abrupt changes in deep atlantic circulation during the transition to full glacial conditions 1 six ocean drilling program odp sites in the northwest atlantic have been used to investigate kinematic and chemical changes in the western boundary undercurrent wbuc during the development of full glacial conditions across the marine isotope stage 5a 4 boundary 70 000 years ago sortable silt mean grain size ss measurements are employed to examine changes in near bottom flow speeds together with carbon isotopes measured in benthic foraminifera and planktic foraminiferal fragmentation as proxies for changes in water mass chemistry a depth transect of cores spanning 1 8 4 6 km depth allows changes in both the strength and depth of the wbuc to be constrained across millennial scale events ss measurements reveal that the flow speed structure of the wbuc during warm intervals interstadials was comparable to modern holocene conditions however significant differences are observed during cold intervals with higher relative flow speeds inferred for the shallow component of the wbuc 2 km depth during all cold stadial intervals including heinrich stadial 6 and a substantial weakening of the deep component 3 4 km during full glacial conditions our results therefore reveal that the onset of full glacial conditions was associated with a regime shift to a shallower mode of circulation involving glacial north atlantic intermediate water that was quantitatively distinct from preceding cold stadial events furthermore our chemical proxy data show that the physical response of the wbuc during the last glacial inception was probably coupled to basin wide changes in the water mass composition of the deep northwest atlantic

iron oxide copper gold iocg deposits through earth history implications for origin lithospheric setting and distinction from other epigenetic iron oxide deposits the iron oxide copper gold iocg group of deposits initially defined following discovery of the giant olympic dam cu u au deposit has progressively become too embracing when associated deposits and potential end members or analogs are included the broader group includes several low ti iron oxide associated deposits that include iron oxide p rich iron oxide f and ree rich fe or cu au skarn high grade iron oxide hosted au cu carbonatite hosted cu ree and f rich and iocg sensu stricto deposits consideration of this broad group as a whole obscures the critical features of the iocg sensu stricto deposits such as their temporal distribution and tectonic environment thus leading to difficulties in developing a robust exploration model the iocg sensu stricto deposits are magmatic hydrothermal deposits that contain economic cu and au grades are structurally controlled commonly contain significant volumes of breccia are commonly associated with presulfide sodic or sodic calcic alteration have alteration and or brecciation zones on a large commonly regional scale relative to economic mineralization have abundant low ti iron oxides and or iron silicates intimately associated with but generally paragenetically older than fe cu sulfides have lree enrichment and low s sulfides lack of abundant pyrite lack widespread quartz veins or silicification and show a clear temporal but not close spatial relationship to major magmatic intrusions these intrusions where identified are commonly alkaline to subalkaline mixed mafic even ultramafic to felsic in composition with evidence for mantle derivation of at least the mafic end members of the suite the giant size of many of the deposits and surrounding alteration zones the highly saline ore fluids and the available stable and radiogenic isotope data indicate release of deep volatile rich magmatic fluids through devolatization of causative mantle derived magmas and variable degrees of mixing of these magmatic fluids with other crustal fluids along regional scale fluid flow paths precambrian deposits are the dominant members of the iocg group in terms of both copper and gold resources the 12 iocg deposits with 100 tonnes t resources are located in intracratonic settings within about 100 km of the margins of archean or paleoproterozoic cratons or other lithospheric boundaries and formed 100 to 200 m y after supercontinent assembly their tectonic setting at formation was most likely anorogenic with magmatism and associated hydrothermal activity driven by mantle underplating and or plumes limited amounts of partial melting of volatile rich and possibly metal enriched metasomatized early precambrian subcontinental lithospheric mantle sclm fertilized during earlier subduction probably produced basic to ultrabasic magmas that melted overlying continental crust and mixed with resultant felsic melts with devolatilization and some penecontemporaneous incorporation of other lower to middle crustal fluids to produce the iocg deposits preservation of near surface deposits such as olympic dam is probably due to their formation above buoyant and refractory sclm which resisted delamination and associated uplift most precambrian iron oxide p rich or magnetite apatite kiruna type deposits have a different temporal distribution apparently forming in convergent margin settings prior to or following supercontinent assembly it is only in the phanerozoic that iocg and magnetite apatite deposits are roughly penecontemporaneous in convergent margin settings the phanerozoic iocg deposits such as candelaria chile occur in anomalous extensional to transtensional zones in the coastal cordillera which are also the sites of mantle derived mafic to felsic intrusions that are anomalous in an andean context this implies that special conditions possibly detached slabs of metasomatized sclm may be required in convergent margin settings to generate world class iocg deposits it is likely that formation of giant iocg deposits was mainly a precambrian phenomenon related to the extensive mantle underplating that impacted on buoyant metasomatized sclm generally smaller and rarer phanerozoic iocg deposits formed in tectonic settings where conditions similar to those in the precambrian were replicated

modeling the role of sodic alteration in the genesis of iron oxide copper gold deposits eastern mount isa block australia liberation of iron and potassium by widespread postmetamorphic albitization of country rocks was one of the likely contributing processes in the formation of both barren and mineralized magnetite chalcopyrite biotite gold hematite clinopyroxene actinolite apatite ironstones in the cloncurry district of the proterozoic mount isa block whole rock geochemical data indicate nearly immobile al ga ti zr during transformation of a variety of least altered rocks toward albitite the data indicate that the addition of na from a brine to the rock accompanied the loss of fe k ba rb ca sr co v mn pb and zn from those altered rocks and enrichment in the brine but that cu was not systematically stripped from a variety of wall rocks during albitization conversely the formation of metasomatic ironstones the immediate hosts to some cu au ores involves addition of most of the same elements that were lost during albitization the correlation between intensity of alteration its distribution and timing e g in breccias cored by ca 1530 1500 ma granitoids and convergence of all rock types toward magmatic stable isotope values provides strong evidence for a substantial component of igneous derived fluid simulations of the albitization process were carried out isothermally at 550 c and 350 mpa and polythermally from these conditions down to 400 c and 200 mpa using the gibbs minimization method with hch software and the unitherm database both simple fluid rock mixing models and more complicated reactor style algorithms used a range of input fluids from fluids equilibrated fluid with two feldspar granite through to na k ratios consistent with fluid inclusion results and geochemical data for initially unaltered wall rocks the apparent paradox of widespread albitization resulting from fluid released by two feldspar granites can be explained by relatively small shifts away from the k feldspar albite equilibrium curve and even isothermal model fluids derived from two feldspar granites produce albitites in calc silicate rocks outboard of granite proximal k feldspar clinopyroxene skarns matching field patterns those models with fluid na k ratios similar to those of fluid inclusions produced the most realistic alteration assemblages dominated by albite for both isothermal conditions and decreasing temperature which approximate those observed in the field pixe and microthermometric data on fluid inclusions from quartz in two feldspar quartz monzonite and pegmatite at the top of the mount angelay pluton indicate bulk na k molar ratios in the fluid of between 10 and 20 considerably higher than our thermodynamically calculated values for fluid in equilibrium with two feldspar granite of around 3 at 550 c 350 mpa such shifts may have been attained by admixture of magmatic hydrothermal fluid with small amounts of nacl brines trapped along grain boundaries in scapolite bearing calc silicate wall rocks by fluid immiscibility due to high initial co2 contents in the felsic intrusions by contributions from mafic magmas or from dissolution of salt rich layers into the intrusions prior to crystallization and fluid release with increasing amounts of fluid rock interaction in the models the fluids were enriched in k fe and ca approaching compositions observed in fluid inclusions in the ore deposits these fluids reacted with pelitic rocks which are common ore hosts would produce magnetite clinopyroxene biotite actinolite alteration at high temperature similar to the proximal alteration around ore deposits we infer that precipitation of sulfides in the cu au deposits was the result of mixing of cu bearing brine of ultimately magmatic origin but modified extensively via albitization with sulfur bearing fluids or reaction of the brine with sulfur bearing rocks when cu was absent from the initial magmatic fluid barren ironstones may have been the result

synchronous and proportional deglacial changes in atlantic meridional overturning and northeast brazilian precipitation changes in heat transport associated with fluctuations in the strength of the atlantic meridional overturning circulation amoc are widely considered to affect the position of the intertropical convergence zone itcz but the temporal immediacy of this teleconnection has to date not been resolved based on a high resolution marine sediment sequence over the last deglaciation we provide evidence for a synchronous and near linear link between changes in the atlantic interhemispheric sea surface temperature difference and continental precipitation over northeast brazil the tight coupling between amoc strength sea surface temperature difference and precipitation changes over northeast brazil unambiguously points to a rapid and proportional adjustment of the itcz location to past changes in the atlantic meridional heat transport

magmatic hydrothermal processes within an evolving earth iron oxide copper gold and porphyry cu mo au deposits iron oxide copper gold iocg deposits formed by magmatic hydrothermal fluids mh iocg share many similarities with but have important differences from porphyry cu mo au porphyry deposits mh iocg deposits predominantly occur in precambrian rocks are fe oxide rich and have volumetrically extensive high temperature alteration zones whereas porphyry deposits occur almost exclusively in phanerozoic rocks are fe sulfide rich and have narrower high temperature alteration zones we propose that these deposit types are linked by common subduction modified magmatic sources but that secular changes in oceanic sulfate content and geothermal gradients at the end of the precambrian caused a transition from the predominance of s poor arc magmas and associated s poor mh iocg systems to s rich arc magmas and associated s rich porphyry deposits in the phanerozoic phanerozoic mh iocg and rare precambrian porphyry deposits are explained by local or periodic fluctuations in oceanic oxidation state and sulfate content or remobilization of previously subduction modified lithosphere in post subduction tectonic settings

