the mesoproterozoic copperwood sedimentary rock hosted stratiform copper deposit upper peninsula michigan copperwood is located in gogebic county upper peninsula michigan within the porcupine mountains copper district it was discovered in 1956 and in 2008 orvana minerals corp began exploration and development work with production projected in the near future stratiform copper mineralization is hosted by gray to black shales and siltstones of the basal nonesuch formation copper mineralization is overlain by laminated gray siltstones of the nonesuch formation and is underlain by red bed sandstones conglomerates and minor siltstones of the copper harbor formation these rocks are part of a thick section of clastic sedimentary rocks that comprise the upper fill of the mesoproterozoic 1 1 1 0 ga midcontinent rift the copper deposit is a tabular body that averages 2 5 m thick lacks significant basal undulations and dips 8 to 12 northward on the southwest limb of the western syncline an open fold with a shallow plunge to the northwest chalcocite is the only cu bearing mineral in the orebody and occurs as concentrations along stratigraphic laminations and as disseminated grains within the orebody there is no mineral or metal zoning cu ag and s are strongly enriched zn is very slightly enriched and pb and co lack enrichment gangue minerals in the orebody are quartz clinochore muscovite illite plagioclase k feldspar calcite and hematite which are consistent with temperatures of less than 130 c only one significant fault a shallow nw dipping reverse fault with displacement of up to 7 m has disturbed the section the mineralized zone at copperwood is stratigraphically equivalent to that at the white pine mine but copperwood lacks the structural complexity and the hydrothermal overprint manifested by the native cu mineralization at white pine reported canadian national instrument 43 101 compliant measured indicated and inferred resources are 33 million metric tonnes mt of 1 60 cu and 4 1 ppm ag for total contained cu of about 1 165 billion lb and 4 32 moz of ag the characteristics of copperwood are consistent with those of reduced facies or kupferschiefer type sedimentary rock hosted stratiform copper deposits the proposed genetic model is chalcocite replacement of pyrite in unlithified sediments during diagenesis as a result of emanating upward focused compaction driven cu bearing saline basinal waters with cu leached from the underlying red bed paleoquifer the simplicity of the mineralizing event and the undeformed nature of the deposit distinguish copperwood from most other examples of reduced facies or kupferschiefer type sedimentary rock hosted stratiform copper deposits throughout the world

hematite u th he thermochronometry constrains intraplate strike slip faulting on the kuh e faghan fault central iran abstract the kuh e faghan strike slip fault system kff located to the northern edge of the lut block in central iran developed through a neogene quaternary pulsed history of eastward fault propagation and fault related exhumation this system is a consequence of the residual stresses transmitted from the arabia eurasia convergent plate boundary here we integrate structural and textural analysis with new and previously published apatite fission track aft and apatite u th he apatite he results chlorite thermomentry and hematite u th he data from hematite coated brittle fault surfaces to constrain the timing of tectonic activity and refine patterns of late miocene pliocene burial and exhumation associated with the propagation of the kff twenty nine hematite u th he hematite he dates from three striated hematite coated slip surfaces from the kff fault core and damage zone yield individual dates from 12 2 ma petrographic analysis and chlorite thermometry of a polyphase fossil fluid system in the kff fault core document that fluid circulation and mineralization transitioned from a closed system characterized by pressure solution and calcite growth to an open system characterized by hot hydrothermal t 239 10 c fluids and hematite formation hematite microtextures and grain size analysis reveal primary and secondary syntectonic hematite fabrics no evidence of hematite comminution and similar hematite he closure temperatures 60 85 c in each sample integration of these results with thermal history modeling of aft and apatite he data shows that kff activity in the late miocene is characterized by an early stage of fault nucleation fluid circulation hematite mineralization and eastward propagation not associated with vertical movement that lasted from 12 to 7 ma hematite he aft and apatite he data track a second phase of fault system activity involving fault related exhumation initiating at 7 ma and continuing until present time our new data constrain the onset of the recognized late miocene pliocene tectonic reorganization in north central iran

u loss associated with laser heating of hematite and goethite in vacuum during u th he dating and prevention using high o2 partial pressure abstract single aliquot u th he dating of hematite has been used to study iron oxide precipitation in various environments but we show there is an important challenge to the method highly retentive hematite samples require temperatures of 1000 c to be completely degassed whereas the temperature for major u loss is 980 c this leads to erroneously high u th he ages through the analysis of u th and sm of hematite and goethite samples we establish the degree of u loss at this temperature and demonstrate that prolonged heating at temperatures of 950 c can lead to u loss we show that loss of u in goethite and hematite samples is associated with phase change from hematite to magnetite as fe is reduced the onset temperature of vacuum reduction of hematite can be increased from about 800 900 c in vacuum to approximately 1250 c in an oxygen partial pressure of 100 mbar we demonstrate that samples can be outgassed to extract helium at 1150 c without u loss in an o2 rich atmosphere during heating which does not increase the analytical blanks we describe our implementation and automation of the procedure an average age calculated on a reference hematite sample from replicate aliquots n 12 which were analyzed using this procedure has a relative uncertainty of 2 1 and is within uncertainty of the previously measured two aliquot age we suggest this o2 degassing procedure as a way to precisely and reproducibly determine single aliquot hematite and goethite u th he ages

