tektites apollo the crust and planets a life with trace elements stuart ross taylor msc university of new zealand phd indiana university scd university of oxford faa ac always called ross grew up on a farm near ashburton new zealand ross has worked on a wide variety of topics in trace element geochemistry including the composition and evolution of the moon the continental crust tektites impact glasses and island arc rocks in 1969 he carried out the first chemical analysis of the first returned lunar sample at nasa in houston he has published 10 books and 240 papers in scientific journals he was awarded the v m goldschmidt award of the geochemical society in 1993 in 1994 he was elected a foreign associate of the national academy of sciences in 1998 he was awarded the leonard medal of the meteoritical society in 2002 the bucher medal of the american geophysical union and in 2012 the shoemaker distinguished lunar scientist medal of the nasa lunar science institute asteroid 5670 is named rosstaylor

palaeoenvironmental significance of rounded pyrite in siliciclastic sequences of the late archaean witwatersrand basin oxygen deficient atmosphere or hydrothermal alteration petrographic and sulphur isotope studies support the long held contention that rounded grains of pyrite in siliciclastic sequences of the late archaean witwatersrand supergroup originated as placer grains the grains areconcentrated at sites where detrital heavy minerals are abundant within quartz pebble conglomerates and quartzose sandstones depositional sites with abundant pyrite are 1 within the matrix of bar type clast supported conglomerates 2 on scoured or winnowed surfaces and 3 on stratification planes the grains are internally compact or porous with truncation of internal structure at outer margins indicating fragmentation and rounding of pyritic source rocks during erosion and sediment transport a large range in textures reflects source rock lithologies with known varieties linked to sedimentary hosted diagenetic pyrite volcanic hosted massive sulphide deposits and hydrothermal pyrite laser ablation sulphur isotope analysis of pyrite reveals a broader range in 3 4 s values 5 3 to 6 7 than that of previously reported conventional bulk grain analyses 1 to 4 rounded pyrite from the steyn reef has significant variation in 3 4 s values 4 7 to 6 7 that establishes heterogeneous sulphur compositions with even adjacent grains having diverse isotopic signatures the heterogeneity supports a placer origin for rounded pyrite euhedral pyrite and pyrite overgrowths which are undoubtedly authigenic have restricted 3 4 s values 0 5 to 2 5 are chemically distinct from rounded pyrite and are probably the products of metamorphism or hydrothermal alteration the placer origin of rounded pyrite indicates that pyrite was a stable heavy mineral during erosion and transport in the early atmosphere its distribution in three sequences witwatersrand supergroup ventersdorp contact reef and black reef and in other sequences not linked to witwatersrand type au u ore deposits implies deposition of redox sensitive detrital heavy minerals during the late archaean consequently rounded grains of detrital pyrite are strong indicators of an oxygen poor atmosphere while not confirming a placer origin for gold in witwatersrand au u ore deposits the palaeoenvironmental significance of rounded pyrite negates its link to hydrothermal mineralization

geology the smile of the cheshire cat little is known about geological processes on earth during the hadean over 4000 million years ago in his perspective kramers discusses evidence for crust formation during this early period the new calibration of the lutetium 176 decay constant reported by scherer et al necessitates a new interpretation of existing data it appears that continental crust existed as long as 4400 million years ago but that it was rare

the 13c12c ratios of siderite and organic matter of a modern metalliferous hydrothermal sediment and their implications for banded iron formations abstract a hydrothermal ferruginous sediment precipitated by the activity of the microaerophilic chemolithotrophic bacterium galionella ferruginea has been sampled in a bay of nea kameni island santorini greece due to high fugacity of carbon dioxide precipitation of siderite also occurred the 13c value pdb was determined to be 6 5 in the siderite and 26 8 in the organic matter of mainly microbiological origin the enrichment of isotopically light carbon in carbonates of banded iron formations 13 c 10 has recently been discussed in literature the dilution of these marine carbonates by isotopically light carbon is suggested to have resulted from bacterial oxidation of reduced organic carbon during early diagenesis it is further suggested that fe iii in the newly precipitated sediment served as electron acceptor during oxidation in a hydrothermal model for the origin of banded iron formations this is consistent with the data presented here it is therefore postulated from the results presented that the reduced organic carbon in banded iron formations originates from microaerophilic chemolithotrophic bacteria

the composition and evolution of the continental crust rare earth element evidence from sedimentary rocks the composition of the present day upper crust inferred from the uniformity of sedimentary rock r e e rare earth element patterns is close to that of granodiorite a revised andesite model is used to obtain total crustal composition the lower crust is the composition remaining assuming that the upper crust one third of the total is derived from intracrustal partial melting the upper crustal r e e pattern has pronounced eu depletion eu eu 0 64 the lower crustal pattern has eu enrichment eu eu 1 17 and the total crust has no eu anomaly relative to chondritic abundances the eu depletion in the upper crust is attributed to retention of eu in plagioclase in the lower crust because plagioclase is not stable below 40 km 10 kbar the anomaly is intracrustal in origin the archaean upper crust has a different r e e pattern to that of the present day upper crust being lower in total r e e and la yb ratios and lacking an eu anomaly these data are used to infer the archaean upper crustal composition which resembles that of the present day total crust except that ni and cr contents are higher the archaean crustal composition can be modelled by a mixture of tholeiites and tonalite trondhjemites the latter have steep light r e e enriched heavy r e e depleted patterns consistent with equilibration with garnet and hence probable mantle derivation there is little reason to suppose that the archaean lower crust was different in composition from the upper crust except locally where partial melting episodes occurred the r e e evidence is consistent with isotopic and geological evidence for a low continental growth rate in the early archaean a massive increase to about 70 of the total crust between about 3000 and 2500 ma b p and a slow increase until the present day the change from archaean to post archaean r e e patterns in the upper crust is not isochronous but is reflected in the sedimentary rock r e e patterns at differing times in different continents on the basis of a model composition for the mantle 36 of the potassium 30 of uranium 15 of lanthanum and 3 of ytterbium are concentrated in the present continental crust this enrichment is related to ionic size and valency differences from common mantle cations e g mg fe pre 3 9 ga b p crusts were obliterated by meteorite bombardment no geochemical evidence exists for primordial anorthositic sialic or mafic crusts

rb cs fractionation a link between granulite metamorphism and the s process abstract high grade metamorphism of pelitic sediments produces large cs losses with little k and rb depletion island arc volcanics contain an enhanced cs component relative to k and rb we suggest a connection between these two processes whereby fluids or melts removed from feldspar bearing subduction assemblages under high grade metamorphic conditions are enriched in cs relative to k and rb these cs enriched components infiltrate subarc mantle and lead to ubiquitous cs enrichment in arc volcanics normal oceanic magmatism is not effective in fractionating rb cs therefore the canonical oceanic basalt value of 85 for rb cs is distinctive relative to processes involving sediments recycling fluid melt metamorphism and arc volcanism

the moon re examined abstract recent geochemical and geophysical data from the moon enable a revision of earlier interpretations regarding lunar origin structure and bulk composition earth and moon show many similarities among their isotopic compositions but they have evolved in totally dissimilar ways probably related to the deficiency of water in the moon as well as the vast differences in size and internal pressure although some global geochemical trends such as volatile depletion based on k u ratios have been established current lunar samples come from differentiated regions making the establishment of a bulk composition more reliant on bulk geophysical properties or isotopic similarities although it remains unclear how the latter relate to whole moon composition the lack of fractionation effects among the refractory and super refractory elements indicates that the proto lunar material seems unlikely to have been vaporized while the depletion of volatile elements may place lower limits on proto lunar temperatures the apparent lack of geochemical evidence of an impacting body enables other possible impactors such as comets to be considered

