application of the crosta technique for porphyry copper alteration mapping using etm data in the southern part of the iranian volcanic sedimentary belt abstract many of the known porphyry copper deposits in iran are situated in the central iranian volcanic belt the area under study is located in the southern part of this belt and covers an area of about 6600 km2 the climate in the area is semi arid given the poor soil development and poor vegetation cover but abundant outcrops the arid semi arid part of the belt is most suitable for remote sensing study enhanced thematic mapper plus etm images have been used for alteration mapping crosta method was found useful for enhancing the areas in which the regolith contains a high proportion of hydroxyl and iron oxide minerals the crosta method has been used on selected 4 and 6 bands areas with iron oxide and hydroxyl minerals have been enhanced by using six bands of etm data

emplacement of the 18 may 1980 lateral blast deposit ene of mount st helens washington facies variations east northeast of mount st helens preserve a record of depositional processes in the 18 may 1980 lateral blast cloud this paper reports new field grain size and component data from the ene sector of the timber blowdown zone and presents a model for blast flow and sedimentation the first erupted ejecta was rich in juvenile components and extends to the distal blowdown limit the last erupted ejecta was rich in accidental lithics and reached no further than a few kilometres from the mountain due to waning discharge the blast cloud was a turbulent stratified flow which transported and deposited sediment in the manner of a high density turbidity current the possibility that the blast was emplaced as a giant shearing fluidised bed is not favoured by compositional zoning patterns depositional conditions were strongly influenced by the rate of suspended load fallout from the blast within about 8 km from vent rapid sedimentation caused deposition under moderate to high concentration conditions and formation of a basal hindered settling zone able to detach gravitationally and drain into local depressions the resulting proximal facies resembles a low aspect ratio ignimbrite fines depletion in the proximal facies is attributed to a combination of residual turbulence and rapid gas escape during particle settling and compaction through the hindered settling zone component data suggest that the blast head played no significant role in the generation of fines depletion in the blast deposit as suggested by previous workers with increasing distance from vent the rate of particle fallout declined and sedimentation took place under increasingly dilute and tractional conditions building up antidune like bedforms wavelengths of these bedforms range from 20 to 1 m and decrease away from vent there is a systematic relationship between antidune migration direction and depositional slope the transition from proximal ignimbrite like to distal surge like facies suggests a possible gradation in transport and deposition processes between conventional pyroclastic surges and high velocity pyroclastic flows

detection of hydrothermal alteration zones in a tropical region using satellite remote sensing data bau goldfield sarawak malaysia abstract remote sensing for geology in tropical environments is very challenging because of the dense vegetation cover and the problem of persistent cloud cover in this research paper we have investigated and demonstrated the detection of hydrothermal alteration zones and structural elements associated with intrusion related gold mineralization using various types of remote sensing data in the bau gold mining district in the state of sarawak east malaysia on the island of borneo the climate of bau is tropical with persistent cloud cover and very dense vegetation ground geological analyses coupled with remote sensing data were used to detect hydrothermally altered rocks and structural elements associated with gold mineralization in the bau area landsat enhanced thematic mapper etm hyperion and phased array type l band synthetic aperture radar palsar data were used to carry out lithological structural mapping of the mineralized zones in the study area and surrounding terrain hydrothermal alteration zones were detected along the ssw to nne structural trend of the tai parit fault that corresponds with the occurrence of other gold mineralization in the bau limestone the results show that the known gold prospects and potential areas of mineralization are recognizable by the methods used despite limited bedrock exposure the approach used in this study is broadly applicable to the detection of gold mineralization using etm hyperion and palsar data in tropical sub tropical regions

electrophoretic mobility of some tropical soil clays effect of iron oxides and organic matter abstract the effect of organic matter and iron oxides on the electrophoretic mobility em behaviour of some colloidal clay fractions of some tropical soils was studied the clays from the a horizon of the soils were treated to remove organic matter oxidation by na hypochlorite treatment ferrihydrite by acid ammonium oxalate and better crystalline iron oxides reductive dissolution by dithionite citrate bicarbonate treatment organic matter and iron oxides particularly better crystalline ones contributed to the ph dependent charge the removal of organic matter resulted in an increase in the em and isoelectric point iep deferration decreased both the em and iep of the soil clays increase in ph resulted in negative em while salt concentration did not have consistent effect on the em and iep values

