application of numerical wave propagation techniques to study local soil effects the case of benevento italy many of the numerical techniques used for seismic zonation studies treat one dimensional structural models and or the incidence of plane polarized body waves these techniques are often not adequate for laterally heterogeneous structures and for sources that are not located beneath the site of interest in such cases a more rigorous treatment of the combined effects of the source the path and the site response is needed this can be accomplished with a hybrid approach combining modal summation and the finite difference technique to demonstrate the differences between these techniques the ground motion in the city of benevento italy is modelled we first compare the results obtained with one and two dimensional structural models for vertical incidence of plane polarized body waves these results are then compared with those obtained with the hybrid approach for two dimensional structural models

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

geology geochronology geochemistry and ore genesis of the wangu gold deposit in northeastern hunan province jiangnan orogen south china abstract the wangu gold deposit in northeastern hunan south china is one of many structurally controlled gold deposits in the jiangnan orogen the host rocks slates of the lengjiaxi group are of neoproterozoic age but the area is characterized by a number of late jurassic cretaceous granites and ne trending faults the timing of mineralization tectonic setting and ore genesis of this deposit and many similar deposits in the jiangnan orogen are not well understood the orebodies in the wangu deposit include quartz veins and altered slates and breccias and are controlled by wnw trending faults the principal ore minerals are arsenopyrite and pyrite and the major gangue minerals are quartz and calcite alteration is developed around the auriferous veins including silicification pyritic arsenopyritic and carbonate alterations field work and thin section observations indicate that the hydrothermal processes related to the wangu gold mineralization can be divided into five stages 1 quartz 2 scheelite quartz 3 arsenopyrite pyrite quartz 4 poly sulfides quartz and 5 quartz calcite the lianyunshan s type granite which is in an emplacement contact with the ne trending changsha pingjiang fracture zone has a zircon la icpms u pb age of 142 2 ma the dayan gold occurrence in the changsha pingjiang fracture zone which shares similar mineral assemblages with the wangu deposit is crosscut by a silicified rock that contains muscovite with a ca 130 ma 40ar 39ar age the gold mineralization age of the wangu deposit is thus confined between 142 ma and 130 ma this age of mineralization suggests that the deposit was formed simultaneously with or subsequently to the development of ne trending extensional faults the emplacement of late jurassic cretaceous granites and the formation of cretaceous basins filled with red bed clastic rocks in northeastern hunan which forms part of the basin and range like province in south china empa analysis shows that the average as content in arsenopyrite is 28 7 atom and the mineralization temperature of the arsenopyrite pyrite quartz stage is estimated to be 245 20 c from arsenopyrite thermometry the high but variable au as molar ratios 0 02 of pyrite suggest that there are nanoparticles of native au in the sulfides an integration of s pb h o he ar isotope systematics suggests that the ore fluids are mainly metamorphic fluids originated from host rocks possibly driven by hydraulic potential gradient created by reactivation of the wnw trending faults initially formed in paleozoic with possible involvement of magmatic and mantle components channeled through regional fault networks the wangu gold deposit shares many geological and geochemical similarities as well as differences with typical orogenic epithermal and carlin type gold deposits and may be better classified as an intracontinental reactivation type as proposed for many other gold deposits in the jiangnan orogen

site amplifications observed in the gubbio basin central italy hints for lateral propagation effects abstract in this study we investigate the site amplification effects observed in the gubbio plain central italy the recordings of 140 local earthquakes 1 2 ml 4 7 observed by two linear arrays installed along the longitudinal and perpendicular basin axis are analyzed both in the time and frequency domains to determine the spatial variation of the local site effects in the basin the time series recorded in the gubbio plain are characterized by locally generated surface waves which cause a significant increase in both ground motion duration and amplitude with respect to a nearby reference station on a rock site in the middle of the basin where the sedimentary cover is thickest ca 600 m the peak ground velocity is amplified on average by a factor of 5 with respect to the reference station installed on rock and the duration is increased by a factor of about 2 the analyses in the frequency domain show that the spectral energy of the basin generated waves is mainly distributed over the range 0 4 2 hz and affects both horizontal and vertical components the site responses estimated by applying two reference site methods show that the overall shape of the amplification functions is similar for the sites located inside the basin with a difference in the amplification levels which can reach values as high as 30 in the middle of the valley amplifications up to a factor of 10 affect the vertical component of ground motion over a broad frequency range for nearly all basin sites with the maximum amplifications occurring at around 1 hz finally although the horizontal to vertical spectral ratios were found to provide a reliable estimation of the fundamental resonance frequency of the site they fail to estimate the shape of the site transfer function

ambient vibration analysis of an unstable mountain slope summary a field experiment with small aperture seismic arrays was performed on the unstable rock slope above the village of randa in the southern swiss alps the aim of this experiment was to constrain the seismic response of a potential future rockslide using ambient vibration recordings weak seismic events were identified on the recordings and site to reference spectral ratios were calculated using a reference site located on the stable part of the slope spectral ratios of up to 30 were observed at sites located within the unstable portion of the slope a strong variation of spectral ratios with azimuth indicates a directional site effect neither amplification nor directionality were observed at sites located in the stable part of the slope furthermore time frequency polarization analysis of the ambient noise was performed to provide robust estimates of frequency dependent directions of the maximum polarization it was found that the unstable part of the slope vibrates within a narrow range of directions 130 10 for the frequency range centred around 5 hz the polarization directions estimated from ambient seismic vibrations are in good agreement with the deformation directions obtained by geodetic and in situ measurements no directionality of ambient vibrations was observed at sites within the stable part of the slope

geochemistry of metalliferous hydrothermal deposits in the aeolian arc tyrrhenian sea abstract in shallow water areas of the submerged volcanic complex around the island of panarea aeolian archipelago hydrothermal precipitation of both low temperature fe oxyhydroxide rich red muds and crusts and high temperature sediment hosted massive sulfides was discovered during an integrated high resolution survey iron rich crusts were also found on the bathymetric high of secca del capo north of salina island the exhalative iron rich sediments occur in small closed depressions or in proximity to faults and scarps at water depths ranging from 55 to 285 m the principal chemical characteristics of these deposits are high but variable fe content ranging from 12 2 to 45 and low contents of the transition elements mn cu zn ni and co the low contents of cu ni and co suggest a hydrothermal origin the fe oxyhydroxide deposits are enriched in light rare earth element ree 35 110 chondrite compared to heavy ree 10 25 chondrite their ree patterns are similar to those of associated calc alkaline volcanics negative slope of light ree and a horizontal distribution of the heavy ones this contrasts with the pattern for iron and manganese oxides of hydrogenous origin which have tilted trends of heavy ree paralleling that of seawater the mineralogy of the polymetallic sulfide deposits consists of galena sphalerite pyrite and barite in the form of silt sand grains and decimeter sized fragments disseminated in clay 30 cm below the seabed at a waterdepth of 80 m the chemistry of the aeolian iron rich low temperature deposits and of the high temperature ba rich pb and zn sulfides suggests that they are genetically analogous to respectively the kuroko type iron formation tetsusekiei and the black ore exposed in the miocene hokuroku district of japan

effects of geometry on the seismic wavefield of alpine glaciers passive seismology allows measurement of the structure of glaciers and ice sheets however most techniques used so far in this context are based on horizontally homogeneous media where parameters vary only with depth 1 d approximations which are appropriate only for a subset of glaciers here we analyze seismic noise records from three different types of glaciers plateau valley and avalanching glacier to characterize the influence of the glacier geometry on the seismic wavefield using horizontal to vertical spectral ratios polarization analysis and modal analysis we show that the plateau glacier and the valley glacier can be seen as 1 d whereas the relatively small avalanching glacier shows 3 d effects due to its bed topography and the deep crevasses in principle the techniques proposed here might allow monitoring such crevasses and their depth and thus to constrain a key parameter of avalanching and calving glacier fronts

geology fluid inclusions and isotope geochemistry of the herenping gold deposit in the southern margin of the yangtze craton china a sediment hosted reduced intrusion related gold deposit abstract the herenping gold deposit is a typical gold deposit in the xuefengshan arcuate tectonic zone in the southern margin of the yangtze craton and the major feature of the gold mineralisation in the zone is the varying degrees of tungsten and antimony mineralisation in the ore deposits the herenping gold deposit occurs in the reddish purple sandy slate in the middle section of the madiyi formation of the neoproterozic banxi group and is controlled by the fault fold zone associated with the liulincha anticlinorium and f8 fault zone however its sources of mineralisation and relationships between hydrothermal fluids and magmatic rocks are unclear which similar to those of many gold deposits in metasedimentary terranes in the worldwide the mineralisation can be divided into four stages an albite quartz stage i an albite quartz pyrite gold stage ii a quartz gold polymetallic sulphide stage iii and a quartz carbonate stage iv the gold mineralisation occurred in albite quartz veins in stage ii and in sulphide rich quartz veins in stage iii in the deposit a study of the fluid inclusions reveals that the homogenisation temperature and salinity were slightly higher in stage ii th 186 348 c w 5 2 17 43 wt nacl equiv than in stage iii th 145 249 c w 2 9 15 57 wt nacl equiv indicating that the temperature and salinity of the ore forming fluid are gradually decreasing the h o d 62 3 to 53 0 18o 4 2 11 8 isotope characteristics reveals that the ore forming fluid is a magmatic hydrothermal source the sulphur 34s 4 8 2 0 isotope characteristics and the alteration mineral assemblage sericite chlorite pyrite indicates that the ore forming fluids was reduced the lead 206pb 204pb 17 419 17 436 207pb 204pb 15 519 15 535 and 208pb 204pb 37 86 37 90 isotope characteristics reflect the ore forming materials were likely derived from a deep magmatic source in addition the geochemical characteristics of albitite veins show that they are silicon rich 64 02 66 26 wt and significantly reduced notably the herenping gold deposit is located in the western portion of the tungsten tin metallogenic provinces in south china is host in epimetamorphic detrital rocks and was formed at least two stages of mineralisation typical gold bearing albite quartz veins developed during the primary stage these characteristics are consistent with those of reduced intrusion related deposits such as the muruntau kumtor and telfer deposits thus the herenping gold deposit may be a sediment hosted intrusion related gold deposit based on the phase transition pattern from sulphide rich quartz veins to albite quartz veins to albitite veins with increasing depth in the deposit we propose that reduced intrusions deep in the herenping gold deposit could be discovered in the future which implies the possible existence of a reduced intrusion related gold system in the xuefengshan arcuate tectonic zone

seismic strain release along the middle america trench mexico we measure the seismic moment of five great ms 7 8 earthquakes from 1928 to 1942 along the mexican portion of the middle american trench directly from recorded seismograms and obtain considerably lower moment values than had previously been estimated from ms such direct moment determinations are inherently more reliable as the average seismic slip rate along this portion of the arc appears to be essentially constant these measurements of the past seismic moment are used to estimate that the current end of 1980 moment deficiency is 46 1027 dyne cm or an average slip of 97 cm along the arc although this is much lower than past estimates at the current rate of increase 1 6 1027 dyne cm yr 3 4 cm yr of seismic displacement the moment deficiency by 1985 will be the equivalent of five magnitude 8 earthquakes and by 1990 six such events the slip along this portion of the middle america trench arc appears to fit shimazaki and nakata s slip predictable model in which the size but not the time of occurrence of future large events may be estimated

a combined inversion of rayleigh wave dispersion and 2 d resonance frequencies summary shear wave velocities of the sediment fill of a deep alpine valley are estimated from ambient noise recorded on linear and circular arrays we propose a combined inversion of 2 d reso nance frequencies identified from site to reference spectral ratios and rayleigh wave dispersion curves obtained from frequency wavenumber analysis the method is tested on synthetic noise data and on noise recorded at three sites in the rhone valley in southern switzerland previous studies have shown that 2 d resonance dominates the ambient vibration wavefield at low fre quencies at the investigated sites inversion techniques which assume that the noise wavefield consists mainly of horizontally propagating surface waves will therefore fail to resolve shear wave velocities at depths below around 500 m we show that standard techniques lead to an overestimation of shear wave velocities at depth when applied to synthetic and observed am bient noise the combined inversion is able to resolve the shear wave velocities in the initial velocity model when applied to synthetic noise records application of the method to observed ambient noise improves resolution at depth and yields realistic shear wave velocities for the lower part of the sediment fill

