modeling susceptibility to landslides using the weight of evidence approach western colorado usa abstract the paonia mcclure pass area of colorado is well known for active mass movements we examined 735 active shallow movement features including debris flows debris slides rock slides and soil slides in this area identification of the hazardous areas is a fundamental component of disaster management and an important basis for promoting safe human occupation and infrastructure development in landslide prone areas bayes theorem based on the weight of evidence woe was used to create a map of landslides that could be hazardous the modeling was accomplished by employing a geographical information system gis and a statistical package seventeen factors that cause landslides were measured and weighted using the woe method to create a map of areas susceptible to landslides the maps of weighted factors were summed on a pixel by pixel basis after performing chi square tests to determine factors that are conditionally independent of each other by combining factors that represent topography hydrology geology land cover and human influences six models were developed the performance of each model was evaluated by the distribution of the observed landslides the validity of the best map was checked against landslides which were not entered in the analysis the resulting map of areas susceptible to landslides has a prediction accuracy of 78

elemental mobilities produced by low grade metamorphic events a case study from the proterozoic supracrustals of southern norway abstract within the sveconorwegian province of southern norway the telemark supracrustals represent the only low grade metamorphic assemblages these supracrustals are composed of metabasalts acid metavolcanics and metasediments which have been subjected to three metamorphic events an early burial type greenschist facies regional and thermal metamorphism within the supracrustal piles each of the events is heterogeneously preserved and has caused variable degrees of elemental redistribution burial metamorphism is a localised phenomenon involving high fluid rock ratios which has produced extremely anomalous compositions in contrast the regional metamorphism greenschist facies has completely obliterated the primary textures in the basaltic formations and has also produced a large degree of scatter in the more mobile elements the late thermal metamorphism is associated with the intrusion of late kinematic granites 950 ma within the thermal aureoles the metabasalts contain randomly orientated porphyroblasts of biotite hornblende and opaque phases in these basalts the more immobile elements i e zr nb ti y have been mobilised to varying degrees this conclusion is of major significance since these are the elements which are frequently used to discriminate ancient tectonic environments if these elements are used for this purpose in the present case spurious conclusions regarding the genesis and tectonic setting of the volcanics may be reached from this study it is apparent that low grade metamorphic events can have a profound effect upon whole rock geochemical compositions and thus ancient volcanic suites must be effectively screened prior to their use in tectonic modelling

panafrican basement and mesozoic gabbro in the zagros orogenic belt in the dorud azna region nw iran laser ablation icp ms zircon ages and geochemistry abstract the dorud azna region of the sanandaj sirjan metamorphic zone ssmz in nw iran is part of the zagros orogenic belt and exposes an amphibolite grade metamorphic succession of mixed continental e g the granitic galeh doz orthogneiss and oceanic or rift e g various amphibolites origin which is intruded by the darijune gabbro laser ablation icp ms u pb zircon ages of 608 18 ma and 588 41 ma of the granitic galeh doz orthogneiss indicate a panafrican basement similar to that of the yazd block of central iran we therefore interpret this part of the ssmz to represent a previously subducted part of the panafrican basement of the iranian microcontinent based on geochemistry amphibolites and metagabbros from the amphibolite unit representially potentially the cover on the panafrican galeh doz orthogneiss are interpreted to have their origin in a likely upper paleozoic to mesozoic rift or e morb ophiolite succession one of the metagabbros here termed dare hedavand metagabbro yield a 206pb 238u mean age of 314 6 3 7 ma talc bearing greenschists to epidote amphibolites of the triassic june complex formed in a similar but younger environment furthermore the metamorphic complex is intruded by the darijune gabbro which yields a mean icp ms u pb zircon age of 170 2 3 1 ma the final stage of likely jurassic greenschist facies grade metamorphism postdates the gabbro intrusion we interpret the darijune gabbro to have resulted from the initial subduction of neotethyan oceanic lithosphere in a continental arc setting the new data combined with data from literature indicate that the ssmz represents a tectonic element of a mixed continental and oceanic origin likely accreted to central iran during a jurassic tectonic process the new data also constrains thick skinned nappe stacking within the sanandaj sirjan zone

ig mapper a new arcgis toolbox for the geostatistics based automated geochemical mapping of igneous rocks abstract this work introduces a user friendly fast and effective tool for the automated geochemical mapping of igneous rocks to provide a geospatial representation of petrological parameters through the application of either deterministic or stochastic interpolation techniques the geostatistical approach allows mapping to be extended to areas where igneous rocks are hidden under sedimentary cover also introducing an estimate of the interpolation reliability this new gis based automated procedure which is mostly constructed with the arcgis model builder as a graphical code designer can generate three main types of outputs 1 interpolation maps of major and trace elements isotopic compositions and derived parameters to provide valuable geospatial information regarding the genetic and structural relationships between magmatic bodies 2 lithological maps that are based on the geostatistical interpolation of major element data and mirror the main geochemical classification diagrams of plutonic rocks and 3 interpolation checking maps which provide an estimate of the geostatistical interpolability for one specific parameter at a time this last output is expressed in the form of an empirical index stochastic interpolation index which highlights the randomness level of a specific value distribution this automated lithological mapping function is an entirely new tool based on five original python scripts which makes it possible to interpolate on a georeferenced map the compositions deriving from the most used geochemical classification diagrams this new tool package is presented here by using a portion of the serre batholith in central calabria southern italy to illustrate the potential of this method to open new research perspectives in igneous petrology

the effect of mixed wettability on pore scale flow regimes based on a flooding experiment in ketton limestone darcy scale multiphase flow in geological formations is significantly influenced by the wettability of the fluid solid system so far it has not been understood how wettability impacts the pore scale flow regimes within rocks which were in most cases regarded as an alteration from the base case of strongly water wet conditions by adjustment of contact angles in this study we directly image the pore scale flow regime in a carbonate altered to a mixed wet condition by aging with crude oil to represent the natural configuration in an oil reservoir with fast synchrotron based x ray computed tomography we find that the pore scale flow regime is dominated by ganglion dynamics in which the pore space is intermittently filled with oil and brine the frequency and size of these fluctuations are greater than in water wet rock such that their impact on the overall flow and relative permeability cannot be neglected in modeling approaches

dynamic fluid connectivity during steady state multiphase flow in a sandstone abstract the current conceptual picture of steady state multiphase darcy flow in porous media is that the fluid phases organize into separate flow pathways with stable interfaces here we demonstrate a previously unobserved type of steady state flow behavior which we term dynamic connectivity using fast pore scale x ray imaging we image the flow of n2 and brine through a permeable sandstone at subsurface reservoir conditions and low capillary numbers and at constant fluid saturation at any instant the network of pores filled with the nonwetting phase is not necessarily connected flow occurs along pathways that periodically reconnect like cars controlled by traffic lights this behavior is consistent with an energy balance where some of the energy of the injected fluids is sporadically converted to create new interfaces

gis based mineral potential modeling by advanced spatial analytical methods in the southeastern yunnan mineral district china this paper demonstrates a modeling procedure of mineral potential mapping based on singularity theory and further presents an idea to look into metallogeny of sn cu polymetallic deposits in southeastern yunnan mineral district china by applying a localized regression method mineralization is a typical cascade process generally accompanied by irregular geological geochemical and geophysical signatures singularity index as an efficient anomaly analytical tool helps to identify anomalies as well as characterize formation processes of these anomalies in this study the singularity based mineral potential mapping method was utilized to characterize hydrothermal mineralization associated with magmatic tectonic and sedimentary processes in this district based on the results a mineral prospectivity model was constructed to delineate target areas in addition to mineral prospectivity controlling effects of geo processes on mineralization are spatially non stationary geographically weighted regression analysis was thus employed to investigate these spatially varied controlling effects and it has contributed to improve understanding to local metallogeny in the study area results of the spatial analysis presented can be used to guide following stages of mineral exploration in the district

phenomenological understanding of poroelasticity via the micromechanics of a simple digital rock modelmicromechanics basis of poroelasticity

some petrologic and oxygen isotopic relationships in the amulet mine noranda quebec and their bearing on the origin of archean massive sulfide deposits a concentrically zoned alteration pipe is present at the amulet a cu zn mine in the archean abitibi greenstone belt the pipe consists of a central core zone of so called dalmatianite spotted cordierite anthophyllite rock surrounded by a zone of biotite bearing grid fracture alteration study of the dalmatianite indicates that these rocks experienced two episodes of recrystallization first the original andesite was completely reconstituted during a hydrothermal event producing a quartz chlorite assemblage this transformation was associated with the formation of the massive sulfide lens and presumably took place in a submarine environment later contact metamorphism associated with the intrusion of the nearby lake dufault granodiorite resulted in partial recrystallization of the chlorite and quartz to cordierite and anthophyllite whole rock delta 18 o values decrease from about 6 to 10 in most of the abitibi belt to 5 to 7 in the country rocks surrounding the ore deposit to values as low as 3 6 in the core of the dalmatianite zone this oxygen isotopic zoning must have been produced by the hydrothermal activity because the dehydration reactions associated with contact metamorphism cannot have affected delta 18 o by more than 0 5 per mil assuming an alteration temperature of 300 degrees or 50 degrees c and a water rock ratio greater than two the hydrothermal fluid must have had delta 18 o 0 5 or 1 0 this indicates that the amulet ore deposit formed from a hydrothermal fluid that had a delta 18 o value similar both to modern seawater and to the fluids which formed the phanerozoic massive sulfide deposits of the kuroko and cyprus types the apparent constancy of delta 18 o of seawater during the precambrian and the continued importance of seawater hydrothermal processes are important constraints which must be considered in developing models of the history of the earth

metabasalts axial hot springs and the structure of hydrothermal systems at mid ocean ridges knowledge of the chemical transfer and mineralogical transformations that occur when sea water reacts with basalt at elevated temperatures and pressures can be used along with geological and geophysical data to deduce the typical structure and evolutionary sequence for hydrothermal systems within the oceanic crust along the axis of a mid ocean ridge studies of metabasalt and metadiabase dredged from fault scarps along the axial valley of the mid atlantic ridge reveal consistent relationships among the bulk chemistry of the altered rocks and their secondary mineralogy mineral abundances and mineral compositions especially for chlorite these relationships can be interpreted in terms of the distribution of alteration with respect to time temperature and water rock ratio in young crust assemblages of chl ab ep act chl ab ep act qtz chl ab qtz and chl qtz are produced at successively higher effective sea water to rock ratios within the temperature range of the greenschist facies 250 to 450 c toward higher ratios chlorites tend to become more mg rich pillow basalts of layer 2 are commonly altered under these conditions by sea water on the descending rather than the ascending limb of a convection system this type of alteration which reflects moderately high water rock ratios may characteristically occur above a still partially molten magma chamber as the magma chamber solidifies and is then penetrated more pervasive alteration of the deeper part of layer 2 and of layer 3 occurs at lower water rock ratios producing solutions such as those recovered from springs on the galapagos rift and the east pacific rise at 21 n localized upwelling limbs of the convection system can produce veins filled with quartz sulfides and fe rich chlorite

