the terrestrial alteration of saharan shergottites dar al gani 476 and 489 a case study of weathering in a hot desert environment abstract rare earth element ree and other selected trace and minor element concentrations were determined in various phases of dar al gani 476 and 489 two basaltic shergottites recently found in the libyan sahara whereas merrillite and feldspathic glass compositions do not seem to have been altered since the fall of these meteorites olivine and pyroxenes commonly show light ree enrichments sometimes accompanied by ce anomalies that are attributed to terrestrial alteration sr and ba enrichments are also observed the calcium carbonate that resides in most cracks is essentially devoid of ree but a fine grained amorphous silicate material that fills some veins and pockets has striking light ree enrichments and elevated p sr and ba it is argued that this material likely to be impact melt as well as the notoriously light ree poor olivine and pyroxenes were preferentially affected by a crustal light ree rich contaminant caution is urged when using whole rock or even mineral separate compositional and isotopic data for hot desert meteorites

application of regional frequency analysis to the estimation of extreme storm surges traditionally extreme value theory is applied to single site series of surge observations in order to estimate the probability of occurrence of extreme events at that particular site however single site analyses give uncertain estimation of extreme quantiles mainly because of the limited duration of observation periods in order to reduce this uncertainty regional frequency analysis rfa approaches suggest collecting information not only from a single site series but also from all statistically similar available series of observation the use of rfa is widely increasing in geosciences but few applications have been attempted yet for surge estimation the aim of this study is to examine the applicability of rfa to extreme storm surges the surge data observed at 18 french harbors located on the atlantic coast from the spanish to belgian borders were collected the series span a period of 30 years on average with the longest series going back to the 19th century stationary and independent samples of extreme surges peaks over a given threshold are extracted and their statistical homogeneity has been tested via heterogeneity and discordancy measures based on l moments homogeneous regions have been identified and in order to merge information on frequency of occurrence of surges from all the sites a surge index pooling method is defined finally a regional frequency distribution has been estimated the hypothesis and the applicability of rfa application are discussed with some ideas for future developments in the research direction

ce anomalies in the lew85300 eucrite evidence for ree mobilization during antarctic weathering abstract there is abundant evidence for widespread ree mobilization in antarctic eucrites resulting in ce and eu anomalies and lower whole rock ree abundances relative to typical eucrites using secondary ion mass spectrometry sims we investigated the microdistribution of ce anomalies in the antarctic polymict eucrite lew85300 ce anomalies positive and or negative are present in all three of the minerals plagioclase pyroxene and silica analysed the anomalies occur in grains from all four clasts as well as in mineral and lithic fragments from the surrounding matrix thus there appears to be no lithologic association silica which has been heavily shocked and altered exhibits a lree enriched pattern with negative ce and eu anomalies consistent with a derivation of the ree from ca phosphate dissolution trivalent ree are leached from the phosphates with preferential retention of tetravalent ce and redeposited on silica pyroxene is also widely affected by ree mobilization due to an extensive shock induced microcrack network along cleavage planes a tendency for the largest ce anomalies to occur at low lree concentrations suggests that pyroxene itself experienced ree leaching with concomitant ce retention ce anomalies are rare in plagioclase because this mineral lacks an extensive network along which ree can be mobilized the widespread ree mobilization and evidence for other forms of weathering requires that trace element data be used cautiously especially for antarctic eucrites

calcite dolomite geothermometry in the system caco3 mgco3 feco3 an experimental study an experimental study of the system caco3 mgco3 feco3 was undertaken in order to calibrate the iron correction to the calcite dolomite geothermometer which is based on the solubility of magnesium in calcite in the assemblage calcite dolomite the experiments at 450 c and lower temperatures resulted in products with a very small grain size and incomplete equilibration however application of a carefully devised automatic data processing algorithm to analyses of the phases in experimental charges combined with a thermodynamic analysis results in geothermometer diagrams which should be preferred to previous theoretical predictions

oxygen isotope studies of achondrites abstract oxygen isotope abundances provide a powerful tool for recognizing genetic relationships among meteorites among the differentiated achondrites three isotopic groups are recognized l snc mars 2 earth and moon and 3 hed howardites eucrites diogenites the hed group also contains the mesosiderites main group pallasites and silicates from iiiab irons the angrites may be marginally resolvable from the hed group within each of these groups internal geologic processes give rise to isotopic variations along a slope 1 2 fractionation line as is well known for terrestrial materials variations of 17o from one planet to another are inherited from the inhomogeneities in the solar nebula as illustrated by the isotopic compositions of chondrites and their constituents among the undifferentiated achondrites five isotopic groups are found 1 aubrites 2 winonaites and iab iiicd irons 3 brachinites 4 acapulcoites and lodranites and 5 ureilites the isotopic compositions of aubrites coincide with the earth and moon and also with the enstatite chondrites these bodies apparently were derived from a common reservoir the isotopic composition of which was established at the chondrule scale by nebular processes isotopic similarities between chondrites and achondrites are seen only for the following instances 1 enstatite chondrites and aubrites 2 h chondrites and he irons and 3 l or ll chondrites and iva irons the isotopic data also support the following genetic associations 1 winonaites and iab iiicd irons 2 acapulcoites and lodranites and 3 ureilites and dark inclusions of c3 chondrites an attempt to reconcile the whole planet isotopic compositions of earth mars and the eucrite parent body with mixing models of their chemical compositions failed it is not possible to satisfy both the chemical and isotopic compositions of the terrestrial planets using known primitive solar system components

40ar 39ar dating of microgram feldspar grains from the paired feldspathic achondrites gra 06128 and 06129 abstract 40 ar 39 ar ages of single feldspar grains from the paired meteorites graves nunatak 06128 gra8 8 grains and 06129 gra9 26 grains are presented plateau ages 70 of the 39 ar released ranged from 4000 to 4600 ma with an average 1 uncertainty of 90 ma the most precise ages obtained were 4267 17 ma for a grain from gra8 and 4437 19 ma and 4321 18 ma for two grains from gra9 isotope correlation diagrams yield less precise ages ranging from 3800 to 5200 ma with an average 1 uncertainty of 250 ma they indicate a negligible trapped component plateau ages integrated total fusion ages and isochron ages are internally concordant at the 95 confidence level the distribution of the plateau ages for gra9 is bimodal with peaks at 4400 and 4300 ma in contrast the plateau age distribution for gra8 peaks at about 4260 ma with broad wings extending toward younger and older ages to explain the distributions of grain ages we prefer a scenario that includes a major post formation event about 4400 ma ago and a later melt intrusion event that heated gra8 more than some parts of gra9

upb zircon and rutile chronology of archean greenstone formation and gold mineralization in the val d or region quebec abstract u pb geochronology provides an absolute time framework for the evolution of the sigma gold deposit and surrounding rocks at val d or southern abitibi subprovince the bourlamaque batholith the largest pluton in the area gives a 2699 8 1 0 ma u pb zircon age this pluton cuts the val d or formation which hosts the mineralization a u pb zircon age of 2704 9 1 1 ma on a felsic volcanic rock the colombiere rhyolite 13 km east of the mine dates that formation the gold bearing quartz vein system at sigma is hosted by andesites and two generations of porphyry intrusions all metamorphosed to the greenschist facies the oldest porphyry porphyritic diorite shows the same deformation as the volcanic rocks and has a 2703 7 2 5 ma u pb zircon age the porphyritic diorite and volcanic rocks are cut by feldspar porphyry dykes which post date regional folding and have a 2694 0 2 2 ma u pb zircon age regional greenschist metamorphism has been dated directly with a u pb date of 2684 7 ma on rutile in the colombiere rhyolite the mineralization and hydrothermal alteration in the mine are superimposed on the metamorphic minerals hydrothermal rutile from an alteration halo around the veins in andesite has a 2599 9 ma u pb age textural evidence clearly indicates that the wall rock alteration and vein filling are contemporaneous and hence the vein system and gold mineralization appear to have developed at least 80 m y after the formation and metamorphism of host greenstones

direct detection of projectile relics from the end of the lunar basin forming epoch the lunar surface a key proxy for the early earth contains relics of asteroids and comets that have pummeled terrestrial planetary surfaces surviving fragments of projectiles in the lunar regolith provide a direct measure of the types and thus the sources of exogenous material delivered to the earth moon system in ancient 3 4 billion years ago ga regolith breccias from the apollo 16 landing site we located mineral and lithologic relics of magnesian chondrules from chondritic impactors these ancient impactor fragments are not nearly as diverse as those found in younger 3 4 ga to today regolith breccias and soils from the moon or that presently fall as meteorites to earth this suggests that primitive chondritic asteroids originating from a similar source region were common earth moon crossing impactors during the latter stages of the basin forming epoch

a petrologic thermodynamic and experimental study of brachinites partial melt residues of an r chondrite like precursor abstract the primitive achondrites provide a window into the initial melting of asteroids in the early solar system the brachinites are olivine dominated meteorites with a recrystallized texture that we and others interpret as evidence of partial melting and melt removal on the brachinite parent body we present a petrologic thermodynamic and experimental study of the brachinites to evaluate the conditions under which they formed and test our hypothesis that the precursor material to the brachinites was feo rich compared to the precursors of other primitive achondrites petrologic analysis of six brachinites brachina allan hills alh 84025 hughes 026 elephant moraine eet 99402 northwest africa nwa 3151 and nwa 4969 and one brachinite like achondrite nwa 5400 shows that they are meteorites with recrystallized texture that are enriched in olivine 80 vol and depleted in other minerals with respect to a chondritic mineralogy silicates in the brachinites are feo rich fa 32 36 brachinite like achondrite northwest africa 5400 is similar in mineralogy and texture to the brachinites but with a slightly lower feo content fa 30 thermodynamic calculations yield equilibration temperatures above the fe ni fes cotectic temperature 950 c for all meteorites studied here and temperatures above the silicate eutectic 1050 c for all but two brachina formed at an f o 2 of iw and the other brachinites and nwa 5400 formed at iw 1 all the meteorites show great evidence of formation by partial melting having approximately chondritic to depleted chondritic mineralogies equilibrated mineral compositions and recrystallized textures and having reached temperatures above that required for melt generation in an attempt to simulate the formation of the brachinite meteorites we performed one atmosphere gas mixing partial melting experiments of r4 chondrite lapaz ice field 03639 experiments at 1250 c and an oxygen fugacity of iw 1 produce residual phases that are within the mineralogy and mineral compositions of the brachinites these experiments provide further evidence for the formation of brachinites as a result of partial melting of a chondritic precursor similar in mineralogy and mineral compositions to the r chondrites

generation of abnormal trace element abundances in antarctic eucrites by weathering processes abstract based on rees antarctic eucrites can be divided into two groups those showing normal trace element characteristics e g similar to juvinas and those showing abnormal trace element abundances many antarctic eucrite polymict eucrite and basaltic clast samples show the abnormal trace element abundances with ree patterns exhibiting positive ce anomalies sometimes negative ce anomalies positive eu anomalies and low abundances of the remainder of the rees with the lrees generally being at lower relative abundances than the hrees most samples of crystalline clasts from the polymict eucrites lew85300 lew85302 and lew85303 show the abnormal patterns while the glassy matrixes of these meteorites show normal patterns exterior samples generally show more abnormal patterns larger anomalies greater depletions than interior samples from the same meteorites comparison of all basaltic eucrite literature data combined with our data shows that positive and negative ce anomalies and positive eu anomalies are found in about 61 of antarctic eucrite analyses and are virtually unknown in non antarctic eucrite analyses further positive ce anomalies and positive eu anomalies are commonly associated with antarctic eucrites having low ree concentrations consideration of mineral melt partition coefficients shows that it is unlikely that ce anomalies are magmatic features from the hed parent body cerium anomalies on earth are generally restricted to the weathering zone where the relative ease of oxidizing ce to the 4 state allows for fractionation of ce from the 3 rees we believe the unusual ree patterns of abnormal antarctic eucrites arise from weathering effects generated in or on the antarctic ice our suggested scenario involves formation of melt water and its equilibration with the atmosphere which promotes dissolution of ree rich phosphates and oxidation of ce tetravalent ce can then be fractionated from the trivalent ree in solution the details of the weathering process are unclear and will require detailed chemical and sem investigations of eucrites for their elucidation we predict that rapidly chilled eucrites with glassy rather than crystalline mesostases will be more likely to survive the antarctic environment without alteration of their ree patterns occasional s se and k enrichments are likely due to weathering in the antarctic environment as well but these enrichments are not well correlated with ce anomalies