sulfur isotopic studies of archean slate and graywacke from northern minnesota evidence for the existence of sulfate reducing bacteria abstract sulfur isotopic studies of pyrite from metasediments in the 2 6 byr old deer lake green stone sequence minnesota have been conducted in order to evaluate the possible importance of sulfate reducing bacteria in sulfide formation pyrite occurs as ovules up to 2 cm in diameter within graphitic slates and as fine disseminations in metagraywacke units sem studies indicate the pyrite is framboidal in morphology 34 s values of pyrite from the deer lake sediments range from 2 3 to 11 1 with a peak at 2 isotopic data are consistent with either high temperature inorganic reduction of circulating seawater sulfate or low temperature bacterial reduction however the lack of sulfide bands or massive occurrences in the sediments the restriction of pyrite mineralization to the sediments and the absence of evidence for hot spring activity suggest that a diagenetic origin of pyrite is more feasible sulfide in such an environment would be produced principally by the action of sulfate reducing bacteria results of the study are in agreement with those of goodwin et al 1976 who suggest that dissimilatory sulfate reduction was operative in the archean ocean some 2 75 byr ago

further sulfur and carbon isotope studies of late archean iron formations of the canadian shield and the rise of sulfate reducing bacteria sulfur and carbon contents and isotope ratios are reported for five archean iron formations helen nakina and finlayson lumby and bending lake areas distributed across 850 km of the canadian shield all 2 7 ga old a 34s profile through a complete stratigraphic column oxide facies excluded of the helen iron formation shows a 34s range of 30 2 mean 34s value of 2 5 and a standard deviation i of 7 3 in sharp contrast to the sulfide and siderite facies the oxide facies in the column shows a uniform 34s value close to zero the 34s values obtained for the other four iron formations are again wide ranging highly variable in the sulfide and pyrite siderite facies but uniform and close to zero for the oxide facies the carbon in the oxide siderite chert facies has 13c values of 2 3 to 1 1 in the range of phanerozoic marine carbonates however the carbonates in the graphite rich sulfide facies have 13c values as low as 7 6 the mixing of reduced carbon with marine carbonate is suggested to explain the light carbonate values the reduced carbon associated with the light carbonate is also relatively light at up to 13corg 33 5 but is in the range of other precambrian values distal high temperature abiogenic sulfate reduction as a source of highly fractionated sulfides in the archean iron formations is ruled out on the basis of both isotopic and geologic evidence it is concluded that only the bacterial reduction of sulfate at low temperatures could produce the wide ranging highly variable 34s values exhibited by these sulfides over large areas

a lower crustal origin for massif type anorthosites the origin of batholith sized masses of plagioclase rich crustal rocks mainly proterozoic in age has mostly been ascribed to aluminous magmas of mantle derivation here we propose that such masses are derived by partial melting of an aluminous lower continental crust which has developed following extraction of a granitic upper crust by intra crustal melting this segregation of upper and lower crusts occurred principally in the late archaean as the lower crust was depleted in heat producing elements during the initial melting to produce granites an external source of heat is required to produce proterozoic massif type anorthosites we speculate that this heat resulted from the continental crust moving over a mantle hotspot or line plume

regional o sr and pb isotope relationships in late cenozoic calc alkaline lavas of the andean cordillera quaternary recent volcanism in the andes has occurred in three regions 45 33 s 28 16 s and 2 s 5 n each of which has a distinct plate tectonic setting and contains volcanic suites with different chemical and isotopic characteristics isotope ratios of o and sr are lowest and those of pb least variable in the southern volcanic zone svz where medium k lavas have isotopic characteristics equivalent to volcanics from intraoceanic arcs where continental crust is absent the svz lavas were probably derived from an asthenospheric mantle source above a shallow benioff zone parental basaltic magmas rose largely unmodified through thin continental crust where differentiation occurred by low pressure crystal fractionation without concurrent modification of isotopic composition the slight enrichment of 206 pb in the northern volcanic zone nvz where the crust is thin and the benioff zone deep suggests a greater subduction zone component for parental medium k magmas the slight 18 o enrichment suggests a small amount of lower crustal interaction isotope ratios of o and sr are highest and those of pb most variable in the central volcanic zone cvz parental magmas in the cvz were probably generated within the same mantle source region as those in the svz and nvz subsequently during transit through the exceptionally thick continental crust of the central andes high k magmas were produced by a combination of bulk contamination in the lower crust and later low pressure fractional crystallization assimilation processes in the upper crust which altered both chemical and isotopic compositions

petrological and stable isotope studies of carbonate and sulfide minerals from the gunflint formation ontario evidence for the origin of early proterozoic iron formation abstract the 1 9 ga gunflint formation in the thunder bay district of ontario principally comprises iron formation overlain by an iron poor limestone dolostone member the upper limestone member rocks are virtually unmetamorphosed retaining primary textures except locally around diabase sills the gunflint presents an opportunity to study both unmetamorphosed and metamorphosed iron formation and to study the changes from iron rich to iron poor sedimentation of the carbonate minerals in iron rich units siderite formed at or near the sediment water interface with ankerite and calcite forming later during diagenesis and during metamorphism around sills heaviest 13c values of siderite and of dolomite in the upper limestone member are consistently near 0 throughout the stratigraphic section indicating that marine bicarbonate was the source of carbon a spread of values between 0 and 7 for unmetamorphosed rocks is the result of the incorporation of oxidized organic matter during diagenesis whereas 13c values more negative than 7 are the result of metamorphism the heaviest 18o values from unmetamorphosed rocks 5 3 pdb for siderite 6 1 for ankerite and 6 7 for calcite are considered to represent the original marine composition lighter values to 17 represent isotopic exchange reactions with pore fluids at higher temperatures and or isotopic exchange with 18o depleted meteoric water low s c ratios and a relatively narrow range of positive 34s values in pyrite throughout most of the formation are consistent with bacterial sulphate reduction of seawater containing sulphate at a significantly lower concentration than the modern ocean locally higher sulfide contents and a wider range of 34s values were the product of the introduction of sulfur after deposition it is proposed that the gunflint formation was deposited in a stratified water column with anoxic bottom water the depositional basin had restricted communication with the open ocean and was affected by distal volcanism hydrothermal activity associated with the volcanism provided a large source of dissolved iron and possibly silica which helped buffer o2 and sulphate in water to low levels low concentrations of sulphate limited the generation of h2s that would otherwise have restricted the solubility of iron during periods of increased hydrothermal activity the anoxic oxic water boundary moved upwards permitting transport of iron to the shallow shelf where it was precipitated as siderite iron hydroxides iron silicates or pyrite depending on physico chemical conditions the transition to the overlying limestone marks a decrease in hydrothermal activity with a contraction of the redox boundary

stable isotope geochemistry of early protezozoic carbonate concretions in the animikie group of the lake superior region evidence for anaerobic bacterial processes abstract thirteen carbonate concretions from the rove thomson and gunflint formations of the early proterozoic 2 0 ga animikie group in the lake superior region were analyzed for variations in carbon and oxygen isotopes the isotope data of ferroan dolomite concretions from the rove formation yield trends comparable to the isotope systematics displayed by authigenic carbonate in modern organic rich marine burial environments the isotope systematics of the ferroan dolomite concretions suggest that carbonate initially precipitated in a zone of bacterial methane production and later at greater burial depths in a zone of thermal decarboxylation recrystallization of calcite concretions in the rove and thomson formations has homogenized the oxygen isotopic composition however because the carbon system was apparently rock dominated the primary 13c signateres have been preserved calcite concretions from the rove formation display a strong correlation between 13c weight percent carbonate and position in the concretion the data suggest that these concretions formed progressively during burial in the zone of bacterial sulfate reduction sulfur isotopic analysis of pyrite disseminated in the concretions yield high positive 34s values isotopic data for the pyrite and the host concretion are consistent with models that suggest that high positive 34s values of early proterozic pyrite result from bacterial reduction of a limited supply of seawater sulfate the isotopic composition of concretions in the gunflint formation suggest early formation in a system open with respect to seawater bicarbonate the detailed isotopic study of precambrian carbonate concretions is a useful approach for investigating precambrian organic matter diagenesis and the evolution of bacteria

