new geochemical and mineralogical constraints on the genesis of the vani hydrothermal manganese deposit at nw milos island greece comparison with the aspro gialoudi deposit and implications for the formation of the milos manganese mineralization abstract the mn ba pb deposit at aspro gialoudi in nw milos is shown to be a fossil inhalative exhalative hydrothermal deposit that represents the deepest part of the vani succession at the western extremity of the main vani manganese deposit the geology of the vani aspro gialoudi area is characterized by upper pliocene lower pleistocene dacitic and rhyodacitic lava domes which are overlain by the vani volcaniclastic unit considered to be part of the 2 66 1 44 ma magmatic event at milos island the presence of in situ and intrusive hyaloclastite breccias surrounding the coherent lava domes at aspro gialoudi and vani areas indicates submarine emplacement for the domes the dacitic rhyodacitic domes are variously altered mainly propylitic and or argillic alteration silicified and in some cases locally exhibiting adularia alteration both aspro gialoudi and main vani deposit are located proximal to fault systems the main vani manganese deposit is adjacent to the nw trending kondaros katsimouti vani dome fault whereas the aspro gialoudi deposit is adjacent to the relatively minor ne trending fault on the west coast of milos at aspro gialoudi mineralization took place in a subseafloor and or seafloor environment and is characterized by a stratabound mn barite rich deposit mainly within a package of propylitized intrusive hyaloclastites and within the overlying sandstones banded epithermal veins trending ne sw and composed of chalcedonic silica quartz barite mn oxide sulfides crosscut the dacitic lavas the hyaloclastites and the overlying volcaniclastic sequence at aspro gialoudi and are considered to represent the feeder zones of the manganese barite mineralization within the veins early sulfide galena sphalerite barite and quartz deposition is followed by manganese oxides and aragonite thus resembling the epithermal style pb zn ag mn mineralization across the nw trending katsimoutis kondaros vani fault mineralization in aspro gialoudi and vani deposits seems to be controlled by alternating cycles of deposition of sulfides and hydrothermal manganese oxides within the faults manganese deposition in both deposits formed in a similar manner namely by transport of hydrothermal fluids through the adjacent fault systems into a reservoir of volcanoclastic sandstone and hyaloclastites to produce a deposit initially consisting of principally of pyrolusite and occasionally ramsdellite which were subsequently replaced by cryptomelane hollandite coronadite and hydrohaeterolite precipitation of hydrothermal manganese oxides took place very quick and under microbial mn ii oxidation compositional data show that metallic elements most enriched in the aspro gialoudi and vani manganese deposits relative to the average continental crust lie in the sequences pb cd mn as sb zn w tl ba cu mo co bi and as sb pb mn tl cd zn w cu ba mo co respectively mineralogical and geochemical e g ree data from both aspro gialoudi and main vani deposit are taken to indicate mainly a seawater source for the hydrothermal fluids these two deposits are genetically and spatially related to base and precious metal intermediate sulfidation epithermal mineralization they formed successively by similar processes and are considered to be integral parts of the same hydrothermal system

sedimentary origin of the mn fe ore of um bogma southwest sinai geochemical and paleomagnetic evidence paleomagnetic mineralogical and geochemical investigations have been carried out to estimate the origin and age of the mn fe ore of um bogma formation of the early carboniferous for this purpose oriented samples were collected from 26 sites in the mn fe ore and host rocks of um bogma formation and the overlying sandstone of abu thora formation the paleomagnetic pole determined from the characteristic remanent magnetization of the mn fe ore from 20 sites and the hosting rocks of um bogma formation is located at 22 s 97 e dp 3 9 dm 7 4 this paleomagnetic pole position falls close to the carboniferous poles of africa suggesting that the mn fe ore and associated rocks of um bogma formation were deposited during the carboniferous furthermore the paleolatitude determined for these rocks based on the mean paleomagnetic inclination suggests that the mn fe ore of um bogma was deposited at a latitude 10 south of the equator i e in tropical conditions mineralogical and geochemical investigations support the paleomagnetic results the ore is enriched with na k ca mg sr co and ni suggesting that the mn fe ore of um bogma is of sedimentary marine origin the enrichment of some ore samples with hydrothermal elements as zn cu pb v w and f is restricted to faulted areas indicating that a younger phase of hydrothermal activity affected the ore after its deposition samples from the overlying abu thora sandstone yield a mean paleomagnetic direction of d 326 i 42 k 19 3 95 17 9 which provides a paleomagnetic pole position at latitude 59 longitude 302 dp 13 5 dm 22 this magnetization is significantly different from that of the mn fe ore and host rocks and is assigned a cretaceous age the porous sandstone acquired its magnetization long after deposition most likely by diagenetic chemical processes associated with red pigmentation

zircon u pb ages and geochemistry of granitoids in the truong son terrane vietnam tectonic and metallogenic implications abstract truong son terrane one of the most important tectonic and metallogenic terranes in indochina block is composed of many volcano plutonic complexes reported here is geochronological and geochemical data obtained from six different volcano plutonic complexes the new data reveals that the granite from the hai van complex is 438 ma in age and shows collision related geochemical characteristics whereas another five samples from five volcano plutonic complexes present consistent emplacement and crystallization ages ranging from 261 to 242 ma dien bien granodiorite phia bioc monzogranite and dong trau rhyolite display typical subduction related calc alkaline affinity e g depletion in nb ta and ti and enrichment in rb and la while monzogranite from song ma complex displays collision related shoshoniteseries and granites from bengiang queson complex are related to post collision calc alkaline series based on these observations in combination with the previous published geochronological data we propose that at least four major stages of magmatic activities occurred during the paleozoic and the early mesozoic through the truong son terrane ordovician silurian 420 470 ma late carboniferous early permian 280 300 ma late permian to mid triassic 245 270 ma and middle late triassic 200 245 ma these magmatic activities are not only attributed to the tethyan song ma ocean southwestward subduction but also related to paleo tamky phuoc son oceanic bidirectional subduction synthesized with regional metallogenic data we identified three metallogenic epochs 1 late carboniferous early permian 280 300 ma arc magmatic hydrothermal cu au fe polymetallic metallogenic system related to the tamky phuoc son ocean north dipping subduction 2 late permian middle triassic 245 280 ma arc magmatic hydrothermal cu au fe and orogenic w sn au polymetallic metallogenic system which linked to both paleo tethyan song ma ocean south dipping subduction and tamky phuoc son ocean closure 3 middle to late triassic 200 245 ma syn collisional magmatic epithermal fe au w sn and post collisional or orogenic au system

tectonics and magmatism in turkey and the surrounding area this volume contains 23 papers from a range of international contributors describing recent research into the tectonics and magmatism of turkey and its surroundings this region is sited at the collision zone between eurasia and afro arabia and as such provides an extraordinarily complete and well exposed record of the staged tectonic evolution of this sector of the alpine himalayan orogen the geological history of this area involves separation of continental fragments from the margin of gondwana their migration across the tethyan oceans the subsequent closure of these oceans and finally the development of the neotectonic regime which continues to evolve to the present day such a comprehensive record is relevant to the understanding of collisional zones worldwide the volume is divided into five sections tethyan evolution neotethyan ophiolites post tethyan basin evolution neotectonics and igneous activity the first two sections deal with tethyan oceans whose growth and subsequent closure dominated the geodynamic framework in the mesozoic and cenozoic the subsequent sections deal with more recent geological developments from the balkan peninsula in the west to the transcaucasus in the east that followed consumption of the tethyan oceans there is a broad mix of papers throughout the volume wide ranging review papers on ocean development and extensional tectonics are followed by detailed descriptions of petrology and geochemistry and geographically focused studies on basin evolution specific aspects of extensional and strike slip tectonics and discussions of the relationship of magmatic activity to the tectonic development of the area tectonics and magmatism in turkey and the surrounding area presents up to date results and ideas from a large number of international contributors on a wide range of current research activity in this region it is essential reading for all geoscientists with an interest in both academic and applied aspects of eastern mediterranean geology

