recycling of iodine in fore arc areas evidence from the iodine brines in chiba japan the distribution of iodine in the earth s crust is dominated by its accumulation in marine sediments if fluxes between terrestrial and marine compartments are considered however a significant imbalance exists between known sources and sinks of iodine we present here evidence from the fore arc area near chiba japan the world s largest brine iodine producing area that iodine is mobilized from marine sediments during the early stages of subduction based on detailed chemical analyses of 22 brines and 129i dating of 13 of these samples collected from the kazusa formation we show that iodine in these fluids is derived from organic rich marine sediments with a minimum age of 50 myr geochemical characteristics of the brines and the age of the iodine indicate that the iodine enrichment is caused by mobilization from subducting marine sediments and not by derivation from the host formation age 1 2 myr the direct return of iodine from marine sediments into the oceans during the subduction of oceanic plates could provide the missing link in the iodine cycle and be an important pathway also in the marine cycle of carbon

geochemistry and geochemical modeling of unsaturated zone in a tropical region in urânia sao paulo state brazil summary the geochemistry of a thick unsaturated zone in a tropical region in ur nia sao paulo state brazil has been investigated the site was instrumented for pressure head measurements and pore water sampling above the water table at 9 5 m depth the composition of the solid phase was determined by x ray diffraction optical microscopy sem and microprobe and icp aes analyses of decomposed samples the unsaturated zone is composed mainly of clayey sand and can be subdivided into three zones a shallow zone down to depth of 2 m corresponding to the evaporation line an intermediate zone between 2 and 7 m where small wetting fronts dissipate and only longer recharge events are evidenced by changes of pressure head and a deep zone between 7 and 9 5 m where pressure heads are generally stable based on data collected during the recharge period in year 2000 the response time of water table to recharge event was of 3 months the solid phase is in an advanced stage of weathering and quartz and kaolinite are principal minerals pore water has a low mineralization and can be characterized as ca hco 3 type with high concentrations of nitrate at shallow depth the main factors that have an impact on pore water chemistry are 1 atmospheric input and nitrate pollution due to human activities 2 evaporation down to a depth of 2 m 3 plant respiration down to a depth of 7 m 4 dissolution of primary silicate minerals such as feldspars and the formation of secondary minerals like kaolinite and 5 adsorption and cation exchange analysis of the solid phase suggests that ferric oxides and hydroxides provide the principal adsorption surfaces inverse geochemical modeling yielded non unique results and both dissolution precipitation of silicates plus cation exchange and dissolution precipitation of amorphous silica plus cation exchange were able to match changes of water chemistry along the presumed flow path

sound velocities of majorite garnet and the composition of the mantle transition region the composition of the mantle transition region characterized by anomalous seismic wave velocity and density changes at depths of approximately 400 to 700 km has remained controversial some have proposed that the mantle transition region has an olivine rich pyrolite composition whereas others have inferred that it is characterized by pyroxene and garnet rich compositions piclogite because the sound velocities in pyrolite estimated from laboratory data are substantially higher than those seismologically observed although the velocities of the olivine polymorphs at these pressures wadsleyite and ringwoodite have been well documented those of majorite another significant high pressure phase in the mantle transition region with realistic mantle compositions have never been measured here we use combined in situ x ray and ultrasonic measurements under the pressure and temperature conditions of the mantle transition region to show that majorite in a pyrolite composition has sound velocities substantially lower than those of earlier estimates owing to strong nonlinear decreases at high temperature particularly for shear wave velocity we found that pyrolite yields seismic velocities more consistent with typical seismological models than those of piclogite in the upper to middle parts of the region except for the potentially larger velocity jumps in pyrolite relative to those observed at a depth of 410 km in contrast both of these compositions lead to significantly low shear wave velocities in the lower part of the region suggesting possible subadiabatic temperatures or the existence of a layer of harzburgite rich material supplied by the subducted slabs stagnant at these depths

breccias and ores part 1 history organization and petrography of breccias abstract although the term breccia is one of the oldest rock names still in use and proliferating in its application a satisfactory definition remains problematic and an overall classification of breccias is non existent the names of breccia varieties several hundred please the heart rather than the computer and there is little interdisciplinary correlation among the more than fifty specialized schools of breccia study this contribution reviews briefly the history of breccia research and provides a list of the present study trends complete with references with emphasis on ore associated breccias wherever possible conventional breccia definitions and their shortcomings are discussed and a case is made for the introduction of the petrographic category of coarse fragmentites of which the typical sedimentary breccias and conglomerates as well as volcanic tectonic hydrothermal impact and other fragmental materials are members whether designated or not as breccia in the conventional literature this is followed by a proposed rational organization classification of coarse fragmentites and breccias based on the regime of formation and architecture fabric gefuge two fundamental end member sequences a b and a transitional suite c can be recognized a disaggregation fragmentites d breccias produced from a solid progenitor by increasing rate of fracturing expansion rotation mixing and attrition the transitional sequence is crackle mosaic rubble melange milled breccia b aggregation fragmentites a breccias generated by gathering aggregation and accumulation of originally dispersed fragments at the site of deposition these materials form a sequence ranging from tightly packed fragment supported matrix free fragmentites through matrix infilled matrix supported fragmentites to lonestone rocks c in transport fragmentites t breccias formed by redeposition of an aggregate gathered in an earlier phase of development as an a fragmentite or by transportation and redeposition of an advanced member i e rubble melange or milled fragmental aggregate of a d fragmentite examples of metallic mineralizations coeval with or superimposed on the fragmentite sequences are reviewed

a first principles approach to supergene enrichment of a porphyry copper protore i cu fe s subsystem abstract a unified description of supergene enrichment of a porphyry copper protore is presented based on the principles of metasomatic zoning mathematically this formulation represents the supergene weathering process as a moving boundary problem a first principles approach is used to describe quantitatively the transport of oxygenated water through a porous host rock consisting of a cu bearing protore mineral reaction rates are represented by kinetic rate expressions for both precipitation and dissolution reaction zones containing mineral alteration products making up a leached zone oxide zone and enrichment blanket propagate downward in the direction of fluid transport the time evolution of the system is completely determined by the governing transport equations once initial and boundary conditions are specified giving the composition of the unaltered host rock and infiltrating fluid entering at the surface of the weathering column the description provides for both fully saturated conditions and undersaturated conditions in the presence of a water table at depth an order of magnitude estimate of the velocity of propagation of a redox front demonstrates that metasomatic effects become increasingly important as the o content of the infiltrating water increases regions of higher permeability resulting in higher fluid flow velocities lead to increased enrichment compared to regions of lower permeability with reduced flow velocities in agreement with field observations results of numerical calculations suggest that the enrichment blanket may be subdivided into three distinct zones 1 1 an enriched zone at the top of the blanket 2 2 the middle blanket in which chemical reactions of cu bearing minerals are absent and 3 3 the nascent blanket forming the interface between the protore and middle blanket both the nascent and middle blanket contain the same cu grade as the protore these results are in agreement with field observations of a high cu grade within a relatively narrow zone in the upper portion of the blanket results of numerical calculations for three different scenarios are presented the first example considers a simplified representation of the enrichment process with chalcopyrite covellite and chalcocite as the major cu minerals in this case chalcocite forms an enriched zone at the top of the blanket which migrates downward increasing in width the second and third examples differ by the presence of a water table at depth and include brochantite tenorite native cu and cuprite as secondary cu minerals in addition to the minerals used in the first example surprisingly in these two examples the enriched blanket zone does not grow indefinitely with time but reaches a steady state profile that is displaced rigidly in the direction of fluid transport without changing shape in the presence of a water table at depth the major enrichment occurs in the oxide zone lying above the blanket

using gemorphological markers to discriminate neogene tectonic activity in the precordillera of north chilean forearc 24 25 s abstract we study the neogene tectonic activity in a sector of the precordillera in the andean forearc analysing aerial photographs satellite images and fieldwork data the interpretation of alluvial landforms drainage organisation and evolution of intermittent river networks affecting post lower miocene deposits allow us to recognize low intensity tectonic processes controlling the landscape evolution all these geomorphological markers indicate no strike slip offsets but repeated and small tectonic pulses that reactivate previous structures originated under a transpressive context the observed deformation pattern is the consequence of e w orthogonal compression resulting in limited shortening related to the accommodation of deformation in the chilean forearc of the neogene uplift of the altiplano puna

phase transition in mgsio 3 perovskite in the earth s lower mantle a new polymorph of mgsio3 more stable than the pbnm perovskite phase has been identified by first principles computations it has the cairo3 structure with cmcm symmetry and consists of sio3 layers intercalated by eightfoldcoordinated mg ions high temperature calculations within the quasiharmonic approximation give a volume change of f1 5 and a clapeyron slope of f7 5f0 3 mpa k at f2750 k and f125 gpa these pressure temperature p t conditions are close to those in which a phase transition in mgsio3 perovskite has been observed by in situ angle dispersive x ray diffraction measurements this transition appears to be associated with the du discontinuity d 2004 elsevier b v all rights reserved

secondary copper enrichment in tailings at the laver mine northern sweden field and laboratory studies of the sulphide bearing tailings at laver northern sweden show that the present release of metals from the tailings is low especially with regard to cu a large part of the cu released by sulphide oxidation is enriched in a distinct zone just below the oxidation front the enrichment zone occurs almost all over the tailings area except in areas with a shallow groundwater table the cu enrichment is caused by formation of covellite and adsorption onto mineral surfaces the transport of zn co cd ni and s seems to be controlled mainly by adsorption no secondary zone or secondary minerals containing these metals have been found just below the groundwater table metals are released into solution when the enrichment zone reaches the groundwater due to the low ph an increased release of metals especially cu can be expected in the future since the enrichment zone is moving towards the groundwater table

