palaeoproterozoic rifting and formation of sulphide deposits along the southwestern margin of the svecofennian domain southern sweden abstract a mineralized palaeoproterozoic volcanic sequence has been identified southwest of vetlanda in southern sweden the sequence which is defined as the froderyd group is surrounded by 1 78 ga granitoids and may be considered as the southernmost segment of svecofennian crust in sweden the froderyd group has a bimodal geochemical character and is dominated by pillow basalts and associated gabbros but rhyolites thin intercalations of marble and stratiform sulphide ores do also occur the carbonate intercalations and the stratiform sulphide ores are interpreted as submarine exhalites formed syngenetically with the volcanic activity the mafic rocks have a typical mid ocean ridge basalt geochemistry with flat rare earth elements patterns the lead isotopic compositions of the mafic rocks and the associated stratiform sulphide ores support such a close affinity to juvenile sources with mantle character in contrast the rhyolites display more evolved geochemical signatures and isotopic patterns and are interpreted to represent remelted products of slightly older sialic crust a model for the formation of the froderyd group is presented suggesting rifting along a continental margin which may have occurred in the final stage of the svecofennian crust forming period

using multiple logistic regression and gis technology to predict landslide hazard in northeast kansas usa abstract landslides in the hilly terrain along the kansas and missouri rivers in northeastern kansas have caused millions of dollars in property damage during the last decade to address this problem a statistical method called multiple logistic regression has been used to create a landslide hazard map for atchison kansas and surrounding areas data included digitized geology slopes and landslides manipulated using arcview gis logistic regression relates predictor variables to the occurrence or nonoccurrence of landslides within geographic cells and uses the relationship to produce a map showing the probability of future landslides given local slopes and geologic units results indicated that slope is the most important variable for estimating landslide hazard in the study area geologic units consisting mostly of shale siltstone and sandstone were most susceptible to landslides soil type and aspect ratio were considered but excluded from the final analysis because these variables did not significantly add to the predictive power of the logistic regression soil types were highly correlated with the geologic units and no significant relationships existed between landslides and slope aspect

instantaneous outbursts in underground coal mines an overview and association with coal type instantaneous outbursts in underground coal mines have occurred in at least 16 countries involving both methane ch4 and carbon dioxide co2 the precise mechanisms of an instantaneous outburst are still unresolved but must consider the effects of stress gas content and physico mechanical properties of the coal other factors such as mining methods e g development heading into the coal seam and geological features e g coal seam disruptions from faulting can combine to exacerbate the problem prediction techniques continue to be unreliable and unexpected outburst incidents resulting in fatalities are a major concern for underground coal operations gas content thresholds of 9 m 3 t for ch4 and 6 m 3 t for co2 are used in the sydney basin to indicate outburst prone conditions but are reviewed on an individual mine basis and in mixed as situations data on the sorption behaviour of bowen basin coals from australia have provided an explanation for the conflicting results obtained by coal face desorption indices used for outburst proneness assessment a key factor appears to be different desorption rates displayed by banded coals which is supported by both laboratory and mine site investigations dull coal bands with high fusinite and semifusinite contents tend to display rapid desorption from solid coal for a given pressure drop the opposite is true for bright coal bands with high vitrinite contents and dull coal bands with high inertodetrinite contents consequently when face samples of dull fusinite or semifusinite rich coal of small particle size are taken for desorption testing much gas has already escaped and low readings result the converse applies for samples taken from coal bands with high vitrinite and or inertodetrinite contents in terms of outburst potential it is the bright vitrinite rich and the dull inertodetrinite rich sections of a coal seam that appear to be more outburst prone this is due to the ability of the solid coal to retain gas even after pressure reduction creating a gas content gradient across the coal face sufficient to initiate an outburst once the particle size of the coal is reduced rapid gas desorption can then take place c 1998 elsevier science

signatures from single airguns the far field signatures from a comprehensive and systematic airgun pulse test have been analyzed empirical relations between the characteristic signature parameters and depth 5 12 m pressure 100 137 bar 10 13 7 mpa and total chamber volume 0 65 9 5 l have been derived also the influence of using waveshape kits in different positions within the chamber has been tested the results indicate that 1 the amplitude is proportional to chamber pressure to the power 3 4 2 the bubble period is nearly independent of the position of the waveshape plate 3 the increase in primary bubble amplitude ratio is inversely proportional to the chamber volume above the waveshape plate 4 the amplitude is independent of airgun depth suggestions and comments regarding this work from dr b ursin and dr a ziolkowski are appreciated the field work was supported by the norwegian petroleum directorate through the continental shelf project at the seismological observatory university of bergen an airgun allowing for continuous variation of the chamber volumes was supplied by geco geophysical company of norway the purchase of two airguns was financed by norske getty exploration a s

calculation of electromagnetic radiation criterion for rockburst hazard forecast in coal mines intensive micro fracturing of rock close to mining operations accompanies an increase in the likelihood of rockbursting this fracturing causes an increase of the electromagnetic radiation emr level by up two orders of magnitude depending on the mining environment several examples of this enhanced emr are presented in this paper we first treat the emr theoretical criterion of rockburst hazard in coal mines and compare it with the empirical criterion of emr activity that was revealed on the basis of more than 400 different hazardous and non hazardous situations in underground coal mines only the following parameters are needed to estimate the emr criterion of rockburst hazard limiting value of gum volume mine working width coal seam thickness and coal elastic properties