mineralogy and geochemistry of epigenetic features in metalliferous sediment atlantis ii deep red sea finely laminated and undisturbed except in the area of the southwest basin in this part bedding resedimentation and brecciation are common in addition some sediment cores contain vein minerals precipitated in open fissures which crosscut unlithified metalliferous sediments these veins are the conduits by which new hot brine vents into the deep vein mineralogy is dominated by anhydrite talc smectite pyrite sphalerite and chalcopyrite vertical zonation due to cooling and reaction of the incoming brine as it rises through the metalliferous sediment near the southwest basin west basin transition metalliferous sediment has been locally recrystallized to a hematite magnetite pyroxene assemblage probably due to the intrusion of basalt into the metalliferous sediments modified journal abstract

the role of migrating oil field brines in the formation of sediment hosted cu rich deposits oil field brines commonly contain ppm quantities of zn pb and h 2 s but negligible quantities of cu theoretical analysis of the water rock interactions expected during migration through evaporitic and red bed sequences suggests that these reducing oil field brines can become transformed into far more oxidized fluids capable of transporting cu pb zn and sulfate and of forming sediment hosted cu rich deposits calculation of the chemical mass transfer accompanying reaction of a typical reducing brine with anhydrite hematite and quartz followed by the assemblage quartz k feldspar muscovite hematite chlorite and cuprite reveals that the aqueous phase becomes greatly undersaturated with respect to sphalerite galena chalcopyrite bornite pyrite and pyrrhotite as it achieves log f sub o 2 values well above the magnetite hematite buffer consistent with saturation with respect to anhydrite hematite and chalcocite and ore forming concentrations of copper and sulfate consequently evaporites are not only possible sources of salinity and oxidized sulfur for evolving basinal brines but may be crucial to the development of the f sub o 2 conditions required to transport cu in ore forming concentrations reaction of the oxidized brine with organic matter approximated by graphite and diagenetic pyrite results in precipitation of the zonation sequence chalcocite bornite chalcopyrite and pyrite with variable amounts of hematite covellite sphalerite and galena depending on the relative rates of reaction of the graphite and pyrite

elemental partitioning into mn and fe oxides derived from dolomitic shale hosted pbzn deposits northwest queensland australia abstract exploration for dolomitic shale hosted base metal mineralization in northwest queensland is largely dependent upon geochemical evaluation of ironstones fe oxides because of their abundance in the weathered zone often quantitatively account for most of the base metal content of an ironstone mn oxides are less well developed but provide particularly good hosts for ba zn and pb and hence assume importance where present the mn fe coatings found in stream coatings vigorously scavenge and concentrate solution transported base metals and hence have to be very carefully evaluated when used during exploration however the present survey of base metal contents in gossans and ironstones in northwest queensland has shown that the ba cu p pb ni s and zn contents of the mn and fe oxides can be used to accurately indicate their parent material only ce and co are possibly preferentially incorporated into mn oxides but neither element is a pathfinder for pb zn mineralization development of the mn oxides chalcophanite todorokite lithiophorite and the cryptomelane group incorporating k ca mg ba co zn and pb reflects acid conditions during sulfide oxidation when an ironstone consistently contains mn oxides with greater than 1 pb or 10 zn it can be regarded as derived from pb or zn rich mineralization as ba is often associated with sulfides and facilitates the incorporation of pb into cryptomelane ba without accompanying base metals in a mn oxide implies derivation from base metal barren pyrite and or pyrrhotite cu pb zn al phosphate sulfate and arsenate are all incorporated into fe oxides however only pb which is more strongly partitioned into hematite and al and phosphate which are preferentially incorporated into goethite show clear partitioning between the fe oxide phases the preferential incorporation of phosphate rather than sulfate into an fe oxide makes areas showing higher sulfate contents particularly good targets knowledge of the nature of the distributions of pathfinder elements helps understanding of the associations seen in whole rock analyses and leads to rational application of geochemical data during exploration

recent mn ag deposits in coastal hydrothermal springs in the baja california peninsula mexico hot springs with associated mn ag mineralization were identified in the intertidal zone of the bahia concepcion bay of the central eastern baja california peninsula hot spring activity is related to a system of nw se faults that are associated with the opening of the gulf of california the hot springs are hosted by miocene volcanic and volcaniclastic units of the comondu group the maximum discharge temperature recorded is 72 c with the ph ranging from 6 2 to 6 5 and salinity values reaching up to 27 g kg veins stockworks breccias crusts and organosedimentary stromatolites of silica carbonate and mn oxides are associated with the hot springs the mn oxide and silica deposits show an association with ag as ba ca cu mg pb sb sr tl v w and zn acanthite and native silver occur along with pyrite in a mineral assemblage rich in opal a todorokite romanechite aragonite high mg calcite and barite three distinct mineral associations characterized by sulfides sulfates and oxides are recognized the silver minerals formed late in the paragenesis textural evidence suggests a microbial mediation for the mn mineral deposition pourbaix diagrams for mn and ag species were constructed for the physicochemical conditions of the coastal hot springs these diagrams show that both mn and ag minerals are stable at low temperature 65 c and near neutral ph under slightly reducing or oxidizing conditions the characteristics of the subaerial to shallow submarine hot springs and the results of the geochemical modeling suggest that the hydrothermal system in the bahia conception bay is formed through convection of meteoric waters intermixed with some saline fluids or seawater

stratigraphic and sedimentological factors controlling the distribution of epigenetic manganese deposits in iron formation of the emily district cuyuna iron range east central minnesota early proterozoic strata of the emily district at the far northern end of the cuyuna iron range define the southwestern closure of the animikie basin in east central minnesota as such the rocks of the emily district are correlative with strata of the well known animikie group of the mesabi range however unlike the monoclinal nature of the mesabi range strata in the emily district are deformed into a series of broad open eastward plunging folds with near vertical axial planes geometric relationships imply that the basal contact of the animikie group overlies an unconformity cut onto older folded rocks of the cuyuna north range that unconformity marks a boundary between twice deformed rocks of the penokean fold and thrust belt and the once deformed rocks of the animikie basin on the mesabi range the animikie group consists of a lower quartz arenitic sequence pokegama quartzite an intermediate iron rich sequence biwabik iron formation and an upper black shale graywacke sequence virginia formation in the emily district however the stratigraphic position of the biwabik is occupied by several lenticular units of iron formation intercalated within both pokegama and virginia like materials the main iron formation termed unit a can be divided into seven lithotopes that were deposited during two transgressive regressive cycles in a basin having a strandline to the west and deeper water to the north and east well rounded grains of terrigenous quartz which persist throughout much of the formation imply that sedimentation occurred relatively close to the strandline although unit a has many mineralogical textural and chemical attributes indicative of ordinary iron formation it locally contains manganese oxides in amounts 10 to 100 times greater than the norm of 0 6 to 0 8 percent in the biwabik iron formation manganese oxides occur principally in the coarser grained parts of unit a as disseminated grains as thin pods or lenses and as layers as thick as 1 5 m that typically contain about 10 percent mn some contain as much as 20 to 30 percent mn manganese oxides are particularly abundant in two laterally persistent zones about 15 to 18 m thick that have manganese tenors enriched to the range of 10 to 50 percent both zones more or less coincide with stratigraphic positions occupied by oolitic pisolitic iron formation the zones contain various proportions of psilomelane and cryptomelane as well as hematite and quartz goethite and manganite are locally abundant where they occur they are secondary phases that formed during a period of intense chemical weathering that modified these rocks in late jurassic or early cretaceous time the manganese oxides are most likely epigenetic they are confined to the porous and permeable parts of unit a rocks with the greatest primary porosity such as the oolitic pisolitic lithotope and quartz arenitic rocks in the epiclastic lithotope have the most manganese we suggest that the manganese was deposited by a refluxing process involving reducing solutions that leached manganese from older rocks of the cuyuna north range the manganese was subsequently precipitated where the reducing solutions came into contact with oxidizing conditions in the depositional basin just below the sediment water interface much of the manganese must have been precipitated early in the diagenetic history of the iron formation because it occupies pore spaces normally filled with silica cement