preliminary evidence for the involvement of budding bacteria in the origin of alaskan placer gold lacelike networks of micrometre size filiform gold associated with alaskan placer gold particles are interpreted as low temperature pseudomorphs of a pedomicrobium like budding bacterium submicron reproductive structures hyphae and other morphological features similar to those of pedomicrobium manganicum occur as detailed three dimensional facsimiles in high purity gold in and on placer gold particles from lillian creek alaska in a scanning electron microscope survey the majority of gold particles at nine alaskan placer deposits appear to include gold that has accumulated chemically at low temperatures in and on the cells of p manganicum similar bacterioform gold from a paleozoic deposit in china and from the precambrian witwatersrand deposit in south africa may indicate that bacterioform gold is widespread

case study numerical modeling of the tidal bore on the qiantang river china the tidal bore at the estuary of the qiantang river in china is one of the most spectacular bores in the world although it is a famous scenic spot it may cause disasters due to its destructive power in this paper a new numerical model based on a godunov type scheme with the water level bottom topography formulation combined with the improved wet dry techniques is constructed to numeri cally simulate the tidal bore on the qiantang river the simulated results using the model agree well with observed data which shows that the model can reproduce the formation evolution and dissipation of the tidal bore on the qiantang river

first principles investigations on the elasticity and phase stability of grossular garnet 1 in order to understand the fate of subducted continental materials by means of mechanisms such as tectonic erosion and sediment subduction it is important to understand the high pressure stability and elastic properties of grossular garnet we study these questions using the first principles computation method grossular garnet was found to dissociate into an assemblage of casio3 ca perovskite pv and al2o3 corundum cor at about 23 4 gpa accompanied by remarkable jumps of compressional wave 8 0 shear wave 11 6 bulk sound 5 7 velocities and density 12 1 although pv with the grossular garnet composition was suggested experimentally after the decomposition reaction this phase was found to be less stable than an assemblage of capv and cor at pressures higher than 20 gpa this indicates that observed pv with the grossular garnet composition is metastable but can be obtained because of the slow kinetics of the garnet decomposition reaction our results imply that the dissociation of grossular garnet as well as that of jadeite included in continental materials subducted into the deep mantle increases the complexity of the 660 km discontinuity and can explain seismically observed multiple reflections we have also investigated the anisotropy of elastic velocities of grossular garnet capv and cor and found that capv is the most anisotropic mineral this implies that capv could produce seismic anisotropy in the uppermost lower mantle

characteristics of undular hydraulic jumps experimental apparatus and flow patterns in open channels the transition from supercritical to subcritical flows is called a hydraulic jump for low upstream froude numbers free surface undulations develop downstream of the jump and the hydraulic jump is called an undular jump new experiments on undular hydraulic jumps were performed in a rectangular channel in which the upstream flows were fully developed turbulent shear flows in this paper the main flow patterns are described visual and photographic observations indicate five types of undular jumps one of the main flow characteristics is the presence of lateral shock waves for froude numbers larger than 1 2 the results show that the disappearance of undular jump occurs for froude numbers ranging from 1 5 to 2 9 and that the wave length and amplitude of the free surface undulations are functions of the upstream froude number and the aspect ratio yc w

sedimentation and preservation of the miocene atacama gravels in the pedernales chanaral area northern chile climatic or tectonic control in recent years longitudinal changes on the thin thick skinned tectonic styles of the central andes has been intensively discussed while other studies have considered the role of mass transfers on the unloading the orogen and on the stress regime along the plate interface arising from changes on the volume of sediment arriving into the peru chile trench the search for paleo climate records is therefore crucial for our understanding of the history of the central andes in this paper we focus on the atacama gravels an extensive blanket of miocene continental deposits filling a neogene paleo valley system along the southern atacama desert in northern chile an east west transect between pedernales and chanaral 26o30 s enabled us to carry out a sedimentological and tectonic study of the atacama gravels based on logging and field observations along the rio salado canyon new 39ar 40ar ages obtained on intercalated and overlying ignimbrites date the beginning of the atacama gravels sedimentation at around the oligocene miocene boundary and cessation of sedimentation in the late miocene thirteen lithofacies included within five facies associations a1 to a5 were identified depositional environments vary from proximal alluvial fan a1 a2 in the precordillera through ephemeral fluvial a3 a4 to distal playa lake a5 in the coastal cordillera no evidences of syn sedimentary deformation have been found showing that the change from sediment removal to sediment preservation cannot be explained by tectonic causes and climate change appears to be the dominant controlling factor of sediment preservation a progressive change from semi arid towards hyper arid climatic conditions during the miocene led to a reduction on the transport capacity of the fluvial system and sediment preservation along the paleovalley system formed during the oligocene

mineralogical and geochemical behavior of mill tailing material produced from lead zinc skarn mineralization hanover grant county new mexico usa mineral extraction and processing especially metal mining produces crushed and milled waste such material exposed to weathering poses the potential threat of environmental contamination in this study mill tailings from inactive pb zn mines in new mexico southwest usa have been examined for their potential environmental impacts by means of detailed mineralogical and geochemical characterization the principal ore minerals remaining in the tailings material are sphalerite chalcopyrite and very minor galena smithsonite and cerrusite accompanied by the gangue minerals pyrite pyrrhotite magnetite hematite garnet pyroxene quartz and calcite white precipitate occurring on tailings surfaces is composed of gypsum and hydrated magnesium sulfates pyrite is mostly unaltered or shows only micron scale rims of oxidation goethite hematite in some surface samples this iron oxide rim on pyrite is the only indication of weathering derived minerals found by microscopy there are variations in element concentrations with depth that reflect primary variations through time as the tailings ponds were filled cadmium and zn concentrations increase with depth and ag and pb are low for the uppermost core samples while cu ni and co concentrations are generally high for the uppermost core samples these elemental distributions indicate that little or no leaching has taken place since emplacement of the tailings because no accumulation or enrichment of these metals is observed in hanover tailings even in reducing portions of tailings piles element concentrations of surface samples surrounding the tailings reflect underlying mineralized zones rather than tailings derived soil contamination we observed no successive decreasing metal concentrations in prevalent wind directions away from the tailings stream sediment samples from hanover creek have somewhat elevated zn cd and pb concentrations in areas that receive sediments from erosion of the tailings however input from tributaries downstream of the ponds appears to be principal source of heavy metals in hanover creek the results of this study indicate that there is low risk for groundwater heavy metal contamination from hanover tailings tailings material do not show significant geochemical oxidation alteration or metal leaching with depth our studies indicate that neutralizing minerals present in the tailings are sufficient to keep the tailings material chemically stable geochemically however tailings materials are being eroded and may pose a threat to hanover creek via siltation

ultra deep oxidation and exotic copper formation at the late pliocene boyongan and bayugo porphyry copper gold deposits surigao philippines geology mineralogy paleoaltimetry and their implications for geologic physiographic and tectonic controls the boyongan and bayugo porphyry copper gold deposits are part of an emerging belt of intrusion centered gold rich deposits in the surigao district of northeast mindanao philippines exhumation and weathering of these late pliocene age deposits has led to the development of the world s deepest known porphyry oxidation profile at boyongan 600 m and yet only a modest 30 70 m oxidation profile at adjacent bayugo debris flows volcanic rocks and fluviolacustrine sediments accumulating in the actively extending mainit graben subsequently covered the deposits and preserved the supergene profiles at boyongan and bayugo there is a vertical transition from shallower supergene copper oxide minerals malachite azurite cuprite to deeper sulfide stable assemblages chalcocite hypogene sulfides this transition provides a time integrated proxy for the position of the water table at the base of the saturated zone during supergene oxidation contours of the elevation of the paleopotentiometric surface based on this mineralogical transition show that the thickest portions of the unsaturated zone coincided with a silt sand matrix diatreme breccia complex at boyongan within the breccia complex the thickness of the unsaturated zone approached 600 m whereas outside the breccia complex e g at bayugo the thickness averaged 50 m contours of the paleopotentiometric surface suggest that during weathering groundwater flowed into the breccia complex from the north south and east and exited along a high permeability zone to the west the high relief 550 m on the elevation of the paleopotentiometric surface is consistent with an environment of high topographic relief and the outflow zone to the west of the breccia complex probably reflects proximity to a steep scarp intersecting the western breccia complex margin stable isotope paleoaltimetry has enabled estimation of the elevation of the land surface which further constrains the physiographic setting during supergene oxidation isotopic measurements of oxygen in supergene kaolinite from boyongan suggest that local paleometeoric water involved in weathering had a 18o composition of approximately 5 7 per mil at the latitude of the southern philippines this value corresponds to pleistocene rain water condensing at elevations between 750 and 1 050 m above contemporary sea level providing a maximum estimate for the surface elevation during weathering of the porphyry systems physiographic reconstructions suggest that the deep oxidation profile at boyongan formed in an environment of high topographic relief immediately east of a prominent 550 m escarpment the high permeability contrast between the breccia complex and the surrounding wall rocks coupled with the proximity of the breccia complex to the escarpment led to a depressed groundwater table and a vertically extensive unsaturated zone in the immediate vicinity of boyongan this thick vadose zone and the low hypogene pyrite copper sulfide ratios 0 6 at boyongan promoted in situ oxidation of copper sulfides with only modest 200 m supergene remobilization of copper in contrast higher hypogene pyrite chalcopyrite ratios 2 3 at bayugo led to greater acid production during weathering and more complete leaching of copper above the base of oxidation this process promoted significant 600 m lateral dispersion of copper down the paleohydraulic gradient into the diatreme breccia comple ultimately leading to the formation of an exotic copper deposit

the high pressure single crystal elasticity of pyrope grossular and andradite high pressure brillouin scattering experiments were conducted on three natural singlecrystal garnets with near end member compositions pyrope mg3al2si3o12 grossular ca3al2si3o12 and andradite ca3fe 31 2si3o12 acoustic velocities of the samples were measured from the samples at pressures to 10 gpa in a diamond anvil cell with a methanolethanol water pressure medium elastic stiffness constants cij and their pressure dependencies cij p were calculated as were aggregate elastic moduli ks and g and their respective pressure derivatives the cauchy relations changed with pressure for both grossular and andradite suggesting that assuming these are constant is not valid for extrapolation to high pressures for these and possibly other minerals the variation in ks dp and g p was sensitive to composition and required a complex mixing model for extrapolation of end member elasticity values from garnets of intermediate compositions

