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

geochemistry and fluid characteristics of the dalli porphyry cu au deposit central iran abstract the miocene dalli porphyry cu au deposit in the central part of urumieh dokhtar magmatic arc is the first reported au rich porphyry cu deposit in the zagros orogenic belt the cu au mineralization is mainly hosted in diorite and quartz diorite intrusions presenting as numerous veinlets in the altered wall rocks with potassic phyllic and propylitic alteration developed based on the mineral assemblages and crosscutting relations of veinlets hydrothermal mineralization alteration occurred in at least three stages characterized by veinlets of 1 qtz kfs mag ccp 2 qtz py ccp bn cv cc and 3 qtz chl bt the ore bearing intrusions exhibit typical geochemical characteristics of subduction zone magmas including lree fractionated pattern strong enrichment in lile cs rb ba pb and u and depletion of hfse with marked negative ti and nb anomalies the adakite like ore hosting porphyry intrusions are characterized by a systematic gradual decreasing and increasing of y and eu eu with increasing sio2 content respectively moreover they exhibit a significant increasing trend of sr y with decreasing of y which indicates progressive hornblende fractionation and suppression of plagioclase fractionation during the evolution toward high water content of parental magma a relatively flat hree pattern with low dyn ybn and nb ta values may represent that amphibole played a more important role than garnet in the generation of the adakitic melts in the thickened lower crust based on the phase assemblages confirmed by detailed laser raman spectroscopy analyses and proportion of solid liquid and gaseous components five types of fluid inclusions were recognized which are categorized as 1 liquid rich two phase liquidh2o vaporh2o iia 2 vapor rich two phase vaporh2o co2 liquidh2o iib 3 high saline simple fluids iiia liquidh2o vaporh2o hl 4 high saline opaque mineral bearing fluids iiib liquidh2o vaporh2o hl hem ccp py and 5 multi phase type iiiab liquidh2o vaporh2o hl anh hem mag ccp in early stage veins the homogenization temperature of multiphase inclusions as high as 620 c with corresponding salinities of up to 75 wt nacl equivalent represent the initial ore forming fluids from early to late stage veins the gradual decrease of homogenization temperature of saline inclusions iiiab iiia and iiib from 620 to 340 c corresponding salinities of 75 35 wt nacl equivalent may reflect fluid boiling and mixing of the early magmatic fluids with circulating groundwater the common association of hematite and anhydrite daughter phases with the most primitive inclusions iiiab in early stage veins and the lack of co2 bearing inclusions in the middle to late stage veins reveal co2 content and oxygen fugacity of the fluids was significantly decreased from early to main stage of sulfide mineralization second generation of veins it seems that magnetite crystallization and co2 escape have a decisive role in oversaturation of s2 and subsequent rapid and large scale precipitation of sulfides in second generation of veins at the dalli deposit

salt precipitation in magmatic hydrothermal systems associated with upper crustal plutons magmatic hydrothermal systems associated with upper crustal plutons strongly influence volcanic and geothermal processes and form important mineral deposits fluids released from plutons are commonly saline and undergo phase separation into high salinity brines and low salinity vapors upon ascent while brine vapor immiscibility has been extensively studied precipitation of solid salt during phase separation in magmatic hydrothermal systems has generally been considered a rare phenomenon here we show that most porphyry deposits exhibit fluid inclusion evidence best interpreted by solid salt precipitation from ore forming solutions this interpretation naturally links thermodynamics numerical simulations and independent estimates of porphyry ore formation depths salt precipitation imposes major changes on the permeability of the system moreover salt precipitation has implications for ore formation along the liquid vapor halite curve the recognition of salt saturated systems is challenging but very relevant for understanding the evolution of magmatic hydrothermal systems

understanding the evolution of magmatic hydrothermal systems based on microtextural relationships fluid inclusion petrography and quartz solubility constraints insights into the formation of the yulong cu mo porphyry deposit eastern tibetan plateau china the evolution of the magmatic hydrothermal system that formed the eocene yulong cu mo porphyry deposit of the eastern tibetan plateau china is reconstructed based on the study of the sequence of stockwork vein sets showing systematic crosscutting relationships in hand specimen early a veins associated with potassic alteration of the porphyritic host are composed of vitreous quartz that is extensively recrystallized and has a dark blue cathodoluminescence fluid inclusions contained in the quartz have been affected by post entrapment modification some of the a veins were reopened and contain ribbons of microscopic molybdenite flakes formation of the molybdenite was associated with recrystallization of the earlier formed quartz and concomitant with the development of a dark purple to brownish cathodoluminescence signature reopening of the early veins also resulted in the formation of ab veins containing euhedral quartz crystals that contain encapsulated molybdenite flakes and are intergrown with coarse laths of molybdenite these euhedral quartz crystals showing a dark purple to brownish cathodoluminescence host vapor rich intermediate density fluid inclusions as well as hypersaline liquid and vapor rich fluid inclusions indicating that fluid immiscibility at hydrostatic pressure conditions occurred during crystal growth later c veins that crosscut and commonly reopen the earlier a and ab veins lack quartz as a gangue mineral and consist entirely of chalcopyrite and pyrite with minor molybdenite sulfide formation was accompanied by chlorite or sericite alteration of the wall rocks late d veins containing quartz and pyrite with associated sericitic alteration of the porphyritic wall rocks crosscut all earlier vein types only minor amounts of molybdenite and chalcopyrite are present euhedral quartz crystals in the d veins contain liquid rich fluid inclusions that have not been affected by post entrapment modification the results of this study indicate that mo and cu mineralization at yulong was introduced by single phase intermediate density magmatic hydrothermal fluids as the porphyry system was transitioning from ductile to brittle conditions the bulk of the mo endowment predated cu mineralization and formed during the change from lithostatic to hydrostatic conditions and associated immiscibility of the magmatic hydrothermal fluids chalcopyrite precipitation followed as the single phase intermediate density magmatic hydrothermal fluids was escaping into the hydrostatic pressured regime cooling of the magmatic hydrothermal fluids appears to have been the principal control on metal precipitation

gold speciation and transport in geological fluids insights from experiments and physical chemical modelling this contribution provides an overview of available experimental thermodynamic and molecular data on au aqueous speciation solubility and partitioning in major types of geological fluids in the earth s crust from low temperature aqueous solution to supercritical hydrothermal magmatic fluids vapours and silicate melts critical revisions of these data allow generation of a set of thermodynamic properties of the auoh aucl 2 auhs and au hs 2 complexes dominant in aqueous hydrothermal solutions however other complexes involving different sulphur forms chloride and alkali metals may operate in high temperature sulphur rich fluids vapours and melts the large affinity of au for reduced sulphur is responsible for au enrichment in s rich vapours and sulphide melts which are important gold sources for hydrothermal deposits thermo dynamic speciation and partitioning data and their comparison with au and s contents in natural fluid inclusions from magmatic hydrothermal gold deposits provide new constraints on the major physical chemical parameters temperature pressure salinity acidity redox and ubiquitous fluid components sulphur carbon dioxide arsenic affecting au concentration transport precipitation and fractionation from other metals in the crust the availability and speciation of sulphur and their changes with the fluid and melt evolution are the key factors controlling gold behaviour in most geological situations

fluid chemistry structural setting and emplacement history of the rosario cu mo porphyry and cu ag au epithermal veins collahuasi district northern chile the rosario cu mo ag deposit is located in the collahuasi district of northern chile it comprises high grade cu ag au epithermal veins superimposed on the core of a porphyry cu mo orebody rosario has mining reserves of 1 094 million metric tons mt at 1 03 percent copper an additional 1 022 mt at 0 93 percent copper occurs in the district at the nearby ujina and quebrada blanca porphyry deposits the rosario reserve contains over 95 percent hypogene ore whereas supergene sulfide ores dominate at ujina and quebrada blanca mineralized veins are hosted within lower permian volcanic and sedimentary rocks lower triassic granodiorite and late eocene porphyritic quartz monzonite the rosario fault system a series of moderate southwest dipping faults has localized high grade cu ag au veins at cerro la grande similar high grade cu ag au veins are hosted in north northeast trending sinistral wrench faults normal movement in the rosario fault system is interpreted to have been synchronous with sinistral strike slip deformation at la grande hydrothermal alteration at rosario is characterized by a k feldspar core focused in the rosario porphyry that grades out to a secondary biotite albite magnetite assemblage paragenetic relationships indicate that magnetite was the earliest formed alteration product but has been replaced by biotite albite vein crosscutting relationships indicate that k feldspar formed during and after biotite albite alteration chalcopyrite and bornite were deposited in quartz veins associated with both k feldspar and biotite albite assemblages the early hydrothermal fluid was a hypersaline brine 40 45 wt nacl that coexisted with vapor between 400 degrees and 600 degrees c weakly mineralized illite chlorite intermediate argillic alteration of the early k and na silicate assemblages was caused by moderate temperature 250 degrees 350 degrees c moderate salinity brines 10 15 wt nacl molybdenite was precipitated in quartz veins that formed between the potassic and intermediate argillic alteration events these fluids were 350 degrees to 400 degrees c with salinities between 10 and 15 wt percent nacl porphyry style ore and alteration minerals were overprinted by structurally controlled quartz alunite pyrite pyrophyllite dickite and muscovite quartz phyllic alteration assemblages the quartz alunite pyrite alteration formed at 300 degrees to 400 degrees c from fluids with a salinity of 10 wt percent nacl the pyrophyllite dickite assemblage formed between 250 degrees and 320 degrees c from dilute 5 wt nacl fluids an upward flared zone of muscovite quartz pyrite altered rocks surrounds the fault controlled domain of advanced argillic alteration thick veins 0 5 2 m wide of fault hosted massive pyrite chalcopyrite and bornite precipitated brines with a salinity of 30 wt percent nacl at temperatures of 250 degrees to 300 degrees c pressure depth estimates indicate that at least 1 km of rock was eroded at rosario between formation of the k na silicate and advanced argillic assemblages this erosion was rapid occurring over a period of 1 8 m y the rosario porphyry intruded immediately after the incaic tectonic phase implying that it was emplaced as the domeyko cordillera underwent gravitational collapse expressed as normal faults in the upper crust gravitational sliding potentially accelerated exhumation and helped to promote telescoping of the high sulfidation environment onto the rosario porphyry the hydrothermal system responsible for porphyry cu mineralization at rosario was partially exhumed prior to the formation of high sulfidation ore and alteration assemblages this implies that emplacement of a second blind intrusion occurred somewhere beneath the rosario and cerro la grande high sulfidation vein systems and is supported by the fault geometry and zoning of precious metals and sulfosalts at the district scale

factors controlling copper solubility and chalcopyrite deposition in the sungun porphyry copper deposit iran the sungun porphyry copper deposit is hosted in a diorite granodioritic to quartz monzonitic stock that intruded eocene volcanosedimentary and cretaceous carbonate rocks copper mineralization is associated mainly with potassic alteration and to a lesser extent with sericitic alteration based on previously published fluid inclusion and isotopic data by hezarkhani and williams jones most of the copper is interpreted to have deposited during the waning stages of orthomagmatic hydrothermal activity at temperatures of 400 to 300 c these data also indicate that the hydrothermal system involved meteoric waters and boiled extensively in this work thermodynamic data are used to delineate the stability fields of alteration and ore assemblages as a function of fs2 fo2 and ph the solubility of chalcopyrite was evaluated in this range of conditions using recently published experimental data during early potassic alteration 450 c copper solubility is calculated to have been 50 000 ppm whereas the copper content of the initial fluid responsible for ore deposition is estimated from fluid inclusion data to have been 1200 3800 ppm this indicates that initially the fluid was highly undersaturated with respect to chalcopyrite which agrees with the observation that veins formed at t 400 c contain molybdenite but rarely chalcopyrite copper solubility drops rapidly with decreasing temperature and at 400 c is approximately 1000 ppm within the range estimated from fluid inclusion data whereas at 350 c it is only 25 ppm these calculations are consistent with observations that the bulk of the chalcopyrite deposited at sungun is hosted by veins formed at temperatures of 360 60 c other factors that in principle may reduce chalcopyrite solubility are increases in ph and decreases in fo2 and acl our analysis shows however that most of the change in ph occurred at high temperature when chalcopyrite was grossly undersaturated in the fluid and that the direction of change in fo2 increased chalcopyrite solubility we propose that the sungun deposit formed mainly in response to the sharp temperature decrease that accompanied boiling and partly as a result of the additional heat loss and decrease in acl which occurred as a result of mixing of acidic cu bearing magmatic waters with cooler meteoric waters of lower salinity