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

late cretaceous miocene sedimentary development of the arabian continental margin in se turkey adiyaman region implications for regional palaeogeography and the closure history of southern neotethys abstract the middle cretaceous late miocene sedimentary successions that are exposed on the arabian continental margin near adiyaman provide valuable insights into sedimentary tectonic and climatic processes that affected the southern neotethys and its continental margins deposition in the region began with aptian early campanian shelf carbonates followed by deepening during the mid campanian lithoclastic bioclastic turbidites accumulated along the downfaulted northern margin of the arabian platform during the campanian a flexurally controlled foredeep developed in advance of the emplacement of mesozoic allochthonous continental margin and oceanic rocks during the latest campanian early maastrichtian e g supra subduction zone kocali ophiolite alluvial detritus was shed from the emplaced allochthon in non marine to shallow marine deltaic settings during latest campanian early maastrichtian a marine transgression resulted in the establishment of a shallow marine shelf during the mid maastrichtian during the latest maastrichtian the platform submerged initiating deeper water hemipelagic sedimentation uplift took place during the palaeocene resulting in sediment instability slumping and formation of high density subaqueous gravity flows in response to regional faulting and tilting some areas in the north and the southwest emerged during the early middle eocene generating alluvial fans in a warm humid climate that favoured oxidation and reddening the likely control of the tectonic instability was far field compression related to the latest stages of subduction of the southern neotethys or the initial stages of collision of the arabian and tauride continents an oligocene hiatus is likely to reflect the formation of a collision related forebulge followed by flexural subsidence to form an early miocene foreland basin this was finally over ridden by the northerly active continental margin of the southern neotethys during early mid miocene regional suture tightening mid late miocene and related non marine coarse clastic sedimentation was followed by westward tectonic escape of the anatolian microplate towards the aegean region during plio quaternary time

relationship between morphology and composition of manganese nodules from the central indian ocean abstract the central indian ocean basin nodules exhibit a wide range of morphologies and compositions based on size shape and surface texture spheroidal nodules having a diameter between 2 and 4 cm and surface textures ranging from smooth to coarsely granular or of intermediate nature are the most common the nodule facies and their compositions are influenced by the underlying sediment through which they receive some of their constituents for example nodules with rough surface texture which are associated with siliceous radiolarian sediments are comparatively large have higher mn fe ratios and higher ni and cu contents and have lower contents of fe and co compared to the smaller smooth surfaced nodules associated with red clays additionally the shapes of the nodules reflect in part the time of initiation of growth of nodules and bottom current characteristics the nature size and abundance of botryoids are perhaps responsible for the coarse mammillated surface texture of the nodules and influence their geochemical characteristics the association of coarse texture with the siliceous sediments reflects the precipitation of larger particles of manganese oxides through the larger pore spaces of the sediment as a result of the enhanced early diagenetic effects the smooth texture in contrast reflects the direct supply of manganese oxides from the overlying bottom water as a result of their precipitation as authigenic oxyhydroxides

lead and uranium isotopic behavior in diagenetic and epigenetic manganese nodules timna basin israel determined by mc icp ms abstract isotope ratios of u and pb were measured in two types of mn nodules from the cambrian timna formation israel type a nodules are mainly composed of pyrolusite and hollandite with mn ba pb and u concentrations of 30 60 0 2 2 5 0 2 1 0 and 500 3500 ppm respectively whereas type b nodules were formed by alteration of the former and contain mainly coronadite with mn ba pb and u concentrations of 7 48 0 2 7 0 6 5 and 10 160 ppm respectively the isotopic composition of u and pb was measured by mc icp ms on mn rich solutions up to 100 mg l without and with chromatographic separation the values for the 207 206 and 208 206 ratios have been determined with precisions of up to 50 ppm and those of 206 204 207 204 and 208 204 up to 200 ppm the values for the 234 238 ratios have been determined with precisions of 0 4 1 the results of the separated and unseparated solutions were shown to be equal within the error thus there is no significant matrix effect while measuring u and pb in mn rich solution using the mc icp ms the isotopic composition of pb and u support the distinction between the two types of mn nodules type a nodules have a wide range of 206pb 204pb ratios 18 278 19 776 and an almost constant ratio of 208pb 204pb in contrast type b nodules have almost constant 206pb 204pb ratios and a wide range of 208pb 204pb ratios 37 986 38 079 type a nodules form a linear array on a 207pb 204pb vs 206pb 204pb diagram while type b nodules form a tight group characterized by lower pb isotope ratios that slightly deviate from the type a array the 234u 238u ratio differs between the two types of nodules type a nodules exhibit a uniform and close to equilibrium 234u 238u ratio while type b nodules show a wide range of 234u 238u ratios above and below the equilibrium value the isotopic composition of pb in type a nodules might reflect pb contributions from plutonic rock weathering exposed at the time of deposition or later to the cambrian sea these nodules have remained unaffected by processes that occurred since the cambrian the higher 208pb 204pb values of type b indicate that these nodules were formed from a th enriched solution probably during epigenetic processes which occurred also during the last 1 ma thus the two isotopic systems of u and pb can record formation leaching and redeposition of mn ores

atlantis ii deep geothermal brine system chemical processes between hydrothermal brines and red sea deep water water samples and suspended matter taken in the atlantis ii deep area red sea during the expedition so 2 with rv sonne in november 1977 were investigated for chemical composition only slight changes have been found for most components since 1966 a strong decrease of the cu content from 100 500 g kg 1 according to brooks et al 1969 to values below 1 g kg 1 has however become evident comparison between theoretical concentrations in the intermediate brine layers resulting when using the lower or the upper homothermal layers respectively as end members of mixing processes with red sea deep water and the concentrations measured prove that precipitation and resolution processes have considerable influence on the concentrations found in solution components strongly involved in such processes are iron manganese copper oxygen sulfate and silica as could be shown from comparison of theoretical and measured concentration profiles along the water column investigations of the metals suspended in the brine confirm these processes compared to 1971 1972 the cu and zn values in suspension preferring the southwestern basin at that time are clearly reduced thus being in agreement with the recently lowered hydrothermal activity remarks on the hypothetical composition of the unknown hydrothermal brine discharging into the deepest basin are also included

isotopic constraints on fluid evolution and precipitation mechanisms for the boleo cu co zn district mexico stable and radiogenic isotope composition of stratiform cu co zn mineralization and associated sedimentary rocks within the boleo district of the miocene santa rosalia basin baja california sur constrains the evolution of seawater and hydrothermal fluids and the mechanisms responsible for sulfide and oxide deposition stable isotope geochemistry of limestone and evaporite units indicates a strong paleogeographic influence on the chemistry of the water column near shore limestone at the base of the boleo formation is characterized by modified marine carbon 13cpdb 6 0 to 4 4 and oxygen 18osmow 19 5 to 26 2 isotope composition due to the influx of 13c and 18o depleted fluvial water sulfate sulfur isotope composition 34scdt 17 21 to 22 3 and 18osmow 10 7 to 13 1 for basal evaporite and claystone facies are similar to miocene seawater strontium isotopes are less radiogenic than expected for miocene seawater due to interaction with volcanic rocks low s c ratios high mn contents and sedimentological evidence indicate the basin water column was oxidizing the oxygenated basin restricted sulfide precipitation to within the sedimentary pile by replacement of early diagenetic framboidal pyrite and pore space filling by cu co zn sulfides to produce disseminated sulfides quartz mn oxide oxygen isotope geothermometry constrains mineralization temperature between 18 and 118 c sulfur isotopes indicate the following sources of sulfide 1 bacterial sulfate reduction within the sedimentary pile produced negative 34s values 20 in framboidal pyrite and 2 bacterial sulfate reduction at high temperature 80 118 c within the sedimentary pile during the infiltration of the metal bearing brines produced cu co zn sulfides with negative but close to 0 34s values isotope modeling of fluid rock reaction and fluid mixing indicates 1 sedimentary and marine carbonates 13c 11 6 to 3 2 and 18o 19 0 to 21 8 precipitated from basin seawater pore water that variably mixed with isotopically depleted meteoric waters and 2 hydrothermal calcite 13c 7 9 to 4 3 and 18o 22 1 to 25 8 formed by dissolution and replacement of authigenic marine calcite by downward infiltrating metalliferous brine and brine sediment exchange that prior to reaction with calcite had mixed with isotopically depleted pore water the downward infiltration of metalliferous brine is inferred from lateral and stratigraphic metal distributions and from the concentration of cu sulfides along the upper contact of pyrite bearing laminae the co existence and textural relationships among framboidal pyrite base metal sulfides carbonate and mn fe oxides including magnetite within mineralized units are consistent with carbonate replacement and high temperature bacterial reduction within the sedimentary pile occurring simultaneously below a seawater column under predominantly oxygenated conditions

