precious metals in volcanic peridotite associated nickel sulfide deposits in western australia ii distribution within the ores and host rocks at kambalda a detailed study of the distribution of pd ir and au in the sulfide component of contact ore layers at lunnon shoot has shown consistent differences between the matrix and massive layers and significant lateral variation within them palladium values in sulfides increase upward in ore sections and when average values are compared with those predicted by the relationship between pd and ni in mined ore ross and keays 1979 loss of pd is indicated the pd au cu enriched footwall sulfide stringers are believed to be the principal repository of remobilized pd iridium has a more uniform distribution and there is no evidence of important loss or gain from contact ore even though massive layer sulfides contain more ir at nearly all sample locations average values of au are higher in matrix layer sulfides and some loss of au from contact ore into footwall stringers and perhaps more distant sites is likely if it is assumed that the distribution of these metals and of ni and cu was uniform during emplacement of sulfide melt their present distribution can be attributed to the following processes redistribution of ir could have occurred during igneous cooling in the presence of a high thermal gradient at the base of the komatiitic volcanic pile and could have been accompanied by some movement of pd in areas of active stress most redistribution of pd is attributed to stress during the existence of metamorphic monosulfide solid solution and significant redistribution of cu may also have been induced by stress the circulation of latestage sulfur bearing solutions through contact ore layers seccombe et al 1981 could have transferred pd au and cu from contact sulfides particularly from the more permeable massive layer to footwall stringers and resulted in the close association of anomalous values of au and cu transfer of about 5 percent of the s in the matrix layer to the massive layer by these solutions would account for the consistently higher ni content of the matrix layer and development of secondary pyrite in the massive layer analyses of sulfide mineral separates from several shoots have consistently shown that pentlandite is the dominant host for pd ir is more uniformly distributed with higher values in pyrite and chalcopyrite and perhaps pyrite is the most important host for au concentrates of secondary pyrite appear to have normal values which suggests some movement of ir during its development the precious metals appear to be uniformly distributed through sulfide mineral hosts but observed variation in ore sections and layers requires that their abundance in the preferred sulfide host must vary considerably further work has strengthened the conclusion of ross and keays 1979 that olivine in the original komatiitic magmas was the principal host for ir and the liquid component was the principal host for pd olivine control lines for pd and ir in primary melts predict values at lower mgo in good agreement with those in hanging wall basalts at kambalda at higher mgo they agree closely with the most recent estimate for pyrolite and a chondritic pd ir ratio of about unity these predicted values result in a substantial increase in pd ir with decreasing mgo results from kambalda and other ni sulfide deposits indicate that the pd ir ratio of the sulfide melt may approximate that of the coexisting silicate melt even though absolute values may vary widely this variation exceeds that expected from the relative volumes of silicate and sulfide melt and may result from differences in factors such as f sub s 2 and f sub o 2 when immiscible sulfides formed measurements of pd and ir offer scope for defining the mgo contents of primary silicate melts associated with immiscible sulfides and may allow a more precise definition of f sub s 2 and perhaps f sub o 2 during formation of immiscible sulfide melts

platinum group minerals in the skouries cu au pd pt te porphyry deposit the skouries deposit is a platinum group element pge enriched cu au porphyry system located in the chalkidiki peninsula greece with associated ag bi and te enrichment the deposit is hosted by multiple porphyritic monzonite and syenite intrusions which originated from a magma chamber at depth an initial quartz monzonite porphyritic intrusion contains a quartz magnetite chalcopyrite pyrite vein stockwork with intense potassic alteration the quartz monzonite intrusion is cross cut by a set of syenite and mafic porphyry dykes and quartz chalcopyrite bornite magnetite veins which host the majority of the cu and au mineralisation late stage quartz pyrite veins with associated phyllic alteration crosscut all previous vein generations electron microprobe and scanning electron microscopy shows that the pge are hosted by platinum group minerals pgm in the quartz chalcopyrite bornite magnetite veins and within potassic alteration assemblages the pge mineralisation in skouries is therefore part of the main high temperature hypogene mineralisation event platinum group minerals at skouries include sopcheite ag4pd3te4 merenskyite pd pt te bi 2 and kotulskite pd te bi with rare telargpalite pd ag 3te isomertieite pd11sb2as2 naldrettite pd2sb testibiopalladite pdte sb te and sobolevskite pdbi the most common platinum group mineral is sopcheite the pgm in skouries are small 52 m2 on average and occur as spherical grains on the boundaries between sulphides and silicates and as inclusions within hydrothermal quartz and sulphides these observations support a semi metal collector model whereby an immiscible bi te melt acts as a collector for pge and other precious metals in high temperature hydrothermal fluids this mechanism would allow the formation of pgm in porphyries without pt and pd fluid saturation

genesis of the huangshannan high ni tenor magmatic sulfide deposit in the eastern tianshan northwest china constraints from pge geochemistry and os s isotopes abstract the huangshannan magmatic ni cu sulfide deposit is one of a group of permian magmatic ni cu deposits located in the southern central asian orogenic belt in the eastern tianshan northwest china it is characterized by elevated ni tenor concentrations in recalculated 100 sulfide in sulfide within ultramafic rocks 9 19 wt with values much higher than other deposits in the region sulfides of the huangshannan deposit are composed of pentlandite chalcopyrite and pyrrhotite and the host rock is relatively fresh indicating that the high ni tenor is a primary magmatic feature rather than formed by alteration processes it is shown that sulfides with high ni tenor can be generated by sulfide olivine equilibrium at an oxygen fugacity of qfm 0 5 for magmas containing 450 ppm ni and 20 olivine ores with 10 wt sulfur have relatively low pge and ni tenors compared to other ores r factor mass ratio of silicate to sulfide liquid modeling of ni indicates that they formed at moderate r values 150 600 based on this constraint on r values ores with 4 5 wt as sulfide rich samples are also depleted in cu and as interstitial sulfides in those samples are physically interconnected at a scale of several cms the low pt and pd anomalies are attributed to solid pt and pd phases crystallization and retention with the monosulfide solid solution mss and cu rich sulfide liquid percolation during mss fractionation this finding indicates that pt anomalies in sulfide rich rocks from magmatic ni cu deposits in the eastern tianshan are the result of sulfide fractionation rather than a hydrothermal effect 187 os 188 os 278ma values of the lherzolite samples vary from 0 27 to 0 37 and os 278ma values vary from 110 to 189 indicating significant magma interaction with crustal sulfides rich in radiogenic os well constrained os values and 34 s values 0 4 to 0 8 indicate that crustal contamination occurred at depth before the arrival of the magma in the huangshannan chamber regionally deposits with high ni tenor have not been reported other than the huangshannan deposit however many intrusions with high ni contents in olivine are present in nw china such as the erhongwa poyi and poshi intrusions those intrusions are capable of forming high ni tenor sulfides due to olivine sulfide silicate equilibrium and relative high ni content in parent magma making them attractive exploration targets

