stratified flow along a corrugated slope separation drag and wave drag abstract lee wave generation and horizontal flow separation in stratified flow along a slope with corrugations or a ridge running directly downslope are explored using analytical and numerical methods both of these processes are important to the drag on alongslope currents the analytical solution for steady wave generation by stratified flow along a corrugated slope is extended to the evanescent flow regimes there are two evanescent regimes having intrinsic frequencies either above the buoyancy frequency n fast flow or below n sin a slow flow for nonrotating fluid and slope angle a streamlines of the low speed evanescent solution tend to follow isobaths while those of wave solutions tend to flow up over ridges and down in canyons an analytical expression is developed for the wave drag felt by an isolated ridge on a slope for a gaussian ridge of alongslope length l the drag becomes small when u ln 1 the fast flow regime or when u ln sin a 1 2 the slow flow regime numerical ex

rare earth element enrichment in post variscan polymetallic vein systems of the harz mountains germany carbonate gangue in historically important post variscan polymetallic pb zn cu ag vein systems in the upper harz mountains has elevated rare earth element contents ree y 1500 340 ppm n 16 in bulk samples this enrichment is due to the occurrence of abundant micrometer sized synchysite inclusions in calcite identified via raman spectroscopy calcite bulk analyses have roof shaped paas normalized ree patterns with a eu peak but without ce or y anomalies and with a steeply dipping hree pattern microbeam analysis electron microprobe and la icpms identifies these patterns as dominated by synchysite ce nd with strong eu enrichment in the weight percent range and lree hree fractionation la lu 100 paas normalized the synchysite component in calcite gangue is detected in polymetallic veins all over the harz mountains which seems to be a diagnostic feature of the region and suggests a large scale mesozoic fluid system however the upper western harz systems with no fluorite have more elevated ree content compared with the lower eastern harz fluorite rich systems with less ree content carbonate gangue in the upper harz systems has homogeneous 87sr 86sri around 0 714 and endi of 9 while carbonate gangue in the lower harz systems has 87sr 86sri around 0 716 and endi of 2 to 5 fluorite in the lower harz mountains has strong positive y anomalies and variable eu anomalies at generally low ree abundances and no ree mineral inclusions both sr and nd isotope compositions in the fluorite are very variable and indicate an open system 87sr 86sri 0 710 0 718 endi 3 to 17 the synchysite mree enrichment in calcite gangue in the upper harz mountains compares favorably with carbonatite related lree dominated bastnasite from china and elsewhere and allows an interesting perspective as a by product of pb zn mining

latitudinal temperature gradient during the cretaceous upper campanian middle maastrichtian y18o record of continental vertebrates latitudinal variations in model biogenic apatite d18o values were calculated using fractionation equations of vertebrates and weighted rainfall y18o values along with mean annual air temperatures provided by iaea wmo meteorological stations the reference equation obtained was used to compute a continental temperature gradient for the late campanian middle maastrichtian interval by using published and new d18o values of phosphate from vertebrates samples are mainly tooth enamel from crocodilians and dinosaurs that lived at paleolatitudes ranging from 83 4 n alaska to 32 3 s madagascar the temperature gradient was less steep 0 4 0 1 c latitude than the present day one 0 6 c latitude with temperatures that decreased from about 30 c near the equator to about 5 c at the poles above 30 of paleolatitude air temperatures were higher than at present the validity of these results is discussed by comparison with climatic criteria inferred from paleontological paleobotanical and sedimentological data the latitudinal distribution of oxygen isotope compositions of continental vertebrates is potentially a powerful tool for quantifying mesozoic terrestrial climates

preservation of primary stable isotope signals in dinosaur remains and environmental gradients of the late cretaceous of montana and alberta abstract although the use of stable isotope data from vertebrate remains is becoming common for the cenozoic their application to mesozoic environments has been rare in part due to the perception that diagenesis has obfuscated all potential primary signal in this paper we illustrate how stable isotope data collected from dinosaur and other vertebrate remains can in fact be used to reconstruct paleoenvironmental conditions during the mesozoic carbon and oxygen isotope ratios were measured from tooth enamel of hadrosaur dinosaurs and from scales of freshwater fish that were collected from sites in the two medicine judith river and dinosaur park formations of montana and alberta these formations represent a coastal to upland gradient along the western margin of the late cretaceous inland seaway isotopic comparisons among skeletal components and among taxa are used as evidence that primary paleoenvironmental information as recorded by isotope data is preserved in tooth enamel and freshwater fish scales a comparison of carbon isotope ratios between hadrosaur tooth enamel and sedimentary organic matter indicates that these animals had a larger isotopic offset compared to bulk diet than modern mammals and that all hadrosaurian isotope data are consistent with the existence of c3 only ecosystems higher and more variable carbon and oxygen isotope ratios from animals occupying the coastal judith river region are interpreted to reflect a range of freshwater to brackish water conditions and plants that were undergoing water stress lower and less variable carbon and oxygen isotope ratios from the upland two medicine and intermediate dinosaur park areas are interpreted to reflect a gradual rainout of moisture from air masses moving inland and more uniform environmental conditions overall these results indicate that stable isotopes from dinosaur and other vertebrate remains have the potential to expand our understanding of terrestrial environments and ecosystems during the mesozoic

structural controls on the base metal vein deposits of the northampton complex western australia abstract the northampton complex is a proterozoic inlier near the west coast of western australia 450 km north of perth the copper lead and zinc vein type deposits occupy dilational sites along brittle ductile shear zones there are four types of structural settings of the ore deposits 1 lens structures 2 shear breccia link shear structures extensional strike slip duplexes 3 intersecting brittle ductile shears and 4 curved brittle ductile shears a model involving n s dextral wrenching along the darling mobile belt best explains the various features of the deposits in this model proterozoic granulite facies paragneisses of the northampton complex were fractured with the development of predominantly extensional fractures and normal faults and to a lesser extent riedel both r and r restraint and principal displacement shears since previous isotopic dating has not resolved the age of mineralisation crosscutting relationships between mineralisation the older dolerite dykes 650 800 ma and younger 330 trending sinistral shears 500 650 ma are used to constrain the timing to between 650 ma and 800 ma ne sw shortening across the paterson and king leopold mobile belts between 650 ma and 800 ma may also have been associated with the dextral movements along the darling mobile belt

determination of crustal fluid residence times using nucleogenic 39ar abstract argon 39 is a radioactive isotope of ar with a half life of 269 years there are two natural sources of 39 ar on earth cosmogenic production in the upper atmosphere and nucleogenic production in rocks cosmogenic 39 ar has been recognized as an ideal tracer for groundwater residence times and oceanic circulation nucleogenic 39 ar has generally been considered problematic for groundwater studies in this work we developed simple models for the evolution of 39 ar 40 ar ratios where 40 ar denotes radiogenic 40 ar produced in the model system in rocks and fluids in rocks both 39 ar and 40 ar are produced and a fraction of the 39 ar and 40 ar is released into the mobile fluid phase in both reservoirs 39 ar reaches production or supply decay equilibrium whereas 40 ar accumulates with time thereby the 39 ar 40 ar ratio in rocks and fluids generally decreases with time our models suggest that the co evolution of these two isotopes in rocks and fluids provides a new chronometer of fluid migration and reaction in the crust this chronometer is relevant to a much wider time range than that limited by radioactive decay of cosmogenic 39 ar i e 1400 years at the current detection limit of 3 modern atmospheric value the 39 ar 40 ar chronometer is applicable to estimating residence times of very old groundwater as well as for studying fluid rock interactions and fluid migration rates such as those occurring during co 2 sequestration and the formation of hydrocarbon reservoirs

transient permeability and reseal hardening in fault zones evidence from dilation breccia textures t is well established that earthquake faulting can create permeability along a fault zone in high competence rocks by mismatch of the fault walls and by secondary fracture in a surrounding damage zone and that this permeability is created repeatedly during successive earthquake cycles less well proven is that such permeability is transient being episodically reduced by precipitation of cements in the fracture porosity the textures of carbonate dilation breccias formed at around 1 7 km depth on the dent fault zone nw england lend support to this economically important concept of transient fracture permeability the key observation is that many breccias reflect only a single episode of brecciation and reseal a generally applicable explanation of such single phase breccias is that they were resealed in the interval between major earthquakes that this reseal made the breccia stronger that the intact rock and that subsequent brecciation in the same rock volume was inhibited this reseal hardening model implies that transient permeability in fault zones may last no longer than the recurrence times of large earthquakes and that the permeability conduits will change position in the damage zone with time unless focused at a major fault jog or termination

review of stagodontidae mammalia marsupialia from the judithian late cretaceous belly river group of southeastern alberta canada although stagodontid marsupials are among the most distinctive mammals of late cretaceous age in north america there remain significant gaps in knowledge of their dental anatomy particularly that of the stratigraphically oldest genus eodelphis matthew 1916 we report here on stagodontid specimens from the judithian belly river group of southeastern alberta canada that document what was until now previously unknown parts of the upper and lower premolar dentition of eodelphis browni matthew 1916 and eodelphis cutleri smith woodward 1916 the new information further confirms the distinctiveness of both nominal species of eodelphis and bolsters previous hypotheses suggesting a close phylogenetic relationship between e cutleri and the advanced stagodontid didelphodon marsh 1889 although the new specimens from alberta suggest that the problematic holotype of boreodon matutinus lambe 1902 is an upper third premolar a referral to eodelphis cannot be made with confidence and the name should conti

carbonate hosted zinc lead deposits in the lower cambrian of hunan south china a radiogenic pb sr isotope study zinc lead deposits hosted by lower cambrian carbonate rocks near huayuan in the hunan guizhou orogenic belt southern china have been studied by means of pb and sr isotopes the deposits are characterized by two mineralization stages 1 a main economic stage comprising cockade style sphalerite galena pyrite marcasite fluorite barite and calcite and 2 a subsequent noneconomic stage with nodular rosette sphalerite saddle dolomite and bitumen both ore stages are postdated by a generation of late calcite main stage sulfides 206pb 204pb 18 162 18 225 display a steep linear trend on conventional pb pb diagrams which indicates binary mixing of lead components bearing the imprint of ancient 207pb dominated crustal rocks and reservoirs with elevated th u ratios possibly located in the lower crust nodular rosette sphalerites fall outside this line but reflect a second mixing trend between mineralizing fluids characterized by 206pb 204pb 18 3 and lead isotopically similar to specific main stage cockade sphalerites suggesting either remobilization of pb from main stage ores or contemporaneous mixing of three distinct lead components in the course of an evolving hydrothermal event the 87sr 86sr ratios of diagenetic and hydrothermal carbonate cements and barites range from 0 70905 to 0 71006 and increase systematically with the paragenetic sequence indicating progressive mixing of marine sr derived from the lower cambrian carbonate host rocks with radiogenic sr supplied by external mineralizing fluids in order to identify possible local metal sources u pb and rb sr analyses were performed on six whole rock samples from the lower cambrian sequence and their time integrated pb and sr isotope evolution was compared to the isotopic signature of the mineralization whereas shales and black shales of the cambrian balang and niutitang formations underlying the ore bearing qingxudong carbonate unit appear to be possible external sources for the radiogenic sr found in hydrothermal carbonates the u pb data do not permit these shales to be considered as primary source rocks for the ore lead both the pb and the sr isotopes indicate mineralizing fluids that had interacted with various external metal sources some of them most probably being located in sedimentary or crystalline basement rocks this refutes prevailing genetic models favoring the hydrocarbon and metal rich lower cambrian niutitang black shales as the most likely source reservoir for the zn and pb in the deposits of the huayuan district the pb and sr isotope mixing trends observed for the ore and gangue preciptates reflect small scale heterogeneous fluid systems that were not capable of producing large deposits this may indicate that the huayuan district is not a favorable target for future exploration of economic ore deposits it also limits the prospects of successful radiometric dating of the mineralization since conventional geochronologic models require initial isotopic homogeneity

influence of till provenance on regional groundwater geochemistry abstract a regional groundwater geochemistry study was conducted in the paskapoo formation of southern alberta canada our study area focused on a region where two continental ice sheets the cordilleran and laurentide met the glacial deposits transported by these ice sheets have different bulk characteristics reflective of the bedrock of the source region of the ice recharge through these two different glacial deposits generates distinctly different water geochemistry within the underlying paskapoo formation such that bedrock aquifer acquires a geochemical signature of the immediately overlying glacial deposits through which recharge occurs oxidation of pyrite in laurentide till generates high sulphate groundwater and associated acid generation leads to enhanced mineral weathering this generates high tds high na so4 groundwater in underlying bedrock aquifers this process appears transitory where thin laurentide drift deposits are completely oxidized and have reduced capacity to generate high sulphate water the same bedrock underlying carbonate dominated cordilleran drift deposits have low tds ca hco3 groundwater

