geochemistry and tectonic setting of the volcanics of the carolina slate belt the carolina slate belt consists of precambrian cambrian metamorphosed mafic to felsic flows volcaniclastics and derived sediments which filled in a volcanic trough presumed to have formed along the leading edge of the north american continent during the early closing of the proto atlantic ocean within the slate belt in central north carolina south carolina and on the south carolina georgia line there are volcanigenic massive sulfide deposits of kuroko affinities and their metamorphically remobilized sulfide and au quartz deposits a total of 296 chemical analyses of volcanic rocks and associated dikes of which 227 are in unpublished theses dissertation and reports are plotted on alkali sio 2 k 2 o na 2 o afm and na 2 o k 2 o cao diagrams in addition selected subsets are compared with standard discriminant plots such as tio 2 sio 2 mgo feo total al 2 o 3 and y zr ti generally speaking the volcanics of the slate belt define a bimodal suite of calc alkaline to tholeiitic rocks with strong affinities to volcanic suites described in the lesser antilles and with the volcanics of the coastal volcanic belt of maine a subduction related orogenic environment is most probable in addition the major element analyses strongly suggest that a pervasive postdepositional alteration process has taken place in general this alteration appears to have affected the fine grained matrix of the volcaniclastics but flows and dikes were not immune an overall alkali depletion and mgo enrichment is characteristic with significant but variable mobility of na 2 o k 2 o cao and sio 2 thus characterization of the magmatogenesis by major element composition alone is not easily done alteration associated with massive sulfide mineralization in the gold hill district north carolina and the lincolnton mccormick district south carolina georgia is similar to but more intense than the pervasive secondary alteration strong silicification alkali addition or subtraction and mgo enrichment is characteristic in general a significant proportion of the mineralization associated alteration falls outside the normal range of compositional variability of typical slate belt suites and thus has a notable signature

global methane emission through mud volcanoes and its past and present impact on the earth s climate mud volcanism is an abundant global phenomenon whereby fluid rich low density sediments extrude both on land and offshore methane which generally exceeds 90 vol of the gas phase is emitted at high rates during and after emplacement of the mud domes and is known for its high global warming potential gwp this comprehensive estimate of the annual contribution of mud volcano degassing assesses the significance of mud volcanism for the accumulation of greenhouse gases in the atmosphere a first order estimate for the earlier pre anthropogenic volume of methane released through mud volcanoes further supports their profound effect on the earth s climate since at least the paleozoic 570 ma

neodymium isotopes in seawater from the barents sea and fram strait arctic atlantic gateways abstract the neodymium concentration c nd and isotopic composition e nd in seawater have been determined in the water column at five sites in the barents sea fram strait area where most of the water exchange between the arctic ocean and the north atlantic takes place in the main arctic ocean inflow branch across the barents sea the concentration and isotopic composition c nd 15 5 pmol kg and e nd 10 8 are similar to those reported for the northeastern nordic seas which is consistent with this region being a source area for the arctic inflow due to the addition of nd from svalbard shelf sediments the c nd in the surface waters above 150 m in the fram strait inflow branch is higher by a factor of 2 and the e nd is shifted to lower values 11 8 in the stratified nansen basin where cold low salinity water overlies warmer atlantic water the c nd and e nd do not vary with the vertical temperature salinity structure but are essentially constant and similar to those of the atlantic inflow throughout the entire water column down to 3700 m depth which indicates that the nd is to a large extent of atlantic origin compared to the atlantic inflow water the nd in the major arctic ocean outflow the fram strait show higher c nd in the surface waters above 150 m and a higher e nd 9 8 throughout the entire water column down to 1300 m depth sources for the more radiogenic nd isotopic composition in deep water of the fram strait outflow most likely involve boundary exchange with sediments on the shelf and slope as the water passes along the canadian archipelago river water is a possible source in the surface water but it also seems likely that pacific water nd modified by interactions on the shelf is an important component in the fram strait surface outflow changes in the relative proportions of inflow of river water and flow of pacific water through the arctic ocean could thus influence the isotopic composition of nd in the north atlantic

comparison of three gis based models for predicting rockfall runout zones at a regional scale site specific information about the level of protection that mountain forests provide is often not available for large regions information regarding rockfalls is especially scarce the most efficient way to obtain information about rockfall activity and the efficacy of protection forests at a regional scale is to use a simulation model at present it is still unknown which forest parameters could be incorporated best in such models therefore the purpose of this study was to test and evaluate a model for rockfall assessment at a regional scale in which simple forest stand parameters such as the number of trees per hectare and the diameter at breast height are incorporated therefore a newly developed geographical information system gis based distributed model is compared with two existing rockfall models the developed model is the only model that calculates the rockfall velocity on the basis of energy loss due to collisions with trees and on the soil surface the two existing models calculate energy loss over the distance between two cell centres while the newly developed model is able to calculate multiple bounces within a pixel the patterns of rockfall runout zones produced by the three models are compared with patterns of rockfall deposits derived from geomorphological field maps furthermore the rockfall velocities modelled by the three models are compared it is found that the models produced rockfall runout zone maps with rather similar accuracies however the developed model performs best on forested hillslopes and it also produces velocities that match best with field estimates on both forested and nonforested hillslopes irrespective of the slope gradient

reduced north atlantic deep water flux to the glacial southern ocean inferred from neodymium isotope ratios the global circulation of the oceans and the atmosphere transports heat around the earth broecker and denton1 suggested that changes in the global ocean circulation might have triggered or enhanced the glacial interglacial cycles but proxy data for past circulation taken from sediment cores in the south atlantic ocean have yielded conflicting interpretations of ocean circulation in glacial times 13c variations in benthic foraminifera2 3 4 5 6 support the idea of a glacial weakening or shutdown of north atlantic deep water production whereas other proxies such as cd ca ba ca and 231pa 230th ratios show little change from the last glacial maximum to the holocene epoch7 8 9 here we report neodymium isotope ratios from the dispersed fe mn oxide component of two southeast atlantic sediment cores both cores show variations that tend towards north atlantic signatures during the warm marine isotope stages 1 and 3 whereas for the full glacial stages 2 and 4 they are closer to pacific ocean signatures we conclude that the export of north atlantic deep water to the southern ocean has resembled present day conditions during the warm climate intervals but was reduced during the cold stages an increase in biological productivity may explain the various proxy data during the times of reduced north atlantic deep water export

effect of impact velocity block mass and hardness on the coefficients of restitution for rockfall analysis abstract one of the most significant input parameters in rockfall trajectory modelling is the coefficient of restitution which controls block rebound in particular in the design of rockfall barriers it can significantly affect their height in practice the coefficients of restitution are acquired by field or laboratory tests back analyses of known events experience or most commonly suggested values connected to the slope material furthermore to account for the effect of impact velocity or block mass scaling factors are available however the suggested values are based on a qualitative description of the slope material and the scaling factors are not well documented nor do they account for the effects of impact velocity and block mass simultaneously in this paper a semi empirical correlation is proposed that takes into account the schmidt hammer rebound value of both the slope and block material as well as the impact velocity and block mass this was derived by an extensive laboratory experimental study 445 impact tests of a one dimensional drop of spherical blocks onto planar surfaces the semi empirical correlation proposed adequately describes the responses observed under the circumstances imposed in the laboratory

trondhjemites tonalites and diorites in the south portuguese zone and their relations to the vulcanites and mineral deposits of the iberian pyrite belt in the south portuguese zone close associations of diorites tonalites and trondhjemites occur north of the pyrite belt the period of their emplacement is pre carboniferous and not as has generally been assumed variscanpostorogen the trondhjemitic intrusive suite and the lower carboniferous spilite keratophyre association are related through their comagmatic derivation both series share sodium dominance low concentrations of large ion lithophile elements indicators of a water rich original magma and a deficient scorification of the element potential which was acummulated in the sulphide and manganese deposits of the pyrite belt through post volcanic hydrothermal processes the mineralogically and geochemically primitive composition of both plutomtes and vulcanites their mode of eruption from acid to basic facies as well as their position in the orogenic process indicate that they represent products of a successively proceeding partial melting of subducting oceanic crust the trondhjemitic intrusives are the initialites in the magmatic orogenic development

landform effect on rockfall and hazard mapping in cappadocia turkey the cappadocia region has unique geomorphological features resulting from differential erosional processes which make it very attractive to tourists besides the fairy chimneys for which the area is best known there are also impressive buttes and mesas buttes and mesas are formed in regions having flat lying strata in which the uppermost levels are composed of well cemented limestones and granular ignimbrites whereas the lower parts and slopes consist of low durability tuff and ignimbrites this durability difference results in serious rockfall events this study involves two dimensional rockfall analyses in and near the avanos zelve and cavusini areas where volcano sedimentary units of neogene age outcrop to provide a rockfall hazard map in which areas of tourism activity are also considered

