multistage intrusion brecciation and veining at el teniente chile evolution of a nested porphyry system the el teniente copper molybdenum deposit is hosted by the late miocene teniente mafic complex a largely subvolcanic package of primarily basaltic andesite porphyry sills and stocks that were emplaced within the mid late miocene farellones formation in the late miocene pliocene a series of intermediate felsic plutons were intruded into the teniente mafic complex these are spatially associated with magmatic hydrothermal breccias and multiple vein types that form individual mineralized complexes here we present detailed observations on mineralogy textures and intrusion breccias and vein crosscutting relationships to constrain the nature and relative timing of magmatic and hydrothermal events our revised classification defines 13 vein types divided lilt three main stages 1 premineralization biotite and or k feldspar quartz anhydrite albite magnetite actinolite epidote veins that formed prior to emplacement of mineralized intrusions and breccias 2 main mineralization stage veins that grade from gangue dominated quartz anhydrite veins potassic alteration halos into sulfide dominated veins with phyllic alteration halos and 3 late mineralization veins containing sulfosalts five breccia types have been observed in the deposit typically forming individual vertically zoned complexes spatially associated with individual intrusions and overlapping in time i igneous cemented breccias 2 k feldspar cemented breccias 3 biotite cemented breccias 4 anhydrite cemented breccias and 5 tourmaline cemented breccias breccia cements display 1 similar paragenetic evolution to main mineralization stage veins indicating a close genetic link between them a distinction can be made between early premineralization vein types types 1 2 that represent veins formed possibly deposit wide prior to emplacement of intrusion breccia complexes late pre and main mineralization vent types types 3 8 which are interpreted to reflect the repeated cycle of fluid release associated with each mineralized intrusive complex and late mineralization vein types types 9 10 that represent it single event linked to the emplacement of the braden breccia pipe the geologic evidence indicates a close spatial and temporal relationship between emplacement of shallow felsic intermediate pipelike intrusions and the development of igneous mid mineralized magmatic hydrothermal breccias and vein halos the magmatic hydrothermal transitions observed in these complexes indicate that the deposit formed from a series of localized pulses of magmatic hydrothermal activity which followed rather similar evolution paths single deposit wide models of fluid evolution and mineralization are therefore inappropriate we conclude that el teniente represents a nested but otherwise rather typical porphyry cu mo system unusual only in thia the teniente mafic complex pi is it particularly efficient physical trap in terms of pervasive fracturing during intrusion of magmatic hydrothermal breccia complexes and its an effective chemical trap for deposition of sulfides the overlapping of mineralized envelopes from successive fertile intrusions and the absence of barren intermineral porphyries resulted in its unusual size and high hypogene grades

subgrain scale decoupling of re and 187os and assessment of laser ablation icp ms spot dating in molybdenite abstract reproducibility of re os molybdenite ages depends on sample size and homogeneity suggesting that re and os are decoupled within individual molybdenite crystals and do not remain spatially linked over time in order to investigate the re os systematics of molybdenite at the subgrain micron scale we report la icp ms re os ages for an archean molybdenite crystal from aittojarvi finland analyzed in situ in a white aplite matrix a related aittojarvi molybdenite a996d in the form of a very fine grained mineral separate is used as one of our in house ntims standards and thus its age of 2760 9 ma is well established measurements of 187 re 187 os 185 re on micron scale spots along 200 m traverses across the crystal yield a wide range of ages demonstrating that in this case microsampling of molybdenite does not produce geologically meaningful ages experimentation with mineral separations and sample size over a 7 yr period predicted that this would be the outcome we suggest that 187 os is more likely to be the mobile species based on its charge and ionic radius and that 187 os becomes decoupled from parent 187 re with time on the micron and larger scale incompatible charge and ionic radius for os ions formed during reduction of molybdenite forming fluids may explain the widely observed absence of common initial os in molybdenite geologically accurate ages for molybdenite can only be obtained for fully homogenized crystals or crystal aggregates so that any post crystallization 187 re 187 os decoupling is overcome a growing number of geologically accurate id ntims 187 re 187 os ages for homogenized molybdenite suggest that postcrystallization mobility of radiogenic 187 os must be limited to within the molybdenite mineral phase we suggest that radiogenic 187 os may be stored in micron scale dislocations kink bands and delamination cracks produced by deformation and that the unusual structure and deformation response of molybdenite results in an increased chemical stability in this mineral migration of 187 os into adjacent silicate phases is highly unlikely but other contacting sulfides may take in os in an example from a proterozoic skarn deposit at pitkaranta western russia we demonstrate minor loss of radiogenic 187 os from molybdenite and a corresponding gain in adjacent chalcopyrite such that the molybdenite age is not perceptibly disturbed whereas the resulting chalcopyrite ages are impossibly old therefore it is unadvisable to perform re os analytical work on any sulfide in contact or intimate association with molybdenite in addition to large errors in the age if the isochron method is employed initial 187 os 188 os ratios could be erroneously high leading to seriously errant genetic interpretations

ages and petrogenesis of the late triassic andesitic rocks at the luerma porphyry cu deposit western gangdese and implications for regional metallogeny abstract the tibetan plateau is one of the most significant cu poly metallic mineralization regions in the world and preserves important information related to subductional and collisional porphyry cu mineralization this study investigates a new occurrence of cu mineralization related andesitic porphyries in the western domain of the gangdese magmatic belt and assesses its petrologic zircon u pb geochronology whole rock chemistry and sr nd hf pb isotope data zircon u pb dating of three ore related porphyries yields crystallization ages of 212 211 ma these ages are consistent with previous molybdenite re os dating indicating a late triassic magmatic and cu mineralization event in the western gangdese magmatic belt nb ta and ti depletion th and lree enrichment and high la yb and th yb ratios in addition to high u yb ratios from zircons suggest that the magma was generated in an active continental arc setting the porphyries have radiogenic isotopic compositions with 87sr 86sr i 0 70431 0 70473 end t 1 1 to 3 8 207pb 204pb i 15 601 15 622 and 208pb 204pb i 38 450 38 693 as well as high positive zircon ehf t values from 6 2 to 10 6 mean value 8 3 corresponding to model ages tdm ranging from 509 ma to 819 ma mean 646 ma this suggests that the andesitic magmatism was dominantly sourced from depleted mantle materials that were modified by subducted oceanic sediment derived melts during the subduction of the neo tethys ocean the mineralization related porphyries contain amphibole and epidote as well as high whole rock fe2o3 feo and zircon ce4 ce3 ratios suggesting hydrous and highly oxidized parent magmas considering the existing cu mineralization and highly oxidized magma of the well preserved triassic andesitic igneous rocks in the western gangdese belt the subduction related continental arc magma system is favorable for subduction related porphyry cu deposits the existence of luerma porphyry mineralization demonstrates that there are at least five generations of porphyry cu mo au mineralization in the gangdese magmatic belt which advances the timeframe of porphyry mineralization to the late triassic

