primary platinum mineralization in the nizhny tagil and kachkanar ultramafic complexes urals russia a genetic model for pge concentration in chromite rich zones the nizhny tagil uralian alaskan type ultramafic complex is composed of a dunite core with a rim of wehrlite and pyroxenite the dunite unit which has a uniform mineral composition olivine fo 89 8 92 1 avg 0 25 wt cao represents an accumulation of olivine and minor chromite from a mafic magma in an open system magma chamber after solidification of the dunite differentiation began with the formation of the wehrlite olivine fo 77 9 88 8 and pyroxenite corresponding to the closure of the magmatic system two main types of chromitite occurrence are observed in the dunite body small 100 5 cm scattered schlieren of chromite crystals within the ultramafic unit and much larger up to 100 5 m concentrations the chromite composition in both types is similar and uniform cr cr al fe 3 66 02 mg mg fe 2 49 05 and cr cr al fe 3 69 14 mg mg fe 2 49 81 respectively the larger concentrations of chromite include brecciated and net textured ore or massive veins that reflect the dynamic accumulation of chromite crystals in cavities along magma conduits inside the dunite body these cavities are analogous to small magma chambers within the consolidated part of the dunite body and similar to podiform chromitites in ophiolites were created by continuous feeding of magma to the system the platinum group element pge content of the chromite free facies of the dunite is relatively low pt being the only significant pge typically between 0 3 35 ppb but as much as 98 ppb in one sample in contrast both types of chromite occurrence are enriched in pge two pge mineralizing episodes are distinguished an ir ru rh os rich pt pd poor episode in which the platinum group minerals pgm are mainly ir alloys and a pt pd rich episode in which the pgm are mainly pt alloys i e pt 2 fe ni cu ptfeni 2 and tetraferroplatinum and tulameenite like compositions along with rare hollingworthite and an unidentified rhnias mineral the primary pgm have been affected locally by a serpentinization related low temperature alteration that is characterized by addition of copper with alteration to complex pt fe ni cu alloys of varied stoichiometry including tulameenite and platinian copper placer concentrations derived from the nizhny tagil complex have a slightly different assemblage of pgm with abundant isoferroplatinum the presence of gold commonly aggregating the pgm and unusual au sn and au pb alloys the kachkanar complex situated 120 km north of the nizhny tagil complex has essentially the same characteristics apart from a slightly different composition of the ultramafic cumulates suggesting that they were derived from a magma of different composition the pgm distribution also differs in that it contains more abundant isoferroplatinum than other pgm the high pt concentrations are the result of the affinity of platinum minerals for chromite and the mode of chromite deposit formation in the cavities in which chromite crystallized pgm tended to be incorporated in chromite or remained attached to chromite crystals to explain the very high concentrations of chromite associated pgm we define a cr factor which is the ratio of the mass of silicate magma to the mass of chromite in contact with the ascending magma where the cr is high i e a relatively low proportion of chromite in contact with a large amount of magma crystallizing the pt minerals the efficiency of the mechanical collection of pt minerals is at a maximum and the pt concentration i e amount of pt minerals will be high possible variations due to the collection of pge by a sulfide liquid have not been established a model is proposed whereby the observed chromite and associated pt mineralization can result from the normal magmatic evolution of the complex provided that a structural hydrodynamic trap is available to concentrate the chromite

the effects of stress paths on acoustic velocities and 4d seismic imaging time shifts on 4d seismic images result from two basic causes 1 acoustic velocity changes due to fluid migration fluid substitution fluid composition and 2 velocity changes resulting from changes in total stresses i e the vertical and horizontal stresses during depletion this paper is concerned only with the latter the effect of changing total stress on rock velocity

anomalous sulfur poor platinum group element mineralization in komatiitic cumulates mount clifford western australia an unusual occurrence of sulfur poor platinum group element pge mineralization has been discovered at mount clifford in the agnew wiluna belt western australia within the lower part of a 1 000 m thick komatiitic dunite body the host body consists primarily of strongly serpentinized olivine adcumulates with accessory chromite high precision whole rock icp ms data show that the pge mineralization extends over tens of meters whereas the lateral extent is unknown palladium and pt abundances are closely associated with base metal sulfides but show offset distribution patterns with maximum concentrations associated with the relatively sulfide poor base of a disseminated sulfide bearing layer whole rock concentrations range up to 4 100 ppb pd and 920 ppb pt iridium rh and ru follow the trends in pd and pt but are strongly depleted ir 0 4 ppb ru 0 5 ppb rh 0 1 ppb platinum group minerals pgm were located in essentially sulfide free serpentine 2 m below the peak in sulfide abundance and can be categorized into three groups pd antimonides pt dominated pgm and pt bearing ni antimonides the pge mineralization zone is underlain by an interval of strong ni depletion within olivine mesocumulates that is characterized by an unusual negative correlation between ni and the mg number of the rock this relationship is interpreted to be the result of an equilibration of olivine of variable forsterite content with a relatively large mass of magmatic sulfide however there is no direct evidence of this sulfide mass anywhere in the entire mount clifford dunite body the ni depletion is accompanied by strong depletion in ipge ir ru and rh the association of the pge zone with a reversal in the mg fe ratio of the host cumulates and a distinctive offset relationship of multiple pt pd and cu s peaks is suggestive of a primary magmatic origin however this is inconsistent with current models for offset reef pge concentrations which involve the onset of sulfide liquid saturation from a previously sulfur undersaturated pge undepleted magma the association of enriched pt and pd with highly depleted ni and ipge in immediately underlying cumulates conflicts with this model we suggest a combination of processes early sulfide segregation at low r values producing ni and ipge depleted olivine partial redissolution and removal of most of this sulfide component during a major replenishment event and subsequent overprint by a migrating pt pd cu rich fluid

mechanical and petrophysical properties of north sea shales one of the problems when evaluating potential borehole stability problems in the drilling of hydrocarbon exploration and production wells is the lack of relevant data to describe the lithologies this relates in particular to the shales since these constitute most of the overburden and are also the most troublesome this paper presents a set of data from a variety of deeply cored shales from the north sea the shales have been extensively characterised and span a wide range of both petrophysical and mechanical properties depending on for example burial history and diagenesis special characteristics of shales have been tested and described including pore size distribution permeability anisotropy and temperature dependence appropriate procedures for sample handling testing and interpretation have been developed or modified from other related sciences

