gold in porphyry copper deposits its abundance and fate abstract porphyry copper deposits are among the largest reservoirs of gold in the upper crust and are important potential sources for gold in lower temperature epithermal deposits whether gold remains in porphyry copper deposits is important both to their economic attractiveness and to the distribution of gold in the upper crust cu au atomic ratios of porphyry copper ore deposits form a continuous range from about 5000 to 5 000 000 with a median near 40 000 which separates gold rich and gold poor deposits gold is found in porphyry copper deposits in solid solution in cu fe and cu sulfides and as small grains of native gold usually along boundaries of bornite sims ion probe analyses of ore minerals from the gold rich batu hijau kingking and skouries porphyry copper deposits show that bornite contains about 1 ppm au whereas chalcopyrite contains about an order of magnitude less chalcocite and covellite contain 10 20 ppm au but are not abundant enough to account for a significant part of the gold endowment in many porphyry copper deposits the amount of gold presently in solid solution in cu fe sulfides is not adequate to account for all the gold in porphyry copper deposits and the remainder is present as micron scale grains of native gold experiments in the cu fe s au system show that bornite and chalcopyrite can contain about 1000 ppm gold at typical porphyry copper formation temperatures of 600 700 c and indicate that bornite and chalcopyrite in porphyry copper deposits were saturated with respect to gold at temperatures of only 200 300 c in contrast cu au ratios of bulk ore in porphyry copper deposits would require bornite and chalcopyrite to be saturated with respect to gold at temperatures similar to those at which primary potassic ore and alteration are thought to form this indicates that the maximum gold endowment of porphyry copper deposits is probably fixed by the amount of gold that will go into solid solution in cu fe sulfides when the deposit forms at high temperature and that gold is not commonly added later from other sources although it can be redistributed during cooling or later events the experimental data also suggest that high temperature 600 700 c vapors can extract considerably more gold from porphyry copper systems than can low temperature 300 c alteration comparison to cu au ratios of volcanic emissions suggests further that high temperature processes remove copper relative to gold from porphyry copper systems whereas low temperature processes remove gold preferentially and that this can account for deposits with extremely low and high cu au ratios respectively deposits with cu au ratios between about 20 000 and 100 000 however probably reflect different degrees of removal of gold or copper by immiscible sulfides

calibration of the ion microprobe for quantitative trace precious metal analyses of ore minerals quantitative ion microprobe analysis because of its sensitivity and low minimum detection limits is uniquely suited for the determination of precious metals in common sulfide and sulfosalt mineral particles since the early work of biirg 1930 1935 the presence of trace amounts of precious metals in common ore minerals like pyrite arsenopyrite sphalerite etc has been debated by many mineralogists in s udies of synthetic gold bearing sulfides kurauti 1941 clark 1960 bulk analyses of ore sulfides and sulfarsenides boyle 1965 badalov and badalova 1967 korobushkin 1970 and in radioisotopic studies of synthetic sulfides mironov and geletiy 1979 mironov et al 1986 the term invisible gold was used by boyle 1979 to denote differences between colloidal and solid solution gold in ore minerals of course one of the major problems in determining the role of invisible gold in sulfides is ascertaining the absence of gold mineral inclusions gold silver and palladium have been determined irectly in sulfides in only a few cases where concentrations exceeded the minimum detection limits of the electron microprobe aubert et al 1964 or proton microprobe cabri et al 1984 1985 data on the invisible precious metal content of common sulfides and sulfosalts are essential for precious metal geochemistry and exploration and for determining the mineralogical distribution of precious metals in samples from processing circuits silver and gold in major sulfide minerals can account for substantial fractions of the total silver cabri 1988 chryssoulis and surges 1988 and gold chryssoulis 1989 in some ores thus affecting the precious metal distribution between flotation products or causing refractoriness in some metallurgical processes the ion microprobe has been used for qualitative determinations oftrace elements in geologic materials andersen 1973 lovering 1975 shimizu et al 1978 however because of difficulties inherent in the technique slodzian 1975 leta and morrison 1980 zinner 1980 metson et al 1983 quantitative determination was hampered for several years mcintyre et al 1984 first attempted to calibrate the ion microprobe on ore minerals in order to quantify the silver and indium content of sphalerite synthetic standards of sphalerite doped with variable amounts of silver and indium were used for calibration because of factors not well understood at the time e g the effect of fe substitution for zn on the ion yields charging effects reprodueibility was not as good as expected nevertheless the results confirmed the proportionality between the secondary ion signal and concentration chryssoulis et al 1986 used quantitative ion implantation to determine the silver concentration in sphalerite pyrite and ehaleopyrite from the brunswick massive sulfide base metal ore luff 1986 quantitative gold ion implantation was developed to determine the gold concentration in common sulfide and sulfarsenide minerals from refractory ores chryssoulis et al 1987 the gold concentration in copper anodes was determined with the ion microprobe using synthetic standards of gold in copper in the current study synthetic sulfides were employed to calibrate the ion microprobe for the platinumgroup elements this study discusses comparatively the methods available to calibrate the ion microprobe for quantitative in situ analysis of precious metals in ore minerals and metallurgieal products