rare earth element geochemistry of clastic and chemical metasedimentary rocks associated with hydrothermal sulphide mineralisation in the olary block south australia abstract analysis of a variety of rock types from the south australian portion of the lower to middle proterozoic willyama inliers by icp ms demonstrate that primary rare earth element ree distributions remained essentially unchanged despite multiphase deformation and amphibolite grade metamorphism variable trends of preferential ree mobilisation are observed only where large amounts of fluid caused the rock to undergo strong retrogression and or hydrothermal alteration except for these conditions ree can be considered immobile and their distribution is generally independent of mineralogy thus providing a powerful tool for the characterisation of provenance of protoliths in a high grade metamorphic terrain ree signatures and other geochemical constraints of some volcanogenic sediments for example point to an andesitic parentage suggesting bimodal and gradually changing volcanism occurring in a developing intracontinental rift zone ree distributions in metasediments associated with sulphide mineralisation reflect both physico chemical characteristics of the ore bearing fluids and rock compositions comparison of their ree profiles allows discrimination between a strata bound redox controlled deposits b exhalative mineralisation and c epigenetic vein type mineralisation ree distributions in the analysed rocks are in agreement with other lines of textural and geochemical evidence for that limited syn tectonic remobilisation low fluid rock ratios unchanged primary ree signatures but widespread late stage mobilisation of sulphides high fluid rock ratios selective mobilisation of ree occurred in the olary block ree signatures of exhalative precipitates associated with sulphide mineralisation do not show a systematic stratigraphic variation but are indicative of fluctuating f o 2 conditions over short distances and display only moderately positive eu anomalies this contrasts with findings for the adjacent broken hill block and highlights the dissimilarities of ore formation processes that were active in the olary and the broken hill block as well as the depositional differences between the two blocks

the seismic response of two dimensional sedimentary deposits with large vertical velocity gradients an extension of the aki larner technique to vertically inhomogeneous media is presented so that vertical velocity gradients may be taken into account in two dimensional models only sh waves are considered here but the theory is valid for p and sv waves as well this method is applied to investigate the seismic response of two dimensional sedimentary deposits with large velocity gradients three different cases are considered a shallow high contrast valley a deep high contrast valley and a deep low contrast valley in each case a comparison is performed with the results of a two dimensional model taking into account only homogeneous sediments and a one dimensional model taking into account the vertical inhomogeneity of sediments the presence of a large velocity gradient does not change a lot the qualitative behavior of a two dimensional deposit local surface waves and or two dimensional resonance patterns are observed as in the case of homogeneous sediments nevertheless the surface waves are much more dispersive with lower phase and group velocities and larger amplitudes only very deep valleys give rise to the development of two dimensional resonance on the other hand the amplifications obtained in such deposits may reach much larger values than those predicted with either two dimensional homogeneous models or one dimensional inhomogeneous models since these results have been obtained for realistic values of valley geometrical and mechanical considerations they should find some application in earthquake engineering or seismic microzonation studies

geochemical implications of rare earth element patterns in hydrothermal fluids from mid ocean ridges abstract rare earth element data are reported for vent fluids collected from eight deep sea hydrothermal areas including samples from sediment hosted and bare rock hydrothermal systems the morb normalized ree patterns from these diverse settings are remarkably similar to each other but distinctly different than seawater or basalt being lree enriched and possessing a strikingly positive eu anomaly the ree concentrations making up these patterns vary widely however both on a spatial and temporal basis when plotted against ionic radii these fluid trends are remarkably linear and show the same fractionation patterns exhibited by plagioclase during magma segregation this analysis suggests that the partitioning of the ree between fluid and rock during high temperature hydrothermal alteration of morb is dominated by crystochemical exchange during dissolution and recrystallization reactions at the exposed surfaces of plagioclase phenocrysts a comparison of ree ionic radii in eight coordination indicate that the partitioning of 3ree and 2eu are dominated by chemical substitution for ca 2 and sr 2 respectively these considerations predict that the total 3ree content of vent fluid varies in a systematic way during the transition from an rich morb plagioclase to ab rich hydrothermal plagioclase and that these parameters can be used as indicators of the average extent of alteration inside active hydrothermal systems

provenance and tectonic setting of the proterozoic turbidites in hunan south china geochemical evidence the geochemical composition of the middle upper proterozoic turbidites in hunan south china is related to provenance and tectonic setting of the sedimentary basin the turbidites are characterized by moderate sio 2 contents al 2 o 3 sio 2 typically 0 1 0 3 and moderate k 2 o na 2 o ratios generally 0 1 0 3 but relatively high fe 2 o 3 mgo contents 5 10 wt and unusually low contents of cao typically 1 wt abundances of ferromagnesian trace elements and incompatible elements are moderate the ree patterns are uniform and similar to the upper continental crust and typical post archean shales with lree enrichment flat hree and significant negative eu anomalies in general the slates show higher contents of fe 2 o 3 mgo and ferromagnesian trace elements and lower ratios of la sc and th sc than the associated graywackes suggesting that more mafic materials were incorporated into the clay size fraction compared to the upper proterozoic banxi group the middle proterozoic lengjiaxi group has higher concentrations for most ferromagnesian trace elements and lower la sc ratios implying more mafic components in the provenance of the latter the relationship among alkali and alkaline earth elements the chemical index of alteration cia and the th u ratios indicate that the source area was affected by a moderate weathering history the main source was old continental crust the yangtze craton dominated by felsic rocks of magmatic origin with a variable admixture of mafic components from continental island arcs e g the fangjingshan dayong and the sibao yiyang island arc chains the flysch deposition took place in a back arc basin rather than a failed intracontinental rift as proposed by some workers we suggest that suturing between the yangtze and cathaysia blocks did not occur until late proterozoic time and that the final assembly of the supercontinent rodinia in south china was probably marked by the jingning orogeny at 0 8 ga

geochemical modeling of the zoned footwall alteration pipe hellyer volcanic hosted massive sulfide deposit western tasmania australia the mineralogy of hydrothermal alteration assemblages siliceous core chlorite zone sericite zone in the footwall pipe of the hellyer volcanic hosted massive sulfide vhms deposit is controlled mainly by the temperature ph and redox state of the hydrothermal fluids based on the results of our numerical modeling the zoned alteration system could have formed by a combination of water rock interaction and cooling with a siliceous core predicted to form at the center of the conduit passing outward to a chlorite dominated zone a sericite rich zone and finally grading out to unaltered andesite these mineralogical changes relate to a gradual evolution of fluid chemistry water rock ratio ph and temperature from the core to the margin of the system initial temperatures were probably close to 350 degrees c and the hydrothermal fluids were reduced h2s dominated at low temperatures 200 degrees c a peripheral alteration zone consisting mostly of k feldspar chlorite sericite and hematite is predicted to form this low temperature zone has not been recognized at hellyer but elevated k2o contents and local k feldspar development have been noted at other vhms deposits suggesting that this zone might form at low temperatures and low water rock ratios in the footwall of vhms deposits if the existence of barren outer k feldspar alteration zones is confirmed the findings could have important implications for exploration specifically with regards to distinguishing ore related alteration zones from barren alteration systems

a natural seismic isolating system the buried mangrove effects the belleplaine test site located in the island of guadeloupe french lesser antilles includes a three accelerometer vertical array designed for liquefac tion studies the seismic response of the soil column at the test site is computed using three methods the spectral ratio method using the vertical array data a numerical method using the geotechnical properties of the soil column and an operative fre quency domain decomposition fdd modal analysis method the belleplaine test site is characterized by a mangrove layer overlaid by a stiff sandy deposit this con figuration is widely found at the border coast of the caribbean region which is exposed to high seismic hazard we show that the buried mangrove layer plays the role of an isolation system equivalent to those usually employed in earthquake engineering aimed at reducing the seismic shear forces by reducing the internal stress within the structure in our case the flexibility of the mangrove layer reduces the distortion and the stress in the sandy upper layer and consequently reduces the potential of liquefaction of the site

array estimators and the use of microseisms for reconnaissance of sedimentary basins a natural field seismic technique is possible to attain by observing microseisms with a suitably designed array and by digitally processing the data to obtain estimates of the phase velocities of rayleigh waves wavelengths of interest in detecting depth to the basement of sedimentary basins are in the range 2 to 20 km and correspond to wave periods from 1 to 7 s an array of five or seven seismometers deployed as an expanding cross configuration simplifies field procedures and is adequate for phase velocity measurements of rayleigh waves in the required wavelength range provided high resolution frequency wavenumber spectral analysis is used this analysis can be implemented on a minicomputer in the field results obtained from observation in a sedimentary basin of known structure show predominantly fundamental mode rayleigh wave propagation the scatter of velocity estimates is small enough to allow inversion by curve matching and depth to the basement can be computed to an accuracy of 30 percent w

strong ground motion from the michoacan mexico earthquake the network of strong motion accelerographs in mexico includes instruments that were installed under an international cooperative research program in sites selected for the high potenial of a large earthquake the 19 september 1985 earthquake magnitude 8 1 occurred in a seismic gap where an earthquake was expected as a result there is an excellent descripton of the ground motions that caused the disaster

geology fluid inclusions and geochemistry of the zhazixi sb w deposit hunan south china abstract the zhazixi sb w deposit in the xuefeng uplift south china exhibits a unique metal association of w and sb where the w orebodies are hosted by interlayer fractures and the sb orebodies are contained within nw trending faults this study proposes that the w and sb mineralization took place in two separate periods the mineral paragenesis of the w mineralization reveals a mass of quartz scheelite and minor calcite the mineral assemblage of the sb mineralization developed after w mineralization and consists of predominantly quartz and stibnite and small amounts of native sb berthierite chalcostibnite pyrite and chalcopyrite fluid inclusions in quartz and coexisting scheelite are dominated by two phase liquid rich aqueous inclusions at room temperature microthermometric studies suggest that ore forming fluids for w mineralization are characterized by moderate temperatures 170 270 c low salinity 3 7 wt nacl equiv low density 0 75 0 95 g cm 3 and moderate to high pressure 57 2 99 7 mpa and these fluids experienced a cooling and dilution evolution during w mineralization ore forming fluids for sb mineralization are epithermal types with low temperatures 150 230 c low salinity 4 6 wt nacl equiv moderate density 0 82 0 94 g cm 3 and high pressure 42 2 122 5 mpa and these fluids display an evident decline in homogenization temperature during sb mineralization laser raman analyses of the vapor phase indicate that the ore forming fluids for both w and sb mineralization contain a small amount of co 2 the ore forming fluids for sb mineralization are identified as predominantly originating from the continental crust as suggested by the low 3 he values 0 009 10 12 cc stp g and 3 he 4 he ratios 0 002 0 056 ra as well as high 36 ar values 1 93 10 9 cc stp g and 40 ar 36 ar ratios 909 5 2279 7 the source of s is identified to be the neoproterozoic wuqiangxi formation as traced by the 34 s v cdt values of stibnite 3 1 9 4 the 208 pb 204 pb 37 643 40 222 207 pb 204 pb 15 456 15 681 and 206 pb 204 pb 17 093 20 042 ratios suggest a mixture of lower crustal and supracrustal pb sources it is thus concluded that the ore genesis of the zhazixi sb w deposit is related to the intracontinental orogeny during the early mesozoic fluid mixing is considered to be the critical mechanism involved in w mineralization whereas a fluid cooling process is responsible for sb mineralization furthermore the absence of au is attributed to the low a s content in sb mineralizing fluids

