evolution of southern caribbean plate boundary vicinity of trinidad and tobago two processes oblique collision of an island arc and strike slip motion parallel to the south american coast have been suggested as dominant in the tectonic evolution of the southeastern corner of the caribbean field work in the el pilar fault zone of trinidad and interpretation of offshore seismic data lead us to conclude that the dominant process was strike slip motion on five or more major fault systems within a 250 km wide east west trending plate boundary zone extending north to south from grenada to the mouth of the orinoco river during the last 30 m y movements in this fault zone 1 diverted the orinoco river eastward 2 juxtaposed blocks with diverse stratigraphic characteristics and 3 generated secondary extensional compressional and strike slip str ctures including anticlines of northeast to north northeast trend of which the tobago arch the central range of trinidad and the deformed mud diapirs off the southeastern coast of trinidad are the most prominent

hydrothermal mounds and young ocean crust of the galapagos preliminary deep sea drilling results leg 70 a total of 32 holes at 5 sites near 1 n 86 w drilled on deep sea drilling project dsdp leg 70 november december 1979 provide unique data on the origin of the hydrothermal mounds on the south flank of the galapagos spreading center hydrothermal sediments primarily mn oxide and nontronite are restricted to the immediate vicinity of the mounds 100 m and are probably formed by the interaction of upward percolating hydrothermal solutions with sea water and pelagic sediments above locally permeable zones of ocean crust mounds as much as 25 m in height form in less than a few 10 5 yrs and geothermal and geochemical gradients indicate that they are actively forming today the lack of alteration of upper basement rocks directly below the mounds and throughout the galapagos region indicates that the source of the hydrothermal solutions is deeper in the crust

manganese deposits of the devonian magnitogorsk palaeovolcanic belt southern urals russia abstract recent studies provide an overview on hydrothermal volcaniclastic sedimentary manganese deposits from the magnitigorsk palaeovolcanic belt in southern urals russia 100 deposits this report presents data on the structures of ore bodies chemical composition and mineralogy of manganese ores these deposits are divided into two types with different ore bearing band structures chemical and mineral ore compositions and ore component accumulation conditions manganese ores of the type 1 deposit are associated with jasperites ores from type 2 deposits are localised within thin banded jaspers type 1 deposits are thought to form during hydrothermal activity in areas where hydrothermal fluids leak into the seafloor type 2 deposits are formed within a closed basin as hydrothermal activity decreases away from hydrothermal vents and typically contain a greater volcaniclastic contribution manganese ores comprised more than 70 mineral types and form three groups of mineral assemblages a minerals formed during low grade regional metamorphism t 200 260 c p 2 3 kbar that compose the main part of ore bodies b mineral assemblages in segregatic and metasomatic veins filling late stage tectonic fractures and c an assemblage of subsurface supergene minerals most of these minerals which total approximately 38 minerals are metamorphic silicates the formation of metamorphic mineral assemblages is controlled by the presence of organic material om in primary sediments the conditions under which type 1 deposits formed favour the accumulation of om the metamorphism of these sediments is responsible for the formation of oxide carbonate silicate reduced ores which consist of mn silicates and carbonates such as tephroite rhodonite caryopilite and rhodochrosite andradite quartz hematite and hausmannite insignificant preserved quantities of om were found in type 2 deposits during the metamorphic alteration of these sediments oxide silicate oxidised ores were formed with the dominance of braunite

manganese metallogenesis a review abstract metallogenesis of manganese in space and time is reviewed here in the light of the progressive development of the atmosphere the hydrosphere and the lithosphere attendant with the varied styles of tectonism economic deposits of manganese first appeared c 3000 ma ago postdating by at least 800 million years the oldest known geological sequence containing iron formation and base metal sulfide ores the development of manganese deposits in the archean as a whole vis a vis that of iron formation and stratiform massive sulfides was minor this is possibly a reflection of the composition of the then endogenic exhalations and or the character of the atmosphere and the hydrosphere the geologic setting of the manganese deposits of this age was always atypical of the archean period deposition of manganese was intensified with the advent of the proterozoic with the changing tectonic style leading to stabilization of the cratons and oxygenation of the hydrosphere and the atmosphere large to superlarge deposits were formed mainly through terrigenous input during this period the mesozoic era ushered in the supremacy of manganese deposition and the peak was reached in cenozoic time this was largely due to the formation of giant shallow water deposits in areas of marine transgression as well as deposition of manganese rich nodules and crusts in deep sea environments three major aspects of manganese metallogenesis stand out as most important but enigmatic these are a the extreme fractionation of iron and manganese in nature and their reverse trend of metallogenic development b the universal record of shallow water deposition of manganese in land based deposits in contrast with the deep sea milieu observed in modern basins and c the common evidence of biological activity in close association with manganese deposition which could be either causal or casual all these aspects merit further in depth study and metallogenic analysis in a broad spectrum

origin of ultramafic hosted magnesite on margarita island venezuela ultramafic hosted deposits of magnesite mgco3 have been studied on margarita island venezuela to elucidate the source of carbon and conditions of formation for this type of ore petrographic mineralogic and 18o data indicate that magnesite precipitated on margarita in near surface environments at low p and t 13c ranges from 9 to 16 pdb within the magnesite and 8 to 10 pdb within some calcite and dolomite elsewhere on the island the isotopically light dolomite fills karst and the calcite occurs as stock work veins which resemble the magnesite deposits these carbon isotopic ratios are consistent with a deep seated source rather than an overlying source from a zone of surficial weathering however there is not much enrichment of precious metals and no enrichment of heavy rare earth elements as would be expected if the carbon had migrated upward as aqueous carbonate ions the carbon probably has risen as a gaseous mixture of co2 and ch4 which partially dissolved in near surface water before leaching cations and precipitating as magnesite and other carbonates the process probably is ongoing given regional exhalation of carbonaceous gases

economic potential of the ultramafic rocks of jamaica and tobago two contrasting geological settings in the caribbean ultramafic rocks in jamaica are dunites with minor lherzolite often serpentinised and are part of a dismembered ophiolite complex in tobago dunites wehrlites pyroxenites and hornblendites form the lower part of a plutonic complex of island arc affinity the mineral assemblages and chemistry reflect these differences chromite in jamaica is high in al and mg whereas in tobago it is rich in fe as in alaskan type intrusives ni cu pge assemblages in jamaica are pentlandite with later low temperature heazlewoodite awaruite and native copper the latter with pt and pd in tobago an assemblage of pentlandite pyrrhotite pyrite and chalcopyrite is much less affected by later alteration pge phases also occur the dunites in jamaica have sufficient mgo to be a potential source of olivine the higher fe in olivine from tobago indicates that olivine cumulates in plutonics from island arc settings are a less suitable source of the mineral ni laterites in jamaica are unlikely because of high topographic relief the prospect for ni laterites in tobago is low as there is little ni in the olivines chrysotile asbestos talc and magnesite are absent in both islands this is probably a consequence of the lack of secondary serpentine recrystallisation to form fibrous chrysotile veins the deep tectonic level and lack of hydrothermal circulation for magnesite to form and the absence of metamorphic metasomatic events and or late stage extension tectonics which might have yielded talc