re os and u pb geochronology of the clear creek dublin gulch and mactung deposits tombstone gold belt yukon canada absolute timing relationships between plutonism and mineralization new re os molybdenite and u pb zircon dates from deposits of the tombstone gold belt provide direct timing constraints for sulphide mineralization and crystallization of spatially associated plutons at clear creek re os molybdenite dates 93 6 0 3 to 92 4 0 4 ma are in excellent agreement with the host intrusion u pb zircon age 92 3 0 3 ma consequently we propose the nominally younger existing 40 ar 39 ar hydrothermal mica ages 91 7 0 4 and 90 0 0 3 ma for clear creek are a result of slow cooling at dublin gulch the re os molybdenite date 93 2 0 3 ma for a late stage vein is nominally younger than the host intrusion u pb zircon age 94 0 0 3 ma in agreement with the deposits paragenesis the u pb zircon date 92 1 0 2 ma for the mactung pluton which lies adjacent to the w skarn has a younger age than the re os molybdenite dates 97 5 0 5 ma fluid inclusion geochemical data for ore fluid indicate a magmatic origin for the w skarn however the u pb and re os age data suggest that the exposed mactung stock is not the source of ore fluid for the w skarn and that the progenitor pluton for ore fluid is unknown the robust age constraints obtained for mineralization and magmatism in this study are in accord with the hypothesis that these deposits are intrusion related ore systems the results are also in agreement with previous studies demonstrating that the re os molybdenite chronometer can provide accurate and precise dates for the timing of metallic mineralization with rigorous sampling protocol

re os geochronology and systematics in molybdenite from the endako porphyry molybdenum deposit british columbia canada precise re os molybdenite ages for the endako porphyry molybdenum deposit and the nithi mountain occurrence british columbia canada yield new information on the timing of molybdenite deposition three episodes of mineralization are indicated 1 154 ma 2 148 to 146 ma and 3 145 ma re os dates agree well with new u pb and 40 ar 39 ar data from granitoids of the nithi phase 155 2 1 5 ma the endako phase 148 4 1 5 ma and a preore dike 147 4 0 6 ma and the casey phase 145 1 0 2 ma plus hydrothermal biotite 144 5 0 75 ma villeneuve et al 2001 the excellent correlation between the re os dates from molybdenite and the ages of granitoids from the area indicates a direct genetic relationship between these plutons and molybdenite mineralization these re os data also provide further insight into the systematics and robustness of re os in molybdenite the endako molybdenum deposit is the product of two episodes of mineralization both associated with moderate salinity 5 15 wt nacl equiv and high temperature 440 c fluids a third low temperature 190 300 c hydrothermal event is associated with eocene faulting selby et al 2000 the clear distinction between two of the re os molybdenite dates in the deposit and the close agreement of these dates to the ages of granitoid intrusions suggest that the re os system in molybdenite is not reset by high temperature 440 c moderate salinity hydrothermal fluids in contrast magmatic biotite in a 147 ma preore dike has a 40 ar 39 ar age of 145 ma identical to the age of the hydrothermal biotite indicating that 440 c fluids reset the ar ar system in biotite hence we interpret that the re os isotope system in molybdenite is resistant to resetting by high temperature fluids 440 c in contrast to the 40 ar 39 ar system in biotite the re os system in molybdenite is also unaffected by postore hydrothermal fluids these data show that molybdenite can provide critical information in understanding sulfide mineral deposition in ore systems which is not recorded by other isotopic systems in alteration minerals

himalayan cu mo au mineralization in the eastern indo asian collision zone constraints from re os dating of molybdenite we present new re os molybdenite age data on three porphyry cu mo au deposits yulong machangqing and xifanping these deposits are associated with the himalayan adakitic magmatism that occurred in a continental collision environment controlled by large scale cenozoic strike slip faults in the eastern indo asian collision zone three distinct episodes of cu mo au mineralization are recognized at yulong re os isotopic data of four molybdenite samples from sulfide quartz veins in the quartz sericite alteration zone yield an isochron with an age of 40 1 1 8 ma 2 coincident to a zircon sensitive high mass resolution ion microprobe shrimp age of 40 9 0 1 ma for the host monzogranite the molybdenite re os dates together with k ar rb sr u pb and 40ar 39ar dates on the pre and intra ore porphyries suggest that cu mo au mineralization formed during the late stage 40 ma of regional porphyry magmatism but hydrothermal activity probably lasted to at least 36 ma at machangqing molybdenite re os data from the k silicate and quartz sericite alteration zones yield an isochron with an age of 35 8 1 6 ma 2 which is identical to the zircon shrimp and bulk rock rb sr ages 35 36 ma of the host granite but older than bulk rock k ar dates 31 32 ma for associated au bearing quartz syenite with advanced argillic alteration at xifanping five molybdenite samples from the k silicate alteration zone yield the youngest re os isochron age in the area at 32 1 1 6 ma 2 the re os molybdenite dates here are younger than k ar ages 33 5 34 6 for hydrothermal biotite and actinolite there is a positive correlation between the absolute age of the deposits and their cu and au reserves in the eastern indo asian collisional zone episodic stress relaxation probably caused multiple magmatic intrusions which most likely resulted in three episodes of cu mo au mineralization in the eastern indo asian collision zone

