geochemical and mineralogical control of different genetic types of deep sea nodules from the pacific ocean deep sea nodules from the northeast pacific nodule belt and the southeast pacific sonne basin being formed in areas bordering the equatorial zone of high biological productivity accumulate by two basically different growth processes a early diagenetic growth by supply from pore water and b hydrogenetic growth by supply from near bottom sea water these growth processes lead to different genetic types of nodules early diagenetic type a hydrogenetic type b and mixed type ab a further type ac very rich in mn is being formed by increasing influence of early diagenesis these types can clearly be distinguished by their shapes surface textures mineral constituents of oxide fraction internal microstructures and geochemistry a genetical classification is being proposed on the basis of statistically computed interelement relationships todorokite very poor in fe is the main mn phase in the early diagenetic substance mno2 intimately intergrown with feooh xh2o is the main phase in the hydrogenetic substance consequently an important difference can be pointed out the metal supply for the growth of the early diagenetic nodules is based on an ionic solution of me2 e g mn2 ni2 cu2 zn2 whereas the supply for the hydrogenetic nodules is caused by transport of colloidal particles mobilization of mn2 and fractionation from fe is controlled by the amount of decomposing organic matter in the peneliquid layer of the sediments the main factor controlling the intensity of early diagenesis is the biological productivity in surface waters the crucial point of reversal at a mn fe ratio of about 5 obtained by hyperbolical regression of the analyses of nodules from the southeast pacific represents best concentrations in ni and cu mn fe quotients greater than 5 cause a decrease of ni and cu content nodules from the northeast pacific nodule belt generally contain higher concentrations in cu than nodules from the southeast pacific this can be explained by an additional supply of cu transported below ccd by siliceous plankton

rare earth element characteristics and k ar ages of the band ziarat ophiolite complex southeastern iran the band ziarat complex of southeastern iran is located on the western boundary c f the jaz murian depression rand is bounded by two ma jar fault systems the principal rock units of this complex are a gabbro sequence that includcs low and high level cumulate gabbros a late intrusive sequence that consists of diorite and plagiogranite and a volcanic sequence that includes diabase dikes and a lesser anaount of basaltic lava mantle rocks are virtually absent because of the presence of the two bounding fault systems but we consider the complex to be an ophiolite in nature rare earth cleislcnt ree whole rock data clearly diffcremtiate the classic ophiolitic lithologies for the crustal rocks in this complex bas4 on the ree data there are two distinct types of basalt presenl at band ziarat i those that formed from an initial basaltic melt with a light rare earth element lree enriched signature similar to intraplate hasalts and ii those that have lree depleted patterns similar to normal mid ocean ridge basalts the data also suggest i that the gabbros are adcumulates and were derived from a source slightly enriched in lree with fractic natioam controlled by removal of clinopyroxene or hornblende and plagioclase and ii that the late intrusive rocks as well as a ma jority of the cliabnse dikes are cogenetic and were derived from thc same lree enriched source k ar ages ranging from 134 4 to 146 5 ma for lowlevel gabbros and from 821 4 to 930 4 ma for high level gabbros were measured on five hornblende and two whole rock samples which suggests that these rocks may have formed early in the cretaceous period

mineral chemistry and geochemical behavior of hydrothermal alterations associated with mafic intrusive related au deposits at the atud area central eastern desert egypt abstract vein type gold deposits in the atud area are related to the metagabbro diorite complex that occurred in gabal atud in the central eastern desert of egypt this gold mineralization is located within quartz veins and intense hydrothermal alteration haloes along the nw se brittle ductile shear zone as well as along the contacts between them by using the mass balance calculations this work is to determine the mass volume gains and losses of the chemical components during the hydrothermal alteration processes in the studied deposits in addition we report new data on the mineral chemistry of the alteration minerals to define the condition of the gold deposition and the mineralizing fluid based on the convenient geothermometers two generations of quartz veins include the mineralized grayish to white old vein trending nw se and the younger non mineralized milky white vein trending ne sw the ore minerals associated with gold are essentially arsenopyrite and pyrite with chalcopyrite sphalerite enargite and goethite forming during three phases of mineralization first second main ore and third supergene phases three main hydrothermal alteration zones of mineral assemblages were identified zones 1 3 placed around mineralized and non mineralized quartz veins in the underground levels the concentrations of au ag and cu are different from zone to zone having 25 790 ppb 0 7 69 6 ppm and 6 93 8 ppm 48 6 176 1 ppb 0 9 12 3 ppm and 39 6 118 2 ppm and 53 9 155 4 ppb 0 7 3 4 ppm and 0 2 79 ppm for zones 1 2 and 3 respectively the mass balance calculations and isocon diagrams calculated using the geoiso windows program revealed the gold to be highly associated with the main mineralized zone as well as sericitization kaolinitization and muscovitization in zone 1 more than in zones 2 and 3 the sericite had a higher muscovite component in all analyzed flakes average x ms 0 89 with 0 10 0 55 phengite content in wall rocks and 0 13 0 29 phengite content in mineralized quartz veins wall rocks had higher calcite caco 3 contents and lower mgco 3 and feco 3 contents than the quartz veins the chlorite flakes in the altered wall rocks were composed of pycnochlorite and ripidolite with estimated formation temperatures of 289 295 c and 301 312 c respectively albite has higher albite content 95 08 99 20 which occurs with chlorite in zone 3

sedimentation at manop site h eastern equatorial pacific over the past 400 000 years climatically induced redox variations and their effects on transition metal cycling gravity cores recovered from manganese nodule project site h 6 33 n 92 49 w show marked downcore variations in the abundance of calcium carbonate organic carbon opal manganese and other components deposited over the past 400 000 years variations in the downcore abundance of organic carbon which ranges from 0 2 to 1 0 can be used to hindcast redox conditions in the surface sediments over this time the results indicate that the depth to the manganese redox boundary varied from about 5 to 25 cm below the seafloor during four major cycles downcore variations in solid phase mn ni and cu can be produced by such changes in redox conditions a model which predicts that solid phase mn can be trapped and buried when the mn redox boundary migrates rapidly upward is consistent with the observed organic carbon and mn records and supports the reconstructed redox variations the history of redox variations at site h can be explained by changes with time in surface water productivity major productivity variations at the site occur over 100 kyr cycles with relatively higher productivity occurring during glacial stages thus quaternary climate changes influence surface water productivity redox conditions in sediments and the cycling of transition metals

the timing of the cape orogeny new 40ar 39ar age constraints on deformation and cooling of the cape fold belt south africa abstract we conducted a 40ar 39ar thermochronological study of samples from three transects across the cape fold belt of south africa metamorphic conditions along these transects decrease from the greenschist facies in the southern hinterland to the anchizonal foreland to the north nine new 40ar 39ar plateau ages and two mini plateau ages from handpicked muscovite are combined with one earlier published biotite mineral age and reveal two age modes the older population ranges from 261 3 to 276 5 ma n 4 and the younger from 248 2 to 254 6 2 1 ma n 4 the remaining three ages 400 ma are detrital and reflect unreset ages electron microprobe analyses and x ray diffraction studies indicate little mineralogical variation of micaceous material across the belt samples dominantly host muscovite clay minerals such as illite or smectite are absent microstructural characterization of rock fabrics across the belt reveals different mechanisms of strain partitioning and heterogenous deformation of different lithologies specifically pressure solution fracture and limited crystal plasticity are the dominant deformation mechanisms in the shale dominated bokkeveld group and witteberg groups in the foreland region resulting in recrystallization of phyllosilicate minerals strain partitioning into narrow locally deformed horizons of the table mountain group is accompanied by dynamic grain boundary recrystallization in quartz a weak trend of southward younging ages is interpreted as the preservation of deformation ages ca 275 260 ma and younger cooling ages ca 255 245 ma although it remains plausible that these populations represent two deformation events these new age constraints significantly narrow the temporal window of cape fold belt tectonic activity and provide a firm basis for evaluating the depositional patterns in the foreland karoo basin

