a submarine hydrothermal manganese deposit from the south west pacific island arc hydrothermal deposits of a wide variety of types are being found with increasing frequency on or near actively spreading mid ocean ridges1 4 however they also have a potential to occur in other submarine volcanic settings including island arcs5 to follow up indications of mineralization associated with submarine hydrothermal activity in the south west pacific island arc6 a joint new zealand oceanographic institute imperial college research cruise was mounted in may 1981 aboard the rv tangaroa during this cruise over 130 sampling stations were occupied at one of which were dredged manganese deposits with strong hydrothermal affinities this is the first report of such deposits from an island arc setting

a high temperature hydrothermal deposit on the east pacific rise near 7 n abstract a seabeam survey of the east pacific rise epr led to the selection of several sites having structural characteristics favorable for hydrothermal activity dredging of such an area located at 7 n on the epr resulted in the recovery of sulfides oxides and fresh basalt chemical analyses and isotopic compositions showed that the recovered pyrites were probably precipitated directly from hot vent hydrothermal waters chemical analyses and isotopic composition of manganese iron oxides indicated that they too were of hydrothermal origin 210 pb pb measurements yielded ages of 90 10years for the deposits this site may still be undergoing hydrothermal activity

geochemistry of ferromanganese nodules from domes site a northern equatorial pacific multiple diagenetic metal sources in the deep sea abstract the major and minor element composition of ferromanganese nodules from domes site a has been determined by x ray fluorescence methods three phases appear to control the bulk compositions mn and fe oxyhydroxides and aluminosilicates relatively wide compositional variations are evident throughout the area nodules with high mn fe ratios high cu mg mo ni and zn concentrations and high todorokite mno 2 ratios have granular surface textures and are confined to an east west trending depression with thin quaternary sediment cover nodules with low mn fe ratios high concentrations of as ca ce co la p sr ti v y and zr and low todorokite mno 2 ratios have smooth surfaces and are confined to shallower areas with relatively thick quaternary sediment to the north and south of the depression all nodules in the area have compositions which are influenced by diagenesis but those with the most marked diagenetic signature high mn fe and cu ni ratios low ce la ratios and more todorokite are found in areas of very slow or non existent sedimentation many of these nodules are actually in contact with outcropping tertiary sediment this paradox may be resolved by postulating by analogy with some shallow water occurrences that the nodules accrete from bottom waters which have enhanced particulate and dissolved metal contents derived from diagenetic reaction in areas remote from the site of nodule formation the metals are supplied in a bottom flow probably antarctic bottom water which also erodes or prevents modern sedimentation in the depression nodules on the flanks of the depression are not evidently affected by this flow and derive at least pan of their constituent metals from diagenetic reaction in the underlying quaternary sediment apparently abyssal diagenetic nodules can have an immediate and a remote diagenetic metal source metal fluxes derived from pore water dissolved metal gradients may not be relevant to particular accreting nodules if a significant fraction of their metals is derived from outside the area in which they form

hydrothermal sulfides from a submarine caldera in the shichito iwojima ridge northwestern pacific abstract a large mineralized block of two pyroxene andesite was dredged from a 913 m deep wall of a submarine caldera of the kaikata seamount about 180 km north of iwojima island the kaikata caldera 26 42 n 141 05 e is a seamount in active volcanic front schichito iwojima ridge to the west of ogasawara bonin trench sulfide minerals observed in the sample are dominantly pyrite with minor amount of sphalerite and cu fe sulfide chalcopyrite they occur in 5 mm thick veinlets together with euhedral quartz and chlorite the high filling temperatures 290 c of fluid inclusions in the quartz crystals and enrichment of gold max 142 ppb in vein materials both indicate a hydrothermal origin of the sulfides this is to our knowledge the first discovery of hydrothermal precious and base metal mineralizations associated with front volcanism in the marine environment