phase relations in the system mgsio 3 al 2 o 3 up to 52 gpa and 2000 k abstract phase relations in the system mgsio3 al2o3 have been determined for pressures from 15 to 52 gpa and at a temperature of 2000 k from in situ synchrotron x ray diffraction measurements obtained using sintered diamond anvils in a multi anvil apparatus a wide two phase region of garnet and corundum is found to exist up to 27 gpa at higher pressures a phase assemblage of aluminous bridgmanite and corundum is stabilized the solubility of al2o3 in bridgmanite and that of mgsio3 in corundum are highly dependent on pressure the al2o3 content in bridgmanite increases from 12 mol at 27 gpa to 29 mol at 52 gpa forming bridgmanite with the pyrope composition 25 mol al2o3 at about 45 gpa in contrast the mgsio3 content in corundum decreases from 24 mol at 27 gpa to 9 mol at 52 gpa the minimum pressure where the pyropic bridgmanite is formed is significantly higher than the result of the earlier study 37 gpa on the pyrope composition these results suggest the al2o3 content in bridgmanite and the mgsio3 content in corundum are good pressure indicators in the mixed phase region at pressures above 30 gpa where virtually no pressure references are available for quench experiments the new phase diagram in the system mgsio3 al2o3 confirms that bridgmanite is the dominant host mineral for al2o3 in the pyrolitic or peridotitic compositions under the pressure and temperature conditions of the earth s lower mantle

supergene features and evolution of gossans capping massive sulphide deposits in the iberian pyrite belt abstract twelve massive sulphide deposits from the iberian pyrite belt ipb show well preserved iron caps some of which were mined during the last century to recover precious metals e g tharsis rio tinto san miguel field observations and correlation assays between the distinct mineral sequences at different deposits suggest that all the gossans were developed under similar conditions and have undergone the same geological events all the gossans have a mushroom like morphology in sharp contact with the underlying massive sulphide orebodies in most cases these are located over an apparent supergene enrichment zone rich in secondary sulphides some gossans extend into tongues of alluvial heterolithic breccias consisting of eroded transported gossans displaced as far as several hundred meters away from their sources the distribution of major minerals throughout the gossan profiles goethite hematite quartz and jarosite and the statistical analysis of the geochemical data distinguish three separate zones with gradual contacts roughly parallel to the current topography 1 the lower zone dominated by goethite and subordinate jarosite with significant enrichment in s as p pb sn sb ag and au 2 the middle or principal zone dominated by goethite and lacking jarosite which is depleted in s and as as well as heavy and precious metals and 3 the upper zone near the surface mainly composed of hematite and quartz with only weak anomalies in p pb and sn the origin and variations occurred in the profiles are explained by a three stage process this involves an initial acidic stage of gossan development centred on the oxidation of sulphides that lead to the formation of the first fe rich oxyhydroxides and sulphates mainly goethite and jarosite respectively over time a progressive stage of maturity is reached progressively downwards through the gossan profile due to the intensification of the oxidation and leaching processes the ongoing gossan formation produced alteration and reprecipitation of pre existing oxyhydroxides the loss of the majority of the previously sorbed heavy metals and a major dilution of trace elements especially in the zones near the surface the main results of this stage of formation are the production of heavy metal depleted oxyhydroxides most commonly goethite and hematite and the disappearance of jarosite subsequently local uplift of the gossanous rocks by neotectonic movements facilitated the rejuvenation of the oxidation of the ores this final stage complicated the previously developed zonation with the formation of jarosite in mature areas possible major breaks in this gossan development ocurred in messinian times 7 8 ma and at the beginning of the early quaternary 1 2 ma

geology of the escondida porphyry copper deposit antofagasta region chile the escondida porphyry copper deposit located in northern chile was one of the two largest copper producers of the world in the 1990s the hydrothermal evolution of this deposit is associated with the emplacement of a late eocene oligocene quartz monzonitic to granodioritic intrusive stock complex composed of at least three intrusive phases and hosted by paleocene andesite this paleocene andesite is underlain by mesozoic and paleozoic sedimentary and volcanic rocks which are characteristic of the basement of the precordillera de domeyko province in northern chile we propose that the intrusive stock associated with the mineralization at escondida was emplaced in a tensional gash formed between sinistral strike slip faults of the regional domeyko fault system the complete evolution of the porphyry system is characterized by overprinting of pervasive and vein associated alteration mineralization styles grouped in three main hydrothermal stages the early stage includes a zone of pervasive biotitization of andesite and development of a silicification shell around the intrusive complex propylitic alteration around the biotitic zone and a vein associated orthoclase quartz anhydrite biotite alteration that mark the end of stage one this early alteration contains magnetite chalcopyrite and bornite with less than 0 5 vol percent of sulfides and a hypogene copper grade of 0 2 wt percent the second hydrothermal stage is represented by vein and vein selvage associated chlorite sericite quartz and by quartz sericite with sulfides including chalcopyrite pyrite and molybdenite in the chlorite sericite and quartz sericite zones the content of sulfides ranges from less than 0 5 to 2 vol percent with a chalcopyrite to pyrite ratio of 3 to 1 and copper grades that range between 0 4 and 0 6 wt percent the intrusion of a rhyolite dike and a dome are at least 3 m y younger than the first and second hydrothermal stages and separate them in time from the late hydrothermal stage the late hydrothermal stage is represented by an acid sulfate mineral association that includes pyrophyllite alunite and quartz as alteration minerals and a variety of sulfides that include bornite chalcopyrite pyrite chalcocite covellite enargite sphalerite tennantite and galena this acid sulfate event occurred mainly in west northwest striking veins and also along the contact of the rhyolite and its host rock where sulfides from this event overprint previous sulfides the primary copper grades range from 0 6 to higher than 1 0 wt percent in the escondida deposit the highest hypogene and supergene copper grades occur in areas where all three hydrothermal stages are present

stable isotope geochemistry of copper carbonates at the northwest extension deposit morenci district arizona implications for conditions of supergene oxidation and related mineralization stable isotope analyses were performed on 39 copper carbonate samples from the las terrazas fault zone of the northwest extension copper oxide deposit morenci district arizona the 18 o values of azurite 23 3 25 5 smow and malachite 21 0 23 5 smow indicate formation in supergene conditions from meteoric water oxygen isotope thermometry suggests oxidation occurred at temperatures between 20 and 34 c with lower temperatures representing ambient air temperatures and higher temperatures reflecting minor heat production by exothermic oxidation of sulfides for malachite a relationship between higher temperatures and higher local oxide copper grade suggests in situ formation from oxidizing copper sulfides whereas for azurite the lack of such a relationship and field evidence suggest formation from copper transported along major structures azurite 13 c values range from 4 2 to 10 7 per mil and exhibit isotopic enrichment with increasing height above the supergene enrichment blanket paleowater table this evidence suggests that azurite samples received significant amounts of organic carbon resulting from the oxidation of bacteria known to be instrumental in supergene sulfide enrichment processes adjoining the water table with upward diffusive enrichment producing the observed enrichment in 13 c with height above the water table malachite 13 c values range from 9 6 to 11 1 per mil and suggest a carbon source from oxidation of surface vegetation and or dissolution of primary or secondary carbonate by a rising water table during supergene processes detailed investigation of millimeter scale isotopic profiles across azurite veins suggests a carbon source that is initially lighter than whole vein sample measurements with progressive isotopic enrichment of the carbon source or reservoir during vein formation this as well as the fact that partial pressures of co 2 must exceed atmospheric levels for azurite formation indicates that these veins formed in a system that was at least partially closed to the atmosphere oxygen isotope thermometry indicates many of the veins formed at temperatures up to 10 c above ambient temperatures with a drop to ambient temperatures during final vein growth isotopic and field evidence indicate that the northwest extension oxide deposit formed when a shallow early stage copper sulfide enrichment blanket was stranded above the water table relatively low temperature oxidation of these sulfides produced copper rich solutions that were transported along major structures and azurite formed when the fluids intersected pockets of high p co 2 possibly produced by seasonal oxidation of supergene related bacteria above the water table over time oxidation and related mineralization reduced permeability along major structures and bacterial populations waned as deeper sulfide enrichment processes slowed lower p co 2 and reduced transport potential produced in situ and highly localized oxidation centered on the high grade zones of the early sulfide blanket remaining in the oxidation zone with malachite as a dominant phase

the deposition of elemental gold from gold i thiosulfate complexes mediated by sulfate reducing bacterial conditions the role of sulfate reducing bacteria in the precipitation of elemental gold through a geologic stratum was investigated using column experiments the mixed culture dominated by sulfate reducing bacteria was isolated from the driefontein consolidated gold mine witwatersrand basin republic of south africa bacterially mediated gold precipitation from the gold i thiosulfate complex was more efficient than the corresponding abiotic experiments in the bacterial systems sulfate reducing bacteria i e desulfovibrio sp deposited gold inside the cells as spherical nanoparticles over time these nanoparticles of gold were released from the cells and deposited at cell surfaces and in the bulk solutions ultimately these nanoparticles of gold contributed to the formation of micrometer scale octahedral gold crystals occasional framboidlike structures 1 5 m diam and millimeter scale gold foils typically surrounding the silicate grains spherical gold particles 1 m diam were precipitated in the abiotic experiments and the formation of octahedral gold framboidlike structures and gold foils were not observed in these experiments the reduction and enrichment of elemental gold by sulfate reducing bacteria occurred without the concomitant death of the bacteria suggesting that in natural systems this process could go on over geologic time scales as long as nutrients and gold i thiosulfate were provided to the system