influence of crustal heterogeneity on normal fault dimensions and evolution southern south africa extensional system abstract the tectonic configuration of southern south africa is dominated by a continental scale mesozoic extensional system superimposed upon a significant and well constrained palaeozoic lithospheric scale heterogeneity through integrating onshore structural analysis with offshore subsurface studies it is possible to evaluate the applicability of established normal fault growth models in a heterogeneous crustal setting at a basin scale for the first time the 480 km long mesozoic extensional system comprises a number of fault arrays that vary in length from 78 to 230 km coupled with displacements of up to 16 km the fault arrays are amongst the longest and largest displacement of high angle normal faults dips of 45 60 documented in continental lithosphere although comprised of co linear segments rather than the en echelon segment configuration typical of many other extensional systems this atypical geometry is considered to be a consequence of the high degree of structural inheritance between the underlying paleozoic cape fold belt and the subsequent extensional system furthermore it is proposed that the overall displacement length dimensions of the extensional faults were inherited from the underlying compressional faults the establishment of a seismic stratigraphic framework for the pletmos and gamtoos offshore basins reveals that the faults established their long lengths 160 and 90 km respectively within 6 myr of rift initiation prior to accruing their substantial displacement 16 km furthermore there is no evidence for the development of intra basin faults the southern south africa extensional system presents an end member case of structural inheritance where extensional structures are parallel to and reactivate underlying compressional structures in this study structural inheritance is considered to have a significant effect on mechanisms of fault growth the pre existing structures not only result in the rapid establishment of fault lengths of up to 160 km but additionally to strain being localised onto the pre existing fabric to such an extent that no intra basin faults evolve and strain is accommodated entirely on the bounding faults

recognition genesis and evolution of manganese ore deposits in southeastern china abstract manganese ore deposits are common in the falang formation of ladinian age middle triassic southeastern yunan china the deposits containing manganese oxide and manganese carbonate ores are not metamorphic in origin and they commonly contain bioclasts concentric ring structures are clearly observed in oolitic and pisolitic manganese ores an integrated approach using sedimentology and paleoenvironment analysis provides new insight into the genesis of these ores systematic research has been conducted on typical deposits dounan yanzijiao laowu tujichong using cathodoluminescence and scanning electron microscope techniques which allow elucidation of changes in laminated microtextures at the mm m scale preliminary results show that manganese enrichment in triassic deposits of this region may be related to microbial activity and mineralization was a consequence of bacterially mediated diagenetic reactions in addition findings of biodetritus in the manganese ore indicate that manganese ore is close to the redox level the concentration of manganese in solution and in precipitates in triassic is controlled by bacterial oxidation and redox conditions corresponding to sea level changes during the ladinian

chemical processes affecting the mobility of major minor and trace elements during weathering of granitic rocks abstract the behaviour of 38 major and trace elements as well as changes in the mineralogy have been examined in 10 weathering profiles developing on some portuguese granitic rocks element mobilities are calculated from geochemical data normalized with respect to ti in the fresh parent rock chemical elements are divided into two groups immobile and mobile on the basis of their geochemical distribution during weathering elements that are immobile during weathering are zr hf fe al th nb sc and the ree very mobile are ca na p k sr ba rb mg and si mobile elements are derived mainly from leachable minerals such as feldspars micas and apatites whereas immobile elements are either concentrated in resistate phases or strongly adsorbed by secondary minerals the geochemical behaviour of mn cr v fe and ce is very dependent on redox conditions redox transformations of these elements can be used to set limits on the oxidation state of a weathering suite the ree are mobilized or fractionated during late stages of weathering but not during moderate stages of weathering this fractionation is caused by selective leaching of rocks composed of both stable and unstable minerals containing ree

rare earth element fluxes and geochemical budget in the eastern equatorial pacific rare earth element ree patterns and flux measurements of sediment traps sediments and nodules from the eastern tropical pacific demonstrate the dominance of ree supply to the sea floor by particle settling quantitative partitioning of the particle flux reveals that biogenic debris is the major ree carrier in shallow depths however the labile particles are surpassed in importance by alumino silicate particles at greater depths regeneration of biogenic associated ree appears responsible for la ce variations in the particle flux with depth and provides the primary source of ree accreted by nodules

sand spherules interpreted as crustacean feeding pellets from an eocene shore environment western carpathians slovakia abstract sand spherules from eocene shallow marine deposits are identified as crab brachyura feeding pellets several points support this interpretation i microscopic study of these structures shows the absence of fine grained matrix ii spatial distribution within shallow water deposits foreshore to upper shoreface is interpreted on the basis of well sorted fine grained sandstones and sedimentary structures such as a low angle wedge shaped tabular type cross bedded units ripples sand bars and intercalated storm layers of coarser material with trace fossils identified as belonging to the archetypal skolithos to cruziana ichnofacies and iii the sand spherules have a bimodal size distribution and all these structures have a regular spherical shape another argument that implies biogenic origin of spherules and supports the interpretation of them as fossil feeding pellets of crabs is their association with other crustacean trace fossils ophiomorpha and the occurrence of identical structures interpreted as fossil feeding pellets associated with a comparable trace fossil assemblage from miocene shallow water deposits in southwest japan the recognition of crustacean sandstone spherules in the sedimentary record is a good indicator of the shoreline palaeoenvironment

rare earth elements in manganese nodules from the south atlantic ocean as indicators of oceanic bottom water flow abstract the mineralogy and geochemistry of a suite of nine manganese nodules from the south atlantic have been determined the ce la ratios of the nodules were investigated to see if they could be used as redox indicators to trace the oxygen content of the ambient water mass and the flow path of the antarctic bottom water as has previously been successfully carried out in the pacific ocean the ce la ratios of the nodules decrease in the sequence lazarev sea weddell sea 10 4 and 9 7 east georgia basin 6 5 and 7 1 argentine basin 5 0 but then increase in the brazil basin 6 2 and angola basin 9 8 and 15 1 a further decrease was observed in the cape basin 7 6 an extremely high ce la ratio of 24 4 had already been determined for nodules sampled north of the nares abyssal plain in the western north atlantic these data reflect the more complicated pattern of bottom water flow in the south atlantic than in the south pacific the penetration of more oxygenated north atlantic deep water into the south atlantic accounts for the higher ce la ratios in the nodules from the angola and brazil basins based on this study the flow path of the antarctic bottom water could only be traced as far north as the argentine basin the unique geochemistry of nodules from the central angola basin high mn fe and ce la ratios high contents of ni cu zn and mo appears to be a function of the nature of the overlying water mass and of the multiple diagenetic sources of metals to the nodules

manganese microchimneys buried in the central pacific pelagic sediments evidence of intraplate water circulation abstract manganese oxide deposits of an irregular tube like shape with unique composition and structure were found within pliocene siliceous sediments from an abyssal hill in the central pacific manganese nodule province effective separation of mn from fe and probably a rapid rate of mn deposition are suggested from the chemical composition a very high mn fe ratio up to 400 and low concentrations of transition metals the ree pattern is similar to other marine low temperature hydrothermal and sub oxic diagenetic mn deposits low total ree abundance and strong negative ce anomaly the deposit consists of major todorokite with minor buserites showing a hydrothermal signature blade like crystals of the minerals typically grow within open tubes several mm thick and lack detrital minerals all data indicate a low temperature hydrothermal or cold seep origin or less likely a sub oxic diagenetic origin this unusual manganese deposit from a pelagic environment is thought to have formed on the sea floor from mn bearing waters that passed through sediments or basement rocks we speculate that intraplate water circulation took place during the late pliocene to pleistocene due to the uplift and or block faulting after the deposition of pelagic pliocene sediments