isobar free neon isotope measurements of flux fused potential reference minerals on a helix mc plus mass spectrometer abstract this work presents new analytical techniques for extraction and analysis of neon from a suite of different mineral phases including quartz pyroxene hematite apatite zircon topaz and fluorite neon was quantitatively extracted at 1100 c from all of these minerals using an in vacuum lithium borate flux fusion technique evolved neon was purified using a cryogenic method capable of separating ne from he present in abundances 8 orders of magnitude higher typical of samples carrying nucleogenic radiogenic noble gases the purified neon was measured on a helix mc plus10k mass spectrometer that permits isobar free measurement of all three neon isotopes when operated at its highest mass resolving power mrp of 10 300 the shoulder representing solely 22ne on the low mass side of the 22ne co2 2 doublet is wide enough to permit measurement of isobar free 22ne operating in this mode comes with the penalty of a 50 reduction in neon sensitivity coupled with a mathematical isobar stripping method this approach excludes 99 5 of the co2 2 while still collecting 99 of the 22ne beam routine edge centering on the dynamic co2 2 peak prior to introduction of a sample permits rapid and robust relocation of the desired measure point in the mass spectrum cosmogenic 21ne and 22ne concentrations obtained using these methods on the cronus a quartz and cronus p pyroxene international reference materials are in excellent agreement with previous work or expectations similarly the concentration of nucleogenic 21ne and 22ne in durango apatite and the cit hematite standard agree well with previous work durango apatite has notable heterogeneity in neon concentrations consistent with previous observations of heterogeneous he u and th concentrations in this apatite nucleogenic neon concentrations are also presented for previously unstudied minerals including a sri lanka zircon slc a topaz from the imperial topaz mine in brazil itp1 and a fluorite w 90 from new hampshire taken together this set of potential reference minerals and the associated dataset provide a starting point for intercalibration among multiple mineral phases carrying 21ne and 22ne of cosmogenic or nucleogenic origin

the basis for earthquake prediction summary recent advances in understanding the behaviour of shear waves propagating in the crust make the routine prediction of earthquakes seem practicable accumulating evidence suggests that most of the earth s crust is pervaded by distributions of fluid filled cracks and microcracks that are aligned by the contemporary stress field so that the cracked rockmass is effectively anisotropic to seismic waves this causes shear waves to split and shear wave splitting is observed whenever shear waves propagating along suitable raypaths in the crust are recorded by three component instruments these distributions of cracks are known as extensive dilatancy anisotropy or eda many characteristics of the crack and stress geometry can be monitored by analyzing shear waves propagating through the cracked rockmass observations of temporal variations of the behaviour of shear wave splitting in seismic gaps confirm these hypotheses and suggest that stress changes before earthquakes may be monitored by analyzing shear waves in particular monitoring earthquake preparation zones with three component shear wave vertical seismic profiles could lead to techniques for the routine prediction of earthquakes

fe oxides in jasperoids from two gold districts in nevada characterization geochemistry and u th he dating abstract this study examines the whole rock geochemistry fe oxide texture and crystal morphology and fe oxide u th he date variation of jasperoids as well as the relationships between these characteristics in order to evaluate jasperoids as an indicator for gold mineralization jasperoid samples with a range of textures appearances and expected gold concentrations were collected from two gold districts in nevada the northern carlin trend gold quarry mine and the battle mountain district marigold mine battle mountain prospect in our jasperoid samples whole rock concentrations of au are positively correlated with as ag pb sb u w and tl the following fe oxide textures are associated with anomalous gold concentrations disseminated submicron crystals feathery and acicular crystal morphologies concentric zonation from hematite to goethite and botryoidal textures calculated closure temperatures for the u th he system in observed jasperoid fe oxide morphologies within our dataset range from 26 to 136 c indicating variable susceptibility to he diffusion at near surface conditions fe oxide u th he dates range from 29 4 0 5 ma to 0 11 0 01 ma displaying intra and intersample variation we attribute the date variation to multiple factors including he implantation parent isotope exchange and he loss through closure temperature sensitivity and alpha ejection the intra and intersample variation within the fe oxide u th he dates limits our ability to make geologic interpretations our case study identifies important limitations of the u th he method in jasperoids and provides insight on how he date variation might be avoided in future studies

hematite and mn oxide u th he dates from the buckskin rawhide detachment system western arizona gaining insights into hematite u th he systematics

strain variations across the proterozoic penokean orogen usa and canada abstract strata in the huron 2 5 2 0 ga and animikie 2 2 1 85 ga basins were deposited on the southern margin of the archean superior province these rocks were deformed during the penokean orogeny 1850 ma followed by subsequent accretionary orogens to the south at 1750 ma yavapai and 1630 ma mazatzal strain patterns are unique to each orogenic belt with no far field effect archean wawa terrane rocks in the penokean foreland preserve deformation associated with archean accretion with no younger penokean yavapai or mazatzal strain overprint the penokean orogeny deformed huron animikie basin sediments into a north vergent fold and thrust belt with no yavapai or mazatzal strain overprint yavapai orogen strains sw ne margin parallel shortening are unique when compared to the younger mazatzal shortening n20 w shortening with no strain overprint penokean deformation is characterized by shortening from the south including uplifted archean gneisses and a northerly thin skinned fold and thrust belt with north vergent nappes and a gently dipping foreland our study of finite and calcite twinning strains n 60 along 1500 km and across 200 km the penokean belt indicate that this orogeny was collisional as layer parallel shortening axes are parallel across the belt or parallel to the tectonic transport direction n s penokean nappe burial near the margin resulted in vertical shortening strain overprints some of which are layer normal the sudbury impact layer 1850 ma is found across the animikie basin and provides a widespread deformation marker with many local unique strain observations we also report new geochronology u pb zircon and apatite for the gneiss mafic dike rocks at wissota chippewa falls wi and arbutus black river falls wi dams respectively which bears on penokean yavapai deformation in the archean marshfield terrane which was accreted during the penokean orogen pseudotachylite formation was common in the superior province archean basement rocks especially along terrane boundaries reactivated by contemporaneous penokean trans hudson cape smith and new quebec deformation in the hinterland south the younger yavapai orogen 1750 ma n 8 deformation is preserved as margin parallel horizontal shortening sw ne in yavapai crust and up to 200 km to the north in the penokean thrust belt as a strain and barrovian metamorphic overprint mazatzal deformation 1630 ma n 16 is preserved in quartzites on yavapai and penokean crust with layer parallel and layer normal shortening strains oriented n20 w

