bolt length requirement in underground openings abstract a parametric study has been carried out using the numerical analysis code flac3d to obtain the influence of various shapes of underground openings on the maximum induced boundary stress five shapes viz circular horseshoe rectangular elongated d shape and elliptical have been considered for each shape four tunnel depths and five horizontal in situ stress models have been taken for the study of induced boundary stresses the values of maximum and minimum induced boundary stresses in the roof and wall have been obtained from the analyses this data has subsequently been used to develop correlations to estimate the normalized maximum and minimum boundary stresses which have been subsequently compared with the strength of the rock mass obtained from the sheorey s non linear failure criterion for three rock masses represented by three values of bieniawski s rmr and three values of crushing strength of intact rock material the values of minimum factor of safety at the roof and the wall have been collected from all the plots using these data sets different correlations have been developed to estimate the minimum factor of safety fmin in the roof and wall since the bolt length should be normalized with the opening size some more computer models have been run with varying tunnel width of 5 and 20 m besides the earlier 10 m size to obtain the correlations for estimating the bolt length the depth of factor of safety contour of 1 5 from the opening periphery has been picked up from all these models and the correlations have been developed for estimating the roof and wall bolt length for the five shapes of underground openings the correlations for bolt length show that in addition to the shape of underground openings and in situ stress the bolt length also varies with the rock mass type these correlations have been verified for field cases of elongated d shape openings

gold bearing arsenian pyrite and marcasite and arsenopyrite from carlin trend gold deposits and laboratory synthesis invisible gold in natural and synthetic arsenian pyrite and marcasite correlates with anomalous as content and fe deficiency and high contents of invisible gold in most natural and all synthetic arsenopyrite correlate with excess as and fe deficiency as rich fe deficient arsenopyrite synthesized hydrothermally contains up to 3 0 wt au uniformly distributed in growth zones of light backscattered electron contrast at the deep star gold deposit carlin trend nevada the sulfide compositions apparently span the full range of metastability from fesz to near feass 40 at s arsenian pyrite contains up to 0 37 wt au but arsenopyrite has excess s and is relatively au poor observed minimum fe contents are 29 1 at in arsenian pyrite and marcasite from the deep star deposit and 31 3 at in synthetic arsenopyrite we suggest that invisible gold in arsenian pyrite and marcasite and arsenopyrite from sediment hosted gold deposits represents au removed from ore fluids by chemisorption at as rich fe deficient surface sites and incorporated into the solids in metastable solid solution however the oxidation state of invisible gold aua au1 remains uncertain because the chemisorption process is intrinsically nonsystematic in terms of crystal chemical parameters and does not result in definitive atomic substitution trends

an observation of the horizontal and vertical diffusion of a passive tracer in the deep ocean an experiment to measure the dispersion of a passive tracer injected at 300 and 1000 m depth in the pacific 600 miles southwest of san diego is described rhodamine dye was released as a very nearly point source and the subsequent growth of the patch was mapped at various times up to 66 2 hours after release using a self propelled underwater research vehicle spurv which carried temperature conductivity pressure and dye sensors on a depth cycling trajectory through the patch the analysis shows that the horizontal diffusion rates decrease with depth that it is difficult to resolve the mixing in terms of a constant diffusion parameter based on any one of a number of models that the 300 m results agree with those obtained by schuert 1970 and that the patch growth began to develop eddy behavior at 66 2 hours when the rms second moment of the dye distribution was r2 l 2 210 m for the purpose of predicting horizontal mixing the results indicate that eddy diffusivities of 1150 and 360 cm2 s at 300 and 1000 m respectively are the best fit values for spatial scales 200 m horizontally although we have focused on horizontal isopycnal diffusion a few aspects of the vertical diapycnal characteristics of the patch are also discussed