the emplacement of intermediate volume ignimbrites a case study from roccamonfina volcano southern italy a model is presented for the emplacement of intermediate volume ignimbrites based on a study of two 6 km3 volume ignimbrites on roccamonfina volcano italy the model considers that the flows were slow moving and quickly deflated from turbulent to non turbulent conditions yield strength and density increased whereas fluidisation decreased with time and runout of the pyroclastic flows in proximal locations on the caldera rim heterogeneous exposures including discontinuous lithic breccias stratified and cross stratified units interbedded with massive ignimbrite suggest deposition from turbulent flows in medial locations thick massive ignimbrite occurs associated with three types of co ignimbrite lithic breccia which we interpret as being emplaced by non turbulent flows multiple grading of different breccia lithic concentration types within single flow units indicates that internal shear occurred producing overriding or overlapping of the rear of the flow onto the slower moving front part this overriding of different parts of non turbulent pyroclastic flows could be caused by at least two different mechanisms 1 changes in flow regime such as hydraulic jumps that may occur at breaks in slope and 2 periods of increased discharge rate possibly associated with caldera collapse producing fresh pulses of lithic rich material that sheared onto the slower moving part of the flow in front

hydrothermal alteration mapping using aster data in the infiernillo porphyry deposit argentina abstract the infiernillo cu mo porphyry deposit is located in the san rafael massif in southern mendoza province argentina it is hosted by and genetically related to lower permian gondwanan volcanic rocks which developed in a magmatic arc tectonic setting the alteration zone has an oval shape about 3 km 2 km in size with a nne ssw strike it consists of a small central quartz neck with appreciable hematite surrounded by an intense quartz injected zone with local pervasive potassic alteration outwards there is a well developed phyllic halo with intense bleaching which consists of pervasive and vein type silicification sericitization and pyritization cu and mo anomalies are approximately coincident and are located between the silicified zone and the phyllic halo in the outer part of the alteration zone small polymetallic veins with pyrite arsenopyrite galena and minor chalcopyrite sphalerite and electrum in quartz gangue crop out an advanced spaceborne thermal emission and reflection radiometer aster with three visible and near infrared vnir bands six shortwave infrared swir bands and five thermal infrared tir bands was used to characterize the infiernillo porphyry deposit alteration area a circular zoning pattern was clearly observed in the vnir swir band combination spectral analysis of the surface reflectance swir detected 2 20 and 2 26 m absorptions field data and sample spectroscopic analyses obtained using a ger 3700 spectral radiometer and a swir reflectance spectrometer portable infrared mineral analyzer pima showed a good correlation with the aster data the 2 20 m absorptions due to al hydroxyl reveal the presence of clay minerals al illite kaolinite and sericite whereas the 2 26 m absorption due to fe hydroxyl resulted from jarosite the field samples were also analyzed with a tir portable spectrometer micro ftir model 102 the tir was useful for detecting surface silica and potassic alteration through analysis of five band surface emissivity data aster images provided preliminary mineralogic information and geo referenced alteration maps at low cost and with high accuracy in this way aster has been proven to be a powerful tool in the initial steps of ore deposit exploration

application of fuzzy logic and geometric average a cu sulfide deposits potential mapping case study from kapsan basin dpr korea abstract in this paper two kinds of knowledge driven methods one using the fuzzy logic and another using geometric average were applied to create the mineral potential maps for cu sulfide deposits in the greenfield kapsan basin dpr korea the ore geology studies for the study area have revealed that cu sulfide deposits of hydrothermal genesis in kapsan basin are closely associated with jurassic intrusions and faulting tectonics based on the conceptual model of cu sulfide deposits and the available spatial datasets in the study area we used five independent evidential maps for cu sulfide deposits potential mapping they include 1 faults 2 aeromagnetic anomaly 3 cu geochemical data 4 pb geochemical data and 5 zn geochemical data the evidential map values were transformed into continuous values of the 0 1 range using the non linear fuzzy membership functions logistic sigmoid and fuzzy gaussian functions because the fuzzy logic and geometric average methods can use the same fuzzification methodology based on suitable membership functions it is very economic and efficient to simultaneously apply two predictive models for mineral potential mapping of the study area the preparation of these evidential layers were performed using spatial analyses supported in arcgis 10 4 gis platform based on geological geophysical and geochemical spatial datasets the validation and comparative analysis results for the two predictive models demonstrated that most of known mineral occurrences are distributed in areas with high potential values the target areas classified by the fuzzy logic occupy 15 of the study area and contain 78 of the total number of known mineral occurrences compared with the fuzzy logic the resulting areas by the geometric average occupy 13 of the study area but contain 93 of the total number of known mineral occurrences although the total number of known mineral occurrences is relatively low for the application of roc receiver operating characteristics technique the areas under the roc curve auc obtained by two predictive models were greater than 0 5 suggesting that both predictive models and their resulting potential maps are useful for evaluating the prospectivity of cu sulfide deposits in kapsan basin

