 3 to 9 0 but 95 of the values are between 4 and 9 the boron isotope compositions of metabasalt hosted tourmaline show a bimodal distribution with peak 11b values at about 2 and 6 the wide range and bimodal distribution of boron isotope ratios in tourmaline require an origin from at least two isotopically distinct fluid sources which entered the hydrothermal system separately and were subsequently mixed the estimated 11b values of the hydrothermal fluids based on the peak tourmaline compositions and a mineralization temperature of 550 c are around 1 and 10 the isotopically lighter of the two fluids is consistent with boron released by metamorphic devolatilization reactions from the greenstone lithologies whereas the 11b rich fluid is attributed to degassing of i type granitic magmas that intruded the greenstone sequence providing heat and fluids to the hydrothermal system

the alkaline porphyry associated yao an gold deposit yunnan china rare earth element and stable isotope evidence for magmatic hydrothermal ore formation the yao an vein type gold deposit is located in the ailaoshan jinshajiang alkaline intrusive belt yunnan province china and is associated both in time and space with 33 5 1 0 ma old alkaline intrusions the gold mineralization is associated with potassic wall rock alteration the ree distribution patterns of secondary k feldspar are generally similar to those of the igneous perthite but with about seven times higher total ree abundances the alteration is ascribed to a high ree magmatic fluid derived from the yao an alkaline intrusive suite the hydrothermal yao an gold deposit formed during two gold bearing stages i e a sulfide pyrite stage and a sulfide oxide stage pyrite specularite the ree abundance of early stage i pyrite is relatively high with strong enrichment in lree la yb n of 40 290 generally positive eu anomalies eu eu 0 86 1 55 and ree patterns very similar to those of secondary feldspar in contrast the later stage ii pyrite has much lower ree concentrations and lower la yb n of 5 5 11 8 eu eu of 0 49 0 76 and flat chondrite normalized spidergram patterns the stage i pyrite has 34s in the range of 2 2 to 3 2 and overlaps with regionally distributed pyrite in least altered syenite porphyry in contrast stage ii pyrite has much higher 34s values between 7 8 and 16 5 carbon isotope data for four samples from stage ii revealed 13c pdb values between 6 and 8 these stable isotope and ree data suggest that magmatic fluids of the alkaline intrusions caused both potassic alteration and stage i sulfide mineralization the system evolved from stage i to stage ii mineralization by influx of meteoric fluids with relatively heavier sulfur although calcite carbon isotope data suggest that the co2 remained dominantly of magmatic origin

plume and arc magmatism in the abitibi subprovince implications for the origin of archean continental lithospheric mantle abstract based on eclogitic mantle xenoliths that appear to be the residue of slab melts it is commonly argued that the formation of distinctive lithospheric keels beneath archean cratons occurred by the tectonic accretion of oceanic crust these models are complicated by evident buoyancy of the keels the varied compositions of the mantle xenolith suite as a whole and a compositional constraint that a large portion of the keels originated in mantle plume melting events resolution of these issues is complicated by the long development history of most cratons 100 s of m y and the multiple cycles of magmatism they represent in contrast the single 50 m y period of arc volcanism in the abitibi subprovince and the immediate onset of orogeny and craton stabilisation avoids many of these uncertainties chemical and isotopic data demonstrate that syn volcanic to syn tectonic adakitic abitibi granitoids were derived via slab melting deep seismic reflection profiles image singular slab like features along the moho these are interpreted as the remnants of oceanic slabs emplaced and torn during orogeny nonetheless their presence directly contradicts subcretion models of keel formation because they occupy regions that should correspond to the top of an earlier formed subcreted keel post adakite shoshonitic granitoids and lamprophyres also attest to the presence of a metasomatised mantle wedge throughout the entire period of abitibi arc magmatism diamond bearing lamprophyres in the abitibi and adjacent wawa subprovince are compositionally equivalent to paleoproterozoic diamondiferous rocks and characteristic of adakite generating shallow subduction rather than evidence of pre existing sub cratonic keels abitibi mantle plume and subduction related volcanism also demonstrates the continuous presence of shallow asthenospheric mantle beneath the belt over a 50 m y period komatiites and then boninites erupted along the central part of the belt halfway through its evolution and rifted arc style volcanism dominated the belt within a few m y of orogeny none of these events are consistent with the development of a progressively thickened continental lithospheric keel the geodynamic evolution of the abitibi belt demonstrates a fact recognised in some xenolith studies the characteristic association of deep keels and archean cratons was not developed gradually during greenstone belt volcanism rather it was initiated by the coupling of shallow imbricated plume and arc related crust with the buoyant residue of mantle plume melting that rose from depths of 80 km to 400 km subduction was active along the southern and eastern margin of the superior province craton before and after ascent of the abitibi plume renewal of subduction in the abitibi as marked by the occurrence of the 2716 ma boninitic volcanic suite delayed the ascent of the deep keel and its coupling to the composite crust final ascent of the plume residue occurred following orogeny and slab loss and may have included entrainment of fragmented slab residue into the rising diapir the coupling of shallow crust and deep keel occurred soon after and the keel s presence beneath the subprovince is recognised by phanerozoic diamond deposits xenolith chemistry and geophysical data