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

timing of rotational motion of apuseni mountains romania paleomagnetic data from tertiary magmatic rocks paleomagnetic results are reported from 8 sites in eocene to oligocene magmatic rocks and 27 sites in middle miocene to upper miocene volcanic rocks of the apuseni mountains following af demagnetization 29 sites were selected for tectonic interpretation these results together with previously published data imply a northward displacement of the area studied between the late cretaceous and oligocene followed by a large clockwise rotation prior to the middle miocene after which no significant movement has occurred these results agree with other data from the carpatho pannonian domain showing a period of great mobility during the early miocene

abyssal mixing where it is not abstract a parameterization based on internal wave wave interaction theory which infers turbulence production from finescale internal wave shear is applied to 114 full water depth velocity profiles in the sargasso sea an average eddy diffusivity of 0 1 10 4 m2 s 1 independent of depth is inferred this value is consistent with full water depth microstructure measurements from abyssal basins in the eastern north atlantic and eastern north pacific it is an order of magnitude smaller than the values inferred from a simple vertical advection diffusion balance or bulk budgets thus the mixing needed to close deep global water mass budgets does not appear to occur over midlatitude abyssal plains this suggests that ocean mixing is either i confined to boundary layers as in ideal thermocline theory or ii localized to hotspots such as over rough topography or restrictive passages abyssal diffusivities do not display any dependence on bottom slope for slopes less than 7 10 2 based on 5 10 km bathy

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

the santa monica basin tracer experiment a study of diapycnal and isopycnal mixing we have studied cross isopycnal diapycnal and lateral mixing and stirring below the sill of santa monica basin by releasing two tracers sulfur hexafluoride and perfluorodecalin as close as possible to an isopycnal surface and measuring their subsequent dispersion the target for the release was a potential temperature surface at about 790 m depth roughly 100 m above the bottom and 50 m below the sill three surveys performed immediately after about 7 weeks after and about 6 months after the release showed that the time scales for lateral stirring and mixing in the basin were between 2 and 5 months the diapycnal diffusivity for the whole period was found to be 0 29 0 06cm2 s near the injection surface where the buoyancy frequency was about 1 1 cph this estimate may include some mixing in the turbulent boundary layer near the walls of the basin our best estimate for the diapycnal diffusivity in the basin interior is 0 25 0 08 cm2 s

dye dispersion in the seasonal thermocline abstract a dye dispersion experiment was performed in september 1979 in the open ocean approximately 180 km off the east coast of florida an initially vertical sheet of dye extending from about 60 to 100 meters in depth and about 10 kilometers long was dispensed into the seasonal thermocline its subsequent evolution was recorded with an instrumented chain that included 25 fluorometers which was towed back and forth across the dye sheet by another vessel the dye sheet was crossed 17 times at ages varying from 6 minutes to slightly less than 4 hours two of the most apparent effects in the data were the important of vertical shear and the presence of intermittency in the dye time series it is found that the depth averaged width of the dye sheet grows as time to the 3 2 power there is good evidence that a shear diffusion interaction is responsible for this growth which implies an effective vertical diffusivity of 1 0 0 5 cm 2 s 1 even though this is an upper ocean experiment there is some cons

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

trace element concentrations in porphyry copper deposits from metaliferi mountains romania a reconnaissance study there are fifteen miocene intrusions with porphyry copper mineralization in the metaliferi mountains romania most are associated with epithermal au ag te bi se ge vein systems the investigation of fifty samples from six deposits rosia poieni bucium tarni a colnic rovina valea morii and bolcana indicated bulk rock mean values of 0 16 0 88 ppm au 1000 ppm in bornite in the porphyry type mineralization galena forms microinclusions in pyrite chalcopyrite and bornite and contains up to 3750 ppm ag 17 380 ppm se 1570 ppm ge and 780 ppm te galena and pyrite from the epithermal mineralization in the m gura bolcana troi a system contain concentrations of ag and se ten times lower than in the same minerals from the porphyry copper mineralization the present data show that te is a significant trace element in the potassic zone of the investigated porphyry systems the data also shows that this does not correlate with the presence or absence of ophiolitic basement or with variation in the chemistry of the host intrusions tellurium enrichment in porphyry type deposits of the metaliferi mountains supports their genetic relationship with the spatially associated epithermal systems