effects of magmatic processes serpentinization and talc carbonate alteration on sulfide mineralogy and ore textures in the black swan disseminated nickel sulfide deposit yilgarn craton the black swan disseminated orebody occurs predominantly within the partially carbonated serpentinite core of a zoned serpentinite talc carbonate ultramafic cumulate body of komatiitic parentage the black swan disseminated sulfides depart significantly from the characteristic pattern observed in otherwise similar deposits in western australia and canada which display magnetite bearing pentlandite rich sulfide aggregates blebs in serpentinites and s rich millerite bearing assemblages in talc carbonates the black swan disseminated ores in contrast are dominated by millerite pyrite polydymite assemblages in both serpentinites and talc carbonates with no evident relationship to the progression of carbonation sulfides show three types of intergrowth with gangue minerals which can occur separately or all together intergrowth with magnetite at least some of which appear to be primary magmatic in origin fine intergrowth with interlocking lath textured antigorite and intergrowth with carbonate minerals carbonate commonly replaces the core of sulfide blebs while retaining the primary magmatic outline carbonate replacement of sulfide roughly parallels the overall progression of carbonation of the whole rock but no systematic relationship of the other intergrowth types to carbonate content is observed in the serpentinites serpentine mineralogy determined by microbeam raman spectroscopy comprises lizardite which occurs in pseudomorphic mesh textures after olivine and antigorite formed by variable degrees of overprinting of original lizardite mesh textures ranging to a completely overprinting interlocking texture with no relic igneous texture this progression is interpreted as the result of mild thermal metamorphism of original lizardite serpentinite this progression is completely independent of carbonate content and is also apparently independent of extent of sulfide antigorite intergrowth which is interpreted as being early and related to volume expansion during initial sea floor serpentinization talc is almost completely absent from serpentinites while carbonate content varies widely whole rock ni and s data are very strongly correlated in millerite poor pentlandite rich samples and poorly correlated in samples where millerite is the dominant ni bearing sulfide on this basis we conclude that the pentlandite assemblages are slightly modified survivors of the original magmatic event while the millerite pyrite assemblages formed during the earliest stages of serpentinization overprinting of the early serpentinization event by talc carbonate had essentially no effect on sulfide mineralogy other than inducing intergrowth with carbonate a number of distinctive features such as magnetite rich bleb cores the association of sulfides with segregation vesicles and chromite shells the subspherical morphology of the blebs and preferential replacement of bleb cores are considered to be inherited from the magmatic phase and are attributed to an original high but variable oxygen and halogen content of the sulfide melt component exsolution of this component during solidification of the blebs in some cases produced sulfide centered bubbles now preserved as segregation vesicles while in other cases oxygen was retained within the bleb forming magnetite sulfide intergrowths chromite shells formed as a result of exsolved oxygen interacting with komatiite magma volatile rich blebs solidified in some cases with hollow or porous cores which were subsequently exploited by carbonate replacement

relative contribution of magmatic and post magmatic processes in the genesis of the thompson mine ni co sulfide ores manitoba canada abstract the ni co pge sulfide deposits of the thompson nickel belt tnb in northern manitoba canada are part of the fifth largest nickel camp in the world based on contained nickel past production from the tnb deposits is 2500 kt ni the thompson deposit is located on the eastern and southern flanks of the thompson dome structure which is a re folded nappe structure formed during collision of the trans hudson orogen with the canadian shield at 1 9 1 7 ga the thompson deposit is almost entirely hosted by p2 member sulfidic metasedimentary rocks of the paleoproterozoic ospwagan group variably serpentinised and altered dunites peridotites and pyroxenites contain disseminated sulfides and have a spatial association with sediment hosted ni sulfides which comprise the bulk of the ore types these rocks formed from rift related komatiitic magmas that were emplaced at 1 88 ga and subsequently deformed by boudinage thinning folding and stacking disseminated sulfide mineralization in the large serpentinised peridotite and dunite intrusions that host the birchtree and pipe ni co sulfide deposits typically has 4 6 wt ni in 100 sulfide the disseminated sulfides in the less abundant and much smaller boudinaged serpentinised peridotite and dunite bodies associated with the thompson deposit have 7 10 wt ni in 100 sulfide the majority of thompson mine sulfides are hosted in the p2 member of the pipe formation which is a sulfidic schist developed from a shale prololith the mineralization in the schist includes both low ni tenor 13 wt ni in sulfide define a systematic trend that mirrors the configuration of the second order doubly plunging f3 structures on the flanks of the dome although moderate to high ni tenor mineralization is sometimes localized in fold hinges more typically the highest ni tenor mineralization is located on the flanks of the fold structures there is no indication of the mineralogical and geochemical signatures of sedimentary exhalative or hydrothermal processes in the genesis of the thompson ores the primary origin of the mineralization is undoubtedly magmatic and this was a critical stage in the development of economic mineralization variations in metal tenor in disseminated sulfides contained in ultramafic rock indicate a higher magma sulfide ratio in the thompson parental magma relative to birchtree and pipe the variation in ni tenor of the semi massive and massive sulfide broadly supports this conclusion but the variations in metal tenor in the thompson ores was likely created partly during deformation the sequence of rocks was modified by burial and loading of the crust d2 events to a peak temperature of 750 c and pressure of 7 5 kbar the third major phase of deformation d3 was a sinistral transpression d3 event which generated the dome and basin configuration of the tnb these conditions allowed for progressive deformation and reformation of pyrrhotite and pentlandite into monosulfide solid solution as pressure and temperature increased this process is termed sulfide kinesis separation of the ductile monosulfide solid solution from granular pentlandite would result in an effective separation of ni during metamorphism and the monosulfide solid solution would likely be spread out in the stratigraphy to form a broad halo around the main deposit to produce the low ni tenor sulfide reformation of pentlandite and pyrrhotite after the peak d2 event would explain the broad footprint of the mineral system the effect of the d3 event at lower pressure and temperature would have been to locally redistribute deform and repeat the lenses of sulfide the understanding of the relationships between petrology stratigraphy structure and geochemistry has assisted in formulating a predictive exploration model that has triggered new discoveries to the north and south of the mine and provides a framework for understanding ore genesis in deformed terrains and the future exploration of the thompson nickel belt

chalcophile and platinum group element pge concentrations in the sulfide minerals from the mccreedy east deposit sudbury canada and the origin of pge in pyrite magmatic sulfide deposits consist of pyrrhotite pentlandite chalcopyrite pyrite and platinum group minerals pgm understanding the distribution of the chalcophile and platinum group element pge concentrations among the base metal sulfide phases and pgm is important both for the petrogenetic models of the ores and for the efficient extraction of the pge typically pyrrhotite and pentlandite host much of the pge except pt which forms pt minerals chalcopyrite does not host pge and the role of pyrite has not been closely investigated the ni cu pge ores from the south range of sudbury are unusual in that sulfarsenide pgm rather than pyrrhotite and pentlandite are the main carrier of pge probably as the result of arsenic contribution to the sulfide liquid by the as bearing metasedimentary footwall rocks in comparison the north range deposits of sudbury such as the mccreedy east deposit have as poor granites in the footwall and the ores commonly contain pyrite our results show that in the pyrrhotite rich ores of the mccreedy east deposit os ir ru rh ipge and re are concentrated in pyrrhotite pentlandite and surprisingly in pyrite this indicates that sulfarsenides which are not present in the ores were not important in concentrating pge in the north range of sudbury palladium is present in pentlandite and together with pt form pgm such as ptpd tebi 2 platinum is also found in pyrite two generations of pyrite are present one pyrite is primary and locally exsolved from monosulfide solid solution mss in small amounts 2 wt together with pyrrhotite and pentlandite this pyrite is unexpectedly enriched in ipge as pt and the concentrations of these elements are oscillatory zoned the other pyrite is secondary and formed by alteration of the mss cumulates by late magmatic hydrothermal fluids this pyrite is unzoned and has inherited the low concentrations of ipge and re from the pyrrhotite and pentlandite that it has replaced