mercury and silver rich ferromanganese oxides southern california borderland deposit model and environmental implications mercury and silver enriched ferromanganese oxide crusts were recovered at water depths of 1 750 to1 300 m from la victoria knoll located about 72 km off the coast of northern baja california no other ferromanganese precipitate found so far in the modern ocean basins is similarly enriched in hg and ag the precipitates consist of submetallic gray brecciated mn oxide layers overlain by brown earthy laminated fe mn oxide crusts both oxide types are rich in hg to 10 ppm and ag to 5 5 ppm the mn rich layers are composed of mno 2 with lesser amounts of 10a and 7a manganates whereas the mn phase in the fe mn crusts is solely mno 2 the fe phase in both layers is x ray amorphous established criteria for distinguishing hydrothermal versus hydrogenetic crusts indicate that the mn rich layers are predominantly of low temperature hydrothermal origin whereas the fe mn crusts are hydrogenetic although there is some overlap in the source of chemical components in both types la victoria knoll is uplifted continental basement rock with basalt andesite and schist cropping out at the surface the knoll may have an intrusive core the hg and ag were derived from leaching by hydrothermal fluids of organic matter rich sediments in basins adjacent to la victoria knoll and to a lesser extent from continental basement rocks underlying the knoll and adjacent basins both rock types are notably enriched in ag and hg faults were the main fluid transport pathway and hydrothermal circulation was driven by high heat flow associated with thinned crust other elements derived from the hydrothermal fluids include tl cd cr and li the main host for hg and ag is feooh although mno 2 likely hosts some of the ag minor sulfide and barite also may contain small amounts of these metals possible analogs in the geologic record for this deposit type are found in the basin and range province of the western united states and mexico the discovery highlights the fact that fluids circulating along faults in the offshore california borderland are transporting potentially toxic metals hg ag tl as cd cr pb and ni and depositing them on and just below the ocean floor

characteristics of manganese nodules from the central indian basin relationship with the sedimentary environment the hydrogenetic and diagenetic manganese nodules from the cib show an unequivocal genetic relationship with neogene sedimentological patterns hydrogenetic nodules were observed at the top of the sedimentary column and interstratified in thin sequences of biosiliceous sediments and underlying miocene red clays in cores from topographic highs early to late pliocene radiolarian fauna were found at the base of the biosiliceous deposits these condensed biosiliceous sediments are less than 4 0 m thick and periods of non deposition and or erosion may have occurred in the central deep area 11 15 s significant biogenic deposition began during the early to late pliocene as a result of the development of a high biogenic productivity belt to the south producing the favourable conditions for diagenetic accretionary processes for mn nodules this indicates growth of hydrogenetic nodules prior to the late pliocene and the subsequent inception of diagenetic accretion formation of the most recent diagenetic nodules is associated with higher rates of sedimentation in the deep sea troughs where the siliceous sediments are much thicker this should promote the diagenetic mobilization of mn and its precipitation under oxic and suboxic conditions nevertheless diagenetic nodules are restricted to the upper 40 cm of sediments younger than 400 000 years suggesting fast growing diagenetic nodules and the dissolution of buried nodules below the first 50 cm of siliceous oozes hydrogenetic nodules are formed by dense layers of mno2 fe oh 3 and amorphous silica and they show smooth texture and botryoidal shapes analysis of bulk and selected portions of layered crust or rind shows very low mnfe ratios 2 and relatively high co and ti contents in most cases the cores of hydrogenetic nodules are fragments of altered ash layers from the indonesian volcanic arc which is located more than 2500 km to the east the ash layers are also interstratified with miocene red clays diagenetic nodules show a granular texture and comprise concentric layers with dendritic or columnar structures mainly of 10 a manganate higher mn ni and cu contents are observed in this phase late diagenetic enrichment of these nodules is continuous within the upper 40 cm of recent ni that enhances the stability of early diagenetic 10 a manganate buserite and c the formation of todorokite some nodules referred to as mixed in the literature show hydrogenetic internal layers which grade outward to a diagenetic crust this transitional character suggests slow changes in the sedimentary environment as growth advances the nodules of the cib and the east equatorial pacific eep are similar in terms of both metallic composition and accretionary patterns however the nodules of the cib are considerably younger and present a continuous accretionary history the history of the manganese nodules from the cib is related to the post late miocene sedimentary and geodynamic evolution of this basin

