biotic geochemical and environmental changes through the early sheinwoodian wenlock silurian carbon isotope excursion escie buttington quarry wales abstract palaeontological sedimentological and geochemical data particularly from la icpms analyses of pyrite from a 12 4 m section through the lower sheinwoodian trewern brook mudstone formation of buttington quarry wales are combined to reveal the environmental changes taking place during the early wenlock epoch of the silurian during the early part of the escie early sheinwoodian carbon isotope excursion the uppermost cyrtograptus murchisoni through to lower monograptus riccartonensis biozones show increased nutrient levels and peaks in palynomorph and graptolite abundance at this time graptolite diversity globally was declining dramatically possibly associated with metal particularly zinc concentrations attaining toxic levels and probably with the base of the euphotic zone being higher in the water column resulting from blooms of phytoplankton causing those graptolites that specialized in feeding on phytoplankton that were outcompeted in this diminished volume of illuminated surface waters to decline in numbers and eventually become extinct correlation of the graptolite and conodont biozonations enables the levels of the main stratigraphically higher ireviken event datum points to be proposed for the buttington section and this in turn allows events recognised elsewhere intervals of malformed palynomorphs and re organization of polychaete faunas together with an oceanic anoxic event to be correlated with the lower part of the studied buttington section the commencement of the oae identified on gotland at ireviken event datum point 4 appears to correlate rather well with a rapid transition marking the top of the butterley mudstone member at buttington from heavily bioturbated mudstones to laminated graptolitic mudstones surprisingly the most rapid change in 13ccarb values within the buttington section from 0 6 at 8 19 8 25 m to 2 09 at 8 50 8 55 m is not associated with any major faunal palynological abundance or geochemical changes these are all coincident with the initial rise in 13ccarb values up to about the 5 m level in the buttington section another unexplained feature of the graptolite record is a sudden change from monograptus dominated to pristiograptus dominated assemblages about half way through the studied section

multistage pyrites in the nibao disseminated gold deposit southwestern guizhou province china insights into the origin of au from textures in situ trace elements and sulfur isotope analyses abstract nibao is a unique thrust fault controlled and strata bound disseminated gold deposit in southwestern guizhou province china in nibao pyrite is the major sulfide mineral and au is structurally bound au within the pyrite lattice in this study we conducted detailed analyses of the pyrite chemistry and s isotope composition in nibao using laser ablation inductively coupled plasma mass spectrometry la icp ms and laser ablation multi collector inductively coupled plasma mass spectrometry la mc icp ms respectively through petrographic and pyrite chemical studies four pyrite generations py1 py4 were distinguished framboidal pyrite py1 pre ore sedimentary stage clean pyrite overgrowing framboidal pyrite py2 pre ore diagenetic stage spongy pyrite py3 early ore stage and overgrowth of narrow pyrite rims surrounding py2 py3 and disseminated pyrite associated with arsenopyrite py4 main ore stage among these py2 and py4 are the most abundant the trace element content in py2 is characterized by a wide range of as cu sb and pb concentrations 2480 58100 ppm 55 4 1610 ppm 29 1 232 ppm and 24 1 376 ppm respectively while py4 has the highest au as cu and se contents 70 ppm 4200 1630 ppm and 38 3 ppm respectively the 34s values of pre ore pyrites measured by la mc icp ms in this study and the available data in the literature range broadly from 53 3 to 114 8 indicating that they were most likely generated by bacterial reduction from marine sulfate during sedimentation diagenesis meanwhile the 34s values of ore pyrites have relative narrow 34s values mostly varying from 5 to 5 and indicating that the s was derived either from the average of sedimentary rocks or from a magmatic source since igneous rocks are scarce in the region and the exposed 77 99 ma are clearly younger than the mineralization age of the nibao gold deposit 141 ma a magmatic source is unlikely in nibao all pyrites in this study show a positive correlation r2 0 71 between co and ni and the co ni and zn ni ratios of main stage py4 are close to or within the range defined for a sedimentary diagenetic origin suggesting a sedimentary source is more likely in nibao

improving understanding of near term barrier island evolution through multi decadal assessment of morphologic change abstract observed morphodynamic changes over multiple decades were coupled with storm driven run up characteristics at fire island new york to explore the influence of wave processes relative to the impacts of other coastal change drivers on the near term evolution of the barrier island historical topography was generated from digital stereo photogrammetry and compared with more recent lidar surveys to quantify near term decadal morphodynamic changes to the beach and primary dune system between the years 1969 1999 and 2009 notably increased profile volumes were observed along the entirety of the island in 1999 and likely provide the eolian source for the steady dune crest progradation observed over the relatively quiescent decade that followed persistent patterns of erosion and accretion over 10 30 and 40 year intervals are attributable to variations in island morphology human activity and variations in offshore bathymetry and island orientation that influence the wave energy reaching the coast areas of documented long term historical inlet formation and extensive bayside marsh development show substantial landward translation of the dune beach profile over the near term period of this study correlations among areas predicted to overwash observed elevation changes of the dune crestline and observed instances of overwash in undeveloped segments of the barrier island verify that overwash locations can be accurately predicted in undeveloped segments of coast in fact an assessment of 2012 aerial imagery collected after hurricane sandy confirms that overwash occurred at the majority of near term locations persistently predicted to overwash in addition to the storm wave climate factors related to variations within the geologic framework which in turn influence island orientation offshore slope and sediment supply impact island behavior on near term timescales

gold in the oceans through time during sedimentation and diagenesis of carbonaceous shales in marine continental margin settings au is adsorbed from seawater and organic matter and becomes incorporated into sedimentary pyrite la icpms analysis of over 4000 sedimentary pyrite grains in 308 samples from 33 locations around the world grouped over 123 determined ages has enabled us to track in a first order sense the au content of the ocean over the last 3 5 billion years gold was enriched in the meso and neoarchean oceans several times above present values then dropped by an order of magnitude from the first great oxidation event goe1 through the paleoproterozoic to reach a minimum value around 1600 ma gold content of the oceans then rose with perturbations through the meso and neoproterozoic showing a steady rise at the end of the proterozoic 800 to 520 ma which most likely represents the effects of the second great oxidation event goe2 gold in the oceans was at a maximum at 520 ma when oxygen in the oceans rose to match current maximum values in the archean and proterozoic the au content of seawater correlates with the time distribution of high mg greenstone belts black shales and banded iron formations suggesting that increases in atmospheric oxygen and marine bio productivity combined with the higher background of au in komatiitic and mg rich basalts were the first order causes of the pattern of au enrichment in seawater we suggest the lack of major au deposits from 1800 to 800 ma is explained by the low levels of au in the oceans during this period

ultrahigh temperature metamorphism followed by two stage decompression of garnet orthopyroxene sillimanite granulites from ganguvarpatti madurai block southern india the mg al granulites from ganguvarpatti consist of orthopyroxene sillimanite garnet quartz as peak assemblage with a few porphyroblasts of cordierite and sapphirine these assemblages were strongly overprinted by late symplectites and coronas orthopyroxene inclusions in garnet and porphyroblast cores have the highest xmg 0 80 and al2o3 content 10 7 wt the estimated near peak metamorphic conditions 1 000 50 c and 11 kbar using garnet orthopyroxene geothermobarometry are consistent with those determined using a petrogenetic grid the proposed multi stage evolution process implies an initial decompression deduced from multi phase symplectites followed by cooling during biotite formation further late decompression is explained from the orthopyroxene rims on biotite this proposed p t path thus suggests a unique and complex evolution history for the uht granulites of southern india present results are comparable with similar adjacent terranes in the gondwana supercontinent but the lack of structural and geochronological data makes a link with any major metamorphic event uncertain

whole rock and discrete pyrite geochemistry as complementary tracers of ancient ocean chemistry an example from the neoproterozoic doushantuo formation china the trace element content of pyrite is a recently developed proxy for metal abundance in paleo oceans previous studies have shown that the results broadly match those of whole rock studies through geologic time however no detailed study has evaluated the more traditional proxies for ocean chemistry for comparison to pyrite trace element data from the same samples in this study we compare pyrite trace element data from 14 samples from the wuhe section of the ediacaran age doushantuo formation south china measured by laser ablation inductively coupled plasma mass spectrometry with new and existing whole rock trace element concentrations total organic carbon fe mineral speciation s isotope ratios and pyrite textural relationships this approach allows for comparison of data for individual trace elements within the broader environmental context defined by the other chemical parameters the results for discrete pyrite analyses show that several chalcophile and siderophile elements ag sb se pb cd te bi mo ni and au vary among the samples with patterns that mirror those of the independent whole rock data a comparison with existing databases for sedimentary and hydrothermal pyrite allows us to discriminate between signatures of changing ocean conditions and those of known hydrothermal sources in the case of the wuhe samples the observed patterns for trace element variation point to primary marine controls rather than higher temperature processes specifically our new data are consistent with previous arguments for pulses of redox sensitive trace elements interpreted to be due to marine oxygenation against a backdrop of mostly o2 poor conditions in the ediacaran ocean with important implications for the availability of bioessential elements the agreement between the pyrite and whole rock data supports the use of trace element content of pyrite as a tracer of ocean chemistry in ways that complement existing approaches while also opening additional windows of opportunity for example unlike the potential vulnerability of whole rock data to secondary alteration the pyrite record may survive greenschist facies metamorphism furthermore early formed pyrite can be identified through textural relationships as a proxy of primary marine chemistry even in the presence of hydrothermal overprints on whole rock chemistry via secondary fluids finally pyrite analyses may allow for the possibility of more quantitative interpretations of the ancient ocean once the elemental partitioning between the mineral and host fluids are better constrained collectively these advances can greatly increase the number of basins that may be investigated for early ocean chemistry especially those of precambrian age

new paleomagnetic results from the ediacaran doushantuo formation in south china and their paleogeographic implications abstract a new paleomagnetic pole is obtained from the top of member 3 of the doushantuo formation in the jiulongwan section of the yangtze gorges area in south china a total of 191 samples from 23 sites were collected and subjected to stepwise alternating field af and thermal demagnetization after the removal of a soft component sc of viscous magnetic remanence acquired in present geomagnetic field a high temperature component hc likely carried by magnetite was isolated the hc includes vectors from 147 samples using principal component analysis and arc constraints from 44 samples using remagnetization great circle analysis both the vectors only and the combined vectors and arc constraints of the hc passed a reversal test this is the first ediacaran paleomagnetic remanence from the south china block scb that passes a reversal test and it is interpreted as a primary remanence the hc vectors were thus used to calculate the paleomagnetic pole and in combination with arc constraints were used for polarity interpretation the vectors give a mean direction of d 75 2 i 41 0 95 2 5 n 147 after bedding correction and a corresponding paleomagnetic pole at 23 9 n 187 0 e dm dp 3 0 1 8 this pole differs significantly from previously published results of the doushantuo formation which may have been subjected to paleozoic remagnetization our results provide a 23 5 1 8 n paleolatitude for the yangtze gorges area of the scb and suggest several alternative paleogeographic options for the ediacaran cambrian amalgamation of east gondwana depending on chronostratigraphic correlations