the estuarine chemistry of rare earth elements comparison of the amazon fly sepik and the gulf of papua systems abstract a comparison of the amazon fly gulf of papua and sepik river systems has shown that there are two distinct processes operating on dissolved rare earth elements ree in estuaries large scale salt induced coagulation in the low salinity region and small to extensive release in the mid to high salinity region fractionation of the ree occurs during both removal and release the order of removal follows lree mree hree and the order of release follows hree mree lree where l m and h refer to light middle and heavy ree respectively hence estuarine reactions can modify the relative abundance of dissolved ree reaching the oceans operating in tandem the removal and release lead to the preferential removal of the lree and the preferential release of hree during estuarine mixing this combination in turn results in an effective river water flux river flux after modifications by estuarine chemistry which is evolved toward the ree composition of seawater which has a heavy ree enriched composition when normalized against the ree composition of rivers or the earth s continental crust the increase of dissolved ree in the mid to high salinity waters of the amazon and fly estuaries suggests a sediment and or suspended sediment source the lack of ree increases in the sepik river estuary strengthens this explanation as the mixing zone of this estuary is located over a deep shelf where there is little physical contact between bottom sediment and estuarine waters in marked contrast the amazon and fly estuaries are dominated by the active resuspension and deposition of bottom sediments the resupply of ree accompanied by fractionation may result from ree carbonate complexation during the reaction of seawater with suspended particles and or bottom sediment estuarine and shelf sediments may be important sources of dissolved nd to the oceans thereby helping to maintain the inter ocean differences in the nd isotopic composition of seawater by reducing the residence time of nd in the oceans

a new approach to the nd residence time in the ocean the role of atmospheric inputs concentrations of rare earth elements ree and nd isotopic ratios were analyzed for seawater filtered suspension and sediment trap samples collected in the tropical atlantic ocean eumeli program eutrophic mesotrophic and oligotrophic sites 20 n 18 21 w this is the first ree nd dataset on solution and different sized particles collected at the same site we present direct evidence of the nd isotopic exchange between particulate lithogenic fraction and seawater without significant mass transfer this exchange is probably one of the main factors that simultaneously constrains the nd concentration and isotopic ratio budget we propose a new approach to estimate the residence time of nd in the ocean nd based on isotopic exchange 200 yr nd 1000 yr the exchange requires a partial dissolution of lithogenic nd we estimate that the fraction of soluble nd proportion in atmospheric dust is of the order of 20 based on the isotopic ratios we suggest that the partial dissolution of atmospheric fallout is probably one of the main ree sources of the ocean

redox zonation of elements at an oxic post oxic boundary in deep sea sediments abstract deep sea sediments generally provide limited evidence of redox control on the post depositional redistributions of elements this is because only a fraction of any element is reactive and observed elemental distributions are the result of a number of competing processes which are simultaneously active so that redox effects are not dominant a detailed investigation is reported of a core which is unusual in showing unequivocal evidence of direct redox control operating in a homogeneous environment that is relatively free from competing processes a progressive oxidation front has migrated slowly downwards into a uniform turbidite over a long period ca 250 ky the reactive fractions of several redox sensitive elements now show a remarkable degree of organisation around the redox boundary of this front with the different elements exhibiting individual responses solid phase enrichments are not coincident but are arranged in a clear succession of concentration peaks along the redox gradient from oxic to postoxic conditions the succession is mn i fe se and pt cu and pb v zn and sb and u the movement directions of most elements can be inferred from the peak shapes against the homogeneous turbidite background composition the system seems to have been essentially isolated within the sediment for most elements so that no loss or gain can be ascribed to redox processes exceptions are u and v which have been augmented by uptake from ocean bottom waters into the sediments by an efficient redox trap mechanism

rift related igneous activity and metallogenesis in sw bergslagen sweden abstract the bergslagen ore belt in central sweden comprises a mid proterozoic complex of broadly coeval volcano sedimentary and plutonic rock units showing overlapping ages between 1 9 and 1 84 ga and formed in a rift tectonic setting the volcano sedimentary rock unit of this complex is referred to as the bergslagen supracrustal sequence and divided into the lower leptite the middle leptite and the upper leptite and slate groups in sw bergslagen the development of the plutono volcano sedimentary complex began about 1 9 ga ago with the early volcanic phase of extrusion of lower leptite group felsic volcanics in the subsequent initial rift phase branching basins were formed in which felsic volcanics and iron formations of the middle leptite group were deposited the succeeding rift phase was marked by the deposition of felsic volcanics volcaniclastic and other sediments of the upper leptite and slate group in rift phase basins the rift phase is characterized by bimodal mafic felsic volcanism and plutonism metabasic flows are found between the felsic metavolcanics and metasediments in the rift basins whereas metabasic sills and dykes are associated with granite intrusions in the horsts between the rift basins the metabasic rocks are referred to as the bergslagen metabasic rock suite and the granites as the bergslagen older granite suite the alkaline to subalkaline chemistry and anorogenic suite trace element enrichments of the older granites their close affinities to associated silicic volcanics the continental tholeiitic character of the metabasite rock suite and the outspoken bimodality of the rift phase magmatism all support the contention of a rift tectonic setting manganese and sulfide ores are found as syngenetic exhalative sedimentary deposits in the rift basins and epigenetic replacement deposits in older formations below the floor of and in the horsts between the rift basins these ore deposits and associated metasomatic alterations are related to widespread sub seafloor hydrothermal metamorphism in connection with hydrothermal convection systems driven by the heat of the various rift phase mafic and felsic intrusions and extrusions the rift phase terminated with cessation of volcanism and was followed by the post rift phase of tectonic compression and the intrusion of about 1 84 ga old hybride rocks of the hyttsjo gabbro tonalite suite

rare earth elements in the nw indian ocean abstract dissolved rare earth element ree distributions have been determined at three stations in the high productivity nw indian ocean nwio upwelling zone dissolved ree distributions within the well oxygenated surface waters and deep portions of the water column are similar to those reported previously from other open ocean locations at depth dissolved ree concentrations are intermediate between those of the atlantic and pacific oceans consistent with the continuous regeneration and enrichment of the strictly trivalent rees in and the progressive oxidative removal of ce from the deep ocean within the mid depth oxygen minimum zone dissolved ree concentrations exhibit a notable enrichment superimposed upon these typical oceanic profiles further dissolved ce concentrations are preferentially enriched within the suboxic horizon compared to the rest of the series indicating the reduction of insoluble ce iv to dissolved ce iii at these depths by analogy with our previous studies of ree distributions in anoxic basins we propose that the more modest enrichments of the strictly trivalent rees observed in the nwio suboxic zone must derive from uptake through scavenging within the well oxygenated portions of the water column and regeneration from sediments and settling particles within the more reducing conditions of the oxygen minimum zone

origin of ree mineralization in the bastnas type fe ree cu mo bi au deposits bergslagen sweden the bastnas type deposits with mineral assemblages of fe oxides ca mg silicates rare earth element ree silicates ree fluorocarbonates and cu fe mo bi sulfides are associated with marble horizons in a strongly na k and or mg altered metavolcanic succession over a distance of at least 80 km in a sw ne trending zone in western bergslagen two subtypes occur 1 enriched relative to the other type in light ree lree and fe exemplified by the bastnas and rodbergsgruvan deposits and 2 enriched in heavy ree hree y mg ca and f represented by deposits in the norberg district bastnasite hosts primary fluid h2o co2 inclusions with salinities of 6 29 eq wt cacl2 and with total homogenization temperatures th tot of ca 300 400 c subtype 2 has late stage fluorite with fluid inclusions that show 1 16 eq wt nacl and th tot of ca 90 150 c molybdenite re os ages obtained from three deposits are 1 904 6 1 863 4 and 1 842 4 ma nd isotopic data from five different ree minerals yielded no defined isochron but a range in end 1 88 ga of 0 2 to 1 6 the oxygen isotope values 18osmow of dolomite and calcite from the associated ree mineralized skarn and recrystallized carbonate assemblages lie in the range 6 1 8 6 overlapping with those of the host marbles carbon isotope values 13cpdb show typical magmatic signatures of 6 7 to 4 4 while the host marbles group around ca 2 4 the sulfur isotope 34scdt values of associated sulfides range between 10 8 and 0 2 the combined evidence suggests ree mineralization beginning at 1 9 ga from mainly svecofennian juvenile magmatic 400 c fluids carrying si f cl s co2 and the ree in addition to other metals mineralization occurred through reactions with dolomitic layers in the supracrustal units coevally with regional metasomatic alteration associated with fluid circulation through an extensive active volcano plutonic complex

sr_nd_pb isotope systematics in amazon and congo river systems constraints about erosion processes abstract 87 sr 86 sr 143 nd 144 nd 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb isotopic ratios and rb sr sm nd u pb and th concentrations have been measured in the suspended loads of the congo and amazon rivers and their tributaries in the dissolved load 87 sr 86 sr rb sr nd sm u pb and th concentrations are also reported these results show that nd sm th and pb are almost insoluble and that their mass balance is controlled by particulates whereas rb sr and u are fractionated between soluble and particulate phases the 87 sr 86 sr ratios can only be interpreted after computing the amount of carbonate recycling and the partitioning for silicates between soluble and insoluble this paper presents a method based on the lead isotopic system that can be used to test the steady state of erosion which is tacitly assumed in many river and erosion studies the results presented show that the steady state is validated in each river of the congo basin and in the lowland rivers of the amazon basin but in not verified in the rivers from the andes rio solimoes and rio madeira 87 sr 86 sr 206 pb 204 pb and 208 pb 204 pb ratios are positively correlated and negatively correlated with 143 nd 144 nd ratios a number of arguments indicate that these correlations are mixing lines the end members being orogenic and shield components respectively for the amazon basin analysis of the river loads shows that the orogenic zone is favoured some 5 times more than the shield on an equal area basis this leads to a reinterpretation of sm nd data for shales and casts some doubts upon the proposition of secular variations in the sm nd ratio of the continental crust

