reply to the comments by marignac and cathelineau on the paper by sanchez espana et al source and evolution of ore forming hydrothermal fluids in the northern iberian pyrite belt massive sulphide deposits sw spain evidence from fluid inclusions and stable isotopes mineralium deposita 38 519 537

post depositional tectonic modification of vms deposits in iberia and its economic significance the original stratigraphic relationships and structure of vms deposits are commonly obscured by deformation this can also affect their economic significance as shown by several iberian pyrite belt ipb sw iberia examples the contrasting rheologic properties of the different lithologies present in an orebody massive sulphide feeder stockwork alteration envelope volcanic and sedimentary rocks play a major role in determining its overall behaviour variscan thin skinned tectonics led to stacking of the massive pyrite and stockwork bodies in duplex structures resulting in local thickening and increased tonnage of minable mineralization furthermore differential mechanical behaviour of the different sulphide minerals localised the detachments along relatively ductile sulphide rich bands the result was a geochemical and mineralogical reorganisation of most deposits which now consist of barren massive pyrite horses bounded by base metal rich ductile shear zones metal redistribution was enhanced by mobilisation of the base metal sulphides from the initially impoverished massive pyrite through pressure solution processes to tensional fissures within the already ductile shear zones in nw iberia vms deposits were also strongly overprinted by the variscan deformation during emplacement of the cabo ortegal and ordenes allochthonous nappe complexes but no stacking of the orebodies was produced original contacts were transposed and the orebodies their feeder zones and the country rock acquired pronounced laminar geometry in lower grade rocks greenschist facies cabo ortegal complex solution transfer mechanisms are common in pyrite which remains in the brittle domain while chalcopyrite shows ductile behaviour in higher grade rocks amphibolite facies ordenes complex metamorphic recrystallisation overprints earlier deformation textures the contrasting behaviour of the ipb and nw iberian deposits is explained by key factors that affect their final geometry composition and economics such as pre deformation structure size and mineralogical composition of the orebody and associated lithologies temperature crustal level deviatoric stress and availability of a fluid phase during deformation and the style and rate of deformation

regional mapping of pre metamorphic spilitization and associated chemical mobility in greenschist facies metabasalts of the sw scottish highlands abstract both spilitic and non spilitic metabasaltic sills are hosted by greenschist facies metasediments in the sw scottish highlands spilitization is mainly characterized by enrichment in na 2 o elevated modal plagioclase and epidote segregations mapping of the spatial distribution of spilitic metabasalts reveals an ancient sub sea floor fluid cell centred on the extrusive tayvallich volcanics fluid circulation was most extensive at shallow levels where most sills were spilitized we attribute this to pervasive flow of saline fluid which was thermally driven by the cooling suite of lava flows and sills spilitization below this lithostratigraphic depth was restricted to only a few sills their spilitization is largely unrelated to specific properties of these sills e g width chemistry or host lithology we conclude that fluid channelling was an intrinsic property of sub sea floor fluid flow either at deeper levels or earlier during fluid circulation by profiling of the size distributions of relic phenocrysts in a partly spilitized sill we conclude that spilitization proceeds with the symmetric propagation of a spilitization front from the sill margins towards the sill interior based on chemical profiling across the margin of an epidote segregation we conclude that spilitization is associated with chemical transport on scales ranging from 0 1 to 10 m

controls on the siting and style of volcanogenic massive sulphide deposits abstract volcanogenic massive sulphide vms deposits form in subaqueous environments from circulating hydrothermal fluids heated by volcanic activity these deposits form as sulphide mounds stratiform exhalative and or replacive bodies and commonly have stockwork vein mineralization in their immediate footwall these various styles are essentially facies of mineralization each one being the product of a particular set of conditions that control the ore forming processes and the consequent geometry and architecture style of the deposits these controls include the physical and or chemical nature of the host rocks the temperature and composition of the hydrothermal fluids and the redox state of the depositional environment the style of exhalative deposits is controlled by the salinity of the vented fluids and the redox state at the seafloor hydrothermal fluids with salinities less than twice that of seawater that vented into open oxic oceanic environments typically formed small mound and chimney complexes unless they were rapidly covered by sediments or volcanic rocks the massive sulphides were rapidly oxidized and partly dissolved by seawater in contrast stratiform sheet like deposits are typically formed in anoxic bottom waters anoxic marine conditions were periodically of global extent particularly prior to 2 4 ga or of a regional nature local anoxic conditions can also be self induced by the exhalation of saline and reducing hydrothermal fluids that ponded in bathymetric depressions such as second or third order basins to form a brine pool these exhalative systems may have been initiated as chimney vent complexes and subsequently overlain by stratiform sulphides formed under the self induced anoxic conditions deposits formed in anoxic environments can be significantly larger than those in oxic settings and this is attributed to several factors that include longer lived hydrothermal circulation more efficient sulphide precipitation and reduced or inhibited oxidation thereof replacement of volcanic and sedimentary strata by sulphide typically occurs within the feeder zones beneath the exhalative mineralization however successions with abundant porous permeable and or reactive rocks such as glassy and or pumiceous volcaniclastic rocks and in some cases limestone favoured the development of large replacive deposits that may have had little surficial expression on the sea floor vms deposits at spreading centres within oceanic crust formed almost exclusively as mounds most of them have not been preserved likely due to oxidation of the sulphides in the prevailing oxic environment and or destruction of oceanic crust during subsequent subduction intra continental rifts arc rifts and back arc rifts commonly have more complexity in their structure and facies architecture and environments and can host all styles of vms mineralization in these settings early extension favoured the formation of restricted basins with ideal conditions for the onset of hydrothermal activity and development of anoxic bottom waters whereas in mature rifts the conditions were less conducive for the formation of regionally extensive anoxic environments formation of replacive deposits was permissible in all settings with porous or reactive subsea floor strata replacive mineralization is the most likely to be preserved in the geological record due to the sulphides being physically shielded from oxidative weathering and mechanical erosion at the seafloor the various styles of vms mineralization can rarely be distinguished using a single criterion in most cases multiple criteria are required mound style mineralization is distinguished by a mound or lens shaped morphology b presence of chimney fragments c presence of abundant sedimented sulphide breccias d location on a stratigraphic boundary ore horizon and e association with a thin horizon or thicker stratigraphic interval of fine grained clastic rocks e g shale mudstone that accumulated at slow sedimentation rates stratiform exhalative mineralization is distinguished by a sheet like morphology prior to deformation b presence of fine grained clastic host rocks that accumulated at relatively slow rates e g mudstone c presence of local or extensive planar stratification replacive mineralization is characterized by a irregular geometry and distribution of sulphide bodies b gradation from massive sulphides to semi massive sulphides and disseminated mineralization with relict textures of the host rock and c originally pumiceous glassy or reactive host rocks emplaced at high depositional rates mass flow deposits lavas carbonate altered mass flow deposits or limestone one deposit or district may comprise two or more of these main styles of mineralization in many cases the main styles of vms mineralization present in a particular region can be predicted from examination of the facies architecture and depositional environments of the host succession recognition of the style s of mineralization that occur in a particular basin or mineral belt enables exploration models to be improved and should influence the strategy of exploration for vms deposits

low temperature low pressure deformation and metamorphism of the vangorda massive sulphide orebody yukon canada the vangorda orebody is a small stratiform massive sulphide orebody located in anvil district yukon canada the orebody consists of fineto medium grained semi massive and massive sulphides with a common sulphide mineralogy of pyrite pyrrhotite sphalerite galena and minor chalcopyrite the host rocks and the sulphide lithofacies have been complexly deformed during two phases of deformation d1 and d2 and associated metamorphism m1 and m2 the effects of d1 and m1 are penetratively overprinted by d2 and m2 d2 and m2 resulted in tight to isoclinal f2 folding of the orebody remobilisation of the sulphides recrystallisation and development of shear zones along the limbs of the f2 folds chlorite thermometry and sulphide thermobarometry have been carried out on the host phyllites and on the sulphides chlorite was analysed from the s1 and s2 foliations in the phyllites to determine m1 and m2 temperatures respectively however no difference was found between chlorite compositions in these foliations and a mean temperature of 363 c was calculated from the tetrahedral a1iv occupancy arsenopyrite thermometry yielded a comparable mean temperature of 336 c sphalerite inclusions in m2 pyrite porphyroblasts from d2 shear zones were analysed for pressure using the sphalerite hexagonal pyrrhotite pyrite barometer inclusions were analysed in an attempt to determine if relic m1 sphalerite and hence pressure signature was preserved inclusion compositions appear to reflect only m2 conditions and yielded a mean pressure of 4 0 kb sphalerite hexagonal pyrrhotite assemblages were analysed from d2 shear zones to determine the m2 pressure using the sphalerite hexagonal pyrrhotite barometer these calculations yielded a mean pressure of 6 1 kb the m2 temperatures and pressures calculated using these calibrations are in good agreement with those estimated from petrogenetic relationships

millennial scale climate variability of the northeast pacific ocean and northwest north america based on radiolaria and pollen abstract radiolaria and pollen abundances in marine sediment cores from the northeast pacific are used to reconstruct oceanographic and continental climate change during the past glacial cycle 0 150 kyr these data allow direct comparison of the climate response of continental and oceanic systems detailed 18 o and ams 14 c measurements provide a link into global stratigraphic frameworks canonical correlation analysis extracts two modes of variation common to both the radiolaria and pollen records the first mode of variation correlates an assemblage of radiolaria associated with coastal upwelling with increased redwood western hemlock and alder pollen this association is consistent with the modern relationship between coastal upwelling coastal fog and redwood forests a second canonical mode relates an oceanic fauna now found in highest abundance in the far north pacific with reduced pine and western hemlock pollen abundance comparison of these records to an ice core 18 o record suggests that at wavelengths 3000 years warm events in greenland are correlated to intervals of increased coastal upwelling off oregon decreases in importance of very cold north pacific fauna suggesting warming and increases in pollen associated with wetter coastal environments radiolarian based sea surface temperature estimates suggest that the variability of the northeast pacific on this time scale is about 2 c warming in the coastal regions reflects reduced advection of the california current but is moderated by increases in cool coastal upwelling we infer that the response of the northeast pacific to millennial scale climate changes is related to changes in atmospheric circulation at mid to high latitudes preliminary analysis suggests that oceanic variability off oregon at wavelengths 18 o records this variability is associated with changes in subtropical faunal elements without similar changes in other faunal elements this finding suggests that unlike longer period millennial scale events the propagation of the shorter wavelength events to the northeast pacific is through subtropical or tropical teleconnections

paragenesis of cobalt and nickel in the black butte shale hosted copper deposit belt basin montana usa the black butte copper deposits formerly known as sheep creek are a group of sediment hosted laterally extensive cu co ag deposits hosted in dolomitic shale of the mid proterozoic newland formation copper cobalt mineralization occurs in zones of massive laminated pyrite that were locally reworked and infiltrated by cu rich fluids during early diagenesis cobalt along with substantial nickel and arsenic mainly occurs as impurities within early porous pyrite or as minute grains of sulpharsenides i e cobaltite glaucodot and or alloclasite later thermal events remobilized the co ni and as to form intergrowths of siegenite co ni 3s4 and tennantite the temperature of this later event is constrained by the mineralogical assemblage to have been relatively low between 125 and 225 c although many of the characteristics of sedex type deposits are present at black butte e g laterally extensive massive pyrite horizons interbedded black shales abundant barite and local phosphate horizons and rifted continental margin setting the lack of economic pb and zn mineralization in the main deposits and the abundance of cu with high co is more typical of sediment hosted stratiform copper deposits the neihart formation a hematitic quartz sandstone resting below the base of the belt supergroup may have been an important source bed for cu co ni ag fluids it is speculated that these fluids ideal for forming cu deposits were expelled along growth faults near the margin of the belt basin and deposited metals on or just below the sea floor in a setting that is typical of sedex deposits this unique mineral deposit model may have applications to other districts where cu co rich sulfides are deposited in an exhalative setting

textures of the hellyer volcanic hosted massive sulfide deposit tasmania the aging of a sulfide sediment on the sea floor the relatively undeformed polymetallic massive sulfide ore of the hellyer deposit retains many textures developed during the early crystallization history common textures in the least modified ore away from the main feeder zone include pyrite framboids concentric and radial textured spheres dendritic and fibrous forms breccias mineral banding veins and reniform and crustification textures many are typical of early crystallization within a medium at high degrees of supersaturation some result from open space filling and others indicate disturbances of the sulfide mass possibly due to tectonic activity and volume adjustment the banding could be due to current winnowing most of these textures are found in modern midocean ridge and kuroko massive sulfide deposits but at hellyer the framboids are much more common hexagonal outlines in ore sphalerite indicate derivation of much of the sphalerite by inversion of wurtzite the high content of chalcopyrite in the wurtzite derived sphalerite appears in most cases to have developed by exsolution rather than replacement or coprecipitation although there is local evidence of both processes having operated possibly resulting from early asymmetrical crystal growth comparison of hellyer ore and typical kuroko ores reveals other differences than framboid abundance e g metal contents and ratios mineralogy and sulfur isotope compositions the most significant of which are the relatively high salinities of the hellyer ore fluids these together with evidence of a coeval basin imply sulfide deposition in a brine pool as previously proposed the development of a quenched sulfide mud at the bottom of a basin filled with spent ore fluid with little or no involvement of seawater explains the different mineral content e g lack of fe oxides scarcity of barite in the massive sulfide and the pyrite arsenopyrite assemblage the high metal content lack of chimney structures and differences in sulfur isotope compositions the sulfide mud dominated by fe s phases would be an ideal growth medium for framboidal pyrite the weight of experimental evidence concerning the development of framboidal pyrite points to involvement of metastable precursor fe s phases such as mackinawite and greigite in a weakly oxidized environment oxygen may have been added to the reduced acid brine pool as a result of inward diffusion of oxygen from overlying seawater which is shown to have been oxic by the presence of sessile benthic dendroids in the shales overlying the ore deposit however the level of oxidation was insufficient to form marcasite