ultrahigh temperature metamorphism in madurai granulites southern india evidence from carbon isotope thermometry abstract ultrahigh temperature uht metamorphism in the madurai block of the southern indian granulite terrain has been verified using the calcite graphite isotope exchange thermometer carbon isotope thermometry has been applied to marbles from a locality near the reported occurrence of sapphirine granulites that have yielded temperature estimates of around 1000 c the 13c and 18o values of calcite are homogenous implying equilibration of the isotopes during metamorphism however the 13c values of single graphite crystals show variations in the order of 1 within a hand specimen detailed isotopic zonation studies indicate that graphite preserves either the time integrated crystal growth history or reequilibrium fractionation during its cooling history the graphite cores preserve higher 13c values than the rims the fractionation between calcite and graphite cores gives the highest metamorphic temperature of about 1060 c which matches the petrologically inferred temperature estimates in the high

crustal evolution in south india constraints from nd isotopes nd isotope analyses from a range of lithologies including charnockites metasediments and granitoids that comprise the high grade terrain of south india define contrasting age provinces north of the palghat cauvery shear zone the karnataka craton and the granulite blocks of nilgiri and madras are characterized by model nd ages from 3 4 to 2 4 ga with significant crustal growth during the late archean south of the palghat cauvery shear zone a pan african granulite facies event resulted in sm nd fractionation as observed in several incipient charnockite localities model nd age calculations that allow for sm nd fractionation at 550 ma yield ages in the range of 2 9 to 1 3 ga this range compares closely with published model nd ages from the high grade terrain of sri lanka mid proterozoic crustal growth 1 1 ga observed in the vijayan complex of sri lanka may have provided source material for metasediments characterized by young model nd ages in southern peninsular india the palghat cauvery shear z

the chemical conditions of the late archean hamersley basin inferred from whole rock and pyrite geochemistry with δ33s and δ34s isotope analyses the well preserved late archean sedimentary rocks of the fortescue and hamersley basins in western australia offer fascinating insights into early earth ocean chemistry prior to the great oxidation event goe in this study we use a combination of whole rock geochemistry la icpms trace element analysis of sedimentary pyrite and pyrrhotite and shrimp si sulfur isotope analyses to elucidate the chemical changes in these sedimentary rocks these proxies are used to examine chemical conditions of the ocean during the late archean two to three periods of oxygen enrichment prior to the deposition of banded iron formations bif can be identified one minor stage of general increase in whole rock enrichment factors and trace element content of pyrite is observed up stratigraphy in the jeerinah formation fortescue basin and a more substantial stage is present in the paraburdoo and bee gorge members of the wittenoom formation hamersley basin some of the trace element enrichments indicate organic matter burial flux ni cr zn co and cu which suggests an increase in biological productivity if the increased biological activity reflects an increase in cyanobacteria activity then an associated increase in oxygen is likely to have occurred during the deposition of the bee gorge member an increase in atmospheric oxygen would result in continental weathering of sulfide and other minerals increasing the trace element content of the water column via erosion and avoiding excessive depletion of trace elements due to drawdown in seawater since some of these trace elements may also be limiting nutrients such as mo and se for the cyanobacteria the degree of biological productivity may have further increased due to the increasing amount of trace elements introduced by oxygenation in a positive feedback loop these periods of increased productivity and oxygen rise stopped prior to the onset of bif deposition in the hamersley basin this may be due to the ocean reaching an oxidation threshold enabling the precipitation of hematite and magnetite bif the bif deposition caused depletion of ocean nutrients such as phosphate severely limiting the growth of cyanobacteria and thus limiting further oxygen production

an improved set of a x parameters for fe mg ca garnets and refinements of the orthopyroxene garnet thermometer and the orthopyroxene garnet plagioclase quartz barometer

vanadium and its isotope composition of river water and seawater analytical improvement and implications for vanadium isotope fractionation abstract investigation of redox variations in recent and paleo oceans has been of particular scientific interest to elucidate the rise and variations of the atmospheric oxygen level by analyses of isotopic signatures of redox sensitive elements like fe mo and u vanadium is another redox sensitive metal that has become the target of stable isotope research during the last decade research of the oceanic v cycle revealed a rather complex interplay of riverine v as a major v source to the oceans on one side with v deposition in sediments and at hydrothermal vents as major sinks on the other the balance between these major v pools is sensitive to the ocean water oxygen level and chemistry the current data set of stable v isotope signatures of seawater is still very small but indicates already subtle variation of the v isotope signatures in the marine environment however the v isotopes of marine sediments and particularly the riverine v isotope composition of dissolved and particulate v i e the major source of v in modern marine environments has not been constrained at all so far in this study we present a new method for efficient v separation from seawater that allows multiple analyses of the v isotope composition of a single sample to separate v from large amounts volume 2 l of seawater samples we employ the bio rad chelex 100 resin and conventional cation and anion resins to yield a high v recovery of 90 from an uv irradiated sample non irradiated samples were marked by lower v recovery rates of ca 75 which was also observed in earlier studies further tests however revealed that even such reduced v yields do not incur significant v isotope fractionation within analytical uncertainty our 51vaa value of 0 27 0 14 2s d n 3 for the nass 6 seawater reference solution perfectly matched earlier results in addition seawater collected in the wadden sea at the german north sea coast is marked by a 51vaa signature of around 0 02 0 19 2s d n 17 which is slightly lower than those of the great oceans and may be related to an influx of river water bioactivity or a tide induced v mobilization to characterize the v isotope composition of the major v source to the oceans we determined for the first time v isotope signatures of 13 selected rivers dissolved and particulate fractions of source water tributary rivers and the yangtze river in the yangtze river basin china a large variation of dissolved v ca 0 07 to 6 0 g l and particulate bound v ca 0 03 to 17 g l was found for the sample suite the obtained 51vaa values of the dissolved v pool span a range of 0 76 0 18 2s d to 0 10 0 22 2s d whereas particulate bound v extends to lower 51v signatures between 2 13 0 30 2s d and 0 11 0 11 2s d notably dissolved v from the river sources and small tributaries scatters between ca 0 4 to 0 7 and agrees well with the predicted average 51vaa value of 0 6 0 3 for continental run off for the lower yangtze river however the dissolved 51vaa signatures increase from the three gorges dam towards the estuary from 0 76 to 0 10 suggesting v isotope fractionation due to adsorption to abundant particulate fe oxides but may also reflect an input of anthropogenic v the low 51vaa of particulate v largely follow this trend and thus indicate ongoing v isotope fractionation during riverine v transport to the ocean our first results of stable v isotope investigation of river waters show that v isotope signatures can indeed carry their host rock signature but are also sensitive to adsorption driven fractionation in oxidized environments the latter strongly depends as predicted from earlier theoretical calculations on the presence of particulate fe oxyhydr oxides and highlights gradual v isotope fractionation during riverine v transport to the ocean

surge of ore metals in seawater and increased bio activity a tracer of vhms mineralization in archaean successions yilgarn craton western australia the nimbus ag zn au deposit is a hybrid vhms deposit with epithermal characteristics formed in the eastern goldfields superterrane yilgarn craton under shallow water 700 mbsl low temperature conditions intersections of some ore lenses are high grade and polymetallic making similar styles of mineralization attractive yilgarn exploration targets the mineralization at nimbus is hosted by a bimodal felsic mafic succession of volcanic rocks which are overlain by a succession of least altered polymict conglomerates with a carbonaceous to dacitic matrix a new re os age 2680 34 ma nodular pyrite and black shale suggests that the overlying polymict conglomerate is coeval to 2 70 ga volcanism and mineralization at nimbus the pyrite within the high grade polymetallic sulfide assemblages has a consistently lower sb ag ratio 1 30 than pyrite from other sulfide phases e g 30 to 1000 in colloform and barren pyrite trace elements tes in sedimentary nodular pyrite from multiple intervals along a single drillhole nbdh010 indicate the existence of an enriched sedimentary interval with higher total te content ag au and sb au lower s se and polymetallic like signature of sb ag within this enriched interval the black shale matrix of the polymict conglomerate shows higher total organic carbon toc mo content and co ni ratios and suggest increased bio activity at that time interpreted to be associated with the ag zn au mineralization the te characteristics in sedimentary pyrite reflecting increased metal content in seawater inferred from in situ pyrite trace element analysis has the potential to be developed into an exploration tool for successions adjacent and coeval to similar ore deposits

diagenetic mobilization of ti and formation of brookite anatase in early cambrian black shales south china abstract titanium ti is typically hosted in detrital minerals in marine sediments and has long been considered to be immobile during diagenesis in this study the authigenic titania minerals brookite and anatase are observed in early cambrian carbonaceous shales from the meishucun and zhajin sections of south china respectively black shales in the meishucun section have total organic carbon toc contents from 1 6 to 3 9 wt and hi hydrogen index values from 3 8 to 20 mg hc g toc whereas black shales in the zhajin section have much higher toc 7 1 15 6 wt but lower hi

ultra high temperature metamorphism and multistage decompressional evolution of sapphirine granulites from the palni hill ranges southern india sapphirine granulites from a new locality in the palni hill ranges southern india occur in a small enclave of migmatitic highly magnesian metapelites mg 85 72 within massive enderbitic orthogneiss they show a variety of multiphase reaction textures that partially overprint a coarse grained high pressure assemblage of bt opx ky grt pl qtz the sequence of reactions as deduced from the corona and symplectite assemblages together with petrogenetic grid considerations records a clockwise p t evolution with four distinct stages 1 equilibration of the initial high p assemblage in deep overthickened crust 12 kbar 800 900 c was followed by a stage of near isobaric heating presumably as a consequence of input of extra heat provided by the voluminous enderbitic intrusives during heating kyanite was converted to sillimanite and biotite was involved in a series of vapour phase absent melting reactions which resulted in the ultra high temperature assemblage opx crd kfs spr sil grt qtz bt coexisting with melt equilibration at c 950 1000 c 11 10 kbar 2 subsequently as a result of decompression of the order of 4 kbar at ultra high temperature a sequence of symplectite assemblages opx sil spr spr crdopx spr crdopx crdopx crd spl crd spl developed at the expense of garnet orthopyroxene and sillimanite this stage of near isothermal decompression implies rapid ascent of the granulites into mid crustal levels possibly due to extensional collapse and erosion of the overthickened crust 3 development of late biotite through back reaction of melt with residual garnet indicates a stage of near isobaric cooling to c 875 c at 7 8 kbar i e relaxation of the rapidly ascended crust to the stable geotherm 4 a second period of near isothermal exhumation up to c 6 5 kbar 850 c is indicated by the partial breakdown of late biotite through volatile phase absent melting reactions available isotope data suggest that the early part of the evolutionary history stages 1 3 is presumably coeval with the early proterozoic metamorphism in the extended granulite terrane of the nilgiri biligirirangan and shevaroy hills to the north while the exhumation of the granulites from mid crustal levels stage 4 occurred only during the pan african thermotectonic event which led to the accretion of the kerala khondalite belt to the south

