lead isotope analyses of gold silver ores from rosia montană romania a first step of a metal provenance study of roman mining activity in alburnus maior roman dacia the rosia montan ore deposit apuseni mountains romania is europe s largest au ag deposit it also corresponds to the roman alburnus maior mining site known by historians and archaeologists due to the discovery of dozens of roman wooden wax tablets during the underground works carried out during the 18th and 19th centuries the present geochemical research is based on a detailed archaeological and geological study of the roman mines at rosia montan making use of archaeologically and geologically documented ore samples the geochemical analyses allowed us to establish an accurate database for the ores exploited during roman times at rosia montan and probably before this approach represents a contribution towards improving the accuracy of metal provenance studies of gold silver ores during antiquity in romania and also at an european level because the studied ore samples represent remnants of the original ores used by the romans for the production of precious metals twenty nine ore samples and one litharge roll have been selected prepared and analysed by mc icp ms high resolution measurements a specific rosia montan pb isotope signature of gold silver ores extracted by the roman miners was obtained this signature is distinct when compared with other ore deposits from the apuseni mountains as well as within a broader region maramures ore district a litharge roll discovered in a roman inclined adit situated close to the surface which attests the presence of metallurgical workshops has also been analysed the different lead isotope values of the litharge roll and the rosia montan gold silver ores suggest that other ore sources from the south apuseni mountains or from elsewhere were also employed by the gold metallurgy developed at rosia montan during roman times

diatreme breccias at the kelian gold mine kalimantan indonesia precursors to epithermal gold mineralization early miocene volcanism associated with a maar diatreme breccia complex preceded main stage epithermal gold mineralization at the kelian gold mine kalimantan indonesia prior to brecciation andesite intrusions 19 7 0 06 ma were emplaced into a package of felsic volcaniclastic rocks and overlying carbonaceous sand stones and mudstones and a weakly mineralized geothermal system was established intrusion of quartz phyric 19 8 0 1 ma and quartz feldspar phyric rhyolite 19 5 0 1 ma into the active geothermal system triggered widespread fragmentation and formation of the maar diatreme complex subsurface phreatomagmatic and phreatic explosions disrupted the preexisting hydrothermal system producing three composite diatreme breccia bodies the tepu runcing and burung breccias the diatremes consist of polymict breccias and sandstones that contain abundant carbonaceous matrix a distinctive facies association comprising coherent rhyohte jigsaw fit rhyolite breccia and matrix rich breccias that contain wispy to blocky juvenile rhyolite clasts define the root zones of the diatremes the surficial products of maar diatreme volcanic activity at kelian are preserved as large blocks of well stratified breccias they contain accretionary lapilli and were deposited by a combination of wet pyroclastic basesurge fallout and cosurge fallout processes evidence for syneruptive resedimentation of the pyroclastic deposits is preserved in poorly stratified breccia beds megablocks of phreatomagmatic base surge deposits were dropped down several hundred meters from the maar environment into the underlying diatremes volcanism in the kelian maar diatreme complex was dominated by a combination of phreatomagmatic and phreatic processes with subordinate hydraulic tectonic and dry magmatic fragmentation the carbonaceous matrix rich diatreme breccias acted as aquicludes during subsequent hydrothermal activity focusing fluid flow into the wall rocks adjacent to the diatremes where epithermal gold mineralization and hydrothermal brecciation occurred 2008 society of economic geologists inc

elastic finite difference modeling of the 1971 san fernando california earthquake finite difference seismograms calculated for the 1971 san fernando earthquake show strong effects due to lateral variation in sediment thickness in the san fernando valley and the los angeles basin using basin structure derived mostly from well logs and teleseismically determined source parameters two dimensional sh and p sv finite difference calculations reproduce the amplitude and duration of the strong motion velocities recorded across the los angeles and san fernando basins for the period range of 2 to 10 sec the edges of basins nearest the seismic source show ground motion amplification up to a factor of 3 over the case without the basin and tend to convert direct shear waves into love and rayleigh waves that travel within the basins

the 1994 northridge earthquake 3 d crustal structure in the rupture zone and its relation to the aftershock locations and mechanisms a detailed 3 d p wave velocity structure of the crust in the epicentral area of the 17 january 1994 northridge earthquake is determined by using 104 709 arrival times from 1673 northridge aftershocks and 2948 other local earthquakes a test performed using the data from the nearby portable stations suggests that the aftershock hypocenters relocated with the obtained 3 d model are accurate to about 2 km we found that regions with high aftershock activity are generally associated with faster p wave velocities the velocity is high around the main south dipping fault of the 1994 northridge earthquake and the north dipping fault of the 1971 san fernando earthquake a linear distribution of strike slip aftershocks was found along a ne sw boundary between high velocity and low velocity structures to the west of this boundary a cluster of large shallow aftershocks with mixed mechanisms occurred in or near the border of a low velocity area while to the east aftershocks with thrust mechanisms occurred in a high velocity area these observations suggest that lateral variations of crustal properties are closely related to the fault segmentation in the transverse ranges a better understanding of these features is important for long term seismic hazard assessment in the los angeles area

mineralogical and chemical variations of ochreous precipitates from acid sulphate waters asw at the rosia montană gold mine romania the mineralogical and chemical variations of ochreous precipitates forming from acid sulphate waters discharged from the lowest mine adit sf cruci din orlea of the rosia montan gold mine romania were investigated by a multianalytical approach xrpd ir tem icp applied to surface precipitates and associated waters the mineralogy of the precipitates changed significantly as a consequence of the variations in the chemical parameters of the circulating solutions mainly ph eh and sulphate concentrations which were mainly controlled by mixing with unpolluted waters of rosia river ochreous precipitates are characterized by high concentrations of potentially toxic elements ptes in particular cr co ni cu zn as cd and pb and consist of a mixture in variable proportion of jarosite and schwertmannite which represent the stable secondary minerals along the investigated transect of rosia river particular regard is given to the ability of authigenic phases to selectively scavenge selected ptes from contaminated solutions during their genesis and minerogenetic evolution furthermore laboratory kinetic batch experiments on natural heterogeneous samples of ochreous precipitates were carried out to investigate the release processes involving ptes and to verify the type and the amount of elements that can be temporarily permanently trapped by the solid phase from the contaminated solutions the comparative analysis of the precipitates and waters of the rosia montan mining area indicated that the role of secondary minerals as mitigating agents can be limited because even minor ph eh oscillations would cause mineralogical transformations that could lead to trace elements mobilization in the environment

modeling of ground motion from a 1994 northridge aftershock using a tomographic velocity model of the los angeles basin the 1994 northridge mainshock and its aftershocks show a complex pattern of peak accelerations at stations located in the los angeles basin the waveforms contain multiples of body wave phases and extensive surface waves at frequencies mostly below 1 hz in particular for stations at distances greater than 18 km secondary arrivals show larger accelerations than the direct s wave arrivals the mainshock waveforms are further complicated by irregularities of the source rupture we use 2d finite difference to evaluate the effect of lateral variations in seismic velocity on the amplitude of shear wave energy and to distinguish the effects of source and propagation path we model waveforms from one aftershock recorded at nine stations deployed along a 60 km long profile extending into the los angeles basin we use a two dimensional slice through the 3d tomography model of the los angeles basin in the 2d finite difference calculations these synthetic waveforms fit the aftershock waveforms significantly better than corresponding waveforms determined from simple 1d velocity models with the addition of a thin low velocity surface layer above the tomography model the finite difference synthetics reproduce most of the important features of the recorded data in particular the large amplitude arrivals 7 to 10 sec following the direct s arrival these arrivals correspond to the ss arrival which is sharply refracted at the basin edge and the s wave with multiple legs trapped by the dipping near surface gradient for large earthquakes located either inside or outside the basin these phases can be the cause of the largest and hence potentially most hazardous shaking in the los angeles basin

magma evolution and the formation of porphyry cu au ore fluids evidence from silicate and sulfide melt inclusions silicate and sulfide melt inclusions from the andesitic farallon negro volcanic complex in nw argentina were analyzed by laser ablation icpms to track the behavior of cu and au during magma evolution and to identify the processes in the source of fluids responsible for porphyry cu au mineralization at the 600 mt bajo de la alumbrera deposit the combination of silicate and sulfide melt inclusion data with previously published geological and geochemical information indicates that the source of ore metals and water was a mantle derived mafic magma that contained approximately 6 wt h2o and 200 ppm cu this magma and a rhyodacitic magma mixed in an upper crustal magma chamber feeding the volcanic systems and associated subvolcanic intrusions over 2 6 million years generation of the ore fluid from this magma occurred towards the end of this protracted evolution and probably involved six important steps 1 generation of a sulfide melt upon magma mixing in some parts of the magma chamber 2 partitioning of cu and au into the sulfide melt enrichment factor of 10 000 for cu leading to cu and au concentrations of several wt or ppm respectively 3 a change in the tectonic regime from local extension to compression at the end of protracted volcanism 4 intrusion of a dacitic magma stock from the upper part of the layered magma chamber 5 volatile exsolution and resorption of the sulfide melt from the lower and more mafic parts of the magma chamber generating a fluid with a cu au ratio equal to that of the precursor sulfide 6 focused fluid transport and precipitation of the two metals in the porphyry yielding an ore body containing au and cu in the proportions dictated by the magmatic fluid source the cu s ratio in the sulfide melt inclusions requires that approximately 4 000 ppm sulfur is extracted from the andesitic magma upon mixing this exceeds the solubility of sulfide or sulfate in either of the silicate melts and implies an additional source for s the extra sulfur could be added in the form of anhydrite phenocrysts present in the rhyodacitic magma it appears thus that unusually sulfur rich not cu rich magmas are the key to the formation of porphyry type ore deposits our observations imply that dacitic intrusions hosting the porphyry cu au mineralization are not representative of the magma from which the ore fluid exsolved the source of the ore fluid is the underlying more mafic magma and unaltered andesitic dikes emplaced immediately after ore formation are more likely to represent the magma from which the fluids were generated at alumbrera these andesitic dikes carry relicts of the sulfide melt as inclusions in amphibole sulfide inclusions in similar dykes of other less explored magmatic complexes may be used to predict the au cu ratio of potential ore forming fluids and the expected metal ratio in any undiscovered porphyry deposit

study of weak and strong ground motion including nonlinearity from the northridge california earthquake sequence abstract this article presents a new method to estimate s wave site response relative to a regional layered crustal model the method is useful for site specific strong motion prediction because the estimated site response functions are referenced to an idealized regional layered model for which we know the ground response exactly we applied this method to the northridge earthquake sequence we determined the site amplifications from aftershocks with magnitudes 2 6 to 4 3 at 21 stations that were colocated with strong motion stations these site response functions were then used to modify synthetic seismogram calculated for the northridge mainshock in the same regional layered crustal model and thus obtain site specific ground motion estimates these site specific synthetic seismograms have higher correlation to observations in comparison to the synthetic seismograms without weak motion site correction they have similar amplitude and frequency content to the observations especially at sites with recorded peak ground accelerations below 0 3 g at sites with larger ground motions however this approach overestimates the strong motion the differences are made clear when we estimate site response functions from the strong motion records and compare them with those from weak motion records we express the differences as the average ratio of the weak to strong motion site response aws ratio when the ground motion is low the aws ratio is near unity indicating that the weak and strong motion site responses agree with each other within the uncertainty however the aws ratio increases as the ground motion amplitude increses the difference in weak and strong motion site responses becomes significant at stations where peak acceleration was above 0 3 g peak velocity was above 20 cm sec or peak strain was above 0 06 during the mainshock this result demonstrates directly from the ground motion observations the relationship between nonlinear site response and peak ground motion parameters the nonlinearity is present on soft rock sites as well as on sediment sites

the nature and genesis of gold silver tellurium mineralization in the metaliferi mountains of western romania precious metal au ag and base metal pb zn deposits in the metaliferi mountains of western romania occur in steeply clipping quartz ca mn carbonate veins which are hosted by miocene andesitic stocks and lava flows and surrounding sedimentary rocks the deposits consist predominantly of sulfides pyrite chalcopyrite sphalerite galena sulfosalts of as and sb and a diverse range of au ag tellurides the igneous host rocks have undergone mild pervasive propylitic alteration whereas immediately adjacent to the veins the wall rock alteration assemblages consist of quartz sericite k feldspar calcite and pyrite fluid inclusion stable isotope and thermodynamic data suggest that the majority of the mineralization and hydrothermal alteration in these deposits was caused by loci salinity 0 5 wt nacl equiv medium temperature 200 degrees 300 degrees c near neutral ph 5 6 fluids which underwent occasional boiling the fluid inclusion and stable isotope data support a model in which a metal bearing magmatic fluid was exsolved from a crystallizing calc alkaline melt and ascended to higher levels in the crust undergoing some isotopic exchange with surrounding sedimentary rocks but limited mixing with ground waters although the deposits in this part of the romanian carpathians exhibit many of the geologic characteristics of classic low sulfidation volcanic hosted au ag epithermal deposits they seem to have formed from essentially magmatic waters and there is little evidence for the incorporation of meteoric fluids into the hydrothermal system

geological setting and timing of the chah zard breccia hosted epithermal gold silver deposit in the tethyan belt of iran the breccia hosted epithermal gold silver deposit of chah zard is located within a high k calc alkaline andesitic to rhyolitic volcanic complex in the central part of the urumieh dokhtar magmatic arc udma west central iran the total measured resource for chah zard is 2 5 million tonnes of ore at 12 7 g t ag and 1 7 g t au 28 6 t ag 3 8 t au making it one of the largest epithermal gold deposits in iran magmatic and hydrothermal activity was associated with local extensional tectonics in a strike slip regime formed in transtensional structures of the dehshir baft strike slip fault system the host rocks of the volcanic complex consist of eocene sedimentary and volcanic rocks covered by miocene sedimentary rocks la icp ms u pb zircon geochronology yields a mean age of 6 2 0 2 ma for magmatic activity at chah zard this age represents the maximum age of mineralization and may indicate a previously unrecognized mineralization event in the udma breccias and veins formed during and after the waning stages of explosive brecciation events due to shallow emplacement of rhyolite porphyry detailed systematic mapping leads to the recognition of three distinct breccia bodies volcaniclastic breccia with a dominantly clastic matrix gray polymict breccia with a greater proportion of hydrothermal cement and mixed monomict to polymict breccia with clay matrix the polymictic breccias generated bulk mineable ore whereas the volcaniclastic breccia is relatively impermeable and largely barren precious metals occur with sulfide and sulfosalt minerals as disseminations as well as in the veins and breccia cements there is a progression from pyrite dominated stage 1 to pyrite base metal sulfide and sulfosalt dominated stages 2 and 3 to base metal sulfide dominated stage 4 breccias and veins hydrothermal alteration and deposition of gangue minerals progressed from illite quartz to quartz adularia carbonate and finally gypsum dominated assemblages free gold occurs in stages 2 and 4 principally intergrown with pyrite quartz chalcopyrite galena sphalerite and ag rich tennantite tetrahedrite and also as inclusions in pyrite high rb sr ratios in ore grade zones are closely related to sericite and adularia alteration positive correlations of au and ag with cu as pb zn sb and cd in epithermal veins and breccias suggest that all these elements are related to the same mineralization event

