review of the modelling of radionuclide transport from u series disequilibria and of its use in assessing the safe disposal of nuclear waste in crystalline rock abstract u series disequilibia from crystalline rocks and u deposits have been used to estimate the timing of hydrogeological events for u and ra mobility and to model the transport rates of u and ra both with some sucess unfortunately activity ratio data alone are not unique to a given process or model and it is shown how inappropriate choice of the model can have quite diverse consequences for interpretation of the data information from other sources is needed to help minimise these non uniqueness problems but as yet the state of methodology is unadequate to assess completely the validity of the models in particular the rate of deposition of u in fractures seems highly dependent upon the availability of trivalent fe and other low temperature minerals whose rates of formation are largely unknown this review reinforces the need to assess closely the suggestion that chemisorption is an effective retardant of fracture borne borne repository source radionuclides

secondary fabrics revealed by remanence anisotropy methodological study and examples from plutonic rocks summary the fabric of fine grained magnetite is isolated by partial remanence anisotropy paar measurements that combine cycles of anhysteretic remanence acquisition and alternating frequency af tumbling demagnetization of the low coercivity fraction since remanence intensities of the most coercive fine grained magnetite are very weak rarely exceeding 10 per cent of the measured remanence in the studied samples a methodological study is presented that defines optimal measurement schemes and examines the role of gyroremanence and background remanences due to hard remanence carriers this procedure is applied to some reddened granites from tana corsica and wichita oklahoma and to the tellnes ilmenite rich norite norway the paar fabrics for fine grained magnetites are compared to the fabrics of the coarse grained primary magnetite grains as shown by both the anisotropy of magnetic susceptibility ams and the remanence anisotropy of the low coercivity fraction in tellnes fine grained magnetite is believed to be of secondary origin this is strongly suggested by the correlation between the paar fabrics and the orientations of sets of microfractures decorated by oxides in the reddened granites although no direct correlation between paar fabrics and microstructures could be evidenced the comparison between unaltered specimens and hydrothermally altered ones reveals changes in magnetic properties and fabrics that are ascribable to this secondary geological process

the sedimentary structure of linear sand dunes linear sand dunes dunes that extend parallel to each other rather than in star like or crescentic forms are the most abundant type of desert sand dune1 but because their development and their internal structure are poorly understood they are rarely recognized in the rock record2 models of linear dune development2 3 4 5 6 have not been able to take into account the sub surface structure of existing dunes but have relied instead either on the extrapolation of short term measurements of winds and sediment transport or on observations of near surface internal sedimentary structures from such studies it has not been clear if linear dunes can migrate laterally2 7 8 here we present images produced by ground penetrating radar showing the three dimensional sedimentary structure of a linear dune in the namib sand sea where some of the world s largest linear dunes are situated these profiles show clear evidence for lateral migration in a linear dune moreover the migration of a sinuous crest line along the dune produces divergent sets of cross stratification which can become stacked as the dune height increases and large linear dunes can support superimposed dunes that produce stacked sets of trough cross stratification these clear structural signatures of linear dunes should facilitate their recognition in geological records

ground penetrating radar and its use in sedimentology principles problems and progress abstract ground penetrating radar gpr also referred to as ground probing radar surface penetrating radar subsurface radar georadar or impulse radar is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface

the henkel petrophysical plot mineralogy and lithology from physical properties the henkel plot logarithm of magnetic susceptibility versus density of rock samples reveals that most rocks fall on either a magnetite trend or a paramagnetic trend i

impact shocked zircons discovery of shock induced textures reflecting increasing degrees of shock metamorphism abstract textural effects specifically characteristic of shock metamorphism in zircons from impact environments have not been reported previously however planar deformation features pdf due to shock metamorphism are well documented in quartz and other mineral grains from these same environments an etching technique was developed that allows sem visualization of pdf and other probable shock induced textural features such as granular polycrystalline texture in zircons from a variety of impact shock environments these textural features in shocked zircons from k t boundary distal ejecta form a series related to increasing degrees of shock that should correlate with proportionate resetting of the u pb isotopic system