geology and magmatic hydrothermal evolution of the giant pebble porphyry copper gold molybdenum deposit southwest alaska the pebble deposit is located 320 km southwest of anchorage alaska it is one of the largest porphyry deposits known with a total resource of 10 78 billion tons bt it comprises the east and west zones which are approximately equal in size with slightly lower grade mineralization in the center of the deposit where the peripheries of the two zones merge the west zone was discovered by cominco america in 1989 and the east zone was discovered by northern dynasty minerals in 2005 the oldest rock in the pebble district is the jurassic cretaceous kahiltna flysch unit which contains basinal turbidites interbedded basalt flows and associated gabbro intrusions these rocks were intruded between 99 and 96 ma by coeval granodiorite and diorite sills followed shortly thereafter by alkalic monzonite intrusions and related breccias subalkalic hornblende granodiorite porphyry plutons of the kaskanak batholith were emplaced at 90 ma similar smaller granodiorite plutons were emplaced around the margins of the batholith and are related to cu au mo mineralization re os dates on molybdenite are between 89 7 and 90 4 ma a late cretaceous volcanic and sedimentary cover sequence completely conceals the east zone whereas the west zone is overlain only by glacial sediments and is exposed in one small outcrop eocene volcanic rocks and subvolcanic intrusions occur east and southeast of the pebble deposit and unconsolidated glacial sediments are widespread the east and west zones represent two coeval hydrothermal centers within a single system the west zone extends from surface to 500 m depth and is centered on four small granodiorite plutons emplaced into flysch diorite and granodiorite sills and alkalic intrusions and breccias the much higher grade east zone extends to at least 1 700 m depth and is hosted by a larger granodiorite pluton and adjacent granodiorite sills and flysch the granodiorite plutons merge with depth on the east side of the deposit high grade mineralization has been dropped 600 to 900 m into the ne trending east graben where the deposit remains undelineated to the east and to depth variations in hypogene grade and metal ratios reflect multiple stages of metal introduction and redistribution hornfels related to the kaskanak batholith formed prior to hydrothermal activity at pebble and is most intensely developed in flysch disseminated and vein hosted cu au mo mineralization dominated by chalcopyrite and locally accompanied by bornite formed with potassic alteration in the shallow part of the east zone and with approximately coeval sodic potassic alteration in the west zone and at depth in the east zone illite kaolinite alteration overprinted potassic and sodic potassic alteration throughout the deposit and variably redistributed copper and gold high grade copper gold mineralization is related to advanced argillic alteration controlled by a synhydrothermal brittle ductile fault zone which overprinted potassic sodic potassic and illite kaolinite alteration in the east zone advanced argillic alteration comprises a core of pyrophyllite alteration associated with chalcopyrite bounded to the west by an upward flaring zone of sericite alteration which contains hypogene bornite digenite covellite and trace enargite and tennantite late quartz veins introduced additional molybdenum in several parts of the deposit grade destructive quartz sericite pyrite alteration forms a halo to the entire deposit and yields outward to propylitic alteration a quartz illite pyrite cap is preserved in the weakly mineralized center of the deposit mineralization at pebble is predominately hypogene a thin incompletely developed zone of supergene mineralization occurs in the west zone and is overlain by a thin leached capping there is no evidence for paleosupergene mineralization or leaching below the cover sequence in the east zone molybdenite contains high concentrations of rhenium throughout the deposit elevated palladium concentrations are associated with pyrophyllite alteration in the east zone the pebble deposit occurs in one of a number of large deep seated magnetic anomalies which are located at the intersection of crustal scale structures both parallel and at high angles to a mid cretaceous magmatic arc this setting is similar to fertile porphyry environments in northern chile and suggests that southwestern alaska is highly prospective for porphyry exploration the large size and high hypogene grades of the pebble deposit may reflect a combination of multiple stages of metal introduction with vertically restricted lateral fluid flow induced by hornfels aquitards in flysch

magmatic epithermal transitions in alkalic systems porgera gold deposit papua new guinea fluid inclusion and stable isotope evidence are presented for the transition from magmatic related mesothermal to meteoric water dominated epithermal activity at the giant porgera gold deposit papua new guinea reflecting this transition au ag mineralization occurs in two main stages disseminated auriferous pyrite in phyllic alteration zones stage i and fault related quartz roscoelite cemented hydrothermal breccias and veins carrying locally abundant free gold and au ag tellurides stage ii the deposit is spatially and temporally associated with a late miocene 6 ma epizonal intrusive complex emplaced in continental crust immediately prior to an early pliocene continent island arc collision stage i ore formation was associated in part with fluids of magmatic origin 200 to 500 c 7 to 12 wt and 31 to 58 wt nacl equivalent eq 18 o 8 1 to 9 4 d 50 to 32 and appears to represent a new type of au rich cu poor porphyritic intrusion related mineralization associated with volatile rich mafic alkalic magmatism in a continent island arc collision environment stage ii vein type mineralization crosscuts this earlier disseminated orebody it formed at depths of 2 to 3 km from lower temperature lower salinity isotopically exchanged ground waters 180 c 3 to 10 eq wt nacl 18 o 3 1 to 6 4 d 62 to 34 similar to fluids from other au ag te epithermal deposits gold in these late veins was probably remobilized from deeper stage i type mineralization and stable isotope and textural evidence suggest that au was deposited following tectonically induced fluid phase separation

deposit scale structural controls on orogenic gold deposits an integrated physical process based hypothesis and practical targeting implications the application of deposit scale structural targeting to orogenic gold deposits is primarily concerned with locating volumes of higher grade mineralisation ore shoots within a broader host structural system although empirical correlations between structural heterogeneities and ore shoots have long been noted and certain key physical processes elucidated no integrated system based synthesis has been previously published however linking the existing understanding with important recent advances in understanding of the dynamic physical processes of emplacement of hydrothermal ore systems now provides the opportunity to develop such a synthesis the most important of these new concepts includes the idea that deposits form in vertically extensive conduit systems linking source to sink and the related concept of the phenomena of injection driven swarm behaviour integration of all of these elements leads to the proposal of a coherent physical process based model for the structural emplacement of orogenic gold systems and the local formation of gold enriched volumes this model considers that an orogenic gold deposit must be viewed from the perspective of three different geometric elements each with a particular meaning in terms of physical process and which typically relate to different scales these elements include a the integrated swarm volume isv which is the rock volume which bounds the limits of the mineralisation hosting structural system and is effectively the geological entity that defines a deposit b fluid pathways which are 3d pathways through the isv where dynamic ore fluid emplacement has been repeatedly strongly focused and c ore shoots which are localised volumes of high grade gold deposition that are interpreted to represent volumes of anomalous dilation or second order valve sites within host fluid pathways consideration of this new framework suggests significant potential to improve the effectiveness of structural targeting at the deposit scale in particular ore shoots are only expected within fluid pathways and equivalent dilatant zones outside such pathways are predicted to be barren a key theme is that the rheological architecture of the host rock mass is the most important predictive input to targeting both at the scale of emplacement of the ore hosting conduit system and the scale of localised ore shoots

evolution of magmatic vapor to gold rich epithermal liquid the porphyry to epithermal transition at nevados de famatina northwest argentina fluid inclusions in the subeconomic porphyry cu mo au system at nevados de famatina and closely associated high sulfidation epithermal cu au ag as sb te veins at la mejicana northwest argentina were studied to reconstruct the evolution of hydrothermal fluids from their deep magmatic source to the shallow epithermal environment field geology vein petrography fluid inclusion microthermometry and single inclusion microanalysis by laser ablation inductively coupled plasma mass spectrometry la icp ms were combined to determine the evolution of pressure temperature and ore metal concentrations in the fluids cathodoluminescence imaging complements transmitted light petrography to constrain the successive stages of quartz formation and the entrapment sequence of the fluid inclusion populations aqueous liquid inclusions of 5 wt percent nacl equiv salinity trapped in quartz sericite pyrite qsp veins between 360 and 325 c contain unusually high concentrations of cu 400 5 000 ppm as 200 ppm sb and te both up to 100 ppm and au several ppm along with other ore forming elements these veins are paragenetically transitional between subeconomic porphyry copper mineralization exposed in the valley floor and high sulfidation epithermal veins with high au grades which are preserved along a high ridge adjacent to the porphyry stock low density vapor and hypersaline liquid i e brine inclusions were trapped in early formed quartz of the porphyry stockwork veins between 450 and 600 c the brine contains lower cu and au concentrations than coexisting vapor inclusions and texturally even earlier inclusions of intermediate density that are trapped in phenocrysts and some stockwork veins the latter may be equivalent to a parental fluid the low and intermediate density fluids compositionally overlap in salinity with the aqueous liquids recorded by the later transitional quartz sericite pyrite veins fluid inclusions and geologic time relations indicate that the transitional quartz sericite pyrite veins were the channelways for metal rich aqueous liquids that generated the high sulfidation epithermal cu au deposit these mineralizing liquids are interpreted to have evolved by continuous density increase contraction from a low salinity s rich magmatic fluid of low to intermediate density this vaporlike fluid was produced by exsolution from a magma that existed at greater depth during the late stages of cooling of the magmatic hydrothermal complex and probably underwent minor brine separation prior to reaching the present level of exposure epithermal mineral precipitation occurred upon dilution of the low salinity magmatic fluid with meteoric water which entered the hydrothermal system as it was cooled and successively eroded during continued magmatic fluid ascent

a review of intermediate sulfidation epithermal deposits and subclassification abstract intermediate sulfidation is veins is one of the subtypes of epithermal deposits formed in subduction related arc settings or post collisional orogenic belts the economic and scientific significance of is deposits has been highlighting importance in ag au pb zn exploration and study of porphyry epithermal systems this epithermal clan of deposits typically have a close relationship with andesitic dacitic volcanic subvolcanic rocks and formed at a depth of 0 3 to as much as 1 km is deposits are typically related to oxidized calcic to calc alkaline magmatism fluid homogenization temperatures and salinities range between 150 and 350 c and 0 and 23 wt nacl equivalent respectively the o and h isotope compositions are consistent with a mixture of magmatic and meteoric water with an increase in meteoric diluent as the hydrothermal system wanes most of the is deposits in the world particularly those in circum pacific metallogenic belts formed during cenozoic time several mesozoic and paleozoic is deposits in the central asian orogenic belt imply great exploration potential for pre cenozoic is deposits in this area the presence of mn carbonate such as rhodochrosite and manganocalcite locally mn silicate e g rhodonite helvite typically in mid to late hydrothermal stages is a common diagnostic feature to discern is from low sulfidation ls deposits in addition the occurrence of intermediate sulfidation state sulfides such as pyrite chalcopyrite sphalerite galena and tetrahedrite tennantite associations are another indicator of the is type light colored fe poor sphalerite is typical of is deposits consistent with relatively oxidized fluids elevated fluid salinity is another characteristic with maximum salinity values of base metal rich is veins usually 5 wt nacl equiv the reported is deposits worldwide show that they develop in compressional volcanic arcs as well as in some extensional settings in this review is deposits are subdivided into nc neutral compressional type is with a low ag au ratio 60 formed in extensional settings such as extensional intra arc post collisional orogenic belts and back arc settings another notable feature of e type is deposits is their large ag endowment compared to nc type is nc type is au ag deposits can be associated with porphyry cu au and or high sulfidation hs au cu deposits and their economic metals are mainly gold and or silver by contrast some e type is deposits can occur on the flanks of porphyry molybdenum deposits e type is veins can also occur together with ls precious metal veins in back arcs or extensional continental margins the most representative examples occurring in mexico the occurrence of the two subtypes of is are largely controlled by the parent magma with parent magma of nc type is primarily derived from depleted mantle or juvenile crust while parent magma of e type is mainly from ancient continental crust the occurrence of is deposits is presumably controlled by tectono magmatic settings and fluid evolution paths neutral to compressive stress regime relatively great depth to an exsolving magma 4 km and low exsolution rate of magmatic fluids plus the presence of syn ore dikes in conjunction with the development of interconnected fracture networks above the porphyry stock could be conducive for the occurrence of is and also hs au veins upon porphyry copper deposits pcds confirmation of sub types and variations of is veins can aid in exploration for spatially and genetic related mineralization types such as porphyry and hs deposits