sensitivity of time lapse seismic to reservoir stress path the change in reservoir pore pressure due to the production of hydrocarbons leads to anisotropic changes in the stress field acting on the reservoir reservoir stress path is defined as the ratio of the change in effective horizontal stress to the change in effective vertical stress from the initial reservoir conditions and strongly influences the depletion induced compaction behaviour of the reservoir seismic velocities in sandstones vary with stress due to the presence of stress sensitive regions within the rock such as grain boundaries microcracks fractures etc since the response of any microcracks and grain boundaries to a change in stress depends on their orientation relative to the principal stress axes elastic wave velocities are sensitive to reservoir stress path the vertical p and s wave velocities the small offset p and sv wave normal moveout nmo velocities and the p wave amplitude versus offset avo are sensitive to different combinations of vertical and horizontal stress the relationships between these quantities and the change in stress can be calibrated using a repeat seismic sonic log checkshot or vertical seismic profile vsp at the location of a well at which the change in reservoir pressure has been measured alternatively the variation of velocity with azimuth and distance from the borehole obtained by dipole radial profiling can be used having calibrated these relationships the theory allows the reservoir stress path to be monitored using time lapse seismic by combining changes in the vertical p wave impedance changes in the p wave nmo and avo behaviour and changes in the s wave impedance

crystallization of sulfide liquids and the interpretation of ore composition we have been exploring ways to quantitatively assess the extent to which fractionation of sulfide melt has effected variations in composition within magmatic sulfide ore bodies our approach has been to determine by experiment the crystallization paths of sulfide liquids in temperature and composition dimensions in this paper the results of new major element partitioning experiments below 1050 c in the nickel free system are presented and summarized along with new and previous work in the fe ni cu s quaternary the partition coefficients d for cu between monosulfid solid solution mss and sulfide liquid in the ni free system dcu wt cu in mss wt cu in liquid cluster near 0 3 but decrease to nearly 0 1 for cu rich s poor liquids near 1000 c dni also declines with decreasing sulfur content of the liquid but increases with decreasing temperature preliminary data indicate that dni exceeds 1 0 in low ni liquids with greater than 16 wt cu at 1050 c the quality of available data on the

partition coefficients for ni cu pd pt rh and ir between monosulfide solid solution and sulfide liquid and the formation of compositionally zoned ni cu sulfide bodies by fractional crystallization of sulfide liquid many nickel copper sulfide orebodies contain cu and fe rich portions the fe rich ore is generally richer in os ir ru and rh and poorer in pt pd and au than the cu rich ore in komatiite hosted ores ni tends to be concentrated in the cu rich ore whereas in tholeiitic ores it tends to be concentrated in the fe rich ore the origin of this zonation could be due to crystal fractionation of fe rich monosulfide solid solution from a sulfide liquid the crystal fractionation would produce an fe rich cumulate enriched in os ir ru and rh and a fractionated liquid enriched in cu pt pd and au this model can be tested for zoned orebodies by applying experimentally determined partition coefficients for the metals into monosulfide solid solution we have compared our experimental results with those of other workers to show that the partition coefficients are strongly influenced by the sulfur content of the system there is a positive correlation between the partition coefficients and sulfur content of th

chalcophile and platinum group element pge concentrations in the sulfide minerals from the mccreedy east deposit sudbury canada and the origin of pge in pyrite magmatic sulfide deposits consist of pyrrhotite pentlandite chalcopyrite pyrite and platinum group minerals pgm understanding the distribution of the chalcophile and platinum group element pge concentrations among the base metal sulfide phases and pgm is important both for the petrogenetic models of the ores and for the efficient extraction of the pge typically pyrrhotite and pentlandite host much of the pge except pt which forms pt minerals chalcopyrite does not host pge and the role of pyrite has not been closely investigated the ni cu pge ores from the south range of sudbury are unusual in that sulfarsenide pgm rather than pyrrhotite and pentlandite are the main carrier of pge probably as the result of arsenic contribution to the sulfide liquid by the as bearing metasedimentary footwall rocks in comparison the north range deposits of sudbury such as the mccreedy east deposit have as poor granites in the footwall and the ores commonly contain pyrite our results show that in the pyrrhotite rich ores of the mccreedy east deposit os ir ru rh ipge and re are concentrated in pyrrhotite pentlandite and surprisingly in pyrite this indicates that sulfarsenides which are not present in the ores were not important in concentrating pge in the north range of sudbury palladium is present in pentlandite and together with pt form pgm such as ptpd tebi 2 platinum is also found in pyrite two generations of pyrite are present one pyrite is primary and locally exsolved from monosulfide solid solution mss in small amounts 2 wt together with pyrrhotite and pentlandite this pyrite is unexpectedly enriched in ipge as pt and the concentrations of these elements are oscillatory zoned the other pyrite is secondary and formed by alteration of the mss cumulates by late magmatic hydrothermal fluids this pyrite is unzoned and has inherited the low concentrations of ipge and re from the pyrrhotite and pentlandite that it has replaced

an overview of the platinum group element nanoparticles in mantle hosted chromite deposits abstract this paper reviews the occurrence of platinum group elements nanoparticles pge nps in mantle hosted chromite deposits showing that pge nps are more frequently found in these deposits than previously thought a comparison of published experimental data with observations in natural samples reveal that pge nps might form at the pressure 1 0 5 gpa temperature 1200 c and f o 2 fmq 1 conditions in which chromite deposits form in the upper mantle the crystallization of pge nps may take place earlier or simultaneously to the segregation of chromite and or sulfide liquids from silicate melts if the pges are dissolved in the silicate melt the segregation of pge nps could be linked to local changes in f o 2 and f s 2 during the early crystallization of chromite and or olivine mobile crystals of chromite and droplets of sulfide melts entrained in the basaltic parent melt may also play an additional role as physical collectors of pge nps providing a complementary or even an alternative mechanism for the fractionation of pges in high temperature silicate melts furthermore hydrothermal alteration of the chromite deposits during seafloor metamorphism or exhumation i e retrograde metamorphism of upper mantle rocks has also a significant effect on the internal structure of the oxides and sulfides that host the pge nps frequently pge nps are found along the replacement contacts between primary and secondary minerals suggesting that pge nps can also form during low temperature alteration events 200 600 c finally heating events overimposed on chromite deposits previously affected by hydrous metamorphism may enhance fluid infiltration subsequently triggering chemical mineralogical or textural responses in the oxide or sulfide matrices hosting the pge nps promoting coarsening of metal nanoparticles the interplay between these processes can explain the wide spectrum of particle sizes of pge inclusions that are observed in many altered chromite deposits which can vary from a few nanometers to larger than a micron these studies provide evidence that pge nps can eventually form under a wide spectrum of thermal and pressure conditions and show that aqueous fluids may play a relevant role in producing pge nps during metamorphism and metasomatism of mantle hosted chromite deposits

controlled laboratory experiments to assess the geomechanical influence of subsurface injection and depletion processes on 4d seismic responses laboratory experiments are performed with soft synthetic reservoir sandstone cemented under stress and with synthetic overburden caprock material consisting of compacted clay kaolinite in brine the rock like materials are loaded mechanically under stress paths representative of stress changes occurring in the subsurface as a result of injection increasing pore pressure or depletion followed by injection into a storage reservoir static stress strain behaviour and multidirectional p and s wave velocities are monitored during the tests the tests with sandstone are performed on dry material and simple poroelastic modelling is performed to relate these data to the behaviour of fluid water co2 saturated samples under the same stress paths the focus is on identifying 4d seismic attributes that may be used in the field to interpret monitoring measurements this could help diagnose stress changes in the overburden signalling the risk of co2 leakage from a reservoir if the compressive or tensile strength limit of the overburden is reached and of course to help quantify amounts of co2 stored

