application of thermochronology to hydrothermal ore deposits thermochronology finds many applications in economic geology utilizing temperature sensitive radiometric dating techniques to reveal low temperature upper crustal processes can elucidate many aspects of deposit genesis including timing and duration of mineralization processes rate of exhumation and erosion of intrusive ore deposits and comparative preservation potential the tools are utilized to best advantage when combined with other thermochronometry techniques that provide complementary information in addition when thermochronometers are combined with geochronometers e g zircon u pb over 800 c of thermal history is revealed from emplacement to erosion fig 1 with the advent of computational algorithms that provide more accurate and detailed models of thermochronology results the economic geologist has a powerful tool to use when assessing economic favorability of a region or prospect this chapter summarizes the various ways that low temperature thermochronometers have been utilized in studies of economic mineralization and primarily focuses on studies of porphyry ore deposits these deposits are well characterized and provide a good platform from which to demonstrate the extended understanding of ore formation processes that is provided by thermochronology studies in this section we review the fundamental application of u th he fission track and 40ar 39ar thermochronometry methods to mineralized systems we then present a synopsis of how these techniques can be used in thermal history analysis either alone or in combination with other chronometers in order to provide more information on deposit genesis the discussion is presented from low through to higher temperature thermochronometers corresponding to their presentation on figure 1 u th he thermochronology as documented earlier in the volume u th he thermochronology is based on measuring the accumulation of radiogenic 4he produced from u and th decay the daughter helium is retained until the mineral is heated to a temperature at which its structure and helium retentivity change this closure temperature varies from

heat flow during the carboniferous and mesozoic of the northwest german basin the temperature history of the northwest german basin has been reconstructed using a one dimensional computer model that accounts for compaction related changes of physical rock properties depth temperature and maturity of organic matter maturity has been modelled by empirically relating vitrinite reflectance to time temperature history heat flow values for the mesozoic and carboniferous have been obtained by matching measured and computed vitrinite reflectance for mesozoic samples agreement between measured and computed maturity can be achieved with a heat flow between 37 and 50 mw m2 0 9 and 1 2 hfu there is no systematic areal variation carboniferous samples are matched best at heat flows between 70 and 96 mw m2 1 7 and 2 3 hfu corresponding to geothermal gradients between 50 and 80 c km depending on lithology and compaction areal variation follows patterns subparallel to the structural grain of the variscan orogeny mesozoic heat flow is compatible with heat flow in stable platform areas carboniferous heat flow and its geotectonic setting are best in agreement with present day back arc areas underlain by continental crust

multi stage ag bi co ni u and cu bi vein mineralization at wittichen schwarzwald sw germany geological setting ore mineralogy and fluid evolution the wittichen co ag bi u mining area schwarzwald ore district sw germany hosts several unconformity related vein type mineralizations within variscan leucogranite and permian to triassic redbeds the multistage mineralization formed at the intersection of two fault systems in the last 250 ma a permo triassic ore stage i with minor u bi quartz fluorite mineralization is followed by a jurassic to cretaceous ore stage ii with the main ag and co mineralization consisting of several generations of gangue minerals that host the sub stages of u bi bi ag ni as bi and co as bi important ore minerals are native elements co and ni arsenides and pitchblende sulphides are absent the miocene ore stage iii comprises barite with the cu bi sulfosalts emplectite wittichenite and aikinite and the sulphides anilite and djurleite besides native bi chalcopyrite sphalerite galena and tennantite the mineral forming fluid system changed from low salinity 5 wt nacl at high temperature around 300 c in permian to highly saline around 25 wt nacl cacl2 at lower temperatures 50 150 c in triassic to cretaceous times thermodynamic calculations and comparison with similar mineralizations worldwide show that the mesozoic ore forming fluid was alkaline with redox conditions above the hematite magnetite buffer we suggest that the precipitation mechanism for native elements pitchblende and arsenides is a decrease in ph during fluid mixing processes ree patterns in fluorite and the occurrence of bi in all stages suggest a granitic source of some ore forming elements whereas e g ag co and ni probably have been leached from the redbeds the greater importance of cu and isotope data indicates that the miocene ore stage iii is more influenced by fluids from the overlying redbeds and limestones than the earlier mineralization stages