importance of vertical geochemical processes in controlling the oceanic profiles of dissolved rare earth elements in the northeastern indian ocean vertical profiles of dissolved rare earth elements rees were obtained in the bay of bengal and the andaman sea the ree concentrations at various depths in the bay of bengal are the highest in the indian ocean this is attributable ultimately to the large outflow of the ganges brahmaputra and irrawaddy rivers but the dissolved ree flux to surface waters alone cannot explain the large and near constant ree enrichment throughout the entire water column the underlying fan sediments serve as not a source but a sink for dissolved ree iii s absence of excess 228ra in the deep waters suggests that lateral input of dissolved rees from slope sediments is also small in these regions partial 0 3 dissolution of detrital particles which are carried by the rivers and lateral surface currents and subsequently settle through the water column appears to be a predominant source for the dissolved rees vertical profiles showing an almost linear increase with depth are common features for the light and middle rees everywhere but their concentration levels are variable from basin to basin and from element to element this suggests that their oceanic distributions respond quickly to the variation of particle flux and its ree composition through reversible exchange equilibrium with suspended and sinking particles much like the case for th the relative importance of the vertical geochemical processes of reversible scavenging over the horizontal basin scale ocean circulation with passive regeneration like nutrients decreases systematically from the light to the heavy rees using a model the mean oceanic residence times of rees in the bay of bengal are estimated to range from 37 years for ce to 140 1510 years for the strictly trivalent rees in the deep water of the andaman sea isolated from the bay of bengal by the andaman nicobar ridge maximum sill depth of 1800 m the ree concentrations are almost uniform presumably due to rapid vertical mixing the ree iii concentrations are similar to that of 1250 m depth water in the bay of bengal consistent with other oceanographic properties however the ree composition of the deep water appears to be altered slightly by preferential scavenging of the light ree iii at the bottom boundary of the basin

sedimentation and shale tectonics of the northwestern niger delta front abstract the modern day slope and outer shelf of the niger delta are characterized by fault bounded sedimentary depocentres and intervening shale structures some of which are diapiric using two dimensional seismic reflection data and stratigraphic information from five wells the neogene history of a 70 30 km portion of the northwestern niger delta shelf and slope has been examined the shale structures were established by late miocene time probably in response to lateral shale withdrawal from beneath the advancing deltaic load combined with compressional uplift and folding of pro delta strata during pliocene and pleistocene time these structures were buried by the prograding delta and extensional growth faulting commenced stacked onlap relationships and stacked erosional channels indicate that the shale structures continued to influence sedimentation patterns throughout this period throughout the pliocene extension and subsidence were concentrated in a graben like depocentre bounded by both regional and counter regional growth faults during the early pleistocene subsidence on the regional growth fault ceased and growth was transferred to the counter regional growth fault set the geometry and history of the depocentre is analogous to salt related depocentres typical of the northern gulf of mexico and atlantic margins of brazil and angola to explain the history of the niger delta study area a model is proposed in which the miocene pleistocene sedimentary package has slid basinward breaking up during extension thereby creating seaward stepping depocentres examples from analogue modelling studies are used to suggest possible origins for the large counter regional growth faults

the rare alkalies in hydrothermal alteration at wairakei and broadlands geothermal fields n z abstract drillcores and waters from wairakei and broadlands geothermal areas new zealand have been analyzed for li rb cs na k mg ca al ti mn and be the drillcores were altered to various degrees at temperatures below 300 c in slightly alkaline chloride water probably derived from rock water interaction in untapped horizons at higher temperature it changes its composition as it leaches ca and na from the rock and adds k rb cs and li evaluation of these changes in relation to the dimensions of the altered zone under observation suggests that a high mass ratio of water to rock e g 100 and a period of up to 1 million years are responsible for the present stage of alteration increase of k and rb in the altered rocks is a result of the formation of abundant adularia in addition to illite the k rb ratio of the rock decreases during alteration but remains higher than that of the fluid only clay materials and zeolites that preferentially absorb rb give slightly lower k rb ratios than the fluid the mineral phases responsible for the uptake of lithium during alteration are chlorite 300 ppm li and quartz up to 430 ppm li li uptake in quartz is considered to be the mechanism by which al rich quartz crystallises from alumino silicates li al atomic ratios of 0 3 0 57 and al concentrations up to 3000 ppm have been observed relatively small concentrations of cs are found in potassic minerals e g 10 ppm cs in adularia 44 ppm cs in illite however 240 ppm cs are found in wairakite from wairakei equilibrated at 235 c lower equilibration temperatures may lead to higher cesium concentrations this effect in conjunction with a more concentrated hydrothermal fluid could explain a content of 4500 ppm cs in wairakite extracted from a drillcore taken in the el tatio geothermal field in chile

geochemical facies model of ore formation in the grythyttan hallefors area bergslagen central sweden the different iron and manganese ore deposits of the grythyttan hallefors area display an arrangement that reflects a systematic change in redox conditions from oxidic banded iron formation into highly reduced graphite bearing slates this phenomenon is explained by a facies model the different environmental conditions are also held to be responsible for the geochemical differentiation of base metal deposits into cu ores associated with minerals of bi co mo as zn pb au and pb zn ag ores associated with minerals of sb mn as sn cu spatial relationships between deposits of these two groups and certain iron and manganese deposits point to a common source of all metals possibly connected with exhalative derivates from basic volcanism

origin of late archean and early proterozoic rocks and associated mineral deposits from the zhongtiao mountains east central china abstract late archean and early proterozoic supracrustal rocks in the zhongtiao mountains of east central china include five successions separated by unconformities or intrusive contacts the oldest successions the shushui complex 2500 ma and the jiangxian 2400 2200 ma and zhongtiao groups 2100 ma are composed chiefly of metapelites quartzites and marbles with small amounts of bimodal felsic mafic volcanics in which felsic ash flow tuffs dominate the overlying danshanshi group includes chiefly quartzites and conglomerates and the xiyanghe group 1830 ma comprises bimodal volcanics and red beds granitoids range from late archean to early proterozoic in age and vary from tonalite to granite in composition precambrian igneous rocks show a subduction zone geochemical component depletion in nb ta relative to lile and early proterozoic granitoids range in composition from i to s types geochemical and isotopic constraints favor an origin for early proterozoic zhongtiao felsic magmas either by melting of sediments or tonalites in the crust or by melting of amphibolite eclogite in a descending slab zhongtiao pelites are similar in composition to phanerozoic shales and exhibit negative eu anomalies on chondrite normalized graphs stratiform copper deposits in the zhongtiao proterozoic rocks are of three types volcanic hosted deposits of hydrothermal or exhalative origin primary sedimentary deposits and remobilized sedimentary deposits the jiangxian and zhongtiao lithologic assemblages of quartzite pelite carbonate together with primary textures and structures in these rocks suggest deposition in shallow marine tectonically stable basins whereas coarse terrigenous sediments in the danshanshi and xiyanghe groups appear to reflect near shore marine to fluvial deposition in tectonically active basins most data are consistent with deposition of the early proterozoic supracrustal rocks in a continental margin back arc basin

chemistry of micas and chlorite in proterozoic acid metavolcanics and associated rocks from the hastefalt area norberg ore district central sweden microprobe analyses are performed on micas biotite muscovite and phlogopite and chlorite from 1 9 1 8 ga acid k or na rich metavolcanics cordierit emica schists and manganiferous rocks from the hastefalt area in central sweden the results indicate that fe rich biotites and muscovites containing 10 to 25 celadonite and or pyrophyllite are common in the k and na rich metavolcanics in the cordierite mica schists the biotites are mg rich and the muscovites contain less than 10 celadonite and or pyrophyllite the predominant mica in the manganiferous rocks are phlogopite and less frequent rather pure muscovite the chlorites show a wide range in composition but principally those occurring in the k and na rich metavolcanics are brunsvigite and diabantite and those in the cordierite mica schists and the manganiferous rocks are mainly sheridanite and clinochlore the chlorites of the manganiferous rocks show enrichment in mn compared to those in other rock types in general the compositional variations in the micas and less commonly chlorites are strongly controlled by rock type and fluid chemistry particularly with respect to the ratio of feo feo mgo estimates of maximum prograde metamorphic temperature based on phyllosilicates and co existing cordierite and garnets indicate a value of up to 500 c

geochemical characterisation of a polyphase deformed altered and high grade metamorphosed volcanic terrane implications for the tectonic setting of the svecofennides south central finland abstract the virtasalmi metavolcanic belt forms part of the early proterozoic svecofennide terrane in central finland the preserved supracrustal lithologies 40 of the assemblage have undergone extensive synvolcanic hydrothermal alteration polyphase regional ductile deformation low pressure regional polyphase metamorphism to granulite facies with subsequent amphibolitisation and extensive emplacement of a synkinematic i type plutonic suite despite these overprinting events three chemically distinct suites of metatholeiites and one suite of coeval coarser grained intrusive lithologies are recognized and their petrogenesis resolved primary igneous geochemistry is preserved mainly by the hfses and cr and ni variable major and lil element mobility is demonstrated significant differences in geochemistry are reflected in different metamorphic assemblages between suites preservation of vesicular pillow lavas indicate subaqueous extrusion of the three metatholeiitic suites trace element geochemistry indicates that suite i compositions are controlled by low pressure fractional crystallization in contrast suite iii amphibolite compositions are controlled by batch partial melting with limited modification by open system fractional crystallization these differences in fractionation history point to the evolution of these two main suites within distinct upper crustal magmatic plumbing systems also differences in more hyg less hyg element and other incompatible element ratios point to derivation of suites i and iii by different degrees of partial melting from different heterogeneous mantle source regions coeval eruption of these suites indicates that variations in source geochemistry and melting processes reflect spatial rather than temporal differences the volumetrically smaller suite ii comprises lava flows and pillowed units that are interlayered with but have a more depleted chemistry than the other suites marked variation in cr and ni contents within a narrow range of zr contents in individual flows in subgroups iia 1 and iia 2 and marked tio 2 enrichment in subgroup iib suggests that the more depleted character of this suite is due to fractional crystallisation and crystal settling in high level magma chambers suite iv amphibolites comprise a number of small intrusive bodies that are emplaced within the volcanic pile they are coarser grained than the enveloping amphibolites and are interpreted as tectonised relics of high level magma chambers and or sills emplaced into the coeval metavolcanic assemblage they have a depleted geochemistry and there is textural and geochemical evidence to suggest a partial cumulate origin similarities in fractionation histories suggest that suite iv intrusions are cogenetic with suites i and ii enrichment in incompatible elements particularly nb demonstrates that the virtasalmi metatholeiites are not related to supra subduction zone magmatism all the amphibolites are within plate basalts or e type morbs with similar compositions known today from a range of tectonic settings however the interlayering of e morb metavolcanic rocks with marbles and voluminous fine grained clastic metasediments is more likely to indicate an intracratonic rift passive margin geotectonic setting subsequent deformation and metamorphism of the volcanics and syn kinematic calc alkaline intrusives are interpreted as accretion at a destructive margin the latter was most probably a continental calc alkaline arc various crustal levels of which are now exposed in the study area