stratigraphy of the tectonically imbricated lithological succession of the neves corvo mine area iberian pyrite belt portugal biostratigraphic research based on palynomorphs and ammonoids of the tectonically imbricated lithological succession of the neves corvo mine in the portuguese part of the iberian pyrite belt has yielded ages for all formerly recognised lithostratigraphic units these can be assembled in three main lithological sequences 1 detrital sandy shale substrate phyllite quartzite formation of late famennian age 2 volcano sedimentary complex divided into a lower and an upper suite in which one basic three dolerite sills and four felsic volcanic units and a mineralised package of massive sulphides are identified with ages which range from the late famennian to the late visean 3 flysch succession mertola formation composed of shale and greywacke dated as late visean to early serpukhovian precise biostratigraphic dating of the sedimentrary host rocks of massive sulphide mineralisation constrains the age of the latter to the late strunian 354 8 354 0 ma three stratigraphic hiatuses corresponding to early middle strunian tournaisian and early visean respectively and a south westward progressive unconformity were also recognised sequences 1 and 2 are related to extensional episodes while sequence 3 marks the beginning of compressive tectonic inversion which gave rise to south westward flysch progradation in close relation to a foreland basin development our results lead to the reinterpretation of the tectonic structure of the neves corvo mine with implications for the interpretation of the regional basin dynamics and metal exploration

a new sulphur isotopic study of some iberian pyrite belt deposits evidence of a textural control on sulphur isotope composition the sulphide deposits of the iberian pyrite belt ipb represent an ore province of global importance our study presents 113 new sulphur isotope analyses from deposits selected to represent the textural spectrum of ores measured 34s values range from 26 to 10 mostly for massive and stockwork ores in agreement with data previously published in situ laser 34s analyses reveals a close correlation of 34s with texture primary diagenetic textures are dominated by relatively low 34s 8 to 2 whereas stockwork feeder textures are dominated by higher 34s 3 to 5 intermediate textures mainly coarse textures in stratiform zones have intermediate 34s although they are mostly dominated by the high 34s component rare barite has a homogeneous 34s around 18 which is consistent with direct derivation from lower carboniferous seawater sulphate a dual source of sulphide sulphur in the ipb deposits has been considered a hydrothermal source derived from reduction of coeval seawater sulphate in the convective systems is represented by sulphide in the feeder zones here variations in 34s are caused by variations in the extent of the sulphate reduction which governs the so4 h2s ratio the second end member was derived from the bacterial reduction of coeval seawater sulphate at or near the surface as reflected in the primary textures a distinct geographical variation in 34s and texture from sw more bacteriogenic and primary textures to ne more hydrothermal textures and 34s which reflects a variation in the relative input of each source was likely controlled by local geological environments given that the sulphur isotope characteristics of the ipb deposits are unlike most vms and kuroko deposits and noting the dominance of a mixed reduced sedimentary and volcanic environment we suggest that the ipb could represent an ore style which is intermediate between volcanic and sedimentary hosted massive sulphide types

a comparison of the horne volcanogenic massive sulfide deposit and intracauldron deposits of the mine sequence noranda quebec most of the massive sulfide deposits of the rouyn noranda area are associated with rhyolite and andesite flows of the mine sequence and occur within the noranda cauldron a volcanic subsidence structure related to partial evacuation of an underlying magma chamber the flavrian pluton the horne massive sulfide orebodies lie within a sequence of rhyolitic breccias located just south of the inferred margin of the subsidence structure and are separated from the mine sequence by the horne creek fault traditionally the horne deposits and the intracauldron deposits have been interpreted to occur within the same stratigraphic interval even though they share some characteristics such as mineral zoning patterns alteration assemblages and an association with synvolcanic faults the two deposit groups are clearly distinguishable intracauldron massive sulfide deposits are small 5 mt cu zn rich concordant mounds associated with interflow horizons and are closely linked to vent zones where synvolcanic faulting provided hydrothermal fluids with cross stratal structural permeability the three major sulfide deposits at the horne mine are much larger 20 150 mt and formed in a fault bounded sediment filled graben on the flank of a rhyolitic vent complex the orebodies are au cu rich but zn poor and have bowl shaped morphologies which resulted from extensive subsea floor sulfide precipitation whereas the intracauldron sulfide deposits lie within a bimodal flow dominated succession consisting mainly of andesite basalt and high silica rhyolite with volumetrically insignificant pyroclastic rocks the horne orebodies occur in felsic fragmental rocks and rhyolite flows which are part of a stratigraphic sequence which contains virtually no mafic volcanic rocks also compared to all intracauldron rhyolites the horne rhyolites show a fundamental depletion in incompatible trace elements such as the high field strength and rare earth elements which implies that the horne rhyolites may have followed a different magmatic evolutionary path such differences in deposit characteristics their paleoenvironments of formation and the physical volcanology and geochemistry of their host volcanic successions suggest that contrary to previous interpretations the massive sulfide deposits of the intracauldron mine sequence and those of the horne sequence may have formed at different stages in the evolution of the noranda cauldron

the experimental ductile deformation of polycrystalline and single crystal pyrite polycrystalline pyrite deformed in triaxial compression tests at a confining pressure of 300 mpa strain rates of 10 super 4 sec super 1 to 10 super 5 sec super 1 and temperatures above about 450 degrees c shortens by dislocation flow mechanisms above 500 degrees c dynamic recovery and recrystallization are important and steady state flow is attained after 10 to 20 percent shortening the dynamically recrystallized grain size d in mu m is related to the flow stress sigma by the relationsigma g k d b super 0 9 where k 16 2 g 7 8 x 10 4 mpa and b 5 42 x 10 super 4 mu m below about 450 degrees c polycrystalline pyrite deforms by brittle mechanisms after less than a few percent strain by dislocation flow the strength of polycrystalline pyrite decreases significantly with increasing temperature and decreasing strain rate over the temperature interval 500 degrees to 700 degrees c at strain rates of 2 x 10 super 5 sec super 1 the steady state flow stress drops from about 500 to 70 mpa pyrite single crystals shortened in the and orientations at 600 degrees c about 10 super 5 sec super 1 and 300 mpa confining pressure exhibit three stage work hardening behavior in which the stage 2 work hardening rates are nearly as high as the elastic modulus for shortening the yield stress 280 mpa and the differential stress at the commencement of stage 3 800 mpa are several times larger than for shortening the strength during shortening is comparable to that of the polycrystalline pyrite tested the single crystal strength data structural considerations and transmission electron microscopy suggest that 100 and possibly 100 are major slip systems the 110 dislocation glide may also be important but has a critical resolved shear stress several times higher than 100 glide the present data indicate that pyrite can be considerably weaker and more ductile than indicated by previous studies and that pyrite is likely to be deformed by dislocation flow mechanisms under a range of geologically realistic conditions

active and relict sea floor hydrothermal mineralization at the tag hydrothermal field mid atlantic ridge the tag hydrothermal field is a site of major active and inactive volcanic hosted hydrothermal mineralization in the rift valley of the slow spreading mid atlantic ridge at 26 degree n the axial high is the principal locus of present magmatic intrusions the tag field contains three main areas of present and past hydrothermal activity 1 an actively venting high temperature sulfide mound 2 two former high temperature vent areas 3 a zone of low temperature venting and precipitation of fe and mn oxide deposits the volcanic centers occur at the intersections between ridge axis parallel normal faults and projected axis transverse transfer faults the intersections of these active fault systems may act as conduits both for magmatic intrusions from sources beneath the axial high that build the volcanic centers and for hydrothermal upwelling that taps the heat sources radiometric dating of sulfide samples and manganese crusts in the hydrothermal zones and dating of sediments intercalated with pillow lava flows in the volcanic center adjacent to the active sulfide mound indicate multiple episodes of hydrothermal activity throughout the field driven by heat supplied by episodic intrusions over a period of at least 140 times 10 sup 3 yr the sulfide deposits are built by juxtaposition and superposition during relatively long residence times near episodic axial heat sources counterbalanced by mass wasting in the tectonically active rift valley of the slow spreading oceanic ridge hydrothermal reworking of a relict hydrothermal zone by high temperature hydrothermal episodes has recrystallized sulfides and concentrated the first visible primary gold reported in a deposit at an oceanic ridge

isotopic exchange in mineral fluid systems ii oxygen and hydrogen isotopic investigation of the experimental basalt seawater system abstract oxygen and hydrogen isotopic exchange reactions between basalt and seawater at t 300 to 500 c were investigated using oceanic tholeiitic basalt 18 o 5 7 d 70 natural seawater 18 o 1 2 d 5 and artificial seawater 18 o 5 3 as starting materials the starting basalts varied in the crystallinity from holocrystalline to glass but were ground to approximately the same grain size 100 mesh the water rock mass ratios ranged from 1 to 3 and the duration of the experiments ranged from 167 to 576 days in general depletion of 18o and enrichment of d in basalts occur at all temperatures with the magnitudes of change being greater as temperature time and to a lesser degree glass content increases the trends in isotopic shifts are directly related to changes in the style and intensity of mineralogic alterations in the basalt e g smectite at 300 c talc actinoiite at 400 500 c the changes in the 18 o values of basalts and seawater in the experimental systems were observed to follow closely with those expected from a first order rate law rate constants for the oxygen isotopic exchange between rock and water range from 10 9 5 to 10 8 0 moles oxygen m2 of solid surface sec for temperatures of 300 to 500 c the activation energy for the isotopic exchange reaction was calculated to be 11 5 kcal mol an application of our experimental rate data to natural systems suggests that the oxygen isotope equilibrium between basalt and seawater in the mid oceanic ridge may take place within approximately 1000 years at 350 c our experimental data also suggest the equilibrium oxygen isotopic fractionation factors between the altered basalt and seawater to be 3 5 0 5 at 300 c 2 0 0 4 at 400 c and 0 5 0 25 at 500 c the observed hydrogen isotopic fractionation factors between the altered basalts and seawater in our experimental systems were about 74 at 300 c about 62 at 400 c and about 48 at 500 c these fractionation factors are probably attributable to the equilibrium fractionation between fe rich secondary phases and seawater

late glacial to holocene changes in winds upwelling and seasonal production of the northern california current system abstract a core 120 km off the coast of southern oregon was examined for changes in lithology diatoms and pollen over the past 30 000 yr primary production during the late pleistocene was about half that of the holocene evidence from diatoms and pollen indicates that summer upwelling was much weaker implying an absence of strong northerly winds early pliocene diatoms found throughout the late pleistocene section were probably derived from diatomites east of the cascades and provide evidence for strong easterly winds over a dry continental interior the findings verify predictions of a climate model based on glacial maximum conditions there is no compelling evidence for a climatic reversal corresponding to the european younger dryas chron during the early holocene 9000 7000 yr b p there may have been years when winds were insufficiently strong to support upwelling so that warm stratified waters lay closer to the coast

the california current system off monterey california physical and biological coupling repeated hydrobiological surveys over the period 1988 2002 perpendicular to the central california coast indicate strong coupling between physical circulation and biological production an equatorward flowing jet about 100 200 km from shore marked the inshore edge of the california current cc this cc jet had its highest velocities during late winter and spring the jet divided inshore biologicallyproductive waters from offshore low production waters mean flow in the inshore waters is poleward however this flow is interrupted in late spring and summer bya surfaceenhanced equatorward flowing coastal upwelling jet the upwelling jet coincides with maxima of nutrients chlorophyll a and primaryproduction annual variabilityin the inshore zone is related to 1 vertical py cnocline movements associated with geostrophic adjustments to accelerations of the california current system and 2 coastal upwelling in offshore waters the annual cycle accounted for a small fraction of the variability indicating the dominance of eddies and meanders in this zone j geophys res 92 1987 12 947 the offshore regime was mesotrophic to oligotrophic with a subsurface chlorophyll a maximum above the nutricline considerable subduction mayoccur under the california current jet and be an important process in the export of biogenic material to the deep sea published byelsevier ltd

a holocene record of ocean productivity and upwelling from the northern california continental slope abstract the holocene upwelling history of the northern california continental slope is examined using the high resolution record of tn062 o550 40 9 n 124 6 w 550 m water depth this 7 m long marine sediment core spans the last 7500 years and we use it to test the hypothesis that marine productivity in the california current system ccs driven by coastal upwelling has co varied with holocene millennial scale warm intervals a combination of biogenic sediment concentrations opal total organic c and total n stable isotopes organic matter 13c and bulk sedimentary 15n and key microfossil indicators of upwelling were used to test this hypothesis the record of biogenic accumulation in tn062 o550 shows considerable holocene variability despite being located within 50 km of the mouth of the eel river which is one of the largest sources of terrigenous sediment to the northeast pacific ocean margin a key time interval beginning at 2900 calibrated years before present cal yr bp indicates the onset of modern upwelling in the ccs and this period also corresponds to the most intense period of upwelling in the last 7500 years when these results are placed into a regional ccs context during the holocene it was found that the timing of upwelling intensification at tn062 o550 corresponds closely to that seen at nearby odp site 1019 as well as in the santa barbara basin of southern california other ccs records with less refined age control show similar results which suggest late holocene upwelling intensification may be synchronous throughout the ccs based on the strong correspondence between the alkenone sea surface temperature record at odp site 1019 and the onset of late holocene upwelling in northern california we suggest that ccs warming may be conducive to upwelling intensification though future changes are unclear as the mechanisms forcing sst variability may differ