u th ne and multidomain u th he systematics of a hydrothermal hematite from eastern grand canyon a hydrothermal hematite from the redwall limestone in eastern grand canyon arizona usa was analyzed for u th he and u th ne systematics the dense polycrystalline aggregate has u and th concentrations of 16 ppm each neon produced by particle capture on 18 o is abundant in the sample it constitutes 90 of total 21 ne and indicates a u th ne age of 217 5 ma this value provides a lower bound for the formation age of the sample but detailed interpretation is not possible given the current absence of neon diffusion data for hematite the 130 2 ma u th he age is much younger than the ne age and therefore must be a cooling age highly reproducible step heating he release experiments reveal the existence of a spectrum of diffusion domain sizes spanning about 3 orders of magnitude in radius corresponding to he closure temperatures ranging from 0 to 150 c these domains may correspond to crystallites in the specimen which are observed to range from smaller than a few nm to a few m 4he 3he age spectra acquired from the same experiments define a distinctive sigmoidal shape with step ages increasing monotonically from 0 to 210 ma this pattern clearly records the presence of the multiple domains as the hematite acquired its radiogenic helium coupling of the 4he 3he spectra and the diffusion data allow modeling of permissible time temperature paths experienced by the hematite these paths can be compared with independent thermal history reconstructions for eastern grand canyon characterized by 170 m yr of sedimentary burial followed by regional unroofing and canyon incision beginning at 80 ma the unroofing portion of the path inferred from the hematite is in good agreement with apatite u th he and fission track data the results permit rapid cooling in late cretaceous early tertiary time suggest a subsequent period of slow cooling through temperatures of 50 70 c with accelerated cooling ensuing after 20 ma in contrast the hematite data demand temperatures in some part s of the mesozoic that are at least 100 c hotter than expected based on burial depth estimates this may indicate that the sample experienced a reheating event associated with the passage of fluids similar to those observed at nearby mineralized breccia pipes overall these data provide motivation for further work to understand he and ne behavior in hematite and their potential use in thermochronometry

genesis of high grade hematite orebodies of the hamersley province western australia a reply sir we are very thankful for the constructive comments provided by kneeshaw and kepert unfortunately the competitive ownership structure of the iron ore mining industry in the hamersley province limits our personal knowledge of the mount whaleback deposit to occasional mine visits and to the available literature published and unpublished we do however have access to the data on the smaller giles mini and lido deposits 50 and 10 km west of mount whaleback respectively and to extensive exploration mapping in the ophthalmia ranges to the north direct proof for rotation of the orebody as it is preserved at paraburdoo in the approximately 50 dip of the overlying proterozoic hematite conglomerates of the mount mcgrath formation is not preserved at mount whaleback however we believe that there is sufficient information available in the literature to think that a rotational model for a large part of the deposit is perfectly plausible first and above all as stated in taylor et al 2001 f2 folds are more upright with axial planes dipping about 50 s in the southern and western part of the deposit away from the whaleback fault e g as shown on section no 315120e fig 4 in powell et al 1999 interestingly the ore controlling faults are also more upright in this part of the deposit which suggests an intimate link between the dip of these fault planes and dip of the axial planes of f2 folds secondly

sinkhole susceptibility mapping using the analytical hierarchy process ahp and magnitude frequency relationships a case study in hamadan province iran abstract since 1989 an increasing number of sinkhole occurrences have been reported in the kabudar ahang and razan qahavand subcatchments krq of hamadan province western iran the sinkhole related subsidence phenomenon poses a significant threat for people and human structures including sensitive facilities like the hamadan power plant groundwater over exploitation from the thick alluvial cover and the underlying cavernous limestone has been identified as the main factor involved in sinkhole development a sinkhole susceptibility model was produced in a gis environment applying the analytical hierarchy process ahp approach and considering a selection of eight factors each categorized into five classes distance to faults df water level decline wld groundwater exploitation ge penetration of deep wells into karst bedrock pka distance to deep wells ddw groundwater alkalinity ga bedrock lithology bl and alluvium thickness at relative weights were preliminarily assigned to each factor and to their different classes through systematic pairwise comparisons based on expert judgment the resulting sinkhole susceptibility index ssi values were then classified into four susceptibility classes low moderate high and very high susceptibility subsequently the model was refined through a trial and error process involving changes in the relative weights and iterative evaluation of the prediction capability independent evaluation of the final model indicates that 55 and 45 of the subsidence events fall within the very high and high susceptibility zones respectively the results of this study show that ahp can be a useful approach for susceptibility assessment if data on the main controlling factors have sufficient accuracy and spatial coverage the limitations of the model are partly related to the difficulty of gathering data on some important geological factors due to their hidden nature the magnitude and frequency relationship constructed with the 41 sinkholes with chronological and morphometric data indicates maximum recurrence intervals of 1 17 2 14 and 4 18 years for sinkholes with major axial lengths equal to or higher than 10 m 20 m and 30 m respectively