the gold content of some archaean rocks and their possible relationship to epigenetic gold quartz vein deposits gold mineralization in archaean granite greenstone environments especially gold quartz veins contributes considerably to the world s gold production the formation of epigenetic gold mineralization in greenstone belts is generally explained by the metamorphic secretion theory this theory is based on the assumption that the source of the gold may be komatiitic or tholeiitic lavas pyritic chemical or clastic sediments and even granitic rocks from which as a result of regional metamorphic overprinting gold was extracted and concentrated in suitable structures it has been shown that in proposed potential source rocks gold is predominantly associated with sulfide minerals and thus relatively easily accessible to secretion and reconstitution processes a large number of various rock types originating from granite greenstone terranes of the kaapvaal and the rhodesian cratons were geochemically investigated and the following ranges for gold determined volcanic rocks komatiitic and tholeiitic 0 1 372 ppb granitic rocks of the basement 0 3 7 8 ppb iron rich chemical sediments 1 0 667 ppb statistical treatment of the data reveals that volcanic rocks as well as iron rich chemical sediments are favorable sources for epigenetic gold mineralization formed by metamorphic secretion while the granitic rocks make less suitable primary gold sources this finding explains the close spatial relationship which is common between gold quartz veins and greenstone belts the conspicuous abundance of epigenetic gold mineralization in the archaean however is attributed to the unique geologic and metamorphic history of the granite greenstone terranes

hindcast of the wave conditions along the west iberian coast this paper describes the development of a wave prediction system for the west iberian coast the implemented wave prediction system is based on two state of the art spectral wave models wam for the ocean area and swan for the nearshore however because of its extended geographical space the swan model will include some generation effects in the coarse swan simulations complemented by wave transformation effects near the coast the system was validated by means of extended hindcast runs in various regions belonging to the continental portuguese coastal environment which were compared with buoy data focusing on the extreme energetic events and both direct comparisons and statistical results are presented

martian gases in an antarctic meteorite significant abundances of trapped argon krypton and xenon have been measured in shock altered phases of the achondritic meteorite elephant moraine 79001 from antarctica the relative elemental abundances the high ratios of argon 40 to argon 36 2000 and the high ratios of xenon 129 to xenon 132 2 0 of the trapped gas more closely resemble viking data for the martian atmosphere than data for noble gas components typically found in meteorites these findings support earlier suggestions made on the basis of geochemical evidence that shergottites and related rare meteorites may have originated from the planet mars

expected characteristics of cometary meteorites recent developments in our understanding of comets provide insights into the topic of cometary meteorites these developments include the identification of comet asteroid transition objects such as 4015 wilson harrington and 3200 phaethon information on the composition of cometary solids and new ideas on the collisional history of jupiter family comets in this work we revisit this question and we conclude that comets do indeed yield macroscopic meteorites which either have not been found or have not been recognized we also consider the expected characteristics of cometary meteorites with an emphasis on those that may help identify and differentiate them from other types of meteorites if cometary meteorites have preserved the main characteristics of cometary dust the mineralogy would be dominated by highly unequilibrated anhydrous silicates and the chemistry would be nearly chondritic but with a high abundance of c and n on the other hand if an unknown process produced extensive aqueous alteration in the material that formed cometary meteorites they would resemble or could even be ci carbonaceous chondrites we do not expect cometary meteorites to have chondrules so far no single meteorite looks unequivocally cometary however we have identified xenoliths in ordinary chondrite regolith breccias that meet most of our criteria for a cometary origin and deserve further study

physical chemical properties and metal budget of au transporting hydrothermal fluids in orogenic deposits we use a set of analytical techniques for fluid inclusion analysis to determine the bulk properties of the ore fluids from five orogenic gold deposits the most common ore fluid is a low salinity 0 4 6 5 wt nacl twoto three phase aqueous carbonic fluid its th total range is 200 400 8c and total homogenization occurs by bubble or liquid disappearance a less common aqueous fluid of similar bulk salinity and t h total is also documented microchemical data show that the ore fluid in the five deposits is chemically uniform and made of na subordinate k and b and minor to trace amounts of cu as li sr rb ba cs sb and au range 0 5 5 mg g thermodynamic modelling carried out for one of the studied deposits indicates that the ore fluid was in equilibrium with vein minerals at the time of gold deposition and that its vapour phase was distinctly enriched in au b as and sb the proposed mechanism of gold precipitation is a combination of fluid decompression and boiling combining these results with 3d geometrical reconstructions of one of the studied deposits sigma we estimate that a minimum ore fluid volume of c 0 1 1 0 km is sufficient to generate a world class orogenic deposit orogenic deposits provide about a third of the global gold production goldfarb et al 2001 frimmel 2008 these deposits are formed within active continental margins in orogenic belts where major tectonic boundaries juxtapose metamorphosed volcanic plutonic and sedimentary terranes the ore bodies consist of au mineralized vein networks filled with quartz carbonates and other silicates that in places crosscut the stacked terranes of the continental margins the veins are dilated portions of vertically extensive brittle ductile to ductile fracture networks that form due to the advection of aqueous hydrothermal fluids within the continental crust ridley et al 1996 groves et al 2003 these ore fluids are generated in still undefined source regions deep in the crust and transported to shallower levels 3 15 km depth through the vein networks along which they deposit gold a number of studies kerrich et al 2000 ridley diamond 2000 groves et al 2003 showed that although these networks do not occur systematically in all orogens they have a set of important geological features in common which include 1 formation during accretionary orogenic events 2 occurrence relatively close to regional tectonic lineaments especially along lower order splays of these structures 3 spatial association with granitoid intrusions 4 occurrence within some metamorphic belts with gold precipitation being synto postmetamorphic in age 5 relatively low sulphide abundance within the veins 6 carbonate sericitealbite sulphide hydrothermal alteration of host rocks postdating metamorphism 7 poorly developed mineral and metal zoning within the ore bodies and 8 genesis from low to moderate salinity ore fluids over a large temperature range 250 700 8c but mostly within 300 350 8c these common traits occur systematically in deposits from different terrains having distinct ages suggesting that a common geological process and au transporting fluid are responsible for their formation here we present a database of fluid inclusion properties from five typical orogenic deposits which show most of the geological characteristics listed above the database was constructed with the aim of determining as accurately as possible the properties of the au transporting fluid in this geological environment in particular laser ablation inductively coupled plasma mass spectrometry la icp ms of single fluid inclusions paragenetically coeval with vein gold provides the concentration of a suite of metals including au in this fluid this dataset when combined with 3d geometrical reconstructions of one of these deposits offers new constraints on the volume of the ore from garofalo p s ridley j r eds gold transporting hydrothermal fluids in the earth s crust geological society london special publications 402 http dx doi org 10 1144 sp402 8 the geological society of london 2014 publishing disclaimer www geolsoc org uk pub ethics by guest on april 3 2014 http sp lyellcollection org downloaded from

teleconnection pattern influence on sea wave climate in the bay of biscay the potential modification of hydrodynamic factors such as waves is a source of concern for many coastal communities because of its potential effect on shoreline evolution in the northern atlantic swell is created by storm winds that cross the atlantic following west east tracks these tracks are shifted more southward or northward depending on the season and on recurring large scale atmospheric pressure anomalies also called teleconnection patterns this study investigates the trends of sea wave patterns in the bay of biscay and relates their interannual variability to teleconnection patterns sea wave parameter time series from the 40 yr european centre for medium range weather forecasts

fe mg fe mn relations of meteorites and primary heterogeneity of primitive achondrite parent bodies abstract we examine fe mg mn relations of meteorites as represented on plots of molar fe mg ratio vs molar fe mn ratio and use them to consider whether it is meaningful to classify achondrites as primitive or evolved first we demonstrate that fe mg fe mn plots can be used to identify some of the major processes that have affected meteorite parent bodies during both the nebular condensation and accretion and the planetary igneous stages of their evolution examination of compositions of chondrites on this diagram reveals distinct patterns that result from three nebular processes 1 volatility controlled mn mg fractionation 2 metal silicate fractionation under highly reducing conditions and 3 subsequent oxidation leading to variations in feo mgo ratio ordinary chondrites ocs show a characteristic pattern that records all three of these processes and suggests that the latter two are coupled examination of the compositions of achondrites on this diagram shows that all of those that have been classified as primitive lodranites acapulcoites winonaites iab silicate inclusions brachinites and ureilites are easily distinguished from those that have been classified as evolved sncs heds and lunar basalts the mn mg ratios of the former are chondritic while those of the latter are superchondritic hence they plot in two graphically distinct regions of the fe mg fe mn diagram a simple melting calculation reveals that this distinction results principally because the former are residues and the latter are melts or cumulate products of melts rather than because the latter are more evolved additionally however some of the groups classified as primitive achondrites show fe mg fe mn patterns similar to that of ocs constant but distinct mno mgo ratios over large ranges of feo mgo ratio we argue that these trends reflect primary heterogeneity resulting from the same nebular processes as those that affected ocs and therefore preserve evidence that more of the materials that accreted to form planetesimals experienced these processes than is apparent from known chondrites this evidence is preserved principally because these meteorites are residues in contrast groups commonly classified as evolved achondrites show fe mg fe mn patterns that reflect only igneous processing and any evidence for primary heterogeneity of their parent bodies has been obliterated again this is principally because these meteorites represent melts rather than beause they are more evolved usage of the terms primitive and evolved to describe achondrites should be clearly defined

estimating the upper tail of flood peak frequency distributions using hydrometeorological information in its 1988 report the national research council committee on estimating the probabilities of extreme floods identified principles for improving the estimation of floods with annual exceedance probabilities of the order of 10 3 or smaller this paper presents a methodology for estimating the probability of extreme floods which makes use of these principles its core is the peak to volume method bradley and potter 1992 which is based on separately estimating the probability distributions of flood volumes and flood peaks conditioned on volumes in its original form it relies on extrapolating a conventionally estimated probability distribution the distribution of flood volumes to strengthen this step we propose use of the gradient of extreme values gradex method guillot and duband 1967 in which the upper tail of the flood volume distribution is deduced from that of precipitation we enhance the gradex method by exploiting the work of smith 1989 who developed a regional model for estimating the upper tail of a frequency distribution based on extreme order statistics an example illustrates the proposed method

fluid wall rock interaction in an archean hydrothermal gold deposit a thermodynamic model for the hunt mine kambalda gold mineralization at the hunt mine kambalda is situated in a 20 m thick steeply dipping shear zone within a sequence of rather uniform metabasalts zonal alteration of the host rocks occurred around fractures which acted as conduits during gold mineralization limited major element mobility ensured assemblages of low variance over most of the alteration zone providing a suitable environment for the application of thermodynamics in conjunction with detailed petrographic geochemical electron microprobe analysis of mineral compositions and fluid inclusion studies microthermometry equilibrium equations involving fluid components and alteration minerals are used to determine conditions during the alteration event and in particular activity gradients of components profiles across the schist zone show increasing f sub h 2 s around auriferous quartz veins log f sub h 2 s 0 6 but constant f sub o 2 log f sub o 2 29 7 these results are near the magnetite pyrrhotite pyrite triple point for the inferred temperature of 350 degrees c and explain the pyrite pyrrhotite magnetite zonation sequence outward from veins the profile of x sub co 2 is very close to the value of 0 25 determined independently from fluid inclusions the k super h super profile shows increases adjacent to auriferous veins corresponding to the zone of biotite stability using a value for fluid salinity of 2 equiv wt percent nacl ph was calculated to be around 6 9 the solubility of gold in solution was estimated for the calculated conditions for the complex au hs super 2 the maximum solubility is around 0 5 mg kg super 1 i e 0 5 ppm for au cl super 2 it is close to 10 super 6 mg kg super 1 indicating the efficacy of sulfide transport of gold compared to chloride transport under these conditions the calculated decrease in f sub h 2 s away from the auriferous quartz veins results in an 80 percent or greater decrease in gold solubility suggesting hat the sulfidation of fe rich wall rocks is a geologically reasonable and very efficient mechanism for precipitating gold from solution at elevated temperatures