40ar 39ar and k ar dating of k rich rocks from the roccamonfina volcano roman comagmatic region italy abstract roccamonfina is the northernmost volcano of the campanian area of the k rich roman comagmatic region of italy it erupted a huge amount of pyroclastics and lavas belonging to both the leucite basanite and leucitite series lbls and the shoshonite series ss spread over an area of about 300 km2 the above series correspond to the high k series hks and low k series lks of appleton 1972 respectively 40ar 39ar and k ar dating of samples from both series gave ages ranging from 0 656 to 0 096 ma for the ss and from 1 03 to 0 053 ma for the lbls these results indicate that the products of the two series were outpoured together at least between 0 7 and 0 1 ma ago i e during both the so called pre caldera phase and the post caldera phase of activity the latest products of the volcanism at roccamonfina were erupted just before the deposition of the grey campanian ignimbrite which erupted from vents located about 50 km to the south in the phlegrean fields near naples and has an age of about 33 000 years taking into account all the available radiometric data we conclude that roccamonfina was active between 1 5 and 0 05 ma ago in excellent agreement with the stratigraphie evidence in this same time span is concentrated the activity of all the centers of the roman region north of naples

bypassing and diachronous deposition from density currents evidence from a giant regressive bed form in the poris ignimbrite tenerife canary islands exceptional longitudinal exposure through an ignimbrite sheet on the southern flanks of las canadas volcano tenerife canary islands reveals a giant regressive bed form 520 m long it comprises sourceward dipping diffuse lenses 50 m long of massive and diffuse bedded lapilli tuff its architectural relationships indicate that at any one moment in time deposition was restricted to an 50 m long longitudinal depositional zone bounded both upslope and downslope by extensive bypassing zones the regressive architecture shows that the zone of deposition gradually migrated sourceward as the current passed nonpersistent scours indicate that the current was locally and momentarily erosive although at many locations there is little evidence for substantial erosion or deposition and most of the pyroclastic load seems to have entirely bypassed subaerial slopes to enter the atlantic ocean 20 km from the source the ignimbrite is diachronous and any single vertical section through it represents only a short phase of the current9s protracted depositional history similarly protracted and complex flow histories elsewhere may be easily overlooked at typical field exposures of ignimbrites turbidites and lahar deposits leading to significantly underestimated flow durations and volumes

hydraulics of the august 7 1980 pyroclastic flow at mount st helens washington open channel hydraulic theory for flow of an inviscid fluid down a channel of changing slope and width yields a longitudinal velocity profile that matches measured velocities of the august 7 1980 pyroclastic flow at mount st helens the model is useful for prediction of zones of erosion deposition and hazards it requires only topographic data estimates of volumetric flow rate and a manning coefficient appropriate for the channel

post collapse volcanic history of calderas on a composite volcano an example from roccamonfina southern italy roccamonfina part of the roman potassic volcanic province is an example of a composite volcano with a complex history of caldera development the main caldera truncates a cone constructed predominantly of this caldera may have been associated with one of the ignimbritic eruptions of the brown leucitic tuff blt around 385 000 yr bp the campagnola tuff the youngest ignimbrite of the blt however drapes the caldera margin and must postdate at least the initial stages of collapse during the subsequent history of the caldera there were several major explosive eruptions the largest of these was that of the galluccio tuff at about 300 000 yr bp it is likely that there was further collapse within the main caldera associated with these eruptions it is of note that despite these subsequent major explosive eruptions later collapse occurred within the confines of the main caldera between eruptions caldera lakes developed producing numerous lacustrine beds within the caldera fill extensive phases of phreatomagmatic activity generated thick sequences of pyroclastic surge and fall deposits activity within the main caldera ended with the growth of a large complex of basaltic trachyandestite lava domes around 150 000 yr bp early in the history of roccamonfina sector collapse on the northern flank of the volcano formed the northern caldera one of the youngest major events on roccamonfina occurred at the head of this northern caldera with explosive activity producing the conca ignimbrite and associated caldera there is no evidence that there was any linkage in the plumbing systems that fed eruptions in the main and northern calderas

space time evolution of monogenetic volcanism in the mafic garrotxa volcanic field ne iberian peninsula we reconstructed the evolution of the volcanic activity within the central garrotxa monogenetic volcanic field the youngest volcanic area of the iberian peninsula by investigating the stratigraphy of the volcanic successions and the morphology of the monogenetic eruptive centres analysis of this volcanic succession has been conducted following the unconformity bounded stratigraphic units criteria the detailed stratigraphy of the volcanic successions shows that the central garrotxa volcanic field gvf evolved through four main periods of volcanic activity synthems represented by the eruptive products of the mafic monogenetic volcanoes and associated syn eruptive reworked deposits eruptive units and by the inter eruptive deposits epiclastic units the distribution and the morphologies of the monogenetic volcanoes suggest that feeder dykes were emplaced under influence of the present stress filed and along pre existing fractures of the basement our facies analysis of the deposits and their distribution shows that migration of volcanism toward the centre of the basin was accompanied by a trend of increasing explosivity episodic hydromagmatism in central garrotxa occurred without a specific geographic locus or obvious temporal correlation finally by integrating field data with the stratigraphy extracted from water wells we determined the volume of the volcanic deposits the small average volume of products emitted during each eruptive period and the long quiescence separating them allow us to classify the gvf as a low output rate volcanic field

