direct dating of sulfides by rbsr a critical test using the polaris mississippi valley type znpb deposit abstract the rb sr dating of sphalerites is a powerful method for directly determining the age of base metal deposits and testing models for large scale fluid flow however the uncertainty over the exact host phases for the trace amounts of rb and sr and the causes of variability in rb sr have caused concern over the reliability of the method here we show that the polaris mvt deposit with a geologically well constrained age of formation confirmed by paleomagnetic measurements and hosted in significantly older sedimentary rocks yields a consistent rb sr age of 366 15 ma providing the first unequivocal vindication of the reliability of the method

lead isotopic patterns of galena in the piedmont and blue ridge ore deposits southern appalachians massive sulfide deposits of the southern appalachians form two distinct groups of lead isotope ratios which correlate with their geologic settings piedmont massive sulfides are associated with volcanic rocks of predominantly cambrian age they have model lead ages which are too young an effect of u pb enrichment of source rocks lead isotope ratios of piedmont massive sulfide define a trend of decreasingly radiogenic values from the mineral district virginia to the stone hill deposit alabama which probably reflects decreasingly ensialic volcanism from northeast to southwest a regression through the data has a slope which corresponds to a secondary isochron age of about 3 7 b y the line is proposed to represent mixing between variable amounts of upper crustal lead decreasing to the southwest with lead from a source relatively depleted in u pb which has however experienced either continuous or episodic enrichment of uranium relative to lead the occurrence of a similar trend in galenas from kings mountain belt ores is further evidence for such a source massive sulfides of the blue ridge geologic province occur in upper precambrian metasedimentary sequences and are typically low in lead content lead isotope ratios of galenas from ducktown and the gossan lead are highly enriched in 206 pb compared to amounts expected for deposits of that age the anomalously radiogenic component is probably the result of lead derived from the predominantly clastic sediments of the host sequences the radiogenic component of the 206 pb coupled with the narrow range of 207 pb 204 pb at ducktown indicates that much older continental crustal rocks were not involved in the ore forming process galenas from a vein in the hamme tungsten district north carolina form a tight grouping which is similar to lead in k feldspars from postorogenic approximately 300 m y old granitic plutons the mineralized veins of the virginia gold pyrite belt have galenas with a wide spread of radiogenic lead isotope ratios and do not appear to be related to massive sulfide deposits of the central virginia piedmont

millennial scale northwest african droughts related to heinrich events and dansgaard oeschger cycles evidence in marine sediments from offshore senegal 1 we present a suite of new high resolution records 0 135 ka representing pulses of aeolian fluvial and biogenic sedimentation along the senegalese continental margin a multiproxy approach based on rock magnetic element and color data was applied on three cores enclosing the present day northern limit of the itcz a strong episodic aeolian contribution driven by stronger winds and dry conditions and characterized by high hematite and goethite input was revealed north of 13 n these millennial scale dust fluxes are synchronous with north atlantic heinrich stadials fluvial clay input driven by the west african monsoon predominates at 12 n and varies at dansgaard oeschger time scales while marine productivity is strongly enhanced during the african humid periods and marine isotope stage 5 from latitudinal signal variations we deduce that the last glacial itcz summer position was located between core positions at 12 26 and 13 40 n furthermore this work also shows that submillennial periods of aridity over northwest africa occurred more frequently and farther south than previously thought

sea surface water variability during the mid brunhes inferred from calcareous plankton in the western mediterranean odp site 975 abstract planktonic foraminifera and calcareous nannoplankton were analyzed in core ocean drilling program site 975 located in the western mediterranean in order to study their response to environmental changes across the mid brunhes interval and specifically through marine isotope stage mis 15 and 8 ca 650 230 ka multivariate analysis of assemblage composition revealed that the calcareous plankton dynamics were mainly driven by surface water temperatures both on glacial interglacial and stadial interstadial time scales throughout the studied interval foraminiferal and nannoplankton assemblages responded to environmental forcing in concert except during mis 15 when multiple environmental factors appear to have been superimposed on the otherwise dominating effect of temperature variability sea surface temperature sst has been estimated from planktonic foraminiferal assemblages using the artificial neural networks method pointing out relevant seasonal variations through the record our reconstructions reveal that calcareous plankton assemblages also responded to other environmental factors than temperature including modification in surface water stratification nutrient availability and detrital input specifically a more stable stratified water column seems to have accompanied the interval through mis 15 13 on the other hand across the mid brunhes interval from mis 12 onwards the enhanced glacial strength affected both planktonic foraminifera and calcareous nannofossils planktonic foraminifera indicate that mixed and productive surface waters developed during glacials and stadials accompanied by episodes of increased detrital input as suggested by calcareous nannoplankton assemblages enhanced food availability was likely driven by wind induced upwelling and or by continental coastal input during dry conditions persisting in the mediterranean region and over north africa finally spectral and wavelet analyses of calcareous plankton time series allowed to identify the pattern of periodic response of the plankton at milankovitch cycles and in some cases at millennial variability the dominant 100 kyr periodicity recorded in surface water temperature proxies clearly reflects a major response of the planktonic community to the global glacial interglacial climate pattern high frequency variation 5 8 11 13 ky of surface water temperature proxies and of selected taxa abundance highlights the occurrence of millennial scale instability superimposed on the paleoenvironmental modifications occurring through the mid brunhes interval climate transition this framework accounts for the occurrence of different surface water dynamics across the mid brunhes interval and is in favor of the hypothesis that the millennial scale surface water temperature variations are modulated by the harmonics of the precession forcing