paragenetic specularite and adularia elba italy concordant u th he and k ar ages abstract in order to test the usefulness of the helium method for detecting young geological events in hematite u th and 4 he concentrations were analyzed in five specularite samples from rio marina type hematite deposits northeastern elba italy four specularite samples define a u 0 235th 4 he isochron age of 5 39 0 46 ma 2 the isochron intercepts the 4 he axis at 49 88 pl g 2 adularia which is paragenetic with specularite in one sample used for the isochron gives a meank ar age of 5 32 0 11 ma in addition two specularite samples one from rio marina and one from terra nera southeastern elba give helium model ages of 6 4 0 4 and 7 3 0 4 ma respectively depending on the model of genesis the high ages reflect incomplete 4 he degassing and or 4 he excess the study demonstrates that geologically meaningful helium ages as young as pliocene can be obtained from specularite in spite of expected interferences from initial helium if the 4 he axis intercept is a general measure of initial 4 he in hematite its effect on the calculated ages in mesozoic hematites in previous studies is negligible the age concordance implies that similar concordance should exist in samples with a known thermal history much older than pliocene moreover the helium method could also work on specularite with a thermal history younger than pliocene

reliability of k ar dating of clays and silicifications associated with vein mineralizations in western europe k ar ages were determined on fine fractions and one massive silicification associated with vein mineralizations in uranium barium fluorine and related base metals in western europe the reliability of the potassic materials analysed once the mineralogical and geochemical relationships to the low temperature mineralization have been established is demonstrated the isotopic ages are concentrated between nearly 190 and 170 ma this epoch corresponds to that of the rifting of the future atlantic and tethys oceans this type of low temperature mineralization thus seems to be better explained by extensional phenomena

reactivated basement structures affecting the sedimentary facies in a tectonically quiescent epicontinental basin an example from nw switzerland abstract the jurassic deposits in the southern part of central europe accumulated in a shallow epicontinental sea and their deposition has usually been believed to have corresponded to a phase of tectonic quiescence neither on conventional seismic records nor in outcrops obvious indications of synsedimentary tectonics were found nonetheless subtle variations in lithofacies and thickness occur above faults in the crystalline basement in fact preexisting structures became reactivated in the jurassic during major extensional phases when the tethys and the north atlantic opened this reactivation led to differential subsidence and or to rotation of fault bounded blocks but the sediments were deformed mainly flexurally as vertical movements in the basement were dissipated by triassic salt thus the depositional area was morphologically differentiated into swells and depressions in siliciclastic muddy environments swells were characterized by hardbottoms and hiatus beds depressions were filled by distal tempestites and gravity deposits in carbonate settings reefs nucleated on swells marls and muds were deposited in depressions many of them gravity deposits reactivation of faults occurred only during short episodes and was not synchronous throughout the study area and reactivation of individual faults was episodic and probably controlled by the palaeostress field and the faults orientation reactivation of deep rooted faults is also documented by hydrothermal activity which led to vein mineralization and alteration of minerals today exposed in nearby basement units the chronostratigraphic ages of the hydrothermal processes coincide with phases of enhanced subsidence during the sinemurian aalenian bajocian bathonian and oxfordian in turn facies changes of the sedimentary cover should be useful to predict basement structures when no seismic records are available