volcanic rocks of the witwatersrand triad south africa ii petrogenesis of mafic and felsic rocks of the dominion group abstract a bimodal suite of volcanic rocks builds the bulk of the dominion group which with an age of 2 72 ga is the oldest cover sequence overlying the granite greenstone archaean basement of the kaapvaal craton in the western transvaal south africa the basic lavas are relatively rich in sio 2 50 58 and aphyric and exhibit a large compositional range this variation is typically tholeiitic in that it is characterized by strong enrichment of ti fe and v in differentiated lavas the different amounts of relative enrichment of these elements allow the basic lavas to be subdivided into two groups one group is characterized by evolution to low ti v ratios in evolved lavas and the other by high ti v ratios for nearly all other elements the composition variation of the two groups is extremely similar and overlaps although the high ti v group contains the most evolved compositions and most of the primitive lavas mg numbers 60 belong to the low ti v group although recognition of the two groups is based on geochemistry they are interlayered in a consistent pattern within the lava pile theoretical modelling indicates that the variation in both lava groups can be explained by low pressure fractional crystallization of phases in a typical tholeiitic sequence primitive basalts of the low ti v group show a large range in major element compositions and a more restricted range of incompatible trace elements and ree abundances in particular fe 2 o 3 total ranges from 9 to 13 5 and correlates positively with mgo cr and ni and negatively with al 2 o 5 and sio 2 there are no correlations of mg number with incompatible trace elements such as zr and ce these lavas also have lree enriched ree abundance patterns and negative nd these features cannot be explained by crustal contamination but are consistent with derivation by uniform amounts of melting of a mantle source which was heterogeneous with regard to major elements particularly fe al and probably ca and na and uniformly enriched in incompatible trace elements at least 0 3 ga before melting the geochemical style of this enrichment is akin to that associated with modern subduction this enrichment is associated with the development of a thick archaean lithosphere the existence of which is corroborated by diamond age and diamond inclusion thermobarometric studies the geochemistry of the dominion basic lavas differs significantly from those of the 3 4 ga barberton komatiitic and tholeiitic suites this suggests that the changing pattern of crustal evolution from metastable greenstone tectonic styles to stable proterozoic styles is reflected in the changing character of the mantle sources tapped by basic magmas the porphyritic dominion rhyodacites or rhyolites exhibit limited compositional variation and are genetically unrelated to the basic lavas nd isotopes and la th and th co ratios suggest that they are partial melts of mafic crustal materials geochemical and petrological features of the dominion suite are entirely consistent with eruption in a continental environment characterized by rifting or lithospheric thinning this is consistent with some models for the tectonic development of the witwatersrand basin

gis based weights of evidence modelling of rainfall induced landslides in small catchments for landslide susceptibility mapping landslide susceptibility mapping is a vital tool for disaster management and planning development activ ities in mountainous terrains of tropical and subtropical environments in this paper the weights of evidence modelling was applied within a geographical information system gis to derive landslide susceptibility map of two small catchments of shikoku japan the objective of this paper is to evaluate the importance of weights of evidence modelling in the generation of landslide susceptibility maps in relatively small catchments having an area less than 4 sq km for the study area in moriyuki and monnyu catchments northeast shikoku island in west japan a data set was generated at scale 1 5 000 relevant thematic maps representing various factors e g slope aspect relief flow accumulation soil depth soil type land use and distance to road that are related to landslide activity were generated using field data and gis techniques both catchments have homogeneous geology and only consist of cretaceous granitic rock thus bedrock geology was not considered in data layering during gis analysis success rates were also estimated to evaluate the accuracy of landslide suscepti bility maps and the weights of evidence modelling was found useful in landslide susceptibility mapping of small catchments

field and geochemical characteristics of mesoarchean to neoarchean volcanic rocks in the storo greenstone belt sw greenland evidence for accretion of intra oceanic volcanic arcs abstract the storo greenstone belt southern west greenland consists of thrust imbricated slices of mesoarchean 3060 ma and neoarchean ca 2800 ma mafic to ultramafic volcanic rocks volcaniclastic sediments and gabbro anorthosite associations the belt underwent polyphase metamorphism at upper amphibolite facies conditions between 2650 and 2600 ma the contacts between the mesoarchean and neoarchean volcanic rocks and surrounding eoarchean to neoarchean tonalite trondhjemite granodiorite ttg gneisses are tectonic and typically bounded by high grade mylonites regardless of age the volcanic rocks are dominated by mafic amphibolites with a tholeiitic basalt composition near flat to slightly enriched light rare earth element lree patterns la smcn 0 91 1 48 relatively flat to slightly depleted heavy ree hree gd ybcn 1 0 1 28 and pronounced negative nb ta anomalies nb nb 0 34 0 73 on chondrite and primitive mantle normalized diagrams these geochemical characteristics are consistent with subduction zone geochemical signatures and partial melting of a shallow

mineralization controls in island arc settings insights from philippine metallic deposits abstract a review of the gold copper volcanogenic massive sulfide and ultramafic hosted i e chromitite nickel sulfide platinum group minerals deposits in the philippines is presented it is critical that a thorough understanding of the spatial and temporal relationship among magmatism structures and mineralization must be gained if the correct evaluation of the economic potential of a particular deposit is to be done structural features conducive to precious and base metal mineralizations are associated with shear zones extensional jogs and collision zones in northern luzon alkali and adakitic magmatism are considered good markers for gold copper mineralization volcanogenic massive sulfide deposits are hosted by either ophiolites of marginal basin origin or metamorphic terranes exploration works on these deposits have been geared in determining the gold content of the massive sulfides chromitite deposits are related with ultramafic rock hosted deposits their occurrence is attributed to crystallization magma mixing and mantle melt interaction processes in subduction related settings the multiple stages of partial melting responsible for the formation of supra subduction zone ophiolites result in the generation of second to third stage melts that are enriched in nickel sulfides and platinum group minerals on the basis of structural geochemical and tectonic controls panay mindoro and central mindanao and the sierra madre leyte and samar are good exploration targets for precious and base metal deposition in the western and eastern sides of the philippines respectively

assessment of ground subsidence using gis and the weights of evidence model abstract the weights of evidence model one of the bayesian probability models was applied in evaluating a ground subsidence spatial hazard near abandoned underground coal mines aucms at magyori area samcheok city in korea using gis using ground subsidence location and a spatial database containing information such as mining tunnel borehole topography geology and land use the weights of evidence model was applied to calculate each relevant factor s rating for the magyori area in korea seven major factors controlling or related to ground subsidence were determined from the probability analysis of the existing ground subsidence area depth of drift and distance from drift from the mining tunnel map slope gradient obtained from the topographical map ground water level and permeability from borehole data geology and land use tests of conditional independence were performed for the selection of factors allowing 6 combinations of factors to be analyzed for the analysis of mapping ground subsidence spatial hazard the contrast values w and w of each factor s rating were overlaid spatially the results of the analysis were validated using receiver operating characteristic roc with the previous ground subsidence locations in the case of all factor used the area under the roc curve auc showed 0 9667 which corresponds to an accuracy of 96 67 in the case of the combinations the case of distance from drift depth of ground water and land use used showed the 90 71 auc 0 9071 accuracy which is the best result produced in this analysis the results can be used for hazard prevention and land use planning near aucm areas

quantified spatial relationships between gold mineralisation and key ore genesis controlling factors and predictive mineralisation mapping st ives goldfield western australia abstract determining the spatial relationships between various geological features and mineralisation is not only important for understanding the ore genesis of mineral deposits but can also help to guide mineral exploration by providing predictive mineral maps in this gis based study we quantify the spatial relationships between gold mineralisation and plausible controlling factors in the central part of the st ives area western australia we weigh plausible control factors including rock types lithological boundaries and faults using gold occurrences in drill cores and then apply the weights to the geological data to generate a predictive map for the entire st ives area the three major findings of this study are 1 all major gold deposits are controlled by faults and small scale fault systems have a stronger correlation with gold mineralisation than large faults 2 felsic to intermediate intrusive rocks show strong correlations with gold mineralisation whereas metamorphic mafic rocks greenstones possibly acted as part of the broad regional environment for the mineral province rather than as a factor controlling the exact locations of the deposits and 3 our predictive mapping indicates that the southeast part of the st ives goldfield has a high potential for discovering new gold mineralisation

spatial analysis and visualization of exploration geochemical data abstract this paper briefly reviews the application of geoinformatics in exploration geochemistry from the perspective of spatial analysis and visualization and demonstrates the advantages of geoinformatics in exploring geochemical patterns and identifying geochemical anomalies in particular the application of geoinformatics to geochemical mapping recognition of geochemical anomalies and simulation of geochemical patterns are discussed the benefits of geoinformatics include 1 overlay of geochemical data on a geological map which helps geochemists to understand spatial geochemical patterns and visualize geochemical anomalies 2 local neighbourhood spatial analysis which considers the local spatial structure of geochemical patterns as a powerful tool to identify weak geochemical anomalies and 3 geochemical patterns simulation based on geological constrains which helps to understand geological processes future researches should focus on development and application of various functions for processing geochemical data in a gis to promote the progress of geoinformatics in both geochemical exploration and environmental studies

data and knowledge driven mineral prospectivity maps for canada s north abstract data and knowledge driven techniques are used to produce regional au prospectivity maps of a portion of melville peninsula northern canada using geophysical and geochemical data these basic datasets typically exist for large portions of canada s north and are suitable for a greenfields exploration programme the data driven method involves the use of the random forest rf supervised classifier a relatively new technique that has recently been applied to mineral potential modelling while the knowledge driven technique makes use of weighted index overlay commonly used in gis spatial modelling studies we use the location of known au occurrences to train the rf classifier and calculate the signature of au occurrences as a group from non occurrences using the basic geoscience dataset the rf classification outperformed the knowledge based model with respect to prediction of the known au occurrences the geochemical data in general were more predictive of the known au occurrences than the geophysical data a data driven approach such as rf for the production of regional au prospectivity maps is recommended provided that a sufficient number of training areas known au occurrences exist

structural control of low sulfidation epithermal gold mineralization in the rosario bunawan district east mindanao ridge philippines the rosario bunawan district is situated about 200 km north of davao city the capital of the mindanao island southern philippines gold is produced from the co o mine containing about 2 034 000 t of ore at 10 9 g t au and in numerous small scale operations by local miners epithermal gold mineralization in the rosario bunawan district and the co o mine is confined to narrow 0 2 4 m low sulfidation quartz chalcedony calcite veins in volcanic and volcaniclastic wall rocks three major vein orientations are distinguished 1 the nnw sse trending set with a sinistral strike slip sense of deformation philippine fault trend 2 the ene wsw trending dextral strike slip set palawan trend and associated veins in the riedel geometry and 3 the wnw ese trending conjugate set co o trend three structural stages are defined 1 extensional shear or shear veins formed in the co o the philippine fault and palawan trends during regional nw se compression and near vertical vein opening d1 2 reactivation of veins in the philippine fault veins associated with the palawan and to a lesser extent the co o trends during e w compression and near horizontal n s oriented vein opening d2 new d2 extensional shear or shear veins formed in the philippine fault and structures associated with the palawan and associated riedel trends 3 the d3 stage block faulting subsequently displaced all of the auriferous veins the auriferous rosario bunawan district is situated between two splays of the philippine fault which acted as a lateral ramp system during the oblique convergence of the philippine sea plate and the eurasian plate the oblique convergence resulted in a change from a compressional d1 to a transpressional d2 regime which was a prerequisite for the two stage vein opening and hydrothermal mineralization leading to an economic gold enrichment d1 compressional tectonics may have caused an elevated geothermal gradient in shallow crustal levels forming the heat source for the fluid plumbing system which is at variance to typical epithermal deposits formed in extensional zones d2 thrusting of a limestone nappe together with syn tectonic diorite intrusions may have further increased the geothermal gradient maintaining the fluid plumbing system the limestone nappe may at the same time have represented an aquitard forcing the hydrothermal fluids into the volcanic and volcaniclastic wall rocks which is regarded as critical for the two stage gold mineralization in the rosario bunawan district