the magnetic susceptibility of granitic rocks as a proxy for geochemical composition example from the saruhan granitoids ne turkey the magnetic susceptibility of rocks is determined by their bulk chemistry and magnetic mineralogy in this case study of the saruhan pluton in turkey a detailed survey based on 925 field measurements and 37 whole rock analyses reveals a strong correlation between magnetic susceptibility and feot r 2 0 8 petrographic observations and calculations based on whole rock major element analyses indicate the presence of magnetite grains further calculations show that magnetite accounts for 88 of the magnetic susceptibility the spatial correlation between feototal and the magnetic susceptibility is particularly spectacular which suggests that km is a proxy for geochemical differentiation the zoning pattern of magnetic susceptibility across the pluton is concentric and reverse with the highest values of magnetic susceptibility in the center this type of zoning is consistent with a previously proposed petrogenetic model the comparison of the saruhan granites with a classic example of paramagnetic granites reveals two contrasted feot km trends this suggests that these variations can be a useful tool to distinguish between leucocratic paramagnetic and leucocratic ferrimagnetic granites 2007 elsevier b v all rights reserved

magnetic susceptibility anisotropy as a predictive exploration tool of metasomatic iron oxide deposits example from the panj kuh iron ore body ne iran abstract the panj kuh iron deposit hosted by late eocene igneous rocks in north of central iran is associated with a syenitic intrusive body magnetic fabric investigations indicate that the panj kuh pluton was emplaced within a sinistral shear zone corridors of sheared and metasomatized rocks show that the shear zone was active after emplacement of the pluton and in the final steps of crystallization the sheared rocks allowed for circulation of hydrothermal fluids during cooling of the magma and caused the pervasive na ca alteration the ferrimagnetic phase in fresh syenite is mostly euhedral or subhedral magnetite and is observed adjacent to or as inclusion in biotite and pyroxene anisotropy of magnetic susceptibility ams in the fresh syenite is due to preferred shape orientation of magnetite grains in na ca altered syenites magnetite has reduced or has been totally absorbed the alteration results in decreased bulk susceptibilities km and higher anisotropy degrees p accompanied by changes in the shape of magnetic susceptibility anisotropy ellipsoid this study of the panj kuh pluton suggests that ams can be used for mapping lithology and hydrothermal alteration types since various types of hydrothermal alteration create transform or destroy ferrimagnetic minerals in a mineralized system susceptibility measurements aid mapping of igneous rock type alteration zoning and mineralization integrating petrography magnetic mineralogy bulk magnetic susceptibility and preferred orientations of principal axes of the ams in fresh and altered rocks can be used to generate predictive magnetic exploration models for metasomatic iron oxide deposits

a simple exact method of 3 d migration theory recently a heuristic and empirical analysis of a method of three dimensional 3 d migration has been presented by gibson larner and levin it consists of sets of two dimensional 2 d migrations in orthogonal directions in this paper we examine this two pass method using scalar wave theory and show its action to be identical to that of so called full 3 d migration for constant velocity media the demonstration of equivalence is carried out in both the frequency space and frequency wavenumber domains the latter providing a particularly transparent view of the mechanism of the two pass approach we then extend our analysis to consider how various approximate algorithms used in practical implementations affect the validity of our conclusion

mapping of apparent magnetic susceptibility and the identification of fractures a case study from the eye dashwa lakes pluton atikokan ontario in situ magnetic susceptibility measurements are only possible on outcrops which are often limited by overburden and water bodies an alternative approach is to derive an apparent susceptibility map from total magnetic intensity tmi surveys which was done in this study for the eye dashwa lakes pluton near atikokan ontario susceptibility logs of cores directly link alteration to systematic changes in the amount and composition of magnetic minerals the surficial distribution of alteration zones was originally estimated from a limited number of in situ magnetic susceptibility measurements here through forward modeling of the tmi data set susceptibility data are used to validate the apparent susceptibility data set the modeling accounts for the bathymetric surface of all lakes that cover the area a two step process of bulk and local scale modeling was used to estimate apparent susceptibility patterns bulk magnetic susceptibility is used as an indicator of overall alteration content and local scale apparent magnetic susceptibility values are computed using a forward modeling routine the new apparent magnetic data set indicates northwest and northeast linears which are the same as those seen in previous studies

three dimensional reverse time migration of ground penetrating radar signals three dimensional 3d ground penetrating radar gpr systems and 3d seismic imaging techniques have been developing fast and evolving rapidly in the last decade ray based migration methods have been successfully applied to processing 3d gpr signals based on the similarity between electromagnetic and seismic waves however reverse time migration rtm of 3d gpr signals has not been well studied in the past in this paper we present a 3d rtm based on maxwell s equations for 3d gpr surveys migration recovers the true subsurface structure from a distorted and unfocused time profile and suppresses common electromagnetic clutter and noise rtm based on maxwell s equations can consider conductivity directly and compensate for the attenuation within a high conductivity zone compared with 2d rtm 3d rtm back propagates both in line and cross line signals simultaneously and can include complex 3d permittivity and conductivity models we have integrated a parallel finite difference time domain fdtd algorithm based on a hybrid mpi and openmp scheme to reduce the computational cost of 3d problems the 3d rtm experiments on an anomaly of em shape and a realistic sand dune model demonstrate the effective recovery of 3d subsurface structures

