intercalibration of astronomical and radioisotopic time the 40ar 39ar radioisotopic dating technique is one of the most precise and versatile methods available for dating events in earth s history but the accuracy of this method is limited by the accuracy with which the ages of neutron fluence monitors dating standards are known calibrating the ages of standards by conventional means has proved difficult and contentious the emerging astronomically calibrated geomagnetic polarity time scale apts offers a means to calibrate the ages of 40ar 39ar dating standards that is independent of absolute isotopic abundance measurements seven published 40ar 39ar dates for polarity transitions nominally ranging from 0 78 to 3 40 ma are based on the fish canyon sanidine standard and can be compared with apts predictions solving the 40ar 39ar age equation for the age of the fish canyon sanidine that produces coincidence with the apts age for each of these seven reversals yields mutually indistinguishable estimates ranging from 27 78 to 28 09 ma with an inverse variance weighted mean of 27 95 0 18 ma normalized residuals are minimized at an age of 27 92 ma indicating the robustness of the solution

new thermochronologic constraints on the evolution of the zaldivar porphyry copper deposit northern chile life spans and thermal evolution of hydrothermal systems are of fundamental metallogenic importance we were able to establish the chronology and cooling history of the zaldivar porphyry copper deposit northern chile by applying a combination of different isotopic dating methods in minerals with different closure temperatures including 40ar 39ar geochronology and zircon fission track thermochronology together with fluid inclusion thermometry and previous published u pb zircon geochronology the hydrothermal mineralization in the zaldivar deposit is genetically related to the llamo porphyry unit samples of igneous biotites from this intrusion yielded 40ar 39ar plateau ages between 35 5 0 7 and 37 7 0 4 ma defining a weighted average of 36 6 0 5 ma 2 in contrast one sample from the zaldivar porphyry one from the andesites and two from the llamo porphyry yielded considerably younger fission track ages of approximately 29 ma with a weighted mean for all ages of 29 1 1 7 ma 2 thermal and compositional constraints for the hydrothermal system in the zaldivar deposit from fluid inclusions thermometry show that at least three fluid types broadly characterize two main hydrothermal episodes during the evolution of the deposit the main mineralization and alteration event is characterized by high temperature above 320 c hypersaline fluids salinity between 30 and 56 wt nacl equivalents coexisting with low density gas rich inclusions salinity less than 17 wt nacl equivalents that homogenizing into the gas phase at temperatures above 350 c the second episode corresponds to a low temperature event which is characterized by liquid rich fluid inclusions that homogenize into the liquid phase at temperatures ranging from 200 c to 300 c with salinities lower than 10 wt nacl equivalents the 40ar 39ar data 36 6 0 5 ma weighted average obtained from igneous biotites represent the minimum age for the last high temperature above 300 c hydrothermal pulse when compared with previously published u pb ages 38 7 1 3 ma in zircons from the llamo porphyry a close temporal relationship between crystallization of the parental intrusion and the thermal collapse of the last high temperature hydrothermal event is evident cooling took place from approximately 800 c crystallization of the intrusive complex defined by zircon u pb ages to below 300 50 c biotite 40ar 39ar closure temperature within approximately 1 5 m y because the thermal annealing of fission tracks in zircons occurs at temperatures of 240 30 the zircon fission track zft ages of 29 1 1 7 ma 2 mark the end of the thermal activity in the zaldivar area specifically the time when the whole area cooled below this temperature well after the collapse of the main hydrothermal event in the zaldivar porphyry copper deposit this cooling age roughly coincides with the age defined for the emplacement of dacitic dikes at 31 2 8 ma 2 published k ar whole rock 5 km south of the zaldivar deposit in the escondida area this late magmatic pulse probably is responsible for high heat flow in the zaldivar deposit as late as 29 ma there is no evidence that the low temperature hydrothermal pulse recognized by fluid inclusion studies is related to this thermal event the zircon fission track cooling ages are interpreted to be related to the time lag required for complete relaxation of the perturbation of the isotherms in the geothermal field imposed by the intrusion of magmatic bodies with or without any association with low temperature hydrothermal activity

the remarkable re os chronometer in molybdenite how and why it works the re os rhenium osmium chronometer applied to molybdenite mos2 is now demonstrated to be remarkably robust surviving intense deformation and high grade thermal metamorphism successful dating of molybdenite is dependent on proper preparation of the mineral separate and analysis of a critical quantity of molybdenite unique to each sample such that recognized spatial decoupling of 187re parent and 187os daughter within individual molybdenite crystals is overcome highly precise accurate and reproducible age results are derived through isotope dilution and negative thermal ion mass spectrometry id ntims spatial decoupling of parent daughter precludes use of the laser ablation icp ms microanalytical technique for re os dating of molybdenite the use of a reference or control sample is necessary to establish laboratory credibility and for interlaboratory comparisons the rb sr k ar and 40ar 39ar chronometers are susceptible to chemical and thermal disturbance particularly in terranes that have experienced subsequent episodes of hydrothermal magmatic activity and therefore should not be used as a basis for establishing accuracy in re os dating of molybdenite as has been done in the past re os ages for molybdenite are almost always in agreement with observed geological relationships and when available with zircon and titanite u pb ages for terranes experiencing multiple episodes of metamorphism and deformation molybdenite is not complicated by overgrowths as is common for some minerals used in u pb dating e g zircon monazite xenotime nor are re and os mobilized beyond the margins of individual crystals during solid state recrystallization moreover inheritance of older molybdenite cores incorporation of common os and radiogenic os loss are exceedingly rare whereas inheritance common pb and pb loss are common complications in u pb dating techniques therefore molybdenite ages may serve as point in time markers for age comparisons