ultrahigh temperature granulite metamorphism 1050 c 12 kbar and decompression in garnet mg70 orthopyroxene sillimanite gneisses from the rauer group east antarctica highly magnesian and aluminous migmatitic gneisses from mather peninsula in the rauer group eastern antarctica preserve ultrahigh temperature uht metamorphic assemblages that include orthopyroxene sillimanite quartz garnet sillimanite quartz and garnet orthopyroxene sillimanite garnet that ranges up to xmg of 71 5 coexists with aluminous orthopyroxene that shows zoning from cores with 7 5 8 5 wt al2o3 to rims with up to 10 6 wt al2o3 adjacent to garnet peak p t conditions of 1050 c and 12 kbar are retrieved from fe mg al thermobarometry involving garnet and orthopyroxene in very good agreement with independent constraints from petrogenetic grids in feo mgo al2o3 sio2 and related chemical systems sapphirine orthopyroxene and cordierite form extensive symplectites and coronas on the early phases the specific reaction textures and assemblages involving these secondary phases correlate with initial garnet xmg with apparent higher pressure reaction products occurring on the more magnesian garnet and are interpreted to result from an initial phase of ultrahigh temperature near isothermal decompression uht itd from 12 to 8 kbar at temperatures in excess of 950 c later textures that involved biotite formation and then partial breakdown along with garnet relics to symplectites of orthopyroxene cordierite or cordierite spinel may reflect hydration through back reaction with crystallizing melts on cooling below 900 850 c followed by itd from 7 to 8 kbar to c 5 kbar at temperatures of 750 850 c the tectonic significance of this p t history is ambiguous as the rauer group records the effects of archean tectonothermal events as well as high grade events at 1000 and 530 ma late stage biotite formation and subsequent itd can be correlated with the p t history preserved in the proterozoic components of the rauer group and hence with either 1000 or 530 ma collisional orogenesis however whether the preceding uht itd history reflects a temporally unrelated event e g archean or is simply an early stage of either the late proterozoic or pan african tectonism as recently deduced for similar uht rocks from other areas of the east antarctica remains uncertain

proterozoic ocean redox and biogeochemical stasis the partial pressure of oxygen in earth s atmosphere has increased dramatically through time and this increase is thought to have occurred in two rapid steps at both ends of the proterozoic eon 2 5 0 543 ga however the trajectory and mechanisms of earth s oxygenation are still poorly constrained and little is known regarding attendant changes in ocean ventilation and seafloor redox we have a particularly poor understanding of ocean chemistry during the mid proterozoic 1 8 0 8 ga given the coupling between redox sensitive trace element cycles and planktonic productivity various models for mid proterozoic ocean chemistry imply different effects on the biogeochemical cycling of major and trace nutrients with potential ecological constraints on emerging eukaryotic life here we exploit the differing redox behavior of molybdenum and chromium to provide constraints on seafloor redox evolution by coupling a large database of sedimentary metal enrichments to a mass balance model that includes spatially variant metal burial rates we find that the metal enrichment record implies a proterozoic deep ocean characterized by pervasive anoxia relative to the phanerozoic at least 30 40 of modern seafloor area but a relatively small extent of euxinic anoxic and sulfidic seafloor less than 1 10 of modern seafloor area our model suggests that the oceanic mo reservoir is extremely sensitive to perturbations in the extent of sulfidic seafloor and that the record of mo and chromium enrichments through time is consistent with the possibility of a mo n colimited marine biosphere during many periods of earth s history

tracking the onset of phanerozoic style redox sensitive trace metal enrichments new results from basal ediacaran post glacial strata in nw canada abstract a global rise in oxygen levels has been proposed to coincide with the ediacaran to cambrian radiation of animals yet the precise timing and nature of this change remains unresolved one hypothesis is that the ocean atmosphere system became temporarily well oxygenated in the earliest ediacaran directly following the marinoan snowball earth glaciation 635 ma the evidence for oxygenation is based on large enrichments of redox sensitive trace elements in black shale from south china presumably deposited under a euxinic water column these enrichments meet or exceed the bulk concentrations of redox sensitive trace elements found in phanerozoic shale deposited under euxinic water columns here we test the early ediacaran post snowball oxygenation hypothesis with new data from a high resolution multi proxy geochemical and sedimentological study of three stratigraphic sections in the earliest ediacaran sheepbed formation of the mackenzie and wernecke mountains nw canada iron speciation data from all sections suggest that the local water column was dominantly ferruginous with a notable exception of probable euxinic conditions recorded in part of one section redox sensitive elements show no appreciable enrichments in the basal sheepbed formation with maximum concentrations of molybdenum vanadium uranium and chromium only slightly above world average shale values the lack of substantial elemental enrichments within the sheepbed formation is consistent with results from coeval ferruginous strata in svalbard the dominance of local ferruginous conditions in nw canada cannot alone account for the muted redox sensitive element enrichments as v u and cr are thought to be enriched under these conditions and samples deposited under euxinic conditions also lack phanerozoic style enrichments these contrasting results from different localities highlight a need to further investigate the veracity of trace metal enrichments in all localities as representing global redox conditions as the results have important implications for the timing of oxygenation with respect to early animal evolution

distinguishing ore deposit type and barren sedimentary pyrite using laser ablation inductively coupled plasma mass spectrometry trace element data and statistical analysis of large data sets faced with ongoing depletion of near surface ore deposits geologists are increasingly required to explore for deep deposits or those lying beneath surface cover the result is increased drilling costs and a need to maximize the value of the drill hole samples collected laser ablation inductively coupled plasma mass spectrometry la icp ms analysis of pyrite is one tool that is showing promise in deep exploration since the trace element content of pyrite approximates the composition of the fluid from which it precipitated and the crystallization mechanism the trace element characteristics can be used to predict the type of deposit with which a pyritic sample is associated this possibility however is complicated by overlapping trace element abundances for many deposit types the solution lies with simultaneous comparison of multiple trace elements through rigorous statistical analysis specifically we used la icp ms pyrite trace element data and random forests an ensemble machine learning supervised classifier to distinguish barren sedimentary pyrite and five ore deposit categories iron oxide copper gold iocg orogenic au porphyry cu sedimentary exhalative sedex and volcanic hosted massive sulfide vhms deposits the preferred classifier utilizes in situ co ni cu zn as mo ag sb te tl and pb measurements to train the random forests testing of the random forests classifier using additional data from the same deposits and sedimentary basins test data set yielded an overall accuracy of 91 4 94 9 for iocg 78 8 for orogenic au 81 1 for porphyry cu 93 6 for sedex 97 2 for sedimentary pyrite 91 8 for vhms similarly testing of the random forests classifier using data from deposits and sedimentary basins that did not have analyses in the training data set yielded an overall accuracy of 88 0 81 4 for orogenic au 95 5 for sedex 90 0 for sedimentary pyrite 73 9 for vhms insufficient data was available to perform a blind test on porphyry cu and iocg the performance of the classifier was further improved by instituting criteria at least 40 of total votes from the random forests needed for a conclusive identification to remove uncertain or inconclusive classifications increasing the classifier s accuracy to 94 5 for the test data 94 6 for iocg 85 8 for orogenic au 87 8 for porphyry cu 95 4 for sedex 98 5 for sedimentary pyrite 94 6 for vhms and 93 9 for the blind test data 85 5 for orogenic au 96 9 for sedex 96 7 for sedimentary pyrite 84 6 for vhms the random forests classification models for pyrite trace element data can be used as a predictive modeling tool in greenfield terrains by providing an accurate indication of ore deposit type this advance will assist mineral explorers by allowing early implementation of predictive ore deposit models when prospecting for ore deposits furthermore the ability of the classifier to accurately identify pyrite of sedimentary origin will allow researchers interested in paleoenvironmental conditions of ancient oceans to effectively screen prospective samples that are affected by a hydrothermal overprint

multistage metamorphic evolution of the trivandrum granulite block southern india abstract the trivandrum granulite block tgb southern india records evidence for three distinct stages of evolution m1 m3 during the pan african high grade metamorphism with possible temperature gradient from north to south of the terrain as detected from mineral phase equilibria thermobarometry in three classic localities namely nuliyam kunnanpara and nellikkala the charnockites both incipient and massive were formed during the first stage m1 at temperatures higher than their host rocks and at appreciably lower pressures charnockite formation was dominantly controlled by an increase in partial pressure of co 2 along structural locales during subisothermal decompression although an increase of potash activity could have also been an important factor in this process the charnockites at nellikkala in the northern margin of tgb were formed under appreciably more h 2 o rich conditions x h 2 o 0 53 0 03 than those at nuliyam x h 2 o 0 25 0 02 in the southern margin it is inferred that during the period between the metamorphic stages m1 and m2 the terrain experienced subisobaric cooling comparison of results from thermobarometry with data on absolute age determinations from geochronology of the metamorphic rocks in tgb allows the interpretation that the m1 metamorphic event took place during 540 600 ma m2 at about 530 ma and m3 in the interval of 440 470 ma mineralogic and thermobarometric evidence for earlier high grade metamorphic processes if any have been erased from these rocks the processes of charnockite formation and post peak retrograde metamorphism in the tgb took place under high geothermal gradients 40 150 km this probably testifies to the existence of a local heat source either magmas at depth or mantle plume beneath the region the general metamorphic cycle in the tgb is estimated to be ca 100 160 ma which is much shorter in time span than that in the other regions of southern peninsular india such as the karnataka craton and the eastern ghats mobile belt during this period the terrain experienced rapid exhumation of approximately 6 7 cm year with the total amplitude of vertical movements estimated to be about 16 17 km

empirical links between trace metal cycling and marine microbial ecology during a large perturbation to earth s carbon cycle abstract understanding the global redox state of the oceans and its cause and effect relationship with periods of widespread organic carbon deposition is vital to interpretations of earth s climatic and biotic feedbacks during periods of expanded oceanic oxygen deficiency here we present a compilation of new and published data from an organic rich locality within the proto north atlantic ocean during the cenomanian turonian boundary event that shows a dramatic drawdown of redox sensitive trace elements iron geochemistry independently suggests euxinic deposition i e anoxic and sulfidic bottom waters for the entire section thus confirming its potential as an archive of global marine metal inventories in particular depleted molybdenum mo and vanadium v concentrations effectively record the global expansion of euxinic and oxygen deficient but non sulfidic waters respectively the v drawdown precedes the oae fingerprinting an expansion of oxygen deficiency prior to an expansion of euxinia molybdenum drawdown in contrast is delayed with respect to v and coincides with the onset of oae2 parallel lipid biomarker analyses provide evidence for significant and progressive reorganization of marine microbial ecology during the oae in this region of the proto north atlantic with the smallest relative eukaryotic contributions to total primary production occurring during metal depleted intervals this relationship may be related to decreasing supplies of enzymatically important trace elements similarly box modeling suggests that oceanic drawdown of mo may have approached levels capable of affecting marine nitrogen fixation predictions of possible nitrogen stress on eukaryotic production locally and globally are consistent with the low observed levels of mo and a rise in 2 methylhopane index values during the peak of the oae at the same time the environmental challenge presented by low dissolved oxygen and euxinia coincides with increased turnover rates of radiolarian clades calcareous nanofossils and foraminifera suggesting that the temporal patterns of anoxia euxinia and associated nutrient limitation may have contributed to the fabric of oae2 related turnover