manganiferous cherts of the franciscan assemblage i general geology ancient and modern analogues and implications for hydrothermal convection at oceanic spreading centers there are several hundred ophiolitic manganiferous chert deposits primarily of late jurassic to early cretaceous age known within the franciscan assemblage of california the sequences typically consist of one to three massive manganiferous chert lenses containing 30 to 50 percent mn and averaging 1 m in thickness by 15 m subcircular diameter these are separated by an average 2 to 10 m of thin bedded radiolarian cherts and overlie basalts or greenstones both their geology and chemistry indicate that the ore lenses are hydrothermal and may have formed on the flanks of a mid ocean ridge or within a back arc basin it is proposed that the sequences developed as a result of sea floor spreading over a series of deep hydrothermal seawater convection cells paralleling a spreading center and spaced roughly 5 to 10 km apart chemical profiles of mn fe si al cu ni zn co ba ti the rare earth elements and 87 sr 86 sr have been determined through two complete sections these profiles indicate hydrothermal input of mn si cu ni zn and ba and detrital or hydrogenous input of al and co they illustrate the use of ti as a measure of relative detrital sedimentation rates fe is strongly fractionated from mn within the ores fe mn 0 1 and fe mn ratios decrease upward throughout each section suggesting preferential deposition of fe within the sediment and of mn at the seawater interface rare earth element distributions reflect the interaction of sea water and underlying basalts sr isotopic ratios of the ores and basalts demonstrate both strong and moderate seawater influences respectively fluid inclusion analyses on veins of undetermined age show seawater salinity temperatures of roughly 200 degrees c and tentative entrapment pressures corresponding to 1 700 m water depth early and intermediate veins were injected into unconsolidated siliceous sediment producing a characteristic bleached and pseudobrecciated texture an analogy is drawn with the present day field of hydrothermal mounds near the galapagos rift and with ophiolitic complexes of the northern apennines and other localities

mineralogy of low grade metamorphosed manganese sediments of the urals petrological and geological applications abstract the paper describes mineralogy of the low grade metamorphosed manganese sediments which occur in sedimentary complexes of the pai khoi ridge and the polar urals and volcanosedimentary complexes of the central and south urals the degree of metamorphism of the rocks studied corresponds to pt conditions of the prehnite pumpellyite deposits of pai khoi and polar and south urals and green schist deposits of the central urals facies one hundred and nine minerals were identified in the manganese bearing rocks on the basis of optical and electron microscopy x ray diffraction and microprobe analysis according to the variations in the amount of major minerals of the manganese rocks of the urals they are subdivided on carbonate i oxide carbonate silicate ii and oxide silicate iii types carbonates various mn 2 bearing silicates associated with oxides and carbonates and braunite mn 3 bearing silicate are the major mn hosts in types i ii and iii respectively because of the different oxidation state of mn the rocks of types i and ii are termed as reduced and the rocks of type iii as oxidized the formation of a certain mineralogical type of metamorphic assemblage is controlled by the content of organic matter in the primary sediments the sequence type i type ii type iii reflects the decrease in the amount of organic matter in metalliferous sediments mineralogical data indicate that manganese in the primary sediments accumulated in a silicate form mn si gel glass etc during diagenesis the mn si phase was transformed to neotokite with subsequent formation of caryopilite and further crystallization of pyroxmangite rhodonite tephroite and other silicates due to reactions involving caryopilite the hydrated mn silicates caryopilite and or friedelite and the spatially associated parsettensite stilpnomelane and other minerals are the index minerals of the low grade metamorphism under pt conditions of prehnite pumpellyite facies nearly 70 of silicate minerals are hydrous the metamorphosed mn bearing sediments are characterized by the low temperature caryopilite or tephroite caryopilite pyroxmangite rhodonite and the high temperature caryopilite free or tephroite pyroxmangite rhodonite facies their pt conditions correspond to zeolite and prehnite pumpellyite the low temperature and green schist and higher grade the high temperature facies

inferring transport characteristics in a fractured rock aquifer by combining single hole ground penetrating radar reflection monitoring and tracer test data 1 investigations of solute transport in fractured rock aquifers often rely on tracer test data acquired at a limited number of observation points such data do not by themselves allow detailed assessments of the spreading of the injected tracer plume to better understand the transport behavior in a granitic aquifer we combine tracer test data with single hole ground penetrating radar gpr reflection monitoring data five successful tracer tests were performed under various experimental conditions between two boreholes 6 m apart for each experiment saline tracer was injected into a previously identified packed off transmissive fracture while repeatedly acquiring single hole gpr reflection profiles together with electrical conductivity logs in the pumping borehole by analyzing depth migrated gpr difference images together with tracer breakthrough curves and associated simplified flow and transport modeling we estimate 1 the number the connectivity and the geometry of fractures that contribute to tracer transport 2 the velocity and the mass of tracer that was carried along each flow path and 3 the effective transport parameters of the identified flow paths we find a qualitative agreement when comparing the time evolution of gpr reflectivity strengths at strategic locations in the formation with those arising from simulated transport the discrepancies are on the same order as those between observed and simulated breakthrough curves at the outflow locations the rather subtle and repeatable gpr signals provide useful and complementary information to tracer test data acquired at the outflow locations and may help us to characterize transport phenomena in fractured rock aquifers

