petrographic observations of iron copper and zinc sulfides in freshwater canal sediment abstract sulfide minerals are known to be important hosts for metals in many freshwater and marine sediments but little is known about their petrography particularly in fine grained recent freshwater sediments in this paper the results of a cryogenic sem investigation of sulfide textures in two fine grained anaerobic canal bed muds are reported the technique allows direct observation of the undisrupted mineral and organic textures in the canal bed mud iron sulfides occur in two forms coatings on biofilms and framboids iron sulfide coated biofilms have iron sulfur ratios in the range fes to fe3s4 framboid structures display a continuum of textures from greigite proto framboids with a poorly developed crystallite texture to pyrite framboids with well developed crystallites proto framboids tend to be smaller than framboids a positive correlation was observed between crystallite diameter and framboid diameter by dividing the framboid diameter by the crystallite diameter it was deduced that framboids tend not to have single crystallites at their centers copper occurs as a discrete sulfide with a composition similar to chalcopyrite zinc occurs as a zinc iron sulfide with metal to sulfur ratios in the range 0 59 to 0 87 copper sulfides tend to nucleate on surfaces whereas the zinc sulfides occur both on surfaces and as floccular precipitates in open pore space

new observations of ambient inclusion trails aits and pyrite framboids in the ediacaran doushantuo formation south china ambient inclusion trails aits are intriguing microtubular structures that commonly occur in association with pyrite in precambrian organic rich cherts and phosphorites they are thought to be created by the migration of pyrite or other crystal grains through a lithified substrate driven by pressure solution from the in situ thermal decomposition of organic matter new phosphorite samples of the ediacaran doushantuo formation south china contain abundant aits exhibiting diverse morphotypes which may be distinguished from filamentous microfossils and endolithic microborings with a suite of morphological criteria based on optical microscopy and scanning electron microscopy sem black shales of the baizhu section contains abundant pyrite framboids whose size distributions reveal significant temporal variations of redox conditions in shallow marine waters that probably promoted the formation of the doushantuo phosphorites aits in the phosphorites are categorized into three types and further into five subtypes i a i b ii a ii b and iii based on their morphologies and observed or interpreted associations with various kinds of terminal pyrite crystals among these subtype ii a single striated microtubes 2 10 m wide are interpreted to have resulted from migration of intact pyrite framboids those of subtype ii b dense clusters of outward radiating microtubes with consistent widths and inward facing cuspate ridges likely have formed by explosive disintegration and propulsion of pyrite framboids due to highly concentrated carbon dioxide gas during the oxidation of organic matter during early diagenesis formation of euhedral and framboidal pyrites involve a suite of biogeochemical and physical processes including non biological oxidation of organic matter and reduction of sulfate in the presence of ferrous iron following the burial of pyrites further oxidative degradation of organic matter produced abundant co2 gas which drives the pyrites to move through the solid but not yet fully lithified phosphatic gel composing granules this model explains the formation of previously reported but unexplained star burst type aits and it may be tested by experimental studies our new observations provide evidence for the widespread occurrence of aits in the doushantuo phosphorites and urge careful petrographic examinations and differentiation between aits and morphologically similar biogenic microstructures

