locating and quantifying geological uncertainty in three dimensional models analysis of the gippsland basin southeastern australia abstract geological three dimensional 3d models are constructed to reliably represent a given geological target the reliability of a model is heavily dependent on the input data and is sensitive to uncertainty this study examines the uncertainty introduced by geological orientation data by producing a suite of implicit 3d models generated from orientation measurements subjected to uncertainty simulations the resulting uncertainty associated with different regions of the geological model can be located quantified and visualised providing a useful method to assess model reliability the method is tested on a natural geological setting in the gippsland basin southeastern australia where modelled geological surfaces are assessed for uncertainty the concept of stratigraphic variability is introduced and analysis of the input data is performed using two uncertainty visualisation methods uncertainty visualisation through stratigraphic variability is designed to convey the complex concept of 3d model uncertainty to the geoscientist in an effective manner uncertainty analysis determined that additional seismic information provides an effective means of constraining modelled geology and reducing uncertainty in regions proximal to the seismic sections improvements to the reliability of high uncertainty regions achieved using information gathered from uncertainty visualisations are quantified in a comparative case study uncertainty in specific model locations is identified and attributed to possible disagreements between seismic and isopach data further improvements to and additional sources of data for the model are proposed based on this information finally a method of introducing stratigraphic variability values as geological constraints for geophysical inversion is presented

constrained 3d modeling of the mesoproterozoic benagerie volcanics australia abstract the benagerie volcanics form part of a hotspot track that affected large sections of eastern australia during the mesoproterozoic understanding the location and controls on eruption centres of the benagerie volcanics and coeval plutons is difficult because they do not outcrop and are known only from limited drillhole data we have applied various combinations of forward and inversion modeling of magnetic and gravity to well constrained petrophysics and drillholes areas to characterize the 3d geometry and extent of the volcanic province and its crustal architecture thereby adding to a better understanding of the emplacement mechanisms involved we interpret the sw limit of the benagerie shear zone corridor to be a major terrane boundary separating relatively magnetic crust to the sw from crust with low magnetic susceptibility to the ne 2d and 3d models show a pronounced thickening of felsic material coincident with the shear zone that may be interpreted as a plutonic root thereby corroborating interpretations that this shear zone acted as a structural conduit for the ascent and emplacement of magma

three dimensional model and late stage warping of the plattengneis shear zone in the eastern alps abstract the plattengneis shear zone is a 250 600 m thick flat lying cretaceous eclogite facies mylonitic shear zone with north over south transport direction that is exposed over almost 1000 km2 in the koralpe region along the eastern margin of the alps although the shear zone is one of the largest in the alps its role in the eoalpine metamorphic evolution and the subsequent exhumation of the region remain enigmatic and its large scale geometry is not well understood the outcrop pattern suggests that the shear zone is made up of a single sheet that is folded into a series of open syn and antiforms with wavelengths of about 10 km eclogite bodies occur above within and below the shear zone and there is no metamorphic grade change across the shear zone in the south the fold axes strike east west and plunge shallowly to the east in the north the fold axes are oriented in north south direction and form a dome shaped structure of the shear zone total shortening during this late stage warping event was of the order of 5 indirect evidence constrains this folding event to have occurred between 80 and 50 ma and the fold geometry implies that the final exhumation in the koralpe occurred somewhat later than further north interestingly the shear zone appears to strike out of the topography in the south and dip into the topography in the north so that north of the shear zone only hanging wall rocks are exposed and south of it only foot wall rocks possibilities for the geometric relationship of the plattengneis shear zone with the surrounding south dipping detachments are discussed

geological modelling from field data and geological knowledge part ii modelling validation using gravity and magnetic data inversion the analysis of multiple data sets is required to select a realistic 3d geological model among an infinite number of possibilities an inverse method that aims at describing the 3d geometry of geological objects is presented the method takes into account the geology and the physical properties of rocks while respecting the topological properties of an a priori model the a priori model is built from the geological data set and its geometry is largely dependent upon assumptions about inaccessible geology at depth this method referred to as total litho inversion is a generalized 3d inversion that results in quantifying the lithology and the distribution of rock property in a probabilistic way its application is demonstrated through i a simple synthetic case and ii the relative distribution characterization of granites and diorites in an orogenic domain