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

empirical green s function study of the january 17 1994 northridge california earthquake the january 17 1994 northridge main shock was analyzed using an empirical green s function approach to estimate the spatial and temporal distribution of fault slip far field source time functions obtained from seismograms recorded by the berkeley digital seismic network bdsn and terrascope stations reveal the distributed nature of the source and the presence of a second large subevent the location of the fault beneath the san fernando valley as well as the updip directivity of the rupture contributed to the locally heavy damage due to this earthquake

nonlinear ground motion amplification by sediments during the 1994 northridge earthquake it has been known since at least 1898 ref 1 that sediments can amplify earthquake ground motion relative to bedrock for the weak ground motion accompanying small earthquakes the amplification due to sediments is well understood in terms of linear elasticity hooke s law 2 but there has been a long standing debate regarding the amplification associated with the strong ground motion produced by large earthquakes the view of geotechnical engineers based largely on laboratory studies is that hooke s law breaks down at larger strains causing a reduced nonlinear amplification seismologists on the other hand have tended to remain sceptical of this nonlinear effect mainly because the relatively few strong motion observations seemed to be consistent with linear elasticity although some recent earthquake studies have demonstrated nonlinear behaviour under certain circumstances3 4 the significance of nonlinearity for the type of stiff soil sites found in the greater los angeles region remains unresolved5 here we report that ground motion amplification due to sediments for the main shock of the 1994 northridge earthquake was up to a factor of two less than the amplification observed for its aftershocks these observations imply significant nonlinearity in such amplification and bring into question the use of measurements of weak ground motion to predict the strong ground motion at sedimentary sites

the 1994 northridge earthquake sequence in california seismological and tectonic aspects the m w 6 7 northridge earthquake occurred on january 17 1994 beneath the san fernando valley two seismicity clusters located 25 km to the south and 35 km to the north northwest preceded the mainshock by 7 days and 16 hours respectively the mainshock hypocenter was relatively deep at 19 km depth in the lower crust it had a thrust faulting focal mechanism with a rake of 100 on a fault plane dipping 35 to the south southwest and striking n75 w because the mainshock did not rupture the surface its association with surficial geological features remains difficult to resolve nonetheless its occurrence reemphasized the seismic hazard of concealed faults associated with the contractional deformation of the transverse ranges the northridge earthquake is part of the temporal increase in earthquake activity in the los angeles area since 1970 the mainshock was followed by an energetic aftershock sequence eight aftershocks of m 5 0 and 48 aftershocks of 4 m 5 occurred between january 17 and september 30 1994 the aftershocks extend over most of the western san fernando valley and santa susana mountains they form a diffuse spatial distribution around the mainshock rupture plane illuminating a previously unmapped thrust ramp extending from 7 10 km depth into the lower crust to a depth of 23 km no flattening of the aftershock distribution is observed near its bottom at shallow depths above 7 10 km the thrust ramp is topped by a dense distribution of aftershock hypocenters bounded by some of the surficial faults the dip of the ramp increases from east to west the west side of the aftershock zoae is characterized by a dense steeply dipping and north northeast striking planar cluster of aftershocks that exhibited mostly thrust faulting these events coincided with the gillibrand canyon lateral ramp along the east side of the aftershock zone the aftershocks also exhibited primarily thrust faulting focal mechanisms the focal mechanisms of the aftershocks were dominated by thrust faulting in the large aftershocks with some strike slip and normal faulting in the smaller aftershocks the 1971 san fernando and the 1994 northridge earthquakes ruptured partially abutting fault surfaces on opposite sides of a ridge both earthquakes accommodated north south contractional deformation of the transverse ranges the two earthquakes differ primarily in the dip direction of the faults and the depth of faulting the 1971 north northeast trend of left lateral faulting chatsworth trend was not activated in 1994

magmatic fluids in the breccia hosted epithermal au ag deposit of rosia montana romania the breccia hosted epithermal au ag deposit of rosia montan is located 7 km northeast of abrud in the northern part of the south apuseni mountains romania estimated total reserves of 214 91 million metric tons mt of ore at 1 46 g t au and 6 9 g t ag 10 1 moz of au and 47 6 moz of ag make rosia montan one of the largest gold deposits in europe at this location miocene calc alkaline magmatic and hydrothermal activity was associated with local extensional tectonics within a strike slip regime related to the indentation of the adriatic microplate into the european plate during the carpathian orogenesis the host rocks of the magmatic complex consist of pre mesozoic metamorphosed continental crust covered by cretaceous turbiditic sediment flysch magmatic activity at rosia montan and its surroundings occurred in several pulses and lasted about 7 m y rosia montan is a breccia hosted epithermal system related to strong phreatomagmatic activity due to the shallow emplacement of the montana dacite the montana dacite intruded miocene volcaniclastic material volcaniclastic breccias and crops out at cetate and c rnic hills current mining is focused primarily on the cetate open pit which was mapped in detail leading to the recognition of three distinct breccia bodies the dacite breccia with a dominantly hydrothermal matrix the gray polymict breccia with a greater proportion of sand sized matrix support and the black polymict breccia which reached to the surface contains carbonized tree trunks and has a dominantly barren clastic matrix the hydrothermal alteration is pervasive adularia alteration with a phyllic overprint is ubiquitous silicification and argillic alteration occur locally mineralization consists of quartz adularia carbonates commonly mn rich pyrite fe poor sphalerite galena chalcopyrite tetrahedrite and native gold and occurs as disseminations as well as in veins and filling vugs within the montana dacite and the different breccias the age of mineralization 12 85 0 07 ma was determined by 40 ar 39 ar dating on hydrothermal adularia crystals from vugs in the dacite breccia in the cetate open pit microthermometric measurements of fluid inclusions in quartz phenocrysts from the montana dacite revealed two fluid types that are absent from the hydrothermal breccia and must have been trapped at depth prior to dacite dome emplacement brine inclusions 32 55 wt nacl equiv homogenizing at t h 460 c and intermediate density fluids 4 9 15 6 wt nacl equiv t h between 345 430 c secondary aqueous fluid inclusion assemblages in the phenocrysts have salinities of 0 2 to 2 2 wt percent nacl equiv and t h of 200 to 280 c fluid inclusion assemblages in hydrothermal quartz from breccias and veins have salinities of 0 2 to 3 4 wt percent nacl equiv and t h from 200 to 270 c the oxygen isotope composition of several zones of an ore related epithermal quartz crystal indicate a very constant 18 o of 4 5 to 5 0 per mil for the mineralizing fluid despite significant salinity and temperature variation over time following microthermometry selected fluid inclusion assemblages were analyzed by laser ablation inductively coupled plasma mass spectrometry la icpms despite systematic differences in salinity between phenocryst hosted fluids trapped at depth and fluids from quartz in the epithermal breccias all fluids have overlapping major and trace cation ratios including identical na k rb sr cs ba consistent with the constant near magmatic oxygen isotope composition of the hydrothermal fluids these data strongly indicate a common magmatic component of these chemically conservative solutes in all fluids cu pb zn and mn show variations in concentration relative to the relatively non reactive alkalis reflecting the precipitation of sulfide minerals together with au in the epithermal breccia and possibly of cu in an inferred subjacent porphyry environment the magmatic hydrothermal processes responsible for epithermal au ag mineralization at rosia montan are however not directly related to the formation of the spatially associated porphyry cu au deposit of rosia poieni which occurred about 3 m y later

neogene quaternary magmatism and geodynamics in the carpathian pannonian region a synthesis in the carpathian pannonian region in neogene times westward dipping subduction in a land locked basin caused collision of two lithospheric blocks alcapa and tisia with the southeastern border of the european plate calc alkaline and alkaline magmatism was closely related to subduction rollback collision and extension from the spatial distribution of the magmatic activity four segments can be defined western segment magmatism occurring on the alcapa block central segment magmatism occurring on both alcapa and the tisia blocks south eastern segment and interior segment both on the tisia block most calc alkaline magmatism in the region resulted from melting of a heterogeneous asthenospheric mantle source modified by addition of fluids and sediment assimilation and fractionation processes at shallow crustal levels occurred in most of the segments strongly masking the deeper source processes long term subduction rollback and or delamination led to contamination of the asthenosphere beneath the western segment here large volume partial melts of the contaminated mantle caused underplating and crustal anatexis leading to mixing of mantle derived calc alkaline magmas with crustal melts in the central segment calc alkaline magmas were formed by subduction and rollback followed by back arc extension and slab breakoff avariable mantle source is indicated in the back arc setting and larger amount of fluid induced metasomatism source enrichment and assimilation nearer to the trench in the interior segment evolution from typical calc alkaline magmas to adakite like ones was related to extension due to fast rotations and transtensional tectonics here calc alkaline magmas formed by decompression melting of a heterogeneous crust mantle lithosphere while adakite like melts resulted from fliud dominated melting of the lithosphere along the south eastern segment slab breakoff was responsible for the generation of typical calcalkaline magmas but in the extreme south of the segment shallow level tearing of the slab followed breakoff strike slip tectonics allowed the rise of hot asthenosphere and generation of adakite like magmas via slab melting along the torn edge of the east european plate alkalic basaltic volcanism with an oib like asthenosphere source followed the calc alkaline stage

stochastic finite fault modeling of ground motions from the 1994 northridge california earthquake i validation on rock sites the stochastic method of simulating ground motions from finite faults is validated against strong motion data from the m 6 7 1994 northridge california earthquake the finite fault plane is subdivided into elements each element is as signed a stochastic o92 spectrum and the delayed contributions from all subfaults are summed in the time domain simulated horizontal acceleration time histories and fourier spectra at 28 rock sites are compared with observations we first perform simulations using the slip distribution on the causative fault derived from strong motion teleseismic gps and leveling data wald et al 1996 we then test the performance of the method using quasi random distributions of slip and alternative hypocenter locations this is important because the rupture initiation point and slip distribution are in general not known for future earthquakes the model bias is calculated as the ratio of the simulated to the observed spectrum in the frequency band of 0 1 to 12 5 hz averaged over a suite of rock sites the mean bias is within the 95 confidence limits of unity showing that the model provides an accurate prediction of the spectral content of ground motions on average the maximum excursion of the model bias from the unity value when averaged over all 28 rock stations is a factor of approximately 1 6 at most frequencies it is below a factor of 1 4 interestingly the spectral bias and the standard deviation of the stochastic simu lations do not depend on whether the fault slip distribution and hypocenter location are based on data or are randomly generated this suggests that these parameters do not affect the accuracy of predicting the average characteristics of ground motion or they may have their predominant effect in the frequency range below about 0 1 hz below the range of this study the implication is that deterministic slip models are not necessary to produce reasonably accurate simulations of the spectral content of strong ground motions this is fortunate because such models are not available for forecasting motions from future earthquakes however the directivity effects controlled by the hypocenter location are important in determining peak ground ac celeration at individual sites although the method is unbiased when averaged over all rock sites the simulations at individual sites can have significant errors generally a factor of 2 to 3 which are also frequency dependent factors such as local geology site topography or basin propagation effects can profoundly affect the recordings at individual stations to generate more accurate site specific predictions empirical responses at each site could be established

gallium germanium indium and other trace and minor elements in sphalerite as a function of deposit type a meta analysis abstract while a significant amount of analytical data on trace and minor element concentrations in sphalerite has been collected over the last six decades no meta analysis of this data has ever been conducted in this study the results of such an analysis are presented while the study focusses on ga ge and in data for six other elements ag cd co cu fe and mn was also included the results show that there are systematic statistically significant differences in the mean concentrations of fe ga ge in and mn in sphalerite from different deposit types while cd and cu concentrations show no such differences and ag and co concentrations are only significantly different for vein type deposits a principal component analysis demonstrates that the differences between deposit types are approximately one dimensional being expressible in terms of a single number this number correlates strongly with the homogenisation temperature of fluid inclusions r 2 0 82 p 16 it may be expressed as follows pc 1 ln c ga 0 22 c ge 0 22 c fe 0 37 c mn 0 20 c in 0 11 with ga ge in and mn concentrations in ppm and fe concentration in wt the relationship is sufficiently strong to be used as a geothermometer ggimfis the empirical relationship between pc 1 and the homogenisation temperature t is t c 54 4 7 3 pc 1 208 10 our results indicate a strong control of sphalerite chemistry by fluid temperature particularly for the concentrations of ga r 2 0 40 ge r 2 0 65 fe r 2 0 30 and mn r 2 0 60 and to a lesser degree in r 2 0 10 the concentrations of ag cd co and cu appear to be independent of temperature as a consequence of the strong temperature control on pc 1 metamorphic overprinting of pb zn deposits even by lower greenschist facies events may lead to significant changes in sphalerite composition namely a relative decrease in ga and ge concentrations and increase in fe mn and to a lesser degree in concentrations the closure temperature of sphalerite in regional metamorphic events appears to be around 310 50 c such that higher grade events will not be reflected in its composition factors other than temperature such as differences in fluid salinity or source rock composition do not appear to be responsible for differences between deposit types but rather appear to cause differences between individual deposits particularly the cu activity in ore forming systems appears to have a strong influence on in concentrations in sphalerite the observed trends in sphalerite compositions provide a useful tool for future studies of different types of pb zn deposits as well as for mineral exploration they should be particularly relevant for the identification of new resources of ga ge and in