a new hypothesis on parameters controlling the formation and size of porphyry copper deposits implications on thermal gradient of subducted oceanic slab depth of dehydration and partial melting along the kerman copper belt in iran abstract porphyry copper deposits in the tethyan metallogenic belt broadly occur in early mesozoic late mesozoic paleogene and neogene within a wide range of tectonic setting these deposits in iran often occur within the cenozoic urumieh dokhtar magmatic arc udma mostly in the kerman porphyry copper belt kpcb located in the southeast of this arc these deposits along the udma are mainly associated with the granitoids of miocene age 18 82 9 20 ma in this research geochemical characteristics pb and sr isotopes tectonic environment oxidizing conditions and source of magmas for the most important porphyry copper deposits of the udma have been compared and discussed on the basis of trace element discrimination diagrams the kerman belt granitoids formed in a volcanic arc type setting whereas the jebal barez granitoids seem to have formed in a different tectonic setting the eu eu of granitoids from the kerman belt are greater than 1 2 representing the oxidizing conditions for the crystallization of the granitoid magma whereas jebal barez granitoids were formed under reducing conditions the sr y ratio for kerman granitoids is greater than 60 indicating adakitic affinities and la yb n for these granitoid rocks is between 17 and 35 suggesting that their parental magma was generated from a deep garnet bearing source based on 87sr 86sr i values for kerman belt granitoids of 0 704 0 705 it is suggested that parental magmas originated from a subducted oceanic slab in the sarcheshmeh porphyry copper deposit the thermal gradient of the oceanic slab at depth was less than 9 c km warm cold slab the oceanic slab was highly hydrated and more than 80 of the water within the oceanic slab was released in the deep zone of the sub arc region at a depth of 110 130 km under saturated conditions the oceanic slab partially melted 20 25 a large volume of magma and magmatic water formed sarcheshmeh as a giant porphyry copper deposit in the iju deposit a small porphyry copper deposit the oceanic slab was slightly hydrated and minor water was released at the depth of 110 130 km a small volume of magma was formed due to water undersaturated melting conditions finally a new hypothesis is introduced regarding the roles of down dip thermal gradient of the oceanic slab water content depth of dehydration and degree of partial melting of oceanic slab which are important controls on the formation and size of the porphyry copper deposits within continental volcanic arcs

geochemistry and textures of gold bearing arsenian pyrite twin creeks nevada implications for deposition of gold in carlin type deposits this study relates morphology size texture and chemistry of arsenian pyrite in the twin creeks carlin type gold deposits to the chemical position and amount of gold that it contains arsenian pyrite is confirmed as the most important gold hosting mineral and four types of gold bearing arsenian pyrite are recognized among these four types the lowest amount of gold and arsenic 1 wt as 17 60 ppm au is contained in arsenian pyrite with relatively large grain sizes 10 30 mu m it formed at relatively high temperatures 250 degrees c and k super h super ratios adularia stable probably relatively slowly the largest amount of gold and arsenic 1 05 2 43 wt as 595 1 465 ppm au is contained in arsenian pyrite with small grain sizes up to 2 mu m that formed at low temperatures 120 degrees 200 degrees c and moderate k super h super ratios illite stable probably by relatively rapid deposition xanes exafs and sims analyses show that gold in arsenian pyrite is both structurally bound au i and in submicroscopic inclusions of free gold au highest amounts of structurally bound gold were observed in the relatively coarse grained arsenian pyrite noted above whereas most inclusions of free gold were observed in fine grained arsenian pyrite in general there is a good correlation between gold and arsenic in arsenian pyrite although au as ratios vary from one pyrite to another it is suggested that gold in arsenian pyrite was deposited by direct deposition of native gold and by adsorption of au i from hydrothermal solutions adsorption of gold by arsenian pyrite can take place from solutions that are not saturated with respect to native gold relative volumes of gold bearing pyrite from different paragenetic stages at twin creeks suggest that as much as 50 percent of the total gold in the deposit could have formed from solutions that were not saturated with respect to native gold because both au and au i are found together in arsenian pyrite it is likely that they were deposited by the same process consideration of possible depositional reactions suggests that a decrease in the activity of reduced sulfur is most likely to cause gold deposition

evolution of mineralizing fluid in the porphyry copper system of the skouries deposit northeast chalkidiki greece evidence from combined pb sr and stable isotope data the porphyritic syenite of the skouries deposit intruded the metamorphic basement of the serbomacedonian massif in the northeast chalkidiki peninsula at 19 ma the final eraplacement was controlled by dominantly northeast southwest trending steep faults that created pathways for the deep seated magma to rise to shallow crustal levels following its eraplacement stage i the porphyritic syenite suffered a pervasive potassic alteration stage ii approximately 590 degrees 640 degrees c two later veining stages with propylitic characteristics stage iiia approximately 480 degrees c stage iiib approximately 380 degrees c brought in most of the cu which was deposited in the form of chalcopyrite quartz sulfide calcite veins transect the porphyritic syenite as well as the country rocks in a narrow 50 m wide halo around the stock only the range of delta 18 o values from 3 5 to 7 6 per rail for the fluids in equilibrium with vein quartz is within the typical range of early ore forming fluids associated with porphyries representing magmatic fluids that may to some extent have interacted with the igneous wall rock a subsequent late propylitic alteration stage iv approximately 210 degrees c more localized and patchy affected the country rocks and the porphyritic syenite and deposited disseminated pyrite and chalcopyrite the delta 34 s values from vein and disseminated sulfides range from 2 1 to 0 3 per rail indicative of a magmatic origin for the sulfur the 207 pb 204 pb ratios from pyrite and chalcopyrite deposited in stage iiia early and stage iiib late veins 15 683 15 687 are markedly lower than those from disseminated sulfides related to stage iv 15 696 15 734 and lie within the range of 15 672 to 15 696 defined by feldspars from the porphyritic syenite the pb isotopes therefore indicate an evolution of the fluid composition from one characterized by magmatic components to one dominated by the country rocks whereas ore hosted in veinlets stage iii contains lead from both sources furthermore they suggest that the lead in the ores developed in continental crustal environments with high mu 2 and w 2 values and evolved in a reservoir with high th pb and low u pb ratios age corrected 87 sr 86 sr ratios from inclusion fluids in vein quartz range from 0 7086 to 0 7099 for veins within the country rock and from 0 7061 to 0 7080 in veins transecting the porphyritic syenite values for porphyry feldspars range from 0 7079 to 0 7081 and country rock from 0 7135 to 0 7342 these data confirm the pb isotope trends and indicate that sr contamination took place where the veins crosscut the country rocks fluids in veins within the porphyry could ascend rapidly from deeper levels without reacting with the porphyry and thus show an unaffected magmatic sr isotope signature pb and sr isotopes in inclusion fluids are shown to be extremely sensitive tracers for elucidating the hypogene leaching processes in the skouries porphyry system