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

geology of the bousquet 2 mine an example of a deformed gold bearing polymetallic sulfide deposit the bousquet 2 mine is a deformed pyritic polymetallic archean gold deposit located within a zone of intense ductile brittle deformation composed of highly sheared and altered metamorphic tectonites of contrasting rheological properties the ore occurs in a metamorphosed zone of aluminous alteration and is composed of foliation parallel massive and semimassive pyritic lenses overprinted by late en echelon extensional veinlets containing au ag cu mineralization structural and textural analyses show that the gold bearing sulfide bodies and enclosing host rocks contain discrete tectono metamorphic features resulting from two principal episodes of metamorphism m 1 and m 2 the earlier prograde event m 1 and coeval regional deformation d 1 were accompanied by overall ductile deformation of sulfides and by recrystallization and remobilization of the mineralization parallel to foliation m 1 caused development of a pervasive east west trending metamorphic layering of the pyritic mineralization transposition and elongation of the pyritic bodies parallel to mineral stretching l 1 lineations meter scale folding of sulfides sulfide brecciation coarsening and annealing recrystallization of pyrite and ductile remobilization of incompetent sulfides and gold into interstices and triple point junctions of juxtaposed pyrite grains extensive differential remobilization of ductile sulfides mainly sphalerite pyrrhotite galena chalcopyrite chalcocite and bornite and gold took place during m 1 and gave rise to planar zones enriched in au ag cu mineralization along the interfaces of pyritic lenses and their adjacent silicate rocks m 2 metamorphism is chronologically related to a late brittle incremental stage of the progressive deformation and is characterized by high fluid influx pervasive retrogression of peak metamorphic minerals and remobilization of sulfides and gold into transgressive structures the retrograde mineralization displays a wide range of small scale structures resulting from fluid assisted remobilization of ductile sulfides including piercement and injection structures as well as foliation oblique extensional veinlets metamorphic remobilization of ore constituents took place mainly at ore wall rock interfaces fe pb zn and au ag cu bearing extensional veinlets generally occur in foliation parallel protores of similar mineralogical composition and are interpreted as having resulted from in situ metamorphic remobilization gold and copper show a corelationship throughout the deposit the highest gold and copper values occur within extensional veins overprinting previously au cu enriched planar zones mineralogical zoning in the sulfide masses is structurally controlled and can be related directly to abundant au cu bearing veinlets that represent mineralized segments of a systematic joint system structural and textural evidence suggests that gold mineralization with its present textural relations formed during m 1 and m 2 but that a large proportion of the structurally controlled vein mineralization resulted from in situ remobilization rather than from additions from an external source

high resolution climatic evolution of coastal northern california during the past 16 000 years holocene and latest pleistocene oceanographic conditions and the coastal climate of northern california have varied greatly based upon high resolution studies ca every 100 years of diatoms alkenones pollen caco 3 and total organic carbon at ocean drilling program odp site 1019 41 682 n 124 930 w 980 m water depth marine climate proxies alkenone sea surface temperatures ssts and caco 3 behaved remarkably like the greenland ice sheet project gisp 2 oxygen isotope record during the balling allerod younger dryas yd and early part of the holocene during the yd alkenone ssts decreased by 3 c below mean bolling allerod and holocene ssts the early holocene ca 11 6 to 8 2 ka was a time of generally warm conditions and moderate caco 3 content generally 4 the middle part of the holocene ca 8 2 to 3 2 ka was marked by alkenone ssts that were consistently 1 2 c cooler than either the earlier or later parts of the holocene by greatly reduced numbers of the gyre diatom pseudoeunotia doliolus 10 and by a permanent drop in caco 3 to 3 starting at ca 5 2 ka coastal redwood and alder began a steady rise arguing for increasing effective moisture and the development of the north coast temperate rain forest at ca 3 2 ka a permanent ca 1 c increase in alkenone sst and a threefold increase in p doliolus signaled a warming of fall and winter ssts intensified higher amplitude and more frequent cycles of pine pollen alternating with increased alder and redwood pollen are evidence that rapid changes in effective moisture and seasonal temperature enhanced el nino southern oscillation enso cycles have characterized the site 1019 record since about 3 5 ka

source and evolution of ore forming hydrothermal fluids in the northern iberian pyrite belt massive sulphide deposits sw spain evidence from fluid inclusions and stable isotopes a fluid inclusion and stable isotopic study has been undertaken on some massive sulphide deposits aguas tenidas este concepcion san miguel san telmo and cueva de la mora located in the northern iberian pyrite belt the isotopic analyses were mainly performed on quartz chlorite carbonate and whole rock samples from the stockworks and altered footwall zones of the deposits and also on some fluid inclusion waters homogenization temperatures of fluid inclusions in quartz mostly range from 120 to 280 c salinity of most fluid inclusions ranges from 2 to 14 wt nacl equiv a few cases with th 80 110 c and salinity of 16 24 wt nacl equiv have been also recognized in addition fluid inclusions from the soloviejo mn fe jaspers 160 190 c and 6 wt nacl equiv and some late to post hercynian quartz veins 130 270 c and 4 wt nacl equiv were also studied isotopic results indicate that fluids in equilibrium with measured quartz 18ofluid 2 to 4 chlorites 18ofluid 8 14 dfluid 45 to 27 whole rocks 18ofluid 4 7 dfluid 15 to 10 and carbonates 18oankerite 14 5 16 13cfluid 11 to 5 evolved isotopically during the lifetime of the hydrothermal systems following a waxing waning cycle at different temperatures and water rock ratios the results fluid inclusions 18o d and 13c values point to a highly evolved seawater along with a variable but significant contribution of other fluid reservoirs such as magmatic and or deep metamorphic waters as the most probable sources for the ore forming fluids these fluids interacted with the underlying volcanic and sedimentary rocks during convective circulation through the upper crust

shale basins sulfur deficient ore brines and the formation of exhalative base metal deposits abstract the massive sulfide deposits of the iberian pyrite belt are interbedded with felsic volcanic rocks and shale and underlain by several thousand meters of siliciclastic sedimentary rocks known as the pq group isotope geochemistry and regional geology are both consistent with equilibration of the ore forming fluids with the pq group prior to ore deposition near the former seafloor the average cu zn pb ratio of the pq group rocks ca 26 55 19 is similar to the weighted average of all the massive sulfide orebodies combined ca 25 52 23 the genetic relationship between massive sulfide deposits and a siliciclastic sedimentary metal source is explained here by a thermodynamic model proposing that mildly reducing redox conditions imposed by equilibration with the sedimentary rocks are most critical for the formation of an effective ore forming fluid relatively metal rich but organic poor pyrite bearing shale undergoing dewatering of saline pore fluids is an effective source for the generation of sulfur deficient but relatively iron and base metal rich brines thus we propose that the giant deposits of the iberian pyrite belt owe their existence not to exceptionally metal enriched e g magmatic fluids but to the existence of a fairly ordinary but large metal source in reactive siliciclastic sediments combined with an underlying igneous heat source and a particularly efficient mechanism of sulfide precipitation by mixing with h 2 s rich fluids at or near the seafloor essentially similar mineral equilibria are imposed when saline fluids are buffered by typical continental basement rocks leaching of retrograde minerals and possibly residual salts from their magmatic or metamorphic prehistory is expected to generate similar variably metal rich but relatively sulfide deficient fluids thus the existence of mildly reducing rocks can be the dominant chemical control in the source of fluids generating many volcanogenic irish type or sedex deposits many of which are known to precipitate their metal load in response to biogenic sulfide addition at the ore deposition site

formation of volcanogenic massive sulfide deposits the kuroko perspective abstract the main objective of this paper is to identify the geochemical hydrological igneous and tectonic processes that led to the variations in the physical size geometry and chemical mineralogy metal ratios and zoning characteristics of volcanogenic massive sulfide deposits with respect to space from a scale of mining district size area to a global scale and time from a all volcanogenic massive sulfide deposits vmsds appear to have formed in extensional tectonic settings such as at mid ocean spreading centers backarc spreading centers and intracontinental rifts and failed rifts all vmsds appear to have formed in submarine depressions by seawater that became ore forming fluids through interactions with the heated upper crustal rocks submarine depressions especially those created by submarine caldera formation and or by large scale tectonic activities e g rifting become most favorable sites for the formation of large vmsds because of hydrological physical and chemical reasons the fundamental processes leading to the formation of vmsds include the following six processes 1 1 intrusion of a heat source typically a 10 3 km size pluton into an oceanic crust or a submarine continental crust causes deep convective circulation of seawater around the pluton the radius of a circulation cell is typically 5 km the temperature of fluids that discharge on the seafloor increases with time from the ambient temperature to a typical maximum of 350 c and then decreases gradually to the ambient temperatures in a time scale of 100 to 10 000 years the majority of sulfide and sulfate mineralization occurs during the waxing stage of hydrothermal activity 2 2 reactions between low temperature t 2 4 as disseminated gypsum and anhydrite in the country rocks 3 3 reactions of the modified seawater with higher temperature rocks at depths during the waxing stage cause the transformation of the seawater to metal and h 2 s rich ore forming fluids the metals and sulfide sulfur are leached from the county rocks the previously formed gypsum and anhydrite are reduced by fe 2 bearing minerals and organic matter providing additional h 2 s the mass of high temperature rocks that provide the metals and reduced sulfur is typically 10 11 tons 40 km 3 in volume the roles of magmatic fluids or gases are minor in most massive sulfide systems except for so 2 to produce acid type alteration in some systems 4 4 reactions between the ore forming fluids and cooler rocks in the discharge zone cause alteration of rocks and precipitation of some ore minerals in the stockwork ores 5 5 mixing of the ore forming fluids with local seawater within unconsolidated sediments and or on the seafloor causes precipitation of primitive ores with the black ore mineralogy sphalerite galena pyrite barite anhydrite 6 6 reactions between the primitive ores with later and hotter hydrothermal fluids cause transformation of primitive ores to matured ores that are enriched in chalcopyrite and pyrite variations in the mineralogical and elemental characteristics the geometry and the size of submarine hydrothermal deposits are controlled by the following four parameters 1 a the chemical and physical characteristics of seawater composition temperature density which depend largely on the geographical settings e g equatorial evaporating basins 2 b the chemical and physical characteristics of the plumbing system lithology fractures 3 c the thermal structure of the plumbing system which is determined largely by the ambient geothermal gradient and the size and temperature of the intrusive and 4 d the physical characteristics of the seafloor depth basin topography for example the submarine hydrothermal deposits developed in basaltic plumbing systems are generally poor in pb and ba compared to those developed in felsic plumbing systems the lower temperature systems are generally poorer in sulfides but richer in iron oxides and sulfates the higher temperature and larger hydrothermal systems tend to produce chalcopyrite and pyrite rich ores contrasts in the metal ratios between the noranda type archean vmsds and the younger vmsds reflect the differences in the geothermal gradient of the plumbing systems the submarine hydrothermal deposits developed in the near equatorial regions tend to form large continuous bedded type ores because of the likeliness of creating large stratified basins the basic processes of submarine hydrothermal mineralization have remained essentially the same throughout the geologic history from at least 3 5 billion year ago to the present

ore genesis age of the tharsis mining district iberian pyrite belt a palynological approach massive sulphide deposits of the tharsis mining district iberian pyrite belt are included in a black shaly series that is stratigraphically conformable with the underlying phyllite quartzite group well preserved palynomorph assemblages have been obtained from this shaly series the miospore assemblages are assigned to the ln biozone indicating a latest devonian age this is consistent with the re os age of 348 6 12 3 ma from both massive sulphides and stockwork mineralization palynological and isotopic results from elsewhere in the pyrite belt are similar suggesting that mineralization was synchronous throughout the region

comparison of rio tinto spain and guaymas basin gulf of california an explanation of a supergiant massive sulfide deposit in an ancient sill sediment complex the volcano sedimentary unit that hosts the stratiform massive sulfide mineralization at rio tinto is reinterpreted as a sill sediment complex that in many respects is analogous to the example that is currently forming in the guaymas basin gulf of california however rio tinto is distinctive because 1 it is a product of bimodal magmatism 2 it has a much higher sill sediment ratio 4 1 lessening the extent of ore forming metal depletion during interaction between hydrothermal fluid and wet sediment and 3 most of the sills were emplaced penecontemporaneously as shown by the ubiquitous development of peperitic sill margins despite the narrowness of the sedimentary screens these data together with evidence for local extrusive behavior imply rapid formation of the complex at exceptionally high levels of emplacement it follows that in the complex variations in thickness of 400 m were directly expressed as basin floor deformation and that troughs in the resultant topography were able to trap exhalative hydrothermal plumes thus preserving the sulfides from dispersion also crucial to the mineralization process was the sheetlike form of the sill complex which by acting as a cap prevented regular convective cell patterns from forming and focused considerable discharge at areas of weakness the intense magmatic pulse the creation of pronounced topography and the capping of the hydrothermal system combined to make a 500 mt supergiant deposit

the role of granites in volcanic hosted massive sulphide ore forming systems an assessment of magmatic hydrothermal contributions assessment of geological geochemical and isotopic data indicates that a significant subgroup of volcanic hosted massive sulphide vhms deposits has a major or dominant magmatic hydrothermal source of ore fluids and metals this group which is typically characterised by high cu and au grades includes deposits such as those in the neoarchean doyon bousquet laronde and cambrian mount lyell districts these deposits are distinguished by aluminous advanced argillic alteration assemblages or metamorphosed equivalents intimately associated with ore zones in many of these deposits 34ssulphide is low with a major population below 3 34ssulphate differs from coexisting seawater and 34ssulphate sulphide 20 30 these characteristics are interpreted as the consequence of disproportionation of magmatic so2 as magmatic hydrothermal fluids ascended and cooled and as a definitive evidence for a significant magmatic hydrothermal contribution other characteristics that we consider diagnostic of significant magmatic hydrothermal input into vhms ore fluids include uniformly high 3 times modern seawater values salinities or very 18o enriched 18o 5 ore fluids we do not consider other criteria e g variable salinity moderately high 18ofluid 2 5 34ssulphide near 0 metal assemblages or a spatial association with porphyry cu or other clearly magmatic hydrothermal deposits that have been used previously to advocate significant magmatic hydrothermal contributions to be diagnostic as they can be produced by non magmatic processes known to occur in vhms mineral systems however in general a small magmatic hydrothermal contribution cannot be excluded in most vhms systems considered conclusive data that imply minimal magmatic hydrothermal contributions are only available in the paleoarchean panorama district where coeval seawater dominated and magmatic hydrothermal systems appear to have been physically separated this district which is characterised by chloritic and sericitic alteration assemblages and lacks aluminous advanced argillic alteration assemblages is typical of many vhms deposits around the world suggesting that for garden variety vhms deposits a significant magmatic hydrothermal contribution is not required other than deposits associated with advanced argillic alteration assemblages the only deposit for which we ascribe a major magmatic hydrothermal contribution is the devonian neves corvo deposit this deposit differs from other deposits in the iberian pyrite belt and around the world in being extremely sn rich with the sn closely associated with cu and in having formed from high 18o rich fluids 18ofluid 8 5 we consider these characteristics particularly the last as diagnostic of a significant magmatic hydrothermal contribution our analysis indicates that two subgroups of vhms deposits have a major magmatic hydrothermal contribution cu au rich deposits with aluminous alteration assemblages and reduced very sn rich deposits in which sn was introduced in a high temperature ore assemblage comparison with normal vhms deposits suggests that these subgroups of vhms deposits may form in specialised tectonic environments the cu au rich deposits appear to form adjacent to magmatic arcs an environment conducive to the generation of hydrous oxidised melts by melting metasomatised mantle in the wedge above the subducting slab this contrasts with the back arc setting of normal vhms deposits in which relatively dry granites in this contribution we use the term granite sensu latto formed by decompression melting drive seawater dominated hydrothermal circulation the tectonic setting of highly sn rich vhms deposits such as neves corvo is less clear however thick continental crust below the ore hosting basin may be critical as it is in other sn deposits