tube fossils from gossanites of the urals vhms deposits russia authigenic mineral assemblages and trace element distributions abstract the occurrence types morphology and mineralogical characteristics of tube microfossils were studied in gossanites from twelve vhms deposits of the urals several types of tube microfossils were recognized including siboglinids polychaetes and calcerous serpulids replaced by a variety of minerals e g hematite quartz hematite chlorite carbonate hematite depending on the nature of the substrate prior to the formation of the gossanites colonial hematite tube microfossils 150 m across 1 2 mm long are composed of hematitic outer and inner walls and may exhibit a cellular structure within their cavities spherical forms are saturated with fe oxidizing bacteria inside the tubes probably analogues of trophosomes colloform stromatolitic outer wall surfaces are characterized by the presence of numerous interlaced filaments of hematite 2 3 m diameter up to 1 2 mm long between tube microfossils the hematitized cement contains bundles of hematitized filaments with structures similar to the hyphae of fungi hematite chlorite tube microfossils are scattered in gossanites mostly as biological debris they are typically 30 to 300 m in diameter and 1 to 5 mm long the layered structure of their tube walls is characterized by hematite quartz and chlorite layers abundant filamentous bacteria coated by glycocalix and chlorite stromatolite are associated with hematite chlorite tubes the carbonate hematite tube microfossils up to 300 m across 2 3 mm long occur in carbonate rich gossanites the tubes are characterized by fine 10 m thick walls of hematite and cavities dominated by relatively dark carbonate or hematite carbonates may be present both in walls and cavities stromatolite like leucoxene or hematite carbonate aggregates were also found in association with tubes randomly oriented filaments are composed of ankerite single filaments are composed of individual cells typically smaller than 100 nm across similar to that of magnetotactic bacteria three dimensional tomographic images of all types of tube microfossils demonstrate a clear wavy microlayering from outer and inner walls which may reflect segmentation of the tube worms the traces of burrowing or fragments of glycocalix with relict spheres are typical of tube microfossils from gossanites the carbon isotopic composition of carbonates associated with tube microfossils from hematite quartz hematite carbonate and hematite chlorite gossanites average 7 2 6 8 22 8 pdb respectively these values are indicative of a biogenic origin for the carbonates the oxygen isotopic composition of these carbonates is similar in all three gossanite types averaging 13 5 14 2 13 0 relative to smow and indicative of active sulfate reduction during the diagenetic and anadiagenetic stages of the sediments evolution the trace element characteristics of hematite from tube microfossils are characterized by high contents of following trace elements average ppm mn 1529 as 714 v 540 w 537 mo 35 and u 5 such high contents are most likely the result of metal and metalloid sorption by fine particles of precursor iron hydroxides during the oxidation of sulfides and decomposition of hyaloclasts via microbially mediated reactions

geochemistry and origin of mn deposits in the waziristan ophiolite complex north waziristan pakistan the waziristan ophiolite complex is located along the western margin of the indian plate in northwestern pakistan the mn deposits in the saidgi and shuidar areas are part of this ophiolite complex these deposits both banded and massive in nature are hosted by metachert and are generally overlying metavolcanics braunite and cryptocrystalline quartz are the main constituents of the manganese ores in both areas hematite occurs in the shuidar deposits as a minor phase metacherts are microcrystalline aggregates of microcrystalline quartz chalcedony and lesser hematite chemically the studied mn deposits and associated metacherts are very similar to those formed by submarine hydrothermal effusive processes the deposits originated along sea floor spreading centers mid ocean ridges within the neo tethys ocean and were later obducted as part of the waziristan ophiolite complex

the hydrothermal component in ferromanganese nodules from the southeast pacific ocean abstract statistical analyses of geochemical data from ferromanganese nodule samples representing a broad area of the southeast pacific ocean indicate nodule compositions are controlled by four factors 1 suboxic diagenesis 2 oxic diagenesis 3 hydrogenous precipitation and 4 hydrothermal precipitation the first three are identical to those identified in studies of nodules from the north pacific the fourth factor represents the first quantitative determination of a significant hydrothermal end member in ferromanganese nodules nodules apparently acquire a hydrothermal component through the accretion of colloidal sized hydrothermal precipitates which are widely dispersed from their origin at vents along the east pacific rise epr nodules recovered from beneath the shadow of the present day hydrothermal plumes emanating from the epr contain significantly higher amounts of hydrothermal material relative to nodules from other areas

microbially mediated iron ore formation silicic superunit rudabanya hungary abstract the mineralogical petrological geochemical and textural characterization of the triassic bodvaszilas sandstone in the rudabanya open pit and aggtelek mts is summarized based on our investigations the pore filling carbonate cement in the lower triassic bodvaszilas sandstone formation of a proximal basin series rudabanya was formed as the result of syngenetic and early diagenetic two step microbially mediated fe mineralization fe oxide formation by chemo lithoautotrophic fe oxidizing microbes feob in a suboxic neutrophylic environment and fe carbonate by heterotrophic microbes in a suboxic to anaerobic environment based on mineralized microbially produced textural evidences the carbonate in the higher parts of the formation transition between the bodvaszilas sandstone and the overlying formation szin marl was formed by the same metasomatic processes that produced the siderite ore in the middle triassic limestones and dolomites these processes led to partial or complete fe replacement of the syngenetic carbonate layers microbially mediated fe enrichment also occurred at distal basin position in the bodvaszilas sandstone aggtelek mts the formation later underwent deep burial diagenesis

geochemical studies on permian manganese deposits in guichi eastern china implications for their origin and formative environments abstract permian manganese ore deposits are widely distributed in southwestern and eastern china guichi permian manganese district in southern anhui province central eastern china is currently the most important manganese metal producers in eastern china manganese ores mno 18 2 45 4 wt in guichi region occur in calcareous argillaceous and siliceous mn bearing sequence of the permian gufeng formation in contrast to mn bearing rocks the ores have higher mn fe p sr more than 1500 ppm and ni contents 480 ppm higher mn fe 5 and lan cen 2 values and lower co ni

ground penetrating radar response to fracture fluid salinity why lower frequencies are favorable for resolving salinity changes time lapse ground penetrating radar gpr surveys exploit signal amplitude changes to monitor saline tracers in fractures and to identify groundwater flow paths however the relationships between gpr signal amplitude phase and frequency with fracture aperture and fluid electrical conductivity are not well understood we used analytical modeling numerical simulations and field experiments of multifrequency gpr to investigate these relationships for a millimeter scale aperturefracturesaturatedwithwaterofvaryingsalinity we found that the response of lower frequency radar signals detects changes in fluid salinity better than the response of higher frequency signals increasing fluid electrical conductivity decreases low frequency gpr signal wavelength which improves its thin layer resolution capability we concluded that lower signal frequencies such as 50 mhz and saline tracers of up to 1 s m conductivity are preferablewhenusinggprtomonitorflowinfracturedrock furthermore we found that gpr amplitude and phase responsesaredetectableinthefieldandpredictablebyemtheory and modeling therefore they can be related to fracture aperture and fluid salinity for hydrologic investigations of fractured rockflowandtransportproperties

