primary platinum mineralization in the nizhny tagil and kachkanar ultramafic complexes urals russia a genetic model for pge concentration in chromite rich zones the nizhny tagil uralian alaskan type ultramafic complex is composed of a dunite core with a rim of wehrlite and pyroxenite the dunite unit which has a uniform mineral composition olivine fo 89 8 92 1 avg 0 25 wt cao represents an accumulation of olivine and minor chromite from a mafic magma in an open system magma chamber after solidification of the dunite differentiation began with the formation of the wehrlite olivine fo 77 9 88 8 and pyroxenite corresponding to the closure of the magmatic system two main types of chromitite occurrence are observed in the dunite body small 100 5 cm scattered schlieren of chromite crystals within the ultramafic unit and much larger up to 100 5 m concentrations the chromite composition in both types is similar and uniform cr cr al fe 3 66 02 mg mg fe 2 49 05 and cr cr al fe 3 69 14 mg mg fe 2 49 81 respectively the larger concentrations of chromite include brecciated and net textured ore or massive veins that reflect the dynamic accumulation of chromite crystals in cavities along magma conduits inside the dunite body these cavities are analogous to small magma chambers within the consolidated part of the dunite body and similar to podiform chromitites in ophiolites were created by continuous feeding of magma to the system the platinum group element pge content of the chromite free facies of the dunite is relatively low pt being the only significant pge typically between 0 3 35 ppb but as much as 98 ppb in one sample in contrast both types of chromite occurrence are enriched in pge two pge mineralizing episodes are distinguished an ir ru rh os rich pt pd poor episode in which the platinum group minerals pgm are mainly ir alloys and a pt pd rich episode in which the pgm are mainly pt alloys i e pt 2 fe ni cu ptfeni 2 and tetraferroplatinum and tulameenite like compositions along with rare hollingworthite and an unidentified rhnias mineral the primary pgm have been affected locally by a serpentinization related low temperature alteration that is characterized by addition of copper with alteration to complex pt fe ni cu alloys of varied stoichiometry including tulameenite and platinian copper placer concentrations derived from the nizhny tagil complex have a slightly different assemblage of pgm with abundant isoferroplatinum the presence of gold commonly aggregating the pgm and unusual au sn and au pb alloys the kachkanar complex situated 120 km north of the nizhny tagil complex has essentially the same characteristics apart from a slightly different composition of the ultramafic cumulates suggesting that they were derived from a magma of different composition the pgm distribution also differs in that it contains more abundant isoferroplatinum than other pgm the high pt concentrations are the result of the affinity of platinum minerals for chromite and the mode of chromite deposit formation in the cavities in which chromite crystallized pgm tended to be incorporated in chromite or remained attached to chromite crystals to explain the very high concentrations of chromite associated pgm we define a cr factor which is the ratio of the mass of silicate magma to the mass of chromite in contact with the ascending magma where the cr is high i e a relatively low proportion of chromite in contact with a large amount of magma crystallizing the pt minerals the efficiency of the mechanical collection of pt minerals is at a maximum and the pt concentration i e amount of pt minerals will be high possible variations due to the collection of pge by a sulfide liquid have not been established a model is proposed whereby the observed chromite and associated pt mineralization can result from the normal magmatic evolution of the complex provided that a structural hydrodynamic trap is available to concentrate the chromite

spatial and temporal distribution of gold deposits in the urals during the past 10 years the paleozoic urals mountain belt has been the subject of internationally based deep seismic and ancillary geologic studies aimed at improving our knowledge of the lithospheric evolution of the orogenic belt in general and its prominent crustal root in particular in view of its wide ranging mineral endowment especially for gold this work also provides important keys to help clarify relationships between collisional tectonic processes and gold mineralization following an outline of current ideas on the tectonic evolution of the urals we present an overview of the distribution of the majority of known gold deposits this information together with the available isotopic and geologic age data of associated alteration assemblages is compared to available geochronological data for various magmatic and deformation episodes spatial and temporal relationships suggest that hydrothermal mineralizing processes and the geodynamic evolution of the orogen are linked in an attempt to analyze the deep structural framework of the orogen down to the mantle we have also examined a number of subcontinental and regional scale continuous geophysical datasets the urals have been subdivided traditionally into a series of north south striking tectonic zones but more recently into three principal tectono magmatic sectors which comprise a suture sector along the main uralian fault zone and two sectors with tectonically imbricated island arc transitional viewed as active continental margin and continental zones gold deposits are found in all tectono magmatic sectors of the orogen minor gold occurs in siluro devonian volcanic hosted massive sulfide deposits magnetite copper skarns and porphyry copper deposits in a number of cases younger structures shear zones faults and their intersections have controlled the deposition of higher gold grades in the urals this has led to the concept of progressive concentration of gold during later tectonic overprinting and the understanding that regional deformation and hydrothermal fluid rock interaction in the late carboniferous to early triassic upgraded gold contents of earlier deposits during the late carboniferous to early triassic gold bearing quartz vein lodes which effectively encompass the majority of the larger gold deposits in the urals were also formed in structural chemical traps some deposits such as mindyak that is hosted by tectonic melanges along the main uralian fault zone are clearly typical late orogenic lode gold deposits others occur within and along the margins of early to middle carboniferous older granite and although local orthomagmatic relationships have been described most recent observations now favor a strong structural control on the lodes and no direct genetic association with granite intrusion in the two largest gold deposits kochkar and berezovskoe gold mineralization was controlled by structural and combined structural chemical traps in dilational jogs in both shear and contact zones locally gold mineralization has been shown to occur during a change from orthogonal to transpressional compression the inferred ages of the lode gold deposits suggest they are mostly coeval with the generally undeformed permian early triassic younger granites however a spatial relationship with gold mineralization has not been observed the younger granites were formed in an extensional regime following ural wide magma generation caused by a thermal flux attributed to underplating of the crust by mantle derived mafic magmas the widespread distribution of this late thermal event during changes in stress regime and the involvement of magma generating mantle processes suggest regional delamination in the lithosphere and concomitant upwelling of the asthenosphere these processes may have largely occurred prior to the formation of the prominent crustal root of the urals which formed during subsequent transpressional convergence another triassic ural wide phase of hydrothermal alteration has been recognized but associated gold deposits have been documented in only two cases we tentatively attribute this phase to destabilization of the lithosphere of the wider altaids reflected by the formation of the west siberian and central asian basins east of the urals during the mesozoic the integrated analysis of magnetic bouguer gravity heat flow and crustal thickness data suggests that a major indenter of the east european craton is responsible for a singular transcrustal sidewall ramp in the subsurface of the middle urals this ramp may extend into the mantle and formed the principal conduit zone for mineralizing fluids the world class kochkar and berezovskoe gold deposits are adjacent to this proposed conduit

electron microprobe and la icp ms study of monazite hydrothermal alteration implications for u th pb geochronology and nuclear ceramics this paper presents new data that quantify the response of magmatic monazite to three main types of hydrothermal alteration namely sericitization chloritization and greisenization the samples were taken from three paleozoic granites the st nectaire granite massif central france the carnmenellis granite cornwall england and the skiddaw granite lake district england fluid inclusion thermometry and hydrothermal parageneses indicate that alteration took place at temperatures ranging from 260 to 340 c and salinities from 3 to 18 wt nacl equivalent possible monazite alteration mechanisms found in the course of this study using backscattered scanning electron microscopy bse sem electron microprobe laser raman spectroscopy and laser ablation inductively coupled plasma mass spectrometry la icp ms include cationic substitutions monoclinic to hexagonal structure transition accompanied by chemical exchanges selective th removal dissolution reprecipitation and dissolution with replacement by a different mineral these results show that despite the compositional and crystallographic simplicity of monazite it exhibits varied chemical responses to different mineral fluid interactions elemental and isotopic measurements by la icp ms for the unaltered monazites yield statistically significant 232th 208pb and 238u 206pb magmatic crystallization ages in some cases it was possible to give a reasonable estimate of the age of mineral fluid interaction using the altered parts of the monazites or newly precipitated crystals for other minerals 232th 208pb and 238u 206pb systematics were strongly disturbed by variable inputs and or depletions of u th and pb the data suggest that monazite like nuclear waste forms would be good hosts for tetravalent actinides but may release the lanthanides and actinides with lower and higher valencies especially if the fluids are oxidizing or tend to dissolve monazite