estimation of surface iron oxide abundance with suppression of grain size and topography effects abstract mineral forms of iron oxide such as hematite goethite and jarosite are important because they are widely distributed at the earth s surface and because they are used as indicators for mineral exploration iron oxide abundance in rocks containing these minerals can be estimated from the absorption depth at wavelengths of around 900 nm in a reflectance spectrum but this depth is also affected by extraneous factors such as grain size and topography this paper investigated the effect of grain size on reflectance spectra and proposed a method for estimating iron oxide abundance in surface rocks by using remotely sensed data with suppression of the effects of grain size and topography reflectance spectra were measured in a laboratory from rock powder samples of different grain sizes containing iron oxide minerals while the reflectance increased with decreasing grain size the presence of ferric iron caused the absorption depth to be almost constant at around 900 nm irrespective of the chemical composition of the sample in addition the difference between the reflectance at 550 nm and 760 nm slope was a function of grain size iron oxide abundance can be estimated accurately by mcr 900d which is the maximum absorption depth at the absorption center after the effect of grain size and topography was suppressed by slope and the continuum removal method which takes the ratio between the original spectrum and its continuum respectively correlation of mcr 900d results with datasets of actual spectral and chemical iron oxide laboratory measurements revealed that the mineral forms also need to be considered mcr 900d results were significantly correlated with rock samples classified as containing different forms of iron oxide minerals hematite goethite and jarosite finally mcr 900d was applied to an aviris dataset for the cuprite site in nevada usa the results represented the enrichment zones of iron oxide within hydrothermally altered areas

mt pelee martinique may 8 and 20 1902 pyroclastic flows and surges abstract the distribution stratigraphic relationships and fragmental components of the may 8 and 20 1902 pyroclastic flows from mt pelee martinique together with eyewitness accounts suggest the following explanation for those eruptions the eruptions were vertically directed magmatic perhaps initiated phreatically and contained abundant juvenile lithics from congealed magma of the dome and neck this resulted in a two part eruption column having 1 a dense lithic charged part which collapsed into the crater and flowed out of a pre existing notch in its side giving rise to pyrochlastic flows and 2 a magmatically derived column containing gases juvenile vitric material and crystals which largely by passed the neck and dome and escaped into the atmosphere all of the energy of the flows was apparently focused through the notch they emerged fully turbulent and flowed down riviere blanche gravity segregation of large and abundant fragments soon resulted in a dense high concentration poorly fluidized block and ash flow confined to the valley leaving above a fully turbulent high energy ash cloud surge as the ash cloud surge moved down the mountain it continued to expand outward the process of gravity segregation continued as the ash cloud surge expanded resulting in secondary block and ash underflows toward st pierre the secondary block and ash flows developed on a gently sloping upland surface 100 m or more above the valley of riviere blanche the turbulent fragment depleted surges above the secondary block and ash flows maintained sufficient energy to devastate the landscape outward to about 3000 m including st pierre the surges refracted around obstacles and in one place moved up a small valley in a direction opposite to the main flows

detecting lithology with advanced spaceborne thermal emission and reflection radiometer aster multispectral thermal infrared radiance at sensor data abstract the advanced spaceborne thermal emission and reflection radiometer aster aboard nasa s terra satellite measures multispectral thermal infrared tir emission from the earth s surface to space based on analysis of tir spectral properties of typical rocks on the earth several mineralogic indices including the quartz index qi carbonate index ci and mafic index mi for detecting mineralogic or chemical composition of quartzose carbonate and silicate rocks with aster tir data are proposed these indices are applied to the aster tir data scenes for selected study areas in china and australia the results show that aster tir can discriminate quartz and carbonate rocks as well as mafic ultramafic rocks even with atmospherically uncorrected radiance at sensor data lithologic interpretations agree well with published geologic data and field observations the mineralogic indices applied to aster tir provide one unified approach for lithologic mapping in arid and semi arid regions of the earth

