styles of failure in late holocene highstand prodelta wedges on the adriatic shelf on the continental shelves of the northern mediterranean basin the late holocene highstand systems tract hst prograded un der the influence of major rivers after the attainment of the present sea level highstand about 5 5 cal kyr bp on the adriatic shelf the thickness distribution of the late holocene hst reflects the location of major deltas on the western side of the basin and the geostrophic cir culation which prevents a more uniform sediment dispersal toward the center of the basin very high sediment accumulation rates 1 to 10 cm year resulted in the construction of a hst depocenter up to 35 m thick this shore parallel depocenter is affected by failure of limited displacement over as much as 40 of its extent gas impregnation is common in the topset region and occurs at very shallow levels a few meters below the sea floor five areas are characterized by a variety of sea floor and subsurface crenulations although locally some of these crenulations have an intriguingly regular geometry sediment failure is the most plausible mechanism for their formation sediment failure better explains the large variety of geometries that characterizes the coastal mud prism of the late holocene hst furthermore we observe that these crenulations occur only where the downlap surface at the base of the hst is disrupted and affected by geometries that are con sistent with fluid escape processes this relationship suggests that the basal surface acts as a weak layer for sediment failure failure occurred in variable water depths from the northern slope of the modern po prodelta 10 20 m water depth to the narrow shelf offshore bari 40 110 m water depth in all these areas the proximal part of the hst prodelta wedge is intensely gas charged the thickness and age of the sediment sections affected by failure are slightly differ ent from place to place but appear everywhere younger than 5 5 cal kyr bp where failure affects the entire hst the detachment occurs on the downlap surface at its base failure geometries characterize the head region whereas compressional features such as pressure ridges and mud diapirs dominate in the toe region ranging in depth between 70 and 110 m where failure is limited to the upper few meters of the hst there is a clear lithologic change decrease in carbonate fraction and grain size across the basal surface this lithological change reflects a switch in sediment supply from local apennine rivers below to po derived mud this change occurred at the onset of the little ice age documenting the indirect control of short term climate change and hu man impact on sediment architecture the deformations affecting the late holocene hst in the various areas show differences in internal geometry but appear everywhere to be characterized by limited downward displacement and can be attri buted to shear dominated retrogressive failure it is suggested that some degree of consolidation occurred immediately after mobilization possibly induced by the escape of fluids nowhere has failure evolved into disintegration and flow likely because the type of cyclic loading that triggered it was not prolonged over a long enough interval short lived radionuclides in the uppermost stratigraphic layers which postdate the failure in the area offshore ortona allowed us to quantify systematic changes in sediment accumulation rates as a func tion of the underlying deformed sea floor in areas of wavy sea floor troughs show sediment accumulation rates of greater than 16 mm yr a figure that is fourfold the rate measured on the flanks of the troughs

evidence for two stages of mineralization in west africa s largest gold deposit obuasi ghana the supergiant obuasi gold deposit is the largest deposit in the paleoproterozoic birimian terranes of west africa with 62 moz of gold past production resources the deposit is hosted in the paleoproterozoic kumasi group sedimentary rocks composed of carbonaceous phyllites slates psammites and volcaniclastic rocks intruded by different generations of felsic dikes and granites a three stage deformation history is defined for the district the d1 ob stage is weakly recorded in the sedimentary rocks as a layer parallel fabric and indicates that bedding parallel shearing occurred during the early stage of deformation at obuasi the d2 ob is the main deformation stage affecting the obuasi district and corresponds to a nw se shortening tight to isoclinal folding as well as intense subhorizontal stretching occurred during d2 ob parallel with the plane of a pervasive ne striking subvertical foliation s2 ob finally a n s shortening event d3 ob refolded previously formed structures and formed a distinct ene striking variably dipping s3 ob cleavage that is domainal in nature throughout the deposit two economic styles of mineralization occur at obuasi and contribute equally to the gold budget these are 1 gold bearing sulfides dominantly arsenopyrite mainly disseminated in metasedimentary rocks and 2 native gold hosted in quartz veins that are as much as 25 m wide microstructural evidence such as strain shadows surrounding gold bearing arsenopyrite parallel with s2 ob but folded by s3 ob indicates that the sulfides were formed during d2 ob concentrations of as much as 700 ppm au are present in the epitaxial growth zones of the arsenopyrite grains although the large mineralized quartz veins are boudinaged and refolded indicating their formation during d2 ob field and microanalytical observations demonstrate that the gold in the veins is hosted in microcracks controlled by d3 ob where the s3 ob cleavage crosscuts the quartz veins in the main ore zones thus these observations constitute the first evidence for multiple stages of gold deposition at the obuasi deposit futhermore three dimensional modeling of stratigraphy structure and gold orebodies highlights three major controls on oreshoot location which are 1 contacts between volcaniclastic units and pre d 1 felsic dikes 2 fault intersections and 3 f3 ob fold hinges the maximum age for the older disseminated gold event is given by the age of the granites at 2105 2 ma which is within error of hydrothermal rutile in the granites of 2098 7 ma the absolute age of the younger gold event is not known

process studies on the po river plume north adriatic sea the coastal processes in the adriatic sea and in particular the development and evolution of the po river plume are studied with a three dimensional primitive equation model experiments are performed to examine the buoyancy driven flow and the interaction with topography wind stress and ambient stratification the pathways of particles released from the po are computed to simulate the transport of land drained materials in the absence of wind forcing the po river plume consists of an offshore bulge that occupies most of the north part of the basin and a southward coastal current that is confined within the narrow coastal region along the italian peninsula when all adriatic rivers are included basinwide buoyancy driven cyclonic coastal flow is established that diminishes the seaward removal of po waters and promotes their southward advection through the coastal current wind stress modifies the above winds that are downwelling favorable for the po discharge site like bora restrict offshore plume development enhance the southward coastal current and confine the plume within the narrow western adriatic shelf conversely upwelling favorable winds like scirocco eliminate the baroclinic coastal current and advect low salinity po waters toward the shallow parts of the northern adriatic when preexisting stratification of basin waters is described the density field is influenced by both temperature and salinity during winter when the coastal waters tend to be colder and fresher than offshore waters the cyclonic circulation is sustained owing to input from rivers and particularly the po the intense spatial and temporal variability of wind stress and river runoff and the resulting variability in the circulation of the coastal adriatic sea are elaborated through a realistic simulation during january 1994

particle transport in the bari canyon southern adriatic sea to define the sediment transport pathways along the southern adriatic shelf and slope two oceanographic cruises were carried out in the southern adriatic in july 2004 and in march april 2005 to study the role of the bari canyon system on sediment dispersal three moorings including sediment traps and current meters have been deployed near the bottom at depths of 600 m for one year march 2004 march 2005 two moorings were deployed within the canyon station b in the northern branch and station c in the southern branch and one on the adjacent open slope north of the canyon system station a total mass fluxes tmfs measured by sediment traps were always higher in the canyon than on the adjacent slope the highest values were measured at station c average 8 07 g m 2 d 1 roughly double those of station b 3 07 g m 2 d 1 and the lowest outside the canyon at station a 1 69 g m 2 d 1 the highest tmf were recorded in spring 2004 a period characterized by the lowest water temperatures and the highest current speeds up to 72 cm 1 which were associated with the highest across slope current component along the canyon axes the simultaneous variations of fluxes occurring at the three stations imply that similar processes are active along the entire southern adriatic margin and that they are amplified inside the canyon in spring a vein of southward flowing north adriatic dense water naddw was observed along the adriatic shelf this was related to an enhanced across slope current component which was responsible for the higher particle fluxes both on the open slope and at the canyon stations these data suggest that the bari canyon is an efficient conduit for sediment from the adriatic continental shelf to the deep basin downcore profiles of 210 pb in sediments collected below the traps have been used to estimate sediment mass accumulation rates mars on a century scale on the open slope the annual trap flux recorded in 2004 2005 was lower than mar on the contrary in the bari canyon the annual trap flux was higher than mar indicating that the lateral advection of particles becomes predominant and that a fraction of the particles intercepted by sediment traps was only in transit through the canyon 2007 elsevier b v all rights reserved

the effect of wind stress over the eastern mediterranean on deep water formation in the adriatic sea abstract we investigate the effect of interannual variability of the wind stress over the eastern mediterranean on adriatic deep water adw formation using an oceanic general circulation model of the mediterranean sea driven by monthly era interim wind stress of the years 1979 2014 this is done by using climatological annual cycle of the surface temperature and freshwater flux but interannually varying wind stress a connection between the wind stress magnitude over the rhodes gyre region and adw outflow is found in association with the formation of levantine intermediate water liw 720 years artificially generated wind stress fields were constructed based on the first 50 empirical orthogonal functions eofs of the wind stress monthly anomalies this simulation strengthen the connection that was found and also reveal a centennial internal variability of both the liw and the adw outflow it is also found that the intensity of the rhodes gyre is almost linearly related to the wind stress amplitude however the adw outflow is non monotonically related to the wind stress amplitude there is an optimal wind stress amplitude for which the adw formation is maximal when the wind stress amplitude is more than 50 the climatological mean wind stress amplitude the adw outflow is weakened this implies a different balance between the saline liw and the fresh atlantic water entering the eastern mediterranean from sicily strait under stronger than present wind stress amplitude

simple shear testing of sensitive very soft offshore clay for wide strain range stiffness and damping properties of sensitive very soft clay sediments of the italian adriatic continental shelf are determined by means of two series of cyclic simple shear tests one with 12 stages and one with two stages the apparatus used in this research is capable of investigating the stress strain behaviour of the soil in a wide range of shear strains from about 0 0004 to 1 test results were expressed in terms of small strain shear modulus g0 normalized equivalent shear modulus geq g0 and damping ratio d versus cyclic shear strain amplitude c these parameters were analyzed in the framework of existing literature by comparison with empirical correlations developed for onshore materials of different plasticity and limited to g0 also for soft soils the dependence of g0 geq g0 c and d c on factors such as void ratio stress history and loading cycles is analyzed and discussed

formation and deformation of pyrite and implications for gold mineralization in the el callao district venezuela the el callao mining district is the most important gold producing region in venezuela it is hosted in the paleoproterozoic guasipati el callao greenstone belt which forms part of the guayana craton the venezuelan extension of the guiana shield of south america it consists of volcanic and volcanosedimentary sequences that were affected by several deformation events particularly localized shear zones the colombia mine the largest active mine in the district produces 4 tonnes t 128 600 oz of gold annually with reserves estimated at 740 t 24 moz and grades of up to 60 g t gold mineralization is concentrated within a vein network in the colombia corridor a shear fracture hosted mesh of interconnected quartz ankerite albite veins enclosing fragments of altered metabasaltic host rocks gold occurs mostly in the metabasaltic fragments and is spatially associated with pyrite in which it occurs as invisible gold micron sized native gold inclusions and filling fractures based on optical and scanning electron microscopy backscattered electron observations two types of pyrite are recognized a simple zoned pyrite and a less common oscillatory zoned pyrite both types consist of a mineral inclusion rich core and a clearer rim however in oscillatory zoned pyrite the latter is composed of complex rhythmic overgrowths of alternating as rich and as poor bands laser ablation inductively coupled plasma mass spectrometry la icp ms analysis and elemental mapping reveal the presence of invisible gold in all generations of pyrite the highest concentrations 5 23 ppm au are found in oscillatory zoned pyrite rims which correlate with the highest as concentrations 16 000 23 000 ppm in as poor bands au up to 1 5 ppm and as 300 6 000 ppm concentrations decrease by about an order of magnitude copper bi te sb pb and ag always occur with invisible gold particularly in pyrite cores suggesting that at least part of the gold occurs in sulfosalt nanoparticles of these metals and metalloids visible native gold grains occur as small inclusions throughout core and rim of both pyrite types as well as in fractures within it in both occurrences chalcopyrite sphalerite tellurobismuthite ankerite albite and chlorite accompany native gold and gold fineness ranges between 900 and 930 at an early stage of vein mesh formation pyrite formed in the metabasaltic fragments at the expense of ankerite which in turn resulted from alteration of fe ti oxides gold together with other chalcophile elements was incorporated within the structure of pyrite most likely by destabilization of metal sulfide complexes during ankerite replacement subsequent cyclic reactivations of the shear zone caused development of pressure shadows around pyrite generating local and repeated decreases in pressure which triggered local boiling of the hydrothermal fluid as evidenced by the presence of primary fluid inclusions containing immiscible liquid rich and vapor rich aqueous carbonic fluids this process was responsible for a number of physical chemical changes in the liquid all of which contributed to the formation of the as and au rich overgrowths in pyrite 1 removal of h 2 o into the vapor phase inducing saturation of dissolved metals in the remaining liquid 2 an increase in ph due to partition of h 2 s and co 2 into the vapor thus decreasing the solubility of sulfide minerals and 3 an adiabatic decrease in temperature lowering the solubility of as and au in the liquid waning of this process restored precipitation of as poor pyrite until the onset of a new cycle because pressure drops are more significant adjacent to open spaces oscillatory zoned pyrite probably crystallized near newly formed veins whereas simple zoned pyrite formed away from them previously formed pyrite underwent fracturing during reactivation of the deformation especially through the brittle deformation events that postdated shearing resulting in local pulverization of pyrite this newly created porosity facilitated fluid circulation and remobilization of structurally bound gold as well as of other chalcophile elements ag cu bi te pb and sb which reprecipitated together with pyrite in the form of native gold sulfides and tellurides either as small inclusions or as larger grains within fractures this remobilization process facilitates the exceptionally high gold tenor found in the deposit where the colombia corridor is intersected by the santa maria fault

