sulfur isotopes in diamonds reveal differences in continent construction neoproterozoic west african diamonds contain sulfide inclusions with mass independently fractionated mif sulfur isotopes that trace archean surficial signatures into the mantle two episodes of subduction are recorded in these west african sulfide inclusions thickening of the continental lithosphere through horizontal processes around 3 billion years ago and reworking and diamond growth around 650 million years ago we find that the sulfur isotope record in worldwide diamond inclusions is consistent with changes in tectonic processes that formed the continental lithosphere in the archean slave craton diamonds that formed 3 5 billion years ago do not contain any mif sulfur younger diamonds from the kaapvaal zimbabwe and west african cratons do contain mif sulfur which suggests craton construction by advective thickening of mantle lithosphere through conventional subduction style horizontal tectonics

alaskan type nature and pge mineralization of the wuxing mafic ultramafic complex in eastern part of the central asian orogenic belt abstract the wuxing mafic ultramafic complex is located in the eastern part of the central asian orogenic belt caob it consists of hornblende olivine clinopyroxenite hornblende clinopyroxenite clinopyroxenite gabbro and diorite hornblende occurs in all the rock types of the complex and is pargasite in composition clinopyroxene is diopsidic in composition with high cao and low tio2 contents the flat ree and sub parallel trace element patterns of both clinopyroxene and hornblende suggest that these rocks were formed by fractional crystallization from common magma with no significant crustal contamination enrichment in large ion lithophile elements relative to high field strength elements of the silicate minerals together with the variable sulfur isotope compositions 34s 2 55 11 01 of the sulfides indicate the involvement of subducted oceanic materials into the mantle source these petrological mineralogical and geochemical features strongly suggest the alaskan type nature of the wuxing complex the hydrous parental magma of the wuxing complex was derived from partial melting of the mantle wedge which had been metasomatized by subducted melts fluids the wuxing complex is a unique pt pd rich ni cu sulfide deposit in the caob the ore minerals which are dominated by pyrite pyrrhotite pentlandite chalcopyrite and platinum group mineral pgm mainly occur in clinopyroxenite and hornblende clinopyroxenite the sulfide ores are predominantly present as net textured and disseminated textures pentlandite and chalcopyrite associated with pyrrhotite commonly occur in the marginal zone of the pyrrhotite grains the pgms occur as interstitial grains at the contact between base metal sulfides and silicate minerals or along the crack of pyrrhotite or clinopyroxene or as inclusions in pyrrhotite the occurrences of sulfides and pgms in the wuxing complex together with sulfur isotope compositions and pge patterns reveal that the pge enrichment of the alaskan type complexes can be attributed to the high degree partial melting of the mantle source sulfur involvement in the source and pge transportation of hydrous melts

gps tec technique for observation of the evolution of substorm particle precipitation 1 one of the signatures of magnetospheric substorms is the precipitation of high energy particles into the high latitude ionosphere in this paper we introduce a new method of tracking substorm particle precipitation using gps total electron content tec and provide some preliminary observations of precipitation signatures from application of this method using tec measurements from several gps receivers we examined particle precipitation signatures associated with two separate substorm events 4 october 2008 and 29 october 2008 and monitored the expansion of the high energy precipitation regions with a higher temporal and spatial resolution than previously available for each event we have observed tec signatures associated with substorm particle precipitation along 20 to 25 separate gps raypaths from up to 7 gps receivers located in the canadian arctic this is in addition to particle injection signatures found in cluster satellite data and precipitation signatures in ground based riometer data signature timing on different raypaths from different stations indicates a mainly northward tailward expansion of the precipitation injection region with a smaller westward azimuthal component for the events studied by applying a triangulation method we also calculated propagation velocity of the precipitation boundary in regions covered by our gps receivers for each substorm expansion velocity ranged from 0 3 2 km s northward and 0 1 km s westward and tended to decrease in magnitude at higher latitudes

distinguishing diapirs from inflated plutons an integrated rock magnetic fabric and structural study on the roundstone pluton western ireland granitoid plutons account for much of the continental crust and are critical in the generation of several economic resources despite over a century of research the fundamental process by which large felsic bodies intrude remains controversial two contrasting models persist 1 mass ascent and subsequent cooling of magma diapirism 2 sheet ascent and subsequent emplacement laccoliths the latter hypothesis is different from the former as distinct ascent and emplacement processes must occur and be identifiable traditional field methods rarely allow this important distinction to be made we present field petrographic and anisotropy of magnetic susceptibility data from the roundstone pluton connemara western ireland which was previously considered a diapiric intrusion the new data reveal anomalous subvertical magmatic lineations in the core of this circular intrusion as well as a suite of magmatic and submagmatic fabrics that parallel nnw sse country rock faults and coeval g2 sheets within the pluton we deduce that these structures reflect a distinct centralized ascent process along a nnw sse conduit lateral emplacement and pluton inflation followed ultimately forming a punched laccolith we conclude that the combined application of the above techniques provides a unique insight into pluton architecture that removes ambiguity between contrasting diapiric and inflated pluton models supplementary material complete rock magnetic data tables and sample site coordinates irish grid are available at http www geolsoc org uk sup18837

sulfur isotope exchange and metal enrichment in the formation of magmatic cu ni pge deposits sulfur isotope measurements provide a useful means of evaluating the source of sulfur in magmatic cu ni pge deposits although low sulfur pge rich deposits e g j m reef of the stillwater complex merensky reef of the bushveld complex show little or no isotopic evidence for the involvement of crustally derived sulfur several high sulfur deposits e g noril sk duluth complex show strong evidence for contamination of mafic magmas by sulfur of crustal origin processes such as magma degassing or redox changes accompanying crystallization are ineffective in significantly modifying sulfur isotope signatures of sulfides that crystallize from immiscible liquids that exsolve from the mafic magmas for this reason 34s values are primarily dependent on sulfur source characteristics and variations can often be treated using a two component mixing approach however deposits such as those at noril sk and voisey s bay that appear to have formed in magma conduit systems present another possibility for modification of sulfur isotope signatures these deposits are thought to have been upgraded in metal tenor by reaction with uncontaminated mantle derived melts that traversed the accumulated sulfide on their way to the surface our calculations illustrate the efficiency of reactions that involve the exchange of fe for cu ni or pge in producing increases in the metal tenor of the accumulated sulfide sulfur isotope exchange between the crustally contaminated sulfide ore accumulation and sulfur of mantle origin may accompany chalcophile element exchange and is capable of masking or limiting the degree of isotopic evidence for the initial stage of ore genesis that involved crustal sulfur sulfur isotope exchange is distinct from the addition of sulfur in the form of immiscible sulfide droplets from a sulfide saturated magma to the accumulated sulfide although both additive mixing and exchange can lead to similar isotopic effects stable isotopic exchange provides a mechanism in addition to additive mixing that may lead to decoupling of different isotopic systems

