vertical profile of artificial radionuclide concentrations in the central arctic ocean abstract the artificial radionuclides 90 sr 137 cs 238 pu 239 240 pu and 241 am have been measured in eight water samples collected in 1979 at intervals from surface to bottom through the ice at the lorex satellite camp ss near the north pole differences in the concentrations and ratios of these nuclides compared with values measured over time in the various water masses that flow into the arctic ocean can be used as semi independent checks on rates of flow to the lorex stations and on residence times in the arctic ocean an unexpected finding was that water labelled with low level liquid waste from the windscale plant on the irish sea is a major component of the 1500 m lorex sample and has reached there in no more than eight to ten years even from this one station in the polar ocean estimation of the inventories of the various radionuclides is good enough to emphasize the importance of horizontal advection of the various supply terms to the arctic

temporal variations in coda duration of local earthquakes in the wellington region new zealand temporal variations of coda duration relative to event magnitude for local earthquakes near wellington have been investigated the region is one of plate convergence and subduction the data consist of routinely made observations for events from 1978 through 1985 1552 events magnitude 1 6 to 5 2 depth 0 5 to 90 0 km the observed average over time correspondence between duration as measured from the origin time and magnitude is reasonably well predicted by the single backscattering theory of coda formation for events of magnitude 4 or less for larger events the observed durations are longer than predicted this theory predicts that a temporal increase in scattering attenuation will reduce the coda duration relative to magnitude thus any temporal changes in the duration magnitude relation can be interpreted in terms of changes inq however it is necessary to consider spatial biases since the observed durations are relatively long for shallow events and for events of all depths at stations situated in the south eastern half of the region usually believed part of the accretionary border for both these situations other evidence would suggest that the scattering coefficient would be relatively high lowq these observations may be due to a relatively high component of surface wave scattering and the importance of multiple scattering in the later part of the coda in regions of lowq as suggested by finite element studies of coda formation despite the lack of any significant earthquakes during the 1978 1985 period there is nevertheless a significant temporal change in duration observed in the wellington region a change from relatively long to relatively short codas occurred in mid 1981 this change correlates well with changes in the rate of activity b value radon emission and ground tilt as derived from lake levels it is not yet clear how all these parameters are related physically but an episode of aseismic slip or creep along the plate interface below the region may have been the cause

jurassic penetrative deformation and cenozoic uplift in the central high atlas morocco a tectonic model structural and orogenic inversions the central high atlas is characterized by a relatively mild deformation with a local development of a more or less penetrative cleavage in the axial part of the belt locally this cleavage and the plutonic bodies which outcrop in the core of most of the north east trending anticlines ridges with intrusions are overlain by a disconformable sequence that comprises red clastic deposits which are capped by cenomano turonian limestones the age of these red deposits are bracketted between bathonian to mid cretaceous therefore the spatial relationship of the cleavage with mafic intrusions in the axial part of the central high atlas suggests that it developed contemporaneously with the emplacement of magmas probably during mid jurassic times during this period the structural inversion occurred from a transtensional regime to a transpressive regime there are few indications that an important shortening persisted within the axial part of the central high atlas after the end of the jurassic along the northern and the southern borders of the belt however cretaceous and cenozoic strata were deposited their sedimentary facies bear witness of successive stages of the atlas evolution especially the rapidly coarsening up of the clastic deposits since the oligocene in these marginal basins indicates the onset of the rising up of the belt i e the orogenic inversion

formation of willemite in hydrothermal environments willemite zinc silicate is the main zinc mineral in some carbonate hosted ore deposits e g franklin new jersey vazante brazil beltana south australia kabwe zambia recent interest in these unconventional zinc deposits has increased because of high zinc grades that exceed 40 wt percent relatively low environmental impact of ore processing owing to the lack of acid generating sulfides in the waste and advances in ore processing technologies in the past most metallogenic studies proposed formation of willemite deposits by supergene or hypogene alteration of preexisting sulfide deposits however recent data on the vazante beltana and kabwe deposits indicate willemite crystallization at temperatures in excess of 150 c raising the possibility of primary precipitation from hydrothermal fluids we use numerical geochemical modeling to examine the formation of willemite under hydrothermal conditions activity activity diagrams reveal that in the presence of dissolved sulfur and quartz willemite instead of sphalerite will precipitate under oxidizing e g hematite stable sulfate predominant and alkaline ph higher than k feldspar muscovite quartz conditions willemite also becomes more stable relative to sphalerite at high temperature and willemite can coexist with magnetite at 300 c the stabilities and solubilities of sphalerite willemite smithsonite hydrozincite and zincite were calculated for wide ranges of temperature 25 300 c chloride concentration dissolved sulfur and carbon concentrations ph quartz saturation and oxidation potential plots of the solubility of the different minerals as a function of two variables e g temperature and redox state ph and redox state allow us to predict the effects of changing chemical conditions which in turn permits an estimate of the efficiency of particular precipitation processes cooling is an effective process for precipitating sphalerite but not willemite whereas ph increase e g by acidic fluids reacting with carbonates is effective for precipitating willemite but not sphalerite dynamic geochemical models that simulate physicochemical processes are used to understand the formation of the beltana willemite deposit in the adelaide geosyncline of south australia this small high grade deposit 850 000 t at 36 zn is hosted in dolomite of the cambrian ajax limestone next to a tectonic contact with the diapiric halite bearing clastic sediments of the callanna group the orebody is associated with hematite alteration and is characterized by the total absence of sulfides willemite is the only zinc ore mineral and the arsenate hedyphane ca 2 pb 3 aso 4 3 cl is the main lead mineral the model results show that willemite will precipitate in response to water rock interaction and fluid mixing processes at temperatures above 120 c the presence of arsenate in the hydrothermal fluid is likely to have been important at beltana in arsenate absent models sulfate is reduced to sulfide by the precipitation of ferrous iron as hematite resulting in the precipitation of sphalerite and galena in contrast in models including arsenate the reduction of sulfate to sulfide is inhibited and willemite is predicted to precipitate

neutralization of sulfuric acid solutions by calcite dissolution and the application to anoxic limestone drain design abstract batch reactor br experiments were conducted to measure the effect of hydrodynamics and gypsum coatings on calcite neutralization rates a factorial array of br experiments measured the h concentration change by calcite dissolution over a ph range of 1 5 3 5 and na2so4 concentrations of 0 1 m the rate of h concentration change with time was determined by numerical differentiation of h concentration versus time regression modeling showed that for uncoated calcite rates are only significantly affected by ph r 10 2 32 a h 0 76 whereas for calcite coated with gypsum only time had a significant effect on calcite dissolution rates r 10 1 96t 0 53 because transport limited dissolution rates for uncoated calcite are a function of the ph and reynolds number a model was developed to express the effects of these two variables on the rate of h consumption for a solution with a darcy velocity q through a porous medium with a particle radius rp such that r 1 08 10 3 q 0 31 r p 0 69 m h 0 87 this equation was integrated via a numerical model to simulate the performance of an idealized anoxic limestone drain ald this model predicts the ph and alkalinity change along the length of an ald the model shows that the efficiency of an ald is greater when the darcy velocity is low and the particle radius is small in addition the growth of gypsum coatings causes the rate of h neutralization to decline as the square root of time as they form and block the h transport to the calcite surface supersaturation with respect to gypsum leading to coating formation can be avoided by diluting the ald feed solution or by replacing limestone with dolomite

seismic guided waves trapped in the fault zone of the landers california earthquake of 1992 a mobile seismic array of seven stations was deployed at 11 sites along the fault trace of the m7 4 landers earthquake of june 28 1992 with a maximum offset of 1 km from the trace we found a distinct wave train with a relatively long period following the s waves that shows up only when both the stations and the events are close to the fault trace this wave train is interpreted as a seismic guided wave trapped in a low velocity fault zone to study the distribution of amplitude of the guided waves with distance from the fault trace and also their attenuation with travel distance along the fault zone we eliminated source and recording site effects by the coda normalization method the normalized amplitudes of guided waves show a spectral peak at 3 4 hz which decays sharply with distance from the fault trace spectral amplitudes at high frequencies 8 15 hz show an opposite trend increasing with distance from the fault trace the normalized amplitudes of guided waves at 3 4 hz also show a systematic decrease with hypocentral distance along the fault zone from which we infer an apparent q of 50 in order to confirm the existence of the guided waves a dense array of 31 stations was deployed at one of the 11 sites the resultant records revealed unequivocal evidence for the existence of guided waves associated with the fault zone by modeling the waveforms as s waves trapped in a low velocity waveguide sandwiched between two homogeneous half spaces with velocity vs 3 0 km s we infer a waveguide width of about 180 m a shear velocity of 2 0 2 2 km s and a q of 50 hypocenters of aftershocks with clear guided waves show a systematic distribution both laterally and with depth delineating the extent of the low velocity fault zone in three dimensions we find that the zone extends to a depth of at least 10 km this zone apparently continues to the south across the pinto mountain fault because guided waves are observed at stations north of the pinto mountain fault for earthquakes with epicenters south of it on the other hand the zone appears to be discontinuous at the fault bend located about 20 km north of the mainshock epicenter guided waves were observed for stations and epicenters which are located on the same sides of the fault bend but not for those on the opposite sides