stratified flow in pyroclastic surges stratified flow theory is applied to pyroclatic surges in an effort to gain insight into transport dynamics during explosive eruptions particle transport is assumed to be by turbulent suspension and calculations contained herein show that this is likely for many cases including the 18 may 1980 blast at mount st helens the discussion centers on the rouse number pn which represents a ratio of particle settling velocity to scale of turbulence the brunt vaisala frequency n which is the maximum possible frequency of internal waves the froude number fr representing the ratio of inertial forces to gravitational forces and the richardson number ri a ratio of buoyant restoring forces to turbulent mixing forces the velocity or flow power dependence of bed form wavelength in surge deposits is related to a velocity dependence of wavelength of internal waves in the turbulent surge this produces a decrease in dune wavelength with increasing distance from vent migration direction of bed forms is related tofr as it is defined for a continuously stratified flow proximal to distal facies variations in surge deposits reflect increasingpn andri as the flows move away from their sources this produces the progression from sandwave to massive to planar facies with increasing distance from vent where the long axis of topography is at low angles to the flow direction massive facies in topographic lows may from concurrently with sandwave facies on highs due to the higher particle concentration in the lows where long axis of topography is at high angles to flow direction denser lower parts of the surge may be dammed or blocked blocked material tends to form massive flows that may move down slope independent of the overriding surge a model incorporating turbulent transport stratified flow and time evolution of pyroclastic surges is proposed for deposits which have been attributed to both pyroclastic flow and pyroclastic surge transport by various workers during the initial high energy waxing phase of the eruptive event pn is sufficiently low that only coarse but poorly sorted material is deposited to form relatively coarse bottom layers as the event wanes remaining finer material is deposited through a thin bed load to produce overlying bedded and cross bedded veneer deposits throughout most of the event blocking occurs to produce relatively thick and massive deposits in valley bottoms

aster spectral analysis for alteration minerals associated with gold mineralization abstract this study presents classifications of advanced spaceborne thermal emission and reflection radiometer aster imagery based on spectral analysis of alteration minerals associated with gold mineralization in abo marawat area which is located in the central eastern desert of egypt spectral analysis of continuum removed reference spectra of alteration minerals alunite kaolinite sericite and calcite from usgs and jpl spectral libraries show shifts in position shape and strength most probably related to changes in sample purity and particle size of analyzed samples spectral information divergence sid classification method proved successful for mapping sericite calcite and clay minerals spectral angle mapper sam classification identified only sericite and calcite alteration minerals the identified alteration zones are coincidence with the field sampling and geological map of the study area the microscopic examination of samples collected from the quartz veins and hydrothermally altered wall rocks from near surface and subsurface at abu marawat gold mine shows sericitization argillaceous and carbonatization alteration zones gold occurs as very fine inclusions in pyrite chalcopyrite and sphalerite and also found filling the fractures between chalcopyrite grains this study concludes that aster image classifications using reference spectra are a stable and reproducible technique for mapping gold related hydrothermal alteration zones in areas with no dominant vegetation cover

alteration mineralogy at the cerro la mina epithermal prospect patagonia argentina field mapping short wave infrared spectroscopy and aster images the cerro la mina prospect located in the los menucos area argentina is currently being explored for epithermal gold mineralization triassic jurassic hydrothermal activity produced intense alteration of rhyolites andesites ignimbrites and tuffs of the late triassic los menucos group in the somun cura massif a detailed surface map of the principal alteration assemblages at cerro la mina was produced employing field mapping supported by short wave infrared swir field spectroscopy petrography x ray diffraction xrd and scanning electron microscopy sem advanced argillic argillic and silicic alteration zones and their internal mineral assemblage variations were recognized at cerro la mina the silicification consists of massive bodies of fine grained quartz and minor vuggy quartz locally containing disseminated aggregates of pyrite and rutile advanced argillic alteration of magmatic hydrothermal origin occurs adjacent to the silicic alteration zones and can be subdivided into three mineral assemblages 1 stage 1 alunite quartz dickite kaolinite pyrophyllite diaspore rutile pyrite barite 2 dickite kaolinite pyrophyllite diaspore pyrite barite and 3 dickite quartz diaspore the advanced argillic and silicic alteration grades to argillic alteration comprising three mineral assemblages 1 kaolinite dickite quartz illite smectite 2 kaolinite illite smectite ferroan clinochlore and 3 illite quartz muscovite kaolinite supergene alteration which locally overprints the prior alteration zones consists of jarosite hematite goethite stage 2 alunite aluminum phosphate sulfate aps poorly crystalline kaolinite consistent discrimination of the main alteration minerals of this prospect was also achieved by means of satellite multispectral remote sensing the application of image processing techniques specifically designed for mineral mapping to selected spectral bands of the terra aster multispectral sensor resulted in a detailed alteration map for the entire prospect comparison between the results achieved through remote sensing with field data on the cerro la mina confirmed the accuracy of the former the silicification and minor vuggy quartz the abundant dickite and the coarse grained hypogene alunite among other advanced argillic alteration assemblages suggest that cerro la mina corresponds to a volcanic hydrothermal leached environment possibly controlled by permeable lithological units these characteristics led us to interpret this prospect as a possible lithocap similar to those that typically host subsequent high sulfidation mineralization

