upper ovetian trilobites from spain and their implications for the palaeobiogeography and correlation of the cambrian stage 3 in gondwana abstract the upper part of the la herreria formation in los barrios de luna leon province n spain has been revised from a palaeontological and biostratigraphical point of view two stratigraphic sections have been studied including their trilobite and ichnofossils contents the ichnofossil assemblages have a high diversity of species characterising the cruziana ichnofacies suggesting a shallow sublittoral environment for the upper part of the la herreria formation the trilobites species recognised are lunagraulos antiquus dolerolenus formosus dolerolenus longioculatus lunolenus lunae metadoxides richterorum metadoxides armatus and sardaspis sp from the upper ovetian lower cambrian stage 3 under discussion by the iscs the new trilobite assemblages make possible a good correlation between the lower cambrian formations of north spain sardinia south china and siberia analysis of the palaeobiogeographical meaning of all trilobite genera that have been identified in the upper ovetian of spain shows a strong connection between the northern peri gondwana margin and west gondwana with a low latitude distribution for the spanish trilobites at this time

duplex style and triangle zone formation insights from physical modeling duplexes are a common feature in thrust belts at many scales their geometries vary significantly from antiformal stacks with significant forethrusting in the cover e g southern pyrennes spain to triangle zones e g foreland canadian rockies to low displacement individually spaced ramp anticlines e g sub andean thrust belt bolivia we present a series of physical experiments demonstrating that the strength of the decollements relative to that of the intervening and overlying rock layers plays a significant role in controlling the duplex style the models comprise brittle layers made of dry quartz sand and decollements made of two types of viscous silicone polymers the strength of the decollements in the models is a function of the shortening rate applied to the model the relative strength of the decollements and surrounding rocks affects the development of active or passive roof duplexes triangle zones it also affects the amount of translation of individual thrust blocks and the spacing of thrust ramps which in turn determine if a duplex evolves into an antiformal stack or into individually spaced ramp anticlines model results indicate that specific associations of structural features form systematically under similar rheological and boundary conditions the presence of relatively strong decollements promotes local underthrusting of the cover individual ramp anticlines internal deformation of thrust sheets low early layer parallel shortening and sequential towards the foreland propagation of structures weak decollements promote forethrusting of the cover antiformal stacks coeval growth of structures and low internal strain with the exception of significant early layer parallel shortening no underthrusting at a regional scale occurred in any model

fold reactivation involving angular unconformable sequences theoretical analysis and natural examples from the cantabrian zone northwest spain abstract during the reactivation of folds truncated by unconformable layers the unconformity surface adopts various geometrical shapes depending on the fold reactivation mechanisms the paleorelief slope is also a determining factor for location and development of cover structures it can be theoretically shown that the reactivation of flexural flow and flexural slip folds below an unconformity produces folds of the same sense of curvature in layers above and below the unconformity viewed in profile that is to say these mechanisms give rise to a cover synform over a basement synform or antiform over antiform when the axes of both folds are subhorizontal folds reactivated by tangential longitudinal strain also behave in the same way in this case the cover folds may become tight even for initially high angles of unconformity which does not happen with flexural mechanisms the reactivation of chevron folds may give rise to opposite curvatures of basement and cover beds hence paradoxical structures such as a cover synform over a basement antiform or viceversa may be produced even if their axes are horizontal when two adjacent parts of the basement sequence are deformed by different folding mechanisms cover beds and unconformity are folded over the homoclinal sequence of each limb in the basement fold during fold reactivation the unconformity surface usually becomes a surface of decollement owing to the structures that have to be developed in the cover in order to accommodate the changes in length of the unconformity the development of extensional or compressional structures in the cover can be predicted from a geometrical study of the unconformity surface natural examples of reactivated folds under unconformable sequences of carboniferous age in the cantabrian zone show a good agreement with the above mentioned theoretical conclusions conclusions obtained on the distribution of folding mechanisms in the limbs and hinge zones and in layers or multilayers of different nature from the geometrical study of folded unconformable sequences in the cantabrian zone also agree with results from published experimental data

effects of magmatic processes serpentinization and talc carbonate alteration on sulfide mineralogy and ore textures in the black swan disseminated nickel sulfide deposit yilgarn craton the black swan disseminated orebody occurs predominantly within the partially carbonated serpentinite core of a zoned serpentinite talc carbonate ultramafic cumulate body of komatiitic parentage the black swan disseminated sulfides depart significantly from the characteristic pattern observed in otherwise similar deposits in western australia and canada which display magnetite bearing pentlandite rich sulfide aggregates blebs in serpentinites and s rich millerite bearing assemblages in talc carbonates the black swan disseminated ores in contrast are dominated by millerite pyrite polydymite assemblages in both serpentinites and talc carbonates with no evident relationship to the progression of carbonation sulfides show three types of intergrowth with gangue minerals which can occur separately or all together intergrowth with magnetite at least some of which appear to be primary magmatic in origin fine intergrowth with interlocking lath textured antigorite and intergrowth with carbonate minerals carbonate commonly replaces the core of sulfide blebs while retaining the primary magmatic outline carbonate replacement of sulfide roughly parallels the overall progression of carbonation of the whole rock but no systematic relationship of the other intergrowth types to carbonate content is observed in the serpentinites serpentine mineralogy determined by microbeam raman spectroscopy comprises lizardite which occurs in pseudomorphic mesh textures after olivine and antigorite formed by variable degrees of overprinting of original lizardite mesh textures ranging to a completely overprinting interlocking texture with no relic igneous texture this progression is interpreted as the result of mild thermal metamorphism of original lizardite serpentinite this progression is completely independent of carbonate content and is also apparently independent of extent of sulfide antigorite intergrowth which is interpreted as being early and related to volume expansion during initial sea floor serpentinization talc is almost completely absent from serpentinites while carbonate content varies widely whole rock ni and s data are very strongly correlated in millerite poor pentlandite rich samples and poorly correlated in samples where millerite is the dominant ni bearing sulfide on this basis we conclude that the pentlandite assemblages are slightly modified survivors of the original magmatic event while the millerite pyrite assemblages formed during the earliest stages of serpentinization overprinting of the early serpentinization event by talc carbonate had essentially no effect on sulfide mineralogy other than inducing intergrowth with carbonate a number of distinctive features such as magnetite rich bleb cores the association of sulfides with segregation vesicles and chromite shells the subspherical morphology of the blebs and preferential replacement of bleb cores are considered to be inherited from the magmatic phase and are attributed to an original high but variable oxygen and halogen content of the sulfide melt component exsolution of this component during solidification of the blebs in some cases produced sulfide centered bubbles now preserved as segregation vesicles while in other cases oxygen was retained within the bleb forming magnetite sulfide intergrowths chromite shells formed as a result of exsolved oxygen interacting with komatiite magma volatile rich blebs solidified in some cases with hollow or porous cores which were subsequently exploited by carbonate replacement

application of high resolution x ray computed tomography to mineral deposit origin evaluation and processing abstract high resolution x ray computed tomography ct is the industrial equivalent of medical cat scanning and provides a mechanism for non destructive studies of the three dimensional nature of geological materials hrxct produces two dimensional images slices that reveal the interior of an object as if it had been sliced open along the image plane for viewing a ct image is generated by differences in x ray attenuation that arise from differences in density and composition within the object by acquiring a contiguous set of slices volumetric data for all or part of a sample can be obtained allowing three dimensional inspection and measurement of features of interest ct is particularly effective in the study of metallic ores that commonly contain minerals spanning the range of densities of natural materials available software can produce grain shape size and orientation data from the scanned volume which can be particularly useful for oriented samples ct is particularly useful for studies of gold and other precious metal bearing minerals that typically have significant contrast even with common metallic mineral phases ct precisely defines the in situ location of mineral grains of interest within a sample which then can be studied in conventional petrographic sections and other forms of data collected e g isotope or trace element geochemistry another area of application is fluid inclusions which can be discerned even in opaque phases and fluid and vapor volumes measured for sufficiently large occurrences we summarize ct principles and review available instrumentation as well as scanning and data reduction protocols that provide unique three dimensional information for diverse ore types and applications in mineral deposits geology ct applications for economic geology and other fields will continue to expand as instruments continue to evolve and as scanning protocols and applications are extended for more precise quantification of three dimensional relationships particularly for fine grained particles and small fluid inclusions in larger volumes and for separation of minerals with limited contrast

hydrate distribution off vancouver island from multifrequency single channel seismic reflection data on the northern cascadia margin single channel seismic data clearly image the bottom simulating reflector bsr that marks the base of the hydrate stability zone airguns with three distinct source frequencies 30 75 and 150 hz were recorded along several coincident lines and at all frequencies the bsr appears as a single pulse bsr reflection coefficients are slightly larger for the 30 hz data than for the 75 or 150 hz data multi frequency analysis indicates that the bsr is due to a single sharp interface at the base of the hydrate zone whereas the velocity structure away from the interface must be gradationally varying so as to produce no separate reflection and no tuning effects at the 75 and 150 hz frequencies in contrast the seafloor reflection in some areas has significantly larger amplitudes for data recorded with the 75 hz source relative to the 30 hz source synthetic seismogram analysis of the two data sets shows that the high amplitudes can be produced by a 2 m thick high velocity layer at the seafloor with velocities and densities corresponding to those of carbonate using the 75 hz source seafloor and bsr amplitudes and reflection coefficients were measured over a tight grid of lines nominally spaced at 200 m maximum bsr reflection coefficients of 0 15 0 18 were observed beneath topographic highs while maximum seafloor reflection coefficients of up to 0 5 0 6 were found on the flanks of the topographic highs this suggests that topography provides a major control on the flow of methane bearing fluids amplitude measurements converted to values of velocity above the bsr were used to estimate hydrate concentrations which reaches a maximum of 15 18 of the total sediment volume with mean values near 5 10 over the 100 km2 survey area the volume of methane gas in the hydrate reservoir is estimated as 6 4 l010 m3 or 2 1 trillion cubic feet

fractional crystallization of sulfide ore liquids at high temperature tie line compositions of fe ni cu sub 1 x s monosulfide solid solution mss and fe ni cu s liquid in the presence of sulfur vapor have been quenched from temperatures between 1 050 degrees and 1 180 degrees c more than 80 bulk compositions on both sulfur rich and sulfur poor sides of the mss field were investigated by sealed silica tube techniques qualitative observations of wetting behavior suggest increasing mobility in a silicate host rock as sulfide liquids become more cu rich partition coefficients for copper or 0 25 d super mss hq cu are obtained from ni bearing experiments with approximately 2 wt percent cu and no quench phases the equation d super mss hq cu 0 0003 x t degrees c 0 0310 x wt s 0 0069 x wt cu 1 3450 describes partitioning observed in ni free experiments above 1 000 degrees c above 1 000 degrees c the ni distribution coefficient d super mss hq cu decreases with increasing temperature and or sulfur content of the liquid these results yield improved models describing the fractional crystallization of natural sulfide liquids major element fe ni cu s compositions of ores from the sudbury district are shown to be entirely consistent with fractional crystallization at temperatures above 1 000 degrees c with the possible exception of rare samples enriched in both ni and cu sulfide liquids fractionating ni fe rich hanging wall ores at sudbury ontario must have been less cu rich than previously thought at temperatures above 950 degrees c reduced sulfur activity in residual liquids can result in massive late stage bornite rich ores