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

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

timing of gold mineralization at red lake northwestern ontario canada new constraints from u pb geochronology at the goldcorp high grade zone red lake mine and the madsen mine the goldcorp high grade zone at the red lake mine has reserves proven and probable established at 1 775 million tons mt at an average grade of 80 6 g t au new u pb geochronologic data combined with detailed mapping and crosscutting relationships provide timing constraints and new insights into the formation of the exceptionally rich goldcorp high grade zone the results show that the main stage of the high grade mineralization in the high grade zone formed before 2712 ma and that a second stage of gold mineralization much smaller in terms of total gold content but spectacular in terms of grade formed after 2702 ma this second stage is attributed to gold remobilization caused by the enhanced thermal gradient and deformation associated with the emplacement of the cat island pluton 2699 ma approximately 7 km east of the deposit or by the ca 2 63 to 2 66 ga postorogenic regional thermal event indicated by hornblende muscovite and biotite ar ar cooling ages from the uchi subprovince it is proposed that the main stage of high grade mineralization formed between ca 2723 to 2712 ma possibly synchronous with emplacement of the dome and mckenzie island stocks the abino granodiorite and hammell lake batholith as well as with penetrative d2 main stage regional deformation lamprophyre dikes spatially associated with the deposit postdate main stage mineralization by at least 10 m y a postore granodiorite dike from the madsen mine the second largest deposit in the district was dated at 2698 1 ma this age is similar to a postalteration and late deformation diorite dike at the creek zone showing near the former starratt olsen mine which was dated at 2696 2 ma the crosscutting relationships confirm that the main stage of mineralization at the madsen mine is pre 2698 ma a folded and metamorphosed polymictic conglomerate located stratigraphically above the campbell red lake deposit and deposited after ca 2747 but before 2712 ma is correlated with the newly recognized huston assemblage crosscutting and overprinting relationships between the conglomerate and the alteration indicate protracted multistage aluminous and iron carbonate quartz veining and or alteration event s before and after deposition of the conglomerate the age of the conglomerate confirms that the campbell red lake deposit is proximal to a folded regional unconformity consistent with the empirical relationship between large gold deposits and unconformities elsewhere in archean greenstone belts this paleosurface represents a key first order exploration target and it is proposed that areas of high potential for gold exploration in red lake occur in the balmer assemblage rocks within 500 m to 1 km of the unconformity