reduced mixing from the breaking of internal waves in equatorial waters in the oceans heat salt and nutrients are redistributed much more easily within water masses of uniform density than across surfaces separating waters of different densities but the magnitude and distribution of mixing across density surfaces are also important for the earth s climate as well as the concentrations of organisms most of this mixing occurs where internal waves break overturning the density stratification of the ocean and creating patches of turbulence predictions of the rate at which internal waves dissipate were confirmed earlier at mid latitudes here we present observations of temperature and velocity fluctuations in the pacific and atlantic oceans between 42 degrees n and 2 degrees s to extend that result to equatorial regions we find a strong latitude dependence of dissipation in accordance with the predictions in our observations dissipation rates and accompanying mixing across density surfaces near the equator are less than 10 of those at mid latitudes for a similar background of internal waves reduced mixing close to the equator will have to be taken into account in numerical simulations of ocean dynamics for example in climate change experiments

pre alpine crust in the apuseni mountains romania insights from sm nd and u pb data abstract the apuseni mountains in romania expose pre alpine crustal basement rocks between the carpathian and dinaride segments of the alpine orogen because of a lack of direct constraints the age and plate affinity of the basement rocks have been largely uncertain new sm nd data for key lithotectonic assemblages and u pb zircon data for crosscutting plutons are presented they show the presence of early proterozoic crustal components and help constrain the age and nature of several contrasting pre alpine crustal domains basement rocks of the apuseni mountains consist of a northern granite gneiss terrane somes bounded by an amphibolite granodiorite belt codru a composite igneous belt overprinted by alpine shearing highis biharia and a southern carbonate lens mica schist gneiss terrane baia de aries the northern terrane has yielded tdm model ages ranging from 1 90 to 1 76 ga and nd 0 values ranging from 15 5 to 12 5 the southern terrane has yielded tdm model ages of 1 82 1 69 ga and nd

mineralogy and geochemistry of sulfosalts from baia sprie ore deposit romania new bismuth minerals occurrence abstract the baia sprie epithermal ore deposit is one of the best known deposits in romania and europe it consists mainly of a vein system with two major veins 1 principal vein and 2 southern vein along fractures that delimitate an andesitic block and a subvolcanic intrusion the principal vein is one of the longest hydrothermal veins in europe with more than 5 km in length a thickness that varies between 0 5 and 22 m and it extends vertically on more than 800 m samples belonging to different levels of principal vein have been analyzed using electron microprobe a new occurrence of bismuth minerals was identified within the deeper part of the deposit bismuthinite lillianite gustavite disordered intergrowths of lillianite homologues heyrovskyite and cosalite the presence of bi sulfosalts suggests temperature of 350 c while the as content in arsenopyrite indicates formation temperatures between 320 and 360 c the oscillatory zoning bands of pyrite and tetrahedrite tennantite members indicate an increased sb and as concentration in hydrothermal solutions the zoning textures suggest a high s and low as concentration in the early fluids followed by multiple pulses of as rich solutions in the late fluids the high content of as in pyrite and the presence of bismuth minerals at baia sprie deposit can represent indicators for significant au concentrations within the lower level of the mineralization from the type locality baia sprie new analytical data for semseyite were presented and for the first time a new occurrence of geocronite jordanite series was identified in the intermediate and upper part of the deposit

