sims zircon u pb geochronology and sr nd isotopes of ni cu bearing mafic ultramafic intrusions in eastern tianshan and beishan in correlation with flood basalts in tarim basin nw china constraints on a ca 280 ma mantle plume zircon sims u pb dating of the poshi hongshishan bijiashan and huangshan ni cu bearing and xiangshan ni cu ti fe bearing mafic ultramafic intrusions in the eastern tianshan and beishan rift yields a relatively restricted range of 278 6 ma to 284 0 ma the histogram of compiled age data of basalts in the tarim basin and mafic ultramafic intrusions in the eastern tianshan and beishan rift has a peak of 280 ma which probably represents the time of mantle plume activity the basalts have lower end t values in the range of 9 2 1 7 and mg of 2 wt indicating that they were generated directly from a peripheral zone of the mantle plume by low degree of melting the mafic ultramafic intrusions have higher end t of 1 3 11 2 and mg of 33 90 and lower tio2

contaminants from cretaceous black shale i natural weathering processes controlling contaminant cycling in mancos shale southwestern united states with emphasis on salinity and selenium abstract soils derived from black shale can accumulate high concentrations of elements of environmental concern especially in regions with semiarid to arid climates one such region is the colorado river basin in the southwestern united states where contaminants pose a threat to agriculture municipal water supplies endangered aquatic species and water quality commitments to mexico exposures of cretaceous mancos shale ms in the upper basin are a major contributor of salinity and selenium in the colorado river here we examine the roles of geology climate and alluviation on contaminant cycling emphasis on salinity and se during weathering of ms in a colorado river tributary watershed stage i incipient weathering began perhaps as long ago as 20 ka when lowering of groundwater resulted in oxidation of pyrite and organic matter this process formed gypsum and soluble organic matter that persist in the unsaturated weathered shale today enrichment of se observed in laterally persistent ferric oxide layers likely is due to selenite adsorption onto the oxides that formed during fluctuating redox conditions at the water table stage ii weathering pedogenesis is marked by a significant decrease in bulk density and increase in porosity as shale disaggregates to soil rainfall dissolves calcite and thenardite na2so4 at the surface infiltrates to about 1 m and precipitates gypsum during evaporation gypsum formation estimated 390 kg m 2 enriches soil moisture in na and residual so4 transpiration of this moisture to the surface or exposure of subsurface soil slumping produces more thenardite most se remains in the soil as selenite adsorbed to ferric oxides however some oxidizes to selenate and during wetter conditions is transported with soil moisture to depths below 3 m coupled with little rainfall relatively insoluble gypsum and the translocation of soluble se downward ms landscapes will be a significant nonpoint source of salinity and se to the colorado river well into the future other trace elements weathering from ms that are often of environmental concern include u and mo which mimic se in their behavior as co cr cu ni and pb which show little redistribution and cd sb v and zn which accumulate in stage i shale but are lost to varying degrees from upper soil intervals none of these trace elements have been reported previously as contaminants in the study area

liquid immiscibility and the evolution of basaltic magma this experimental study examines relationships between alternative evolution paths of basaltic liquids the so called bowen and fenner trends and silicate liquid immiscibility synthetic analogues of natural immiscible systems exhibited in volcanic glasses and melt inclusions were used as starting mixtures conventional quench experiments in 1atm gas mixing furnaces proved unable to reproduce unmixing of ferrobasaltic melts yielding instead either turbid opalescent glasses or crystallization of tridymite and pyroxenes in contrast experiments involving in situ high temperature centrifugation at 1000g g 1 4 9 8 m s did yield macroscopic unmixing and phase separation centrifugation for 3 4 h was insufficient to complete phase segregation and resulted in sub micron immiscible emulsions in quenched glasses for a model liquid composition of the middle zone of the skaergaard intrusion at super liquidus temperatures of 1110 11208c centrifugation produced a thin silicic layer 64 5 wt sio2 and 7 4 wt feo at the top of the main fe rich glass 46 wt sio2 and 21 wt feo the divergent compositions at the top and bottom were shown in a series of static runs to crystallize very similar crystal assemblages of plagioclase pyroxene olivine and fe ti oxides we infer from these results that unmixing of complex aluminosilicate liquids may be seriously kinetically hampered presumably by a nucleation barrier and thus conventional static experiments may not correctly reproduce it in the light of our centrifuge experiments immiscibility in the skaergaard intrusion could have started already at the transition from the lower to the middle zone thus magma unmixing might be an important factor in the development of the fe enrichment trend documented in the cumulates of the skaergaard layered series

simulations of nearshore particle pair dispersion in southern california knowledge of horizontal relative dispersion in nearshore oceans is important for many applications including the transport and fate of pollutants and the dynamics of nearshore ecosystems two particle dispersion statistics are calculated from millions of synthetic particle trajectories from high resolution numerical simulations of the southern california bight the model horizontal resolution of 250m allows the investigation of the two particle dispersion with an initial pair separation of 500m the relative dispersion is characterized with respect to the coastal geometry bathymetry eddy kinetic energy and the relative magnitudes of strain and vorticity dispersion is dominated by the submesoscale not by tides in general headlands are more energetic and dispersive than bays relative diffusivity estimates are smaller and more anisotropic close to shore farther from shore the relative diffusivity increases and becomes less anisotropic approaching isotropy 10km from the coast the degree of anisotropy of the relative diffusivity is qualitativelyconsistentwiththat foreddy kinetic energy thetotal relative diffusivity asa functionof pairseparation distance r is on average proportional to r 5 4 additional lagrangian experiments at higher horizontal numerical resolution confirmed the robustness of these results structures of large vorticity are preferably elongated and aligned with the coastline nearshore which may limit cross shelf dispersion the results provide useful information for the design of subgrid scale mixing parameterizations as well as quantifying the transport and dispersal of dissolved pollutants and biological propagules

turbulence and entrainment in a buoyant surface plume in winter tidal outflow from the leschenault estuary forms a buoyant sheared stratified plume in koombana bay on each outgoing tide the turbulence in the plume and the local entrainment into the plume are examined based on measurements collected in an intensive field program coherency measurements between horizontally separated sensors are used to examine the anisotropy of the turbulence the effects of viscosity and buoyancy on the turbulence are studied using an activity diagram which is also an indicator of the mixing efficiency and total mixing the osborne cox model is tested and found to be valid in the plume

geological characteristics of tulargen magmatic cu ni co deposit in eastern xinjiang and its exploration direction the tulargen cu ni deposit a great breakthrough in cu ni exploration in xinjiang in the past ten years is obviously controlled by secondary fractures in the kangguer huangshan regional ductile sheer zone similar to things of the known huangshan and xiangshan cu ni deposits ore bodies are hosted in ultramafic complexes which consist of hornblende peridotite pyroxene peridotite hornblende pyroxenite and gabbro the proved nickel 125000 tons and cobalt reserves 10 000 tons have reached large size and copper reserves have reached medium size the richest massive ore body with an average grade of ni 4 56 and cu 2 52 can reach 37 98 m in thickness in no 1503 drill hole the ore district remains under prospecting now the deposit was formed through deep seated magma segregation and is characterized by bulk mineralization it has experienced a single intrusion with multiple pulsant inburst the m f values are between 3 1 and 4 8 falling into the category of ferrous ultramafic rocks the intrusion has low ti total alkali and al2o3 and contains high sulfur usually higher than 1 suggesting a good ore forming potential ore minerals consist of pyrrhotite pyrite pentlandite chalcopyrite and violarite ni and co elements occur as isolated sulfides and sulfur arsenic mineral components geochemical exploration reveals that the deposit is located in a cu ni co anomaly area with the ni peak value of 133 10 6 and cu value of 83 10 6 geophysical characteristics of this district show that high gravity high polarization and high magnetic anomalies are associated with low electric resistance the exploration direction is also pointed out in this paper new ore bearing ultramafic intrusions will be possibly found along the central weak shear zone between the strong shear zones on both sides and the southwestern extension of no i intrusion with well developed hornblende peridotite is the pipe center for magma upwelling and may be a mineralization enrichment center