non chondritic platinum group element ratios in the earth s mantle the earth s upper mantle has an overabundance of highly siderophile elements platinum group elements gold and rhenium relative to what would be expected from equilibrium with the metallic core1 3 this excess is now widely believed to have been introduced as a late veneer by meteorite bombardment during early earth history but after separation of the core4 here we report high precision analyses of platinum group elements pges from fertile upper mantle iherzolites which show variations in relative abundances that exceed those in the chondritic meteorites that are thought to have furnished the late veneer5 in particular the pd ir ratio at about 1 76 is significantly greater than that of known chondritic meteorites6 our results combined with previous indications of both non chondritic and nearly chondritic pge ratios in the few other fertile mantle iherzolites that have been analysed2 3 7 11 strongly suggest that the mantle is heterogeneous in its pge content on scales of 100 kilometres if the observed pge ratios can be reconciled with a plausible meteoritic source the observed heterogeneity may reflect an original spatial variation in the late veneer otherwise an additional fractionation mechanism seems to be required

ultrasonic velocity and shear wave splitting behavior of a colton sandstone under a changing triaxial stress ultrasonic experiments on a dry colton sandstone placed in a triaxial pressure machine show that effective stress changes lead to distinct anisotropic velocity changes in compressional waves and shear waves the stress imprint can be recognized from the associated velocity pattern by relating the velocities to the three normal stress directions the ultrasonic velocities indicate that the sensitivity of the different waves to stress predominantly depends on stresses applied in the polarization and propagation directions of the particular wave mode also stress induced changes in shear wave splitting are observed

rocks under strain strain induced time lapse time shifts are observed for depleting reservoirs pressure depletion as a result of oil and gas production creates changes in the stress and strain fields of the rock material both inside and outside the reservoir seismic waves propagating through these rocks have different traveltimes before and after depletion because the layer thicknesses change and the seismic velocity is altered by the changes in the stress and strain fields the cumulative change in two way traveltimes with depth is referred to as time lapse time shift

impact of fabric microcracks and stress field on shale anisotropy summary few data are available on shales in terms of seismic to ultrasonic properties and anisotropy although all are important with regards to imaging problems often encountered in such lithologies additionally mechanisms causing changes in these properties are not well documented due to the fine grain size of such materials and time required for testing under controlled pore pressure conditions the results presented here are derived from a set of experiments run on muderong shale with pore pressure control in order to evaluate the effect of stress magnitude and stress anisotropy on ultrasonic response this shale was noted to have a linear velocitymean effective stress response and extremely high anisotropy both likely the result of the presence of fluid filled cracks in a low permeability porous medium changes in velocity and vp vs ratios are dependent on both stress and smectite content s wave velocity is significantly affected by the presence of smectite in this and other shales and at low stress 20 mpa is less sensitive to stress change than p wave velocity vp vs ratios are noted to increase in this shale up to 20 mpa effective stress then decrease slightly due to stress induced loss of interlayer water in smectite intrinsic anisotropy comes from composition a strong compaction fabric and the presence of microfractures changes to ultrasonic anisotropy are the result of the magnitude of the stresses their orientation with respect to the fractures and the degree of stress anisotropy

seismic anisotropy in sedimentary rocks part 2 laboratory data part one of this paper presents a method for measuring seismic velocities and transverse isotropy in rocks using a single core plug this method saves at least two thirds of the time for preparing core samples and measuring velocities in transversely isotropic ti rocks using this method we have measured velocity and anisotropy of many shale and reservoir rocks from oil and gas fields around the world we present some of the data in this paper which include seismic velocity and anisotropy in 17 brine saturated shale samples 1 gas and brine saturated coal sample 8 brine saturated sands 12 gas saturated sands 32 gas saturated carbonate samples and 25 brine saturated carbonate samples the results show that clays and fine layering in sedimentary rocks are the main causes of seismic anisotropy very little intrinsic anisotropy exists in unfractured reservoir rocks such as sands sandstones and carbonates under reservoir conditions in contrast all shales were found seismically anisotropic anisotr

estimation of layer thickness and velocity changes using 4d prestack seismic data in some hydrocarbon reservoirs severe compaction of the reservoir rocks is observed this compaction is caused by production and is often associated with stretching and arching of the overburden rocks time lapse seismic data can be used to monitor these processes since compaction and stretching cause changes in layer thickness as well as seismic velocities it is crucial to develop methods to distinguish between the two effects we introduce a new method based on detailed analysis of time lapse prestack seismic data the equations are derived assuming that the entire model consists of only one single layer with no vertical velocity variations the method incorporates lateral variations in relative velocity changes by utilizing zero offset and offset dependent time shifts to test the method we design a 2d synthetic model that undergoes severe reservoir compaction as well as stretching of the overburden rocks finally we utilize the method to analyze a real 2d prestack time lapse seismic line from t

platinum group element gold silver and base metal distribution in compositionally zoned sulfide droplets from the medvezky creek mine noril sk russia concentrations of ag au cd co re zn and platinum group elements pge have been determined in sulfide minerals from zoned sulfide droplets of the noril sk 1 medvezky creek mine the aims of the study were to establish whether these elements are located in the major sulfide minerals pentlandite pyrrhotite chalcopyrite and cubanite to establish whether the elements show a preference for a particular sulfide mineral and to investigate the model which suggests that the zonation in the droplets is caused by the crystal fractionation of monosulfide solid solution mss nickel cu ag re os ir ru rh and pd were found to be largely located in the major sulfide minerals in contrast less than 25 of the au cd pt and zn in the rock was found to be present in these sulfides osmium ir ru rh and re were found to be concentrated in pyrrhotite and pentlandite palladium and co was found to be concentrated in pentlandite silver cd and zn concentrations are highest in chalcopyrite and cubanite gold and platinum showed no preference for any of the major sulfide minerals the enrichment of os ir ru rh and re in pyrrhotite and pentlandite exsolution products of mss and the low levels of these elements in the cubanite and chalcopyrite exsolution products of intermediate solid solution iss support the mss crystal fractionation model because os ir ru rh and re are compatible with mss the enrichment of ag cd and zn in chalcopyrite and cubanite also supports the mss fractionation model these minerals are derived from the fractionated liquid and these elements are incompatible with mss and thus should be enriched in the fractionated liquid gold and pt do not partition into either iss or mss and become sufficiently enriched in the final fractionated liquid to crystallize among the iss and mss grains as tellurides bismithides and alloys during pentlandite exsolution pd appears to have diffused from the cu rich portion of the droplet into pentlandite