methane derived authigenic carbonates mdac in northern central adriatic sea relationships between reservoir and methane seepages abstract in the adriatic basin gas venting characterized by pockmarks gas bubbling and other fluid escape related features is diffused and has been linked or to shallow gases trapped in the late pleistocene and below the holocene maximum flooding surface or to leakage from more deeply buried pliocene to pleistocene foredeep succession some seepages are associated with carbonate crusts but a possible correlation between methane leakage and carbonate precipitation in this basin never reached a clear definition carbonate concretions recovered by different areas of the adriatic sea northern central and southern at different depths from ca 30 to ca 300 m have been analysed different fabrics petrography and mineralogy can be evidenced for the different sets of samples all of them show a carbonate content mainly represented by high mg calcite up to 66 in weight of total carbonates for the samples from central adriatic close to bonaccia gas field offshore ancona and 79 to 96 of the total carbonate weight for the other samples that are mainly biogenic these differences are also reflected by the 13 c values ranging between 19 and 29 vpdb for the samples collected in the bonaccia area and moderately positive values for all the other samples bonaccia samples contain carbonate cements that record the contribution of methane derived carbon and have been interpreted as formed below the sea floor in correspondence of the sulphate methane transition zone carbonates recovered from the southern and northern adriatic basin do not show clear evidence of methane derived carbon and are mainly made up by organisms typically recovered in the adriatic coralligenous assemblage nonetheless micro morphological evidences suggest influence of bacterial sulphate reduction and methanogenesis in precipitation of some of these carbonates

kinematics of large syn orogenic intrusions example of the lower proterozoic saraya batholith eastern senegal the large saraya batholith intruded the lower proterozoic sequences of eastern senegal structural analysis indicates that this large granitic batholith corresponds to a composite body consisting of several coalescent plutons and interfering diapirs interpretation of the structural fabric patterns in these plutons and in the host rocks constitutes the basis of a hypothetical model of initiation ascent and emplacement as follows 1 development of a deep n s granitic ridge controled by a major crustal fracture generated by an earlier extensional phase re activated by a strike slip fault which probably would facilitate segregation collection and ascent of magmas 2 intrusion and splitting up of the ridge into several diapirs which ascended simultaneously and separately in a setting of a n s sinistral transcurrent deformation inducing a transverse nw se shortening and forceful emplacement of plutons and 3 final emplacement characterized by interference between regional deformation and pluton ballooning the latter leading to the coalescence of intrusions and to the formation of a larger apparently homogeneous body

structural and gold mineralizing evolution of the world class orogenic mana district burkina faso multiple mineralizing events over 150 million years abstract the mana district located in the northern part of the birimian hounde greenstone belt in western burkina faso is a world class paleoproterozoic orogenic gold district 8 moz including five gold deposits fofina nyafe siou wona kona and yaho these deposits are located in specific lithostratigraphic domains and gold is controlled by various structural features deposit and regional scale mapping intrusion age and geochemistry as well as airborne aeromagnetic and electrical resistivity geophysical data were used to decipher the tectonic evolution of each gold deposit and the district five deformational and four gold mineralizing events were recognized the first deformation event d1md e w oriented shortening affected the metamorphosed volcanic and sedimentary rocks of the lower birimian group this early deformation episode was correlated with the formation of gently n plunging folds f1md and n s striking thrusts faults coeval with emplacement of the pre to synkinematic wona kona and siou plutons dated at 2172 ma under greenschist facies metamorphism the quartz carbonate veins v1md at fofina and siou formed during d1md at eoeburnean time manifesting the first gold event at approximately 2172 ma the following deformation event d2md e w oriented extension is associated with the deposition of the upper birimian group mana basin overlying the lower birimian group the geometry of the mana basin is controlled by the mana and maoula shear zones the tarkwaian type rock formation overlying the upper birimian group controlled by the wona kona and siou shear zones is constrained at the end of d2md or at the beginning of the d3md event with a maximum deposition age at 2113 ma the third deformation event d3md e w to wnw ese transpression affected the entire supracrustal rock such event is correlated with the formation of map scale f3md folds and dextral shear zones during the eburnean orogeny 2113 2090 ma a second gold mineralizing event occurred during d3md and is manifested by quartz carbonate veins v3md and disseminated sulfides at the yaho fofina and nyafe and possibly wona kona deposits the fourth deformation event d4md nnw sse transpression is correlated with sinistral shearing along the major transcurrent faults and the development of asymmetric nne striking folds f4md associated with vertical fold axes syn d4md mineralization is characterized mainly by a strong silicification si4md with disseminated pyrite and arsenopyrite along the wona kona shear zone and by tiny quartz carbonate veinlets v4md this event is considered the main gold bearing event in the western margin of the mana district the fifth and last deformation event d5md is brittle in character and was responsible for the formation of e w subvertical crenulation cleavages and reverse faults under overall n s shortening this late deformation event is tentatively associated with a last gold event recorded as free gold associated with muscovite in brittle fractures developed in competent orebodies at the wona kona and siou deposits this event could be as young as 2022 ma the age obtained from ar ar datation of muscovite schists at the wona kona deposit our main contribution is that we decipher multiple gold mineralizing events at the district scale based on deposit and regional scale mapping it is interpreted that gold was introduced as early as 2172 ma and possibly as late as 2022 ma during at least 3 or even 4 shortening tectonic events in a timeframe not yet recognized at the district scale for all the birimian belts

modeling the northern adriatic double gyre response to intense bora wind a revisit 1 a combination of recent intensive observations and simulations with two numerical models is used to revisit the issue of the northern adriatic response to strong bora episodes new observed and simulated data reinforce the view that an episode of strong bora wind provokes a double gyre cyclonic trieste and anticyclonic rovinj response north of the po delta pula line during an intense bora episode both measured and modeled statistics picture a downwind highly polarized and almost depth independent flow within the trieste gyre nw arm its ne arm maintains a sharp polarization and strong depth dependence while exhibiting lower speeds with models in good accord with observations the current statistics for rovinj gyre provide lower maximum and average speed values and less polarized but still rather depth independent flow while exhibiting clockwise rotation the north arm of the senj gyre positioned south of the po delta pula line enjoys more lateral freedom and exhibits less rectilinear flow our review reinforces the notion that modeling studies based on ecmwf wind forcing fail to properly take into account the orographic control of the dinaric alps and to produce correct bora induced gyral pattern the coamps model successfully simulated the onset duration and decay of the wind peaks but exhibited a tendency to overpredict the strength of the bora wind our simulations have identified the shallow nw coastal strip as an important source of colder water observed in a sequence of remotely sensed sst fields derived from avhrr data

mapping turbidity patterns in the po river prodelta using multi temporal landsat 8 imagery abstract thirty meters resolution turbidity maps derived from landsat 8 l8 images were used to investigate spatial and temporal variations of suspended matter patterns and distribution in the area of po river prodelta italy in the period from april 2013 to october 2015 the main focus of the work was the study of small and sub mesoscale structures linking them to the main forcings that control the fate of suspended sediments in the northern adriatic sea a number of hydrologic and meteorological events of different extent and duration was captured by l8 data quantifying how river discharge and meteo marine conditions modulate the distribution of turbidity on and off shore at sub mesoscale peculiar patterns and smaller structures as multiple plumes and sand bars were identified thanks to the unprecedented spatial and radiometric resolution of l8 sensor the use of these satellite derived products provides interesting information particularly on turbidity distribution among the different delta distributaries in specific fluvial regimes that fills the knowledge gap of traditional studies based only on in situ data a novel approach using satellite data within model implementation is then suggested

a fluid inclusion and stable isotope study at the loulo mining district mali west africa implications for multifluid sources in the generation of orogenic gold deposits the world class loulo mining district 15 5 moz resource in the birimian terrane of western mali contains a range of mineralogically diverse styles of orogenic gold mineralization the district is distinguished by as rich orebodies as at yalea as well as tourmaline bearing fe rich orebodies as at gara new fluid inclusion and stable isotope data presented here constrain the nature of the hydrothermal fluids responsible for these different types of mineralization and point towards the role of multifluid sources metamorphic and magmatic in the formation of orogenic gold deposits microthermometric and laser raman studies from yalea main and two other similar orebodies loulo 3 and baboto reveal the dominance of coexisting co 2 n 2 ch 4 type 1 and h 2 o nacl type 2 fluid inclusions these inclusions show evidence of fluid unmixing from reduced quartz faylite magnetite qfm buffered low salinity 10 wt nacl equiv co 2 rich h 2 o nacl n 2 ch 4 primary ore fluids the combination of microthermometric data and geothermometry based on ore and alteration assemblages indicate trapping temperatures and pressures of 270 to 340 c at 1 4 to 1 8 kbar the p t x state of the yalea style mineralizing fluids along with the 18 o fluid compositions of 8 8 to 10 7 is consistent with the derivation of auriferous fluids during greenschist facies regional metamorphism of the host terrane similar fluid compositions were previously reported elsewhere in the birimian crust of west africa and in other orogenic gold districts worldwide the precipitation of gold from the h 2 s rich metamorphic fluid is primarily linked to phase separation of the ore fluid which is controlled by p t fluctuations and or fluid rock interaction with carbonaceous host sedimentary rocks confirmed by low 13 c values of 21 7 to 15 8 fluid inclusion investigations from gara and a similar style orebody yalea north indicate the presence of coexisting co 2 n 2 ch 4 type 1 and mixed salinity 5 21 wt nacl equiv co 2 rich h 2 o nacl inclusions type 3 inclusion assemblages also contain common oxidized hematite magnetite hm buffered high temperature 400 c hypersaline 35 50 wt total dissolved solids metalliferous na fe ca cu ni w pb zn multiphase h 2 o rich co 2 nacl fecl 2 inclusions type 4 this inclusion type has not been previously reported in other birimian terranes the composition of the brines along with carbon isotope data 13 c of 14 4 to 4 5 suggests a magmatic input to the gara style hydrothermal system the coexistence in the fluid inclusion assemblages of the magmatic brines with yalea style co 2 rich metamorphic fluids and the positive correlation between salinity and homogenization temperatures suggest mineralization was locally controlled by fluid mixing the interaction of these two chemically contrasting fluids explains the distinctive petrographic characteristics of the gara style orebodies this includes the growth of widespread multi stage fe 3 rich tourmaline b rich granite source and sodic alteration and ore assemblages consisting of abundant nickeloan pyrite ree phosphates ni co pb zn minor trace sulfides and scheelite gold deposition in the gara style hydrothermal system is related to physical and chemical changes of the two fluids during mixing e g decreases in f o2 and t in the brines and retrograde boiling of the co 2 component in the metamorphic fluids a salting out effect

chemical and boron isotope composition of tourmaline from the kiaka orogenic gold deposit burkina faso west african craton as a proxy for ore forming processes the kiaka orogenic gold deposit burkina faso located in the paleoproterozoic domain of the west african craton is characterized by a two stage gold mineralization hosted in volcano sedimentary metamorphic rocks that was formed during the eoeburnean 2 20 2 13 ga and eburnean 2 13 2 05 ga orogenic cycles these two stages include an early disseminated low grade gold mineralization and a late vein hosted high grade gold mineralization paragenetic studies indicate that the first gold stage was coeval with the deposition of hydrothermal tourmaline the aim of this paper is twofold i to determine the processes responsible for deposition of the economic disseminated gold mineralization and ii to identify the source of the mineralizing fluids for this purpose we performed an in situ study on tourmaline by combining electron probe microanalysis and secondary ion mass spectrometry measurements of boron isotopes hydrothermal tourmaline hosted in metamafic volcanic rocks and metagreywackes has a dravite composition but shows different 11b values falling within the two intervals of 25 1 to 22 0 and 19 6 to 15 1 respectively our results suggest that tourmaline formed from a distal high temperature ca 400 c reduced and low salinity hydrothermal fluid that interacted with the local host rocks based on the modeling of tourmaline fluid boron isotope fractionation we propose a metamorphic fluid origin derived from devolatilization of deeply buried muscovite schists during the regional prograde to peak metamorphism prior ca 2 13 ga this metamorphic fluid rock interaction model may possibly extend to other orogenic gold deposits in the west african craton

geostrophic circulation patterns in the northeastern adriatic sea and the effects of air sea coupling may september 2003 1 ctd data were collected weekly during 20 cruises from may to september 2003 over a 19 station grid in a coastal region of the northeastern adriatic sea as part of the adriatic sea integrated coastal areas and river basin management system pilot project adricosm relative geostrophic velocities indicated fine scale circulation patterns in the area consisting of two pronounced circulation cells of cyclonic and anticyclonic character and that were present in the area for most of the investigated period these motions were induced primarily by spatial variations in the temperature field and may be strengthened during episodes of very strong northeasterly bora wind when the investigated region is not heated cooled uniformly