sedimentary rocks and crustal evolution tectonic setting and secular trends a significant change in the composition of turbidites deposited at active tectonic settings is seen at the archean post archean transition in comparison to post archean active margin turbidites archean greenstone turbidites exhibit more uniform th sc ratios but with a similar average greater hree depletion gd n yb n 2 less eu depletion eu eu mostly 0 85 and an absence of low th u ratios th u 3 these data indicate that differing mantle sources and or conditions of mantle melting existed during the archean and that intracrustally differentiated rocks older cratons or young differentiated arcs were relatively unimportant as provenance components for archean turbidites in contrast some sedimentary rocks preserved in archean platformal sequences of high grade terranes display significant negative eu anomalies similar to the majority of post archean shales indicating that the general process of cratonization including intracrustal differentiation has taken place since at least 3

no water no granites no oceans no continents water is essential for the formation of granite and granite in turn is essential for the formation of continents earth the only inner planet with abundant water is the only planet with granite and continents the moon and the other inner planets have little or no water and no granites or continents

the composition and petrogenesis of the lower crust a xenolith study granulite facies lower crustal xenoliths from a single basaltic vent hill 32 in the mcbride volcanic province north queensland australia illustrate the extreme lithologic diversity of the deep crust these xenoliths are dominantly mafic but intermediate and felsic granulites represent a significant proportion 20 of the xenolith population all xenoliths have high grade mineralogies and generally well equilibrated textures as well as decompression features which are indicative of derivation from deep crustal levels 0 7 1 0 gpa major and trace element chemistry for 12 xenoliths chosen to span the observed lithologic range are used to constrain the petrogenesis of these rocks in the smaller layered samples metamorphic differentiation may lead to nonrepresentative sampling however in most instances such secondary processes can be identified and the original chemical characteristics delineated the mafic xenoliths formed through a variety of processes including crystallization of mafic magma crystal accumulation from mafic and felsic magmas and partial melting of intermediate compositions to yield a mafic residuum the two analyzed intermediate xenoliths are metasediments based upon high alumina to alkali ratios and rare earth element patterns whereas the two felsic xenoliths have compositions similar to igneous rocks comparisons of noncumulate and or restite xenoliths with unmetamorphosed rock types show that k and rb are variably depleted whereas th and u are strongly depleted in all rock types the large ion lithophile element depletion patterns for xenoliths are similar to those of rocks from granulite facies terrains suggesting similar processes were operative suggestions of an anomalously ba and sr rich lower crust are not supported by the data by using the observed lithologic proportions of xenoliths at hill 32 and the chemical analyses presented here a weighted mean composition of the lower crust can be obtained and compared with recently proposed lower crustal compositions the weighted mean composition is mafic and formed through a combination of basaltic underplating crystal accumulation tectonic underplating and partial melting no simple model of lower crust formation through basaltic or andesitic underplating nor intracrustal melting is sufficient to explain lower crust formation in phanerozoic continental margin settings

sulfur and carbon isotopes in archean banded iron formations implications for sulfur sources abstract sulfur isotope ratios of pyrite from two late archean banded iron formations were used to constrain possible sources of sulfur the iron formations studied were the temagami iron formation which hosts the sherman mine near temagami and the boston iron formation including the adams mine south of kirkland lake both in ontario in both cases algomantype oxide facies magnetite chert ores predominate the sulfur studies were supplemented by limited carbon isotopic data for the sherman mine iron formation in the sherman mine occurs on both limbs of a regional synformal structure each iron formation unit caps a thick calc alkaline andesite dominated volcanic sequence with one band hosted in sedimentary rocks of turbidite origin the adams mine includes four major iron formation bands interbedded with mafic and ultramafic volcanic rocks and greywacke of turbidite origin the sulfur isotope statistics for averages of pyrites from these three units are sherman mine volcanic hosted suite 34 s 1 7 4 6 n 14 sherman mine sediment hosted suite 34 s 1 4 1 6 n 43 and adams mine 34 s 1 8 2 9 n 17 these averages differ by from juvenile sulfur and together with their limited dispersions suggest a predominantly unfractionated source of sulfur it is argued that this sulfur has been derived from the associated volcanic piles most of the pyrite occurs as disseminated grains in oxide facies iron formation and interbedded clastic sediments a distinctive nodular pyrite in the sherman mine sediment hosted suite occurs in cherty graphitic sulfide facies iron formation while the sulfur isotopic properties of this subset 34 s 0 0 0 8 are not suggestive of biogenic sulfur the geological setting and carbon isotopic compositions of associated graphite 13 c 34 imply that anaerobic bacterial processes were active in this reducing environment the apparent lack of biogenic sulfide is rationalized by models suggesting that archean marine basins differed from phanerozoic analogues in various parameters which influence sulfur isotopic characteristics it is argued that biogenic sulfide is probably a significant component of the sulfur in sherman mine nodular pyrite

the isotopic record of lunar volcanism abstract the timing and extent of lunar volcanism was determined primarily by the internal thermal evolution of the moon a late heavy bombardment produced most of the observable lunar basins easily recognized stratigraphic markers and also may have influenced lunar volcanism most of the nearside basins seem to have been produced 3 8 4 0 ga ago during a period often referred to as the lunar cataclysm the pre cataclysm period was characterized by formation of the lunar crust plutonic rocks within the crust and pre mare volcanism isotopic analysis of breccia clasts pre dating the cataclysm has yielded an outline of this period the isotopic record of post cataclysm mare volcanism is clear but incomplete because samples from the youngest mare areas are lacking specifically the isotopic data show that some lunar anorthosites formed 4 45 ga ago consistent with early formation of an anorthositic lunar crust some mg suite norites troctolites and dunites also formed approximately contemporaneously with the oldest anorthosites but others are up to 200 300 ma younger more evolved rocks granites and quartz monzodiorites also formed between 4 4 and 4 0 ga ago the earliest known pre mare volcanism at 4 25 ga ago included aluminous mare like basalts and an olivine gabbronorite similar to apollo 12 basalts kreep basalt volcanism began at least 4 1 ga ago approximately contemporaneously with that of the ancient mare like basalts and continued during the cataclysm recorded instances of high ti mare basalt volcanism began during or immediately after the cataclysm low ti mare basalt volcanism is the most recent for which samples are available the isotopic data record an early primary lunar differentiation during which mare basalt sources formed probably by crystallization of cumulus minerals from a lunar magma ocean the isotopic record of post cataclysm basalts indicates a heterogeneous lunar mantle and can be explained by partial melting of cumulate sources but more complex petrogenesis also has been suggested more complex petrogenetic processes including assimilation and assimilation fractional crystallization afc seem to be required for pre mare volcanics the isotopic data contain a hint that petrogenesis of the oldest pre mare volcanics may be linked to formation of the so called procellarum basin possibly the oldest and largest lunar basin such a basin would provide a geologic context for the pre mare volcanics and its formation may have been a defining moment in lunar history

a 3 800 million year isotopic record of life from carbon in sedimentary rocks an increased ratio of 12c to 13c an indicator of the principal carbon fixing reaction of photosynthesis is found in sedimentary organic matter dating back to almost four thousand million years ago a sign of prolific microbial life not long after the earth s formation partial biological control of the terrestrial carbon cycle must have been established very early and was in full operation when the oldest sediments were formed