the formation of pt ir alloys and cu pd rich sulfide melts by partial desulfurization of fe ni cu sulfides results of experiments and implications for natural systems abstract we propose a model of high temperature formation of platinum group element pge alloys from base metal sulfides subjected to decreasing sulfur fugacity f s 2 for this purpose we experimentally investigated the effect of partial desulfurization of monosulfide solid solution mss with variable ni and cu contents on the distribution behaviour of pt ir and pd at 1000 c we partially removed sulfur from the pge bearing mss using the tube in tube technique and pyrrhotite as an f s 2 buffer we found that mss undergoing s loss can produce 1 pt and ir exsolution from the mss matrix in the form of pge bearing alloys 2 partial melting of the cu ni bearing mss to form fe rich mss cu ni pd rich sulfide liquid and fe ir pt alloy both of these processes are geologically important the partial melting of the s depleted sulfides could explain the presence of two types of sulfides found in the mantle mss dominated sulfides and s poor sulfides consisting mainly of pentlandite and chalcopyrite we also suggest that the cu ni pd rich liquid formed by partial melting of the sulfides could migrate away from the mss and fe ir pt alloys thus spatially decoupling ir pt and cu pd as observed in reefs and mantle nodules in addition the formation of pge alloys in response to the desulfurization processes potentially could occur 1 after pressure falls during transport of the basalt magma with entrained sulfide droplets 2 after sulfur removal by s undersaturated melts or fluids from pge enriched sulfide proto ore 3 after degassing of the sulfide droplets occurring in a sub volcanic chamber and 4 as a result of sulfide interaction with chromite

ultrasonic velocities in cretaceous shales from the williston basin compressional and shear wave velocities were measured in the laboratory from 1 bar to 4 kbar confining pressure for wet undrained samples of cretaceous shales from depths of 3200 and 5000 ft in the williston basin north dakota these shales behave as transversely isotropic elastic media the plane of circular symmetry coinciding with the bedding plane for compressional waves the velocity is higher for propagation in the bedding plane than at right angles to it and the anisotropy is greater for the 5000 ft shale for shear waves the sh wave perpendicular to bedding and the sv wave parallel to bedding propagate with the same speed which is about 25 percent lower than that for the sh wave parallel to bedding in general compressional and shear velocities are higher for the indurated 5000 ft shale than for the friable 3200 ft shale all velocities increase with in increasing confining pressure to 4 kbar the 3200 ft shale exhibits velocity hysteresis as a function of pressure whereas this effect is a

a study of the organic matter in tunisian phosphates series relevance to phosphorite genesis in the gafsa basin tunisia abstract in the gafsa basin tunisia peloidal fracolite is interbedded with shales limestones and rocks of intermediate lithology the rocks were deposited in an epicontinental sea and have been buried no more than 500 m the organic matter they contain is therefore thermally immature and in all units derived mainly from marine plankton particularly dinoflagellates the organic matter in the phosphorite units is composed predominantly of humic acids ha which are essentially located within the pellets these pellets are surrounded by an outer matrix in which the organic matter is similar to the kerogen comprised in the shally strata alternating with the phosphorite and limestone beds during weathering the content of the organic matter assocciated with the matrix decreases more rapidly than that of the organic matter entrapped within the pellets geochemical and palynological study of the organic matter in interbedded rocks of different lithology shale limestone phosphorite suggest that the shales were deposited in a reducing environment the limestones in one that was oxic whilst the phosphorites were formed in a redox environment inermediate between the two the interpretation of the data presented in this paper is that the genesis of shales phosphate and some carbonate beds excluding coquinas did not result from the deposition of initially sharply differentiated sediments but resulted from differences in diagenesis of sediments initially containing planktonic organic matter associated with clay and carbonate minerals

ni cu au and platinum group element contents of sulphides associated with intraplate magmatism a synthesis the tectonic setting of intraplate magmas typically a plume intersecting a rift is ideal for the development of ni cu platinum group element bearing sulphides the plume transports metal rich magmas close to the mantle crust boundary the interaction of the rift and plume permits rapid transport of the magma into the crust thus ensuring that no sulphides are lost from the magma en route to the crust the rift may contain sediments which could provide the sulphur necessary to bring about sulphide saturation in the magmas the plume provides large volumes of mafic magma thus any sulphides that form can collect metals from a large volume of magma and consequently the sulphides will be metal rich the large volume of magma provides sufficient heat to release large quantities of s from the crust thus providing sufficient s to form a large sulphide deposit the composition of the sulphides varies on a number of scales i there is a variation between geographic areas in which sulphides from the noril

petrogenesis of pelitic xenoliths at the babbitt cuni deposit duluth complex minnesota u s a abstract the babbitt deposit consists of disseminated cu fe ni sulfides found within mafic rocks of the duluth complex generally near contacts with underlying metasedimentary rock types host rocks for the deposit include troctolites olivine gabbros gabbronorites norites and occasionally country rock hornfels xenoliths of country rocks are abundant in the deposit and suggest a relationship between sulfide mineralization and country rock contamination country rocks in the babbitt area include those of the middle precambrian biwabik iron formation and both calcareous and non calcareous pelites of the virginia formation xenoliths contain the assemblage cordierite plagioclase biotite orthopyroxene and are thought to have been derived from virginia formation protoliths comparison of protoliths and xenoliths using composition volume element ratio and mass balance techniques suggests that xenoliths have been strongly depleted in volatiles alkalis and si footwall rocks show only a depletion in volatiles neither fluid phase transport nor diffusion through an intergranular fluid can account for the mass of material transferred extensive partial melting of xenoliths with residual enrichment of feo mgo and al2o3 is the most viable transfer process the lack of sio2 concentration gradients around xenoliths and anomalous igneous rock compositions suggest that desilicification occurred at a time when physical mixing of extracted partial melt and host magma was possible and prior to final emplacement sulfide saturation may have been initiated due to si assimilation with an auxiliary magma chamber however the composition of ores in the babbitt deposit is consistent with saturation being achieved by addition of sediment derived volatile sulfur independent of major element assimilation

platinum group element chromitite associations in the bushveld complex new and recently published platinum group element data of chromite rich layers in the bushveld complex are evaluated chondrite normalized platinum group element plots of these data show that trends for chromitite layers differ from that of the merensky reef the data furthermore indicate remarkable consistencies in compositional trends for many kilometers along strike of individual layers suggesting that the conditions of formation of chromitite layers and their associated platinum group element mineralization were very uniform over large areas of the magma chamber significant differences in the proportions of platinum group elements within a particular layer are only evident on a regional scale the platinum group minerals of the middle group of chromitite layers in the marikana area of the western bushveld are mainly sulfides and arsenides laurite is the most common platinum group mineral and is mostly enclosed by chromite a variety of other platinum group minerals occur in close association with base metal sulfides extremely low bulk sulfur content in the chromitite layers is ascribed to a postcumulus loss of sulfur postcumulus loss of sulfur and the existence of laurite enclosed within chromite casts doubt on the validity of any petrogenetic models for platinum mineralization in chromitite rich layers based on partition coefficients and the r factor