intrusion related affinity and orogenic gold overprint at the paleoproterozoic bonikro au mo deposit cote d ivoire west african craton the bonikro gold deposit and satellite hire open pits are located at the southern tip of the oume fettekro granite greenstone belt in cote d ivoire country rocks in the region have undergone polyphase deformation and prolonged arc magmatism during the paleoproterozoic eburnean orogeny intrusive host rocks at hire and bonikro have been dated at 2180 6 and 2086 4 ma u pb on zircon respectively these plutonic bodies acted as favourable sites for fluid flow due to their brittle rheological characteristics gold mineralisation at bonikro is hosted by i a sheeted quartz vein array characterised by an au w bi te ag metal association in the cupola of a porphyritic granodiorite and ii an overprinting swarm of fault fill smoky quartz molybdenite veins gold mineralisation at hire is shear hosted and shares a similar relative timing with the latter set of auriferous veins this second phase of gold mineralisation occurred during a period of transcurrent tectonics late in the eburnean tectono magmatic history soon after the cessation of compressional deformation it is responsible for the bulk of gold resources in the region e g bonikro hire agbahou and has been dated at 2074 16 ma re os on molybdenite the integration of structural paragenetic relationships with high precision dating of magmatic and hydrothermal events highlights the superposition of late eburnean orogenic gold mineralisation on an earlier intrusion related gold system linked to the local emplacement of a porphyritic granodiorite at bonikro and illustrates the genetic diversity of paleoproterozoic granitoid hosted gold mineralisation in the west african craton it also further supports that gold mineralisations in the west african craton occurred diachronously throughout the eburnean orogeny through a variety of deposit types including au skarn intrusion related au orogenic au and porphyry cu au

on the origin of a chain of eddies in the gulf of eilat aqaba abstractthe gulf of eilat aqaba is a terminal elongated basin that exchanges water with the northern red sea via the straits of tiran this study used energy budgets of mean kinetic energy mke and eddy kinetic energy eke differentiated by a simple horizontal averaging filter instability analysis and numerical simulations to study the horizontal circulation of the gulf which is characterized by the existence of a chain of eddies along its main axis the kinetic energy is predominantly in the form of eke energy conversion between mke and eke is negligible where the main sources for both energy reservoirs are the conversions from the available potential energy ape this term is balanced by the work done by pressure at the straits in case of mke and by dissipation in the case of eke the mke balance represents the coupling between the exchange flow at the straits and the wintertime dense water formation the dense water exits through the straits while sinking adiabatically along the gulf the stro

dense low salinity outflow from the adriatic sea under mild 2001 and strong 1999 winter conditions 1 quasi synoptic temperature salinity and oxygen measurements in the adriatic and northern ionian seas mediterranean sea during two different winter conditions are presented in addition to the confirmation of previous knowledge about deepwater formation in the eastern mediterranean measurements give more insight into processes in the adriatic sea in winter and especially into the fate of the dense low salinity water masses transported by the west adriatic current wac and its spreading into the ionian sea a mild winter season without dense water production in the shallow areas of the adriatic sea was encountered during a cruise in february 2001 dense water outflow restricted to the deeper parts of the strait of otranto was nevertheless present during that mild winter and also in previous records of a cruise in autumn 1999 thus even in times of no deepwater production in the southern adriatic sea observations reveal a continuous flow of adriatic deep water adw through the strait of otranto and downslope in the northern ionian sea strong winter conditions are represented by a cruise carried out in february 1999 at that time cold and fresh water with density higher than that of south adw was observed on the italian shelf the dense coastal current is continued around cape santa maria di leuca at the heel of the italian boot in the gulf of taranto where the width of the shelf rapidly decreases dense coastal water is released to depth and transformed by intrusion and mixing with ambient water plumes and patches with horizontal extensions smaller than distances of a station grid are resolved by towed measurements in the 200 m upper layer with a multisensor chain products of coastal water transformation may be found at any depth on the western slopes of the ionian sea the new observations of dense water carried by the wac and plunging down to the level of neutral buoyancy in the gulf of taranto seem to confirm the hypothesis that the wac could be the origin of cold lenses found below the thermocline in the central ionian sea sellschopp and onken 2000

the hydrothermal fluid of archaean lode gold deposits at different metamorphic grades compositional constraints from ore and wallrock alteration assemblages a low salinity mixed aqueous carbonic fluid is common to all archaean lode gold deposits throughout the range of mineralising conditions from sub greenschist to lower granulite facies temperatures alteration assemblages and fluid inclusion data give constraints on the fluid composition fluid xco2 is 0 1 0 3 in typical greenschist facies mesothermal deposits at higher temperatures the assemblages are consistent with formation from a fluid of similar composition but slightly higher or lower xco2 cannot be ruled out and fluid inclusion data indicate that ch4 may be an important component in ore fluids at these temperatures fluid ph is neutral or weakly alkaline at all conditions a range of relative oxidation states of four orders of magnitude fo2 is indicated at any temperature with deposits more oxidising relative to qfm at lower temperature sulphur contents of the fluids vary from 10 to 10 3 5m s with a trend towards lower sulphur contents at lower temperatures the relative concentrations of major cations in solution are similar at all conditions with na k ca although ca may be less abundant at low temperatures the broad similarities in ore fluid composition at all temperatures give support to crustal continuum models in which archaean lode gold mineralisation involved either a single fluid moving through the middle and upper crust or derivation of ore fluids by similar processes at different crustal levels many of the compositional differences between high and lowtemperature ore fluids may be attributed to evolution of deep sourced hydrothermal solutions as they rise along structurally controlled conduits the constancy of major ore fluid component concentration e g co2 cl k suggests fluid buffering and high fluid rock ratios along fluid pathways fluid buffered conditions can also explain the ore fluid fo2 temperature relations with equilibria between oxidised and reduced aqueous carbon or sulphur species controlling the oxidation state in contrast the concentrations of components present in lesser abundance in archaean gold ore fluids e g s ca h were probably controlled either by saturation of one or more mineral phases brought on by decreasing temperature or were rock buffered through fluid rock reactions extrapolation to high temperatures of the k na and ca contents of the gold bearing fluids indicates that their composition is consistent with derivation from or final equilibration with rocks of intermediate granitic composition thus giving support to isotopic and geological arguments for ore fluid source regions external to the greenstone belts the fluid oxidation states are characteristic of a wide range of potential source rocks including mantle derived igneous rocks calc alkaline granitoids and magmas and seaflooraltered metabasalts strongly oxidised magmatic sources or unusually oxidising source processes e g co2 streaming during granulitisation of the lower crust are therefore not required in the genesis of arch an lode gold deposits

is the southeastern adriatic sea coastal strip an eutrophic area abstract this study intends to understand and assess the effects of the discharge from the buna bojana river delta watersheds on the eutrophic status of the southeastern adriatic sea and contrast this area with the northwestern adriatic region where the po river dominates the freshwater discharge into the coastal ocean we compare observations of inorganic nutrients turbidity and physical variables from the two regions and use numerical model results to characterize the physical circulation of the two areas the area affected by the po river discharge extends at least one hundred kilometers southward from the delta and approximately 20 km offshore maximum chlorophyll concentrations typically occur within the river plume similarly in the southeastern adriatic sea the buna bojana river discharge extends northward along the coasts for approximately one hundred kilometers and contains a large maxima in the regional chlorophyll distribution the two coastal areas tend to have opposing physical forcing processes the po river tends to be affected area by northerly to northeasterly winds that cause downwelling whereas the buna bojana river on the opposite side of the basin is typically characterized by northerly upwelling favorable winds however during the study period upwelling is not a dominant feature of the circulation and both the shelf slope current southeastern adriatic sead current and the along shore currents in the southeastern adriatic sea are northward the along shore current probably dominated by the river runoff is here described for the first time and called the southeastern shelf coastal sesc current under these conditions primary productivity is high in both regions leading us to conclude that river plume dynamics and the associated nutrient inputs determine the eutrophication status of the coastal strip regardless of the circulation regime in the southeastern adriatic sea area the adriatic southeastern coastal area is an eutrophic area that is strongly affected by freshwater inputs particularly from the buna bojana river system

west africa gold preface west africa with an approximate 10 000 metric ton t gold endowment is one of the world s great gold provinces and the largest paleoproterozoic gold producing region the gold resources are concentrated within the 2250 to 2000 ma greenstone belts of the man leo shield forming the southern part of the west african craton the gold endowment of the eburnean gold deposits mainly orogenic type equals that of the world s other great precambrian lode gold provinces however the exploration and mining is much less mature in west africa than it is in other great precambrian gold provinces with much of the development throughout the man leo shield taking place during just the past 25 years the contributions included in this west africa gold special issue of economic geology collectively document the paleoproterozoic gold endowment observed in the southern part of the west african craton from west mali guinea to east burkina faso ghana from large to deposit scales and throughout the eburnean orogeny goldfarb et al 2017 present a broad scale overview of the paleoproterozoic gold endowment of man leo shield southern part of the west african craton the eburnean orogeny generated the world s most significant paleoproterozoic gold accumulation in the greenstone belts of ghana mali burkina faso and adjacent countries this paper documents successively the geology of the region gold deposit distribution in the man leo shield the

membrane effect of geosynthetic reinforcement subjected to localized sinkholes a membrane effect often occurs in geosynthetic reinforced structures where subsoil may have voids or sinkholes an analytical model is proposed to estimate membrane effect of a geosynthetic reinforcement subjected to localized sinkholes the upper interface friction in the subsided area and vertical deformation of supporting soil in the anchorage area are considered simultaneously the maximum geosynthetic strain and maximum surface settlement serving as key design points can be determined based on the proposed method verified using a full scale experiment a parametric study is conducted the results show that ignoring upper interface friction results in significant undervaluation of maximum geosynthetic strain and ignoring vertical deformation of supporting soil leads to obvious undervaluation of maximum surface settlement a practical design framework is also proposed and it is an applicable tool for preliminary design of geosynthetic reinforced structures especially for cases with soft ground

seafloor evidence for the interaction between cascading and along slope bottom water masses 1 the steep slope of the sw adriatic margin central mediterranean is impacted today by two water masses having markedly different origin but a similar southward flow component the levantine intermediate water liw and the north adriatic deep water naddw the liw forms through evaporation in the eastern mediterranean and enters the adriatic along a counterclockwise path the naddw forms through winter cooling on the north adriatic shelf and cascades across the western slope of the south adriatic basin bathymetric and side scan sonar tobi images of the sw adriatic margin accompanied by chirp sonar profiles define an area of extreme seafloor complexity characterized by a variety of sediment waves erosional scours longitudinal furrows and giant comet marks these distinctive bottom current features are not randomly distributed but appear genetically linked and have a consistent down current arrangement we ascribe this seafloor pattern to the constructive interference of the highly saline liw flowing along the slope between 200 and 600 m water depth and the cold naddw plunging off shelf obliquely to the slope stratigraphic data indicate that this oceanographic regime has been active since the last glacial interglacial transition the cascading naddw is density driven but is not short lived as a turbidity current would be consequently the interaction between downslope and along slope currents is here more dynamical as two water masses act simultaneously over a prolonged interval somewhat diverting their paths and leading to locally enhanced energetic conditions at the seafloor

mineralisation footprints and regional timing of the world class siguiri orogenic gold district guinea west africa siguiri is a world class orogenic gold district hosted in the weakly metamorphosed upper birimian to lower tarkwa group sedimentary rocks of the siguiri basin guinea the district is characterised by a protracted deformation history associated with four main deformation events d1s is a n s compression d2s is an e w compression progressively evolving into an early d3s transpression and then into a late d3s nnw sse transtension and d4s is a ne sw compression field observations petrography and geochemistry at three key deposits of the siguiri district bidini sintroko pb1 and kosise suggest a polyphase hydrothermal history that can be subdivided into four hydrothermal events the first hydrothermal event was associated with the development of barren bedding parallel and en echelon v2s quartz dominated pyrite veins the second hydrothermal event is characterised by the development of v3a pyrite ankerite veins late during d3s laser ablation icp ms data show that this vein set contains high gold contents of up to 43 3 ppm in substitution in pyrite crystal lattice representing a minor first gold mineralisation event the third and most prominently developed hydrothermal event is late d3s and represents the second and principal gold mineralisation event this mineralisation event led to two distinct mineralisation textures the first texture is best exposed in the kosise deposit and is characterised by gold bearing quartz ankerite arsenopyrite conjugate v3b veins although the bulk of the gold is hosted in native gold grains in v3b veins la icp ms analyses show that gold also substitutes in the arsenopyrite crystal lattice up to 55 5 ppm the second mineralisation texture is best expressed in the sanu tinti deposit and consists of disseminated barren pyrite hosted in a polymict conglomerate the second and third hydrothermal events are both structurally controlled by a series of early d3s n s ne sw wnw ese and e w sub vertical incipient structures expressed as fracture zones of higher v3s vein density a composite geochemical cross section across fracture zones from the kosise deposit indicates that gold mineralisation in the siguiri district is associated with enrichments in ag au as bi co mo sb s te and w relative to background geochemical variations associated with the ore shoots in the siguiri district are consistent with petrographic observations and highlight an albite carbonate sulphide sericite alteration the fourth and last hydrothermal event is associated with the development of a late penetrative s4s cleavage during d4s deformation which overprints all pre existing hydrothermal features and is associated with the deposition of free gold chalcopyrite and galena along fractures in v3a pyrite and v3b pyrite and arsenopyrite mineralogical and geochemical footprints as well as timing of the gold mineralising events in the siguiri district when compared with other deposits of the west african craton highlight the synchronicity of gold mineralisation in siguiri syn d3s and syn d4s events with other similar events in this part of the craton such as the early au sb bi te w mineralisation at the morila deposit in southeast mali our results support the hypothesis that late eburnean age gold mineralisation in the siguiri district and in the west african craton as a whole was polyphase