subseafloor hydrothermal alteration during the early proterozoic at garpenberg central sweden the early proterozoic sulfide deposit at garpenberg is located in the metallogenetic province of central sweden it is a strata bound massive sulfide deposit contained in a supracrustal sequence of mainly acid metavolcanic rocks stratiform zn pb cu mineralization is underlain by cu bearing stockwork ore and an extensive alteration zone the sulfide ores and their altered wall rocks were formed by subseafloor hydrothermal activity the alteration pattern observed in the wall rocks of this deposit is consistent with a hydrothermal system where the fluid consists mainly of seawater and a high water rock mass ratio predominates the hydrothermal activity caused the destruction of the primary mineralogy mainly feldspars and a general redistribution of the chemical elements in the altered wall rocks which were principally depleted in ca na and eu and enriched in mg eu was redeposited with the ore metals near or at the seafloor and ca was deposited as limestone most of the major and trace elements show large mobility during the alteration only ti zr y and ree excluding eu behaved as relatively immobile elements

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

age and geochemistry of granites associated with momineralizations in western bergslagen sweden abstract the bergslagen area south central sweden where large amounts of fe cu zn pb au ag mo and w have been produced for several centuries is one of the oldest mining districts in europe two episodes of magmatism and ore formation can be distinguished 1 an older early svecofennian phase that generated 1890 1850 ma old calc alkaline continental margin volcanic and plutonic units related to the svecofennian orogeny and 2 a younger phase comprising potassiumrich granitoids which intruded over a period extending from 1825 to 1680 ma during the final stage of or subsequent to the regional metamorphism and deformation related to the svecofennian orogeny in recent years considerable confusion has dominated the discussion concerning the timing and setting of the mo w forming granites in western bergslagen in this study one of the most important intrusions of undeformed granite in western bergslagen has been investigated in regard to geochemistry and u pb zircon age the granite skalhojden has a peraluminous silica and potassium rich chemistry as well as a uniformly flat ree pattern with a marked negative eu anomaly the u pb data yielded an age of 1758 8 ma these data show convincingly that the granite is comparable to other 1800 1680 ma mo w bearing granitoids elsewhere in the fennoscandian shield but are in strong conflict with hypotheses on early svecofennian rift related crust and ore forming processes recently proposed for western bergslagen a revision of the models of crustal growth and ore formation in that area is suggested

tourmaline in the central swedish ore district more than 40 recently discovered tourmaline occurrences have been investigated in the mid proterozoic bergslagen ore district of central sweden some are spatially associated with ores others with zones of leaching remobilization and migmatization among the tourmaline bearing ore deposits are the dammberg znpb fe sulphide deposit the sala pb zn ag deposit the dalkarlsberg pershyttan and haksberg fe oxide deposits the leja cu deposit and the zinkgruvan zn pb ag deposit tourmaline has been recorded a as tourmalinites and tourmaline bearing chemical sediments b in tourmaline bearing skarns c in tourmaline quartz veins d as disseminations along the foliation in schists e in tourmaline pegmatites f in tourmalinized haloes in metavolcanites along tourmaline pegmatites and g in late joints tourmalinites tourmaline bearing chemical sediments and tourmaline bearing skarns are spatially associated with sulphide and oxide mineralizations the dravite components in these tourmalines are proportional to the size of zn pb sulphide mineralizations tourmalines from quartz veins close to and within ore deposits contain high zr and cr contents with increasing distance away from these deposits the zr and cr contents fall significantly tourmalines from pegmatites have inherited a number of trace element enrichments through partial melting and assimilation of volcaniclastic sediments into granitic melts despite magmatic homogenization zn contents in these tourmalines reflect the proximity of zn pb sulphide deposits decreasing away from them tourmalines from late joints with zn contents above the 100 ppm level are also indicative for the proximity of zn pb sulphide mineralizations thus some trace elements in these tourmalines may represent suitable exploration tools

a coupled approach to simulate initiation of outbursts of coal and gas model development an outburst of coal and gas is a major hazard in underground coal mining it occurs when certain conditions of coal stress strength and gassiness are met the outburst is recognized as a two step process i e initiation and development each step has its own characteristics and requires different approaches in numerical modeling as a first step the initiation process of the outburst is numerically simulated with a coupled simulator the simulator models the deformation and failure of a coal seam adsorption and desorption of gas and flow of gas and water in coal the simulator is developed by linking and sequentially executing two numerical codes flac3d and comet3 flac3d is a widely used commercial code designed for engineering mechanics computation while comet3 is a well established code to model gas and water production from desorption controlled reservoirs in this paper these two codes are linked and sequentially executed through coupling modules including a user designed c module and several modules developed with the build in fish language in flac3d these coupling modules are used to transfer relevant data between the codes a simple example to simulate the initiation of the outburst is also presented in this paper to demonstrate the capability of the coupled simulator