the role of early sulfide saturation in the formation of the yulong porphyry cu mo deposit evidence from mineralogy of sulfide melt inclusions and platinum group element geochemistry abstract sulfide melt inclusions enclosed in silicate minerals have been observed in many oxidized cu bearing porphyries the origin of such sulfide melt inclusions could bear critical information of metal enrichment or depletion during magma evolution of porphyry systems the giant yulong porphyry cu mo deposit in eastern tibetan plateau consists of a series of felsic intrusions among which the mineralized yulong intrusion emplaced at a late stage of the magmatic activity this study reports detailed texture and composition of sulfide melt inclusions from barren and mineralized intrusions as well as platinum group elements of these intrusions to evaluate potential role of early sulfide saturation in the porphyry mineralization system these sulfide melt inclusions occurring as globules or droplets are preserved in zircon amphibole and quartz grains most of them are composed of a major phase of pyrrhotite and minor pyrite chalcopyrite and pentlandite smooth boundaries between these phases suggest the origin of fractionation from sulfide melt upon cooling small amounts of cu and ni are heterogeneously distributed in the pyrrhotite the sulfide melt inclusions could be observed in both the pre and syn mineralization intrusions at yulong indicating that sulfide saturation had commonly occurred during magma evolution magnetite mineral inclusions could be observed in zircon and amphibole grains as well the mineral assemblage of magnetite pyrrhotite pyrite of the mineral inclusions constrains the yulong magmatic system to redox conditions near the magnetite pyrite pyrrhotite buffer and above the fayalite magnetite quartz buffer fmq high eu eu values 0 56 0 78 of the hosting zircons and high calculated nno values 0 5 of the hosting amphibole indicate highly oxidized nature of the parental magma both pre and syn mineralization intrusions have low pge contents pt 0 04 to 0 17 ppb pd 0 19 0 60 ppb with compositions plotting in the au poor porphyry cu fields in discriminating diagrams early sulfide saturation may have been reached and small amounts of sulfides have been segregated from magma most pges and au but little cu have been removed from the evolved magma because the partition coefficient of cu between sulfide and silicate melt is about two orders of magnitude lower than pge or au as a consequence the evolved magma would have high cu but very low pge and au resulting in the au poor porphyry cu mineralization at yulong

zircon crystallization and the lifetimes of ore forming magmatic hydrothermal systems magmatic hydrothermal copper ore formation involves multiple pulses of subvolcanic porphyry intrusion vein opening and hydrothermal ore deposition it is driven by larger subjacent magma reservoirs acting as the source of fluid and ore forming components high precision u pb ages of individual zircon crystals from porphyries immediately predating and postdating cu au mineralization at bingham canyon utah united states and bajo de la alumbrera northwestern argentina show a significant spread of reliably concordant ages this demonstrates zircon crystal formation over a protracted period of 1 m y which is interpreted to record the lifetime of the magma reservoir from which porphyries and ore fluids were extracted the youngest zircons in all pre ore and post ore intrusions overlap within a much shorter time interval of 0 32 m y at bingham canyon and 0 090 m y at alumbrera these youngest zircons of each intrusion are interpreted to bracket the maximum duration of porphyry emplacement and ore formation to short periods consistent with thermal constraints this study illustrates that age brackets based on individual magmatic zircon grains are geologically more informative than the calculation of means and standard deviations based on apparently normal age distributions in zircon populations

a comparison of measured and predicted broadband acoustic arrival patterns in travel time depth coordinates at 1000 km range broadband acoustic signals were transmitted from a moored 250 hz source to a 3 km long vertical line array of hydrophones 1000 km distant in the eastern north pacific ocean during july 1989 the sound speed field along the great circle path connecting the source and receiver was measured directly by nearly 300 expendable bathythermograph xbt conductivity temperature depth ctd and air launched expendable bathythermograph axbt casts while the transmissions were in progress this experiment is unique in combining a vertical receiving array that extends over much of the water column extensive concurrent environmental measurements and broadband signals designed to measure acoustic travel times with 1 ms precision the time mean travel times of the early raylike arrivals which are evident as wave fronts sweeping across the receiving array and the time mean of the times at which the acoustic reception ends the final cutoffs for hydrophones near the sound channel axis are consistent with ray predictions based on the direct measurements of temperature and salinity within measurement uncertainty the comparisons show that subinertial oceanic variability with horizontal wavelengths shorter than 50 km which is not resolved by the direct measurements significantly 25 ms peak to peak affects the time mean ray travel times the final cutoffs occur significantly later than predicted using ray theory for hydrophones more than 100 200 m off the sound channel axis nongeometric effects such as diffraction at caustics partially account for this observation

how accurately can we date the duration of magmatic hydrothermal events in porphyry systems an invited paper determining the absolute duration of magmatic hydrothermal events leading to the formation of porphyry systems i e including porphyry copper skarn and epithermal deposits is one of the key questions in ore geology this is so because the duration of magmatic hydrothermal events in porphyry systems is instrumental to the development of genetic models necessary to explore a category of mineral deposits that provide most of the copper and significant amounts of base and precious metals to our economy the problem of determining the absolute duration of magmatic hydrothermal events in porphyry systems has been addressed through thermal modeling of cooling intrusions and time needed to precipitate specified metal amounts from active hydrothermal systems with known metal concentrations and fluid fluxes both these methods have shown that the likely duration of hydrothermal systems is on the order of a few tens of kilo annum ka isotopic dating in contrast is the only possible way to determine the life span of magmatic hydrothermal events in fossil porphyry systems analytical and methodological developments during the last decade in the fields of the most robust isotopic systems commonly used for absolute dating u pb 40ar 39ar re os allow us to date minerals with internal precisions 0 2 2 for a 10 ma old mineral this corresponds to a 20 ka uncertainty which is marginally sufficient to discriminate the duration of hydrothermal systems at the tens of kilo annum scale however many geochronological studies on fossil porphyry systems have shown that these are most often formed through repeated cycles of several intrusion events which extend the overall life of the porphyry systems to a few 0 x and up to 2 ma in some cases internal precisions of the above mentioned dating methods allow us in theory to comfortably discriminate events at the 0 x scale and the combination of u pb 40ar 39ar and reos geochronology is a tool widely used by ore geologists to bracket the duration of cyclic magmatic hydrothermal events in porphyry systems in this review we discuss some fundamental problems that are systematically overlooked in most geochronological studies trying to bracket the life span of porphyry systems we show that if these problems are not adequately taken into account and tackled the result will be that fundamentally wrong life spans of porphyry systems will be estimated we also provide basic guidelines to follow when trying to resolve the duration of magmatic hydrothermal events in porphyry systems with the highest accuracy and precision currently achievable

