deciphering the hydrothermal evolution of a vms system by la icp ms using trace elements in pyrite an example from the bracemac mcleod deposits abitibi canada and implications for exploration textural and chemical characterization of pyrite was used to reconstruct the hydrothermal evolution of the bracemac mcleod archean volcanogenic massive sulfide vms deposits 6 mt in the matagami district abitibi canada the mineralization hosted in a bimodal volcanic sequence is divided into a 1 zn rich zone concordant to the key tuffite a marker horizon at the district scale 2 a cu rich zone which locally crosscuts the stratigraphic pile and 3 some localized magnetite rich zones replacing sphalerite and pyrite detailed petrographic and laser ablation inductively coupled plasma mass spectrometry la icp ms studies of whole pyrite grains including inclusions and zonation from the key tuffite and from the different ore zones of the deposits has revealed five pyrite types nodular pyrites i in the key tuffite and subidiomorphic pyrites from the low temperature 250 c zn rich zone ii have the same chemical signature suggesting that both precipitated under similar physicochemical conditions a wide range of trace elements cu zn ag sn sb te au pb bi tl are present in both but compared to the other types of pyrite they are significantly enriched in sb and tl subidiomorphic pyrites from the copper rich zone iii have a different signature enriched only in se co in pb and bi these pyrites commonly overgrow the nodular pyrites and are related to later higher temperature fluids 300 c pyrite preserved during a later magnetite replacement 350 c stage iv also are enriched in se but are depleted in all other elements a similar signature is found in idiomorphic metamorphic pyrite v which occurs at the district scale during high temperature recrystallization of pyrite iv and v only the contents of ni co as and se are mostly preserved whereas other base metals are expelled from the pyrite structure consequently only ni co as se sb and tl were useful to reconstruct the hydrothermal evolution of the vms system and used to build a suite of discrimination diagrams specifically the ratio se tl can discriminate pyrites from mineralized zn rich zone se tl 10 000 the innovative approach of this study based on la icp ms acquisition of the chemistry of entire pyrite grains makes our results directly applicable for exploration consequently pyrite concentrate samples analyzed for as tl and se by more classical mass spectrometric techniques have the potential to be used for vectoring to ore by using the proposed discrimination diagrams

on the subsurface cfc maxima in the subtropical north pacific thermocline and their relation to mode waters and oxygen maxima the spatial structure of the subsurface chlorofluorocarbon cfc concentration maxima in the subtropical north pacific is examined using data from the pacific ocean sector of the world ocean circulation experiment woce hydrographic program collected in the period 1991 1994 comparison with potential vorticity pv sections reveals that the cfc maxima coincide with the pv minimum associated with subtropical mode water stmw in the western pacific as suggested by earlier observations warner et al 1996 in the eastern part of the central pacific the cfc maxima appear to be shallower than the central mode water cmw while they are deeper than the eastern subtropical mode water in the eastern pacific a subsurface oxygen maximum also coincides with stmw and the cfc maxima in the west is located between the cfc maxima and cmw in the central pacific and is absent in the east the collocation in the west is explained by the fact that stmw is the densest water to outcrop in the recirculation to the south of the kuroshio and the kuroshio extension while denser water is not directly ventilated in this region data from two post woce cruises and results from a steady state age model indicate that the cfc maxima are transient and are deepening such that the collocation of the cfc maxima and stmw does not persist in the late 1990s model experiments based on a smooth age profile demonstrate that the deepening of the cfc maxima is closely related to changes in the atmospheric cfc growth rates

the presence of carbonic dominant volatiles during the crystallization of sulfide bearing mafic pegmatites in the north roby zone lac des iles complex ontario mafic pegmatites in the platinum group element pge mineralized roby zone lac des iles complex northwest ontario canada comprise dikes veins and irregular pods of coarse grained magnesiohornblende pyroxene and labradorite andesine with minor biotite apatite fe ti oxides and intercumulus quartz that grades into massive quartz or graphic quartz base metal sulfide vysotskite pd ni s intergrowth at their cores quartz apatite and magnesiohornblende host primary and secondary assemblages of one or two phase carbonic fluid co 2 up to 10 ch 4 minor h 2 o n 2 inclusions that contain ore metals ni cu pd bi te fe rare trails of late stage high salinity aqueous fluid inclusions are secondary in origin and therefore unrelated to the crystallization of the pegmatites assemblages of primary carbonic fluid inclusions show considerable variation in mode and temperature of homogenization reflecting large fluctuations in confining pressure at the time of quartz crystallization of as much as 1 kbar in single quartz crystals and 2 8 kbars all data independent thermobarometric methods constrain conditions for the following two stages of pegmatite formation and carbonic fluid entrapment 1 the crystallization of magnesiohornblende plagioclase intergrowth at t 650 to 850 c and p 1 to 3 kbars and 2 the crystallization of quartz at t 535 to 650 c and p 0 4 to 3 2 kbars setting the maximum depth of emplacement of the lac des iles complex north roby zone magma at 10 to 12 km the results indicate that aqueous dominant volatile phases were absent during the crystallization of pegmatitic gabbroic rocks at the lac des iles complex and that water poor carbonic fluid entrapment persisted to well below solidus conditions a role played by carbonic fluid as a potential transport medium for ligands involved in the precipitation and remobilization of the pge and base metals is strongly suggested and warrants further investigation

changes in sulfides and platinum group minerals with the degree of alteration in the roby twilight and high grade zones of the lac des iles complex ontario canada the lac des iles complex hosts pd deposits with unusually high pd pt and pd ir ratios these high ratios have been attributed to the introduction of pd by late magmatic hydrothermal fluids the presence of hydrous silicates and low temperature sulfide mineral assemblages has been advanced as evidence for fluid overprint this idea has been investigated by documenting the change in silicate sulfide and platinum group mineralogy and texture in samples from the deposit ranging from fresh gabbronorite to extensively altered chlorite actinolite schist in addition whole rock analysis combined with laser ablation analysis of the sulfides was used to determine which phase controlled each of the pge in fresh gabbronorite the sulfide assemblage is igneous pyrrhotite pentlandite chalcopyrite and pd is present mainly in pentlandite and kotulskite pdte inclusions associated with the sulfide minerals all other pge except pt are present in solid solution in pyrrhotite and pentlandite platinum is present as sperrylite ptas2 and montcheite ptte2 inclusions associated with the sulfide minerals these observations suggest that the pge in the fresh gabbronorite were all collected by magmatic sulfide liquid in the chlorite actinolite schist the sulfide assemblage is a low temperature assemblage consisting of chalcopyrite pyrite millerite a minor amount of palladium is present in millerite but most is present as bismuth rich kotulskite and pd arsenides both of which are associated with hydrous silicate all other pge except pt are hosted by pyrite a minor amount of pt is present in pyrite but most is found as sperrylite and montcheite associated with hydrous silicate minerals the pyrite could have formed by fe loss from pyrrhotite resulting in the pyrite inheriting os ir ru and rh and fe loss from pentlandite to form millerite resulting in the millerite inheriting some pd the pge concentrations of the whole rock show there is no direct correlation between the sulfide assemblage the degree of alteration of the silicate minerals and ore grade thus although fluids have clearly altered the sulfide silicate and platinum group mineralogy and their textures it is not clear that these fluids have changed the pge content of the rocks

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

precious and base metal geochemistry and mineralogy of the grasvally norite pyroxenite anorthosite gnpa member northern bushveld complex south africa implications for a multistage emplacement the grasvally norite pyroxenite anorthosite gnpa member within the northern limb of the bushveld complex is a mineralized layered package of mafic cumulates developed to the south of the town of mokopane at a similar stratigraphic position to the platreef the concentration of platinum group elements pge in base metal sulfides bms has been determined by laser ablation inductively coupled plasma mass spectrometry these data coupled with whole rock pge concentrations and a detailed account of the platinum group mineralogy pgm provide an insight into the distribution of pge and chalcophile elements within the gnpa member during both primary magmatic and secondary hydrothermal alteration processes within the most unaltered sulfides containing pyrrhotite pentlandite and chalcopyrite only the majority of ipge rh and some pd occur in solid solution within pyrrhotite and pentlandite with an associated pt as and pd bi te dominated pgm assemblage these observations in conjunction with the presence of good correlations between all bulk pge and base metals throughout the gnpa member indicate the presence and subsequent fractionation of a single pge rich sulfide liquid which has not been significantly altered in places the primary sulfides have been replaced to varying degrees by a low temperature assemblage of pyrite millerite and chalcopyrite these sulfides are associated with a pgm assemblage characterized by the presence of pd antimonides and pd arsenides which are indicative of hydrothermal assemblages the presence of appreciable quantities of ipge pd and rh within pyrite and to a lesser extent millerite suggests these phases directly inherited pge contents from the pyrrhotite and pentlandite that they replaced the replacement of both the sulfides and pgm occurred in situ thus preserving the originally strong spatial association between pgm and bms but altering the mineralogy precious metal geochemistry indicates that fluid redistribution of pge is minimal with only pd au and cu being partially remobilized and decoupled from bms this is also indicated by the lower concentrations of pd evident in both pyrite and millerite compared with the pentlandite being replaced the observations that the gnpa member was mineralized prior to intrusion of the main zone and that there was no local footwall control over the development of sulfide mineralization are inconsistent with genetic models involving the in situ development of a sulfide liquid through either depletion of an overlying magma column or in situ contamination of crustal s we therefore believe that our observations are more compatible with a multistage emplacement model where preformed pge rich sulfides were emplaced into the gnpa member such a model explains the development and distribution of a single sulfide liquid throughout the entire 400 800 m thick succession it is therefore envisaged that the gnpa member formed in a similar manner to its nearest analogue the platreef notable differences however in pge tenors indicate that the ore forming process may have differed slightly within the staging chambers that supplied the platreef and gnpa member

