structural controls on sulfide mobilization at the high grade flying fox ni cu pge sulfide deposit forrestania greenstone belt western australia the flying fox komatiite hosted ni deposit is located in the forrestania greenstone belt of the yilgarn craton in western australia the host volcanosedimentary succession has been metamorphosed to amphibolite facies and deformation has sheared and dismembered the orebody creating 11 distinct ore shoots the ore shoots are hosted at the base of a komatiite sequence structurally overlying deformed metasedimentary rocks the ni sulfide orebody has undergone six phases of deformation 1 d 1areg e w compression resulted in tilting of the stratigraphy 2 d 1bff continued e w compression resulted in coaxial flattening along the footwall sedimentary rock sulfide komatiite contact and the basalt hanging wall sedimentary rock contact 3 d 2ff ene wsw compression resulted in noncoaxial shearing of the d 1bff structures 4 d 3ff ese wnw compression resulted in shallow angle thrusts 5 d 4ff during e w extension normal ductile brittle faults formed by the pooling and dilation of granitic magma along the f 2 structural contact between the footwall sedimentary and komatiite rocks and 6 d 5ff intrusion of a proterozoic dolerite dike during n s extension accompanied by late stage brittle normal faulting during deformation the ni sulfides reverted to monosulfide solid solution mss and were mechanically relocated along the footwall sedimentary rock komatiite contact offset into the footwall sedimentary rocks and entrained in the granitic magma creating atypical granite hosted sulfides the ni sulfides were mobilized up to 5 m away from the ultramafic rocks during the d 1 and d 2 events however subsequent dismemberment of the original orebody into separate ore shoots along flat lying faults during the d 3 event led to offsets of up to 300 m the detailed structural analysis of the flying fox deposit has shown that restoration of the lithostratigraphy along known faults can be used to define the volcanic stratigraphy including primary ni ore horizons this information can be used as a guide to the location of concealed extensions to known ore shoots or completely unknown orebodies at depth or along strike

structural analysis and interpretation of the surface deformations of the el asnam earthquake of october 10 1980 the el asnam earthquake of october 10 1980 represents the major seismotectonic event of these last decades in the west mediterranean area it has induced a large amount of surface breaks this earthquake reveals the importance of compressional phenomena that characterize nowadays the tectonics of north africa the tectonic analysis of surface rupture shows the complexity of the deformation mechanism the principal mechanism consists of the activation of a nw se trending thrust fault accompanied with a left lateral motion and with an intense deformation of the northwestern overthrusting block an accurate description of these deformations shows that for a large part the breaks geometry depends closely on the substratum structure finally the analysis of the dislocations on irrigation ducts just above the fault traces allowed a quantitative study of the deformation

precise u pb zircon ages for the molson dyke swarm and the fox river sill constraints for early proterozoic crustal evolution in northeastern manitoba canada precise u pb zircon ages have been obtained for samples from the molson dyke swarm and the fox river sill in ne manitoba canada the ages determined for the cross lake and cuthbert lake dykes are 1 883 7 1 5 1 7and 1 883 2 ma respectively and are in excellent agreement with the 1 882 9 1 4 1 5ma age obtained for the fox river sill these results support the contention that the emplacement of the fox river sill and the molson dyke swarm was contemporaneous and also demonstrate the potential for correlating mafic igneous activity in widely spaced localities the timing of early proterozoic mafic magmatism in the western superior province appears to be synchronous with igneous activity in other parts of the circum superior belt and in the trans hudson orogen to the west the emplacement of the molson dyke swarm at 1 883 ma indicates a 700 ma interval of quiescence between the final igneous activity that is recorded in the archean basement and dyke intrusion the presence of deformed equivalents of molson dykes in the thompson nickel belt indicates that the intense deformation in this belt occurred sometime after 1 883 ma

relative contribution of magmatic and post magmatic processes in the genesis of the thompson mine ni co sulfide ores manitoba canada abstract the ni co pge sulfide deposits of the thompson nickel belt tnb in northern manitoba canada are part of the fifth largest nickel camp in the world based on contained nickel past production from the tnb deposits is 2500 kt ni the thompson deposit is located on the eastern and southern flanks of the thompson dome structure which is a re folded nappe structure formed during collision of the trans hudson orogen with the canadian shield at 1 9 1 7 ga the thompson deposit is almost entirely hosted by p2 member sulfidic metasedimentary rocks of the paleoproterozoic ospwagan group variably serpentinised and altered dunites peridotites and pyroxenites contain disseminated sulfides and have a spatial association with sediment hosted ni sulfides which comprise the bulk of the ore types these rocks formed from rift related komatiitic magmas that were emplaced at 1 88 ga and subsequently deformed by boudinage thinning folding and stacking disseminated sulfide mineralization in the large serpentinised peridotite and dunite intrusions that host the birchtree and pipe ni co sulfide deposits typically has 4 6 wt ni in 100 sulfide the disseminated sulfides in the less abundant and much smaller boudinaged serpentinised peridotite and dunite bodies associated with the thompson deposit have 7 10 wt ni in 100 sulfide the majority of thompson mine sulfides are hosted in the p2 member of the pipe formation which is a sulfidic schist developed from a shale prololith the mineralization in the schist includes both low ni tenor 13 wt ni in sulfide define a systematic trend that mirrors the configuration of the second order doubly plunging f3 structures on the flanks of the dome although moderate to high ni tenor mineralization is sometimes localized in fold hinges more typically the highest ni tenor mineralization is located on the flanks of the fold structures there is no indication of the mineralogical and geochemical signatures of sedimentary exhalative or hydrothermal processes in the genesis of the thompson ores the primary origin of the mineralization is undoubtedly magmatic and this was a critical stage in the development of economic mineralization variations in metal tenor in disseminated sulfides contained in ultramafic rock indicate a higher magma sulfide ratio in the thompson parental magma relative to birchtree and pipe the variation in ni tenor of the semi massive and massive sulfide broadly supports this conclusion but the variations in metal tenor in the thompson ores was likely created partly during deformation the sequence of rocks was modified by burial and loading of the crust d2 events to a peak temperature of 750 c and pressure of 7 5 kbar the third major phase of deformation d3 was a sinistral transpression d3 event which generated the dome and basin configuration of the tnb these conditions allowed for progressive deformation and reformation of pyrrhotite and pentlandite into monosulfide solid solution as pressure and temperature increased this process is termed sulfide kinesis separation of the ductile monosulfide solid solution from granular pentlandite would result in an effective separation of ni during metamorphism and the monosulfide solid solution would likely be spread out in the stratigraphy to form a broad halo around the main deposit to produce the low ni tenor sulfide reformation of pentlandite and pyrrhotite after the peak d2 event would explain the broad footprint of the mineral system the effect of the d3 event at lower pressure and temperature would have been to locally redistribute deform and repeat the lenses of sulfide the understanding of the relationships between petrology stratigraphy structure and geochemistry has assisted in formulating a predictive exploration model that has triggered new discoveries to the north and south of the mine and provides a framework for understanding ore genesis in deformed terrains and the future exploration of the thompson nickel belt

modelling hanging wall accommodation above rigid thrust ramps abstract experimental models are used to study the role of material rheology in hanging wall accommodation above rigid flat ramp flat thrust footwalls the deformation in the hanging wall was accomplished by forwards sliding along a rigid basal staircase trajectory with a variable ramp angle ranging from 15 to 60 we model different ramp angles to examine hanging wall accommodation styles above thrust ramps of overthrust faults ranging from 15 to 30 as well as above pre existing normal faults ranging from 45 to 60 for the hanging walls we used stratified frictional sand and viscous silicone putty materials in this paper we study three types of models type 1 models represent purely frictional hanging walls where accommodation above thrust ramps was by layer parallel thickening and by generating a series of back thrusts type 2 and 3 models represent stratified frictional viscous hanging walls in these models accommodation was by a complex association of reverse and normal faults mainly controlled by the rheological anisotropy as well as by the ramp inclination angle in type 2 models the silicone covered only the lower flat while in type 3 models it also covered the rigid ramp for 30 in type 2 models and 45 in type 3 models the viscous layer inhibited the development of back thrusts in the frictional hanging wall instead the silicone thickened to develop a ductile ramp for values higher than 30 in type 2 models and 45 in type 3 models back thrusts develop in response to the bulk compression the experiments simulate many structures observed above natural thrust ramps with 30 and pre existing normal faults with 45 the models emphasise the importance of a basal ductile layer which allows the hanging wall to step up over the rigid ramp by building up its own ductile ramp the models also emphasise that foreland directed normal faulting can develop at a thrust front in the case that the vertical stress due to gravity exceeds the horizontal stress due to end loading within a thrust wedge