os nd o and s isotope constraints on country rock contamination in the conduit related eagle cu ni pge deposit midcontinent rift system upper michigan abstract the eagle cu ni pge deposit is hosted by mafic to ultramafic intrusive rocks associated with the marquette baraga dike swarm in northern michigan sulfide mineralization formed in a conduit system during early stages in the development of the 1 1 ga midcontinent rift system the conduit environment represents a prime location for melt rock interaction in order to better assess the extent of country rock contamination in the eagle system a combined trace element nd os o and s isotope study of country rocks sulfide bearing igneous rocks and massive sulfide was undertaken both the eagle and the weakly mineralized east eagle intrusion show trace element patterns that are similar to those of picritic basalts that formed during early stages of rift development the trace element os nd and o isotopic values of the igneous rocks are consistent with os 1100 and e nd 1100 values for the magmas are 34 and 2 18 o values of pyroxene in feldspathic pyroxenite range from 6 5 to 6 6 and provide the only indication that bulk contamination may locally have exceeded 20 sulfur isotopic values of disseminated and massive sulfide in the eagle intrusion range from 0 3 to 4 6 the 34 s values are much lower than those that characterize most of the country rocks but could still be indicative of a contribution of s from country rocks of up to 50 33 s values of the disseminated and massive sulfides range from 0 10 to 0 09 indicating a source in paleoproterozoic country rocks semi massive sulfide in the eagle deposit has 34 s values between 2 2 and 5 3 and 33 s values show a broad range between 0 86 and 0 86 indicating a major contribution from an archean source isotopic data from the eagle deposit strongly indicate that multiple sources of sulfur were involved in the generation of the ni cu pge mineralization and magmas which traversed variable paths through the mantle and crust were focused and utilized the same conduit at the level of the eagle deposit our results emphasize the fact that the sulfur isotopic values of immediate country rocks may not be appropriate as end member values for mixing calculations sulfur derivation from deeper in the conduit system may have involved rocks with very different sulfur isotope ratios in addition sulfur isotopic exchange reactions between passing magma and accumulated crystals or sulfide liquid in the conduit may have led to decreased sulfur isotope variability and 34 s values near those of mantle sulfur

sulfur isotope composition of metasomatised mantle xenoliths from the bultfontein kimberlite kimberley south africa contribution from subducted sediments and the effect of sulfide alteration on s isotope systematics abstract sulfur isotopes are a powerful geochemical tracer in high temperature processes but have rarely been applied to the study of mantle metasomatism in addition there are very limited s isotope data on sub continental lithospheric mantle sclm material for cratonic regions these data are restricted to sulfide inclusions in diamonds to provide new constraints on the s isotope composition of the sclm and on the source s of mantle metasomatic fluids beneath the diamondiferous kimberley region south africa we investigated the s isotope systematics of five metasomatised mantle xenoliths from the bultfontein kimberlite pentlandite and chalcopyrite in these xenoliths were analysed by in situ secondary ion mass spectrometry sims with bulk rock material measured by gas source isotope ratio mass spectrometry techniques based on previous studies the xenoliths experienced different types of metasomatism to one another at distinct times 180 and 90 80 ma contained pentlandite grains show variable alteration to heazlewoodite i e ni sulfide magnetite the in situ s isotope analyses of pentlandite exhibit a relatively restricted range between 5 9 and 1 4 34 s compared to vcdt with no statistically meaningful differences between samples chalcopyrite only occurs in one sample and shows 34 s values between 5 4 and 1 0 the bulk rock ssulfide isotope analyses vary between 3 4 and 0 8 34 s importantly the only sample hosting dominantly fresh sulfides shows a bulk rock 34 s value consistent with the mean value for the sulfides whereas the other samples exhibit higher bulk 34s 32s ratios the differences between bulk rock and average in situ 34 s values are directly correlated with the degree of sulfide alteration this evidence indicates that the elevated 34s 32s ratios in the bulk samples are not due to the introduction of heavy s commonly as sulfates and are best explained by isotopic fractionation coupled with the removal of light s during serpentinisation when pentlandite is altered to s poor mixtures of heazlewoodite and magnetite available bulk ssulfide isotopic data for sclm peridotite xenoliths are dominated by positive 34 s values which contrasts with the negative values of the sulfides these results imply that the mantle s isotope values from bulk peridotite samples are commonly modified by isotopic fractionation during serpentinisation therefore the s isotopic composition of the sclm may require revision the limited isotopic variability shown by sulfides in the bultfontein mantle xenoliths is probably due to intermittent tapping of a mantle source with a relatively restricted s isotope composition while the asthenospheric mantle 34 s 1 4 is a viable candidate 34 s values as low as 5 9 require input from recycled crustal material possibly represented by the sulfur reservoir with negative 34 s signature that is missing in the 500 ma sedimentary record and could have been subducted and stored in the earth s mantle

in situ multiple sulfur isotope analysis by sims of pyrite chalcopyrite pyrrhotite and pentlandite to refine magmatic ore genetic models with growing interest in the application of in situ multiple sulfur isotope analysis to a variety of mineral systems we report here the development of a suite of sulfur isotope standards for distribution relevant to magmatic magmatic hydrothermal and hydrothermal ore systems these materials include sierra pyrite fes2 nifty b chalcopyrite cufes2 alexo pyrrhotite fe 1 x s and vmso pentlandite fe ni 9s8 that have been chemically characterized by electron microprobe analysis isotopically characterized for 33s 34s and 36s by fluorination gas source mass spectrometry and tested for homogeneity at the micro scale by secondary ion mass spectrometry beam sample interaction as a function of crystallographic orientation is determined to have no effect on 34s and 33s isotopic measurements of pentlandite these new findings provided the basis for a case study on the genesis of the long victor nickel sulfide deposit located in the world class kambalda nickel camp in the southern kalgoorlie terrane of western australia results demonstrate that precise multiple sulfur isotope analyses from magmatic pentlandite pyrrhotite and chalcopyrite can better constrain genetic models related to ore forming processes data indicate that pentlandite pyrrhotite and chalcopyrite are in isotopic equilibrium and display similar 33s values 0 2 this isotopic equilibrium unequivocally fingerprints the isotopic signature of the magmatic assemblage the three sulfide phases show slightly variable 34s values 34schalcopyrite 2 9 0 3 34spentlandite 3 1 0 2 and 34spyrrhotite 3 9 0 5 which are indicative of natural fractionation careful in situ multiple sulfur isotope analysis of multiple sulfide phases is able to capture the subtle isotopic variability of the magmatic sulfide assemblage which may help resolve the nature of the ore forming process hence this sims based approach discriminates the magmatic sulfur isotope signature from that recorded in metamorphic and alteration related sulfides which may not be resolved during bulk rock fluorination analysis the results indicate that unlike the giant dunite hosted komatiite systems that thermo mechanically assimilated volcanogenic massive sulfides proximal to vents and display negative 33s values the kambalda ores formed in relatively distal environments assimilating abyssal sulfidic shales