40ar 39ar dating of west african lateritic cryptomelanes abstract dating weathering processes is an innovative approach to understanding climate dependant modifications of the earth s surface potassium bearing manganese oxides are a ubiquitous feature of weathering mantles developed from mn bearing parent rocks recent studies have demonstrated the possibility of dating k rich manganese oxides from the hollandite group such as cryptomelane k 1 2 mn 8 o 16 nh 2 o using 40 ar 39 ar argon ion laser probe method this work applies that approach to cryptomelanes formed in the lateritic manganese ore deposit of tambao northern burkina faso a present unexploited deposit among the cryptomelane richest in the world two samples of massive mn rich concretions 10mm and 4mm in thickness were collected from the massive 80 m high mn rich hill at tambao a detailed petrographical study shows that these cortical formations are composed of successive na rich cryptomelane layers with na na k ba up to 20 seven and five subsamples from these two concretions were studied with a 40 ar 39 ar laser probe the age spectra indicate ages that are coherent with the general organization of the concretions showing a regular decrease from cores towards rims within the two concretions ages range from 49 8 0 4 ma to 48 1 0 1 ma and from 47 5 0 3 ma to 44 5 0 4 ma respectively the youngest ages being obtained for the most external layers the integrated rates of cryptomelane precipitation are estimated at 1 and 5 mm ma these ages clusters show that weathering at tambao was functioning during the early eocene and thus suggest that there is a relationship between the formation of the bauxites of the african surface and the mn fe laterites

synthesis and model of formation water flow alberta basin canada based on a large amount of publicly available data several studies have previously examined the flow of formation waters in different parts of the alberta basin offering various interpretations as to the causes of the observed pressure regime and flow pattern however there has been no synthesis of these diverse studies on a basin wide basis accordingly these studies are critically reviewed in this paper and synthesized in a new basin scale model of the flow of formation waters in the alberta basin the proposed regional scale model has significant implications for understanding hydrocarbon migration pathways ore genesis the geothermal regime and deep waste disposal in the alberta basin several flow systems each one driven by a different mechanism are identified together with the main processes leading to the nonhydrostatic pressures observed in the basin two megahydrostratigraphic successions and associated flow systems are recognized the first succession corresponds to the pre cretaceous passive margin stage of basin development and consists of thick carbonate dominated aquifer systems separated by shaly aquitards and evaporitic aquicludes a northeastward basin scale flow system is driven by basin topography with recharge in montana and discharge in northeastern alberta southwest to northeast regional scale flow adjacent to the fold and thrust belt is probably the result of past tectonic processes the salinity of formation water in pre cretaceous aquifers is high and generally increases both northward and with depth this variability is the result of increased water rock reactions mineral solubility with increased temperatu e and of incomplete flushing by meteoric water as a result of salinity variations flow retarding buoyancy effects can be important the second megahydrostratigraphic succession corresponds to the post jurassic foreland stage of basin evolution and consists of thick shaly aquitard systems and relatively thin sandstone aquifers in the southwestern part of the basin flow in isolated aquifers is driven southwestward by erosional rebound in the thick intervening shales downdip toward the fold and thrust belt the salinity of formation waters in the post jurassic aquifers is low mixing of waters and interference between the major flow systems takes place along the pre cretaceous unconformity where successively older pre cretaceous aquifers subcrop from west to east flow in shallow lo al systems at the top of the sedimentary succession is driven by local topography

low temperature thermochronology of the flanks of the southern upper rhine graben the upper rhine graben urg is the most perceptible part of the european cenozoic rift system uplifted variscan basement of the black forest and the vosges forms the flanks of the southern part of the graben apatite and zircon fission track ft analyses indicate a complex low temperature thermal history of the basement that was deciphered by inverse modelling of ft parameters the models were tested against the observed data and independent geological constraints the zircon ft ages of 28 outcrop samples taken along an e w trending transect across the black forest and the vosges range from 136 to 312 ma the apatite ft ages from 20 to 83 ma the frequency distributions of confined track lengths are broad and often bimodal in shape indicating a complex thermal history cooling below 120 c in the early cretaceous to palaeogene was followed by a discrete heating episode during the late eocene and subsequent cooling to surface temperature the modelled time temperature t t paths point to a total denudation of the flanks of urg in the range of 1 0 1 7 km for a paleogeothermal gradient of 60 c km and 1 3 2 2 km for a paleogeothermal gradient of 45 c km since the late eocene