a 3d geological model for the ruiz tolima volcanic massif colombia assessment of geological uncertainty using a stochastic approach based on bezier curve design abstract the ruiz tolima volcanic massif rtvm is an active volcanic complex in the northern andes and understanding its geological structure is critical for hazard mitigation and guiding future geothermal exploration however the sparsity of data available to constrain the interpretation of this volcanic system hinders the application of standard 3d modelling techniques furthermore some features related to the volcanic system are not entirely understood such as the connectivity between the plutons present in its basement i e manizales stock el bosque batholith we have developed a methodology where two independent working hypotheses were formulated and modelled independently i e a case where both plutons constitute distinct bodies and an alternative case where they form one single batholith a monte carlo approach was used to characterise the geological uncertainty in each case bezier curve design was used to represent geological contacts on input cross sections systematic variations in the control points of these curves allows us to generate multiple realisations of geological interfaces resulting in stochastic models that were grouped into suites used to apply quantitative estimators of uncertainty this process results in a geological representation based on fuzzy logic and in maps of model uncertainty distribution the results are consistent with expected regions of high uncertainty near under constrained geological contacts while the non unique nature of the conceptual model indicates that the dominant source of uncertainty in the area is the nature of the batholith structure

geodiversity exploration of 3d geological model space abstract the process of building a 3d model necessitates the reconciliation of field observations geophysical interpretation geological data uncertainty and the prevailing tectonic evolution hypotheses and interpretations uncertainty is compounded when clustered data points collected at local scales are statistically upscaled to one or two points for use in regional models interpretation is required to interpolate between sparse field data points using ambiguous geophysical data in covered terranes it becomes clear that multiple interpretations are possible during model construction the various interpretations are considered as potential natural representatives but pragmatism typically dictates that just a single interpretation is offered by the modelling process uncertainties are introduced into the 3d model during construction from a variety of sources and through data set optimisation that produces a single model practices such as these are likely to result in a model that does not adequately represent the target geology a set of geometrical geodiversity metrics are used to analyse a 3d model of the gippsland basin southeastern australia after perturbing geological input data via uncertainty simulation the resulting sets of perturbed geological observations are used to calculate a suite of geological 3d models that display a range of geological architectures the concept of biodiversity has been adapted for the geosciences to quantify geometric variability or geodiversity between models in order to understand the effect uncertainty has models geometry various geometrical relationships depth volume contact surface area curvature and geological complexity are used to describe the range of possibilities exhibited throughout the model suite end member models geodiversity metrics are classified in a similar manner to taxonomic descriptions further analysis of the model suite is performed using principal component analysis pca to determine important geometrical characteristics the configuration of the model space is determined through identifying outlier model examples which potentially represent undiscovered model species

on the rheology of till the deformation of subglacial till is instrumental in causing certain glacier surges the motion of rapid ice streams in ice sheets and ice sheet surges which are associated with heinrich events and consequent rapid climatic shifts during the last ice age it may also be the means whereby drumlins are formed and these in turn may act as a brake on large scale ice flow it is therefore important in building models to understand the rate at which till deforms and how this controls the basal ice velocity in recent years two paradigms have emerged on the one hand theoreticians have tended to use a viscous rheology though this lacks quantitative support on the other hand field and laboratory studies suggest that till behaves plastically in this paper i will examine some of the dynamic consequences of this latter assumption and show how the dichotomy between viscous and plastic may be less clearcut than previously thought

constrained inversion of geologic surfaces pushing the boundaries during the past 10 years there has been a shift in modelling for geophysical interpretation away from idealized geometrical bodies floating in air and toward fully three dimensional representations this transition has been driven by a number of factors both technological and conceptual the principal conceptual driver has been the growing recognition of the importance of integrated interpretations interpretation is a shared responsibility of geoscientists the common goal being an earth model consistent with all available information