u th he thermochronometry reveals pleistocene punctuated deformation and synkinematic hematite mineralization in the mecca hills southernmost san andreas fault zone abstract the timing tempo and processes of punctuated deformation in strike slip fault systems are challenging to resolve in the rock record faults in the mecca hills adjacent to the southernmost san andreas fault california accommodate active deformation and exhumation in the plio pleistocene sedimentary rocks and underlying crystalline basement we document the spatiotemporal patterns of san andreas fault related deformation as recorded in crystalline basement rocks of the mecca hills using fault microstructural observations geochemical data and hematite n 24 and apatite n 44 u th he hematite he apatite he thermochronometry data reproducible mean hematite he dates from minor hematite coated fault surfaces in the painted canyon fault damage zone range from 0 7 0 4 ma and are younger than 1 2 ma apatite he dates from adjacent crystalline basement host rock these data reveal concomitant pleistocene pulses of fault slip fluid flow and synkinematic hematite mineralization hematite textures crystal morphology and hematite he data patterns imply some damage zone deformation occurred via cyclic crack seal and creep processes apatite he data from crystalline basement define distinct date eu patterns and indicate cooling across discrete fault blocks in the mecca hills uniform 1 2 ma apatite he dates regardless of eu are located exclusively between the painted canyon and platform faults outside of this fault block samples yield individual apatite he dates from 30 1 ma that define a positive apatite he date eu correlation these patterns reveal focused exhumation away from the main trace of the san andreas fault at 1 2 ma low temperature thermochronometry of fault related rocks provides an unprecedented window into the 10 5 10 6 yr record of san andreas fault related deformation in the mecca hills and documents hematite deformation mechanisms that may be operative in other strike slip faults world wide

environmental geology and the marine dimension this paper reviews the role of environmental geology and the practice of environmental geology mapping in the context of the geological geophysical and geochemical factors which are relevant to human activity and safety it is concluded that informed planning policies for the offshore areas are necessary these would allow mutually acceptable and sensible exploitation of all natural resources engineering and military developments and recreational uses and would also take account of natural and man made hazards to such activities the policies would follow from multidisciplinary systematic environmental studies involving international cooperation the imperative for the earth science practitioner to remain sensitive to the requirements of the users of such information is recognized as is the need to communicate unambiguously it is concluded that geologists should look increasingly from the past to the future

u th ne chronometry abstract production of 21ne from the reaction 18o n 21ne in u and th rich minerals such as apatite zircon monazite and titanite can potentially be used for chronometry based on a review of the available cross section data we reevaluated the production of 21ne from this reaction using a thin target approach and compared the results against thick target situations the 21ne 4he production ratio in these minerals is about 4 10 8 but varies with oxygen content and th u ratio 21ne has a stopping range of about 1 m compared to about 20 m for particles thus the 21ne 4he production ratio also depends on crystal size when the crystals are small enough that ejection is important using a monte carlo model we computed the effects of ejection on the 21ne 4he ratio for various geometries and grain sizes we also present measurements of the 21ne 4he ratio on few mg aliquots of well dated volcanic apatites and zircons for which the duration of retention of 21ne and 4he is the same values of 4 4 1 1 10 8 and 3 5 1 2 10 8 for apatite and zircon respectively are in agreement with the theoretical values of 4 16 0 14 10 8 3 54 0 13 10 8 based on our production rate estimates the durango apatite and fish canyon tuff zircon give ne ages of 34 2 8 6 and 28 12 ma respectively which are in agreement with independently known ages our results demonstrate that the 21ne production is well understood and can be used to measure the neon retention time for slowly cooled minerals the 4he and 21ne content of zircons from the deeply exhumed crustal section in gold butte nevada crystallization age of 1 4 ga imply u th ne ages of 963 164 and 777 122 ma far older than their he ages of 16 7 1 3 and 19 1 1 5 ma respectively to explain the age difference a neon closure temperature for zircon between the values given by the thermochronometers u pb on apatite and ar ar on muscovite is derived probably 400 50 c

low long term erosion rates and extreme continental stability documented by ancient u th he dates zircon and apatite crystals from the western canadian shield yield u th he dates that are the oldest yet reported for terrestrial rocks zircon dates from 1 73 to 1 58 ga are consistent with independent geological and thermochronological constraints and indicate that the rocks were at temperatures 180 c and crustal depths 7 10 km since ca 1 7 ga apatite dates from 0 95 to 0 55 ga suggest residence of rocks at temperatures 40 50 c and crustal depths 1 5 2 km for 1 0 0 6 b y when interpreted using conventionally accepted apatite he diffusion kinetics and considering the proposed effect of radiation damage on apatite he retentivity our analysis implies long term integrated unroofing rates of 2 5 m yr since ca 1 7 ga these rates are significantly lower than the long term rates suggested by previous thermochronological data sets in continental interiors but are within the range of short term erosional estimates the results are consistent with the extreme stability of this region since the proterozoic

iron oxides constrain bif evolution in terranes with protracted geological histories the iron count prospect middleback ranges south australia abstract when studied at appropriate scales of observation and using complementary methods the intrinsic textural and geochemical complexity of iron oxides can provide unparalleled insights into the evolution of iron ore resources from banded iron formation deposition to ore formation iron count is one of 20 deposits and prospects within the archean middleback ranges iron ore belt south australia in which iron oxides from bifs and ores display variable textural and trace element signatures integrated petrography iron oxide laser ablation mapping and geochemistry and in situ dating of bif derived ores was undertaken to assess whether features observed in samples from this representative prospect might be attributed to localized and superimposed overprint processes the prospect consists of a west and east ridge each characterized by a sequence of overprints expressed as interconversions between iron hydr oxides and accompanying variation in trace element concentrations pseudomorphic replacement of early magnetite by hematite martite followed by replacement by iron hydroxides is recognized in samples from the east ridge further overprints are expressed as veining brecciation and crystallization of micro platy hematite rich in granitophile elements sn mo w u martitization of early magnetite in the west ridge is accompanied by enrichment in zn co and ni in martite subsequent recrystallization of martite iron hydroxides by granoblastic hematite is marked by enrichment in ti ta nb ree and granitophile elements and co crystallization of ree minerals this is followed by crystallization of micro platy hematite similarly rich in these elements enrichment in ti and granitophile elements in granoblastic hematite is interpreted to infer crystallization from highly saline fluids generated by interaction between evaporite bearing sedimentary rocks and granite derived fluids post archean australian shale normalized rey fractionation trends of iron oxides from the east ridge are consistent with precipitation of iron rich minerals from a mixture of anoxic seawater and hydrothermal vent fluids analogous trends from the west ridge lack a seawater signature contrasts in rey fractionation trends between the two ridges is interpreted as a combination of the loss of primary seawater signature due to severe overprinting in the west ridge and to lateral variation in the marine depositional environment results validate the hypothesis that variation in iron oxide trace element signatures seen throughout the middleback ranges iron ore belt results from overprinting due to superimposed tectono magmatic events that have locally affected each deposit despite undergoing different sequences of ore forming stages as well as possibly distinct depositional environments the two ridges share a common overprint dated here at 1790 ma using in situ u pb geochronology of co existing hematite monazite and xenotime this age is considered to represent the timing of interaction between granite derived fluids with ore hosting rock such interpretation is supported by the geochemical signatures of the dated iron oxides showing enrichment in granitophile elements and coincident ages for the wertigo granite and myola volcanics which occur proximal to the prospect and were emplaced erupted during intracontinental rifting the approach undertaken here combining petrography iron oxide geochemistry and in situ dating of bif derived ores is generically applicable to other iron resources within the middleback ranges or analogous terranes elsewhere