paragenesis of the grasberg cu au deposit irian jaya indonesia results from logging section 13 the grasberg cu au deposit is hosted within the grasberg igneous complex gic a pliocene volcanic and intrusive complex situated in the highlands of irian jaya indonesia the gic is composed of intrusive and volcanic rocks that were disrupted by formation of the dalam diatreme and intruded by later multistaged grasberg and kali intrusions each intrusive phase is overprinted by extensive hydrothermal infill and alteration based on drillcore logging on section 13 35 separate stages of alteration and infill have been recognized and their spatial distribution mapped in 14 drillholes that represent approximately 1 8 km of vertical section using intrusions as timelines the hydrothermal stages can be timed as post dalam pre mgi main grasberg intrusion post mgi pre kali and post kali and linked into seven groups that are interpreted as separate hydrothermal systems pre kali systems include ten of the recognized stages and are mostly high temperature alteration k feldspar and or biotite devoid of sulfide mineralization sulfides are restricted to post kali time and excluding early quartz anhydrite sulfide and molybdenite veins can be grouped into three main stages 1 heavy sulfide zone hsz mineralization 2 grasberg copper gold stage and 3 late copper mineralization mixed copper sulfides covellite enargite pyrite and pyrite covellite marcasite the hsz is dominated by fine grained replacement pyrite and distributed mainly towards the periphery of the gic with only minor occurrences towards the central zones it is suspected that a high proportion of the copper and gold content of the hsz is due to overprinting by the grasberg copper gold stage and late copper mineralization

evolution of hydrothermal fluid characteristics at the santa rita new mexico porphyry copper deposit mineralogic and fluid inclusion investigations conducted in the laboratory combined with in situ observations of temporal relationships among geologic features demonstrate that systematic changes in hydrothermal fluid characteristics occurred with time during evolution of mineralization and alteration of the granodiorite stock at the santa rita porphyry copper deposit the earliest fluids to circulate are recorded in potassically altered orthoclase and biotite stable veins as vapor rich h 2 o co 2 inclusions and hypersaline 30 70 equiv wt nacl or kcl inclusions which homogenize over a wide temperature range from 240 degrees to greater than 800 degrees c the high salinity fluid inclusions are complex chloride brines with significant concentrations of sodium potassium copper iron and sulfur but sulfide minerals are not associated with the early potassic assemblage produced by this fluid oxygen isotope ratios of quartz in the orthoclase and biotite stable veins are identical to phenocryst quartz in the intrusion 8 2ppm later solutions circulated through newly formed fractures and older reopened veins and are recorded in low salinity less than 15 equiv wt nacl fluid inclusions which homogenize primarily in the temperature range of 220 degrees to 360 degrees c these hydrothermal fluids formed two distinct alteration assemblages as they reacted with potassically altered rock chlorite is the dominant silicate gangue mineral of the earlier chalcopyrite bearing orthoclase and clay stable assemblages and sericite characterizes the later phyllic alteration assemblage with quartz and pyrite oxygen isotope ratios of quartz of the later assemblages 8 6 10 4ppm are heavier than quartz of the earlier potassic assemblages it is concluded that the earliest hydrothermal fluids to circulate within the stock localizing the orebody at santa rita could have been derived by phase separations of fluids exsolved from crystallizing magma into condensed hypersaline liquids and h 2 o co 2 vapors as these fluids moved through fractures potassic alteration of rock occurred without concomitant deposition of sulfides later solutions of dominantly meteoric origin progressively formed hypogene copper mineralization associated with chlorite stable alteration and then phyllic alteration

platinum group minerals in the santo tomas ii philex porphyry copper gold deposit luzon island philippines mineralized quartz diorites of the santo tomas ii porphyry copper gold deposit carry high au contents average 1 8 ppm as well as 160 ppb pd and 38 ppb pt values of other platinum group elements pge and rhenium are below the analytical detection limits there is a significant positive correlation between au and cu the highest pd values were detected in the most au and cu rich rocks platinum group minerals pgm occur exclusively as inclusions in chalcopyrite and bornite potential pd and pt contents in sulphide concentrates are estimated at 1 5 g t and 0 4 g t respectively the precious metal assemblages consist of merenskyite main pgm kotulskite moncheite native gold electrum hessite and petzite polyphase fluid inclusions in quartz veinlets associated with a pgm bearing bornite chalcopyrite magnetite assemblage are characterized by high salinity 35 to 60 eq wt nacl and high trapping temperatures between 380 and 520 c they may represent primary magmatic hydrothermal fluids which have been responsible for the transport of pd pt and au as chloride complexes