mineralogy and geochemistry of two metamorphosed sedimentary manganese deposits sierra nevada california usa abstract laminated to massive rhodochrosite hausmannite and mn silicates from the smith prospect and manga chrome mine sierra nevada california were deposited as ocean floor sediments associated with chert and shale the principal lithologies at smith are chert argillite rhodochrosite hausmannite and chlorite rich layers and relatively uncommon layers of jacobsite the manga chrome mine also contains layers rich in manganoan calcite and caryopilite tephroite rhodonite spessartine and accessory alleghanyite and sonolite formed during metamorphism volcaniclastic components are present at manga chrome as metavolcanic clasts and as mn poor red garnet and hematite rich layers there is no evidence such as relict lithologies that mn was introduced into mn poor lithologies such as chert limestone or mudstone replacement of mn poor phases by mn rich phases is observed only in the groundmass of volcanic clasts that appear to have fallen into soft mn rich mud manganiferous samples from the smith prospect and manga chrome mine have high mn fe and low concentrations of ni cu zn co u th and the rare earth elements that are similar to concentrations reported from other ancient mn deposits found in chert greenstone complexes and from manganiferous sediments and crusts that are forming near modern sea floor vents the sierra nevada deposits formed as precipitates of mn rich sediments on the sea floor probably from mixtures of circulating hydrothermal fluids and seawater the composition of a metabasalt from the smith prospect is consistent with those of island arc tholeiites metavolcanic clasts from the manga chrome mine are compositionally distinct from the smith metabasalt and have alkaline to calc alkaline affinities a back arc basin is considered to be the most likely paleoenvironment for the formation of the mn rich lenses at the manga chrome mine and by association the smith prospect layers of rhodochrosite hausmannite and chert preserve the composition and some textures of the sedimentary protoliths at both sierra nevada deposits jacobsite rich layers probably represent a fe rich protolith caryopilite and manganoan calcite represent additional protoliths at the manga chrome mine the metamorphic assemblage prehnite chlorite epidote calcite in a metabasalt from the smith prospect constrains regional metamorphic conditions to a maximum temperature of 325 c and a pressure of 2 kbar slightly higher temperatures are indicated by the presence of actinolite in another metabasalt compositions of mn rich minerals in smith samples are consistent with these metamorphic conditions

bedded jaspers of the ordovician lokken ophiolite norway seafloor deposition and diagenetic maturation of hydrothermal plume derived silica iron gels sedimentary beds of jasper red hematitic chert in the ordovician lokken ophiolite of norway are closely associated with volcanogenic massive sulphide vms deposits the jaspers occur in the immediate hangingwall and laterally peripheral to the large lokken 25 30 mt and small hoydal 0 1 mt vms deposits and are exposed discontinuously for several kilometres along strike massive or laminated types predominate jasper sulphide debris flow deposits are also abundant near vms deposits the jaspers contain hematite rich laminae showing soft sediment deformation structures and microtextural evidence that record the presence of a colloidal precursor and an origin as gels early textures include 1 straight or curved chains of hematitic filaments 3 10 m in diameter and 20 100 m long 2 branching networks of 15 25 m thick tubular structures surrounded by cryptocrystalline hematite and filled with quartz and euhedral hematite 3 small up to 10 m spherules composed of cryptocrystalline hematite and silica and 4 up to 50 m silica spherules with hematitic cores the small filaments seem to have been deposited in varying proportions in the primary laminae possibly together with hematitic and siliceous microspheroids diagenetic changes are represented by polygonal syneresis cracks and the presence of cryptocrystalline originally opaline silica chalcedony quartz carbonate and cryptocrystalline hematite and or goethite forming botryoidal masses and spheroids 10 m to 5 mm in diameter coarser euhedral grains of quartz carbonate and hematite are integral parts of these textures bleached silica rich jaspers preserve only small relics of fine grained hematite rich domains and locally contain sparse pockets composed of coarse euhedral hematite epidote

low temperature hydrothermal deposits of franklin seamount woodlark basin papua new guinea abstract hydrothermal deposits of siliceous fe mn oxides from a few cm to 7 m in height are widespread at the summit and caldera floor of franklin seamount a 250 m high edifice of basaltic andesite lava tubes pillows and talus located near the western propagating tip of the woodlark spreading axis some deposits are venting clear fluid at about 30 c the hydrothermal constructions are composed predominantly of x ray amorphous protoferrihydrite mixed with variable amounts of opaline silica and greenish nontronite most deposits are covered by mm thick black crusts of vernadite and feroxyhyte which are mineralised bacterial formations genus leptothrix of hydrogenous origin microbes also influenced formation of the fe rich parts of the deposits as evidenced by filamentous protoferrihydrite pseudomorphs of gallionella blocky inorganic particles of protoferrihydrite and ferrihydrite occur as rare interior phases nontronite formed by precipitation from hydrothermal solutions commonly involving replacement of microbial protoferrihydrite and silica patchy and lenticular birnessite partly altered by biogenic processes to vernadite occurs within siliceous protoferrihydrite matrices in dark cm thick outer margins of some edifices this is considered hydrothermal in origin reflecting percolation of hydrothermal fluids through porous protoferrihydrite opal aggregates to more oxidised conditions near the exterior related to mixing with seawater the different mineralogical associations are reflected by geochemistry trace elements in the manganiferous phases were derived partly from the primary hydrothermal solution and partly from seawater with which this was extensively diluted at the depositional site and also deeper within the volcanic structure of franklin seamount most of the fe mn cu zn and pb was derived from the primary hydrothermal fluid from limited data nontronitic portions of the deposits contain more cu zn and pb than the siliceous protoferrihydrite rich portions migration of redox boundaries and redistribution of elements during flow through processes influence development of the typical zoned structure of the deposits uranium thorium decay series equilibria at both actively venting and inactive sites at franklin seamount yield ages not exceeding 43 years

tobago west indies a fragment of a mesozoic oceanic island arc petrochemical evidence the pre cenozoic rocks of tobago west indies represent an exceptional cross section through a portion of a composite mesozoic arc system other parts of which may be found in the villa de cura klippe the aruba blanquilla island chain and perhaps in the western cordillera of colombia and ecuador the geochemical data from tobago presented in this paper provide a basis from which a regional view of the petrologic character of the accreted mesozoic arc of the southern caribbean mountain system can be deduced the mesozoic rocks of tobago can be divided into four main groups the north coast schist the ultramafic to mafic plutonic complex the tobago volcanic group and late mafic dykes rocks of the north coast schist served as wallrock for the plutonic volcanic dyke complex which evolved during the mid cretaceous geochemical and nd and sr isotopic data presented demonstrate the oceanic island arc character of all the pre cenozoic rocks of the island all suites span the calc alkaline and tholeiitic regions on discrimination diagrams rare earth element ree patterns for the north coast schist tobago volcanic group and plutonic suite are essentially identical and are moderately lree enriched la yb 1 1 2 7 the dykes exhibit the most unevolved ree patterns and are interpreted as most closely representative of parental liquid compositions initial nd 6 6 to 9 4 and 87 sr 86 sr 0 70303 0 70364 for all samples except north coast schist and tobago volcanic group argillites are similar in value and overall range to other oceanic island arcs limited isotopic data from argillite samples from tobago suggest an important change in the continental derived sediment contribution during mesozoic arc growth nd isotopic data from north coast schist siliceous argillite indicate virtually no continental detritus in this neocomian sediment while nd isotopic data from the tobago volcanic group argillite suggest a definite continental contribution during albian arc growth

