manganiferous phyllosilicate assemblages occurrences compositions and phase relations in metamorphosed mn deposits mn rich members of the pyrosmalite family mn fe 8si6o15 oh cl 10 friedelite and schallerite have been identified as rock forming minerals together with caryopilite in several metamorphosed carbonate mn deposits the phase assemblages and mineral compositions are described for eight of these localities each of which represents a distinct geologic situation friedelite is always cl bearing and occurs both as a prograde phase in low grade metamorphic rocks pyrenees haute maurienne and as a secondary phase formed by retrogressive replacement of primary anhydrous phases in higher grade rocks schallerite an asbearing relative of friedelite occurs in the greenschist metamorphic deposit of the kodnitztal austria together with other as minerals in these deposits caryopilite is typically formed during retrograde metamorphism by alteration of generally anhydrous mn silicates based upon these occurrences a qualitative petrogenetic grid for the system mno sio2 co2 h2o with the phases friedelite caryopilite pyroxmangite rhodonite tephroite rhodochrosite quartz co2 and h2o is proposed the phase relations imply that cl or as free friedelite is not stable in hydrous systems with respect to caryopilite from the mineral assemblages containing hydrous mn silicates waterrich fluids are inferred during the retrograde metamorphic evolution of the investigated deposits chemical data for mn rich chlorites which are basically members of the clinochlore pennantite series which coexist with the pyrosmalite minerals show the absence of intermediate mn mg ratios this supports the existence of a miscibility gap as previously hypothesized by other authors

tungsten accumulation in pacific ferromanganese deposits tungsten has often been reported in marine ferromanganese deposits and the question arises as to how the large oxyanionic species wo42 enters the appropriate phases very low w concentrations in seawater less than 0 0002 g kg suggest that it is not directly related to precipitation processes of all the comparable marine samples manganese micronodules have the highest w contents in the range 1 4 to 3 6 times 3 higher than in the associated macronodules a depositional record for more than 60 million years obtained for a thick manganese crust shows that the tungsten distribution with depth correlates best with as and to a lesser extent with fe the mechanism favoured for enrichment of w is precipitation onto fine hydrothermal manganese rich particles supplied by ridge volcanic activity such particle plumes are usually released in cycles stay for comparatively long periods in the water column and are then transported from the hydrothermal centres to the deep basins where they settle and probably contribute to the growth of ferromanganese oxide phases on the ocean floor which is mainly by diagenetic and hydrogenetic processes

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

geology and geochemistry of middle eocene maden complex ferromanganese deposits from the elazig malatya region eastern turkey abstract in the study region the puturge precambrian permian metamorphic rocks the upper jurassic lower cretaceous guleman ophiolites the upper cretaceous lower eocene hazar unit the campanian lower maastrichtian aged elazig magmatics and the middle eocene maden complex crop out extensively the maden complex containing ferromanganese mineralization unconformably overlies the puturge metamorphic rocks the guleman ophiolites and the hazar unit and is unconformably overlain by plio quaternary sediments the ferromanganese mn fe ores in the elazig malatya region eastern turkey are hosted in the mudstone member of the volcano sedimentary part of the middle eocene maden complex as lenses or interbedded layers in the elazig malatya region mn fe ores occur at eight localities namely beyhan palu sarikamis kockale germili hazar alihan and kom mn fe ores are found in the kockale and palu deposits as a single bed but in the hazar and kom deposits as two beds and in the sarikamis germili and alihan deposits in three levels the thickness of these mineralized levels ranges from 0 3 m to 10 m all the investigated mineralizations are conformable with the foot wall mudstones braunite bixbyite jacobsite pyrolusite manganite and psilomelane are the main manganese oxide minerals hematite barite and pyrite are also found in variable amounts in the ferromanganese ores the trace element content of all studied ferromanganese deposits is generally in low concentrations and tends to enrichment in the assemblage of ba sr v cu pb zn and as with a geochemical characteristic similar to hydrothermal deposits rare earth element ree patterns of the maden complex mn fe deposits support a hydrothermal origin with a slight enrichment in the middle ree 4 04 29 91 ppm average 16 49 and a slightly high concentration of total ree 92 40 738 23 ppm average 517 85 in all the investigated deposits ree patterns displayed negative ce 0 08 to 0 72 average 0 15 and eu 0 55 to 0 82 average 0 72 anomalies this shows that low temperature hydrothermal fluids played an important role in the formation of mineralization the ore deposition is similar to that of sedimentary exhalative mineralization deposited within the maden marginal basin

measured shear rates in large dry and wet snow avalanches we present estimates of internal shear rates of real scale avalanches that are based on velocity measurements optical velocity sensors installed on the instrument pylon at the swiss vallee de la sionne test site are used to measure flow velocities at different flow heights of three large dry and wet snow avalanches possible sources of error in the correlation analysis of the time lagged reflectivity signals measured by optical sensors are identified for real size avalanches these include spurious velocities due to noise and elongated peaks an appropriate choice of the correlation length is essential for obtaining good velocity estimates placing restrictions on the maximum possible accelerations in the flow improves the analysis of the measured data coherent signals are found only in the dense flowing cores we observe the evolution of shear rates at different depths between the front and tail of the flowing avalanche at the front large shear rates are found throughout the depth at the tail plug flows overriding highly sheared layers near the bottom of the flow are observed the measured velocities change strongly with height above the ground and fluctuations around the measured mean velocity can be identified we find that the dense flows are laminar undergoing a transition from supercritical to subcritical flow behaviour from the head to the tail furthermore we provide real scale experimental evidence that the mean shear rate and the magnitude of velocity fluctuations increase with the mean discharge

manganese in pelagic carbonates indication of major tectonic events during the geodynamic evolution of a passive continental margin the jurassic european margin of the tethys ligurian sea abstract mid oceanic hydrothermal activity is the main source of manganese in the pelagic realm consequently long term fluctuations of manganese in bulk carbonates could represent the variations in the hydrothermal flow intensity through time depending on global tectonic activity within this scope we analysed three jurassic sedimentary series in the southeastern basin france thus providing valuable information for further palaeogeographic and geodynamic reconstructions of the european tethyan passive margin the long term variations of the manganese curve can be correlated with second order sea level changes the main transgressive phases early toarcian late aalenian to bajocian and late bathonian to callovian are marked by a manganese content increase whereas the regressive phases late pliensbachian late toarcian to middle aalenian early bathonian to middle bathonian oxfordian are characterized by decreasing trends furthermore some manganese positive anomalies can be superimposed on the global geochemical record of sea level changes these coincide with periods of increasing subsidence rate early toarcian late bajocian middle and late oxfordian and also with phases of extension early aalenian of the european margin of the ligurian ocean the major event is the very sharp increase of manganese content localised in the athleta zone late callovian and corresponds to the first occurrence of oceanic crust moreover the manganese enrichments recorded in carbonates deposited before callovian times may have resulted from hydrothermal emanations during the first stages of rifting