unravelling the formation histories of placer gold and platinum group mineral particles from corrego bom successo brazil a window into noble metal cycling abstract gold and platinum group metals pgm are cycled through earth s environments by interwoven geological physical chemical and biological processes leading to the trans neoformation of metallic particles in placers the placer deposit at corrego bom successo cbs brazil is one of the few localities worldwide containing secondary gold and pgm particles placer gold consists of detrital particles from nearby hydrothermal deposits that were transformed in the surface environment processes that have affected these particles include short distance transport chemical de alloying of the primary gold silver and bio geochemical dissolution re precipitation of gold leading to the formation of pure secondary gold and the dispersion of gold nanoparticles the latter processes are likely mediated by non living organic matter om and bacterial biofilms residing on the particles the biofilms are largely composed of metallophillic and proteobacteria abundant mobile gold and platinum nanoparticles were detected in surface waters suggesting similar mobilities of these metals earlier hydrothermal processes have led to the formation of coarsely crystalline arborescent dendritic potarite pdhg on potarite surfaces biogeochemical processes have then led to the formation of platinum and palladium rich micro crystalline layers which make up the botryoidal platinum palladium aggregates subsequently potarite was dissolved from the core of many aggregates leaving voids now often filled by secondary anatase tio2 containing biophilic elements the presence of fungal structures associated with the anatase suggests that fungi may have contributed to its formation for the first time a primary magmatic pgm particle comprising a mono crystalline platinum palladium alloy with platinum iridium osmium inclusions was described from this locality finally defining a possible primary source for the pgm mineralisation in conclusion the formation of modern day placer gold and pgm particles at cbs began 100s of millions of years ago by magmatic and hydrothermal processes these provided the metal sources for more recent biogeochemical cycling of pges and gold that led to the trans neoformation of gold and pgm particles

formation processes of framboidal pyrite abstract pyrite framboid formation may be the result of four consecutive processes 1 nucleation and growth of initial iron monosulfide microcrystals 2 reaction of the microcrystals to greigite fe 3 s 4 3 aggregation of uniformly sized greigite microcrystals i e framboid growth and 4 replacement of greigite framboids by pyrite the uniform morphology uniform size range and ordering of the microcrystals in individual framboids as well as the range of observed framboid structures from irregular aggregates to densely packed spherical aggregates and polyframboids are consequences of these processes using dlvo theory derjaguin landau verwey and overbeek we have evaluated the stability of colloidal iron monosulfide suspensions with ionic strengths typical of marine and lacustrine waters in addition to van der waals attractive and double layer repulsive forces a term is included to account for the ferrimagnetic properties of greigite numerical models predict that magnetically saturated greigite particles 0 1 m in diameter will rapidly aggregate in either marine or fresh water the aggregation model is in agreement with the sequence of greigite formation followed by pyrite framboid formation established in a previous experimental study sweeney and kaplan 1973 and is consistent with the occurrence of framboids composed of other magnetic minerals e g greigite magnetite and magnesioferrite based on the temperature dependent magnetic properties of greigite and aging experiments in hydrothermal solutions this mechanism for framboid formation via precursor greigite could operate to temperatures of 200 c consistent with the occasional occurrence of pyrite framboids in the paragenesis of metalliferous ore deposits

composition and pore characteristics of black shales from the ediacaran lantian formation in the yangtze block south china the ediacaran period was critical in the evolution of the biosphere and ocean in the history of the earth shales rich in organic matter om are well developed for this period in the yangtze block china and have recently been related to shale gas exploration in south china to date detailed characterisation of the ediacaran shales is not available the present work sets out a detailed investigation of the composition and pore characteristics of samples from a shallow drill core in the ediacaran lantian formation in the lower yangtze area and the effects of shale composition on the pore growth are discussed the 90 m thick lantian black shales are highly over mature equivalent vitrinite reflectance evro value approximately 4 0 with a total organic carbon toc content up to 12 they are dominated by quartz 33 72 generally with low clay or feldspar content bulk porosities of the shales range from 1 0 to 7 9 and are positively correlated with toc content high magnification scanning electron microscopy sem images support the crucial importance of om content on pore development generally pore volume shows excellent positive correlation with toc content for micropores good correlation for mesopores and relatively poor correlation for macropores two samples with mostly high toc content showed very low macropore volume and medium mesopore volume these results suggest a close relationship between om with relatively small pores and enhanced compaction effect on large pores in highly om enriched shales