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

north atlantic ocean circulation and abrupt climate change during the last glaciation the most recent ice age was characterized by rapid and hemispherically asynchronous climate oscillations whose origin remains unresolved variations in oceanic meridional heat transport may contribute to these repeated climate changes which were most pronounced during marine isotope stage 3 the glacial interval 25 thousand to 60 thousand years ago we examined climate and ocean circulation proxies throughout this interval at high resolution in a deep north atlantic sediment core combining the kinematic tracer protactinium thorium pa th with the deep water mass tracer epibenthic 13c these indicators suggest reduced atlantic overturning circulation during every cool northern stadial with the greatest reductions during episodic hudson strait iceberg discharges while sharp northern warming followed reinvigorated overturning these results provide direct evidence for the ocean s persistent central role in abrupt glacial climate change

ice shelf collapse from subsurface warming as a trigger for heinrich events episodic iceberg discharge events from the hudson strait ice stream hsis of the laurentide ice sheet referred to as heinrich events are commonly attributed to internal ice sheet instabilities but their systematic occurrence at the culmination of a large reduction in the atlantic meridional overturning circulation amoc indicates a climate control we report mg ca data on benthic foraminifera from an intermediate depth site in the northwest atlantic and results from a climate model simulation that reveal basin wide subsurface warming at the same time as large reductions in the amoc with temperature increasing by approximately 2 c over a 1 2 kyr interval prior to a heinrich event in simulations with an ocean model coupled to a thermodynamically active ice shelf the increase in subsurface temperature increases basal melt rate under an ice shelf fronting the hsis by a factor of approximately 6 by analogy with recent observations in antarctica the resulting ice shelf loss and attendant hsis acceleration would produce a heinrich event

geochemistry of hypersaline fluid inclusions from the starra fe oxide au cu deposit cloncurry district queensland studies of liquid vapor multisolid l v ns and liquid vapor halite fluid inclusions suggest that at least three fundamentally different brines were involved in the genesis of the proterozoic ironstone hosted starra au cu deposit element concentrations determined from proton induced x ray emission pixe analysis of groups of l v ns inclusions from the early barren magnetite ironstone stage 400 550 c and the younger mineralization stage 220 360 c covary over concentration ranges greater than the deduced analytical errors the l v ns inclusions in the two stages are very different with higher ratios of fe and k to ca mn cu zn sr ba and pb in the ironstone stage quite distinct pseudosecondary nacl cacl h o inclusions are abundant in mineralization stage quartz calcite and anhydrite high concentrations of cu ca 1 000 ppm are present in some l v ns inclusions of both stages and the data suggest that large amounts of cu mn zn as ba and pb passed through the starra system as it evolved cl br ratios in the inclusions are mostly less than 0 002 and clearly different from those of ore fluids of the giant sedimentary hosted copper orebody at mount isa this could reflect a major magmatic contribution to the salinity at starra that is consistent with the preferred origin of the water in published stable isotope studies ba concentrations of at least several wt percent in some mineralization stage l v ns inclusions are associated with oxidized sulfur bearing mineral parageneses given the low solubility of barite this suggests that a s2 f o2 relationships varied during mineralization

tectonomagmatic evolution of the southern great bear magmatic zone northwest territories canada implications for the genesis of iron oxide alkali altered hydrothermal systems the great bear magmatic zone in northwestern canada is a paleoproterozoic volcano plutonic belt of high k calc alkaline to shoshonitic affinity interpreted as a continental arc that formed between 1 87 and 1 85 ga following the short lived calderian orogeny tectonomagmatic evolution of this magmatic zone favored the formation of multiple iron oxide and alkali alteration systems within a time frame of 10 m y as constrained geochronologically within error between 1875 and 1865 ma this illustrates a temporal and genetic relationship between shoshonitic to high k calc alkaline continental arc magmatism and the formation of iron oxide rich deposits and alkali alteration associated with iron oxide copper gold iocg mineralization early rhyolitic magmatism formed the basal sequence of the lou assemblage under a compressive or transpressive tectonic regime between 1872 and 1867 ma an apparent higher magmatic production is linked to a marked change in composition of the volcanic and plutonic rocks from rhyolite to intermediate felsic and locally mafic compositional homogeneity of the intrusive and volcanic rocks of the mazenod and bea assemblages termination of ductile to brittle ductile deformation along the main deformation zones and transition to widespread brittle fracturing and breccia formation are interpreted to reflect a change in the regional stress regime from compressional transpressional to extensional transtensional this change in stress regimes is associated with iron oxide rich mineralization that initially formed the nico au bi co deposit followed by iocg mineralization in the nico and sue dianne deposits as well as albitite hosted u mineralization in the southern breccia

an intrusion related origin for cu au mineralization in iron oxide copper gold iocg provinces major cu au deposits of iron oxide copper gold iocg style are temporally associated with oxidized potassic granitoids similar to those linked to major porphyry cu au deposits stable and radiogenic isotope evidence indicates fluids and ore components were likely sourced from the intrusions iocg deposits form over a range of crustal levels because co2 rich fluids separate from the magmas at higher pressures than in co2 poor systems thereby promoting partitioning of h2o cl and metals to the fluid phase at deep levels the magma fluid system cannot generate sufficient mechanical energy to fracture the host rocks as in porphyry systems and the iocg deposits therefore form in a variety of fault related structural traps where the magmatic fluids may mix with other fluids to promote ore formation at shallow levels the iocg deposits form breccia and fracture hosted mineralization styles similar to the hydrothermal intrusive breccias and sulphide vein systems that characterize many porphyry cu au deposits the fluids associated with iocg deposits are typically h2o co2 salt fluids that evolve by unmixing of the carbonic phase and by mixing with fluids from other sources in contrast fluids in porphyry systems typically evolve by boiling of moderate salinity fluid to produce high salinity brine and a vapor phase commonly with input of externally derived fluids these different fluid compositions and mechanisms of evolution lead to different alteration types and parageneses in porphyry and iocg deposits porphyry cu au deposits typically evolve through potassic sericitic and intermediate and or advanced argillic stages while iocg deposits typically evolve through sodic calcic potassic and carbonate rich stages and at deeper levels generally lack sericitic and argillic alteration the common association of porphyry and iocg cu au deposits with potassic oxidized intermediate to felsic granitoids together with their contrasting fluid compositions alteration styles and parageneses suggest that they should be considered as part of the broad family of intrusion related systems but that they are typically not directly related to each other

translating the mineral systems approach into an effective exploration targeting system abstract holistic mineral systems approaches are being increasingly adopted in the study of ore deposits but application in industry has been suboptimal because of the lack of a conceptual framework to help translate the mineral system understanding to practical application a four step process is proposed for linking the conceptual mineral system with data available to support exploration targeting these steps include translation from 1 critical processes of the mineral system to 2 constituent processes of the mineral system to 3 targeting elements reflected in geology and 4 targeting criteria used to detect the targeting elements directly or by proxy this translation process is illustrated using examples from komatiite hosted ni cu pge and orogenic au mineral systems ranking of targets must be at the critical process level rather than the current practice of mixing processes elements and proxies the significance of targeting elements and their mappable criteria changes as a function of the scale at which the critical processes operate and the availability of relevant geoscience datasets this scale dependence is rarely recognised in current practice sources of uncertainty when translating the mineral system understanding into an effective exploration targeting system include 1 resolution of a mappable criterion in a dataset 2 how well the targeting criterion reflects the targeting element 3 how well the targeting element reflects the critical process and 4 whether the process being mapped is critical for the genesis of a mineral deposit the first three sources of uncertainty collectively are termed the representativeness of the targeting criteria i e how representative is a mappable criterion of the constituent process for which it is a proxy the last source of uncertainty reflects our lack of understanding of the processes that control mineralisation and highlights areas for further research

muted change in atlantic overturning circulation over some glacial aged heinrich events several periods of massive iceberg discharge into the north atlantic and widespread cooling marked the last glacial period reconstructions of northward flow along the florida margin suggest that not all cold events were associated with a change in the strength of the atlantic meridional overturning circulation

reducing subjectivity in multi commodity mineral prospectivity analyses modelling the west kimberley australia predicting realistic targets in underexplored regions proves a challenge for mineral explorers knowledge driven prospectivity techniques assist in target prediction and can significantly reduce the geographic search space to a few locations the mineral prospectivity of the underexplored west kimberley region was investigated following interpretation of regional gravity and magnetic data emphasis was placed on identifying geological structures that may have importance for the mineral prospectivity of the region subsurface structure was constrained through combined gravity and magnetic modelling along three transects crustal scale structures were interpreted and investigated to determine their depth extent these interpretations and models were linked to tectonic events and mineralization episodes in order to map the distribution of minerally prospective regions using a knowledge driven mineral systems approach a suite of evidence layers was created to represent geological components that led to mineralization and then applied to each mineral system where appropriate this approach was taken to provide a more objective basis for prospectivity modelling the mineral systems considered were 1 magmatic ni sulphide 2 carbonate hosted base metals 3 orogenic au 4 stratiform hosted base metals and 5 intrusion related base metals including sn w fe oxide cu au and cu au porphyry deposits these analyses suggest that a geologically complex belt in the kimberley basin at the boundary to the king leopold orogen is prospective for magmatic related hydrothermal mineral systems including ni au and cu the lennard shelf is prospective for carbonate hosted base metals around a feature known as the 67 mile high and parts of the king leopold orogen are prospective for stratiform hosted base metals these results show that knowledge driven mineral system modelling is effective in identifying prospectivity in regional scale studies of underexplored areas as well as drastically reducing the search space for explorers working in the west kimberley