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

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

velocity distribution in snow avalanches in order to investigate the detailed structure of snow avalanches we have made snow flow experiments at the miyanomori ski jump in sapporo and systematic observations in the shiai dani kurobe canyon in the winter of 1995 1996 a new device to measure static pressures was used to estimate velocities in the snow cloud that develops above the flowing layer of avalanches measurements during a large avalanche in the shiai dani which damaged and destroyed some instruments indicate velocities increased rapidly to more than 50 m s soon after the front velocities decreased gradually in the following 10 s velocities of the lower flowing layer were also calculated by differencing measurement of impact pressure both recordings in the snow cloud and in the flowing layer changed with a similar trend and suggest a close interaction between the two layers in addition the velocity showed a periodic change power spectrum analysis of the impact pressure and the static pressure depression showed a strong peak at a frequency between 4 and 6 hz which might imply the existence of either ordered structure or a series of surges in the flow

tectonic control of guadalupian lopingian cherts in northwestern sichuan basin south china abstact cherts have been considered to be formed mainly through processes involving biosilicification riverine inputs and hydrothermal activities in the permian massive cherts are widely distributed in south china bearing significant implications for the reconstruction of paleogeography and paleoceanography of the eastern paleo tethys ocean the origin of the permian cherts in south china however remains inconclusive due to a lack of systematic petrographic and geochemical study in this article we analyze the petrologic and geochemical characteristics of the cherts collected from five outcrops in the northwestern sichuan basin south china these cherts are found from the upper guadalupian maokou formation ca 268 259 ma and upper lopingian dalong formation ca 254 252 ma field and microscopic observations suggest that cherts from the maokou formation occur mainly in nodular forms and consist of microcrystalline quartz silicified bioclasts and siliceous fossil debris both petrographic observation and geochemical analysis suggest that the maokou cherts are mainly of hydrothermal origin near deep faults in the southwest and of biogenetic origin with less hydrothermal influence in the northeast of the studied area the dalong cherts occur in both nodular and bedded forms with more abundant siliceous fossil debris than the maokou cherts major trace and rare earth element data support that the dalong cherts are influenced by both biosilicification and hydrothermal activities the spatial heterogeneity of the cherts origin in south china is largely controlled by tectonic activities associated with the emeishan large igneous province elip event and the closure of the paleo tethys ocean the troughs formed by the extensional tectonic activity linked to the elip could provide accommodation space and activate deep faults allowing the rise of silicon rich hydrothermal fluids from the deep and nutrient rich water from volcanogenic upwellings subsequent cooling may have facilitated the precipitation of large amounts of silica and the formation of cherts in the study region this work demonstrates that the origin of the guadalupian lopingian cherts in south china is predominantly controlled by tectonic and biological activities which sheds light on the global permian chert event

decouverte de microstructures de nodules polymetalliques dans les mineralisations manganesiferes metamorphiques de falotta et de parsettens grisons suisse les mineralisations manganesiferes de falotta et de parsettens grisons suisse se manifestent dans les radiolarites du jurassique superieur et elles sont deposees sur les ophiolites du domaine pennique ce minerai presente des microstructures botryoidales caracteristiques des nodules polymetalliques les phases mineralogiques des nodules sous l effet du metamorphisme alpin se transforment de facon progressive en braunite faiblement cristallisee avec un important exces en sio2 a la peripherie des structures botryoidales par contre vers la partie centrale de ces structures la braunite est souvent largement cristallisee sa teneur en sio2 est normale de fines veinules constituees de termes intermediaires de la serie isostructurale de la cryptomelanehollandite recoupent la mineralisation de braunite et indiquent la deuxieme etape dans l evolution du minerai oxyde de falotta et parsettens la troisieme etape est representee par la presence de la todorokite et de la birnessite due a l oxydation des veinules posterieures de rhodonite ces deux oxydes n ont aucun rapport direct avec la mineralisation primaire l existence de structures sedimentaires et volcaniques non deformees dans les ecailles superieures de la nappe de platta permet d expliquer la conservation de microstructures primaires de nodules polymetalliques dans le minerai de braunite la variation de la teneur en sr2 observee lorsque l on va de falotta vers parsettens dans les termes intermediaires de la serie isostructurale de la cryptomelane hollandite ainsi que la destabilisation de la braunite au voisinage des veinules seraient liees a la difference du degre de deformation entre ces deux zones il est important de remarquer que les parametres geochimiques fe mn ou mn co cu ni couramment utilises dans les travaux sur les nodules polymetalliques sont inadequats meme dans les structures les mieux preservees

geochemical constraints on the depositional setting of palaeozoic cherts from the new england orogen nsw eastern australia despite widespread occurrences of radiolarian cherts within the new england orogen neo their age geochemistry and sedimentology have not been studied recent radiolarian age determinations of these cherts have markedly changed previous conceptions as to their age geochemical analyses constrain the depositional setting of two distinctive types of chert facies within two terranes of the orogen type i are ribbon bedded cherts of the djungati terrane and varicoloured ribbon bedded cherts of the anaiwan terrane low values of al al fe mn and corresponding high values of fe2o3 indicate a possible hydrothermal contribution while mnotio2 ratios indicate accumulation far from terrigenous sedimentary influences high si si al fe ratios indicate a high biogenic content type ii are tuffaceous cherts which are common in both terranes high values of al al fe mn and low si si al fe and mnotio2 values indicate deposition in an environment which is more proximal to a terrigenous source than that of type i cherts the abundance of both na2o and al2o3 increases relative to silica in type ii cherts and indicates dilution by the input of volcanic ash this is further substantiated by the ternary k ba v 10 plot an al 1bfe 1bmn diagram indicates that type ii cherts are non hydrothermal in origin both chert types were conveyed into a trench by subduction processes as subduction continued hemipelagic sedimentation was swamped by the influx of coarse grained volcaniclastic sediments deposited from turbidity currents reaching the trench the diverse sedimentary types were tectonically intercalated to form sequences of imbricate thrust slices within two distinctly different subduction complexes which have subsequently been tectonically juxtaposed