fluxes of metals to a manganese nodule radiochemical chemical structural and mineralogical studies fluxes of metals to the top and bottom surfaces of a manganese nodule were determined by combining radiochemical 230th 231pa 232th 238u 234u and detailed chemical data the top of the nodule had been growing in its collected orientation at 4 7 mm myr 1 for at least 0 5 myr and accreting mn at 200 g cm 2 kyr 1 the bottom of the nodule had been growing in its collected orientation at about 12 mm myr 1 for at least 0 3 myr and accreting mn at about 700 g cm 2 yr 1 although the top of the nodule was enriched in iron relative to the bottom the nodule had been accreting fe 50 faster on the bottom 232th was also accumulating more rapidly in the bottom despite a 20 fold enrichment of230th on the top the distribution of alpha emitting nuclides calculated from detailed radiochemical measurements matched closely the pattern revealed by 109 day exposures of alpha sensitive film to the nodule however the shape and slope of the total alpha profile with depth into the nodule was affected strongly by226ra and222rn migrations making the alpha track technique alone an inadequate method of measuring nodule growth rates diffusion of radium in the nodule may have been affected by diagenetic reactions which produce barite phillipsite and todorokite within 1 mm of the nodule surface however our sampling interval was too broad to document the effect we have not been able to resolve the importance of nodule diagenesis on the gross chemistry of the nodule

a geochronological 40ar 39ar and 87rb 87sr study of k mn oxides from the weathering sequence of azul brazil k mn oxides of hollandite group minerals such as cryptomelane k1 2 mn3 mn4 8o16nh2o are often precipitated authigenically in weathering profiles the presence of structural k allows these minerals to be dated by the k ar and 40ar 39ar methods making it possible to study the progression of oxidation fronts during weathering processes within the context of a recent 40ar 39ar study of cryptomelane from the azul mn deposit in the carajas region amazonia brazil vasconcelos et al 1994 defined three age clusters 65 69 51 56 and 40 43 ma and proposed that they correspond to the episodic precipitation of the three generations of mn oxide that have been identified in the deposit beauvais et al 1987 we performed a laser probe 40ar 39ar and 87rb 87sr study on new samples from the same mn deposit our 40ar 39ar data confirm that cryptomelane is a suitable mineral for 40ar 39ar dating although in some cases we clearly identify the existence of 39ar recoil effects although the corresponding age spectra are generally strongly disturbed our results also confirm that the earliest cryptomelane generation is of upper cretaceous paleocene age we obtained good plateau ages from veins and concretions of the second cryptomelane generation some of these results allow definition of a well constrained age cluster at 46 7 48 1 ma not observed by vasconcelos et al 1994 a petrographic study confirms that none of the samples analyzed in the present study contained material associated with the third generation of cryptomelane we propose that these new results support the idea of a more or less continuous crystallization of k mn oxides mainly constrained by local factors rather than the model advanced by vasconcelos et al 1994 which suggests that each cryptomelane generation corresponds to distinct weathering events related to global climatic changes 87sr 86sr data show large variations clearly inherited from the 2 1 ga parent rock of the mn protore the rb sr results demonstrate that minimum fractionation occurs during cryptomelane crystallization except for the latest generation which is depleted in sr this precludes use of the rb sr radiochronometer for dating secondary mn oxides in laterites

isotopic dating of supergene manganese oxides from the groote eylandt deposit northern territory australia a total of 51 conventional k ar dates on 22 manganese oxide samples from the groote eylandt manganese deposit is presented because most of the samples contained detrital mica from the bedrock k ar ages and their standard errors were corrected using material balance equations following determination of the contribution of radiogenic argon and potassium from the silicate residue in this way the times of formation of cryptomelane ba todorokite and romanechite and probably also vernadite were estimated in addition high resolution 40 ar 39 ar dating was used to date growth bands of pure void filling cryptomelane corrected k ar ages show that cryptomelane and ba todorokite the latter previously thought to be of diagenetic origin were precipitated between 18 and 6 ma early to late miocene as a result of chemical weathering through widespread dissolution and in situ replacement of pisoliths and ooliths romanechite in the lower part of the profile in the g south quarry must be older than 43 7 or 1 2 ma in the upper part of the g south quarry profile romanechite formed at about 30 ma these ages together with the cryptomelane and ba todorokite ages appear to define several episodes of intense chemical weathering in this deposit during the tertiary a pre late eocene episode older than 43 7 or 1 2 ma an oligocene episode around 30 ma and a miocene weathering megacycle 6 18 ma it is suggested that these weathering related processes had a much more significant effect on development of the deposit than previously thought the present mineralogy was produced by replacement processes during the tertiary associated with intense chemical weathering and not by sedimentary or diagenetic processes isotopic ages on manganese oxides from groote eylandt are similar to those determined on manganese oxides from northwestern australia and brazil indicating that periods of intense weathering in the tertiary recording humid climatic conditions were relatively widespread

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

geologic setting and origin of the lucifer manganese deposit baja california sur mexico high grade stratiform manto hosted by sandy tuff of the lower pliocene boleo formation with which it is in part syngenetic ore deposition occurred in a shallow marine basin mineralized fractures and hydrothermal alteration observed in the vicinity of the proposed source area suggest that the ore solutions originated from hot springs two types of alteration are related to mineralization 1 destruction of mafic silicate minerals in volcanic rocks and 2 argillization of glassy groundmass material modified journal abstract

timing of weathering induced alteration of manganese deposits in western australia evidence from k ar and 40 ar 39 ar dating under particular climatic conditions tetravalent k mn oxides can be formed during terrestrial chemical weathering of mn ores in this study the results of k ar and 40 ar 39 ar dating of weathering related k mn oxides mainly cryptomelane k ba mn 8 o 16 xh 2 o from supergene mn deposits in the pilbara and peak hill mn provinces nw australia and from scattered occurrences of k mn oxides found in deeply weathered rocks in western australia are presented in ideal circumstances k ar and 40 ar 39 ar ages will reflect the time since the formation of k mn oxides however 40 ar 39 ar and k ar dating of k mn oxides which formed as a result of chemical weathering may be complicated by admixture of mica inherited from bedrock and by mixing of different generations of weathering related k mn oxides to correct for admixture of inherited mica a two stage k ar dating technique was applied some samples of dated cryptomelane had finely banded textures and therefore might represent several generations the age differences between these generations were investigated using microsampling and laser microprobe 40 ar 39 ar dating total fusion age determinations of several groups of growth bands of a late oligocene densely layered cryptomelane from the woodie woodie mn deposit nw australia suggest an averaged growth rate of 0 8 or 0 3 mm m y however the growth rate calculated for much of the band sequence is 1 5 mm m y which is five times greater than for the remaining youngest group of bands 0 3 mm m y thus suggesting uneven growth rates the low growth rate might be the result of very slow growth of cryptomelane and or the presence of hiatuses in cryptomelane precipitation total fusion ages measured on void filling banded and colloform cryptomelane in samples from a vertical profile through a mesalike deposit near horseshoe nw australia show peaks at 52 to 48 44 to 43 40 to 39 35 30 to 29 and 7 ma these results are interpreted as reflecting formation of weathering products in the deposit over a remarkably extended period possibly in an episodic manner related to alternation of more humid and drier climatic periods during the tertiary the results from this study show some evidence of episodic formation of weathering related manganese oxides within the deposits studied although modification of age patterns by local hydrological and geomorphological factors allows only a limited degree of correlation of these periods on a regional scale