lead isotopes as a provenance tool for quartz examples from plutons and quartzite northeastern minnesota usa abstract the u pb isotope system in plutonic quartz samples approximates the crystallization age of the host granitoid and thus provides a useful provenance tool for detrital quartz grains we present lead isotopic data and u and pb concentrations of quartz from three late archean granitoids and from the early proterozoic pokegama quartzite all in northeastern minnesota lead in granitic quartz is considerably more radiogenic than in its associated whole rock host but it is similar or only slightly more thorogenic than its host pb pb ages obtained from quartz whole rock leached feldspar from the late archean granitic plutons are consistent with existing geochronology suggesting that the u pb system in quartz remained closed since crystallization u pb isotopic data for detrital clear quartz populations in the pokegama quartzite record late archean ages 2550 2650 consistent with a source from the superior province lead isotopic compositions of detrital k feldspar populations and lead and neodymium isotopic compositions of whole rocks samples from the pokegama quartzite also support a superior province source this study highlights the potential of the lead isotope system in detrital quartz k feldspar and whole rocks in provenance studies of sandstones

genesis of the stratiform zhenzigou pb zn deposit in the north china craton rb sr and c o s pb isotope constraints abstract isotopes rb sr c o s and pb were investigated from the zhenzigou pb zn deposit in the qingchengzi mineral field qmf of the north china craton as an aid to determine the genesis of stratiform pb zn deposits in the liao ji rift a step dissolution rb sr age of 1798 8 ma with 206pb 204pb ratios of 17 7477 17 8527 were obtained from sphalerite sulfur isotopic ratios for pyrite 5 14 4 sphalerite 2 4 8 6 and galena 0 3 8 6 from zhenzigou have a narrower range than those from the host paleoproterozoic dashiqiao formation and granite in the area calcite and limestone from ore and wallrocks at the deposit have similar c and o isotope compositions with 13cpdb ranging from 6 0 to 2 3 and 18osmow from 9 8 to 13 7 which are similar to those of carbonatite and the mantle comprehensive analysis of the pb isotopic composition of the sulfide from the zhenzigou deposit and pb zn deposits in adjacent area show that the pb originated from the upper crust and mixed with pb from the mantle sulfur isotopes from zhenzigou deposit indicate that the mineralization has a volcanic eruption source the 13cpdb and 18osmow values indicate that the co2 originated from a mixed mantle marine carbonate and organic source combined with the study of regional metallogenic background this paper proposes that deposition of stratiform pb zn mineralization in the qmf began ca 2052 ma during development of the liaoji rift the mineralization extended to ca 1798 ma prior to deformation associated with the lvliang movement which dismembered the stratiform pb zn mineralization the veined mineralization in the region cross cuts the stratiform deposits and represents remobilized and redeposited deposits associated with the emplacement of triassic plutons such as the xinling and shuangdinggou granites

recent developments in dating ancient crustal fluid flow several isotopic techniques have recently been developed or substantially improved allowing the accurate determination of the timing of fluid related processes these include k ar rb sr and sm nd dating of diagenetic minerals in clastic rocks u pb dating of carbonates sm nd dating of fluorite and uraninite re os and rb sr dating of sulfides 40ar 39ar and rb sr dating of fluid inclusions and u pb dating of ilmenite magnetite sphene and rutile while many of these techniques require further evaluation some have already resulted in new constraints on a variety of crustal fluid flow models

groundwater flow to a well in a layered porous medium 1 steady flow analytical solutions of steady multiple aquifer problems usually assume the flow of groundwater to be essentially horizontal in aquifers and vertical in aquitards these assumptions yield formulae that are economical to evaluate the simplifications however ask for a theoretical check this paper is dealing with the derivation of an analytical formula that may serve as such it considers steady flow of groundwater to a partially screened well in a layered porous medium both horizontal and vertical flow components are taken into account

permeability anisotropy and its relations with porous medium structure 1 the complete permeability tensor of 18 porous rock cores was determined by means of x ray tomography monitoring during the displacement of a salty tracer to study the effect of the pore space geometry on the anisotropy of permeability we compared the three dimensional shape of the invasion front with the x ray porosity maps obtained before injection the samples clean and shale bearing sandstones limestones and volcanic rocks belong to a broad variety of granulometry and pore space geometry their porosity ranges from 12 to 57 and their permeability ranges from 1 5 10 14 to 4 10 12 m2 for sandstones the permeability anisotropy is well correlated with the presence of bedding for volcanic rocks it is clearly related to the orientation of vesicles or cracks however for limestones no evident link between the geometry of the porous network and the permeability anisotropy appears probably because of the influence of the nonconnected porosity that does not contribute to the hydraulic transport this systematic work evidences the ability and the limitations of the tracer method to characterize the anisotropy of permeability in the laboratory in a simple and rapid way

transient dupuit interface flow with partially penetrating features a comprehensive potential is presented for dupuit interface flow in coastal aquifers where both the fresh water and salt water are moving the resulting potential flow problem may be solved for incompressible confined aquifers using analytic functions the vertical velocity of the interface may then be computed analytically and the change of the position of the interface may be simulated by numerical integration through time starting with a known or estimated initial position the upconing of the interface below a partially penetrating ditch or well may be studied if dupuit solutions for such features are available a new dupuit solution is derived for a ditch that penetrates the aquifer partially from above a dupuit solution for a partially penetrating well may be obtained following a similar derivation the new dupuit solution is combined with the interface solution to simulate the upconing of an initially horizontal interface below a series of partially penetrating ditches the interface converges to the known steady state position

simulating groundwater flow in multi aquifer systems with analytical and numerical dupuit models abstract analytic dupuit solutions for multi aquifer flow are compared to exact solutions for two dimensional flow in the vertical plane to determine the error in discharge that is introduced by adopting the dupuit approximation specifically the problem of flow in the bottom aquifer of a two aquifer system is studied where flow is caused by a piecewise constant head in the top aquifer the difference between the exact and dupuit solutions is small if the leakage factor a characteristic length of the aquifer system is large relative to the thickness of the aquifer even for anisotropic hydraulic conductivities the accuracy of discharges obtained with a dupuit solution improves when the aquifer is divided up in a number of layers separated by leaky layers representing the vertical resistance to flow of the aquifer in a second comparison analytic dupuit solutions are compared to numerical dupuit solutions obtained with the finite difference method to determine reasonable cell sizes and domain sizes for finite difference models accurate discharges were obtained with the finite difference method when the cell size is chosen equal to or smaller than the smallest leakage factor and the domain size is at least six times the largest leakage factor both a two aquifer system with one leakage factor and a three aquifer system with two leakage factors were studied

intense silicification of ordovician carbonates in the tarim basin constraints from fluid inclusion rb sr isotope dating and geochemistry of quartz an unconventional porous silicified carbonate reservoir was unveiled in the middle ordovician fractured limestone within a strike slip fault zone in the tarim basin nw china the silicified carbonates are mainly composed of fine to medium crystalline fascicular quartz matrix and coarse crystalline bladed to columnar quartz cement fluid inclusion leachate residue paired rb sr isotopic dating of the quartz cement yields an isochron age of 167 15 ma attesting to a causal link to the jurassic yanshanian orogeny pervasive replacement of matrix quartz and subsequent precipitation of cement quartz through nonisothermal effervescence probably induced by episodic influxes of the hot silica and sr 87 rich basinal brines from the neighbouring deeper manjiaer depression this study thus signifies the usefulness of using rb sr isotope dating method in constraining the timing of carbonate alteration enabling to establish the deterministic relationship of basinal fluid evolution with the major tectonic activity