evidence for magmatic hydrothermal fluids and ore forming processes in epithermal and porphyry deposits of the baguio district philippines the baguio district contains a diverse array of epithermal porphyry and skarn deposits together with a large broadly strata bound advanced argillic lithocap magmatism mineralization and alteration occurred in response to subduction of the south china sea plate and the scarborough ridge beneath northern luzon over the past 3 m y rapid uplift and exhumation resulted in epithermal veins overprinting several porphyry cu au deposits most of the epithermal au ag deposits of the baguio district including antamok and acupan the two largest au deposits are intermediate sulfidation state quartz carbonate adularia illite base metal sulfide veins that contain electrum and minor au ag tellurides in contrast high sulfidation mineralization at kelly includes enargite tennantite electrum and precious metal tellurides and is associated with advanced argillic alteration although the mineralizing fluids that formed the porphyry and epithermal deposits had distinct temperatures and salinities stable and radiogenic data provide evidence for direct magmatic contributions into each deposit type the epithermal mineralizing fluids were dilute generally 600 c hypersaline brines 30 to 70 wt nacl equiv and low density vapor sulfur isotope compositions of sulfides in the porphyry skarn and intermediate sulfidation epithermal veins of the southern and central baguio district are mostly between 1 and 6 per mil consistent with a predominance of h2s in the mineralizing fluids i e reducing conditions in contrast sulfides from the high sulfidation porphyry and intermediate sulfidation deposits located adjacent to the baguio lithocap mostly have negative sulfur isotope values 6 9 to 0 8 consistent with oxidizing so42 predominant mineralizing fluids intermediate sulfidation epithermal veins at acupan have crosscut a well mineralized porphyry cu au stock work at ampucao the two deposits cannot be distinguished on the basis of radiometric age determinations ampucao 0 51 0 26 ma acupan 0 65 0 07 ma and are interpreted to be cogenetic with telescoping of the two environments caused by the rapid uplift and exhumation associated with ridge subduction measured 34ssulfide 1 1 to 6 6 34ssulfate 10 4 to 31 8 values and initial strontium ratios of anhydrite 0 70378 0 70385 are consistent with identical and predominantly magmatic sources of these components for the ampucao porphyry and acupan epithermal veins helium isotopes provide further evidence of mantle derived components in the epithermal veins r ra values of 6 0 and 6 7 oxygen deuterium and carbon isotopes provide evidence for predominantly magmatic water at ampucao and for hybrid magmatic meteoric waters at acupan that precipitated precious metals due to boiling the proportion of magmatic water relative to meteoric water and precious metal grades both decreased with time during epithermal vein formation at acupan the common observation of cross cutting relationships between porphyry and epithermal veins observed throughout the baguio district imply that the evolution of porphyry style to intermediate sulfidation style mineralization was a common phenomenon in this region and contributed significantly to its rich metal endowment

fluid fluid interactions in magmatic hydrothermal ore formation hydrothermal ore deposits have provided some of the first geological evidence for the interaction of multiple fluids in the earth s interior including fluid mixing as well as fluid phase separation physical evidence comes from veins and breccias documenting the impact of fluids in breaking rocks and creating fracture permeability for ore formation as a result of the fluid expansion that is commonly associated with phase separation between melts and multiple fluids chemical evidence of fluid fluid interaction includes the precipitation of minerals in veins as a result of fluid boiling or mixing between chemically contrasting fluids fluid inclusions record interactions of multiple fluids especially in magmatic hydrothermal ore deposits and associated igneous rocks fig 1 in recent years fluid inclusions have contributed to a more quantitative understanding of the role of fluid fluid interactions since new microanalytical techniques allow determination of element concentrations in all types of fluids from low density vapor through aqueous and hypersaline liquids to hydrous salt melts roedder 1984 samson et al 2003 figure 1 geological evidence for fluid phase separation in ore forming magmatic hydrothermal systems a bonanza grade gold 1 wt that was precipitated together with fine grained pyrite in a fluidized breccia resulting from instantaneous boiling and expansion of magmatic fluids ascending from an underlying andesite porphyry intrusion the breccia consists of adularia sericite altered clasts of sedimentary wall rock s and nodules of originally colloidal pyrite with bright specks of gold p g both cemented by roscoelite r vanadium rich muscovite and late calcite c zone vii ore body porgera papua new guinea ronacher et al 2004 b bladed manganocalcite the characteristic habit of calcite precipitated from aqueous epithermal fluids as a result of the ph change following loss of co2 to a separating vapor phase madan bulgaria kostova et al 2004 c growth band in a euhedral quartz

nonlinear sediment response during the 1994 northridge earthquake observations and finite source simulations we have addressed the long standing question regarding nonlinear sediment response in the los angeles region by testing whether sediment amplification was similar between the northridge earthquake and its aftershocks comparing the weak and strong motion site response at 15 sediment sites we find that amplification factors were significantly less for the main shock implying systematic nonlinearity the difference is largest between 2 and 4 hz a factor of 2 and is significant at the 99 confidence level between 0 8 and 5 5 hz the inference of nonlinearity is robust with respect to the removal of possibly anomalous sediment sites and how the reference site motion is defined furthermore theoretical ground motion simulations show no evidence of any bias from finite source effects during the main shock nonlinearity is also suggested by the fact that the four sediment sites that contain a clear fundamental resonance for the weak motion exhibit a conspicuous absence of the peak in the strong motion although we have taken the first step of establishing the presence of nonlinearity it remains to define the physics of nonlinear response and to test the methodologies presently applied routinely in engineering practice the inference of nonlinearity implies that care must be exercised in using sediment site data to study large earthquakes or predict strong ground motion

thermal regime reconstruction and fluid inclusion la icp ms analysis on intermediate sulfidation epithermal pb zn veins implications for porphyry cu deposits exploration in the xianhualing district anhui china abstract the xianhualing district at jinzhai in the northern dabie orogen china is a significant area for pb zn cu au polymetallic exploration the main rocks in the area are mica quartz schist of the neoproterozoic foziling group and magmatic rocks which are controlled by two sets of faults striking nne and nw recent drilling has revealed that the orebody occurs mainly in mica quartz schist in the form of breccia and veinlets major ore minerals include pyrite sphalerite galena chalcopyrite magnetite gold silver and silver sulfosalts with alteration assemblages of predominantly quartz sericite calcite and chlorite three types of fluid inclusions occur in quartz sulfide vein samples collected from eight drill holes two phase liquid rich inclusions type i two phase vapor rich inclusions type and halite bearing inclusions type iii microthermometric studies of type i and fluid inclusions indicate homogenization temperatures of 161 378 c and salinities of 0 5 7 8 wt nacl equivalent fluid inclusion microthermometric data and mineralization and alteration characteristics indicate an intermediate sulfidation epithermal environment current exploration is focused on the location of potential deep porphyry mineralization associated with epithermal mineralization in this study 28 drill core samples from different levels were selected for fluid inclusion microthermometry to elucidate fluid evolution pathways and hence to determine the likelihood of porphyry bodies the consistent fluid inclusion petrography distribution patterns and fluid evolution trends indicate that the deeper part of the dongchong area may have been the regional thermal center of fluid flow the estimated mineralization depths of type iii fluid inclusions are in the range 0 4 1 5 km indicating a relatively shallow formation fluid chemical compositions obtained from single inclusion laser ablation inductively coupled plasma mass spectrometry la icp ms analyses support the occurrence of a single magmatic hydrothermal fluid source which has a degree of mixing with meteoric water and a small amount of basinal brines during the migration path and the fluid evolution pattern agrees well with the fluid inclusion mapping result quartz vein hosted fluid inclusions contain significant amounts of pb zn and cu indicating good exploration prospects for porphyry cu mineralization at depth

felsic maar diatreme volcanoes a review felsic maar diatreme volcanoes host major ore deposits but have been largely ignored in the volcanology literature especially for the diatreme portion of the system here we use two mexican tuff rings as analogs for the maar ejecta ring new observations from one diatreme and the economic geology literature on four other mineralized felsic maar diatremes to produce an integrated picture of this type of volcano the ejecta rings are up to 50 m thick and extend laterally up to 1 5 km from the crater edge in two mexican examples the lower part of the ejecta ring is dominated by pyroclastic surge deposits with abundant lithic clasts up to 80 at hoya de estrada these deposits display low angle cross bedding dune bedforms undulating beds channels bomb sags and accretionary lapilli and are interpreted as phreatomagmatic rhyolitic juvenile clasts at tepexitl have only 0 25 vesicles in this portion of the ring the upper parts of the ejecta ring sequences in the mexican examples have a different character lithic clasts can be less abundant the grain size is typically coarser and the juvenile clasts can be different in character with some more vesicular fragments fragmentation was probably shallower at this stage the post eruptive maar crater infill is known at wau and consists of reworked pyroclastic deposits as well as lacustrine and other sediments underneath are bedded upper diatreme deposits interpreted as pyroclastic surge and fall deposits the upper diatreme and post eruptive crater deposits have dips larger than 30 at wau with approximately centroclinal attitudes at still lower structural levels the diatreme pyroclastic infill is largely unbedded montana tunnels and kelian are good examples of this at cerro de pasco the pyroclastic infill seems bedded despite about 500 m of post eruptive erosion relative to the pre eruptive surface the contact between the country rocks and the diatreme is sometimes characterized by country rock breccias kelian mt rawdon pyroclastic rocks in the diatreme are typically poorly sorted and ash rich they contain a heterolithic mix of juvenile clasts and lithic clasts from various stratigraphic levels megablocks derived from the ejecta ring or the country rocks are often found in the diatremes evidence for multiple explosions is in the form of steep crosscutting pyroclastic bodies within some diatremes and fragments of pyroclastic rocks within other pyroclastic facies pyroclastic rocks are cut by coherent felsic dikes and plugs which may have been feeders to lava domes at the surface allowing for the difference in magma composition felsic maar diatreme volcanoes have many similarities with their ultramafic to mafic equivalents differences include a common association with felsic domes inside the crater or just outside wau although the domes within the crater may be destroyed during the eruption hoya de estrada tepexitl the dikes and plugs feeding and invading felsic diatremes seem larger the processes of phreatomagmatic explosions involving felsic magmas may be different

kinematic evolution of the romanian carpathians abstract the regional pattern of contraction and extension directions and the evolution of the strain field from paleogene to neogene times enabled a reconstruction of the migration path of the carpathian collision front the carpathian nappes were thrust around the moesian plate during paleogene and early neogene times and protruded into a small oceanic embayment between the moesian and european plates the arc structure of the carpathian fold thrust belt was formed in late neogene times as a result of the eastward escaping tisza dacia block due to n directed convergence of the adriatic plate and the retreating subduction of an oceanic slab brittle deformation structures in the romanian carpathians suggest three tectonic events related to major plate motions 1 paleogene to middle miocene ne to ene contraction caused right lateral curved strike slip faults 2 middle miocene to pliocene fan shaped orientations of contraction directions were caused by right lateral oblique convergence in the southern carpathians frontal convergence in the southern eastern carpathians and left lateral convergence in the northern eastern carpathians 3 pleistocene to holocene general e w extension and n s contraction in the carpathian arc and local ese wnw contraction in the vrancea area is related to the late roll back stage and break off of the subducted slab in the bend area

