seismic pore space compressibility and gassmann s relation the pore space compressibility of a rock provides a robust model independent descriptor of porosity and pore fluid effects on effective moduli the pore space compressibility is also the direct physical link between the dry and fluid saturated moduli and is therefore the basis of gassmann s equation for fluid substitution for a fixed porosity an increase in pore space compressibility increases the sensitivity of the modulus to fluid substitution two simple techniques based on pore compressibility are presented for graphically applying gassmann s relation for fluid substitution in the first method the pore compressibility is simply reweighted with a factor that depends only on the ratio of fluid to mineral bulk modulus in the second technique the rock moduli are rescaled using the reuss average which again depends only on the fluid and mineral moduli

influence of water column anoxia and sediment supply on the burial and preservation of organic carbon in marine shales abstract previous work has suggested that the laminated organic rich and bioturbated organic poor shales of the camp run member of the late devonian early mississippian new albany shale formed under anoxic and oxygenated bottomwater conditions respectively and that the interbedding of the two facies was due to the vertical oscillation of a water column anoxic oxic boundary where it impinged on the basin margin we have extended this analysis by examining the chemical and mineralogical differences between the two shale facies in a single borehole core by seeking evidence for deposition of the laminated shales under bottom water oxia or anoxia and by determining whether the laminated shales formed when the carbon supply to the sea floor was higher the results of this study show that the laminated and bioturbated shales are mineralogically and chemically distinct relative to al an index of the aluminosilicate content si ti fe p na ba co cr cu mo ni v zn and zr are all higher whereas mn ca mg and sr are lower in the laminated compared with the bioturbated shales the differences are due to a higher quartz feldspar titanite ilmenite and zircon content in the laminated shales probably indicating a coarser grain size and the greater abundance of manganoan calcite in the bioturbated shales dissolved oxygen was present in bottom waters during the deposition of some of the laminated shale intervals because of the presence of manganoan calcite a phase that can only form in sediments with an oxic surface in addition the organic matter preserved in the two shale types is isotopically different 13corganic values are 1 9z permil lighter on average in the laminated compared with bioturbated intervals possibly indicating a larger fraction of terrestrial organic matter in the latter 15n values are 1 9z permil lighter on average in laminated compared with bioturbated intervals possibly indicating a larger fraction of terrestrial organic matter in the latter 15n values are 1 9z permil lighter on average in laminated compared with bioturbated intervals suggesting that nutrient drawdown was less during the deposition of the organic rich laminated shales the chemical mineralogical and isotopic contrasts between the two shale facies of the camp run member indicate that the conditions of sedimentation were different during their deposition the difference was possibly related to variations in sea level which would have caused the camp run shoreline to move closer to and farther from the core site causing in turn the deposition of coarser and finer grained sediments that contained different mixtures of marine and terrestrial organic matter bottomwater conditions were anoxic during deposition of most laminated intervals bottom water anoxia or dysoxia led to decreased burial and preservation of the essential nutrient phosphorus in the laminated organic rich shales relative to the rocks deposited beneath better oxygenated bottomwaters increased availability of phosphorus in the water column on long timescales leads to increased productivity and a higher settling flux of organic matter causing bottom water oxygen levels to fall this is consistent with the nitrogen isotope evidence suggesting that production was probably higher during the deposition of the organic rich shales thus production variations coupled with enhanced sedimentary regeneration of phosphorus from sediments related to low oxygen bottom water concentrations provide a general mechanism for the formation of the alternating facies of this member of the new albany shale

fluid inclusion characteristics of intrusion related gold mineralization tombstone tungsten magmatic belt yukon territory canada intrusion hosted low sulfide sheeted vein systems are common within many plutons and stocks of the middle cretaceous tombstone tungsten magmatic belt yukon territory and host significant gold mineralization fluid inclusion characteristics of five such systems namely emerald lake dublin gulch scheelite dome mike lake and mactung constrain the vein forming fluid composition formation temperatures and pressures hydrothermal fluid processes and potential fluid sources the veins contain a wide range of fluid inclusion types ubiquitous type 1a and 1b inclusions are low salinity 1a xnacl 1 kbar at emerald lake and dublin gulch and 2 kbar at mactung and scheelite dome that potentially control fluid composition and evolution a variety of fluid processes may have been responsible for gold precipitation including immiscibility and or release of an evolving magmatic fluid

empirical relationships among seismic velocity effective pressure porosity and clay content in sandstone we use a multivariate analysis to investigate the influence of effective pressure pe porosity and clay content c on the compressional velocity vp and shear velocity vs of sandstones laboratory measurements on water saturated samples of 64 different sandstones provide a large data set that was analyzed statistically for each sample relationships between effective pressure and vp and vs have been determined all samples were well fit by relationships that have an exponential increase in velocity at low pe tapering to a linear increase with pe for pe greater than 0 2 kbar there are differences in the pressure dependences of velocity for different rocks particularly at very low pressures however the differences cannot be attributed to or c for the combined set of measurements from all samples the best fitting formulations are vp 5 77 6 94 1 73c 0 446 pe e 16 7pe and vs 3 70 4 94 1 57c 0 361 pe e 16 7pe while this is admittedly a very simplified parameterization it is remarkable how well

geology and geochemistry of the clear creek intrusion related gold occurrences tintina gold province yukon canada the clear creek gold occurrences lie within deformed lower greenschist facies rocks of the western selwyn basin they consist of auriferous sheeted quartz veins that cut six cretaceous stocks and their hornfels the veins contain 1 2 combined pyrite and arsenopyrite with lesser pyrrhotite bismuthinite and scheelite as well as 2 5 g t au new 40ar 39ar geochronology of hydrothermal micas indicates that the veins formed within 1 2 million years of granitoid emplacement fluid inclusion microthermometry defines a parent ore fluid of 81 mol h2o 14 mol co2 4 mol nacl kcl and 1 mol ch4 which unmixed into a low and high salinity immiscible pair this suggests a more saline parent fluid and a greater degree of fluid unmixing relative to the other occurrences in the eastern tintina gold province inclusions trapped in as and bi rich high gold grade veins have homogenization temperatures of 300 350 c whereas inclusions found in more ag and pb rich veins are characterized by temperatures of

origin ore forming fluid evolution and timing of the logrosan sn w ore deposits central iberian zone spain the logrosan sn w ore deposits in the metallogenic sn w province of the european variscan belt consist of endo and exogranitic greisen type and quartz cassiterite veins associated with a s type granite mineral characterization fluid inclusion study isotope geochemistry and ar ar geochronology have been combined in order to reconstruct the conditions for sn w mineralization the endo and exogranitic mineralization must have been developed in a relatively long lived system 308 303 ma during or soon after the emplacement of the logrosan related granite at ca 308 ma the mineralizing fluids are characterized by complex aqueous and volatile h2o n2 co2 ch4 nacl fluid inclusions microthermometry and raman analyses indicate that fluid composition evolved from n2 ch4 to n2 rich followed by co2 rich fluids with varying amounts of h2o the presence of n2 and ch4 suggests the interaction with fluids derived from the nearby metasedimentary host rocks a model of host rock interaction assimilation and mixing of metamorphic and magmatic fluids resulting in change of the redox conditions is proposed for tin deposition later sulfide minerals were precipitated as a result of pressure and temperature release

compressional and shear wave velocities as a function of confining stress in dry sandstones a laboratory study was carried out to investigate the influence of confining stress on compressional and shear wave velocities for a set of rock samples from gas producing sandstone reservoirs in the cooper basin south australia the suite of samples consists of 22 consolidated sublitharenites with helium porosity ranging from 2 6 to 16 6 we used a pulse echo technique to measure compressional and shear wave velocities on dry samples cylindrical 4 6 2 cm at room temperature and at elevated confining stress 60 mpa compressional and shear wave velocities in samples increase non linearly with confining stress a regression equation of the form v a be dp gives a good fit to the measured velocities with improved prediction of velocities at high confining stresses compared with equations suggested by other studies the predicted microcrack closure stresses of the samples show values ranging from 70 mpa to 95 mpa and insignificant correlation with porosity permeability or clay content there is a positive correlation between change in velocity with core porosity and permeability but this association is weak and diminishes with increasing confining stress experimental results show that pore geometry grain contact type and distribution and location of clay particles may be more significant than total porosity and clay content in describing the stress sensitivity of sandstones at in situ reservoir effective stress the stress dependence of cooper basin sandstones is very large compared with data from other studies the implication of our study for hydrocarbon exploration is that where the in situ reservoir effective stress is much less than the microcrack closure stress of the reservoir rocks the variation of reservoir effective stress could cause significant changes in velocity of the reservoir rocks the velocity changes induced by effective stress in highly stress sensitive rocks can be detected at sonic log and probably surface seismic frequencies

a simple effective medium model for water saturation in porous rocks a general equation for water saturation is derived from effective medium theory a simpler low frequency equation is also derived both equations are directly solvable for water saturation the model should be applicable to any granular water wet formation additional relationships are derived specifically for application to shaly sandstones but the model should be applicable to a wide range of rock types water conductivities and tool frequencies in the derivation hydrocarbons are included in the matrix component of the equation and the combined matrix elements are treated as resistors in parallel the low frequency equation is compared to various approaches to calculation of water saturation such as dual water waxman smits and bussian the general equation is compared to three component effective medium porosity index and complex refractive index models crim the model is proven to work on experimental data under a wide range of frequencies and water conductivities it is recommended that

middle cretaceous calcareous nannofossil biogeography and preservation in the atlantic and indian oceans implications for paleoceanography abstract the quantitative study of calcareous nannofossil preservation and biogeographic distribution puts constraints on paleoceanographic models for the atlantic and indian oceans during the middle cretaceous we establish a dissolution ranking of middle cretaceous calcareous nannofossils based on susceptibility to dissolution a positive correlation of organic carbon content of the sediments and the relative abundance of watznaueria indicates that much of the carbonate dissolution was caused by the release of carbon dioxide during oxidation of organic matter the depth distribution of the most dissolution resistant species watznaueria barnesae shows relative abundance maxima at the deepest sites and a maximum where intermediate waters impinge on slopes this reflects stagnant oxygen poor bottom waters and possibly a mid water oxygen minimum zone with increased deposition and catabolic breakdown of organic matter factor analyses are performed on various data sets for three different time slices ranging in age from late aptian to early albian middle albian and late albian to cenomanian the resulting factors can be related to paleoceanographic conditions such as colder water at high latitudes high fertility upwelling conditions and neritic conditions for all three time intervals a wide tropical to subtropical zone was flanked by boreal and austral zones upwelling conditions probably existed along the north african margin and over the falkland plateau zonal upwelling is tentatively postulated for the northwestern and northeastern margin of the north atlantic in the middle albian and for the eastern margin of the north atlantic off western europe for the late albian to cenomanian we speculate on surface water current patterns location of upwelling regions and haline driven deep circulation for the middle cretaceous