gis based 3d prospectivity mapping a case study of jiama copper polymetallic deposit in tibet china abstract this paper reports a deposit scale gis based 3d mineral potential assessment of the jiama copper polymetallic deposit in tibet china the assessment was achieved through a sequential implementation of metallogenic modelling and 3d modelling of geology geochemistry and prospectivity a metallogenic model for the jiama deposit and 3d modelling workflow were used to construct multiple 3d layers of volumetric and triangular mesh models to represent geology geochemistry and ore controlling features in the study area a gis based 3d weights of evidence analysis was then used to estimate the subsurface prospectivity for cu mo orebodies in the area which led to the identification of three prospective deep seated exploration targets additionally the geochemical modelling indicates three potential fluid flow pathways based on the 3d zonation of major geochemical elements and their ratios particularly the zn pb ratios which support the results of the weights of evidence model

a multidisciplinary study of a syntectonic pluton close to a major lithospheric scale fault relationships between the montmarault granitic massif and the sillon houiller fault in the variscan french massif central 2 gravity aeromagnetic investigations and 3 d geologic modeling 1 new gravity and aeromagnetic investigations have been carried out to understand the emplacement mechanisms of a granitic pluton and the relationships with a nearby lithospheric scale fault this paper concerns the second part of a methodological multidisciplinary study and complements previous geochronologic and anisotropy of magnetic susceptibility ams studies on the same pluton in the northern part of the variscan french massif central fmc the montmarault massif crops out along the sillon houiller fault shf bouguer and aeromagnetic anomaly maps imply thickening of the pluton along the shf and suggest laccolitic spreading northwestward on the basis of petrophysical measurements direct two dimensional 2 d joint gravity and magnetic modeling has been performed along 10 cross sections in order to quantitatively constrain the 3 d pluton geometry and its relationships with surrounding geologic units these geophysical cross sections new structural information field and ams measurements and petrophysical data have been integrated into a regional 3 d geological and geophysical model altogether the results obtained from geochronology petromagnetic fabrics part 1 gravity and aeromagnetic investigations as well as 3 d modeling part 2 demonstrate that the montmarault pluton was emplaced during the namurian period along the shf our results further show that at that time in response to a nw se regional extension if the shf existed it behaved as a normal fault mylonites attesting for synmagmatic normal motion on the northeastern part of the montmarault pluton strengthen this tectonic scenario during the late carboniferous the fmc experienced ne sw extension along the shf by 80 km of brittle left lateral wrench offset this second tectonic event is well recorded in the stephanian coal basins which were formed along nw se listric brittle faults and constrain the present day shape of the montmarault pluton

three dimensional seismo tectonics in the po valley basin northern italy the po valley northern italy is a composite foreland foredeep basin caught in between the southern alps and northern apennine mountain belts by integrating the 3d structural model of the region with the public earthquake dataset the seismo tectonics of the basin is shown at different scales of observation the three dimensional geo volumeis used to reviewthe seismicity around the region and validate the structure earthquake association for such a complex tectonic framework despite the overall uncertainty due to the original data distribution quality as well as the crustal scale model dimension the direct correlation between structures and seismicity a confirms the po valley region as an active tectonic system and b allows the whole structural architecture to be revised by a unique three dimensional perspective and approach this study also indicates that 3d methodology is a powerful tool for better understanding of highly complex seismo tectonic situations at both regional and local scales

a multidisciplinary study of a syntectonic pluton close to a major lithospheric scale fault relationships between the montmarault granitic massif and the sillon houiller fault in the variscan french massif central 1 geochronology mineral fabrics and tectonic implications 1 because of its location along one of the major faults the sillon houiller fault shf of the french massif central fmc the montmarault granitic pluton is well suited to better understand the place of the late orogenic magmatism in variscan orogeny through a methodological approach the close spatial association of the pluton with the lithospheric shf is investigated in order to clarify the relationships between faulting and magmatic processes during the late carboniferous therefore a multidisciplinary study has been carried out on the montmarault massif combining geochronology field and laboratory microstructural observations and anisotropy of magnetic susceptibility ams methods presented in this paper and gravity and aeromagnetic modeling part 2 as well as similar studies from other plutons in the fmc allows us to draw the following conclusions 1 the montmarault pluton dated by the chemical u th pb method on monazite at 321 2 ma was emplaced in a nw se maximum stretching trend which is consistent with the regional extensional tectonic regime 2 the montmarault pluton is rooted in its eastern part along the shf with a laccolite like shape in its western part 3 at circa 320 ma the proto shf acted probably as a normal fault considered as the feeding channel for the magma emplacement and 4 late carboniferous ne sw extensional tectonics reworked the montmarault pluton in a brittle postsolidus stage