millennial scale tropical atmospheric and atlantic ocean circulation change from the last glacial maximum and marine isotope stage 3 abstract abrupt millennial scale climate oscillations known as dansgaard oeschger d o cycles characterized the climate system of the last glacial period although proxy evidence shows that d o cycles resulted in large scale changes in atmospheric circulation patterns around the planet an understanding of how atlantic meridional overturning circulation amoc varied across these events remains unclear here we take advantage of the fact that both tropical atmospheric circulation changes corresponding to north south shifts in the intertropical convergence zone itcz and large scale changes in ocean circulation associated with amoc variability can be reconstructed in the same sediment core from the florida straits to examine the relationship between atmospheric and ocean circulation changes across d o events to reconstruct surface water conditions mg ca paleothermometry and stable isotope measurements were combined on the planktonic foraminifera globigerinoides ruber white variety from sediment core knr166 2 jpc26 24 19 61 n 83 15 14 w 546 m depth to reconstruct a high resolution record of sea surface temperature and o seawater 18 a proxy for upper mixed layer salinity during marine isotope stages mis 2 and 3 from 20 35 ka bp as an additional proxy for upper water column salinity change we also generate a faunal abundance record of the salinity sensitive planktonic foraminifera neogloboquadrina dutertrei our results suggest that rapid reductions in sea surface salinity occurred at the onset of d o interstadials while stadials are characterized by increased surface salinities the most likely cause of these salinity changes was variation in the strength and position of the itcz across d o events finally we examine the relationship between millennial scale atmospheric circulation changes recorded in the planktonic records and ocean circulation changes inferred from the benthic o 18 record from our core our results provide some of the first evidence that amoc strength did vary across at least one of the millennial scale d o cycles of mis 3

reduced and oxidized au cu bi iron oxide deposits of the tennant creek inlier australia an integrated geologic and chemical model iron oxide associated au cu bi deposits of the tennant creek gold field range from magnetite pyrrhotite pyrite reduced cu rich deposits through sulfide poor magnetite rich high grade au bi intermediate f o2 deposits to hematite rich high grade au oxidized deposits discordant magnetite hematite chlorite quartz ironstone bodies that host the ore formed hydrothermally during the 1840 to 1860 ma barramundi orogeny at temperatures up to 350 to 400 c and 2 5 to 5 kbars deposition of ironstone minerals was localized by dilatency that was generated during d1 reverse shearing and folding a separate au cu bi hydrothermal stage overprinted selected ironstones during d2 at or before 1825 to 1830 ma where favorable d1 structures and fluid pathways were reactivated the extremes of the reduced to oxidized deposit spectrum represent divergent chemical conditions that cannot be reconciled by the action of a single fluid we have identified both reducing and oxidizing fluids that helped to form the au cu bi deposits at the west peko deposit which represents the reduced end member subtype constraints from oxide silicate sulfide mineral stabilities fluid inclusions and chlorite thermochemistry indicate that au cu bi ore was introduced into ironstone at 300 to 340 c by a reducing pyrrhotite stable weakly acidic sulfur rich and n2 ch4 rich aqueous fluid containing 3 to 10 wt percent nacl equiv an ore fluid source outside the relatively oxidized metasedimentary host sequence warramunga formation is implied we suggest similar ore fluids for other reduced cu and sulfide rich deposits in the district chemical mass transfer modeling of reactions between reducing fluid and ironstone incorporating estimated thermodynamic properties for aqueous bismuth complexes indicates that highly efficient gold and native bi deposition was predominantly in response to desulfidation and oxidation of the fluid chalcopyrite precipitated mainly in response to increased ph gold bismuth ore in the eldorado deposit an oxidized and hematitic end member is interpreted to have involved mixing of an oxidizing hematite stable ca na cl brine with an intermediate f o2 low to moderate salinity ore fluid as well as reaction of both fluids with ironstone furthermore the mass transfer modeling suggests that mixing of reducing and oxidizing fluids in the absence of ironstones could have resulted in high grade au deposits lacking fe oxides a subtype that has received comparatively little exploration attention in the tennant creek district

timing of palaeoproterozoic au cu bi and w mineralization in the tennant creek region northern australia improved constraints via intercalibration of 40ar 39ar and u pb ages abstract the magnitude of systematic uncertainties inherent in comparisons of proterozoic 40ar 39ar and u pb based ages is illustrated via a consideration of age constraints on two contrasting styles of palaeoproterozoic mineralization in northern australia published 40ar 39ar ages for au cu bi mineralization in the tennant creek region range from 1825 to 1829 ma apparently younger than the timing of deformation bracketed by 207pb 206pb zircon ages of igneous rocks at 1850 ma despite this apparent age offset propagation of systematic uncertainties in the 40ar 39ar ages shows that they are indistinguishable from the 1850 ma zircon ages recalculation using revised estimates of the 40k decay constant and age of the 40ar 39ar standard shifts the 40ar 39ar ages to 1847 1851 ma in excellent agreement with 207pb 206pb zircon ages from tennant supersuite igneous rocks and with local geological constraints to the south of tennant creek in the davenport ranges numerous small w prospects have been interpreted to be coeval with post tectonic granites of the devils suite at 1710 1720 ma new 40ar 39ar ages from muscovite selvages on wolframite bearing veins range from 1697 to 1703 ma these ages shift to 1711 to 1717 ma when recalculated using revised estimates for 40k decay constant and age of standard material bringing them into agreement with existing 207pb 206pb zircon ages for devils suite granitoids and consistent with field and geochemical interpretations these examples highlight the importance of considering systematic sources of uncertainty when comparing radiometric ages determined via different isotopic methods particularly in the proterozoic and archean parts of the timescale ongoing work to calibrate the 40ar 39ar and u pb based timescales will further enhance the application of multiple isotopic methods to constrain geological processes

sources of mineralising fluids for the olympic dam deposit south australia smnd isotopic constraints abstract the olympic dam cu u au ag deposit south australia is hosted by the olympic dam breccia complex a high level hematite rich hydrothermal breccia system the deposit is characterised by extreme enrichments of ree which are a product of the ore forming process therefore making the sm nd isotopic system an ideal tool for clarifying the complex relationships between the different ore and breccia types pyrite chalcopyrite and bornite chalcocite rich hematitic ores share an initial end signature of 2 5 which suggests that these ore types are cogenetic these ores together with sulphide poor hematitic breccias yield a 14 point sm nd isochron age of 1572 99 ma the host roxby downs granite has an initial nd of 5 and therefore cannot alone have been the source of the mineralising fluids for the hematitic ores in contrast to hematitic rocks volumetrically minor magnetite rich assemblages have the same initial nd signature as the host granite suggesting that they are cogenetic assuming that both hematite and magnetite were precipitated from solution their contrasting isotopic signatures require that ore deposition involved two distinct fluids the isotopic data do not allow the distinction between a model involving concurrent activity of such fluids in a mixing regime and a model involving temporally separate overprinting of magnetite by hematite cu sulphides the ore signature of nd 2 5 cannot have been derived solely from pre existing crustal rocks of the gawler craton it must have involved a contribution from a mantle derived source rock or magma the most likely source of this nd component are the mantle derived rocks produced during the gawler range volcanics event e g altered alkaline mafic ultramafic dykes within the deposit which have initial isotopic signatures as high as nd 4 assuming end member compositions equivalent to these dykes and the roxby downs granite the ore signature implies that 30 of the nd in the ores was derived from the mafic ultramafic source if nd was leached from source rocks rather than derived from magmatic volatiles the inferred rock fractions contributing ree to the deposit are 13 mafic ultramafic rocks and 87 roxby downs granite or its volcanic equivalent massbalance calculations indicate that 13 rock fraction of mafic ultramafics can account for 50 of the cu contained in the deposit the involvement of mafic ultramafic rocks is therefore inferred to have been crucial to the genesis of the cu enriched ores at olympic dam

a comparison of mineral deposits at the gecko and white devil deposits implications for ore genesis in the tennant creek district northern territory australia detailed geologic metal zonation paragenetic fluid inclusion and stable isotope studies have been undertaken of the cu rich gecko k44 and the au rich white devil deeps zone orebodies in the proterozoic tennant creek district of the northern territory australia despite differences in the grade and mineral abundances in the ores three paragenetic stages are present in both deposits 1 an early synkinematic oxide stage at which time the ironstones formed 2 a syn to postkinematic sulfide stage at which time cu au and bi were introduced and 3 a late minor carbonate stage with minor pb and zn the oxide stage involved precipitation of magnetite hematite quartz and chlorite this stage was subsequently foliated the sulfide stage involved the precipitation of gold chalcopyrite bi minerals chlorite and quartz and the hematization of magnetite the carbonate stage involved precipitation of carbonate talc galena and sphalerite and the alteration of chalcopyrite to bornite and covellite fluid inclusion studies indicate that oxide stage minerals formed from low temperature 250 degrees c high salinity 15 20 wt nacl equiv fluids whereas the sulfide stage formed from high temperature 350 degrees c high salinity 20 wt nacl equiv fluids that show evidence of phase separation sulfur isotope studies indicate that lower delta 34 s values occur in au rich pods whereas higher delta 34 s values occur in cu rich halos metal zonation studies indicate that in the white devil deeps zone orebody a basal au rich zone is surrounded by a bi rich shell this zonation is broadly similar to zonation at the juno deposit au bi cu pyrite large 1975 owing to its very low grades the distribution of cu in the white devil deeps orebody is erratic conversely the gecko k44 orebody is only weakly zoned with au enrichment at the top of the orebody in the sulfide tongue mineral deposition occurred in well zoned au rich e g juno and white devil and weakly zoned chalcopyrite hematite rich e g gecko deposits owing to the reduction of highly oxidized sulfide stage fluids through hematization of magnetite in ironstones the fluids evolved through the hematite field in f sub o 2 ph space to the hematite pyrite join and then followed the hematite pyrite join toward the hematite pyrite magnetite triple point this fluid evolution caused early gold precipitation in the hematite field but chalcopyrite precipitated only along the hematite pyrite join which accounts for metal zonation in well zoned au rich deposits in chalcopyrite hematite rich deposits fluid evolution was restricted to the hematite pyrite join and minor gold precipitated with chalcopyrite the k44 sulfide tongue is inferred to be a small zoned au rich system adjacent to the main k44 orebody differences in metal abundance and zonation can be interpreted in terms of varying proportions of highly oxidized magmatic hydrothermal fluids relative to more reduced connate basinal fluids introduced into the ore forming systems a large component resulted in well zoned au rich deposits an intermediate component resulted in chalcopyrite hematite rich au poor deposits and a small component resulted in unzoned chalcopyrite rich pyrrhotite bearing deposits with intermediate au grades e g peko