thermal infrared 2 5 13 5 μm spectroscopic remote sensing of igneous rock types on particulate planetary surfaces fundamental molecular vibration bands are significantly diminished by scattering thus such bands in spectra of fine particulate regoliths i e dominated by 5 m particles or regoliths displaying a similar scale of porosity are difficult to use for mineralogical or rock type identification consequently other spectral features have been sought that may be more useful in spectroscopic remote sensing of composition we find that mineralogical information is retained in overtones and combination tones of the fundamental molecular vibrations in the 3 0 to 7 0 m region but that relatively few minerals have a sufficiently distinctive band structure to be unambiguously identified with currently available techniques more significantly identification of general rock type as defined by the scfm chemical index scfm sio2 sio2 cao feo mgo is possible using spectral features associated with the principal christiansen frequency and with a region of relative transparency between the si o stretching and bending bands however environmental factors may affect the appearance and wavelengths of these features finally prominent absorption bands may result from the presence of relatively small amounts of water hydroxyl or carbonate because absorption bands exhibited by these materials in the 2 7 to 4 0 m region where silicate spectra are otherwise featureless increase strongly in spectral contrast with decreasing particle size such materials are thus detectable in very small amounts in a particulate regolith composed predominantly of silicate minerals

forestepping backstepping stacking pattern of volcaniclastic successions roccamonfina volcano italy abstract we use unconformity bounded stratigraphie units ubsu to reconstruct the chronostratigraphy of volcaniclastic deposits of roccamonfina volcano southern italy significant discontinuities of different hierarchical order in the stratigraphic succession of the volcano have allowed us to identify the ubsu supersynthems synthems and subsynthems the hierarchical order has been determined by the importance and duration of the discontinuities bounding such units and by their geographic distribution supersynthems are bounded by regional scale unconformities that may correspond to important tectonic events changes in the style of eruptive activity or volcano tectonic collapses synthems are bounded by unconformities marked by paleosols that are representative of considerable hiatus and extended all over the synthem they are composed of complex sequences of depositional units at roccamonfina the synthems reveal cyclical eruptive activity unconformities bounding the subsynthems have been recognized through a detailed facies analysis more than 100 stratigraphic sections have been analyzed and correlated restoring them to single successive datum planes it has been possible to reconstruct the original stratigraphic relationships the geometry of the units and the effects of syn eruptive tectonic activity this procedure revealed that the unconformity surfaces bounding depositional units show different physical expression in the proximal medial and distal areas a erosive surfaces may become amalgamation surfaces b amalgamation of several depositional units can locally produce a single lithostratigraphic unit in this case the unconformity surfaces bounding the units can be identified by the presence of discontinuous pumice and lithic concentration zones c non depositional surfaces in proximal areas bypassing surfaces or in interfluve areas may correspond to downslope deposits d unconformity surfaces can bound different lithostratigraphic units that are the result of down current facies variation the pyroclastic units at roccamonfina are organized as forestepping backstepping sequences we interpret this organization as resulting from waxing waning processes associated with eruption and emplacement in fact the internal geometry of each synthem indicates a forestepping phase until the maximum eruption rate is achieved as it later declines deposition occurs upslope backstepping this mechanism is also reproduced at smaller scale within each subsynthem the forestepping backstepping organization of the deposits provides an explanation for the variability of physical chemical and sedimentological parameters observed in the roccamonfina volcaniclastic deposits

identifying high potential zones of gold mineralization in a sub tropical region using landsat 8 and aster remote sensing data a case study of the ngoura colomines goldfield eastern cameroon abstract climatic conditions and vegetation constrain the use of optical satellite imagery as an exploration tool for hydrothermal ore mineralization in tropical and subtropical regions in this investigation landsat 8 and aster satellite imagery were used to detect hydrothermal alteration zones associated with gold mineralization in the ngoura colomines region eastern cameroon the study area contains several gold bearing quartz veins associated with zones of pyritization muscovite sericite iron oxides and silicification principal component analysis pca independent component analysis ica and specialized spectral band ratios were used to extract spectral information related to vegetation iron oxide hydroxide minerals al oh fe mg oh carbonate group minerals and silicification using landsat 8 data at regional scale linear spectral unmixing lsu algorithm was implemented to aster vnir swir bands for detailed discrimination of hematite jarosite kaolinite muscovite chlorite and epidote at district scale the automated spectral hourglass ash technique was employed to extract reference spectra directly from the aster bands for producing fraction images of end members using the lsu a comprehensive field survey was used to verify the remote sensing results petrographic study x ray diffraction analysis and reflectance spectroscopy indicated the presence of quartz goethite and sericite as well as the absorption features of fe3 fe2 al oh oh h2o and sio2 in the alteration zones several hydrothermal alteration zones of iron oxide hydroxide clay carbonate minerals and silicification zones were identified which are spatially associated with known mining areas and gold occurrences in the study area high potential prospects were also delineated including the ngoura colomines prospects and the newly discovered yangamo ndatanga and tapare tapondo prospects in the southwestern and southeastern parts of the study area consequently satellite based mineral prospectivity maps at regional and district scales were generated for the study area by implementing the fuzzy logic model to the most informative thematic layers derived from image processing results the satellite based prospectivity maps are reliable for exploration of new gold prospective zones in the ngoura colomines goldfield