bismuth and cobalt minerals as indicators of stringer zones to massive sulphide deposits iberian pyrite belt the stringer zones and commonly the interaction zone at the base of the massive sulphide mounds in the iberian pyrite belt contain bismuth and cobalt minerals that are not found in the overlying massive sulphides these are fairly rare cobalt sulphoarsenides cobaltite alloclasite galucodot that were formed at the beginning of the massive sulphide genesis and fairly common bismuth sulphides bismuthinite hammarite wittichenite cosalite kobellite joseite etc including species rare at world scale nuffieldite giessenite jaskolskiite that were deposited from last stage high temperature 300 c copper bearing fluids containing bi te se the last stage fluids precipitated chalcopyrite containing cu bi te se sulphosalts at the base of the sulphide mound to form a high cupriferous zone their interaction with the massive sulphides is reflected by the formation of an exchange zone a few metres thick showing chalcopyrite disease textures at the base of the mound this zone forms the upper limit of potentially economic copper enrichment and of bismuth minerals gold is undoubtedly in part if not totally related to this last phase the bismuth concentrations being equivalent in the massive sulphides and the stringers the presence of bismuth minerals in the stringer zones results from high temperature conditions combined with a rarity of galena which impedes absorption of available bi the distribution of these bismuth minerals provides a basic mineralogical zoning in the stringer zone with a deep low as2 zone containing native bismuth and tellurides and a shallow higher as2 zone in contact with the massive ore sensu stricto and containing complex bismuth sulphides these results make it possible to distinguish between sulphide veinlets belonging to stockwork zones of massive orebodies and veinlets of an ambiguous nature and provide mineralogical criteria for the proximity of copper rich zones they enrich the very complex mineralogy of the iberian pyrite belt

response of diatom and silicoflagellate assemblages to climate change in the santa barbara basin during the past 178 years and the rise of the toxic diatom pseudo nitzschia australis

evolution and source of ore fluids in the stringer system hellyer vhms deposit tasmania australia evidence from fluid inclusion microthermometry and geochemistry the hellyer deposit is a classic large tonnage high grade mound style volcanic hosted massive sulphide vhms deposit in the cambrian mt read volcanic belt of western tasmania in the footwall directly underlying the deposit there is an extensively altered pipe which cootains a well developed and preserved stringer zone the vein paragenesis at hellyer indicates that premineralization stage i veins consist entirely of quartz and occur throughout the alteration pipe the synmineralization stage 2 veins are the most abundant veins in the stringer zone and consist of three sub stages stage 2a veins of crustiform quartz pyrite and carbonate with minor amounts of chalcopyrite sphalerite and galena stage 2b veins with abundant base metal sulphides minor quartz carbonate and barite gangue and stage 2c veins of coarsely crystalline barite with variable amounts of pyrite sphalerite galena and carbonate stages 3 6 veins are postmineralization veins and are related to the devonian tabberabberan orogeny textural petrographic and microthermometric investigations of fluid inclusions in the hellyer stringer system indicate that type i primary liquid vapour inclusions occur along growth planes of crustiform quartz crystals or within colour banding of zoned sphalerite these inclusions are 10 15 m in size and yielded homnogenisation temperatures of 170 220 c in early 2a veins 165 322 c in main stage 2b veins and 190 256 c io late stage 2c veins these data suggest a waxing and waning thermal history however the average salinity remained between 8 11 naci equiv wt in all stage 2 veins chalcopyrite bearing primary fluid inclusions have been recognised in the base metal rich stage 28 veins no evidence for presence of co2 e g formation of clathrates was recorded by rnicrothermometry however laser raman spectroscopic lrs analysis indicates the presence of co2 1 mole in the stage 2b veins and no detectable co2 in 2a and 2c vein stages semi quantitative sem wds microprobe analyses of fluid inclusion decrepitates indicate that the hellyer ore fluid was enriched in potassium and calcium but depleted in magnesium relative to seawater pixe microanalysis of fluid inclusions in quartz indicates that the stage 2b ore fluids have a significantly higher base metal concentration compared to the stage 2a veins the postmineralization stage 4 veins have a variable but lower base metal content in this study there was no fluid inclusion evidence of boiling cation composition higher salinities relative to seawater and the presence of co2 suggest that recycled seawater alone cannot be the sole source of the ore fluids this interpretation is in agreement with previous isotopic studies in the hellyer stringer system although direct input of bulk ore constituents from a magma chamber cannot be demonstrated from the present fluid inclusion data such a contribution of ore fluids from a magmatic source cannot be ruled out the possible input from the magmatic source may have occurred during the base metal rich stage 2b vein formation characterised by the intensifying temperature of deposition higher base metals and co2 contents

high resolution paleoceanography of the guaymas basin gulf of california during the past 15 000 years abstract deep sea drilling project site 480 27 54 10 n 111 39 34 w 655 m water depth contains a high resolution record of paleoceanographic change of the past 15 000 years for the guaymas basin a region of very high diatom productivity within the central gulf of california analyses of diatoms and silicoflagellates were completed on samples spaced every 40 50 yr whereas icp aes geochemical analyses were completed on alternate samples sample spacing 80 100 yr the bolling allerod interval 14 6 12 9 ka note ka refers to 1000 calendar years bp throughout this report is characterized by an increase in biogenic silica and a decline in calcium carbonate relative to surrounding intervals suggesting conditions somewhat similar to those of today the younger dryas event 12 9 11 6 ka is marked by a major drop in biogenic silica and an increase in calcium carbonate increasing relative percentage contributions of azpeitia nodulifera and dictyocha perlaevis a tropical diatom and silicoflagellate respectively and reduced numbers of the silicoflagellate octactis pulchra are supportive of reduced upwelling of nutrient rich waters between 10 6 and 10 0 ka calcium carbonate and a nodulifera abruptly decline at dsdp 480 while roperia tesselata a diatom indicative of winter upwelling in the modern day gulf increases sharply in numbers a nearly coincident increase in the silicoflagellate dictyocha stapedia suggests that waters above dsdp 480 were more similar to the cooler and slightly more saline waters of the northern gulf during much of the early and middle parts of the holocene 10 to 3 2 ka at about 6 2 ka a stepwise increase in biogenic silica and the reappearance of the tropical diatom a nodulifera marks a major change in oceanographic conditions in the gulf a winter shift to more northwesterly winds may have occurred at this time along with the onset of periodic northward excursions el nino driven of the north equatorial countercurrent during the summer beginning between 2 8 and 2 4 ka the amplitude of biogenic silica and wt fe al and ti proxies of terrigenous input increase possibly reflecting intensification of enso cycles and the establishment of modern oceanographic conditions in the gulf increased numbers of o pulchra after 2 8 ka suggest enhanced spring upwelling

hydrothermal alteration of felsic volcanic rocks associated with massive sulphide deposition in the northern iberian pyrite belt sw spain abstract massive sulphide deposits of the northern iberian pyrite belt ipb are mainly hosted by felsic volcanic rocks of rhyolitic to dacitic composition beneath most of the massive ores of this area e g concepcion san miguel aguas tenidas este or san telmo deposits there is usually a wide hydrothermal alteration halo associated with stockwork type mineralization within these alteration envelopes there are two principal rock types 1 chlorite rich rocks linked to the inner and more intensely altered zones and dominantly comprising chlorite pyrite quartz sericite carbonate rutile zircon chalcopyrite and 2 sericite rich rocks more common in the peripheral zones and showing a dominant paragenesis of sericite quartz pyrite chlorite carbonate rutile zircon sphalerite mass balance calculations comparing altered and least altered felsic volcanic rocks suggest that sericitization was accompanied by moderate enrichment in mg fe and h 2 o with depletion in si na and k and a slight net mass loss of about 3 chloritization shows an overall pattern which is similar to that of the sericitic alteration but with large gains in fe mg and h 2 o and minor enrichment in si s and mn and a significant loss of na and k and a minor loss of ca and rb however chloritization has involved a much larger net mass change mass gain of about 28 only a few elements such as nb y zr ti p and lree appear to have remained inert during hydrothermal alteration whilst ti and al have undergone very minor mobilization the results point to the severity of the physico chemical conditions that prevailed during the waxing stage of the ore forming hydrothermal systems further mineralogical and geochemical studies of the altered footwall rocks in the studied deposits indicate that hydrothermal ore bearing fluids reacted with host rocks in a multi stage process which produced a succession of mineralogical and chemical changes as the temperature increased

a new geodynamic interpretation for the south portuguese zone sw iberia and the iberian pyrite belt genesis 1 the south portuguese zone spz constitutes the southernmost segment of the variscan iberian massif it is bounded to the north by the beja acebuches ophiolitic complex and related accretionary wedge to the south lie the iberian pyrite belt ipb and flysch deposits forming the southern extent of the zone structural analysis within the spanish side of the spz supports continuous south propagating deformation evolving from early synmetamorphic thrusting in the internal zone to thin skinned tectonics in the southern external domain the accretion of the spz to the ossa morena zone is also witnessed by the presence of various melanges observed throughout the investigated area part of the melanges observed in the ipb are related to the volcanics and mineralizations setting a key point to understand the ipb mineralizations genesis is to constrain the volcanogenic model one underestimated feature is the large amount of submarine calc alkaline ignimbritic facies implying the presence of caldera structures within the province such correlation between caldera environment and ore deposits strongly suggests that the ipb developed in a continental arc our geodynamic model proposes an early north directed subduction associated with the obduction of the oceanic crust toward the south southward this episode is immediately followed by the development of the accretionary prism while farther south a second subduction zone responsible for the arc setting of the ipb initiates subsequent visean continental collision is associated with the deposit of the south propagating flysch and the present geometry of the spz

comment on the paper by sanchez espana et al source and evolution of ore forming hydrothermal fluids in the northern iberian pyrite belt massive sulphide deposits sw spain evidence from fluid inclusions and stable isotopes mineralium deposita 38 519 537 the recent paper by sanchez espana et al 2003 presents new fluid inclusion fi and stable isotope data on several massive sulphide deposits of the northern iberian pyrite belt ipb using these results together with previously published data on some large deposits of the southern ipb they concluded that the ore forming fluids in the ipb were a mixture of highly evolved seawater exchanged with the underlying sedimentary and magmatic rocks and a significant deep fluid component either of metamorphic or magmatic origin the latter is the favoured conclusion however this conclusion essentially depends on the fundamental assumption that neither fis nor stable isotope records were disturbed during the late variscantectono thermal event s yet according to the current knowledge on metamorphosed deposits e g marshall and spry 2000 marshall et al 2000 fis in such deposits generally do not preserve data pertinent to the pre metamorphic ore stage and the stable isotope data are usually difficult to interpret here we would like 1 to discuss the possibility of finding pristine fis in the ipb massive sulphide deposits that would have survived the late variscan low grade tectono thermal event 2 to present evidence for a significant gold depositing post kinematic hydrothermal stage in the ipb deposits with the concomitant development of pervasive lateto post kinematic fluid percolation through the ore bodies and 3 to discuss the real significance of the o h stable isotope data our discussion is mainly based on our study of the tharsisstockwork marignac et al 2003 with additional information from the la zarza and rio tintostockworks diagana2001 and from the nevescorvo deposit moura et al 1997a b we conclude that all fi data and many stable isotope data are in fact a record of the late variscan post kinematic hydrothermal overprint and that only few data may be of significance for the early syn sedimentary ore forming event in the ipb massive sulphide deposits

remobilisation of base metals and gold by variscan metamorphic fluids in the south iberian pyrite belt evidence from the tharsis vms deposit the tharsis massive sulphide deposit one of the major vms type deposits in the iberian pyrite belt ipb was severely deformed by the variscan tectono thermal events the question of whether or not these events affected the metal distribution in the deposit has been addressed by simultaneously studying the mineral parageneses tharsis stockwork and the fluid circulation at local and regional scales the results are 1 the early paragenesis in the stockwork q1 quartz pyrite chlorite phengitefcobaltitefankerite was strongly overprinted by a late post kinematic mineral deposition including new quartz veins q3 quartz and base metal sulphides chalcopyrite sphalerite bi and te minerals pyrite and galena and gold 2 at a regional scale fluids accompanying the peak metamorphism conditions ca 300 mpa ca 300 jc were of c o h n nacl type co2 dominated with ch4 and n2 and are considered to be metamorphic on the basis of microthermometry and geochemistry the late to post kinematic evolution retrograde stage was characterised by a pressure drop down to 40 mpa lithostatic to hydrostatic transition and a heat input leading to temperatures z430 jc then decreasing to temperature around 170 jc fluids of the retrograde type exhibit both dilution of the c o h n nacl fluid by a low salinity meteoric water and progressive loss of volatile components 3 fluids of the retrograde type pervasively percolated through the tharsis stockwork and were responsible for the strong mineral overprint on the early deformed paragenesis all the measurable fluid inclusions f i record these late fluids there are primary fluid inclusions in q1 but they are systematically imploded due to the external overpressure generated by the variscan tectonic events although base metal distribution in the stockwork is basically the result of the