lunar and terrestrial crusts a constrast in origin and evolution abstract planetary crusts differing in composition from that of the bulk planet and containing large concentrations of incompatible elements such as k u and th may arise in two distinctly different ways the first exemplified by the moon involves flotation of a feldspathic crust during an initial melting episode in which much of the planetary body was molten the second probably more common type of crust is formed as a consequence of partial melting in response to radioactive heating in the planetary interior and the eruption of basaltic lavas examples include the lunar maria and the oceanic crust of the earth subsequent partial melting episodes involving recycling into the mantle or lower crustal melting episodes produce more acidic crusts of which the terrestrial continental crust forms the type example the upper crust requires at least three successive partial melting events

isotopic composition of disseminated sulfur in precambrian sedimentary rocks abstract isotopic analyses of trace sulfur in precambrian carbonates and clastic sedimentary rocks support the results of previous studies which have shown that 34s measurements of archean sedimentary sulfur cluster mostly around mantle like values and that a significant overall dispersion of 34 s 32 s ratios commenced at about 2 7 ga ago the outstanding feature of the proterozoic record is the predominance of heavy 34ssulfide values mostly in excess of 0 cdm consideration of these data in combination with the sparse 534s record for proterozoic sulfates suggests that 34ssulfide sulfide may have been smaller than was the case during the phanerozoic a possible scenario that is compatible with the above data is based on a proposition that the terrestrial exogenic sulfur cycle evolved in a tripartite manner in the archean it was coupled to and controlled by the magmatic endogenic cycle the proterozoic for the most part represents a transitional stage into a phanerozoic like exogenic cycle the latter essentially decoupled from its endogenic counterpart and its redox balance maintained and mediated by the biosphere the indication that the mean combined 34s of proterozoic sulfate and sulfide may have significantly exceeded the phanerozoic mean value of 2 cdm is enigmatic and poses problems for balance considerations

origins of stratiform and stratabound fe cu zn horizons in the lower proterozoic moran lake group labrador central mineral belt zn cu and fe are concentrated as stratiform and stratabound sulphide rich beds in the lower proterozoic warren creek formation moran lake group central labrador upper member sedimentary rocks have a hydrothermal like fe enrichment but a dominantly hydrogenous signature as indicated by high al2o3 relative to sio2 and high al and fe relative to mn the upper member shales and sulphide rich beds were deposited as fe rich pelagic sediments the paucity of mn and abundance of fe in typical shale samples and lack of cu pb and zn fractionation in stratiform massive sulphide beds that contain up to 4702 ppm zn 533 ppm cu and 15 ppm pb suggest that deposition occurred in restricted brine pools i e cu and zn were precipitated rapidly and were not fractionated stratabound sphalerite mineralization containing 3 7 zn and 121 ppm cu but no pb was deposited in a porous lithology at the top of the warren creek formation and represents a unique style of metal concentration the stratiform deposits proba

microbial dolomite precipitation using sulfate reducing and halophilic bacteria results from qinghai lake tibetan plateau nw china past studies have revealed the important roles of certain types of microbes in precipitating dolomite in coastal hypersaline lakes and lagoons and marine sediments however it is still poorly known if other types of microbes can precipitate dolomite in low salinity lakes without any marine influence the objective of this study was therefore to expand the microbial dolomite precipitation model by investigating the origin of dolomite in the sediments of qinghai lake an inland slightly saline lake salinity 12 5 g l on the tibetan plateau nw china this objective was accomplished via an integrated approach combining geochemical investigations of natural dolomite present in the lake sediments with laboratory precipitation experiments a 5 m sediment core was collected and pore water chemistry was analyzed calculation of saturation index indicated that dolomite was oversaturated in sediment pore water sub spherical grains of dolomite with abundant pores and microstructures similar to microbially precipitated dolomite were found in the sediments suggesting a biogenic origin dolomite precipitation experiments were set up in the laboratory to simulate the natural conditions of the qinghai lake dolomite was precipitated using sulfate reducing bacterium srb desulfotomaculum ruminis and aerobic halophilic bacterium halomonas marina present in the qinghai lake sediments aqueous geochemistry and mineral characterization data collectively suggest that dolomite precipitation was accomplished via increase of ph and alkalinity to overcome the kinetic inhibitors and exopolymeric substances eps and cell walls as possible nucleation sites these results expand the current microbial dolomite precipitation model and have implications for dolomite formation in slightly saline inland lake environments

sulfur isotopes in early proterozoic volcanogenic massive sulfide deposits new data from arizona and implications for ocean chemistry the 34s range of sulfides from early proterozoic volcanogenic massive sulfides of arizona is narrow 129 out of 133 measurements lying within a range of 2 8 to 3 2 other early proterozoic and archean deposits of comparable type and mineralogy have similar s isotope characteristics these deposits unlike phanerozoic analogues do not appear to have incorporated reduced sulfur derived from marine sulfate early proterozoic oceans are known to have contained sulfate in this paper it is a major tenet that sulfate was confined to an upper water layer it is proposed that most volcanogenic massive sulfide hydrothermal systems prior to 1 7 ga were recharged with sulfate free water from an anoxic lower layer and in general discharged into reducing environments rare deposits with exceptional mineralogy or s isotope compositions may reflect hydrothermal recharge from the oxidized upper layer or deposition from fluids discharging into and mixing with the upper water layer

multiple sulfur isotopes and the evolution of earth s surface sulfur cycle abstract the distribution of sulfur isotopes in geological materials reveals information about earth history and biogeochemical processes research during the last several decades has used sulfur isotope geochemistry as a tool to better understand microbial processes harrison and thode 1958 kaplan 1975 monster et al 1979 peck 1959 peck 1962 rees 1973 and sediment diagenesis berner 1969 berner 1982 canfield et al 1993b earth historians also realized this potential as there exists a rich record of environmental change within the sedimentary records canfield and teske 1996 claypool et al 1980 goodwin et al 1976 habicht et al 2002 kah et al 2004 monster et al 1979 shen et al 2001 strauss 1993 thode and goodwin 1983 these applications have championed the use of the two most abundant sulfur isotopes 32s and 34s and provide a rich introduction to what the sulfur isotope record has to offer see canfield 2004 canfield and raiswell 1999 within the last decade this information has been supplemented by new data derived from the less abundant isotopes 33s and 36s the measurement of all four stable sulfur isotopes multiple sulfur isotope geochemistry has expanded our understanding of biological evolution and activity atmospheric chemistry and transport crustal recycling and many more fields related to earth surface processes see farquhar and wing 2003 here i present a review of recent works in multiple sulfur isotope geochemistry with a focus on results that inform our understanding of biogeochemical processes and earth surface evolution

carbon and sulfur isotopes in precambrian sediments from the canadian shield carbon and sulfur isotope ratios have been determined for more than 200 samples of precambrian graphitic and sulfidic metasediments from the superior and churchill provinces of canada the sediments were deposited in small sedimentary basins related to various canadian greenstone belts the age of the archean samples is approximately 2 7 ga the proterozoic samples about 1 8 ga the archean organic material shows c isotope values between 47 and 15 vs pdb the proterozoic metasediments show a smaller range with 13c between 30 and 17 a few carbonate samples yielded c isotopic compositions between 5 9 and 4 7 associated iron sulfides have 34s values ranging from 6 to 8 which are consistent with isotopic fractionation effects either by inorganic or bacterial reactions in the sedimentary sulfur cycle the great variability of organic c isotopic composition especially in the late archean although affected by extensive postdepositional alteration might indicate differences in the environmental conditions and or the organic content of these sedimentary basins some extremely 13c depleted organic carbon values support a global occurrence of environments likely dominated by methanotrophic organisms at the end of the archean

