amethyst bearing lava flows in the parana basin rio grande do sul brazil cooling vesiculation and formation of the geodic cavities size distribution data obtained from detailed field study of bubbles and amethyst geodes in the basaltic lava flows of the serra geral formation ametista do sul rio grande do sul brazil are used in cooling and vesiculation models to infer the origin and the formation processes of the geodic cavities coupled field observations and modelling results emphasize that 1 the formation of geodes in the studied lava flow can be explained qualitatively and quantitatively by the exsolution of magmatic gas from the supersaturated melt with no need for external surface water supply 2 the vertically elongated habits of the geodes result from higher cooling rate of the magma in contact with the accumulating bubbles and 3 the abnormal metre sized geodes with their branching habits result not only from the diffusive decompressive bubble growth but also from the coalescence of inwards progressing tubular cavities

reworked tsunami deposits by bottom currents circumstantial evidences from late pleistocene to early holocene in the gulf of cadiz abstract younger sand layers ysls have been identified in drill cores of a late glacial to early holocene muddy contourite succession from the gulf of cadiz in this study we evaluate the grain size characteristics of the ysl which display bi gradational grading with inverse grading from silt to fine or medium grained sand followed by normal grading from fine or medium grained sand to silt radiocarbon dating shows that the ysl formed at three distinct times 1 the bolling allerod sites u1387 and u1386 2 the younger dryas site u1390 and 3 the beginning of the boreal site u1389 ichnological analyses and radiocarbon dating of cores from drill site u1389c indicate that the ysls consist of reworked materials deposited at a high sedimentation rate the results of sedimentological analyses ichnological treatment spatial distributions and radiocarbon dating of the ysls suggest that the possibility of an origin of the ysls is tsunami related but later reworked by bottom current however the source areas of the sandy sediments remain unclear although our results show them to be variable and area dependent some sandy deposits are transported by the mediterranean outflow water mow from the proximal sector of the gulf of cadiz contourite depositional system cds which is close to the strait of gibraltar however in other cases it is more probable that local gravity flows which are the result of instability on adjacent margins provide the sandy material

high resolution image treatment in ichnological core analysis initial steps advances and prospects abstract ichnological studies have become popular during the last decades particularly those associated with the development of two major concepts the ichnofacies model and ichnofabric approach they have driven ichnology into diverse fields of earth sciences including paleoecology sedimentology paleoceanography and basin analysis as well as applied fields for the oil and gas industry and aquifer characterization whereas early ichnological analyses focused on outcrops later the number of ichnological studies on well cores increased noticeably still ichnological research on cores is hampered by certain limitations i e mainly narrow exposed surface and the characterization of ichnological properties is complicated when cores are involved to facilitate ichnological analysis in cores from modern deposits several techniques among them x rays magnetic resonance and computed tomography have been used with the development of computer software a new high resolution image treatment has emerged as a powerful tool in different branches of ichnological studies especially for cores from modern marine deposits because applications are numerous and perhaps not familiar to all the scientific community this paper provides an overview of the usefulness of image treatment in ichnological analysis its first steps and subsequent development the novel techniques most recently used in the study of cores from modern marine deposits and some challenges for future research

controls on prolate and oblate geode geometries in the veia alta basalt flow largest world producer of amethyst parana volcanic province brazil abstract variable intensity of hydrothermal alteration of the veia alta basalt flow ametista do sul brazil exerted the fundamental control on the shape and size of the amethyst geodes the loss on ignition loi of the host basalt is used as a proxy for intensity of alteration and has direct relationship with the height of the geodes up to 150 cm in the three study mines and with the prolaticity of geodes all rocks with loi 5 wt host prolate geodes and all oblate geodes are hosted in rocks with loi 2 k 2 o and rb the hydrothermal origin of the geodic cavities is thus established and their shapes explained by the empirical observation of the results from a previous numerical simulation experiment

oxidized and reduced mineral assemblages in greenstone belt rocks of the st ives gold camp western australia vectors to high grade ore bodies in archaean gold deposits hydrothermal sulfide oxide gold mineral assemblages in gold deposits in the archaean st ives gold camp in western australia indicate extremely variable redox conditions during hydrothermal alteration and gold mineralization in space and time reduced alteration assemblages pyrrhotite pyrite occur in deposits in the southwest of the camp e g argo junction deposits and moderately to strongly oxidized assemblages magnetite pyrite hematite pyrite occur in deposits in the central corridor in the northeast e g north orchin revenge deposits reduced mineral assemblages flank the central corridor of oxidized deposits and locally cut across it along e w trending faults oxidized mineral assemblages in the central corridor are focused on gravity lows which are interpreted to reflect abundant felsic porphyritic intrusions at about 1 000 m below present surface hydrothermal magnetite predates and is synchronous with early phases of gold associated albite carbonate pyrite biotite chlorite hydrothermal alteration later stage gold associated pyrite is in equilibrium with hematite the spatial distribution and temporal sequence of iron sulfides and oxides with gold indicate the presence of at least two spatially restricted but broadly synchronous hydrothermal fluids with contrasting redox states sulfur isotope constraints support the argument that the different mineral assemblages reflect differences in redox conditions the 34s values for pyrite for the st ives gold camp range between 8 4 and 5 1 with the negative values occurring in oxidized magnetite rich domains and slightly negative or positive values occurring in reduced pyrrhotitic domains preliminary spatial and paragenetic analysis of the distribution of iron sulfides and oxides in the st ives camp suggests that gold grades are highest where the redox state of the hydrothermal alteration assemblages switches from relatively reduced pyrrhotite pyrite to relatively oxidized magnetite pyrite and hematite pyrite both in space and time gold deposition is inferred to have occurred where fluids of contrasting redox state mixed

mineralisation of amethyst bearing geodes in ametista do sul brazil from low temperature sedimentary brines evidence from monophase liquid inclusions and stable isotopes fluid inclusion studies in combination with hydrogen oxygen and sulphur isotope data provide novel insights into the genesis of giant amethyst bearing geodes in early cretaceous parana continental flood basalts at amestita do sul brazil monophase liquid inclusions in colourless quartz amethyst calcite barite and gypsum were analysed by microthermometry after stimulating bubble nucleation using single femtosecond laser pulses the salinity of the fluid inclusions was determined from ice melting temperatures and a combination of prograde and retrograde homogenisation temperatures via the density maximum of the aqueous solutions four mineralisation stages are distinguished in stage i celadonite chalcedony and pyrite formed under reducing conditions in a thermally stable environment low 34sv cdt values of pyrite 25 to 32 suggest biogenic sulphate reduction by organotrophic bacteria during the subsequent stages ii amethyst goethite and anhydrite iii early subhedral calcite and iv barite late subhedral calcite and gypsum the oxidation state of the fluid changed towards more oxidising conditions and microbial sulphate reduction ceased three distinct modes of fluid salinities around 5 3 3 4 and 0 3 wt nacl equivalent characterise the mineralisation stages ii iii and iv respectively the salinity of the stage i fluid is unknown due to lack of fluid inclusions variation in homogenisation temperatures and in 18o values of amethyst show evidence of repeated pulses of ascending hydrothermal fluids of up to 80 90 c infiltrating a basaltic host rock of less than 45 c colourless quartz and amethyst formed at temperatures between 40 and 80 c while the different calcite generations and late gypsum precipitated at temperatures below 45 c calculated oxygen isotope composition of the amethyst precipitating fluid in combination with d values of amethyst hosted fluid inclusions 59 to 51 show a significant 18o shift from the meteoric water line this 18o shift high salinities of the fluid inclusions with chloride sulphate composition and high 34s values of anhydrite and barite 7 5 to 9 9 suggest that sedimentary brines from deeper parts of the guarani aquifer system must have been responsible for the amethyst mineralisation

source requirements for the golden mile kalgoorlie significance to the metamorphic replacement model for archean gold deposits the golden mile at kalgoorlie represents a giant archean hydrothermal gold system localized by ductile shear zones and hosted mainly by a differentiated tholeiitic sill chlorite carbonate and pyrite alteration zones cover the whole mineralized area 1 km 3 km and calculations suggest that for the golden mile production around 1200 t au the amounts of components added to these alteration zones are 340 mt co2 20 mt k and 5 mt s if one adopts a metamorphic replacement model for gold mineralization in which all ore components derive from devolatilization of greenstones at amphibolite facies or above these data suggest that a source area involving a 5 km thick greenstone slab of area 8 km 8 km could produce the necessary co2 k s h2o and au this is considered a reasonable volume of greenstone belt and under such a model the minimum spacing of large gold deposits would be approximately 20 km along strike neither special au enriched source rocks nor unreasonably large volumes of greenstone b

geochemical and scintillometric characterization and correlation of amethyst geode bearing parana lavas from the quarai and los catalanes districts brazil and uruguay geochemical studies of the six lowermost lava flows of the cretaceous serra geral formation parana volcanic province in quarai brazil and artigas uruguay were combined with flow by flow field studies of structures and scintillometric profiles to establish a consistent regional stratigraphic framework over at least 100 km this greatly improves exploration capability for amethyst and agate geodes a basalt colada mata olho alegrete facies serra geral formation was the first lava to flow over the ancient botucatu desert in the region but an andesite colada catalan overstepped this basalt in many places perhaps palaeohighs four basaltic andesites complete the lava stratigraphy in this formation adding up to 300 m of lavas the stratigraphic sequence of contrasting lava compositions is 51 0 wt sio 2 in the first lava followed by 57 5 52 5 56 0 53 0 and finally 54 5 wt sio 2 overall mgo variation is between 2 and 7 wt all lavas in the two districts are low ti 2 of the gramado type the characteristic contents of most major and trace elements 124 rock samples analysed allow the ready identification of each lava contrasting rock chemistry also results in strong variation in scintillometric values 270 points measured in the field and nineteen continuous borehole profiles from bottom to top of the stratigraphy the cps values are 49 3 2 123 10 3 62 4 7 94 4 6 45 and 85 colada catalan has the structure of aa lava particularly the contorted igneous banding and autobreccias in the upper and lower crusts in some places a 2 m thick silicified sandstone layer lies on top of some coladas and silicified sandstone forms breccias with volcanic rocks geochemistry of the six lavas indicates complex evolution involving melting of lithospheric mantle injection into the crust and assimilation of crust followed by fractional crystallization this study indicates the possibility of world class deposits of amethyst geodes on the brazilian side of the border with uruguay