temperature induced 4he degassing of specularite and botryoidal hematite a 4he retentivity study degassing of radiogenic 4he induced by stepwise heating in a vacuum was carried out on various grain size fractions of specular and botryoidal hematite in order to place constraints on their 4he retentivities samples from the vosges odenwald saarbergland and cumbria were used below 900 c specularite yields straight lines in arrhenius plots this is consistent with volume diffusion the diffusion distances correspond with the macroscopic mean grain size by contrast botryoidal hematite yields curved lines which are straight only below 250 c the actual diffusion distances appear to be commensurate with the microscopic size of the constituent crystals 0 1 to 10 m the diffusion coefficients of specular d20 and botryoidal hematite d20 r2 are 10 28 cm s 1 and 10 22 s 1 and the activation energies range from 110 to 130 and 130 to 210 kj mol respectively helium 4 closure temperatures tc of specularite grains with diameters of about 5 mm are above 200 c and for all grain fractions in botryoidal hematite 10 m the tc is above 90 160 c on the basis of tc both hematite varieties should be useful thermochronometers low temperature 4he losses of the order of a few percent during a few 100 m y are conceivable for botryoidal hematite

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

calculation of oxygen isotope fractionation in metal oxides abstract a theoretical model calculating the thermodynamic isotope factors of oxygen in metal oxides of geochemical interest is presented for temperatures between 0 and 1200 c on the basis of the modified increment method the following order of 18o enrichment is obtained cassiterite rutile magnetite ilmenite ulvospinel hematite uraninite chromite corundum spinel the results are expressed as 103 in a 106 t2 b 103 t c which compare well with existing theoretical experimental and empirical calibrations on quartz oxides and oxides water systems the present calculations enable not only estimation of the oxygen isotope composition of fluids from which the metal oxides were precipitated when independent temperature information is available but can also be applied as oxygen isotope geothermometers to igneous and metamorphic rocks

dating of vein specularite using internal u th 4he isochrons hematite an ubiquitous iron oxide is commonly found enriched with uranium and other elements supplied by the ore solution from which it had formed the decay of the incorporated uranium to stable lead produces alpha particles which become 4he atoms via electron capture in hematite this helium production may provide a convenient clock which records the time elapsed since the iron oxide became closed enough to prevent quantitative helium escape wernicke and lippolt 1993a 1993b recently lippolt et al 1993 reported high retention qualities of specular hematite for 4he over geologic periods of time activation energies above 116 kj mol and diffusion coefficients smaller than 10 30 m2 s 1 at room temperature and closure temperatures above 200 c here the concentrations of u and th have been measured together with radiogenic 4he at four different locations inside two specularites the u he concentrations co varied sufficiently among the locations for an internal helium isochron of late jurassic age to be obtained from each specularite the study suggests that specularite is a prolific chronometer and might allow a routine approach of the helium isochron method to obtain crystallization cooling ages

ree systematics in hydrothermal fluorite abstract ree patterns of fluorite from 63 post variscan hydrothermal veins of the schwarzwald area germany can be divided into two major groups type a fluorite shows roof shaped paas normalized patterns with enriched mree the turning point of the curvature is at ho or er position all patterns of type a show a distinct positive eu anomaly type b fluorite shows roof shaped patterns with enriched mree and strongly depleted hree and a characteristic steep slope between nd and sm the turning point of the curvature is at gd to dy all patterns of type b show negative or no eu anomalies laser ablation icp ms traverses through single grains combined with cathodoluminescence imagery revealed either i identical ree patterns and total ree concentrations from core to rim ii identical ree patterns but concentration gradients or iii variable ree patterns and concentration gradients from core to rim these features are explained by different degrees of supersaturation or different fluid fluorite ratios during crystallization and by complexly controlled precipitation processes under closed system conditions petrographically late fluorites from several deposits show the characteristics of new fluid batches rather than the expected remobilization features lree enrichment close to the crystal faces in some grains may result from the copreciptiation of a submicrometer sized lree enriched phase or from lree clustering in late cool fluids by comparison with literature data on natural waters from gneissic and granitic aquifers and of leachates of granites and gneisses we show that the hydrothermal vein fluorite preserves the characteristic source related ree feature of the hydrothermal fluid that migrated through either gneissic type a or granitic type b host rocks the immediate host rocks of the veins however are not the source rocks of the ree which indicates large scale fluid convection in the basement gneiss related type a fluorite shows tb ca tb la trends of primary hydrothermal crystallization whereas granite related type b fluorite indicates remobilization of possibly pegmatitic or variscan fluorite

