sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

rare earth thhfta and large ion lithophile element variations in metabasites from the proterozoic amphibolite granulite transition zone at arendal south norway abstract the proterozoic arendal metabasites are minor intrusions which possess wholly metamorphic textures and mineral assemblages data are presented for eight selected samples chondrite normalised ree patterns are relatively flat between 10 and 20 chondrite abundances they are characterised by 1 ce n yb n n nd n 1 normalised to primordial mantle values the incompatible elements reveal variable enrichment in the large ion lithophile elements except th and low ta they are similar to many destructive plate margin basalts on a th hf ta diagram the rocks plot in a sub linear trend reflecting variation in th hf samples with high th hf ratios come from the zone of highest metamorphic grade where the host gneisses are deficient in th consequently the patterns in the metabasites could not have been produced by any secondary metamorphic fractionation or by bulk contamination by the country rocks there is no evidence for any post magmatic mobility of any of the elements except rb which is depleted in the highest grade rocks relative to their lower grade counterparts the trace element distributions are largely reflecting those of the parental magmas but consideration of bulk distribution coefficients shows how they may have been modified in some aspects e g ce n nd n by the imposition of the metamorphic mineralogies the data are consistent with a model involving a derivation from a mantle source region which had been affected by subduction related hydrous metasomatism or partial melting and b crystallisation of the magmas directly under the high grade conditions

ree th hf ta in bamble gabbros southern norway and their amphibolitized equivalents implications for gabbro tectonic setting abstract the bamble gabbros hyperites are a group of partly metamorphosed proterozoic basic intrusions in the bamble sector of southern norway they are discordant to structures formed during the kongsbergian 1 54 ga high grade metamorphism yet are themselves partially amphibolitized in some localities transitions from gabbro to amphibolite occur over only a few metres a previous study of closely spaced gabbro amphibolite sample pairs revealed that amphibolitization was accompanied by increases in k fe3 p h2o rb cl zr and decreases in ca fe2 s zn si co new data for ree th hf ta in the same samples indicate that the only possible metamorphic modification of these elements is a barely significant increase in la in one locality eu eu ratios are preserved this adds confidence to the use of ree as petrogenetic indicators in amphibolitized basic rocks the resistance of sm nd and lu hf ratios to the amphibolitization may indicate that these isotopic systems could be used to gain geochronological and petrogenetic information from the gabbros and their amphibolitized equivalents the combined chemical data fingerprint the gabbros as similar to present day destructive plate margin related basic rocks this is surprising as it has previously been widely supposed that they are an expression of the tensional alkaline magmatism that was widespread in the north atlantic province at 1 25 ga it thus seems more likely that the bamble gabbros are related to renewed subduction after the 1 25 ga anorogenic period the geochemistry of these widespread gabbros must be accounted for in future proterozoic scandinavian tectonic reconstructions

a sulphur isotope study of the broken hill deposit new south wales australia sulphur isotopic compositions of sulphides within garnet rich rocks and high grade ore from the broken hill deposit new south wales australia have been determined and show a range of values of 3 3 to 6 7 per mil thermochemical considerations including the spread of values of 34s suggest that the deposit was derived from a mixed source of sulphur in which seawater reduced by inorganic processes mixed with magmatic sulphur or that sulphate from contemporaneous seawater was reduced biogenically at low temperatures thermochemical considerations also suggest that pyrrhotite formed by desulphidation of pyrite so that the original fe s o assemblage was pyrite magnetite

oxide and sulphide minerals in highly oxidized rb depleted archaean granulites of the shevaroy hills massif south india oxidation states and the role of metamorphic fluids the shevaroy hills of northern tamil nadu southern india expose the highest grade granulites of a prograde amphibolite facies to granulite facies deep crustal section of late archaean age these highly oxidized quartzofeldspathic garnet charnockites generally show minor high tio2 biotite and amphibole as the only hydrous minerals and are greatly depleted in the incompatible elements rb and th peak metamorphic temperatures garnet orthopyroxene and pressures garnet orthopyroxene plagioclase quartz are near 750 degrees c and 8 kbar respectively pervasive veinlets of k feldspar exist throughout dominant plagioclase in each sample and show clean contact with orthopyroxene they are suggested to have been produced by a low h2o activity migrating fluid phase under granulite facies conditions most likely a concentrated chloride carbonate brine with high alkali mobility accompanied by an immiscible co2 rich fluid silicate oxide and sulphide mineral assemblages record high oxygen fugacity pyroxenes in the felsic rocks have high mg mg fe 0 5 0 7 the major oxide mineral is ilmenite with up to 60 mole per cent exsolved hematite utilizing three independent oxygen barometers ferrosilite magnetite quartz ferrosilite hematite quartz and magnetite hematite in conjunction with garnet orthopyroxene exchange temperatures samples with x hm ilm 0 1 yield a consistent oxygen fugacity about two log units above fayalite stability less oxidized samples x hm ilm 0 4 pyrite is the dominant sulphide and pyrrhotite is absent pyrite grains in these samples have marginal alteration to magnetite along the rims signifying a high temperature oxidation event moderately oxidized samples 0 1 x hm ilm 0 4 have abundant co existing pyrrhotite pyrite and magnetite the most reduced granulite samples have pyrrhotite as the dominant sulphide with little or no pyrite and no coexisting magnetite chalcopyrite is a common accessory mineral of pyrite and pyrrhotite in all the samples textures in some samples suggest that it formed as an exsolution product from pyrrhotite extensive vein networks of magnetite and pyrite associated principally with the pyroxene and amphibole give evidence for a pervasive highly oxidizing fluid phase thermodynamic analysis of the assemblage pyrrhotite pyrite and magnetite yields consistent high oxidation states at 700 800 degrees c and 8 kbar the oxygen fugacity in our most oxidized pyrrhotite bearing sample is 10 12 65 bar at 770 degrees c there are strong indications that the shevaroy hills granulites recrystallized in the presence of an alkali rich low h2o activity fluid probably a concentrated brine it cannot be demonstrated at present whether the high oxidation states were set by initially oxidized protoliths or effected by the postulated fluids the high correspondence of maximally rb depleted samples with the highest recorded oxidation states suggests that the rb depletion event coincided with the oxidation event probably during breakdown of biotite to orthopyroxene k feldspar we speculate that these alterations were effected by exhalations from deep seated alkali basalts which provided both heat and high oxygen fugacity low a h2o fluids it will be of interest to determine whether greatly rb depleted granulites in other precambrian terranes show similar highly oxidizing signatures