geology of the hope brook mine newfoundland canada a preserved late proterozoic high sulfidation epithermal gold deposit and its implications for exploration the hope brook gold mine is a high sulfidation epithermal gold deposit hosted by late proterozoic rocks of the northern appalachian avalon zone it is located within the whittle hill sandstone which is intruded by a late proterozoic quartz feldspar porphyry sill dike complex of the roti intrusive suite the deposit 45 t au is enclosed within a zone of hydrothermal alteration 3 km long and up to 400 m wide this zone of alteration is characterized by extensive advanced argillic alteration with pyrophyllite kaolinite andalusite and alunite which is developed mostly in the structural hanging wall of the ore zone and two main stages of massive silicic alteration the first a buff colored stage of massive silicic alteration extends for or 3 km laterally away from the deposit it constitutes a barren to weakly auriferous unit and most likely results from the pervasive acid leaching of the original host s the second stage of gray massive silicic alteration is spatially coincident with gold mineralization and is characterized by vuggy quartz the mineralization consists of several percent of pyrite and lesser amounts of chalcopyrite and bornite and some tennantite with local traces of enargite in addition to au and cu there is a very limited amount of other metals in the deposit although it has anomalously high amounts of sb bi pb and as the ages of altered pre and late ore quartz feldspar porphyry and of an unaltered postore intermediate dike cutting altered rocks bracket the age of mineralization alteration between 578 and 574 ma this temporally and genetically links mineralization alteration and roti intrusive suite plutonism despite a strong spatial relationship between a major fault zone cinq cerf fault zone and gold mineralization the hope brook deposit bears no genetic relationship to major ductile deformation the deposit was formed approximately 150 m y prior to the development of this fault zone the existence of hope brook along with a few mesozoic pueblo viejo paleozoic temora neoproterozoic brewer and paleoproterozoic deposits enaasen highlights the potential for discovery of such au cu intrusion related deposits in older terranes despite their emplacement at high levels in the crust the potential for preservation of such high sulfidation deposits in older terranes may be high if tilting and or burial took place early in the geologic evolution of the host volcano plutonic arc although the nature and distribution of the initial buff silicic stage of alteration are critical indications of a large scale hydrothermal system the ore at hope brook is only localized in rocks displaying the gray colored second silicic stage of alteration consequently the recognition of the two stages of massive silicic alteration was critical in understanding the genesis of the hope brook deposit and constitutes an important exploration tool in discriminating between potentially mineralized and barren zones

identifying 2d resonance in microtremor wave fields to predict local site effects during earthquakes we must know the geometrical and mechanical properties of local sedimentary structures and their resonance behavior we present a concept to identify resonance modes for 2d structures this is done for synthetic as well as measured microtremor wave fields the microtremor data were investigated by using the reference station and horizontal to vertical h v methods analyzing the synthetic microtremor data in profiles across 2d structures the reference station method rsm turned out to be much more suitable for the detection of 2d resonances than the h v method we therefore focused on rsm when analyzing the measurement data from two test sites in switzerland the st jakob tullingen trough near basel in the north and a site in the rhone valley near the village vetroz in the south the results of these two test sites led to different conclusions whereas the spectral peaks in data of the st jakob tullingen trough were not well developed and could only tentatively be interpreted those from the rhone valley clearly exhibited 2d resonance effects the sh 00 and the sv fundamental mode could be successfully identified at 0 32 0 03 and 0 35 0 03 hz respectively

complex polarization analysis of particle motion knowledge of particle motion polarization aids in identifying phases on three component seismograms the scheme of montalbetti and kanasewich 1970 is extended to analytic three component seismograms where the imaginary part of the signal is the hilbert transform of the real part this scheme has only one free parameter the length of the time window over which the polarization parameters are estimated so it can be applied in a routine way to three component data the azimuth and dip of the direction of maximum polarization and the degree of elliptical polarization as a function of time for the seismograms are obtained polarization analysis of strong motion data from the 1971 san fernando earthquake aids in the discrimination between wave types which is important for the understanding of the complicated earthquake induced shaking observed in basins most arrivals are incident on the receivers in the direction of the back azimuth to the epicenter which suggests that despite the complicated motions two dimensional finite difference methods are sufficient to understand the effect on seismic waves of the los angeles and san fernando basins vidale and helmberger 1986b

seismic soil effect in an embanked deep alpine valley a numerical investigation of two dimensional resonance this paper presents a 2d numerical study of the seismic response of a deep embanked sediment filled valley rhone valley switzerland to incident sh and sv waves the 2d modeling is performed with a program developed by pedersen et al 1995 based on the ibem technique this valley exhibits variation in subsurface geometry therefore three representative cross sections are considered in order to investigate the influence of symmetric and asymmetric morphology on the seismic response comparison between 1d and 2d modeling shows that both resonant frequencies and amplification values differ to a large extent looking in the central part of the valley the 2d predicted amplification value is about twice higher than in the 1d case whereas the fundamental resonant frequency value is higher by a factor of 1 7 moreover 2d modeling results show that this valley presents a twodimensional resonance due to its shape ratio and shear wave velocity contrast the main characteristic is the unchanged position of the fundamental resonance frequency regardless of the surface site along the cross section under consideration and the incidence angle however the asymmetric cross section induces a specific spectral amplification pattern at the surface site and along the cross section which is also a function of the direction of incidence of the seismic wave such results show the importance of considering the morphology of a deep and narrow valley when investigating the local seismic response

rare earth element behaviour associated with strata bound scheelite mineralisation broken hill australia abstract strata bound scheelite mineralisation occurs within calc silicates of a metamorphosed proterozoic volcano sedimentary sequence and is spatially related to lenticular bodies of basaltic volcanics tourmalinites and quartz gahnite rocks a pre metamorphic alteration halo has been detected within the enclosing basalts in the form of elevated fe as and eu contents which were formed by reducing and or high temperature hydrothermal fluids changing eh conditions during alteration gave rise to ce enriched basalts and sediments proximal and distal to the mineralisation the calc silicate horizon represents a hydrothermally altered and metamorphosed carbonate rich sediment as indicated by calc silicate pods containing primary sedimentary ree patterns the calc silicate horizon displays a lateral zonation from an unmineralised hydrothermally altered lree depleted core to mineralised lree depleted hree and eu enriched margins the wide range of ree patterns and the distinctive variation in ree spectra from the centre to the margins is due to the progressive dissolution of carbonates and the deposition of scheelite with decreasing temperature from the w fe as eu enriched ore fluids

genesis of the banxi sb deposit south china constraints from wall rock geochemistry fluid inclusion microthermometry rb sr geochronology and h o s isotopes abstract the banxi sb deposit is located in the world class central western hunan sb belt in south china with quartz vein type sb only mineralization hosted by neoproterozoic epimetamorphic clastic sedimentary rocks in this contribution microthermometric rb sr geochronological and h o isotopic analyses on fluid inclusions trapped in quartz s isotopic studies on stibnite and major trace elemental measurements on fluid altered and unaltered wall rocks are presented to constrain the genesis of the deposit the fluid inclusions are characterized by low homogenization temperature 170 260 c and low salinity 3 7 wt nacl equiv with a low fluid density of 0 72 0 93 g cm3 and a ph of 5 59 the low dw fluid 2h 140 to 107 whereas positive 18ov smow 15 9 17 2 and 18ow fluid 18o 5 9 8 4 values in quartz indicate that the mineralizing fluid was generated from the low grade metamorphic basement rocks and received a certain input of meteoric water the rb sr isotopic compositions of quartz samples yielded an isochron age of 196 4 ma 1 mswd 0 70 for quartz stibnite ores a highly radiogenic 87sr 86sr value 0 72663 0 74002 initial 87sr 86sr 0 72640 indicates that ore forming materials are derived mainly from basement rocks and a direct material contribution from local granitic rocks can be ruled out the 34sv cdt values of stibnite range narrowly from 4 81 to 6 72 and are in the 34sv cdt range of the metamorphic rocks indicating that the sulfur was sourced from the basement rocks by sulfate reduction compositional differences between fluid altered decolorized and unaltered wall rocks are obvious the migrated sio2 so3 lree hf nb zr ta th u mo sn w into altered wall rocks suggests a deep basement metamorphic rocks derived si rich alkaline brine for the fluid rock interaction while the leached fe2o3 mgo mno tio2 ba cs rb as co v ni sb sc cu pb and zn from the altered rocks imply a material contribution of banxi group wall rocks during the sb mineralization process consequently we conclude that the quartz stibnite stage of the banxi sb deposit was formed during the late triassic orogeny in the xuefeng mountain region heated by granitic magmatism sb and s were leached from the basement rocks forming an initial si rich and alkaline ore bearing fluid precipitation of stibnite from the fluid resulted from interacting with wall rocks and mixing of meteoric water coupled by releasing of stress decreasing of temperature and lowering of the ph at higher crustal levels

rare earth element systematics in hydrothermal fluids abstract rare earth element concentrations have been measured in hydrothermal solutions from geothermal fields in italy dominica valles caldera salton sea and the mid atlantic ridge the measured abundances show that hydrothermal activity is not expected to affect the ree balance of either continental or oceanic rocks the ree enrichment of the solutions increases when the ph decreases high temperature solutions 230 c percolating through different rock types may show similar ree patterns

origin of the eskay creek precious metal rich volcanogenic massive sulfide deposit fluid inclusion and stable isotope evidence the eskay creek deposit is an unusual polymetallic au ag rich volcanogenic sulfide sulfosalt deposit located in the iskut river area of northwestern british columbia canada economic concentrations of precious and base metals are contained in the 21 zone which is divided into a number of subzones as of december 31 1998 total production and proven probable reserves are 1 9 million tons mt at 60 2 g t au 2 652 g t ag 3 2 percent pb 5 2 percent zn and 0 7 percent cu the 21b zone which contains the bulk of the reserves began production in 1995 the mineralization occurs mainly as well preserved stratiform clastic beds of sulfide sulfosalt debris and also as discordant footwall quartz sulfide veins the hydrothermal system that formed the eskay deposit was low temperature

rare earth element distribution in exhalites associated with broken hill type mineralisation at the pinnacles deposit new south wales australia abstract rare earth element ree concentrations in exhalites and pelites associated with strata bound base metal broken hill type mineralisation have been measured for the early proterozoic pinnacles deposit in western new south wales garnetites garnet rich rocks and sulphide rich garnet gahnite bearing rocks exhibit a wide variety of ree concentrations particularly lree and eu which cannot be related entirely to changes in mineralogy but show some correlation with stratigraphic position relative to the main orebody exhalites lying in the footwall to the mineralised rocks have negative eu anomalies and steep lree enriched patterns whereas exhalites in the hanging wall to the ores and silicate rich rocks from within the ore lenses have zero or positive eu anomalies and less lree enriched patterns hree have more consistent values throughout the deposit but in places are strongly depleted non mineralised pelites are slightly enriched in the ree relative to shale composite values and have negative eu anomalies it is argued in this paper that because the variations in data can be related to the stratigraphic location of samples relative to the orebodies that the observed ree distributions are due to fluctuations in ree concentrations in the primary exhalative fluids rather than differential mobilisation of ree during a second post depositional episode of hydrothermal alteration or mobilisation of the ree during prograde granulite facies metamorphism or retrograde amphibolite facies metamorphism which has affected the area the lack of association between metamorphic mineral assemblages and ree distribution and the absence of any homogenisation of the ree concentrations suggest that the data reflect the primary exhalative fluid composition and that the variations in ree data reflect changes in palaeoenvironmental conditions such as f o 2 and temperature a corollary to this conclusion is that there was minimal mobilisation of the ree during subsequent metamorphism