fluid chemical evolution as a factor in controlling the distribution of gold at the archean golden crown lode gold deposit murchison province western australia the golden crown lode gold deposit is one of a number of northwest southeast to north south trending quartz veins hosted by a steeply dipping 500 m thick differentiated dolerite sill the great fingall sill and adjacent graphitic shale in the day dawn district of the murchison province in the archean yilgarn craton western australia quartz veins of the golden crown deposit are shear zone hosted crosscut the dominant host rock stratigraphy at a high angle and are laminated partly boudinaged and generally bifurcate at their extremities veins are dominated by dark gray or milky white quartz with subordinate calcite and ankerite and in order of abundance arsenopyrite pyrrhotite pyrite galena chalcopyrite and minor sphalerite the vein sulfides coexist with native gold and are most abundant at vein margins textural evidence indicates that precipitation of the majority of these minerals overlapped and that most phases can be considered to have been in equilibrium during vein genesis mineral chemistry fluid inclusions alteration and ore assemblages show that there are significant systematic gradients in intensive variables within the golden crown deposit these are recorded over the approximately 450 m of vertical exposure of the vein system and over up to 30 m into the wall rocks based on proximal alteration assemblages and zoning patterns zoned wall rock alteration haloes are divisible into four sequences three of which are closely related to gold mineralization specific alteration sequences occur within different parts of the vein system biotite alteration predominates in the deeper portions whereas muscovite alteration characterizes the upper and southern portions of the system higher grade gold zones within the golden crown deposit are limited to the northern end of the system in the deeper portion of the veins and expand along strike to the south in the upper portions fluid inclusions interpreted to be trapped during gold mineralization are low salinity 10 wt nacl equiv h2o co2 ch4 inclusions with variable carbonic to aqueous contents that are interpreted to be due to fluid immiscibility inferred methane concentrations in the carbonic phase vary significantly from 19 7 mole percent in the vicinity of the shale contact to 5 2 mole percent in the shallower southern end of the deposit carbon and oxygen isotope compositions of carbonates 13ccalcite 10 5 to 1 9 13cankerite 5 3 to 4 1 18ocalcite 7 0 18 3 and 18oankerite 7 7 9 2 and oxygen isotope compositions of vein quartz 18oquartz 10 2 12 5 are well within the range of known archean orogenic lode gold deposits combining the results of all geothermometers and geobarometers a temperature of 300 to 400 c and pressure of 2 5 0 5 kbars are determined with temperature variations over the exposed quartz vein of less than 40 c the as content at of arsenopyrite and au ag ratios of native gold show significant compositional variation which appears to be controlled by parameters such as a h2s aq and f o2 not temperature gradients on the basis of the variations in fluid composition determined in the reefs the two major processes responsible for high grade gold mineralization are interpreted to have been phase separation in the deeper portions of the ore forming system approximately below 400 m level and above these levels mixing between two modified ore fluids one reduced fluid that had reacted with graphitic shale and a relatively oxidized fluid that had partly equilibrated with dolerite

mineralogic fluid inclusion and stable isotope studies of several gold mines in the mother lode tuolumne and mariposa counties california gold bearing quartz veins in the southern part of the mother lode california formed from fluids which contained si k co 2 ca s and metals and which were focused into permeable fault zones in the coulterville district of the mother lode these fluids altered serpentinite to a talc chlorite magnesite quartz assemblage which is crosscut by veins containing quartz dolomite sericite sulfides tellurides and gold textural relationships among the vein filling minerals reveal that galena tellurides pb ni ag au ag and native gold precipitated last among the vein minerals observations from the oro rico and mcalpine mines coulterville district indicate that these deposits were subjected to deformation during and after their formation fluid inclusions in the milky vein quartz exhibit only a narrow range in t sub m ice but a large range in t h which probably reflects posttrapping deformation microthermometry of fluid inclusions from vug filling quartz in the alleghany district in the northern portion of the mother lode reveals low salinity 2 h 2 o fluids with t sub mco 2 56 7 degrees c t sub m clathrate 9 5 degrees c and t sub h total 150 degrees to 200 degrees c visual estimates of co 2 content indicate a maximum of 10 mole percent co 2 in contrast inclusions from vug filling quartz in the coulterville district are filled with low salinity low t h 110 degrees 140 degrees c h 2 o rich fluids which were probably later than and unrelated to the gold mineralizing fluids oxygen isotope values of vein quartz from the southern mother lode indicate formation by 18 o enriched fluids in the range 6 to 11 per mil vs smow these values are similar to estimates of 8 to 15 per mil from vein quartz of the alleghany district taylor 1981 boehlke and kistler 1986 the average delta 13 c values for magnesite and dolomite of 4 5 or 0 6 per mil vs pdb from the southern mother lode are identical to results from the alleghany district 200 km to the north rosenbaum and taylor 1984 these data suggest either a single or well mixed source of oxidized carbon for the fluids oxygen isotope compositions of magnesite calculated using an experimentally derived phosphoric acid fractionation factor at 50 degrees c of 1 0096 are enriched in 18 o relative to coexisting dolomite as predicted for isotopic equilibrium the chemistry of the mother lode ore forming fluids is characterized by several approaches with an x sub co 2 estimate of 0 1 from fluid inclusions quartz magnesite assemblages in the coulterville serpentinite alteration zones limit the temperature of formation to below 325 degrees c for p 2 h 2 o fluid coupled with the assumption of trapping temperatures of 300 degrees c suggests minimum trapping pressures of 1 000 to 2 000 bars assuming equilibrium the assemblage of daughter minerals described by coveney 1981 indicates neutral ph conditions of 5 5 to 6 0 at the prevailing p t conditions sulfide mineral stabilities imply that h 2 s was the dominant sulfur species and that a sub o 2 of the mineralizing fluids was in the range 10 super 32 to 10 super 35 our preferred model for the formation of the mother lode vein system involves magmatic activity associated with a subducting slab in this model generation of ore forming fluids is possible by a variety of mechanisms including metamorphic devolatilization reactions in rocks adjacent to the plutons direct magmatic input and deep circulation of meteoric water any of these mechanisms is possible given the available data on the mother lode deposits

the silidor deposit rouyn noranda district abitibi belt geology structural evolution and paleostress modeling of an au quartz vein type deposit in an archean trondhjemite late orogenic gold bearing quartz vein deposits within the rouyn noranda mining district occur mainly within archean tonalitic plutons of the blake river group southern abitibi belt the silidor deposit is a representative example of a pluton hosted lode gold deposit the silidor mine contained 2 95 million tons mt mined and estimated reserves grading 5 1 g t au 15 t au the mineralized zone is 900 m in length and has a vertical extent of 900 m an average thickness of 3 5 m and trends northwest southeast with a dip of 50 to 70 ne its alteration envelope consists of a red hematite altered trondhjemite measured 18 o values for quartz veins 7 7 10 9 and 34 s values for pyrite 6 1 to 9 4 imply oxidizing conditions during gold deposition the mineralized zone comprises vein quartz white gray and smoky varieties beige mineralized trondhjemite and green carbonate sericite fuchsite breccia which resulted from shearing and metasomatism of an early northwest southeast dioritic dike a quantitative microtectonic study 400 measurements was carried out on the powell tonalitic sill in the silidor mine area to reconstruct the deformation before during and after the mineralizing events the reduced stress tensors display large variations in 1 orientation trending successively northwest southeast northeast southwest and finally north south the silidor deposit is the result of several vein filling events which occurred during evolution from strike slip faulting to reverse faulting regimes with 1 remaining northeast southwest but with exchange of orientation of 2 and 3 such variations may reflect an oblique collision and processes of stress permutation paleostress mapping of archean terranes can be used as a targeting tool for mesothermal lode gold deposits reduced stress tensors were used for the computation of paleostress maps using a distinct element model the silidor au quartz mineralization appears on these paleostress maps in an area characterized by low mean stress throughout the deformation history of the area near the horne creek fault this study emphasizes the role of second order faulting in the location of low and high pressure zones in the archean crust and the possible role of a tectonic indentor in the location of au mineralization

carbonate sulfide equilibria and stratabound disseminated epigenetic gold mineralization a proposal based on examples from alleghany california u s a abstract stratabound disseminated pyritic au ore bodies were produced by reactions between wall rocks and through flowing fluids in mesozoic epigenetic au quartz vein systems in the sierra nevada metamorphic belt equilibrium relations among fe bearing carbonate and sulfide minerals were critical in determining which rock types were likely to host disseminated mineralization along portions of discordant veins the compositions of metasomatic carbonates in hydrothermally altered wall rocks at alleghany california u s a were larely predetermined by the relative proportions of fe mg and ca in the unaltered wall rocks thus coexisting solid solutions in the magnesite siderite and dolomite ankerite series from a variety of different wall rocks yield an empirical phase diagram for a large part of the ca co 3 mgco 3 feco 3 system at the temperature of metasomatism 325 50 c because fe mg silicates were unstable in alteration zones adjacent to the veins wall rock fe was partitioned between carbonates and sulfides pyritization and disseminated au mineralization occur in a variety of igneous and metasedimentary wall rocks in which the initial molar fe fe mg 0 5 in altered wall rocks with initial molar fe fe mg 0 5 fe was incorporated almost entirely within mg rich carbonates x feco 3 0 6 in magnesite siderite solutions it is proposed that the co 2 rich vein fluid responsible for the alteration and mineralization was partially buffered with respect to h 2 s co 2 h 2 ratios by equilibrium between pyrite and mg 0 4 fe 0 6 co 3 graphite as it traversed and altered intermediate volcanic and sedimentary rocks this fluid then locally reacted with lower fe fe mg rocks to form fe bearing dolomite magnesite assemblages and reacted with higher fe fe mg rocks to form ankerite pyrite assemblages gold precipitated from saturated solutions of bisulfide complexes partly in response to fluid desulfidation and reduction caused by the pyritization reactions in terranes dominated by intermediate metavolcanic and metasedimentary rocks favorable host rocks for this type of mineralization need not have high fe contents but do require high fe fe mg ratios they may include felsic volcanic and plutonic rocks fe rich tholeiitic differentiates banded fe formations and a variety of siliceous and argillaceous sedimentary rocks rocks which tend not to be heavily sulfidized because they have low initial fe fe mg ratios include ultramafic and mafic igneous rocks and some argillaceous sedimentary rocks exploration guidelines based on these principles may be useful elsewhere in the sierra nevada and in other comparable heterogeneous metamorphic terranes if modified to reflect the dominant buffering rock types in a given fluid flow path carbonate sulfide equilibria are capable of approximately buffering the carbonate sulfide ratios of co 2 rich vein fluids f co 2 10 2 8 at 325 c 200mpa or 2000 bar the alleghany fluid f co 2 10 3 2 or 10 mol co 2 had a molar co 2 h 2 s ratio of approximately 10 3 assuming graphite saturation at lower co 2 fugacities fe bearing silicates entered the buffering assemblages carbonatization reactions could potentially de sulfidize some wall rocks releasing s and associated metals to the fluid this would be most likely to occur in pyrite bearing mafic and ultramafic rocks and some argillites

gold abundance and an aluminosilicate rich alteration zone in the val d or mining district abitibi quebec examples of the fossil geothermal fields abstract investigation of gold abundance in a gold rich mining district by accurate analytical techniques e g instrumental neutron activation and or radiochemical neutron activation shows that gold is anomalously distributed in some parts of the val d or mining district of quebec it is possible to distinguish 1 background values 1 4 3 5 ppb au 2 zones of primarily anomalous gold values around the lamaque sigma mines median 15 ppb au 3 enrichment halos around gold orebodies median 70 ppb au 4 secondary gold enrichment in shear zones and 5 high background values for the east sullivan monzonitic stock the bourlamaque batholith is considered to be a gold enriched intrusion because of areas shear zones that are anomalously enriched in gold median 10 ppb au it is concluded that there are auriferous geological units in the val d or mining district such as the bourlamaque batholith and val d or formation the latter contains the lamaque sigma gold mines representing 49 6 of the total gold production in the district it is interpreted that the val d or formation is part of a central volcanic complex within an island arc system that the centre of this complex is located in the main lamaque plug and that this environment may be compared to high temperature active geothermal systems which are commonly responsible for the formation of epithermal gold deposits the lamaque sigma area is considered to be a fossil geothermal field potentially explaining the anomalous gold values in addition a dumortierite bearing aluminosilicate rich zone of hydrothermal alteration in the val d or mining district is considered as for other similar occurrences to be the result of hydrothermal alteration within a geothermal field producing an al and si rich leached protholith which has subsequently been metamorphosed and deformed a model is proposed for the formation of the gold deposits within the primary gold rich environment by mobilisation of gold in the volcanic rocks due to metamorphism and deformation therefore two distinct and successive events are postulated 1 gold rich synvolcanic geothermal activity and 2 late remobilisation from the host rocks followed by deposition of gold ore within favourable structures

