combining in situ isotopic trace element and textural analyses of quartz from four magmatic hydrothermal ore deposits this study couples in situ 16o 17o and 18o isotope and in situ trace element analyses to investigate and characterize the geochemical and textural complexity of magmatic hydrothermal quartz crystals euhedral quartz crystals contemporaneous with mineralization were obtained from four magmatic hydrothermal ore deposits el indio au ag cu deposit summitville au ag cu deposit north parkes cu au deposit and kingsgate quartz mo bi w deposit the internal features of the crystals were imaged using cathodoluminescence and qualitative electron microprobe maps quantitative isotopic data were collected in situ using 157 nm laser ablation inductively coupled plasma mass spectrometry for 40 trace elements in quartz and sensitive high resolution ion microprobe for 3 isotopes in quartz imaging revealed fine oscillatory zoning sector zoning complex macromosaic textures and hidden xenocrystic cores in situ oxygen isotope analyses revealed a 18o range of up to 12 4 0 3 in a single crystal the largest isotopic range ever ascribed to oscillatory zonation in quartz some of these crystals contain a heavier 18o signature than expected by existing models while sector zoned crystals exhibited strong trace element variations between faces no evidence for anisotropic isotope fractionation was found we found 1 isotopic heterogeneity in hydrothermal quartz crystals is common and precludes provenance analysis e g d 18o using bulk analytical techniques 2 the trace element signature of quartz is not an effective pathfinder toward noble metal mineralization and 3 in three of the four samples both textural and isotopic data indicate non equilibrium deposition of quartz

synthetic fluid inclusions in natural quartz iii determination of phase equilibrium properties in the system h2o nacl to 1000 c and 1500 bars phase equilibria in the system h2o nacl have been determined to 1000 c and 1500 bars using synthetic fluid inclusions formed by healing fractures in inclusion free brazilian quartz in the presence of the two coexisting immiscible h2o nacl fluids at various temperatures and pressures petrographic and microthermometric analyses indicate that the inclusions trapped one or the other of the two fluids present or mixtures of the two salinities of the two coexisting phases were obtained from heating and freezing studies on those inclusions which trapped only a single homogeneous fluid phase results of the present study are consistent with previously published data on the h2o nacl system at lower temperatures and pressures and indicate that the two phase field extends well into the p t range of most shallow magmatic hydrothermal activity as a consequence chloride brines exsolved from many epizonal plutons during the process of second boiling should immediately separate into a high salinity liquid phase and a lower salinity vapor phase and produce coexisting halite bearing and vapor rich fluid inclusions this observation is consistent with results of numerous fluid inclusion studies of ore deposits associated with shallow intrusions particularly the porphyry copper deposits in which halite bearing and coexisting vapor rich inclusions are commonly associated with the earliest stages of magmatic hydrothermal activity

the berit transect of the tauride thrust belt s turkey late cretaceous early cenozoic accretionary collisional processes related to closure of the southern neotethys abstract we report on an integrated study of a critical segment of the tauride thrust belt in se turkey berit area units related to two sutures are exposed in the northerly and southerly parts of the area studied in the north the upper cretaceous binboga melange reflects the closure of a northerly mesozoic oceanic basin in the south contrasting units document the closure of the southern neotethys in the south the berit or goksun ophiolite formed as an incipient oceanic arc within the southern neotethys during the late cretaceous c 90 ma intercalated amphibolite granulite facies rocks may record a dismembered metamorphic sole an underlying meta sedimentary meta volcanic unit is interpreted as accreted continental rift and oceanic seamount lithologies the berit ophiolite was accreted to the tauride active continental margin to the north around 85 ma and was then intruded by calc alkaline granites c 70 85 ma northerly margin units were exhumed and covered by shelf carbonate sediments during latest cretaceous early cenozoic time northward subduction during the mid cenozoic c 45 ma resulted in back arc extension along the tauride active margin and subduction influenced volcanism possibly controlled by slab roll back during oligocene early miocene time the southern neotethys closed and the tauride active margin was telescoped to create the present south vergent thrust stack this was accompanied by mass wasting of the advancing allochthon to form sub aqueous frontal olistostromes the arabian platform was over ridden by mid miocene time followed by left lateral strike slip along the east anatolian fault zone as anatolia began to escape westwards towards the aegean sea

trace element composition of quartz from porphyry systems a tracer of the mineralizing fluid evolution trace element composition of hydrothermal quartz reflects the p t x conditions of the mineralizing fluids and can be a potential tracer of the fluid evolution to explore this potential quartz trace element data from 21 porphyry cu au mo and epithermal polymetallic deposits were compiled in addition quartz trace element data from six granite related systems granite pegmatite greisen sn w mo veins and from a subset of calc alkaline arc related volcanic rocks were also compiled for comparison for porphyry cu au mo deposits quartz compositions are from publications in which the sequence of quartz bearing veins and their potential reopening were documented as well as their precipitation temperatures and pressures the compiled dataset shows that trace element composition of quartz continuously evolved between the different porphyry veins and quartz generations a b c d and e the observed evolution reflects the cooling and or compositional variations of the hydrothermal fluids the quartz al ti sb ti ge ti and sb ge ti ratios allow for the discrimination of quartz from different vein generations of porphyry cu au mo deposits this study shows that quartz composition preferentially combined with cathodoluminescence images is an efficient proxy for tracing the evolution of the hydrothermal fluids in porphyry systems and can be used as a vectoring tool to target the centers of porphyry systems