consistent joint elastic electrical differential effective medium modelling of compacting reservoir sandstones abstract improved reservoir characterization and monitoring can be achieved by combining seismic and controlled source electromagnetic techniques this requires developing coherent rock physics descriptions in this paper we demonstrate consistent joint elastic electrical modelling according to the differential effective medium theory we test our modelling against data from a compaction experiment on a set of 11 sandstone core samples from the same quarry location the presented approach is analogous to calibrating a rock physics model to a particular reservoir based on data from possible well logs and core samples for simplicity we choose to use multivariable non linear regression in the inversion it shows that this technique is able to identify solutions that are physically sound however a more rigorous inversion method might be considered in future implementations to identify the critical parameters we test the elastic electrical sensitivity of the various unknown variables involved the most sensitive parameters identified are then perturbed during the modelling the mineralogy consists mainly of quartz which we assume to be spherical and kaolinite we use the resistivity to calibrate the aspect ratio of the clay grains and estimate the porosity reduction due to compaction these values are in turn used in inverse modelling of the bulk and shear moduli the solid minerals make up the inclusion material in the differential effective medium modelling for both the elastic and electrical properties hence this formulation constitutes a consistent joint elastic electrical modelling scheme we achieve good fits between the model results and the laboratory measurements for most of the samples the reason for the less good fit with some of the samples might be due to measurement errors in the laboratory this is supported by the observed abnormal stiffness compaction trends associated with those samples

geological storage of carbon dioxide carbon dioxide co2 is the main compound identified as affecting the stability of the earth s climate a significant reduction in the volume of greenhouse gas emissions to the atmosphere is a key mechanism for mitigating climate change geological storage of co2 or the injection and long term stabilization of large volumes of co2 in the subsurface in saline aquifers in existing hydrocarbon reservoirs or in unmineable coal seams is one of the more technologically advanced options available a number of studies have been carried out and are reported here they are aimed at understanding the safety physical and chemical behaviour and long term fate of co2 when stored in geological formations until efficient alternative energy options can be developed geological storage of co2 the subject of this volume provides a mechanism to reduce carbon emissions significantly whilst continuing to meet the global demand for energy

cross property rock physics relations for estimating low frequency seismic impedance trends from electromagnetic resistivity data estimating the low frequency seismic impedance trend is critical for reservoir characterization based on seismic inversions conventional seismic reflection data have an information gap between 2 and 10 hz and do not contain information about the background impedance trend on the other hand controlled source electromagnetic csem data are typically low resolution and contain information about the earth s resistivity structure thus cross property rock physics relations between elastic and electrical properties can extract information from the csem data to provide constraints on the low frequency seismic impedance trend this concept is tested with well log data and applied to a resistivity section inverted from csem data results show that appropriate cross property rock physics relations can capture the background low frequency impedance trend and provide useful constraints on models for inversion

fracturing in saturated rocks undergoing triaxial deformation using complex electrical conductivity measurements experimental study frequency dependent complex electrical conductivity measurements have been made on sandstones saturated with distilled water during triaxial deformation in both drained and undrained regimes the resulting electrical and mechanical data show how the rock undergoes compaction followed by dilatancy due to new crack formation crack growth interlinkage and failure as axial strain is increased electrical data are particularly good at indicating how early the formation of new cracks begins showing that the quasi linear portion of the stress strain curve for triaxial deformation of saturated rocks does not represent truly elastic behaviour but the combined effects of i crack closure perpendicular to the strain axis and ii the formation of tensile cracks parallel to the strain axis a difference in the stress strain behaviour between the drained and undrained samples was also observed with the undrained samples developing a pronounced strain softening phase before failure the experimental data have also been used to derive the volumetric porosity electrical porosity cementation exponent and electrical tortuosity of the pore crack network during deformation the relative importance of crack closure and dilatation a during the progress of deformation and b between crack populations controls these parameters and the electrical data over a wide range of frequencies however the frequency dependence of the micro structural parameters and the electrical data was found to be not affected significantly by the hydrostatic pressurisation or the triaxial deformation the development of large scale crack connectivity is observed to be confined to just prior to failure and is controlled by the loss of cracks perpendicular to the axis of current flow and deformation c 2000 elsevier science b v all rights reserved

calcareous nannofossil biostratigraphy and assemblages of the cenomanian turonian boundary interval implications for the origin and timing of oceanic anoxia a detailed nannofossil zonation has been derived for the cenomanian turonian boundary interval consisting of three zones two subzones and nine additional biohorizons this biostratigraphy based on the investigation of numerous sections from europe north america and africa allows accurate correlation of sections from shelf and deep sea environments the increased resolution helps solve several pertinent paleoceanographic and sedimentologic problems in this time period facies patterns are variable in this interval for numerous reasons a widespread hiatus occurred in the latest cenomanian and earliest turonian in much of northwest europe and may have been an indirect result of peak marine transgression in parts of the deep tethys dissolution of carbonate took place in undersaturated bottom waters or during early diagenesis only a few boundary sections mostly within the western interior united states are characterized by continuous carbonate deposition in many sections a 13c excursion which has been associated with the burial of large amounts of marine organic matter coincides with a facies change lower ratios of coccolith carbonate to micrite and poorer nannofossil preservation this excursion therefore may be strongly overprinted by diagenesis numerous nannofossil events indicate that the carbon excursion is slightly diachronous between sequences of the western interior and that the shift occurred distinctly later in this region than in northwest germany the data obtained do not invalidate the concept of a cenomanian turonian ocean wide anoxic event but show how local tectonic climatic and oceanographic perturbations have masked the global scenario in particular they indicate that carbon shifts may be basinal and not always oceanic phenomena a conclusion which can be rationalized with overall sluggish middle cretaceous circulation nannofossil assemblages in almost all sequences observed contain exceptionally high abundances of two dissolution resistant taxa in particular samples eprolithus floralis and broinsonia sp however the overall composition of assemblages does not change dramatically in the boundary interval in contrast to the macrofossils and foraminifera which suffered widespread extinctions

seismic attenuation and pore fluid viscosity in clay rich reservoir sandstones the frequency dependence of seismic attenuation in a suite of clay rich reservoir sandstones was investigated in the laboratory compressional and shear wave velocities vp and vs and quality factors qp and qs were measured as functions of pore fluid viscosity at an effective pressure of 50 mpa and at an experimental frequency of about 0 8 mhz using the pulse echo technique the experimental viscosity ranged from 0 3 to 1000 centipoise which gives equivalent frequencies for a water saturated sandstone of 2 6 mhz to 780 hz assuming a global flow loss mechanism two types of behavior were observed high permeability greater than 100 millidarcies sandstones tend to show variable qp and qs which are similar in magnitude to those predicted by the biot theory over the viscosity range 0 3 to about 20 centipoise equivalent frequency range 2 6 mhz to about 39 khz low permeability less than 50 millidarcies sandstones tend to show almost constant qp and qs over the experimental viscosity range that are

chloritization of the hydrothermally altered bedrock at the igarape bahia gold deposit carajas brazil the igarape bahia gold deposit has developed from weathering of a near vertical hydrothermal cu au mineralization zone the unweathered bedrock composed of chlorite schists is mainly metamorphosed basalts pyroclastic and clastic sedimentary rocks and iron formation contents and fe fe mg ratios of chlorites increase from distal country rock towards the mineralization zone which can be attributed to different water rock ratios and locations in a hydrothermal system in the hydrothermal system high salinity fluids convected through basin floor rocks stripping metals from the recharge zones with precipitation in discharge zones the chlorite with lower fe fe mg ratios indicates alteration by relatively unreacted mg rich fluids occurring within recharge zones by contrast the chlorite with higher fe fe mg ratios in the mineralization zone formed from solutions rich in fe mn au cu h2s and sio2 within a discharge zone the iron formation could also be formed within the discharge zone or on the basin floor from the fe rich fluids the distal country rock with less chlorite content is a hydrothermal product at low water rock ratios whereas the proximal country rock and the host rock with more chlorite content formed at high water rock ratio conditions the al iv contents of chlorites indicate that the formation temperatures of these rocks range from 204 to 266 c with temperatures slightly increasing from distal country rock towards the mineralization zone

a laboratory study of the dependence of elastic wave velocities on pore scale fluid distribution laboratory data have been collected during a continuous imbibition drainage experiment that show a clear dependence of elastic wave velocities on the details of the pore scale distribution of water and air in a sandstone compressional wave velocity vp was measured at a frequency of 1 mhz shear wave velocity vs was measured at a frequency of 600 khz during the experiment vp showed little variation with the level of water saturation sw during increasing sw through imbibition until sw 0 80 at which point vp increased dramatically when sw was decreased pronounced saturation induced hysteresis was observed in the region 03 0 4 as a simple model we consider the imbibition process as producing a partially saturated state in all pores i e all pores contain both air and water the drainage process in contrast favors the existence of either air filled or water filled pores as elastic wave velocities are very sensitive to the saturation state in the smaller crack like pores these variations in fluid distribution cause related variations in velocities

revised mesozoic cenozoic orogenic architecture and gold metallogeny in the northern circum pacific abstract the orogenic collages of the northern circum pacific between japan and alaska revealed an endowment of about 450 moz au in various deposit types and diverse mesozoic cenozoic tectonic settings the area consists of predominantly late paleozoic to cenozoic turbidite to island arc terranes as well as precambrian cratonic terranes that can be grouped into the kolyma alaska kamchatka aleutian and nipponide collages the latter can be linked via the mongol okhotsk suture with the late paleozoic to early mesozoic terranes in the mongolides the early yanshanian magmatic arc terranes in the fossil kolyma alaska collage host copper gold porphyry deposits which have only recently received much attention exploration has revealed a large and growing gold endowment of more than 30 moz au in some individual deposits with smaller role of epithermal deposits this mineralization formed at 140 125 ma is partly coeval with the collisions of magmatic arcs with the passive margin sequences of the siberian craton and related granitoid magmatism about 200 moz of gold is known in the kolyma alaska collage in the mesozoic orogenic gold deposits and related quaternary placers the central kolyma indigirka south verkhoyansk and north chukotka subprovinces of the collage revealed an endowment of more than 10 moz au each a similar and coeval event in the mongolides in relation to the collision between siberia and north china is largely reflected in still poorly dated intrusion related gold deposits clustered along the mongol okhotsk suture the overlapping yanshanian magmatic arcs in transbaikalia and northeast china and the okhotsk chukotka magmatic arc in the russian far east stitch the kolyma alaska collage with the paleozoic central asian supercollage and adjacent cratons while the okhotsk chukotka arc reveals a relatively simple and broad oroclinal pattern the yanshanian arcs in mongolia and ne china form a tightly deformed giant z shaped feature that was bent in response to the southward movement of the siberian craton and northward translation of the nipponides and north china craton to close the mongol okhotsk suture in late jurassic to cretaceous times the yanshanian arcs host mostly small to medium sized 100 70 ma au ag deposits with the largest endowment discovered in the baley district in transbaikalia and at kupol in the northern part of the okhotsk chukotka arc some intrusion related gold deposits were formed synchronously with this arc magmatism with the largest known examples in the tintina belt in alaska formed at 104 and 93 91 ma the kamchatka aleutian collage is still evolving in front of the westward subducting pacific plate it s late cretaceous to paleogene magmatic arc rocks form immature island arc terranes extending from the aleutian islands towards the nipponides via kamchatka peninsula kuril islands and eastern sakhalin however in the nipponides the sikhote alin portion of the magmatic arc overlaps the mesozoic turbidite terranes the oroclinal pattern of this more than 8000 km long magmatic arc indicates its westward translation in agreement with the movement of the pacific plate so that the arc is presently colliding with itself along the island of sakhalin a seismically active intraplate lineament and a boundary between the nipponide and kamchatka aleutian collages this magmatic arc is usually interpreted to be of intra oceanic origin with subsequent docking to asia from the south however presence of the sea of okhotsk cratonic terrane between sakhalin and kamchatka suggests that it may be rather considered as an external arc system that separated from the rest of asia due to backarc spreading events therefore forming the most external arc system at the active margin with the pacific plate the subduction related events in the collage produced numerous late mesozoic to cenozoic 1 3 moz gold epithermal deposit in kamchatka and sikhote alin as well as au cu porphyry deposits with currently largest gold endowment in the pre tertiary pebble copper deposit in alaska the westward translation of the kamchatka aleutian collage might have controlled the emplacement of this porphyry deposit as well as up to 30 moz into intrusion related gold deposits at 70 65 ma in the kuskokwim belt immediately north from the porphyry cluster