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

magmatic and hydrothermal chronology of the giant rio blanco porphyry copper deposit central chile implications of an integrated u pb and 40ar 39ar database the history of hypabyssal intrusion and hydrothermal activity in the northeastern and central parts of the be hemothian sensu clark 1993 rio blanco los bronces porphyry copper molybdenum deposit is clarified on the basis of integrated u pb and 40ar 39ar geochronology isotope dilution thermal ion mass spectrometry id tims u pb dates for zircon separates and id tims and sensitive high resolution ion microprobe shrimp dates for single zircon grains in pre syn and late mineralization volcanic and intrusive host rocks in the rio blanco don luis and sur sur mining sectors provide a temporal framework for interpretation of incremental heating and spot fusion 40ar 39ar dates for respectively magmatic biotite and hydrothermal biotite muscovite and orthoclase the ore deposit is hosted in part by 16 77 0 25 to 17 20 0 05 2 ma andesitic volcanic strata of the farellones formation but the major host rocks are units of the san francisco batholith including the 11 96 0 40 ma rio blanco granodiorite mine terminology the 8 40 0 23 ma cascada granodiorite and the 8 16 0 45 ma diorite hypabyssal dacitic intrusions late porphyries emplaced into the batholith yield 206pb 238u id tims dates ranging from 6 32 0 09 ma quartz monzonite porphyry through 5 84 0 03 ma feldspar porphyry to 5 23 0 07 ma don luis porphyry the late mineralization rio blanco dacite plug yields a shrimp zircon age of 4 92 0 09 ma the 40ar 39ar plateau ages for phenocrystic biotites in quartz monzonite porphyry feldspar porphyry and don luis porphyry as well as the preore diorite range only from 5 12 0 07 to 4 57 0 06 ma all are significantly younger than the corresponding zircons and exhibit no correlation with intrusive sequence the 40ar 39ar ages for hydrothermal biotite and orthoclase veins within the san francisco batholith units fall in a narrow interval from 5 32 0 27 to 4 59 0 11 ma hydrothermal sericites muscovite one associated with chalcopyrite yielded spot fusion ages of 4 40 0 15 ma rio blanco granodiorite hosted and 4 37 0 06 ma don luis porphyry hosted comparison with the id tims and shrimp zircon ages indicates that most of the 40ar 39ar ages even 95 percent plateaus do not record initial magmatic cooling or hydrothermal alteration mineralization events evidence for quasipervasive reheating to at least 300 c by successive intrusions published re os ages for two molybdenite samples range from 5 4 to 6 3 ma and overlap extensively with the zircon u pb ages for the late porphyries they imply that cu mo mineralization overlapped temporally with the emplacement of at least quartz monzonite porphyry and feldspar porphyry units of the late porphyry suite and was therefore contemporaneous with the rise of dacitic melts to subvolcanic levels hydrothermal activity is inferred to have continued until 4 37 0 06 ma following intrusion of the don luis porphyry and the early stages of emplacement of the rio blanco dacite plug complex hypogene cu mo mineralization therefore probably persisted for 2 m y the geochronologic data do not resolve whether ore formation was continuous or episodic but the observed crosscutting relationships between intensely altered and mineralized country rocks and less altered and mineralized late porphyry bodies support a model in which the ascent of metal rich brines from an unexposed zone of the parental magma chamber was periodically stimulated by magma perturbation and hypabyssal intrusion