an analysis of dense water production on the north adriatic shelf abstract the aim of this paper is to investigate the mechanism of dense water formation in the northern shelf region of the adriatic sea and its spreading towards the middle and south adriatic the analyses encompass temperature salinity sigma t and dissolved oxygen data collected during 1951 1989 interval in the deep trench located in the middle of the adriatic hydrographic sections as well as current and temperature time series collected in the north and middle adriatic were analysed too the data outline linear trends of salinity by 0 0036 0 0017 year 1 and of dissolved oxygen content by 0 022 0 008 ml l 1 year 1 whereas temperature data reveal three periods having different attributes strong fluctuations 1951 1962 higher 1966 1980 and lower 1981 1989 temperature values two types of north adriatic dense water naddw formation result from the analysis the first with rather low temperatures high rates of surface buoyancy losses e g 1956 1981 1984 and the second with high salinity large inflow of levantine intermediate water liw e g 1955 1968 after formation on the shelf naddw can bifurcate and goes close to the western main branch and or eastern secondary branch flanks by correlating hydrological data collected at the bottom of the trench with the north adriatic surface buoyancy fluxes and the po river discharges main naddw current velocity is calculated to be higher than 8 cm s 1 therefore reaching the jabuka pit about 1 month after generation whereas the secondary branch arrives there about 1 month later naddw current lasted for about 2 months spring 1984 preconditionings favourable for the naddw formation are achieved too by correlating both surface buoyancy fluxes and the po river discharges with temperature data measured at the bottom of the jabuka pit

short lived eburnian orogeny in southern mali geology tectonics u pb and rb sr geochronology abstract this work is based on a comprehensive field survey including mapping of the massigui degree sheet in southern mali the investigated area belongs to the northern part of the man shield which is mainly composed of lower proterozoic volcano sedimentary sequences birimian and of large areas of granitoids the whole being affected by the eburnian orogeny structural and geochronological u pb and rb sr results from this study point to a short period of time 30 ma for the eburnian orogenesis between 2100 and 2070 ma the events recorded later 1984 30 ma being due to tectonic reactivations on the other hand no trace of events older than 2100 ma have been found coupled with geochemical and rb sr isotopic systematics this leads to invoke a fundamental link between birimian volcanics and eburnian granitoids both being high k calc alkaline in composition and coming from a single evolving mantle source in a palaeo environment which has some of the characteristics of modern subduction including back arc or docking zones the main regional structure of the area strikes roughly nne ssw with an important strike slip component escorted by a greenschist metamorphism the deformation is the most intense in the n40 to n10 5 km large banifin shear zone where metamorphism reached the lower amphibolite facies here one observes subvertical strong foliation non cylindrical folding locally sheath folds and subhorizontal pencil lineations the deformation being regionally recorded by light subisoclinal folds with subvertical axes compatible with a sinistral movement this regional shear tectonics d2 2074 9 8 ma is preceded by an isoclinal deformation d1 bracketed between 2098 5 ma and d2 only known as relics from which it likely derived a later phase d3 occurred along the banifin shear belt at a more superficial level even if still ductile generated by a dextral movement and having induced retrograde metamorphism this last tectonic phase which is not accompanied by plutonism nor volcanism has been dated at 1982 30 ma being responsible for the complete resetting of the rb sr isotopic system in the plutons present in the banifin corridor

transcurrent tectonics and polycyclic evolution in the lower proterozoic of senegal mali abstract outcrops of the early proterozoic birimian series within the kedougou inlier straddling the mali senegal border have traditionally been described as being composed of a basal volcanic mako series overlain by a detrital carbonate dialle dalema series this geosynclinal context was later reinterpreted in terms of oceanization and subduction as the mako series contains successively basaltic pillow lavas of tholeiitic affinity and a calc alkaline complex however the sedimentary dialle dalema series lie in the core of a major anticlinorium and the rocks show overprinting of an earlier by a later tectonic phase the volcanic and sedimentary rocks of the mako series were affected only by the later tectonic phase in addition a fan delta deposit intercalated between the tholeiitic and calc alkaline rocks contains pebbles of schistose and folded sedimentary rock that clearly belong to the dialle dalema series these observations necessitate a complete revision of the local stratigraphy thus the clastic deposits of the dialle dalema are attributed to the lower birimian and are interpreted as having been deposited in intra cratonic basins the first tectonic phase took place before emplacement of the volcanic sereis which shows evidence of an extensional setting with major crustal fracturing the second deformation affected both the sedimentary and volcanic series structural analysis furthermore shows that the formation of the second cleavage s2 was contemporaneous with the emplacement of major granite bodies as well as with major transcurrent sinistral shear zones finally this evolution is shown to be comparable with that in other lower proterozoic terranes of the west african craton

february 2003 marine atmospheric conditions and the bora over the northern adriatic 1 a winter oceanographic field experiment provided an opportunity to examine the atmospheric marine conditions over the northern adriatic mean february winds are from a northeasterly direction over most of the adriatic and a more northerly direction along the western coast wind speeds are fastest in jets over the ne coast during bora events and weakest in the mid northwestern adriatic diurnal air temperature cycles are smallest on the ne coast and largest in the midwestern adriatic the maximum sea air difference is 10 c on the eastern coast and near zero on the midwestern adriatic boras are northeasterly from wind events that sweep off croatia and slovenia bringing slightly colder and drier air over the northern adriatic the main bora season is december to march winter 2002 2003 was normal for bora events synoptic scale temporal variations are correlated over the northern adriatic fastest bora winds and highest wind stress over the northern adriatic is concentrated in four topographically controlled jets the strongest is the senj jet while the trieste jet extends across the entire northern adriatic between each two jets is a weak wind zone the greatest mean net heat loss is in bora jets in the ne adriatic where it was 438 w m 2 and is weakest in the midwestern northern adriatic where it was near zero wind stress is concentrated over the ne half of adriatic in four bora jets while wind stress is weak in the nw adriatic there is significant variation in wind stress mean and standard deviation structure over the northern adriatic with each bora event

stable c o and s isotope record of magmatic hydrothermal interactions between the faleme fe skarn and the loulo au systems in western mali the gara yalea and gounkoto au deposits of the 17 moz loulo mining district largely hosted by the kofi series metasediments are located several kilometers to the east of the 650 mt fe skarn deposits in the adjacent faleme batholith the au deposits are interpreted to have formed through phase separation of an aqueous carbonic fluid which locally mixed with a hypersaline brine of metaevaporite origin recognition of an intrusive relationship between the faleme batholith and kofi series opens the possibility that the fe skarns and au deposits are part of the same mineral system in this paper we combine new 13c 18o and 34s data from the karakaene ndi skarn au occurrences along the western margin of the kofi series and zircons within plutonic rocks of the faleme batholith we combine these with existing data from the loulo au deposits to model the contribution of magmatic volatiles to au mineralization c and o isotope compositions of auriferous carbonate quartz sulfide veins from the loulo au deposits have wide ranges 13c 21 7 to 4 5 and 18o 11 8 to 23 2 whereas values from carbonate veins in kofi series au prospects close to the faleme batholith and the karakaene ndi fe skarn deposit have more restricted ranges 13c 16 8 to 3 7 18o 11 4 to 17 2 and 13c 3 0 1 18o 12 6 1 respectively kofi series dolostones have generally higher isotopic values 13c 3 1 to 1 3 and 18o 19 1 to 23 3 pyrite from kofi series au prospects adjacent to the faleme batholith have a wide range of 34s values 4 6 to 14 2 similar to pyrite from the karakaene ndi skarn 2 8 to 11 9 whereas 34s values of pyrite and arsenopyrite from the loulo deposits are consistently 6 comparison of the c and o isotope data with water rock reaction models indicates the loulo au deposits formed primarily through unmixing of an aqueous carbonic fluid derived from the devolatilization of sedimentary rocks with an organic carbon component isotopic data are permissive of the hypersaline brine that enhanced this phase separation including components derived from both kofi series evaporite horizons interlayered with the dolostones and a magmatic hydrothermal brine this magmatic hydrothermal component is particularly apparent in o c and s isotope data from the gara deposit and au prospects immediately adjacent to the faleme batholith

structural controls on granitoid hosted gold mineralization and paleostress history of the edikan gold deposits kumasi basin southwestern ghana the 9 moz total aggregate gold endowment at the edikan mine kumasi basin ghana is contained within a cluster of orogenic gold deposits located along the akropong fault zone the granitoid hosted orebodies at edikan e g ag2 ag3 fobinso esuajah essentially an interconnected mesh of gold bearing quartz veins formed during deformation event d3edk which postdates the penetrative regional d2edk deformation the gold bearing quartz veins developed in and adjacent to n s and nw se trending low angle thrust faults that crosscut lithological contacts and earlier formed steeply dipping d2edk faults our paleostress analysis shows that the d3edk deformation during which the mineralized fault system developed was characterized by a wnw ese hybrid compression that evolved to a strike slip regime this progressive deformation is best described with the following stress regimes wnw ese transpression pure compression t1 associated with low angle thrusting subsequent transpression strike slip t2 and later strike slip transtension t3 associated with steeply dipping strike slip faulting the bulk of the granitoid hosted gold mineralization at edikan is associated with two principal sets of gold bearing quartz veins including low angle fault fill veins controlled by thrusts and shallow dipping oblique extension veins that developed during t1 the activation of the reverse and sinistral strike slip faults led to the development of restraining jogs characterized by abundant shallow and steeply dipping gold quartz veins with moderately ne plunging ore shoots the geometry of the mineralized fault fracture meshes is consistent with fault valve behavior in a horizontal compressive stress regime under sustained conditions of supralithostatic fluid pressures at low differential stress

mediterranean sea large scale low frequency ocean variability and water mass formation rates from 1987 to 2007 a retrospective analysis abstract we describe a synthesis of the mediterranean sea circulation structure and dynamics from a 23 year long reanalysis of the ocean circulation carried out by adani et al 2011 this mesoscale permitting dynamical reconstruction of past ocean variability in the mediterranean sea allows the study of the time mean circulation and its low frequency decadal components it is found that the time mean circulation is composed of boundary and open ocean intensified jets at the border of cyclonic and anticyclonic gyres the large scale basin circulation is generally characterized in the northern regions by cyclonic gyres and in its southern parts by anticyclonic gyres and eddy dominated flow fields with the exception of the tyrrhenian and the northern ionian sea the time mean tyrrhenian sea circulation is dominated by cyclonic gyres of different intensity and intermittency the northern ionian sea circulation however reverses in sign in two ten year periods the first in 1987 1996 and the second in 1997 2006 which is here called the northern ionian reversal phenomenon this reversal is provoked by the excursion of the atlantic ionian stream from the middle to the northern parts of the basin the decadal variability of other parts of the basin is characterized by changes in strength of the basin scale structures the water mass formation rates and variability are dominated by event like periods where the intermediate and deep waters are formed for 2 3 years at higher rates the largest deep water formation events of the past 23 years occurred separately in the western and eastern mediterranean basin the first coincided with the eastern mediterranean transient roether et al 1996 and the second with the western mediterranean deep water formation event in 2005 2006 smith et al 2008 a new schematic of the basin scale circulation is formulated and commented

coastal mixing in multiple mouth deltas a case study in the po delta italy abstract satellite imagery provides evidence of complex mixing dynamics in the coastal zone in front of multiple mouth deltas one peculiar feature identified in front of the po delta italy consists in warmer water bulges present in some periods in the coastal zone between the river mouths such features are evident during both high and low river discharge through an integrated approach based on the analysis of satellite imagery in situ field data and a high resolution oceanographic model representing the whole river delta sea system we investigated the relative contribution of the different forcing in controlling coastal mixing of riverine waters the results evidence that the occurrence of these warmer saltier water bulges is due to upwelling induced by the combined action of tides and wind regimes aligned along coastline winds from the land and along the coast drive the upwelling through the well known mechanism described by ekman the presence of river discharge enhance the water column stratification creating the conditions in which tidal action follows the tidal straining theory both processes are identified in modelling results the occurrence of these localized coastal waters with peculiar thermohaline characteristics detectable on satellite imagery of the area can be relevant in the definition of the freshwater areas of influence and the mechanisms of riverine water mixing in the near coastal zone this can shed some light eventually on characterizing the sediment dynamics as well as the thermohaline properties of waters in the area and also to identify eventual impacts on the local ecosystems and fishery

general circulation of the northern adriatic sea results of long term measurements abstract residual sea currents of the northern adriatic were analysed in the sense of the general global circulation over a period of 42 months in one main and two control stations at the end of the summer season and the beginning of autumn in the so called inversion period residual surface 6 m sea currents at the main station showed characteristic seasonal behaviour a change of direction from the north nw n ne to the south east se the sequence with se directions lasted about 1 5 months after that directions changed again to the nw or n the direction of bottom residual currents 37 m in this inversion period had the same pattern as the surface ones this behaviour of the currents can be associated with the change of the cyclonic gyre into the anticyclonic in all other periods at the main station the surface residual sea currents have predominant north directions bottom residual currents mainly followed the pattern of surface currents for all stations and periods except during the periods from january to june 1990 and 1992 when they were of opposite direction at station b