the calamine nonsulfide zn pb deposits of belgium petrographical mineralogical and geochemical characterization abstract the belgian nonsulfide zn deposits represent the historical basis for the zinc mining and smelting industry in europe the zinc ores were called calamines and consist of a mixture of zn carbonates smithsonite hydrozincite and zn silicates hemimorphite willemite and zn clays with a variable content of pb minerals the calamines are considered to be oxidation products of primary sulfide ores the most important was the la calamine orebody more than 600 000 tons of zn metal that was continuously exploited for several centuries nonsulfide ores were also exploited at schmalgraf engis dickenbusch fossey rocheux oneux welkenraedt and in other smaller deposits all no longer accessible for study where the calamines extended from the surface to an average depth of 40 to 50 m the primary zn pb sulfide mineralization consists of post variscan hydrothermal veins and replacement bodies mostly occurring in the dinantian visean limestones the sulfides intersect the paleozoic rocks and are truncated and unconformably covered by late cretaceous sediments santonian aachen fm the same setting has been observed for the nonsulfide ores suggesting an early to mid cretaceous weathering consistent with other geological and geochronological data on paleoweathering in europe the extensive occurrence of willemite that appears to be the first deposited nonsulfide mineral is a striking particularity of the belgian calamines most fluid inclusions in willemite 80 and all inclusions in smithsonite are monophase aqueous ice melting temperatures suggest salinities between 0 and 5 wt nacl equiv homogenization temperatures of rare two phase inclusions liquid vapor in willemite display a large variation between 80 and 190 an interval matching the temperature ranges of other willemite ores throughout the world so far considered of hydrothermal origin the stable isotope variation of belgian smithsonites and cerussites is very similar to the range measured in other supergene nonsulfide deposits similar to those of sw sardinia belgian smithsonites exhibit a limited range of 18o values from 27 1 to 30 6 averaging 28 4 0 8 v smow this limited range points to a relatively uniform isotope composition of the oxidizing waters and constant temperatures of smithsonite crystallization carbon isotope values even from the same mine show a considerable range from 11 6 to 1 6 this extensive range indicates at least two carbon sources 13c depleted carbon derived from the organic matter in the soils and 13c enriched carbon originating from marine carbonate host rocks cerussites have oxygen isotope values ranging from 16 8 to 19 3 averaging 17 8 1 0 and carbon isotope values of 18 4 to 14 7 the metallic deposits of eastern belgium have undergone a polyphase history which started with a possibly jurassic sulfide mineralization followed by oxidation under high silica activities and consequently by supergene weathering owing to structure and mineralogical association we do not consider the high homogenization temperatures as reliable minimum temperature estimates of willemite formation however it is possible that the willemite concentrations could have been derived from low temperature localized hydrothermal processes caused by deeply reaching oxidizing fluids smithsonite and hemimorphite often developed at the expenses of willemite have all the characteristics of supergene oxidation products

zincian dolomite a peculiar dedolomitization case a peculiar dedolomitization phenomenon is associated with the supergene alteration of zn pb sulfide ores resulting in the precipitation of newly formed carbonate phases in addition to the deposition of calcite and several metal carbonates this phenomenon results in a widespread replacement of host rock dolomites by zincian dolomite phases dolomite samples have been collected in the oxidation zone of the mining districts of southwestern sardinia italy yanque peru and jabali yemen and the results compared with data sets from upper silesia poland and namibia in all districts zn dolomite as much as 20 zno replaces the previous dolomite phases through fractures and along crystal growth zones and smithsonite znco 3 may be high in mg to 15 mgo zn dolomites are produced by the reaction of metal carrying and o rich meteoric fluids with preexisting dolomite bodies hosting zn sulfide ores subjected to active weathering their occurrence in the oxidation zone of the sulfide deposits corroborates their supergene origin the ample extent of the zn dolomite replacement bodies underestimated so far is important for the exploration of nonsulfide zn ores because it may lead to an incorrect evaluation of the extractable metallic resources calculated from the assay data

simulations of anomalous seismogram envelopes at coda portions abstract two models of coda wave envelope formation based on single isotropic scattering in complicated inhomogeneous structures are tested to explain anomalous seismogram envelopes observed at the coda portion one is a hybrid model with a reflector embedded in a scattering medium the seismogram envelope composed of scattered waves is calculated from the summation of the energy density of coda waves for the real source and the mirror image source the size of the reflector affects the duration of the anomalously large amplitude coda envelope following the reflected wave the second model is a simulation of coda waves in a medium which is composed of many small cubic blocks three dimensional variation of the attenuation and scattering intensity is represented adequately by combination of blocks the energy density of coda waves is calculated with the scattering coefficient of the block which includes the scattering point and the attenuation factor integrated along the ray path of each scattered wave coda envelopes based on the two models are simulated in order to explain anomalous seismogram envelopes which are observed in japan in the kanto area central part of japan reflected s waves from the upper boundary of the subducting pacific plate are observed for shallow events and generate large amplitude wave trains in the coda portion the parallel distribution of coda decay curves following the direct s wave and the reflected s wave is explained by the large extension of the reflector the large amplitude offset requires a two layer structure in the distribution of the scattering and attenuation intensity in awaji island western part of japan the coda amplitude does not decrease for about 10 s after the arrival of the direct s wave for shallow local events the simulation of coda waves with a two layer strong scattering body for s waves ranging from about 20 to 30 km in depth might explain the flat portion of the observed s coda envelope the simulation of p wave seismogram envelopes for the artificial blast suggests that there exists a strong scattering body for p waves ranging from 20 to 25 km in depth the lower crust beneath the northern part of awaji island might be strongly inhomogeneous not only for s waves but also for p waves

supergene nonsulfide zn pb mineralization in the mehdiabad world class sub seafloor replacement sedex type deposit iran the world class mehdiabad nonsulfide deposit consists of several accumulations of zn pb fe nonsulfide minerals derived from supergene of a vent proximal sub seafloor replacement sedex type deposit hosted in lower cretaceous clastic carbonate rocks of the taft and abkuh formations the main sulfides are galena sphalerite pyrite and minor amounts of chalcopyrite which have been partially or completely transformed into nonsulfide minerals by supergene processes currently the zn mineralization in the abkuh formation ore horizon ii is almost fully oxidized the mehdiabad deposit which can be assigned to both direct replacement and wall rock replacement types the time of the formation of the nonsulfide deposit has not been determined but it is probable that the main supergene metallogenesis happened during tertiary possibly between post cretaceous to present the mineralogy of the nonsulfide mineralization is generally complex and consists of smithsonite hydrozincite and hemimorphite as the main economic minerals accompanied by cerussite anglesite iron manganese oxy hydroxides sauconite and zn rich clays commonly nonsulfide minerals in this deposit consist of two types of ore red zinc ore rzo rich in zn fe pb as and white zinc ore wzo typically with very high zinc grades but low concentrations of iron and lead the proposed three step scenario for the deposition of nonsulfide mineralization in the mehdiabad deposit comprises 1 the deposition of primary sulfides contemporaneous with lower cretaceous clastic carbonate host rocks to form sedex type mineralization 2 during the late cretaceous to present regional uplift leads to deformation folding and thrusting of sulfide bearing lower cretaceous sequence and 3 as a result zn pb fe sulfides hosted in carbonates experienced oxidation under an arid warm climate to form the supergene nonsulfide ore mineralizations

artificial radionuclide tracer supply to the denmark strait overflow between 1972 and 1981 measurements of the concentrations of the artificial radionuclides 3h 137cs and 90sr in the northern irminger sea in 1972 and 1981 are reported in both years tracer measurements from this area included data from samples of the dense overflow water from the north through denmark strait all three tracers were strongly correlated inversely with salinity in the dense outflows the tracer maxima being related directly to the salinity minimum when the tracer characteristics in the outflows in 1972 and 1981 were compared concentrations of all in 1981 were observed to be about double the 1972 values the individual tracer concentrations on a decay corrected density normalized basis were higher in increasing order 90sr 93 3h 115 137cs 150 the relatively greater increases for 3h and 137cs were attributed to contributions of new sources of these tracers in northern surface waters the 3h source is argued to derive from atmospheric hydrological recycling whereas the 137cs source is identified as the input to the greenland and iceland seas of advected european nuclear fuel reprocessing wastes both the tracer and hydrographic data are used to identify northern locations of intermediate water formation capable of supplying the observed dense overflow water characteristics it is argued from the time taken for the overflow water to reflect the new surface 137cs source that transport from the source to the overflow can be quite rapid about 2 years

the residence time of the freshwater component in the arctic ocean the time function of bomb tritium concentrations in river runoff to the arctic ocean has been reconstructed from published data on tritium in precipitation 1959 1975 tritium measurements on oceanic samples through the halocline exhibit strong linear relationships between tritium concentrations tu values and salinity these waters thus look like binary mixtures of atlantic source water and freshwater runoff combining these data the vintage of the freshwater component in the arctic basin has been determined assuming no other major tritium source the relation indicates the average age of the freshwater component to be 11 1 years in the nansen basin and the outflow and somewhat higher in the canada basin according to tritium salinity data a surface layer of 10 60 m is affected by sea ice melting and freezing in the nansen basin and the thickness of this layer increases to 150 170 m toward the canada basin there is tritium also in the deeper waters the unmixed atlantic water which points at residence times for that water not to exceed 17 years the appendix is available with the entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j81 012 1 00 payment must accompany order

can moroccan atlas lithospheric thinning and volcanism be induced by edge driven convection terra nova 24 27 33 2012 abstract the moroccan lithosphere is characterized by an anomalously thinned area located beneath the atlas domains which forms a singular narrow ne sw directed strip overlain by cenozoic alkaline volcanism the origin of this thinning and volcanism is still a matter of debate the proposed models invoke processes either related to the mediterranean slab or mantle plumes herein we propose an alternative edge driven convection edc model involving small scale convection at the boundary between the west african craton and the atlas lithosphere our comparison of the atlas lithosphere velocity and volcanism episodes during the last 80 ma points out that volcanism occurs when plate moves at velocities c 1 cm a 1 a velocity sufficiently low to trigger edc this is the first process that could explain the c 20 ma volcanism shutdown separating the two volcanic episodes of the atlas in addition it may successfully account for the lithosphere thinning location and geometry and volcanism geochemistry