paragneiss assimilation in the genesis of magmatic ni cu co sulfide mineralization at voisey s bay labrador δ34s δ13c and se s evidence the voisey s bay ni cu co deposit is located in ca 1 33 ga troctolitic rocks of the nain plutonic suite northern labrador it is widely regarded as a prime example of sulfide mineralization associated with a magmatic conduit system previous geological and geochemical studies have indicated that the voisey s bay intrusion was contaminated by interaction with both sulfide poor archean gneisses and with paleoproterozoic sulfide bearing tasiuyak metasedimentary gneiss limited sulfur isotope data previously indicated that only one of the four ore zones at voisey s bay is characterized by 34s values outside the range considered normal for uncontaminated mantle derived mafic magmas 0 2 new s isotope data presented here extends the previously reported range in 34s values for the tasiuyak gneiss from 17 0 to 18 3 per mil with an average of 1 4 per mil assimilation of this sulfur followed by isotope homogenization in the magmatic system is consistent with the isotope data from the ore zones and in line with the wealth of evidence that suggests that interaction with tasiuyak gneiss was an essential ingredient for ore formation in all the zones se s values of sulfide minerals in the ore zones at voisey s bay are also in the same range as those of whole rock samples from the tasiuyak gneiss 13c values of both mineralized and nonmineralized parts of the voisey s bay intrusion are anomalous 18 3 to 24 8 and similar to values of graphite in the tasiuyak gneiss both s and c contamination of the voisey s bay intrusion via diffusive transfer in a fluid phase derived from inclusions and wall rocks are considered unlikely because the area had been subjected to granulite grade metamorphism prior to emplacement of the nain plutonic suite either fractional melting or total fusion of xenoliths is considered a more likely mechanism for s addition to the mafic magma via pyrrhotite melting and for c addition in the form of co2 and ch4 produced by reaction of graphite with o and h bearing melt species

district to camp controls on the genesis of komatiite hosted nickel sulfide deposits agnew wiluna greenstone belt western australia insights from the multiple sulfur isotopes the agnew wiluna greenstone belt of western australia is the largest komatiite hosted nickel sulfide belt in the world and contains two world class ni cu pge deposits and a host of smaller deposits this study focuses on the broader scale geology of this greenstone belt in order to understand the key controls on the genesis of the komatiite hosted ni cu pge deposits with specific focus on camp to district controls we apply multiple sulfur isotopes to this geologic framework and conclude not only that the addition of crustal sulfur is a prerequisite for ore genesis in komatiite systems but above all that the sulfur required to generate world class deposits is most likely derived from barren volcanic massive sulfide lenses which are spatially and genetically associated with felsic volcanic and volcaniclastic sequences that were emplaced coevally with large komatiitic sills and channelized lava flows multiple sulfur isotope data can be utilized in exploration at the deposit to district scales at the deposit scale the spatial pattern of mass independent s isotope values 33 s provides crucial insight into the identification of proximal high grade and high tenor ores in mineralized systems in fact sulfur data reflect the assimilation process that occurred upon komatiite emplacement whereby hot turbulent magma thermomechanically eroded and assimilated exhalative sulfides spatially located close to vent with negative to near zero 33 s values whereas less turbulent flows interacted with distal sulfidic shales having 33 s values above 0 per mil accordingly the spatial variation of multiple sulfur isotope values in magmatic sulfides and associated host rocks may be utilized as a vector towards high grade ores of poorly known systems at the district scale rather than ascertaining what controls the distribution of komatiite hosted ni cu pge deposits the appropriate question to ask is what controls the distribution of country rock sulfides considering that exhalative sulfides may be crucial to ore genesis in komatiite systems we propose that felsic lava domes unambiguously mark their vents and can be directly mapped or inferred from gravity data this work provides the first step in identifying district scale control on komatiite hosted ni cu pge deposits this is the scale that has high impact on exploration for new komatiite hosted nickel sulfide belts globally

characteristics of gps tec variations in the polar cap ionosphere this paper presents statistical characteristics occurrence rate amplitude and frequency of low frequency 100 mhz variations in total electron content tec observed in the polar cap ionosphere tec variations were primarily associated with mesoscale tens to hundreds of kilometers ionization structures and were observed by five global positioning system gps receivers over a 6 year period 2009 2014 the altitude of ionization structures was estimated by using colocated ionosonde radars high data rate receivers combined with broad spatial coverage of multisatellite tec measurements provided high resolution magnetic local time latitude maps of tec variation characteristics which were examined as a function of solar cycle and season these high resolution maps improve upon the current observational picture of mesoscale structuring in the polar cap and provide accurate links to particular magnetospheric source regions occurrence of tec variations was consistently highest in dayside regions mapping to low latitude and plasma mantle boundary layers while largest amplitude tec variations were observed in dayside regions close to the polar cusp and lower latitudes around midnight occurrence and amplitude of tec variations increased significantly during the ascending phase of the solar cycle independent of solar wind conditions while seasonal statistics showed highest dayside occurrence and amplitude in winter months lowest in summer and highest nightside occurrence and amplitude around equinox a surprising result in the frequency distributions of tec variations was discrete frequencies of about 2 and 4 mhz which appeared to originate from regions corresponding to the plasma mantle immediately poleward of the polar cusp