1 1 porphyry cu au and epithermal au ag deposits in the southern apuseni mountains romania 1 1 porphyry cu au and epithermal au ag deposits in the southern apuseni mountains romania south apuseni mountains district lat 46 03 n long 22 58 e k kouzmanov p iv scanu g o connor a isotope geology and mineral resources eth sonneggstrasse 5 8092 zurich switzerland b geological institute of romania caransebes str 1 78344 bucharest romania c gabriel resources ltd suite 1501 110 yonge st toronto on m5c 1t4 canada received 19 november 2004 accepted 1 may 2005

northridge aftershocks a source study with terrascope data broadband and long period displacement waveforms from a selection of northridge aftershocks recorded by the terrascope array are modeled to study source characteristics source mechanisms and moments are determined with long period data using an algorithm developed by zhao and helmberger 1994 these results are compared with those by hauksson et al 1995 and thio and kanamori 1996 the width of the direct pulses at the nearest stations pas and calb are measured as indications of the source duration another measurement of the source time functions of these earthquakes is obtained by comparing the short period to long period energy ratio in the data to that in the synthetics these measurements are used to estimate the relative stress drop using a formula given by cohn et al 1982 the depth distribution of the relative stress drops indicates that the largest stress drops are in the depth range of 5 to 15 km for an aftershock population of 24 events a correlation of extended surface wave train with source depth is demonstrated for paths crossing the san fernando basin

on the variability of aftershock ground motions in the san fernando valley we analyze aftershocks of the 1 17 94 mw6 7 northridge earthquake recorded at a 3 element small aperture array within the town of northridge above the mainshock rupture plane many of the m4 5 aftershocks are observed to have a prolonged shaking duration up to 8 seconds with conspicuous longer period 1 s arrivals in the latter part of the wave train recordings of a m4 0 aftershock that occurred at 23 49 gmt on 1 17 show the origin of these waves a slant stack cross correlation method on each of the three components shows that the late arrivals are characterized by low apparent velocities and a back azimuth that is approximately 10 degrees off that of the direct arrivals based on the inferred apparent velocities and consideration of studies in other sedimentary basins we conclude that these later arrivals consist of surface waves generated within the san fernando valley similar results are obtained for a m3 4 event recorded across the array the surface waves are not however a ubiquitous feature of the aftershock recordings we show that other m 4 events recorded at the same site are characterized by simple displacement pulses and durations that are typical for their magnitude suggesting that 3 dimensional site response may be difficult to predict in cases where the sources are close to a valley or basin and or the basin structure is complex

cretaceous collision and indentation in the west carpathians view based on structural analysis and numerical modeling 1 a model of indentation of a rigid promontory into weak metasedimentary rocks during cretaceous convergence is suggested for tectonic evolution of southern part of west carpathians an early arcuate cleavage fan has developed in front of northward moving southern rigid basement block the interaction of the moving indenter with western stationary basement promontory is responsible for development of the boundary parallel shear zone along which the main southern indenter is shifted to the east this results in development of a new steep transpressional cleavage overprinting the early fabric eastward displacement of the southern indenter causes the development of a thrust zone parallel to the margin of the eastern stationary promontory a proposed numerical model of the deformation of a thin viscous sheet in front of oval rigid indenter reliably simulates the development of the observed deformation pattern modeled discrete partitioning between the western promontory and the indenting block fully agrees with the observed secondary cleavage associated with the transpressional shear zone our numerical model interconnects this complex kinematic frame with finite strain pattern which was to date possible only for simple boundary conditions in addition the model explains the polyphase cleavage patterns in terms of complex shapes of promontories and changes in movements of indenting blocks

hydrothermal breccias and veins at the kelian gold mine kalimantan indonesia genesis of a large epithermal gold deposit mineralized hydrothermal breccias and veins formed during and after the waning stages of maar diatreme related volcanic activity at kelian kalimantan indonesia subsurface phreatic explosions occurred around the margins of the diatreme breccia complex focusing high temperature fluid flow and generating several large mineralized hydrothermal breccia bodies tectonic phreatomagmatic and hydraulic processes also contributed to hydrothermal brecciation explosive phreatic brecciation was followed by in situ hydraulic brecciation and then by minor veining as the system returned to steady state geothermal conditions brecciation and mineralization mostly occurred 400 to 700 m below the paleowater table the kelian deposit contained more than 240 t au prior to mining precious metals occur with sulfide minerals as disseminations in sheeted and conjugate veins and as breccia cement there is a progression from pyrite dominated stage 1 to base metal sulfide dominated stages 2 and 3 to sulfosalt dominated hydrothermal breccias and veins stage 4 in terms of gangue minerals the system evolved from illite quartz to adularia and or quartz and or illite dominated and then carbonate dominated boiling produced abundant bladed carbonate during stages 3 and 4 overall carbonate and base metal sulfide minerals are abundant whereas quartz is comparatively minor free gold is most abundant in stages 3 and 4 but also occurs in stages 1 and 2 native gold occurs principally as inclusions in pyrite sphalerite galena arsenopyrite quartz bladed carbonate and sulfosalts hydrothermal alteration assemblages are zoned about contacts faults breccias and veins and consist of secondary quartz illite pyrite chlorite and various carbonate minerals kelian preserves evidence of a magmatic component to the mineralizing fluids fluid inclusion analyses revealed the presence of saline fluid inclusions in particular from stage 3 isothermal mixing of low salinity 0 to 2 wt nacl equiv with moderate salinity fluids 10 to 25 wt nacl equiv rather than boiling resulted in the range of salinity and homogenization temperatures of fluid inclusions in sphalerite carbonate and quartz deposited during stage 3 salinities of 4 to 6 wt percent nacl equiv for inclusions in adularia and quartz from stages 2 and 4 and in rhodochrosite and proustite pyrargyrite from stage 4 may also reflect a component of mixing of low salinity water with a moderately saline fluid sulfur isotope values from kelian sulfides 34s 1 4 to 5 5 per mil are consistent with a magmatic sulfur source both boiling and fluid mixing contributed to high grade au mineralization at kelian rapid formation hundreds of years or less is inferred for the individual hydrothermal breccia bodies 2008 society of economic geologists inc

three dimensional simulation of a magnitude 7 75 earthquake on the san andreas fault simulation of 2 minutes of long period ground motion in the los angeles area with the use of a three dimensional finite difference method on a parallel supercomputer provides an estimate of the seismic hazard from a magnitude 7 75 earthquake along the 170 kilometer section of the san andreas fault between tejon pass and san bernardino maximum ground velocities are predicted to occur near the fault 2 5 meters per second and in the los angeles basin 1 4 meters per second where large amplitude surface waves prolong shaking for more than 60 seconds simulated spectral amplitudes for some regions within the los angeles basin are up to 10 times larger than those at sites outside the basin at similar distances from the san andreas fault

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

observations of loma prieta aftershocks from a dense array in sunnyvale california a small aperture 300 m four station array was deployed in sunnyvale california for 5 days to record aftershocks of the loma prieta earthquake of october 1989 the purpose of the array was to study the seismic response of the alluvium filled santa clara valley and the role of surface waves in the seismic shaking of sedimentary basins strong motion records of the loma prieta mainshock indicate that surface waves produced the peak velocities and displacements at some sites in the santa clara valley we use the recordings from the dense array to determine the apparent velocity and azimuth of propagation for various arrivals in the seismograms of four aftershocks with magnitudes between 3 6 and 4 4 apparent velocities are generally observed to decrease with increasing time after the s wave in the seismograms phases arriving less than about 8 sec after the s wave have apparent velocities comparable to the s wave and appear to be body waves multiply reflected under the receiver site or reflected by crustal interfaces for times 10 to 30 sec after the direct s wave we observe long period 1 to 6 sec arrivals with apparent velocities decreasing from 2 5 to 0 8 km sec we interpret these arrivals to be surface waves and conclude that these surface waves produce the long duration of shaking observed on the aftershock records much of the energy in the 40 sec after the s wave is coming approximately from the direction of the source although some arrivals have backazimuths as much as 60 different from the backazimuths to the epicenters two of the aftershocks show arrivals coming from 30 to 40 more easterly than the epicenters this energy may have been scattered from outcrops along the southeastern edge of the basin in contrast the deepest aftershock studied d 17 km displays later arrivals with backazimuths 30 to 40 more westerly than the epicenter a distinct arrival for one of the aftershocks propagates from the southwest possibly scattered from the western edge of the basin synthetic seismograms derived from a plane layered crustal model do not produce the long period love waves observed in the waveforms of the ml 4 4 aftershock these love waves may be generated by the conversion of incident s waves or rayleigh waves near the edge of the basin

fluid evolution in zoned cordilleran polymetallic veins insights from microthermometry and la icp ms of fluid inclusions abstract fluid inclusion analysis through the paragenetic sequence of one symmetrically zoned vein sample is used to reconstruct the p t x fluid evolution of a porphyry intrusion related cordilleran polymetallic vein from morococha central peru results record an evolution from initial deep seated precipitation of quartz pyrite and base metal sulphides to final near surface deposition of carbonates demonstrating progressive mineralisation during uplift and erosion this is the first detailed study addressing meso to epithermal zn pb ag cu rich ore in a magmatic hydrothermal system by combination of fluid inclusion microthermometry with laser ablation inductively coupled plasma mass spectrometry la icp ms quantifying metal as well as sulphur concentrations in the evolving hydrothermal fluid scanning electron microscopy cathodoluminescence sem cl imaging of quartz and detailed transmitted and reflected light petrography provide textural evidence that early moderately saline 4 5 wt nacl eq and co 2 bearing fluids with homogenisation temperatures of 340 380 c precipitate cu bearing minerals in this open hydrothermal system the fluids record decreasing salinities co 2 contents and temperatures while zn pb and ag sulphides precipitate fluids related to early precipitation in the vein have metal contents of several 1000 g g s and fe over 1000 g g cu 100 g g pb 10 g g ag and several 100 g g zn sulphur concentrations in the fluid are sufficiently high to precipitate all metals in solution as sulphides the latest generation of fluid inclusions associated with abundant carbonate precipitation in the centre of the vein has homogenisation temperatures ranging from 260 to 220 c low metal concentrations and no measurable co 2 during vein formation cooling and several kilometres of erosion resulted in telescoping of consecutively precipitated mineral assemblages the deep input fluid dominating in the early vein stage is interpreted to be of magmatic origin most likely a single phase magmatic fluid of intermediate salinity and density it cooled to an aqueous liquid separated minor co 2 rich vapour and was eventually diluted by meteoric water in the late stages of vein formation when the progressively eroded land surface was only several hundred meters above the vein location

1 subduction slab detachment and mineralization the neogene in the apuseni mountains and carpathians abstract the inner carpathians comprise several distinct neogene late stage orogenic pb zn cu ag au ore districts the mineral deposits in these districts are closely related to volcanic and subvolcanic rocks and represent mainly porphyry and epithermal vein deposits which formed within short periods of time in each district here we discuss possible geodynamic and structural controls that suggest why some of the neogene volcanic districts within the carpathians comprise abundant mineralization while others are barren the neogene period has been characterized by an overall geodynamic regime of subduction where primary roll back of the subducted slab and secondary phenomena like slab break off and the development of slab windows could have contributed to the evolution location and type of volcanic activity structural features developing in the overlying lithosphere and visible in the carpathian crust such as transtensional wrench corridors block rotation and relay structures due to extrusion tectonics have probably acted in focusing hydrothermal activity as a result of particular events in the geodynamic evolution and the development of specific structural features mineralization formed during fluid channelling within transtensional wrench settings and during periods of extension related to block rotation in the slovakian ore district of the western carpathians neogene volcanism and associated mineralization were localized by sinistral ne trending wrench corridors which formed part of the extruding alcapa block the baia mare ore district in the eastern carpathians reflects a transtensional wrench setting on distributed oversteps close to the termination of the dragos voda fault there mineralization was spatially controlled by the transtensional dragos voda master fault and associated cross fault systems the golden quadrangle cu au ore district of the southern apuseni mountains reflects an unusual rotated transtensional extensional setting close to the termination of a graben system there fluid flow was probably localized by fault propagation at the inner tip of the graben system the spatial and temporal evolution of the magmatism and its changing geochemical signature from n w to s e strongly suggests a link with the contemporaneous northeastward roll back of the subducted slab and a progressive southeastward detachment during accelerating roll back this geodynamic evolution is further supported by the present day overall and detailed mantle lithospheric density images the present day heat flow patterns the crustal architecture and its interpreted evolution and the spatial and temporal evolution of depocentres around the carpathian arc in contrast to all these features the mineral deposits in the west carpathians east carpathians and apuseni mountains are too synchronous with respect to their individual volcanic history and contrast too much with younger volcanics of similar style but barren in southeastern parts of the carpathians to simply link them directly to the slab evolution in all three districts the presence of magmatic fluids released from shallow plutons and their mixing with meteoric water were critical for mineralization requiring transtensional or extensional local regimes at the time of mineralization possibly following initial compressional regimes these three systems show that mineralization was probably controlled by the superposition of favourable mantle lithospheric conditions and partly independent evolving upper crustal deformation conditions in the 13 to 11 ma period the dominant mineralization formed all across the carpathians and was superimposed on structurally favourable crustal areas with at that time volcanic hydrothermal activity the period may reflect the moment when the upper part of the crust failed under lithospheric extension imposed by the slab evolution this crustal failure would have fragmented the overriding plate possibly breaking up the thermal lid to provoke intensive fluid flow in specific areas and allowed subsequent accelerated tectonic development block rotation and extrusion of a family of sub blocks that are arbitrarily regarded as the tisia dacia or alcapa blocks even though they have lost their internal entity

hydrothermal evolution of the copler porphyry epithermal au deposit erzincan province central eastern turkey the copler au deposit measured and indicated resource of 122 8 million tonnes at 1 7 g t au 4 8 g t ag and 0 1 wt cu is centered around shallow level dioritic to granodioritic intrusive rocks of the middle eocene copler kabatas magmatic complex which have been emplaced into a succession of regionally metamorphosed late paleozoic mesozoic sedimentary and carbonate rocks the deposit comprises a centrally located subeconomic porphyry cu au system characterized by a potassically altered biotite k feldspar magnetite core overprinted by a more extensive phyllic quartz sericite alteration zone the potassic alteration zone is associated with early m type hairline magnetite and crosscutting b type quartz magnetite sulfide veinlets whereas the enveloping phyllic altered rocks contain abundant d type quartz pyrite and lesser polymetallic quartz sulfide veinlets intermediate sulfidation epithermal au mineralization that overprints the porphyry occurred in two stages main stage epithermal mineralization is characterized by carbonate sulfide veinlets consisting of manganocalcite arsenical pyrite arsenopyrite marcasite chalcopyrite tennantite tetrahedrite galena and sphalerite late stage sooty pyrite veinlets contain some realgar and orpiment and are associated with zones of extensive carbonate alteration in the carbonate sulfide veinlets invisible gold is primarily hosted within arsenical pyrite and to a lesser extent by arsenopyrite tetrahedrite and tennantite in sooty pyrite veinlets invisible gold is associated with fine grained arsenical pyrite manto type carbonate replacement zones occur in the distal portions of the porphyry system and constitute a significant gold resource these carbonate replacement bodies display a mineral paragenesis similar to that of the epithermal carbonate sulfide veinlets in that they contain abundant arsenical pyrite together with lesser chalcopyrite arsenopyrite and marcasite and sparse sphalerite galena tennantite and tetrahedrite invisible gold in these ores is contained mainly within pyrite and chalcopyrite and to a lesser extent in arsenopyrite tetrahedrite and tennantite polyphase brine inclusions 47 62 wt nacl equiv in early b type quartz magnetite sulfide veinlets were trapped together with low salinity 3 5 5 wt nacl equiv vapor rich inclusions at temperatures 390 c and at a depth of 1 5 km under lithostatic conditions fluids associated with the overprinting phyllic alteration were slightly cooler 370 c and less saline 37 42 wt nacl equiv fluid inclusions in manganocalcite and sphalerite from epithermal carbonate sulfide veinlets trapped moderate salinity 4 15 wt nacl equiv fluids at 290 c whereas fluid inclusions hosted in barite and realgar from sooty pyrite veinlets were formed from low temperature 100 c and low to moderate salinity 1 14 wt nacl equiv fluids these data indicate that the au mineralizing system at copler progressed from a high temperature porphyry system to a relatively low temperature intermediate sulfidation epithermal system deposition of gold in the early stages of epithermal mineralization resulted from cooling sulfidation and neutralization of predominantly magmatic sourced hydrothermal fluids whereas a meteoric water component is evident in the latest stage of mineralization deposit scale geologic observations combined with fluid inclusion and stable isotope evidence suggest that mineralization at copler records activity of a relatively deep epithermal system and that its formation was structurally and lithologically controlled specifically the thick premineralization carbonate sequence once overlying the deposit acted as a pressure seal and also as a neutralizing agent during the build up of the magmatic hydrothermal system the weakening of this carbonate cover by igneous intrusion and subsequent hydrothermal activity may have contributed to later selective erosion of the alteration zone thereby telescoping the intermediate sulfidation epithermal system onto the earlier porphyry system and creating the copler window