testing the basin centered gas accumulation model using fluid inclusion observations southern piceance basin colorado the upper cretaceous mesaverde group in the piceance basin colorado is considered a continuous basin centered gas accumulation in which gas charge of the low permeability sandstone occurs under high pore fluid pressure in response to gas generation high gas pressure favors formation of pervasive systems of opening mode fractures this view contrasts with thatofothermodelsoflow permeabilitygasreservoirsinwhich gas migrates by buoyant drive and accumulates in conventional traps with fractures an incidental attribute of these reservoirs we tested the aspects of the basin centered gas accumulation model as it applies to the piceance basin by determining the timing of fracturegrowth and associated temperature pressure and fluid composition conditions using microthermometry and raman microspectrometry of fluid inclusions trapped in fracture cement that formed during fracture growth trapping temperatures of methane saturated aqueous fluid inclusions record systematic temperature trends that increase from approximately 140 to 185 c and then decrease to approximately 158 c over time which indicates fracture growth during maximum burial conditions calculated pore fluid pressures for methanerich aqueous inclusions of 55 to 110 mpa 7977 15 954 psi indicate fracture growth under near lithostatic pressure conditions consistent with fracture growth during active gas maturation and charge lack of systematic pore fluid pressure trends

atlantic ocean circulation changes preceded millennial tropical south america rainfall events during the last glacial during the last glacial period greenland s climate shifted between cold stadial and warm interstadial phases that were accompanied by ocean circulation changes characterized by reduced atlantic meridional overturning circulation amoc during stadials here we present new data from the western tropical atlantic demonstrating that amoc slowdowns preceded some of the large south american rainfall events that took place during stadials based on 231pa 230th and ti ca measurements in the same sediment core we determine that the amoc started to slowdown 1420 250 and 690 180 1 years before the onset of two large precipitation events associated with heinrich stadials our results bring unprecedented evidence that amoc changes could be at the origin of the large precipitation events observed in tropical south america during heinrich stadials in addition we propose a mechanism explaining the differences in the extent and timing of amoc slowdowns associated with shorter and longer stadials

predictive mineral discovery in the eastern yilgarn craton western australia an example of district scale targeting of an orogenic gold mineral system abstract the eastern yilgarn craton eyc is one of the world s premier gold provinces subject to over a century of mineral exploration prolonged interest in the terrane has led to the assembly of multiple world class data sets suitable for testing district scale targeting methodologies district scale targeting is concerned with identifying a mineral camp 60 km 60 km in size within a prospective region or province 1000 km 1000 km in size exploration at the district scale necessitates the development of predictive exploration models which can be applied to large regions recent advances in the study of the geodynamic evolution and 3d architecture of the eyc together with an understanding of their interrelationship with the orogenic gold mineral system has resulted in identification of critical mineralisation processes responsible for the region s rich gold endowment here we describe and map these critical processes using them as a basis for district scale targeting we relate gold mineralisation to three temporally constrained geodynamic periods integrated with regional hydrothermal alteration unlike many targeting methodologies this methodology does not incorporate the location of known gold deposits in the analysis yet it predicted 75 of known gold mineralisation in 5 of the area the methodology allows critical mineralisation processes to be identified and mapped through time and space these critical processes are mostly generic and can be applied to other granite greenstone orogenic gold regions such as the abitibi in canada an important outcome of this work for the eyc is the identification of a number of new target areas not known currently for significant gold mineralisation in what is otherwise thought to represent a mature terrane for gold exploration

simulation of abrupt climate change induced by freshwater input to the north atlantic ocean temperature records from greenland ice cores1 2 suggest that large and abrupt changes of north atlantic climate occurred frequently during both glacial and postglacial periods one example is the younger dryas cold event broecker3 speculated that these changes result from rapid changes in the thermohaline circulation of the atlantic ocean which were caused by the release of large amounts of melt water from continental ice sheets here we describe an attempt to explore this intriguing phenomenon using a coupled ocean atmosphere model in response to a massive surface flux of fresh water to the northern north atlantic of the model the thermohaline circulation weakens abruptly intensifies and weakens again followed by a gradual recovery generating episodes that resemble the abrupt changes of the ocean atmosphere system recorded in ice and deep sea cores4 the associated change of surface air temperature is particularly large in the northern north atlantic ocean and its neighbourhood but is relatively small in the rest of the world

a framework of overprinting orogens based on interpretation of the mount isa deep seismic transect a deep seismic reflection transect and coincident refraction study reveal the crustal structure developed during mesoproterozoic orogenesis preserved in the mount isa inlier of northwest queensland australia geologic interpretation of the reflection data indicates a two stage evolution for east west shortening the first stage involved west directed folding and thrusting above a decollement in the eastern part of the terrane this decollement system was the forehand of an orogenic system rooted east of the present day inlier the second stage is characterized by a network of basement cutting reverse and strike slip faults that dissected the decollement this overprinting system was linked to crustal thickening within the mount isa terrane the refraction profile indicates the crust beneath the inlier is currently approximately 55 km thick rocks with transitional velocities 7 km s in the lower 15 km are interpreted as mafic underplate formed during the pre orogenic rift history of the inlier the refraction profile also reveals two west dipping high velocity layers within the crust evaluating the origin of these layers in light of the kinematics of crustal thickening suggests they are portions of the underplated material thrust to midcrustal levels during the second stage of shortening the overprinting orogenic scenario has implications for the geodynamic evolution of the inlier that should have a direct bearing on mineralizing systems localized by reverse faults developed during the second stage of shortening this basement cutting stage established a linked fault network able to tap deeper crustal circulation during the intrusion of late to postorogenic granitoids

contrasting tectonic settings and sulfur contents of magmas associated with cretaceous porphyry cu mo au and intrusion related iron oxide cu au deposits in northern chile porphyry cu mo au and iron oxide copper gold iocg deposits share many similarities e g fe cu and au contents but also have important differences e g the predominance of sulfide minerals in porphyry deposits and iron oxides in iocg deposits genetic comparisons are complicated by the broad definition of iocg deposits here we restrict our study to iocg deposits that are related to igneous intrusive systems in the mesozoic coastal cordillera of northern chile both porphyry and iocg deposits occur in close spatial and temporal proximity offering the chance to examine what controls their different modes of formation from detailed examination of the timing geochemistry and tectonic setting of associated igneous rocks based on new and published data we find that rocks associated with mid cretaceous iocg deposits 125 110 ma are largely indistinguishable from those associated with slightly earlier 125 ma and later 110 ma porphyry cu mo au deposits magmas related to iocg deposits were formed during a brief period of back arc transtension in the mid cretaceous and are on average somewhat more mafic dioritic locally alkaline and isotopically primitive compared to granodioritic magmas associated with porphyry deposits formed during normal contractional arc tectonics in the later cretaceous however these compositional ranges overlap and the differences are not clear enough to be diagnostic we measured the so3 content of igneous apatite from selected samples of these rocks to test the hypothesis that the difference in sulfur content of the ore deposits was due to differences in sulfur content of the associated magmas early igneous apatite crystals occurring as inclusions in silicate phenocrysts from the carmen de andacollo porphyry cu au deposit re os molybdenite ages of 103 9 0 5 ma 103 6 0 5 ma are significantly richer in s 0 25 0 17 wt so3 n 69 than similar apatite crystals from two iocg deposits candelaria casualidad and a sample of regional mid cretaceous igneous rock from near productora 0 04 0 02 wt so3 n 76 using published partition coefficients for s between apatite and oxidized silicate melt we semi quantitatively estimate corresponding magmatic sulfur contents of 0 02 wt s in the carmen de andacollo magmas versus 0 001 to 0 005 wt s in the iocg associated magmas this is an order of magnitude difference and the opposite of what would be expected if the difference were due to bulk magma composition sulfur solubility is generally higher in mafic magmas whereas here the s content is higher in the more felsic porphyries we conclude that the porphyry forming magmas indeed had higher s contents than the iocg related magmas and suggest that these differences reflect different petrogenetic processes during normal subduction magmas derived from the metasomatized mantle wedge are hydrous moderately oxidized and s rich and have the potential to generate s rich porphyry type deposits in contrast in back arc extensional settings upwelling asthenospheric melts carry a weaker subduction signature including lower s contents interaction of these s poor magmas with previously subduction modified upper plate lithosphere is more likely to give rise to s poor iocg deposits