mn ba hg mineralization at shallow submarine hydrothermal vents in bahia concepcion baja california sur mexico coastal submarine hydrothermal venting occurs on the west shore of the fault bounded bay of bahia concepcion along a stretch of about 700 m of rocky shoreline diffuse hydrothermal seepage of water and continuous gas bubbling mainly co2 and n2 take place through the sediment covered seafloor at shallow depth 5 to 15 m in addition at about 500 m se a cluster of hot springs occurs within the intertidal zone the temperature and ph of the hydrothermal fluids varies from 72 to 87 c and 5 95 to 6 02 in the submarine diffuse venting area and reaches 62 c and ph of 6 68 in the intertidal hot springs mn ba hg mineralization is presently forming as a result of the hydrothermal venting at the intertidal hot springs moss like crusts of manganese oxides and structureless detrital aggregates cemented by opal a barite and calcite occur around the main discharge conduits these aggregates are overlaid by silica carbonate fine layered stromatolitic aggregates that extend some meters from the hot springs forming crusts and coalescing rims over volcanic pebbles and boulders manganese crusts are made up of barium rich x ray amorphous todorokite like and romanechite phases and represent a rare example of a manganese deposit formed in a shallow submarine hydrothermal environment in the submarine diffuse venting area the hydrothermal precipitates are less conspicuous and consist in millimeter thick iron oxyhydroxide coatings on volcanic cobbles and boulders these coatings are composed of poorly crystallized six line ferrihydrite accompanied by minor cinnabar and fine grained colloform pyrite textures and fabrics of the mineral assemblages suggest microbial mediation for mineral deposition the vent precipitates display a significant enrichment of hg as and sb arsenic is probably adsorbed onto mn and fe oxide substrates the nasc north american shale composite normalized ree patterns of the vent precipitates show a pronounced positive eu anomaly that is probably inherited from the hydrothermal fluid

genesis of manganese deposits in southwestern amazonia mineralogy geochemistry and paleoenvironment abstract chemical analysis xrd sem and empa were carried out on five manganese deposits in southwestern amazonia brazil to determine their sources of mn their lithostratigraphic units the environment in which mn accumulated during the proterozoic and the effects of weathering since the late cretaceous on the mineralization process the sedimentary hydrothermal and lateritic environments in this area produced a wide and complex variety of structures textures minerals and geochemical features where coronadite hollandite and romanechite as the main mn minerals changed their chemical compositions during the lateritization process in this context during lateritization more mobile elements mgo cao na 2 o and k 2 o were removed while concentrations of sio 2 al 2 o 3 fe 2 o 3 mno pb and co increased the high concentrations of cu pb and tl and the presence of positive gd anomalies galena and nuggets of ag and zn ni mno 2 in both the protoliths and duricrusts indicate that the ze juliao apui and novo natal deposits record the influences of sulfide and hydrothermal activity the ree zr hf vs tio 2 1000 co ni ratios indicate that felsic and mafic rocks were the sources of mn in these samples

age and duration of weathering by 40k 40ar and 40ar 39ar analysis of potassium manganese oxides supergene cryptomelane k1 2 mn3 mn4 8o16 h2o samples from deeply weathered pegmatites in southeastern brazil subjected to 40k 40ar and 40ar 39ar analysis yielded 40k 40ar dates ranging from 10 1 0 5 to 5 6 0 2 ma million years ago laser probe 40ar 39ar step heating of the two most disparate samples yielded plateau dates of 9 94 0 05 and 5 59 0 10 ma corresponding within 2 to the 40k 40ar dates the results imply that deep weathering profiles along the eastern brazilian margin do not reflect present climatic conditions but are the result of a long term process that was already advanced by the late miocene weathering ages predate pulses of continental sedimentation along the eastern brazilian margin and suggest that there was a time lag between weathering and erosion processes and sedimentation processes

geochemical constraints on the genesis of the montana de manganeso vein type mn deposit mexican plateau abstract manganese mineralization at montana de manganeso san luis potosi state consists of oxide ores that form sharp contacts with volcanic host rocks the orebodies are generally in the form of veins and irregular masses and locally as mineralized breccias petrographic analyses indicate that the mineralization is multi episodic with colloform and crustiform textures predominating the x ray diffraction and electron microscopy show that manganese oxides todorokite birnessite pyrolusite romanechite and cryptomelane are the main ore minerals while iron oxides goethite and hematite are accessory the most common gangue minerals are calcite and quartz with subordinate amounts of barite according to fluid inclusion microthermometry the mineralization is associated with aqueous solutions of intermediate salinity 8 to 16 wt nacl equivalent and temperatures between 101 and 140 c stable isotope analysis of calcite 13cpdb 7 76 to 6 32 18opdb 8 01 to 4 71 and barite 34s 7 9 to 13 6 shows a contribution of magmatic volatiles to hydrothermal fluids dominated by meteoric water calculated 18ofluid 6 58 to 13 14 relative to smow argillic alteration is the most widespread hydrothermal alteration at montana de manganeso and indicates fluid temperature below 150 c and near neutral ph much more local advanced argillic alteration revealed by the occurrence of kaolinite is interpreted as a steam heated overprint which in turn suggests a boiling process that must have happened at greater depths the mn ores formed through a process of mixing of a boiled off hydrothermal fluids with b cold diluted meteoric water our results support a hot spring deposit model according to which montana de manganeso corresponds to the shallowest portion of an epithermal system formed in a continental volcanic arc setting

contrasting mineralogical geochemical signatures of manganese oxides guides to metallogenesis manganese oxides have a strong sorption capacity for cationic species in the depositional fluid this sorption capacity is reflected in the chemistry of the oxides which is different from that for the oxides precipitated from fresh water seawater and hydrothermal fluids characteristic mineralogical geochemical enrichment and geochemical association defined statistically signatures in conjunction with several diagnostic plots can be employed to distinguish between the following different genetic types of manganese deposits supergene hydrothermal supergene marine terrestrial supergene dubhite and supergene marine hydrothermal sedimentary exhalative sedex dubhites are manganese oxides derived from the weathering of a mineralized sequence i e base and precious ore minerals and gangue hydrothermal deposits characteristically show geochemical enrichments in the assemblage as ba cu li mo pb sb sr v zn and an mn as geochemical association supergene marine deposits show na k ca mg sr and co cu ni geochemical enrichments whereas supergene terrestrial deposits tend to have very high ba contents and an mn ba association dubhites contain high levels of pb and zn show an mn pb base metal association and are composed of significant quantities of base metal bearing manganese oxides bixbyite braunite hausmannite huebnerite jacobsite and pyrochroite occur predominantly only in hydrothermal deposits whereas chalcophanite coronadite crednerite delta mno 2 groutite hollandite lithiophorite manganite nsutite quenselite ramsdellite romanechite todorokite and woodruffite are generally of supergene origin in addition to established plots presently used to identify marine sedimentary exhalative deposits the following diagnostic graphs were devised na vs mg distinguishes deposits of marine and fresh water origin co ni vs as cu mo pb v zn discriminates between hydrothermal and supergene oxides and pb vs zn can be used to recognize dubhites and therefore prospective sequences