geological and isotopic constraints on ore genesis huangjindong gold deposit jiangnan orogen southern china abstract the huangjindong gold deposit with gold resources of 80 t is hosted in neoproterozoic slates along the chang ping fault in the jiangnan orogen southern china the orebodies are dominated by auriferous arsenopyrite pyrite quartz scheelite veins quartz rich breccias that are cemented by late arsenopyrite pyrite muscovite and quartz auriferous stibnite quartz veins and disseminated gold in arsenopyrite pyrite sericite quartz altered rocks neither significant alteration zoning nor ore element zoning are recognized within the orebodies although the orebodies at shallower crustal levels are slightly more stibnite rich at the regional scale the first order control on the distribution of gold deposits is the nne to ne trending crustal scale sinistral strike slip chang ping fault as in other gold provinces globally this controlling fault is not gold mineralized the gold occurrs in wnw to e w trending zones of thrusts and fracture arrays associated with tight locked up asymmetrical folds the broadly e w trending orebodies formed independently within approximately ne trending fault bounded corridors defined by the first order chang ping and second order ni wan and keng shang chang long faults hydrothermal activity was initiated at the ductile brittle transition but evolved to brittle dominated deformation all within a transpressional environment oxygen and hydrogen isotope compositions of fluids d 44 4 to 34 2 18o 8 6 to 9 5 calculated from gold related hydrothermal quartz and hydrothermal sericite respectively are consistent with a metamorphic source sulfur isotope compositions of the gold bearing arsenopyrite and pyrite median values between 8 0 and 6 0 are generally distinct from 34s of the regional neoproterozoic slates in the jiangnan orogen but overlap the compositions of pyrites in global sediment hosted orogenic gold deposits lead isotope compositions of the gold bearing arsenopyrite and pyrite 206pb 204pb 17 049 to 18 417 207pb 204pb 15 263 to 15 712 208pb 204pb 37 597 to 39 220 suggest that the lead was sourced from metamorphic rocks involved in the orogenic events therefore both the stable and radiogenic isotopic data indicate that ore forming fluids and metals were derived from a metamorphic source although the precise nature of that source is unclear on the basis of these geological and isotopic data huangjindong is interpreted as an orogenic gold deposit the gold ore bodies show classic structural controls being adjacent at the province scale to the crustal scale chang ping fault but located in thrusts and associated tight anticlinal fold hinges that lie in corridors between markedly oblique relatively brittle fault arrays that parallel the chang ping fault

contrasted monazite hydrothermal alteration mechanisms and their geochemical implications in spite of the major importance of monazite as a repository for the rare earths and th in the continental crust for u th pb geochronology and as a possible form for high level nuclear waste very little work has been carried out so far on the behaviour of this mineral during fluid rock events this contribution describes two contrasting examples of the hydrothermal alteration of monazite the first case comes from a sample of the carnmenellis granite cornwall southwest england chloritized at 284 16 c whereas the other occurs in the skiddaw granite lake district northwest england which underwent greisenization at 200 30 c an integrated study involving backscattered scanning electron microscopy electron microprobe analyses and laser ablation inductively coupled plasma mass spectrometry la icp ms reveals that the chloritization event was characterized by the coupled substitution 2ree3 th4 ca2 in the altered parts of the monazite thus leaving the p o framework of the crystal untouched in contrast greisenization led to the coupled substitution ree3 p5 th4 si4 and therefore involved a partial destruction of the phosphate framework the resulting rare earth element patterns are quite different for these two examples with a maximum depletion for dy and er in the altered parts of the carnmenellis monazite whereas the skiddaw monazite shows a light rare earth depletion but an yb and er enrichment during alteration this latter enrichment accompanied by an increase in u but roughly unchanged pb concentrations probably resulted from a decrease in the size of the 9 coordinated site in monazite thereby favouring the smaller rare earths these contrasted styles of monazite alteration show that the conditions of fluid rock interaction will not only affect the aqueous geochemistry of the lanthanides actinides and lead and the relative stability of the different minerals holding these elements variations in these conditions will also lead to various possible chemical exchanges between the crystalline phases and the hydrothermal fluids the occurrence of common lead along penetrative cracks in the carnmenellis monazite shows that only a leaching prior to the u pb analyses of the whole grain will permit an accurate determination of the magmatic crystallization age in contrast for the skiddaw case it may be possible to date the fluid rock event by in situ 207pb 206pb geochronology the observation that the altered parts of both monazite examples display nd leaching and no significant sm nd fractionation indicates that they should not affect the host whole rock nd isotopic signatures finally it appears that monazite like ceramics designed for the containment of high level nuclear wastes will retain th and the geochemically equivalent transuranic elements during fluid rock events similar to those documented in this study but may release nd u and the corresponding radionuclides to the environment

siderophile element abundances in the upper mantle evidence for a sulfide signature and equilibrium with the core abstract measurements of the intrinsic oxygen fugacities of samples from the earth s upper mantle have shown that the characteristic oxidation state ranges from values close to fe ni metal saturation to more oxidized values tectonic processes can account for the progressive and variable oxidation of a mantle that was originally in equilibrium with metal so that the oxygen fugacity data give strong support to the possibility of protocore protomantle equilibrium the data for apparently overabundant siderophile elements in the mantle are reviewed and 2 groups group a ge au pd pt ru rh ir re os group b sn sb ag ga cu as co ni w mo are recognized group a abundances result from an overprinting by a late accreting chondritic component of a mantle that had suffered major extraction of the indigenous complement by core forming metal chou 1978 group b however are 10 more abundant than group a and may be distinguished as a group by their greater chalcophile tendencies this is highlighted for example by the large cl normalized sn ge ratio of the mantle which is unexpected as a result of metal silicate fractionation alone but can be accounted for if some sn together with sulfur was retained in the mantle during core separation industrial experience in the equilibrium of molten fe and silicate slags shows that sulfur is not overwhelmingly partitioned into metal so that the concept of partial 20 of original accreting component retention of sulfur and group b elements in the mantle has experimental and theoretical support following core separation progressive loss of sulfide from the mantle is indicated by the anomalously high ni at a given mg number in archaean basalts and siliceous mg poor sediments it is also a feature of oceanic and continental basalts that some u pb fractionation must have occurred in the mantle source regions following core separation and this is most satisfactorily achieved if pb is partially removed from u in a sulfide phase

upscaling experiments conducted on a block of volcanic tuff results for a bimodal permeability distribution permeability upscaling is physically investigated by making over 31 000 permeability measurements on a meter scale block of volcanic tuff the experiments are made possible by a specially adapted minipermeameter test system here we present and analyze 5185 permeability values corresponding to five different sample supports i e sample volumes collected from one of the six block faces the results show that the measured spatial permeability patterns bimodal permeability distribution and semivariogram structure length scales are closely related to the strong textural contrast characterizing the tuff sample i e highly porous pumice fragments embedded in a tight rock matrix each of the summary statistics shows distinct and consistent trends with increasing sample support i e upscaling as the sample support increases the mean and variance decrease according to a power law relation and the semivariogram range increases linearly while the general structure of the semivariogram isotropic spherical model remains unchanged interpretation of these results is pursued from two very different points of view one addresses upscaling of the ensemble statistics while the second examines upscaling from a local or pointwise perspective we find the general upscaling trends exhibited by the ensemble statistics given above to be consistent with the basic concepts of volume averaging albeit nonlinear volume averaging the bimodal characteristics of the tuff sample and the nonuniform flow conditions imparted by the minipermeameter contribute to the nonlinearity the local analysis reveals strong variability in permeability upscaling from point to point throughout the sampling domain specifically the permeability upscaling exhibited by zones rich in pumice is very different from zones dominated by matrix unless the averaging volume is significantly larger than the spatial correlation scale