variability of outcrop magnetic susceptibility and its relationship to the porphyry cu centers in the highland valley copper district abstract the highland valley copper porphyry cu mo centers compose canada s largest porphyry cu mining district and are hosted in plutonic rocks of the late triassic guichon creek batholith in the quesnel terrane british columbia here we evaluate the relationship between variations in magnetic susceptibility and alteration in order to define a footprint around the porphyry cu centers using a district scale dataset of 1610 minimally weathered outcrops and 11 432 magnetic susceptibility measurements statistical analysis of the outcrop based measurements revealed changes in outcrop geometric mean magnetic susceptibility and the coefficient of variation extent of variability in relation to the mean are proportional to vein frequency and altered rock volume estimates at a confidence interval of 95 and 9 degrees of freedom the average standard error uncertainty of the geometric mean and coefficient of variation from 10 magnetic susceptibility outcrop measurements is 7 3 and 13 2 respectively modeling of outcrop magnetic susceptibility data shows that domains of coefficient of variation of 0 3 extend 1 4 km away from the porphyry centers whereas pronounced susceptibility lows of

ballooning emplacement and alteration of the chah musa subvolcanic intrusion ne iran inferred from magnetic susceptibility and fabric the porphyritic diorite chah musa subvolcanic intrusion is located in the toroud chah shirin magmatic arc in the northern central iranian structural zone the elliptical chah musa body hosts a copper deposit and intrudes an eocene sequence of volcanic breccia agglomerate and red tuffaceous sediment high magnetic susceptibility values are attributed to the presence of magnetite as a magnetic carrier changes in bulk magnetic susceptibility correlate with zonation of alteration in the intrusion although the degree of anisotropy of magnetic susceptibility decreases due to hydrothermal alteration the field observations confirm that this parameter can be used as a strain marker strongly oblate magnetic ellipsoids are found in the eastern half of the intrusion where isolated outcrops of flat lying tuffaceous host cover dioritic rocks roof zone stations with prolate ellipsoids mostly belong to the centre of the intrusion where the magnetic lineations plunge steeply they are interpreted as indicating the main feeder zone the concentric fabric pattern at the periphery of intrusion the oblate magnetic ellipsoids at the roof the highest anisotropy degree along the small diameter of the intrusion and an intense deformation of the host rocks especially at the western margin all are evidence that the intrusion was ballooning during the late stages of its emplacement ascent and emplacement of the chah musa body is ascribed to the tensional space provided by a dextral shear zone created by the regional left lateral movement on the bounding anjilow and toroud strike slip faults

exhuming norwegian ultrahigh pressure rocks overprinting extensional structures and the role of the nordfjord sogn detachment zone 1 the nordfjord sogn detachment zone nsdz is widely cited as one of the primary structures responsible for the exhumation of norwegian ultra high pressure uhp rocks here we review data from the considerable volume of research describing this shear zone and compile a strikeparallel cross section along the nsdz from the solund basin in the south to the soroyane uhp domain in the north this cross section highlights several previously unrecognized patterns revealing a shear zone with top to the west asymmetric fabrics that 1 initiated at amphibolite facies 2 overprints metamorphic breaks and tectonostratigraphic contacts and 3 has a gradational continuum of muscovite cooling ages these patterns constrain the kinematic evolution of the nsdz and suggest a new three step model for the exhumation of norwegian u hp rocks the initial stages of exhumation were characterized by the rise of crustal rocks from u hp depths to the base of the crust by buoyancydriven mechanisms not specified in this paper mantle exhumation was followed by top to thewest normal sense displacement within a broad noncoaxial ductile shear zone near the base of the crust that overprinted tectonostratigraphic contacts formed previously during mantle exhumation in the final stages of crustal exhumation top w brittleductile detachments soled into and partially excised this ductile shear zone dropping the devonian basins into contact with rocks of varying tectonostratigraphic levels this new interpretation of the nsdz is significant as it accounts for the extreme crustal excision observed in western norway using three sequentially overprinting structures active at different stages of uhp rock exhumation citation johnston s m b r hacker and t b andersen 2007 exhuming norwegian ultrahigh pressure rocks overprinting extensional structures and the role of the nordfjord sogn detachment zone tectonics 26 tc5001