genesis and exploration implications of epithermal gold mineralization and porphyry style alteration at the endeavour 41 prospect cowal district new south wales australia endeavour 41 is a deep level structurally controlled epithermal gold deposit hosted by early ordovician subaqueous volcanosedimentary rocks calc alkalic to shoshonitic mafic to intermediate sills dikes and stocks intruded the volcanosedimentary units in the middle ordovician the most felsic intrusions together with pyroxene bearing dikes are temporally related to gold mineralization postmineralization intrusions are exclusively of mafic character endeavour 41 evolved from early high temperature porphyry style veins and alteration to lower temperature epithermal style gold mineralization early magnetite and garnet bearing veins stage 1 and 2 respectively associated with actinolite magnetite and biotite bearing alteration assemblages have been cut by gold bearing veins and associated alteration assemblages there were two main epithermal style gold mineralizing events 1 quartz pyrite calcite adularia chlorite veins stage 3 and 2 carbonate base metal sulfide veins calcite ankerite quartz pyrite sphalerite galena chalcopyrite ag tellurides arsenopyrite apatite hematite illite muscovite and chlorite stage 4 gold occurs principally as a refractory phase in pyrite it also occurs as grains of au ag tellurides and as inclusions of free gold in pyrite sphalerite and chalcopyrite hydrothermal alteration associated with gold mineralized veins produced early epidote and k feldspar epidote bearing alteration halos and later stage illite muscovite k feldspar and calcite rich alteration halos the highest gold grades are associated with muscovite and illite alteration stable isotope analyses and fluid inclusion data provide evidence of a magmatic hydrothermal component to the mineralizing fluids fluid inclusion data suggest that gold precipitated from boiling saline waters 9 0 wt nacl at temperatures of about 310 c stage 3 veins are estimated to have formed approximately 1 km below the paleosurface at hydrostatic pressure 90 bars stage 4 illite formed at temperatures below 280 c stage 3 calcite has 13 c calcite and 18 o calcite values that range from 5 2 to 4 6 and from 11 6 to 12 1 respectively calculated fluids for these mineral values at 300 c 13 c fluid 3 18 o fluid 6 are consistent with a magmatic hydrothermal source of carbon and oxygen during stage 3 a component of meteoric waters is inferred for stage 4 because 13 c carbonate and 18 o carbonate values range from 6 9 to 0 5 and from 10 9 to 30 1 respectively corresponding to 13 c fluid and 18 o fluid values of 5 and 2 at 200 to 250 c the 34 s sulfide values for early vein stages range between 4 9 and 0 5 stage 3 has 34 s sulfide values ranging from 5 2 to 0 8 with the most 34 s enriched values deposited away from the mineralized center stage 4 sulfides have isotopic compositions from 7 5 to 2 5 the negative isotopic values are consistent with oxidized sulfate predominant magmatic hydrothermal fluids sulfur isotopic zonation patterns show that the most negative 34 s values correlate with gold enriched domains and also with areas that contain high temperature porphyry style alteration facies the negative sulfur isotope values define zones of upflow for the mineralizing magmatic hydrothermal fluids the paragenetic history of endeavour 41 records a transition from deep level to shallow level magmatic hydrothermal activity this transition implies erosion and unroofing of the system synchronous with mineralization high temperature assemblages e g actinolite magnetite biotite and k feldspar epidote indicate that epithermal mineralization occurred proximal to a magmatic hydrothermal center and that there is potential for the discovery of porphyry copper gold mineralization below the current level of diamond drilling

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

the goonumbla porphyry copper deposits new south wales significant porphyry copper gold deposits have been discovered at goonumbla near parkes in central new south wales australia exploratory drilling to date has defined a resource in excess of 250 million metric tons of mineralization with mean grades of 0 70 percent cu and 0 28 g metric ton au this mineralization is contained within the three largest deposits of nine so far located all of which occur toward the top of a calc alkaline volcanic pile of middle silurian age the host volcanics range from trachyte to andesite in composition and have been deposited in the central part of what is believed to have been a large collapse caldera vertical pipelike bodies of vein and disseminated bornite chalcopyrite and chalcocite mineralization are associated with small irregular quartz monzonite porphyry intrusions these porphyries have been derived as late stage quartz rich differentiates of a more mafic monzonitic magma and have migrated upward along and close to the contacts of larger earlier mafic intrusions pervasive pink k feldspar flooding of the volcanics with lesser development of secondary biotite is indicative of the intense potassic alteration which has accompanied the deposition of sulfides quartz vein stockwork systems are invariably developed at or near the porphyry andesite contacts and contain above average abundances of copper gold and silver the mineralizing hydrothermal solutions were low in sulfur content with the result that pyrite is almost totally absent from the central parts of the mineral bodies subsequent oxidation and secondary enrichment although present have not played an important role in the ore forming process bed rock geochemical sampling for copper and gold supported by ground magnetic and induced polarization surveys have proven to be the most effective exploration methods for detecting the soil covered mineralization the goonumbla deposits are high level volcanic to subvolcanic examples of the porphyry copper type and have been formed in a continental margin arc environment in the eastern side of the bogan gate trough

the bingham canyon porphyry cu mo au deposit i sequence of intrusions vein formation and sulfide deposition the bingham canyon porphyry copper gold molybdenum deposit is one of the largest and highest grade porphyry orebodies in the world this study focused on the northwest side of the deposit where quartz mon zonite porphyry qmp the first and largest porphyry intrusion hosts the bulk of the high grade copper gold ore 1 0 cu 1 0 ppm au the north northeast trending high grade zone had pre mining dimensions of 1 500 m strike 300 m vertical and 500 m width and contained more than 500 million tonnes mt of ore associated with potassic alteration and abundant quartz veins the lack of superimposed sericitic alteration yielded ideal exposures in which to study the early high temperature stages of ore formation a style of mineralization that in many porphyry deposits represents the major period of copper introduction we mapped multiple porphyry dikes in the sequence 1 qmp 2 latite porphyry lp 3 biotite porphyry bp 4 quartz latite porphyry breccia qlpbx and 5 quartz latite porphyry qlp porphyry dikes faults and quartz veins are steeply dipping and have two dominant orientations north northeast and northwest striking dikes have a north northeast strike but they thicken and develop northwest trending apophyses and host high grade copper gold zones at intersections with northwest faults indicating that magmatic hydrothermal fluids were focused by these structural intersections each porphyry intrusion was accompanied by a similar sequence of veins potassic alteration and sulfides biotite veinlets were followed by fractures with early dark micaceous edm halos of sericite k feldspar biotite andalusite and local corundum containing disseminated bornite chalcopyrite gold edm halos are cut by multiple generations of a quartz veins representing the main cu au ore forming event postdating all intrusions are quartz molybdenite veins followed by quartz sericite pyrite veins cathodoluminescence cl petrography identified distinct a quartz veinlets consisting of dark luminescing quartz filling fractures and dissolution vugs in earlier a quartz veins and adjacent porphyry wall rock these veinlets contain abundant bornite and chalcopyrite and minor k feldspar and are closely linked in time to the introduction of the bulk of the copper and gold although a similar sequence of veins was repeated on emplacement of all porphyry intrusions the vein density and intensity of potassic alteration declined with time the youngest porphyry qlp is mostly weakly mineralized and locally unaltered these observations indicate that magmatic hydrothermal fluids underwent a similar physiochemical evolution during and immediately following emplacement of each of several porphyry dikes the relationship between edm veins and a quartz veins requires that the flux of magmatic fluid from the magma chamber occurred in an episodic manner as opposed to a continuous discharge vein truncation relationships coupled with abrupt changes in copper gold grades sulfide ratios and potassic alteration intensity at porphyry intrusive contacts indicate that the mass of introduced copper and gold decreased significantly during successive porphyry intrusive hydrothermal cycles presumably due to depletion of metals and volatiles in the underlying magma chamber