from crucible to graben in 2 3 ma a high resolution geochronological study of porphyry life cycles boyongan bayugo copper gold deposits philippines the boyongan and bayugo porphyry copper gold deposits are part of a belt of gold rich copper deposits in the surigao district of northeast mindanao philippines the detailed age relationships described in this study provide insight into the geologically short life cycles that characterize porphyry formation in dynamic arc environments since their late pliocene emplacement 2 3 2 1 ma shrimp sensitive highresolution ion microprobe u pb zircon dating at depths of 1 2 2 0 km these deposits were exhumed deeply weathered and buried weathering of these deposits led to the development of the world s deepest known porphyry oxidation profile 600 m thick at boyongan and a modest 30 70 m oxidation profile at adjacent bayugo this earlymiddle pleistocene supergene event followed a period of rapid uplift and exhumation in northeast mindanao 2 5 km ma u th he apatite age elevation spectrum subsequent rapid subsidence 0 34 km ma radiocarbon age elevation spectrum and burial of these deposits are attributed to a mid pleistocene shift from transpressional tectonics to the present day transtensional setting in northeast mindanao during this period debris flows volcanic material and fluviolacustrine sediments accumulating in the actively extending mainit graben covered the weathered deposits preserving the supergene profiles beneath 50 500 m of cover this detailed geochronological study documents the geologically short 2 3 ma time scales over which these major intrusion centered mineral deposits evolved from emplacement exhumation deep oxidation and burial highlighting the dynamism of tectonic processes in environments such as the philippine mobile belt 2012 geological society of america

timing and duration of hydrothermal activity at the los bronces porphyry cluster an update new geochronological data from the los bronces cluster of the rio blanco los bronces mega porphyry cu mo district establish a wide range of magmatism hydrothermal alteration and mineralization ages both in terms of areal extent and time the northern el plomo and southernmost los piches exploration areas contain the oldest barren porphyritic intrusions with u pb ages of 10 8 0 1 ma and 13 4 0 1 ma respectively a hypabyssal barren intrusion adjacent northwesterly to the main pit area yields a slightly younger age of 10 2 0 3 ma san manuel sector u pb whereas in the los bronces lb open pit area the present day mineral extraction zone porphyries range from 8 49 to 6 02 ma u pb hydrothermal biotite and sericite ages are up to 0 5 ma younger but consistent with the cooling of the corresponding intrusion events of each area two quartz molybdenite b type veins from the lb open pit have re os molybdenite ages of 5 65 0 03 ma and 5 35 0 03 ma consistent with published data for the contiguous rio blanco cluster the san manuel exploration area within the los bronces cluster located about 1 5 2 km southeast of the open pit extraction zone shows both the oldest hydrothermal biotite 7 70 0 07 ma 40ar 39ar and breccia cement molybdenite ages 8 36 0 06 ma re os registered in the entire rio blanco los bronces district these are also older than those reported from the el teniente porphyry cu mo deposit suggesting that mineralization in the late miocene to early pliocene porphyry belt of central chile commenced 2 ma before the previously accepted age of 6 3 ma

how long can a hydrothermal system be sustained by a single intrusive event published numerical calculations show that the convective systems which produce near surface geothermal systems or ore deposits are likely to cool their intrusion heat source in at most a few tens of thousands of years even if the intrusion is large generally hydrothermal circulation near surface geothermal activity and magmatic intrusion should be closely tied in time and space long lived approximately 1 m y hydrothermal activity normally suggests multiple pulses of intrusion with associated pulses of hydrothermal circulation however if the permeability of the intruded environment is just above that which allows convection and the volume of the intrusion is very large calculations presented here show that a single episode of intrusion can sustain hydrothermal circulation and near surface geothermal activity for approximately 800 000 yr for a deep sill heat source these unusually long lived hydrothermal systems can vent through a few very widely separated discharge sites and have the potential to produce isolated massive sulfide deposits of unusually large size

giant ore deposits formed by optimal alignments and combinations of geological processes giant ore deposits are priority targets for mining companies a review of the characteristics of several giant porphyry and epithermal deposits worldwide suggests that they formed from ordinary processes that were fortuitously operating at maximum efficiency

re os geochronology of quartz enclosed ultrafine molybdenite implications for ore geochronology re os molybdenite geochronology relies on the aliquant analysis taken from a mineral separate although suitable for coarse grained molybdenite samples traditional mineral separation techniques are not ideally suited for samples possessing fine grained molybdenite m and thus hamper the application of re os geochronology for such samples here we demonstrate a room temperature hydrofluoric acid hf chemical separation technique that is capable of isolating ultrafine molybdenite i e m for re os geochronology six re os molybdenite model ages from four molybdenite in house control and nist reference material rm8599 samples exposed to concentrated hf are indistinguishable from the re os molybdenite model ages for aliquants not exposed to hf thus hf exposure at room temperature has no effect on re os molybdenite systematics our hf chemical separation technique was then applied to six ultrafine molybdenite samples from the lupa goldfield southwest tanzania three samples from the kenge deposit provide a weighted average re os molybdenite model age of 1953 5 ma mswd 0 6 n 3 whereas three samples and one repeat analysis from the porcupine deposit provide a weighted average re os molybdenite model age of 1886 5 ma mswd 1 5 n 4 our proposed analytical protocol has allowed us to determine reproducible ages from ultrafine molybdenite samples within the lupa goldfield that were previously unsuitable for molybdenite re os geochronology using conventional mineral separation techniques

geology mineralization alteration and structural evolution of the el teniente porphyry cu mo deposit sir the el teniente cu mo deposit in central chile is an extraordinary accumulation of cu mo ore fig 1 and we welcome the opportunity provided by skewes and stern 2007 to discuss and clarify several important issues regarding its classification and interpretation and to address several incorrect assertions that they make regarding our manuscript cannell et al 2005 we have interpreted el teniente to be a typical porphyry deposit in terms of its alteration assemblages vein and breccia styles and spatial and temporal relationships between cu mo mineralization and felsic porphyries skewes and stern 2007 dispute our claims that mineralization occurred primarily in veins and was related to felsic intrusive activity they also take issue with our interpretations of the various geochronological datasets from el teniente and our classification of el teniente as a porphyry cu mo deposit we address each of these in turn below in order to facilitate the following discussion table 1 correlates the geologic nomenclature of skewes and stern 2007 with that of cannell et al 2005 figures 1 and 2 illustrate the location of the main geologic units on underground mine level 6 at el teniente also shown on figure 1 are the approximate locations of the hypogene sulfide mineral zones figure 2 shows the block model of mo grades in the mine for more details of geologic relationships at el teniente refer to figure 4 of cannell et al 2005 and figures 4 and 5 of skewes et al 2002 although the dacite porphyry dike is shown as a single unit on figure 1 note that rojas 2002 2003 mapped multiple phases within this composite intrusive body skewes and stern 2007 criticized our use of what they assert to be an outdated map of hypogene mineralization