high grade iron ore deposits of the mesabi range minnesota product of a continental scale proterozoic ground water flow system the mesabi range along the north edge of the paleoproterozoic penokean orogen in northern minnesota has produced 3 6 billion metric tons of ore since its discovery in 1890 of that amount 2 3 billion metric tons were extracted from hematite or goethite rich deposits generally referred to as high grade ores the high grade ores formed as the biwabik iron formation was oxidized hydrated and leached by solutions flowing along open faults and fractures the source of the ore forming solutions has been debated since it was first proposed that the ores were weathering products formed by descending meteoritic ground water flowing in late mesozoic time subsequently others believed that the ores were better explained by ascending solutions possibly hydrothermal solutions of pre phanerzoic age neither wolff nor gruner could reconcile their observations with a reasonable source for the solutions in this paper i build on modern mapping of the mesabi range and mine specific geologic observations summarized in the literature to propose a conceptual model in which the high grade ores formed from ascending solutions that were part of a continent scale topographic or gravity driven ground water system i propose that the ground water system was active during the later stages of the development of a coupled fold and thrust belt and foreland basin that formed during the penokean orogen

multi aliquot method for determining u th he ages of hydrothermal hematite returning to elba abstract we have used a multi aliquot method to obtain precise u th he ages of hydrothermal hematite and to assess the extent to which he loss from fine grained hematite caused by diffusion and recoil hematite n 6 from the rio marina mine elba italy yields u th he ages that range from 5 36 0 33 to 5 64 0 11 ma giving a weighted mean age of 5 53 0 14 ma and an isochron age of 5 25 0 20 ma 40ar 39ar data from cogenetic adularia yield flat age spectra with analytically indistinguishable plateau ages 5 575 0 008 and 5 583 0 013 ma an additional adularia has a more complex spectrum and yields an interpreted age of 5 64 0 03 ma the hematite u th he ages overlap the 40ar 39ar ages albeit they are less precise 2 6 vs 0 2 0 5 this indicates that the loss of in situ radiogenic 4he from complex fine grained hematite either by diffusion and recoil is insignificant the study shows that multi aliquot method has the potential to reliably deliver precise and accurate ages for iron oxide mineralisation that has not suffered significant post crystallisation thermal perturbation

single crystal hematite u th he dates and fluid inclusions document widespread cryogenian sand injection in crystalline basement abstract the tavakaiv quartzite informal in colorado usa is one of the world s largest basement hosted clastic injectite systems and provides a glimpse into the tectonic and near surface environment of ancient north america the age origin and significance of tavakaiv injectites has been debated for over a century owing to inherent difficulties with assigning absolute age constraints to unfossiliferous sandstone intrusions here we apply an innovative combination of single crystal hematite u th he thermochronometry and fluid inclusion microthermometry to hematite mineralization associated with the injectites to document the age and ambient fluid conditions of tavakaiv injectite formation our approach confirms individual hematite crystals comprising commonly analyzed polycrystalline aggregates are the he diffusion domains and that hematite u th he closure temperature increases with crystal size we apply apatite and zircon fission track thermochronometry to the tavakaiv quartzite and host rock to account for the consequences of phanerozoic orogenic episodes on the hematite u th he dates and explain the observed trends between hematite he date and crystal size our results indicate that hematite formed 676 26 million years ago arithmetic mean date 1 constraining the timing of the tavakaiv injection event fluid inclusion studies reveal that this mineralizing fluid was at least 200 c and saline 20 wt cacl2 equiv comparison of new and previously published detrital zircon u pb age populations from quartzite samples yield a sediment source common to tavakaiv bodies across a broader region and illuminate the greater areal extent of the cryogenian injection event we interpret that formation of basement penetrating fracture arrays was associated with crustal extension within rodinia at this time this was accompanied by sand remobilization that promoted widespread sand injection within horsts bounding neoproterozoic rift basins the resulting sand injectites served as permeable pathways for contemporaneous circulation of saline groundwater driven by fluid gradients in extensional and or transtensional basins

evaluating and comparing methods of sinkhole susceptibility mapping in the ebro valley evaporite karst ne spain abstract multiple sinkhole susceptibility models have been generated in three study areas of the ebro valley evaporite karst ne spain applying different methods nearest neighbour distance sinkhole density heuristic scoring system and probabilistic analysis for each sinkhole type separately cover collapse sinkholes cover and bedrock collapse sinkholes and cover and bedrock sagging sinkholes the quantitative and independent evaluation of the predictive capability of the models reveals that 1 the most reliable susceptibility models are those derived from the nearest neighbour distance and sinkhole density these models can be generated in a simple and rapid way from detailed geomorphological maps 2 the reliability of the nearest neighbour distance and density models is conditioned by the degree of clustering of the sinkholes consequently the karst areas in which sinkholes show a higher clustering are a priori more favourable for predicting new occurrences 3 the predictive capability of the best models obtained in this research is significantly higher 12 5 82 5 than that of the heuristic sinkhole susceptibility model incorporated into the general urban plan for the municipality of zaragoza although the probabilistic approach provides lower quality results than the methods based on sinkhole proximity and density it helps to identify the most significant factors and select the most effective mitigation strategies and may be applied to model susceptibility in different future scenarios