new evidence of magmatic fluid related phyllic alteration implications for the genesis of porphyry cu deposits the phyllic alteration in a number of circum pacific porphyry cu au deposits is related to high temperature saline magmatic fluids this contradicts the widely used genetic models wherein phyllic alteration formed as the result of mixing between magmatic and meteoric fluids at the endeavour 26 north porphyry deposit in eastern australia the transition from early potassic to the main stage phyllic alteration is associated with fluids that with time decline in total salinity nacl kcl and temperature from 600 to 550 degrees c calculated and measured delta 18 o and delta d compositions of fluids 5 1 8 5 parts per thousand 57 to 73 parts per thousand delta d confirm a primary magmatic origin for both the early potassic and main stage phyllic alteration these results are consistent with other recent studies e g el salvador chile far southeast philippines and panguna and porgera papua new guinea and suggest that rather than these results being unusual a major revision of porphyry cu genetic models is required

isotopic and geochemical characteristics of laramide magmatic systems in arizona and implications for the genesis of porphyry copper deposits major element trace element and nd sm and rb sr isotope data are described from igneous rocks in 11 multiphase magmatic complexes of laramide age in arizona eight complexes contain barren stocks as well as productive plutons associated with the formation of porphyry base metal deposits whereas in three complexes porphyry orebodies have not been recognized most of the complexes evolved through similar stages early dominantly intermediate volcanic rocks were intruded by multiphase complexes temporally characterized by increases in sio 2 changes in the ferromagnesian mineral assemblage increasingly porphyritic textures and a progression from barren to subproductive to productive intrusions within complexes the sequence is independent of both the absolute age of initiation of local magmatism and its duration analytical data and field relationships are combined to show elements of the petrogenetic history of these complexes potential relationships between productive and barren magmas and factors which may have influenced formation of the characteristic magmatic hydrothermal sequence the isotopic composition of laramide igneous rocks forms an array from epsilon ndt and 87 sr 86 sr initial values of 0 and 0 704 to 14 and 0 710 respectively early volcanic rocks have a more primitive signature consistent with retention of a significant mantle component subsequent intrusions were derived predominantly from isotopically heterogeneous precambrian lower crust but probably also contain an undefined amount of mantle component individual complexes do not exhibit any consistent isotopic trends over time and unique types of source rocks are not indicated for productive magmas in contrast rare earth elements ree in several complexes display temporally systematic behavior progressively younger intrusions in a given complex follow a path of decreasing concentration of ree steepening profiles greater upward concavity in heavy ree profiles and changes in the eu anomaly from negative to either markedly less negative or positive the ree data from individual complexes suggest an increasing petrogenetic involvement of amphibole either in the restite of the source region or as a fractionating phase and similar paths of petrogenetic evolution in spite of chronologic and trace element evidence which argues against completely comagmatic development productive and barren intrusions cannot be clearly distinguished by the isotopic data but the systematic ree trends parallel increasing productivity of magmas in individual complexes models which reconcile isotopic variation systematic ree behavior protracted local but largely noncomagmatic magmatism and the increasing development of porphyry mineralization include 1 progressive metasomatism of the crustal component 2 increasing assimilation of amphibolitic crust by mantle basalts and 3 migration of crustal anatexis from deep anhydrous rocks to shallower amphibolites the relative importance of these processes cannot yet be clearly assessed from the data but a plausible metallogenic impact of each would be upon the concentration and possibly the composition of magmatic volatiles in the primary melts and or during subsequent fractionation in this light existing models which propose that the principal control upon intrusion productivity is a balance between crystal fractionation and the timing of saturation and release of magmatic hydrothermal fluids may be strongly influenced by processes operative either in their source regions or during their interaction with the crust initiation of such processes may be a response to abrupt changes in tectonic regime in the volcanic are environment

melt and fluid inclusions in hydrothermal veins the magmatic to hydrothermal evolution of the elatsite porphyry cu au deposit bulgaria the magmatic to hydrothermal transition in the late cretaceous elatsite porphyry cu au mo platinum group element deposit has been studied in a suite of samples with clear timing relations between porphyry dikes magmatic hydrothermal veins silicate melt inclusions in quartz veins fluid inclusion generations and ore minerals ore mineralization occurs late at temperatures 200 to 300 c below those of the early multistage interplay between magmatic and hydrothermal processes at near magmatic temperature pressure conditions crosscutting relations and petrography indicate that shortly after the intrusion of the earliest monzodioritic dikes fluids precipitated a first generation of granular quartz veins accompanied by potassic alteration the second vein generation with crystalline quartz textures and k feldspar alteration halos formed at the same time as the second granodioritic pulse of porphyry intrusions cathodoluminescence imaging of quartz growth textures reveals that the earliest fluid inclusions in the crystalline quartz veins are of intermediate density and 8 wt nacl equiv salinity probably trapped at near lithostatic pressures of 1 200 to 1 300 bars at near magmatic temperatures 730 c and implies a depth of 4 to 5 km depressurization led to phase separation indicated by a first generation of coexisting brine and vapor inclusions trapped at temperatures of 640 c and suprahydrostatic pressures of 920 bars a second quartz generation in crystalline quartz veins precipitated during progressive depressurization and hosts assemblages of coexisting brine vapor and silicate melt inclusions trapped at temperatures in excess of 600 c and suprahydrostatic pressures of 630 to 880 bars some open spaced quartz veins were filled with aplite during this stage field relations and geochemical evidence suggest that the aplites as well as the silicate melt inclusions in hydrothermal quartz veins represent volumetrically minor residual melts that evolved directly from granodiorite porphyries at the level of deposit formation and do not represent aliquots of metal supplying magma at depth fluid inclusions coexisting with the silicate melt inclusions are metal rich but these fluids predate sulfide precipitation and are therefore not the dominant fluids responsible for the cu au mineralization at elatsite melt fluid metal separation processes recorded in these co trapped silicate melt and fluid inclusions in vein quartz are small scale local phenomena and do not appear to be suited for understanding and quantifying metal segregation in the deeper source microthermometry data of fluid inclusions trapped during the later stages of the formation of the second quartz generation show further depressurization to 260 to 325 bars and cooling to 460 c representing a hot hydrostatic regime bornite chalcopyrite and magnetite seem to be slightly later precipitated at temperatures 460 c in separate veins or opened spaces of preexisting veins dissolution textures of the second quartz generation indicate a subsequent local redissolution of vein quartz most likely as a result of passing through a window of retrograde quartz solubility upon further cooling below 460 c the next economically most important chalcopyrite pyrite stage is largely devoid of quartz precipitation and is mostly expressed as paint veins due to the lack of fluid inclusions the temperature pressure conditions of formation of these veins could not be constrained the waning phase of hydrothermal activity is represented by a quartz carbonate zeolite stage formed at low temperature 145 c as indicated by microthermometry of fluid inclusions trapped in quartz from this stage laser ablation inductively coupled plasma mass spectrometry analyses of fluid inclusions show very high cu contents in early intermediate density fluid inclusions and in the first vapor inclusion generation followed by a drastic decrease in the second generation of vapor inclusions the decrease correlates with the appearance of anhydrite inclusions in the second quartz generation and may indicate that a lack of sulfur in these later vapor inclusions led to cu partitioning into the brine alternatively it is also possible that unlike early vapor inclusions the later vapor inclusions were not susceptible to postentrapment copper enrichment in accordance with recent experiments a progressive cu enrichment in the brine phase correlates well with depressurization prior to mineralization mass balance considerations based on analyzed fluid components and fluid phase relations indicate that brine was volumetrically minor and therefore likely stagnant but this may have prepared ore precipitation by accumulating cu stripped from ascending vapor