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

physical modeling of an underground roadway excavation in geologically 45 inclined rock using infrared thermography abstract physical modeling of excavation of a roadway tunnel in the geologically 45 inclined rock strata by using a newly developed physical modeling approach the so called physically finite elemental slab assemblage pfesa together with infrared ir thermography were conducted for visualization and observation of the progressive development of the excavation damaged zone edz the excavation was schemed as two phases i e phase 1 the full face excavation and phase 2 the staged excavation the experiment was performed under unbalanced confinement found in underground coal mining the relative temperatures of the excavation zone were mapped by the ir camera in real time and over the entire field into thermography series which were processed using such procedures as statistics noise removal and spectral frequency analysis for image feature extraction irt defined as the statistical mean of the thermography matrix was used as a measure of rock responses characterizing the full face excavation and the staged excavation as a multi linearity and nonlinearity processes respectively by its time marching scheme the temporal and spatial evolutions of the edz were described in detail by the denoised thermographies directional propagations of the excavation induced stress wave were characterized by the spectral frequency analysis of the resultant thermographies

evidence for enhanced mixing over rough topography in the abyssal ocean the overturning circulation of the ocean plays an important role in modulating the earth s climate but whereas the mechanisms for the vertical transport of water into the deep ocean deep water formation at high latitudes and horizontal transport in ocean currents have been largely identified it is not clear how the compensating vertical transport of water from the depths to the surface is accomplished turbulent mixing across surfaces of constant density is the only viable mechanism for reducing the density of the water and enabling it to rise however measurements of the internal wave field the main source of energy for mixing and of turbulent dissipation rates have typically implied diffusivities across surfaces of equal density of only approximately 0 1 cm2 s 1 too small to account for the return flow here we report measurements of tracer dispersion and turbulent energy dissipation in the brazil basin that reveal diffusivities of 2 4 cm2 s 1 at a depth of 500 m above abyssal hills on the flank of the mid atlantic ridge and approximately 10 cm2 s 1 nearer the bottom this amount of mixing probably driven by breaking internal waves that are generated by tidal currents flowing over the rough bathymetry may be large enough to close the buoyancy budget for the brazil basin and suggests a mechanism for closing the global overturning circulation

mineralogy and textural relationships among sulphosalts and related minerals in the bleikvassli zn pb cu deposit nordland norway several distinct assemblages of pb sb pb as cu pb sb and cu fe zn sn sulphosalts are identified in sulphide samples from bleikvassli mine norway detailed optical microscopy and electron probe microanalysis have permitted investigation of textural relationships between minerals and compositional variations between different ore types tetrahedrite typically containing 10 16 wt ag rare freibergite containing 25 30 wt ag has also been identified in two samples stannite cu2 fe zn sns4 and meneghinite cupb13sb7s24 are widely distributed as trace constituents throughout massive pyritic and galena rich ores native antimony and pyrargyrite occur in trace amounts in all ore types as the breakdown products of earlier sulphosalts several distinct types of wall rock mineralisation are present at bleikvassli of considerable mineralogical interest are the coarse grained sulphide mobilisates within the wall rock which contain a distinct and characteristic suite of pb as sulphosalts tennantite jordanite pb14as6s23 seligmannite cupbass3 dufrenoysite pb2as2s5 bournonite cupbsbs3 is the only sb bearing sulphosalt recognised in significant amounts within the mobilisates meneghinite and tetrahedrite being conspicuously absent these mobilisates display considerable au enrichment electrum can be confirmed intimately associated with jordanite and tennantite appreciable sb up to 3 wt is contained within galena in the mobilisates in contrast to galena from massive ores which contains only negligible sb contents of ag and bi in galena vary considerably in all ore types but confirm earlier suggestions that galena is a major ag carrier at bleikvassli boulangerite pb5sb4s11 jamesonite fepb4sb6s14 and gudmundite fesbs occur in trace amounts sn sulphosalts are represented by kesterite cu2 zn fe sns4 but commonly zoned with respect to zn fe ratio in the mobilisates rather than by stannite a rare type of mobilisate also in the wall rock in which chalcocite and bornite are the main minerals contains native ag stromeyerite agcus mckinstryite ag cu 2 s ag free tetrahedrite an unnamed cu ag fe sulphide cu3ag2fes4 and native bi myrmekitically intergrown with chalcocite although a comprehensive genetic model for the wall rock mineralisation at bleikvassli is largely impossible given the limitations in the present state of knowledge regarding mechanisms involved in remobilisation processes a multi stage model of remobilisation during regional metamorphism is considered to best explain the observations an interplay of different solid and liquid state remobilisation mechanisms in various combinations is required to account for the macro and microscopic observations remobilisation probably began during the earlier stages of metamorphism with crystallisation and further remobilisation taking place during the entire metamorphic cycle giving rise to the extensive chemical and mineralogical diversity observed today preserved mineral assemblages and their textural relationships reflect a complex sequence of replacement and decomposition reactions taking place during the latest phase of late metamorphic crystallisation and subsequent cooling