investigation on the role of microorganisms in manganese mineralization from abadeh tashk area fars province southwestern iran by using petrographic and geochemical data abstract hydrothermal manganese and ferromanganese deposits associated with neyriz ophiolite colored melange occurred as small ore deposits in the abadeh tashk area se of fars province sw iran the deposits are found in three types a banded syngenetic ores b massive boudin and lens shaped diagenetic ores and c vein and veinlet epigenetic ores microtextural geochemical and mineralogical data associated with petrographic raman ftir and sem studies indicated that the primary fe compounds formed series of microbially mediated biomats and mn compounds were precipitated as an amorphous oxide on an active oxide surface accompanying silica gels field relationships between ore and host rock high mn fe ratio 17 43 to 40 79 lree positive eu and negative ce anomalies in syngenetic ore types reveal that the ores were formed by hydrothermal fluid in an oceanic floor environment manganese was fractionated from iron due to physicochemical changes as well as microbial activities in the sedimentary environment microbial remains as filamentous beads with regular circular shapes vermiform structures series of fe rich biomats traces of embedded organic material besides trace metals and ree concentrations in mn ores emphasize the role of microorganisms in fe and mn precipitation syngenetic mineralization took place under suboxic neutrophilic conditions while diagenetic processes resulted in variably reduced fe and mn oxides via organic matter decomposition forming rhodochrosite as the end product braunite formation occurred most probably as a biogeochemically mediated early diagenetic product diagenetic and epigenetic mn ores were formed when primary mn deposits underwent subsequent diagenetic and remobilization redeposition events respectively

discrete dual porosity model for electric current flow in fractured rock the identification of fractures and the characterization of their properties are of critical importance in a wide variety of research fields and applications to this end geophysical methods are of significant interest as they can provide information regarding the spatial distribution of a number of subsurface physical properties in a rapid and noninvasive manner electrical resistivity surveying in particular has been shown in several previous investigations to exhibit sensitivity to the presence of fractures suggesting that geoelectrical experiments may contain important information regarding how fractures are distributed and connected in the subsurface however a lack of suitable numerical modeling tools for electric current flow in fractured media has prevented a detailed and systematic exploration of this concept to address this issue we present a novel discrete dual porosity modeling approach that is specifically tailored to the electrical resistivity problem with our approach an analytical formulation for fracture matrix current flow exchange at the fracture scale is integrated into a discrete fracture network model which is then combined with a block scale finite volume representation of the rock matrix our methodology allows for low cost and accurate simulation of electric current flow through both the fractures and matrix and is readily applicable to complex fracture networks at relatively large scales although formulated here in two dimensions this work represents an important first step toward investigating the effect of fracture network characteristics on bulk electrical properties as well as toward the simulation of geoelectrical survey data in realistic fractured rock environments

genetic diversity of manganese deposition in the terrestrial geological record terrestrial manganese deposits formed by hydrothermal sedimentary and supergene processes ancient analogues of modern oceanic hydrothermal deposits formed in spreading centre and subduction related settings and those deposited from terrestrial hot springs are discussed sedimentary mn oxide deposits formed in shallow water at the margins of stratified oceans above the redoxcline during sea level changes mn carbonate deposits probably formed by diagenesis through mn oxyhydroxide reduction coupled with organic matter oxidation climatic variation and basin water stratification responsible for mn concentration were manifestations of atmospheric coz content prompted by tectonism supergene manganese enrichment in continental weathering profiles was mainly dictated by climate topography and drainage systems manganese deposits of diverse genetic types occur in the terrestrial geological record roy 1981 these were produced by direct hydro thermal activity sedimentary processes and continental weathering although the processes may be interrelated each involves distinct mechanisms that place the deposits into specific genetic types some of these processes are best understood in preset day depositional sites the ancient environments were determined by the intensity and style of tectonism volcanism and hydrothermal activity the composition of the atmosphere and the hydrosphere and the development of the biosphere which all varied with time it is my intention to unfold the total panorama of the environmental evolution during different time envelopes that produced a variety of manganese deposits in the past only major deposits and those providing distinctive evidence of their environment of deposition will be considered here

which fractures are imaged with ground penetrating radar results from an experiment in the aspo hardrock laboratory sweden abstract identifying fractures in the subsurface is crucial for many geomechanical and hydrogeological applications here we assess the ability of the ground penetrating radar gpr method to image open fractures with sub mm apertures in the context of future deep disposal of radioactive waste gpr experiments were conducted in a tunnel located 410 m below sea level within the aspo hard rock laboratory sweden using 3 d surface based acquisitions 3 4 m 19 m with 160 mhz 450 mhz and 750 mhz antennas the nature of 17 identified gpr reflections was analyzed by means of three new boreholes bh1 bh3 9 9 5 m deep out of 21 injection and outflow tests in packed off 1 m sections only five provided responses above the detection threshold with the maximum transmissivity reaching 7 0 10 10 m2 s most gpr reflections are situated in these permeable regions and their characteristics agree well with core and optical televiewer data a 3 d statistical fracture model deduced from fracture traces on neighboring tunnel walls show that the gpr data mainly identify fractures with dips between 0 and 25 since the gpr data are mostly sensitive to open fractures we deduce that the surface gpr method can identify 80 of open sub horizontal fractures we also find that the scaling of gpr fractures in the range of 1 10 m2 agrees well with the statistical model distribution indicating that fracture lengths are preserved by the gpr imaging no measurement bias our results suggests that surface gpr carries the resolution needed to identify the most permeable sub horizontal fractures even in very low permeability formations thereby suggesting that surface gpr could play an important role in geotechnical workflows for instance for industrial scale siting of waste canisters below tunnel floors in nuclear waste repositories

manganese scavenging and oxidation at hydrothermal vents and in vent plumes abstract hydrothermal vents provide a major source of dissolved mn ii to the oceans where concentrations range from 5 mm within the 350 c hot smokers to just above ambient seawater concentration in far field vent plumes the mn ii rich environments within warm vents and vent plumes provide a suitable habitat for mn ii oxidizing bacteria in order to compare rates of scavenging and oxidation of mn ii proximally within vent fields