the ocean s role in setting the mean position of the inter tropical convergence zone through study of observations and coupled climate simulations it is argued that the mean position of the inter tropical convergence zone itcz north of the equator is a consequence of a northwards heat transport across the equator by ocean circulation observations suggest that the hemispheric net radiative forcing of climate at the top of the atmosphere is almost perfectly symmetric about the equator and so the total atmosphere plus ocean heat transport across the equator is small order 0 2 pw northwards due to the atlantic ocean s meridional overturning circulation however the ocean carries significantly more heat northwards across the equator order 0 4 pw than does the coupled system there are two primary consequences first atmospheric heat transport is southwards across the equator to compensate 0 2 pw southwards resulting in the itcz being displaced north of the equator second the atmosphere and indeed the ocean is slightly warmer by perhaps 2 c in the northern hemisphere than in the southern hemisphere this leads to the northern hemisphere emitting slightly more outgoing longwave radiation than the southern hemisphere by virtue of its relative warmth supporting the small northward heat transport by the coupled system across the equator to conclude the coupled nature of the problem is illustrated through study of atmosphere ocean ice simulations in the idealized setting of an aquaplanet resolving the key processes at work

dansgaard oeschger cycles interactions between ocean and sea ice intrinsic to the nordic seas dansgaard oeschger d o cycles are the most dramatic frequent and wide reaching abrupt climate changes in the geologic record on greenland d o cycles are characterized by an abrupt warming of 10 5 c from a cold stadial to a warm interstadial phase followed by gradual cooling before a rapid return to stadial conditions the mechanisms responsible for these millennial cycles are not fully understood but are widely thought to involve abrupt changes in atlantic meridional overturning circulation due to freshwater perturbations here we present a new high resolution multiproxy marine sediment core monitoring changes in the warm atlantic inflow to the nordic seas as well as in local sea ice cover and influx of ice rafted debris in contrast to previous studies the freshwater input is found to be coincident with warm interstadials on greenland and has a fennoscandian rather than laurentide source furthermore the data suggest a different thermohaline structure for the nordic seas during cold stadials in which relatively warm atlantic water circulates beneath a fresh surface layer and the presence of sea ice is inferred from benthic oxygen isotopes this implies a delicate balance between the warm subsurface atlantic water and fresh surface layer with the possibility of abrupt changes in sea ice cover and suggests a novel mechanism for the abrupt d o events observed in greenland ice cores

iron oxide copper gold deposits an andean view iron oxide copper gold iocg deposits defined primarily by their elevated magnetite and or hematite contents constitute a broad ill defined clan related to a variety of tectono magmatic settings the youngest and therefore most readily understandable iocg belt is located in the coastal cordillera of northern chile and southern peru where it is part of a volcano plutonic arc of jurassic through early cretaceous age the arc is characterised by voluminous tholeiitic to calc alkaline plutonic complexes of gabbro through granodiorite composition and primitive mantle derived parentage major arc parallel fault systems developed in response to extension and transtension induced by subduction roll back at the retreating convergent margin the arc crust was attenuated and subjected to high heat flow iocg deposits share the arc with massive magnetite deposits the copper deficient end members of the iocg clan as well as with manto type copper and small porphyry copper deposits to create a distinctive metallogenic signature

exploration targeting for orogenic gold deposits in the granites tanami orogen mineral system analysis targeting model and prospectivity analysis abstract a major challenge for mineral exploration geologists is the development of a transparent and reproducible approach to targeting exploration efforts particularly at the regional to camp scales in terranes under difficult cover where exploration and opportunity costs are high in this study a three pronged approach is used for identifying the most prospective ground for orogenic gold deposits in the paleoproterozoic granite tanami orogen gto in western australia a key input to the analyses is the recent development of a 4d model of the gto architectural evolution that provides new insights on the spatio temporal controls over orogenic gold occurrences in the area in particular on the role of pre mineralization pre 1795 ma d gtoe d gto1 d gto2 architecture in localization of gold deposits and the spatial distribution of rock types in 3d this information is used to build up a model of orogenic gold minerals system in the area which is then integrated into the three mutually independent but complementary mineral prospectivity maps namely a concept driven manual and fuzzy analysis and a data driven automated analysis the manual analysis involved 1 generation of a process based gold mineral systems template to aid target selection 2 manual delineation of targets 3 manual estimation of the probability of occurrence of each critical mineralization process based on the available information and 4 combining the above probabilities to derive the relative probability of occurrence of orogenic gold deposits in each of the targets the knowledge based geological information system gis analysis attempts to replicate the expert knowledge used in the manual approach but queried in a more systematic format to eliminate human heuristic bias this involves representing the critical mineralization processes in the form of spatial predictor maps and systematically querying them through the use of a fuzzy logic model to integrate the predictor maps and to derive the western gto orogenic gold prospectivity map the data driven empirical gis analysis uses no expert knowledge instead it employs statistical measures to evaluate the spatial associations between known deposits and predictor maps to establish weights for each predictor layer then combines these layers into a predictive map using a weights of evidence wofe approach application of a mineral systems approach in the manual analysis and the fuzzy analysis is critical potential high value targets identified by these approaches in the western gto lie largely under cover whereas traditional manual targeting is biased to areas of outcrop or sub crop amenable to direct detection technology such as exploration geochemistry and therefore towards areas that are data rich the results show the power of combining the three approaches to prioritize areas for exploration while the manual analysis identifies and employs human intuition and can see through incomplete datasets it is difficult to filter out human bias and to systematically apply to a large region the fuzzy method is more systematic and highlights areas that the manual analysis has undervalued but lacks the intuitive power of the human mind that refines the target by seeing through incomplete datasets the empirical woe method highlights correlations with favorable host stratigraphy and highlights the control of an early set of structures potentially undervalued in the knowledge driven approaches yet is biased due to the incomplete nature of exploration datasets and lack of abundant gold deposits due to the extensive cover the results indicate that the most prospective areas for orogenic gold in western gto are located in the central part of the study area largely in areas blind to previous exploration efforts according to our study the procedure to follow should be to undertake the analyses in the following order manual prospectivity analysis followed by the conceptual fuzzy approach followed by the empirical gis based method undertaking the manual analysis first is important to prevent explorationists from being biased by the automated gis based outputs it is however emphasized that all of the prospectivity outputs from these three methods are possible and they should not be treated as treasure maps but instead as decision support aids therefore a final manual prospectivity analysis redefined by the mutual consideration of output from all of the methods is required the strategy employed in this study constitutes a new template for best practice in terrane to camp scale exploration targeting that can be applied to different terranes and deposit types particularly in terranes under cover and provides a step forward in managing uncertainty in the exploration targeting process

stochastic atmospheric forcing as a cause of greenland climate transitions abstractan unforced simulation of the community climate system model version 4 ccsm4 is found to have greenland warming and cooling events that resemble dansgaard oeschger cycles in pattern and magnitude with the caveat that only three transitions were available to be analyzed it is found that the transitions are triggered by stochastic atmospheric forcing the atmospheric anomalies change the strength of the subpolar gyre leading to a change in labrador sea sea ice concentration and meridional heat transport the changed climate state is maintained over centuries through the feedback between sea ice and sea level pressure in the north atlantic indications that the initial atmospheric pressure anomalies are preceded by precipitation anomalies in the western pacific warm pool are discussed the full evolution of the anomalous climate state depends crucially on the climatic background state

timing of iron oxide cu au u hydrothermal activity and nd isotope constraints on metal sources in the gawler craton south australia the eastern gawler craton hosts australia s premier uranium bearing iron oxide copper gold iocg belt the 500 km long olympic cu au u province in addition to the olympic dam cu u au and prominent hill cu au deposits numerous barren and weakly mineralized iocg prospects are present in the province new geochronological data for hydrothermal minerals combined with constraints from host rock ages demonstrate that alteration and associated iocg mineralization formed between 1570 and 1600 ma in three districts of the province this iocg hydrothermal activity temporally overlaps with magmatism of the hiltaba suite and gawler range volcanics titanites in paragenetically early magnetite bearing alteration in the olympic dam and prominent hill districts yield u pb ion probe ages of 1576 5 and 1567 10 ma respectively molybdenite in veins crosscutting magnetite biotite and albitic alteration in the moonta wallaroo district have re os ages of 1574 6 and 1599 6 ma respectively these represent minimum ages of the iocg alteration assemblages in this district a muscovite 40ar 39ar age of 1575 11 ma provides a minimum age of paragenetically later hematitic alteration in the olympic dam district neodymium isotope compositions were determined for 44 whole rock samples from barren and weakly mineralized cu au prospects and host rocks in the olympic dam and prominent hill districts the new geochronological framework enables comparison of the nd isotope data across two iocg districts at the time of formation of the olympic dam deposit ca 1590 ma magnetite rich weakly cu mineralized alteration from five prospects yields a relatively narrow range end 1590 values of 5 8 to 4 1 both hematite and magnetite rich alteration yield generally similar end 1590 values that match values from fresh and weakly altered paleoproterozoic metasedimentary and metagranitic rocks 6 6 to 3 5 as well as from most felsic hiltaba suite intrusions and gawler range volcanics in the eastern gawler craton ca 6 to 4 these data are consistent with crustal sources for ree and by implication for associated copper in the barren and weakly mineralized prospects mineralization and alteration in these minor iocg systems can be geochemically discriminated from the giant olympic dam deposit where greater inputs of mantle derived ree and other ore components are evident 2007 society of economic geologists inc