determination of diapycnal diffusion rates in the upper thermocline in the north atlantic ocean using sulfur hexafluoride 1 the apparent diapycnal diffusivity below the wind driven surface mixed layer of the ocean was determined in an anticyclonic eddy in the eastern north atlantic using sulfur hexafluoride sf6 tracer data collected in june 1998 in this tracer experiment the downward penetration of sf6 was measured for 3 weeks following the deliberate injection of sf6 in the surface mixed layer the resulting data were used to constrain the one dimensional fickian diffusion model to estimate the diapycnal diffusivity the model also includes the lateral diffusion component so that it can more accurately represent the time evolution of the sf6 concentrations along the isopycnal surface this affects the estimation of the diapycnal diffusivity for the upper thermocline immediately below the surface mixed layer we estimated the diapycnal diffusivity for the 3 week period as 0 3 0 2 cm2 s 1 at a buoyancy frequency of 8 2 cph

mixing of a tracer in the pycnocline a patch of sulfur hexafluoride was released in may 1992 in the eastern north atlantic on an isopycnal surface near 300 m depth and was surveyed over a period of 30 months as it dispersed across and along isopycnal surfaces the diapycnal eddy diffusivity k estimated for the first 6 months was 0 12 0 02 cm2 s while for the subsequent 24 months it was 0 17 0 02 cm2 s the vertical tracer distribution remained very close to gaussian for the full 30 months as the root mean square rms dispersion grew from 5 to 50 m lateral dispersion was measured on several scales the growth of the rms width of the tracer streaks from less than 100 m to approximately 300 m within 2 weeks implies an isopycnal diffusivity of 0 07 m2 s at scales of 0 1 to 1 km larger than expected from the interaction between vertical shear of the internal waves and diapycnal mixing teasing of the overall patch initially about 25 km across into streaks with an overall length of 1800 km within 6 months supports predictions of exponential growth by the mesoscale strain field at a rate of 3 0 5 10 7 s 1 the rms width of these streaks estimated as 3 km and maintained in the face of the streak growth indicates an isopycnal diffusivity of 2 m2 s at scales of 1 to 10 km much greater than expected from internal wave shear dispersion the patch was painted in albeit streakily by 12 months confirming expectations from analytical and numerical models homogenization of the patch continued during the subsequent 18 months while the patch continued to spread with an effective isopycnal eddy diffusivity on the order of 1000 m2 s acting at scales of 30 to 300 km

hydrothermal alteration associated with gold mineralization in the southern apuseni mountains romania preliminary sr isotopic data precious metal mineralization in the southern apuseni mountains of western romania is hosted by mid miocene 14 ma andesitic stocks and lava flows the mineralized veins are surrounded by aureoles of hydrothermal alteration consisting of quartz sericite k feldspar pyrite and calcite the alteration process caused a total homogenization of initial 87sr 86sr in the rocks ages determined for the hydrothermal alteration are 13 7 15 7 ma indicating that hydrothermal alteration immediately followed igneous activity furthermore a large influx of radiogenic sr took place during alteration this sr probably being derived from the hydrothermal leaching of continental meta sedimentary rocks in the basement