calcareous nannofossil paleoecology of the mid cretaceous western interior seaway and evidence of oligotrophic surface waters during oae2 abstract analysis of calcareous nannofossils total organic carbon toc values and carbon isotope records from outcrop and drill cores in the central colorado and kansas and southern texas western interior basin wib indicates predominantly oligotrophic surface water conditions during the late cenomanian turonian oceanic anoxic event 2 oae2 high resolution bio chemostratigraphy of this interval allows for detailed correlation of changes in nannofossil assemblages and toc across the wib and aids comparison with other global records prior to and at the onset of oae2 the a interval in the 13c positive excursion identified by pratt and threlkeld 1984 mesotrophic to eutrophic nannofossil taxa biscutum and zeugrhabdotus are relatively high in abundance and foraminiferal assemblages record a high diversity benthonic zone toc sharply declines at the start of oae2 despite evidence of high surface productivity and benthic diversity implying that the seafloor was briefly oxygenated during a period of enhanced mixing in the expanding western interior seaway during the latter two thirds of oae2 intervals b and c in the excursion toc periodically increases suggesting that anoxic conditions returned at the substrate despite persistently low abundances of biscutum and zeugrhabdotus implying oligotrophic surface water conditions the divergence of these two proxies suggests a highly stratified water column in the wib not higher productivity which resulted in anoxic conditions during oae2 if productivity was not the primary cause of increased carbon burial in the wib it is probable that increased terrestrial runoff and incursion of warm saline tethyan waters from the south led to salinity stratification in the absence of mixing warm and saline bottom waters would have been isolated from freshened boreal currents and become stagnant allowing for preservation of greater amounts of organic material in the substrate nannofossil records from cuba ks are an exception and reveal relatively high productivity throughout suggesting that occasional mixing of nutrients to the surface may have continued along the eastern margin of the central wib

solid inclusions of halite in quartz evidence for the halite trend abstract compositions of fluid inclusions containing halite and sylvite daughter minerals can define a linear trend of decreasing salinity when plotted in the nacl kcl h 2 o ternary system this is termed the halite trend and is attributed to halite precipitation from the fluid before trapping salt crystals observed in vein quartz crystals from mineralized zones in the capitan mountains nm usa using an electron microprobe are evidence of halite precipitation causing the halite trend the crystals observed on both polished and broken sample surfaces are often euhedral and enclosed in quartz with little suggestion of associated fluid cavities based on the textural evidence these salt crystals are interpreted as solid inclusions that were trapped during the growth of quartz given halite saturated fluids trapping of heterogeneous liquid halite fluid inclusions is possible leading to the potential to overestimate the fluid inclusion salinities

prediction of archie s cementation factor from porosity and permeability through specific surface based on archie s cementation factor as measured on north sea chalk and on published data we explore how the cementation factor depends on other physical properties of the chalk a relationship between cementation factor and specific surface with respect to bulk volume is obtained for chalk this leads to how archie s cementation factor may be predicted from porosity and permeability for chalk as well as for sandstone a common relationship between cementation factor and specific surface with respect to bulk volume calculated from porosity and permeability is obtained as an alternative the a factor in archie s equation is related to specific surface with respect to bulk volume but the relationship is less clear than the simple relationship between cementation factor and specific surface

integrated paleoenvironmental analysis of the niobrara formation cretaceous western interior seaway northern colorado abstract this study presents a regional chronostratigraphic framework and paleoenvironmental reconstruction of the niobrara formation in northern colorado based upon multidisciplinary biostratigraphic and lithostratigraphic data a local biostratigraphic zonation is described for the coniacian to earliest campanian of this region of the western interior seaway based primarily upon the distribution of calcareous nannofossils three key paleoenvironmental packages are also identified and linked to the evolution of regional sedimentary facies during the early to late coniacian tethyan water masses interacted with boreal surface currents to produce regional upwelling along tectonically controlled bathymetric highs a well mixed relatively well oxygenated water column with warm surface water temperatures and high fertility sustained a rich microflora fauna and promoted higher carbonate production enhanced fluvial input and a weakening of tethyan influence during the early santonian mark the onset of a regional environmental shift this period of transition extends through the middle santonian and is characterized by pulses of transported material and relatively frequent turnover of faunal associations increased terrigenous runoff likely produced eutrophic surface waters and intensified water column stratification leading to a general deterioration of the bottom water environment in a progressively dysoxic setting continued strengthening of fluvial input during the late santonian to early campanian resulted in surface water freshening and sustained primary productivity this surface water environment in conjunction with stifled vertical mixing promoted the development of a stagnant and intensely stratified water column the basin was therefore severely dysoxic possibly anoxic and corrosive with chemically reducing bottom waters and an expanded oxygen minimum zone thereby limiting biotic development and causing the deposition of finely laminated mud rich carbonate poor seciments

effects of fluid displacement pattern on complex electrical impedance in berea sandstone over frequency range 104 106 hz to better understand the effect of fluid distribution on the electric response of rocks saturated with oil and brine we conducted experimental studies on the complex electrical impedance in a berea sandstone together with in situ acquisitions of oil distribution images employing a high resolution medical x ray computed tomography we performed two tests of brine displacement by oil under high 10 mpa and low 5 mpa pressures which were accompanied by fingering and stable displacement patterns respectively the measured complex impedance data were fitted to the cole model to obtain the resistance capacitance peak frequency of the imaginary impedance and the exponent of the rock fluid system with increasing oil saturation the resistance showed an increasing trend whereas the other three parameters decreased the fingering displacement exhibited lower resistance and capacitance than the stable displacement the analysis of the resistance changes using a simple parallel connection model indicates that there are more components of residual brine in parallel connections in the fingering pattern than in the stable displacement pattern at the same saturation we also interpreted the normalised changes in the capacitance or apparent dielectric constant with respect to the oil saturation via an analysis of the shape factor of fluid distribution based on the maxwell wagner brugermann hanai model the changes in the shape factor suggest that the pinch off of the brine in parallel connection by the oil is a dominant mechanism reducing the capacitance in the stable displacement most of the connections in the brine phase are immediately pinched off by oil displacement front at a local oil saturation of 65 conversely in the fingering displacement there is a transition from the bulk or layered brine to the pinched off at a local oil saturation below 60 the analyses indicate that the difference in the fluid distribution under different fluid conditions is responsible for the non archie behaviour

evaluation of porosity and saturation degree by laboratory joint measurements of velocity and resistivity a model improvement this paper illustrates the laboratory procedures and experiments carried out on samples with different lithologies and reconstructed samples in order to test and implement an electroseismic model carrara et al 1994 which allows the evaluation of porosity and the saturation degree of rocks the testing was conducted by comparing porosity and saturation degree s w values obtained from measured resistivity and elastic wave velocity v p by means of appropriate formulations with the values of and s w previously calculated by geotechnics and employed as standards the experimental results have led to a good definition of the model to be proposed as an application method in the field of hydrogeology

geoelectrical and seismic prospections in hydrogeology model and master curves for the evaluation of porosity and water saturation the prevailing purpose of geoelectrical exploration is the location of acquifers as resistivity is strongly sensitive to the presence of water through this method valuable information on the structure and volume of storage rocks may be acquired however the evaluation of saturation and porosity which plays a strong role in the estimation of hydraulic parameters is hitherto affected by a large uncertainty therefore it is necessary to carry out expensive and often numerous drillings in addition to the calibration ones in this paper we argue how the uncertainty can be substantially reduced by carrying out a joint seismic and geoelectrical prospection

cross property relations between electrical conductivity and the seismic velocity of rocks cross property relations are useful when some rock properties can be measured more easily than other properties relations between electrical conductivity and seismic velocity stiffness moduli and density can be obtained by expressing the porosity in terms of those properties there are many possible ways to combine the constitutive equations to obtain a relation each one representing a given type of rock the relations depend on the assumptions to obtain the constitutive equations in the electromagnetic case the equations involve archie s law and its modifications for a conducting frame the hashin shtrikman hs bounds and the self similar and complex refraction index method crim models in the elastic case the stress strain relations are mainly based on the time average equation the hs bounds and the gassmann equation also expressions for dry rocks and for anisotropic media using backus averaging are analyzed the relations are applied to a shale saturated with brineoverburden and to a sandstone saturated with oilreservoir tests with sections of a north sea well log show that the best fit is given by the relation between the gassmann velocity and the crim selfsimilar and archie models for the conductivity

velocities and quality factors of sedimentary rocks at low and high effective pressures summary techniques for measuring acoustic velocities and quality factors q of sedimentary rocks in the laboratory are sufficiently accurate to establish closely fitting regression curves which represent the variation of these acoustic properties with pressure ultrasonic p and s wave measurements of velocity v v and q q q were made on 16 different water saturated sandstone samples at various effective pressures using an ultrasonic reflection technique and the data were fitted using a simple regression equation containing a constant plus linear and exponential pressure dependent terms the redundancy of the linear term in the regression of q data suggests that microcracks alone govern the pressure variation of q whereas velocities are additionally dependent on another mechanism consistent with the changes in elastic moduli caused by intergranular compression causing small reductions in porosity the implied rates of microcrack closure with increasing effective pressure in all samples were found to be comparable the regression equations describe the data closely enough to enable the extrapolation of acoustic properties to both low and high effective pressures this is of practical use since laboratory techniques can produce uncertain results at low pressures due to coupling problems and low signal strengths whilst high pressures require large confining vessels low pressure and high pressure data are applicable to shallow seismic surveys and hydrocarbon exploration respectively