fractional crystallization of sulfide ore liquids at high temperature tie line compositions of fe ni cu sub 1 x s monosulfide solid solution mss and fe ni cu s liquid in the presence of sulfur vapor have been quenched from temperatures between 1 050 degrees and 1 180 degrees c more than 80 bulk compositions on both sulfur rich and sulfur poor sides of the mss field were investigated by sealed silica tube techniques qualitative observations of wetting behavior suggest increasing mobility in a silicate host rock as sulfide liquids become more cu rich partition coefficients for copper or 0 25 d super mss hq cu are obtained from ni bearing experiments with approximately 2 wt percent cu and no quench phases the equation d super mss hq cu 0 0003 x t degrees c 0 0310 x wt s 0 0069 x wt cu 1 3450 describes partitioning observed in ni free experiments above 1 000 degrees c above 1 000 degrees c the ni distribution coefficient d super mss hq cu decreases with increasing temperature and or sulfur content of the liquid these results yield improved models describing the fractional crystallization of natural sulfide liquids major element fe ni cu s compositions of ores from the sudbury district are shown to be entirely consistent with fractional crystallization at temperatures above 1 000 degrees c with the possible exception of rare samples enriched in both ni and cu sulfide liquids fractionating ni fe rich hanging wall ores at sudbury ontario must have been less cu rich than previously thought at temperatures above 950 degrees c reduced sulfur activity in residual liquids can result in massive late stage bornite rich ores

partition coefficients for ni cu pd pt rh and ir between monosulfide solid solution and sulfide liquid and the formation of compositionally zoned ni cu sulfide bodies by fractional crystallization of sulfide liquid many nickel copper sulfide orebodies contain cu and fe rich portions the fe rich ore is generally richer in os ir ru and rh and poorer in pt pd and au than the cu rich ore in komatiite hosted ores ni tends to be concentrated in the cu rich ore whereas in tholeiitic ores it tends to be concentrated in the fe rich ore the origin of this zonation could be due to crystal fractionation of fe rich monosulfide solid solution from a sulfide liquid the crystal fractionation would produce an fe rich cumulate enriched in os ir ru and rh and a fractionated liquid enriched in cu pt pd and au this model can be tested for zoned orebodies by applying experimentally determined partition coefficients for the metals into monosulfide solid solution we have compared our experimental results with those of other workers to show that the partition coefficients are strongly influenced by the sulfur content of the system there is a positive correlation between the partition coefficients and sulfur content of th

os pb nd isotope and highly siderophile and lithophile trace element systematics of komatiitic rocks from the volotsk suite se baltic shield abstract highly siderophile element hse ru pd re os ir and pt abundances and re os isotope systematics in combination with lithophile trace element and sm nd and pb pb isotopic data are reported for komatiites and basalts from the volotsk suite in the se baltic fennoscandian shield the new sm nd and pb pb whole rock isochron ages of 2850 84 and 2861 150 ma respectively define the emplacement age of the volcanic sequence this age is statistically indistinguishable from the emplacement age of the lower mafic ultramafic sequences of the adjacent sumozero kenozero greenstone belt the re os internal isochron derived from the analysis of a whole rock b2 4 cumulate and three chromite separates yields an age of 2878 81 ma which is consistent with the ages obtained from the lithophile element isotopic systems the komatiites of the volotsk suite were derived from a mantle source characterized by depletions in highly incompatible lithophile trace elements with the magnitude of the time integrated lree depletion initial nd 2 7 0 2 typical of this period in the earth s mantle history yet this source had an initial 187os 0 4 0 4 and thus evolved with a time integrated re os that was identical within uncertainty to that of the carbonaceous chondritic reference in addition the calculated relative abundances of os ir ru and pt in the komatiite source are similar to chondrites and may be explained by late post core segregation accretion to the earth of materials with high absolute and chondritic relative abundances of hse or by re entrainment of the core if the former interpretation is correct the late accreted materials were well homogenized within the upper mantle by 2 9 ga like many other archean komatiites the studied rocks have radiogenic nd isotopic composition indicative of their long term relative depletions in highly incompatible lithophile trace elements yet the long term re os in their source remained near chondritic modeling indicates that the komatiite source must have experienced only a small degree of partial melting 2 3 and extraction of basaltic melts ca 150 ma prior to emplacement of the komatiitic sequences larger degrees of melting would otherwise have led to loss of a substantial fractionation of re in the source which would then have evolved to a subchondritic 187os 188os by the time of komatiite formation

fine structure of auroral roar emissions in september 1994 a narrowband downconverting receiver was installed at circle hot springs alaska to complement ongoing stepped frequency receiver observations of auroral roar a relatively narrowband emission at frequencies roughly 2 and 3 times the ionospheric electron gyrofrequency ce by good fortune auroral roar events were captured at 0957 ut 0057 lt on september 6 1994 and at 1015 ut 0115 lt on october 23 1994 the narrowband recording with a center frequency of 2 853 mhz and bandwidth of 10 khz revealed that these auroral roar events were composed of multiple narrowband features which drift in frequency in a complicated pattern both rising tones and falling tones were observed and the slopes of the discrete features varied from nearly flat to 100 khz s when the downconverted signals are played through a loudspeaker they resembled structured vlf emissions such as chorus these data show that auroral roar like auroral kilometric radiation is at least sometimes characterized by fine frequency structures previously not resolved by stepped frequency analyzers the existence of such fine structures has significance for theories of the generation mechanism of auroral roar which remains unexplained

platinum group minerals in the limoeiro ni cu pge sulfide deposit brazil the effect of magmatic and upper amphibolite to granulite metamorphic processes on pgm formation the limoeiro ni cu platinum group elements pge deposit is a recent discovery associated with an igneous tubular conduit system in northeastern brazil representative ores from the deposit have been used for platinum group minerals pgm identification and for pge in base metal sulfides bms quantification ninety eighty percent of the pgm in the massive sulfide ores is homogeneous pt ni bi bearing merenskyite pdte2 enclosed primarily by pyrrhotite suggesting that it is formed by exsolution from monosulfide solid solution mss merenskyite gradually but systematically becomes poorer in pt and ni with increasing fractionation which is interpreted to reflect a transition to a more evolved sulfide liquid that segregated in the eastern parts of the intrusion in massive sulfide ores merenskyite forms unusually large up to 5000 m2 euhedral grains commonly in contact with spherical silicate inclusions bms hosts 12 16 of the pd with the remainder hosted by pgm which is interpreted to indicate that merenskyite recrystallized from a pge bearing bismuthotelluride metamorphic melt formed during high grade metamorphism sperrylite ptas2 is the second most abundant pgm 18 of pgm in disseminated ore and in contrast to merenskyite occurs mainly as very small median of 25 m2 inclusions in high temperature silicates and oxides interpreted to have crystallized at high temperatures directly from sulfide blebs that formed and were transported within the limoeiro magma conduit

can biological toxicity drive the contrasting behavior of platinum and gold in surface environments abstract in spite of the similar chemical properties of gold au and platinum pt au is highly mobile in surface environments whereas pt appears to be far less so in this study we assess if geomicrobial processes are likely to cause these differences as the mobility of pt and au should differ little based on thermodynamic solubility alone to achieve an accurate comparison it is important that both metals occur in the same environment mineral and groundwater samples were obtained from the fifield pt au field in new south wales australia where pt and au nuggets occur in a series of tertiary eluvial and alluvial paleo placers in particular we studied the m scale dispersion of au and pt within an extraordinary 10 mm sized fragment of ferruginous paleochannel material which contained abundant native au and isoferroplatinum grains gold grains displayed complex secondary morphologies indicative of biogeochemical transformations whereas isoferroplatinum grains appeared smooth and well rounded and showed no signs of supergene transformation gold grains were surrounded by a dusting of highly pure metallic au particles 10 m in diameter whereas no metallic pt particles were detected a search for ionic pt was also unsuccessful a series of biotic and abiotic incubation experiments was conducted to investigate the hypothesis that these differences in mobility are driven by interactions with microbiota biofilms consisting of metallophilic bacteria formed on ultraflat au surfaces and caused significant surface transformations in contrast only subtle changes were observed on pt surfaces incubated under similar conditions minimal inhibitory concentrations for au complexes are more than an order of magnitude lower than those measured for pt complexes in cupriavidus metallidurans cells this higher cell toxicity of mobile au compared to pt complexes can lead to toxic levels of mobile au in the vicinity of au grain surfaces the elevated toxicity drives the formation of au detoxifying biofilms that catalyze the biomineralization of spheroidal nano particulate and bacteriomorphic au in contrast this does not occur on isoferroplatinum grains due to the lower toxicity of pt in conclusion these results are consistent with microbial adaptation to element toxicity driving the cycling of precious metals in surface environments