fluid inclusion h o s isotope and rare earth element constraints on the mineralization of the dong an sb deposit south china abstract systematic geochemical study on the cambrian strata hosted dong an sb deposit in the central hunan sb belt would provide key information on the origin of the low temperature mineralization in south china in this study microthermometric h o isotopic and fluid composition analyses on ore bearing quartz s isotopic analyses on sulfides and rare earth element ree analyses on wall rocks and monominerals stibnite pyrite and quartz in ores were conducted to constrain the genesis of the dong an sb deposit two major stages of mineralization were identified in the dong an deposit 1 an early pyrite stibnite quartz stage mineralization with intense wall rock alteration occurring at depth of the deposit and 2 a late quartz stibnite stage mineralization occurring at shallow depths microthermometric analyses reveal a low temperature 150 to 230 c low salinity 4 5 7 0 wt nacl equiv low density 0 88 0 96 g cm3 low pressure 4 5 mpa and weakly acid ph 5 74 fluid for the sb mineralization compositional analyses for fluid inclusions show that the main ion compositions are na k mg2 ca2 f cl and so42 while the gas compositions are dominated by h2o and co2 this suggests that the ore forming fluids were enriched in alkali metals sulfur and halogen the h o isotopic compositions 18oh2o 2 52 to 7 13 2hh2o 88 6 to 58 3 of fluid inclusions in quartz suggest a mixture of magmatic water metamorphic rocks derived brine and meteoric water the 34s values of stibnite 1 32 to 2 86 and pyrite 17 4 to 23 6 are very different suggesting multi sulfur sources involving buried magmatic rocks ore bearing meta sedimentary rocks and deep basement rocks the decreasing of ree contents from early to late mineralization stages reflects a decrease of temperature reduction of fluid rock interaction and input of meteoric water along with the stibnite precipitation we propose that precambrian strata that underwent regional metamorphism during early paleozoic acted as a sb source bed whereas strong tectono magmatism in the early mesozoic provided thermal driving force for the sb mineralization occurring under a tensile stress in secondary faults at the shallow crust this study highlights the use of multi geochemical methods to constrain the genesis of large scale sb mineralization in south china

australian volcanic hosted massive sulfide deposits features styles and genetic models the cambro ordovician period has yielded the major development of volcanic hosted massive sulfide vhms deposits in australia resulting in about 12 million metric tons of contained metal copper lead and zinc concentrated in the mount read volcanics tasmania and the mount windsor volcanics queensland the archean 4 million metric tons of metal and the silurian 3 5 million metric tons of metal constitute the next important episodes while the devonian and permian have produced isolated deposits the deposits range from cu type to zn cu type to zn pb cu type the zn cu type deposits are restricted to the archean and silurian whereas the cu type and zn pb cu type occur sporadically throughout the time span from early archean to permian in general terms the major vhms bearing districts are calc alkaline in character and display a thick basal pile of rhyolitic volcanics 1 3 km thick including lavas epiclastics and subvolcanic intrusions which is overlain by a polymodal sequence containing various proportions of rhyolite dacite andesite basalt and sediments the major deposits are commonly located at the top contact of the rhyolite pile or within the lower part of the overlying polymodal sequence there is a wide range in variability of styles of australian vhms deposits including mounds pipes sheets layered deposits stacked deposits stockwork and disseminated deposits distal reworked deposits and cyclic layered deposits although these various styles show a range of features there is a consistent theme across the spectrum of metal zonation alteration mineralogy alteration chemistry sulfur isotopes macrotextures microtextures and host volcanic relationships which strongly suggests that they all belong to the one genetic group of ore deposit the classic mound style deposits such as hellyer have a series of key features subsets of which are represented in the other deposit styles the mound deposits are considered to form from deposition of metal sulfides on the sea floor immediately around the hydrothermal vent growth of the mound occurs by upward replacement of sulfide assemblages stable at higher fluid temperatures leading to zone refining and lead zinc silver gold enrichment in the outer and upper parts of the mound departure from the classic mound style of deposit is related principally to three key factors the chemistry of the ore fluid salinity temperature f02 and ah2s the nature permeability and chemistry of the volcanic pile and the sea hoor environment sea hoor topography and seawater depth these factors control the aspect ratio of the deposit the extent of stringer zone development the degree of subsea floor replacement mineralization the nature and spatial development of footwall alteration and the development and style of related distal mineralization sulfur isotope studies of australian vhms deposits indicate that reduced seawater sulfate is a major source of sulfur in the deposit whereas lead and strontium isotope results are compatible with the metals being derived by seawater convection and leaching from the volcanic pile and basement rocks this conclusion is supported by the application of various leaching models which demonstrate the availability of an adequate source of both base and precious metals in the footwall volcanic sequences the input of metals directly from volcanic magma chambers is not precluded by the available data and one likely scenario involves the contribution of gold and copper from a magmatic vapor plume rising to mix with convective seawater fluids which contribute lead zinc silver and gold leached from the footwall volcanics and basement rocks the relative importance of the magmatic input compared with the seawater convective input may help to explain the spectrum of deposit styles arid their spatial relationship to volcanic centers or adjacent sedimentary basins

sediment in the black smoker area of the east pacific rise 18 5 s abstract a sediment profile perpendicular to the east pacific rise epr was investigated in an area in which massive sulfides have been observed along the axis of the epr a holocene to late pleistocene age is concluded for all of the up to 3 m long cores leading to sedimentation rates of 0 3 2 6 cm 1000 a the sediments are composed of hydrothermal precipitate calcareous tests and in traces hyaloclastic material the proportion of carbonate increases with increasing distance from the spreading center the hyaloclastic material is more or less weathered and is concentrated near the spreading center the hydrothermal component is composed mainly of iron and manganese hydroxides the proportion of hydrothermal matter in the sediment is higher near the axis of the epr also near the axis the elements b p cr and v are enriched in the hydrothermal component whereas mn zn cu fe and as are depleted the core profiles show a fluctuation in the proportion of hydrothermal material periods of higher hydrothermal input correlate with periods of the best calcite preservation diagenetic alteration of the sediment increases with increasing distance from the spreading center i e with decreasing sedimentation rate mo zr co ni rb th y ba la and ree are enriched in the sediment by diagenetic processes

rare earth element geochemistry of hydrothermal deposits from the active tag mound 26 n mid atlantic ridge the rare earth element ree geochemistry of various phases from the active tag hydrothermal mound has been examined and related to their mineralogy and fluid chemistry the mound deposits range from black and white smoker chimneys massive anhydrite sulphide mixtures oxides and ochres all phases except black smoker chimney anhydrite demonstrate a positive eu anomaly when normalised to chondrite ree values ree substitution into sulphide and sulphate phases appears to be strongly influenced by crystallographic control for all ree other than eu precipitation of anhydrite within the tag mound is the major mechanism for removal of ree during mound circulation and 0 15 0 35 g anhydrite is inferred to precipitate from every kg of fluid venting from the white smoker chimneys oxides from the mound fall into three different categories with distinct ree patterns oxide rims on sulphides atacamite bearing oxides and silica rich fe oxides and ochres the oxide rim phases contain sulphide and seawater derived rees whereas the atacamite bearing oxides and the ochreous material exhibit no seawater signature which suggests precipitation from or alteration by a modified hydrothermal fluid

assessment of site effects in alpine regions through systematic site characterization of seismic stations abstract in the framework of the renewal project of the swiss strong motion network ssmnet a procedure for site characterization has been established the aim of the procedure was to systematically derive realistic 1d velocity profiles at each station it is mainly based on the analysis of surface waves particularly from passive experiments and includes cross checks of the derived amplification functions with those obtained through spectral modeling of recorded earthquakes the systematic use of three component surface wave analysis allowing the derivation of both rayleigh and love dispersion curves also contributes to the improvement of the quality of the retrieved profiles the procedure is applied to the 30 ssmnet stations installed on various site types within the project covering different aspects of seismic risk the characterization of these 30 sites gives an overview of the variety of possible effects of surface geology on ground motion in the alpine area such effects ranged from deamplification at hard rock sites to amplification up to a factor of 15 in lacustrine sediments with respect to the swiss reference rock velocity model the derived velocity profiles are shown to reproduce observed amplification functions from empirical spectral modeling although many sites are found to exhibit 1d behavior the procedure allows the detection and qualification of 2d and 3d effects the sites are therefore classified with respect to the occurrence of 2d 3d resonance and edge generated surface waves in addition to the large and deeply incised alpine valleys of the rhone the rhine and the aar smaller structures such as local alpine valleys and alluvial fans are shown to exhibit 2d 3d behavior

geochemical characteristics of the triassic tethys turbidites in northwestern sichuan china implications for provenance and interpretation of the tectonic setting the triassic tethys graywacke slate turbidites in the northwestern sichuan china have been analysed for major and trace elements and petrographically studied compared to phanerozoic turbidites the turbidites in this study are quartz intermediate average 55 in composition and are characterized geochemically by their moderate fe2o 3 mgo 9 28 2 84 tio2 0 72 0 17 contents and al2o3 sio2 0 25 0 10 ratios moderate abundances of ferromagnesian trace elements co 15 8 ppm cr 113 72 ppm ni 14 9 ppm sc 12 4 ppm etc and moderate contents of incompatible elements such as th 11 3 ppm u 3 0 7 ppm zr 170 64 ppm hf 4 1 ppm and total rees 159 33 ppm in general the slates show systematically higher fe2o 3 mgo sc co and eueu but lower sollasc and thsc than the associated graywackes suggesting that various provenance components may separate into different grain size fractions during sedimentary sorting processes that is the more mafic materials tended to incorporate into the sedimentary record for the clay size fraction framework modes and geochemical data indicate that the turbidites were mainly derived from a recycled orogenic provenance characterized chiefly by sedimentary metasedimentary rocks and granite gneisses similar to the upper continental crust but with a variable admixture of continental island arc volcanic components flysch deposition took place in a back arc basin situated between an active continental margin the kunlun qinling fold belt and a continental island arc the yidun island arc weathering conditions in the source area significantly influenced the composition and distribution of elements in the sediments with the elapse of time during sedimentation the degree of chemical weathering in the provenance became intense while the tectonic activity decreased gradually

infrared microthermometric and noble gas isotope study of fluid inclusions in ore minerals at the woxi orogenic au sb w deposit western hunan south china abstract the woxi au sb w deposit hosted by the neoproterozoic low grade metamorphic clastic rocks is located in a brittle ductile shear zone within the xuefengshan range south china orebodies are predominantly banded quartz veins which are strictly controlled by bedding faults and display significant vertical extents up to 2 km without obvious vertical metal zoning fluid inclusions hosted in quartz scheelite and stibnite from quartz scheelite and quartz sulfide gold veins have been studied using conventional and infrared microscopy respectively four types of fluid inclusions were identified based on petrography including type i two phase liquid rich aqueous inclusions type ii two or three phase co 2 rich inclusions type iii two phase vapour rich aqueous inclusions and type iv single phase aqueous inclusions the fluid inclusions in ore minerals scheelite and stibnite and their coexisting quartz largely share similar characteristics in terms of their types homogenization temperatures and salinities this is consistent with the fact that these ore minerals are always intergrown with quartz microthermometric and laser raman data indicate a low to moderate temperature 140 240 c low salinity 2 rich n 2 bearing aqueous ore forming fluid such fluid is further identified as a deeply non magmatic crustal fluid rather than a mantle source fluid by the significantly low 3 he 4 he ratios 0 002 0 281 ra and a small amount of meteoric water or host rock buffered fluid could be involved w ore precipitation was probably associated with mixing between a deeply originated crustal fluid and host rock buffered fluid based on the fluid inclusion features in scheelite and quartz i however au and sb ore deposition probably resulted from boiling which was caused by the marked pressure drop geological features such as banded structure and crack sealing structure also indicate that fluid pressure fluctuation induced by fault valve mechanism occurred during ore precipitation these characteristics of the ore forming fluids in the woxi deposit are in good agreement with the definition of orogenic gold deposits and the woxi au sb w deposit is probably an atypical orogenic gold deposit for its unique ore forming element association

anthropogenic sources stimulate resonance of a natural rock bridge the natural modes of vibration of bedrock landforms as well as the sources and effects of stimulated resonance remain poorly understood here we show that seismic energy created by an induced earthquake and an artificial reservoir has spectral content coincident with the natural modes of vibration of a prominent rock bridge we measured the resonant frequencies of rainbow bridge utah using data from two broadband seismometers placed on the span and identified eight distinct vibrational modes between 1 and 6 hz a distant induced earthquake produced local ground motion rich in 1 hz energy stimulating a 20 db increase in measured power at the bridge s fundamental mode moreover we establish that wave action on lake powell an artificial reservoir generates microseismic energy with peak power 1 hz also exciting resonance of rainbow bridge these anthropogenic sources represent relatively new energy input for the bridge with unknown consequences for structural fatigue