geology of the escondida porphyry copper deposit antofagasta region chile the escondida porphyry copper deposit located in northern chile was one of the two largest copper producers of the world in the 1990s the hydrothermal evolution of this deposit is associated with the emplacement of a late eocene oligocene quartz monzonitic to granodioritic intrusive stock complex composed of at least three intrusive phases and hosted by paleocene andesite this paleocene andesite is underlain by mesozoic and paleozoic sedimentary and volcanic rocks which are characteristic of the basement of the precordillera de domeyko province in northern chile we propose that the intrusive stock associated with the mineralization at escondida was emplaced in a tensional gash formed between sinistral strike slip faults of the regional domeyko fault system the complete evolution of the porphyry system is characterized by overprinting of pervasive and vein associated alteration mineralization styles grouped in three main hydrothermal stages the early stage includes a zone of pervasive biotitization of andesite and development of a silicification shell around the intrusive complex propylitic alteration around the biotitic zone and a vein associated orthoclase quartz anhydrite biotite alteration that mark the end of stage one this early alteration contains magnetite chalcopyrite and bornite with less than 0 5 vol percent of sulfides and a hypogene copper grade of 0 2 wt percent the second hydrothermal stage is represented by vein and vein selvage associated chlorite sericite quartz and by quartz sericite with sulfides including chalcopyrite pyrite and molybdenite in the chlorite sericite and quartz sericite zones the content of sulfides ranges from less than 0 5 to 2 vol percent with a chalcopyrite to pyrite ratio of 3 to 1 and copper grades that range between 0 4 and 0 6 wt percent the intrusion of a rhyolite dike and a dome are at least 3 m y younger than the first and second hydrothermal stages and separate them in time from the late hydrothermal stage the late hydrothermal stage is represented by an acid sulfate mineral association that includes pyrophyllite alunite and quartz as alteration minerals and a variety of sulfides that include bornite chalcopyrite pyrite chalcocite covellite enargite sphalerite tennantite and galena this acid sulfate event occurred mainly in west northwest striking veins and also along the contact of the rhyolite and its host rock where sulfides from this event overprint previous sulfides the primary copper grades range from 0 6 to higher than 1 0 wt percent in the escondida deposit the highest hypogene and supergene copper grades occur in areas where all three hydrothermal stages are present

timing and formation of porphyry cu mo mineralization in the chuquicamata district northern chile new constraints from the toki cluster the recently discovered toki cluster which includes the toki quetena genoveva miranda and opache porphyry cu mo prospects is located 15 km south southwest of the chuquicamata radomiro tomic mines in northern chile these prospects occur in an area of 5 6 km and are completely covered with neogene alluvial deposits inferred resources for the cluster are estimated at about 20 mt of fine copper with toki and quetena contributing 88 of these resources mineralization in these deposits is associated with tonalite porphyries that intruded andesites and dacites of the collahuasi group and intrusions of the fortuna los picos granodioritic complex hypogene mineralization in the toki cluster consists mainly of chalcopyrite bornite with minor molybdenite with mineralization grading outward to a chalcopyrite pyrite zone and ultimately to a pyrite halo alteration is dominantly of the potassic type with k feldspar and hydrothermal biotite sericitic alteration is relatively restricted to late quartz pyrite veins d type veins previous k ar geochronology for the cluster yielded ages within a range of 34 to 40 ma four new re os ages for toki indicate that molybdenite mineralization occurred in a single pulse at 38 ma re os ages for three different molybdenite samples from quetena are within error of the toki mineralization ages these ages are concordant with a new zircon u pb age of 38 6 0 7 ma from the tonalite porphyry in quetena two re os ages for genoveva 38 1 0 2 and 38 0 0 2 ma are also within error of the toki and quetena molybdenite ages four re os molybdenite ages for opache range between 36 4 and 37 6 ma the miranda prospect is the youngest with an age of 36 ma four new re os ages for the chuquicamata deposit range between 33 and 32 ma whereas nine new 40ar 39ar ages of biotite muscovite and k feldspar range between 32 and 31 ma analyzed molybdenites have re and os concentrations that vary between 21 3 099 ppm and 8 1 231 ppb respectively the highest re and os concentrations are found in the toki prospect three new 40ar 39ar ages for the toki cluster are younger than the re os mineralization ages the age spectra for these three samples show evidence of excess argon and have similar inverse isochron ages of 35 ma that probably reflect a late hydrothermal phyllic event the new geochronological data presented here for the toki cluster indicate that molybdenite mineralization occurred within a very short period probably within 2 ma and synchronously at 38 ma in three mineralization centers toki quetena and genoveva furthermore mineralization at the toki cluster preceded the emplacement of the chuquicamata deposit 35 31 ma and indicates that porphyry cu mo mineralization occurred episodically over a period of several million years in the chuquicamata district

two ages of porphyry intrusion resolved for the super giant chuquicamata copper deposit of northern chile by ela icp ms and shrimp zircon u pb ages measured in situ by excimer laser ablation inductively coupled plasma mass spectrometry ela icp ms and verified by sensitive high resolution ion microprobe shrimp on ore bearing felsic porphyries from the chuquicamata porphyry copper molybdenum deposit northern chile identify two discrete igneous events the volumetrically dominant east porphyry has an age of 34 6 0 2 ma whereas the bench and west porphyries yield ages of 33 3 0 3 ma and 33 5 0 2 ma respectively the age of the east porphyry is indistinguishable from a re os age for early molybdenite mineralization 35 ma and the oldest reported 40 ar 39 ar ages for hydrothermal alteration confirming a genetic link with mineralization previous geological studies and 40 ar 39 ar and re os geochronology identify two main hydrothermal events high temperature potassic alteration with chalcopyrite at 33 4 0 3 ma followed by lower temperature quartz sericite alteration with pyrite at 31 1 0 3 ma the ages of the west and bench porphyries match the ages for potassic alteration younger quartz sericite alteration may reflect an additional fourth intrusion concealed at depth the anomalously large size of chuquicamata appears to be due to a protracted igneous history resulting in the superposition of at least two temporally distinct magmatic hydrothermal systems