predictive mapping of prospectivity for orogenic gold giyani greenstone belt south africa we present a mineral systems approach to predictive mapping of orogenic gold prospectivity in the giyani greenstone belt ggb by using layers of spatial evidence representing district scale processes that are critical to orogenic gold mineralization namely a source of metals fluids b active pathways c drivers of fluid flow and d metal deposition to demonstrate that the quality of a predictive map of mineral prospectivity is a function of the quality of the maps used as sources of spatial evidence we created two sets of prospectivity maps one using an old lithologic map and another using an updated lithological map as two separate sources of spatial evidence for source of metals fluids drivers of fluid flow and metal deposition we also demonstrate the importance of using spatially coherent or geologically consistent deposit occurrences in data driven predictive mapping of mineral prospectivity the best predictive orogenic gold prospectivity map obtained in this study is the one that made use of spatial evidence from the updated lithological map and spatially coherent orogenic gold occurrences this map predicts 20 of the ggb to be prospective for orogenic gold with 89 goodness of fit between spatially coherent inactive orogenic gold mines and individual layers of spatial evidence and 89 prediction rate against spatially coherent orogenic gold prospects in comparison the predictive gold prospectivity map obtained by using spatial evidence from the old lithological map and all gold occurrences has 80 goodness of fit but only 63 prediction rate these results mean that the prospectivity map based on spatially coherent gold occurrences and spatial evidence from the updated lithological map predicts exploration targets better i e 28 smaller prospective areas with 9 stronger fit to training gold mines and 26 higher prediction rate with respect to validation gold prospects than the prospectivity map based on all known gold occurrences and spatial evidence from the old lithological map

alteration mineralogy lithochemistry and stable isotope geochemistry of the murgul artvin ne turkey volcanic hosted massive sulfide deposit implications for the alteration age and ore forming fluids abstract the murgul artvin ne turkey massive sulfide deposit is hosted dominantly by late cretaceous calc alkaline to transitional felsic volcanics the footwall rocks are represented by dacitic flows and pyroclastics whereas the hanging wall rocks consist of epiclastic rocks chemical exhalative rocks gypsum bearing vitric tuff purple vitric tuff and dacitic flows multi element variation diagrams of the hanging wall and footwall rocks exhibit similar patterns with considerable enrichment in k rb and ba and depletion in nb sr ti and p the chondrite normalized rare earth element rees patterns of all the rocks are characterized by pronounced positive negative eu anomalies as a result of different degrees of hydrothermal alteration and the semi protected effects of plagioclase fractionation mineralogical results suggest illite illite smectite chlorite kaolinite and chlorite in the footwall rocks and illite smectite kaolinite and chlorite illite in the hanging wall rocks overall the alteration pattern is represented by silica sericite chlorite and chlorite carbonate epidote sericite and quartz albite zones increments of ishikawa alteration indexes resulting from gains in k 2 o and losses in na 2 o and the chlorite carbonate pyrite index towards to the center of the stringer zone indicate the inner parts of the alteration zones calculations of the changes in the chemical mass imply a general volume increase in the footwall rocks abnormal volume increases are explained by silica and iron enrichments and a total depletion of alkalis in silica zone relative k increments are linked to the sericitization of plagioclase and glass shards and the formation of illite smectite in the sericite zone in addition fe enrichment is always met by pyrite formation accompanied by quartz and chlorite illite is favored over chlorite smectite and kaolinite in the central part of the ore body due to the increase in the al k na ca ratio although the rees were enriched in the silicification zone light rees show depletion in the silicification zone and enrichment in the other zones in contrast to the heavy rees behavior hydrothermal alteration within the hanging wall rocks apart from the gypsum bearing vitric tuffs is primarily controlled by chloritization with proportional fe and mg enrichments and sericitization the 18 o and d values of clay minerals systematically change with increasing formation temperature from 6 6 to 8 7 and 42 to 50 for illites and 8 6 and 52 for chlorite respectively the o and h stable isotopic data imply that hydrothermal alteration processes occurred at 253 332 c for illites and 136 c for chlorite with a temperature decrease outward from the center of the deposit the positive 34 s values 20 3 to 20 4 for gypsum suggest contributions from seawater sulfate reduced by fe oxide hydroxide phases within altered volcanic units thus the hydrothermal alteration possibly formed via a dissolution precipitation mechanism that operated under acidic conditions the k ar dating 73 62 ma of the illites indicates an illitization process from the maastrichtian to early danian period

alteration geochemistry and fluid inclusion characteristics of the greenstone hosted gold deposit of hutti eastern dharwar craton india gold mineralization of the hutti mine southern india is situated in closely spaced laminated quartz veins and associated alteration haloes along steeply dipping shear zones within a sequence of rather uniform amphibolites intense shearing has resulted in large scale mylonitization of the wall rocks anastomosing shear zones with intervening lensoid bodies of unsheared amphibolites are characteristic features of the deposit the general pattern of symmetrical alteration comprises a distal zone of chlorite rich rock with a proximal biotite rich zone adjacent to laminated quartz veins arsenopyrite thermometry yielded a temperature range of 350 477 c for the biotite alteration zone which preceded the formation of the laminated quartz veins mass balance calculations on the alteration zones indicate a gradual mass and volume loss during alteration the alteration is accompanied by intense potash metasomatism and addition of sulfur which resulted in the formation of arsenopyrite pyrrhotite and pyrite results of fluid inclusion studies suggest that low salinity 3 9 13 5 wt nacl equivalent h2o co2 rich fluids were responsible for gold rich laminated quartz vein formation in the hutti deposit these fluids constituted a later counterpart of the protracted fluid activity that first formed the biotite alteration zone the estimated p t values range from 1 0 to 1 7 kbar at 280 320 c these data along with the alteration assemblages and the characteristic gold sulfide association both in the altered wall rock and laminated quartz veins suggest that gold transported as reduced bisulfide complexes was deposited in response to sulfidation reactions in the wall rocks comparison of p t conditions of formation of gold quartz veins at hutti with two other large gold deposits in the eastern dharwar craton namely kolar 1 8 kbar 280 c and western ramagiri 1 45 1 7 kbar 240 270 c indicates broadly similar lode gold forming conditions in the dharwar craton

geochemistry of archean alkalic volcanic rocks from the crystal lake area east of kirkland lake ontario canada abstract twelve samples of timiskaming volcanics from the crystal lake area were analyzed for major and trace elements ta th zr hf v cr sc rare earth elements ree y etc by x ray fluorescence and instrumental neutron activation analysis techniques the samples which include mafic trachytes trachytes and leucite trachytes represent several batches of archean alkalic magmas differentiated at shallow depths the cr sc cr systematics and ree zr th and zr y characteristics show however that their primary magmas generated at great depths in the enriched mantle where garnet remained in the refractory residue of partial melt the chemical similarity between the timiskaming samples and modern alkalic rocks in mature volcanic arcs strongly implies that the timiskaming volcanism represents the last stage of a late archean island arc volcanism present in the southwestern abitibi belt superior province the occurrence of timiskaming type alkalic rocks is not rare in archean greenstone belts thereby suggesting that a tectonic setting similar to modern volcanic arc system might have been common in late archean time

stratigraphy and geochemistry in the proterozoic mafic volcanic rocks of the nagu korpo area sw finland the volcanic rocks of the nagu korpo area in sw finland form a thin 1000 m formation that is folded into narrow synforms separated by migmatite filled antiforms in nagu the volcanic formation comprises three units a lower unit of subvolcanic banded gabbro sills a middle unit of amphibolitic volcanic rocks and an upper unit consisting of a thin ultramafic volcanic rock layer the volcanic formation is interlayered within a thicker sequence of metasedimentary gneisses geochemically the metavolcanic rocks are tholeiitic and plots based on ti y zr and other trace elements show that they resemble recent within plate lavas morb and mantle normalised trace element plots show patterns strongly differing from those of recent arc lavas indicating a tectonic environment of plate boundary related initial rifting the upper ultramafic lavas are enriched in lree relative to the lavas of the much thicker amphibolitic middle unit below a model for the initial formation of the volcanic rocks of the svecofennian fold belt must acknowledge both the episode of initial rifting and the later evolution of an island arc like environment

integrated gis based modelling for the quantitative prediction of magmatic ti v fe deposits a case study in the panzhihua xichang area of southwest china abstract the estimation of undiscovered mineral resources is an important part in the potential value of a mineral field and its long term use this manuscript documents six procedures for estimating the volume of potential mineral resources in an area that is based on integrated geological information forming part of a metallogenic model the technique for this methodology includes 1 the development a metallogenic model or models for mineral deposits in the study area 2 the integration of the characteristics of known mineral anomalies with geology geochemistry and geophysics to establish a predictive model for mineralization 3 the definition of possible mineral resources incorporating predictive models with characteristic analyses the knowledge driven delphi method and magnetic anomalies 4 calculate the parameters for the quantitative prediction areas of known mineral deposits and their estimated dip extension ore bearing coefficients and their similarity coefficients based on explored ore deposits in the area studied 5 complete quantitative predictions using an synthetic volumetric equation and 6 assess zones that are considered prospective for mineral resources the procedure is tested for magmatic ti v fe resources in a known mineralized zone in the sichuan province of china

combining fractal analysis of mineral deposit clustering with weights of evidence to evaluate patterns of mineralization application to copper deposits of the mount isa inlier nw queensland australia the clustering of mineral occurrences and their spatial associations with particular geological features are critical aspects of mineral distributions for exploration and understanding ore genesis variations in the degree of clustering of mineral occurrences or geological features can be measured by fractal dimensions obtained from a shifting box counting method spatial associations between mineral occurrences and geological features can be quantified by the weights of evidence wofe method using the contrast value which increases with the strength of the spatial relationship a new method is proposed to evaluate mineral occurrence distributions by combining the power of fractal analysis of clustering with the wofe approach the method compares the correlation between the variation in degree of clustering of mineral occurrences and a geological feature in a study area with the contrast value of the same feature the possible outcomes can be simplified into four scenarios depending on whether the correlation in variation of clustering and the contrast are high or low respectively each outcome has specific exploration implications if either a high correlation in variation of clustering or a high contrast value is obtained the geological feature can be used for exploration targeting the integrated fractal and wofe approach is applied to copper occurrences in the proterozoic mount isa inlier nw queensland australia which hosts large numbers of copper deposits 1 869 occurrences including the world class mount isa copper deposit variation in clustering of copper occurrences has a positive correlation with variation in clustering of fault bends r 0 823 fault intersections r 0 862 and mafic rocks r 0 885 wofe results indicate that the copper occurrences are spatially associated with fault intersections and bends and with mafic rocks analyses were carried out separately for the two major lithostratigraphic sequences in the inlier the eastern and western successions the western succession copper occurrences are apparently more clustered than those of the eastern succession which may reflect a lower degree of exploration and or geological factors the association of copper occurrences with mafic rocks compared with fault bends and intersections is greater in the eastern succession which may reflect genetic factors correlations in the variation of clustering of mineral occurrences and geological features have a linear relationship with the contrast values and the spatial association between all geological features and copper occurrences constitute high correlation high contrast cases the linear relationship suggests that the geological features that control the clustering of the copper occurrences could be the same features that control their localization