origin of ultramafic hosted vein magnesite deposits abstract large deposits of magnesite mgco3 occur either as carbonated ultramafic rocks or as sedimentary beds the origins of both sedimentary and ultramafic hosted deposits remain controversial as does the relationship between them ultramafic hosted deposits are reviewed herein with an emphasis on veins rather than massive bodies magnesium apparently has been supplied to magnesite veins by their ultramafic host uncertainties concerning ultramafic hosted deposits include the source state and mode of transportation of carbon the cause of its precipitation and the mineralogy of the initial precipitate genetic questions about ultramafic hosted vein deposits are summarized with the aid of flow charts the preferred route through these charts attributes most vein magnesite to an influx of metamorphic degassing co2 and ch4 into groundwater which flows through serpentinite or peridotite the source of co2 ch4 is considered to be deeper than 10 km because metamorphism 300 c is required to release carbonaceous volatiles of the type which apparently induced observed magnesite mineralization however vein magnesite precipitation generally has occurred within just a few hundred meters of the earth s surface vein deposits are considered to be genetically related to massive bodies but the massive bodies typically contain less 12c the 12c rich co2 which has produced vein deposits is attributed to a fluid phase variably mixed ch4 co co2 which rose until it reached upper crustal groundwater the hypothetical water poor fluid presumably became slightly oxidized hence richer in soluble co2 as it encountered near surface sulfate bearing water co2 enriched water is envisioned to have been expelled regionally due to tectonic processes leaving little mineralogical evidence of its expulsion through non ultramafic rock co2 rich water which happened to encounter either serpentinite or peridotite presumably has produced magnesite vein deposits and a common silicate byproduct nontronite according to the following reaction 12 mg3si2o5 oh 4 serpentine 36 hco3 4 fe3o4 o2 12 fesi2o5 oh nontronite 36 mgco3 magnesite 36 oh 18h2o

comparing flux averaged and resident concentration in a fractured bedrock using ground penetrating radar this is the published version copyright 2010 by the american geophysical union all rights reserved

single hole gpr reflection imaging of solute transport in a granitic aquifer 1 identifying transport pathways in fractured rock is extremely challenging as flow is often organized in a few fractures that occupy a very small portion of the rock volume we demonstrate that saline tracer experiments combined with single hole ground penetrating radar gpr reflection imaging can be used to monitor saline tracer movement within mm aperture fractures a dipole tracer test was performed in a granitic aquifer by injecting a saline solution in a known fracture while repeatedly acquiring single hole gpr sections in the pumping borehole located 6 m away the final depth migrated difference sections make it possible to identify consistent temporal changes over a 30 m depth interval at locations corresponding to fractures previously imaged in gpr sections acquired under natural flow and tracer free conditions the experiment allows determining the dominant flow paths of the injected tracer and the velocity 0 4 0 7 m min of the tracer front

geology tectonic settings and iron ore metallogenesis associated with submarine volcanism in china an overview abstract submarine volcanogenic iron oxide svio deposits are one of the most important sources of high grade iron ores in china the spatial distribution of the deposits is controlled by the tectonic settings including arc back arc and rift environments with the svio deposits mostly concentrated in the western part of china namely the southwestern yangtze craton western and eastern tianshan and altay orogens and the kaladawan iron ore district in the eastern part of the altyn tagh region the chinese svio deposits range in age from paleoproterozoic to mesozoic and were formed during two main metallogenic epochs in the proterozoic and paleozoic more than 70 of the svio deposits formed in the paleozoic with three important svio metallogenic provinces recognized in the altay eastern and western tianshan orogens these svio deposits are hosted in lithofacies that are related to submarine magmatism such as lavas and associated pyroclastic and volcaniclastic sedimentary rocks the iron orebodies are hosted in different volcanic lithofacies with different features moreover the different volcanic lithofacies in which the fe ores are hosted also provide information as to their spatial relationship ranging from distal to proximal to the eruption center or vent many of these deposits are characterized by well developed skarns and could be interpreted either by a distal position of the ore system in question and or exposed igneous rocks or active magma chamber or a relationship to early metamorphism and continuous alteration at relatively high temperature followed by retrograde alteration as temperatures decline geological and geochemical evidence suggests that these deposits were formed as a result of submarine magmatic activity including subaqueous volcanic eruptions associated volcano sedimentary lithofacies and related post magmatic hydrothermal activity iron oxide ore probably formed the hydrothermal fluids which generated the skarns could be a mixture of evolved magma derived water and convecting sea water driven by the heat from the shallow active magma chamber whereas volcano sedimentary deposits could be formed by the fallout of the ore bearing materials to the sea floor emanating from submarine eruption columns or fractional precipitation of iron which had been introduced locally into the bottom water by volcanic origin hydrothermal solutions and by leaching from the relatively iron rich volcanic rocks the formation of these various styles of fe ore deposits is controlled by several key factors such as magma differentiation lithofacies of host rocks temperature and chemical compositions of hydrothermal fluids as well as the depth of sea water in combination with their geological characteristics geodynamic mechanisms and metallogenesis we propose a genetic model in which the origin of these deposits can be related to the space time evolution of the submarine volcanism and their relationship to volcanic lithofacies variation such as central proximal and distal environments of ore formation

time lapse imaging of saline tracer transport in fractured rock using difference attenuation radar tomography 1 accurate characterization of fractured rock aquifer heterogeneity remains one of the most challenging and important problems in groundwater hydrology we demonstrate a promising strategy to identify preferential flow paths in fractured rock using a combination of geophysical monitoring and conventional hydrogeologic tests cross well differenceattenuation ground penetrating radar was used to monitor saline tracer migration in an experiment at the u s geological survey fractured rock hydrology research site in grafton county new hampshire radar data sets were collected every 10 min in three adjoining planes for 5 hours during each of 12 tracer tests an innovative inversion method accounts for data acquisition times and temporal changes in attenuation during data collection the inverse algorithm minimizes a combination of two functions the first is the sum of weighted squared data residuals second is a measure of solution complexity based on an a priori space time covariance function subject to constraints that limit radarattenuation changes to regions of the tomograms traversed by high difference attenuation ray paths the time series of tomograms indicate relative tracer concentrations and tracer arrival times in the image planes from these we infer the presence and location of a preferential flow path within a previously identified zone of transmissive fractures these results provide new insights into solute channeling and the nature of aquifer heterogeneity at the site index terms 0910 exploration geophysics data processing 0915 exploration geophysics downhole methods 1829 hydrology groundwater hydrology 1832 hydrology groundwater transport 1894 hydrology instruments and techniques keywords radar tomography fractured rock ground penetrating radar geophysics hydrogeophysics

comparison of alternative methodologies for identifying and characterizing preferential flow paths in heterogeneous aquifers one of the main difficulties encountered when characterizing the hydrodynamic properties of a fractured aquifer is to identify the preferential flow paths within it different methods may be applied to determine the variability of the permeability at the borehole scale and to image the structure of the main flow zones between boreholes in this paper we compare the information obtained from different measurement techniques performed in a set of three 100 m depth wells well to well spacing 5 10 m in a fractured crystalline rock setting geophysical logging and borehole wall imaging are used to identify open and closed fractures intersecting the boreholes and their orientation the comparison with flowmeter and single packer tests shows that few of the fractures interpreted as open from geophysical logs are significantly transmissive cross borehole connectivity is first investigated from single packer tests with pressure monitoring in adjacent boreholes to determine fracture zone connectivity we propose a methodology simply based on the variation with packer depth of the ratio of the drawdown in the observation well and the drawdown in the pumping well the results are compared to the analysis of cross borehole flowmeter tests we show that both methods provide consistent results with a similar level of information on connectivity