systematics of chlorite alteration at the phelps dodge massive sulfide deposit matagami quebec hydrothermal alteration at the phelps dodge archcan volcanogenic massive sulfide deposit has converted rhyodacite and rhyolite footwall rocks into the following mineral assemblages quartz chlorite albite epidote or sericite quartz chlorite or sericite chlorite or sericite and chlorite talc or stilpnomelane alteration at constant al was initiated by hydration addition of fe mg silicification and leaching of ca na which produced al saturated chlorites with a wide range of fe fe mg ratios within the assemblage quartz chlorite albite epidote or sericite with continued addition of fe and less mg combined with extensive leaching of quartz the chlorite became al undersaturated quartz chlorite talc assemblage and ultimately formed a rock composed essentially of chlorite the chlorite talc or stilpnomelane assemblage is stable in late crosscutting veinlets and in the ore zone chlorites in the si al mg fe system form a rectangular solid solution plane with limited substitution of al for si and extensive substitution of fe for mg in si al space the solid solution plane is outlined by al saturation presence of other al rich mineral and al undersaturation presence of al poor or al free mineral boundaries al iv substitution for si in the chlorites increases from 2 3 to 3 01 formula units based on 8 si al iv with fe fe mg whereas al iv occupancy decreases from 2 88 to 2 65 the valence charge balance is compensated by octahedral site vacancies or by the conversion of fe super 2 to fe super 3 the al iv content of chlorite also increases with temperature chlorites on the al saturated boundary of the solid solution field form a potentially useful geothermometer t degrees c 106 al iv 18 al iv is corrected for changes with the fe fe mg ratio as al iv corrected al iv 0 7 fe fe mg the fe fe mg ratios of bulk rock and contained chlorite correlate well birefringence colors of the chlorite change from green to brown violet and berlin blue as fe fe mg changes from 0 18 to 0 64 the fe fe mg variation apparently depends largely on the proportions of mg rich seawater and fe rich hydrothermal fluid in the altering brine

distribution and mineral assemblages of bedded manganese deposits in shikoku southwest japan implications for accretion tectonics abstract numerous bedded manganese and manganese iron ore deposits occur in shikoku southwest japan the mineralogy wall rock characteristics and fossil age data of the deposits are synthesized in this paper their mineral assemblages correlate well with the progressive metamorphic grade of the accretionary complexes in shikoku based on the plate tectonic framework of subduction accretion process the deposits are considered to have formed by metamorphism of mn fe nodule bearing siliceous sediments on the ocean floor

hydrothermal activity associated with off axis volcanism in the peru basin abstract products of low temperature hydrothermal activity are widespread in the peru basin and are associated with late tertiary oceanic island type intraplate volcanics hydrothermal activity is still taking place as indicated by a series of sharp high and narrow temperature anomalies over one of the volcanic cones submarine hydrothermal activity associated with off axis volcanism has been frequently observed elsewhere but was usually found to be limited to seamounts in the peru basin a hydrothermal halo was found in sediments surrounding hydrothermally active seamounts in addition to hydrothermal precipitates on the tops of the seamounts todorokite birnessite fe nontronite goethite and silica were found on top of young volcanic edifices and occur as coatings on volcanic rocks and in nuclei of manganese nodules the hydrothermal precipitates in the sediments are mg fe silicates as is the case in the adjacent bauer basin the proportion of hydrothermal precipitates in the sediments increases with depth in the cores down to the appearance of the basalt that indicates the beginning of intraplate volcanism 5 million years ago sediments overlying late tertiary volcanic rocks are locally enriched in hydrothermal material by solutions percolating upwards directly into the sediment in these sediments apatite and phillipsite appear to have been precipitated directly from these ascending hydrothermal solutions

the continental margin of uruguay crustal architecture and segmentation abstract the uruguayan continental margin comprises three sedimentary basins the punta del este pelotas and oriental del plata basins the genesis of which is related to the break up of gondwana and the opening of the atlantic ocean herein the continental margin of uruguay is studied on the basis of 2d multichannel reflection seismic data as well as gravity and magnetic surveys as is typical of south atlantic margins the uruguayan continental margin is of the volcanic rifted type large wedges of seaward dipping reflectors sdrs are clearly recognizable in seismic sections sdrs flat lying basalt flows and a high velocity lower crust hvlc form part of the transitional crust the sdr sequence subdivided into two wedges has a maximum width of 85 km and is not continuous parallel to the margin but is interrupted at the central portion of the uruguayan margin the oceanic crust is highly dissected by faults which affect post rift sediments a depocenter over oceanic crust is reported deepwater pelotas basin and volcanic cones are observed in a few sections the structure of continental crust sdrs flat flows oceanic crust is reflected in the magnetic anomaly map the positive free air gravity anomaly is related to the shelf break while the most prominent positive magnetic anomaly is undoubtedly correlated to the landward edge of the sdr sequence given the attenuation interruption and or sinistral displacement of several features most notably sdr sequence magnetic anomalies and depocenters we recognize a system of nw se trending transfer faults here named rio de la plata transfer system rpts two tectono structural segments separated by the rpts can therefore be recognized in the uruguayan continental margin segment i to the south and segment ii to the north

mineralogical and geochemical constraints on the origin of ferromanganese crusts from the rivera plate western margin of mexico abstract marine hydrogenetically precipitated ferromanganese crusts are widespread in the pacific ocean they occur as pavements coating volcanic or sedimentary hard rock substrates mainly on the slopes of seamounts plateaus and hills in ocean basins and continental margins we studied three ferromanganese crusts from one dredge haul from the rivera plate western margin of mexico which are up to 15 mm thick and grow directly on a substrate of pillow basalt fragments they consist of laminated botryoidal porous aggregates mostly of fe and mn oxyhydroxides and up to 10 silicates xrd analysis showed the predominance of poorly crystallized mineral phases in the crusts that include mn feroxyhyte and vernadite and an authigenic smectite like clay detrital minerals probably derive from granodiorites of the eastern wall of the neighboring middle america trench scattered barite grains occur on the crust surface and suggest plume fall out derived from hydrothermal vents although a possible pelagic source cannot be dismissed ratios between major fe mn si and trace co ni cu elements reveal that such crusts are predominantly hydrogenetic in origin although they show a hydrothermal influence that increases in the outer layers iron contents range from 16 2 to 25 2 wt and manganese from 3 4 to 14 5 wt the fe mn ratio ranges from 1 6 to 7 0 the sio 2 al 2 o 3 ratio ranges from 4 3 to 6 6 indicating the presence of biogenic silica radiolarians the concentrations of copper up to 383 ppm and cobalt up to 534 ppm are significantly below those of the typical hydrogenetic crusts whereas ni up to 1320 ppm is about the same or slightly lower ree normalized profiles and ree values 486 to 732 ppm match those reported for hydrogenetic crusts but suggest a hydrothermal contribution for the later crust layers the inferred crust growth rates using the co chronometer 44 and 229 mm myr are higher than those reported for pure hydrogenetic crusts mostly 1 to 6 mm myr thus indicating an increasing hydrothermal influence the highest growth rate 229 mm myr corresponding to the outer crust layers suggests a regional hydrothermal input of iron and manganese to seawater the intensification of regional submarine hydrothermal activity began about 13 000 yr ago and may be related to the tectonic activity in the complex junction of the rivera cocos pacific and north america plates