dynamics of the polish and eastern slovakian parts of the carpathian accretionary wedge insights from palaeostress analyses the arcuate outer carpathian accretionary wedge formed in front of the east alpine carpathian pannonian alcapa megablock during the eocene sarmatian the wedge accreted sediments of the subducting remnants of the carpathian flysch basin a large oceanic tract left in front of the alpine orogen the palaeostress data for the orogenic hinterland particularly the data related to the early miocene extension that was expanding towards the ne combined with coeval subduction related volcanism that was expanding towards the ne indicate that the uneven roll back of the subduction zone was the main mechanism controlling the development of the northern west carpathian arc the palaeostress data for the tertiary accretionary wedge from the same time period are characterized by outward fanning 1 trajectories that changed gradually during the wedge development in contrast the palaeostress data for the hinterland are characterized by preferred directional stress events that changed abruptly during the wedge development these palaeostress results are in accordance with the behaviour of the wedge and the hinterland as the wedge behaved as a weak continuum and the hinterland behaved as a block mosaic with weak boundaries the fault traces of the northern west carpathian arc converge to both ends of the arc and suggest that the pre existing basin was the factor that controlled the arc location these fault trace patterns are asymmetric indicating a slightly oblique overall convergence in a ne sw direction in accordance with this convergence the palaeostress data for the accretionary wedge indicate that the western part of the wedge which is characterized by nw se oriented maximum principal compressional stress 1 was undergoing sinistral transpression meanwhile the eastern part which is characterized by ne sw oriented 1 was undergoing compression apparently the dynamics of the accretionary wedge was further influenced by the shape of an elongated ne sw trending alcapa megablock which was located behind the wedge and advanced in the direction of the general early miocene convergence during the most pronounced stages of the wedge development this megablock served as the local indenter as its strength surpassed that of the accretionary wedge located to its front further dynamic complexities were added because of the complex shape of the magura unit which was located in the most proximal portion of the wedge and was stronger than the units in front of it wedge outcrops indicate that the large scale shortening which is characterized by the development of detachments and ramps was preceded by an initial layer parallel shortening this is indicated by scaly fabrics and minor reverse faults that rotated into locked positions during the later accretion several outcrops with a wedge detachment fault indicate that there was a relatively low amount of friction during its development the decollement zone is several hundred metres thick and shows evidence of transient fluid flow that was driven by pressure gradients this is documented by frequent hydrofracturing sandstone dykes and fibrous veins that opened against the weight of the whole wedge all of which indicate cycles of higher pore fluid pressures that lowered the basal friction

thrust fault mechanics and origin of a frontal ramp several features of thrust sheets in nonmetamorphic and relatively low grade metamorphic terrains indicate that the modes of faulting included both gradual and stick slip types of motion a first order quantitative analysis is made of the mechanics of this type of faulting in the analysis part of a wedge shaped thrust belt slips forward over a fault area of length l and unit width w producing a strain concentration in subhorizontal strata at the front of the growing thrust where a frontal ramp develops by shear fracturing equations for net slip x and the conditions for ramping are evaluated with limit equilibrium principles and coupled oscillator theory the quantitative analysis takes into account anisotropy resulting from contrasts in competency and facies changes a special case solution for maximum net slip associated with stick slip is lw ki 1 cos ot o 12 1 cos 1t where is the stress drop ki are spring constants of the strata 0 and 1 are natural frequencies of the system and t evaluated from another equation is the time for net slip the spring constants and natural frequencies can be evaluated from seismic and stratigraphic data a preliminary solution for piggy back thrusting indicates that ramp spacing can be systematic and that it depends upon the thickness of the deforming package the elastic parameters of the deforming package the slope of the topographic surface and the stresses along the trailing edge of the package

3d geometry of range front blind ramp and its effects on structural segmentation of the southern longmen shan front eastern tibet abstract a 3d fault morphology model has been constructed from seismic profiles covering the piedmont of the southern longmen shan lms eastern margin of the tibetan plateau it reveals a spatial correlation between an 3 5 km high geometrical bump on the range front blind ramp rfbr and the gap between the 2008 m w 7 9 wenchuan and 2013 m w 6 6 lushan earthquakes sandbox modeling is then used to probe the effects of the geometrical irregularity of the rfbr on fault behaviors and the lms range front deformation sand wedges are designed to thrust over artificial blind ramps analogous to the thrusting of the lms orogenic wedge toward the sichuan basin through the rfbr the experiments reproduce the first order deformation features presented in the southern lms range front confirming that along strike geometrical variations of the rfbr have induced the segmentation of both fault motion and the range front deformation their results also suggest that the gap between the wenchuan and lushan earthquakes is located directly within the structural transition zone originating from the geometrical bump on the rfbr additionally there is a duplex structure occurring in the hanging wall of the geometrical bump which localizes significant shear strain with progressive shortening and represents a fracture zone corresponding to the observed geophysical anomaly low seismic velocity underneath the seismic gap it is likely that this fractured body protected the gap from the ruptures of the wenchuan and lushan earthquakes

computerized x ray tomography analysis of sandbox models examples of thin skinned thrust systems computerized x ray tomography applied to analog sandbox experiments performed in a normal gravity field makes possible the analysis of the kinematic evolution as well as the three dimensional geometry of models that simulate tectonic deformations most of the plastic or viscous analog materials generally used in a normal gravity field for such models have x ray attenuations compatible with medical scanner images models using soft cohesionless granular materials were studied faults in granular materials corresponding to dilatant zones with lower by 30 50 x ray attenuation are thus clearly visible in the tomography images kinematic analysis was done on imbricate thrust propagation in materials with an internal friction angle of 30 thrust propagation is controlled mainly by a triangular pop up structure resulting from the nucleation of two conjugate thrusts at the basal decollement the pop up structure is created immediately in front of the previous thrust three dimensional geometry analysis was tested on lateral ramps parallel to the transport direction lateral ramps were induced by changing the frictional boundary conditions at the bottom of the model though the lateral ramps strike almost parallel to the transport direction their dip angle is comparable to the dip angle of frontal ramps

global trends and environmental issues in nickel mining sulfides versus laterites abstract nickel ni is an important metal in modern infrastructure and technology with major uses in stainless steel alloys electroplating and rechargeable batteries economic ni resources are found in either sulfide or laterite type ores although the majority of economic resources are contained in laterite ores the bulk of historic ni production has been derived from sulfide ores since laterites require more complex processing to meet future demand for ni there is an increasing amount of ni being mined from laterite ores leading to increasing energy and greenhouse gas emission costs for ni production in many of the major ni fields of the world environmental impacts have also been significant especially in sudbury in canada and the taimyr and kola peninsulas in russia a major gap in the literature remains on historical trends in global ni mining especially with respect to primary aspects such as production known economic resources and ore grades and type this paper compiles and analyses a wide array of data on global ni mining presenting a coherent picture of major historical trends and the current industry configuration the paper includes unique historical data sets for major ni fields especially the sudbury basin and thompson fields in canada and the kambalda field in australia by understanding these critical mega trends in the ni industry it is possible to better understand unfolding global issues such as environmental impacts greenhouse gas emissions climate change and potential industry responses and whether peak nickel is a viable concept and the implications these issues have for ni production and demand the data trends and issues synthesized in this paper therefore provide a compelling picture of the ni industry and should help to inform current research and policy directions

an introduction to remobilization information from ore body geometry and experimental considerations abstract mobilization involves the translocation and concentration of originally dispersed metallic constituents remobilization is the translocation resulting in modified concentration and distribution of pre existing metalliferous concentrations mobilization and remobilization proceed by chemical liquid state mechanical solid state and mixed processes the paradox of remobilization is that the more complete the process the more difficult becomes substantiation regional metamorphic remobilization is commonly invoked to explain the morphology of supposedly once stratiform massive sulphides and their feeder and alteration systems analysis of the principal dimensions of stratiform massive sulphides in non metamorphic and regionally metamorphosed deposits shows that whereas comparative morphology may be a guide to remobilization it does not constitute proof similarly feeder and alteration morphology suggests that geometric analysis may be of value in establishing mechanical remobilization but the more complex alteration distributions which exist could well lead to misinterpretation in highly deformed terranes ore composition internal structure and zonation influence the ore s capacity to be remobilized mechanical remobilization requires rheological divergence between sulphides and their host rocks experimental deformation of dry sulphides shows that most common sulphides pass through the brittle ductile transition before entering the field of regional metamorphism but that the strength order of sulphides silicates and carbonates remains dynamic until all are undergoing steady state flow within this context experimental strength orders support galena weakest experimental considerations indicate that during diagenesis and early prograde metamorphism the brittle ductile transition will result in widely distributed micro and mesoscale mechanical remobilization nevertheless there is usually insufficient gross behavioural contrast to engender discordant macroscale remobilization possible exceptions particularly in relation to thrusting are outlined but we conclude that macroscale mechanical remobilization during the brittle ductile transition is an uncommon occurrence experimental data were also examined relative to subsequent prograde to peak metamorphism and strength contrasts during decaying and retrogressive metamorphism because the largest strength difference between sulphides and the host sequence is in the lower part of the 350 650 c metamorphic range we contend that macroscale mechanical remobilization is more probable during prograde metamorphism in the 350 500 c interval we similarly believe that macroscale mechanical remobilization is more likely during deformation accompanying retrogressive cooling in the range 500 350 c and we note that it may also result from deformation exploiting the brittle ductile contrasts between silicate and sulphide rocks during the water deficient non retrogressive metamorphic decay cycle chemical mobilization and remobilization require the dissolution of base metals by metamorphic fluids the compositions of hydrothermal low grade metamorphic fluids and their precipitates in active geothermal systems show that the fluids can dissolve transport and form concentrations of base and precious metals similarly fluid inclusion compositions from low to medium grade metamorphic rocks show that such fluids can dissolve a few ppm of base metals in both cases low salinities and low dissolved base metal contents raise doubts over whether such metamorphic fluids can form ore grade base metal concentrations we submit that they can metamorphogenesis is favoured by high initial base metal concentrations preferential dissolution of sulphides over silicates and fluid dominated metamorphism as found in a multiple pass fluid system preferential dissolution of sulphides and the need for high water rock ratios are supported by theoretical considerations experimental work on mafic felsic and sedimentary source rocks and field based studies in the context of mobilization the work strongly implies that prograde metamorphic devolatilization and a mobile fluid phase have substantial ore forming capability retrograde revolatilization does not remobilization is more complex although favoured by high initial metal concentrations dissolution is inhibited by the low permeability of homogeneous low silicate massive sulphides and the consequent peripheral fluid channeling it is conversely enhanced by fine grainsize in discordant fluid focussing retro grade shear zones in all cases for remobilization to form a new ore body both fluid flow and the precipitation process must be focussed and efficient