composition volume changes during hydrothermal alteration of andesite at buttercup hill noranda district quebec abstract hydrothermally altered andesites in the upper member of the amulet formation at buttercup hill noranda quebec represent part of the aquifer and cap of a self sealing geothermal system that focussed the discharge of hydrothermal fluids during the formation of massive cu zn sulfide deposits five alteration facies are recognized 1 pervasive greenschist facies regional metamorphism least altered andesite 2 epidotization silicification 3 albitization silicification 4 chloritization 5 sericitization silicification alteration is localized on permeable zones such as amygdules fractures flow tops discordant breccia dikes and conformable breccia horizons epidotized silicified andesite is enriched in ca sr eu and depleted in mg and first transition series metals ftsm relative to least altered andesite albitized silicified andesite is significantly enriched in na and depleted in most ftsm relative to least altered andesite the abundances and inter element ratios of the rare earth elements ree and most high field strength elements hfs y zr th u hf ta are similar in least altered epidotized silicified and albitized silicified andesites the most silicified andesites are strongly enriched in na si strongly depleted in mg and divalent ftsm and slightly but systematically depleted in ree and most hfs elements serialized andesites were previously silicified they are very strongly enriched in k rb cs ba very strongly depleted in na ca sr eu and slightly depleted in light ree relative to silicified andesite chloritized andesitic rocks exhibit heavy ree and hfs element ratios similar to those of leastaltered andesite but are relatively strongly enriched in mg and divalent ftsm strongly depleted in si and large ion lithophile lil elements and slightly depleted in light ree the coupled behavior of the heavy ree and most hfs elements during epidotization albitization silicification chloritization and serialization suggests that they were inert during hydrothermal modification of the andesite mass balance calculations suggest that volume was conserved during epidotization silicification and albitization silicification but that intense silicification was accompanied by volume increases up to 30 percent

crustal assimilation in the burnt lake metavolcanics grenville province southeastern ontario and its tectonic significance three intimately interbedded suites of volcanic rocks are identified geochemically in the burnt lake area of the belmont domain in the central metasedimentary belt and their petrogenesis is evaluated the burnt lake back arc tholeiitic suite comprises basalts similar in trace element signature to tholeiitic basalts emplaced in back arc basins formed in continental crust the burnt lake continental tholeiitic suite comprises basalts and andesites similar in trace element composition to continental tholeiitic sequences the burnt lake felsic pyroclastic suite comprises rhyolitic pyroclastics having major and trace element compositions that suggest that they were derived from crustal melts rare earth element models suggest that the burnt lake back arc tholeiitic rocks were formed by fractional crystallization of mafic magmas derived by approximately 5 partial melting of an amphibole bearing depleted mantle enriched in light rare earth elements by a subduction component the modelling also suggests that t

comparison of 3d prospectivity modeling methods for fe cu skarn deposits a case study of the zhuchong fe cu deposit in the yueshan orefield anhui eastern china abstract three dimensional 3d metallogenic prospectivity modeling has become increasingly important in deep fe cu skarn mineralization prospecting the selection of prediction models and their comparison are of great significance in this paper we integrated the geological and geophysical data from the zhuchong fe cu deposit in the yueshan orefield anhui eastern china to establish the local 3d geological framework we extracted the 3d ore controlling factors quantitatively by means of 3d spatial analysis methods and compared the 3d mineralization locations predicted by the weight of evidence method and the artificial neural network method the results show that both methods can locate most of the known orebodies suggesting that both are relatively reliable in addition the weight of evidence method performed distinctly better than the artificial neural network method in terms of both prediction effectiveness and efficiency therefore the weight of evidence method may be more applicable in 3d prospectivity modelling for fe cu skarn deposits in the region finally the composite area predicted by the two methods is taken as the final prediction result of the mineralization area of the deposit and it is suggested that in the quantitative 3d prediction multiple selection of different methods with good adaptability should be involved in the prediction at the same time and compound prediction method should be used to delineate the target area our work has guiding significance for future deep prospecting and exploitation for other similar fe cu skarn deposits

primary geochemical characteristics of mineral deposits implications for exploration extract the old adage mineral exploration is like finding a needle in a haystack recaps the difficulty of finding economic mineral deposits near or beneath the surface in general two main approaches can be used to detect the presence of mineral deposits near or beneath the ground surface one employs a mineral deposit model and the other aims at the identification of a primary halo about a mineral deposit a mineral deposit model provides systematic empirical descriptive and or theoretical genetic descriptions of the essential geological geochemical and geophysical features of a type of mineral deposits cf cox and singer 1986 and roberts et al 1988 the primary halo of a mineral deposit as defined originally by safronov 1936 is an area including rock surrounding mineral deposit ore bodies and enriched elements that make up that deposit thus descriptions of primary haloes may form part of a mineral deposit model but both deposit model and primary halo approaches to mineral exploration are based on studies of primary geochemical characteristics of mineral deposits because chemical processes during mineralization are the ones that ultimately bring about metal precipitation or mineral formation however a deposit model approach to mineral exploration is apt for identifying which haystacks contain a needle whereas a primary halo approach to mineral exploration is proper for deducing where in a needle bearing haystack is the needle located

geochemistry of neoarchean mafic volcanic rocks and late mafic dikes in the zanhuang complex central orogenic belt north china craton implications for geodynamic setting abstract an archean melange belt has been recognized in the zanhuang complex central orogenic belt cob north china craton ncc all units of the melange belt are intruded by a ca 2 5 ga granite pluton and cross cut by undeformed 2 5 ga pegmatites which constrains the archean formation age of the melange some exotic mafic ultramafic blocks are tectonically dispersed in the metasedimentary matrix to the melange and mainly consist of metabasaltic rocks deformed pillow lavas with epidosite cores gabbros and ultramafic rocks both metabasalts and epidosites are characterized by enrichment in light rare earth elements lree and pronounced negative nb and zr anomalies on chondrite and primitive mantle normalized diagrams these geochemical characteristics are consistent with supra subduction zone geochemical signatures based on the pillow structures and seafloor hydrothermal alteration combined with the geochemical characteristics an intra oceanic arc forearc setting is proposed for the formation of these exotic blocks furthermore a west dipping intra oceanic subduction zone is proposed to have formed in an ocean between the eastern block and an arc terrane prior to 2 5 ga the collision between the arc and the eastern block of the ncc happened at ca 2 5 ga resulting in the formation of the archean melange belt in the zanhuang complex all of the units of the melange belt were intruded by late mafic dikes which are present as boudinaged or lenticular shapes in the melange and surrounding gneisses and are intruded by younger ca 2 5 ga pegmatites geochemical characteristics of the late mafic dikes are consistent with an arc related mantle source region rather than an oib like source accordingly pending determination of their precise age an arc polarity reversal event is proposed to have occurred following the arc continent collision resulting in east dipping subduction beneath the newly accreted arc and eastern block forming the swarm of arc affinity mafic dikes the new subduction zone further resulted in ponded magma below the accreted arc block which induced the partial melting of thickened crust and the intrusion of ca 2 5 ga granitic and pegmatitic melts into the melange and the mafic dikes the mafic dikes were then deformed and metamorphosed when the remaining open part of the ocean between the arc collision modified margin of the eastern block collided with the western block of the ncc

landslide susceptibility analysis and verification using the bayesian probability model the bayesian probability model using the weight of evidence method was applied to the task of evaluating landslide susceptibility using gis data the location chosen for the study was the janghung area in korea which suffered substantial landslide damage following heavy rain in 1998 using the location of the landslides as well as topographic factors such as soil forest and land use the weight of evidence method was used to calculate each factor s rating tests of conditional independence were performed for the selection of the factors allowing the large number of combinations of factors to be analyzed for each factor rating the contrast values w and w were overlaid for landslide susceptibility mapping the results of the analysis were verified using the observed landslide locations and among the combinations the slope aspect curvature soil material and wood types show the best results

the queensborough mafic ultramafic complex a fragment of a meso proterozoic ophiolite grenville province canada abstract the queensborough mafic ultramafic complex occurs as a fault bounded block up to 10 km wide and having an area 220 km2 it lies in the grimsthorpe domain of the bancroft elzevir mazinaw sharbot lake terrane in the central metasedimentary belt of the grenville province it has been suggested without adequate supporting data that the complex may represent oceanic crust a fragment of an ophiolite or even a metavolcanic sequence made up of basaltic and komatiitic flows the geological and tectonic significance of the complex is assessed using field relationships petrography and geochemistry structurally the lowest part of the complex comprises a series of ultramafic rocks characterized by metre scale compositional layering represented by several different metamorphic assemblages of talc chlorite carbonate anthophyllite and actinolite tremolite these assemblages indicate that the original rocks were cumulate peridotites and pyroxenites the ultramafic rocks are overlain structurally by a series of mafic rocks predominantly massive to highly sheared gabbros the gabbros are penetrated by a series of mafic dykes and include a few small enclaves of pillowed mafic volcanics major and trace element chemistry shows that the mafic rocks represent a fractionally crystallized sequence of tholeiitic gabbros lavas and mafic dykes and that the ultramafic cumulates are co genetic the regional geological setting and the trace element signatures of the mafic rocks suggest that they were formed in a back arc basin comparison of the queensborough complex with proterozoic and phanerozoic igneous complexes suggests that it represents a partially preserved crustal section of a mesoproterozoic ophiolite in addition the rocks of the queensborough complex are petrographically and geochemically similar to those of the vavilov basin which occurs in the deepest part of the tyrrhenian sea by analogy with this neogene back arc basin we suggest that the central metasedimentary belt which contains the queensborough complex formed by attenuation of the continental crust the complex is preserved along a suture and is interpreted as having formed during the collision of a continental island arc with the continental margin of laurentia the characteristics and preservation of the queensborough mafic ultramafic complex are very similar to those of many phanerozoic ophiolites and suggest that mesoproterozoic thermotectonic processes are also similar to those presently operating

mapping singularities with stream sediment geochemical data for prediction of undiscovered mineral deposits in gejiu yunnan province china abstract this paper proposes the concept of singularity for characterizing hydrothermal mineralization processes a singular physical process may result in anomalous amounts of energy release or material accumulation within a narrow spatial temporal interval mineralization can be considered as a type of singular process due to large amounts of material accumulation and element enrichment a spatial singularity mapping technique is developed based on the local singularity involved in the context of multifractal theory it assembles geochemical map at different scales and calculates an index indicating the scaling characteristics of enrichment and depletion of geochemical concentration at multiple scales this index was used for quantifying spatial singularity of mineralization associated geochemical anomalies a case study for the gejiu tin polymetallic mineral district yunnan province china demonstrates that the concepts of singularity and the singularity mapping technique are applicable and useful for delineating anomalies caused by mineralization and for predicting the locations of undiscovered mineral deposits

geochemistry of two metavolcanic arc suites from the central metasedimentary belt of the grenville province southeastern ontario canada samples of two subalkaline metavolcanic suites the tudor formation ca 1 28 ga and the overlying kashwakamak formation have been analysed for major elements and 27 trace elements including rare earth elements the tudor formation is tholeiitic and contains mainly basaltic flows whereas the kashwakamak formation is calc alkaline and contains mainly andesitic rocks with minor felsic rocks the succession has been regionally metamorphosed to upper greenschist lower amphibolite facies trace element abundances and ratios indicate that rocks of the tudor and kashwakamak formations are island arc type geochemical modelling using rare earth elements zr ti and y indicates that the tudor volcanic rocks are not derived from a single parental magma through simple fractional crystallization equilibrium partial melting of a heterogeneous proterozoic upper mantle can explain the trace element abundances and ratios of tudor formation volcanic rocks the intermediate to felsic rocks of the kashwakamak formation appear to have been derived from a separate partial melting event the data are consistent with an origin of the arc either on oceanic crust or on thinned continental crust and with accretion of the arc to a continental margin between the time of extrusion of tudor volcanic rocks and that of kashwakamak volcanic rocks