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

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

extreme enrichment of se te pge and au in cu sulfide microdroplets evidence from la icp ms analysis of sulfides in the skaergaard intrusion east greenland the platinova reef in the skaergaard intrusion east greenland is an example of a magmatic cu pge au sulfide deposit formed in the latter stages of magmatic differentiation as is characteristic with such deposits it contains a low volume of sulfide displays peak metal offsets and is cu rich but ni poor however even for such deposits the platinova reef contains extremely low volumes of sulfide and the highest pd and au tenor sulfides of any magmatic ore deposit here we present the first la icp ms analyses of sulfide microdroplets from the platinova reef which show that they have the highest se concentrations up to 1200 ppm and lowest s se ratios 190 700 of any known magmatic sulfide deposit and have significant te enrichment in addition where sulfide volume increases there is a change from high pd tenor microdroplets trapped in situ to larger low tenor sulfides the transition between these two sulfide regimes is marked by sharp peaks in au and then te concentration followed by a wider peak in se which gradually decreases with height mineralogical evidence implies that there is no significant post magmatic hydrothermal s loss and that the metal profiles are essentially a function of magmatic processes we propose that to generate these extreme precious and semimetal contents the sulfides must have formed from an anomalously metal rich package of magma possibly formed via the dissolution of a previously pge enriched sulfide other processes such as kinetic diffusion may have also occurred alongside this to produce the ultra high tenors the characteristic metal offset pattern observed is largely controlled by partitioning effects producing offset peaks in the order pt pd au te se cu that are entirely consistent with published d values this study confirms that extreme enrichment in sulfide droplets can occur in closed system layered intrusions in situ but this will characteristically form ore deposits that are so low in sulfide that they do not conform to conventional deposit models for cu ni pge sulfides which require very high r factors and settling of sulfide liquids

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

comment on changes in sulfides and platinum group minerals with the degree of alteration in the roby twilight and high grade zones of the lac des iles complex ontario canada by mln djon and sj barnes i wish to raise three main issues arising out of a carefulreading of the paper by djon and barnes 2012 1 it employs a fundamentally flawed technique by usingthin sections polished blocks to measure the absoluteand relative abundances of base metal sulfide bms minerals and trace platinum group minerals pgms insilicate whole rocks resulting in errors in calculationsfor mass balance and pge deportment 2 it describes poor analytical methods for electron probemicro analysis epma of pgm and laser ablationinductively coupled plasma mass spectrometry la icp ms analyses of the bms resulting in errors inthe reported concentrations for some elements 3 it shows poor preparation of the manuscript omittingimportant details on which values for pge concentra tions were used in calculations for mass balance andpge deportment and why this makes for the inabilityof the results to be checked and evaluated critically byreaders it is also unfortunate that the authors do not acknowledgeany referees for their efforts which make it impossible forthe reader to judge whether a the referees were knowl edgeable in applied process mineralogy and epma la icp ms and b the authors implemented the obvious rec ommendations that would have been made by such experts because this journal is mainly devoted to the study ofmineral deposits some background is relevant to put theabove criticisms in context studies of pge mass balancesand their deportment in rocks is a well developed techniquein the discipline of applied process mineralogy similarly well established procedures have been developed in theanalytical geochemistry community for in situ analyses ofpges in sulfide minerals by la icp ms nonetheless bothapplied process mineralogy and la icp ms analyses ofminerals are relatively new areas of scientific endeavor formany mineral deposit geologists and academics perhapsexplaining some of the mistakes made applied process mineralogy only evolved internationallywith the first international council for applied mineralogy icam conference in 1981 having been developed in someof the major mining companies and some governmentresearch laboratories e g canmet canada csiro aus tralia and mintek south africa unfortunately there areveryfew universitieswherestudentscanbecomeproficientinappliedandprocessmineralogy mostexpertshavinglearntonthe job schouwstra and smit 2011 there are also very fewbooks devoted to the subject a rare one being by petruk 2000 most case studies being found in conference proceed ings e g canadian mineral processors icam and theminerals metals and material society tms aime ormore recently in the conference of metallurgists e g fordet al 2009 2011 and minerals engineering e g lotter2011 thus proper procedures for pge mass balances anddeportment are not well known outside the applied processmineralogy community secondly la icp ms of mineralswasdevelopedonly20yearsago fromthepioneeringworkofjackson et al 1992 and proper procedures for analyses ofbms has been only widely possible more recently

textural mineralogical and stable isotope studies of hydrothermal alteration in the main sulfide zone of the great dyke zimbabwe and the precious metals zone of the sonju lake intrusion minnesota usa stratigraphic offsets in the peak concentrations of platinum group elements pge and base metal sulfides in the main sulfide zone of the great dyke and the precious metals zone of the sonju lake intrusion have in part been attributed to the interaction between magmatic pge bearing base metal sulfide assemblages and hydrothermal fluids in this paper we provide mineralogical and textural evidence that indicates alteration of base metal sulfides and mobilization of metals and s during hydrothermal alteration in both mineralized intrusions stable isotopic data suggest that the fluids involved in the alteration were of magmatic origin in the great dyke but that a meteoric water component was involved in the alteration of the sonju lake intrusion the strong spatial association of platinum group minerals principally pt and pd sulfides arsenides and tellurides with base metal sulfide assemblages in the main sulfide zone of the great dyke is consistent with residual enrichment of pt and pd during hydrothermal alteration however such an interpretation is more tenuous for the precious metals zone of the sonju lake intrusion where important pt and pd arsenides and antimonides occur as inclusions within individual plagioclase crystals and within alteration assemblages that are free of base metal sulfides our observations suggest that pt and pd tellurides antimonides and arsenides may form during both magmatic crystallization and subsolidus hydrothermal alteration experimental studies of magmatic crystallization and hydrothermal transport deposition in systems involving arsenides tellurides antimonides and base metal sulfides are needed to better understand the relative importance of magmatic and hydrothermal processes in controlling the distribution of pge in mineralized layered intrusions of this type

roots of an archean volcanic arc complex the lac des iles area in ontario canada abstract the lac des iles area is located in the wabigoon subprovince an archean granite greenstone terrain in the superior province in ontario canada the area consists of several unmetamorphosed plutons of biotite and hornblende tonalite and mafic and ultramafic intrusions which are emplaced into an older tonalitic gneiss the mafic ultramafic bodies are concentric in shape and consist of periodotite pyroxenite gabbro and hornblende gabbro cumulates and diorite the largest intrusion the lac des iles complex consists of several mafic and ultramafic centers an internal sm nd isochron from the southern ultramafic complex gives an intrusion age of 2736 28 ma mswd 1 5 nd t 1 2 this age is also assumed to be representative of the time of emplacement of the other mafic and ultramafic bodies as well as the unmetamorphosed tonalite plutons the tonalitic gneiss represents older continental crust and had an nd value of 1 at this time the nd t values of the felsic and mafic ultramafic suites are positive ranging from 0 to 2 this range can be explained if primary magmas derived from a depleted mantle reservoir assimilated continental crust such as the tonalite gneiss during their ascent this implies that the tonalite magmas in the lac des iles area represent mixtures of the tonalite country rock and mantle magmas which formed by partial melting of depleted mantle or of mafic rocks underplated beneath the continental lithosphere the morphology and the rock assemblages of the mafic and ultramafic intrusions in the lac des iles area resemble alaskan type intrusions which are common components of phanerozoic magmatic arcs associated with subduction zones in addition the crystallization sequence in the mafic ultramafic intrusions suggests that they are derived from a parental magma with high al basalt affinities the mafic ultramafic rocks are depleted in high field strength elements but enriched in large ion lithophile elements and the tonalites belong to calc alkaline rock series displaying fractionation trends towards trondhjemitic compositions thus the archean lac des iles area and the root zones of phanerozoic active continental margins share many geological geochemical and petrological features which would suggest that the lac des iles area formed in an andean type continental margin