geochemistry of halogens in the milk river aquifer alberta canada abstract analytical data are presented for cl br and i on a regional scale for the milk river aquifer the three halides show strikingly similar spatial distributions and are highly correlated concentrations are low in the freshwater portions of the aquifer but increase by as much as two orders of magnitude along the margins however halide ratios reach nearly constant values moving down gradient suggesting the dominance of a common subsurface source for these ions ratios of cl i and cl br are less than those of seawater and fit an origin derived from the diagenesis of organic matter in the sediments halide ratios rule out leakage and or diffusion from the underlying colorado group as a major influence on the chemistry the favored hypothesis is altered connate seawater diffusing from low permeability units within the milk river formation as the primary source of salts this hypothesis of an internal source has important implications for solute sources in other aquifers affected by saline waters because it does not require the importation of a distant fluid the129i i ratio has a meteoric value in groundwater collected near the recharge area but ratios for downflow waters are only 8 70 of this value due to the 16 ma half life of129i these data indicate that most of the increase in dissolved i cannot derive from concentration of a meteoric source by ion filtration but must have a subsurface origin concentrations of129i producedin situ by spontaneous fission of238u attain measurable levels only in the oldest waters sampled ages 105a in which it may account for nearly 90 of the total dissolved129i concentration water ages based upon36cl cl data range up to 2 ma if uncorrected for any dilution by subsurface sources of dead cl if one assumes that the subsurface contributions of cl contribute at least 90 of total cl in the distal portion then the36cl based ages are reduced to 1ma somewhat greater than those estimated by hydrodynamic modeling

correlation of grassy lake and cedar lake ambers using infrared spectroscopy stable isotopes and palaeoentomology the late cretaceous grassy lake and cedar lake amber deposits of western canada are among north america s most famous amber producing localities although it has been suggested for over a century t

origin and distribution of sulfate in a fractured till in southern alberta canada glacial till in a 22 km sup 2 area of the interior plains region of southern alberta canada consists of an upper brown gypsiferous weathered zone up to 20 m thick and a lower discontinuous grey nonweathered zone up to 25 m thick although the total sulfur content of the two till zones is the same 0 34 the mean total sulfate content of the weathered till 4 0 mg g sup 1 exceeds that the nonweathered till 0 8 mg g sup 1 similarities suggest that all so sub 4 sup 2 in the nonweathered till and 20 of the sulfate in the weathered till was derived from sulfate rich bedrock fragments incorporated in the till during deposition laboratory experiments and delta sup 18 o and delta sup 34 s analyses of total so sub 4 sup 2 and the sulfur forms in the two zones show that the majority of the sulfate in the weathered till was derived from the oxidation of organic s at some time after the till was deposited mass balance and flux calculations indicate that this oxidation occurred under partially saturated conditions groundwater flow simulations suggest that the water table was much lower and that a thick partially saturated zone was possible during the drier altithermal period 11 000more to 3000 years b p the following chemical processes account for the major ions that are found in the groundwater but were generated when the partially saturated zone existed the oxidation of reduced s produced so sub 4 sup 2 and h sup the h sup reacted with carbonate minerals under elevated p sub co2 with ca sup 2 loss by exchange for na sup and gypsum precipitation volume shrinkage in the weathered till resulting from these geochemical processes may have enhanced the development of fractures and caused the associated increased hydraulic conductivity less

cockade breccia product of mineralisation along dilational faults cockade breccias are fault fills in which individual clasts are completely surrounded by concentric layers of cement they occur particularly in low temperature near surface hydrothermal veins at least six mechanisms have been proposed for the formation of cockade breccia like textures but only two repeated rotation accretion and partial metasomatic replacement of clast minerals have been supported by detailed evidence a typical example of cockade breccia from the gower peninsula south wales shows clear evidence for the rotation accretion mechanism in particular overgrown breakage points in cement layers where cockades were previously touching each other and rotated geopetal infills of haematitic sediment based on the available evidence it is proposed that cockade textures result from low rates of cement growth compared to high rates of dilational fault slip seven criteria are given for the correct identification of cockade breccias

chaotic breccia zones on the pembroke peninsula south wales evidence for collapse into voids along dilational faults chaotic breccias and megabreccias locally called gash breccias hosted within the pembroke limestone group visean mississippian lower carboniferous of southwest wales are re mapped along with spatially related crackle and mosaic breccias of thirteen studied megabreccia bodies seven lie along steep nnw or nne striking strike slip faults originating during north south variscan late carboniferous shortening though reactivated during later extension four bodies are conformable with e w striking steeply dipping bedding and two have irregular or indeterminate margins the bedding parallel zones are interpreted as the dilational tips of listric normal faults and the cross strike faults as transtensional transfer zones sub horizontal clast fabrics suggest brecciation by gravitational collapse into opening fissures rather than by cataclasis along the faults most fissures have geometrically matched margins produced by this dilational faulting and only locally have the indented margins indicating solutional processes the most likely age for the main fissure extension and fill is late triassic based on analogous dated fills at the eastern end of the bristol channel basin the pembroke megabreccias blur the distinction between fault rocks formed by deformation and those formed by redeposition along fault zones

geochemistry s vital contribution to solving water resource problems abstract as part of the events celebrating 40 a of iagc it is fitting to trace the modern evolution and development of hydrogeochemistry however fascination with water quality can be traced back more than 2 ka in the post war years hydrogeochemistry was influenced heavily by the advances in other disciplines including physical chemistry metallurgy and oceanography hydrological applications of isotope science also developed rapidly at this time and important advances in analytical chemistry allowed multi element and trace element applications to be made experimental studies on equilibrium processes and reaction kinetics allowed bench scale insight into water rock interaction consolidation of knowledge on processes in groundwaters and the current awareness of hydrogeochemistry by water professionals owe much to the work of robert garrels john hem and co workers in the early 1960s studies of down gradient evolution enabled a field scale understanding of groundwater quality and geochemical processes as a function of residence time dissolution and precipitation processes in carbonate and non carbonate aquifers redox processes cation exchange and salinity origins emerging water resource and water quality issues in the 1960s and 70s permitted the application of hydrogeochemistry to contaminant and related problems and this trend continues the impacts of diffuse pollution from intensive agriculture waste disposal and point source pollution from urban and industrial sources relied on geochemistry to solve questions of origin and attenuation in semi arid regions facing water scarcity geochemical approaches have been vital in the assessment of renewability and characterising palaeowaters the protection and new incoming regulation of water resources will rely increasingly on a sound geochemical basis for management

an alternative view on the origin of chemical and isotopic patterns in groundwater from the milk river aquifer canada the milk river artesian aquifer underlies 15 000 km2 of southern alberta canada it consists of thin 30 75 m thick sandstone and is confined above by the pakowki shale typically 120 m thick and below by the colorado shale the aquifer subcrops in southern alberta and northern montana groundwater movement is to the north west and east from the outcrop area dominant recharge area cl and i concentrations increase in the direction of flow from less than 0 05 and 0 001 mmol l respectively near the recharge area to more than 140 and 0 15 mmol l at the northern edge of the aquifer similarly waters become more enriched in oxygen 18 and deuterium from less than 21 0 and 167 near the recharge area to values approaching 8 0 and 70 0 in the north isotope values in the recharge area plot on the global meteoric water line and indicate that the recharge waters are isotopically unaltered meteoric waters downgradient from the recharge area the data deviate from the meteoric water line slope of 6 3 instead of 8 0 three mechanisms have been advanced to explain the origin of the chemical and isotopic patterns the introduction of connate formation water through the colorado shale and subsequent mixing with infiltrating meteoric water a finite source of meteoric recharge mixing with more saline water in the aquifer and chemical and isotopic enrichment due to ion filtration hydraulic conductivity and hydraulic head data cl concentrations of drill cuttings and isotopic values from groundwater from the colorado shale provide arguments for reevaluating these ideas an alternative mechanism based on diffusion between saline isotopically enriched water in the colorado shale and fresher isotopically depleted water in the aquifer is tested using an analytical mass transport model although uncertainty exists in the model parameters results showed that the patterns in cl i 18o and 2h in the aquifer can be explained by aquitard diffusion further aquitard diffusion must be considered when using chlorine 36 dating methods in aquifer aquitard systems such as the milk river aquifer

application of isotopic methods to dating of very old groundwaters milk river aquifer alberta canada the aim of this joint project was to evaluate the usefulness of available geochemical and isotope techniques for dating very old groundwater this paper represents a synthesis of an iaea sponsored study for which purpose the milk river aquifer groundwaters were sampled from 16 wells during 1985 and subsequent years for the following measurements 2h 3h 13c 18o 14c 39ar 81kr 85kr noble gases including222rn 36cl 129i and u isotopes the milk river aquifer was selected for this study because several preceding investigations had established that this groundwater system contains waters whose ages range from recent to 1ma the present study has established that the milk river aquifer system is very complex both in terms of groundwater origin and in terms of the evolution of its chemical and isotopic contents however this apparent complexity proved to be an interesting challenge with respect to the use of different and complementary approaches to interpretation of the geochemical and isotope data in terms of groundwater residence time thus the groundwater ages based on the hydrodynamic model should be considered as a lower limit of the average groundwater age in the milk river aquifer 0 25ma while those based on the36cl cl data uncorrected for any dilution by dead cl should be considered as an upper limit 2ma the milk river aquifer international project is an excellent illustration of the variety of insight and increased confidence possible in flow system analysis when multiple independent dating methods are combined with detailed hydrogeological studies the conclusion of the present study is that the potential for dating of very old groundwaters by a variety of isotope techniques is very high provided a combination of methods is applied never a simple method by itself

basement reservoir plumbing fracture aperture length and topology analysis of the lewisian complex nw scotland upfaulted ridges of neoarchean crystalline basement rocks formed in the faeroe shetland basin as a consequence of mesozoic rift processes and are an active target for oil exploration we carried out a comprehensive fault and fracture attribute study on the extensive exposures of geologically equivalent crystalline basement rocks onshore in nw scotland lewisian gneiss complex as an analogue for the offshore oil and gas reservoirs of the uplifted rona ridge basement high our analysis shows a power law distribution for fracture sizes aperture and length with random to clustered spacing and high connectivity indices regional variations between the scottish mainland and the outer hebrides are recognized that compare directly with variations observed along the rona ridge in the faeroe shetland basin here we develop a model for the scaling properties of the fracture systems in which variations in the aperture attributes are a function of the depth of erosion beneath the top basement unconformity more generally the combination of size spatial and connectivity attributes we found in these basement highs demonstrates that they can form highly effective well plumbed reservoir systems in their own right supplementary material additional methods and results are available at https doi org 10 6084 m9 figshare c 5017139 thematic collection this article is part of the the geology of fractured reservoirs collection available at https www lyellcollection org cc the geology of fractured reservoirs

pore geometry as a control on rock strength the strength of rocks in the subsurface is critically important across the geosciences with implications for fluid flow mineralisation seismicity and the deep biosphere most studies of porous rock strength consider the scalar quantity of porosity in which strength shows a broadly inverse relationship with total porosity but pore shape is not explicitly defined here we use a combination of uniaxial compressive strength measurements of isotropic and anisotropic porous lava samples and numerical modelling to consider the influence of pore shape on rock strength micro computed tomography ct shows that pores range from sub spherical to elongate and flat ellipsoids samples that contain flat pores are weaker if compression is applied parallel to the short axis i e across the minimum curvature compared to compression applied parallel to the long axis i e across the maximum curvature numerical models for elliptical pores show that compression applied across the minimum curvature results in relatively broad amplification of stress compared to compression applied across the maximum curvature certain pore shapes may be relatively stable and remain open in the upper crust under a given remote stress field while others are inherently weak quantifying the shape orientations and statistical distributions of pores is therefore a critical step in strength testing of rocks

the structure of shear related vein type gold deposits a review abstract the structure of vein type gold deposits is defined by the shapes and geometrical relationships of mineralized bodies the form of the mineralization making up these bodies and the sequence of vein forming events most mineralized zones occur within or are spatially associated with shear zones especially shear zones in larger systems of intersecting shear zone sets they range in shape from tabular to linear and in form from disseminated to breccia to stockwork or sheeted veinlet zones to single veins there typically is a complex history of mineral deposition which overlaps and is genetically related to the deformation that generated the host structural zone the purpose of this paper is to consider the structural features of vein type deposits in relation to the geometrical properties and evolution of veinhosting fractures particularly shear zones the evidence indicates that veins are localized by tectonically generated dilatancy in an environment of low mean stress caused by high fluid pressure it is proposed that a major cause of tectonic dilation of shear zones is the interference between intersecting shears during bulk inhomogeneous flattening by movement on systems of intersecting shear zone sets