sulfide remobilization during low temperature alteration of seafloor basalt abstract the behavior of sulfide minerals during the physical and chemical changes accompanying seafloor alteration was studied in three basalt flows from the bottom of d s d p hole 418a leg 53 the rocks are mildly altered and contain primary authigenic and vein sulfide minerals sulfide habit mineralogy and trace element content are inter related and are correlated with the extent and type of silicate and oxide alteration incipient alteration at 90 100 c was accompanied by low temperature reequilibration of pyrrhotite and locally by the oxidation of pyrrhotite to pyrite plus magnetite the dominant stage of alteration at 90 c is characterized by dissolution and local redistribution of pyrite and chalcopyrite whose precipitation appears to be controlled by the water rock ratio and the extent to which the water has been modified by reaction with the basalt chalcopyrite was concentrated relative to pyrite by slight changes in fluid composition caused by reaction with other minerals concurrent precipitation of smectite causes a net increase in rock volume tending to restrict seawater access calculations of rock cooling rate through time suggest that the most prolonged hydrothermal circulation occurs at low temperatures giving rise to pervasive low temperature alteration assemblages

isotopic constraints on the timing of crustal accretion of the bamble sector norway as evidenced by coronitic gabbros abstract this paper presents the first sm nd data for coronitic gabbros hyperites from the high grade proterozoic bamble sector norway sm nd whole rock isochron ages of the vestre dale gabbro 1 11 0 14 ga the jomasknutene gabbro 1 77 0 19 ga and the flosta gabbro 1 64 0 23 ga indicate that contrary to earlier ideas intrusion of these gabbros is not exclusively bound to the sveconorwegian orogeny 1 2 0 9 ga some of the gabbros were already emplaced at the onset of or during the gothian orogeny 1 75 1 5 ga initial nd values of about 5 5 of jomasknutene and flosta gabbros provide clear evidence of a depleted mantle reservoir beneath this part of the southwest scandinavian domain this highly positive value differs from the nd isotope evolution curve for the southwest scandinavian mantle as postulated by mearns et al 1986 which assumes that depletion of the mantle beneath this part of scandinavia started at c 1 74 ga however the initial nd value of the vestre dale gabbro plots close to this curve whereas 143nd 144nd ratios of the mantle sources of the tromoy and arendal gabbros evolved with approximately chondritic 144sm 144nd ratios their nd 1 1 ga values range from 5 1 0 3 to 6 0 0 3 gothian metasomatism of a depleted mantle source by lile and lree bearing fluids provides a mechanism to obtain low nd isotope ratios in magmas represented by the vestre dale gabbro examples of low nd isotope magmas have also been found in the telemark sector and in southern sweden the marked depletion in nb indicates that the metasomatic fluids were possibly related to gothian subduction

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

geochemical behavior of sulfur in granitoids during intrusion of the south mountain batholith nova scotia canada abstract a detailed stable isotope s o and elemental major trace s content study of peraluminous s type granites and granodiorites of the south mountain batholith and the meguma group metasediments into which the batholith was intruded has been conducted on a regional and local scale near mt uniacke sulfur contents of the metasediments range from 5 to 2440 ppm and 34 s ranges from 3 7 to 26 3 sulfur contents of the igneous rocks range from 6 to 570 ppm with the granites 20 ppm having lower sulfur contents than the granodiorites 300 ppm approximately 30 to 60 of the sulfur in the granodiorites is present as pyrrhotite a late phase with most of the remainder being present as sulfur substituted into biotite an early phase 18 oq quartz values of the mt uniacke granodiorites are heavy a 12 2 indicating formation of the magmas by partial melting of sedimentary rocks major element variations suggest that the granites are related to the granodiorites by fractional crystallization of plagioclase quartz and biotite comparison of the sulfur contents of the granodiorites with experimental determinations of sulfur solubility suggest that the distribution coefficient of sulfur d s between the cumulate and the magma during fractional crystallization 4 the regional granodiorites have a relatively restricted range of 34 s values 5 4 to 8 4 while the regional granites have a wide range of 34 s values 1 6 to 15 0 granodiorites at mt uniacke with normal magmatic values 0 76 to 1 42 for 18 o quartz feldspar have 34 s values between 6 6 and 12 3 and show good negative correlations between 34 s and s feo and mgo contents some granodiorites at mt uniacke have anomalously low sulfur contents for their major element composition and 18 o quartz feldspar values 0 45 to 0 67 indicate that these samples have undergone hydrothermal alteration and this alteration event is probably responsible for the low sulfur contents a number of processes have been considered in order to understand the variations of 34 s partial melting of inhomogeneous source rocks may be responsible for some of the regional 34 s variations but this implies that the granites are not genetically related to the granodiorites inhomogeneous source rocks are an unlikely explanation for the systematic variations of 34 s observed over only a few kilometres at mt uniacke rayleigh fractionation accompanying the fractional crystallization of biotite 34 s pyrrhotites silicate s 0 5 to 1 0 can account for only a small component of the observed 34 s variations the assimilation of isotopically variable sulfur derived from the meguma group metasediments during fractional crystallization combined assimilation fractional crystallization or afc provides the best explanation for the 34 s variations transfer of sulfur from the country rock may have been possible by either bulk afc where all of the country rock material is incorporated into the magma or by selective afc where sulfur and other volatile elements only are transferred from the country rock into the magma selective afc could have been effected by a sloping mechanism of intrusion followed by the heating of country rock xenoliths to the point where extensive desulfidation reactions took place with sulfur being transferred from the country rock to the magma by a fluid phase

proterozoic copper deposits in nw queensland australia sulfur isotopic data sulfur isotopic disequilibrium is commonly observed between associated pyrite and copper sulfides in nw queensland a sulfur isotopic study of copper mineralization in dolomites at paradise valley and arenites at mammoth has allowed the significance of such disequilibrium to be evaluated copper mineralization at paradise valley is characterized by a greater enrichment in 34s with 34s values often greater than 30 for both copper sulfides and associated syngenetic diagneetic pyrite at mammoth copper sulfides have isotopic compositions 34s 15 9 to 0 3 transitional between disseminated syngenetic diagenetic pyrite 34s 5 7 to 1 7 and epigenetic vein pyrite 34s 17 9 to 7 1 suggesting progressive reaction and replacement of syngenetic diagenetic pyrite by a copper bearing mineralizing fluid under oxidizing conditions the isotopic data within the constraints imposed by geological and geochemical factors support a model of reaction between copper bearing mineralizing fluids and pre existing syngenetic diagenetic pyrite for both the carbonate and arenite hosted deposits