duration of the early cambrian u pb ages of volcanic ashes from avalon and gondwana volcanic zircons from three ashes give a u pb date of 511 1 ma on trilobite bearing upper lower cambrian upper branchian series strata of southern new brunswick that correlate into the siberian middle botomian toyonian stage interval this very young age on the late but not latest early cambrian of avalon is consistent both with a 519 1 ma age on the older caerfai bay shales of south wales that are tentatively correlated into strata with the oldest avalonian trilobites lower branchian and with a 517 1 5 ma age on the antatlasia gutta pluviae zone trilobites of morocco determination of a 522 2 ma zircon age on the moroccan subtrilobitic lower cambrian lie de vin formation is consistent with an earlier reported 521 7 ma age from the lie de vin but suggests that a 526 4 ma age on australian trilobite bearing lower cambrian rocks may be too old a 33 ma duration of the avalonian early cambrian and an 8 ma length of the avalonian trilobite bearing lower cambrian support proposals that

basement controls on sediment hosted zn pb deposits a pb isotope study of carboniferous mineralization in central ireland lead isotope ratios of galenas from carbonate hosted zn pb or ba or cd or ag deposits in central ireland are homogeneous within individual deposits but vary between deposits the variation correlates directly with geographic position defining isoplumbs and not with style of mineralization age of host rock or structural or physico chemical factors the least radiogenic pb occurs in the northwest and the most radiogenic in the southeast this pattern elegantly reflects irish pre caledonian basement geology lewisian gneisses in the northwest and late proterozoic upper crustal rocks in the southeast that the northwestern end member of the irish pb mixing trend is ultimately lewisian is demonstrated by the concordance of the irish pb isotope trend with the trends defined in proterozoic to tertiary rocks and ores of scotland which contain pb of demonstrably lewisian derivation although geologic relations and pb isotope ratios unambiguously implicate basement in the ore forming process we are unable to discriminate between lewisian gneisses themselves and detritus derived from lewisian rocks in the caledonian metamorphic complex as the direct source of pb comparison of the irish deposits with mcarthur river and mississippi valley deposits leads us to conclude that style of mineralization syngenetic syndiagenetic epigenetic is not a fundamental aspect of sediment hosted zn pb deposits but is a reflection of local stress regimes and physico chemical conditions the fundamental link between the types of sediment hosted zn pb deposits may be the onset of a condition such as extension or compression that provides a mechanism for driving fluids in extensional regimes seismic pumping processes may channel fluids toward the surface or into fractures or favorable pore spaces resulting in a wide variety of styles of mineralization the lack of dilatency in sediments in compressional regimes however may inhibit surface exhalation and favors epigenetic styles of mineralization

surface and deep ocean circulation in the subpolar north atlantic during the mid pleistocene revolution 1 we investigated surface and deep ocean variability in the subpolar north atlantic from 1000 to 500 thousand years ago ka based on two ocean drilling program odp sites feni drift site 980 55 29 n 14 42 w and bjorn drift site 984 61 25 n 24 04 w benthic foraminiferal stable isotope data planktic foraminiferal faunas ice rafted debris data and faunally based sea surface temperature estimates help test the hypothesis that oceanographic changes in the north atlantic region were associated with the onset of the 100 kyr world during the mid pleistocene revolution based on percentage of neogloboquadrina pachyderma s records from both sites surface waters during interglacials and glacials were cooler in the mid pleistocene than during marine isotope stages mis 5 and 6 in particular interglaciations at bjorn drift site 984 were significantly cooler faunal evidence suggests that the interglacial arctic front shifted from a position between the two sites to a position northwest of bjorn drift site 984 after ca 610 ka as during the late pleistocene we find faunal evidence for lagging surface warmth at most of the glacial initiations during the mid pleistocene each initiation is associated with high benthic 13c values that are maintained into the succeeding glaciation which we term lagging nadw production these findings indicate that lagging warmth and lagging nadw production are robust features of the regional climate system that persist in the middle to late pleistocene

sea surface temperatures did not control the first occurrence of hudson strait heinrich events during mis 16 1 hudson strait hs heinrich events ice rafting events in the north atlantic originating from the laurentide ice sheet lis are among the most dramatic examples of millennial scale climate variability and have a large influence on global climate however it is debated as to whether the occurrence of hs heinrich events in the eastern north atlantic in the geological record depends on greater ice discharge or simply from the longer survival of icebergs in cold waters using sediments from integrated ocean drilling program iodp site u1313 in the north atlantic spanning the period between 960 and 320 ka we show that sea surface temperatures ssts did not control the first occurrence of hs heinrich like events in the sedimentary record using mineralogy and organic geochemistry to determine the characteristics of ice rafting debris ird we detect the first hs heinrich like event in our record around 643 ka marine isotope stage mis 16 which is similar as previously reported for site u1308 however the accompanying high resolution alkenone based sst record demonstrates that the first hs heinrich like event did not coincide with low ssts thus the hs heinrich like events do indicate enhanced ice discharge from the lis at the end of the mid pleistocene transition not simply the survivability of icebergs due to cold conditions in the north atlantic