paleohydrologic evolution and geochemical dynamics of cumulative supergene metal enrichment at la escondida atacama desert northern chile quantitative limonite mapping within the leached capping of the porphyry copper deposit at la escondida chile permits reconstruction of the paleohydrologic and chemical evolution of a well developed supergene ore forming system the mineralogy textures and relative abundance of supergene limonite minerals hematite goethite and jarosite are used to reconstruct the former ratio of pyrite to chalcocite and the preoxidation copper grade based on empirical limonite sulfide correlations after locke 1926 blanchard 1968 and loghry 1972 estimates of preoxidation copper grades in surface exposures and tops of drill holes at la escondida are significantly lower than actual copper grades in the underlying enrichment blanket at depth this apparent inconsistency is explained by a progressive increase in the copper grade of the sulfide enrichment blanket as it descended to its present location in response to a descending water table this systematic trend of reconstructed grades of supergene enriched copper sulfide increasing with depth offers the first quantitative proof of cumulative downward enrichment in a supergene profile as proposed by locke 1926 the consistent trends of limonite mineralogy and abundance in vertical profiles indicate that water table descent at la escondida was relatively continuous in space although not necessarily in time evidence for cumulative downward enrichment in vertical profiles through leached capping allows quantitative analysis of chemical mass balance in dynamic supergene systems slopes of linear regressions for profiles of reconstructed enriched copper grades vs depth indicate lateral fluxes into or out of a given vertical profile this method provides independent verification of conclusions from a previous study of copper mass balance at la escondida brimhall et al 1985 which showed that lateral fluxes of copper were a significant factor during supergene leaching and enrichment

iodine rich waters involved in supergene enrichment of the mantos de la luna argentiferous copper deposit atacama desert chile recent studies have suggested the involvement of highly saline deep formation waters that modified preexisting cu assemblages to form atacamite during supergene oxidation of cu deposits in the atacama region in this report we document the occurrence of ag i inclusions hosted by supergene chalcocite from mantos de la luna an argentiferous upper jurassic stratabound cu deposit in the coastal range of northern chile the presence of this unusual mineral assemblage indicates that iodargyrite precipitated from reducing iodine rich waters suggesting that the fluids involved in supergene enrichment of cu deposits in the coastal range were more complex than previously thought this suggests the prevalence of hyperarid conditions during the latest stages of supergene enrichment of the mantos de la luna cu deposit in the atacama region supporting the notion that supergene enrichment processes in hyperarid areas are dynamic in nature and do not exclusively require the presence of meteoric water

magmatic relationships and ages between adakites magnesian andesites and nb enriched basalt andesites from hispaniola record of a major change in the caribbean island arc magma sources abstract located in the cordillera central of the dominican republic the late cretaceous tireo fm tf records a major change of the magma sources in the caribbean island arc it comprises a 3 km thick sequence of arc related volcanic and volcano sedimentary rocks with variable geochemical characteristics combined detailed mapping stratigraphy geochemistry and u pb ar ar geochronology show that the volcanic rocks of the tireo fm include two main volcanic sequences the lower volcanic sequence is dominated by monotonous submarine vitric lithic tuffs and volcanic breccias of andesite to basaltic andesite with minor interbedded flows of basalts and andesites fossil and u pb and 40ar 39ar geochronological data show that arc magmatism in the lower sequence began to accumulate before 90 ma from the aptian to turonian these rocks constitute an island arc tholeiitic suite derived from melting by fluxing of a mantle wedge with subduction related hydrous fluids the upper volcanic sequence is characterized by a spatial and temporal association of adakites high mg andesites and nb enriched basalts which collectivelly define a shift in the composition of the subduction related erupted lavas a dacitic to rhyolitic explosive volcanism with subaerial and episodic aerial eruptions and sub volcanic emplacements of domes characterize mainly this stratigraphic interval the onset of this volcanism took place at turonian coniacian boundary and continued in the santonian to lower campanian with minor events in the late campanian adakites represent melts of the subducting slab magnesian andesites the product of hybridization of adakite liquids with mantle peridotite and nb enriched basalts melts of the residue from hybridization we propose a model of oblique ridge subduction at 90 ma and possibly subsequent slab window formation as principal cause of magmatic variations recorded in the caribbean island arc above a southwestern dipping subduction zone

in situ measurements of the phase transition boundary in mg3al2si3o12 implications for the nature of the seismic discontinuities in the earth s mantle abstract here we report the phase boundary of pyrope garnet mg3al2si3o12 to al bearing silicate perovskite plus corundum with the highest transition pressure determined by in situ measurements in a multi anvil apparatus at high temperature the consistency of the pressure scales by different standards of au nacl pt w and mo at high temperature was also evaluated by in situ x ray measurements our results together with recent in situ measurements of the post spinel transition in mg2sio4 irifune et al science 279 1998 1698 1700 and the ilmenite perovskite transition in mgsio3 ono et al geophys res lett 2000 submitted show that pressures determined in conventional quench experiments ito and takahashi j geophys res 94 1989 10637 10646 could have been overestimated by more than 2 gpa at pressures corresponding to the bottom of the transition zone on the basis of the in situ measurements the post spinel transition occurs at a depth 600 km that is too shallow to match with the 660 km seismic discontinuity in the earth s mantle therefore an olivine dominant mantle compositional model may be inconsistent with the seismic observations alternatively we propose a pyroxene garnet dominant transition zone with an appropriate al2o3 content ca 6 8 mol in which majorite garnet transforms to perovskite at the depth of the 660 km discontinuity any alternative models would have to consider chemical stratification in the mantle

influence of varying shape and depth on the generation of tidal bores understanding the formation of tidal bores is of great importance to the changing morphology of estuaries this study investigates how the slope of tidal bores front changes by influence of varying shape and depth in estuaries a new analytical solution of the slope was derived from the 1d shallow water equation and two numerical models were developed based on the upwind scheme and superbee schemes to simulate the propagation of tidal waves six cases were utilized to investigate the influences of decreasing width and depth on the generation of tidal bores analytical results suggest that the initial depth is considered to have more significant influence on the generation of tidal bore than the initial width compared with the analytical results scheme 2 which is based on superbee scheme is found to be superior to the other scheme and its results show a good agreement with the new analytical solution both analytical and numerical results show that the decrease of width and depth can promote the generation of tidal bores in contrast tidal bores may weaken or even not form due to the energy dissipation bottom friction induced

atacamite in the oxide zone of copper deposits in northern chile involvement of deep formation waters atacamite a copper hydroxychloride is an important constituent of supergene oxide zones of copper deposits in northern chile whereas in similar deposits elsewhere it is rare in chile it has generally been assumed to be a primary constituent of the supergene zones there are two difficulties with this supposition the first is that atacamite requires saline water for its formation whereas supergene oxidation was caused by percolating oxygenated meteoric water mainly rainwater the second is that atacamite dissolves rapidly or undergoes phase change when exposed to fresh water supergene enrichment of copper deposits in northern chile extended over a long period 44 to 9 ma being terminated by the onset of hyperaridity during this period there was at least intermittent rainfall exposing previously formed atacamite to dissolution or phase change furthermore atacamite bearing oxide zones in several deposits are directly overlain by thick miocene alluvial gravels the stream waters that transported these gravels would have permeated the oxide zones in some deposits atacamite bearing assemblages occur both in the oxide zones and in contiguous gravels we suggest that atacamite bearing oxide assemblages are more likely to have been a replacement of preexisting oxide phases after the onset of hyperaridity at about 9 ma a hyperarid climate made possible evaporation and concentration of chloride in meteoric waters in this paper we discuss another source of saline waters to modify oxide zones dewatering of the domeyko basin expelled brines along faults some of which had earlier guided the location of porphyry deposits at the spence porphyry copper deposit saline waters which d vs 18o isotope analyses identify as basinal brines are presently rising through the deposit then flowing away along the base of the covering gravels compositions of these waters lie within the stability fields of atacamite and brochantite the two minerals that comprise the oxide zone evidence is presented for other porphyry deposits radomiro tomic and gaby sur that basinal brines may have been involved in the late formation of atacamite

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

stable isotopic composition of soil calcite o c and gypsum s overlying cu deposits in the atacama desert chile implications for mineral exploration salt sources and paleoenvironmental reconstruction abstract soils overlying two porphyry cu deposits spence gaby sur and the pampa del tamarugal atacama desert northern chile were collected in order to investigate the extent to which saline groundwaters influence soil chemistry in regions with thick miocene and younger sediment cover soil carbonate calcite was analyzed for c and o isotopes and pedogenic gypsum for s isotopes soil calcite is present in all soils at the spence deposit but increases volumetrically above two fracture zones that cut the miocene gravels including gravels that overlie the deposit the c isotope composition of carbonate from the soils overlying fracture zones is indistinguishable from pedogenic carbonate elsewhere at the spence deposit all 13 c vpdb values fall within a narrow range 1 40 4 23 consistent with the carbonate having formed in equilibrium with atmospheric co 2 however 18 o vpdb for carbonate over both fracture zones is statistically different from carbonate elsewhere average 18 o vpdb 0 82 vs 2 23 respectively suggesting involvement of groundwater in their formation the composition of soils at the tamarugal anomaly has been most strongly affected by earthquake related surface flooding and evaporation of groundwater 13 c vpdb values 4 28 to 2 04 are interpreted to be a mixture of dissolved inorganic c dic from groundwater and atmospheric co 2 at the spence deposit soils only rarely contain sufficient so 4 for s isotope analysis the so 4 bearing soils occur only above the fracture zones in the gravel results are uniform 3 7 4 9 34 s cdt which is near the middle of the range for so 4 in groundwater 0 9 7 3 sulfur in soils at the gaby sur deposit 3 8 6 1 34 s cdt is dominated by gypsum which primarily occurs on the flanks and tops of hills suggesting deposition from so 4 rich fogs sulfate in gaby sur deposit gypsum is possibly derived by condensation of airborne so 4 from volcanic so 2 from the nearby andes at the gaby sur deposit and tamarugal anomaly pedogenic stable isotopes cannot distinguish between s from porphyry or redeposited so 4 from interior salars the three sites studied have had different histories of salt accumulation and display variable influence of groundwater which is interpreted to have been forced to the surface during earthquakes the clear accumulation of salts associated with fractures at the spence deposit and shifts in the isotopic composition of carbonate and sulfate in the fractures despite clear evidence of relatively recent removal of salts indicates that transfer from groundwater is an ongoing process the interpretation that groundwaters can influence the isotopic composition of pedogenic calcrete and gypsum has important implications for previous studies that have not considered this mechanism