the geologic setting of the platiniferous ug 2 chromitite layer on the farm maandagshoek eastern bushveld complex the platiniferous ug 2 chromitite layer forms part of the upper chromitite group of the critical zone on the farm maandagshoek 254kt in the eastern bushveld complex the upper chromitite group is made up of four cyclic units namely ug 1 ug 2 ug 3 and ug 3a each of which consists of a basal chromitite layer with or without olivine overlain successively by melanorite and norite and terminated with anorthosite the ug 2 chromitite layer and its associated basal pegmatoid is found close to the base of the ug 2 cyclic unit the cyclic units are separated by sharp contacts and have a remarkable persistence along strike and downdip whole rock cu total ni pt and pd show an upward enrichment from the base of the ug 2 unit reaching a maximum in the main chromitite layer they are depleted in the hanging wall sequence of melanorite bulk analyses of the ug 2 chromitite and its enclosing lithologies for pt pd ru rh ir au s sulfide ni cu and co show that the platinum group elements and base metals are concentrated 1 close to the top and base of the main chromitite layer 2 in the leader layer and 3 in minor chromitite lenses and layers both in the footwall pegmatoid and the hanging wall melanorite the pt pt pd and cu ni ratios are low in the footwall pegmatoid and base of the main chromitite layer values of these ratios however increase upward with pt pt pd decreasing at the upper contact of the ug 2 layer the calculated concentration of platinum group metals in the sulfide phase in the ug 2 chromitite layer ranges from 3 000 to just under 12 000 ppm the above determination is primarily controlled by the concentration of s in the layer with the average precious metal distribution remaining relatively constant the calculated d super sulfide liquid sub silicate liquid with the parental liquid values in parentheses are pt 52 575 40 ppb pd 132 940 16 ppb rh 22 080 8 ppb ir 730 000 0 4 ppb and au 2 190 21 ppb evidence of an influx of magma into the eastern lobe of the bushveld complex at a level between the upper and middle chromitite groups is indicated by discontinuous and disturbed layers in borehole drilling on maandagshoek it is suggested that this magma batch was slightly more enriched in the platinum group elements in order to produce the increased value of these elements in the ug 2 chromitite layer it is proposed that preexisting sulfides in the ug 2 chromitite layer collected platinum group elements from upward migrating highly fractionated intercumulus fluids under highly reducing conditions during the early stages of formation of the layer the relatively large volume of sulfide initially present in the layer was later reduced by volatiles enriched in o 2 passing through the layer resorbing the sulfides and blowing off so 2 the partial resorption of the sulfides accounts for the presence of minor pt fe alloys and the abnormally high partition coefficients of the platinum group elements in the sulfide liquid of the ug 2 chromitite layer

in situ stress dependence of wave velocities in reservoir and overburden rocks seismic waves propagate through a stressed earth sonic waves recorded by a borehole sonic logging tool propagate in the near well environment which is also stressed albeit under different stress conditions than the untouched formation far away cores excavated from within the earth undergo stress release and are then reloaded in the laboratory but hardly ever to the complete fully anisotropic in situ state of stress and pore pressure based on this we easily recognize that stress sensitivity affects our ability to compare and correlate geophysical and petrophysical measurements of wave velocities on the other hand it also provides an avenue to extract information about rock stresses as an example the presence of abnormally low velocities in seismic or log data is evidence of high pore pressure

velocity anisotropy and attenuation of shale in under and overpressured conditions the seismic velocity and attenuation of fully saturated shales were measured for the first time under overpressured conditions using the ultrasonic reflection technique shale cores from naturally overpressured horizons in the north sea were tested in the laboratory at confining and pore pressures relevant to in situ conditions a single frequency tone burst pulse wave was used to determine the seismic wave velocities and quality factors of the shale samples with errors less than 0 3 and 0 1 db cm respectively at a frequency of 0 75 mhz sample length changes with varying confining and pore pressure were measured and the pore pressure equilibration time was monitored for each sample the anisotropy of the seismic attributes vp vs qp and qs was determined over a range of differential pressures from 5 to 60 mpa with respect to the predominant foliation the ultrasonic velocity data followed a transversely isotropic pattern depending on the direction of wave propagation with respect to the laminations the poisson s ratio was found to rise by 5 as the shale material progressed from a normally pressured to an overpressured state the quality factor q characteristics were interpreted in terms of pore geometry and connectivity as well as the directional permeability of the transversely isotropic shale material the results were converted to bulk and shear loss modulus defects and a positive bulk loss was observed for waves propagating perpendicular to the lamination plane even above differential pressures of 20 mpa this indicates different levels of biot flow and squirt flow attenuation mechanisms acting within the shale structure depending on the wave propagation and vibration directions

mineralogy of the hse in the subcontinental lithospheric mantle an interpretive review abstract the highly siderophile elements hse os ir ru rh pt pd re au exist in solid solution in accessory base metal sulfides bms as well as nano to micron scale minerals in rocks of the subcontinental lithospheric mantle sclm the latter include platinum group minerals pgm and gold minerals which may vary widely in morphology composition and distribution the pgm form isolated grains often associated with larger bms hosted in residual olivine located at interstices in between peridotite forming minerals or more commonly in association with metasomatic minerals pyroxenes carbonates phosphates and silicate glasses in some peridotite xenoliths the pgm found inside residual olivine are mainly os ir and ru rich sulfides and alloys in contrast those associated with metasomatic minerals or silicate glasses of peridotite xenoliths consist of pt pd and rh bonded with semimetals like as te bi and sn nanoscale observations on natural samples along with the results of recent experiments indicate that nucleation of pgm is mainly related with the uptake of hse by nanoparticles nanominerals or nanomelts at high temperature 900 c in both silicate and or sulfide melts regardless of the residual or metasomatic origin of their host minerals a similar interpretation can be assumed for gold minerals our observations highlight that nanoscale processes play an important role on the ore forming potential of primitive mantle derived magmas parental to magmatic hydrothermal deposits enriched in noble metals the metal inventory in these magmas could be related with the physical incorporation of hse bearing nanoparticles or nanomelts during processes of partial melting of mantle peridotite and melt migration from the mantle to overlying continental crust