platinum group element gold silver and base metal distribution in compositionally zoned sulfide droplets from the medvezky creek mine noril sk russia concentrations of ag au cd co re zn and platinum group elements pge have been determined in sulfide minerals from zoned sulfide droplets of the noril sk 1 medvezky creek mine the aims of the study were to establish whether these elements are located in the major sulfide minerals pentlandite pyrrhotite chalcopyrite and cubanite to establish whether the elements show a preference for a particular sulfide mineral and to investigate the model which suggests that the zonation in the droplets is caused by the crystal fractionation of monosulfide solid solution mss nickel cu ag re os ir ru rh and pd were found to be largely located in the major sulfide minerals in contrast less than 25 of the au cd pt and zn in the rock was found to be present in these sulfides osmium ir ru rh and re were found to be concentrated in pyrrhotite and pentlandite palladium and co was found to be concentrated in pentlandite silver cd and zn concentrations are highest in chalcopyrite and cubanite gold and platinum showed no preference for any of the major sulfide minerals the enrichment of os ir ru rh and re in pyrrhotite and pentlandite exsolution products of mss and the low levels of these elements in the cubanite and chalcopyrite exsolution products of intermediate solid solution iss support the mss crystal fractionation model because os ir ru rh and re are compatible with mss the enrichment of ag cd and zn in chalcopyrite and cubanite also supports the mss fractionation model these minerals are derived from the fractionated liquid and these elements are incompatible with mss and thus should be enriched in the fractionated liquid gold and pt do not partition into either iss or mss and become sufficiently enriched in the final fractionated liquid to crystallize among the iss and mss grains as tellurides bismithides and alloys during pentlandite exsolution pd appears to have diffused from the cu rich portion of the droplet into pentlandite

mineralogical variation in platinum group element within altered chromitite of the kondapalli layered igneous complex southern india implication on magmatic evolution and its petrogenetic significance abstract the kondapalli layered igneous complex klic is deformed and dismembered stratiform type of mafic ultramafic complex emplaced into high grade metamorphic rocks of eastern ghat belt egb which contains chromite with relatively oxidized compositions that occur as bands pockets pods stringer and dissemination this chromite hosts traces of pgm eg laurite irarsite ir ru rh pt ass os ir ru alloys and fe ni as s minerals the present study helps to understand the changes and or reworking of chromite and pgm due to the effect of alteration petrographic observations and epma study indicate that the chromite core is still consistent with magmatic fractionation processes whereas sequential alteration of the chromite rim suggests upper greenschist to lower amphibolite facies of metamorphism 500 to 550 c the platinum group minerals pgm however display evidence of partial hydrothermal metamorphic reworking especially laurite and irarsite which occur near the chromite grain boundary in contrast the primary ones which probably formed at high t and low fs2 and occur in the chromite cores are relatively less affected by alteration the calculated parental magma composition was similar to that of modern primitive boninitic tholeiitic basalt formed by a high degree of mantle melting present study ascribes the formation of the subduction generated arc mafic ultramafic magmatism in the kondapalli to the closure of the ocean that led to the formation of the suture between eastern dharwar craton edc and egb the parent magma of the klic is interpreted as mantle derived arc related boninites with s undersaturated nature like other layered intrusions this is indicating that an initial percolation of sulphur poor melts for long period without significant contamination for the genesis of klic the mineral chemistry supports the very limited crustal contamination and non availability of the sufficient meta sediments during assimilation precludes the sulphur saturation in the klic which is mainly constrained for the development of potential ni cu pge mineralization as a result the klic fever the deposition of only primary orthomagmatic chromite pge mineralization these findings determined that the investigated klic are low priority ni cu pge targets the compositions of the chromites can be used to determine the petrologic history of the intrusions and may prove to be a useful exploration tool in such mineralised belt

magma mixing and constitution zone refining in the lac des iles complex ontario genesis of platinum group element mineralization the lac des iles complex is a 2 74 ga old composite intrusion emplaced into a granite and or granite gneiss terrane of the wabigoon subprovince northwestern ontario the complex consists of a gabbroic and ultramafic part the latter has been subdivided into northern and southern intrusive phases both the gabbroic and ultramafic parts contain platinum group element bearing ni cu sulfide mineralization although only the roby zone in the gabbro is of economic importance the southern ultramafic complex consists of a wehrlite to olivine clinopyroxenite core which is surrounded by websterite and gabbronorite cumulates petrographic and geochemical studies suggest that the northern ultramafic complex consists of at least eight cyclic units which ideally are composed of dunite and wehrlite to olivine clinopyroxenite cumulates at the base followed by clinopyroxenite and websterite locally grading into gabbronorite this indicates similar crystallization sequences in both ultramafic centers olivine olivine clinopyroxene clinopyroxene clinopyroxene orthopyroxene or plagioclase in the ultramafic complex platinum group element bearing sulfide mineralization occurs at the top of cyclic units in websterite and orthopyroxenite cumulates sulfide bearing samples up to 1 wt sulfide are enriched in au pd pt and cu relative to ni ir os and ru with pd ir ratios on the order of 250 sulfide immiscibility probably was caused by mixing of fractionated residual melt with more primitive liquid which periodically intruded the magma chamber evidence of mixing is seen in gradational chemical variations across the interface of cyclic units and in the occurrence of inclusions of olivine crystals and crystal aggregates in websterite and gabbronorite cumulates these inclusions are not in equilibrium with their present host rock and presumably formed before mixing in the more primitive magma a mineralized orthopyroxenite cumulate at the top of cyclic unit 2 could not have been produced by the normal crystallization sequence consideration of the phase relationships in the ternary system olivine clinopyroxene plagioclase quartz suggests that these cumulates are the crystallization product of a hybrid magma formed during magma mixing at the interface of cyclic units the gabbroic complex consists mainly of largely altered gabbro and gabbronorite cumulates and is intruded by mafic ultramafic dikes the center of the gabbroic complex contains the economically important roby zone with its platinum group element bearing cu ni sulfide mineralization this is a lithologically and texturally very complex zone in which high grade platinum group element mineralization is associated with pegmatite and mafic ultramaflc dikes the roby zone is characterized by strong enrichments of au pd and pt relative to ir and os and by variable but extremely high pd ir ratios of greater than 10 000 high au pt and pd pt ratios indicate a fractionation of pt from au and pd it is suggested that the high volatile content of the residual magma of the gabbroic complex triggered partial remelting of surrounding gabbro cumulates a process called constitutional zone refining by mcbirney 1987 during the partial melting event compatible elements such as ir and os are buffered by the residual silicate and oxide mineralogy whereas incompatible elements such as au pd and pt as well as volatile components such as h 2 o and h 2 s become highly concentrated in the partial melt phase eventually this newly formed magma may become sulfide saturated either by cooling and fractional crystallization or due to the continuous dissolution of sulfides when the zone of melting proceeds through the gabbro cumulates ratios such as pd ir and pd pt would strongly depend on the degree of remelting and fractional crystallization until the time of sulfide saturation the matrix of the varitextured zone is interpreted as the residuum of this melting process whereas pegmatoids and pegmatites segregationlike gabbro phases and quartz bearing plagioclase and incompatible element rich dikes are regarded as the final crystallization products of the partial melting

using the high mobility of palladium in surface media in exploration for platinum group element deposits evidence from the lac des iles region northwestern ontario platinium group element pge mineralization is commonly accompanied by large amounts of ni fe sulfides which are explored for using a variety of geophysical and geochemical methods appreciation of a new type of pge mineralization is emerging hosted by gabbroic rocks with low concentrations 5 vol of disseminated sulfides the host rocks commonly display textural complexity such as brecciation pods and veins of pegmatite and magma mingling of different lithological units examples include the lac des iles deposit in northwestern ontario the east bull lake suite in eastern ontario and several intrusions in the kola peninsula and northern finland such mineralization does not result in prominent geophysical and geochemical anomalies thus posing a challenge for exploration we initiated a project to develop new geochemical exploration approaches for such pge deposits with low sulfides and selected the lac des iles district northern ontario canada which contains one producing mine and many pd showings mineralization is hosted by gabbroic rocks with low concentrations 5 vol of sulfides enriched elements include pd pt au ni cu and co in separate sulfide rich mineralization base metals can be abundant up to 1 wt percent but pd is insignificant 200 ppb this reduces the relevance of ni cu and co as possible pathfinders for sulfide poor pge mineralization leaving pd pt and au a detailed study in the baker zone at the lac des iles mine and the legris lake property indicates the essentially immobile nature of pt in these surface environments by contrast pd is depleted in b horizon soil suggesting its removal during the conversion of c to b horizon soils the loss of pd in b horizon soil reflects the transport of pd as neutral and anionic complexes probably with oh and possibly with organic ligands which are not adsorbed by fe oxyhydroxides in the soils instead pd migrates in solution to accumulate in humus in swamps and organic rich lake sediments downslope from mineralization the distribution of pd in humus therefore provides a distal indicator of nearby mineralization total digestion of humus using fire assay or aqua regia yielded up to 160 ppb pd whereas a variety of commercially available leaching methods extracted few ppb pd the results indicate that pd is tightly held in organic matter this behavior of pd contrasts with many metallic elements such as cu and ni that are enriched in b horizon soil and may be extracted by a variety of leaching techniques palladium arsenides tellurides antimonides and sulfides are unstable in weathering environments and their dissolution releases pd to surface waters therefore pd can be used to indicate other pge mineralization as it is always abundant among pge where pge mineralization is associated with high concentrations of fe sulfides their oxidation produces acidic waters which further promotes pd dispersion thus the findings of this study are applicable to exploration for both sulfide rich and poor pge mineralization