ancient synsedimentary structural control on thrust ramp development an example from the northern apennines italy the umbria marche sabina foreland fold and thrust belt northern apennines italy provides excellent test cases for the hypothesis of ancient syndepositional structural features controlling thrust ramp development the sedimentary cover late triassic to miocene in age is made of platform and pelagic carbonates whose deposition was controlled by significant synsedimentary extension normal faulting mainly during the jurassic and the late cretaceous palaeogene determined sensible lateral thickness variations within the relative sequences by late miocene the sedimentary cover was detached from its basement along a mainly evaporitic horizon and was deformed by means of eastward verging folds and thrusts in order to locate the points where thrust ramps branch off the basal detachment both line length and equal area techniques were used in the construction of a balanced cross section through three major fault related folds in southeastern umbria the nucleation of thrust ramps was controlled by the occurrence of jurassic and cretaceous palaeogene synsedimentary normal faults these interrupted the lateral continuity of the evaporitic unit the late triassic anidriti di burano fm at the base of the sedimentary cover and acted as obstacles to the eastward propagation of the thrust system giving rise to major folds which originated from tip line folding processes therefore the inferred relationships between ancient normal faults and late thrusts indicate that synsedimentary tectonic structures and the related lateral stratigraphic variations can be envisaged as mechanically important perturbations which effectively control the nucleation and development of thrust ramps

three dimensional geometry and kinematics of experimental piggyback thrusting the three dimensional geometry and kinematics of piggyback stacks of imbricate thrust sheets are illustrated and discussed using a single model shortened in a squeeze box strike parallel geometric elements simulated include lateral ramps eyed sheath folds splays and thrust thrust interference fine details of these structures were exposed by eroding a shortened wedge of sand using a newly developed vacuum eroding technique a kinematic analysis of the model shows a stepwise increase in imbricate thrust spacing and or a decrease in rate of nucleation of imbricate thrusts in the direction of thrust transport despite the steady forward advance of a rear wall the piggyback wedge accreted episodically recording different strain domains in longitudinal cross sections strain partitioning in single layers by bed length balancing showed an increase in layer shortening with volume loss and a corresponding decrease in imbricate thrusting and ramp folding with depth

thrust surface geometry implications for thrust belt evolution and section balancing techniques abstract the application of modern concepts of thrust tectonics to orogenic belts has yielded many detailed restorable sections thrusts generally restore with a staircase geometry onto the undeformed stratigraphic template since the work of rich 1934 it has been generally assumed that thrusts have propagated with a staircase trajectory and that hangingwall structures result from the movement of the thrust sheet up footwall ramps however thrusts often cut through previously folded strata with a smooth trajectory smooth trajectory thrusts can be identified from footwall geometry and strain state once a smooth trajectory thrust has been identified it is insufficient to produce a balanced deformed section and its restored counterpart sequential balanced sections must be constructed reversing the deformation history the restoration of thrusts to a staircase trajectory has no mechanical significance as the thrust is merely acting as a marker if restored back beyond the time at which it propagated thrust ramps are not necessarily actual steps in the thrust surface they are often just zones where the thrust cuts through bedding in a smoothly curving trajectory ductile deformation in thrust belts can reduce bed length at depth thus removing the need for structures which are necessary to preserve constant bed lengths ductile deformation in the internal zones of orogenic belts renders the construction of balanced sections in these zones highly problematical

modelling the geometry of coulomb thrust wedges internal geometry and detachment of coulomb thrust wedges is examined in a combined gravity and pressure force field under various boundary conditions and coulomb parameters frontally buttressed sand wedges accreted with narrow tapers above soles with negligible friction in these models serial imbricates stepped up in conjugate sets which operated synchronously or serially with increases in sole friction model coulomb wedges accreted in piggyback style with enhanced taper but narrower spacing of imbricates in this mode flat topped box fold anticlines nucleated at the frontal tip of a sole thrust prior to the fore limb failing as a ramp the initial ramp thrusts subsequently rotated and steepened to acquire concave upwards listric geometry when cohesion was a significant component of strength and the sand grains interlocked thoroughly ramp climb during piggyback thrusting occurred through the generation of a stack of backthrusts the taper of cohesionless sand wedges which lack any length scale was consistent with the critical cohesionless coulomb wedge taper in contrast the taper of experimental cohesive sand wedges which are scale dependent was consistent with the theoretical cohesive coulomb narrow taper only when the cohesive length scale was lr sr rar 10 6 this was constrained by comparing geometry of cohesive sand wedges shortened at different body force per unit mass

alternative model of thrust fault propagation a widely accepted explanation for the geometry of thrust faults is that initial failures occur on deeply buried planes of weak rock and that thrust faults propagate toward the surface along a staircase trajectory we propose an alternative model that applies gretener s beam failure mechanism to a multilayered sequence invoking compatibility conditions which demand that a thrust propagate both upsection and downsection we suggest that ramps form first at shallow levels and are subsequently connected by flat faults this hypothesis also explains the formation of many minor structures associated with thrusts such as backthrusts wedge structures pop ups and duplexes and provides a unified conceptual framework in which to evaluate field observations

the role of salt in fold and thrust belts davis d m and engelder t 1985 the role of salt in fold and thrust belts in n l carter and s uycda editors collision tectonics deformation of continental lithosphere tectonophysics 119 67 88 the style of deformation in thin skinned fold and thrust belts is critically dependent upon the resistance to sliding along the detachment between the mass of deforming sediments and the underlying rocks evaporites can provide an extremely weak horizon within which a basal detachment can form and along which only a relatively small shear traction can be supported fold and thrust belts that form atop a salt layer such as the appalachian plateau the franklin mountains in northwestern canada and the jura of the alps among others share several readily observable characteristics as predicted by a simple mechanical model for fold and thrust belts a detachment in salt permits a thrust belt to have an extremely narrow cross sectional taper in addition predicted orientations of the principal stress axes over a salt dtcollement are consistent with the commonly observed lack of a consistently dominant vergence direction of structures within the thrust belt other common attributes of salt basal thin skinned deformation include the presence of several widely but regularly spaced folds and abrupt changes in deformational style at the edge of the salt basin

lithostratigraphy and geochemistry of the high grade metasedimentary rocks in the thompson nickel belt and adjacent kisseynew domain manitoba implications for nickel exploration exploration for nickel in the thompson nickel belt is focused on specific paragneiss units within the paleoproterozoic sedimentary and volcanic cover succession ospwagan group on the northwestern margin of the archean superior craton these units host ultramafic bodies and all significant nickel deposits in the thompson nickel belt knowledge of the lithostratigraphy is therefore essential for finding the units with the highest potential for the discovery of new nickel deposits this is made practical by a distinctive stratigraphic succession with numerous marker units including metamorphosed quartzite carbonate pelite iron formation and graywacke as summarized in this paper however the sedimentary rocks are generally highly deformed and metamorphosed making the recognition of some units difficult and their sedimentary origin obscure to better recognize the sedimentary protoliths of orehosting and related units a simple plot of sio 2 versus al 2 o 3 is used to estimate the approximate proportions of siliciclastic and chemical sedimentary components this demonstrates that much of the succession which was previously considered to be derived from calcareous and ferruginous chemical sediments is a hybrid containing a substantial siliciclastic component thus explaining the present mineralogy and geochemistry and assisting in the recognition of units at various metamorphic grades extended element plots using the most abundant metapelite unit in the ospwagan group as the normalizing factor show a common provenance for the entire group they also illustrate a clear difference between the ospwagan group and the underlying basements gneiss and allow the ospwagan group to be distinguished from petrographically similar but economically barren younger paragneiss units of the burntwood and grass river groups unlike the ospwagan group the younger units which predominate in the kisseynew domain adjoining the thompson nickel belt were derived mainly from an exotic paleoproterozoic arc related source and therefore have a different geochemical signature this geochemical difference can be utilized in areas of sparse geologic information such as beneath phanerozoic or glacial cover where initial exploration drilling tests new geophysical targets combined litho and chemostratigraphy improve insight into basin evolution which probably occurred on a ca 2 ga passive continental margin or shelf the ca 1880 ma maficultramafic magmatism related to the nickel deposits may have formed in a different tectonic environment possibly in a continental back arc associated with a recently proposed episode of felsic calc alkaline plutonism

possible effects of pre existing basement topography on thrust fault ramping finite element models show that one way in which thrust ramps may arise is through the mechanical interaction between basement and overlying sediments in the simplest case shear coupling between a planar basement sediment causes the differential stresses in the sediments to die out with depth and distance from the applied load for such cases curved thrust faults may result if the strength of the rock is exceeded basement topography may also affect the location and shape of ramps by acting as a stress concentrator by producing a stress shadow and by changing principal stress orientations modeling suggests that whether or not these basement topographic features cause ramping will depend on the height and angularity of the feature as well as the rock types that overlie it under the assumption of linear elasticity and for given boundary conditions the poisson s ratio plays an important role in determining the orientation and magnitude of the principal stresses calculations using experimentally measured poisson s ratios predict that the earliest maximum compressive stress directions should be nearly vertical in the more cratonward portions of thrust belts however the stress directions which are inferred to have occurred earliest in this part of thrust belts are nearly horizontal this suggests that non elastic or ductile processes have an effect on the propagation of thrust faults