reverse time migration migration of stacked or zero offset sections is based on deriving the wave amplitude in space from wave field observations at the surface conventionally this calculation has been carried out through a depth extrapolation we examine the alternative of carrying out the migration through a reverse time extrapolation this approach may offer improvements over existing migration methods especially in cases of steeply dipping structures with strong velocity contrasts this migration method is tested using appropriate synthetic data sets

results of 3 d georadar surveying and trenching the san andreas fault near its northern landward limit abstract as part of a program to determine the location and geometry of the san andreas fault saf buried beneath shallow sediments near its northern landward limit three 20 m long parallel trenches were constructed at positions distributed over a distance of 55 m the majority of excavated material comprised unconsolidated fluvial sediments deposited in a number of paleochannels single zones of active faulting identified in each of the trenches were initially interpreted in terms of a solitary strand of the saf to map the saf between and beyond the trenches and to detect other active fault zones hidden by the young sedimentary cover we collected a dense ground penetrating radar georadar data set across a 23 2 72 m area the data were recorded using a semi automated acquisition system that included a conventional georadar unit coupled to a self tracking laser theodolite with automatic target recognition capabilities since these data were plagued by system ringing as a result of the moderate to high electrical conductivities of the surficial sediments an extensive data processing scheme was required to extract meaningful subsurface information the final processed georadar volume cuboid contained numerous subhorizontal and trough shaped reflections that originated from the fluvial paleochannels using the geological interpretation of the trench walls as a guide to pick semi automatically the times of the most important reflecting horizons we discovered that alignments of the nearly linear boundaries of these horizons defined two nw se trending strands of the saf within the survey area the georadar expression of the eastern saf strand could only be traced over a distance of 38 m it had been intersected in the northern trench in contrast the western saf strand extended over the entire length of the georadar volume and had been intersected in the central and southern trenches prominent reflections on georadar cross sections were found to be vertically displaced by 0 2 0 3 m across both saf strands a conspicuous linear trending feature observed on horizontal sections at 3 3 3 6 m depth was laterally offset by 4 5 5 5 m along the eastern saf strand the interpreted vertical and horizontal offsets could have been generated by the 1906 san francisco earthquake and or earlier events undetermined amounts of aseismic slip may also have occurred along the newly defined saf strands

examples of reverse time migration of single channel ground penetrating radar profiles a single channel ground penetrating radar gpr profile portrays a distorted unfocused image of subsurface structure due to apparent position shifts associated with dipping reflectors and to diffractions from corners and edges a focused image may be produced from such data by using any of the migration algorithms previously developed for seismic data we use reverse time migration based on the scalar wave equation field work was performed over a simple stratigraphic soil sequence and a complicated fluvial environment in the migrated images reflector continuity is enhanced and the level of detail available for high resolution interpretation is significantly increased

on the lognormal distribution of oxides in igneous rocks using magnetic susceptibility as a proxy for oxide mineral concentration summary trace element concentrations in igneous rocks are frequently lognormally distributed and shaw 1961 suggested that minor minerals in igneous rocks might also be lognormally distributed there is accumulating evidence to show that bulk magnetic susceptibility bms often closely follows a lognormal distribution in fresh igneous rocks but because bms is dependent upon oxide grain size and mineralogy it is not obvious why this should be so we have adopted shaw s simple theoretical model as an argument to account for the lognormal distribution of bms the obvious prevailing conditions must be that the original melt was uniform that pressure temperature and oxygen fugacity were constant and that the minerals were formed at equilibrium in addition because bms is also a function of grain size and mineralogy the distribution of these latter parameters must be insensitive to changes in p t etc at equilibrium it appears that there must be a limit to the lognormal law in trying to apply it to minerals of greater concentration however bms proxies for oxide content and because it does closely follow the lognormal distribution it thus appears that in crystalline igneous rocks the lognormal law is obeyed by minerals of concentrations at least up to a few percent knowledge of the mean and variance of such distributions can be useful in a variety of petrological applications especially in drillcore logging a simple example is presented

hydrothermally induced changes in mineralogy and magnetic properties of oxidized a type granites abstract the changes in magnetic mineralogy due to the hydrothermal alteration of a type granitic rocks have been thoroughly investigated in samples from the granite of tana corsica france and compared with other a type granites meruoca ne brazil bushveld south africa mount scott wichita mountains oklahoma usa and the stratoid hypersolvus granites of madagascar the altered red colored samples and their non altered equivalents were magnetically characterized by means of magnetic susceptibility measurements hysteresis loops remanent coercivity spectra and lowrie test it is shown that hydrothermalization in magnetite bearing granites is related to the formation of fine grained magnetite and hematite and to coeval depletion in the content of primary low coercive coarse grained magnetite these mineralogical changes give typical rock magnetic signatures namely lower susceptibility magnitudes and anisotropy degrees prolate ams anisotropy of magnetic susceptibility fabrics and increased coercivities optical microscopy and sem scanning electronic microscopy images suggest that the orientation of the secondary magnetic minerals is related to fluid pathways and micro fractures formed during the hydrothermal event and therefore may be unrelated to magma emplacement and crystallization fabrics changes in magnetic mineralogy and grain size distribution have also to be considered for any paleomagnetic and iron isotope studies in granites