overburden 4d time shifts indicating undrained areas and fault transmissibility in the reservoir abstract production induced geomechanical stress changes cause velocity changes in the overburden that might be detected as 4d seismic time shifts the strength of the velocity changes depends on the degree of pressure changes and the elastic properties of the reservoir and overburden layers even small velocity changes less than 1 might accumulate into detectable seismic time shifts at the top reservoir since the overburden thickness typically ranges from one to several kilometers reservoir pressure changes inducing seismic time shifts are observed in the overburden of the snorre heidrun and statfjord fields all located on the norwegian continental shelf the strong correlation between overburden time shifts geomechanics and reservoir pressure changes is used to indicate undrained areas and transmissibility across faults which is useful information for increased oil recovery well planning and reservoir model updating 4d geomechanical models are built with input from simulated reservoir pres

platinum group minerals in the middle group of chromitite layers at marikana western bushveld complex indications for collection mechanisms and postmagmatic modification the platinum group minerals in a drill core taken through the middle group of chromitite layers in the critical zone at marikana in the western bushveld complex were found to consist mainly of laurite as inclusions in chromite grains the platinum group minerals containing pt pd and rh are concentrated in the intercumulus silicates and frequently associated with base metal sulphides up to about 20 of all platinum group minerals in the investigated chromitite layers contain sub stantial amounts of as the base metal sulphides are strongly modified in the postmagmatic stage which led to a significant loss of fe and s in this way concentrating cu ni and the platinum group elements by factors of up to 10 interaction between chromite and base metal sulphides cannot account for all the fe lost in chromite poor samples and the importance of additional processes is indicated inclusions in chromite and orthopyroxene indicate the formation of discrete platinum group minerals and as rich phases before the

seismic anisotropy of shales the seismic properties and preferred clay mineral orientation of a suite of shales are investigated using laboratory velocity measurements as a function of confining pressure x ray diffraction techniques and electron microprobe backscatter bse imaging the velocity measurements indicate that these shales are transversely isotropic with the main symmetry axis perpendicular to bedding anisotropy at elevated pressures caused mainly by preferred orientation of clays illite parallel to bedding ranges from 20 vp and 19 vs for a sample of new albany shale to 30 vp and 35 vs for a sample of chattanooga shale the degree of clay mineral alignment in the shales is constrained by orientation indices produced using simple x ray diffraction techniques a strong positive correlation is found between the degree of preferred orientation as expressed in the orientation indices and seismic anisotropy bse images of the shale fabrics confirm in a qualitative manner the results of the x ray study to investigate wave propagation in the shales elastic constants of each sample are calculated and used to produce phase and group wave velocity surfaces which describe variation in velocity as a function of angle to the bedding normal the calculated velocity surfaces constrained by independent velocity measurements display a lack of shear wave splitting at near normal incidence in even the most anisotropic shales for the highly anisotropic chattanooga shales group velocity surfaces differ significantly from corresponding phase velocity surfaces

physical properties of shale at temperature and pressure deformational properties p wave and s wave velocities and electrical resistivity were measured for three north sea malm shales in the laboratory under pressures to 800 bars and temperatures to 100 c these data were used to evaluate how factors such as mineralogy microstructure compaction and pore fluid conductivity affect a shale s seismic and electrical responses deformation in the shales is dominated by inelastic processes which cause time dependent changes in velocity resistivity and pore pressure overall shales are less sensitive to pressure changes as compared to sandstones of similar porosity however changes in temperature result in large changes in physical properties as compared to sandstones or shaly sands p wave and s wave velocities may decrease by as much as 10 percent over the temperature range studied and calculated activation energies for surface conduction are nearly twice those observed in shaly sands these comparisons emphasize fundamental differences in fabric among the

the lower banded series of the stillwater complex montana whole rock lithophile chalcophile and platinum group element distributions the principal rock types of the lower banded series of the stillwater complex are gabbronorite and norite with minor troctolite and anorthosite the whole rock composition is largely controlled by the cumulate minerals plagioclase and pyroxene olivine the rocks are very poor in incompatible elements at the 0 1 to 2 times mantle levels indicating 10 liquid fraction the pd and pt are enriched in a layer known as the j m reef which occurs in a zone containing olivine bearing rocks ob i this zone contains the same rock types as the rest of the lower banded series but troctolite olivine gabbronorite and anorthosite are more abundant in ob i the concentrations of lithophile elements in ob i are similar to the rocks above and below ob i in particular the reef rocks show no additional signs of continental crust contamination such as additional th or lree enrichment and the reef rocks are not enriched in incompatible elements the strongly chalcophile elements cu ni se bi and au all correlate with s indicating that these elements are controlled by sulfides the pge show two trends the rocks below the j m reef and the reef rocks have high pge au to s ratios and fall on a single trend whereas those above the reef have low metal to s ratios these low ratios for the rocks above the reef could arise because the magma was depleted in pge au as it had already segregated some pge au rich sulfides the relatively high pge au cu and se concentrations of the rocks below the reef imply that the rocks contain 0 1 wt cumulate sulfides however they have very low s contents 300 ppm the low s se ratios of these rocks 2000 and most of the rocks outside of the reef suggest that they have lost more than half of their s the pd pt and pd ir ratios of the reef 3 4 and 800 respectively are much higher than those of the rocks below and above the reef the high pd pt and pd ir ratios of the reef imply that the sulfides formed from a fractionated magma however there is no correlation between the pd ir and pd pt ratios and the host rock type these ratios are dissimilar to the bushveld reefs and the main sulfide zone of the great dyke they more closely resemble the reefs in more fractionated rocks such as the ap reef of the penikat intrusion the roby zone of the lac des iles complex or the disseminated sulfides of the noril sk i intrusion the very high pd s and low cu pd ratios of the j m reef require that the sulfides collected pd from a very large volume of magma none of the current models is entirely satisfactory however we favor a model where at depth the ob1 magma partially melted a komatiitic massive sulfide and then transported the sulfide droplets into the magma chamber at the level of the j m reef

metamorphic evolution of sulphide rich chromitites from the chernichevo ultramafic massif se bulgaria abstract the upper mantle rocks of the metamorphosed ophiolite of chernichevo rhodope metamorphic complex in southern bulgaria host small chromite ores with unusual mineralization of base metal sulphides rich in platinum group elements mineralogical and chemical data indicate that after their formation in the mantle the chernichevo s chromite ores were modified by the intrusion of an alkaline mafic melt which resulted in the precipitation of a suite of metasomatic minerals sulphides calcite apatite and ilmenite accompanied by an increase in feo tio2 ga zn vn mn and especially ti and fe2o3 contents in the chromite the degree of chemical modification and abundance of metasomatic minerals are positively correlated and mark the extent of reaction of the chromitite with the intruding melt sulphide segregation promoted the concentration of high amounts of pges up to 3661 ppb particularly pt and pd yielding chromite ores with a typical flat to positive sloped chondrite normalized pattern subsequently the chromite ores were deformed and metamorphosed together with their host rocks at ultra high pressure uhp 2 5 gpa 1200 c to be later retrograded under eclogite and finally hydrous amphibolite facies conditions giving rise to three microstructural types metamorphism of the most metasomatized i e sulphide rich chromitites at temperatures 700 c within the conditions of uhp and eclogite facies resulted in the formation of 1 non porous recrystallized chromite consisting of a granoblastic microstructure made up of coarse grained blasts and finer grained chromite neoblasts in contrast hydrous metamorphism on the less metasomatized i e sulphide poor chromitite under the conditions of amphibolite facies ca 482 483 c resulted in the formation of 2 partly altered chromite characterized by unaltered cores surrounded by fe2 rich and al depleted porous chromite containing abundant clinochlore and 3 porous chromite corresponding to a chromite that was entirely transformed by the metamorphic alteration to fe2 rich and al depleted porous chromite during metamorphism magmatic ni fe cu sulphides originally formed during the metasomatic event in the mantle were altered resulting in a major leaching of cu rich sulphides leading to significant remobilization of pt and pd