centrifuge assisted percolation of fe s melts in partially molten peridotite time constraints for planetary core formation the mechanism which segregates molten fe s into metallic cores of planetary bodies is still not fully understood due to the high interfacial energy and wetting angle between fe s melts and silicate mantle minerals the continuous percolative flow of such melts cannot be efficient for the core segregation in planetary bodies a series of percolation experiments has been realized on a partially molten fertile garnet peridotite employing a centrifuging piston cylinder a high temperature garnet peridotite with mg 0 90 composed of 60 vol olivine 15 vol orthopyroxene 6 vol clinopyroxene and 19 vol garnet has been used as the silicate matrix peridotite powders with the 100 200 or 20 30 m grain size were mixed with 5 30 vol fe s of eutectic composition fe70s30 the aggregates were centrifuged at 500 700 g at temperatures below and above the melting point of the peridotite the centrifuge experiments revealed a negligible percolation of fe s melts through the unmolten peridotite matrix only at t 1260 c i e above the solidus of the peridotite and starting with 5 vol of fe70s30 the vertical melt gradient achieved 1 2 vol mm in samples with 15 vol fe70s30 the vertical separation achieved 2 2 5 vol mm after 10 h of centrifuging at 500 g an increase in the degree of partial silicate melting in the peridotite leads to an increase of the fe s separation rate from the peridotite matrix fe s contents 10 vol cause an increase of the fe s melt droplet size and of the effective percolation velocity of fe s melt a threshold dividing fast 10 cm per year and slow percolations 1 mm per year of fe s melt is found around 14 15 vol of fe70s30 the experimentally determined permeabilities of fe s melt in the unmolten peridotite with 7 10 vol of fe70s30 melt are 10 18 10 19 m2 which is 2 3 orders of magnitude lower than the values calculated previously from static experiments the presence of the silicate melt increases the segregation velocity of fe s melt in a partially molten peridotite by more than one order of magnitude with respect to the unmolten peridotite matrix this could provide an effective segregation of fe s melt in a planetary mantle down to 2 5 vol of residual fe s melt the extremely slow percolation of fe s melt in the absence of the partial silicate melting precludes a scenario of metallic core formation via percolation before temperatures allow a substantial partial melting of mantle silicates in planetary bodies

polymetallic sulfide exploration on the deep sea floor the feasibility of the mini moses experiment the recent discoveries of polymetallic sulfide deposits on the deep sea floor have created an interest in geophysical techniques for mapping them a magnetometric resistivity method mini moses has been developed for detecting the distribution of sub sea floor electrical resistivity a vertical long wire bipole feeds electric current into the ocean some of the current enters the sea floor and its magnetic field is measured at various distances by a low frequency induction coil magnetometer the method is sensitive to conductive and resistive zones at depth and information about three dimensional resistivity structures can be obtained the small load resistance of an electric transmitter grounded in the ocean allows high current to be driven by a battery powered instrument the induction coil receiver is more sensitive and less noisy than conventional flux gate magnetometers over the selected frequency band this receiver is therefore well adapted to the almost noise free deep sea floor environment b

mapping of seafloor hydrothermally altered rocks using geophysical methods marsili and palinuro seamounts southern tyrrhenian sea hydrothermal alteration processes involve mineralogical chemical and textural changes as a result of hot aqueous fluid rock interaction under evolving boundary conditions these changes affect the physico chemical properties of the rocks enabling high resolution geophysical prospecting to be an important tool in the detection of seafloor hydrothermal alteration here we present the results of recent geophysical investigations of the marsili and palinuro volcanic complexes southern tyrrhenian sea during the 2010 tir10 and 2011 mava2011 cruises by the r v urania the new dataset includes a dense grid of multibeam bathymetry seafloor reflectivity magnetic and gravity lines and high resolution single chirp and multichannel seismic profiles the surveys were focused on areas known to host intense hydrothermal alteration in order to provide a more detailed description of the marsili and palinuro hydrothermal systems ground truthing was based on earlier discoveries of hydrothermal vents and their associated deposits and on direct observations made by rov dives high resolution morpho bathymetry sonar reflectivity rock magnetization and density distribution together enabled us to assess the extent of seafloor hydrothermal alteration and its relationship to local volcanic and tectonic structures hydrothermal alteration associated with the marsili seamount is largely distributed along primary volcano tectonic structures at the ridge crest by contrast at palinuro hydrothermal alteration is mostly associated with secondary volcanic structures such as collapsed calderas and volcanism reactivation along ring faults in particular evidence for intense hydrothermal activity occurs at palinuro where volcanotectonic features interact with regional tectonic structures

passive roof thrusting and forelandward fold propagation in scaled brittle ductile physical models of thrust wedges a set of scaled analogue models was performed to investigate the role of a decollement layer in the structural style of fold and thrust belts silicone putty sgm 36 has been employed to represent the ductile decollement while frictional material quartz sand has been used to simulate the brittle behavior of roof and floor sequences situated above and below the decollement respectively in order to explore a wide combination of strength profiles models have been deformed under five distinct rates of compression 0 15 0 3 0 45 0 6 and 1 5 cm h 1 employing four different thicknesses for the silicone layer 0 1 0 2 0 4 and 0 8 cm experimental results indicate that roof sequences exhibit two distinct styles of deformation 1 passive roof duplex prd geometry e g banks and warburton 1986 and 2 outward propagation of folding ofp along the decollement e g davis and engelder 1985 in prd geometry the roof sequence remains relatively stationary being underthrust by a wedge shaped floor duplex while in ofp displacement along the floor thrusts is transferred horizontally along the decollement layer experiments suggest the occurrence of a genetic relationship between shear stresses at the base of the roof sequence b and within the ductile layer d and the development of prd or ofp geometry for a given strain rate the deformation pattern of roof sequences depends upon the b d ratio as well as the absolute b and d values the transition field between ofp and prd styles has been approximated by curvilinear regression of transition style experimental data points with a minimum value of d varying between about 112 and 160 pa to enter the prd field syntectonic sedimentation in the molasse basin is found to inhibit development of folding into the foreland but to promote prd style experiments simulate many of the principal characteristics of fold and thrust belts developed above a basal evaporite decollement as well as the development of passive roof duplexes at mountain fronts shear stress values inferred for many fold and thrust belts correlate well the deformation fields predicted by the present experimental study allowing to propose a simple model describing the mechanical behavior of natural roof sequences underlain by a decollement layer

on electric fields produced by inductive sources on the seafloor abstractthe transient electromagnetic tem method has recently been proposed as a tool for mineral exploration on the seafloor similar to airborne tem surveys conducted on land marine tem systems can use a concentric or coincident wire loop transmitter and receiver towed behind a ship such towed loop tem surveys can be further augmented by placing additional stationary receivers on the seafloor throughout the survey area we examine the electric fields measured by remote receivers from an inductive source transmitter within a 1d layered earth model at sea it is conceivable to deploy either a horizontal transmitter such as the analogous standard airborne configuration or a more exotic vertical transmitter therefore we study and compare the sensitivity of the vertical and horizontal towed loop systems with a variety of seafloor conductivity structures our results indicate that the horizontal loop system is more sensitive to the thickness of a buried conductive layer and would be advantageous over

intraplate deformation and basin formation during the tertiary within the northern iberian plate origin and evolution of the almazan basin the tertiary almazan basin was a topographic high during the mesozoic rifting at the northern part of the iberian plate it was bordered by two mesozoic basins 1 the castilian basin with a maximum thickness of more than 2000 m to the south and 2 the cameros basin with a maximum thickness of 9000 m to the north to the east the almazan basin is bordered by paleozoic rocks of the nw se trending aragonian range which underwent little subsidence during the mesozoic the two mesozoic basins show an e w direction during the tertiary nne ssw compression mainly late eocene early miocene both mesozoic basins were inverted and uplifted and the almazan basin with an overall synclinal geometry was filled with syn tectonic terrestrial sediments reaching a maximum thickness of 3500 m deformation during the tertiary was strongly controlled by preexisting structures both mesozoic extensional faults and reactivated variscan folds the depocenter of the tertiary basin migrated southward during the paleogene this migration is consistent with a piggyback transport of the whole basin northward due to the movement on the underlying crustal scale north verging cameros thrust the geometry and sedimentary evolution of the almazan thick skinned piggyback basin was controlled by the uplift associated with the main crustal scale thrust which was the main source area and was separated from the foreland basin since the early stages of filling late eocene this makes the main difference with thin skinned piggyback basins controlled by the foreland thrust belt and separated from the foreland basin only at their late stages

chromite in komatiites 3d morphologies with implications for crystallization mechanisms high resolution x ray computed tomography has been carried out on a suite of komatiite samples representing a range of volcanic facies chromite contents and degrees of alteration and metamorphism to reveal the wide range of sizes shapes and degrees of clustering that chromite grains display as a function of cooling history dendrites are spectacularly skeletal chromite grains formed during very rapid crystallization of supercooled melt in spinifex zones close to flow tops at slower cooling rates in the interiors of thick flows chromite forms predominantly euhedral grains large clusters up to a dozen of grains are characteristic of liquidus chromite whereas fine dustings of mostly individual 20 m grains form by in situ crystallization from trapped intercumulus liquid chromite in coarse grained olivine cumulates from komatiitic dunite bodies occurs in two forms as clusters or chains of euhedral crystals developing into chicken wire texture where chromite is present in supra cotectic proportions and as strongly dendritic semi poikilitic grains these dendritic grains are likely to have formed by rapid crescumulate growth from magma that was close to its liquidus temperature but supersaturated with chromite in some cases this process seems to have been favoured by nucleation of chromite on the margins of sulphide liquid blebs this texture is a good evidence for the predominantly cumulus origin of oikocrysts and in situ origin of heteradcumulate textures our 3d textural analysis confirms that the morphology of chromite crystals is a distinctive indicator of crystallization environment even in highly altered rocks

district to camp controls on the genesis of komatiite hosted nickel sulfide deposits agnew wiluna greenstone belt western australia insights from the multiple sulfur isotopes the agnew wiluna greenstone belt of western australia is the largest komatiite hosted nickel sulfide belt in the world and contains two world class ni cu pge deposits and a host of smaller deposits this study focuses on the broader scale geology of this greenstone belt in order to understand the key controls on the genesis of the komatiite hosted ni cu pge deposits with specific focus on camp to district controls we apply multiple sulfur isotopes to this geologic framework and conclude not only that the addition of crustal sulfur is a prerequisite for ore genesis in komatiite systems but above all that the sulfur required to generate world class deposits is most likely derived from barren volcanic massive sulfide lenses which are spatially and genetically associated with felsic volcanic and volcaniclastic sequences that were emplaced coevally with large komatiitic sills and channelized lava flows multiple sulfur isotope data can be utilized in exploration at the deposit to district scales at the deposit scale the spatial pattern of mass independent s isotope values 33 s provides crucial insight into the identification of proximal high grade and high tenor ores in mineralized systems in fact sulfur data reflect the assimilation process that occurred upon komatiite emplacement whereby hot turbulent magma thermomechanically eroded and assimilated exhalative sulfides spatially located close to vent with negative to near zero 33 s values whereas less turbulent flows interacted with distal sulfidic shales having 33 s values above 0 per mil accordingly the spatial variation of multiple sulfur isotope values in magmatic sulfides and associated host rocks may be utilized as a vector towards high grade ores of poorly known systems at the district scale rather than ascertaining what controls the distribution of komatiite hosted ni cu pge deposits the appropriate question to ask is what controls the distribution of country rock sulfides considering that exhalative sulfides may be crucial to ore genesis in komatiite systems we propose that felsic lava domes unambiguously mark their vents and can be directly mapped or inferred from gravity data this work provides the first step in identifying district scale control on komatiite hosted ni cu pge deposits this is the scale that has high impact on exploration for new komatiite hosted nickel sulfide belts globally