the jurassic danba hypozonal orogenic gold deposit western china indirect derivation from fertile mantle lithosphere metasomatized during neoproterozoic subduction the genesis of hypozonal orogenic gold deposits is highly controversial with both crustal metamorphic fluids and variously derived sub crustal fluids suggested as fluid and metal sources the lower jurassic danba gold deposit a rare phanerozoic hypozonal orogenic gold deposit on the western margin of the yangtze craton china provides an opportunity to resolve these controversies danba is characterized by biotite amphibole alteration and pyrrhotite dominant ore assemblages formed at 500 600 c the 34s values of ore related pyrrhotite range from 3 1 to 9 9 in sharp contrast to those of syn sedimentary pyrrhotite from devonian host rocks which are between 6 8 and 9 5 the pb isotope compositions of ore related pyrrhotite with 206pb 204pb 17 85 18 25 and 207pb 204pb 15 48 15 67 are less radiogenic and more variable than those of unaltered host rocks these differences combined with the hypozonal feature of the deposit indicate that ore metals and sulfur were derived from a sub crustal rather than a local crustal source the pge patterns of ore related pyrrhotites are similar to those of sulfides in baltic mantle lithosphere that was metasomatized by aqueous fluids in terms of marked enrichment of pd and ru but significantly differ from those of magmatic intrusions and related magmatic hydrothermal deposits this suggests that the metals that formed the danba deposit were transported via aqueous fluid from metasomatized mantle lithosphere rather than from a magmatic source the 18o of mantle fluid calculated from hydrothermal quartz and biotite ranges from 10 to 12 the anomalously high s and o isotope ratios and variable pb isotope ratios together with pge data support a model in which the inferred mantle lithosphere source was significantly hydrated metasomatized and fertilized by fluid derived from subducted oceanic sediments with elevated 34s and 18o values geological evidence suggests that this subduction event was neoproterozoic in age this study defines a model in which hydrated and metasomatized mantle lithosphere was formed during early subduction but it was over 500 million years later during later lower jurassic asthenosphere upwelling that metal and sulfur rich fluid was released into the crust to form the danba gold deposit

criteria for the recognition of metamorphosed or altered lamprophyres a case study from the archaean of kambalda western australia abstract the ability to distinguish ancient lamprophyres from other mafic and ultramafic intrusive rock types has become increasingly important lamprophyres have been used as marker horizons in the mapping of several precambrian terranes they have been recognized for decades as possible indicators of gold mineralization and their presence has implications for the tectonic interpretation of ancient greenstone belts whilst fresh undeformed lamprophyres are readily recognized metamorphosed altered and or deformed examples are more problematical the intrusive ages of kambalda lamprophyres are constrained by available field and geochronological evidence including direct dating of one kersantite to the period 2684 2660 ma these rocks therefore belong to the world s oldest group of alkaline rocks and lamprophyres so far recognized which also includes contemporaneous examples from canada zimbabwe and probably tanzania despite their extreme age and low to medium grade regional metamorphic history these rocks still preserve characteristic lamprophyric textures chemistry and mineralogy only where metamorphism has been overprinted by gold related alteration and deformation do the lamprophyres cease to be recognizable petrographically however their unique chemistry persists and despite losses of the most mobile elements from presumed magmatic compositions altered and deformed specimens still retain far higher contents of sr k ba th nb p zr and ce than basalts of the local greenstone succession even lamprophyres which have been converted to biotite plagioclase carbonate pyrite schists retain this distinctive chemical signature during both alteration and metamorphism mobile elements k rb sr ba display far larger changes than archetypal immobile elements ce nb zr p ti clearly sanctioning traditional preference for the latter in assessing altered rocks however the surprising loss of nb during biotitization of hornblende indicates that negative nb anomalies conventionally regarded as indicators of subduction related magmatism can also be induced purely by alteration processes