on the mechanisms for low sulfide high platinum group element and high sulfide low platinum group element mineralization in the eastern gabbro coldwell complex canada evidence from textural associations s se values and platinum group element concentrations of base metal sulfides

the role of komatiitic and picritic magmatism and s saturation in the formation of ore deposits abstract the introduction of high temperature high magnesium komatiitic and picritic magmas into the earth s upper crust has given rise either directly or indirectly to many of the world s major ore deposits there is a direct association between komatiitic magmatism and kambalda style ni cu pge deposits the link between magma type and mineralization is not as clear cut in the case of the noril sk cu ni pge deposits but nevertheless there is an association between picritic magmatism and ore deposit development komatiitic and or picritic magmatism may also have contributed to the formation of many types of hydrothermal ore deposits recent nd isotope data generated by kent et al 1994 provide strong evidence for the hypothesis proposed by keays in 1983 that the au in archaean au deposits was derived either directly or indirectly from komatiites through the action of metamorphic fluids the importance of komatiitic and picritic magmas in ore forming processes arises from the fact that they are among the few mafic ultramafic magma types that are s undersaturated at the time of magma formation s saturation of magmas leads to marked depletion in the chalcophile metals for example czamanske and moore 1977 estimated that a third of the original cu and ni contents of morb were lost from the magmas due to extraction into magmatic sulphides the depletion in au and the pge is much greater due to their much larger partition coefficients keays and scott 1976 komatiitic and picritic magmas are s undersaturated because they are high temperature magmas produced by large degrees of partial melting of upper mantle sourc regions that were already depleted in s through earlier partial melting events most mafic magmas produced by less than 25 partial melting are s saturated and hence depleted in the ore forming chalcophile elements in contrast komatiitic and picritic magmas have their full complement of chalcophile metals when they do become s saturated they form sulphides that are strongly enriched in ni cu au pge and other strongly chalcophile metals these may accumulate to form ore deposits directly e g magmatic ni cu pge sulphides or be dispersed in komatiitic picritic rocks or their fractionation products making these source rocks for hydrothermal au or vms deposits

subepithermal au pd mineralization associated with an alkalic porphyry cu au deposit mount milligan quesnel terrane british columbia canada at the mount milligan cu au porphyry deposit quesnel terrane british columbia canada barren and weakly mineralized late stage hydrothermal veins occur in volcanic rocks adjacent to zones of cu au porphyry mineralization and have overprinted the porphyry stage veins the earliest of the late stage hydrothermal veins are barren and consist of quartz pyrite carbonate chlorite tourmaline these veins are similar to transitional to late stage hydrothermal veins in other alkaline porphyry cu au deposits and we consider these to be the equivalent of transitional post porphyry pre epithermal quartz sericite pyrite veins in calc alkaline porphyry environments a later generation of volumetrically minor mineralized veins are composed of pyrite hg and as bearing quartz carbonate chlorite and contain early electrum arsenopyrite tetra hedrite tennantite platinum group element pge tellurides galena sphalerite barite and chalcopyrite as inclusions in pyrite and a later assemblage of electrum pge tellurides arsenides and antimonides galena sphalerite chalcopyrite and various au ag te bi minerals in annealed fractures and open space infillings in quartz and pyrite metal precipitation in these veins was temporally and spatially associated with the deposition and later recrystallization of pyrite primary fluid inclusions in quartz in the barren and weakly mineralized veins are two phase l v homogenize to liquid over a narrow range in t 170 270 c n 96 12 veins and show a wide range in salinity 4 2 wt nacl equiv to 28 7 wt cacl2 equiv when all samples are considered however individual veins show narrow ranges in salinity and homogenization temperature la icp ms analyses indicate that the fluids were highly enriched in as to 2 260 ppm sb to 230 ppm b to 5 400 ppm au 1 2 ppm and pd 0 5 1 ppm but depleted in cu 80 ppm compared to typical porphyry stage fluids metal ratios in the fluids overlap with bulk rock metal ratios in the mineralized veins the inclusions are interpreted to contain a contracted magmatic vapor produced by boiling that lost cu during the formation of porphyry stage veins at depth fluids show decreasing b as sb and increasing sr ca and salinity with time stable c o and h isotope analyses of vein minerals indicate that mixing of this magmatic fluid with meteoric water was not responsible for metal deposition rather metal precipitation was possibly the result of mixing of the magmatic derived fluid with a heated saline groundwater the precious and accessory metal mineralogy of the hydrothermal veins is similar to that found in low to intermediate sulfidation epithermal systems fluid inclusion microthermometry and chlorite thermometry constrain the approximate formation conditions of the veins between 200 and 1 500 bars and 240 and 280 c after the formation of the mineralized veins circulation of low salinity metal depleted fluids occurred these latest stage fluids may have formed by mixing of the saline magmatic fluid groundwater hybrid with meteoric water the results of this study suggest a genetic link between porphyry stage events and the deposition of au and pge in late stage veins in an alkalic igneous environment recognition of hydrothermal processes involving the transport of au pge as sb bi te b rich fluids in the subepithermal regimes implies that low sulfidation epithermal au deposits may have been present in the shallower parts of the magmatic hydrothermal complex and that there is potential for the discovery of pge rich epithermal veins in less deeply exhumed terranes on the other hand the formation of high grade low sulfidation epithermal au pge deposits may be prohibited if porphyry epithermal transitional fluids precipitate ore metals through mixing with groundwater prior to reaching the level where meteoric water mixing and epithermal boiling normally occur

further investigation of auroral roar fine structure in april 1996 a downconverting receiver was operated in churchill manitoba canada to increase the statistics about the recently discovered fine structure of auroral roar emissions auroral roar is found to be both structured and unstructured a wide variety of previously unknown tonal features drifting in a complicated manner were recorded these structured features can be classified according to their duration frequency drift and grouping with like features typically 95 of the structured features last less than 1 s the slope of drifting features is more commonly negative than positive with a magnitude typically less than a few khz s 1 and a maximum of 800 khz s 1 the minimum bandwidth of features is 6 hz or less and typical separation between similar features is 400 hz these measurements form a basis for reviewing proposed generation mechanisms of auroral roar including a localized source model and laser cavity mechanism

observations of nightside auroral cavities radar observations of field aligned auroral f region density depletions cavities have been identified in a portion of the sondre stromfjord incoherent scatter radar isr data base covering the period february 1986 to january 1988 these auroral cavities are nightside phenomena with localized field aligned f region density depletions of 20 to 70 percent below surrounding values they occur during moderate to quiet geomagnetic conditions when the pillared edge of the auroral oval is within view of sondre stromijord seasonally they are a wintertime phenomena occurring just pillared of the statistical auroral oval unlike the previously reported polar hole the average width of the cavities is less than 100 km case studies show that the cavities closely track the pillared edge of the most pillared auroral arc sequential radar scans show that cavities appear on time scales as short as several minutes suggestive of local electrodynamic formation or rapid transport data from january 24 1987 collected during coordinated optical radar and satellite observations spanning an hour of local time were examined for possible cavity formation mechanisms the cavity formation processes examined herein include locally enhanced chemical loss vertical diffusion drifting horizontal gradients in the background plasma and evacuation as a result ofmore field aligned currents the formation time scales calculated evacuation fluxes close proximity to e region aurora and field aligned current signatures seen in magnetometer and radar observations suggest a strong association of the cavities with upward flowing electrons carrying region 1 downward field aligned currents 46 refs 9 figs 1 tab less