low rhenium molybdenite by metamorphism in northern sweden recognition genesis and global implications abstract re os dating of molybdenite is an accurate means to date intrusions and intrusion related ore deposits using the model age or isochron approach but molybdenite has a new niche in the greenschist to granulite facies metamorphic environment re os ages for metamorphic molybdenite may be used to construct regional metamorphic histories age significance and accuracy are established by analyzing multiple molybdenite separates extracted from single petrographically characterized molybdenite occurrences in this study twelve geologically distinct molybdenite bearing samples from two small mo districts in northern sweden trace a 150 m y paleoproterozoic svecofennian metamorphic history from 1900 to 1750 ma these data reveal a little known widespread and protracted late svecofennian anatexis in northern sweden the kataberget mo cu f deposit is located in the moskosel granite batholith north of the economically renown skellefte district four different molybdenite samples from outcrop at kataberget indicate an intrusion age of 1895 6 ma with the formation of later pegmatite aplite at 1875 6 ma the allebuoda bjorntjarn and munka mo w deposits in the rappen district are represented by three outcrop and five drill core samples of molybdenite bearing aplite pegmatite granite these two deposits were previously described as intrusion related climax type mo mineralization re os ages for molybdenites from these deposits range from 1865 to 1750 ma and significantly re concentrations are markedly low extending to the sub ppm level age agreement within the deposits is conspicuously lacking whereas with one exception age agreement within any single sample geologic occurrence as established by analysis of additional molybdenite separates is very good these data together with fundamental geologic observations discussed in this paper suggest that mo w mineralization in northern sweden is not intrusion related but the local product of episodic melting of archean paleoproterozoic supracrustal gneisses related to the svecofennian orogeny petrographic traverses across the boundary between widespread foliation parallel units of aplitic to pegmatitic pink granite and hosting biotite gneiss directly capture the process of ore formation dehydration breakdown of zircon rich biotite aligned with the foliation in the gneiss is accompanied by formation of new pristine post deformational biotite plus sulfides oxides hydrothermal zircon and fluorite all associated with microcline dominant leucosomes this process has profound implication for the traditional leucogranite intrusion related genesis attributed to the broad classification of mo w sn base and precious metal mineralization e g south mountain batholith nova scotia okiep namaqualand south africa mactung yukon pogo liese tintina alaska carajas and goias rio tocantins brazil new england batholith nsw australia bergslagen sweden nevoria western australia alpeinerscharte austria erzgebirge germany sardinia corsica batholith in addition to biotite metallogenic contributions e g mo w sn u bi cu pb zn fe ni co au ag te as sb ree in various combinations may also be controlled by breakdown of amphibole in effect the trace element composition of dehydrating or recrystallizing components in a gneissic rock essentially defines the local and district metallogenic suite in the absence of focusing structures e g shear zones sheeted vein development this process will generally form small and disconnected subeconomic deposits with erratic and unpredictable grades low re content in associated molybdenite is a key indicator for a subeconomic origin by local melting of biotite gneiss mo w or muscovite schist sn w

from a long lived upper crustal magma chamber to rapid porphyry copper emplacement reading the geochemistry of zircon crystals at bajo de la alumbrera nw argentina the formation of world class porphyry copper deposits reflect magmatic processes that take place in a deeper and much larger underlying magmatic system which provides the source of porphyry magmas as well as metal and sulphur charged mineralising fluids reading the geochemical record of this large magmatic source region as well as constraining the time scales for creating a much smaller porphyry copper deposit are critical in order to fully understand and quantify the processes that lead to metal concentration within these valuable mineral deposits this study focuses on the bajo de la alumbrera porphyry copper deposit in northwest argentina the deposit is centred on a dacitic porphyry intrusive stock that was mineralised by several pulses of porphyry magma emplacement and hydrothermal fluid injections to constrain the duration of ore formation we dated zircons from four porphyry intrusions including pre syn and post mineralisation porphyries based on intersection relations between successive intrusion and vein generations using high precision ca id tims based on the youngest assemblages of zircon grains which overlap within analytical error all four intrusions were emplaced within 29 ka which places an upper limit on the total duration of hydrothermal mineralisation re os dating of hydrothermal molybdenite fully overlaps with this high precision age bracket however all four porphyries contain zircon antecrysts which record protracted zircon crystallisation during the 200 ka preceding the emplacement of the porphyries zircon trace element variations ti in zircon temperatures and hf isotopic compositions indicate that the four porphyry magmas record a common geochemical and thermal history and that the four intrusions were derived from the same upper crustal magma chamber trace element zoning within single zircon crystals confirms a fractional crystallisation trend dominated by titanite and apatite crystallisation however zircon cathodoluminescence imaging reveals the presence of intermediate low luminescent dark growth zones in many crystals from all intrusions characterised by anomalously high th u and ree concentrations and transient excursions in trace element ratios a return to the same fractionation trend after this excursion excludes external compositional forcing such as magma mixing instead we interpret the dark zones to record zircon crystallisation during a transient event of rapid growth that resulted from mafic magma injection into the base of the magma chamber releasing a co2 rich vapour phase into the dacitic crystal mush we propose that this vapour phase then migrated upwards to the apical part of the magma chamber from where it was expelled together with successive batches of magma to form the porphyry copper deposit within a short time span of less than a few 10 000 years the short duration of host rock emplacement hydrothermal alteration and mineralisation presented in this study provides critical constraints on fluid storage in magma chambers and the genesis of large porphyry copper deposits