geochemistry of th u ree mineralizing magmatic fluids capitan mountains new mexico the capitan mountains in south central new mexico are formed by an east west trending tertiary 28 3 ma alkali feldspar granitic pluton which intruded permian sedimentary rocks of the yeso and san andres formations several widely distributed th u ree veins which occur along the western end and flanks of the pluton are characterized by smoky and clear quartz fluorite adularia hematite calcite thorite titanite allanite chlorite and clay minerals four main types of fluid inclusions representing a large range in temperature and salinity occur in the quartz and fluorite type 1 inclusions are the dominant type and represent high temperature high salinity fluids with th up to 600 degrees c and bulk salinities up to 84 wt percent nacl kcl equiv inclusion types 2 3 and 4 have decreasing t h and salinities type 1 and 2 inclusions define a halite trend when plotted in the nacl kcl h 2 o system the observed t h salinity trends suggest a fluid evolution from the original parent fluid by cooling and crystallization of halite the chemical composition of the inclusion fluid was determined by a crush and leach extraction and analysis by icp ms icp aes and ion chromatography the cations are dominated by na k ca mn and fe other cations analyzed include mg al ba li sr rb cs pb zn and ree cu was below detection the dominant anions are cl and so 4 levels of i and br were usually low the main controls on fluid compositional variations are thought to be partitioning during vapor exsolution from the magma and mineral precipitation in the veins the delta 18 o from quartz and delta d from inclusion fluids in quartz values of the fluids are 7 1 to 8 0 and 54 to 80 per mil respectively based on field relations fluid inclusion microthermometry stable isotope data petrographic data and inclusion fluid chemistry the fluids responsible for the th u ree mineralized zones in the western half of the capitan mountains are most likely of magmatic origin as a result of cooling induced fracturing of the outer carapace of the capitan pluton the exsolved magmatic fluids were introduced into brecciated zones halogen ratios and sulfate concentrations are suggestive of evaporite assimilations into the magma before fluid exsolution

a new fe mn geothermometer for hydrothermal systems implications for high salinity fluids at 13 n on the east pacific rise abstract field and experimental investigations demonstrate the chemistry of mid ocean ridge hydrothermal vent fluids reflects fluid mineral reaction at higher temperatures than those typically measured at the seafloor to account for this and in turn be able to better constrain sub seafloor hydrothermal processes we have developed an empirical geothermometer based on the dissolved fe mn ratio in high temperature fluids using data from basalt alteration experiments the relationship t c 331 24 112 41 log fe mn has been calibrated between 350 and 450 c the apparent fe mn equilibrium demonstrated by the experimental data is in good agreement with natural vent fluids suggesting broad applicability when used in conjunction with constraints imposed by quartz solubility associated sub seafloor pressures can be estimated for basalt hosted systems as an example this methodology is used to interpret new data from 13 n on the east pacific rise where high temperature fluids both enriched and depleted in chloride 339 646 mmol kg relative to seawater are actively venting within a close proximity accounting for these variable salinities active phase separation is clearly taking place at 13 n yet the fluid fe mn ratios and the silica concentrations suggest equilibration at temperatures less than those coinciding with the two phase region these data show the chloride enriched fluid reflects the highest temperature and pressure 432 c 400 bars of equilibration consistent with circulation near the top of the inferred magma chamber this is in agreement with the elevated co 2 concentration relative to the chloride depleted fluids the noted temperature derived from the fe mn geothermometer is higher than the critical temperature for a fluid of equivalent salinity this carries the important implication that despite being chloride enriched relative to seawater these fluids evolved as the vapor component of even higher salinity brine

geophysical modeling via simultaneous joint inversion of seismic gravity and electromagnetic data application to prestack depth imaging geophysical modeling of multiple geophysical parameters can take place reliably through the simultaneous joint inversion of the different geophysical domains the desired objective is the derivation of a model expressing different geophysical properties of the earth but at the same time showing consistency among the parameters this concept generally referred to as data integration is widespread in geophysics but the way of achieving it is not obvious several authors have proposed different approaches where data interpretation and experience all contributed to the task the result is that no general workflows could be defined that left ample margins for uncertainties and personal judgment

stable isotope o h s c and n systematics of quartz vein systems in the turbidite hosted central and north deborah gold deposits of the bendigo gold field central victoria australia constraints on the origin of ore forming fluids the central and north deborah gold deposits are located in one of 15 mining centers of the bendigo gold field central victoria australia a major world class gold province developed in a turbidite terrane gold mineralization occurs primarily within domes and reverse fault systems in multiply deformed lower ordovician metaturbidites deformation and thrusting occurred between 450 and 420 ma coevally with regional metamorphism at zeolite to greenschist facies in the central and north deborah deposits six stages of quartz veining each with characteristic geometry and mineral paragenesis developed sequentially stages 1 2 and 4 are gold bearing whereas stages 3 5 and 6 are barren gold related quartz veins were deposited at temperatures of 350 25 c based on oxygen isotope geothermometry of silicate phases quartz muscovite and sulfur isotope compositions of coexisting sulfide mineral pairs sphalerite galena this result is consistent with temperatures inferred from fluid inclusions the 18o values of gold bearing vein quartz and coexisting hydrothermal muscovite are uniform within and between the six vein stages ranging from 15 9 to 17 2 per mil and 11 6 to 12 8 per mil respectively the d values of hydrothermal muscovites are also uniform at 68 to 55 per mil ore fluids have calculated 18o values of 8 to 11 per mil and d values of 37 to 17 per mil pyrite of synsedimentary diagenetic origin in slate and sandstone displays sulfur isotope compositions of 23 5 to 8 0 per mil and 0 1 to 11 9 per mil respectively sulfides from gold bearing quartz veins have a range of 7 4 to 8 1 per mil median ca 2 5 the relatively uniform vein pyrites indicate a large uniform sulfur source most likely from desulfidation reactions of sulfide minerals interaction of the ore forming fluid with depleted sulfides at the site of deposition may have shifted the sulfur isotope signatures of source sulfides to more negative values carbon isotope compositions of carbonates range from 5 1 to 9 0 per mil median ca 6 5 nitrogen concentrations and nitrogen isotope compositions of hydrothermal muscovite from quartz veins are 652 to 895 ppm and 2 84 to 4 49 per mil respectively collectively the data define a band in n content vegh rsus 15n coordinate space from higher n and lower 15n in the phanerozoic metasedimenary hosted central and north deborah gold deposits to lower n and higher 15n in predominantly meta igneous hosted neoarchean gold provinces collectively the h o s c and n isotope compositions of ore related hydrothermal minerals indicate that the dilute aqueous carbonic and n bearing ore forming fluids were generated from metamorphic dehydration reactions at deeper crustal levels and were variably influenced by exchange with wall rocks during transport to the site of deposition this genetic model for the central and north deborah gold deposits is consistent with other turbidite hosted lode gold deposits and counterparts in volcanic plutonic terranes in contrast these data are not consistent with either mantle derived fluids or magmatic fluids nor do they support a deeply circulated meteoric surface water model for vein formation

simultaneous core sample measurements of elastic properties and resistivity at reservoir conditions employing a modified triaxial cell a feasibility study adaptations of existing triaxial cells for ultrasonic p and s wave measurements are well documented this paper proposes further modification of such a cell so that also resistivity measurements can be carried out simultaneously at reservoir conditions by employing the top cap and the pedestal of the cell as electrodes axial resistivity measurements are now feasible in order to minimize the polarization effect of this two electrode arrangement careful analyses have been carried out to optimize the choice of electrode coating and measurement frequency band radial resistivity measurements are also included in the system by introducing a strap electrode system in a reservoir under production changes in both saturations temperature if steam injection and stresses can take place therefore the modified triaxial system should be able to measure the integrated effects on the acoustic parameters and electric responses caused by variations in each of these parameters the feasibility of the system to obtain such reliable information is demonstrated employing a small selection of core samples in the future such combined measurements on reservoir core samples can be used to link both seismic and electromagnetic observations to the actual earth model and constrain both modelling and inversion

nannoplankton productivity fluctuations and rhythmically bedded pelagic carbonates of the greenhorn limestone upper cretaceous abstract comparison of calcareous nannofossil assemblages from rhythmically interbedded calcareous shales and adjacent bioturbated chalks of the greenhorn limestone cenomanian turonian of the western interior basin indicate significant changes in phytoplankton paleocommunity structure between lithotypes significantly higher shannon diversity and evenness values in the chalk assemblages indicate more stable surface water conditions with lower fertility three taxa indicative of high surface water fertility are significantly more abundant in marlstone assemblages which suggests that calcareous shale marlstone deposition corresponded with fluctuating surface water conditions with relatively high fertility the higher surface fertility and concomitant production of organic matter resulted in sediment anoxia during marlstone deposition leading to high rates of organic carbon storage reduced phytoplankton production during chalk deposition allowed oxygenation of the sea floor and establishment of diverse benthic invertebrate communities

a carbon and oxygen stable isotopic study of the siderite alteration in the black ridge gold deposit clermont central queensland gold mineralisation in the black ridge gold deposit clermont central queensland is associated with extensive siderite alteration and is most concentrated along a locally sheared unconformity between the proterozoic anakie metamorphics and the overlying basal conglomerates of the permian blair athol coal measures the carbon and oxygen isotopic compositions of 49 siderite specimens from all rock units show a systematic variation spatially related to the unconformity the 13c values of siderite decrease with depth from about 0 to 19 while the siderite 18o values of siderite from the overlying conglomerates are lighter average 20 5 than those from the underlying anakie metamorphics average 23 5 both isotopes show the largest variations in the samples from the unconformity itself the data are best interpreted as the result of the mixing of two isotopically and thermally distinct fluids the upper cooler fluid has a marine signature and was derived from the pore water of the conglomerate the lower geothermal fluid which carried most of the gold was not locally derived but was probably modified in the upper part of the anakie metamorphics as a consequence f geothermal gradients imposed by instrusive rocks common throughout the clermont area mixing of the two fluids along the unconformity led to gold solubility in the geothermal fluid dropping more than four orders of magnitude causing gold mineralisation there

chlorine isotopes in fluid inclusions determination of the origins of salinity in magmatic fluids abstract thermal ionisation mass spectrometry tims of the cs 2 cl ion has been used to determine the 37 cl value of paleofluids trapped in fluid inclusions modifications to the existing published method have lowered the precision by a factor of 2 0 09 1 thereby allowing real differences to be measured with greater certainty the method has been applied to determine 37 cl of two sets of magmatic fluids trapped in fluid inclusions samples were studied from the capitan pluton in new mexico and the sw england batholith both of which have high temperature fluids whose d and 18 o signatures are distinctly magmatic relative to standard mean ocean chloride smoc the 37 cl values of the capitan samples cluster around 0 whereas those from sw england cluster around 1 8 the br cl ratios of the capitan fluid inclusions are low indicative of halite dissolution and are comparable to local high salinity waters derived from leaching permian evaporites the br cl ratios of the sw england fluid inclusions are much higher and within the range of values normally considered to be magmatic we conclude that the 37 cl value of the capitan magmatic fluids confirms the evidence from br cl ratios that cl was derived from an evaporite source whereas the 37 cl value of the sw england fluids appears to be more representative of a deep magmatic source