progressive mixing of meteoritic veneer into the early earth s deep mantle komatiites are ancient volcanic rocks mostly over 2 7 billion years old from the archaean era that formed through high degrees of partial melting of the mantle and therefore provide reliable information on bulk mantle compositions1 in particular the platinum group element pge contents of komatiites provide a unique source of information on core formation mantle differentiation and possibly core mantle interaction2 3 4 5 6 7 8 most of the available pge data on komatiites are from late archaean 2 7 2 9 gyr old or early proterozoic 2 0 2 5 gyr old samples here we show that most early archaean 3 5 3 2 gyr old komatiites from the barberton greenstone belt of south africa and the pilbara craton of western australia are depleted in pge relative to late archaean and younger komatiites early archaean komatiites record a signal of pge depletion in the lower mantle resulting from core formation this signal diminishes with time owing to progressive mixing in to the deep mantle of pge enriched cosmic material that the earth accreted as the late veneer during the early archaean 4 5 3 8 gyr ago meteorite bombardment

pt and pd mobility in hydrothermal fluids evidence from komatiites and from thermodynamic modelling abstract komatiite host rocks and ores provide a natural laboratory for the study of pt and pd during hydration and carbonation of ultramafic rocks the degree of correlation between pt and pd and of those elements with lithophile elements such as ti in komatiitic rocks and ores is strongly dependent on the magmatic sulfide content of the rock pt and pd are typically very strongly correlated within s poor komatiites and in disseminated ores containing 5 volume or less magmatic sulfides in contrast they are almost completely decoupled in sulfide rich ore samples thermodynamic modelling based on the existing body of published experimental data on pt and pd solubilities suggests that pd and pt can be readily transported as bisulfide complexes in acidic neutral solutions under reduced and moderate oxidation condition at 300 c and chloride complexes are only important under extremely acidic oxidised conditions pd is much more soluble than pt in the case of fluids in sulfide rich environments in equilibrium with the characteristic assemblages found within altered and metamorphosed komatiites solubilities of both elements are much lower in sulfide poor environments especially where ph values are constrained to neutral values by the near ubiquitous presence of carbonate minerals in the alteration assemblage this accounts for the evident near immobility of pt and pd in even the most altered silicate host rocks as compared with their wide dispersion in sulfide rich ores

platinum group element and nickel sulphide ore tenors of the mount keith nickel deposit yilgarn craton australia a set of platinum group element pge analyses of about 120 samples from a 250 m continuous drill core through the mount keith komatiite hosted nickel orebody combined with ni cu co s and major elements reveals a complex trend of covariance between the original cumulus components of a thick sequence of nearly pure olivine sulphide liquid adcumulates the intersection is divided into informal chemostratigraphic zones defined primarily by combinations of fine scale cyclicity in original olivine composition defined by mg and sulphide composition defined by pt s and ni s contents of ni and pge in 100 sulphides tenors were determined from linear regressions of the ni s and pge s covariance for each zone inferred olivine compositions range from about fo92 to fo94 6 and show a broad decrease from bottom to top of the sequence complicated by numerous reversals revealing crystallisation in an open conduit system ni and pge tenors of mount keith sulphide ores have typical values similar to the type i deposits of the kambalda dome mobility of s at least on the scale of 2 m sample composites is evidently relatively minor tenors for the various zones range 12 22 ni 370 1540 ppb pt 970 3670 ppb pd 100 460 ppb ir 170 460 ppb rh and 710 1260 ppb ru pt pd and rh tenors are very strongly correlated but the iridium group of platinum group elements ipges ir and ru less so tenor variations are predominantly controlled by variations in magma sulphide ratio r 100 350 with a minor component of variance from equilibrium crystallisation trends in the parent magma pge depletion in the silicate melt due to sulphide liquid extraction is limited by entrainment of sulphide liquid droplets and continuous equilibration with the transporting silicate magma ratios of the pges to one another are similar to those in the host komatiite magma with the exception of pt which is systematically depleted in ores relative to rh and pd and relative to host magma by a consistent factor of about 2 to 2 5 this anomalous pt depletion relative to pge element ratios in unmineralized komatiitic rocks matches that observed in bulk compositions of many komatiite hosted orebodies the highly consistent nature of this depletion and particularly the very strong correlation between pt pd and rh in the mount keith deposit argue that this depletion is a primary magmatic signal and not an artefact of alteration differential diffusion rates between pt and the other pges giving rise to a low effective partition coefficient for pt into sulphide liquid is advanced as a possible but not definitive explanation

u pb ages of granitoid rocks in the northwestern makkovik province labrador evidence for 175 million years of episodic synorogenic and postorogenic plutonism new u pb zircon titanite and monazite ages reported here along with existing age data demonstrate that granitoid bodies in the northwestern segment of the paleoproterozoic makkovik province labrador are of three distinct ages the redefined island harbour bay plutonic suite consists of varied dioritic to granitic units that were syntectonically emplaced into archean crust of the kaipokok domain between ca 1895 ma and 1870 2 ma this plutonism occurred during the early stages of the makkovikian orogeny in an obliquely convergent andean continental margin setting the hares islands and drunken harbour granites form smaller discrete plutons that were emplaced in or adjacent to the island harbour bay plutonic suite at 1805 5 ma and 1791 2 ma respectively during dextral strike slip deformation that accompanied accretion of an outboard juvenile terrane magmatic activity during this period was preferentially sited along active structural zones but also occurred outside of these zones the undeformed blacklers bight a type granite was emplaced in the kaipokok domain at 1716 1 ma late in the development of the orogen a type granites of this age form a significant component of the southeastern makkovik province and their generation is linked to mafic underplating and heterogeneous regional extension the new age data support the conclusion of earlier workers that crustal growth via synorogenic and postorogenic plutonism was episodic and allow along with field and geochemical data inferences to be made regarding the tectonic setting of individual plutonic events

latitudinal dynamics of auroral roar emissions auroral roar a narrowband f f 0 1 emission near 2 and 3 times the ionospheric electron gy rofrequency 2fce and 3fce is observed with a merid ional chain of lf mf hf radio receivers located in northern canada spanning 67 to 79 invariant latitude observations of these emissions are compared with the auroral electrojet location inferred from the canadian auroral network for the open program unied study canopus magnetometer array variations in the intensity of the observed auroral roar emissions and in the invariant latitude of the most intense emissions are correlated with movements of the poleward boundary of the electrojet for example substorm onsets which appear as rapid poleward expansions of this boundary result in screening of the emissions from the underlying ground stations because of precipitation induced ioniza tion in the lower ionosphere in four of the v e study days the peak emission intensity is located 0 9 pole ward of the poleward electrojet boundary inferred from the magnetometers in one case the peak emission in tensity is up to 10 equatorward of the poleward electro jet boundary in all cases there is a tendency for the latitude of the most intense auroral roar emissions to track the movements of the electrojet location inferred from the magnetometer data for two examples the footprint of the fast auroral snapshot fast satellite passes within 3 of one or more of the ground stations and the satellite detects unstable electron populations in the polewardmost auroral arc reinforcing the sce nario that auroral roar emissions are generated by these electrons in the polewardmost arc and propagate into the polar cap where conditions are often favorable for their detection at ground level