precious metal mineralogy in porphyry skarn and replacement type ore deposits of the ertsberg gunung bijih district irian jaya indonesia petrographic and electron microprobe analyses of native au and a variety of sulfide minerals indicate a generally high but widely varying native au fineness and a cu fe sulfide host for most ag in the gunung bijih timur complex of cu au skarn deposits the big gossan and dom cu skarn deposits and the grasberg porphyry cu au deposit native au rims bornite in veins and forms inclusions in bornite and chalcopyrite in samples from grasberg and from the gunung bijih timur complex as well as filling open space in quartz veins in the complex skarn and quartz veins in the big gossan area host native au in association with pyrite pyrrhotite galena chalcopyrite sphalerite and arsenopyrite native au from the gunung bijih timur complex has a wide but bimodal range of fineness 920 to 990 and 340 to 820 avg 860 native au from grasberg samples is or 930 fine avg 960 fineness of big gossan au ranges from 540 to 960 avg 830 although compositional ranges are small within most individual samples native au from grasberg falls into two groups with respect to pd pd bearing or 3 500 ppm avg 1 800 ppm and with no detectable pd fire assay of grasberg ore reveals trace but detectable 10 ppb pd 500 ppb avg or 50 ppb concentrations of pd and no detectable pt native au from the gunung bijih timur complex averages twice as much cu as that from grasberg 1 7 vs 0 8 wt cu native au from big gossan has uniformly low cu contents or 1 200 ppm cu avg 300 ppm mass balance calculations and analytical data indicate that the bulk of the ag in the gunung bijih timur complex is contained by bornite indicating a partitioning of ag into bornite relative to native au or a discrete ag mineral this is supported by the consistent positive correlation of cu and ag throughout the gunung bijih timur complex as well as in grasberg and dom ag bearing galena occurs in the big gossan area but is rare in the grasberg the gunung bijih timur complex and the dom orebodies the high fineness of native au from the gunung bijih district represents the upper end of the reported range for porphyry and skarn type cu au deposits but is similar to values reported elsewhere in indonesia the fineness of native au in the gunung bijih timur complex does not appear to be controlled by depth or distance from the local intrusive contact mineral assemblage or paragenetic relationship the fineness of native au from the big gossan area shows a positive correlation with elevation suggestive of a lower temperature more distal character than in the other skarns of the district differences in pd contents may be related to acidity and redox conditions during native au deposition high cu high pd and low ag compositions of au grains in pan concentrates suggest a porphyry or cu skarn source relative to a more distal source compositional characteristics identified in this study may have applications to exploration within the ertsberg district and elsewhere

sulfide mineral in intrusive and volcanic rocks of the bingham park city belt utah we report here the results of a reconnaissance study of sulfide inclusions in some intrusive and volcanic rocks from the bingham park city belt in central utah the study was undertaken to determine whether primary sulfides were preserved in these rocks and if so to assess their role in the geochemistry of copper in the magmas numerous samples were studied from the alta clayton peak and flagstaff stocks and a few samples were also studied from the little cottonwood last chance and soldier canyon stocks as well as from the phoenix dike and the keetley volcanics our results show that sulfides are present in unaltered intrusive and volcanic rocks although most of these inclusions lack hematite and pyrite that are typical products of degassing at least some inclusions appear to have been modified possibly by reaction with enclosing iron bearing host minerals measurements of the sizes of inclusions suggest that sulfides contain only 20 to 50 percent of the copper in the rock whereas sulfide selective analyses suggest that all of the copper in the rock is hosted by sulfides despite this uncertainty compositions of sulfides vary systematically from unit to unit the distribution of sulfide inclusions in different minerals suggests that mafic intrusions were saturated with sulfur over a longer period of time during their crystallization history than were felsic intrusions although there are exceptions chalcopyrite is most abundant in intrusions emplaced at deeper levels bornite is found in intrusions emplaced at intermediate levels and pyrrhotite is found in the shallowest intrusions and volcanic rocks finally apparently unaltered samples of the last chance soldiers canyon and phoenix bodies contain talnakhite a copper bearing sulfide mineral that was not observed in the other intrusive rocks in view of the close association of the last chance and phoenix bodies with the bingham porphyry copper deposit this relationship could be of use in evaluation of the mineral potential of felsic intrusive rocks

the evolution of a porphyry cu au deposit based on la icp ms analysis of fluid inclusions bajo de la alumbrera argentina the chemical and physical evolution of magmatic to hydrothermal processes in the porphyry cu au deposit of bajo de la alumbrera northwestern argentina has been reconstructed with a quantitative fluid inclusion study fluid inclusion petrography microthermometry and single inclusion microanalysis by excimer laser ablation inductively coupled plasma mass spectrometry la icp ms are combined to determine the evolution of pressure temperature and ore metal concentrations including cu and au in the fluids complementary hydrogen and oxygen isotope analyses are used to further constrain the water sources in the evolving system the combined data provide a new level of insight into the mechanisms of metal sourcing and ore mineral precipitation in a porphyry style magmatic hydrothermal system based on previously reported observations of the igneous geology alteration geochemistry and veining history of the subvolcanic porphyries at alumbrera the distribution of fluid inclusion types in space and time is documented six major inclusion types are distinguished the highest temperature brine inclusions up to 750 c p 1 kbar are mainly recorded in barren quartz magnetite veins in the core of the alteration system these polyphase brine inclusions halite sylvite multiple opaque and transparent daughter crystals are interpreted as the most primitive magmatic fluid recorded at the level of the deposit they are of moderately high salinity 50 60 wt nacl equiv dominated by nacl kcl and fecl 2 and contain on average 0 33 wt percent cu and 0 55 ppm au upon cooling and decompression these saline liquids exsolve a vapor phase which is preferentially enriched in cu relative to its main salt components but probably plays a minor role in the formation of this particular deposit because of the inferred small mass fraction of vapor cooling and decompression from the highest initial p t conditions down to about 450 c causes magnetite k silicate alteration but no saturation in au or cu sulfides as recorded by continually high ore metal concentrations in the fluid inclusions coprecipitation of cu and au as chalcopyrite and native gold some early bornite occurs over a narrow range of decreasing fluid temperature with cooling from 400 to 305 c the cu concentration in the brine drops by about one order of magnitude to less than 0 07 wt percent without a proportional decrease in major salt components ore mineral precipitation extracts 85 percent of the cu and au from the fluid it is associated with potassic alteration as shown by a concomitant decrease in the k na ratio of the cooling magmatic brine and by an increase in its ba and sr concentrations elements which are probably liberated in the destruction of calcic igneous minerals the fluid chemical data demonstrate that the metal ratios in this and probably many other porphyry style ore deposits are primarily controlled by the magmatic source of the ore brines on the other hand the final hypogene ore grade of the deposit is controlled by the efficiency of ore mineral precipitation at alumbrera metal extraction is governed by the efficiency of cooling a high flux of magmatic fluid within a small rock volume dilution of residual magmatic fluids as recorded by aqueous fluid inclusions of decreasing salinities and temperatures below 295 c follows after the main stage of copper introduction and is associated with feldspar destructive phyllic alteration geometric relationships fluid analyses and stable isotope data together indicate that phyllic alteration results from postmineralization hydrothermal activity involving minor mixing between meteoric water residual brine and a waning input of magmatic vapor