sulfide silicate textures in magmatic ni cu pge sulfide ore deposits massive semi massive and sulfide matrix breccia ores abstract much of the value of magmatic ni cu pge sulfide orebodies is contained within massive or semi massive ores that show a wide variety of textural relationships to included or adjacent silicate rocks we identify five mutually gradational textural types 1 pure inclusion free massive sulfide ores 2 sulfide matrix ore breccias of sharp wall soft wall or mixed character 3 emulsion textured ores formed by frozen mixtures of molten silicate and sulfide most commonly developed as melt films at thermal erosion contacts 4 vein hosted sulfides formed at late magmatic or high temperature post emplacement deformation stage close to the brittle ductile transition in the country rocks or host igneous bodies and 5 tectonic durchbewegung breccias formed by mechanical inter shearing of less ductile silicate inclusions and more ductile solid sulfides some deposits the moran shoot at kambalda being the type example record the invasion of country rock footwall by downward or sideways percolating superheated molten sulfide liquid generating vertical sequences of pure massive sulfide emulsion textured ores and finely spaced invasive sulfide veins these are referred to as sulfide melting infiltration fronts and may provide a clue to the mechanism of formation of sulfide rich magmatic ores as whole sulfide matrix ore breccias are particularly well developed in the voisey s bay and aguablanca deposits where they developed by flooding of percolating sulfide melt through the silicate matrix of magmatic intrusion breccias displacing silicate melt the lithology of the silicate or carbonate rock inclusions determines the nature of the inclusion matrix relationships non refractory inclusions typically disaggregate along original grain boundaries to leave coherent inclusions surrounded by clouds of inclusion derived or matrix derived crystals with the low melting silicate component preferentially displaced by sulfide liquid whereas refractory inclusions retain sharp boundaries zonation of inclusions and overgrowths preserves reaction between inclusion and silicate matrix that pre dates invasion of the intrusion breccia by sulfide liquid the process of percolation of dense low viscosity sulfide liquid into pore space and fractures within partially molten or melting silicate rock is a unifying theme that links sulfide matrix ore breccias and emulsion textured ores with distinctive textures in less sulfide rich rocks such as net texture matrix ore texture leopard texture poikilitic net texture and interspinifex ore vein hosted massive sulfides may be emplaced under magmatic conditions where the excess pressure of the sulfide liquid column drives or enhances fracturing of the country rock and injection of sulfide into the cracks such veins are commonly referred to as remobilised a term which may obscure process understanding and should be reserved for cases where tectonic solid state mobilisation of sulfide can be demonstrated on textural and structural grounds the tendency of sulfide liquids to invade country rocks and potentially to drive the propagation of their own magmatic containers may be a critical feedback loop in the development of magmatic sulfide mineral systems

pt and pd mobility in hydrothermal fluids evidence from komatiites and from thermodynamic modelling abstract komatiite host rocks and ores provide a natural laboratory for the study of pt and pd during hydration and carbonation of ultramafic rocks the degree of correlation between pt and pd and of those elements with lithophile elements such as ti in komatiitic rocks and ores is strongly dependent on the magmatic sulfide content of the rock pt and pd are typically very strongly correlated within s poor komatiites and in disseminated ores containing 5 volume or less magmatic sulfides in contrast they are almost completely decoupled in sulfide rich ore samples thermodynamic modelling based on the existing body of published experimental data on pt and pd solubilities suggests that pd and pt can be readily transported as bisulfide complexes in acidic neutral solutions under reduced and moderate oxidation condition at 300 c and chloride complexes are only important under extremely acidic oxidised conditions pd is much more soluble than pt in the case of fluids in sulfide rich environments in equilibrium with the characteristic assemblages found within altered and metamorphosed komatiites solubilities of both elements are much lower in sulfide poor environments especially where ph values are constrained to neutral values by the near ubiquitous presence of carbonate minerals in the alteration assemblage this accounts for the evident near immobility of pt and pd in even the most altered silicate host rocks as compared with their wide dispersion in sulfide rich ores

deformation and remobilization in some western australian nickel ores abstract volcanic associated nickel deposits in the archaean greenstone belts of western australia show a variety of features related to post depositional deformation and medium to high grade regional metamorphism deformation and accompanying remobilization have resulted in changes to the gross structure shape and orientation of ore shoots and have led to the development of separate offset ores tectonic breccia ores and irregular sulphide stringers physical remobilization of ore has been mainly on a mesoscopic scale up to 150 m and largely by mechanical processes but with some fluid assisted and stress induced chemical remobilization of sulphur and possibly copper most of the present ore fabrics and textures are the result of combined deformation metamorphically induced phase changes and recrystallization massive and matrix ores show well developed tectonite fabrics defined by mineralogical layering preferred orientation of pyrrhotite and alignment of silicate and spinel inclusions layering in the ores is probably the result of both strain controlled exsolution from high temperature phases and mechanical segregation of different minerals within polyminerallic aggregates during deformation observational and experimental data suggest that sulphide deformation was dominantly by dislocation type mechanisms kinking and twinning at medium temperatures 300 550 c with diffusional mechanisms becoming important at high temperature 500 c dynamic recrystallization during deformation probably accounts for the annealed state of individual mineral grains within most ores except those deformed at a late stage

rheological and tectonic modeling of salt provinces abstract technological improvements and a more rigorous research approach have led the petroleum industry to renew and expand its interest in physical modeling of faulting associated with halokinesis salt tectonics and the formation of structural hydrocarbon traps can be reproduced in models using viscous polymers for the substratum and frictional plastic granular materials for the overburden the fault patterns simulated in these dynamically scaled models are remarkably similar to those in depth converted seismic sections scale models are therefore useful for generating new concepts and for reconstructing the structural evolution of hydrocarbon traps although even unsealed models may help generating ideas the full transfer of quantitative data requires that models be dynamically scaled to their natural prototypes previously published scaling theory for salt tectonics has erroneously assumed fluid behaviour of the overburden this paper provides a sound scaling approach for geological deformations involving brittle overburdens on ductile substrata rheological data from overburden rocks and salt are compiled and compared to model rheologies using dimensions of laboratory analogs and other intrinsic material properties scaling approaches are compared and rules are formulated for achieving dynamic similarity in models of salt tectonics including those with synkinematic sedimentation

the terminology of structures in thrust belts abstract a review of structures and geometric relationships recognized in thrust belts is presented a thrust is defined as any contractional fault a corollary being that thrusts must cut up section in their transport direction flats are those portions of a thrust surface which were parallel to an arbitrary datum surface at the time of displacement and ramps are those portions of thrusts which cut across datum surfaces ramps are classified on the basis of their orientation relative to the thrust transport direction and whether they are cut offs in the hangingwall or footwall of the thrust lateral variations in the form of staircase trajectories are joined by oblique or lateral ramps which have a component of strike slip movement an array of thrusts which diverge in their transport direction may form by either of two propagation models these are termed piggy back propagation which is foreland directed and overstep propagation which is opposed to the thrust transport direction an array of thrust surfaces is termed an imbricate stack and should these surfaces anastamose upwards a duplex will result the fault bounded blocks are termed horses a duplex is bounded by a higher roof thrust and a lower floor thrust the intersection of any two thrust planes is termed a branch line thrusts can be classified on the basis of their relationship to asymmetric fold limbs which they cut a further classification arises from whether a particular thrust lies in the hangingwall or footwall of another one the movement of thrust sheets over corrugated surfaces or the local development of thrust structures beneath will fold higher thrust sheets these folds are termed culminations and their limbs are termed culmination walls accommodation of this folding may require movement on surfaces within the hangingwall of the active thrust these accommodation surfaces are termed hangingwall detachments and they need not root down into the active thrust this category of detachment includes dip slip hangingwall drop faults which are developed by differential uplift of duplex roofs and out of the syncline thrusts which develop from overtightened fold hinges back thrusts as well as forming as hangingwall detachments may also form due to layer parallel shortening above a sticking thrust or by rotation of the hangingwall above a ramp

platinum group element and nickel sulphide ore tenors of the mount keith nickel deposit yilgarn craton australia a set of platinum group element pge analyses of about 120 samples from a 250 m continuous drill core through the mount keith komatiite hosted nickel orebody combined with ni cu co s and major elements reveals a complex trend of covariance between the original cumulus components of a thick sequence of nearly pure olivine sulphide liquid adcumulates the intersection is divided into informal chemostratigraphic zones defined primarily by combinations of fine scale cyclicity in original olivine composition defined by mg and sulphide composition defined by pt s and ni s contents of ni and pge in 100 sulphides tenors were determined from linear regressions of the ni s and pge s covariance for each zone inferred olivine compositions range from about fo92 to fo94 6 and show a broad decrease from bottom to top of the sequence complicated by numerous reversals revealing crystallisation in an open conduit system ni and pge tenors of mount keith sulphide ores have typical values similar to the type i deposits of the kambalda dome mobility of s at least on the scale of 2 m sample composites is evidently relatively minor tenors for the various zones range 12 22 ni 370 1540 ppb pt 970 3670 ppb pd 100 460 ppb ir 170 460 ppb rh and 710 1260 ppb ru pt pd and rh tenors are very strongly correlated but the iridium group of platinum group elements ipges ir and ru less so tenor variations are predominantly controlled by variations in magma sulphide ratio r 100 350 with a minor component of variance from equilibrium crystallisation trends in the parent magma pge depletion in the silicate melt due to sulphide liquid extraction is limited by entrainment of sulphide liquid droplets and continuous equilibration with the transporting silicate magma ratios of the pges to one another are similar to those in the host komatiite magma with the exception of pt which is systematically depleted in ores relative to rh and pd and relative to host magma by a consistent factor of about 2 to 2 5 this anomalous pt depletion relative to pge element ratios in unmineralized komatiitic rocks matches that observed in bulk compositions of many komatiite hosted orebodies the highly consistent nature of this depletion and particularly the very strong correlation between pt pd and rh in the mount keith deposit argue that this depletion is a primary magmatic signal and not an artefact of alteration differential diffusion rates between pt and the other pges giving rise to a low effective partition coefficient for pt into sulphide liquid is advanced as a possible but not definitive explanation