fractionation of the platinum group elements and gold in some komatiites of the abitibi greenstone belt northern ontario the noble element patterns from four nickel sulfide deposits in komatiites of the abitibi greenstone belt exhibit various degrees of fractionation pd ir ratios for dundonald texmont hart and alexo are 10 5 12 and 116 respectively the noble element patterns could have been affected by metamorphism including hydrothermal alteration contamination of the magma by a sulfide rich sediment crystal fractionation of monosulfide solid solution solubility of os ir alloys and rus2 and timing of sulfur saturation noble element patterns of samples from the deposits dundonald and alexo of the lowest metamorphic grade prehnite pumpellyite facies are smooth and exhibit no or very small au and pt anomalies however some samples from texmont mid greenschist facies metamorphism contain pt and au anomalies further all samples from the hart deposit which has experienced carbonate alteration have large negative pt and au anomalies contamination of the komatiites with fe sulfide rich sediments found in their vicinity will not change the noble element patterns appreciably a 10 percent contamination of the komatiites will change the pd ir ratio of the sulfides from approximately 5 to 7 5 the massive sulfide at the base of the alexo deposit has a pd ir ratio of 44 the overlying net textured ore has a pd ir ratio of 171 this change in pd ir ratios could be due to the fractionation of monosulfide solid solution from the sulfide liquid the difference in noble element fractionation between the four deposits does not appear to be related to differences in the lithophile element composition of the silicate liquid from which the sulfides separated since all four deposits have a similar lithophile chemistry it is proposed that the differences in the fractionation of the noble element between the deposits is the combined result of the timing of sulfur saturation and the lower solubility of os ir and rus2 in the silicate melt compared to rh pt and pd

komatiites and nickel sulphide orebodies of the black swan area yilgarn craton western australia 1 petrology and volcanology of host rocks the black swan succession is a bimodal association of dacitic and komatiitic volcanic rocks located about 50 km nne of kalgoorlie within the 2 7 ga eastern goldfields greenstone province of the yilgarn craton the komatiite stratigraphy comprises a steep dipping east facing package about 700 m in maximum thickness and about 2 5 km in strike length fig 1 which hosts a number of economically exploitable ni sulphide orebodies including the silver swan massive ore shoot approximately half a million tonnes at about 10 5 ni the sequence can be subdivided into a lower felsic unit comprising coherent and autobrecciated facies of multiple dacite lava flows an upper eastern and lower western ultramafic unit each showing marked lateral facies variation and an upper felsic unit coeval with the eastern ultramafic unit the komatiite sequence has been metamorphosed at sub greenschist facies in the presence of high proportions of co2 rich fluid giving rise to pervasive talc carbonate and talc carbonate quartz assemblages with extensive preservation of pseudomorphed igneous textures cores of lizardite serpentinite are present in the thickest parts of the ultramafic succession the degree of penetrative deformation is generally very low and original stratigraphic relationships are largely intact in much of the sequence the eastern ultramafic unit and western ultramafic unit are interpreted as components of a single large komatiite flow field representing overlapping stages in the emplacement of a series of distributory lava pathways and flanking sheet flows the western ultramafic unit which hosts the bulk of the high grade massive and disseminated ores is a sequence dominated by coarse grained olivine cumulates 2 km wide and up to 500 m thick with major magma pathways represented by thick homogenous olivine mesocumulate piles at its northern and southern ends respectively 400 and 200 m thick the sequence between the two major pathways consists of olivine orthocumulates ooc with minor spinifex textured intervals the unit is capped by a persistent spinifex textured crust less than 1 m thick and is locally vesicular the eastern ultramafic unit contains the black swan cumulate zone a 500 m thick sequence of very coarse grained hopper textured locally vesicular ooc containing disseminated sulphides in its lower 200 m the zone is flanked to the north and south by complexly interdigitated sequence of highly irregular spinifex capped olivine cumulate rich flow lobes between 1 and 100 m thick and dacitic lavas and tuffs the complexity of the 3 d spatial relationship of these units suggests a combination of simultaneous eruption of dacite and komatiite combined with thermal or thermomechanical erosion the eastern and western units are interpreted as the result of more or less continuous prolonged eruption of olivine charged komatiite lava which developed localised thermo mechanical erosion channels in the dacitic substrate komatiite and dacite eruption was synchronous giving rise to complex interdigitation and extensive contamination and hybridisation

komatiites and nickel sulfide ores of the black swan area yilgarn craton western australia 4 platinum group element distribution in the ores and genetic implications the black swan komatiite sequence in the eastern goldfields province of the archaean yilgarn craton in western australia is a body of dominantly olivine rich cumulates with lesser volumes of spinifex textured rocks interpreted as a section through an extensive komatiite lava flow field the sequence hosts a number of nickel sulfide orebodies including the silver swan massive shoot and the cygnet and black swan disseminated orebodies the massive sulfide orebodies of the black swan succession are pervasively depleted in all platinum group elements pges particularly pt and pd despite very high ni contents this depletion cannot be explained by r factor variations which would also require relatively low ni tenors the pge depletion could be explained in part if the ores are enriched in a monosulfide solid solution mss cumulate component but requires some additional fractional segregation of sulfide melt upstream from the site of deposition the silver swan orebody shows a remarkably consistent vertical zonation in pge contents particularly in ir ru rh os which increase systematically from very low levels at the stratigraphic base of the sulfide body to maxima corresponding roughly with the top of a lower layer of the orebody rich in silicate inclusions platinum shows the opposite trend but is somewhat modified by remobilisation during talc carbonate alteration a similar pattern is also observed in the adjacent white swan orebody this zonation is interpreted and modelled as the result of fractional crystallisation of mss from the molten sulfide pool the strong ipge depletion towards the base of the orebody may be a consequence of sulfide liquid crystallisation in an inverted thermal gradient between a thin rapidly cooling upper rind of komatiite lava and a hot substrate

the calculated solubility of platinum and gold in oxygen saturated fluids and the genesis of platinum palladium and gold mineralization in the unconformity related uranium deposits thermodynamic calculations on the solubility of platinum and gold indicate that saline 1 m nacl fluids saturated with atmospheric oxygen can transport geologically realistic concentrations of platinum group elements pge gold and uranium as chloro complexes a number of calculations involving fluid rock interaction suggest that the oxygen saturated fluids flowing through rocks containing quartz muscovite kaolinite magnetite and hematite initially oxidize any magnetite to hematite allowing subsequent batches of ore fluids to retain their high oxidation state during their migration through the aquifer the oxidizing fluids would move the oxidation reduction interface deeper into the aquifer leaching and redepositing platinum and gold the redissolution of earlier precipitated platinum and gold depends on the fluid rock ratio and the associated increase in the oxidation state therefore lowering of fluid rock ratios and or mixing of the oxidized fluids with a large amount of reduced fluid will precipitate uranium pge and gold it is suggested that this model can explain the genesis of gold and pge mineralization in the unconformity related uranium deposits of the alligator rivers uranium field in the northern territory australia