the rb sr geochronological evolution of the ras gharib segment of the northern nubian shield rb sr whole rock isochron ages have been determined for six igneous rock suites from the ras gharib these represent all major crustal components of the northern nubian shield and are from oldest to youngest diorite tonalite extrusive rocks granodiorite adamellite and leucogranite muscovite trondhjemite orogenic pan african suites dyke swarms and anorogenic peralkaline granites the ages obtained are 881 58 ma 620 16 ma 552 7 ma 516 7 ma 493 7 ma and 476 2 ma the initial 87 sr 86 sr ratios of the pan african suites and the dykes are in the range 0 7039 to 0 7047 the initial ratio of the anorogenic peralkaline granites is 0 7110 0 0012 higher than any previously reported for igneous rocks from the egyptian belt the 493 7 ma age of the dyke swarms represents a younger limit for the pan african compression accretion event and an upper older limit for an extensional tectonic regime linked with this is the anorogenic peralkaline granite magmatism 476 2 ma which is the last manifestation of igneous activity in this region the low initial ratios of the pan african suites provide no support for the existence of an older archaen sialic continental crust in the region the anorogenic peralkaline granite with the high initial ratio was produced by partial melting of earlier pan african suites the age data are used to construct a tentative correlation scheme for shield rocks of egypt sudan and saudi arabia

importance of different types of marine particles for the scavenging of heavy metals in the deep sea bottom water abstract in experiments of 7 days duration using voltammetric and radiotracer measurement techniques the role of different particle types in the sorption of dissolved metal species in a disturbed deep sea bottom seawater system were investigated resuspension of oxic to suboxic surface sediment into the bottom water in the deep sea either by natural events or industrial activities like mn nodule mining has been shown to be followed quickly by scavenging of dissolved heavy metals e g released from interstitial water on the resuspended particles compared to other deep sea particles like clay minerals calcite and apatite mn and fe oxides and oxyhydroxides were found to be by far the most important phases in scavenging many dissolved heavy metals only pb was sorbed strongly on all particles used with highest affinity to carbonate fluorapatite caesium was significantly scavenged only by clay minerals like illite the sorption experiments support a simple electrostatic model hydrated cations and labile cationic chloro complexes in seawater like mn2 mncl co2 ni2 cu2 zn2 ba2 and pbcl are preferentially adsorbed or ion exchanged on the negatively charged surfaces of mn oxides in contrast oxyanions and neutrally or negatively charged complexes like hvo42 moo42 haso42 uo2 co3 22 and pbco30 associate with neutral to slightly positive amphoteric fe oxyhydroxide particles metals forming strong chloro complexes in seawater like cd cdcl20 are less readily sorbed by oxides than others a comparison of the results of voltammetric and radiotracer techniques revealed that after fast sorption within the first hour isotopic exchange dominated reactions on mno2 rich particles in the following days this was especially pronounced for mn and co which are bound to the mn oxide surface via a redox transformation

geological and geochemical constraints on the cheshmeh frezi volcanogenic stratiform manganese deposit southwest sabzevar basin iran abstract the cheshmeh frezi mn deposit belongs to the southwest sabzevar basin to the north of the central iranian microcontinent this basin which hosts abundant mineral deposits including mn exhalative and besshi type cu zn volcanogenic massive sulfide deposits followed an evolution closely related to the subduction of the neo tethys oceanic crust beneath the central iranian microcontinent two major sedimentary sequences are recorded within this basin i the lower late cretaceous volcano sedimentary sequence llcvss and ii the upper late cretaceous sedimentary dominated sequence ulcss the cheshmeh frezi mn deposit is hosted within red tuff with interbeds of green tuffaceous sandstone of the llcvss mineralization occurs as stratiform blanket like and tabular orebodies psilomelane pyrolusite and braunite are the main minerals of the ore which display a variety of textures such as layered laminated disseminated massive replacement or open space fillings the footwall and hanging wall volcanic rocks are predominantly andesite and trachyandesite rocks footwall and hangingwall volcanic rocks at cheshmeh frezi are enriched in light rare earth elements lrees compared to chondrite have steep ree patterns and generally show ta and nb depletions relative to chondrite which are characteristic of back arc environments the significant geochemical characteristics of ore such as high mn content 12 41 33 14 wt average 19 41 wt low concentration of fe 0 64 2 27 wt average 1 63 wt high ba 49 7 9901 ppm average 2728 67 ppm lree hree and negative ce and eu anomalies reveal a primary distal hydrothermal exhalative source for mineralization cheshmeh frezi deposit in comparison with different types of volcanogenic manganese deposits shows broad similarities with the cuban type mn deposits such as tectonic host and associated rock types geometry textures structures mineralogy and lithogeochemistry

growth of a manganese nodule from peru basin a radiochemical anatomy abstract attempts have been made to study the entire growth history of a manganese nodule from the northern part of peru basin in the pacific using radiochemical profiles of 230 th 232 th 227 th 230 th and 10 be 9 be combined with the observations on fe mn contents and textural variation the radiochemical data indicate that the nodule grew more or less concentrically throughout most of its existence since it formed 1 5 my ago receiving mn from both bottom water and pore water this condition appeared to have changed about 180 ky ago when the growth became asymmetric in that the top and bottom sides became fixed in their relative positions on the sea floor since then the bottom side accreted with a fast rate of close to 200 mm my apparently fueled by the supply of diagenetically remobilized mn in pore water from the sediment substrate in the meantime the top side accumulated at about 6 mm my a value which is in the normal range for deep sea nodules having their mn supplied from the hydrogenous source

geochemical and sedimentological studies of a box core from the western sector of the peru basin abstract the distribution of sediments micronodules and manganese nodules which has been studied in a number of cores from the peru basin is clearly related to the proximity of the basin to the c c d and to the equatorial high productivity zone one core from the peru basin has been looked at in considerable detail in this core an extensively bioturbated calcareous siliceous rich upper sedimentary unit is underlain by an overconsolidated dark brown clay characteristic differences in mineralogy and chemistry are observed in the composition of these sediment types with the dark brown clays having higher contents of mn fe co ni cu zn and p than the sediments of the upper horizon in addition these dark brown clays contain montmorillonite as the principal clay mineral whereas the sediments of the upper sediment horizon consist of montmorillonite kaolinite and illite micronodules are much more abundant in the coarse fraction 40 m of the dark brown clay horizon than in the upper sedimentary unit and are characterized by higher mn fe ratios and higher ni and cu contents than those from the upper sediment horizon this reflects the fact that these overconsolidated sediments are well oxidized and that element remobilization from the micronodules has not taken place within this sediment type in the upper sedimentary unit there is a sharp drop in the mn fe ratio and ni and cu contents of the micronodules immediately beneath the sediment surface reflecting the selective migration of mn and other transition elements such as ni and cu from the micronodules buried managanese nodules are found at two horizons within the sediment column these nodules show characteristic differences in their surface texture compared to surface nodules but no marked difference in composition the buried nodules are not associated with any well defined feature such as a sedimentary hiatus it is suggested that nodules are maintained at the sediment surface by bioturbation buried nodules are simply those nodules that have failed to be maintained at the sediment water interface