ensialic spreading subsidence in the mesozoic and palaeogene andes of central chile an oceanic plate subducting eastwards below a continental margin and resulting in crustal shortening can be inferred to have been active in central chile during the palaeozoic however the geological record for the mesozoic and palaeogene shows evidence of a persistent tensional regime and absence of crustal shortening although lateral asymmetry inherent to a subducting model is shown by this record a bilateral symmetry is also well substantiated a coupled action of plate subduction and spreading subsidence the latter taking place within the margin of a continental plate is suggested to explain these features

genesis of lavas of the taupo volcanic zone north island new zealand the taupo volcanic zone forms part of the taupo hikurangi subduction system and comprises five volcanic centres tongariro taupo maroa okataina and rotorua tongariro volcanic centre is formed almost entirely of andesite while the other four centres contain predominantly rhyolitic volcanics and later fissure eruptions of high al basalt estimated total volume of each lava type are as follows 2 km3 of high al basalt 10 000 km3 of rhyolite and ignimbrite 97 4 the location of the andesites and vent alignments suggest a source from a subduction zone underlying the area however the lavas differ chemically from island arc andesites such as those of tonga in particular by having higher contents of the alkali elements light ree and sr and pb isotopes this suggests some crustal contamination and it is considered that this may occur beneath the wide accretionary prism of the subduction system amphibolite of the subduction zone will break down between 80 and 100 km and a partial melt will rise a multi stage process of magma genesis is then likely to occur high al basalts are thought to be derived from partial melting of a garnet free peridotite near the top of the mantle wedge overlying the subduction zone locations of the vents controlled largely by faults within the crust rhyolites and ignimbrites were probably derived from partial melting of mesozoic greywacke and argillite under the taupo volcanic zone initial partial melting may have been due to hydration of the base of the crust the water having come from dehydration of the downgoing slab the partial melts would rise to form granodiorite plutons and final release of the magma to form rhyolites and ignimbrites was allowed because of extension within the taupo graben dacites of the bay of plenty probably resulted from mixing of andesitic magma with small amounts of rhyolitic magma but those on the eastern side of the rotorua taupo area were more likely formed by a higher degree of partial melting of the mesozoic greywacke argillite basement this may be due to intrusion of andesite magma on this side of the taupo volcanic zone

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

early proterozoic continental tholeiites from western bergslagen central sweden iii geodynamic inferences abstract the 1 88 ga old within plate continental tholeiites belong to the mainly metavolcanic bimodal bergslagen supracrustal series bss in the svecofennian domain of the baltic shield the bss evolved in an intracontinental rift despite only moderate lithospheric extension the tholeiites are the near surface expression of a 10 20 km thick magmatic crustal underplate that probably underlies most of the sw svecofennian domain and caused the svecofennian crust to be three layered thick but yet isostatically stable underplating strengthened the lithosphere sufficiently to control the time of cratonization geodynamic models for the origin of the bss consistent with our interpretations are gravitational collapse of an overthickened continental accreted terrane margin or back arc processes related to a marginal volcanic arc 250 km further south a tentative reconstruction of relative plate motions during svecofennian time indicates predominantly longitudinal motion of the plates in question and complies with the relatively slow latitudinal drift of the shield at the time recent ion microprobe u pb ages of proterozoic zircons in svecofennian metasediments imply about 0 2 ga of pre svecofennian crustal evolution while the nd model ages of the most primitive metatholeiites may be indicative of initial mantle differentiation as early as 2 4 ga bp accompanying protocrust formation

the svecofennian orogen a tectonic model abstract recent geological studies have provided new concepts concerning the timing of the final break up of the archaean craton age data on detrital zircons from sedimentary rocks in sweden and finland show marked similarities and indicate pervasive homogenization of accumulated material geochemical and isotopic studies in sweden and finland suggest the existence of two volcanic belts separated by an area dominated by sedimentary rocks however the ages of metamorphism and plutonism differ in particular the late post 1 85 ga granitoid magmatism was more voluminous in sweden than in finland the svecofennian crust in finland is anomalously thick up to 65 km and is characterized by a high velocity lower crust of variable thickness the evolution of the svecofennian orogen is modelled by opening of the pre svecofennian ocean at 1 95 ga and progressive accretion of two arc complexes to the archaean craton between 1 91 1 87 ga initial accretion at 1 91 ga led to thrusting of the slices of an island arc complex and proterozoic marine strata onto the thickening craton margin subduction reversal with simultaneous anti clockwise rotation of the converging plate or convergence of another plate resulted in subduction below the newly accreted arc complex the tectonic style at the craton margin changed from thrusting to lateral displacement in the east in finland in the west in sweden the subduction zone retreated along a transform fault a large sedimentary basin closed in the east 1 89 ga ago when another arc complex collided against the accreted one collision resulted in lithospheric thickening subsequent delamination of the thickened lithosphere and compensation by a hot mantle underplate and large scale granitoid magmatism as a result of mixing between mantle magma and remelted arc complex material the thick dense layer that formed in the lower crust as the result of underplating kept the thickened crust in isostatic balance thus the exhumation rate in this area was similar to the rate in areas of thinner crust subduction and sediment accumulation continued in the west until at least 1 87 ga when large areas in the east were already stabilized an intracratonic transpressional zone developed as the result of continued convergence subsequent extensional collapse along the transpressional zone caused melting of svecofennian sedimentary rocks migmatization and generation of the 1 84 1 82 ga anatectic granites of southern finland and central sweden the voluminous post 1 85 ga granitoid magmatism in sweden is tentatively associated with an east west extension that is not related to the extensional collapse