mineralogical and geochemical characterization of the riopar non sulfide zn fe pb deposits prebetic zone se spain abstract the present paper reports the first detailed petrological and geochemical study of non sulfide zn fe pb deposits in the riopar area prebetic zone of the mesozoic betic basin se spain constraining the origin and evolution of ore forming fluids in riopar both sulfide and non sulfide zn fe pb calamine ores are hosted in hydrothermally dolomitized lower cretaceous limestones the hypogene sulfides comprise sphalerite marcasite and minor galena calamine ores consist of zn carbonates smithsonite and scarce hydrozincite associated with abundant fe hydr oxides goethite and hematite and minor pb carbonates cerussite three smithsonite types have been recognized i sm i consists of brown anhedral microcrystalline aggregates as encrustations replacing sphalerite ii sm ii refers to brownish subhedral aggregates of rugged appearance related with fe oxi hydroxides in the surface crystals which replace extensively sphalerite and iii sm iii smithsonite appears as coarse grayish botryoidal aggregates in microkarstic cavities and porosity hydrozincite is scarce and appears as milky white botryoidal encrustations in cavities replacing smithsonite also two types of cerussite have been identified i cer i cerussite consists of fine crystals replacing galena along cleavage planes and crystal surfaces and ii cer ii conforms fine botryoidal crystals found infill porosity calcite and thin gypsum encrustations were also recognized the field and petrographic observations of the riopar non sulfide zn fe pb revealed two successive stages of supergene ore formation under meteoric fluid processes i gossan and red calamine formation in the uppermost parts of the ore with deposition of fe hydr oxides and zn and pb carbonates sm i sm ii and cer i occurring as direct replacements of zn pb sulfides and ii gray calamine ore formation with deposition of sm iii cer ii and hydrozincite infilling microkarst cavities and porosity the stable isotope variation of riopar smithsonite is very similar to those obtained in other calamine ore deposits around the world their c o isotope data 18 o 27 8 to 29 6 v smow 13 c 6 3 to 0 4 v pdb puts constrains on i the oxidizing fluid type which was of meteoric origin with temperatures of 12 to 19 c suggesting a supergene weathering process for the calamine ore formation under a temperate climate and ii the carbon source that resulted from mixing between two co 2 components derived from the dissolution of host dolomite 13 c enriched source and vegetation decomposition 13 c depleted component

mixing in the west spitsbergen current abstract twenty eight profiles of temperature and salinity down to 1 km depth have been measured in the area north from the coast of svalbard to latitude 84 40 n between 0 and 32 e longitude they show atlantic waters of the west spitsbergen current entering the arctic ocean in a bifilimentary mode one filament following the coastline and the other 300 km farther north apparently following the continental shelf break the profiles show these filaments mixing into the ambient water in a series of intrusive layers which are remarkably uniform over distances of hundreds of kilometers a triple peak structure at the atlantic water maximum is the dominant oceanographic characteristic of the area with salt fingering occurring on the upper surface of the cold intrusions and indications of double diffusive exchanges through the lower surface a system or eddies or meanders is postulated as the mechanism for the production of multiple fronts allowing the intrusive layers to extend to distances much greater t

pb zn deposits and salt bearing diapirs in southern europe and north africa many diapirs with triassic evaporite successions in southern europe and north africa are accompanied by strata bound pb zn mineral deposits these are of two types 1 epigenetic mineralization filling cavities exhibiting analogies with mississippi valley type deposits and 2 syndiagenetic mineralization in sediments rich in organic materials this second type is very similar to the so called volcanic exhalative type in most of these ore deposits diapirism seems to be a determining factor in the development of base metal concentrations diapir growth can be divided into four distinct stages initiation ascent piercement and subsequent deformation study of north african and southern european deposits has led to a genetic model of diapir emplacement and associated pb zn mineralization the source of these metals is unknown the transport of the metals is provided or facilitated by the brine from adjacent triassic evaporites deposition of sulfides occurs where the deep fluids meet the upper beds these deposits can be remobilized with each new phase of diapir growth

detection of localized small scale heterogeneities in the hanshin awaji region japan by anomalous amplification of coda level we estimated the spatial distribution of small scale heterogeneities in and around the hanshin awaji region including the coseismic fault area of the 1995 hyogo ken nanbu japan earthquake by using the amplification factor of the coda level as a measure of scattering strength we analyzed 137 earthquakes recorded at 64 stations because the coda level is strongly affected by site amplification the determination of the amplification factor of the coda level requires the following three major steps 1 checking the stability of coda waves among different stations such as coda q and lapse time 2 estimating the site amplification of coda waves for events outside the fault region and 3 taking the spectral ratio of coda waves for events inside the fault zone after correcting the site characteristics obtained in step 2 the coda decay rate batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document q mathrm c 1 end document is common among stations for each event the site amplification factor at each site estimated from 25 events correlates with the surface geological setting the most important result is that coda amplification anomalies exist as clusters along the coseismic fault area depending on frequency beneath awaji island in the range of 1 4 hz and beneath the area southwest of kobe 8 16 hz these high coda levels imply that strong heterogeneities exist there the scales of these heterogeneities are estimated to be about 0 2 1 4 and 0 06 0 18 km corresponding to the observed dominant frequencies 1 4 and 8 16 hz respectively manuscript received 10 january 2000

geology mineralogy and stable isotope geochemistry of the kabwe carbonate hosted pb zn deposit central zambia abstract the carbonate hosted kabwe pb zn deposit central zambia has produced at least 2 6 mt of zn and pb metal as well as minor amounts of v cd ag and cu the deposit consists of four main epigenetic pipe like orebodies structurally controlled along ne sw faults sphalerite galena pyrite minor chalcopyrite and accessory ge sulphides of briartite and renierite constitute the primary ore mineral assemblage cores of massive sulphide orebodies are surrounded by oxide zones of silicate ore willemite and mineralized jasperoid that consists largely of quartz willemite cerussite smithsonite goethite and hematite as well as numerous other secondary minerals including vanadates phosphates and carbonates of zn pb v and cu galena sphalerite and pyrite from the pb zn rich massive orebodies have homogeneous negative sulphur isotope ratios with mean 34 s cdt permil values of 17 75 0 28 1 16 54 0 0 27 and 15 82 0 25 respectively the zn rich and pb poor no 2 orebody shows slightly heavier ratios of 11 70 0 5 34 s for sphalerite and of 11 91 0 71 34 s for pyrite the negative sulphur isotope ratios are considered to be typical of sedimentary sulphides produced through bacterial reduction of seawater sulphate and suggest a sedimentary source for the sulphur carbon and oxygen isotope ratios of the host dolomite have mean 13 c pdb and 18 o smow values of 2 89 and 27 68 respectively which are typical of marine carbonates the oxygen isotope ratios of dolomite correlate negatively to the sio 2 content introduced during silicification of the host dolomite the depletion in 18 o in dolomite indicates high temperature fluid rock interaction involving a silica and 18 o rich hydrothermal solution two types of secondary fluid inclusions in dolomite both of which are thought to be related to ore deposition indicate temperatures of ore deposition in the range of 257 to 385 and 98 to 178 c respectively the high temperature fluid inclusions contain liquid vapour solid phases and have salinities of 15 to 31 eq wt nacl whereas the low temperature inclusions consist of liquid vapour with a salinity of 11 5 eq wt nacl fluid transport may have been caused by tectonic movements associated with the early stages of the pan african lufilian orogeny whereas ore deposition within favourable structures occurred due to changes in pressure temperature and ph in the ore solution during metasomatic replacement of the host dolomite the termination of the kabwe orebodies at the mine club fault zone and observed deformation textures of the ore sulphides as well as analysis of joint structures in the host dolomite indicate that ore emplacement occurred prior to the latest deformation phase of the neoproterozoic lufilian orogeny

cesium 137 transport into the arctic ocean through fram strait cesium 134 and 137cs activities were measured in water samples collected in march april 1981 at the fram 3 ice station located 200 km north of fram strait the water depth profiles of these isotopes reveal the presence of two pathways for the entry of anthropogenic tracers into the arctic ocean through fram strait atlantic water passing across the yermak plateau at the 100 200 m level is labeled by elevated concentrations of 134cs and 137cs associated with inputs from the sellafield reprocessing plant in the united kingdom the 134cs 137cs ratio is consistent with a transit time into the nansen basin from the sellafield united kingdom vicinity of 5 6 years an elevated concentration of 137cs at the 1500 m level is associated with inputs of recently ventilated water from the greenland norwegian seas or as a consequence of brine formation and off shelf transport from the barents sea

greenland sea convection in the winter of 1987 1988 during february 1988 a layer of almost uniform temperature and salinity between 100 and 1250 m depth was observed in the central greenland sea this feature indicative of previous deep convection is explained in terms of a conceptual penetrative convection model

site amplification from s wave coda in the long valley caldera region california following the work of phillips 1985 we have computed site amplification factors for coda waves at many sites in the long valley region in the eastern sierra nevada we computed ratios of coda amplitudes measured at 15 stations in and around long valley caldera relative to a granitic site mmpm for six frequency bands centered at 1 5 3 0 6 0 9 0 12 0 and 15 0 hz all station sites located within the caldera experienced large ground motion amplification at 1 5 and 3 0 hz ranging between five and 17 times that of the reference site however at higher frequencies these same sites exhibited significantly less amplification than the reference granite site this is attributed to the competing effects of an impedance contrast between the basement rock and caldera fill and very high absorption in the caldera fill at high frequencies station mmlm located on top of a volcanic plug displayed the largest amplitudes of all the sites studied for frequencies between 9 0 and 15 0 hz a dike structure attached to the plug couples the basement rock to the surface at high frequencies the resulting large amplitudes at mmlm are not due to amplification resulting from a strong impedance contrast rather the absorption under this site is very low perhaps lower than at the reference site mmpm outside the caldera another hard rock site located at devil s postpile mdpm generally behaved like the reference site for all frequencies the lowest amplifications observed came from a site outside the caldera mdcm located on thin pyroclastic ash deposits overlying granitic basement this can be attributed to a dominance of absorption over the amplification caused by lower impedance of this layer variations among sites on similar surface geology may be due to small local variations in impedance and absorption under and adjacent to the site the range in the spectral decay parameter between caldera and rock sites are comparable to results of anderson and hough 1984 for sites on alluvium and rock in the san fernando region these surprisingly different amplifications support the need for additional site specific studies amplifications determined in this study for the frequency range 1 5 and 3 0 hz correlate remarkably well with eaton s 1990 residuals for duration magnitude fmag and amplitude magnitude xmag for the usgs northern california seismic array further supporting the use of coda waves in determining site specific amplification