nickel sulfide deposits in australia characteristics resources and potential abstract australia s nickel sulfide industry has had a fluctuating history since the discovery in 1966 of massive sulfides at kambalda in the eastern goldfields of western australia periods of buoyant nickel prices and high demand speculative exploration and frenetic investment the nickel boom years have been interspersed by protracted periods of relatively depressed metal prices exploration inactivity and low discovery rates despite this unpredictable evolution the industry has had a significant impact on the world nickel scene with australia having a global resource of nickel metal from sulfide ores of 12 9 mt five world class deposits 1 mt contained ni and a production status of number three after russia and canada more than 90 of the nation s known global resources of nickel metal from sulfide sources were discovered during the relative short period of 1966 to 1973 australia s nickel sulfide deposits are associated with ultramafic and or mafic igneous rocks in three major geotectonic settings 1 archean komatiites emplaced in rift zones of granite greenstone belts 2 precambrian tholeiitic mafic ultramafic intrusions emplaced in rift zones of archean cratons and proterozoic orogens and 3 hydrothermal remobilized deposits of various ages and settings the komatiitic association is economically by far the most important accounting for more than 95 of the nation s identified nickel sulfide resources the ages of australian komatiitic and tholeiitic hosted deposits generally correlate with three major global scale nickel metallogenic events at 3000 ma 2700 ma and 1900 ma these events are interpreted to correspond to periods of juvenile crustal growth and the development of large volumes of primitive komatiitic and tholeiitic magmas caused by large scale mantle overturn and mantle plume activities there is considerable potential for the further discovery of komatiite hosted deposits in archean granite greenstone terranes including both large and smaller high grade 5 to 9 ni deposits that may be enriched in pges 2 to 5 g t especially where the host ultramafic sequences are poorly exposed analysis of the major komatiite provinces of the world reveals that fertile komatiitic sequences are generally of late archean 2700 ma or paleoproterozoic 1900 ma age have dominantly al undepleted al 2 o 3 tio 2 15 to 25 chemical affinities and often occur with sulfur bearing country rocks in dynamic high magma flux environments such as compound sheet flows with internal pathways facies kambalda type or dunitic compound sheet flow facies mt keith type most precambrian provinces in australia particularly the proterozoic orogenic belts contain an abundance of sulfur saturated tholeiitic mafic ultramafic intrusions that have not been fully investigated for their potential to host basal ni cu sulfides voisey s bay type mineralization the major exploration challenges for finding these deposits are to determine the pre deformational geometries and younging directions of the intrusions and to locate structural depressions in the basal contacts and feeder conduits under cover stratabound pge ni cu cr deposits hosted by large archean proterozoic layered mafic ultramafic intrusions munni munni panton of tholeiitic affinity have comparable global nickel resources to many komatiite deposits but low grades

textural evidence for remobilization in metamorphic environments remobilization of stratabound massive sulphide deposits involves both dislocation flow mechanical remobilization and fluid state processes chemical remobilization textural support for such remobilization is presented at micro meso and macroscales microscale evidence establishes the degree the amount of a deposit affected of remobilization likewise mesoscale textures establish the degree and may provide mesoscale models of macroscale remobilization processes but still do not establish the extent the distance over which translocation may have occurred of remobilization where macrotexture indicates a departure from an original conformable relationship gross remobilization is suggested and may be the consequence of mechanical and or chemical processes the case for gross mechanical and or chemical remobilization is often difficult to sustain because alternative hypotheses e g hydrothermal replacement may be compatible with the observed relationships remobilization of a conformable ore layer may involve internal redistribution during which sulphides have been modified by dislocation flow and or fluid state processes within the layer constraints or external where the layer constraints have been substantially transgressed during dislocation flow and or fluid phase remobilization if mesoscale textures indicate remobilization of the external type then macroscale gross remobilization remains a possibility subject to substantiation

u pb zircon and re os isotope geochronology of mineralized ultramafic intrusions and associated nickel ores from the thompson nickel belt manitoba canada a u pb zircon age 1880 5 ma has been obtained from a mineralized ultramafic body in the setting lake area of the thompson nickel belt this crucial new age for ultramafic magmatism in the thompson belt in conjunction with the precise age determinations established for the molson dike swarm cross lake dike 1883 7 1 7 1 5 ma cuthbert lake dike 1883 2 ma and the fox river sill 1882 9 1 5 1 4 ma by heaman et al 1986 provides the first direct evidence for the contemporaneous nature of mafic ultramafic magmatism along the northwest margin of the superior craton this magmatic event also appears to be synchronous with mafic magmatism in other parts of the circum superior belt and the trans hudson orogen re os isotope systematics of mineralized samples from seven deposits that span the length of the belt produce an age similar to the u pb zircon age but with a much larger error 1885 49 ma with an initial os of 4 6 the os isotope data demonstrate that the source of the thompson belt ores including those orebodies hosted in ultramafic rocks and those hosted in pelitic rocks was dominantly mantle derived establishing that thompson belt magmatism is synchronous with the molson dike swarm and the extensive fox river sill has important new exploration implications and requires modification of existing concepts which have presumed that thompson belt magmatism is significantly older than these other intrusive suites also it would appear that other important ni and ni cu deposits elsewhere in the circum superior belt and in the trans hudson orogen formed at or near 1 88 ga and thus this age could be considered an important and widespread nickel mineralizing metallogenic interval during the early proterozoic

machine learning classification of debris covered glaciers using a combination of sentinel 1 2 sar optical landsat 8 thermal and digital elevation data abstract debris cover on glacier surfaces hampers the accurate detection of debris covered ice using traditional techniques based on image band ratios therefore this study tests a new automatic classification scheme for hierarchical mapping of glacier surfaces based on machine learning classifiers including k nearest neighbors knn support vector machine svm gradient boosting gb decision tree dt random forest rf and multi layer perceptron mlp several raster layer combinations synthetic aperture radar sar coherence image derived from sentinel 1 data visible near infrared to short wave infrared bands from sentinel 2 thermal information from landsat 8 and geomorphometric parameters from the advanced land observing satellite alos world 3d 30 m mesh aw3d30 digital elevation model were tested to delineate the debris covered glaciers in the gilgit baltistan pakistan and shaksgam valley china the highest over classification accuracy 97 was obtained using the rf classifier followed by the gb and svm with radial basis function kernel and utilizing all of the multisensor sentinel landsat alos data notably the rf classifier showed to be robust to parameter settings fast and accurate for mapping debris covered ice gb classifier showed similar performance as rf despite it has a moderately lower accuracy compared to rf although svm classifier has a slower in the speed of tuning hyper parameter it still performs the third best classification accuracy as the multisensory data we used is freely and near globally available our methodology potentially could be applied for precise delineation of debris covered glaciers in other areas

effect of ramp geometry on deformation in a ductile decollement level abstract a theoretical model is presented to explain the relation between the different strain regimes in a ductile decollement level and the ramp geometry this model accounts for a simple shear regime in the basal flat level and a less rotational and more flattening strain regime along the ramp the model is applied to a field example where the ramp dip and the shear value on the basal flat are estimated from pressure shadow data

analogue modelling of thrust systems passive vs active hanging wall strain accommodation and sharp vs smooth fault ramp geometries we present new analogue modelling results of crustal thrust systems in which a deformable brittle hanging wall is assumed to endure passive internal deformation during thrusting i e exclusively as a consequence of having to adapt its shape to the variable geometry of a rigid footwall building on previous experimental contributions we specifically investigate the role of two so far overlooked critical variables a concave convex cc vs flat ramp flat frf thrust ramp geometry and b presence vs absence of a basal velocity discontinuity vd regarding the first variable we compare new results for considered cc smoother ramp types against classical experiments in which frf sharp ramp geometries are always prescribed our results show that the considered sharp vs smooth variation in the thrust ramp geometry produces important differences in the distribution of the local stress field in the deformable hanging wall above both lower and upper fault bends with corresponding styles of strain accommodation being expressed by marked differences in measured morpho structural parameters regarding the second variable we for the first time report analogue modelling results of this type of experiments in which basal vds are experimentally prescribed to be absent our results critically show that true passive hanging wall deformation is only possible to simulate in the absence of any basal vd since active shortening accommodation always necessarily occurs in the hanging wall above such a discontinuity i e above the lower fault bend in addition we show that the morpho structural configuration of model thrust wedges formed for prescribed vd absence conditions complies well with natural examples of major overthrusts wherein conditions must occur that approximate a frictionless state along the main basal thrust plane