endeavour 26 north a porphyry copper gold deposit in the late ordovician shoshonitic goonumbla volcanic complex new south wales australia endeavour 26 north is the largest of 12 pipelike porphyry cu au deposits found near parkes in central west new south wales within the late ordovician goonumbla volcanic complex the dominant volcanic rocks of the complex the goonumbla volcanics are latitic flows and volcanic breccias which are overlain by the trachytic wombin volcanics the volcanic rocks are characterized by high k 2 o and high k 2 o na 2 o ratios which are typical of the shoshonite association as well as an enrichment in large ion lithophile elements and a low concentration of high field strength elements the nelungaloo volcanics form an early ordovician nonshoshonitic volcanic substrate to the complex which initially developed in a submarine and subsequently subaerial setting the 87 sr 66 sr epsilon nd and pb isotope data indicate the magmas were derived from mantle sources the shoshonitic magmas may be products of high pressure fractionation in the subcontinental lithosphere the porphyry deposits are associated with a gravity low which is taken to reflect a subvolcanic chamber beneath the center of the complex all deposits are located within a pronounced circular feature in the aeromagnetic data that is interpreted as the margin of a collapsed caldera dioritic to monzonitic stocks which in part define the caldera rim represent a resurgent phase of magmatism the endeavour 31 stock which was part of this phase is ringed by six porphyry cu au deposits including endeavour 26 north the deposits are centered on fingerlike quartz monzonite porphyries which cut the endeavour 31 stock at depth geochemical anomalies of cu and zn in the bedrock define the size of the alteration system associated with the stock in part the distribution of the cu au deposits is controlled by the endeavour lineament in comparison to most other volcanic and intrusive rocks of the goonumbla volcanic complex the endeavour

porphyry gold deposits of the refugio district maricunga belt northern chile the porphyry gold deposits of the refugio district and similar deposits in the maricunga belt contain the lowest known copper to gold ratios cu ppm au 0 03 of any porphyry type deposit the gold deposits are associated with subvolcanic andesitic to dacitic intrusions emplaced into coeval volcanic rocks both the verde and pancho deposits are zoned in space from a deeper zone of banded quartz veinlets associated with chlorite magnetite albite and or pyrite albite clay alteration to a shallow zone of pyrite albite clay and local quartz alunite ledges pancho contains an additional deepest porphyry copperlike zone with quartz veinlets a veinlets and potassic alteration relative to verde pancho is telescoped with all three zones present within a 400 m vertical interval the porphyry copperlike zone at pancho is characterized by a veinlets and pervasive potassic alteration both restricted to intrusive rocks a veinlets range from hairline streaks of magnetite biotite with minor quartz and chalcopyrite and k feldspar alteration envelopes to sugary quartz veinlets 1 cm in width with magnetite and chalcopyrite and no alteration envelopes hypersaline liquid inclusions coexisting with vapor rich inclusions indicate temperatures above 600 c and salinities as high as 84 wt percent nacl equiv a pressure estimate of 250 bars indicates a depth of 1 000 m assuming lithostatic pressure potassic alteration consists of a central zone of magnetite k feldspar oligoclase that changes outward to a biotite rich zone total sulfide content predominately as chalcopyrite is generally 1 vol percent whereas magnetite content is 2 to 5 percent where a veinlets and potassic alteration predominate grades are typically 0 1 wt percent hypogene copper and 0 5 to 1 ppm gold banded quartz veinlets are present at both verde and pancho where they occur mostly above a veinlets and cut a veinlets where they overlap they are less than 2 cm in thickness and lack alteration envelopes dark gray bands whose color is due to abundant vapor rich fluid inclusions and micrometer sized grains of magnetite commonly occur as symmetric pairs near the vein walls the bands are commonly botryoidal and are continuous through quartz grains suggesting that the quartz recrystallized from a silica gel rare liquid rich fluid inclusions in quartz indicate temperatures 350 c and salinities 35 wt percent nacl equiv estimated pressures are 200 bars suggesting depths of 190 to 1 500 m under hydrostatic pressure gold occurs both in the dark bands with magnetite and outside the dark bands with pyrite chlorite illite and k feldspar banded veinlets occupy steeply dipping radial and shallowly dipping concentric fractures zones of abundant banded veinlets without early a veinlets generally contain 0 5 to 2 ppm gold and 0 05 wt percent hypogene copper most of the differences between porphyry gold deposits at refugio and porphyry copper deposits can be attributed to shallower depths of formation less than 1 km compared to 1 5 to 4 km that is typical for porphyry copper deposits shallower depths resulted in lower sulfide concentrations local garnet veinlets widespread albite bearing alteration and most importantly banded quartz veinlets which are unique to porphyry gold deposits banded quartz veinlets are a direct result of episodic intrusion of magma to within 1 km of the surface and exposure of high temperature magmatic fluids to hydrostatic pressures episodic rupturing of a brittle ductile boundary surrounding the intrusive centers at verde and pancho led to flashing of magmatic fluids loss of sulfur to vapor and low sulfide gold ratios in ore

