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assemblage paragenetic relationships indicate that magnetite was the earliest formed alteration product but has been replaced by biotite albite vein crosscutting relationships indicate that k feldspar formed during and after biotite albite alteration chalcopyrite and bornite were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

along strike segmentation of the abanico basin central chile new chronological geochemical and structural constraints the andes of central chile are composed mostly of cenozoic volcanic rocks erupted during the opening and subsequent inversion of the intra arc volcano tectonic abanico basin until recently the internal segmentation of this inverted basin was poorly understood based on a combination of u pb geochronology u th he thermochronology whole rock geochemistry and structural data we propose that the abanico basin can be divided into two main segments separated by the nw striking piuquencillo fault and conjugate ne striking faults stratigraphic units defined in the northern segment abanico and farellones formations cannot be correlated with the rocks of the southern segment coya machali formation and teniente volcanic complex in terms of lithofacies depositional ages and geochemistry the northern and southern segments also show temporal differences in their tectonic evolution an early deformation event beginning at 22 ma affected only the northern segment and is associated with the formation of progressive unconformities between the abanico and farellones formations and also with crustal thickening as reflected in the geochemistry of the farellones formation a second stage of crustal thickening and exhumation began at 12 ma as suggested by a sharp increase of the la yb ratios in the northern segment in the southern segment this event is reflected by only a moderate increase of la yb ratios and by the transition between the coya machali formation and the teniente volcanic complex finally a third stage of exhumation and crustal thickening beginning at 7 ma affected both the northern and southern segments this last stage was the main exhumation event affecting the rocks of the andes of central chile and is recorded in the geochemistry of igneous rocks by a sharp increase in the la yb ratios in the southern segment

tectonic trigger for the formation of late miocene cu rich breccia pipes in the andes of central chile during the late miocene the decreasing angle of subduction below the andes of central chile caused a reduction in the influx of new magma and heat into the base of magmatic systems that had been active throughout the miocene this led to their cooling and solidification triggering the release of large volumes of metal rich magmatic fluids from middle and upper crustal magma chambers and generating a group of economically significant cu rich breccia pipes the sr and nd isotopic compositions of the magmatic fluids that formed these brecccas determined from breccia matrix minerals were variable implying that these fluids were not exsolved from a specific cu porphyry magma as is often invoked to explain andean cu deposits instead the formation of the late miocene deposits in central chile was tectonically triggered by cooling of a variety of magma types during the last stages of existence of long lived andean magmatic systems as both subduction angle and as a result subarc magma supply decreased

tectonic affinity of nisutlin and anvil assemblage strata from the teslin tectonic zone northern canadian cordillera constraints from neodymium isotope and geochemical evidence we present geochemical and isotopic data for nisutlin assemblage metasedimentary rocks and anvil assemblage greenstones from the teslin tectonic zone of the northern canadian cordillera this study aims to establish the tectonic setting of formation for the sedimentary and basaltic protoliths of these highly deformed and metamorphosed rocks and thereby place constraints on the origin of these enigmatic rocks for which differing tectonic models have been proposed for the nisutlin assemblage metasedimentary rocks the geochemical and isotopic data show that two widely different source regions contributed detritus to the original sediments one source region was felsic upper crustal material with nd isotopic compositions compatible with ultimate derivation from the north american continent depleted mantle model age tdm 2 5 2 8 ga the second source region is deduced to be chemically primitive crust basaltic andesitic with a short crustal residence history 0 9 ga for the anvil assemblage greenstones immobile trace element abundances are dissimilar to within plate oceanic arc and normal mid ocean ridge basalts and similar to calc alkaline basalts in active continental margin settings we interpret the paleosetting for the nisutlin assemblage to be at the outermost margin of the ancestral north american continent in an area which received detrital input from the distal north american craton in the early paleozoic however this area also received detritus from a chemically and isotopically juvenile magmatic arc source a source type not known from paleozoic metasedimentary rocks from the miogeoclinal sequence on the basis of similar nd isotopic relationships recorded elsewhere in deformed paleozoic rocks of the orogen we infer that these geochemical signals reflect tectonic processes of regional extent the trace element geochemistry of the anvil assemblage greenstones does not support a correclation with known paleozoic greenstones of the slide mountain terrane which some tectonic models have advocated