paleomagnetism of alkaline complexes and remagnetization in the kapuskasing structural zone ontario canada the shenango and nemegosenda alkaline complexes of the southern kapuskasing structural zone ksz an uplifted crustal block in northern ontario preserve primary thermoremanent magnetizations with mean directions d 112 i 46 k 13 95 13 n 9 sites and d 304 i 51 k 31 95 10 n 7 sites for shenango and d 124 i 57 k 13 9520 n 4 sites and d 312 i 54 k 17 95 13 n 7 sites for nemegosenda their average paleomagnetic pole is 45 n 189 e dp 6 dm 8 falling on the keweenawan track of the north american apparent polar wander path apwp between 1098 1107 ma reverse polarity r and 1087 1098 ma normal polarity n poles of lake superior lavas and dikes unlike the keweenawan paleopoles which have a reversal asymmetry of 30 the shenango and nemegosenda r and n poles are almost 180 reversed which was found also by lewchuk and symons 1990b this symmetry of r and n poles casts doubt on the previously accepted predominance of asymmetric reversals of the earth s field in keweenawan time the archean shawmere anorthosite is overprinted by a b magnetization with mean direction d 97 i 68 k 12 95 10 n 18 sites the shawmere b paleopole at 38 n 226 e dp 13 dm l6 falls between the carbonatite poles and 1850 ma cratonic poles and the b magnetization seems to be a composite of middle and late proterozoic overprints sites in the western part of the shawmere body close to the carbonatite line of faults linking the various alkaline complexes are severely altered with an abundance of secondary magnetite and hematite virtual geomagnetic poles for these sites fall close to the keweenawan track and have an average pole of 189 53 n dp 15 dm 20 suggesting that the b nrm at these sites is an 1100 ma thermochemical overprint caused by hydrothermal fluids at the time of carbonatite intrusion more easterly sites are less altered their vgps resemble 1850 ma cratonic poles and average to 235 e 30 n dp 15 dm 17 these b natural remanent magnetizations are probably thermochemical remanent magnetizations impressed by middle proterozoic hydrothermal activity associated with intrusion of early alkaline bodies fault movement on the ivanhoe lake fault zone or late stage uplift of the ksz

formation of planar deformation features pdfs in zircon during coseismic faulting and an evaluation of potential effects on u pb systematics abstract zircons from pseudotachylyte and cataclasite veins in the svarthumlevatnet metagabbro sw norway are faulted brecciated and display multiple sets of planar deformation features pdfs that we assign to coseismic deformation in the middle crust during caledonian continent collision the zircons give a u pb upper intercept age of 1507 4 ma interpreted as a minimum age of the gabbro and a lower intercept age of 968 31 ma likely indicating the time of granulite facies metamorphism but they do not record the caledonian coseismic faulting even when the fault planes are healed by thin veins of low u zircon the work indicates that pdfs are not exclusive to meteorite impacts but may also develop during seismic faulting

3d reverse time migration using the acoustic wave equation an experience with the seg eage data set kirchhoff is the most commonly used 3d prestack migration algorithm because of its speed and other economic advantages but it uses a high frequency ray approximation to the wave equation and therefore has difficulties in imaging complex geologic structures where multipathing occurs e g beneath rugose horizons such as faulted salt domes where traveltime calculations become difficult