contribution of early impact events to metal silicate separation thermal annealing and volatile redistribution evidence in the pultusk h chondrite three dimensional x ray tomographic reconstructions and petrologic studies reveal voluminous accumulations of metal in pultusk h chondrite at the contact of these accumulations the chondritic rock is enriched in troilite the rock contains plagioclase rich bands with textures suggesting crystallization from melt unusually large phosphates are associated with the plagioclase and consist of assemblages of merrillite and fluorapatite and chlorapatite the metal accumulations were formed by impact melting rapid segregation of metal sulfide melt and the incorporation of this melt into the fractured crater basement the impact most likely occurred in the early evolution of the h chondrite parent body when post impact heat overlapped with radiogenic heat this enabled slow cooling and separation of the metallic melt into metal rich and sulfide rich fractions this led to recrystallization of chondritic rock in contact with the metal accumulations and the crystallization of shock melts phosphorus was liberated from the metal and subsumed by the silicate shock melt owing to oxidative conditions upon slow cooling the melt was also a host for volatiles upon further cooling phosphorus reacted with silicates leading to the formation of merrillite while volatiles partitioned into the residual halogen rich dry fluid in the late stages the fluid altered merrillite to patchy cl f apatite the above sequence of alterations demonstrates that impact during the early evolution of chondritic parent bodies might have contributed to local metal segregation and silicate melting in addition postshock conditions supported secondary processes compositional textural equilibration redistribution of volatiles and fluid alterations

microchemical and sulfur isotope constraints on the magmatic and hydrothermal evolution of the black swan succession western australia the black swan succession consists of an archean bimodal dacite komatiite association largely dominated by ultramafic cumulates hosting a number of massive and disseminated magmatic sulfide orebodies although it was affected by multiple alteration events the low degree of penetrative deformation allowed the preservation of magmatic textures and stratigraphic relationships in this context we apply a combined multiple sulfur isotope and microchemical approach to unravel the potential of sulfides to simultaneously retain information about their magmatic and hydrothermal history negative 33s signatures in both massive 0 56 and disseminated 0 66 sulfide orebodies reflect the assimilation of photochemically derived sulfur into the komatiite magma which attained sulfide liquid supersaturation through the assimilation of crustal material analogous to the intercalated breccia dacite hosting colloform sulfides 33s 0 91 the slightly different 33s signatures between disseminated and massive orebodies reflect the assimilation of different proportions of crustally derived sulfur and imply that the respective sulfide liquids segregated from distinct komatiite magma pulses subsequent alteration episodes imparted to the black swan succession a concentric zonation consisting of a serpentinite core and talc carbonate margins the black swan disseminated orebody extends through both alteration styles without major variations in the dominant millerite pyrite sulfide assemblage pyrite in both serpentinite and talc carbonate samples exhibits a consistent trace element signature suggesting a relative immobile behavior of ni and co during the percolation of the talc carbonate fluids conversely variable 34s signatures between the two alteration styles reflect mobilization of sulfur during talc carbonate alteration whereas the 2 range of 34s values in serpentinites can be attributed to moderate equilibrium fractionation processes the 10 range of 34s values in talc carbonate rocks suggests that highly oxidizing fluids promoted the mobilization of sulfur as so42 which decreased the 34s of the disseminated sulfides furthermore sulfur isotope and microchemical signatures of euhedral pyrite from intercalated dacitic breccia indicate that this pyrite generation was deposited from a late hydrothermal event which is characterized by variable and least negative 33s signatures between 0 20 and 0 48 relative to all sulfide orebodies these features suggest that the late fluids developed in a heterogeneous hydrothermal system with a minor component of sulfur recycled from the sulfide orebodies

the role of komatiitic and picritic magmatism and s saturation in the formation of ore deposits abstract the introduction of high temperature high magnesium komatiitic and picritic magmas into the earth s upper crust has given rise either directly or indirectly to many of the world s major ore deposits there is a direct association between komatiitic magmatism and kambalda style ni cu pge deposits the link between magma type and mineralization is not as clear cut in the case of the noril sk cu ni pge deposits but nevertheless there is an association between picritic magmatism and ore deposit development komatiitic and or picritic magmatism may also have contributed to the formation of many types of hydrothermal ore deposits recent nd isotope data generated by kent et al 1994 provide strong evidence for the hypothesis proposed by keays in 1983 that the au in archaean au deposits was derived either directly or indirectly from komatiites through the action of metamorphic fluids the importance of komatiitic and picritic magmas in ore forming processes arises from the fact that they are among the few mafic ultramafic magma types that are s undersaturated at the time of magma formation s saturation of magmas leads to marked depletion in the chalcophile metals for example czamanske and moore 1977 estimated that a third of the original cu and ni contents of morb were lost from the magmas due to extraction into magmatic sulphides the depletion in au and the pge is much greater due to their much larger partition coefficients keays and scott 1976 komatiitic and picritic magmas are s undersaturated because they are high temperature magmas produced by large degrees of partial melting of upper mantle sourc regions that were already depleted in s through earlier partial melting events most mafic magmas produced by less than 25 partial melting are s saturated and hence depleted in the ore forming chalcophile elements in contrast komatiitic and picritic magmas have their full complement of chalcophile metals when they do become s saturated they form sulphides that are strongly enriched in ni cu au pge and other strongly chalcophile metals these may accumulate to form ore deposits directly e g magmatic ni cu pge sulphides or be dispersed in komatiitic picritic rocks or their fractionation products making these source rocks for hydrothermal au or vms deposits

high resolution x ray computed tomography and its application to ore deposits from data acquisition to quantitative three dimensional measurements with case studies from ni cu pge deposits high resolution x ray computed tomography hrxct is a nondestructive technique that allows exploration of the three dimensional distribution of minerals and pore space in natural and synthetic rock samples recent technological developments allow the characterization of samples up to few centimeters in diameter at a resolution down to 0 7 m this combined with the development of dedicated workflows algorithms and softwares is opening new doors for the quantitative three dimensional characterization of ores at the sample scale when combined with three dimensional image analysis hrxct provides quantitative three dimensional mineralogical and textural measurements volume shape three dimensional relationship that are impossible to assess accurately by any other method this manuscript describes the principles of hrxct and presents dedicated methodologies from data acquisition throught to quantitative three dimensional measurements these methodologies are applied to ni cu pge ore samples but are suitable for a range of geologic materials the combination of hrxct with quantitative three dimensional image analysis applied to geologic materials hosting ore deposits provides a better understanding of ore mineralogy ore forming processes and parameters required for mineral or metallurgical processing with benefit for both academic studies and mineral industry applications

marine dipole dipole controlled source electromagnetic and coincident loop transient electromagnetic experiments to detect seafloor massive sulphides effects of three dimensional bathymetry seafloor massive sulphides smss are regarded as a potential future resource to satisfy the growing global demand of metals including copper zinc and gold aside from mining and retrieving profitable amounts of massive sulphides from the seafloor the present challenge is to detect and delineate significant sms accumulations which are generally located near mid ocean ridges and along submarine volcanic arc and backarc spreading centres currently several geophysical technologies are being developed to detect and quantify sms occurrences that often exhibit measurable contrasts in their physical parameters compared to the surrounding host rock here we use a short fixed offset controlled source electromagnetic csem system and a coincident loop transient electromagnetic tem system which in theory allow the detection of sms in the shallow seafloor due to a significant electrical conductivity contrast to their surroundings in 2016 csem and tem experiments were carried out at several locations near the trans atlantic geotraverse hydrothermal field to investigate shallow occurrences of massive sulphides below the seafloor measurements were conducted in an area that contains distinct sms sites located several kilometres off axis from the mid atlantic ridge some of which are still connected to hydrothermal activity and others where hydrothermal activity has ceased based on the quality of the acquired data both experiments were operationally successful however the data analysis indicates bias caused by three dimensional 3d effects of the rough bathymetry in the study area and thus data interpretation remains challenging therefore we study the influence of 3d bathymetry for marine csem and tem experiments focusing on shallow 3d conductors located beneath mound like structures we analyse synthetic inversion models for attributes associated with 3d distortions of csem and tem data that are not sufficiently accounted for in conventional 1d tem and 2d csem interpretation schemes before an adequate quantification of sms in the region is feasible these 3d effects need to be studied to avoid over underestimation of sms using the acquired em data the sensitivity of csem and tem to bathymetry is investigated by means of 3d forward modelling followed by 1d tem and 2d csem inversion of the synthetic data using realistic error conditions subsequently inversion models of the synthetic 3d data are analysed and compared to models derived from the measured data to illustrate that 3d distortions are evident in the recorded data sets

the santa rita nickel sulfide deposit in the fazenda mirabela intrusion bahia brazil geology sulfide geochemistry and genesis the santa rita ore zone within the fazenda mirabela intrusion is an unusual example of high tonnage magmatic ni cu pge sulfide mineralization developed as a stratiform layer within the main cumulus sequence of a layered intrusion the intrusion as a whole is about 4 2 5 km in outcrop dimensions and at least 3 km in original maximum stratigraphic thickness with an original boat shaped morphology the ore zone comprises a 50 to 200 m thick interval containing up to 5 wt percent disseminated sulfides within a sequence of mostly unaltered harzburgites and orthopyroxenites this orthopyroxene dominated sequence lies between the dominantly olivine rich cumulates that comprise the lower half of the intrusion and the gabbroic cumulates that make up the upper half sulfide tenor variations and silicate host rock compositions have been derived from a very large database of continuous assays of more than 500 diamond drill cores consistent patterns of sulfide tenor gradually decreasing ni from over 20 to about 10 wt percent near constant cu and gradually decreasing pges with cyclically varying pt pd ratios are found within the santa rita ore zone across the entire intrusion and display relatively little lateral variability the position of the sulfide mineralization envelope within the harzburgite orthopyroxenite package migrates to higher stratigraphic levels from the northern to the southern margin of the intrusion maximum grades and thicknesses correlate with the maximum thickness of orthopyroxene bearing cumulates asymmetrically disposed toward the southern margin of the intrusion nickel tenors of the sulfides range from 15 to 25 wt percent exceptionally high for rocks with relatively low values of mgo mgo feo and are closer to the typical values observed in komatiite hosted deposits although cu tenors typically 5 8 wt are much higher than komatiite values sulfide pge tenors range from less than 100 ppb to greater than 10 ppm of both pt and pd with maximum values in s poor rocks at the base of the sulfide bearing interval pges become significantly more depleted toward the top of the santa rita zone we attribute these features along with the localization of the sulfide bearing interval at the contact between ultramafic and mafic cumulates to mixing of an initially s undersaturated moderately ni enriched resident magma with a relatively low ni pge depleted significantly lower temperature replenishing magma charged with suspended sulfide liquid droplets

high resolution x ray computed microtomography a holistic approach to metamorphic fabric analyses an intrinsic limitation of studying microstructures in thin section is that their spatial three dimensional 3 d distribution shape and orientation have to be inferred by combining 2 d data from different sections this procedure always involves some degree of interpretation that in some cases can be ambiguous recent advances in high resolution x ray computed microtomography have made possible the direct imaging in 3 d of volumes of rock to centimeter scale this rapidly evolving technology is nondestructive and provides a holistic approach of microstructural analysis that eliminates interpretative procedures associated with 2 d methods spatial images can be generated through any part of the rock sample and used as virtual petrographic sections our application of this technique to an oriented drill core sample from the classic orijarvi metamorphic region of southern finland reveals a number of in situ 3 d aspects including 1 the spatial distribution and shape of andalusite porphyroblasts 2 the geometry of a matrix foliation anastomosing around the porphyroblasts 3 a millimeter scale compositional layering that controlled the oscillation of porphyroblasts and sulfide mineralization and 4 distinct inclusion trail patterns characterizing porphyroblast core versus rim zones the combined data indicate that the steeply dipping bedding subparallel foliation that characterizes the orijarvi area formed by bulk north south crustal shortening and associated vertical stretching