iron isotope systematics from the batu hijau cu au deposit sumbawa indonesia abstract this study examines the fractionation of iron isotopes as a reflection of processes that govern the co magmatic formation of a hydrothermal ore system of a classic porphyry copper deposit we present iron isotope analyses measured using multi collector icpms of magmatic intrusive rocks and coeval hypogene ore minerals from the batu hijau porphyry copper gold deposit in sumbawa indonesia isotopic analysis were made of the intrusive magmatic host rocks to the deposit ranging from sub volcanic andesite and quartz diorite to tonalite and of hypogene chalcopyrite bornite and magnetite ore mineral separates iron isotope values of andesite and quartz diorite range from 57fe 0 17 0 05 to 0 26 0 05 the more felsic differentiated dacite and tonalite have heavier iron isotope values 57fe 0 27 0 08 to 0 32 0 08 than the intermediate and mafic rocks heavy iron isotopes are positively correlated with sio2 and negatively correlated with mgo cao tio2 and v suggesting that crystallisation of clinopyroxene amphibole and magnetite is the primary control on isotopic evolution of the melt these isotopic trends are supported by thermodynamic rhyolite melts modelling of crystal fractionation using published mineral melt fractionation factors and demonstrate that the isotopic evolution of the batu hijau melts was controlled by crystal fractionation magnetite from the batu hijau ore deposit is isotopically heavier 57fe range from 0 24 0 14 to 0 74 0 14 than coexisting chalcopyrite from 0 62 0 04 to 0 16 0 05 and bornite from 0 72 0 23 to 0 08 0 03 consistent with theoretical fractionation factors derived from spectroscopy comparison of our mineral data with data from other deposits defines a range of 57fe values for hypogene chalcopyrite from porphyry copper deposits from 1 26 to 0 29 models of rayleigh type fractionation assuming an initial hydrothermal fluid composition which is isotopically light 57fe between 0 5 and 0 1 produces mineral compositions that match our analytical data the modelled isotope values are in agreement with experiments demonstrating that hypogene chalcopyrite has isotopic compositions reflecting the isotopic value of the hydrothermal fluid however hypogene chalcopyrite from this study is significantly lighter than values of chalcopyrite separates from the renison tin deposit which span a range of 0 28 0 06 to 1 32 0 06 we propose that the presence or absence of pyrrhotite influences the relative differences in 57fe values of chalcopyrite between porphyry copper and tin deposits because of its preference for isotopically light iron which in turn is controlled by both oxygen and sulfur redox conditions in the fluid

unidirectional solidification textures and their significance in determining relative ages of intrusions at the henderson mine colorado a variety of igneous textures displayed by stocks associated with the henderson molybdenite deposit are interpreted to result from unidirectional growth from the walls of magma chambers inward these igneous textures are present in layers and multilayered sequences consisting of crenulate quartz and feldspar pegmatites crenulate quartz dendritic alkali feldspar and quartz and dendritic and micrographic alkali feldspar quartz intergrowths minerals or intergrowths defining a layer within any one stock consistently terminate or branch inward away from the stock contacts the layers are separated by aplite or aplite porphyry and are most common in the apical and marginal parts of an individual stock layering generally parallels intrusive contacts differences in morphologies of phases among the various layers suggest changing conditions of growth from an undercooled melt and or aqueous solution changes in these physical and chemical conditions as the stock crystallized inward produced the observed textural and compositional layering unidirectional solidification textures can be used to determine the relative ages of individual stocks as well as the approximate orientation of stock contacts in the absence of other independent evidence unidirectional textures can also be used to indicate proximity to an intrusive contact these features are an invaluable aid in detailed mapping of multiple intrusion systems in which the units are compositionally identical or nearly identical

sulfur isotopic zonation in the cadia district southeastern australia exploration significance and implications for the genesis of alkalic porphyry gold copper deposits the alkalic porphyry gold copper deposits of the cadia district occur in the eastern lachlan fold belt of new south wales australia the district comprises four porphyry deposits ridgeway cadia quarry cadia hill and cadia east and two iron copper gold skarn deposits big cadia and little cadia almost 1 000 tonnes of contained gold and more than four million tonnes of copper have been discovered in these systems making cadia the world s largest known alkalic porphyry district in terms of contained gold porphyry gold copper ore at cadia is associated with quartz monzonite intrusive complexes and is hosted by central stockwork and sheeted quartz sulfide carbonate vein systems the cadia porphyry deposits are characterized by cores of potassic and or calc potassic alteration assemblages and peripheral halos of propylitic alteration with late stage phyllic alteration mostly restricted to fault zones hematite dusting is an important component of the propylitic alteration assemblage and has produced a distinctive reddening of feldspar minerals in the volcanic wall rocks around the mineralized centers sulfide mineralization is strongly zoned at ridgeway and cadia east with bornite rich cores surrounded by chalcopyrite rich halos and peripheral zones of pyrite mineralization the cadia hill and cadia quarry deposits have chalcopyrite rich cores and pyrite rich halos and cadia hill contains a high level bornite rich zone distinctive sulfur isotopic zonation patterns have been identified at ridgeway cadia hill and cadia east the deposit cores are characterized by low 34ssulfide values 10 to 4 consistent with sulfide precipitation from an oxidized sulfate predominant magmatic fluid at 450 to 400 c pyrite grains that occur in the propylitic alteration halos typically have 34ssulfide values near 0 there is a gradual increase in 34ssulfide values outwards from the deposit cores through the propylitic halos water rock interaction during propylitic alteration caused magmatic sulfate reduction and concomitant oxidation of ferrous iron bearing minerals resulting in enrichment of 34s in pyrite and also producing the distinctive reddened hematite rich alteration halos to the cadia deposits these results show that sulfur isotope analyses have potential applications in the exploration of alkalic porphyry style deposits with zones of depleted 34ssulfide values most prospective for high grade mineralization