elasticity of pyrope and majorite pyrope solid solutions to high temperatures abstract majorite garnet solid solutions are major mineral phases in the earth s upper mantle and transition zone here we present the first brillouin scattering measurements of the elasticity of majorite mj mg 4 si 4 o 12 pyrope py mg 3 al 2 si 3 o 12 solid solutions mj 50 py 50 and mj 80 py 20 and single crystal elasticity of pure synthetic pyrope at temperatures up to 800 c the temperature derivatives of the adiabatic bulk k s and shear moduli for all compositions along the mj py join are the same within the experimental uncertainties k s t 14 0 14 5 20 mpa k t 8 3 9 2 10 mpa k the temperature dependence of the acoustic velocities for mj py solid solutions is about half that of other major transition zone minerals this implies that temperature variations in the transition zone inferred from lateral velocity heterogeneity can be significantly underestimated if the properties of majoritic garnet are not taken into account

observations on the behavior of gold during supergene oxidation at summitville colorado u s a and implications for electrum stability in the weathering environment abstract the textural relations morphology and composition of gold grains in both oxidized and unoxidized ore from the summitville colorado au cu ag deposit have been investigated in this study gold from oxidized summitville ore is finer grained than that from unoxidized ore and occurs exclusively in intimate intergrowths with goethite of presumed supergene origin these oxide gold grains show no evidence of silver depletion and are enriched in silver relative to primary gold in a few cases this trend can be explained using the stability relations of silver in electrum at 25 c at this temperature electrum with up to 20 wt ag may be relatively stable in the weathering environment provided that chloride contents are sufficiently low in the coexisting aqueous phase this is in accord with the maximum silver values observed in gold grains in the oxidized zone of the summitville deposit and with the negligible chloride content of present mine drainage the absence of chloride that is implied by these electrum compositions effectively rules out gold chloride complexes as an explanation for the local remobilization of gold in the oxidized zone at summitville it strongly suggests that gold chloride complexes are not necessary to transport gold at least on a local scale in the acidic environment that characterizes many weathering sulfide ore bodies local gold mobilization in this environment is believed to reflect the formation of transient gold thiosulfate complexes

age of the los ranchos formation dominican republic timing and tectonic setting of primitive island arc volcanism in the caribbean region this study reports u pb ages for zircons from the los ranchos formation which is part of the primitive island arc sequence the oldest volcanic rocks in the greater antilles zircons were analyzed from three samples quartz porphyry quartz keratophyre from the lower part of the formation quita sueno member fragmental quartz porphyry from the upper part of the formation pueblo viejo member and the cotui quartz diorite stock that intrudes the lower part of the formation the lower part of the los ranchos formation represented by the quita sueno sample formed at either 113 9 0 8 or 118 6 0 5 ma depending on interpretation of the data whereas the upper part represented by the pueblo viejo sample formed ca 110 9 0 8 ma the cotui stock rd 73 601 was emplaced ca 111 8 0 6 ma or 112 9 0 9 ma depending on whether eight grains reflect subtle inheritance these results show that the los ranchos formation was emplaced during the aptian albian transition that the cotui stock could have supplied magma to the volcanic sequence and fluids to the pueblo viejo gold silver deposit in the upper part of the formation and that carbonaceous sediments in the upper part of the formation formed at the same time as ocean anoxic event 1b paquier caribbean plate tectonic models involving invasion of anomalous pacific crust into the caribbean region appear to agree best with this age because they provide a mechanism for the change from primitive island arc pia to calcalkaline magmatism and account for the restricted ocean circulation necessary to generate regional anoxic conditions

copper isotopes as a means of determining regional metallurgical practices in european prehistory a reply to jansen abstract we present a detailed response to the critique by mr jansen of the paper digging deeper insights into metallurgical transitions in european prehistory through copper isotopes when we consider cu isotope ratios of european eneolithic and early bronze age artifacts in the context of their local geological settings climates and archaeological contexts mr jansen s hypothesis that 63 cu enrichment results from the adoption of fahlore ores is untenable in both serbia and central europe the earliest copper production is associated with 65 cu enriched ores and subsequently produced artifacts yield lower ranges 65 cu this shift in cu isotopic composition correlates with the initial use of predominantly hypogene ores not with variations in their trace element content essentially the expanded dataset supports the conclusions that were presented in the original paper cu isotopes are an effective means of delineating the transition from oxide based smelting to methodologically more complex smelting of sulphide ores in prehistoric europe with its relatively limited production and trade mixing did not mask the critical cu isotope signatures in this setting therefore cu isotope compositions of artifacts can be used to interpret the mineralogical character of the ores from which they were produced regardless of their provenance as long as trade networks remained within a region of similar climatic history

bioleaching of waste material from the salobo mine brazil recovery of refractory copper from cu hosted in silicate minerals abstract in this study we demonstrate the recovery of refractory copper from cu sulphide inclusions in silicate minerals of waste rocks by acidithiobacillus ferrooxidans mediated silicate dissolution acidophilic iron oxidising bacteria and waste rock samples were collected at the salobo 3 alpha iron oxide copper gold iocg mine in para state brazil bench top column leaching trials of seven different waste rocks with complex gangue mineralogy were run with and without endemic a ferrooxidans in acidic media pre and post leach materials characterisation and continuous monitoring of leaching column effluents were used to investigate the amenity of low sulphide waste material to leaching by a ferrooxidans and the mechanisms controlling solution chemistry the data presented here suggests that in lieu of other fe ii sources iron oxidising bacteria utilise solubilised ferrous iron from fe bearing silicate minerals such as chlorite biotite and amphiboles as alternative energy sources the microbially mediated weathering of fe ii bearing silicates provides access to refractory sulphides trapped as cu sulphide inclusions in these minerals the dissolution of these silicate minerals controls the ph of the leach solution a ferrooxidans thereby indirectly causes the leach solution ph of biotic systems to buffer at ph 3 2 to 5 0

controls on the 129i i ratio of deep seated marine interstitial fluids old organic versus fissiogenic 129 iodine iodine and its radioisotope 129i have been successfully used to trace the origin of pore waters in submarine fluid escape structures because of their close association with organic material in deeply buried sediments we report here halogen concentrations and 129i i ratios for fluids of five mud volcanoes sampled along an e w transect across the gulf of cadiz in the ne atlantic ocean concentrations of iodide and bromide increase consistently seaward accompanied by a decrease in 129i i ratios from 6490 10 15 to 663 10 15 the exceptionally high 129i i ratios at the near shore locations reflect the presence of fissiogenic 129i produced in situ by spontaneous fission of 238u within terrigenous sediments and released into pore water during clay mineral diagenetic processes the observed 129i i and halogen trends together with similar changes in 87sr 86sr ratios indicate a progressive seaward transition from inorganic terrigenous to organic marine fluid sources comparison of our results with literature data for varying geological settings reveals a general relationship between fissiogenic 129i radiogenic 87sr and the lithology or provenance of rocks and sediments respectively while 129i i ratios in continental rock hosted aquifers and terrigenous sedimentary systems are dominated by in situ production of fissiogenic 129i iodine isotopes in oceanic settings or volcanogenic marine sediments reflect the release of old iodine from deeply buried organic matter the gulf of cadiz represents the full transition between these continental and oceanic 129i i and 87sr 86sr end members this is the first systematic investigation of fissiogenic 129i production in marine sedimentary environments

quantitative geochemical approach to pedogenesis importance of parent material reduction volumetric expansion and eolian influx in lateritization abstract using mass balance techniques we test the prevalent view that laterite genesis is dominated by in situ residual enrichment during chemical weathering of bedrock through calculation of net mass fluxes through the laterite soils in mali west africa we show that residual enrichment by removal of mobile elements with a corresponding increase in bulk porosity and decrease in bulk density contributes only a very minor fraction of the enrichment of al fe si and au instead we demonstrate that the abundance of these elements is due to the influx and accumulation by selective retention of chemically mature detritus of local and foreign origin clearly evident in micromorphological infilling features at the same sample depths that accumulation reaches extreme values we show that volumetric expansion in excess of 200 has occurred locally we infer that these spatially coincidental zones of mass influx of rock forming metals fe al si and also au with dilational hyperstrains result from a mutually reinforcing mechanical interaction between material influx and the effects of subsurface deformational processes such as shrink swell cycles and root growth and decay we propose that with progressive infilling of available connected voids by illuvial microsedimentary deposits of insoluble resistate and neoformed minerals the capacity for the combined skeleton and plasma to remain isovulumetric is exceeded we speculate that the resultant space problem is relieved by upwards expansion towards the overlying free surface continued translocation and void infilling occur and are limited to the depth where the size of translocational particles is smaller than that of the connected voids consequently progressive hyperstrains accumulate above this critical depth by the long term influence of a proposed translocational wedge of chemically resistant minerals against which numerous generations of plant roots have exerted stresses eclectic surficial contaminants involved are continuously derived from above leaving no indication of a relict source region within the present soil profile from which they might have been extracted instead the source region is largely the existing regolith column itself which releases local material and in addition is supplemented by deposition of colluvial detritus shed nearby by escarpment retreat

exploring for deeply covered mineral deposits formation of geochemical anomalies in northern chile by earthquake induced surface flooding of mineralized groundwaters northern chile is a major producer of copper from porphyry deposits most ores worked to date were exposed near the surface exploration is now focused on deposits along a basement unconformity buried under piedmont gravels deposited by ca 10 ma two recent discoveries the spence and gaby sur deposits are covered by gravel soils above these deposits have anomalies for elements present in saline mineralized groundwaters the anomalies occur above fracture zones in the gravels believed to represent the upward propagation of basement faults that guided emplacement of the porphyries we propose that during earthquakes in this seismically active region there was pumping of saline basement waters up the faults and fracture zones entraining mineralized groundwaters from the deposits after surface flooding and evaporation elements were redistributed by infrequent rains sampling shows that surface active cations such as cu 2 1 were adsorbed and retained in the top few centimeters of soil whereas nacl and porphyry indicator elements that dissolve as anions se re and as are not adsorbed and are removed to 40 cm depth given the 10 m y interval since the gravels were deposited and the hyperarid climate of the atacama desert anomalies may have formed by repeated episodes of seismically induced flooding company geochemical surveys show that such features are numerous in northern chile producing linear zones of saline soils plus other constituents of local groundwaters e g b and i where faults controlling these features intersect mineralization elements specific to the mineralization are also present saline zones may be outlined in the field by measuring the conductivity of soil plus water slurries sampling for full geochemical analyses can be limited to areas so defined anomalies may be generated along fault lines in other seismically active wetter climates but only for elements that are adsorbed on soil minerals although the context of the study is mineral exploration the process may be relevant to the formation of geochemical features of environmental interest above major faults