cataclastic rocks of the san gabriel fault an expression of deformation at deeper crustal levels in the san andreas fault zone the san gabriel fault a deeply eroded late oligocene to middle pliocene precursor to the san andreas was chosen for petrologic study to provide information regarding intrafault material representative of deeper crustal levels cataclastic rocks exposed along the present trace of the san andreas in this area are exclusively a variety of fault gouge that is essentially a rock flour with a quartz feldspar biotite chlorite amphibole epidote and fe ti oxide mineralogy representing the milled down equivalent of the original rock anderson and osborne 1979 anderson et al 1980 likewise fault gouge and associated breccia are common along the san gabriel fault but only where the zone of cataclasis is several tens of meters wide at several localities the zone is extremely narrow several centimeters and the cataclastic rock type is cataclasite a dark aphanitic and highly comminuted and indurated rock the cataclastic rocks along the san gabriel fault exhibit more comminution than that observed for gouge along the san andreas the average grain diameter for the san andreas gouge ranges from 0 01 to 0 06 mm for the san gabriel cataclastic rocks it ranges from 0 0001 to 0 007 mm whereas the san andreas gouge remains particulate to the smallest grain size the ultra fine grain matrix of the san gabriel cataclasite is composed of a mosaic of equidimensional interlocking grains the cataclastic rocks along the san gabriel fault also show more mineralogiec changes compared to gouge from the san andreas fault at the expense of biotite amphibole and feldspar there is some growth of new albite chlorite sericite laumontite analcime mordenite and calcite the highest grade of metamorphism is laumontite chlorite zone zeolite facies mineral assemblages and constrained uplift rates allow temperature and depth estimates of 200 30 c and 2 5 km thus suggesting an approximate geothermal gradient of 50 c km such elevated temperatures imply a moderate to high stress regime for the san andreas which is consistent with experimental rock failure studies moreover these results suggest that the previously observed lack of heat flow coaxial with the fault zone may be the result of dissipation rather than low stress much of the mineralogy of the cataclastic rocks is still relict from the earlier igneous or metamorphic history of the protolith porphyroclasts even in the most deformed rocks consist of relict plagioclase oligoclase to andesine alkali feldspar quartz biotite amphibole epidote allanite and fe ti oxides ilmenite and magnetite we have found no significant development of any clay minerals illite kaolinite or montmorillonite for many sites the compositions of these minerals directly correspond to the mineral compositions in rock types on one or both sides of the fault whole rock major and trace element chemistry coupled with mineral compositions show that mixing within the zone of cataclasis is not uniform and that originally micaceous foliated or physically more heterogeneous rock units may contribute a disproportionally large amount to the resultant intrafault material as previously found for the gouge along the san andreas chemical mobility is not a major factor in the formation of cataclastic rocks of the san gabriel fault we see only minor changes for si and alkalies however there is a marked mobility of li which is a probable result of the alteration and formation of new mica minerals the gouge of the san andreas and san gabriel faults probably formed by cataclastic flow there is some indication presently not well constrained that the fine grained matrix of the cataclasite of from the san gabriel fault formed in response to superplastic flow

geostatistical analysis of aquifer heterogeneity from the core scale to the basin scale a case study this study examines the spatial variability of conductivity within the sandstone wabiskaw member of the lower cretaceous middle mannville in the alberta basin the wabiskaw is an important regional hydrostratigraphic unit vertical variability within the aquifer is characterized by downhole variograms of log conductivity from core measurements they are found to exhibit pseudoperiodic structures due to alternating sand and shale layers horizontal spatial variability is characterized using variograms of log transmissivity and indicator data these variograms show a steady increase in spatial variability over length scales ranging from 400 m to 100 km characteristic of self similar or fractal behavior they also reveal distinct correlation structures related to both high and low transmissivity depositional features this study also considers the upscaling of conductivity vertically from the core to the well scale and horizontally from the well to the basin scale it is shown that traditional vertical upscaling of conductivities by arithmetic averaging causes an overestimation of transmissivity in two dimensional areal flow models an alternative approach based on power averaging is proposed transmissivities derived by vertical upscaling of core measurements are compared with values derived from drill stem tests in the same well no correlation between these quantities is observed an average transmissivity for the wabiskaw in the study area is determined by geometric spatial averaging however the highly clustered spatial distribution of well locations requires a weighting of sample values using ordinary kriging

re os isotopic constraints on the source of platinum group minerals pgms from the vestřev pyrope rich garnet placer deposit bohemian massif abstract mineralogical studies of the heavy fraction from a holocene pyrope rich garnet placer deposit at vest ev krkonose piedmont basin bohemian massif have identified the presence of very rare grains of platinum group minerals pgm pt fe alloy grains are accompanied by os ir ru minerals native osmium iridium and ruthenium with inclusions of pt fe alloy and hongshiite ptcu this mineral assemblage is typical for several mantle settings including ophiolites the chemistry of the os ir ru minerals shows an enrichment of the pgm in ru which is typical of ophiolites the grain morphology of pgm and pyrope rich garnet mostly rounded with numerous euhedral subhedral grains does not exclude a common source in situ laser ablation mc icp ms was used to measure the re os isotopic compositions of single os rich grains which show heterogeneous subchondritic os isotopic compositions 187 os 188 os 0 12082 0 12505 0 00003 this precludes their low temperature origin and indicates derivation of platinum group elements pges essentially from mantle derived rocks without a significant contribution of crustal os the mantle model age t ma and re depletion model age t rd model ages range from 0 4 to 1 0 ga and most likely reflect a long history of melt depletion that affected the mantle sources of pgm

determination of radiogenic isotopes rbsr smnd and pbpb in fluid inclusion waters an example from the bluebell pb zn deposit british columbia canada abstract rb sr pb nd and sm isotopes were determined in fluid inclusion waters extracted from quartz samples of the bluebell pb zn deposit british columbia the results demonstrate that radiogenic isotopes in fluid inclusion waters can constitute useful geochronological and genetic tools when applied in conjunction with geological geochemical and other geochronological studies rb sr isotopes of fluid inclusion waters and of mineralized marbles hosting the deposit indicate a tertiary mineralization age of 19 2 5 9 ma and an initial 87 sr 86 sr ratio of 0 7143 this rb sr date is in general agreement with a cenozoic age suggested by geologic field relations described by irvine 1957 and fyles 1967 pb isotope data suggest two isotopically distinct fluids one less radiogenic and similar to values measured on galenas and the other more radiogenic this is in agreement with ohmoto and rye s 1970 hypothesis of two meteoric hydrothermal fluids and lecouteur s 1973 convection cell model nd and sm isotope also suggest mixing of fluids both pb pb and nd sm data suggest very old lower and upper crustal materials as possible source of the metals

an early paleozoic orogenic gold belt along the jiang shao fault south china evidence from fluid inclusions and rb sr dating of quartz in the huangshan and pingshui deposits abstract there are several gold deposits in the eastern section of the regional jiang shao fault between the yangtze and cathaysia blocks in south china auriferous quartz veins in these deposits are strictly hosted in second order ne trending ductile shear zones the ores generally contain low amounts of sulfide minerals

