geochemical characteristics of deep sea sediments from the arabian sea a high resolution study abstract five deep sea cores from the arabian sea covering a time interval of 170 ky were sampled at high resolution and analysed for major and trace elements the stratigraphy of the cores was obtained by comparing the ba al ratio with the specmap data this method is based on the close correlation between ba concentrations or ba al ratios and oxygen isotope ratios 18o of foraminifera in arabian sea sediments ba al ratios used as a productivity proxy are variable but high in all deep sea cores of the arabian sea indicating a basin wide influence of nutrient rich water masses compared to glacial intervals the warmer periods are characterised by higher element al ratios of proxies which are directly ba ca sr p i e hard parts of organisms or indirectly u 230thex related to biological productivity 230thex provides evidence for intense boundary scavenging caused by high productivity due to enhanced upwelling and terrigenous input from the indus fan the mn distribution in a core from the western arabian sea shows enrichments during interglacial periods and may indicate mn export owing to the presence of a stronger oxygen minimum zone several processes limit the applicability of proxies intercalated turbidites in the deep sea cores can be identified by means of si al ti al and zr al ratios versus depth due to the enrichment of quartz ti minerals and zircon in the basal layer these elements are also important for the reconstruction of the history and extent of the eolian dust input diagenetic redistribution of redox sensitive elements occurs at the boundaries between turbidites and normal pelagic sedimentation and may mask or destroy primary signals

the role of event beds in the preservation of organic carbon in fine grained sediments analyses of the sedimentological processes operating during deposition of the whitby mudstone formation toarcian lower jurassic preserved in northeast england abstract geologists have recently observed that source rocks commonly contain a wide variety of microfabrics including diminutive ripples and burrows the existence of these fabrics challenges the assumption that persistent bottom water anoxia and low energy conditions are necessary prerequisites for enhanced organic carbon preservation in these units in order to enhance our understanding of the depositional and diagenetic processes responsible for organic carbon preservation in these strata the lower jurassic whitby mudstone formation which contains mudstones with up to 14 2 total organic carbon has been investigated using optical electron optical and geochemical methods four thinly bedded mudstone lithofacies were identified a silt bearing clay rich mudstones b clay rich mudstones c clay calcareous nannoplankton and organic carbon bearing mudstones and d cement rich mudstones internally individual beds are typically sharp based and normally graded they are either laminated partially bioturbated or homogenized where depositional fabrics are preserved pellets silt lags ripple lamination shell pavements wave enhanced sediment gravity flows of fluid mud and organo minerallic aggregates have been observed the presence of up to 14 2 toc in units that are sharp based and normally graded suggests that mass flows possibly generated by storms likely influenced sedimentation during deposition of these mudstones the abundant organo minerallic fabrics in these units indicates that at least some of the organic carbon was delivered to the seafloor as marine snow aggregates that likely formed in the water column following phytoplankton blooms homogenization of bed tops indicates that between sediment delivery episodes an infauna was able to colonize the seafloor implying that the bottom waters were at least partly oxygenated during these intervals these fabrics suggest that during deposition of the whitby mudstone formation organic carbon was being preferentially preserved below regions of high primary organic production the close association between sharp based graded beds and organo minerallic aggregates indicates that large volumes of organic carbon were delivered episodically to the seafloor and that conditions at the sediment water interface were episodically dynamic here organic carbon is likely to have been preferentially preserved because the frequency of depositional events was sufficiently high to minimize both oxidant diffusion into the sediment and organic carbon mineralization while bottom water anoxia may have developed during the phytoplankton blooms it was unlikely to have been persistent because the microfabrics present indicate that there was sufficient time and oxygen available for an infauna to disrupt the sediment between deposition events

lack of enhanced preservation of organic matter in sediments under the oxygen minimum on the oman margin the impingement of oxygen minima on continental margins is widely thought to promote the accumulation of sedimentary facies enriched in well preserved organic matter it is shown here however that such a relationship does not clearly apply to the productive oman margin in the arabian sea which hosts one of the most severe oxygen minima in the oceans measurements made on the 0 1 cm depth interval from fourteen box cores collected from the outer shelf upper continental slope area off oman show that 1 1 deposited organic matter is overwhelmingly of marine origin 2 2 there is no significant correlation between the abundance of sedimentary organic carbon corg and the bottom water o2 concentration 3 3 there is no relation between the sedimentary corg n ratio and bottom water o2 4 4 there is no correlation between the hydrogen index hi of the organic matter and bottom water oxygen there are however significant correlations between the corg n ratio and the i corg cr al and zr al ratios as well as between the corg n ratio and the hydrogen index these relationships are interpreted as being the result of winnowing and attendant reworking which produce a progressive increase in the corg n ratio and a decrease in the hi and the i corg ratio as organic matter becomes progressively degraded commensurate rises in the cr al and zr al ratios result from the increased proportion of heavy minerals associated with winnowed lag deposits overall these data suggest that the bottom water oxygen concentration has little effect in governing either the distribution or the degree of preservation of organic matter on this margin thus the generally high but spatially variable corg content of the sediments on the oman margin may not reflect the occurrence of an oxygen minimum but instead be the result of a high settling flux of organic matter supported by monsoon driven upwelling and post depositional redistribution of the organic material by hydrodynamic influences

lack of organic matter accumulation on the upwelling influenced somalia margin in a glacial interglacial transition abstract monsoon induced upwelling has been operating off somalia for at least the last 160 000 years making the nw indian ocean one of the most productive oceanic areas in the world we have studied the sediments recovered during the indusom cruise of the r v marion dufresne from three different environments off this margin a core from the highly productive surface waters core md85 674 a core where the oxygen minimum intersects the slope core md85 664 and a reference core from the deep basin with normal bottom oxygen levels and moderate primary production core md85 668 though the first two environments are a priori favourable to organic matter om accumulation no marine om enrichment can be observed in the cores to understand this anomaly emphasis is placed upon the transition from isotopic stage 6 to stage 5 because the end of the glacial stage 6 is characterised by intensified upwelling and primary productivity in this region whereas stage 5 experienced a marked decrease in productivity various palaeoenvironmental markers such as om v ni cu zn ba and p have been used to identify periods of high productivity and or bottom water oxygen depletion the results suggest that 1 the lack of marine om in two settings favourable to organic carbon storage may be due to the nature of primary productivity coccolithophorid production would not be prone to om accumulation in contrast to the contribution of om by diatoms or particularly naked phytoplankton dinoflagellates or other peridinians 2 ba is not an accurate palaeoproductivity marker in this region although the oceanic environment would have been a priori suitable for the use of ba as a proxy indicator 3 the period of intensified upwelling in stage 6 as well as the stage 6 5 transition left no geochemical imprint on the sediments this means that some upwelling systems may not be accompanied by marked enrichments in marine organic matter within the underlying sediments in other words the somalia upwelling does not participate to the so called biological pump and has no positive effect upon long term carbon storage

lack of evidence for enhanced preservation of sedimentary organic matter in the oxygen minimum of the gulf of california a test of the hypothesis that hydrogen rich organic matter accumulates preferentially in sediments under oxygen minima has been carried out by examining the composition of laminated and homogeneous diatomaceous sediments of the guaymas basin in the gulf of california the laminated sediments occur where an intense oxygen minimum intersects the slope around the margins of the basin above and below the depth of the oxygen minimum the sediments are homogenized by a burrowing infauna the two sediment types have very similar bulk chemical and mineral compositions and the organic matter is overwhelmingly marine the total organic carbon contents and rock eval parameters hydrogen and oxygen indices of the two sediment types are not significantly different whereas a road organic carbon maximum in the homogeneous sediments is centered at roughly 1200 m depth on the slope of the basin this maximum lies deeper than the core of the oxygen minimum thus both the concentration and the nature of the organic matter in the sediments of this highly productive marginal marine basin are not related to the concentration of dissolved oxygen in the bottom waters

lithologically controlled invisible gold yukon canada the newly discovered cretaceous coffee orogenic gold deposit 4 moz resource consists of an extensive oxidised zone developed on primary sulphidic rock the primary mineralised rock is characterised by invisible gold in arsenian pyrite that has replaced biotite in selected host rocks the deposit has a cryptic surface expression and is an example of an extremely subtle exploration target hydrothermal emplacement was controlled by extensional fractures with breccias but most mineralisation was focused on biotite bearing granitic gneiss metasedimentary gneisses and younger biotite granite fine grained 0 1 mm arsenian pyrite replaced biotite along mineral cleavage planes and followed biotite rich metamorphic and post metamorphic structural fabrics arsenian pyrite also formed overgrowths on earlier coarse grained up to 2 mm barren hydrothermal pyrite arsenian pyrite is concentrically zoned on the 1 10 m scale with respect to as sb and au contents and typically contains 5 wt as 500 mg kg sb and 500 mg kg au in solid solution biotite replacement was accompanied by sericitisation silicification and ankerite impregnation hydrothermal alteration involved dilution and localised depletion of k na and al in silicified host rocks but most ca mg and fe concentrations remained broadly constant magnesium rich ultramafic host rocks were only weakly mineralised with auriferous arsenian pyrite and have fuchsite and magnesite alteration near surface oxidation has liberated nanoparticulate and microparticulate supergene gold which remains essentially invisible varying degrees of oxidation extend as deep as 250 m below the present subdued topographic surface well beyond the present vadose zone and this deep oxidation may have occurred during post mineralisation uplift and erosion in the cretaceous oxidation has leached some as from the surficial mineralised rocks decreasing the geochemical signal which is also obscured by the localised presence of high background as up to 100 mg kg in metasedimentary quartzites in the region antimony provides more reliable soil anomalies than as but most sb anomalies are 100 mg kg the persistence of invisible gold into the extensive supergene zone with little gold particle size enhancement has ensured that no placer deposits have formed in nearby streams further restricting the surface footprint and au dispersal halo of this subtle exploration target