microchemical and sulfur isotope constraints on the magmatic and hydrothermal evolution of the black swan succession western australia the black swan succession consists of an archean bimodal dacite komatiite association largely dominated by ultramafic cumulates hosting a number of massive and disseminated magmatic sulfide orebodies although it was affected by multiple alteration events the low degree of penetrative deformation allowed the preservation of magmatic textures and stratigraphic relationships in this context we apply a combined multiple sulfur isotope and microchemical approach to unravel the potential of sulfides to simultaneously retain information about their magmatic and hydrothermal history negative 33s signatures in both massive 0 56 and disseminated 0 66 sulfide orebodies reflect the assimilation of photochemically derived sulfur into the komatiite magma which attained sulfide liquid supersaturation through the assimilation of crustal material analogous to the intercalated breccia dacite hosting colloform sulfides 33s 0 91 the slightly different 33s signatures between disseminated and massive orebodies reflect the assimilation of different proportions of crustally derived sulfur and imply that the respective sulfide liquids segregated from distinct komatiite magma pulses subsequent alteration episodes imparted to the black swan succession a concentric zonation consisting of a serpentinite core and talc carbonate margins the black swan disseminated orebody extends through both alteration styles without major variations in the dominant millerite pyrite sulfide assemblage pyrite in both serpentinite and talc carbonate samples exhibits a consistent trace element signature suggesting a relative immobile behavior of ni and co during the percolation of the talc carbonate fluids conversely variable 34s signatures between the two alteration styles reflect mobilization of sulfur during talc carbonate alteration whereas the 2 range of 34s values in serpentinites can be attributed to moderate equilibrium fractionation processes the 10 range of 34s values in talc carbonate rocks suggests that highly oxidizing fluids promoted the mobilization of sulfur as so42 which decreased the 34s of the disseminated sulfides furthermore sulfur isotope and microchemical signatures of euhedral pyrite from intercalated dacitic breccia indicate that this pyrite generation was deposited from a late hydrothermal event which is characterized by variable and least negative 33s signatures between 0 20 and 0 48 relative to all sulfide orebodies these features suggest that the late fluids developed in a heterogeneous hydrothermal system with a minor component of sulfur recycled from the sulfide orebodies

the role of paragneiss assimilation in the origin of the voisey s bay ni cu sulfide deposit labrador multiple s and fe isotope evidence isotopic and geochemical studies conducted on the voisey s bay deposit labrador canada suggest crustal contamination of the primary magma as a trigger for sulfur saturation and formation of the deposit the use of multiple s isotopes has allowed for the identification of a bacterial sulfate reduction biosignature in the tasiuyak gneiss in the footwall to the voisey s bay deposit this putative biosignature is preserved in the deposit even at high silicate magma sulfide melt ratios r factor and links the s present in the voisey s bay deposit to the tasiuyak gneiss iron isotopes in the voisey s bay deposit have been reset to magmatic values at r factors 100 but s isotope data can be used to model higher r factors a contamination model results in calculated r factors of 433 177 the multiple s isotope data are a new proxy to directly link s from the deposit to crustal s sources even in deposits with high r factors where the equilibration with large amounts of silicate magma can make interpreting a link between the deposit and the sulfur source difficult

multiple sulfur isotopes reveal a magmatic origin for the platreef platinum group element deposit bushveld complex south africa the platreef ore horizon of the bushveld complex south africa is the third largest platinum group element ore deposit in the world but the origin of its ore remains enigmatic a complex contact relationship between the igneous and footwall rocks of the bushveld complex coupled with evidence for widespread late stage hydrothermal processing obscures the original mineralization history of the platreef we constrain the parental magmatic origin of the platreef by exploiting multiple sulfur isotope contrasts across bushveld complex contact zones in order to see through the effects of postmineralization hydrothermal activity we report s isotope measurements made on samples collected along two profi les through the platreef into underlying metapelitic and metacarbonate footwall rocks in both profi les igneous rocks far from the contact have low 33 s values average 33 s 0 15 whereas metasedimentary rocks far from the contact have high 33 s values 33 s to 5 04 with a smoothly varying profi le between the two end members the midpoint in both isotope profi les is displaced into the footwall defi ning a classic advective dispersive tracer geometry this geometry is not present in the associated 34 s values the displacement of the 33 s front suggests fl uid transport and advection of s into the country rocks this was accompanied by back diffusion of the s isotope tracer into the platreef the platreef magma was apparently s saturated prior to emplacement and counterintuitively lost s during the formation of the present platreef ore horizon

multiple s isotopes zircon hf isotopes whole rock sr nd isotopes and spatial variations of pge tenors in the jinchuan ni cu pge deposit nw china previous geochemical data for the jinchuan ni cu platinum group elements pge deposit the single largest magmatic sulfide deposit in the world are derived primarily from the upper parts of the deposit this paper reports new pge and s hf sr nd isotope data for the lower parts of the deposit that have become accessible for sampling by ongoing underground mining activity new pge data from this study together with previous results indicate that pge tenors in the bulk sulfide ores of the deposit increase eastward except for two fault offset ore zones which occur together within the western part of the deposit generally these two ore zones show depletions in ipge ir ru rh but not in ppge pt pd and cu and more fractionated olivine and cr spinel compositions than the rest of the deposit these differences can be explained by a more evolved parental magma for the ipge depleted ore zones the eastward increase of pge tenors in the rest of the deposit can be explained by upgrading of preexisting sulfide liquid in a subhorizontal conduit by a new surge of magma moving through the conduit from west to east which took place before the formation of the ipge depleted ore zones the jinchuan ultramafic rocks are characterized by elevated initial 87sr 86sr ratios from 0 7077 to 0 7093 negative e nd values from 9 2 to 10 5 and zircon e hf values from 4 to 7 these data indicate up to 20 of crustal contamination in the jinchuan magma four of nine multiple sulfur isotope analyses for the jinchuan deposit show anomalous 33s values varying from 0 12 to 2 67 these results together with elevated 34s values 2 for some of the samples analyzed previously by other researchers indicate the involvement of external sulfur from archean and proterozoic sedimentary rocks modeling results based on our olivine data and magma compositions estimated previously by other researchers indicate that fractional crystallization did not play a major role in triggering sulfide saturation in the jinchuan magma and that the parental magma experienced previous sulfide segregation during ascent or in staging chambers

multiple sulfur isotope evidence for surface derived sulfur in the bushveld complex abstract the rustenberg layered suite of the bushveld complex originated in the mantle but is characterized by variably radiogenic strontium neodymium lead and osmium initial isotope ratios and more elevated 18 o values than expected from a partial melt of primitive mantle it is not clear whether bushveld magmas assimilated material from the crust or whether they were instead generated from an eclogitic mantle source that contained crustal material here we report the 33 s of fifteen whole rock and sulfide separate samples from both the main and critical zones of the bushveld including the ug2 chromitite and the merensky reef all samples have positive 33 s values 0 11 0 02 1 and 34 s values 2 2 0 6 1 non zero 33 s is fundamentally a surface process since high temperature processes are not known to produce significant change in 33 s the positive 33 s indicates that the bushveld sulfur contains a sedimentary or surface derived component the homogeneity of 33 s values for this suite of samples contrasts with the heterogeneity displayed by strontium neodymium lead and osmium initial isotope ratios of the bushveld and requires that the sulfur contamination occurred prior to the emplacement of the bushveld in the upper crust possible sources of contamination include lower crust and sub continental lithospheric mantle limited multiple sulfur isotopic measurements of these reservoirs exist more work needs to be done to constrain whether they contain surface derived sulfur with non zero 33 s and if they do whether the concentrations and isotopic compositions of these reservoirs can explain the measured 33 s of the bushveld