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

production and decay of random kinetic energy in granular snow avalanches any model of snow avalanches must be able to reproduce velocity profiles this is a key problem in avalanche science because the profiles are the result of a multitude of snow ice particle interactions that in the end define the rheology of flowing snow recent measurements on real scale avalanches show that the velocity profiles change from a highly sheared profile at the avalanche front to a plug like profile at the avalanche tail preventing the application of a single simple rheology to the avalanche problem in this paper we model not only the velocity profiles but also the evolution of the velocity profiles by taking into account the production and decay of the kinetic energy of the random motion of the snow granules we find that the generation of this random energy depends on the distribution of viscous shearing within the avalanche conversely the viscous shearing depends on the magnitude of the random energy and therefore its collisional dissipation thus there is a self consistency problem that must be resolved in order to predict the amount of random energy and therefore the velocity profiles we solve this problem by stating equations that describe the production and decay of random energy in avalanches an important guide to the form of these equations is that the generation of random energy is irreversible we show that our approach successfully accounts for measured profiles in natural avalanches

cherts of the barberton greenstone belt interpreted as products of submarine exhalative activity cherts studied from the southern barberton greenstone belt are identified as replacement products of various pillow lavas pyroclastic deposits and sedimentary deposits silica filled fracture systems within the cherts have been found to be associated with this silicification process these systems include 1 silica filled fractures 2 silica vein stockworks 3 silica cemented breccias and 4 pseudoconglomerate bodies some of the silica filled fracture systems can be shown to have formed soon after sedimentation silica vein stockworks can be seen to develop laterally into silica cemented breccias the fragments of which have sometimes become rounded within the fracture systems to form pseudoconglomerate the cherts are interpreted as silicified hemi pelagic sediments that overlie pillow lavas some of which are now also cherts cells of convective sea water interacted with oceanic crust to produce silica rich fluids these fluids silicified lava and sediments on re entering the near surface env

geochemistry of manganese bearing cherts associated with alpine ophiolites and the hawasina formations in oman abstract based on correlation coefficients and analogies with studies on recent mn enrichments the major and trace elements of mn occurrences associated with ophiolites that have been variously affected by regional alpine metamorphism were attributed to different origins mn zn v ce nd and la are hydrothermal al ti k zr rb ga sc and some fe and pb are detrital and si p u y nb and the remainder of the fe are biogenic preliminary studies of mn occurrences in the wahrah formation of oman reveal a very similar geochemistry as the extensive exposure of this formation does not display any evidence of hydrothermal systems only a hydrothermal supply of mn to seawater from a distant source is envisaged for these and other deposits

geochemistry and origin of piemontite bearing and associated manganiferous schists from arrow junction western otago new zealand abstract closely spaced analyses for major minor and trace elements have been made through 3 m of manganiferous quartzose schists and immediately overlying quartzofeldspathic schists at arrow junction otago new zealand chemically the quartzose schists correspond to pelagic siliceous muds or brown clays rather than to typical cherts whole rock oxidation ratios fe 3 100 fe 3 fe 2 increase from 16 to 99 with increasing mn apart from sio2 al2o3 is the most abundant oxide in these rocks al2o3 correlates negatively with sio2 and positively with all other components analysed in the manganiferous quartzose schists including fe2o3 mno tio2 mgo cao na2o k2o ba cr cu ni pb rb v y zn and zr parameters such as al 2 o 3 100 al 2 o 3 mno and fe ti indicate that the quartzose schists have a higher hydrothermal plus hydrogenous component than average pelagic clays but a larger terrigenous component than typical metalliferous sediments from the crest and proximal flanks of the east pacific rise close covariance of al2o3 with tio2 and zr results in ratios ti al 50 10 3 and zr al 2 10 3 conforming closely with average shale and average new zealand alpine schist metasediments but less closely with average andesite the data exclude basalt or rhyolite as the dominant aluminous detrital component al ti and zr are regarded as being of predominantly terrigenous origin normalized for constant al2o3 the following elements are enriched in grey green and in pink piemontite bearing arrow junction quartzose schists relative to average new zealand alpine metase dimentary rocks by average factors indicated mn 32 44 ni 15 15 cu 5 12 si 3 6 2 6 pb 2 4 zn 2 8 2 5 fe 1 8 1 9 y 1 7 1 8 ba 1 2 1 6 and sr 1 0 2 0 the metal enrichment trend can be regarded as being imposed on the products of a silica dilution trend in which al2o3 was reduced to 4 by dilution of end member terrigenous sediment with non terrigenous silica about 97 98 of the mn 93 of the ni 79 91 of the cu 73 61 of the sio2 and 43 48 of the fe is considered to be of a non terrigenous hydrothermal hydrogenous biogenic origin in the quartzose schists covariance of elements other than si with al2o3 within the single bed investigated is attributed firstly to accumulation of femn oxides at a rate essentially constant relative to that of clay minerals and other aluminous phases though diluted by varying amounts of largely biogenic silica and secondarily to the sorptive scavenging properties of the femn oxides and of clay mineral components of the sediment although the base metals may ultimately have been introduced to the ocean from submarine hydrothermal systems these sediments originated at a site relatively remote from a fast spreading ridge or other active submarine hydrothermal source

influence of palaeoclimate and hydrothermal activity on organic matter accumulation in lacustrine black shales from the lower cretaceous bayingebi formation of the yin e basin china abstract the lacustrine black shales of the lower cretaceous bayingebi formation are an important hydrocarbon source rock in the yin e basin it is important to understand the mechanism of organic matter accumulation in these shales to reconstruct the palaeoenvironment and palaeoclimate in the early cretaceous in northwestern china and search for potential oil and gas resources based on petrological elemental geochemical and organic geochemistry analyses of typical field profile samples the influence of palaeoclimate and hydrothermal activity on organic matter accumulation in different sedimentary units unit i ii and iii is revealed unit ii has the highest total organic matter abundance tocavg 5 95 mainly type i kerogen lamalginite which is in the immature to low mature stage organic carbon isotope data 13corg element ratios sr cu and c value and weathering indexes including cia ciw and pia together revealed that the region experienced a semihumid to semiarid palaeoclimate in the middle of the early cretaceous the increase in rainfall in unit ii enhanced the abundance of lake algae and surrounding terrestrial vascular vegetation and elevated the lake level which contributed to adequate sources and favourable preservation conditions for organic matter accumulation several lines of evidence including high sulfur contents the combination of vein pyrite and micritic dolomite positive eu anomalies and element geochemical correlations confirm the existence of intermittent low temperature white smoker type hydrothermal activity the decrease of oxygen content in lake bottom water may be related to the input of hydrothermal fluid which provided necessary nutrient elements for biological productivity according to palaeontological and radioisotope dating data it can be inferred that the black shales of the bayingebi formation are the product of the combined effect of global palaeotemperature rise in the early aptian stage of the early cretaceous and intermittent low temperature hydrothermal activity