three dimensional vp and vp vs velocity models of the los angeles basin and central transverse ranges california we use p and s arrival times from 5225 earthquakes and 53 explosions recorded by the southern california seismographic network to invert for the three dimensional p velocity v p and the p and s velocity ratio v p v s in the central transverse ranges and the los angeles basin to model long wavelength features of the velocity structure we invert for the models by interpolating models determined successively from a sparse medium to a dense grid with 40 20 and 10 km spacing of horizontal grid nodes layers of grid nodes are placed at depths of 1 4 6 8 12 16 and 20 km the data variance decreased about 80 in the gradational inversion ample data from the 1994 northridge and other earthquake sequences the rich background seismicity and the dense station distribution along with controlled sources made the model well resolved except along the edges to the southwest in the offshore region and at depths greater than 20 km the v p model images the shape of the los angeles and east ventura basins down to depths of 8 and 12 km three low velocity areas at 1 km depth in the los angeles basin that coincide with recent sediment depositional areas are also imaged the north edge of the peninsular ranges the santa monica and the san gabriel mountains form discontinuous high velocity ridges extending to depths of 20 km the high v p v s ratios in the near surface are consistent with high pore fluid pressures in the basin sediments at depth beneath the east ventura basin the high v p v s and high v p suggest the presence of ophiolitic assemblages or mid miocene volcanics in contrast a body with normal v p and low v p v s that is identified in the upper crust beneath santa monica bay may be a fragment of quartz rich continental crust the v p model of both the ventura and the los angeles basins shows features that suggest deformation of the hanging wall or basin closure at seismogenic depths of 16 km the hypocenters of moderate sized and large earthquakes are located within or adjacent to high v p velocity bodies in most cases these high velocity bodies form the upper block consistent with shortening of the lower crust as described in thick skinned tectonic interpretations

tectonothermal evolution of the apuseni mountains romania resolution of variscan versus alpine events with 40ar 39ar ages abstract polyphase alpine transcurrent faulting and thrusting in the apuseni mountains in romania resulted in the juxtaposition of contrasting structural units that include both metamorphic assemblages and permian mesozoic cover resolution of the chronology of alpine events and distinction from pre alpine evolution has been possible by systematic 40ar 39ar mineral dating of medium and low grade assemblages hornblende and muscovite within nonretrogressed northern sectors of the somes gneissic assemblage record rapid postmetamorphic cooling between 317 and 300 ma following a regionally penetrative late variscan tectonothermal overprint the codru amphibolite granodiorite assemblage records markedly older 40ar 39ar mineral ages 400 365 ma hornblende 340 335 ma muscovite that date delayed postmetamorphic cooling following early variscan tectonothermal activity although variably overprinted during mesozoic tectonism late variscan tectonothermal activity 320 300 ma is also evident from analysis

waste rock dump investigation at rosia montană gold mine romania a geostatistical approach rosia montan the largest european gold mine could be re opened environmental problems led to severe pollution of the rosia and abrud rivers the two main potentially toxic element pte sources in mine sites are in general the abandoned underground workings and the piles of waste rock since the composition of waste rocks is often heterogeneous this study faces the problem of estimating their mineralogical and chemical features starting from a set of sampling point twenty five samples were collected on the main waste dump of the rosia montan mine following a virtual squared grid knots distance about 25 m grain size color bulk chemistry mineralogy acid mine drainage potential and a set of selected pte ag as cu ni pb and zn concentrations were determined on each sample in a first approximation two main waste rock groups were identified wr1 bulk composition is dacite dominated while wr2 is andesite dominated in both of them the concentrations of ptes are below the regulatory limits for soils with the exception of as in terms of acid mine drainage wr1 has a net acid producing potential while wr2 has a net neutralizing potential the anisotropy of wr properties were analysed by means of semi variograms and displayed with contour maps application of positive matrix factorization for the analysis of all the data relative to waste rocks allowed defining in a semi quantitative way the factors controlling pollution and their spatial distribution the processing of score matrix g factor associated with the geostatistical elaboration promises to be a powerful tool to discern the composition of mine dumps and support the exploitation and remediation phases

source complexity of the 1994 northridge earthquake and its relation to aftershock mechanisms we determined the source process of the 1994 northridge earthquake in relation to the aftershock mechanisms to study the source complexity of the mainshock we inverted the p and sh waveforms recorded by the iris and ida iris networks using the method of kikuchi and kanamori 1991 in which the rupture is represented by a series of discrete subevents with varying mechanisms the waveforms show that the rupture consisted of several subevents with about 2 sec in between our solution consists of three subevents with essentially the same mechanism viz strike dip and slip of 130 42 and 116 respectively the first subevent occurred at a depth of about 19 km followed after 2 sec by the second and largest subevent at a depth of 17 km and the third subevent again 2 sec after the second at a depth of about 13 km the total moment from the body waves of this sequence is about 1 1 10 26 dyne cm m w 6 6 with a source duration of 7 sec the large depths of these subevents explain the lack of any surface rupture furthermore the upward propagation of the subevents is consistent with the depth of the hypocenter and the distribution of the aftershocks which are shallower and more northerly than the mainshock hypocenter the aftershocks were analyzed using data from the terrascope network we inverted short period surface waves to determine the moment tensor for 70 events with m w 3 5 the aftershocks can be grouped into three regions based on the mechanisms the eastern part of the aftershock zone where we find thrust events with mechanisms very similar to the main event a central area with predominantly strike slip events and an area to the west where we find oblique thrust events but with more northerly p axes than in the eastern region this distribution suggests that the fault system on which the northridge earthquake occurred is segmented and that the extent of the northridge rupture is controlled by a change in geometry of the fault we find a high stress drop 270 bar for the mainshock we propose that the changes in the fault geometry prevented a slip pulse from propagating thereby causing a high ratio of slip to rupture length

basin structure effects on long period strong motions in the san fernando valley and the los angeles basin from the 1994 northridge earthquake and an aftershock the strong ground motions recorded within the san fernando valley and in the los angeles basin during the 17 january 1994 northridge earthquake show complex waveforms and complicated patterns of peak acceleration and veloc ity this complexity persists even at long periods 1 to 10 sec we investigate basin structure effects on long period wave propagation in the san fernando valley and in the los angeles basin by the two dimensional finite difference modeling of the mainshock and one selected aftershock with m 4 1 the aftershock ground motion records in the san fernando valley and in the los angeles basin can be explained by basin structure effects assuming a simple point source model the structural effects and a source model composed of two subevents can explain the most prominent characteristics of the strong motion waveforms ob served during the mainshock at sites south of the epicenter while such a combination is not enough to explain the large strong motions observed in the north this result suggests that the rupture propagation effects significantly amplified the ground mo tions at sites north of the epicenter

noble metals in thetford mines ophiolites quebec canada part ii distribution of gold silver iridium platinum and palladium in the lac de l est volcano sedimentary section the gold silver iridium palladium and platinum contents of basic volcanics and argillaceous sedimentary rocks from the lac de l9est thetford mines area quebec were determined by radiochemical neutron activation analysis copper and sulfur were also determined in this suite by atomic absorption spectroscopy and leco gas analysis respectively the basic volcanics are part of the thetford mines ophiolite complex of the southern quebec appalachians they rest in fault contact on a complex consisting of tectonite peridotite ultramafic and mafic cumulates and hypabyssal metagabbro the basalts are divisible into a lower and an upper unit separated by argillaceous sediments three different petrographic chemical lithologies were recognized in the lac de l9est volcanic section including high tio 2 and low tio 2 basalts in the lower unit and low tio 2 basalts in the upper unit the main purpose of the study was to compare the relative mobility of platinum group metals pt pd and ir with au ag and cu in a basic volcanic ophiolite setting which was subject to significant thermal metamorphism and possibly some hydrothermal activity based on the distribution of metals in a stratigraphic profile across approximately 425 m of ophiolitic basalt it is concluded that pt pd and ir show no trends related to stratigraphic setting and that these metals were not redistributed by thermal or hydrothermal activity their abundances which in some cases differ greatly from one basalt type to another are probably characteristic of the lavas at the time of eruption au ag and cu show some tendency to concentrate in sulfur rich rocks or near the stratigraphic tops of flow units some redistribution within flow units may have occurred but metal profiles indicate no significant displacement of these metals toward the top of the pile the lack of a well developed sheeted dike complex at lac de l9est suggests a fracture system conducive to large scale deep circulation of seawater in the pile was lacking

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

fluid evolution in a volcanic hosted epithermal carbonate base metal gold vein system alto de la blenda farallon negro argentina alto de la blenda is a 6 6 ma intermediate sulphidation epithermal vein system in the farallon negro volcanic complex which also hosts the 7 1 ma porphyry cu au deposit of bajo de la alumbrera the epithermal vein system is characterised by a large extent and continuity 2 km 400 m open to depth 6 m maximum width and an average gold grade of 8 g t the vein is best developed within an intrusion of a fine grained equigranular monzonite interpreted as the central conduit of a stratovolcano whose extrusive activity ended prior to porphyry cu au emplacement at bajo de la alumbrera which is in turn cut by minor epithermal veins the alto de la blenda vein consists predominantly of variably mn rich carbonates and quartz with a few percent of pyrite sphalerite galena and other sulphide and sulphosalt minerals four phases of vein opening hydrothermal mineralisation and repeated brecciation can be correlated between different vein segments stages 2 and 3 contain the greatest fraction of sulphide and gold they are separated by the emplacement of a polymictic breccia containing clasts of quartz feldspar porphyry as well as basement rocks fluid inclusions in quartz related to stages 2 to 4 are liquid rich with 2 4 wt nacl eq they homogenise between 160 and 300 c with very consistent values within each assemblage vapour inclusions are practically absent in the epithermal vein quartz fragments in the polymictic breccia contain inclusions of intermediate to vapour like density and similar low salinity 3 wt nacl eq besides rare brine inclusions containing halite laser ablation inductively coupled plasma mass spectrometry la icp ms analyses of epithermal inclusions indicate high concentrations of k fe as sb cs and pb that significantly vary within and through subsequent vein stages careful consideration of detection limits for individual inclusions shows high gold concentrations of 0 5 to 3 ppm dissolved in the ore fluid which contains variably high sulphur concentrations in excess over fe and other chalcophile metals compositional variations are interpreted to reflect cooling and contraction of lower density magmatic fluids at depth like those preserved in porphyry clasts that were mechanically transported up by the polymictic breccia ore mineral precipitation from the magmatic fluid occurred by further cooling and possibly minor mixing with surface derived water leading to sulphide saturation de sulphidation of the magmatic fluid and consequent gold precipitation the absence of flash boiling and or reduction by carbonaceous host rocks has led to relatively modest but constant gold grades in the carbonate base metal gold veins of alto de la blenda

site response for urban los angeles using aftershocks of the northridge earthquake ground motion records from aftershocks of the 1994 northridge earthquake are used to estimate site response in the urban los angeles area over 1300 shear wave records from 61 sources and 90 sites are used in a linear inversion for source and site response spectra the methodology makes no assumptions about the shape of the source spectrum to obtain a stable unique inverse a q model and geometrical spreading factor are assumed in addition the site response at a hard rock site is constrained to be approximately 1 0 with a kappa of 0 02 the site response spectra compare favorably with the results of previous and on going investigations in los angeles a couple of first order effects are lower site response in the surrounding mountains dominated by mesozoic and tertiary rocks and higher values in the san fernando and los angeles basins containing surficial pleistocene and holocene alluvial deposits results show good correlation of high site response spectral values with localized areas of severe damage interstate 10 collapse sherman oaks northridge interstate 5 14 collapse however widespread trends in site response across the sedimentary basins are not obvious the data suggest that site responses are lower near the southern margin of the san fernando valley for sources to the north due to north dipping sedimentary structures but the general pattern of site response is characterized by high variability on length scales less than a kilometer variations of a factor of 2 in site response are observed over the length scale of 200 m and for the same surficial geologic unit for some of the alluvial basin sites surface wave generation is a significant contributor to elevated site response at lower frequencies below 2 hz the total damage pattern for the northridge earthquake is influenced by strong source directivity to the north and strong local site effects the correlation of weak motion site response estimates with areas of significant damage demonstrates the value of these field measurements in future urban planning and in the reduction of seismic risk in urban areas

