exhumation driven devolatilization as a fluid source for orogenic gold mineralization at the damang deposit ghana gold mineralization at the damang deposit is unique among currently known orogenic gold deposits in ghana comprising gold hosted within metasediments of the tarkwaian system and contained in a subhorizontal extensional quartz vein array that formed during regional compression the damang region has an extended paragenesis involving numerous structural metamorphic igneous and metasomatic events orogenic gold mineralization occurred late in the geologic paragenesis at damang postdating regional metamorphism and an earlier episode of hydrothermal alteration locally termed pink hematite alteration associated with the intrusion of mafic sills and dikes this earlier pink hematite alteration event involves extensive silicification that changed the rheology of the altered rocks and promoted later fracturing following peak regional metamorphism at around 2005 ma the damang region underwent a short period of rapid exhumation as constrained through numerical thermal modeling of existing pressure temperature time data this exhumation triggered the generation of a subhorizontal fracture array that was fed by fluids released through decompression driven metamorphic devolatilization the interaction between these fluids and the host rock resulted in precipitation of gold in association with sulfide carbonate potassic alteration halos around quartz veins such postpeak metamorphic exhumation driven devolatilization is unlikely to be a singular occurrence and represents a potentially important source of fluid for orogenic gold deposits elsewhere in ghana west africa and globally

scavenging of thorium isotopes in the canada basin of the arctic ocean abstract investigations on the distribution of thorium isotopes in the water column have been utilized as powerful tracers to investigate the geochemical pathways of particle reactive material in the ocean we measured th 228 th 230 th 232 th and 234 th isotopes in samples collected along a horizontal profile from barrow ak to the canada basin as well as two vertical profiles in the canada basin the suspended particle concentrations were also measured to investigate the role of suspended particulate matter spm in th scavenging the spm inventory is more than an order of magnitude higher than that reported for the alpha ridge ice station indicating that the spm inventories vary over an order of magnitude in the deep arctic basins the conditional partition coefficient of th isotopes between suspended particulate matter and dissolved phase generally appears to be higher than those in non polar regions and this is attributed to more reactive suspended particulate matter the residence times of total 230 th are significantly lower than those calculated for the alpha ridge station while higher than those found in the eurasian basin and beaufort sea in the canadian basin the calculated residence time in all the deep basins of the arctic ocean varied between 13 1 and 45 1 years a reversible scavenging model applied to the distribution of th isotopes 230 th 228 th in the deep waters and 234 th 228 th in the upper 100 m indicates that the forward removal rate constant is higher than the value reported for the alpha ridge while the reverse rate constant is comparable to the alpha ridge station suggesting faster removal onto particulate matter and slower desorption of th from the particulate matter

fluid inclusion studies of the abawso gold prospect near the ashanti belt ghana the major ghanaian lode gold deposits are preferentially aligned along the western and eastern contacts of the kumasi basin with the ashanti and sefwi belts respectively the investigated area of the abawso small scale concession covering the workings of the old ettadom mine is situated 3 km west of the lithological contact of the birimian metavolcanic rocks of the akropong belt in the east with the birimian metasedimentary rocks of the kumasi basin in the west the rocks of the abawso concession represent a steeply nw dipping limb of a se verging anticline with an axis plunging to the sw quartz veining occurs predominantly in the form of en echelon dilatational veins along nne ssw striking shear zones of a few metres width and shows evidence of brittle and ductile deformation also stockwork style quartz veining occurs in the vicinity of the main shaft of the old ettadom mine hydrothermal alteration includes sericitisation sulphidation and locally carbonatisation the auriferous quartz veins mainly follow the trend of brittle to ductile deformed quartz veins however some occur in stockwork fluid inclusion studies reveal a large number of h2o inclusions along intragranular trails in auriferous quartz vein samples as well as an overall dominance of h2o and h2o co2 inclusions over co2 inclusions textural observations and physico chemical fluid inclusion properties indicate post entrapment modifications for all quartz vein samples due to grain boundary migration recrystallisation this process is interpreted to be responsible for the generation of the co2 inclusions from a h2o co2 parent fluid in comparison with mineralisation at the ashanti and prestea deposits which are characterised by co2 n2 inclusions the observed inclusion assemblage may be due to a shallower crustal level of mineralisation or different degrees and styles of recrystallisation or a less pronounced development of laminated quartz veins due to comparably restricted pressure fluctuations furthermore the microthermometric observations allow the reconstruction of a possible retrograde p t path depicting near isothermal decompression in the p t range of the brittle ductile transition