quantifying exhumation at the giant pulang porphyry cu au deposit using u pb he dating the triassic pulang porphyry cu au deposit located in the south yidun terrane is the oldest and one of the largest porphyry deposits in the southeastern tibetan plateau the mineralization occurs mostly in the potassic alteration zone of the pulang intrusive complex u pb he triple dating namely apatite u th he zircon u pb and zircon u th he dating together with inverse thermal modeling reveals that the pulang complex was emplaced at a paleodepth of 5 0 to 6 5 km at 215 2 ma the deep level emplacement of the complex coupled with the episodic replenishment of the magma chamber gave rise to the establishment of a prolonged magmatic hydrothermal system at pulang although a range of single grain zircon and apatite u th he ages were obtained on each sample the weighted mean zircon and apatite u th he ages vary systematically with elevation defining a multistage cooling denudation history at pulang specifically three phases of cooling were recognized from inverse thermal modeling including rapid cooling 80 120 c m y in the late triassic moderate cooling 3 5 c m y from the late triassic to early cretaceous and a protracted slow cooling period 50 m y of extremely slow cooling and erosion at pulang could be related to the formation and preservation of a peneplain on the southeastern tibetan plateau since the late cretaceous a relict peneplain thus signifies a favorable tectonic environment for the preservation of ancient porphyry systems worldwide

high precision 40ar 39ar dating of two consecutive hydrothermal events in the chuquicamata porphyry copper system chile 40ar 39ar data have been used to resolve the relatively high temperature 350 c potassic alteration event at chuquicamata from the lower temperature 350 c quartz sericite alteration phase four k feldspars from the potassic zone yielded plateau large domain ages in the range 32 9 33 8 ma mean 33 4 0 3 ma the fact that apparent ages of co existing biotites span a similar range suggests that there was very rapid cooling through feldspar and biotite closure temperatures especially if these minerals closed at substantially different temperatures multi domain diffusion modelling of the feldspar data suggests that at this time cooling was rapid ca 60 80 my through closure temperatures of 330 440 c as these closure temperatures are substantially higher than the ones normally assumed for biotite i e about 300 c they and or the calculated cooling rates may be unreliable four sericites from the quartz sericite zone yielded variably discordant age spectra the least discordant of these has a plateau at 31 1 0 3 ma and this is interpreted as the time of this alteration event some k feldspars in the quartz sericite zone were completely overprinted at this later time and most of the other ones studied show partial overprinting overprinting appears to decrease as distance from the central quartz sericite zone increases in the more remote areas effects of the later event appear constrained to narrow fault controlled alteration zones the data are consistent with a conceptual model proposed by zentilli et al zentilli m leiva g rojas j graves m c 1994a the chuquicamata system revisited extended abstract society of economic geologists symposium copper deposits of the andes new developments concepcion chile october 17 18 1994 proceedings 2 1647 1651 wherein potassic alteration by late magmatic fluids occurred at depth prior to rapid exhumation of the system quartz sericite alteration perhaps caused by a new pulse of porphyry intrusion at depth occurred some 2 3 my later principally in the core of the deposit although alteration did propagate outwards through the action of hydrothermal fluids passing through a brittle relatively shallow fracture system

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

40ar 39ar and re os geochronology of porphyry copper molybdenum deposits and related copper silver veins in the collahuasi district northern chile the rosario and ujina porphyry cu mo deposits together with porphyry copper mineralization at the nearby quebrada blanca deposit constitute the third largest concentration of copper mineralization associated with the domeyko fault system in northern chile at rosario fault hosted cu ag rich massive sulfide veins are associated with pyrophyllite alunite quartz altered rocks the rosario massive sulfide veins cut biotitealbite magnetite k feldspar and illite chlorite altered rocks associated with porphyry style copper molybdenum mineralization similar massive sulfide veins occur in the la grande area 1 to 2 km south of rosario copper ore at ujina is associated with a k feldspar biotite altered quartz monzonite intrusion the k feldspar biotite assemblage has been overprinted by white mica chlorite alteration new geochronologic data presented in this paper constrain the ages of hydrothermal activity in the rosario and ujina deposits the 40ar 39ar biotite illite and alunite dates at 2 sigma error and a re os molybdenite date at 0 5 error are reported for porphyritic rocks and hydrothermal alteration from the rosario and ujina mineralized centers a weighted mean 40ar 39ar plateau age of 34 4 plus or minus 0 3 ma is obtained for igneous biotite in a monzonite porphyry that hosts copper mineralization at the rosario deposit illite and hypogene alunite from separate overprinting alteration events yielded 40ar 39ar ages of 34 5 plus or minus 0 5 ma plateau age and 32 6 plus or minus 0 3 ma plateau age respectively an re os age of 33 3 plus or minus 0 2 ma for molybdenite at rosario is slightly younger than the 40ar 39ar age of illite but older than the alunite a weighted mean plateau age of 32 7 plus or minus 1 6 ma for hypogene alunite from the la grande cu ag au vein south of rosario is indistinguishable from the age of rosario alunite at ujina the weighted mean 40ar 39ar plateau age of igneous biotite for a monzonite intrusion that hosts copper mineralization is 35 2 plus or minus 0 3 ma the monzonite is intruded by postmineralization porphyry dikes of similar composition from which igneous biotite yielded a 40ar 39ar age of 34 7 plus or minus 0 3 ma igneous biotite in the rosario porphyry cooled through its closure temperature during and after the formation of illite implying that porphyry style ore and alteration minerals in the rosario deposit had formed by 34 3 ma the age of alunite at rosario and la grande indicate that a second discrete episode of hydrothermal activity was superimposed 1 8 plus or minus 0 4 m y later onto the earlier formed porphyry cu system hydrothermal activity at ujina is constrained by the 40ar 39ar ages of igneous biotite in the premineralization and postmineralization intrusions and occurred during a minimum interval of 0 5 plus or minus 0 4 m y the biotite granite at la profunda 1 5 km east of ujina has a igneous biotite age of 81 2 plus or minus 2 9 ma indicating that this intrusion is unrelated to the mineralized eocene oligocene porphyry intrusions at ujina rosario and quebrada blanca the 40ar 39ar data for igneous biotite in the rosario and ujina porphyries are cooling ages after multiple hydrothermal events in most cases these are minimum hydrothermal ages i e ages of the last high temperature hydrothermal event to have affected the samples not magmatic ages however the biotite age for the inca porphyry is possibly only slightly younger than the intrusion age because biotite has not been affected by later hydrothermal alteration