extension and compression in the northern apennines italy hinterland evidence from the late miocene pliocene siena radicofani basin and relations with basement structures 1 the northern apennines na hinterland area is characterized by a complex neogene quaternary tectonics where both crustal extension associated with the tyrrhenian basin opening and crustal shortening in the onshore area took part in the deformation analysis of synorogenic deposits preserved in the nnw trending siena radicofani basin srb extending along a large part of the na hinterland documents the evolution of deformation of this sector during the last 9 ma information from subsurface geology deep seismic lines commercial seismic lines and deep wells surface geology mapping and structural analysis and from analogue modeling was integrated and used to infer the tectono sedimentary history of the srb and its relation with structures in the substratum as well as the possible implications for the evolution of the na hinterland the results we obtain indicate that the srb and the adjoining hinterland basins were bounded by thrust anticlines controlling basin development and deformation seismic lines across the srb display various examples of compressional structures affecting the basin fill and the substratum such as thrust anticlines and reverse faults notably these basin scale structures exhibit a good correlation with those observed in the field and are consistent with the kinematics of the outcrop scale compressional structures the thrust anticlines bounding the basins are often cored by triassic evaporites burano formation suggesting that this weak layer decoupling the sedimentary cover from the underlying crystalline basement controlled their evolution in this circumstance three series of scaled brittle ductile physical models have been used to investigate the development of a basement cover system with a decollement ductile layer at the base of the sedimentary cover these models simulate the evolution of the northern apennines hinterland where the basement is involved in the thrusting and the sedimentary cover is shortened above a basal ductile layer given by the burano formation longitudinal models cross sections display similar deformation patterns to those observed in the na hinterland such as characteristic wavelength of both basement and cover structures as well as detachment and fault propagation folding in the cover extensional tectonics is instead found to control sedimentation in the southern part of the srb at 8 ma or representing recent deformation the older extensional event is here related to the forelandward propagation of tyrrhenian related extension that could reactivate suitably oriented basement thrusts transfer zones produced a differential propagation of extension such that along strike sectors of the hinterland were eventually deformed by different stress fields analysis of the srb and of other adjoining basins reveals that the na hinterland experienced alternated periods of forward and backward migration of the compression extension transition in our interpretation the competition between extension and compression in the hinterland is related to the nnw directed africa pelagian indentation responsible for the lateral extrusion of the na and the contemporaneous opening of the tyrrhenian basin in the inner zone increased marginal loading at the foreland promoting reactivation of hinterland thrusts may have influenced this process as well

dynamic rupture activation of backthrust fault branching we perform dynamic rupture simulations to investigate the possible reactivation of backthrust branches triggered by ruptures along a main thrust fault simulations with slip weakening fault friction and uniform initial stress show that fast propagation speed or long propagation distance of the main rupture promotes reactivation of backthrust over a range of branch angles the latter condition may occur separately from the former if rupture speed is limited by an increasing slip weakening distance towards the junction direction the results suggest a trade off between the amplitude and duration of the dynamic stress near the main rupture front for backthrust reactivation termination of the main rupture by a barrier can provide enhanced loading amplitude and duration along a backthrust rooted near the barrier facilitating its reactivation especially with a high frictional resistance the free surface and depth dependent initial stress can have several additional effects the sign of the triggered motion along the backthrust can be reversed from thrust to normal if a deeply nucleated main rupture breaks the free surface while it is preserved as thrust if the main rupture is terminated by a barrier at depth the numerical results are discussed in relation to several recent megathrust earthquakes in sumatra chile and japan and related topics such as branch feedbacks to the main fault the dynamic view on backthrust fault branching provided by the study fills a gap not covered by quasi static models or observations a specific examined case of antithetic fault branching may be useful for indicating a barrier like behavior along the main fault

the influence of intrabasinal faults on the development of a linked thrust system the mesozoic and cenozoic rocks exposed in the arve valley region of the external french alps are used to assess the role of early intrabasinal faults on later thrust fault evolution the early intrabasinal faults produced at some time from latest upper cretaceous to tertiary strike parallel or subparallel to later neo alpine thrusts where early faults dip away from the thrusts they are generally cut through and occasionally are overturned during this process in one example extreme overturning has allowed partial reactivation early faults dipping in the same direction as thrusts may a be reactivated b initiate ramping of the thrust ahead of the preexisting fault c be cut through by the thrust d cause pinning of the thrust at the footwall of the fault and folding against the fault as displacement continues buttressing from this work it is evident that intrabasinal faults exerted a major influence on the distribution of mechanical heterogeneities these heterogeneities include variations of stratigraphic thickness and type across faults fault related unconformities and the presence of the fault itself during the period of contraction such features strongly controlled the development of the stress field produced ahead of an advancing thrust and hence influenced the position of thrust fault propagation within the stratigraphy

creep of rocksalt abstract a review is presented of the fundamental flow properties and processes in experimentally deformed natural and synthetic halite single crystals and polycrystalline aggregates included in the summary are discussions of a microstructures induced during steady state creep b creep rupture of rocksalt c experiments associated with project salt vault and more recent field studies and d brine migration a representative steady state flow law determined for natural aggregates and maximum natural deviatoric stresses deduced from subgrain sizes are applied briefly to considerations of creep in waste repositories and of salt dome dynamics while the mechanical behavior of rocksalt is probably better understood than for all other rock types further investigations especially on load path stress history and creep rupture are clearly mandated furthermore additional investigations of brine migration and of bench and field scale deformations are needed the latter incorporating realistic rocksalt flow properties into numerical simulations of natural rock mass response

textural development in sulfide matrix ore breccias in the aguablanca ni cu deposit spain revealed by x ray fluorescence microscopy abstract the intrusion hosted ni cu sulfide deposit at aguablanca in south western spain contains a high proportion of ores in the form of sulfide matrix ore breccias these are polymict comprising autoliths and xenoliths in sulfide rich and or sulfide poor matrices inclusion lithologies include calc silicate skarn rocks from the adjacent marbles ultramafic and mafic cumulates and remelted and recrystallized mafic rocks containing spinifex like textures breccia textures have been investigated at mm to cm scale using desk top and synchrotron based microbeam xrf mapping which reveal a number of distinctive common features disaggregation of inclusions into adjacent sulfide along original silicate grain boundaries complex reverse and oscillatory zoning in cr content of clinopyroxene grains within sulfide and inside inclusions narrow reaction rims between country rock clasts and enclosing silicates and preferential disposition of pyroxene crystals within pyrrhotite pentlandite aggregates original mss relative to inclusion poor chalcopyrite the observed range of textures is explained by a model of percolation of molten sulfide through a pre existing silicate matrix intrusion breccia preferentially displacing a cotectic or eutectic plagioclase pyroxene melt the process is analogous to that believed to have formed interspinifex ore in komatiite hosted deposits and also to that responsible for superficially similar sulfide matrix ore breccias at voisey s bay the preserved range of textures is interpreted as being due to late stage gravity driven percolation of sulfide liquid from above into a pre existing partially molten intrusion breccia this intrusion breccia itself may have been emplaced into the neck of the aguablanca stock in the waning stages of magma flow

growth stratal records of instantaneous and progressive limb rotation in the precordillera thrust belt and bermejo basin argentina analysis of synorogenic deposits preserved near the thrust front zone of the precordillera fold and thrust belt and in the bermejo foreland basin in central argentina documents the evolution of deformation during the last 5 myr as well as the thrust system kinematics seismic lines across the area display examples of progressive and instantaneous limb rotations the easternmost thrust plate of the central precordillera the niquivil thrust experienced episodic motion in two main stages a first thrust movement as a fault propagation fold and a second movement as a high angle anticlinal breakthrough fault after a period of quiescence growth strata deposited in the la pareja intermontane basin and the las salinas and bermejo anticline recorded continuous growth of eastern precordilleran structures beginning at 2 7 ma with uplift rates of 0 3 mm yr for the niquivil anticline 1 08 mm yr for the las salinas anticline and between 0 6 and 0 38 mm yr during the last 2 myr for the bermejo anticline once the eastern precordillera began to grow the propagation of the niquivil thrust stopped restricting the deformation to the young vallecito out of sequence thrust the complex geometry of growth strata deposited on the back limb of the las salinas anticline can be explained by using a model of a two step fault propagation fold with constant layer thickness the bermejo anticline of the eastern precordillera is formed by the simultaneous propagation of a shallow fault responsible for the fold shape and a deep fault that produced vertical uplift a growth triangle that documents instantaneous forelimb rotation for a fault propagation fold is recorded for the first time in a published seismic line

geology geochemistry and genesis of the longhua low temperature hydrothermal ni co arsenide deposit in sedimentary rocks guangxi south china abstract the longhua ni co deposit hosted in cambrian carbonaceous sandstone and siltstone in south china consists of disseminated niccolite mineralization and high grade ni co arsenides quartz carbonate vein mineralization the disseminated mineralization is characterized by niccolite hosted in the center of quartz fragments and in argillaceous concretions in cambrian banded pisolitic carbonaceous silty mudstone and by parallel niccolite grains in cambrian pisolitic pelite these characteristics indicate that the disseminated niccolite originated through redeposition the ni co vein mineralization forms high grade ores and is composed mainly of ni co arsenides the homogenization temperatures of fluid inclusions in the mineralized vein quartz range from 118 to 219 c with corresponding salinities of 1 2 to 8 8 wt nacl equiv the ore forming fluids yield dv smow and 18oh2o values of 54 to 66 and 3 0 to 7 7 respectively indicating that the source was circulating meteoric water the longhua ni co vein mineralization gives a niccolite re os isochron age of 462 6 8 5 ma mswd 1 03 the geological and geochemical characteristics of the longhua ni co deposit indicate that it formed as follows 1 precambrian quartz niccolite mineralization was eroded and transported to the longhua sediment trap forming low grade disseminated niccolite mineralization or ni co rich source beds during the cambrian 2 high grade ni co arsenide vein mineralization was formed by further enrichment of ni co from the ni rich source beds by circulated meteoric water during the ordovician caledonian orogeny the formation of the longhua low temperature high grade ni co vein ore indicates that ni can be transported in low temperature fluids that are rich in arsenic and hco3 or co32 the longhua ni co deposit might represent a new type of sedimentary hosted low temperature hydrothermal ni deposit