uptake and fractionation of rare earth elements on hydrothermal plume particles at 9 45 n east pacific rise abstract particulate samples 0 45 m from a neutrally buoyant hydrothermal plume at 9 45 n on the northern east pacific rise were collected using large volume in situ filtration and analyzed for fe al mn ni and fourteen rare earth elements ree the sm fe ratio a proxy for overall ree fe and nd er light heavy ree fractionation increased moderately with decreasing particulate fe chemically the sense of these relationships matched that documented previously in the tag plume on the mid atlantic ridge german et al 1990 although particulate fe was about 10 fold lower at 9 45 n spatial trends relative to the vent source however were opposite of expectation because slow fe ii oxidation and fe iii colloid aggregation over this interval led to increased particulate fe 10 26 nm with distance from source field and sherrell submitted after subtraction of non plume background particle composition plume particles at 9 45 n and tag had indistinguishable ranges of light ree enriched fractionation relative to ambient seawater and had very similar sm fe therefore kd for fe oxyhydroxides demonstrating that plume particles in both oceans reflect to a first degree the local seawater ree composition within plume ree variations at 9 45 n were investigated using a simple mixing model which accounts for the bulk fe al mn variations in the plume using two endmembers fresh hydrothermal oxyhydroxide precipitates and ridge crest background particles composed largely of locally resuspended sediment sm fe and nd er plot linearly with mixing ratio r 0 96 implying that the observed ree trends result from mixing of these two endmembers extrapolation to the composition of pure hydrothermal precipitates suggests that nd er is fractionated relative to seawater by a factor of 1 8 during adsorption onto fresh fe oxyhydroxide particles the ridge crest background particles are 5 fold higher in sm fe and nd er is 2 49 relative to seawater partly a result of enriched terrigenous component in the resuspended matter a reinterpretation of ree at tag reveals that positive curvature in ree vs fe plots argued previously to reflect continuous ree uptake i e increasing kd german et al 1990 may result from local depletion of the dissolved ree pool by partitioning onto fe particles at fe 100 nm similar drawdown effects could contribute to the variable degrees of curvature observed for all seawater source particle reactive species in plumes that are sampled at high particulate fe concentration in sum ree behavior in hydrothermal plumes is more consistent with equilibrium adsorption and mixing of distinct particle types than with kinetic uptake control precise measurements of rees in modern ridge crest metalliferous sediments could be compared to the endmember composition calculated from the plume data to evaluate long term changes in ree of the hydrothermal component

geochemistry and geochronology of the banxi sb deposit implications for fluid origin and the evolution of sb mineralization in central western hunan south china abstract central western hunan in south china hosts the largest antimony belt in the world with two types of sb deposits identified sb au woxi type and sb only xikuangshan type banxi is the most representative deposit in the region with vein type sb mineralization hosted in neoproterozoic clastic rocks stibnite developing in ores and arsenopyrite mainly occurring in altered country rocks trace element contents including rare earth elements ree and isotopic ratios s pb sr nd he and ar in stibnite and or arsenopyrite were analyzed to determine the timing of ore formation and to elucidate fluid origin and evolution processes most sulfides have high ree contents 45 103 ppm moderate fractionation between lree and hree lree hree 6 38 11 56 and slightly negative eu anomalies eu eu 0 53 0 72 the 34 s values are 3 88 5 81 for stibnite and 9 25 11 82 for arsenopyrite the 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios range from 18 617 to 18 635 15 695 to 15 739 and 38 965 to 38 981 for stibnite and from 18 594 to 18 609 from 15 587 to 15 698 and from 38 893 to 38 926 for arsenopyrite the 87 rb 86 sr and 87 sr 86 sr ratios are 0 3016 3 538 and 0 711463 0 717591 respectively for stibnite and 0 2251 2 214 and 0 711244 0 711565 respectively for arsenopyrite the 147 sm 144 nd and 143 nd 144 nd ratios are 0 1174 0 9816 and 0 511942 0 512768 for stibnite with end t values t 130 ma ranging from 12 4 to 6 6 and two stage model ages t 2dm ranging from 1457 to 1932 ma the 40 ar 36 ar and r ra ratios where ra is the atmospheric 3 he 4 he ratio of 1 4 10 6 are 409 545 and 0 0088 0 0348 respectively for stibnite the rb sr and sm nd isotopic analyses of the sulfides yield isochron ages of 129 4 2 4 ma 2 mswd 1 3 and 130 4 1 9 ma 2 mswd 1 6 respectively the combined trace element and isotopic data set indicates that the ore forming fluids were a mixture of dominantly deep basement derived solute rich parent water and a small amount of dilute heated meteoric water the decreases in ree 34 s 206 pb 204 pb 207 pb 204 pb 208 pb 204 pb 87 rb 86 sr 87 sr 86 sr 147 sm 144 nd and 143 nd 144 nd and increases in 40 ar 36 ar and 4 he contents in the stibnite from the earlier quartz stibnite mineralization stage stage ii through to the later stibnite mineralization stage stage iii indicate that the influx of meteoric water increased during sb mineralization the deep sourced relatively high temperature rock reacted fluid mixed with increasing amounts of more oxidized low temperature meteoric fluids causing the precipitation of arsenopyrite and stibnite sequentially at the banxi deposit a two period genetic model has been proposed for the world class sb mineralization in the central western hunan region the woxi type sb au deposits were derived from orogenic fluids generated from folding and shearing during the caledonian and indosinian orogeny whereas the xikuangshan type sb deposits were formed by mixing heated basement derived hydrothermal fluid circulating during the flare up of magmatism in south china with lower temperature meteoric water

seismogenesis of the 1985 great ms 8 1 michoacan mexico earthquake the size and source complexity of the great ms 8 1 michoacan mexico earthquake can be attributed to both a restriction of the downdip width of the seismic interface between the overriding and downgoing plates and a uniform distribution of asperities the seismogenic evidence of strain accumulation during the 20 years prior to the 19 september 1985 mainshock closely resembles that observed prior to the smaller mw 7 6 earthquakes in the adjacent colima 1973 and petatlan 1979 regions the subsequent rupture zones are seismically quiescent mb 4 0 for 2 5 4 years prior to the mainshocks the locked thrust interface is loaded by aseismic slip and normal faulting within the downgoing plate below 25 30 km there is evidence that the 1981 playa azul earthquake mw 7 3 is an integral stage of the evolutionary process of strain accumulation and release in the michoacan area and could thus be considered a foreshock to the great 1985 earthquake

on the limitation of the h v spectral ratio using seismic noise as an exploration tool application to the grenoble valley france a small apex ratio basin the h v spectral ratio method based on seismic noise hvsrn was used in the grenoble basin france an alpine valley characterized by a small apex ratio the resonance frequencies obtained in the experiments were compared to the thickness of the sediments deduced from a microgravimetric survey and to the 1 d theoretical assessment of site responses given the abundance of data on the sediments and depth of the basin the values of the theoretical resonance frequency fo can be determined quite accurately however it has been observed that the effects of basin geometry can disturb fo measurements using the hvsr method in particular for a case like the grenoble basin which has a small apex ratio w h and strong suspected 2 d and or 3 d effects interpretation of fo values in terms of bedrock depth gives rise to estimation errors of about 10 in certain cases with the most significant errors 50 occurring on the edges of the basin where subsurface layers are characterised by larger heterogeneities and where the basin topography is accentuated this study suggests that great care must be taken when using the hvsrn method as an exploration tool at least in valleys with a small apex ratio

geochemistry and petrogenesis of placer nephrite from hetian xinjiang northwest china article the yurungkash and karakash rivers also known respectively as the white jade and black jade rivers located in hetian xinjiang province northwest china are the two main sources in china of white green and black placer nephrite with a long history 5000 years of exploration and mining the twenty nine placer nephrite samples collected from both rivers and analyzed in the present study possess fine grained and compact microstructures the mineral assemblages in the samples provide clues to the metamorphic metasomatic processes that formed the nephrite which was the result of one of the following reactions dolomitic marble tremolite or dolomitic marble diopside tremolite white nephrite from the yurungkash river and green nephrite from the karakash river are predominantly tremolite based on electron probe microanalytical data backscattered electron images and raman spectra two kinds of black nephrite from the karakash river are identified one dominated by actinolite aggregates and another consisting of tremolite aggregates with graphite crystals up to 2 mm in length compared with black nephrite white and green nephrites contain fewer mineral inclusions and have lower feo and mno contents all the amphiboles in the nephrites have very low contents of cr2o3 0 00 0 07 wt and nio 0 00 0 05 wt relative to serpentinite related nephrite 0 07 0 43 wt cr2o3 0 08 0 36 wt nio most of the nephrite samples have low total rare earth element ree contents ranging from 12 22 to 49 40 ppm in two nephrite samples relatively high ree concentrations 161 and 190 ppm are related to the presence of ree bearing minerals whole rock ree chondrite normalized patterns of all samples are characterized by strong negative eu anomalies 0 16 0 48 moderate light ree enrichment la ndn 1 8 5 0 and nearly flat heavy ree distributions gd ybn 0 3 1 7 nephrite samples from both river locations have 18

yttrium and rare earth elements in fluids from various deep sea hydrothermal systems rare earth element ree and yttrium y concentrations were measured in fluids collected from deep sea hydrothermal systems including the mid atlantic ridge mar i e menez gwen lucky strike tag and snakepit the east pacific rise epr i e 13 n and 17 19 s and the lau vai lili and manus vienna woods pacmanus desmos back arc basins bab in the south west pacific in most fluids y is trivalent and behaves like ho chondrite normalized y ree y reen concentrations of fluids from mar epr and two bab sites i e vai lili and vienna woods showed common patterns with lree enrichment and positive eu anomalies ree analysis of plagioclase collected at lucky strike strengthens the idea that fluid ree contents are controlled by plagioclase phenocrysts other processes however such as ree complexation by ligands cl f so42 secondary phase precipitation and phase separation modify ree distributions in deep sea hydrothermal fluids ree speciation calculations suggest that aqueous ree are mainly complexed by cl ions in hot acidic fluids from deep sea hydrothermal systems ree concentrations in the fluid phases are therefore influenced by temperature ph and duration of rock fluid interaction unusual y reen patterns found in the pacmanus fluids are characterized by depleted lree and a positive eu anomaly the demos fluid sample shows a flat y reen pattern which increases regularly from lree to hree with no eu anomaly these manus basin fluids also have an unusual major element chemistry with relatively high mg so4 h2s and f contents which may be due to the incorporation of magmatic fluids into heated seawater during hydrothermal circulation ree distribution in pacmanus fluids may stem from a subseafloor barite precipitation and the ree in demos fluids are likely influenced by the presence of sulfate ions

infrared microthermometric and stable isotopic study of fluid inclusions in wolframite at the xihuashan tungsten deposit jiangxi province china the xihuashan tungsten deposit jiangxi province china is a world class vein type ore deposit hosted in cambrian strata and mesozoic granitic intrusions there are two major sets of subparallel ore bearing quartz veins the ore mineral assemblage includes wolframite and molybdenite with minor amounts of arsenopyrite chalcopyrite and pyrite there are only two phase aqueous rich inclusions in wolframite but at least three major types of inclusions in quartz two or three phase co2 rich inclusions two phase pure co2 inclusions and two phase aqueous inclusions indicating boiling fluid inclusions in wolframite have relatively higher homogenization temperatures and salinities 239 380 c 3 8 13 7 wt nacl equiv compared with those in quartz 177 329 c 0 9 8 1 wt nacl equiv these distinct differences suggest that those conventional microthermometric data from quartz are not adequate to explain the ore formation process enthalpy salinity plot shows a linear relationship implying mixing of different sources of fluids although boiling occurred during vein type mineralization it seems negligible for wolframite deposition mixing is the dominant mechanism of wolframite precipitation in xihuashan 34s values of the sulfides range from 1 6 to 0 1 indicative of a magmatic source of sulfur 18o values of wolframite are relatively homogeneous ranging from 4 8 to 6 3 oxygen isotope modeling of boiling and mixing processes also indicates that mixing of two different fluids was an important mechanism in the precipitation of wolframite