the influence of co2 on the solubility of quartz in single phase hydrothermal fluids implications for the formation of stockwork veins in porphyry copper deposits

fluid density control on vapor liquid partitioning of metals in hydrothermal systems hot aqueous fluids both vapor and saline liquid are primary transporting media for metals in hydrothermal magmatic systems despite the growing geological evidence that the vapor phase formed through boiling of magmatic ore bearing fluids can selectively concentrate and transport metals the physical chemical mechanisms that control the metal vapor liquid fractionation remain poorly understood we performed systematic experiments to investigate the metal vapor liquid partitioning in model water salt gas systems h2o nacl kcl hcl at hydrothermal conditions measurements show that equilibrium vapor liquid fractionation patterns of many metals are directly related to the densities of the coexisting vapor and liquid phases despite differences in the vapor phase chemistry of various metals that form hydroxide chloride or sulfide gaseous molecules of contrasting volatile properties water solute interaction is a key factor that controls the metal transfer by vapor like fluids in earth s crust these findings allow quantitative prediction of the vapor liquid distribution patterns and vapor phase metal transport in a wide range of conditions our density model accounts well for the vapor brine distribution patterns of na si fe zn as sb and ag observed in fluid inclusions from magmatic hydrothermal deposits for au and cu the partitioning in favor of the liquid phase predicted in a sulfur free system contrasts with the copper and gold enrichment observed in natural vapor like inclusions the formation of stable complexes of cu and au with reduced sulfur may allow for their enhanced transport by sulfur enriched magmatic hydrothermal vapors

magmatic evolution and related w mo mineralization in the larong deposit eastern tibet evidence from zircon u pb ages geochemistry and sr nd hf isotopes abstract the late cretaceous ca 92 ma larong porphyry w mo deposit 39 44 mt wo3 0 1541 is the first discovered giant w mo deposit in the leiwuqi zogang metallogenic belt sanjiang region multi stage granitoids including the dacite porphyry dp granodiorite porphyry gp biotite granite porphyry bgp monzogranite porphyry mp biotite granite bg and granite aplite ga have been identified in the larong deposit however the magmatic evolution and related w mo mineralization in this deposit are still poorly understood la icp ms zircon u pb dating of the dp gp bgp mp bg and ga yield weighted mean 206pb 238u ages of 214 0 0 7 ma 213 8 1 3 ma 104 4 0 9 ma 93 9 1 3 ma 91 7 0 5 ma and 36 2 0 6 ma respectively the late triassic dp and gp should be classified as peraluminous a cnk values of 0 95 1 57 s type granitoids they are characterized by pronounced negative end t values 10 01 to 13 92 and ehf t values 8 5 to 16 6 with old tdm2 nd and tdm2 hf ages 1 81 2 12 ga and 1 79 2 30 ga respectively indicating that the dp and gp were mainly derived from partial melting of ancient crustal materials after break off of the paleo tethyan oceanic slab the late cretaceous bgp mp and bg and late eocene ga have low a cnk ratios 0 92 1 06 but high sio2 70 57 77 34 and differentiation index di 87 55 98 06 similar to the characteristics of highly fractionated i type granite detailed elemental e g depletion in nb ta ti sr ba eu and p and isotopic data 87sr 86sr i 0 71192 0 72932 end t 11 81 to 9 11 ehf t 10 4 to 1 4 demonstrate that they were the result of magma mixing between ancient crust derived melts and mantle derived melts the bgp was produced during the final stage of bangong nujiang tethyan ocean bnto subduction the mp and bg were formed under a post collisional tectonic setting related to slab break off of the bnto and the ga was likely associated with delamination of the thickened eclogitic lower crust together with lithospheric mantle the w mo mineralization in the larong deposit is genetically associated with the mp with four favorable factors that can account for the formation of this deposit 1 high w background 2 multi stage magmatism 3 highly evolved relatively oxidized and f rich magmatic system and 4 sufficient calcium obtained by intense fluid rock interaction

copper deposition during quartz dissolution by cooling magmatic hydrothermal fluids the bingham porphyry abstract scanning electron microscope cathodoluminescence imaging is used to map successive generations of fluid inclusions in texturally complex quartz veinlets representing the main stage of ore metal introduction into the porphyry cu au mo deposit at bingham utah following conventional fluid inclusion microthermometry laser ablation inductively coupled plasma mass spectrometry la icpms is applied to quantify copper and other major and trace element concentrations in the evolving fluid with the aim of identifying the ore forming processes textures visible in cathodoluminescence consistently show that the bulk of vein quartz q1 characterized by bright luminescence crystallized early in the vein history cu fe sulfides are precipitated later in these veins in a microfracture network finally filled with a second generation of dull luminescing q2 quartz mapping of brine and vapor inclusion assemblages in these successive quartz generations in combination with la icpms microanalysis shows that the fluids trapped before and after cu fe sulfide precipitation are very similar with respect to their major and minor element composition except for copper copper concentrations in inclusions associated with ore formation drop by two orders of magnitude in a tight pressure temperature interval between 21 and 14 mpa and 425 350 c several hundred degrees below the temperature of fluid exsolution from the magma copper deposition occurs within a limited p t region in which sulfide solubility shows strong normal temperature dependence while quartz solubility is retrograde this permits copper sulfide deposition while secondary vein permeability is generated by quartz dissolution the brittle to ductile transition of the quartz feldspar rich host rocks occurs in the same temperature range which further enhances vein reactivation and promotes cooling and expansion of fluids ascending across the transition from lithostatic to hydrostatic conditions

sediment hosted gold deposits in guizhou china products of wall rock sulfidation by deep crustal fluids sediment hosted gold deposits in guizhou china are hosted in late paleozoic and early mesozoic sedimentary rocks along the southwest margin of the precambrian yangtze craton they have characteristics similar to carlin type gold deposits in nevada and are notably enriched in as sb hg and tl the shuiyindong and yata deposits consist of disseminated strata bound sulfides in permian bioclastic limestone and fault controlled mineralization in middle triassic calcareous clastic rocks respectively mineralization in both deposits consists of barren milky quartz veins disseminated gold bearing arsenian pyrite and arsenopyrite stibnite realgar and orpiment the barren milky quartz veins occur in the ore controlling structures with an envelope of gold mineralization in the host rock consisting of disseminated gold bearing arsenian pyrite and arsenopyrite and replacement style quartz veinlets later drusy quartz stibnite realgar and orpiment fill fractures and vugs on the periphery of gold mineralization petrography microthermometry laser raman spectroscopy and laser ablation inductively coupled plasma mass spectrometric la icp ms analyses of fluid inclusions are used to characterize the chemical evolution of ore fluids at shuiyindong and yata early barren milky quartz veins trapped aqueous fluid with moderate salinity 6 0 wt nacl equiv and minor co2 2 4 mol at a temperature of 230 30 c this fluid contains measurable b na k cs sr as sb and au 3 8 0 5 5 7 2 3 g g determined by la icp ms and is interpreted to approximate the mineralizing fluid responsible for precipitation of early barren quartz veins low salinity 0 9 2 3 wt nacl equiv co2 bearing 6 3 8 4 mol aqueous fluids are recorded in replacement style quartz veinlets they formed gold bearing arsenian pyrite and arsenopyrite and quartz veinlets at a temperature of 210 20 c and pressures of 450 to 1 150 bars corresponding to depths between 1 7 and 4 3 km under lithostatic conditions fluid inclusions in late stibnite orpiment realgar quartz veins contain high co2 58 64 mol and n2 19 2 23 7 mol with trace ch4 up to 1 6 mol the increasing content of co2 and decrease in the concentrations of au and as in aqueous carbonic inclusions are interpreted to result from carbonate dissolution at the level of the deposits during gold mineralization covariance of au as sb and sr concentrations in the fluids is interpreted to reflect deposition of as and sb sulfides and gold concurrent with carbonate crystallization iron is below detection limit 400 g g in all fluid inclusion types suggesting that the ore fluids were fe poor but possibly sulfur rich possibly explaining their exceptionally high gold contents iron in sulfide minerals was probably derived from dissolution of ferroan minerals in the host rocks sulfidized by h2s rich fluids to precipitate arsenian pyrite arsenopyrite and gold pressure fluctuation induced by faulting resulted in local fluid immiscibility and led to late deposition of realgar orpiment stibnite and calcite hydrogen and oxygen isotope compositions of ore fluids d h2o 35 to 68 18o h2o 4 16 5 indicate a metamorphic origin possibly related to crustal thickening and prograde metamorphism during the late yanshanian orogeny

geochronology and geochemistry of porphyritic intrusions in the duolong porphyry and epithermal cu au district central tibet implications for the genesis and exploration of porphyry copper deposits abstract the duolong district in central tibet hosts a number of porphyry as well as high sulfidation epithermal copper gold deposits and prospects associated with voluminous calc alkaline volcanism and plutonism in this study we present new geochronological geochemical isotopic and mineralogical data for both economically mineralized and barren porphyritic intrusions from the duobuza and naruo porphyry cu au deposits zircon u pb analyses suggest the emplacement of economically mineralized granodiorite porphyry and barren granodiorite porphyry at naruo deposit took place at 119 8 1 4 ma and 117 2 0 5 ma respectively four molybdenite samples from the naruo deposit yield an isochron re os age of 119 5 3 2 ma indicating mineralization occurred synchronously with the emplacement of the early granodiorite porphyry at duobuza deposit the barren quartz diorite porphyry intruded at 119 5 0 7 ma and two economically mineralized intrusions intruded at 118 5 1 2 ma granodiorite porphyry and 117 5 1 2 ma quartz diorite porphyry respectively petrographic investigations and geochemical data indicate that all of the porphyritic intrusions were oxidized water rich and subduction related calc alkaline magmas zircons from the porphyritic intrusions have a wide range in the ehf 0 11 1 indicating that they were sourced from mixing of mantle derived mafic and crust derived felsic melts moreover the variation of trace element content of plagioclase phenocrysts indicates that the magma chambers were recharged by mafic magmas comparison of the composition of amphibole phenocrysts indicates the porphyry copper gold mineralization at duolong was generated in magma chambers at low crystallization temperatures and pressures 754 to 791 c 59 m to 73 mpa n 8 and under highly oxidizing conditions nno 2 2 to 2 7 n 8 in contrast barren intrusions were sourced from the magma chambers with higher crystallization temperatures and pressures 816 to 892 c 111 to 232 mpa n 22 that were less oxidizing nno 0 6 to 1 6 n 22 the requirement for a thermal contrast is supported by the declining of ti content in magnetite crystals in barren intrusions 12 550 to 34 200 ppm versus those from economically mineralized intrusions 600 to 3400 ppm moreover the v content in magnetite crystals from economically mineralized intrusions 990 to 2510 ppm is lower than those recorded from barren intrusions 2610 to 3510 ppm which might reflect the variation in oxidation state of the magma the calculated water solubility of the magma forming the economically mineralized intrusions 3 2 3 7 wt is lower than that of magma forming the barren intrusions 4 6 6 4 wt based on the chemical physical characteristics of economically mineralized magma our study suggests that the development of porphyry cu au mineralization at duolong was initiated by shallow level emplacement of a magma that crystallized at lower temperatures and pressures experimental studies show that copper and water solubilities in silicate melts decrease with falling temperatures and pressures indicating metals and ore forming fluids are more likely to be released from a magma reservoir emplaced at shallow crustal levels we propose the magnetite might be a convenient exploration tool in the search for porphyry copper mineralization because the variations in ti and v content of mineral concentrates and rock samples are indicative of barren versus mineralized intrusions