the case for a martian origin of the shergottites nitrogen and noble gases in eeta 79001 abstract nitrogen and noble gases were measured in samples of a glass inclusion and the surrounding basaltic matrix from the antarctic shergottite eeta 79001 a nitrogen component trapped in the glass but not present in the matrix has a 15n value at least as high as 190 ratios of40ar 14n and15n 14n in the glass are consistent with dilution of a martian atmospheric component 15n 620 160 40ar 14n 0 33 0 03 by either terrestrial atmosphere adsorbed on the samples or by indigenous nitrogen from the minerals of the rock trapped noble gases in the glass reproduce within error the elemental and isotopic compositions measured in mars atmosphere by viking and are in general agreement with previous measurements except for much lower abundances of neutron generated krypton and xenon isotopes the most reasonable explanation at the present time for the noble gas pattern and the isotopically heavy nitrogen is that a sample of martian atmosphere has been trapped in the eeta 79001 glass and that this meteorite and thus the shergottites and probably the nakhlites and chassignites as well originated on mars nitrogen in the non glassy matrix of eeta 79001 amounts to less than 0 5 ppm and has a spallation corrected 15n value in the range 0 to 20 it may reflect indigenous nitrogen in the basalt or a mixture of indigenous and adsorbed terrestrial nitrogen spallogenic noble gases yield single stage exposure ages between 400 000 and 900 000 years depending on irradiation geometry trapped argon may have an unusually low36ar 38ar ratio trapped krypton except for a small excess at80kr is smoothly mass fractionated with respect to either terrestrial or chondritic kr the trapped xenon composition is consistent with addition of neutron capture radiogenic and fissiogenic isotopes to a base composition resembling terrestrial atmospheric xe the elemental84kr 132xe ratio of 25 is close to the terrestrial value and very different from the chondritic ratio

gold quartz veins and auriferous granite at the oriental mine alleghany district california in the vicinity of serpentinite wall rocks the three fissure veins at the oriental mine alleghany district california contain small high grade ore shoots carrying hundreds of troy ounces of gold per ton in addition minable zones of albitized wall rock granite ore contain an average of 0 2 ounces of gold per ton in the veins most native gold is associated with arsenopyrite but in the granite it occurs as microscopic inclusions within the pyrite various geothermometers and paragenetic relations suggest that vein gold deposition occurred during the end stages of mineralization at temperatures between approximately 200 degrees and 300 degrees c at pressures between 670 and 2 500 bars and at depths exceeding 2 5 km during the early stages of mineralization when most hydrothermal alteration and gold deposition in granite probably occurred temperatures were above 340 degrees c and possibly as high as 491 degrees c muscovite paragonite calcite dolomite dawsonite and albite fluid inclusion daughter minerals have been identified in situ by refractive index measurements and by x ray powder diffraction the near neutral to alkaline character of the mineralizing fluids implied by the presence of 0 34 m dissolved dawsonite and the low equivalent nacl contents of fluid inclusions suggest that gold may have been complexed with sulfur or arsenic rather than occurring as chloride complexes wall rock alteration effects include envelopes of intense carbonatization and desilication surrounding the principal gold quartz veins but also occurring along splits and fractures emanating from the main vein structures for example in granite the main alteration effects dissolution of original quartz and formation of albite occur along nearly flat lying fractures chiefly in the footwall of the oriental vein chemical analyses suggest that desilication of granite and removal of silica during ankeritization of mafic minerals in the other rock types liberated sufficient amounts of silica to form the vein quartz at the oriental mine beyond the fringes of the main alteration envelopes is an outer essentially pervasive alteration zone characterized by sericitization and chloritization which grades into greenschist facies country rocks and may predate mineralization gold in high grade ore shoots may have been precipitated by reactions involving reducing fluids derived from the wall rock serpentinite near which all high grade vein ores occur limited fluid inclusion data for ore shoot quartz however seem to be consistent with the alternative possibility of temperature controls for ore deposition

formation of homogeneous regions for regional frequency analysis of extreme significant wave heights regional frequency analysis rfa can reduce uncertainties in the estimations of return levels provided that homogeneous regions can be delineated in the framework of extreme marine events a physically based method to form homogeneous regions by identifying typical storms footprints is proposed first a spatiotemporal declustering procedure is employed to detect storms generating marine extremes second the identification of the most typical storms footprints relies on a clustering algorithm based on a criterion of storm propagation the resulting regions are readily explicable sites from a given region are likely to be impacted by the same storms and any storm impacting a region is likely to remain enclosed in this region this procedure is fairly simple to implement as the only information required is the time of occurrence of the observed extremes an application to the estimation of extreme significant wave heights from the numerical sea state database anemoc 2 is given six regions both physically and statistically homogeneous are delineated in the north east part of the atlantic ocean it is shown that the identification of storms footprints allows the increase of the overall statistical homogeneity combined with rfa the proposed method highlights regional differences in the spatial extent and intensity of storms

common asteroid break up events of eucrites diogenites and howardites and cosmic ray production rates for noble gases in achondrites we determined the cosmic ray produced noble gas abundances in eight diogenites four eucrites and four howardites using these and additional noble gas and chemical data from the literature composition and shielding dependent production rates of achondrites for 3he 21ne 38ar 78kr 83kr and126xe were derived based on 81krkr exposure ages the cosmogenic ratio 22ne 21ne is found to be a valid shielding indicator for all howardites eucrites and diogenites heds this ratio correlates with other shielding dependent ratios such as 78kr 83kr 80kr 83kr 124xe 131xe 126xe 131xe and 128xe 131xe we show that strong correlations for these ratios also exist for basaltic lunar rocks the new production rates were used for the calculation of exposure ages for all heds with known noble gas abundances two major exposure age clusters at 21 ma and 38 ma are observed in all three classes we find that five asteroid break up events characterized by exposure ages 6 1 ma 12 2 ma 21 4 ma 38 8 ma and 73 3 ma produced all diogenites fifteen out of seventeen howardites and twenty eight out of thirty nine eucrites we conclude that asteroidal or cometary impact events at such times on one or several parent bodies are responsible for the ejection of eucrites howardites and diogenites probable parent bodies are multiple 4 vesta derived kilometer sized objects of basaltic achondritic composition reaching the 3 1 resonance region a proposed source area for meteorites the direct ejection from vesta and capture by earth of basaltic meteorites has been shown to be dynamically difficult in such a scenario large events 38 ma and 21 ma ago are required liberating simultaneously material representing vesta s surface eucrites howardites and interior regions diogenites

the role of geoscience breakthroughs in gold exploration success yilgarn craton australia abstract australia experienced a major increase in gold production during the 1980s and this is reflected in the production of 250 tonnes of gold per annum since then much of the production has come from the archean yilgarn craton of western australia and mostly from gold only deposits discovery is the factor best accounting for the outperformance of yilgarn gold production in a global context and both greenfield and brownfield exploration success have been essential scientific input to gold exploration evolved rapidly from 1980 and is implicated in the exploration success in the yilgarn six scientific breakthroughs had changed the nature of almost all yilgarn gold exploration thinking by 1990 and appear to have been important components of the exploration success breakthroughs relate to primary gold geology timing and structural control favourable host rocks gold related alteration and gold in the regolith environment landscape evolution gold geochemistry targeted sampling these six breakthroughs changed paradigms from which the western australian industry has not reverted these breakthroughs were not necessarily a key part of the original aims of the researchers common features in the development of the breakthroughs were small but persistent research groups with an understanding of industry a willingness to challenge dogma development of informal industry linkages and the ability to formulate and tackle key questions breakthroughs led to applications not considered when the research was conceived the breakthrough ideas were eventually available globally but they were not equally applicable and not equally accepted and adopted an openness to new ideas may correlate with the massive and ongoing exploration success witnessed in the yilgarn goldfields

the record of cosmogenic radiogenic fissiogenic and trapped noble gases in recently recovered chinese and other chondrites abstract we performed a comprehensive study of the noble gas isotopic abundances in thirty six chondrites including twenty seven chondrites recovered in china the large data base allows us to recognize some new characteristics of the nuclear record in chondritic matter the comparison of the trapped noble gas release pattern for ordinary and carbonaceous chondrites shows that the planetary trapped noble gases in ordinary chondrites are released mainly above 1200 c whereas 85 of these gases in carbonaceous chondrites are degassed at 200 c there exists a clear correlation of the fraction of trapped xe released at 1200 c and petrologic type of chondrites it thus appears that the carrier phases of the trapped noble gases in ordinary and in carbonaceous chondrites may not be the same the ngawi ll3 chondrite is solar gas rich the solar gases in meteorites and lunar surface material are mixtures of solar wind sw and solar energetic particles sep we show that the variations of the 3 he 4 he and 20 ne 22 ne ratios for solar gas rich meteorites and lunar surface material could be either due to preferential diffusive losses of the lighter isotopes of he and ne or due to a change of the sw sep flux ratio with time furthermore we demonstrate that the 81kr concentration is a function of the shielding depth of a sample within the meteoroid deviations from this depth dependency curve are observed for jilin h5 lishui l5 suizhou l6 and dongtai ll6 a complex exposure history for jilin is thus confirmed and is possible for the other three chondrites cosmic ray exposure ages are calculated based on six different nuclides 3he 21ne 38ar 83kr 126xe and 81kr kr in most cases good agreement is observed for the ages derived from the different methods quality classes are assigned to the exposure ages and the age distributions are discussed in some meteorites we observe effects induced by secondary cosmicray produced neutrons epithermal neutron fluxes jn 30 300 ev and fast neutron fluxes jn 5 mev are derived based on the reactions 79br n 80kr and 24mg n 21ne respectively and preatmospheric masses of the meteoroids are estimated we show that the ratio j n 30 300 ev j n 5 mev increases with increasing preatmospheric mass we introduce a 3he exposure age 21ne exposure age vs 4he gas retention age 40ar gas retention age diagram that is a powerful tool for distinguishing different thermal histories of meteoroids finally in some chondrites we observe xe produced by 244pu fission and calculate the time span between fission xe retention in these chondrites and that of the angra dos reis achondrite we find that the ordinary chondrites started to retain fission xe 48 30 ma earlier than angra dos reis we do not observe systematic differences between h l and ll or type 5 and 6 chondrites with respect to the time of fission xe retention

cat mountain a meteoritic sample of an impact melted asteroid regolith cat mountain is a new ordinary chondrite impact melt breccia that contains several shocked chondrule bearing clasts of l5 material these clasts are surrounded by a total impact melt of similar composition material which appears to have cooled over a period of a few thousand years probably within a melt breccia lens in the bottom of a large 1 km diameter crater on an l chondrite asteroid noble gas isotopes indicate that the sample was involved in at least two different impact events approximately 880 and 20 myr ago following the 4 55 ga accretion of primitive chondritic material the 880 ma event is responsible for the impact breccia texture of the sample and the 20 ma event reduced the sample to a meter sized object we also infer that another impact occurred between 880 and 20 ma possibly the 500 ma event recorded in many other l chondrites to jettison the material from the asteroid belt into an orbit that evolved into an earth crossing trajectory the shock metamorphic processes that occurred at 880 ma redistributed the opaque phases in the meteorite and altered the crystalline characteristics of silicate phases this reduced the reflectance of the l5 material and decreased the amplitude of its spectral absorption features these characteristics are consistent with the spectral characteristics of some c class asteroids and suggest that some dark asteroids that appear to belong to the c class could be covered with shocked ordinary chondrite material if one assumes that cat mountain came from the same asteroid as other l chondrites with the same cosmic ray exposure age then the juxtaposition of these different materials suggests asteroids are rubble piles which are heterogeneous on a scale less than 100 m furthermore the structural integrity of cat mountain and other l chondrites suggests the strengths of asteroid rubble piles are limited by fractures and contrasting material properties and are thus inherently weak in a ram pressure regime produced when they enter a planetary atmosphere however in a regime where the asteroid is the target of impact fragmentation rather than the projectile the added porosity of a rubble pile structure will compensate for the presence of fractures and absorb a large amount of the impact energy in this case the structural integrity of the asteroid may appear to be the same as a previously unshocked chondritic material

a high resolution hindcast of wind and waves for the north sea the norwegian sea and the barents sea 1 a combined high resolution atmospheric downscaling and wave hindcast based on the era 40 reanalysis covering the norwegian sea the north sea and the barents sea is presented the period covered is from september 1957 to august 2002 the dynamic atmospheric downscaling is performed as a series of short prognostic runs initialized from a blend of era 40 and the previous prognostic run to preserve the fine scale surface features from the high resolution model while maintaining the large scale synoptic field from era 40 the nested wam wave model hindcast consists of a coarse 50 km model covering the north atlantic forced with era 40 winds and a nested 10 11 km resolution model forced with downscaled winds a comparison against in situ and satellite observations of wind and sea state reveals significant improvement in mean values and upper percentiles of wind vectors and the significant wave height over era 40 improvement is also found in the mean wave period era 40 is biased low in wind speed and significant wave height a bias which is not reproduced by the downscaling the atmospheric downscaling also reproduces polar lows which cannot be resolved by era 40 but the lows are too weak and short lived as the downscaling is not capable of capturing their full life cycle