the cortlandt complex evidence for large scale liquid immiscibility involving granodiorite and diorite magmas abstract granodiorite and diorite plutons of the rosetown complex n y which are associated with the nearby cortlandt complex have chemical and textural characteristics indicating that large scale liquid immiscibility played a major role in their petrogenesis rare earth element zirconium niobium and phosphorus abundances are much greater in the diorite precluding the possibility that the rosetown diorite and granodiorite are related by fractional crystallization the trace element data also eliminate the possibility that the granodiorite represents 1 a partial melt of crustal rocks including basalt 2 a granitic cumulate or 3 a residue from an aqueous fluid derived either from a silicate melt or crustal rocks liquid immiscibility appears to be viable model for the origin of the rosetown granodiorite and iron rich diorite this model is supported by the following 1 the major element compositions occur in a two liquid field on a greig diagram 2 both bodies have similar sr isotope compositions 3 common phases in the two rock types have overlapping compositions 4 the major and trace element data of the diorite and granodiorite are similar to the experimentally determined partition data of immiscible liquid pairs and 5 possible ocelli of iron rich diorite are found in the granodiorite

a review of the western part of the altaids a key to understanding the architecture of accretionary orogens abstract the altaids is one of the largest accretionary collages in the world and the tectonic styles of the accretionary processes have been interpreted in several ways including as an amalgamation of multiple terranes as a result of oroclinal bending of a long single arc or as a caledonian continental collision based on recent tectonostratigraphic analyses together with paleomagnetic data the tectonic styles of the neoproterozoic to paleozoic accretionary processes of the altaids are discussed the western altaids is the main focus of the study which was mainly composed of several independent linear components such as arcs and microcontinents with proterozoic basement and cover rocks various kinds of arcs existed in the paleo asian ocean including a complicated type of arc alaskan type which is a combination of the japan and mariana type intra oceanic arcs and the cordillera type continental arcs these linear components rotated and collided with each other with multiple subduction polarities which could have been an important result of multiple linear element amalgamation and which has contributed greatly to the architecture of the eurasian continent the basic tectonic styles of the altaids can be summarized as arc arc collision oroclinal bending and large scale rotation and multiple subductions with a complicated archipelago paleogeography these basic features of accretionary orogens in general can be attributed to the amalgamation of complicated multiple linear elements some mesozoic to cenozoic accretionary orogens in the world are also characterized by processes of multiple linear element amalgamation more attention should be paid to the multiple linear element amalgamation of ancient accretionary orogens which will shed light on lateral and vertical continental growth

sea surface temperature variability at the scripps institution of oceanography pier abstractsea surface temperature sst has been measured from near the end of the scripps institution of oceanography sio pier daily since 1916 it is one of the world s longest instrumental time series of sst it is widely used in studies of climate and marine ecosystems and in fisheries management the authors hypothesized that a discontinuity exists in 1988 when the old pier was replaced with the present pier a regression of annual mean sst at sio sstsio on the pacific decadal oscillation index for 1916 87 was used to predict annual mean sst sstsio pdo for 1916 present the residual ressstsio sstsio sstsio pdo time series shows a positive discontinuity in 1988 when the present sio pier was first used to measure sstsio no discontinuity in 1988 was observed for ressst at 12 other shore stations or in nearby waters use of the first principal component of other shore station time series of annual mean sst as the predictor yields similar results sstsio measured over 3 days shows a diel cyc

understanding seismic heterogeneities in the lower mantle beneath the americas from seismic tomography and plate tectonic history we combine results from seismic tomography and plate motion history to investigate slabs of subducted lithosphere in the lower mantle beneath the americas using broadband waveform cross correlation we measured 37 000 differential p and s traveltimes 2000 pcp p and scs s times along a wide corridor from alaska to south america we invert the data simultaneously to obtain p and s wave velocity models we interpret slab structures and unravel subduction history by comparing our v s tomographic images with reconstructed plate motion from present day up to 120 myr convergence of the pacific with respect to the americas is computed using either 1 the pacific and indo atlantic hot spot reference frames or 2 the plate circuit passing through antarctica around 800 km depth four distinctive fast anomalies can be associated with subduction of the nazca cocos and juan de fuca plates beneath south central and north america respectively and of the pacific plate beneath the aleutian island arc the large fast anomalies in the lowermost mantle which are most pronounced in the s wave models can be associated with late cretaceous subduction of the farallon plate beneath the americas near 2000 km depth the images record the post 80 myr fragmentation of the proto farallon plate into the kula plate in the north and the farallon plate in the northeast near 1000 km depth we infer separate fast anomalies interpreted as the kula pacific juan de fuca and farallon slabs this interpretation is consistent with the volume and length of slabs estimated from the tomographic images and the plate history reconstruction

u pb ages and hf o isotopes of zircons from late paleozoic mafic ultramafic units in the southern central asian orogenic belt tectonic implications and evidence for an early permian mantle plume abstract u pb age and hf o isotope data of zircons from the mafic ultramafic complexes and their related rhyolites and granites in the eastern tianshan and beishan regions were obtained by sims and la icpms the hf o isotopic composition and hf model age of the zircons are closely related to their tectonic setting and formation age the zircons from the mafic ultramafic complexes in the bogeda haerlike and jueluotage belts have higher ehf t 8 17 and lower 18o 4 6 whereas most of the zircons in the gabbros granites and rhyolite from the middle tianshan massif and beishan rift display lower ehf t 0 8 and higher 18o 5 8 the positive ehf t and relatively lower 18o values suggest that these mafic ultramafic complexes were derived from depleted mantle which was subjected to subduction related modification processes the hf isotopic composition of zircons in the granites has revealed that the growth of juvenile crust was also very significant in the southern margin of the central asian orogenic belt during the paleozoic the hf model ages of the analyzed zircons together with the regional geology suggest that the beishan area had a northward subduction possibly from ca 900 ma to ca 400 ma whereas the eastern tianshan had a south directed subduction most likely from ca 600 ma to ca 310 ma additionally zircons with ca 280 ma u pb ages display wider and more scattered ehf t and 18o variations than the relatively older and younger ones which further support the early permian mantle plume model

ebb tide dynamics and spreading of a large river plume abstract momentum balances in the near field region of a large tidally pulsed river plume are examined the authors concentrate on a single ebb tide of the columbia river plume using the regional ocean modeling system roms configured to hindcast flow conditions on the washington and oregon shelves and in the columbia river estuary during ebb plume interior streamwise balances are largely between advection pressure gradient and frictional forces stream normal balances in this region reduce to centrifugal cross stream pressure gradient and coriolis terms i e the gradient wind balance commonly assumed in river plume bulge investigations temporal derivatives are most important at the plume front and as the ebb progresses winds were light and contributed little to the force balance midebb stress and vertical salt flux were largest at a midplume depth where stratification and vertical shear were also high consistent with shear induced mixing internal stress slows the spreading plume consi