iodine content of the carbonates from the doushantuo formation and shallow ocean redox change on the ediacaran yangtze platform south china abstract the ediacaran period 635 541 ma is characterized by remarkable carbon isotope 13c excursions significant ocean redox changes and rapid diversification of eukaryotes including early animals these biological and geochemical events are commonly thought to be linked but their causal relationships remain controversial a particular point relates to the shallow ocean redox change across the negative 13c excursions most existing geochemical proxy data focused on tracking the redox conditions of deep or bottom water columns and provided limited information about the surface ocean ratios of iodine to calcium magnesium i ca mg from carbonates represent one of the few redox proxies that track the oxidation state of the shallow oceans here we report paired carbonate carbon isotopes 13ccarb and i ca mg ratios of the doushantuo formation from a drillcore section at daotuo paleogeographically located at the slope of the ediacaran yangtze platform south china in addition we compare the i ca mg ratios across the shuram upper doushantuo 13ccarb excursion in four sections of a shelf to slope transect in the slope section at daotuo the 13ccarb of the doushantuo formation shows three negative anomalies that are correlatable with those documented from the yangtze gorges area shelf and the siduping section slope the i ca mg ratios of the doushantuo formation from the drillcore are dominated by low but non zero

theoretical phase relations involving cordierite and garnet revisited the influence of oxygen fugacity on the stability of sapphirine and spinel in the system mg fe al si o the theoreticalp t grid for stability relations of the phases cordierite cd sapphirine sa hypersthene hy garnet ga spinel sp sillimanite si and quartz qz of hensen 1971 has proved useful in the interpretation of metamorphic mineral assemblages formed at low oxygen fugacity both experimental data and evidence from natural rocks indicate that at high oxygen fugacity compatability relations change as a result of the enlargement of the stability field of spinel which causes a topological inversion and the stabilisation of the invariant points sa ga and cd this implies the stable existence of the univariant equilibria for f text o text 2 buffered conditions sp qz ga hy si o2 sa cd cd sp qz hy si o2 sa ga and sa sp qz hy si o2 ga cd and the divariant reaction sp qz hy si o2 sa ga cd these redox equilibria are restricted to conditions of high oxygen fugacity the proposed theoreticalp t grids for both low and high oxygen fugacity satisfactorily explain all experimental data and metamorphic mineral assemblages so far found in granulites

mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions 1 sedimentary molybdenum mo s has been widely used as a proxy for benthic redox potential owing to its generally strong enrichment in organic rich marine facies deposited under oxygen depleted conditions a detailed analysis of mo s total organic carbon toc covariation in modern anoxic marine environments and its relationship to ambient water chemistry suggests that 1 mo s while useful in distinguishing oxic from anoxic facies is not related in a simple manner to dissolved sulfide concentrations within euxinic environments and 2 patterns of mo s toc covariation can provide information about paleohydrographic conditions especially the degree of restriction of the subchemoclinal water mass and temporal changes thereof related to deepwater renewal these inferences are based on data from four anoxic silled basins the black sea framvaren fjord cariaco basin and saanich inlet and one upwelling zone the namibian shelf representing a spectrum of aqueous chemical conditions related to water mass restriction in the silled basin environments increasing restriction is correlated with a systematic decrease in mo s toc ratios from 45 5 for saanich inlet to 4 5 1 for the black sea this variation reflects control of mo s by mo aq which becomes depleted in stagnant basins through removal to the sediment without adequate resupply by deepwater renewal the basin reservoir effect the temporal dynamics of this process are revealed by high resolution chemostratigraphic data from framvaren fjord and cariaco basin sediment cores which exhibit long term trends toward lower mo s toc ratios following development of water column stratification and deepwater anoxia mo burial fluxes peak in weakly sulfidic environments such as saanich inlet owing to a combination of greater mo aq availability and enhanced mo transport to the sediment water interface via fe mn redox cycling and are lower in strongly sulfidic environments such as the black sea and framvaren fjord these observations demonstrate that at timescales associated with deepwater renewal in anoxic silled basins decreased sedimentary mo concentrations and burial fluxes are associated with lower benthic redox potentials i e more sulfidic conditions these conclusions apply only to anoxic marine environments exhibiting some degree of water mass restriction e g silled basins and are not valid for low oxygen facies in open marine settings such as continent margin upwelling systems

carbon isotope variability across the ediacaran yangtze platform in south china implications for a large surface to deep ocean δ13c gradient new isotope data obtained from relatively conformable carbonate rich strata of the ediacaran yangtze platform in south china reveal substantial 13 c variability in platform sections four negative 13 c anomalies with a nadir down to 8 pdb are present in the interval between the cap carbonate level 635 ma and the precambrian cambrian boundary 542 ma while in slope and basinal sections 13 c values are negative through the entire doushantuo formation 635 551 ma if these 13 c values are close to their primary seawater signature they imply a strong 10 surface to deep ocean 13 c gradient that is consistent with long term deep ocean anoxia and the presence of a large dissolved organic carbon doc reservoir the two prominent negative 13 c excursions within the doushantuo formation above the cap carbonate level are associated with shoaling and local exposure of the platform the anomalies may thus record remineralization of a large oceanic doc pool via sulfate reduction that transferred 13 c depleted carbon from the oceanic doc reservoir to the surface ocean during regression inconsistencies in ediacaran 13 c profiles globally and variations in south china in particular highlight the need for further evaluation of local departures in 13 c from an inferred average seawater signature

pyritization of trace metals in anoxic marine sediments the pyritization of reactive trace elements in different anoxic marine sediments was investigated to determine the importance of factors such as h2s reactive fe pyrite content and salinity in controlling this process the areas studied included anoxic sulfidic sediments baffin bay a hypersaline coastal lagoon from texas and green canyon a hemipelagic oil seepage area anoxic nonsulfidic sediments with high sedimentation rates atchafalaya bay mississippi delta system hemipelagic anoxic nonsulfidic sediments with low sedimentation rates gulf of mexico shelf and slope and orca basin an euxinic hypersaline basin and organic rich marsh sediments atchafalaya bay results indicate that the degree of trace metal pyritization dtmp of all trace metals except cd increased with increasing degree of pyritization dop irrespective of the type of sedimentary environment involved however for as hg and mo the dtmpdop values were generally above the 1 1 ratio line whereas the transition metals co cu mn and ni displayed a close to linear increase in dtmp with dop and moderate incorporation into pyrite chromium and the class b metals pb and zn were also gradually incorporated into the pyrite phase but without reaching the dtmp levels exhibited by the transition metals cadmium was not incorporated to a significant extent these results are consistent with the chemical attributes of these different classes of trace elements availability of dissolved trace metals and organic matter content are apparently important factors controlling the incorporation of co cr cu and ni into pyrite in anoxicsulfidic fe poor and h2s rich environments

multistage sedimentary and metamorphic origin of pyrite and gold in the giant sukhoi log deposit lena gold province russia gold mineralization at sukhoi log in eastern siberia is hosted in a deformed neoproterozoic organic bearing and pyritic black shale and siltstone sequence that is folded into a tight overturned anticline the deposit contains about 30 million ounces of gold at an average grade of 2 0 g t au and is one of the largest known undeveloped gold resources the high grade gold zone forms a gently dipping tabular body in the core of the anticline the best gold grades occur in narrow bedding parallel pyrite quartz veinlets that have been folded during the main deformation event lower grade gold is associated with disseminated pyrite developed in and around the high grade core of the deposit detailed paragenetic studies of the mineralization and host rocks have defined six stages of pyrite development in the carbonaceous sediments the two earliest forms of pyrite termed py1 and py2 are commonly developed in stratiform layers of micron sized crystals framboids and fine euhedra which are interpreted as synsedimentary to early diagenetic in origin coarser grained bedding parallel aggregates of inclusion rich pyrite termed py3 contain inclusions of arsenopyrite native gold and gold tellurides and are interpreted to form during late diagenesis and earliest deformation coarse euhedral pyrite py4 overgrows the earlier pyrite py1 py2 and py3 and the slaty cleavage developed in the host rocks indicating a syndeformation timing late stage inclusion free pyrite py5 overgrows and replaces earlier sulfides and is considered to be syn to late deformation laser ablation inductively coupled plasma mass spectrometry la icpms analyses of the various pyrite types indicate that the synsedimentary py1 contains the highest levels of invisible gold varying from 0 4 to 12 1 ppm with a mean of 3 22 ppm au and 1 900 ppm as py1 is also enriched in a suite of trace elements mo sb ni co se te ag cu pb zn mn ba cr u v which are similar to those concentrated by organic processes in euxinic sedimentary environments later generations of pyrite from py2 to py5 including pyrite in bedding parallel pyrite quartz veinlets contain progressively lower contents of invisible gold and most other trace elements however this metamorphic and postmetamorphic pyrite contains microinclusions of free gold arsenopyrite pyrrhotite sphalerite and chalcopyrite the paragenetic textural and chemical relationships at sukhoi log suggest that gold was clearly initially introduced prior to cleavage development accompanying sedimentation of the organic rich shales and fixed during diagenesis within the structure of diagenetic arsenian pyrite subsequently accompanying deformation gold was liberated from recrystallized diagenetic pyrite to become concentrated as free gold and gold tellurides within metamorphic pyrite and folded bedding parallel pyrite quartz veinlets two key processes are considered vital to the formation of the sukhoi log deposit original synsedimentary and early diagenetic concentration of gold dissolved within arsenian pyrite in organic rich black shales and metamorphic processes that liberated gold from the early forms of arsenian pyrite to be concentrated as free gold and gold tellurides within late diagenetic and metamorphic pyrite and associated pyrite quartz veinlets in the core of an overturned anticline these ore forming processes are unlikely to be unique to sukhoi log other black shale and turbidite hosted deposits that occur in rifted continental margin environments which have undergone collision and basin inversion may form by similar processes

silica undersaturated sapphirine spinel and kornerupine granulite facies rocks ne strangways range central australia small pods of silica undersaturated al rich and mg rich granulite facies rocks containing sapphirine pleonastic spinel kornerupine cordierite orthopyroxene corundum sillimanite and gedrite are scattered throughout the ne strangways range central australia these are divided into four distinct rock types namely orthopyroxene rich aluminous granofels and metapelitic gneisses containing sapphirine spinel or kornerupine two granulite facies metamorphic events are recognized of which only the first m1 is considered in this paper peak metamorphic mineral parageneses indicate that the m1 thermal maximum occurred at approximately 900 950 c and 8 9 kbar all samples are characterized by profuse and diverse coronitic and symplectic reaction textures these are interpreted as evidence for the sequential crossing of the following reactions in the system fmas cordierite spinel corundum sapphirine sillimanite cordierite spinel orthopyroxene sapphirine sillimanite sapphirine spinel sillimanite orthopyroxene corundum sapphirine sillimanite cordierite orthopyroxene corundum phase stability relationships in fmas and mash indicate an anticlockwise p t path terminated by isobaric cooling such a path is exemplified by early low p mineral parageneses containing spinel corundum and gedrite and the occurrence of both prograde and retrograde corundum reaction textures preserve evidence for an increase in ah2o and ab2o3 with progressive isobaric cooling this hydrous retrogression resulted from crystallization of intimately associated m1 partial melt segregations there is no evidence for voluminous magmatic accretion giving rise to the high m1 thermal gradient the m1 p t path may be the result of either lithospheric thinning after both crustal thickening and burial of the supracrustal terrane or concomitant crustal thickening and mantle lithosphere thinning