platiniferous chromitite and the tectonic setting of ultramafic rocks in cabo ortegal nw spain high cr number cr chromitites with exceptional concentrations of platinum up to 7000 ppb and palladium up to 4400 ppb occur in sulphide poor dunites exposed along the western side of the ultramafic herbeira massif at cabo ortegal nw spain the pt pd enriched chromitites are restricted to the exposed top of the c 800 m thick herbeira layered complex which comprises two dunite dominated units lower and upper dunites separated by a garnet bearing pyroxenite dominated unit the herbeira layered complex is interpreted as lower crustal and is underlain by high al spinel harzburgite interpreted as mantle tectonite dunite lenses within this underlying tectonized harzburgite also contain high cr chromitites but these are pt pd depleted pt and pd have been strongly fractionated into the overlying herbeira layered complex highest pt and pd concentrations are restricted to the top of the upper dunite where a negative ru anomaly also becomes apparent the cabo ortegal ultramafics form part of a high grade terrane with hp granulites garnet pyroxenites and eclogites and are similar to pge rich chromite concentrations in arc root complexes in pakistan jijal and alaska talkeetna and tonsina the cabo ortegal chromitites are interpreted as having crystallized from a sulphide poor mantle derived suprasubduction melt deep within an arc massif subsequently thrust over the gondwanan continent during variscan collision

refined insight into 40ar 39ar progressive crushing technique from k cl ar correlations in fluid inclusions abstract hydrothermal fluid activity associated with geological processes can now be dated by 40ar 39ar progressive crushing of minerals thanks to recent advances in high precision mass spectrometry however methods of data analysis and interpretation for these high resolution measurements still need to be refined in this study we report further insights into using k cl ar diagrams as tools for interpreting ages of secondary and primary fluids from 40ar 39ar stepwise crushing experiments three paragenetic mineral pairs of muscovite and wolframites from a southern china tungsten deposit were investigated using the 40ar 39ar technique through laser incremental heating and progressive crushing of single minerals incremental heating analyses of muscovites yielded flat age spectra defining plateau ages of 156 153 ma progressive crushing experiments of wolframites yielded anomalously old apparent ages due to excess 40ar however the apparent ages decline quickly after the initial steps and stabilize to form age plateaus of 156 153 ma without excess 40ar the plateau age steps interpreted as ages of gases derived from primary fluid inclusions pfis yield well defined isochrons with ages ranging from 157 to 153 ma and initial 40ar 36ar values that are indistinguishable from the modern atmospheric value digitally created 2d and 3d diagrams of k cl ar correlations can easily reveal distribution trends and correlation planes from the crushing steps interpretations of these diagrams further reveal the ages of secondary fluid inclusions sfis 87 to 83 ma and primary fluid inclusions pfis 159 to 150 ma raw data from sfis degassed during the initial crushing steps form scatters on inverse isochron plots however 2d and 3d k cl ar diagrams yield sfi ages that agree with 40ar 39ar ages of k feldspar veins cutting the tungsten ore bodies

steady groundwater flow through many cylindrical inhomogeneities in a multi aquifer system a new approach is presented for the simulation of steady state groundwater flow in multi aquifer systems that contain many cylindrical inhomogeneities the hydraulic conductivity of all aquifers and the resistance of all leaky layers may be different inside each cylinder the approach is based on separation of variables and combines principles of the theory for multi aquifer flow with principles of the analytic element method the solution fulfills the governing differential equations exactly everywhere the head flow and leakage between aquifers may be computed analytically at any point in the aquifer system the boundary conditions along the circumference of the cylinder are satisfied approximately but may be met at any precision two examples are discussed to illustrate the accuracy of the approach and the significance of inhomogeneities in multi aquifer systems the first application simulates the vertical and horizontal advective spreading of a conservative tracer in a homogeneous aquifer that is overlain by an aquifer with cylindrical inclusions of higher permeability the second application concerns the three dimensional shape of the capture zone of a well that is screened in the bottom aquifer of a three aquifer system the capture zone extends to the top aquifer due to cylindrical holes of lower resistance in the separating clay layers

variations of olivine fo ni contents and highly chalcophile element abundances in arc ultramafic cumulates southern alaska abstract recent drilling in the duke island complex shows that some olivine clinopyroxenites from hall cove contain low s but high pt pd in contrast dunites from the duke island complex and the yellow hill intrusion on nearby annette island are low in pt pd as well as s new data from this study show that the low s ultramafic rocks from duke and annette islands are extreme cumulates of olivine and or clinopyroxene and all contain trace to minor amounts of cumulus sulfide as a result the ratios of the least mobile highly chalcophile elements in these rocks mainly reflect those of original sulfide liquids which in turn reflect those of their parental magmas our data also show that all dunite samples from annette island contain ni depleted primitive olivine with fo contents 90 mol and ni contents

how accurately can we date the duration of magmatic hydrothermal events in porphyry systems an invited paper determining the absolute duration of magmatic hydrothermal events leading to the formation of porphyry systems i e including porphyry copper skarn and epithermal deposits is one of the key questions in ore geology this is so because the duration of magmatic hydrothermal events in porphyry systems is instrumental to the development of genetic models necessary to explore a category of mineral deposits that provide most of the copper and significant amounts of base and precious metals to our economy the problem of determining the absolute duration of magmatic hydrothermal events in porphyry systems has been addressed through thermal modeling of cooling intrusions and time needed to precipitate specified metal amounts from active hydrothermal systems with known metal concentrations and fluid fluxes both these methods have shown that the likely duration of hydrothermal systems is on the order of a few tens of kilo annum ka isotopic dating in contrast is the only possible way to determine the life span of magmatic hydrothermal events in fossil porphyry systems analytical and methodological developments during the last decade in the fields of the most robust isotopic systems commonly used for absolute dating u pb 40ar 39ar re os allow us to date minerals with internal precisions 0 2 2 for a 10 ma old mineral this corresponds to a 20 ka uncertainty which is marginally sufficient to discriminate the duration of hydrothermal systems at the tens of kilo annum scale however many geochronological studies on fossil porphyry systems have shown that these are most often formed through repeated cycles of several intrusion events which extend the overall life of the porphyry systems to a few 0 x and up to 2 ma in some cases internal precisions of the above mentioned dating methods allow us in theory to comfortably discriminate events at the 0 x scale and the combination of u pb 40ar 39ar and reos geochronology is a tool widely used by ore geologists to bracket the duration of cyclic magmatic hydrothermal events in porphyry systems in this review we discuss some fundamental problems that are systematically overlooked in most geochronological studies trying to bracket the life span of porphyry systems we show that if these problems are not adequately taken into account and tackled the result will be that fundamentally wrong life spans of porphyry systems will be estimated we also provide basic guidelines to follow when trying to resolve the duration of magmatic hydrothermal events in porphyry systems with the highest accuracy and precision currently achievable

sediment transport storage relations for degrading gravel bed channels 1 in a drainage network sediment is transferred through a series of channel valley segments natural sediment storage reservoirs that are distinguished from their neighbors by their particular capacity to store and transport sediment we propose that the sediment transport capacity of each reservoir is a unique positive function of storage volume which influences sediment mobility and availability through variations in bed surface texture channel gradient and availability of valley floor sediments for erosion examinations of the form of transport storage relations of degrading alluvial reservoirs using published field studies flume experiments and simulations support a conceptual model that includes two phases in phase i filled channels respond to variations in supply primarily by changes in stored sediment volume with little change in transport rate in phase ii channel mobility is responsive to supply through armoring and form roughness although these phases could represent idealized transport limited phase 1 or supply limited phase ii states we propose that every alluvial reservoir responds to changes in sediment inputs by changing both storage and transport rate the propensity for either depending on reservoir characteristics and the sediment exchange processes in the channel transport storage relations for phase ii are approximately linear but examination of numerical simulations and flume experiments indicates that armoring imparts positive curvature simulations of degradation of an alluvial reservoir with channel and valley floor surfaces indicate that interactions between channel lowering and lateral erosion are critical in the manifestation of a transport storage relation better knowledge of transport storage relations could lead to improved sediment routing models for drainage basins wherein component sediment reservoirs dynamically adjust to varying sediment loads