geology of the post collisional porphyry copper molybdenum deposit at qulong tibet porphyry deposits are usually thought to form from subduction related calc alkaline magmas in magmatic arc settings although some porphyry deposits also occur in post collisional extensional settings the post collisional deposits remain poorly understood here we describe the igneous geology alteration mineralogy and mineralization history of qulong a newly discovered porphyry cu mo deposit in southern tibet that belongs to the post collisional class the deposit is associated with miocene monzogranite granodiorite intrusions and is hosted partly by jurassic andesitic dacitic volcanic rocks the deposit contains 7 1 mt cu and 0 5 mt mo metal the 19 5 ma granodioritic monzogranitic rongmucuola pluton with diorite enclaves is the earliest miocene intrusive unit it was intruded by a regularly shaped stock p porphyry and then thin dikes x porphyry of monzogranite at about 17 7 ma the main cu mo mineralization is associated with the p porphyry a barren diorite porphyry intruded the p and x porphyries around 15 7 ma petrologic trends of the intrusions suggest that the miocene intrusions have similar origins and probably formed by fractionation of a deeper magma chamber emplacement of miocene porphyries controlled by the qulong anticline is in direct response to the rapid uplift erosion of the gangdese arc batholiths in southern tibet miarolitic cavities and unidirectional solidification textures key evidence for volatile separation have been recognized in the p and x porphyries respectively early potassic alteration characterized by quartz k feldspar anhydrite pervades the p porphyry and rongmucuola pluton laterally this alteration grades into quartz biotite anhydrite k feldspar which affects all miocene intrusions except the latest dioritic porphyry wall rocks of rongmucuola pluton and jurassic andesitic dacitic volcanics within 1 1 5 km of the porphyries are dominated by pervasive potassic alteration an outer halo of propylitic alteration epidote chlorite calcite extends up to 2 km away from the deposit feldspar destructive alteration sericite chlorite clay minerals has overprinted most of the potassic and part of the propylitic alteration the alteration is strongly pervasive in the interior of the porphyry bodies and occurs as vein halos away from the porphyry bodies the earliest quartz k feldspar alteration and veins are barren whereas approximately 60 of the cu reserves is associated with slightly later quartz biotite anhydrite alteration barren assemblages are related to irregular quartz k feldspar anhydrite veins which are truncated by the x porphyry cu sulfide bearing assemblages are associated with discontinuous chalcopyrite biotite and continuous quartz anhydrite chalcopyrite molybdenite veins deposition of cu mo with abundant anhydrite occurred during or between emplacement of closely related porphyries from high temperature magmatically derived fluids and was probably caused by the disproportionation of so

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

fluid inclusion and h o c isotope geochemistry of the yaochong porphyry mo deposit in dabie shan china a case study of porphyry systems in continental collision orogens the yaochong porphyry mo deposit in xinxian county henan province china is located in the hong an terrane that is the western part of the dabie orogen the dabie orogen is part of a 1 500 km long triassic continental collision belt between the north china block and the south china block four types of vein are present paragenetically from early to late they are as follows stage 1 quartz k feldspar pyrite magnetite vein stage 2 quartz k feldspar molybdenite pyrite vein stage 3 quartz polymetallic sulfides k feldspar vein and stage 4 quartz carbonate fluorite vein four compositional types of fluid inclusion pure co2 co2 bearing aqueous and solid bearing are present in quartz from the first three stages only low salinity aqueous fluid inclusions occur in quartz from the last stage all the estimated salinities are 13 1 wt nacl eq and no halite crystals were identified homogenization temperatures for the fluid inclusions from stages 1 to 4 are in the ranges of 262 501 202 380 168 345 and 128 286 c respectively and estimated depths decrease from 6 9 to 8 9 km through 6 2 7 2 to 4 7 km quartz separates from the veins yielded a 18o value of 7 7 11 2 corresponding to 18oh2o values of 1 3 to 6 9 using temperature estimates from fluid inclusion data dh2o values of fluid inclusion vary from 80 to 55 and 13cco2 from 2 3 to 2 7 suggesting that the ore fluids evolved from magmatic to meteoric sources we conclude that the ore forming fluid system at yaochong was initially high temperature high salinity and co2 rich and then progressively evolved to co2 poor lower salinity and lower temperature by mixing with meteoric water which results in ore precipitation

sodium calcium metasomatism chemical temporal and spatial relationships at the yerington nevada porphyry copper deposit tilting associated with extensional tectonics has exposed 1 800 m of continuous palcovertical relief through the jurassic age yerington porphyry copper deposit the rarely observed root zones of a porphyry system are characterized at yerington by sodium calcium metasomatism the principal hydrothermal reactions involve the replacement of primary k feldspar by oligoclase and of primary biotite by actinolite copper has been removed sodic calcic alteration developed at deep intrusive contacts nearly simultaneously with potassic alteration and copper mineralization at shallow intrusive contacts the reactions accompanying potassic alteration are the reverse of those accompanying sodic calcic alteration plagioclase reacted to form k feldspar hornblende reacted to form biotite the potassic and sodic calcic alteration couplet principally accompanied each of two separate intrusive events 1 luhr hill granite stock and associated porphyry dikes and 2 walker river granite porphyry dikes the younger walker river intrusion was emplaced at slightly deeper levels than the older luhr hill complex vertically stacked and partially superimposed alteration and mineralization patterns resulted from differences in depth and in timing of emplacement at lower temperatures late sodic alteration was superimposed on early sodic calcic alteration at deeper levels in the system whereas late quartz sericite pyrite alteration was superimposed on potassic alteration at higher levels sodic alteration is characterized by the replacement of k feldspar by albite and of biotite by chlorite copper deposited during potassic alteration was remobilized the transition to lower temperature alteration is associated only with the walker river intrusion the hydrothermal system associated with the emplacement of the luhr hill complex had not evolved to lower temperature assemblages prior to emplacement of the walker river dikes phase equilibria and geologic reconstruction of depth of emplacement suggest that temperatures during early sodic calcic alteration were limited to the range of 360 degrees to 480 degrees c at pressures between 300 and 800 bars late sodic alteration took place at similar pressures but at temperatures less than 360 degrees c nearly simultaneous development of potassic and sodic calcic alteration resulted from the flow of fluids away from intrusions at shallow levels potassic alteration and from the flow of fluids toward intrusions at deeper levels sodic calcic alteration because k na and na ca activity ratios of a fluid in equilibrium with granitic rocks decrease with decreasing temperature cooling of high temperature fluids can generate potassic alteration and heating of fluids to high temperatures can generate sodic or sodic calcic alteration