origin of two distinct multiple sulfur isotope compositions of pyrite in the 2 5ga klein naute formation griqualand west basin south africa abstract quadruple sulfur isotope ratios 32s 33s 34s 36s were measured by a high precision sf6 method for early diagenetic pyrite in the 2 5 ga upper prieska facies of the griqualand west basin from the agouron drill core gkp01 measured 33s 33s 0 515 34s values range between 2 3 and 8 5 with no apparent meter scale stratigraphic trend for 70 m section it was found that early diagenetic pyrites occur in two texturally and isotopically distinct populations such that bulk rock isotope data would reflect mixing of these two sulfur pools nodular and layered pyrite yield mostly negative down to 2 3 and relatively constant 33s values over a few tens of cm scale disseminated pyrites in contrast yield positive 0 0 8 5 33s values that are heterogeneous in sub cm scales the former pyrite sulfur was likely derived from seawater sulfate through microbial sulfate reduction and the latter preferentially sampled aqueous h2s s0 reservoirs in late archean oceans relatively constant 33s values for layered pyrite suggest archean sulfate reservoirs had residence times of a few million years most data yield a well defined 36s 33s ratios of 0 9 suggesting predominance of a single s mif source reaction four analyses of a two cm length sample 306 5 m yield 36s 33s slope of 1 6 this slope is consistent with the relationship expected for a symmetry breaking isotope effect during the s s2 reaction but deviations from the main archean array i e 36s 33s 0 9 may also result from various combinations of so photolysis and so2 oxidation high spatial resolution high precision sf6 measurements of archean pyrite provide significant new insights into the origin of archean sulfur mass independent fractionation s mif and the late archean sulfur cycle

gps total electron content variations associated with a polar cap arc 1 we report an example of total electron content tec variations using global positioning system gps measurements associated with a polar cap arc detected by an all sky imager and ionosonde at a polar cap station during the transit of the arc gps signals along the arc length showed an increase of 2 tec units whereas gps signals perpendicular to the arc showed only an increase of 0 3 tec units this indicates that the gps tec variations associated with a polar cap arc are dependent on the geometry of the gps raypaths with respect to the arc ionosonde measurements confirm that this arc was an e region feature at 110 km with peak electron density of 5 4 1011 el m3 estimated speed of the arc using a gps triangulation method was about 300 m s

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

how do metals escape from magmas to form porphyry type ore deposits abstract many precious and base metals cu au ag mo w sn in porphyry type deposits are extracted from a granitic to granodioritic silicate melt and transported by magmatic hydrothermal fluids to the site of ore deposition metals abundance increases from some ppb in the melt to in ore bodies assuming a unique magmatic source for metals it implies an exceptional combination of enrichment process acting over up to 4 orders of magnitude previous models of magma differentiation and hydrothermal circulations omitted to consider the role of metal segregation during magma chamber evolution models for the formation and evolution of intrusions have recently shifted from the so called melting storage assimilation homogenization mash paradigm basically steady state to the mantle melting segregation ascent emplacement m m sae paradigm dynamic and discontinuous in time successive magma injections of variable compositions progressively build the magma chamber this is supported by field relations e g cross cutting dykes and stocks textures e g partially resorbed enclaves or mineral fabrics geochemistry e g hybridization signatures and age dating aswell as istopic studies as melt crystallizes and forms a mush 50 crystals volatiles also exsolve forming a magmatic volatile phase mvp while melt motion slows down metals partition between the three phases melt crystals and mvp they generally prefer the mvp owing to more favorable partition coefficients this is indicated by metal content in coeval melt and fluid inclusions with homogenization temperatures above 600 c or in volcanic fumaroles here by simulating the physical interactions between the three phases we suggest a model of fluid sparging during which metals segregate towards the mvp by diffusion and are further transported by advection as metal complexes the model also provides estimates of metal enrichment an undimensional peclet number rules the competition between diffusion and advection basically scaling with respect to the inverse of the product of melt viscosity by metal diffusivity d the threshold value of the peclet number between diffusion and advection is roughly 10 9 fast diffusive metals au cu ag w readily diffuse from silicate melt and towards bubbles of the mvp to escape the mush through tubular structures the mvp must overcome a critical gas saturation level about 20 vol usually reached after several magma injections advection then takes over and transports the metal enriched mvp towards the top of the magma chamber this leads to nearly coeval 1 separation between a high salinity liquid phase and a low salinity vapor phase 2 fluid rock interactions resulting in potassic advanced argillic and phyllic alterations and 3 metal deposition the metal enrichment scales as the ratio between partition coefficient i e related to the gradient in chemical potential diffusivity i e related to the gradient of concentration and melt viscosity i e related to the gradient of momentum the rates at which all such gradients relax determe metals enrichment inducing chemical and physical instabilities leading to a cyclic process the whole cycle also encompasses the case of a partial non completed full enrichment yielding to barren intrusions a tentative model generalizes the sparging fluid model to other metal deposits linked to an intrusion such generalization should be interpreted as predicting metal enrichment by 3 4 orders of magnitude rather than predicting an exact value

large amplitude gps tec variations associated with pc5 6 magnetic field variations observed on the ground and at geosynchronous orbit large amplitude variations in gps total electron content tec at pc5 6 6 67 mhz frequencies have been observed using a high data rate global positioning system gps receiver of the canadian high arctic ionospheric network tec variations with peak to peak amplitudes of 2 7 tec units 1 tecu 1016 el m 2 were observed over a 2 5 h period in the postnoon sector on 9 september 2011 during a period of high auroral activity within a moderate geomagnetic storm tec observations were from the sanikiluaq nunavut 56 54 n 280 77 e gps receiver located in the auroral region over this same time period compressional pc5 6 magnetic field variations were observed by the geosynchronous goes 13 magnetometer and the ground based sanikiluaq magnetometer goes 13 has a northern magnetic footprint in close proximity to sanikiluaq cross correlation analysis indicates that magnetic field and tec variations were possibly linked no natural hazards or nuclear explosions capable of exciting tec perturbations were reported on this day using a triangulation technique involving tec measurements of multiple gps satellites the propagation velocity of tec variations in the ionosphere was also calculated this calculation revealed two distinct events lower frequency 0 9 mhz tec variations that propagated westward consistent with the westward propagation of compressional pc5 waves observed by goes 13 and 15 satellites and higher frequency 3 3 mhz tec variations that propagated southward this is the first report of variations in ionospheric tec linked to satellite observations of pc5 6 ulf waves