drilling shallow water massive sulfides at the palinuro volcanic complex aeolian island arc italy a subseafloor replacement style barite and sulfide occurrence was drilled in shallow waters at the palinuro volcanic complex the northernmost aeolian arc volcano in the tyrrhenian sea italy using a lander type drilling device 11 successful drill holes yielded a total of 13 5 m of core from a sediment filled depression located at a water depth of 630 to 650 m the longest continuous drill core recovered consists of 4 84 m of massive to semimassive barite and sulfides with abundant late native sulfur overprint seafloor observations suggest that the hydrothermal system associated with the formation of the subseafloor barite and sulfide ore zone is still active although black smoker activity does not occur on the seafloor the recovered drill core shows that the subseafloor deposit is zoned with depth the top of the mineralized zone is comprised of a variably silicified vuggy barite sulfide facies that shows notable polymetallic metal enrichment while the deeper portion of the mineralized zone is dominated by massive pyrite having distinctly lower base and precious metal grades metal zonation of the barite and sulfide deposit is related to the evolution of the hydrothermal fluids in space and time the barite cap and the massive pyrite present in the deeper portion of the mineralized zone appear to have formed early in the paragenesis during the main stage of the mineralization the barite cap was brecciated and cemented by a polymetallic assemblage of barite and pyrite with minor chalcopyrite and tetrahedrite trace famatinite and rare cinnabar lower temperature precipitates formed during the main stage of mineralization include sphalerite galena pyrite opal a and barite which are associated with traces of pb sb as sulfosalts such as bournonite seligmannite or semseyite a distinct mineral assemblage of fine grained anhedral enargite hypogene covellite chalcopyrite and galena is commonly associated with colloform sphalerite galena and pyrite as a late phase of this main stage colloform pyrite and marcasite are the last sulfides formed in the paragenetic sequence the deposit is interpreted to have formed from fluids having an intermediate sulfidation state although excursions to high and very high sulfidation states are indicated by the presence of abundant enargite and hypogene covellite laser ablation and conventional sulfur isotope analyses show that pyrite formed close to the seafloor within the zone of polymetallic metal enrichment has a variable sulfur isotope composition 34s 39 to 3 whereas a more narrow range is observed in the massive pyrite at depth 34s 10 to 0 similar variations were also documented for the late native sulfur overprint overall the negative sulfur isotope ratios at depth the intermediate to very high sulfidation conditions during mineralization and the abundance of native sulfur suggest contributions of magmatic volatiles to the mineralizing fluids from a degassing magma chamber at depth biological processes are interpreted to have played a major role during late stages of ore formation the combination of a subseafloor replacement deposit with a massive to semimassive barite cap rock overlying massive pyrite the intermediate to high sulfidation characteristics and the strong biological influence on the late stages of mineralization are distinct from other modern seafloor massive sulfide deposits and represents a style of submarine mineralization not previously recognized in a modern volcanic arc environment the barite and sulfide occurrence at palinuro shares many characteristics with porphyry related base metal veins and intermediate sulfidation epithermal deposits suggesting that metallogenic processes associated with arc related magmatic hydrothermal systems are not restricted to the subaerial environment

constraints on the formation of platinum group element deposits in igneous rocks mechanisms of concentration of the platinmn group and other chalcophile elements iu several platinum group element deposits in layered intrusions are evaluated in light of recently published data on element partitioning between immiscible sulfide and silicate melts the similarity of the partition coefficieut d super sulfide melt silicate melt of ir to that of pd indicates that the observed fractionation of these elements in nature resulted from a process other than or in addition to sulfide liquid immiscibility in experiments designed to test the possibility that this fractionation was due to the presence of os ir alloy sulfide and silicate melts were equilibrated with ir metal at 1 450 degrees c 8 kbars total pressure and under sulfur and oxygen fugacity conditions appropriate for nature the ir content of the sulfide liquid was found to be or 3 7 wt percent and that of the coexisting silicate melt inferred to be or 1 000 ppb these concentrations are far in excess of the ir contents of natural sulfides or rocks and indicate that os ir alloys are not stable in the presence of sulfide or silicate melts in nature using our preferred values of d super sulfide melt silicate melt for the chalcophile elements and their estimated concentrations in the mantle limits are determined for the possible ranges of concentrations and relative abundances of these elements in immiscible sulfide liquid formed in magma derived by partial melting of the mantle the ratios of highly chalcophile to moderately chalcophile elements and of metal to sulfur of several deposits including the j m reef stillwater complex the ug 2 bushveld complex and the lac des isles complex are inconsistent with concentration solely by segregation of sulfide liquid in contrast the merensky reef fits the geochemical criteria for formation by accumulation of magmatic sulfide stratigraphic variations in chalcophile element concentrations through the ug 2 and the main sulfide zone of the great dyke also indicate that metals must have been redistributed on at least the meter scale our analysis implies either different relative mobilities of the chalcophile elements relative to one another in a process postdating initial sulfide liquid deposition or concentration by a different mechanism

ten years of marine csem for hydrocarbon exploration marine controlled source electromagnetic csem surveying has been in commercial use for predrill reservoir appraisalandhydrocarbonexplorationfor10 years althougha recent decrease has occurred in the number of surveys and publications associated with this technique the method has become firmly established as an important geophysical tool intheoffshoreenvironment thisisaconsequenceoftwoimportant aspects associated with the physics of the method first it is sensitive to high electrical resistivity which although not an unambiguous indicator of hydrocarbons is an important property of economically viable reservoirs second although the method lacks the resolution of seismic wave propagation it has a much better intrinsic resolution than potential field methods such as gravity and magnetic surveying which until now have been the primary nonseismicdatasetsusedinoffshoreexploration althoughbymany measures marine csem is still in its infancy the reliability and noise floors of the instrument systems have improved significantly over the last decade and interpretation methodology has progressed from simple anomaly detection to 3d anisotropic inversion of multicomponent data using some of theworld sfastestsupercomputers researchdirectionspresently include tackling the airwave problem in shallow water by applying time domain methodology continuous profiling tools and the use of csem for reservoir monitoring during production

interfacial tension between magmatic sulfide and silicate liquids constraints on kinetics of sulfide liquation and sulfide migration through silicate rocks we have measured the interfacial tension sf between sulfide and silicate melts over the temperature range from 1250 to 1325 c by in situ measurement of the shapes of sessile drops of sulfide immersed in silicate melt sitting upon level alumina substrates the silicate melt was an alkali free synthetic basaltic liquid the sulfide melts were synthetic mixtures of fe cu ni s or fe s o the interfacial tension ranges from about 500 mj m 2 for sulfide of fes composition to approximately 600 mj m 2 for sulfide containing 16 wt cu or 6 5 wt ni and up to 650 mj m 2 for fe s o liquid containing 4 wt o contact angles vary from 150 to 180 showing that sulfide liquid does not wet oxide minerals in silicate magmas the density of sulfide melt does not depend strongly on cu or ni content remaining between 4 0 and 4 5 g cm 3 over the range of cu and ni contents expected in sulfide magmas but increases substantially to about 5 5 g cm 3 in fe s o melts containing 4 wt o our results can be combined with conventional concepts of nucleation theory to indicate that when silicate magmas exist at small degrees of supersaturation sulfide drops may nucleate rarely and at widely spaced intervals leading to kinetic control of the compositions of the resulting droplets in light of our results we use simple scaling arguments to argue that sulfide magmas are not capable of migrating through partially molten silicate rocks by capillary forces alone but may be forced through narrow grain boundaries or grain edges only by the flow of the enclosing silicate melt during melt extraction by compaction of partially molten mantle peridotite it is highly unlikely that silicate flow rates could be sufficiently rapid to permit the entrainment of droplets of sulfide liquid at temperatures below the solidus of enclosing silicate rocks sulfide melt will be free to travel along fractures or grain boundaries the mobility of sulfide melts through completely solidified silicate rocks may account for the widespread observation that late stage highly fractionated sulfide liquids have escaped from cooling bodies of massive sulfide to form veins and disseminations of cu rich sulfide minerals in their silicate host rocks

rapid resistivity imaging for marine controlled source electromagnetic surveys with two transmitter polarizations an application to the north alex mud volcano west nile delta to image the internal resistivity structure of the north alex mud volcano offshore egypt the marine electromagnetics group at the helmholtz centre for ocean research kiel geomar developed and conducted a novel transient marine controlled source electromagnetic experiment the system which was specifically developed to image the mud volcano is also generally suitable for surveys of other small seafloor targets such as gas hydrate reservoirs fluid flow features and submarine massive sulfide deposits an electric bipole antenna is set down by a remotely operated vehicle on the seafloor sequentially in two perpendicular polarizations at each transmission station two orthogonal horizontal electric field components are recorded on the seabed by an array of independently deployed nodal receivers rxs with two transmitter polarizations the unique acquisition geometry of the system provides a very rich data set however for this geometric setup conventional marine electromagnetic interpretation schemes such as normalized magnitude variation with offset plots have been difficult to implement we have developed a simple imaging technique which can be used for a first step mapping of seafloor apparent resistivity with the geomar system images can be produced in just a few minutes on a regular laptop computer and the robustness of the approach was demonstrated using two synthetic data sets from simple seafloor models the method was then applied to the real data acquired at the north alex mud volcano in 2008 results found increased apparent sediment resistivities of up to 4 omega m near the center of the mud volcano occurring at source rx offsets greater than 500 m which mapped to apparent depths of greater than 150 m this may be caused by large quantities of free gas or freshwater in the sediment pore space