a simplified energy and mixing budget for a small river plume discharge 1 the formation and evolution of a tidally modulated river plume that spreads and mixes into english channel waters is investigated by combining results from two observational studies remote sensing imagery showed a near semicircular plume expansion as its diameter increased linearly during the ebb tide subsequent ship surveys made repeated transects across the plume front and showed that regions of mixing and instability froude numbers 1 were confined to horizontal length scales 1 suggesting that a plume cannot form

copper solubility in a basaltic melt and sulfide liquid silicate melt partition coefficients of cu and fe the solubility of copper in a sulfur saturated basaltic melt has been determined at 1245 c as a function of fo2 and fs2 copper solubilities at log fo2 values between 8 and 11 fall into two distinct populations as a function of fs2 at log fs2 values 1 65 sulfide liquid that coexists with the basaltic glass quenches to sulfur poor bornite solid solution at log fs2 values in excess of 1 65 the sulfide liquid quenches to a complex intergrowth of sulfur rich bornite and intermediate solid solution copper solubilities in the low fs2 population range from 594 to 1550 ppm whereas those in the high fs2 population range from 80 to 768 ppm sulfide liquid silicate liquid partition coefficients d for cu and fe range from 480 to 1303 and 0 7 to 13 6 respectively metal sulfur complexing in the silicate liquid is shown to be insignificant relative to metal oxide complexing for fe but permissible for cu at high fs2 values on log dfe sulfide silicate and log dcu sulfide silicate vs log fs2 log fo2 diagrams both fs2 populations show distinct but parallel trends the observation of two d values for any fs2 fo2 ratio indicates nonideal mixing of species involved in the exchange reaction the two distinct trends observed for both cu and fe are thought to be due to variations in activity coefficient ratios e g feo fes and cuo0 5 cus0 5 results of the experiments suggest that accurate assessments of fs2 fo2 ratios are required for the successful numerical modeling of processes such as the partial melting of sulfide bearing mantle and the crystallization of sulfide bearing magmas as well as the interpretation of sulfide mineralogical zoning in addition the experiments provide evidence for oxide or oxy sulfide complexing for cu in silicate magmas and suggest that the introduction of externally derived sulfur to mafic magma may be an important process for the formation of cu rich disseminated magmatic sulfide ore deposits

subduction induced mantle heterogeneity beneath eastern tianshan and beishan insights from nd sr hf o isotopic mapping of late paleozoic mafic ultramafic complexes abstract extensive late paleozoic mafic ultramafic complexes in the eastern tianshan and beishan regions in the southern central asian orogenic belt caob represent an ideal opportunity to assess the characteristics of the mantle in this area whole rock nd sr and zircon hf o isotopic data from the mafic ultramafic complexes of the jueluotage belt middle tianshan massif and beishan rift were compiled for isotopic mapping end t and 87sr 86sr i values range from 5 5 to 9 5 and 0 702 to 0 706 respectively in the jueluotage belt and from 2 to 11 and 0 703 to 0 710 respectively in the middle tianshan and beishan zircon ehf t and 18o values are in the range of 6 0 17 0 and 4 14 8 00 respectively in the jueluotage belt 1 8 and 5 17 6 30 respectively in the middle tianshan and show large variations of 1 17 and 4 12 respectively in the beishan spatially the 87sr 86sr i ratios of mafic ultramafic complexes increase from the jueluotage belt and beishan to the middle tianshan while the end t values show an opposite trend and reflect a mixing character between depleted mantle and em ii reservoirs zircon ehf t and 18o values exhibit an apparent southward decreasing and increasing trends respectively from the jueluotage belt through middle tianshan to beishan rift their corresponding hf model ages increase continuously from north to south these observations demonstrate that the mantle sources beneath the eastern tianshan and beishan are compositionally heterogeneous which presumably result from significant and variable degrees of subduction related modification we therefore suggest that the late paleozoic subcontinental lithospheric mantle beneath the jueluotage belt was modified by slab derived melts and fluids during the subduction of the junggar ocean whereas the mantle beneath the beishan rift was influenced mainly by slab derived fluids during the subduction of the south tianshan ocean the unique similarities of the middle tianshan mafic ultramafic complexes reflect a two stage modification of their mantle source namely the sequential subduction of the early south tianshan ocean followed by subduction of the junggar ocean thus the subduction induced mantle heterogeneity beneath the caob is probably regional in scope

chalcophile elemental compositions of morbs from the ultraslow spreading southwest indian ridge and controls of lithospheric structure on s saturated differentiation article i nfo sulfide globules in mid ocean ridge basalts morbs from the ultra slow spreading southwest indian ridge swir are present in olivine crystals and in the matrix glass indicating s saturated fractionation during mag matic evolution most of the sulfides were in equilibrium with the magmas based on the ni contents of the sul fides the major element trends of morbs from zone c 48 51 e of the swir define two distinct liquid lines of descent lld including one which is composed of morbs depleted in hree the morbs have variable pge con centrations with pd contents ranging from 0 056 to 1 572 ppb they are pge depleted relative to ni and cu with high cu pd ratios 55 000 1 785 000 quantitative modeling using pd vs ni correlations yields relatively low amounts of segregated sulfides for both groups assuming complete equilibration between the sulfides and the melt however the correlation of calculated sulfur contents with mgo suggests much higher amounts of segre gated sulfides indicating that the segregated sulfides are incompletely equilibrated with the magma there are no obvious correlations between pge concentrations and spreading rates for morbs globally morbs from the swir show slowly decreasing pge contents during magmatic evolution but exhibit higher sulfide seg regation rates compared to morbs from faster spreading ridges largely due to the poor equilibration between the segregated sulfides and the magma such incomplete equilibration could result from thicker lithosphere and an absence of steady magma chambers and conduits beneath ultra slow spreading ridges

platinum group element geochemistry of cu ni mineralization in the basal zone of the babbitt deposit duluth complex minnesota the babbitt cu ni sulfide deposit located in the duluth complex of minnesota contains associated low grade platinum group element pge mineralization interelement correlations show that for both massive and disseminated ore zones rh ru os re and ir are positively correlated to s abundance and suggest that they have behaved as immobile elements however pt pd and au are strongly decoupled from the rh ru os re ir group and show no significant correlation with s cu or ni a pge enriched zone up to 3 000 ppb pt and 1 100 ppb pd is located laterally adjacent to the highest grade cu ni ore the pge enriched zone is characterized by abundant bornite lower sulfide delta 34 s values 1 4 to 8 9ppm than those from other sulfide bearing zones at babbitt and oxide assemblages that include cr bearing hercynite and magnetite rich spinels as well as ilmenite sperrylite ptas 2 is the only discrete pge mineral identified in the babbitt deposit synchrotron x ray fluorescence microprobe analyses indicate that some rocks with a high bulk pge content are characterized by ppm quantities 16 132 of pd in cubanite chalcopyrite maucherite and mackinawire although cl contents of biotite and apatite from mineralized units range from 0 10 to 0 71 and 0 87 to 1 43 wt percent respectively no direct relationship between pge enrichment and cl content of volatile rich phases has been observed geochemical data suggest that both magmatic and hydrothermal processes have been important in the localization of pge at the babbitt deposit the distribution of rh ru os re and ir reflects magmatic concentration processes whereas pt pd and au have been locally mobilized and redistributed during hydrothermal alteration