the east greenland polar front in autumn closely spaced salinity and temperature measurements in the region of the east greenland polar front from 75 n to 79 n in october november 1981 are presented the return atlantic current rac having a core of relatively warm and saline atlantic intermediate water aiw t 0 5 to 3 0 c s 34 9 to 35 0 was found everywhere along a steep front separating it from the colder fresher polar water a narrow frontal jet was found to have velocities greater than 0 80 m s where the station density was great enough to resolve its concentrated character notable fine structure was present especially in the warm aiw just east of the front a cold saline water forming a knee in the temperature salinity correlation was present in the upper margins of the rac the knee is formed primarily by warm aiw or atlantic water flowing under the upper layers of water flowing from the arctic ocean calculations are presented to show that an initially isothermal underflow could be modified to a thick thermocline by double diffusion calculations of the rate of cooling of fine structure elements by double diffusion indicate that the fine structure would have a limited lifetime about 12 days if its waters were not continually replenished

numerical simulation and a geochemical model of supergene carbonate hosted non sulphide zinc deposits abstract the proposed metallogenetic model presented in this paper is based on observations from the iranian non sulphide zinc deposits mehdi abad iran kuh and kuh e surmeh the emplacement of non sulphide ore can be generally subdivided into an oxidation stage followed by a post oxidation stage the formation of carbonate hosted non sulphide zinc deposits is primarily controlled by three factors climate protore composition and geology lithology and structure of the wall rocks the climate controls the oxidation and metal transport predominantly through the amount of meteoric water and the availability of oxygen which indirectly is controlled through the thickness of the soil cover and biogenic oxygen consumption favourable conditions for oxidation are an arid climate with minimal biogenic activity within the soil as a consequence oxygen can reach the sulphides easily resulting in higher metal concentrations of the supergene aqueous solutions dry climates are associated with a low water table preventing descending zn bearing fluids from contact with the aquifer and thus from dilution dispersion and removal of metals commonly non sulphide zinc deposits consist of two types of ore red zinc ore rich in zn 20 fe 7 pb as and white zinc ore typically with very high zinc grades up to 40 but low concentrations of iron 4 2 ions during the oxidation stage leads to the precipitation of highly insoluble anglesite which results in low pb 2 concentration within the fluid most of the zinc up to 80 at ph 6 or 97 at ph 5 leaves the oxidation zone and precipitates as zinc carbonates in adjacent parts of the carbonate host rock the neutralisation processes of the sulphuric acid with the carbonates of the host rock during the oxidation stage lead to the formation of co 2 g consequently the co 2 partial pressure p co2 g increases drastically and forms a co 2 g halo around the active oxidation zone thus most of the zinc precipitates as smithsonite which is stable and occurs exclusively in a high p co2 g environment the p co2 g decreases during the post oxidation stage and reaches the level of atmospheric p co2 g under these conditions hydrozincite becomes stable and starts to replace smithsonite most of the stage i smithsonite becomes corroded and is altered to stage ii hydrozincite the post oxidation stage is also associated with the successive formation of local zinc hydro silicates depending on the availability of sio 2 within the solution generally arid climates provide the best conditions for the preservation of non sulphide deposits the limited availability of meteoric water and deep to very deep water tables protect the non sulphide ore from subsequent dissolution

the carbonate hosted willemite prospects of the zambezi metamorphic belt zambia zambian willemite zn2sio4 deposits occur in the metasedimentary carbonate rocks of the proterozoic katangan supergroup the most important orebodies are located around kabwe and contain both sulphides and willemite in dolomites of low metamorphic grade the star zinc and excelsior prospects lusaka area discovered in the early 1920s occur in the metamorphic lithotypes of the late proterozoic zambezi supracrustal sequence which were deposited in a transtensional basin formed during the oblique collision of the kalahari and congo cratons the deposits are hosted by the limestone and dolomitic marbles of the cheta and lusaka formations structural analysis indicates that several fracture sets host the deposits which may be genetically related to the pan african mwembeshi dislocation zone a major geotectonic boundary between the lufilian arc and the zambezi belt in both prospects willemite replaces the marbles and is found along joints and fissures with open space filling textures and locally may develop colloform and vuggy fabrics as well silver as well as traces of germanium and cadmium have been detected within the willemite ore and lead or zinc sulphides are scarce or absent calcite locally replaces willemite willemite is associated with specular hematite and franklinite and post dates the zn spinel gahnite in the paragenesis genthelvite zn4be3 sio4 3s occurs as a minor phase in irregular aggregates the willemites from the lusaka area though mn poor show green cathodoluminescence colours and bright green fluorescence in short wave uv as the high temperature willemites in usa thermometric analyses of primary fluid inclusions in willemite yield homogenization temperatures that range from 160 c to 240 c and salinities of 8 16 wt equiv nacl the homogenization temperatures suggest a hypogene hydrothermal origin for the willemite concentrations the geochemistry of fluid inclusion leachates suggests that the hydrothermal fluids were brines derived from highly evaporated seawater precise age constraints are currently lacking for the lusaka area deposits though the deposits are not deformed indicating that they post date the lufilian orogeny 520 ma the possibility of precursor ores exists the gahnite franklinite willemite deposits could have been derived from a metamorphosed primary sulphide or even nonsulphide concentration that has subsequently been completely destroyed however there is no real evidence of such a primary source for the willemite mineral association the lusaka zinc ores may have been produced by an extensive hydrothermal system with fluids discharging along basinal fracture zones controlled by the pre pan african rifting stage a paragenesis similar to that of the lusaka prospects has been proposed to be a vector towards massive sulphide ores in several parts of the world therefore it is possible that these small willemite showings in zambia may be part of a much bigger and still unexplored zinc province

the contribution of the greenland and barents seas to the deep water of the arctic ocean the deep waters of the arctic ocean are traditionally held to be fed by an influx of norwegian sea deep water nsdw via the northward flowing west spitsbergen current discrete sample and ctd observations obtained from the greenland spitsbergen passage in august 1981 during the transient tracers in the ocean tto north atlantic expedition showed a 100 m thick layer of modified greenland sea deep water gsdw colder and fresher than nsdw at 2500 m spreading northward along the bottom of a deep unimpeded channel underneath the nsdw since the available data indicate that arctic ocean deep water aodw has a higher salinity than nsdw mixing of nsdw and gsdw can not produce aodw therefore other sources such as the peripheral arctic shelf seas must contribute dense saline water to the arctic ocean concentrations of 137cs and 90sr observed in aodw are greater than those observed in gsdw and nsdw the concentrations of these radionuclides on the barents sea shelf are sufficiently high and in the correct relative proportions to support this proposition

site amplification factors in central and southern california determined from coda waves abstract site amplification factors at frequencies of 1 5 3 6 and 12 hz were determined for 158 stations of the southern california seismic network scsn from coda waves of 306 local earthquakes using a recursive stochastic inverse method our results for southern california are consistent with those of central california obtained by su et al 1992 in that the site amplification at a station is systematically related to the surface geology of the station site the site amplification is high for young quaternary sediments and decreases with increasing geologic age at all frequencies between 1 5 and 12 hz this decreasing rate is higher for younger rock sites gradually becomes lower with increasing geologic age and appears to be insignificant when the site reaches mesozoic age or older the relationship between site amplification and geologic age obtained for southern california agrees with that for central california amplification factors at 158 sites in southern california were combined with those at 132 sites in central california through a common reference site the result is a unique data base of site specific uniformly referenced amplification factors throughout central and southern california

characterization and origin of low t willemite zn2sio4 mineralization the case of the bou arhous deposit high atlas morocco willemite zn2sio4 usually reported in hypogene non sulfide deposits is described as the main ore mineral in the carbonate hosted bou arhous zinc deposit this deposit is located in the high atlas intracontinental range that formed during the tertiary based on a set of microscopic observations it was possible to establish that willemite replaces primary sphalerite on the basis of cathodoluminescence imaging three successive generations of willemite are distinguished with evidence of dissolution reprecipitation processes willemite is also variably enriched in ge up to 1000 ppm while ge contents lower than 100 ppm are reported in the primary sulfide minerals depending on the willemite generation this substitution was positively or negatively correlated to the zn pb substitution according to the nature of zoning sector versus oscillatory the incorporation of ge was either controlled by crystallographic factors or by the nature of the mineralizing fluids willemite is associated with other oxidation related mineral species like cerussite pbco3 but is not in isotopic equilibrium and therefore not considered to be cogenetic oxygen isotope compositions support the formation of willemite at temperatures below 130 c from mixed meteoric and deeper hydrothermal fluids the formation of the high atlas belt during the tertiary has contributed to the exhumation of the sulfide minerals and the development of vertical conduits for percolation of meteoric water and ascending hydrothermal fluids in addition to a local contribution of silicate minerals of the host limestone hydrothermal fluids probably transported si and ge that are incorporated in willemite

the distribution of aluminium in the greenland sea and its relationship to ventilation processes during two cruises to the greenland sea in 1988 and 1989 a total of 690 on board aluminium al determinations were performed on samples collected from profiles located along four transects in the greenland sea as part of the greenland sea project al concentrations range from extremely low values 0 4 nm in the polar waters of the east greenland current draining the arctic ocean to 17 9 nm in the newly formed norwegian sea deep water nsdw at the periphery of the greenland gyre the al content in the component water masses serves to constrain the make up of these water masses from the various mixing products of the region the enrichment of al in the nsdw both at its site of formation within the greenland sea up to 17 9 nm and in the lofoten basin of the norwegian sea up to 40 3 nm leads to the conclusion that there must be an additional external source of al to these water masses the apparent inability of water column or sedimentary diagenetic processes to provide this enrichment and the observation of enriched al values associated with a high salinity shelf brine leads us to the conclusion that these brines may be responsible for the observed enrichments the high concentration of al in the greenland sea deep water compared with the water masses that produce it suggests that al may be acting as an inverse tracer of the processes that ventilate this basin by convective overturn i e the al concentration which increases with time as a result of continuous brine or other external inputs is reduced during convective events it is also argued that this flushing of elevated al water during convective events may have a similar counterpart in the iceland sea and that this mechanism could go some way toward solving the al deficit that exists between the enriched north atlantic deep water and its depleted precursor water masses observed in the intermediate waters of the greenland and iceland seas