dalton wells geology and significance of debris flow hosted dinosaur bonebeds in the cedar mountain formation lower cretaceous of eastern utah usa the lower cretaceous dalton wells dinosaur locality north of moab utah consists of a 2 m thick stacked succession of four fossil rich bonebeds with an estimated collective lateral extent of more than 4000 m2 to date 215 m2 of the bonebeds have been excavated and more than 4200 vertebrate fossil field specimens have been collected the site occurs at the base of the yellow cat member of the cedar mountain formation and lies unconformably on upper jurassic strata of the morrison formation the age of the assemblage is tentatively accepted as barremian nine dinosaur taxa are recognized making dalton wells one of the richest abundance and diversity lower cretaceous dinosaur localities in the world the bonebeds are rare examples of fossiliferous subaerial debris flow deposits at least four flows originated an undetermined distance up slope from an early cretaceous site of dinosaur bone concentration and flowed through the site carrying bones short distances toward an adjacent area of lakes ponds and wetlands host sediments most likely accumulated on the eastward dipping slopes of a backbulge in a foreland basin the overall depositional setting was alluvial lacustrine in a warm to hot and seasonally wet and dry climate the consistent expression and location of lacustrine facies in both the brushy basin member of the morrison formation and the yellow cat member of the cedar mountain formation indicate that high rates of subsidence typified the dalton wells area both before and after the j k transition and further suggest that there was some form of long term to episodic and localized influence on subsidence the depositional slope required to generate debris flows may have been established by forebulge crustal flexure but could also have been established or amplified by the high rates of subsidence that maintained the lacustrine paleoenvironments in the field area concretionary deposits in the yellow cat member at dalton wells are diagenetic and apparently resulted from groundwater precipitation likely enhanced by the presence of organics bones and lacustrine carbonates the regional and cross facies expression of calcretes in the yellow cat member combined with the rarity of pedogenic indicators confirms that they are not paleosols mineral precipitation likely occurred as groundwater flow was established in response to foreland basin development it remains unknown under what specific circumstances animals died and carcasses accumulated prior to being reworked by debris flows however the stratigraphic association of seasonally wet and dry facies throughout the yellow cat member suggests that drought induced mortality events were probably common in a seasonally wet and dry environment debris flows may have been triggered by intense rainfall or seismic events

fissure fills along faults variscan examples from gower south wales the extent to which persistent rather than transient fissures wide planar voids can exist along upper crustal faults is important in assessing fault permeability to mineral and hydrocarbon bearing fluids variscan late carboniferous faults cutting dinantian lower carboniferous limestones on the gower peninsula south wales host clear evidence for fissures up to several metres wide evidence includes dendritic hematite growth and elongate calcite growth into open voids spar ball and cockade breccia formation laminated sediment infill and void collapse breccias detailed mapping reveals cross cutting geometries and brecciation of earlier fissure fills showing that fissures were formed during rather than after active faulting fissures therefore probably formed by geometric mismatch between displaced fault walls rather than by solution widening along inactive faults

on the arrangement of solid inclusions in fibrous veins and the role of the crack seal mechanism the arrangement of solid inclusions in veins was examined in three different rock types and tectonic settings common to all samples is a new type of sinusoidal inclusions associated with inclusion bands oriented parallel to the vein wall and inclusion trails at high angle to the vein wall crosscutting relationships of inclusion bands and the sinusoidal inclusions imply that inclusion bands do not reflect individual crack seal increments in our veins inclusion bands are not a sufficient criterion to infer the crack seal mechanism further evidence for solid inclusions not formed by the classic crack seal mechanism is given by inclusion bands in gypsum crystals grown in soft clay during incorporation solid inclusions can become folded or boudinaged depending on their orientation with respect to the opening direction the complex displacement field within the vein is recorded by curved crystal fibres which track the opening direction based on the arrangement of solid inclusions within the vein we suggest that our veins grew continuously during syntectonic vein formation solid inclusions formed by a fluctuation of adhesion at the vein wall interface rather than by crack sealing and vein growth was at least partly driven by the force of crystallisation q 2005 elsevier ltd all rights reserved

genesis of cockade breccias in the tectonic evolution of the cirotan epithermal gold system west java the pliocene cirotan gold deposit provides an exceptional example of mineralized breccias and in particular cockade breccias analysis of these breccias approached through both field observation and image analysis on photographs made it possible to determine their method of graded formation the mineralized structure as much a 25 m thick in places is a right lateral strike slip fault that evolved to a normal fault at the end of the system s development it consists of juxtaposed breccia bodies separated by major slip or septa which formed at a major inflection of the host fault the breccia bodies all show a similar internal organization from footwall to hanging wall one passes from a siliceous breccia with angular clasts to a thick infill of cockade breccia showing a reverse grading with small centimetre size cockades aspect ratios of 1 10 passing to larger up to 1 m more equant cockades aspect ratios 1 3 in contact with the hanging wall the different stages of cockade formation demonst

intense fracturing and fracture sealing induced by mineral growth in porous rocks article i nfo mineral precipitation in the pores of a rock may exert a force which is called crystallization pressure this process has been studied experimentally and results bring a new look on the way fractures may develop and seal in natural systems cylindrical core samples of porous limestone and sandstone were left for several weeks in contact with an aqueous solution saturated with sodium chloride at 30 or 45 c under axial normal stress in the range 0 02 0 26 mpa the fluid was allowed to rise in the core samples by capillary forces up to a controlled height where evaporation and precipitation occurred the uniaxial deformation of the samples was measured using high resolution displacement sensors the samples were characterized using computed x ray tomography allowing therefore imaging in 3d the intensity and localization of the damage two kinds of damage could be observed firstly small rock fragments were peeled from the sample surface secondly

strontium isotopic evidence on the chemical evolution of pore waters in the milk river aquifer alberta canada abstract strontium isotope ratios were measured on 13 rock 18 leachate and 28 pore water samples from the milk river aquifer the confining argillaceous formations and the glacial till mantling the recharge area strontium isotope ratios 87sr 86sr of pore waters from the aquifer confining units and the glacial till ranged from 0 7069 to 0 7082 the 87sr 86sr ratios in aquifer pore waters decrease with increasing distance from the aquifer recharge area and this is interpreted to be the result of mixing and water rock interaction within the aquifer the solute composition of the recharging groundwater is modified by the local lithology causing distinct geochemical patterns along different flow paths within the aquifer whole rock 87sr 86sr ratios indicate that the shales and till are generally more radiogenic than the aquifer sandstone the authigenic carbonate cements and rock forming minerals comprising the major lithologic units had little apparent influence on the pore water sr chemistry carbonate cement leachates from the till and the aquifer sandstone are more radiogenic than those from the confining shale formations feldspar separates from the aquifer sandstone have relatively radiogenic sr isotope ratios whereas bentonites from the milk river and colorado shale formations have whole rock and leachate sr isotope ratios that are relatively unradiogenic ratios of most milk river aquifer pore waters are lower than those of any leachates or whole rocks analyzed except the bentonites the 87sr 86sr ratios of exchangeable sr in the bentonites are similar to ratios found in the more evolved pore waters simple rock water interaction models calculated for the whole rock leachate and exchangeable ion pore water pairs indicate that ion exchange with bentonite clays within the milk river and colorado shale formations appears to influence the isotopic evolution of the pore water sr in each of these units

three dimensional unified geological model of the milk river transboundary aquifer alberta canada montana usa the milk river transboundary aquifer canada usa has been so intensively used over the 20th century that concerns have risen about the durability of this resource since the mid 1950s this aquifer actually corresponds to the middle virgelle member of the upper cretaceous milk river formation called eagle formation in montana to assess the conditions needed for a sustainable use of the aquifer a comprehensive and unified portrait of the aquifer is needed across its international boundary the stratigraphic framework and geometry of geological units on both sides of the international border were thus unified in a 50 000 km2 three dimensional 3d geological model the virgelle member is 0 60 m thick and it subcrops near the border and along both sides of the sweetgrass arch it dips away from the subcrop areas in a semi radial pattern the medicine hat gas field hosted by the alderson member alberta which is separated from the other members by a regional unconformity and the tiger ridge gas field n

quantifying fault breccia geometry dent fault nw england a geometric classification of fault breccia borrowed from the cave collapse literature has been suggested as an alternative to available genetic classifications here image analysis is used to explore geometric discrimination between the visually assigned classes of crackle breccia mosaic breccia and chaotic breccia using samples from the well understood dent fault northwest england clast sphericity and surface roughness show some correlation with the breccia classes but particle size distributions and their fractal dimension show none a more useful parameter is the percentage of sample area occupied by clasts crackle breccia has 75 clasts mosaic breccia 60 75 clasts and chaotic breccia has 60 clasts the eye is also good at judging the tessellation goodness of fit of clasts and a semi quantitative approach to assessing this parameter is explored the average degree of rotational misfit of the clasts is strongly related to breccia class crackle breccia involves less than 10 average rotation mosaic breccia 10 20 and chaotic breccia more than 20 rotation comparison charts are provided for semi quantitative classification of fault breccias

seismic cycle recorded in cockade bearing faults col de teghime alpine corsica abstract few fault rocks are known to be associated undoubtedly with seismic faulting here we investigated the formation mechanism of cockade breccias found in transtensional faults cutting marbles and quartzites from the col de teghime area alpine corsica france field surveys coupled with detailed microanalytical investigations indicated that i the core clasts of the cockades are composed of host rock fragments 310 m in size that are suspended in the slipping zones and arranged in inverse grading ii the concentric rims of the cockades show a cyclic zoning made of saddle dolomite mg calcite goethite anatase iii the cockade bearing veins are associated with minor fault veins filled with fine fragments we propose that the cockade bearing faults formed at shallow crustal depths

synkinematic skarns and fluid drainage along detachments the west cycladic detachment system on serifos island cyclades greece and its related mineralization back arc extension in the aegean sea has been accommodated by several large scale detachments such as the west cycladic detachment system wcds in the oligocene and miocene the wcds especially crops out on serifos island cyclades with a synkinematic granodioritic intrusion as skarns represent metasomatic reactions near the contact between intrusions and the host rocks they sign the position of the main drains used by fluids while the mineralogy of the serifos skarns is well known geometrical and kinematic relations between the detachments and ore bodies remains poorly studied this study allows us to distinguish different types of skarn high temperature skarns correspond to 1 massive garnet endoskarns 2 ribbon and bubble garnet pyroxene endoskarns 3 garnet pyroxene cracks exoskarns whereas medium temperature pyroxene ilvaite bearing skarn breccias within the meghalo livadhi and kavos kiklopas detachments belonging to the wcds our observations show that skarn formation is associated with the activity of detachments and the syntectonic pluton emplacement endo and exoskarn deposits formed coeval with the ductile and brittle structures resulting from the activity of the wcds such as echelon veins veins with antithetic shear and boudinaged veins wrapped within sheath folds with a top to the ssw or sw shear senses compatible with the regional kinematics some skarn breccias formed within detachment planes far from the contact of the main granodioritic body attesting for the intense flow of magmatic fluids along these discontinuities these over pressurized fluids play a major role in the mechanical behaviour of the detachments and strain localization the two detachments acting as preferential crustal scale drains the pattern of magmatic fluid flows is not centred on the intrusion in this context iron rich skarns and associated primary magnetite deposits have been remobilized during late brittle increments of motion along the detachments together with surface derived fluids responsible for deposition of the economic fe ba mineralization

crystallization pressure versus crack seal as the mechanism for banded veins banded fibrous veins are often pointed to as evidence for episodic crack opening driven by oscillations in fluid pressure or bulk strain advances in understanding the geochemistry of precipitation data on veins and experiments suggest that pressure due to growing crystals may be an alternate explanation for many observations on these types of veins we propose that some veins originate at sites of precipitation and then propagate due to the pressure exerted by the crystal growth as materials precipitate the vein walls are pushed apart the resulting veins have shapes typical for mode i cracks except that mechanically crystallization pressure replaces the role of internal fluid pressure in their propagation a nonzero remote differential stress serves to align veins mechanical and geochemical considerations suggest that this process will be most important in fine grained rocks such as greenschist grade pelites where diffusion from sites of dissolution rather than advection is the dominant mass transport process veins may owe their orientation to tectonism but their initiation and growth are due to processes that supersaturate the pore fluid veins formed by this mechanism involve cracking to the extent that precipitation forces an original flaw to extend during precipitation cyclic quartz mica bands may indicate geochemical self organization at the vein wall driven by pressure solution enhanced supersaturation in the pore fluid and nonlinear precipitation kinetics at the vein wall

erosion of a surface vortex by a seamount abstract numerical experiments are carried out on the f plane using a shallow water isopycnal model to analyze the behavior of a surface intensified anticyclonic vortex when it encounters an isolated seamount the advection by the vortex of deep fluid parcels across the isobaths is known to generate deep anticyclonic and cyclonic circulations above and near the bathymetry respectively these circulations are shown to exert a strong shear on the upper layers which causes an erosion of the initial vortex by filamentation the erosion often results in a subdivision of the eddy while the eroded original structure forms a dipole with the deep cyclone and is advected away the filaments torn off from the original core aggregate into a new eddy above the seamount splitting in more than two structures is sometimes observed the erosion process is quantified by the bulk volume integral of the eddy potential vorticity anomaly a sensitivity study to different parameters of the configuration distance between