four dimensional mapping of tracer channelization in subhorizontal bedrock fractures using surface ground penetrating radar 1 to observe flow channeling in situ surface ground penetrating radar gpr was used to detect a saline tracer moving through a sub horizontal bedrock fracture the tracer is mapped using amplitude variations resulting from the significant difference in electromagnetic properties between the tracer and natural ground water within the fracture results show that hydrogeophysical investigations using gpr can successfully image tracer movement in a variety of flow configurations in three spatial dimensions through time hence 4d observed tracer travel paths demonstrated meter scale spatial variability that may be attributed to heterogeneity in fracture aperture

formation of jasper and andradite during low temperature hydrothermal seafloor metamorphism ongeluk formation south africa andradite and andradite grossular solid solutions have repeatedly been described as minor constituents of weakly metamorphosed ocean floor metabasites and associated calcareous or siliceous sediments the conditions of garnet formation however have remained rather elusive here wedescribe the discovery of andradite as a minor but widespread constituent of chert and jasper closely associated with only very weakly metamorphosed basaltic andesites of the early paleoproterozoic ongeluk formation transvaal supergroup south africa the andradite is most commonly fine grained and forms skeletal crystals that poikilotopically enclose and replace quartz and hematite macroscopically coarse grained andradite is scarce and was recognized at one locality only up to 3 mm largeandradite grains occur closely associated with quartz in short veins that crosscut thin beds of andradite bearing jasper the cogenetic association of quartz and andradite was studied in detail to constrain the conditions of garnet formation our results indicate that andradite crystallized at temperatures well below 200 c in the sub seafloor environment in siliceous sediments of hydrothermal origin that provided an ample source of sio2 and fe2o3 andradite formed when hydrothermally modified seawater introduced ca that was leached when seawater interacted with plagioclase and clinopyroxene in the surrounding volcanic pile other important preconditions for garnet formation were the lack of mixing between the hydrothermal fluid and cold seawater and low fco2 it appears reasonable to extend the findings of this study to other recorded occurrences of andradite in modern and ancient ocean floor metabasites

environments and processes of manganese deposition concentration of manganese in solution and its deposition takes place by redox controlled processes in a variety of modern and ancient geologic and geochemical environments modern mn deposition occurs predominantly in deep sea areas rather than shallow water domains although deep sea sedimentary deposits dominate hydrothermal contribution of mn to the ocean system may be substantial mn deposition from hydrothermal solutions at or near sea floor spreading centers and less commonly in island arc areas is known in addition near and far field dispersion of mn from vent sites is also substantial such distributions are controlled by the flow rate and egress temperature of the solution and the residence time of mn in seawater thus even in sedimentary deposit domains at least partial derivation of mn from a hydrothermal source is possible sedimentary fe mn crusts on older volcanic substrates on seamounts form by hydrogenous deposition of metal concentrated from terrigenous sources in the mid water column oxygen minimum zones thus the presence or absence of volcanic rocks is not a clear indication of whether sedimentary mn deposits particularly in the ancient geologic record are the result of a totally terrigenous or a totally volcanogenic source abyssal fe mn nodules are considered to form from a basin water hydrogenous and or pore water early diagenetic supply of metals but in most cases the extent of supply from either of the sources is unknown the metal incorporation mechanisms of free moving nodules is little understood and it is possible that in most cases both sources contribute to the nodule composition therefore no nodule should be considered as totally hydrogenous or totally early diagenetic based only on its bulk composition the determined growth rate giving only an average value cannot by itself reveal the growth history of the nodules biological participation directly or indirectly controls mn deposition the stratified black sea demonstrates the concentration of mn in solution in an anoxic zone its advection toward the redox interface and its precipitation in an oxygenated condition similar stratified basins are contemplated for ancient mn deposition in shallow water basin margin areas geologic and geochemical signatures indicate that during sea level highstands stratified basins formed in which mn was concentrated in solution in the anoxic part corresponding transgression led to the impingement of the redox interface on the continental shelf and precipitation of mn oxides could take place across the interface during transgression regression cycles offshore in anoxic or dysaerobic conditions mn carbonate could form by early diagenetic reaction of mn super 2 with co 2 or hco 3 super produced by organic carbon oxidation critical mn deposits occurring in transgressive glaciogenic and black shale bearing ancient sequences support this paleoenvironmental model for mn deposition

ferruginous and manganiferous haloes around massive sulphide deposits of the urals proximal brecciform ferruginous and manganiferous rocks related to vms deposits of the urals are subdivided into jasperites gossanites and umbers in addition to thin bedded jaspers and cherts the coherence of host rock composition and mn fe fertility of the sediments have been established fe poor pink hematitic and gray sulphidic chert are typical of the felsic class of vms deposits in contrast the contents of fe vary from high to moderate in ferruginous rocks enclosed in basaltic units associate with vms deposits fe and mn rich ferruginous rocks and umbers occur in association with limestones and calcareous sedimentary rocks in both types of volcanic sequences a common feature of jasperites and umbers is the abundance of replacement textures of hyaloclastites and carbonates by hematite and silica in addition replacement of clastic sulphides by hematite and magnetite is a characteristic genetic feature of gossanites all of these sedimentary rocks are accompanied by pseudomorphs of hematite and quartz formed after bacterial filaments the abundance of replacement textures are supportive of the halmyrolysis model in addition to hydrothermal sedimentary and sub seafloor hydrothermal replacement theories study of chemical zonation of altered hyaloclasts shows depletion of their rims not only in mobile na k mg but also in immobile al ti and ree whereas si and fe are concentrated in situ the halmyrolysis model presented here involving organic rich calcareous hyaloclastic sediments resolves the problem of subtraction of al ti ree and other elements which are commonly immobile under hydrothermal conditions the evolution of the halmyrolysis process from acidic reducing to alkaline oxidized conditions infers a possible range in transformation from fe ii mg smectites to fe silicates and fe si oxides as precursors of brecciform jasperite and thin bedded jasper the higher acidic initial stage of gossanite formation seems to be required for oxidation of organic matter and or pyrite the acidic condition facilitates the temporal preservation of immobile elements al ti ree in immature chlorite hematite gossanites another peculiarity of the gossanite forming processes is the likely sorption of p u and v by iron hydroxides displacing sulphides the general evolution of all ferruginous sediments results in complete fe 2 oxidation and silicification accompanied by subtraction of other elements the vertical diagenetic differentiation leads to concentration of mn carbonates silicates and oxyhydroxides into the tops of jasperite and gossanite layers mn oxyhydroxides scavenge positively charged hydrated cations like co and ni near vent bacterial communities may activate the processes of volcanic glass and sulphide degradation the proposed processes of halmyrolysis followed by silicification in situ may resolve the enigma of silica rich sediment formation in a silica undersaturated ocean the discrimination between gossanite and jasperite is useful for elaboration of new criteria for local exploration of vms and mn deposits halo dispersion of gossanites covering an area about two to three times that of the massive sulphide deposit is a good vector for ore body discovery proximal gossanites can be differentiated from jasperites by presence of relic sulphide clasts or elevated contents of chalcophile elements cu fe zn pb bi te as sb ba noble metals au ag and distinct ree patterns with la and eu positive anomalies the development of halmyrolysis and biomineralization models merit further elaboration and testing in on going research in order to add or revise theories of iron and manganese deposit formation 2012 elsevier b v