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

accumulation of transition metals and metalloids in sulfidized stromatolites of the 3 48 billion year old dresser formation pilbara craton abstract stromatolites of the 3 48 billion year old dresser formation pilbara craton western australia provide some of the oldest convincing evidence of life on earth here we augment previous evidence with a detailed investigation of the concentrations and distributions of various transition metals cr mn co ni cu zn mo se ag sn au hg and pb and metalloids as sb and te in unweathered samples of strongly sulfidized stromatolites from drill cores high resolution elemental mapping and in situ compositional analysis of sulfides pyrite and sphalerite show that these sedimentary and hydrothermally sourced elements are strongly concentrated in texturally distinctive nano porous pyrite enriched in autochthonous organic matter which forms the major petrogenetically earliest component of wrinkly laminated and digitate growth fabrics within the stromatolites repeated cyclic alternations of various transition metals and metalloids most importantly ni and zn plus the presence of disconformities and overgrowth relationships between wrinkly stromatolite laminae suggest that these element accumulations were primarily established by depositional processes during continuous stromatolite formation because transition metals and metalloids generally have strong affinities for organic matter and can play active roles in biochemical processes we interpret these element accumulations in the dresser formation stromatolites to be the result of binding to organic matter of living microbial communities and or dead biomass and perhaps also microbial utilization collectively our results show that the precise characterization of transition metal metalloid concentrations and distributions can unveil element enrichment patterns suggestive of biological activity even in some of earth s oldest stromatolites

resolving miss conceptions and misconceptions a geological approach to sedimentary surface textures generated by microbial and abiotic processes the rock record contains a rich variety of sedimentary surface textures on siliciclastic sandstone siltstone and mudstone bedding planes in recent years an increasing number of these textures have been attributed to surficial microbial mats at the time of deposition resulting in their classification as microbially induced sedimentary structures or miss research into miss has developed at a rapid rate resulting in a number of misconceptions in the literature here we attempt to rectify these miss misunderstandings the first part of this paper surveys the stratigraphic and environmental range of reported miss revealing that contrary to popular belief there are more reported miss bearing rock units of phanerozoic than precambrian age furthermore miss exhibit a pan environmental and almost continuous record since the archean claims for the stratigraphic restriction of miss to intervals prior to the evolution of grazing organisms or after mass extinction events as well as claims for the environmental restriction of miss appear to result from sampling bias in the second part of the paper we suggest that raised awareness of miss has come at the cost of a decreasing appreciation of abiotic processes that may create morphologically similar features by introducing the umbrella term sedimentary surface textures of which miss are one subset we suggest a practical methodology for classifying such structures in the geological record we illustrate how elucidating the formative mechanisms of ancient sedimentary surface textures usually requires consideration of a suite of sedimentological evidence from surrounding strata resultant interpretations microbial or non microbial should be couched within a reasonable degree of uncertainty this approach recognizes that morphological similarity alone does not constitute scientific proof of a common origin and reinstates a passive descriptive terminology for sedimentary surface textures that cannot be achieved with the current miss lexicon it is hoped that this new terminology will reduce the number of overly sensational and misleading claims of miss occurrence and permit the means to practically separate initial observation from interpretation furthermore this methodology offers a scientific approach that appreciates the low likelihood of conclusively identifying microbial structures from visual appearance alone informing the search for true miss in earth s geological record and potentially on other planetary bodies such as mars

the depth of the convective boundary layer on mars abstract we are using observations obtained with mars express to explore the structure and dynamics of the martian lower atmosphere we consider a series of radio occultation experiments conducted in may august 2004 when the season on mars was midspring of the northern hemisphere the measurements are widely distributed in latitude and longitude but the local time remained within a narrow range 17 0 17 2 h most of the atmospheric profiles retrieved from these data contain a distinct well mixed convective boundary layer cbl we have accurately determined the depth of the cbl and its spatial variations at fixed local time through analysis of these profiles the cbl extends to a height of 3 10 km above the surface at the season and locations of these measurements its depth at fixed local time is clearly correlated with variations in surface elevation on planetary scales with a weaker dependence on spatial variations in surface temperature in general the cbl is deep 8 10 km where the surface elevation is high as in tharsis montes and syrtis major and shallow 4 6 km where the surface elevation is low as in amazonis and utopia this variability results from the combined effects of conditions near the surface and in the atmosphere above the cbl convection arises from solar heating of the ground and the impact of this heat source on thermal structure is largest where the surface pressure and atmospheric density are smallest at high surface elevations the vertical extent of the cbl is in turn constrained by the static stability of the overlying atmosphere these results greatly reduce the long standing uncertainty concerning the depth of the cbl