hydrothermal alteration and mineralization in the neves corvo volcanic hosted massive sulfide deposit portugal i geology mineralogy and geochemistry the neves corvo volcanic hosted massive sulfide deposit is one of the largest 300 mt and richest known deposits of the iberian pyrite belt the deposit is unique because of its extremely high cu and sn grades 45 mt at 6 cu plus 4 5 mt at 12 cu and 2 2 sn more than 300 000 metric tons t of tin metal is contained in several types of tin mineralization that grade from 500 ppm to 60 percent sn the deposit consists of five orebodies including corvo the focus of the present study the volcanic volcaniclastic and sedimentary lithofacies that directly host the neves corvo mineralization consist of a rhyolitic dome cryptodome hyaloclastite complex facies interpretation indicates that volcanic activity occurred at moderate water depth below storm wave base in variably subsiding basins of different orders several syn and postore modification events included gravity driven mass transport processes and subsequent low angle thrusting and asymmetric detachment folding which shaped the present deposit the ore geology and geochemistry and the textural mineralogical and geochemical aspects of the ore forming process in the corvo orebody collectively suggest that ore formation resulted from a long lived hydrothermal system including two main mineralizing events an early stage of stringer and massive cassiterite deposition and a subsequent episode of massive sulfide ore generation two spatially independent stockworks fed these genetically related mineralizing systems the early deposition of stringer and massive cassiterite ores took place almost exclusively in the tin corridor a structural alignment bounded by synvolcanic faults textural analysis and geochemical data both indicate minimal fluid rock interaction during ascent of the tin bearing fluid the massive and semimassive cassiterite ores at corvo most likely formed by direct venting into seawater and or emplacement in water laden unlithified sediments and early hydrothermal products that mantled the footwall volcanic sequence stringer and massive cassiterite precipitation is thought to have been a product of a short lived episode in the overall ore forming system the vein filling mineral assemblage in the cassiterite stockwork quartz cassiterite pyrite donbassite kaolinite chamosite coupled with whole rock and mineral geochemical data indicate that the tin bearing fluid had a low ph and relatively high temperature 380 c the massive sulfide related hydrothermal alteration in corvo is essentially strata bound the permeability contrasts in the uppermost portion of the footwall succession played an important role in controlling the fluid flow the hydrothermal alteration is zoned and consists of an inner chlorite donbassite quartz sulfide sericite core that grades outward into successive enveloping k sericite quartz sulfide and na sericite quartz sulfide halos textural evidence from the mine to the microscopic scale and mass balance considerations indicate that extensive silicate replacement in the coherent volcanic rocks of the footwall sequence and disseminated replacement mineralization in the uppermost volcaniclastic and or sedimentary units were major mechanisms of massive sulfide deposition at corvo alteration mineralogy and geochemistry indicate that the neves corvo ore fluids were hotter and more acidic than typical ore forming fluids of the iberian pyrite belt the geochemical characteristics of the tin and copper mineralization also differ from the ores of typical deposits of the iberian pyrite belt and imply the involvement of additional metal sources possibly magmatic in the ore forming system copper enrichment due to mechanical and fluid assisted tectonometamorphic remobilization processes accounts for the formation of extremely high grade ore shoots in the deposit

response of california current forcing to mid holocene insolation and sea surface temperatures 1 we find that mid holocene insolation causes systematic changes in wind forcing of the california current system suppressing wind stress in the spring and enhancing wind stress in the summer and autumn both large and regional scale processes play an important role in the insolation enhancement of wind stress with elevated summer insolation magnifying both large scale sea level pressure gradients and regional scale land sea thermal contrast we find that prescribed changes in large scale sea surface temperatures ssts amplify the response of nearshore wind stress to mid holocene insolation with sst magnification of changes in large scale sea level pressure gradients overcoming sst muting of changes in regional scale land sea thermal contrast the climate model simulations are supported by proxy inferred cooler than present sea surface temperatures in the northern california current system as well as by high nitrogen isotope values in the southern california current system our results highlight the importance of multiscale dynamical interactions in regulating the response of regional environments to global scale changes in radiative forcing

impact of local morphology on sedimentation in a submarine canyon rov studies in eel canyon northern california u s a abstract despite existing paradigms about marine sedimentation some submarine canyons are receiving large amounts of sediment during the present highstand of sea level these modern examples can be used to unlock secrets of past canyon sedimentation however submarine canyons have complex morphology and consequently dramatic variations in sedimentary processes and deposits can occur over a range of spatial scales as small as meters to tens of meters operations from surface ships usually cannot place sampling devices on the canyon seabed with this level of accuracy the purpose of the present study was to investigate the variability of sedimentation over a range of scales in order to delineate accurate trends along and among channels at the head of a canyon sampling with the rov ventana facilitated detailed examination of microenvironments i e wall thalweg in eel submarine canyon the combination of intense sedimentation from nepheloid layers and gravity flows in a complicated morphologic system leads to clear distinctions between microenvironments as well as some recognizable and unifying trends in sedimentation inherent small scale variability due to canyon morphology is evident in narrow and steep channels at 1 m horizontal resolution cores exhibit consistent sediment fabric but laminae can differ between cores at the 10 m horizontal scale the fabric is not consistent broader more gently sloping channels reveal consistent sediment fabric at the 10 m scale in most cases physical stratification decreases along the thalwegs of channels as water depths increase in contrast channel walls generally exhibit elevated impacts of bioturbation and variable amounts of physical stratification radiochemical profiles 210pb 137cs and the predominance of physical stratification including discrete laminae with high sand content suggest that the northern entrants are receiving more sediment than their southern counterparts however 210pb profiles in this study demonstrate rapid accumulation of sediment everywhere in the head of eel canyon with the highest rates of accumulation 40 mm yr found in the channel thalwegs in thalwegs evidence from sedimentary structures e g erosional bases cross bedded sand layers demonstrates that gravity flows occur frequently many times each year and have been linked by other investigations to storm impacts on the adjacent continental shelf on decadal timescales these processes are temporarily depositing sediment in the head of the canyon which is removed over longer timescales probably as larger gravity flows triggered by earthquakes the radiochemical and sedimentological data collected at the base of entrant channels confirm that modern sediment is moving to deeper portions of the canyon

diatoms in northeast pacific surface sediments as paleoceanographic proxies abstract fossil diatom total abundances valves g in 54 surface sediment samples from the northeast ne pacific ocean reflect the position of high primary production associated with coastal upwelling and that possible biases associated with dilution or dissolution are small diatom species assemblages defined by q mode factor analysis in 30 samples with abundant diatoms are related to modern oceanographic properties five statistical assemblages given by five specific diatom species and or groups are related to upwelling chaetoceros spores subtropical thalassionema nitzschioides subarctic rhizosolenia hebetata transitional neodenticula seminae and freshwater freshwater diatoms ecological environments these factors are significantly correlated with primary productivity temperature nutrient concentrations and salinity although the strongest relationship is that between diatom assemblages and productivity however it is not possible to distinguish between coastal and open ocean curl driven upwelling based on chaetoceros spores relative percentages by themselves or on the floral factors

tectonic style and structural analysis of the puebla de guzman antiform iberian pyrite belt south portuguese zone sw spain

4 transpressional tectonics lower crust decoupling and intrusion of deep mafic sills a model for the unusual metallogenesis of sw iberia abstract sw iberia is interpreted as an accretionary magmatic belt resulting from the collision between the south portuguese zone and the autochthonous iberian terrane in variscan times 350 to 330 ma in the south portuguese zone pull apart basins were filled with a thick sequence of siliciclastic sediments and bimodal volcanic rocks that host the giant massive sulphides of the iberian pyrite belt massive sulphides precipitated in highly efficient geochemical traps where metal rich but sulphur depleted fluids of dominant basinal derivation mixed with sulphide rich modified seawater massive sulphides formed either in porous reactive volcanic rocks by sub seafloor replacement or in dark shale by replacement of mud or by exhalation within confined basins with high biogenic activity crustal thinning and magma intrusion were responsible for thermal maturation and dehydration of sedimentary rocks while magmatic fluids probably had a minor influence on the observed geochemical signatures the ossa morena zone was a coeval calc alkaline magmatic arc it was the site for unusual mineralization particularly magmatic ni cu and hydrothermal fe oxide cu au ores iocg most magmatism and mineralization took place at local extensional zones along first order strike slip faults and thrusts the source of magmas and iocg and ni cu deposits probably lay in a large mafic ultramafic layered complex intruded along a detachment at the boundary between the upper and lower crust here juvenile melts extensively interacted with low grade metamorphic rocks inducing widespread anatexis magma contamination and further exsolution of hydrothermal fluids hypersaline fluids 18 o fluid 5 4 to 12 were focused upward into thrusts and faults leading to early magnetite mineralization associated with a high temperature 500 c albite actinolite salite alteration and subsequent copper gold bearing vein mineralization at somewhat lower temperatures assimilation of sediments by magmas led in turn to the formation of immiscible sulphide and silicate melts that accumulated in the footwall of the layered igneous complex further injection of both basic and sulphide rich magmas into the upper crust led to the formation of ni cu rich breccia pipes younger 330 to 280 ma peraluminous granitoids probably reflect the slow ascent of relatively dry and viscous magmas formed by contact anatexis these granitoids have w sn and pb zn related mineralization that also shows geochemical evidence of major mantle crust interaction late epithermal hg cu sb and pb zn ag mineralization was driven by convective hydrothermal cells resulting from the high geothermal gradients that were set up in the zone by intrusion of the layered igneous complex in all cases most of the sulphur seems to have been derived from leaching of the host sedimentary rocks 34 s 7 to 20 with only limited mixing with sulphur of magmatic derivation the metallogenic characteristics of the two terranes are quite different in the ossa morena zone juvenile magmatism played a major role as the source of metals and controlled the styles of mineralization in the south portuguese zone magmas only acted as heat sources but seem to have had no major influence as sources of metals and fluids which are dominated by crustal signatures most of the magmatic and tectonic features related to the variscan subduction and collision seem to be masked by those resulting from transpressional deformation and deep mafic intrusion which led to the development of a metallogenic belt with little resemblance to other accretionary magmatic arcs

hydrothermal alteration and mineralization in the neves corvo volcanic hosted massive sulfide deposit portugal ii oxygen hydrogen and carbon isotopes the oxygen hydrogen and carbon isotope compositions of hydrothermally altered rocks and minerals from massive and stockwork ores of the neves corvo volcanic hosted massive sulfide deposit have been used to infer its thermal history and the origins of the hydrothermal fluids quartz and cassiterite separated from the stringer and massive cassiterite ores of the corvo orebody tin corridor have 18o values of 12 5 to 13 6 and 1 4 to 0 4 per mil respectively quartz cassiterite oxygen isotope fractionation indicates temperatures of 174 to 207 c avg 191 c for precipitation of this mineral pair the calculated oxygen isotope composition of the fluid 18oh2o 0 4 to 0 7 avg 0 1 suggests that cassiterite precipitation resulted from extensive mixing of a tin bearing fluid with seawater at sea floor hydrothermal vents the whole rock oxygen isotope composition of the hydrothermally altered felsic volcanic rocks hosting the sulfide stockwork of the corvo orebody varies from the central stockwork chloritic alteration zone i 18o 8 7 9 6 to the peripheral zones sericitic and paragonitic alteration zones iia 18o 11 6 13 1 and iib 18o 11 0 14 1 the 18o values of quartz also increase from alteration zone i avg 13 9 to alteration zone iia avg 14 4 to alteration zone iib avg 15 0 quartz from the hanging wall jasper unit yielded higher 18o values of 15 5 to 17 9 per mil chlorite from alteration zone i has 18o values of 6 1 to 8 4 per mil avg 7 4 sericite has 18o and d values that vary slightly from 18o 9 3 to 10 1 per mil avg 9 9 and d 59 to 47 per mil avg 53 in alteration zone i to 18o 9 8 to 11 4 per mil avg 10 5 and d 50 per mil in alteration zone iia to 18o 9 4 to 11 7 per mil avg 10 6 and d 61 to 36 per mil avg 45 in alteration zone iib siderite associated with waning hydrothermal activity has low 13c values 11 1 to 5 8 suggesting the incorporation of oxidized organic carbon from the footwall sequence and or the addition of magmatic carbon in alteration zone i quartz chlorite fractionation indicates temperatures of 249 to 402 c avg 335 c and 18oh2o values of 6 1 to 10 2 per mil avg 8 3 quartz sericite pairs gave isotopic equilibrium temperatures of 250 to 289 c avg 269 c and 18oh2o values of 5 8 to 7 0 per mil avg 6 4 in alteration zone iia and 170 to 318 c avg 223 c and 18oh2o 1 4 to 8 3 per mil avg 4 5 in alteration zone iib the oxygen isotope data show that in the core of the feeder system alteration zone i the temperature and the 18oh2o values were very high the d values calculated for the ore fluids d 37 to 11 are also significantly lower than seawater outward from the central stockwork alteration zones iia and iib the ore fluid was depleted in 18o and the temperatures were lower the oxygen hydrogen and carbon isotope signatures of the neves corvo ore fluids are best explained by incorporation of magmatic and or metamorphic fluids into a seawater dominated hydrothermal system magmatic fluids in particular were a likely source for the tin and much of the copper in the neves corvo ores

supergene enrichment of precious metals by natural amalgamation in the las cruces weathering profile iberian pyrite belt sw spain abstract natural au ag hg alloys occur in the las cruces ore deposit in the eastern part of the iberian pyrite belt they are mainly concentrated in the lower part of the gossan profile including a sheared black shale level where the gossan makes contact with a barren pyrite zone within the supergene cu rich mineralization drill core analyses show a heterogeneous distribution of au ag and hg within the weathering profile with mean values of 5 1 ppm 155 ppm and 52 ppm respectively in general the absolute tenures increase towards the bottom of the weathered profile mineralogical studies conducted on samples from the active mine workings indicate that hg and precious metals occur mainly as au ag hg alloys these associations constitute the best potential resource for precious metals at the las cruces deposit this paper describes how this unusual precious metal enrichment is produced along the weathering profile by supergene processes combining paragenetic information mineral chemistry and the data pertaining to the solubilities of au ag and hg in a weathering profile we suggest a two stage genetic model for the formation of the las cruces au ag hg mineralization 1 release of au ag and hg from the massive sulfide deposit by weathering processes during the gossan formation at ph 0 9 v conditions au ag and hg are mobilized downward through the weathering profile as chloride complexes and fixed as elemental au halides oxides and sulfates and 2 remobilization of hg ag and au in the gossan after the deposit was buried beneath the neogene carbonate rich sedimentary cover the buffering capacity of the percolating fluids due to their interaction with the carbonate rich sedimentary pile leads to significant mineralogical and geochemical changes at near neutral conditions ph 6 7 eh 0 v hg ag and au are newly remobilized as thiosulfate sulfate and hydroxide complexes and newly fixed by sorption during ferric hydroxide formation and as sulfates several cycles of dissolution precipitation of au ag and hg near the redox front occur by oscillations in the water table and changes in the ph eh conditions the interaction of downward migrating fluids with high reductant lithologies black shales and massive sulfides seems to be responsible for the reduction of different complexes and for the precipitation of cinnabar ag sulfides and sulfosalts as well as the precipitation of au ag hg amalgams