bimodal grain size distribution of chinese loess and its palaeoclimatic implications grain size analysis indicates that chinese loess generally shows a bimodal distribution with a coarse and a fine component the coarse component comprising the main part of the loess has pronounced kurtosis and is well sorted which is interpreted to be the product of dust storms generated by low altitude northwesterly winds its grain size reflects the strength of the low altitude circulation in the dust seasons of the year and its percentage provides an indicator of the source area aridity and the frequency of dust storms conversely the fine component has a wide grain size range and is poorly sorted sedimentary illustrations based on the grain size distribution characteristics of bulk samples and of detrital quartz suggest that the fine component probably represents the background dust load of the atmosphere and is mainly transported by high altitude westerly airstreams its grain size provides an estimate of the westerly air stream intensity the coarse and fine components of a loess sample can be mathematically separated by fitting a designated mathematical distribution function to the measured grain size data and this procedure constitutes an approach for reconstructing the palaeowind system of northern china c 2003 elsevier b v all rights reserved

two modes of back arc spreading back arc spreading is initiated with rifting along the volcanic zone of an island arc under extensional tectonics the width of the volcanic zone of the arc which is closely related to the dip angle of the subducting slab should cause a variation in the style of initial rifting and subsequent back arc spreading two modes of back arc spreading single rift type and multirift type are introduced from the comparative study of the bonin arc and the japan sea divergent tectonics in an island arc above a steeply dipping slab will cause a single rift system in a narrow volcanic zone but will cause a multirift system in a broad volcanic zone which is related to a shallow dipping angle of subduction

geochemistry of hydrothermal mn oxide deposits from the s w pacific island arc abstract hydrothermal mn oxide crusts have been removed from the tonga kermadec ridge the first such hydrothermal deposits to be reported in the s w pacific island arc in several respects the deposits are similar to hydrothermal mn crusts from oceanic spreading centre settings they are limited in areal extent comprise well crystalline birnessite and generally display extreme fractionation of mn from fe they are strongly depleted in many elements compared to hydrogenous mn deposits but are comparatively enriched in li zn mo and cd the group ia and group iia metals show strong intercorrelations and the behaviour of mg in the purest samples may indicate the extent to which normal seawater has influenced the composition of the deposits certain aspects of the deposits are not typical of hydrothermal mn deposits in particular at least some of the crusts have developed on a sediment or unconsolidated talus substrate some crusts or specific layers within some crusts display a chemical composition which suggests a significant input from normal seawater

possible formation mechanisms for the modal coarse silt quartz particles in loess deposits abstract the first major event in the formation of a loess deposit is the production of silt sized quartz particles many particle production methods have been proposed the bulk of loess particles appear to be produced by a glacial grinding to give ice sheet loess or b cold weathering in high regions to give mountain loess there are close relationships between mountain loess and desert loess loess material can be seen as a product of the cold phase of the glacial cycle