ferromanganese nodules from manop sites h s and r control of mineralogical and chemical composition by multiple accretionary processes abstract the chemical composition of ferromanganese nodules from the three nodule bearing manop sites in the pacific can be accounted for in a qualitative way by variable contributions of distinct accretionary processes these accretionary modes are 1 1 hydrogenous i e direct precipitation or accumulation of colloidal metal oxides in seawater 2 2 oxic diagenesis which refers to a variety of ferromanganese accretion processes occurring in oxic sediments and 3 3 suboxic diagenesis which results from reduction of mn 4 by oxidation of organic matter in the sediments geochemical evidence suggests processes 1 and 2 occur at all three manop nodule bearing sites and process 3 occurs only at the hemipelagic site h which underlies the relatively productive waters of the eastern tropical pacific a normative model quantitatively accounts for the variability observed in nearly all elements zn and na however are not well explained by the three end member model and we suggest that an additional accretionary process results in greater variability in the abundances of these elements variable contributions from the three accretionary processes result in distinct top bottom compositional differences at the three sites nodule tops from h are enriched in ni cu and zn instead of the more typical enrichments of these elements in nodule bottoms in addition elemental correlations typical of most pelagic nodules are reversed at site h the three accretionary processes result in distinct mineralogies hydrogenous precipitation produces mno2 oxic diagenesis however produces cu ni rich todorokite and suboxic diagenesis results in an unstable todorokite which transforms to a 7 a phase birnessite upon dehydration the presence of cu and ni as charge balancing cations influence the stability of the todorokite structure in the bottoms of h nodules which accrete dominantly by suboxic diagenesis na and possibly mn 2 provide much of the charge balance for the todorokite structure limited growth rate data for h nodules suggest suboxic accretion is the fastest of the three processes with rates at least 200 mm 106 yr oxic accretion is probably 10 times slower and hydrogenous 100 times slower since these rates predict more suboxic component in bulk nodules than is calculated by the normative analysis we propose that suboxic accretion is a non steady state process variations in surface water productivity cause pulses of particulate flux to the sea floor which result in transient mn reduction in the surface sediments and reprecipitation on nodule surfaces

growth rates of manganese rich nodules at manop site h eastern north pacific abstract estimates of the growth rates of ferromanganese nodules at manop site h 6 33 n 92 49 w lie between 7 and 1200 mm my the most probable range estimated from nodule size distributions nodule chemistry accumulation rates of authigenic elements and u series modeling is 30 300 mm my such rates are much faster than measured values for most pelagic nodules the distributions of u series and stable elements suggest that a typical nodule consists of two compositionally distinct non detrital components one rich in mn u and sb and the other in fe co ree ni cu and th when the uncorrected u series data which do not show simple decay patterns with depth are normalized to the relative proportion of the fe rich component the data yield well constrained growth rates of 55 mm my for a nodule top and 200 mm my for its bottom the component enriched in mn which is most abundant on nodule bottoms appears to accrete much faster than the component enriched in fe

diagenetic mobilization of manganese in peru basin sediments abstract the mn contents and sedimentation rates of two cores from different areas of the peru basin have been determined the southern core is associated with mn nodules of conventional slow accretion rates mm 106 yr while the northern one accompanies nodules with very high growth rates 102 mm 106 yr the depletion of mn observed within the top 40 cm of the cores is interpreted as resulting from a diagenetic remobilization of mn 2 due to the oxidative characteristics of the sedimentary column in both cores the calculated flux of mn provided by the sediment is higher than the total mn recovered in the overlying nodules this indicates that the mn content of the peru basin nodules can be supplied by diagenetic processes from the sediment not only for the slowly growing nodules but also for the extremely fast growing concretions found in the north of the basin

biological pumping upwards of the coarse fraction of deep sea sediments abstract in a restricted part of an area intensively sampled by box coring approximately 50 samples from a 2 4 km rectangle a stiff muddy glacial gravel till is encountered at a depth of 30 40 cm x radiographs of the upper 15 to 20 cm of the cores reveal gravel in overlying foraminiferal mud only from the area where there is the deeper till layer the localization strongly suggests that the material in the top of the cores has its source in the deeper layer i postulate that burrowing organisms move gravel upward by pushing aside the particles that are too large to be eaten because the strength of the enclosing mud decreases upwards the gravel particles move preferentially upward the upward decrease in shear strength of he sediment is rapid at an interface occurring 4 cm below the surface on average thus hydrostatic pressures of 20 to 200 g cm2 exerted by vermiform burrowing animals act within an environment of asymmetrical sediment property permitting an asymmetrical response to the uniformly directed body pressure this asymmetrical response a pumping mechanism affecting material that does not pass through the gut is contrasted with the mixing of finer sediments that are eaten and excreted documented by many other workers dimensional arguments suggest the flux of material is related to the ratio of biological mixing rate to sedimentation rate the mechanism is also applicable to maintenance of mn nodules and their nuclei at the surface if macrofossils have behaved like gravel some s ell beds may have been generated and some stratigraphic anomalies caused by this means

compositional changes of surface sediments and variability of manganese nodules in the peru basin abstract two types of manganese nodules were observed in the peru basin large botryoidal nodules in basins and small ellipsoidal nodules on slope positions the sediment in areas with large botryoidal nodules contains a thinner and weaker oxidation zone than the sediment under small ellipsoidal nodules indicating that diagenetic processes in the sediment which supply manganese nodules with metals for their growth are stronger in sediments on which large botryoidal nodules grow organic matter which activates remobilization of metals occurs mostly in the form of refractory lipidic compounds in the inner capsule of radiolaria this material needs bacterial degradation to act as a reducing agent easily oxidizable organic components could not be found in the sediments other changes in sediment composition do not have a link to manganese nodule growth biogenous components radiolarians organogenic barite and apatite increase towards the equatorial high productivity zone authigenous clay minerals nontronite as well as montmorillonite with high fe 3 incorporation on positions of ochtaedral al increase with distance from the continent the assessment of environmental impacts will have to take into account the regional differences in sediment composition and the small scale variability of manganese nodules

growth history of manganese nodules and crusts of the peru basin abstract in the nodule field of the peru basin situated south of the zone of high bioproductivity a relatively high flux of biogenic matter explains a distinct redox boundary at about 10 cm depth separating very soft oxic surface sediments from stiffer suboxic sediments maximum abundance 50 kg m 2 of diagenetic nodules is found near the calcite compensation depth ccd currently at 4250 m there the accretion rate of nodules is much higher 100 mm ma 1 than on ridges 5 mm ma 1 highest accretion rates are found at the bottom of large nodules that repeatedly sink to a level immediately above the redox boundary there distinct diagenetic growth conditions prevail and layers of dense laminated mn oxide of very pure todorokite are formed the layering of nodules is mainly the result of organisms moving nodules within the oxic surface sediment from diagenetic to hydrogenetic environments the frequency of such movements is much higher than that of climatic changes two types of nodule burial occur in the peru basin large nodules are less easily moved by organisms and become buried consequently buried nodules generally are larger than surface nodules this type of burial predominates in basins at ridges where smaller nodules prevail burial is mainly controlled by statistical selection where some nodules are not moved up by organisms