microfossils of sulphur metabolizing cells in 3 4 billion year old rocks of western australia sulphur isotope data from early archaean rocks suggest that microbes with metabolisms based on sulphur existed almost 3 5 billion years ago leading to suggestions that the earliest microbial ecosystems were sulphur based 1 5 however morphological evidence for these sulphur metabolizing bacteria has been elusive here we report the presence of microstructures from the 3 4 billion year old strelley pool formation in western australia that are associated with micrometre sized pyrite crystals the microstructures we identify exhibit indicators of biological affinity including hollow cell lumens carbonaceous cell walls enriched in nitrogen taphonomic degradation organization into chains and clusters and 13 c values of 33

interpretation of the nitrogen isotopic composition of precambrian sedimentary rocks assumptions and perspectives nitrogen isotope compositions in sedimentary rocks d 15 n sed are routinely used for reconstructing cenozoic n biogeochemical cycling and are also being increasingly applied to understanding the evolution of ancient environments here we review the existing knowledge and rationale behind the use of d 15 n sed as a proxy for the precambrian n biogeochemical cycle with the aims of i identifying the major uncertainties that affect analyses and interpretation of nitrogen isotopes in ancient sedimentary rocks ii developing a framework for interpreting the precambrian d 15 n sed record iii testing this framework against a database of precambrian d 15 n sed values compiled from the literature and iv identifying avenues of focused research that should increase confidence in interpreting precambrian d 15 n sed data this review highlights the intrinsic complexity of the d 15 n sed proxy and the significant effort that remains to realize its potential specifically it is crucial to gain a better understanding of how and when diagenesis and metamorphism affect the d 15 n of bulk and kerogen bound nitrogen ultimately more data are required to apply statistics to interpreting d 15 n sed variability within given geological time intervals finally numerical modeling of the d 15 n sed variability expected in different environments under varying redox scenarios is necessary to establish a predictive template for interpreting the ancient nitrogen isotope record in spite of the challenges facing the application of this proxy to the precambrian the existing d 15 n sed record shows several features possibly related to the stepwise oxygenation of the surface environment underlining the potential for nitrogen isotopes to reveal clues about the evolution of early earth

sulfur isotope evidence for a paleoarchean subseafloor biosphere barberton south africa the archean sub seafloor has been proposed as an environment for the emergence of life with septate clusters of titanite microtextures in pillow lava rims argued to be the earliest traces of microbial microboring here we use nanoscale secondary ion mass spectrometry nanosims to test possible geochemical traces of life in ca 3 45 ga pillow lavas of the barberton greenstone belt south africa sulfide inclusions in the titanite microtextures record strongly negative sulfur isotope fractionations of 34 s vcdt 39 8 to 3 2 vcdt vienna canyon diablo troilite these represent the largest range and most negative 34 s values so far reported from the archean and are consistent with an early biogenic origin for the sulfides extensive in situ elemental mapping did not find any organic linings associated with the microtextures despite the high spatial resolution and sensitivity of the nanosims the absence of organic linings thus excludes a key line of evidence previously used to support the biogenicity of the microtextures in contrast in situ sulfur isotope analysis of basalt hosted sulfides provides an alternative approach to investigating the existence and nature of an archean subseafloor biosphere