ore paragenesis of recent hydrothermal deposits at the cocos nazca plate boundary galapagos rift at 85 51 and 85 55 w complex massive sulfide mineralizations non sulfidic mineralizations and mineralized basalts complex massive sulfide ores black smokers as well as mineralized basalts and unconsolidated sediments were sampled during the german research expedition garimas 1 in the eastern portions of the galapagos rift at 85 50 w longitude the massive sulfide ores are characterized by a porous layered compositional texture with typical colloidal and or gel textures local occurrences of organism remains worm tubes which are embedded in the ore were also found the composition of the massive sulfide ores exhibits a considerable range from iron sulfide ores pyrite melnikovite pyrite marcasite to copper rich ores chalcopyrite and or zinc dominated ores sphalerite wurtzite schalenblende additional new types of hydrothermal mineralizations were found which consist primarily of manganese hydroxide limonite or fe rich smectite fe rich protosmectite together with limonite and opaline silica hydrothermally altered basalts may be characterized by significant sulfide contents primarily pyrite and locally by hematite sediments in the vicinity of the black smokers frequently contain fragments of complex massive sulfide ores with increasing distance from the black smokers these massive sulfide fragments exhibit complete replacement and pseudomorphism by limonite some replacement and pseudomorphism of microorganisms in unconsolidated sediments by limonitic material is also observed in places the unconsolidated sediments contain manganese hydroxide mineralizations of hydrothermal origin

structural stability of marine 10 a manganates from the ogasawara bonin arc implication for low temperature hydrothermal activity abstract hydrothermal 10 a manganate deposits with distinct differences in structural stability when exposed to air were found on the kaikata seamount of the ogasawara arc western pacific the most stable 10 a manganates are concentrated near the center of the hydrothermal field while the unstable ones occur towards the field margins all manganates are characterized by very high mn fe ratios and extremely low contents of transition elements such as cu co and ni the variation in 10 a stability of the hydrothermal manganates is not regulated by mineral chemistry or aging but appears to be determined by other factors e g the hydrothermal fluid temperature at mineral deposition we propose a structural model for marine manganates showing two continuous series of increasingly stabilized 10 a manganates one series is of hydrothermal origin structurally similar to todorokite with a tunnel structure fixed at deposition and the other is a buserite like series of diagenetic origin comprising phyllomanganates all the marine 10 a manganates can be progressively stabilized in two different manners the todorokite like series by the establishment of smaller tunnels and the buserite like series by post depositional uptake of 10 a stabilizing interlayer cations both series are linked together with a common end member the most unstable 10 a manganate which appears to be formed at low temperature and easily transforms to a 7 a manganate in air

stabilization of 10a manganates by interlayer cations and hydrothermal treatment implications for the mineralogy of marine manganese concretions abstract experimental substitutions of transition and alkaline earth cations into synthetic 10a na manganate show that cation uptake and the stability of the cation substituted mineral increase with stability of the hydroxide of the cation hydrothermal treatment of synthetic 10a manganates with different metal contents as well as marine diagenetic and hydrothermal 10a manganates shows that the stabilities of their structures are enhanced with increasing temperature the stabilization is due to reinforcement of the tunnel walls supporting the mn4 o2 6 octaheral layers the diagenetic 10a manganates have initially unstable buserite like structures with each interlayer wall composed of two mn2 o2 3 x oh 3 x octahedra 0 x 3 with either a na o2 2x oh n 2x unit n 6 and or 8 or less frequently a mn2 o2 2x oh 2 2x octahedron in between some of these cations in the walls are post depositionally substituted by highly hydrated divalent metal cations particularly cu2 and ni2 while some of the mn2 ions are slowly oxidized to mn4 these interlayer changes result in higher crystal field stabilization energy and shifts from interlayer van der waal s forces and weak coordination links to strong coordination links which stabilize the mineral structures low temperature hydrothermal 10a manganates have todorokite like structures with tunnel walls constructed predominantly of mn2 o2 3 x oh 3 x and mn2 o2 2x oh 6 2x octahedra high temperature hydrothermal 10a manganates have stable todorokite structures with the walls constructed of mn4 o2 6 octahedra the positive correlation between the formation or post depositional alteration temperatures and the mineral stability is due to the increase in oxidation rate of interlayer mn2 ions with increasing temperature of the hydrothermal fluids marine 10a manganates can be used as genetic indicators for manganese concretions and the sediments in which they occur and as a geothermometer in the search of ancient and modern hydrothermal vents where massive sulphide deposits are often found