variability of surface sediments in the peru basin dependence on water depth productivity bottom water flow and seafloor topography abstract we investigated surficial sediments for physico chemical composition from numerous sites of seven study areas in the manganese nodule field of the northern peru basin as part of a deep sea environmental study major results from this study are strong variability with respect to water depth productivity in surface waters locality bottom water flow and seafloor topography sediment sites are located mostly in 3900 to 4300 m water depth between the lysocline and the carbonate compensation depth ccd large fluctuations in carbonate content 0 to 80 determine sediment density and compressional wave velocity and by dilution contents of opal and non biogenic material mass accumulation rates of biogenic components as well as geochemical proxies barium and phosphorus distinguish areas of higher productivity in the northwest near equatorial upwelling and in the northeast close to coastal upwelling from areas of lower productivity in the west and south comparisons between the central peru basin area discol and western peru basin area sediperu reveals for the sediperu area a shallower ccd more carbonate but less opal organic carbon and non biogenic material in sediments at the same water depth as well as larger down core fluctuations of organic carbon and mno2 bottom water flow in the abyssal hill topography causes winnowing of material from summits of seamounts and ridges where organic carbon preservation is poor to basins where organic carbon preservation is better down core measurements in box cores indicate a three fold division in the upper 50 cm of the sediment column an uppermost semi liquid top layer is dark brown 5 15 cm thick and contains most of the ferro manganese nodules a 5 15 cm thick transition zone of light sediment color has increasing shear strength lowest opal contents and compressional wave velocities but highest carbonate contents and sediment densities the lowermost layer contains stiffer light gray sediments

mesozoic break up of sw gondwana implications for regional hydrocarbon potential of the southern south atlantic abstract this work provides new palinspastic palaeofacies reconstructions of sw gondwana incorporating rotation of a falkland malvinas microplate we discuss the implications of this for the tectonic evolution of the southern south atlantic and hence for the regional hydrocarbon potential existing gondwana reconstructions display good fits of major continents but poorly constrained fits of microcontinents in most continental reconstructions the falkland malvinas plateau was assumed to be a rigid fragment of pre permian south american crust however it has been suggested on the basis of palaeomagnetic data that the falkland malvinas islands were rotated by 180 after 190 ma this rotation hypothesis has been successfully tested on the basis of devonian stratigraphy and palaeontology permian stratigraphy and sedimentology and late palaeozoic and early mesozoic structure making it unlikely that the plateau behaved as a rigid structure during breakup we have explored the consequences of accepting this hypothesis for the tectonic evolution of sw gondwana by compiling new palaeogeographic maps for the permian cretaceous of the southern atlantic area to achieve a realistic close fit we have devised a pre rift proxy for the ocean continent boundary for the south atlantic in order to produce the best fit it is necessary to subdivide south america into four plates the consequences of this are far reaching our work suggests that although sedimentary basins were initiated at different times three major tectonic phases can be recognised in regional terms these can be thought of as pre syn and post rift during the pre rift time until the late triassic the area was dominated by compressional tectonism and formed part of the gondwana foreland the falkland malvinas islands lay east of africa the falkland malvinas plateau was 33 shorter and patagonia was displaced east with respect to the rest of south america in part along the line of the gastre fault system potential source facies are dominantly post glacial black shales of late permian age deposited in lacustrine or hyposaline marine environments these rocks would also be an effective regional seal sandstones deposited in the late permian would be dominantly volcaniclastic with poor reservoir qualities triassic sandstones tend to be more mature there was significant extension from about 210 ma end triassic until the south atlantic opened at about 130 ma early cretaceous in the early syn rift phase extension was accompanied by strike slip faulting and block rotation later extension was accompanied by extrusion of large volumes of lava early opening of the south atlantic was oblique which created basins at high angle to the trend of the ocean on the argentine margin and resulted in microplate rotation in ne brazil intermittent physical barriers controlled deposition of upper jurassic cretaceous anoxic sediments during breakup some of these mudrock units are effective seals with likely regional extent during crustal reorganisation clastic sediments changed from a uniform volcaniclastic provenance to local derivation with variable reservoir quality in the late rift and early post rift phase continental extension changed from oblique to normal and basins developed parallel to the continental margins of the south atlantic this change coincides with the main rifting in the equatorial basins of brazil and the early impact of the santa helena plume it resulted in widespread development of unconformities the abandonment of the reconcavo tucano jatoba rift and the end of ne brazil plate rotation which remained attached to south america there was extensive deposition of evaporites concentrated in but not restricted to the area north of the rio grande rise walvis ridge widespread deposits can be used to define potential regional elements of hydrocarbon systems and to provide a framework for relating more local elements our main conclusion is that the regional hydrocarbon potential of the southern south atlantic has been constrained by the tectonic evolution

paleozoic crustal blocks of onshore and offshore central argentina new pieces of the southwestern gondwana collage and their role in the accretion of patagonia and the evolution of mesozoic south atlantic sedimentary basins abstract the southwestern gondwana basement block configuration in the central argentinean offshore area was analyzed using gravimetric magnetic and seismic data and existing onshore tectonic models the resultant maps the distribution of the mesozoic and cenozoic basins and paleozoic structural features were used to validate the interpretations and to produce a new regional tectonic model pre carboniferous southwestern gondwana of south america was interpreted as an open margin formed from east to west by the dom feliciano belt the rio de la plata craton the pampean belt and the pampia and cuyania terranes the collision of the patagonia allochthonous terrane during the late paleozoic resulted in the development of the ventania cape fold belt which was mapped for the first time off the argentinean coast out to 600 km from the shore a strong change in the orientation of the fold belt is referred to as the colorado syntaxis a mirror image of the cape syntaxis in south africa this change reflects the buttressing effect of the cratonic blocks that hamper the northward propagation of syncollisional deformation and resulted in a 180 km shift of the orogenic front the mesozoic basins and the basement block distribution were analyzed the pampean belt a deformed area produced by the pampia accretion to the cratonic area is the locus to two episutural basins the general levalle and macachin basins the salado basin was interpreted as an episutural basin controlled by a 2 1 2 0 ga suture within the rio de la plata craton the colorado basin is composed of four segmented depocenters that reflect different emplacement controls the location of the western colorado basin was controlled by the upper paleozoic orogen the distributions of the central and eastern colorado depocenters orthogonal to the continental boundary were also strongly influenced by the upper paleozoic structures and were offset by lineaments that reflect dom feliciano fabric the colorado basin external depocenter that parallels the continental margin was also controlled by these lineaments we interpret a time gap of some 50 ma between the beginning of the evolution of the margin orthogonal depocenters and the atlantic breakup

submarine hydrothermal manganese deposits from the ogasawara bonin arc off the japan islands abstract numerous submarine hydrothermal sulfide and oxide deposits have been found in the mid ocean ridge systems but until now no activity has been found in an island arc system the geological survey of japan gsj has started a geological geophysical and geochemical investigation program in the bonin mariana arc since 1984 aiming at evaluation of submarine hydrothermal metal deposits and understanding of their geological background during the reconnaissance survey by r v hakurei maru in june 1984 thick hydrothermal manganese crusts were recovered from three seamounts of the bonin arc at a depth of ca 1000 m the chemical and mineralogical features and characteristic structure and occurrence of associated calcareous fossils and nontronite claystones suggest the quaternary low temperature hydrothermal activity forming well crystallized todorokite pyrolusite goethite and nontronite deposits thin hydrogenous ferromanganese encrustations on the hydrothermal crusts from a guyot of the northern arc indicate that the recent very active hydrothermal activities around this area may be declining or already finished whereas the fresh hydrothermal manganese crusts from the kaikata seamount suggest recent hydrothermal activity