microseismic monitoring and stability evaluation for the large scale underground caverns at the houziyan hydropower station in southwest china abstract the stability of underground caverns and the excavatability of rock masses are important for geotechnical engineering practices during the design and construction stages the risks associated with underground caverns at the houziyan hydropower station in southwest china are growing due to excavation induced unloading to assess the instability of underground caverns and resolve the complex subsurface conditions of the highly fractured rock mass a high resolution microseismic monitoring system was established in deep underground caverns this system was used to determine the relationship between the measured microseismic activities and the excavation damage zones of the surrounding rock mass the excavation damage zones and potential risk regions in the underground caverns were identified by analyzing the tempo spatial distribution of microseismic activities in addition the correlation between microseismic activities and pre existing geological structures was determined and traditional monitoring results were analyzed to validate the correlation between seismicity and the excavation damaged zones of the underground caverns a numerical model was employed to further evaluate the deformation and stability of the surrounding rock mass the monitoring results demonstrate that microseismic events mainly occurred in high stress concentration regions corresponding with the results obtained from the numerical analysis therefore this comprehensive method which incorporates microseismic monitoring numerical analysis traditional monitoring and field observations is promising for predicting the deformation and instability of surrounding rock masses in the underground caverns subjected to excavation

deformation forecasting and stability analysis of large scale underground powerhouse caverns from microseismic monitoring abstract to assess the stability of the underground powerhouse caverns and analyse the failure mechanism of the surrounding rock mass at the baihetan hydropower station in southwest china a high resolution microseismic ms monitoring system was implemented in the left bank underground powerhouse caverns based on the temporal and spatial distribution of ms events the correlation between ms activities and construction was established and three damage regions for the surrounding rock mass during excavation were identified ms clusters were found to occur most often in stress concentration regions of the underground powerhouse caverns and to result from various factors including excavation induced unloading and geological structure activation the seismic source parameters i e moment magnitudes and s wave to p wave energy ratios e s e p of the three ms clusters demonstrate the different failure modes and risks of the surrounding rock mass the temporospatial evolution of the ms activities apparent stress and cumulative apparent volume in localized rock mass during the period of a typical large deformation were used to develop a comprehensive analytical method for forecasting the deformation of the surrounding rock mass thus this comprehensive analytical method which incorporates ms monitoring conventional monitoring geological survey and construction is promising for identifying the damage zones and forecasting the macro deformation of the surrounding rock mass in underground powerhouse caverns subjected to excavation

a fractional crystallization model for the deposition of argentian tetrahedrite electron microprobe analyses of natural hydrothermal tetrahedrites reveal that most specimens are heterogenous in composition a simplified formula for natural tetrahedrite showing the three common solid solutions is cu ag 10 fe zn 2 sb as 4 s 13 variations in ag and sr are positively correlated within each individual sample however the mathematical slopes and intercepts of the linear correlations are different for different samples and the bulk composition of the samples varies with position within the ore deposit nearly 5 000 new point analyses are presented for tetrahedrites from coeur d9alene idaho and orcopampa and julcani peru to document these observations heterogeneity within a single sample could arise when a particular depositional site receives more and less evolved fluids at different times modified journal abstract

sulphur hexafluoride as a tracer of biogeochemical and physical processes in an open ocean iron fertilisation experiment abstract the first open ocean experiment to test the iron hypothesis in the equatorial pacific was undertaken using the tracer gas sulphur hexafluoride sf 6 to locate and track the fertilised surface water continuous surface measurements showed that the sf 6 patch spread rapidly in the first 24 h from an initial release area of 64 km 2 to a total area of 214 km 2 and remained relatively constant in size for the following three day period sf 6 data was mapped in a lagrangian frame of reference by the use of a drogued gps buoy released at the centre of the patch the sf 6 patch remained coherent and exhibited a slow anti cyclonic oscillation during the first four days the buoy was transported downwind of the patch in a northwesterly direction within two days which has implications for the future use of buoys in surface water advection studies following subduction below a low salinity front 3 4 days after release the patch centre was relocated by its sf 6 signal at a depth of 25 30 m to the east of the residual surface patch the latter spread rapidly to the southwest during the remainder of the experiment whilst the subducted patch remained relatively stationary density corrected sf 6 profiles were used to calculate a mean vertical eddy diffusivity of 0 25 cm 2 s across the thermocline following the subduction event a vertical flux of nitrate of 2 5 mmol m 2 d 1 into the mixed layer was estimated which implied an f ratio value of 0 4 on comparison with productivity data the results demonstrate that sf 6 is a successful tracer of water masses and emphasise the potential of this technique for the in situ measurement and manipulation of open ocean processes