segregation and fractionation of magmatic ni cu pge sulfides in the western jinchuan intrusion northwestern china insights from platinum group element geochemistry the jinchuan ni cu pge deposit is one of the world s largest magmatic sulfide deposits recent studies have suggested that the jinchuan intrusion originally comprised two individual intrusions the eastern and the western intrusions the western intrusion consists of an upper and a lower unit the upper unit is largely free of sulfides with weakly disseminated sulfides only at the base of the unit these sulfides are characterized by moderate cu pd ratios of 5 500 to 14 900 and relatively high pge tenors pge in 100 sulfides in the range of 510 to 1 000 ppb irsul 420 to 1 200 ppb rusul and 2 900 to 8 000 ppb pdsul disseminated net textured and minor massive sulfides in the lower unit comprise the no 24 orebody the third largest at jinchuan the disseminated ores have remarkably high cu pd ratios 24 200 85 600 and low pge tenors in the range of 120 to 560 ppb irsul 100 to 480 ppb rusul and 430 to 3 600 ppb pdsul the net textured and massive ores contain high ipge contents 240 820 ppb irsul and 170 630 ppb rusul and ni cu ratios 1 7 11 3 low pd ru ratios 0 53 3 1 and exhibit significant pt depletion 300 ppb ptsul additionally small cu rich orebodies occur at the base of the no 24 orebody or in small intrusions within footwall schists marbles and granites beneath the western intrusion the cu rich sulfides have very low ipge tenors 1 9 16 ppb irsul and 6 4 21 ppb rusul and ni cu ratios 0 3 2 8 high pd ru ratios 37 3 378 and highly variable ptsul between 43 and 11 000 ppb the pge geochemistry and model calculations indicate that the disseminated sulfides of the upper and lower units segregated from pge undepleted and depleted parental magmas respectively the pge depleted magma had undergone a minor amount of earlier sulfide liquid extraction at depth furthermore this pge depleted parental magma had slightly higher pge contents than the magma from which the sulfides of the nos 1 and 2 orebodies in the eastern intrusion segregated the significant variations in base and precious metal ratios of the net textured and massive sulfide ores are attributed to fractionation of the sulfide melts that formed these ores this led to both migration of the residual cu rich sulfide melts away from the early formed monosulfide solid solution mss to form cu rich ores as well as back intrusion of the cu rich ores into the mss the negative pt anomalies of the net textured and massive sulfides resulted from preferential extraction of pt into the cu rich residual melts due to the presence of as te and bi

crustal contamination and sulfide immiscibility history of the permian huangshannan magmatic ni cu sulfide deposit east tianshan nw china abstract the huangshannan mafic ultramafic intrusion is a permian ni cu sulfide bearing intrusion in the southern margin of the central asian orogenic belt the intrusion consists of an ultramafic unit which is composed of lherzolite and olivine websterite and a mafic unit which is composed of olivine gabbronorite gabbronorite and leuco gabbronorite this intrusion was formed by two separate pulses of magma a more primitive magma for the early ultramafic unit and a more evolved magma for the late mafic unit u pb isotope geochronology of zircon from the mafic unit yields an age of 278 2 ma according to its olivine and cr rich spinel compositions the estimated parental magma of lherzolite for the huangshannan intrusion has 12 4 wt mgo indicating picritic affinity fractional crystallization modeling results and the presence of rounded sulfide inclusions in an olivine crystal fo 86 7 indicate that sulfide immiscibility was achieved at the beginning of olivine fractionation co magmatic zircon crystals from gabbronorite have a 18o value close to 6 5 which is 1 2 higher than the typical mantle value and suggests significant crustal contamination 20 the positive ehf t values of co magmatic zircon which vary from 9 2 to 15 3 and positive whole rock end t values which vary from 4 7 to 7 8 also indicate that the parental magma was derived from a depleted mantle source and contaminated by 5 20 juvenile arc crust and then by 5 upper crustal materials however modeling results of sulfur content at sulfide saturation reveal that such a large amount of crustal contamination is not sufficient to trigger sulfide saturation in the parental magma which strongly suggests that external sulfur addition probably during contamination has played a critical role in causing sulfide immiscibility furthermore the arc magmatism geochemical signatures of the huangshannan intrusion such as significant nb and ta depletion relative to la and low ca contents in olivine are interpreted as the result of slab derived fluid modification during previous subduction we speculate that the contamination of juvenile arc crust may have occurred in the lower crust because of picritic magma underplating and that partial melting in the mantle was triggered by the impingement of a mantle plume or lithosphere delamination in a post subduction environment

pt and pd mobility in hydrothermal fluids evidence from komatiites and from thermodynamic modelling abstract komatiite host rocks and ores provide a natural laboratory for the study of pt and pd during hydration and carbonation of ultramafic rocks the degree of correlation between pt and pd and of those elements with lithophile elements such as ti in komatiitic rocks and ores is strongly dependent on the magmatic sulfide content of the rock pt and pd are typically very strongly correlated within s poor komatiites and in disseminated ores containing 5 volume or less magmatic sulfides in contrast they are almost completely decoupled in sulfide rich ore samples thermodynamic modelling based on the existing body of published experimental data on pt and pd solubilities suggests that pd and pt can be readily transported as bisulfide complexes in acidic neutral solutions under reduced and moderate oxidation condition at 300 c and chloride complexes are only important under extremely acidic oxidised conditions pd is much more soluble than pt in the case of fluids in sulfide rich environments in equilibrium with the characteristic assemblages found within altered and metamorphosed komatiites solubilities of both elements are much lower in sulfide poor environments especially where ph values are constrained to neutral values by the near ubiquitous presence of carbonate minerals in the alteration assemblage this accounts for the evident near immobility of pt and pd in even the most altered silicate host rocks as compared with their wide dispersion in sulfide rich ores

immiscible silicate liquid partition coefficients implications for crystal melt element partitioning and basalt petrogenesis this study investigates partitioning of ele ments between immiscible aluminosilicate and boro silicate liquids using three synthetic mixtures doped with 32 trace elements in order to get a good spatial separation of immiscible liquids we employed a high temperature centrifuge experiments were performed at 1 050 1 150 c 1 atm in sealed fe and pt containers quenched products were analysed by electron micro probe and la icp ms nernst partition coefficients d s between the fe rich and si rich aluminosilicate immiscible liquids are the highest for zn 3 3 and fe 2 6 and the lowest for rb and k 0 4 0 5 the plots of d values against ionic potential z r in all the composi tions show a convex upward trend which is typical also for element partitioning between immiscible silicate and salt melts the results bear upon the speciation and structural position of elements in multicomponent silicate liquids the ferrobasalt rhyolite liquid immis cibility is observed in evolved basaltic magmas and may play an important role in large gabbroic intrusions such as skaergaard and during the generation of unusual lavas such as ferropicrites

detachment of buoyant surface jets discharged on slope characteristics of a buoyant surface jet discharged on a sloping bottom are reviewed and a numerical experiment is performed to evaluate the depth at the point where the jet detaches from the bottom this calculation is important in the context of predicting dilution and spreading characteristics of buoyant discharges for example associated with heated discharges from power plants the experiment is based on a direct numerical solution of the longitudinally integrated momentum equation which takes into account entrainment and bottom friction results are compared with laboratory and field data reported in the literature as well as previous empirical relations for calculating this depth it is found that the appropriately scaled detachment depth varies with the inverse of the discharge densimetric froude number the scaled depth decreases with increases in either the entrainment or bottom friction coefficient but increases with increasing slope a minor effect of discharge aspect ratio is also shown