the source of ore fluids and solutes in archaean lode gold deposits of western australia abstract the ore fluids which produced archaean lode gold deposits in sub amphibolite facies rocks of the yilgarn block western australia are characteristically low to moderate salinity h 2 o co 2 ch 4 fluids wall rock alteration and ore deposition were from a generally reducing near neutral fluid at 200 350 c and 1 3 kbar although more oxidising fluids produced some assemblages in the giant golden mile deposit gold was transported as reduced sulphur complexes the ore fluid composition and stable and radiogenic isotope data indicate multiple sources for the fluid and solute deep plumbing systems are invoked with the fluids being either metamorphic fluids that derived solutes from the lower and upper crusts or fluids exsolved from deep seated granitoids formed by anatexis of such crust

in situ pb isotope analysis of pyrite by laser ablation multi collector and quadrupole icpms pb isotope ratios measured in the mineral pyrite provide a valuable petrogenetic tool with widespread applicability in order to interpret complex structural and mineralogical textures however a method of in situ analysis is essential while laser ablation icpms is ideally suited to this task the low melting point of sulfide the highly variable and often high pb contents and the potential presence of relatively radiogenic inclusions introduce a number of analytical problems unique to pyrite pb isotope analysis here we address these issues using results obtained on two very different analytical systems based around multi collector and quadrupole icpms instruments respectively we suggest that controlled ablation of pyrite is only achieved at low laser fluence and that under these conditions standardisation using silicate reference materials is inappropriate and natural pyrite standards are to be preferred the inherent variability in pb and sometimes u concentrations in pyrite requires careful selection of detector systems for optimal analysis and in this regard both quadrupole and multi collector icpms instruments can play important and complimentary roles multi collector instruments provide higher precision analyses but detector configurations can prohibit simultaneous measurement of u th and pb furthermore the micrometer scale variability in pb concentrations can cause problems for both faraday cup and ion counting detection systems in contrast quadrupole icpms systems allow simultaneous measurement of u th and pb and have more flexible detection systems with many orders of magnitude dynamic range but are unable to produce high precision data results are presented for two different analytical systems and demonstrate a very strong dependence of data quality upon signal size in addition they allow some estimation of the limiting precision obtainable by these methods finally a geological example is provided from the giant sukhoi log sedimentary au deposit of russia

architecture of the neoarchaean jaguar vhms deposit western australia implications for prospectivity and the presence of depositional breaks abstract the duration and nature of breaks in archaean volcanosedimentary packages recently re evaluated in the abitibi greenstone belt has been assessed at jaguar an archaean cu zn rich volcanic hosted massive sulphide vhms deposit in the teutonic bore volcanic complex tbvc the eastern goldfields of the yilgarn craton western australia the deposit is hosted by coherent volcanic facies and associated volcaniclastic facies with minor non volcanic facies the hypothesis that vhms ore lies on the intersection of volcanic centres and depositional breaks is found to be valid for the jaguar deposit with the site being an active volcanic complex at footwall time with further dome development close to the final ore location at mineralised package time and then reoccurring volcanic complexes andesitic and basaltic at several points in the hangingwall succession broadly tied into the ore position at jaguar the entire stratigraphic sequence faces west with no major structural complications making it ideal for stratigraphic analysis the footwall evidences prolific volcanism with no intervening sedimentation the mineralised package mp consists of intercalated dacite breccia conglomerate sandstone and mudstone the footwall volcanic rocks and the mp dacite appear to be differentiation products from the same magma chamber a major volcanic geochemical boundary is identified between the footwall mp tholeiitic to transitional affinities and the immediate hangingwall succession calc alkaline the hangingwall package includes four distinct volcanic units intercalated with mass flow deposits and graphitic argillites vhms mineralisation occurred across a distinct change in the geochemistry of erupted volcanic facies at a time of increased volcaniclastic sedimentation and extension this break is comparable to member level hiatuses seen in the abitibi gb i e the most brief of breaks because there is no silicification of sedimentary unit tops by silicic seawater exposure and there is minimal development of black shales a third time sensitive criteria was the development of peperite on the base of hanging wall hw andesite lavas the mp closely resembles breaks within interpreted deeper water domains of the abitibi gb for instance the deloro tisdale assemblage interface south of timmins the recognition of the change in the rate of emplacement of volcanic units and particularly the change in chemistry of volcanic rocks are critical exploration lithologic guides to use in the absence of chemical sediment deposits exhalites although crustal extension and basin subsidence were factors in the shaping of the succession their effects were too subtle to use as an exploration tool a corollary of the recognition of a member level vhms bearing interval in the teutonic bore volcanic complex is that like the kidd munro assemblage stratigraphy abitibi gb where several ore bearing depositional breaks are known below the great kidd creek deposit there is scope for the discovery of further potentially larger deposits on higher formation or group level breaks in the tbvc

epigenetic formation of amethyst bearing geodes from los catalanes gemological district artigas uruguay southern parana magmatic province abstract giant geodes up to 4 m long in the massive central portions of altered basalt lavas from the parana magmatic province southern brazil and uruguay form a world class source of amethyst and agate although the origin of the cavities has been ascribed to degassing of the lava at 1150 c field evidence is conclusive that the giant amethyst agate filled geodes were formed by hydrothermal processes at low temperatures we propose an epigenetic and hydrothermal model for the origin of giant geodes this model includes hydrothermal brecciation during an early brittle stage and the late formation of the cavities geodes in the brittle stage an overpressured aqueous fluid affected the basalt in a p t field delimited by temperatures between 100 and 150 c and vapor pressures between 1 2 and 5 5 bar the fluids were capable of lifting the roof and fracturing the host rock along new subhorizontal and subvertical fractures and breccias in the massive lava the formation of these structures occurred at shallow depths unit by unit to open the cavities dissolution of the now altered basalt to clay minerals is necessary the process is closely linked to the highest alteration grade of mineralized lavas in los catalanes gemological district dissolution processes are observed in micrometer scale in the studied basalts the primary mineralogy consisting of labradorite andesine augite pigeonite mesostasis k rich was altered during the interaction of large volumes of hot aqueous fluid with the rock the alteration of pigeonite and its replacement by smectite is observed around the cavities followed by the precipitation of amorphous silica and microcrystalline quartz in clay rich sites associated zeolites heulandite clinoptilolite fill the newly formed cavities in progressive stages of hydrothermal alteration our data indicate that the temperatures were less than 200 c and probably less than 150 c cavity formation occurred after alteration of the basalt to more than 60 vol clay minerals we thus suggest that cavities related to geode formation are of epigenetic origin

ethological implications from a detailed x ray radiograph and 14c study of the modern deep sea zoophycos the modern zoophycos found in deep sea sediments from the portuguese continental margin differs markedly from most zoophycos described from the fossil record a detailed x ray radiograph analysis revealed that the trace consists of an upwards constructed helically coiled spreite that is connected to the sediment surface through a single shaft comparison of 14c dates from spreiten material and directly surrounding sediment revealed age differences of up to more than 2500 years the spreiten material always being younger this clearly shows that the spreiten material was collected on the seafloor and transported into the sediment together with raised levels of organic carbon in the spreiten compared to the surrounding sediment this indicates a selective detritus feeding behavior of the tracemaker detailed studies of the bathymetrical and regional distribution of zoophycos in archived x ray radiographs stored at kiel university germany reveal that the trace is strictly confined to deep calm settings where most organic carbon reaches the seafloor in pulses on the basis of these findings the traditional interpretation of zoophycos as a deposit feeder is rejected in favor of a combined detritus feeder and cache model for the modern deep sea zoophycos

the granny smith gold deposit the role of heterogeneous stress distribution at an irregular granitoid contact in a greenschist facies terrane the granny smith gold deposits formed late in the structural history of the yilgarn block at a high crustal level in a largely brittle structural regime gold mineralisation is located along a n s striking fault which wraps around the contact of a small granitoid intrusion in different sections of the fault mineralisation may be developed in the granitoid in the adjacent sedimentary sequence and or along the contact between them in the granitoid gold mineralisation is in conjugate networks of thin carbonate quartz veins and their alteration halos small displacements along veins are common in contrast veins and faults in the sedimentary rocks are subparallel to bedding spatial variations in the conjugate vein orientations indicate that the local stress field was heterogeneous and controlled by the shape of the granitoid contact the greatest variations in vein and implied stress orientations occur in zones where the contact is most irregular these are also the areas of richest mineralisation fluid flow was thus focused in a regional scale low mean stress region created by the geometry of the granitoid intrusion its irregular contact caused deposit scale variations in fluid flow and resulted in heterogeneous gold grades along the contact zone