ore forming mechanism and physicochemical evolution of gutaishan au deposit south china perspective from quartz geochemistry and fluid inclusions abstract the gutaishan is an important gold deposit of the jiangnan orogen in south china the deposit is characterized by multiphase alteration mineralization including barren quartz pre ore stage i quartz dolomite pyrite arsenopyrite stage ii quartz dolomite native gold pyrite arsenopyrite stibnite stage iii and quartz dolomite pyrite stage iv cathodoluminescence cl observations show that each of stage ii and iii quartz comprises two sub stages stage ii qii1 and qii2 stage iii qiii1 and qiii2 and stage iv quartz qiv contains no sub stages qiii1 has distinct core rim texture with the cl intensity decreasing from core to rim qii1 qii2 qiii2 and qiv are texturally more homogeneous variations of aluminium concentration correlate with the cl intensity and reveal the determinated of ph in fluids during stage ii and iii with marked decline to stage iv fluid inclusions fis trapped in quartz are liquid rich and co2 rich suggesting a co2 h2o nacl fluid system fluid inclusion microthermometry data suggest that the ore forming fluids were under conditions of medium low salinity stage ii 1 02 11 46 wt nacl equiv stage iii 0 83 9 84 wt nacl equiv stage iv 4 39 8 10 wt nacl equiv and temperature stage ii 190 285 c stage ii 170 270 c stage ii and 163 240 c consistent with the low ti content

rare earth element study of exhalites within the willyama supergroup broken hill block australia a wide variety of unusual rock types exhalites are commonly associated with or host to exhalative mineralisation within the willyama supergroup chondrite normalised ree patterns of feldspar gahnite calcite magnetite and garnet rich lithologies in the vicinity of stratiform broken hill type pb zn ag mineralisation are lree and eu enriched similar to the ree patterns of pure metalliferous sediments and hydrothermal fluids of the east pacific rise and the red sea in contrast tourmaline garnet amphibole feldspar and gahnite rich exhalites in strike extension of broken hill type orebodies possess lree enrichments and negative eu anomalies and also hree enrichments and negative ce anomalies these ree patterns are the result of decreasing temperatures of the hydrothermal fluids changing oxidation reduction conditions and increasing influence of basic volcanism with increasing distance from the sulphide mineralisation

syngenetic origin for the sediment hosted disseminated gold deposits in nw sichuan china ore fabric evidence abstract sediment hosted disseminated gold deposits in nw sichuan china have many features in common with the well known carlin type deposits in the western united states they are hosted by middle upper triassic turbidites composed of 1300 4300 m of rhythmically interbedded slightly metamorphosed calcareous sandstone siltstone and slate the ore bodies are typically layer or lens like in shape and generally extend parallel to the stratification of the host sedimentary rocks with a strike length of tens to several hundreds of meters the immediate host rocks consist mainly of calcareous slate and siltstone characterized by high contents of organic matter and diagenetic pyrite the main primary ore minerals associated with gold mineralization include pyrite arsenopyrite realgar and stibnite gangue minerals comprise mostly quartz calcite and dolomite gold is extremely fine grained usually less than 1 m and cannot be seen with an electron microscope two types of ore mineralization have been recognized in the deposits the stratiform ores are composed of rhythmical interbeds of sulfides e g pyrite arsenopyrite realgar stibnite interpreted to be authigenic and detrital quartz quartzite sericite and graphite of allogenic origin they were folded and deformed concordantly with host rocks and grade both vertically and laterally into normal country rocks another type of ore forms a network of numerous gold bearing veins and veinlets of quartz calcite sulfides of millimeter centimeter decimeter and even meter scale in width the network ore randomly fills fissures microfissures and cleavages but still is stratabound in character detailed studies on ore fabrics show abundant evidence for synsedimentary origins although subsequent diagenesis metamorphism tectonic deformation and epigenetic hydrothermal activity have significantly remolded the primary fabrics primary fabrics are shown either by rhythmical interbeds of different mineral components parallel to the bedding or by the change of grain size of the same minerals such as pyrite realgar and stibnite the layer inhomogeneity of the stratiform ore is clarified by parallel overprints of later schistosity planes resulting in distinct grain orientation and elongation aggregate polarization and undulating extinction of ore minerals especially of mechanically and chemically extremely mobile ones such as realgar and stibnite it is proposed that the stratiform ores in these chinese deposits were most probably formed concurrently with their host middle upper triassic turbidites in submarine hot spring environments while the network mineralization was formed as a result of complicated processes such as diagenesis weak metamorphism tectonic deformation and epigenetic hydrothermal activity responsible for the remobilization or reworking of the pre existing stratiform ores geochemical data also support this genetic model

fluid zircon interaction during low temperature hydrothermal processes implications for the genesis of the banxi antimony deposit south china abstract fluid zircon interaction in hydrothermal systems may provide key information on fluid characterization and ore precipitation in this study in situ analyses of hf isotopes in zircon combined with u pb ages and major and trace element data provide new insights into fluid genesis at the banxi antimony deposit the zircons separated from typical quartz stibnite ores and altered wall rocks have undergone fluid modification to different degrees showing hydrothermal overprints in reflected transmitted light back scattered electron bse and cathodoluminescence cl images and variable concentrations of si zr hf u th pb ti nb ta p f y and rare earth elements they possess identical u pb ages to the banxi group and underlying lengjiaxi group clastic rocks but distinct 176hf 177hf 176lu 177hf and 176yb 177hf ratios indicating the possible changing of lu hf systematics during the hydrothermal alteration the evidence suggests a contribution of ore material from the banxi group and a deeper fluid source derived from the lengjiaxi group and the crystalline basement beneath it a fluid mixing model is proposed wherein the deep sourced high radiogenic hf fluid mixed with circulating near surface meteoric component dominated fluid triggering antimony precipitation the u pb chronometer was not reset during this low temperature mineralization event whereas the lu hf systematics in the fluid altered zircons show evidence of lattice breakdown of the old zircons during fluid mixing coupled with external input of highly radiogenic hf from the crystalline basement this research highlights the potential to use zircon structure and geochemistry in tracing complex fluid evolutionary processes

dispersion of u th and ree by water rock interaction around an intragranitic u vein jalerys mine morvan france abstract the dispersion of u th and ree from a u vein type deposit localized in an intragranitic vein through the surrounding host rock has been characterized by combining petrological mineralogical and geochemical major and trace elements radiogenic isotopes studies the different stages of hydro thermal alteration have been identified including those leading to changes in the major or trace element concentrations the distances over which u th and ree have migrated are estimated and correlated with the main water rock interaction processes the role of co precipitation with secondary minerals in the retention of these elements is stressed these processes are considered as analogous to those which could take place around a radioactive waste repository in a similar rock type the main geochemical implications of this work for the safety assessment of such a disposal are discussed

fine structure of a postfailure wadati benioff zone the hypocentral distribution of locally recorded aftershocks of the great ms 8 1 michoacan mexico earthquake of september 19 1985 defines a narrow wadati benioff zone structure roughly 10 km thick dipping 14 at n23 e this is in good agreement with the source geometry obtained by waveform modeling of the 1985 michoacan mainshock and the large 1979 petatlan earthquake in the adjoining region we inverted for the crustal velocity structure in the epicentral region by applying the levenberg marquardt non linear least squares algorithm to our local aftershock data the velocity model consists of a layer with linearly increasing velocity in depth overlying a dipping constant velocity halfspace our hypocentral location program uses a velocity model of the same form together with ray tracing the earthquake hypocentral resolution obtained with this program is significantly better than that from conventional approaches hypo and looks very promising for use in velocity structures with an important dipping interface like subduction zones

age constraints on the devonian shale hosted zn pb ba deposits gataga district northeastern british columbia canada sedimentary exhalative barite and barite sulfide deposits occur in upper devonian basinal clastic sedimentary rocks of the earn group of the gataga district northern canadian cordillera the deposits formed in a stratigraphic sequence from which conodont species and assemblages range in age from the upper triangularis zone to the lower praesulcata zone of the early to late famennian a time span of no more than 7 m y at the driftpile deposit which is the best constrained example conodonts bracket at least two distinct mineralization events during the middle famennian the older event is the lower upper marginifera zone or north trench zone and east zone and the younger event is the uppermost marginifera trachytera zone or main zone the other gataga deposits although somewhat less well defined are roughly of these ages or somewhat younger one barite pyrite unit at cirque is late famennian postera and expansa zones the youngest unit so far recognized in the gataga district exhalation of metalliferous brines into the gataga basin was of relatively short duration and episodic and the sites of active venting probably migrated along extensional faults through time this data allow temporal correlation of these sedimentary exhalative deposits with other devonian mississippian mineralization events on the north american margin such as other sedimentary exhalative sulfide deposits and volcanogenic sulfide deposits located on the outermost western margin of the miogeocline the sedimentary exhalative deposits of the kechika trough formed during a brief geologic episode within a much longer lived time span of are and back arc rifting and sea floor hydrothermal mineralization

1 d and 2 d resonances in an alpine valley identified from ambient noise measurements and 3 d modelling summary h v spectral ratios are regularly used for estimating the bedrock depth in 1 d like basins exhibiting smooth lateral variations in the case of 2 d or 3 d pronounced geometries observational and numerical studies have shown that h v curves exhibit peculiar shapes and that the h v frequency generally overestimates 1 d theoretical resonance frequency to investigate the capabilities of the h v method in complex structures a detailed comparison between measured and 3 d simulated ambient vibrations was performed in the small size lower romanche valley french alps which shows significant variations in geometry downstream and upstream the sechilienne basin analysing the h v curve characteristics two different wave propagation modes were identified along the valley relying on previous geophysical investigation a power law relationship was derived between the bedrock depth and the h v peak frequency which was used for building a 3 d model of the valley geometry simulated and experimental h v curves were found to exhibit quite similar features in terms of curve shape and peak frequency values validating the 3 d structure this good agreement also evidenced two different propagation modes in the valley 2 d resonance in the sechilienne basin and 1 d resonance in the external parts this study underlines the interest of h v curves for investigating complex basin structures

geochemistry of a hydrothermal sediment core from the obs vent field 21 n east pacific rise abstract we report a geochemical investigation of near vent hydrothermal sediment from the east pacific rise collected in a short 11 cm core by submersible from the obs vent site at 21 n the sediment has high concentrations of fe 23 25 cu 10 22 zn 4 13 and s 22 30 but low mn concentrations 108 279 ppm indicating a much fresher sulfidic input than in previously reported near vent sediments from the mid atlantic ridge further studies are required to fully characterise near field hydrothermal sediments but the data in this study allow the first comparisons with similar near vent material collected previously from the mid atlantic ridge as well as ridge flank data from the epr and juan de fuca ridge compared to ridge flank sediments the near field sediments exhibit high ratios of fe mn cu fe and zn fe unlike cu and zn pb is not so significantly enriched pb isotope compositions are indistinguishable from local morb indicating a dominant hydrothermal source for this element in these sediments this may not necessarily be the case for ridge flank sediments however where scavenging from seawater may also be important ree distributions throughout the core exhibit low concentrations and characteristics typical of vent fluids with lree enrichments and pronounced positive eu anomalies these patterns are similar to those of relatively fresh sulfides but there is also evidence for progressive oxidation downward into the core by ingressing seawater