timing of superposed volcanism in the proterozoic mount isa inlier australia metamorphosed proterozoic successions in the mount isa inlier contain a variety of volcanic suites interspersed at several intervals throughout the 30 km thick stratigraphic pile the u pb isotopic systematics of zircons crystallised in superposed felsic volcanic units allow detailed definition of the chronology of this volcanism and therefore of the major depositional cycles this supracrustal development spanned a 270 ma interval in the early to mid proterozoic new u pb zircon data from the earliest recognised volcanic cycle leichhardt metamorphics yield a pooled age for this event at 1867 5 ma a far northern segment of the same basement succession contains a geochemically similar felsic sequence 1852 7 ma old these results confirm the coevality between this felsic volcanism and nearby intrusive bodies of the same age the second major cycle of volcanism is 60 80 ma younger than the first this interval representing the maximum duration of the intervening regional unconformity dacitic and mafic volcanic rocks bottletree formation which unconformably overlie the western flank of the 1870 ma basement are dated in two areas at 1790 810 and 1808 1722 rhyodacites argylla formation on the eastern side of the basement have a similar age 1783 5 ma so for purposes of correlation and crustal evolution these two sequences flanking either side of the basement can be considered to comprise a single volcanic cycle subsequent cycles of felsic volcanism are recognised in stratigraphically younger sequences which include rhyolites with well resolved u pb zircon discordance patterns indicating ages of 1720 7 ma doherty formation and 1678 3 ma carters bore rhyolite the youngest volcanic cycle 1603 6 ma is evidenced by rhyolitic lavas in a part of the sequence previously considered to be much older at least 1740 ma recognition of such a young volcanic episode has an important economic bearing for it implies that rocks equivalent in age to the prospective pb zn rich mount isa group in the west ca 1670 ma could well exist in the eastern succession of the inlier

distribution mineralogy and geochemistry of selenium in felsic volcanic hosted massive sulfide deposits of the finlayson lake district yukon territory canada three significant base metal deposits were recently discovered in the finlayson lake district yukon territory canada however widely varying selenium contents e g 1 100 ppm avg se at wolverine 200 ppm avg se at kudz ze kayah and 7 ppm avg se at gp4f have hindered their rapid exploitation observations and data from the deposits in the finlayson lake district show a strong positive correlation between high temperature 300 c copper rich sulfide assemblages at the base of volcanic hosted massive sulfide vhms and the selenium content of all sulfide minerals thermodynamic calculations for selenide and sulfide minerals indicate significantly higher temperatures of formation and lower solubilities of selenide versus sulfide minerals which is consistent with petrographic observations and can explain the distribution of selenium in zone refined vhms and volcanic sediment hosted massive sulfide deposits volumetric mass balance calculations indicate that some selenium could be sourced from contemporaneous volatile degassing of seo 4 its rapid reduction to h 2 se and subsequent entrainment into hydrothermal ore fluid however estimates for the kudz ze kayah and wolverine deposits suggest an additional large se reservoir volumetric mass balance estimates indicate that contemporaneous volcanic rocks and black shales are likely selenium reservoirs for the kudz ze kayah and wolverine deposits respectively

variations of sulfur isotopes in metamorphic rocks from bamble sector southern norway a laser probe study abstract variations of sulfur isotopes in metamorphic rocks from bamble sector southern norway are investigated using a q switched pulsed mode laser combustion technique the results indicate that laser related fractionations are reproducible 1 0 2 provided uniform conditions are maintained during analysis bamble is a precambrian high grade metamorphic terrain a transition from amphibolite to granulite facies occurs across the 25 km width of the sector supracrustal rocks of mid proterozoic ages were intruded by felsic and mafic magmas and metamorphosed during the sveconorwegian orogenic episode earlier studies indicated that bamble rocks equilibrated under a relatively high f o 2 2 3 log units above qfm buffer during peak metamorphism j geochemical exploration 31 1989 149 j geology 100 1992 447 contrib mineral petrol 1139 2000 180 which led to phase changes in sulfides pyrrhotite or po mss has variably been replaced by pyrite magnetite mantling of pyrite by magnetite is common metasupracrustal rocks display a large variation in 34 s cdt 1 to 12 consistent with data from sedimentary rocks of similar age no distinction can be made between amphibolite transition and granulite zones the isotopic signature of sulfides was determined by bacteriogenic reduction of seawater sulfate with an initial 34 s value of 20 30 tonalitic trondhjemitic gneisses from granulite zone show a large scatter in 34 s cdt 0 to 8 implying that the parent magmas were contaminated by sedimentary materials this is supported by s se ratios mafic rocks from various metamorphic zones display a clustering of 34 s cdt values around 0 and s se ratios in the range 3 10 3 to 6 10 3 this is consistent with a mantle source for s ni cu sulfide ores locally associated with the mafic rocks however are enriched in 34 s indicating the involvement of sedimentary s in the formation of the ores mass and isotopic balance calculations indicate that oxidation of pyrrhotite or po mss proceeded without significant addition or removal of s sulfur liberated during mantling of fe sulfides by magnetite was in a reduced form and reprecipitated in short distances as secondary overgrowth and fracture filling pyrite the large variation of 34 s values for the supracrustal rocks and the preservation of the original isotopic features for various rock units suggest that no isotopic homogenization occurred in spite of the high grade metamorphism

sulfur and oxygen isotopic evidence of country rock contamination in the voisey s bay ni cu co deposit labrador canada abstract the emplacement of basaltic magma into sulfide bearing country rocks provides a favorable geologic environment for magmatic sulfide ore formation related either directly to assimilation of country rock sulfur or indirectly to a depression of sulfide solubility caused by assimilation induced changes in magma composition pelitic country rocks of the proterozoic tasiuyak gneiss in the area of the voisey s bay ni cu co deposit contain sulfidic layers that may have provided sulfur to basaltic magmas during emplacement of the voisey s bay intrusion sulfur isotopic compositions of the tasiuyak gneiss range from 0 9 to 17 0 values typical for sulfides produced via bacterial sulfate reduction in an open marine environment archean gneisses in the area contain low amounts of sulfide and are less likely to have served as a source of externally derived sulfur sulfur isotopic compositions of the sulfide minerals from the voisey s bay deposit show consistent variations both spatially and with rock types disseminated and massive sulfides show a decrease in 34 s to the west with values typically between 0 and 2 in the eastern deeps ovoid and discovery hill zone and between 2 and 4 in the reid brook zone 34 s values of the mushua intrusion to the north and the normal troctolite in the eastern deeps are more positive ranging between 0 5 and 1 8 this range is taken to represent the isotopic composition of primary mantle derived sulfur in the area because the mushua intrusion and normal troctolite show the least geochemical evidence for contamination by country rocks sulfur isotopic data from the reid brook zone are consistent with up to a 50 sulfur contribution from the tasiuyak gneiss correspondingly lower proportions are indicated for the eastern portion of the deposit where country rocks are predominantly low sulfide enderbitic and quartzofeldspathic gneisses oxygen isotopic values of gneiss fragments in the basal breccia sequence and feeder breccia suggest that the assimilation process involved a greater proportion of high 18 o contaminant to the west 18 o values of the tasiuyak gneiss 5 9 to 14 0 enderbitic gneiss 6 4 to 8 7 and archean quartzofeldspathic gneiss 9 5 to 9 7 are consistent with an increased proportion of tasiuyak gneiss contaminant to the west isotopic data strongly indicate that sulfur from the tasiuyak gneiss has been involved in ore deposition at the voisey s bay deposit however sulfur and oxygen isotopic data also strongly suggest that the addition of externally derived sulfur was not the sole process responsible for mineralization and that assimilation of both proterozoic and archean country rocks played a key role in depressing sulfide solubility prior to sulfide localization via dynamic physical mechanisms