the bingham canyon porphyry cu mo au deposit iii zoned copper gold ore deposition by magmatic vapor expansion fluid inclusion microthermometry and laser ablation icpms microanalysis are combined with geological and textural observations to reconstruct the spatial and temporal evolution of magmatic fluids that formed the subvolcanic porphyry cu au mo ore deposit at bingham canyon utah the bingham canyon orebody is exposed over 1 6 km vertically and has the shape of an inverted cup with distinct metal zoning fluid inclusions in the barren but highly veined and potassically altered deep center of the system have intermediate density 0 6 g cm 3 and a salinity of 7 wt percent nacl equiv they have subequal concentrations of na k fe and cu and contain minor co2 the intermediate density fluids were trapped as a single phase mostly at 500 c and 800 bars the au cu rich center near the top of the orebody contains low density vapor inclusions 0 2 g cm 3 coexisting with brine inclusions containing 45 wt percent nacl equiv the vertical transition of different inclusion types indicates phase separation of the single phase input fluid upon volume expansion associated with a pressure drop to 200 100 bars mass balance calculation based on all analyzed inclusion components indicates that the mass of the vapor phase exceeded that of the brine by 9 1 the vapor contained cu as its dominant cation 1 5 wt and contributed about 95 percent of the total amount of copper transported to the base of the orebody bornite chalcopyrite and native gold were precipitated in a narrow temperature interval from 430 to 350 c into secondary pore space created by local redissolution of vein quartz as a result of retrograde quartz solubility in the vapor dominated fluid system intermediate density fluid inclusions in the deepest parts of the peripheral copper ore zone have identical density and composition including similar gold contents as those in the deep center microthermometry and statistical estimation of phase proportions in the inclusions show that the vapor in the peripheral cu rich but au poor ore zone remained denser and the separating brine was less saline 36 wt nacl equiv compared to vapor and brine in the central au cu ore zone this indicates that the peripheral fluids experienced a lower degree of phase separation due to slightly higher fluid pressure at equivalent temperature compared to more strongly expanding fluids in the center of the system the systematic zoning of au cu within the ore shell despite compositionally similar input fluids is interpreted to have resulted from slightly different pressure temperature density evolution paths of magmatic fluids copper was selectively precipitated in the peripheral ore zone in contrast to complete coprecipitation of au and cu in the central upflow zone of the vapor plume the formation of particularly rich cu au ore in the center of the upward expanding fluid plume is consistent with published experimental data showing that the solubility of metals in hydrous vapor decreases sharply with falling pressure due to destabilization of the hydration shell around metal complexes in expanding vapor this interpretation supports the classic vapor plume model for porphyry copper ore formation but additionally emphasizes the role of sulfur bearing complexes as a key chemical control on magmatic hydrothermal metal transport and the deposition of cu and au in porphyry ores our interpretation of selective cu au precipitation as a function of vapor density can explain the more general observation that most gold rich porphyry copper deposits are formed in shallow sub volcanic environments whereas deeper seated porphyry cu mo deposits are generally gold poor

ore geology and fluid inclusions of the hucunnan deposit tongling eastern china implications for the separation of copper and molybdenum in skarn deposits abstract the hucunnan ore deposit is a representative skarn cu mo deposit in the tongling district an important ore district of the renowned middle lower yangtze river metallogenic belt of china the deposit shows distinct zonation of metals with cu mineralization distributed mainly in the exoskarn zone at shallow depths and mo mineralization occurring chiefly in the endoskarn zone located at deeper depths field evidence and petrographic observations indicate that the ore forming processes can be divided into the skarn quartz molybdenite quartz chalcopyrite and carbonate stages five types of fluid inclusions fis are present in the deposit solid bearing type 1 liquid rich type 2 vapor rich type 3 pure vapor type 4 and co 2 bearing type 5 the skarn stage contains mainly type 1 and 2 but also minor type 3 and 4 fis the fis display homogenization temperatures of 434 570 c and salinities of 2 07 66 0 wt nacl equiv the existence of hematite daughter minerals in the type 1 inclusions together with the presence of magnetite in skarn implies that the skarn stage fluid was oxidizing the skarnization of the granodiorite porphyry is commonly accompanied by potassic alteration suggesting that the fluids were rich in alkali similar to the skarn stage the quartz molybdenite stage contains type 1 and 2 and minor type 3 and 4 fis which yield homogenization temperatures of 280 458 c and salinities of 1 40 54 2 wt nacl equiv the presence of sulfide instead of hematite daughter minerals in the type 1 inclusions in quartz molybdenite veins associated with sericitization indicates that the fluids of the quartz molybdenite stage were more reducing and more acidic than the fluids in the skarn stage the decrease in oxygen fugacity and increase in acidity could have resulted from magnetite crystallization and the consumption of alkali cations and oh respectively during the skarn stage the quartz chalcopyrite stage contains all types of fis which show homogenization temperatures of 203 392 c and salinities of 1 22 46 6 wt nacl equiv observations of hematite bearing type 1 fis in quartz chalcopyrite veins containing anhydrite associated with biotitization suggest that the fluids of the quartz chalcopyrite stage were oxidizing and alkali rich probably on account of the inflow of meteoric water and boiling in an open system in the carbonate stage only type 2 fis are present these fis yield the lowest homogenization temperatures of 156 276 c and the lowest salinities of 1 05 12 3 wt nacl equiv microthermometry and h o isotope data indicate that the ore forming fluids were dominated by magmatic water in the early stages skarn and quartz molybdenite stages and that the magmatic water gradually mixed with circulating meteoric water during the late stages quartz chalcopyrite and carbonate stages the coexistence of saline and vapor rich fis as internal trails or clusters within individual crystals with similar homogenization temperatures but contrasting salinities and homogenization modes to the liquid and vapor respectively in the first three stages strongly suggests that three episodes of fluid boiling occurred in these stages as further supported by the hydrogen isotopic compositions of the fluids which are lower than those of magmatic water based on the above data we conclude that temporal changes in redox conditions acidity and temperature in the mineralizing fluids resulted in the temporal separation of cu and mo by selective sulfide precipitation in the hucunnan skarn deposit the competition among metals e g mo and cu for sulfur in magmatic fluids along with vapor brine immiscibility fluid boiling are major factors that contributed to the spatial separation of cu and mo in the deposit

mineralium deposita change and continuity 2012 has been a year of transition for mineralium deposita after 4 years as co editor patrick j williams has steppeddown in june to fully concentrate on his consulting busi ness during patrick s tenure mineralium deposita hascontinued to grow as a top journal for research on mineraldeposits we are grateful for his dedicated work and wishhim the best of luck for the future the council of the society for geology applied tomineral deposits sga has appointed georges beaudoinfrom universite laval quebec canada as the new co editor of the journal georges has been on the editorialboard since 2001 bernd lehmann from technischeuniversitat clausthal clausthal germany remains asco editor three new associate editors joined the editorialboard in 2012 these are david craw university of otago dunedin new zealand albert gilg technische universitatmunchen munich germany and robert linnen westernuniversity london canada associate editor noel c whitehas stepped down after many years of service and we thankhim for his energic and careful work the journal continues to attract a high level of sub missions of about 120 140 papers per year since 2011 a mineralium deposita volume contains about 1 000printed pages with color print free of charge to allauthors we have a wide distribution across the world through subscriptions and more than 300 online dealswith aggregators and consortia mineralium deposita isaccessible to more than 7 700 institutions worldwide this is a strong incentive to submit research to mineraliumdeposita and to gain large exposure the world of scientificpublishing is changing quickly and direct download ofpapers published in mineralium deposita has grownfrom about 98 000 in 2008 to 133 000 in 2011 for anannual rate of increase of approximately 10 approx imately 20 of downloads are for papers publishedonline first and for the calendar year whereas about60 of downloads are for papers published since 1997 roughly 44 of downloads are from the asia pacificregion china 18 australia 10 whereas europeaccounts for 28 germany 6 uk 4 northamerica for 16 usa 8 canada 7 and bothafrica and south america each account for 6 as editors of mineralium deposita we are committed todiligent review of submissions in 2011 the average timefrom submission to acceptance including author correctionsof revised versions was 217 days slightly down from239 days in 2010 however this distribution is highlyskewed and most papers were handled within 150 days after acceptance a paper is published online with a doiwithin approximately 3 weeks this ensures rapid publica tion and allows the new papers to be read downloaded andcited immediately such that your work reaches the scientificcommunity quickly the research submitted to mineraliumdeposita is sourced from a large number of countries withtop contributors in 2011 being china 30 canada 15 and australia 11 as we wish to ensure high scientificquality we accept on merit approximately 40 of thesubmissions from year to year since 2006 the annualimpact factor if of mineralium deposita has variedbetween 1 25 and 2 06 with a value of 1 68 in 2011 close to the average 10 year if of 1 66 we are dedi cated to publish high quality innovative and challeng ing papers in mineralium deposita and we work toimprove the standing of the journal the two most citedpapers to date published in mineralium deposita in2010 were by r r keays and p c lightfoot on thecrustal sulfur contamination that causes formation ofmagmatic ni cu sulfide deposits keays and lightfoot2010 andbyn koglin h e frimmel w e lawrieminter and h braetz on the trace element compositionof pyrite from mesoarchean and paleoproterozoic placerdeposits koglin et al 2010

the porphyry cu mo au deposit at altar argentina tracing gold distribution by vein mapping and la icp ms mineral analysis the altar porphyry cu mo au deposit occurs in the miocene to early pliocene copper belt of the high andes of western argentina close to the chilean border a cluster of late miocene porphyries intruded a more extensive complex of early miocene rhyolitic to andesitic volcanic and subvolcanic rocks potassic alteration in the central porphyry was partially overprinted by feldspar destructive alteration and finally by argillic to advanced argillic alteration early stockwork veins have been cut successively by quartz pyrite veins tourmaline veins and enargite veins based on correlation analysis of assay results and mapped abundances of these four vein types we estimate that approximately 11 to 26 of the copper in the altar orebody is associated with enargite veins whereas the remainder is associated with the early stockwork veining and potassic alteration gold concentration is low compared with typical cu au porphyries of the andean back arc region but higher than in the giant miocene deposits of chile at an average au cu ratio of 0 14 10 4 by weight across the central porphyry orebody at altar gold is dominantly associated with chalcopyrite in the domain of stockwork veining and potassic alteration small scale assays in combination with petrographic observations and laser ablation inductively coupled plasma mass spectrometry microanalyses show that a significant fraction of the gold in the stockwork veins is enclosed in pyrite as submicroscopic particles attached to inclusions of a bi te pb ag enriched cu fe sulfide phase microscopic grains of native gold also occur along grain boundaries between pyrite and chalcopyrite and rarely as larger particles in enargite veins

metal fractionation between magmatic brine and vapor determined by microanalysis of fluid inclusions the major and trace element compositions of individual fluid inclusions from a range of magmatic hydrothermal ore deposits were analyzed by laser ablation inductively coupled plasma mass spectrometry to explore the behavior of ore forming components during fluid phase separation boiling in high temperature saline fluid systems data from 13 samples showing unambiguous evidence for coeval trapping of a liquid brine and a coexisting vapor phase identify two groups of elements with drastically different geochemical behavior na k fe mn zn rb cs ag sn pb and tl preferentially partition into the brine probably as cl complexes whereas cu as au probably as hs complexes and b selectively partition into the vapor fluid phase separation is probably a major previously underestimated process in the chemical differentiation that contributes to the extreme range of selective element enrichments in magmatic hydrothermal systems from deep plutons through porphyry style and greisen deposits to epithermal mineralization and volcanic fumaroles