local variability of manganese nodule facies on small abyssal hills of the central pacific basin abstract local variability of manganese nodule facies and associated sediments were studied around abyssal hills 60 60 km 2 located in the equatorial zone of the central pacific basin small scale variations in nodule occurrence mineralogy chemistry and internal structure are discussed in relation to seismic records and sediment lithology the slow sedimentation rate from the late tertiary to the quaternary appear to have promoted formation of nodules around the abyssal hills although the plio pleistocene hiatus at depths below sediment surface suggests no clear evidence of increased growth of nodules during the period in the area of rapid and continuous sedimentation away from the hill areas nodules are rare probably because of insufficient lifting force for nodules mineralogical and chemical studies reveal that the two principal nodule morphologies smooth and rough surfaces result from preferential deposition of hydrogenous or diagenetic manganese minerals in relation to early diagenesis of surface siliceous sediments regional variability of nodule surface morphology and composition suggests a very local change in sedimentary conditions in space and internal mineral variation suggests changes in sedimentary conditions with time the geological factors controlling the small scale variability of nodule facies seem to be similar to those controlling regional scale variations

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

ni cu co rich hydrothermal manganese mineralization in the wallis and futuna back arc environment sw pacific abstract the wallis and futuna back arc system is a complex area composed of at least two active oceanic spreading centers the futuna and alofi spreading centers and young volcanic zones characterized by diffuse magmatism locally affected by the samoan hotspot this geological setting is favorable to the establishment of hydrothermal systems in the form of either high temperature ht hydrothermal venting or low temperature lt diffuse flow during the 2010 futuna cruise aboard the r v l atalante three remarkable inactive lt fe si mn deposits were discovered utu uli anakele and utu sega some of the mn rich precipitates discovered exhibit the highest base metals concentrations so far recorded in ferromanganese rocks including in the well documented hydrogenetic crusts and polymetallic nodules the deposits lie on top of volcanoes and formed in close association with the volcanic facies the manganese mineralization occurs in the form of massive layered crusts and mn rich cements within strongly altered basaltic pyroclastic rocks brecciated lavas and more rarely in sediments field observations and mineralogical and chemical studies support a hydrothermal origin for the mineralization and show that nickel cobalt and copper enrichments are controlled by the precipitation of 7 a and 10 a manganates the conventional geochemical classifications e g bonatti et al 1972 used to decipher the origin of mn mineralization cannot be used for this new type of deposit and new robust discrimination diagrams need to be established we suggest that the unusual enrichment of metals recorded in our samples is due to i a lack of precipitation of high temperature massive sulfides at depths that would have retained metals e g cu ni co ii isolation of the hydrothermal system thereby avoiding ni co and cu losses in the water column and iii the ability of birnessite and buserite todorokite to scavenge co ni and cu from aqueous fluids the utu uli and anakele deposits share certain characteristics with the active hydrothermal system at loihi seamount e g the depth of mineralization relationships with pyroclastic volcanoes and the influence of a mantle plume source and thus might represent late stage products of this specific type of hydrothermal activity elsewhere the co rich mineralization of the calatrava volcanic field cvf in spain may be a potential analog of the utu sega deposit the mn co deposits of the cvf formed in close proximity to pliocene volcanic rocks metals were transported by epithermal hydrothermal solutions with high fo 2 and cobalt was scavenged by mn oxides together with the well documented stratabound mn deposits gonzalez et al 2016 hein et al 2008 hein et al 1996 the mn deposits discovered in the wallis and futuna back arc provide crucial insights into lt hydrothermal activity in the deep ocean the metal rich character of this lt hydrothermal activity may be of major importance for future research on the net flux of hydrothermally derived metals e g ni co cu to the open ocean