holocene climatic change in morocco a quantitative reconstruction from pollen data annual precipitation july and january temperatures were reconstructed from a continuous holocene pollen sequence from the middle atlas morocco using the best modern analogues method the reconstructions show a clear difference between the early and late holocene from 10 ka to 6 5 ka the climate was drier and warmer than during the period since 6 5 ka the average value of annual precipitation was 870 mm until 6 5 ka then rose to 940 mm between 10 ka and 6 5 ka january and july temperatures were about 4 c higher than the present both temperatures show a marked decrease between 7 ka and 6 ka after 6 5 ka july and january temperatures fluctuated between 21 and 23 c and 2 5 and 5 c respectively january temperatures show a period of intermediate values 3 5 c between 4 ka and 5 5 ka the reconstructed climate values generally match palaeolimnological data from the same core which show five intervals of low lake level during the holocene they are also consistent with regional scale cohmap simulated palaeoclimate that shows contrasting patterns of rainfall variation between the northwesternmost part of africa and the intertropical band

site amplification of coda waves from local earthquakes in central california the goals of this study are two fold 1 to examine the site effect of coda waves believed to be the average site effect of shear waves in order to understand its spatial and frequency dependent behavior and 2 to learn what we can about the processes that generate the coda itself we use digital data from over 90 earthquakes each recorded by a subset of some 150 stations in the coast ranges of central california between san francisco and san luis obispo results from the band 1 5 to 24 hz indicate that site amplification depends strongly on surface geology and frequency at low frequencies 1 5 to 3 0 hz changes in amplification up to a factor of 20 are observed amplification generally varies inversely with deposit age at sediment sites and is lowest at granite and franciscan basement sites at high frequencies 6 to 24 hz the pattern changes many granite sites the majority in the gabilan range exhibit increasing amplification with frequency relative to the average station this behavior differs strikingly from that observed at sediment and franciscan sites which roll off at an intermediate rate and many sediment sites adjacent to the san andreas fault zone which decay away even more rapidly with frequency these results can be explained qualitatively by appealing to variable near site impedance and attenuation however complicating phenomena such as mode excitation in valley sediments must exist at low frequencies peaked behavior at a few hard rock sites at high frequency 12 hz currently lacks explanation at a few sediment sites the low frequency excitation is so strong that the coda envelopes begin to take on different shapes this contradicts the assumption based on previous observations that the coda shape is independent of source receiver location thus some site measurements may be artificially high the working model of coda waves as body wave energy backscattered from randomly distributed inhomogeneities must be modified to include the possibility of efficient near site resonance excited by incident direct and coda wave energy

characteristics of small scale heterogeneities in the hidaka japan region estimated by coda envelope level we estimated the spatial distribution of small scale heterogeneities as anomalous amplification of coda level in the hidaka japan region we analyzed 2768 seismograms in a frequency range of 1 32 hz for 24 earthquakes recorded at 62 stations first we estimated the site effect of each station using the coda nor malization method with regional earthquake data of large epicentral distances all the data processing was done after the correction of this site effect next we deter mined coda amplitude factor caf that is the amplitude ratio of coda waves on each source station pair relative to the averaged coda amplitude over stations for earthquakes inside the region we found systematic spatial variations of caf im plying the existence of localized heterogeneities at frequencies lower than 2 hz the caf is relatively large in the west of the hidaka mountains implying the possibility of strong heterogeneities with a scale of 0 6 1 3 km there in a high frequency range 16 hz caf values are large on paths crossing the hidaka mountains from the corresponding lapse time of coda 65 sec there may be a zone of concentrated heterogeneities beneath the hidaka mountains at the depth of 100 120 km

40ar 39ar ages and duration of the central atlantic magmatic province volcanism in morocco and portugal and its relation to the triassic jurassic boundary the central atlantic magmatic province camp is the world s largest known continental igneous province and is 15 contemporaneous with the triassic jurassic t j boundary that marks one of the five largest biological extinctions in the last 16 600 ma although constraints on the duration of the camp volcanism remain yet poorly defined the assumption that the camp 17 may have had a causal relationship with the climatic and biotic crisis was suggested marzoli a bertrand h knight k cirilli 18 s buratti n verati c nomade s renne p r youbi n martini r allenbach k neuwerth r rapaille c zaninetti l 19 bellieni g 2004 synchrony of the central atlantic magmatic province and the triassic jurassic boundary climatic and biotic 20 crisis geology 32 973 976 in this paper we present new 40ar 39ar ages on basaltic flows from moroccan central high atlas 21 oujda and argana and portuguese algarve and santiago do cacem basins where camp lava flows are interlayered with t j 22 sedimentary sequences 23 in the moroccan basins where the basalts were erupted across the t j boundary well defined 40ar 39ar plateau ages n 12 24 for more than 90 of the total erupted volume of camp basalts range from 197 8 0 7 ma to 201 7 2 4 ma and display a main 25 restricted peak at 199 1 1 ma providing a precise estimate of the 40ar 39ar age of the t j boundary concordant with the current 26 u pb age 199 6 0 3 ma palfy j mortensen j k carter e s smith p l friedman r m tipper h w 2000 timing the 27 end triassic mass extinction first on land then in the sea geology 28 39 42 the topmost lava flows recurrent unit yield a 28 significantly younger mean age of 196 6 0 6 ma highlighting late episodic eruption of camp magmas these late basalts 29 represent a small magma volume b10 of the total which was erupted most likely due to asthenospheric upwelling and 30 lithospheric extension within the t j central high atlas basins 31 in the portuguese basins stratigraphical and palynological studies of the associated continental sedimentary sequence 32 underlying the volcanic units suggest an age close to the t j boundary for the camp basaltic flows this is confirmed by new 33 40ar 39ar data for the portuguese basalts which provide the first accurate radio isotopic ages for lava flows in the european 34 camp with two plateau ages yielding a mean value of 198 1 0 4 ma these plateau ages plus three concordant mini plateau 35 ages suggest synchronous rifting and volcanism both in south western europe and morocco central high atlas and oujda basins in summary the eruptive history of the camp with an early extremely widespread and intense peak at 199 1 ma and a tail of 37 episodic eruption events until 196 6 ma is consistent with the biotic turnover at the t j boundary which was likely caused by 38 devastating effects of extensive volcanic eruptions

geology of the beltana willemite deposit flinders ranges south australia beltana is a high grade hypogene willemite deposit hosted in lower cambrian carbonate rocks in the arrowie basin northern flinders ranges south australia it is situated adjacent to a major growth fault on the basin margin ooid grainstone units of the woodendinna dolomite and units of archaeocyathid rich wilkawillina limestone are the main host lithologies lead minerals in subeconomic quantities are also present in karstic collapse breccias surrounding the willemite orebodies mineralization is structurally controlled and associated with brecciation and extensive hematite rich hydrothermal zincian dolomitization ore minerals include willemite and coronadite with lesser mimetite hedyphane and smithsonite late stage gangue minerals include manganocalcite dolomite and minor quartz the texture of willemite is heterogeneous resulting from various depositional mechanisms such as partial to massive replacement of the carbonate host rock internal sedimentation fracture fill brecciation and vein fill on the periphery of the deposit smithsonite formed by weathering of willemite beltana is centered on a karstic collapse breccia that extends at least 100 m vertically formed in part through corrosion by acidic ore solutions the geochemical signature of the orebody includes high levels of zn pb cd as and mn notably silver is absent from the deposit and sulfur concentrations are low 20 ppm fluid inclusion studies yield a low minimum temperature range of ore deposition between 50 and 170 c k ar dating of coronadite associated with the willemite orebody indicates an age of formation of 435 5 ma premining resources of willemite ore were 850 000 t at 36 percent zn and an associated body of subeconomic lead contained more than 800 000 t at 8 9 percent pb 3 9 percent zn and 1 percent as the deposit has some similarities with mississippi valley type deposits but differs in ore and alteration mineral assemblages

the nonsulfide zinc deposit at accha southern peru geological and mineralogical characterization the accha yanque zinc belt is located in the southern altiplano of peru a major zinc rich metallogenic province hosting a number of economic mineral deposits porphyry copper and skarn ores several nonsulfide type occurrences showings and mineral deposits are situated in a belt peripheral to the northern northeastern and northwestern edge of the oligocene miocene yauri apurimac batholith mineralization is hosted in breccias of both sedimentary and tectonic origin in the limestones of the middle to upper cretaceous ferrobamba formation primary ores belong to the carbonate replacement deposit type and are at least in part structurally controlled currently the zn mineralization is almost fully oxidized the accha deposit can be assigned to both direct replacement and wall rock replacement types the mineralized zone indicated resources 5 1 mt 8 2 zn and 0 9 pb occupies the hinge of an anticlinal dome that has been exposed by erosion the southern limb of the structure dips about 55 to the south southwest whereas its northern limb is truncated by faults the nonsulfide concentrations consisting of a mineralized zone 5 to 20 m thick are continuous along strike to the west for at least 700 m the mineralogy of the accha deposit shares many characteristics with that of the typical carbonate hosted calamine type nonsulfide zn ores the nonsulfide mineral association consists mainly of smithsonite and hemimorphite replacing both primary ore minerals and carbonate host rocks hydrozincite has been detected only in samples near the surface smithsonite occurs in zoned concretions with goethite mn hydr oxides and zn clays as well as replacive cement in the limestone intervals one of the most peculiar nonsulfide zn minerals at accha is a sauconite like zincian smectite variably concentrated throughout the deposit locally sauconite occurs as replacement of detrital feldspars and or detrital fragments occurring in marly sediments or in infills of karst cavities it also replaces both hemimorphite and smithsonite deposited during earlier stages the age of the supergene products in the whole belt is poorly constrained although there is geomorphologic evidence that the formation of supergene minerals postdates by more than 10 m y the last large scale secondary enrichment event that terminated with central andean climatic desiccation at 15 ma the age of the accha deposit may be consistent with a pliocene k ar date of 3 3 0 2 ma obtained for supergene alunite from the top part of the leached cap in the nearby cotabambas cu deposit