combining field and modelling techniques to assess rockfall dynamics on a protection forest hillslope in the european alps adequate management of a mountain forest that protects downslope areas against impacts of rockfall requires insight into the dynamics of the hillslope environment therefore we applied a combined approach using field and modelling techniques to assess the determining factors for rockfall source areas rockfall tracks and rockfall runout zones on a forested slope in mountainous terrain the first objective of this study was to understand why rockfall occurs in the study area the second objective was to translate the knowledge obtained in the field into a model that simulates rockfall dynamics on a forested slope realistically the third objective was to assess which hillslope characteristics primarily determine the distribution of active rockfall tracks to achieve these objectives we made a geomorphological map of the whole study area and we measured the major discontinuity planes in the bedrock that are exposed in the rockfall source areas furthermore a test site for simulation modelling within the larger study area was defined in which both a forest and a hillslope inventory were carried out the available data and our developed rockfall simulation model allowed us to assess the slope characteristics that mainly determine the distribution of areas affected by rockfall we found that in decreasing order of importance both standing and felled trees the surface roughness and rockfall resistant shrubs primarily determine the distribution of rockfall affected areas simulation tests without a forest cover produced similar rockfall runout zones as fossil rockfall events identified in the field we believe that the combined field and modelling approach is a prerequisite for understanding how forests can protect against rockfall

hydrothermal plumes along the east pacific rise 8 40 to 11 50 n particle distribution and composition the discovery of a volcanic eruption at the 9 45 52 n site on the east pacific rise epr led us to investigate how the composition of suspended matter in hydrothermal plumes may be used to provide a better understanding of the relative age and vent fluid characteristics of a ridge crest system during surface ship surveys during the troughs tropical ridge observations of underwater geochemical hydrothermal signals expedition we collected hydrothermal plume particles along a 350 km section extending from approximately 8 40 n to 11 50 n of the epr north and south of the clipperton transform fault over the segment south of the clipperton transform fault the sfe ratio in the particles ranged from about 0 9 to 10 with the highest values immediately over the new vent field at the 9 45 52 n site these enrichments exactly coincide with the elevated 3he heat and ch4mn ratios in the plumes over the same vent field the s rich particles are primarily organic and may be related to the bacteria blizzard associated with the eruption in addition very high cufe and znfe ratios were observed in the hydrothermal plumes south of the clipperton transform fault these high ratios are indicative of the predominance of high temperature h2s rich vents between 9 35 n and 9 50 n in contrast the samples from the segment north of clipperton transform fault had sfe ratios which ranged from 0 04 to 0 82 typical of mature fe rich hydrothermal plumes these results suggest that the gas rich vent fluids at the 9 45 52 n site produced the sulfur enriched particles in the water column gas rich plumes and sulfur enriched plume particles were also observed underneath the 1986 megaplume on the juan de fuca ridge jdfr suggesting a similar mode of formation north of the clipperton transform fault the hydrothermal particles are dominated by fe rich oxyhydroxide particles characteristic of mature high temperature vent fields the plume maximum is centered at 11 08 n the fe oxyhydroxide particles scavenge ca si p v cr and as from seawater for p and v the mean element fe ratios in the epr hydrothermal particles are intermediate between jdfr and tag hydrothermal systems for as the mean element fe ratios of all three systems are about the same new evidence for si scavenging by hydrothermal fe oxyhydroxide particles indicates that this sink for dissolved si in the oceans is small

rockfall activity index rai a lidar derived morphology based method for hazard assessment abstract in this paper we introduce the rockfall activity index rai a point cloud derived high resolution morphology based approach for assessing rockfall hazards with the rai methodology rockfall hazards are evaluated in a two step procedure first morphological indices local slope and roughness are used to classify mass wasting processes acting on a rock slope these classifications are then used with estimated instability rates to map rockfall activity across an entire slope face the rockfall hazard is quantified as the estimated annual kinetic energy produced by rockfall along 1 m length segments of a slope face field assessment of the rai method at multiple study sites indicates that the morphology derived classification and hazard assessment routines provide results that closely match the observed behavior and performance of rock slopes

toward objective rockfall trajectory simulation using a stochastic impact model the accuracy of rockfall trajectory simulations depends to a large extent on the calculation of the rebound of falling boulders on different parts of a slope where rockfalls could occur the models commonly used for rebound calculation are based on restitution coefficients which can only be calibrated subjectively in the field to come up with a robust and objective procedure for rebound calculation a stochastic impact model associated with an objective field data collection method was developed and tested in this study the aims of this work were to assess the adequacy of this approach and to evaluate the minimum amount of field data required to obtain simulation results with a satisfactory level of predictability to achieve these objectives the rebound calculation procedure developed was integrated into a three dimensional rockfall simulation model and the simulated results were compared with those obtained from field rockfall experiments for rocky slopes the simulations satisfactorily predict the experimental results this approach is advantageous because it combines precise modelling of the mechanisms involved in the rebound and of their related variability with an objective field data collection procedure which basically only requires collecting the mean size of soil rocks the approach proposed in this study therefore constitutes an excellent basis for the objective probabilistic assessment of rockfall hazard

an experimental investigation of high temperature interactions between seawater and rhyolite andesite basalt and peridotite natural seawater was allowed to react with rhyolite andesite basalt and peridotite at 200 500 c and 1 000 bars at water rock mass ratios of 5 and 50 in order to investigate the effects of rock type water rock ratio and temperature on solution chemistry and alteration mineralogy the results indicate that interactions of seawater with various igneous rocks are similar in the production of a hydrous mg silicate and anhydrite as major alteration products fluids involved in the interactions lose mg to alteration phases while leaching fe mn and si from the rocks the ph of the solutions is primarily controlled by mg oh silicate formation and therefore varies with mg and si concentration of the system other reactions which involve mg such as mg ca exchange or which produce free h cause major differences in fluid chemistry between different seawater rock systems high water rock ratio systems 50 1 are generally more acidic and more efficient in leaching than low ratio systems 5 1 due to relatively more seawater mg available for mgsilicate production the experiments show that large scale seawater rock interaction could exert considerable control on the chemistry of seawater as well as producing large bodies of altered rock with associated ore deposits

assessment of rockfall hazard around afyon castle turkey the afyon castle is a tourist destination and a historical site in the city of afyon in turkey the castle is located on a steep hill with a height of 226 m in close proximity to the castle there are settlements the hill consists of trachitic andesite the rock contains columnar joints and flow layering owing to these discontinuities blocks of varying sizes had fallen down the settlement areas near the castle are now in danger because of the rockfall risk in this study rockfall analysis was carried out along nine profiles of the hill fall out distance bounce height kinetic energy and velocity of the rocks along each profile were investigated the results of the analyses were evaluated and the areas delineated as susceptible to rockfall risk are highlighted remedial measures including rock bolts and protective fences were suggested on the basis of the field observations and the rockfall risk evaluation

spatio temporal evolution of the west african monsoon during the last deglaciation on the basis of a multi proxy data set from the gulf of guinea eastern equatorial atlantic we reconstruct the spatio temporal evolution of the west african monsoon wam and present evidence for a decoupling between latitudinal shifts of the rain belt and wam intensification the onset of deglacial monsoon invigoration at 16 600 years before present lagged northward migration of a weak rainfall zone by 2800 years conversely during the younger dryas yd time interval wam precipitation was severely reduced but we find no evidence for a large scale retreat of the rainfall front this observation is not in agreement with the hypothesis of a large scale shift of the intertropical convergence zone south of the tropical wam region during the yd our results can be better reconciled with the newly emerging concept of a strong influence of tropical easterly and african easterly jets on modern wam