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

trace element characteristics and pb isotopic evolution of metasediments and associated proterozoic rocks from the amphibolite to granulite facies bamble sector southern norway abstract a study of trace element distribution and rb sr sm nd and pb isotopic compositions has been performed on amphibolite and granulite facies metasediments mafic granulites dioritic gneiss intrusive enderbitic veins and calc alkaline tonalitic gneisses from the proterozoic bamble sector southern norway the lile content of the granulite facies metapelites is similar to the average of the upper crust and post archaean average shales the k rb ratios of the amphibolite and granulite facies semipelites and impure quartzites are similar and the k rb ratios of the metapelites show overall similarities to the ratios of undepleted metapelites sr isotopic system and a poor correlation in the sm nd system the calculated t dm model ages for the metasediments can represent crustal residence times of 1 67 to 2 05 ga the present day lead isotopic data can be reproduced by a three stage model of pb evolution in which t 0 4 57 ga t 1 1 9 or 1 5 ga t2 1 1 ga 1 238 u 204 pb 7 9 1 232 th 238 u 2 5 2 4 15 where t 1 and t 2 are related to separation from the mantle and the sveconorwegian orogeny respectively the protolith of the metasediments the dioritic gneiss and the mafic granulites evolved in high u pb environments prior to sveconorwegian times 2 16 32 19 and18 45 respectively most of these rock units experienced conditions of 2 3 and 2 3 suggesting a large scale fractionation in the u th pb system connected to u mobility during the medium to high grade metamorphism there are no unambiguous differences in the pb isotopic composition between the amphibolite and granulite facies rocks but the mafic granulites from the classical depleted granulite area of tromoy island evolved in overall lower 2 238 u 204 pb environments than similar rocks from the neighbouring hisoy island this suggests that the similar u content of these rocks largely can be due to local pre sveconorwegian 238 u 204 pb variations sveconorwegian intrusive enderbitic dykes and veins crystallized with low lile and nb concentrations at granulite facies p t aco 2 conditions pre sveconorwegian granulite facies tonalitic gneisses show a less depleted trace element pattern and low nb concentrations and the hornblende free tonalitic gneisses have significantly lower u content than their hornblende bearing counterparts the investigated metasediments have very low contents of the less mobile elements nb sr cu and p 2 o 5 which probably represent characteristics of the pre sedimentary protolith

age and lead isotope systematics of uranium enriched cobalt mineralization in the modum complex south norway abstract in the modum complex in the precambrian kongsberg sector of south norway cobalt sulphides and arsenides chalcopyrite and pyrite occur in stratiform bands and lenses the cobalt ore minerals are intimately associated with thorian uraninite both on a regional and on a microscopic scale due to the presence of coeval inclusions and intergrowths of uraninite in the cobalt minerals hand picked separates of ore minerals show a large range of u pb ratios this has led to a very large range of present day lead isotopic composition 206 pb 204 pb 18 1 to 277 207 pb 204 pb 15 6 to 36 208 pb 204 pb 37 to 57 two groups of samples can be discerned group 1 defines an imperfectly fitted pb pb lead isochron with an age of 1434 29 ma group 2 defines a pb pb correlation line with an age of 1146 66 ma these results indicate that the uranium bearing cobalt ore was deposited during the orogenic interlude commonly thought to separate the gothian kongsbergian ca 1 5 ga and sveconorwegian 1 2 0 9 ga orogenies in the baltic shield multi stage lead modelling indicates that the initial isotopic composition of the lead in the ores is indistinguishable from that of lead in the country rock metasediments suggesting that it was extracted from such a source the group 2 leads were affected by a strongly localized hydrothermal reworking process during the sveconorwegian orogeny which led to small scale partial pb isotopic homogenization and to strong fractionation of uranium thorium and lead the 1 43 ga age for primary mineralization defines a definite lower age limit for the onset of clastic sedimentation in the kongsberg sector the crustal precursor of the sediments must have retained a high lile upper continental crust character for several hundred million years prior to sedimentation

titaniferous magnetite ilmenite thermometry and titaniferous magnetite ilmenite orthopyroxene quartz oxygen barometry in granulite facies gneisses bamble sector se norway implications for the role of high grade co 2 rich fluids during granulite genesis oxygen fugacities have been estimated for a wide distribution of samples from the granulite facies terrane region c of the bamble sector se norway using both the titaniferous magnetite ilmenite and orthopyroxene titaniferous magnetite quartz oxygen barometers these oxygen fugacities are estimated using temperatures calculated from the titaniferous magnetite ilmenite thermometer of ghiorso and sack 1991 and are both internally consistent with each other as well with the thermometer in samples for which the estimated temperature is high the two oxygen barometers show good agreement whereas agreement is poor for low temperature samples in these low temperature samples oxygen fugacities estimated from titaniferous magnetite ilmenite are considerably less than those estimated from orthopyroxene titaniferous magnetite quartz an increase in this discrepancy with decrease in temperature appears to reflect preferential resetting of the hematite component in the ilmenite grains without significant alteration of the more numerous titaniferous magnetite grains this is due in part to greater re equilibration of the ilmenite grains during retrograde interoxide resetting between the ilmenite grains and the titaniferous magnetite grains the mean temperature for the non reset samples 791 17 c 1 is in good agreement with temperatures obtained from garnet orthopyroxene kd exchange thermometry in the same region 785 795 c 1 harlov 1992 2000a most non reset oxygen fugacities range from log10 f o2 14 to 11 8 or approximately 0 5 1 5 log units above quartz fayalite magnetite at 7 5 kbar both these temperatures and the range of oxygen fugacities are in good agreement with those estimated using the titaniferous magnetite ilmenite thermometer oxygen barometer of andersen et al 1991 the quilp equilibrium quartz ulvospinel ilmenite pyroxene is used to project self consistent equilibrium temperatures and oxygen fugacities for samples reset due to hematite loss from the ilmenite grains these projected temperatures and oxygen fugacities agree reasonably well with the non reset samples the mean projected quilp temperature is 823 6 c 1 this result supports the conclusion that low titaniferous magnetite ilmenite temperatures down to 489 c and accompanying low oxygen fugacities are the result of hematite loss from the ilmenite grains non reset oxygen fugacities lie approximately 1 5 log10 units above the upper graphite stability curve indicating that the stable c o h fluid phase interacting with these gneisses whether regionally or locally was co2 this is borne out by the presence of numerous co2 rich fluid inclusions in these rocks

subannual to interannual variabilities of sst in the north atlantic ocean abstractbased on observational data this work examines the multi time scale feature of the sea surface temperature sst variability averaged in the whole north atlantic ocean to be referred to a