observations of seamount attached eddies in the north pacific satellite tracked drifters were used to examine eddy activity in the vicinity of the emperor seamount chain esc in the north pacific during 1991 1993 the trajectories of two drifters drogued at a depth of 120 m revealed a pair of counterrotating mesoscale eddies attached to the leeside of ojin jingu seamount in the summer of 1992 the eddies had diameters of 75 100 km and rotational speeds of 20 40 cm s at 120 m sea surface height anomalies derived from blended topex ers 1 satellite altimetry revealed that the eddies had a surface manifestation as well one of the drifters made five loops within the cyclonic eddy over a period of 62 days during which time the eddy translated westward toward the seamount at 2 9 cm s this is one of the first observations demonstrating an extended attachment of a topographically generated eddy to a seamount drifters drogued at a depth of 15 m which crossed the esc in the summer of 1991 and winter of 1993 revealed no eddy activity most likely because of a decoupling of the topographic influence to the 15 m flow at their crossing latitude over the nintoku seamount summit depth at 1000 m the implication is that eddy formation within the mixed layer near the esc is confined to the region around the taller ojin jingu and kinmei seamounts summit depths at 800 m and 100 m respectively it is suggested that long lived eddies attached to the leeside of the esc can profoundly influence local biological production and water exchange between the western and eastern basins of the north pacific

uranium series radionuclides in fluids and solids milk river aquifer alberta canada abstract samples from 21 wells completed in the milk river aquifer were sampled and analysed for u isotopes in general u concentrations decrease with distance from the recharge area groundwater samples can be delineated into a small oxic group u content 101t 5 mmol 1 and a more predominant anoxic group u content of 10 7 mmol 1 all groundwater samples were undersaturated with respect to the common u minerals such as uraninite coffinite and rutherfordine the dominant u complexes were uranyl carbonates the234u 238u activity ratios increased from 2 to 11 with distance downflow of the outcrop the highest activity ratio of 11 8 was measured at a well defined redox front whereupon a steady decrease downdip to 4 was observed this decrease was interpreted to be due to the decay of234u excess with age of the groundwater and due to u loss by sorption precipitation processes from solution to solid surfaces two u isotope dating models were used to estimate the age of the groundwater in the milk river aquifer model 1 is a simple model of downdip decay of234u excess in solution under steady state conditions model 2 is a phenomenological model for the evolution of u isotope groundwater composition downdip based on a transport dispersion equation incorporating radioactive decay and assuming that sorption processes are of first order kinetics both models were applied to the u isotope data collected along the same flow path in the aquifer they yielded flowrates of 0 1 0 2 m a and 0 2 0 6 m a respectively the latter range is in good agreement with flowrates of 0 3 m a obtained from hydraulic considerations the lower value derived from model 1 is interpreted in terms of u migration velocity rather than as groundwater flowrate model 2 was also applied to an additional flowpath the calculated flowrate range of 0 1 0 4 m a is in excellent agreement with the hydraulic model flowrate of 0 2 m a the main conclusion of this work is that u isotopes can be used for dating very old groundwaters provided the local hydrogeology and u geochemistry are understood well

geometry and formation of gypsum veins in mudstones at watchet somerset sw england gypsum veins and faults were studied in red mudstones of the upper triassic mercia mudstone group in the bristol channel basin exposed in e w trending cliffs at watchet on the somerset coast sw england in nodular gypsum horizons individual gypsum nodules are connected by subhorizontal gypsum veins in evaporite free mudstone layers however dense anastomosing networks of gypsum veins occur in a 300 m long profile dissected by 28 mostly normal faults with small displacements 24 faults have veins following them indicating palaeofluid transport along the fault planes ninety seven cross cutting relationships and mostly perpendicular vein fibres indicate that the veins are primarily extension fractures the thickest veins in the vein network are subhorizontal 160 measurements indicating a vertical orientation of the minimum principal compressive stress horizontal basin compression such a stress state may have existed during basin inversion associated with alpine compression late cretaceous to early tertiary i propose that the gypsum veins are the result of hydrofracturing in the gypsum nodules then presumably consisting of anhydrite overpressure was generated related to the hydration of anhydrite to gypsum stress concentration around the nodules led to rupturing and injection of thin subhorizontal hydrofractures some of the calcium sulphate saturated fluids were then transported upwards along the faults and gained access to evaporite free mudstone layers where dense anastomosing vein networks developed most veins were arrested during their propagation by layers with contrasting mechanical properties stress barriers some veins however propagated through the barriers along faults to shallower levels the dense networks of mineral veins observed in watchet indicate that hydrofractures can generate a very high temporary permeability in fluid reservoirs

palaeoseismic events recorded in archaean gold quartz vein networks val d or abitibi quebec canada archaean gold quartz vein deposits are commonly hosted in high angle reverse shear zones and are interpreted to have formed in a regime of horizontal compression and high fluid pressure environment this paper presents the results of a combined structural and fluid inclusion study on three gold quartz vein deposits of the val d or area abitibi quebec consisting of subhorizontal extensional veins and e w steeply dipping shear veins crack seal structures tourmaline fibres stretched quartz crystals and open space filling textures indicate that the subhorizontal veins formed by hydraulic fracturing under supralithostatic fluid pressure co2 rich and h2o nacl fluid inclusions interpreted as two coexisting immiscible fluids occur typically in microcracks of different orientations interpreted to have formed in the 1 2 plane horizontal co2 rich fluid inclusion planes are contemporaneous with the opening of these veins 3 vertical vertical h2o nacl fluid inclusion planes as well as some microstructures such as deformed minerals indicate that the same extensional veins have experienced episodic vertical shortening 3 horizontal alternating with the opening events deformation and slip opening also occurred in shear veins in which preferred orientation of fluid inclusion planes is not clear except that the h2o nacl fluid inclusion planes tend to be oriented at high angles to the slip direction the successive opening and collapse events in subhorizontal extensional veins are correlated with deformation and slip opening events in shear veins respectively and are attributed to cyclic fluid pressure fluctuations in the system they are thus consistent with the fault valve model sudden drop in fluid pressure from supralithostatic to lower values induces fluid unmixing and occurs immediately post failure following seismic rupturing along the shear zone sealing of the shear veins allows the fluid pressure to build up again and the subhorizontal extensional veins to form the intermittent change in orientation of 3 in horizontal extensional veins is ascribed to a total shear stress release along the neighbouring shear veins after rupture the complex internal structures of the gold quartz veins provide an excellent record of archaean seismic activity along high angle reverse faults

constraints of deep crustal structures on large deposits in the cloncurry district australia evidence from spatial analysis abstract deep structures are commonly recognized as critical factors for controlling the formation of large hydrothermal deposits it is of great importance for the metallogenic studies to quantitatively describe the spatial associations of deep structures with mineral deposits in the cloncurry district of the mt isa province australia many large deposits have been discovered and district scale deep structures have also been recognized from the magnetic gravity seismic and magnetotelluric data in this paper we delineate the 3d configuration of the deep structures by 3d geometric modeling and gaussian curvature analysis and quantify spatial associations of the deep structures with the large deposits by the weights of evidence method the results demonstrate that the configuration of deep structures has a positive spatial constraint on the distribution of deposits many deposits are located close to the high curvature portion of the deep structures according to this rule there are some potential target areas where curvature of the deep structural surfaces is high but no deposits have been discovered such results can be used to identify targets with potential for finding undiscovered deposits

red bed and basement sourced fluids recorded in hydrothermal mn fe as veins sailauf germany a la icpms fluid inclusion study the hydrothermal mn fe as vein mineralization at sailauf germany hosts a complex sequence of oxide and carbonate minerals that record a protracted fluid history the mineralization is related to a major unconformity that separates permian zechstein sedimentary rocks from underlying variscan crystalline basement the hydrothermal veins contain two principal mineralization stages which are mn oxides associated with calcite and hematite associated with mn calcite the fluid evolution of the hydrothermal system has been reconstructed from fluid inclusion petrography microthermometry and la icpms microanalysis coupled with stable isotope geochemistry of carbonate and oxide minerals the fluid inclusions are high salinity sodic calcic brines and the bulk fluid properties show no major differences between the mn oxide and the hematite stage la icpms analysis of major and trace elements demonstrates that the mineralization formed from chemically distinct fluid pulses characterized by variations in their k li b pb and zn concentrations the fluid that precipitated the mn oxide stage has anomalous pb zn and li b ratios which closely resemble fluids found in fracture fillings in red beds of the permian rotliegend basin by contrast the fluids associated with the hematite stage have pb zn and li b ratios typical of crustal fluids that were derived from interaction with crystalline basement both fluids possess characteristic element ratios including cl br but variable absolute concentrations of most metals this suggests that both fluids were modified by mixing with a common metal depleted brine that had a similar cl br ratio most likely a formation water from the overlying zechstein sedimentary rocks the sailauf mineralization provides insight into the protracted post variscan fluid evolution at the basement cover interface the compositionally anomalous fluid that precipitated the mn oxides is comparable to brines derived from interaction with red beds and likely represents the ore fluid of kupferschiefer type sediment hosted cu deposits conversely the fluid that deposited the hematite mineralization resembles fluids that typically form basement and sediment hosted pb zn deposits

comment on an alternative view on the origin of chemical and isotopic patterns in groundwater from the milk river aquifer canada by m j hendry and f w schwartz the milk river aquifer in southern alberta combines apparently simple classical confined aquifer hydrodynamics with somewhat enigmatic groundwater geochemistry of conservative solutes over the past 10 years five major papers have focused on the geochemistry of milk river aquifer groundwater most recently hendry and schwartz 1988 have proposed a different mechanism aquitard diffusion to explain the milk river geochemistry they described and evaluated previously proposed geochemical processes especially ion filtration hendry and schwartz 1988 concluded that ion filtration and the other proposed mechanisms were not supported by the data they then described the aquitard diffusion mechanism and used a simple analytical model to simulate observed aquifer trends in cl sup minus and sup 18 o from the results of this exercise they concluded that diffusion from the aquitards was controlling the solute distributions in the aquifer finally they interpreted previously published sup 36 cl data and new profiles of cl sup minus in the aquitards in terms of the diffusion model upon review the authors do not find the arguments against ion filtration to be as damaging as hendry and schwartz indicate nor do they find the evidence for aquitard diffusion to be as persuasive in this study they will first evaluate hendry andmore schwartz s arguments against ion filtration then they will review the arguments in favor of aquitard diffusion and finally the authors will address the implications for the interpretation of the vertical cl sup minus profiles and the sup 36 cl data less

effects of the fieberling seamount group upon flow and thermohaline structure in the spring of 1991 the circulation and thermohaline structure around fieberling fieberling ii and hoke seamounts are examined on the basis of two high resolution surveys in april and may 1991 the large scale flow approached the seamounts from the southeast impinging first on hoke then splitting with one branch meandering westward in jetlike fashion over the fieberling ii and fieberling seamounts and the other turning to the northeast the jets were typically 10 20 km wide with core speeds of 0 2 0 5 m s and were accompanied by pairs of cyclonic and anticyclonic eddies with diameters of 10 30 km located near the seamounts while the large scale flow pattern persisted over a week significant changes were observed in the shape of the meanders and the locations of the eddies over this period transient bottom intensified upwelling cones 20 km in diameter and 150 220 m high were encountered on all three seamounts investigated as were pronounced 60 m deep mixed layers above the summits their persistence at a given location was less than a week geopotential height perturbations of the order of 0 8 j kg equivalent to 0 08 m in elevation were observed in the vicinity of the seamounts these perturbations are dominated by mesoscale ridges troughs peaks and depressions the positions of which vary with depth as well as time in general the surface geopotential topographies differ in shape from those observed at depths where the seamount peaks occur which is attributed to the vanishing influence of the california current beneath 200 m

integrated climate model oxygen isotope evidence for a north american monsoon during the late cretaceous abstract during the late cretaceous western north america was characterized by a close geographic association between the sevier highlands and the western interior seaway in this paper an atmospheric general circulation model agcm is used to simulate the impact of this geographic association on surface pressure wind direction and precipitation and it is predicted that seasonal changes in these variables resulted in a strong monsoon along the eastern flank of the sevier highlands confirmation that these model simulations are accurate is provided by isotopic data from foreland basin sediments in particular oxygen isotope records from different environments large rivers small streams and ponds and proxies unionid bivalve shells and paleosol carbonates indicate that foreland basin streams were recharged by local precipitation with high oxygen isotope ratios while large trunk rivers were recharged by high elevation precipitation this hydrologic pattern is observed from alberta to utah and is consistent with east to west monsoonal air mass movements and associated seasonal rainfall recognition of a highland driven monsoon has implication in regard to studies of fossil taphonomy of water vapor transport and of links between climate and mountain uplift and exhumation in this region