the genesis of the amethyst geodes at artigas uruguay and the paleohydrology of the guarani aquifer structural geochemical oxygen carbon strontium isotope and fluid inclusion study the amethyst bearing geodes found in the flood basalts of the arapey formation at artigas uruguay were formed as protogeodes by bubbles of co2 rich basalt derived fluids the formation of the celadonite rim and the lining of the geodes by agate followed by quartz and amethyst were driven by the artesian water of the guarani aquifer percolating the basalts from below the temperature of the amethyst formation is estimated from fluid inclusion data to be between 50 and 120 c oxygen stable isotope data suggest a crystallization temperature of calcite of about only 24 c the actual wellhead temperature of the water produced from the guarani aquifer in the study area is around 29 c

chemical stratigraphy of the parana lavas south america classification of magma types and their spatial distribution a new classification scheme has been developed to assign the lava flows of the parana continental flood basalt province south america into geochemically distinct magma types with six basaltic major and trace element abundances and or ratios by mapping out the spatial distribution of these magma types within the lava sequences it has been possible to determine the internal stratigraphy of the lava pile on a regional scale previous studies on road profiles traversing the well exposed coastal serra geral escarpment of southern brazil are summarised together with results from some new sampled sections more widespread stratigraphical investigations of the parana lavas have been hampered by the lack of sufficient topographic relief and the cover of sedimentary rocks however access to drill core chippings from nine boreholes in the central parana region has provided a unique opportunity to investigate the stratigraphy of the otherwise inaccessible deeper levels of the lava pile and to map out stratigraphic variations in three dimensions the borehole samples have indicated cated a stacking of units of different magma types all overlapping towards the north which suggests that the main locus of magmatism moved northwards with time within the parana basin this migration could be related to the northward propagation of rifting during the initiation of the south atlantic ocean maps of the surface distribution of samples of each magma type show a pattern consistent with the stratigraphy inferred from the boreholes although suggesting that the shift in magmatism may have been towards the northwest on the basis of geochemical similarities between magma types and their inferred stratigraphical relationships it is proposed that the parana can be divided into two principal magmatic centres 1 an older one in the south comprising the gramado esmeralda and urubici magma types and 2 a younger one developed about 750 km to the north formed by the pitanga paranapanema and ribeira magma types

archean high mg monzodiorite syenite epidote skarn and biotite sericite gold lodes in the granny smith wallaby district australia u pb and re os chronometry of two intrusion related hydrothermal systems the granny smith 37 t au production and wallaby deposits 38 t out of a 180 t au resource are located northeast of kalgoorlie in 2 7 ga greenstones of the eastern goldfields province the youngest orogenic belt of the yilgarn craton western australia at granny smith a zoned monzodiorite granodiorite stock dated by a concordant titanite zircon u pb age of 2 665 3 ma cuts across east dipping thrust faults the stock is fractured but not displaced and sets a minimum age for large scale 1 km thrust faulting d2 regional folding d1 and dynamothermal metamorphism in the mining district the local gold pyrite mineralization controlled by fractured fault zones is younger than 2 665 3 ma in augite hornblende monzodiorite alteration progressed from a hematite stained alkali feldspar quartz calcite assemblage and quartz molybdenite pyrite veins to a late reduced sericite dolomite albite assemblage gold related monazite and xenotime define a u pb age of 2 660 5 ma and molybdenite from veins a re os isochron age of 2 661 6 ma indicating that mineralization took place shortly after the emplacement of the main stock perhaps coincident with the intrusion of late alkali granite dikes at wallaby a ne trending swarm of porphyry dikes comprising augite monzonite monzodiorite and minor kersantite intrudes folded and thrust faulted molasse the conglomerate and the dikes are overprinted by barren 1 600 m long replacement pipe which is intruded by a younger ring dike of syenite porphyry pervasively altered to muscovite calcite pyrite skarn and syenite are cut by pink biotite calcite veins containing magnetite pyrite and subeconomic gold silver mineralization au ag 0 2 the veins are associated with red biotite sericite calcite albite alteration in adjacent monzonite dikes structural relations and the concordant titanite u pb age of the skarn constrain intrusion related mineralization to 2 662 3 ma the main stage gold pyrite ore au ag 10 forms hematite stained sericite dolomite albite lodes in stacked d2 reverse faults which offset skarn syenite and the biotite calcite veins by up to 25 m the molybdenite re os age 2 661 10 ma of the ore suggests a genetic link to intrusive activity but is in apparent conflict with a monazite xenotime u pb age 2 651 6 ma which differs from that of the skarn at the 95 confidence level the time relationships at both gold deposits are inconsistent with orogenic models invoking a principal role for metamorphic fluids released during the main phase of compression in the fold belt instead mineralization is related in space and time to late orogenic magnetite series high mg monzodiorite syenite intrusions of mantle origin characterized by mg mg fetotal 0 31 0 57 high cr 34 96 ppm ni 22 63 ppm ba 1 056 2 321 ppm sr 1 268 2 457 ppm th 15 36 ppm and rare earth elements total ree 343 523 ppm at wallaby shared ca k co2 metasomatism and th ree enrichment in allanite link au ag mineralization in biotite calcite veins to the formation of the giant epidote skarn implicating a th ree rich syenite pluton at depth as the source of the oxidized hydrothermal fluid at granny smith lead isotope data and the rb th u signature of early hematite bearing wall rock alteration point to fluid released by the source pluton of the differentiated alkali granite dikes

gold mineralization in as rich mesothermal gold ores of the bogosu prestea mining district of the ashanti gold belt ghana remobilization of invisible gold the bogosu prestea mining district of southwestern ghana is a 33 km section of the early proterozoic ashanti gold belt greenschist facies carbonaceous and carbonate bearing turbidites and greywackes and mafic dikes host numerous economic mesothermal gold deposits structurally higher ores in the bogosu concession have brittle deformation and consist of disseminated sulphide lodes in tectonically disrupted sedimentary rocks and carbonate altered mafic dikes most gold occurs as micrometre size particles in arsenian pyrite and as invisible gold in arsenian pyrite and arsenopyrite the structurally deeper ores of the adjoining prestea concession are associated with brittle ductile deformation and consist of extensive crack seal quartz veins and graphitic shear zones only minor amounts of invisible gold were detected in these deeper lodes gold occurs dominantly as abundant microscopic and larger particles in sulphide arsenide minerals and in gangue the gold distribution patterns revealed by sims microprobe analysis and ion maps emp and colour staining suggest that most of the primary gold in the bogosu prestea system precipitated in solid solution with sulphide arsenide minerals however post depositional concentration and redistribution occurred in increasing degree with 1 increase in metamorphic hydrothermal gradients in the gold system depth 2 decrease in the refractory properties of the host mineral and 3 increase in the amount of post depositional host mineral recrystallization and deformation gold evolved from primary solid solution within sulphide arsenide minerals to colloidal and micrometre size particles concentrated in voids fractures and internal grain boundaries and finally to microscopic and larger particles at sulphide arsenide grain margins and in the gangue assemblage the general conclusions presented here are applicable to as rich gold deposits of all ages worldwide the presence of gold in late fractures is insufficient evidence for late stage introduction of gold in mesothermal gold systems

geometallurgy of the pebble porphyry copper gold molybdenum deposit alaska implications for gold distribution and paragenesis the pebble cu au mo deposit in southwest alaska is one of the world s largest porphyry deposits the deposit contains over 80 billion pounds blbs cu 107 million ounces moz au and 5 6 blbs mo in all resource categories copper and gold grades vary across diverse hydrothermal alteration assemblages with higher grades associated with sericite and pyrophyllite rich assemblages in an advanced argillic alteration zone moderate grades are associated with the potassic and sodic potassic alteration assemblages that dominate the deposit and low grades are found in quartz illite pyrite assemblages these variations reflect fluctuations in both the temperature and composition of the magmatic hydrothermal fluids in time and space qemscan scanning electron microscope based mineral mapping and in situ laser ablation inductively coupled plasmamass spectrometry methods designed to document the spatial and temporal variations in metal deportment across alteration zones show that gold occurs as inclusions of electrum and high fineness gold in chalcopyrite and pyrite and as free grains hosted by silicate minerals with the proportion of each related to the principal host alteration assemblage gold associated with the earliest high temperature sodic potassic and potassic assemblages occurs as electrum inclusions in chalcopyrite and to a lesser extent pyrite and pyrite trace element signatures have high gold silver and copper concentrations pyrite 1 during cooling of the hydrothermal system lower temperature illite and illite kaolinite alteration overprinted the earlier assemblages with varying degrees of recrystallization and precipitation of more pyrite rich assemblages with pyrite having a gold poor trace element composition pyrite 2 gold released during recrystallization formed high fineness gold inclusions in newly formed pyrite and narrow gold rich pyrite rims pyrite 3 a second magmatic hydrothermal event resulted in a sericite and pyrophyllite rich advanced argillic overprint which introduced more copper and gold to the system and recrystallized preexisting sulfides into both high and low sulfidation assemblages with high fineness gold inclusions in pyrite and chalcopyrite and solid solution gold in bornite a second generation of pyrite 1 with elevated palladium concentrations is associated with this hydrothermal fluid pulse and also possibly high arsenic pyrite pyrite 4 understanding the controls on gold deportment provides genetic constraints on ore deposit genesis alteration and sulfide assemblages and gold compositions provide information on the hydrothermal fluid compositions ph and temperature evolution of the magmatic hydrothermal system the presence of electrum inclusions in chalcopyrite and pyrite in potassic and sodic potassic alteration is consistent with these zones forming from early high temperature magmatic fluids because both gold and silver are transported together in such fluids high fineness gold inclusions in younger pyrite related to low temperature clay alteration are evidence that the gold in early electrum was partially remobilized and reprecipitated the low temperature clay alteration most likely formed from a mixture of h2s rich vapor with meteoric waters conditions where gold is transported as a bisulfide complex and silver is not resulting in the separation of the two metals a second structurally controlled pulse of magmatic fluids formed a well mineralized advanced argillic alteration assemblage containing high fineness gold inclusions in chalcopyrite and pyrite the only part of the deposit where high fineness gold is hosted by chalcopyrite in the pyrophyllite stability field acidic fluid compositions transport gold and silver as different complexes and gold solubility is significantly lower than silver leading to the precipitation of highfineness gold inclusions palladium is transported by the same complex as gold under these conditions consistent with the elevated palladium content of pyrite in the advanced argillic alteration assemblage the temporal and spatial studies of variations in gold deportment across the pebble deposit provide critical inputs to optimization of mineral processing design the greatest influence on metallurgical gold recovery at pebble is the proportion of gold that is hosted by pyrite pyrite hosted gold may require different mineral processing methodologies compared with gold hosted by chalcopyrite therefore defining domains of consistent hydrothermal alteration and sulfide mineralogy and gold deportment is the key to the geometallurgical characterization of the deposit