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

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

the thermal significance of potassium feldspar k ar ages inferred from age spectrum results 40ar39ar age spectrum analyses of three microcline separates from the separation point batholith northwest nelson new zealand which cooled slowly 5 c ma 1 through the temperature zone of partial radiogenic 40ar accumulation are characterized by a linear age increase over the first 65 percent of gas release with the lowest ages 80 ma corresponding to the time that the samples cooled below about 100 c the last 35 percent of 39ar released from the microclines yields plateau ages 103 99 and 93 ma which reflect the different bulk mineral ages and correspond to cooling temperatures between about 130 to 160 c theoretical calculations confirm the likelihood of diffusion gradients in feldspars cooling at rates 5 c ma 1 diffusion parameters calculated from the 39ar release yield an activation energy e 28 8 1 9 kcal mol 1 and a frequency factor grain size parameter d0l2 5 6 3 9 14sec 1 this arrhenius relationship corresponds to a closure temperature of 132 13 c which is very similar to the independently estimated temperature from the observed diffusion compensation correlation this d0l2 implies an average diffusion half width of about 3 m similar to the half width of the perthite lamellae in the feldspars the range in microcline k ar ages from the separation point batholith is the result of relatively small temperature differences within the pluton during cooling comparison of the diffusion laws determined for microcline with those for anorthoclases and other homogeneous k feldspars e 40 to 52 kcal mol 1 reveals that ar diffusion is more highly temperature dependent in the disordered structural state than in the ordered structural state previously published u shaped age spectra are probably the result of the superimposition of excess 40ar upon diffusion profiles of the kind described here

neotectonics seismicity and stress in glaciated regions the melting of large ice caps over the span of many centuries to several millennia is an important agent of dynamic change within the solid earth fig 1 it induces significant redistributions of mass on the surface of the earth drives sea level and land elevation changes and readjusts lithospheric stresses in formerly glaciated areas and adjacent regions effects manifest as increased seismicity and eventually in powerful earthquakes it was an understanding that was apparent a century ago de geer 1888 kolderup 1913 but has found increased support during the 20th century in particular the discovery of the end glacial faults of northern scandinavia kujansuu 1964 lagerback 1979 olesen 1988 proved definitively that glacial loads and therefore climate can act as tectonic drivers over very short geological times fig 1 simplifed loading history for central fennoscandia during the last weichselian major glaciation modified after talbot 1999 ice thickness appears above the time axis and consequent crustal depression appears below the model illustrates how rapid vertical ice loading and unloading changes lead to far slower crustal depression or rebound and that the scale of crustal response is considerably less than the imposed ice mass fluctuations reflecting viscous flow of the

late cretaceous to miocene volcanism sedimentation and upper crustal faulting and folding in the principal cordillera central chile field and geochronological evidence for protracted arc volcanism and transpressive deformation