paleoproterozoic gold deposits hosted by albite and carbonate altered tonalite in the chirano district ghana west africa paleoproterozoic birimian supergroup rocks of southwest ghana host numerous mesothermal lode gold deposits including the 38 million ounce moz ashanti deposit at obuasi and other multimillion ounce deposits at bogoso konongo prestea bibiani and in the yamfo sefwi region gold deposits of the chirano district are localized along the chirano lode horizon a 9 km segment of the chirano and related shear zones on the southeast margin of the sefwi bibiani belt economically significant mineralization at chirano is largely hosted by altered tonalite intrusions weaker alteration and subparts per million gold grades extend into adjacent birimian mafic igneous rocks and tarkwaian group sedimentary rocks pink albite alteration albite quartz pyrite hematite rutile leucoxene chalcopyrite gold and later pale carbonate alteration ankerite sericite quartz pyrite hematite gold fineness 910 940 ag au telluride characterize the gold deposits of the chirano district alteration assemblages and the bi te and mo contents of the mineralized rocks at chirano are more typical of lode gold deposits than orthomagmatic gold deposits alteration assemblages at chirano contrast with the graphite carbonate pyrite arsenopyrite pyrrhotite assemblages that dominate the lode gold deposits in southwest ghana which are hosted by graphitic shear zones and birimian sedimentary rocks differences between alteration assemblages at chirano and those in graphitic shear zones may reflect the different wall rock assemblages with which the hydrothermal fluid equilibrated rather than different fluid sources mineralization in the chirano district formed during a relatively late episode of small displacement brittle cataclasis on the chirano lode horizon after reverse ductile shearing associated with regional scale shortening this structural history is similar to that documented at the larger ashanti and bogoso deposits on the opposite side of the kumasi basin timing relationships are compatible with all three deposits forming during a single mineralizing event late in the eburnean 2 orogeny at chirano limited fault vein geometric relationships imply a component of reverse movement during mineralization whereas sinistral strike slip movement accompanied mineralization at ashanti and bogoso no consistent correlation was observed between the asymmetry of bends and splays in the strike of the chirano lode horizon and the location or style of individual gold deposits unlike at ashanti and bogoso the structural settings of deposits in the chirano district indicate that an exploration strategy which assumes mineralization occurred during sinistral offset in the host structures similar to relationships at ashanti and bogoso may result in significant targets being ignored

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

the african humid period and the record of marine upwelling from excess 230th in ocean drilling program hole 658c using a high resolution 230 th normalized record of sediment flux we document the deglacial and holocene history of north african aridity and coastal upwelling at ocean drilling program hole 658c at both the end of the younger dryas and after the 8 2 ka event there are significant drops in terrigenous accumulation at our site indicating an increase in the monsoon moisture flux over africa at this time at 5 5 ka there is an abrupt end to the african humid period and a return to stronger upwelling conditions for carbonate and opal fluxes the 230 th normalization completely changes the shape of each record based on percentage variations alone this site is a clear example of how variations in one sediment component can obscure changes in the others and it demonstrates the need for radionuclide measurements more generally in paleoceanography by taking our new records and a large amount of previous data from this site we conclude that increases in african moisture are tightly coupled to decreases in coastal upwelling intensity

high co2 content of fluid inclusions in gold mineralisations in the ashanti belt ghana a new category of ore forming fluids a reply fluid inclusions were studied in samples from the ashanti konongo southern cross prestea abosso damang and ayanfuri gold deposits in the ashanti belt ghana primary fluid inclusions in quartz from mineralised veins of the ashanti prestea konongo southern cross and abosso damang deposits contain almost exclusively volatile species the primary setting of the gaseous i e the fluid components co2 ch4 and n2 fluid inclusions in clusters and intragranular trails suggests that they represent the mineralising fluids microthermometric and raman spectroscopic analyses of the inclusions revealed a co2 dominated fluid with variable contents of n2 and traces of ch4 water content of most inclusions is below the detection limits of the respective methods used aqueous inclusions are rare in all samples with the exception of those from the granite hosted ayanfuri mineralisation here inclusions associated with the gold mineralisation contain a low salinity co2 and low salinity 6 eq wt nacl however fluid inclusions in quartz from the gold mineralisations in the ashanti belt point to distinctly different fluid compositions specifically the predominance of co2 and co2 h2o have to be emphasized fluid systems with this unique bulk composition were apparently active over more than 200 km along strike of the ashanti belt fluids rich in co2 may present a hitherto unrecognised new category of ore forming fluids

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

trapping efficiencies of sediment traps from the deep eastern north atlantic the 230th calibration bottom tethered sediment traps deployed in the deep eastern north atlantic between 54 n 20 w and 33 n 20 w l1 l2 l3 at the european continental margin at 49 n omex and off the canary islands estoc were investigated for the determination of 230th trapping efficiencies the ratios of 230th flux measured in the traps fa to the expected 230th flux from the production rate of 230th in the overlying water column fp ranged between 0 09 and 1 26 for the traps with deployment periods 300 days the interannual variation of fa fp ratios different years but same location and water depth were up to 10 suggesting that the average 230th flux to the sediment traps did not vary significantly the influence of lateral advection on the 230th flux was taken into account either by applying a mass balance of 230th and 231pa or by assuming a constant removal rate of 230th from the water column an assumption based on similar 230th concentration depth profiles observed at most locations investigated 230th trapping efficiencies were between 9 and 143 showing a trend of increasing efficiencies with increasing water depth no relation was found between current velocities and 230th trapping efficiencies our investigations suggest that the observation of constant or even increasing particle flux rates with increasing water depths in several sediment trap arrays investigated may be a result of sediment trap biases the correction for the trapping biases is important for the understanding of the regional differences in the particle flux in the eastern north atlantic