episodic accretion and strain partitioning in a model sand wedge we model led thrust wedge accretion and deformation partitioning in a passively layered sand detached and shortened above a smooth rigid decollement the thrust wedge accretes in piggyback style during forward advance of a rear wall the passively layered sand accommodates the shortening penetratively by kinking ramp folding and by imbrication in single layers the style of compression changes with time and or stratigraphic position within the sand prism initial penetrative layer shortening above a slipped zone of decollement is succeeded by formation of monoclinal or conjugate shear bands at temporary terminations of decollement the shear bands subsequently narrow down and lock as thrust ramps the model sand wedge accrets episodically rather than steadily episodicity is controlled by the stick slip mode of decollement propagation and by volume loss and compaction of the wedge material in response to convergence this results in formation of a wedge with a convex upwards cross sectional topography

a metamorphosed proterozoic carbonaceous shale hosted co ni cu deposit at kalumbila kabompo dome the copperbelt ore shale in northwestern zambia the kalumbila co ni cu prospect 12 15 s 25 20 e is located 300 km west of the zambian copperbelt on the southeastern flank of the kabompo dome in the middle unit of the lufilian arc kalumbila contains a drill indicated resource of 3 04 mt at 0 67 wt percent ni 0 2 wt percent co and 0 11 wt percent cu using a 0 08 wt percent co and 0 3 wt percent ni cutoff with an average thickness of 12 75 m ni co cu mineralization occurs as strata bound disseminated to finely laminated locally semimassive to locally discordant chalcopyrite pyrrhotite violarite and siegenite within a finely laminated highly carbonaceous and pyritic metapelite 300 500 m thick surface rock exposure in this low relief terrain of woodland and seasonal swamp is 1 percent and geophysics magnetic and electromagnetic surveys is an essential exploration tool detrital zircons in the kalumbila metasediments shrimp u pb ages of 2004 1884 ma are derived from the underlying paleoproterozoic granitic gneiss such as that exposed in the adjacent kabompo basement dome the metasedimentary sequence grades upward from siliciclastic rocks mica schists to the carbonaceous metapelite which hosts the co ni cu these units are overlain by dolomitic and mg rich schists possible meta evaporites which are in turn succeeded by calc silicate rocks and a deformed diamictite this sequence is broadly similar to the stratigraphy in the zambian copperbelt and suggests that the kalumbila carbonaceous metapelite may be the chronostratigraphic equivalent of the katangan roan ore shale a significant exploration target kalumbila occurs within a moderately 40 north northwest dipping band of wamikumbi formation carbonaceous metapelite on the flank of a recumbent south southeast verging f1 or f2 back fold during the lufilian orogeny peak metamorphic conditions at f1 were of amphibolite facies grade 650 c 13 kbars both monazites and rutiles within the kalumbila metasediments have metamorphic characteristics and late orogenic lufilian shrimp u pb ages 548 6 7 6 ma and 531 21 ma respectively sulfides in the metasediments display metamorphic textures and therefore predate the peak of lufilian tectonism and thermal metamorphism a suite of spatially associated apparently late lufilian gabbros intrude the metasedimentary rocks these gabbros are unmineralized but the thermal effects of their emplacement may have modified ore distribution a genetic model in which synsedimentary pyrite in a carbonaceous pelite was partially replaced by syndiagenetic or metamorphic co ni cu bearing fluids of unknown origin is favored

measurements of friction coefficients and cohesion for faulting and fault reactivation in laboratory models using sand and sand mixtures abstract simple laboratory tests have been made on dry quartz sand and on mixtures of sand and clay and sand and cement tests were made on both low and high density specimens of each mixture as determined by physical handling techniques the tests included measurements of density estimates of the coefficient of internal friction based on fault orientation and estimates of the friction coefficients and cohesion values for fault initiation and reactivation in a shear frame apparatus which was also used to test artificial fault zones made from pure clay glass microspheres and wheat flour the results suggest that density is determined more by handling technique than by composition and that friction coefficients and perhaps cohesion both increase with increasing density the shear testing revealed a consistent drop in cohesion for fault reactivation in all densely packed mixtures tested although small this drop may be significant for some types of laboratory models

the influence of pre existing thrust faults on normal fault geometry in nature and in experiments relations between normal faults and pre existing thrust faults are classically described in terms of three basic situations normal faults can cross cut thrust faults they can branch out from thrust faults at depth on a de collement level or they can entirely reactivate thrust planes the mechanical aspects of these types of interaction were studied by analogue modelling in which sand simulates the brittle rocks and silicone putty an interlayered de collement the models underwent compression producing thrust faults with variable dips followed by extension three possible ways of interaction are described here a no interaction occurs in the case of low dip thrust faults 32 1 and normal faults are developed independently displaying a listric geometry b branching at depth on the de collement level occurs when dip of the thrust faults reaches 32 1 in this case the dip of the normal faults whose geometry becomes planar decreases with increasing thrust dip we suggest that this change in dip of normal faults depends upon the rotation of stress tensor axes along the pre existing fault zone where a drop in the friction coefficient is likely to occur c reactivation occurs in brittle material when dip of the pre existing fault exceeds 41 1

active folding in the algerian earthquake of 10 october 1980 a fold controlling the form of the local topography near el asnam algeria increased in amplitude at the time of the earthquake of 10 october 1980 the deformation occurred rapidly in an elastic brittle manner and not in the gradual ductile fashion in which folds are normally thought to develop

constraints on friction coefficients by an inverse analysis of sand box thrust dips abstract we measured the dips of thrusts forming in a uniform sand layer under horizontal shortening by a rigid emerging ramp in conditions of full erosion various ramp dips and four types of ramp material were used throughout the 12 experiments in three experiments the ramp was shortcut by a less steep thrust forming a spontaneous ramp in the sand the forward modelling proposed to predict these observations involves i computing the total dissipation in the structure by using global force equilibrium and a parameterised kinematic framework including the possibility of shortcut development and ii minimising the total dissipation of mechanical work with respect to the kinematic parameters i e the thrust dips for which two analytic solutions are found the inverse problem involves computing probability densities over the parametric space of friction coefficients including the internal friction angle of the sand and friction angles of the four materials used on the rigid ramps practically this involves computing a misfit using the l2 norm between the observed and predicted thrust dips for every possible value of the friction angles the resulting probability density provides all the quantitative information that can be retrieved from the experiments in the light of our forward modelling ramp friction angles exhibit sharp probability changes at values that trigger the occurrence of shortcuts thus yielding non trivial bounds on the ramp friction values that are directly related to the observations of ramp and back thrust geometry also the probability distribution of the internal sand friction and those of the ramp frictions is in good agreement with independent measurements this approach is designed to be applicable to field studies of brittle deformation where geometries are observed and rheological parameters are sought

a new multilayered visco elasto plastic experimental model to study strike slip fault seismic cycle nowadays technological advances in satellite imagery measurements as well as the development of dense geodetic and seismologic networks allow for a detailed analysis of surface deformation associated with active fault seismic cycle however the study of earthquake dynamics faces several limiting factors related to the difficulty to access the deep source of earthquake and to integrate the characteristic time scales of deformation processes that extend from seconds to thousands of years to overcome part of these limitations and better constrain the role and couplings between kinematic and mechanical parameters we have developed a new experimental approach allowing for the simulation of strike slip fault earthquakes and analyze in detail hundreds of successive seismic cycle model rheology is made of multilayered visco elasto plastic analog materials to account for the mechanical behavior of the upper and lower crust and to allow simulating brittle ductile coupling postseismic deformation phase and far field stress transfers the kinematic evolution of the model surface is monitored using an optical system based on subpixel spectral correlation of high resolution digital images first results show that the model succeed in reproducing the deformation mechanisms and surface kinematics associated to the main phases of the seismic cycle indicating that model scaling is satisfactory these results are comforted by using numerical algorithms to study the strain and stress distribution at the surface and at depth along the fault plane our analog modeling approach appears then as an efficient complementary approach to investigate earthquake dynamics

basin inversion and contractional reactivation of inherited normal faults a review based on previous and new experimental models abstract compressional inversion of former extensional sedimentary basins is a particularly common phenomenon given that passive margins share the same destiny of being subsequently incorporated into fold and thrust belts during basin inversion pre existing faults may concentrate stress and localise future thrust ramps or may be reactivated recording reversal of movement from extension to reverse this process has attracted attention largely because of its economic implications related to petroleum and ore deposit prospects and seismic hazard assessment since more than two decades analogue modelling has been used to indentify and or test a number of parameters relevant for the inversion process this paper aims therefore to offer a reasoned review of the analogue modelling work done on the subject coupling such previous results with those of a new experimental series inspired to the northern apennines stratigraphy and evolution past models have explored the role of main factors governing fault reactivation susceptibility such as fluid pressure fault weakness fault steepness angle of shortening and sediment loading the new models have addressed the role played by geometry and strength of a basal ductile layer during inversion two sets of sand silicone models were first extended orthogonally at different velocities to produce dissimilar pre inversion internal geometries and then shortened coaxially at different velocities to vary the brittle ductile coupling the experimental results confirm the selectiveness of fault inversion and reveal strong similarities with structural styles of tectonic inversion reported from the northern apennines and various areas worldwide the preferred geological model inferred from this modelling involves contribution of 1 syn inversion rotation of pre existing faults to shallower dip and 2 rotation of principal stress axes which could explain the invariable reactivation of only one of the two oppositely dipping graben bounding faults these factors would thus interact with the other well established parameters controlling the fault reactivation process

critical stress difference and orientation of faults in rocks with strength anisotropies the two dimensional case abstract equations are derived for the critical stress difference on thrust normal and strike slip faults with finite cohesive strength both in homogeneous isotropic rock and along pre existing strength anisotropies with different cohesion and coefficient of friction subject to the limitation that the plane of anisotropy contains the intermediate axis of stress the range of orientations for which sliding occurs along pre existing planes of weakness rather than along a new fault is given as a function of material parameters and critical stress difference for the intact rock given the principal stress directions the equations allow the direct calculation of the stress and orientation conditions for the three faulting regimes