alteration facies linkages among iron oxide copper gold iron oxide apatite and affiliated deposits in the great bear magmatic zone northwest territories canada high temperature metasomatism driven by ascent of voluminous saline fluid columns in the upper crust plays a major role in the genesis of iron oxide alkali alteration ore systems but fundamental questions remain on genetic linkages among iron oxide copper gold iocg iron oxide apatite ioa albitite hosted uranium and skarn deposits that they produce excellent surface exposures of such systems in the great bear magmatic zone of northernwestern canada record the depth to paleosurface prograde evolution of iron oxide alkali alteration facies and mineralization across the belt albitite corridors that are tens of kilometers in length record the earliest reactions between highly saline fluids and host rocks along fault zones and subvolcanic intrusions pervasive albitization partitioned metals from the host rocks into the ascending fluid column leaving behind structurally weakened corridors of porous albitite these corridors were cut replaced and overprinted by amphibole and magnetite bearing calcic iron alteration assemblages in extreme cases the discharge of calcium iron and specialized metals formed iron oxide apatite deposits vanadium rare earth elements while recharging the outgoing fluids in sodium potassium and base and precious metals as temperatures declined and fluid chemistry evolved through fluid rock reactions the formation of potassic iron alteration assemblages breccias and sulfides resulted in magnetite and hematite group iocg mineralization within carbonate units skarns formed prior to are replaced by and evolved to calcic iron alteration facies skarns can locally host base metal mineralization tectonically uplifted albitite breccias replaced by potassic iron alteration assemblages became a preferential host for uranium mineralization the results of this study also illustrate that permutations and cyclical build up of alteration products can arise from a combination of faulting differential uplift and renewed magmatism framed within an alteration facies deposit model alteration zones and mineral occurrences play a pivotal role in predicting the mineral potential of iron oxide and alkali altered systems at district to deposit scales

electrical conductors in archean mantle result of plume interaction 1 from long period magnetotelluric data across the gawler craton we obtain a three dimensional resistivity image of the lithosphere and provide constraints on tectonothermal events dating back to the proterozoic contrary to common observations of archean cratons displaying high electrical resistivity in the mantle lithosphere the magnetotelluric data show low resistivity of around 10 m at 80km depth underneath the 1595ma gawler range volcanics a silicic large igneous province the resistivity distribution appears to be a signature of plume modified orogenesis with low degree partial melting at the base of the lithosphere in a back arc setting the enhanced conductivity is explained through higher hydrogen and iron content in the crystal lattice and also along the grain boundaries of the mantle constituting minerals older arc related magmatism to the southwest across 1620 1610ma st peter suite does not display enhanced conductivity and suggests a depleted mantle lithosphere the data show that yellowstone type mantle plume analogues are preserved through time and still display an elevated electrical signature in the lithosphere today

a new constraint on the size of heinrich events from an iceberg sediment model abstract heinrich layers anomalously thick layers of ice borne sediment in the north atlantic ocean have long been associated with abrupt climate changes in glacial times however there is still no consensus on either the exact amount of ice needed to transport this sediment or how such a large volume of ice could be produced using an iceberg model that includes sediment we simulate the delivery of sediment to the north atlantic during such an event our model assumes that sediment is uniformly distributed within the ice with a concentration of 4 unlike sediment models which assume that the sediment lies in a single layer this model can carry sediment all the way from the western to the eastern north atlantic we use a variety of different estimates for the total volume of ice released to model the sediment layer thickness and we show that to best fit the observations 60 10 4 km 3 with a plausible range of 30 120 10 4 km 3 of ice needs to be released this is equivalent to a 0 04 sv 10 6 m 3 s 1 with a plausible range of 0 02 0 08 sv release of freshwater over the 500 yr of a typical heinrich event this is a smaller flux of water than is required to show a significant impact on the global climate in most current state of the art gcms

uranium in iron oxide copper gold iocg systems the olympic dam iron oxide copper gold iocg deposit is currently the world s largest producer of uranium other iocg deposits generally have anomalous though uneconomic uranium grades the fluids that generate iocg deposits are thought to be saline and highly oxidized and would be capable of leaching and transporting significant uranium the reasons for uranium enrichment in certain iocg deposits remain speculative but could include the composition of mineralization related magmas of the wall rocks altered by hydrothermal fluids or of the fluids mixing at the site of mineralization there is sparse data available on uranium abundance in iocg ores there is even less reliable data on the uranium content of unaltered wall rocks for the deposits however the data that is available suggest that the uranium grade of iocg deposits may be primarily related to the uranium content of their unaltered host rocks many iocg deposits appear to have approximately 10 to 40 times enrichment in the ore compared to unaltered host rocks this suggests that exploration for uranium rich iocg deposits should focus on areas with anomalously high uranium contents in host rock sequences

coupling of trade winds with ocean circulation damps itcz shifts abstractthe position of the intertropical convergence zone itcz is sensitive to the atmosphere s hemispheric energy balance lying in the hemisphere most strongly heated by radiative and turbulent surface energy fluxes this study examines how the ocean circulation through its cross equatorial energy transport and associated surface energy fluxes affects the itcz s response to an imposed interhemispheric heating contrast in a coupled atmosphere ocean general circulation model shifts of the itcz are strongly damped owing to a robust coupling between the atmosphere s hadley cells and the ocean s subtropical cells by the trade winds and their associated surface stresses an anomalous oceanic wind driven cross equatorial cell transports energy across the equator strongly offsetting the imposed heating contrast the circulation of this cell can be described by the combination of trade wind anomalies and the meridional gradient of sea surface temperature which sets the temperature contrast between its up

introduction to the special issue mineral prospectivity analysis and quantitative resource estimation abstract this introduction provides an overview of the history present status and future perspective of research in the fields of mineral prospectivity analysis and quantitative resource estimation it also summarizes the papers included in the special issue

moho geometry along a north south passive seismic transect through central australia abstract receiver functions from a temporary deployment of 25 broadband stations along a north south transect through central australia are used to retrieve crustal and uppermost mantle structural constraints from a combination of different methods using h k stacking as well as receiver function inversion overall thick crust with significant thickness variation along the profile 40 to 55 km is found bulk crustal v p v s values are largely in the felsic to intermediate range with the southernmost stations on the gawler craton exhibiting higher values in excess of 1 8 a common conversion point ccp stacking profile shows three major discontinuities of the crust mantle boundary 1 a two sided moho downwarp beneath the musgrave province which has previously been associated with the neoproterozoic to early cambrian petermann orogeny 2 a moho offset along the redbank shear zone further north attributed to the middle to late paleozoic alice springs orogeny and 3 another moho offset further north located at the boundary between the davenport and warramunga provinces which has not been imaged before in all cases the difference in crustal thickness between the two sides of the offset is 8 10 km unlike the two southern moho offsets the northernmost one does not coincide with a prominent gravity anomaly its location and the absence of known reactivation events in the region make it likely that it belongs to a proterozoic suture zone that marks a previously unknown block boundary within the north australian craton

timing of multiple hydrothermal events in the iron oxide copper gold deposits of the southern copper belt carajas province brazil the southern copper belt carajas province brazil hosts several iron oxide copper gold iocg deposits including sossego cristalino alvo 118 bacuri bacaba castanha and visconde mapping and u pb sensitive high resolution ion microprobe shrimp iie zircon geochronology allowed the characterization of the host rocks situated within regional wnw ese shear zones they encompass mesoarchean 3 08 2 85 ga ttg orthogneiss granites and remains of greenstone belts neoarchean ca 2 74 ga granite shallow emplaced porphyries and granophyric granite coeval with gabbro and paleoproterozoic 1 88 ga porphyry dykes extensive hydrothermal zones include albite scapolite biotite scapolite tourmaline magnetite alteration and proximal potassium feldspar chlorite epidote and chalcopyrite formation u pb laser ablation multicollector inductively coupled mass spectrometry la mc icp ms analysis of ore related monazite and re os ntims analysis of molybdenite suggest multiple neoarchean 2 76 and 2 72 2 68 ga and paleoproterozoic 2 06 ga hydrothermal events at the bacaba and bacuri deposits these results combined with available geochronological data from the literature indicate recurrence of hydrothermal systems in the southern copper belt including 1 90 1 88 ga ore formation in the sossego curral ore bodies and the alvo 118 deposit although early hydrothermal evolution at 2 76 ga points to fluid migration coeval with the carajas basin formation the main episode of iocg genesis 2 72 2 68 ga is related to basin inversion coupled with neoarchean ca 2 7 ga felsic magmatism the data suggest that the iocg deposits in the southern copper belt and those in the northern copper belt 2 57 ga salobo and igarape bahia alemao deposits do not share a common metallogenic evolution therefore the association of all iocg deposits of the carajas province with a single extensive hydrothermal system is precluded

oceanic link between abrupt changes in the north atlantic ocean and the african monsoon abrupt changes in the african monsoon which have been recorded throughout the late pleistocene and early holocene epochs tend to coincide with changes in north atlantic thermohaline circulation a numerical simulation shows that the interaction between thermohaline circulation in the north atlantic ocean and wind driven currents in the topical atlantic ocean contributes to the rapidity of african monsoon transitions during abrupt climate change events