broad synchroneity of three gold mineralization styles in the kalgoorlie gold field shrimp u pb and 40ar 39ar geochronological evidence there has been a long standing controversy regarding the timing and number of gold mineralization events at kalgoorlie uranium pb dating of zircons and hydrothermal monazite and xenotime as well as ar 40 ar 39 analysis of metasomatic fuchsite and white mica are used to date pre to synore dikes alteration and orebodies in order to resolve this issue the majority of gold mineralization at kalgoorlie including ductile brittle fimiston brittle ductile oroya and brittle mount charlotte style gold are different expressions of a complex mineralizing system that was active at broadly the same time at ca 2 64 ga gold mineralization was thus deposited in both ductile and brittle structures at approximately the same crustal level at broadly the same time limier similar pt conditions this giant ore system formed after ea 2 69 ga basic magmatism intrusion of the golden mile dolerite sill at 2680 9 ma and intrusion or calc alkaline feldspar quartz porphyry dikes at 2670 5 ma gold mineralization was broadly coeval with lamprophyre dike intrusion at 2642 6 ma and overlapped the waning stages of hornblende and albite bearing porphyry dike emplacement at 2650 6 ma and regional metamorphism subsequent brittle deformation in the kalgoorlie gold held way accompanied by hydrothermal activity that may have led to some late gold mineralization or remobilization in extensional quartz vein arrays in the golden mile between about 2 61 and 2 60 ca this late hydrothermal activity and associated brittle deformation marks the last event to significantly affect the rocks it kalgoorlie and may be related to uplift lift and final cooling of the terrane despite this late event the geometry of the kalgoorlie gold field and its contained lode systems has remained essentially the same since the time of gold mineralization

geochronological constraints on pre syn and postmineralization events at the world class cleo gold deposit eastern goldfields province western australia recent geological and geochronological studies have led to a reevaluation of whether or not the majority of the lode gold deposits of the yilgarn craton formed nearly synchronously during an archean craton wide hydrothermal event as previously proposed the majority of reliable data indicate that gold mineralization took place at ca 2640 to 2625 ma however recent work in the far north of the eastern goldfields province provides structural evidence for instances of earlier gold mineralization and geochronological data for interpreted postore rocks that are considerably older than 2640 ma the documentation of xenotime and monazite in association with ore minerals at the cleo deposit provides a valuable means of determining the absolute age of gold mineralization at the cleo deposit high grade western lodes veins crosscut the sunrise shear zone at a high angle with only centimeter scale offset given that the stratigraphic sequence indicates at least several hundred meters offset across the shear zone the minimal offset of the western lodes veins indicates that gold mineralization was late in the history of movement in the shear zone the absolute ages of pre syn and postmineralization elements in the mine stratigraphic succession have been determined using a variety of geochronological techniques fuchsite micas formed in the sunrise shear zone yield an 40ar 39ar isochron age of 2667 19 ma rhyodacite porphyry dikes postdate the formation of the shear zone but predate the main phase of gold mineralization dike intrusion is constrained to 2674 3 ma by shrimp ii u pb analysis of zircons from these dikes rhenium os analysis of molybdenite from quartz chalcopyrite molybdenite veins that crosscut the porphyry dikes gives an age of formation at 2663 11 ma consistent with their relationship to the porphyry dikes both the dikes and these veins are crosscut by gold bearing western lodes veins mutually crosscutting relationships with ore minerals indicate that microscopic xenotime and monazite grains were deposited during ore formation in the western lodes ore zones shrimp ii u pb analyses of xenotime and monazite grains indicate that western lodes mineralization took place at 2654 8 ma at least 9 m y after the intrusion of the porphyry dikes 95 confidence evidence for substantial temporal separation between intrusive activity and gold mineralization is recorded by other researchers for other deposits associated with granitic intrusions in the leonora laverton area phlogopitic micas from a lamprophyre that crosscuts the whole succession including the sunrise shear zone yield an ar ar plateau age of 2080 4 ma this study constrains the timing of multiple events at cleo including the main phase of gold mineralization during a relatively short span of time however in the context of the larger debate about the existence of a dominant 2640 to 2625 ma period of gold mineralization and the extent of a proposed widespread pre 2660 ma mineralization event in the yilgarn craton the data from cleo are equivocal the 2654 8 ma age for mineralization being significantly older than 2640 ma but not significantly pre 2660 ma even if the maximum possible age is accepted

p t x conditions of hydrothermal fluids and precipitation mechanism of stibnite gold mineralization at the wiluna lode gold deposits western australia conventional and infrared microthermometric constraints the wiluna lode gold deposits are located in the archean wiluna greenstone belt in the northern sector of the norseman wiluna belt in the yilgarn craton of western australia they are hosted in subgreenschist facies meta basalts and controlled by the wiluna strike slip fault system and associated shear veins and breccias the 13 individual lode gold deposits have produced around 115 t au from 1901 to 1946 and 1986 to today historically they also produced 38 3 t as and 3 5 t sb gold formed in two stages stage 1 gold pyrite arsenopyrite is finely disseminated in the wallrock and breccia fragments whereas stage 2 gold stibnite is located in massive shear veins and breccia matrix as fracture fill and in banded colloform textured veins stibnite gold orebodies only occur in some of the deposits e g moonlight and northern part of the west lode and also display a restricted vertical extent being preserved only in the uppermost 200 m of stibnite bearing lodes petrographic conventional and infrared microthermometric and laser raman analysis on stibnite bearing quartz veins and breccias reveal that the antimony and gold rich hydrothermal fluid was of mixed h2o nacl co2 ch4 type microthermometric measurements reveal maximum homogenization temperatures of 340 c average 290 25 c and a wide range of salinities between 0 2 and 23 eq wt nacl aqueous carbonic fluid inclusions contain variable xco2 ch4 0 03 to 0 82 with the carbonic phase containing a maximum xch4 of 0 21 combined petrographic and microthermometric evidence suggests that the fluid inclusion properties reflect fluid immiscibility of a low salinity medium xco2 ch4 homogeneous parent fluid at about 290 c and pressures between 700 and 1 700 bar fluid immiscibility was triggered by cyclic pressure release during fault zone movement the decompression adiabatic cooling of the hydrothermal fluids shifted the ore fluid to lower temperatures significantly reduced the degree of stibnite undersaturation and caused stibnite to precipitate the deposition of stibnite reduced the ore fluid h2s concentration thereby destabilized gold bisulfide complexes in solution and caused gold precipitation locally this mechanism explains the intimate spatial association of stibnite and gold in quartz veins and breccias in the stibnite gold orebodies at wiluna

the archean chalice gold deposit a record of complex multistage high temperature hydrothermal activity and gold mineralisation associated with granitic rocks in the yilgarn craton western australia abstract the chalice gold deposit 20 t au produced in the southwestern portion of the late archean norseman wiluna greenstone belt of the yilgarn craton western australia is hosted both in a sequence of intercalated mafic and ultramafic amphibolites and a post peak metamorphism monzogranite dike the deposit is flanked on the western side by calc alkaline plutonic rocks and to the east by a predominantly monzogranitic pluton with at least four generations of monzogranitic dikes that intrude the local mine stratigraphy locally four deformation events d 1 d 4 have affected this sequence of amphibolites and two stages of gold mineralisation are recognised controlled by the progressive d 2 event main stage gold mineralisation 95 of the resource which is demonstrably later than all granitic bodies except second generation and subsequent monzogranite dikes is controlled by localised d 2 asymmetric folds developed in the mafic amphibolite it is expressed as veins and wall rock replacement characterised by a prograde assemblage of quartz diopside plagioclase k feldspar titanite pyrrhotite pyrite magnetite garnet hornblende scheelite and biotite second stage gold mineralisation 5 of the resource is associated with the intrusion of a monzogranite dike and is expressed as disseminated gold in the dike as well as foliation discordant veins of quartz gold quartz diopside gold actinolite gold and molybdenite tellurobismuthite gold detailed field mapping and petrography suggest that main stage gold mineralisation at chalice is equivalent to hypozonal orogenic lode gold mineralisation in other archean greenstone belts of the yilgarn craton whereas monzogranite associated second stage gold mineralisation is atypical of such deposits the main stage mineralisation cannot be correlated to any particular granitoid in the local environment although temporally it is bracketed by granitic magmatism a deep magmatic or metamorphic source cannot be resolved from the field data it is also uncertain as to whether second stage mineralisation represents a true magmatic gold event or is a product of the assimilation and remobilisation of main stage gold during the intrusion of the monzogranite dike however its distinctive metal association of au bi mo te w suggests the former irrespective of this uncertainty chalice remains as a deposit which is more intimately related both spatially and temporally to granitic magmatism than other yilgarn deposits