copper arsenic decoupling in an active geothermal system a link between pyrite and fluid composition abstract over the past few decades several studies have reported that pyrite hosts appreciable amounts of trace elements which commonly occur forming complex zoning patterns within a single mineral grain these chemical zonations in pyrite have been recognized in a variety of hydrothermal ore deposit types e g porphyry cu mo au epithermal au deposits iron oxide copper gold carlin type and archean lode au deposits among others showing in some cases marked oscillatory alternation of metals and metalloids in pyrite growth zones e g of cu rich as au ag depleted zones and as au ag rich cu depleted zones this decoupled geochemical behavior of cu and as has been interpreted as a result of chemical changes in ore forming fluids although direct evidence connecting fluctuations in hydrothermal fluid composition with metal partitioning into pyrite growth zones is still lacking in this study we report a comprehensive trace element database of pyrite from the tolhuaca geothermal system tgs in southern chile a young and active hydrothermal system where fewer pyrite growth rims and mineralization events are present and the reservoir fluid i e ore forming fluid is accessible we combined the high spatial resolution and x ray mapping capabilities of electron microprobe analysis empa with low detection limits and depth profiling capacity of secondary ion mass spectrometry sims in a suite of pyrite samples retrieved from a 1 km drill hole that crosses the argillic 20 450 m and propylitic 650 1000 m alteration zones of the geothermal system we show that the concentrations of precious metals e g au ag metalloids e g as sb se te and base and heavy metals e g cu co ni pb in pyrite at the tgs are significant among the elements analyzed as and cu are the most abundant with concentrations that vary from sub ppm levels to a few wt i e up to 5 wt as 1 5 wt cu detailed wavelength dispersive spectrometry wds x ray maps and sims depth vs isotope concentration profiles reveal that pyrites from the tgs are characterized by chemical zoning where the studied elements occur in different mineralogical forms arsenic and co occur as structurally bound elements in pyrite cu and au in pyrite can occur as both solid solution and submicron sized particles of chalcopyrite and native au or au tellurides respectively pyrites from the deeper propylitic zone do not show significant zonation and high cu co as concentrations correlate with each other in contrast well developed zonations were detected in pyrite from the shallow argillic alteration zone where cu co rich as depleted cores alternate with cu co depleted as rich rims these microanalytical data were contrasted with chemical data of fluid inclusions in quartz and calcite veins high cu as ratios and borehole fluid low cu as ratios reported at the tgs showing a clear correspondence between cu and as concentrations in pyrite forming fluids and chemical zonation in pyrite these observations provide direct evidence supporting the selective partitioning of metals into pyrite as a result of changes in ore forming fluid composition most likely due to separation of a single phase fluid into a low density vapor and a denser brine capable of fractionating cu and as

a critical look at iron paleoredox proxies new insights from modern euxinic marine basins enrichments in reactive iron occur under euxinic marine conditions that is where dissolved sulfide is present in the water column these enrichments result primarily from the export of remobilized iron from the oxic shelf which is scavenged from the euxinic water column during syngenetic pyrite formation and deposited in the underlying sediments strongly elevated ratios of highly reactive iron to total iron fehr fet and total iron to aluminum fet al and high degrees of pyritization dop are each products of this enrichment process these paleoredox proxies are among the most faithful recorders of ancient euxinia contrary to previous arguments iron enrichment is decoupled from biogenic sediment inputs but it does appear to be a uniquely euxinic phenomenon in other words we can rule out a major contribution from preferential physical transport of fehr rich detrital sediment to the deep basin which could also operate under oxic conditions furthermore enrichment via the shuttling of iron remobilized from oxic shelves appears to be limited by inefficient transport and trapping processes in deep oxic basins elevated fet al ratios in the euxinic sediments also cannot be a product of internal enhancement of the reactivity of the detrital iron pool without net fehr addition these conclusions are supported by observations in the modern black sea orca basin and effingham inlet fet al ratios are unambiguous recorders of paleoredox even in sediments that have experienced high degrees of metamorphic alteration however this study suggests that high siliciclastic accumulation rates can swamp the enrichment mechanism resulting in only intermediate dop values for euxinic sediments and fet al ratios that mimic the oxic shelf such dilution effects are well expressed in black sea basinal turbidites and rapidly accumulating muds on euxinic basin margins under conditions of persistent euxinia varying extents of fehr enrichment can illuminate spatial and temporal gradients in siliciclastic sedimentation the magnitude of enrichment is a function of the source shelf to sink ocean basin areal ratio suggesting that iron proxies can also record ocean scale paleoenvironmental properties through muted enrichments at times of very widespread euxinia for the first time manganese data are interpreted in light of the redox shuttle model as for the iron data the black sea orca basin and effingham inlet show enrichments in total manganese in the deep euxinic basin suggesting export from the suboxic porewaters of the oxic shelf and scavenging and burial in the basin the black sea data reveal iron and manganese enrichment across the broad deep euxinic basin suggesting efficient lateral transport and deep water mixing tied to the physical properties of the water column

pyrite geochemistry in the toarcian posidonia shale of south west germany evidence for contrasting trace element patterns of diagenetic and syngenetic pyrites authigenic pyrite grains from a section of the lower toarcian posidonia shale were analysed for their trace element contents and sulphur isotope compositions the resulting data are used to evaluate the relationship between depositional conditions and pyrite trace element composition by using factor analysis trace elements in pyrite may be assigned to four groups i heavy metals including cu ni co pb bi and tl ii oxyanionic elements as mo and sb iii elements partitioned in sub microscopic sphalerite inclusions zn and cd and iv elements related to organic or silicate impurities ga and v results indicate that trace element contents in pyrite depend on the site and mechanism of pyrite formation with characteristic features being observed for diagenetic and syngenetic pyrites diagenetic pyrite formed within anoxic sediments generally has a high heavy metals content and the degree of pyritization of these elements increases with increasing oxygen deficiency similar to the degree of pyritization of reactive fe the highest gradient in the increase of the degree of trace element pyritization with bottom water oxygenation was found for the elements ni cu mo as tl in contrast syngenetic pyrite formed within a euxinic water column typically is enriched in as mo and sb but is low in heavy metals and the geochemical variation reflects changes in sea water composition

uncovering framboidal pyrite biogenicity using nano scale cnorg mapping framboidal pyrite has been used as a paleo redox proxy and a biomarker in ancient sediments but the interpretation of pyrite framboids can be controversial especially where later overgrowths have obscured primary textures here we show how nano scale chemical mapping of organic carbon and nitrogen cn org can detect relict framboids within precambrian pyrite grains and determine their formation mechanism pyrite grains associated with an ediacaran fossil lagerstatte from newfoundland ca 560 ma hold significance for our understanding of taphonomy and redox history of the earliest macrofossil assemblages they show distinct chemical zoning with respect to cn org relict framboids are revealed as spheroidal zones within larger pyrite grains whereby pure pyrite microcrystals are enclosed by a mesh like matrix of pyrite possessing elevated cn org replicating observations from framboids growing within modern biofilms subsequent pyrite overgrowths also incorporated cn org from biofilms with concentric cn org zoning showing that the availability of cn org progressively decreased during later pyrite growth multiple framboids are commonly cemented together by these overgrowths to form larger grains with relict framboids only detectable in cn org maps in situ sulfur isotope data 34 s 24 to 15 show that the source of sulfur for the pyrite was also biologically mediated most likely via a sulfate reducing microbial metabolism within the biofilms relict framboids have significantly smaller diameters than the pyrite grains that enclose them suggesting that the use of framboid diameters to infer water column paleo redox conditions should be approached with caution this work shows that pyrite framboids have formed within organic biofilms for at least 560 m y and provides a novel methodology that could readily be extended to search for such biomarkers in older rocks and potentially on other planets

uranium and molybdenum isotope evidence for an episode of widespread ocean oxygenation during the late ediacaran period abstract to improve estimates of the extent of ocean oxygenation during the late ediacaran period we measured the u and mo isotope compositions of euxinic anoxic and sulfidic organic rich mudrocks orm of member iv upper doushantuo formation south china the average 238 u of most samples is 0 24 0 16 2sd relative to standard crm145 which is slightly higher than the average 238 u of 0 02 0 12 for restricted black sea deep water unit i euxinic sediments and is similar to a modeled 238 u value of 0 2 for open ocean euxinic sediments in the modern well oxygenated oceans because 238 u is preferentially removed to euxinic sediments compared to 235 u expanded ocean anoxia will deplete seawater of 238 u relative to 235 u ultimately leading to deposition of orm with low 238 u hence the high 238 u of member iv orm points to a common occurrence of extensive ocean oxygenation ca 560 to 551 myr ago the mo isotope composition of sediments deposited from strongly euxinic bottom waters h 2 s aq 11 m either directly records the global seawater mo isotope composition if mo removal from deep waters is quantitative or represents a minimum value for seawater if mo removal is not quantitative near the top of member iv 98 mo approaches the modern seawater value of 2 34 0 10 high 98 mo points to widespread ocean oxygenation because the preferential removal of isotopically light mo to sediments occurs to a greater extent in o 2 rich compared to o 2 deficient marine environments however the 98 mo value for most member iv orm is near 0 relative to standard nist srm 3134 0 25 suggesting extensive anoxia the low 98 mo is at odds with the high mo concentrations of member iv orm which suggest a large seawater mo inventory in well oxygenated oceans and the high 238 u hence we propose that the low 98 mo of most member iv orm was fractionated from contemporaneous seawater possible mechanisms driving this isotope fractionation include 1 inadequate dissolved sulfide for quantitative thiomolybdate formation and capture of a seawater like 98 mo signature in sediments or 2 delivery of isotopically light mo to sediments via a particulate fe mn oxyhydroxide shuttle a compilation of mo isotope data from euxinic orm suggests that there were transient episodes of extensive ocean oxygenation that break up intervals of less oxygenated oceans during late neoproterozoic and early paleozoic time hence member iv does not capture irreversible deep ocean oxygenation instead complex ocean redox variations likely marked the transition from o 2 deficient proterozoic oceans to widely oxygenated later phanerozoic oceans