laramide porphyry cu mo mineralization in northern mexico age constraints from re os geochronology in molybdenite twenty five new re os molybdenite ages for nine porphyry copper molybdenum deposits from northern mexico constrain the timing of mineralization and the longevity of porphyry systems in this region the ages of all the deposits are between 50 and 61 ma i e paleocene to early eocene and are associated with the laramide orogeny the oldest deposits are those from the cananea district and include the el alacran prospect 61 ma the maria deposit 60 ma the current cananea mine and la colorada breccia 59 ma the age of mineralization at cumobabi also is 59 ma and it was followed by the emplacement of deposits at suaqui verde and cuatro hermanos at about 57 to 56 ma the malpica prospect the southernmost porphyry copper prospect in western mexico was emplaced at 54 ma the la caridad deposit in nacozari and the el creston prospect both have re os molybdenite ages of 54 ma the tameapa prospect has a protracted hydrothermal mineralization history with multiple molybdenite mineralization events at 57 52 to 53 and 50 ma total re and 187 os concentrations for molybdenites range from 10 424 to 26 ppm and from 6 641 to 14 ppb respectively the deposit with the highest re and os concentrations is el alacran and the lowest concentrations are found in el creston the ages determined support the formation of porphyry copper deposits in northern mexico during the laramide orogeny in general the ages of porphyry copper deposits in the north american province range from 76 ma at bagdad arizona to 50 ma at tameapa sinaloa the ages also show that porphyry copper mineralization occurred continuously between these two dates with two main episodes at 60 ma cananea district mexico and sierrita and copper creek united states and at 54 ma la caridad el creston malpica in mexico and morenci united states

periodic hot spot distribution on io the jovian satellite io has active volcanic hot spots the point to point correlation of the hot spot distribution indicates that the hot spots preferentially make chains the arrangement of the chains is periodic with a typical spacing of 120 kilometers the chains exhibit concordant trends with stresses imposed by the tidal deflection of the lithosphere suggesting that the hot spots are formed along fissures in the lithosphere the typical spacing may be controlled by lithosphere thickness

the genesis of the ores and intrusions at the yuhai cu mo deposit in eastern tianshan nw china constraints from geology geochronology geochemistry and hf isotope systematics abstract the yuhai porphyry cu mo deposit is located in the eastern tianshan orogenic belt of the southern central asian orogen belt being an economically important porphyry cu deposit in nw china the deposit comprises sixteen buried orebodies that are predominantly associated with dioritic and granodioritic intrusions and are structurally controlled by roughly ne trending faults la icp ms zircon u pb dating yielded crystallization ages of 441 6 2 5 ma mswd 0 03 n 24 for diorite and 430 4 2 9 ma mswd 0 04 n 19 and 430 3 2 6 ma mswd 0 09 n 24 for granodiorite in situ zircon hf isotope data on a diorite sample show e hf t values from 8 7 to 18 6 and two granodiorite samples exhibit similar e hf t values from 12 6 to 19 6 and 12 6 to 18 9 respectively the dioritic and granodioritic intrusions belong to a low k tholeiite series and are relatively enriched in large ion lithophile elements k ba pb and sr and are depleted in high field strength elements th nb ta and ti moreover these intrusions have high sio 2 al 2 o 3 and mgo contents low na 2 o p 2 o 5 and tio 2 contents low nb ta ratios and slightly positive eu anomalies re os dating of molybdenite intergrowth with chalcopyrite yielded a well constrained 187 re 187 os isochron age of 351 7 2 9 ma mswd 1 5 with a weighted average age of 355 7 2 4 ma mswd 0 69 ma indicating that the yuhai cu mo deposit is younger than the intrusion of the diorite and granodiorite combined with the regional geological history and above mentioned data we suggest that the yuhai intrusions were most likely derived from the partial melting of mantle components that were previously metasomatized by slab melts formed by the northward subduction of the ancient tianshan ocean plate beneath the dananhu tousuquan island arc during the silurian to carboniferous under the subduction related tectonic setting the metasomatized mantle magma was emplaced into the shallow crust and induced the formation of the early carboniferous yuhai cu mo deposit and the hydrothermal fluids of enriched sulfides probably played an important role in the cu mo mineralization