three dimensional mineral prospectivity modeling for targeting of concealed mineralization within the zhonggu iron orefield ningwu basin china abstract the zhonggu iron orefield is one of the most important iron orefields in china and is located in the south of the ningwu volcanic basin within the middle and lower yangtze metallogenic belt of eastern china here we present the results of new 3d prospectivity modeling that enabled the delineation of areas prospective for exploration of concealed and deep seated baixiangshan type mineralization and yangzhuang type mineralization within the zhonggu orefield both of these deposits are kiruna type fe apatite deposits but are hosted by different formations within the ningwu basin the modeling approach used during this study involves 3 steps 1 combining available geological and geophysical data to construct 3d geological models 2 generation of 3d predictive maps from these 3d geological models using 3d spatial analysis and 3d geophysical methods 3 combining all of the 3d predictive maps using logistic regression to create a prospectivity map this approach integrates a large amount of available geoscientific data using 3d methods including 3d geological modeling 3d 2d geophysical methods and 3d spatial analysis and data integration methods the resulting prospectivity model clearly identifies highly prospective areas that not only include areas of known mineralization but also a number of favorable targets for future mineral exploration the 3d prospectivity modeling approach showcased within this study provides an efficient way to identify camp scale concealed and deep seated exploration targets and can easily be adapted for regional and deposit scale targeting

evolution of the archean abitibi greenstone belt and adjacent terranes new insights from geochronology geochemistry structure and facies analysis

geochemistry and geochronology of the metamorphic sole underlying the xigaze ophiolite yarlung zangbo suture zone south tibet abstract strongly foliated amphibolite clasts are found embedded within the ophiolitic melange underlying the xigaze ophiolite near bainang and angren yarlung zangbo suture zone southern tibet these high grade amphibolites are interpreted as remnants of a dismembered subophiolitic metamorphic sole that would have formed during the inception of a subduction they include garnet clinopyroxene amphibolites clinopyroxene amphibolites and common amphibolites petrographic descriptions mineral chemistry and thermobarometry of these rocks can be found in a companion paper guilmette c hebert r dupuis c wang c s li z j 2008 metamorphic history and geodynamic significance of high grade metabasites from the ophiolitic melange beneath the yarlung zangbo ophiolites xigaze area tibet journal of asian earth sciences 32 423 437 the geochemistry of the amphibolites confirms that their protoliths were igneous mafic rocks of basaltic to pyroxenitic composition that were likely part of an upper oceanic crust rare earth elements contents are suggestive of an n morb origin however enriched liles and depleted nb ta ti when compared to n morbs rather suggest a suprasubduction zone influence a large proportion of the overlying ophiolitic mafic rocks share the same geochemical characteristics suggesting the protoliths of the amphibolites might have crystallized in the same environment as the xigaze ophiolitic crust likely in a back arc basin 40 ar 39 ar step heating dating of hornblende concentrates from three samples yielded ages of 123 6 2 9 ma 127 7 2 2 ma and 127 4 2 3 ma these cooling ages are slightly younger or overlapping magmatic and sedimentary ages obtained from the overlying ophiolite all these new data support a model in which the ophiolitic crust and the protolith of the amphibolites were formed along the same spreading center above a subduction zone the demise of the early subduction circa 130 ma forced the inception of a new subduction zone at the ssz spreading axis burying ssz mafic rocks underneath a ssz ophiolitic mantle

adakitic rocks in the masara gold silver mine compostela valley mindanao philippines different places varying mechanisms abstract the presence of adakites has been used as an indicator for the occurrence of gold mineralization in many mineral prospecting works traditionally the unique geodynamic controls to adakite formation particularly the high temperature gradient and other slab melting requirements have been taken as key elements that must be present during their formation however several studies have suggested alternative mechanisms this paper presents fractional crystallization as the most viable mechanism for the generation of adakitic rocks in the masara gold silver mine in eastern mindanao philippines furthermore this paper also argues that the occurrence of adakitic rocks does not necessarily indicate the presence of mineralization depending on the scale their occurrence may be an exploration marker at a regional or district level but at the mine level other more localized parameters will have to be considered

archean metavolcanics from the rouyn noranda district abitibi greenstone belt quebec 2 mobility of trace elements and petrogenetic constraints qualitative evaluation of altered mafic pillows from the rouyn noranda district of the abitibi metavolcanic belt reveals that for low grade metamorphism the high field strength elements hfs zr y ti and the rare earth elements ree are immobile however where alteration is extreme the ree elements are leached and redeposited by carbonate rich and k rich metasomatic fluids whilst zr y and zr ti remain unchanged rubidium ba and to a lesser extent sr are mobile at all levels of alteration however provided certain filters are applied the original geochemical values of the lavas for the alkaline elements the hfs elements and the ree can be defined the geochemical variations thus identified for the volcanic series of the rouyn noranda district are ascribed to a combination of contamination and fractional crystallization of a primitive tholeiitic magma

alteration and lithogeochemistry in the masara gold district eastern mindanao philippines as tools for exploration targeting abstract the intermediate to low sulfidation epithermal gold deposit in masara compostela valley eastern mindanao philippines is associated with a diorite porphyry from the late miocene lamingag intrusive complex detailed mineralogical investigation of the host rocks in the deposit reveals five major alteration zones and at least two mineralizing events a potassic alteration zone characterized by stockwork magnetite veins secondary biotite and magnetite and an early stage chlorite sericite alteration composed of quartz chlorite illite sericite pyrite biotite magnetite calcite assemblages are interpreted to be linked with an earlier porphyry copper system in the area these were overprinted by late stage chlorite sericite alteration consisting of quartz chlorite illite sericite pyrite adularia magnetite epidote and sericite assemblages which generally contain quartz illite sericite pyrite these alteration overprints are inferred to be related to a younger low to intermediate sulfidation epithermal gold mineralization which involved near neutral fluids advanced argillic alteration comprising quartz kaolinite magnetite dickite illite calcite was also observed in the area isocon analysis shows that alteration zones associated with epithermal mineralization are generally characterized by enrichment in sio 2 and k 2 o and depletion of cao and na 2 o as well as additions of au cu zn and pb pearce element ratio per analysis indicates high degrees of sericitization in the altered diorite porphyry tuff and quartz diorite units at least three major alteration centers are defined based on the spatial distribution of the alteration index of surface samples calculated from the per analysis the results of this study support the use of whole rock geochemistry as a complement to traditional techniques in exploration geochemistry

pore scale morphology and wettability characteristics of xenon hydrate in sand matrix laboratory visualization with micro ct abstract the properties of gas hydrate bearing sediments ghbs depend on their changing morphology and wettability characteristics which are in turn important for efficiency and safety issues during production we present the results of xenon hydrate formation experiments using quartz sand packs at different salinities direct 3d visualization of hydrate distribution in the pore space was obtained with the help of high resolution micro computed tomography ct four phases xenon hydrate xenon gas brine and quartz sands were segmented and labelled in the raw micro ct scanned images a 3d reconstruction reveals typical pore scale patterns of hydrate occurrence pore filling grain coating and shows that hydrate preferentially aggregates at the gas water interface reflecting greater local access to xenon gas molecules the hydrate cluster shape factor ranges from 2 to 10 indicating that xenon hydrate forms with a complex and irregular microstructure consistent with random growth nature of hydrate the hydrate saturation is found to decrease with salinity under excess gas condition which we interpret in terms of the hydrate formation kinetics to indicate that gas hydrate prefers to grow into the gas phase at the gas water interface a total of 270 local contact angles of water at the gas and hydrate interfaces in pores were measured with a micro ct image analysis method to obtain information on the wettability variation of hydrate surfaces the average was calculated to be 47 6 indicating that xenon hydrate surface is hydrophilic our analysis of the xenon hydrate morphology provides a new method for revealing hydrate growth behavior at pore scale the wettability characterization offers key parameters for accurate numerical simulation of multiphase flow prediction and seepage behavior in ghbs

geology and timing of mineralization at the cangshang gold deposit north western jiaodong peninsula china the cangshang gold deposit of the north western jiaodong peninsula contains reserves of greater than 50 tonnes t and is developed by the largest open pit gold mine in china this deposit is a jiaojia style i e disseminated and veinlet deposit it is controlled by the san cang fault zone which trends 040 and dips 40 75 se at the mine site the main no 1 orebody lies between a hanging wall of precambrian metamorphic rocks mainly amphibolite of the fenzishan group and a footwall composed of the mesozoic linglong granitoid the ore zone is mainly composed of pyritized sericitized and silicified granitoid which has undergone variable degrees of cataclasis shrimp u pb dating of zircon indicates that the protolith of the hanging wall amphibolite was formed at 2530 17 ma and underwent metamorphism at 1852 37 ma the footwall granodiorite has been dated at 166 4 ma whereas zircons from the ore zone yield a younger age of 154 5 ma cathodoluminescence images of zircons from the granodiorite and ore zone show oscillatory zonation indicative of an igneous origin for both and the ages of these zircons therefore are all interpreted to be representative of magmatic crystallization dating of sericite by 40ar 39ar has been used to directly determine the timing of formation of the cangshang deposit providing the first time absolute age on formation of the jiaojia style gold deposits the well defined age of 121 3 0 2 ma provides the precise timing of gold mineralization at the cangshang deposit this age is consistent with those of linglong style vein type gold mineralization also from the north western jiaodong peninsula at between 126 and 120 ma therefore our work indicates that both styles of gold deposits in the jiaodong peninsula were formed during the same mineralization event

ratio correlations and major element mobility in altered basalts and komatiites attempts have been made in the recent literature to constrain major element mobility in altered basalts and komatiites using the molecular proportion ratio mpr diagrams developed by t h pearce 1970 the method involves ratioing the molecular proportions of two oxides against a third oxide and presenting the results as an oxide oxide ratio plot the transformation appears to clean up scatter plots with low correlations and produces highly correlated ratio plots these plots have been taken to be indicative of igneous fractionation trends and thus of minimal bulk chemical change during alteration there are however inherent statistical problems in ratio correlation which have received much attention in the mathematical literature this paper explains the implications of enhanced correlations for work on altered rocks using ratio plots and suggests that extreme caution must be exercised in the interpretation of mpr diagrams

pore scale imaging and analysis of phase topologies and displacement mechanisms for co2 brine two phase flow in unconsolidated sand packs co2 storage in saline aquifers is considered a potential solution for co2 mitigation owing to its significant capacity and worldwide distribution capability it is therefore becoming more important to understand the underground co2 brine flow mechanisms co2 migration is primarily controlled by the pore scale subsurface flows in different saline aquifer sites with variable reservoir formation compositions and reservoir conditions variations occur in the state of co2 phase gas versus supercritical brine salinity and rock wettability under different reservoir conditions and may result in different subsurface co2 brine migration phenomena in this study we investigate the drainage and imbibition procedures of co2 and brine by injecting fluids into unconsolidated sand packs under different conditions of co2 phase states brine salinity and wettability of sand packs the pore scale fluid distribution is visualized using micro x ray computed tomography micro ct it is found that the phase states of co2 brine salinity and wettability have low impacts on co2 distribution during drainage however the increase in brine salinity significantly damages the connectedness of the water phase in pore structures and further decreases the co2 brine interfacial areas in addition a pore scale event called the droplet fragmentation of nonwetting phase is found to occur in the imbibition procedure which is considered to be beneficial to the dissolution trapping in co2 geological storages it is experimentally demonstrated that the pore structure of rock cores is a factor that significantly contributes to droplet fragmentation