high latitude gps tec changes associated with a sudden magnetospheric compression 1 using ionospheric total electron content tec measured by global positioning system gps receivers of the canadian high arctic ionospheric network chain we provide clear evidence for a systematic and propagating temporary tec enhancement produced by compression of the magnetosphere due to a sudden increase in solar wind dynamic pressure the magnetospheric compression is evident in themis goes satellite data application of a gps triangulation technique revealed that the tec changes propagated with a speed of 3 6 km s in the antisunward direction near noon and 8 km s in the sunward direction in the pre noon lower latitude sector characteristics of these tec changes along with riometer absorption measurements seems to indicate that the tec change is due to electron density enhancement in the f region and is possibly due to particle precipitation associated with sudden magnetospheric compression

sulfur isotope variations within the platreef ni cu pge deposit genetic implications for the origin of sulfide mineralization the platreef the world s third largest platinum group element pge deposit is a 10 400 m thick pyroxenitic unit at the base of the northern limb of the mafic bushveld complex hosting pge mineralization in association with base metal sulfides the sulfide mineralization is thought to have been either largely magmatic in origin with contamination by assimilation of local floor rocks considered an ore modifying process or a product of assimilation of country rock s and silicic contamination which caused s saturation in the magma with the contamination being fundamental to the ore forming process we have performed an extensive and detailed sulfur isotope study of the platreef which indicates that magmatic signatures 34s 0 to 2 are preserved in early formed sulfide droplets within the platreef pyroxenites in the area from sandsloot to witrivier these values are comparable to sulfide inclusions in diamonds in the nearby klipspringer kimberlite and are considered to have a primary mantle origin there is no indication of any significant external s in any of the primary sulfides in the sandsloot witrivier area however later sulfides found in calc silicate floor rocks at sandsloot and zwartfontein and in xenoliths of calc silicate throughout the section indicate an input of country rock s anhydrite bearing horizons in the malmani dolomites may have exchanged s with magmatic platreef sulfide during platreef intrusion imparting a heavier s isotope signature in the fluid affected rocks than those in the early sulfides the archean basement although containing minor amounts of sulfide with a negative 34s value is not a significant contributor to the s budget of the platreef previous studies have indicated that in areas where the sedimentary floor rocks contain appreciable sulfides rather than sulfates such as at turfspruit the platreef sulfides are extensively contaminated with country rock s assimilation of pyrite bearing shales in the turfspruit area has locally upgraded the s content of the platreef and given the basal platreef sulfides a heavier isotopic signature sulfur saturation in the platreef magma took place before contamination probably in a staging chamber prior to intrusion a major pulse of magma entrained the preformed pge rich sulfides and was injected to form the platreef where assimilation of country rock sulfides upgraded the s content on a strictly local scale and hydrothermal leaching introduced s from country rock sulfates into later stage sulfides again on a local scale south of zwartfontein it is proposed that the platreef was intruded into sediments of the transvaal supergroup which formed the floor and the roof of the platreef north of zwartfontein the platreef intruded the boundary between the malmani supergroup sediments and the archean basement this could have potentially mineralized the roof calc silicates north of zwartfontein in a manner similar to the floor in the sandsloot area the later intrusion of the main zone magma formed a magmatic unconformity on top of the cold platreef and entrained large rafts of mineralized calc silicate for tens of kilometers north of the last footwall outcrop of calc silicate

magnetic dipolarization with substorm expansion onset 1 we compare the timing and spatial extent of dipolarization with auroral breakup by using magnetic field data 1 min time resolution from goes 8 and goes 9 and global auroral images 37 s frame rate from the polar ultraviolet imager we survey the entire year of 1997 data and obtain 32 unambiguous dipolarization events that had ionospheric footprints within 2 hours in magnetic local time mlt from their associated auroral breakups it is found that the auroral breakup preceded the arrival of dipolarization at goes by an average of 1 7 2 7 min 1 0 2 1 min for events 1 hour from the auroral breakup the delay of geosynchronous dipolarization represents a propagation time as the substorms rarely initiated at the goes location propagation velocities derived from the propagation time are 60 km s 1 eastward 75 km s 1 westward and 270 km s 1 earthward at geosynchronous orbit we also show for the first time that auroral bulge and dipolarization region closely map the bulge is the region of currents out of the ionosphere the eastern edge of the dipolarization region where field aligned currents are flowing into the ionosphere is based on the t89 magnetic field model located at 0 5 hour in mlt eastward of the eastern edge of the auroral bulge within the initiation site meridian the dipolarization onset was observed 1 min prior to the auroral breakup at the goes altitude this time is associated with alfven transit time and therefore depends on the radial location of the onset the azimuthal scale of the initiation site is found to be 0 5 hour in mlt in the ionosphere or less than 1 earth s radius at 6 6 re these results support current diversion into the ionosphere as a critical part of substorms finally a simple timing analysis of specific substorm onset time features suggests that near earth reconnection cannot occur before current disruption and therefore cannot be the cause of substorm

mineralogic and stable isotope studies of hydrothermal alteration at the jinchuan ni cu deposit china the jinchuan intrusion hosts one of the largest magmatic ni cu sulfide deposits in the world net textured and disseminated pyrrhotite pentlandite and chalcopyrite are found in olivine rich rocks 60 80 vol that occur as a northwest southeast striking dike olivine in the intrusion has been variably converted to mixtures of serpentine and fine grained magnetite interstitial pyroxene and minor plagioclase have been altered to mixtures of chlorite amphibole epidote clinozoisite na rich feldspar and lesser amounts of calcite although the interstitial net texture of sulfide minerals surrounding olivine grains is preserved up to 30 vol percent of sulfide minerals are replaced by magnetite serpentine and chlorite an external origin for mg and si needed for the isovolumetric replacement of sulfides cannot be discounted but a local origin related to olivine and pyroxene alteration is favored serpentine and chlorite may be enriched in cu and ni but the enrichment can account for less than 1 percent of the metals lost during the replacement of sulfide minerals by silicates and oxides some of the metals and sulfur that were removed from the net textured sulfide assemblages have been redeposited on a centimeter scale in fine ribbons and veins within serpentine chlorite and amphibole sulfur isotope values of the pyrrhotite pentlandite chalcopyrite assemblage at jinchuan fall in the range of 2 to 8 per mil with over 80 percent of the values between 2 and 2 per mil immediate country rocks in the jinchuan area are precambrian granitoids schists and marbles with sulfur concentrations less than 100 ppm although the 34 s values of the main sulfide assemblage at jinchuan are in the range that is characteristic of mantle derived sulfur assimilation of sulfur from unexposed country rocks cannot yet be discounted secondary pyrite occurs in veins and stringers and rarely as a replacement of pyrrhotite and is characterized by 34 s values between 7 and 27 per mil the strongly negative 34 s values of secondary pyrite are thought to be a result of oxidation of primary magmatic sulfide assemblages and partial reduction of aqueous sulfate oxygen and hydrogen isotope values of silicate minerals suggest that at least two fluids have been involved in the hydrothermal alteration at jinchuan the 18 o values of plagioclase amphibole and serpentine all suggest the involvement of a fluid with a 18 o value between 2 and 5 per mil at 300 to 400 c the d values of amphibole and one population of serpentine suggest a d value for the fluid in the range of 45 to 63 per mil these values are consistent with the involvement of evolved seawater or a metamorphic fluid in the early stages of alteration the possible involvement of evolved seawater in hydrothermal alteration is consistent with a rift setting for the emplacement of the jinchuan intrusion however the wide range in serpentine d values computed d of the fluid 45 to 103 suggest either that serpentinization involved a mixture of evolved seawater and or metamorphic water and meteoric water or more likely that serpentine continued to exchange hydrogen isotopes with late stage meteoric waters after it formed