geochemistry of early frasnian late devonian pyrite ammonoid level in the kostomloty basin poland and a new proxy parameter for assessing the relative amount of syngenetic and diagenetic pyrite abstract pyrite geochemistry isotope and trace element composition degree of pyritization s c org ratio was used in context of selected lithogeochemical parameters major and trace elements including sulphur organic carbon and 13 c of carbonate carbon to constrain fluctuations in depositional conditions during the early to middle frasnian carbon isotopic perturbation punctata event in the kostomloty basin poland based on the ratio between the sum of oxyanionic elements and transition metals in pyrite a new proxy parameter index of syngenetic pyrite isyp is proposed for assessing the relative amount of syngenetic pyrite in a sample the distribution of the isyp along the kostomloty male gorki section upper szydlowek to the basal kostomloty beds is in concert with conclusions inferred from paleoecologic data and other geochemical parameters degree of pyritization s c org 34 s pyrite according to these the lower segment of the szydlowek beds was deposited in a normally oxygenated environment but undergoing increasing primary productivity in surface water as indicated by an increase in 13 c carb and in cu zr ratio in bulk rock which triggered the periodic deposition of sediments slightly enriched in organic matter notably within the pyrite ammonoid level goniatite level fluctuating but in general high s c org ratios dop r values and isyp values suggest that during this time against the background of a generally dysoxic environment shorter or longer lasting episodes of more restricted anoxic and possibly even euxinic bottom water conditions developed low sedimentation rates enabled a continuous and practically unlimited supply of sulphate during bacterial sulphate reduction bsr which in turn led to a strong depletion of pyrite sulphur in 34 s in this interval constantly around 29 in contrast below and above the goniatite level higher 34 s values up to 3 are compatible with closed system conditions and higher sedimentation rates the styliolina horizon is distinguished by the overall highest portion of syngenetic pyrite which suggests that in this marker layer most of the pyrite precipitated from euxinic bottom waters

identifying global vs basinal controls on paleoproterozoic organic carbon and sulfur isotope records abstract paleoproterozoic sedimentary successions are important archives of the redox evolution of earth s atmosphere and oceans efforts to unravel the dynamics of our planet s early oxygenation from this archive rely on various geochemical proxies including stable carbon and sulfur isotopes however ancient metasedimentary rocks often experienced early and late stage bio geochemical processes making it difficult to discern primary environmental signals from bulk rock 13corg and 34s values such complexity in carbon and sulfur isotope systematics contributes to uncertainty about the redox structure of paleoproterozoic oceans a currently popular idea is that following the great oxidation event global changes led to low oxygen environments and temporally fluctuating ocean redox conditions that lasted until the neoproterozoic the volcano sedimentary rocks of the onega basin have figured prominently in this concept particularly the exceptionally organic rich rocks of the 1 98 ga zaonega formation however a growing body of evidence shows that local depositional processes acted to form the 13corg and pyrite 34s records of the zaonega formation thus calling for careful assessment of the global significance of these isotope records placing new and existing organic carbon and sulfur isotope data from the zaonega formation into the context of basin history and by comparing those results with key paleoproterozoic successions of the francevillian basin gabon the pechenga greenstone belt nw russia and the animikie basin canada we show that the stratigraphic 13corg and pyrite 34s trends can be explained by local perturbations in biogeochemical carbon and sulfur cycling without requiring global drivers despite their temporal disparity we also demonstrate that individual successions share certain geological traits e g magmatic and or tectonic activity hydrocarbon generation basin restriction suggesting that their pyrite 34s and 13corg trends were governed by common underlying mechanisms e g similar basinal evolution and biogeochemical feedbacks and are not necessarily unique to certain time intervals we further show that pyrites in these successions that are most likely to capture ambient seawater sulfate isotopic composition have consistent 34s values of 15 18 which hints at remarkable stability in the marine sulfur cycle over most of the paleoproterozoic era

geochemistry of ediacaran cap dolostones across the yangtze platform south china implications for diagenetic modification and seawater chemistry in the aftermath of the marinoan glaciation cap dolostones of the ediacaran doushantuo formation yangtze platform south china from various palaeo water depths were studied to evaluate the extent of their diagenetic alteration and to assess temporal and spatial variations of seawater chemistry in the aftermath of the marinoan glaciation diagenetic fluid overprint is common in cap dolostone lithologies however the mobilization of trace elements and the modification of sr and o isotopic compositions are variable and were controlled by multiple stages of fluid overprint the highest 87 sr 86 sr ratios up to 0 7246 occur in cap dolostones from the palaeo slope environment at the huanglianba section whereas cap dolostones deposited in platform settings and in one of the distal basinal settings reveal 87 sr 86 sr ratios close to the proposed late neoproterozoic seawater composition 0 7077 shale normalized ree y patterns of carbonate leachates display enrichments of heavy over light ree and superchondritic y ho ratios typical of seawater however y ho ratios in the cap dolostones are always lower than modern seawater values which is interpreted to reflect dilution of the seawater signal by continent derived meltwater influx during deglaciation negative ce anomalies in carbonate leachates from platform and slope sections suggest that oxidized conditions existed in shallow marine environments shortly after the marinoan glaciation whereas positive or no resolvable ce anomalies in basin settings indicate that the latter remained anoxic redox stratification of the yangtze margin at the beginning of the ediacaran is further supported by the relative enrichment of redox sensitive trace metals in basinal sections these data may indicate moderately anoxic less than 10 m dissolved o 2 and presumably manganous conditions during the deposition of cap dolostones in the deeper realms of the yangtze basin supplementary material supplementary data for this paper are available at https doi org 10 6084 m9 figshare c 3770957

the stability of sapphirine quartz and hypersthene sillimanite quartz assemblages an experimental investigation in the system feo mgo al 2 o 3 sio 2 under h 2 o and co 2 conditions phase relations and mineral chemistry involving the phases garnet gt spinel sp hypersthene hy sapphirine sa cordierite cd sillimanite sil and quartz qz have been experimentally determined in the system fmas feo mgo al2o2 sio2 under low fo2 and for various h2o co2 conditions several compositions were studied with 100 mg mg fe ratio ranging from 64 to 87 with excess quartz and sillimanite our data do not show any differences in gt cd stability and composition as a function of h2o co2 and h2o co2 ch4 content in good agreement with a previous experimental study at lower temperature aranovich and podlesskii 1983 at 1 000 c and 11 kbar under co2 saturated conditions cordierite grew from a crystalline mix unseeded with cordierite thus under water absent conditions cordierite will have a high p stability field in the presence of co2 if water has a pressure stabilizing effect on cordierite then our results would indicate that the effects of h2o and co2 are of the same magnitude at high temperature our data support the theoretical p t grid proposed by hensen 1986 for high t metapelites and are largely consistent with the high temperature experimental data of hensen and green 1973 the univariant boundary gt cd hy sil qz which marks the disappearance of hy sil qz assemblages has a negative dp dt slope above 1 000 c and a positive one below this temperature extrapolation of our data to iron free systems shows that the high p breakdown limit of mg cordierite has a negative slope in the range 1 025 1 300 c and probably positive below 1 000 c this indicates a maximum of stability for mg cordierite at around 1 000 c and 13 kbar because of the curvature of the univariant reactions en sil py qz mg cd en sil qz and gt cd hy sil qz the iron free invariant point involving the phases py en cd sil and qz probably does not exist sapphirine qz bearing assemblages are stable only at temperatures above 1 050 c at 1 075 c the joint gt sa is stable up to 11 kbar at higher pressure garnet sapphirine and quartz react according to the reaction gt sa qz hy sil reequilibrated sapphirines are more aluminous than the theoretical endmember mg2al4sio10 due to alal mgsi substitutions 100 al2o3 al2o3 feo mgo in experimental sapphirines ranges from 50 5 to 52 2 sapphirine in the assemblage sa cd sil qz shows a decrease in al content with decreasing temperature and pressure such that the alumina isopleths for sapphirine have a slight negative dp dt slope a similar decrease in al content of sapphirine with temperature is also observed in sa sil qz assemblages

pyrite compositions from vhms and orogenic au deposits in the yilgarn craton western australia implications for gold and copper exploration abstract the archaean yilgarn craton western australia is a world class metallogenic province hosting considerable resources of au ag ni cu zn and fe here we present trace element compositions of pyrite from 30 orogenic au and 5 volcanic hosted massive sulphide vhms deposits across the yilgarn pyrites from vhms deposits tend to have higher sn se cu pb bi and lower ni relative to orogenic deposits vhms deposit pyrites commonly have co ni as 100au te au se te orogenic gold deposits could be subdivided based on association of au with as or te pyrites from au as ores generally have pb bi 5 se te 5 pb sb 100 and the majority of au is refractory in pyrite structure at the same time au te association pyrites are characterised by lower values of pb bi se te and tl te higher values of ag au pb sb and au generally resides in inclusions of different compositions our data can be used at the exploration stage to distinguish between vhms vs orogenic au signatures for all studied deposits inclusion populations are summarised with implications for au and ag deportment orogenic au deposits from the yilgarn mostly have multistage formation histories reflected in the presence of multiple generations of pyrites however only some deposits record multiple high au mineralisation events

multiple negative molybdenum isotope excursions in the doushantuo formation south china fingerprint complex redox related processes in the ediacaran nanhua basin abstract the ediacaran doushantuo formation offers one of the most complete and extensively studied records of end neoproterozoic biotic and environmental change here we report multiple coeval negative molybdenum mo isotope excursions to as low as 98monist 0 25 2 24 0 10 2sd in shales from four separate sites in south china rongxi taoying wuhe and yuanjia that preserve the doushantuo formation the negative 98mo excursions appear coincident with previously discovered and seemingly peculiar redox sensitive element rse patterns in the same sedimentary rocks we propose that these geochemical trends can be explained by some combination of a enhanced local marine oxygenation in the sedimentary basin where the doushantuo formation was originally deposited the nanhua basin and b changes in the degree of connectivity between this paleo basin and the open ocean enhanced local marine oxygenation by exposing more sediments in the nanhua basin to h2s poor conditions could have hindered quantitative tetrathiomolybdate formation within these sediments local marine oxygenation could have also stimulated the operation of a mn oxide shuttle today both of these processes are shown to promote the retention of lighter mass mo isotopes in sediments and also govern rse enrichment patterns alternatively or in addition the nanhua basin may not have maintained an uninterrupted connection with the open ocean during the entirety of the ediacaran period the negative 98mo excursions occur coincident with sea level highstands that could have also exposed more sediments in the basin to h2s poor conditions and or catalyzed the operation of a local mn oxide shuttle when trying to infer temporal changes in ancient global ocean redox it is important to consider the influence of sea level changes and associated variations in local depositional conditions on stratigraphic trends in rse enrichments and isotope compositions