the ridgeway gold copper deposit a high grade alkalic porphyry deposit in the lachlan fold belt new south wales australia ridgeway is a high grade gold copper porphyry deposit 54 mt at 2 5 g t au and 0 77 cu related to an alkalic intrusive complex of monzonitic composition the deposit occurs within the cadia district of new south wales australia which consists of a cluster of four late ordovician gold copper porphyry deposits and two iron copper gold skarn deposits with a combined gold resource in excess of 574 metric tonnes t the deposits lie on a 7 km long northwest oriented corridor of alteration and mineralization transverse to the axis of the postulated volcanic arc alteration and mineralization at ridgeway are zoned around a vertically attenuated intrusive complex of monzodioritic to quartz monzonitic composition distinct styles of veining and alteration are related to different intrusive phases of the monzonite complex with the intensity of alteration and grade of mineralization decreasing from early to late mineral intrusions early mineral intrusions are associated with intense actinolite magnetite biotite calc potassic alteration and up to four stages of high grade quartz magnetite sulfide veining bornite is the most abundant sulfide formed during early stage alteration and correlates well with gold moderate to weak intensity orthoclase biotite plus or minus magnetite potassic alteration accompanies the inter and late mineral intrusions this alteration being associated with chalcopyrite and pyrite rich quartz orthoclase veins propylitic and sodic albite pyrite alteration assemblages are peripheral to and locally overprint the potassic alteration phyllic alteration is restricted to the margins of late stage faults the fluid inclusion assemblage comprises one and two salt bearing brine inclusions in addition to aqueous liquid vapor inclusions of low to moderate salinity no low density vapor rich inclusions are present indicating that the fluids from which the quartz veins precipitated did not enter the liquid vapor field of the h2o nacl system the brine inclusions undergo final homogenization to liquid via halite dissolution this phenomenon in addition to the absence of low density vapor inclusions suggests that the mineralizing fluids at ridgeway were nonboiling hypersaline brines that exsolved directly from the crystallizing magma the presence of mineralized aplitic vein dikes and comb quartz layering are interpreted to indicate that the early and transitional stages of mineralization at ridgeway formed at the transition between magmatic and hydrothermal conditions

the tectonic significance of ordovician magmatism in the eastern lachlan fold belt abstract the shoshonitic rock series is a suite of igneous rocks derived from the mantle and containing high potassium plus low abundances of high field strength elements it is commonly associated with calcalkaline igneous rocks but in most modern examples a contemporary active subduction zone is not present mantle derived shoshonitic magmatism in the lachlan fold belt commenced in the early ordovician and terminated at the end of the ordovician when it was replaced by tholeiitic magmatism and the onset of wholesale melting of the lower to middle crust associated calcalkaline igneous rocks are insignificant the shoshonites are widely distributed across the eastern part of the fold belt in a series of discontinuous belts and volcanic centres the largest of which is the orange wellington belt extending from east of cowra to dubbo the broad geographical distribution is not typical of the curvilinear belts of volcanics associated with subduction zones and would be even greater if the intervening basins or troughs were unfolded all rocks analyzed to date are either clearly shoshonitic or show chemical features that indicate shoshonitic affinities prior to alteration and metamorphism in some areas lavas rich in olivine and clinopyroxene potassic trachybasalts dominate in others the more evolved plagioclase rich shoshonites are most abundant it is suggested that the ordovician magmatism was not accompanied by coeval subduction as has been generally assumed more likely the lithospheric mantle beneath the lachlan fold belt was modified during an earlier subduction event associated with the assembling of the basement blocks recognized from granite studies the cause of melting in the ordovician may be related to lithospheric heating or overturning prior to the upwelling of unmodified asthenosphere the hot 1200 c asthenosphere was the source for the silurian tholeiites and provided conductive heat for the melting of the lower to middle crust

direct evolution of brine from a crystallizing silicic melt at the questa new mexico molybdenum deposit molybdenum mineralization in the southwest orebody at the questa deposit is associated with crystallization of aplite porphyry explosive brecciation and exsolution of magmatic hydrothermal fluids quartz k feldspar fluorophlogopite and molybdenite precipitated from exsolving aqueous fluids and cemented aplite porphyry and andesite wall rock clasts forming a magmatic hydrothermal breccia ore fluid inclusions in quartz in the breccia matrix trapped aqueous fluids that transported and precipitated molybdenum two fluid inclusion populations associated with molybdenite mineralization were identified the largest population commonly contains liquid vapor halite sylvite and one or more opaque daughter crystals these inclusions homogenize between 200 degrees and 500 degrees c and have a prominent mode at 360 degrees to 400 degrees c salinities vary from 31 to 57 wt percent nacl equiv low first ice melting temperatures suggest that additional fluid components possibly calcium or magnesium chlorides may be present approximately 80 percent of these inclusions homogenize by halite dissolution phase equilibria constraints require that these inclusions trapped fluids in the vapor absent field the remaining saline inclusions homogenize to liquid at temperatures above halite dissolution temperatures significantly the saline fluid did not coexist with a low density aqueous fluid a second population of inclusions contains fluids with salinities of 2 7 to 25 0 wt percent nacl equiv and homogenizes by vapor bubble disappearance vapor bubble expansion or critical behavior textural relationships and phase behavior during microthermometry indicate that these inclusions constitute a single population which formed as pressure and temperature fluctuated at near critical conditions pressure changes related to brecciation followed by crystallization and system resealing produced the observed fluids saline fluids were trapped as the system sealed following a major brecciation event these high salinity fluids were produced as the melt under pressure that increased from hydrostatic to lithostatic partitioned increasing amounts of chlorine into the exsolving aqueous fluid renewed fracturing and abrupt pressure decrease to hydrostatic conditions reduced the mass of chlorine partitioning to the exsolving fluid lower salinity fluids exsolved at near critical conditions and were trapped by inclusions that homogenize to liquid to vapor or by critical behavior the lack of cogenetic liquid and vapor rich fluid inclusions and phase equilibria constraints indicate that high salinity fluids or 57 wt nacl equiv were generated directly by the crystallizing magma and were not a product of aqueous fluid immiscibility

fluid inclusion study of the wunugetu cu mo deposit inner mongolia china hydrothermal alteration and mineralization at the wunugetu porphyry cu mo deposit china include four stages i e the early stage characterized by quartz k feldspar and minor mineralization followed by a molybdenum mineralization stage associated with potassic alteration copper mineralization associated with sericitization and the last pb zn mineralization stage associated with carbonation hydrothermal quartz contains three types of fluid inclusions namely aqueous w type daughter mineral bearing s type and co2 rich c type inclusion with the latter two types absent in the late stage fluid inclusions in the early stage display homogenization temperatures above 510 c with salinities up to 75 8 wt nacl equivalent the presence of s type inclusions containing anhydrite and hematite daughter minerals and c type inclusions indicates an oxidizing co2 bearing environment fluid inclusions in the mo and cu mineralization stages yield homogenization temperatures of 342 508 c and 241 336 c and salinities of 8 6 49 4 and 6 3 35 7 wt nacl equivalent respectively the presence of chalcopyrite instead of hematite and anhydrite daughter minerals in s type inclusions indicates a decreasing of oxygen fugacity in the late stage fluid inclusions yield homogenization temperatures of 115 234 c and salinities lower than 12 4 wt nacl equivalent it is concluded that the early stage fluids were co2 bearing magmatic in origin and characterized by high temperature high salinity and high oxygen fugacity phase separation occurred during the mo and cu mineralization stages resulting in co2 release oxygen fugacity decrease and rapid precipitation of sulfides the late stage fluids were meteoric in origin and characterized by low temperature low salinity and co2 poor