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

u pb geochronology of the syn orogenic knaben molybdenum deposits sveconorwegian orogen norway paired isotope dilution thermal ionization mass spectrometry id tims and secondary ion mass spectrometry sims zircon u pb data elucidate geochronological relations in the historically important knaben molybdenum mining district sveconorwegian orogen south norway this polyphase district provided c 8 5 mt of ore with a grade of 0 2 it consists of mineralized quartz veins silica rich gneiss pegmatites and aplites associated with a heterogeneous locally sulphide bearing amphibolites facies gneiss called knaben gneiss and hosted in a regional scale monotonous commonly weakly foliated granitic gneiss an augen gneiss at the knaben i deposit yields a 1257 6 ma magmatic zircon age dating the pre sveconorwegian protolith of the knaben gneiss mineralized and non mineralized granitic gneiss samples at the knaben ii and kvina deposits contain some 1488 1164 ma inherited zircon and yield consistent intrusion ages of 1032 4 1034 6 and 1036 6 ma this age links magmatism in the district to the regional 1050 1020 ma sirdal i type granite suite corresponding to voluminous crustal melting during the sveconorwegian orogeny a high u low th u zircon rim is present in all samples it defines several age clusters between 1039 6 and 1009 7 ma peaking at c 1016 ma and overlapping with a monazite age of 1013 5 ma the rim records protracted hydrothermal activity which started during the main magmatic event and outlasted it this process was coeval with regional high grade sveconorwegian metamorphism molybdenum deposition probably started during this event when silica rich mineralizing fluids or hydrous magmas were released from granite magma batches an analogy between the knaben district and shallow short lived porphyry mo deposits is inappropriate

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

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

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

mineralogical and isotopic zonation in the sur sur tourmaline breccia rio blanco los bronces cu mo deposit chile implications for ore genesis the sur sur tourmaline breccia is located in the southeast part of the rio blanco los bronces porphyry copper molybdenum deposit central chile the breccia hosts approximately one quarter of the total resource of 57 mt of fine copper at rio blanco the breccia is hosted within and contains altered clasts of granodiorite from the 12 to 8 ma san francisco batholith which intruded a sequence of miocene volcanic and volcaniclastic rocks a series of weakly mineralized to barren felsic porphyries cut the breccia and indicate a minimum age of approximately 6 ma for mineralization at sur sur the sur sur breccia dike is at least 3 km long 0 2 km wide and has a vertical extent of at least 1 km the breccia has been cemented by early biotite and anhydrite at depth and by tourmaline and specularite at higher altitudes these early formed cements have been overgrown and in some cases replaced by chalcopyrite magnetite pyrite and quartz mineralogical zonation in the breccia includes a transition from biotite cement and related biotite alteration upward to tourmaline cement and quartz sericite tourmaline alteration at approximately 3 000 m elevation iron oxide minerals are also zoned with a transition upward from a magnetite dominated zone below 3 330 m to a specularite dominated zone above 3 600 m pyrite is the dominant sulfide at altitudes above 4 000 m secondary liquid rich vapor rich and hypersaline fluid inclusions are preserved in quartz and tourmaline cement measured homogenization temperatures are mostly between 300 degrees and 450 degrees c and salinities range from 0 to 69 wt percent nacl equiv sulfur isotope compositions of sulfide cement range from 4 1 to 2 7 per mil the lowest delta 34s sulfide values are in samples from between 3 700 and 4 000 m elevation where they correspond to the highest copper grades in the tourmaline breccia this high grade zone also contains abundant specularite locally replaced by magnetite modeling of sulfate sulfide equilibrium indicate that approximately 150 degrees c of cooling over a vertical interval of 100 m would be required to account for the zonation of sulfide isotope compositions at sur sur making conductive cooling an unlikely ore forming mechanism measured 206pb 204pb values of lead in anhydrite cement in the sur sur tourmaline breccia and the rio blanco magmatic breccia range from 17 558 to 18 479 207pb 204pb values range from 15 534 to 15 623 and 208pb 204pb values range from 37 341 to 38 412 the lead in anhydrite is considerably less radiogenic than that indicated by values obtained previously for lead in sulfide ores and igneous host rocks at rio blanco los bronces the source of lead in anhydrite must have been from rocks external to the main magmatichydrothermal system probably the precordilleran basement a magmatic hydrothermal explosion from a deep seated crystallizing intrusion triggered breccia formation at sur sur hydrostatic pressures catastrophically exceeded lithostatic load plus the tensile strength of the confining granodiorite leading to widespread brecciation and subsequent invasion by large volumes of magmatic gas and hypersaline brine the low density gas phase carrying h2o so2 hcl and b2o3 separated physically from the dense copper bearing brine and flushed through the breccia column first where it condensed into ground waters of uncertain derivation anhydrite specularite and tourmaline were deposited from this lowsalinity acidic oxidized hybrid solution subsequent upwelling of magmatic hydrothermal brine resulted in sulfide deposition high grade copper deposition is interpreted to have occurred in response to mixing of the oxidized acidic water with the copper bearing magmatic hydrothermal brine