character and kinematics of faults within the turbidite dominated lachlan orogen implications for tectonic evolution of eastern australia reply fault zones within turbidite dominated orogenic systems typified by the lachlan orogen of eastern australia are characterised by higher than average strain and intense mica fabrics transposition foliation and isoclinal folds poly deformation with overprinting crenulation cleavages and steeply to moderately plunging meso and micro folds they have a different character compared to the brittle ductile fault zones of classic foreland fold and thrust belts such as the appalachians and the canadian rocky mountains multiple cleavages and transposition layering record a progressive shear related deformation history an intense mica fabric evolves initially during shortening of the overlying sedimentary wedge but is progressively modified during rotation and emplacement to higher structural levels along the steep parts of inferred listric faults the deformed wedge outside the fault zones generally undergoes one phase of deformation shown by a weak to moderately developed slaty cleavage which is parallel to the axial surface of upright subhorizontally plunging chevron folds other faults within the turbidites of the lachlan orogen include the steep zones of ductile strike slip deformation that bound a centrally located high t low p metamorphic complex characterised by s c mylonites these ductile shear zones indicate a southward passage of the metamorphic complex as a crustal wedge with emplacement to higher structural levels along a leading edge ductile thrust fault ar ar dating constrains the timing of regional deformation to be mostly late ordovician through silurian across the lachlan orogen faults in the low grade turbidite sequences record the kinematic evolution of the developing lachlan orogen and indicate progressive deformation associated with simultaneous eastward propagating and migrating deformation fronts in both the western and eastern parts of the fold belt these deformation fronts are related to accretionary style deformation at the leading edges of overriding plates in an inferred southwest pacific type subduction setting from the late ordovician to the mid devonian along the former gondwana margin the fault zones effectively accommodate and preserve movements within the structurally thickening migrating and prograding accretionary wedge

stochastic structure constrained image guided inversion of geophysical data abstractinverse modeling of geophysical data involves the recovery of a subsurface structural model and the distribution of petrophysical properties independent information regarding the subsurface structure is usually available with some uncertainty from the expertise of a geologist and possibly accounting for sedimentary and tectonic processes we have used the available structural information to construct a model covariance matrix and to perform a structure constrained inversion of the geophysical data to obtain a geophysical tomogram m we have considered that the geologic models y were built from random variables and were described with a priori probability density function in the bayesian framework we have explored for the a posteriori probability density of the geologic models i e the structure of the guiding image with the markov chain monte carlo method and we inverted at the same time in a deterministic framework the geophysical data the sampling of the geologic models was performed

evolution of the mount woods inlier northern gawler craton southern australia an integrated structural and aeromagnetic analysis structural mapping integrated with interpretation and forward modelling of aeromagnetic data form complimentary and powerful tools for regional structural analysis because both techniques focus on architecture and overprinting relationships this approach is used to constrain the geometry and evolution of the sparsely exposed mount woods inlier in the northern gawler craton the mount woods inlier records a history of poly phase deformation high temperature metamorphism and syn and post orogenic magmatism between ca 1736 and 1584 ma the earliest deformation involved isoclinal folding and the development of bedding parallel and axial planar gneissic foliation s1 this was accompanied by high temperature upper amphibolite to granulite facies metamorphism at ca 1736 ma during subsequent north south shortening d2 open to isoclinal south southeast oriented f2 folds developed as the palaeoproterozoic successions of the inlier were thrust over the archaean nuclei of the gawler craton the syn d2 engenina adamellite was emplaced at ca 1692 ma the post d2 history involved shear zone development and localised folding exhumation of metamorphic rocks and deposition of clastic sediments prior to the emplacement of the ca 1584 ma granite balta suite the mount woods inlier is interpreted as the northern continuation of the kimban orogen