flow system controls of the chemical evolution of groundwater abstract isotopic and major ion analyses of 130 fresh and brackish groundwater samples reveal a strikingly consistent pattern of variation over 28 000 km 2 of the western canada sedimentary basin hydrodynamic interpretations based on drill stem tests and piezometric data reveal a pattern of broad regional flow from south to north however there is some evidence to suggest that patterns of groundwater flow have been influenced in the past by wisconsin glaciation all the permeable units appear to be recharged by meteoric water in the south where they outcrop or come close to the surface samples of groundwater collected down dip in each of six major sandstone units are progressively enriched in d 18 o na and cl for example the deepest waters of the artesian milk river aquifer are enriched by up to 70 and 15 with respect to the d and 18 o of the modern recharge waters the pattern of chemical evolution is strongly related to the hydraulic characteristics of individual units the isotopic composition is determined by the extent to which hydraulic conductivity has facilitated meteoric water flushing of connate water thus more permeable units and permeable zones within a unit tend to be isotopically lighter because of a more complete and more rapid invasion of meteoric water interestingly the largest conductivity values are found in some of the deepest units 1500 m consequently water in these deeper units have d and 18 o values which approach that of the recharge the major ion chemistry is controlled both by this process and a complex set of rock water interactions in addition to providing information about the chemical evolution of groundwater this study can begin to quantify the complex pattern of flushing in a large sedimentary basin

hydrogeology and hydrochemistry of the milk river aquifer system alberta canada a review abstract the milk river aquifer system consists of 30 60 m of cretaceous sandstone located within the milk river formation southern alberta canada the milk river formation is confined below by 500m of shale of the colorado group and above by up to 120 m of shale the pakowki formation the dominant recharge area for the aquifer is the sweetgrass hills montana where the aquifer crops out from the recharge area the groundwater flows to the north east and west calculated groundwater residence times at the north end of the aquifer about 100 km north of the recharge area range from 250 to 510 ka limited hydrological data from the confining shales suggest that cross formational flow does not occur systematic patterns are observed in major ions na cl hco 3 co 3 and so 4 stable isotopes 18 o and deuterium and field ph on a regional scale several mechanisms have been proposed to explain the geochemical evolution of the groundwaters

numerical simulations of stratified rotating flow over finite amplitude topography abstract a primitive equation numerical ocean model is used to investigate the response of an basic flow initially horizontally and vertically uniform to the presence of an isolated seamount at the center of a 4000 m deep periodic channel the model is configured with 5 km horizontal resolution and 15 constant density layer in the vertical the coriolis parameter fluid stratification coefficient of lateral friction and length scale or the topography are held constant while the men downstream flow speed and height of the obstacle vary up to an extreme case of a 20 cm s 1 current impinging on a 3500 seamount the results include the familiar anticyclonic vortex straddling the topograhy while a cyconic vortex propagates downgstream both advective and vorticity interaction effects are noted in the experiment with the extent of perturbations to the density field being influenced by variations in the mean flow speed and obstacle height possible modifications to the model are discussed in relation to obse

a fracture loop thermal balance model of black smoker circulation abstract this time dependent model examines the thermal balance between hot rocks and hydrothermal circulation during the formation of volcanogenic ore deposits in order to establish whether the major heat supply to black smoker systems comes from the rock or from an underlying magma chamber flow is modelled as an open thermosyphon in a single fault which is parallel and very close to the mid ocean ridge axis this configuration is based on seafloor and ophiolite evidence of black smoker systems and their structural location the fault is represented in the model by a series of pipes carrying turbulent flow which is driven by the buoyancy difference between upflow and downflow hydraulic resistance to flow is predominantly in the discharge zone the fault is allowed to propagate downwards the horizontal conductive heat flux from the rock is computed analytically with the water flow treated digitally so that the heat exchange at the rock water interface at every position in the loop can be calculated for each time step the model thus provides the exit water temperature and mass flow rate throughout the lifespan of a hot spring enabling the resulting ore mass to be estimated results show that this system cannot obtain sufficient heat from a thin layer of rock such as the 1 2 km thick layer of lavas and dykes overlying an axial magma chamber to sustain long lived ore forming black smokers if the circulation penetrates through a greater volume of hot rock to the base of a recently solidified magma chamber ore masses of a few million tonnes can be formed if conditions are particularly favourable we conclude that systems producing larger ore masses must tap a magmatic heat supply

reply to comment on an alternative view on the origin of chemical and isotopic patterns in groundwater from the milk river aquifer canada by m j hendry and f w schwartz

radiocarbon and stable isotopes in water and dissolved constituents milk river aquifer alberta canada abstract origin and age of groundwater in the milk river aquifer alberta canada was the focal point of the present study to answer related questions wells in this aquifer were sampled and 2 h and 18 o in water 13 c and 2 h in methane 34 s and 18 o in so 4 13 c and 14 c in dissolved inorganic carbon dic and dissolved organic carbon doc and tritium contents determined stable isotope analyses on ground water permitted the recognition of at least three different zones within the aquifer starting at the recharge zone modern type groundwaters are encountered for the first few kilometers these are followed by groundwater with slightly higher 18 o and 2 h contents i e waters which do not show a glacial signature and were probably recharged under warmer climatic conditions groundwater in the third zone is characterized by higher salinities and a pronounced oxygen isotope shift they show the gradual admixture of far more saline formation waters from the alberta basin sulphate s and sulphate o isotope values indicate a till source for the so 4 however so 4 in wells close to the area where so 4 virtually disappears show isotopic values which suggest that so 4 reduction is occurring although other studies could not find bacterial populations of so 4 reducers methane is present in most wells and based on c and h isotope data has a biogenic origin methane production occurs close to some wells and or it diffuses from the confining shales into the aquifer radiocarbon is measurable only in the first 20 km from the recharge zone however transformation of measured concentrations to water ages is very difficult because of the complexity of the geochemical system comparison with 14 c data on doc was therefore very interesting and this new technique may complement the dic radiocarbon dating two wells near the recharge zone yielded dic doc high molecular weight hmw and doc low molecular weight lmw results the dic dates were much older than doc dates but the differenve in years between the wells for all three types of c were within 1000 a of each other the doc dates led to the conclusion that the initial dic radiocarbon content was as low as 30 modern when the water entered the aquifer the age of the water 20 km from the recharge zone was assessed at 20 000 a resulting in a velocity of 1 m a this result is much higher than estimates by other techniques

the displacement of connate water from aquifers a mathematical model is developed for the mixing of meteoric and original formation waters in homogeneous aquifers the theoretical analysis indicates that geologic formations that have had a few to a few tens of pore volumes of meteoric water pass through them may be at steady state with respect to further displacement of their contained fluids depending on constraints in the recharge area the steady state may vary from near meteoric water throughout the whole formation to a spatial variation in concentration ranging from meteoric water in the recharge areas to highly concentrated water at the discharge ends of the system the former condition is attained when the recharge area incorporates the total depth and breadth of the formation where this condition is not satisfied the concentrations that evolve are controlled by the original concentration of the formation water the composition of recharging meteoric water the dispersion parameters and the size of the recharge area in comparison to the total breadth of the formation as measured along its strike for heterogeneous formations the concentration patterns that evolve seem to depend further on contrasts in hydraulic conductivity this is demonstrated in the milk river sandstone which is characterized by several extensive zones of dilute water within narrow high conductivity pathways and marked increases in concentration in adjacent lower permeability rock in parts of the aquifer where higher permeability pathways appear to be absent the isochlores form a broad linear band with a marked increase in concentration in the flow direction

on subinertial oscillations trapped by the juan de fuca ridge northeast pacific spectra of currents measured along the 2100 m deep juan de fuca ridge in the northeast pacific have prominent tidal inertial and weather band 3 7 day period spectral peaks the weather band peak in particular has a number of interesting features it is strongest in close lateral proximity to the ridge and strongest near ridge depth intensification near the ridge is characteristic of trapped motion spectral peak intensities vary seasonally with largest amplitudes occurring in autumn and winter seasonal variation suggests that surface weather is forcing flow at depth together trapping and seasonality indicate opportunistic amplification of oscillatory motion at the ridge at all frequencies forcing topography and stratification together shape current and hydrographic distributions near the ridge effects of those interactions for subinertial motion are quantified here using a primitive equation numerical model forcing period 1 10 days and friction are the principal dependencies examined results show that flow over the juan de fuca ridge can be amplified by factors of 3 4 for diurnal and up to a factor of 7 for weather band frequencies amplification is ridge trapped with effects extending many hundreds of meters upward and extending 5 10 km laterally for 5 day period flow the strength and area of amplification increase with increasing period over the 1 to 10 day period band oscillatory weather band flow leads to vertical velocities on the order of 0 3 cm s 1 on ridge flanks which in turn cause periodic temperature t and salinity s variations with amplitudes of as much as 0 05 c and 0 01 practical salinity units respectively the vertical motion and consequent vertical displacement 100 m lead to isotherms that plunge below the crest alternately each side of the ridge a distribution observed in conductivity temperature depth transect data near the ridge crest cross ridge baroclinic pressure gradients caused by cyclically plunging isopycnals are in near geostrophic balance with the coriolis force associated with along ridge flow along ridge current amplification is therefore closely tied to isopycnal movement up and down ridge flanks since weather band oscillations lead to much larger cross ridge baroclinic pressure gradients than do diurnal motions of the same amplitude weather band forcing causes greater along ridge current amplification results vary strongly with forcing period and direction of forcing with respect to the ridge but depend only moderately on friction and turbulent mixing coefficients

ammonoid habitats and habits in the western interior seaway a case study from the upper cretaceous bearpaw formation of southern alberta canada abstract multidisciplinary research on the habitats and life habits of ammonoids of the upper cretaceous bearpaw formation is based on hydrostatics and hydrodynamic aspects of shell shapes occurrence in lithofacies evidence of predation and stable isotopic data the large and well streamlined oxyconic placenticeras with large chitinous anaptychus had the weakest shells known and suffered mosasaur tooth perforations at minimal ambient pressure anomalously light 18 o signatures preserved in their aragonitic shells suggest that they grew in brachyhaline water juveniles and some adults of orthoconic baculites had a vertical life orientation and primarily resided in the lower to middle levels of the water column flourishing during oxygenation events some adults however may have changed to a mainly horizontal swimming habit in mid water attitudinal change is indicated by relative shortening of the body chamber during late ontogeny neutral buoyancy at maturity could have been achieved only with a partially liquid filled phragmocone implying the exceptional use of cameral liquid as an apical counterweight juvenile scaphitids were planktic or sluggishly nektic as implied by sphaeroconic and discoconic immature whorls respectively the adults had different habits as indicated by their strongly modified body chambers which gave high stability suited to vertical swimming adult hoploscaphites and most jeletzkytes with open hooked scaphitoconic body chambers were demersal and lived close to the sea floor during oxygenation events whereas adult rhaeboceras with an elliptical contracted body chamber elliptosphaerocone lived in mid water

decoupling of solutes and water in regional groundwater systems the murray basin australia documenting the origins residence times and movement of groundwater and the solutes that it contains is critical to understanding hydrogeological systems this study uses cl mass balance to determine the cl accession time i e the time required for cl to accumulate and cl to estimate the residence times of cl in the victorian portion of the murray basin southeast australia much of the murray basin contains saline groundwater with total dissolved solids tds concentrations commonly 14 000 mg l and locally up to 300 000 mg l the total mass of cl stored in the victorian portion of the basin is estimated as between 12 400 and 47 100 mt using present day rainfall totals and cl concentrations in rainfall the cl accession time is 170 to 650 ka aquifer thicknesses and groundwater salinity both increase westwards in this part of the murray basin consequently the cl accession times increase westward from 0 1 0 6 ka to 286 1080 ka by contrast c activities of the majority of the groundwater are 2 pmc and commonly much higher notwithstanding the difficulty in correcting c residence times the widespread occurrence of groundwater with above background c activities implies that groundwater residence times are generally 30 ka which is substantially shorter than the cl accession times rcl the ratio of cl to total cl 10 values of the groundwater are between 20 and 230 and are uncorrelated with cl concentrations while it is difficult to determine precise cl residence times the observation that the rcl values are significantly higher than those that represent secular equilibrium with the aquifer matrix rcl of 5 to 10 indicates that they are up to a few hundred thousand years and similar to the cl accession times the rcl values together with the geology of the aquifers stable isotope ratios and major ion geochemistry precludes halite dissolution incorporation of connate water or the long term diffusion of cl from clays as mechanisms of producing the elevated cl concentrations rather it is most likely that the high cl concentrations result from recycling of solutes in saline lakes and playas or repeated cycles of evapotranspiration in the unsaturated zone