influence of sedimentary environment on organic matter enrichment in shale a case study of the wufeng and longmaxi formations of the sichuan basin china abstract as two essential controls on the formation of organic matter om enriched shales both paleoproductivity and preservation models remain controversial for the wufeng and longmaxi shales in the sichuan basin southwest china this study provides geochemical parameters as proxies for the paleoproductivity characteristics ba p al and ni cu al bottom water redox status u th v v ni v cr and mo and terrigenous clastic flux th and al of the wufeng longmaxi formations in the sichuan basin a back deep basin in a foreland basin system in southwest china combining these data with total organic carbon toc content and sedimentation rate data obtained from graptolite zones allowed us to discuss the validity of these popular indices and to identify the main factors that controlled om enrichment in the formations toc contents exceed 4 wt in the upper wufeng formation to the bottom part of the longmaxi formation lm1 3 which are the most om rich intervals the average p al ratio for well jy2 in the jiaoshiba area is 0 009 which is lower than those for well yy1 0 028 in the yongchuan area and well dy1 0 02 in the dingshan area indicating the lowest productivity levels were in the jiaoshiba area based on the redox proxies the samples from well dy1 reflect less reducing bottom water conditions than those from wells jy2 and yy1 the th and al indices increase upwards indicating that the terrigenous clastic input increased and that those in the yongchuan area were lower than those in the jiaoshiba and dingshan areas the sedimentation rate was too low to dilute the om in the sichuan basin especially during the depositional time of the om rich intervals such that the redox status of the water became more critical given the more strongly reducing conditions of the sedimentary environment and the high thermal maturity of the om in this formation the ba concentrations appeared anomalously low and became inaccurate as a paleoproductivity index as well as the validity of v v cr and v v ni anomalously decreased as redox indices

a reappraisal of kerogen formation abstract comparative microscopical and chemical studies of recognizable entities in kerogen and their extant counterparts suggest a new and simple mechanism of kerogen formation which clarifies the interrelationships between extant biomass kerogen and fossil fuels

the inorganic geochemistry of cretaceous black shales dsdp leg 41 in comparison to modern upwelling sediments from the gulf of california

occurrence and origin of ultralaminar structures in amorphous kerogens of various source rocks and oil shales abstract forty low maturity type i ii kerogens from source rocks and oil shales ranging in age from infra cambrian to miocene were examined by transmission electron microscopy tem when previously observed by light microscopy and or uv fluorescence microscopy the above samples like a very large number of kerogens seemed homogeneous and amorphous in fact tem revealed the presence of ultralaminar structures in 22 of these amorphous kerogens the abundance of ultralaminae depends on the considered sample and some of the tested kerogens are nearly exclusively composed of ultralamina accumulations based on thickness three main groups of ultralaminae can be identified parallel studies on extant algae indicated that some of the above ultralaminae likely derived from the resistant outer walls of microalgae the fossilization of such outer walls should occur via the selective preservation pathway and result in the formation of highly aliphatic ultralaminar kerogens the lack of ultralaminae in infra cambrian kerogens is consistent with a cyanobacterial origin

remobilization of barium in continental margin sediments abstract the rate of ba release from california continental margin sediments has been measured using an in situ benthic flux chamber and the range of values 25 50 nmol cm 2 y 1 is larger than any previously published benthic flux estimate for this element the magnitude of the ba flux suggests that a significant fraction of the ba raining from the euphotic zone is recycled at the seafloor ba si regeneration ratios from these margin sediments increase with depth demonstrating that ba is decoupled from si during the earliest stages of diagenesis on the other hand ba regeneration rates and caco3 dissolution rates covary the coupling between these two constituents is supported by the observation that the ba caco3 dissolution flux ratio 1 7 0 4 10 3 is independent of bottomwater depth even in sediments underlying the oxygen minimum zone along the continental margin furthermore this flux ratio is consistent with both the water column ba alkalinity ratio for the world s ocean as well as the ba caco3 ratio in sediment trap solid phases from the equatorial pacific 1 1 2 2 10 3 however the constancy of the ba alkalinity ratio over geologic time remains in question because the mechanism that controls this relationship remains a mystery our flux measurements suggest that diagenesis does not significantly influence the ba ca ratio in the upper 0 5 mm of pacific sediments thereby supporting the idea of using the ba concentration in surface dwelling benthic forams as a proxy for deep water chemical conditions lea and boyle 1989 1990 on the other hand we predict that if a foraminifer lives 0 5 mm or more below this interface then diagenetic effects could influence the ba ca ratio that foram species would record the carrier phase of the particulate ba reactive during early diagenesis does not appear to be organic matter oxyhydroxides or calcium carbonate but rather a mineral phase related to marine barite or perhaps celestite

organic rich and manganese sedimentation during the cenomanian turonian boundary event in the outer carpathian basins a new record from the skole nappe poland abstract upper cenomanian lower turonian strata in the splawa section of the skole nappe outer carpathians poland provide a detailed palaeoenvironmental record of the oceanic anoxic event oae 2 from a deep water basin below the ccd at the northern margin of the western tethys the oae 2 succession consists of black parallel laminated radiolarian shales enriched in organic matter of mainly marine origin toc up to 8 organic carbon isotope variations together with microfossil datum events allowed to correlate the studied organic rich facies with other black shale successions along the outer carpathians and other areas of the western tethys the mean values of sedimentation rate 3 5 5 5 mm kyr and organic matter accumulation rate 0 5 g m2 year calculated for the oae 2 interval in the outer carpathian basins are comparable to the values from other deep water marginal basins in the western tethys the average redox sensitive trace metal contents and their enrichment factors indicate water column anoxia in the outer carpathian basins intensified during the interval of the largest shift in 13c values the periods of bottom anoxia were interrupted by intervals of variable eh conditions with sedimentation of hemipelagic green shales including poor agglutinated foraminiferal assemblages an increase in productivity of organic and siliceous plankton during the oae 2 is documented based on increased values of silica and barium enrichments this closely corresponds to an interval of the largest positive stable carbon isotope excursion related to the beginning of the largest sea level rise linked with intensive coastal upwelling extremely low sedimentation rate or even hiatuses and the increase in deep water circulation causing basin oxygenation resulted in precipitation of two ferromanganese layers their formation was related to changes in hydrodynamic conditions at the basin floor expressed by precipitation of fe mn carbonates some chemical indices seem to suggest that the primary metal enrichments could be related to hydrothermal activity however the concentrations of some elements show also on hydrogenic to diagenetic influences in these metalliferous sediments the precipitation of these fe mn sediments was probably synchronous with the manganese enrichment across the c t transition recorded in other western tethyan basins and in the adjacent epicontinental seas

tectonic subsidence modelling of the polish basin in the light of new data on crustal structure and magnitude of inversion abstract the polish basin pb is one of a set of basins developed on the paleozoic platform of western europe in the late paleozoic between the variscan orogen and the east european craton eec its main depocentral axis the mid polish trough mpt was active during most of the basin development as a maximum subsidence zone with almost uninterrupted sedimentation the present base of the permian in the mpt ranges in depth from ca 3000 to 3500 m near the baltic coast to up to 8000 m to the southeast the mpt lies parallel and adjacent to the edge of the eec and appears to be related to a distinct structural zone within the crust the tornquist teisseyre zone ttz subsidence of the mpt can be explained in terms of crustal extension transtension and related lithosphere cooling coupled with the structural predetermination of the underlying ttz tectonic subsidence analysis of the preserved and reconstructed stratigraphic record suggests the occurrence of a late permian early triassic rifting phase however there is a deficit of geologically observable extensional features faulting of this age implying an important relationship between this phase of apparent basin subsidence and earlier post variscan late carboniferous early permian tectonism the match between crustal structure implied by basin modelling studies and available deep seismic sounding dds data is not always clear this is probably related to the heterogeneous basement which comprises the outer zone of the variscan belt in the southwest eec crust in the northeast and a complex of caledonian reworked precambrian crustal blocks in the central part of the basin changes to crustal architecture as a result of alpine tectonics may also play a role increased tectonic subsidence rates during oxfordian kimmeridgian times late jurassic correlate with intensified rifting and wrench activity within the arctic north atlantic rift system and along the northern tethyan margin in contrast accelerating tectonic subsidence beginning in the cenomanian is a precursor of compressional deformations in the basin that culminated in alpine related basin inversion during the latest late cretaceous and earliest tertiary taking inversion into account the maximum depth of the base zechstein structural surface at the end of the cretaceous is estimated to have been as much as 5000 m near the baltic sea to more than 10 000 m in the southeasternmost part of the basin because of the erosion of these sediments however constraints on cretaceous subsidence and in turn the magnitude and exact timing of late cretaceous paleogene inversion are poor

late pleistocene variability of arabian sea summer monsoon winds and continental aridity eolian records from the lithogenic component of deep sea sediments the modern indian ocean summer monsoon is driven by differential heating between the asian continent and the indian ocean to the south this differential heating produces a strong pressure gradient which drives southwest monsoon winds during june july and august satellite and meteorological observations aerosol measurements sediment trap studies and mineralogical studies indicate an atmospheric mode of transport for modern lithogenic sediments in the northwest arabian sea analyses of lithogenic grain size and mass accumulation rate mar records from the owen ridge indicate that eolian transport has been the primary mode of transport for the past 370 kyr visual inspection shows that the mar record is positively correlated with global ice volume as indicated by the marine 18o record in contrast the grain size record varies at a much higher frequency showing little correlation to either the mar or the 18o records spectral analyses confirm these relationships indicating that the lithogenic grain size and mar records are coherent only over the precession band whereby the grain size leads the mar by 124 8 kyr we conclude that an eolian transport mechanism is the only mechanism that allows for this phase difference and at the same time is supported by comparison of the grain size and mar with independent eolian records we use lithogenic grain size as a paleoclimatic indicator of summer monsoon wind strength and lithogenic mar as a paleoclimatic indicator of source area aridity these interpretations are supported by comparison of the lithogenic records to independent indicators of wind strength globigerina bulloides upwelling record and aridity a loess record from central china such comparisons indicate high coherence and zero phase relationships our work supports the findings of previous studies which have documented the link between monsoon strength and the earth s axial precession cycles both the lithogenic mar and the grain size records have high coherency with precessional insolation maximum lithogenic mar source area aridity is in phase with 18o global ice volume and leads maximum precessional insolation by 88 6 kyr we attribute this lead to the influence of glacial conditions on the aridity and therefore the deflation potential of the source areas maximum lithogenic grain size summer monsoon wind strength lags maximum precession by 148 9 kyr we attribute this lag both to the influence of global and or local ice volume and to the availability of latent heat from the southern hemisphere indian ocean the two of which combine to determine the strength of the indian ocean monsoon