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

hematite geochemistry and geochronology resolve genetic and temporal links among iron oxide copper gold systems olympic dam district south australia abstract the wirrda well and acropolis prospects 25 km south from the olympic dam deposit are among several dozen examples of iron oxide copper gold iocg mineralisation forming a 600 km long province in the eastern gawler craton south australia iocg systems across the province differ in terms of host lithology iron oxide mineral associations intensity of brecciation and grade of cu u au mineralisation previous efforts to provide a geochronological framework for mineralisation and correlate this with igneous activity were inhibited by a lack of clear crosscutting features particularly in breccia hosted systems and a scarcity of reliable hydrothermal mineral geochronometers the earliest generation of hematite characterised by enrichment in u w sn mo and previously reported from olympic dam provides confident u pb dates and insights into hydrothermal fluid signatures similar hematite is recognised from wirrda well and acropolis allowing direct comparison between the three iocg systems relationships between early silician wirrda well and titaniferous acropolis magnetite and u bearing hematite at the two prospects differ inferred martitisation of magnetite at acropolis has generated zoned hematite with u w mo enrichment at constant sn concentration but with a marked loss of ree y rey and ti whereas at wirrda well single crystal zoned hematite resembling that from olympic dam retains high rey and sn concentrations although morphologies textures and compositions of u bearing hematite at olympic dam wirrda well and acropolis vary significantly a common u pb laser ablation inductively coupled plasma mass spectrometry age of 1590 ma is obtained from the most reliable data 207pb 206pb 1598 9 6 3 ma at wirrda well and 1590 6 6 5 ma at acropolis the geochemical signatures of iron oxides from the two prospects share common trends for u w sn mo high field strength and siderophile elements comparable with signatures of fe oxides from the outer shell of the olympic dam deposit given that datable iron oxides would seem to be ubiquitous phases throughout the eastern gawler craton the commonality in geochemistry and age of u bearing hematite from the olympic dam district is significant as it provides a single traceable mineral to compare iocg systems across the province

evolution of the breccia hosted porphyry cu mo au deposit at agua rica argentina progressive unroofing of a magmatic hydrothermal system detailed geologic mapping has been used to show that agua rica is a porphyry style cu mo au deposit that was first overprinted by polystage brecciation associated with a high sulfidation epithermal event and then by a barren surface venting phreatomagmatic diatreme prior to a final stage of supergene enrichment it was emplaced in the miocene 8 5 ma as an outlier of the farallon negro volcanic complex in northwestern argentina the agua rica deposit lies next to the contact between precambrian or lower paleozoic metasedimentary rocks and coarse grained ordovician granites in a first pulse of miocene magmatism equigranular to porphyritic intrusions were emplaced with minor potassic alteration and weak cu mo mineralization subsequent intrusion of feldspar porphyries was associated with intense porphyry style stockwork veining potassic and propylitic alteration and disseminated cu mo au mineralization molybdenite chalcopyrite bornite pyrite the present alteration and mineralization pattern is dominated by an almost pervasive overprint of high sulfidation epithermal assemblages phyllic and advanced argillic alteration and cu au ag as pb zn mineralization in breccia cements and as void fillings covellite is the dominant copper mineral in the ore and seems to have partly or completely replaced chalcopyrite and bornite of the earlier porphyry events the high sulfidation epithermal assemblages are closely related to the emplacement of a largely clast supported hydrothermal breccia three major bodies of this breccia have been mapped on the basis of clast lithology clast shape and size degree of alteration and composition of breccia matrix igneous breccia with a fine grained porphyritic matrix is intimately associated and interfingers with the base of the hydrothermal breccia columns a final phase of magmatic hydrothermal activity formed a matrix supported and commonly bedded crater infill breccia it formed by a surface venting phreatomagmatic eruption as shown by a continuous downward transition from bedded breccias to clast supported breccias with sandy or pumiceous matrix to a solid igneous breccia with a fine grained porphyritic matrix in the lower core of the conical crater infill breccia body graded matrix rich epiclastic sediments subsequently filled the crater magmatic activity was terminated by a dike of unmineralized biotite porphyry which intruded the crater infill breccia talus breccia was shed into the crater from the rim supergene leaching and enrichment which replaced covellite pyrite chalcopyrite and bornite by chalcocite and secondary covellite formed an enrichment blanket that was dissected by the present day steeply incised topography the distinctive feature of the agua rica hydrothermal system is the occurrence of early weakly mineralized intrusions later feldspar porphyries with stockwork hosted chalcopyrite bornite molybdenite mineralization hydrothermal breccias with an epithermal pyrite covellite overprint and barren surface venting breccias all exposed at one location within 1 000 m of vertical exposure reconstruction of the time sequence of these geologic elements indicates that agua rica is the result of a protracted history of magmatic hydrothermal activity with superposition of several intrusion events that probably extended over several million years during progressive regional uplift erosion and explosive unroofing

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

relationships between a porphyry cu mo deposit base and precious metal veins and laramide intrusions mineral park arizona in the wallapai mining district porphyry style copper molybdenum mineralization occurs within and near laramide granitoid stocks at the center of an elongate zone of polymetallic quartz veins the principal mineralized veins form a well defined paragenetic sequence with a simplified mineralogy progressing through 1 anhydrite molybdenite am veins of quartz k feldspar anhydrite pyrite biotite molybdenite 2 quartz molybdenite qm veins with quartz molybdenite pyrite 3 anhydrite chalcopyrite ac veins containing quartz k feldspar anhydrite pyrite magnetite chalcopyrite chlorite rutile 4 quartz pyrite qp veins of quartz sericite pyrite and quartz pyrite chalcopyrite epidote chlorite and 5 polymetallic quartz pmq veins with a gangue assemblage of quartz sericite calcite kaolinite epidote chlorite and a variety of base and precious metal minerals the coexistence of vapor and liquid rich fluid inclusions in vein quartz shows that the molybdenite bearing anhydrite and quartz veins formed at 360 degrees to 410 degrees c from boiling low salinity brines chalcopyrite deposition in the anhydrite chalcopyrite veins was at 380 degrees to 420 degrees c from nonboiling brines averaging 20 equiv wt percent nacl and 25 equiv wt percent kcl the quartz pyrite veins formed at 320 degrees to 350 degrees c from brines of 1 to 13 equiv wt percent nacl the polymetallic quartz veins formed from dilute brines of 1 to 7 equiv wt percent nacl temperatures in the first stage of mineralization of the polymetallic quartz veins abruptly increased to 400 degrees to 450 degrees c in and near mineral park but declined outward to less than 300 degrees c on the district periphery in subsequent stages fluid temperatures decreased across the district to less than 200 degrees c pressures were 250 to 300 bars probably in a hydrostatic pressure regime during boiling related to molybdenite mineralization but they may have increased to about 1 100 bars lithostatic pressure during chalcopyrite deposition in the anhydrite chalcopyrite veins a depth during mineralization of 3 to 4 km is suggested copper and molybdenum mineralization occurred in a lithocap environment above a progenitor intrusion but was not directly related to the exposed ithaca peak stocks the evolution from hypersaline fluids in the anhydrite chalcopyrite veins to low salinity lower temperature fluids in the quartz pyrite veins suggests an influx of meteoric water into the waning porphyry style hydrothermal system brines up to 100 degrees c hotter appeared during the formation of the paragenetically later polymetallic quartz veins and constituted a new and much larger hydrothermal system the heat source presumably an unexposed intrusion was much larger than the porphyry style system the zonation in base metal ratios of polymetallic quartz veins is symmetrical with respect to the proposed heat source

physiographic and tectonic settings of high sulfidation epithermal gold silver deposits of the andes and their controls on mineralizing processes abstract gold and silver ores in the vast majority of andean high sulfidation epithermal au ag deposits occur at high present day elevations and typically 200 500 m below low relief landforms situated at 3500 to 5200 m a s l most deposits are middle miocene and younger and include el indio tambo pascua lama veladero el indio belt chile argentina cerro de pasco central peru pierina lagunas norte yanacocha northern peru quimsacocha ecuador and the california vetas mining district santander colombia jointly accounting for 130 moz au resources slightly older examples are only preserved in the atacama desert and include the middle eocene el guanaco and el hueso and the late oligocene early miocene la coipa deposits the absence of paleocene and older high sulfidation epithermal deposits can be explained by limited preservation potential imposed by transpressional tectonics within overall contractile episodes and surface uplift these conditions prevailed predominantly in segments of shallow angle subduction of the nazca or caribbean plate below the south american continent a tectonic setting also common for porphyry style cu au mo deposits stratovolcanoes are uncommon ore hosts and volcanic rocks coincident with mineralization are in most cases volumetrically restricted or absent recording the terminal stages of local arc magmatism however dacitic domes are important at e g yanacocha and la coipa at lagunas norte a small stratovolcano largely pre dating but temporally overlapping with mineralization occurs immediately east of the deposit and volcanic sector collapse may have occurred during hydrothermal activity mineralization is typically located near the backscarp of pediments or the heads of valleys incising now high elevation low relief surfaces in the california vetas mining district and el indio belt hydrothermal alunite ages become generally younger upstream along the incising valleys indicating that hydrothermal activity and by inference ore deposition were facilitated by erosion the lowering of the water table and reduction of hydrostatic and lithostatic pressure at these sites of high local relief are believed to have enhanced both boiling and mixing of magmatic with meteoric fluids ultimately enhancing ore deposition the host rock composition permeability and location of the water table control the distribution of alteration zones and ore intermediate volcanic rocks are the most common ore hosts but they typically pre date mineralization by several ma however high sulfidation epithermal mineralization can be hosted in any conceivable rock type including high grade metamorphic rocks california vetas mining district significantly older plutonic rocks pascua lama or quartzites lagunas norte large vuggy quartz alteration zones and commonly oxidized low grade large tonnage mineralization are best developed in relatively permeable volcaniclastic rocks or hydrothermal breccia bodies whereas coherent volcanic plutonic or metamorphic rocks may host fault and breccia controlled ores the near surface steam heated zone can attain a thickness of several hundred meters in dry climates e g veladero pascua lama tambo but is typically poorly developed and less than 20 m thick in humid climatic zones the physiographic and tectonic settings of high sulfidation epithermal deposits are distinct from low sulfidation epithermal districts such as those of patagonia el penon chile or fruta del norte ecuador the latter range to significantly older ages jurassic to early eocene occur at mainly lower elevations and were emplaced in extensional settings a temporal coincidence between uplift erosion and mineralizing processes as well as a spatial and temporal association with porphyry style mineralization is not evident for these low sulfidation districts

hydrothermal evolution of the el teniente deposit chile porphyry cu mo ore deposition from low salinity magmatic fluids the magmatic hydrothermal evolution of the el teniente porphyry cu mo deposit in the central andes in chile is reconstructed based on field relationships scanning electron microscopy cathodoluminescence petrography and fluid inclusion analysis by microthermometry and laser ablation inductively coupled plasma mass spectrometry la icpms three major stages of cu mo mineralization are observed following the barren hydrothermal stage 1 the stage 2 mineralization is characterized by quartz anhydrite stockwork veins and breccias with chalcopyrite bornite and molybdenite both stages 1 and 2 are associated with pervasive potassic alteration quartz anhydrite veins with chalcopyrite bornite and molybdenite associated with phyllic alteration represent stage 3 mineralization stage 4 mineralization linked to the formation of the large braden diatreme is characterized by breccias and rare veins containing a lower temperature assemblage with tourmaline sericite and lesser tennantite bornite and chalcopyrite with late gypsum in local vugs ten fluid types are distinguished in this study based on petrographic and microthermometric criteria such as phase proportions daughter minerals homogenization behavior and salinity the hydrothermal evolution across the stages of cu deposition is characterized by the contraction of a vapor phase originating by phase separation during stage 2 overall cooling of the system at pressures fluctuating around the two phase fluid surface led to a transition from a two phase fluid state dominated by vapor at 410 c and 300 bars in stage 2 to a single phase low salinity fluid derived from cooling and contraction of magmatic vapor to a liquid which dominates during stage 3 mineralization at 350 c and 200 bars copper mineralization mainly formed from the vapor phase and its low salinity liquid derivatives representing a large volume of fluid with an initially high cu content 1 2 0 4 wt cu copper sulfides precipitated upon cooling between 410 and 320 c indicated by a drop of cu na k mn fe ratios of over four orders of magnitude through the evolution of the deposit from stage 2 to stage 4 the highest mo concentrations occur in residual brines resulting from extreme boiling as indicated by concurrent halite saturation recent geochronology cannell 2005 maksaev et al 2004 suggests a relatively long lived magmatic hydrothermal system at el teniente our fluid chemical data show no evidence for major crystal fractionation in a large fluid generating upper crustal magma chamber because cs na k mn fe is constant from pre ore to all syn ore fluids however the initiation of copper mineralization was associated with a 4 to 10 fold increase in the concentration of cu mo li and fe in the inferred main ore forming input fluid compared with pre ore fluids of intermediate salinity and otherwise very similar major and trace element ratios these data indicate that injection from depth of an exceptionally cu mo li and probably also s rich volatile phase into an already actively evolving upper crustal magmatic hydrothermal system triggered the formation of this unusually large and rich copper deposit