iron framboids in the hydrocarbon related middle devonian hollard mound of the anti atlas mountain range in morocco evidence of potential microbial biosignatures iron framboids in the context of a middle devonian hydrocarbon seep conical mound anti atlas morocco have been thoroughly investigated through a combination of techniques including optical and high resolution scanning electron microscopy x ray diffraction energy dispersive x ray spectroscopy raman microscopy and time of flight secondary ion mass spectroscopy framboids occur embedded in laminated carbonates of the mound and are precipitated along the veins that crosscut it and served as the conduits for channeled reduced hydrocarbon rich fluids the morphology structure and composition of the framboids contribute to the reconstruction of the complex interplay between the advected fluids and the associated biological and or abiological processes a comparison of our dataset with that from modern framboids formed under similar conditions indicates that the fe rich framboids represent replaced primary pyrite framboids produced as a consequence of bacterial sulfate reduction and the anaerobic oxidation of methane

two sulphur isotope provinces deduced from ores in the mount isa eastern succession australia the sulphur isotopic characteristics of ore deposits in the australian mount isa eastern succession are not well known unlike those of the western succession in this study new detailed analyses are provided for recently discovered eastern succession mineralisation such as the starra and osborne bif hosted cu au ores the dugald river sediment hosted pb zn prospect and four vein hosted cloncurry style cu au deposits hampden mt elliot swan mt cobalt and the answer mine all of the deposits of the eastern succession have 34ssulphide between 8 and 9 regardless of their genesis empirically a moderate 34s range averaging close to 0 characterises starra style cu au and pegmont pb zn bif ores whereas shear and vein style cu mineralisation populations are tighter and do not average close to 0 this is a particularly surprising result for dugald river where a larger isotopic variation more typical of stratiform sediment hosted pb zn ores in the region might have been expected by comparison western succession stratiform pb zn and vein style cu deposits span a huge range of 15 to 51 large sulphur isotope ranges typify sulphate evaporite or organic sulphur rich sedimentary successions the lack of such variation in the eastern succession in turn suggests that primary evaporite sequences there were halite dominated but sulphate poor and or contained only limited volumes of organic sulphur rich sediment eastern succession sequences were therefore less likely hosts for giant stratiform pb zn deposits because of their paucity of sulphur although local sulphur sources permitted small deposits such as dugald river to develop sedimentary conditions were more favourable for the development of sulphur poor synsedimentary hydrothermal systems such as starra osborne and pegmont although sulphur isotope evidence is equivocal about the origin of these epigenetic deposits close to the williams batholith mt dore hampden owe their clustering around 0 to their granitic fluid source

multiple sulfur and carbon isotope composition of sediments from the belingwe greenstone belt zimbabwe a biogenic methane regulation on mass independent fractionation of sulfur during the neoarchean abstract to explore the linkage between mass independent sulfur isotope fractionation mif s and 13corg excursions during the neoarchean as well as the contemporary redox state and biogeochemical cycling of carbon and sulfur we report the results of a detailed carbon and multiple sulfur 34s 33s 36s isotopic study of the 2 7 ga manjeri and 2 65 ga cheshire formations of the ngezi group belingwe greenstone belt zimbabwe multiple sulfur isotope data show non zero 33s and 36s values for sediments older than 2 4 ga i e prior to the great oxidation event goe indicating mif s thought to be associated with low atmospheric oxygen concentration however in several 2 7 2 5 ga neoarchean localities small scale variations in mif s signal magnitude seem to correlate with negative excursion in 13corg possibly reflecting a global connection between the relative reaction rate of different mif s source reaction and sulfur exit channels and the biogenic flux of methane into the atmosphere during periods of localized microbiologically mediated shallow surface water oxygenation the manjeri formation black shales studied here display a wide range of 13corg between 35 4 and 16 2 average of 30 3 6 0 1 while the cheshire formation shales have 13corg between 47 7 and 35 1 average 41 3 3 1 the 34s values of sedimentary sulfides from manjeri formation vary between 15 15 and 2 37 average 1 71 4 76 1 showing very small and mostly negative 33s values varying from 0 58 to 0 87 average 0 02 0 43 1 cheshire formation black shale sulfide samples measured in this study have 34s values ranging from 2 11 to 2 39 average 0 25 1 08 1 and near zero and solely positive 33s anomalies between 0 14 and 1 17 average 0 56 0 29 1 moreover 36s 33s in the two formations are comparable with a slope of 1 38 manjeri formation and 1 67 cheshire formation respectively this differs from the archean reference line i e 0 9 the sulfur and carbon isotopic signatures recorded here likely reflect different environmental conditions and or ecosystems within the sampled cheshire and manjeri formations paleofacies the differences in carbon isotopes in different sedimentological facies are interpreted as recording different metabolic pathways including photosynthesis methanogenesis and methanotrophy low 13corg values in the cheshire formation black shales suggest a strong influence of methanotrophy likely preceded by bacterial methanogenesis while the large range of manjeri formation 34s may record bacterial sulfate reduction the c and multiple s isotopic variations recorded here may imply different patterns of c and s fractionation perhaps dependent on variations in the biogenic egress of methane to the atmosphere

microbial fixation of methane carbon at 2 7 ga was an anaerobic mechanism possible 1 in earth s history the most extreme episode of 13c depletion in sedimentary organic matter occurred about 2 7 billion years ago this isotopic excursion is widely interpreted as resulting from increased burial of organic carbon derived from microbial fixation of 13c depleted methane modern microbial physiologies involve either oxygen or sulfate as electron acceptors in such processes until now the isotopic signal has been exclusively assigned to growth of aerobic methanotrophic bacteria and consequently interpreted as an indication for the presence of molecular oxygen in late archaean surface environments the alternative anaerobic pathway involving sulfate as the electron acceptor was dismissed because this process has been considered inefficient in producing biomass sufficient to account for significant fractions of 13c depleted carbon in some archaean rocks calculations based on recent findings at two modern sites now show however that anaerobic processes could account for the archaean signal

uranium bearing stratiform organic matter in paleoplacers of the lower huronian supergroup elliot lake blind river region canada the elliot lake blind river ontario paleoplacer deposits in the basal matineda formation lowermost member of the 2 25 2 45 ga old huronian supergroup contain organic matter chemically consistent with kerogen this substance is also referred to as thucholite uranium ores and some gold occur here and these minerals may be in close association with the kerogen two uraniferous and auriferous stratiform kerogens obtained from the denison mines limited s denison mine and rio algom limited s stanleigh mine have been analyzed by combined high vacuum pyrolysis gas chromatography mass spectrometry and by neutron activation the reflectances of these samples have also been determined related samples containing dispersed kerogen have been examined by backscattered scanning electron microscopy the polymer like matrix of the two stratiform kerogens consists of aromatic alkyl aromatic hydrocarbon and sulphur moieties and contains 20 and 32 uranium with gold abundances in the parts per billion range

geochemistry of archean metasedimentary rocks from west greenland abstract archean metasedimentary rocks occur as components of the isua supracrustals akilia association and malene supracrustals of southern west greenland primary structures in these rocks have been destroyed by metamorphism and deformation their chemistry and mineralogy is consistent with a sedimentary origin but other possible parents e g acid volcanics altered pyroclastic rocks cannot be excluded for some of them there is little difference in the composition of metasedimentary rocks from the early archean isua supracrustals and probable correlative akilia association both have a wide range in rare earth element ree patterns with la n yb n ranging from 0 61 5 8 the ree pattern of one akilia sample with low la n yb n compares favourably with that of associated tholeiites and it is likely that such samples were derived almost exclusively from basaltic sources other samples with very steep ree patterns are similar to felsic volcanic boulders found in a conglomeratic unit in the isua supracrustals samples with intermediate ree patterns are best explained by mixing of basaltic and felsic end members metasedimentary rocks from the malene supracrustals can be divided into low silica 55 sio2 and high silica 77 sio2 varieties these rocks also show much variation in la n yb n 0 46 14 0 and their origin is explained by derivation from a mixture of mafic volcanics and felsic igneous rocks the wide range in trace element characteristics of these metasedimentary rocks argues for inefficient mixing of the various source lithologies during sedimentation accordingly these data do not rigorously test models of early archean crustal composition and evolution the systematic variability in trace element geochemistry provides evidence for the bimodal nature of the early archean crust