carbonate hosted zinc lead deposits in the lower cambrian of hunan south china a radiogenic pb sr isotope study zinc lead deposits hosted by lower cambrian carbonate rocks near huayuan in the hunan guizhou orogenic belt southern china have been studied by means of pb and sr isotopes the deposits are characterized by two mineralization stages 1 a main economic stage comprising cockade style sphalerite galena pyrite marcasite fluorite barite and calcite and 2 a subsequent noneconomic stage with nodular rosette sphalerite saddle dolomite and bitumen both ore stages are postdated by a generation of late calcite main stage sulfides 206pb 204pb 18 162 18 225 display a steep linear trend on conventional pb pb diagrams which indicates binary mixing of lead components bearing the imprint of ancient 207pb dominated crustal rocks and reservoirs with elevated th u ratios possibly located in the lower crust nodular rosette sphalerites fall outside this line but reflect a second mixing trend between mineralizing fluids characterized by 206pb 204pb 18 3 and lead isotopically similar to specific main stage cockade sphalerites suggesting either remobilization of pb from main stage ores or contemporaneous mixing of three distinct lead components in the course of an evolving hydrothermal event the 87sr 86sr ratios of diagenetic and hydrothermal carbonate cements and barites range from 0 70905 to 0 71006 and increase systematically with the paragenetic sequence indicating progressive mixing of marine sr derived from the lower cambrian carbonate host rocks with radiogenic sr supplied by external mineralizing fluids in order to identify possible local metal sources u pb and rb sr analyses were performed on six whole rock samples from the lower cambrian sequence and their time integrated pb and sr isotope evolution was compared to the isotopic signature of the mineralization whereas shales and black shales of the cambrian balang and niutitang formations underlying the ore bearing qingxudong carbonate unit appear to be possible external sources for the radiogenic sr found in hydrothermal carbonates the u pb data do not permit these shales to be considered as primary source rocks for the ore lead both the pb and the sr isotopes indicate mineralizing fluids that had interacted with various external metal sources some of them most probably being located in sedimentary or crystalline basement rocks this refutes prevailing genetic models favoring the hydrocarbon and metal rich lower cambrian niutitang black shales as the most likely source reservoir for the zn and pb in the deposits of the huayuan district the pb and sr isotope mixing trends observed for the ore and gangue preciptates reflect small scale heterogeneous fluid systems that were not capable of producing large deposits this may indicate that the huayuan district is not a favorable target for future exploration of economic ore deposits it also limits the prospects of successful radiometric dating of the mineralization since conventional geochronologic models require initial isotopic homogeneity

using radar sounding data to identify the distribution and sources of subglacial water application to dome c east antarctica basal radar reflectivity is the most important measurement for the detection of subglacial water however dielectric loss in the overlying ice column complicates the determination of basal reflectivity dielectric attenuation is a function of ice temperature and impurity concentration temperature distribution is a function of climate history basal heat flow and vertical strain rate all of which can be partially inferred from the structure of dated internal layers using 11 dated layers isotope records from dome c east antarctica and a model of the spatial variation of geothermal flux we calculate the vertical strain rate and accumulation rate history allowing identification of areas where the basal melt rate exceeds 1 5 mm a 1 the accumulation rate history and vertical strain rates are then used as inputs for a transient temperature model the model outputs for the present day temperature distribution are then combined with depth dependent ionic concentrations to model dielectric loss and infer basal reflectivity the resulting reflection coefficients are consistent 5 db across a variety of subglacial water bodies we also identify a high reflectivity 15 db in concordia trench and along suspected subglacial water flow routes in vincennes basin highland areas tend to have highly variable reflection coefficients near 30 db consistent with an ice bedrock interface this combined model also identifies three areas of enhanced basal melting along concordia ridge concordia subglacial lake and vincennes basin melt at concordia subglacial lake exceeds 5 mm a 1 the inferred basal melt at these locations is not possible without enhanced geothermal flux we demonstrate how radar sounding data can provide both input and verification for a self consistent model of vertical strain vertical temperature distribution and meltwater distribution

mixing line isochrons a new interpretation of galena lead isotope data from southeastern british columbia ainsworth bluebell slocan and moyie camps mixing of lead from two different sources both of which follow simple growth curve lead evolution the more radiogenic source is thought to represent evolution of lead in the upper crustal continentally derived sedimentary rocks which host these deposits the two stage bluebell growth curve provides an estimate of the uranium poor lead source which may be the lower crust the upper mantle or a mixture of both mixing line isochrons drawn between these two curves at ages corresponding to the best estimates for the mineralization ages at these three mining camps closely fit the lead isotope data this supports the age estimates for all three camps and in particular substantiates a lower cambrian age for the original mineralization in the ainsworth and bluebell deposits mixing is assumed to take place at the time of mineralization and may be attributed to magmatic activity in the moyie and slocan camps applicability of the model to a large part of the omineca belt may be used to date both epigenetic and syngenetic or penecontemporaneous deposits of unknown age modified journal abstract