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

sulfidization of 3 48 billion year old stromatolites of the dresser formation pilbara craton constraints from in situ sulfur isotope analysis of pyrite abstract this study reports in situ sulfur isotope analyses 32s 33s 34s and 36s of pyrite in strongly sulfidized stromatolites from the 3 48 billion year old dresser formation pilbara craton australia these data shed light on sulfur reservoirs and sulfide precipitation processes and provide clues for the contribution of sulfur cycling microbes to sulfidization sulfur isotope signatures derived from mass dependent fractionation mdf monitored by 34s and mass independent fractionation mif here 33s and 36s of pyrite in stromatolites and of microscopic pyrite within associated barite allow for the identification of distinctive sulfur sources i magmatic hydrothermal sulfide h2s with 34s and 33s 0 ii magmatic hydrothermal sulfate so42 with a mdf signature mdf so42 34s 10 and 33s 0 iii photochemically derived sulfate with a mif signature mif so4 34s 6 and 33s 3 0 iv photochemically derived elemental sulfur s0 with 34s 0 and 33s 0 the sulfur isotope data suggest that sulfidization was largely driven by reduction of intermixed mdf so42 and mif so42 bulk signature of 34s 5 and 33s 1 4 and dilution of produced h2s 34s 12 and 33s 1 4 by native h2s in magmatic hydrothermal fluids the 34s shifts up to 17 generated by sulfate reduction are consistent with both thermochemical reactions and influence of sulfate cycling microbes the latter which may have facilitated rapid pyrite precipitation and preservation of microbial remains that are entombed within the petrogenetically earliest pyrite generation of stromatolites collectively our data are consistent with ancient stromatolite growth in proximity to shallow marine hydrothermal vents where hydrothermal fluids contributed to sulfidization that may have been further influenced by sulfur cycling microbes

pathways for neoarchean pyrite formation constrained by mass independent sulfur isotopes it is generally thought that the sulfate reduction metabolism is ancient and would have been established well before the neoarchean it is puzzling therefore that the sulfur isotope record of the neoarchean is characterized by a signal of atmospheric mass independent chemistry rather than a strong overprint by sulfate reducers here we present a study of the four sulfur isotopes obtained using secondary ion ms that seeks to reconcile a number of features seen in the neoarchean sulfur isotope record we suggest that neoarchean ocean basins had two coexisting significantly sized sulfur pools and that the pathways forming pyrite precursors played an important role in establishing how the isotopic characteristics of each of these pools was transferred to the sedimentary rock record one of these pools is suggested to be a soluble sulfate pool and the other pool atmospherically derived elemental sulfur is suggested to be largely insoluble and unreactive until it reacts with hydrogen sulfide we suggest that the relative contributions of these pools to the formation of pyrite depend on both the accumulation of the insoluble pool and the rate of sulfide production in the pyrite forming environments we also suggest that the existence of a significant nonsulfate pool of reactive sulfur has masked isotopic evidence for the widespread activity of sulfate reducers in the rock record