magma mixing in late archean tonalitic and mafic rocks of the lac des iles area western superior province abstract plutonic rocks in the lac des iles area of the western superior province provide a record of contemporaneous late archean mafic and tonalitic magmatism this suite of rocks consists of mafic to ultramafic intrusions mafic to intermediate dikes hornblendite and hornblende tonalite the tonalite contains net veined and disaggregated mafic to intermediate dikes mafic schlieren and zones of hornblendite to mela tonalite with skeletal hornblende these textures are interpreted to be the result of magma mixing the hornblende tonalite is geochemically characterized by high al 2 o 3 high na 2 o k 2 o low rb moderate sr and fractionated ree the hornblendite mafic to intermediate dikes and tonalite show whole rock trends of decreasing total ree increasing depletion of hree and increasing eu eu with increasing sio 2 amphiboles range in composition from edenitic and pargasitic hornblende to hornblende in dike rocks mela tonalite and hornblendite and from hornblende to actinolite in tonalite the development of skeletal amphiboles with strong normal zoning and resorbed hornblende with weak reverse zoning are attributed to conditions of supercooling and superheating respectively in zones of magma mixing the least fractionated dike rocks geochemically resemble lamprophyres derived from alkali basaltic magma variation of ree among the mafic to intermediate dikes suggests that they fractionated hornblende hornblendites and mela tonalites can be modeled as hornblende cumulates from the dike rocks the amphiboles probably crystallized rapidly during mixing leaving a feldspathic residue variation in hornblende tonalites is consistent with mixing of sio 2 rich tonalite melt with mafic to intermediate dike phases and associated hornblende cumulates and feldspathic residue open system magmatic processes at lac des iles result in a continuum of disequilibrium textures reflecting emplacement of mafic magma into a crystallizing felsic host the plutonic rocks probably formed from a zoned magma chamber with a mafic base and tonalitic top breccia zones in the tonalite suggest that explosive degassing of the chamber occurred structures similar to those reported here are common in other granitoids in the superior province and suggest that mafic magmatism and magma mixing played an important role in the development of late archean granitoid plutons

the lac des iles palladium deposit ontario canada part ii halogen variations in apatite analysis of apatite from the mine block intrusion mbi of the lac des iles igneous complex shows two pronounced trends in the halogens apatite from relatively fresh norite and melanorites from the pd sulfide zone contain up to 57 mol chlorapatite endmember with significant hydroxyapatite component in contrast in altered rock amphibolite and greenschist assemblages the chlorapatite component is typically less than 10 mol with wide variation in the f and oh endmember components the latter trend is attributed to cl loss to degassing and alteration whereas the former is attributed to cl enrichment in the ore bearing rocks it is suggested that the relatively h2o rich and intermediate cl content of the early igneous fluids degassed from the deeper levels of the mbi can explain the high pd pt and pd ir ratios of the deposit a model is presented in which disseminated pd rich sulfides are initially introduced by a high temperature magmatic fluid that also influenced crystallization to produce the gross modal variations of the igneous host rock this high temperature mineralization event was subsequently modified by the influx of late igneous and country fluids at amphibolite to greenschist conditions

new mineralogical and isotopic constraints on main zone hosted pge mineralisation at moorddrift northern bushveld complex the northern limb of the bushveld complex south africa contains a number of occurrences of platinum group element pge mineralisation within main zone rocks whereas the rest of the complex has pge depleted main zone units on the farm moorddrift cu ni pge sulphide mineralisation is hosted within the upper main zone in a layered package of gabbronorites mottled anorthosites and thin pyroxenites our observations indicate that a 10 m thick reef style package of mineralisation has been extensively disturbed forming a mega breccia which in some localities may distribute mineralised rocks over intersections of over 300 m the sulphides are made up of pyrrhotite pentlandite and chalcopyrite heavily altered around their margins and overprinted by secondary pyrite platinum group mineral assemblages typical of primary magmatic deposits with pt and pd tellurides and sperrylite are present in the reef style package whereas there is a decrease in tellurides and an increase in antimonides in the disturbed package interpreted to be related to hydrothermal recrystallization during veining and brecciation sulphur isotopes show that all sulphides within the mineralised package on moorddrift have a crustal signature consistent with local country rock sediments of the transvaal supergroup we interpret the mineralisation at moorddrift as a primary sulphide reef likely produced as a result of the mixing of crustally contaminated magmas in the upper main zone which has been locally disrupted post crystallisation at present there are no firm links between moorddrift and the other known pge occurrences in the main zone at the aurora and waterberg projects although the stratigraphic position of all may be similar and thus intriguing nonetheless they do demonstrate that the main zone of the northern limb of the bushveld complex unlike the eastern and western limbs can be considered a fertile unit for potential pge mineralisation

platinum group element chromitite associations in the bushveld complex new and recently published platinum group element data of chromite rich layers in the bushveld complex are evaluated chondrite normalized platinum group element plots of these data show that trends for chromitite layers differ from that of the merensky reef the data furthermore indicate remarkable consistencies in compositional trends for many kilometers along strike of individual layers suggesting that the conditions of formation of chromitite layers and their associated platinum group element mineralization were very uniform over large areas of the magma chamber significant differences in the proportions of platinum group elements within a particular layer are only evident on a regional scale the platinum group minerals of the middle group of chromitite layers in the marikana area of the western bushveld are mainly sulfides and arsenides laurite is the most common platinum group mineral and is mostly enclosed by chromite a variety of other platinum group minerals occur in close association with base metal sulfides extremely low bulk sulfur content in the chromitite layers is ascribed to a postcumulus loss of sulfur postcumulus loss of sulfur and the existence of laurite enclosed within chromite casts doubt on the validity of any petrogenetic models for platinum mineralization in chromitite rich layers based on partition coefficients and the r factor

pgm facies variations for cu pge deposits in the coldwell alkaline complex ontario canada abstract accurate characterization of the platinum group mineral pgm assemblages for cu ni pge deposits are typically constrained by sample size and the difficulty of finding statistically significant numbers of grains which is expected given the low concentrations of platinum group elements 75 m can account for large fractions of total mass despite these limitations an accurate survey of pgm from different deposit types would have significant value towards developing deposit models and respective exploration strategies in this study we present results for a comprehensive evaluation of pgm at four copper pge occurrences hosted within separate but co genetic gabbro or troctolite intrusions in the coldwell alkaline complex and confirm that accurate surveys are possible with sufficient sample material and efficient pgm concentration methods the pgm concentration methods used include 1 hydroseparation of sieved size fractions of pulverized material and 2 panning of grain separates produced by electric pulse disaggregation of drill core specimens a favourable comparison of the results has verified the reliability of each method and added confidence that the pgm assemblages identified at three of the four locations are fully characterized precious metal mineral pmm assemblages are determined for the main zone and w horizon at the marathon deposit and the main zones at each of the geordie lake deposit and area 41 occurrence a total of 10 824 pmm grains pge and au ag and 68 mineral species including 16 unknown minerals were identified of which 768 grains and 31 species occur at the main zone 523 grains and 41 species at area 41 9485 grains and 43 species at w horizon and 56 grains and 12 species at geordie lake the pmm are grouped as follows pd ge pge s as pt fe alloy pd cu pb au pd ni s pd pt sn pt as pd as pd pt sb as pd pt bi te and au ag all of the deposits were found to contain similar proportions of pd pt sb as pd pt bi te and au ag minerals but the w horizon and area 41 are distinguished from the marathon main zone and geordie lake deposits by the presence of minerals in the pge s as pt fe alloy pd cu pb au and pd ge groups taken together the pmm assemblages for deposits in the coldwell exhibit a strong correlation to pge enrichment relative to the range for mantle cu pd values 1000 10 000 and there is no relationship between the abundances of pd pt bi te and pd pt sb as minerals that are commonly associated with hydrous phases and the intensity of hydrothermal alteration thus minerals found only at the w horizon and area 41 where significant pge upgrading has occurred including pt fe alloys rustenburgite marathonite palladogermanide unknown rh ni fe sulfide au pd cu alloy braggite coldwellite laurite zvyagintsevite laflammeite and unknown phases pd 5 as 2 pd 3 as pd 3 as pb bi might be considered as index minerals for pge enriched types of mineralization in the coldwell