trace element variations in olivine from the eastern deeps intrusion at voisey s bay labrador as a monitor of assimilation and sulfide saturation processes ni cu co sulfide mineralization in the mesoproterozoic voisey s bay intrusion is spatially and genetically associated with magmatic breccia zones within an extensive dike system and in particular with the entry point of this system into a larger intrusion eastern deeps intrusion the massive sulfide and breccia bearing inner basal margin of this upper intrusion is enveloped by weakly mineralized variable textured troctolite that progressively decreases in sulfide content contains fewer paragneiss fragments and eventually grades into a largely sulfide barren homogeneous plagioclase and olivine meso cumulate termed normal troctolite toward the top of the intrusion olivine from the troctolite lithologies the mineralized basal breccia sequence and the uppermost olivine gabbro in the eastern deeps intrusion was analyzed with secondary ion mass spectrometry sims we present multitrace element data including petrogenetically important elements v cr mn co ni zn sr and y which indicate that four petrological processes important to ore formation are recorded by the compositional diversity of olivine the heterogeneous ni co fo contents of olivine in the eastern deeps intrusion co ni ratios in olivine gabbro 0 18 1 1 normal troctolite 0 07 0 26 variable textured troctolite 0 11 0 29 basal breccia sequence 0 20 0 34 are due to variable modification of original compositions by reequilibration with trapped silicate and sulfide liquids the abrupt changes of fe fo79 fo66 and ni 2 500 to 80 ppm contents and some trace elements up to 1 5x more sr up to 3x more y than average normal troctolite olivine in olivine from intervals in the barren upper normal troctolite indicate that olivine crystallized from separate pulses of magma with variable degrees of differentiation the severe ni depletion of one troctolite melt batch 10 ppm ni vs 290 ppm ni for average normal troctolite magma is likely a result of sulfide saturation and segregation either in a deeper staging chamber or in the conduit prior or contemporary to olivine precipitation and emplacement the gradational increase of fe from fo80 to fo62 mn from 4 000 to 10 000 ppm and zn from 400 to 620 ppm in olivine from the weakly mineralized and contaminated lower part of the variable textured troctolite downward into the massive sulfide bearing and strongly contaminated basal breccia sequence is consistent with olivine fractionation from an increasingly country rock contaminated sulfide saturated silicate magma olivine here crystallized prior to or contemporaneously with the segregation of an immiscible sulfide liquid olivine grains that are enclosed by sulfide display homogeneous forsterite contents fo62 with pronounced intragrain trace element zonation mn ni co zn diffusion profiles mn ni indicate a relatively short immersion time 1 000 years of these olivine grains in sulfide liquid which likely resulted in the partial retention of ni in the olivine olivine in the vicinity of massive sulfides in the eastern deeps intrusion from variable textured troctolite to basal breccia sequence has a distinct minor and trace element signature v cr mn co ni zn compared to olivine from the barren troctolite and olivine gabbro a multiple regression analysis using these data yields an index that describes the relative vertical proximity of olivine to massive sulfides in conjunction with the stratigraphic context of the host lithology this information could potentially be used as a vector toward massive sulfide mineralization in the eastern deeps intrusion and also support ni exploration in other olivine bearing mafic intrusions with similar style of sulfide mineralization

wetting of mantle olivine by sulfide melt implications for re os ratios in mantle peridotite and late stage core formation this study investigates the effects of variations in the relative fugacities of oxygen and sulfur on the wetting of mantle olivine by molten sulfide experiments were performed on mixtures of san carlos olivine and synthetic fes at 1 bar and 1350 c crucibles were fabricated from san carlos olivine and the fugacities of oxygen and sulfur were controlled by mixing co2 co and so2 gases experimental conditions ranged from logfo2 7 9 to 10 3 and from logfs2 1 5 to 2 5 our experimental results demonstrate that at a given temperature and pressure the olivine sulfide melt dihedral angle is controlled by the concentration of o dissolved in an anion rich melt trace amounts of o dissolve in sulfide melt at fo2 conditions near the iron wustite oxygen buffer and the dihedral angle is 90 at fo2 conditions near the fayalite magnetite quartz oxygen buffer the concentration of dissolved o is near 9 wt and the dihedral angle is 52 allowing small amounts of sulfide melt to form an interconnected network in olivine rich rocks and to migrate via porous flow these results indicate that sulfide melt is likely to be mobile at current upper mantle fo2 and fs2 conditions in mantle peridotite the addition or removal of sulfide melt by porous flow will variably fractionate re os u pb and th pb ratios because os and pb are more chalcophile than re u and th the re os ratio of the peridotite is especially sensitive to this process the mobility of sulfide melt at oxidizing conditions implies that the addition of oxidized chondritic material during the later stages of the accretion of the earth may have facilitated the segregation of core forming material by porous flow if temperatures were in excess of the sulfide solidus

on mapping seafloor mineral deposits with central loop transient electromagnetics electromagnetic methods are commonly employed in exploration for land based mineral deposits a suite of airborne land and borehole electromagnetic techniques consisting of different coil and dipole configurations have been developed over the last few decades for this purpose in contrast although the commercial value of marine mineral deposits has been recognized for decades the development of suitable marine electromagnetic methods for mineral exploration at sea is still in its infancy one particularly interesting electromagnetic method which could be used to image a mineral deposit on the ocean floor is the central loop configuration central loop systems consist of concentric transmitting and receiving loops of wire while these types of systems are frequently used in land based or airborne surveys to our knowledge neither system has been used for marine mineral exploration the advantages of using central loop systems at sea are twofold 1 simplified navigation because the transmitter and receiver are concentric and 2 simplified operation because only one compact unit must be deployed we produced layered seafloor type curves for two particular types of central loop methods the in loop and coincident loop configurations in particular we consider models inspired by real marine mineral exploration scenarios consisting of overburdens 0 to 5 m thick overlying a conductive ore body 5 to 30 m thick modeling and resolution analyses showed that using a 50 m 2 transmitting loop with 20 a of current these two configurations are useful tools to determine the overburden depth to a conductive ore deposit and its thickness in the most extreme case absolute voltage errors on the order of 10 nv are required to resolve the base of a 30 m thick ore deposit whether such noise floors can be achieved in real marine environments remains to be seen

cu ni pge fertility of the yoko dovyren layered massif northern transbaikalia russia thermodynamic modeling of sulfide compositions in low mineralized dunite based on quantitative sulfide mineralogy the geology and major types of sulfide mineralization in the yoko dovyren layered massif northern transbaikalia russia are presented this study focuses on the structure mineralogy and geochemistry of poorly mineralized plagiodunite and dunite in the lower part of the intrusion assuming these rocks contain key information on the timing of sulfide immiscibility in the original cumulate pile we apply a novel approach which combines estimates of the average sulfide compositions in each particular rock with thermodynamic modeling of the geochemistry of the original sulfide liquid to approach the goal an updated sulfide version of the comagmat 5 model was used results of simulations of sulfide immiscibility in initially s undersaturated olivine cumulates demonstrate a strong effect of the decreasing fraction of the silicate melt due to crystallization of silicate and oxide minerals on the composition of the intercumulus sulfide liquid comparison of the observed and modeled sulfide compositions indicates that the proposed modeling reproduces well the average concentrations of cu cd ag and pd in natural sulfides this suggests the sulfide control on the distribution of these elements in the rocks conversely data for pt and au suggest that a significant portion of these elements could present in a native form thus depleting the intercumulus sulfide melt at an early stage of crystallization

analog experimental insights into the formation of magmatic sulfide deposits abstract magmatic sulfide deposits result from transport and settling of dense sulfide liquid droplets in basic magma to model these processes we carried out analog experiments in which dense silicone oil droplets were transported in a viscous aqueous polymer solution the results of the experiments indicate that sulfide droplets can be carried in suspension by magma flowing at typical velocities due to the large surface tension of sulfide droplets coalescence does not occur during transport transport ceases when upward magma velocity decreases because of conduit enlargement or change from vertical to horizontal flow coalescence of droplets is controlled by magma viscosity and the presence of crystals

unraveling multiple thermotectonic events accommodated by crustal scale faults in northern iberia spain insights from k ar dating of clay gouges

first results from a marine controlled source electromagnetic survey to detect gas hydrates offshore oregon 1 submarine gas hydrate is a hazard to drilling a potential hydrocarbon resource and has been implicated as a factor in both submarine slope stability and climate change bulk in situ electrical resistivities evaluated from electromagnetic surveys have the potential to provide an estimate of the total hydrate volume fraction more directly than by using seismic and well log data we conducted a marine controlled source electromagnetic sounding at hydrate ridge oregon usa in august 2004 electromagnetic fields transmitted by a deep towed horizontal electric dipole source were measured by a linear array of 25 seafloor electromagnetic receivers positioned 600 m apart to produce a dense coverage in the recorded electric field data results are presented in simple form by apparent resistivity pseudosections which produce an approximate image of lateral resistivity variations across the study region resistivity values are consistent with those from well logs collected in the area and pseudosection features are correlated with seismic reflectors archie s law based on pseudosection apparent resistivities predicts volumetric hydrate concentrations vary from 0 30 across the ridge

sulfur saturation and second stage melts application to the bushveld platinum metal deposits a model is presented for the formation of platinum group element ores by precipitation from sulfur deficient platinum group element rich second stage magmas numerous investigations indicate that basaltic magmas originating from undepleted or mildly depleted source regions are sulfur saturated at the time of eruption mantle derived peridotites residual from midocean ridge basalt magma genesis have pd abundances that are uniformly too high for it to have originated solely from silicate melt retained in the source region at the time of segregation they imply the presence of an accessory immiscible sulfide melt to host the platinum group elements the very high sulfide melt silicate melt partition coefficients of the platinum group elements would result in strong fractionation of these metals into the accessory sulfide component during the melting event the extreme platinum group element enrichment of this accessory sulfide component is evidenced by the discovery ofplatinoid minerals in residual mantle nodules containing pd and pt abundances at the low ppb level keays et al 1981 magmas generated by low to moderate degrees of partial melting of undepleted mantle are therefore sulfur saturated at the time of segregation these first stage magmas become impoverished in platinum group elements during the early stages of fractional crystallization because of coprecipitation of an immiscible sulfide phase e g midocean ridge basalt glasses average

the assessment of marine gas hydrates through electrical remote sounding hydrate without a bsr marine gas hydrates prevalent in offshore sediments in canada and japan are a possible hydrocarbon resource a hazard to drilling and a source of a major greenhouse gas quantitative estimates of hydrate concentrations in deep sea sediment are difficult to obtain by conventional methods we have sought novel techniques specifically designed for assessment such as transient electric dipole dipole electromagnetics the latter method is based on the assumption of a reduced electrical conductivity in hydrate rich zones field trails of new apparatus on the cascadia margin have proven successful excellent data were collected and analysed using a differential phase method to reduce systematic error apparent resistivities collected on three lines demonstrate that the resistivity of the seafloor is remarkably uniform over the whole survey area the average hydrate concentration deduced with the aid of a reference model based on the electrical logs of odp holes 888 and 889 is about 17 26 of pore space 9 13 of sediment volume in the 100 m interval above the bsr the values are consistent with those obtained by other analyses further the presence of hydrate is predicted in a region to the east of 889b where there is no visible bsr