a petrologic chemical and isotopic study of monument draw and comparison with other acapulcoites evidence for formation by incipient partial melting abstract we have conducted petrologic chemical and isotopic studies of acapulcoites acapulco monument draw yamato 74063 alh a77081 alh a81261 alh a81315 alh 78230 alh a81187 and alh 84190 in an attempt to constrain their genesis acapulcoites have distinctly different oxygen isotopic compositions than silicate inclusions in iab and iiicd irons winonaites and ureilites and thus formed on a different parent body oxygen isotopic compositions which are slightly heterogeneous within the group overlap with lodranites indicating a likely origin on a common parent body these groups can be distinguished on the basis of mafic silicate grain size all acapulcoites have mafic silicate compositions intermediate between e and h chondrites roughly chondritic mineralogies achondritic equigranular textures micrometer to centimeter sized veins of fe ni fes which cross cut silicate phases rapid metallographic cooling rates at 600 400 c 103 105 c myr and trapped noble gas abundances comparable to type 3 4 ordinary chondrites they exhibit variable mafic silicate zoning abundance of fe ni fes veins ree abundances and patterns and possibly cosmic ray exposure ages 5 7 ma momument draw and yamato 74063 retain rare relict chondrules phosphates are associated with fe ni fes veins or form separate veins in monument draw and acapulco heating and cooling of acapulcoites occurred very early in the history of the solar system as evidenced by the 39ar 40ar ages of 4 51 ga these ages appear distinctly younger than the likely formation time for acapulco of 4 557 ga but are older than analogous 39ar 40ar ages for most chondrites acapulcoites formed from a precursor chondrite which differs from known chondrites in mineral and oxygen isotopic compositions heating to 950 1000 c resulted in melting at the fe ni fes cotectic but silicates did not melt silicate textures resulted from extensive solid state recrystallization heating was by noncollisional sources e g 26al electromagnetic induction despite uncertainties owing to a lack of data acapulcoites may have experienced a three stage thermal history of slow cooling at high temperature rapid cooling at intermediate temperatures and slow cooling at low temperatures possibly resulting from breakup and gravitational reassembly of the parent body the complex thermal history is also reflected in disequilibrium ree abundances one or at most two impact events 7 ma and possibly 5 ma ago are consistent with the cosmic ray exposure ages of all four acapulcoites for which cosmogenic noble gas data exist

extreme wave climate variability in southern europe using satellite data 1 a time dependent generalized extreme value gev model for monthly significant wave height maxima from satellite databases is used to model the seasonal and interannual variability of the extreme wave climate throughout southern europe in order to avoid a misleading use of the maxima time series the classical extreme value model has been modified to cope with nonhomogeneous monthly observations seasonality is represented using intraannual harmonic functions in the model while interannual variability is modeled including north atlantic and mediterranean regional scale sea level pressure predictors such as the north atlantic oscillation nao the east atlantic ea or the east atlantic western russian ea wr patterns the results quantify the strong spatial variability detected in the seasonal location and scale gev parameters in general prominent zonal west east and meridional north south gradients of these location and scale parameters reveal the predominance of low pressure centers located in the nao region e g a gradient of 4 m for the location parameter and 1 5 units for the scale parameter between north south is shown in the month of september the model also quantifies the influence of regional climate patterns on extreme wave climate results show a great influence of nao and ea on the atlantic basin e g every unit of the monthly nao index explains 25 cm of the extreme wave height in the gulf of biscay and the ea index explains 20 cm while the negative phases of ea wr contribute greatly to the western mediterranean basin

brachina a new type of meteorite not a chassignite the brachina meteorite previously classified as a chassignite is found to be a nearly primitive and unique meteorite it is a fine grained unshocked equigranular igneous rock containing small melt inclusions it contains 80 olivine fo70 5 5 clinopyroxene wo38en49fs13 10 plagioclase an22 0 5 chromite 0 5 chlorapatite 3 fe sulfide 0 3 pentlandite and a trace of ni rich metal orthopyroxene en70 and anorthoclase rich glass are found only in melt inclusions siderophiles are high in the sulfides and the oxidation state is similar to that of ll chondrites major element and mineralogic data of brachina are similar to chassigny but trace element data are dramatically different the major differences are higher feo mno ga al and k la ratios w depletion high siderophile content near horizontal ree pattern at about 1 chondrite level high refractory nonrefractory metal ratios e g ir au and chalcophile element depletion compositionally brachina is close to c2 chemistry but has undergone some segregation of fe ni s melt these data in addition to its near 4 5 b y age and oxygen isotopic signature within the eucritic field suggest that brachina is not related to chassigny or snc meteorites it may be related to primitive meteorites such as silicate inclusions in iab irons and winonaites but is more oxidized reduction would make it very similar to winonaites the assemblage may have experienced the beginning of melting in its parent body since it has characteristics that differ from any other meteorite we suggest it be called a brachinite

regional frequency analysis of extreme waves in a coastal area abstract this study analysed the wave data from several locations in a coastal region to identify the areas with comparable wave height statistics and to estimate regional extreme significant wave heights of designated return periods the regional frequency analysis algorithm executed in this work utilised the significant wave height data from 35 sites 35 45 n 6 5 11 0 w in a coastal grid 0 25 0 25 off portugal in the north atlantic ocean extracted from 44 years hipocas hindcast wave database regional frequency analysis algorithms based on l moments identified the discordant sites discordant site statistics are substantially diffused from the group of sites statistics assisted in the formation of homogeneous regions by cluster analyses data vectors include site characteristics and site statistics and consequently selected appropriate regional frequency distributions by z goodness of fit test statistic at 90 level of significance to estimate regional extreme significant wave height quantiles of designated return periods the regional frequency analysis algorithm recognised in certain cases neighbouring sites as members of diverse regions revealing that geographical proximity of sites are not ascertaining factors to form homogeneous regions at site analyses along with regional frequency analysis enabled to apprehend the precision of the regional extreme quantile as genuine feature of its at site extreme quantiles

modification of ree distribution of ordinary chondrites from atacama chile and lut iran hot deserts insights into the chemical weathering of meteorites the behavior of rare earth elements rees during hot desert weathering of meteorites is investigated ordinary chondrites ocs from atacama chile and lut iran deserts show different variations in ree composition during this process inductively coupled plasma mass spectrometry icp ms data reveal that hot desert ocs tend to show elevated light ree concentrations relative to oc falls chondrites from atacama are by far the most enriched in rees and this enrichment is not necessarily related to their degree of weathering positive ce anomaly of fresh chondrites from atacama and the successive formation of a negative ce anomaly with the addition of trivalent rees are similar to the process reported from antarctic eucrites in addition to rees sr and ba also show different concentrations when comparing ocs from different hot deserts the stability of atacama surfaces and the associated old terrestrial ages of meteorites from this region give the samples the necessary time to interact with the terrestrial environment and to be chemically modified higher ree contents and lree enriched composition are evidence of contamination by terrestrial soil despite their low degrees of weathering special care must be taken into account while working on the ree composition of atacama meteorites for cosmochemistry applications in contrast chondrites from the lut desert show lower degrees of ree modification despite significant weathering signed by sr content this is explained by the relatively rapid weathering rate of the meteorites occurring in the lut desert which hampers the penetration of terrestrial material by forming voluminous fe oxide oxyhydroxides shortly after the meteorite fall

new noble gas data of primitive and differentiated achondrites including northwest africa 011 and tafassasset this work reports on the noble gas inventory of 3 new acapulcoites 3 brachinites 2 new eucrites from the dar al gani region in libya the unique achondrite dar al gani dag 896 from the same locality the new eucrite like achondrite northwest africa nwa 011 and the controversial sample tafassasset we determined cosmic ray exposure and gas retention ages evaluated shielding conditions and discuss the trapped noble gas component of the specimens all exposure ages are within the known range of stony meteorites and partly confirm previously established age clusters shielding conditions vary suggesting substantial shielding for all 3 brachinites and tafassasset we cannot exclude however that the mg rich composition of brachinites simply simulates heavy shielding regarding the trapped component we found q like compositions only for the acapulcoite thiel mountains til 99002 the brachinite elephant moraine eet 99402 yields a high subsolar 36ar 132xe ratio of 400 along with a slightly elevated 84kr 132xe ratio indicating minor atmospheric contamination all the other samples particularly the eucrite dag 983 are characterized by clearly elevated ar kr xe ratios due to significant terrestrial alteration tafassasset exhibits noble gas parameters that are different from those of cr chondrites including a relatively high cosmic ray exposure age the absence of a solar component low 132xe concentrations a low trapped 36ar 132xe ratio of 30 and a noticeable amount of radiogenic 129xe similar attributes have been observed for some primitive achondrites these attributes are also consistent with the metamorphic character of the sample we therefore consider tafassassets noble gas record to be inconclusive as to its classification primitive achondrite versus metamorphosed cr chondrite

development of regional flood duration frequency curves based on the index flood method abstract the aim of this research paper is to develop a statistical model that provides a more complete description of a basin s flood regime the approach adopted in this paper is based on the flood duration frequency qdf analysis which takes into account the temporal variability of floods this approach is analogous to the intensity duration frequency idf model commonly used for rainfall analysis the proposed model allows qdf curves for a given basin to be estimated while using a minimum number of parameters this model is called converging model because of the observed convergence of distributions towards small return periods a local at site model and a regional approach are developed the regional approach uses classical concepts of regional hydrologic frequency analysis index flood if method and can be used for basins where no streamflow data is available results from 158 catchments located in the provinces of quebec and ontario canada are used to illustrate the method

chemistry of the calcalong creek lunar meteorite and its relationship to lunar terranes the calcalong creek lunar meteorite is a polymict breccia that contains clasts of both highlands and mare affinity reported here is a compilation of major minor and trace element data for bulk clast and matrix samples determined by instrumental neutron activation analysis inaa petrographic information and results of electron microprobe analyses are included the relationship of calcalong creek to lunar terranes especially the procellarum kreep terrane and feldspathic highlands terrane is established by the abundance of thorium incompatible elements and their kreep like ci chondrite normalized pattern feo and tio2 the highlands component is associated with apollo 15 kreep basalt but represents a variant of the kreep derived material widely found on the moon sources of calcalong creek s mare basalt components may be related to low titanium lt and very low titanium vlt basalts seen in other lunar meteorites but do not sample the same source the content of some components of calcalong creek are found to display similarities to the composition of the south pole aitken terrane what appear to be vlt relationships could represent new high aluminum low titanium basalt types

on the sheltering effect of islands in ocean wave models 1 the effect of resolving relatively small islands in a third generation wave model covering the whole north atlantic is shown to have noticeable effects at long distances from the islands in addition to the local effects that have been reported earlier to resolve the islands a very fine grid is adopted locally which is then nested in the overall model the examples presented show the shadowing effect of azores islands for three specific wave conditions when they come from the southwest from the west and from the northwest the sheltering effect of the islands was demonstrated by a reduction of the significant wave height in the region on the leeward side of azores archipelago when comparing the wave model results with the island resolved and unresolved

the northwest africa 1500 meteorite not a ureilite maybe a brachinite the northwest africa nwa 1500 meteorite is an olivine rich achondrite containing approximately 2 3 vol augite 1 2 vol plagioclase 1 vol chromite and minor orthopyroxene cl apatite metal and sulfide it was originally classified as a ureilite but is currently ungrouped we re examined the oxygen three isotope composition of nwa 1500 results of ultra high precision 0 03 for d 17 o laser fluorination analyses of two bulk chips and high precision 0 3 secondary ion mass spectrometry sims analyses of olivine and plagioclase in a thin section show that the oxygen isotope composition of nwa 1500 d 17 o 0 22 from bulk samples and 0 18 0 06 from 16 mineral analyses is within the range of brachinites we compare petrologic and geochemical characteristics of nwa 1500 with those of brachinites and other olivine rich primitive achondrites including new petrographic mineral compositional and bulk compositional data for brachinites hughes 026 reid 013 nwa 5191 nwa 595 and brachina modal mineral abundances texture olivine and pyroxene major and minor element compositions plagioclase major element compositions rare earth element abundances and siderophile element abundances of nwa 1500 are within the range of those in brachinites and in most cases well distinguished from those of winonaites iab silicates acapulcoites lodranites ureilites and divnoe nwa 1500 shows evidence of internal reduction in the form of reversely zoned olivine fo 65 73 core to rim and fine grained intergrowths of orthopyroxene metal along olivine grain margins the latter also occur in reid 013 hughes 026 nwa 5191 and nwa 595 we argue that reduction olivine fi enstatite fe 0 o 2 is the best hypothesis for their origin in these samples as well we suggest that nwa 1500 should be classified as a brachinite which has implications for the petrogenesis of brachinites fe mn mg compositions of brachinite olivine provide evidence of redox processes among bulk samples nwa 1500 provides evidence for redox processes on a smaller scale as well which supports the interpretation that these processes occurred in a parent body setting sims data for 26 al 26 mg isotopes in plagioclase in nwa 1500 show no 26 mg excesses beyond analytical uncertainties 1 2 the calculated upper limit for the initial 26 al 27 al ratio of the plagioclase corresponds to an age younger than 7 ma after cai compared to 53 mn 53 cr data for brachina wadhwa et al 1998b this implies either a much younger formation age or a more protracted cooling history however brachina is atypical and this comparison may not extend to other brachinites