trace element content of pyrite from the kapai slate st ives gold district western australia the kapai slate is a continuous pyrite rich carbonaceous shale horizon within the st ives au district that is spatially related to high grade au mineralization in situ laser ablation inductively coupled mass spectrometry la icpms trace element analyses in situ sensitive high resolution ion microprobe stable isotope shrimp si s isotope analyses and optical microscopy pyrite texture analyses were used to examine the different pyrite types in the kapai slate and au deposits these data were also used to confirm that the trace element signature of sedimentary pyrite can be preserved in rocks that underwent upper to mid greenschist facies metamorphism and significant hydrothermal overprint the data were further utilized to gain a more detailed understanding of the ocean conditions during deposition of the kapai slate and determine whether some of the au and s in the st ives district could have been sourced from the kapai slate seven different types of pyrite were identified fine grained sedimentary pyrite py 1 nodular sedimentary pyrite py 2 remobilized sedimentary pyrite py 3 coarse grained inclusions poor late pyrite py 4 inclusion rich magnetite series pyrite py 5 ore stage pyrite py 6 and pyrite associated with the mafic units py 7 each type of pyrite was found to have distinctive trace element compositions and s isotope signatures the results of the la icpms analyses provide evidence for early trace element enrichment in the kapai slate sedimentary pyrite median values of 158 ppm ni 387 ppm co 82 ppm cu 727 ppm as 1 91 ppm mo 13 ppm se 0 25 ppm au 7 72 ppm te and 3 36 ppm ag for py 1 and 223 ppm ni 158 ppm co 99 ppm cu 856 ppm as 1 27 ppm mo 10 2 ppm se 0 57 ppm au 10 09 ppm te and 6 62 ppm ag for py 2 concentrations of ni and co are low relative to other late archean sedimentary pyrite median of 813 and 465 ppm respectively and mo levels are near that of the euxinic shales of the similar aged jeerinah formation in the hamersley basin western australia these data suggest that the kapai slate was deposited in an anoxic to euxinic basin with relatively low biological productivity the 33 s and 34 s signatures of the sedimentary pyrite suggest two different sources of s positive 34 s and negative 33 s signatures indicate bacterial reduction of so 4 2 from seawater whereas positive 34 s and positive 33 s signatures indicate an elemental s 8 source indicating the pyrite formed later during diagenesis this s isotope signature is consistent with a transition between a near sediment environment to a more distal environment source analyses of the ore phase pyrite yield weakly positive 33 s values this suggests there was a minor contribution of sedimentary s to the more significant oxidized ore forming fluids which is consistent with a small contribution of au from a sedimentary source approximations of the degree of sedimentary pyrite destruction in the pyrrhotite pyrite dominated zones and pyrrhotite magnetite pyrite zones of the northern part of the st ives district were used to calculate the amount of au released from the early sedimentary pyrite the calculation suggests that a minor though possibly locally significant amount of au could have been sourced from the kapai slate

stratigraphic position of the ediacaran miaohe biota and its constrains on the age of the upper doushantuo δ13c anomaly in the yangtze gorges area south china abstract the siliceous shale unit that hosts the ediacaran miaohe biota in the yangtze gorges area commonly referred to as the miaohe member has an age of 551 0 7 ma this unit is thought to be time equivalent with the doushantuo member iv which marks the top of the upper doushantuo negative 13 c excursion new bio sequence and chemostratigraphic studies presented here demonstrate that the miaohe member is significantly younger than the doushantuo member iv most likely time equivalent with the lower shibantan member of the dengying formation the new findings indicate that the top of the doushantuo formation i e the top of the upper doushantuo shuram 13 c excursion should be much older than 551 ma likely 560 ma the ocean oxygenation event documented from the doushantuo member iv black shales should also be older than 560 ma and predate the miaohe biota for more than 10 ma

precambrian tectonics and crustal evolution in south india about 3 4 ga ago voluminous calc alkaline magmas represented by the granitoid gneisses of southern india were emplaced into a now poorly preserved non continental crust unstable ensialic basins initiated at about 3 0 ga were filled with volcanic and sedimentary rocks up to about 2 6 ga this basement cover sequence was deformed at the close of the archaean first by northward accretion and thickening of several crustal slabs formerly separated by prisms of stable shelf sediments structures produced by this episode were refolded and dislocated by large n s strike slip shear belts to impart intense steep planar fabrics to large volumes of the crust fluids rich in co possibly derived from sedimentary material driven beneath the crustal slabs by the thickening mechanism purged the deep crust of h o to form granulites upward migration of hot h o rich fluids encouraged partial melting at intermediate crustal levels these late archaean tectonic and thermal events began soon after the close of basin f

molybdenum contents of sulfides in ancient glacial diamictites implications for molybdenum delivery to the oceans prior to the great oxidation event abstract in order to determine whether sulfides are major reservoirs for mo in the upper continental crust ucc we determined the composition and mode of occurrence of sulfides and evaluated their contribution to the molybdenum budget in twelve glacial diamictites with ages ranging from 2900 to 300 ma the diamictites provide a snapshot of ucc mineralogy and composition at the time of their deposition and show systematic depletion in bulk rock mo concentrations after the great oxidation event goe reflecting the effects of oxidative weathering in their provenance gaschnig et al 2014 li et al 2016 sulfides are generally confined to archean and paleoproterozoic diamictites although they also have been found in one phanerozoic sample with an ancient provenance we classify the sulfides based on their compositions and morphologies detrital sulfides are generally rounded may be a single mineral or an assemblage of minerals and show a very wide range in mineralogy including a single molybdenite grain sedimentary sulfides are pyrites generally with framboidal like textures pyrites also include non framboidal textured authigenic pyrites epigenetic sulfides consist of irregular pyrrhotite aggregates sometimes pyrrhotite intergrown with chalcopyrite and cobaltite late stage euhedral pyrites and pyrite aggregates in veins high mo concentrations up to 230 ppm are found in some sedimentary framboidal like pyrites from the mesoarchean coronation and paleoproterozoic makganyene formations epigenetic pyrrhotite aggregates and chalcopyrite in the ramsay lake diamictite and in detrital sulfides in timeball hill diamictites that may have originated from hydrothermal fluids in the sedimentary basins other detrital sulfides have widely variable mo concentrations 0 5 36 ppm mass balance calculations show that sulfides can account for only

highly heterogeneous poikiloredox conditions in the early ediacaran yangtze sea abstract although there has been a sustained effort to reconstruct ocean redox conditions throughout the ediacaran a lack of high resolution data across time equivalent strata shelf to basin has hindered our ability to understand redox dynamics at the basinal scale we measured iron species trace and major element concentrations toc and corg p ratios of black shale from six high resolution sections from the early ediacaran yangtze sea i e the inner shelf jiulongwan outer shelf zhongling slope siduping and mingle and basinal yuanjia and long e sections which were integrated with published data from these sections and seven other correlative sections from the same region for a basinwide perspective on redox tracers these results document strong spatiotemporal redox variability during the early ediacaran including transitions between ferruginous euxinic suboxic and oxic conditions at high frequencies and short distances a pattern for which we coin the term poikiloredox conditions our results also suggest that multiple geochemical proxies including iron species redox sensitive trace element concentrations and enrichments and corg p ratios show different responses to poikiloredox conditions accounting for conflicting redox interpretations in early ediacaran studies this study thus demonstrates the importance of multiple proxies high stratigraphic resolution and a basin scale perspective in paleomarine redox studies underlining the potential for overgeneralization of redox patterns based on analysis of a single or a limited number of proxies or sections

p t grids for silica undersaturated granulites in the systems mas n 4 and fmas n 3 tools for the derivation of p t paths of metamorphism abstract considering the minerals cordierite cd sapphirine sa hypersthene hy garnet ga spinel sp sillimanite si and corundum co in the system feo mgo al2o3 sio2 fmas the stable invariant points are co ga cd and sa constraints imposed by experimental data for the system mas indicate that under low ph2o conditions the invariant points occur at high temperature 900 c and intermediate pressure 7 10 kbar this temperature is higher than that commonly advocated for granulite facies metamorphism in granulites fe mg exchange geothermometers may yield temperatures of 100 150 c below peak metamorphic conditions and evidence for peak temperatures is best preserved by relict high temperature assemblages and by al rich cores in orthopyroxene application of the fmas grid to some well documented granulite occurrences introduces important constraints on their p t histories rocks of different bulk compositions occurring in close proximity in the field may record distinct segments of their p t paths this applies particularly to rocks with evidence for reaction in the form of coronas symplectites and zoned minerals consideration of curved reaction boundaries and xms isopleths may explain apparently contradictory results for the stability of cordierite obtained from low temperature experiments and thermochemical calculations on the one hand and hightemperature experimental data on the other

the formation mechanisms of sedimentary pyrite nodules determined by trace element and sulfur isotope microanalysis abstract redox sensitive trace elements in pyrite including nodules are increasingly used to infer the chemical conditions of ancient oceans but considerable uncertainty remains regarding the mechanism and timing of nodule formation resolving these uncertainties is important because pyrite nodules must form in connection with the overlying water column rather than during late diagenesis to reflect the composition of the global ocean existing models for pyrite nodule formation have been specific to pyrite textures from individual sites and we lack a unified model that can explain the compositional and textural diversity observed in nodules from different localities in this study we examine ten pyrite nodules from several geological periods neoarchean to carboniferous using in situ la icp ms and shrimp si analyses we present transects of spot analyses of trace elements as ag cu co ni sb and se and s isotope ratios for each nodule the pyrite nodules can be classified according to three main categories those with 1 little to no trace element or isotopic zonation of the nodule from core to margin 2 strong zonation from core to margin and 3 minor zonation near the core but more significant zonation near the margin of the nodule we further illustrate this zonation with a nanosims element map from an additional pyrite nodule these results are interpreted to indicate nodule formation along a spectrum between two end member mechanisms we suggest that the absence of trace element or isotopic zonation reflects nodule growth by a pathway that is analogous to the pervasive growth mechanism for carbonate nodules this model involves the production of many nucleation sites that are evenly distributed within the volume that the nodule eventually occupies consequently this mechanism results in a chemically homogenous nodule pyrites formed this way are suitable for paleoceanographic reconstruction the other end member mechanism is analogous to the concentric growth model for carbonate concretions in this scenario the core of the nodule forms first and is followed by the addition of concentric layers each with a progressively different trace element content and 34s signature as diagenesis progresses despite having limited utility for reconstructing ancient seawater these late forming nodules may track the evolving availability of bioessential trace elements for the subsurface biosphere with important implications for global biogeochemical cycles spatial trends in trace elements and s isotopes thus speak to the mechanisms of pyrite nodule formation and provide a framework for evaluating nodule suitability for a range of paleoenvironmental studies

pyrite as a record of hydrothermal fluid evolution in a porphyry copper system a sims empa trace element study porphyry copper deposits are currently the world s largest source of copper and molybdenum and are also among the largest reservoirs of gold in the upper crust despite the fact that pyrite is a ubiquitous mineral phase in these deposits and secondary cu enrichment processes are commonly controlled by the abundance of this sulfide the major and trace element chemistry of pyrite from porphyry systems remains unconstrained in this study we report the first comprehensive trace element database of pyrite from the dexing deposit china s largest porphyry cu deposit by combining high spatial resolution and x ray mapping capabilities of electron microprobe analysis empa with low detection limits and depth profiling capabilities of secondary ion mass spectrometry sims in a suite of samples from the dexing deposit we show that the concentrations of precious metals e g au ag metalloids e g as sb se te and heavy metals e g cu co ni zn hg in pyrite from porphyry systems are more significant than previously thought among the elements analyzed cu as au and ni are the most abundant with concentrations that vary from sub ppm levels to a few wt i e 6 wt cu 3 wt as 0 25 wt au and 0 2 wt ni detailed wavelength dispersive spectrometry wds x ray maps and sims depth vs isotope concentration profiles reveal that pyrite from the dexing deposit is characterized by complex chemical zoning where the studied elements occur in different mineralogical forms while as occurs as a structurally bound element in pyrite cu and au can occur as both solid solution and micro to nano sized particles of chalcopyrite and native au or au tellurides respectively indicating that pyrite can control metal speciation and partitioning during porphyry cu mineralization the well developed oscillatory zoning detected in pyrite where cu rich as depleted growth zones alternate with cu depleted as rich layers indicates that cu is geochemically decoupled from as suggesting that this selective partitioning of metals into pyrite is most likely the result of changes in hydrothermal fluid composition