porphyry copper and tourmaline breccias at los bronces rio blanco chile the los bronces rio blanco deposit is located on the west side of the andes in central chile about 69 km from santiago los bronces is a breccia complex superimposed on the west side of an earlier major porphyry copper system the rio blanco mine currently exploits the north central part of this porphyry deposit and has started operating a large copper bearing tourmaline breccia sur sur about 2 km south of the present mine the los bronces rio blanco deposit was formed on the east side of the san francisco batholith this intrusion is strongly peraluminous and has a calc alkaline composition with an alkali calcic affinity the batholith took a minimum of 11 5 m y to form from the early miocene 20 1 m y to the late miocene 8 6 m y the porphyry copper mineralization alteration and copper tourmaline breccias were formed over a period of at least 2 5 m y between 7 4and 4 9 m y ago a postmineral volcanic neck or diatreme at la copa erupted within and removed a large segment of the northern part of the porphyry copper system thus marking the last evidence of magmatic activity in the area k ar age determinations of biotites indicate the diatreme erupted in the early pliocene between 4 9 and 3 9 m y ago the prebreccia porphyry system exhibits propylitic sericitic silicic and potassic alteration a unique alteration feature of this system is the replacement of mafic minerals by specularitc and or tourmaline within the propylitic zone the porphyry system contains disseminated and stockwork copper iron molybdenum sulfide mineralization within an area of about 12 km 2 los bronces is composed of at least seven different copper bearing tourmaline breccias that form one large contiguous kidney shaped body about 2 km long and 0 7 km wide at the present erosion surface the breccia body crops out at elevations between 4 150 and 3 450 m the various breccias are characterized by their locations matrices clasts shapes types and degrees of mineralization and alteration the breccias are usually monolithic but in some cases are bilithic or heterolithic with most clasts consisting of quartz monzonite or andesitc with locally minor amounts of quartz latite porphyry monzodiorite and vein quartz the breccia matrices consist of variable amounts of quartz tourmaline specularitc anhydrite pyrite chalcopyrite bornitc molybdenite sericite chlorite and rock flour the seven different breccias types are identified from oldest to youngest as ghost central western infiernillo anhydrite fine gray and donoso the breccia complex has sharp contacts with the surrounding intrusive rocks and andesites internally the breccia contacts are locally well defined but elsewhere they coalesce interfinger or display gradational contacts breccias at los bronces are interpreted as being emplaced explosively followed by collapse after pressure release of hydrothermal fluids the primary mineral distribution is best known in the donoso breccia which has been the center of mining activity since its discovery in 1864 in spite of the coarse and irregular nature of the sulfides in the matrix chalcopyrite pyrite and specularitc at the 3 670 m open pit operating level show a tendency to be distributed in irregular shells in which one of the three minerals predominates in any one shell the transitions between shells are rapid several semiellipsoidal shells of alternating high and low copper grades are also apparent from the copper distribution of underground level 3640 and from various cross sections the shells are approximately vertical subparallel to the donoso breccia contacts which dip inward secondary enrichment enhanced the primary grade in the southern two thirds of the los bronces breccia complex and in much of the surrounding porphyry copper system the degree and depth of enrichment are a function of breccia and fracture permeability and extend to a depth of more than 500 m in certain favorable sectors the shape and depth of the enrichment blanket and overlying leached capping suggest that the enrichment process is related to the present ground water regime and is still active

magmatic sulfides and au cu ratios in porphyry deposits an experimental study of copper and gold partitioning at 850 c 100 mpa in a haplogranitic melt pyrrhotite intermediate solid solution gold metal assemblage at gas saturation abstract the behavior of copper and gold in the phase assemblage pyrrhotite po intermediate solid solution iss haplogranitic melt gold metal capsule at 850 c 100 mpa and gas saturation ah2o 0 9 has been investigated the results are presented as nernst partition coefficients the partition coefficient dcupo melt 2 6 0 3 103 1 was determined for po and melt in equilibrium with an iss of composition cu 19 1 fe 30 1 s 51 1 2 for gold the partition coefficients are dauiss melt 5 7 2 2 103 1 between iss and melt and daupo melt 140 40 1 between po and melt these imply dauiss po 42 9 1 between iss and po the oxygen fugacity for the experiments log f o 2 13 2 0 3 1 was determined by using the hydrogen sensor technique the sulfur fugacity log f s 2 1 0 0 7 1 was calculated from the composition of po in our experiments melts at iss saturation have cu fe by weight of ca 1 100 the results indicate that crystallization of iss may deplete a melt in gold and crystallization of po may deplete a melt in copper however a melt saturated with iss at a given bulk composition temperature pressure oxygen and sulfur fugacity and feo concentration will have a fixed concentration of cu preventing strong depletion of the melt in cu until iss is fractionated from the melt or changes in environmental conditions destabilize iss a thermodynamic model for the partitioning of cu and au between po and melt in terms of oxygen and sulfur fugacity indicates that dcupo melt and daupo melt may increase greatly with increasing sulfur fugacity and decreasing oxygen fugacity within the po stability field the model also suggests that destabilization of both iss and po relative to magnetite due to changes in oxygen and sulfur fugacities can result in the release of cu and au from the sulfides to the melt