the hakkari nonsulfide zn pb deposit in the context of other nonsulfide zn pb deposits in the tethyan metallogenic belt of turkey abstract the hakkari nonsulfide zinc deposit is situated close to the southeastern border of turkey here both sulfide and nonsulfide zn pb ores are hosted in carbonate rocks of the jurassic cudi group with features typical of carbonate hosted supergene nonsulfide zinc mineralization the regional strike extent of the mineralized district is at least 60 km the age of the supergene deposit has not been determined but it is probable that the main weathering happened during upper tertiary possibly between upper miocene and lower pliocene the hakkari mineralization can be compared to other carbonate hosted zn pb deposits in turkey and an interpretation made of its geological setting the zinc mineral association at hakkari typically comprises smithsonite and hemimorphite which apparently replace both sulfide minerals and carbonate host rock two generations of smithsonite are present the first is relatively massive the second occurs as concretions in cavities as a final filling of remnant porosity some zinc is also hosted within fe mn hydr oxides lead is present in cerussite but also as partially oxidized galena lead can also occur in mn hydr oxides max 30 pbo the features of the supergene mineralization suggest that the hakkari deposit belongs both to the direct replacement and the wall rock replacement types of nonsulfide ores mineralization varies in style from tabular bodies of variable thickness

the calamines and the others the great family of supergene nonsulfide zinc ores abstract nonsulfides is a term which comprises a series of oxidized zn pb ore minerals it has also been used to define a special deposit type mainly considered as derived from the weathering of zn pb sulfide concentrations however nonsulfide zinc deposits have been distinguished between supergene and hypogene according to their mineralogy geological characteristics and genetic setting the supergene deposits formed by weathering and oxidation at ambient temperatures whereas the hypogene ones are considered hydrothermal or associated with metamorphic processes on primary sulfide ores in this review paper a comparison between a number of several nonsulfide deposits has been carried out typical calamines peculiar calamines and others the whole group comprises deposits of typical supergene origin mixed supergene hypogene mineralizations and oxidized concentrations characterized by different metals only locally associated with zinc the zn pb nonsulfide concentrations hosted in carbonate rocks which are mainly attributed to wall rock replacement and direct replacement supergene processes are the typical calamines liege district belgium iglesias district italy silesia cracow district poland peculiar calamine deposits are those mineralizations that have been generally considered as supergene but which are instead genetically related at least partly to hypogene processes e g angouran iran jabali yemen though mineralogically and texturally similar to supergene nonsulfide deposits the others are prevailingly supergene nonsulfide zinc deposits not hosted in carbonate rocks skorpion namibia yanque peru or characterized by other metals as main commodities like lead magellan australia silver sierra mojada mexico wonawinta australia or vanadium otavi mountainland namibia minerals of current economic importance in most calamine deposits are smithsonite hydrozincite and cerussite this mineralogical association is generally simple but when the calamines are dolomite hosted one of the consequences of the wall rock replacement process is the generation of a series of economically useless zn and mg bearing mixed carbonate phases secondary deposits hosted in silicatic sedimentary or volcanic rocks mainly contain hemimorphite and or sauconite lead ag and v rich nonsulfide ores are characterized by a more complex mineralogical association mixed pb carbonates pb sulfates pb phosphates pb arsenates various ag sulfosalts and zn pb cu vanadates carbon and oxygen stable isotope studies allow distinguishing between supergene and hypogene nonsulfide deposits evaluating the effects of oxidative heating and even gaining indirect paleoclimatic information the oxygen isotope variation of the individual carbonate minerals within a deposit is relatively small indicating constant formation temperatures and a single meteoric fluid source carbon isotope values are highly variable thus suggesting several isotopically distinct carbon sources periods of paleoclimatic switch overs from seasonally humid arid to hyperarid have been considered as the most favorable conditions for the formation and preservation of supergene nonsulfide deposits however while several recent nonsulfide deposits throughout the world are positioned between 15 and 45 n latitude thus pointing to a warm and humid weathering climate others have been deposited in sub arctic regions the economic value of the nonsulfide zn pb ag v ores is highly variable because more than in the case of metallic sulfide deposits it resides not only on the geological setting but also on their mineralogy that can directly influence processing and metallurgy

apatite fission track analyses on basement granites from south western meseta morocco paleogeographic implications and interpretation of aft age discrepancies abstract this work is based on apatite fission track analysis of samples mostly granites from the basement of the cretaceous tertiary phosphate and ganntour plateaus exposed in the jebilet and rehamna massifs western meseta morocco this basement belongs to the carboniferous early permian variscan belt and the earlier marine onlap is late triassic in age however the aft ages are post triassic and different in the jebilet 186 203 ma and rehamna 148 153 ma track length modelling support the occurrence of moderate heating events during the jurassic and the eocene respectively with cooling during the permian and cretaceous intervals these results are partly accounted for by considering a moderate subsidence during the late triassic liassic which is a noticeable change in the regional paleogeographic concept of west moroccan arch however the discrepancies between the aft results from the studied massifs make necessary to explore further explanation we interpret the observed discrepancies by the difference in age and depth of crystallization of the sampled granites in the variscan orogen i e 330 ma 5 6 km in the jebilet versus 300 ma 8 10 km in the rehamna the importance of the late jurassic early cretaceous uplift and erosion of the entire meseta and that of its late eocene burial are emphasized

thermohaline circulation in the arctic mediterranean seas the renewal of the deep north atlantic by the various overflows of the greenland scotland ridges is only one manifestation of the convective and mixing processes which occur in the various basins and shelf areas to the north the arctic ocean and the greenland iceland and norwegian seas collectively called the arctic mediterranean the traditional site of deep ventilation for these basins is the greenland sea but a growing body of evidence also points to the arctic ocean as a major source of deep water this deep water is relatively warm and saline and it appears to be a mixture of dense brine enriched shelf water with intermediate strata in the arctic ocean the deep water exits the arctic ocean along the greenland slope to mix with the greenland sea deep water conversely very cold low salinity deep water from the greenland sea enters the arctic ocean west of spitsbergen within the arctic ocean the lomonosov ridge excludes the greenland sea deep water from the canadian basin leaving the latter warm saline and rich in silica in general the entire deep water sphere of the arctic mediterranean is constrained by the greenland scotland ridges to circulate internally therefore it is certain of the intermediate waters formed in the greenland and iceland seas which ventilate the north atlantic these waters have a very short residence time in their formation areas and are therefore able to rapidly transmit surface induced signals into the deep north atlantic

supergene processes in zinc lead silver sulfide ores in carbonates eh ph relations have been examined for assemblages of the burgin mine east tintic district utah at the temperature of 60 degrees c of local subsurface waters and at 25 degrees c for the tynagh mine ireland and the matagente deposit cerro de pasco peru modified journal abstract

zinc rich clays in supergene non sulfide zinc deposits the nature and the origin of zinc clays are poorly understood with the example of the bou arhous zn pb ore deposit in the moroccan high atlas this study presents new data for the mineralogical and chemical characterization of barren and zinc clays associated with non sulfide zinc ores in the field white to ocher granular clays are associated with willemite zn2sio4 while red clays fill karst related cavities cutting across the non sulfide ore bodies red clays kaolinite chlorite illite and smectite present evidence of stratification that reflects internal sedimentation processes during the karst evolution white clays contain 7 a clay mineral smectite irregular interstratified minerals with less than 20 of smectite layers willemite is partially dissolved and is surrounded by authigenic zinc clay minerals together with xrd results wds analyses on newly formed clay aggregates suggest that this interstratified mineral is composed of fraipontite and sauconite cec measurements support that zinc is only located within the octahedral sheets these new results support the following process i dissolution of willemite leading to release of si and zn ii interaction between zn si rich solutions and residual detrital clays and iii dissolution of kaolinite and formation of interstratified zinc clay minerals that grew over detrital micas

site amplification from coda waves validation and application to s wave site response abstract the subject of this article is to see if the response to s waves at a specific site can be determined from coda waves we used aftershock records of the 1992 landers and big bear earthquakes observed at four terrascope stations pas pfo svd and gsc in southern california the wide dynamic range of the terrascope instrument provided a broadband seismogram for s waves and at the same time coda waves over a long lapse time window we analyzed a total of 708 three component waveforms from 65 events whose magnitudes ranged from 3 3 to 5 4 the station svd is located on quaternary alluvium and the remaining stations are on rocks of cretaceous age we first evaluated the coda site amplification factor using a spectral ratio method may eda et al 1991 koyanagi et al 1992 for frequency bands centered at 0 75 1 0 1 5 2 0 3 0 4 0 and 6 0 hz for lapse time windows after 70 sec from the origin time we found that the site amplification factor for the radial component is similar to that for the transverse component this similarity was expected because codas consist of backscattered waves coming from all directions into the station resulting in a directionally averaged site response we then evaluated the s wave site amplification factor using an inversion method andrews 1986 on the direct s wave portion of the same data set we found that the coda site response agrees with the s wave site response within a factor of about 1 5 supporting the earlier findings by tsujiura 1978 and justifying the use of coda waves in determining site specific amplification for s waves this agreement between s wave site response and coda site response is understandable if we assume that coda waves are dominated by s waves as theoretically predicted by aki 1992 and zeng 1993

inversion tectonics and the evolution of the high atlas mountains morocco based on a geological geophysical transect an edited version of this paper was published by the american geophysical union agu copyright 1998 agu see also http www agu org pubs crossref 1999 1998tc900015 shtml http atlas geo cornell edu morocco publications beauchamp1999 htm

mineralogical and geochemical characterization of supergene cu pb zn v ores in the oriental high atlas morocco in the moroccan high atlas two sulfide deposits hosted by jurassic dolostones underwent significant weathering in the cu deposit of jbel klakh several stages of supergene mineralization are distinguished 1 the replacement of hypogene sulfides in the protolith chalcopyrite by secondary sulfides in the cementation zone bornite digenite chalcocite covellite 2 the formation of oxidized minerals in the saprolite malachite azurite brochantite where the environment becomes more oxidizing and neutral and 3 the precipitation of late carbonates calcite and iron hydr oxides in the laterite the precipitation of carbonates is related to the dissolution of dolomitic host rocks which buffers the fluid acidity due to the oxidation of sulfides in the jbel haouanit pb zn deposit the mineral assemblage is dominated by typical calamine minerals cu minerals chalcocite covellite malachite and a cu pb zn vanadate mottramite galena is successively weathered in anglesite and cerussite sphalerite is weathered in smithsonite which is rapidly replaced by hydrozincite late iron hydr oxides are mainly found at the top of both deposits laterite both deposits are thus characterized by specific mineral zoning from laterite to protolith related to variations in the mineralogy and ore grades and probably caused by varying eh ph conditions