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

arc oblique fault systems their role in the cenozoic structural evolution and metallogenesis of the andes of central chile abstract the evolution of the main cordillera of central chile is characterized by the formation and subsequent inversion of an intra arc volcano tectonic basin the world s largest porphyry cu mo deposits were emplaced during basin inversion statistically the area is dominated by ne and nw striking faults oblique to the n striking inverted basin margin faults and to the axis of cenozoic magmatism this structural pattern is interpreted to reflect the architecture of the pre andean basement stratigraphic correlations syn extensional deposits and kinematic criteria on fault surfaces show several arc oblique structures were active as normal faults at different stages of basin evolution the geometry of syn tectonic hydrothermal mineral fibers in turn demonstrates that most of these structures were reactivated as strike slip reverse faults during the middle miocene early pliocene fault reactivation age is constrained by 40 ar 39 ar dating of hydrothermal minerals deposited during fault slip the abundance and distribution of these minerals indicates fault controlled hydrothermal fluid flow was widespread during basin inversion fault reactivation occurred under a transpressive regime with e to ene directed shortening and was concentrated around major plutons and hydrothermal centers at the margins of the former intra arc basin deformation was largely accommodated by reverse faulting whereas in its central part strike slip faulting was predominant

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

reos dating of molybdenites from ore deposits in japan implication for the closure temperature of the reos system for molybdenite and the cooling history of molybdenum ore deposits abstract rhenium and osmium abundances were determined on molybdenites from eighteen ore deposits in japan fifteen vein type a skarn type a greisen type and a pegmatite type deposit re os ages obtained for molybdenites from northeastern central and southwestern japan are 100 130 ma 50 75 ma and ca 10 ma respectively reflecting the ages of regional igneous activities in individual areas for vein type ore deposits re os ages for molybdenites agree with rb sr whole rock ages of host granitoids while they are 3 12 ma older than k ar mineral ages of the host rocks on the other hand re os ages of molybdenites from skarn pegmatite and greisen type ore deposits agree with k ar ages of the host rocks the comparison of re os ages for molybdenites with rb sr and k ar ages of host rocks in vein type deposits suggests that re os closure temperature for vein molybdenite is close to whole rock rb sr closure temperature for host granitic rocks i e roughly estimated to be around 500 c and higher than k ar closure temperature for host granodiorites i e 230 370 c if the thermal history of vein molybdenites is essentially equivalent to that of host rocks one possible explanation for age discrepancies of 3 12 ma between re os ages for molybdenites and k ar ages for the wall rocks observed in vein type molybdenum deposits is that later thermal events after formation of molybdenum ores may reset k ar ages hydrothermal alteration might have occurred in such a temperature condition as to disturb k ar mineral systems in wall rocks and made them younger but not the re os system in molybdenite the other explanation might be that the age discrepancies correspond to a cooling interval from ca 500 to 300 c of host granitoid on the other hand the agreement of re os ages of molybdenites and k ar ages of host rocks in skarn pegmatite and greisen type deposits in this study indicates no later disturbance for k ar system in the wall rock or the rapid cooling of the ore and wall rocks after the formation of molybdenite deposits