the origin and hydrothermal mobilization of carbonaceous matter associated with paleoproterozoic orogenic type gold deposits of west africa abstract the chemical and physical properties of carbonaceous matter cm were studied in paleoproterozoic metasediment hosted orogenic type gold deposits in burkina faso the inata deposit in mali the syama deposit and in ghana the obuashi and bogoso deposits two types of cm occur in all the studied deposits metamorphosed and hydrothermal metamorphosed cm prevails in all the deposits hydrothermal cm occurs in small veinlets in hydrothermally altered rocks and in quartz veins or forms irregular accumulations parallel or sub parallel to c type cleavage within the shear zones the origin of hydrothermal cm which occurs in paragenesis with au bearing arsenopyrite or pyrite seems to have been due to supersaturation of hydrothermal fluids with carbon at the deeper or middle crustal levels the isotopic composition of carbon in bulk cm 33 1 to 26 2 vpdb indicates its biogenic origin the isotopic composition of carbon in hydrothermal carbonates ranges from 14 5 to 4 4 vpdb which suggest mixing of carbon derived from a deep seated source with carbon derived from an organic source the interaction of hydrothermal fluids with metamorphosed cm could be one of the causes of the reduction of hydrothermal fluids and formation of the respective mineralization the optical properties and raman spectra of the metamorphosed cm particles in the individual studied mineral deposits differ considerably the temperatures calculated on the basis of the raman spectra of metamorphosed cm vary between 280 and 440 c depending on the thermometer used and correspond to temperatures of metamorphism of upper sub grenschist and greenschist facies the temperatures calculated for hydrothermal cm at the individual deposits are only slightly lower compared to the metamorphosed cm at the same deposits which indicates approximately the same temperature of the metamorphic and hydrothermal processes

synmetamorphic carbon mobility and graphite enrichment in metaturbidites as a precursor to orogenic gold mineralisation otago schist new zealand the macraes orogenic gold deposit is hosted by a graphitic micaceous schist containing auriferous porphyroblastic sulphides the host rock resembles zones of unmineralised micaceous graphitic pyritic schists derived from argillaceous protoliths that occur locally in background pelitic otago schist metasediments this study was aimed at determining the relationship between these similar rock types and whether the relationship had implications for ore formation argillites in the protolith turbidites of the otago schist metamorphic belt contain minor amounts of detrital organic matter 50 million years of evolution of the metamorphic belt from development of sheared argillite in the jurassic to postmetamorphic ductile extension in the cretaceous introduced graphite is structurally controlled and occurs with metamorphic muscovite and chlorite as veins and slicken sided shears with some veins having 50 noncarbonate carbon graphitic foliation seams in low grade micaceous schist and metamorphic quartz veins contain equant graphite porphyroblasts up to 2 mm across that are composed of crystallographically homogeneous graphite crystals graphite reflectance is anisotropic and ranges from 1 to 8 green light texturally similar porphyroblastic pyrite has grown in micaceous schist up to 10 wt s metamorphic quartz veins and associated muscovite rich shears these pyritic schists are weakly enriched in arsenic up to 60 ppm the low grade metamorphic mobility and concentration of graphite in micaceous schists is interpreted to be a precursor process that structurally and geochemically prepared parts of the otago schist belt for later more restricted gold mineralisation economic amounts of gold and associated arsenic were subsequently introduced to carbonaceous sulphidic schists in the macraes gold deposit by a separate metamorphic fluid derived from high grade metaturbidites fluid flow at all stages in these processes occurred at metamorphic rates mm year and fluids were broadly in equilibrium with the rocks through which they were passing

10be and ba concentrations in west african sediments trace productivity in the past particle reactive elements are scavenged to a higher degree at ocean margins than in the open ocean due to higher fluxes of biogenic and terrigenous particles in order to determine the influence of these processes on the depositional fluxes of10be and barium we have performed high resolution measurements on sediment core geob 1008 3 from the congo fan because the core is dominated by terrigenous matter supplied by the congo river it has a high average mass accumulation rate of 6 5 cm kyr biogenic10be and ba concentrations were calculated from total concentrations by subtracting the terrigenous components of10be and ba which are assumed to be proportional to the flux of al2o3 the meanba al weight ratio of the terrigenous component was determined to be 0 0045 the unusualy high terrigenous10be concentrations of 9 1 109 atoms g al2o3 are either due to input of particles with high10be content by the congo river or due to scavenging of oceanic10be by riverine particles the maxima of biogenic10be and ba concentrations coincide with maxima of the paleoproductivity rates time series analysis of the10be and of ba concentration profiles reveals a strong dominance of the precessional period of 24 kyr which also controls the rates of paleoproductivity in this core during the maxima of productivity the flux of biogenic ba is enhanced to a larger extent than that of biogenic10be applying a model for coastal scavenging we ascribe the observed higher sensitivity of ba to biogenic particle fluxes to the fact that the ocean residence time of ba is approximately 10 times longer than that of10be

the netherlands indian ocean expedition 1992 1993 first results and an introduction the netherlands indian ocean programme was carried out with the rv tyro in the nw indian ocean the arabian sea and off kenya and the seychelles during 1992 1993 with the objective to study the effect on both spatial and temporal scales of the monsoon on the climate system in the northern indian ocean the programme included five research foci studied in different projects project a was directed towards the effects of the seasonally reversing monsoonal system on the coastal ecosystems in kenya especially to gain a clear understanding of the physical chemical and biological processes occurring in the coastal zone this includes the development of the marine flora and fauna in response to the changing conditions in the coastal zone the second project b aimed at a study of the dynamics of the pelagic system including a quantification of the carbon flux and biogeographical studies with the emphasis on distribution and taxonomy of plankton part of this project was designed as pilot project for the jgofs northwest indian ocean study carried out in 1994 95 covering most of the jgofs core measurements these studies were planned in close cooperation with the geological project c tracing a seasonal upwelling system aimed at determining the spatial and temporal variability of biological chemical and geological parameters that define an upwelling system and recognizing these in the sedimentary record as proxies for upwelling in the waters off somalia and yemen project d concentrated on two main issues the first was the late quaternary productivity and the dynamics of the oxygen minimum zone in the northeast arabian sea the second was the depositional architecture and sediment facies of the middle and lower indus fan the biology of oceanic reef systems of the seychelles formed the last project e within the netherlands indian ocean programme and was mainly directed towards biogeographical taxonomical and ecological studies of the reefs the studies comprised within these projects were and are being carried out at a range of different institutes and preliminary results were discussed at an arabian sea workshop held at nioz texel the netherlands from 13 16 february 1995 the papers in this special form the first group of results from the progamme and as a consequence the articles have a strongly variable character the first paper by kromkamp et al describes temporal and spatial variability of primary production along the kenyan coast and their relationship to the development of the cyanobacterium trichodesmium

vanadium accumulation in carbonaceous rocks a review of geochemical controls during deposition and diagenesis abstract published data relevant to the geochemistry of vanadium were used to evaluate processes and conditions that control vanadium accumulation in carbonaceous rocks reduction adsorption and complexation of dissolved vanadium favor addition of vanadium to sediments rich in organic carbon dissolved vanadate v v species predominate in oxic seawater and are reduced to vanadyl ion v iv by organic compounds or h 2 s vanadyl ion readily adsorbs to particle surfaces and is added to the sediment as the particles settle the large vanadium concentrations of rocks deposited in marine as compared to lacustrine environments are the result of the relatively large amount of vanadium provided by circulating ocean water compared to terrestrial runoff vanadium rich carbonaceous rocks typically have high contents of organically bound sulfur and are stratigraphically associated with phosphate rich units a correspondence between vanadium content and organically bound sulfur is consistent with high activities of h 2 s during sediment deposition excess h 2 s exited the sediment into bottom waters and favored reduction of dissolved v v to v iv or possibly v iii the stratigraphic association of vanadiferous and phosphatic rocks reflects temporal and spatial shifts in bottom water chemistry from suboxic phosphate concentrated to more reducing euxinic conditions that favor vanadium accumulation during diagenesis some vanadium organic complexes migrate with petroleum out of carbonaceous rocks but significant amounts of vanadium are retained in refractory organic matter or clay minerals as carbon in the rock evolves toward graphite during metamorphism vanadium is incorporated into silicate minerals

cretaceous and paleogene saline lacustrine source rocks discovered in the southern junggar basin nw china abstract saline lacustrine source rocks in china provide the resource basis for many giant oil fields here we report the first discovery of such source rocks in the piedmont area of the northern tianshan mountains in the southern junggar basin of nw china these source rocks are cretaceous and paleogene in age organic geochemistry and trace element data suggest that these mudstones were formed in a brackish saline lacustrine environment characterized by deep water and reducing conditions and in a warm and dry paleoclimate evidence for this environment includes mudstone pr ph values of 0 4 and negative ce and eu anomalies the total organic carbon toc contents of these cretaceous and paleogene mudstones are typically 0 5 with maximum values of 1 45 and 2 22 respectively signifying moderate to high organic matter abundance rock eval and kerogen analyses suggest that the organic matter was dominated by type ii kerogen the mudstones are generally thermally mature suggesting favorable conditions for hydrocarbon particularly oil generation oil source correlation confirms the oil generation of these two sets of source rocks whose development are controlled mainly by reducing environments these cretaceous and paleogene mudstones should therefore be a target for regional exploration in the southern junggar basin in addition to the known gas producing jurassic rocks this oil bearing potential is unique amongst the early cretaceous and eocene oligocene central asian petroliferous basins as the eastern portion of this realm is considered to host predominantly jurassic coal based source rocks giving rise to numerous large gas fields rather than oil resources

transport and release of transition elements during early diagenesis sequential leaching of sediments from manop sites m and h part i ph 5 acetic acid leach sediments from manop sites m and h in the eastern tropical pacific ocean can be partitioned into operationally defined phases by means of a sequential leach procedure this paper reports the results of the first leach in the sequence an acetic acid solution buffered as p h 5 with sodium acetate this leach is designed to remove carbonate bound and sorbed cations the only cation bound in a consistent ratio to calcium in the carbonate is strontium the molar ratio is 2 10 3 in contrast transition metals are sorbed onto the surfaces of other sedimentary particles the proportions sorbed range from 2 to 10 of the total manganese about 10 of the total nickel and copper and less than 1 of the total iron the pool of sorbed metals in surface sediments is sufficiently large and the rate of biological stirring is sufficiently rapid for this metal reservoir potentially to dominate the porewater reservoir in supplying metals to ferromanganese nodules a simple model for nodule growth based upon transfer of metals through this reservoir suggests that only 1 of the sedimentary sorbed metals within a radius of 2 to 9 cm is required to support typical nodule growth rates