brachinites igneous rocks from a differentiated asteroid we have done petrologic studies of brachinites allan hills alh 84025 elephant moraine eet 99402 and eet 99407 bulk geochemical studies of eet 99402 and eet 99407 ar ar studies of brachina and eet 99402 and a xe isotopic study of brachina textural mineral compositional and bulk compositional evidence show that eet 99402 and eet 99407 are paired alh 84025 eet 99402 and eet 99407 have igneous textures petrofabric analyses of alh 84025 and eet 99407 demonstrate the presence of lineations and probable foliations of olivine grains that support formation as igneous cumulates mineral minor element chemistry and bulk rock incompatible lithophile element contents of the brachinites are distinct from those of acapulcoite lodranite clan meteorites a suite of high grade metamorphic rocks and anatectic residues the differences demonstrate a higher blocking temperature of equilibration for the brachinites and that cumulus plagioclase is present in eet 99402 eet 99407 and probably alh 84025 thus indicating an igneous origin brachinites are differentiated ultramafic achondrites and are not part of a suite of primitive achondrites we infer that their parent asteroid is a differentiated body brachina has an excess of 129xe correlated with reactor produced 128xe demonstrating that short lived 129i was present at the time of formation this plus literature data attests to early formation of the brachinites within a few ma of the formation of chondrites ar ar age data show that brachina and eet 99407 were degassed about 4 13 ga ago possibly by a common impact event eet 99402 and eet 99407 show petrographic evidence for shock including possible conversion of plagioclase to maskelynite followed by devitrification brachina is unshocked making a direct association between the ar ar age and textures ambiguous

differentiated achondrites asuka 881371 an angrite and divnoe noble gases ages chemical composition and relation to other meteorites abstract we present a study of the noble gas isotopic abundances in two achondrites divnoe and the asuka 881371 angrite for divnoe we also performed chemical analyses of the major elements and of some minor and trace elements that are relevant for the comparison with other meteorite types and for the interpretation of the noble gas data based on the cosmic ray produced noble gases an exposure age of 5 4 0 7 ma for asuka 881371 was obtained this ejection time from the parent asteroid differs from those of the other three angrites angra dos reis 55 5 ma lew 86010 17 6 ma and lew 87051 0 2 ma whereas the u th 4 he and k 40 ar gas retention ages of asuka 881371 are 3750 1000 ma and 3910 500 ma respectively we derive for the 244 pu 136 xe system a formation age of 4533 40 ma which is contemporaneous with that of the other angrites angra dos reis and lew 86010 for divnoe the abundance patterns of the major lithophile siderophile refractory and volatile elements the isotopic abundance pattern for primordial trapped xe and the oxygen isotopes indicate that this unique meteorite is related to the brachinite achondrites assuming no pre exposure to cosmic rays on the parent body divnoe s asteroid ejection event occurred 17 2 2 3 ma ago

thresholds for storm impacts on an exposed sandy coastal area in southern portugal abstract storms are one of the most important phenomena responsible for coastal erosion their destructive power presents major challenges for coastal management and knowledge of their characteristics and associated consequences is therefore of paramount importance in this study thresholds for storm impacts are defined for a sandy coast in southern portugal faro beach ria formosa using two different approaches i hydrodynamic conditions associated with historical storm impacts i e infrastructural damage and ii computed maximum wave run up values r high compared with beach morphology damage thresholds are defined as limits above which the action of a storm exceeds beach front response capability and starts to act directly on human infrastructures according to method i four different thresholds were defined for individual storms directed from the sw the threshold is a significant wave height of 4 7 m with a storm duration of 2 days and for storms directed from the se is a significant wave height of 6 m with a storm duration of at least 2 days regarding storm groups for those directed from the sw the threshold is 2 storms lasting at least 2 days each with significant wave heights greater than 3 5 m whilst for those directed from the se the threshold is 3 short storms lasting 1 day each with significant wave height over 3 9 m the return period for the sw storm group threshold is just 1 7 years for method ii beach morphological parameters d high highest elevation of the frontal dune d low elevation of the dune base and tan f foreshore slope were determined for five chosen cross shore profiles along the study area and r high computed for different hydrodynamic conditions results were validated through field observations of storm impacts the lowest thresholds for overwash are along the central part of the study area where a dune crest is absent due to human occupation the highest thresholds for overwash are on those profiles where a frontal dune is well developed or a foredune ridge is present western and eastern parts of the study area this study presents a methodological strategy to compute realistic thresholds for storm impacts along faro beach based on historical datasets of hydrodynamics and storm impacts information the approach could be implemented in other coastal areas to provide a comprehensive assessment of the storm impact requiring only simple information like offshore storm hydrodynamics characteristics beach morphology and reports of coastal infrastructure damage

storminess and surges in the south western approaches of the eastern north atlantic the synoptic climatology of recent extreme coastal storms abstract the climatology of intense winter cyclone events in the eastern north atlantic responsible for high magnitude surge generation top 1 of events within the region of the south western approaches to northwest france and southwest england is extracted from daily sea level and 500 hpa level atmospheric pressure analyses cluster analysis yields discrete cyclone track regimes linked to upper airflow patterns being responsible for the generation of intense storms central pressure at sea level 990 hpa which promote severe surge events 60 cm along the french coast of the south western approaches fluctuations in storminess are strongly influenced by the southward intrusion and strengthening of the jet stream in mid atlantic these occurrences are often associated with negative sea surface temperature sst anomalies near newfoundland and a strengthening of the thermal gradient across the atlantic well to the south of its normal position resultant cyclogenesis promotes storms displaying a delay in minimum central pressure attainment until well east of 14 w encouraging enhancement of surge flow stepwise multiple regression analysis indicates that the most influential variables in promoting severe surge events in the south western approaches are trans atlantic sea surface temperature gradients the most important influence is the prevailing west east sea surface temperature gradient during the month of the storm followed by that for the prior month of the storm and thirdly the north south sea surface temperature gradient prevailing during the month of the event other influential variables reflect the character of the cyclone storm duration mean deepening rate of storm central pressure the value of the outermost closed isobar around the storm centre and the longitudinal position of the outermost closed isobar to the right of the cyclone track in contrast the north atlantic oscillation nao is not very effective as a discriminator of surge activity this may reflect the greater intra month volatility of parameters used to derive the nao index than of other monthly variables considered in the study the lack of resolvability at the individual storm level probably also arises because of the monthly detailing of the nao against storms of 2 3 days duration this behavioural model of extreme storminess in the south western approaches to northwest france provides the basis by which extremes of coastal susceptibility can be calibrated

hydrothermal alteration zoning and gold concentration at the kerr addison archean lode gold deposit kirkland lake ontario kerr addison a major archcan lode gold deposit of the abitibi belt with a production of approximately 10 x 10 6 oz au approximately 320 metric tons up to 1983 is localized in a zone of talc carbonate and chlorite carbonate rocks immediately south of a regional structural break the kirkland lake larder lake fault zone relict volcanic textures taken in conjunction with the ratios of diag nostic relatively less mobile elements collectively indicate that most of the wall rocks of the mine were originally mafic and ultramafic rocks along with their clastic derivatives regional greenschist facies metamorphism is locally superposed by a distinct zonation of gold associated hydrothermal alteration characterized by massive introduction of co 2 coupled with variable enrichments of alkali metals and calcium which produced systematic trends of alteration mineral assemblages alteration types of the initial stage contain chlorite which is replaced by muscovite or albite in the advanced stage of alteration with a concomitant increase in the proportion of carbonate minerals numerous generations of crosscutting veins are enveloped by alteration borders in which the sequence of the al bearing minerals namely albite mus covite and chlorite develop from the vein to the wall rocks always in a systematic sequence the same sequence is observed at a larger scale from the ore zone to the periphery of the mine area the intensity of alteration can be monitored by saturation indices co 2 ca fe mg for carbonates and 3k na al 3k al and na al for muscovite albite muscovite and albite respectively molar ratios plots of the moving averages of these indices across the 3 850 ft level of the mine reveal a remarkable correspondence to variations of gold abundance suggesting a genetic relationship of gold enrichment to hydrothermal alteration on a broad scale gold is concentrated to the south of the kirkland lake larder lake fault zone and at a more detailed scale in the transition zone between carbonate muscovite and carbonate albite alteration types during advanced alteration fluid x sub co 2 was approximately 0 1 and na k asymp 10 volcanics of the kinojevis and larder lake groups are 18 o enriched relative to pristine tholeiites and possess distinct mineral delta 18 o values probably due to different conditions of marine water alteration during or shortly after extrusion in domains of advanced alteration these are all shifted down to a common narrow bracket here 18 o 16 o and d h data indicate fairly constant temperatures 270 degrees 300 degrees c and a common isotopic composition of hydro thermal fluids delta 18 o 5ppm delta d 30 to 50ppm across the alteration zoning these results are in common with many other archcan lode gold deposits fe dolomite has a uniform delta 13 c value of 2 8 or 0 42 per mil 1sigma throughout the footwall and ore zones but it is enriched by approximately 1 per mil in the graphite free hanging wall rocks fluid delta 13 c value was 4 or 1 per mil reflecting either a magmatic carbon reservoir or mixtures of marine carbonate carbonaceous and magmatic sources the enrichment of gold at one side of the kirkland lake fault zone is interpreted to be the result of development of a metasomatic zoning induced by gradients in oxidation state the precious metal being concentrated in the reducing side zonation of alteration types south of the kirkland lake larder lake fault zone represents various steps of a continuous process of incremental changes of the rocks to adapt to the composition of an externally generated fluid successive generations of fracture arrays and veins have the same alteration patterns and thus the composition of the incoming hydrothermal fluid seems to have remained essentially unchanged through time gold mineralization at the kerr addison mine and its contiguous alteration halo are interpreted to be the result of repeated cycles of hydraulic fracturing fluid penetration and local reaction with rocks fluid rock interaction produced lateral variations of fluid composition which led to gold concentration probably due to gradients in ph preferentially at the interface between the carbonate muscovite and carbonate albite alteration types which is also the site of pyrite concentration the alteration assemblages and specific site of gold pyrite concentration at kerr addison are common to several other described archcan lode gold deposits

chemical alteration and ree mobilization in meteorites from hot and cold deserts the effects of terrestrial weathering on ree mobilization are evaluated for a variety of uncommon meteorites found in antarctica and in hot deserts the meteorites analyzed include 7 non cumulate eucrites 10 shergottites 3 nakhlites 2 lunar meteorites 4 angrites 10 acapulcoites 1 winonaite and 1 brachinite in situ concentration measurements of lanthanides and selected other minor and trace elements were made on individual grains by secondary ion mass spectrometry sims in antarctic meteorites oxidation converts ce 3 to ce 4 which is less soluble than the trivalent ree resulting in ce anomalies the mineral most affected is low ca pyroxene however not all grains of a given mineral are and distinct analyses of a single grain can even yield ree patterns with and without ce anomalies the effect is most pronounced for antarctic eucrites in which ce anomalies are observed not only in individual minerals but also in whole rock samples although ce anomalies are observed in meteorites from hot deserts as well the most characteristic signs of chemical alteration in this environment are a lree enrichment with a typical crustal signature as well as sr ba and u contaminations these can modify the whole rock ree patterns and disturb the isotope systematics used to date these objects the lree contamination is highly heterogeneous affecting some grains and not others of a given mineral mainly olivine and low ca pyroxene the two minerals with the lowest ree concentrations the major conduit for ree movement is through shock induced cracks and defects and the highest levels of contamination are found in altered material filling such veins and cracks meteorites that experienced low shock levels and those that are highly recrystallized are the least altered copyright 2003 elsevier ltd