palaeomagnetic and rock magnetic investigations of the sipoo subjotnian quartz porphyry and diabase dykes southern fennoscandia abstract the sipoo quartz porphyry dyke swarm u pb zircon age 1 63 ga in southern finland carries an intermediate to high coercivity remanent magnetization a n d 22 2 i 1 8 k 34 2 95 13 3 n 5 dykes which is regarded as primary the sipoo diabase dykes emplaced slightly before the granite porphyries yield a highly scattered antiparallel direction a r d 198 0 i 6 5 k 6 2 95 40 1 n 4 dykes isolated in intermediate to high coercivities based on positive contact test results remanence a r is primary in the diabases the best preserved diabase dyke as determined by petrographic and bulk magnetization properties carries both the a r magnetization and the a n magnetization as a secondary component in some samples the most altered diabase dyke is almost completely overprinted by a n the overprinting has taken place as a result of hydrothermal alteration and formation of new magnetite during the emplacement of quartz porphyry dykes and rapakivi granite the quartz porphyries and diabases carry mixed sd and md magnetic grain sizes the large md grains being responsible for a relatively large present earth s field pef magnetization in addition a high coercivity magnetization b d 23 9 i 52 2 k 215 8 95 6 3 n 4 dykes presumably a chemical overprint has been isolated in the quartz porphyries the b magnetization is interpreted to be either an intermediate direction between a n and pef with no geological significance or to represent a separate reactivation of the crust at about 1 32 ga ago

migration by extrapolation of time dependent boundary values migration of an observed zero offset wavefield can be performed as the solution of a boundary value problem in which the data are extrapolated backward in time this concept is implemented through a finite difference solution of the two dimensional acoustic wave equation all depths are imaged simultaneously at time 0 the imaging condition and all dips right up to vertical are correctly migrated numerical examples illustrate this technique in both constant and variable velocity media

paleomagnetism of ordovician alkalic intrusives and host rocks from the pedernal hills new mexico positive contact test in remagnetized rocks jackson m van der voo r and geissman j w 1988 paleoma etism of ordovician alkalic intrusives and host rocks from the pedemal hills new mexico positive contact test in remagnetized rocks tectonophysics 147 313 323 a set of thin dikes from central new mexico dated at 469 7 ma rb sr loring and armstrong 1980 have yielded a virtual geomagnetic pole which lies on the late paleozoic segment of the north american apparent polar wander path the remanence of the dikes appears to be a product of late paleozoic hydrothermal alteration paradoxically however the magnetization of the host rocks is most simply explained in terms of a positive contact test samples collected between 0 2 and 0 5 dike widths from the contact contain a component of remanence parallel to the magnetization in the dikes with unblocking temperatures which decrease with distance from the dikes host rocks from a distance of more than 1 dike width show no evidence of the characteristic dike magnetization there are two possible resolutions of this paradox 1 the magnetization of the host rocks is secondary despite the apparent positive contact test and is a product of hydrothe al fluid migration through the dikes or along the contact zones or 2 the magnetization of the dikes is primary but not representative of the ordovician paleofield for north america possible reasons for inaccurate representation include a incomplete averaging of secular variation b tectonic rotation with respect to the stable craton or c erroneous age determination for the rocks we argue that explanation 1 is the most likely

evidence for dune reactivation from gpr profiles on the maputaland coastal plain south africa the maputaland area of northeastern south africa is characterized by extensive dune fields which developed during polyphase reworking of regional aeolian cover sand from the mid pleistocene to the holocene extended parabolic dunes many preserved only as wind rift trailing limbs as well as areas of sinuous crested dunes hummocky dune systems and the high composite accretionary coastal barrier dune cordon are the dominant dune forms there are few natural sections exposing the stratigraphic succession and unequivocal relative age relationships between dune systems are uncommon a ground penetrating radar gpr survey of dunes and representative aeolian sand stratigraphic units was undertaken in order to investigate the internal structure of the different dune forms and identify stratigraphic relationships between buried sedimentary units the gpr profiles revealed that the trailing limbs of almost all the parabolic dunes that were surveyed comprise stacked sand units separated by low angle reflections interpreted as bounding surfaces which accumulated through polyphase vertical accretion most extended parabolic dunes are aligned north south and the upper parts of the dunes are characterized by inclined reflections in gpr profile interpreted as large scale sets of cross stratification with apparent dips toward the west a hummocky dune revealed cross stratified aeolian sand superimposed on a truncated dune form and probably formed through deflation of pre existing dunes using 100 mhz and 200 mhz antennae it is clear that gpr is capable of imaging very fine sedimentary structures and buried erosional surfaces in the homogeneous aeolian sand of maputaland at some of the sites investigated the buried sand units identified were sampled by hand augering for infrared stimulated luminescence dating the age determinations on these samples suggest that vertical accretion of up to 7 m of sand occurred intermittently over variable time scales up to 25 000 years on some parabolic dune limbs during the late pleistocene in some complex dunefields adjacent dunes were mobilized at different times suggesting that remobilization was localized the implications of the complex internal structure and vertical accretion of extended parabolic dunes are discussed in the context of changes in vegetation cover and water table due to seasonal and short term cyclical climate variations as well as long term climate change patterns during the last glacial cycle and the holocene