oxide mineralization at the radomiro tomic porphyry copper deposit northern chile the main copper oxide minerals in the radomiro tomic deposit are atacamite copper clays chrysocolla and copper wad their relative abundance provides the basis for dividing the oxide zone into two major geologic units the upper oxide unit and the lower oxide unit furthermore the study of mineral abundances in the oxide zones allowed the definition of an oxide mineral zonation that consists of five mineral assemblages based on the relative proportion of the three main copper oxide components atacamite copper clays and chrysocolla these classifications allow both an understanding of the distribution of copper minerals throughout the zone and an interpretation of the supergene processes that formed it the upper oxide unit is mineralogically heterogeneous the copper content is furnished on average by 40 vol percent atacamite 31 vol percent copper clays with minor chysocolla and copper wad the lower oxide unit is more homogeneous atacamite accounts for 70 vol percent of the copper ore minerals with minor amounts of copper clays and chrysocolla copper and chlorine concentrations and porosity are greater in the upper oxide unit whereas hematite chalcocite and molybdenite concentrations and specific gravity are greater in the lower oxide unit the vertical distribution of the cl cu ratio shows a chlorine deficient zone located between elevations of 2 780 and 2 870 m between these elevations the proportion of atacamite is lower and the proportion of copper clays chrysocolla and copper wad is higher than in other portions of either the upper oxide or lower oxide units the oxide zone at radomiro tomic was originated through the in situ oxidation of a preexisting secondary sulfide enrichment blanket oxidation produced an extensive zone of atacamite accompanied by weakly developed argillic alteration the upper part of the deposit was further enriched by lateral migration of copper rich solutions to the north and east where copper precipitated as chrysocolla copper wad and copper in clays in these areas strong argillic alteration characterized by the presence of montmorillonite was developed this second alteration phase impacted only the uppermost portion of the oxide zone and the base of overlying gravels

aeromagnetic signature of porphyry copper systems in northern chile and its geologic implications the compilation of a large aeromagnetic high resolution dataset acquired for base metals exploration in northern chile between lat 19 45 s and 27 15 s revealed a pattern of transorogenic regional magnetic anomalies these anomalies occur as generally east west stripes of negative residual magnetic intensity of more than 100 nanotesla nt they have an east west extension of some tens of kilometers and a north south width of some 5 to 10 km some of them can be observed continuously from the coast to the volcanic belt their residual intensity is typically more than 100 nt they also show a loose north south spacing it is observed that all known porphyry copper deposits of the investigated segment are spatially related to these transverse magnetic anomalies we propose that the transverse magnetic anomalies are the magnetic response to the loci of emplacement of intrusive bodies of batholithic size along paths of the advancing magmatic front of the active continental margin the occurrence of several important porphyry copper deposits grouped in clusters within a district is explained as being related to a common parental intrusive complex which is geophysically signaled by a corresponding transverse magnetic anomaly a possible implication of the observed relationship between porphyry copper deposits and transverse magnetic anomalies is the quasideterministic restriction of porphyry copper deposits to certain orogen transverse loci necessary condition and the corresponding consequences for future exploration strategies

geochronology of the porphyry copper deposits and related mineralization of mexico k ar dating demonstrates that all but eight of 41 dated porphyry copper and related ore deposits of mexico were emplaced during the laramide episode of maximum plate convergence one older deposit is related to the jurassic volcanic arc of western north america one is pre laramide cretaceous four are oligocene in age and two late cenozoic deposits are within the modern trans mexican chiapenecan volcanic arc thirty three of the deposits lie within a long narrow belt that continues into arizona and new mexico and widens from 100 km to over 300 km in the region of maximum extension in the southern basin and range province eighty five percent of the deposits were emplaced during the eastward transgression of the cordilleran volcanic arc in middle cretaceous through eocene time the occurrence of the porphyry copper deposits of mexico appears to be independent of the terrane intruded and the copper content of the wall rocks where the wall rocks predate the volcanic arc which is syngenetic with the porphy