mineralogy geochemistry and genesis of the ferromanganese ores from hazara area nw himalayas northern pakistan abstract ferromanganese ores occur in hazara area near abbottabad within the hazira formation of the kalachitta margala thrust belt of the nw himalayas of the indo pakistan plate in pakistan the hazira formation of cambrian age is a relatively thin unit up to 150 m thick which consists of either thin ferruginous siltstone with variable amounts of clay shale ferromanganese ores phosphorite and barite or thicker evenly bedded reddish brown siltstone it has a conformable lower contact with the abbottabad formation cambrian and an unconformable upper contact with the samana suk limestone jurassic the ferromanganese ores of the hazara area were studied in terms of their mineral and geochemical composition mineralogically a variety of mn and fe phases have been noticed in kakul galdanian and chura gali ferromanganese ores bixbyite is the principal mn phase while pyrolusite hollandite partridgeite and braunite occur in lesser amounts hematite however is the only fe phase in these ores gangue minerals include carbonates cryptocrystalline quartz iron clay and variable amounts of apatite plumbogummite and barite glauconite occurs in traces textural features suggest remobilization and subsequent precipitation of early diagenetic mn and fe phases along the fractures and interstices of the gangue minerals during later metamorphism chemical analyses show that the mn fe ratio in the ores is highly variable and ranges from 0 46 to 5 25 these ores exhibit a line of descent from lree to hree with a small positive ce anomaly their ree is higher than the hydrothermal mn deposits and lower than the hydrogenous crust the petrochemical characteristics suggest a mixed hydrothermal hydrogenetic source for the ferromanganese ores which have formed in shallow water or continental shelf environment due to the upwelling of anoxic deep seated water

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

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

manganese deposits in turkey distribution types and tectonic setting abstract manganese deposits in turkey are divided into four main groups on the basis of their age host rocks and processes of formation the first is hydrothermal hydrogenetic and rarely diagenetic type manganese deposits which are chiefly associated with radiolarian chert series these deposits occur as lenses and small ore beds within ophiolitic melanges zones of paleo tethyan karakaya and neo tethyan north anatolian and south anatolian suture belts the second is black shale hosted manganese deposits that is found in black shale calcareous shale and calciturbiditic limestone horizons of the passive margin sediments of late cretaceous age in the western taurides these deposits generally are metamorphosed to greenschist facies and include mn carbonate silicate and oxide minerals the third is volcanic arc hosted ores along the black sea margin which occur in different types of metasomatic hydrothermal and stratabound settings rock associations include upper cretaceous dacitic tuff reddish limestone marl and hemipelagic claystone the fourth is oligocene hosted ores in the thrace basin these deposits are similar to those of the paratethyan oligocene belt which occur on the eastern and northern margin of black sea and includes the chiatura georgia nikopol ukraine and varna bulgaria respectively the oligocene mn deposits of the thrace basin were formed by diagenetic replacement processes during a marine regression

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

mineralogy and geochemistry of neoproterozoic siliceous manganese formations from ntui betamba cameroon pan african fold belt implications for mineral exploration the siliceous manganese formations from ntui betamba area have been studied with the aim to constrain their mineralogy geochemistry and genesis neoproterozoic manganese bearing rocks at ntui betamba include garnet galaxite bearing quartzite and galaxite bearing quartzite that besides a characteristic quartz spessartine garnet and galaxite mnal2o4 assemblage comprises also graphite and rutile galaxite crystals show chemical zoning from core to rim due to the change in composition from galaxite to cryptomelane bulk rock geochemistry reveals that the studied rocks are characterized by high sio2 content 52 83 wt they are enriched in fe2o3 and al2o3 and display mn fe ratio of 1 2 mno concentrations are high in galaxite bearing quartzite 16 wt and moderate 8 03 wt in garnet galaxite bearing quartzite the transition trace metal co cu and ni contents are lower with co and cu markedly depleted relative to ni and variable contents of zn the ree pattern of garnet galaxite bearing quartzite shows ce positive anomaly similar to the hydrogenous sediment but differs from the later with strong eu negative anomaly and the lack of weak positive anomaly in yb whereas the galaxite bearing quartzite is characterized by the lack of ce anomaly and the weak eu negative anomaly both rocks show hree content close to that of hydrothermal sediment and exhibit flat hree trend the high contents of silica iron and aluminum together with the co zn ratios 0 3 and the contrasting behavior of ree suggest that the studied manganese bearing rocks are of sedimentary origin probably derived from a mixed hydrothermal hydrogenous source the high content of mn bearing minerals in these rocks represents indicators of concealed or buried mineralization and could be used as exploration guide

manganese ores in tunisia genetic constraints from trace element geochemistry and mineralogy abstract northern and central tunisia hosts few small scale stratiform and stratabound mn deposits low to medium in grade mn

impact of hydrothermal activity on organic matter quantity and quality during deposition in the permian dalong formation southern china abstract the very high temperature at the center of a hydrothermal system is detrimental for the deposition of organic rich sediments however it s not known how the petroleum source rock develops at the boundary of a hydrothermal system where the seawater temperature was only slightly elevated the petroleum generation potential using pyrolysis gc gc ms and ft icr ms techniques of eight organic rich permian shale samples from shangsi section china were systematically investigated principal component analysis reveals that the quantity and quality of the organic matter in the shale is dominated by biomass productivity the redox condition and terrestrial organic matter input rare earth element distribution pattern reveals that the two samples with highest toc contents show a slight eu anomaly which indicates the sample was influenced by a hydrothermal system to some degree a depositional model showing how the influences from hydrothermal event promote the development of petroleum source rock is summarized 1 at the edge of a hydrothermal system the seawater temperature can be elevated by 5 10 c which further promotes the development of phytoplankton and zooplankton 2 an upwelling can be intrigued and chemical weathering will be accelerated which both introduce excessive nutrients and increase the biota productivity 3 flux with the terrestrial advanced plant can also be accelerated to the shelf area by the volcano induced climate change 4 the consumption of the extensive biomass induced by the hydrothermal activity would expand the oxygen minimum zone and further enable more organic matter to be preserved in shale