the ti saturation surface for low to medium pressure metapelitic biotites implications for geothermometry and ti substitution mechanisms the ti content of biotite can serve as a geothermometer for graphitic peraluminous metapelites that contain ilmenite or rutile and have equilibrated at roughly 4 6 kbar the relationship between ti content temperature and mg mg fe value was calibrated empirically using an extensive natural biotite data set 529 samples from western maine and south central massachusetts in combination with the petrogenetic grid of spear et al 1999 the calculated ti saturation surface is curved such that for a given mg mg fe value ti concentration increases as a function of temperature in a nonlinear fashion and for a given temperature ti concentrations decrease with an increase in mg mg fe the fit to the ti saturation surface can be reformulated as the geothermometric expression t ln ti a c x mg 3 b 0 333 in which t is temperature in degrees celsius ti is the number of atoms per formula unit apfu normalized on the basis of 22 o atoms x mg is mg mg fe a 2 3594 b 4 6482 10 9 and c 1 7283 the calibration range for this expression is x mg 0 275 1 000 ti 0 04 0 60 apfu and t 480 800 c precision of the ti in biotite geothermometer is estimated to be 24 c at the lower temperature range and improves to 12 c at higher temperatures application of the ti in biotite geothermometer to ilmenite or rutile bearing graphitic peraluminous metapelites equilibrated at 3 6 kbar is generally consistent with independent temperature determinations but with some deviations that represent local reequilibration consequently the ti systematics in biotite can also serve as the basis of a very sensitive indicator of chemical equilibrium or lack thereof application of the geothermometer to metapelites not containing the requisite mineral assemblages can lead to minor to significant errors in estimated temperatures biotite ti substitution mechanisms are controlled by several factors based on the biotite calibration data set magnesian biotites x mg 0 65 incorporate ti in accordance with the exchange vector tial2r 1si 2 where r is the sum of the divalent cations mg fe mn this substitution mechanism is primarily a response to misfit of the octahedral and tetrahedral layers in magnesian biotites intermediate biotites x mg 0 65 particularly at higher temperatures exhibit enhanced ti concentrations most consistent with the ti deprotonation tio2r 1 oh 2 exchange vector dominance of ti deprotonation substitution is largely a function of reduction of h2o activity at higher metamorphic grades supplementary biotite data from metaluminous amphibolites and mafic granulites metamorphosed isothermally with variable h2o activities reveal that low al biotite incorporates significantly higher concentrations of ti relative to peraluminous biotite as a result of a combination of the exchange vectors tio2r 1 oh 2 and rsial 2 substituting in roughly an 8 1 ratio

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

the nassara gold prospect gaoua district southwestern burkina faso abstract the nassara au prospect is located in the birimian boromo greenstone belt in southwestern burkina faso it is part of a larger mineralized field that includes the cu au porphyry system of gaoua to the north at nassara mineralization occurs within the west batie shear zone that follows the contact between volcanic rocks basalt and andesite and volcano sediments pyroclastics and black shales at the southern termination of the boromo belt gold is associated with pyrite and other fe bearing minerals that occur disseminated within the sheared volcanic and volcano sedimentary rocks in particular highest grades are distinguished in alteration halos of small quartz albite ankerite veins that form networks along the shear zone here pyrites are marked by as poor and as rich growth zones the latter containing gold inclusions gold mineralization formed during d2na subsequent shear fractures related to d3na related are devoid of gold nassara is a classical orogenic gold occurrence where gold is associated to disseminated pyrite along quartz veins

230th normalization an essential tool for interpreting sedimentary fluxes during the late quaternary there is increasing evidence indicating that syndepositional redistribution of sediment on the seafloor by bottom currents is common and can significantly affect sediment mass accumulation rates notwithstanding its common incidence this process generally referred to as sediment focusing is often difficult to recognize if redistribution is near synchronous to deposition the stratigraphy of the sediment is not disturbed and sediment focusing can easily be overlooked ignoring it however can lead to serious misinterpretations of sedimentary fluxes particularly when past changes in export flux from the overlying water are inferred in many instances this problem can be resolved at least for sediments deposited during the late quaternary by normalizing to the flux of 230th scavenged from seawater which is nearly constant and equivalent to the known rate of production of 230th from the decay of dissolved 234u we review the principle advantages and limitations of this method notwithstanding its limitations it is clear that 230th normalization does provide a means of achieving more accurate interpretations of sedimentary fluxes and eliminates the risk of serious misinterpretations of sediment mass accumulation rates

mineralogical fluid inclusion and stable isotope characteristics of birimian orogenic gold mineralization at the morila mine mali west africa abstract gold mineralization at morila is hosted in flat lying meta graywacke associated with a birimian aged massigui schist belt in mali three major events of deformation metamorphism fluid flow d 1 d 2 and d 3 are recognized at morila with mineralization associated with various increments of deformation and fluid flow during d 2 three distinct vein sets v 1 v 3 associated with d 1 d 3 respectively have also been recognized v 1 vein sets are thin poorly defined quartz feldspar metamorphic segregations broadly parallel to the regional fabric v 2 veins are generally boudinaged foliation parallel quartz feldspar veins or occur as felsic melt segregations in the form of quartz k feldspar muscovite biotite blebs located essentially within the ore zone v 3 veins occur as sub parallel to high angle biotite arsenopyrite gold veins that appear to be extensional in nature the ore zone is characterized by compositionally distinct biotite higher mgo and lower feo and more calcic plagioclase than otherwise texturally identical minerals in the footwall and hanging wall of the mineralized zone suggesting that prograde metamorphic minerals were modified by post metamorphic mg and ca rich mineralizing fluids gold forms discrete grains in the v 2 veins or in the adjacent host rock and is closely associated with pyrrhotite and arsenopyrite gold also occurs with sb bi ore minerals in rare microfractures numerous thin biotite arsenopyrite gold veinlets cut d 1 and d 2 fabrics and often carry significant gold associated with kink bands in the d 2 fabric fluid inclusion and oxygen isotope study provide evidence that morila fluids are intermediate salinity 12 16 wt nacl equivalent nacl cacl 2 mgcl 2 h 2 o ch 4 n 2 fluids of magmatic origin 18 o water 10 9 0 3 the ore forming fluid subsequently unmixed to form a compositional range of vapor rich ch 4 n 2 dilute nacl ch 4 n 2 aqueous and liquid rich brine associated with the opening of a micro fracture network and vein development quartz biotite isotope geothermometry indicates that mineralization occurred between 350 to 450 c gold mineralization at morila was an integral part of coeval plutonism deformation and regional metamorphism while the modification of the ore fluid by unmixing was the most important factor associated with the concentration of economically viable gold grades at morila