a modified genetic model for the huangshandong magmatic sulfide deposit in the central asian orogenic belt xinjiang western china the huangshandong ni cu deposit is the largest magmatic sulfide deposit discovered to date in the central asian orogenic belt in northern xinjiang western china the host intrusion is a 274 ma composite mafic ultramafic intrusion consisting of four separate intrusive units a large layered gabbroic sequence phase i a sheet like ultramafic body phase ii a dyke like gabbronorite body phase iii and an irregular ultramafic unit phase iv important sulfide mineralization is present in the last three intrusive units predominantly as disseminated and net textured sulfides pyrrhotite pentlandite and chalcopyrite the huangshandong mafic ultramafic intrusive rocks are characterized by arc like geochemical signatures such as low ca content in olivine and negative nb ta anomalies in whole rocks this together with a post subduction setting for the east tianshan in the permian suggests that the source mantle was modified previously by slab derived fluids in the carboniferous the mantle derived magma was ponded in a staging chamber in the lower part of the newly formed arc crust the first batch of magma to arrive at huangshandong was most fractionated and depleted in ni crystallizing fe rich and ni depleted olivine fo67 300 ppm ni the second batch of magma was more primitive crystallizing more primitive olivine fo81 84 the third batch of magma was also highly fractionated and depleted in ni crystallizing fe rich and ni depleted olivine fo72 600 ppm ni the final batch of magma became more primitive again crystallizing the most primitive olivine fo81 86 the occurrence of rounded sulfide inclusions in olivine primocrysts in the huangshandong ultramafic rocks indicates that immiscible sulfide liquid droplets were present during olivine crystallization the ni tenors of disseminated sulfide ores in the gabbronorite dyke vary mainly between 5 and 8 wt which are too high to have been produced by the parental magma of the dyke the ni cu and platinum group elements pge tenors of disseminated sulfide ores in the dyke phase iii and the ultramafic sheet phase ii are remarkably similar these observations together with the sequence of magma emplacement suggest that the sulfide liquids entrapped in the magma of the dyke formed at depth by a previous pulse of more primitive magma the estimated parental magma for the most primitive lherzolites in the huangshandong intrusion contains 10 wt mgo modeling shows that sulfide saturation in the parental magma of the huangshandong lherzolites could have resulted from fractional crystallization significant pge depletions relative to ni and cu in the disseminated sulfide ores of the huangshandong deposit may be due to sulfide retention in the source mantle

ni cu au and platinum group element contents of sulphides associated with intraplate magmatism a synthesis the tectonic setting of intraplate magmas typically a plume intersecting a rift is ideal for the development of ni cu platinum group element bearing sulphides the plume transports metal rich magmas close to the mantle crust boundary the interaction of the rift and plume permits rapid transport of the magma into the crust thus ensuring that no sulphides are lost from the magma en route to the crust the rift may contain sediments which could provide the sulphur necessary to bring about sulphide saturation in the magmas the plume provides large volumes of mafic magma thus any sulphides that form can collect metals from a large volume of magma and consequently the sulphides will be metal rich the large volume of magma provides sufficient heat to release large quantities of s from the crust thus providing sufficient s to form a large sulphide deposit the composition of the sulphides varies on a number of scales i there is a variation between geographic areas in which sulphides from the noril

microgranitoid enclaves in granites globules of hybrid magma quenched in a plutonic environment microgranitoid enclaves autoliths cognate xenoliths mafic inclusions are common in high level granitoid plutons they have relatively fine grained igneous microgranitoid microstructures1 and many show evidence of having flowed in a magmatic condition2 these features counter interpretations that the enclaves represent transformed solid fragments of diverse wall rocks3 5 or restite6 11 an alternative interpretation is that the enclaves represent globules of mafic magma that have mingled commingled and quenched in the granitoid host magma12 16 a detailed review of the literature occurrence morphology and composition of micro granitoid enclaves strongly supports this view hut indicates that the enclave magmas range in composition from mafic to felsic and that magma mixing may be involved in their formation17 i summarize here the main features of microgranitoid enclaves and briefly outline the possible processes leading to their incorporation as magma globules in the host granitoid

speciation and weathering of selenium in upper cretaceous chalk and shale from south dakota and wyoming usa abstract in geologic materials petroleum and the environment selenium occurs in various oxidation states vi iv 0 ii mineralized forms and organo se complexes each of these forms is characterized by specific chemical and biochemical properties that control the element s solubility toxicity and environmental behavior the organic rich chalks and shales of the upper cretaceous niobrara formation and the pierre shale in south dakota and wyoming are bentoniferous stratigraphic intervals characterized by anomalously high concentrations of naturally occurring se numerous environmental problems have been associated with se derived from these geological units including the development of seleniferous soils and vegetation that are toxic to livestock and the contamination of drinking water supplies by se mobilized in groundwater this study describes a sequential extraction protocol followed by speciation treatments and quantitative analysis by hydride generation atomic absorption spectroscopy this protocol was utilized to investigate the geochemical forms and the oxidation states in which se occurs in these geologic units organic se and di selenide minerals are the predominant forms of se present in the chalks shales and bentonites but distinctive variations in these forms were observed between different sample types chalks contain significantly greater proportions of se in the form of di selenide minerals including se associated with pyrite than the shales where base soluble humic organo se complexes are more prevalent a comparison between unweathered samples collected from lithologic drill cores and weathered samples collected from outcrop suggest that the humic organic se compounds in shale are formed during oxidative weathering and that se oxidized by weathering is more likely to be retained by shale than by chalk selenium enrichment in bentonites is inferred to result from secondary processes including the adsorption of se mobilized by groundwater from surrounding organic rich sediments to clay mineral and iron hydroxide surfaces as well as microbial reduction of se within the bentonitic intervals distinct differences are inferred for the biogeochemical pathways that affected sedimentary se sequestration during periods of chalk accumulation compared to shale deposition in the cretaceous seaway mineralogy of sediment and the nature of the organic matter associated with each of these rock types have important implications for the environmental chemistry and release of se to the environment during weathering

nickel copper occurrences in the belleterre angliers belt of the pontiac subprovince and the use of cu pd ratios in interpreting platinum group element distributions within the belleterre angliers greenstone belt of the pontiac subprovince there are a number of ni cu sulfide occurrences associated with synvolcanic gabbros the stratigraphy and geochemistry of the belt suggest that it is a rifted island arc and that the gabbros which contain the ni cu sulfides were derived from the mantle plume that rifted the island arc the conditions under which the sulfides formed may be modeled either by recalculating the sulfide compositions to 100 percent sulfide or by using the cu pd ratios both approaches suggest that most of the sulfide occurrences formed from an enriched morb magma with r factors of 200 to 1 000 one of the occurrences la force is depleted in platinum group elements pge relative to cu and this depletion may be the result of the removal of sulfides from the magma prior to emplacement at this stratigraphic level the advantage of using the cu pd ratio rather than recalculating to 100 percent sulfide is that it is not necessary to have s analyses to model the conditions of formation of the sulfides further the cu pd ratio may be used as a prospecting tool rocks with ratios greater than mantle values formed from magmas depleted in pd possibly due to removal of sulfide from the magma this implies the potential for a pge bearing sulfide deposit at stratigraphically lower levels such an approach has been applied to pge targets in the eastern abitibi subprovince samples from four ni cu occurrences with cu pd ratios close to mantle ratios have the potential to produce pge as a by product samples from seven ni cu sulfide occurrences and the layered intrusions lac dore bell river and cummings complex have cu pd ratios much greater than mantle ratios indicating that these intrusions and sulfides are not good targets for pge at this stratigraphic level although there may be pge rich sulfides present at depth