methane discharge into the black sea and the global ocean via fluid flow through submarine mud volcanoes during the margasch cruise m52 1 in 2001 with rv meteor we sampled surface sediments from three stations in the crater of the dvurechenskii mud volcano dmv located in the sorokin trough of the black sea and one reference station situated 15 km to the northeast of the dmv we analysed the pore water for sulphide methane alkalinity sulphate and chloride concentrations and determined the concentrations of particulate organic carbon carbonate and sulphur in surface sediments rates of anaerobic oxidation of methane aom were determined using a radiotracer 14ch4 incubation method numerical transport reaction models were applied to derive the velocity of upward fluid flow through the quiescently dewatering dmv to calculate rates of aom in surface sediments and to determine methane fluxes into the overlying water column according to the model aom consumes 79 of the average methane flux from depth 8 9 10 6 mol a 1 such that the resulting dissolved methane emission from the volcano into the overlying bottom water can be determined as 1 9 10 6 mol a 1 if it is assumed that all submarine mud volcanoes smvs in the black sea are at an activity level like the dmv the resulting seepage represents less than 0 1 of the total methane flux into this anoxic marginal sea the new data from the dmv and previously published studies indicate that an average smv emits about 2 0 10 6 mol a 1 into the ocean via quiescent dewatering the global flux of dissolved methane from smvs into the ocean is estimated to fall into the order of 10 10 mol a 1 additional methane fluxes arise during periods of active mud expulsion and gas bubbling occurring episodically at the dmv and other smvs

geochemical mass transfer patterns as indicators of the architecture of a complete volcanic hosted massive sulfide hydrothermal alteration system panorama district pilbara western australia outstanding exposure across the panorama district in the archean pilbara block of western australia reveals a cross section through a complete volcanic hosted massive sulfide vhms hydrothermal alteration system in an area of low metamorphic grade and very low strain geochemical maps in combination with alteration maps document mass transfer across this alteration system feldspar bearing rocks at the top of the volcanic pile are enriched in k and si but depleted in na in contrast to those at the bottom of the volcanic pile that are enriched in na and depleted in k sericite quartz altered rocks are typically enriched in si and depleted in ca na and fe whereas chlorite quartz altered rocks which dominate transgressive feldspar destructive alteration zones are marked by k ca na depletion and mg fe enrichment copper and zn are strongly depleted in rocks at the base of the volcanic pile and to a lesser extent in transgressive feldspar destructive alteration zones the amount of metal leached from the volcanic pile is far greater than that contained in known deposits and thus a magmatic metal source is not necessary to explain the formation of the panorama vhms deposits mass transfer patterns at panorama have similarities to existing models for regional vhms hydrothermal alteration systems including the distribution of alkali elements in feldspar bearing semiconformable alteration zones and the presence of a base metal depleted zone at the base of the volcanic pile however there are significant differences both in the architecture of the hydrothermal alteration system and in mass transfer patterns these include si enrichment rather than depletion at the top of the volcanic pile widespread mg enrichment outside of the upper semiconformable alteration zones the absence of a silica cap rock above the base metal depleted zone more hydrous alteration assemblages in the zones of base metal depletion and extensive zones of transgressive feldspar destructive alteration

rare earth elements in cold seep carbonates from the niger delta abstract the circulation of methane rich fluids at cold seeps often leads to precipitation of authigenic carbonates mediated by microbial activity which can be used as archives of fluid seepage on continental margins in this study we have investigated the potential of using rare earth element ree concentrations in authigenic carbonates for tracing fluid sources and providing information on associated biogeochemical processes at cold seeps we have examined various chemical procedures for the analysis of ree in authigenic carbonates and present a robust method using dilute acetic acid solution that allows the extraction of ree from carbonate phases with reduced contamination from fe mn oxides and detrital minerals using this method we analysed a series of carbonate samples collected at various deep sea sites of active fluid seepage on the niger delta for their ree and trace element concentrations 13c and 18o values and 87sr 86sr isotope compositions we show that the ree composition of cold seep carbonates is controlled primarily by that of the fluid from which they have precipitated our results also suggest that significant ree fractionation can occur during carbonate precipitation which can be related to various degrees of ree complexation by organic versus carbonate ligands in response to changing pore water chemical composition for parameters such as carbonate alkalinity

particle geochemistry in the rainbow hydrothermal plume mid atlantic ridge we report the analysis of 18 large volume 500 1500 l in situ filtered samples of particulate material from the largest hydrothermal plume on the mid atlantic ridge overlying the ultramafic hosted rainbow hydrothermal field at 36 deg 14 n measured particulate iron concentrations reach 614 nm high concentrations of particulate fe oxyhydroxides result from the extremely high fe concentration 24 mm and fe h2s ratio 24 of the vent fluids and persist to at least 10 km away from the vent site due to the advection of plume material with the ambient along axis flow two of the nine pairs of pump deployments appear to have intercepted the buoyant or otherwise very young portion of the hydrothermal plume these samples are characterized by anomalously compared to neutrally buoyant plume samples high concentrations of mg u and chalcophile elements and low concentrations of mn ca v y and the rare earth elements ree within the neutrally buoyant plume elemental distributions are largely consistent with previously observed behaviors preferential removal of chalcophile elements conservative behavior of oxyanions p v and u and continuous scavenging of y and the ree this consistency is particularly significant in light of the underlying differences in fluid chemistry between rainbow and other studied sites chalcophile elements are preferentially removed from the plume in the order cd zn co cu phosphorus iron and vanadium iron ratios for the neutrally buoyant plume are consistent with global trends with respect to the concentration of dissolved phosphate in ambient seawater comparison of buoyant and neutrally buoyant plume ratios with data from hydrothermal sediments underlying the rainbow plume cave et al 2002 indicates however that while p fe ratios are indeed constant v fe ratios increase progressively from early stage plume particles to sediments ree distributions in the buoyant and neutrally buoyant plume appear most consistent with a continuous scavenging process during dispersion through the water column

spatial and temporal diversity of early proterozoic volcanic sequences comparisons between the baltic and laurentian shields abstract early proterozoic volcanic supracrustal sequences in the baltic shield exhibit considerable diversity in their geochemical composition sedimentary and metallogenetic associations the earliest volcanic sequences are calc alkaline associations whose age and mode of origin is poorly understood at present tholeiitic metabasalts erupted at about 2 2 2 0 ga form a significant component of lapponian and jatulian supracrustal sequences in the northern part of the shield these lavas were erupted in marine basins and rifts within archaean cratonic lithosphere ultramafic lavas are present but appear to be spatially restricted to certain supracrustal belts marginal to possible crustal suture zones e g the karasjok belt tholeiitic metabasalts of slightly younger age 1 96 ga form part of an ophiolitic association at jormua in north central finland other kalevian suites of similar age at outokumpu and in northern finland may have formed in marginal basins adjacent to a proterozoic ocean the svecofennian domain of central sweden and southern finland locally contains primitive oceanic arc like terranes representing a juvenile addition to the proterozoic crust most of the svecofennian complex is however composed of turbiditic sediments felsic calc alkaline volcanics dated at 1 92 1 87 ga and plutonic suites which reflect sedimentary and igneous reprocessing of the juvenile arc terranes the porphyry volcanics of norrbotten were subaerially erupted between 1 9 and 1 87 ga they reflect maturation of the svecofennian arc system to an andinotype continental margin terrestrial calc alkaline volcanism continued until 1 6 ga in the transscandinavian granite porphyry belt all the volcanic components of the classic wilson cycle have now been recognised in the baltic shield the early proterozoic history of which is thus readily explicable in terms of plate tectonic concepts in the laurentian shield tholeiitic metabasalts are associated with ultramafic lavas in the cape smith belt and elsewhere along the northern margin of the superior craton the ophiolitic association has recently been described from the cape smith belt the trans hudson and svecofennian belts are complex accretional orogens with comparable magmatic and tectonic histories pre grenville reconstructions suggest that the continuation of the transscandinavian granite porphyry belt is to be found in labrador and possibly in the southern part of the concealed mid continent region in the usa the numerous similarities between the two shields suggest they underwent a parallel and possible juxtaposed evolution in early proterozoic time

towards rational use of baffle arrays on sloped and horizontal terrain for filtering boulders baffle arrays are used to filter boulders from granular flows such that the impact load exerted on barriers is reduced however current guidelines provide limited recommendations on baffle design

a seismic model of the precambrian crust along the coast of southeastern sweden the coast profile wide angle airgun experiment and the southern part of fennolora revisited abstract within the framework of the eurobridge project the p wave velocity structure along the coast of southeastern sweden was determined from 2 d forward modeling of seismic refraction and wide angle reflection airgun data on a profile named the coast profile previously obtained results of the fennolora profile were also used the studied traverse extends from the ca 1 90 1 86 ga svecofennian orogenic domain in the north to the blekinge bornholm region bbr in the south where the dominant crust forming granitoid rocks were emplaced between ca 1 78 and 1 72 ga in the intervening area the crust has ages between these extremes the rocks of the different age groups and lithologies mostly being arranged in roughly ew trending belts however there are also substantially younger shear zones and granite intrusions the obtained results show a crustal structure typical of shield areas with velocities of ca 5 9 6 5 km s in the upper and 6 5 6 9 km s in the lower parts of the final model the crustal levels below approximately 40 km have velocities above 7 km s the moho is situated at depths of ca 36 km beneath the bbr and 40 42 km beneath most of the modeled part of the svecofennian orogen the thickest now identified crust is about 52 km it forms a wide belt along the southern edge of the latter domain the variations of crustal thickness do not appear to occur smoothly but rather stepwise the particulars of the resultant moho topography are described in a genetic interpretation it is suggested that the metamorphic island arc environment in the southern part of the svecofennian domain developed by a subduction related process ending ca 1 85 ga ago but that similar developments including mafic underplating continued still later until at least ca 1 77 ga farther to the south between ca 1 55 and 1 45 ga the bbr and adjoining area were affected by largely granitoid magmatism associated with foliation and the formation of major zones of shearing together the various episodes of underplating subduction and crustal stacking appear to have been responsible for the varying depths and present step like topographies of moho and the crust