the geochemistry and mixing of leakage in a semi confined aquifer at a municipal well field memphis tennessee usa abstract the memphis aquifer in southwestern tennessee is confined to a semi confined unconsolidated sand aquifer and is the primary municipal water source in the memphis metropolitan area past studies have identified regions in the metropolitan area in which the overlying upper claiborne confining unit lacks significant clay and provides a hydraulic connection between the shallow aquifer and the memphis aquifer in this study major solute chemistry 3h and 3h 3he groundwater dating are used to investigate the extent and chemical effects of leakage through the confining unit to the memphis aquifer in the vicinity of a municipal well field the 3h 3he dates and geochemical modeling of the chemical data are used to constrain mixing fractions and the timing of modern recharge tritium activities of as much as 2 8 tu are observed in shallow production wells but deeper production wells have 3h activities that approach the detection limit trends in water chemistry indicate vertical mixing in the aquifer of shallow na so4 cl rich water and deeper ca mg hco3 rich water water chemistry does not vary consistently with seasonal pumping but 3h activity generally decreases during low use periods stable o and h isotopes show little variation and are not useful groundwater tracers for this study the 3h bearing na so4 cl rich water is interpreted to reflect recharge of modern water through the upper claiborne confining unit the 3h 3he dates from 5 production wells indicate modern recharge that infiltrated 15 20 a ago is present in the shallow production wells geologic data and hydrologic boundary conditions suggest that the most likely source for continued leakage is a nearby stream nonconnah creek geochemical reaction modeling using the netpath computer code suggests that proportions of shallow aquifer water leaking into the memphis aquifer range from 6 to 32 the 3h 3he dating and netpath modeling results correlate well suggesting that these complementary analytical tools provide an effective means to evaluate proportions of modern water leaking into semi confined aquifers these results also indicate a need to carefully consider connections between surface water and semi confined groundwater resources in wellhead protection programs

texture mineralogy and geochemistry of hydrothermally altered submarine volcanics recovered southeast of cheshire seamount western woodlark basin the western woodlark basin lies within a gold rich metallogenic province this area is characterized by detachment faults that record ongoing extension and act as major pathways for the circulation of hydrothermal fluids dredging from the flanks of a submarine ridge southeast of cheshire seamount western woodlark basin retrieved hydrothermally altered monomictic to polymictic crackle mosaic and chaotic breccias with at least 30 clasts n2 mmin diameter the precursor rocks are andesitic to rhyolitic in composition but have been intensely hydrothermally altered with about 90 of the volcanic glass replaced by secondaryminerals the breccias show five generations of quartz growth with the first being related to magmatic processes and the remaining four to alteration stages including silicification chloritization illitization sericitization albitization and sulfidation needle like crystals ofmordenite zeolite withmultiple growth centers growon the fourth generation of quartz notable textural variants in the breccias are vesicles perlitic cracks and zoned alteration halos that mantle the rims of clasts electron microprobe analyses on chlorite from breccia samples have identified clinochlore as the main chlorite type and indicate a formation temperature in the range of 210 304 c this and the elevated au as ag hg zn pb sb contents of a mineralized sample indicate hydrothermal alteration temperatures n200 c suggesting that these breccias may represent the upflow zone of a hydrothermal system and highlight the potential for seafloor massive sulfides in the area the breccias show elevated contents of immobile trace elements and lree as well as a depletion in ta and nb suggesting that the precursor rocks were formed in a rift related suprasubduction environment

the nature and significance of rift related near surface fissure fill networks in fractured carbonates below regional unconformities fissure fill networks are a widely recognized but relatively little described near surface phenomenon supplementary material appendix a is available at https doi org 10 6084 m9 figshare c 5023103

continental basinal origin of ore fluids from southwestern massif central fluorite veins albigeois france evidence from fluid inclusion and stable isotope analyses the most important fluorspar mining district in france is located in the palaeozoic basement of the albigeois in southwestern french massif central the massive fluorite is hosted within large e w striking fractures crosscutting cambro ordovician clastics associated with large zones of hypersilicified tectonic breccia which form the wall of the mined deposits fluid inclusion data for pre fluorite and fluorite stage fluids have salinities between 20 26 wt nacl equiv with homogenisation temperatures between 85 170 c furthermore low first ice melting temperatures around 50 c indicates the presence of significant cacl2 and possibly mgcl2 together with nacl calculated fluid 18o for pre fluorite quartz ranges from 9 1 to 5 2 with d between 55 to 64 placing the data directly on the present day meteoric water line fluorite stage fluids have 18o between 0 1 to 3 2 and d ranging from 53 to 75 indicating an interacted meteoric fluid origin combining the fluid inclusion and stable isotope data illustrates that the main fluorite depositing fluid has characteristics typical of a basinal brine the authors have no evidence that a magmatic system was involved in the deposit genesis the proposed model highlights that mineralisation was related to major mesozoic extensional events coinciding with the gradual opening of the atlantic and tethys oceans in order to account for the chemistry of the fluids and the siting of the deposits the authors postulate a genetic relationship with local continental evaporite bearing basins coincident with and controlled by the e w fractures

paleosol barometer indicates extreme fluctuations in atmospheric co2 across the cretaceous tertiary boundary we present an atmospheric p co 2 p is partial pressure curve showing extreme fluctuations for the interval between ca 77 and 63 ma in southern alberta canada using a paleosol barometer paleosol carbonate nodules micrite were collected from 40 bk horizons among 6 stratigraphic sections for stable carbon isotope analysis based on results from the study area declining atmospheric p co 2 from 1200 ppmv v is volume in the campanian to 780 ppmv in the maastrichtian correlates with late cretaceous climate cooling and falling sea level as documented in global records the remarkable rise in atmospheric p co 2 near 65 5 ma 1440 ppmv correlates with volcanic activity associated with the deccan traps rising sea level and warmer global climates the decline in atmospheric p co 2 760 ppmv at the cretaceous tertiary boundary and subsequent sharp rise into the danian 1000 ppmv occurred during static terrestrial temperatures and sea level this work provides compelling evidence that atmospheric p co 2 curves modeled for the phanerozoic do not offer the resolution needed to understand environmental conditions during catastrophic events in earth9s history

peloids in stratabound zn pb deposits and their genetic importance peloids from sediment hosted zn pb deposits in belgium ireland and poland are composed of zn calcite siderite smithsonite silica pyrite melnikovite sphalerite galena thiosulphates and zn as bearing limonite the size of peloids is between 7 and 60 m the core and the shell of peloids are composed of different minerals and the shell is usually coarsely crystalline peloids are present in collapse breccias of karst cavities stromatactis cavities debris flow breccias and fractures cross cutting carbonates hosting the mineralization in places peloids form a major microtexture of the sulfide mineralization peloids are cemented and replaced by sulfides organic acids extracted from sulfide peloids are composed of amido acids considered to be characteristic of bacterial origin the size and specific texture of peloids are independent of mineralogy location and age of the mineralization therefore the peloids disussed are considered as forms induced by bacterial activity rather than forms precipitated inorganically

the pb zn ag vein system at montevecchio ingurtosu southwestern sardinia italy a summary of previous knowledge and new mineralogical fluid inclusion and isotopic data abstract the montevecchio ingurtosu district sw sardinia was among the largest historical pb zn producers of italy with significant ag output and yields of metallic byproducts such as cd co cu bi sb ge in and ga despite this importance detailed descriptions of orebodies and mineral assemblages are surprisingly scarce and old here we summarize all previously available information and contribute new textural microchemical fluid inclusion and c o isotopic data deriving from a recent sampling of currently exposed orebodies mineralization occurs as steeply dipping veins extending for almost 20 km at the northern and western flanks of the variscan arbus pluton veins are hosted in phyllites of the arburese unit close to the thermometamorphic aureole ore enrichments range from massive to coarsely nodular stockwork and brecciated vein filling consists of siderite locally zn rich quartz sphalerite galena remarkably rich in micro inclusions with accessory chalcopyrite fahlore bournonite barite and ni co sulfarsenides vein assemblages may vary even within a single vein from sphalerite to galena dominated cu rich assemblages fahlore chalcopyrite were locally observed wallrock is affected by silicification sericitization and pyrite dissemination sphalerite shows a complex mineral chemistry with marked variations in fe 0 08 to 8 9 mol fes and in cd contents from 1 wt trace element analyses la icp ms document the presence of measurable amounts of ga ge in ag ni co tl and mo fahlore varies from the sb tetrahedrite and the as tennantite endmembers with ag rich compositions corresponding to sb endmembers the occurrence of cd rich tetrahedrite up to 14 5 wt is remarkable fluid inclusion studies on sphalerite and quartz are in agreement with previous literature data and indicate comparatively low in the range 90 130 c homogenization temperatures th and high salinities 14 to 25 equiv mass nacl both microthermometric data and sem eds analyses of decrepitated inclusions indicate the presence of ca and k beside na pressure correction to th is presumably low in the order of 10 c considering a hydrostatic pressure regime application of the sphalerite based ggimfis thermometer provided temperatures in excellent agreement with fluid inclusion data for the montevecchio mineralization isotopic data on montevecchio carbonates define mildy negative 13cpdb values between 1 and 5 per mil and a larger spread of 18osmow values between 14 and 20 per mil other isotopic data from literature include a limited set of 34s values for galena sphalerite and pyrite and a fairly large body of pb isotopic data on galena comparatively narrow ranges for sulfur isotope signatures suggest a homogeneous possibly igneous sulfur source whereas the large spread in pb isotope signatures reflects the large scale character of the hydrothermal process and indicates that the arbus pluton may have been just one of the sources of ore lead the montevecchio vein system shows affinities with other late to post variscan european deposits the nature of the mineralizing fluids at montevecchio is analogous to low temperature basinal brines and typical of several regional scale late to post variscan hydrothermal events across europe mineralization at montevecchio obviously postdates the emplacement of the arbus plutonic complex but its exact age remains unknown

repeated reactivation of clogged permeable pathways in epithermal gold deposits kestanelik epithermal vein system nw turkey this study presents a detailed study of the dimensions geometry textures and breccias of a well exposed epithermal vein system the kestanelik gold deposit in the biga peninsula nw turkey and investigates the permeability enhancement mechanisms in epithermal gold deposits here mineralization is associated with quartz veins up to 13 6 m thick vein textures and breccia components indicate repeated sealing and subsequent brecciation of wall rock and pre existing vein infill field and petrographic analyses characterize east west trending veins as left lateral faults whereas ne sw trending veins are extensional mode i fractures cataclasite and tectonic breccia of wall rocks and early quartz hydrothermal crackle breccias and matrix supported chaotic breccias of pre existing vein infill all of which are cemented by late iron oxide bearing quartz indicate that co seismic rupturing and hydraulic fracturing are two major permeability enhancement mechanisms in addition transient variations in local stress direction caused by syn mineralization dyke intrusion may have enhanced permeability on misoriented surfaces and at locations where the dip changes this study emphasizes the importance of understanding structural geology and kinematics as controls on the location of boiling and mineralization mechanisms in epithermal gold deposits

breccia formation by particle fluidization in fault zones implications for transitory rupture controlled fluid flow regimes in hydrothermal systems breccias in the rusey fault cornwall uk and the roamane fault porgera gold deposit papua new guinea provide insights about the dynamics of fluid flow and flow velocities when fault ruptures breach overpressured reservoirs of hydrothermal fluid these faults contain cockade like breccias in which rock fragments are mantled by spheroidal overgrowths of hydrothermal minerals at rusey the overgrowths are quartz dominant whereas in the roamane fault overgrowths are composed of calcite quartz or gold rich pyrite although none of the rock fragment cores of accretionary spheroids are in contact with their neighbours the spheroidal overgrowths do contact each other and are at least partially cemented together the hydrothermal overgrowths mostly comprise either outwards coarsening crystals that radiate from the surface of the core rock fragment or finer grained inequigranular to mesh like intergrowths concentric textural banding and oscillatory growth zones are present in some hydrothermal mantles the breccias occur as fault parallel layers and lenses each up to several tens of centimeters thick adjacent layers are characterized by texturally distinct ranges of clast sizes and different proportions of clasts to hydrothermal overgrowths in the rusey fault many texturally distinct breccia layers are present within a 3m wide fault core some layers truncate others and many breccia layers exhibit grainsize grading or banding clasts in the breccias include fragments of wall rock veins and various fault damage products including fragments of earlier generations of cemented breccia brecciation was episodic and separated by periods of cementation the distinctive textures of the breccias are interpreted to have formed by fluidization of fault damage products in a high fluid flux regime hydrothermal coatings developed while clasts were in a suspended state during fluid ascent through dilatant fault segments layered breccias record multiple episodes of particle fluidization and indicate that the faults provided conduits for repeated transitory fluid upflow particle size distributions indicate that fluid velocities during fluidization were in the range 0 1 ms 1 to 1 ms 1 the maximum flow rates correspond to fluid fluxes of 10 to 100 l s 1 per meter strike length of fault through dilatant fault apertures up to several tens of centimeters wide such high flow rates characteristically induce intense swarm seismicity rather than mainshock aftershock seismicity and have implications for the dynamics and rates of formation of fault related hydrothermal ore deposits