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

the selbaie zn cu ag deposits quebec canada an example of evolution from subaqueous to subaerial volcanism and mineralization in an archean caldera environment the selbaie deposits of western quebec are hosted in calc alkalic pyroclastic rocks of the abitibi subprovince rocks range upward from subaqueous debris flows through pumiceous tuff to densely welded ignimbrite they form an intracaldera sequence over 1 200 m thick which records evolution from subaqueous to subaerial deposition mineralization occurred within this sequence on the southwest flank of the brouillan tonalite a central intrusion and possibly a resurgent dome and includes regionally extensive and temporally early exhalite local massive sulfide and later epithermal veins these veins were emplaced by open space filling along synvolcanic structures and make up the bulk of the economic resource mineralization and alteration show similarities to both massive sulfide and epithermal deposits cu zn increases with depth but also increases laterally toward veins and toward the intrusion ag cu in veins is higher in the upper levels of the system whole rock mass balance calculations indicate enrichment in si fe mg and mn with proximity to mineralization and depletion in ca k and na na metasomatism common in host rocks to archean massive sulfide deposits is absent in subaerially emplaced tuff at selbaie and k feldspar is preserved selbaie is unusual 1 as an archean example of a subaerial caldera that evolved from subaqueous to subaerial volcanism 2 in representing economically important archean epithermal mineralization and 3 in demonstrating the link between subaqueous volcanogenic massive sulfide deposits and subaerial volcanogenic epithermal veins it is perhaps unique in preserving so well all three of these aspects in a single mineralized system the rarity of similar mineralized subaerial volcanic settings in the abitibi subprovince reflects its primitive crustal development but may also be due to incomplete preservation of subaerial environments

an 11 300 yr record of paleoclimatology and paleoceanography of the central california coast in a gravity core from pioneer seamount abstract diatom pollen silicoflagellate and biogenic opal analyses from a 155 cm long gravity core from pioneer seamount offshore santa cruz california ps1410 06 gc latitude 37 3 n longitude 123 4 w water depth 2165 m are compiled for the last 11 300 years and compared with those of odp 1019 and tn062 o550 from northern california the relative abundance record of the subtropical diatom fragilariopsis doliolus has similar bimodal holocene patterns in all three cores suggesting that sea surface temperatures sst were lower during the middle part of the holocene than they were during the later and earlier parts the relative abundance of coastal redwood sequoia sempervirens pollen a proxy for fog and coastal upwelling displays stepwise increases in odp 1019 and tn062 o550 between 4000 and 3000 cal yr bp but its relative abundance in ps1410 06 gc increases gradually throughout the past 10 200 yr without any major steps similarly biogenic silica opal displays stepwise increases at 3600 and 2900 cal yr bp in odp 1019 and tn062 o550 respectively whereas opal increases more gradually in ps1410 06 gc during the past 10 100 yr with relatively minor steps at 3100 and 2600 cal yr bp together coastal redwood and opal argue for a more gradual late holocene increase in coastal upwelling along the coast of central california compared with that off northern california where onshore offshore gradients are more distinct

effects of greenschist facies metamorphism and related deformation on the mobrun massive sulfide deposit quebec canada the mobrun zn cu ag au deposit in the noranda mining camp is hosted by archean mafic and felsic submarine volcanic rocks the deposit comprises three massive sulfide complexes the main and satellite lenses near surface and the 1100 orebody at depth the rocks have been subjected to lower greenschist facies metamorphism and related deformation which resulted in changes in ore textures development of shear zones and veins systems remobilization of gold and formation of a new mineral electrum within the orebodies both mechanical and chemical processes operated to produce secondary textures and structures resulting from brittle deformation ductile deformation and annealing the specific deformation mechanisms include brittle failure and cataclastic flow dislocation glide dislocation creep and solution precipitation creep the main and satellite lenses are characterized by excellent preservation of primary sulfides deposited from and reworked by synvolcanic hydrothermal fluids these orebodies were affected to a limited degree by mechanical processes of deformation in contrast the 1100 orebody is characterized by a higher degree of development of textures and structures related to metamorphism and deformation especially those formed by chemical processes the differences may be due to the greater depth of the 1100 orebody relative to the other lenses as regional metamorphic isograds are subhorizontal and more extensive interaction between metamorphic fluids and the 1100 lens

seasonal variations in the formation of al and si rich fe stromatolites in the highly polluted acid mine drainage of agua agria creek tharsis sw spain abstract the study of the different biotic and abiotic processes involved in the current formation of fe stromatolites in rivers affected by acid mine drainage amd is essential not only to understand this unique and extreme environment but also to achieve a better understanding of the past iron formation on the earth and on mars the fe stromatolites studied in the highly polluted amd in tharsis sw spain revealed a unique mineral assemblage with jarosite and rostite as the most unexpected fe and al phases and goethite and schwertmannite as the main constituents seasonal variations in this region greatly affected the composition of the precipitates and the distribution of diatoms within the fe stromatolites drought and flood events were also recognized in the sedimentary textures and in the mineral assemblages observed of particular layers within the fe stromatolites the characterization of the chemical and mineralogical composition of fe stromatolites in tharsis as well as the different formation mechanisms proposed complement the existing literature on newly formed fe stromatolites and provides new observations to increase our understanding of those extreme environments

coastal upwelling in the california current system abstract coastal upwelling in the california current system has been the subject of large scale studies off california and baja california and of small scale studies off oregon recent studies of the winds along the entire coast from 25 n to 50 n indicate that there are significant along shore variations in the strength of coastal upwelling which are reflected in the observed temperature distribution active upwelling appears to be restricted to a narrow coastal band about 10 25 km wide along the entire coast but the region influenced by coastal upwelling may be much wider intensive observations of the upwelling zone during summer off oregon show the presence of a southward coastal jet at the surface a mean vertical shear a poleward undercurrent along the bottom and persistently sloping isopycnals over the continental shelf most of the upwelling there occurs during relatively short periods several days long of upwelling favorable winds during the upwelling season off oregon the offshore ekman transport is carried by the surface ekman layer and the onshore return flow occurs through a quasi geostrophic interior it is not known whether the structure and dynamics observed off oregon are typical of the upwelling zone along the entire coast though some of the same features have been observed off baja california current and future research will eventually show whether the oregon results are also applicable in the region of persistently strong upwelling favorable winds off northern california and in the region of complex bathymetry off central and southern california

groundwater gossan interaction and the genesis of the secondary siderite rock at las cruces ore deposit sw spain abstract part of the las cruces secondary siderite deposit has sparked an interest in the scientific community because of its unique mineralogy the original gossan formed by goethite and hematite has been replaced by a siderite and galena rock we postulate that this rock can be formed by the interaction of iron oxides with groundwater similar in composition to that of the present day hydrochemical and isotopic characteristics of groundwater support this hypothesis the negative eh values the existence of h 2 s and the tendency toward high sulfate isotope values indicate a reducing groundwater condition the high ammonium boron and iodine concentrations as well as the low 13 c values of dissolved inorganic carbon dic confirm the organic matter oxidation the reductive dissolution of pb bearing goethite at the expense of dissolved organic carbon doc leads to the precipitation of fe sulfides galena and siderite the formation of siderite from this process is confirmed by the low amount of dissolved fe in groundwater 13 c values and thermodynamic calculations one dimensional reactive transport modeling demonstrated that the present day groundwater flux and chemical composition could form the siderite rock in less than 1 ma with no external supply of reactants sensitivity analyses revealed that the time of formation depends on the structure of the groundwater flux spaced fractures or pervasive the flow rate and especially the doc concentration in fact calculations with the highest doc measured concentration resulted in a mineral zonation one zone formed by fe sulfides and other zone formed by siderite with galena in both zones reactive transport calculations and the similarity of its high 34 s values indicate that the sulfur of galena came from the current groundwater reactive transport calculations and the similarity of its high 34 s values indicate that the sulfur of galena came from the current groundwater

productivity contribution of paleozoic woodlands to the formation of shale hosted massive sulfide deposits in the iberian pyrite belt tharsis spain the geological materials produced during catastrophic and destructive events are an essential source of paleobiological knowledge the paleobiological information recorded by such events can be ric

explanation for many of the unusual features of the massive sulfide deposits of the iberian pyrite belt newly published fluid inclusion data from quartz in stockwork veins beneath seven massive sulfide lenses in the iberian pyrite belt suggest that the lenses were formed from fluids that on reaching the sea reversed buoyancy and ponded in basins sulfides quenched in the resulting brine pool would have settled to form a sulfide mud this process provides a relatively efficient trapping mechanism for metal in the fluids and effectively excludes ambient seawater accounting for the deposits tending to have the characteristics of large size sheet like form absence of relict chimney structures and a mineral content characterized by pyrite arsenopyrite and absence or scarcity of barite marcasite and fe oxides if total s was less than total metals in the stockwork fluids some or all of the more soluble zn and pb could have been swept from the basin at the overflow accounting for the variable but generally low zn and pb contents of the ores the lack of sedimentary source for the high salinities implicates magmatic intrusions possibly similar to those related to sn w mineralization

type of volcanoes hosting the massive sulfide deposits of the iberian pyrite belt the volcanic sedimentary complex vsc of the iberian pyrite belt ipb in southern portugal and spain comprises an upper devonian to lower carboniferous submarine succession with a variety of felsic volcanic lithofacies the architecture of the felsic volcanic centres includes felsic lavas domes pyroclastic units intrusions and minor mafic units that define lava cryptodome pumice cone volcanoes the diversity of volcanic lithofacies recognized in different areas of the ipb mainly reflects variations in proximity to source but also differences in the eruption style the ipb volcanoes are intrabasinal range in length from 2 km to 8 km and their thickest sections vary from 400 m to 800 m these volcanoes are dominated by felsic lavas domes that occur at several stratigraphic positions within the volcanic centre however the pyroclastic units are also abundant and are spatially related to the lavas domes the intrusions are minor and define cryptodomes and partly extrusive cryptodomes the hydrothermal systems that formed the neves corvo and lousal massive sulfide ore deposits are associated with effusive units of felsic volcanic centres at neves corvo the massive sulfide orebodies are associated to rhyolitic lavas that overlie relatively thick fiamme rich pyroclastic unit in several other locations within the belt pyroclastic units contain sulfide clasts that may have been derived from yet to be discovered coeval massive sulfide deposits at or below the sea floor which enhances the exploration potential of these pyroclastic units and demonstrates the need for volcanic facies analysis in exploration

brine pool deposition for the zn pb cu massive sulphide deposits of the bathurst mining camp new brunswick canada i comparisons with the iberian pyrite belt abstract the ordovician zn pb cu massive sulphide ore deposits of the bathurst mining camp share many features with those of the devonian carboniferous iberian pyrite belt particularly the tendency to large size tonnage and metal content shape as far as can be determined after allowing for deformation metal content particularly fe cu pb zn and sn mineral assemblages pyrite arsenopyrite pyrrhotite and lack or rarity of sulphates sulphide textures particularly framboidal pyrite lack of chimney structures and rubble mounds irregular metal or mineral zoning and the low degree of zone refining compared to hokuroku ores the major differences between the provinces are the lack of vent complexes and the presence of sn cu ores in the iberian pyrite belt there are also similarities in the geological setting of the two camps both lie within continental terranes undergoing arc continent and continent continent collision and in each case massive sulphide mineralisation followed ophiolite obduction the ore deposits are associated with bimodal volcanic rocks derived from morb and continental crust and marine shales and mineralisation was locally accompanied or followed by deposition of iron formations fluid inclusion data from veins in stockworks from at least six of the iberian massive sulphide deposits point to sulphide deposition having taken place in basins containing mostly spent saline ore forming fluids brine pools and it is suggested that most of the major features of the bathurst deposits can be explained by similar processes the proposed model is largely independent of ocean sulphate and o 2 content whereas low values of each are requisites for the current spreading plume model of sulphide deposition in the bathurst camp

syn to late tectonic stockwork emplacement within the spanish section of the iberian pyrite belt structural textural and mineralogical constraints in the tharsis and la zarza areas in deformed massive sulfide deposits it is commonly difficult to distinguish between primary stockwork mineralization and remobilized sulfides that occupy late cleavages and deformation structures and the mechanism of formation of the deformation veins is not always clear an analysis of sulfide vein networks associated with two massive sulfide deposits of the iberian pyrite belt is presented as an example of this complexity variscan deformation has affected the massive sulfide related stockworks at la zarza and tharsis and led to the formation of sulfide bearing deformation veins the primary feeder stockwork has a complex mineralogical composition with pyrite rich veins rimmed by narrow co as assemblages e g cobaltite and arsenopyrite interstitial galena chalcopyrite and sphalerite minerals are also observed the vein set developed during deformation was emplaced within cleavage and shear planes characteristic of the regional south verging tectonics away from massive sulfides the characteristic minerals of the syntectonic veins are pyrite and quartz however deformation veins developed in contact with primary feeder veins and massive sulfide have co as rich rims and base metal sulfides similar to the primary feeder veins the development of the complex vein paragenesis within the stockwork zones is explained in terms of regional scale deformation models