high pressure elastic properties of major materials of earth s mantle from first principles the elasticity of materials is important for our understanding of processes ranging from brittle failure to flexure to the propagation of elastic waves seismologically revealed structure of the earth s mantle including the radial one dimensional profile lateral heterogeneity and anisotropy are determined largely by the elasticity of the materials that make up this region despite its importance to geophysics our knowledge of the elasticity of potentially relevant mineral phases at conditions typical of the earth s mantle is still limited measuring the elastic constants at elevated pressure temperature conditions in the laboratory remains a major challenge over the past several years another approach has been developed based on first principles quantum mechanical theory first principles calculations provide the ideal complement to the laboratory approach because they require no input from experiment that is there are no free parameters in the theory such calculations have true predictive power and can supply critical information including that which is difficult to measure experimentally a review of high pressure theoretical studies of major mantle phases shows a wide diversity of elastic behavior among important tetrahedrally and octahedrally coordinated mg and ca silicates and mg ca al and si oxides this is particularly apparent in the acoustic anisotropy which is essential for understanding the relationship between seismically observed anisotropy and mantle flow the acoustic anisotropy of the phases studied varies from zero to more than 50 and is found to depend on pressure strongly and in some cases nonmonotonically for example the anisotropy in mgo decreases with pressure up to 15 gpa before increasing upon further compression reaching 50 at a pressure of 130 gpa compression also has a strong effect on the elasticity through pressure induced phase transitions in several systems for example the transition from stishovite to cacl2 structure in silica is accompanied by a discontinuous change in the shear s wave velocity that is so large 60 that it may be observable seismologically unifying patterns emerge as well eulerian finite strain theory is found to provide a good description of the pressure dependence of the elastic constants for most phases this is in contrast to an evaluation of birch s law which shows that this systematic accounts only roughly for the effect of pressure composition and structure on the longitudinal p wave velocity the growing body of theoretical work now allows a detailed comparison with seismological observations the athermal elastic wave velocities of most important mantle phases are found to be higher than the seismic wave velocities of the mantle by amounts that are consistent with the anticipated effects of temperature and iron content on the p and s wave velocities of the phases studied an examination of future directions focuses on strategies for extending first principles studies to more challenging but geophysically relevant situations such as solid solutions high temperature conditions and mineral composites

high pressure transformation of pyrope mg3al2si3o12 in a sintered diamond cubic anvil assembly transformation of pyrope garnet was investigated at 1600 c and at pressures higher than 35 gpa using a sintered diamond cubic anvil assembly in a double staged split sphere apparatus pyrope transformed into orthorhombic perovskite at ca 37 gpa whereas a small amount of corundum coexisted with perovskite at lower pressures the unit cell dimensions of perovskite were determined to be a 4 771 2 a b 4 947 2 a c 6 950 3 a and v 164 0 2 a a trace of stishovite observed in the run products may be evidence of nonstoichiometry in the perovskite these results support the view that perovskite is the major host phase of al2o3 in the lower mantle

supergene sulphides and related minerals in the supergene profiles of vhms deposits from the south urals abstract the mineralogy and structure of the supergene profile in recently exploited volcani hosted massive sulphide vhms deposits of cyprus uralian and kuroko type in the south urals russia have been studied specific subzones enriched in secondary sulphides and associated minerals have been distinguished in residual pyrite and quartz pyrite sands at the gayskoye zapadno ozernoye dzhusinskoye and alexandrinskoye deposits besides minerals which are common to the cementation subzones covellite chalcocite and acanthite non stoichiometric colloform and framboidal pyrite pyrite dzharkenite pyrrhotite like and jordanite like minerals metacinnabar sphalerite selenium enriched tetrahedrite and unidentified as sb sulphosalts of pb or hg and ag sulphur bearing clausthalite naumannite and tiemannite were also found secondary sulphide minerals in vhms deposits of the south urals region are characterized by light sulphur isotope compositions 8 1 to 17 2 superposition of the advanced oxidation of colloform pyrite an enrichment in impurities sphalerite galena and tennantite from the primary ores stagnant water conditions an elevation of the water table during oxidation and bacterial activity led to supergene concentrations of the base metals as sulphide selenides or sulphosalts

an experimental study of the garnet perovskite transformation in the system mgsio3mg3al2si3o12 phase transformations in the system mgsio3 mg3al2si3o12 have been studied at pressures between 22 and 28 gpa at 1500 c using a multi anvil apparatus majorite garnet with less than about 10 wt al2o3 was found to completely transform into an orthorhombic perovskite structure over a pressure interval between 24 and 27 gpa whereas pyrope garnet disproportionated into sub aluminous perovskite plus corundum solid solutions at pressures greater than 26 5 gpa alumina contents in the perovskite structure are dependent on temperature and increase from 11 wt at 1500 c to 17 wt at 1800 c at a pressure of 27 gpa the alumina content of perovskite also in creases with increasing pressure such that aluminous perovskite with the pyrope composition 25 mol al2o3 should be formed by about 30 40 gpa these observations are consistent with our recent experimental results on a pyrolite composition which demonstrated that no separate aluminous phase exists in the upper part of the lower mantle the entire inventory of al2o3 in pyrolite can be accommodated in solid solution in magnesium silicate perovskite

ore mineralogy fluid inclusion and stable isotopic characteristics of stratiform copper deposits in the coastal cordillera of northern chile late jurassic stratiform copper deposits in the coastal range of northern chile susana lince and buena vista of the carolina de michilla district and mantos de la luna are hosted in an andesite dominant volcanic pile of the jurassic la negra formation which is extensively intruded by gabbroic to granodioritic plutons and dikes primary copper mineralization is characterized by chalcocite cu1 90s digenite bornite chalcopyrite hematite supergene alteration of these minerals has produced chalcocite djurleite covellite atacamite chrysocolla and copper oxides copper wad fluid inclusion data indicate a variable temperature of formation 200 to 380 c and a wide range of fluid salinities 7 to 34 wt nacl carbon and oxygen isotopic compositions of calcite from the susana lince deposit 13c 2 6 to 3 6 18o 13 7 to 18 7 combined with the thermometric data suggest that the fluid responsible for the calcite mineralization derives from mixing of high temperature meteoric water with cooler basinal brines these data imply that the stratiform copper deposits of the coastal cordillera are epigenetic and formed from non magmatic moderately oxidized hydrothermal solutions

phase stability and elastic properties of the nal and cf phases in the namg2al5sio12 system from first principles new hexagonal aluminous nal phase and orthorhombic calcium ferrite cf type phase are considered to be major mantle components of the mid ocean ridge basalt morb at pressure and temperature conditions in the lower mantle which can potentially host alkali elements with large ionic radii the high pressure stability and elastic properties of both nal and cf phases are therefore of fundamental importance for understanding the fate of subducted morb here we report those properties of the namg2al5sio12 system studied by means of the first principles computation method nal was found to transform to the cf phase at 39 6 gpa accompanied by discontinuities in density 1 8 as well as compressional wave 0 2 shear wave 0 9 and bulk sound 1 0 velocities the property of subducted morb was evaluated using these results and the velocity contrast between pyrolite and morb of 5 was found to be quite comparable to the shear velocity anomaly observed for seismic scatterers at depths from 1100 to 1800 km however since the transformation of the nal to cf phase within morb produces insignificant increases in the seismic velocities it would be seismologically undetectable on the other hand the anisotropy change associated with the phase transition is significant and could be seismically detectable using observations such as shear wave splitting measurements since the cf phase is considerably more anisotropic compared to the nal phase

the role of discontinuous magma inputs in felsic magma and ore generation for a long time granites have been considered as passive bodies ascending under intrinsic negative density and viscosity contrasts with their host rocks chemical variations within a granitic body resulted from in situ differentiation and crystal fractionation since the mid 1980s this global view has been significantly modified by i shifting melting from water saturated conditions to fluid absent reactions ii increasing the role played by the mantle during granite generation iii reassessing the rheology of partially molten rocks iv demonstrating stepwise segregation and ascent of magmas by analogue and numerical models v combining structural geophysical and geochemical studies to reveal the internal structures in granitic plutons it results that a granitic body is built up by a discontinuous accumulation of successive magma intrusions the discontinuous nature of magma emplacement has also significant consequences for its ability to generate ore the processes that lead to ore deposits are examined with a brief review of the magmatic and fluid phases that concentrate ore forming elements examples are taken from crustal derived granites and porphyry type deposits those are considered as the two end members of magmatic and hydrothermal ore deposits the source characteristics of the magma the emplacement mechanisms and magma mixing processes are the frame that controls the potential to carry base metals with the magma the distribution of elements is controlled by diffusion partition between minerals and melt solubility and redox conditions variations of those parameters are examined by considering their activation energy which controls the exponential dependence with temperature a characteristic length depending on the activation energy temperature variation and time is estimated for a characteristic time lag of 30 ka the intrusion of a magma into a magma chamber of similar composition hence temperature has few effects on diffusion partition coefficient and redox conditions because of a too low temperature contrast the intrusion of a mafic magma into a felsic one induces a variation of 300 c in both magmas the characteristic length of diffusion may vary by up to two orders of magnitude whereas the variation of partition coefficients is only one order of magnitude the redox conditions are about 2 5 log unit in the mafic magma but they can vary by 7 log units in the felsic magma hence a strong decrease in d values is observed in porphyry type deposits the effect is a removal of the elements with higher activation energy w sn zr from the mafic to the felsic magma deformation during the late stages of emplacement also controls ore formation