the ophiolitic bath dunrobin formation jamaica significance for cretaceous plate margin evolution in the north western caribbean two neighbouring areas of tholeiitic basalts dolerites isotropic gabbros and tonalites in eastern jamaica are recognized as the upper section 2 5 km thick of an ophiolite limestones associated with this bath dunrobin formation contain a fauna of upper campanian and lower maestrichtian age the basalts are overlain by a thick sequence of maestrichtian volcaniclastic rocks and are faulted against a blueschist terrain since its emplacement the ophiolite has been subjected to uplift and major left lateral strike slip tectonism beginning in the eocene recognition of this subduction zone complex and regional considerations of island arc polarity necessitates that ocean crust must have been consumed by a southward dipping subduction zone the overlying late cretaceous palaeogene arc stretched from guatemala through jamaica to oriente province cuba this arc separated the yucatan basin to the n where active spreading accompanied subduction from the colombian basin and the southern nicaraguan rise to the se where tholeiitic magmatism b penetrated older ocean crust the bath dunrobin formation probably represents ocean crust from the yucatan basin obducted during the maestrichtian the major ophiolite terrains of guatemala and oriente cuba are by inference also derived from a proto yucatan basin

fracture network characterization using stress based tomography information on structural features of a fracture network at early stages of enhanced geothermal system egs development is mostly restricted to borehole images and if available outcrop data however using this information to image discontinuities in deep reservoirs is difficult wellbore failure data provides only some information on components of the in situ stress state and its heterogeneity our working hypothesis is that slip on natural fractures primarily controls these stress heterogeneities based on this we introduce stress based tomography in a bayesian framework to characterize the fracture network and its heterogeneity in potential egs reservoirs in this procedure first a random initial discrete fracture network dfn realization is generated based on prior information about the network the observations needed to calibrate the dfn are based on local variations of the orientation and magnitude of at least one principal stress component along boreholes a markov chain monte carlo mcmc sequence is employed to update the dfn iteratively by a fracture translation within the domain the markov sequence compares the simulated stress profile with the observed stress profiles in the borehole evaluates each iteration with metropolis hastings acceptance criteria and stores acceptable dfn realizations in an ensemble finally this obtained ensemble is used to visualize the potential occurrence of fractures in a probability map indicating possible fracture locations and lengths we test this methodology to reconstruct simple synthetic and more complex outcrop based fracture networks and successfully image the significant fractures in the domain

hydrogeophysical characterization of transport processes in fractured rock by combining push pull and single hole ground penetrating radar experiments the in situ characterization of transport processes in fractured media is particularly challenging due to the considerable spatial uncertainty on tracer pathways and dominant controlling processes such as dispersion channeling trapping matrix diffusion ambient and density driven flows we attempted to reduce this uncertainty by coupling push pull tracer experiments with single hole ground penetrating radar gpr time lapse imaging the experiments involved different injection fractures chaser volumes and resting times and were performed at the fractured rock research site of ploemeur in france h network hplus ore fr en for the gpr acquisitions we used both fixed and moving antenna setups in a borehole that was isolated with a flexible liner during the fixedantenna experiment time varying gpr reflections allowed us to track the spatial and temporal dynamics of the tracer during the push pull experiment during the moving antenna experiments we clearly imaged the dominant fractures in which tracer transport took place fractures in which the tracer was trapped for longer time periods and the spatial extent of the tracer distribution up to 8 meters at different times this demonstrated the existence of strongly channelized flow in the first few meters and radial flow at greater distances by varying the resting time of a given experiment we identified regions affected by density driven and ambient flow these experiments open up new perspectives for coupled hydrogeophysical inversion aimed at understanding transport phenomena in fractured rock formations

supergene sulphides and related minerals in the supergene profiles of vhms deposits from the south urals abstract the mineralogy and structure of the supergene profile in recently exploited volcani hosted massive sulphide vhms deposits of cyprus uralian and kuroko type in the south urals russia have been studied specific subzones enriched in secondary sulphides and associated minerals have been distinguished in residual pyrite and quartz pyrite sands at the gayskoye zapadno ozernoye dzhusinskoye and alexandrinskoye deposits besides minerals which are common to the cementation subzones covellite chalcocite and acanthite non stoichiometric colloform and framboidal pyrite pyrite dzharkenite pyrrhotite like and jordanite like minerals metacinnabar sphalerite selenium enriched tetrahedrite and unidentified as sb sulphosalts of pb or hg and ag sulphur bearing clausthalite naumannite and tiemannite were also found secondary sulphide minerals in vhms deposits of the south urals region are characterized by light sulphur isotope compositions 8 1 to 17 2 superposition of the advanced oxidation of colloform pyrite an enrichment in impurities sphalerite galena and tennantite from the primary ores stagnant water conditions an elevation of the water table during oxidation and bacterial activity led to supergene concentrations of the base metals as sulphide selenides or sulphosalts

hydrothermal manganese deposits in island arcs and related to subduction processes a possible model for genesis abstract submarine hydrothermal manganese deposits have recently been recovered from a number of island arc settings such as the tonga kermadec ridge ogasawa arc trench bonin arc mariana arc and bismarck archipelago it has also been shown that large volumes of fluid are released during dewatering of subducting sediments the amount of water subducted globally 1 5 10 15 g yr 1 is about two orders of magnitude less than that advected at ocean spreading centres hydrothermal manganese deposits may be precipitated from these waters the distribution of terrestrial manganese deposits around the circum pacific belt and elsewhere suggests that some of these deposits may be of hydrothermal origin related to subduction processes at present most of these terrestrial deposits are inadequately described to permit the establishment of the precise tectonic setting at the time of deposition of the manganese deposits and therefore an unambiguous assessment of this hypothesis