exploring the method of optical dating and comparison of optical and 14c ages of late weichselian coversands in the southern netherlands a study was made of the applicability of three different techniques for equivalent dose de determination in the optical dating of quartz the single aliquot regenerative dose technique sar the single aliquot additive dose technique saad and the multiple aliquot additive dose technique maad for this purpose quartz grains were extracted from a sequence of upper pleniglacial to late glacial coversands exposed at the locality of ossendrecht in the southwestern netherlands a site for which both radiocarbon and earlier luminescence dates are available providing independent age control upon testing the different assumptions underlying each of the three osl techniques investigated the sar protocol was found to be the technique of choice the optical ages obtained with this protocol were in good agreement with the chronostratigraphical position of the sediments investigated and with the available chronostratigraphical information on the same and equivalent deposits this confirms the suitability of the sar technique for dating coversands furthermore a small laboratory intercomparison of sar based de determinations yielded results that were in fair overall agreement copyright 2004 john wiley sons ltd

zircon ce4 ce3 ratios and ages for yulong ore bearing porphyries in eastern tibet yulong ore bearing porphyries along the northwestern extension of the red river ailao shan fault system in eastern tibet consist of five porphyry deposits containing a total of more than 8 million tons of copper resources u th pb laser inductively coupled plasma mass spectrometry dating of zircon shows that the porphyries were emplaced in early tertiary 41 2 36 9 ma covering a period of 4 3 ma with formation ages decreasing systematically from northwest to southeast the start of porphyry magmatism coincided with the onset of transpressional movement along the red river ailao shan fault system implying a close link between these two events age sequence in intrusions can be plausibly explained by assuming that a region of melting in the lower northwestern plate moved southeasternward along the tuoba mangkang fault relative to the upper plate zircon grains from the yulong ore bearing porphyries have higher ce4 ce3 than those from barren porphyries in the region this suggests that the ore bearing porphyries crystallized from a relatively oxidized magma which has important implications for future ore exploration in the region and other cu deposits in convergent margin environments in general

the distribution and timing of molybdenite mineralization at the el teniente cu mo porphyry deposit chile this journal is published under the terms of green open access authors may post a copy of the accepted i e post peer review version of their paper https doi org 10 2113 econgeo 110 2 387 in a repository of their choice or to their personal website after the relevant embargo period has passed the embargo period will be 12 months from formal online publication

re os ages for archean molybdenite and pyrite kuittila kivisuo finland and proterozoic molybdenite kabeliai lithuania testing the chronometer in a metamorphic and metasomatic setting seven 187re 187os ages were determined for molybdenite and pyrite samples from two well dated precambrian intrusions in fennoscandia to examine the sustainability of the re os chronometer in a metamorphic and metasomatic setting using a new 187re decay constant 1 666 10 11y 1 with a much improved uncertainty 0 31 we determined replicate re os ages for molybdenite and pyrite from the kuittila and kivisuo prospects in easternmost finland and for molybdenite from the kabeliai prospect in southernmost lithuania these two localities contain some of the oldest and youngest plutonic activity in fennoscandia and are associated with newly discovered economic au mineralization ilomantsi finland and a cu mo prospect kabeliai lithuania two re os ages for vein hosted kabeliai molybdenite average 1486 5 ma in excellent agreement with a 1505 11 ma u pb zircon age for the hosting kabeliai granite pluton the slightly younger age suggests the introduction of cu mo mineralization by a later phase of the kabeliai magmatic system mean re os ages of 2778 8 ma and 2781 8 ma for kuittila and kivisuo molybdenites respectively are in reasonable agreement with a 2753 5 ma weighted mean u pb zircon age for hosting kuittila tonalite these re os ages agree well with less precise ages of 2789 290 ma for a rb sr whole rock isochron and 2771 75 ma for the average of six sm nd tdm model ages for kuittila tonalite three re os analyses of a single pyrite mineral separate from the same sample of kuittila pluton that yielded a molybdenite separate provide individual model ages of 2710 27 2777 28 and 2830 28 ma re 17 4 12 1 and 8 4 ppb respectively with a mean value of 2770 120 ma in agreement with the kuittila molybdenite age the re and 187os abundances in these three pyrite splits are highly correlated r 0 9994 and provide a 187re 187os isochron age of 2607 47 ma with an intercept of 21 ppt 187os mswd 1 1 it appears that the re os isotopic system in pyrite has been reset on the millimeter scale and that the 21 ppt 187os intercept reflects the in situ decay of 187re during the 160 to 170 m y interval from 2778 ma time of molybdenite pyrite deposition to 2607 ma time of pyrite resetting when the re os data for molybdenites from the nearby kivisuo prospect are plotted together with the kuittila molybdenite and pyrite data a well constrained five point isochron with an age of 2780 8 ma and a 187os intercept 2 4 3 8 ppt of essentially zero results mswd 1 5 we suggest that the pyrite isochron age records a regional metamorphic and or hydrothermal event possibly the time of au mineralization a proposed re os age of 2607 ma for au mineralization is in good agreement with radiometric ages by other methods that address the timing of archean au mineralization in deposits worldwide so called late au model molybdenite in contrast provides a robust re os chronometer retaining its original formation age of 2780 ma despite subsequent metamorphic disturbances in archean and proterozoic time

patterns of mineralization and alteration below the porphyry copper orebody at el salvador chile three diamond drill holes angled below the lowest haulage level at el salvador have doubled the vertical exposure of the deposit and revealed very different features of alteration and mineralization below this major porphyry copper orebody sulfide assemblages persist with depth but the total sulfide content diminishes magnetite becomes a part of all sulfide assemblages except very late pyritic d veins residual traces of pyrrhotite chalcopyrite found locked in quartz and as abundant and wide spread inclusions in pyrite apparently represent the remains of an early prograde mineralization obliterated by intense sulfidation of subsequent events relicts of specularite veinlets may be a similar phenomenon vein types change newly recognized early biotitic eb veinlets with and without sulfides quartz albite anhydrite and actinolite have varied alteration halos containing albite k feldspar biotite green sericite anhydrite and andalusite they appear to be deeper equivalents of a quartz veins veinlets descriptively similar to both eb and a quartz veins formed as a second generation within the young intramineral l porphyry complex which truncates similar veinlets in older and better mineralized rocks granular a quartz k feldspar sulfide anhydrite veins diminish in abundance and in content of sulfide and k feldspar with depth and are hard to distinguish from b quartz anhydrite veins with characteristic molybdenite the latter have much better developed k feldspar alteration halos than seen above younger g sulfide veins with green sericite biotite and anhydrite and halos with green sericite alkali feldspar and andalusite cut b veins they are older than relatively sparse d pyrite quartz veins with sericite pyrite calcite anhydrite halos and occasional tourmaline pervasive sericite chlorite in the pyritic fringe terminates downward and biotitic alteration of andesite diminishes revealing more restricted and residual actinolite hornfels ilmenite and then sphene appear as residual accessory minerals and minor vein constituents minor andalusite with alkali feldspar extends to deepest exposures mostly within halos of b and c veins traces of corundum and cordierite occur with andalusite