trace fossils as a paleoceanographic tool evidence from late quaternary sediments of the southwestern iberian margin biogenic structures in late quaternary sediments from the southwestern iberian continental slope were studied by using x ray images from two cores from 580 and 1750 m water depth eight different ichnocoenoses were observed indistinct bioturbation planolites dominated thalassinoides dominated chondrites dominated planolites and thalassinoides dominated pyritized microburrows such as trichichnus and mycellia dominated chondrites trichichnus and mycellia dominated and zoophycos variations of the ichnocoenoses within the cores show a striking correlation with climatically induced changes in the hydrographical regime i e current strength and bathymetric position of the mediterranean outflow water mow comparison of the response of the ichnocoenoses to changes in bottom water conditions and substrate between the two cores studied indicate that bottom water oxygenation and enrichment of particulate organic matter at the base of the mow layer are the primary factors controlling the ichnocoenoses the traces even recorded short term climatic changes such as the younger dryas cold event the spatial and temporal distribution patterns are in good agreement with earlier models of the mow history which gives reason to see a refinement of trace fossils as a complementary tool for paleoceanographical studies

australian volcanic hosted massive sulfide deposits features styles and genetic models the cambro ordovician period has yielded the major development of volcanic hosted massive sulfide vhms deposits in australia resulting in about 12 million metric tons of contained metal copper lead and zinc concentrated in the mount read volcanics tasmania and the mount windsor volcanics queensland the archean 4 million metric tons of metal and the silurian 3 5 million metric tons of metal constitute the next important episodes while the devonian and permian have produced isolated deposits the deposits range from cu type to zn cu type to zn pb cu type the zn cu type deposits are restricted to the archean and silurian whereas the cu type and zn pb cu type occur sporadically throughout the time span from early archean to permian in general terms the major vhms bearing districts are calc alkaline in character and display a thick basal pile of rhyolitic volcanics 1 3 km thick including lavas epiclastics and subvolcanic intrusions which is overlain by a polymodal sequence containing various proportions of rhyolite dacite andesite basalt and sediments the major deposits are commonly located at the top contact of the rhyolite pile or within the lower part of the overlying polymodal sequence there is a wide range in variability of styles of australian vhms deposits including mounds pipes sheets layered deposits stacked deposits stockwork and disseminated deposits distal reworked deposits and cyclic layered deposits although these various styles show a range of features there is a consistent theme across the spectrum of metal zonation alteration mineralogy alteration chemistry sulfur isotopes macrotextures microtextures and host volcanic relationships which strongly suggests that they all belong to the one genetic group of ore deposit the classic mound style deposits such as hellyer have a series of key features subsets of which are represented in the other deposit styles the mound deposits are considered to form from deposition of metal sulfides on the sea floor immediately around the hydrothermal vent growth of the mound occurs by upward replacement of sulfide assemblages stable at higher fluid temperatures leading to zone refining and lead zinc silver gold enrichment in the outer and upper parts of the mound departure from the classic mound style of deposit is related principally to three key factors the chemistry of the ore fluid salinity temperature f02 and ah2s the nature permeability and chemistry of the volcanic pile and the sea hoor environment sea hoor topography and seawater depth these factors control the aspect ratio of the deposit the extent of stringer zone development the degree of subsea floor replacement mineralization the nature and spatial development of footwall alteration and the development and style of related distal mineralization sulfur isotope studies of australian vhms deposits indicate that reduced seawater sulfate is a major source of sulfur in the deposit whereas lead and strontium isotope results are compatible with the metals being derived by seawater convection and leaching from the volcanic pile and basement rocks this conclusion is supported by the application of various leaching models which demonstrate the availability of an adequate source of both base and precious metals in the footwall volcanic sequences the input of metals directly from volcanic magma chambers is not precluded by the available data and one likely scenario involves the contribution of gold and copper from a magmatic vapor plume rising to mix with convective seawater fluids which contribute lead zinc silver and gold leached from the footwall volcanics and basement rocks the relative importance of the magmatic input compared with the seawater convective input may help to explain the spectrum of deposit styles arid their spatial relationship to volcanic centers or adjacent sedimentary basins

architecture and geodynamic evolution of the st ives goldfield eastern yilgarn craton western australia abstract a new structural evolution consisting of both extensional and contractional events has been defined for the st ives goldfield in the south central kalgoorlie terrane of the eastern yilgarn craton in western australia these events shaped the development of the fault architecture which controlled the location of the regional anticlines the magmatic centres and the deposition of the archaean greenstone successions the fundamental grain of the st ives goldfield is north northwest trending this trend is marked by faults which developed during d1 extension which was oriented east northeast west southwest across these faults we map major stratigraphic changes in the thickness and composition of units especially of the previously undivided black flag group volcaniclastic rocks the centre of the st ives goldfield is dominated by the kambalda anticline this north northwest trending regional fold was likely established early during the d1 extensional history and was fully established during subsequent east northeast oriented d2 contraction the regional anticline is an important architectural element because 1 magmatism and gold mineralising fluids were focussed into this domed region and 2 deformation was partitioned across the limbs and crest of this structure the d3 event involved regional uplift and extension resulting in the formation of late basins merougil conglomerate locally and the emplacement of granitoids sourced from a metasomatised mantle wedge mafic type porphyries the most significant gold event in terms of endowment occurred during d4b sinistral strike slip shearing and associated thrusting e g tramways and republican thrusts these thrusts were previously interpreted as the first contractional structures to deform the area d1 but are here reinterpreted as relatively late d4b in this d4b event the north northwest trending faults underwent sinistral strike slip shearing and were linked across the kambalda anticline by accommodation structures represented by generally east to east northeast trending thrusts reactivation of d1 transfer structures may have influenced the location of these later accommodation structures late stage mineralisation during d5 was the result of dextral strike slip brittle shearing

young porphyries old zircons new constraints on the timing of deformation and gold mineralisation in the eastern goldfields from shrimp u pb zircon dating at the kanowna belle gold mine western australia abstract the kanowna belle gold mine is a late archaean orogenic lode gold deposit hosted by felsic volcaniclastic and intrusive rocks porphyries of the kalgoorlie terrane western australia rare gold occurs in fragments of veins and alteration that form clasts within the black flag group volcaniclastic rocks at the kanowna belle mine indicating that epithermal gold mineralisation accompanied black flag group volcanism the shrimp u pb zircon age of the volcaniclastic unit is 2668 9 ma and xenocrystic zircons with 2 68 2 70 and 2 71 ga age groupings are common the black flag group rocks are faulted by a d1 thrust and 2670 ma is thus an older limit for regional d1 deformation although shrimp u pb zircon ages of felsic porphyries commonly give the best constraints on the timing of deformation and structurally controlled gold mineralisation the data are complex and dates from single samples can be ambiguous four porphyry samples from the kanowna belle gold mine were analysed backscattered electron and cathodoluminescence imaging show that most magmatic zircon in the porphyries is either high u and metamict or restricted to rims on older xenocrysts that are too narrow to be dated by shrimp some porphyries appear to have been saturated with zircon at source and contain only xenocrystic zircons zircons that are interpreted to be magmatic in a sample of the mineralised kanowna belle porphyry gives a mean age of 2655 6 ma the kanowna belle porphyry is cross cut by regional d2 fabrics and 2655 ma is thus the maximum age for regional d2 deformation this is a maximum age for epigenetic lode gold mineralisation the age of resetting of high u zircon grains 2 63 ga and the age of ore related pb pb galenas 2 63 ga serves as an approximate date for lode gold mineralisation if the complex zircon history of the felsic porphyries at kanowna belle is typical of this suite throughout the eastern goldfields province it is clear that existing single zircon dates from this province require reevaluation backed up by careful backscattered and cathodoluminescence imaging and textural studies

geology of the golden grove prospect western australia a volcanogenic massive sulfide magnetite deposit potentially economic deposit stratabound two phases of sulfide precipitation separated by a major phase of fe oxide development metamorphosed under lower greenschist facies hydrothermal alteration of host rocks fe oxide abundance is due to either sea floor weathering or to a change with time in the trend of the ore solution seawater mixing path modified journal abstract

ichnological analysis of contourites past present and future abstract contourite deposits are significant facies in deep water sedimentary environments because they record critical paleoclimatological and paleoceanographic data contourite research also informs slope stability geological hazard assessment and petroleum exploration scientific consensus has not converged on several key aspects of contourite interpretation however some researchers interpret bioturbation as a diagnostic feature that differentiates contourites from associated facies e g turbidites while other researchers consider bioturbation to be of second order importance this work reviews existing literature and relevant field data to better define the role of ichnological analysis in contourite research review of significant contributions by earlier studies including formalization of terminology bioturbation burrow etc can help constrain wider usage of ichnological concepts e g ichnofacies and ichnotaxonomic analysis this paper also revisits ichnological data in paleoenvironmental interpretations reservoir characterization and the rare example of ichnofacies and ichnofabric analyses designation of diagnostic criteria can promote the use of ichnological information in contourite research regardless of consensus concerning bioturbation as a diagnostic criterion in contourite characterization ichnological data can still inform interpretations and integrate with other techniques to advance understanding of contourite sedimentary facies for a broad range of applications