early proterozoic ore deposits and tectonics of the birimian orogenic belt west africa abstract the early proterozoic of the west african craton comprises a series of volcanic troughs and sedimentary basins the birimian with granitic terranes accreted on archean nuclei in the man and reguibat shields studies of the birimian of the man shield indicate a model of polycyclic evolution with a major collision event d 1 2 1 ga thrusting part of the proterozoic terrane over the archean before individualization of numerous volcanic troughs and clastic infill basins the proposed evolution for the birimian orogenic belt comprises 1 deposition of the sedimentary lower birimian b1 with minor tholeiitic volcano sedimentary intercalations containing chert and or mn formations and with most of the detritus being derived from early proterozoic sources apart from contamination near the proterozoic archean contact 2 pre b2 crustal thickening related to d 1 thrusting 3 formation over about 40 ma of the upper birimian b2 with numerous volcanic troughs of different composition tholeiitic and rare komatiitic bimodal tholeiitic to calc alkaline volcano plutonic and tarkwaian clastic infill basins and 4 major transcurrent tectonics with sinistral d 2 and dextral d 3 strike slip faults such a tectonic evolution from a collision d 1 phase to a transcurrent d 2 d 3 phase is typical of collision belts and in the present case the evolution of the birimian orogenic belt can be extended into guyana the metallogenic history of the birimian shows a three phase evolution coinciding with the orogenic evolution and extends over almost 150 ma from the perkoa massive zn ag sulfides 2 12 ga with a clear mantle affinity to the latemesothermal au quartz veins 2 ga with according to lead isotopes a high crustal participation the economic mineralization of belt thus consists of 1 1 pre orogenic pre d 1 deposits related to early extension zones this was diverse with stratiform au tourmalinite type 1 au loulo in mali dorlin in guyana stratiform fe cu faleme in senegal and mn nsuta in ghana tambao in burkina faso and a single massive zn ag sulfide deposit perkoa in burkina faso associated with regional volcanosedimentary variably tholeiitic stratigraphic marker beds 2 2 syn orogenic post d 1 to syn d 2 d 3 deposits with disseminated au sulfides type 2 au yaoure in the ivory coast in extensional zones of the b2 followed by auriferous paleoplacers type 3 au in b2 extensional zones tarkwaian banket conglomerate or syn d 2 transtensional zones debris flow of orapu in guyana 3 3 late orogenic post peak d 2 d 3 deposits with mesothermal au mineralization evolving from a disseminated gold bearing arsenopyrite and au quartz lode type type 4 au ashanti in ghana to a quartz vein type with free gold and cu pb zn ag bi paragenesis most of the gold in west africa comes from this phase finally the metallogeny of the birimian appears as rich in au and mn formations and poor in volcanogenic mineralization and bif it differs from the archean metallogeny of west africa and other regions through the presence of certain deposit types such as au stratiform tourmalinite gold bearing conglomerate with au and fe ti oxides but no uranium or sulfides and au arsenopyrite rich shear zone deposits that are very common in but not exclusive to the proterozoic and paleozoic

observations of event scale sedimentary dynamics with an instrumented bottom boundary layer tripod abstract a new approach to examine event scale sedimentation is described that establishes a direct connection between water column signals and changes in the seabed the po river italy shelf is a good case study due to the dominant impact of winter storm events on sediment transport and the availability of coincident measurements necessary for the analysis repeated deployments of an instrumented bottom boundary layer tripod at this site have produced a nearly continuous record of sediment transport over 2 5 y sediment cores were collected every 3 mo during this time and seabed inventories of 7 be half life 53 3 d were used to determine net sediment deposition or erosion during each deployment comparison of these values with the net elevation change obtained from the tripod altimeter shows good agreement varying from 2 cm deposition to 1 cm erosion the altimeter s use is extended to quantify the net seabed change that results from individual storm induced sediment resuspension events lasting from days to weeks within each event analysis of the altimeter record has proved challenging likely due to changes in sediment porosity that occur during a storm event however net erosion and deposition that occurs over an event can be evaluated and was found to be

deposition and flux of sediment from the po river italy an idealized and wintertime numerical modeling study abstract recent studies of sediment dynamics and clinoform development in the northern adriatic sea focused on winter 2002 2003 and provided the data and motivation for development of a detailed sediment transport model for the area near the po river delta we used both idealized test cases and more realistic simulations to improve our understanding of seasonal sediment dynamics there we also investigated the relationship between physical processes and the observed depositional products e g the accumulation of sediment very near the po river distributary mouths sediment transport near the po river was evaluated using a three dimensional ocean model coupled to sediment transport calculations that included wave and current induced resuspension suspended sediment transport multiple grain classes and fluvial input from the po river high resolution estimates from available meteorological and wave models were used to specify wind wave and meteorological forcing model results indicated that more than half of the discharged sediment remained within 15 km of the po river distributary mouths even after two months of intensive reworking by winter storms during floods of the po river transport in the middle to upper water column dominated sediment fluxes otherwise sediment fluxes from the subaqueous portion of the delta were confined to the bottom few meters of the water column and correlated with increases in current speed and wave energy spatial and temporal variation in wind velocities determined depositional patterns and the directions of sediment transport northeasterly bora winds produced relatively more eastward transport while southwesterly sirocco winds generated fluxes towards both the north and the south eastward transport accounted for the majority of the sediment exported from the subaqueous delta most likely due to the frequent occurrence of bora conditions progradation of the po river delta into the adriatic sea may restrict the formation of the western adriatic coastal current increasing sediment retention at the po delta and reducing the supply of sediment to the apennine margin a positive morphodynamic feedback may therefore be present whereby the extension of the delta into the adriatic increases sediment accumulation at the delta and facilitates further progradation

variability of the large scale general circulation of the mediterranean sea from observations and modelling a review abstract in this paper we present an overview of the most recent findings about the mediterranean sea present day circulation structure both historical observations and numerical model simulations are presented outlining the differences and agreement the model simulations are presented for both an eddy resolving and a coarse resolution numerical model and the results are intercompared the importance of the mesoscales in modifying the large scale flow field is elucidated the critical point is the discovery of the large amplitude interannual variability of the circulation and water mass structure associated with the anomalies of atmospheric forcing over the basin the seasonal variability can be strictly related to changes in heat and momentum fluxes while the interannual variability has a component which is related to the mesoscale field the latter is very intense in the algerian current region and levantine basin but different in structure in the two regions results are shown which confirm the importance of wind driving in establishing the kinetic energy of the flow field by comparing the current transport at the strait of corsica with observations in conclusion the essential characteristics of the present day circulation are associated with the atmospheric forcing and the basin topographic structure results from palaeoceanographic simulations for the last 20 000 years show that changing the atmospheric forcing can cause large changes in the circulation structure which may have affected sapropel formation

the alamoutala carbonate hosted gold deposit kedougou kenieba inlier west africa the alamoutala gold deposit is located in the kedougou kenieba inlier a window of paleoproterozoic rocks that crop out in eastern senegal and western mali the deposit is part of the 3 moz au yatela district and produced 308 400 oz au between 2002 and 2012 country rocks in the alamoutala open pit consist of carbonate rocks arenites wackes and siltstones the sedimentary rocks have been subjected to polycyclic deformation and regional greenschist facies metamorphism synkinematic calc alkaline intermediate quartz feldspar porphyry stocks intruded the metasedimentary rocks at 2083 7 ma u pb zircon amphibolite facies contact metamorphism of carbonate rocks resulted in the formation of a high temperature low pressure magnetite bearing skarn field relationships and microtextural data however indicate that economic gold mineralization is shear hosted and occurred during retrograde contact metamorphism geometric and kinematic analyses indicate that the ore hosting structures were undergoing sinistral reverse displacement at the time of mineralization ore minerals deposited synchronous with a potassic hydrothermal alteration assemblage defined as biotite calcite pyrite k feldspar actinolite tremolite quartz muscovite and tourmaline petrographic studies reveal that ore related sulfides largely consist of pyrite with lesser pyrrhotite and chalcopyrite the ore also contains accessory ag sb as hg bi te mo w zn pb ni co u bearing mineral species the alamoutala deposit represents two distinct hydrothermal systems in which a locally developed magnetite bearing skarn was overprinted by a region wide orogenic gold event in the late eburnean

the geology and mineralogy of the loulo mining district mali west africa evidence for two distinct styles of orogenic gold mineralization loulo is a world class orogenic gold mining district in the birimian terrane of western mali orebodies are located along second or higher order shears associated with the senegal mali shear zone with gold mineralization largely linked to a transtensional event the mine camp is divided into two distinct styles of gold deposit on the basis of differing geologic characteristics one group is typified by the gara deposit whereas the other by the yalea deposit both deposit styles are hosted by similar rock types calcareous graywackes and calciticdolomitic marbles gara style orebodies occur as sulfide disseminations or ankerite rich shear vein stockworks hosted in folded tourmalinized sandstones and breccias mainly within 2 km of the senegal mali shear zone these deposits are characterized by intense multi stage albitization and tourmalinization pre syn and postmineralization gold lodes are fe rich dominated by nickeloan pyrite contain cu ni co minor and trace sulfides e g chalcopyrite gersdorffite pentlandite cobaltite millerite and show consistently high levels of p ree w bearing phases apatite monazite xenotime and scheelite base metal concentrations show a marked increase in marble host rocks with the formation of nickeloan pyrite cobaltite clausthalite ores in contrast yalea style deposits are associated with quartz ankerite vein lodes and disseminated sulfide stringer zones mineralization occurs along highly altered tourmaline absent brittle ductile shears up to 8 km away from the senegal mali shear zone wall rock alteration is characterized by addition of k 2 o cao co 2 h 2 o and sio 2 with mineral assemblages consisting of chlorite sericite carbonate quartz albite ore paragenesis is enriched in as mainly as multistage growth of arsenopyrite and arsenian pyrite base metal sulfides scheelite and ree phosphates are extremely rare the diversity in the ore paragenesis is controlled by a dynamic hydrothermal system that sourced fluids and metals from different reservoirs within the region the as rich yalea style deposits have characteristics typical of birimian gold mineralization in ghana and auriferous fluids are likely derived from the dewatering of sedimentary rocks during regional metamorphism on the other hand the polymetallic fe b rich gara style orebodies show atypical features for birimian gold mineralization instead field relations and the mineralogy and geochemistry of the gara style lodes indicate a strong hydrothermal influence from surrounding intrusive stocks with possible links between gold mineralization and iron oxide skarn development in the region the data collected at loulo highlight the diverse nature of orogenic gold deposits especially in west africa this style of ore deposit can form from a variety of fluid sources both metamorphic and magmatic

simulation of the northern adriatic circulation during winter 2003 1 numerical simulations of the adriatic sea were conducted with the navy coastal ocean model during the adriatic circulation experiment in the fall and winter of 2002 2003 and results were compared with observations the ocean model used a 1 km resolution grid over the entire adriatic sea model forcing included atmospheric fluxes from the coupled ocean atmosphere mesoscale prediction system coamps tides boundary conditions from a global model and freshwater river and runoff inflows model tidal elevation showed good agreement with international hydrographic organization station data and model tidal currents showed good agreement with tidal currents determined from acoustic doppler current profiler adcp measurements detided model currents showed good agreement with adcp currents with rms errors along the principal variance axes ranging from 6 to 12 9 cm s and correlations ranging from 0 16 to 0 81 correlations between model and adcp currents along the minor variance axes were generally low comparison of the model simulated temperature and salinity profiles during january and february with conductivity temperature depth measurements indicated that the model captured some of the spatial structure of the observed fields the model response to several bora wind events in january and february showed a recurring pattern of cyclonic and anticyclonic gyres that generally agreed with observations and reflected the pattern of wind stress curl from the coamps wind stress forcing during strong bora forcing two large cyclonic circulation gyres form in the northern adriatic with a smaller anticyclonic circulation between them near the istrian peninsula additionally a couple of large meanders frequently occur within the eastern adriatic current southeast of kvarner bay and these meanders sometimes close to form small gyres

benthic foraminiferal evidence for the formation of the holocene mud belt and bathymetrical evolution in the central adriatic sea detailed analyses of modern and fossil benthic foraminiferal assemblages collected in the central adriatic sea are used as tools to reconstruct the environmental changes that occurred between the last deglaciation and the present last 14 kyrs in particular we focus on the timing and formation of the mud belt the modern benthic foraminiferal assemblages display a parallel zonation to the italian coast controlled by the interaction between food oxygen availability and water depth cluster analysis of 4 sediment cores separates the fossil foraminiferal assemblages in 6 groups cluster a is dominated by three ammonia species cluster b consists of ammonia papillosa nonionella turgida elphidium advenum and elphidium decipiens cluster c is composed of two taxa hyalinea balthica and trifarina angulosa cluster d is dominated by 5 species cibicides lobatulus buccella granulata reussella spinulosa textularia agglutinans and elphidium crispum cluster e contains bulimina spp gavelinopsis praegeri bolivina spp cassidulina neocarinata and asterigerinata mamilla and cluster f is dominated by bulimina marginata valvulineria bradyana globocassidulina subglobosa and melonis padanum the cluster analysis and contemporary distribution patterns of these taxa are used together with ecological preferences of the most frequent species to reconstruct the spatial and temporal distribution of the different biofacies in the past this reveals information about holocene palaeoenvironmental changes that are related to water depth fluctuations and the installment of the coast parallel mud belt the benthic assemblage records the transition from a infralitoral environment biofacies i to deeper marine condition biofacies iii after that the sea level reached about the modern level biofacies iv the benthic foraminiferal community evidences the development of the mud belt and the subsequent transformation of the ecological niches linked to the trophic evolution of the environment