geology sulfide mineralogy and petrogenesis of the angstberg ni cu pge sulfide mineralization lausitz block bohemian massif germany a potential ni cu exploration target in central europe abstract germany s largest known magmatic ni cu pge sulfide enrichment is associated with the gabbroic angstberg intrusion that is one of several small scaled ni cu sulfide bearing intrusions in the northern bohemian massif central european variscan belt the intrusions are part of a middle devonian to early carboniferous mafic ultramafic magmatic system that emplaced within cadomian granodiorites of the lausitz block the angstberg intrusion represents an exposed sub vertical dike like body 320 60 m in plan view and comprises olivine gabbronorite olivine gabbro gabbro olivine hornblende gabbro and hornblende pyroxene gabbro the hornblende bearing and hornblende free lithologies originate from at least two variably fractionated basaltic parental magma batches which differ in their ti lree hree and volatile contents fractionation probably took place in deeper seated sections of the magmatic system possibly within staging magma chamber s overall enriched incompatible trace element patterns suggest that the angstberg lithologies are linked with intra plate magmatism likely associated with a transtensional setting in the course of the variscan orogeny the previously suggested devonian age of the intrusion is confirmed by an 40ar 39ar biotite age of 373 4 0 9 ma for the olivine gabbro the magmatic sulfide mineralization is predominated by disseminated sulfides that are hosted in the olivine richest parts of the olivine gabbronorite and olivine hornblende gabbro lithologies in addition some sulfide matrix breccias up to 70 modal sulfides occur directly on the footwall contact of the intrusion to granodiorite both mineralization types are characterized by a predominance of pyrrhotite over pentlandite and chalcopyrite with minor secondary violarite and pyrite and accessory pge au and ag phases nickel rich bismuthotellurides of the melonite merenskyite solid solution series and froodite are the most common platinum group minerals disseminated sulfides are characterized by high ni moderate cu and low pt and pd tenors 4 9 wt ni 2 6 wt cu 200 800 ppb pt 200 1000 ppb pd sulfide matrix breccias feature comparable ni but lower cu pt and pd tenors 4 6 wt ni 0 3 1 wt cu 10 100 ppb pt 40 200 ppb pd fractional crystallization and wall rock assimilation of granodiorite are regarded as key factors for sulfide saturation in the magmas associated with the angstberg intrusion sulfur isotope compositions of pyrrhotite pentlandite chalcopyrite assemblages 1 4 to 0 2 vcdt propose a mantle origin of s whereas addition of crustal s cannot be completely ruled out as the s isotope values of the sulfides overlap with those of the granodiorite 7 to 4 vcdt olivine and sulfide textures suggest that disseminated sulfides likely originate from sulfide melts that were entrained in an olivine rich crystal mush during magma rise to upper levels the sulfide matrix breccias also resulted from entrained sulfide melts or from gravity driven downward percolation of sulfide melts from stratigraphically higher now eroded levels in both cases the formation of sulfide matrix breccias most likely was amplified by in situ thermomechanical erosion of the granodioritic wall rock caused by flash boiling of thermally dehydrating biotite despite spatial limitations of the mineralized zones and limited information about the architecture of the intrusions in the northern bohemian massif the angstberg intrusion as well as other neighboring magmatic sulfide occurrences may represent a new exploration target for ni and cu in central europe

the agnew nickel deposit western australia part ii sulfide geochemistry with emphasis on the platinum group elements nickel sulfide mineralization in the agnew deposit comprises matrix or net textured ores primary in situ massive sulfides structurally remobilized massive sulfides and low grade disseminated or cloud suifides matrix and massive sulfides are also present at the laterally correlative rocky s reward deposit 2 km to the north systematic compositional contrasts are noted between the different ore types when analyses are normalized to abundances in 100 percent sulfides matrix ores are enriched in ni co cu pt pd and au but depleted in os ir ru and rh relative to adjacent massive ores both at the agnew deposit and at rocky s reward cloud sulfides are similar to matrix sulfides in os ir ru and rh but are enriched in ni co cu pt pd and au relative to both massive and matrix ores overall abundances of all the above elements are slightly lower at rocky s reward than at agnew and both deposits are depleted in these elements relative to ores at kambalda remobilized and in situ massive sulfides are identical in composition implying that remobilization occurred by tectonic not hydrothermal processes massive sulfides could not have originated by metamorphic upgrading of matrix ore the nickel content of olivine within the mineralized flow at agnew is strongly depleted relative to typical komatiitic olivines olivine in the cloud sulfide zone is depleted to a lesser extent quantitative modeling shows that the observed olivine mg fe ratios and nickel contents as well as the ni contents of the agnew sulfides formed by extensive preemplacement extraction of olivine and sulfide liquid from a primitive komatiite parent olivine and sulfides in the cloud zone show less extensive differentiation in a model compositional contrasts between the agnew and rocky s reward deposits are attributed to lateral differentiation within lava flows since agnew is closer to the site of eruption the difference in os ir ru and rh concentrations between matrix and massive ore cannot be the result of in situ fractionation of the sulfide liquid or of hydrothermal remobilization the different ore types must have formed from discrete batches of sulfide liquid which segregated under different fugacities of sulfur and or oxygen

geochemical investigation of the lower cambrian mineralised black shales of south china and the late devonian nick deposit canada abstract lower cambrian tommotian black shales of the niutitang formation south china host a thin accumulation 5 20 cm of ni mo platinum group elements pge au ni as zn cu v and rare earth elements ree of all known deposits the late devonian ni mo pge sulphide horizon in black shales of the nick deposit selwyn basin in canadian yukon presents the strongest similarity with the niutitang formation polymetallic layer in the present study samples of the mineralised layer and host shales in south china from two mine sites zunyi and sancha were investigated in order to further characterise the prevailing redox conditions and mechanisms involved in the metal concentration process at both sites additional comparison with the nick deposit mineralised layer was also undertaken bulk geochemical analysis including pge analysis were conducted on all samples along with m scale investigation of metal distributions and associations by x ray fluorescence xrf mapping and synchrotron xrf mapping the comparison of the two sites from south china highlights strong similarities in metal enrichment factors pge and ree distribution patterns are also highly similar and suggest a source from seawater strong variations in elemental distributions at m scale were observed at both sites most likely related to intense variations in redox conditions in the sediment the comparison with the nick deposit highlights a stronger enrichment in ni and zn in the nick deposit and a greater variety of minerals in the niutitang shales the pge and ree distributions of both the nick deposit and the niutitang shales however present highly similar patterns and support an origin from seawater the present study provides further insight into mineralisation style and processes in these mineralised black shales highlighting the importance of redox conditions and re emphasizing the role of organic matter in the formation of these mineralised layers

speciation and solubility of palladium in aqueous magmatic hydrothermal solutions combining thermodynamic data at 25c and 1 bar with correlation algorithms enables prediction of equilibrium dissociation constants for aqueous platinum group element pge complexes at high pressures and temperatures we used these data 1 to calculate the speciation of pd ii in nacl solutions at temperatures to 750c pressures to 2 kbar and values from 3 to 8 and 2 to predict the solubility of palladium at 2 kbar as a function of temperature oxygen fugacity f sub o2 ph and total chloride concentration m sub t cl sup minus calculations indicate that as ph increases there is a sharp transition from chloride to hydroxide complex dominance at all chloride concentrations this shift occurs at or below neutral ph in dilute solution but at m sub t cl sup minus ge 1 0 pd ii chloride complexes account for the majority of dissolved pd ii well into alkaline conditions solubility of palladium increases with increasing temperature m sub t cl sup minus and f sub o2 at 700c 2 kbar and the f sub o2 set by the fmq buffer palladium solubility in a 3 0 m nacl solution is approximately 0 3 ppm at a ph of 4 and one unit ph variation can change palladium solubility by two orders of magnitude these results suggest that pge can be transported as chloridemore complexes in cl rich magmatic hydrothermal solutions like those inferred from petrologic studies of the stillwater and bushveld complexes less