magnetic effects of hydrothermal alteration in porphyry copper and iron oxide copper gold systems a review abstract magnetic anomaly patterns can be used as a tool for mapping lithology metamorphic zones and hydrothermal alteration systems as well as identifying structures that may control passage of magmas or hydrothermal fluids associated with mineralisation reliable geological interpretation of mineralised systems requires an understanding of the magmatic metamorphic and hydrothermal processes that create alter and destroy magnetic minerals in rocks predictive magnetic exploration models for porphyry copper and iron oxide copper gold iocg deposits can be derived from standard geological models by integrating magnetic petrological principles with petrophysical data deposit descriptions and modelling of observed magnetic signatures of these deposits even within a particular geological province the magnetic signatures of similar deposits may differ substantially due to differences in the local geological setting searching for look alike signatures of a known deposit is likely to be unrewarding unless pertinent geological factors are taken into account these factors include the tectonic setting and magma type composition and disposition of host rocks depth of emplacement and post emplacement erosion level depth of burial beneath younger cover post emplacement faulting and tilting remanence effects contingent on ages of intrusion and alteration and metamorphism because the effects of these factors on magnetic signatures are reasonably well understood theoretical magnetic signatures appropriate for the local geological environment can qualitatively guide exploration and make semiquantitative predictions of anomaly amplitudes and patterns the predictive models also allow detectability of deposit signatures to be assessed for example when deposits are buried beneath a considerable thickness of nonmagnetic overburden are covered by highly magnetic heterogeneous volcanic rocks or there is a strong regional magnetic gradient this paper reviews the effects of hydrothermal alteration on magnetic properties and magnetic signatures of porphyry copper and iron oxide copper gold systems and presents examples of predictive magnetic exploration models and their predicted signatures in various geological circumstances

petrophysics and mineral exploration a workflow for data analysis and a new interpretation framework abstract as mineral exploration seeks deeper targets there will be a greater reliance on geophysical data and a better understanding of the geological meaning of the responses will be required and this must be achieved with less geological control from drilling also exploring based on the mineral system concept requires particular understanding of geophysical responses associated with altered rocks where petrophysical datasets of adequate sample size and measurement quality are available physical properties show complex variations reflecting the combined effects of various geological processes large datasets analysed as populations are required to understand the variations we recommend the display of petrophysical data as frequency histograms because the nature of the data distribution is easily seen with this form of display a petrophysical dataset commonly contains a combination of overlapping sub populations influenced by different geological factors to understand the geological controls on physical properties in hard rock environments it is necessary to analyse the petrophysical data not only in terms of the properties of different rock types it is also necessary to consider the effects of processes such as alteration weathering metamorphism and strain and variables such as porosity and stratigraphy to address this complexity requires that much more supporting geological information be acquired than in current practice the widespread availability of field portable instruments means quantitative geochemical and mineralogical data can now be readily acquired making it unnecessary to rely primarily on categorical rock classification schemes the petrophysical data can be combined with geochemical petrological and mineralogical data to derive explanations for observed physical property variations based not only on rigorous rock classification methods but also in combination with quantitative estimates of alteration and weathering to understand how geological processes will affect different physical properties it is useful to define three end member forms of behaviour bulk behaviour depends on the physical properties of the dominant mineral components density and to a lesser extent seismic velocity show such behaviour grain and texture behaviour occur when minor components of the rock are the dominate controls on its physical properties grain size and shape control grain properties and for texture properties the relative positions of these grains are also important magnetic and electrical properties behave in this fashion thinking in terms of how geological processes change the key characteristics of the major and minor mineralogical components allows the resulting changes in physical properties to be understood and anticipated

geophysical inversion contributions to mineral exploration lessons from the footprints project magnetic and gravity inversions are used to create 2d or 3d models of the magnetic susceptibility and density respectively using potential field data unconstrained inversions generate an output