analysis of sand woven geotextile interface shear behavior using discrete element method dem the interaction between soil and geotextile is essential for the performance of reinforced soil this study reveals the microscopic mechanism of interface shear between sand and geotextile based on

extreme cooling and dense water formation estimates in open and coastal regions of the adriatic sea during the winter of 2012 generation of dense waters in the adriatic sea during an extreme cooling event in the winter of 2012 including its preconditioning and spreading phases have been investigated using the one way coupled roms and the aladin hr modeling system both climatological and real river fluxes are used in the simulations aside from the convenient dense water formation areas located at the northernmost adriatic shelf we found that a similar amount of dense water with slightly lower density was formed in the eastern and deeper adriatic coastal area which was subjected to extreme heat losses up to 2000 w m2 during peak cooling periods this part of the adriatic has been known for extreme cooling during wintertime bora outbreaks nevertheless no ocean model study has previously reproduced dense water formation in this area the most likely reason for that was an overestimate of river discharges introduced to ocean models from newly available data we estimated that the contribution of eastern adriatic rivers between the neretva river and rijeka bay is more than six times lower than what has been previously documented transport of dense water toward the middle adriatic had a peak value of about 0 6 sv while the speed of initial bottom density current surpassed 40 50 cm s which is several times faster than past events different pathways of the dense water toward the middle and south adriatic depressions have also been documented the contribution of the eastern coastal adriatic area to the overall north adriatic dense water formation has been quantified and discussed for average and low freshwater load conditions indicating that this part of the adriatic is a common place for dense water generation

sadiola hill a world class carbonate hosted gold deposit in mali west africa the 8 moz sadiola hill gold deposit is located in the kedougou kenieba inlier a window of deformed ca 2200 to 2050 ma rocks that crop out in eastern senegal and western mali the geology of the inlier differs from other paleoproterozoic granite greenstone belts and sedimentary basins by the abundance of carbonate rocks the sadiola hill gold deposit occurs within 3 km of the senegal mali shear zone and country rocks in the region have undergone polycyclic deformation the lithostratigraphy of the open pit consists of impure limestones overlain by younger sequences of detrital sedimentary rocks which include arenite wacke and siltstone the sedimentary rocks have been subjected to regional greenschist facies metamorphism and have been intruded by multiple generations of synkinematic calc alkaline stocks and dikes the bulk of the ore is hosted within a n s to nnw trending 10 to 50 m wide brittle ductile dilational shear zone defined as the sadiola shear zone gold lodes also occur along an array of steep nne trending shear zones geometric and kinematic analyses indicate that the ore hosting structures were undergoing sinistral displacement at the time of mineralization locally defined as the d3s nnw sse shortening event hydrothermal alteration is polyphase and includes an early high temperature calc silicate phase i e porphyroblastic growth of actinolite tremolite followed by a potassic phase i e biotite calcite quartz k feldspar tourmaline actinolite that was synchronous with ore mineral deposition paragenetic studies reveal a multistage ore development that includes an as rich sulfide stage followed by an au sb stage the ore is associated with a metal enrichment suite of au as sb cu fe w mo ag bi zn pb te the sadiola hill deposit shares a similar relative timing and structural setting to that of other world class orogenic gold systems in the west african craton e g ashanti loulo with gold deposition occurring during a period of transcurrent tectonics after the cessation of region wide compressional deformation the high temperature paragenesis at sadiola hill is atypical of gold mineralization in the craton and indicates that the late eburnean tectono magmatic activity between ca 2080 and 2060 ma played an important role in the dynamics of hydrothermal fluid circulation along the senegal mali shear zone

interactions among adriatic continental margin morphology deep circulation and bedform patterns abstract within the mediterranean region the adriatic basin is one of the key sites for the formation and spreading of dense shelf water once formed in the northern shallow region as a response to strong wintry cold air outbreaks dense water masses move southeastwards as bottom hugging gravity currents eventually reaching the south adriatic continental margin a fraction of the dense water mass is thus intercepted by the shelf break whence it flows down the continental slope driven by its negative buoyancy and interacting with ambient water and seafloor topography this process generates a wide variety of dynamics and morphological features such as erosional moats furrows giant comet marks sediment drifts and sediment waves in this study we merge the outcomes of a state of the art wave ocean coupled numerical model with the geological evidence from the analysis of southern adriatic bedform patterns the model was run to reproduce an exceptional cold event that occurred in winter 2012 and benefits from a high resolution bottom topography produced from data collected during recent bathymetric surveys model results allow the identification of flow pathways along and across the continental shelf and slope with particular emphasis on the role of large scale margin geometry in controlling morphodynamic processes and its implications in terms of resolution requirements for modelling purposes although modelled overall water fluxes and basin renewal ratios are mostly controlled by regional circulation and large scale morphology local topographic features and singularities appear crucial in triggering concentrating and modulating bottom currents dynamics and sediment transport towards the south adriatic pit as well as enhancing mixing and entrainment of ambient water as long as this degree of information is provided within the bathymetric constraint modelled hydrodynamic pathways in the study case are consistent with observed bedform morphology and their spatial pattern for different zones in the continental slope temporal variability of the flows has been investigated permitting to disentangle the relative contribution of dense water cascading and background circulation at the basin and sub basin scale in controlling bedform dynamics this study gives a first quantitative insight on the hydrodynamic mechanisms responsible for south adriatic margin reshaping suggesting a modelling approach to the interpretation of the high resolution bathymetric and stratigraphic data made available by recent survey technologies

anatomy of a compound delta from the post glacial transgressive record in the adriatic sea abstract on the mediterranean continental shelves the post glacial transgressive succession is a complex picture composed of seaward progradations related to sea level stillstands and or increased sediment supply to the coasts and minor flooding surfaces associated with phases of enhanced rates of sea level rise among late pleistocene examples major mid shelf progradations have been related to the short term climatic reversal of the younger dryas event a period during which the combination of increased sediment supply from rivers and reduced rates of sea level rise promoted the formation of progradations up to tens meter thick while the documentation of coastal and subaqueous progradations recording the younger dryas interval is widely reported in literature the model of compound progradation within transgressive deposits has not yet been proposed here we present the documentation of a deltaic system where both delta front sands and related fine grained subaqueous progradations prodeltaic to shallow marine have been preserved the paleo gargano compound delta pgcd formed offshore the modern gargano promontory southern adriatic sea and is composed of a coastal coarse grained delta of reduced thickness and a muddy subaqueous clinoform up to 30 m thick the pgcd probably the first worldwide documentation of a compound delta within the transgressive record provides the opportunity to investigate the processes controlling the formation of a compound delta system during an overall sea level rise and the factors that allowed its preservation the finding of the pgcd provides the opportunity for a comparison with modern worldwide compound systems

surface circulation in the gulf of trieste northern adriatic sea from radar model and adcp comparisons 1 high resolution high frequency hf radar observations of surface currents in the gulf of trieste got are presented and compared to moored subsurface current measurements and to high resolution simulations from the northern adriatic princeton ocean model napom oceanographic model dominant circulation modes of the got were resolved and numerical model capabilities in reconstructing them were assessed the time frame covers march 2011 through october 2012 napom reconstructs the dominant surface circulation features observed by the radar such as the general basin wide cyclonic circulation scheme and the coastal jet outflowing the got but is in general less energetic than radar currents comparisons between radar adcp and model currents suggest that the model underestimates originate within the low frequency diurnal semidiurnal and inertial bands and that both radar and model currents do not reproduce the diurnal tidal ellipse structure observed by the moored current meter however radar model results for the semidiurnal tides are spatially consistent using empirical orthogonal function eof decomposition the coherent spatial scales and corresponding temporal scales were extracted findings suggest that hf radar current observations complement model simulations in regions of enhanced topographic variability where variance of model currents at the surface is distorted by the effects of the sigma layer grid on the contrary model results complement radar observations in areas with poor radar coverage and furthermore provide spatial and temporal continuity of ocean state forecasts

direct shear tests on reinforced sand new data are presented from internal measurements in direct shear tests on sand an interpretation is given for the plane strain angle of friction and the angle of dilation of sand in a direct shear test the direct shear angle of friction deduced from the conventional analysis is shown to under estimate the frictional shearing resistance of sand by about 20 results are presented from direct shear tests on reinforced samples and these are fitted by a limit equilibrium analysis in which all the parameters are independently measured plastic incremental strains cause dilation in dense sand and dominate the deformation with increasing stress ratio the rate of increase of the reinforcement force in shearing sand is shown to depend on the angle of dilation the maximum bond angle of friction between sand and the rough surface of reinforcement is also determined by plastic deformation in the sand a theoretical analysis for the bond is supported by the test results which show that the maximum bond angle of f

lithospheric controls on the formation of provinces hosting giant orogenic gold deposits ages of giant gold systems 500 t gold cluster within well defined periods of lithospheric growth at continental margins and it is the orogen scale processes during these mainly late archaean palaeoproterozoic and phanerozoic times that ultimately determine gold endowment of a province in an orogen a critical factor for giant orogenic gold provinces appears to be thickness of the subcontinental lithospheric mantle sclm beneath a province at the time of gold mineralisation as giant gold deposits are much more likely to develop in orogens with subducted oceanic or thin continental lithosphere a proxy for the latter is a short pre mineralisation crustal history such that thick sclm was not developed before gold deposition in constrast orogens with protracted pre mineralisation crustal histories are more likely to be characterised by a thick sclm that is difficult to delaminate and hence such provinces will normally be poorly endowed the nature of the lithosphere also influences the intrinsic gold concentrations of potential source rocks with back arc basalts transitional basalts and basanites enriched in gold relative to other rock sequences thus segments of orogens with thin lithosphere may enjoy the conjunction of giant scale fluid flux through gold enriched sequences although the nature of the lithosphere plays the crucial role in dictating which orogenic gold provinces will contain one or more giant deposits the precise siting of those giants depends on the critical conjunction of a number of province scale factors such features control plumbing systems traps and seals in tectonically and lithospherically suitable terranes within orogens

summer breakout of trapped bottom dense water from the northern adriatic 1 the paper deals with an intriguing dense water breakout episode in mid august 2004 which has been observed in the bottom layers of the oil rig located in the middle of the northern adriatic various data temperature series and vertical t s profiles currents meteorological measurements and satellite images have been analyzed in order to understand conditions which preceded were active and followed the breakout episode a stationary bottom pool of dense water generated during the previous winter has been suspected to be a source of the dense water observed during the breakout with a permanent position established by a stationary northern adriatic cyclonic anticyclonic gyre system the breakout lasted for 3 days advecting the bottom waters more than 2 c colder than residing waters at the oil rig site the main result of modeling experiments concerns the generative force for the observed breakout which was found to be a mesoscale storm that occurred over the open north adriatic on 8 august 2004 the storm has been reproduced by the coupled ocean atmosphere mesoscale prediction system coamps atmospheric model which was then used to force the princeton ocean model pom at the surface results of simulations reveal the capability of the storm to break the thermohaline fronts through the wind induced baroclinic transport and downwelling at the exposed shorelines this is the first study in the adriatic which evaluates the impact of mesoscale summer storm to the sea driving bottom layer circulation through the convergence divergence dynamics in addition to the direct impact on the sea surface through the wind stress forcing

resonant coupling of a traveling air pressure disturbance with the east adriatic coastal waters 1 exceptional sea level oscillations and strong current reversals observed in the east adriatic on 27 june 2003 are analyzed using available meteorological and tide gauge measurements and numerical model results it is shown that the variability in the atmosphere sea system was characterized by high frequencies 0 01 0 1 min 1 and sea level and current amplitudes surpassing 1 m and 1 m s 1 respectively the event was related to the occurrence of a gravity disturbance in the atmosphere above the adriatic the disturbance traveled toward the east southeast at a speed of 22 m s 1 and was resonantly coupled with a wave in the sea 50 m deep the resulting forced wave was further amplified when entering funnel shaped bays opened to it there are indications that the forcing disturbance and its counterpart in the sea excited normal modes of the bays and harbors in the area moreover nonlinear steepening of the forced wave seemingly occurred resulting in the formation of high frequency wave trains this process along with the generation of coastal seiches could explain the observed and modeled differences between the spectra of coastal variability and the spectrum of forcing wave

age constraints on gold mineralization and paleoproterozoic crustal evolution in the ashanti belt of southern ghana abstract u pb isotopic dating in the region of the ashanti belt in ghana has been carried out to improve understanding of crustal evolution and gold mineralization in this paleoproterozoic terrane a u pb zircon age of ca 2174 2 ma for a belt type granitoid from sekondi accords with previous ages on belt type plutons in ghana but metamorphic titanite within this granitoid gives an age of 2092 3 ma coeval with intrusion of the late basin type granitoids the within belt granitoid at banso village has an age close to 2097 3 ma which falls into the age range typical for basin type granitoids 2116 2088 ma these results indicate that widespread plutonism in the birimian sedimentary basins also produced magmatic and metamorphic effects within the volcanic belts most dated detrital zircons from birimian metasediment samples at the ashanti gold mine agree in age at 2155 2 ma with others that are slightly older this gives a maximum estimate for the depositional age of the sediments and for gold mineralization at the ashanti gold mine hydrothermally altered and auriferous granitoid plutons along the western flank of the ashanti belt at anyankyerim nhyiaso yaomensakrom and esuajah ayanfuri all have intrusion ages within error of 2105 2 ma this is also the age of metamorphic titanite in an unmineralized basin type granitoid at kwapia rutiles from the hydrothermally altered yaomensakrom and the mineralized esuajah ayanfuri granitoid were dated at 2098 7 and 2086 4 ma respectively and probably provide minimum ages on gold mineralization these data indicate a close temporal association among auriferous granitoid plutons near the western margin of the ashanti belt at 2105 ma gold mineralization may be only slightly younger than magmatic emplacement of the plutons granitic plutonism in the sedimentary basins metamorphism and hydrothermal gold mineralization in southern ghana are all part of a major crust formation event the eburnean orogeny that can be constrained to the time range 2120 2080 ma