pioneer nannofossil assemblages from the initial transgression of the niobrara seaway in the turonian san juan basin new mexico usa abstract nannofossils of the north american late cretaceous western interior seaway have been extensively studied but these investigations have primarily focused on the diverse communities of the niobrara and greenhorn sea level highstands we lack a firm understanding of the nature of early nannofossil communities from the initial stages of the transgression and of how the diverse assemblages of the coniacian santonian became established we investigated nannofossils in a core from the san juan basin new mexico with concentrated sampling across this transgression we then compared nannofossil assemblages from the initial transgression of the seaway to the more established cosmopolitan assemblages of the niobrara highstand the initial stages of transgression were characterized by unusual low diversity assemblages dominated by holococcoliths and seldom reported and previously undescribed species of hetero and holococcoliths herein we describe five new species and one new genus from these assemblages ahmuellerella frankiae sp nov gartnerago waszczakii sp nov orastrum schollei sp nov pharus clarescopoli sp nov and wisea sanjuanensis gen et sp nov these initial assemblages transitioned to more cosmopolitan higher diversity assemblages coincident with an unconformity that likely represents subaqueous erosion or prolonged non deposition above this unconformity the nannoplankton were abundant diverse and characterized by open marine cosmopolitan taxa that persisted through the coniacian and santonian x ray fluorescence data collected from the core show a high abundance of the detrital elements al and ti in the section indicating substantial detrital clay input into the area coincident with deposition of the holococcolith dominated assemblages the detrital influence lessened as cosmopolitan nannoplankton became more abundant in the area we suggest that the initial holococcolith rich assemblages are representative of a shallow marine potentially hyposaline turbid or unstable environment such assemblages have been observed from the late turonian elsewhere in northern new mexico and may represent typical pioneer nannofloras of the late cretaceous western interior marine transgressions our integrated investigation of nannofossils and x ray fluorescence geochemistry adds to the meager knowledge base of pioneer nannofloral communities in the initial phases of continental marine transgression

pressure effects on the joint elastic electrical properties of reservoir sandstones we conducted a laboratory study of the joint elastic electrical properties of sixty three brine saturated sandstone samples to assess the likely impact of differential pressure confining minus pore fluid pressures in the range 8 60 mpa on the joint interpretation of marine seismic and controlled source electromagnetic survey data the samples showed a wide range of petrophysical properties representative of most sandstone reservoirs we found that a regression equation comprising both a constant and an exponential part gave a good fit to the pressure dependence of all five measured geophysical parameters ultrasonic p and s wave velocity attenuation and electrical resistivity electrical resistivity was more pressure sensitive in clay rich sandstones with higher concentrations of low aspect ratio pores and micropores than in clean sandstones attenuation was more pressure sensitive in clean sandstones with large open pores macropores than in clay rich sandstones pore shape did not show any influence on the pressure sensitivity of elastic velocity as differential pressure increases the effect of the low aspect ratio pores and micropores on electrical resistivity becomes stronger than the effect of the macropores on attenuation further analysis of correlations among the five parameters as a function of pressure revealed potentially diagnostic relationships for geopressure prediction in reservoir sandstones

gold deposits and gold metallogeny of far east russia abstract the russian far east or far east russia fer is host to a huge gold endowment and has produced more than 6500 t of gold since the 1860s much of this gold has come from several mining districts aldan upper amur lower amur okhotsk allakh yun yana kolyma priokhotie omolon and chukotka these districts include several gold deposits mostly of orogenic and epithermal nature as well as large and very large alluvial placer deposits the main gold districts are of late mesozoic age but there are also three districts aldan omolon and southern primorie with pre mesozoic gold ores and three districts kamchatka sakhalin south kurile and lower amur with gold ores of cenozoic age this review paper attempts to marshal on the regional scale all available data aiming to provide a framework for generating and testing new ideas on the gold deposits of fer the focus is on 1 gold metallogeny 2 details of key gold deposits and 3 relationship between gold ore forming processes metamorphic processes and granitoid intrusions in different geodynamic settings the largest gold metallogenic belts in fer were formed in the late mesozoic namely in the late jurassic yana kolyma early cretaceous eastern flank of mongol okhotsk aldan oloy chukotka okhotsk koryak and late cretaceous sikhote alin the mesozoic era was also the time when most of the gold hosting orogens were formed paleozoic mesozoic and cenozoic orogens resulted from the interaction between the pacific oceanic plates with the siberian craton and the north china craton these orogens are products of diverse geodynamic settings and can be divided into four types 1 collisional e g yana kolyma 2 accretionary or uncompleted collisional e g okhotsk koryak or kamchatka 3 combined collisional and transform margin mongol okhotsk and 4 active transform margin sikhote alin the first two types are typical of north east russia whereas the third and fourth types are in the southern part of fer the late cretaceous okhotsk chukotka and east sikhote alin gold provinces are associated with continental margin magmatic arcs and are post accretionary post orogenic comparison of lode gold deposits from different geodynamic settings reveals specific features in metallogeny of the late mesozoic orogens at the southern and eastern margins of the siberian craton yana kolyma collisional orogen okhotsk koryak accretionary orogen and mongol okhotsk transform margin orogen these orogens possess different metal associations the yana kolyma belt contains au sn w and cu pb zn lode deposits the late jurassic transbaikalian sector of the mongol okhotsk orogen contains au mo pb zn sn ta nb w hg sb lode deposits whereas early cretaceous au cu mo hg sb lode deposits are present in the amur sector finally the okhotsk koryak orogen hosts au cu mo cu w bi ag co bi as and be sn li w deposits of early cretaceous age epithermal gold deposits occur in two different geodynamic settings 1 island arcs kamchatka kurile islands and magmatic belts at active continental margins omolon okhotsk chukotka and eastern sikhote alin and 2 rift related magmatism linked with orogenic events and strike slip kinematics such as transform like continental margin settings aldan and upper amur in the mongol okhotsk orogen mineralogic geochemical and isotope systematics indicate a metamorphic magmatic origin of hydrothermal plutonic systems in collisional settings yana kolyma okhotsk koryak and oloy chukotka orogens and active continental margin okhotsk chukotka and east sikhote alin settings with source contributions from the lower crust and mantle the mongol okhotsk and sikhote alin orogens are of transform fault related origin and suggest a source of the ore forming fluids mostly from the mantle

an effective medium algorithm for calculating water saturations at any salinity or frequency an algorithmic approach is used to mix the conductivities and geometric factors of the disperse components the rock and hydrocarbon particles with the host conductivity formation water the theoretical basis for the algorithm is the hanai bruggeman hb equation which itself incorporates only one disperse component the new approach the incremental model accommodates geometric factors such as sand and shale porosity exponents saturation exponent and also accommodates the associated grain conductivities its advantage over previous methods is that it works at any water salinity or tool frequency while allowing saturation and porosity exponents to have values other than 1 5 the algorithm is general and is written to accommodate simultaneous mixing of up to three disperse components and the formation water but it can be extended to accommodate any number of disperse components in its application to shaley sands hydrocarbon and sand elements are set to zero conductivity at low frequency but they can be nonzero for calculating saturations at higher frequencies the reason for this is that hydrocarbon and sand conductivities are real and very close to zero at low frequencies but at high frequencies the dielectric constants become significant making the complex conductivities nonzero the incremental model compared well with the waxman smits model on multiple water conductivity saturation data from two published experimental data sets the model is adaptable to other rock conductivity problems such as vuggy porosity vuggy water saturation and clay coated sand grains the potential exists for the algorithm to be part of a comprehensive computer program for calculating rock conductivities and saturations using many different combinations of rock fabrics and compositions

the berezovsk giant intrusion related gold quartz deposit urals russia evidence for multiple magmatic and metamorphic fluid reservoirs abstract the berezovsk gold deposit in the middle urals has been mined for 270 years its endowment past production and gold reserves is estimated to be 490 t of gold the deposit is located in the greenschist metamorphosed silurian volcanogenic sedimentary rocks intruded by granitoid dykes to the north east of late carboniferous shartash granite massif mineralisation is represented by sulphide quartz veins in the granitoid dykes ladder veins and in the host rocks krassyk veins formed in the following four stages ankerite quartz quartz pyrite gold polymetallic and carbonate ore veins are accompanied by halos of gumbeite quartz orthoclase carbonate beresite quartz sericite ankerite pyrite and listvenite quartz fe mg carbonate fuchsite pyrite the veins mainly consist of quartz with sulphide minerals commonly 3 5 vol about 180 minerals have been identified in ores but the most abundant minerals are quartz calcite ankerite pyrite galena tennantite chalcopyrite aikinite native gold and sphalerite native gold was deposited during quartz pyrite au i and gold polymetallic au ii stages fineness of gold ranges from 863 to 984 and from 723 to 848 for au i and au ii respectively the mineral and metal zoning was identified relative to the roof of the shartash granite massif the fluid inclusion study revealed that the gold mineralisation at the berezovsk deposit was formed at 300 230 c and 0 3 2 3 kbar mostly 0 5 1 2 kbar from a h2o co2 nacl fluid with salinity of 7 3 18 2 wt nacl equiv the fluid was separated into h2o co2 nacl and co2 rich fluids due to temperature and or pressure drop at the deposition site calculated 18o and d values are 5 2 8 1 and 39 to 63 respectively for the fluid in equilibrium with alteration assemblages the average 13c value for the fluid equilibrated with carbonates from the inner zones of metasomatic halos is 5 3 the calculated 18o and 13c values are 3 0 9 6 and 3 to 9 respectively for ore forming fluids the 34s values are 1 4 12 9 and 1 6 to 11 7 for the fluid in equilibrium with early and late sulphides respectively in addition to the isotopic data the geological mineralogical and fluid inclusion data confirmed the predominant contribution of the magmatic fluid to formation of the berezovsk hydrothermal system the light c o and s isotope enrichment of the fluid was mainly caused by fluid phase separation fluids generated by decarbonation and dehydration reactions due to the contact metamorphism of the host rocks during the shartash massif emplacement were responsible for additional 34s input the ore forming fluid was enriched in the light 16o isotope on the deposit flanks indicating the mixing with heated meteoric water