microbial origin of australian coalbed methane bituminous coal seam gases from the permian sydney and bowen basins australia are characterized by 1 methane ethane ratios greater than or equal to 1000 2 dgr13c and dgrd values for methane of 60 10 pmil pdb and 217 17 pmil smow respectively 3 carbon dioxide contents of less than 5 and 4 dgr13c co 2 ch4 values of 55 10 pmil pdb these data suggest that microbial reduction of co2 rather than traditional thermogenic reactions is mainly responsible for gas composition invasions by co2 of deep seated external origins are readily recognized by their isotopic compositions 7 2 pmil pdb

fractal and seismic b value study during dynamic roof displacements roof fall and surface blasting for enhancing safety in the longwall coal mines abstract mining of coal has always been a very risky task from older times and is often associated with various fatal accidents in form of rock bursts gas outbursts slope bench failure studies carried out by various safety agencies around the world such as msha usa dgms india state administration china have reported higher fatality rates in underground mines and are mostly resulting from the sudden roof falls most of the roof falls occur suddenly in the running mine due to support failure or adverse strata conditions the present study focuses on the monitoring of the roof falls in the longwall mine of central india as the presence of stable roof has resulted in several roof fall related accidents in various indian longwall panels including churcha mine kothadi mine and gdk 11a incline the aforesaid accidents was also responsible for the poor performance of longwall mines in india which is considered to be one of the best mining practices in majority of the coal producing countries of the world the paper incorporates the spatial distribution and magnitude of microseismic events released before during the roof falls and surface blasting in terms of fractal dimension as well as b value these two parameters helped in getting precursory signatures for spatio temporal forecasting of minor and major roof falls as well as helped in monitoring strata behavior during surface blasting a total of sixty four minor falls lf1 lf64 seventy six major falls rf1 rf76 and fifteen surface blasting sb1 sb15 the results showed decreasing trend in the both fractal dimension d and b value before roof fall as microseismic events emitted were highly clustered and had higher magnitude whereas higher fractal dimension d and lower b value was seen during surface blasting when the emitted microseismic events had higher magnitude but were found to be dispersive in nature

gis modelling of slope stability in phewa tal watershed nepal abstract hazards are an inherent but dangerous and costly element of mountainous environments conventional maps of mountain hazards provide useful inventories of hazardous sites but provide little insight into the operation of the hazards furthermore this approach tends to rely heavily on subjective interpretation of the landscape which means that the results can not be replicated or transferred to other areas thus alternative approaches employing the quantitative capabilities of geographic information systems gis to model and predict slope stability are receiving increasing attention this paper reports on the use of a diverse gis database compiled primarily from existing maps and aerial photographs to construct a regional model of slope stability in phewa tal watershed nepal an integral part of the research was to explore an alternative approach to the commonly used grid cell approach by employing geomorphometrically significant terrain units the terrain units employed were created by generating line networks representing local maxima and minima extracted from elevation and curvature surfaces one of the chief benefits of applying gis technology in this research was the ability to georeference all of the attribute data to these terrain units in doing so it allowed the database to be exported into an external statistical package where the terrain units could be statistically explored as the basic analytical unit the application of a variety of statistical techniques resulted in logistic regression being selected as the most useful logistic regression successfully predicted terrain units as being either stable or unstable at a rate of approximately 90 concordance with a conventionally produced map of slope stability the statistical probabilities of terrain unit stability were imported back into the gis to produce a map of predicted slope stability that compared well with the conventional map of slope stability the findings of this research suggest that the use of geomorphometrically significant terrain units extracted from a digital elevation model dem are an efficient alternative to approaches using regular grid cells in particular the terrain units facilitated the use of logistic regression and significantly decreased the amount of computing costs finally this research also suggests that important information can be gathered from existing information sources such as maps aerial photographs and written documents thereby limiting the need for costly and time consuming field work at the reconnaissance level based on this latter finding other information sources such as satellite imagery should be examined

svecofennian detrital zircon ages implications for the precambrian evolution of the baltic shield metasediments intruded by 1 90 1 87 ga old plutonic rocks form the oldest major proterozoic crustal component in the svecofennian domain of the baltic fennoscandian shield their ndtdm model ages and conventional multigrain zircon u pb ages between 2 4 and 2 1 ga have previously been interpreted either as mixing ages between 1 9 ga old juvenile materials and a minor archaean component or as actual rock and protolith ages to resolve the ensuing controversy 120 individual detrital zircons from svecofennian metasediments in sweden and finland were analysed using the shrimp ion microprobe the oldest materials in this array are a 3 44 ga old zircon from the tampere schist belt in finland and a 3 32 ga old crystal from southeastern sweden about 30 of the analysed crystals are 2 97 2 60 ga old while 65 have ages between 2 12 and 1 88 ga thus there is no evidence of 2 6 2 1 ga old protoliths but the age range of the proterozoic zircons indicates that a major area of 2 1 1 9 ga old crust was in erosional position 1 9 ga ago this implies that the formation of palaeoproterozoic crust in the baltic shield or its one time close neighbourhood must have commenced 100 200 ma earlier than hitherto assumed in conjunction with previously obtained isotopic data the youngest detritus ages of the present study constrain the age of svecofennian sedimentation it can also be concluded that the archaean zircons found in quartzites from southern sweden may have been derived from source areas to the southwest of the central svecofennian marine depositional basin the so called bothnian basin separating southern sweden from the archaean craton in the northeastern part of the shield