comparative reos smnd and rbsr isotope and trace element systematics for archean komatiite flows from munro township abitibi belt ontario abstract a series of komatiite flows from munro township ontario have re and os concentrations that range from 0 545 to 1 27 ppb and 1 00 to 2 20 ppb respectively the187re 186os in the suite range from 14 05 to 52 37 and the187os 186os range from 1 49 to 3 22 giving a crystallization age of2726 93ma and an of initial187os 186os of0 873 0 035 this age is in good agreement with the crystallization ages that have been reported for these rocks using other isotopic systems the re os isochron indicates that the system was resistant to the low grade metamorphism that altered the rocks the initial os isotopic composition is consistent with the derivation of the melts from a mantle source s that originated with a chrondritic 187os 186os i and evolved with an approximately chondriticre os sm nd data for the same suite cluster about anend value at 2 72 ga of 2 to 3 rb sr isotope data indicate significant mobilization of these elements by the greenschist grade metamorphism that has altered the rocks comparisons of re and os concentrations with those of mgo feo ni cr and s suggests that re was incompatible d 1 os concentrations were likely controlled by the presence or precipitation of trace metallic or sulfide phases both during melting and crystallization and not by the modally predominant silicate minerals

tertiary and quaternary magmatism in mindanao andleyte philippines geochronology geochemistry and tectonic setting abstract a set of 230 igneous rock samples from leyte and mindanao philippines has beenstudied for their major and trace element chemistry mineralogy and geochronology 40k 40ar dating several volcanic sectors have been distinguished according to their geographic position tectonic framework and geologic history a in leyte the ophiolitic basement at 50 ma is morb type but characterized by negative nb 0 anomalies typical of back arc basalts miocene 20 and 11 ma and late pliocene to quaternary magmas 2 5 0 4 show typical island are talc alkaline characteristics in eastern mindanao eocene 47 46 ma magmatic rocks are arc tholeiitic while those of miocene 18 6 ma and early pliocene 4 5 ma age are generally talc alkaline dacites of 12 ma age have adakitic compositions the young 3 ma volcanics in surigao and north davao are mostly adakitic although talc alkaline basalts and basaltic andesites dated at 0 9 ma overlie adakites in surigao b in daguma oligocene 30 ma arc tholeiitic diorites intrude older arc sequences miocene0 17 0 7 7 ma dikes and flows in both daguma and sarangani peninsula are mostly talc alkaline andesites although minor adakites dated back to 18 ma have been found overlying undated breccias in daguma in southeast daguma the tale alkaline volcanic substratum of pliocene recent volcanoes is 8 6 ma old quaternary 1 83 ma to present andesitec and dacitic volcanics in mt parker and mt matutum southwest daguma are either talc alkaline or adakitic while mt blit northwest daguma is built up by 2 5 ma old hfse enriched basalts 1 ma old normal talc alkaline andesites and 0 8 ma old adakites c in central mindanao miocene andesites yield ages of 20 and 16 ma pliocene 2 5 ma 0 volcanism is dominated by talc alkaline and hfse enriched basalts and basaltic andesites quaternary lavas i ma to present range in character from tale alkaline to shoshonitic and exhibit wide variations in their trace element behavior d miocene lavas of 19 11 ma age in zamboanga are mostly talc alkaline though a lone 0 18 ma old adakite was also encountered pliocene quaternary basalts and basaltic andesites dated back to 2 2 1 ma are hfse enriched such that some display positive nb anomalies in spidergrams adakites of 3 8 0 7 ma age are located nearer the sulu trench the compositional variety of tertiary recent island arc magmatism in leyte and mindanao couldbe linked to the tectonic settings prevailing during each magmatic phase and is here utilized to refine paleokinematic reconstruction of the tectonic history of the philippine archipelago the identification of adakites at certain time periods is used to date timings of subduction initiations and arc polarity reversals major and abrupt changes in geochemical compositions are well exhibited by the pliocene pleistocene volcanism involving the collision related shift from talc alkaline to shoshonitic volcanism in central mindanao and adakite production in all the volcanic sectors defined the origin of the hfse enrichments among lavas younger than 3 ma could be attributed to the presence in their mantle source of an oib component or alternatively to the enrichment of this mantle source through percolation of slab derived melts

evidence for hfse and ree mobility during calc silicate metasomatism mesoarchean 3075ma ivisaartoq greenstone belt southern west greenland abstract the mesoarchean ca 3075 ma ivisaartoq greenstone belt consists dominantly of variably deformed and metamorphosed mafic to ultramafic flows basalts to picrites in addition there are minor serpentinites gabbros clinopyroxene rich cumulates and volcaniclastic and siliciclastic sedimentary rocks primary volcanic structures such as pillows and volcanic breccia are well preserved in low strained zones the belt underwent intense metasomatic hydrothermal alteration between 3075 and 2961 ma an early stage of calc silicate metasomatism stage i resulted in the formation of epidosites in pillow cores pillow interstitials and intrusive margins of gabbroic dykes this alteration appears to have resulted from sea floor hydrothermal alteration a second stage of calc silicate metasomatism stage ii formed centimeter to meter scale layers concordant to discordant relative to the regional foliation these layers consist of diopside garnet epidote plagioclase quartz titanite vesuvianite calcite actinolite scheelite the second stage calc silicate rocks are associated with shear zones and their origin is attributed to interaction of reactive fluids with mafic and ultramafic rocks during regional metamorphism both stages of calc silicate metasomatism caused significant mobilization of major elements si mg ca fe na k and mn lile rb cs sr ba pb and lree heavy rare earth elements hree and hfse th nb ta zr ti remained relatively immobile during stage i metasomatic alteration but were variably disturbed during the stage ii metasomatism accordingly the stage ii calc silicate rocks exhibit evidence for significant mobility of th nb and ta on a local scale 1 4 m whereas zr and ti were not significantly mobilized this resulted in calc silicates with complementary trace element patterns displaying extreme negative to positive nb anomalies nb nb 0 19 7 28 transition metals ni v co cr and sc were relatively immobile during both metasomatic events amphibolites spatially related to the second stage calc silicate rocks preserve mineralogical and major element characteristics consistent with a mafic to ultramafic composition however their near primary magmatic trace element compositions were variably modified due to strong ree mobility during the stage ii metasomatic event this gave rise to various ree characteristics including lree enriched lree depleted and u shape ree patterns some of these element patterns resemble those shown by modern boninites and mid ocean ridge basalts n morb in contrast the least altered amphibolites exhibit similar trace element patterns to those displayed by the least deformed non metasomatized mafic and ultramafic pillow flows they possess relatively flat trace element patterns with negative nb ta anomalies indicating a subduction zone geochemical signature

whole rock geochemical techniques for evaluating hydrothermal alteration mass changes and compositional gradients associated with epithermal au ag mineralization volcanic rocks hosting quartz calcite adularia illite epithermal deposits undergo elemental mass changes associated with k metasomatism k h metasomatism and h metasomatism that are developed progressively upward and outward from the site of mineralization as hydrothermal fluid ascends boils and cools resultant hydrothermal mineral zonation shows increasingly k rich mineral assemblages with proximity to deposits thus patterns of k enrichment provide a vector toward those deposits we describe whole rock geochemical techniques for identifying these patterns and for evaluating attendant hydrothermal mineral zonation whole rock geochemical anomalies are evaluated by calculating mass changes associated with hydrothermal alteration using a modified version of gresens 1967 equation to compare the composition of altered rocks to fresh rock equivalents hydrothermally altered rocks most affected by k metasomatism will be characterized by the largest k gains and generally na and ca losses mass changes associated with k metasomatism are also evaluated graphically using plots of molar 2ca na k al versus molar k al since molar values are used to construct the plot compositions of altered rocks can be compared to the compositions of primary and secondary k na ca and al bearing minerals that are located in the same compositional space allowing identification of important hydrothermal minerals e g adularia illite smectite and alteration processes that are reflected in trends from fresh rock compositions toward the compositions of hydrothermal minerals the intensity of k metasomatism encompassing both k gains and na and ca losses can be represented by the slope of the line between an altered rock composition and the origin i e the molar k 2ca na k value determinations of mass changes in altered rocks surrounding selected epithermal deposits demonstrate the predominance of k metasomatism proximal to and commonly increasing in intensity toward mineralized veins comparisons of k mass changes to trace element concentrations indicate that the area affected by k metasomatism is more extensive 100s to 1 000s of meters than that containing anomalous concentrations of precious metals base metals and pathfinder elements 10s to 100s of meters therefore whole rock geochemical techniques potentially extend the area over which geochemical targeting may be effective data from this study show that intensity of k metasomatism molar k 2ca na k values and concentrations of precious metals and pathfinder elements increase toward ore and are greatest proximal to ore so that pathfinder element and whole rock geochemical anomalies are complementary

time dependent pore filling this research was funded by the kaust endowment j jang was supported in part by the u s geological survey s gas hydrates projects g abelskamp edited the manuscript data sets presented in this study are available from the kaust repository http hdl handle net 10754 627427

exploration tools for linked porphyry and epithermal deposits example from the mankayan intrusion centered cu au district luzon philippines the mankayan mineral district of northern luzon philippines hosts several significant ore deposits and prospects of various types within an area of similar to 25 km 2 including the far southeast porphyry cu au deposit the lepanto high sulfidation epithermal cu au deposit the victoria intermediate sulfidation epithermal au ag vein deposit the teresa epithermal au ag vein deposit the guinaoang porphyry cu au deposit and the buaki old palidan porphyry cu au prospects all having formed in a period of about 2 m y from similar to 3 ma the geologic units include 1 a basement composed of late cretaceous to middle miocene metavolcanic rocks volcaniclastic rocks 2 the miocene 12 to 13 ma tonalitic bagon intrusive complex 3 the pliocene similar to 2 2 to 1 8 ma imbanguila dacite porphyry and pyroclastic rocks and 4 postmineralization cover rocks including die similar to 1 2 to 1 0 ma bato dacite porphyry and pyroclastic rocks and the similar to 0 02 ma lapangan tuff extensive advanced argillic alteration crops out for similar to 7 kin along the inconformity between the basement rocks and the imbanguila dacite formation consists of quartz alunite pyrophyllite or diaspore with local zones of silicic alteration and a halo of dickite kaolinite the alteration and its subhorizontal geometry indicate that it is a lithocap or coalesced lithocaps the northwest striking portion is similar to 4 km long and hosts the lepanto enargite au ore deposit also controlled by the lepanto fault the lepanto epithermal deposit is related to the underlying far southeast porphyry the quartz alunite alteration halo of lepanto is contemporaneous with the similar to 1 4 ma potassic alteration of the porphyry there are also silicic advanced argillic alteration patches similar to 600 m above the far southeast orebody at the present surface these are interpreted to be perched alteration there is no systematic mineralogical or textural zoning in the lepanto lithocap that indicates direction to the intrusive source most surface samples of the lithocap contain less than 50 ppb au despite many being less than a few hundred meters from underground cu au ore this study found that several characteristics of the lepanto lithocap change systematically with distance from the causative intrusion the alunite absorption peak at similar to 1 480 nm in the short wavelength infrared swir spectrum shifts to higher wavelengths where the sample is closer to the intrusive center due to higher na and lower k content in the alunite published experimental studies indicate that high na na k is related to higher formation temperature high ca alunite including huangite also occurs at locations proximal to the intrusive center alunite mineral composition analyzed by laser ablation inductively coupled plasma mass spectrometry la icp ms indicates that the pb content decreases toward the intrusive center whereas sr la sr ph and la pb increase markedly whole rock compositions using only nonmineralized taken as cu similar to 350 m above the upper extent of the veins an airborne geophysics survey indicates that the far southeast orebody is associated with a wide zone of demagnetization due to extensive magnetite destructive phyllic alteration such low magnetic anomalies on the margin of a large lithocap elsewhere may deserve attention the directional indicators and mineralization signatures found in this study have the potential to indicate direction to the intrusive center during exploration of similar porphyry epithermal districts