intrusion related gold bismuth deposits of north east russia ptx parameters and sources of hydrothermal fluids abstract intrusion related au bi deposits of north east russia are related to late mesozoic orogenic s and i type granites of ilmenite series the studied deposits differ in their position relatively to the plutons alteration ore body morphology and sulphide content in ores based on mineral composition of ores studied deposits are divided into bismuth sulphotelluride quartz bismuth arsenide sulpharsenide and bismuth siderite polysulphide types bismuth sulphotelluride quartz deposits levo dybinskoe kurum ergelyakh tuguchak basugunya are characterised by low sulphide 3 vol mineralisation native gold associates with bismuth minerals bismuthinite sulphotellurides and tellurides maldonite jonassonite native bismuth bismuth arsenide sulpharsenide deposits myakit chepak dubach chistoe kandidatskoe host as rich mineralisation lollingite and arsenopyrite are main minerals and their contents vary from 5 to 60 vol commonly 10 the intergrowths of native gold with bismuth minerals sulphotellurides tellurides native bismuth occur mainly in arsenopyrite bismuth siderite polysulphide arkachan type is characterised by high sulphide 5 15 vol and high carbonate up to 35 vol ores native gold associates with bismuthinite and other sulphobismuthites minerals of tellurium are rare fluid inclusion and stable isotope study of samples from eighteen au bi deposits constrains the fluid composition formation temperatures pressures and fluid sources four types of fluid inclusions fi were revealed i two phase fi consisting of h2o liquid and co2 vapour and three phase fi with h2o liquid co2 vapour and co2 liquid ii vapour rich co2 one or two phase fi with minor rarely dominant ch4 and n2 sometimes with a thin liquid rim iii two phase liquid vapour aqueous inclusions iv three or multiphase fi consisting of h2o liquid gas bubble and one or more daughter minerals au bi mineralisation formed at 437 200 c mainly from 400 to 250 c and 0 1 1 9 kbar from a h2o co2 nacl fluid which forms an immiscible brine and co2 bearing vapour at low pressure 1 3 kbar as well as low to moderate salinity co2 h2o mixtures without brines at higher pressure 1 3 kbar the studied deposits formed at shallow ergelyakh tuguchak arbatskoe at 1 2 km kurum levo dybinskoe at 2 3 km and deep chuguluk shkolnoe arkachan at 4 km dubach at 5 km depth bismuth sulphotelluride quartz deposits commonly occur at shallow depth whereas bismuth arsenide sulpharsenide and bismuth siderite polysulphide deposits are mainly formed in deeper environment the stable isotope data suggest predominantly magmatic source of gold bearing fluids but magmatic fluid was enriched in light o c and s isotopes as a result of fluid immiscibility the magmatic source is consistent with the overlap in lead isotope compositions of ores and related intrusions as well as synchronism of magmatism and hydrothermal activity according to geochronology data

effects of fluids and dual pore systems on pressure dependent velocities and attenuations in carbonates theeffectsoffluidsubstitutiononp ands wavevelocitiesin carbonates of complex texture are still not understood fully the often used gassmann equation gives ambiguous results when compared with ultrasonic velocity data we present theoretical modelingofvelocityandattenuationmeasurementsobtainedata frequency of 750 khz for six carbonate samples composed of calcite and saturated with air brine and kerosene although porosities 2 14 and permeabilities 0 74 md are relatively low velocity variations are large differences between the highest and lowest p and s wave velocities are about 18 and 27 for brine saturated samples at 60 and 10 mpa effective pressure respectively s wave velocities are measured for two orthogonal polarizations forfourofsixsamples anisotropyisrevealed the gassmann model underpredicts fluid substitution effects by 2 for three samples and by as much as 5 for the rest of the six samples moreover when dried they also show decreasing attenuationwithincreasingconfiningpressure tomodelthisbehavior we examine a pore model made of two pore systems one constitutesthemainanddrainableporosity andtheotherismade ofundrainedcracklikeporesthatcanbeassociatedwithgrain tograincontacts inaddition thesedriedrocksamplesaremodeled to contain a fluid filled pore system of grain to grain contacts potentiallycausinglocalfluidflowandattenuation forthetheoretical model we use an inclusion model based on the t matrix approach whichalsoconsiderseffectsofporetextureandgeometry and porefluid global and local fluidflow by using a dualpore system we establish a realistic physical model consistently describingthemeasureddata

the late cretaceous donlin creek gold deposit southwestern alaska controls on epizonal ore formation the donlin creek gold deposit southwestern alaska has an indicated and inferred resource of approximately 25 million ounces moz au at a cutoff grade of 1 5 g t the ca 70 ma deposit is hosted in the late cretaceous kuskokwim flysch basin which developed in the back part of the arc region of an active continental margin on previously accreted oceanic terranes and continental fragments a hypabyssal mainly rhyolitic to rhyodacitic and commonly porphyritic 8 3 km dike complex part of a regional ca 77 to 58 ma magmatic arc formed a structurally competent host for the mineralization this deposit is subdivided into about one dozen distinct prospects most of which consist of dense quartz carbonate veinlet networks that fill north northeast striking extensional fractures in the northeast trending igneous rocks the sulfide mineral assemblage is dominated by arsenopyrite pyrite and typically younger stibnite gold is refractory within the arsenopyrite sericitization carbonatization and sulfidation were the main alteration processes fluid inclusion studies of the quartz that hosts the resource indicate dominantly aqueous ore fluids with also about 3 to 7 mol percent co2 ch4 and a few tenths to a few mole percent nacl kcl the gold bearing fluids were mainly homogeneously trapped at approximately 275 to 300 c and at depths of 1 to 2 km some of the younger stibnite may have been deposited by late stage aqueous fluids at lower temperature measured 18o values for the gold bearing quartz range between 11 and 25 per mil the estimated 18o fluid values range from 7 to12 per mil suggesting a mainly crustally derived fluid a broad range of measured d values for hydrothermal micas between 150 and 80 per mil is suggestive of a contribution from devolatilization of organic matter and or minor amounts of mixing with meteoric fluids gold associated hydrothermal sulfide minerals are characterized by 34s values mainly between 16 and 10 per mil with the sulfur derived from diagenetic pyrite and organic matter within the flysch basin a smaller group of 34s measurements which shows values as depleted as 27 per mil suggests a different local sulfur reservoir in the basin for the later hydrothermal episode dominated by stibnite initial nd of 8 7 to 3 1 and 87sr 86sr measurements of 0 706 to 0 709 for the ore hosting dikes also indicate a crustal reservoir for some of the late cretaceous magmatism overlapping lead isotope data for these intrusive rocks and for sulfide minerals suggest a crustal contribution for the lead in both copper and gold bearing stockwork veinlets in hornfels occur at dome a prospect located at the northern end of the donlin creek deposit these stockworks are cut by the younger auriferous gold veins that define the main donlin creek gold mineralization highly saline gas rich heterogeneously trapped fluids deposited the stockworks at temperatures approximately 100 c hotter than those of the main gold forming event at donlin creek the genetic relationship of the dome prospect to the main donlin creek gold resource is equivocal the epizonal donlin creek deposit shows affinities to the gold systems interpreted by various workers as orogenic or intrusion related it shows important differences from typical epithermal and carlin like deposits the ore forming fluids were derived by either broad scale metamorphic devolatilization above rising mantle melts or exsolution from a magma that was dominated by a significant flysch melt component

effects of porosity and clay content on wave velocities in sandstones the ultrasonic compressional vp and shear vs velocities and first arrival peak amplitude ap were measured as functions of differential pressure to 50 mpa and to a state of saturation on 75 different sandstone samples with porosities ranging from 2 to 30 percent and volume clay content c ranging from 0 to 50 percent respectively both vp and vs were found to correlate linearly with porosity and clay content in shaly sandstones at confining pressure of 40 mpa and pore pressure of 1 0 mpa the best least squares fits to the velocity data are vp km s 5 59 6 93 2 18c and vs km s 3 52 4 91 1 89c deviations from these equations are less than 3 percent and 5 percent for vp and vs respectively the velocities of clean sandstones are significantly higher than those predicted by the above linear fits about 7 percent for vp and 11 percent for vs which indicates that a very small amount of clay 1 or a few percent of volume fraction significantly reduces the elastic moduli of sandstones for shaly

vein type tungsten deposits of china and adjoining regions abstract taking the south china tungsten province as representative this paper deals systematically with the geological setting geometry paragenesis wallrock alteration and geochemical characteristics of asian vein type tungsten deposits on the basis of data acquired since the 1970 s the regional metallogenic conditions and the genesis of the deposits are discussed the large scale distribution of vein type tungsten deposits in asia is inferred to be controlled by tungsten enriched formations multi period and multi stage granitic activity and favourable tectonic environment the deposits are not only controlled by magmatic differentiation but also by the overall evolution of the continental crust

resistivity of partially saturated triassic sandstone the variation in resistivity with saturation of poorly cemented triassic sandstone samples from a site in the english midlands has been measured the measurements were obtained using an adapted four electrode technique which utilizes conductive gelling agents between electrodes avoiding the need to sputter electrodes directly on to samples a difficult process with such friable samples the measurements provide important information regarding the way in which resistivity varies with saturation in the triassic sandstone the resulting variation in the observed resistivity versus saturation curves indicates the presence of significant pore scale variation between samples measurements have also been conducted on fully saturated samples these indicate significant variation in the matrix conductivity between samples the results have important implications for field scale monitoring of the unsaturated zone

seismic wave attenuation and dispersion resulting from wave induced flow in porous rocks a review one major cause of elastic wave attenuation in heterogeneous porous media is wave induced flow of the pore fluid between heterogeneities of various scales it is believed that for frequencies below 1 khz the most important cause is the wave induced flow between mesoscopic inhomogeneities which are large compared with the typical individual pore size but small compared to the wavelength various laboratory experiments in some natural porous materials provide evidence for the presence of centimeter scale mesoscopic heterogeneities laboratory and field measurements of seismic attenuation in fluid saturated rocks provide indications of the role of the wave induced flow signatures of wave induced flow include the frequency and saturation dependence of p wave attenuation and its associated velocity dispersion frequency dependent shear wave splitting and attenuation anisotropy during the last four decades numerous models for attenuation and velocity dispersion from wave induced flow have been developed with varying degrees of rigor and complexity these models can be categorized roughly into three groups according to their underlying theoretical framework the first group of models is based on biot s theory of poroelasticity the second group is based on elastodynamic theory where local fluid flow is incorporated through an additional hydrodynamic equation another group of models is derived using the theory of viscoelasticity though all models predict attenuation and velocity dispersion typical for a relaxation process there exist differences that can be related to the type of disorder periodic random space dimension and to the way the local flow is incorporated the differences manifest themselves in different asymptotic scaling laws for attenuation and in different expressions for characteristic frequencies in recent years some theoretical models of wave induced fluid flow have been validated numerically using finite difference finite element and reflectivity algorithms applied to biot s equations of poroelasticity application of theoretical models to real seismic data requires further studies using broadband laboratory and field measurements of attenuation and dispersion for different rocks as well as development of more robust methods for estimating dissipation attributes from field data