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

komatiites and nickel sulfide ores of the black swan area yilgarn craton western australia 2 geology and genesis of the orebodies the black swan ultramafic succession hosts a number of magmatic fe ni cu pge sulfide ore shoots ranging from high grade massive ore to low grade disseminated sulfides of these the most economically significant is the silver swan massive sulfide orebody associated with the basal contact of the succession the deposit varies in thickness between 5 and 20 m reaches a n s strike length of 75 m extends for at least 1 2 km of vertical plunge and is open at depth overlying matrix net textured ore is rare inclusions of dacite are abundant within the lower 5 m of the massive sulfide they range from angular fragments through smooth sinuous and plumose morphologies to fine lace like intergrowths with the sulfide matrix and comprise variable proportions of cores of porphyritic dacite and carapaces with skeletal plagioclase phenocrysts dynamic crystallisation and kinetic melting textures in the carapaces indicate that the inclusions have been heated to various temperatures some well above their liquidus temperature the composition of the inclusions ranges from a perfect match with the immediate footwall dacites to mixtures of dacite with up to 30 komatiite the consistent thickness of the inclusion bearing basal layer within the massive sulphide is interpreted as the extent of 3 d physical connectivity between the inclusions and a partially molten underlying hybrid layer primary contacts between the silver swan massive sulfide orebody and overlying ultramafic rocks are marked by thin rinds containing coarse grained chevron textured chromites with skeletal textures compositions of these chromites match those from kambalda perseverance and other localities and are inconsistent with a metamorphic origin they are interpreted as markers of primary magmatic contacts the combination of this feature with the general paucity of matrix ore implies that the massive ore accumulated and solidified before the accumulation of the overlying thick sequence of olivine cumulates taken together with observations on the internal fractionation of platinum group elements within the massive ores these observations are consistent with a model where the massive ore were emplaced at the floor of a small partially drained lava tube the floor of the tube had been previously heated by passage of large volumes of lava such that it had reached its melting range the felsic inclusions within the ore are the result of buoyant ascent of partially molten substrate into the ore magma this constitutes strong evidence for the operation of thermo mechanical erosion during ore emplacement the disseminated cygnet and black swan orebodies show a number of distinctive features cygnet contains a assemblage of clasts and inclusions which are interpreted as the result of rip up transport and redeposition of sulfides from a pre existing massive sulfide orebody of which black duck may be a remnant the black swan orebody by contrast does not show xenolithic features but is characterised by an association of sulfide blebs with segregation vesicles and by unusually coarse grained olivine the black swan orebody is interpreted as the result of transport of sulfide droplets within a lava charged with a suspended load of coarse olivine crystals

near bottom magnetic signatures of submarine hydrothermal systems at marsili and palinuro volcanoes southern tyrrhenian sea italy near bottom magnetic field data were collected using a towed magnetometer over selected parts of palinuro and marsili submarine volcanoes in the southern tyrrhenian sea italy we obtained equivalent magnetizations maps at these sites by inverting the corresponding magnetic anomalies highlighting the seafloor expression of hydrothermal alteration zones of reduced magnetization are interpreted as evidence for alteration related to hydrothermal processes they are associated with water column and seafloor observations of hydrothermal activity and altered host rocks at marsili volcano a large elliptical area of reduced magnetization is located south of the summit cone and perpendicular to the trend of marsili volcano itself this confirms the presence of a large hydrothermal system centered over the more recent eastern volcanic ridge and its associated magma chamber similarly areas of reduced magnetization over palinuro caldera are consistent with hydrothermal venting occurring along the caldera walls consistent with permeability structures related to caldera ring faults providing preferred pathways for the upflow of hydrothermal fluids

a first application of a marine inductive source electromagnetic configuration with remote electric dipole receivers palinuro seamount tyrrhenian sea we study a new marine electromagnetic configuration which consists of a ship towed inductive source transmitter and a series of remote electric dipole receivers placed on the seafloor the approach was tested at the palinuro seamount in the southern tyrrhenian sea at a site where massive sulfide mineralization has been previously identified by shallow drilling a 3d model of the palinuro study area was created using bathymetry data and forward modeling of the electric field diffusion was carried out using a finite volume method these numerical results suggest that the remote receivers can theoretically detect a block of shallowly buried conductive material at up to 100 m away when the transmitter is located directly above the target we also compared the sensitivity of the method using either a horizontal loop transmitter or a vertical loop transmitter and found that when either transmitter is located directly above the mineralized zone the vertical loop transmitter has sensitivity to the target at a farther distance than the horizontal loop transmitter in the broadside direction by a few 10s of meters furthermore the vertical loop transmitter is more effective at distinguishing the seafloor conductivity structure when the vertical separation between transmitter and receiver is large due to the bathymetry as a horizontal transmitter is logistically easier to deploy we conducted a first test of the method with a horizontal transmitter apparent conductivities are calculated from the electric field transients recorded at the remote receivers the analysis indicates higher apparent seafloor conductivities when the transmitter is located near the mineralized zone forward modeling suggests that the best match to the apparent conductivity data is obtained when the mineralized zone is extended southward by 40 m beyond the zone of previous drilling our results demonstrate that the method adds value to the exploration and characterization of seafloor massive sulfide deposits

evaluation of gas hydrate deposits in an active seep area using marine controlled source electromagnetics results from opouawe bank hikurangi margin new zealand several known gas seep sites along the hikurangi margin off the east coast of new zealand were surveyed by marine controlled source electromagnetic csem experiments a bottom towed electric dipole dipole system was used to reveal the occurrence of gas hydrate and methane related to the seeps the experiments were part of the international multidisciplinary research program new vents carried out on german r v sonne in 2007 cruise so191 to study key parameters controlling the release and transformation of methane from marine cold vents and shallow gas hydrate deposits two csem lines have been surveyed over known seep sites on opouawe bank in the wairarapa region off the se corner of the north island the data have been inverted to sub seafloor apparent resistivity profiles and one dimensional layered models clearly anomalous resistivities are coincident with the location of two gas seep sites north tower and south tower on opouawe bank a layer of concentrated gas hydrate within the uppermost 100 m below the seafloor is likely to cause the anomalous resistivities but free gas and thick carbonate crusts may also play a role seismic data show evidence of fault related venting which may also indicate the distribution of gas hydrates and or authigenic carbonate geochemical profiles indicate an increase of methane flux and the formation of gas hydrate in the shallow sediment section around the seep sites takahe is another seep site in the area where active venting higher heat flow shallow gas hydrate recovered from cores and seismic fault planes but only moderately elevated resistivities have been observed the reasons could be a the gas hydrate concentration is too low even though methane venting is evident b strong temporal or spatial variation of the seep activity and c the thermal anomaly indicates rather temperature driven fluid expulsion that hampers the formation of gas hydrate beneath the vent

komatiites and nickel sulphide orebodies of the black swan area yilgarn craton western australia 1 petrology and volcanology of host rocks the black swan succession is a bimodal association of dacitic and komatiitic volcanic rocks located about 50 km nne of kalgoorlie within the 2 7 ga eastern goldfields greenstone province of the yilgarn craton the komatiite stratigraphy comprises a steep dipping east facing package about 700 m in maximum thickness and about 2 5 km in strike length fig 1 which hosts a number of economically exploitable ni sulphide orebodies including the silver swan massive ore shoot approximately half a million tonnes at about 10 5 ni the sequence can be subdivided into a lower felsic unit comprising coherent and autobrecciated facies of multiple dacite lava flows an upper eastern and lower western ultramafic unit each showing marked lateral facies variation and an upper felsic unit coeval with the eastern ultramafic unit the komatiite sequence has been metamorphosed at sub greenschist facies in the presence of high proportions of co2 rich fluid giving rise to pervasive talc carbonate and talc carbonate quartz assemblages with extensive preservation of pseudomorphed igneous textures cores of lizardite serpentinite are present in the thickest parts of the ultramafic succession the degree of penetrative deformation is generally very low and original stratigraphic relationships are largely intact in much of the sequence the eastern ultramafic unit and western ultramafic unit are interpreted as components of a single large komatiite flow field representing overlapping stages in the emplacement of a series of distributory lava pathways and flanking sheet flows the western ultramafic unit which hosts the bulk of the high grade massive and disseminated ores is a sequence dominated by coarse grained olivine cumulates 2 km wide and up to 500 m thick with major magma pathways represented by thick homogenous olivine mesocumulate piles at its northern and southern ends respectively 400 and 200 m thick the sequence between the two major pathways consists of olivine orthocumulates ooc with minor spinifex textured intervals the unit is capped by a persistent spinifex textured crust less than 1 m thick and is locally vesicular the eastern ultramafic unit contains the black swan cumulate zone a 500 m thick sequence of very coarse grained hopper textured locally vesicular ooc containing disseminated sulphides in its lower 200 m the zone is flanked to the north and south by complexly interdigitated sequence of highly irregular spinifex capped olivine cumulate rich flow lobes between 1 and 100 m thick and dacitic lavas and tuffs the complexity of the 3 d spatial relationship of these units suggests a combination of simultaneous eruption of dacite and komatiite combined with thermal or thermomechanical erosion the eastern and western units are interpreted as the result of more or less continuous prolonged eruption of olivine charged komatiite lava which developed localised thermo mechanical erosion channels in the dacitic substrate komatiite and dacite eruption was synchronous giving rise to complex interdigitation and extensive contamination and hybridisation

preliminary interpretation of electromagnetic heat flow seismic and geochemical data for gas hydrate distribution across the porangahau ridge new zealand porangahau ridge located offshore the wairarapa on the hikurangi margin is an active ocean continent collision region in northeastern new zealand coastal waters bottom simulating reflections bsrs in seismic data indicate the potential for significant gas hydrate deposits across this part of the margin beneath porangahau ridge a prominent high amplitude reflection band has been observed to extend from a deep bsr towards the seafloor review of the seismic data suggest that this high amplitude band is caused by local shoaling of the base of gas hydrate stability due to advective heat flow and it may constitute the location of elevated gas hydrate concentrations during r v tangaroa cruise tan0607 in 2006 heat flow probing for measurements of vertical fluid migration sediment coring for methane concentrations and additional seismic profiles were obtained across the ridge in a subsequent 2007 expedition on r v sonne cruise so191 a controlled source electromagnetic csem experiment was conducted along the same seismic geochemical and heat flow transect to reveal the electrical resistivity distribution csem data highlight a remarkable coincidence of anomalously high resistivity along the western landward flank of the ridge which point to locally higher gas hydrate concentration above the high amplitude reflection band measured sediment temperature profiles also along the western flank consistently show non linear and concave geothermal gradients typical of advective heat flow geochemical data reveal elevated methane concentrations in surface sediments concomitant with a rapid decline in sulfate concentrations indicating elevated methane flux and oxidation of methane in conjunction with sulfate reduction at the landward ridge base together these data sets suggest that the western rim of porangahau ridge is a tectonically driven zone of rising fluids that transport methane and cause an upward inflection of the base of gas hydrate stability and the formation of locally enriched gas hydrate above the reflective zone

copper ore grade hydrothermal mineralization discovered in a seamount in the tyrrhenian sea mediterranean is the mineralization related to porphyry coppers or to base metal lodes abstract a luzonite and tennantite tetrahedrite bearing massive sulfide mineralization was discovered when sampling the crater of the palinuro seamount located within a probable island arc or marginal basin tectonic setting the mineralization is made up of indurated sulfide crusts interpreted to have been deposited by a seawater sediment interface and mixed with ooze of organic and volcanic origin a preliminary investigation of the economic minerals showed besides luzonite and tennantite tetrahedrite native rare copper all associated with pyrite predominantly and baryte native silver bismuthinite and stibnite were also found a dust like white precipitate was observed by submersible close to the mineralized zone but no structures or edifices resembling black smokers have yet been identified massive pyrite deposits associated with such uncommon mineral assemblages are found in the high level volcanic parts of porphyry copper systems or associated with base metal lodes the massive sulfide discovery is suggested to have a volcanogenic exhalative origin and a genetic relationship with porphyry coppers or base metal sulfide lodes

vulcan a deep towed csem receiver we have developed a three axis electric field receiver designed to be towed behind a marine electromagnetic transmitter for the purpose of mapping the electrical resistivity in the upper 1000 m of seafloor geology by careful adjustment of buoyancy and the use of real time monitoring of depth and altitude we are able to deep tow multiple receivers on arrays up to 1200 m long within 50 m of the seafloor thereby obtaining good coupling to geology the rigid body of the receiver is designed to reduce noise associated with lateral motion of flexible antennas during towing and allows the measurement of the vertical electric field component which modeling shows to be particularly sensitive to near seafloor resistivity variations the positions and orientations of the receivers are continuously measured and realistic estimates of positioning errors can be used to build an error model for the data during a test in the san diego trough offshore california inversions of the data were able to fit amplitude and phase of horizontal electric fields at three frequencies on three receivers to about 1 in amplitude and 1 in phase and vertical fields to about 5 in amplitude and 5 in phase the geological target of the tests was a known cold seep and methane vent in 1000 m water depth which inversions show to be associated with a 1 km wide resistor at a depth between 50 and 150 m below seafloor given the high resistivity 30 m and position within the gas hydrate stability field we interpret this to be massive methane hydrate