gold mineralization in the ashanti belt of ghana genetic constraints of the stable isotope geochemistry the ashanti belt of ghana is the key district of gold mineralization in the paleoproterozoic terrane of west africa the area considered in southwest ghana is covered by lithologies of the volcanic sedimentary birimian supergroup and the overlying elastic sedimentary tarkwaian group which were jointly folded and metamor phosed under greenschist facies conditions during the eburnean teetonothermal event at about 9 1 ga regional fotiation md subparallel shear zones hosting mesothermal gold mineralization developed during deformation coeval with metamorphism four major tsoes of primary gold mineralization are present in the ashanti belt 1 mesothermal generally steeply dipping quartz veins in shear zones mainly in birimian sedimentary rocks 9 sulfide ores with auriferous arsenopyrite and pyrite spatialty dosely associated with the quartz veins 3 sulfide disseminations and stockworks in granitoids and 4 paleoplaeers of the tarkwaian group this study concentrates on types 1 and 9 of the hydrotherlnal gold mineralization stable isotope analyses of host rock and ore components were performed with the ailn of obtaining parameters relevant to the origin and evolution of the fluids that produced gold mineralization carbonaeeous matter in the birimian metasediments displays 93c values ranging from 11 4 to 9 8 3 per mil relative to pdb indicating an organogenie origin carbonates display a unimodal distribution of 9ac values ranging from 9 9 to 17 0 per rail relative to pdb coz extracted from fluid inclusions in the auriferous quartz veins has 93c values ranging from 9 5 to 15 7 per mil relative to pdb it is proposed that these carbon isotope compositions of carbonates and coz reflect extensive interaction of the co 2 rieh hydrothermal fluids with reduced carbon in birimian sediments in the deeper parts of the hydrothermal systems carbonates and auriferous vein quartz have 6 so values ranging from 19 9 to 9 9 9 and 19 8 to 15 6 per mil relative to smow respectively carbonates and quartz were deposited in near isotopic equilibrium with respect to 6 so indicating fluid dominated conditions during ore formation from fluids of metamorphic or magmatie origin such an origin is corroborated bysd values of water extracted from fluid inclusions in vein quartz 37 to 53 relative to smoxv pyrite of synsedimentary diagenetie origin in birimian schists displays sulfur isotope compositions ranging from 7 3 to 9 0 9 per rail median ca 10 relative to cdt similar compositions and wide ranges are usually attributed to sulfide generation by bacterial sulfate reduction from seawater arsenopyrite and eogenetie pyrite from the sulfide ores generally have 534s values in the range 5 3 to 10 9 per rail relative to cdt the tight unimodal distribution of 534s values indicates a large homogeneous fluid reservoir the low 534s values are interpreted as source inherited not related to unusual ph eh temperature or depositional conditions sulfides in birimian sediments represent the most likely sulfur reservoir tapped by the fluid systems the c o h and s isotope compositions of ore related hydrothermal minerals and fluid inclusion compo nents indicate that the mineralizing fluids interacted extensively with the paleoproterozoie rocks especially birimian sediments at deeper crustal levels and at high temperatures the isotopic compositions are most compatible with the formation of fluids from devolatilization reactions invomng birimian strata during pro grade metamorphism at depth metamorphic fluids

fluid immiscibility in natural processes use and misuse of fluid inclusion data ii interpretation of fluid inclusion data in terms of immiscibility abstract phase equilibrium analysis of the relevant systems together with the application of the principles of chemical equilibrium put severe constraints on the interpretation of fluid inclusion data in terms of immiscibility in part i following from that point the major limits on the accuracy and even the validity of fluid inclusion quantitative data and their interpretation in terms of fluid composition and density are briefly discussed the practical implications of the general constraints temperature pressure topology of the fluid systems are envisaged emphasis is laid on some important consequences such as the use of isochore intercepts and the possible resulting interpretation of fluid mixing rather than unmixing the case of highly saline inclusions the identification and interpretation of heterogeneous trapping the composition and density constraints on coexisting fluids are presented and illustrated by natural examples taking into account all the measurable parameters in fluid inclusions volume temperature and nature of phase transitions more or less complete individual spectroscopic analyses all the available experimental data and all the theoretical constraints may be long and difficult however it is most generally very informative and productive although part of these data is often sufficient to deny unmixing nevertheless a final example on metamorphic fluids demonstrates how such an approach can prove and also characterize a fluid unmixing during a geologic process

detection and processing of bistatically reflected gps signals from low earth orbit for the purpose of ocean remote sensing we will show that ocean reflected signals from the global positioning system gps navigation satellite constellation can be detected from a low earth orbiting satellite and that these signals show rough correlation with independent measurements of the sea winds we will present waveforms of ocean reflected gps signals that have been detected using the experiment onboard the united kingdom s disaster monitoring constellation satellite and describe the processing methods used to obtain their delay and doppler power distributions the gps bistatic radar experiment has made several raw data collections and reflected gps signals have been found on all attempts the down linked data from an experiment has undergone extensive processing and ocean scattered signals have been mapped across a wide range of delay and doppler space revealing characteristics which are known to be related to geophysical parameters such as surface roughness and wind speed here we will discuss the effects of integration time reflection incidence angle and examine several delay doppler signal maps the signals detected have been found to be in general agreement with an existing model based on geometric optics and with limited independent measurements of sea winds a brief comparison is presented here these results demonstrate that the concept of using bistatically reflected global navigation satellite systems signals from low earth orbit is a viable means of ocean remote sensing