sea level rise due to polar ice sheet mass loss during past warm periods background although thermal expansion of seawater and melting of mountain glaciers have dominated global mean sea level gmsl rise over the last century mass loss from the greenland and antarctic ice sheets is expected to exceed other contributions to gmsl rise under future warming to better constrain polarice sheetresponse to warmer temperatures we draw on evidence from in terglacial periods in the geologic record that ex perienced warmer polar temperatures and higher gmsls than present coastal records of sea level from these previous warm periods dem onstrate geographic variability because of the influence of several geophysical processes that operate across a range of magnitudes and time scales inferring gmsl and ice volume changes from these reconstructions is nontrivial and generally requires the use of geophysical models advances interdisciplinary studies of geo logic archives have ushered in a new era of deciphering magnitudes rates and sources of sea level rise advances in our understanding of polar ice sheet response to warmer climates have been made through an increase in the number and geographic distribution of sea level reconstructions better ice sheet constraints and the recognition that several geophysical processes cause spatially complex patterns in sea level in particular accounting for glacial isostatic processes helps to decipher spatial variability in coastal sea level records and has reconciled a number of site specific sea level reconstructions for warm periods that have oc curred within the past several hundred thou sand years this enables us to infer that during recent interglacial periods small increases in

strontium isotope trends during diagenesis in ore bearing carbonate basins strontium isotope studies 120 analyses were carried out on ore and gangue minerals from five ore districts in different carbonate basins most of the samples were separated from consecutive diagenetic generations even for diverse stratigraphic positions and mineralogies very consistent trends are recognized in all cases87sr 86sr ratios increase with advancing diagenetic stage however each district shows a different behaviour in the magnitude of increase over the first diagenetic generation which ideally is close to contemporaneous seawater the increase of the strontium ratios in the subsequent diagenetic generations is explained by equilibration during crystallization with fluids evolving towards more radiogenic compositions this is interpreted as a consequence of the reaction of the fluids with rb bearing phases mainly detrital clay minerals variation ranges of87sr 86sr ratios can constitute a sensitive tool for determining the stage of basin evolution in a similar way as vitrinite reflectance or illite crystallinity this method has the disadvantage that the increase of radiogenic strontium depends not only on the evolution stage i e temperature pressure and time but also on the amount of rb bearing minerals present in the basin on the other hand this method has the important advantage that within a given basin this last parameter can be modelled each evolution stage is recorded in the cements or crystallization generations by its strontium isotope signatures which tend towards increased radiogenic values with advancing diagenesis

variability of surface water characteristics and heinrich like events in the pleistocene midlatitude north atlantic ocean biomarker and xrd records from iodp site u1313 mis 16 9 1 a reconstruction of milankovitch to millennial scale variability of sea surface temperature sst and sea surface productivity in the pleistocene midlatitude north atlantic ocean marine isotope stage mis 16 9 and its relationship to ice sheet instability was carried out on sediments from integrated ocean drilling program iodp site u1313 this reconstruction is based on alkenone and n alkane concentrations u37k index total organic carbon toc and carbonate contents x ray diffraction data magnetic susceptibility and accumulation rates increased input of ice rafted debris occurred during mis 16 12 and 10 characterized by high concentrations of dolomite quartz and feldspars and elevated accumulation rates of terrigenous matter minimum input values of terrigenous matter on the other hand were determined for mis 13 and 11 peak values of dolomite coinciding with quartz plagioclase and kalifeldspar peaks and maxima in long chain n alkanes indicative for land plants are interpreted as heinrich like events related to sudden instability of the laurentide ice sheet during early and late deglacial phases of the glacials the coincidence of increased toc values with elevated absolute concentrations of alkenones suggests increased glacial productivity probably due to a more southern position of the polar front alkenone based sst reached absolute maxima of about 19 c during mis 11 3 and absolute minima of 10 c during mis 12 and 10 within mis 11 prominent cooling events mis 11 22 and 11 24 occurred the absolute sst minima recorded directly before and after the glacial maxima mis 10 2 and 12 2 are related to heinrich like event meltwater pulses as supported by the coincidence of sst minima and maxima in c37 4 alkenones and dolomite these sudden meltwater pulses especially during terminations iv and v probably caused a collapse of phytoplankton productivity as indicated by the distinct drop in alkenone concentrations ice sheet disintegration and subsequent surges and outbursts of icebergs and meltwater discharge may have been triggered by increased insolation in the northern high latitudes