mapping iron oxide cu au iocg mineral potential in australia using a knowledge driven mineral systems based approach abstract iron oxide copper gold iocg deposits are consequences of lithospheric to deposit scale earth processes and form where there was a coincidence of ore forming processes in space and time building on previous conceptualisations we view a mineral system as an ore forming geological system in which four components are required to have operated efficiently and coincidentally namely 1 available sources of ore metals i e copper gold uranium rare earth elements and hydrothermal fluids 2 energy sources to drive fluids in the ore forming system 3 active crustal and mantle lithospheric architecture representing hydrothermal fluid and or magma flow pathways and 4 physico chemical gradients along which ore metals were deposited to form ore bodies this holistic multi scale mineral systems framework has been used to develop a practical knowledge based yet data rich prospectivity mapping method applicable at regional to continental scales for hydrothermal and orthomagmatic ore forming systems we demonstrate how the mineral system components can be translated into mappable criteria and show how maps of mineral potential are generated by integrating diverse and rich input data sets the method enables prediction of mineral potential not only in brownfields areas but also in greenfields and covered terranes with no previously known mineralisation here we report the application of this methodology in regional scale mapping of the potential for iocg deposits in australia using examples from five studies over the last decade in northern queensland eastern south australia and southern and central eastern northern territory uncertainties in the results arising from assignment of weightings to input data layers were investigated by the application of monte carlo type probabilistic simulations the results of 500 iterations using randomly assigned weightings overall support the deterministic results but also show that modelled prospectivity is controlled mainly by variations in intrinsic values of the input geoscientific data sets e g highs and lows of gravity values rather than by the weightings the results of the knowledge driven data rich analyses of iocg potential have been validated against known iocg deposits not used directly in the analysis we find in all five studies queensland south australia and northern territory a good spatial correspondence with few exceptions statistical analysis of prospectivity mapping results from the tennant creek mt isa study area demonstrate that 15 of 16 iocg deposits occur in the highest modelled prospectivity areas within 4 2 of the study area representing an area reduction of 95 8 moreover several new discoveries of cu au mineralisation have been made within areas previously highlighted as highly prospective this success and validation support the utility of geoscience australia s approach as a decision support tool to assist exploration companies and governments in craton to regional scale area selection for discovery of iocg and other mineral systems

fluid evolution and origins of iron oxide cu au prospects in the olympic dam district gawler craton south australia geologic observations suggest two stages of hydrothermal activity at a number of presently subeconomic iron oxide copper gold systems in the olympic dam district eastern gawler craton they contain high and moderate to low temperature fe oxide rich hydrothermal alteration the mineral assemblages include magnetite calc silicate alkali feldspar fe cu sulfides and hematite sericite chlorite carbonate fe cu sulfides u ree minerals in all documented prospects the minerals of the hematitic assemblages replace the minerals of the magnetite rich assemblages the bulk of the subeconomic cu au mineralization is associated with the hematitic alteration assemblages microanalysis by proton ion probe pixe of hypersaline fluid inclusions in magnetite rich assemblages however demonstrates that significant amounts of copper 500 ppm were transported by the early stage high temperature 400 c fluids responsible for the magnetite rich alteration these brine inclusions contain multiple solid phases liquid vapor multiple solids including chalcopyrite in some cases in comparison inclusions of the hematitic stage are relatively simple liquid vapor types with homogenization temperatures of 200 to 300 c and containing 1 to 8 wt percent nacl equiv the br cl ratios of the magnetite forming fluids measured by pixe lie beyond the range of typical magmatic and or mantle values allowing for the possibility that the fluids originated as brines from a sedimentary basin or the crystalline basement sulfur isotope compositions of chalcopyrite and pyrite demonstrate that sulfur in both alteration assemblages was derived either from cooling magmas and or crystalline igneous rocks carried by relatively oxidized fluids so42 h2s 34ssulfides from 5 to 2 or from crustal sedimentary rocks 34ssulfides from 5 to 10 oxygen and hydrogen isotope compositions of waters calculated for minerals of the magnetite rich assemblage have 18o values of 7 7 to 12 8 per mil and d values of 15 to 21 per mil the only available 18o and dfluid values for the hematitic assemblage are 4 7 and 9 per mil respectively the isotopic compositions of both fluids coupled with the available literature data can be explained in terms of fluid reequilibration with felsic gawler range volcanics or other felsic igneous rocks in the region and with metasedimentary rocks of the wallaroo group at low water to rock ratios prior to their arrival at the mineralization sites the lack of significant copper mineralization associated with magnetite forming fluids that carried copper suggests that there was no effective mechanism of saturation of copper minerals or the quantity of these fluids was not sufficient to produce appreciable copper mineralization association of the copper gold mineralization with the hematitic alteration in the subeconomic prospects can be explained by a two stage model in which preexisting hydrothermal magnetite with minor associated copper gold mineralization was flushed by late stage oxidized brines that had extensively reacted with sedimentary or metamorphic rocks the reduction of these brines driven by conversion of magnetite to hematite resulted in precipitation of copper and gold the oxidized brines may have contributed additional copper and gold to the system in addition to upgrading preexisting subeconomic cu au mineralization when compared to published models for the olympic dam deposit the new data for fluids in subeconomic fe oxide cu au prospects of the olympic dam district indicate the diversity of origins of iron oxide copper gold systems even within the same geologic region

evaporitic source model for igneous related fe oxide ree cu au u mineralization we propose that many igneous related fe oxide rich ree cu au u bearing deposits form by hydrothermal processes involving evaporitic ligand sources either coeval salars or older evaporites these deposits are abundant in both phanerozoic and proterozoic extensional continental and continent margin settings they commonly form in global arid zones but they also occur where magmatism is superimposed upon older evaporites magmatic compositions exert only second order control mainly on alteration mineralogy and on element abundances hot s poor brines generated by interaction with evaporitic materials are consistent with geologic settings and help rationalize the distinctive element enrichments siderophile lithophile and hydrothermal alteration sodic locally alkaline found in these systems this model contrasts with immiscible oxide melt and magmatic hydrothermal origins commonly proposed for these deposits although all three mechanisms can occur 31 refs 3 figs 1 tab

sea ice switches and abrupt climate change we propose that past abrupt climate changes were probably a result of rapid and extensive variations in sea ice cover we explain why this seems a perhaps more likely explanation than a purely thermohaline circulation mechanism we emphasize that because of the significant influence of sea ice on the climate system it seems that high priority should be given to developing ways for reconstructing high resolution in space and time sea ice extent for past climate change events if proxy data can confirm that sea ice was indeed the major player in past abrupt climate change events it seems less likely that such dramatic abrupt changes will occur due to global warming when extensive sea ice cover will not be present

controls on the tropical response to abrupt climate changes abrupt climate change events during glacial times have distinct tropical imprints despite their cause being at high latitudes the mechanisms by which high latitudes affect low latitudes are currently unclear we present climate model simulations of a set of different abrupt events and find changes in tropical rainfall can not be comprehensively explained by either changes in sea ice extent or ocean circulation changes in tropical meridional temperature gradients are the clearest way to explain tropical rainfall changes across all events we find some tropical regions are unlikely to record heinrich events because the rainfall is moved far enough away from them during stadial periods that they are insensitive to further change greenland temperature responds linearly to atlantic sea ice extent suggesting that the absence of change in greenland temperature during heinrich events implies no sea ice expansion despite major changes in the climate system elsewhere

timing and nature of fluid flow and alteration during mesoproterozoic shear zone formation olary domain south australia the development of shear zones at mid crustal levels in the proterozoic willyama supergroup was synchronous with widespread fluid flow resulting in albitization and calcsilicate alteration monazite dating of shear zone fabrics reveal that they formed at 1582 22 ma at the end of the olarian d3 deformational event and immediately prior to the emplacement of regional s type granites two stages of fluid flow are identified in the area first an albitizing event which involved the addition of na and loss of si k and fe and a second phase of calcsilicate alteration with additions of ca fe mg and si and removal of na fluid fluxes calculated for albitization and calcsilicate alteration were 5 56 109 to 1 02 1010 mol m 2 and 2 57 108 5 20 109 mol m 2 respectively these fluxes are consistent with estimates for fluid flow through mid crustal shear zones in other terranes the fluids associated with shearing and alteration are calculated to have 18o and d values ranging between 8 and 11 and 33 and 42 respectively and nd values between 2 24 and 8 11 our results indicate that fluids were derived from metamorphic dehydration of the willyama supergroup metasediments fluid generation occurred during prograde metamorphism of deeper crustal rocks at or near peak pressure conditions shear zones acted as conduits for major crustal fluid flow to shallow levels where peak metamorphic conditions had been attained earlier leading to the apparent retrograde fluid flow event thus the peak metamorphism conditions at upper and lower crustal levels were achieved at differing times prior to regional granite formation during the same orogenic cycle leading to the formation of retrograde mineral assemblages during shearing

a metasomatic origin for the iron oxide au cu starra orebodies eastern fold belt mount isa inlier the starra ironstone hosted au cu deposit in northwest queensland australia displays evidence of a polyphase history of late post metamorphic structurally controlled metasomatism the mineralisation is hosted within several massive ironstone units which occur at a lithological contact of metamorphosed sandstone and siltstone sequences and foliated chlorite biotite magnetite schists the ironstones strike north south and occur as discontinuous lenses that cross cut the host rocks in places magnetite ironstone textures are generally massive in appearance but relict deformed breccia and foliation textures are locally preserved sulphide ore textures are more brittle and consist of fine pervasive brecciation of the ironstones and host rocks petrological and textural observations support a hydrothermal origin for both ironstone and mineralisation three dominant post peak metamorphic paragenetic stages of alteration and mineralisation are recognised 1 early widespread na ca metasomatism consisting of albite quartz actinolite scapolite 2 localised k fe metasomatism consisting of biotite magnetite hematite quartz pyrite and 3 the mineralising stage consisting of anhydrite calcite hematisation of magnetite pyrite chalcopyrite gold and extreme chloritisation of biotite the na dominant alteration occurs throughout the eastern fold belt and for at least 50 km to the east and 150 km to the north of starra the ironstones were products of localised fe metasomatism associated with shearing and brecciation of previously na metasomatised host rocks gold and copper mineralisation resulted from the interaction of magnetite a late oxidising fluid and an increase in ph this produced variable hematisation of magnetite and caused the solubility of chloride complexed gold to decrease dramatically high gold copper ratios can be explained in terms of the solubility differences of gold and copper in the thermochemical conditions that existed at starra