secular variation in greenstone sequence development emphasizing superior province canada abstract evidence from the superior province of the canadian shield suggests the existence of several distinct lithostratigraphic associations in greenstone belts 1 quartz arenite and carbonate bearing sequences 2 mafic ultramafic volcanic sequences 3 mafic to felsic volcanic cycles and 4 timiskaming type sequences of fluviatile sediments and calc alkaline to alkaline volcanics recently recognized quartz arenite bearing sequences in the sachigo and wabigoon subprovinces are from base to top quartz arenite stromatolite bearing carbonate oxide facies iron formation and komatiite or tholeiite primary structures in the quartz arenites indicate shallow water deposition and represent mature sedimentation granitoid provenance of these sediments is postulated based upon petrography of coarse arenites and clasts of associated conglomerates the few dated superior province quartz arenite bearing sequences are 2 85 ga the shallow water origin of the primary structures and biota and the areal extent of the quartz arenite and carbonate sequences invite comparison with platform sediments at passive margins platform sequences unconformably overlie 3 ga granitoid rocks and older mafic volcanics where original lower contacts are preserved in two localities mafic volcanic sequences contain sheet flows iron formations and deep water argillites based on physical volcanology and sedimentology these sequences are compared to modern deep water mafic plain and hawaiian volcanism they generally underlie mafic to felsic volcanic cycles and overlie platform sequences mafic sequences are 2740 2700 ma in age mafic to felsic volcanic cycles consist of deep water tholeiitic flows overlain by shallow water to subaerial intermediate to felsic pyroclastics and flows the facies style of volcanism petrography and geochemistry of the mafic to felsic cycles most closely resemble the characteristics of crust in continental magmatic arc systems this type of lithostratigraphic association varies in age from 2775 to 2700 ma in the superior province with minor exceptions timiskaming type sequences consist of fluviatile conglomerate immature arenites and wackes with subaqueous to subaerial volcanics of variable chemistry longitudinal and lateral variation within fault bounded basins is extreme and the sequences have generally been affected by only late stages of deformation the combination of rock types facies distribution the fault bounded nature of the repositories and the locus of sedimentation along zones of transcurrent displacement suggest timiskaming sequences are best compared with modern pull apart basins superior province timiskaming sequences are within the superior province platform sequences are the earliest postorogenic lithostratigraphic unit in greenstone belts followed by mafic plain sequences arc volcanics and pull apart basins we suggest that platform sequences based upon limited evidence are preceded by an orogeny and that pull apart basins represent a subsequent orogeny the lithostratigraphic units above have distinct metallogenic associations 1 platform sequences based upon compilation of several shields may contain detrital au and u and oxide facies iron formations associated felsic volcanics contain no recognized volcanogenic cu zn deposits in the superior province the following metallogenic associations are noted 2 mafic plain sequences contain komatiite flow related ni deposits cu ni and platinum group deposits are associated with flows and coeval intrusions 3 arc volcanic sequences contain volcanogenic cu zn sulphide deposits and scarce deposits of porphyry type cu mo and 4 timiskaming sequences and related plutonism are related to lode au

single zircon age constraints on the tectonic juxtaposition of the archean abitibi greenstone belt and pontiac subprovince quebec canada abstract zircons from metasediments and granitoids in the high grade lacorne block within the low grade archean abitibi greenstone belt have been dated by the single zircon pb evaporation technique yielding 207pb 206pb minimum ages detrital zircons in the mature clastic metasediments of the lacorne block display a range of ages from 2691 8 ma to 3042 6 ma the younger zircon ages 2691 8 2695 4 2715 16 and 2719 4 ma thus impose an upper limit for deposition and indicate that the high grade lacorne block is not basement to the abitibi supracrustal sequence 2747 2680 ma existence of abundant 69 older detrital zircons 2750 ma suggests in turn that the abitibi supracrustal rocks are not the source of the lacorne sediments two generations of granitoids occur in the lacorne block an early monzodiorite monzonite granodiorite syenite series mmgs 2671 4 to 2675 24 ma and a younger s type garnet muscovite granite series gmg 2630 20 to 2655 8 ma this contrasts with granitoid magmatism in the abitibi greenstone belt which ended at 2675 ma the pontiac subprovince to the south of the abitibi greenstone belt shares all of the above features of the lacorne block including detrital zircon ages as well as the composition and timing of granitoid magmatism this is interpreted to indicate that the lacorne block was originally part of the same tectonic terrane as the pontiac subprovince after development of the mmgs magmatism 21670 2680 ma the pontiac subprovince locally underthrust the abitibi greenstone belt and crustal thickening promoted partial melting of underthrust pontiac metasediments to form the 2644 13 ma s type granites later differential uplift exposed the lacorne block as a high grade tectonic window in the abitibi greenstone belt