reactions of hydrothermal solutions with organic matter in paleoproterozoic black shales at talvivaara finland evidence from multiple sulfur isotopes abstract stable isotopic studies of archean paleoproterozoic sedimentary rocks older than 2 4 ga have documented large mass anomalous fractionations of sulfur isotopes 33 s 0 0 2 while younger rocks record little to no anomalous fractionation of sulfur isotopes this change from large anomalous fractionations to sulfur isotope values that fall on the terrestrial fractionation line has been proposed to represent the transition from an essentially anoxic archean atmosphere to an oxygenated atmosphere here we present 34 s and 33 s data for 28 core samples from paleoproterozoic 2 1 1 9 ga metamorphosed black shales and associated sulfide ores in eastern finland previous 34 s of studies of the talvivaara and outokumpu deposits of eastern finland focused on single grain analyses of sulfides while this study presents data from sequentially extracted sulfur fractions e g acid soluble sulfides chrome reducible sulfides elemental sulfur the sulfur isotope results range between 16 6 and 11 6 for 34 s 8 6 and 6 0 for 33 s and 1 25 and 0 55 for 33 s the anomalously fractionated samples are not consistent with previous findings that large anomalous fractionations of sulfur isotopes are absent in sedimentary metasedimentary rocks younger than 2 4 ga it is unlikely that talvivaara sulfides are the products of ultraviolet photolysis of volcanic so 2 in an oxygen poor atmosphere alternatively these sulfides could in part be the products of diagenetic reactions between sediments enriched in organic matter c org and hydrothermal solutions rich in sulfate i e thermochemical sulfate reduction laboratory experiments on thermochemical sulfate reduction have shown that mass anomalous fractionations of sulfur isotopes can be recorded in reduced sulfur products from reactions between simple amino acids and sulfate at 150 300 c a thermochemical sulfate reduction pathway for the mass anomalous signatures in talvivaara samples is consistent with previous genetic models proposed for the origin of the sulfur and organic carbon rich black shales now schists associated with the talvivaara and outokumpu ore deposits at talvivaara metalliferous black shales apparently were deposited under an anoxic to sulfidic marine water column the reported multiple sulfur isotopic data are key geological evidence for mass anomalous fractionations of sulfur isotopes during hydrothermal alteration of fine grained organic rich sediments approximately 20 of samples in this study show large offsets in 33 s values between different extracted sulfur fractions from the same sample which can be explained by classical isotope effects associated with the formation of hydrothermal alteration products that predominantly are retained within the precursor fine grained organic rich units

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

a review of the application of multiple s isotopes to magmatic ni cu pge deposits and the significance of spatially variable δ33s values the determination of 33 s values in conjunction with 34 s values provides an effective means of evaluating the importance of s derivation from archean country rocks in magmatic ni cu pge ore genesis particularly where 34 s values of potential s source rocks are near 0 and similar to most s of mantle derivation however 33 s values of sulfides in some archean rocks may also be near 0 care should be taken in the evaluation of s derivation from archean rocks based solely on this parameter although anomalous 33 s values are found primarily in archean rocks rare occurrences of nonzero 33 s values have been identified in sulfides from younger rocks and hence knowledge of the multiple s isotope composition of potential contaminants is essential for an accurate assessment of s contamination of mantle derived magmas restricted ranges in 33 s values may be characteristic of particular archean formations and when used in conjunction with mixing calculations may fingerprint a distinct s source rock spatial variability in 33 s values within different types of mineralized systems may be caused by the emplacement of isotopically distinct magma pulses by locally variable mixing proportions and the addition of secondary sulfide to the primary assemblage in the case of conduit type deposits in the midcontinent rift system three component mixing calculations show that both high and low 33 s values in some units that are similar to end member values in the archean country rocks must be a function of assimilation of primarily archean s even though proterozoic carbonaceous sedimentary country rocks contain in excess of 1 wt s and are particularly viable s source rocks

spatial distribution of sulfur isotope ratios associated with the eagle ni cu sulfide deposit in upper peninsula michigan implications on country rock contamination in a dynamic magma conduit abstract the eagle ni cu magmatic sulfide deposit in the upper peninsula of michigan is hosted in mafic ultramafic rocks associated with the 1 1 ga midcontinent rift event the deposit consists of massive semi massive and disseminated sulfide textural zones located in two closely spaced funnel shaped intrusive bodies called the eagle and eagle east intrusions the intrusions are surrounded by metamorphosed supracrustal paleoproterozoic rocks of the michigamme formation and at depth by a neoarchean migmatitic banded gneiss 34s values were obtained from sulfide minerals separated by micro drilling from different parts of the intrusions and the surrounding rocks the 34s values from the intrusions cluster within a small range between 1 and 3 relative to v cdt regardless of the mode of occurrence textural type mineral type and location of the sample however disseminated sulfide minerals in the metasedimentary country rocks of the michigamme formation show a substantially greater range in 34s values between 4 and 35 with a median of 7 7 while disseminated sulfides in the basement granite gneiss show values ranging from 9 to 13 with a median of 2 5 the narrow range of 34s values within the intrusions despite wide variabilities in the surrounding country rocks can be explained by the incorporation of crustal sulfur by a mantle derived magma followed by a homogeneous mixing of the immiscible sulfide liquid with a silicate liquid to sulfide liquid ratio r factor of 200 or more the assimilation of crustal rocks and the mixing of the resultant immiscible sulfide liquid must have been facilitated by the rapid movement of magma along a narrow conduit system