finite difference seismograms for sh waves the accuracy of the finite difference method for generating synthetic seismograms of sh wave propagation in cylindrically symmetric media is discussed the finite difference method has the advantage that arbitrary density and velocity fields in the medium may be specified a point source is generated by a simple transformation of a line source the accuracy of the finite difference seismograms in flat and dipping layered media is confirmed by comparison with the generalized ray method a source radiation pattern is inserted by introducing a near field which has permanent displacement near the source strong motion synthetics are constructed with this new method for the 1968 borrego mountain earthquake as recorded at el centro good fits to the data are achieved using the laterally varying model determined by a detailed refraction survey and the source parameters determined by teleseismic waveform modeling shallow faulting is no longer necessary to explain the long period surface wave development

a geology based 3d velocity model of the los angeles basin sediments abstract seismic hazard studies of the los angeles basin area require a realistic seismic velocity model we use geologic information about depth to crystalline basement depths to sedimentary horizons uplift of sediments and surface geology in a velocity depth age function to construct a three dimensional velocity model in earthquake location tests the model predicts travel times satisfactorily and in earthquake ground motion simulations the model correctly determines the timing and amplitude of late arriving waves

geology geochemistry and genesis of axi a paleozoic low sulfidation type epithermal gold deposit in xinjiang china abstract axi is a low sulfidation type epithermal gold deposit hosted in paleozoic subaerial volcanic rocks in the western tianshan orogenic belt xinjiang china the resource is more than 50 t gold at an average grade of 4 4 ppm the deposit occurs in the tulasu volcanic fault basin in the paleozoic active continental margin on the northern side of the yili central tianshan plate the host rocks are andesitic volcaniclastic rocks of the paleozoic dahalajunshan formation and the orebodies occur as veins in annular faults of a paleocaldera mineralization at axi can be subdivided into five stages quartz and or chalcedony vein quartz vein quartz carbonate vein sulfide vein and carbonate vein there are two types of ore host quartz vein and altered rocks ore minerals are native gold electrum pyrite marcasite arsenopyrite hematite limonite and trace amounts of pyrargyrite polybasite naumannite cerargyrite sphalerite chalcopyrite tetrahedrite galena pyrrhotite and clausthalite gangue minerals are mainly quartz chalcedony illite calcite siderite dolomite adularia and laumontite the main wall rock alteration is silicification and phyllic alteration carbonatization and propylitization the deposit is characterized by an enrichment relative to crustal abundance of au ag as sb bi hg se te and mo depletion in base metals cu pb and zn and a low ag au ratio 0 5 3 7 three types of fluid inclusions were recognized in quartz from the major mineralization stages liquid aqueous inclusions liquid rich two phase inclusions and small amounts of vapor rich two phase inclusions microthermometric measurements indicate that the final ice melting temperatures are 0 3 to 4 4 c corresponding to salinities of 0 5 6 9 wt nacl equiv 2 2 wt nacl equiv in average the peak temperatures of ice melting varies from 0 4 to 1 9 c corresponding to salinities of 0 7 3 1 wt nacl equiv homogenization temperatures range mainly between 120 and 240 c with an average of 190 c and a maximum of 335 c the fluid density is 0 73 to 0 95 g cm 3 and thus the estimated maximum mineralization depth is about 700 m hydrogen and oxygen isotopic compositions of the ore fluids lie within a narrow range d h2o is 98 to 116 and 18 o h2o 1 8 to 0 4 3 he 4 he ranges from 0 0218 to 0 138 ra with an average of 0 044 ra indicating that he derived predominantly from crust with negligible mantle he in the ore fluids by contrast the 40 ar 36 ar ranges from 317 7 to 866 0 suggesting that crust derived radioactive 40 ar accounts for 7 0 to 66 and atmospheric 40 ar about 43 to 93 in the ore fluids hydrogen oxygen carbon sulfur and noble gas isotopes indicate that the ore forming fluids of the axi gold deposit consisted predominantly of circulating meteoric water ore forming metals may have derived mainly from the host volcaniclastic rocks of the dahalajunshan formation and basement rocks the occurrence of adularia platy calcite and quartz or sulfide aggregates as pseudomorphs after bladed calcite in ore veins and occurrence of aqueous liquid and liquid rich and vapor rich two phase inclusions indicates that boiling of the ore forming fluid have occurred leading to supersaturation of the hydrothermal solution and deposition of ore metals this is the main mineralization mechanism for quartz vein type ores in axi the ore forming fluid was buffered to a near neutral ph in a reduced environment during mineralization the preservation of this paleozoic axi deposit and its discovery required a rapid accumulation of sediments in the basin after formation of the deposit and minimal amount of erosion after late cenozoic uplift

stochastic finite fault modeling of ground motions from the 1994 northridge california earthquake ii widespread nonlinear response at soil sites on average soil sites behaved nonlinearly during the m 6 7 1994 north ridge california earthquake this conclusion follows from an analysis that combines elements of two independent lines of investigation first we apply the stochastic finite fault simulation method calibrated with 28 rock site recordings of the north ridge mainshock to the simulation of the input motions to the soil sites that recorded this event the calibrated model has a near zero average bias in reproducing ground motions at rock sites in the frequency range from 0 1 to 12 5 hz the soil sites selected are those where there is colocation of strong motion acce lerographs and temporary instruments from the northridge aftershock observation network at these sites weak motion amplification functions based on numerous aftershock records have been empirically determined in three separate investigations reported in the literature these empirical weak motion amplification factors can be applied to the simulated input rock motions at each soil site to determine the ex pected motions during the mainshock i e neglecting nonlinearity these expected motions can then be compared to the actual recordings during the mainshock this analysis shows that the recorded strong motion spectra are significantly over estimated if weak motion amplifications are used the null hypothesis stating that the inferred differences between weak and strong motion amplifications are statis tically insignificant is rejected with 95 confidence in the frequency range from approximately 2 2 to 10 hz on average the difference between weak and strong motion amplifications is a factor of 2 nonlinear response at those soil stations for which the input peak acceleration exceeded 150 to 200 cm sec 2 contributes most to this observed average difference these findings suggest a significant nonlinear re sponse at soil stations in the los angeles urban area during the northridge main shock the effect is consistent with the increase in damping of shear waves at high levels of strain which is well known from geotechnical studies of soil properties

nonlinear dimensional analysis of trapezoidal valleys subjected to vertically propagating sv waves this paper studies the seismic response of soil basins emphasizing the sensitivity of 2d dynamic response to geometric and material properties this is accomplished through a formal dimensional analysis accounting for fully inelastic soil response thus augmenting the generalization potential of the results and provid ing a novel framework for future research on the subject it is shown that 2d valley response may be described through the following key dimensionless parameters 1 the valley shape factor s expressing the slope inclination 2 the impedance ratio i which expresses the stiffness of the soil relative to the bedrock 3 the wavelength ratio s which is a function of soil stiffness and seismic excitation frequency 4 the rigidity ratio v expressing the stiffness of the soil relative to its strength and 5 the resistance ratio r which expresses the degree of soil nonlinearity the effectiveness of the dimensional formulation is verified through the numerical analysis of equivalent valleys assuming elastic and nonlinear soil response finally a parametric study is conducted to gain insight on the effects of the introduced dimensionless parameters on the dynamic response of trapezoidal alleys it is shown that decreasing thevalley slope or the wavelength ratio promotes wave reflections within the wedge thus enhancing the possibility of wave interferences and subsequently leading to 2d aggravation on the valley surface on the other hand the geometry dependent parasitic vertical accel eration increases as the valley slope becomes steeper as the degree of soil nonlinear ity increases 2d phenomena tend to become localized close to the valley edges

magnitude of nonlinear sediment response in los angeles basin during the 1994 northridge california earthquake the study of nonlinear site response has practical difficulties due to large ambiguities in isolating local response from other competing effects we chose a sedimentary site lf6 in los angeles basin that 1 has the closest reference rock sites available compared to other stations allowing an accurate estimation of local amplification and 2 illustrates clear resonance in the near surface in our opinion this case represents the least ambiguity in the identification of possible nonlinearity the site responses during the northridge the 1987 whittier narrows events and the northridge aftershocks are compared the station shows a fundamental resonance frequency change between the higher and lower amplitude motions in the entire ensemble of 17 events used the net shear modulus reduction during the northridge event is a factor of 1 3 to 1 4 compared to the whittier narrows event and is a factor of 1 7 compared to the aftershocks this result provides guidance of what to expect at other sites in the basin where the nonlinear response is less easy to characterize

geology of the sandaowanzi telluride gold deposit of the northern great xing an range ne china geochronology and tectonic controls abstract the sandaowanzi gold telluride deposit is a new discovery with dominance in gold tellurides in northeastern china the deposit is hosted in quartz veins intruding sub alkaline volcanic rocks there are two types of gold telluride ores in the sandaowanzi ore deposit i e the vein ores and the disseminated ores calaverite krennerite sylvanite petzite empressite hessite and stuetzite are the dominant au ag bearing minerals either in vein ores or in disseminated ores minor amount of other tellurides e g coloradoite altaite and sulfides e g pyrite sphalerite galena chalcopyrite and chalcocite mostly occur in the disseminated ores the gold bearing quartz veins crosscut volcanic host rocks which are dated at 135 3 124 7 ma by la icp ms u pb zircon method the latter unconformably overly a monzogranite dated as 181 6 ma diabase dikes dated at 116 6 ma intrude the gold bearing quartz veins the age data thereby bracket the timing of gold mineralization between 125 3 and 116 6 ma these geochronologic data are consistent with field relations regional comparison reveals that the widespread volcanism in the great xing an range is a product of the subduction of the izanagi plate beneath the eurasian plate gold telluride mineralization was contemporaneous with regional extension and magmatism as the subducting izanagi plate rolled back

edge diffracted 1 sec surface waves observed in a small size intramountain basin colfiorito central italy during the umbria marche central italy seismic sequence a small aperture 200 m four station array was operating in the colfiorito plain a few kilometers away from the epicenters of the ml 5 6 and 5 8 mainshocks of 26 september 1997 the array was deployed approximately 500 m from the eastern edge of the basin we analyze the three component seismograms of 12 aftershocks in a magnitude range of 2 5 to 4 1 amplitudes of the horizontal components are systematically higher than those of the vertical component with an average horizontal to vertical spectral ratio of about 3 at 1 hz in this frequency band earthquake induced ground shaking is highly coherent across the array a 1 sec running window zero lag cross correlation algorithm is used to compute apparent velocity and backazimuth of coherent wave trains in the frequency band 0 5 to 2 hz apparent velocity and backazimuth show a different behavior in the first part of the seismograms compared to the late coda the largest amplitude waves that is s waves and early coda are characterized by low apparent velocities mostly between 400 and 1200 m sec this suggests that near the rock edge the most significant part of seismic energy propagates horizontally in the basin backazimuth of these low frequency coherent wavetrains never coincides with the array to source direction the predominant backazimuth is peaked around n110 corresponding to the nearest steep outcrop of the basin edge the observed 1 sec coherent wave trains are interpreted as locally generated surface waves that are persistently diffracted from the nearby basin edge as long as a significant level of seismic radiation is incident to the bedrock when the bedrock excitation decreases a much larger variability of both apparent velocity and backazimuth is observed suggesting that in the coda randomly scattered waves within the basin and late arrivals of deeper origin become more important multipathing from the source to the site as well as multipathing within the basin are therefore interpreted as the main causes of the observed long duration coherent low frequency basin shaking

zoned base metal mineralization in a porphyry system origin and evolution of mineralizing fluids in the morococha district peru porphyry related base metal vein and replacement mineralization i e cordilleran polymetallic mineralization in the morococha district central peru is part of a large magmatic hydrothermal system associated with the emplacement of several late miocene porphyry intrusions and formation of important cu mo mineralization zn pb ag cu veins overprint the giant toromocho porphyry cu mo deposit in the center of the district and display a typical concentric base metal zonation cu zn pb ag covering an area of approximately 50km2 a detailed fluid inclusion study supports the hypothesis that base metal mineralization precipitated from cooled and evolved metal rich intermediate density porphyry type fluids in early stages of cordilleran base metal vein formation fluid inclusions have low salinities of 2 to 5 wt nacl equiv co2 contents of 3 to 10mol and homogenization temperatures th of 380 to 340 c they are similar to intermediate density fluid inclusions trapped in a milky quartz vein predating cordilleran polymetallic mineralization with similar low salinities 3 0 3 8 wt nacl equiv and low co2 contents 6 5 8 mol but higher th of 420 to 410 c during cooling of the intermediate density fluids from 400 to 300 c the lithostatic pressure regime changed to a hydrostatic one the fluids underwent pressure drop as well as phase separation i e unmixing and lost most of their co2 they acquired moderate salinities in some cases intermediate up to 16 wt nacl to brine compositions however the bulk of the magmatic fluid retained low salinity while it continued to cool under open system conditions and precipitated tennantite tetrahedrite chalcopyrite enargite sphalerite and galena upon cooling below 270 c the fluids deposited abundant rhodochrosite and quartz while following the boiling curve toward lower p t conditions these data record an evolution of mineral precipitation from deep minimum depth of 2 1 5 km to shallow environments 300 800 m oxygen hydrogen and carbon stable isotope data indicate that the hydrothermal fluids have a dominantly magmatic signature and were diluted by meteoric waters during the carbonate stage copper 5 000 18 000 g g sulfur up to 12 000 g g and iron 2 100 6 000 g g concentrations in the intermediate density fluid inclusions in the milky quartz veins are approximately 5 to 10 times higher than in intermediate density inclusions of the early cordilleran base metal veins the base metals zn pb and mn have comparable concentrations between 100 and 1 000 g g for both types of fluid these findings suggest that the fluids identified in cordilleran polymetallic veins are compositionally similar to the porphyry type fluids and could have derived from the latter after precipitation of cu and fe bearing sulfides in a deeper porphyry environment the new data explain the commonly observed base and precious metal zonation patterns encountered in porphyry centered districts e g bingham butte and show that both porphyry and polymetallic mineralization can precipitate from similar magmatic hydrothermal fluid pulses