multistage genesis of the late cretaceous manganese karst hosted tasdremt deposit high atlas morocco the eastern part of the souss basin morocco contains several mn deposits in the tasdremt district three mn orebodies occur within the cenomanian turonian dolostones and the senonian coniacian to maastrichtian detrital series the main orebody being located at the boundary between them the mn ores consist of coronadite group minerals mostly coronadite and hollandite in a karstified dolostone new field observations petrographic analyses and geochemical data define the tasdremt deposits as a karst hosted accumulation 11 60 wt mn particularly enriched in ba 1 5 8 2 wt and pb 1 0 5 0 wt with poor contaminations in al fe and p this study shows that the ore forming process is similar to that occurring in the imini c3 level located 100 km to the north east such similarities with the high grade pyrolusite bearing ore suggest that the tasdremt deposit is a lateral equivalent of the imini deposits however the scarcity of pyrolusite in tasdremt results in lower mn grades the tasdremt ores being considered an aborted incomplete system in comparison with the imini deposits 40ar 39ar geochronology of k bearing mn oxides yields late cretaceous ages defining three phases at 91 5 ma 77 5 82 ma and 65 67 ma although the source of metals remains hypothetical mineralizing fluids were carried by o2 free groundwater that mixed with o2 rich shallow meteoric waters at the tasdremt depositional site the dissolution of the host dolostones and the karst environment have provided suitable conditions for the precipitation of mn oxides causing the coeval increase of ph and eh respectively the early atlasic deformation during the late cretaceous is associated with mineralization events and was responsible for creation of low stand reliefs from tasdremt to imini this period enabled karstification and mineralization connecting the tasdremt deposits to other african mn deposits is difficult since the latter consist of laterite resting above paleoproterozoic mn protores and consequently formed under different conditions from karst hosted deposits it is likely that other mn occurrences formed along the atlas belt in similar settings

late quaternary climatic reconstruction for the maghreb north africa abstract the paleoclimatic evolution of the maghreb since 40 000 yr b p is not yet known in great detail for that purpose data from more than 35 sites have been collected although only about 11014c dates and a few prehistoric remains can be used to correlate these data however the sites are well distributed over the maghreb and the convergent results from paleosoils paleolakes alluvian or eolian deposits pollen analysis etc induce one to draw up a certain pattern in climatic evolution for the period between 40 000 and 20 000 yr b p the data are still fragmentary but are concordant in indicating wetter environments generalized as far as the northern sahara the effect of dropping temperatures on the increasing water budget and soil moisture is not yet clear but rainfall could have been more regular and more abundant as a consequence of the shifting of middle latitude cyclone paths towards the south in both summer and winter the environmental indicators show that between about 20 and 18 000 yr b p rainfall progressively became more irregular however proofs of aridity in the south maghreb and the northern sahara is evident only for the period between 12 10 000 yr b p at that time the saharan high pressure belt was reinforced and well established at higher latitudes than at present this dry climate lasted more or less until the thermal optimum after 6000 yr b p there is some evidence that the climate became wetter again but the environmental conditions were rather different from those of before 20 000 yr b p for instance the middle holocene dark humic sois are the result of a pedogenesis different from that of the late pleistocene reddish paleosoils for the last two millennia it is not easy to distinguish between a natural trend towards aridification and desertification through man s intervention

arctic ocean water mass balance from isotope data the distributions of the oxygen 18 and tritium isotopes and of salinity yield a residence time of 10 years for the surface and halocline waters of the arctic basin we find a yearly net production of 0 59 m of sea ice and an input of 1 16 m of freshwater from continental river runoff local precipitation and bering strait salinity deficiency using the basin area value with these numbers gives long term average total net production and transport rates of 0 15 sv of ice and 0 18 sv of meteoric component bering strait water not included if in addition a reasonable depth profile of relative current velocity is assumed for the outflow a yearly input of 2 8 sv of atlantic and bering strait water is needed to replenish the upper and halocline waters these numbers should be good to 20 and are multiyear averages the isotope data clearly indicate that the barents sea is an inflow area for atlantic water to the basin but that net export of ice occurs there

large scale oceanography in fram strait during the 1984 marginal ice zone experiment the pattern of large scale circulation in fram strait during summer 1984 is inferred from hydrographic data and water mass analysis and direct current observations by use of surface and subsurface floats the west spitsbergen current carrying warm and salty atlantic water splits into several branches two flowing northward into the arctic ocean and two turning westward causing a recirculation across the main axis of fram strait the individual flow paths are topographically controlled suggesting a strong barotropic component of the circulation

the origin of norwegian sea deep water a nearly homogeneous water mass the norwegian sea deep water is found below 2000 m depth in the norwegian and lofoten basins of the norwegian sea recent observations indicate that this water is a mixture of relatively cold and fresh greenland sea deep water with warmer saltier eurasian basin deep water from the arctic ocean we have found this mixture along the western and southern periphery of the greenland sea near the level where the pressure compensated densities of the parent water masses are equal the along isopycnal mixing produces a remarkably uniform water mass which can be traced only a short distance away from its entry into the norwegian sea through gaps in the mid ocean ridge north of jan mayen island direct measurements of flow through these gaps confirm motion in the proper sense to accomplish this connection

non sulfide zinc deposits of the moroccan high atlas multi scale characterization and origin six non sulfide zn pb ore deposits were investigated in the moroccan high atlas to understand processes and timing of their formation sulfide and non sulfide ores are hosted in lower jurassic reefal to para reefal limestone zn pb carbonates zn silicates and associated hydrated phases directly replace the stratabound primary ore bodies or fill cavities along fractures related to the atlasic compression field observation has been complemented by a multidisciplinary approach e g xrd raman sem epma for the mineralogical characterization all six ore deposits present similar parageneses revealing three successive stages for ore deposition 1 formation of the protore sulfides 2 early supergene weathering with formation of zn pb bearing carbonates and iron oxi hydroxides and 3 late supergene weathering with deposition of zn carbonates zn silicates and hydrated phases direct replacement of primary sulfides is accompanied by precipitation of zinc non sulfide minerals in cavities or internal sediments filling the proposed three step scenario can be placed within the tectonic evolution of the moroccan high atlas belt deposition of primary sulfides is contemporaneous with opening of the tethyan and atlantic oceans during the tertiary intracontinental deformation has given rise to the high atlas fold and thrust belt and to regional uplift as a result zn pb sulfides hosted in carbonates experienced oxidation under an arid climate to form karst related zn pb non sulfide ore bodies

from sandstone to carbonate hosted stratabound deposits an isotope study of galena in the upper moulouya district morocco the upper moulouya district displays three main types of lead ores in the hercynian domain 1 aouli vein type deposits hosted in the hercynian basement 2 zeida triassic sandstone hosted and 3 mibladen carbonate hosted stratabound and karstic mineralisations in the mesozoic cover lead and sulfur isotope studies indicate that the aouli vein type and zeida sandstone hosted stratabound mineralisations are formed by a mixing of two fluids one formed by the leaching of the aouli granite massif and the other by leaching of the saharian basement these deposits may correspond to the same triassic metallogenic event focused along fault systems or within permeable sandstone deep fluids were mobilised during the early extensional movements associated with the opening of the atlas rifting basin the mississippi valley type mibladen mineralisation is related to a distinct metallogenic event superimposed on the earlier one and represents a remobilization of earlier concentrations or a more recent leaching of the same sources but with a more pronounced contribution of the local organic matter the upper moulouya area demonstrates the close relationship between vein type and sandstone hosted lead zinc mineralisations and their major differences with mississippi valley type deposits

stability of biological and inorganic hemimorphite implications for hemimorphite precipitation in non sulfide zn deposits abstract hemimorphite zn 4 si 2 o 7 oh 2 h 2 o one of the most common minerals in non sulfide zn deposits together with smithsonite and hydrozincite is one of the most abundant minerals in the calamine deposits in sw sardinia in spite of their importance for the development of ore genesis models the stability properties of hemimorphite are poorly known this paper presents solubility experiments on two different types of hemimorphite a geological hemimorphite from a supergene non sulfide zn deposit of supposed abiotic origin and a hemimorphite precipitated by bacterial activity both specimens were characterized before and after the experiment by synchrotron radiation x ray powder diffraction scanning electron microscopy and x ray absorption spectroscopy the calculated solubility product constants logk s are similar for both geological and biogenic hemimorphite 30 3 0 4 and 30 5 0 1 respectively during the solubility experiment biological hemimorphite undergoes an amorphous to crystalline phase transition and the distinctive features mineralized bacterial sheaths and organic filaments that allowed us to demonstrate its biological origin are no longer recognizable by scanning electron microscopy the results of this study may be useful for developing ore genesis models including evolution in a supergene environment and in general for performing geochemical speciation and equilibrium calculations moreover our findings open the way for a new interpretation of hemimorphite forming processes and suggest the possibility that bacteria may have played a role in the formation of this mineral in ore deposits