tectonothermal history of the schwarzwald ore district germany an apatite triple dating approach abstract exceptionally large u rich apatite from the schwarzwald ore district germany was triple dated using id tims u pb fission track ft and u th he dating methods the aim of adopting the multi dating approach on a single sample was to i further constrain thermo tectonic evolution of the schwarzwald from the formation of crystalline basement through to cooling and exhumation and ii test potential and limitations of in situ ft u th he double dating the apatite u pb age of 289 5 4 5 ma records the cooling of the basement through the 550 c during the early permian and brackets the age of the apatite hosting rhyolite between 289 5 4 5 ma and 314 6 ma which is the age of rhyolite hosting granite this is in excellent agreement with radiometric ages of related rhyolites and fits with the magmatic evolution of the schwarzwald during variscan orogeny in the eocene between 50 and 40 ma the basement resided at 100 c and then cooled to surface temperatures as revealed by the ft age 37 6 1 3 ma and thermal modelling results based on track lengths during the cooling event the basement was likely exhumed as a rift shoulder of newly formed upper rhine graben rift nine apatite grains yielded u th he ages from 30 7 1 5 to 65 0 2 6 ma mean age 45 7 1 3 ma three possible reasons for the lack of reproducibility are i non homogeneous distribution of parent isotopes evidenced by strong u zoning ii bad neighbourhood causing implantation of extraneous he and iii radiation damage leading to increased he retentivity implied by the high 250 ppm u concentration these problems could not be circumvented by mechanical abrasion of outermost rim of dated crystals which yielded u th he ages from 26 0 1 0 to 56 2 2 2 ma mean age 37 2 1 4 ma in situ ft and traditional u th he double dating of single apatite crystals revealed that the vast majority of u th he ages were younger than indistinguishable from or overlap within error with corresponding ft ages proving the robustness of this approach the results also show that apparent discrepancies between ft and u th he ages reported in the literature may arise simply as a result of statistical misconceptions and conventional data treatment considering the range of single grain ft ages and the oldest single grain ft age in addition to the central ft age may provide an effective basis on which to evaluate the viability of u th he data

botryoidal hematite from the schwarzwald germany heterogeneous uranium distributions and their bearing on the helium dating method abstract neutron induced fission tracks of small grain mounts of two co genetic botryoidal hematites eisenbach hematite manganese mineralization district mittelschwarzwald germany reveal substantial heterogeneous 235 u distributions 235 u fission tracks in the three shells of one hematite yield total uranium concentrations of 26 48 and 160 ppm 2 errors of approximately20 respectively the other hematite consists of a coherent mineralogical unit devoid of shell type features in which four localities have been probed with a range in total uranium between 26 and 600 ppm induced fission tracks from a larger section of the single unit hematite show a subparallel arrangement of five well defined 235 u zones with densities ranging from about 10 6 tracks cm 2 in zone 5 to approximately 25 10 6 tracks cm 2 in zone 2 additionally in zones 3 5 gradual internal track density variations of over 100 can be recognized a traverse shows that there is an overall decrease in radioactivity from zone 1 to zone 5 an autoradiograph confirms the existence of five zones with different activities and allows correlation of the high activity zone 2 with a 0 5 mm thin internal hematite micro layer analyses by mass spectrometer of the triple shell hematite resulted in the following concentrations 26 45 and 166 ppm uranium 2 errors of1 and 0 55 3 25 l g 4 he 2 errors of3 the four probed localities in the single unit hematite show smaller variations at 40 73 ppm uranium 2 errors of0 5 and 0 75 1 37 l g 4 he 2 errors of3 spectrometry of thorium yields values in the 1 5 ppm range for both hematites the uranium and 4 he concentration differences measured allow construction of two internal u th he isochrons yielding identical ages 2 error of 156 1 ma and 155 6 ma concordance of both isochrons in our opinion is strong evidence for a geologically significant age we interpret the data as emplacement ages further we suggest that botryoidal hematite has the potential to be a prolific chronometer for the helium method on mesozoic hematite bearing mineralizations