venus s shield terrain plains planitiae or lowlands expanses of gentle long wavelength 1000 km basins cover 80 of venus s surface these regions are widely accepted as covered by volcanic fl ows although the mechanism s responsible for resurfacing remains elusive in addition a volcanic origin for the lowland surface may be open to question lowland resurfacing is typically attributed to catastrophic emplacement 10 100 m y of globally extensive thick 1 3 km fl ood type lava this model of resurfacing has been postulated on the basis of impact crater distribution taken together with a lack of obvious volcanic fl ows or edifi ces and a lack of viable alternative models ongoing geologic mapping of 15 000 000 km2 0 25n 90 150e using 225 m pixel and 75 m pixel nasa magellan sar synthetic aperture radar data indicates that small edifi ces called shields 1 15 km diameter edifi ces 1 km high play a major role in lowland resurfacing individual shields are radar smooth or rough quasi circular to circular features with or without a central pit shield shapes which have been previously documented range from shield dome or cone to fl at topped or fl at shield deposits typically coalesce forming a thin regionally extensive but discontinuous mechanically strong layer herein called shield paint shield paint conforms to delicate local topography providing evidence of its thin character and indicating generally low viscosity during emplacement shield terrain shields and shield paint covers more than 10 000 000 km2 within the study area detailed mapping of fi ve 2 2 regions using coregistered normal and inverted right and left illumination sar imagery indicates shield densities of 3500 33 500 shields 106 km 2 thus the map area hosts more than 35 000 335 000 shields shield terrain generally postdates but is also locally deformed by fractures and wrinkle ridges indicating time transgressive formation relative to local deformation and or reactivation the regional scale crust was strong throughout shield terrain formation shield terrain may extend across much of venus s surface

geology fluid inclusion and isotope constraints on ore genesis of the post collisional dabu porphyry cu mo deposit southern tibet abstract the dabu cu mo porphyry deposit is situated in the southern part of the lhasa terrane within the post collisional gangdese porphyry copper belt gpcb it is one of several deposits that include the qulong and zhunuo porphyry deposits the processes responsible for ore formation in the dabu deposit can be divided into three stages of veining stage i quartz k feldspar biotite chalcopyrite pyrite stage ii quartz molybdenite pyrite chalcopyrite and stage iii quartz pyrite molybdenite three types of fluid inclusions fis are present liquid rich two phase l type vapor rich two phase v type and solid bearing multi phase s type inclusions the homogenization temperatures for the fis from stages i to iii are in the ranges of 272 475 c 244 486 c and 299 399 c and their salinities vary from 2 1 to 49 1 1 1 to 55 8 and 2 9 to 18 0 wt nacl equiv respectively the coexistence of s type v type and l type fis in quartz of stage i and ii with similar homogenization temperatures but contrasting salinities indicate that fluid boiling is the major factor controlling metal precipitation in the dabu deposit the ore forming fluids of this deposit are characterized by high temperature and high salinity and they belong to a h2o nacl magmatic hydrothermal system the h o s pb isotopic compositions indicate that the ore metals and fluids came primarily from a magmatic source linked to miocene intrusions characterized by high sr y ratios similar to other porphyry deposits in the gpcb the fluids forming the dabu deposit were rich in na and cl derived from metamorphic dehydration of subducted oceanic slab through which nacl brine or seawater had percolated the inheritance of ancient subduction associated arc chemistry without shallow level crustal assimilation and or input of the meteoric water was responsible for the generation of fertile magma as well as co2 poor and halite bearing fis associated with post collisional porphyry deposits the estimated mineralization depths of qulong dabu and zhunuo deposits are 1 6 4 3 km 0 5 3 4 km and 0 2 3 0 km respectively displaying a gradual decrease from eastern to western gangdese deep ore forming processes accounted for the generation of giant sized qulong deposit because the exsolution of aqueous fluids with large fraction of water and chlorine in deep or high pressure systems can extract more copper from melts than those formed in shallow systems however the formation of small sized dabu deposit can be explained by a single magmatic event without additional replenishment of s metal or thermal energy in addition the ore forming conditions of porphyry cu mo deposits in gpcb are comparable to those of porphyry cu au mo deposits formed in oceanic subduction related continental or island arcs but differ from those of porphyry mo deposit formed in the dabie qinling collisional orogens the depth of formation of the mineralization and features of primary magma source are two major controls on the metal types and ore fluid compositions of these porphyry deposits

3 1 the elatsite porphyry cu au deposit bulgaria ore deposit lat 42 45 n long 24 02 e

experimental study of the behavior of copper and zinc in a boiling hydrothermal system vapor liquid partitioning coefficients for cu and zn in aqueous fluid were determined under boiling conditions at 500 650 c and 35 100 mpa in sulfur bearing and sulfur free systems a synthetic fluid inclusion technique was used to sample the experimental system of coexisting vapor rich and liquid rich fluid inclusions the cu and zn concentrations in individual fluid inclusions were then analyzed by synchrotron radiation x ray fluorescence the vapor liquid distribution constant of cu k d m cu vapor m cu liquid where m denotes the molality of metal is found to be strongly dependent on the sulfur content in the experimental solutions in sulfur bearing systems cu preferentially partitions into the vapor phase whereas zn preferentially fractionates into the hypersaline liquid the k d values for cu and zn obtained in this study correspond well with those obtained from natural fluid inclusions in hydrothermal ore deposits the results suggest that differential volatility of metals is an important factor affecting the enrichment of certain metals in different hydrothermal ore deposits

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

climate and interior coupled evolution on venus climate interior coupled evolution is investigated for venus by merging a partial melting parameterized mantle convection model with a gray radiative convective atmospheric model a positive feedback process can operate by the release of water to the atmosphere via mantle melting leading to an increase in atmospheric opacity and the radiative temperature gradient the resulting amplification of the greenhouse surface temperature raises the mantle temperature leading to an increase in the partial melting rate using thin lid convection a coupled model for venus running over an interval of 3 to 1 ga shows a significant increase in surface temperature partial melting extent and extrusive magma flux compared to a model where there is no communication between greenhouse modulated surface temperature and partial melting in the interior coupled and uncoupled models that transition with variable timing to stagnant lid convection either shut down partial melting via lithospheric thickening or evolve to large amounts of melt due to increased interior temperatures

summary of seismological constraints on the structure of the earth s core we review the current state of the seismological constraints on core structure the evidence supports a simple two layer model of the core the fluid outer core seems to have properties which are consistent with those of a vigorously convecting region the inner core has a sharp boundary characterised by a 0 5 0 6 g cc density jump a 0 6 0 7 km s jump in p velocity and a jump in shear velocity to 2 5 km s or greater there is weak evidence for an anomalously steep shear velocity gradient at the top of the inner core finally the attenuation of both body waves and free oscillations indicate that the inner core is strongly attenuating near its surface though the data suggest that the attenuation is frequency dependent

venus crater distribution and plains resurfacing models detailed analysis of the distribution of craters on venus using mth nearest neighbor analysis coupled with models based upon surface morphology constraints indicates that the hypothesis of complete spatial randomness csr cannot be rejected but is not a unique model of the observed crater distribution based on morphologic mapping the extensive volcanic plains can be divided into four units that have a spread in age of the order of 0 5t the mean surface age of the planet this four unit plains model along with its derivatives produce test statistics that indicate such models also cannot be rejected further the probability of obtaining a result at least as extreme as the observed test statistic given that the null hypothesis model corresponds to venus is true is lowest for the csr model there is no particular reason to pick a csr model along with its implications for catastrophic resurfacing as a constraint on the evolution of venus and there are geological reasons to choose the multiage models we find that we cannot distinguish statistically among models that have two three or four distinct production ages within the plains however the hypothesis that the variation in crater density within all of the plains is due to a single random process can be rejected for two reasons first the binomial probability that such a process could exist within each of the plains units is 0 05 except the smallest and youngest unit pl1 second using a chi squared statistic to test the hypothesis that four plains units have the same age gives a p value of 10 4 indicating confident rejection of the hypothesis thus csr cannot be used as a constraint on models of resurfacing or planetary evolution of venus because of the non uniqueness in matching such a model to the observed crater distribution and the strong indication of distinct ages within the plains with a significant spread in age geological and geophysical constraints provide our best clues for understanding venus

the relation between cu au ratio and formation depth of porphyry style cu au mo deposits constraints on gold and copper ore grades in porphyry style cu au mo deposits are re examined with particular emphasis on published fluid pressure and formation depth as indicated by fluid inclusion data and geological reconstruction defining an arbitrary subdivision at a molar cu au ratio of 4 0 104 copper gold deposits have a shallower average depth of formation 2 1 km compared with the average depth of copper molybdenum deposits 3 7 km based on assumed lithostatic fluid pressure from microthermometry the correlation of cu au ratio with depth is primarily influenced by the variations of total au grade despite local mineralogical controls within some ore deposits the overall cu au ratio of the deposits does not show a significant correlation with the predominant type of cu fe sulfide i e chalcopyrite or bornite primary magma source probably contributes to metal endowment on the province scale and in some individual deposits but does not explain the broad correlation of metal ratios with the pressure of ore formation by comparison with published experimental and fluid analytical data the observed correlation of the cu au ratio with fluid pressure can be explained by dominant transport of cu and au in a buoyant s rich vapor coexisting with minor brine in two phase magmatic hydrothermal systems at relatively shallow depth approximately 3 km and greater confining pressure is likely to precipitate copper molybdenum only while sulfur complexed gold remains dissolved in the relatively dense vapor upon cooling this vapor may ultimately contract to a low salinity epithermal liquid which can contribute to the formation of epithermal gold deposits several kilometers above the au poor porphyry cu mo deposit these findings and interpretations imply that petrographic inspection of fluid inclusion density may be used as an exploration indicator low pressure brine vapor systems are favorable for coprecipitation of both metals leading to au rich porphyry copper gold deposits epithermal gold deposits may be associated with such shallow systems but are likely to derive their ore forming components from a deeper source which may include a deeply hidden porphyry copper molybdenum deposit exposed high pressure brine vapor systems or stockwork veins containing a single type of intermediate density inclusions are more likely to be prospective for porphyry copper molybdenum deposits