nd isotope data on 1 9 1 2 ga old basic rocks and metasediments from the bothnian basin central sweden abstract sm nd data are presented for basic rocks and metagreywackes from the early proterozoic bothnian basin in central sweden the basic rocks include synsedimentary metabasalts early orogenic intrusions and anorogenic dolerites covering the age range 1 9 1 2 ga the samples thus span the entire period from the early part of the svecokarelian thermo tectonic episode to the time when this region of the baltic shield had been a stable craton for about 0 4 ga all these samples have slightly positive nd values up to 2 for synorogenic rocks and up to 3 5 for anorogenic dolerites if these values are representative for the contemporaneous mantle they suggest a less depleted character for this mantle than that shown for several other proterozoic shield areas three metagreywacke samples have nd values of 2 4 to 3 1 indicating a significant influx of detrital older crustal material into the bothnian basin

the role of spatial variability in coal seam parameters on gas outburst behaviour during coal mining abstract gas outburst is recognized as a potentially fatal hazard to be managed during the mining of gassy coal seams gas outbursts in australian coal mines have been associated with the presence of geological structures in the coal and surrounding rocks having a range of spatial scales from millimetres to metres the contributing mechanisms are influenced by coal gas reservoir variables including gas composition fluid pressure desorption pressure and rate porosity intrinsic permeability and relative permeability they are also influenced by geomechanical variables such as strength in situ stress and mining induced stress the work described here concerns the influence of variability of permeability and strength on outburst behaviour key coal properties are characterised for a field site in an operational underground coal mine and then used in a series of hypothetical simulations of outburst initiation at the field site an array of horizontal holes was cored in seam well tests for permeability and stress were performed in the holes and recovered core was tested in the laboratory for permeability strength and sorption properties for permeability and strength sufficient numbers of measurements were obtained to describe these properties statistically assuming that the measurements are uncorrelated spatially analysis of the cumulative probability distributions of the field and laboratory permeability data shows a strong size effect that cannot be linearly up scaled using monte carlo techniques these statistical descriptions are used to generate realisations of property values across the model grid used in the simulation analyses the stochastic model approach demonstrates that the variability of the permeability and strength fields can lead to both outburst and non outburst outcomes from the same measured input data depending on the corresponding spatial distribution of permeability and strength at the face these results suggest the potential application of this approach as a tool for outburst risk analysis and assessment

bimodal early proterozoic volcanism in the grythytte field and associated volcano plutonic complexes bergslagen central sweden the grythytte field sequence forms a nnw belt of acid basic metavolcanic and metasedimentary rocks the geology shows characteristics of a dynamic process of trough forming and infilling which to a large extent post dates the hjulsjo volcanoplutonic complex situated to the east in the latter complex acid metapyroclastics strike around a centre of granite and granophyre which cut and are cut by basic sills and dykes field and petrochemical evidence points to a distinct bimodal magmatism that ist manifested during one short phase of a rifting period

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

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

control and prevention of gas outbursts in coal mines riosa olloniego coalfield spain abstract underground coal mines have always had to control the presence of different gases in the mining environment among these gases methane is the most important one since it is inherent to coal despite of the technical developments in recent decades methane hazards have not yet been fully avoided this is partly due to the increasing depths of modern mines where methane emissions are higher and also to other mining related circumstances such as the increase in production rates and its consequences difficulties in controlling the increasing methane levels increasing mechanization the use of explosives and not paying close attention to methane control systems the main purposes of this paper are to establish site measurements using some critical parameters that are not part of the standard mining control methods for risk assessment and to analyze the gas behavior of subvertical coal seams in deep mines in order to prevent gas incidents from occurring the ultimate goal is the improvement in mining conditions and therefore in safety conditions for this purpose two different mines were instrumented for mine control and monitoring both mines belong to the riosa olloniego coalfield in the asturias central basin spain and the areas instrumented are mined via subhorizontal sublevels at an actual depth of around 1000 m under the overburden of mount lusorio during this research a property favoring gas outbursts was site measured for the first time in an outburst prone coal 8th coalbed gas pressure and its variations which contributed to complete the data available from previous characterizations and to set some guidelines for assessing the potential outburst prone areas a gas measurement tube set has been designed for measuring gas pressure as well as its variation over time as a result of nearby workings and to calculate permeability the paper establishes the effect of overlapping of works but it also shows the efficacy of two preventive measures to be applied high pressure water infusion and the exploitation of a protective coal seam 7th coalbed that must be mined preferably two complete sublevels before commencing the advance in the outburst prone coalbed both measures constitute an improvement in the mining sequence and therefore in safety and should be completed with a systematic measurement to control the risk gas pressure in the 8th coalbed in the area of influence of other workings to establish the most suitable moment to renew the advance further researches could focus on ascertaining the permeability not only in mined areas but also in areas of the mine that are still not affected by mining work and on tuning more finely the ranges of influence of overstress time and overlap distance of the workings of the 7th coalbed in the 8th coalbed