the bow city structure southern alberta canada the deep roots of a complex impact structure geological and geophysical evidence is presented for a newly discovered probable remnant complex impact structure the structure located near bow city southern alberta has no obvious morphological expression at surface the geometry of the structure in the shallow subsurface mapped using downhole geophysical well logs is a semicircular structural depression approximately 8 km in diameter with a semicircular uplifted central region detailed subsurface mapping revealed evidence of localized duplication of stratigraphic section in the central uplift area and omission of strata within the surrounding annular region field mapping of outcrop confirmed an inlier of older rocks present within the center of the structure evidence of deformation along the eastern margin of the central uplift includes thrust faulting folding and steeply dipping bedding normal faults were mapped along the northern margin of the annular region isopach maps reveal that structural thickening and thinning were accommodated primarily within the belly river group evidence from legacy 2 d seismic data is consistent with the subsurface mapping and reveals additional insight into the geometry of the structure including a series of listric normal faults in the annular region and complex faulting within the central uplift the absence of any ejecta blanket breccia suevite or melt sheet based on available data is consistent with the bow city structure being the remnant of a deeply eroded complex impact structure accordingly the bow city structure may provide rare access and insight into zones of deformation remaining beneath an excavated transient crater in stratified siliciclastic target rocks

intermediate sulfidation epithermal gold base metal deposits in tertiary subaerial volcanic rocks sahinli tespih dere lapseki western turkey abstract gold in the sahinli and tespih dere intermediate sulfidation gold base metal deposits in western turkey occurs in relatively deep epithermal quartz veins along with base metal minerals which have epithermal textures including plumose quartz vug infills comb and cockade textures and matrix supported milled breccias the total sulfide content of the veins in the area is variable ranging from fluid inclusions in main stage quartz at sahinli are only liquid rich with homogenization temperatures ranging from 220 to 322 c and the majority of th values between 250 and 300 c salinity ranges from 4 3 to 6 9 wt nacl equiv first ice melting temperatures tmf between 24 5 and 19 0 c indicate that the fluids were dominated by nacl h2o during mineralization the relatively higher average th at the tespih dere deposit 295 c is attributed to a relatively deeper level of exposure calculated 18o values indicate that ore forming hydrothermal fluids in the study area had 18oh2o ranging from 1 1 to 9 7 average 3 8 strongly 18o enriched compared with present day hydrothermal meteoric water in the area 18o 8 5 d values of fluid inclusions in quartz range from 58 to 93 and d values of clay minerals and alunite from 40 to 119 d values from intermediate argillic alteration average 68 in the study area are very similar to d values of the present day local geothermal system average d 54 whereas d values from advanced argillic alteration average d 33 are very different from the present day local geothermal system the 34s values in samples from the sahinli and tespih dere deposits average 2 9 for pyrite 3 3 for chalcopyrite 5 4 for sphalerite and 7 6 for galena these data are consistent with derivation of the sulfur from either igneous rocks or possibly from local wallrock

multistage evolution of the calera epithermal ag au vein system orcopampa district southern peru first results in the orcopampa district southern peru the calera vein and its splits comprise a complex multistage epithermal fissure vein system of early miocene age hosted by slightly older silicic and intermediate volcanic rocks the several veins of the district are hosted by normal faults that strike n 45 degrees e to east west the calera vein system is the largest and economically most important yet discovered in the district produced ore and reserves contain over 40 million ounces of silver and 0 4 million ounces of gold five paragenetic stages as well as multiple episodes of fracturing faulting and hydrothermal brecciation are recognized the early stage is defined by quartz or adularia or sericite or pyrite altered wall rock and by mineralogically similar veinlets altered wall rock rich in adularia borders the vein at depth and yields laterally to sericite rich rock within a few meters of the vein whereas altered wall rock with abundant sericite borders the vein in upper levels early stage material is cut and brecciated by several substages of the mn stage which are characterized by abundant rhodonite and rhodochrosite containing bands composed largely of sphalerite and other sulfide minerals or tetrahedrite rich ores contain 10 2 to 10 3 ppm te mainly in hessite ag 2 te the mn stage is followed by two quartz rich substages the second substage contains tetrahedrite this quartz stage is in turn succeeded by the bonanza stage which contains native gold miargyrite pyrargyrite and several other silver sulfosalts and precious and base metal tellurides in quartz gangue this stage contains about 50 percent of the precious metal values of the calera system late quartz and sphalerite galena veins with barite marcasite and stibnite and hydrothermal breccia dikes of the late stage are volumetrically minor ore shoots typically occur in zones of intense fracturing indicated by abundant stockwork veins and vein splits based on the form and zoning of the west plunging main ore shoot ore forming fluids appear to have moved diagonally upward several superimposed stages have different distributions within the main ore shoot the mn stage is better developed at depth and the quartz stage is dominant in upper levels the au rich ores of the bonanza stage are found preferentially in a zone of intersection of vein splits that appears to have controlled fluid flow mineralization throughout the district is very similar the bonanza stage however has been identified only in the calera vein the paragenetic sequence has resulted from a series of progressively evolving hydrothermal fluids initial abundant rhodonite is replaced by rhodochrosite and eventually by quartz as the dominant gangue mineral the base metal sulfide and tetrahedrite bands must have formed from compositionally very different hydrothermal fluids the bonanza stage also represents a distinct fluid with much lower ag au relatively high a te a s and low manganese content the close spatial and temporal association with dacite dikes and flows the relatively high te content of the ores and the high a te a s ratios implied by some of the phase assemblages suggest the involvement of deep seated hydrothermal fluids

magnesite deposits and occurrences in the west carpathians of czecho slovakia abstract magnesite occurrences in the west carpathians a part of the alpine orogenic system have been known since the second half of the 19th century they are hosted by cambrian silurian devonian carboniferous permian lower and upper triassic sedimentary units economically most important are crystalline magnesite veitsch type and locally associated talc in the devonian sequence of the veporides and in the caboniferous of the gemerides yearly production 2 3 million tonnes traditionally the slovak magnesite deposits had been interpreted as hydrothermal metasomatic related to magmatically derived fluids more recently a sedimentary diagenetic origin of the magnesite with mg derived in full or in part from the contemporaneous submarine basaltic volcanism is considered more probable after deposition and diagenesis the magnesites and their host rocks were metamorphosed in greenschist carboniferous of the gemerides to amphibolite devonian of the veporides facies

widespread basement erosion during the late paleocene early eocene in the laramide rocky mountains inferred from 87sr 86sr ratios of freshwater bivalve fossils reconstruction of the timing and pattern of exhumation of basement involved uplifts during the laramide is essential to the understanding of the mechanisms of crustal shortening and thickening in the region we use reconstructions of the 87 sr 86 sr ratios of late cretaceous early cenozoic river water from fossil shells in six basins of the rocky mountains contextualized by modern river water sr chemistry studies to trace the erosion of precambrian basement cores in the laramide ranges the 87 sr 86 sr ratios and sr concentration of modern river water in the rocky mountains are controlled by river bedrock lithology weathering of precambrian silicate rocks in the cores of laramide ranges produces high 87 sr 86 sr ratios in highland rivers weathering of paleozoic and mesozoic carbonates along the basin margins reduces the 87 sr 86 sr ratios and increases sr concentration of rivers as they flow basinward lowland rivers that have headwaters in precambrian basement mostly have 87 sr 86 sr ratios 0 711 whereas rivers confined to or with very long reaches in basins have 87 sr 86 sr ratios between 0 709 and 0 711 river water 18 o values do not change in response to changes in catchment elevation our results from fossil shells show that carbonate weathering dominated the river water sr chemistry in the alberta foreland williston and crazy mountains basins and that proterozoic low grade metamorphic carbonates in the belt purcell supergroup were not exposed in the canadian rocky mountains during late cretaceous early paleocene time silicate weathering influenced the sr chemistry of surface waters in the powder river basin during the late paleocene and the washakie basin during the early eocene suggesting precambrian silicate basement rock was extensively exhumed and eroded the observation that precambrian basement was eroded earlier around the powder river basin than around the washakie basin is consistent with a previous study that suggests laramide ranges in northeast wyoming reached high elevation earlier than the ranges adjacent to the sevier thrust belt widespread basement erosion in late paleocene early eocene time was controlled by tectonic exhumation and may have been intensified by the wet and warm global climate

flow rates in the axial hot springs of the east pacific rise 21 n implications for the heat budget and the formation of massive sulfide deposits abstract the first in situ measurements of flow rates in submarine hot springs temperatures between 275 and 350 c were made in the hot springs of the east pacific rise at 21 n during november 1981 the flow rates ranged between 0 7 and 2 4 m s we estimate that the total rates at which heat and mass are transported from the three hot spring areas obs national geographic and southwest vents are ca 2 2 108 w and 150 kg of fluid s respectively the very high rate of heat loss precludes the existence of hot springs as steady state features of the east pacific rise at 21 n we estimate that hot springs are active for a maximum of ca 40 000 years chemical and or mechanical clogging of the vents can drastically reduce the lifetime of the hot springs using a simple model of plume development 1 we calculated that less than 3 of the sulfide particles that are entrained in the hydrothermal plumes at 21 n settle from the plumes before dispersal by a lateral submarine current at a height of ca 250 m above the seafloor 2 the time that is required to form the sulfide mounds that surround the hot springs by the accumulation of sulfide particles that settle from the plumes is ca 70 85 years the current rate at which sulfide particles settle from the hydrothermal plumes and accumulate near the hot springs appears to be too small to lead to the formation of large massive sulfide deposits such as the mavrouni deposit on cyprus 3 within the time limits that are suggested by our thermal energy balance calculations

a new crocodylian archosauria from the basal paleocene of the red deer river valley southern alberta borealosuchus griffithi sp nov is described on the basis of an incomplete skeleton from the basal paleocene southern alberta this new species records one of a few basal cenozoic occurrences o

macrofossil magnetobiostratigraphy for the upper santonian lower campanian interval in the western interior of north america comparisons with european stage boundaries and planktonic foraminiferal zonal boundaries magnetostratigraphic samples were collected from the milk river and pakowki formations of southeastern alberta to determine the polarity chron 34 33r boundary this boundary was located in the upper half of the deadhorse coulee member and is below the first local occurrence of the western interior ammonite baculites obtusus comparison with the laterally equivalent eagle sandstone of montana and niobrara formation of colorado indicates that the 34 33r contact is within either the baculites sp smooth or baculites sp weak flank ribs ammonite zone in the western interior of north america direct correlation of the desmoscaphites erdmanni through baculites asperifomis western interior ammonite zones with magnetobiostratigraphic sections of the upper santonian lower campanian stages in europe suggests that i the santonian campanian boundary as defined in europe is within the lower baculites obtusus zone and ii the western interior appearance of some ammonites and crinoids scaphites hippocrepis trachyscaphites spiniger marsupites uintacrinus is profoundly time transgressive relative to the appearance of these same species in europe the date of 84 ma for the santonian campanian boundary is too old and a date of around 80 ma may be more accurate the santonian campanian boundary defined by ammonites crinoids and belemnites in europe is within the lower part of chron 33r and is younger than the santonian campanian boundary as determined by planktonic foraminifera at gubbio italy