direct dating of tin tungsten mineralization of the piaotang tungsten deposit south china by 40ar 39ar progressive crushing abstract dating ore minerals is the most direct method to determine the mineralization age of a deposit but only a few ore minerals can be directly dated by traditional isotopic geochronometers the aim of this study is to investigate the possibility of direct dating of the ore minerals cassiterite and wolframite from the piaotang tungsten deposit using the 40ar 39ar stepwise crushing technique comparing the age to coexisting k rich muscovite dated by 40ar 39ar laser stepwise heating the cassiterite wolframite and muscovite samples were separated from four pieces of ore hand specimens the 40ar 39ar isochron ages of cassiterite and wolframite are concordant with ages of their coexisting muscovite indicating that cassiterite and wolframite are suitable ore minerals for directly dating the ore forming event by 40ar 39ar stepwise crushing

nd sr pb isotopic constraints on metal and fluid sources in w sb au mineralization at woxi and liaojiaping western hunan china this paper presents nd sr pb isotope data on scheelite inclusion fluids and residues of gangue quartz and sulfides from the w sb au ore deposits at woxi and liaojiaping ljp in the xuefeng uplift belt xub western hunan china sm and nd concentrations in scheelite from woxi are much lower than in scheelite from ljp and can be distinguished by their high 147sm 144nd ratios of 1 25 from the much lower ratios around 0 26 in scheelites from the ljp end values compared to values at 200 ma which is the average timing of granitoid emplacement during the indosinian yanshanian periods in the xub are around 10 for the ljp and compare well with the range of 5 to 11 defined by the granitoids whereas they are around 27 for scheelite from woxi this might indicate that rees in the mineralizing fluids at ljp originated from granitoids that are concentrated along the southern border of the xub whereas in the case of woxi the original fluids might have been masked by rees released during intense high temperature wall rock alteration of unexposed precambrian basement rocks at depth sr isotopes of scheelite from these two deposits show similar relations to host nearby rocks in that 87sr 86sr t 200 ma ratios of 0 721 for ljp scheelite agree with values ranging between 0 718 0 726 for granitoids whereas these ratios are much higher i e 0 745 for scheelite from woxi and correspond to the 87sr 86sr t 200 ma ratio range of 0 743 0 749 for precambrian host slates crushing experiments to release inclusion fluids from gangue quartz and sulfides deposited during later stages of ore deposition in both deposits failed to provide accurate and geologically meaningful two point fluid residue tie lines in rb sr isochron diagrams however sr released from fluid inclusions generally reveals lower initial 87sr 86sr ratios than the respective residues and shows affinities to 87sr 86sr t 200 ma values of indosinian yanshanian granitoids both at woxi and ljp pb stepwise leaching of scheelite and sulfides did not result in sufficient spreads in pb isotope diagrams and therefore no information regarding exact mineralization ages in the two deposits could be deduced overall ore pb isotopes reveal upper crustal signatures and are compatible with pb isotope signatures of the predominant precambrian slates in the woxi area steep trajectories through late stage quartz sulfide mineralization in pb isotope diagrams may hint at mixing scenarios involving pb from the host rocks and a component with lower 207pb 204pb and 208pb 204pb ratios relative to 206pb 204pb ratios which cannot be linked to any known reservoir in the xub mining district sr isotopes of four out of seven residual sulfide samples from woxi plot along a paleomixing line at an age of 199 8 ma supporting a mixing scenario for the fluids indicated by the pb isotopes and pointing to a possible genetic relationship with the emplacement of indosinian yanshanian granitoids the budgets of rees rb sr and pb in the original fluids were severely affected by contamination of these elements apparently during intense wall rock alteration but after sealing of the major pathways the mineralizing fluids tend to have better preserved their original signatures these attest a genetic relationship between the metallogeny in the xub w sb au province and the emplacement of indosinian yanshanian granitoids during mesozoic intracontinental tectonic uplift and thrusting

on the diversity of the pge content in chromitites hosted in ophiolites and in porphyry cu systems controlling factors abstract the present study on the diversity of the platinum group elements pge content in chromitites and porphyry cu deposits from greece and everywhere literature data aims to define factors controlling precious metal enrichment in ophiolite complexes and the unknown pd and pt potential in porphyry cu systems through an integrated set of mineralogical and geochemical approaches the pge content in chromitites associated with ophiolite complexes is commonly low a few 100 s of ppb however a significant pge enrichment up to 10 s of ppm is a feature of relatively small chromite occurrences regardless their major element composition plots of the pd ir versus normalized pt pt ratios defined separate fields corresponding to various chromitite types large chromite deposits exhibit low pd ir values reflecting low degree of fractionation primitive magmas negative pt pt partial melting of already depleted mantle and increasing partial melting trend from high al towards to high cr deposits the association with hydrous silicates cr bearing hydrogrossular chlorite and serpentine and texture features of os ir ru rich compatible or ipge minerals coupled with very low pd ir and negative pt pt values were attributed to an origin by partial melting of already depleted mantle and increased partial melting degree during a subsequent crustal mantle recycling stage via fluid driven processes assuming that the increasing pd ir reflects a fractionation trend of parent magma a significant enrichment in pt and pd incompatible or ppge occurring in small occurrences either high cr or high al type may be a sensitive fingerprint for the orientation in the mantle sequence of the ophiolites and exploration for chromite commonly the pge content in porphyry cu mo au deposits is less than 10 ppb however elevated pd pt contents over 6 ppm in sulfide rich samples are a characteristic feature of certain porphyry cu au alkaline intrusions evidence of a favorable tectonic setting post collisional for the origin of porphyry cu au pd pt elevated porphyry deposits include elevated up to hundreds of ppm contents in cr co ni and re and elevated 187 os 188 os ratios reflecting mixing and contribution to the magma composition the oxidized nature of parent magmas abundant magnetite and the evolved mineralized fluid system in porphyry deposits are considered to be critical requirements for the transportation and deposition of sufficient au and pge elevated pd pt and au contents in porphyry deposits combined with the association of the major pd mineral merenskyite with bornite and chalcopyrite major cu minerals are encouraging economic factors for the contribution to the global pd pt production

rb sr dating of sphalerite based on fluid inclusion host mineral isochrons a clarification of why it works nakai et al 1990 1993 brannon et al 1992 and christensen et al 1995a b recently published precise rb sr formation ages of sphalerites from various mississippi valleytype deposits this important advance in direct radiometric dating of ore deposition is based on a crush leach procedure in which the rb sr isotope composition of the fluid inclusion fraction termed leachate is analyzed separately from the residual host crystal termed residue isochron arrays were obtained by combining the fluid host mineral data pairs from several samples the resulting ages have yielded decisive chronological constraints on controversial genetic models as summarized for example by christensen et al 1995a where few alternative methods for dating are available although the method appears successful the above authors were unable to explain why the separation of sphalerite samples into fluid inclusion and residual solid fractions should yield an isochron age at all without an explanation the accuracy of the ages remains uncertain the aims of the present communication are to clarify the origin of the isochron patterns and to evaluate their age significance in the way they have been interpreted hitherto that is in the absence of independent geochronologic information our arguments are based first on analyses of synthetic fluid inclusions in quartz which we use as an experimental analogue of fluid inclusion bearing sphalerites in building on the analytical approach of shepherd and darbyshire 1981 for fluid inclusion dating pettke and diamond 1995a synthesized rbsr bearing aqueous fluid inclusions in quartz under high temperatures and pressures subsequent analysis of the separate fluid inclusion and quartz host fractions revealed rb sr patterns which are very similar to those found in natural sphalerite by nakai eta 1990 although recognizing that the analogy between the synthetic and natural samples is limited by important differences in crystal chemical behavior between sphalerite and quartz we are confident that the similarities between the isotopic results of these studies justify inferences being drawn regarding the dating of natural sphalerites second by manipulating the data published by nakai et a 1990 1993 brannon et a 1992 and christensen et a 1995a b we examine the nature of partitioning of rb and sr between sphalerite and hydrothermal parent fluid and thus arrive at conclusions on the validity of dating with fluid inclusion host sphalerite isotope arrays