changes in planktic and benthic foraminifer assemblages in the gulf of lions off south france response to climate and sea level change from mis 6 to mis 11 1 a multidisciplinary study involving micropaleontological and geochemical tools was carried out in borehole prgl1 promess 1 with the aim of reconstructing the impact of climate change and sea level variation between 133 ka and 406 ka in the upper slope of the gulf of lions we used factor analysis to obtain three main benthic assemblages related to eutrophic mesotrophic and oxygenated environments planktic foraminifers were grouped as warm water and cold turbulent species these results were compared with records of caco3 and major and trace elements al ca k sr as well as the c n ratio of organic matter power and cross spectral analysis showed a straightforward relationship between precession minima and thermal stratification of the water column as well as the occurrence of eutrophic bottom conditions during lowstand periods and mesotrophic environments at times of highstand these eutrophic mesotrophic oscillations usually driven by global eustatic change also involved regional variations in caco3 source to this environment during periods of precession maxima enhancement of northwesterly winds increased primary productivity by mixing enhancing the percentage of cold turbulent species in the water column and the proportion of oxygenated benthic species on the bottom during interglacial stages these events were recorded by lower biogenic carbonate at the expense of higher silicate related components most likely due to a higher supply from pyrenees rivers the record of oxygenated benthic species can be a good proxy to monitor past changes in winter intermediate water dynamics driven by northwesterly winds

surface ocean temperatures in the north east atlantic during the last 500 000 years evidence from foraminiferal census data changes in north atlantic sea surface temperature sst are regarded as a key element of the climate during the quaternary however there are relatively few long term records providing quantitative sst estimates from this region using planktic foraminiferal derived ssts together with changes on species level and iceberg rafted debris the last 500 ka were studied pronounced sst changes as determined from the last glacial interglacial cycle characterize most colder periods peak interglacial temperatures were found for marine isotope stages mis 1 5e and 11 the latter two being the warmest the warm substages within mis 7 and 9 are marked by enhanced dissimilarity coefficients indicating that ssts obtained for these times appear to be overestimated this is corroborated by differences within the species assemblage which show enhanced cold water components it is therefore concluded that detailed analysis down to species level is a crucial prerequisite to better reconstructions of sst

decadal resolution record of winter monsoon intensity over the last two millennia from planktic foraminiferal assemblages in the northeastern arabian sea the indian monsoon system is an important climate feature of the northern indian ocean small variations of the wind and precipitation patterns have fundamental influence on the societal agricultu

87 sr 86 sr ratio measurements on sulfides carbonates and fluid inclusions from pine point northwest territories canada an 87 sr 86 sr ratio increase accompanying the mineralizing process crystallization of fine grained early diagenetic dolomite and later coarse dolomite has occurred in sr isotope equilibrium with devonian sea water 87 sr 86 sr 0 7082 extraction of radiogenic sr from silicates in the metal source sediments by mineralizing brines modified journal abstract

cockade breccia product of mineralisation along dilational faults cockade breccias are fault fills in which individual clasts are completely surrounded by concentric layers of cement they occur particularly in low temperature near surface hydrothermal veins at least six mechanisms have been proposed for the formation of cockade breccia like textures but only two repeated rotation accretion and partial metasomatic replacement of clast minerals have been supported by detailed evidence a typical example of cockade breccia from the gower peninsula south wales shows clear evidence for the rotation accretion mechanism in particular overgrown breakage points in cement layers where cockades were previously touching each other and rotated geopetal infills of haematitic sediment based on the available evidence it is proposed that cockade textures result from low rates of cement growth compared to high rates of dilational fault slip seven criteria are given for the correct identification of cockade breccias

fluid inclusion and carbon oxygen and strontium isotope study of the polaris mississippi valley type zn pb deposit canadian arctic archipelago implications for ore genesis the polaris deposit is one of the largest mississippi valley type deposits in the world with 22 million tonnes of ore at 14 zn and 4 pb contained in a single compact orebody surrounded by dolomitized host rocks using detailed sampling of carbonates in the orebody and the dolostone halo this paper aims to characterize the temporal and spatial evolution of the mineralizing system and to understand the mechanisms that controlled the accumulation of this large compact zn pb deposit five types of dolomite have been distinguished including three replacement rd and two pore filling dolomites pd the paragenetic order is rd1 rd2 rd3 pd1 and pd2 pore filling calcite pc postdates all other minerals in most cases sulfides and dolomite did not co precipitate but sphalerite and galena largely overlap with rd3 and pd1 various dolomites are dissolved or replaced by sulfide precipitating fluids sulfides in turn can be overgrown by dolomites colloform texture in sphalerite is widespread fluid inclusions were studied in rd3 pd1 pd2 sphalerite and pc the overall ranges of homogenization temperatures t h and last ice melting temperatures t m ice for fluid inclusions in dolomites and sphalerite are from 67 to 141 c and from 46 7 to 27 0 c respectively consistent with warm basinal brines with high salinities and ca na ratios gas chromatographic analysis of these fluid inclusions indicates low concentrations of hydrocarbons 0 06 mol c o and sr isotopes were analyzed for all dolomites and pc as well as for the fine grained host limestone and early diagenetic calcite sc rc the isotopic values of rd2 rd3 pd1 and pd2 cluster tightly and form largely overlapping domains with respect to the host limestone they are depleted in 18o similar in 13c and slightly enriched in 87sr there are no regular spatial variations for fluid inclusion and isotope data indicating an overall geochemical homogeneity in the hydrothermal system however certain samples close to the fracture zones in the orebody with slightly elevated t h and 87sr 86sr values and depleted 18o values suggest that the fracture zone was the conduit for the hot brines based on the geological and geochemical characteristics of the deposit we propose that sulfide precipitation at polaris was caused by mixing of a reduced metal rich sulfur poor fluid with a reduced metal poor sulfur rich fluid at the site of mineralization the metal carrying fluid ascended along fractures from below the deposit and was hotter than the host rocks whereas the reduced sulfur carrying fluid was delivered to the site of mineralization laterally and was in thermal equilibrium with the host rocks this model can readily explain the dissolution of dolomite during sulfide precipitation and the abundance of colloform sphalerite as well as the low concentrations of hydrocarbons in fluid inclusions