spectral amplification in a sediment filled valley exhibiting clear basin edge induced waves various site response estimates are presented for a linear array deployed in the coachella valley california during the 1992 landers big bear aftershock sequence this systematic comparison is unique in that the response of the site is clearly dominated by basin edge induced waves average sediment to bedrock spectral ratios for long s wave windows which include the basin edge induced waves exhibit amplification factors as high as 18 below 7 hz the deep basin structure which gives rise to the obvious multi dimensional effects produces a fundamental resonant peak that shifts between basin sites from 0 23 to 0 48 hz as the depth to bedrock changes above 0 6 hz where the largest amplifications occur the response is remarkably similar between sites and appears to be dominated by a near surface layer that is relatively uniform across the valley the apparent fundamental resonant frequency of this layer is between 0 8 and 1 hz sediment to bedrock spectral ratios computed using shorter windows that exclude the basin edge induced waves imply that the multi dimensional effects are significant only below 4 hz where they increase amplifications by an approximate factor of 2 spectral ratios computed using coda windows taken at twice the s wave travel time exhibit amplifications that are an average factor of 1 7 greater between 1 and 4 hz than those of the s wave estimates this discrepancy does not improve by taking coda windows later at four times the s wave travel time horizontal to vertical component s wave spectral ratios do not agree with the sediment to bedrock ratios however they do exhibit a clear peak at the fundamental resonant frequency of the deep basin structure sediment to bedrock spectral ratios of ambient seismic noise are also inconsistent with the s wave estimates however horizontal to vertical noise ratios exhibit clear peaks near the fundamental resonant frequencies of both the deep basin structure below 0 6 hz and the suspected near surface layer between 0 8 and 1 hz therefore ambient noise data appear to provide valuable constraints on the basin structure ongoing efforts involve multi dimensional modeling of the observed basin edge induced phases and resonant frequencies

geology lithogeochemistry and alteration of the battle volcanogenic massive sulfide zone buttle lake mining camp vancouver island british columbia volcanogenic polymetallic massive sulfide deposits within the buttle lake mining camp occur within the felsic volcanic and volcaniclastic rocks of the myra formation that immediately overlies price formation andesite these units comprise the lower exposed part of the paleozoic sicker group in the buttle lake uplift in central vancouver island the sicker group represents a volcanic island arc that forms the base of the allochthonous wrangell terrane the battle main zone contains 2 3 million tons mt of proven and probable reserves grading 1 3 g t au 25 3 g t ag 2 5 percent cu 0 5 percent pb and 13 2 percent zn overall the buttle lake camp hosts geologic reserves of about 12 5 mt the battle main massive sulfide zone occurs within the h w horizon the lowest member of the myra formation immediately above the price formation andesite price formation andesite is over 300 m thick in the vicinity of the camp and consists of feldspar or pyroxene porphyritic basaltic andesite flows synvolcanic block faulting of this unit formed the regional scale buttle lake camp basin with a strike length of at least 10 km local sub basins in this major structure contain the sulfides and felsic volcanic rocks of the h w horizon the h w horizon is a 15 to 200 m thick felsic package that extends throughout the basin it consists of eight members three of which represent periods of massive sulfide deposition from the stratigraphic base to the top of these members are 1 the battle main massive sulfide lens 2 fine rhyolitic tuffaceous deposits 3 h w mafic sills 4 gap massive sulfide lens 5 coarse rhyolite pyroclastic deposits 6 rhyolite tuffaceous and cherry sediments 7 battle upper massive sulfide lenses and 8 a tripartite rhyolite flow dome complex consisting of quartz porphyritic rhyolite quartz feldspar porphyritic rhyolite and green quartz feldspar porphyritic rhyolite volcaniclastic units in the felsic package evolved with interfingering of subaerial and submarine pyroclastic processes flow dome units evolved by fractionation of quartz and feldspar alteration evaluated petrographically and with pearce element ratios is most intense close to synvolcanic and synmineral feeder faults that channeled solutions through the price formation andesite proximal to the battle main massive sulfide lens envelopes to the feeder faults have distinctive mg addition anomalies and contain the mineral assemblage pyrite sericite quartz chlorite discharge feeder stockworks immediately below the battle main massive sulfide lens contain varying proportions of sericite quartz and pyrite but lack significant chlorite deposition of the h w horizon rhyolitic units on top of the battle main massive sulfide lens did not halt mineralization rather fluids continued to percolate upward through the newly deposited rhyolitic units and deposited the battle upper lenses close to the new sediment water interface alteration below the battle upper lenses consists of quartz sericite and pyrite with minor galena sphalerite and tennantite overall hydrolysis of feldspar in both the price formation and the h w horizon resulted in a halo surrounding the ore lenses marked by addition of k and concomitant na and ca depletion

rare earth element geochemistry of the woxi w sb au deposit hunan province south china the woxi w sb au deposit in hunan south china is hosted by proterozoic metasedimentary rocks a turbiditic sequence of slightly metamorphosed greenschist facies gray green and purplish red graywacke siltstone sandy slate and slate the mineralization occurs predominantly 70 as stratabound stratiform ore layers and subordinately as stringer stockworks the former consists of rhythmically interbedded banded to finely laminated stibnite scheelite quartz pyrite and silty clays whereas the latter occurs immediately beneath the stratabound ore layers and is characterized by numerous quartz pyrite gold scheelite stringer veins or veinlets that are typically either subparallel or subvertical to the overlying stratabound ore layers the deposit has been the subject of continued debate in regard to its genesis rare earth element geochemistry is used here to support a sedimentary exhalative sedex origin for the woxi deposit the ree signatures of the metasedimentary rocks and associated ores from the woxi w sb au deposit remained unchanged during post depositional processes and were mainly controlled by their provenance the original ore forming hydrothermal fluids as demonstrated by fluid inclusions in quartz from the banded ores are characterized by variable total ree concentrations 3 5 to 136 ppm marked lree enrichment lan ybn 28 248 lree hree 16 to 34 and no significant eu anomalies eu eu 0 83 to 1 18 they were most probably derived from evolved seawater that circulated in the clastic sediment pile and subsequently erupted on the seafloor the bulk banded ores are enriched in hree lan ybn 4 6 11 4 lree hree 3 to 14 and slightly depleted in eu eu eu 0 63 to 1 14 relative to their parent fluids this is interpreted as indicating the influence of seawater rather than a crystallographic control on ree content of the ores within a single ore layer the degree of hree enrichment tends to increase upward while the total ree concentrations decrease reflecting greater influence and dilution of seawater there is a broad similarity in chondrite normalized ree patterns and the amount of ree fractionation of the bandedoresinthisstudyandexhalitesfromothersedex typepolymetallicoredeposits suggestingasimilargenesisforthesedeposits

geochemistry and petrology of nephrite from alamas xinjiang nw china abstract the hetian nephrite deposit is one of the largest nephrite deposits worldwide located within the hetian deposit xinjiang northwest china the alamas ore body occurs as veins on the contact between the late variscan granodiorite and precambrian dolomitic marble petrographic studies and electronic microprobe analyses reveal two possible nephrite formation processes 1 dolomitic marble tremolite and 2 dolomitic marble diopside tremolite nephrite veins show continuous coloration zones ranging from white and white green zones to a green zone towards the granodiorite with increasing concentrations of cr feo and tfe2o3 all these nephrite samples have quite low cr and ni contents 8 95 178 7 ppm and 0 05 3 95 ppm respectively relative to serpentinite related nephrite cr2o3 0 07 0 43 wt nio 0 08 0 36 wt their bulk rock ree patterns exhibit strong negative eu anomalies 0 03 0 21 with declined lree flat hree and low ree concentration 2 84 84 81 ppm similar to those of host dolomitic marble samples with negative eu anomalies 0 15 0 23 declined lree flat hree and lower ree concentration 8 48 11 1 ppm indicating a close genetic relationship between them homogenization temperatures analyses on the fluid inclusions in tremolite yield a minimum temperature 293 c for the nephrite formation nephrites have oxygen and hydrogen isotope compositions in the range from 3 2 to 6 2 per mil and 83 0 to 94 7 per mil respectively the corresponding equilibrated fluids have isotope compositions of 18o 3 1 to 6 1 293 c combined with field observation there are at least three possible fluid sources meteoric water magmatic water and co2 derived from decarbonation of dolomite and a metasomatic and dolomite related origin is suggested for the alamas ore body in the hetian nephrite deposit xinjiang nw china

observation of 1 to 5 second microtremors and their application to earthquake engineering part ii evaluation of site effect upon seismic wave amplification due to extremely deep soil deposits abstract the usefulness of long period microtremor observation for earthquake engineering problems at extremely deep soil deposit site was examined in this study microtremor observations were made in the niigata plain japan and in los angeles california where depths to the basement rock are several kilometers these two locations were selected because strong motion records obtained during the niigata earthquake of 1964 and the san fernando earthquake of 1971 contain large long period amplitudes understanding why these predominate long period motions were recorded is important for the evaluation of seismic input motions for large scale structures long period microtremor observations were carried out in both areas in order to evaluate the characteristics of deep soil observations were performed simultaneously at a number of stations to distinguish the nature of deep soil deposit the result of fourier analysis showed that amplitude of microtremors in long period range increases systematically from the point of basement rock outcrop to deep deposit site with the increase corresponding to the depth to basement rock this relationship coincides with that observed in the strong motion earthquake records these analyses indicated that simultaneous observation of long period microtremors at a number of stations can provide insight to the characteristic of deep soil amplification and therefore permit estimation of seismic input motions for large scale structures

the effect of topography on earthquake ground motion a review and new results a brief review of experimental and theoretical results about the effect of topography on seismic motion shows that they are consistent only on a qualitative basis amplification at mountain tops for wavelengths comparable with mountain widths is predicted and observed but the numerical simulations often underestimate the actual observed effects we propose that this disagreement is because current models are not complex enough we therefore computed the response to incident sh waves of a set of different complex configurations that include two dimensional surface topography with or without periodic ridges and subsurface layering the results show that 1 the topographic effect in itself is difficult to isolate from other effects like surface layering and therefore the amplification on top of geomorphologically complex sites cannot be predicted by a priori estimations based solely on topography and 2 the high crest base amplification ratio observed in the field cannot usually be matched even with complex two dimensional structures with incident plane sh waves which suggests that more complex models are needed to incorporate more complex wave fields e g sv surface and three dimensional geologic configurations

the use of rayleigh wave ellipticity for site specific hazard assessment and microzonation application to the city of lucerne switzerland summary the sediments underlying the city of lucerne switzerland consisting of fluvio lacustrine deposits of quaternary age have the potential to produce strong amplification of the seismic wavefield to obtain a reliable estimation of the deep soil structure we combine different methodologies based on ambient noise recordings such as single station horizontal to vertical ratios and three component array analysis two novel techniques to estimate rayleigh wave ellipticity from ambient noise recordings are tested these are based on a single and a multistation approach respectively the first utilizes the continuous wavelet transform to perform a decomposition of the noise wavefield and to isolate and extract the rayleigh wave contribution the second conversely relies on a high resolution f k method to achieve the same result we compare the results from the two techniques to provide an evaluation of their capabilities and limitations a two step inversion scheme is then presented to improve resolution on the bedrock depth in particular the surface wave dispersion information is initially used to constrain the soft sediment part while the rayleigh wave ellipticity peak is subsequently used for constraining the bedrock depth it is shown that such an approach is beneficial to map the bedrock geometry over dense urban areas the output velocity model is then used to compute the local seismic amplification by means of gridded 1 d approximation

rare earth element patterns in archean high grade metasediments and their tectonic significance abstract metasediments from two contrasting types of archean high grade terrains are interpreted as being derived from distinct tectonic settings the kapuskasing structural zone canada represents the deep roots of a typical greenstone belt whereas the limpopo province southern africa and western gneiss terrain australia mainly consist of shelf sediments deposited on a granitic basement and then buried to the depths required for granulite fades metamorphism upper amphibolite to granulite fades paragneisses from the kapuskasing structural zone have ree patterns similar to those of greenstone belt sediments except where partial melting has occurred forming restites with eu enrichment and melts with eu depletion except in this latter instance metamorphism has not affected the primary ree patterns ree patterns in archean upper amphibolite to granulite facies metasediments from the central limpopo province and western gneiss terrain show wide differences ranging from patterns which resemble those in post archean terrigenous sediments to typical archean sedimentary rock patterns the diversity in ree patterns for these shallow shelf metasediments is interpreted as resulting from derivation from local provenances samples with post archean patterns displaying eu depletion are interpreted as being derived from k rich granitic plutons which were portions of small stable early archean terrains precursors of the widespread late archean proterozoic episode of major cratonic development