noble metal enrichment processes in the merensky reef bushveld complex we have analysed sulphides silicates and chromites of the merensky introduction reef for platinum group elements pges re and au using laser the enrichment of noble metals in layered gabbroic ablation inductively coupled plasma mass spectrometry and synthetic intrusions to form stratiform merensky type ore horizons pyrrhotite standards annealed with known quantities of noble metals is an extremely efficient yet poorly understood process os ir and ru reside in solid solution in pyrrhotite and pentlandite metal enrichment must be related to the formation of rh and part of the reef s pd in pentlandite whereas pt au re magmatic layering as the ore horizons form an integral and some pd form discrete phases olivine and chromite often part of the magmatic stratigraphies of their host insuspected to carry os ir and ru are pge free all phases analysed trusions metal concentration is also related to the prescontain noble metals as discrete micro inclusions with diameters ence of magmatic sulphides because the noble metals are either dissolved in base metal sulphides or occur as typically 100 nm inclusions in sulphides commonly have the discrete noble mineral phases intergrown with sulphides element combinations os ir pt and pt pd au inclusions in vermaak hendriks 1976 ballhaus ryan 1995 olivine and chromite are dominated by pt au pd few inclusion ballhaus ulmer 1995 spectra can be related to discrete noble metal phases and few there is considerable controversy as to where the inclusions have formed by sub solidus exsolution rather some metals came from and how metal enrichment worked pge inclusions notably those in olivine and chromite are earlyfor a stratiform platinum group element pge deposit magmatic nuggets trapped when their host phases crystallized we inside the magmatic stratigraphy of a layered intrusion suggest that the silicate melt layer that preceded the merensky reef there are two possibilities either the metals were derived was pge oversaturated at early cumulus times experiments from the melt column above the ore horizon or they came combined with available sulphide silicate partition coefficients sugfrom the magma equivalent to the cumulate package gest that a silicate melt in equilibrium with a sulphide melt underlying the ore owing to the large density contrast containing the pge spectrum of the merensky ore would indeed be between silicate and sulphide melt a popular view is that oversaturated with respect to the least soluble noble metals sulphide the metals were enriched by gravitational settling of melt apparently played little role in enriching the noble metals in sulphide melt i e out of the magma column above the the merensky reef rather its role was to immobilize a pre existing ore campbell et al 1983 barnes naldrett 1985 in situ stratiform pge anomaly in the liquid stratified magma naldrett et al 1987 on the other hand it is well chamber established that gravitational crystal settling plays little role in producing magmatic layering and magmatic stratigraphies mcbirney noyes 1979 morse 1986 campbell 1987 and this cannot remain without consequence for stratiform noble metal deposits a third alternative is noble metal enrichment by late

stress induced anisotropy in brine saturated shale summary this paper reports the intrinsic and crack induced anisotropic properties of a set of preserved brine saturated shale samples and their response to external stresses we used undrained multistage triaxial tests to evaluate how the ultrasonic wave velocities and their anisotropy changed with increasing isotropic and differential stress conditions in addition the impact of stress orientation with respect to fabric orientation was evaluated an array of ultrasonic transducers allowed to measure five independent wave velocities which were used to calculate the elastic properties of the shale results indicate that in this shale p and s wave velocities vary with stress in a different manner dependent on the maximum principal stress orientation with respect to the fabric where the maximum stress is normal to bedding vpv and vs1 increase monotonically with increasing effective stress however vph and vsh decrease during individual loading stages but increase from stage to stage as confining pressure increases the reverse occurs when the microfabric is parallel to the maximum principal stress where the maximum stress is bedding normal velocity anisotropy decreases as differential stress increases when maximum stress is fabric parallel anisotropy increases elastic anisotropy is related to the initial composition and the spatial distribution of the different minerals fabric in the sediment and the presence of microfractures while changes in elastic anisotropy result from the applied stresses their orientation with respect to the rock fabric and the degree of stress anisotropy

review paper a semi empirical model of strain sensitivity for 4d seismic interpretation we reformulate the original model of hatchell and bourne and roste stovas and landro that couples fractional velocity change to subsurface strain via a fundamental constant r the new model combines elastic compressibility of a dual porosity system for a sand shale mixture with horizontal planes of inter granular weakness the majority of observed r factor magnitudes from post stack 4d seismic data in both the reservoir and overburden can thus be explained r is predicted to depend strongly on lithology and also initial strain state the model is also extended to predict the observed angle dependence of time lapse time shifts from pre stack data an expression for the gradient of time shift with incidence angle is obtained in terms of the background vp vs and also the ratio of tangential to normal compliances bt bn representing loss or creation of inter granular coupling if accurately estimated from data this compliance ratio can be used as an additional parameter to assess the post production state of the overburden it is concluded that whilst r remains the over arching parameter controlling the magnitude of time shifts measured from 4d seismic data bt bn is a subtler parameter that may also prove of future value

nonlinear rock physics model for estimation of 3d subsurface stress in anisotropic formations theory and laboratory verification we develop a rock physics model based on nonlinear elasticity that describes the dependence of the effective stiffness tensor as a function of a 3d stress field in intrinsically anisotropic formations this model predicts the seismic velocity of both p and s waves in any direction for an arbitrary 3d stress state therefore the model overcomes the limitations of existing empirical velocity stress models that link p wave velocity in isotropic rocks to uniaxial or hydrostatic stress to validate this model we analyze ultrasonic velocity measurements on stressed anisotropic samples of shale and sandstone with only three nonlinear constants we are able to predict the stress dependence of all five elastic medium parameters comprising the transversely isotropic stiffness tensor we also show that the horizontal stress affects vertical s wave velocity with the same order of magnitude as vertical stress does we develop a weakanisotropy approximation that directly links commonly measured anisotropic thomsen parameters to the principal stresses each thomsen parameter is simply a sum of corresponding background intrinsic anisotropy and stressinduced contribution the stress induced part is controlled by the difference between horizontal and vertical stresses and coefficients depending on nonlinear constants thus isotropic rock stays isotropic under varying but hydrostatic load whereas transversely isotropic rock retains the same values of dimensionless thomsen parameters only unequal horizontal and vertical stresses alter anisotropy since thomsen parameters conveniently describe seismic signatures such as normal moveout velocities and amplitudevariation with offset gradients this approximation is suitable for designing new methods for the estimation of 3d subsurface stress from multicomponent seismic data