scenarios for the evolution of life on mars received 10 march 2005 revised 2 august 2005 accepted 7 september 2005 published 22 november 2005 1 as the environmental histories of earth and mars have diverged drastically after the first few hundred million years so would the history of any life on them while earth has had liquid water on its surface for billions of years mars most likely had long dry and cold environments interspersed with warmer and wetter periods life thrived on earth but may have been severely restricted on mars there it could be present today in liquid water in or beneath ice sheets or glaciers in subterranean aqueous reservoirs especially in regions of elevated heat flow or in protected habitats such as lava tubes caves or cracks and fissures the potential for life is enhanced in regions where elevated heat flow may occur such as in parts of the tharsis and elysium volcanic provinces possible organisms would be chemoautotrophic psychrophiles adapted to a nutrient poor environment or photoautotrophic life in selected near surface habitats alternatively life may have evolved alternating cycles between active and dormant forms in which case microbes could be present in dormant forms close to the surface and in active forms in protected environments periodic liquid water on mars could have provided opportunities for biologic activity as well as evolutionary progress at the surface during the short lived climatic perturbations ancient organisms from any of these environments may also have left a detectable fossil record

flood basalts basalt floods or topless bushvelds lunar petrogenesis revisited a critical comment the lengthy paper on this subject by m j o hara tompkins 1999 and studies of crustal thickness e g 2000 contains an interesting reassessment of lunar evoluneumann et al 1996 these papers are also not cited tion although it differs little in its conclusions from his this new evidence has led to a revision of the al2o3 original views published over a quarter of a century ago content of the bulk lunar crust from 24 6 the value to answer all the arguments in detail would demand a used by taylor 1975 that o hara discusses to 30 paper of equal length however it is possible to discern lucey et al 1995 some basic underlying assumptions among the extensive to account for this amount of feldspar plagioclase has discussion and i have chosen to concentrate on these to 36 al2o3 close to 50 of the al and eu in the bulk display some of the fundamental fallacies that underlie moon has to be concentrated in the crust shortly after o hara s case the formation of the moon flotation of feldspar in a dry crucial to his argument is his statement that there is magma ocean is the only viable hypothesis accounting no positive europium anomaly in the average lunar incidentally for the parallel ree patterns excluding eu highland crust p 1545 see also p 1551 and this leads observed in most highland samples thus much new him to deny the existence of a magma ocean from which evidence ignored by o hara has only served to subthe crust formed by plagioclase flotation consequently stantiate the traditional interpretation there is no negative europium anomaly in the average o hara wishes in fact to form the thick feldspathic mantle to be inherited by later mare basalts p 1545 crust by partial melting of wet peridotite and claims that see also p 1555 partial melting in the presence of water followed by as these two factors an enrichment of eu in the near surface fractionation and volatile losses can explain highland crust and a corresponding depletion in the the feldspathic character high incompatible element conmantle inherited by the later mare basalts are corcentrations and lack of eu anomaly in the lunar highlands nerstones of the standard model for lunar evolution p 1545 see also p 1553 this view heavily based on based on a magma ocean the remainder of o hara s terrestrial analogues is unfortunately negated by the conclusions stand or fall on their validity completely anhydrous nature of all lunar minerals and his claim that there is no overall enrichment of eu in total absence of any evidence for water on the moon the average highland crust is based on the data from the even at ppb levels the famous rusty rock 66095 was apollo 16 site as interpreted by korotev haskin 1988 hydrated in the terrestrial atmosphere epstein taylor the fundamental difficulty is that the apollo 16 site 1974 is more basic than the average highlands subsequent o hara also seems unwilling to accept the data that extensive coverage of the farside highlands by the clemshow that there is a great depletion of other volatile entine and lunar prospector missions has revealed that elements in the moon preferring a scenario as in much they are dominated by ca rich anorthosite as discussed of the rest of the paper based heavily on terrestrial by lucey et al 1995 a paper that does not appear in experience however he also appeals to the example of the extensive reference list of o hara s paper other io as a model for getting rid of volatiles such as na and evidence of the highly feldspathic nature of the highlands sulphur that unfortunate body in the close embrace of jupiter six jupiter radii distant from a body of 318 earth comes from studies of the lunar farside e g pieters

carbon isotope distribution in organic matter and siderite of a modern metalliferous hydrothermal sediment and possible implications for gold associated with banded iron formation abstract the carbon isotope distribution in organic matter and siderite has been determined in the metalliferous ferruginous sediments of santorini greece the sediments were precipitated by the microaerophilic chemolithotrophic bacterium galionella ferruginea from reduced hydrothermal solutions in siderites precipitated due to high co2 fugacity the 13 c 12 c isotope ratio pdb was 6 5 permil whereas the ratio was 26 8 permil in organic matter produced by the bacteria the common occurrence of isotopically light carbon 13c 10 permil pdb in carbonates of banded iron formations bif s was proposed some years ago to be the result of the dilution of carbon of marine carbonates by isotopically light carbon originally present in organic matter the explanation for this dilution would be that fe iii in newly precipitated oxide hydroxides served as an electron acceptor during oxidation of the organic carbon to carbonate the corresponding redistribution of some reduced carbon in the newly precipitated ferruginous sediment to carbonate minerals in the proportions found in some bif s has been modelled in the present study the isotopic shift to 13c 11 2 permil of the carbonate minerals of such a dilution by carbon of biological origin is close to the values observed in the geological record therefore organic matter appears to have been much more abundant during the early phases of bif development the association of gold and reduced organic carbon is well established in for instance the witwatersrand type conglomerates and some archaean bif s of hydrothermal origin this association may therefore make it worthwhile evaluating once again the role of organic activity in the deposition of bif s and their potential as a source of gold

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

u pb zircon geochronology of the selbaie cu zn ag au mine abitibi subprovince canada the selbaie mine is a large tonnage low grade cu zn ag au deposit with both stratiform and epithermal characteristics mineralization comprises lower grade disseminated zn ag ore and pyritic siliceous sinter of the a1 zone at the surface and higher grade cu zn ag au quartz sulfide lenses of the a2 zone below and transitional with the a1 zone and of the b zone 1 km to the west the copper rich quartz sulfide lenses comprise networks of subvertical quartz sulfide veins vein arrays and breccia they have irregular locally gradational boundaries and variable attitudes with dips from 25 o to 90os the mineralization is within a volcanic stratigraphic succession of heterolithic breccias and felsic and intermediate tuffs and flows which are cut by mafic and felsic intrusions and felsite dikes the felsic volcanic rocks and a tonalitic marginal phase from the adjacent brouillan pluton are calc alkalic and have geochemical signatures that support a cogenetic relationship the mineralization and mine stratigraphic succession are truncated by the brouillan faults a series of subparallel west directed predominantly brittle thrusts with the brouillan pluton on the upper plate above the mine stratigraphic succession galenas from stratiform and vein ore have uniform lead isotope compositions of 2o6pb 2o4pb 13 184 to 13 211 2o7pb 2o4pb 14s351 to 14 369 and 2ospb 2o4pb 33s039 to 33 100 with model values of 8 1 8 2 and model k values of 4 1 to 4 2 n 5 among the most primitive of abitibi volcanic associated massive sulfide depositss they have model ages that range from 2 71 to 2 68 ga a u pb zircon age of 2729 ma for a sericite altered calc alkalic quartz porphyry flow 150 m up section from stratiform mineralization closely approximates the age for this mineralization type a u pb zircon age for a felsite dike that cuts postore east west foliation is 2726 3 ma slightly younger but overlapping at the 20 level with the age for the quartz feldspar porphyry flow indicating that the copper rich quartz sulfide lenses are essentially coeval with the lower grade stratiform mineralization a sample of sheared chloritic granodiorite taken from one of the brouillan faults near the margin of the brouillan pluton has a complex zircon opulation six concordant anal ses of abraded multigrain fractions individual grains or grain tips 20 p 206 s