probabilistic sinkhole modelling for hazard assessment a method for quantitatively assessing sinkhole susceptibility spatial probability and hazard spatio temporal probability has been developed and independently tested in a 50 km2 sector of the ebro valley evaporite karst three genetic types of sinkholes have been mapped in the floodplain and a terrace surface 947 small cover collapse sinkholes type 1 terrace large collapse sinkholes type 2 floodplain and large subsidence depressions type 3 floodplain the type 1 sinkhole inventory includes two temporal populations 447 sinkholes formed before 24 november 2005 and 500 between that date and 2 november 2006 sinkhole susceptibility models have been elaborated analysing the statistical relationships between the sinkholes of the 2005 inventory and a set of potential conditioning factors the independent evaluation validation of the susceptibility models by means of several strategies random sequentially excluded and temporal has allowed us to select the most significant variables for each sinkhole type and assess quantitatively the quality of models which are reasonable for the three sinkhole types validation has also provided information on the contribution of specific variables and the effect of changing their accuracy to the prediction capability of models susceptibility models for type 3 sinkholes have been validated satisfactorily with the 2006 sinkhole inventory temporal validation the best susceptibility model has been transformed into a hazard map considering the frequency of sinkholes that occurred in each susceptibility class between 2005 and 2006 as well as their average size the susceptibility and hazard models obtained could be used as an objective basis for the application of mitigation measures either of preventive or corrective nature copyright 2008 john wiley sons ltd

a matter of minutes breccia dike paleomagnetism provides evidence for rapid crater modification during an impact event a crater s transient structure adjusts gravitationally within medium sized complex craters a central uplift rises and collapses resulting in large scale rotations of the target rock estimated crater modification rates from numerical models indicate that complex impact craters modify to a structurally stable state within tens of seconds to several minutes after excavation however there is little direct geologic evidence constraining these rates we show how paleomagnetic measurements of lithic breccia dikes emplaced during crater excavation can be used to constrain the rate of crater modification within the central uplift of the 34 km diameter slate islands impact structure ontario canada the uniformity and linearity of paleomagnetic directions among the clasts and matrix of breccia dikes throughout the impact structure indicate that breccia dikes were frictionally heated above the magnetite curie temperature 580 c during their emplacement and subsequently cooled in situ through magnetic blocking temperatures the tight grouping of these paleomagnetic directions implies that these breccia dikes cooled and locked in magnetic remanence over a time interval in which the impact structure was not experiencing structural rotations and had already reached a stable state conductive cooling of the thinnest sampled breccia dike would have led to the recording of magnetic remanence approximately six minutes after emplacement this constraint necessitates a stable crater structure only minutes after impact and presents a rare case in which a geological process can be resolved on such a short time scale

ahp based evaluation of the karst collapse susceptibility in tailai basin shandong province china karst sinkholes began to appear in tailai basin of china in the 1970s and have been increasingly exacerbating ever since evaluation of the sinkhole susceptibility has been challenging the lithology li distance to fault df overburden type oty overburden structure os overburden thickness oth groundwater depth gd relative location between the groundwater table and bedrock rl pumping wells pw are chosen as conditioning factors the weights of the factors are obtained based the analytic hierarchy process ahp further a gis based evaluation of the karst sinkholes susceptibility in the tailai basin is made the tailai basin is divided into extremely susceptible area highly susceptible area moderately susceptible area and weakly susceptible area and their corresponding areas are 60 15 85 80 61 69 and 19 88 km2 respectively the extremely and highly susceptible areas are mainly distributed in taian city and encompass an area of 145 95 km2 results of this study provide a decision basis for prevention and treatment of karst sinkholes in the tailai basin

tsunami risk in northwestern europe a holocene example a thin regionally extensive laterally persistent sand layer is present within the holocene coastal sequences of eastern scotland dated to 7000 yr bp it is proposed that this deposit was caused by a tsunami wave generated by a catastrophic submarine landslide the second storegga slide on the norwegian continental slope the distribution of this tsunami deposit indicates that the wave penetrated at least 2 km beyond the contemporary coastline and a minimum of 4 m above the contemporary high water mark although the frequency of tsunamis may be low in this region their effects should be considered for very long term or very sensitive strategic developments at coastal sites

development and validation of sinkhole susceptibility models in mantled karst settings a case study from the ebro valley evaporite karst ne spain abstract a preliminary sinkhole susceptibility analysis has been carried out in a stretch 50 km 2 in area of the ebro valley alluvial evaporite karst ne spain a spatial database consisting of a sinkhole layer and 27 thematic layers related to causal factors was constructed and implemented in a gis three types of sinkholes were differentiated on the basis of their markedly different morphometry and geomorphic distribution large subsidence depressions 24 large collapse sinkholes 23 and small cover collapse sinkholes 447 the susceptibility models were produced analysing the statistical relationships between the mapped sinkholes and a set of conditioning factors using the favourability functions approach the statistical analyses indicate that the best models are obtained with 6 conditioning factors out of the 27 available ones and that different factors and processes are involved in the generation of each type of sinkhole the validation of two models by means of a random split strategy shows that reasonably good predictions on the spatial distribution of future dolines may be produced with this approach around 75 of the sinkholes of the validation sample occur on the 10 of the pixels with the highest susceptibility and about 45 of the area can be considered as safe