subsea floor replacement in volcanic hosted massive sulfide deposits abstract recent research on volcanic hosted massive sulfide vms deposits indicates that syngenetic subsea floor replacement ores form an important component of many deposits in the context of vms deposits subsea floor replacement can be defined as the syn volcanic formation of sulfide minerals within pre existing volcanic or sedimentary deposits by infiltration and precipitation in open spaces fractures inter and intra granular porosity as well as replacement of solid materials there are five criteria for distinguishing subsea floor replacement in massive sulfide deposits 1 mineralized intervals are enclosed within rapidly emplaced volcanic or sedimentary facies lavas intrusions subaqueous mass flow deposits pyroclastic fallout 2 relics of the host facies occur within the mineral deposit 3 replacement fronts occur between the mineral deposit and the host lithofacies 4 the mineral deposit is discordant to bedding and 5 strong hydrothermal alteration continues into the hanging wall without an abrupt break in intensity criteria 1 3 are diagnostic of replacement whereas criteria 4 and 5 may suggest replacement but are not alone diagnostic because clastic sulfide ores contain accessory rock fragments collected by the parent sediment gravity flow s during transport criteria 2 can only be applied to massive semi massive disseminated or vein style deposits and not clastic ores the spectrum of vms deposit types includes deposits that have accumulated largely subsea floor and others in which sedimentation and volcanism were synchronous with hydrothermal activity and precipitation of sulfides occurred at and below the sea floor over the life of the hydrothermal system deposits that formed largely subsea floor are mainly hosted by syn eruptive or post eruptive volcaniclastic facies gravity flow deposits water settled fall autoclastic breccia however some subsea floor replacement vms deposits are hosted by lavas and syn volcanic intrusions sills domes cryptodomes burial of sea floor massive sulfide by lavas or sediment gravity flow deposits can interrupt sea floor mineralization and promote subsea floor replacement and zone refining the distance below the sea floor at which infiltration and replacement took place is rarely well constrained with published estimates ranging from less than 1 to more than 500 m but mainly in the range 10 200 m the upper few tens to hundreds of metres in the volcano sedimentary pile are the favoured position for replacement as clastic facies are wet porous and poorly consolidated in this zone and at greater depths become progressively more compacted dewatered altered and less amenable to large scale infiltration and replacement by hydrothermal fluids furthermore sustained mixing between the upwelling hydrothermal fluid and cold seawater is regarded as a major cause of sulfide precipitation in vms systems and this mixing process generally becomes less effective with increasing depth in the volcanic pile the relative importance of subsea floor replacement in vms systems is related principally to four factors the permeability and porosity patterns of host lithofacies sedimentation rate the relative ease of replacement of host lithofacies especially glassy materials and early formed alteration minerals during hydrothermal attack and physiochemical characteristics of the hydrothermal fluid

geochemistry and architecture of the host sequence of the massive sulfides in the northern iberian pyrite belt abstract the northernmost iberian pyrite belt hosts several small felsic volcanogenic massive sulfide orebodies geochemically the volcanic sedimentary complex is dominated by andesitic to rhyolitic calc alkaline magmatic rocks with a significant proportion of dacite and andesite the lower felsic and upper felsic units are geochemically identical and probably represent dismembered parts of a single volcanic felsic complex if that holds true massive sulfide deposits of the northern ipb are hosted by volcaniclastic rocks located in the hanging wall of a single unit dominated by dacite rhyolite dome complexes this volcanic unit is characterized by zr contents structural analysis and the geochemistry suggest that the volcanic sequence is tectonically imbricated with the youngest units located at the lowest structural position the proposed reconstructed stratigraphic sequence comprises an andesitic footwall overlain by the felsic complexes of the middle felsic and lower upper felsic units thus the massive sulfide deposits formed toward the top of the whole sequence and associated with the youngest felsic rocks having a specific geochemistry

surface patterns in temperature flow phytoplankton biomass and species composition in the coastal transition zone off northern california satellite thermal imagery and in situ biological and physical data are presented that describe the spatial variability of phytoplankton biomass and species composition in relation to the physical structure at the sea surface during persistent upwelling off northern california surface patterns in temperature geostrophic velocity chlorophyll and particle size structure show that the coastal zone was dominated by two water masses separated by a well defined physical boundary this boundary is apparent in satellite thermal imagery as a cold front and in dynamic height as a meandering jet in the california current on the landward side of the front jet we observed cold coastal water that was relatively enriched in phytoplankton biomass due to the presence of large diatoms on the seaward side of the front jet we observed relatively warm water where the phytoplankton biomass was low and the diatoms were largely absent broad tongues and narrow filaments of cold chlorophyll rich water that extended over 100 km offshore were present in our study area these features were bounded by the meandering coastal jet the coldest most chlorophyll rich water in these tongues and filaments was located between the onshore and offshore flows in relatively slow moving water but entraimnent of coastal water into the jet was apparent

ore mineralogy and sulfur isotope study of the massive sulfide deposit of filon norte tharsis mine spain the volcanogenic massive sulfide deposit of filon norte at tharsis is hosted by carbonaceous black slate and connected only partly with stockwork veins the massive ores are usually composed of fine grained pyrite with subordinate amounts of sphalerite chalcopyrite galena and arsenopyrite monoclinic pyrrhotite sometimes occurs in massive pyritic ores in the apparently middle and upper horizons of the orebody and siderite rich ores are interstratified with compact pyritic ores in the apparently lower horizons from the occurrence of monoclinic pyrrhotite together with the fes contents of sphalerite mostly ranging from 11 to 16 mol it is inferred that the sulfide minerals of the massive orebody were precipitated in euxinic muds on the sea floor at temperatures below 250 c the negatively shifted highly variable 34s values of the massive ores and their close similarity to those of the underlying black slates strongly suggest that the sulfide sulfur of the massive orebody and the slates is cognate and biogenic

the filon norte orebody tharsis iberian pyrite belt a proximal low temperature shale hosted massive sulphide in a thin skinned tectonic belt the filon norte orebody tharsis iberian pyrite belt is one of the largest pyrite rich massive sulphide deposits of the world the present structure of the mineralization consists of an internally complex low angle north dipping thrust system of variscan age there are three major tectonic units separated by thick fault zones each unit with its own lithologic and hydrothermal features they are internally organized in a hinterland dipping duplex sequence with high angle horses of competent rocks igneous and detritic rocks and massive sulphides bounded by phyllonites the mineralization is within the lower unit and is composed of several stacked sheets of massive sulphides and shales hosting a stockwork zone with no obvious zonation the intermediate unit is made up of pervasively ankeritized shales and basalts spilites here hydrothermal breccias are abundant the upper unit is the less hydrothermally altered one and consists of silicified dacites and a diabase sill the tectonic reconstruction suggests that the sequence is inverted and the altered igneous rocks were originally below the orebody carbon oxygen and sulphur isotopes in the massive sulphides and hydrothermal rocks as well as the mineral assemblage and the paragenetic succession suggest that the sulphide precipitation in the sea floor took place at a low temperature 150 c without indication at least in the exposed section of a high temperature copper rich event sporadic deep subsea floor boiling is probably responsible for the formation of hydrothermal breccias and the wide extension of the stockwork its co au enrichment is interpreted as being related with the superposition of some critical factors such as the relationship with black shales the low temperature of formation and the boiling of hydrothermal fluids the present configuration and thickness of the orebody is due to the tectonic stacking of a thin and extensive blanket 2 4 km2 of massive sulphides with low aspect ratio they were formed by poorly focused venting of hot modified seawater equilibrated with underlying rocks into the seafloor massive sulphide precipitation took place by hydrothermal fluid quenching bacteriogenic activity and particle settling in an unusual restricted euxinic and shallow basin brine pool with a low detritic input but with important hydrothermal activity related to synsedimentary extensional faulting resedimentation of sulphides seems to be of major importance and responsible for the observed well mixed proximal and distal facies the tectonic deformation is largely heterogeneous and has been mostly channelled along the phyllonitic tectonized shales deformation bands thus sedimentary and diagenetic textures are relatively well preserved outside the deformation bands in the massive sulphides superimposed variscan recrystallization is not very important and only some early textures are replaced by metamorphic tectonic ones the stockwork is much more deformed than the massive sulphides the deformation has a critical effect on the present morphology of the orebody and the distribution of the ore minerals this deposit is a typical example of the sheet like shale hosted anoxic low temperature and zn rich massive sulphides developed in a ensialic extensional basin

isotope geochemistry tracks the maturation of submarine massive sulfide mounds iberian pyrite belt the massive sulfide deposits of the southern iberian pyrite belt ipb occur as shale hosted exhalative mounds or shallow sub seafloor replacive bodies that formed at the devonian carboniferous boundary in anoxic bottoms the geochemistry of the mineralization and the host shale from some of the major deposits including a detailed 50 m thick section through the migollas orebody shows a marked textural and vertical zonation that is also reflected in the chemical textural and isotopic variations of pyrite and carbonates pyrite evolves from primary framboids and colloform aggregates to late euhedral crystals which accompanies a redistribution of the contained base metals and grain coarsening sims analyses depict an extreme variability of 34s values from 42 3 to 4 4 with a gradual increase that is related to the textural maturation there is also a systematic rise in the 87sr 86sr ratios 0 70846 to 0 71354 13c 12 2 to 5 2 and 18o values 14 1 to 27 8 of the associated carbonates which evolve from early dolomite to late siderite this evolution evidences the maturation of the exhalative mineralization during mixing between two fluids modified seawater enriched in biogenically derived reduced sulfur and upflowing hydrothermal fluids early sulfides precipitated in the seawater mound interface towards the core of the mounds there was an increasing influence of deep fluids that modified the early mineral textures and the isotopic signatures this evolution is similar to that observed in modern submarine hydrothermal systems and confirms the importance of mound refining in the evolution of fossil exhalative mounds and the formation of economic ores

high resolution paleoclimatology of the santa barbara basin during the medieval climate anomaly and early little ice age based on diatom and silicoflagellate assemblages in kasten core spr0901 02kc abstract diatom and silicoflagellate assemblages documented in a high resolution time series spanning 800 to 1600 ad in varved sediment recovered in kasten core spr0901 02kc 34 16 845 n 120 02 332 w water depth 588 m from the santa barbara basin sbb reveal that sbb surface water conditions during the medieval climate anomaly mca and the early part of the little ice age lia were not extreme by modern standards mostly falling within one standard deviation of mean conditions during the pre anthropogenic interval of 1748 1900 no clear differences between the character of mca and the early lia conditions are apparent during intervals of extreme droughts identified by terrigenous proxy scanning xrf analyses diatom and silicoflagellate proxies for coastal upwelling typically exceed one standard deviation above mean values for 1748 1900 supporting the hypothesis that droughts in southern california are associated with cooler or la nina like sea surface temperatures ssts increased percentages of diatoms transported downslope generally coincide with intervals of increased siliciclastic flux to the sbb identified by scanning xrf analyses diatom assemblages suggest only two intervals of the mca at 897 to 922 and 1151 1167 when proxy ssts exceeded one standard deviation above mean values for 1748 to 1900 conversely silicoflagellates imply extreme warm water events only at 830 to 860 early mca and 1360 to 1370 early lia that are not supported by the diatom data silicoflagellates appear to be more suitable for characterizing average climate during the 5 to 11 year long sample intervals studied in the spr0901 02kc core than diatoms probably because diatom relative abundances may be dominated by seasonal blooms of a particular year

extreme 18o enriched volcanics and 18o evolved marine water aljustrel iberian pyrite belt transition from high to low rayleigh number convective regimes abstract quartz eye keratophyric tuffs at aljustrel s portugal iberian pyrite belt possess unusually high uniform whole rock values up to 18 1 with a mean of 16 7 0 7 because the quartz eye cores have 18o 12 0 to 13 5 the felsic tuffs may have had an original whole rock oxygen isotope composition of 10 to 11 the deduced enrichments of up to 8 in keratophyric derivatives is attributed to isotope exchange with abundant marine water under temperatures which diminished to 100 c during thermally driven convective cooling the isotopic uniformity requires elevated permeability of 10 8 cm2 such that the second critical rayleigh number was exceeded and drifting non steady state convection cells dominated with relatively smooth thermal structures in mineralised counterparts of the tuffs beneath the feitais estacao zn pb cu massive sulphide orebodies whole rock values are 12 and quartz 13 3 15 4 chlorite 3 2 6 3 fractionations correspond to temperatures of 220 270 c and a calculated fluid 18o of 1 4 to 5 7 this local isotopic overprinting in vent domains of the regionally high 18o was induced by a stable second stage convective regime imposed by drastic reduction of permeability accompanying capping of the geothermal discharge by hydrothermal cherts and or progressive spilitisation of the tuffs at lower water rock coupled with higher temperatures the recirculating marine water underwent variable 18o enrichment up to 5 7 by exchange with the high 18o tuffs an upwards increase in 18o quartz and quartz reflects progressive cooling of the geothermal discharge from 15 4 270 c in the stockwork through 18 3 220 240 c in the orebody to 20 1 110 130 c in overlying hydrothermal cherts probably induced by entrainment of ambient marine bottom water in sub seafloor aquifers

dissolved and particulate metals and arsenic species mobility along a stream affected by acid mine drainage in the iberian pyrite belt sw spain abstract intensive mining has taken place in the iberian pyrite belt since 3000 b c generating acid mine drainage amd and releasing high amounts of so 4 acidity metals and metalloids into surface water concentrations of elements in amd impacted waters are regulated by the precipitation of fe rich materials and particulate matter can influence the mobility and the bioavailability of metals in this paper a study on the dissolved as species concentration along a polluted stream has been performed two sampling campaigns were conducted during the dry and the rainy seasons concentrations of dissolved elements are higher during the dry season and increase progressively along the water course in both seasons concentrations up to 80 g l 1 of as 3 and 5 mg l 1 of as 5 were determined the concentration of as species increases and the as 3 as 5 ratio decreases downstream the fe 2 fe 3 and as 3 as 5 ratios show the same pattern with respect to ph for all the examined samples except those taken from au cyanidation wastes the particulate phase is mainly composed of fe as and pb with as being associated with the fe minerals while pb seems to be associated with the clay colloids