geodynamics of the eastern yilgarn craton abstract over the last decade there have been significant advances in our understanding of the stratigraphy magmatism deformation metamorphism and timing of mineralisation in the eastern yilgarn craton eyc of western australia the integration of these disciplines has enabled a holistic review of the tectonic history of the eyc which favours a paraautochthonous tectonic model a significant advance has been the recognition of a 2810 ma rifting event off the eastern margin of the youanmi terrane which set up the north northwest trending architecture of the eyc rifting was followed by a 100 myr long phase of tectonic activity initiated by the establishment of a convergent margin at 2715 ma characterised by a west dipping subduction zone to the east of the eyc subduction was associated with the deposition of 2715 2670 ma volcanic stratigraphy and the emplacement of voluminous tonalite trondhjemite granodiorite magmatism which resulted in magmatic thickening of the crust volcanism was terminated by a 5 myr pulse of east northeast contraction followed by mid orogenic extension possibly linked to lithospheric and lower crustal delamination the lack of ultra high pressure metamorphism and the presence of high geothermal gradients preclude this contractional event from recording continent continent collision mid orogenic extension at 2665 ma resulted in the introduction of metasomatised mantle melts mafic granites and syenites deposition of siliciclastic basins which record metamorphic anticlockwise ptt paths and the start of significant economic gold mineralisation in the eyc high stretching factors and or delamination associated with this extension event resulted in significant heat input into the base of the crust which eventually led to the emplacement of low ca crustal melt granites and cratonisation of the eyc major gold mineralisation postdates mid orogenic extension and was associated with renewed compression transpression 2650 ma and the development of steep predominantly north northwest striking sinistral and later north to north northeast striking dextral strike slip faults during low ca granite emplacement

zoophycos in deep sea sediments indicates high and seasonal primary productivity ichnology as a proxy in palaeoceanography during glacial interglacial variations trace fossils provide valuable palaeoenvironmental information in hemipelagic settings this is particularly true in the case of zoophycos an easily recognizable trace fossil in core at iodp site u1385 zoophycos was found throughout an interval representing 1 5 ma covering 45 glacial interglacial cycles mediated by obliquity 41 ka and short term eccentricity 100 ka zoophycos is most common in sediments deposited during glacial times and when the sedimentation rate was intermediate and primary production was high and seasonal occurrences of zoophycos elsewhere support a similar relationship with seasonal organic matter deposition this is particularly significant considering that seasonality of organic matter deposition is difficult to decipher from the sediment record zoophycos appears to represent a useful proxy to characterize high and seasonal organic matter deposition and primary productivity in neogene hemipelagic deposits

geochemical stratigraphy of lavas and fault block structures in the ametista do sul geode mining district parana volcanic province southern brazil abstract the parana volcanic province is the world s largest producer of amethyst geodes mostly from the ametista do sul mining district 20 by 30 km in southern brazil the description of the lava flows in the ametista do sul mining district and adjacent areas combined with flow by flow geochemistry and scintillometry defines the stratigraphy of the flows nine flows were identified in the ametista do sul region and four additional flows were identified in the frederico westphalen region totalizing 13 flows in the stratigraphy of the ametista do sul mining district six of the flows belong to pitanga magma type more than 3 wt tio 2 which occur at the base of the local stratigraphy and the other seven flows belong to paranapanema magma type 2 3 wt tio 2 at the top of the stratigraphy the amethyst bearing geodes occur in the uppermost three pitanga flows known as veia alta main producer veia do meio and veia baixa these flows were highly altered more than 60 vol to clay minerals by a low temperature alteration process the massive presence of clay minerals is an important component that controls the rheology of the rock transforming the basalt into a very low grade smectite and celadonite metabasalt two paranapanema flows coogamai and linha alta from ametista do sul were identified in a lower position at the base of the section in frederico westphalen which were correlated using scintillometry and flow by flow geochemistry in addition veia alta and veia do meio flows were also identified in lower positions compared to ametista do sul thus the identification of these flows in different places with different elevations is an evidence of the presence of downthrown blocks in a fault block structure lowering the stratigraphy more than 200 m to the west in four steps the tectonic patterns that generate this structure are three nw strike lineaments the identification of the coogamai flow at the base of the frederico westphalen region suggests that the veia alta geode hosting flow is below the ground or below the elevation of 250 m in this region these evidences show that the fault block structure is controlling vertically the deposit of amethyst bearing geodes and is of major significance in the exploration for new amethyst geode deposits in the region

synmetamorphic lode gold deposits in high grade archean settings lode gold deposits that formed under conditions of the middle to upper amphibolite and granulite facies have been identified in the yilgarn block of western australia these deposits which form a continuum with lower metamorphic grade mesothermal gold depos its show that at least some of the fluids responsible for mesothermal gold deposits originated in or below the middle crust studies of 18 o suggest that fluid compositions were controlled by the wall rocks at least for some elements these more proximal gold deposits provide more information about deep fluid sources than do investigations of higher level mineralization deposited from fluids strongly modified by wall rock interaction during the early part of their ascent

granite cored domes and gold mineralisation architectural and geodynamic controls around the archaean scotia kanowna dome kalgoorlie terrane western australia abstract granite cored domes are associated with many of the larger gold deposits of the archaean eastern yilgarn craton of western australia the scotia kanowna dome is eroded to sufficiently deep levels to provide insights into the role granite cored domes play in controlling fluid flow and gold deposition at the centre of the scotia kanowna dome is a granite batholith which is surrounded by outward dipping greenstone belts and associated shear zones this upper crustal dome sits above mid crustal domes providing a series of stacked geometries favourable to focussed fluid flow a number of small to medium sized gold deposits occur on the limbs and the centre of the dome and the world class kanowna belle gold mine occurs on the nose of the dome at least three separate gold mineralising events are defined each of regional significance which can be correlated with other well known gold deposits of the eastern yilgarn craton the palaeostress across this region was dominated by both maximum contractional and extensional vectors oriented perpendicular to the north northwest trending grain the resultant strain is seen in the architecture of the scotia kanowna dome with its margins and associated shear zones controlling the distribution of stratigraphy which is relatively linear and parallel to the margin throughout most of the tectonic history the flanking shear zones were high strain domains that recorded multiple stages of contraction with thrust and mostly sinistral strike slip shear kinematics in contrast the dome nose region was a relatively low strain domain as it was located in the strain shadow of the regional contractional events for example the early extensional record has been preserved at the nose with late stage basins formed in the hangingwall to the extensional faults adding to the stratigraphic complexity of the local region these late basins also may have contributed to the fluid budget in contrast along the flanks of the domes there is no record of these late basins or the extensional faults that controlled their deposition the architecture of the dome played an important role in controlling mineralisation during a significant deviation in the maximum contractional stress vector to an east southeast west southwest orientation at this time basins in the nose region underwent inversion with thrusting to the north and northwest shortening was accommodated along the dome flanks by sinistral strike slip shearing which was relatively free to move due to the mostly linear stratigraphy combined with limited anisotropy and perturbations along the flank however the stratigraphic and geometrical complexity around the dome nose resulted in localised maximum dilation and gold deposition at this time the dome nose area was also a favoured locus for gold enriched dominantly mafic type magmas which are seen as the extensive porphyry swarms in the region these felsic intermediate rocks also may have contributed to the complex fluid budget and are considered as indicators of particular fertility for gold they may have been the primary source for much of the metal endowment the architecture of granite cored domes has played a critical role in focussing magma as well as mineralising fluids into regions of maximum dilation they did this by virtue of their inherent competence and by influencing the position and geometry of shear zones fluid pathways and hence distribution of stratigraphy depositional sites across the region the scotia kanowna dome is a good example of this effect and inferences can be made in favour of similar controls by concealed domes such as beneath kalgoorlie

mid depth oxygen drawdown during heinrich events evidence from benthic foraminiferal community structure trace fossil tiering and benthic δ13c at the portuguese margin abstract the distribution of trace fossils and benthic foraminiferal assemblages in two sediment cores from 2160 m water depth at the northern and 1100 m at the southern portuguese continental margin was used to reconstruct the bottom water oxygenation during the last 40 ka emphasis was given to the heinrich events during which enhanced meltwater flux associated with the iceberg surges reduced or even halted deep water formation in the north atlantic condensed trace fossil tiering structures and high proportions of low oxygen tolerant benthic foraminifera suggest a major drawdown of bottom water oxygenation during heinrich events using the benthic foraminiferal oxygenation index bfoi of kaiho 1991 1994 that links benthic foraminiferal communities to ambient bottom water oxygenation we extracted apparent oxygen concentrations from benthic assemblages bfoi values suggest low oxic conditions during heinrich events 1 and 4 with mean oxygen levels of 2 6 to 2 8 ml l 1 and high oxic conditions with 4 1 ml l 1 during heinrich event 2 at the shallower site high proportions of low oxygen tolerant foraminiferal species and bfoi minima are recorded a few centimetres below the maximum concentrations of ice rafted debris indicating that the original microhabitat depth of dysoxic species is preserved beneath the heinrich layers even though bioturbation continued during the events trace fossil tiering calibrated with the redox boundary in low oxic environments and dysoxic ichnotaxa commonly associated with black shales indicate oxygen levels lower than those implied by the bfoi oxygenation estimates derived from trace fossil tiering denote low oxic conditions during h1 13 3 ka with oxygen concentrations slightly above 1 ml l 1 and dysoxic conditions during h2 20 6 ka h3 27 ka and h4 33 5 ka with oxygen concentrations between 0 1 and 1 ml l 1 during the younger dryas bottom waters likely were low oxic negative excursions of benthic carbon isotope values provide independent control on the oxygen drawdown during heinrich events considering a bottom water oxygenation of 6 1 to 6 5 ml l 1 during the last glacial the benthic 13 c minima reveal an oxygen depletion to values between 3 4 and 5 0 ml l 1 during h1 through h4 at the shallower core site differences between estimates from benthic 13 c bfoi and trace fossil tiering suggest that benthic foraminiferal communities are rather robust to oxygen depletion if the level does not fall below 3 ml l 1 whereas burrowing organisms react sensitively to depth variations of the redox boundary in near surface sediments due to even small changes of bottom water oxygenation