timing of magmatism and deformation in the kamiskotia kidd creek area western abitibi subprovince canada abstract the kamiskotia kidd creek area comprises well preserved granitoid greenstone belt lithologies of the western most abitibi subprovince similar in composition and structural style to other late archean granitoid greenstone terranes e g kalgoorlie norseman western australia belingwe zimbabwe slave province canada it contains the kidd creek volcanogenic massive sulfide deposit and lesser deposits of the kamiskotia district and lode gold deposits associated with the destor porcupine fault zone near the prolific porcupine gold district the magmatic and tectonic history for the area is provided through detailed structural mapping and high precision u pb geochronology field observations support the following sequence of magmatic and structural events in the kamiskotia area 1 formation of older mafic and intermediate volcanic rocks followed by the emplacement of the kamiskotia gabbroic complex kgc and cogenetic massive sulfide bearing bimodal volcanic rocks kv also accompanied by coeval intrusion of granitoid a into the crystallizing kgc 2 regional bulk rotation about a sub horizontal axis of this stratigraphy to form a ne facing monocline 3 emplacement of three large granitoid intrusions imparting their respective contact strain aureoles on the stratigraphy 4 regional sub horizontal bulk north south shortening that formed a non penetrative east west flattening fabric with an element of 5 late dextral transpression that formed high strain zones related to western destor porcupine fault zone dpfz within less competent volcanic units and 6 emplacement of alkalic dikes associated with the late stages of transpressive deformation u pb ages help substantiate this chronology and aid in the correlation of kamiskotia lithologies across the southern abitibi subprovince zircon ages for the kgc and a kamiskotia rhyolite are 2707 2 ma and 2705 2 ma respectively these ages are coeval with the reid rhyolite with a zircon age of 2706 2 ma but are significantly younger than the kidd creek rhyolite and the prosser rhyolite with zircon ages of 2717 2 ma data refined by the addition of an abraded concordant analysis and 2716 6 3 ma respectively two of the granitoid intrusions have zircon ages of 2696 1 5 and 2694 4 ma the older granitoid intrusion has a titanite population with a 207 pb 206 pb minimum age of 2692 5 ma which may represent a protracted cooling history or a metamorphic event after the setting of the zircon u pb system two zircon fractions from the younger granitoid intrusion exhibit inheritance with 207 pb 206 pb minimum ages up to 2926 ma indicating the presence of significantly older crust in this region timing of north south compression and late transpression may be constrained by a u pb garnet titanite age on a late to post tectonic alkalic dike at 2687 3 ma

noble metal abundances of late archean 2 7 ga accretion related shoshonitic lamprophyres superior province canada abstract shoshonitic magmatism occurred in transpressive geodynamic settings within the superior province during the diachronous accretion of allochthonous subprovinces over 2720 to 2680 ma which culminated in stabilization of this archean craton the dikes are interpreted to have formed from low degrees of partial melting of depleted mantle metasomatically enriched in lile and lree during a prior subduction accretion event selenium contents of the dikes range from 50 130 ppb and s from 150 1000 ppm with s se ratios of 1150 18 000 signifying open system behaviour of s during autometasomatic and late hydrothermal alteration based on the se contents and assuming magmatic s se ratios of 5 000 primary s contents of the alkaline magmas were undersaturated at 650 ppm mgo and ni are correlated and ir during evolution of the shoshonitic magmas olivine pyroxene controlled ir concentrations and probably rh platinum and palladium correlate with ti implying that these pge were controlled by timagnetite fractionation

the scale of ore depositional systems an important restraint on epigenetic vs remobilized syngenetic origins for archaean mesothermal gold deposits there is general consensus that the majority of gold deposits in the important group hosted by volcanic or intrusive host rocks within archaean granitoid greenstone terrains have an epigenetic origin however there is controversy surrounding those stratabound deposits hosted by fe rich sedimentary rocks such as banded iron formation bif for which epigenetic syngenetic and remobilized syngenetic lateral secretion origins have all been proposed in western australia such controversial gold deposits in fe rich sedimentary units have similar ore mineralogies ore element ratios and in places alteration assemblages and on the craton scale show very similar structural controls to the other deposits equivalent relationships are recorded for similar deposits in other cratons all western australian deposits occur along kilometre scale shear or fault zones linked to trans craton obliqueto strike slip shear zones that were a focus for i carbonation with a mantle like isotopic signature and ii emplacement of high level a and i type granitoids felsic porphyries and or calc alkaline lamprophyres the scale of the mineralizing systems and the broad contemporaneity of mineralization as indicated by radiogenic isotope studies is much larger than that envisaged in conceptual secretion models which involve volumetrically small locally enriched source rocks instead archaean gold mineralization in western australia at least is probably the result of high fluid flux during deformation hightemperature metamorphism and magmatism which may be related to tectonism at convergent plate margins as in modern examples there is strong evidence for similar tectonic and mineralizing processes from the canadian shield

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