40 ar 39 ar and u pb geochronology of the goonumbla porphyry cu au deposits new south wales australia the 40 ar 39 ar technique of k ar dating has been used to determine the age of hydrothermal sericite associated with mineralization in the goonumbla porphyry copper gold deposits lachlan fold belt new south wales australia the 40 ar 39 ar age spectra from goonumbla hydrothermal sericite indicate that vein and groundmass potassic and phyllic alteration were broadly contemporaneous at 439 2 or 1 2 ma 1sigma the 40 ar 39 ar dates obtained from hydrothermal alkali feldspar are considerably younger than those from coeval hydrothermal sericite u pb dating of magmatic zircons by ion microprobe yields an age of 438 5 or 3 6 ma 1sigma for the nelungaloo volcanics which underlie the mineralized goonumbla sequence providing a maximum age for mineralization and suggesting that the two successions are largely coeval the 40 ar 39 ar age spectra obtained in this investigation from fine grained sericite illustrate the amenability of this hydrothermal phase to dating by the 40 ar 39 ar technique and suggest that there is considerable potential for application of this dating method to phanerozoic ore deposits the close agreement in ages between the 40 ar 39 ar and u pb results gives confidence in the application of both dating techniques to altered paleozoic rocks

quartz vein emplacement mechanisms at the e26 porphyry cu au deposit new south wales porphyry cu au mo deposits are characterized by numerous fracturing events brittle fracture of mineralized intrusions and the surrounding host rocks is a consequence of hydraulic breakage caused by the interplay of the changing physiochemical properties of magmatic fluids and or the local tectonic regime we have mapped more than 1 400 quartz sulfide vein sets at the ordovician endeavour 26 north e26 deposit central new south wales in order to constrain the processes influencing fracture development around small 200 m porphyritic intrusions veins from intermediate levels in the e26 deposit define complicated patterns within 10 m of the porphyritic intrusions whereas more systematic patterns occur up to 50 m from the intrusive contact the outer parts of the ore deposit are characterized by quartz veins with orientations of 340 and subordinate orthogonal sets of bisecting veins at 240 and 290 the data show a broad range of vein orientations that define a conical distribution around a vertical axis there is a rare subset of near horizontal veins that formed early relative to the main stage of ore bearing vein emplacement many quartz veins exhibit fault displacements at both micro and macroscopic scales and fabrics including serrate fractures slickenlines and asymmetric fiber trails the distribution of veins suggests that the dominant fracture array developed perpendicular to the direction of bulk finite extension but significant vein dilation also occurred in orientations with a component of shear strain we propose a physical model that combines intrusion driven hydraulic fracturing into a preexisting fracture mesh to help explain the observed vein patterns and to better link fracture development and vein emplacement hydraulically driven deformation was important locally at e26 contributing to the formation of the irregular fracture stockwork immediately adjacent to the small intrusive bodies the more predictable vein patterns that occur away from the porphyritic intrusions require part of the hydraulically driven extension to have reactivated the existing fracture mesh parts of this more systematic geometry including the occurrence of flat veins are probably related to the emplacement of larger 10 km diameter magma bodies adjacent to e26 with doming causing the subordinate fracture arrays including the gross conical distribution fluctuating fluid pressures combined with hydraulically driven extension caused dilation of preexisting and synmineralization fractures and superposition of veins with similar orientations vein patterns suggest that the regional stress state that existed prior to or synchronously with porphyry ore deposit formation strongly influenced vein orientation to within tens of meters away from the mineralizing intrusions fractures that localized ore in the e26 porphyry deposit developed in response to the infiltration of fluid batches including magma and magmatic hydrothermal fluids into a regional deformation environment

controls on skarn mineralization and alteration at the cadia deposits new south wales australia the cadia fe cu au skarns in eastern new south wales australia are associated with the late ordovician shoshonitic cadia intrusive complex which hosts the largest mineralized intrusion related system in eastern australia both the big cadia and little cadia skarns are developed within a 40 m thick volcanic derived calcareous sandstone and adjacent units which represent the most important control on skarn formation the ore zones have undergone postore displacement along steeply dipping predominantly reverse faults without significant remobilization of ore chalcopyrite and minor native gold formed in intimate association with epidote chlorite quartz calcite and in the interstices of bladed hematite and magnetite aggregates the age of the au cu mineralizing event at cadia is constrained by 40ar 39ar dating of accompanying muscovite at 438 2 4 2 ma 1 gold to copper ratios within the skarns are generally lower than for porphyry au cu deposits at cadia particularly the high tonnage low grade cadia hill deposit ore and calc silicate gangue mineralogy are similar to other oxidized fe cu au skarns associated with porphyry deposits iron skarn at big cadia occurs several hundred meters distant from the margin of a mineralized intrusion of quartz monzonite porphyry magmatic dominated fluids reacted with carbonate in the wall rocks and produced classic skarn zonation over an 800 m interval from the intrusive contact located at cadia quarry toward more distal environments at big cadia skarn zonation comprises 1 proximal garnet pyroxene 2 intermediate garnet pyroxene scapolite and 3 distal fe au cu skarn alteration of noncalcareous metavolcanic rock units fine grained pyroxene phyric volcanic rocks and volcaniclastic rocks adjacent to the mineralizing quartz monzonite porphyry includes hydrothermal biotite k feldspar quartz hornfels and magnetite quartz biotite hornfels gold copper mineralization formed adjacent to garnet bearing veins peripheral to the main garnet rich zone indicating that garnet forming fluids carried the ore metals at little cadia and cadia east mineralization and skarn zonation similar to big cadia developed above additional intrusions of quartz monzonite porphyry retrograde hydrous alteration replaced much of the prograde garnet dominant mineralogy at cadia with the strongest overprint at little cadia the styles and distribution of alteration and mineralization suggest that the big cadia skarn formed from fluids that migrated laterally within calcareous units from strongly altered quartz monzonite phases of the cadia intrusive complex at cadia quarry at little cadia skarn formation was probably related to fluids derived from the cadia intrusive complex that migrated vertically and laterally within permeable calcareous units structural controls were important in focusing fluids and localizing the emplacement of late mineralizing phases of the cadia intrusive complex