the petrology and geochemistry of alkaline granites from nigeria abstract the nigerian younger granites as well as the petrologically similar but chronologically older northern centres in air and south niger constitute the best example of epidosically migrating mid plate magmatism the nigerian anorogenic ring complexes provide a classic example of alkaline granitoid evolution each anorogenic centre represents the exposed roots of an eroded volcano volcanic assemblages preserved by caldera collapse at some centres confirm that early erupted liquids evolved from olivine basalt through hawaiite mugearite and trachyte although there are volumetrically abundant rhyolitic ignimbrites there are no volcanic equivalents of biotite granite however at the subvolcanic level biotite granites are extensively mineralized with rich deposits of columbite sphalerite cassiterite and wolframite related peralkaline granites contain enriched concentrations of ore elements but apart from pyrochlore thorium rich monazite and topaz most potential ores are contained in alkali amphiboles or alkali pyroxene fluid interaction in the granite cupolas has caused subsolidus mineral growth and modified original element abundances in some instances fluid reaction has been so intense that original granite has been locally converted to albite microclinite and greisen these reactions can be monitored by the new mineral assemblages the major element chemistry trace elements e g the rare earths and isotopically by the initial strontium isotopic ratios

application of the trace element and isotope geochemistry of strontium to studies of carbonate diagenesis carbonate rocks and natural waters exhibit a wide range in the concentration and isotopic composition of strontium this wide range and the quantifiable covariation of these parameters can provide diagnostic tools for understanding processes of fluid rock interaction careful consideration of the uncertainties associated with trace element partitioning sample heterogeneity and fluid rock interaction mechanisms is required to advance the application of the trace element and isotope geochemistry of strontium to studies of diagenesis goundwater evolution ancient seawater chemistry and isotope stratigraphy a principal uncertainty involved in the application of sr concentration variations to carbonate systems is the large range of experimental and empirical results for trace element partitioning of sr between mineral and solution this variation may be a function of precipitation rate mineral stoichiometry crystal growth mechanism fluid composition and temperature calcite and dolomite in ancient limestones commonly have significantly lower sr concentrations 20 70 p p m than would be expected from published trace element distribution coefficient values and sr ca ratios of most modern sedimentary pore waters this discrepancy probably reflects the uncertainties associated with determining distribution coefficient values as techniques improve for the analytical measurement and theoretical modelling of sr concentration and isotopic variations the petrological analysis of carbonate samples becomes increasingly important the presence of even small percentages of non carbonate phases with high rb concentrations and high 87 sr86 sr values such as clay minerals can have significant effects on the measured 87 sr 86 sr values of carbonate rocks due to the decay of 87rb to 87 sr for example a permian marine limestone with 50 p p m sr and 1 p p m rb will have a present day 87 sr 86 sr value that is 2 10 4 higher than its original value this difference is an order of magnitude greater than the analytical uncertainty and illustrates the importance of assessing the need for and accuracy of such corrections a quantitative evaluation of the effects of water rock interaction on sr concentrations and isotope compositions in carbonates strengthens the application of these geochemical tracers geochemical modelling that combines the use of trace elements and isotopes can be used to distinguish between different mechanisms of water rock interaction including diffusive and advective transport of diagenetic constituents in meteoric pore fluids during the recrystallization of carbonate minerals quantitative modelling may also be used to construct diagnostic fluid rock interaction trends that are independent of distribution coefficient values and to distinguish between mixing of mineral end members and fluid rock interaction

effect of the spatial variability of transmissivity on the groundwater flow and budget of the takelsa multilayer aquifer tunisia groundwater models are vulnerable to uncertainties especially those that are developed based on incomplete knowledge of the hydraulic parameters transmissivity is often the most uncertain parameter in groundwater modeling this work evaluates the effect of the spatial variability of transmissivity on the outputs of the groundwater flow model of the takelsa multilayer aquifer the study was based on a combination of deterministic and stochastic modeling groundwater flow modeling and stochastic simulations were made using the pmwin software a version of modflow initially the groundwater flow model was developed in the steady state the criteria used for the calibration process were based on the comparison between the observed and the simulated hydraulic level then a stochastic approach was used and 100 simulations of transmissivity were performed the simulated transmissivity values were used to recalculate the hydraulic head and the water budget of the saouaf deep aquifer finally the consequent 100 results obtained by running modflow were analyzed the results showed variations in the hydraulic head levels but the flow direction remained the same the impact of the spatial variability of transmissivity on the water budget shows a range of inflow and outflow rates of saouaf aquifer with special relevance to the sea intrusion which may cause a probable deterioration of the quality of the groundwater

transient well flow in leaky multiple aquifer systems abstract a previously developed eigenvalue analysis approach to groundwater flow in leaky multiple aquifers is used to derive exact solutions for transient well flow problems in leaky and confined systems comprising any number of aquifers equations are presented for the drawdown distribution in systems of infinite extent caused by wells penetrating one or more of the aquifers completely and discharging each layer at a constant rate since the solution obtained may be regarded as a combined analytical numerical technique a type of one dimensional modelling can be applied to find approximate solutions for several complicating conditions numerical evaluations are presented as time drawdown curves and include effects of storage in the aquitard unconfined conditions partially penetrating wells and stratified aquifers the outcome of calculations for relatively simple systems compares very well with published corresponding results the proposed multilayer solution can be a valuable tool in aquifer test evaluation as it provides the analytical expression required to enable the application of existing computer methods to the determination of aquifer characteristics

the giant chromite deposits at kempirsai urals constraints from trace element pge ree and isotope data the investigation of stable and radiogenic isotopes and of platinum group pge and rare earth elements ree in chromitites and associated ultramafic rocks of the kempirsai massif southern urals gives strong evidence for a multistage formation of giant ophiolitic podiform chromite deposits present in the southeastern part of the massif the kempirsai ophiolite massif is divided by a shear zone into two parts in the northwestern area small bodies of al rich chromite formed from basaltic melts between 420 to 400 ma according to sm nd mineral isochrons of harzburgite pyroxenite websterite and gabbro harzburgites and pyroxenites in this area are enriched in light ree and have nd 400 6 and sr 400 5 chromitites have scattered pge distributions pd ir 0 4 7 0 being partly enriched in pd and pt os 400 of one chromitite is 4 4 the southeastern part of the kempirsai massif well known for its world class deposits of podiform low al magnesiochromite is characterized by harzburgite and dunite enriched in light ree with very low nd 400 4 3 to 17 1 and positive sr 400 10 values chromitites are strongly enriched in ir os and ru and depleted in pd and pt os 400 of three chromitites is uniform and approaches c1 and dmm compositions in veins and pods postdating crystallization of massive chromite pargasitic amphibole formed in equilibrium with fluid inclusion bearing chromite at temperatures close to 1000 c these amphiboles give 40ar 39ar stepwise heating ages of 365 to 385 ma and are characterized by low nd 400 0 6 to 4 6 and general enrichment in ree the cooling ages correspond to a 379 3 1 6 ma rb sr mineral isochron produced from amphibole and phlogopite of a pyroxenite vein in the western part of the massif from these data it is concluded that parts of the kempirsai massif have been pervasively metasomatized by large amounts of fluids and melts derived from a subducted slab composed of oceanic crust and sediments subduction occurred at least 15 35 ma after a melting event that produced a typical ophiolitic sequence in the paleozoic sakmara zone we conclude that large chromite orebodies formed from second stage high mg melts that interacted with depleted mantle and fluids on their way upward in a suprasubduction zone regime and in a fore arc position to the magnitogorsk island arc

perturbation analysis of flows in a three layer confined unconfined aquifer system abstract perturbed solutions of the coupled non linear equations governing essentially horizontal flows in a rigid three layer confined unconfined aquifer system are obtained in the form of asymptotic series in the dimensionless leakage parameters of the intervening semi pervious strata the uppermost layer is phreatic while the remaining two are semi confined the solutions are particularized for the flow towards a fully penetrating well which is screened for the bottommost confined aquifer a numerical example for this case is added