highly siderophile and strongly chalcophile elements in magmatic ore deposits an ore deposit by definition must be economically viable that is to say it must contain sufficient material at high enough grade to make it possible to mine and process it at a profit bates and jackson 1987 this requires the elements to be collected and concentrated by some phase and for them to be deposited close to the surface of the earth at the oxygen fugacities found in the crust native fe is not normally stable and thus the highly siderophile elements defined as ru rh pd re os ir pt and au cannot behave as siderophile elements except in rare cases such as on disko island klock et al 1986 where the magma is sufficiently reduced for native fe to be present however if mafic magmas become saturated in a base metal sulfide liquid the highly siderophile elements behave as highly chalcophile elements table 1 thus these elements are generally found in association with base metal sulfide minerals which crystallized from a magmatic sulfide liquid namely pyrrhotite pentlandite chalcopyrite cubanite pyrite an exception to this is au although au is strongly chalcophile and is produced as a by product from many platinum group element pge deposits table 2 most primary au deposits consist of native au groves et al 1998 these will not be discussed in this chapter there are many pge deposits i e accumulations of pge minerals and base metal sulfides containing pge bates and jackson 1987 around the world but most of these do not constitute pge ore deposits because they are either too small or their grade is too low or other political or infrastructure factors prevent the economic exploitation of the deposit bates and jackson 1987 for the purpose of this work we have defined pge ore deposits as those which have significant production 2 of the annual world

geochemistry and mineralogy of pd in the magnetitite layer within the upper gabbro of the mesoarchean nuasahi massif orissa india palladium concentrations of 1 3 ppm with an average pt pd ratio of 0 15 have been located for the first time in a magnetitite layer in the nuasahi massif in orissa india this layer occurs at a high stratigraphic level in the complex and is nearly 4 km long and 5 12 m thick the sections of the pd rich zone identified to date extend over a distance of 1 km at the southern end of the layer several phases of mineralization are evident the first primary assemblage of platinum group minerals pgm contains pd sulfides vysotskite pd pb alloys zvyagintsevite and a pd in alloy a mineral probably new to mineralogy these pgm are confined to central magnetite grains in the magnetitites the magnetite grains with exsolved fine laths of ilmenite at centers are referred to as central magnetite grains these central magnetite grains are commonly surrounded by blebs of ilmenite and magnetite that contain the majority of the pgm these are dominated by pd antimonides variably altered to pd oxides and other pgm including ptas2 sperrylite rus2 laurite and irrhass irarsite hollingwothite many of these pgm also occur in the interstitial silicates with rare occurrences in the central magnetite grains we propose that the platinum group elements pge crystallized during a minor sulfide saturation event that occurred as the magnetitites crystallized this event produced the minor cu sulfides in these magnetitites later introduction of antimony and arsenic during the alteration event that produced the blebby ilmenite and magnetite led to the more primary pgm being succeeded by the main pgm assemblage dominated by pd antimonides these are associated with secondary cu minerals and sperrylite subsequent oxidation during weathering in the hot wet indian climate produced the pd oxides the nuasahi massif is a sill like archean layered ultramafic mafic intrusion genetically linked to high mg siliceous basalt or boninites and is characterized by unusually thick layers of chromitite pge are concentrated in these chromitites and in the base metal sulfide bearing breccias in the overlying gabbro the pd in the magnetitites described here indicates the presence of a third level where pge are concentrated and a magma that crystallized to produce pge concentrations at three stratigraphic levels in the massif this indicates that similar thin sill like intrusions hosting unusually thick chromitites may also have pge concentrations at a number of stratigraphic levels

fold and thrust partitioning in a contracting fold belt insights from the 1931 mach earthquake in baluchistan 1 surface deformation associated with the 27 august 1931 earthquake near mach in baluchistan is quantified from spirit leveling data and from detailed structural sections of the region interpreted from seismic reflection data constrained by numerous well logs mean slip on the west dipping dezghat bannh fault system amounted to 1 2 m on a 42 km 72 km thrust plane with slip locally attaining 3 2 m up dip of an inferred locking line at 9 km depth slip also occurred at depths below the interseismic locking line in contrast negligible slip occurred in the 4 km near the interseismic locking line the absence of slip here in the 4 years following the earthquake suggests that elastic energy there must either dissipate slowly in the interseismic cycle or that a slip deficit remains pending its release in a large future earthquake elastic models of the earthquake cycle in this fold and thrust belt suggest that slip on the frontal thrust fault is reduced by a factor of 2 to 8 compared to that anticipated from convergence of the hinterland a partitioning process that is presumably responsible for thickening of the fold and thrust belt at the expense of slip on the frontal thrust near the latitude of quetta gps measurements indicate that convergence is 5 mm yr hence the minimum renewal time between earthquakes with 1 2 m mean displacement should be as little as 240 years however when the partitioning of fold belt convergence to frontal thrust slip is taken into account the minimum renewal time may exceed 2000 years

mineralogy of the hse in the subcontinental lithospheric mantle an interpretive review abstract the highly siderophile elements hse os ir ru rh pt pd re au exist in solid solution in accessory base metal sulfides bms as well as nano to micron scale minerals in rocks of the subcontinental lithospheric mantle sclm the latter include platinum group minerals pgm and gold minerals which may vary widely in morphology composition and distribution the pgm form isolated grains often associated with larger bms hosted in residual olivine located at interstices in between peridotite forming minerals or more commonly in association with metasomatic minerals pyroxenes carbonates phosphates and silicate glasses in some peridotite xenoliths the pgm found inside residual olivine are mainly os ir and ru rich sulfides and alloys in contrast those associated with metasomatic minerals or silicate glasses of peridotite xenoliths consist of pt pd and rh bonded with semimetals like as te bi and sn nanoscale observations on natural samples along with the results of recent experiments indicate that nucleation of pgm is mainly related with the uptake of hse by nanoparticles nanominerals or nanomelts at high temperature 900 c in both silicate and or sulfide melts regardless of the residual or metasomatic origin of their host minerals a similar interpretation can be assumed for gold minerals our observations highlight that nanoscale processes play an important role on the ore forming potential of primitive mantle derived magmas parental to magmatic hydrothermal deposits enriched in noble metals the metal inventory in these magmas could be related with the physical incorporation of hse bearing nanoparticles or nanomelts during processes of partial melting of mantle peridotite and melt migration from the mantle to overlying continental crust

an experimental study on the geochemical behavior of highly siderophile elements hse and metalloids as se sb te bi in a mss iss pyrite system at 650 c a possible magmatic origin for co hse bearing pyrite and the role of metalloid rich phases in the fractionation of hse abstract pyrite the most abundant sulfide in the earth s crust is an accessory mineral in several magmatic sulfide deposits although most pyrite is hydrothermal previous experimental studies have shown that pyrite can also have a primary magmatic origin by exsolving from monosulfide solid solution mss during cooling of a sulfide melt if sulfur fugacity is sufficiently high pyrite from some localities has significant amounts of co and complex zonation in some low melting point chalcophile elements lmce such as as se sb te bi henceforth referred to as metalloids and some platinum group elements pge ru rh pd os ir pt however the origin of such pyrite and the causes of zonation are not clear because the distribution of some of these elements is heterogeneous and seems to be developed in concentric zones the zonation has been interpreted to represent growth stages some of them secondary and caused partly by hydrothermal fluids better constraints on the origin of co pge bearing pyrite could help unravel the geochemical processes affecting the sulfide assemblages in which it is found thus an experimental study was undertaken to characterize pyrite formation in magmatic sulfide environments and its relationship with metalloids and highly siderophile elements hse pge re au natural pyrrhotite chalcopyrite pentlandite and elemental s were mixed and doped with approximately 50 ppm of each hse a mixture of metalloids was added at 0 2 wt or 3 wt to aliquots of sulfide mixtures starting materials were sealed in evacuated silica tubes and fused at 1200 c the temperature was subsequently reduced to 750 c at 60 c h then to 650 c at 0 5 c h to produce relatively large euhedral pyrite crystals then quenched the experiments were analyzed using reflected light sem epma and la icp ms experimental products contained euhedral pyrite mss intermediate solid solution iss and metalloid rich phases interpreted as quench product of an immiscible metalloid rich liquid the results show that co ni hse bearing pyrite with complex zonation in ru rh os ir and pt can form by a subsolidus reaction involving both mss and iss and does not require secondary e g hydrothermal processes because such pyrite results from the cooling of a sulfide melt after mss and iss it can be described as magmatic among the hse ru rh os re and ir have identical zonation patterns in pyrite pt is also zoned but differently and au and pd are essentially excluded previously documented natural hse bearing pyrite also display identical zonation patterns in ru rh os and ir the complex zoning is likely preserved due to the extremely slow diffusion rates for those elements in pyrite thus the presence of pyrite with similar characteristic in natural sulfide assemblages is consistent with a magmatic origin and does not require hydrothermal processes the results also show that if a metalloid rich liquid is present it will significantly sequester au pd and pt but will not affect ru rh os re and ir in the absence of metalloid rich phases au partitions strongly into iss and pd partitions preferentially into mss