mineralogy and crystal chemistry of mn fe co ni and cu in a deep sea pacific polymetallic nodule minor element concentrations in marine ferromanganese nodules are primarily controlled by the mineralogy which itself depends on redox conditions at the sediment water interface results are presented for the first in depth x ray microstructural and microspectroscopic investigation of a mixed hydrogenetic diagenetic nodule which is representative of ferromanganese deposits on abyssal plains the measurements were conducted by micro x ray diffraction and x ray absorption spectroscopy both xanes and exafs on hydrogeneous and diagenetic regions of the nodule the hydrogenetic diagenetic interface was imaged by x ray microfluorescence after which regions of interest were chosen to represent mineralogical and chemical transformations that occurred at the early stage of suboxic diagenesis in the hydrogenetic nodule oxic environment mn is speciated as fe vernadite a nanocomposite material composed of intergrown feroxyhite feooh and monodispersed phyllomanganate layers having no interlayer mn vernadite in the diagenetic nodule suboxic environment mn is speciated dominantly as mg rich 10 a vernadite which consists of a random intergrowth of vernadite and its transformation product todorokite the authigenic 10 a vernadite precipitated from the components of vernadite in fe vernadite that were dissolved in suboxic microenvironments of the sediment direct evidence supporting a redox driven dissolution reaction is provided by the valence composition of mn as measured by micro xanes which is 0 69mn4 0 24mn3 0 07mn2 average 3 62 0 04 v u for fe vernadite and 0 61mn4 0 23mn3 0 16mn2 average 3 28 0 04 v u for 10 a vernadite ni and cu derived mainly from dissolved vernadite and oxidized organic matter replace structural mn3 4 in both the mno2 layer and todorokite domains of 10 a vernadite pure todorokite in highly diagenetic regions of the nodule has an average formula of mg2 0 167 mn4 0 783 mn3 0 099co3 0 002ni2 0 076cu2 0 040 o2 n h2o with an atomic ratio of cu ni co mn 0 13 which is slightly lower than 0 167 1 6 the maximum metal uptake capacity reported for marine nodules by analogy with synthetic todorokites we infer that mg2 which has a hydrated diameter close to that of the 3 3 tunnel size of todorokite and mn3 and cu2 which prefer jahn teller distorted octahedra play a crucial role in templating the topotactic transformation of 10 a vernadite to todorokite and stabilizing todorokite in suboxic marine sediments

a model for the formation of hydrothermal manganese crusts from the pitcairn island hotspot the distribution of elements in the hydrothermal mn crusts from the pitcairn island hotspot can be explained by considering processes occurring within the hotspot volcano these include the role of boiling of the ascending hydrothermal fluid which leads to sulphide deposition and seawater intrusion into the upper part of the volcano this in turn results in the development of an oxycline above which feooh can precipitate the high mn fe ratios and low contents of ni and zn in the massive crusts are thought to reflect the rapid incorporation of the ore elements into sulphide minerals such that only a small proportion of these elements are available for incorporation in the crusts the small positive eu anomaly in the crusts on a nasc normalized basis reflects the lower temperatures in the hydrothermal fluids at the pitcairn island hotspot 25dgc compared to those at mid ocean ridges c 350 c the oxyanions cro42 vo43 aso43 and po43 the rare earth elements ree and th are scavenged by feooh particles within the upper part of the seamount and can therefore be incorporated into the crusts associated with the fe rich phase molybdenum and uranium are scavenged in only negligible amounts by the feooh molybdenum is therefore most probably scavenged from seawater by manganese oxides during the actual formation of the mn crusts the alkali metals li rb and cs remain in solution in the hydrothermal fluids and are selectively incorporated into the buserite structure of the mn crusts in the absence of strong competition from the divalent transition metal ions the compositional characteristics of the hydrothermal mn crusts can therefore be explained in terms of a simple model of element scavenging and uptake occurring mainly within the seamount a laser ablation icpms profile in one of the hydrothermal crusts ds 63 4 revealed varying ree concentrations and patterns in the different layers of the crust these data indicate that the hydrothermal component was variable during the formation of the crust it was calculated to be almost 100 in the upper 18 0 mm of this crust apart from the samples at 6 0 8 0 mm and about 80 in the lower layers