multi scale integrated structural and aeromagnetic analysis to guide tectonic models an example from the eastern musgrave province central australia abstract in many polydeformed precambrian provinces the understanding of their tectonic history is limited by insufficient exposure which leads to difficulty in developing links between local and regional architecture and results in poorly constrained models of their regional scale architecture high resolution aeromagnetic data allows interpretation and modelling at a scale comparable to structural mapping and by integrating these methods these links can be developed with high confidence as an example we integrate structural mapping aeromagnetic data interpretation and 3d magnetic inversions in a multi scale structural analysis of the polydeformed eastern musgrave province in central australia deformation during the ca 1200 ma musgravian orogeny is characterised by an originally northeast trending structural grain defined by shear zones and tight to isoclinal folds at all scales 3d magnetic inversion models of syn to post musgravian granites indicate that this structural grain is predominantly west dipping this architecture suggests that a northeast oriented fold and thrust belt developed as a result of northwest southeast compression in central australia during the musgravian orogeny the next deformation event is characterised by an array of originally east southeast trending shear zones that truncate and offset the musgravian structural grain with apparent dextral displacements of up to 1 km these shear zones are commonly co located with mafic and granitic dykes suggesting a dilational origin and they are interpreted to have initiated under northeast southwest extension during the ca 1080 ma giles event the architecture of these two mesoproterozoic events was later extensively overprinted by two deformation events during the pan african aged ca 550 ma petermann orogeny the first is characterised by the widespread reactivation of mesoproterozoic structures resulting in a network of shear zones of variable orientation and the second is characterised by the development of crustal scale transpressional shear zones motion on which has caused the rotation of lithospheric blocks and the reorientation of prior structural trends by up to 90 collectively the architecture of these two events suggests broadly north south crustal shortening in central australia as an intraplate response to gondwana assembly this example demonstrates that the integration of structural geology with aeromagnetic interpretation and modelling can be used to develop high confidence links between local and regional structures these links permit the derivation of better constrained models of major tectonic events particularly in regions where outcrop is poor and the structural architecture is complex

simplifying drill hole domains for 3d geochemical modelling an example from the kevitsa ni cu pge deposit abstract a 3d geology model is a simplified version of the true geology designed to give a visual summary of the geometry and distribution of major geological elements in a specified region drill holes provide detailed data of the subsurface that can be classified into geological units that are the fundamental elements of the 3d model due to software limitations upscaling lumping is usually required to reduce the number of geological units in the drill holes prior to model building upscaling is a subjective process which means that different geologists will group in different ways and will typically not record the rationale behind their decision this means the experiment is not reproducible in our study we use a method of upscaling geological units in this case based on assay data using the continuous wavelet transform cwt and tessellation methods this method reduces subjectivity and can easily be repeated e g on an updated or new drill hole by using the same parameters ensuring that the upscaling process is consistent over all drill hole data we apply this technique to a large assay database 90 000 samples from the kevitsa nickel copper platinum group element pge deposit in finland the kevitsa ni cu pge disseminated sulfide orebody is hosted in a proterozoic layered intrusion in northern finland internal geological subdivision and correlation within the intrusion is very difficult to do consistently using lithological observations owing to general homogeneity of rock types and an overprint of alteration but distinct variability is evident in ni and pge sulfide tenors in its raw form the tenor variation dataset appears noisy and unsystematic we have applied the tessellation method to classifying ore types based on tenor variations consistently and objectively reducing the number of units in each drill hole to create a simplified 3d model of the orebody our results reveal shallow inward dipping cryptic layering defined by sulfide composition which are interpreted as reflecting an increase in ni and pge tenor with time during emplacement of the sulfide bearing cumulates we interpret this as a progressive increase in silicate sulfide mixing efficiency r factor as the intrusion developed from an interconnected sill sediment complex choked with country rock inclusions into a freely convecting magma chamber based on this case study we show that the tessellation method can add considerable value by distinguishing the wood from the trees in large 3d geochemical databases the method may be widely applicable in other ni cu pge deposits where tenor variations appear at first sight to be chaotic and uninterpretable

structural model creation the impact of data type and creative space on geological reasoning and interpretation the authors would like to thank participants in the interpretation exercises bond was funded by midland valley exploration and a scottish executive score award whilst collecting the cohort 1 interpretation dataset midland valley exploration s move software was used to create the geological model and borehole dataset fiji image j software was used to create figure 5a and c ion gxt are thanked for creation of the synthetic seismic image dataset