some new lead isotope determinations from the proterozoic sulfide ores of central sweden lead isotope determinations were made on galenas from three strata bound sulfide ores in the early proterozoic svecokarelian bergslagen district of central sweden and four epigenetic deposits in the alvdalen and vansbro districts in the early to middle proterozoic post svecokarelian belt the leads from the strata bound bergslagen deposits show exceptional isotopic homogeneity over large areas their isotopic composition suggests the existence of a pre svecokarelian crust in the district and is consistent with exhalative sedimentary ore formation in an active continental margin environment the vansbro and alvdalen leads display constant compositions within each district but marked divergence between the districts their compositions preclude derivation exclusively from recycled svecokarelian lead and suggest a substantial lead contribution from a mantle like source the difference between model ages and geologic ages for many of the deposits with a small but significant excess of radiogenic lead suggests a significant deviation of the fennoscandian shield from conventional global lead evolution models

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

early proterozoic continental tholeiites from western bergslagen central sweden i petrology geochemical petrogenesis and geotectonic setting abstract the early proterozoic bergslagen supracrustal series bss of western bergslagen consists of a pile of felsic volcanites and intercalated carbonates with in the upper part an alternating succession of volcaniclastics and basic flows this pile is intruded by a bimodal sequence of granites and basic sills and dikes major and trace element data reveal the influence of several processes that have acted upon the basic magma crustal contamination or supra subduction zone ssz modification fractional crystallization and potassic and sodic alteration due to sub seafloor processes are recognized using geochemical and petrological criteria the basic rocks are divided in two least altered la and two alkali altered aa sets geochemically the least altered basalts resemble phanerozoic continental within plate tholeiites and thus contradict the interpretation by many previous authors of bergslagen as an active margin volcanic arc alkali alteration leads to pseudo calc alkaline or pseudo alkaline signatures however a ssz component observable in part of the la set indicates a relation in space and time to a convergent margin

wavelets well ties and the search for subtle stratigraphic traps we examine the conventional methodology for tying wells to processed seismic data and show why this methodology fails to allow for reliable interpretation of the seismic data for stratigraphy we demonstrate an alternative methodology that makes the tie without the use of synthetic seismograms but at the price of measuring the seismic source signature the cost of such measurements being about 1 of data acquisition costs the essence of the well tie is 1 to identify geological and seismic interfaces from the logs and core 2 to measure the one way traveltime to these interfaces using downhole geophones and 3 to use the polarity information from 1 and the timing information from 2 to identify the horizons on the zero phase processed seismic data conventional processing of seismic data usually causes the wavelet to vary from trace to trace and conventional wavelet extraction at a well using the normal incidence reflection coefficients relies on a convolutional relationship between these coeff

modeling acoustic propagation of airgun array pulses recorded on tagged sperm whales physeter macrocephalus in 2002 and 2003 tagged sperm whales physeter macrocephalus were experimentally exposed to airgun pulses in the gulf of mexico with the tags providing acoustic recordings at measured ranges and depths ray trace and parabolic equation pe models provided information about sound propagation paths and accurately predicted time of arrival differences between multipath arrivals with adequate environmental information a broadband acoustic pe model predicted the relative levels of multipath arrivals recorded on the tagged whales however lack of array source signature data limited modeling of absolute received levels airguns produce energy primarily below 250hz with spectrum levels about 20 40db lower at 1khz some arrivals recorded near the surface in 2002 had energy predominantly above 500hz a surface duct in the 2002 sound speed profile helps explain this effect and the beampattern of the source array also indicates an increased proportion of high frequency sound at near horizontal launch angles these findings indicate that airguns sometimes expose animals to measurable sound energy above 250hz and demonstrate the influences of source and environmental parameters on characteristics of received airgun pulses the study also illustrates that on axis source levels and simple geometric spreading inadequately describe airgun pulse propagation and the extent of exposure zones

numerical simulation of stress distributions and displacements around an entry roadway with igneous intrusion and potential sources of seam gas emission of the barapukuria coal mine nw bangladesh abstract this paper uses two dimensional boundary element method bem numerical modeling to analyze the deformation and failure behavior of a coal seam and to understand the nature of gas flow into a roadway entering the barapukuria coal mine in bangladesh the barapukuria basin contains permian aged gondwana coals with high volatile b bituminous rank three models a b and c are presented here model a assumes horseshoe shaped geometry model b assumes trapezoid shaped geometry and model c assumes horseshoe shaped geometry coupled with a roof fall induced cave generated by the break up of rock materials along the vertical dimension of an igneous dyke the simulation results show that there is little difference in strata deformation between models a and b in model a there is no horizontal tensional stress and the overall horizontal stress patterns are compressive while the distribution and magnitude of vertical stress show higher tensional stresses on the immediate rib sides and floor in model b both horizontal and vertical stress distributions indicate low to medium tensional stresses on the immediate roof floor and rib sides but compressive stresses are prominent toward the interior of the coal seam deformation vectors indicate that failure extends laterally to about 7 5 m around the excavation geometry on the contrary for model c the distributions and magnitudes of horizontal and vertical stress show higher tensional stresses in both rib sides of the roof fall zone the deformation around the dyke induced perturbation zone affects a large volume of coal the deformation vectors with high magnitudes are nearly horizontal and propagate laterally up to 30 m whereas low magnitude deformation vectors extend about 25 m toward the roof and 20 m toward the floor the vertical tensional displacement which is concentrated in the floor and the left and right hand sides of the roof propagates about 30 m on both sides and about 22 m in the floor from these simulation results it is thought that the extension of the dyke induced perturbation zone toward the roof floor and rib sides of the entry roadway initially creates small tensional cracks that gradually grow into large scale tensional features these features could also be responsible for high concentrations of gas which are emitted into the mine from fractured coals due to insufficient mine ventilation and low atmospheric pressure