ultrasonic properties of sedimentary rocks effect of pressure saturation frequency and microcracks seismic velocities and attenuations are influenced by lithology porosity and permeability as well as the kind and quantity of the pore fluids the microstructure of rocks is another important factor influencing seismic properties this influence can be used to investigate the pressure dependent closure of microcracks for this purpose velocities and attenuations of p and s waves have been determined at ultrasonic frequencies in three different rocks vacuum dry and partially saturated with water as a function of hydrostatic pressure up to 200 mpa a new combined model has been developed with this model an explicit description of the microstructure local fluid flow lf and macrostructure gassmann effect global fluid flow is possible assuming a patchy saturation i e inhomogeneous distribution of the fluid in the pores and modulus reduction both the saturation dependent measurements and the pressure dependent data can be explained the modelling and the phenomenological interpretation of the data gained under increasing hydrostatic pressure yields consistent results concerning the amount of crack closure as well as the range in which crack closure appears in high porosity sandstones bentheimer and obernkirchner sandstone a strong closure of cracks already with a small increase of pressure must be concluded in a low porosity harzer greywacke a significantly lower closure of cracks can be concluded within the pressure range of 0 100 mpa it is shown however that there must be open cracks in all rocks even under elevated hydrostatic pressure resulting in a measurable effect due to lf

acoustic signatures of partial saturation the relationship between elastic wave velocities and water saturation in a water gas reservoir depends strongly on whether saturation is heterogeneous patchy or homogeneous heterogeneity in saturation may result from lithologic heterogeneity because under conditions of capillary equilibrium different lithologies within a reservoir can have different saturations depending on their porosities and permeabilities we investigate this phenomenon by generating models of a reservoir in which we control the distribution of lithologic units and theoretically determine the corresponding velocity saturation relationship we assume a state of capillary equilibrium in the reservoir and determine the saturation level of each region within the reservoir from the corresponding capillary pressure curve for the lithologic unit at that location the velocities we calculate for these models show that saturation heterogeneity caused by lithologic variation can lead to a distinct dependence of velocity on saturation in a water gas saturated reservoir a patchy distribution of the different lithologic units is found to cause p wave velocity to exhibit a noticeable and almost continuous velocity variation across the entire saturation range this is in distinct contrast to the response of a homogeneous reservoir where there is only a large change in velocity at water saturations close to 100

a quantitative analysis of calcareous nannofossil bioevents of the late cretaceous late cenomanian coniacian western interior seaway and their reliability in established zonation schemes abstract calcareous nannofossil assemblages from 8 localities in the upper cenomanian coniacian strata of central colorado and kansas and southern texas western interior seaway usa were analyzed to produce a new high resolution biostratigraphic framework for the greenhorn formation eagle ford formation and basal austin chalk eighteen datasets from coeval successions around the world including the global stratotype section and point gssp at pueblo co and proposed reference sections for the base of the turonian and candidate gssps for the base of the coniacian in germany poland and new mexico were incorporated from literature sources additional discussion is devoted to the basal turonian and coniacian boundaries as they reflect paleoceanographic phenomena e g oae2 widespread late turonian regression where high resolution biostratigraphy has academic as well as industrial application ranking and scaling of 48 selected bioevents produces a quantitatively derived optimum sequence of first and last occurrences scaling of events along a relative time scale reveals an 8 9 evolutionary turnover during oae2 comparison with the qualitatively developed nannofossil zonations known as the cc zonation of perch nielsen and uc zonation of burnett reveals inconsistencies largely due to the recognition of new amended species concepts discrepancies near the turonian coniacian boundary reflect changes to its placement in recent revisions to the geologic timescale a recently documented sequence of bioevents provides an accurate proxy for the boundary in the absence of the inoceramid index fossil cremnoceramus deformis erectus meek fifteen bioevents from the optimum sequence are given greater priority based on their interpreted reliability between the sections examined and the cc and uc zonations

seismic attenuation in partially saturated berea sandstone submitted to a range of confining pressures using the forced oscillation method we measure the extensional mode attenuation and young s modulus of a berea sandstone sample at seismic frequencies 0 5 50 hz for varying levels of water saturation 0 100 and confining pressures 2 25 mpa attenuation is negligible for dry conditions and saturation levels 80 for saturation levels between 91 and 100 attenuation is significant and frequency dependent in the form of distinct bell shaped curves having their maxima between 1 and 20 hz increasing saturation causes an increase of the overall attenuation magnitude and a shift of its peak to lower frequencies on the other hand increasing the confining pressure causes a reduction in the attenuation magnitude and a shift of its peak to higher frequencies for saturation levels above 98 the fluid pressure increases with increasing confining pressure when the fluid pressure is high enough to ensure full water saturation of the sample attenuation becomes negligible a second series of comparable experiments reproduces these results satisfactorily based on a qualitative analysis of the data the frequency dependent attenuation meets the theoretical predictions of mesoscopic wave induced fluid flow wiff in response to a heterogeneous water distribution in the pore space so called patchy saturation these results show that mesoscopic wiff can be an important source of seismic attenuation at reservoir conditions

application of the bisq model to clay squirt flow in reservoir sandstones 1 an understanding of the variations of compressional wave velocity and attenuation in sandstones as a function of pore fluid properties is important for the identification and monitoring of hydrocarbon reservoirs in order for seismic inversion to be well constrained a rock physics model that describes accurately the observed behavior is required a number of such models have been proposed but have not been extensively tested against laboratory data the unified biot and squirt flow model was applied to data obtained from ultrasonic experiments conducted on a wide range of sandstone types when saturated with different pore fluids with viscosities ranging from 0 3 to 1000 cp this model was seen to match well all the observed velocity and attenuation values as opposed to the biot model which was only successful for clean sandstones saturated with low viscosity fluids this has led to the conclusion that a squirt flow mechanism is important at the grain scale in addition an increase in the dynamic uniaxial strain modulus of the dry frame with increasing pore fluid viscosity was observed in the absence of free gas or grain contact microcracks the laboratory data were collected at 60 mpa effective pressure this can be linked to decreasing local flow and decreasing relaxation in the soft pore space of the sandstone the extent of which is in turn connected to the clay content and pore structure of the sandstone these results imply that at ultrasonic frequencies the squirt flow is due to the presence of clay

a new approach for deriving pseudovelocity logs from resistivity logs1 this paper describes a method of generating pseudovelocity logs using measurements of electrical resistivity a theoretical relation between electrical resistivity and transit time which is applicable to a wide range of lithologies has been developed the application of this relation using a method which defines lithoresistivity zones as lithological intervals related to the same formation and showing small resistivity variations has been tested in the reconcavo sedimentary basin in bahia brazil a comparison of derived pseudovelocity logs with actual sonic logs for five wells shows the validity of the present approach

laboratory measurements of porosity permeability resistivity and velocity on fontainebleau sandstones the relations among the resistivity elastic wave velocity porosity and permeability in fontainebleau sandstone samples from the ile de france region around paris france were experimentally revisited these samples followed a permeability porosity relation given by kozeny carman s equation for the resistivity measurements the samples were partially saturated with brine archie s equation was used to estimate resistivity at 100 water saturation assuming a saturation exponent n 2 using self consistent sc approximations modeling with grain aspect ratio 1 and pore aspect ratio between 0 02 and 0 10 the experimental data fall into this theoretical range the sc curve with the pore aspect ratio 0 05 appears to be close to the values measured in the entire porosity range the elastic wave velocity was measured on these dry samples for confining pressure between 0 and 40 mpa aloading and unloading cycle was used and did not produce any significant hysteresis in the velocity pressure behavior for the velocity data using the sc model with a grain aspect ratio 1 and pore aspect ratios 0 2 0 1 and 0 05 fit the data at 40 mpa pore aspect ratios ranging between 0 1 0 05 and 0 02 were a better fit for the data at 0 mpa both velocity and resistivity in clean sandstones can be modeled using the sc approximation in addition a linear fit was found between the p wave velocity and the decimal logarithm of the normalized resistivity with deviations that correlate with differences in permeability combining the stiff sand model and archie for cementation exponents between 1 6 and 2 1 resistivity was modeled as a function of p wave velocity for these clean sandstones

geochemical constraints on the genesis of the scheelite dome intrusion related gold deposit tombstone gold belt yukon canada the scheelite dome intrusion related gold deposit western selwyn basin yukon is hosted in hornfelsed metasedimentary strata that lie adjacent to the exposed apices of a monzogranite to quartz monzonite plutonic complex of the mid cretaceous tombstone tungsten magmatic belt tintina gold province alaska and yukon a variety of mineralization styles occur throughout a 10 3 km east trending corridor and include reduced au and w rich skarns au w and ag pb zn sb rich quartz tension vein arrays and multiphase fault veins and isolated zones of au rich sericite carbonate altered rock integrated u pb shrimp data for magmatic zircon and ar ar data for magmatic and hydrothermal biotite indicate that gold mineralization occurred within 1 to 2 m y of magma emplacement fluid inclusion oxygen isotope and arsenopyrite geothermometry data indicate that hydrothermal minerals formed at depths of 6 to 9 km over a temperature range from 550 c high temperature au rich skarns formed at 400 c whereas vein hosted mineralization formed at 280 to 380 c in skarns au is strongly associated with enrichments of bi te w and as whereas a variety of au rich veins occur with as rich type 1 and te and w rich type 2 end members silver pb zn sb veins are typically au poor and represent the latest and lowest temperature phase in the hydrothermal paragenesis the fluid inclusion data indicate that all mineralization styles were formed from low salinity 4 wt nacl equiv aqueous carbonic fluids consistent with the composition of fluid inclusions within infilled miarolitic cavities in the intrusive rocks however the nonaqueous fluid was predominantly ch 4 in skarn co 2 in au te and au w veins and a fluid with roughly equal amounts of co 2 ch 4 and n 2 in au as and ag pb zn sb veins oxygen isotope data are consistent with a mineralizing fluid of predominantly magmatic origin that was variably modified to more positive 18 o values during interaction with 18 o enriched metasedimentary strata sulfur isotope data suggest two possible sources of sulfur a magmatic source characterized by 34 s values of approximately 5 to 0 per mil and sulfur from the metasedimentary country rocks characterized by more negative 34 s values of approximately 15 to 10 per mil collectively the data indicate that gold at scheelite dome was deposited from a magmatic hydrothermal system interaction of magmatic fluids with graphitic hornfels rocks resulted in reduction of the ore fluids higher ch 4 co 2 ratios and modification of the oxygen and sulfur isotope values of the ore fluids toward those of the metasedimentary hornfels progressive reduction and cooling of hydrothermal fluids in addition to phase separation in vein hosted mineralization were the mechanisms for gold deposition compared to other intrusion related gold deposits associated with the tombstone tungsten magmatic belt magmatism exposed mineralization at scheelite dome is predominantly hosted by hornfelsed metasedimentary rocks this results in more diverse mineralization styles and a greater spread of isotope and fluid inclusion data