the relationship between manganese minerals and metallic elements in deep sea manganese nodules abstract the relationship between manganese minerals and the concentration of fe cu ni zn and al in mn rich crystalline areas in deep sea manganese nodules were investigated using microdiffraction and electron microprobe analysis thirty three microsamples were obtained from eight polished sections of five pacific ocean manganese nodules birnessite and todorokite are the principal manganese minerals in the x ray diffraction powder patterns on polished sections kept in a vacuum only birnessite was identified in sixteen microsamples only todorokite was identified in one microsample another sixteen microsamples were mixtures of birnessite and todorokite microsamples in which only birnessite was identified contain cu ni and zn in the same concentrations as the microsamples in which both birnessite and todorokite were identified it appears that birnessite as well as todorokite can incorporate cu ni and zn with the exception that no todorokite was observed in microsamples with very small amounts of fe cu and ni there is no systematic correlation between the manganese mineralogy and the concentration of fe cu ni and zn in the microsamples the microsamples examined in this study contain varying amounts of al 0 01 2 57 wt 0 92 wt on average todorokite appeared in the microsamples which contained more than 0 7 wt al mineralogical considerations suggest that at least part of the al detected may be incorporated in todorokite

ferruginous vernadite in an indian ocean ferromanganese nodule select area electron diffraction and microanalysis of the optically dark component of a ferromanganese nodule from the south east indian ocean manganese field indicate that this is composed of a random stratification of crystallites of vernadite mno 2 r 2 o ro r 2 o 3 x y h 2 o where r represents elements such as k ba na ca mg and a disordered hydrated iron oxide possibly ferrihydrite 5fe 2 o 3 9h 2 o or feroxyhyte feooh whether the dark component is an irregular mixed layer hybrid mineral or a layered accumulation resulting from epitaxy of the above phases is uncertain

regional variation of manganese nodule facies on the wake tahiti transect morphological chemical and mineralogical study abstract during the gh80 1 cruise of rv hakurei maru january to march 1980 conducted by the geological survey of japan a significant regional variation of manganese nodule facies was found on the 4000 km long transect from wake to tahiti more than 190 bottom samplings and 120 sea bed photography using box corer free fall grab and piston corer revealed three characteristic nodule facies each extending over hundreds of kilometers in the northern central pacific basin and the mid pacific mountains area zeolitic pelagic clay surface sediment discoidal to irregular shaped smooth surface nodules are dominant they consist of inner fragmented older nodules composed of mno2 and surrounding 2 5 mm thick layers of mno2 and 10 a manganate mn fe and cu ni are low averages 1 4 and 0 85 wt consistent with mineralogy in the central to southern central pacific basin siliceous clay or ooze surface sediment spherical and rough surface nodules with concentric structure predominate each concentric layer consists of 10 a manganate yielding high mn fe and cu ni averages 4 1 and 2 41 wt in the penrhyn basin zeolitic clay surface sediment spherical to discoidal shaped smooth surface nodules of simple internal structure are distributed they consist mostly of mno2 and consequently mn fe and cu ni are low averages 1 3 and 0 85 wt the manihiki plateau covered with thick calcareous sediments is a barren area these regional variation in surface and internal structures and chemical characteristics are principally due to preferential growths of the two ferromanganese minerals the mode of regional variation of the minerals and its close relationship to surface sediments variability are consistent with the two supply route model of these minerals the 10 a manganate forming rough surface dominantly developed within surface sediments as a result of diagenesis of siliceous sediments in the central and southern central pacific basin whereas mno2 develops through direct supply of metal elements from the overlying bottom waters forming smooth surface nodules in the northern central pacific basin and penrhyn basin