introduction to the special issue devoted to alkalic porphyry cu au and epithermal au deposits this special issue is devoted to alkalic porphyry cu au and epithermal au deposits and focuses on two regions british columbia canada fig 1 and the southwest pacific region australia and papua new guinea fig 2 the special issue commences with a review of triassic to jurassic metallogeny of british columbia logan and mihalynuk 2014 then documents ore zones from several alkalic deposits central zone galore creek micko et al 2014 southwest zone galore creek byrne and tosdal 2014 northeast zone mt polley pass et al 2014 lower main zone lorraine bath et al 2014 mt milligan jago et al 2014 and provides a comprehensive overview of mineralization in the lorraine district devine et al 2014 four contributions document alkalic porphyry and epithermal deposits in new south wales northparkes harris and holcombe 2014 endeavour 41 zukowski et al 2014 endeavour 42 henry et al 2014 cadia harris et al 2014 the final contribution uses the results of mapping and core logging in order to resolve the physical volcanology and hydrothermal evolution of the giant ladolam alkalic epithermal gold deposit papua new guinea blackwell et al 2014 eight of these papers are the outcome of a collaborative project between the mineral deposit research unit mdru at the university of british columbia the australian research council s centre for excellence in ore deposits codes at the university of tasmania and industry partners the remaining are based on work by the british columbia geological survey logan and mihalynuk 2014 teck resources ltd devine et al 2014 a research collaboration between codes and newcrest mining ltd harris et al 2014 and the university of queensland harris and holcombe 2014 fig 1 terrane map and location of selected alkalic porphyry cu au deposits of british columbia deposits that are the subject of

endeavour copper gold porphyry deposits northparkes new south wales intrusive history and fluid evolution four economic porphyry copper gold deposits endeavour 22 26 27 and 48 occur within the late ordovician goonumbla volcanic complex of central west new south wales australia together these deposits have a combined ore reserve of 63 6 million metric tons mt at 1 1 percent copper and 0 5 g t gold mineralization is centered in narrow pipelike quartz monzonite porphyry qmp intrusive complexes we have recognized at least nine intrusive phases within the endeavour deposits these are in order of emplacement as follows a premineral equigranular monzodiorite early mineral equigranular to weakly porphyritic biotite quartz monzonite bqm stocks and dikes synmineral k feldspar qmp k qmp pipes and dikes late mineral augite biotite k feldspar qmp ka qmp intrusions and biotite qmp b qmp dikes and postmineral basaltic trachyandesite dikes augite monzonite porphyry dikes and basaltic dikes early stage biotite magnetite and propylitic alteration of the host volcanic rocks and k feldspar alteration of the bqm occurred at each deposit during the intrusion of the bqm stocks and early mineral b qmp dikes transitional stage unidirectional solidification textures and other related anisotropic textures formed mostly during the emplacement of k qmp and ka qmp intrusions main stage sulfide mineralization at all four deposits is spatially and temporally associated with the k qmp and to a lesser extent ka qmp intrusions and their associated k feldspar and sericite hematite alteration assemblages and is characterized by multiple generations of stockwork and sheeted quartz k feldspar bornite chalcopyrite and gold bearing veins late stage sericite quartz copper sulfide carbonate hematite alteration and vein assemblages formed prior to the emplacement of the postmineral intrusions weak to moderate postmineral propylitic alteration assemblages were the last alteration event related to the qmp intrusive complexes intrusive activity and associated biotite alteration occurred between 446 and 437 ma based on 40ar 39ar analyses of biotite and hornblende based on microthermometric analyses of fluid inclusions from early transitional main and late stage veins the endeavour deposits formed at depths between 1 000 and 1 700 m below the paleosurface with a lithostatic pressure regime prevailing throughout the early transitional and main stages and near hydrostatic pressures during the late stage sericitic events the first three stages were dominated by high temperature 460 550 c magmatic hydrothermal brines with salinities of 55 to 60 wt percent nacl kcl equiv although the late stage fluids were cooler 350 400 c and less saline 40 wt nacl equiv their compositions are consistent with the magmatic hydrothermal origin indicated by previous oxygen and hydrogen isotope studies confirming that the endeavour porphyry deposits are representatives of the orthomagmatic end member of the porphyry continuum

chlorite and epidote mineral chemistry in porphyry ore systems a case study of the northparkes district new south wales australia propylitic alteration characterized by the occurrence of chlorite and epidote is typically the most extensive and peripheral alteration facies developed around porphyry ore deposits however exploration within this alteration domain is particularly challenging commonly owing to weak or nonexistent whole rock geochemical gradients and the fact that similar assemblages can be developed in other geologic settings particularly during low grade metamorphism we document and interpret systematic spatial trends in the chemistry of chlorite and epidote from propylitic alteration around the e48 and e26 porphyry cu au deposits of the northparkes district new south wales australia these trends vary as a function of both distance from hydrothermal centers and alteration paragenesis the spatial trends identified in porphyry related chlorite and epidote at northparkes include 1 a deposit proximal increase in ti as sb and v in epidote and ti in chlorite 2 a deposit distal increase in co and li in chlorite and ba in epidote and 3 a pronounced halo around deposits in which mn and zn in chlorite as well as mn zn pb and mg in epidote are elevated chlorite al si ratios and epidote al fe ratios may show behavior similar to that of mn zn or may simply decrease outward and v and ni concentrations in chlorite are lowest in the peak mn zn zone in comparison to porphyry related samples chlorite from the regional metamorphic assemblage in the district contains far higher concentrations of li ca ba pb and cu but much less ti similarly metamorphic epidote contains higher concentrations of sr pb as and sb but less bi and ti these chlorite and epidote compositional trends are the net result of fluid mineral partitioning under variable physicochemical conditions within a porphyry magmatic hydrothermal system they are most easily explained by the contribution of spent magmatic derived ore fluid s into the propylitic domain it is envisaged that such fluids experience progressive cooling and reduction in 119891 s2 during outward infiltration into surrounding country rocks with their ph controlled by the extent of rock buffering experienced along the fluid pathway

quantifying the three dimensional shapes of spheroidal objects in rocks imaged by tomography abstract the shapes of objects in rocks are sometimes measured through tomographic sections either physical sections or virtual x ray computed tomography approximation of these objects as ellipsoids is often sufficient in these analyses here we present an easily implemented algorithm to best fit an ellipsoid to a set of n points n 9 distributed on the surface of a spheroidal object observed in tomographic sections the method is demonstrated on x ray computed tomography data of 90 chondrules in a cr2 chondrite by averaging the ellipsoids for all the objects measured in a rock one can then readily describe its fabric by an average ellipsoid and if that average ellipsoid is interpreted as a strain ellipsoid and assuming all objects have undergone the same strain each object can be retro deformed and the inferred initial population of objects studied