oxygen and sulfur isotope geochemistry revealing a significant crustal signature in the genesis of the post collisional granitoids in central anatolia turkey abstract late cretaceous granitoid rocks from central anatolia comprise s i a type plutons derived from the collisional stages of the neo tethyan convergence system in central turkey these granitoids intrude the tectonic imbrication zone consisting of blocks of supra subduction zone type ssz type central anatolian ophiolite and crustal metasediments which are present in the izmir ankara erzincan suture zone the plutons are overlain by late palaeocene early eocene or younger detrital sediments granitoid formation is thought to be related to magma generation processes occurring in a post collisional lithospheric detachment related geodynamic setting that resulted from slab break off or lithospheric delamination whole rock s and quartz feldspar o isotope data from these plutons yields a broad range of values and both parameters indicate a nearly exclusively supracrustal origin for the s type granites as well as a significant crustal contribution in the genesis of the hybrid i type and a type granitoids the more mafic i type and a type granitoid rocks of any given suite have lower s and o values indicative of their larger degree of mantle component the combined stable isotope geochemical compositions when coupled with major trace and ree geochemistry and regional geology provide evidence that the significant crustal contribution originated from a metasomatized mantle layer which was affected by earlier ssz derived fluids and then accreted into the subcontinental lithosphere as collision occurred the partial melting of such a metasomatized mantle layer in a post collisional extensional geodynamic setting supplied either by the slab break off or lithospheric delamination mechanisms provided the significant crustal signature in the hybrid magmas of the late cretaceous i type and a type granitoids in central anatolia turkey

petrology and geothermobarometry of granulite facies metapelites from the hisoy torungen area south norway new data on the sveconorvegian p t t path of the bamble sector the high grade rocks metapelite quartzite metagabbro of the hisoy torungen area represent the south westernmost exposures of granulites in the proterozoic bamble sector south norway the area is isoclinally folded and a metamorphic p t t path through four successive stages m1 m4 is recognized petrological evidence for a prograde metamorphic event m1 is obtained from relict staurolite chlorite albite staurolite hercynite ilmenite cordierite sillimanite fine grained felsic material quartz and hercynite biotite sillimanite within metapelitic garnet the phase relations are consistent with a pressure of 3 6 0 5 kbar and temperatures up to 750 850 c m1 is connected to the thermal effect of the gabbroic intrusions prior to the main m2 sveconorwegian granulite facies metamorphism the main m2 granulite facies mineral assemblages quartz plagioclase k feldspar garnet biotite sillimanite are best preserved in the several metre wide al rich metapelites which represent conditions of 5 9 9 1 kbar and 790 884 c these p t conditions are consistent with a temperature increase of 80 100 c relative to the adjacent amphibolite facies terranes no accompanying pressure variations are recorded up to 1 mm wide fine grained felsic veinlets appear in several units and represent remnants of a former melt formed by the reaction bt sil qtzgrt lq this dehydration reaction together with the absence of large scale migmatites in the area suggests a very reduced water activity in the rocks and xh2o 0 25 in the c o h fluid system was calculated for a metapelitic unit a low but variable water activity can best explain the presence or absence of fine grained felsic material representing a former melt in the different granulitic metapelites the strongly peraluminous composition of the felsic veinlets is due to the reaction grt former melt silcrd bt qtz h2o which has given poorly crystalline cordierite aggregates intergrown with well crystalline biotite the cordierite and biotite producing reaction constrains a steep first stage retrograde relative to m2 uplift path decimetre to metre wide strongly banded metapelites quartz plagioclase biotite garnet sillimanite inter layered with quartzites are retrograded to m3 amphibolite facies assemblages a p t estimate of 1 7 5 6 kbar 516 581 c is obtained from geothermobarometry based on rim rim analyses of garnet biotite plagioclase sillimanite quartz assemblages and can be related to the isoclinal folding of the rocks m4 greenschist facies conditions are most extensively developed in millimetre wide chlorite rich calcite bearing veins cutting the foliation

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

p t conditions for the arendal granulites southern norway implications for the roles of p t and co2in deep crustal lile depletion the orthopyroxene clinopyroxene garnet orthopyroxene and garnet clinopyroxene geothermometers and the garnet orthopyroxene plagioclase garnet clinopyroxene plagioclase and anorthite ferrosilite grossular almandine quartz geobarometers are applied to metabasites and the garnetplagioclase sillimanite quartz geobarometer is applied to a metapelite from the proterozoic arendal granulite terrain bamble sector norway p t conditions of metamorphism were 7 3 0 5 kbar and 800 60 c this terrain shows a regional gradation from the amphibolite facies into normal lile content granulite facies rocks and finally strongly lile deficient granulite facies gneisses neither p nor t vary significantly across the entire transition zone the change in grade parallels the increasing dominance of co2 over h2o in the fluid phase lile depletion is not a pre condition of granulite facies metamorphism granulites may have either depleted or normal chemistries the results presented herein show that lile deficiency in granulite facies orthogneisses is not necessarily related to variations in either p or t the important mechanisms in the arendal terrain were a direct synmetamorphic crystallization from magma with primary lile poor mineralogies imposed by the prevailing fluid regime and b metamorphic depletion involving scavenging of liles during flushing by mantle derived co2 rich fluids the latter process is constrained by u pb and rb sr isotopic work to have occurred no later than 50 ma after intrusion of the acid intermediate gneisses and was probably associated with contemporary basic magmatism in a tectonic environment similar to a present day cordilleran continental margin

are stable isotopic trends in amphibolite to granulite facies transitions metamorphic or diagenetic an answer for the arendal area bamble sector southeastern norway from mid proterozoic carbon bearing rocks the isotopic 3 i3 c and 3 18 0 compositions of primary marbles and secondary veins calcites and primary fahlbands and metapelites and secondary veins graphites sampled across the am phibolite to granulite facies transition in the bamble sector southeast ern norway have been investigated the primary calcites display a regional trend in a 3 i3c 3i80 plot which is the reverse of the expected trend the granulite grade primary calcites essentially preserved most of their initial sedimentary compositions whereas the amphibolite grade calcites have increasingly lower 3 i3 c values the 3 18 0 composi tions of amphibolite grade primary calcites and of some vein tlpes appear to be buffered by the o reservoir of the country rock the 3 1 c of graphite of different types is specific for a certain lithology but not spatially related to the metamorphic zoning reaction progress calculations and rayleigh fractionation model ling prove that prograde metamorphic decarbonation reactions alone cannot be held responsible for the isotopic trend in the marbles the reversed isotopic trend in the marbles themselves combined with the lack of any trend in the primary graphites is not compatible with pervasive flushing with a homogeneous mantle derived co2 rich fluid at granulite facies metamorphism the marble trend and the constant 3 i3 c composition of j rimary graphite throughout the metamorphic zoning are best explamed by low grade processes that did affect the stable isotopic compositions of the marbles but left the graphites unaffected the processes may even occur under diagenetic conditions later amphibolite granulite facies metamorphism preserved the trend despite the production of calcsilicates subsequent retrograde hydro thermal action produced graphite quartz veins and several types of calcite veins without resetting stable isotope systematics on a regional scale