a minimum thermodynamic model for the bipolar seesaw 1 the simplest possible model is proposed to explain a large fraction of the millennial climate variability measured in the isotopic composition of antarctic ice cores the model results from the classic bipolar seesaw by coupling it to a heat reservoir in this thermal bipolar seesaw the heat reservoir convolves northern time signals with a characteristic timescale applying the model to the data of grip and byrd we demonstrate that maximum correlation can be obtained using a timescale of about 1000 1500 years higher correlations are obtained by first filtering out the long term variability which is due to astronomical and greenhouse gas forcing and not part of the thermal bipolar seesaw the model resolves the apparent confusion whether northern and southern climate records are in or out of phase synchronous or time lagged

submarine hydrothermal contribution for the extreme element accumulation during the early cambrian south china throughout the geological history of the earth submarine hydrothermal activity has played an important role in seawater chemistry biological evolution and enrichment of metals in the earth crust however the prospect of hydrothermal activity for extreme element accumulation during the early cambrian a key geological period in south china has not been well constrained this study reports geochemical e g ree and sr isotope investigations of a coarse grained limestone layer and associated calcite veins in zunyi and nayong areas guizhou province to constrain the hydrothermal activity and evaluate the significance of hydrothermal contribution to extreme element accumulation during the early cambrian south china our results reveal positive eu anomalies and higher initial 87sr 86sr ratios 0 7083 0 7150 for carbonate samples than those of early cambrian seawater indicating the presence of hydrothermal processes combined with constraints from the spatial relationships and coincidence with adjacent mineralization these hydrothermal processes provide the most probable contribution for polymetallic ni mo pge mineralization furthermore there are abundant hydrothermal dolomite and barite calcite veins in the dolostone of the dengying formation indicating the occurrence of a variety of hydrothermal fluids overall multi stage hydrothermal pulses with different fluid compositions spanned the ediacaran cambrian transition in south china in particular these hydrothermal fluids with positive eu anomalies and enriched radiogenic sr originating from proterozoic mafic ultramafic rocks may have flowed through the underlying precambrian silicate clastic rocks e g xiajiang banxi and lengjiaxi groups and may have been crucial for the marine environment biological diversity and extreme element accumulation during the early cambrian south china

lead isotope geochemistry of mississippi valley type deposits of the southern appalachians lead isotope compositions of sphalerite fluorite barite and sparry dolomite in mississippi valley type deposits of the southern appalachians fall into four different isotopic groups most sphalerite forms two small clusters whereas barite fluorite and sparry dolomite compositions are more scattered these lead isotope compositions reflect the distribution of the deposits which are hosted by two main palcoaquifers lower cambrian clastic and carbonate rocks host the austinville zn pb cartersville ba embreeville zn and doughtery zn deposits all of which fall in a cluster of lead isotope compositions near 207 pb 204 pb 15 73 and 206 pb 204 pb 19 45 lower ordovician carbonate rocks of the knox group host the copper ridge zn eve mills zn greeneville fall branch ba f mascot jefferson city zn powell river zn pb russell tazewell ba f and sweetwater ba zn f deposits which have more complex compositions sphalerite from mascot jefferson city eve mills sweetwater and russell tazewell plots in a cluster around 207 pb 204 pb 15 67 and 206 pb 204 pb 19 0 whereas that from copper ridge plots in both clusters fluorite from sweetwater falls on a long array in 207 pb 204 pb 206 pb 204 pb space that has a two stage age of 1 55 to 1 9 ga for t 2 360 ma the previously published 87 sr 86 sr isochron age obtained for the mascot jefferson city district barite and sparry dolomite compositions are relatively similar and have lower 207 pb 204 pb and 208 pb 204 pb ratios than most sphalerite and fluorite the spatial distribution of lead isotope compositions indicates that there were at least two mineralizing solutions represented by the two lead clusters the upper cluster solution dominated the lower ordovician palcoaquifer whereas the lower cluster dominated the lower cambrian palcoaquifer and that the two solutions mixed in most areas except the mascot jefferson city district where zinc mineralization is strongest although the specific sources of these leads cannot be determined from available data on possible source rocks the two lead clusters probably came from relatively young well mixed sedimentary basins and the lead in the fluorite must have come from a source with an unusally high u th ratio such as phosphoritc this study confirms that the isotopic composition of lead in southern appalachian mississippi valley type deposits differs significantly from that found in mid continent deposits