the influence of particle composition on thorium scavenging in the ne atlantic ocean pomme experiment abstract 230th 232th and 234th were analyzed in sinking particles collected by moored and drifting sediment traps in the ne atlantic ocean pomme experiment in order to constrain the phase s carrying th isotopes in the water column it reveals a contrasted behaviour between 234th and 230th 234th is correlated to the particulate organic carbon suggesting that it is primarily scavenged by organic compounds in the surface waters 230thxs is correlated with mn ba and the lithogenic fraction that are enriched in small suspended particles and incorporated in the sinking particulate flux throughout the water column the lack of correlation between 230thxs and caco3 or biogenic silica bsi indicates that caco3 and bsi are not responsible for 230th scavenging in the deep waters of this oceanic region 230th is generally correlated with the lithogenic content of the trapped material but this correlation disappears in winter during strong atmospheric dust inputs suggesting that lithogenic matter is not directly responsible for 230th scavenging in the deep waters or that sufficient time is required to achieve particle solution equilibration mno2 could be the prevalent 230thxs bearing phase the narrow range of kd mno2th obtained for very contrasted oceanic environments supports a global control of 230thxs scavenging by mno2 and raises the possibility that the 230th 231pa fractionation is controlled by the amount of colloidal mno2 in seawater

scavenging of 230th 231pa and 10be in the southern ocean sw pacific sector the importance of particle flux particle composition and advection abstract the scavenging of 230 th 231 pa and 10 be was studied in the pacific sector of the southern ocean along 170 w using measurements from surface sediments time series sediment traps and the water column all sediment traps collected an annual flux of 231 pa greater than the integrated rate of production by 235 u decay up to 5 5 times greater and a flux of 10 be greater than the global average deposition rate of 10 be up to 3 4 times greater fluxes of 230 th were on average close to the production rate in the overlying water column these large fluxes of 231 pa and 10 be and high unsupported 231 pa 231 th and 10 be 230 th ratios in the sediments are not associated with depletion of nuclides in the water column and therefore are not the result of the classical boundary scavenging mechanism we estimate that of the 231 pa and 230 th advected into the southern ocean as part of the large scale overturning circulation only those nuclides associated with the upper limb of this circulation i e those that pass through the surface as part of the wind driven ekman flow are scavenged efficiently the majority of the nuclides advected into the southern ocean and associated with the bottom water limb are not scavenged to the sediments of the southern ocean but are returned northward throughout the year the unsupported 231 pa 230 th and 10 be 230 th ratios of material reaching sediment traps at 1000 m at a given site increase with increasing particle flux this behavior is explained by a conceptual model in which th pa and be are scavenged reversibly by fine grained suspended particles at all depths while pa and be are in addition scavenged strongly by diatom rich aggregates in surface waters spatial variability in the annually averaged unsupported 231 pa 230 th and 10 be 230 th ratios of sinking particulate matter reflects primarily the variability in particle composition and in the ratio and quantity of nuclides upwelled to the mixed layer rather than variability in particle flux

tellurium magmatic fluids and orogenic gold an early magmatic fluid pulse at cononish gold deposit scotland significant tellurium enrichment occurs in many orogenic gold deposits but the factors causing this are little understood some authors suggest this demands a magmatic input whereas others suggest it need not fractionation of te from se and s could offer insight into source pathway processes of auriferous fluids the metasedimentary hosted cononish vein gold deposit scotland is unusually te rich compared to many orogenic gold deposits with te au 2 4 whereas most orogenic deposits have te au 1 here ag in au ag alloy increases from 10 to 90 wt through the paragenesis correlating with decreasing hessite ag2te abundance this suggests the au ag alloy composition was controlled by the fluid te activity and that this decreased through time this is coupled to an increase in pyrite 34s from 2 0 to 11 4 through the paragenesis thus the deposit formed from a primary fluid with a low 34s and high te au ag that evolved to a high 34s low te pb cu bearing fluid the high 34s of the later fluid suggests it can only be sourced from specific nearby metamorphosed sedex horizons the early fluid that deposited most of the gold could be sourced from other metasedimentary units in the stratigraphy or be magmatic in origin we argue that two observations taken together suggest it is most likely that this fluid was magmatic the age of the mineralisation is identical to the last stage of crystallization of nearby granite batholiths and the fluid has a s isotope signature consistent with a magmatic source gold deposits in orogenic belts are almost certainly polygenetic and this study demonstrates evidence for te rich orogenic deposits having a significant magmatic component