countermeasures to treat collapse during the construction of road tunnel in fault zone a case study from the yezhuping tunnel in south qinling china to ensure the safety of the tunnel construction it is very important to take the appropriate treatment measures after the collapse happened especially the tunnel goes through the fault fracture zone this paper sets forth the process of the collapse that occurred in the yezhuping tunnel affected by the fault fracture zone and introduces the treatment for the collapse the deformation characteristics of the surrounding rock are analyzed according to the monitoring results based on the research regarding the effect of the fault on the tunnel by using the general hoek brown failure criterion and the field monitoring results it is shown that the fault is the main reason for the collapse it induces the attenuation of the young modulus and the compressive strength and the enlargement of the plastic zone the research results have some reference significance for similar projects

glacial incisions indicating middle and upper pieistocene ice limits off britain from the recognition that major incisions formed at lowland or tidewater ice sheet margins during each of the last three glacial stages it is assumed that a standard quaternary stratigraphy is applicable to the deposits geophysically profiled on the continental shelf off britain ice limits for each glacial stadial can be mapped from the geographical distribution of the incisions during the next glacial stage major incisions will be downcut on the present continental shelf or coastal lowlands to some 350 m below the ambient surface this will have important environmental consequences regarding the long term burial of hazardous wastes

hydrothermal oxidation in the biwabik iron formation mn usa precambrian iron formations throughout the world notably in australia brazil and south africa show evidence of hypogene 110 c mostly 250 c oxidation alteration and silica dissolution as a result of tectonic or magmatic activity although hydrothermal oxidation has been proposed for the prototype lake superior type iron formation the biwabik iron formation in minnesota usa it has not been documented there by examining oxidized and unoxidized biwabik iron formation in three mines including material from high angle faults that are associated with oxidation we document an early hypogene oxidation event 175 c involving medium salinity aqueous fluids 8 4 4 9 wt nacl equiv that infiltrated iron formation along high angle faults at the hibbing taconite mine hydrothermal fluids oxidized iron carbonates and silicates near faults producing goethite quartz in contrast with much of the oxidized iron ores on the mesabi range silica was not removed but rather recrystallized during this event perhaps lying in a rock dominated system at low cumulative fluid flux during the hydrothermal oxidation event in the hibbing taconite deposit quartz filled microfractures and irregular inclusions commonly formed in coarse variably oxidized magnetite currently the ore mineral these inclusions degrade the ore by introducing excess silica in magnetic concentrate hydrothermal oxidation at hibbing taconite mine is overprinted by later relatively minor supergene oxidation both along faults and near the surface which locally dissolved quartz at the fayal reserve mine widespread silicate and carbonate gangue dissolution and iron oxidation was followed by precipitation of pyrite mn siderite apatite and other minerals in void spaces which prevented post oxidation compaction and significant volume loss in the sampled rocks although definitive temperature data for this assemblage are needed the weight of evidence indicates that this mineralization is hypogene the association of oxidation with epithermal conditions constrains the oxidation and subsequent mineralization to have taken place during the precambrian the only time when these rocks would have experienced the necessary temperatures the mineralization at fayal reserve shows little supergene overprint pyrite is largely unoxidized hydrothermal oxidation in both mines was likely produced by basinal fluids that were expelled during the 1 83 1 87 ga penokean orogeny and mixing with meteoric fluids along faults although a 1 1 ga rift related fluid flow event is also possible later supergene overprinting of the iron formation was minor

karst collapse susceptibility mapping considering peak ground acceleration in a rapidly growing urban area abstract karst collapse occurrences represent a geological hazard that can cause damage to man made structures in the present study a karst collapse susceptibility map was produced using a multivariate statistical method and a geographical information system the case under study is the northern suburbs of athens greece the karstic features of the study area were recorded physical processes slope angle and aspect hydrographic network springs lithology tectonic features along with anthropogenic road network and land use parameters were chosen as major factors affecting the karst collapse occurrences the innovative method was combining karst collapse occurrences with seismic hazard assessment which was achieved by calculating peak ground acceleration pga the pga was determined for a return period of 475 years corresponding to a 90 probability of not being exceeded in 50 years the logistic regression lr method was applied to evaluate these factors slope angle pga lithology and distance to springs and roads were statistically significant for the applied model among these factors the slope angle and pga have a negative effect while the lithology and distance to springs and roads have a positive effect on the karst collapse occurrences the validation of the applied lr model indicated that the results are reliable and that the produced map is accurate the karst collapse susceptibility map was classified into four classes the areas of very high and high susceptibility were observed mainly in the eastern and southwestern parts of the study area almost 30 of the existing urban growth boundary of the study area is located in areas of very high and high susceptibility the karst collapse susceptibility map can be used by planners and engineers for sustainable urban development

multiple episodes of hematite mineralization indicated by u pb dating of iron ore deposits marquette range michigan usa high grade hematite ore so called hard ore was first mined in the lake superior region of north america in a d 1848 the development of ore deposit models from the region has strongly influenced research on the origin of this deposit type worldwide the inability to date high grade hematite ores has hindered the testing of competing genetic models in the marquette range northern michigan usa high grade hematite ore is hosted by the 1 9 1 85 ga negaunee iron formation and unconformably overlying goodrich quartzite field relations and new in situ u pb geochronology of monazite and xenotime intergrown with hematite from six mines across the marquette range michigan indicate that the formation of high grade hematite ore bodies involved up to three events the presence of pebbles of hematite ore in basal conglomerate of the goodrich quartzite indicates that the first episode of iron oxide mineralization occurred after deposition and deformation of the negaunee iron formation but before the ca 1 85 ga sudbury impact monazite in iron ore deposits within the hinges of penokean aged folds yields an age of ca 1 8 ga which is interpreted to record a second phase of hematite enrichment monazite and xenotime in iron ore deposits along the limbs of regional folds give ages of ca 1 77 ga and are interpreted to record a later episode of hematite upgrading the ca 1 8 ga and ca 1 77 ga phosphate ages coincide with the timing of regional tectonic events suggesting hematite mineralization was coeval with the penokean orogeny and yavapai interval accretion our results support the proposal that the formation of high grade hematite ore bodies is a multistage process linked to discrete orogenic events