the use of 7be to identify event and seasonal sedimentation near the po river delta adriatic sea in october 2000 a major flood event of the po river occurred the resulting seabed deposit was initially sampled in december 2000 and most sites were reoccupied on subsequent cruises over a 3 yr period using the maximum penetration depth of the short lived radioisotope 7be half life 53 3 d the flood deposit was found to be up to 15 cm thick individual depocenters of thick strata were located immediately adjacent to the distributaries at the river mouth in relatively shallow water 30 m these flood deposit thicknesses are minimum estimates because the depth of 234th half life 24 1 d exceeds that of 7be in physically stratified flood sediment indicating that the first sediment deposited during the flood event likely originated from the river channel 30 55 of the estimated sediment load delivered to the shelf during the flood event can be accounted for using 7be penetration depths seasonal deposition also can be quantified using 7be after removing the effects of biological mixing seasonal deposition rates are a maximum of 6 cm yr 1 near the pila distributary decreasing to 2 cm yr 1 in the southern portions of the dispersal system

adcp observations of the western adriatic slope current during winter of 2001 abstract data from an acoustic doppler current profiler adcp mooring maintained during the winter of 2001 in 57 m of water near senigallia italy are used to describe the winter conditions of the western adriatic current in the northern adriatic sea wind and water temperature measurements from the acqua alta tower in 19 m water depth off venice and winds from a 4 km resolution reanalysis model coamps are used to interpret the adcp data especially with respect to currents generated by bora winds at the adcp site mean depth average current for the winter deployment period was 10 4 cm s toward 140 roughly aligned with local bathymetric contours both mean currents and fluctuations about the means were highly barotropic during the winter southeastward along shore mean currents increased slightly 1 8 cm s with depth between 7 and 47 m following a nearly linear trend offshore cross slope mean currents only increased 2 0 cm s deep in the water column between 35 and 51 m current variability was dominated by four bursts of currents in which flow toward the southeast greatly increased these bursts followed bora winds the timing of which was identified by measured winds at the acqua alta tower depth averaged de tided currents exceeded 30 cm s during all four events and reached 45 cm s during one event correlations between these along shore currents and simulated wind stress from the coamps model were calculated over the whole north adriatic the cross covariance between currents and wind stress had a spatial pattern similar to the bora wind itself reaching maxima along the northern adriatic coast off the southern tip of istria and near ilovik island 14 5 n 44 4 e wind stress in these regions had stronger correlation with currents at the mooring than did wind stress anywhere near the mooring bottom water at the mooring was too warm for it to have been north adriatic dense water except perhaps for a brief pulse of cold water associated with the third current burst on april 1st

transport in an idealized three gyre system with application to the adriatic sea abstract motivated by observations of surface drifters in the adriatic sea transport in a three gyre system is studied with the aid of dynamical systems techniques particular attention is paid to the issue of intergyre transport the velocity field is assumed to be two dimensional and incompressible and composed of a steady three gyre background flow on which a time dependent perturbation is superimposed two systems of this type are considered 1 an observationally motivated analytically prescribed model consisting of a steady background on which a multiperiodic time dependent perturbation is superimposed and 2 an observationally based model of the adriatic sea consisting of the mean surface circulation derived from surface drifter trajectories on which a time dependent altimetry based perturbation velocity field is superimposed it is shown that for a small perturbation to the steady three gyre background two of the gyres exchange no fluid with the third gyre when the perturbation strength excee

multi stage and multi sourced fluid and gold in the formation of orogenic gold deposits in the world class mana district of burkina faso revealed by la icp ms analysis of pyrites and arsenopyrites abstract mana is a world class paleoproterozoic orogenic gold district 8 0 moz that includes five gold deposits fofina nyafe siou wona kona and yaho hosted in various rocks in the northern part of the birimian hounde greenstone belt western burkina faso the gold deposits recorded different styles of mineralization associated with sulfides during polyphase deformation events detailed petrographic and la icp ms analyses of pyrites and arsenopyrites from the main mineralization of each deposit provide new information on the potential gold and arsenic sources and timing of fluids responsible for mineralization at mana four hydrothermal fluid events associated with two distinct source reservoirs and at least two hydrothermal systems were recognized the first hydrothermal fluid event was generated during the eoeburnean d1md md for mana district shortening event 2172 ma evidence of which is preserved in the fofina and siou deposits and occurred under greenschist metamorphic facies conditions economic gold deposits at fofina are associated with metamorphic disseminated pyrite py1f in black shale zoned pyrite py2f enriched in as ni cu ag sb w au and pb and arsenopyrite in folded v1f quartz carbonate veins in contrast the siou deposit exhibits au in porous pyrite cores py1s which are associated with ag bi te and w sb in v1s quartz veins hosted in the siou granodiorite these two trace element suites are interpreted as having been induced by a metamorphic source in the fofina deposit and by a local contribution of a magmatic source in the siou deposit the second hydrothermal fluid event occurred during the eburnean d3md transpressional event 2113 2090 ma in the nyafe deposit this event is defined by au as rich rims in hydrothermal pyrite py3n and by the co precipitation of au rich arsenopyrite in the v3n quartz veinlets v3n controlled by a second order dextral shear zone the third and main hydrothermal fluid event during the d4md transpressional event 2090 ma is characterized by the development of strong silicification and by zoned pyrites py3wk and py2y and au rich arsenopyrite in the wona kona and yaho deposits however the same late au as rich rims in hydrothermal pyrite are observed in both deposits and in the nyafe deposit and these rims are interpreted to be related to the same economic gold source related to the lower birimian metamorphic reservoir composed of black shale diagenetic framboidal pyrite and tholeiitic basalts the diagenetic framboidal py1wk in black shale lower birimian group is enriched in au median of 0 8 ppm low in as median of 70 ppm with other trace elements ni cu zn ag sb and pb the last hydrothermal event is associated with free gold remobilization in late microfractures in the wona kona and siou deposit during the reactivation of major transcurrent shear zones during the d4md event or the d5md shortening event as late as 2022 ma a binary diagram of as ag vs sb bi appears to be effective at separating the diagenetic magmatic and metamorphic pyrites and could be used in orogenic gold exploration to ascertain potential gold endowment at the district scale

the gounkoto au deposit west africa constraints on ore genesis and volatile sources from petrological fluid inclusion and stable isotope data the loulo gounkoto complex in the kedougou kenieba inlier hosts three multi million ounce orogenic gold deposits situated along the senegal mali shear zone this west malian gold belt represents the largest west african orogenic gold district outside ghana the gounkoto deposit is hosted to the south of the gara and yalea gold mines in the kofi series metasedimentary rocks the ore body is structurally controlled and is characterised by sodic and phyllic alteration as and fe rich ore assemblages with abundant magnetite and overall enrichment in fe as cu au ag w ni co ree minor te pb se cd fluid inclusion analysis indicates that the deposit formed at p t conditions of approximately 1 4 kbar and 340 c and that two end member fluids were involved in mineralisation 1 a moderate temperature 315 340 c low salinity 10 wt nacl equiv low density 1 g cm 3 h2o co2 nacl h2s n2 ch4 fluid 2 a high temperature up to 445 c hypersaline 40 wt nacl equiv high density 1 3 g cm 3 h2o co2 nacl fecl2 fluid partial mixing of these fluids within the jog zone at gounkoto enhanced phase separation in the aqueo carbonic fluid and acted as a precipitation mechanism for au these findings demonstrate the widespread if heterogeneously distributed nature of fluid mixing as an ore forming process in the loulo gounkoto complex operating over at least a 30 km strike length of the shear zone stable isotope analyses of ore components at gounkoto indicate a dominant metamorphic source for h2o h2s and co2 and by extension au it thus can be reasoned that both the aqueo carbonic and the hypersaline fluid at gounkoto are of metamorphic origin and that the high levels of salinity in the brine are likely derived from evaporite dissolution

orogenic disseminated gold in phanerozoic fold belts examples from victoria australia and elsewhere abstract orogenic gold mineralisation in the lachlan orogen of southeastern australia and in other phanerozoic fold belts has generally been assumed to be confined entirely to quartz veins however an improved understanding of the tectonic structural and geochronological framework in which these occurrences form and recent advances towards the extent of wallrock alteration around these veins cast doubt on the validity of this deeply entrenched lode gold paradigm ore grade orogenic disseminated gold mineralisation has been recognised in a number of fold belts that are known to host significant orogenic lode gold deposits lachlan orogen australia buller terrane and otago schist new zealand meguma terrane canada tien shan mountains in uzbekistan and kyrgyzstan yana kolyma province baikal verhoyansk and allakh yun fold belts in north central mongolia and far east russia disseminated mineralisation in these collisional belts is invariably hosted by pervasively altered greenschist to subgreenschist facies rocks these occurrences also share a number of characteristics with some carlin type gold deposits in the great basin of western north america e g getchell regarding structural relationships fluid composition mineral paragenesis and a common association of carbonaceous matter with mineralisation features of alteration physico chemical characteristics of the ore bearing fluids and strong structural control in all of the studied occurrences point to a close genetic association with lode gold mineralisation the two styles are considered to represent end members of a crustal continuum of orogenic gold emplacement in phanerozoic fold belts with disseminated mineralisation more likely to develop at shallower levels and within more permeable units during the waning stages of uplift and exhumation these conditions facilitate ground preparation via brittle fracturing and the development of intricate stockwork systems efficient gold segregation from bisulphide complexes is largely controlled by fluid mixing of an evolved metamorphic fluid with either more oxidised ascending fluids or meteoric fluids and accelerated by the presence of carbonaceous matter at the site of deposition

the massawa gold deposit eastern senegal west africa an orogenic gold deposit sourced from magmatically derived fluids the massawa gold project is situated on the senegalese side of the highly prospective productive palaeo proterozoic birimian kedougou kenieba inlier which hosts several world class orogenic gold deposits districts in western mali e g loulo and sadiola the massawa ore body has a strike length of at least 4 km and a current resource of 3 61 moz at a grade of 2 8 g t 1 the ore body is structurally controlled and located within a package of low grade regionally metamorphosed volcaniclastic sediments agglomerates tuffs and ash tuffs quartz feldspar and lithic wackes carbonaceous shales hydrothermal breccias and gabbro and porphyry sills these rocks have undergone pervasive silica alteration followed by a sericite ankerite chlorite alteration event related to mineralization two major styles of mineralization are recognized at massawa from field and laboratory studies the first stage of sulphide au mineralization is associated with disseminated arsenopyrite pyrite which follows shear zones in the sedimentary and volcano sedimentary host rocks the second stage consists of quartz stibnite tetrahedrite veining distinguished by coarse visible gold and represents a late stage overprint on the primary mineralization the two stages of gold mineralization are separated by a phase of quartz molybdenite veining a distinctive base metal trace assemblage is linked to stibnite formation including multiple sb phases such as chalcostibite zinkenite roshchinite aurostibite jamesonite and robinsonite secondary ion mass spectroscopy based gold deportment data indicate that up to 90 of stage 1 gold is held as a solid solution within either arsenopyrite or arsenian pyrite stable isotope data yield 34ssulphide values of between 0 and 4 1 and 18oh2o values of 5 5 10 9 for all stages of mineralization suggesting a magmatic fluid influence this is consistent with field data that suggest that mineralization is synchronous with emplacement of a sequence of concordant felsic sheets that mineralization occurred at shallow 6 km depths is suggested both by the presence of stibnite and by fluid inclusion studies low temperature homogenization temperatures between 150 c and 230 c h2o nacl fluids 6 wt nacl equiv and coeval co2 ch4 inclusions observed in both phases of mineralization indicate trapping conditions of 220 315 c at 1 1 65 kbar a combination of phase petrology fluid inclusion and stable isotope data suggests deposition of gold from low salinity magmatic fluids most probably released from felsic rocks similar to those emplaced into the massawa sequence during mineralization

lagrangian turbulence in the adriatic sea as computed from drifter data effects of inhomogeneity and nonstationarity 1 the properties of mesoscale lagrangian turbulence in the adriatic sea are studied from a drifter data set spanning 1990 1999 focusing on the role of inhomogeneity and nonstationarity a preliminary study is performed on the dependence of the turbulent velocity statistics on bin averaging and a preferential bin scale of 0 25 is chosen comparison with independent estimates obtained using an optimized spline technique confirms this choice three main regions are identified where the velocity statistics are approximately homogeneous the two boundary currents west east adriatic current wac eac and the southern central gyre cg the cg region is found to be characterized by symmetric probability density function of velocity approximately exponential autocorrelations and well defined integral quantities such as diffusivity and timescale the boundary regions instead are significantly asymmetric with skewness indicating preferential events in the direction of the mean flow the autocorrelation in the along mean flow direction is characterized by two timescales with a secondary exponential with slow decay time of 11 12 days particularly evident in the eac region seasonal partitioning of the data shows that this secondary scale is especially prominent in the summer fall season possible sampling issues as well as physical explanations for the secondary scale are discussed physical mechanisms include low frequency fluctuations of forcings and mean flow curvature inducing fluctuations in the particle trajectories consequences of the results for transport modeling in the adriatic sea are discussed