the detection of potassic alteration by gamma ray spectrometry recognition of alteration related to mineralization canadian case histories document the use of airborne and ground gamma ray spectrometry to detect and map potassium alteration associated with different styles of mineralization these include volcanic hosted massive sulfides cu pb zn pilley s island newfoundland polymetallic magmatic hydrothermal deposits au co cu bi w as lou lake northwest territories and porphyry cu au mo deposits at mt milligan british columbia and casino yukon territory mineralization in two of these areas was discovered using airborne gamma ray spectrometry in each case history alteration produces potassium anomalies that can be distinguished from normal lithologic potassium variations by characteristic lows in eth k ratios interpretations incorporating airborne and ground spectrometry surficial and bedrock geochemistry and petrology show that gamma ray spectrometric patterns provide powerful guides to mineralization this information complements magnetic electromagnetic geological and conventional geochemica

geochemistry and tectonomagmatic affinities of the metavolcanic rocks of the early proterozoic tampere schist belt southern finland abstract the c 1 9 ga old tampere schist belt is part of the svecofennian province of finland and sweden which was formed by extensive mantle derived crustal growth during the early proterozoic the volcanic rocks of the belt range widely in chemical composition part of the variation is due to alteration and reworking but the main control are primary compositional characteristics the rocks range from almost low k tholeiitic units to shoshonitic and trachytic units intermediate rocks of calc alkaline affinities being most common by and large the volcanic rocks resemble those of present day volcanic arcs calc alkaline intermediate rocks dominate and the contents of tio2 in mafic rocks are often low some units are exceptional by exhibiting non arc affinities they are fairly high in ti and may thus mark extensional tectonic events the percentage of andesites dacites rhyolites or percent adr mostly exceeds 50 which suggests that the crust was more than 20 km thick during the eruption of most of the studied rocks the tampere schist belt thus resembles mature island arcs or volcanic arcs at or close to active continental margins rather than immature intra oceanic island arcs archaean crust is absent and it can be inferred that the crust was segregated from the mantle during the proterozoic the svecofennian province as a whole appears to differ from present day convergent plate margins by the rapidity of its crustal evolution

temporal stability of the neodymium isotope signature of the holocene to glacial north atlantic the neodymium isotopic composition of marine precipitates is increasingly recognized as a powerful tool for identifying changes in ocean circulation and mixing on million year to millennial timescales unlike nutrient proxies such as 13 c or cd ca nd isotopes are not thought to be altered in any significant way by biological processes and thus they can serve as a quasi conservative water mass tracer however the application of nd isotopes in understanding the role of thermohaline circulation in rapid climate change is currently hindered by the lack of direct constraints on the signature of the north atlantic end member through time here we present the first results of nd isotopes measured in u th dated deep sea corals from the new england seamounts in the northwest atlantic ocean our data are consistent with the conclusion that the nd isotopic composition of north atlantic deep and intermediate water has remained nearly constant through the last glacial cycle the results address long standing concerns that there may have been significant changes in the nd isotopic composition of the north atlantic end member during this interval and substantiate the applicability of this novel tracer on millennial timescales for paleoceanography research

sulphur isotope compositions in the ammeberg zn pb ore deposit south central sweden genetic implications the distribution of sulphur isotope compositions in the ammeberg sulphide ore deposit is discussed the 34s values for various sulphides show a complex pattern of fluctuations between isotopic equilibrium and non equilibrium conditions this feature as well as the observed variations in the 34s values of galena and sphalerite are interpreted to have originated from successive pulses of sulphide forming solutions on the basis of geological field criteria and sulphur isotope data the ammeberg deposit is considered to be a typical distal mineralization belonging to the volcanic exhalative group of ore deposits the banded structure of the ore the spatial separation of pb and zn and the presence of discrete persistant ore layers probably relate to the type of convective system that created the mineral forming solutions and to the various processes taking place when the brines were expelled onto the sea floor

neodymium isotopic composition and rare earth element concentrations in the deep and intermediate nordic seas constraints on the iceland scotland overflow water signature neodymium isotopic composition and rare earth element concentrations were measured in seawater samples from eleven stations in the nordic seas these data allow us to study how the iceland scotland overflow water isow acquires its neodymium signature in the modern ocean the waters overflowing the faroe shetland channel are characterized by nd 8 2 0 6 in good agreement with the only other data point published 19 years ago in the greenland and iceland seas the water masses leading to the formation of the isow display lower neodymium isotopic composition with nd around 11 and 9 respectively since no water masses in the nordic seas are characterized by nd 8 the radiogenic signature of the isow likely reflects inputs from the highly radiogenic norwegian basin basaltic margins jan mayen iceland faroe with nd 7 in addition to the neodymium isotopic composition the rare earth element patterns suggest that these inputs occur via the remobilization which includes resuspension and dissolution of sediments deposited on the margins whereas the neodymium isotopic composition behaves conservatively in the oceans in the absence of lithogenic inputs and can be used as a water mass tracer these results emphasize the role of interactions between sediments deposited on margins and seawater in the acquisition of the neodymium isotopic composition of water masses these results should allow a better use of this parameter to trace the present and the past circulation in the north atlantic

lateral variations in supracrustal geology within the swedish part of the southern svecokarelian volcanic belt abstract the southern volcanic belt of the proterozoic svecokarelian orogen exhibits significant lateral changes of lithology and stratigraphy in the swedish part of the belt metavolcanites dominate the stratigraphic column to the west whereas they form only minor interbeds in the predominant metasediments to the east the metavolcanites of the western area are almost exclusively rhyolitic while the eastern area also contains mafic and intermediate rocks mg rich quartz mica schists which are believed to have been formed by synvolcanic alteration at depth appear to be restricted to the western area these features are compatible with an area of rhyolitic volcanic centres in the west supplying tephra into a sedimentary basin in the east this episode of volcanism thus appears to represent an interlude in the deposition of sediments it has been suggested that this rhyolitic volcanism originated from a continental crust which was activated by extensional tectonics

proterozoic seawater felsic volcanics interaction w bergslagen sweden evidence for high ree mobility and implications for 1 8 ga seawater compositions mg enrichment in diffusely bounded schistose alteration zones occurring in proterozoic submarine felsic volcanics ne of hjulsjo w bergslagen is shown to result from felsic rock seawater interaction in a sub seafloor hydrothermal system the alteration is apparently in two stages feldspar being altered first to a kaolinite type clay which is then replaced by mg chlorite

rockfall induced block propagation on a soil slope northern italy this paper reports the field evidence and the kinematical study of the motion of two blocks a and b mobilised by a rockfall in lavone valtrompia northern italy on 14 february 1987 the two sequences of impact marks left by the blocks on the ground surface were measured and the lithostratigraphical features of the debris slope were surveyed on the basis of the field collected input data several computer simulations were carried out to calculate the coefficients of restitution e satisfying the trajectory conditions the computed output values show that rebound trajectories require high coefficients of restitution 0 8 e 0 9 back calculated impact velocities range from 9 2 to 19 8 m s trajectory heights vary from 0 to 2 4 m above the slope surface block trajectories differ considerably according to the circumstances of initial air projection i e to initial rebound angle r the calculated values of r denote a considerable range 36 emphasising the random nature of this parameter the described case history shows that rockfall computer analyses can be an effective tool to describe the bouncing propagation of single blocks but care must be taken in choosing the restitution coefficient e and the geometrical parameters of initial air projections

tectonic styles of early proterozoic ore deposition in the fennoscandian shield the early proterozoic metallogenic events of the fennoscandian shield are connected with two major stages of crustal evolution the karelian continental development 2 5 2 1 ga and the svecofennian orogeny 2 0 1 75 ga the karelian continental development was dominated by deposition of terrestrial sediments and tholeiitic volcanism on archaean crust a tensional regime probably associated with a mantle plume and partial melting of the upper mantle culminated in the generation of an ene wsw trending rift zone which was intruded by tholeiitic magma 2 44 ga ago some 15 layered igneous bodies hosting cr pge ni cu and fe v ti deposits are known in the kemi suhanko and koillismaa belts these mafic ultramafic bodies originally formed either several lopoliths or one single layered igneous complex with a minimum length of 260 km nw se and nnw sse trending dolerite dykes intruded the rifted and attenuated archaean crust 2 25 2 0 ga ago preceding ocean opening the coeval ne sw trending dolerite dykes in the northern part of the shield are interpreted as manifestation of an aulacogen the failed arm of a triple armed rift system oceanic crust is preserved in 1 96 ga old ophiolite complexes the cu co zn ni and cr contents of the outokumpu type deposits derive from hydrothermal leaching of oceanic crust and were discharged together with chemogenic cherts and carbonates from ascending hydrothermal fluids on the seafloor above fissure vents in the northern part of the shield rifting and probably ocean opening resulted in the formation of the layered tholeiitic sedimentary complex of the petsenga ni cu district intruded by mineralized mafic ultramafic magma the age of this event is poorly constrained the basin was subsequently closed and continental collision of the kola suture was accompanied by southward obduction of the lapland granulite belt on the archaean crust during the svecofennian orogeny the divergent continental margin was converted into an active margin early subduction of oceanic crust produced oceanic island arcs intruded by 1 93 1 9 ga old tonalites and trondhjemites subsequent subduction of oceanic crust generated 1 9 1 87 ga old continental island arcs associated with massive sulphide cu zn pb ag au deposits the island arcs were accreted to the archaean crust in a concave belt containing the ore districts of kiruna skellefte vihanti pyhasalmi aijala orijarvi and bergslagen bimodal volcanic suites with felsic calc alkaline and mafic tholeiitic volcanites are attributed to rifting of the overriding plate above subduction zones ni cu deposits in synorogenic 1 9 1 87 ga old mafic ultramafic intrusions occur in linear fault controlled belts at the margin of the archaean crust the generation of ni bearing tholeiitic to komatiitic magma is explained by partial melting of the mantle wedge above the early subduction zone magma differentiation and magma upwelling along transcurrent faults on the continental margin sulphur was probably assimilated from the supracrustal wall rocks 1 89 1 87 ga old early svecofennian granitoids are associated with porphyry type cu mo au deposits widespread late svecofennian s type 1 84 1 75 ga granitic magmatism generated minor mo u w sn and ree deposits emphasis is laid on the importance of geotectonic models as a basis for further exploration in the fennoscandian shield