geology of the skorpion supergene zinc deposit southern namibia the skorpion zinc deposit in southwestern namibia comprises a significant nonsulfide orebody 24 6 mt at 10 6 zn and subordinate amounts of primary base metal sulfide mineralization which structurally underlies the nonsulfide ores at depth the host rocks of the blind nonsulfide orebody and relict sulfide mineralization consist of a mixed volcano sedimentary sequence of neoproterozoic age that has formed in an initial continental rift system between the kalahari cratonic province and the rio de la plata cratonic province the metavolcanic and subvolcanic rocks display a distinct bimodal geochemical composition of within plate affinity and have been emplaced under an extensional crustal regime zircons from a rhyolitic vesicular flow extruded approximately contemporaneously with the volcanic hosted sulfide mineralization have been dated by shrimp u pb analysis and yield an age of 751 9 5 5 ma the basin that hosts the skorpion deposit has been shaped by horst and half graben tectonics which also controlled the sedimentary deposition of siliciclastic and carbonate sediments within both shallow and deeper water environments the rock sequence was affected by a major tectono metamorphic event the pan african brasiliano orogeny at approximately 550 to 545 ma metamorphism reached uppermost greenschist to lowermost amphibolite facies and the complex deformational style of the region is the result of intense faulting folding and thrusting the skorpion orebody is hosted by arkosic metaarenites and subordinately by volcaniclastic metasedimentary rocks it is irregularly shaped transgressive to sedimentary layering and has a relatively flat top which is covered by a blanket of unmineralized overburden consisting of calcrete boulder beds and recent sand dunes at depth the orebody has a relatively sharp contact with a barren marble unit on the east and south and a more gradational boundary within the siliciclastic host rocks on the west and north the nonsulfide ore minerals comprise predominantly sauconite zn smectite substantial amounts of hemimorphite and smithsonite and subordinate amounts of scholzite tarbuttite atacamite hydrozincite and hetearolite the ore minerals are mainly euhedral and subhedral crystals and occur as open space fillings in intergranular voids fractures and breccias and as replacements of feldspar and mica the metasedimentary host rocks of the nonsulfide ore contain abundant iron hydroxide pseudomorphs after disseminated sulfides and stringers and after rare semimassive stratiform layers of sulfides gossanous manganese and iron hydroxide rich siliciclastic metasedimentary rocks are common in the western and northwestern vicinity of the nonsulfide orebody alteration of the supergene mineralized host rocks includes removal of calcite cement and the breakdown of detrital albite rich plagioclase and of minor orthoclase local alteration phenomena also include silicification and rare secondary barite both a result of the alteration and breakdown of feldspar minor base metal sulfide mineral deposits occur in metarhyolitic flows and felsic hyaloclastic rocks structurally below the nonsulfide orebody the primary sulfide minerals comprise pyrite pyrrhotite sphalerite minor chalcopyrite and galena as well as secondary chalcocite and colloidal sphalerite brunckite the volcanic hosted sulfide ore minerals are deformed and partly recrystallized and thus of premetamorphic and predeformation origin in contrast the skorpion nonsulfide zinc deposit is of postmetamorphic origin as shown by two hydrous low p low t ore assemblages the secondary assemblages occur at least partly as delicate euhedral and subhedral crystals in secondary pore space open fractures veins and breccias the nonsulfide ore contains pseudomorphs from in situ oxidation and replacement of preexisting sulfides and ore and also from the remobilization or precipitation of base metals the skorpion nonsulfide zinc deposit is of supergene origin and formed from the oxidation of sulfide protore by circulating meteoric water as suggested by textural evidence and by initial stable isotope data the timing of ore formation is still undefined but lies within the large age bracket between 545 ma peak metamorphism and subsequent partial exhumation and the deposition of the nonmineralized overburden of namib desert gravels 21 ma and dune sands

the formation of goethite jarosite and alunite during the weathering of sulfide bearing felsic rocks quantities of goethite and jarosite produced by weathering correlate with abundance and composition of sulfide minerals originally in rocks to characterize processes forming these minerals chemical weathering of sulfide bearing rocks was simulated using differential equations which describe mass transfer between aqueous solutions and minerals helgeson 1968 goethite begins precipitating during reaction between meteoric water f sub o 2 10 super 06 atm and sulfides after dissolution of 6 7 x 10 super 9 g pyrite or 6 0 x 10 super 9 g chalcopyrite per 1 000 g h 2 o reaction of the oxygen dissolved in 1 000 g water that is initially saturated with the atmospheric abundance of oxygen consumes 0 0085 g pyrite or 0 013 g chalcopyrite goethite is the only reaction product the calculations predict that weathering produces jarosite or alunite after goethite when 0 04 moles of oxygen have been consumed per 1 000 g h 2 o and where rates of oxygen replenishment approximately equal or exceed consumption simultaneous reactions between k feldspar an aqueous solution and pyrite or chalcopyrite produce alunite and goethite if the irreversible molar flux of fe al is less than 0 5 reactions with fluxes of fe al between 0 5 and 1 0 produce alunite goethite and jarosite those with fe al fluxes greater than 1 0 generate only jarosite after goethite following saturation of the solution with jarosite the mass ratio goethite goethite jarosite decreases smoothly from 1 0 to 0 0 accompanying continuous dissolution of pyrite and chalcopyrite the interval of reaction progress over which goethite and jarosite coexist increases relative to pyrite and k feldspar reactions when weathering involves muscovite or chalcopyrite in simulations whose sulfides have been totally oxidized this ratio varies antithetically with the volume percent sulfide and or ratio of pyrite pyrite chalcopyrite initially present a prediction consistent with geologic observations

isotope dating of waters at fram iii measurements of tritium helium 3 together with salinity yield 11 years as arctic basin residence time of the halocline waters in the arctic outflow in the fram strait radiocarbon and tritium data on the deeper waters point at some penetration of surface waters down to 1500 m during the last 20 years even at 2500 m the 14c activity is within 1 80 years of modern pre bomb values

a ground water mixing model for the origin of the imini manganese deposit cretaceous of morocco the imini deposit just south of the atlas mountains of morocco consists of three beds of manganese oxide ore in a slightly deformed dolomite unit about 10 m thick of cenomanian turonian late cretaceous age the dolomite host is sugary textured massive and permeable dolomite occurs as nearly euhedral rhombs each ore bed is about a meter thick and consists almost entirely of intergrowths of pyrolusite and hollandite family minerals bao up to 11 and pbo up to 28 with a flattened geode structure overlying the ore beds are solution collapse breccias with dolomite clasts janggunite mn fe oxide and dolomite matrix and pyrolusite hollandite calcite cement the ore solution collapse breccia and coarsely recrystallized pure dolomite are coextensive a zone only 400 to 1 000 m wide but 25 km long and elongate east northeast west southwest diagenetic features of the deposit are recrystallized texture of the dolomite flattened geode structure of the ore solution collapse breccia and associated draped laminae of the insoluble residues fossil replacement by mn oxides and zoned chert nodules with inclusions a mineralogic paragenesis shown independently in each of these features from older to younger is 1 precursor carbonates 2 dolomite janggunite and 3 hollandite pyrolusite chert calcite diagenesis probably occurred during the late cretaceous in a mixing zone of fresh and saline ground water as similar diagenetic sequences without manganese deposits are widely reported to have formed in such environments carbon and oxygen isotope compositions of carbonates and oxygen isotope compositions of chert show that an increasing component of fresh meteoric ground water was present as diagenesis proceeded falling sea level allowed the mixing zone to occupy various positions within the carbonate unit and convert the primary calcareous carbonate rocks to dolomite with chert nodules anoxic seawater is known both worldwide and from the local depositional basin atlas gulf in the cenomanian turonian this is believed to be the key to manganese deposition because anoxic conditions greatly enhance manganese solubility two specific versions of the mixing zone model are presented for manganese deposition one in which a primary sedimentary manganese precipitate formed along margins of the anoxic basin and was recrystallized during diagenesis in the mixing zone and the other in which anoxic saline ground water brought manganese into the mixing zone where it precipitated

the west spitsbergen current disposition and water mass transformation recent work suggests that the west spitsbergen current which provides the principal contribution to the arctic ocean of salt and sensible heat as well as of a variety of anthropogenic tracers is a rather complex circulation feature north of 79 n where the isobaths diverge markedly the current contains two separate warm cores that follow different isobaths the western core carried by the offshore branch of the current follows the western flank of the yermak plateau and north of 80 n at least part of this flow detaches from the plateau probably to contribute to the recirculation in fram strait in contrast the inshore branch follows the shelf break into the arctic ocean it is this inshore branch that provides the primary focus in this paper during the transit of the inshore waters past northwestern spitsbergen the core properties change primarily through vertical heat flux which during ice free conditions in winter is estimated to be of the order of 200 w m 2 from the core layer alone together with some freshening within the arctic ocean this process is responsible for fully transforming the original atlantic water into arctic intermediate water within about 600 km of fram strait

imaging of three dimensional small scale heterogeneities in the hidaka japan region coda spectral analysis summary while large scale heterogeneities have been studied intensively by seismic tomography with traveltime data small scale heterogeneities are not fully investigated yet we obtained the 3d spatial distribution of small scale heterogeneities as relative scattering coefficients in the hidaka japan region using the spatial variation of high frequency coda power spectra we analysed 530 seismograms recorded at 62 stations for nine local earthquakes in the frequency range of 1 32 hz after correcting source station and propagation effects we assigned the spatial and temporal variations of observed power spectra of coda waves into the 3 d distribution of scattering coefficient based on single and isotropic scattering models small scale heterogeneities are distributed not only in a non uniform manner but also differently among scale lengths estimated from their frequency dependence an area of large relative scattering coefficient in 2 and 16 hz is located at a depth shallower than 45 km in the southwest of the hidaka mountains correlating well with a highly active area of microearthquakes at a depth of 60 120 km two dipping zones of large scattering coefficient are imaged beneath the summit of the hidaka mountains these zones may imply two layers of strong seismic wave reflection consistent with the upper and lower planes of the double seismic zone in the subducting pacific plate as determined by the hypocentral distribution in this region

iodine 129 cfc 11 transit times for denmark strait overflow water in the labrador and irminger seas 1 iodine 129 discharged from nuclear fuel reprocessing plants in france and the united kingdom is transported into the nordic seas on timescales of 3 5 years tracer 129i is subsequently injected into intermediate waters that overflow the sills between greenland iceland and scotland and ventilate the north atlantic deep waters nadw during the early 1990s discharges of 129i increased by 600 resulting in a large well resolved tracer front whose passage through the nordic seas is presently being observed by a time series of 129i measurements on the woce ar7w section in the labrador sea the highest 129i levels were measured below depths of 3000 m in denmark strait overflow water dsow these levels increased by about 300 between 1997 and 2001 to values 40 107 atoms l indicating that the leading edge of the tracer front from the early 1990s was being observed entering the nadw using a simple mixing advection model 129i and cfc 11 results were used to calculate transit times of 0 4 2 6 years for the flow of dsow from formation regions in the nordic seas to the labrador sea measurements on samples collected in the irminger sea in 2001 gave transit times of 0 3 years for core dsow immediately south of denmark strait and about 2 years for locations off the southern tip of greenland an increase in dsow transit times observed in the labrador sea between 1999 and 2001 probably reflects a more general weakening in the subpolar gyre of the north atlantic during the 1990s