evaluation of the role of sulfidation in deposition of gold screamer section of the betze post carlin type deposit nevada this study was undertaken to evaluate the relation between sulfidation and gold deposition in the screamer section of the betze post carlin type deposit we also attempted to determine the source of sulfur in the deposit and the possibility that more than one gold depositing event contributed metal to the screamer system gold ore at screamer forms a generally stratiform body hosted largely by the wispy member of the devonian popovich formation and lacks obvious alteration of wall rock gangue minerals gold at screamer is hosted by arsenian pyrite that forms disseminated grains and overgrowths on diagenetic pyrite a strong correlation is observed between the gold content of rock samples and their proportion of ore related arsenian pyrite as determined by point counts isocon plots show that mineralization at screamer involved addition of both sulfur and iron along with gold arsenic antimony tungsten and local silica barium and phosphorus fe al vs s al plots show that most ore samples at screamer do not contain enough sulfur to account for all of their iron as pyrite petrographic examination shows that the iron occurs in pyrite ferroan dolomite and iron bearing micas in order of decreasing abundance the fe al vs s al plots also show that screamer samples with high gold contents contain more pyrite than samples with low gold contents and that samples inside the ore zone have more pyrite than those in the surrounding area these relations are interpreted to indicate that screamer has undergone at least two pyrite forming events the first event which probably took place during diagenesis involved incomplete sulfidation that left some iron in carbonate and silicate minerals the second event which probably took place during gold mineralization sulfidized most remaining iron and added pyrite in the screamer ore zone the 34 s values of chemically extracted sulfur from disseminated pyrite at screamer range from 13 8 to 16 5 per mil and 34 s values for hand picked separates of pyrite and other sulfides in veins cutting these rocks range from 21 2 to 11 7 per mil a significant fraction of samples with high gold contents and of samples in the ore zone regardless of gold content have 34 s values between 1 and 5 per mil these data suggest that early diagenetic sulfur with a wide range of 34 s values was overprinted by sulfur with isotopic compositions in the 1 to 5 per mil range that was associated with gold mineralization the 34 s values for gold related sulfur at screamer are lower than those reported for bulk mineral separates from most other carlin type deposits and from sims analyses of sulfides from the proximal post part of the betze post system and could be magmatic limited evidence can be found for multiple gold forming events in the screamer zone tungsten which might have been introduced by the jurassic age goldstrike stock is widespread in the deposit and correlates closely with gold a few samples with high tungsten gold ratios found along fault zones might be part of an earlier phase of mineralization related to the goldstrike stock a 34 s value for pyrite in one of these samples is similar to the high values reported for sulfides in auriferous polymetallic mineralization in the post section of the deposit but this mineralization is not reported to contain tungsten other veins containing sphalerite have lower 34 s values and lack consistent gold values whereas there is no correlation between gold values and the degree to which the host rocks have undergone sulfidation there is a strong and highly significant correlation between gold values and the abundance of ore related pyrite this shows that simple sulfidation of immediately adjacent wall rock cannot account alone for gold deposition at screamer and it might not be the only ore depositing process in some other carlin deposits a more general extended sulfidation process could be important however one likely process involves mixing of an invading mineralizing fluid containing sulfur and gold with a wall rock fluid containing iron derived from adjacent or distal wall rocks recognition of the source s for this iron and fluid flow pathways responsible for introducing it to the ore zone could provide useful guidance in exploration for the next carlin trend

the role of sulfur in the formation of magmatic hydrothermal copper gold deposits abstract essential resources of many rare metals including copper zinc molybdenum silver and gold occur in natural sulfide mineral deposits understanding the origin of these metal resources has been limited by a lack of data about the geochemistry of sulfur the most important and abundant element of ore deposits we report the first directly measured sulfur concentrations in high temperature fluids together with their ore metal contents using a new method for sulfur quantification in fluid inclusions by laser ablation inductively coupled plasma mass spectrometry la icp ms co genetic brine and vapor inclusions from magmatic hydrothermal ore deposits and granitic intrusions show an excess of sulfur over ore metals as required for efficient ore mineral precipitation the results demonstrate that s cu and au are highly enriched in vapor like magmatic fluids implying that such low salinity fluids are the key agent for the formation of porphyry copper and epithermal gold deposits

giant versus small porphyry copper deposits of cenozoic age in northern chile adakitic versus normal calc alkaline magmatism cenozoic magmatic activity in northern chile led to the formation of two contrasting porphyry copper belts 1 a paleocene early eocene belt comprising small porphyry copper deposits e g lomas bayas of normal calc alkaline affinity and 2 a late eocene early oligocene belt hosting huge porphyry copper deposits e g chuquicamata of adakitic affinity although the first belt comprises both volcanic and plutonic rocks andesitic basaltic and rhyolitic lavas and tuffs and associated sub volcanic porphyries and felsic stocks the latter only includes intrusions mostly granodioritic types including porphyry copper deposits we suggest that the late eocene early oligocene belt formed when fast and oblique convergence between the south america and farallon plates led to flat subduction and direct melting of the subducting plate hence giving rise to plutonic rocks of adakitic affinity the absence of volcanism under prevailing compressional conditions prevented the escape of so2 from the adakitic sulfur rich highly oxidized magmas closed porphyry system which allowed formation of huge mineral deposits on the contrary coeval volcanic activity during formation of the paleocene early eocene calc alkaline porphyries allowed development of open systems hence to outgassing and therefore to small mineral deposits

origin of the lengshuigou porphyry skarn cu deposit in the zha shan district south qinling central china and implications for differences between porphyry cu and mo deposits porphyry cu and mo deposits are two economically important types of metal deposits worldwide but factors controlling their difference remain enigmatic compared with the well studied large porphyry mo province in the south margin of the north china block s ncb the origin of newly discovered porphyry cu deposits in the south qinling sqb is poorly constrained integrated zircon la icpms u pb and molybdenite re os ages and geological evidence indicate three stages of magmatism at lengshuigou 1 late neoproterozoic 718 to 704 ma quartz diorite albitite granite association during the pre ore stage 2 146 to 145 ma granodiorite porphyry during the syn ore stage and 3 145 ma granite porphyry during the post ore stage elemental and sr nd isotopic evidence provide important constraints on their magma source pre ore neoproterozoic quartz diorite albitite granite was derived by re melting of a mixture of crustal and juvenile mantle materials and stronger fractional crystallization was involved in these ore hosting intrusions than in contemporary granitoids hosted in the douling group syn ore granodiorite porphyry was derived from mantle derived magma with contributions from different proportions of crustal components post ore granite porphyry was derived mainly from a crustal source nearly contemporaneous porphyry cu and mo systems were identified in qinling province including the 147 139 ma porphyry mo systems in the s ncb and 150 146 ma porphyry cu systems in the sqb granitic stocks related to porphyry cu systems in the sqb are characterized by moderate sio2 contents 58 01 69 07 and less radiogenic nd hf isotopes end t 3 8 to 6 3 ehf t 4 5 to 1 6 whereas the granitic stocks related to porphyry mo deposits in the s ncb have high sio2 concentrations 64 00 76 00 and more radiogenic nd hf isotopes end t 18 0 to 11 6 ehf t 26 3 to 13 5 in addition molybdenite from the chigou and lengshuigou porphyry cu deposits in the s ncb show higher re contents 77 50 394 3 ppm than those from nearly contemporaneous porphyry mo deposits 9 34 49 7 ppm in the s ncb these lines of evidence indicate that a higher proportion of mantle component was involved in the formation of porphyry cu deposits in the sqb than nearly contemporaneous porphyry mo deposits in the s ncb it is most likely that the nature of the magma source plays an essential role in the differences between porphyry cu and mo deposits

origin of the ore forming fluids of the zefreh porphyry cu mo prospect central iran constraints from fluid inclusions and sulfur isotopes abstract the zefreh porphyry cu mo prospect is located in the central part of the nw trending cenozoic urumieh dokhtar metallogenic belt 75 km ne of isfahan city central iran chalcopyrite and molybdenite mainly occur as disseminated sulfides in the host rocks and to a lesser extent in the surrounding volcanic rocks four types of fluid inclusions were identified in quartz rich veins i e two phase liquid rich two phase vapor rich simple brine and multi phase brine inclusions liquid rich inclusions in ore bearing a type quartz veins homogenized between 350 and 370 c suggesting that fluids trapped in these inclusions were derived from magmatic fluids at high temperatures simple and multi phase brine inclusions exhibited homogenization or partial homogenization over a wide range from 350 to 1209 c the very high homogenization temperatures and the presence of up to six solid phases in multi phase brine inclusions indicate heterogeneous trapping of melt fluid and vapor the zefreh porphyry prospect is thought to have formed from hypersaline liquids and vapors that exsolved from a magmatic intrusion assembled in the shallow crust the 34s values of sulfides from the zefreh porphyry prospect range from 0 8 to 10 7 this indicates that the early ore bearing quartz veins dominated by high 34s pyrites may have interacted with later hydrothermal fluids or alternatively the pyrites are paragenetically late products of propylitic and k feldspar dominated potassic alteration assemblages another plausible explanation for significantly enriched 34s values of sulfides may be mixing of hydrothermal fluids of magmatic origin with the cenozoic seawater 34s 22 it is suggested that the zefreh prospect likely would be a poor target for further exploration

porphyry copper deposits of the cis and the models of their formation abstract deposits of the porphyry family essentially porphyry copper and gold porphyry copper gold bearing porphyry molybdenum copper gold containing porphyry copper molybdenum and porphyry molybdenum deposits are associated in time and space with granitoid magmatism mainly in phaerozoic volcano plutonic belts whatever their age the deposits belong to two types of belts basaltic belts representing axial zones of island arcs or andesitic belts formed within active continental andean type margins the petrochemistry of ore bearing magmatism related to the nature of the substratum of volcano plutonic belts reveals a number of essential characteristics both in composition and zonation of wallrock alteration and ore mineralization these characterisics enabled previous researchers to establish four models of porphyry copper deposits based on their lithologic associations e g diorite granodiorite monzonite and granite pophyry copper deposits are thought to be the product of self generating two fluid mixing ore magmatic systems porphyry intrusions are pathways for energy and metals from deep seated magma chambers of which the upper mineralized parts are accessible for observation the relationship between magmatic fluids and meteoric water participating in the ore forming processes dependent on the structural petrophysical conditions of formation provide a subdivision for the porphyry copper ore magmatic systems into three types open closed and transitional concurrently a common trend in the evolution of the systems has been established from a nearly autoclave regime of structural and ore forming processes to a gradual increase in the importance of hydrothermal recycling the completeness of the oms ore magmatic system development according to this scheme which determines the existence of various oms types depends on many factors the most important being the depth of formation of porphyry intrusive bodies the petrophysical peculiarities of the host rocks and the palaeohydrogeological conditions of ore deposition although rock fracturing especially defluidization second boiling and contraction are caused by the same mechanisms the stockwork growth in open and closed systems relative to the wall rock takes place in opposite directions primarily due to different petrophysical parameters of the near stock environment in open systems structural and ore metasomatic processes are finalized fractures extend progressively from porhyry stocks into the marginal parts of the intrusive framework and extension of large scale recycling of magmatic and activated meteoric water in the same direction result in the formation of ore bearing stockworks these are large in all dimensions cover mainly hanging wall zones and are characterized by clearly defined concentric mineral zoning and extensive geochemical haloes in a closed oms with centripetal growing fractures hydrothermal convection is stunted the vertical extension of recycling cells is restricted and the volume of meteoric water involved in circulation during the period of ore deposition is relatively small as a result relatively small intra intrusive lenticular stockworks are developed which are characterized by close co existence of several generations of mineralization with fragmentary preservation of the earliest ones these are characterized by the elements of reverse zoning increased density of the veinlets and metal content as well as poorly developed hanging wall dispersion haloes

distribution and composition of gold in porphyry gold systems example from the biely vrch deposit slovakia the biely vrch deposit in the western carpathians is assigned to the shallow sulfide poor porphyry gold deposit type and has an exceptionally low cu au ratio according to 3 d geochemical models there is a limited spatial correlation between au and cu due to the primary introduction of gold by a salt melt and cu by low density vapor despite a rough spatial correlation of gold grades with quartz stockwork intensity gold is hosted mostly by altered rock exclusively in native form three main gold mineral assemblages were recognized here in the deepest parts of the system the k and ca na silicate gold assemblage is associated with minerals of high temperature alteration plagioclase k feldspar actinolite with gold grades and fineness depending on depth and potassium content of the host rock k silicate alteration hosts the lowest fineness gold 914 whereas ca na silicate alteration has the highest 983 the intermediate argillic gold assemblage is the most widespread with gold hosted mainly by chlorite illite smectite and interstratified illite chlorite smectite minerals the gold fineness is mostly variable 875 990 and inherited from the former gold mineral assemblages the latest advanced argillic gold assemblage has its gold mostly in kaolinite the extremely high fineness 994 results from gold remobilization by late stage aqueous magmatic hydrothermal fluids uncommon bonanza grade appears where the earlier gold mineral assemblages were further enriched by this remobilized gold primary precipitation of gold occurred during ascent and cooling of salt melts at 450 to 309 c mostly during retrograde quartz solubility