origin of a giant orebody at navan ireland the navan base metal deposit in ireland formed 360 myr ago1 and is one of the world s largest orebodies with 70 million tonnes of 12 zn pb much of the mineralization was sedimentary exhalative other well known examples of this class of the so called sedex deposits are mount isa in australia sullivan in canada and meggen in germany several models for the formation of such deposits have been suggested here we report the first systematic stratigraphic pb isotopic study of galenas in any giant exhalative zn pb orebody we document evidence that the sources of pb in the navan orebody evolved to produce increased dispersion and less radiogenic averages of lead isotopic compositions this is as expected if the orebody formed from a hydrothermal convection cell which expanded to scavenge metals from progressively deeper parts of the continental crust

interglacial intensity in the north atlantic over the last 800 000 years investigating the complexity of the mid brunhes event the mid brunhes event mbe represents a step like increase between marine isotope stages mis 13 11 in the intensity of interglacial warmth a transect of palaeoclimatic records in the north atlantic from 40 n to the nordic seas indicates strong differences in the expression of the mbe within this region between 40 and 56 n sea surface and air temperature records suggest that all interglacials of the past 800 000 years were characterized by similar levels of warmth so there is no evidence for an mbe in these latitudes of the north atlantic north of 56 n there is increasing evidence for interglacials mis 19 13 being cold relative to mis 11 1 as most records of long term interglacial diversity suggest the mbe is a global event the north atlantic is clearly anomalous furthermore the strong spatial difference in temperature conditions during interglacials mis 19 13 in the north atlantic means that the temperature gradient across this region would have been enhanced in fact effectively doubled in magnitude during this interval copyright 2013 john wiley sons ltd

strontium isotopic evidence for the origin of barites and sulfides from the mississippi valley type ore deposits in southeast missouri several barites from the lead barite district contain between 1 170 and 1 633 ppm sr their 87 sr 86 sr ratios range from 0 7098 to 0 7118 in contrast to the values of 0 7082 to 0 7089 for the host carbonate rocks four galenas from the viburnum mine in southeast missouri provide a rb sr age of 392 or 21 m y and an initial isotopic composition of 0 7104 or 0 0004 indicating the period of mineralization to be early devonian modified journal abstract

revised tuning of ocean drilling program site 964 and kc01b mediterranean and implications for the δ18o tephra calcareous nannofossil and geomagnetic reversal chronologies of the past 1 1 myr 1 high resolution color reflectance records of kc01 and kc01b calabrian ridge ionian sea are presented and compared with a modified spliced high resolution color reflectance record of ocean drilling program odp site 964 this comparison revealed that kc01b is characterized by intensive deformation between 27 and 28 5 m piston depth and that some sapropels are tectonically reduced in thickness moreover the piston coring has caused considerable stretching in the top of kc01 and kc01b using a new splice of odp site 964 as guide previous astronomical tuned timescales of kc01b and odp site 964 were evaluated this evaluation resulted in a new sapropel based astronomical timescale for the last 1 1 myr the new timescale implies a much more uniform change in sedimentation rate for the ionian sea cores two prominent excursions to lighter values in the 18o record of the planktonic foraminiferal species globigerinoides ruber occur during marine isotopic stages 12 and 16 applying the new timescale these shifts correspond with maxima in obliquity and are punctuated by minima in the precession cycle they are absent in global ice volume records and are interpreted as reflecting a summer low salinity surface water lens that floats on top of extremely saline intermediate and deep waters at times of the very low sea levels during these glacial periods all biostratigraphic and magnetostratigraphic events found in kc01b and odp site 964 were re dated according to the new timescale and the ages of 33 tephra layers were reviewed the new ages for the calabrian ridge 2 and 3 magnetic events in the brunhes are concordant with minima in the global sint800 composite record derived from worldwide deep sea records of relative paleointensity and have been attributed to the big lost and la palma excursions respectively

isotopic footprints of the giant precambrian caixiashan zn pb mineralization system abstract carbonate replacement zn pb deposits are formed through fluid circulation within carbonate rocks and are an important global source of zn and pb the caixiashan carbonate replacement deposit is one of the largest zn pb systems in china the mesoproterozoic syn sedimentary stage i of the caixiashan deposit is characterized by sulfides with negative 34s values 25 3 to 8 6 generated by organic sulfate reduction which co precipitated with the host rocks the neoproterozoic main sulfide precipitation stage ii was caused by thermo sulfide reduction resulting in positive 34s values 7 9 12 3 carbonates from stage i have 13cpdb of 1 2 to 2 8 and 18osmow of 17 1 24 0 similar to those of marine carbonate rocks dolomite and calcite from stage ii have 13cpdb ranging from 5 1 to 0 2 and 18osmow of 14 1 19 7 consistent with dissolution of carbonate rock in contrast dolomite and calcite from stage iii have mantle c o signatures with the 13cpdb ranging from 7 5 to 0 4 and 18osmow from 5 8 to 13 2 c o isotopic signatures suggest that the original carbonates were dissolved by the acid generated from sulfide precipitation consistent with the sulfide precipitation process subsequent precipitation of carbonates created large volumes of dolomite alteration that coated the sulfides and possibly contributed to the preservation of the ore as dolomite would dissolve more slowly than calcite carboniferous magmatism stage iii resulted in a magmatic overprint on the stage ii sulfide the metal sources of these sulfide ore packets are mainly derived from the mesoproterozoic carbonate rocks as indicated by the lead isotopes of sulfides and also c o isotopes of carbonates the deposit is characterized by a complex paragenesis with multiple overprinting sources of hydrothermal fluids and sulfide over 700 m y the syn sedimentary stage 1019 ma and main mineralization stage 859 837 ma at caixiashan are chronologically and tectonically associated with the assembly and break up of the rodinia supercontinent whereas the magmatic hydrothermal modification stage 353 ma is associated with the closure of the paleo asian ocean during the early carboniferous