carbonate preservation history in the peru basin paleoceanographic implications we studied preservation dissolution cycles and paleoproductivity in eight sediment cores from the peru basin south of the highly productive surface waters of the eastern equatorial pacific stratigraphy is based on stable oxygen isotopes and on combined magnetostratigraphy and biostratigraphy sediment cores which span the last 8 m y were retrieved during cruise 79 with rv sonne close to the carbonate compensation depth ccd in general sediments show pacific type carbonate cycles we interpret a pronounced carbonate peak between 6 and 7 ma as the result of a western and northern extension of the highly productive peru current decreased carbonate contents from the late miocene to the late pliocene might be associated with a slow contraction of the latitudinal extent of the high productivity belt north of the study areas during the pliocene carbonate variations showed 400 kyr cycles indicating the growth and decay of ice sheets which should have been associated with pulsations of the antarctic ice cap an abrupt collapse of the carbonate system occurred at 2 4 ma higher frequency variations of the carbonate record indicate the major increase of the northern hemisphere glaciation during the quaternary carbonate fluxes are high during glacials and low during interglacials large amplitude variations with long broad minima and maxima associated with small migrations of the lysocline and the ccd 200 m are indicative of the preservation dissolution history in the peru basin during the early pleistocene climatic forcing by the 41 kyr obliquity cycle is not observed in the carbonate record during the last 800 kyr variability in the carbonate record was dominated by the 100 kyr eccentricity cycle fluxes of biogenic material calcium carbonate organic carbon opal and barium were greatest during glacials which imply higher productivity and export production of the peru current during cold climatic periods dissolution was greatest during interglacials as inferred from the relatively poor preservation of planktonic foraminifera and from the low accumulation rate of carbonate after the mid brunhes event 400 ka we observe a plateaulike shift to enhanced dissolution and to intensified productivity

sediments and micronodules in the northern and central peru basin the mineralogy and composition of sediments and manganese micronodules from the northern and central sectors of the peru basin are discussed because of the proximity of the basin to the carbonate compensation depth c c d surface sediments vary between calcareous oozes and siliceous muds besides biogenic components clay minerals are important by far the most abundant clay mineral is smectite which is thought to be of diagenetic origin on a carbonate free basis the surface sediments are rather uniform in composition throughout the basin and are similar in composition to those of the equatorial pacific sedimentation rates for the uppermost core sections are in the range of 3 to 5 mm 1000 yr

element supply to surface manganese nodules along the aitutaki jarvis transect south pacific supply of metals to manganese nodules in the south equatorial pacific is heavily dependent on variations in biological productivity in the northern part of the aitutaki jarvis transect under high biological productivity in the surface waters there is a high flux of mn ni cu and zn to the nodules diagenetically cycled through the interstitial waters of the uppermost sediments together in the nodules with the formation of 10a manganite to the south of the high productivity zone these elements decrease in the nodules at the expense of fe co and pb of hydrogenetic provenance and mno2 is more abundant however nodule compositions also reflect the position of the deposits relative to the carbonate compensation depth ccd which deepens northwards throughout the region with mn ni cu and zn being enriched in 10a manganite bearing nodules from near the ccd under high productivity waters and fe co and pb being more abundant in x ray amorphous or mno2 bearing nodules away from the ccd and or in the south of the transect under low productivity waters

periodic events of bottom transport of peru basin sediment during the late quaternary 230th and 231pa depth profiles in cores from the peru basin suggest that the sediment accumulation during the late quaternary was characterized by a sequence of periods with normal slow accumulation of siliceous rich muds that were interrupted by shorter periods of up to one order of magnitude higher accumulation of carbonate rich sediments faster sediment accumulation is caused by deposition of miocene carbonate rich sediments eroded in the southern regions of the peru basin the periods of faster accumulation occurred at 70 000 161 000 181 000 and 294 000 314 000 a and coincide with periods of global climatic cooling

style of rifting and the stages of pangea breakup pangea results from the progressive amalgamation of continental blocks achieved at 320 ma assuming that the ancient concept of active versus passive rifting remains pertinent as end members of more complex processes we show that the progressive pangea breakup occurred through a succession of rifting episodes characterized by different tectonic evolutions a first episode of passive continental rifting during the upper carboniferous and permian led to the formation of the neo tethys ocean then at the beginning of triassic times two short episodes of active rifting associated to the siberian and emeishan large igneous provinces lips failed the true disintegration of pangea resulted from 1 a triassic passive rifting leading to the emplacement of the central atlantic magmatic province 200 ma lip and the subsequent opening of the central atlantic ocean during the lowermost jurassic and from 2 a lower jurassic active rifting triggered by the karoo ferrar lip 183 ma which led to the opening of the west indian ocean the same sequence of passive then active rifting is observed during the lower cretaceous with in between the parana etendeka lip at 135 ma we show that the relationships between the style of rifts and their breakdown or with the type of resulting margins as magma poor or magma dominated are not straightforward finally we discuss the respective role of mantle global warming promoted by continental agglomeration and mantle plumes in the weakening of the continental lithosphere and their roles as rifting triggers

genesis of zixi gold deposit in xuefengshan jiangnan orogen south china age geology and isotopic constraints abstract the medium sized zixi gold deposit is hosted in a meta gabbro diabase dike and located geologically in the xuefengshan belt of the jiangnan orogen in south china gold bearing quartz carbonate sulfide veins and the ore hosting meta gabbro diabase dike are structurally controlled by the ne trending first stage faults which are secondary faults to the regional xupu jingzhou fault metallic minerals at zixi include arsenopyrite and pyrite along with minor chalcopyrite sphalerite galena bournonite and native gold ore related alteration includes silicic carbonate sericite and chlorite based on vein crosscutting relationships and mineral paragenesis the alteration mineralization is divided into three stages 1 arsenopyrite pyrite native gold quartz mineralization 2 polymetallic sulfides native gold chlorite carbonate quartz mineralization and 3 post ore carbonate quartz alteration to constrain any temporal relationship between the gold mineralization and the ore hosting meta gabbro diabase dike we obtained a re os isochron age for the gold bearing arsenopyrite 425 28 ma n 5 mswd 0 47 which is 350 myr younger the meta gabbro diabase zircon u pb age 783 08 0 97 ma n 30 mswd 0 39 this precludes the dike from any direct metallogenetic link with the gold deposit the ore forming fluids have calculated 18oh2o and d values of 3 5 to 9 1 and 68 1 to 55 5 respectively indicating a metamorphic source probably through dehydration breakdown of chlorite sulfur isotope compositions of the gold bearing pyrite 5 8 to 3 6 are distinct from those of the lengjiaxi group metamorphic rocks but marginal overlap with those from the banxi group metamorphic rocks lead isotope compositions of the gold bearing pyrite 206pb 204pb 17 08 to 17 63 207pb 204pb 15 48 15 54 208pb 204pb 37 64 37 94 suggest that the lead was sourced from metamorphic rocks the h o s pb isotopic data indicate that ore forming materials were derived from a metamorphic source however the precise nature of that source is unclear the zixi gold mineralization displays many typical features of orogenic gold deposits such as being structurally controlled and have similar alteration and mineralization styles ore mineral assemblages and h o s stable isotopic features the zixi gold deposit was likely formed during the early paleozoic intracontinental orogeny of the jiangnan orogen