taphonomy of very ancient microfossils from the 3400ma strelley pool formation and 1900ma gunflint formation new insights using a focused ion beam abstract focused ion beam fib milling permits the accurate extraction of ultrathin c 100 nm cross sectional lamellae from microfossils found in geological thin sections subsequent tem analysis of these lamellae can provide unique insights into the ultrastructure chemistry and taphonomy of precambrian microfossils at the micrometer to nanometer scale combining serial fib milling with sem imaging extends this capability to three dimensional 3d tomographic reconstruction and visualization of precambrian microfossils revealing information not available in light microscopy here we apply these techniques to two iconic silicified microfossil assemblages from the 3400 ma strelley pool formation of western australia and the 1900 ma gunflint formation of canada all the examined microfossils have carbonaceous walls surrounded by pure silica impregnation of microfossil walls by nano grains of silica is common together with variable degrees of wall displacement and replacement by silica all microfossils are rigidly preserved in 3d and show little or no folding or compression however there are also notable differences in taphonomic preservation our examples of the spheroidal gunflint microfossil huroniospora showed the highest fidelity of preservation with a continuous carbonaceous wall fossilized by spheroidal nano silica grains that resemble those found on bacterial surfaces in modern silicifying hot spring environments the nucleation of these silica nano spheres on the microfossil walls has induced an artificial saw tooth like ridged wall texture that may subsequently hinder species level identification the strelley pool microfossils in comparison show a lower fidelity of preservation with small parts of the microfossil walls completely replaced by silica plus extensive recrystallization of spheroidal silica nano grains to angular micro quartz our examples of the sheath like filamentous gunflint microfossil siphonophycus showed the lowest fidelity of preservation with many gaps in the carbonaceous walls and significant redistribution of carbon by recrystallizing silica grains a model is presented to explain these observations criteria for distinguishing highly probable microfossils from non cellular carbonaceous microstructures e g botryoids and grain coatings using fib based imaging are put forward for the first time here using examples drawn from the strelley pool formation and comparisons with younger gunflint material the combined in situ techniques of fib tem and fib sem nano tomography potentially provide a wealth of new nano scale information regarding the biogenicity antiquity and taphonomy of precambrian microfossils however the destructive nature of both techniques makes their application to unique palaeontological specimens problematical

microbial structures and possible bacterial sulfide fossils in the giant jinding zn pb deposit yunnan sw china insights into the genesis of zn pb sulfide mineralization abstract the jinding zn pb sulfide deposit lanping yunnan china is one of the youngest sediment hosted giant zn pb deposit in the world it is also a well known deposit in china the large scale of the mineralization and especially the huge volume of h 2 s that was required to precipitate the zn pb sulfide are of great interest to ore geologists ore microscopy shows microbial structures such as framboidal sphalerite spherical aggregates of galena sphalerite oolite sphalerite dendritic colloidal sphalerite pyrite metacolloidal sphalerite pyrite multinuclear metacolloidalring like sphalerite pyrite botryoidal sphalerite pyrite framboidal pyrite and bacterial plate like of galena sphalerite detailed observations and analyses of the microbial structures at micron to nanometer scales by field emission scanning electron microscopy fesem and energy dispersive spectrometry eds reveal that the bacteria fossils are composed of sphalerite galena or pyrite or of multiple sulfide minerals with calcite and that they are distributed in bacterial colonies in the ore the individual bacteria fossils are spherical botryoidal or ring like with a diameter of 200 500 nm filamentous mucoid and tubular extracellular polymeric substances eps are commonly observed that are closely associated with and have the same composition as the bacteria fossils secondary ion microprobe analysis sims by in situ sulfur micro isotopic analysis of the microbial sulfide structures and bacteria fossils yield 34 s v cdt values varying from 48 6 to 9 5 per mil indicating that there was a high percentage of sulfate reducing bacteria in the zn pb sulfide mineralization process previous analyses have shown that the zn pb mineralization was formed at a shallow depth and low temperature with barely visible hydrothermal alteration the presence of evaporitic sulfate layers and paleo oil reservoir characteristics the authors believe that bacterial sulfate reduction might be the key h 2 s production mechanism in the jinding dome that was required to form this giant pb zn sulfide ore body