towards an integrated inversion of geoscientific data what price of geology abstract the inversion of multiple geoscientific datasets to define structures in hard rock terrains has for the most part been limited to geophysical methods supported by rock property constraints in this paper we expand the range of constraints available to geological modellers by defining a series of misfit functions that are used to define the quality of a given geological model with respect to the available geological data these misfit functions encompass both spatial and temporal observations and include primary data such as the location of an outcrop or bore hole location of a given rock type the orientation of its different generations of foliations as well as secondary geologic observations such as age relationships when we combine geologic conditions with geophysical misfit functions which already exist for many geophysical measures we have the potential to better constrain two and 3d models of the earth as a first test a subset of these misfit functions are applied to a set of synthetic three dimensional volumetric models built with an implicit surface modelling scheme by perturbing the input structural data within a narrow range we can simulate a range of significantly different three dimensional models for which we can then apply both geological and geophysical misfit functions several joint geological geophysical inversion schemes may be developed based on this methodology with the ultimate goal being an inversion scheme that simultaneously minimizes both geological and geophysical misfit

towards incorporating uncertainty of structural data in 3d geological inversion abstract all geological models are subject to several kinds of uncertainty these can be classified into three different types data imprecision and quality inherent randomness and incomplete knowledge with our approach we address uncertainties introduced by input data quality in complex three dimensional 3d models of subsurface structures geological models as input data we consider parameters of geological structures i e formation and fault boundary points and orientation measurements our method consists of five steps construction of an initial geological model with an implicit potential field method assignment of probability distributions to data positions and orientation measurements simulation of several input data sets construction of several model realisations based on these simulated data sets and finally the visualisation and analysis of the uncertainties we test our approach in two generic models a simple graben setting and a complex dome structure the first model shows that our approach can evaluate uncertainties from different structures and their interaction furthermore it indicates that the final uncertainty of the model is not simply the sum of all input data uncertainties but complex interactions exist the second example demonstrates that our approach can handle full three dimensional settings with overturned surfaces results of the uncertainty simulation can be visualised and analysed in several ways ranging from borehole histograms to uncertainty maps for complex 3d visualisation and analysis we use indicator functions when we apply these we can treat the visualisation of uncertainties in complex settings in a self consistent manner with our simulation method it is possible to analyse and visualise the uncertainties directly introduced by imprecision in the input data our approach is intuitive and straight forward and suitable in both simple and complex geological settings it enables detailed insights into the model quality even for the non expert in cases where a geological model is the basis for geophysical simulation it opens up the way to geological data driven ensemble modelling and inversion

the miocene palaeoenvironmental and palaeoceanographic evolution of the gippsland basin southeast australia a record of southern ocean change abstract the gippsland basin in southeastern australia preserves up to 2 5 km thick tertiary to recent marine carbonate sediments included in the seaspray group during the neogene the seaspray group carbonates of the mackerel and flounder petroleum fields lay at the shelfal to bathyal palaeoenvironmental transition an ideal palaeoceanographic setting to study the neogene history of events in the evolving southern ocean seismic foraminiferal and facies analyses of the miocene seaspray group sediments at the mackerel 1 and flounder 1 wells have revealed the following palaeoenvironmental history of the area relatively cool to temperate upwelling conditions prevailed in the area during the earliest miocene during this time low energy upper slope globigerina ooze calcareous mudstone was deposited in the oxygen minimum zone during the early to lower middle miocene upper slope marl was deposited in oligotrophic conditions the presence of neritic subtropical foraminifera and abundant shallow and deep dwelling warm to cool temperate plankton in the upper slope suggests that warm poorly stratified oceanic conditions prevailed in the region this upper early miocene warm phase and mid miocene climatic optimum in gippsland corresponds to a time when global ocean conditions were much warmer and less vertically and latitudinally stratified than at present these oceanic conditions were associated with a reduced east antarctic ice sheet a higher sea level a relatively weak antarctic circumpolar current and weak atmospheric and wind driven circulation during the upper middle miocene to late miocene cool phase after c 14 5 ma strong upwelling and cooler oceanic conditions prevailed in the outer shelf to upper slope canyon facies in gippsland the occurrence of common deep dwelling plankton taxa in this interval suggests that regional oceanic conditions became more vertically stratified during this time from 14 5 and 5 million years ago the middle to late miocene palaeoenvironmental change recorded in seaspray group sediments corresponds to global cooling and major antarctic ice sheet expansion when the world s oceans became more vertically and latitudinally stratified from around 14 5 million years the transition from a warm miocene optimum to cooler oceanic conditions was associated with a strengthened antarctic circumpolar current and more intense wind driven atmospheric circulation in the southern ocean