new basin modelling results from the polish part of the central european basin system implications for the late cretaceous early paleogene structural inversion combined subsidence and thermal 1d modelling was performed on six well sections located in the north western mid polish trough swell in the eastern part of the central european basin system the modelling allowed constraining quantitatively both the mesozoic subsidence and the magnitude of the late cretaceous paleocene inversion and erosion the latter most probably reached 2 400 m in the mid polish swell area the modelled upper cretaceous thickness did not exceed 500 m and probably corresponded to 200 300 m in the swell area as compared with more than 2 000 m in the adjacent non inverted part of the basin such upper cretaceous thickness pattern implies early onset of inversion processes probably in the late turonian or coniacian our modelling coupled with previous results of stratigraphic and seismic studies demonstrates that the relatively low sedimentation rates in the inverted part of the basin during the late cretaceous were the net result of several discrete pulses of non deposition and or erosion that were progressively more pronounced towards the trough axis the last phase of inversion started in the late maastrichtian and was responsible for the total amount of erosion which removed also the reduced upper cretaceous deposits according to our modelling results a late cretaceous heat flow regime which is similar to the present day conditions about 50 mw m2 was responsible for the observed organic maturity of the permian mesozoic rocks this conclusion does not affect the possibility of late carboniferous permian and late permian early triassic thermal events

geochemistry of late metamorphic hydrothermal alteration and graphitisation of host rock macraes gold mine otago schist new zealand abstract the macraes gold deposit in the otago schist new zealand formed during late metamorphic fluid flow through a lower greenschist facies shear zone mineralisation occurred near to the brittle ductile transition at about 300 c large volumes of host rock in a shear zone up to 120 m thick have been hydrothermally altered by this fluid activity most alteration is not structurally controlled apart from proximity to the shear zone ductile and brittle microshears traverse the most mineralised rocks and some structural control of fluid flow occurred as well fluid flow was slow similar to that in metamorphic rocks mm year and diffusion through interconnected fluid was a significant chemical process localised extensional hydrofractures m scale are filled with mineralised quartz most alteration of the host rocks was isochemical with respect to the lithophile elements and mineralised rocks have been variably enriched in as au sb w mo and bi but not co or cd addition of sulphur has occurred to both host rocks and mineralised rocks up to 1 wt above a background of 0 1 wt host rock sulphur is mainly pyritic and is not structurally controlled mineralised rocks have pyrite and arsenopyrite along microshears pyrite chalcopyrite sphalerite and galena have formed from sulphidation of silicates with no addition of metals graphite has been added to mineralised rocks along microshears up to 3 wt locally above a background of 0 1 wt noncarbonate carbon graphite deposition may have occurred as a result of mixing of two fluids water methane and water carbon dioxide graphitisation and sulphidation reactions released low d water which accumulated in the slow moving mineralising fluid distinction between this low d reaction water and meteoric water incursion is difficult

varve calibrated records of carbonate and organic carbon accumulation over the last 2000 years in the black sea sedimentologic and geochemical studies of box and gravity cores recovered from the black sea during the first leg of a multileg international black sea expedition in 1988 allow reconstruction of the basinwide holocene environmental history of the black sea in the deeper parts of the basin box cores typically recovered a flocculent surface layer fluff laminated coccolith marls of unit i 25 45 cm thick and the upper 5 10 cm of finely laminated dark colored sapropels of unit ii fine grained homogeneous mud turbidites are interbedded with units i and ii over much of the basin but the stratigraphie position of these turbidites differs from site to site the deposition of individual turbidites up to 15 cm thick does not appear to have significantly disturbed underlying laminae sediment trap deployments in the black sea suggest that light and dark laminae couplets represent annual increments of sedimentation i e varves we have therefore constructed a varve chronology for the sequence in order to correlate and date distinctive sedimentation and paleoenvironmental events distinctive groups of laminae in unit i can be correlated across the entire deeper basin a distance of more than 1000 km this implies a remarkable homogeneity in production accumulation and preservation of biogenic material over much of the black sea during deposition of unit i the change from deposition of finely laminated organic carbon rich sapropels unit ii to laminated more calcareous coccolith rich marls unit i is thought to represent the crossing of a salinity threshold for emiliania huxleyi the varve chronology sets this change at about 1 63 ka 1633 100 yr b p but the record of magnetic secular variation measured in several cores produces an age estimate of about 2 0 ka for the base of unit i or about 1 2 times the varve age the average of six calibrated accelerator mass spectrometry radiocarbon ages for the base of unit i is 2 7 ka or about 1 7 times the varve age following the initial change to coccolith dominated sedimentation deposition of sapropel resumed for at least one significant period 1 56 1 25 ka since 1 25 ka cycles of carbonate deposition with quasi decadal periodicities have produced characteristic darker and lighter assemblages of laminae these cycles may have been climatically driven geochemical analyses coupled with the varve ages adopted herein indicate that accumulation rates of carbonate are nearly an order of magnitude higher in unit i averaging 35 45 g m 2 yr 1 than in sapropelic unit ii which contains primarily detrital carbonate the accumulation of lithogenic components in parts of unit i is only 1 5 times the rate in unit ii deepwater organic carbon accumulation rates are somewhat higher in unit i 3 5 4 5 g m 2 yr 1 than in the upper part of unit ii organic carbon accumulation rates in unit i are somewhat antithetic to those of carbonate and on the basis of this and additional constraints placed by pyrolysis and carbon isotopic analyses of organic material it appears that terrestrial organic matter is an important component perhaps 25 of total organic carbon burial in the basin unit i in the western part of the black sea has a higher terrestrial organic component and higher accumulation rates of terrigenous clastic material than unit i in the eastern part this difference between eastern and western black sea is to be expected because of the major rivers that empty into the western black sea from eastern europe ukraine and russia shallow slope sites but still within euxinic bottom waters have lower organic carbon accumulation rates and lower pyrolysis hydrogen indices than deepwater basinal sites suggesting selective resuspension and oxidation of organic matter at basin margins and focusing of organic matter deposition toward the basin center a comparison of the black sea data with those from several open ocean sites with similar water depths showed no significant difference between organic carbon accumulation rates under oxic and anoxic conditions for a given bulk accumulation rate the organic carbon accumulation rates normalized to primary productivity are about the same in both settings

pyritization of trace metals in anoxic marine sediments the pyritization of reactive trace elements in different anoxic marine sediments was investigated to determine the importance of factors such as h2s reactive fe pyrite content and salinity in controlling this process the areas studied included anoxic sulfidic sediments baffin bay a hypersaline coastal lagoon from texas and green canyon a hemipelagic oil seepage area anoxic nonsulfidic sediments with high sedimentation rates atchafalaya bay mississippi delta system hemipelagic anoxic nonsulfidic sediments with low sedimentation rates gulf of mexico shelf and slope and orca basin an euxinic hypersaline basin and organic rich marsh sediments atchafalaya bay results indicate that the degree of trace metal pyritization dtmp of all trace metals except cd increased with increasing degree of pyritization dop irrespective of the type of sedimentary environment involved however for as hg and mo the dtmpdop values were generally above the 1 1 ratio line whereas the transition metals co cu mn and ni displayed a close to linear increase in dtmp with dop and moderate incorporation into pyrite chromium and the class b metals pb and zn were also gradually incorporated into the pyrite phase but without reaching the dtmp levels exhibited by the transition metals cadmium was not incorporated to a significant extent these results are consistent with the chemical attributes of these different classes of trace elements availability of dissolved trace metals and organic matter content are apparently important factors controlling the incorporation of co cr cu and ni into pyrite in anoxicsulfidic fe poor and h2s rich environments

monitoring the variations of the socotra upwelling system during the last 250 kyr a biogenic and geochemical approach abstract a combination of changes in the species composition of the radiolarian populations and in the sediment chemical composition content and mass accumulation rates of carbonate organic carbon and selected major and trace elements with special attention paid to ba is used to reconstruct the variations in upwelling activity over the last 250 kyr in the socotra gyre area somali socotra upwelling system nw indian ocean in the socotra gyre core md 962073 at 10 n the variations in upwelling intensity are reconstructed by the upwelling radiolarian index uri while the thermocline surface radiolarian index tsri testifies to productivity variations during non upwelling intervals despite an origin related both to marine and terrigenous inputs the geochemical records of organic carbon silica and trace elements ba p cu and zn normalized to al are controlled by the variations in surface paleoproductivity the data indicate a continuous increase in upwelling intensity during the last 250 kyr with a maximum activity within the mis 3 while high productivity periods in between the upwelling seasons occurred both during glacial and interglacial intervals a comparison of our data with published observations from another gyre of the somalian upwelling area located at 5 n in the somali gyre area shows differences regarding periods of upwelling activity and their geochemical imprint three hypotheses are proposed to explain these differences 1 changes in the planktonic community resulting in more silica rich deposits in the socotra gyre and more carbonate rich deposits in the somali gyre that are controlled by differences in the source water of the upwelling 2 a more important terrigenous input in the southern gyre and 3 a different location of the sites relative to the geographic distribution of the upwelling gyres and hydrologic fronts

can sediment geochemistry record changes in coastal upwelling palaeoproductivity evidence from northwest africa and the arabian sea abstract the causes and consequences of organic carbon c org burial in sediments underlying regions of coastal upwelling are of profound importance to studies of palaeoceanography and palaeoclimatology alike the primary control on coastal upwelling wind stress and resulting ekman transport is linked intimately to variation in the earth s insolation record via a variety of feedback mechanisms in comparison the nutrients required to sustain productivity and the factors affecting the c org content of the sediment are related to variation in global glacial boundary conditions using a variety of geochemical indicators it is apparent that the record of upwelling off northwest africa driven by the northeast trade winds is characterized by arid glacial conditions and high wind stress sustaining elevated euphotic zone productivity the resulting c org accumulation record reflects higher palaeoproductivity during glacial episodes in contrast the arabian sea upwelling is seasonal faunal and geochemical ba al u th ratios indicators suggest strong interglacial 23 ka cyclicity in the southwest monsoon the c org record is spatially and temporally consistent but in disagreement with other palaeoproductivity indicators these results point to the decoupling of surface ocean productivity in areas of coastal upwelling from deep ocean circulation and nutrient supply this result has important consequences for driving atmospheric p co 2 changes on timescales less than that of oceanic mixing further applications of geochemical tracers to areas of coastal upwelling such as northwest africa and peru are needed urgently