seismogenic zone temperatures and heat flow anomalies in the to nankai margin segment based on temperature data from iodp expedition 333 and thermal model the location of the seismogenic zone across the to nankai margin segment has been widely investigated using geodetic tsunami seismologic and heat flow data as well as thermal models seafloor heat flow measurements show large scatter raising questions about the thermal state of the incoming and overriding plates in this study new temperature and conductivity measurements recorded in the philippine sea plate psp and in the accretionary prism during iodp expedition 333 are integrated with recent data on the margin structure and seismicity to improve constraints on the thermal structure of the incoming plate and the subduction zone as well as the thermal conditions within the seismogenic zone iodp expedition 333 measurements provide heat flow values that are lower than the average of nearby seafloor measurements thermal modeling for the psp suggests that hydrothermal warming is insignificant in the trench thus an observed widespread positive thermal anomaly in the shikoku basin that peaks at the kashinozaki knoll more likely results from vigorous thermal convection in the upper mantle in back arc context the modeled thermal structure of the margin from the trench to the mantle shows a significantly colder interplate contact than in previous studies the seismogenic zone is likely to be 30 170 km from the deformation front corresponding to the 100 340 c temperature range the 1944 co seismic slip zone extends farther southward where temperatures are about 60 c slow slip earthquakes are located in the downdip transition zone between 340 and 440 c across the intersection of the moho and the megathrust fault this improved thermal structure from the trench to the mantle results mainly from a better estimate of oceanic plate age slab dip and sedimentation rate variations in the trench this last parameter cools the interplate contact until a depth of 35 km shifting the thermally defined seismogenic zone landward by 20 km and significantly diminishing its influence near the corner flow area

gold in porphyry copper deposits experimental determination of the distribution of gold in the cu fe s system at 400 to 700 c experiments in the system au cu fe s were carried out at temperatures of 400 to 700 c to determine how much gold could be accommodated by bornite and chalcopyrite the two most common ore minerals in porphyry copper gold deposits our results show that for all temperatures bornite contains one order of magnitude more gold than chalcopyrite or intermediate solid solution iss its high temperature equivalent the range of gold concentrations in bornite and chalcopyrite or iss decreases with decreasing temperature from 1 280 to 8 200 ppm au in bornite and 100 to 125 ppm au in iss at 600 c to 235 to 364 ppm au in bornite and 5 to 16 ppm au in chalcopyrite or iss at 500 c and to 13 to 80 ppm au in bornite and 2 to 4 ppm au in chalcopyrite or iss at 400 c the amount of gold in bornite is also strongly dependent on the composition of bornite being highest in stoichiometric bornite compositions cu5fes4 and decreasing toward cu rich and cu poor compositions phase equilibrium constraints for solutions with geologically reasonable reduced sulfur contents indicate that high temperature porphyry copper gold deposits will contain bornite and magnetite whereas lower temperature deposits whether primary or overprinted by phyllic alteration will contain chalcopyrite and pyrite if gold is present in the ore forming solutions more of it will be deposited in high temperature porphyry copper gold deposits where it will be closely associated with bornite coexisting magnetite in these deposits should generate magnetic anomalies lower temperature deposits will contain less gold which is hosted by pyrite as well as chalcopyrite and will lack magnetic anomalies comparison of the amount of gold hosted by natural porphyry copper gold ores to that hosted by bornite and chalcopyrite in our experiments suggests that significant amounts of gold can be lost from these deposits into surrounding hydrothermal systems

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

origin and ore forming consequences of the advanced argillic alteration process in hypogene environments by magmatic gas contamination of meteoric fluids metasomatic effects have been thermodynamically computed for magma derived sulfur gases which may contaminate convecting meteoric fluids in the monzonite k silicate protore and are compared with natural assemblages in the butte district of montana the advanced argillic assemblage with covellite is produced in hypogene environments at 300 degrees c by sulfur metasomatism of protore only for a limited range of net sulfur valences essentially 1 to 2 placing limiting constraints on the possible ratios of so 2 and h 2 s gases a second important factor is the relative reaction rates of protore and contaminating sulfur gases contamination by sulfur gases is a third factor of importance a final factor is that a minimum negative net volume of reaction causes by wall rock dissolution and fracture enlargement the high permeability necessary for circulation of enormous quantities of hydrothermal fluids and vein growth characteristic of this extreme alteration facies modified journal abstract

magmatism and metallogeny associated with mantle upwelling zircon u pb and lu hf constraints from the gold mineralized jinchang granite ne china abstract the jinchang gold deposit is located in the easternmost portion of the central asian orogenic belt caob and represents one of the major gold districts in eastern jilin heilongjiang provinces of china the gold ore bodies are hosted mainly in altered mesozoic granitoids breccia pipes and ring and radial faults gold mineralization consists of alteration stockwork in hydrothermally altered granites breccia and quartz sulfide vein types alteration assemblages around the alteration style ore body show a vertical sequence of potassic phyllic and propylitic zones in this study we present u pb and lu hf isotope data on zircons derived from mineralized granophyric granite biotite monzogranite granodiorite and granite porphyry and sericite rb sr ages from the jinchang gold deposit the results show 206pb 238u ages of 201 3 ma mswd 1 1 203 4 ma mswd 1 4 201 5 ma mswd 2 1 and 110 3 ma mswd 1 6 respectively sericite from the gold mineralized phyllic altered granodiorite and granite porphyry returns rb sr isochron ages of 110 4 ma mswd 1 04 and 107 5 ma mswd 0 91 respectively our new data indicate that the gold mineralization at jinchang took place at ca 110 ma and was temporally related to intrusion of the granite porphyry zircon e hf 200 ma values of the ca 200 ma granites vary from 4 8 to 8 1 with tcdm model ages of 727 1535 ma reflecting their derivation mainly by partial melting of juvenile proterozoic crust the gold bearing 110 ma granite porphyry returns e hf 110 ma values in the range of 1 6 to 9 8 with tcdm model ages of 542 1069 ma suggesting partial melts of juvenile proterozoic crust with notable input of mantle components as compared to the ca 200 ma granites compiled oxygen 18osmow 0 7 10 1 and hydrogen dsmow 99 to 70 stable isotopic values of quartz from ores indicate that the ore forming fluids were predominantly exsolved from magmas with minor amount of meteoric water in quartz sulfide veins at the late stage the hf isotope data from the granite porphyry integrated with the results from previous data on s and pb isotopic composition of ores constrain the source of ore forming components as lower crust with discernible mantle inputs and wall rock assimilation our results have implications bearing on the widespread magmatism and metallogenic event during the early cretaceous time in east china and link them to mantle upwelling that contributed both heat and volatiles for crustal melting and scavenging of metals which in turn were concentrated in upper crustal levels through exsolution for the magmas