mantle derived archaean monozodiorites and trachyandesites the 2 680 2 750 myr old1 5 intrusive granite greenstone terranes6 8 in the rainy lake region ontario and in and adjacent to the vermilion district minnesota of the superior province in north america include a wide variety of volcanic and intrusive rocks with initial pb sr and nd isotope ratios close to those for the mantle4 5 9 12 the isotopic constraints require the production of large volumes of silica oversaturated magmas from silica undersaturated mantle within 100 200 myr we present here geochemical data on monzodiorites and trachyandesites from the rainy lake area which are strongly enriched in large ion lithophile elements lile we conclude that they are derived by direct melting of the mantle at depths of 50km in either anhydrous or hydrous conditions their rare earth element ree abundances and initial 143nd 144nd ratios suggest that their mantle sources were enriched in lile shortly before melting the monzodiorites trachyandesites and their granodioritic derivatives may comprise up to 20 of the exposed igneous rocks in the rainy lake region and vermilion district if these rocks are as abundant in other archaean terranes a significant part of the early continental crust could have formed by direct melting of lile enriched mantle

a carbon oxygen hydrogen and sulfur isotopic study of the gold mineralization at loulo mali abstract the isotopic compositions of oxygen hydrogen carbon and sulfur have been determined on silicate carbonate and sulfide samples from auriferous tourmalinized sandstone its footwall and hanging wall of birimian age 2 1 ga at loulo in mali the sandstones have undergone two phases of deformation the samples were taken from three different orebodies loulo 0 loulo 3 and p64 for loulo 0 18o values for vein quartz are consistently between 16 1 and 16 6 smow for oxygen with one exception at 11 6 the 18o values for detrital quartz grains from the tourmalinized sandstone are also 16 1 tourmaline has a high 18 o of 13 9 the 18o values for total rocks are also relatively homogeneous at 13 2 to 15 7 the lowest values 13 2 and 14 being those for the footwall samples dolomites from loulo 0 and p64 have 18o values between 15 1 and 19 5 smow for oxygen and 13c values of 13 5 to 2 0 pdb with the exception of one sample from the hanging wall which is of sedimentary origin 13 c 0 5 18 o 22 2 the sampled dolomites are in veinlets or veins or disseminated in rocks and were deposited by hydrothermal fluids the 34s values of samples from the three orebodies range between 6 0 and 12 9 cdt they fall into different groups according to location but pre and post schistosity sulfides within each group are indistinguishable the results are interpreted as indicating the existence of two hydrothermal systems enriched in 18o at different times one of these gave rise to tourmalinization silicification and dolomitization of the sandstone and the deposition of sulfides the high d values of the tourmalines in agreement with petrological data indicate that the fluid of this system was of marine origin the two phases of folding intervened between the activity of this hydrothermal system and the initiation of the second system which gave rise to the stockwork this fluid rich in 18o was possibly of metamorphic origin with a low water rock ratio it remobilized the pre schistosity sulfides concentrating them into post schistosity veins the partly remobilized silica and carbonates were deposited under temperature conditions such that their isotopic compositions were similar to those observed for the tourmalinized sandstone the vertical extent of this hydrothermal system is as yet poorly known it is very extensive horizontally and strongly pervasive in the tourmalinized sandstone but in the vertical sense appears to be confined to fractures in the footwall

rare earth element patterns in archean high grade metasediments and their tectonic significance abstract metasediments from two contrasting types of archean high grade terrains are interpreted as being derived from distinct tectonic settings the kapuskasing structural zone canada represents the deep roots of a typical greenstone belt whereas the limpopo province southern africa and western gneiss terrain australia mainly consist of shelf sediments deposited on a granitic basement and then buried to the depths required for granulite fades metamorphism upper amphibolite to granulite fades paragneisses from the kapuskasing structural zone have ree patterns similar to those of greenstone belt sediments except where partial melting has occurred forming restites with eu enrichment and melts with eu depletion except in this latter instance metamorphism has not affected the primary ree patterns ree patterns in archean upper amphibolite to granulite facies metasediments from the central limpopo province and western gneiss terrain show wide differences ranging from patterns which resemble those in post archean terrigenous sediments to typical archean sedimentary rock patterns the diversity in ree patterns for these shallow shelf metasediments is interpreted as resulting from derivation from local provenances samples with post archean patterns displaying eu depletion are interpreted as being derived from k rich granitic plutons which were portions of small stable early archean terrains precursors of the widespread late archean proterozoic episode of major cratonic development

evidence for an intrabasinal source and multiple concentration processes in the formation of the carbon leader reef witwatersrand supergroup south africa laser ablation inductively coupled plasma mass spectrometer la icp ms trace element maps of pyrite and gold from the carbon leader reef in the witwatersrand basin provide new evidence that a significant proportion of the pyrite and gold was intrabasinal derived from the west rand group or equivalent shales stratigraphically below this reef rounded detrital pyrite grains in the carbon leader reef vary from compact to porous to sooty with similar textures and composition to diagenetic pyrites reported from sedimentary rocks in the west rand group detrital porous and sooty pyrites contain 0 4 to 11 3 ppm solid solution gold sulfur isotope 34s values from 17 to 16 and high levels of as and te plus a wide range of other trace elements in decreasing order ni co sb cr cu u pb bi mo zn and ag the sooty pyrite is the most au te and mo rich and is intergrown with alumino silicates and organic matter the detrital pyrite textures s isotopes and geochemistry resemble diagenetic pyrite developed under suboxic to anoxic bottom water conditions the laicp ms maps also show that the detrital pyrite grains have euhedral hydrothermal pyrite overgrowths containing micro inclusions of gold brannerite and ni as sulfides the pyrite overgrowths are also enriched in solid solution gold tellurium and other trace elements including in decreasing order as co ni cr cu mn pb bi and ag fractured and brecciated pyrite associated with brittle bedding parallel fracture zones in the carbon leader reef are also enriched in these elements due to alteration of pyrite surrounding the fractures laser icp ms pb isotope determinations on the cores of detrital pyrite indicate an age between 2750 and 2950 ma with hydrothermal overgrowths originating between 2100 and 2020 ma incorporating highly radiogenic pb this study demonstrates that both of the two competing theories for the origin of the witwatersrand gold reefs are likely to be correct we suggest that the hydrothermal event was widespread kilometer scale and involved basinal fluids that scavenged gold tellurium arsenic and trace elements co ni cr cu mn pb bi ag from gold bearing sedimentary units in the central rand group 2013 society of economic geologists inc

iron and sulfur in the pre biologic ocean tentative geochemical cycles for the pre biologic earth are developed by comparing the relative fluxes of oxygen dissolved iron and sulfide to the atmosphere and ocean the flux of iron is found to exceed both the oxygen and the sulfide fluxes because of the insolubility of iron oxides and sulfides the implication is that dissolved iron was fairly abundant and that oxygen and sulfide were rare in the atmosphere and ocean sulfate produced by the oxidation of volcanogenic sulfur gases was the most abundant sulfur species in the ocean but its concentration was low by modern standards because of the absence of the river borne flux of dissolved sulfate produced by oxidative weathering of the continents these findings are consistent with the geologic record of the isotopic composition of sedimentary sulfates and sulfides except in restricted environments the sulfur metabolism of the earliest organisms probably involved oxidized sulfur species not sulfide