strain indicators and magnetic fabric in intraplate fault zones case study of daroca thrust iberian chain spain abstract anisotropy of magnetic susceptibility ams has been applied to the study of shallow fault zones although interpretation of the results requires establishing clear relationships between petrofabric and magnetic features magnetic behaviour of fault rocks and an extensive knowledge of p t conditions in this work we demonstrate that magnetic methods can be applied to the study of heterogeneous fault zones provided that a series of requisites are met a major fault zone within the iberian plate daroca thrust showing transpressional movements during cenozoic time was chosen for this purpose because of the exceptional outcrops of fault gouge and microbreccia and its relevance within the context of the northeastern iberian plate magnetic fabrics were analysed and the results were compared with foliation and s c structures measured within the fault zone clay mineral assemblages suggest maximum burial depths shallower than 2 km

sequences of thrusts and displacement transfer in the superposed duplexes of the esla nappe region cantabrian zone nw spain abstract in a cross section through the southern arm of the cantabrian zone several duplexes have been identified below the esla nappe which is the uppermost and main thrust sheet of the area the folds deforming the esla nappe are culmination walls linked to frontal and lateral ramps belonging to the lower thrust sheets the thrust sequence can be established on the basis of quantitative analysis of displacement transfer and out of sequence thrusting the primitive footwall ramps of the esla nappe region were often subsequently broken by decollements developed in successively lower stratigraphic levels of these footwalls the kinematics of the lowest duplex are more complicated than those of typical duplexes described elsewhere some thrusts transfer only part of their displacement to the roof thrust while the remaining part is accommodated along the higher thrusts of previously emplaced duplexes cutting out of sequence one or more floor or roof thrusts cumulative displacement of the thrusts in this region is about 90 km giving a present thickness 3 times that of the original pre orogenic sequence together with a translation of at least 60 km for the synorogenic basin

physical constraints on the migration of immiscible fluids through partially molten silicates with special reference to magmatic sulfide ores the migration of dense fe rich immiscible liquids through partially molten silicates is of critical importance to several issues including the formation of magmatic sulfide ore deposits and the formation of metallic cores in terrestrial planets the migration of immiscible dense liquids can be considered to occur in three distinct regimes dictated by the relative sizes of the dense liquid droplets and the crystals making up the silicate crystal mush or partially melted silicate rock if dense microdroplets are smaller than the diameter of the narrowest portions of pore throats between silicate crystals then downward motion is possible the maximum rate of downward settling in loosely packed crystal mushes occurs when the droplet size is approximately one tenth the crystal size as long as the silicate melt between crystals remains microdroplets are capable of migrating distances of hundreds to thousands of meters vertically through crystal mushes contained in cooling dikes with typical grain sizes stranding of larger droplets similar in size to the crystals results from capillary forces preventing droplet deformation as they attempt to pass into pore throats narrower than themselves only in very coarse grained mushes with grain sizes greater than about 2 cm can droplets the size of intergranular pores migrate downwards on the other hand coalescence of many microdroplets into pre existing stranded droplets may generate connected net textured domains of the dense liquid that are many times larger than the grain size of the mush when the vertical height of the connected domain is great enough the pressure gradient inside the dense phase exceeds the capillary force impeding downward motion through narrow pore throats and the immiscible phase is able to move down along vertically oriented networks these networks should not suffer stranding until they reach a solid layer or the base of the intrusion we suggest that in most cases sulfide droplets formed by fractional segregation in large magma bodies should come to rest at the top of the crystal pile whereas sulfides introduced to magmas by assimilation of fine grained sulfidic sediments should be capable of passing downward through crystal mushes to form massive or net textured accumulations at the bottom of the partially molten zone

olivine crystallographic control and anisotropic melt distribution in ultramafic partial melts in the upper mantle physical properties permeability electrical conductivity and seismic velocity are highly dependent on the melt geometry both flat and curved melt interfaces exist in olivine basalt partial melts to further understand anisotropic wetting behavior of partial melting within the mantle crystal orientation studies have been conducted to determine the miller indices of flat interfaces wetted by the melt in olivine basalt partial melt samples the samples were equilibrated at pressures of 1 2 gpa and temperatures of 1350 1400 c for 142 549 hours crystal orientation studies show that lower miller indices of crystals are associated with wetted flat melt interfaces and melt films specifically 010 110 and 021 olivine faces in these studies were dominantly wetted indicating that they may be potentially large contributors to permeability and seismic anisotropy in the upper mantle where partial melts occur with high degrees of preferred crystallographic alignment

multiple sulfur and iron isotope composition of magmatic ni cu pge sulfide mineralization from eastern botswana we report here high precision multiple sulfur and iron isotope compositions for a series of mineralized samples from ni cu pge sulfide deposits in the archean tati greenstone belt and the phikwe complex of eastern botswana mineralized samples from the phoenix and selkirk ni cu pge deposits in the tati greenstone belt display slightly positive 34s isotope values ranging from 0 2 to 0 8 v cdt 33s values of sulfides at phoenix and selkirk are 0 01 to 0 08 v cdt suggesting either a dominantly mantle sulfur source or effective eradication of a crustal 33s anomaly through equilibration with large amounts of silicate melt in the selebi phikwe belt a granite gneiss terrane with abundant amphibolite lenses of either volcanic and or intrusive nature mineralized lower grade samples from the phikwe phokoje and dikoloti ni cu pge deposits have more variable 34s values ranging from 3 1 to 0 3 and display significant mass independent anomalies 33s values ranging from 0 89 to 0 27 suggesting that barren sulfides associated with distal or low temperature sea floor hydrothermal activity contributed sulfur to these deposits iron isotopes of sulfides from these deposits show a relatively small range of negative 56fe values 0 29 to 0 04 consistent with high temperature fractionations in magmatic systems with the exception of one sample from the dikoloti ni cu pge deposit of the selebi phikwe greenstone belt which shows a more negative 56fe value of 0 61 consistent with assimilation of sedimentary or hydrothermal sulfides rather than fractionations in high temperature magmatic systems data from this study highlight the complexity and variability that characterize ore forming processes in magmatic systems we suggest that the presence of sulfur bearing lithologic units in host rocks of mafic and ultramafic intrusions may not be essential toward the assessment of the prospectivity of a province to host orthomagmatic nickel sulfides geologic settings without any or little sulfur in the stratigraphy which have been traditionally neglected in terms of their prospectivity should thus be revisited and possibly reassessed considering the potential importance of external source of sulfur to generate ore deposits

stabilities of laurite rus2 and monosulfide liquid solution at magmatic temperature we have reversed the equilibria ru s2 rus2 and 2feo s2 2fes o2 under controlled temperature oxygen fugacity fo2 and sulfur fugacity fs2 at 1 atm to test if the platinum group mineral laurite rus2 has a stability field at magmatic temperature outside that of magmatic monosulfide liquid the fs2 in equilibrium with ru and rus2 is given by log fs2 6 9 12190 t 1173 to 1673 k whereas the fs2 at sulfide saturation of a basaltic melt may be approximated from log fs2 6 7 12800 t 2 log xfeo log fo2 1473 to 1673 k our experiments support the notion that the sulfide mineral laurite can crystallize directly out of a sulfur bearing sulfide undersaturated silicate melt as implied by laurite chromite intergrowth textures in natural chromite ore

a time domain electromagnetic survey of the tag hydrothermal mound a conductivity survey of the tag mound was made using innovative transient electric dipole dipole instrumentation the receiver was deployed on the sulfide mound 30 m south of the central black smoker while the submersible alvin carried the transmitter on a survey path around the receiver at a radius of approximately 70 m conductivity measurements of the seafloor between the transmitter and receiver were made at 5 minute intervals the survey lasted 4 hours measurements made at 12 sites are initially interpreted in terms of an apparent conductivity of a uniform seafloor a more complex model in which the seafloor has two layers is then used apparent conductivities range from 1 4 to 15 9 s m generally higher than that of seawater the results suggest possible focusing of hydrothermal convection in the northern quadrant of the mound adjacent zones of anhydrite accumulation and fluid convection in the north eastern quadrant heterogeneity and layering in the kremlin zone and unexpected spatial variability in the western quadrant the data from several sites show evidence of distortion attributed to 3 d anomalies

strain partitioning in the footwall of the somiedo nappe structural evolution of the narcea tectonic window nw spain abstract the somiedo nappe is a major thrust unit in the cantabrian zone the external foreland fold and thrust belt of the north iberian variscan orogen exposed at the narcea tectonic window are precambrian rocks below the basal decollement of the somiedo nappe which exhibit a different deformation style than the overlying paleozoic rocks above the basal decollement during variscan deformation folding and widespread subhorizontal bedding parallel decollements were produced in the hanging wall within the paleozoic rocks vertical folding with related axial planar cleavage at a high angle to the decollement planes developed simultaneously in the upper proterozoic narcea slates of the footwall below the detachment the relative magnitude of finite strain measured in the footwall rocks diminishes towards the foreland these observations indicate that 1 significant deformation may occur in the footwall of foreland fold and thrust belts 2 the shortening mechanism in the footwall may be different from that of the hanging wall and 3 in this particular case the partitioning of the deformation implies the existence of a deeper blind decollement surface contemporaneous with the first stages of the foreland development that does not crop out in the region this implies a significant shortening in the footwall which must be taken into account when restoration and balancing of cross sections is attempted a sequential diagram of the evolution of the narcea tectonic window with a minimum shortening of 85 km is proposed explaining the complete variscan evolution of the foreland to hinterland transition in the north iberian variscan orogen

deformation structures and processes within the continental crust an introduction the collection of research papers in this volume provides an overview of current trends in the study of deformation structures and deformation processes in rocks from the continental crust the volume has been divided into three sections to reflect the current interest in structures and processes shear zones and folds the interactions between magmatism and structure and the relationship between microstructure and rheology the range of topics includes the geometry of natural structures from field observations the detailed analysis of the microstructure of deformed rocks the timing of deformation by various geochronological techniques the modelling of deformation processes to constrain the development of structures in rocks and the use of labora tory experimentation to reproduce deformation fabrics in rocks the mixture of techniques and methods treated illustrate the broad and multidisciplinary approach to the study of rock defor mation in the continental crust

the concentration of deep sea gas hydrates from downhole electrical resistivity logs and laboratory data abstract the concentration of gas hydrate at an ocean drilling program site on the continental slope off the coast of vancouver island has been estimated using a combination of downhole electrical resistivity logs resistivity and porosity of recovered core and core pore fluid salinity from a depth of 100 m to the base of gas hydrate stability bottom simulating reflector or bsr at about 225 m the log resistivities have an average of about 2 0 ohmm compared to 1 0 ohmm at a nearby deep sea reference site where no gas hydrate is present the downhole high resistivities result from a combination of 1 high resistivity hydrate filling part of the pore space and 2 low salinity in situ pore water the low salinity fluids are probably produced at greater depths by hydrate dissociation as the base of the stability field has moved upward with time both the hydrate concentration and the in situ salinity can be calculated if the hydrate concentration vs resistivity relation is known assuming that the effect of hydrate may be approximated by porosity reduction the relation is given by archie s law with exponent about two the hydrate affects the core pore fluid salinity through the dilution of the pure water produced by hydrate dissociation upon core recovery the core fluid salinity results from a combination of this dilution and of in situ freshening the in situ pore fluid salinity in the hydrate zone above the bsr is calculated to be about 80 of seawater whereas the measured salinity in the recovered cores is 60 of seawater the computed hydrate concentration in the 100 m interval above the bsr is 25 30 of pore space 12 15 of sediment volume in general agreement with the 20 estimated from the velocity data