mineralogy and geochemistry of pb sb as sulfosalts from coranda hondol ore deposit romania conditions of telluride deposition abstract electron microprobe analyses are reported on newly identified occurrences of pb sb as sulfosalts from the coranda hondol ore deposit certej area south apuseni mountains romania the coranda hondol deposit is an intermediate sulfidation au ag epithermal system hosted in propylitic altered andesitic rocks covered by cretaceous and neogene sediments the main base metal sulfides are sphalerite pyrite and galena subordinate amounts of chalcopyrite arsenopyrite pyrrhotite marcasite tetrahedrite tennantite bournonite seligmannite geocronite jordanite stibnite and au ag tellurides complete the paragenetic sequence gangue minerals are quartz calcite and barite hydrothermal alteration is expressed as pyritisation silicification potassic alteration carbonitisation and phyllic or sericitic alteration minerals of the bournonite seligmannite and geocronite jordanite series are described for the first time in samples from different levels of the coranda hondol open pit both series show chemical variations in terms of sb as sb ratio and display a general spatial trend within the deposit in which the sb content of both series tends to increase towards upper levels textural relationships between the two sulfosalt series and their chemical variations suggest that the presence of sb in hydrothermal fluids favors precipitation of bournonites whereas as favors precipitation of jordanites compositions of minerals from the bournonite seligmannite and geocronite jordanite series extend from bnn35 to bnn98 and from gcn14 to gcn76 respectively back scattered electron imaging reveals grain scale compositional heterogeneity in bournonite seligmannite seen as concentric and layered oscillatory zoning patterns these zoning patterns were observed only in the upper parts of the deposit and suggest an increasing as content in late fluids trace elements te se and fe are preferentially incorporated into sb rich members of bnn slg series this is consistent with the association of gold silver tellurides and bournonites identified at the coranda hondol deposit variable conditions within the coranda hondol hydrothermal system suggest that precipitation of au ag tellurides occurred via two possible mechanisms i te vapor condensation into precious metal brines during boiling and ii by fluid throttling with periodic release of volatiles

lead isotope signatures of epithermal and porphyry type ore deposits from the romanian carpathian mountains lead isotope analyses have been performed on the two major miocene mining districts of romania baia mare and apuseni mountains these two districts have different non overlapping 206pb 204pb isotopic signatures ranging from 18 752 to 18 876 and 18 497 to 18 740 in the baia mare district epithermal deposits are overall homogeneous in their lead isotopic compositions and have values similar to the average of the calc alkaline volcanic rocks these results suggest a magmatic signature for the pb and possibly other metals in the hydrothermal fluids however magmas in this district show isotopic evidence of crustal assimilation in the southern apuseni mountains the lead isotope compositions of sulfide minerals in porphyry copper deposits are clustered confirming that pb and probably other metals were derived principally from associated porphyry stocks on the other hand lead isotope data on sulfides in epithermal ore deposits are much more scattered indicating a notable contribution of pb from local country rocks in the apuseni mountains fertile volcanics are few and appear to come from a more primitive mantle derived source most of the analysed volcanic rocks seem barren differences in lead isotopic compositions between the baia mare district and the apuseni mountains are due to a different basement and probably to variations in crustal assimilation superimposed on variations in the mantle source composition in the apuseni mountains pb may be partly inherited from the previous mesozoic magmatic hydrothermal stage from a geodynamic point of view it seems that the nature and the source of volcanic rocks and their position related to the collision area of the carpathian arc are not the only factors controlling the fertility of a volcanic district