the fluid evolution of the nimbus ag zn au deposit an interplay between mantle plume and microbial activity abstract the nimbus ag zn au volcanic hosted massive sulfide vhms deposit represents an exceptional orebody in the yilgarn craton of western australia it is located in a zone of juvenile crust running n s through the eastern goldfields superterrane however unlike most other vhms occurrences associated with the 2690 2680 ma rift sequence teutonic bore jaguar bentley erayinia it is hosted by the ca 2705 ma plume related stratigraphy which is more typically associated with komatiite hosted nickel sulfide mineralization the nimbus deposit displays hybrid vhms epithermal characteristics resulting from low temperature and shallow water conditions which developed a quartz carbonate sericite dominated alteration assemblage in the dacite host rocks sulfide mineralization comprises pyrite sphalerite galena arsenopyrite ag sb pb bi sulfosalts and rare chalcopyrite in this study we applied a combination of in situ analytical techniques to monitor the evolving sulfur isotope signature of the mineralizing fluids and propose that the nimbus vhms deposit developed as a result of a bimodal fluid history in the first stage the hydrothermal system powered by plume related magmatism deposited a series of barren pyrite lenses with colloform textures their variable but consistently negative mass independent sulfur isotope fractionation signature 33s 0 81 reflects the interaction between mantle derived magmatic fluids and archean seawater the ubiquitous presence of carbon rich porous textures and the remnants of carbonaceous nests in colloform pyrite also indicate a significant contribution of microbial sulfate reducers during the incipient stages of sulfide precipitation the gradual formation of colloform lenses eventually sealed the hydrothermal system establishing a physical barrier that limited the interaction with seawater this process promoted the onset of higher temperature and pressure conditions required to form the high grade zn ag mineralization sourcing sulfur and fluids largely from a magmatic reservoir 33s 0 09 whereas the identification of a predominantly magmatic sulfur source is supported by sulfur isotope signatures the recognition of a magmatic origin of the fluid may only be inferred indirectly it is consistent with the observed quartz sericite alteration style and the proposed mechanism of sulfide deposition via decompression which does not require any interaction with seawater the trace element distribution of the ore related sulfides also supports a closed hydrothermal system developed through multiple fluid pulses indeed this ore forming scenario is commonly favored by high confining pressures which at nimbus were established following the deposition of the colloform pyrite lenses that progressively sealed the hydrothermal system creating the favorable conditions for mineralization

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

genesis and evolution of framboidal pyrite and its implications for the ore forming process of carlin style gold deposits southwestern china abstract southwestern guizhou an indispensable component of the golden triangle area of southwestern china is famous for its numerous carlin style gold deposits unlike other sulfides in the deposits that have been well studied the genesis of framboidal pyrite is still controversial because of its tiny size here we first determined the chemical and in situ sulfur isotopic compositions of framboidal pyrites from three typical carlin style gold deposits namely shuiyindong taipingdong and nibao using secondary electron image sei back scattered electron bse electron probe micro analysis epma and nanometer scale secondary ion mass spectroscopy nano sims methods our epma data show that the framboidal pyrites contain a minor amount of trace elements ni

sulfur isotope variability in biogenic pyrite reflections of heterogeneous bacterial colonization the top 20 cm of sediments at active cold seeps in monterey bay coastal california contain framboidal pyrite that occurs as infillings and pseudomorphs of the chambers of the tests of foraminifera and rarely as irregularly shaped grains sulfur isotope compositions obtained with the ion microprobe show depletions in 34 s d 34 s 52 41 to 25 cdt and large variations both within and among these pyrite grains intergranular differences in d 34 s values in the same sediment are as large as 35 and intragranular zoning reaches 15 zoning is regular in some grains with systematic isotope changes from core to rim or from one foraminiferal chamber to another but irregular in others the regular zoning is consistent with an increase in 34 s through time backscattered electron imaging reveals three types of pyrite isolated framboids in a porous aggregation pf pyrite agglomerated framboids with cementing interstitial pyrite f 1i pyrite and recrystallized pyrite with isolated relicts of framboids rf pyrite in individual grains rf pyrite cores grade into f1i pyrite toward grain rims and f1i pyrite grades into pf pyrite at the grain edges these textures are consistent with a paragenetic sequence whereby framboids first agglomerate pf pyrite then cement f1i pyrite and finally recrystallize rf pyrite the d 34 s values of rf pyrite are generally lower than that of f1i pyrite if the paragenetic sequence is correct then this trend parallels the regular core rim isotopic zoning observed in some grains the implied increase in d 34 s with time is consistent with rayleigh fractionation of sulfur in a closed system bacteria are intimately involved in the production of pyrite from our samples and heterogeneous colonization by bacteria provides a simple explanation for the sulfur isotope heterogeneity among and within grains the foraminifera provide open space for colonization and local nutrients for bacterial growth whereas the cell walls of the bacteria may provide a local nucleation site for sulfides if so then initial colonization is reflected in lower d 34 s values whereas later bacterial emigration to other foraminifera chambers is indicated by higher d 34 s values