chronostratigraphy of proposed turonian coniacian upper cretaceous stage boundary stratotypes salzgitter salder germany and wagon mound new mexico usa

cyclostratigraphy of the upper cretaceous niobrara formation western interior u s a a coniacian santonian orbital timescale abstract the turonian campanian niobrara formation of the western interior basin u s a is characterized by decimeter scale rhythmic alternations of chalk and marl beds and decameter scale oscillations of chalky and marly facies this study applies recent advances in quantitative cyclostratigraphic analysis to high resolution geophysical records in order to test for an orbital signal we studied records of the entire formation 85 m from two wells in colorado 40 17 n 104 38 w 40 14 n 104 41 w the study utilized high resolution time series of borehole resistivity measured from formation microimager tools fmi advanced spectral techniques indicate the presence of eccentricity obliquity and precession periodicities throughout the study interval deviations of bundling ratios in the lower fort hays member from those predicted by simple eccentricity modulation of precession previously reported in the literature are likely due to the influence of obliquity deconvolution and frequency tracking of orbital components were used to reconstruct sedimentation rates for the niobrara formation and thus develop a high resolution orbital timescale which permits calculations of accumulation rates for sedimentary components and the duration of inclusive stages substages and in some cases biozones the niobrara formation in the studied cores appears to be hiatus free and therefore provides a continuous record of rhythmic deposition for astronomical timescale development the relationship between carbonate content and sedimentation rate throughout the niobrara formation indicates that the decameter scale oscillations of chalk and marl are dominantly driven by variations in siliciclastic flux dilution the duration derived from the orbital timescale between the turonian coniacian and coniacian santonian boundaries is 3 40 0 13 myr which is generally consistent with radiometric estimates for the coniacian the orbitally derived duration of the santonian stage is 2 39 0 15 myr which is very similar to estimates based on curve fitting between radiometric dates development of high resolution orbital chronometers provides excellent time resolution in intervals that lack radiometric time control or where control points are widely spaced

joint elastic electrical properties of reservoir sandstones and their relationships with petrophysical parameters we measured in the laboratory ultrasonic compressional and shear wave velocity and attenuation 0 7 1 0 mhz and low frequency 2 hz electrical resistivity on 63 sandstone samples with a wide range of petrophysical properties to study the influence of reservoir porosity permeability and clay content on the joint elastic electrical properties of reservoir sandstones p and s wave velocities were found to be linearly correlated with apparent electrical formation factor on a semi logarithmic scale for both clean and clay rich sandstones p and s wave attenuations showed a bell shaped correlation partial for s waves with apparent electrical formation factor the joint elastic electrical properties provide a way to discriminate between sandstones with similar porosities but with different clay contents the laboratory results can be used to estimate sandstone reservoir permeability from seismic velocity and apparent formation factor obtained from co located seismic and controlled source electromagnetic surveys

calcareous nannofossil paleoceanography of the cretaceous greenhorn sea two distinctive laterally traceable bentonite beds were used to construct three isochronous time slices through the marine sediments of the upper cretaceous greenhorn cyclothem of the western interior basin calcareous nannofossil assemblages from these time slices were analyzed from 40 localities to examine the paleoceanographic conditions in the basin deposition of the lower time slice x bentonite approximately corresponded to the time at which free communication between the basin and open oceanic systems first occurred the most striking trend is the presence of common to abundant nannofossils in the center of the basin and their absence from the eastern and western margins this indicates that open oceanic conditions conducive to large standing crops of calcareous nannoplankton existed only in a narrow centrally located channel conditions at the basin margins were probably unsuitable for large populations due to salinity constraints multivariate analyses indicate two distinct biofacies northern and southern which are interpreted to represent distinct surface water masses the geometry of the water mass boundary suggests that the northern surface water mass actively flowed southward into or over the relatively passive southern water mass the upper time slice hl 3 bentonite samples the nannofossil distributions at or near the maximum transgression of the greenhorn sea in this time slice nannofossils occur beyond the limits of the study area except in proximity to the frontier delta system diversities are significantly higher indicating water mass conditions more similar to those in open oceanic settings multivariate analyses indicate three distinct surface water masses northern southern and western the northern and southern water masses exhibit relationships similar to those during the x bentonite time slices the interaction between the northern and southern water masses promoted vertical stratification of the water column and resultant sediment anoxia the western biofacies may be indicative of a surface water mass with significant contributions from nearby fresh water influx

saturation pore pressure and effective stress from sandstone acoustic properties 1 acoustic velocity and vp vs ratio show different responses in saturated and dry rocks under increasing differential pressures velocity is also shown to be sensitive to pore pressure not just differential pressure under identical low differential pressure conditions velocity is higher in sandstones when pore pressure is high during simulation of inflationary overpressure conditions vp vs ratios of sandstones with high fluid pressures are shown to lie between dry conditions and saturated conditions with constant and low pore pressure thus the velocity differential pressure relationship is not unique however the use of the measured biot effective stress coefficient results in a unique relationship it is postulated that higher velocity and different vp vs ratios are caused by loss of compliance in microfractures due to stiffening by increasing fluid pressure

compressional wave velocity and attenuation at ultrasonic and sonic frequencies in near surface sedimentary rocks laboratory ultrasonic measurements of compressional wave velocity and attenuation were made as a function of effective pressure on samples of limestone sandstone and siltstone taken from a shallow borehole test site the results indicate that the sandstones are pervaded by grain contact microcracks which dramatically affect their compressional wave attenuations clean sandstone shows a compressional wave quality factor q sub p of 24 2 at 5 mpa effective pressure close to the estimated in situ burial pressure and a q sub p of 83 29 at 60 mpa the q sub p of limestones and siltstones at the site show negligible and small increases with pressure in the laboratory respectively the strong pressure dependence of q sub p in clean sandstone was used to infer the presence of in situ microcracks sediment velocities measured in the laboratory at about 1 mhz were compared with those from the full waveform sonic log at about 10 khz implies that they must also be highly attenuating over a significant part of the frequency range 10 khz to 1 mhz to account for the magnitude of the observed velocity dispersion assuming the laboratory q sub p values measured at 5 mpa remain constant down to 10 khzmore predicts the observed dispersion quite well furthermore the sonic log velocities of sandstones limestones and siltstones after normalizing each lithology for porosity and clay content were found to reflect the same pressure depth trends observed in the laboratory the results provide evidence for the existence of in situ microcracks in near surface sediments less

tectonic setting of the plutonic belts of yakutia northeast russia based on 40ar 39ar geochronology and trace element geochemistry samples from plutonic belts and individual intrusions in the sakha republic yakutia northeastern russia were analyzed using 40ar 39ar geochronology and trace element geochemistry four phases of activity were identified a subduction event along the southwest margin of the kolyma omolon superterrane with apparent ages of ca 160 140 ma a superposed collisional event dated at 143 138 ma a subduction event along the northern margin of the superterrane dated at 130 123 ma with a slightly older to contemporaneous extensional event to the west and intrusions associated with east west extension between 106 and 92 ma these phases are interpreted to represent 1 subduction under and 2 accretion to asia of kolyma omolon followed by local extension 3 subduction along the northern edge of this superterrane and 4 regional extension following closure of the south anyui suture and or the start of subduction associated with the okhotsk chukotka volcanic belt

squirt flow in fully saturated rocks we estimate velocity frequency dispersion and attenuation in fully saturated rocks by employing the squirt flow mechanism of solid fluid interaction in this model pore fluid is squeezed from thin soft cracks into the surrounding large pores information about the compliance of these soft cracks at low confining pressures is extracted from high pressure velocity data the frequency dependence of squirt induced pressure in the soft cracks is linked with the porosity and permeability of the soft pore space and the characteristic squirt flow length these unknown parameters are combined into one expression that is assumed to be a fundamental rock property that does not depend on frequency the appropriate value of this expression for a given rock can be found by matching our theoretical predictions with the experimental measurements of attenuation or velocity the low frequency velocity limits as given by our model are identical to those predicted by gassmann s formula the high frequency limits may sign

laboratory study of the electrical and hydraulic properties of rocks under simulated reservoir conditions abstract experimental results are presented for resistivity and permeability measurements on clay free sandstone and shaly synthetic rock samples at simulated reservoir conditions of pressure and temperature some details of a novel multi sample high pressure and temperature rock testing system and a new technique for making synthetic shaly samples are also presented a significant influence of pressure and temperature on both the electrical and the hydraulic properties of sandstone and synthetic rocks has been observed the combined effect of pressure and temperature on the electrical properties of the sandstones tested is approximately the sum of their individual effects the effect of clay minerals on the electrical and hydraulic properties of rocks has also been investigated the experimental results obtained lead to a better understanding of the mechanisms of the pressure and temperature effects on the geophysical properties of sedimentary rocks

diagnostics of seismic time lapse effects of sandstones based on laboratory data we evaluated a viscoelastic modeling of p and s wave velocity dispersion attenuation pressure and fluid effects for a set of siliciclastic rock samples our analysis used a published laboratory data set of 63 sandstones with a wide range of compositional heterogeneities we observed a notable correlation between the velocity and attenuation pressure sensitivity and the abundance lack of quartz in the samples we included compliant pores low aspect ratio proportionally to the content of secondary minerals to account for the differential sensitivity to pressure the observed velocity and attenuation were well reproduced by the applied viscoelastic modeling we found that pores of significantly different scale required pore fluid relaxation time constants of proportionally different magnitudes to reproduce the velocity and attenuation measurements the relaxation time constant of crack sized pores can be one order of magnitude smaller than the constant of mesopores moreover the velocity dispersion and attenuation signatures revealed that a pore textural model dependent on lithological composition is critical in the prediction of time lapse fluid and pressure responses

what is the cementation exponent a new interpretation in 2003 182 billion barrels of oil reserves worth about us 4 5 trillion were discovered worldwide johnson et al 2004 moreover between 1950 and 2002 the total volume of reserves discovered has run to more than 1500 billion barrels for oil and 7 5 trillion cubic feet for gas bentley 2002 more than half of these resources have already been produced and have driven the global economy for the last 50 years

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

compressional velocity and porosity in sand clay mixtures laboratory measurements of porosity and compressional velocity were conducted on unconsolidated brine saturated clean ottawa sand pure kaolinite and their mixtures at various confining pressures a peak in p velocity versus clay content in unconsolidated sand clay mixtures at 40 percent clay by weight was found the peak in velocity is 20 30 percent higher than for either pure clay or clean sand a minimum in porosity versus clay content at 20 40 percent clay by weight is also observed such behavior is explained using a micro geometrical model for mixtures of sand and clay in which two classes of sediments are considered 1 sands and shaley sands in which clay is dispersed in the pore space of load bearing sand and thus reduces porosity and increases the elastic moduli of the pore filling material and 2 shales and sandy shales in which sand grains are dispersed in a clay matrix for these sediments the model reproduces the extrema in velocity and porosity and accounts for much of the scatter in