a multidisciplinary study of invisible gold in arsenopyrite from four mesothermal gold deposits in siberia russian federation characterization of gold in four siberian mesothermal gold deposits was done through a multidisciplinary investigation including ore microscopy inaa sims epma and 197 au moessbauer spectroscopy the deposits are olympiada and veduga in the enisei mountain range and nezhdaninskoye and sentachan in the verkhoyansk kolyma area in which vein and disseminated orebodies are hosted by sedimentary sequences metamorphosed to amphibolite olympiada and greenschist facies ore minerals include arsenopyrite and pyrrhotite or pyrite as major constituents with minor scheelite and sphalerite chalcopyrite and native gold as minor constituents with or aurostibite galena gudmundite tetrahedrite stibnite and berthierite some of the gold mineralization is metallurgically refractory in all four deposits largely due to the presence of invisible gold in arsenopyrite and to a lesser extent in pyrite several generations of arsenopyrite are recognized in the auriferous zones of the veduga nezhdaninskoye and sentachan deposits textural observations indicate late deposition of native gold with respect to arsenopyrite no evidence was found of arsenopyrite recrystallization and the crystallization of native gold is considered to result from an evolution of fluids rather than redeposition of gold wide variations in the gold contents of arsenopyrite occur within deposits within samples and within individual grains inna analyses of individual arsenopyrite grains 30 70 mu m in size show that the gold concentration ranges from 197 au moessbauer spectra of arsenopyrite concentrates from the veduga nezhdaninskoye and sentachan deposits exhibit mainly a component with isomer shifts between 3 3 and 3 6 mm s which is interpreted as strong evidence of the presence of chemically bound gold in the arsenopyrite crystal structure the spectra of samples from the veduga deposit also contain minor amounts of native gold for which negative isomer shifts near 1 2 mm s are expected metallic gold dominates in the 197 au moessbauer spectra of samples from the olympiada deposit but varying amounts of chemically bound gold are also visible in the spectra some attributed to aurostibite it is concluded that the ores from these deposits are refractory partly because the gold occurs in arsenopyrite as chemically bound gold as well as submicroscopic metallic particles probably as small as 2 nm this study also shows that au bearing arsenopyrite is usually depleted in as with respect to its stoichiometric composition but correlation of au enrichment to fe deficiency was not found it is inferred from 197 au moessbauer spectroscopy that substitution of fe super 3 for au super 3 is most likely the temporal change in different modes of gold occurrence i e as native gold or invisibly in sulfides in the mineralized zones and veins is interpreted to result from an evolution of fluids rather than to be a recrystallization phenomenon dissemination of au bearing sulfides within the altered halos infers that a pervasive fluid rock interaction was an effective mechanism for deposition of minerals and gold absorption of gold complexes onto sulfide surfaces is also suggested to have played an important role in the deposition of native gold during the latest episodes in the formation of the deposits

the nature and age of basement host rocks and fissure fills in the lancaster field fractured reservoir west of shetland hosting up to 3 3 billion barrels of oil in place the upfaulted precambrian crystalline rocks of the lancaster field offshore west of shetland give key insights into how fractured hydrocarbon reservoirs can form in such old rocks the neoarchean c 2700 2740 ma charnockitic basement is cut by deeply penetrating oil mineral and sediment filled fissure systems seen in geophysical and production logs and thin sections of core mineral textures and fluid inclusion geothermometry suggest that a low temperature supplementary material analytical methods and isotopic compositions and ages are available at https doi org 10 6084 m9 figshare c 4763237 thematic collection this article is part of the geology of fractured reservoirs collection available at https www lyellcollection org cc the geology of fractured reservoirs

tectonic stratigraphic and sedimentologic significance of a regional discontinuity in the upper judith river group belly river wedge of southern alberta saskatchewan and northern montana the lithostratigraphic interval between the taber and lethbridge coal zones in the upper portion of the nonmarine judith river group of southeastern alberta is divisible into two lithostratigraphic units separated by a regionally extensive and diachronous discontinuity the lower unit referred to here as the oldman formation is characterized by very fine grained to fine grained sandstones that contain fewer than 2 volcanic rock fragments sandstone bodies with numerous sets of horizontally stratified sandstone showing little or no evidence of lateral accretion siliceous paleosols ganisters and a relatively high gamma ray signal in the upper half of the formation the oldman formation comprises deposits of a low sinuosity perhaps ephemeral fluvial system that originated in the southern cordillera of canada and northern montana and flowed northeastward perpendicular to the axis of the alberta basin the upper unit is assigned to a new formation the dinosaur park formation and is characterized by

chlorine 36 dating of very old groundwater 2 milk river aquifer alberta canada the milk river aquifer in southern alberta canada consists of sandstone interbedded between thick shale units the groundwater is confined and discharges by both upward and downward leakage through the shales the concentration of cl increases by about 2 orders of magnitude downgradient through the aquifer this cl increase complicates 36cl dating of the system climatic changes flushing of connate water introduction of cl from older water below the aquifer and ion filtration have been proposed as possible explanations for the increase the 36cl data show a consistent decrease of the 36cl cl ratio downgradient but an increase in the 36cl concentration downgradient in certain parts of the aquifer dates calculated from the 36cl cl ratio show a reasonable distribution in light of the hydraulic controls on the system whereas dates calculated from the 36cl concentration give negative ages this suggests that ion filtration is responsible for the cl increase and that the 36cl cl dates are to be preferred we estimate water ages to be more than 2 m y near the distal end of the aquifer

provenance of upper cretaceous paleogene sandstones in the foreland basin system of the sierra madre oriental northeastern mexico and its bearing on fluvial dispersal systems of the mexican laramide province sandstone petrography and detrital zircon u pb analysis of upper cretaceous paleogene sandstones in the foreland basin of the sierra madre oriental in northeastern mexico indicate long distance sediment transport from arc basement and thrust belt sources lying to the west northwest and south the basin fill termed the difunta group consists of sublitharenites litharenites feldspathic litharenites and lithic arkoses derived from mixed sources that included sedimentary rocks magmatic arc rocks and subordinate basement rocks six age populations comprise the detrital zircon content of the sandstones proterozoic 1900 900 ma early paleozoic 500 400 ma late paleozoic early triassic 288 235 ma jurassic 180 151 ma early cretaceous 150 111 ma and late cretaceous paleogene 110 54 ma these grains were derived from several arc terranes ranging in age from permian to paleogene in western mexico and the southwestern united states from sedimentary rocks and possibly interbedded tuffs of the sierra madre oriental orogen and from basement sources or their derivative sandstones of the southwestern united states the petrographic and geochronologic provenance data corroborate existing models for derivation of much foreland detritus from arc sources to the west identify the sierra madre orogen itself as an important source for sediment and these data modify the late cretaceous paleogene paleogeography of mexico to include a long orogen parallel fluvial system with headwaters in the southwestern united states the difference in average ages of the youngest grains in the sandstones and their inferred depositional ages is 10 5 m y indicating that the initial coarse fill of the foreland basin was derived from early laramide uplift and eastward arc migration in northwestern mexico and the southwestern united states

fluid evolution in the baia mare epithermal gold polymetallic district inner carpathians romania the baia mare district romania represents a complex segment of the neogene quaternary subduction related volcanic chain of the carpathians in this province the calc alkaline volcanism and associated mineralization are closely related to a major strike slip fault and an underlying pluton the ore deposits of the district have many features typical of low sulfidation or adularia sericite epithermal deposits the combination of fluid inclusion microthermometry raman spectroscopy bulk crush leach analysis laser ablation optical emission spectrometry la oes of individual fluid inclusions and stable isotope data has been used to characterize the ore forming solutions involved with gold polymetallic mineralization in three of the largest deposits ore fluids at baia sprie cavnic and sasar deposits had temperatures of 320 to 150 c and salinities in the range 0 21 wt nacl equiv during phreatomagmatic activity fracturing and periods of vein dilation the pressure fluctuations may have caused boiling the hydrothermal fluids were na k li ca chloride solutions with lesser amounts of so4 and f the na k ratios and the stable isotope compositions are consistent with equilibration of the fluids with country rocks at progressively lower temperatures the halogen ratios br cl 103 in the range 0 13 1 21 together with sulfur isotopic systematics 34s 0 3 5 2 per mil are consistent with a dominantly magmatic origin of the solutes and probably of the ore fluids themselves

multi stage fluid incursion in the palaeozoic basement hosted saint salvy ore deposit nw montagne noire southern france abstract the saint salvy vein hosted zn ge deposit occurs in an e w fault system which flanks the southern margin of the late variscan sidobre granite and cross cuts cambrian black shales of the palaeozoic basement comprehensive mineralogical and geochemical studies of vein samples have revealed four mineralizing events m1 m4 related to late and post variscan tectonic events a further late stage event may be related to weathering m1 skarn deposits and m2 patchily mineralized quartz veinlets are associated with granite emplacement quartz contains low salinity h2o co2 nacl dominated fluids 6wt nacl equiv of relatively high temperature 300 580 c trapped under moderate to high pressure estimated m1 fluid d and calculated fluid 18o plot within the metamorphic water field there appears to be no involvement of magmatic fluids by contrast m3 barren quartz and m4 zinciferous economic mineralization stages have h2o co2 nacl cacl2 fluid inclusions with high salinities 23 25 wt nacl equiv and low temperatures 80 140 c which were trapped under low pressure conditions the high salinity and nacl cacl2 content of both m3 and m4 indicates that their parent fluids leached evaporitic salts m3 fluids are meteoric water dominated falling close to the meteoric water line d and 18o averaging 64 and 8 respectively m4 fluids have highly distinctive d averaging 101 and calculated fluid 18o varying from 1 2to 7 1 the unusually low d composition of m4 suggests the involvement of organic fluids in which h is derived directly or indirectly from organic matter the relatively high 18o of m4 fluids indicates that considerable isotopic exchange with sedimentary material took place displacing the 18o from the meteoric water line the data imply interaction of meteoric waters with evaporite and hydrocarbon bearing sedimentary sequences most probably the adjacent aquitain basin the main economic mineralization m4 stage took place during a tensional event probably coincident with the lias dogger transition calculated 34sh2s of m4 sulphide 5 4to 8 2 is almost identical to 34s of local cambrian sulphides 4 7to 9 4 suggesting a genetic link abundant siderite associated with m4 sphalerite has 13c ranging from 2 6to 4 4 indicating that carbon was sourced from sedimentary carbonate mobilized by or equilibrated with the hydrothermal fluid late stage sulphides exhibit extraordinary and highly distinctive 34s sphalerite has extremely low 34s 42 5to 50 5 whereas pyrite has an extraordinary large range from 33 2 to 74 3 closed system sulphate reduction is held to be responsible for the extremely high 34s whereas more open system reduction produces the very low values the coincidence of isotopically low 13c 7 6to 11 9 for co genetic calcite suggests the involvement of organic matter in the reduction process

oxygen isotope evidence for high altitude snow in the laramide rocky mountains of north america during the late cretaceous and paleogene the 18 o values of river waters in late cretaceous and paleogene basins of alberta montana wyoming and colorado are calculated from the isotopic composition of unaltered aragonite mollusk fossils the isotopic composition of these river waters has significant implications for the uplift and climate history of the mountains surrounding the basins our data show that the 18 o values of river water varied dramatically ranging from 23 to 5 relative to vienna standard mean ocean water with an uncertainty of 2 close stratigraphic association of river deposits with very different isotopic values indicates two different water sources rainfall in the warm low elevation basins and snowfall in surrounding mountains the 18 o difference between basinal and highland precipitation suggests that local relief was similar to today9s on the order of 2 5 3 km seasonal variation in shell 18 o values also indicates that there are times when large snow fields in the maastrichtian and paleocene mountains of montana and wyoming survived summer melting and were multiannual features

the archean lode gold deposits at wiluna western australia high level brittle style mineralization in a strike slip regime the wiluna lode hosted gold deposits comprise a group of individual archean lode hosted gold deposits located in the northern part of the norseman wiluna belt western australia collectively they are the fifth largest gold producer in the yilgarn block the deposits are hosted in a series of very low grade metamorphosed prehnite pumpellyite facies mafic and ultramafic lava flows with abundant primary igneous textures preserved lode hosted gold mineralization is controlled by the wiluna strike slip fault system which consists of north and northeast trending and west and east dipping sets of principal displacement faults and associated subsidiary structures the movement on all faults was dextral with minor oblique reverse or oblique normal motion and maximum apparent displacement of 1 350 m the lode deposits are centered on structural inhomogeneities in the principal displacement faults e g divergent bends and dilational jogs including horsetail splays and or subsidiary structures e g overstepping and intersecting faults the plunge of the ore shoots is generally moderately to steeply to the south and is controlled by the intersections between 1 lithologic layering and fault planes 2 two or more fault planes 3 a fault plane and an earlier formed barren or weakly mineralized quartz reef that is semiconcordant to the regional stratigraphy and 4 a fault plane and a felsic intrusion the shape and orientation of ore shoots becomes more complex downdip where they are controlled by additional features such as drag folds and link structures fault hosted ore breccias including implosion and net veined breccias and brecciated veins are significant loci of gold mineralization in all lode deposits they contain mainly quartz chalcedony carbonates fuchsite and arsenopyrite pyrite and or stibnite mineralization occurs also in shear veins and extensional veins and finely disseminated along foliation planes of the mineral fabric formed oblique to the principal displacement faults textures of implosion breccias at wiluna indicate a history of incremental extensional opening across dilational sites and multiple episodes of brecciation and hydrothermal recementation quartz textures such as vugs cavities comb textures and cockade textured quartz are ubiquitous indicating the preservation of open space due to low effective confining pressure geologic relations indicate that the mineralized strike slip fault system was generated late in the tectonic history of the greenstone belt and that high grade ore zones formed late in the strike slip deformation event the very low grade metamorphic facies and the brittle style of deformation in the host rocks combined with the style of mineralization indicate that the fault and mineralizing system formed in a shallow near surface crustal environment textural evidence combined with the tectonic setting of the lode deposits favors the suction pump mechanism as a fluid infiltration mechanism for the lode hosted gold deposits within the wiluna strike slip fault system