geology and alteration in the golden mile kalgoorlie the giant kalgoorlie gold deposit 1 200 metric tons au recovered is surrounded by a wide wall rock alteration halo 1 x 3 km this alteration primarily represents the selectively pervasive formation of carbonate chlorite and localized intense pyrite and muscovite alteration which all formed synchronously with gold mineralization the carbonate alteration halo is interpreted as epigenetic because of evidence that carbonate chlorite assemblages overprint regional metamorphic fabrics furthermore the geometry of the alteration zone boundaries is controlled by ductile shear zones formed during regional deformation and the geochemistry of all the alteration zones suggests that one fluid was responsible for all assemblages there is no evidence of intense premetamorphic carbonation in the kalgoorlie area kalgoorlie is situated in the highly auriferous eastern goldfields province of the yilgarn block within a narrow corridor rift zone that contains several large gold deposits regional metamorphism has produced upper greenschist facies assemblages but has retained original rock textures at kalgoorlie the most important gold host is the golden mile dolerite 80 of gold produced a differentiated tholeiitic sill intruded between a lower mafic ultramafic pile including the paringa basalt the next most important gold host and overlying felsic rocks and metasediments the kalgoorlie syncline is the dominant tectonic structure in the main gold producing area of the golden mile adjacent to this infold of metasediments the golden mile dolerite and paringa basalt are the site of a number of ductile shear zones which formed synchronously with the syncline these zones and the many smaller shear zones between them have provided fluid channelways throughout the golden mile and are the site of most economic gold mineralization three alteration zones have been mapped in the golden mile dolerite on the basis of the mineralogic siting of fe i e the chlorite carbonate and pyrite zones the additional actinolite zone representing the unaltered regional metamorphic mafic assemblage has been converted to chlorite zone assemblages throughout the mined areas of the golden mile the carbonate zone bleached dolerite can be traced for 2 km through the main mineralized parts of the golden mile and to the full depth of lake view mine the boundary between the chlorite and carbonate alteration zones is locally sharp and controlled by ductile shear zones but is generally strata bound and preferentially developed in the more fe rich parts of the dolerite the pyrite zone which includes all economically gold mineralized areas is the site of the strongest muscovite alteration and is most intense and continuous in ductile shear zones the chlorite zone chlorite calcite or ankerite forms from mild carbonation of actinolite zone assemblages the carbonate zone ankerite siderite is a more local expression of this carbonation even after extensive carbonate alteration relative major element abundances are little changed and the main added components are limited to co 2 s k and rb the pyrite zone i e the gold lodes has ankerite muscovite quartz albite pyrite and minor siderite bearing assemblages it represents significant addition of sulfur the three alteration zones not only reflect differing degrees of alteration intensity but are also strongly influenced by host rock fe mg and this ratio largely determines the stability of chlorite favored by low fe mg and thus the distribution of the carbonate zone favored by high fe mg progressive deformation within the shear zones reworked existing mineralization kalgoorlie fits a metamorphic replacement model of gold formation by auriferous metamorphic fluids interacting with fe rich host rocks its great size is a function of a very well developed fluid channelway system via ductile shear zones and later fault zones and the favorable chemical nature of the host rocks especially the golden mile dolerite the full width of carbonation chlorite and carbonate zones reflects overlapping alteration envelopes around the closely spaced fluid pathways the processes responsible for the formation of most of the gold at kalgoorlie were essentially similar to those at several other archean gold deposits but on a larger scale

host rock and structural controls on the nature and timing of gold mineralization at the holloway mine abitibi subprovince ontario the holloway mine a mesothermal gold deposit is located within the western abitibi subprovince ontario mineralized zones that contain microscopic gold within pyrite are hosted by a sequence of metakomatiites mafic to felsic metavolcanic and metasedimentary rocks there were two mineralization events however the early one was the main event in terms of the amount of gold mineralization this event was associated with albitization silicification chloritization and sericitization in addition to pyritization the later mineralization is associated with sericitization and pyritization carbonate and sericite alterations are associated with both mineralizing events results of u pb zircon age dating of rocks within the sequence constrains the main mineralization event to 2672 ma ore lenses of the holloway deposit are enveloped by 080 striking steeply south dipping zones of intense deformation and fabric development within the porcupine destor deformation zone the shear zones are characterized by a strong foliation and locally an associated extension lineation the ore lenses are interpreted to represent lithons that were formed by boudinage of the more competent mineralized zones which are pervasively albitized analysis of geochemical data demonstrates that the ree th nb hf ti fe and al were largely immobile with respect to the albite quartz chlorite sericite and hematite alterations locally preserved textures such as abundant varioles and spherulites indicate that the host metavolcanics were relatively evolved rocks geochemical data show they have an iron enrichment trend typical of tholeiitic mafic to felsic suites and that they were derived through fractional crystallization of parent basalt because of their high fe mg ratios the rocks reacted with hydrothermal solutions carrying gold presumably as thio complexes to form pyrite which scavenged the gold

the tafassasset primitive achondrite insights into initial stages of planetary differentiation abstract tafassasset is an exceptional meteorite that has been linked to both the cr chondrites and the primitive achondrites because previous evidence suggests it might be a primitive achondrite from a known chondrite type we have undertaken a study of the petrology geochemistry and formation history of the meteorite tafassasset is predominantly feo rich olivine 58 yet contains abundant fe ni metal 10 vol and sulfide 3 vol other phases include high and low ca pyroxene plagioclase chromite and phosphate it has a recrystallized texture containing equigranular grains that often meet at 120 triple junctions there are no relict chondrules in the thin sections examined although they have been reported previously electron microprobe analyses reveal homogeneous olivine fa 28 6 both low and high ca pyroxene fs 23 6 wo 3 7 and fs 12 2 wo 39 3 1 a range of plagioclase composition an 23 47 fe ni metal with 5 3 36 6 wt ni and 0 1 0 8 wt co troilite chromite and ca phosphate bulk composition analyses reveal two chips depleted in refractory lithophile and some siderophile elements compared to ci chondrites exceptions are enrichments in fe ni and co a third chip is essentially chondritic in bulk composition different stones of the meteorite have slightly different oxygen isotope composition yet all lie in the cr chondrite trend with one in the acapulcoite lodranite field thermodynamic calculations show that tafassasset equilibrated at a temperature above the fe ni fes eutectic and at an oxygen fugacity of iw 1 the texture heterogeneous distribution of mineral phases plagioclase composition two mineral closure temperatures and bulk composition all provide evidence that tafassasset partially melted on its parent body a comparison with the cr chondrites the brachinites and two anomalous achondrites indicates that tafassasset is most similar to ungrouped primitive achondrites lewis cliff lew 88763 and divnoe and to the brachinites in overall petrography modal mineralogy mineral compositions oxidation state and bulk composition the comparison also excludes the possibility that tafassasset formed by partial melting of a cr chondrite tafassasset is a primitive achondrite and likely evolved on a parent body that experienced incomplete melting never reached isotopic homogeneity and was from the same oxygen isotopic reservoir as the cr chondrite parent body

geochemical and stable isotope studies of the no 4 lode kalgoorlie western australia the no 4 lode is a silicified pyritic shear zone with gold telluride mineralization which is located in the golden mile dolerite along the western limb of the kalgoorlie syncline wallrocks in this zone have undergone a series of metamorphic and metasomatic events this alteration is characterized by an increase in the ko nao ratio introduction of co and s and significant enrichment of au ag te and other ore forming constituents major and trace element and isotopic data are presented 40 chemical analyses ore mineralization is thought to have formed by reaction of chloritic host rocks with a moderately reduced near neutral hydrothermal fluid at t 250 or 50oc isotope and geochemical data suggest that these ore fluids were of metamorphic derivation and may have incorporated magmatic c s and possibly precious metals at deeper levels in the crust j e s

iodine xenon studies of allende inclusions eggs and the pink angel the iodine xenon systems of six allende inclusions five eggs and the pink angel appear to have been altered by non nebular secondary processes evidence for this includes temperature ordered variations in the initial i isotopic composition within several objects with older apparent i xe ages associated with higher extraction temperatures and the absence of primitive i xe ages the span of apparent ages seen in allende objects 10 ma or more is probably too long to reflect any nebular process so at least some alteration probably occurred on the parent body the range in initial 244pu238u ratios for the eggs 3 14 10 3 includes the current best estimates of the bulk solar system value 4 7 10 3 for egg 3 the puu ratio varies by a factor of two between extractions probably the result of fractionation of pu from u among different phases

44 year wave hindcast for the north east atlantic european coast this paper describes a 44 year from 1958 to 2001 wave hindcast conducted for the north atlantic using a fine grid in the north east atlantic coastal areas of europe the wind fields were obtained by a local area model that was applied in the areas adjacent to the european coasts which was forced by the results of the ncep reanalysis while the ncep results have a spatial distribution of 2 and a time step of 6 h the wind fields produced by the local area model have a spatial resolution of 0 5 and a time step of 1 h which is important for accurate descriptions of the conditions in coastal areas and in rapidly changing storms a version of the wam model that allowed two way nesting was adopted and calculations were made with nested grids allowing a fine resolution in the coastal areas of europe this paper includes the description of the set up of the wave model and the validation performed vs in situ measurements so as to allow assessments of the quality of the data produced in this study

geothermal mineral equilibria the dominant reaction determining the chemistry of fluids in a geothermal system of the new zealand type consists of the conversion of primary plagioclase by co2 to calcite and clays with log pco2 15 26 7850 t 273 2 temperature t in c subsequent reactions involving secondary minerals control relative co2 h2s contents the distribution of mineral phases throughout a geothermal system reflects the stepwise conversion of thermodynamically unstable primary phases through a series of intermediate metastable phases to a thermodynamically stable secondary assemblage the relative stabilities of these phases was evaluated on the basis of their solubilities the least soluble aluminiumsilicate representing the thermodynamically most stable phase under a given set of conditions observed assemblages of secondary minerals in geothermal systems represent indicators allowing mineral fluidinteraction conditions to be evaluated on the basis of multi component mineral stability diagrams

oxygen isotope variation in primitive achondrites the influence of primordial asteroidal and terrestrial processes a detailed oxygen isotope study of the acapulcoites lodranites winonaites brachinites and various related achondrites has been undertaken to investigate the nature of their precursor materials high levels of terrestrial alteration displayed by many of these samples have been mitigated by leaching in ethanolamine thioglycollate eatg solution due to their high metal and sulphide content acapulcoite lodranite and winonaite samples show much greater isotopic shifts during weathering than brachinites as observed in previous studies antarctic weathered finds are displaced to lighter oxygen isotope compositions and non antarctic finds to heavier values leached primitive achondrite residues continue to show high levels of oxygen isotope heterogeneity this variation is reflected in the 2 error on group mean 17o values which decrease in the following order acapulcoite lodranite clan brachinites winonaites on an oxygen three isotope diagram the acapulcoite lodranite clan define a limited trend with a slope of 0 61 0 08 and an intercept of 1 43 0 27 r2 0 78 a broad positive correlation between 17o and olivine fayalite contents displayed by both acapulcoite and lodranite samples may be the result of early aqueous alteration and subsequent dehydration winonaites experienced a greater degree of differentiation than the acapulcoite lodranite clan and define a distinct mass fractionation line with a slope of 0 53 0 01 and an intercept of 0 53 0 04 r2 1 a number of samples currently classified as acapulcoites nwa 725 nwa 1052 and dho 1222 have oxygen isotope compositions indicating that they are winonaites the relatively high level of oxygen isotope heterogeneity displayed by the brachinites supports their designation as primitive achondrites a number of ungrouped olivine rich achondrites divnoe nwa 4042 nwa 4363 nwa 4518 nwa 5400 zag b as well as the unique plagioclase rich achondrites gra 06128 and gra 06129 have similar oxygen isotope compositions to the brachinites it remains unclear whether the brachinites and related olivine rich achondrites are from a single or multiple parent bodies the primitive achondrites and related samples represent material from at most only 18 parent bodies compared to an estimated 65 for the iron meteorites this suggests that asteroidal mantle material is underrepresented in the meteorite record early fragmentation of differentiated asteroids followed by preferential destruction of their silicate rich mantles offers a possible explanation for this discrepancy on an oxygen three isotope diagram primitive chondrule bearing winonaites dho 1222 nwa 725 nwa 1052 nwa 1463 mt morris wisconsin plot close to the young russell y r slope 1 line with more evolved samples extending away from it towards the ccam line a similar relationship is shown by the cr chondrites the acapulcoite lodranite clan plots between the slope 1 and ccam lines however the precursor material to the clan may have had a composition close to the slope 1 line prior to parent body processing these relationships support the view that primordial oxygen isotope variation in the early solar system is best represented by the slope 1 y r line