pyrite compositions from vhms and orogenic au deposits in the yilgarn craton western australia implications for gold and copper exploration abstract the archaean yilgarn craton western australia is a world class metallogenic province hosting considerable resources of au ag ni cu zn and fe here we present trace element compositions of pyrite from 30 orogenic au and 5 volcanic hosted massive sulphide vhms deposits across the yilgarn pyrites from vhms deposits tend to have higher sn se cu pb bi and lower ni relative to orogenic deposits vhms deposit pyrites commonly have co ni as 100au te au se te orogenic gold deposits could be subdivided based on association of au with as or te pyrites from au as ores generally have pb bi 5 se te 5 pb sb 100 and the majority of au is refractory in pyrite structure at the same time au te association pyrites are characterised by lower values of pb bi se te and tl te higher values of ag au pb sb and au generally resides in inclusions of different compositions our data can be used at the exploration stage to distinguish between vhms vs orogenic au signatures for all studied deposits inclusion populations are summarised with implications for au and ag deportment orogenic au deposits from the yilgarn mostly have multistage formation histories reflected in the presence of multiple generations of pyrites however only some deposits record multiple high au mineralisation events

anatomy of heinrich layer 1 and its role in the last deglaciation this research used data acquired at the xrf core scanner lab at the marum center for marine environmental sciences university of bremen germany this research used samples provided by the international ocean discovery program iodp funding for this research was provided by the uk natural environmental research council nerc to hodell the nerc radiocarbon facility supported two radiocarbon dates and wally broecker generously supported the remainder with funding from the comer family foundation research by rodriguez tovar and dorador was financed by project cgl2015 66835 p b m acknowledges support from the csic ramon y cajal postdoctoral programme ryc 2013 14073 j f e would like to acknowledge funding under erc advanced grant 320750 nanopaleomagnetism

lateral variability of ichnofabrics in marine cores improving sedimentary basin analysis using computed tomography images and high resolution digital treatment abstract major ichnofabric attributes may be related to a number of limiting marine parameters for tracemakers with paleoenvironmental significance including ocean atmosphere dynamics this is why ichnofabric analysis has proven to be a very useful tool in sedimentary basin analysis as well as in other earth science disciplines although it is a comparatively recent approach in ichnological research ichnofabric characterization is usually based on 2d visual observations of a single view in both outcrops and cores yet ichnofabric features can vary vertically and laterally within a very short distance which may lead to misinterpretations here a new methodological approach is presented allowing for a more objective evaluation of ichnofabric features based on the high resolution digital treatment of computed tomography images on marine sediments cores the method evaluates variations in ichnoassemblages cross cutting relationships and the degree of bioturbation structures in nearby selected images pertaining to several sections of the same interval of a core average values of the obtained data imply a significant improvement of the resolution than 2d observations and therefore a more precise and objective characterization of ichnofabrics the usefulness of the method and its differences with respect to traditional ichnofabric analysis are exemplified by a study of the gravity core fsg09 10 galicia bank domain nw iberian peninsula showing as a very significant tool to interpret paleoenvironmental changes i e sedimentation rate nutrient availability and bottom water oxygenation from the last glacial maximum lgm to heinrich event 1 he1 this example reveals the importance of proposed methods in order to characterize the ichnofabrics including their lateral variability with clear implications for future research on basin analysis

stratigraphic variation in ichnofabrics at the shackleton site iodp site u1385 on the iberian margin paleoenvironmental implications abstract ichnofabric analysis was conducted on cores from site u1385 iodp expedition 339 to interpret paleoenvironmental conditions at the southwest margin of the iberian peninsula during the pleistocene site u1385 provides an important record for the study of orbital and suborbital scale climate variability changes related to ocean atmosphere dynamics and affected environmental parameters a detailed study of the ichnofabric characterization is presented focusing on the types of ichnofabrics relative abundance amount of bioturbation grouping ichnofabric succession transitions and vertical distribution seven ichnofabrics were differentiated green mottled ichnofabric planolites ichnofabric taenidium planolites ichnofabric thalassinoides like palaeophycus ichnofabric planolites thalassinoides thalassinoides like ichnofabric zoophycos ichnofabric and chondrites ichnofabric they exhibit significant differences in terms of ichnofabric features as well as in their stratigraphic distribution the most abundant ichnofabrics are planolites thalassinoides thalassinoides like ichnofabric and green mottled ichnofabrics with a dominance of the middle tier ichnofabrics the degree of bioturbation is moderate with a mean bi around 3 but showing a clear bimodal distribution one group of intervals is characterized by high bioturbation bi 6 while another displays low moderate bi values bi 1 2 in general ichnofabric features confirm generally good environmental conditions oxic environment and high food availability for the macrobenthic tracemaker community especially favorable in the uppermost part of the sediment a complete ichnofabric succession from deep to shallow tier ichnofabrics is commonly registered i e zoophycos ichnofabric or chondrites ichnofabric to planolites thalassinoides thalassinoides like ichnofabric and then either to green mottled ichnofabric or to planolites ichnofabric and then green mottled ichnofabric however there are some intervals where an incomplete succession between deep and shallow ichnofabrics is observed i e chondrites ichnofabric to green mottled ichnofabric or zoophycos ichnofabric to green mottled ichnofabric indicating relevant modifications of environmental parameters such as oxygen or food supply types of ichnofabrics and the bioturbation index show significant short term changes through the studied core such variations are probably correlated to millennial scale climatic perturbations such as glacial terminations and related phenomena heinrich events ice rafting events etc or long term cyclic patterns related to orbital climate variability the patterns could be tied to a significant change in the climate system such as the one associated with the middle pleistocene transition

fluid sources and the role of abiogenic ch4 in archean gold mineralization constraints from noble gases and halogens abstract the st ives goldfield of western australia hosts high grade gold mineralization in a variety of lithologies within 2 7 ga greenstone belts the low salinity co 2 bearing fluids responsible for gold mineralization could have been generated either by metamorphic processes within the greenstones or from external magmatic sources and independently sourced abiogenic ch 4 has been suggested as an important control on gold mineralization in order to better constrain possible fluid sources we applied a combination of he ne ar kr xe isotope and cl br i analyses to quartz and carbonate veins containing h 2 o co 2 fluid inclusions pyrite magnetite hematite and quartz veins containing ch 4 rich fluid inclusions pyrrhotite pyrite samples containing h 2 o co 2 fluid inclusions have higher br cl and i cl values and less radiogenic noble gas isotope signatures than suggested for ch 4 rich fluid inclusions the samples containing ch 4 fluid inclusions have maximum 40 ar 36 ar of 50 000 20 ne 22 ne of 9 8 and maximum 21 ne 22 ne of 0 56 in contrast h 2 o co 2 fluid inclusions have maximum 40 ar 36 ar of only 20 000 and maximum 21 ne 22 ne of 0 14 the use of 40 ar 39 ar methodology to measure k simultaneously with 40 ar 36 ar enables us to show the highest 40 ar 36 ar ratios are representative of the fluids trapped at 2 65 ga and have not been significantly modified by post entrapment 40 ar r production 40 ar r radiogenic 40 ar furthermore the 40 ar 36 ar ratio is correlated with the 21 ne 22 ne and 136 xe 130 xe ratios demonstrating that other heavy noble gas isotope ratios are also close to their original composition the highly radiogenic noble gas isotope signatures are unlikely to have been generated within the greenstone host rocks because seawater altered volcanic rocks have high abundances of non radiogenic atmospheric noble gas isotopes in contrast the strongly radiogenic noble gas isotope signatures are likely to have been generated in ancient basement rocks underlying the greenstones at 2 65 ga the combined noble gas and halogen data are consistent with models in which redox reactions triggered by interaction of independently and distally sourced h 2 o co 2 and ch 4 localized high grade gold mineralization we suggest that the fluids were intimately associated with crustal magmatism in the st ives goldfield and that abiogenic ch 4 could be an important moderator of redox processes in other crustal environments

silver rich telluride mineralization at mount charlotte and au ag zonation in the giant golden mile deposit kalgoorlie western australia the gold deposits at kalgoorlie in the 2 7 ga eastern goldfields province of the yilgarn craton western australia occur adjacent to the d2 golden mile fault over a strike of 8 km within a district scale zone marked by porphyry dykes and chloritic alteration the late golden pike fault separates the older d2 shear zone system of the golden mile 1 500 t au in the southeast from the younger d4 quartz vein stockworks at mt charlotte 126 t au in the northwest both deposits occur in the golden mile dolerite sill and display inner sericite ankerite alteration and early stage gold pyrite mineralization replacing the wall rocks late stage tellurides account for 20 of the total gold in the first but for 30 g t au is characterized by au ag 2 54 and as sb 2 6 30 the latter ratio caused by arsenical pyrite golden mile type d2 lodes occur northwest of the golden pike fault but the hidden secret orebody the only telluride bonanza mined 10 815 t at 44 g t au was unusually rich in silver au ag 0 12 0 35 due to abundant hessite we describe another array of silver rich d2 shear zones which are part of the golden mile fault exposed on the mt charlotte mine 22 level they are filled with crack seal and pinch and swell quartz carbonate veins and are surrounded by early stage pyrite pyrrhotite disseminated in a sericite ankerite zone more than 6 m wide gold grade 0 5 0 8 g t varies little across the zone but au ag 0 37 2 40 and as sb 1 54 13 9 increase away from the veins late stage telluride mineralization 23 g t au sampled in one vein has a much lower au ag 0 13 and as sb 0 48 and comprises scheelite pyrite native gold 830 854 fine hessite and minor pyrrhotite altaite bournonite and boulangerite assuming 250 300 c gold hessite compositions indicate a fluid log fte2 of 11 5 to 10 values well below the stability of calaverite the absence of calaverite and the dominance of hessite in the d2 lodes of the mt charlotte area point to a kilometer scale mineral and au ag zonation along the golden mile master fault which is attributed to a lateral decrease in peak tellurium fugacity of the late stage hydrothermal fluid the as sb ratio may be similarly zoned to lower values at the periphery the d4 gold quartz veins constituting the mt charlotte orebodies represent a younger hydrothermal system which did not contribute to metal zonation in the older one