k ar dating of episodic mesozoic fluid migrations along the fault system of gernsbach between the moldanubian and saxothuringian northern black forest germany along the sw ne trending fault zone of gernsbach northern black forest over a distance of about 45 km between baden baden and pforzheim basal series of the sedimentary cover are extensively altered by hydrothermal solutions the fluids were conveyed in the fault zone and because of favourable permeabilities they spread out along the unconformity between the basement and sedimentary cover k ar dates on authigenic white micas illites and hydrothermally altered detrital micas point to the occurrence of two major episodes of fluid migration the extensive alteration along the entire fault system occurred about 150 ma ago during the jurassic in relation to these hydrothermal activities the epigenetic strata bound uranium deposit of mullenbach originated in upper carboniferous sediments near the fault and the fluorite quartz vein type mineralization of kafersteige was formed along the fault about 100 ma ago during the cretaceous the results indicate various geological processes of the fault system of gernsbach which is located between the saxothuringian and moldanubian zone the mobilization of the fluids and the formation of the ore deposits were probably caused by and connected with tectonic activities in mid europe

4he diffusion in 40ar retentive minerals abstract 4he vacuum diffusion experiments were carried out by stepwise degassing minerals normally used in k ar chronometry such as hornblende nepheline and others the study aims at 4he diffusion parameters for uppermost crustal temperatures and thus at he retentivities of the minerals the results indicate long time near quantitative 4he retention in hornblende pyroxene langbeinite and perhaps nepheline for 0 5 mm grains at least at temperatures below about 70 c sanidine and muscovite lose 4he over geologic periods at lower temperatures only the minerals of the first group are possible u th he chronometers or geothermometers provided that other dating problems such as alpha loss and u migration can be settled closure temperatures for rapidly cooling 2 mm hornblende crystals are found to be in the range of 190 to 170 c tentative u he indices indicate that diffusion parameters of the same order of magnitude as determined for the he retentive minerals may be used to select minerals to be further examined for their u th he datability e g ore minerals

inclusions of sedimentary brines in post variscan mineralizations in the federal republic of germany a study by neutron activation analysis abstract the post variscan vein mineralizations in the federal republic of germany are characterized by highly saline fluid inclusions t e t mice 26 to 20 c t h 1 ca 22 000 60 000 mg kg 1 cl 85 000 200 000 mg kg 1 and br 550 2 600 mg kg 1 composition and salinity of the inclusion solutions are similar to brines in deep sedimentary basins it is assumed that formation waters of the na ca cl type migrated out of permo triassic sediment troughs into culmination zones of the variscan orogen where they were heated and caused mineralizations through cooling and mixing with sulfate bicarbonate waters when reascending

structural controls and timing of fault hosted manganese at woodie woodie east pilbara western australia abstract high grade fault hosted manganese deposits at the woodie woodie mine east pilbara are predominantly hydrothermal in origin with a late supergene overprint the dominant manganese minerals are pyrolusite braunite and cryptomelane the ore bodies are located on or near the unconformities between the neoarchean carawine dolomite and the paleoproterozoic pinjian chert breccia weathering product of carawine dolomite and sedimentary units of the overlying ca 1300 1100 ma manganese group stratabound manganese is typically located above or adjacent to steep fault hosted manganese the ore bodies range in size from 0 2 to 5 5 mt with an average of 0 5 mt historically over 35 mt of manganese has been mined at woodie woodie and current ore resources are 29 94 mt at 39 94 mn 6 96 fe resource and reserves statement june 2011 consolidated minerals pty ltd manganese mineralization at woodie woodie is related to northwest southeast directed extension and basin formation during the mesoproterozoic basin architecture is generally well preserved and major manganese occurrences are localised along growth faults which down throw the pinjian chert breccia into local extensional basins manganese ore bodies are typically located on steep 2nd and 3rd order structures that extend off the major growth faults mineralized structures display a dominant northeast trend reflecting the direction of maximum dilation during northwest southeast extension a paragenetic sequence is identified for the manganese ore at woodie woodie with early hydrothermal braunite pyrolusite cryptomelane todorokite hausmannite overprinted by late supergene oxides preliminary fluid inclusion studies in quartz crystals intergrown with pyrolusite and cryptomelane indicate that primary and pseudosecondary inclusions display a range of salinities from 1 to 18 eq wt nacl and trapping temperatures estimated to be from 220o to 290o at 1 kbar pressure a lead manganese oxide coronadite is common in manganese ores at woodie woodie and pb isotope studies of 40 lead rich ore samples from 16 pits indicate mineralization occurred within an age range of 955 1100 ma a mixed source is suggested for the lead but was predominantly basalts and or volcanogenic sedimentary units e g jeerinah formation of the ca 2700 ma fortescue group the typically high mn fe ratios and enrichment in elements such as pb as cu mo zn are consistent with a dominantly hydrothermal origin for the manganese at woodie woodie supergene manganese is distinguished from hypogene manganese by a marked enrichment in ree in the supergene manganese an early structural framework established during neoarchean rifting provides a major structural control on manganese ore distribution the woodie woodie mine corridor is located in a zone of oblique strike slip extension on major northwest trending transform faults and north trending oblique normal faults a major transform structure at the southern end of the woodie woodie mine corridor jewel southwest fault zone likely acted as a major fluid conduit for manganese bearing hydrothermal fluids and this would account for the concentration of significant manganese ore occurrences to the north and south of this structure