platinum group element and gold contents in the skouries porphyry copper deposit chalkidiki peninsula northern greece the skouries porphyry copper deposit is located in the eastern chalkidiki peninsula northern greece along with several other porphyry copper occurrences this deposit establishes the northeastern part of the servomacedonian zone as a porphyry copper region amphibolite mica schist and two mica gneiss are the predominant rock types exposed in the skouries area these rocks have been intruded by the skouries porphyry stock which is of subalkaline composition and is tertiary in age 18 ma the skouries porphyry intrusion and the surrounding country rocks are strongly fractured and intensely altered by hydrothermal fluids in addition to intense silicification a prominent alteration type is potassic whereas phyllic and propylitic types are less common mineralization mainly includes chalcopyrite pyrite bornite chalcocite and magnetite in the form of veins stockworks and disseminations native gold and electrum commonly are present as small inclusions in chalcopyrite although lateral zoning is not defined clearly a vertical zoning in terms of both metal mineralogy and overall metal content is apparent a zone of oxidation azurite malachite covers the upper part of the ore and is underlain by a zone of reduced rock rich in covellite and chalcocite which in turn is underlain by the most important ore type including a chalcopyrite pyrite bornite magnetite assemblage both weakly and intensively altered porphyry samples from the deposit were analyzed for major oxides trace elements and all platinum group elements pge the stock exhibits high levels of cu au ag b bi co se and te barium and sr contents are also high while rb is low resulting thereby in high k rb and low rb sr ratios palladium concentrations range from less than 2 to 480 ppb ruthenium content ranges from 8 to 41 ppb and pt from 2 to 10 ppb osmium ir and rh content is below detection limit the average au ag ratio is 0 87 which is consistent with the range of several worldwide porphyry copper deposits on the basis of factor analysis of selected geochemical data a strong positive interelement correlation r or 0 83 between au ag pd nd te coupled with their association with silica appears to support a correlation of these precious metals with silicification rather than potassic type alteration such a relationship may suggest similar behavior of these metals and a common origin a positive correlation of cu with iron r 0 86 which is consistent with the association of chalcopyrite with magnetite and the low correlation of te and pd with cu may suggest that these metals and to a lesser extent copper have been redistributed during a late stage of evolution of the skouries porphyry system furthermore the close association of te with precious metals combined with the relatively low temperature for telluride minerals stability may indicate that at least partly precious metal tellurides have been formed in a relatively shallow and less hot environment

imaging of oceanic features by ers 1 synthetic aperture radar data from the european space agency s ers 1 satellite synthetic aperture radar sar covering the region of the east australian current during late 1991 have been analyzed in conjunction with ship and airborne data and infrared imagery apart from wind effects the largest differences in backscatter seem to be associated with different water masses these differences probably being caused by wave damping due to natural surfactants slicklike features in the tasman sea are common even in the deep ocean when the winds are light ocean currents are often visible but as relatively subtle features it is unlikely that changes in atmospheric boundary layer stability due to changing sea surface temperature are the dominant mechanism for radar imaging of ocean currents it is suggested that c band radar backscatter will prove to be more directly correlated with biological activity and ocean color than with sea surface temperature particularly at higher latitudes surfactants could cause errors of 20 or more in wind speeds derived from satellite scatterometers

metamorphic evolution of sulphide rich chromitites from the chernichevo ultramafic massif se bulgaria abstract the upper mantle rocks of the metamorphosed ophiolite of chernichevo rhodope metamorphic complex in southern bulgaria host small chromite ores with unusual mineralization of base metal sulphides rich in platinum group elements mineralogical and chemical data indicate that after their formation in the mantle the chernichevo s chromite ores were modified by the intrusion of an alkaline mafic melt which resulted in the precipitation of a suite of metasomatic minerals sulphides calcite apatite and ilmenite accompanied by an increase in feo tio2 ga zn vn mn and especially ti and fe2o3 contents in the chromite the degree of chemical modification and abundance of metasomatic minerals are positively correlated and mark the extent of reaction of the chromitite with the intruding melt sulphide segregation promoted the concentration of high amounts of pges up to 3661 ppb particularly pt and pd yielding chromite ores with a typical flat to positive sloped chondrite normalized pattern subsequently the chromite ores were deformed and metamorphosed together with their host rocks at ultra high pressure uhp 2 5 gpa 1200 c to be later retrograded under eclogite and finally hydrous amphibolite facies conditions giving rise to three microstructural types metamorphism of the most metasomatized i e sulphide rich chromitites at temperatures 700 c within the conditions of uhp and eclogite facies resulted in the formation of 1 non porous recrystallized chromite consisting of a granoblastic microstructure made up of coarse grained blasts and finer grained chromite neoblasts in contrast hydrous metamorphism on the less metasomatized i e sulphide poor chromitite under the conditions of amphibolite facies ca 482 483 c resulted in the formation of 2 partly altered chromite characterized by unaltered cores surrounded by fe2 rich and al depleted porous chromite containing abundant clinochlore and 3 porous chromite corresponding to a chromite that was entirely transformed by the metamorphic alteration to fe2 rich and al depleted porous chromite during metamorphism magmatic ni fe cu sulphides originally formed during the metasomatic event in the mantle were altered resulting in a major leaching of cu rich sulphides leading to significant remobilization of pt and pd

postmagmatic variability in ore composition and mineralogy in the t4 and t5 ore shoots at the high grade flying fox ni cu pge deposit yilgarn craton western australia the high grade flying fox komatiite hosted ni sulfide deposit located in the forrestania greenstone belt of the archean yilgarn craton western australia is hosted in a deformed and metamorphosed volcano metasedimentary succession postmineralization events have sheared and modified the texture and composition of the original massive sulfide ore creating up to 11 distinct ore shoots including massive stringer vein and breccia sulfides composed of pyrrhotite pentlandite chalcopyrite and variable abundances of pyrite ranging up to 40 vol nickel and platinum group elements pge tenor variations were investigated in two ore shoots t4 and t5 all mineralization styles show considerable variability in ni tenor pges show strong linear correlations between ir os ru and rh but poor correlation between pt pd and cu the normalized molar proportions of fe ni and s projected into the fe ni s ternary system show a distinct linear trend of pyrite addition to a typical primary magmatic composition and no correlation with mineralization style the high pyrite content present throughout the flying fox ore is also associated with elevated cu and as contents and is interpreted to be primarily due to the addition of pyrite from circulating fe s cu and as enriched fluids creating pyrite pentlandite intergrowths localized mechanical segregation of pyrite sulfidation of pyrrhotite to pyrite and oxidation of pyrrhotite to pyrite magnetite has also contributed to these increased pyrite contents although to a lesser extent the addition and segregation of pyrite has diluted the ni tenor with no evidence to suggest chemical mobilization of ni

platinum group element fractionation in a komatiitic basalt lava lake precise pge os ir ru pt pd abundance data for bulk rock samples and mineral separates from a deep differentiated komatiitic basalt lava lake in the vetreny belt baltic shield were obtained using an icp ms id technique the composition of the erupted liquid mgo 5 15 is characterized by a highly fractionated pge pattern pd os n 5 48 with subchondritic os ir n 5 0 43 analysis of separated olivine and chromite revealed that ru os and ir were slightly compatible to moderately incompatible in olivine d 5 1 7 0 8 and were compatible with chromite d 5 100 150 platinum and pd were highly incompatible with olivine d 5 0 08 0 03 and moderately compatible with chromite d 5 1 6 3 3 bulk solid liquid partition coefficients for pges ni cr and cu estimated from the whole rock regressions were os 7 9 ir 6 6 ru 4 5 pt 0 53 pd 0 09 ni 6 2 cr 4 4 and cu 0 01 the highly incompatible behavior of cu and pd indicates that there was no separation of fenicu immiscible sulfide liquid during the differentiation of the lava lake comparison of the bulk partition coefficients with those calculated from the olivine and chromite compositions implies that the fractionating mineral assemblage included 10 2561 mass fraction of pyrrhotite the data obtained provide new constraints on the effects of fractional crystallization on the pge compositions of mafic ultramafic magmas copyright 2001 elsevier science ltd