quantitative estimation of bioturbation based on digital image analysis quantitative determination of modification of primary sediment features by the activity of organisms i e bioturbation is essential in geosciences some methods proposed since the 1960s are mainly based on visual or subjective determinations the first semiquantitative evaluations of the bioturbation index ichnofabric index or the amount of bioturbation were attempted in the best cases using a series of flashcards designed in different situations recently more effective methods involve the use of analytical and computational methods such as x rays magnetic resonance imaging or computed tomography these methods are complex and often expensive this paper presents a compilation of different methods using adobe photoshop software cs6 for digital estimation that are a part of the idiap ichnological digital analysis images package which is an inexpensive alternative to recently proposed methods easy to use and especially recommended for core samples the different methods similar pixel selection method spsm magic wand method mwm and the color range selection method crsm entail advantages and disadvantages depending on the sediment e g composition color texture porosity etc and ichnological features size of traces infilling material burrow wall etc the idiap provides an estimation of the amount of trace fossils produced by a particular ichnotaxon by a whole ichnocoenosis or even for a complete ichnofabric we recommend the application of the complete idiap to a given case study followed by selection of the most appropriate method the idiap was applied to core material recovered from the iodp expedition 339 enabling us for the first time to arrive at a quantitative estimation of the discrete trace fossil assemblage in core samples

interpretation of post entrapment fluid inclusion re equilibration at the three mile hill marvel loch and griffins find high temperature lode gold deposits yilgarn craton western australia abstract fluid inclusions that are interpreted to be related to vein filling of quartz veins at the three mile hill and marvel loch gold deposits in amphibolite facies rocks and the griffins find deposits in granulite facies rocks in the yilgarn craton of western australia are dominantly low salinity h 2 o co 2 ch 4 mixtures or co 2 ch 4 fluids at each deposit inclusions have a wide range of compositions with respect to both the aqueous carbonic ratio and the co 2 ch 4 ratio of the carbonic phase and most fluids could not have been in equilibrium with the mineral assemblage in the vein and adjacent rock inclusion densities suggest a range of p t conditions of entrapment and are in general not consistent with the conditions of vein formation indicated by vein assemblages diffusional addition of h 2 into inclusions diffusional loss of h 2 o and reduction of inclusion volume are possible during cooling and uplift along the inferred p t path the inclusion populations could have been derived from an originally uniform population of low salinity aqueous dominated h 2 o co 2 inclusions by a combination of these processes inclusion modification as the cause of the complex inclusion populations is supported by relations of molar volume to composition and to an extent by variations in fluid salinity if inclusion re equilibration is the cause of inclusion variability it was of variable intensity within a single vein system and within individual clusters of inclusions in some samples and is suggested to have been a function of the local petrological and textural environment

the coupled geochemistry of au and as in pyrite from hydrothermal ore deposits the ubiquity of au bearing arsenian pyrite in hydrothermal ore deposits suggests that the coupled geochemical behaviour of au and as in this sulfide occurs under a wide range of physico chemical conditions despite significant advances in the last 20years fundamental factors controlling au and as ratios in pyrite from ore deposits remain poorly known here we explore these constraints using new and previously published empa la icp ms sims and pixe analyses of as and au in pyrite from carlin type au epithermal au porphyry cu cu au and orogenic au deposits volcanogenic massive sulfide vhms witwatersrand au iron oxide copper gold iocg and coal deposits pyrite included in the data compilation formed under temperatures from 30 to 600 c and in a wide variety of geological environments the pyrite au as data form a wedge shaped zone in compositional space and the fact that most data points plot below the solid solubility limit defined by reich et al 2005 indicate that au1 is the dominant form of au in arsenian pyrite and that au bearing ore fluids that deposit this sulfide are mostly undersaturated with respect to native au the analytical data also show that the solid solubility limit of au in arsenian pyrite defined by an au as ratio of 0 02 is independent of the geochemical environment of pyrite formation and rather depends on the crystal chemical properties of pyrite and post depositional alteration compilation of au as concentrations and formation temperatures for pyrite indicates that au and as solubility in pyrite is retrograde au and as contents decrease as a function of increasing temperature from 200 to 500 c based on these results two major au as trends for au bearing arsenian pyrite from ore deposits are defined one trend is formed by pyrites from carlin type and orogenic au deposits where compositions are largely controlled by fluid rock interactions and or can be highly perturbed by changes in temperature and alteration by hydrothermal fluids the second trend consists of pyrites from porphyry cu and epithermal au deposits which are characterised by compositions that preserve the au as signature of mineralizing magmatic hydrothermal fluids confirming the role of this sulfide in controlling metal ratios in ore systems

a novel sedimentological method based on ct scanning use for tomographic characterization of the galicia interior basin abstract non destructive techniques of core analysis especially of marine cores are being broadly employed for sedimentary paleoceanographic and paleoclimate research in particular computed tomography scanning ct scanning allows acquisition of 3d and 2d images according to desired planes and thus the identification of sedimentary structures large grains and their distributions as well as direct measurements of material densities the most significant contribution of this technique is the possibility of getting results before opening the core in this work ct scan data obtained for five cores from the galicia interior basin gib nw peninsula iberia are presented and discussed focussing on 1 methodology of the ct scan use 2 tomographic description of sedimentary facies identified in the gib 3 treatment of the numeric data obtained with ct scanning using specific software anidoc and 4 comparison of tomographic data with data obtained by conventional methodologies of core analysis the most singular feature of gib cores is the presence of ice rafted debris ird deposited during late pleistocene heinrich events he which can be easily recognized using the ct scan by the presence of high radio density grains immersed in a low radio density matrix comparison of ct scan data with analytical sedimentary data and he proxies performed on the cores validates the ct scanning method as a powerful tool to improve correlations identify well constrained events and make more accurate basin reconstructions without opening all the cores in an oceanographic study

lateral variability in shallow marine ichnofabrics implications for the ichnofabric analysis method ichnological analysis commonly undertaken both in the field and in core studies is generally carried out in vertical logged successions this work documents the results of a detailed ichnofabric study of two highly bioturbated sandstone beds separated by a mudstone within the thick lower jurassic succession of the yorkshire coast uk the two sandstone beds contain relicts of hummocky cross stratification and rare bioclasts of bivalves and belemnites bioturbation of the beds is intense and the diversity of trace fossils is considerable trace fossils present include teichichnus rectus teichichnus isp a thalassinoides isp palaeophycus heberti diplocraterion parallelum rhizocorallium rosselia socialis schaubcylindrichnus isp chondrites isp planolites isp and phycosiphon incertum ichnofabrics were studied at 5 m intervals parallel to the modern cliff line which is parallel to the inferred jurassic palaeo coastline the results demonstrate that there is considerable patchiness to ichnofabric even in a comparatively simple depositional setting such as a storm influenced shelf this observation is in line with studies of the modern sea floor the implications of patchiness in ichnofabric are broad ranging but most importantly suggest that caution is needed in the use of ichnofabric analysis for intra regional correlations

stable isotope and mineralogical investigation of the genesis of amethyst geodes in the los catalanes gemological district uruguay southernmost parana volcanic province stable isotopes c o s and mineralogical studies of the world class amethyst geode deposits of the los catalanes gemological district uruguay constrain processes operative during mineral deposition the mineralized basaltic andesites from the cretaceous parana volcanic province are intensely altered to zeolites clinoptilolite and clay minerals variations in the 18o values of silica minerals in geodes chalcedony quartz and amethyst are much larger and the values generally somewhat lower 21 2 31 5 in the uruguayan deposits than in the ametista do sul area of southern brazil the range of 34s values 15 0 to 0 3 of altered basaltic rocks requires in addition to sulfur of magmatic origin the involvement of 34s depleted sedimentary sulfur from bacterial sulfate reduction the results delimit the mineralizing processes to a post eruption environment characterized by low temperature and strong interaction of the lava flows with meteoric water

testing ethological hypotheses of the trace fossil zoophycos based on quaternary material from the greenland and norwegian seas abstract despite the fact that the trace fossil zoophycos has been found in rocks from most of the phanerozoic little consensus has been reached on how and why this intricate burrow was constructed the cenozoic morphotypes of zoophycos typically include a helically coiled spreite arranged around a vertical shaft connected to the sediment surface morphological details and environmental preferences of the zoophycos producer were studied using 156 cores from the norwegian and greenland seas in order to test the different ethological hypothesis proposed for this trace fossil the spreiten were constructed during interglacial or interstadial intervals and consist of a repeated alternation of lamellae consisting of fine grained pelleted material and coarse grained unpelleted material respectively spreiten were encountered in vigorously bioturbated sediment in turbidite layers and in layers dominated by coarse ice rafted debris this indifference to the composition of the substrate effectively rules out ethological models based on different forms of deposit feeding and the large size and wide spacing of the whorls of the spreiten also make the cesspit model unlikely rather the observed features best agree with a cache behaviour where the main purpose of the deep penetration was to store food and to prevent access by other burrowers likely combined with some gardening of microbes however no indubitable evidence of a reworking of the cached material could be found and probably the answer to how the cache was accessed by the producer is to be found in the marginal tube the difference in diameter between marginal tube and spreiten lamellae together with the presence of both open and filled marginal tubes indicate that the marginal tube is the result of a far more complex behaviour than simply a lateral shift through the sediment