late diagenetic changes in manganese ores of the upper proterozoic penganga group india sedimentary manganese oxide ores occur interstratified with chert and minor calcareous shale and enclosed in limestone in the transgressive upper proterozoic marine sequence of the penganga group andhra pradesh india this sequence shows no evidence of volcanism or hydrothermal activity and is not metamorphosed the manganeseoxide ores show unusual coexistence of the primary sedimentary minerals todorokite and birnessite with their diagenetic conversion products manganite braunite and bixbyite the mineralogical characters and chemical compositions of the important phases as well as their texture are discussed braunite occurs in two generations one earlier or contemporaneous with bixbyite and the other later than bixbyite the different stages of conversion of todorokite and birnessite to braunite and todorokite to manganite are preserved the general observations suggest that bixbyite was also produced by conversion of todorokite birnessite pyrolusite and cryptomelane conventionally considered as diagenetic products of mn oxide hydroxide precursors deposited as primary sediments are here rarely present and then only as supergene derivatives this documentation of diagenetic transformation of primary todorokite and birnessite directly to braunite and bixbyite should be considered while extrapolating the progenitor mineralogy of the metamorphosed manganese oxide ores that abound in the precambrian

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

cenozoic exhumation history of the alborz mountains iran new constraints from low temperature chronometry the alborz mountains in the north of the turkish iranian plateau mainly developed in the cenozoic as a consequence of the closure of neo tethys and continental collision between arabia and eurasia cenozoic growth of the fold and thrust belt exploited an older palaezoic mesozoic crustal fabric but the extent to which this governed the overall form of the mountain belt is unclear to determine when and how the alborz mountain belt has grown apatite fission track aft and u th he ahe thermochronometry were performed on 46 bedrock samples collected along 8 transects across the range aft central ages range from 157 24 ma to 10 1 ma with most ages falling between 40 ma and 10 ma ahe ages range from 17 2 ma to 6 1 ma the data revealed enhanced exhumation ca 35 5 ma minor exhumation between ca 30 20 ma and an increase in exhumation thereafter this pattern matches the tripartite mid cenozoic stratigraphy of central iran where upper oligocene lower miocene carbonates are sandwiched between terrestrial clastic formations the most intriguing thermochronometric signal found is a major acceleration of exhumation that initiated in the late miocene to early pliocene recorded by the ahe data there does not appear to be a direct tectonic cause for pliocene intensified erosion as convergence rates between arabia and eurasia have remained relatively constant enhanced exhumation at this time may reflect a climatically induced intensification of erosion during caspian isolation and base level fall or a regional tectonic re organization of the arabia eurasia collision or both

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

hydrothermal mn deposits of the franciscan assemblage ii isotope and trace element geochemistry and implications for hydrothermal convection at spreading centers abstract major element trace element and sr nd pb and o isotopic data for a franciscan mn deposit suggest an origin by seafloor hydrothermal circulation based on q mode factor analysis the cherts and mn lenses of the blue jay mine formed from a combination of 4 components representing 1 biogenic 1 hydrothermal and 2 detrital sources rb sr u th pb and o isotopic systematics in the mn lenses were affected by input from the hydrothermal circulation of material leached from the underlying basalts nd isotopic compositions in both cherts and mn lenses are identical and within the range measured for pacific ocean water suggesting the ree were not mobilized by hydrothermal activity correlation of 18 o with sio 2 and mno 2 in the mn lenses implies the lenses formed by simple mixing of hydrothermally derived mn oxides with seawater and biogenic silica 18 o of the cherts is both uniform and depleted relative to dsdp jurassic cherts but similar to microquartz bearing cherts of the monterey formation this suggests that diagenetic activity exerted more control on oxygen isotope compositions then hydrothermal alteration or metamorphism finally a well defined rb sr isochron of 158 5myr was obtained for these cherts and opens the possibility of determining absolute radiometric ages for similar cherts throughout the geologic record

petrological geochemical and hydrothermal characteristics of ordovician cherts in the southeastern tarim basin nw china and constraints on the origin of cherts and permian tectonic evolution abstract cherts occur extensively as stratal wedges embedded in the middle lower ordovician carbonate successions in the circum tangguzibasi areas south east tarim basin where thick up to 2 km dark grey well stratified limestones deposited in shelf and platform environments are prominent based on detailed core and thin section observations with petrographic microthermometric and geochemical data for the middle lower ordovician cherts in some key wells two lithotypes of chert are identified across the marginal zone in the western tangguzibasi areas replacement and filled cherts replacement chert is characterized by granular microcrystalline quartz or radially fibrous chalcedony and commonly retains the pre existing dolomite rhombs and elliptical ooids floating in these cherts filled chert the most common type is generally rimmed by fine gained euhedral quartz that grades abruptly into vein cavity fill mega quartz compositionally these chert deposits are strongly enriched in cr zn ba and u and generally show apparent right convex ree patterns with low ree values avg 4 24 ppm weak negative ce anomalies ce ce avg 0 93 and low to intermediate positive eu anomalies eu eu avg 1 19 particularly the replacement cherts microthermometry of fluid inclusions from coarse quartz reveals high homogenization temperatures from 135 to 195 c for trapped primary fluids with high salinities 11 0 18 9 wt these siliceous deposits also have low la ho and th u relatively high y ho and ba sr high ce ce 1 06 intermediate to high lu la n 0 5 1 0 and low la ce n mostly 1 31 1 45 all these data suggest that the cherts formed under the strong influence of hydrothermal fluids originating from detritus poor hydrogenetic fe mn crusts at deep continental margins extensive silicification occurred after intense dolomitization and calcitization while fracturing faulting were greatly intensified in the host carbonates induced by intense extension because of the uplift force of the magma cushion under oblique collision during the early permian most silica could have directly precipitated from hydrothermal fluids to chalcedony fibres around voids and vein cherts along fracture conduits these petrological and geochemical data also provide a useful clue to better understand the extensive silica precipitation intense tectono hydrothermal activity and significant lithospheric fracturing events as a result of the closure of the south tienshan and palaeo tethys oceans during the early middle permian