dust deposition in the central mediterranean tyrrhenian and adriatic seas relationships with marine sediments and riverine input major al ca fe mg mn si and minor cd pb zn elements of aeolian dust samples collected onboard ship around italy were analysed and the concentrations of metal in the dusts were in good agreement with previously published data from the mediterranean sea the elemental composition of dust samples collected in four subareas adriatic ionian tyrrhenian and sicily channel was compared with the composition of marine deep sediments obtained in the same regions mn al cd and zn contents differentiated between the four areas in both sets of samples suggesting a possible geochemical signature of the atmospheric crustal contribution in marine deep sediments an estimate of the relative contribution of atmospheric dry deposition of cd pb and zn and riverine discharge indicates that a the metals deposited from the atmosphere to the adriatic basin are a small fraction 2 5 of those discharged by the po and adige rivers b almost the same amounts of cd pb and zn are delivered to the tyrrhenian sea by the atmosphere and by the arno and tiber rivers

hematite replacement of iron bearing precursor sediments in the 3 46 b y old marble bar chert pilbara craton australia the history of atmospheric oxygen prior to the great oxidation event 2 45 2 2 ga is not well understood hematite in the marble bar chert from a nasa funded drill hole abdp1 in the pilbara craton australia has been cited as evidence for an oxygenated ocean 3 46 b y ago however isotopic data from the same drill hole have been used to argue for an anoxic ocean it is generally agreed that the hematite is primary representing either a direct hydrothermal precipitate or a dehydration product of iron oxyhydroxides that formed during anoxygenic photosynthesis here we present new petrographic evidence from the marble bar chert in drill hole abdp1 that shows that hematite in jasper bands formed via mineral replacement reactions the hematite mostly occurs as sub micron sized inclusions within chert so called dusty hematite that are typically arranged into polygonal clusters surrounded by a rim of clear quartz resembling shrinkage structures the lateral transition from laminated chert enclosing minute inclusions of greenalite siderite and magnetite to chert dominated by dusty hematite provides evidence for in situ replacement of iron bearing minerals the presence of hematite rich bands containing octahedral crystals with residual cores of magnetite indicates that some of the hematite was derived from the replacement of magnetite this interpretation is supported by the widespread occurrence of magnetite in jasper displaying progressive stages of replacement from unaltered octahedral inclusions in quartz to hematite pseudomorphs along quartz grain boundaries the occurrence of dusty hematite in fractures sedimentary laminae and the outer margins of polygonal clusters containing greenalite is consistent with fluid mediated oxidation of iron rich precursor minerals the presence of syn sedimentary chert breccias comprising rotated fragments of laminated chert indicates that the precursor sediment was silicified shortly after deposition the abundance of dusty greenalite inclusions which are texturally the earliest components of the laminated chert suggests that the precursor sediment contained an iron rich clay mineral our results show that hematite has replaced ferrous rich minerals after deposition and provide a mechanism to explain the origin of hematite in the marble bar chert which is consistent with the origin of hematite in adjacent basalts a secondary origin for hematite invalidates arguments for an oxygen bearing ocean 3 46 b y ago and provides a viable explanation for the formation of archean jasper bands our findings show that misinterpretations about the origin of hematite in early precambrian cherts could lead to false conclusions about the chemistry of the ancient ocean and atmosphere

radiometric dating and temperature history of banded iron formation associated hematite gogebic iron range michigan usa newly developed techniques were used to characterize the age origin and temperature history of coarse hematite contained in high grade iron ore three botryoidal specimens from two different mines in the gogebic iron range near ironwood michigan usa yielded u th 21 ne ages concordant with plateau 4he 3he ages these data reveal that while two of the specimens grew at ca 772 41 ma the third formed 300 m y later 453 14 ma 4he 3he polydomain thermochronometry indicates hematite formation at 80 c for the older specimens and 60 c for the younger fe mobilization and recrystallization in open cavities at 3 5 km subsurface has occurred episodically or possibly continuously over hundreds of millions of years despite a quiescent tectonic setting throughout this interval while the analyzed specimens are distinct from typical fe ore their ages along with structural relationships constrain the onset of iron enrichment to between 1060 and 770 ma cooling of 0 5 c m y ensued between ca 800 and ca 550 ma declining to 0 1 c m y for the last 550 m y these data suggest an erosion rate of 6 m m y and 5 km of total erosion of the superior upland province through the phanerozoic and limit unroofing associated with pleistocene glaciation to 1 km

hematite fault rock thermochronometry and textures inform fault zone processes abstract minerals on fault surfaces record fluid rock interaction strain and or heat during fault slip fault hosted hematite is amenable to u th he he thermochronometry hematite he dates reflect fault related processes or exhumation depending on hematite growth above or below the grain size controlled closure temperature and processes that promote open system behavior deconvolving these phenomena requires multi scale hematite textural characterization and constraints on the ambient thermal history from conventional thermochronometry two examples of this approach include investigations of hematite coated fault surfaces from exhumed damage zones in the seismically active wasatch fault zone wfz ut and painted canyon fault pcf paralleling the southern san andreas fault mecca hills ca wfz fault mirrors preserve sub m scale polygonal grain textures and hematite he data patterns that together with host rock apatite he data are consistent with localized friction generated heat hematite he loss and hematite recrystallization during damage zone seismicity