the distribution of platinum group elements pge and other chalcophile elements among sulfides from the creighton ni cu pge sulfide deposit sudbury canada and the origin of palladium in pentlandite concentrations of platinum group elements pge ag as au bi cd co mo pb re sb se sn te and zn have been determined in base metal sulfide bms minerals from the western branch 402 trough orebodies of the creighton ni cu pge sulfide deposit sudbury canada the sulfide assemblage is dominated by pyrrhotite with minor pentlandite chalcopyrite and pyrite and they represent monosulfide solid solution mss cumulates the aim of this study was to establish the distribution of the pge among the bms and platinum group minerals pgm in order to understand better the petrogenesis of the deposit mass balance calculations show that the bms host all of the co and se a significant proportion 40 90 of os pd ru cd sn and zn but very little 35 of the ag au bi ir mo pb pt rh re sb and te osmium and ru are concentrated in equal proportions in pyrrhotite pentlandite and pyrite cobalt and pd 1 ppm are concentrated in pentlandite silver cd sn zn and in rare cases au and te are concentrated in chalcopyrite selenium is present in equal proportions in all three bms iridium rh and pt are present in euhedrally zoned pge sulfarsenides which comprise irarsite irass hollingworthite rhass pge ni rich cobaltite coass and subordinate sperrylite ptas2 all of which are hosted predominantly in pyrrhotite and pentlandite silver au bi mo pb re sb and te are found predominantly in discrete accessory minerals such as electrum au ag alloy hessite ag2te michenerite pdbite and rhenium sulfides the enrichment of os ru ni and co in pyrrhotite pentlandite and pyrite and ag au cd sn te and zn in chalcopyrite can be explained by fractional crystallization of mss from a sulfide liquid followed by exsolution of the sulfides the early crystallization of the pge sulfarsenides from the sulfide melt depleted the mss in ir and rh the bulk of pd in pentlandite cannot be explained by sulfide fractionation alone because pd should have partitioned into the residual cu rich liquid and be in chalcopyrite or in pgm around chalcopyrite the variation of pd among different pentlandite textures provides evidence that pd diffuses into pentlandite during its exsolution from mss the source of pd was from the small quantity of pd that partitioned originally into the mss and a larger quantity of pd in the nearby cu rich portion intermediate solid solution and or pd bearing pgm the source of pd became depleted during the diffusion process thus later forming pentlandite rims of coarse granular veinlets and exsolution flames contains less pd than early forming pentlandite cores of coarse granular

structural interpretation of frontal folds and hydrocarbon exploration western sulaiman fold belt pakistan abstract seismic reflection profiles and borehole data combined with geological mapping was used to analyze foreland structures with 3 d structural variation estimates of shortening and kinematic evolution of western sulaiman fold belt sfb pakistan the western sfb is interpreted with passive roof duplex geometry the floor thrust decollement is interpreted in triassic strata rather than its inference in precambrian cambrian evaporites whereas the roof thrust upper detachment of hinterland vergence is located in eocene ghazij shale based on seismic data the folds in the frontal duplex are interpreted as fault propagation and fault bend type they are located over curved and staircase geometry of blind back thrusts the folds and thrusts of ew trend show right hand en echelon stepping along nw se oriented mountain front due to drag along the western margin of the fold belt the blind thrusts cut across the hanging wall flat of the duplex horse with roots in base triassic at depth of 4 4 5 km 3d surfaces of reservoir strata show three areas of closed elliptical contours as potential prospects over blind thrusts with maximum structural relief of 2200 m shortening of 2100 22 and 9950 m 47 is calculated along with thrusts in the frontal duplex with the interpretation of out of sequence structures passive roof duplex structures between foreland and hinterland vergent back thrusts are reported from mountain belts around the world we have identified out of sequence deformation in the frontal duplex with stacked structures identification of these features adds to our understanding of the development of mountain fronts in the context of anderson s theory of faulting with the presence of a conjugate set of faults and foreland propagation of mountain fronts with secondary out of sequence deformation subsurface seismic data appears to be critical in their recognition for analysis of active foreland deformation and assessment of hydrocarbon plays in the fold belts

fractional crystallization induced variations in sulfides from the noril sk talnakh mining district polar siberia russia abstract the distribution of platinum group elements pge within zoned magmatic ore bodies has been extensively studied and appears to be controlled by the partitioning behavior of the pge during fractional crystallization of magmatic sulfide liquids however other chalcophile elements especially tabs te as bi sb and sn have been neglected despite their critical role in forming platinum group minerals pgm tabs are volatile trace elements that are considered to be mobile so investigating their primary distribution may be challenging in magmatic ore bodies that have been somewhat altered magmatic sulfide ore bodies from the noril sk talnakh mining district polar siberia russia offer an exceptional opportunity to investigate the behavior of tabs during fractional crystallization of sulfide liquids and pgm formation as the primary features of the ore bodies have been relatively well preserved in this study new petrographic 2d and 3d and whole rock geochemical data from cu poor to cu rich sulfide ores of the noril sk talnakh mining district are integrated with published data to consider the role of fractional crystallization in generating mineralogical and geochemical variations across the different ore types disseminated to massive despite textural variations in cu rich massive sulfides lenses veins and breccias these sulfides have similar chemical compositions which suggests that cu rich veins and breccias formed from fractionated sulfide liquids that were injected into the surrounding rocks numerical modeling using the median disseminated sulfide composition as the initial sulfide liquid composition and recent dmss liq and diss liq predicts the compositional variations observed in the massive sulfides especially in terms of pt pd and tabs therefore distribution of these elements in the massive sulfides was likely controlled by their partitioning behavior during sulfide liquid fractional crystallization prior to pgm formation our observations indicate that in the cu poor massive sulfides the pgm formed as the result of exsolution from sulfide minerals whereas in the cu rich massive sulfides the pgm formed by crystallization from late stage fractionated sulfide liquids we suggest that the significant amount of sn bearing pgm may be related to crustal contamination from granodiorite whereas as bi te and sb were likely added to the magma along with s from sedimentary rocks large pgm that are scarce and randomly distributed may account for most of the whole rock pt budget based on our results we propose a holistic genetic model for the formation of the magmatic sulfide ore bodies of the noril sk talnakh mining district

geochemistry of the j m howland reef of the stillwater complex minneapolis adit area i sulfide chemistry and sulfide olivine equilibrium platinum mineralization in the stillwater complex occurs within a complex sequence of olivine bearing plagioclase rich cumulates about 400 m above the base of the banded zone the reef consists of a 2 m thick layer of disseminated sulfides extending over the entire strike length of the complex in the area of this study the host rock to the reef sulfides shows a lateral transition over a strike length of 700 m from a heterogeneous olivine plagioclase cumulate mixed rock to a plagioclase olivine cumulate containing a high proportion of postcumulus bronzite with olivine preserved only as rare resorbed cores on bronzite grains platinum group elements within the reef correlate strongly with abundances of sulfides which show convincing textural evidence for having originated as immiscible sulfide liquid strong correlations are also observed between all six platinum group elements ni and cu despite the gradation in host rock mineralogy the sulfide fraction of the reef displays a constant bulk composition over 700 m of strike length containing 9 3 percent ni 6 9 percent cu and approximately 0 7 percent total platinum group elements principally pd these platinum group element concentrations are two to three orders of magnitude higher than those found in typical magmatic sulfide deposits and are attributed to equilibration of sulfide liquid with a very large volume of silicate melt olivines from the reef show a range of compositions from fo 71 to fo 85 and from 2 400 to 4 500 ppm ni a positive correlation is observed between nio and feo in olivines from sulfide bearing samples indicating ni fe exchange between olivine and sulfides on a local scale such that ni contents of olivines were buffered by that of the sulfide phase a value of 9 70 or 1 49 is obtained for the ni fe distribution coefficient between sulfide and olivine in agreement with values obtained at magmatic temperatures by boctor 1982 these observations may be interpreted in the framework of the plume model of campbell et al 1983 a pulse of replenishing magma enters the stillwater chamber as a buoyant plume and subsequently spreads to form a layer of hybrid melt sulfide liquation and olivine crystallization occur within the plume and the hybrid layer in response to mixing and subsequent cooling sulfide liquid attains high platinum group element concentrations during turbulent ascent and spreading of the plume crystallization of olivine from the hybrid layer gives rise to olivine sulfide boulders which settle to the floor of the chamber reaction between the boulders and the evolved liquid at the bottom of the chamber causes olivine to become more iron rich subsequent reequilibration between olivine and sulfide grains gives rise to the observed ni fe distribution