sulfur isotope and mineralogical studies of ni cu sulfide mineralization in the bovine igneous complex intrusion baraga basin northern michigan the bovine igneous complex referred to as the bic intrusion occurs within the marquette baraga dike swarm in the upper peninsula of michigan the intrusion is likely related to the 1 1 ga midcontinent rift system based on chemical similarities with the nearby eagle mine and other midcontinent rift related picrites the lack of deformation fabric and well developed hornfels that overprints penokean deformation fabrics however there is currently no age date for the bic intrusion to confirm that it is a rift related intrusion the bic is a relatively small layered intrusion with dimensions of 1 100 400 732 m thick units include feldspathic wehrlite olivine melagabbros feldspathic olivine clinopyroxenite and gabbro the little bic a satellite intrusion located 100 m from the main intrusion is primarily feldspathic wehrlite ni cu sulfide mineralization occurs in both intrusions with a higher relative proportion in the little bic intrusion sulfide assemblages are comprised predominantly of pyrrhotite chalcopyrite and pentlandite textural types vary from disseminated through globular to semimassive net textured and locally massive the 34s values of sulfide minerals in the bic intrusion range from 6 0 to 1 5 with 80 of the values between 0 and 1 5 the proterozoic michigamme formation country rocks show 34s values between 3 0 and 9 8 the 34s values of the semimassive sulfides in the little bic intrusion are similar to those in country rock 3 8 6 7 whereas the massive sulfide values are similar to those of the sulfide minerals in the bic intrusion although many values are near those of mantle derived sulfur the presence of strongly negative values in both intrusions indicates that crustally derived sulfur was involved in the mineralization process in addition the distinctly positive values of disseminated sulfides in the little bic intrusion indicate that a large fraction of the sulfur involved in the mineralization was of country rock origin and that at least two pulses of sulfide saturated liquids were involved in its genesis the 33s values for sulfide minerals in the bic and the little bic intrusions range from 0 33 to 0 35 indicating that a component of archean sulfur was also involved in the mineralization olivine fo and ni contents are consistent with rock types being related via fractional crystallization but this process cannot account for the wide range of sulfide zones found throughout both intrusions multiple pulses of magma several sulfide saturated and with distinct sulfur isotope compositions were involved in the formation of the bic and the little bic intrusions both sulfide concentration and isotopic composition suggest that sulfide saturation was promoted via the addition of country rock derived sulfur

multiple sulfur isotopes and the evolution of the atmosphere interest in multiple sulfur isotope analyses has been fueled by recent reports of mass independent sulfur isotope signatures in the geologic record a non zero multiple isotopic signature of sulfur 33s and 36s is produced primarily through photochemical reactions and it is an almost perfect tracer of the source of sulfur once the signature is passed on to a given sulfur reservoir it will be preserved unless there is addition of sulfur with a different 33s or 36s in the geological record this signature has been used to study the evolution of the earth s atmosphere and to trace movement of sulfur through geological systems early in earth s history recently small but significant mass independent signatures have been reported for some younger samples raising the possibility of additional applications of multiple isotope studies the purpose of this review is to introduce and discuss the implications of multiple isotope studies and to focus attention on these anomalous but not uncommon isotopic signatures

multiple s isotope studies of the stillwater complex and country rocks an assessment of the role of crustal s in the origin of pge enrichment found in the j m reef and related rocks abstract the j m reef in the stillwater complex of montana is the highest grade pd deposit in the world averaging approximately 14 ppm pd one suggestion for the origin of the enrichment centers on the sequestration of metals in staging chambers via immiscible sulfide liquids that formed in response to the addition of crustal s because 34s values alone are often insufficient to document in igneous rocks the assimilation of s from archean sedimentary rocks a combined study of both 33s and 34s values and computed 33s values was undertaken 34s and 33s values of cordierite bearing hornfels as well as massive sulfides in the metasedimentary rocks of the contact aureole can be divided into two populations one is characterized by anomalous positive 33s values from 0 to 0 32 and 34s values from 0 5 to 1 6 whereas the other is characterized by anomalous negative 33s values from 0 to 0 22 and 34s values from 1 5 to 5 8 34s and 33s values for rocks from the basal series of the complex range from 0 9 to 3 0 and 0 01 to 0 18 respectively the anomalous s isotope ratios indicate that for some samples at least 50 of the their s was of crustal origin in contrast most of the rocks from the j m reef are characterized by 34s and 33s values between 1 3 and 1 8 and 0 06 to 0 06 respectively these values deviate only slightly if at all from those thought to be representative of mantle s and suggest that i contamination was not an important process for pge enrichment in the complex ii the contaminant was also characterized by near 0 33s values or iii s isotopic exchange in the staging chambers was an important process upgrading of pge values via reaction between sulfide in the chamber and uncontaminated mantle derived magma may also have resulted in the conversion of s isotopic ratios that may have been indicative of crustal s addition to mantle like values rare 34s values up to 7 2 in the j m reef and 8 2 in chromitite from the ultramafic series provide strong evidence for localized assimilation of crustal s which did not experience isotopic homogenization the s isotopic ratios of the j m reef are non unique in terms of a specific genesis as they may be interpreted in either a downward sulfide collection model or an upward fluid transport model

comparing orthomagmatic and hydrothermal mineralization models for komatiite hosted nickel deposits in zimbabwe using multiple sulfur iron and nickel isotope data trojan and shangani mines are low grade 0 8 ni komatiite hosted nickel sulfide deposits associated with ca 2 7 ga volcano sedimentary sequences of the zimbabwe craton at both mines nickel sulfide mineralization is present in strongly deformed serpentinite bodies that are enveloped by a complex network of highly sheared silicified and sulfide bearing metasedimentary rocks strong polyphase structural metamorphic metasomatic overprints in both the trojan and shangani deposits make it difficult to ascertain if sulfide mineralization was derived from orthomagmatic or hydrothermal processes or by a combination of both multiple s fe and ni isotope analyses were applied to test these competing models massive ores at shangani mine show mass dependent fractionation of sulfur isotopes consistent with a mantle sulfur source whereas s isotope systematics of net textured ore and disseminated ore in talcose serpentinite indicates mixing of magmatic and sedimentary sulfur sources potentially via post magmatic hydrothermal processes a restricted range of strongly mass independent 33s values in ore samples from trojan mine likely reflects high temperature assimilation of sulfur from supracrustal rocks and later superimposed low temperature hydrothermal remobilization iron isotope values for most ni bearing sulfides show a narrow range suggesting that in contrast to sulfur nearly all of iron was derived from an igneous source negative ni isotope values also agree with derivation of ni from ultramafic melt and a significant high temperature fractionation of ni isotopes fe isotope values of some samples from shangani mine are more fractionated than expected to occur in high temperature magmatic systems further suggesting that hydrothermal processes were involved in either low grade ore formation liberation of ni from olivine by sulfur bearing hydrothermal fluids or remobilization of existing sulfides potentially inducing secondary ni sulfide mineralization