do microplates in subduction zones leave a geological record active microplate boundaries in ocean continent subduction zones may induce deformation of the overlying plate and spatial or geochemical variations in the volcanic arc we discuss two modern cases the first is the south gorda juan de fuca plate boundary in the cascadia subduction zone where there is little or no effect on the overriding plate and the oceanic plate takes up much of the deformation the second case is the cocos rivera plate boundary in the middle america trench where the overlying colima graben contains substantial deformation in a zone extending from the trench to the volcanic arc and the sub duction related volcanism is spatially and geochemically complex we apply these observations to boundaries of the arguello monterey guadalupe and magdalena microplates which existed in the subduction zone west of baja california at various times from 20 to 12 5 ma the past positions of these boundaries relative to baja california are constrained by global plate reconstructions closure of the gulf of california and an estimate of extension in the mexican basin and range province existing regional mapping and our additional reconnaissance mapping show that paleocene to eocene fluvial and marine sedimentary rocks south of ensenada along the western baja california peninsula and eastward to the mid miocene volcanic arc are undeformed limited available data reveal no major spatial or geochemical variations in the mid miocene volcanic arc that might correlate with the past positions of the microplate boundaries thus these microplate boundaries had little to no effect on the overriding continental plate the nature of guadalupe and magdalena interactions with north america may have been closer to the south gorda juan de fuca example with possible internal deformation of the microplates the monterey and arguello microplates may have behaved like the modern explorer plate with largely strike slip motion relative to north america during their last stages of existence tectonic patterns similar to these examples may be expected from other plate boundaries where a plate is fragmenting as it enters a subduction zone e g the aluk plate in the trench beneath west antarctica in early tertiary time whether these microplates subsequently become attached to the overriding continental plate or to a larger oceanic plate and whether this causes deformation in the region of the former subduction zone may depend on the velocities of the nearby major plates and the relative orientations of the microplate boundaries

rare earth elements in pore waters of marine sediments abstract the rare earth elements rees were measured in pore waters of the upper 25 cm of sediment from one site off peru and three sites on the california margin the pore water ree concentrations are higher than sea water and show systematic down core variations in both concentration and normalized pattern from these analyses and from comparison to other chemical species measured dissolved fe mn ba oxygen nitrate phosphate it is suggested that pore water rees can be grouped into three categories those that are from an fe source those that are from a poc source and cerium oxide rees from the fe source appear where anoxia is reached they have a distinctive middle ree mree enriched pattern the concentrations in this source are so elevated that they dominate ree trends in the fe oxide reduction zone the net result of flux from the poc source is relative enrichment of heavy rees hrees over light rees lrees reflecting remineralizing poc and complexation with doc a common linear ree pattern seen in both oxic and anoxic sediments is associated with this poc source as well as a hree enriched pattern that is seen in surficial sediments at the peru site overall the pore water results indicate that mn oxides are not an important carrier of rees in the oceans a ree biogeochemical model is presented which attempts to reconcile ree behavior in the water and sediment columns of the oceans the model proposes that poc fe oxide and ce oxide sources can explain the ree concentration profiles and relative abundance patterns in environments ranging from oxic sea water to anoxic pore water the model is also consistent with our observation that the ce anomaly of pore water does not exceed unity under any redox condition

variability of mn fe ni cu and co in manganese nodules from the central indian ocean basin abstract the trace element variations in manganese nodules from the central indian ocean basin have been related to the underlying sediment type percentages of mn cu and ni are high in nodules occurring in siliceous sediments compared with nodules from the red clays which contain higher fe and co clustering of analyses shows that ni and cu are geochemically associated with mn and co with fe in both sediment types however the degree of correlation between all the elements is higher in the nodules from red clay sediments compared to the siliceous ooze area nodules similarly there is an increase in the ni and cu values and a decrease in co content with increasing mn fe ratio but the scatter plot of the elements from the red clay sediments show more linearity than the siliceous sediments where the plots are more scattered the variations in the mn fe ratio reflect variability in the composition of bottom water which in turn influences the type of underlying sediments and supply of metal to the deposits the higher concentrations of mn ni and cu in the nodules from siliceous sediments reflect the influence of early diagenesis of the biogenic components whereas the higher fe and co contents in the nodules occurring in red clay areas are a result of their precipitation as authigenic oxyhydroxides

structural controls and timing of fault hosted manganese at woodie woodie east pilbara western australia abstract high grade fault hosted manganese deposits at the woodie woodie mine east pilbara are predominantly hydrothermal in origin with a late supergene overprint the dominant manganese minerals are pyrolusite braunite and cryptomelane the ore bodies are located on or near the unconformities between the neoarchean carawine dolomite and the paleoproterozoic pinjian chert breccia weathering product of carawine dolomite and sedimentary units of the overlying ca 1300 1100 ma manganese group stratabound manganese is typically located above or adjacent to steep fault hosted manganese the ore bodies range in size from 0 2 to 5 5 mt with an average of 0 5 mt historically over 35 mt of manganese has been mined at woodie woodie and current ore resources are 29 94 mt at 39 94 mn 6 96 fe resource and reserves statement june 2011 consolidated minerals pty ltd manganese mineralization at woodie woodie is related to northwest southeast directed extension and basin formation during the mesoproterozoic basin architecture is generally well preserved and major manganese occurrences are localised along growth faults which down throw the pinjian chert breccia into local extensional basins manganese ore bodies are typically located on steep 2nd and 3rd order structures that extend off the major growth faults mineralized structures display a dominant northeast trend reflecting the direction of maximum dilation during northwest southeast extension a paragenetic sequence is identified for the manganese ore at woodie woodie with early hydrothermal braunite pyrolusite cryptomelane todorokite hausmannite overprinted by late supergene oxides preliminary fluid inclusion studies in quartz crystals intergrown with pyrolusite and cryptomelane indicate that primary and pseudosecondary inclusions display a range of salinities from 1 to 18 eq wt nacl and trapping temperatures estimated to be from 220o to 290o at 1 kbar pressure a lead manganese oxide coronadite is common in manganese ores at woodie woodie and pb isotope studies of 40 lead rich ore samples from 16 pits indicate mineralization occurred within an age range of 955 1100 ma a mixed source is suggested for the lead but was predominantly basalts and or volcanogenic sedimentary units e g jeerinah formation of the ca 2700 ma fortescue group the typically high mn fe ratios and enrichment in elements such as pb as cu mo zn are consistent with a dominantly hydrothermal origin for the manganese at woodie woodie supergene manganese is distinguished from hypogene manganese by a marked enrichment in ree in the supergene manganese an early structural framework established during neoarchean rifting provides a major structural control on manganese ore distribution the woodie woodie mine corridor is located in a zone of oblique strike slip extension on major northwest trending transform faults and north trending oblique normal faults a major transform structure at the southern end of the woodie woodie mine corridor jewel southwest fault zone likely acted as a major fluid conduit for manganese bearing hydrothermal fluids and this would account for the concentration of significant manganese ore occurrences to the north and south of this structure

direct dating of weathering phenomena by 40ar39ar and k ar analysis of supergene k mn oxides abstract potassium bearing manganese oxides cryptomelane k1 2 mn3 mn4 8 o16 xh2oand hollandite k ba 1 2 mn3 mn4 8 o16 xh2o are often authigenically precipitated in weathering profiles the presence of structural potassium in manganese oxides makes these minerals datable by the k ar and 40 ar 39 ar methods dating of these phases allows us to time the progression of oxidation fronts during weathering and pedogenic processes detailed age resolution of the weathering history allows us to use deep weathering profiles as land based stratigraphic records of past climatic and geomorphic events complementing evidence from the marine sedimentary and paleontological record potential problems in manganese oxide dating such as ar and or k losses excess argon 39ar loss by recoil during neutron irradiation contamination by primary minerals resistant to weathering the presence of multiple generations of manganese oxides and proportionately low radiogenic ar yield due to adsorbed atmospheric gases are addressed the k ar and 40 ar 39 ar analytical results indicate that ar and or k losses excess 40ar and 39ar recoil seem not to pose problems in manganese oxide dating this investigation suggests that fine scale laser probe 40 ar 39 ar technique is most appropriate for dating of weathering phenomena because this technique permits us to identify contaminating phases and the presence of multiple generations of weathering minerals in the inherently complex mineral assemblage characteristic of weathering profiles k ar and 40 ar 39 ar dating of supergene k bearing manganese oxides formed during lateritization of archean and proterozoic bedrocks in the caraj s region amazonia brazil indicates that weathering started before 72 6 ma petrographic electron microscope and electron microprobe investigation reveal multiple generations of manganese oxide precipitation k ar and 40 ar 39 ar laser probe step heating results independently confirm the presence of these various generations of manganese oxides age clusters at 65 69 51 56 40 43 33 35 20 24 12 17 ma and zero age 0 2 0 2 ma suggest episodic precipitation of k mn oxides resulting from changing weathering conditions in the amazon throughout the cenozoic k ar and 40 ar 39 ar dating of supergene cryptomelane from weathering profiles in eastern minas gerais southeastern brazil suggests continuous weathering from 10 to 5 6 ma ago possibly reflecting local climatic conditions due to the proximity with the atlantic ocean