three dimensional simulation of earthquakes on the los angeles fault system we have used a 3d finite difference method to simulate ground motion from elastodynamic propagating ruptures with constant slip on faults in the metropolitan area of los angeles california simulations are carried out for hypothetical m 6 75 earthquakes on the palos verdes and elysian park faults and for comparison an approximation to the 17 january 1994 m 6 7 northridge earthquake the dominant subsurface features of this area are the deep sedimentary los angeles basin and the smaller and shallower san fernando basin simulated ground motions are restricted to the frequency range 0 0 to 0 4 hz ground motion time histories show that in general sites associated with the largest particle velocities and cumulative kinetic energies are located 1 in the epicentral area 2 above the deepest parts of the basins and 3 near the steepest edges of the los angeles basin we find maximum particle velocities for the palos verdes elysian park and northridge simulations of 0 44 0 67 and 0 58 m sec respectively in each case both the directivity of the rupture and the lower impedance of the basins significantly amplify the ground motion although the gross radiation pattern from these ruptures is observable the 3d basin structure distorts the wave field and becomes a source for edge generated waves signal durations at some basin sites last beyond 90 sec due to love waves and refracted s waves that propagate into the sediments from the basin edges compared with the palos verdes event the durations are generally smaller for the elysian park earthquake due to a smaller amount of love waves generated at the basin edges a simple approximation to the northridge earthquake reproduces the overall spatial pattern of the long period particle velocities successfully predicts the timing of late arriving waves and matches the peak velocities with discrepancies generally less than a factor of 2 however for localized areas immediately north and south of the santa monica mountains the computed ground motion underpredicts the observed horizontal peak velocities but matches the vertical ones the pattern of simulated total cumulative kinetic energies is similar to that for the damage intensities observed near the epicenter of the northridge event while the northridge earthquake caused damage in the los angeles area the 3d simulations show that earthquakes with the same magnitude on the palos verdes or elysian park faults produce more severe ground shaking in the los angeles basin

finite difference modeling of two aftershocks of the 1994 northridge california earthquake recent evidence for nonlinear behavior of strong motions generated by the northridge california earthquake relies explicitly on the analysis of aftershock data thus correcting these observations for propagational and source effects becomes a crucial step in these studies here we demonstrate that the dipping structure near the edges of the san fernando valley can strongly alter the local site responses especially for shallow events we model two aftershocks with similar epicenters but with shallow 4 km and deep 16 km hypocentral depths waveforms from 12 portable instruments deployed across the basin and recording these events were processed and studied in the 0 3 4 hz bandpass for the shallow event distinctive features are a broad direct s phase and large amplitude surface waves at the basin stations and high frequency s phases at stations in the santa monica mountains the deep event is less strongly affected by the basin but displays strong evidence of the source radiation pattern an array analysis indicates 2d propagation for most of the strong arrivals some of these features are explained by a simple 2d basin model containing a strong shallow contrast a factor of 2 jump in seismic velocity at a depth of 1 km within the basin and a moderate deeper gradient

bonanza grade accumulations of gold tellurides in the early cretaceous sandaowanzi deposit northeast china the sandaowanzi epithermal gold deposit 0 5 moz or ca 14 tons located at the northern edge of the great xing an range ne china is unique in that nearly all the gold 95 is contained in gold tellurides mostly in bonanza grade ore shoots the highest grade being up to 20 000 g t the bonanza ores are hosted in the central parts of large scale 3 m wide 200 m long quartz veins which crosscut early cretaceous andesitic trachyte and trachytic andesite and are in turn crosscut by diabase dykes of similar age there are two ore types low grade disseminated ores and high grade vein ores in the former very fine grains of ag rich tellurides mainly hessite and petzite coexist with sulfides pyrite sphalerite galena and chalcopyrite occurring as disseminated grains or sometimes as grain aggregates in the high grade vein ores coarse grained au ag tellurides calaverite sylvanite krennerite and petzite form a major part of quartz telluride veins chalcopyrite forms separate monomineralic veins emplaced within the quartz telluride veins spectacular textures among coarse grained up to 3 cm in diameter tellurides and micron scale bamboo shoot like grains are observed two and three phase telluride symplectites are common in the vein ores fluid inclusion studies suggest that the mineralizing fluids are a mixture of magmatic and meteoric fluids that homogenized in the temperature range of 260 280 c sulfur isotope compositions of pyrite and chalcopyrite 34s 1 64 to 1 91 support the origin of fluids from a deep source it is suggested that faulting temperature changes and variation in fs2 and fte2 were major factors contributing to the two main types of mineralization and the differences between them early rapid cooling and subsequent slow cooling of the later fluids along fault and fracture zones were instrumental in formation of the two superposed ore types open space filling and crack sealing along fractures predominates over replacement during telluride mineralization the sandaowanzi deposit is a unique bonanza grade accumulation of gold tellurides genetically related to subalkaline magmatism which was genetically associated with early cretaceous regional extension

how precisely can the temperature of a fluid event be constrained using fluid inclusions u s national science foundation ear 1624589 chemical sciences geosciences and biosciences division office of basic energy sciences office of science u s department of energy de fg02 03er15430 bureau of economic geology jackson school of geosciences university of texas austin

the slip history of the 1994 northridge california earthquake determined from strong motion teleseismic gps and leveling data we present a rupture model of the northridge earthquake determined from the joint inversion of near source strong ground motion recordings p and sh teleseismic body waves global positioning system gps displacement vectors and permanent uplift measured along leveling lines the fault is defined to strike 122 and dip 40 to the south southwest the average rake vector is determined to be 101 and average slip is 1 3 m the peak slip reaches about 3 m our estimate of the seismic moment is 1 3 0 2 10 26 dyne cm potency of 0 4 km3 the rupture area is small relative to the overall aftershock dimensions and is approximately 15 km along strike nearly 20 km in the dip direction and there is no indication of slip shallower than about 5 to 6 km the up dip strong motion velocity waveforms are dominated by large s wave pulses attributed to source directivity and are comprised of at least 2 to 3 distinct arrivals a few seconds apart stations at southern azimuths indicate two main s wave arrivals separated longer in time about 4 to 5 sec these observations are best modeled with a complex distribution of subevents the initial s wave arrival comes from an asperity that begins at the hypocenter and extends up dip and to the north where a second larger subevent is centered about 12 km away the secondary s arrivals at southern azimuths are best fit with additional energy radiation from another high slip region at a depth of 19 km 8 km west of the hypocenter the resolving power of the individual data sets is examined by predicting the geodetic gps and leveling displacements with the dislocation model determined from the waveform data and vice versa and also by analyzing how well the teleseismic solution predicts the recorded strong motions the general features of the geodetic displacements are not well predicted from the model determined independently from the strong motion data likewise the slip model determined from geodetic data does not adequately reproduce the strong motion characteristics whereas a particularly smooth slip pattern is sufficient to satisfy the geodetic data the strong motion and teleseismic data require a more heterogeneous slip distribution in order to reproduce the velocity amplitudes and frequency content although the teleseismic model can adequately reproduce the overall amplitude and frequency content of the strong motion velocity recordings it does a poor job of predicting the geodetic data consequently a robust representation of the slip history and heterogeneity requires a combined analysis of these data sets

the seismic response of the los angeles basin california using strong motion data recorded in the los angeles region from the 1992 mw 7 3 landers earthquake we have tested the accuracy of existing three dimensional 3d velocity models on the simulation of long period 2 sec ground motions in the los angeles basin and surrounding san fernando and san gabriel valleys first the overall pattern and degree of long period excitation of the basins were identified in the observations within the los angeles basin the recorded amplitudes are about three to four times larger than at sites outside the basins amplitudes within the san fernando and san gabriel valleys are nearly a factor of 3 greater than surrounding bedrock sites then using a 3d finite difference numerical modeling approach we analyzed how variations in 3d earth structure affect simulated waveforms amplitudes and the fit to the observed patterns of amplification significant differences exist in the 3d velocity models of southern california that we tested magistrale et al 1996 graves 1996a hauksson and haase 1997 major differences in the models include the velocity of the assumed background models the depth of the los angeles basin and the depth location and geometry of smaller basins the largest disparities in the response of the models are seen for the san fernando valley and the deepest portion of the los angeles basin these arise in large part from variations in the structure of the basins particularly the effective depth extent which is mainly due to alternative assumptions about the nature of the basin sediment fill the general ground motion characteristics are matched by the 3d model simulations validating the use of 3d modeling with geologically based velocity structure models however significant shortcomings exist in the overall patterns of amplification and the duration of the long period response the successes and limitations of the models for reproducing the recorded ground motions as discussed provide the basis and direction for necessary improvements to earth structure models whether geologically or tomographically derived the differences in the response of the earth models tested also translate to variable success in the ability to successfully model the data and add uncertainty to estimates of the basin response given input scenario earthquake source models

u th pb and 230th 238u disequilibrium isotope systematics precise accessory mineral chronology and melt evolution tracing in the alpine bergell intrusion in order to investigate the potential of combined th u pb isotope and 230th 238u disequilibrium systematics for tracing magmatic crystallization and melt evolution conventional high resolution single crystal tims techniques have been applied to zircon titanite and fragments of geochemically characterized growth zones of allanite these minerals were extracted from a single tonalite specimen collected from the feeder zone of the tertiary bergell pluton southern steep belt s switzerland n italy the isotopic results document an extended history of crystallization and melt evolution of at least 5 ma with well resolved zircon ages defining an early interval of 33 0 to 32 0 ma followed by crystallization of zoned allanite from 32 0 to 28 0 ma and formation of magmatic epidote possibly as late as 26 ma trace and major element patterns in zoned allanite closely mirror melt evolution characterized by increase of u concentration and sharp decrease of th and lree reflecting early crystallization of phases low in u and in particular the dominating control by allanite precipitation preservation of substantial quantities of excess 206pb derived from initial excess 230th in all analyzed allanite grains indicates that their isotopic systems have not been reset by loss of radiogenic pb during prolonged residence at magmatic conditions and regional metamorphic cooling and that the measured sequence of 208pb 232th dates translates into a real age sequence major loss of radiogenic pb from compositionally zoned allanite by volume diffusion would have resulted in a data pattern grossly different from the observed one as demonstrated by numerical modeling of 232th 208pb 238u 230th 206pb isotopic evolution the results therefore suggest closure temperatures 700 c for magmatic allanite quantification of 230th 238u disequilibrium relationships reveals a smooth initially steep decrease of th u in the magma from values of 2 9 at 32 0 ma to 0 1 at 28 0 ma in equilibrium with sequential allanite zoning comparison of calculated th u magma with measured total rock th u 0 79 requires fractional crystallization of allanite at an early stage this process of removal of allanite and thus th from the melt was operative at least until 31 5 ma providing an upper limit for the time of emplacement of the studied magma batch the fact that bulk zircon and a large part of allanite crystallization predate emplacement cautions against equating ages determined on refractory minerals from deep seated plutons with intrusion ages the persistence of magmatic conditions over a period of 5 ma concentrated in a narrow collision zone between the european and the african plate has been a major controlling factor for the oligocene evolution of the adjacent insubric fault the main tectonic lineament of the alps being active from late cretaceous to miocene times

an overview of the pge concentrations in the shetland ophiolite complex extremely anomalous platinum group element pge concentrations are known at one site cliff in the shetland ophiolite complex systematic pge analysis of all the mafic and ultramafic igneous and alteration lithologies in the ophiolite has revealed many lower grade anomalous pge occurrences throughout the cumulate ultramafic sequence and their distribution is described here more sites with pge enrichments as anomalous as those at cliff have not been found at cliff the anomalous values of over 60 ppm pt pd are restricted to a chromite rich sulphide bearing dunite forming a small part of a 200 m dunite lens in mantle harzburgite close to the basal thrust of the ophiolite lower values of up to 6 4 ppm pt pd occur in chromite poor sulphide rich dunites also within this dunite lens the only other chromite rich dunite lens in the cliff area also has detected pt and pd but with low pt pd values of 200 ppb in contrast harzburgites metasediments underlying the basal thrust serpentinites from the basal thrust and internal faults are all barren of pt and pd detection limit 20 ppb in the cliff area therefore detected pge values are restricted to magmatic chromite rich dunite lenses pge analyses of drill core from beneath the disused chromite quarries at cliff are low 227 ppb pt pd indicating that the extremely anomalous pge values are very restricted this supports the idea that pge concentrated magmatically within the dunite lens at cliff may have been remobilized locally to produce extremely anomalous pge values in an alteration zone only a few metres in diameter elsewhere in the ophiolite anomalous pt pd values of up to 4 ppm occur in chromite rich sulphide bearing dunite within the dunite unit which stratigraphically overlies the harzburgite pt pd concentrations of up to 1 ppm are present in the pyroxenites and wehrlites of the upper part of the ultramafic sequences high level wehrlites and pyroxenites within the gabbro unit representing late ultramafic differentiates contain lower levels of pge of up to 310 ppb pt pd the gabbros all have less than 20 ppb pt and pd this distribution indicates that the pge concentrations occur in specific primary magmatic lithologies and pathfinder analysis shows that they are associated with ni cu au and cr pge have not been found above detection limits in fault zones away from primary pge mineralization sites and it is concluded that pge are not significantly hydrothermally reconcentrated at cliff remobilization may have occurred over short distances of only a few metres at most