insights into the genesis of orogenic gold deposits from the zhengchong gold field northeastern hunan province china abstract the zhengchong gold deposit is located in the central jiangnan orogen belt where gold ore occurs mainly as quartz veins altered slates and minor breccias hosted by shear zones in the lengjiaxi group based on its vein crosscutting relationships mineral assemblages and paragenetic sequences mineralization in this deposit is divided into four stages stage 1 quartz q1 pyrite stage stage 2 quartz q2 pyrite arsenopyrite stage stage 3 quartz q3 pyrite polymetallic sulfide mineral stage and stage 4 quartz q4 carbonate stage two types of fluid inclusions have been recognized in the quartz grains co2 bearing fluid inclusions c type and aqueous fluid inclusions w type fluid inclusions in hydrothermal quartz yield homogeneous temperatures and salinities of 312 406 c and 4 65 9 21 wt naclequiv stage 1 252 324 c and 2 20 8 10 wt naclequiv stage 2 193 296 c and 2 24 14 04 wt naclequiv stage 3 and 127 209 c and 2 57 6 59 wt naclequiv stage 4 the co occurrence of these inclusion types despite their variable fluid salinities can be explained by fluid boiling during stages 2 and 3 of mineralization possibly as a result of episodic pressure decreases linked to fault valve activity laser raman spectroscopic analysis results reveal that small quantities of ch4 and n2 are present in the stage 2 3 fluid inclusions fluid inclusion data and microthermometric results show that the ore fluids were low salinity and co2 rich yielding both co2 inclusions c type and aqueous inclusions w type the trapping pressures estimated from the c type inclusions are 80 180 mpa for stages 2 and 3 yielding gold mineralization depths of 7 8 km the mineralizing fluids had calculated 18oh2o values ranging from 3 7 to 8 2 and d values from 75 2 to 61 8 indicating derivation mainly from metamorphic fluids the sulfide minerals yield 34s values of 8 9 to 0 1 and 206pb 204pb 207pb 204pb and 208pb 204pb ratios of 17 83 18 12 15 67 15 76 and 38 03 38 62 respectively which differ significantly from the isotopic composition of the granodiorite 34s 2 4 to 1 0 206pb 204pb 18 57 19 28 207pb 204pb 15 69 15 76 208pb 204pb 38 97 40 34 however the s pb isotopic compositions of the sulfide minerals are similar to those of slates of the lengjiaxi group in the study area the zhengchong gold deposit probably originated from a metamorphic fluid system characterized by low salinity low density and co2 enrichment with limited admixture of magmatic fluids based on similarities to other orogenic gold deposits we infer that the zhengchong orebody represents an orogenic gold deposit formed during the late ordovician jiangnan orogeny caused by collision of the yangtze and cathaysia blocks

calculation of oxygen isotope fractionation in hydroxyl bearing silicates abstract the modified increment method has been applied to the calculation of oxygen isotope fractionation factors for hydroxyl bearing silicate minerals the order of 18o enrichment obtained in common rock forming minerals is pyrophyllite kaolinite tourmaline talc prehnite topaz illite phengite lepidolite muscovite staurolite epidote glaucophane serpentine chlorite tremolite hornblende phlogopite biotite humite norbergite ilvaite hydroxyl bearing silicates are enriched in 18o relative to hydroxyl groups but depleted in 18o relative to anhydrous counterparts three sets of self consistent fractionation factors between quartz and the hydroxyl bearing silicate minerals between calcite and the silicate minerals and between the silicate minerals and water have been calculated for a temperature range of 0 1200 c the fractionation factors calculated for mineral pairs are applicable to isotopic geothermometry in igneous metamorphic and sedimentary petrology they can be used as a test of isotopic equilibrium or disequilibrium in natural mineral assemblages over all temperature ranges of geological interest the difference in oxygen isotope composition between the hydroxyl bearing mineral and the oh group is quantitatively demonstrated to be temperature dependent and therefore can be used as a single mineral geothermometer

thorium isotopes in the western mediterranean sea an insight into the marine particle dynamics we present a detailed view of the 230 th 232 th systematics in the western mediterranean sea in order to constrain water and particle fluxes the conclusions obtained at the regional scale are also relevant at a more global scale although they may be more difficult to establish in the open ocean 230 th and 232 th were analyzed in size fractionated seawater and marine particle samples collected in the ligurian alboran and ionian seas the 230 thxs 230 th produced by the radioactive decay of 234 u in seawater profiles at dyfamed and in the alboran sea site are not linear due to the formation of deep waters the difference of 230 thxs concentration between these two sites is related to the aging of the water masses and to different scavenging conditions the 230 th 232 th ratio is used as a tracer during mixing processes to provide information on the pathways followed by the matter in the water column at dyfamed filtered 6 0 2 wm and ultrafiltered 6 1 kda solutions have similar 230 th 232 th ratios suggesting that an equilibrium exists between truly dissolved and colloidal th the change of the th flux and of the 230 th 232 th ratio of trapped particles observed in august between 200 m and 1000 m is best explained by aggregation of filtered large particles on the trapped particles the residence time of filtered large particles with respect to aggregation on trapped particles is of the order of 8 80 days the combined budget of 230 th and 232 th inputs to the western mediterranean sea requires the dissolution of 3 5 of the th associated with all the continental particulate inputs including particles sequestered in margins suggesting that eolian inputs are not the only source of refractory elements to the mediterranean sea and may be to the whole ocean fl 2002 elsevier science b v all rights reserved