coalbed methane from hazard to resource abstract coalbed gas which mainly consists of methane has remained a major hazard affecting safety and productivity in underground coal mines for more than 100 years coalbed gas emissions have resulted in outbursts and explosions where ignited by open lights smoking or improper use of black blasting powder and machinery operations investigations of coal gas outbursts and explosions during the past century were aimed at predicting and preventing this mine hazard during this time gas emissions were diluted with ventilation by airways e g tunnels vertical and horizontal drillholes shafts and by drainage boreholes the 1970 s energy crisis led to studies of the feasibility of producing the gas for commercial use subsequent research on the origin accumulation distribution availability and recoverability has been pursued vigorously during the past two decades since the 1970 s research investigations on the causes and effects of coal mine outbursts and gas emissions have led to major advances towards the recovery and development of coalbed methane for commercial use thus coalbed methane as a mining hazard was harnessed as a conventional gas resource

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

a fluid inclusion and light element stable isotope study of the gold bearing quartz vein system falun sweden the falun gold quartz vein mineralization is located ca 230 km nw of stockholm sweden within the early proterozoic volcano sedimentary sequence of bergslagen the mineralization consists of a system with subparallel quartz veins that crosscut the alteration zone to the falun massive sulphide deposit early barren and late gold bearing quartz veins follow tectonic structures postdating the formation of the massive sulphide ore both generations of veins are epigenetic to the massive sulphide ore and were formed by hydrothermal processes fluid inclusion study of the gold bearing quartz veins indicates a low moderately saline fluid 0 3 to 17 4 equiv wt nacl heterogeneous trapping is indicated by coexisting inclusions showing a variable co2 content from 100 co2 ch4 to 100 aqueous fluid temperatures of total homogenization also show a wide spread from 116 350 c with a slightly bimodal distribution with peaks at ca 180 c and 280 c measured d values 69 to 63 0 smow of inclusion fluid and calculated 18o values of hydrothermal fluids 7 5 to 1 4 0 smow strongly suggest a meteoric origin for the fluids the quite consistent d values and the range in 18o values indicate that major water rock interaction led to the evolution in 18o of the hydrothermal fluids

electromagnetic radiation induced by mining rock failure abstract anticipating roof fall in mine workings has been a problem for centuries the focus in the search for early warning indicators has been on observing seismic acoustic events prior to the fall these precursors have been studied in great detail at many places but none has been fully successful so far no valid effective early warning system based on low frequency seismic precursors has been established in this paper we investigated a promising new technique which is not yet completely understood or been widely tested in mines the new method is the sensing of the embryonic stages of roof fall by detection of high frequency electromagnetic radiation emr emitted from rock microcracks two examples of combined observations of emr and low frequency acoustic emission prior to roof fall at moonee colliery are presented anomalously high emr was detected more than 1 h before roof fall giving a significant time advantage over the first indicators of low frequency acoustic emission analysis of benioff strain release diagrams of emr emanating from developing medium scale failure in the mine enabled us to fill the gap between previously known microscale rock fracture in lab and macroscale earthquake emr observations and to conclude that indeed a common fundamental relationship must lie behind this multi scale phenomenon

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

marine seismic sources qc of wavefield computation from near field pressure measurements a commercial marine seismic survey has been completed with the wavefield from the n element single guns and clusters airgun array measured for every shot using an array of n 2 near field hydrophones n of which were required to determine the source wavefield the remaining two providing a check on the computation the source wavefield is critical to the determination of the seismic wavelet for the extraction of reflection coefficients from seismic reflection data and for tying the data to wells the wavefield generated by the full array of interacting airguns can be considered to be the superposition of n spherical pressure waves or notional source signatures the n hydrophone measurements providing a set of n simultaneous equations for each shot the solution of the equations for the notional source signatures requires three ingredients the geometry of the gun ports and near field hydrophones the sensitivity of each hydrophone recording channel and the relative motion between the near field hydrophones and the bubbles emitted by the guns the geometry was measured on the back deck using a tape measure a calibration data set was obtained at the approach to each line in which each gun was fired on its own and the resulting wavefield was measured with the near field hydrophones and recorded the channel sensitivities or conversion from pressure at the hydrophones to numbers on the tape were found for each near field hydrophone channel using the single gun calibration data the measured geometry and the peak pressure from each gun known from the manufacturer s calibration the relative motion between the guns and hydrophones was obtained from the same calibration data set by minimizing the energy in the computed notional source signatures at the guns which did not fire the full array data were then solved for the notional source signatures and the pressure was computed at the two spare hydrophones and compared with the actual recordings the rms errors were 5 3 and 2 8 and would have been smaller if the hydrophone channel sensitivities had been properly calibrated beforehand and if the movement of the guns with respect to the hydrophones had been more restricted this comparison of the predicted and measured signatures at spare hydrophones can in principle be done on every shot and we recommend that this be implemented as a standard quality control procedure whenever it is desired to measure the wavefield of a marine seismic source