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

geology geochemistry and re os systematics of manganese deposits from the santa rosalia basin and adjacent areas in baja california sur mexico the manganese ores in the santa rosalia region western mexico are mainly stratiform horizons or mantos constrained to the initial stages of sedimentary cycles of the miocene boleo formation the manganese mineralization is generally restricted to isolated paleo basins and related to nw se faults formed during the early stages of the opening of the gulf of california jasper fe and mn oxides associated to the nw se structures may represent feeder zones for the mineralized system the manganese oxide minerals include pyrolusite cryptomelane todorokite hollandite jacobsite and pyrochroite trace elements in the manganese ores indicate a hydrothermal origin for the deposits of the santa rosalia area rare earth elements ree patterns obtained for manganese minerals from the lucifer and el gavilan deposits also support a hydrothermal origin whereas the middle ree enrichment observed in samples from the boleo district indicates mixing between hydrothermal and hydrogenous sources osmium and rhenium concentrations of the manganese minerals range between 33 173 ppt and 0 14 89 ppb respectively the initial 187os 188os ratios in the manganese oxides from lucifer and the boleo district range between 0 43 to 0 51 and 0 70 to 0 74 respectively these ratios are different from seawater at 7 ma 0 84 0 89 which suggests important contributions of osmium from underlying rocks such as the miocene volcanic rocks and the cretaceous quartz monzonite basement field evidence manganese oxide mineralogy coupled with major and trace element geochemistry and re os systematics support a hydrothermal origin for the manganese deposits from the santa rosalia region the ore deposition style indicates an exhalative intraformational environment restricted to isolated basins in a diagenetic stage related to the initial evolution of the gulf of california

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

geochemistry of supergene manganese oxide deposits groote eylandt australia some 20 different supergene mn oxide ores and associated secondary rocks from the groote eylandt manganese deposit were analyzed for their major minor and trace element content this is the first detailed account of the trace element geochemistry from this deposit and the data presented here should aid in future comparative studies due to the complex nature of the secondary ores and rocks at groote eylandt it is difficult to differentiate supergene products purely on the basis of their trace element composition however we are able to correlate groups of trace elements to individual minerals using a quantitative normalization technique that determines the mineralogical composition of the samples members of these groups tend to be elements with specific ionic radii contained in the following host phases pyrolusite approximately 0 4 aa and or 1 aa cryptomelane and todorokite approximately 0 7aa romanechite no significant correlation detected kaolinite approximately 0 6 0 8 and 1 0 aa and goethite approximately 0 4 aa generally distinctive supergene horizons enriched in certain elements e g zn sr and minerals develop within the stratigraphic section kaolinite in particular seems to form laterally continuous layers that crosscut primary sedimentary units most other minerals also show a stratigraphy controlled abundance cryptomelane todorokite romanechite and gibbsite usually concentrate in higher parts of the profile whereas pyrolusite and quartz increase down the section

k ar dating young rhyolitic rocks a case study of the sierra la primavera jalisco mexico this study demonstrates the feasibility of dating by the k ar method an eruptive sequence of silicic volcanic rocks with ages close to the limits of conventional 14 c dating forty six conventional k ar analyses of sanidine and glass from rhyolites of the sierra la primavera mexico yielded dates of 5 to 150 ka thousand years one sigma errors range from 3 to 39 ka although the samples contain small amounts of extraneous argon most of the dates are consistent with relative ages determined in the field the exceptions are dates on immediately postcaldera eruptive units which are older than the dates for the caldera producing ash flow tuff a similar result has been obtained on dating tuffs and lavas of some other pleistocene calderas this effect is attributed to incomplete outgassing of the larger amount of extraneous argon dissolved in magma that occupied a position deeper in the chamber than the ash flow tuff magma and that erupted immediately after caldera collapse we present two new error equations one a simple extension of the commonly used equation demonstrates the importance of including a term for the uncertainty in the spectrometer mass discrimination factor in the error equation the second equation is a more rigorous formulation of the propagation of errors in the calculation of the age it yields meaningful error estimates for all proportions of radiogenic 40 ar and because it expresses the error in absolute rather than relative terms it can be used to put an upper limit on the age of a sample when no radiogenic 40 ar has been resolved

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

manganese oxide mineralogy petrography and genesis pilbara manganese group western australia supergene manganese oxides occurring in shales breccias and dolomites of proterozoic age in the western australian pilbara manganese group have mn fe ranging from 1 9 to 254 and mn4 to mn total of 0 49 0 94 the manganese mineralogy is dominated by tetravalent manganese oxides especially by cryptomelane with lesser amounts of pyrolusite nsutite manjiroite romanechite and other manganese oxide minerals the manganese minerals are commonly associated with iron oxides chiefly goethite indicating incomplete separation of mn from fe during tertiary age arid climate weathering of older manganiferous formations these manganese oxides also contain variable amounts of braunite and very minor hausmannite and bixbyite the braunite occurs in three generations sedimentary diagenetic recrystallised sedimentary diagenetic and supergene the mode of origin of the hausmannite and bixbyite is uncertain but it is possible that they resulted from diagenesis and or low grade regional metamorphism the supergene manganese deposits appear to have been derived from manganiferous lower proterozoic banded iron formations and dolomites of the hamersley basin and overlying middle proterozoic bangemali basin braunite containing sediments

irregular plate boundary controls on foreland basin sedimentation miocene kahramanmaras foreland basin se turkey abstract the northern movement of the arabian plate led to the development of a compressional regime in the south eastern part of turkey after the late cretaceous the collision of the arabian plate with the anatolide taurides platform and subsequent development of the kahramanmaras foreland basin at the beginning of the miocene evolved as a result of this movement an irregular plate geometry or promontory of the arabian plate caused partitioning of the plate margin precollision collision postcollision this irregular plate boundary was delimited by western and northern boundary faults and an interior basin fault the nw oriented small wedge top basins on the overlying anatolide taurides platform obliquely cut through the foredeep basin the region across the wedge top basin on the irregular promontory of the underlying arabian plate contains different sedimentation depocentres small fining upward submarine fan deposits including pebbly channel deposits and coarsening upward lobe sequences are located at the centre of the irregular part of the plate in the tanir region and overlie planktic foraminifera bearing claystones these submarine fan sediments pass outboard into distal interbedded turbidite claystones and siltstones in a downdip direction s se the boundary fault intersection of the promontory led to the development of a submarine slope environment with irregular sea floor topography in the firniz area 4 5 km south east of the tanir region the slump deposits sandy debrites and fine grained thin bedded turbidites filled this region structural alignments and seismicity associated with the plate margin were the main controlling factors on the geometry of the depocentre sediment quantity sediment input sedimentary facies local sea level changes and post sedimentary deformation in the kahramanmaras foreland basin

a hydrothermal manganese deposit from the eratosthenes seamount eastern mediterranean sea abstract a manganese crust horizon is described from the eratosthenes seamount south of cyprus in the eastern mediterranean sea its morphological and geochemical features coupled with its geotectonic setting suggest that submarine hydrothermal activity is responsible for its formation