lead isotope geochemistry of mississippi valley type mineralization in the central appalachians lead isotope compositions of sulfide minerals from mississippi valley type deposits in cambrian ordovician and silurian rocks in the central appalachians plot in distinct groups one for each major district data for deposits in the nittany arch and shawangunk districts form circular clusters whereas data for the timberville and friedensville districts form more elongated fields comparison of these data to isotopic compositions of possible source rocks suggests that lead in the nittany arch shawangunk and timberville clusters came largely from paleozoic igneous rocks or sediment derived from these rocks whereas lead in the friedensville deposits came from grenville age basement rocks additional lead from the timberville district appears to have come from triassic diabase suggesting that as least some mineralization there is unusually young these results contrast strongly with those for the southern appalachians where different mississippi valley type districts have similar isotopic compositions over large areas only lead from the ordovician hosted timberville deposits in the central appalachians has an isotopic composition similar to that of any of the southern appalachian deposits and its composition is similar to that of deposits in the lower cambrian paleoaquifer of the southern appalachians rather than the ordovician paleoaquifer these relations indicate that although mississippi valley type brines in the central appalachians participated in significant cross formational flow they were not as regionally extensive as those in the southern appalachians a factor that might account for the relative scarcity of large mississippi valley type deposits in the central appalachians area

evolution of millennial scale climate variability during the mid pleistocene 1 we use the oxygen isotopic composition of planktonic foraminifera globigerinoides ruber white from ocean drilling program site 1058 in the subtropical northwestern atlantic to construct a high resolution 800 year climate record spanning the mid pleistocene climate transition 410 ka to 1350 ka we investigate whether or not millennial scale instabilities in the proxy record are associated with the extent of continental glaciation g ruber 18o values display high frequency fluctuations throughout the record but the amplitude about mean glacial and interglacial 18o values increases at marine isotope stage mis 22 880 ka and is highest during mis 12 these observations support that millennial scale climate instabilities are associated with ice sheet size time series analysis illustrates that these variations have significant concentration of spectral power centered on periods of 10 12 ka and 5 ka the timing of these fluctuations agrees well or coincides with the periodicities of the second and fourth harmonics respectively of precessional forcing at the equator an insolation based origin of the millennial scale instabilities would be independent of ice volume and explains the presence of these fluctuations before the mid pleistocene climate transition as well as during interglacial intervals e g mis 37 and 17 because the amplitude of the millennial scale variations increases during the mid pleistocene transition feedback mechanisms associated with the growth of large 100 ka paced polar ice sheets may be important amplifiers of regional surface water hydrographic changes

strontium isotopic geochemistry of mississippi valley type deposits east tennesse implications for age and source of mineralizing brines strontium isotopic ratios of wall rock ore and gangue minerals from the mascot jefferson city copper ridge and sweetwater mississippi valley type mvt districts and from the lost creek barite deposit in east tennessee were measured in an effort to determine the age of this mineralization and its relation to the tectonic evolution of the appalachian orogen the lower ordovician knox group which hosts the mvt mineralization contains limestones and dolomite karst breccias with 87sr 86sr ratios of 0 70900 to 0 70916 that are similar to those of early ordovician sea water primary diagenetic knox dolomite as well as recrystal line dolomite which formed by later alteration of limestone exhibits 87sr 86sr ratios of 0 70930 to 0 71024 reflecting varying degrees of contamination by solutions with more radiogenic strontium 87sr 86sr isotopic ratios of mineralization in the districts increase in the order lost creek sweetwater copper ridge mascot jefferson city and extend to values significantly higher than those of the enclosing rocks of the three possible source basins for the mvt brines the late proterozoic ocoee cambrian luttrell and ordovician sevier basins the sevier basin appears to be the only one that could have supplied brines of the appropriate composition at geologically reasonable times estimates of the change with time in the isotopic composition of sevier basin brines indicate that the maximum ages of the lost creek sweetwater copper ridge and mascot jefferson city mineralization are 520 460 405 and 395 m y respectively comparison of fluid inclusion temperatures for the sweetwater and mascot jefferson city minerlization with the thermal evolution curve for the sevier basin supports these estimates these ages suggest that the lost creek barite minerlization formed as an exhaltive deposit in the sevier basin and that the sweetwater fluorite barite mineralization formed during the later part of taconic orogeny the copper ridge and mascot jefferson city minerlization could have formed either prior to or during the alleghanian orogeny but prior to deformation of the enclosing rocks depending on the rate of istopic evolution of the sevier basin brines