bay sedimentation as controlled by regional crustal behaviour local tectonics and eustatic sea level changes coquimbo formation miocene pliocene bay of tongoy central chile abstract the north facing bay of tongoy in central chile is flanked by topographic highs in the west and east during the miocene and pliocene the bay extended inland at least 30 km farther south than a present it was filled with muds sands coquinas and gravel during a series of transgressions and regressions related to regional and local tectonic movements combined with global sea level variations 87sr 86sr and microfossil dating indicates transgressions between 11 9 11 2 ma 10 1 9 5 ma 9 0 7 3 ma 6 3 5 3 ma 4 3 2 2 ma and 1 7 1 4 ma the regional tectonic behaviour of the crust shows general uplifting from 10 5 ma to 6 9 ma associated with subduction of the juan fernandez ridge jfr beneath this part of the continent subsidence followed between 6 9 and 2 1 ma in the wake of the southeastward migrating jfr the subsequent subduction of an oceanic plateau similar to the jfr caused rapid uplift that led to the final emergence of the bay above sea level the puerto aldea normal fault along the western limit of the study area was reactivated during the regional uplift and subsidence events with reverse faulting occurring during the latter phase sporadic fault reactivation probably triggered the rapid changes in water depth reflected in the recorded vertical succession of facies

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

radial viscous fingering of hot asthenosphere within the icelandic plume beneath the north atlantic ocean abstract the icelandic mantle plume has had a significant influence on the geologic and oceanographic evolution of the north atlantic ocean during cenozoic times full waveform tomographic imaging of this region shows that the planform of this plume has a complex irregular shape with significant shear wave velocity anomalies lying beneath the lithospheric plates at a depth of 100 200 km the distribution of these anomalies suggests that about five horizontal fingers extend radially beneath the fringing continental margins the best imaged fingers lie beneath the british isles and beneath western norway where significant departures from crustal isostatic equilibrium have been measured here we propose that these radial fingers are generated by a phenomenon known as the saffman taylor instability experimental and theoretical analyses show that fingering occurs when a less viscous fluid is injected into a more viscous fluid in radial miscible fingering the wavelength and number of fingers are controlled by the mobility ratio i e the ratio of viscosities by the peclet number i e the ratio of advective and diffusive transport rates and by the thickness of the horizontal layer into which fluid is injected we combine shear wave velocity estimates with residual depth measurements around the atlantic margins to estimate the planform distribution of temperature and viscosity within a horizontal asthenospheric layer beneath the lithospheric plate our estimates suggest that the mobility ratio is at least 20 50 that the peclet number is o 10 4 and that the asthenospheric channel is 100 20 km thick the existence and planform of fingering is consistent with experimental observations and with theoretical arguments a useful rule of thumb is that the wavelength of fingering is 5 1 times the thickness of the horizontal layer our proposal has been further tested by examining plumes of different vigor and planform e g hawaii cape verde yellowstone our results support the notion that dynamic topography of the earth s surface can be influenced by fast irregular horizontal flow within thin but rapidly evolving asthenospheric fingers

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

the altar porphyry cu au mo deposit argentina a complex magmatic hydrothermal system with evidence of recharge processes altar 31 29 s 70 28 w is a large porphyry cu au mo deposit with associated epithermal au ag cu veins located in the cordillera principal of southwest san juan province argentina altar is a complex magmatic hydrothermal system formed from several magmatic and hydrothermal pulses during the middle late miocene new la icpms u pb ages in zircons from the altar porphyries indicate four discrete events of intrusions over an extended magmatic life time of ca 3 m y it comprises a premineralization porphyry 11 75 0 24 ma three mineralized porphyries 11 62 0 21 and 11 68 0 27 ma 11 13 0 26 ma 10 35 0 32 ma related to hydrothermal breccias two postmineralization intrusions and a postmineralization breccia 8 9 0 4 ma the three mineralized porphyries porphyries 2 3 and 4 were emplaced within 0 7 to 1 3 m y amphibole phenocrysts from the porphyries crystallized from oxidized magmas f o2 nno 1 to 2 at temperatures of 780 to 850 c and pressures between 0 9 and 1 8 kbars corresponding to depths of 4 to 7 km anorthite and fe rich rims in the plagioclase phenocrysts suggest that the magmatic chambers were episodically recharged by a less evolved magma the middle late miocene intrusions are interpreted to have been derived from a deeper and relatively large magmatic reservoir that supplied magmas to smaller chambers located in the upper crust the focused magmatic output to shallow levels during a period of a few million years in the altar area has been a main requirement in the formation of this large porphyry copper deposit