transient tidal circulation and momentum balances at a shallow inlet an analysis of transient momentum balances is carried out to elucidate circulation dynamics and exchange mechanisms at shallow barotropic tidal inlets circulation is computed using a depth integrated fully nonlinear time stepping finite element model with variably spaced grids having horizontal resolution down to 50 m velocity and elevation fields from the model are used to directly evaluate the contribution of each term in the momentum equations to the overall momentum balance a transformation of the x y momentum terms into an s n coordinate system is used to simplify the interpretation of the dynamics and provide vivid illustrations of the forces and resulting accelerations in the flow the analysis is conducted for an idealized inlet and contrasted with a highly detailed model of beaufort inlet north carolina results show that momentum balances in the immediate vicinity of these inlets vary significantly in time and space and oscillate between two dynamical states near maximum ebb or flood the alongstream momentum balances are dominated by advective acceleration pressure gradient and bottom friction cross stream balances are dominated by centrifugal acceleration and pressure gradients near slack balances more closely follow linear wave dynamics with local accelerations balancing pressure gradients and to a lesser degree coriolis comparisons between the idealized inlet and beaufort inlet show broad similarities in these momentum balances however natural inlet geometry and bottom topography as well as the tidal transmission characteristics of the sounds behind beaufort inlet produce strong asymmetries moreover momentum balances are highly localized often with subkilometer length scales the dynamics are used to explain the physical mechanisms for inlet exchange in particular the results indicate that the cross stream dynamics generate a wall along the length of an inlet during the stronger phases of the tide the wall is established by opposing cross inlet pressure gradients and centrifugal forces and it poses a significant barrier to cross inlet exchange during the stronger phases of the tide but is absent near slack

mobilization of selenium from the mancos shale and associated soils in the lower uncompahgre river basin colorado abstract this study investigates processes controlling mobilization of selenium in the lower part of the uncompahgre river basin in western colorado selenium occurs naturally in the underlying mancos shale and is leached to groundwater and surface water by limited natural runoff agricultural and domestic irrigation and leakage from irrigation canals soil and sediment samples from the study area were tested using sequential extractions to identify the forms of selenium present in solid phases selenium speciation was characterized for nonirrigated and irrigated soils from an agricultural site and sediments from a wetland formed by a leaking canal in nonirrigated areas selenium was present in highly soluble sodium salts and gypsum in irrigated soils soluble forms of selenium were depleted and most selenium was associated with organic matter that was stable under near surface weathering conditions laboratory leaching experiments and geochemical modeling confirm that selenium primarily is released to groundwater and surface water by dissolution of highly soluble selenium bearing salts and gypsum present in soils and bedrock rates of selenium dissolution determined from column leachate experiments indicate that selenium is released most rapidly when water is applied to previously nonirrigated soils and sediment high concentrations of extractable nitrate also were found in nonirrigated soils and bedrock that appear to be partially derived from weathered organic matter from the shale rather than from agricultural sources once selenium is mobilized dissolved nitrate derived from natural sources appears to inhibit the reduction of dissolved selenium leading to elevated concentrations of selenium in groundwater a conceptual model of selenium weathering is presented and used to explain seasonal variations in the surface water chemistry of loutzenhizer arroyo a major tributary contributor of selenium to the lower uncompahgre river

lateral spreading of a near field river plume observations and numerical simulations 1 data collected from the near field region of the merrimack river massachusetts plume were analyzed to examine plume spreading estimates of the plume spreading rate were derived from a direct assessment of the spreading of clustered surface drifters and from density and velocity data along a cross plume arc additionally plume spreading rates were also derived from highly resolved numerical model output roms these three distinct observational and numerical approaches have reasonable agreement and are compared favorably with observations using a control volume approach in a previous study it is demonstrated that these three methods are valid to estimate the plume spreading rate the observations and numerical simulations also allowed estimation of terms in the lateral momentum balance along streamline normals perpendicular to surface layer streamlines one principal finding of this study is that the dominant terms in the lateral momentum balance are the centrifugal force term associated with streamline curvature the buoyancy term the coriolis term and the interfacial stress term furthermore the lateral momentum balance shows that the lateral spreading process is significantly affected by interfacial stress within the first 1 to 2 km but thereafter is locally inviscid however turbulent mixing continues to play an important role in modifying the spreading rate by adjusting the internal wave speed

mafic felsic magma mixing limited by reactive processes a case study of biotite rich rinds on mafic enclaves article history mafic enclaves in felsic plutons are often used to argue that intermediate magmas are formed by mafic felsic magma mixing but the extent and nature of mixing remains unclear here we examine biotite rich rinds on mafic enclaves from the cretaceous bernasconi hills pluton in the peninsular ranges batholith of southern california to gain insight into magma mixing processes rinds differ from the enclave interior and the host monzogranite in being more fine grained and more mafic and potassic rinds are also 2 5 times more enriched in rare earth elements than the host monzogranite and up to 3 times more enriched than enclave interiors these observations indicate that the rinds were not generated by isochemical quenching binary mixing between enclave and host monzogranite or in situ magmatic differentiation instead rinds appear to have been formed by chemical reaction between the solidified enclave and a hydrous k rich residual melt or fluid formed after progressive crystallization and cooling of the host magma body transforming amphibole in the enclave into biotite rich rinds field observations show snapshots of biotite rich rinds being eroded away and new rinds simultaneously forming on freshly eroded surfaces of enclaves consistent with rinds being formed by chemical reaction instead of as quenching products deformation of enclaves is accommodated primarily by ductile attenuation of the thin rind while the enclave as a whole tends to rotate as a rigid body with minimal internal deformation other than localized brittle failure a comparison of the aspect ratios and cross sectional areas of mafic bodies in the pluton shows that those with high aspect ratios indicating greater accumulated strain are systematically more biotite rich and have smaller cross sectional areas than those with lower aspect ratios which are amphibole rich these relationships not only confirm that biotite rich lithologies are more deformable but also indicate that the high aspect ratio biotite rich bodies also known as schlieren derive from small parent bodies consistent with a derivation from eroding enclave rinds rather than from the enclave itself finally geochemical and thermodynamic modeling indicates that the biotite rich rinds formed when the host felsic magma had cooled to a low melt fraction state f 0 15 0 3 700 760 c suggesting that such reactions occur late in the lifespan of a magma body thus mafic felsic mixing may not be an efficient process for making intermediate magmas unless the magma body can reside at this low temperature range long enough to permit rind formation and subsequent deformation

nitrogen and carbon flow from rock to water regulation through soil biogeochemical processes mokelumne river watershed california and grand valley colorado 1 soil denitrification is an ecologically important nitrogen removal mechanism that releases to the atmosphere the greenhouse gas n2o an intermediate product from the reduction of no3 to n2 in this study we evaluate the relationship between soil carbon and denitrification potential in watersheds with bedrock acting as a nonpoint source of nitrogen testing the hypothesis that nitrate leaching to stream water is in part regulated by denitrification two sites one in a mediterranean climate and the other in an arid climate were investigated to understand the interplay between carbon and denitrification potential both sites included carbonaceous bedrock with relatively high nitrogen concentrations 1 000 mg n kg 1 and had low background nitrogen concentrations in surface and groundwater there was a net accumulation of carbon and nitrogen in soil relative to the corresponding bedrock with the exception of carbonaceous shale from the arid site there the concentration of carbon in the soil 15 620 mg c kg 1 was less than the shale parent 22 460 mg c kg 1 consistent with the bedrock being a source of soil carbon rates of denitrification potential 0 5 83 g n kg 1 hr 1 derived from laboratory incubations appeared to be related to the ratio of dissolved organic carbon and nitrate extracted from soils these data indicate that microbial processes such as denitrification can help maintain background nitrogen concentrations to tens of m n in relatively undisturbed ecosystems when nitrogen inputs from weathering bedrock are accompanied by sufficient organic carbon concentrations to promote microbial nitrogen transformations