oceanic ridge crest processes oceanic ridge crest processes constitute a vigorous frontier of multidisciplinary research with global ramifications in the earth atmospheric and biologic sciences this deep ocean frontier is gradually opening in response to investigations which are elucidating the role of these processes in the lithosphere hydrosphere atmosphere and biosphere and the application of advanced instrumental and interpretive techniques which are increasing the quality and quantity of data these techniques include crustal drilling with borehole logging deep sea drilling project reports high resolution bathymetry sea beam etc side scan sonar seamarc i and ii gloria etc imagery with video and photography multichannel seismics determination of water column properties ctd with rosette sampler etc and submersible applications

metallogeny and temporal spatial distribution of manganese mineralizations in iran implications for future exploration abstract there are a lot of manganese mn deposits and numerous mineral occurrences of this type of mineralization in iran the major tectonic structural zones of iran that host manganese deposits are 1 urumieh dokhtar magmatic assemblage udma 2 the central iran ci 3 the sabzevar zone sz 4 the alborz magmatic belt amb and 5 the cretaceous ophiolites these manganese deposits were formed during discrete time periods 1 late neoproterozoic early cambrian narigan and halab deposits in the ci 2 jurassic halalan deposit in the sz 3 cretaceous mn mineralizations in the late cretaceous volcano sedimentary sequence of southwest sabzevar basin in the sz nasirabad abadeh tashk alashtar sorkhvand esfandagheh benvid gugher kamar talar sardasht and safou manganese deposits in the southeast of birjand dehoo and north of sabzevar deposits which occur in the upper cretaceous ophiolites and 4 eocene miocene e g venarch jalal shahrestanak boznein garab menamin robat karim qaleh mohammad khan rabiei zarashlou narkan sarikand jokandy gharaeh tavaragh and barout aghaji deposits in the udma and amb magmatic arcs intra arc rifts and back arc basins are the principal plate tectonic settings for iranian manganese deposits all of the manganese deposits of the udma and amb formed within tertiary arc and back arcs respectively that developed during subduction of the neo tethyan crust beneath the iranian plate intra oceanic or continental back arc spreading settings are recognized in the neo tethys domain in iran and these host several manganese deposits in the sz and ophiolites the trace element content of all studied manganese deposits is generally low in concentrations and tends to enrichment in the assemblage of v cu pb zn and as with geochemical characteristics similar to hydrothermal deposits rare earth element ree patterns of the iranian manganese deposits support a hydrothermal origin the main time period of formation of manganese mineralization in iran was from cretaceous to miocene the udma and sz are the most favourable metallogenic provinces in iran for manganese exploration because these zones host the most and the largest manganese deposits including venarch and shahrestanak deposits in the udma and manganese mineralizations in the late cretaceous volcano sedimentary sequence of the southwest sabzevar in the sz

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

manganese and ferromanganese ores from different tectonic settings in the nw himalayas pakistan abstract in pakistan manganese and ferromanganese ores have been reported from the hazara area of north west frontier province waziristan agencies in the federally administered tribal areas and the lasbela khuzdar regions of baluchistan this study is focused on comparison of mineralogy and geochemistry of the continental ferromanganese ores of hazara and the ophiolitic manganese ores of the waziristan area of pakistan in the hazara area ferromanganese ores occur at kakul galdanian and chura gali near abbottabad within the hazira formation of the kalachitta margala thrust belt of the nw himalayas of the indo pakistan plate the cambrian hazira formation is composed of reddish brown ferruginous siltstone with variable amounts of clay shale ferromanganese ores phosphorite and barite in waziristan manganese ores occur at shuidar mohammad khel and saidgi within the waziristan ophiolite complex on the western margin of the indo pakistan plate in nw pakistan these banded and massive ores are hosted by metachert and overlie metavolcanics the ferromanganese ores of the hazara area contain variable amount of bixbyite partridgeite hollandite pyrolusite and braunite bixbyite and partridgeite are the dominant mn bearing phases hematite dominates in fe rich ores gangue minerals are iron rich clay alumino phosphate minerals apatite barite and glauconite are present in variable amounts in both fe rich and mn rich varieties the texture of the ore phases indicates greenschist facies metamorphism the waziristan ores are composed of braunite with minor pyrolusite and hollandite hematite occurs as an additional minor phase in the fe rich ores of the shuidar area the only silicate phase in these ores is cryptocrystalline quartz the chemical composition of the ferromanganese ores in hazara suggests that the mn fe was contributed by both hydrogenous and hydrothermal sources while the manganese ores of waziristan originated only from a hydrothermal source it is suggested that the fe mn ores of the hazara area originated from a mixed hydrothermal hydrogenetic source in shallow water in a ontinental shelf environment due to the transgression and regression of the sea while the mn ores of waziristan were formed at sea floor spreading centers within the neo tethys ocean and were later obducted as part of the waziristan ophiolite complex

field experiments and numerical modeling of mass entrainment in snow avalanches 1 snow entrainment alters the speed and hence the run out distance of avalanches yet little is known about this significant process we studied entrainment in snow avalanches using observations from 1 the swiss vallee de la sionne test site 2 the italian pizzac site 3 catastrophic avalanches that occurred during the winter 1998 1999 in switzerland and 4 a medium sized spontaneous avalanche that occurred in 2000 in davos switzerland we determined mass and energy balances for 18 avalanche events on average the mass increased by a factor of 4 the primary mode of entrainment appeared to be frontal ploughing although entrainment behind the avalanche front was also observed step entrainment where a snow cover layer fractures and is entirely consumed by the avalanche also occurred basal erosion was negligible mass availability and snow cover structure were the limiting factors governing entrainment other factors such as track topography and avalanche dimension played a secondary role using the experimental results we introduced an entrainment model into a saint venant type flow model where the internal shear deformation of the avalanche is governed by a bagnold law and the shear stress at the basal layer is treated as a voellmy fluid the model with entrainment not only improves the prediction of the velocities and flow heights in comparison to measurements but also reproduces the variations in run out distances which characterize avalanches with similar terminal velocities but different masses