structural controls on an orogenic gold system the world class siguiri gold district siguiri basin guinea west africa orebodies in the siguiri district a world class paleoproterozoic orogenic gold camp located in the birimian of northeastern guinea are typically represented by cryptic subvertical damage zones that host a high density of mineralized veins although no large regional fault system was recognized observations from five representative deposits of the siguiri district sanu tinti bidini kami kosise and sintroko pb1 show that these orebodies are locally controlled by incipient structures and spread across three distinct structural and lithostratigraphic domains two shale dominated peripheral domains adjoin a central domain whose lithostratigraphy is dominated by medium to coarse grained graywacke and this domain hosts the bulk of the gold endowment of the district the three domains exhibit similar structural elements that can be described within a four stage deformation scheme the first deformation event d 1s is poorly constrained and interpreted to have been an n s compressional event it included development of minor folds with w to wnw gently plunging fold axes without a clear axial planar cleavage the main and second deformation event d 2s is interpreted to have been associated with e w to ene wsw directed compression the d 2s event was responsible for forming the dominant n trending structural grain of the district and creating interference patterns between f 1s and f 2s folds the third event d 3s developed progressively from d 2s compression into an early d 3s e w to enewsw directed transpression and a late d 3s nnw sse directed transtension responsible for most of the gold mineralization in the siguiri district the fourth and last event d 4s was an nw se oriented compressional event responsible for the localized overprinting of veining by a steep to shallowly dipping nne ssw ductile cleavage late d 3s gold bearing mineral occurrences formed along subvertical n s reverse faults ne trending dextral shear zones wnw trending sinistral faults and e trending normal relay faults developed or reactivated early d 3s mineralization is expressed as mineralized shear zones or subvertical damage zones characterized by a 10 to 15 m wide zone of dense quartz carbonate sulfide veining or disseminated gold bearing sulfides the mineralized veins consistently strike ene wsw are steeply dipping and commonly have a conjugate geometry at the mesoscale finite strain analysis of deformation including analysis of folds faults and conjugate mineralized vein sets is consistent with a stress switch from a compressional d 2s to transpressional deformation termed early d 3s results of paleostress analysis on conjugate mineralized vein sets that formed late during d 3s indicate that the stress field ranged from extensional to strike slip sometimes within the same vein locality the late d 3s deformation is interpreted to have been a transtensional event the first change in the orientation of the principal stress axes is related to a switch from a far field dominated to a body force dominated stress field reducing the deviatoric component on the stress tensor the second change in the orientation of the principal stress axes from early d 3s transpression to late d 3s transtension suggests that 1 and 2 were similar in magnitude which facilitated localized stress switches in the siguiri district the early d 3s and late d 3s stress switches which occurred at both a local and regional scale enhanced the fracture permeability and were critical for the establishment of active fluid pathways leading to the formation of a world class gold system

short term evolution of po della pila delta lobe from time lapse high resolution multibeam bathymetry 2013 2016 abstract over the last few years 2013 2016 repeated high resolution multibeam surveys were carried out at the recent most delta lobe of the po river in correspondence to po della pila the collected multibeam bathymetry together with backscatter data seabed samples and high resolution seismic profiles provided insights on the short term morphological and sedimentological evolution of this extremely dynamic submarine portion of the delta a high variety of geomorphological features and depositional bodies were observed from the mouth bar to the prodelta slope such as for example the alongshore and transverse bars formed under the effect of marine currents gravitational instability phenomena and collapse depressions driven by fluid expulsion concurrently the analysis of the seabed reflectivity and sediment samples allowed the identification of two main dominant types of seafloor sediment corresponding to sandy and muddy seabed and the mapping of their variable distribution in the study area the comparison of time lapsed high resolution dems showed that the main changes occurred on the northern side of the prodelta slope where a new lobe shaped fine sediment deposit built up to 4 5 m adding roughly a volume of 1 16 mm3 of new sediments at the same time in the prodelta slope transverse depositional bars showed a clear migration toward the south of the system and local subsidence phenomena up to 1 5 m between 7 and 10 m water depth are observed

timing and structural controls on gold mineralization at the bogoso gold mine ghana west africa the bogoso gold deposit comprises 20 open pits scattered along 18 km of a major fault zone which separates birimian supergroup turbiditic sedimentary rocks to the northwest from tarkwaian group rocks to the southeast individual pits are centered on 200 to 400 m long ore shoots which are located in three broad structural settings steeply pitching relatively high grade orebodies are commonly localized in left hand dilational jogs in the strike of the controlling faults these jogs often coincide with intersecting minor faults gold is largely confined to the graphitic mylonite which defines the fault and imbricated slices of carbonate altered rock gently dipping mineralized quartz vein stockworks and disseminated auriferous pyrite and arsenopyrite form broader zones between more steeply dipping bounding faults in the vicinity of right hand bends and splays in these faults smaller zones of disseminated sulfide mineralization coincide with areas where bedding and or foliation in the adjacent birimian sedimentary rocks is strongly discordant with the adjacent mineralized fault generally where the faults cut the short limbs of tight upright east trending folds approximately 75 percent of the gold extracted from the bogoso district has been mined from a cluster of pits that coincides with the densest and most highly connected concentration of larger faults in the bogoso concession the majority of ore shoots are located along the largest of these faults the narrower faults generally host smaller and less frequent ore shoots the fault network originated during an early episode of regional scale shortening involving thrusting and isoclinal folding the structural setting and geometry of the ore shoots implies that mineralization occurred during a later minor episode of sinistral strike slip movement on the controlling faults after development of the fault network the undeformed nature of the auriferous sulfides implies that this was the last phase of ductile brittle deformation on the host faults this conclusion is consistent with earlier work indicating that the giant ashanti deposit 150 km along strike from bogoso also developed during a period of small displacement sinistral offset late in the history of the host fault network

po river plume on the adriatic continental shelf dispersion and sedimentation of dissolved and suspended matter during different river discharge rates abstract suspended matter and dissolved nutrients were studied in the prodelta of the po river northern adriatic sea immediately after one of the greatest floods of the last century which occurred in october 2000 and in four successive seasonal conditions hydrology total suspended matter tsm particulate organic carbon poc and particulate nitrogen pn content organic carbon stable isotopes 13 c poc particle grain size spectra phytoplankton and dissolved inorganic nutrients i e nitrate nitrite ammonium phosphate and silicate were measured in different discharge conditions to describe processes occurring in the po river delta the main effect of high river discharge was a large volume of low salinity water at the surface that extended over the entire study area the concentration of most sampled variables decreased along a dilution gradient from the po river distributaries mouths to the offshore for tsm at the surface riverine input and dilution were the main factors affecting its distribution at the bottom however increased tsm in the nearshore was due to rapid sinking of suspended matter at the river mouth while resuspension and advection dominated the transport of near bottom sediments offshore at 15 20 m depth in the offshore where resuspension was active an increase in ammonium and decrease in oxygen supported the presence of regeneration processes occurring at the bottom during the october 2000 flood event high nutrient concentrations promoted new production triggering an algal bloom in the southern region of the study area the origin of particulate organic carbon in the river delta was then estimated from a mixing model based on 13 c poc values and carbon nitrogen c n molar ratios and as the contribution of three distinct sources of organic carbon were determined i e marine riverine and terrestrial the riverine end member accounted for 50 of the surface poc and generally decreased towards the offshore the terrestrial carbon contribution was generally the least abundant 20 28 at the surface and at depth respectively and exhibited peak values 30 40 during the october 2000 flood last the marine contribution was the most abundant at the bottom 40 and generally increased offshore during the october 2000 flood the fluvial contribution of particulate organic carbon that is the terrestrial and riverine fractions represented approximately 80 of the total particulate organic carbon in the po river delta

regional setting structure and descriptive geology of the middle proterozoic syama gold deposit mali west africa the syama gold deposit lies in a birimian 2 0 2 2 ga greenstone belt in southern mali gold mineralization is hosted by a thin 0 5 2 0 km but regionally extensive sequence of basalt and andesite interbedded graywacke and argillite and andesitic lamprophyric intrusions this sequence is bounded on the east by andesitic conglomerate and graywacke and on the west by interbedded graywacke and argillite in the syama mine area this ore bearing sequence is structurally layered overturned and east vergent massive competent basalt and conglomerate bound the hanging wall and footwall respectively of the mineralized interval lateritic weathering developed an oxide orebody that overlies sulfide mineralization the oxide orebody extends to 35 to 40 m below the surface sulfide mineralization extends to a depth of at least 500 m mineable oxide reserves are 3 0 million tons with an average grade of 3 20 g ton geologic sulfide reserves from the top of sulfides to 320 m below the surface are 21 million tons with an average grade of 4 02 g ton the oxide deposit was expressed on the surface as a series of 3 to 15 m deep ancient mine workings which extended 800 m along the strike of the deposit and sparse outcrops of silicified rock oxide ore occurs as two deposits a surficial deposit consisting of ancient tailings and dump material which are 0 1 to 5 m thick and extend up to 200 m away from the ancient workings and an in situ lode or saprolite deposit which lies immediately below the ancient workings and extends downward into sulfide mineralization the sulfide deposit consists of lenticular bodies of intense ankerite quartz veinlet stockworks zones of sheeted ankerite quartz veinlets and breccia bodies pyrite is the principal gold bearing mineral and occurs disseminated in veinlet halos and breccia clasts green chloritic basalt is the preferred but nonexclusive host of the mineralization it is commonly bleached by ankerite albite and sericite alteration in the pyritic gold bearing zones silica na 2 o au co 2 s and c have been added to mineralized zones hosted by basalt fe 2 o 3 al 2 o 3 and trace metals have been removed andesitic lamprophyric intrusions and graywacke argillite layers also host disseminated pyrite mineralization faulted beds of graphitic graywacke argillite and zones of silicification bound most individual orebodies the volcanic rocks at syama were probably originally deposited in a narrow rift or graben in an intra arc setting gold mineralization overlapped with compressional deformation and intrusive activity the mineralized horizons at syama lie within a sequence of rocks which has been either stacked or attenuated by layer parallel reverse faults these faults coincide with abrupt regional and mine scale contrasts in rock competency intrusive rocks form a volumetrically significant part of the mineralized sequence and may have aided hydrothermal alteration as a source of heat both the graywacke argillite layers and the altered basalt and intrusions may have been a source for some of the elements and fluids responsible for the mineralization and alteration the mineralization at syama is similar to other middle proterozoic gold deposits in the birimian shield of west africa and to archean gold deposits hosted by mafic volcanic rocks in terms of tectonic setting wall rock alteration form of mineralization and associated structures

the adriatic sea general circulation part ii baroclinic circulation structure abstract in the second part of the paper dedicated to the adriatic sea general circulation the horizontal structure of the hydrographic parameters and dissolved oxygen fields is described on a seasonal timescale maps of temperature and salinity climatological fields reveal the enhanced seasonal variability of the adriatic sea which at the surface is associated with the major dilution effects of river runoff the density and derived dynamic height fields show for the first time the baroclinic geostrophic structure of the general circulation winter is dominated by compensation effects between temperature and salinity fronts along the western coastline the resulting baroclinic circulation is weak and suggests the presence of barotropic current components not accessible by the dataset spring and summer seasons have the smallest spatial scales in the temperature and salinity fields and stronger subbasin scale gyres and current systems which have been classified in a schematic representation of the circu

late eburnean granitization and tectonics along the western and northwestern margin of the archean kenema man domain guinea west african craton abstract recent mapping of the eastern part of guinea has revealed a vast plutonic belt that rims the margin of the archean kenema man craton and that is made up of a variety of granitic rocks granodiorite biotite granite monzogranite two mica granite granodiorite with common clinopyroxene being the most abundant single zircon dating by stepwise pb evaporation carried out on characteristic rock types granodiorite monzogranite two mica granite reveals their age to be late eburnean c 2090 2070 ma and indicates that their emplacement occurred within a relatively short time interval 20 ma the granodiorite biotite granite and monzogranite of the plutonic belt all present a calc alkaline and highly potassic nature and show numerous analogies with the neogene calc alkaline rocks of the central andes there is evidence to suggest strong contamination from the archean crust these analogies make it possible to envisage the emplacement of the plutonic belt directly above a subduction zone the occurrence of peraluminous two mica granite at the northern extension of the plutonic belt in the siguiri basin may suggest that the convergence here was associated with the local melting of metasedimentary rocks in the deep part of the basin contemporaneously with its emplacement the late eburnean plutonic belt accommodated regional convergence by major wnw ese sinistral movements along the northwestern margin of the archean block horizontal shortening towards the wsw is envisaged at the scale of eastern guinea in relation with these kinematics the late eburnean plutonic belt of eastern guinea is a key element of the archean proterozoic transition zone in the southern part of west africa evidence along the western and northwestern border of the archean kenema man domain leads us to interpret this transition zone as an active margin along which strike slip tectonism accommodated regional convergence towards the end of the eburnean cycle