metal source and tectonic setting of iron oxide copper gold iocg deposits evidence from an in situ nd isotope study of titanite from norrbotten sweden titanite occurs as a widespread accessory phase in mineralized zones and alteration associated with iron oxide copper gold iocg and iron oxide apatite ioa deposits of norrbotten county sweden and is a major host of the ree in these deposits in situ analyses of sm nd isotope ratios in titanites previously analysed for u pb geochronology and trace element composition confirms previous interpretations of grain scale isotopic heterogeneity initial nd isotope ratios expressed relative to chur range from 3 to 8 in ioa deposits from 1 to 9 in iocg deposits and from 2 to 4 in the most cu rich deformed iocg deposits of the nautanen deformation zone within individual ioa deposits at valkommen malmberget from 1 4 to 5 7 in grain cores and 7 2 to 8 2 in grain rims rim at gruvberget and from 3 0 to 6 0 in grain cores and from 5 8 to 7 1 in grain rims at luossavaara in iocg deposits at rakkurijarvi iocg dpeosits at nautanen from 1 3 to 2 3 these values are consistent with the derivation of the ree and potentially economically enriched metals from the local volcanic sequence either via granitic melts or directly by leaching by metasomatic fluids the most cu rich deposits reflect the involvement of more basic protoliths the age distribution of these deposits suggest ioa deposit formation during the collisional phase of the svecofennian orogeny 1 9 1 8 ga and iocg mineralization during this phase and during post orogenic collapse 1 8 1 7 ga whilst model ages indicate the ultimate enrichment of the continental crust in these metals during pre collisional extensional and subduction related basic magmatism these processes underscore the importance of continental cycles both in producing the preserved geological record of orogenic ore deposition and in the generation of fertile continental crust from which metals can be mobilised by subsequent events nd varies relative to chur from 3 1 to 4 0 nd varies from 6 1 to 7 1 and in deformed iocg dpeosits at nautanen from 1 3 to 2 3 these values are consistent with the derivation of the ree and potentially economically enriched metals from the local volcanic sequence either via granitic melts or directly by leaching by metasomatic fluids the most cu rich deposits reflect the involvement of more basic protoliths the age distribution of these deposits suggest ioa deposit formation during the collisional phase of the svecofennian orogeny 1 9 1 8 ga and iocg mineralization during this phase and during post orogenic collapse 1 8 1 7 ga whilst model ages indicate the ultimate enrichment of the continental crust in these metals during pre collisional extensional and subduction related basic magmatism these processes underscore the importance of continental cycles both in producing the preserved geological record of orogenic ore deposition and in the generation of fertile continental crust from which metals can be mobilised by subsequent events

u pb geochronological constraints on the genesis of the olympic dam cu u au ag deposit south australia the olympic dam cu u au ag deposit is hosted by the olympic dam breccia complex a high level hematite rich hydrothermal breccia system which occurs entirely within and clearly postdates the roxby downs granite the u pb zircon age of the roxby downs granite is well constrained at 1588 or 4 ma field evidence indicates that brecciation hydrothermal alteration and cu u au ag ree mineralization in the olympic dam breccia complex were penecontemporaneous but this is inconsistent with differing ages from previous u pb and rb sr isotopic data on pitchblende and sericite new shrimp u pb zircon data for three olympic dam breccia complex igneous rock units confirm that cu u au ag ree mineralization was contemporaneous with brecciation and alteration and directly followed cooling of the roxby downs granite by as little as several 8 million years two of the dated olympic dam breccia complex rock units are interpreted as autobrecciated felsic dikes one crosscuts laminated hematite quartz sandstones and the other crosscuts cu u mineralized hematite rich breccias zircons from these dikes yielded ages of 1592 or 8 and 1584 or 20 ma respectively the third unit dated is a disrupted ash fall tuff horizon from within a diatreme which crosscuts hematite quartz breccias near the center of the deposit the northern extremities of this diatreme also crosscut hematitic breccias containing a substantial cu u ore zone zircons from this tuff horizon have an age of 1597 or 8 ma the tuff and associated subaerial or subaqueous volcaniclastics were unconsolidated or only weakly lithified at the time of their incorporation into the diatreme so the age of the tuff also reflects the age of diatreme activity these new isotopic data indicate that the olympic dam breccia complex has an age of approximately 1590 ma and therefore imply that brecciation closely followed emplacement and cooling of the roxby downs granite because these breccias contain sulfide fragments and polyminerallic ore fragments exhibit penecontemporaneous sulfide oxide textural relationships and show a close association between cu or u or ag or ree mineralization and fe rich breccias we argue that the metals of economic interest were introduced

postsubduction porphyry cu au and epithermal au deposits products of remelting of subduction modified lithosphere porphyry cu mo au and some epithermal au deposits are formed from hydrothermal fluids exsolved from cooling water rich calc alkaline magmas emplaced in volcanoplutonic arcs above subduction zones these magmas originate by partial melting of the metasomatized asthenospheric mantle wedge however there is increasing evidence for the existence of a suite of porphyry cu au and epithermal au deposits related to magmas generated after subduction beneath the arc has ceased associated magmas tend to be mildly alkaline relatively sulfur poor and emplaced as isolated complexes rather than in voluminous volcanoplutonic arcs they are likely formed by remelting of previously subduction modified arc lithosphere triggered by postsubduction lithospheric thickening lithospheric extension or mantle lithosphere delamination metasomatized mantle lithosphere or hydrous lower crustal cumulates residual from first stage arc magmatism contain small amounts of chalcophile and siderophile element rich sulfides and constitute a fertile source for hydrous au rich but relatively sulfur poor magmas during later remelting the recognition that porphyry cu au and related epithermal au systems can also form in postsubduction and collisional tectonic settings expands the range of geological environments and geographical terranes that are prospective for such deposits

southern ocean forcing of the north atlantic at multi centennial time scales in the kiel climate model internal multi centennial variability of open ocean deep convection in the atlantic sector of the southern ocean impacts the strength of the atlantic meridional overturning circulation amoc in the kiel climate model the northward extent of antarctic bottom water aabw strongly depends on the state of weddell sea deep convection the retreat of aabw results in an enhanced meridional density gradient that drives an increase in the strength and vertical extent of the north atlantic deep water nadw cell this shows for instance as a peak in amoc strength at 30 n about a century after weddell sea deep convection has ceased the stronger southward flow of nadw is compensated by an expansion of the north atlantic subpolar gyre and an acceleration of the north atlantic current indicating greater deep water formation contractions of the north atlantic subpolar gyre enable warm water anomalies which evolved in response to deep convection events in the southern ocean to penetrate farther to the north eventually weakening the amoc and closing a quasi centennial cycle gyre contractions are accompanied by increases in sea level of up to 20 cm century in some areas of the north atlantic in the southern ocean itself the heat loss during the convective regime results in a sea surface height decrease on the order of 10 cm century with a maximum of 30 cm century in the weddell sea hence the impact of the southern ocean centennial variability socv on regional as well as north atlantic sea level is of the same order of magnitude as the rise of global average sea level during the 20th century which amounts to about 15 20 cm this suggests that internal variability on a centennial time scale cannot be neglected a priori in assessments of 20th and 21st century amoc and regional sea level change

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

magnetotelluric evidence for a deep crustal mineralizing system beneath the olympic dam iron oxide copper gold deposit southern australia the iron oxide copper gold olympic dam deposit situated along the margin of the proterozoic gawler craton south australia is the world s largest uranium deposit and sixth largest copper deposit it also contains significant reserves of gold silver and rare earth elements gaining a better understanding of the mechanisms for genesis of the economic liberalization is fundamental for defining exploration models in similar crustal settings to delineate crustal structures that may constrain mineral system fluid pathways coincident deep crustal seismic and magnetotelluric mt transects were obtained along a 220 km section that crosses olympic dam and the major crustal boundaries in this paper we present results from 58 long period 10 104 s mt sites with site spacing of 5 10 km a two dimensional inversion of mt data from 33 sites to a depth of 100 km shows four notable features 1 sedimentary cover sequences with low resistivity 1000 m archean crustal core from a more conductive crust and mantle to the north typically 500 m 3 to the north of olympic dam the upper middle crust to 20 km is quite resistive 1000 m but the lower crust is much more conductive 100 m and 4 beneath olympic dam we image a low resistivity region 100 m throughout the crust coincident with a seismically transparent region we argue that the cause of the low resistivity and low reflectivity region beneath olympic dam may be due to the upward movement of co2 bearing volatiles near the time of deposit formation that precipitated conductive graphite liberalization along grain boundaries simultaneously annihilating acoustic impedance boundaries the source of the volatiles may be from the mantle degassing or retrograde metamorphism of the lower crust associated with proterozoic crustal deformation