mineral precipitation sequence and formation of the lacustrine hydrothermal sediments in the lower cretaceous tenggeer formation in the baiyinchagan sag china abstract cores from the lower cretaceous tenggeer formation in the baiyinchagan sag of the erlian basin present dolomitic mudstones and argillaceous dolostone with white grains and laminae thin section x ray diffraction xrd electron microprobe empa and scanning electron microscopy sem analyses show that in addition to terrigenous clastics dolomite analcime natrolite pyrite pistomesite fluorite talc barite etc are abundant compared with the conventional lacustrine sediments these rocks contain highly abundant exhalative textures and structures such as laminae and banded textures disseminated textures mesh vein structures breccia structures and contemporaneous deformations these types of mineral associations rock textures and structures are specific and uncommon previous works indicate that these rocks are of hydrothermal origin in this study we provide supplementary evidence and recognition to support the lacustrine hydrothermal sediment origin and further study the mineral precipitation sequence and formation conditions and processes with the use of 3d seismic data the magmatic intrusions hydrothermal ducts and hydrothermal vents are first identified on seismic sections the ni co zn and fe mn cu ni co 10 ternary diagrams confirm the hydrothermal origin of these sediments the sr ba ratio v v ni ratio oxygen and carbon isotope values of carbonate ph and eh values suggest anoxic reducing and alkaline sedimentary conditions based on the analysis of fluid inclusions rock textures and structures we find that the precipitation of minerals occurred in a specific sequence pyrite pistomesite analcime natrolite dolomite the nature of the magmatic intrusions the changes in environmental variables and fluid energy and the flow distance may be the controlling factors of this specific sequence a mode of lacustrine white smoker type hydrothermal sedimentation is presented in this study as the hydrothermal fluid sourced from the intermediate basic magmatic basement enriched in fe2 mg2 al3 si4 ca2 na and co32 rose and mixed with cool lake water ferromagnesian aluminosilicate and carbonate minerals formed successively from the ducts to the vicinity of the vents pulsing exhalation and overflow formed alternating deposits of hydrothermal sediments and lacustrine mudstones

giant pyritic base metal deposits the example of feitais aljustrel portugal detailed study of hanging wall rocks and alteration above the giant feitais orebody of aljustrel iberian pyrite belt portugal shows that cherts that constitute the immediate hanging wall to the sulfide deposit result from hydrothermal alteration of laterally equivalent fe and or mn rich jaspers textures geochemistry and lack of fossil radiolarians indicate that these jaspers are hydrothermal precipitates hydrothermal alteration of the jaspers took place concomitantly with sulfide precipitation through reaction with hot 150 c reduced fluids with replacement of hematite by magnetite pyrite and fe2 phyllosilicates on the basis of the above and considering also the results of previous studies on hydrothermal activity in the aljustrel volcanic rocks and sulfide ores we propose that sulfide precipitation may have taken place under a thin veneer of siliceous sediments present day massive sulfide formation in the guaymas basin and in the salton sea under hundreds of meters of sediments may be approximate analogues in the sense that the presence of a caprock reduces dispersion of black smoke and causes more efficient precipitation

rare earth element study of exhalites within the willyama supergroup broken hill block australia a wide variety of unusual rock types exhalites are commonly associated with or host to exhalative mineralisation within the willyama supergroup chondrite normalised ree patterns of feldspar gahnite calcite magnetite and garnet rich lithologies in the vicinity of stratiform broken hill type pb zn ag mineralisation are lree and eu enriched similar to the ree patterns of pure metalliferous sediments and hydrothermal fluids of the east pacific rise and the red sea in contrast tourmaline garnet amphibole feldspar and gahnite rich exhalites in strike extension of broken hill type orebodies possess lree enrichments and negative eu anomalies and also hree enrichments and negative ce anomalies these ree patterns are the result of decreasing temperatures of the hydrothermal fluids changing oxidation reduction conditions and increasing influence of basic volcanism with increasing distance from the sulphide mineralisation

effects of flow regime and sensor geometry on snow avalanche impact pressure measurements impact pressures of snow avalanches have been measured at the vallee de la sionne experimental test site using two kinds of sensors with different sizes placed at different locations in the avalanche flow pressures measured for a fast dry snow avalanche and a slow wet snow avalanche are compared and discussed the pressures recorded in the dense flow of a dry snow avalanche agree well for the two types of sensors used showing negligible dependence on the measurement device on the other hand significantly different pressures are measured in the slow dense flow of a wet snow avalanche this is attributed to the slow drag and bulk flow of this type of avalanche leading to the formation and collapsing of force chain structures against the different surfaces of the sensors at a macroscopic scale limit state analysis can be used to explain such a mechanism by a shear failure occurring between freely flowing snow and a confined snow volume against the sensor according to a mohr coulomb failure criterion the proposed model explains how impact pressure can be up to 8 times higher than the hydrostatic snow pressure in wet cohesive slow avalanches and its dependence on sensor geometry

impact pressures and flow regimes in dense snow avalanches observed at the vallee de la sionne test site 1 a fundamental problem in avalanche engineering is to determine the impact pressures exerted on structures this task is complicated because snow avalanches flow in a variety of regimes primarily depending on snow temperature and moisture content in this paper we address this problem by analyzing measured impact pressures flow velocities and flow depths of five vallee de la sionne avalanches the measurements are made on a 20 m high tubular pylon instrumented with high frequency pressure transducers and optoelectronic velocity sensors in the observed avalanches we find both subcritical and supercritical flow regimes typical froude numbers were smaller than 6 the subcritical regime fr 1 is characterized by a flow plug riding above a highly sheared basal layer the measured pressures are large and velocity independent in contradiction to calculation procedures pressure fluctuations increase with flow depth indicating a kinematic stick slip phenomena which is largest at the basal layer supercritical flow regimes 1 fr 6 are characterized by a sheared flow all over the avalanche depth in this regime the impact pressure is velocity dependent we derive relationships governing impact pressure as a function of the froude number and therefore flow regime encompassing all the observed avalanches

modeling mass dependent flow regime transitions to predict the stopping and depositional behavior of snow avalanches 1 how terrain snow cover properties and release conditions combine to determine avalanche speed and runout remains the central problem in avalanche science here we report on efforts to understand how surface roughness snow properties and internal mass fluxes control the generation of granular fluctuation energy within the basal shear layers of dense flowing snow avalanches and the subsequent influence on avalanche speed and deposition patterns for this purpose we augment the depth averaged equations of motion to account for the generation of the kinetic energy associated with the particle fluctuations and dissipation of this energy by collisional and frictional material interactions using high resolution laser scans of the preevent snow cover and postevent deposits from two avalanches released at the swiss vallee de la sionne observation station we compare measured and calculated deposition heights the model captures flow velocities and deposition heights without ad hoc adjustments of the constitutive parameters according to avalanche size the model parameters are separated into a terrain and other pure material snow parameters the investigations reveal how release conditions and snow entrainment influence the internal mass distribution and control flow regime transitions between the fluidized regime head and plug regime tail the comparison between the measured and calculated velocities and deposition heights demonstrates why standard voellmy type submodels are suitable for many practical mitigation problems but also why they are limited to cases where the calibrated parameters already accounting for terrain snow cover properties avalanche size and mass intake are known