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

jorn an early proterozoic intrusive complex in a volcanic arc environment north sweden abstract the jorn complex is an early svecokarelian granitoid suite intruded into a volcanic arc environment on the southern margin of a major proterozoic continental area both the complex and its country rocks have been affected by hydrothermal alteration and low grade regional metamorphism four phases can be distinguished on geological chemical and geophysical criteria in particular a heterogeneous calcic outer zone and a more evolved central diapir the rock types vary from granodiorite to granite and have major and trace element abundances similar to those phanerozoic subduction related granitoids from relatively immature volcanic arcs zircon populations from the different phases are rather heterogeneous but do not show significant differences in u distribution or u pb age between the phases while pooled u pb data 13 points give an upper intercept of 1890 7 8 ma a two stage model assuming an age difference between cores and rims gives a more probable crystallisation age of 1876 2 ma with significant lead loss at 1720 ma and 410 ma epsilon nd values range from 1 8 to 3 2 indicating that the source material for the jorn complex was derived from an lree depleted mantle with a small contribution of older crustal material and had a relatively short crustal residence period metaluminous compositions and oxygen isotope ratios suggest non pelitic sources the jorn complex probably originated as a series of subduction related melts of basic to intermediate composition which underwent varying degrees of subsequent differentiation and secondary alteration

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

early proterozoic ensialic spreading subsidence evidence from the garpenberg enclave central sweden abstract the early proterozoic metavolcanic complex in the garpenberg enclave of central sweden displays bimodal basaltic rhyolitic volcanism reflecting alternating compressional and tensional tectonic regimes the acid metavolcanics show a continuous calcalkaline differentiation trend geochemically unrelated to the associated interbedded metabasalts a dacitic horizon indicates mixing of the two end member magmas during a compressional stage bimodal volcanism is characteristic of the early proterozoic supracrustals leptite formation throughout the central swedish province of the baltic shield the paucity of ocean floor rocks and high pressure metamorphism together with the lack of abundant andesites suggest that this province does not represent an island arc rather the combination of an ensialic edifice with alternating compressional and tensional tectonic regimes suggests andinotype subduction coupled spreading subsidence within the margin of a continental plate

effects of volatiles on mixing in calc alkaline magma systems the intimate mixing between different magmas of disparate densities characteristic of some calc alkaline magma systems is explained by a new mechanism involving the emplacement of a layer of wet undersaturated mafic magma at the base of a magma chamber containing more differentiated magma turbulent transfer of heat between the mafic magma and the overlying magma leads to crystallization and exsolution of volatiles in the lower layer for an initial water content of a few per cent the bulk density of the mafic magma can become equal to that of the overlying magma causing overturning and intimate mixing of the magmas the mechanism is most probable in the low pressure environment of a high level magma chamber

the application of a coupled artificial neural network and fault tree analysis model to predict coal and gas outbursts this paper proposes the use of a coupled fault tree analysis fta and artificial neural network ann model to improve the prediction of the potential risk of coal and gas outburst events during the underground mining of thick and deep chinese coal seams the model developed has been used to investigate the gas emission characteristics and the geological conditions that exist within the huaibei coal mining region anhui province china the coal seams in this region exhibit a high incidence of coal and gas outbursts an analysis of the results obtained from an initial application of an fta model identified eight dominant model parameters related to the gas content or geological conditions of the coal seams which characterize the potential risk of in situ coal and gas outbursts the eight dominant model parameters identified by the fta method were subsequently used as input variables to an ann model the results produced by the ann model were used to develop a qualitative risk index to characterize the potential risk level of occurrence of coal and gas outburst events four different potential risk alarm levels were defined safe potential high and strong solutions to the prediction model were obtained using a combination of quantitative and qualitative data including the gas content or gas pressure and the geological and geotechnical conditions of coal seams the application of this combined solution method identified more explicit and accurate model relationships between the in situ geological conditions and the potential risk of coal and gas outbursts an analysis of the model solutions concluded that the coupled fta and ann model may offer a reliable alternative method to forecast the potential risk of coal and gas outbursts

source signature determination by inversion a new method for estimating the pressure wavefield generated by a marine air gun array is presented it is assumed that data is acquired at a ministreamer located below the source array effective source signatures for each air gun are estimated by an inversion algorithm the forward modeling scheme used in the inversion algorithm is based upon a physical modeling of the air bubble generated by each air gun this means that typical inversion parameters are gun depths empirical damping coefficients and reflection coefficient of the sea surface variations in streamer depth are also taken into account by the inversion scheme the algorithm has been successfully tested on examples with unknown streamer positions gun parameters reflection coefficient of sea surface and ministreamer data contaminated with white noise