verifying pore network models of imbibition in rocks using time resolved synchrotron imaging at the pore scale slow invasion of a wetting fluid in porous materials is often modelled with quasi static approximations which only consider capillary forces in the form of simple pore filling rules the appropriateness of this approximation often applied in pore network models is contested in literature reflecting the difficulty of predicting imbibition relative permeability with these models however validation by sole comparison to continuum scale experiments is prone to induce model overfitting it has therefore remained unclear whether difficulties generalizing the model performance are due to network extraction the pore filling rules or whether a quasi static description is useful at all here we address this by examining whether such a model can predict the pore scale fluid distributions underlying the behaviour at the continuum scale to this end we compare the fluid arrangement evolution measured in fast synchrotron micro ct experiments on two rock types to quasi static simulations which implement capillary dominated pore filling and snap off including a sophisticated model for cooperative pore filling the results indicate that pore network models with appropriate pore filling rules can in principle obtain a good first order prediction of the upscaled flow properties of strongly wetted rocks at low capillary numbers

the geochemical nature of the igneous rocks of the sharbot lake domain central metasedimentary belt ontario two bimodal mafic silicic suites of igneous rocks the sharbot lake volcanic rocks and the lavant igneous complex are identified geochemically in the sharbot lake domain of the central metasedimentary belt in ontario and their genesis and thermotectonic environment are evaluated the sharbot lake volcanic rocks comprise a series of basalts characterized by light rare earth element lree depletion and relatively high concentrations of fe2o3 tio2 mno v and y together with rhyolites and silicic pyroclastic rocks they are intruded by rocks of the lavant igneous complex which comprises tholeiitic gabbros characterized by lree enrichment and low concentrations of fe2o3 tio2 mno v and y and granitoid rocks the trace element signatures of the mafic rocks of the sharbot lake volcanic sequences are most like those of back arc tholeiitic basalts and those of the lavant igneous complex are comparable to those of low k tholeiitic basalt suites the trace element signatures of the silicic rocks ass

archean mafic metavolcanics from the rouyn noranda district abitibi greenstone belt quebec 1 mobility of the major elements reply in a suite of archean mafic pillows from the rouyn noranda region of quebec s abitibi greenstone belt including both tholeiitic and calc alkaline varieties spanning the prehnite pumpellyite to upper greenschist metamorphic facies three types of alteration can be defined i chlorite epidote actinolite ii chlorite epidote and iii chlorite sericite the number of mineral phases decreases as a result of progressive hydration from type i to type iii alteration albitization resulting from substitution of in calcic plagioclase is highly variable in type i alteration but in types ii and iii the plagioclase is totally albitized and in some cases silicified chloritization is closely linked to increasing hydration and ca leaching with mgo and feo substituting for cao in ferromagnesian minerals calcium was mobilized and carried by solutions as evidenced by the variable concentration of epidote at the margins of pillows this calcium leaching generated an excess of al2o3 with respect to the combine

predictive modelling of rainfall induced landslide hazard in the lesser himalaya of nepal based on weights of evidence abstract landslide hazard mapping is a fundamental tool for disaster management activities in mountainous terrains the main purpose of this study is to evaluate the predictive power of weights of evidence modelling in landslide hazard assessment in the lesser himalaya of nepal the modelling was performed within a geographical information system gis to derive a landslide hazard map of the south western marginal hills of the kathmandu valley thematic maps representing various factors e g slope aspect relief flow accumulation distance to drainage soil depth engineering soil type landuse geology distance to road and extreme one day rainfall that are related to landslide activity were generated using field data and gis techniques at a scale of 1 10 000 landslide events of the 1970s 1980s and 1990s were used to assess the bayesian probability of landslides in each cell unit with respect to the causative factors to assess the accuracy of the resulting landslide hazard map it was correlated with a map of landslides triggered by the 2002 extreme rainfall events the accuracy of the map was evaluated by various techniques including the area under the curve success rate and prediction rate the resulting landslide hazard value calculated from the old landslide data showed a prediction accuracy of 80 the analysis suggests that geomorphological and human related factors play significant roles in determining the probability value while geological factors play only minor roles finally after the rectification of the landslide hazard values of the new landslides using those of the old landslides a landslide hazard map with 88 prediction accuracy was prepared the methodology appears to have extensive applicability to the lesser himalaya of nepal with the limitation that the model s performance is contingent on the availability of data from past landslides

footprints of spontaneous fluid redistribution on capillary pressure in porous rock pore scale imaging of two phase flow in porous media shows that pore filling occurs as cooperative events with accompanying spontaneous fluid redistribution in other parts of the pore space we present a level set method that controls saturation quasi statically to model experiments controlled by low constant flow rates and demonstrate that our method can describe the observed displacement mechanisms the level set approach determines states of capillary equilibrium which generally are different for displacement protocols constrained by saturation and pressure saturation controlled simulations of drainage in sandstone show spontaneous fluid redistributions with abrupt pressure jumps and cooperative behavior including snap off and interface retraction events consistent with experimental observations drainage capillary pressure curves are lower when saturation rather than pressure controls displacement remarkably these effects are less significant for imbibition processes where the development of hydraulically connected wetting phase moderates the cooperative behavior and associated pressure jumps

mineralization parameters and exploration targeting for gold copper deposits in the baguio luzon and pacific cordillera mindanao mineral districts philippines a review abstract the baguio mineral district in luzon philippines is known to host several world class epithermal gold porphyry copper deposits the interplay of tectonic setting magma composition structural control and hydrothermal systems contributed to the generation of these deposits ridge subduction scarborough seamount resulting to flat subduction and a transpressional regime could also be related to the formation of epithermal gold porphyry copper deposits in baguio subduction processes leading to the formation of calc alkaline rocks associated with high water pressure oxygen fugacity and late sulfur saturation are almost always associated with the gold copper deposits in the district compared to the baguio mineral district less exploration work mine development and production were done in the pacific cordillera mineral district mindanao in southern philippines it is worth noting however that both mineral districts show similarities and overlapping features in terms of geological geophysical and geochemical characteristics this leads one to conclude that the pacific cordillera mineral district has ore deposits waiting to be discovered

regional scale hydrothermal alteration in the central blake river group western abitibi subprovince canada implications for vms prospectivity the late archean blake river group is a thick succession of predominantly mafic volcanic rocks within the southern zone of the abitibi greenstone belt it contains a number of silicic volcanic centers of different size including the large noranda volcanic complex which is host to 17 past producing volcanogenic massive sulfide deposits the noranda complex consists of a 7 to 9 km thick succession of bimodal mafic and felsic volcanic rocks erupted during five major cycles of volcanism massive sulfide formation coincided with a period of intense magmatic activity cycle iii and the formation of the noranda cauldron hydrothermal alteration in these rocks is interpreted to reflect large scale hydrothermal fluid flow associated with rapid crustal extension and rifting of the volcanic complex the alteration includes abundant albite chlorite epidote and quartz silicification which exhibit broad stratigraphic and structural control and correlate with previously mapped whole rock oxygen isotope zonation the mine sequence volcanic rocks are characterized by abundant iron rich chlorite fe fe mg 0 5 hydrothermal amphibole ferroactinolite and coarse grained epidote of clinozoisite composition 10 wt fe2o3 lacking the clinozoisite solid solution alteration in the mine sequence volcanic rocks persists along strike well beyond the limits of the main ore deposits as far as several tens of kilometers and can be readily distinguished from greenschist facies metamorphic assemblages at a regional scale the lack of similar alteration in the pre cauldron sequences is consistent with limited 18o depletion and suggests that the early history of the volcanic complex did not support large scale high temperature fluid flow in these rocks comparisons with a much smaller barren volcanic complex in nearby ben nevis township reveal important differences in the alteration mineralogy between volcanoes of different size with implications for area selection during regional scale mineral exploration the ben nevis complex consists of a 3 to 4 km thick succession of mafic intermediate and felsic volcanic rocks centered on a small subvolcanic intrusion alteration of the volcanic rocks comprises mainly low temperature assemblages of prehnite pumpellyite magnesium rich chlorite fe fe mg 10 wt fe2o3 and calcite actinolite magnetite alteration occurs proximal to the intrusive core of the complex but the limited extent of this alteration indicates only local high temperature fluid circulation adjacent to the intrusion a distal zone of carbonate alteration is located 4 6 km from the center of the volcano although iron bearing carbonates are present locally within this zone the absence of siderite argues against a high temperature origin for this alteration these observations do not offer positive encouragement for the existence of a fossil geothermal system of sufficient size or intensity to have produced a large massive sulfide deposit

geochemistry and tectonic significance of the ongarbira metavolcanic rocks singhbhum district india abstract the volcanic sedimentary sequence of ongarbira occurs to the south of the singhbhum shear zone and rests uncomformably on a basement topographic low between the chakradharpur granite and the singhbhum granite structural analysis reveals that the ongarbira synform and other adjoining structures are kilometre scale first generation folds on e w striking axial planes these structures are in marked contrast with the corresponding kilometre scale first generation folds typical of the iron ore group synclinorium towards the south of the ongarbira belt the ongarbira metavolcanic rocks exhibit a limited range of tholeitic basalt compositions the basalts are grouped according to their mg and the details of their ree patterns groups i and ii are relatively unevolved and very similar to lree and lil depleted ocean ridge tholeiites the most evolved group iii with lree enrichment is most similar to lil enriched ocean floor basalts but may be contaminated with crustal materials in general the ongarbira volcanics evolve upward stratigraphically petrogenetic major element modelling of the ongarbira basalts suggests that the primary melt was generated by batch melting 30 of lherzolite at pressures of at least 1 5 gpa sequential fractionation of ol o1 cpx pl and cpx pl followed comparison of incompatible and compatible element distributions indicates a very similar batch m melting fractional crystallization sequence for ongarbira groups i and ii basalts group iii basalts may have been derived from a batch melt initially more enriched in incompatible elements trace element discrimination of the ongarbira basalts suggests that they were generated in an extensional environment primordial mantle normalized element distributions indicate that the basalts are similar to continental rift basalts but with oceanic affinities the chemical data along with the associated sediments indicate that the ongarbira basalts were probably emplaced in a mature continental rift although a back arc origin cannot be completely disregarded it is concluded that the ongarbira volcanics were emplaced as part of the same rifting event that resulted in outpourings of the proterozoic dalma and dhanjori volcanics implying that the ongarbira suite is proterozoic and not part of the archaean iron ore group the structural geometry of the ongarbira rocks is more conformable to that of the singhbhum mobile belt than to the iron ore group synclinorium in the singhbhum craton it is likely that the southern limit of the singhbhum mobile belt is defined by the interface of its e w structures with the nne structures of the iron ore group rocks thus the singhbhum shear zone does not mark the interface between the archaean singhbhum craton and the proterozoic singhbhum mobile belt in the eastern indian shield