geomorphological markers of faulting and neotectonic activity along the western andean margin northern chile in the atacama desert northern chile some ephemeral channels are developed in the plio quaternary alluvial sequence that caps the neogene atacama gravels formation geomorpho logical studies and high resolution digital elevation data gps along a structural transect in the cen tral depression are used to document modern growth history of subtle folding and faulting in the fore arc region outcrop data of the most recent deposits are combined with observations of warped and faulted late quaternary pediments alluvial fans and terrace surfaces to propose unsuspected neotec tonic processes on the western flank of the domeyko cordillera neotectonic process recognition is here based largely upon the interpretation of alluvial landforms drainage organisation and evolution as the intermittent river network shows systematic patterns of course deflections successive incisions or deposition processes as it encounters the fault scarps or folds in the superficial deposits this area presents both n s trending active vertical faults in the topographically higher pampas and n s trending active folding in the lower pampas these faults seem to accommodate e w extension and compression that could be related to uplift of the western andean margin within a compressive context uplift may have taken place unevenly over the past few million years after the deposition of the superficial alluvial surfaces that cap the neogene atacama gravels copyright 2003 john wiley sons ltd

weathering profile of the cerro de maimon vms deposit dominican republic textures mineralogy gossan evolution and mobility of gold and silver abstract cerro de maimon in the central dominican republic is currently the only vms deposit under production in the caribbean region it is hosted in the maimon formation of early cretaceous age which is part of the oldest and chemically most primitive island arc in the caribbean from bottom to top this deposit can be divided into i a primary sulfide zone ii a supergene enrichment zone and iii an oxidized zone this study reports new data on the textural and mineralogical characteristics of the oxidized zone gossan leached capping zone with emphasis in the au ag bearing phases the mineral paragenesis of the oxidized zone is essentially composed of goethite hematite quartz and barite botryoidal cellular and brecciated textures can be distinguished botryoidal and brecciated textures dominate in the upper parts of the oxidized zone whereas cellular textures are more common in the intermediate and lower parts however the weathering profile is very heterogeneous the leached capping profile shows evidence of both transported and indigenous gossans gold in the oxide paragenesis is extremely pure 99 au suggesting that chemical refining took place silver occurs mainly as iodargyrite agi and minor agbr agcl in botryoidal aggregates particles of au ag alloy in the primary mineralization exposed to a weathering environment can be leached and transported by various agents chemical and biochemical that may exist simultaneously in the presence of halides gold and silver can be leached and transported in a wide range of ph eh conditions especially if iodine is present silver is leached more rapidly and over a broader range of ph eh conditions and is preferentially transported as iodine complexes than other halides the presence of iodargyrite in the cerro de maimon gossan fully developed under tropical conditions suggests that this mineral cannot be considered an indicator of extremely arid environments as typically claimed by many authors iodargyrite occurrence would rather point to the presence of saline halide rich groundwater in oxide deposits

geochemistry of secondary copper minerals from proterozoic porphyry copper deposit malanjkhand india abstract three assemblages of ores have been recognized at the proterozoic porphyry copper deposit malanjkhand india they are 1 primary ore containing chalcopyrite and pyrite 2 moderately oxidized ore containing chalcocite covellite bornite and other secondary copper sulfides and 3 intensely oxidized ore containing copper sulphates carbonates chlorides oxides and native copper the malanjkhand chalcopyrite alters by continued oxidation to the following sequence of minerals chalcopyrite cufes2 bornite cu5fes4 idaite cu3fes4 covellite cus yarrowite cu9s8 spionkopite cu39s28 geerite cu1 60s anilite cu1 75s djurleite cu1 943s chalcocite cu2s the alteration beyond chalcocite follows the reverse sequence to covellite i e chalcocite djurleite anilite geerite spionkopite yarrowite covellite the excess copper from the reverse sequence produces copper sulphates carbonates oxides chlorides and native copper additional formation of copper sulphates carbonates etc is due to variable conditions of eh ph mineral solubilities in water and dissolution of pyrite at relatively high eh ph values these factors give rise to different complex ions such as so42 cu oh 2 cu so 4 cu co3 22 and cucl the chalcopyrite in the primary ore tarnishes by the formation of films of feo oh bornite idaite covellite anilite and chalcocite the tarnish varies in color from deep yellow purple yellow purple violet orange pink blue peacock blue and dark grey to black the alteration of malanjkhandchalcopyrite has been considered to be due to galvanic interactions probable and possible stability relations among various phases are suggested in terms of eh ph and attendant galvanic reactions in oxygenated and carbonated waters percolating through the rock and orebody several electrochemical equations are proposed for the reactions and stability fields of the minerals are constructed using available thermodynamic data

undular tidal bore dynamics in the daly estuary northern australia measurements in the macro tidal daly estuary show that the presence of an undular tidal bore contributed negligibly to the dissipation of tidal energy no recirculation bubble was observed between a trough and the following wave crest in the lee waves following the undular bore this differs to stationary undular bores in laboratory experiments at larger froude numbers where a recirculation bubble exists secondary motions and the turbulence generated by the undular bore had no measurable influence on the sediment transport this situation contrasts with the intense sediment resuspension observed in breaking tidal bores the tidally averaged sediment budget in the daly estuary was controlled by the asymmetry of tidal currents the undular bore may widen the river by breaking along the banks that it undercuts leading to bank slippage a patch of river wide macro turbulence of 3 min duration occurred about 20 min after the passage of the bore during accelerating tidal currents

bacterially mediated supergene alteration and redistribution of copper in mineralised rocks at the salobo iocg deposit brazil abstract the primary ore at the giant salobo iron oxide copper gold iocg deposit in brazil is dominated by magnetite and fe rich silicates with minor 1 disseminated cu fe sulphides and a distinctive absence of pyrite supergene fe silicate and sulphide oxidation has been mediated by bacteria commonly within micrometre scale acidic environments but silicate dominated acid neutralisation has maintained ambient circumneutral ph supergene cu mobility has been controlled by the highly localised fe dominated biogeochemical processes with cu redistribution on the micrometre to metre scales and negligible supergene cu enrichment silicates especially the phyllosilicates biotite and chlorite have variably altered to the clay minerals vermiculite and or smectite and ultimately to kaolinite leaching of mn fe mg and si accompanied silicate alteration with minor addition of cu to clay mineral structures and along cleavage planes iron mobilised by bacterial oxidation processes initially precipitated as ferrihydrite with up to 10 wt cu most cu and mn mobilised in localised acidic environments were precipitated nearby metre scale at circumneutral ph and reflect the immediate supergene biogeochemical environments cu carbonates pseudomalachite chrysocolla and cu mn oxides copper wad the early stages of these natural supergene processes were simulated in laboratory leaching studies using a range of fresh rocks inoculated with an endemic iron oxidising strain of acidithiobacillus ferrooxidans previously cultured from the salobo site bacterially mediated precipitation of ferrihydrite commonly cu bearing in these experiments strongly resembles that seen in the natural outcrops these leaching experiments confirmed the effectiveness of silicate dominated acid neutralisation especially when accompanied by bornite oxidation which is also acid consuming in contrast chalcopyrite oxidation is acid producing and leads to more effective localised cu mobility in solution our combination of field and laboratory observations at the salobo iocg deposit shows that the biogeochemical environment dominated by fe silicates with little sulphides typical for these systems has led to an entirely different style of supergene cu redistribution from that seen at many other cu deposits such as chalcopyrite and pyrite rich porphyry copper deposits where substantial supergene cu enrichment has occurred

lower mantle scattering profiles and fabric below pacific subduction zones abstract the earth s mantle is compositionally evolving principally through the process of mid ocean ridge basalt production 95 by lithospheric area but also by way of arc magmatism 5 and continental growth reymer a schubert g 1984 phanerozoic addition rate to the continental crust and crustal growth tectonics 3 63 77 rowley d b 2002 rate of plate creation and destruction 180 ma to present geol soc am bull 114 927 933 convection eventually must mix these products back into the mantle but the details of the mixing process are unknown we report here new observational data documenting the location of differentiated material in the present day lower mantle and scattering power profiles with depth small scale 10 km objects which efficiently scatter short period s waves are present in the mantle lying below the pacific ocean rim at depths between 1100 and 1800 km we also observe a reduction in scattering power with depth indicating that the objects represent bodies richer in differentiated basalt than the surrounding mantle the scattering objects appear to be deformed to various degrees and usually form clusters separated from each other by a distance of 100 to 200 km the clusters probably represent folds of the order of 100 km probably corresponding to early stage of mixing process because the scattering power does not increase with depth neither does a permanent barrier to flow exist in the mid mantle nor does the intrinsic density of basalt prevent re entrainment into mantle flow from the bottom of the mantle

iodargyrite from zalas cracow area poland as an indicator of oligocene miocene aridity in central europe abstract iodargyrite the hexagonal silver iodide was found in the permian rhyodacite quarry at zalas near cracow southern poland in a fault zone cutting middle jurassic sandy limestone it occurs within a tectonic breccia encrusted by chalcopyrite pyrite ag containing chalcocite covellite galena native bismuth malachite cuprite fe and mn dominant oxides cu sulfates and barite the hydrothermal encrustacion is most likely connected with rejuvenation of old paleozoic faults in the sava phase of the alpine orogeny on the oligocene miocene boundary the periods of aridity when iodargyrite precipitated determined by evaporation of salt lakes or the inland miocene sea that delivered halide ions to the groundwater oxidation system or leaching of weathered ag containing mineralization by saline i rich deep formation waters derived from paleogene sediments during folding and formation of the carpathians nappe structure are connected rather with the low to middle miocene period at this time steppe areas with a dry climate existed on the north foreland of the carpathians in southern poland as a result of a displacement to the north of a dry subtropical zone because of uplift of the carpathians and regression of the inland miocene sea