sr ca and mg ca ratios in niger delta sediments implications for authigenic carbonate genesis in cold seep environments we report on a reconnaissance analysis of the geochemical composition of authigenic carbonates and sediment samples collected from various seepage sites on the niger deep sea fan our aim has been to investigate whether evidence for the presence of authigenic carbonates and gas hydrates within sediments is discernible from solid phase sediment geochemistry we show that sedimentary sr ca and mg ca ratios can be used to infer the presence of authigenic aragonite sr rich and mg rich carbonate phases high mg calcite dolomite in cold seep settings using sr ca and mg ca ratios the proportion wt of authigenic carbonates in niger fan sediments can be calculated from a mixing model between sediment fractions of terrigenous material biogenic calcite aragonite and high mg calcite this approach was applied to high resolution geochemical profiles along sediment cores recovered from various cold seep settings mud volcano diapirs pockmarks gas hydrate bearing sediments our data reveal that authigenic carbonates occur as discrete phases in sediments from gas hydrate bearing areas suggesting that such carbonate rich sediment layers may represent paleo indicators for ancient methane seepage in marine sediments possibly associated to gas hydrate reservoirs

hybridisation in middle proterozoic high level ring complexes aland sw finland abstract the 1800 ma ring complexes of the aland archipelago sw finland were emplaced shortly after the cessation of the major svecofennian orogenic activity during a subsequent period of continuous but episodic mantle crust interaction and crustal adjustment culminating in the 1600 1500 ma rapakivi event chemical data for these complexes indicate that their range of compositions are a result of a complex mixing sequence at depth involving an alkaline lamprophyric magma an aluminous hfs element enriched tholeiitic magma associated with anorthositic magmatism and contamination by a disrupted crystallines mid crustal rapakivi granite body the complexes represent premature local tappings of a developing rapakivi granite source region in the lower crust contamination was a result of thermo mechanical stoping by a hot alkaline basic magma impounded beneath a granite sheet rapakivi granite genesis in southern finland is considered to be an integral part of both lower crustal and upper mantle responses and evolution subsequent to svecofennian orogenic development

a model for the formation of the iron manganese and sulphide ores of central sweden the non apatitic iron ores manganese ores and sulphide ores of central sweden which occur in a volcano sedimentary complex of early proterozoic age have a common volcanogenic origin the close association between specific ore types and metavolcanics suggests a stratigraphic control of the ores on a regional scale deposited in basins the ores formed with increasing water depth increasing ph and decreasing eh in the following order quartz banded iron ores mostly lacking sulphides non man ganiferous skarn iron ores with cu fe sulphides manganiferous skarn iron ores with zn pb sulphides and fe2 mn2 silicates eulysites the latter two ore types occur adjacent to argillites greywackes indicating a reducing environment the manganese oxide ores of the langban type represent a formation intermediate between the quartzbanded iron ores and the manganiferous skarn iron ores

hydrothermal alteration as a control of regional geochemistry and ore formation in the central baltic shield in a geochemical study of the proterozoic volcano sedimentary bergslagen ore province in central sweden more than 1000 eruptive rocks were analyzed for main and trace elements the volcanic rocks form a bimodal suite dominated by rhyolites but deficient in andesites igneous geochemical variation bears little relevance to the occurrence and distribution of ores which mostly appear related to secondary alteration patterns hydrothermal metasomatic alteration occurs on a regional scale and has affected markedly more than half of the 732 analyzed macroscopically fresh porphyritic volcanic rocks metasomatism produced extreme na and k differentiation and fe mg si relationships incompatible with igneous variation patterns enrichment in na and mg and leaching of ore forming metals are prominent in the lower parts of the volcanic pile whereas meta volcanics enriched in k and volcanogenic sediments associated with ores and marbles dominate the upper levels the metasomatic alteration of the volcanic rocks and the formation of most ores are two aspects of a comprehensive process of hydrothermal convection which circulated sea water extracted the ore forming elements from the lower levels of the volcanic pile and enriched them at or close to the top of the volcanic sequence

ore deposition in a proterozoic incipient rift zone environment a tentative model for the filipstad grythyttan hjulsjo region bergslagen sweden the 1 9 1 8 ga bergslagen supracrustal series comprises an early volcanic stage represented by the lower leptite group an initial rift stage by the middle leptite group a rift stage by the upper leptite halleflinta and slate group metabasites and the granite granophyre suite and a post rift stage by conglomerate beds remobilized granite granophyres and the hyttsjo gabbro tonalite suite the formation and subsequent alteration of iron manganese and sulfide skarn ores in the supracrustal series involve

global comparisons of volcanic associated massive sulphide districts although volcanic associated massive sulphide vms deposits have been studied extensively the geodynamic processes that control their genesis location and timing remain poorly understood compar

the lovisa stratiform zn pb deposit bergslagen sweden structure stratigraphy and ore genesis medium to high grade metamorphosed 1 9 ga stratiform syngenetic zn pb ag sulfide deposits comprise an economically important type of ore deposit in the bergslagen lithotectonic unit of the fenn

high element mobility in 1 9 1 86 ga hydrothermal alteration zones bergslagen central sweden relationships with exhalative fe ore mineralizations abstract the 1 9 1 86 ga ensialic belt of western bergslagen sweden comprizes a 12 km thick felsic volcano sedimentary sequence intruded by syn volcanic granitic plutons and mafic dykes and sheets developed in a rifted continental setting regional low temperature alteration of the supracrustal sequence produced greenschist to low amphibolite facies mineral assemblages localized cross cutting zones of intense alteration are developed in felsic volcanics which have been affected by the regional alteration producing drastic changes in both mineralogy and chemistry these zones are found close to the hjulsjo granite granophyre intrusive complex most probably the heat source for the hydrothermal system and related to the exhalative sirsjoberg osjoberg fe oxide deposits the hjulsjo zones are subdivided into inner and outer zones based on differences in mineralogy and chemistry resulting from the variable intensity of alteration while the degree to which most elements are leached increases from the outer into the inner zones mg increases with alteration intensity and si and al stay unchanged although they were mobilized during alteration initially k rb fe and mn increase in the outer zones but are depleted in the inner zones rare earth elements ree are depleted with the light ree being more depleted than the heavy ree a pronounced negative eu anomaly is generally present the hydrothermal fluid was enriched in ore forming metals during alteration and leaching ree patterns of exhalative minerals indicate that the fe oxide deposits were derived from these hydrothermal fluids

the mineral chemistry of hydrothermally altered and metamorphosed wall rocks at the stollberg fe pb zn mn ag deposit bergslagen sweden the c 1 9 ga old stollberg sulphide and mnrich skarn iron ores and sulphide ores in bergslagen south central sweden are hosted by hydrothermally altered and metamorphosed felsic volcanic and volcaniclastic rocks the ores are underlain by comformable alteration zones characterized by albite gedrite quartz and biotite muscovite plagioclase k feldspar quartz garnet assemblages the present mineralogies are interpreted as medium grade metamorphic equivalents to the original alteration mineral assemblages pt conditions during prograde regional metamorphism are semiquantatively determined to be 510 to 560 c at approximately 3 kbar with increasing modal content of gedrite and biotite in the alteration zones the mg fe ratios and xmg s in octahedral positions of these minerals also increase in the gedrite bearing strata whole rock mg fe ratios remain constant whereas in the biotite rich unit the wholerock mg fe trend is parallel to that of the biotites

evidence for intense ree scavenging at cold seeps from the niger delta margin for many trace elements continental margins are the location of intense exchange processes between sediment and seawater which control their distribution in the water column but have yet to be fully understood in this study we have investigated the impact of fluid seepage at cold seeps on the marine cycle of neodymium we determined dissolved and total dissolvable td concentrations for ree and well established tracers of fluid seepage ch4 tdfe tdmn and nd isotopic compositions in seawater samples collected above cold seeps and a reference site i e away from any fluid venting area from the niger delta margin we also analyzed cold seep authigenic phases and various core top sediment fractions pore water detrital component easily leachable phases uncleaned foraminifera recovered near the hydrocast stations methane tdfe and tdmn concentrations clearly indicate active fluid venting at the studied seeps with plumes rising up to about 100 m above the seafloor depth profiles show pronounced ree enrichments in the non filtered samples td concentrations within plumes whereas filtered samples dissolved concentrations exhibit slight ree depletion in plumes relative to the overlying water column and display typical seawater ree patterns these results suggest that the net flux of ree emitted into seawater at cold seeps is controlled by the presence of particulate phases most probably fe mn oxyhydroxides associated to resuspended sediments at the reference site however our data reveal significant enrichment for dissolved ree in bottom waters that clearly relates to diffusive benthic fluxes from surface sediments neodymium isotopic ratios measured in the water column range from end 15 7 to 10 4 evidence that the end values for antarctic intermediate waters aaiw differed from those reported for the same water mass at open ocean settings shows that sediment water interactions take place in the gulf of guinea at each site however the bottom water end signature generally differs from that for cold seep minerals easily leachable sediment phases and detrital fractions from local sediments ruling out the possibility that seepage of methane rich fluids and sediment dissolution act as a substantial source of dissolved nd to seawater in the gulf of guinea taken together our data hence suggest that co precipitation of fe mn oxyhydroxide phases in sub surface sediments leads to quantitative scavenging of dissolved ree at cold seeps preventing their emission into bottom waters most probably it is likely that diffusion from suboxic surface sediments dominates the exchange processes affecting the marine nd cycle at the niger delta margin