complete miscibility between silicate melts and hydrous fluids in the upper mantle experimental evidence and geochemical implications the phase relationships between silicate melts and hydrous fluids were studied by direct visual observation in an externally heated diamond anvil cell complete miscibility of silicate melt and water was observed for a wide range of melt compositions including nepheline jadeite dacite haplogranite and ca bearing granite some evidence for complete miscibility was also observed in the system basalt h2o the critical temperatures in all systems decrease rapidly with pressure at 15 kbar the critical temperature for nepheline is around 550 c for jadeite around 800 c and for granitic compositions it is close to 900 c in general the critical temperatures appear to increase with silica content in the system our results suggest that there is complete miscibility between silicate melts and water in most of the upper mantle except at very shallow depths this means that a water saturated solidus cannot be defined any more in the deeper parts of the upper mantle very silica rich melt inclusions found in spinel lherzolites associated with fluid inclusion are probably the result of the unmixing of a supercritical fluid containing comparable amounts of water and silicate components the decomposition of amphibole in a subducted slab occurs at conditions where the miscibility gap between fluid and silicate melt is not yet closed while the decomposition of phengite and lawsonite occurs far beyond the critical curve accordingly the fluids released by the breakdown of these minerals should have very different properties highly mobile hydrous fluids containing little dissolved silicate should be produced by amphibole breakdown while the decomposition of lawsonite and phengite will lead to much more silicate rich and less mobile fluid phases

petrogenesis and ni cu co sulfide formation of mafic enclaves in tulaergen mafic ultramafic intrusive rocks eastern tianshan northwest china implications for liquid immiscibility and hydrothermal remobilization of platinum group elements

measuring flood output from 110 coastal watersheds in california with field measurements and seawifs the 1300 km long california coast receives output from watersheds that range from 10 km 2 within the coastal mountain ranges to 120 000 km 2 for the drainage basins of the sacramento and san joaquin rivers results from a combination of field and remote sensing data modeling and digital techniques show that during the el nino winter of 1998 the impact of sediment and water transport on nearshore waters from coastal watersheds was spatially extensive varied with depth and was comparable to the impact of output from large rivers the mass of sediment estimated from seawifs data for 25 discrete and coalesced buoyant river plumes emanating from 110 watersheds was 2 2 10 6 t although the mass of all of the plumes represents only 1 2 of the total sediment output from the rivers the plumes covered an area of 29 500 km 2 of coastal waters an important cautionary note is that the surface plumes visible in the remote sensing data even though nearly coincident with flooding do not represent mass output from the rivers

large scale silicate liquid immiscibility during differentiation of tholeiitic basalt to granite and the origin of the daly gap the dearth of intermediate magmatic compositions at the earth s surface referred to as the daly gap remains a major issue in igneous petrology the initially favored explanation invoking silicate liquid immiscibility during evolution of basalt to rhyolite has lost support because of the absence of any firm geological evidence for separation of fe and si rich liquids in igneous rocks this work presents a record of large scale magmatic differentiation due to immiscibility in the tholeiitic sept iles intrusion canada one of the largest layered plutonic bodies on earth gabbroic cumulate rocks from the critical zone of this intrusion show a bimodal distribution in density and p2o5 content despite identical major element chemistry of the principal magmatic phases immiscibility is supported by the presence of contrasting fe rich and si rich melt inclusions trapped in cumulus apatite phase diagrams and well documented occurrences of small scale immiscibility confirm that liquid liquid unmixing and the separation of fe rich and si rich liquids may contribute significantly to the daly gap along the tholeiitic liquid line of descent

large scale silicate liquid immiscibility a possible example from northeastern brazil abstract ultrapotassic peralkalic silica saturated plutons 580 ma are widespread in the cachoeirinha salgueiro foldbelt northeastern brazil they consist of alkali feldspar syenites with pyroxenite as co magmatic inclusions and syn plutonic or late stage dikes pyroxenite and syenite have the same mineral phases aegirine augite microcline sphene apatite blue amphibole magnetite but only in different proportions rare inclusions of a mixed rock about 60 syenite 40 pyroxenite in an emulsion like texture are also present pyroxenes in the three units are all only slightly zoned silica saturated and extremely low in al2o3 0 2 1 4 amphiboles are mostly k rich richterite characterized by high sio2 low al2o3 and tio2 contents and low mg the three rock types have similar ree chondrite normalized patterns with negative slopes and lack of eu anomaly with the total ree in the pyroxenite greater than that of the syenite trace element patterns for the mixed rock are intermediate between those for the pyroxenite and syenite major element partitioning between pyroxenite and syenite has the same sense as that one observed between immiscible liquids in volcanic lavas and trace element partitioning is similar to the experimentally determined partition of immiscible liquid pairs the rocks have similar high 18o values avg w r 8 smow corrected from pyroxene high initial 87 sr 86 sr ratios about 0 710 and low 143 nd 144 nd avg 0 51104 field and geochemical characteristics indicate chemical equilibrium among the three rock types and suggest liquid immiscibility between syenite and pyroxenite the mixed rock representing the original magma composition

spreading dynamics of small river plumes off the northeastern coast of the black sea observed by landsat 8 and sentinel 2 abstract we use near simultaneous ocean color satellite imagery from nasa s landsat 8 and esa s sentinel 2 missions to reconstruct surface currents along the northeastern shore of the black sea and study the spread of a small river plume formed in this area several times a year landsat 8 and sentinel 2 satellites both pass over the study area within a time interval of

kinetics of selenium release in mine waste from the meade peak phosphatic shale phosphoria formation wooley valley idaho usa abstract phosphorite from the meade peak phosphatic shale member of the permian phosphoria formation has been mined in southeastern idaho since 1906 dumps of waste rock from mining operations contain high concentrations of se which readily leach into nearby streams and wetlands while the most common mineralogical residence of se in the phosphatic shale is elemental se se 0 se is also an integral component of sulfide phases pyrite sphalerite and vaesite pyrite ss in the waste rock it may also be present as adsorbed selenate and or selenite and fese 2 and organo selenides se release from the waste rock has been observed in field and laboratory experiments release rates calculated from waste rock dump and column leachate solutions describe the net overall se release from all of the possible sources of se listed above in field studies se concentration in seepage water ph 7 4 7 8 from the wooley valley unit 4 dump ranges from 3600 g l in may to 10 g l by sept surface water flow q from the seep also declines over the summer from 2 l s in may to 0 03 l s in sept se flux se q reaches a steady state of q se release mg l follows a first order reaction with a rate constant k 1 35 6 35e 3 h 1 11 8 55 6 yr 1 laboratory experiments were performed with the waste shale in packed bed reactors residence time varied from 0 09 to 400 h and outlet ph 7 5 here se concentration increased with increasing residence time and release was modeled with a first order reaction with k 2 19e 3 h 1 19 2 yr 1 rate constants reported here fall within an order of magnitude of reported rate constants for oxidation of se 0 formed by bacterial precipitation this similarity among rate constants from both field and laboratory studies combined with the direct observation of se 0 in waste shales of the phosphoria formation suggests that oxidation of se 0 may control steady state se concentration in water draining the wooley valley waste dump