u th he evidence of jurassic continuous hydrothermal activity in the schwarzwald basement germany abstract u th he model and isochron ages of 21 botryoidal hematites collected from the hohberg base metal vein system in the triberg granite complex mittelschwarzwald germany cover most of the jurassic period the possibility of quantitative 4 he loss triggered by successive hydrothermal events although conceivable for individual hematites based on a 4 he retentivity study and calculated opening temperatures of hematite for 4 he of 90 180 c can largely be ruled out thus the range of model and isochron ages indicates that the majority of the hematites are not cogenetic this is supported by a broad range of pb total concentrations in the hohberg botryoidal hematites 150 2700 ppm by comparison with virtually identical pb total concentrations found in cogenetic hematites from four different vein systems in the schwarzwald the th u ratios of the hematites vary by a factor of 700 0 01 7 25 mainly as a result of the range of th concentrations 0 1 74 ppm the incorporation of substantial amounts of th in hematite is thought to result from increased th transport mobility possibly caused by association with colloids and or complexing in the ore solution 18 o analyses of a 160 ma old cogenetic hematite quartz pair indicate that precipitation occurred from a fluid of magmatic origin at a temperature of 180 c the regional temperature peak in the basement at the present erosional surface during the jurassic 130 c provides a lower temperature limit of hematite formation this implies that hematite emplacement occurred at temperatures roughly ranging between 130 and 180 c the jurassic continuous hydrothermal activity suggests that the pre rifting european craton is characterized by local thermal fluxes during a long time span

4he age discordance and release behavior of a double shell botryoidal hematite from the schwarzwald germany abstract microprobe analyses of a double shell botryoidal hematite from the fahlenbach vein system schwarzwald germany show an fe3 depletion of 3 4 with respect to al3 and silicon within a 0 5 mm wide zone of alteration which separates both shells and probably is the result of a subsequent hydrothermal event induced 235u fission tracks of grain mounts from both shells reveal several grain populations within a range of 3 to 22 ppm total uranium mass spectrometer u and photometer analyses th of various localities probed within each shell vary significantly at about 5 and 12 ppm u as well as at 11 and 19 ppm th the th u ratios vary from 1 5 to 2 4he concentrations correlate with u 0 23 th heterogeneities which permits construction of two shell internal isochrons the 4he ages are discordant inner shell although mineralogically older 150 ma outer shell 182 ma 4he release by stepwise heating of one sample from each shell yielded activation energies of 124 8 and 142 7 kj mol the extrapolated 4he diffusion coefficients at 20 c logd 20 r 2 values of 19 7 0 7 and 22 2 0 6 sec 1 reveal a higher 4he retentivity at earth s surface temperatures for the outer shell 4he closure temperatures after dodson 1973 are lower for the inner shell hematite by 50 c probably also indicating earlier opening during heating the age discordance could be the result of a younger hydrothermal event which probably also has caused the observed alteration zone such an event is potentially related to the emplacement of the nearby rappenloch hematite generation ii 156 ma ago complete rejuvenation of the inner shell hematite had occurred whereas the 4he age of the outer shell was only slightly lowered due to the higher 4he retentivity