gold mineralization without quartz veins in a ductile brittle shear zone macraes mine otago schist new zealand greenschist facies schist which hosts the macraes mine in east otago new zealand has been pervasively altered by post metamorphic lower greenschist facies fluids over a 120 m thick section perpendicular to foliation metamorphic titanite has been replaced by rutile and epidote has been replaced by a variety of metamorphic minerals including siderite chlorite muscovite and calcite the early stages of this alteration occurred during development of a ductile cleavage associated with kilometre scale recumbent folding the cleavage was widely overprinted by a subparallel set of spaced mm scale microshears which are locally enriched in rutile and hydrothermal graphite strain was then concentrated into narrow m scale zones where more intensely deformed portions of the rock are crossed and highly disrupted by closely spaced 100 m scale microshears the highly strained rocks show a combination of mylonitic and cataclastic microstructures including crystal plastic grain size reduction and recrystallization of micas to form a new foliation muscovite has grown at the expense of albite in the mylonitic cataclasites hydrothermal alteration was accompanied by addition of pyrite arsenopyrite and gold without development of quartz veins gold precipitated with sulphides during reduction of the fluid by hydrothermal graphite the whole altered rock sequence was later cut sporadically by mesothermal quartz veins which contain gold scheelite rutile pyrite and arsenopyrite this deposit displays a continuum of post metamorphic processes and hydrothermal fluid flow which occurred during uplift of the schist belt

chemical evidence of kerogen formation in source rocks and oil shales via selective preservation of thin resistant outer walls of microalgae origin of ultralaminae abstract new structures termed ultralaminae were recently observed by transmission electron microscopy usually in high amounts in a number of kerogens from oil shales and source rocks morphological similarities were noted between ultralaminae and the thin ca 15 nm resistant outer walls composed of non hydrolyzable macromolecules algaenans commonly occurring in extant chlorophyceae especially in the cosmopolitan genus scenedesmus identification of the pyrolysis products of s quadricauda algaenan showed i a highly aliphatic structure based on a macromolecular network of long up to c32 polymethylenic chains probably cross linked by ether bridges and ii a close correlation based on the formation of n alkylnitriles between this algaenan and two ultralaminar kerogens the rundle oil shale mainly composed of ultralamina accumulations and the green river shale ultralaminae dispersed within an amorphous matrix these fossil ultralaminae therefore likely originated from the selective preservation of the thin algaenan containing outer walls of scenedesmus and or of other chlorophyceae containing outer walls of a similar morphology and composition relative distributions of n alkylnitriles and of n alkanoic acids in the pyrolysates of s quadricauda algaenan and of the rundle oil shale indicated that nitriles are not derived from secondary reactions of carboxylic acids but originate from preexisting nitrogen functions likely amides previous evidence of kerogen formation via selective preservation of algaenans was restricted to rather uncommon kerogens the present results added to ultralamina common occurrence and abundance point to a wide involvement and to a large contribution of the selective preservation of algaenan containing thin outer walls of chlorophyceae in the formation of kerogens in a number of lacustrine source rocks and oil shales all the available information suggest that the three way correlation selective preservation of algaenans from thin resistant chlorophycean outer walls formation of fossil ultralaminae presence of n alkylnitriles with a typical distribution in the pyrolysates of ultralaminar kerogens observed in this study might be of a general character

modeling the late quaternary indian ocean circulation an ocean general circulation model ogcm of the indian ocean is forced by paleoclimate simulations for five time slices over the last 126 000 years using an annual period sinusoidal fit to the perpetual january and july paleoclimatic model forcing the ogcm produces seasonal cycles in velocity fields both vertical and horizontal and temperature salinity fields at these five times the simulations indicate that the southern hemisphere upper ocean circulation of the indian ocean is essentially invariant to climatic fluctuation on this time scale they also suggest that the low insolation 18 000 years b p northern hemisphere upper ocean summer circulation was very much weaker compared to high insolation periods such as 9000 years b p and 126 000 years b p by perhaps an order of magnitude by contrast the simulated low insolation winter northern hemisphere upper ocean circulation was substantially stronger than during high insolation periods equatorial upwelling as simulated is shown to be a mainly boreal summer event reduced by an order of magnitude during low insolation conditions a similar reduction in upwelling is seen along the arabian coast but a less severe decrease along the somalian coast the model simulation of february and august sea surface temperature at 18 000 years b p the height of the last glaciation is generally within 1 2 c of paleoclimate reconstructions the effect of lower glacial sea level on the circulation is shown to be only local

relation between sedimentation rate and burial of organic phosphorus and organic carbon in marine sediments organic carbon and organic phosphorus concentrations in marine sediment cores with known sedimentation rates were determined and collected from the literature with the exception of organic rich sediments from upwelling areas organic phosphorus concentrations in marine sediments do not correlate linearly with organic carbon concentrations the c p ratios of organic matter buried in marine sediments vary systematically with sedimentation rate over the range studied 0 0001 to 2 5 cm y low c p ratios 200 atomic occur in sediments with sedimentation rates both less than 0 002 cm y and greater than 1 cm y higher c p ratios up to 600 are found at intermediate sedimentation rates a simple steady state model is developed for the early diagenesis of organic carbon and organic phosphorus in marine sediments the processes included are sediment burial pore water diffusion and bacterial decomposition of organic matter by oxic respiration and sulfate reduction preferential regeneration of phosphorus relative to carbon is assumed to take place during oxic respiration the modeling shows that both organic matter preservation and the degree of elemental fractionation between phosphorus and carbon depend strongly on the overall sedimentation rate very high sedimentation rates coastal deltaic environment result in a good preservation of deposited organic matter with an initial c p ratio close to the redfield value at very slow sedimentation rates pelagic environment the oxidation of the sedimentary organic matter is nearly complete and produces a low c p residual organic material this residual organic matter may represent either refractory detrital organic compounds enriched in phosphorus or in situ synthesized low c p bacterial remains the high c p ratios at intermediate sedimentation rates slope and shelf environment reflect the preferential regeneration of phosphorus during the incomplete decomposition of the metabolizable organic matter

distribution of organic carbon in surface sediments along the eastern arabian sea a revisit abstract one hundred twelve surface sediment samples along the western continental margin of india were analyzed for organic carbon oc elevated oc concentrations are associated with sediments deposited in areas where productivity is moderate to high very high oc concentrations as reported in earlier studies even for regions where productivity is comparatively low could not be confirmed the re analysis of selected samples by coulometry shows that oc concentrations determined previously by the wet oxidation method may be too high by up to more than a factor of two a broad similarity in the distribution of oc and bioproductivity is observed which is in accordance with other productivity proxies such as the abundance of planktonic foraminiferal species g bulloides and hydrogen indices hi our results indicate the importance of bioproductivity for oc accumulation along the western continental margin of india even though low dissolved oxygen concentrations in the water column sedimentation rate sediment texture clay mineral content dilution by quartz and carbonate as well as topography are considered responsible for the general oc distribution in this area

round hill shear zone hosted gold deposit macraes flat otago new zealand evidence of a magmatic ore fluid the 0 8 moz round hill shear zone hosted gold deposit is one of several located on or near the hyde macraes shear zone macraes flat new zealand field relationships show stockwork veins are the oldest part of the hydrothermal system followed by flat and ramp veins hanging wall shear veins formed early but have been modified by late deformation fluid inclusion microthermometric results for dominant type i inclusions show that flat and ramp veins have the same average wt percent nacl equiv values 2 2 0 6 and were precipitated from the same fluid salinity data for these veins overlap with those from hanging wall veins average 1 3 0 3 and stockwork veins 1 6 0 6 for vein margins 0 9 0 3 for vein centers although both of the latter trend toward lower overall wt percent nacl equiv values suggesting mixing between relatively dilute and more saline end members all of the above veins have similar temperatures of homogenization t h ranging between 110 and 188 c fluid inclusion trapping temperatures are considered to be 300 c equating to a 10 km depth of formation carbon dioxide dissolved in the hydrothermal fluid is responsible for up to one third of fluid inclusion apparent salinities stockwork and hanging wall veins thus have true salinities of 1 wt percent nacl equiv 0 17 molal and flat and ramp veins have true salinities of fluid inclusion volatiles from round hill and other macraes deposits are dominated by h 2 o 99 02 99 69 mol with lesser co 2 0 14 0 76 mol n 2 0 03 0 32 mol and ch 4 0 06 0 17 mol noticeable concentrations of hydrocarbons occur in many of the samples fluid inclusion cation and anion data show few components of relatively low concentration are dissolved in the hydrothermal fluid consistent with co 2 corrected microthermometric measurements a range in fluid inclusion d h 2 o values obtained for the round hill deposit is coincident with the different vein types and also indicates mixing between two fluids one fluid is considered to be o isotope shifted meteoric water as trapped by the early stockwork veins and has the lowest d h 2 o values of 80 per mil the other fluid is represented by flat and or ramp and hanging wall veins that have d h 2 o values up to 40 per mil the macraes d h 2 o data show a trend toward the magmatic water end member for geothermal systems associated with convergent plate boundaries and are consistent with a 25 to 50 percent magmatic component in the macraes hydrothermal system

contrasting coeval paragenesis of gold and scheelite in an orogenic hydrothermal system macraes mine new zealand abstract the macraes deposit 10 moz resource is a cretaceous orogenic system hosted in the hyde macraes shear zone hmsz which was mineralised under lower greenschist facies during later stages of lower greenschist facies metamorphism of host metasedimentary schists gold is encapsulated primarily in sulphides that have replaced silicates in ductile shears that are focussed in micaceous rocks the shears anastomose around structurally competent lenses and were enhanced by hydrothermal graphite deposition and alteration of albite to muscovite in contrast scheelite with minor auriferous sulphides occurs in multigenerational quartz veins that filled fractures in competent lithologies hence scheelite was deposited coevally with gold from the same hydrothermal fluid but in different structural settings from most gold at all scales from millimetres to hundreds of metres consequentially there is weak correlation between au and w at all scales in the deposit multigenerational gold and scheelite mineralisation occurred during progressive deformation in the shear zone in two contrasting structural and mineralogical styles in syn deformationally weakening gold bearing micaceous shears and in syn deformationally hardened competent rocks that became silicified and veined with quartz and scheelite hydrothermal fluid flow in the gold bearing shears occurred at the grain boundary microshear and microfracture scales and was slow hundreds of m year and was controlled by fracture permeability the au and w enrichment in the macraes deposit resulted from regional scale metal mobility driven by coeval recrystallisation in higher grade upper greenschist to amphibolite facies metamorphism that persisted structurally below the macraes deposit for at least 10 ma after mineralisation ceased