multidisciplinary constraints on the cadomian compression and early cambrian extension in the iberian chains ne spain abstract this paper presents a multidisciplinary approach stratigraphic sedimentologic structural and mineralogic to document the evidences for cadomian and earliest cambrian tectonic processes recorded in the iberian chains which were strongly overprinted during variscan and alpine deformation episodes the contact of the neoproterozic paracuellos group and the lower cambrian bambola formation is commonly identifiable by the presence of a distinct erosive unconformity related to the onset of alluvial plain sequences or associated with synsedimentary faults a meso structural analysis of the deformation recorded in the paracuellos slates reveals the existence of an earlier slaty cleavage s 1n overprinted by variscan contractional structures some of them related to positive inversion of pre variscan normal faults the comparative geometrical study with structures observed in the bambola formation essentially a single nw se to n s striking cleavage s 1c is not conclusive about the record of the cadomian orogeny however micro scale deformation associated with the earliest cleavage is much more intense in the paracuellos slates in addition the metamorphic grade and the pressure conditions of the lower cambrian anchizonal shales contrast with the neoproterozoic epizonal slates both observations are consistent with a cadomian contractional deformation associated with a low grade intermediate pressure metamorphism absent in the overlying rocks postdating both processes stratigraphically marked by a tectono thermal discontinuity located at the paracuellos bambola contact the onset of the lowermost cambrian bambola formation is accompanied by strong palaeogeographic transformations in the sedimentary basin including i a sharp relative sea level fall leading to deposition of alluvial plain sediments and ii an increase in sedimentation rates and tectonically induced subsidence at fault bounded depressions all these changes together with the presence of normal or transtensional faults at the base of bambola formation point to an earliest cambrian extensional regime similar to that described for other neighbouring post cadomian basins

multiple melting in a four layered barred olivine chondrule with compositionally heterogeneous glass from ll3 0 semarkona chondrule k7p from ll3 0 semarkona consists of four nested barred olivine bo chondrules the innermost bo chondrule chondrule 1 formed by complete melting of an olivine rich dustball after formation the chondrule was incorporated into another olivine rich dustball a second heating event caused this second dustball to melt the mesostasis and some of the olivine in chondrule 1 were probably also melted at this time but the chondrule 1 structure remained largely intact at this stage the object was an enveloping compound bo chondrule this two step process of melting and dustball enshrouding repeated two more times the different proportions of olivine and glass in chondrules 1 4 suggest that the individual precursor dustballs differed in the amounts of chondrule fragments they contained and the mineral proportions in those fragments the final dustball which ultimately formed chondrule 4 was somewhat more ferroan after melting crystallizing and quenching chondrule 4 contained olivine and glass with higher feo and mno contents than those of the earlier formed chondrules subsequent aqueous alteration on the ll parent body transformed the abundant metal blebs and stringers at the chondrule surface into carbide iron oxide and minor ni rich metal portions of the mesostasis underwent dissolution producing holes and adjacent blades of more resistant material much of the glass in the chondrule remained isotropic even after minor hydration and leaching the sharp moderately lobate boundary between the extensively altered mesostasis and the isotropic glass represents the reaction front beyond which there was little or no glass dissolution

element migration of pyrites during ductile deformation of the yuleken porphyry cu deposit nw china abstract the strongly deformed yuleken porphyry cu deposit ypcd occurs in the kalaxiangar porphyry cu belt kpcb which occupies the central area of the central asian orogenic belt caob between the sawu er island arc and the altay terrane in northern xinjiang the ypcd is one of several typical subduction related deposits in the kpcb which has undergone syn collisional and post collisional metallogenic overprinting the ypcd is characterized by three pyrite forming stages namely a hydrothermal stage a py i a syn ductile deformation stage b py ii characterized by cu au enrichment and a fracture filling stage c py iii in this study we conducted systematic petrographic and geochemical studies of pyrites and coexist biotite which formed during different stages in order to constrain the physicochemical conditions of the ore formation euhedral fragmented py i has low pb and high te and se concentration and ni contents are low with co ni ratios mostly between 1 and 10 average 9 00 py i is further characterized by enrichments of bi as ni cu te and se in the core relative to the rim domains anhedral round py ii has moderate co and ni contents with high co ni ratios 10 average 95 2 and average contents of 46 5 ppm pb and 5 80 ppm te py ii is further characterized by decreasing bi cu pb zn ag te mo sb and au contents from the rim to the core domains annealed py iii has the lowest co content of all pyrite types with co ni ratios mostly

three dimensional morphology of magmatic sulfides sheds light on ore formation and sulfide melt migration the morphology of magmatic sulfides in igneous cumulates is controlled by the wetting properties of sulfide liquids against silicates the formation of nickel sulfide ores the behavior of sulfide liquids during mantle melting and potentially the segregation of the earth9s core are all controlled by the ability of sulfide liquids to migrate through the pore space of partially molten silicates three dimensional x ray tomographic images of sulfide aggregates in komatiitic olivine cumulates indicate that sulfide liquids have a limited tendency to wet olivine crystals forming interconnected networks only in the absence of silicate melt consequently the ability of sulfide liquids to migrate through the pore space of olivine cumulates is limited we conclude that disseminated sulfide ores in komatiites formed by accumulation of transported sulfide blebs a few millimeters in size and not by settling of sulfide olivine aggregates and that sulfides accumulated in the proportions in which they are now found rather than by percolation through cumulate pore space it is unlikely that sulfide droplets can be entrained and carried from the mantle at low degrees of partial melting our results also support the hypothesis that segregation of the earth9s core took place from a magma ocean rather than by percolation of sulfidic melt through partially molten mantle

komatiites of the wildara leonora belt yilgarn craton wa the missing link in the kalgoorlie terrane abstract the wildara leonora belt in the kalgoorlie terrane is located between the world class nickel provinces of the agnew wiluna belt to the north and the kambalda domain to the south it extends from the wildara station to the gold mining center of leonora and consists of a deformed package of mafic komatiitic and sedimentary rocks this package of rocks which hosts a number of small nickel sulfide occurrences has been explored extensively for komatiite hosted nickel deposits most recently within the sullivans unit in the south east of the wildara leonora belt lithostratigraphic similarities together with shared physical geochemical and textural properties support a common affiliation between the wildara leonora and the agnew wiluna belts on this evidence the wildara leonora belt represents the southern extension of the largest komatiite hosted nickel camp in the world the apparently lesser prospectivity for nickel sulfide deposits is interpreted as a consequence of contrasting volcanic facies assemblages komatiites in the wildara leonora belt present geochemical and volcanological characteristics consistent with turbulent lava flow emplacement however compared with the agnew wiluna belt the wildara leonora belt komatiites are not spatially associated with felsic volcanic units but rather overlie a thick sequence of pillowed basalts and sulfidic sediments the lower proportion of adcumulate greater degrees of fractionation and lower degrees of contamination are consistent with komatiites in the wildara leonora belt having been emplaced in a more distal position to the rift environment with lower magma flux and more tranquil emplacement than the agnew wiluna belt komatiites and consequently having lower potential for giant nickel sulfide deposits such as those at perseverance and mt keith

microscale data to macroscale processes a review of microcharacterization applied to mineral systems microanalysis can provide rapid quantitative characterization of mineral systems that complements the field and core scale observations traditionally made in ore deposits we review recent innovations in microanalytical procedures and their application to studies of ore deposits case studies are presented examining how microanalysis can provide constraints on macroscopic processes within mineral systems synchrotron x ray fluorescence shows centimetre scale chemical variations associated with proximity to mineralization in samples from sunrise dam gold mine western australia pseudomorphs of igneous plagioclase and chemically driven recrystallization interpreted from electron backscatter diffraction suggest that the system was dominated by fluid driven brecciation with very little shearing both the fluid chemistry and fluid pressure evolved during a protracted sequence of vein formation and alteration accompanying gold mineralization a second case study of sulphide mineralogy at the mt keith nickel sulphide deposit western australia demonstrates how x ray computed tomography combined with trace element mapping can constrain the chemistry and dynamics of magmatic systems large scale interaction between silicate and sulphide melts shown by homogenous palladium enrichment in pentlandite leads to a large proportion of globular ores with a high nickel content increasing use of microanalysis in ore deposit geology is resulting in the constant reassessment of established models for ore genesis though a combination of micro and macroscale datasets

cotectic precipitation of olivine and sulfide liquid from komatiite magma and the origin of komatiite hosted disseminated nickel sulfide mineralization at mount keith and yakabindie western australia an empirical equation for the relationship of sulfur solubility to silicate magma composition and temperature has been combined with numerical simulations of the fractional crystallization of olivine from komatiite magma to predict the relative proportions of olivine and sulfide liquid which should segregate at equilibrium from a fractionating komatiite the predicted cotectic ratio of olivine to sulfide is higher and the s content of the cumulate assemblage lower by a factor of about three compared with the peak observed in type ii mount keith type dunite hosted disseminated ni sulfide deposits for the observed range of olivine compositions in the dunites this implies that a purely cotectic precipitation model for this deposit type is incorrect and that most of the sulfide liquid found in type ii deposits is transported and mechanically deposited

on the theory of sea floor conductivity mapping using transient electromagnetic systems the electrical conductivity of the sea floor is usually much less than that of the seawater above it a theoretical study of the transient step on responses of some common controlled source electromagnetic systems to adjoining conductive half spaces shows that two systems the horizontal in line electric dipole dipole and horizontal coaxial magnetic dipole dipole are capable of accurately measuring the relatively low conductivity of the sea floor in the presence of seawater for these systems the position in time of the initial transient is indicative of the conductivity of the sea floor while at distinctly later times a second characteristic of the transient is a measure of the seawater conductivity the diagnostic separation in time between the two parts of the transient response does not occur for many other systems including several systems commonly used for exploration on land a change in the conductivity of the sea floor produces a minor perturbation in what is essentially a seawater response some transient responses which could be observed with a practical deep towed coaxial magnetic dipole dipole system located near the sea floor are those for the half space the layer over a conductive or resistive basement and the half space with an intermediate resistive zone the system response to two adjoining half spaces representing seawater and sea floor respectively is derived analytically the solution is valid for all time provided the conductivity ratio is greater than about ten or less than about one tenth the analytic theory confirms the validity of numerical evaluations of closed form solutions to these layered earth models a lateral conductor such as a vertical infinite conductive dike outcropping at the sea floor delays the arrival of the initial crustal transient response the delay varies linearly with the conductance of the dike this suggests that time delay could be inverted directly to give a measure of the anomalous integrated conductance of the sea floor both between and in the vicinity of the transmitter and the receiver dipoles

passive roof duplex geometry in the frontal structures of the kirthar and sulaiman mountain belts pakistan abstract exploration for hydrocarbons over the past few years has greatly improved our understanding of the geometry of frontal mountain belt structures in this study we introduce and discuss the concept of the passive roof duplex using as the main example the kirthar and sulaiman ranges in the baluchistan province of pakistan structures similar to those described here have been recognized previously in other mountain belts and they appear to exist as a common feature in many more frontal regions of mountain belts our example of a passive roof duplex which we describe from pakistan is compared briefly with similar structures reported by others the passive roof duplex is here defined as a duplex whose roof thrust has backthrust sense passive roof thrust and whose roof sequence those rocks lying above the roof thrust remains relatively stationary during foreland directed piggy back style propagation of horses within the duplex