the geology of the taparko gold deposit birimian greenstone belt burkina faso west africa the taparko gold deposit located in the eastern branch of the proterozoic birimian bouroum yalogo greenstone belt burkina faso consists of a network of quartz veins developed in a n 170 trending shear zone 250 m wide 4 km long superimposed on the regional birimian structural pattern the quartz vein network is composed of a a dominant array of quartz veins type 1 parallel to the shear zone and comprising strongly deformed dark quartz exhibiting foliation layering ribbon tension gashes etc b oblique and subparallel related veins type 2 of gray to white weakly deformed quartz crosscutting the dominant quartz veins resulting in breccia structures and c shallow dipping veins type 3 cross cutting veins types 1 and 2 and filled by undeformed white buck structure quartz cross cutting relationships and different quartz types in different veins and within individual veins imply a concomitant filling of the veins during the progressive deformation initial sinistral transcurrent shearing evolved with time to sinistral reverse shearing metallic minerals occur only in type 1 and 2 veins and were deposited in two stages with native gold being related to second stage sulfides gold and chalcopyrite precipitated preferentially upon the surfaces of fractured pyrite grains in low pressure sites pressure shadow zones around and or within the sulfide grains along subsequently annealed fractures the formation of the south taparko deposit can be divided into a succession of events a during the first event n 170 directed sinistral transcurrent shearing resulted in a n 20 mylonitic foliation and fractured rock which allowed h2o co2 and sio2 rich fluids to circulate and deposit quartz with buck texture b during the second event type 1 quartz was strongly deformed and type 2 veins formed with sigmoidal shapes as viewed on a horizontal plane and c during the third event the sinistral transcurrent shearing evolved to sinistral reverse shearing and the deformation style evolved correspondingly from ductile to brittle ductile during the last phase of deformation gold nucleated and deposited in low pressure zones

savers a simulator of gnss reflections from bare and vegetated soils the mean power of the reflected global navigation satellite system gnss signals acquired by a gnss reflectometry gnss r receiver can be modeled through the integral bistatic radar equation by weighting the contributions of all scatterers on the surface by the system impulse response the geophysical properties of the scattering surface affect the magnitude of the reflected navigation signals through the bistatic scattering coefficient which in case the observed surface is land is a function of the soil dielectric properties surface roughness and vegetation cover in this paper the gnss r signal simulator developed in the framework of the land monitoring with navigation signal leimon project supported by european space agency is presented the simulator is able to predict the power reflected by land taking as input the system and observation parameters as well as the land surface parameters the latter are used to simulate both the coherent and the incoherent scattering taking advantage of widely used theoretical models of bistatic scattering from bare soils and vegetated surfaces first the geometrical formulation is discussed and then the problem of polarization mismatch due to real antennas at circular polarization is faced following the polarization synthesis approach finally a comparison with some experimental data collected during the leimon campaign is presented the simulations display the same trend of the experimental data thus showing that the simulator can be used as an efficient tool for the interpretation of gnss r measurements

carbon isotope studies of auriferous quartz carbonate veins from two orogenic gold deposits from the neoarchean chitradurga schist belt dharwar craton india evidence for mantle magmatic source of auriferous fluid abstract carbon and oxygen isotopic compositions of carbonates from auriferous quartz carbonate veins qcvs of two orogenic gold deposits ajjanahalli and guddadarangavvana halli g r halli from the neoarchean chitradurga schist belt of the dharwar craton southern india are examined to understand the origin of the mineralizing fluids the average carbonate carbon 13cpdb and oxygen 18osmow isotope compositions of qcvs of ajjanahalli are 5 5 1 3 and 14 1 2 7 respectively the same ratios for the qcvs of g r halli are 6 2 1 9 and 14 1 0 5 the corresponding average fluid 13c and 18o compositions are 5 81 1 14 13 78 5 1 for ajjanahalli and 4 64 0 7 6 50 0 6 for g r halli the 13cpdb of syn sedimentary carbonates of bif of ajjanahalli 1 8 0 1 carbonated metabasalts of ajjanahalli 1 4 and g r halli 1 3 fall in the compositional range of marine carbonates 0 2 as dissolution decarbonation reactions during metamorphism of pre existing carbonate carbonated rocks produce co2 with 13c values similar to or more enriched than parent rock the carbonate or fluid 13c ratios of the qcvs which fall in the compositional range of mantle magmatic derived co2 or carbonates obtained in this work cannot be the result of metamorphism it is proposed that gold mineralizing fluids were derived from juvenile magmatic melts and were channeled through crustal scale shear zones to give rise to the gold deposits

the kalana vein hosted gold deposit southern mali abstract the kalana gold deposit occurs within metamorphosed paleoproterozoic volcano sedimentary series of the birimian baoule mossi domain of the west african craton in the south of mali these formations are intruded successively by small dioritic bodies as well as andesitic and tonalitic dykes which exhibit volcanic arc setting signatures mineralization is hosted by two sets of quartz veins that intersect the regional schistosity the first set of veins is the most important in terms of grades and size and consists of thick veins up to meter size that range in trend from n s to e w with shallow plunges the second set consists of much thinner centimeter size sub vertical quartz veins oriented ne sw the two sets of veins are interpreted to have formed during the evolution of late gently dipping thrust faulting two episodes of gold precipitation are recognized a first episode during early stages of vein growth formed micron size native gold inclusions in arsenopyrite a later episode during vein shearing and fracturing of the quartz lodes precipitated native gold in free form in quartz in fractured arsenopyrite and associated with chalcopyrite galena sphalerite bi sulfides and native bismuth all evidence suggests that the kalana deposit represents orogenic gold mineralization formed during a relatively long lived hydrothermal system at a late stage of the tectonic history of the greenstone belt

a weathered skarn type mineralization in ivory coast the ity gold deposit abstract although the ity deposit is the oldest operating mine in ivory coast very few studies exist on this deposit it is situated in western ivory coast some 700 km northwest of abidjan the mine is presently operated and mined by smi societe des mines d ity society of ity mines and has produced one million ounces of gold since its opening in 1991 all mined ore bodies are hosted in laterite and clay formations the gold deposits in the ity area form a cluster of mining operations of various sizes flotouo zia mont ity hosted in a birimian volcano sedimentary belt the mineralization is mostly located at the contact between a granodiorite tonalite intrusive body and sediments primary gold mineralization occurs in the form of veinlets and mostly skarn at the contact between the granitic intrusion and limestone calc silicate minerals such as diopside and andradite dominate the skarn however the economic gold mineralization at ity is associated with the saprolitic zone 50 120 m thick and consists of several mineralized lenses of clayey and ferruginous material terres noires and of sedimentary breccia layers a thick laterite horizon a minimum of 10 m overlies the saprolite and covers the land throughout the region it is mineralized in the deposit area this contribution provides a summary of the geological and mineralogical relationships at the ity deposit presents new data on skarn type gold mineralization and summarizes its history from the first findings through exploration and mining assessment