the role of co2 in the chemical modification of deep continental crust compositional differences between granulite facies rocks and equivalent amphibolite facies rocks and the observation of co2 rich fluid inclusions in granulites have led to the suggestion that co2 must play a role in modifying the composition of deep continental crust how co2 effects this change has remained unclear using the thermodynamic properties of aqueous ions in a fluid of evolving co2h2o ratio it is possible to model the incongruent dissolution of feldspars under conditions appropriate for granulite facies metamorphism the results demonstrate that dissolution will be strongly enhanced at high co2h2o ratios with ion solubilities being na k ca this enhancement is compatible with the reported compositional contrasts between granulite and amphibolite facies rock but requires large fluid volumes to test the dissolution model a detailed field and petrologic study was conducted in a well exposed granulite facies terrane in west greenland strong correlation between fluid composition and bulk rock chemistry can be documented co2 rich regions contain rocks which consistently have low ana2oacao ratios while h2o rich regions consistently have high ana2oacao ratios magnetite rims on sulfide grains are ubiquitous in high co2 regions and are absent in high h2o regions and they provide evidence that co2 was introduced into the region these correlations and observations are predictable from the properties of the dissolution process these considerations along with observations regarding graphite petrogenesis provide strong arguments that the total fluid volume interacting with the rock during metamorphism was very large in some cases equaling or exceeding total rock volume such large fluid volumes can lead to significant compositional modification of the crust and will mask the original protolith chemistry such processes should lead to ca and al enriched na k s and si depleted residues in the deep crust

sulfur isotope behavior during metamorphism and anatexis of archean sedimentary rocks a case study from the ghost lake batholith ontario canada abstract recycling of surface derived sulfur into the deep earth can impart distinct sulfur isotope signatures to magmas the details of sulfur transfer from sedimentary rocks to magmas and ultimately igneous rocks through metamorphism and devolatilization and or partial melting however is difficult to trace to understand this process in detail we studied multiple sulfur isotope compositions of sulfides in the archean c 2685 ma ghost lake batholith glb and its surrounding host metasedimentary rocks of the superior craton ontario canada by high spatial resolution secondary ion mass spectrometry complemented by high precision gas source isotope ratio mass spectrometry measurements the glb comprises strongly peraluminous biotite cordierite biotite muscovite and muscovite garnet tourmaline granites to leucogranites which are thought to represent the partial melts of surrounding metagreywackes and metapelites the metasedimentary rocks display a range of metamorphic grades increasing from biotite chlorite 280 380 c at 5 km away from the glb to sillimanite k feldspar grade 660 c immediately adjacent to the batholith thus providing a natural experiment to understand sulfur isotope variations from low to high grade archean sedimentary rocks as well as granites representative of their partial melts we find that metasedimentary sulfide 34 s values increase with progressive metamorphism at most 2 3 from 1 up to 1 to 2 an increase in 34 s values in pyrrhotite during prograde metamorphism can be explained through rayleigh fractionation during pyrite desulfidation reactions pyrite from all but one of the granite samples preserve 34 s values similar to that of the high grade metasedimentary rocks indicating that partial melting did not result in significant fractionation of 34 s the exception to this is one granite sample from a part of the batholith characterized by abundant metasedimentary inclusions this sample contains pyrite with heterogeneous and low 34 s values down to 16 which likely resulted from incomplete homogenization of sulfur between the granitic melt and metasedimentary inclusions small several tenths of a permil mostly positive 33 s are observed in both the metasedimentary rocks and granites our results suggest that archean strongly peraluminous granites could be a high fidelity archive to quantify the bulk sulfur isotope composition of the archean siliciclastic sediments further our findings indicate that subduction of reduced sulfur bearing sediments in the archean with 34 s at or near 0 should result in release of sulfur bearing fluids in the mantle wedge with similar values within a few permil s mif if initially present in archean surface material may be preserved during this process however the absence of s mif in igneous rocks does not preclude assimilation of archean sedimentary material as either s mif may not be originally present in the archean sedimentary sulfur and or homogenization or dilution could obscure any s mif originally present in assimilated archean sediments

comparative oxygen barometry in granulites bamble sector se norway oxygen fugacities have been estimated for the high grade portion of the bamble granulite facies terrane se norway using both titaniferous magnetite ilmenite and orthopyroxene titaniferous magnetite quartz oxygen barometers the two oxygen barometers show good agreement for samples indicating high titaniferous magnetite ilmenite temperatures whereas agreement is poor for low temperature samples oxygen fugacities estimated from titaniferous magnetite ilmenite are considerably lower than those estimated from orthopyroxene titaniferous magnetite quartz this discrepancy increases with a decrease in temperature which appears to reflect preferential resetting of the hematite content in the ilmenite grains without much alteration of the more numerous titaniferous magnetite or orthopyroxene grains the mean temperature for the non reset samples 795 60 c 1 agrees well with temperatures obtained from garnet orthopyroxene k d exchange thermometry in the same region 785 60 c 1 most non reset o

mobilization of gold in the deep crust evidence from mafic intrusions in the bamble belt norway abstract the location of mesothermal gold deposits in the upper part of major transcurrent shear zones suggests that gold was derived from the deep wider portions of the shears the 30 km wide bamble belt south norway is a deep shear belt metamorphosed to upper amphibolite and granulite grade at about 1 1 ga preliminary studies showed that its rocks are strongly depleted in gold and other chalcophile elements mafic rocks were chosen for more detailed study of the mobilization of gold during metamorphism gold in mafic rocks largely partitions into the sulphide phase which is mainly comprised of pyrrhotite modification of this phase was required to liberate gold bamble has two main groups of mafic rock the first metabasites intruded before peak metamorphism are uniformly low in gold their o2 at peak metamorphism obtained from ilmenite orthopyroxene equilibria indicates a strongly oxidized mineral assemblage well above fmq pyrrhotite was stable at peak temperature of 800 c but on cooling below 600 c internal mineralogical buffering by the oxidized assemblage caused the o2 to cross into the stability field of pyrite following conversion of pyrrhotite to pyrite the latter was partly replaced by magnetite these serial changes in the mineralogical form of iron sulphide was conducive to the extraction of gold as was the oxidized nature of the mineral assemblage that would have buffered metamorphic fluids to high o2 the second group of mafic rocks hyperites intruded after peak metamorphism record intermediate steps in the extraction of gold these intrusions of coronitic gabbro were metamorphosed in whole or in part to amphibolite there is a decrease in gold and other chalcophile elements across a hyperite dyke from the pyrrhotite bearing coronitic gabbro interior to the pyrite bearing amphibolite margin