a new discrimination scheme for oceanic ferromanganese deposits using high field strength and rare earth elements abstract ferromanganese fe mn deposits constitute a ubiquitous mineral type in oceanic settings with metal cu ni zn co pt and rare earth element ree enrichments of potential economic interest routine analysis of trace elements by icp ms has advanced our understanding of the impact of hydrogenetic diagenetic and hydrothermal processes on the mobility and interaction of high field strength elements hfse zr and ti and ree and yttrium rey with fe mn oxyhydroxides recent discoveries in the french exclusive economic zone eez of wallis and futuna southwest pacific ocean have brought new insight into the formation of low temperature lt hydrothermal mn deposits and lead us to reconsider the classification and discrimination diagrams for fe mn deposits and ore forming processes using a suite of lt hydrothermal fe mn crusts from wallis and futuna we investigate how contrasting genetic processes influence the distribution of metals mn fe cu ni and co hfse and rey in hydrogenetic diagenetic hydrothermal and mixed type deposits from different environments in the global ocean the interaction of the different metal oxide forming processes indicates that i enrichment of co hfse and rey is favored by hydrogenetic precipitation ii diagenetic processes produce higher mn cu and ni concentrations with oxic remobilization in the sedimentary column while suboxic conditions promote greater mn and fe remobilization that competes with the incorporation of cu and ni ions in nodules hfse and rey derived from seawater are usually low in diagenetic precipitates which discriminate between hydrogenetic and diagenetic inputs within nodules iii hydrothermal fe mn deposits show strong depletion in hfse and rey due to rapid formation and high contents of either fe or mn oxides we present a new discrimination scheme for the genetic types of fe mn deposits using a 10 cu ni co 100 zr y ce fe mn 4 ternary diagram the use of hfse and rey in the classification allows for a more robust discrimination of i each ore forming process with well delimited fields without overlap of metal rich hydrothermal samples and hydrogenetic samples ii oxic and suboxic diagenesis within nodules iii trends between hydrogenetic and diagenetic end members forming a continuum and iv mixed genetic types such as the presence of hydrothermal particles within hydrogenetic crust layers alternatives are also explored to adapt our discriminative diagram to elements measurable by on board instruments to aid in exploration at sea

fine scale study of major and trace elements in the fe mn nodules from the south china sea and their metallogenic constraints abstract many marine fe mn polymetallic nodules may contain high concentrations of mn cu ni zn co and rare earth elements plus yttrium rey to determine the occurrence and enrichment processes of these metals in the fe mn nodules we conducted high resolution mineralogical and geochemical studies on the fe mn nodules collected from the south china sea in situ epma and la icp ms analyses and elemental imaging were performed on individual microlayers of the nodules to reveal the major and trace element distributions the whole rock mineralogical and chemical compositions of the fe mn nodules indicate a hydrogenetic origin the mn mineral phases are mainly composed of nanocrystalline vernadite with interlayered 10 a and 7 a phyllomanganates such as todorokite birnessite and buserite fe ti oxides hydroxides are intergrown and essentially x ray amorphous feroxyhyte and goethite we recognize two main types of microlayers type a layer suboxic diagenetic precipitates containing a high mn fe ratio and high concentrations of cu ni zn ba li and mg and type b layer oxic hydrogenetic accretions with low fractionation of mn and fe and high contents of co rey ti sr and pb furthermore elemental mapping indicates that the enrichments of co and rey are mainly associated with fe mineral phases rather than mn ones which are enriched in mg cu ni zn li and ba two mineralization processes and metal distributions in the individual microlayers are identified in the fe or mn mineral phases the occurrence of 10 a and 7 a phyllomanganates in type a layers are commonly enriched in trace metals such as ni cu zn li ba and mg whereas the metals for the type b layers include co ti pb sr rey which may be carried by the intergrowing fe ti oxyhydroxides and vernadite thus hydrogenesis and diagenesis facilitate the enrichment of fe co ti sr pb rey and mn ni zn cu li ba mg respectively during the mineralization of the south china sea nodules

mobility of metals over the redox boundary in peru basin sediments abstract downcore variations and phase distribution of metals in the quaternary sediments from six areas of the peru basin were investigated the sediments are characterised by a 5 20 cm thick oxic layer at the water sediment interface formed under the influence of dissolved oxygen in the bottom water in deeper sediment sections suboxic conditions are found due to the degradation of organic matter variations in the downcore abundance of metals e g fe mn co ni cu zn v mo cr were determined by bulk chemical methods a significant accumulation of manganese is observed at the depth of the manganese redox boundary caused by diagenetic remobilisation under suboxic conditions and reprecipitation under oxic conditions to investigate their phase distributions partitioning of elements in selected samples over the sediment column was carried out in sequential leaching experiments a comparison between the surface layer and deeper sediment layers shows a distinct change in the element distribution between operationally defined host phases carbonates oxy hydroxides detrital components above the redox boundary at the sediment surface transition metals are enriched in the reducible mn oxide fraction when the horizontal position of the mn redox boundary moves upward influenced by naturally occurring enhancement of surface water productivity these elements are mobilised and available to the manganese nodule accretion process if the redox boundary reaches the level of growth of the nodules in contrast to the naturally induced mobilisation of metals a technical impact e g mining of manganese nodules would be a rapid event occurring under completely different redox conditions metals would be released into the bottom water an oxic environment where scavenging of dissolved metals and resedimentation takes place in relatively short periods of time presumably a long distance transport of contaminants will not happen

the argentine continental margin north of 48 s sedimentary successions volcanic activity during breakup abstract new seismic data and geophysical results from the outer argentine continental margin and from seismic flow line transects across the oceanic argentine brazil and cape angola basins are presented the results document that the early cretaceous south atlantic continental breakup and initial sea floor spreading were accompanied by large scale transient volcanism emplacing voluminous extrusive constructions on the conjugate outer continental margins of the south atlantic on the argentine margin we interpret three major tectono volcanic crustal units beneath a thick and tectonically undisturbed sedimentary succession of cretaceous and tertiary age 1 syn rift basins and even pre rift features are present on the outer shelf 2 a deeply buried 60 120 km wide and several thousand metres thick volcanic wedge occupies most of the slope the wedge is characterized by seaward dipping reflectors and is associated with the distinct magnetic anomaly g 3 the seaward adjacent oceanic crust of cretaceous age shows isochronous changes of the seismic images along our flow line transects suggesting some form of episodicity of rich magma and poor to moderate magma supply at the pre existing mid ocean ridge of the south atlantic during cretaceous time

sequential leaching of peru basin surface sediment for the assessment of aged and fresh heavy metal associations and mobility abstract sequential leaching experiments were carried out using the upper 25 cm of oxic to suboxic sediment from the peru basin and ferromanganese nodules in order to assess potential mobility and the associations of heavy metals in the mineral phases the general leaching pattern confirmed that in the nodules as well as in the upper dark brown sediment layer significant proportions of heavy metals like mn co ni zn cu and cd are associated with mno2 and would be released under reducing conditions in the underlying mn poor layers mn oxide hosted metals are minor to distinguish the leaching behaviour of aged and fresh sorbents radiotracers were adsorbed on the solids before leaching the dominant role of the mn oxide phase for scavenging dissolved heavy metals was confirmed for the upper sediment layer and the nodules for sorption equilibration times of 5 h and 7 days respectively the sorption process was rapid freshly sorbed metals were leached mostly in the same fractions as those in aged sorbents and little difference was found for sorption times of 5 h and 7 days in contrast in the mn poor sediment layers a significant amount of adsorbed radiotracers was easily remobilised by simple ion exchange especially cs and cd and an ageing effect shift to less easily leachable fractions was observed after 7 days when surface sediment is resuspended into the bottom water the mn oxide rich surface layer and nodule particles represent a much more effective heavy metal scavenger under oxic conditions compared to other mn poor sediment phases however at the same time the mn rich particles are a stronger potential source of toxic heavy metals in a shift to more reducing conditions

dry bulk density and caco3 relationships in upper quaternary sediments of the eastern equatorial pacific abstract results from 1110 paired caco3 and bulk density measurements from cores raised from the eastern equatorial pacific permit formulation of well constrained caco3 dbd relationships for that region the cores lie along a n s transect at 110 w from 10 n to 3 s underneath the different currents of the equatorial current system and along an e w transect from 110 to 90 w at approximately 3 s two distinct crescent shaped dry bulk density caco3 relationships are observed for equal caco3 percentages sediments from those sites at 110 w which are situated in the high productivity zone have lower dry bulk density cores raised from closer to shore have relatively greater dbd