geological controls on refractory ore in an orogenic gold deposit macraes mine new zealand the macraes mine is hosted in an orogenic mesothermal gold deposit in metasedimentary rocks of the otago schist belt much gold occurs within altered schist with minimal silica addition and this study focuses on altered schist ore types the unmineralized host schists are chemically and mineralogically uniform in composition but include two end member rock types feldspathic schist and micaceous schist both rock types have undergone hydrothermal alteration along a shallow dipping foliation parallel shear zone but their different rheological properties have affected the style of mineralisation micaceous schist has been extensively recrystallized and hydrothermally altered during ductile deformation to form ores characterized by abundant disseminated millimetre scale pyrite cubes typically 1 2 wt s and minor silicification the earliest pyrite contained ni and or as in solid solution and no gold was imaged in these pyrites or later arsenopyrite grains the ore type is refractory and gold recovery by cyanide leaching is less than 50 with lowest recovery in rocks that have been less affected by later brittle deformation in contrast hydrothermally altered feldspathic schist is characterized by mineralised black microshears and veinlets formed during shear zone related brittle deformation microsheared ore has relatively low sulphur content 0 7 wt and muscovite has been illitised during hydrothermal alteration pyrite and arsenopyrite in microshears are fractured and deformed and contain 1 10 m blebs of gold later pyrite veinlets also contain micron to submicron scale inclusions of sphalerite chalcopyrite galena and gold 10 microns gold in microsheared ore is more readily recoverable than in the refractory ore although encapsulation of the fine gold grains inhibits cyanidation both microsheared ore and disseminated pyritic ore pass laterally into mineralised black shears which contain hydrothermal graphite and late stage cataclastic sulphides this black sheared ore releases gold readily but the gold is then adsorbed on to gangue minerals preg robbed and net cyanidation recovery can be less than 50 hence low gold recovery during cyanidation results from 1 poor liberation of gold encapsulated in microcrystalline quartz and unfractured sulphide grains and 2 preg robbing of liberated gold during cyanidation introduction of pressure oxidation of ore prior to cynidation has mitigated these issues

application of high resolution 2d 3c seismic for characterization of the perspective jurassic shale play in central poland abstract here we show the application of broadband 4 120 hz 2d 3c seismic for characterization of the perspective jurassic shale play in central poland data were acquired along a network of 250 km 2d profiles using single point densely spaced receivers digital 3c sensors and acquisition was focused on providing both high resolution and broadband seismic that would enable structural imaging and quantitative interpretation of the key stratigraphic horizons in the mesozoic sedimentary cover such acquisition parameters resulted in good quality data and allowed for more flexibility during processing e g unaliased f k filtering or digital group forming for ground roll removal processing was oriented to preserve relative amplitudes and the broadband character of the dataset as the input for future quantitative interpretation we obtained a high resolution stratigraphic image of the target upper jurassic upper kimmeridgian tithonian sequence as well as overall structural portrait of this part of mid polish trough characterized by strong imprint of the salt tectonics lateral continuity of particular stratigraphic sequences has been determined and a more precise structural context for deposition and present day structure of the upper kimmeridgian tithonian has been established

paleohydrographic changes in the somali basin 5 n upwelling and equatorial areas during the last 160 kyr based on correspondence analysis of foraminiferal and radiolarian assemblages this study documents the biological signatures impressed upon the sedimentary record underlying both the 5 n upwelling system of the somali current and the equatorial area of the somali basin out of the upwelling influence the evolution of these two distinct hydrographic systems is compared for the last 160 kyr correspondence and cluster analyses are performed on combined radiolarian and planktonic foraminiferal quantitative data in order to study the changes of the planktonic assemblages through time and space the upwelling radiolarian index uri is used as a productivity proxy the water temperature and hydrographic structure of the upper water masses appear to be the major factors controlling the distribution patterns of the fauna the relative abundances of three groups of foraminifera cold water form dextral n pachyderma mixed layer dwellers g trilobus g ruber g sacculifer g conglobatus and g glutinata and thermocline dwellers g menardii g tumida n dutertrei g crassaformis and p obliquiloculata follow distinct evolutionary patterns at the two sites during the last 160 kyr at the equatorial site core md 85668 downcore fluctuations in the relative abundances of the three groups are closely related to the glacial interglacial cyclicity and provide some insights into the interpretation of hydrographic changes the dominance of the mixed layer foraminifera at the transition intervals between isotope stages 6 5 and 2 1 combined with weak uri values is thought to reflect the reorganization of the oceanographic circulation these short term events with a duration of 5000 year could be related to the rapid inflow of oxygen depleted water through the indonesian straits as a result of sea level rise during deglaciation underneath the 5 n gyre core md 85674 the response to global climatic changes is overprinted by the regional effect of the somalian upwelling which has been persistent over the last 160 kyr

anoxia vs productivity what controls the formation of organic carbon rich sediments and sedimentary rocks discussion the prevailing explanation for the origin of organic rich sediments and rocks invokes deposition under conditions of anoxia however recent research suggests that high primary production and not water column anoxia provides the first order control on the accumulation of organic rich facies in the modern oceans oxygen minima do not appear to have any direct effect on carbon accumulation in continental margin or marginal sea environments sediments accumulating in the modern black sea the type euxinic basin are not particularly enriched in organic matter despite the presence of an anoxic water column although a sapropel containing extremely high carbon concentrations was deposited during the holocene at a time when the basin was oxic results of a recently published co pled ocean atmosphere model indicate that during the cretaceous thermohaline and surface circulation in the oceans was similar to or more intense than modern conditions despite the overall equable climate such conditions confound the idea that circulation in the cretaceous atlantic for example was punctuated by oceanic anoxic events brought about by more sluggish circulation sporadic temporal and spatial increases in primary production reflecting changes in the behavior and or state of the ocean atmosphere system constitute a more tenable explanation for the occurrence of modern and quaternary carbon rich sediments and cretaceous black shales consequently the fundamental control on the accumulation of carbon rich facies in the oceans and marginal seas is not the presence or absence of anoxia

tectonic evolution of the mid polish trough modelling implications and significance for central european geology abstract the polish basin forms the easternmost part of the permian mesozoic northwest european basin the depocentral axis of the polish basin the mid polish trough mpt is superimposed on the boundary between the west european phanerozoic and east european proterozoic crustal domains within the trans european suture zone the presence of this fundamental crustal boundary may be paramount in structurally controlling the position of the mpt concentrating stresses during post variscan wrench and extensional tectonics in central europe tectonic subsidence analysis of the preserved and reconstructed stratigraphic record of the polish basin indicates the occurrence of an initial late permian early triassic 255 241 ma rifting phase that was followed by subsequent episodes of increased tectonic subsidence during the oxfordian kimmeridgian 157 152 ma and beginning in the cenomanian 97 ma the oxfordian kimmeridgian episode is interpreted as corresponding to a second extensional event which correlated with intersified rifting and wrench activity within the arctic north atlantic rift system and along the northern tethyan margin while the cenomanian may be considered a precursor of compressional deformations in the basin which culminated in basin inversion in the latest cretaceous and paleocene forward modelling results in view of existing geophysical interpretations which show the presence of a deep moho and a very velocity lower crustal layer beneath thempt suggest that permo mesozoic basic development may be related at least in part to the intrusion of mantle material into and densification of the lower crust rather than exclusively to crustal extension and thinning

geochemistry of eastern mediterranean sediments primary sediment composition and diagenetic alterations abstract two cores recovered in the eastern mediterranean were analysed for major minor and trace elements the primary chemical composition of the sediment is different at each location probably because the lithological sources and the relative biogenic contributions differ carbonates are important for the concentration of ca mg and sr whereas aluminosilicates determine the concentration of si al k li y and be and to a lesser extent that of fe cr ti mg zn and zr in sapropels organic carbon and sulphur seem to be closely related bromine mo p fe v cu zn co ni and cr are closely associated with organic and sulphidic compounds the concentration versus depth profile for organic carbon in two sapropels points to a rapid establishment of conditions that gave rise to sapropel formation followed by a gradual transition back to normal conditions the primary composition is overprinted by diagenetic processes sulphate reducing conditions occurred during and just after sapropel deposition a progressive oxidation front mechanism which became active after sapropel deposition is responsible for additional major geochemical changes this diagenetic phenomenon has strong implications for the chemistry of fe mn ni co zn cu cr v u as and sb

late quaternary biogenic productivity and organic carbon deposition in the eastern arabian sea abstract paleoproductivity variations in the eastern arabian sea during the late quaternary period 42 ka bp to present have been studied using accumulation rates of sedimentary biogenic components organic carbon corg nitrogen n caco3 sr and ba such a multi proxy approach reveals decreased surface productivity during the last glacial interglacial transition the observed change of surface water productivity during the last glacial interglacial period is in antiphase to those observed in other low and mid latitude upwelling areas however consistent with some of the upwelling regions like nw africa and nw mexico sedimentary corg and n are found to be decoupled from surface productivity trend with significant enrichments in corg and n during the last glacial maximum lgm this is interpreted in terms of increase in sedimentation rates by a factor of 3 4 resulting in the better preservation of corg during the lgm

pelagic productivity changes in the equatorial area of the northwest indian ocean during the last 400 000 years abstract major and selected trace element al fe mg k ba p mn v cu ni and ti records were analyzed in two cores recovered from the northwestern indian ocean core md 90940 on the madingley rise and core md 85668 in the somali basin in order to monitor the sedimentary response to pelagic productivity in this area during the last 400 000 years geochemical proxies such as bulk mass accumulation rate mar al normalized major and trace element contents major and trace element mars were compared to biologic markers of palaeoproductivity a new radiolarian index rad ratio and the variations of foraminiferal and radiolarian assemblages special attention being paid to the barium record a sequential leaching procedure determined the main ba carrier fraction in the sediment and thus the amount of biogenic barium the blue ocean sedimentation on the madingley rise core md 90940 is characterized by a low mar and an insignificant terrigenous input the bulk mar variations are directly related to the variations of the rad ratio reflecting a direct link between surface productivity and pelagic sedimentation at this site in this sediment barium is mainly found as barite and can be considered as a palaeoproductivity proxy in the somali basin core md 85668 the terrigenous inputs are relatively higher but the bulk mar variations are still related to the variations of surface productivity no barite was found and barium is mainly linked to the terrigenous input a comparison of the two pelagic sites of the madingley rise and the somali basin points out the differences between the barium records at both sites despite the location of both cores in the pelagic domain the geochemical record and especially the barium one is different from one core to the other the comparison of the variations of the bulk mar which reflects the variations of the surface productivity presents significant discrepancies between both sites in the blue ocean core md 90940 the productivity peak values are mainly recorded during glacial intervals but their maximum values are observed during interglacial isotope stage 9 in the somali basin core md 85668 high bulk mar periods occurred during glacial isotope stages the interglacial episode of high productivity recorded on the madingley rise the absence of significant variations of productivity at the 8 7 transition in the somali basin as well as the absence of a time lag between both records indicate that the surface productivity is in this area controlled more by the local variations of the palaeoceanographic patterns than the global climatic changes e g the glacial interglacial alternations