late stage oxide growth associated with hydrothermal alteration of the western granite isle of rum nw scotland 1 the paleogene western granite isle of rum nw scotland represents a westward tilted shallow level felsic intrusion associated with the early growth stages of the classic early paleogene rum igneous centre rock magnetic data reveal an east to west variability in magnetic properties across the intrusion that is also reflected in petrographic and geochemical observations it is argued that the subtle intraplutonic variations in oxide grain size and composition observed in the western granite might be a common feature of shallow epizonal igneous intrusions as these mineralogical differences are not easily detectable without detailed rock magnetic study this research underscores the need for comprehensive rock magnetic studies when interpreting the postemplacement history of shallow level plutons paleomagnetic data indicate that the eastern part of the intrusion represents the shallower part of the exposed intrusion as further evidenced by roof pendants of lewisian gneiss and abundant drusy miarolitic cavities indicative of shallow emplacement in contrast the western part represents a deeper 900 m part of the intrusion as evidenced by the lack of roof pendants and existence of only minor drusy cavities rock magnetic data indicate that the dominant magnetic phase is low ti titanomagnetite with some titanomaghemite magnetic grain sizes range from pseudosingle domain in the west and multidomain in the east with a slight increase in ti content of the titanomagnetite phases in the east as revealed by curie point estimates we interpret these data to indicate that late stage subsolidus hydrothermal deuteric fluids associated with emplacement of the stage 2 rum layered suite produced secondary growth of fe ti oxide mineral phases along silicate grain boundaries in the eastern part of the intrusion the secondary oxide growth resulted in a slightly coarser magnetic grain size fraction and an increase in ti content of the titanomagnetite grains the deeper structural levels of the western part of the intrusion and its distance from the contact of the rum layered suite inhibited secondary oxide growth and thus this part of the intrusion preserves a primary magmatic oxide phase of a smaller magnetic grain size and near pure magnetite chemistry

interpretation of magnetic susceptibility a new approach to geophysical evaluation of the degree of rock alteration magnetic susceptibility measurements on cores from boreholes in the eye dashwa lakes pluton an archean granitic pluton near atikokan ontario give a quantitative evaluation of the alteration leve

ground penetrating radar for environmental applications abstract ground penetrating radar gpr is a near surface geophysical technique that can provide high resolution images of the dielectric properties of the top few tens of meters of the earth in applications in contaminant hydrology radar data can be used to detect the presence of liquid organic contaminants many of which have dielectric properties distinctly different from those of the other solid and fluid components in the subsurface the resolution approximately meter scale of the radar imaging method is such that it can also be used in the development of hydrogeologic models of the subsurface required to predict the fate and transport of contaminants gpr images are interpreted to obtain models of the large scale architecture of the subsurface and to assist in estimating hydrogeologic properties such as water content porosity and permeability its noninvasive capabilities make gpr an attractive alternative to the traditional methods used for subsurface characterization

characterization of the shallow structures of active fault zones using 3 d ground penetrating radar data 1 where they can be correlated with geological exposures and trenches 3 d ground penetrating radar gpr data can contribute critical subsurface information to paleoseismic investigations because active faults are typically characterized by complicated near surface structures that vary with the styles of faulting and the types of rock that are ruptured gpr data can be difficult to interpret we have acquired 3 d gpr data sets across three active fault zones within new zealand that have different deformation styles the strike slip wellington fault zone reverse faults of the ostler fault zone and normal faults of the maleme fault zone to improve our interpretation of the processed gpr volumes we employed two suites of geometric attributes the first suite was computed using a coherence based algorithm it provided estimates of the coherency azimuth and dip of reflections the second suite quantified the volumetric textures of reflections which allowed different reflection facies to be defined objectively we have demonstrated how some attributes were more successful at visualizing certain structural or depositional characteristics than others for example the coherency attribute was an excellent tool for highlighting normal faults within volcanic deposits of the maleme fault zone whereas the texture based attributes were most useful for discriminating between the gravel and metasediment units juxtaposed by the wellington fault zone our gpr data sets and associated attribute volumes showed details of near surface fault geometry that were not obvious from surface mapping and they revealed evidence of off fault deformation gravitational collapse and topple structures

interpreting regional 3d fault networks from integrated geological and geophysical data sets an example from the guichon creek batholith british columbia abstract the effects of fault processes on rocks commonly include a lowered magnetic susceptibility and an increased predisposition to erosion we present a workflow that uses these characteristics of faults and geological observations to interpret a 3d fault network the location of faults on the topographic surface is first interpreted by a multi layer lineament mapping method that includes geological and geophysical data sets we then demonstrate how magnetic intensity data can be used to estimate the dip of fault related magnetic anomalies by performing 2d inverse modeling along profiles extracted from a magnetic intensity grid the accuracy of the method is assessed by modeling the dip of low magnetic anomalies of known geometry created in a synthetic 3d magnetic susceptibility model modeled dips are consistently accurate to better than 5 for input dips 60 a requirement of the method however is that the magnetic susceptibility contrast between the background field and the magnetic anomaly must be 75 for the anomaly to be accurately modeled comparison between fault orientations modeled from magnetic data and measured in the field in the guichon creek batholith confirms that the methodology can be successfully applied to brittle faults in real albeit relatively simple geological environments