fluid immiscibility in natural processes use and misuse of fluid inclusion data abstract many occurrences of fluid immiscibility in natural geologic systems have been reported recently most often from fluid inclusion studies however the interpretation of fluid inclusion data in terms of immiscibility sometimes suffers from ambiguity of the vocabulary insufficient knowledge of the immiscibility constraints and insufficient knowledge of the topology in the tpx space of natural fluid systems for such reasons some authors have been misled to erroneous interpretations the term chemical immiscibility is unambiguously redefined as a multiphase multicomponent equilibrium the consequences of this definition are directly derived from the phase rule and concern the possible equations that relate the various parameters temperature pressure volumes compositions to each other these equations already put constraints on the topology of the phase equilibria in fluid systems a particular expression of the phase rule is proposed which takes into account the multiphase constant bulk volume constant bulk composition constraints in fluid inclusions the consequences of such an expression are of major importance in fluid inclusion studies the phase relations of some simple systems that approximate quite efficiently the natural complex fluids are then detailed h2o nacl co2 ch4 h2o co2 h2o co2 nacl the effects of these topologies and of the supplementary constraints constant bulk composition and constant bulk volume assumed for fluid inclusions isopleth isochoric systems are discussed

scobi veg a generalized bistatic scattering model of reflectometry from vegetation for signals of opportunity applications scobi veg stands for signals of opportunity coherent bistatic scattering model for vegetated terrains it simulates polarimetric reflectometry of vegetation canopy over a flat ground using a monte carlo scheme the model is aimed at assessing the value of navigation and communication satellite signals of opportunity in a range of frequencies from p to s bands for remote sensing of a number of geophysical land parameters such as soil moisture and biomass a fully polarimetric expression for bistatic scattering from a vegetation canopy is first formulated for a general case and is then specialized to the practical case of ground based low altitude platforms with passive receivers overlooking vegetation using the signals transmitted from large distances using analytical wave theory in conjunction with distorted born approximation the transmit and receive antenna effects i e polarization crosstalk mismatch orientation and altitude are explicitly accounted for the forward model developed here enables the understanding of the effect of different geophysical parameters and system configurations on the coherent and incoherent components of the reflected signatures it can thus help developing robust inverse algorithm for extraction of soil moisture and biomass the model is applied to p band signals of geostationary communication satellites to describe polarimetric reflections from tree canopies as observed from down looking platforms at various altitudes the relative contributions of diffuse and specular scattering on total reflected power and reflectivity are quantified for various observing scenarios

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

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

land geophysical parameters retrieval using the interference pattern gnss r technique in the past years the scientific community has placed a special interest in remotely sensing soil moisture and vegetation parameters radiometry and radar techniques have been widely used for years global navigation satellite systems opportunity signals reflected gnss r over the earth s surface are younger but they have already shown their potential to perform these observations this paper presents a gnss r technique based on global positioning system gps measurements that allows the retrieval of several geophysical parameters from land surfaces this technique measures the power of the interference signal between the direct gps signal and the reflected one after scattering over the land so it is called interference pattern technique ipt this paper presents the results obtained after applying the ipt for topography soil moisture and vegetation height retrievals over vegetation covered soils

the influence of particle composition on thorium scavenging in the mediterranean sea abstract sediment trap data are crucial for the study of marine biochemical cycles but they need careful validation by thorium th isotopes in the present study 230th 232th uranium u aluminum al barium ba and manganese mn were analyzed in sinking particles collected by moored sediment traps in the ligurian sea dyfamed site in order to determine the collection efficiency of the traps and to constrain which particulate phase s carries th isotopes in a region with strong lithogenic inputs the 230thxs evaluation was based on the u content of each sample rather than on the 232th content of each sample and the average 238u 232th ratio of the continental crust because the latter method introduced too much uncertainty in the calculation high trapping efficiencies 187 85 at 200 m and 87 11 at 1000 m indicated no evidence of particle under collection by the traps the lack of correlation between 230thxs and the carbonate or the organic matter fraction suggests that these phases are not major 230thxs carrying phases in the deep ocean for most samples of the time series the 230thxs concentration is correlated with the lithogenic fraction and the mn concentration but pulses of particles with high lithogenic and mn content and low 230thxs concentration occur in winter assuming that 230thxs is only carried by lithogenic particles we estimate kd lithoth ranges from 0 42 0 04 107 ml g to 0 8 0 2 107 ml g assuming that 230thxs is only carried by authigenic mn oxide precipitates mno2 we estimate that kd mno2th ranges from 0 6 0 1 1010 ml g to 1 1 0 4 1010 ml g the relative variation of kd mno2th a factor 7 between different oceanic sites is significantly lower than the relative variation of kd lithoth a factor 50 suggesting that 230thxs has a tighter link with mno2 rather than with lithogenic particles and hence that 230thxs may be more likely scavenged by mno2 than by lithogenic particles the unambiguous determination of the particles carrying 230thxs remains to be done