paragenesis of multiple platinum group mineral populations in shetland ophiolite chromitite 3d x ray tomography and in situ os isotopes abstract chromitite from the harold s grave locality in the mantle section of the shetland ophiolite complex is extremely enriched in ru os and ir at g g concentrations high resolution x ray computed tomography on micro cores from these chromitites was used to determine the location size distribution and morphology of the platinum group minerals pgm there are five generations of pgm in these chromitites small average 5 m in equivalent sphere diameter esd euhedral laurites often with os ir alloys are totally enclosed in the chromite and are likely to have formed first by direct crystallisation from the magma as the chromite crystallised also within the chromitite there are clusters of larger 50 m esd aligned elongate crystals of pt rh ir os and ru bearing pgm that have different orientations in different chromite crystals these may have formed either by exsolution or by preferential nucleation of pgms in boundary layers around particular growing chromite grains thirdly there is a generation of large 100 m esd composite os ir ru rich pgm that are all interstitial to the chromite grains and sometimes form in clusters it is proposed that os ir and ru in this generation were concentrated in base metal sulfide droplets that were then re dissolved into a later sulfide undersaturated magma leaving pgm interstitial to the chromite grains fourthly there is a group of almost spherical large 80 m esd laurites hosting minor os ir ru rich pgm that form on the edge or enclosed in chromite grains occurring in a sheet crosscutting a chromitite layer these may be hosted in an annealed late syn or post magmatic fracture finally a few of the pgm have been deformed in localised shear zones through the chromitites the vast majority of the pgm including small pgm enclosed within chromite larger interstitial pgm and elongate aligned pgm have os isotope compositions that give re depletion model ages approximately equal to the age of the ophiolite at 492 ma a number of other pgm not confined to a single textural group fall to more or less radiogenic values with four pgm giving anomalously unradiogenic os corresponding to an older age of 1050 ma the 187 os 188 os isotopic ratios for pgm from cliff and quoys from the same ophiolite section are somewhat more radiogenic than those at harold s grave this may be due to a distinct mantle source history or possibly the assimilation of radiogenic crustal os

stress induced versus lithological anisotropy in compacted claystones and soft shales shales are anisotropic most definitions of shale in corporate this attribute either by referring to fissility and existence of cleavage planes or to anisotropic texture resulting in anisotropy of physical properties on many length scales definitions of shale scatter though some focus on a high content of clay minerals as characteristic of a shale while others consider a large amount of fine grains 2 m as sufficient in a rock mechanical context it is natural to define shale as a rock in which clay minerals constitute the load bearing framework this means that gas shales in oil field terminology are strictly speaking not shales according to a geological or a geomechanical perspective still these materials have a lot in common with classically defined shales e g low permeability and anisotropy

trace elements in sulfide inclusions from yakutian diamonds sulfide inclusions in diamonds may provide the only pristine samples of mantle sulfides and they carry important information on the distribution and abundances of chalcophile elements in the deep lithosphere trace element abundances were measured by proton microprobe in 50 sulfide inclusions sdi from yakutian diamonds about half of these were measured in situ in polished plates of diamonds providing information on the spatial distribution of compositional variations many of the diamonds were identified as peridotitic or eclogitic from the nature of coexisting silicate or oxide inclusions known peridotitic diamonds contain sdis with ni contents of 22 36 consistent with equilibration between olivine monosulfide solid solution mss and sulfide melt whereas sdis in eclogitic diamonds contain 0 12 ni a group of diamonds without silicate or oxide inclusions has sdis with 11 18 ni and may be derived from pyroxenitic parageneses eclogitic sdis have lower ni cu and te than peridotitic sdis the ranges of the two parageneses overlap for se as and mo the mo and se contents range up to 700 and 300 ppm respectively the highest levels are found in peridotitic diamonds among the in situ sdis significant zn and pb levels are found in those connected by cracks to diamond surfaces and these elements reflect interaction with kimberlitic melt significant levels of ru 30 1300 ppm and rh 10 170 ppm are found in many peridotitic sdis sdis in one diamond with wustite and olivine inclusions and complex internal structures have high levels of other platinum group elements pges as well and high chondrite normalized ir pd comparison with experimental data on element partitioning between crystals of monosulfide solid solution mss and sulfide melts suggests that most of the inclusions in both parageneses were trapped as mss while some high cu sdis with high pd rh may represent fractionated sulfide melts spatial variations of sdi composition within single diamonds are consistent with growth histories shown by cathodoluminescence images in which several stages of growth and resorption have occurred within magmatic environments that evolved during diamond formation

anisotropy of elastic wave velocities in deformed shales part 1 experimental results elastic wave velocity measurements in the laboratory are used to assess the evolution of the microstructure of shales under triaxial stresses which are representative of in situ conditions microstructural parameters such as crack aperture are of primary importance when permeability is a concern the purpose of these experiments is to understand the micromechanical behavior of the callovo oxfordian shale in response to external perturbations the available experimental setup allows for the continuous simultaneous measurement of five independent elastic wave velocities and two directions of strain axial and circumferential performed on the same cylindrical rock sample during deformation in an axisymmetric triaxial cell the main results are 1 identification of the complete tensor of elastic moduli of the transversely isotropic shales using elastic wave velocity measurements 2 assessment of the evolution of these moduli under triaxial loading and 3 assessment of the evolution of the elastic ani

experimental laboratory determination of the dynamic elastic properties of wet drained shales the ultrasonic anisotropic elastic properties of drained saturated shales were measured as a function of confining pressure two shales were characterized in this study a jurassic outcrop shale retrieved under the sea in a saturated state and a kimmeridge clay shale cut from a north sea borehole both shales were highly anisotropic both texturally as revealed by scanning electron microscopy analysis and elastically as measured ultrasonically in the laboratory the strongest anisotropy was seen in the kimmeridge clay shale where up to 38 compressional wave anisotropy thomsen s parameter e and up to 58 shear wave anisotropy thomsen s parameter were observed in addition for both shales e and were found to decrease as a function of increasing confining pressure with the pore pressure drained to atmosphere while the anellipticity deviation of the slowness surfaces from ellipses was found to be positive and decreased as a function of increasing confining pressure accompanying these changes in elastic properties was a decrease in porosity with increasing confining pressure from 10 5 to 8 5 for the jurassic shale the decrease in overall anisotropy of the shales with increasing confining pressure was found to be consistent with theoretical modeling of shale properties where the shale anisotropy and anellipticity were predicted to decrease as a function of decreasing fluid filled porosity