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

geological and geochemical constraints on the origin of the giant lincang coal seam hosted germanium deposit yunnan sw china a review abstract the lincang germanium deposit yunnan sw china contains at least 1000 tonnes of ge at an average grade of 850 ppm ge and is one of the largest ge deposits in the world the deposit is hosted within coal seams of the miocene bangmai formation deposited on top of a ge rich granite batholith the bangmai formation is divided into eight units among which three are coal bearing the ge bearing coal seams are inter layered with siliceous rocks and siliceous limestones in the basal coal bearing unit the coal seams of the other two coal bearing units are not interbedded with siliceous rocks and siliceous limestones and are also barren with respect to ge equant or elongate ge orebodies are generally located at fault intersections germanium is mainly associated with organic matter within the coal seams and is concentrated at the top and bottom of the coal seams where the latter are in contact with the layered siliceous rocks or siliceous limestones major and trace element contents and o and c isotopes of the siliceous rocks and siliceous limestones are similar to those of hydrothermal sediments indicating formation by hydrothermal sedimentation compared with barren coals ge rich coals are notably rich in nb li sb w bi and u and show substantial enrichment of hree which increase together with ge germanium rich coals contain disseminated pyrite with 34 s ranging from 17 2 to 51 4 similar to pyrite in barren coals and thin vein like pyrite with 34 s ranging from 5 4 to 1 9 similar to sulfides in granite related quartz veins we propose that circulating hydrothermal fluids leached abundant ge and other elements from ge rich granites in the basement and were then discharged into the basin mainly along fault intersections to form layer like siliceous rocks and siliceous limestones by depositing si and ca the deposit was formed via interaction between ge in the fluids and organic matter in the coal seams

observations of the dynamic structure of snow avalanches during two winters 1990 92 the dynamic structures of snow avalanches were studied in western norway artificially released wet snow avalanches ran down the avalanche chute and stopped in front of the retaining dam running velocity distributions were obtained not only by video tape recorder but also by various other recording instruments internal velocity was derived for the last avalanche by frequency analysis of impact pressure and optical sensor data the vertical velocity shear of the avalanche flow has been estimated to be in the range 1los

velocity profile inversion in dense avalanche flow we present a velocity time series of a dry mixed real scale avalanche that was recorded at different heights on a mast at the swiss vall ee de la sionne avalanche test site the dataset is of extraordinary quality in terms of completeness and spatio temporal resolution and allows the evolution of distinct flow phases of the avalanche to be traced in particular we found velocity profile inversions at the transition from the avalanche front to the avalanche body we provide a tentative empirical description of the profile inversions and briefly discuss our observations in the light of theoretical considerations

rare earth elements and hydrothermal ore formation processes abstract the geochemical behaviour of ree is influenced by nearly all important hydrothermal ore formation processes including fluid rock interactions fluid precipitations adsorption and scavenging onto particles and changes in fluid temperature pressure ph eh alkalinity and ligand concentration destabilization of ree complexes in response to these physicochemical changes and possible chemical crystallographic controls determine the concentration and distribution of ree within hydrothermal minerals mineraloids and amorphous phases alteration assemblages of intrusive related mineralisations may exhibit a wide range of ree distributions and ree fractionation trends the ree distribution within these hydrothermally altered lithologies will depend on the ree concentration in the rock and the fluid the partitioning behaviour of the ree between the rock phases and the fluid and the types of alteration reactions which take place reactive rocks such as carbonate rich lithologies of skarn deposits may gain or loose significant amounts of ree during fluid rock interactions ree geochemical investigations combined with fluid inclusion and stable isotope studies may point to the origin of alteration products and the source s of ore fluids ancient massive sulphide ores commonly exhibit anomalous eu concentrations similar to many recent submarine hydrothermal precipitates the recognition of hydrothermal fluid seawater sedimentary or volcanically derived ree distributions within ores chemical sediments and hydrothermally altered lithologies may help to constrain genetic modelling of massive sulphide deposits care should be taken with the interpretation of ree distributions from metamorphosed hydrothermal ore deposits becase metamorphic and diagenetic alteration reactions may change the ree distributions mobility of ree may occur during diagenesis of carbonate rich rocks and during the development of shear zones and migmatites in contrast very large fluid rock ratios are necessary to cause significant changes in ree patterns of silicate rich rocks during diagenesis and regional metamorphism

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

plate tectonics and pelagic facies late jurassic to early cretaceous deep sea sediments of the ybbsitz ophiolite unit eastern alps austria abstract pelagic sediments of the ybbsitz unit are part of an ophiolite sequence within the penninic unit in the eastern alps cherts and calpionellid limestones of late jurassic to early cretaceous age were deposited on oceanic basement sedimentation near an oceanic spreading center below the calcium compensation depth ccd is represented by chert clay rhythmites cherts display hydrothermal fe and mn mineralizations that are characterized by low contents of co ni and cu as well as by high fe2o3 tio2 and mno tio2 ratios as the site of deposition migrated away from the spreading center hydrothermal influence ceased due to the late jurassic drop of the ccd calcareous radiolarian ooze was deposited on intrabasinal topographic heighs downslope transport of this ooze to sites below the ccd by turbidity currents resulted in intercalations of calcareous and carbonate free sediments apparently the drop of the ccd was greater than the rate of cooling induced basement subsidence as calcareous radiolarites overly this sequence carbonate contents gradually increase upsection and micritic limestones terminate purely pelagic sedimentation at the jurassic cretaceous boundary plate drift moved the site of deposition towards an active continental margin producing a coarsening upward clastic sequence this sequence starts with turbidite and breccia intercalations in pelagic limestones followed by the deposition of early cretaceous flysch it marks the onset of subduction of the ybbsitz unit under the austroalpine continental margin