platinum group elements in a 3 5 ga nickel iron occurrence possible evidence of a deep mantle origin the bon accord ba ni fe deposit occurs in chemically depleted ultramafic rocks of the circa 3 5 ga jamestown ophiolite complex in the barberton greenstone belt of the kaapvaal craton south africa the host rocks of the ba body are high temperature ultramafic tectonites which probably represent the upper mantle residue from which the overlying magmatic rocks were separated during partial melting ba is unusual both mineralogically and chemically it consists of a rare ni rich assemblage ni oxide bunsenite spinels trevorite nichromite and silicates e g liebenbergite the ni end member olivine and their altered equivalents nio average 38 and feo fe2o3 average 34 are the major chemical constituents the cu and s contents are very low both 2000 c lower mantle high ni fe and ni co ratios relative to c 1 chondrite suggest that ba might have been derived from siderophile rich material that remained in the lower mantle after inefficient core formation a model is presented wherein such a metal silicate heterogeneity is fractionated and oxidized during ascent through the mantle in a thermal plume which originates in the lowermost mantle the d layer some of its residue is finally incorporated as pods into the lithospheric mantle during formation of the archean oceanic crust inclusion of such fractionated pods in the old subcontinental keel of the kaapvaal craton might constitute a potential pge source which could have been tapped by subsequent magmatic activity

seismic waveform modeling in the los angeles basin the proximity of several recent earthquakes to the los angeles sedimentary basin provides an opportunity to isolate the effects of the basin on wave propagation the 4 october 1987 aftershock m l 5 3 of the whittier narrows sequence and the 28 june 1991 sierra madre mainshock m l 5 8 are on a similar azimuth to stations overlying the deepest part of the basin a distinctive feature of records from basin stations recording the 4 october after shock is the large amplitude of multiple s ss etc the multiples have up to twice the amplitude of the direct s phase on the tangential component at such a short range less than 25 km a horizontal seismic velocity gradient is needed to turn rays rapidly enough for large amplitude multiples to form a forward modeling approach is employed using finite difference numerical techniques that produce double couple point source solutions a model based on a recent geologic cross section constructed for the east edge of the los angeles basin generates more phases than are seen in the seismic records simpler models based on dipping layers with low shear velocities in the top few layers fit the data better the seismic velocity depth and dip of the layers are varied to fit the timing between the direct p the direct s and the first s multiple the timing and amplitude of the direct and first multiple s pulses are well modeled though the phase of the first multiple does not match the data including a steeply dipping west edge in the basin model has little effect on the synthetic waveforms except at distances near that basin edge the amplitude of ss is greatest in the deepest part of the basin where it is two times larger than direct s the coda duration increases from 8 sec to more than 20 sec from the ne to the sw the sierra madre mainshock occurred about 25 km to the ne of the whittier narrows sequence the model for whittier narrows was extended to this distance with a shallow basin between whittier and the sierra madre hypocenter to simulate the san gabriel sedimentary basin phases generated by the edge of the deep basin continue to dominate the synthetic waveforms but this model generates a lengthy coda this study shows that specific phases with frequencies up to 1 hz that have traveled through deep sedimentary basins can be explained by two dimensional seismic velocity models

nonlinear soil response in the vicinity of the van normal complex following the 1994 northridge california earthquake ground motion recordings obtained at the van norman complex from the 1994 northridge california mainshock and its aftershocks constitute an excellent data set for the analysis of soil response as a function of ground motion amplitude we searched for nonlinear response by comparing the fourier spectral ratios of two pairs of sites for ground motions of different levels using data from permanent strong motion recorders and from specially deployed portable instruments we also compared the amplitude dependence of the observed ratios with the amplitude de pendence of the theoretical ratios obtained from 1 d linear and 1 d equivalent linear transfer functions using recently published borehole velocity profiles at the sites to provide the low strain material properties one pair of sites was at the jensen filtra tion plant jfp the other pair was the rinaldi receiving station r n and the los angeles dam lad most of the analysis was concentrated on the motions at the jensen sites portable seismometers were installed at the jfp to see if the motions inside the structures housing the strong motion recorders differed from nearby flee field motions we recorded seven small earthquakes and found that the high fre quency low amplitude motions in the administration building were about 0 3 of those outside the building this means that the lack of high frequencies on the strong motion recordings in the administration building relative to the generator building is not due solely to nonlinear soil effects after taking into account the effects of the buildings however analysis of the suite of strong and weak motion recordings indicates that nonlinearity occurred at the jfp as predicted by equivalent linear analysis the largest events the mainshock and the 20 march 1994 aftershock show a significant deamplification of the high frequency motion relative to the weak mo tions from aftershocks occurring many months after the mainshock the weak mo tion aftershocks recorded within 12 hours of the mainshock however show a relative deamplification similar to that in the mainshock the soil behavior may be a con sequence of a pore pressure buildup during large amplitude motion that was not dissipated until sometime later the motions at r n and lad are from free field sites the comparison among spectral ratios of the mainshock weak motion coda waves of the mainshock and an aftershock within ten minutes of the mainshock indicate that some nonlinearity occurred presumably at rin because it is the softer site the spectral ratio for the mainshock is between that calculated for pure linear response and that calculated from the equivalent linear method using commonly used modulus reduction and damping ratio curves in contrast to the jensen sites the ratio of motions soon after the high amplitude portion of the mainshock differs from the ratio of the mainshock motions indicating the mechanical properties of the soil returned to the low strain values as the high amplitude motion ended this may indicate a type of nonlinear soil response different from that affecting motion at the jensen administration building

interplay of tectonics and neogene post collisional magmatism in the intracarpathian region abstract distribution of the neogene calc alkaline magmatism of the carpathian arc is directly related in space and time to the kinematics of the two major terranes of the intracarpathian area alcapa tisia getia along the south eastern border of the european plate in the west carpathians and adjacent areas the volcanic activity occurred between 20 11 ma with large volumes of both acidic and intermediate rocks generally distributed randomly sometimes transversally to the orogenic belt and as rare small occurrences along the flysch belt in the east carpathians the volcanic rocks are distributed along the northern margin of the zemplin block the north easternmost part of the alcapa and eastward along the front of the getic block at the contact with european plate between tokaj slanske vihorlat up to northern calimani mountains the magmatism occurred between 14 9 ma and along the calimani harghita chain between 9 0 2 ma the calc alkaline magmatic rocks of the apuseni mountains are located in the interior of the tisia block and occurred between 14 9 ma the generation of the calc alkaline magmatism is considered here as the result of complex interplay between plate roll back and lithospheric detachment tectonic processes and the break off of the subducted plate mostly in a post collisional setting 1 the magmatites of the western carpathians and the pannonian basin were generated in direct relation to subduction roll back processes over the downgoing slab during the period of lateral extrusion and back arc extension in this area characterized by maximum crustal shortening we can infer further delamination processes to explain the generation of magmas 2 the magmatic rocks from the northern sector of the east carpathians tokaj slanske vihorlat up to the northern calimani mountains resulted after subduction roll back processes and an almost simultaneous break off of the descending plate all along the arc segment during main clockwise rotation of the intracarpathian terranes 3 in the eastern sector of the east carpathians calimani up to harghita mountains the magmatic rocks were generated through partial melting of the subducted slab followed by gradual break off of the subducted plate along strike north to south 4 the apuseni mts magmatic activity resulted in transtensional tectonic regime by decompressional melting of lithospheric mantle during the translation and rotation of tisia getia block

ore related breccias in volcanoplutonic arcs an overview of breccias related to a variety of base metal precious metal and lithophile element deposits in volcanoplutonic arcs permits definition of six possible mechanisms for subsurface brecciation 1 release of magmatic hydrothermal fluids from high level hydrous magma chambers during second boiling and subsequent decompression generates a spectrum of breccia types in which fragments may suffer collapse and or ascent single or multiple intrusion related breccia pipes and pre and intermineral breccias in porphyry copper deposits provide widespread examples 2 magmatic heating and expansion of meteoric pore fluids may lead to brecciation commonly of late or postmineral age and including pebble dikes in porphyry type and related deposits magmatic heating of rocks saturated with seawater may cause submarine hydrothermal eruptions late in the emplacement histories of kuroko type massive sulfide deposits many of the resultant breccias underwent limited sedimentary transport overpressuring of heated fluids beneath semipermeable partly self sealed cap rocks may lead to brecciation and subaerial hydrothermal eruptions in shallow epithermal precious metal settings magmatic heating or tectonic disturbance may have triggered brecciation 3 interaction of cool ground waters with subsurface magma can generate phreatomagmatic explosions postmineral phreatomagmatic diatremes associated with porphyry systems and premineral diatremes with epithermal precious or base metal deposits were generated in this manner these attained the palcosurface to produce pyroclastic base surge and fall deposits that accumulated as tuff rings around maar craters 4 magmatic hydrothermal brecciation may lead to disruption of rocks through to the paleosurface decompression and fragmentation and eruption of the top part of an underlying magma chamber pre and postmineral magmatic diatremes of this sort are inferred to accompany a few porphyry type and other base and precious metal systems they were manifested at the palcosurface by accumulations of pyroclastic fall and flow deposits 5 breccias may result from mechanical disruption of wall rocks during subsurface movement of magma any intrusion related deposit may include such intrusion breccias 6 tectonic breccias resulting from fault displacement may accompany any type of ore deposit a continuum exists between many of these breccia types and it is difficult to identify unique criteria for their unambiguous distinction

rosia poieni copper deposit apuseni mountains romania advanced argillic overprint of a porphyry system the rosia poieni deposit is the largest porphyry copper deposit in the apuseni mountains romania hydrothermal alteration and mineralization are related to the middle miocene emplacement of a subvolcanic body the fundoaia microdiorite zonation of the alteration associated with the porphyry copper deposit is recognized from the deep and central part of the porphyritic intrusion towards shallower and outer portions four alteration types have been distinguished potassic phyllic advanced argillic and propylitic potassic alteration affects mainly the fundoaia subvolcanic body the andesitic host rocks are altered only in the immediate contact zone with the fundoaia intrusion mg biotite and k feldspar are the main alteration minerals of the potassic assemblage accompanied by ubiquitous quartz chlorite and anhydrite are also present magnetite pyrite chalcopyrite and minor bornite are associated with this alteration phyllic alteration has overprinted the margin of the potassic zone and formed peripheral to it it is characterized by the replacement of almost all early minerals by abundant quartz phengite illite variable amounts of illite smectite mixed layer minerals minor smectite and kaolinite pyrite is abundant and represents the main sulfide in this alteration zone advanced argillic alteration affects the upper part of the volcanic structure the mineral assemblage comprises alunite kaolinite dickite pyrophyllite diaspore aluminium phosphate sulphate minerals woodhouseite svanbergite series zunyite minamyite pyrite and enargite luzonite alunite forms well developed crystals veins with enargite luzonite and pyrite in a gangue of quartz pyrophyllite and diaspore are present within and around the subvolcanic intrusion this alteration type is partially controlled by fractures a zonal distribution of alteration minerals is observed from the centre of fractures outwards with 1 vuggy quartz 2 quartz alunite 3 quartz kaolinite alunite and in the deeper part of the argillic zone quartz pyrophyllite diaspore 4 illite illite smectite mixed layer minerals kaolinite alunite and e chlorite albite epidote propylitic alteration is present distal to all other alteration types and consists of chlorite epidote albite and carbonates mineral parageneses mineral stability fields and alteration mineral geothermometers indicate that the different alteration assemblages are the result of changes in both fluid composition and temperature of the system the alteration minerals reflect cooling of the hydrothermal system from 400 c biotite to 300 200 c chlorite and illite in veinlets and to lower temperatures of kaolinite illite smectite mixed layers and smectite crystallization hydrothermal alteration started with an extensive potassic zone in the central part of the system that passed laterally to the propylitic zone it was followed by phyllic overprint of the early altered rocks nearly barren advanced argillic alteration subsequently superimposed the upper levels of the porphyry copper alteration zones the close spatial association between porphyry mineralization and advanced argillic alteration suggests that they are genetically part of the same magmatic hydrothermal system that includes a porphyry intrusion at depth and an epithermal environment of the advanced argillic type near the surface

direct analysis of ore precipitating fluids combined ir microscopy and la icp ms study of fluid inclusions in opaque ore minerals laser ablation inductively coupled plasma mass spectrometry la icp ms in combination with near infrared microscopy of fluid inclusions hosted by ore minerals that are opaque to visible light can provide the composition of ore precipitating fluids we applied the two techniques to well constrained fluid inclusion assemblages hosted by pyrite enargite and quartz to trace the source and evolution of the fluids in high sulfidation epithermal veins overprinting a porphyry copper deposit at rosia poieni romania despite some analytical limitations caused by the sulfide host minerals the data demonstrate that fluids trapped in apparently cogenetic quartz and ore minerals are chemically different systematic changes in major and trace element ratios between liquid vapor vapor rich and brine fluid inclusion assemblages in the three minerals record an evolving fluid source at the porphyry to epithermal transition regarding their cs na k ratios most of epithermal quartz hosted fluid inclusion assemblages form a well defined cluster which coincides with the narrow range of the porphyry stage fluids trapped in early quartz of the porphyry stockwork veins their cu na k ratios are 10 to 100 times lower compared to the pyrite hosted inclusions and correspond to the lowest cu na k ratios recorded for the porphyry stage fluids by contrast pyrite hosted vapor rich fluid inclusions have the highest cu na k similar to the highest cu na k ratios measured in the porphyry stage fluid inclusions the results led to the conclusion that the gangue and ore minerals in the high sulfidation epithermal veins at rosia poieni formed by successive pulses of chemically distinct hydrothermal fluids that were successively exsolved from residual melt batches of a progressively crystallizing magma at greater depth these results are consistent with detailed textural observations but petrography alone could not have led to this unambiguous conclusion