crustal trajectory of sapphirine bearing granulites from ganguvarpatti south india evidence for an isothermal decompression path abstract ganguvarpatti is part of a precambrian terrane characterized by granulite facies rocks including charnockites mafic granulites sapphirine bearing granulites leptynites and gneisses a sequence of reactions deduced from the multiphase reaction textures provide information on the metamorphic history of this area as they formed in response to decompression during uplift geothermobarometry and constraints from reaction textures define a segment of a p t path traversed by the granulites of ganguvarpatti near peak metamorphic conditions of c 800 c and 8 kbar were succeeded by a symplectitic stage at a significantly lower pressure c 700 c and 4 5 kbar documenting a nearly isothermal decompression p t path and rapid uplift c 12 km followed by cooling the presence of many fluid inclusions of extremely low density in the charnockites is consistent with a nearly isothermal uplift path attainment of a maximum pressure of c 8 kbar indicates c 27 km depth of burial during metamorphism this would imply a total crustal thickness of c 65 70 km at 2 6 2 5 ga such a profound crustal thickness and a clockwise decompressive p t path is interpreted as a consequence of tectonic thickening of crust accomplished by collision tectonics of the southern granulite terrane against the dharwar craton along the palghat cauvery shear zone via northward subduction

the coupled geochemistry of au and as in pyrite from hydrothermal ore deposits the ubiquity of au bearing arsenian pyrite in hydrothermal ore deposits suggests that the coupled geochemical behaviour of au and as in this sulfide occurs under a wide range of physico chemical conditions despite significant advances in the last 20years fundamental factors controlling au and as ratios in pyrite from ore deposits remain poorly known here we explore these constraints using new and previously published empa la icp ms sims and pixe analyses of as and au in pyrite from carlin type au epithermal au porphyry cu cu au and orogenic au deposits volcanogenic massive sulfide vhms witwatersrand au iron oxide copper gold iocg and coal deposits pyrite included in the data compilation formed under temperatures from 30 to 600 c and in a wide variety of geological environments the pyrite au as data form a wedge shaped zone in compositional space and the fact that most data points plot below the solid solubility limit defined by reich et al 2005 indicate that au1 is the dominant form of au in arsenian pyrite and that au bearing ore fluids that deposit this sulfide are mostly undersaturated with respect to native au the analytical data also show that the solid solubility limit of au in arsenian pyrite defined by an au as ratio of 0 02 is independent of the geochemical environment of pyrite formation and rather depends on the crystal chemical properties of pyrite and post depositional alteration compilation of au as concentrations and formation temperatures for pyrite indicates that au and as solubility in pyrite is retrograde au and as contents decrease as a function of increasing temperature from 200 to 500 c based on these results two major au as trends for au bearing arsenian pyrite from ore deposits are defined one trend is formed by pyrites from carlin type and orogenic au deposits where compositions are largely controlled by fluid rock interactions and or can be highly perturbed by changes in temperature and alteration by hydrothermal fluids the second trend consists of pyrites from porphyry cu and epithermal au deposits which are characterised by compositions that preserve the au as signature of mineralizing magmatic hydrothermal fluids confirming the role of this sulfide in controlling metal ratios in ore systems

comparison of metal enrichment in pyrite framboids from a metal enriched and metal poor estuary the accumulation of metals and metalloids in diagenetic pyrite framboids is of interest because framboids can be a sink for heavy metal contaminants a source of metals in ore deposits and a tool to interpret paleo ocean chemistry in this study we have used laser ablation inductively coupled plasma mass spectrometry la icpms to analyze pyrite framboids from both the contaminated derwent estuary and the uncontaminated huon estuary in tasmania australia while the enrichment of many trace metals in the huon estuary followed expected trends the trends in the derwent were quite different in addition to the expected high contents of pb zn and cu in the contaminated interval it was found that several elements are not as strongly incorporated into pyrite within the contaminated zone it is suggested that this is due to over competition for adsorption sites on the growing iron sulfides in the contaminated zone resulting in diffusion of several elements to deeper levels in the sediments this results in an increase of these elements in pyrite below the zone of major contamination the la icpms technique also provided the opportunity to obtain accurate data on gold silver and tellurium in pyrite something rarely achieved in sequential leach extractions due to the low concentrations of these metals observed in nature

pyrite morphology and redox fluctuations recorded in the ediacaran doushantuo formation abstract recent geochemical studies of the doushantuo formation ca 635 551 ma in south china suggested that the ediacaran ocean was strongly stratified with an oxic surface layer above a euxinic wedge that was sandwiched within ferruginous deep waters this ocean redox model however was derived largely from the data obtained from stratigraphic sections in the yangtze gorges area that according to recent paleogeographic reconstruction were deposited in a restricted intrashelf lagoon in order to test the redox conditions in open ocean deep water environments we have conducted a detailed morphological analysis of authigenic pyrites from the upper to lower slope sections of the doushantuo formation in analogy to modern euxinic basins such as the black sea framboidal pyrites with smaller and less variable size distribution are taken as evidence for sulfide precipitation in euxinic water column while larger and more variable framboidal and euhedral pyrites are formed or diagenetically altered in sediments with an overlying oxic dysoxic water column except for a few brief intervals pyrites from the doushantuo formation in upper slope sections siduping and taoying sections are mainly of early diagenetic origin and do not record water column euxinia during deposition in contrast pyrites from the doushantuo formation in the lower slope section wuhe section are dominated by fine grained framboids indicative of pervasive water column euxinia below chemocline in both upper and lower slope sections temporal changes in genetic pyrite types occur at centimeter to decameter scales suggesting frequent chemocline fluctuations the overall decrease in abundance of framboidal pyrites toward the upper doushantuo formation in upper slope sections suggests increasing water column oxygenation and deepening of the chemocline macroalgae and metazoan fossils are found mainly from shale intervals without syngenetic pyrites in upper slope sections indicating the sensitivity of macroscopic eukaryotes to the ocean chemocline the redox fluctuations recorded by the doushantuo pyrites compels for comprehensive geochemical data in deep water successions to further test the existing paleoceanographic models of the ediacaran ocean

origin of the triassic qilinchang pb zn deposit in the western yangtze block sw china insights from in situ trace elemental compositions of base metal sulphides abstract the qilinchang pb zn deposit 5mt of sulphide ore at mean grades of 2 3 9 2 pb and 2 7 22 5 zn is hosted in early carboniferous carbonate rocks and mainly controlled by ne ns and nw trending structural belts between the xiaojiang and zhaotong qujing buried faults ore minerals are sphalerite galena pyrite chalcopyrite and marmatite whereas gangue minerals are dolomite calcite and quartz three generations of pyrite are recognized these include fine grained anhedral pyrite py i medium grained anhedral to subhedral hydrothermal pyrite py ii and coarse grained subhedral to euhedral hydrothermal pyrite py iii while the sphalerite occurs in two forms as fine grained intergrown with galena and associated with py i and py ii laser ablation inductively coupled plasma mass spectrometry la icp ms analysis was performed to evaluate trace element compositions of pyrite and sphalerite from different generations of ores py i has relatively higher concentrations of mg mn co ni and tl py ii in cu as se mo and sb relative to pyrite of other generations the contents of trace elements in py iii are variable but significantly enriched in ti v bi ag and pb compared to py i and py ii this variation indicates that these elements occur as micro mineral inclusions of possible ag pb bearing phases sphalerite of stage i has higher concentrations of mn fe co ni cu ga ge as ag cd in sb hg and pb than stage ii these elements are homogeneously distributed in all samples analyzed the incorporation of these elements is primarily through simple substitution mechanisms e g 2zn2 cu in3 as indicated from binary plots principal component analyses pca applied to la icp ms dataset for pyrite reveal two main clusters py i enriched in ni co and as py ii and py iii high in with v mn cu zn se mo ag sb au and bi likewise the pca also confirms two clusters of elements for sphalerite ge cu as sb ag fe and cd corresponding to sph i and in sn and ga corresponding to sph ii py i has higher co ni ratio ranging from 0 04 to 1 6 compared to py ii and py iii having co ni ratios from 0 to 0 706 and 0 0 696 respectively we report that the pyrites from the qilinchang deposit have co ni ratios slightly lower than typical mississippi valley type mvt deposits 0 2 7 2 and different from iron oxide copper gold iocg and porphyry cu deposits considering these geochemical signatures it can be suggested that the qilinchang deposit was not related to magmatic activities we thus propose that the ore forming fluids responsible for the formation of the deposit were generated from a low temperature environment similar to typical mvt deposits

internally consistent recalibrations of mineral equilibria for geothermobarometry involving garnet orthopyroxene plagioclase quartz assemblages and their application to the south indian granulites abstract three reactions are calibrated as geothermobarometers for garnet orthopyroxene plagioclase quartz assemblages namely 1 2 ferrosilite 1 3 pyrope 1 2 enstatite 1 3 almandine a ferrosilite anorthite 2 3 almandine 1 3 grossularite quartz b and enstatite anorthite 2 3 pyrope 1 3 grossularite quartz c the internally consistent geothermobarometers based on reactions a b and c are calibrated from experimental data only the thermodynamic parameters of reaction a are derived from published experimental data in the fmas system n 104 in the range 700 1400 c and 5 50 kbar while those for reaction b are derived by summation of the existing reversed experimental data of the mineral equilibria ferrosilite fayalite quartz d and anorthite fayalite 2 3 almandine 1 3 grossularite e the retrieved thermodynamic parameters for reactions a b and c are respectively h0 cal 3367 209 2749 350 and 3985 545 s0 cal k 1 1 634 0 163 8 644 0 298 and 5 376 0 391 and v01 298 cal bar 1 0 024 0 60946 and 0 5614 on a one cation basis the derived margules parameters of the ternary ca fe mg in garnet are wfe mg 1256 1 0 0 23 t k wmg fe 2880 1 7 0 13 t k wca mg 4047 77 1 5 t k wmg ca 1000 77 1 5 t k wca fe 723 0 332 0 02 t k wfe ca 1090 cal and the ternary constant c123 4498 1 516 0 265 t k cal subregular solution model of non ideal mixing and fe mg al in orthopyroxene wfe mg 948 200 0 34 0 10 t k wfe al 1950 500 and wmg al 0 cal regular solution model of non ideal mixing the anorthite activity in plagioclase is calculated by the al avoidance model of subregular ca na mixing commonly used for geobarometry based on reactions b and c when the geothermobarometers are applied to garnet orthopyroxene plagioclase quartz assemblages n 45 of wide compositional range from the precambrian south indian granulites temperature ranges of 690 860 c x 760 45 c and pressure ranges of 5 10 kbar were obtained the p t values were estimated simultaneously and there is no difference in the pressure calculated from pmg reaction c and pfe reaction b in the existing calibrations this difference is 1 kbar or more furthermore there is no compositional dependence of the ln k of the experimental data in the fmas n 104 and the cfmas n 78 systems at different temperatures and the estimated temperatures of the south indian granulites