euxinic conditions recorded in the ca 1 93 ga bravo lake formation nunavut canada implications for oceanic redox evolution abstract the composition of seawater changed dramatically during the initial rise of atmospheric oxygen in the earliest paleoproterozoic but the emerging view is that atmosphere ocean system did not experience an irreversible transition to a well oxygenated state instead it has been suggested that the oxygen content of the atmosphere ocean system decreased considerably after ca 2 06 billion years ago ga which resulted in a crash in marine sulfate concentrations the end of the deposition of major granular iron formations at ca 1 85 ga has been linked either to the development of extensive euxinic conditions along continental shelves or a decrease in hydrothermal flux the record of oceanic redox state is not well constrained for the period between ca 2 06 ga the end of the lomagundi positive carbon isotope excursion and ca 1 88 ga when major granular iron formations appeared we address this gap by presenting new iron speciation major and trace element data as well as sulfur organic carbon and molybdenum isotopic data for greenschist facies organic matter rich mudrocks orms of the ca 1 93 ga bravo lake formation piling group baffin island the iron speciation data suggest deposition of the bravo lake formation under a euxinic anoxic and sulfidic water column trace metal enrichments and mo isotope data suggest extensive marine euxinia ca 90 million years before the disappearance of large scale economic granular iron formations the addition of new mo data in this time interval is important as it contributes to filling in the sparse proterozoic record lastly this work provides further support for the idea that there was widespread anoxia shortly after the end of the lomagundi event

multiple sulfur and iron isotope composition of magmatic ni cu pge sulfide mineralization from eastern botswana we report here high precision multiple sulfur and iron isotope compositions for a series of mineralized samples from ni cu pge sulfide deposits in the archean tati greenstone belt and the phikwe complex of eastern botswana mineralized samples from the phoenix and selkirk ni cu pge deposits in the tati greenstone belt display slightly positive 34s isotope values ranging from 0 2 to 0 8 v cdt 33s values of sulfides at phoenix and selkirk are 0 01 to 0 08 v cdt suggesting either a dominantly mantle sulfur source or effective eradication of a crustal 33s anomaly through equilibration with large amounts of silicate melt in the selebi phikwe belt a granite gneiss terrane with abundant amphibolite lenses of either volcanic and or intrusive nature mineralized lower grade samples from the phikwe phokoje and dikoloti ni cu pge deposits have more variable 34s values ranging from 3 1 to 0 3 and display significant mass independent anomalies 33s values ranging from 0 89 to 0 27 suggesting that barren sulfides associated with distal or low temperature sea floor hydrothermal activity contributed sulfur to these deposits iron isotopes of sulfides from these deposits show a relatively small range of negative 56fe values 0 29 to 0 04 consistent with high temperature fractionations in magmatic systems with the exception of one sample from the dikoloti ni cu pge deposit of the selebi phikwe greenstone belt which shows a more negative 56fe value of 0 61 consistent with assimilation of sedimentary or hydrothermal sulfides rather than fractionations in high temperature magmatic systems data from this study highlight the complexity and variability that characterize ore forming processes in magmatic systems we suggest that the presence of sulfur bearing lithologic units in host rocks of mafic and ultramafic intrusions may not be essential toward the assessment of the prospectivity of a province to host orthomagmatic nickel sulfides geologic settings without any or little sulfur in the stratigraphy which have been traditionally neglected in terms of their prospectivity should thus be revisited and possibly reassessed considering the potential importance of external source of sulfur to generate ore deposits

an evaluation of the solubility of sulfide sulfur in silicate melts from experimental data and natural samples abstract an evaluation of the solubility of sulfur in silicate melts from experimental data obtained under a wide variety of experimental conditions has been undertaken under reducing conditions fo2 below qfm sulfur is present as sulfide ii oxidation state and precipitates as pyrrhotite or an fe s o sulfide phase when the sulfur concentration in the silicate melt is sufficiently high the basic solubility reaction is 1 2 s 2 g o 2 silicate melt 1 2 o 2 g s 2 silicate melt for silicate melts with high feo contents 10 wt feo sulfur dissolves as an fe3so2 or 2feo fes species when saturated with pyrrhotite fes sulfide melt 2feo silicate melt fe 3 so 2 silicate melt log k log x s 21ogx feo 0 8 at 1200 c 1 bar under saturated and unsaturated conditions 1 2 s 2 g 3feo silicate melt fe 3 so 2 silicate melt 1 2 o 2 g log k log x s 1 2 1og o 2 3 log x feo 1 2 log s 2 4 1 at 1200 c 1 bar log k also shows a positive pressure dependence 0 1 per kbar for silicate melts with low feo contents fes sulfide melt o 2 silicate melt feo silicate melt s 2 silicate melt log k log x s log x feo 5 8 9007ndash 1000 c 1 6 kbar for silicate melts with intermediate feo contents 1 10 wt feo the behavior of sulfur is more complex with sulfur probably present as an fes species fes sulfide melt fes silicate melt log k log x s 1 05 3000 t k 850 1200 c 1 bar 2 2 kbar the effects of temperature pressure melt composition and other experimental conditions have been assessed the ability to predict the solubility of sulfur in silicate melts has implications for the formation of ore deposits associated with igneous systems application of the results to natural systems shows that some samples have a concentration of sulfur higher than that which could have been dissolved in the silicate melt indicating that the magma carried excess sulfur and or sulfur has been added after crystallization of the magma

petrology of the st stephen intrusion and the genesis of related nickel copper sulfide deposits the st stephen intrusion is a tholeiitic mafic ultramafic intrusion of devonian age occurring in the gander terrane of the appalachian orogen the intrusion is dominated by olivine plagioclase cumulates olivine cumulates and plagioclase cumulates olivine ranges in composition from fo 61 to fo 85 and plagioclase from an 43 to an 89 variations in the compositions of clinopyroxene and orthopyroxene are within wo sub 42 47 en sub 37 50 fs sub 6 18 and wo sub 3 3 en sub 50 71 fs sub 26 47 respectively the cr cr al and mg mg fe super 2 ratios of chromites range from 0 25 to 0 75 and 0 01 to 0 65 respectively this appears to have resulted from the changes in the composition of the melt from which chromites were crystallized and reaction of the early formed cumulus chromites with the intercumulus melt the observed crystallization sequence olivine chromite olivine plagioclase olivine plagioclase clinopyroxene plagioclase clinopyroxene orthopyroxene olivine plagioclase orthopyroxene clinopyroxene plagioclase clinopyroxene appears to have resulted from simple fractional crystallization of a common tholeiitic parent magma the composition of the parent magma seems to have an affinity to the mid ocean ridge basalts the intrusion contains numerous zones of significant ni cu sulfide mineralization the principal sulfide minerals are those typical of magmatic assemblages pyrrhotite pentlandite and chalcopyrite ni and cu concentrations reach 2 40 and 3 90 percent respectively platinum group element concentrations are generally low with maximum abundances in massive sulfides for example not exceeding 62 ppb attainment of sulfur saturation in the st stephen magma during the early stages of the differentiation corresponds to the appearance of plagioclase on the liquidus following crystallization of about 10 percent of the olivine the nickel depleted nature of olivines at this interval can be explained by fractional crystallization of olivine and sulfide in the proportion of 50 1 an earlier segregation of sulfide from the parental magma seems to be responsible for the very low levels of platinum group elements in the interstitial sulfides associated with the olivine cumulates preferential assimilation of the sulfide rich portions of the country rock metasediments and attainment of sulfide silicate equilibrium on a local scale are believed to have played important roles in the formation of large pyrrhotite rich sulfide bodies