pan african strike slip tectonics in eastern cameroon magnetic fabrics ams and structure in the lom basin and its gneissic basement abstract field microstructural and anisotropy of magnetic susceptibility ams or magnetic fabric studies were applied to identify the sequence and character of the pan african structures in the basement of eastern cameroon at both sides of the regional scale betare oya shear zone bosz the ne sw trending bosz separates older gneisses and migmatites towards se domain i from the younger rocks of the lom meta volcano sedimentary basin towards nw domain ii in domain i early ductile compressional deformation occurred in two events d1 and d2 under relatively high t conditions during subsequent cooling strain partitioned between the competent basement gneisses with only mild compression and the bordering shear zone bosz with intense simple shear wrenching d3 strain in the less competent rocks of domain ii is dominated by simple shear strike slip wrenching d3 with an earlier stage of compressional deformation preserved only in some low strain pods magnetic fabrics ams document a progressive change from oblate ellipsoids towards prolate ellipsoids in domain i when proceeding from the south towards the bosz foliations are mostly steep but define a girdle with a pole plunging gently towards wsw the magnetic lineations also plunge mostly towards wsw at shallow angles these fabrics indicate a compression approximately normal to the bosz which is also the se margin of the lom basin in the lom metasediments domain ii ams ellipsoids are typically oblate foliations trend ne sw with mostly steep dips magnetic lineations plunge gently ne or sw this fabric with foliations mostly steep and subparallel with the major bosz combined with generally subhorizontal lineations implies the bosz as a pan african strike slip shear zone with a subordinate component of compression at a larger scale the area is part of a continent scale shear zone separating external pan african domains of compression along the northern margin of the congo craton from internal domains dominated by high angle strike slip and transpressional deformation together with published data the present study thus demonstrates that transpression is a regional phenomenon in the pan african orogen of central and eastern cameroon

decoupling of pyroclastic currents hazards assessments gravitational settling of fragments gas elutriation and boundary layer processes cause concentration values to change within different parts of sediment gravity flows during movement these processes result in flow transformations density stratification and decoupling of single currents into separate sediment gravity flows density can change by an increase in solids concentration in basal zones of currents by downward fall of particles or by incorporation of particles from the substrate thereby leaving their upper parts more dilute in some flows upward streaming gases and elutriation of fines cause dilute turbulent currents to develop at the top of a dense current increasing concentration dampens turbulent action transforming the turbulent to the nonturbulent state commonly at the current s base conversely dilute parts of currents become or remain turbulent currents consisting of turbulent and nonturbulent parts can decouple by shearing past one another because of differing flow properties with each part taking separate paths the manner by which a pyroclastic flow moves affects its predicted runout distance its distribution as continuous sheets or in isolated basins and whether it can cross barriers such as high mountain ranges or water bodies during the eruption of unzen volcano on june 3 1991 decoupling of a pyroclastic surge from the top of a pyroclastic flow caused the deaths of harry glicken maurice krafft katia krafft and 40 japanese citizens mapping volcanic hazard zones requires that consideration be given to decoupling processes to help prevent similar tragedies in the future

targeting iron ore in banded iron formations using aster data weld range greenstone belt yilgarn craton western australia advanced spaceborne thermal emission and reflection radiometer aster image analysis is a proven method for mapping mineral and geochemical zonation associated with a variety of ore types including orogenic au porphyry cu mo porphyry skarn pb zn au and mn systems only recently has this technique been applied in a general sense to mineral alteration mapping and exploration for fe ore deposits hosted by banded iron formations bifs for this reason the archean weld range greenstone belt that hosts the beebyn and madoonga fe ore deposits has been chosen as a case study area to test the effectiveness of aster imaging techniques for the identification of fe orebodies banded iron formations in the weld range district crop out as a series of parallel 10 to 500 m wide 55 wt fe iron ore deposits host archean hypogene magnetite and specular hematite orebodies that are locally replaced by more recently formed supergene goethite hematite ore within several hundred meters of the present erosion surface a common feature of all ore types hosted by bifs is a high fe content relative to sio2 consequently all types of fe ore in the weld range district are best identified by the ferric iron to silica index and the opaques to silica index for the reason that these aster image products detect surfaces that are rich in opaque fe oxide minerals and have a low silica abundance gabbro dolerite and basalt country rocks located within 20 m of high grade fe ore zones in bifs are altered to hypogene fe rich chlorite and more rarely are altered by fe rich talc these hypogene alteration zones are best detected by the ferrous iron content in mgoh minerals and carbonates and the feoh group abundance products which identify hypogene fe chlorite and fe talc this study demonstrates that integrated remote spectral sensing techniques aster airborne hyperspectral and radiometric used in conjunction with geophysical surveys aeromagnetic and gravity are useful for district scale exploration for fe orebodies hosted by bifs the spectral sensing techniques are a rapid cost effective and efficient means for generating and ranking exploration targets that are located in areas with restricted physical access