part ii a demonstration of integrating multiple scale 3d modelling into gis based prospectivity analysis a case study of the huayuan malichang district china abstract this paper constitutes the second part of a study called mineral system modelling prospectivity analysis for mvt pb zn deposit in northwestern hunan province china the methodology is described in part 1 part 2 demonstrates the value of 3d modelling at the district and ore deposit scales the process employed in this paper is as follows i 3d models are constructed at multiple scales i e at the district and ore deposit scales ii an interpretation of the 3d models is presented based on a conceptual geological model iii a map of the mineral potential at depth relying on the conceptual geological model and 3d geometry data is delineated and discussed iv calculations of the volume and ore bearing ratio are improved using 3d geometry v the similarity coefficient used in part 1 is replaced with the quantitative uncertainty of the 3d models and vi the undiscovered mineral resources are estimated in the study area to be consistent with part 1 a case study of the mississippi valley type mvt pb zn mineralization in the huayuan malichang district 36 24 km 2 in northwestern hunan province china is conducted

correlation of the askyn river section southern urals russia with the mid carboniferous boundary gssp bird spring formation arrow canyon nevada usa implications for global paleoceanography abstract isotopic data of unaltered low mg calcite brachiopods from type bashkirian strata of the askyn river section southern urals russia are correlated with those from the mid carboniferous boundary global stratotype section and point gssp at arrow canyon southern nevada usa strontium isotope and conodont data of precisely located samples from the sub to tropical locations spanning the mid carboniferous boundary facilitate the correlation of the two sequences and support the discontinuous nature of the sequence at askyn carbon isotopic trends of the two sites are generally divergent and demonstrate the influence overprinting of local oceanographic conditions on global parameters oxygen isotopes show a similar divergence for the latest mississippian time period with concurrence of values for the earliest pennsylvanian at the two sites in both instances differences variations in water temperature currents salinity and burial rate amount of organic matter or combinations of these factors may have played roles of influencing water chemistry at the local level it is possible to achieve global correlations at a finer scale than biozones with precisely located material from stratotype and ancillary sections especially if a global stratotype point has been identified and selected according to universally accepted biostratigraphic criteria consequently it is possible to resolve oceanographic influences at the local level and reconcile them with truly global oceanographic conditions and ultimately define global causes effects such as cryospheric and tectonic events seawater chemistry at arrow canyon probably represents panthalassan global mid carboniferous oceanic conditions supported by its similarity with data from other locations and modern global oceanographic parameters askyn represents paleotethys and global oceanographic conditions but in part overprinted by local influences the mid carboniferous seems to be a time of expansion of the cryosphere as documented by a positive shift in seawater oxygen isotope composition of about 0 5 smow from the latest mississippian 1 2 to earliest pennsylvanian 0 7

the historical development of the magnetic method in exploration the magnetic method perhaps the oldest of geophysical exploration techniques blossomed after the advent of airborne surveys in world war ii with improvements in instrumentation navigation and platform compensation it is now possible to map the entire crustal section at a variety of scales from strongly magnetic basement at regional scale to weakly magnetic sedimentary contacts at local scale methods of data filtering display and interpretation have also advanced especially with the availability of low cost high performance personal computers and color raster graphics the magnetic method is the primary exploration tool in the search for minerals in other arenas the magnetic method has evolved from its sole use for mapping basement structure to include a wide range of new applications such as locating intrasedimentary faults defining subtle lithologic contacts mapping salt domes in weakly magnetic sediments and better defining targets through 3d inversion these new applications have increased the method s utility in all realms of exploration in the search for minerals oil and gas geothermal resources and groundwater and for a variety of other purposes such as natural hazards assessment mapping impact structures and engineering and environmental studies