siliceous phytoplankton response to a middle eocene warming event recorded in the tropical atlantic demerara rise odp site 1260a abstract the middle eocene diatom and silicoflagellate record of odp site 1260a demerara rise is studied quantitatively in order to throw light on the changes that siliceous phytoplankton communities experienced during a middle eocene warming event that occurred between 44 0 and 42 0 ma both pianka s overlap index calculated per couple of successive samples and cluster analysis point to a number of significant turnover events highlighted by changes in the structure of floristic communities the pre warming flora dominated by cosmopolitan species of the diatom genus triceratium is replaced during the warming interval by a new and more diverse assemblage dominated by paralia sulcata an indicator of high productivity and two endemic tropical species of the genus hemiaulus the critical warming interval is characterized by a steady increase in biogenic silica and a comparable increase in excess ba both reflecting an increase in productivity in general it appears that high productivity not only increased the flux of biogenic silica but also sustained a higher diversity in the siliceous phytoplankton communities the microflora preserved above the critical interval is once again of low diversity and dominated by various species of the diatom genus hemiaulus all assemblages in the studied material are characterized by the total absence of continental and benthic diatoms and the relative abundance of neritic forms suggesting a transitional depositional environment between the neritic and the oceanic realms

deep water facies succession around the cenomanian turonian boundary in the outer carpathian basin sedimentary biotic and chemical records in the silesian nappe poland abstract facies succession organic carbon stable isotopes and chemical data together with benthic foraminiferal records from the barnasiowka trzeme nia composite section silesian nappe poland reflect changing oceanographic conditions across the cenomanian turonian transition in one of the largest basins of the outer carpathians whose floor was situated beneath the calcium compensation depth the sediments consist of non calcareous radiolarian shales turbidite intercalations rich in foraminifers and sponge spicules as well as siliciclastics and black shales with marine type of organic matter toc up to 6 5 wt corresponding to global oceanic anoxic event 2 the base of oae 2 has been identified on the basis of organic carbon isotope data as a positive excursion from 26 0 to the peak of 23 2 in the latest cenomanian the top of the oae 2 lies within a succession of oxidized siliceous manganiferous sediments including a fe mn layer with macronodules the organic rich sedimentation continued for about 400 kyr at a rate of ca 5 5 mm kyr and finished before the start of the turonian deep water agglutinated foraminiferal diversification and extinction of several taxa occurred during the early part of the oae 2 due to expanding bottom water anoxia chemical indices and benthic foraminiferal assemblages reveal periodic intervals of intensification and expansion of oxygen minimum zone at the basin floor before and after the oae 2 two early diagenetic ferromanganese layers with macronodules and siliceous manganiferous red and green shales directly overlying the organic rich facies reflect changes in oxygenation of the bottom water related to changes in their dynamics which took place near the c t boundary and in the earliest turonian this condensed fe mn succession records the maximum flooding of the late cenomanian early turonian transgression

late miocene early pliocene manganese redirection in the central indian ocean expansion of the intermediate water oxygen minimum zone decomposition of organic matter combined with density stratification generate a pronounced intermediate water oxygen minimum zone omz in the northwest indian ocean this zone currently lies between water depths of 200 and 2000 m and extends approximately 5000 km southeast from the arabian coast based upon benthic foraminiferal assemblage changes it has been suggested that this omz was even more extensive during the late miocene early pliocene 6 5 3 0 ma with a maximum volume and or intensity at approximately 5 0 ma while this inference may contribute to an understanding of the history of northwest indian ocean upwelling corroborating geochemical evidence for this interpretation has heretofore been lacking ocean drilling program odp sites 752 754 and 757 on broken and ninetyeast ridges are located within central indian ocean intermediate water depths 1086 1650 m but outside the present lateral dimensions of the indian ocean omz high resolution chemical analyses of sediment from these sites indicate significant reductions in the flux of mn and normalized mn concentrations between 6 5 and 3 0 ma that are most pronounced at approximately 5 0 ma because late miocene pliocene paleodepths for these sites were essentially the same as at present and because extremely low sedimentation rates 0 3 1 3 cm ky most likely precluded sedimentary metal oxide diagenesis we suggest that the observed mn depletions reflect diminished deposition of reducible mn oxyhydroxide phases within o2 deficient intermediate waters and that this effect was most intense at approximately 5 0 ma this interpretation implies that waters with less than 2 0 ml l o2 extended at least 1500 km beyond their present limits and is consistent with changes in benthic foraminifera assemblages we further suggest this expanded indian ocean omz is related to regionally and or globally increased biological productivity

geochemical study of organic matter rich cycles from the kimmeridge clay formation of yorkshire uk productivity versus anoxia abstract in this contribution we study two meter scale cycles from the kimmeridge clay formation cored near marton yorkshire which shows cyclic organic matter om distribution our aim is to try to understand the factors responsile for om accumulation the first cycle called lower cycle shows a total organic carbon toc content between 1 and 10 whereas the second called upper cycle shows a toc content varying between 5 and 35 the geochemical composition major elements and trace elements the organic geochemistry toc hi palynofacies and mineralogy of the sediments have been determined in both cycles the cyclicity is expressed through variations in the nature and in the relative abundance of the various types of organic matter constituents furthermore dilution effects by inorganic components of the sediment cannot account for the toc cyclicity for lower cycle the mo v and u content is low and little variable as is the intensity of the oxidation which om suffered from this indicates that variations in phytoplanktonic productivity may be held responsible for the cyclicity in steady and mildly reducing redox conditions in the upper cycle cyclicity also appears to depend on productivity but variations in the concentration of mo v and u and in the oxidation state of the om suggest the environment was temporarily more reducing it is proposed that larger amounts of h 2 s were released into marine bottom waters as a result of initial om decomposition forced the oxic anoxic boundary to rise in the water column and thus favoured om storage the main driving force for variations in the om concentration was the productivity of organic matter walled phytoplankton redox conditions of the depositional environment could have had a positive action but only by acting as a positive feedback effect

resolving the role of carbonaceous material in gold precipitation in metasediment hosted orogenic gold deposits carbonaceous material cm is commonly associated with gold and sulfides in metasediment hosted orogenic gold deposits the role of cm in au deposition is controversial cm has been proposed to contribute to gold deposition by reducing au bisulfide complexes or by facilitating sulfidation which destabilizes au in bisulfide complexes with resultant au deposition integration of petrographic observations thermodynamic models and geochemical data from metasediment hosted orogenic gold deposits in new zealand australia canada and west africa reveals genetic links between sulfides cm and mineralization the results are consistent with the coexistence of cm and pyrite as a consequence of their codeposition from ore fluids with a minor proportion of cm originally in situ in the host rocks au is deposited when pyrite and cm deposition decreases h 2 s concentration in ore fluids destabilizing au hs 2 complexes most cm in gold deposits is deposited from co 2 and ch 4 in ore fluids these findings are applicable to similar deposits worldwide

benthic phosphorus regeneration net primary production and ocean anoxia a model of the coupled marine biogeochemical cycles of carbon and phosphorus we examine the relationships between ocean ventilation primary production water column anoxia and benthic regeneration of phosphorus using a mass balance model of the coupled marine biogeochemical cycles of carbon c and phosphorus p the elemental cycles are coupled via the redfield c p ratio of marine phytoplankton and the c p ratio of organic matter preserved in marine sediments the model assumes that on geologic timescales net primary production in the oceans is limited by the upwelling of dissolved phosphorus to the photic zone the model incorporates the dependence on bottom water oxygenation of the regeneration of nutrient phosphorus from particulate matter deposited at the water sediment interface evidence from marine and lacustrine settings modern and ancient demonstrates that sedimentary burial of phosphorus associated with organic matter and ferric oxyhydroxides decreases when bottom water anoxia dysoxia expands steady state simulations show that a reduction in the rate of thermohaline circulation or a decrease of the oxygen content of downwelling water masses intensifies water column anoxia dysoxia and at the same time increases surface water productivity the first effect reflects the declining supply of oxygen to the deeper parts of the ocean the second effect is caused by the enhanced benthic regeneration of phosphorus from organic matter and ferric oxyhydroxides sedimentary burial of organic carbon and authigenic calcium phosphate mineral francolite on the other hand is promoted by reduced ocean ventilation according to the model global scale anoxia dysoxia leads to a more efficient recycling of reactive phosphorus within the ocean system consequently higher rates of primary production and organic carbon burial can be achieved even when the continental supply of reactive phosphorus to the oceans remains unchanged

new evidence for enhanced preservation of organic carbon in contact with oxygen minimum zone on the western continental slope of india paropkari a l prakash babu c and mascarenhas a 1993 new evidence for enhanced preservation of organic carbon in contact with oxygen minimum zone on the western continental slope of india mar geol i 11 7 13 in order to evaluate the reason for organic enrichment on the western continental slope of india we provide rock eval pyrolysis data of 25 surficial sediment samples from this area results show that the organic matter on the slope is hydrogenrich type ii kerogen which suggests that the organic carbon there is mostly marine the low productivity of overlying waters rules out surface productivity as a possible cause of organic enrichment the association of higher hydrogen index hi values average 306 and higher organic carbon contents av 3 28 wt with the sediments of the upper slope in contact with the oxygen minimum zone omz clearly indicates enhanced preservation under reducing conditions in the anoxic waters of the omz it is suggested that the sediments of the upper slope in contact with the omz have excellent hydrocarbon generation potential and that these slope beds deserve preferential attention for hydrocarbon exploration