studies of the base metal sulfide deposits at mcarthur river northern territory australia iii the stable isotope geochemistry of the h y c ridge and cooley deposits new measurements of s c and o isotopic ratios in the cooley ridge and h y c deposits at mcarthur river place important constraints on the formation of the deposits s isotope ratios in the discordant cooley and ridge mineralization and concordant ridge mineralization have absolute values and distributions similar to those of the h y c mineralization with galena and sphalerite having relatively constant values and pyrite having widely varying values galena sphalerite isotopic fractionations indicate higher equilibrium isotopic temperatures for the cooley deposits 290 degrees to 275 degrees c than for the ridge and h y c deposits 260 degrees to 100 degrees c correlating with a systematic temperature decrease away from the emu fault c and o isotope ratios for carbonates in the discordant and concordant deposits are related describing a single linear trend on a delta 13 c vs delta 18 o plot ratios for carbonates from unmineralized sediments do not plot on the line suggesting that the line does not reflect mixing of a hydrothermal and a sedimentary carbonate but rather reflects equilibrium between carbonates and a hydrothermal fluid over a temperature range similar to that indicated by the s isotopic fractionations in the discordant mineralization the isotopic equilibration occurred during the precipitation of ore stage carbonates whereas in the concordant mineralization the equilibration occurred during chemical exchange between preexisting carbonates and the mineralizing fluid and possibly also during the precipitation of some ore stage carbonates the new data provide additional support for the hypothesis that the discordant and concordant deposits are related and that both types of deposits formed from a common mineralizing fluid which flowed from the emu fault zone the data do not place unequivocal constraints on whether the concordant deposits formed syngenetically or epigenetically but they do indicate that in the concordant deposits the mineralizing process was operating at least in part below the sediment water interface

micro analysis of sulfur isotope ratios and zonation by laser microprobe the university of wisconsin laser microprobe mass spectrometer system combines high spatial resolution with precise accurate and rapid analysis of sulfur isotope ratios spot sizes of 100 200 m are routine and much higher spatial resolution may be possible analytical precision ranges from 1 0 15 pyrite pyrrhotite sphalerite to 1 0 43 galena chalcopyrite comparison of laser microprobe and conventional combustion analyses indicates that laser 34s values are approximately equal to or lower than combustion values for these minerals and an empirical correction of 0 1 sphalerite to 1 4 pyrrhotite is required variations in 18o of so2 laser power density and burn duration affect the magnitude of this correction thus consistent technique is critical natural samples were analyzed by laser microprobe to evaluate the extent of sulfur isotope ratio zonation coexisting sulfide mineral pairs from the rua cove mine alaska show that isotopic equilibrium exists in the stockwork feeder zone while disequilibrium characterizes coexisting pairs from the overlying more rapidly cooled massive sulfide blanket conventional sulfur isotope extraction data on these samples are not valid due to the fine grained intergrown nature of the sulfide phases which precludes satisfactory mineral separation isotopically homogeneous sphalerite and pyrite crystals were found in samples from the amphibolite facies balmat mine while isotopically heterogeneous pyrite crystals were found in a sample from the upper greenschist facies sullivan mine sulfur isotope zonation up to 2 9 in 200 m was found in banded sphalerite blacksmoker chimney material from the bayda mine oman retrograde sulfides from the marcy anorthosite massif vary by 4 2 over 1 cm and finely disseminated sulfides from an amphibolite granulite facies transition zone sample southern india are in disequilibrium across the 25 cm facies transition these results show that sulfur isotope homogeneity may be attained in the cores of annealed high grade metamorphic minerals while lower temperature retrograde or hydrothermally deposited minerals are often isotopically zoned due to temporal variations in fluid chemistry and temperature

sulfur isotope and pge systematics of metasomatised mantle wedge abstract at convergent margins fluids liberated from subducting slabs metasomatise the overlying mantle wedge enriching it in volatiles incompatible elements and possibly ore forming metals despite the genetic link between this process the genesis of arc magmas and formation of porphyry cu au deposits there is currently little understanding of the behaviour of chalcophile and siderophile elements during subduction related mantle metasomatism in this study we report sulfur isotopic compositions and pge concentrations of sulfides in a suite of garnet peridotites from the western gneiss region of norway sampling mantle wedge from 100 to 250 km depth sulfides hosted in metasomatised samples have 34 s deviated from typical mantle values ranging between 10 0 and 5 4 indicating derivation of sulfur from subducted crust sulfides in pervasively metasomatised samples have atypical pge signatures with strong enrichment in os and ru relative to ir whereas channelised fluid flow produced sulfides extremely enriched in pd up to 700 times the concentration found in non metasomatised samples these signatures are reconcilable with a high oxidation state of the metasomatising agents and demonstrate that subduction can recycle chalcophile and siderophile elements into and within the mantle along with sulfur we further show that because the solubility of os and ru in fluids is redox sensitive and pd is more soluble than the i pge ratios such as os ir ru ir plotted against pd ir can be used to trace the metasomatic oxidation of mantle samples mantle derived magmas and porphyry cu au deposits this geochemical insight is used to show that au rich porphyry cu deposits are derived from more oxidised mantle wedge than au poor porphyry deposits

age relationships in the proterozoic high grade gneiss regions of southern norway abstract the proterozoic high grade gneiss regions of southern norway bamble kongsberg rogaland and ostfold historically belong to the so called sveconorwegian 1 2 0 9 ga zone this has long been correlated with the grenville province of north america and features prominently in proterozoic reconstructions across the north atlantic several recent radiometric studies have provided compelling evidence for an earlier high grade gneiss forming event at 1 6 1 5 ga ago in parts of southern norway it has also been shown that at least a section of the bamble sector suffered only a relatively low grade thermal deformational event during the sveconorwegian cycle in this paper new rb sr age determinations for metasediments and an anatectic granite from the same area confirm a pre grenvillian age for the high p t event and preclude the possibility of later high grade reworking previously published age determinations for all sectors are compared with the available radiometric data from the adjoining gneissic terrane of southwest sweden and reviewed in the light of the new data from bamble and recent evidence that relatively low grade events are capable of disturbing and possibly resetting both rb sr total rock and u th pb zircon isotope systems the conclusions are that the main high grade gneiss forming event may have been pre grenvillian in all sectors and that there may have been no regional high grade reworking during the period 1 2 0 9 ga ago

a sulfur isotope study of pyrite genesis the mid proterozoic newland formation belt supergroup montana abstract different generations of sedimentary pyrite from the mid proterozoic newland formation usa have been analysed for their sulfur isotopic compositions the results indicate bacterial sulfate reduction as the pyrite forming process the 34 s values for early diagenetic pyrite around 14 are in contrast to dominantly more positive values for many other middle proterozoic units a progressive reduction of sulfate availability during diagenesis can be recognized by an increase in 34 s content rayleigh distillation as well as through detailed petrographic observations contemporaneous seawater had a sulfur isotopic ratio between 14 and 18 as measured from sedimentary barite within the unit