aftershock area expansion and mechanical heterogeneity of fault zone within subduction zones we investigate global variations in the pattern of aftershock area expansion associated with large subduction zone earthquakes the expansion of aftershock areas with time is relatively small in the subduction zones of alaska the aleutians mexico and parts of the kuriles and south america these subduction zones are interpreted to be characterized by moderate to strong interplate coupling in contrast the extent of aftershock expansion is greater for events within the subduction zones of northeast japan and western and south pacific where interplate coupling is inferred to be weak these results are interpreted in terms of an asperity model where a fault zone is represented by a distribution of strong spots asperities and weaker zones the immediate aftershock area is assumed to extend over an area occupied by asperities and the subsequent expansion to occur into the surrounding weaker zones if large asperities abut each other on a fault plane interplate coupling is strong and little expansion of aftershock area occurs smaller and more sparsely distributed asperities cause weak interplate coupling and significant expansion of aftershock area small and densely distributed asperities result in moderate interplate coupling and little aftershock expansion

the oxygen isotope composition of hercynian granites and pre hercynian gneisses from the schwarzwald sw germany the oxygen isotope composition of 56 hercynian granites and 42 pre hercynian gneisses has been investigated in addition some mineral 18o data and 5 d values of whole rocks have been obtained the granites from the n schwarzwald show in general relatively uniform 18o values between 11 5 and 13 5 those from the s schwarzwald are less uniform and lighter in 18o and range from 2 3 to 11 5 the gneisses from the pre hercynian basement exhibit more or less the same variation and range from 1 7 to 10 4 18o values 6 only occur in the s schwarzwald and obviously indicate hydrothermal interactions of meteoric waters which probably took place after the emplacement and solidification of the granites and which equally affected granites and gneisses due to the nearly identical 18o 16o ratios of s schwarzwald granites and gneisses it is proposed that such gneisses in the pre hercynian basement qualify as the precursor rocks of the s schwarzwald granites whereas for the n schwarzwald granites crustal rocks with heavier 18o values unknown from the present surface have to be postulated this distribution is also reflected on a 87sr 86sr 18o 16o diagram

kar ages of clay size concentrates from the mineralisation of the pedroches batholith spain and evidence for mesozoic hydrothermal activity associated with the break up of pangaea abstract the k ar ages of 32 clay concentrates extracted from samples of ore gangue and wallrock associated with mineralisation in the pedroches batholith lie in the range 119 285 ma although some of the mineralisation is of permian age more than half of the ages lie between 210 and 230 ma and indicate a hydrothermal event at this triassic time a comparison with age data for mineralisation and certain anorogenic magmatism in other areas of the north atlantic reveals a consistent pattern of a major event at ca 210 230 ma and a minor event at ca 160 ma with little cretaceous or tertiary activity it is proposed that the ca 210 230 ma event was related to an initial rapid fracturing of the crust associated with the break up of pangaea which was related with an increase in the geothermal gradient and penetration of the deep crust by surface waters which returned via both new and rejuvenated fissure systems

the fossil geothermal system of the baden baden trough northern black forest f r germany abstract limnic sediments of the upper carboniferous lower permian and triassic from the baden baden trough were hydrothermally altered during the jurassic concentric alteration halos each having a characteristic mineral composition were formed from center to margin zones of sericitization albitization and weak alteration covering an area of 100 km2 are evident these zones indicate decreasing hydrothermal influence whereby the solutions must have risen in the center the chemistry of mica changing systematically from a muscovitic toward an illitic composition also reflects this trend the boron content increases from 75 to 205 ppm the estimated maximum alteration temperature ranges between 240 and 290 c these remarkable changes are obviously early manifestations of geothermal events related to the development of a continental rift rhine graben

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