rare earth element geochemistry of australian paleozoic graywackes and mudrocks provenance and tectonic control abstract in the paleozoic graywackes of eastern australia there is an increase in the total abundance of rare earth elements ree a light to heavy ree ratio and a decrease in the chondrite normalized eu anomaly with the increase in sio2 al2o3 and k2o na2o ratios this is due to the change in the dominant source rocks from andesite to dacite to granite gneiss and sedimentary rocks similarly an increase in total ree and a decrease in eu anomaly is also seen in the associated mudrocks with the increase in total clay content this correlation in paleozoic sedimentary rocks suggests that the ree characteristics of terrigenous sedimentary rocks reflect the depositional tectonic setting of the basin the oceanic island arc type graywackes are characterised by their lower total ree abundance only slight enrichment of lree over hree and the absence of a negative eu anomaly on chondrite normalised plots the continental island arc type graywackes are discriminated by their higher ree abundance and la yb ratio the presence of a small negative eu anomaly on the chondrite normalised plots and the significant enrichment of eu compared to paas post archean average australian shale the sedimentary rocks deposited on andean type active continental margins passive margins platform and cratonic basins are all characterised by the high enrichment of lree over hree and the presence of a pronounced negative eu anomaly on chondrite normalised plots and can not be discriminated from each other by ree patterns alone

microtremor measurements used to map thickness of soft sediments the observations about the behavior of microtremor spectra presented here show that noise measurements can be used as a powerful tool to determine the thickness of soft cover layers the most suitable method for this determination is nakamura s technique which is the ratio of the horizontal component noise spectrum and that of the vertical component i i v spectrum the frequency of the main peak in these spectral ratios correlates well with the sediment thickness at the site using an extensive database of microtremor measurements carried out in the western lower rhine embayment germany it was possible to show that this correlation is clearly valid for a wide range of thickness namely from tens of meters to more than 1000 m a simple formula was derived that for the sediments to be found in the area investigated directly calculates the cover thickness from the frequency of the main peak in the h v spectrum a comparison with calculated resonant frequencies sug gests the relation derived from the noise measurements depending on the velocity depth function of the shear wave classical spectral ratios are shown to be strongly influenced by the noise level and are therefore less reliable in determining the res onant frequency of the subsoil the practical relevance of the investigation is illus trated by means of cross sections constructed from results of the microtremor anal yses which provide a convincing image of the surficial structure of the areas investigated

the subsea floor replacement origin of the ordovician highway reward volcanic associated massive sulfide deposit mount windsor subprovince australia the highway reward massive sulfide deposit is hosted by a submarine below storm wave base silicic synsedimentary intrusion dominated volcanic succession the succession includes at least 13 porphyritic units in a volume of 1 x 1 x 0 5 km peperitic upper margins suggest that most of the rhyolites rhyodacites and dacites were emplaced as small 300 degrees c h 2 s dominant fluids by replacement of rhyolite rhyodacite and peperite lower temperature 300 degrees c fluids that diffused from the margins of the pipes deposited a halo of sphalerite rich ore

are microtremors useful in site response evaluation we have reviewed the applicability of microtremor measurements to evaluate site response of soft soils to this end we evaluated three different techniques commonly used to estimate site effects from microtremor measurements interpretation of fourier amplitude spectra computation of spectral ratios relative to a firm reference station and finally computation of spectral ratios of horizontal components relative to the vertical component of ground motion nakamura s technique these techniques are applied to microtremor records obtained in three cities in mexico mexico city oaxaca and acapulco these cities differ in their local geological conditions and in their seismotectonic environment in order to evaluate the results obtained from microtremor measurements we compare them with standard spectral ratios of the intense s wave part of weak or strong motion records obtained at the same sites our results showed that microtremor measurements can be used to estimate the dominant period of a site with very acceptable reliability in the range 0 3 to 5 hz the best results were obtained with nakamura s technique which also gives a rough estimate of amplification of seismic waves when the local geology is relatively simple simple numerical simulations indicate that the underlying assumptions of nakamura s technique are consistent with the propagation of rayleigh waves these simple numerical simulations also explain why different researchers have been able to successfully characterize 1d site effects using microtremor records regardless of whether they consider microtremors to consist of surface or body waves our results strongly suggest that the technique by nakamura effectively compensates for source effects in microtremor measurements which eliminates a major limitation to their application in earthquake engineering

the ree content of some hydrothermal fluids ree concentrations were determined in solutions from submarine hydrothermal vents on the east pacific rise and for the first time from continental geothermal fields in tibet and bulgaria they indicate that in hydrothermal systems ree are immobile at temperatures below 350 c and for water rock ratios of 105 nd values of submarine solutions and anhydrites 4 7 to 6 2 suggests recharge on the sedimentcovered flanks of the ridge carbonate anions as measured by alkalinity appear to increase the solubility of heavy ree somewhat but not to the extent that substantial amounts of ree could be driven out from rocks by hydrothermal activity

mineralogical and chemical variations castellanos shale hosted zn pb ba deposit northwestern cuba the shale hosted castellanos sedimentary exhalative zn pb ba deposit of jurassic age in northwestern cuba consists of pyrite sphalerite and galena in a hydrothermal quartz carbonate barite matrix with very little clastic or shale matrix the northeastern end of the zn pb ba lens overlies a transgressive cu stringer zone which is interpreted as the vent or feeder channel for the exhalative mineralization abundance patterns in the sulfide assemblage define layering within the deposit in the southwestern part of the deposit sphalerite and galena increase and pyrite decreases stratigraphically upward within individual layers to the northeast near the vent sphalerite and galena decrease upward parallel to pyrite in the area of the vent the basal carbonate is exclusively dolomite however calcite abundance increases rapidly upward remote from the vent dolomite is the dominant carbonate from the base to the top of the deposit carbonate and barite are the main gangue minerals near the discharge site quartz is the major gangue mineral in the southwestern section these and other variations result from differences in a ca super 2 f oh2 temperature and sigma s relative to sulfide forming cations especially fe super 2 at the discharge site and in the depositional basin some distance from the vent

continuous measurements of microtremors on sediments and basement in los angeles california abstract continuous measurement of microtremors at two sites on basement rock and sediments was carried out in los angeles california in order to understand the fundamental characteristics of microtremors a predominant peak with a period of about 6 5 sec was found in the microtremor spectra in both media the spectral amplitude of the peaks varied gradually with time in a similar manner at the two sites their time variant characteristics are in agreement with change in oceanic swell height observed at an oceanic buoy in the southwest of los angeles this suggests that they originate from an oceanic disturbance on the other hand a clear daily variation of spectral amplitudes at a period of 0 3 sec indicates that short period microtremors are caused by cultural noises it was found that the spectral ratio of long period microtremors between the basement and the sediments was repeatable although the spectral amplitudes at the two sites were time variant the spectral ratio of the long period microtremors was similar to that derived from strong motion records this suggests the applicability of spectral ratios of microtremors to assess the effects of deep sediments on long period earthquake ground motion

the effect of quaternary alluvium on strong ground motion in the coyote lake california earthquake of 1979 abstract the effect of alluvium on strong ground motion can be seen by comparing two strong motion records of the coyote lake california earthquake of 6 august 1979 m l 5 9 one record at a site on franciscan bedrock had a peak horizontal acceleration of 0 13 g and a peak horizontal velocity of 10 cm sec the other at a site 2 km distant on 180 meters of quaternary alluvium overlying franciscan had values of 0 26 g and 32 cm sec amplifications by factors of 2 and 3 horizontal motions computed at the alluvial site for a linear plane layered model based on measured p and s velocities show reasonably good agreement in shape with the observed motions but the observed peak amplitudes are greater by a factor of about 1 25 in acceleration and 1 8 in velocity about 15 per cent of the discrepancy in acceleration and 20 per cent in velocity can be attributed to the difference in source distance the remainder may represent focusing by refraction at a bedrock surface concave upward there is no clear evidence of nonlinear soil response fourier spectral ratios between motions observed on bedrock and alluvium show good agreement with ratios predicted from the linear model in particular the observed frequency of the fundamental peak in the amplification spectrum agrees with the computed value indicating that no significant nonlinearity occurs in the secant shear modulus computations show that nonlinear models are compatible with the data if values of the coefficient of dynamic shear strength in terms of vertical effective stress are in the range of 0 5 to 1 0 or greater the data illustrate that site amplification may be less a matter of resonance involving reinforcing multiple reflections and more the simple effect of the low near surface velocity application of traditional seismological theory leads to the conclusion that the site amplification for peak horizontal velocity is approximately proportional to the reciprocal of the square root of the product of density and shear wave velocity

rare earth elements and hydrothermal ore formation processes abstract the geochemical behaviour of ree is influenced by nearly all important hydrothermal ore formation processes including fluid rock interactions fluid precipitations adsorption and scavenging onto particles and changes in fluid temperature pressure ph eh alkalinity and ligand concentration destabilization of ree complexes in response to these physicochemical changes and possible chemical crystallographic controls determine the concentration and distribution of ree within hydrothermal minerals mineraloids and amorphous phases alteration assemblages of intrusive related mineralisations may exhibit a wide range of ree distributions and ree fractionation trends the ree distribution within these hydrothermally altered lithologies will depend on the ree concentration in the rock and the fluid the partitioning behaviour of the ree between the rock phases and the fluid and the types of alteration reactions which take place reactive rocks such as carbonate rich lithologies of skarn deposits may gain or loose significant amounts of ree during fluid rock interactions ree geochemical investigations combined with fluid inclusion and stable isotope studies may point to the origin of alteration products and the source s of ore fluids ancient massive sulphide ores commonly exhibit anomalous eu concentrations similar to many recent submarine hydrothermal precipitates the recognition of hydrothermal fluid seawater sedimentary or volcanically derived ree distributions within ores chemical sediments and hydrothermally altered lithologies may help to constrain genetic modelling of massive sulphide deposits care should be taken with the interpretation of ree distributions from metamorphosed hydrothermal ore deposits becase metamorphic and diagenetic alteration reactions may change the ree distributions mobility of ree may occur during diagenesis of carbonate rich rocks and during the development of shear zones and migmatites in contrast very large fluid rock ratios are necessary to cause significant changes in ree patterns of silicate rich rocks during diagenesis and regional metamorphism

an earthquake doublet in ometepec guerrero mexico on june 7 1982 an earthquake doublet occurred in a gap near ometepec guerrero mexico which had been given a high seismic potential the two earthquakes first event m s 6 9 m b 6 0 16 3 n 98 4 w d 25 km second event m s 7 0 m b 6 3 16 4 n 98 5 w d 8 km of the doublet occurred within five hours of each other we determine the source parameters of these events by inverting surface wave data at a period of 256 s the results are for the first event strike 116 dip 77 slip 88 and seismic moment of 2 8 10 26 dyne cm and for the second event strike 116 dip 78 slip 89 and seismic moment of 2 8 10 26 dyne cm modeling of long period p waves suggests that the first event has a depth of 20 km and is represented by a single trapezoidal source time function with an effective duration of 6 s the second event is best modeled by two sources at depths of 15 and 10 km the combined effective source duration time for the two sources is about 10 s the ratio of the seismic moment obtained from body waves to that from surface waves is 0 5 for the first event and 1 for the second adding the seismic moment of the two events and considering the first week aftershock area 3200 km 2 the stress drop is 4 bars these results suggest that the first event that involved a deeper asperity caused an incremental stress change large enough to trigger the second event if the two events of the doublet broke distinct areas of the subduction zone the coseismic slip is 0 58 m and accounts for about 25 of the total plate motion between the cocos plate and the north america plate accumulated since the last large earthquake in the region other doublets similar to the ometepec doublet have occurred along the middle america trench during the past 70 years a regional distribution of comparable size asperities may be responsible for this relatively frequent occurrence of doublets and for the simplicity of earthquakes in the region the high convergence rate which produces rapid strain accumulation and short recurrence intervals for large earthquakes and the smooth sea floor subducted along the middle america trench may contribute to the homogeneous distribution of comparable size asperities we found a relation log t 1 3 log m 0 t is the average recurrence time and m 0 is the average seismic moment for large earthquakes along the subduction zone in the guerrero oaxaca region where the convergence rate and the properties of the subducted plate are considered relatively uniform a simple asperity model predicts this relation