southern ocean evidence for reduced export of north atlantic deep water during heinrich event 1 deep sea corals form unique high resolution archives of ocean circulation that can be dated using the decay of uranium to thorium they are abundant in the southern ocean and can provide unprecedented insights into ocean circulation and ocean chemistry on sub millennial time scales in areas where application of traditional paleoceanographic proxies is difficult here we present the first coupled neodymium nd isotope and radiocarbon data from deep sea corals in the drake passage southern ocean adding new constraints on ocean circulation during the last heinrich event h1 16 7 ka the modern day drake passage water column is homogeneous with respect to nd isotopes expressed in epsilon units nd its isotopic value of close to 9 is largely controlled by the mixture of north atlantic deep water and pacific deep water the aragonite of modern drake passage corals reflects this water column value whereas a fossil coral from h1 is significantly higher at 6 4 0 4 we interpret this 2 5 unit shift as a reduction in the influence of north atlantic sourced nd in the southern ocean during h1 this interpretation is supported by a series of radiocarbon analyses on the same sample and is consistent with a twofold or greater reduction in export of north atlantic waters from the atlantic basin combining analyses of radiocarbon and nd isotopes on u series dated deep sea coral skeletons holds great potential for quantification of past ocean ventilation rates

metamorphism of magnesium altered felsic volcanic rocks from bergslagen central sweden a transition from mg chlorite to cordierite rich rocks abstract the ca 1 9 ga old felsic volcanic rocks of the bergslagen province have been affected by synvolcanic hydrothermal mg metasomatism a spatial relationship exists between mg alteration zones and calc silicate carbonate banded iron mineralizations and a genetic link is suggested this is supported by the occurrence of the mg rich tourmaline dravite which exists in the mg alteration zones as well as in the wall rocks to iron oxide mineralizations following later regional metamorphism and deformation these rocks occur as large zones of mg rich schists parallel to sub parallel with the regional foliation s1 the dravite crystals have been affected by this regional deformation a second deformational episode folded s1 along steeply dipping fold axes locally this resulted in a crenulation cleavage and the development of a new generation of micas s2 crosscutting s1 in the westernmost areas the mg schists contain a fine grained network of mg chlorite and muscovite with little or no preferred orientation indicating low pressures and low grade metamorphic conditions the grade of recrystallization and deformation increase towards the east and a boundary between low and medium grade metamorphic terrains is crossed the metamorphic boundary is marked by the disappearance of chlorite and the appearance of cordierite in the mg schists porphyroblasts of mg chlorite or cordierite grew across s1 and cordierite porphyroblasts are transected by s2 micas this indicates that the peak of regional metamorphism occurred between the two deformational episodes retrogression of cordierite to chlorite and muscovite is confined to the vicinity of crosscutting s2 micas

a lead isotope study of two sulphide deposits and adjacent igneous rocks in south central sweden two sulphide ore deposits svardsjo and ammeberg occurring in the bergslagen ore district in south central sweden have been examined for their pb isotope compositions analyses of the ore lead reveals a great isotopic homogeneity with compositions that nearly coincide with results obtained from other deposits in the area the stacey and kramers growth model for pb in conformable ores yields model ages however that are 100 150 ma too low in comparison with the accepted geological ages isotopic data from whole rocks and mineral separates indicate an open system behaviour with respect to u and pb on the basis of geological geochemical evidence the sulphide ores in bergslagen are considered to have formed by volcanic exhalative processes the ore lead is interpreted as a mixture of newly added mantle material and a minor archean component it is likely that the main part of the ore lead was derived from volcanic source rocks but most probably sediments interbedded in the volcanic succession also played some role

systematics of hydrothermal alteration at the falun base metal sulfide deposit and implications for ore genesis and exploration bergslagen ore district fennoscandian shield sweden the paleoproterozoic falun zn pb cu au ag pyritic sulfide deposit in the bergslagen ore district sweden is enveloped by hydrothermally altered rocks metamorphosed to the lower amphibolite facie

neodymium budget in the modern ocean and paleo oceanographic implications the oceanic nd budget is calculated using a steady state 10 box model and a compilation of field data this is the first attempt to propose consistent estimates of the nd fluxes entering the ocean as well as indicating possible nd sources and the proportion of nd fluxes exchanged between dissolved and particulate fractions with presently available nd data the best estimates give a total nd influx of 9 x 10 9 g yr which leads to an oceanic nd residence time of 500 years from modeling tests we suggest that the authigenic nd scavenged by particulates is 100 remineralized in the deep ocean the total exchanged nd flux may be as high as 2 x 10 10 g yr the epsilon nd 0 values of the influxes are 22 11 1 and 4 for the north atlantic surface atlantic north pacific and surface indo pacific regions respectively atmospheric and riverine nd fluxes are insufficient to explain the magnitude and regional variability of calculated nd influxes and epsilon nd 0 we propose continental margins as an additional source supplying nd to the ocean using the model calibrated for nd we examine the sensitivity of deep water epsilon nd 0 to variations of nd inputs to the ocean deep water nd concentrations and epsilon nd 0 vary with the changes in nd influxes and their epsilon nd 0 as nd sources to the ocean may change during glacial interglacial periods the epsilon nd 0 shifts recorded in ferromanganese nodules and crusts do not necessarily reflect changes in paleoceanic circulation the effects of continental erosion should be considered in reconstructing patterns of ocean circulation using nd isotopes

rockfall rebound comparison of detailed field experiments and alternative modelling approaches the accuracy of rockfall trajectory simulations mainly rests on the calculation of the rebound of fragments following their impact on the slope this paper is dedicated to the comparative analysis of two rebound modelling approaches currently used in rockfall simulation using field experiments of single rebounds the two approaches consist in either modelling the rock as a single material point lumped mass approach or in explicitly accounting for the fragment shape rigid body approach a lumped mass model accounting for the coupling between translational and rotational velocities and introducing a slope perturbation angle was used a rigid body approach modelling the rocks as rigid locally deformable in the vicinity of the contact surface assemblies of spheres was chosen the comparative analysis of the rebound models shows that both of them are efficient with only a few parameters the main limitation of each approach are the calibration of the value of the slope perturbation roughness angle for the lumped mass approach and the estimation of the rock length and height from field geological and historical analyses for the rigid body approach finally both rebound models require being improved in a pragmatic manner to better predict the rotational velocities distribution copyright 2012 john wiley sons ltd

geotechnical characterization and rockfall simulation of a slope a practical case study from south tyrol italy abstract rockfalls occur often along the state road ss241 val d ega in the val d ega valley south tyrol italy in order to protect the road and the traffic stabilization works are necessary detailed geological and geomorphologic mapping along structural and geomechanic sections was carried out and experimental rockfall trails were examined on the slope above the state road between km 3 550 and 3 830 rockfall simulation rock mass classification and an interpretation of field data especially concerning joints wrapped up the investigations they helped find the specific need for stabilization work and its positioning along the slope the stabilization works were completed on february 2002 another important aspect concerns ongoing geotechnical investigations and stabilization works urgently realised during autumn 1999 this paper is a practical approach in solving rockfall problems along public roads it should be considered as a workbook for university personnel and also for professional geologists

metamorphic ore remobilization in the hallefors district bergslagen sweden constraints from mineralogical and small scale sulphur isotope studies the marble and metavolcanic hosted pb zn ag sb as deposits of the hallefors district located in the palaeoproterozoic bergslagen ore province south central sweden comprise both stratabound sulphides and discordant ag rich sulphide sulphosalt veins the complex sulphide sulphosalt assemblages of the alfrida jan olof mines at hallefors were investigated by a combination of ore microscopy electron microprobe analysis and in situ laser sulphur isotope analysis the massive ore is characterized by positive and homoge neous d 34 s 1 4 to 2 7 v cdt whereas vein hosted sulphides and sulphosalts exhibit similar but generally less positive to slightly negative d 34 s 0 6 to 2 0 comparison of the observed ore mineral assemblages with calculated phase equilibria in the sys tem fe as s o h and isotopic fractionation as a function of temperature oxygen fugacity and ph indi cates that the vein type mineralization was formed from relatively reduced and rather alkaline hydrothermal fluids at these reduced conditions fractionation of d 34 s via changes of fo2 is insignificant and thus the isotopic signatures of the vein minerals directly reflect the com position of the sulphur source we therefore conclude that the vein type ore essentially inherited the sulphur isotope signature from the pre existing massive sulp hides via metamorphic remobilization at approximately 300 400c and 2 3 kbar scales of remobilization observable are on the order of about 5 mm to 30 cm overall the sulphide sulphosalt assemblages from the alfrida jan olof mines exhibit d 34 s values which are comparable to a majority of metasupracrustal hosted deposits in the bergslagen province thereby suggesting a common origin from ca 1 90 1 88 ga volcanic hydro thermal processes