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

development of tectonic cyclothems in rift pull apart and foreland basins sedimentary response to episodic tectonism the thickest part of asymmetric rift pull apart and foreland basin fills commonly consists of large scale hundreds to thousands of metres thick tectonically generated cyclothems of fine grained marine lacustrine or longitudinal fluvial deposits and coarse grained transverse braid plain or alluvial fan deposits the appearance of coarse clastics in these basin fills is typically noted as the time of tectonically rejuvenated source area uplift based on the conceptual tie between relief and coarse grain size and on the application of the davis theory of landform development we propose the opposite interpretation that the commencement of fine grained sedimentation above coarse grained deposits in a tectonic cyclothem is the best indicator of renewed tectonic activity this reinterpretation is more consistent with 1 modern examples 2 the consideration of source area and sedimentary basin geomorphology 3 the disparity between the reaction rates of the various environments to subsidence 4 the disparity between the rates of tectonic uplift and erosion and 5 the controls on elastic wedge progradation in our model extensive coarse grained clastic wedge progradation is an indicator of tectonically quiescent phases

potential toxicity of chemical elements in beach sediments near santa rosalia copper mine baja california peninsula mexico abstract a total of 17 beach sediment samples were analyzed for the determination of thirty one chemical elements to generate a geochemical data set from the santa rosalia mining area in the state of baja california sur south mexico results indicate that the beach sediments were enriched in cu zn co pb cd 3856 2599 635 236 240 mg kg 1 respectively and in mn 2 01 due to a century of mining and smelting activities comparison of these concentration with ecotoxicological sediment quality criteria erl erm lel sel indicated the values of as cd co cr cu ni pb sr zn and mn were higher than the permissible limits average values of the calculated geoaccumulation index i geo suggest that the key elements such as mn ba cd co mo pb sr zn are categorized in class 4 to 6 encompassing the strongly polluted to extremely polluted groups the association and enrichment of the above elements are also well supported statistically factor analysis which points to the role of fe mn oxides as the main scavengers for retaining these chemical elements

pre pliocene extension around the gulf of california and the transfer of baja california to the pacific plate late miocene 12 5 ma extension around the edges of the gulf of california has been alternatively attributed to basin and range extension back arc extension or development of the pacific north america plate boundary this extension was ene directed and similar in structural style to extension in the basin and range province timing constraints permit nearly synchronous onset of this deformation in a belt extending sse from northernmost baja california to the mouth of the gulf where this extensional faulting continued through pliocene time to the present synchronous with motion on the modern transform plate boundary in the gulf of california no change in direction of extension can be resolved revised constraints on pacific north america plate motion support the development of this late miocene extension as a component of pacific north america displacement that could not be accommodated by strike slip displacement along the existing plate boundary west of the baja california peninsula this scenario implies that transfer of baja california from the north america plate to the pacific plate was a gradual process beginning about 12 10 ma when motion of the pacific plate relative to north america was partitioned into separate regimes of strike slip and dip slip displacement on opposite sides of baja california

metalliferous manganese oxide mineralization associated with the boleo cu co zn district mexico apart from its large reserves of cu co zn mineralization contained within stratiform ore beds or mantos the boleo district of central baja mexico also contains significant concentrations of mn oxides typically 2 3 wt mn interspersed with hydrothermal sulfides and both hydrothermal and weathering related metal oxide minerals within the mantos mn oxides occur as concentric nodules disk shaped concretions laminae granules or aggregates veins dendrites and various replacements the oxides are composed of varying amounts of hollandite cryptomelane todorkite romanechite pyrolusite and x ray amorphous mn oxide chemically the manto oxides are unique owing to their extraordinarily high abundances of co cu pb and zn typically 2 5 wt but up to 23 wt existing mineralogical and geochemical classifications are ambiguous regarding the genetic classification of mn oxides within the mantos a new mno 2 fe 2 o 3 t mgo diagram is proposed in order to discriminate among highly metalliferous mn oxides based on the new classification scheme manto mn oxides record a complex interaction between hydrothermal and diagenetic processes to better understand the mechanism of oxide deposition radiogenic isotopes sr and pb and ree geochemistry were used to delineate fluid and metal sources isotopic and ree constraints indicate that the boleo mn oxides are largely hydrothermal in origin however they show varying degrees of modification resulting from diagenetic processes hydrothermal mn oxides are syngenetic synsedimentary to syndiagenetic in origin and were precipitated in association with sulfides reflecting localized variations in redox conditions within the manto sequence due to the downward infiltration of metal bearing brines apart from morphological and stratigraphic evidence e g occurrence of nodular crusts along the upper contact of the manto a syngenetic origin is supported by a single k ar date of 7 0 0 2 ma which is within the estimated age range for deposition of boleo formation clastic sediments interaction between brine and seawater or brine and pore fluid as it infiltrates the sedimentary pile produced hydrothermal precipitates with certain hydrogenetic attributes i e positive ce anomaly lree enrichment on the other hand oxides with hydrogenetic and with mixed hydrothermal hydrogenetic affinities represent diagenetic alteration and remobilization of earlier formed hydrothermal oxides by meteoric fluids by far the greatest degree of remobilization occurred in response to compactional dewatering of the manto where the dewatering pore waters enriched the uppermost manto strata in mn fe zn co and to lesser degrees cu later diagenetic modifications coincided with the development of a supergene overprint which typifies boleo formation strata at elevations above the present day water table

a hydrothermal deposit from explorer ridge in the northeast pacific ocean abstract crusts composed of nontronite and ferromanganese oxides were recovered from explorer ridge a spreading ridge segment in the northeastern pacific ocean located off the west coast of canada the chemical and mineralogical composition of the crusts closely resembles that of the mound like hydrothermal deposits recently discovered at the famous site on the mid atlantic ridge and on the galapagos spreading centre compositional anomalies suggest that the crusts are precipitates of hydrothermal vent solutions which were ejected discontinuously and subsequently mixed with seawater

an age constraint on gulf of california rifting from the santa rosalia basin baja california sur mexico marine rocks of the santa rosalia basin baja california sur were sampled in a pilot study to determine their suitability for magnetostratigraphy and geochronology with the goal of providing an age constraint on gulf of california rifting progressive demagnetization of samples from the boleo formation the earliest marine sequence overlying the deeply eroded basement reveals a high coercivity characteristic remanent magnetization chrm in addition to a low coercivity overprint the chrm appears to be a primary magnetic remanence with stratigraphically bound normal and reversed polarity directions a single 40 ar 39 ar isotopic age of 6 76 0 90 ma 2 was obtained for the cinta colorada a tephra deposit of reversed paleomagnetic polarity within the boleo formation the age of the cinta colorada is refined by calculating isotopic age probabilities for each of the reversed polarity intervals of the geomagnetic polarity time scale gpts in the 2 range 5 86 7 66 ma the interval with the highest probability is 6 57 6 94 ma in conjunction with the isotopic age preliminary magnetostratigraphy of the boleo formation is correlated with the gpts in order to further delineate the onset of marine sedimentation the most likely correlation yields an age of 6 93 7 09 ma gpts subchron c3bn for the base of the boleo formation and 6 14 6 27 ma for the top this correlation indicating an average sedimentation rate of 28 4 cm k y could be significantly altered if a more thorough magnetostratigraphy proved the existence of additional polarity intervals in the boleo formation however even if the isotopic age of the cinta colorada is used as the only age constraint the result is consistent with data from the northern gulf of california and shows that rifting started much earlier than the ca 3 6 ma commencement of sea floor spreading at the mouth of the gulf of california the deposition of the boleo formation was probably related to an early phase of gulf rifting caused by a change in pacific north american plate motions