remote sensing for porphyry copper deposits in southern arizona landsat multispectral scanners landsat 4 thematic mapper three porphyry copper deposits used as test sites landsat data useful for delineating areas of iron oxide on the surface limited spatial resolution of mss hampered mapping of some critical geologic relationships synoptic view well suited for examining regional tectonic patterns landsat 4 thematic mapper is an improved mapping tool compared to the previous landsat scanners modified journal abstract

transport and deposition of a pyroclastic surge across an area of high relief the 18 may 1980 eruption of mount st helens washington the 08 32 pdt 18 may 1980 mount st helens eruption began as an explosion blast that produced a laterally flowing pyro clastic current blast surge it moved outward in a 180 arc at supersonic speeds and then slowed to subsonic speeds supersonic flow severely eroded the ground and produced a ground layer formerly layer a0 above the ground layer lies the deposit derived from the blast surge the blast surge deposits formed in three continuous and concurrent stages the first stage was movement of the transport system that is the blast surge carrying fragments most of the distance from the vent the next two stages involved the depositional system this system developed from rapidly accumulating sediment by gravity segregation at the base of the blast surge two stages of sediment gravity flows with independent flow regimes formed sequentially in rapid succession from the moving blast surge each moved downhill due to gravity independently of the generating blast surge that was driven by explosive expansion units repeated in some sections are deposits derived from divergent and crossing surge lobes caused by irregular topography locally ponded massive deposits in valleys and depressions formed from gas rich pyroclastic flows and originated in two ways 1 topographic blocking by steep volcano facing slopes blocking includes diversion or damming of the lower elevation high density part of the blast surge that could not surmount high ridges 2 also occurring to form valley ponds was drainage of just deposited or almost deposited material from steep slopes 30 35 moving downhill in all slope directions into separate valleys or depressions distances traveled by the blast surge and rates at which coarsest fragments decrease laterally are related to the topographic grain surge runout was farther where flow directions paralleled topographic trends and least where trends were at right angles to the flow obstacle interference depositional patterns thinning thickening rapid fine to coarse facies changes caused a spread in median diameter values that are as great in local areas near the volcano as they are over the width of the devastated region

characterization of aster spectral bands for mapping of alteration zones of volcanogenic massive sulphide deposits abstract in this study the oxidized and hydrothermally altered zones including propylitic argillic and phyllic zones associated with volcanogenic massive sulphide deposits in the sohar shinas region of the sultanate of oman are studied based on absorption characters of spectral bands of advanced spaceborne thermal emission and reflection radiometer aster in this work we have used selected imaging processing methods including decorrelation stretching band ratios linear spectral unmixing lsu and mixture tuned matched filtering mtmf as well as petrological and geochemical characteristics of the alteration zones to map and understand the distribution of these alteration zones results indicate that 1 the decorrelation of aster spectral bands 3 6 and 8 discriminate extrusive basalts and the host lithology of altered zones 2 the application of aster band ratios 5 3 1 2 oxidized zone 4 6 5 argillic zone and 5 7 6 phyllic zone delineate alteration zones spatially associated with mineralized zones 3 the utilization of aster indices for oh bearing altered minerals e g kaolin and alunite indices confirmed the presence of alteration minerals in the mineralized zone 4 alteration end members derived using the spectral angle mapper sam method in combination with linear spectral unmixing lsu can be used to map the distribution of the weathering and alteration zones 5 short wavelength infrared swir measurements on field samples were used to confirm spectral measurements from aster data and 6 microscopic study and xrd analysis of field samples confirmed the presence of hematite and goethite in the oxidized zone chlorite epidote and calcite in the propylitic zone kaolin and chlorite in the argillic zone sericite and illite in the phyllic zone the major minerals responsible to absorptions of aster bands 3 8 5 and 6 respectively this study demonstrated the sensor capability of aster and the potential use of the image processing methods and documented the spectral absorptions values of the altered minerals and the field and mineralogical characters of alteration zones of the volcanogenic massive sulphide deposits to map similar deposits elsewhere