giant porphyry deposits characteristics distribution and tectonic controls more than half of the 25 largest known porphyry copper deposits defined in terms of contained copper metal formed during three time periods the paleocene to eocene eocene to oligocene and middle miocene to pliocene these giant deposits are clustered within three provinces central chile northern chile and southwest arizona northern mexico other giant deposits occur in montana utah panama peru argentina irian jaya mongolia and iran compressive tectonic environments thickened continental crust and active uplift and erosion were associated with the formation of many of these deposits calc alkalic magmas are most favorable for the formation of giant porphyry copper deposits although several of the largest systems are associated with high k calc alkalic intrusions the 25 largest gold rich porphyry deposits are concentrated in the southwest pacific and south america with other occurrences in eurasia british columbia alaska and new south wales many of the deposits formed in the last 13 m y the largest of the deposits are associated with high k calc alkalic intrusions many calc alkalic porphyritic intrusions have also produced giant gold rich porphyries in the last 20 m y the formation of giant porphyry copper molybdenum and copper gold deposits in the circum pacific region has been closely associated with subduction of aseismic ridges seamount chains and oceanic plateaus beneath oceanic island and continental arcs in several examples these tectonic perturbations have promoted flat slab subduction crustal thickening uplift and erosion and adakitic magmatism coeval with the formation of well endowed porphyry and or epithermal mineral provinces similar tectonic features are inferred to be associated with the giant porphyry copper molybdenum provinces of northern chile eocene oligocene and southwest united states cretaceous paleocene topographic and thermal anomalies on the downgoing slab appear to act as tectonic triggers for porphyry ore formation other factors such as sutures in the overriding plate permeability architecture of the upper crust efficient processes of ore transport and deposition and in some cases formation and preservation of supergene enrichment blankets are also vital for the development of high grade giant ore deposits a low grade geochemical anomaly may be the final product of mineralization if ore forming processes do not operate efficiently even in the most favorable geodynamic settings

refinement of the time space evolution of the giant mio pliocene rio blanco los bronces porphyry cu mo cluster central chile new u pb shrimp ii and re os geochronology and 40ar 39ar thermochronology data representing one of the largest known estimated 5 gt at 1 cu and 0 02 mo porphyry system the rio blanco los bronces deposit incorporates at least five hypabyssal intrusive and hydrothermal centres extending for about 5 km from the rio blanco and los bronces mines in the north through the don luis mine to the sur sur mine la americana and los sulfatos in the south the new geochronology data which now include data on different molybdenite vein types confirm the u pb ages of the pre mineralisation intrusions but slightly increase their age range from 8 8 to 8 2 ma the distinct magmatic pulses of the mineralisation associated porphyritic intrusives late porphyries indicate an age interval instead of the previously suggested individual ages the quartz monzonite porphyry ranges from 7 7 to 6 1 ma sur sur 5 74 0 13 ma the feldspar porphyry shows an interval from 5 8 to 5 2 ma and the don luis porphyry from 5 2 to 5 0 ma the new re os data on distinct molybdenite vein types confirm the protracted history of cu mo mineralisation inferred previously the vein development occurred at least from 5 94 to 4 50 ma indicating a time span of 1 5 ma for the hydrothermal activity hydrothermal minerals dated by the 40ar 39ar method are generally too young to record the age of early high temperature mineralisation the majority of the 40ar 39ar data in the rio blanco porphyry cluster record reheating by either the youngest member of the late porphyry suite or the post mineralisation dacite or rhyolite plug formations at around 4 9 4 7 ma

assessment of the 187re decay constant by cross calibration of re os molybdenite and u pb zircon chronometers in magmatic ore systems the past decade has seen renewed interest in 187re 187os geochronology using a variety of matrices including sulfide minerals shales and meteorites the most widely used value of the 187re decay constant 187re is 1 666 0 005 10 11 a 1 0 31 which is based on cross calibration of re os and pb pb chronometers for certain meteorites smoliar m i walker r j and morgan j w 1996 re os isotope constraints on the age of group iia iiia iva and ivb iron meteorites science 271 1099 1102 however other recent studies have yielded alternate values of 187re based upon either direct counting experiments or analysis of meteorites here we provide an independent assessment of 187re using methodology sample materials and preparation of os standard solutions different from those of smoliar et al 1996 combining re os age data for molybdenite formed in magmatic ore deposits with the u pb zircon age of the magmatic rocks a refined 187re value is determined by averaging 11 individual cross calibration experiments spanning ca 2700 ma of earth history using the u decay constants of jaffey jaffey a h flynn k f glendenin l e bentley w c and essling a m 1971 precision measurement of half lives and specific activities of 235u and 238u phys rev 4 1889 1906 a value for 187re of 1 6668 0 0034 10 11 a 1 is determined using the 238u value of jaffey et al 1971 and 235u value of schoene schoene b crowley j l condon d j schmitz m d and bowring s a 2006 reassessing the uranium decay constants for geochronology using id tims u pb data geochim cosmochim acta 70 426 445 a value for 187re of 1 6689 0 0031 10 11 a 1 is determined these values are nominally higher ca 0 1 and ca 0 2 than the value determined by smoliar et al smoliar m i walker r j and morgan j w 1996 re os isotope constraints on the age of group iia iiia iva and ivb iron meteorites science 271 1099 1102 but within calculated uncertainty further refinement of 187re by cross calibrating the molybdenite and u pb zircon chronometers should be possible by utilizing high precision single grain chemical abrasion zircon u pb analyses