the structure of mountain fronts commonly the part of a mountain front which is visible at the surface consists of foreland dipping thrust belt rocks elevated above their regional structural position and overlain more or less conformably by molasse several explanations for their geometry are possible 1 major detachments exist within or beneath the molasse resulting in transport of the foreland basin examples of this geometry come from the swiss molasse plain the southern pyrenees and the mackenzie mountains of canada 2 displacement is lost on major backthrusts beneath the frontal monocline examples cited here are the rockies of alberta the sulaiman ranges of pakistan the mackenzies and the andes in peru 3 thrust sheets travelled over an old land surface and syntectonic molasse contemporaneously offlaps the topographic high of the thrust front this phenomenon occurs along the alpine thrust front in haute provence 4 the frontal fold represents deformation above a large scale thrust tip no unequivocal example of tip line strain at this scale has been recorded although this type of deformation may occur in the brooks range of alaska in many areas mountain fronts show a combination of these idealized geometries

platinum group elements in sulphide minerals platinum group minerals and whole rocks of the merensky reef bushveld complex south africa implications for the formation of the reef the concentrations of platinum group elements pge co re au and ag have been determined in the base metal sulphide bms of a section of the merensky reef in addition we performed detailed image analysis of the platinum group minerals pgm the aims of the study were to establish 1 whether the bms are the principal host of these elements 2 whether individual elements preferentially partition into a specific bms 3 whether the concentration of the elements varies with stratigraphy or lithology 4 what is the proportion of pge hosted by pgm 5 whether the pgm and the pge found in bms could account for the complete pge budget of the whole rocks in all lithologies most of the pge 65 up to 85 are hosted by pgm essentially pt fe alloy pt pd sulphide pt pd bismuthotelluride lesser amounts of pge occur in solid solution within the bms in most cases the pgm occur at the contact between the bms and silicates or oxides or are included within the bms pentlandite is the principal bms host of all of the pge except pt and contains up to 600 ppm combined pge it is preferentially enriched in pd rh and co pyrrhotite contains rh os ir and ru but excludes both pt and pd chalcopyrite contains very little of the pge but does concentrate ag and cd platinum and au do not partition into any of the bms instead they occur in the form of pgm and electrum in the chromitite layers the whole rock concentrations of all the pge except pd are enriched by a factor of five relative to s ni cu and au this enrichment could be attributed to bms in these layers being richer in pge than the bms in the silicate layers however the pge content in the bms varies only slightly as a function of the stratigraphy the bms in the chromitites contain twice as much pge as the bms in the silicate rocks but this is not sufficient to explain the strong enrichment of pge in the chromitites in the light of our results we propose that the collection of the pge occurred in two steps in the chromitites some pgm formed before sulphide saturation during chromitite layer formation the remaining pge were collected by an immiscible sulphide liquid that percolated downward until it encountered the chromitite layers in the silicate rocks pge were collected by only the sulphide liquid

the lac des iles palladium deposit ontario canada part i the effect of variable alteration on the offset zone the recently discovered offset zone of the mine block intrusion of the lac des iles complex hosts palladium mineralization with unusually high pd pt and pd ir ratios in rocks that range from relatively unaltered norite to amphibolites and chlorite actinolite talc schist quantitative assessment of the effect of progressive alteration using mineral modes was done using total silicate h2o as a monitor of reaction progress moles h2o added to form alteration minerals per 100 g of rock major mineral modal variations define three reaction regions 1 0 00 0 03 characterized by epidote clinozoisite formation and some amphibole 2 0 03 0 23 characterized by formation of chlorite amphibole quartz muscovite sericite and calcite after plagioclase pyroxene and 3 0 23 0 28 characterized by the formation of talc after earlier formed amphibole epidote occurs as an incongruent product from the destruction of plagioclase that is itself lost as the reaction proceeds pyroxene is altered at about twice the rate of plagioclase resulting in pyroxene rich protoliths to be more altered than those relatively enriched in plagioclase major elements variations largely reflect variations in the plagioclase pyroxene ratio of the protolith but compositional trends suggest a loss of na with reaction progress the base metal sulfides chalcopyrite pyrrhotite and pentlandite show decreasing abundance with reaction progress forming pyrite magnetite as an intermediate reaction product that also is lost as the reaction proceeds millerite is overall low but increases slightly a more limited data set on the platinum group minerals suggests that platinum group element pge arsenides increase whereas pge sulfides and pge bi tellurides decrease with reaction progress assuming ore element concentrations in the protolith were constant and similar to relatively fresh norites pd increases modestly by 5 whereas pt decreases by about 65 in the most altered rocks similarly cu au and s decrease by 60 82 and 94 respectively in the most altered rocks the antithetical behavior of pd and the fact that pd enrichment is not seen in altered dikes suggest that the pd originally was enriched in the more melanocratic protoliths that are most extensively altered and that pd also was lost in part these results are consistent with the mineralization having been a high temperature event that predated the amphibolite greenschist alteration

distribution of chalcophile and platinum group elements among pyrrhotite pentlandite chalcopyrite and cubanite from the noril sk talnakh ores implications for the formation of platinum group minerals in most magmatic sulfide deposits platinum group elements pge are found both within the structure of the base metal sulfides bms pyrrhotite po pentlandite pn chalcopyrite ccp and cubanite cbn and as platinum group minerals pgm tellurium as bi sb and sn tabs are essential elements in many of these pgm the potential role of tabs in collecting pge and thus forming a pge deposit has not been closely investigated we have determined the concentrations of a full suite of chalcophile elements in po pn ccp and cbn using laser ablation inductively coupled plasma mass spectrometry on samples from the noril sk talnakh ni deposits in these deposits the po rich ore is thought to represent monosulfide solid solution mss cumulate of the initial sulfide liquid and the ccp rich ore a mixture of the fractionated sulfide liquid and intermediate solid solution iss the bms from the po rich ore contain lower concentrations of tabs pd pt and au and higher concentrations of mo ru rh re os and ir than bms from the ccp rich ores this observation is consistent with experimental results which show that tabs pd pt and au are incompatible with mss whereas the other elements are compatible in mss counter intuitively in the po rich ore the bulk of the pd and tabs is hosted by bms this is because during crystallization although only a small amount of the incompatible elements partitioned into the bms the fractionated liquid has migrated away thus the po rich ores represent mss adcumulates therefore as the po rich ores contain very little trapped liquid fraction the bms host the bulk of pd and tabs in contrast in the ccp rich ore the bulk of au pd pt and tabs is present as pgm or electrum grains this is because more trapped liquid is present and as tabs au pd and pt are not compatible with iss they concentrated into the very last sulfide liquid and crystallized as intergrowths of pd pt tabs pgm the tabs then do not appear to collect pd pt and au but rather all elements are concentrated in the most fractionated sulfide liquid by crystal fractionation

the occurrence of platinum group element and gold minerals in the bon accord ni oxide body south africa two samples from the enigmatic ni oxide body of bon accord barberton greenstone belt south africa have been investigated with the hydroseparation technique to obtain heavy mineral concentrates the concentrates contain abundant pt pd and gold minerals never reported before from the bon accord ni oxide body the grains occur as 1 minute inclusions 3 m in trevorite ideally nife3 o4 and 2 larger 5 70 m free aggregates liberated from the host phase the first group comprises several pgm compounds of pd sb pd sb as pd cu sb pt sb pt as s ru as s ru s along with free grains of ni fe as the second consists of sperrylite ptas2 members of the sobolevskite kotulskite series and electrum these results are in good agreement with previous analyses of pge au in bulk rock paragenetic relationships indicate that the pgm and electrum are of secondary origin probably generated during low temperature metamorphism of the ni rich mineralization they have a terrestrial origin and are related with a low sulfidation regime that usually accompanies hydrothermally driven serpentinization of mafic ultramafic bodies the ligands in the newly formed pgm as sb bi te and o probably proceed from the same source of the hydrothermal solutions in this model the metals ni pge au were original components of the primary mineral assemblage of the bon accord precursor whereas as sb bi te and o might have been contributed by the metasomatizing fluids during near surface evolution of the ore body the data on the high grade heavy mineral concentrates obtained by hydroseparation have provided new knowledge about the mineral deportment of pd pt and au