armalcolite bearing fe ti oxide assemblages in graphite equilibrated salic volcanic rocks with native iron from disko central west greenland native iron bearing strongly sediment contaminated andesitic to dacitic lavas from the malig t formation on disko contain an early phenocryst assemblage of plagioclase low ca pyroxene s and ilmenite the phenocrystic ilmenite has reacted to form complex fe ti oxide metal sulphide aggregates which contain one or more of the oxides ilmenite armalcolite and rutile the armalcolite is very similar to the lunar type 1 armalcolite of haggerty 1973 and approximate compositionally the ternary system feti2o5 mgti2o5 ti3o5 92 to 97 mol when evidence from several salic rocks is combined the fe ti oxide metal sulphide aggregates display reactions which may represent one isobaric invariant assemblage ilmenite armalcolite rutile iron and the 3 boundary univariant reactions in the system fe ti o the compositional and textural features of ferro magnesian silicates oxides and metals show that most rocks were affected by a rapidly declining fo2 during magma ascent and cooling as displayed in the fe ti oxide metal sulphide aggregates by the cross cutting of one or several t fo2 buffer curves in the system fe ti o prominent sulphidation reactions are observed in the oxide aggregates and are always of the type where feo in oxide is replaced by fes while the liberated oxygen is consumed in a reduction process carbon bound as graphite or cohenite occurs throughout the rocks and is mostly enclosed in phenocrysts and xenocrysts when the salic magmas ascended from pre eruption reservoirs at 1 to 1 5 kb the reduction was largely controlled by strongly pressure dependent carbon oxygen equilibria resulting in rapidly declining t fo2 paths recorded by the oxide assemblages in the simplified c o gas system carbon barometry sato 1979 applied to the selected rocks would indicate final equilibrium pressures of between 10 and 100 bars the scarcity of preserved graphite in the lavas would suggest that the carbon controlled reductions were terminated when available carbon was exhausted during the magma ascent and solidification

early magnetite amphibole plagioclase alteration mineralization in the island copper porphyry copper gold molybdenum deposit british columbia the initial hydrothermal event in the evolution of the ca 377 mt 0 41 percent cu island copper porphyry cu au mo deposit northern vancouver island was the formation of an extensive alteration mineralization facies dominated by magnetite calcic amphibole and intermediate to sodic plagioclase early stage quasipervasive magnetite rich alteration and associated magnetite rich veinlets in this middle jurassic island arc hosted hydrothermal system developed in both an axial dacitic porphyry dike and contiguous basaltic flows and pyroclastic strata the magnetite rich alteration zone 500 to 700 m wide and originally extending over at least 450 m vertically exhibits an outward zonation from quartz magnetite albite an sub or 6 amphibole trace apatite trace through quartz magnetite amphibole albite an sub 6 10 or oligoclase andesine an sub 15 36 apatite trace or scapolite trace to amphibole magnetite oligoclase or sodic andesinc an sub 15 39 or quartz or apatite trace assemblages definition of early stage mineral assemblages impeded by unusually intense later intermediate argillic alteration and more local phyllic and advanced argillic alteration was facilitated by the use of novel petrographic techniques including incident light nomarski differential interference contrast microscopy early stage mineralization comprises several well defined vein veinlet types which were demonstrably emplaced prior to the main stage chalcopyrite pyrite stockwork and associated k silicate alteration minor chalco pyrite and pyrite occur in some early stage veins and magnetite is a constituent of many later main stage sulfide rich veins but the distinction between these two major vein systems is clear mass exchange calculations demonstrate that early alteration involved intense iron metasomatism of both felsic and mafic country rocks with an fe enrichment approaching 450 percent 20 g 100 cc in the dacite dike and lesser and more variable na enrichment with both ti and al behaving as mobile constituents paragenetically early fluid inclusions in the quartz phenocrysts of the dike are tentatively correlated with the magnetite rich alteration mineralization and imply that this event was initiated above 650 degrees c and at pressures of at least 1 kbar and was generated by fecl 2 rich brines at first single phase and moderately saline avg 15 wt nacl equiv but latterly boiling at ca 560 degrees to 645 degrees c and or ca 0 55 kbars the main stage potassic alteration zone has the configuration of an annulus ca 100 to 150 m in width which was entirely superimposed on the more extensive early alteration mineralization zone at ca 430 degrees to 575 degrees c and below 450 bars gold although correlated overall with cu and potassic alteration was probably extensively introduced in the early stage it is inferred that the scarcity of sulfides in the early alteration assemblages reflects the highly oxidized nature of the initial fluids in which so super 2 exceeded both h 2 s and so super 2 4 the deposition of abundant magnetite and the widespread and intense fe metasomatism which define the early stage record the high solubility of fe as fecl 2 in high temperature brines in equilibrium with magnetite bearing quartzofeldspathic rocks as well as the retrograde solubility of magnetite between ca 550 degrees and 750 degrees c whereas the high so 2 h 2 o so 4 ratios of the initial hydrothermal fluids at island copper and in other similar deposits may have resulted from the high inherent oxygen fugacity of the parental dacitic magmas they may have directly reflected the composition of supercritical fluids expelled on quenching of underplating s rich mafic melts the mineral assemblages of the early stage veins and associated quasi pervasive alteration cannot be assigned to the accepted alteration mineralization facies of porphyry systems such as a veins and potassic alteration and record specific and distinct conditions of fluid rock interaction