development of the california current during the past 12 000 yr based on diatoms and silicoflagellates detailed diatom and silicoflagellates records in three cores from the offshore region of southern oregon to central california reveal the evolution of the northern part of the california current during the past 12 000 yr the early holocene prior to 9 ka was characterizedbyrelativelywarmseasurfacetemperatures sst owingtoenhancednortherlyflowofthesubtropicalwaterscomparable tothemoderndavidsoncurrent progressivestrengtheningof thenorthpacifichighleadtointensificationofthesouthwardflowofthe california current at 8 ka resulting in increased coastal upwelling and relatively cooler sst which persisted until 5 ka reduced southward flow of the california current between 4 8 ka and 3 6 ka may have been responsible for a period of decreased upwelling modern seasonal oceanographic cycles as evidenced by increased spring early summer coastal upwelling and warming of early fall sst evolved between 3 5 and 3 2 ka widespread occurrence of paleoceanographic and paleoclimatic change between 3 5 3 0 ka along the eastern margins of the north pacific was likely a response to increasing enso variability in the tropical pacific published by elsevier b v

association between catastrophic paleovegetation changes during devonian carboniferous boundary and the formation of giant massive sulfide deposits abstract the iberian pyrite belt sw iberia is one of the largest sulfur anomalies in the earth s crust in the southern iberian pyrite belt more than 820 mt of exhalative massive sulfides were deposited in less than one million years at the devonian carboniferous boundary the shale of the ore bearing horizon contains biomarkers indicating major biogenic activity in a methanogenic setting including a five fold increase in typical vascular plant biomarkers and a significant anomaly in those probably indicating the presence of thermophilic archaea this contrasts with signatures in the average sedimentary rocks of the basin that indicate the sediments settled in oxic to sub oxic environments and that they have only minor biomarkers derived from continental paleoflora these data show that the formation of the mineralization was not only related to major hydrothermal activity synchronous with volcanism but may also have been controlled by the input of large amounts of organic matter mostly derived from the degradation of woodland detritus sourced in the nearby continent this massive influx of organic matter could have accelerated extremophilic microbial activity that used short chain hydrocarbons as electron donors for seawater sulfate reduction resulting in concomitant massive sulfide precipitation we propose that the giant massive sulfide deposits resulted from overlapping of geological and biological processes that occurred at the devonian to carboniferous transition including 1 continent collision during the onset of the variscan orogeny leading to major paleogeographic changes and volcanism 2 dramatic stress of continental ecosystems due to the combination of climatic change volcanism variations in the sea level and erosion on a regional scale 3 major biomass destruction and increase of organic supply to marine environments and 4 generation of anoxic conditions and the thriving of sulfate reducing microorganisms under these conditions massive sulfide deposits formed where venting sulfur poor but metal rich hydrothermal brines flowed into a hydrogen sulfide rich anoxic water column the data presented strongly suggest that there was a temporal and causal relationship between the devonian carboniferous geotectonic climatic and biological crises and the formation of the giant volcano sedimentary massive sulfide deposits of the southern iberian pyrite belt

mineralogy and geochemistry of the masa valverde blind massive sulphide deposit iberian pyrite belt spain abstract masa valverde is a blind volcanic hosted massive sulphide deposit recently discovered in the spanish sector of the iberian pyrite belt ipb the deposit is more than 1 km long and is located at depths between 400 and 850 m in direct spatial association with a residual gravimetric anomaly the ore body is concealed beneath culm sedimentary rocks which cover the western extension of a hercynian age anticline a few kilometers west of an area where older massive sulphide workings existed the masa valverde deposit consists of two main ore bodies composed dominantly of massive and banded pyrite which are hosted by a volcano sedimentary sequence made up of felsic tuffs interlayered with shale siliceous exhalite and radiolarian chert the abundance of sedimentary host rocks to the deposit is a feature shared by other large massive sulphide deposits in the eastern sector of the ipb and is interpreted as significant with respect to the origin of the deposit a break in volcanic activity the thickness of the upper massive sulphide orebody varies between a few meters and 70 m and it consists of lenses and blankets of massive sulphides with interbedded tuff and shale and occasionally stockwork zones the lower orebody is smaller and thinner than the upper one but this may be due to incomplete drilling two types of stockwork occur beneath the massive sulphide bodies the more common type consists of irregular and anastomosing sulphide veinlets and irregular blebs formed by replacement stockwork with cross cutting generally straight sided sulphide veins is by contrast suggestive of formation by hydraulic fracturing the mineralogy and alteration processes of the ore and host rocks at masa valverde are analogous to those of other ipb massive sulphides the average temperature of formation of the components of the ore zones estimated on the basis of chlorite thermometry are as follows siliceous exhalites 290 c massive sulphides 325 c and stockworks 305 c rare earth element measurements indicate that the lowest metal concentrations occur in chloritites which occasionally host cu rich stockwork and are characterised by a strongly negative eu anomaly by contrast rocks hosting the sulphide lenses where silicification sericitization and carbonatization are more intense are enriched in lree two main stages of hydrothermal activity are suggested for the masa valverde deposit during an early stage ore fluids would have discharged onto the sea floor resulting in the deposition of pyrite with sphalerite and galena later on with continued input of high temperature fluids 290 to 315 c chalcopirite precipitated especially in the stockworks and at the base of the sulphide lenses at masa valverde this late cu rich hydrothermal event would have produced an ascending cu front which overpassed the stockwork zone and reached a higher temperature 325 c at the base of the massive sulphide lenses the combination of geological mineralogical and geochemical features of the masa valverde deposit provide guidelines for exploration for new blind orebodies in this part of the ipb where tuffs and sedimentary rocks are the dominant host lithologies the masa valverde deposit can be considered as a vhms subtype transitional to shms

zn pb cu massive sulfide deposits brine pool types occur in collisional orogens black smoker types occur in backarc and or arc basins volcanic hosted massive sulfide deposits of zn pb cu type were derived either from seawater dominated buoyant fluids that built mounds on the seafloor e g the ores of the hokuroku basin japan or from saline fluids that reversed buoyancy on mixing with seawater and filled basins on the seafloor e g several ores of the iberian pyrite belt and the mount read province in tasmania the hokuroku ores formed above subduction zones during protracted periods of regional extension but both the iberian pyrite belt and the mount read province formed under extensional stress during continent continent iberia or arc continent mount read collision and orogenesis in the iberian pyrite belt oblique convergence resulted in transcurrent faulting and this may also be the case for the mount read province transcurrent faulting may have allowed easy vertical access for the ore related magmas some of which were sourced in the asthenosphere as well as the blueschist and eclogitic facies emplaced in adjacent terrains and possibly also saline fluids exsolved from the magmas

late hercynian polymetallic vein type base metal mineralization in the iberian pyrite belt fluid inclusion and stable isotope geochemistry s o h cl late variscan vein type mineralization in the iberian pyrite belt related to the rejuvenation of pre existing fractures during late variscan extensional tectonism comprises pyrite chalcopyrite quartz galena sphalerite quartz stibnite arsenopyrite quartz pyrite quartz cassiterite scheelite fluorite galena sphalerite chalcopyrite and quartz manganese oxide mineral assemblages studies of fluid inclusions in quartz stibnite and barite as well as the sulfur isotopic compositions of stibnite galena and barite from three occurrences in the central part of the iberian pyrite belt reveal compelling evidence for there having been different sources of sulfur and depositional conditions quartz stibnite mineralization formed at temperatures of about 200 c from fluids which had undergone two phase separation during ascent antimony and sulfide are most probably derived by alteration of a deeper lying volcanic hosted massive sulfide mineralization as indicated by 34s signatures from 1 45 to 2 74 sub critical phase separation of the fluid caused extreme fractionation of chlorine isotopes 37cl between 1 8 and 3 2 which correlates with a fractionation of the cl br ratios the source of another high salinity fluid trapped in inclusions in late stage quartz from quartz stibnite veins remains unclear by contrast quartz galena veins derived sulfide and metals by alteration of a sedimentary source most likely shale hosted massive sulfides the 34s values in galena from the two study sites vary between 15 42 and 19 04 barite which is associated with galena has significantly different 34s values 0 2 to 6 44 and is assumed to have formed by mixing of the ascending fluids with meteoric water

gold mineralisations in the sw iberian pyrite belt the occurrence and distribution of gold in the massive sulfide orebodies of the upper palaeozoic volcano sedimentary environment of the sw iberian pyrite belt have long been assumed to be quite uniform recent investigations in several working mines indicate that the gold content of the ores varies between ore types and is controlled by physico chemical and time factors during deposition above average gold grades occur in the following ore types lead zinc rich ores situated laterally and on top of the massive sulfide lenses copper rich siliceous basal ore facies footwall stringer sulfides and gangue rich massive sulfides siliceous carbonate rich baryte bearing or carbonaceous matrix exploration possibilities therefore are promising in foot and hanging wall environments within an orebody as well as in disseminated and stringer ores in its footwall

high resolution climate of the past 7300 years of coastal northernmost california results from diatoms silicoflagellates and pollen piston core tn062 o550 collected about 33 km offshore of eureka california contains a high resolution record of the climate and oceanography of coastal northernmost california during the past 7 34 kyr chronology established by nine ams ages on a combination of planktic foraminifers bivalve shell fragments and wood yields a mean sedimentation rate of 103 cm kyr 1 marine proxies diatoms and silicoflagellates and pollen transported by the nearby eel river reveal a stepwise development of both modern offshore surface water oceanography and coastal arboreal ecosystems beginning at 5 4 cal ka the relative abundance of coastal redwood pollen a proxy for coastal fog displays a two fold increase suggesting enhanced coastal upwelling a decline in the relative contribution of subtropical diatoms at 5 0 cal ka implies cooling of sea surface temperatures ssts at 3 6 cal ka an increase in the relative abundance of alder and oak at the expense of coastal redwood likely signals intensified riverine transport of pollen from inland environments cooler offshore ssts and increased precipitation characterize the interval between 3 6 and 2 8 cal ka a rapid stepwise change in coastal climatology and oceanography occurs between 2 8 and 2 6 cal ka that suggests an enhanced expression of modern pacific decadal oscillation like pdo cycles a three fold increase in the relative abundance of the subtropical diatom fragilariopsis doliolus at 2 8 cal ka appears to mark an abrupt warming of winter ssts soon afterwards at 2 6 cal ka a two fold increase in the relative abundance of coastal redwood pollen is suggestive of an abrupt intensification of spring upwelling after 2 8 cal ka a sequence of cool warm pdo like cycles occurs wherein cool cycles are characterized by relative abundance increases in coastal redwood pollen and decreased contributions of subtropical diatoms whereas opposite proxy trends distinguish warm cycles

evolution of hydrothermal fluids in the ashanti gold belt ghana stable isotope geochemistry of carbonates graphite and quartz the oxygen and carbon isotope systematics of ankerite siderite calcite quartz and graphite from the bogosu and prestea mining districts of the ashanti gold belt ghana are used to speculate on the processes leading to hydrothermal alteration and gold deposition the geologic environment of this turbidite and graywacke hosted gold system was a sediment dominated accretionary complex the gold ores are localized within the ashanti structural belt which we suggest became a conduit for deep seated fluids during uplift and dilatancy ankerite and siderite in mineralized sedimentary rocks are broadly similar in oxygen and carbon isotope compositions to corresponding minerals in the metasedimentary country rocks evidence of alteration that preceded gold mineralization is best preserved in spatially associated altered mafic dikes the compositions of fluids responsible for the gold mineralization and associated alteration have been reconstructed using temperatures from carbonate mineral geothermometry alteration of country rocks occurred under rock dominant greenschist facies conditions the isotopic composition of the least altered mafic dikes was influenced by interaction with fluids generated from birimian greenschist facies metasedimentary rocks later extensive carbonate alteration of mafic dikes adjacent to the structural conduit occurred during slow upward migration of fluids lateral diffusion of hydrogen into the structural conduit permitted partial conversion of co 2 to methane resulting in 13 c enrichment of both the residual co 2 and the deposited carbonate minerals rapid even explosive expulsion of deep seated fluids and co 2 h 2 o phase separation occurred episodically throughout the evolution of the hydrothermal system this caused precipitation of sulfides arsenides and gold at relatively high crustal levels and low ambient pressure and temperature during mineralization fluid ascent was too rapid for isotopic and chemical reequilibration between the deep seated ore fluid and adjacent country rocks the ore fluid had chemical and isotopic compositions consistent with deep seated metamorphic fluids that were subsequently modified by preferential partitioning of 18 o and 13 c into a gas phase the composition of the deep seated metamorphic fluid determined using chemical equilibria co 2 h 2 o rich 7 25 mole co 2 is in approximate agreement with that required to produce the isotopic depletion of the residual fluid via phase separation

the high grade las cruces copper deposit spain a product of secondary enrichment in an evolving basin the las cruces deposit iberian pyrite belt includes a large high grade cementation zone capped by unusual rocks that contain carbonates galena iron sulphides and quartz between the late cretaceous and tortonian the volcanogenic massive sulphides were exhumed and affected by subaerial oxidation that formed paired cementation and gossan zones onset of alpine extension produced accelerated growth of the cementation zone along extensional faults leading to formation of the high grade copper ore at ca 11 ma later replacement of the overlying gossan by sulphide and carbonate rich rocks beneath sealing marl sediments is thought to have involved microbial processes occurring between the messinian ca 7 2 ma and today isotope data show that the cementation zone formed by the mixing of descending acidic waters derived from oxidation of the massive sulphides with upwelling geothermal waters flowing at temperatures above 100 c the c o and sr isotope values of the mineralization 87sr 86sr 0 7101 0 7104 and of the local groundwater 0 7102 0 7104 reflect equilibration with basement rocks and indicate that influence on the ore forming process by marl equilibrated water 0 7091 0 7093 or miocene seawater 0 7086 0 7092 was negligible the high sulphur isotope values of the sulphides in the biogenic zone most 19 to 24 are well above those of the primary sulphides 34s ca 6 8 to 10 3 and likely reflect formation of the biogenic sulphides by reduction of aqueous sulphate in the groundwaters sulphur isotope values of the cementation zone 34s ca 2 4 to 21 7 are also consistent with some contribution of sulphur from the biogenic reduction of aqueous sulphate