a special issue devoted to porphyry copper deposits of northern chile chile is known worldwide as the site of one of the largest copper concentrations on earth a total resource including production of about 400 million tons mt of fine copper has been identified in 50 porphyry copper deposits and numerous prospects fig 1 considering 10 mt of contained fine copper as a minimum tonnage to classify a porphyry copper deposit as a giant ore deposit the chilean cordillera contains nine of the 16 giant porphyries along the circum pacific belt among them are the three largest of all el teniente rio blanco los bronces and chuquicamata fig 1 all containing resources plus production of more than 50 mt of fine copper currently chile annually produces about 4 6 mt of fine copper that represents about 37 percent of the world production this enormous geologic potential has triggered numerous international mining companies to concentrate their exploration efforts in the central andes with emphasis in chile during the past 25 years exploration expenditures have surpassed a figure on the order of us 2 billion as a result a total of 76 copper and gold discoveries have been made 24 of which are already in production cabello 2000 among them the most relevant discoveries are the porphyries at la escondida escondida norte zaldivar rosario and ujina in the collahuasi mining district quebrada blanca lomas bayas and in the last 5 years spence and gaby sur the presence of such a significant number and large size of copper porphyries intrigued several generations of researchers during the twentieth century the ongoing exploration efforts have enhanced the interest in understanding the andean geological evolution and metallogenesis the geological processes that are common factors in controlling the emplacement of these orebodies have been the subject of research by numerous individuals in chile and elsewhere the support of mining companies has been

dating the giant zhuxi w cu deposit taqian fuchun ore belt in south china using molybdenite re os and muscovite ar ar system abstract the recently discovered zhuxi w cu ore deposit is located within the taqian fuchun ore belt in the southeastern edge of the yangtze block south china its inferred tungsten resources based on new exploration data are more than 280 mt by 2016 at least three paragenetic stages of skarn formation and ore deposition have been recognized prograde skarn stage retrograde stage and hydrothermal sulfide stage secondly greisenization marmorization and hornfels formation are also observed scheelite and chalcopyrite are the dominant metal minerals in the zhuxi deposit and their formation was associated with the emplacement of granite stocks and porphyry dykes intruded into the surrounding carboniferous carbonate sediments huanglong and chuanshan formations and the neoproterozoic slate and phyllites the scheelite was mostly precipitated during the retrograde stage whereas the chalcopyrite was widely precipitated during the hydrothermal sulfide stage a muscovite 40ar 39ar plateau age of about 150 ma is interpreted as the time of tungsten mineralization and molybdenite re os model ages ranging from 145 9 2 0 ma to 148 7 2 2 ma for the subsequent hydrothermal sulfide stage of activity as the time of the copper mineralization our new molybdenite re os and muscovite 40ar 39ar dating results along with previous zircon u pb age data indicate that the hydrothermal activity from the retrograde stage to the last hydrothermal sulfide stage lasted up to 5 myr from 150 6 1 5 to 145 9 1 ma and is approximately coeval or slightly later than the emplacement of the associated granite porphyry and biotite granite the new ages reported here confirm that the zhuxi tungsten deposit represents one of the mesozoic magmatic hydrothermal mineralization events that took place in south china in a setting of lithospheric extension during the late jurassic 160 150 ma it is suggested that mantle material played a role in producing the zhuxi w cu mineralization and associated magmatism

re os isotopic dating of molybdenites in the xiaoliugou w mo deposit in the northern qilian mountains and its geological significance abstract the xiaoliugou is a large scale w mo deposit newly explored in the northern qilian mountains caledonian fold belt northwestern china it is a vein and skarn type deposit genetically associated with the xiaoliugou caledonian granodiorite stock re os isotopic dating for the molybdenite in the deposit yields an isochron age of 462 13 ma 2 and model ages of 436 to 496 ma these results suggest that w mo mineralization occurred before the collision of plates and mineralized substances mainly originated from the crust

late paleozoic early triassic magmatism on the western margin of gondwana collahuasi area northern chile abstract the basement in the altiplano high plateau of the andes of northern chile mostly consists of late paleozoic to early triassic felsic igneous rocks collahuasi group that were emplaced and extruded along the western margin of the gondwana supercontinent this igneous suite crops out in the collahuasi area and forms the backbone of most of the high andes from latitude 20 to 22 s rocks of the collahuasi group and correlative formations form an extensive belt of volcanic and subvolcanic rocks throughout the main andes of chile the frontal cordillera of argentina choiyoi group or choiyoi granite rhyolite province and the eastern cordillera of peru thirteen new shrimp u pb zircon ages from the collahuasi area document a bimodal timing for magmatism with a dominant peak at about 300 ma and a less significant one at 244 ma copper mo porphyry mineralization is related to the younger igneous event initial hf isotopic ratios for the 300 ma zircons range from about 2 to 6 indicating that the magmas incorporated components with a significant crustal residence time the 244 ma magmas were derived from a less enriched source with the initial hf values ranging from 2 to 6 suggestive of a mixture with a more depleted component limited whole rock 144nd 143nd and 87sr 86sr isotopic ratios further support the likelihood that the collahuasi group magmatism incorporated significant older crustal components or at least a mixture of crustal sources with more and less evolved isotopic signatures