transvaporite model of ore genesis and an exploration strategy for new giant ore deposits abstract in the current work we stand for the revival of the transvaporite ore genesis model which was introduced by hungarian academician e szadeczky kardoss more than half a century ago but has now fallen out of favor and superseded by the orthomagmatic model our arguments in support of the transvaporite model are based on the contemporary overpressure theory developed for mesozoic cenozoic petroleum basins we propose a new variant of the transvaporization model whereby the formation of giant ore deposits occurs in the areas where former petroleum rich basins are intersected by large igneous provinces lips at such sites structural magmatic activity leads to hydrocarbon deposits being destroyed and many new ore deposits being created beneath a new regional volcanic fluid seal built by rapidly accumulating up to 3 4 km in 1 ma lava flows in such conditions a zone of significant overpressure that is 1 4 1 8 times higher than hydrostatic pressure develops subsequently under the influence of compressive mechanism of mass transfer gas saturated brines of sedimentary rocks migrate toward intruding melts and then mix with them as a result unusual rocks transvaporites are formed and giant ore deposits created here we review six supergiant ore deposits of various types and ages with different associations of metals and host rocks including the norilsk district in russia cu ni co pt pd el teniente los bronces district in chile cu mo almaden deposit in spain hg ermakovskoe deposit in russia be pebble copper deposit in southern alaska cu mo au and olympic dam deposit in southern australia u cu au ree noting that all listed metals in each and every deposit do reach giant reserves in all these deposits transvaporization appears to play the key role in ore genesis given the 1 short duration of the main ore genesis stage a significant practical implication of the transvaporite model is that it should modify future strategies for ore deposits exploration instead of pursuing just any deposit exploration efforts should focus specifically on giant ore deposits concentrating search efforts at the sites where former petroleum basins have been intersected by lips basin analysis of enriched oil and gas provinces is already being conducted in detail by seismic transects involving two dimensional cross sections and areal surveys followed by three dimensional mapping of productive reservoirs the same strategy should be applied to ore bearing regions but at better precision and accuracy given the smaller velocity contrast in seismic wave propagation in ore rocks compared with oil and gas bearing sedimentary rocks important advances in the ore geology of lips such as geological mapping and gravity and magnetic surveys have already produced significant new data these studies can be divided into two types which first involve a general description of the lip and are then followed by an investigation of major intrusions likely to be directly linked to ore genesis a combination of these investigations into hydrocarbon basins and lips will lay the foundation for transvaporite exploration which will be the key criterion for the successful search for new giant ore deposits

determining the neogene behavior of the nazca plate by geohistory analysis geohistory analysis was performed on neogene deposits south and north of la serena central chile to determine the behavior of the crust since the middle miocene the tectonic history of both study areas was found to be similar but the timing of uplift and downwarp events at the two localities differs by 1 3 and 0 8 m y respectively which we attribute to the approach and passing of the juan fernandez ridge from trigonometric relationships between the ridge trend the plate vector and the trend between the study areas we calculated a plate convergence rate of 6 2 cm yr between 11 8 and 10 5 ma and 10 1 cm yr between 7 7 and 6 9 ma rapid uplift commenced ca 2 3 ma with a delay of 0 3 m y between the two study areas trigonometric constraints suggest the presence of a hitherto unsuspected oceanic plateau trending 014 subducted below the present continental margin flat plate subduction may thus be better developed where it is assisted by the combined buoyancy of ridge clusters instead of single subducting plateaus