distribution of platinum group elements in the platreef at overysel northern bushveld complex a combined pgm and la icp ms study detailed mineralogical and laser ablation inductively coupled plasma mass spectrometry studies have revealed the physical manifestation of the platinum group elements pge within the platreef at overysel northern bushveld complex south africa the pge in the platreef were originally concentrated in an immiscible sulfide liquid along with semi metals such as bi and te as the sulfide liquid began to crystallize virtually all the os ir ru and rh partitioned into monosulfide solid solution mss which on further cooling exsolved to form pyrrhotite and pentlandite with os ir and ru remaining in solid solution in both phases with rh prefentially partitioning into pentlandite platinum some pd and au were concentrated in the residual sulfide liquid after mss crystallization and were then concentrated in an immiscible late stage melt along with semi metals which was expelled to the grain boundaries during crystallization of intermediate solid solution iss to form pt and pd tellurides and electrum around the margins of the sulfide grains tiny droplets of this melt trapped in the crystallizing mss and iss cooled to form pt bi te microinclusions in all sulfide phases whilst the excess pd was accommodated in solid solution in pentlandite minor redistribution and recrystallization by hydrothermal fluids occurred around xenoliths and at the very base of the mineralized zone within the footwall however the overall lack of secondary alteration coupled with the volatile poor nature of the gneissic footwall have allowed the preservation of what may be the most primary style of platreef mineralization the lack of pgm inclusions within early liquidus phases suggests very early sulfur saturation in the platreef lending support to theories involving s saturation occurring prior to intrusion of the platreef possibly within a staging chamber

sulphide mineral evolution and metal mobility during alteration of the oceanic crust insights from odp hole 1256d fluxes of metals during the hydrothermal alteration of the oceanic crust have far reaching effects including buffering of the compositions of the ocean and lithosphere supporting microbial life an

geochemistry and mineralogy of platinum group element mineralization in the river valley intrusion ontario canada a model for early stage sulfur saturation and multistage emplacement and the implications for contact type ni cu pge sulfide mineralization the river valley intrusion within the 2 48 ga east bull lake intrusive suite in ontario canada is an example of a mafic igneous intrusion with contact type ni cu pge sulfide mineralization along its base whereas many contact type deposits are thought to form from in situ contamination of the magma by the addition of crustal s during emplacement there are some intrusions including the river valley intrusion which appear to have a much more complex history where the timing of s saturation and thus the critical ore genesis processes may have occurred much earlier prior to emplacement the river valley intrusion is made up of a basal 100 m of unlayered inclusion bearing units overlain by layered cumulates the basal units contain autoliths of gabbroic rocks and inclusions of footwall gneiss and amphibolites all within a gabbroic matrix platinum group element rich magmatic sulfide mineralization occurs throughout both the inclusions and the matrix as blebby and disseminated sulfides the matrix and inclusions can be separated into two distinct textural types hydrothermally altered greenschist assemblages and unaltered metamorphic amphibolite assemblages the platinum group mineral pgm assemblages vary only between textural types and not between inclusions and matrix being dominated tellurides in all rock types the hydrothermally altered rocks however have fewer tellurides and an increased amount of sb and as bearing pgm indicative of minor fluid interaction although the pgm have not been mobilized significantly away from the base metal sulfides precious and base metal geochemistry shows all rock types to have an excellent correlation between all the platinum group elements pge indicating the presence of a single well homogenized pge rich sulfide liquid however au and cu appear to be decoupled from the pge at low concentrations although correlate well with each other which is interpreted to be due to minor fluid redistribution and alteration of sulfide bleb margins the overlying layered units above the mineralized units are not pge depleted trace element data including th yb pm and nb th pm ratios demonstrate that all river valley rocks were formed from crustally contaminated magmas following interaction with local country rocks in a deeper subchamber although some samples have s se ratios indicative of crustal s most have s se ratios lower than the mantle range indicative of s loss we propose a multistage model for the formation of the mineralization in the river valley intrusion with a major contamination event at depth with the addition of s from local crustal rocks inducing sulfide saturation sulfide droplets were then enriched in pge within a conduit system with possible further upgrading of sulfide metal tenors and reduction of s se ratios via partial dissolution of sulfide the pge enriched sulfide liquid then settled in a staging chamber and partially crystallized before a major pulse of magma entrained sulfide liquid eroded blocks of precrystallized and mineralized gabbro and footwall rocks and emplaced an inclusion bearing package as the lower 100 m or so of the river valley intrusion later emplacement of main river valley magma was from an s undersaturated pge fertile magma the river valley intrusion is thus an example whereby contact type mineralization is purely a function of the earliest magma intruded containing preformed sulfide mineralization rather than contamination triggering sulfide saturation in situ in such cases processes at depth determine the generation and subsequent tenor of the mineralization in particular dissolution of the sulfide can upgrade metal tenor but subsequently will reduce s se ratios masking the signature of crustal contamination in addition a multistage emplacement such as this will not necessarily preserve the characteristic increase in cu pd ratios in the overlying cumulates that is often used in exploration for pge deposits in mafic intrusions thus a full understanding of all the field geochemical and mineralogical factors is required to construct genetic models for such deposits and especially in the interpretation of s se and cu pd ratios as an indicator of crustal contamination and the presence of pge mineralization

an overview of chalcophile element contents of pyrrhotite pentlandite chalcopyrite and pyrite from magmatic ni cu pge sulfide deposits we have compiled the trace element concentrations in pyrrhotite pentlandite chalcopyrite and pyrite from magmatic ni cu pge ore deposits with the aim of understanding their petrogenesis and whether these minerals can be used as indicator minerals among the samples there are some of the most studied world class ni cu aguablanca duluth jinchuan noril sk talnakh kharaelakh sudbury voisey s bay and others and pge dominated bushveld lac des iles stillwater great dyke and penikat deposits crustal assimilation may be constrained using as se and sb se ratios in pentlandite the degree of interaction between the silicate and sulfide liquids r factor can be estimated by the content of highly chalcophile elements dsulf liq sil liq above 1000 in sulfide minerals the fractional crystallization of the sulfide liquid can be traced using se te ratios of pentlandite pyrite formed by exsolution from mss has higher rh ru ir and os than co existing pyrrhotite whereas pyrite formed by hydrothermal alteration of pyrrhotite inherits the rh ru ir and os contents of the pyrrhotite it replaced sulfide minerals are preserved in transported glacial cover and their trace element chemistry can be used to discriminate their source pentlandite from ni cu deposits has much lower rh and pd concentrations than those from pge dominated deposits pyrite from magmatic deposits has higher co sb and se as ratios relative to pyrite from hydrothermal deposits and chalcopyrite from magmatic deposits has much higher ni and lower cd concentrations than those from hydrothermal deposits

geology petrography geochemistry and genesis of sulfide rich pods in the lac des iles palladium deposits western ontario canada the lac des iles pd deposits are known for their pd rich sulfide poor mineralization however previously undocumented sulfide rich pods also occur within the intrusion that hosts the deposits given the complex magmatic and hydrothermal history of the mineralization at lac des iles the sulfide rich pods could have crystallized from magmatic sulfide liquids or precipitated from hydrothermal fluids sulfide rich pods occur throughout the stratigraphy in all rock types and along comagmatic shear zones and contain net textured to massive sulfides they can be divided into four main groups based on the variation in mineral assemblages 1 pyrrhotite pentlandite pyrite chalcopyrite magnetite ilmenite 2 chalcopyrite pyrrhotite pentlandite pyrite magnetite ilmenite 3 pyrite pentlandite chalcopyrite pyrrhotite magnetite ilmenite and 4 magnetite ilmenite pyrrhotite pentlandite pyrite chalcopyrite whole rock metal contents and s isotopic compositions do not change with the amount of pyrite present except for slight enrichments in as and bi the presence of an essentially magmatic sulfide mineral assemblage pyrrhotite pentlandite chalcopyrite with pentlandite exsolution flames in pyrrhotite in some pods suggests that the pods crystallized from magmatic sulfide liquids the very low cu contents of the pods suggests that they are mainly cumulates of monosulfide solid solution mss we propose a model whereby sulfide liquids were concentrated into dilation zones prior to crystallizing cumulus mss intermediate solid solution crystallized from the fractionated liquids at the edges of some pods leaving residual liquids enriched in pt pd au as bi sb and te these residual liquids are no longer associated with the pods during subsequent alteration pyrite replaced mss pyrrhotite but this did not affect the platinum group element contents of the pods