paleoproductivity and carbon burial across the california current the multitracers transect 42 n the multitracers experiment studied a transect of water column sediment trap and sediment data taken across the california current to develop quantitative methods for hindcasting paleoproductivity the experiment used three sediment trap moorings located 120 km 270 km and 630 km from shore at the oregon california border in north america we report here about the sedimentation and burial of particulate organic carbon corg and caco3 in order to observe how the integrated caco3 and corg burial across the transect has changed since the last glacial maximum we have correlated core from the three sites using time scales constrained by both radiocarbon and oxygen isotopes by comparing surface sediments to a two and a half year sediment trap record we have also defined the modern preservation rates for many of the labile sedimentary materials our analysis of the corg data indicates that significant amounts 20 40 of the total corg being buried today in surface sediments is terrestrial at the last glacial maximum the terrestrial corg fraction within 300 km of the coast was about twice as large such large fluxes of terrestrial corg obscure the marine corg record which can be interpreted as productivity when we corrected for the terrestrial organic matter we found that the mass accumulation rate of marine corg roughly doubled from the glacial maximum to the present because preservation rates of organic carbon are high in the high sedimentation rate cores corrections for degradation are straightforward and we can be confident that organic carbon rain rate new productivity also doubled as confirmation the highest burial fluxes of other biogenic components opal and ba also occur in the holocene productivity off oregon has thus increased dramatically since the last glacial maximum caco3 fluxes also changed radically through the deglaciation however they are linked not to caco3 production but rather to changes in deepwater carbonate chemistry between 18 ka and now

influence of water column anoxia on the burial and preservation of carbon and phosphorus in marine shales abstract organic p and organic c concentrations were measured in several well characterized phanerozoic marine shale sequences with the primary focus being the camp run member of the devonian mississippian new albany shale sequences were selected with close spatial association of bioturbated and laminated sediments which reflect deposition from oxic and anoxic waters respectively average organic c p mole ratios calculated from the data are 150 for bioturbated shales and 3900 for the laminated shales of the new albany differences in the extent and mechanisms of early diagenesis related to the oxygenation of waters at the sediment water interface can account for the c p ratios of buried organic matter low c p ratios of bioturbated sediments are attributed to 1 1 the increased ability of bacteria to store p in well oxygenated environments which leads to the production of low c p ratio bacterial biomass and 2 2 the extensive oxidation of sedimentary organic matter resulting in the formation of residual organic phases with low c p ratios high organic c p ratios of laminated sediments are explained by a combination of 1 1 the limited ability of bacteria to store p under anoxic conditions 2 2 extensive p regeneration from sedimentary organic matter 3 3 enhanced c preservation relative to the bioturbated shales it is also shown that relative to organic c laminated shales are not as effective a p sink as are bioturbated shales this provides a mechanism in anoxic environments for burying large quantities of organic matter without simultaneously sequestering the p needed to sustain further productivity

structural controls on gold bearing quartz mineralization in a duplex thrust system hyde macraes shear zone otago schist new zealand the hyde macraes shear zone in east otago new zealand is a low angle north to northeast dipping thrust system in which gold bearing quartz veins have been deposited mineralization accompanied deformation in the shear zone which is preferentially developed in graphitic pelitic schist the shear zone is a duplex system dominated by steep hinterland dipping thrust faults between well defined shallow dipping upper and lower bounding thrusts imbrication and stacking have occurred in the shear zone especially where intrashear schist is psammitic and relatively brittle this stacking contributes to lateral thickness changes from 2 up to 125 m mineralized veins formed mainly in dilational jogs or localized extensional zones on the relatively shallow dipping parts of the intrashear thrust faults late stage shallow south dipping extensional veins crosscut the duplex structures but are related to the same overall deformation from analysis of the shear zone structure it is possible to make predictions about the geometry of mineralized schist within unexposed parts of the shear zone this is a potentially useful tool for further prospecting and mining in hydrothermally mineralized duplex systems

geochemistry of au bearing pyrite from the sepon mineral district laos dpr southeast asia implications for ore genesis abstract the sepon gold copper district occurs along the truong son foldbelt in a 10 km 40 km east trending corridor in southern laos this study has investigated the nature of gold in pyrite and ore forming fluid characteristics using laser ablation inductively coupled plasma mass spectrometry la icp ms and proton induced x ray emission pixe techniques gold is present as invisible gold au 1 and as nanoparticles of gold au0 in both sedimentary rock hosted gold and skarn cu au deposits gold is present in an early syngenetic pyrite generation pyrite 2b with concentrations to 0 5 ppm post sedimentation processes included formation of quartz veins which host pyrite 3b with concentrations to 1 8 ppm au the highest concentrations of gold were found in the rims of hydrothermal vein hosted pyrite 4a and in skarn related pyrite suggesting gold concentration at a later stage during the ore forming processes and not during sedimentation as rhyodacite porphyry is proximal to calcareous shale and dolomite that host ores it is plausible that the emplacement of rhyodacite porphyry introduced significant amount of hydrothermal fluids that circulated through fractures and favoured high grade to 293 ppm au in pyrite 4a and pyrite skn2 gold is preferentially concentrated in as rich zones and in areas that underwent brittle deformation as evidenced by fracture fill coarse grained pyrite 4a indicating a structural control to ore formation the predominance of se bi and te in pyrite skn1 and the elevated concentrations of bi cu se sn and mo in pyrite skn2 raise the possibility of derivation from a magmatic source the presence of primary hematite associated with the skarn suggests prevailing oxidising fluid conditions during au mineralisation in pyrite skn2 there is a striking chemical similarity between pyrite 4a core and py skn1 and rimmed zones of pyrite 4a and pyrite skn2 which indicates possibility of two types of hydrothermal fluids the as rich fluids with elevated concentrations of au se sb tl and cu recorded in pyrite 4a rims and pyrite skn2 the as poor fluids with elevated concentrations of ni and pb yielded in pyrite 4a cores and pyrite skn1 the chemistry of pyrite has also shown that both ore forming fluids are undersaturated in au similar to au bearing pyrite in the carlin type deposits nevada usa

noble gases fingerprint a metasedimentary fluid source in the macraes orogenic gold deposit new zealand the world class macraes orogenic gold deposit 10 moz resource formed during the late metamorphic uplift of a metasedimentary schist belt in southern new zealand mineralising fluids metals and metalloids were derived from within the metasedimentary host helium and argon extracted from fluid inclusions in sulphide mineral grains three crush extractions from one sample have crustal signatures with no evidence for mantle input r ra 0 03 xenon extracted from mineralised quartz samples provides evidence for extensive interaction between fluid and maturing organic material within the metasedimentary host rocks with 132xe 36ar ratios up to 200 times greater than air similarly i cl ratios for fluids extracted from mineralised quartz are similar to those of brines from marine sediments that have interacted with organic matter and are ten times higher than typical magmatic mantle fluids the macraes mineralising fluids were compositionally variable reflecting either mixing of two different crustal fluids in the metasedimentary pile or a single fluid type that has had varying degrees of interaction with the host metasediments evidence for additional input of meteoric water is equivocal but minor meteoric incursion cannot be discounted the macraes deposit formed in a metasedimentary belt without associated coeval magmatism and therefore represents a purely crustal metamorphogenic end member in a spectrum of orogenic hydrothermal processes that can include magmatic and or mantle fluid input elsewhere in the world there is no evidence for involvement of minor intercalated metabasic rocks in the macraes mineralising system hydrothermal fluids that formed other smaller orogenic deposits in the same metamorphic belt have less pronounced noble gas and halogen evidence for crustal fluid rock interaction than at macraes but these deposits also formed from broadly similar metamorphogenic processes

microscale data to macroscale processes a review of microcharacterization applied to mineral systems microanalysis can provide rapid quantitative characterization of mineral systems that complements the field and core scale observations traditionally made in ore deposits we review recent innovations in microanalytical procedures and their application to studies of ore deposits case studies are presented examining how microanalysis can provide constraints on macroscopic processes within mineral systems synchrotron x ray fluorescence shows centimetre scale chemical variations associated with proximity to mineralization in samples from sunrise dam gold mine western australia pseudomorphs of igneous plagioclase and chemically driven recrystallization interpreted from electron backscatter diffraction suggest that the system was dominated by fluid driven brecciation with very little shearing both the fluid chemistry and fluid pressure evolved during a protracted sequence of vein formation and alteration accompanying gold mineralization a second case study of sulphide mineralogy at the mt keith nickel sulphide deposit western australia demonstrates how x ray computed tomography combined with trace element mapping can constrain the chemistry and dynamics of magmatic systems large scale interaction between silicate and sulphide melts shown by homogenous palladium enrichment in pentlandite leads to a large proportion of globular ores with a high nickel content increasing use of microanalysis in ore deposit geology is resulting in the constant reassessment of established models for ore genesis though a combination of micro and macroscale datasets

numerical modelling of mechanical controls on coeval steep and shallow dipping auriferous quartz vein formation in a thrust zone macraes mine new zealand the hyde macraes shear zone hmsz is a regionally continuous low angle ne dipping 15 late metamorphic thrust zone in the mesozoic otago schist the shear zone which is host to large volumes of mineralised schist consists of foliated fissile schist with some massive schist pods two sets of quartz veins are found within the hmsz thrust related shallowly dipping veins that were emplaced parallel or sub parallel to the shears and swarms of steeply dipping extensional veins which cut across the metamorphic foliation the latter are restricted to the massive schist pods mutual cross cutting relationships occur between steep extensional veins and shallow dipping veins suggesting that they formed contemporaneously the co existence of these two vein types locally implies local rotation of the principal stress axes to produce extensional veins within a regional thrust setting the steep extensional veins are spatially related to lateral and oblique ramps within the hmsz three dimensional mechanical models show that these lateral or oblique ramps can produce favourable conditions for extensional vein formation when combined with a high fluid pressure and oblique convergence mechanical requirements include a reduced differential stress a positive volumetric strain and an increase in the horizontal shear stress our models show that under certain conditions it is possible for extension related structures to form during shortening because of local changes in the stress state without the need for a regional scale switch in the imposed stress field the convergence direction across the hmsz during formation of the steep extensional veins was wnw

a novel selective extraction of barite and its application to eastern mediterranean sediments abstract a sequential extraction method basex was developed to determine the different ba fractions in sediments calibration of basex with pure barite and a home made mixed mineral standard showed that barite is separated from all other major ba containing mineral phases such as clay minerals and fe and mn oxides this method permits the direct determination of sedimentary barite content and of the ba al ratio of clay and is therefore a useful tool in palaeoclimatic studies application of basex to eastern mediterranean sediments including sapropel s1 revealed that the enrichment in ba concentrations observed in this sapropel consists predominantly of barite the relationship of barite ba with organic carbon in sapropel s1 sediments appears to be independent of water depth of organic matter fluxes and of the sedimentation rate for cores ranging from 2150 to 3300 m water depth apparently organic carbon remineralisation has been virtually absent in the water column deeper than 2150 m this might have been caused by suboxic to anoxic conditions present in the deep eastern mediterranean basin during the formation of sapropel s1 because of the constant relationship between barite and organic carbon in sapropelic sediments we suggest that the barite content can be used to quantify the initial organic carbon content of the sediment in the oxidised sapropel interval