minor and trace elements in bornite and associated cu fe sulfides a la icp ms studybornite mineral chemistry abstract in situ laser ablation inductively coupled mass spectroscopy la icp ms has been used to provide a baseline dataset on the minor element contents in hypogene bornite and accompanying cu sulfides from 12 deposits with emphasis on syn metamorphic cu vein systems in norway and skarn porphyry and epithermal systems in se europe bornite contains significant concentrations of both ag and bi especially in the vein and skarn deposits studied and has the potential to be a major ag carrier in such ores concentrations of up to 1 wt of both elements are documented measured concentrations appear to be independent of whether discrete ag and or bi minerals are present within the analyzed sulfide where bornite and chalcocite or mixtures of cu sulfides coexist ag is preferentially partitioned into chalcocite over co existing bornite and bi is partitioned into the bornite bornite is a relatively poor host for au which mimics ag by being typically richer in coexisting chalcocite most anomalous au concentrations in bornite can be readily tracked to micron and submicron scale inclusions but bornite and chalcocite containing up to 3 and 28 ppm au in solid solution can be documented selenium and te concentrations in bornite may be as high as several thousand ppm and correlate with the abundance of selenides and tellurides within the sample selenium distributions show some promise as a vector in exploration offering the possibility to track a fluid source bornite and chalcocite are poor hosts for a range of other elements such as co ni ga and ge etc which have been reported to be commonly substituted within sulfides hypogene bornite and chalcocite may have significantly different trace element geochemical signatures from secondary supergene bornite

the global resurfacing of venus the impact cratering record on venus is unique among the terrestrial planets fully 84 of the craters are in pristine condition and only 12 are fractured remarkably only 2 5 of the craters and crater related features are embayed by lava although intense volcanism and tectonism have affected the entire planet furthermore the spatial and hypsometric distribution of the craters is consistent with a completely random one including stochastic variations monte carlo simulations of equilibrium resurfacing models result in a minimum of 17 times more embayed craters than observed or unobserved nonrandom crater distributions for resurfacing areas between 0 03 and 100 of the planet s surface these models also are not consistent with the number and nonrandom distribution of volcanoes and the nonrandom distribution of embayed and heavily fractured craters the constraints imposed by the cratering record strongly indicate that venus experienced a global resurfacing event about 300 m y ago followed by a dramatic reduction of volcanism and tectonism this global resurfacing event ended abruptly 10 m y the present crater population has accumulated since then and remains largely intact thermal history models suggest that similar global resurfacing events probably occurred episodically in the past the tesserae statistically have the same average surface age crater retention age as the rest of the planet but they probably represent older rock units deformed by earlier episodes of global resurfacing although they largely survived the latest global resurfacing event their surfaces were severely deformed by it monte carlo simulations indicate that only about 4 6 of the planet has been volcanically resurfaced since the global event and that the lava production rate has been no more than 0 01 0 15 km3 yr during this time this rate is significantly less than the current rate of intraplate volcanism on earth 0 33 0 5 km3 yr most of venus recent volcanism occurs in the beta atla themis region and most of the recent tectonism is associated with the major global scale tectonic disruption zones that lie within and connect the equatorial highlands the approximately 33 of the planet s surface bounded by latitudes 30 n and 30 s longitudes 60 and 300 e contains twice as many heavily fractured craters and 1 4 times more lava embayed craters as the planetary average this region includes most of the major tectonic belts in the equatorial region because the craters are indistinguishable from a statistically random distribution both spatially and hypsometrically this concentration of strongly fractured and embayed craters is considered indicative of a continuing low level of limited extension and volcanic activity in this region over the past 300 m y however these craters are simply fractured and or embayed and very few have been subjected to complete tectonic disruption complete burial and subsequent removal from the surface as was the case during the global resurfacing event we show that neither the present level and style of geologic activity nor anything less than global resurfacing could have produced the observed cratering record the effects of recent geologic activity are much less than those of the earlier global resurfacing event when the record of all the early heavy bombardment and much of the later light bombardment was erased from the surface by massive volcanism and tectonic activity episodic regional resurfacing events that had global effects also occurred on earth e g the mid cretaceous superplume and probably on mars on mars they may have triggered the catastrophic releases of water that formed the outflow channels

oyu tolgoi mongolia siluro devonian porphyry cu au mo and high sulfidation cu mineralization with a cretaceous chalcocite blanket the oyu tolgoi porphyry cu au mo deposit is located in the gobi desert of southern mongolia the deposit consists of three main mineralized zones north central and south oyu interpreted to constitute at least two separate porphyry copper centers oyu tolgoi is associated with a series of small structurally controlled stocks and dikes of monzonitic and dioritic composition which intrude a sequence of siluro devonian volcanic and sedimentary rocks country rocks consist of pillow basalt and basaltic andesite interbedded with fine grained clastic sedimentary horizons the sequence is interpreted to have formed in a subaqueous island arc volcanic environment which formed part of the extensive paleozoic tuva mongol arc these island arc rocks are covered by carboniferous terrigenous sequences and are intruded by carboniferous syenite and granite and permian alkaline granite much of the area is covered by poorly consolidated cretaceous sedimentary sequences central oyu consists of a multiple phase hydrothermal breccia crosscutting an altered fine grained feldspar porphyry containing porphyry type alteration and mineralization the breccia underwent texture destructive advanced argillic alteration characterized by several associations of quartz alunite dickite pyrophyllite sericite and zunyite plus lesser svanbergite and fluorite these associations overprint earlier formed k silicate and quartz sericite illite assemblages copper mineralization at central oyu is present in a supergene chalcocite blanket that formed at the expense of a pyrite rich hypogene chalcocite covellite tennantite arsenosul vanite sulvanite chalcopyrite bornite sulfide suite that accompanied the advanced argillic alteration event at south oyu a feldspar hornblende porphyry of monzonitic composition intrudes a sequence of fine grained andesite and basaltic andesite hypogene copper gold mineralization occurs as early magnetite rich pyrite poor quartz chalcopyrite bornite stockworks and sheeted veinlets hydrothermal alteration is composed of biotite and k feldspar with apatite and minor albite magnetite averages 7 to 10 vol percent and copper and gold grades vary sympathetically these early assemblages are overprinted by a sericite chlorite event with ore grade copper and erratic gold and molybdenum values and also by structurally controlled pyrite rich advanced argillic alteration k ar ages show that the hypogene copper gold mineralization at south oyu is latest silurian earliest devonian 411 3 ma and that the entire district was intruded by postmineralization syenite during the carboniferous 307 4 ma the supergene chalcocite blanket at central oyu formed in the early cretaceous earliest late cretaceous based on ages for supergene alunite of 117 1 and 93 1 ma which makes central oyu one of the oldest preserved chalcocite blankets in the world chalcocite blanket preservation was favored by climatic desiccation into the late cretaceous and the tertiary it is inferred that significant regional uplift took place at the silurian devonian boundary this synmineral ization uplift and erosion may have been in part responsible for the telescoping of the hydrothermal systems at oyu tolgoi including the superposition of epithermal style associations over higher temperature deeper seated assemblages typical of the porphyry environment

separation of molybdenum and copper in porphyry deposits the roles of sulfur redox and ph in ore mineral deposition at bingham canyon the giant bingham canyon porphyry cu mo au deposit utah is associated with eocene subvolcanic intrusions it shows a distinct metal zonation above a barren core with dominantly shallow cu au mineralization cu stage following the early quartz monzonite porphyry qmp intrusion and spatially deeper mo mineralization mo stage occurring in a separate vein set exclusively after a late quartz latite porphyry qlp intrusion that truncates earlier cu au veins to understand this metal separation and the geochemical process of molybdenite mineralization we investigated fluid inclusions by microthermometry raman spectroscopy and laser ablation inductively couple plasma mass spectrometry la icp ms microanalysis in low and high grade quartz veins of both mineralization stages in deep low grade quartz veins interpreted to represent the root zone of the cu stage we found high concentrations of cu s and mo in the fluid inclusions whereas in low grade mo stage veins we found lower cu but similar concentrations of s and mo compared to the inferred input fluids to the cu stage sulfur and copper concentrations were similar in intermediate density type fluid inclusions in deep low grade cu stage samples whereas intermediate density type inclusions in low grade mo stage veins have s contents that exceed their cu contents in high grade mo stage vein we found large variations of mo concentrations in coexisting brine and vapor inclusions compared to the p t conditions of the cu precipitation stage 90 260 bars and 320 430 c the mo precipitating fluids were trapped at higher pressures and temperatures of 140 to 710 bars and 360 to 580 c mass balance calculation based on the compositions of intermediate density inclusions and brine vapor assemblages interpreted to be derived by phase separation during decompression of the ascending single phase intermediate density fluid indicate that the mass of vapor phase exceeded that of brine by about 9 1 in both mineralization stages combining this mass balance with the analyzed vapor brine partitioning data indicates that more than 70 of mo and s by mass in the deposit were deposited from the vapor phase earlier cu au deposition was similarly dominated by vapor but recently published data about postentrapment cu diffusion in and out of fluid inclusions cast doubt on previous quantifications suggesting that almost none of the copper was deposited by brine mo is less likely to be modified by selective diffusion and high mo contents max 0 0054 mo na in intermediate density 380 g g mo in brine in the hydrothermal fluids were maintained from the early cu stage to the late mo stage this indicates that mo concentration was not the decisive factor for separate precipitation of late mo ore at bingham canyon instead the metal separation may be explained by a reduction in redox potential and an increase in acidity in the evolving source region of the fluids i e a large subvolcanic magma reservoir this is indicated by the stoichiometry of chalcopyrite and molybdenite precipitation reactions a tentative difference in the fe mn ratio in fluids of both veining stages incipient muscovite alteration along high temperature molybdenite veins and an increasing tendency for mo to fractionate from brine to vapor we suggest that the early cu stage fluids were slightly more oxidized and neutral allowing cu fe sulfides to saturate first while molybdenite saturation was suppressed and mo was lost from the early ore stage by contrast during the later mo stage the fluids were more reduced and acidic thereby allowing selective saturation of molybdenite as the first precipitating sulfide in the cooling and expanding two phase fluid consistent with textural observations this interpretation may imply more generally that small differences in redox potential and acid base balance of the magmatic source of porphyry mineralizing systems may be decisive in the temporal and spatial separation of the two metals

adakite like signature of late miocene intrusions at the los pelambres giant porphyry copper deposit in the andes of central chile metallogenic implications adakite like features are recognized in the late miocene 10 ma porphyritic intrusions of the los pelambres giant porphyry copper deposit central chile 32 s located within the southern portion of the flat slab segment 28 33 s of the chilean andes the al and na rich porphyries of los pelambres display distinctly higher sr y 100 300 and lan ybn 25 60 ratios than contemporaneous and barren magmatic units e g la gloria pluton cerro aconcagua volcanic rocks of the same andean magmatic belt strong fractionation of heavy rare earth elements hree absence of eu anomalies high sr y and zr sm and low nb ta ratios suggest melt extraction from a garnet amphibolite source the late miocene adakite like porphyritic intrusions at los pelambres formed closely related in time and space to the subduction of the juan fernandez ridge jfr hotspot chain along the chilean margin current tectonic reconstructions reveal that at the time of formation of the los pelambres rocks a w e segment of the jfr started to subduct beneath them producing a slow down of a previously rapid southward migration of a ne ridge trench collision these particular tectonic conditions are favorable for the origin of the los pelambres porphyry suite by melting of subducting young hotspot rocks under flat slab conditions the incorporation of crustal components into the oceanic lithopheric magma source by subduction erosion is evidenced by the sr nd isotope composition of the los pelambres rocks different from the morb signatures of true adakites a close relationship apparently exists between the origin of this adakite like magmatism and the source of the mineralization in the los pelambres porphyry copper deposit

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