exploration applications of copper isotopes in the supergene environment a case study of the bayugo porphyry copper gold deposit southern philippines copper isotope compositions of secondary phases from the supergene profile of the bayugo porphyry copper gold deposit philippines show significant isotopic fractionation relative to hypogene sulfide phases and reveal systematic patterns of isotopic enrichment in the leached cap iron oxides and supergene copper sulfides thirty nine iron oxide copper oxide and copper sulfide minerals yielded 65 cu values between 3 4 and 6 9 per mil samples of hypogene sulfides have a narrow range of values near zero per mil 0 6 to 1 0 in contrast samples of supergene sulfides chalcocite and djurleite collected from the exotic and enriched copper zones define a trend of decreasing 65 cu from the enriched source area and proximal exotic zone 3 downgradient to the distal portions these findings are significant because within exotic copper zones the copper isotope values of supergene sulfides can provide an indication both of proximity and direction to the source area the technique could be applied in the search for unrecognized porphyry centers upgradient from headless exotic copper occurrences by exploring for the supergene copper phases with the highest 65 cu values independently copper isotope ratios of iron oxides in surface samples or fossil leached caps might be used to rank prospects and to focus drilling in areas with the greatest potential for mature enrichment profiles by mapping the distribution of isotopically enriched leached cap iron oxides the leached cap screening and targeting tool could enhance the iron oxide mapping techniques traditionally applied in leached cap interpretation and exploration

enhanced permeability due to apparent oil brine slippage in limestone and its dependence on wettability acknowledgments this material includes work supported by a society of petrophysicists and well log analysts foundation grant and an aberdeen formation evaluation society scholarship m c was supported by a university of aberdeen college of physical sciences studentship the authors gratefully acknowledge amer syed for his assistance with the assembly and maintenance of the coreflood rigs jim anderson for helpful discussions and the two anonymous reviewers for their comments and suggestions all data used in this study will be made available from the corresponding author upon request

spatially quantitative characterization of geological processes associated with polymetallic sn w mineralization in the malipo mineral district southeastern yunnan china abstract the current geographic information system gis based mineral prospecting models focus on delineating high probability locations for mineral deposits these models do not attempt to characterize the geological evolution of the area under study either spatially or quantitatively the study described in this paper demonstrates an innovative approach that quantitatively describes the mineralization processes in a spatial way this improves predictions by adding information concerning the areas geologic evolution this study quantitatively characterizes the mineralization in the malipo mineral district china in relation to tectono magmatic activity from caledonian to yanshanian time these findings extend the existing geological knowledge of the study area a critical step for further investigating and interpreting the geochemical signatures the malipo mineral district is a well studied area and thus appropriate for evaluating a new modeling technique our preliminary results show that the quantitative spatial characterizations retrieved from our model offer highly correlated predictive information regarding geologic evolution when compared with the information obtained from traditional ground truthing investigations therefore employing our model in a new and under studied area would potentially provide significant benefits and advance the level of knowledge in the new area

low potassium hydrothermal alteration in low sulfidation epithermal systems as detected by irs and xrd an example from the co o mine eastern mindanao philippines abstract detailed hydrothermal alteration investigations including petrography infrared reflectance spectroscopy irs and xrd of the low sulfidation epithermal co o mine located in eastern mindanao philippines revealed that both distal and intermediate hydrothermal alteration zones contain dominantly illite and chlorite whereas the proximal alteration zone comprises mainly illite chalcopyrite and pyrite the gold bearing veins and the proximal hydrothermal alteration zone display a distinct absence of k rich hydrothermal alteration minerals such as k feldspar adularia gold mineralization in the co o mine is controlled by an extensive quartz breccia vein system which is characterized by three distinct stages of vein incl breccias formation gold is mainly observed in stages 2 and 3 veins stage 1 veins appear as fragments in stage 2 veins and display boiling textures such as quartz pseudomophs after bladed calcite these veins further display colloform to crustiform banding and contain pyrite chalcopyrite and minor gold located in the colloform bands and between bladed quartz pseudomorphs stage 2 veins comprise mostly banded to massive quartz and contains sulfides parallel to bands or disseminated these veins are fine grained with mosaic jigsaw quartz and contain calcite blebs and or fragments of stage 1 veins gold is in textural equilibrium with chalcopyrite sphalerite and locally pyrite stage 3 veins consist of quartz and carbonate locally mn rich and display irregular banded and comb textures in auriferous veins of this stage gold is in textural equilibrium with chalcopyrite and pyrite with local abundance of sphalerite other sulfide minerals observed with gold in stages 2 and 3 are galena acanthite and locally jalpaite the xrd and irs provide inconsistent results regarding the abundance of k rich clays e g illite associated with auriferous veins illite with possibly interlayered swelling clays such as al smectite was identified in auriferous vein stages 2 and 3 using irs but could not be confirmed by xrd comparative analysis of the results of these techniques with respect to the ordering of micaceous minerals suggest less ordered white mica proximal to the veins vein textures such as banded quartz the absence of k feldspar and the abundance of illite interlayered al smectite suggest relatively low temperatures of formation of the hydrothermal alteration system and point to a potential boiling horizon located deeper or marginal to the currently exploited levels of the co o mine the absence of k feldspar may also be related to relatively low temperatures of the hydrothermal fluid the medium potassium rich magma series of the host rocks and or a relatively low oxidation state of the hydrothermal fluid

accreted terranes in the northern part of the philippine archipelago the philippine archipelago consists of a complex array of ophiolites continental fragments and island arc elements that can be identified as accreted terranes similar to those increasingly recognized as components of orogenic zones the northern philippines including luzon mindoro and nearby smaller islands can be divided into at least six of these tectonic elements from west to east across central luzon there are the neogene accretionary prism of the west luzon arc the eocene zambales ophiolite the cretaceous angat ophiolite and a late cretaceous early paleogene volcanic arc built on an older metamorphic basement this arc terrane is repeated by offset along the philippine fault to the south the western luzon terranes are juxtaposed against the metamorphic basement block of mindoro which itself is colliding with the north palawan microcontinental fragment the ophiolites appear to have originated in back arc basins rather than in oceanic plateaus and the metamorphic belts have protoliths indicating deformation along active margins perhaps deep within accretionary prisms the philippine terranes are interpreted as fragments that originated within the complex pacific eurasian plate boundary rather than as intra pacific basin units these terranes have been assembling at least since the oligocene by strike slip and convergent displacements strike slip displacement either along transcurrent faults or as a component of convergence played a very important if not dominant role in this assembly most terranes identified in the northern philippine appear to be plate fragments with attached crust and upper mantle their characteristics contrast with those usually interpreted for terranes in the north american cordillera where near orthogonal convergence and shallow dipping terrane sutures are favored

imaging of oil layers curvature and contact angle in a mixed wet and a water wet carbonate rock we have investigated the effect of wettability of carbonate rocks on the morphologies of remaining oil after sequential oil and brine injection in a capillary dominated flow regime at elevated pressure the wettability of ketton limestone was altered in situ using an oil phase doped with fatty acid which produced mixed wet conditions the contact angle where oil contacted the solid surface measured directly from the images 180 while brine filled regions remained water wet whereas the untreated rock without doped oil was weakly water wet 47 9 using x ray micro tomography we show that the brine displaces oil in larger pores during brine injection in the mixed wet system leaving oil layers in the pore corners or sandwiched between two brine interfaces these oil layers with an average thickness of 47 17 m may provide a conductive flow path for slow oil drainage in contrast the oil fragments into isolated oil clusters ganglia during brine injection under water wet conditions although the remaining oil saturation in a water wet system is about a factor of two larger than that obtained in the mixed wet rock the measured brine oil interfacial area of the disconnected ganglia is a factor of three smaller than that of oil layers

effective use and interpretation of lithogeochemical data in regional mineral exploration programs application of geographic information systems gis technology abstract a geographic information system gis in concert with statistical and geostatistical software has been used to compile manipulate analyze and visualize a large lithogeochemical dataset collected from the archean age swayze greenstone belt sgb located in northern ontario canada altered samples from this database have been identified using a variety of univariate and multivariate statistical and visualization techniques alteration maps are produced for each method and compared to known gold mineralization using the weights of evidence wofe technique major oxide data are interpolated using different sample groups all altered unaltered normalized samples and anomalous concentrations are separated from background using breakpoints on probability plots of the data as well as statistics generated from wofe analysis these maps are also evaluated using wofe analysis with respect to locations of known gold prospects the atypical normative mineral method is more sensitive for identifying alteration in felsic rocks felsic volcanic rocks granitoids whereas the volatile method is more sensitive for detecting alteration in mafic volcanic rocks and sedimentary rocks altered samples are characterized by higher sio2 k2o and mno concentrations and lower mgo and tio2 concentrations areas within the greenstone belt characterized by high concentrations of cao fe k2o and al2o3 were found to the best predictors of the known gold prospects anomalously high concentrations of these oxides reflect carbonatization fe carbonate alteration and potassic alteration trends and indicate that these alteration styles are spatially related to gold mineralization the wofe method is a useful technique with which to evaluate the geochemical maps produced in this paper the wofe technique is useful not only for comparing geochemical anomalies to the location of known gold prospects but also for providing a quantitative measure of association between anomalies and gold prospects furthermore the gold potential maps generated using wofe not only highlight or predict known areas of gold mineralization but also identify high potential areas where no known mineralization occurs a number of areas within the sgb have been identified as having high gold potential on many of the geochemical maps produced in this paper many of these areas coincide with areas of known gold mineralization however others are enigmatic and await follow up exploration

geochemistry and petrogenesis of early proterozoic amphibolites west central colorado u s a abstract early proterozoic supracrustal rocks exposed in west central colorado include amphibolites intimately associated with felsic volcanics and associated volcaniclastic sediments three successions are recognized the dubois succession 1770 1760 ma is comprised chiefly of amphibolites and felsic volcanics the amphibolites exhibit low concentrations of light ree and hfse and are broadly similar in composition to tholeiites from immature island arcs and in some respects to nmorb the cochetopa succession 1745 1730 ma includes large amounts of felsic volcanics and volcaniclastic sediments together with amphibolites that exhibit variable but slight incompatible element enrichment similar to basalts from evolved island arc systems and associated back arc basins the black canyon succession is coeval with the cochetopa succession and is comprised chiefly of volcaniclastic sediments with minor amphibolite these amphibolites exhibit significant incompatible element enrichment similar to basalts from continental margin arc systems geochemical modeling indicates that the amphibolites evolved by closed system fractional crystallization of depleted for the dubois succession to variably enriched parental basalts for the cochetopa and black canyon successions chiefly at shallow depths incompatible element distributions in the amphibolites indicate that mantle sources changed with time from relatively depleted 1770 1760 ma to variable but slightly enriched 1745 1730 ma a provisional model calls upon the dubois succession forming in an island arc system followed by collision with the archean wyoming province at 1750 ma the cochetopa succession was deposited in an intra arc basin developed within a new continental margin arc and the black canyon succession formed in a back arc basin associated with this arc