a re os study of sulfide minerals from the bagdad porphyry cu mo deposit northern arizona usa rhenium and osmium isotopes in sulfide minerals from the bagdad porphyry cu mo deposit have been used to determine timing of mineralization and the source of osmium and by inference ore metals molybdenite chalcopyrite and pyrite were analyzed mainly from the quartz monzonite and porphyritic quartz monzonite units which are characterized by moderate to strong potassic alteration secondary biotite and k feldspar rhenium concentrations in molybdenite are between 330 and 642 ppm four re os analyses of two molybdenite samples from the quartz monzonite and porphyritic quartz monzonite yield a weighted average age of 71 8 0 2 ma 2 analyses of a third sample from a molybdenite vein in precambrian rocks outside of the main ore zone yield a weighted average age of 75 9 0 2 ma 2 and provide evidence of two separate mineralization episodes chalcopyrite samples contain 6 to 12 ppt os and 1 7 to 4 1 ppb re 187os 188os initial ratios are between 0 1 and 0 8 pyrite samples have osmium and rhenium concentrations varying in the range 8 17 ppt and 3 9 6 8 ppb respectively analyses from these pyrite samples yield an eight point isochron with an age of 77 15 ma 2 and an initial 187os 188os ratio of 2 1 0 8 mswd 0 90 the results presented here add to the growing body of work indicating that porphyry type mineralization is produced by long term multiple episodes of magmatism and associated mineralization the data also support the hypothesis that a significant part of the metals and magmas may have a crustal source as has been suggested for other copper deposits and districts in arizona

a revised late eocene age for porphyry cu magmatism in the escondida area northern chile new u pb zircon and 40 ar 39 ar single crystal incremental heating biotite dates are reported for porphyritic rocks from three mineralized centers in the escondida region of northern chile all dates are reported with 2sigma errors at the chimborazo porphyry cu prospect a weighted mean 40 ar 39 ar plateau age of 38 09 or 0 30 ma has been obtained for igneous biotite from a syn or postmineralization feldspar biotite quartz porphyry intrusion at the zaldivar porphyry cu mine zircon and biotite have been analyzed from a similar synmineralization feldspar biotite quartz porphyry the llamo porphyry the zircon u pb age is 38 7 or 1 3 ma whereas the weighted mean 40 ar 39 ar plateau age of igneous biotite is slightly younger at 37 40 or 0 18 ma u pb dating of two other rhyolitic quartz feldspar porphyry bodies that host much of the ore at zaldivar shows that these rocks are paleozoic in age antigua porphyry 290 or 4 ma zaldivar porphyry broadly coeval with antigua but age poorly defined at the escondida deposit the reportedly synmineralization escondida porphyry is dated by u pb at 37 9 or 1 1 ma whereas the reportedly postmineralization rhyolitic porphyry returned a u pb age of 34 7 or 1 7 ma these results indicate a single pulse of synmineralization magmatism in the escondida district at approximately 38 ma followed by minor largely nonmineralizing intrusive events the timing of main stage porphyry mineralization at escondida is apparently bracketed by the ages of the escondida 37 9 or 1 1 ma and rhyolitic porphyries 34 7 or 1 7 ma previously published k ar dates for intrusive rocks and alteration minerals at escondida which range from 39 to 31 ma are interpreted to reflect variable degrees of disturbance of the k ar system by later intrusive events and or by supergene weathering processes an age of approximately 38 ma for ore forming porphyry magmatism in the escondida region is significantly older than previously accepted best estimates based on k ar and u pb dating 32 34 ma but still falls within the age range of other large porphyry systems within the north south trending west fissure zone of northern chile 31 42 ma a common feature of the porphyry intrusions at zaldivar and escondida and also at chuquicamata and el salvador is the presence of zircons with inherited upper paleozoic cores these cores are interpreted to reflect interaction between arc magmas and crustal rocks during melting assimilation storage and homogenization mash and assimilation and fractional crystallization afc processes at various crustal levels

the upper pleistocene on the northern face of the guadarrama mountains central spain palaeoclimatic phases and glacial activity abstract the present paper provides new information on pleistocene glacial activity in a mountainous area of the iberian central system a sediment analysis associated with pleistocene modelling was carried out using 1 granulometric and morphometric procedures 2 quartz grain microtexture techniques sem to discriminate between glacial and no glacial origins of sediments 3 clay x ray diffraction study to determine intra pleistocene climate variability and 4 optically stimulated luminescence osl absolute dating the results show that the sediments were formed in two different phases associated with glacial dynamics one of them was 35 30 ky bp and another was 25 20 ky bp separated by a short intermediate warm wet period identification of glacial phenomena is new for the northern slopes of the guadarrama mountains facing the north meseta duero basin although they are not unusual within the general context of the iberian central system from the data provided we deduce that glaciation in these mountains was much more intense and widespread than had previously been thought because on the northern slopes glaciers occupied large areas reaching the base of the mountains the evidence favours new interpretations of pleistocene morphology in the centre of the iberian peninsula and by extension on the southwestern edge of europe it also highlights the sensitivity of mountainous areas with regard to quaternary climate changes