noble gases bulk chemistry and petrography of olivine rich achondrites eagles nest and lewis cliff 88763 comparison to brachinites eagles nest and lewis cliff lew 88763 are olivine rich achondrites that have been suggested to be related to brachina and alh 84025 both are ultramafic although lew 88763 has 10 plagioclase which eagles nest lacks olivine in eagles nest fo68 is virtually identical in composition to that in brachina fo68 70 and that in lew 88763 is only slightly different fo63 64 the meteorites cosmic ray exposure ages differ from each other and from brachina and alh 84025 like brachina eagles nest has a substantial amount of radiogenic 129xe and an apparent k ar age of 4 5 ga lewis cliff 88763 on the other hand has no detectable radiogenic 129xe an apparent k ar age of 4 5 ga and a substantial amount of trapped xe the chemical composition of lew 88763 is within a factor of two of chondritic for virtually every element analyzed including siderophiles which suggests that it was melted or at least heated and recrystallized in a closed system analyses of the chemical composition of eagles nest are hampered by extensive terrestrial weathering but it appears to be broadly chondritic also although it like brachina is depleted in siderophiles our data suggest that eagles nest is genetically related to brachina but that lew 88763 is not which is a conclusion that is consistent with the o isotopic data of clayton and mayeda 1996

noble gases and halogens in graves nunataks 06129 the complex thermal history of a felsic asteroid crust the meteorite graves nunataks 06128 06129 is a rare example of felsic asteroidal crust knowledge of its history can help shed light on the evolution processes of planetesimals the noble gases can be used to constrain both the chronology of meteorites and the processes that result in movements of volatile elements on asteroidal bodies we have examined the i xe and ar ar systems of the plagioclase rich achondrite graves nunataks 06129 by high resolution laser step heating of irradiated samples iodine and 129xe are both present but are released at different temperatures and do not show a correlation therefore the i xe system in gra 06129 has no chronological significance we propose that radiogenic 129xe was lost from primary phases and parentless 129xe was later introduced into the rock by interaction with a fluid sourced from a reservoir that evolved with a high i xe ratio this could have been the same halogen rich fluid that induced the conversion of merrillite and pyroxene into chlorapatite inherited 40ar i e not generated by in situ decay of 40k is also present in one of three fragments studied here and may have been introduced at the same time as parentless 129xe

archean gold bearing quartz veins at the sigma mine abitibi greenstone belt quebec part ii vein paragenesis and hydrothermal alteration the sigma deposit consists of an archean gold bearing vein system in deformed volcanic rocks intruded by two generations of porphyries the veins cut all rock types and wall rock alteration is superposed on greenschist facies metamorphic assemblages there are two related vein sets subvertical veins in ductile shears and subhorizontal veins in extensional fractures between shear zones this paper reports on the paragenesis of extensional veins and related hydrothermal alteration tension veins are composed chiefly of quartz and tourmaline and subordinate amounts of carbonates chlorite pyrite pyrrhotite scheelite and free gold the veins formed by one or more episodes of open space filling the paragenetic sequence consists essentially of successive deposition of carbonate scheelite tourmaline pyrite pyrrhotite carbonate chlorite and quartz most of the gold and tellurides was introduced into fractures and along grain boundaries of recrystallized vein minerals during a postfilling episode of deformation veins are surrounded by zoned alteration envelopes consisting of an outer zone of cryptic alteration characterized by a chlorite carbonate white mica assemblage and an inner zone of visible alteration characterized by a carbonate white mica outer subzone and a carbonate albite inner subzone alteration zones represent reaction fronts advancing into the wall rocks and resulted from progressive interaction of wall rocks with a single hydrothermal fluid the chlorite carbonate white mica zone is characterized by replacement of epidote by calcite and white mica accompanied by fixation of co 2 and k and by release of small amounts of si in carbonate white mica and carbonate albite subzones of visible alteration chlorite biotite and white mica were replaced by calcite albite and quartz variable amounts of gold tourmaline pyrite pyrrhotite and ilmenite were also introduced visible alteration zones are characterized by additions of ca co 2 na b s p and au and by important losses of mg fe al and h 2 o mass balance calculations show that ca na si co 2 s and b in vein minerals were contributed from the hydrothermal fluid whereas fe mg and al were derived from the walls the development of alteration envelopes began with the infiltration of hydrothermal fluids into open extensional fractures and it ceased before complete filling of the veins when continuous mineral coatings formed along vein walls deposition of carbonate accompanied development of cryptic alteration including initial co 2 additions to the wall rocks subsequent deposition of tourmaline pyrite and pyrrhotite carbonate chlorite accompanied the progressive development of visible alteration which encroached on cryptically altered rocks visible alteration is characterized by additions of ca and co 2 to the wall rocks and by release of mg fe and al later bulk quartz deposition which filled the vein openings generally took place after complete development of the alteration envelopes except for this late quartz deposition of vein minerals is attributed to chemical changes in the fluid resulting from progressive wall rock alteration bulk quartz deposition is attributed to progressive cooling of the hydrothermal fluid

a petrologic and isotopic study of winonaites evidence for early partial melting brecciation and metamorphism we have conducted detailed petrologic chemical and isotopic studies of winonaites to ascertain the genesis of this group of meteorites winonaites have reduced mineral compositions and mineralogy and oxygen isotopic compositions distinct from primitive achondrite groups other than silicate inclusions in iab and iiicd irons however winonaites differ from iab and iiicd irons in that they lack the metallic matrices of the latter and consist mostly of silicates on the basis of these criteria winona mount morris wisconsin tierra blanca pontlyfni y 74025 y 75300 y 8005 and que 94535 are winonaites and y 75305 and y 75261 may be winonaites winonaites are fine to medium grained mostly equigranular rocks pontlyfni and mount morris wisconsin contain what appear to be relict chondrules several winonaites contain mm sized areas that differ substantially in grain size and or silicate mineralogy from the surrounding matrix fe ni fes veins are common in many winonaites mineral compositions are intermediate between e and h chondrites and reduced sulfides are observed in low feo winonaites bulk major element compositions are roughly chondritic although ree elements are fractionated the 39ar 40ar ages of three winonaites range from 4 40 ga mount morris wisconsin to 4 54 ga pontlyfni cosmic ray exposure ages are 20 80 ma trapped noble gases in these winonaites resemble those in enstatite chondrites we suggest that the winonaites formed from a chondritic precursor material unlike that of known chondrites in mineral and oxygen isotopic compositions and this material may have been heterogeneous in composition extensive heating caused metamorphism and partial melting of both fe ni fes and silicate material impact brecciation during cooling mixed lithologies with different thermal histories and subsequent metamorphism produced recrystallization grain growth and reduction of mafic silicates the 39ar 40ar ages indicate that cooling may have been more rapid than observed in iab irons although later resetting may have occurred

extreme wave statistical methods and implications for coastal analyses abstract this work reviews methods for extreme value analysis of ocean waves including site specific univariate analysis environmental contour analysis and spatial analysis a variation of regional frequency analysis is proposed based on the hypothesis that the distribution of extreme wave events at different sites within a homogeneous region are identical except for a shift due to a location parameter with this assumption the shape and scale parameters of the distribution can be determined with greater certainty by pooled measurements while the spatial variation is captured by the location parameter which is equal to a threshold wave height and may be more reliably sourced from a computational model as compared to the extreme values themselves this approach attempts to overcome the lack of accuracy of most wave models in extreme wave events by basing the shape and scale parameters on measurements while using a wave hind cast in a range where it is acceptably accurate to find the spatially varying location parameter the methods are applied to a case study of the canadian pacific coast un sheltered measurement sites were found to satisfy statistical homogeneity and were used to define a regional shifted extreme value distribution a high resolution numerical model was used to define the spatially varying location parameter equal to the 98th percentile of significant wave heights in general the results are satisfactory and suggest this approach may be a useful tool in understanding the spatial variability of wave extremes however it is acknowledged that this approach relies on the availability of multiple measurement sites with sufficient duration to support extreme value analysis

a hybrid efficient method to downscale wave climate to coastal areas long term time series of sea state parameters are required in different coastal engineering applications in order to obtain wave data at shallow water and due to the scarcity of instrumental data ocean wave reanalysis databases ought to be downscaled to increase the spatial resolution and simulate the wave transformation process in this paper a hybrid downscaling methodology to transfer wave climate to coastal areas has been developed combining a numerical wave model dynamical downscaling with mathematical tools statistical downscaling a maximum dissimilarity selection algorithm mda is applied in order to obtain a representative subset of sea states in deep water areas the reduced number of selected cases spans the marine climate variability guaranteeing that all possible sea states are represented and capturing even the extreme events these sea states are propagated using a state of the art wave propagation model the time series of the propagated sea state parameters at a particular location are reconstructed using a non linear interpolation technique based on radial basis functions rbfs providing excellent results in a high dimensional space with scattered data as occurs in the cases selected with mda the numerical validation of the results confirms the ability of the developed methodology to reconstruct sea state time series in shallow water at a particular location and to estimate different spatial wave climate parameters with a considerable reduction in the computational effort

distinguishing barren and auriferous veins in the sigma mine val d or quebec the sigma mine is an archean lode gold deposit located in the abitibi greenstone belt quebec barren quartz veins occur subparallel to auriferous veins within the mine and also occur north of the

on the origin of archean vein type gold deposits with reference to the larder lake break of ontario and quebec the vein type gold deposits of middle to late archean age constitute one of the major sources of gold production in the world these deposits are highly diverse in character but are invariably found in proximity to mafic and ultramafic volcanic rocks and closely associated with tectonically disturbed zones or breaks in the ancient crust using the larder lake break of northern ontario and quebec as a model a general theory of genesis for such deposits is proposed

northwest africa 011 a eucritic basalt from a non eucrite parent body we have carried out a detailed petrographic mineralogical and trace element study of northwest africa nwa 011 this meteorite bears many similarities to the eucrites it was initially identified with although oxygen isotopic compositions rule out a genetic relationship like many eucrites nwa 011 crystallized from a source with approximately chondritic proportions of ree although a slightly lree enriched bulk composition with a small positive eu anomaly as well as highly fractionated fe mg ratios and depleted sc abundances korotchantseva et al 2003 suggest that the nwa 011 source experienced some pyroxene and or olivine fractionation thermal metamorphism resulted in homogenization of ree abundances within grains but nwa 011 did not experience the intergrain ree redistribution seen in some highly metamorphosed eucrites despite a similarity in oxygen isotopic compositions nwa 011 does not represent a basaltic partial melt from the acapulcoite lodranite parent body the material from which nwa 011 originated may have been like some ch or cb chondrites members of the cr chondrite clan which are all related through oxygen isotopic compositions the nwa 011 parent body is probably of asteroidal origin possibly the basaltic asteroid 1459 magnya

rb sr k ar and stable isotope evidence for the ages and sources of fluid components of gold bearing quartz veins in the northern sierra nevada foothills metamorphic belt california gold bearing quartz veins occur in and near major fault zones in deformed oceanic and island arc rocks west of the main outcrop of the sierra nevada composite batholith veins typically occupy minor reverse faults that crosscut blueschist to amphibolite grade metamorphic rocks whose metamorphic ages range from early paleozoic to jurassic vein micas and carbonate quartz mica assemblages that formed by hydrothermal metasomatism of ultramafic wall rocks in the alleghany grass valley washington and mother lode districts yield concordant k ar and rb sr ages the dated veins are significantly younger than prograde metamorphism penetrative deformation and accretion of their host rocks to the continental margin new and previously published mineralization ages from 13 localities in the sierra foothills range from about 140 to 110 m y ago with mean and median between 120 and 115 m y the age relations suggest that mineralizing fluids were set in motion by deep magmatic activity related to the resumption of east dipping subduction along the western margin of north america following the late jurassic nevadan collision event co 2 bearing fluids responsible for metasomatism and much of the vein mica carbonate albite and quartz deposition in several northern mines were isotopically heavy delta 18 o asymp 8 14ppm delta d between about 10 and 50ppm and do not resemble seawater magmatic or meteoric waters metasomatic and vein filling mica dolomite magnesite and quartz in altered ultramafic rocks generally formed from fluids with similar sr and o isotope ratios at a given locality consistent quartz mica delta 18 o fractionations delta 18 o sub q m 4 5 4 9ppm from various localities imply uniform equilibration temperatures probably between 300 degrees and 350 degrees c on a local mine scale fluids responsible for both carbonate alteration of mafic and ultramafic wall rocks and albitic alteration of felsic and pelitic rocks had similar sr isotope ratios samples from three veins in the central alleghany district fit a 115 7 or 3 m y rb sr isochron with a 87 sr 86 sr i value of approximately 0 7119 inferred 87 sr 86 sr ratios of metasomatic fluids from mines in different parts of the foothills region vary considerably 0 704 0 718 suggesting that sr was derived from sources ranging from western assemblage mesozoic ophiolitic or arc volcanic rocks to early paleozoic continent derived clastic rocks of the shoo fly complex systematic geographic variations in both sr and o isotopes can be rationalized by assuming extensive fluid interaction with rocks similar to the ones that are exposed within a few kilometers of the veins but the ultimate sources of the fluids and of au and other constituents may be independent of these isotopically lighter meteoric fluids deposited some late quartz overgrowths and occupied secondary fluid inclusions in earlier vein quartz