ab initio investigation of high pressure phase relation and elasticity in the naalsi2o6 system 1 subducted crusts contain aluminous phases with incompatible elements such as sodium in order to understand the fate of subducted crusts and how they recycle within the earth it is important to investigate high pressure stability and elastic properties of host phases here we have studied naalsi2o6 jadeite a naalsio4 calcium ferrite cf type phase and sio2 stishovite by means of a first principles computation method jadeite was found to dissociate into an assemblage of the cf type phase and stishovite at about 18 gpa associated with remarkable increases of compressional wave 18 7 shear wave 26 4 bulk sound 13 3 velocities and density 15 1 proximity of this transition condition to the 660 km discontinuity in the mantle transition zone suggests that seismically observed splitting of the reflection could be related to this phase transition implying subduction of crustal materials down to the mantle transition zone

chlorine isotope fractionation recorded in atacamite during supergene copper oxidation abstract in the atacama desert of northern chile large amounts of the copper hydroxy chloride mineral atacamite cu2cl oh 3 are formed in the supergene oxidation zone of cu deposits since atacamite requires saline water to form and is commonly preserved under hyperarid conditions it has been proposed as a climate sensitive mineral marker that can also provide relevant geochemical information regarding halogen in particular chlorine fluid sources during supergene cu oxidation however chlorine stable isotope data for atacamite in cu deposits are scarce and no experimental data for chlorine isotope fractionation between atacamite and water are currently available that could provide constraints on the possible mechanisms of fractionation in this study we report 37cl values of atacamite along a thick 100 m and well developed supergene enrichment profile at the barreal seco iron oxide copper gold iocg deposit in the atacama desert the 37cl values of atacamite along this profile range from 2 1 to 0 6 mean 0 4 0 7 median 0 3 and show a distinct trend with depth characterized by higher 37cl values towards the top of the profile with lower values at the bottom in addition the chlorine isotope compositions of experimentally synthetized atacamite crystals and coexisting cucl2 solutions were determined at room temperature 23 c the per mil fractionation factor 37clatacamite cl was determined at 0 75 showing that the heavy isotope 37cl is preferentially incorporated into atacamite we used numerical models to test two possible scenarios that might explain the observed 37cl profile at barreal seco a first scenario involves lowering of the water table with concomitant precipitation of atacamite which removes cl from solution following a rayleigh fractionation process this model qualitatively fits our observations but does not explain the full magnitude of the observed 37cl shift along the supergene profile in contrast a model that simulates cl diffusion following the upward injection of a deep brine that overlies fresh groundwater reproduces well the observed 37cl data suggesting that seismic pumping of basinal brines followed by cl diffusion is a feasible mechanism to explain the formation of atacamite at barreal seco these data are a first step towards interpreting 37cl profiles of atacamite in cu deposits in the atacama desert and exploring the potential use of stable chlorine isotopes to monitor cu weathering and enrichment in supergene environments

pleistocene recycling of copper at a porphyry system atacama desert chile cu isotope evidence we present cu isotope data of hypogene and supergene minerals from the late paleocene spence cu mo porphyry in the atacama desert of northern chile chalcopyrite displays a restricted range of 65cu values within the values reported for primary porphyry cu sulfides 0 28 to 0 34 n 6 supergene chalcocite samples show heavier and remarkably homogeneous 65cu values between 3 91 and 3 95 n 6 consistent with previous models of cu leaching and enrichment in porphyry systems secondary cu minerals from the oxide zone show a wider range of composition varying from 1 28 and 1 37 for chrysocolla n 6 to very light cu isotope signatures reported for atacamite between 5 72 to 6 77 n 17 these data suggest redox cycling of cu during supergene enrichment of the spence cu deposit characterized by a first stage of supergene chalcocite formation from acidic isotopically heavy leach fluids of meteoric origin down flowing in a semi arid climate 44 to 15 9 ma reworking of the initial supergene copper assemblage during the pleistocene by rising neutral and chlorine rich deep formation waters under well established hyper arid climate conditions lead to the formation of atacamite with extremely fractionated cu compositions essentially coeval chrysocolla formed by dissolution of atacamite during short episodes of wetter climatic conditions occurring in the latest pleistocene

geochemical characteristics of the rio verde complex central hispaniola implications for the paleotectonic reconstruction of the lower cretaceous caribbean island arc abstract new geochronological trace element and sr nd isotope data for metabasalts dolerites and amphibolites from the rio verde complex central hispaniola are integrated with existing geochemical data for mafic volcanic rocks and metamorphic derivatives from the los ranchos amina and maimon formations giving new insights into magma petrogenesis and paleotectonic reconstruction of the lower cretaceous caribbean island arc back arc system u pb and 40ar 39ar age data show that the rio verde complex protoliths were in part coeval with volcanic rocks of the los ranchos formation upper aptian to lower albian the geochemical data establish the existence of gradients in trace element parameters nb yb th yb zr yb zr ba and normalized ti sm y and yb abundances and nd isotope compositions from throughout hispaniola which reflect differences in the degree of mantle wedge depletion and contributions from the subducting slab the rio verde complex mafic rocks and some mafic sills and dykes intruding in the loma caribe peridotite have a transitional iat to n morb geochemistry and a weak subduction related signature and are interpreted to form in a rifted arc or evolving back arc basin setting the los ranchos amina and maimon formations volcanic rocks have arc like characteristics and represent magmatism in the volcanic front trace element and nd isotope modeling reproduce observed data trends from arc to back arc and suggest that the variations in several geochemical parameters observed in a sw direction across the caribbean subduction system can be explained from the progressively lower subduction flux into a progressively less depleted mantle source the low nb contents and high end i values in both arc and back arc mafic rocks imply however the absence of a significant lower cretaceous plume enriched component in order to explain these observations a model of proto caribbean oceanic lithosphere subducting to the sw at least in the 120 110 ma interval is proposed to cause the observed magmatic variations in the lower cretaceous caribbean island arc back arc system in this context arc rifting and initial sea floor spreading to form the rio verde complex protoliths occurred in the back arc setting of this primitive island arc built on the ne edge of the caribbean plate

precise determination of post stishovite phase transition boundary and implications for seismic heterogeneities in the mid lower mantle abstract the phase transition boundary between stishovite and cacl2 type structure in pure sio2 was investigated at 45 75 gpa and 300 2490 k based on the in situ x ray diffraction measurements in a laser heated diamond anvil cell lhdac results show that the boundary has a positive dp dt slope of 11 1 mpa k and the transition occurs about 70 gpa at 2200 k along the typical mantle geotherm this corresponds to a depth of 1700 km somewhat shallower than the previous estimate seismic heterogeneities have been found in a wide depth range from 800 to 1850 km in the upper to middle layers of the lower mantle the post stishovite phase transition is known to be ferroelastic type which causes a considerable reduction in shear modulus leading to a large slow shear velocity anomaly the almost pure sio2 phase included in subducted crustal materials may be therefore responsible for the relatively deep mid lower mantle seismic heterogeneities the shallow lower mantle anomalies are possibly caused by the similar phase transition in sio2 phase containing al2o3 and h2o or by the phase transition in al bearing casio3 perovskite from cubic to tetragonal structure

thrust emplacement of the hispaniola peridotite belt orogenic expression of the mid cretaceous caribbean arc polarity reversal articulo sobre el emplazamiento fallero en la zona de peridotitas de la hispaniola republica dominicana estudiando si es la expresion orogenica de la polaridad reversa en la zona del caribe en el cretacico medio

elasticity and phase stability of pyrope garnet from ab initio computation abstract we study the high pressure stability and elastic properties of mg3al2si3o12 pyrope garnet using the density functional first principles computation method pyrope garnet is found to dissociate into an assemblage of mgsio3 mg perovskite pv and al2o3 corundum cor solid solutions at 19 7 gpa at static conditions then this assemblage undergoes a phase transition to pyropic al bearing pv at 65 gpa the enthalpy of an assemblage of mgal2o4 calcium ferrite cf mgpv and stishovite st is less stable than that of mgpv plus cor a continuous reaction in the mgsio3 al2o3 system suggested by this study is consistent with previous experimental and computational studies but not with a recently modeled phase diagram this implies that the formation of pyropic pv could not cause any seismic scatterers in the mid lower mantle the investigated anisotropy of elastic velocities further indicates that pyrope garnet is a very isotropic mineral our results suggest that seismological anisotropy inferred in the upper mantle could not be due to garnet

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

hydrogeochemistry and stable isotopes of ground and surface waters from two adjacent closed basins atacama desert northern chile the geochemistry and stable isotopes of groundwaters surface waters and precipitation indicate different sources of some dissolved constituents but a common source of recharge and other constituents in two adjacent closed basins in the atacama desert region of northern chile 24 15 24 45 s waters from artesian wells trenches and ephemeral streams in the punta negra basin are characterized by concentrations of na ca mg and cl so4 with tds mg ca and so4 cl with tds also mg ca and so4 cl but with tds up to 40 g l the deep mine waters have ph between 3 2 and 3 9 and are high in dissolved co2 13c 4 8 pdb indicating probable interaction with oxidizing sulfides the deep mine waters have 18o values of 1 8 compared with values 3 5 for other hamburgo basin waters thus the mine waters may represent a mixture of meteoric waters with deeper metamorphic waters which had interacted with rocks and exchanged oxygen isotopes at elevated temperatures alternatively the deep mine waters may represent fossil meteoric waters which evolved isotopically along an evaporative trend starting from values quite depleted in 18o and dd relative to either precipitation or shallow groundwaters high i br ratios in the hamburgo basin waters and la escondida mine waters are consistent with regionally high i in surficial deposits in the atacama desert region and may represent dissolution of a wind blown evaporite component rain and snow collected during june 1984 indicate systematic 18o and d fractionation with increasing elevation between 3150 and 4180 m a s l 0 21 18o and 1 7 d per 100 m excluding the deep mine waters from la escondida the waters from the hamburgo and punta negra basins have similar d and 18o values and together show a distinct evaporative trend d 5 0 18o 20 2 snowmelt from the central andes cordillera to the east is the most likely source of recharge to both basins some of the waters in the hamburgo basin may have been recharged during late pleistocene when the climate was wetter and a lake filled the intervening punta negra basin as suggested by recent archaeological and geomorphological studies