longevity of porphyry copper formation at quellaveco peru metal introduction at the late paleocene to early eocene quellaveco porphyry copper molybdenum deposit in southern peru spans several phases of quartz monzonite porphyry emplacement and is bracketed by a precursor granodiorite pluton and a late mineral porphyry body that postdates essentially all copper introduction together the u pb ages of zircons from these intrusive rocks show that 1 08 0 58 m y elapsed between the precursor pluton and initiation of stock emplacement the porphyry system was active intermittently for at least 3 25 m y 4 07 0 82 m y and at least three quarters of the copper inventory was deposited in a maximum of 3 12 m y 2 51 0 61 m y recent u pb zircon dating of several other major central andean porphyry copper deposits in combination with other isotopic techniques suggests that 2 5 to 4 m y life spans are commonplace the longevity of porphyry copper systems implied by these studies appears to reflect the protracted time gaps between the multiple intrusions that intermittently replenished porphyry stocks other precise isotopic methods re os 40 ar 39 ar typically document shorter life spans because it is more difficult if not impossible to date the full sequence of events involved in porphyry copper formation

high water contents of magmas and extensive fluid exsolution during the formation of the yulong porphyry cu mo deposit eastern tibet abstract the yulong porphyry cu mo ore district in eastern tibet features a series of eocene felsic porphyry intrusions only one of which is intensively mineralized in this study zircon u pb ages and major and trace element compositions of whole rock samples and in situ accessory minerals zircon apatite and titanite from these various intrusions were analyzed to determine the factors controlling cu mineralization new zircon u pb dating together with published zircon u pb ages suggest that these porphyry intrusions were emplaced over a relatively short period of time 43 9 0 6 ma to 40 9 0 3 ma with the mineralized yulong intrusion emplaced at a late stage of the magmatic activity 41 1 0 3 ma to 40 9 0 3 ma these intrusions have indistinguishable whole rock major and trace element compositions but the mineralized yulong intrusion has higher apatite and titanite la yb ratios average apatite la yb 115 1 28 5 n 52 average titanite la yb 22 4 4 9 n 38 than the earlier subeconomic intrusions average apatite la yb 50 4 12 3 n 72 average titanite la yb 12 4 3 5 n 58 suggesting more fractionation of amphibole from the magmas that sourced it additionally a negative relationship between la yb and cen cen ratios in apatite and titanite are interpreted to reflect increasing oxidation states through magma evolution indistinguishable zircon eun eun values and apatite core so3 contents from the mineralized zircon eun eun 0 69 0 06 n 25 apatite so3 0 65 0 24 wt n 21 and subeconomic intrusions zircon eun eun 0 62 0 05 n 64 apatite so3 0 61 0 27 wt n 15 suggest that the entire magmatic suite was relatively oxidized hydrous and sulfur rich and was therefore fertile for ore formation however apatite crystals from the mineralized yulong intrusion have significantly lower cl contents 0 08 0 03 wt n 72 and higher f cl ratios 47 80 21 97 n 72 than those from the subeconomic intrusions cl 0 29 0 29 wt f cl 12 87 5 16 n 78 these data may reflect more extensive fluid exsolution from the parental magma chamber at the time of emplacement of the mineralizing yulong magmas sudden and voluminous release of volatiles coeval with emplacement of the yulong intrusion was triggered by an as yet unidentified process but possibly including magmatic recharge

gold in magmatic hydrothermal solutions and the rapid formation of a giant ore deposit the ladolam hydrothermal system on lihir island papua new guinea hosts one of the youngest and largest gold deposits in the world several deep more than 1 kilometer geothermal wells were drilled beneath the ore bodies to extract water at 275 c and to facilitate open pit mining using a titanium down hole sampler we determined that the deep geothermal brine of magmatic origin contains 15 parts per billion gold at the current gold flux of 24 kilograms per year this deposit could have formed within 55 000 years the combination of sustained metal flux and efficient metal precipitation led to the formation of a giant hydrothermal gold deposit in a short period

triggers for the formation of porphyry ore deposits in magmatic arcs porphyry ore deposits supply much of the copper molybdenum gold and silver used by humans a review of the main processes that trigger porphyry ore formation suggests that sulphide saturation of the magmas that supply the metals could be the overriding mechanism that helps control the temporal and spatial distribution of the ore deposits

geological and chronological constraints on the long lived eocene yulong porphyry cu mo deposit eastern tibet implications for the lifespan of giant porphyry cu deposits the yulong porphyry cu mo deposit the third largest porphyry cu deposit in china contains proven reserves of 6 5 million metric tons mt cu and 0 4 mt mo previous radiometric dating studies have provided numerous ages for this deposit but the timing and duration of the process governing the deposition of cu and mo remains not well constrained in this paper we first document multiple stages of mineralization and hydrothermal alteration associated with distinct magmatic pulses at yulong by field and textural relationships and then present high precision molybdenite re os ages of 14 quartz molybdenite chalcopyrite veins representing these stages to precisely constrain the timing and duration of cu mo mineralization the ore hosting yulong composite stock consists of three successive porphyry intrusions 1 monzonitic granite porphyry mgp 2 k feldspar granite porphyry kgp and 3 quartz albite porphyry qap the vein formation cu mo mineralization and ore related alteration are grouped into early transitional and late stages with respect to the intrusive history the first two porphyry intrusions are followed by cyclical sequences of veining that are mainly associated with potassic alteration and have formed 1 me vein ustt 2 ebe t veins 3 a1e t veins 4 a2e bt veins and 5 a3e t veins a2e bt and a3e t veins of the early and transitional stages are dominated by quartz and chalcopyrite pyrite respectively and represent the main cu mo mineralization events more than 80 of cu and mo at yulong were deposited in the early stage with the remainder being formed in the transitional stage the late stage pyrite quartz veins dl which are characterized by sericitic alteration halos postdate the intrusion of qap dikes and have no economic significance molybdenite re os ages of a2e and bt veins indicate that sulfide deposition at yulong was episodic over a prolonged history lasting over 5 13 0 23 m y 1 however the bulk cu mo ores formed in a shorter time interval of 1 36 0 24 m y 1 with most cu precipitated in a more restricted timespan of 0 82 0 24 m y 1 in the early stage these results combined with geochronologic data from porphyry copper deposits elsewhere confirm that multiple magmatic hydrothermal pulses with a lifespan of tens to hundreds of thousands of years are sufficient to form a giant porphyry copper deposit factors such as metal concentration volume and focusing efficiency of ore forming fluids could have played important roles in producing a giant porphyry cu deposit regardless of a short or long lived magmatic hydrothermal system