postmagmatic variability in ore composition and mineralogy in the t4 and t5 ore shoots at the high grade flying fox ni cu pge deposit yilgarn craton western australia the high grade flying fox komatiite hosted ni sulfide deposit located in the forrestania greenstone belt of the archean yilgarn craton western australia is hosted in a deformed and metamorphosed volcano metasedimentary succession postmineralization events have sheared and modified the texture and composition of the original massive sulfide ore creating up to 11 distinct ore shoots including massive stringer vein and breccia sulfides composed of pyrrhotite pentlandite chalcopyrite and variable abundances of pyrite ranging up to 40 vol nickel and platinum group elements pge tenor variations were investigated in two ore shoots t4 and t5 all mineralization styles show considerable variability in ni tenor pges show strong linear correlations between ir os ru and rh but poor correlation between pt pd and cu the normalized molar proportions of fe ni and s projected into the fe ni s ternary system show a distinct linear trend of pyrite addition to a typical primary magmatic composition and no correlation with mineralization style the high pyrite content present throughout the flying fox ore is also associated with elevated cu and as contents and is interpreted to be primarily due to the addition of pyrite from circulating fe s cu and as enriched fluids creating pyrite pentlandite intergrowths localized mechanical segregation of pyrite sulfidation of pyrrhotite to pyrite and oxidation of pyrrhotite to pyrite magnetite has also contributed to these increased pyrite contents although to a lesser extent the addition and segregation of pyrite has diluted the ni tenor with no evidence to suggest chemical mobilization of ni

a note on fault reactivation reactivation of existing faults whose normal lies in the 1 3 plane of a stress field with effective principal compressive stresses 1 2 3 is considered for the simplest frictional failure criterion n n p where and n are respectively the shear and normal stresses to the existing fault p is the fluid pressure and is the static friction for a plane oriented at to 1 the stress ratio for reactivation is 1 3 1 cot 1 tan this ratio has a minimum positive value at the optimum angle for reactivation given by 12tan 1 1 but reaches infinity when 2 beyond which 3 0 is a necessary condition for reactivation an important consequence is that for typical rock friction coefficients it is unlikely that normal faults will be reactivated as high angle reverse faults or thrusts as low angle normal faults unless the effective least principal stress is tensile

emplacement of foreland thrust systems emplacement driving mechanisms for thrust systems have been briefly reviewed and compared with distinctive structural styles in thrust belts a b type mode which implies a push from the rear and an elastic brittle behavior of the rock mass appears to be suitable as a general model for the emplacement of thrust sheets in thin skinned fold and thrust belts where stratal shortening of sedimentary covers and imbrication of upper level crustal rocks occur in such an environment that the mechanical behavior of the crustal section involved the mode and timing of deformation and the geometry of thrust systems are all strongly dependent upon the coupling between induced tectonic strain and transient close to lithostatic pore fluid pressure buildup over a critical areal extent the model presented here does not require a weak basal horizon for the detachment of thrust sheets and pore pressure pp does not need to be high at once under the entire length of the thrust wedge rather the transient buildup of pp and hence the spatial and temporal progressive weakening of the rock mass are directly coupled with deformation

direct dating of ultramafic sills and mafic intrusions associated with ni sulfide mineralization in the thompson nickel belt manitoba canada the paleoproterozoic thompson nickel belt a segment of the northwest margin of the archean superior craton in manitoba is one of the largest nickel producing regions in the world and the second largest ni cu pge platinum group elements mining camp in canada after sudbury the nickel sulfide ores are hosted in or associated with ultramafic sills of komatiitic affinity that were emplaced into sulfur rich metasedimentary rocks of the ospwagan group and subsequently strongly deformed and metamorphosed amphibolite to granulite facies during the trans hudson orogeny a u pb zircon age of 1880 2 1 4 ma for a metaperidotite olivine orthopyroxenite from the upper part of a boudinaged ultramafic sill at the pipe 2 deposit is interpreted as the age of crystallization of the intrusion the first age from an ultramafic sill containing mined nickel sulfide in the thompson nickel belt this age confirms a direct petrogenetic relationship between ni cu pge mineralization and widespread mafic ultramafic magmatic activity molson igneous events at ca 1 88 ga along the superior province craton margin e g thompson nickel belt fox river belt cape smith belt new quebec orogen at the south pit of the thompson mine a u pb zircon age of 1860 7 0 7 ma for a composite mafic intrusion garnet amphibolite to layered metagabbro identifies a new age of mafic magmatic activity in the thompson nickel belt that is unrelated to nickel sulfide mineralization the thermal effects of the trans hudson orogeny are recorded by a range of zircon dates and ca 1760 ma metamorphic titanite from the south pit intrusion and are consistent with interpretations that regional metamorphism occurred as a single progressive event the results of this study open up the possibility of using the high precision u pb geochronology of mineralized ultramafic rocks to precisely constrain the duration of mafic ultramafic magmatism in the thompson nickel belt and assess potential age differences between ultramafic sills across and along strike of this world class nickel metallotect

far field contractional polarity changes in models and nature abstract a change in contractional polarity occurs when the direction of tectonic transport switches along strike this switch is conditioned by lateral variations in rheology or inherited asymmetries such as contrasts in structure or changes in the polarity of subduction zones the parameters controlling contractional polarity changes are less understood in situations when the strain is transferred at large distances from indenters analysing this type of strain transfer is critical for understanding the mechanics of thrusting in fore or back arc settings of orogenic areas comparison of crustal scale analogue modelling with the inversion of the black sea back arc and the formation of the new guinea new britain fore arc suggest that far field changes in contractional polarity are related to rheological contrasts across inherited normal faults the initial extension creates rheological weak zones that localize the subsequent far field contractional deformation along groups of thrusts with opposite vergence along the strike of the system the largest amount of far field contractional deformation is recorded in the transfer zone located between the two indenters moving in opposite directions and is particularly high when inverting oblique extensional systems

duplex structures and imbricate thrust systems geometry structural position and hydrocarbon potential duplexes and imbricate thrust systems form some of the most complex hydrocarbon traps in overthrust belts the geometry of a duplex is controlled by the ramp angle thgr and height hr the final spacing between adjacent thrusts a prime and the relative displacements on them d1 d2 for constant thgr and hr three different classes are recognized 1 independent ramp anticlines and hinterland sloping duplexes 2 true duplexes and 3 overlapping ramp anticlines imbricate thrust systems consist of several thrust faults each of which loses displacement upsection and eventually dies out by progressively transferring its displacement to a fold at its tip or by distributing it among several splays hybrid duplexes are ormed from systems of fault propagation folds that are subsequently carried over ramps so they have a more complex geometry and a greater structural relief these different types of thrust systems occur as outcrops and prospect scale structures and they define the regional structural styles of most fold and thrust belts second and third order duplexes and imbricate thrust systems occur in specific structural positions such as footwalls hanging walls and frontal zones of major thrust ramps and in cores of major anticlines several types of duplexes and imbricate thrust systems form important hydrocarbon traps examples include the system of independent anticlines of the turner valley and highwood oil and gas fields the hinterland sloping duplex consisting of the chestnut ridge sandy ridge system of the ben hur oil field the partly overlapping anticlines of the waterton and savanna creek gas fields and the completely overlapping anticlines of the rose hill oil field

the langmuir volcanic peridotite associated nickel deposits canadian equivalents of the western australian occurrences the 2 7 b y old abitibi greenstone belt is a crudely s shaped zone of metamorphosed volcanic subvolcanic and sedimentary rocks and associated intrusions through it are scattered a dozen small nickel deposits in volcanic peridotites their hosts are volcanic and subvolcanic ultramafic rocks typically containing 40 to 45 percent anhydrous mgo with spinifex tops and overlain by thinner peridotitic to pyroxenitic flows at least one deposit dumont is hosted by a dunitic intrusion others e g dundonald langmuir 2 are partially hosted in sulfidic iron formations mining of the langmuir 2 deposit permitted extensive underground mapping core logging and sample collecting the other deposits are known mainly from poor surface exposures and drill core the langmuir 1 and 2 deposits provided sufficient data to evaluate models for their origin and to compare them to nickel sulfide deposits associated with volcanic peridotites in western australia a magmatic origin is supported by the localization of the main ore zone in a paleotrough by the presence of a possible volcanic feeder beneath the ore and by the regular sequence through the basal ultramafic flow of massive ore overlain by net textured ore then by barren peridotite and lastly by a spinilex textured cap to the flow an unusual spinilex textured and sulfide bearing rock and skeletal chromite also support a magmatic origin as do the base and precious metal contents of the ores the high s se ratios averge 23 000 and slightly lower sulfur isotopic ratios average 0 5 per mil delta 34 s compared to most magmatic nickel sulfide deposits are similar to the ratios for windarra western australia and may be explained by assimilation of sulfide rich cherty iron formation other features incompatible with a purely maginatic origin include the presence of sheared and breccia ore and the high sulfur content of some ores these features result from deformation and greenschist facies metamorphism but surviving features of an earlier magmatic history argue against the ores being formed metamorphically evidence of contemporaneous fumarolic activity was found at the south end of the mine but its importance as an ore forming process was not supported by detailed petrological and geochemical studies limited data from the other deposits in the abitibi belt suggest a common origin for the langmuir deposits with minor variations attributable to the volume of ultramafic magma emplaced the volume of contained nickel sulfides the presence of sulfidic iron formations and the severity of alteration and metamorphism the deposits in western australia probably were formed by similar processes in particular the langmuir deposits display strikingly similar sulfide chemistries to the windarra deposits which are probably dae to assimilation of sulfide rich cherty iron formation