bacteria as nucleation sites for authigenic minerals in a metal contaminated lake sediment abstract sediment samples contaminated with metals arising from mine tailings drainage were obtained from lower moose lake in the onaping region near sudbury ontario canada the samples were examined by electron microscopy selected area electron diffraction and energy dispersive x ray spectroscopy individual bacterial cells and their remains were prominent as nucleation sites for both metal sulfides and a complex polymorphic fe al silicate the principal metal sulfide species associated with the bacteria were amorphous mackinawite fes 1 x and microcrystalline millerite nis trace amounts of cu and zu were also detected in some of the sulfide precipitates at least two structural forms of the fe al silicate were present and energy dispersive x ray spectroscopy point analyses revealed corresponding differences in chemical composition poorly ordered limonitic clay type phases had a granular morphology and contained less fe than well developed crystalline material which generated hexagonal diffraction patterns with reflections d 4 60 and 2 55 characteristic of an interstratified chamositic clay

principles of drainage basin analysis from multisource data application to the structural analysis of the zaire basin abstract classifications which attempt to combine descriptive and genetic aspects of types of drainage basins must take into account the application of new techniques satellite imagery high precision topographic maps and digital terrain models in addition the use of new concepts such as neotectonics and drainage basin history will lead to a reassessment of classification schemes after a review of current classifications we propose a genetic scheme that is based on the development of drainage networks and which includes integration of local and regional scale perturbations state of the art methods of drainage basin analysis are applied to the zaire basin to provide new information on deep structures the influence of basin and block tectonics is revealed in the context of major late proterozoic shear faults which have been rejuvenated up to the present day this is demonstrated from an analysis of the drainage network in the light of geological and geophysical observations

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

development of framboidal pyrite during diagenesis low grade regional metamorphism and hydrothermal alteration distribution patterns microstructural relationships and compositional variations for framboidal pyrite in the paleozoic sedimentary host rocks to gold deposits on the northern carlin trend nevada and at fosterville in central victoria collectively demonstrate that it is not all of synsedimentary early diagenetic origin framboidal pyrite also nucleated in hydrothermal veins formed at several kilometers depth and along dissolution surfaces stylolites and crenulation cleavages formed during metamorphism at up to anchizonal grade i e prehnitepumpellyite facies there are no obvious differences in either the size range or internal morphology of framboids formed in these various settings suggesting that a single relatively simple crystallization path may operate over a wide depth range in the upper crust at fosterville anomalously metal rich including au framboidal pyrite is most abundant adjacent to laminated shear veins that developed by slip along bedding surfaces during folding of the sedimentary host rocks microstructural relationships and pb isotope compositions for the framboidal pyrite and other similarly distributed early formed sulfides support development in response to the localized episodic influx of metal enriched h 2s bearing hydrothermal fluids during regional deformation between 440 and 400 ma these findings may have implications for other similarly deformed metasedimentary successions where the discovery of au bearing framboidal pyrite has recently been cited as evidence for significant au enrichment during sedimentation 2009 society of economic geologists inc

diagenetic evolution of a sedimentary system michigan basin insights from petrography and s isotope micro analysis of pyrite abstract the study presents a detailed investigation of s isotope systematics of pyrite from cambrian ordovician sedimentary rocks along the eastern flank of the michigan basin ontario canada whole rock and secondary ion mass spectrometry sims pyrite analyses of 34s 32s were undertaken in association with a detailed petrographic investigation of the different crystal morphologies to better constrain the diagenetic history of the sedimentary rocks by informing about the processes of pyrite formation the broad range of sims isotopic data i e 37 1