a small s mif signal in martian regolith pyrite implications for the atmosphere abstract the past martian atmosphere is often compared to the archean earth s as both were dominated by co2 rich and o2 poor chemistries archean earth rocks preserve mass independently fractionated sulfur isotopes s mif non zero 33s and 36s originating from photochemistry in an anoxic atmosphere thus martian crustal rocks might also be expected to preserve a s mif signature providing insights into past atmospheric chemistry we have used secondary ion mass spectrometry sims to investigate in situ the sulfur isotope systematics of nwa 8171 paired to nwa 7034 a martian polymict breccia containing pyrite that formed through hydrothermal sulfur addition in a near surface regolith setting in this meteorite pyrite grains have a weighted mean of 33s of 0 14 0 08 and 36s 0 70 0 40 2 s e m so the s mif signature is subtle sulfur isotope data for four additional shergottites yield 33s values that are not resolvable from zero as in previous studies of shergottites at first glance the result for the polymict breccia might seem surprising but no martian meteorite yet has yielded a s mif signature akin to the large deviations seen on earth we suggest that s mif bearing aerosols h2so4 and s8 were produced when volcanic activity pushed a typically oxidising martian atmosphere into a reduced state after rain out of these aerosols s8 would tend to be oxidised by chlorate dampening the s mif signal which might be somewhat retained in the more abundant photolytic sulfate then in the regolith mixing of aqueous surface derived sulfate with igneous sulfide the latter with zero mif to form the abundant pyrite seen in nwa 8171 would further dampen the s mif signal nonetheless the small negative 33s anomalies seen in martian meteorites imply that volcanic activity was sufficient to produce a reducing atmosphere at times this volcanically driven atmospheric evolution would tend to produce high levels of carbonyl sulfide ocs given that ocs is a relatively long lived strong greenhouse gas the s mif signal implies that volcanism periodically generated warmer conditions perhaps offering an evidence based solution to the young wet mars paradox

fe c and o isotope compositions of banded iron formation carbonates demonstrate a major role for dissimilatory iron reduction in 2 5 ga marine environments abstract combined fe c and o isotope measurements of 2 5 ga banded iron formation bif carbonates from the kuruman iron formation and underlying bif and platform ca mg carbonates of the gamohaan formation south africa constrain the biologic and abiologic formation pathways in these extensive bif deposits vertical intervals of up to 100 m were sampled in three cores that cover a lateral extent of 250 km bif fe carbonates have significant fe isotope variability 56fe 1 to 1 and relatively low 13c down to 12 and 18o values 18o 21 in contrast gamohaan and stratigraphically equivalent campbellrand ca mg carbonates have near zero 13c values and higher 18o values these findings argue against siderite precipitation from seawater as the origin of bif fe rich carbonates instead the c o and fe isotope compositions of bif fe carbonates reflect authigenic pathways of formation in the sedimentary pile prior to lithification where microbial dissimilatory iron reduction dir was the major process that controlled the c o and fe isotope compositions of siderite isotope mass balance reactions indicate that the low 13c and low 18o values of bif siderite relative to those expected for precipitation from seawater reflect inheritance of c and o isotope compositions of precursor organic carbon and ferric hydroxide that were generated in the photic zone and deposited on the seafloor carbon fe isotope relations suggest that bif fe carbonates formed through two end member pathways low 13c low 56fe fe carbonates formed from remobilized low 56fe aqueous fe2 produced by partial dir of iron oxide whereas low 13c high 56fe fe carbonates formed by near complete dir of high 56fe iron oxides that were residual from prior partial dir an important observation is the common occurrence of iron oxide inclusions in the high 56fe siderite supporting a model where such compositions reflect dir in place in the soft sediment in contrast the isotopic composition of low fe carbonates in limestone dolomite may constitute a record of seawater environments although our petrographic studies indicate that the presence of pyrite in most low fe carbonates may influence the fe isotope compositions the combined fe c and o isotope data from kuruman bif carbonates indicate that bif siderites that have negative near zero or positive 56fe values may all record biological fe cycling where the range in 56fe values records differential fe mobilization via dir in the sediment prior to lithification our results demonstrate that the inventory of low 56fe marine sedimentary rocks of neoarchean to paleoproterozoic age although impressive in volume may represent only a minimum of the total inventory of fe that was cycled by bacteria

petrograph a new software to visualize model and present geochemical data in igneous petrology a new software petrograph has been developed to visualize elaborate and model geochemical data for igneous petrology purposes the software is able to plot data on several different diagrams including a large number of classification and petrotectonic plots petrograph gives the opportunity to handle large geochemical data sets in a single program without the need of passing from one software to the other as usually happens in petrologic data handling along with these basic functions petrograph contains a wide choice of modeling possibilities from major element mass balance calculations to the most common partial melting and magma evolution models based on trace element and isotopic data results and graphs can be exported as vector graphics in publication quality form or they can be copied and pasted within the most common graphics programs for further modifications all these features make petrograph one of the most complete software presently available for igneous petrology research

growth of planetary crusts the planets and satellites of the solar system show much diversity but most have formed crusts which differ substantially from their bulk compositions three principal types of crust may be broadly distinguished primary formed after accretional heating e g lunar highlands secondary formed following partial melting in planetary mantles e g lunar maria terrestrial oceanic crust and tertiary formed by processing of secondary crusts of which the continental crust of the earth is the only identifiable example crustal growth before 3800 m y was complicated by the heavy planetesimal bombardment active erosion on the earth is likely to have destroyed the brecciated rubble resulting from over 200 mare orientale scale events in this period the mercurian crust is probably primary perhaps analogous to the lunar highlands in contrast the observable martian and venusian crusts are secondary dominated by basaltic volcanism the icy crusts of the satellites of the outer planets are mixtures of both primary and secondary crusts with complex histories ganymede is of special interest in displaying a secondary grooved terrain water ice crust which has split an older more heavily cratered possibly primary crust slight expansion has resulted probably from polymorphic transitions from high density ice viii to low density ice i the primary lunar crust 12 of lunar volume grew in 108 years secondary crusts derived by partial melting of mantles grow at a much slower rate total production of terrestrial oceanic crust over 4000 m y is only 2 of planetary volume whereas terrestrial continental crustal growth is even slower producing over the same period a volume only about 0 33 that of the earth crustal growth on the other planets appears to be an irreversible process without evidence of recycling no evidence for massive planetary expansion as required by expanding earth hypotheses is apparent on the other planets or satellites of the solar system

multielement geochemistry of offshore sediments in the southeastern yellow sea and implications for sediment origin and dispersal abstract in total 116 surface sediments were collected from an offshore area of the southeastern yellow sea including a large mud belt southeastern yellow sea mud seysm and analyzed for grain size and geochemical composition organic carbon and 42 elements principal component analysis revealed that elemental compositions of the offshore sediments were mostly controlled by common aluminosilicate clay minerals and quartz most elements heavy minerals hf zr u th rare earth elements rees biogenic calcium carbonates ca sr feldspar and mica k ba pb and mn oxides mn oxide coatings on sand grains notably total ree concentrations may be associated with heavy minerals possibly zircon and monazite especially in silty grains even though heavy ree hrees concentrations are more strongly controlled by clay minerals in muddy sediments the diagnostic discrimination plots of geochemical compositions e g fe vs al mg vs al light ree vs hree and la lu ucc vs la y ucc suggested that the offshore sediments especially in seysm deposits were composed of a mixture of korean river derived silts and chinese river derived clays this demonstrated that chinese river sediments especially clay particles largely contributed to the formation of the giant mud belt in the korean coastal area furthermore the observed geochemical end members provide new markers of sediment provenance which can be used to track dispersal patterns and sediment limits from chinese and or korean rivers