s saturation history of nain plutonic suite mafic intrusions origin of the voisey s bay ni cu co sulfide deposit labrador canada the voisey s bay deposit is hosted in a 1 34 ga intrusion composed of troctolite olivine gabbro and ferrogabbro the sulfide mineralization is associated with magmatic breccias that are enveloped by weakly mineralized olivine gabbros and troctolites and also occurs as veins along structures in adjacent paragneiss a dyke is connected to the base of the north wall of the eastern deeps intrusion and the entry point of this dyke into the chamber is the locus of the eastern deeps nickel sulfide deposit a detailed exploration in the area between the eastern deeps and the ovoid has shown that these intrusions and ore deposits are connected by a splayed dyke the eastern deeps deposit is surrounded by a halo of moderately to weakly mineralized variable textured troctolite vtt that reaches a maximum thickness above the axis of the eastern deeps deposit along the northern wall of the eastern deeps intrusion the massive sulfides and breccia sulfides are petrologically and chemically different when compared to the disseminated sulfides in the vtt and there is a marked break in ni tenor of sulfide between the two sulfides hosted in the dyke tend to have low metal tenors ni 100 2 5 3 5 sulfides in eastern deeps massive and breccia ores have intermediate ni tenors ni 100 3 5 4 and disseminated sulfides in overlying rocks have high ni tenors ni 100 4 8 four principal processes control the compositions of the voisey s bay sulfides coarse grained loop textured ores consisting of pyrrhotite crystals separated by chalcopyrite and pentlandite exhibit a two orders of magnitude variation in the pd ir ratio which is due to mineralogical variations where pentlandite is enriched in pd and ir is dispersed throughout the mineral assemblage a decrease in ir and rh from the margin of the ovoid toward cubanite rich parts at the central part of the ovoid is consistent with fractionation of the sulfide from the margins toward the center of the ovoid the ovoid ores have higher ni and pd tenor than the eastern deeps massive sulfides this is consistent with both a higher r factor and greater degree of silicate parental magma evolution in the ovoid than the eastern deeps the disseminated sulfides surrounding the eastern deeps deposit have some of the highest ni and pd tenors at voisey s bay which are indicative of not only more primitive magmas but also higher r factors than the ovoid or the eastern deeps vtt and normal textured troctolite of the eastern deeps that contain trace sulfide have 0 1 3 ppb pt and 0 1 3 ppb pd whereas weakly to heavily mineralized variable troctolites in the same unit have one to two orders of magnitude higher abundances of pt and pd troctolites and olivine gabbros from other parts of the voisey s bay intrusion and other nain plutonic suite intrusions including the kiglapait newark bay barth island mushua and nain bay south intrusion also have low platinum group element abundances although it is possible that this is a signature of a widespread sulfide saturation event that pre dated ore formation at voisey s bay it is more likely that platinum group element pge depletion is a product of the source melting process where low degrees of melting resulted in the retention of pge in the mantle source if so this indicates that pge depletion should be used with caution as an exploration tool in the nain plutonic suite

iridium and palladium as discriminants of volcanic exhalative hydrothermal and magmatic nickel sulfide mineralization neutron activation of pd au and ir in samples from 1 economically significant ni sulfide deposits of western australia 2 the host rocks of these deposits 3 hydrothermal and or metasomatic ni sulfide mainly millerite mineralization in peridotite at nullagine western australia 4 hydrothermal replacement volcanic exhalative ni cu sulfide mineralization at sherlock bay western australia and 5 volcanic exhalative sulfides in inter flow sediments at kambalda are used to show that ir and pd can be used to discriminate between the various origins magmatic volcanic exhalative hydrothermal metasomatic and metamorphic ascribed to ni sulfide deposits all the economically significant ni sulfide deposits in western australia are strongly enriched in the precious metals relative to other crustal rocks and have similar pd ni and ir ni ratios to each other these ratios persist regardless of whether the nickel sulfides occur at the base of volcanic ultramafic piles e g kambalda or as centrally disposed interstitial sulfides in intrusive dunite bodies the strong similarities of the pd ir ratios of the ni sulfide ores and of the spinilex textured komatiites which represent ultramafic liquids from which the ni sulfide liquids were derived together with other features of the precious metal geochemistry of the ores and host rocks of the ni sulfide deposits are used to show that the deposits had magmatic origins in contrast the pd ir and ir ni ratios of the hydrothermal and or metasomatic ni sulfide mineralization at nullagine are distinctly different from those of the major ni deposits the former contains high au moderate but variable pd and exceptionally low ir similarly the volcanic exhalative sulfides at kambalda and sherlock bay contain negligible quantities of pd and ir all the ir in both the interflow sediments and the hydrothermal metasomatic mineralization is contributed by the host rocks and not by the sulfides the western australian data together with precious metal data for other examples of hydrothermal ni cu sulfide mineralization strongly suggest that although ni au and pd may be transported in aqueous solution ir cannot hence the relative abundance of ir can be used as a discriminant of magmatic sulfides

buoyant surface jets a combination of dimensional analysis simple physical reasoning and data inspection is used to define distinct geometrical properties and mixing characteristics within the near field of buoyant surface jets for deep stagnant receiving water the jet has a transition length a maximum penetration depth and a limited dilution capacity which is primarily met through bottom entrainment these characteristics are found to scale with a densimetric froude number based on kinematic momentum and buoyancy fluxes and a characteristic source length a criterion for shallow water is developed based on observations of reduced entrainment relationships for shallow water dilution and bottom attachment lengths are given a criterion is presented to distinguish free and shoreline attached jets in crossflowing receiving water and a simple trajectory relationship appears to describe jet trajectories in crossflowing deep receiving water

analysis of petrologic hypotheses with pearce element ratios pearce element ratios can test whether the members of a rock suite are comagmatic and can illustrate the causes of chemical diversity in comagmatic suites comagmatic rocks have constant ratios for elements conserved in the system during changes that led to the chemical diversity in basaltic systems the incompatible elements ti k and p are often conserved the slope of the trend on a pearce element ratio diagram is sensitive to the stoichiometry of the crystallizing and segregating phases a judicious choice of ratios as axes for the diagram provides a signature for the phases involved and estimates of their compositions in basaltic rocks diagrams with ti k vs p k can provide a test of the comagmatic hypothesis diagrams with 0 5 mg fe k vs si k have trends that are distinct for each comagmatic suite and different mineral assemblage different suites are distinguished by the intercepts in diagrams whereas mineral assemblages are recognized by the slopes of the trends for example if olivine is the sole crystallizing and segregating phase the trend will have a slope of 1 diagrams with 2ca na k vs al k distinguish plagioclase from augite assemblages and in conjunction with 0 5 mg fe k diagrams unravel the crystallization sequences of suites that have suffered three phase crystallization and segregation analyses from the uwekahuna laccolith kilauea the 1955 and 1967 68 eruptions of kilauea diamond craters volcanic field oregon and experimental data on morb glasses provide illustrations of the interpretations that can be obtained from pearce element ratios

the chromite deposits of the troodos complex cyprus evidence for the role of a fluid phase accompanying chromite formation the troodos ophiolite of cyprus hosts chromite deposits both as podiform bodies within the basal harzburgite and as lesser layers and schlieren within the overlying dunites and clinopyroxene dunites of the metacumulate sequence all chromitite types have been studied from both field and mineralogical aspects with particular emphasis on the chemistry of the ubiquitous silicate inclusions within chromite grains two distinct inclusion assemblages have been documented chromites from podiform bodies contain abundant hornblende serpentine ortho and clinopyroxene and lesser olivine while those from the metacumulates host pargasite albite serpentine and rare pyroxenes this implies that no single silicate inclusion assemblage in chromite can be considered typically ophiolitic the presence of an alkalirich fluid phase during chromite crystallization as evidenced by the unusual mineralogy of these inclusions has already been widely discussed in the literature however the marked stratigraphic control of inclusion types in chromite as reported here enables more complete modelling of the evolution of this phase to be made