unexpectedly high pge chromitite from the deeper mantle section of the northern oman ophiolite and its tectonic implications unusually high platinum group element pge enrichments are reported for the first time in a podiform chromitite of the northern oman ophiolite the chromitite contains 1 5 ppm of total pge being highly enriched in the ipge subgroup ir os and ru and strongly depleted in the ppge subgroup rh pt and pd its platinum group minerals pgms are classified into three types arranged in order of abundance 1 sulphides os rich laurite laurite erlishmanite solid solution and an unnamed ir sulphide 2 alloys os ir alloy and ir rh alloy and 3 sulpharsenides irarsite and hollingworthite the high pge concentrations are observed only in a discordant chromitite deep in the mantle section which has high cr 0 7 spinel with an olivine matrix all the other types of chromitite in the moho transition zone mtz and concordant pods in the deeper mantle section are poor in pges and tend to have spinels with lower cr up to 0 6 this diversity of chromitite types suggests two stages of magmatic activity were responsible for the chromitite genesis in response to a switch of tectonic setting the first is residual from lower degree partial melting of peridotite which produced low cr pge poor chromitites at the moho transition zone and to a lesser extent within the mantle possibly beneath a fast spreading mid ocean ridge the second chromitite forming event involves higher degree partial melting which produced high cr pge rich discordant chromitite in the upper mantle possibly in a supra subduction zone setting

distribution of platinum group elements and gold within the vourinos chromitite ores greece a geochemical study of chromite ores and host rocks of the vourinos ophiolite complex leads to the distinction of three geotectonic units corresponding to the north vourinos south vourinos and kissavos geographic areas this is based on the range and variability of cr cr al pt pd os ir ru and pd ir ratios and the relative abundance of compatible platinum group elements pge os ir and ru within the three blocks the platinum group element and gold contents are low average concentrations in ppb are os 23 ir 19 ru 58 rh 12 pt 5 9 pd 3 3 and au 2 7 however a few pge enriched chromite samples up to 3 030 ppb were also found the south vourinos area differs from north vourinos as far as its remarkably constant chemical composition major and trace elements its lower pd ir and pt pd os ir ru ratios its greater abundance of the os ir sum relative to ru and its absence of pge enriched chromite ores there is no significant correlation between chromite composition and pge data throughout the complex the only exception is the kissavos area where the pge content is higher and the pd ir ratio lower in cr rich ores than in al rich ones showing a strong negative correlation between the cr cr al and pd ir ratios r 0 8 the low pge content in the majority of the vourinos chromite ores may reflect a lack of sulfur saturation during an early stage of their crystallization whereas pge enrichment may suggest a mixing of primitive and partially fractionated magmas assuming that the vourinos complex formed in a suprasubduction zone environment it seems likely that south vourinos chromitites formed directly above the spreading center whereas the north vourinos chromitites formed at a distance from the spreading center in addition the strong depletion of pge in the kissavos cr rich ores particularly os ir and ru may suggest that these chromitites were crystallized from magmas derived by partial melting of an already depleted mantle source the geochemical trend throughout the vourinos complex seems to provide valuable confirmation of a stratigraphic orientation in the mantle sequence of the complex

compositional variations of chromite and solid inclusions in ophiolitic chromitites from the southeastern turkey implications for chromitite genesis abstract chromitites associated with upper mantle peridotites of ophiolites from southeastern turkey are lenticular bodies or veinlets made up of massive banded and disseminated chromite chromite shows a wide range of cr cr cr al varying between 0 42 and 0 81 and mg mg mg fe2 of 0 45 to 0 75 geochemically they are divided into two compositional groups such as high cr cr 0 7 and high al cr

response of leaky aquifers to earth tides interpreted with numerical simulation abstract the response of aquifers to earth s solid tides earth tides has increasingly been used as a tool for monitoring the hydraulic properties of groundwater systems recent studies of the tidal response of the arbuckle aquifer opened to a usgs deep well in oklahoma wang et al 2018 barbour et al 2019 which has been injected with an enormous amount of toxic wastewater showed evidence that this aquifer may be leaking quantitative interpretation of the tidal response of this aquifer was made with a one dimensional analytical solution wang et al 2018 that showed that substantial leakage is occurring however the analytical model has inherent simplifications such as conductivity isotropy small aquifer thickness absence of aquitard storage and no basement leakage in this study we revisit the tidal response of leaky aquifers with a finite element multi layered model where such simplifications are removed we found that the simplifications in the analytical model lead to overly conservative estimates of leakage we revisit the tidal response of the arbuckle aquifer in oklahoma with the numerical simulation and estimate an average vertical hydraulic conductivity of 2 10 6 t o 7 10 5 m s for the aquitard overlying the arbuckle thus the aquitard above the arbuckle is not confining at this location but is as conductive as the aquifer itself given the fast rise of fluid level in many arbuckle wells in response to the injection of hundreds of millions of barrels of wastewater into this aquifer across oklahoma and kansas the present result calls for vigilant monitoring of leakage of wastewater from the arbuckle aquifer into the overlying freshwater reservoirs and the surface environment plain language summary earthquakes can damage the confinement of groundwater aquifers and thus can cause seismic hazard by letting freshwater in some aquifers to be contaminated or stored toxic wastewater in other aquifers to leak out into the environment thus it is important to monitor possible leakage of aquifers in earthquake countries analysis of the aquifer response to earth s solid tides in a usgs deep well in oklahoma wang et al 2018 barbour et al 2019 which has been used as the repository of an enormous amount of injected toxic wastewater shows that the aquifer may be leaking an analytical solution wang et al 2018 that contains several simplifications was used to quantify the aquifer leakage from the tidal response here we use a two dimensional multilayered numerical simulation without these simplifications to explore the limitations of the analytical model we find that aquitard storage and basement leakage have important effects on the tidal response of aquifers and the omission of these factors in the analytical solution may have caused underestimation of the aquifer leakage we then apply the numerical model to interpret the tidal response of water level documented in a usgs deep monitoring well installed in the arbuckle aquifer in oklahoma where an enormous amount of toxic wastewater has been stored with reasonable estimates of the aquitard storage our simulations yield an estimate of 2 10 6 t o 7 10 5 m s for the vertical hydraulic conductivity of the aquitard thus the aquitard is not at all confining but is as conductive as the aquifer itself given the fast rise of fluid level in many arbuckle wells in response to the injection of hundreds of millions of barrels of wastewater into this aquifer across oklahoma and kansas the present result calls for vigilant monitoring of leakage of wastewater from the arbuckle aquifer into the overlying freshwater reservoirs and the surface environment

platinum group elements as petrological indicators in mafic ultramafic complexes of the central and southern urals preliminary results abstract platinum group elements pge and gold were analyzed by icp ms after the ni sulphide fire assay pre concentration step in 44 rocks from 5 orogenic mafic ultramafic massifs of the central and southern urals they comprise a ring zoned ural alaskan type bodies of the pt bearing belt kachkanar tagil uktus and b lherzolite harzburgite complexes overlain by layered wehrlite gabbro and diorite nurali mindyak supposed to be ophiolite type suites total pge and au contents are generally higher in ural alaskan type complexes compared with lherzolite harzburgite complexes mantle normalized pge patterns range from nearly unfractionated in the dunites pd ir 0 57 3 68 to mildly and strongly fractionated in wehrlite clinopyroxenite and gabbro pd ir 9 1 187 exceptionally high values of pd ir 761 2622 are observed in amphibole rich lithologies at kachkanar possibly indicating a relationship between fractionation of the less refractory pd and increased fluid activity in the parental magma pronounced positive pt anomalies up to 20 times the mantle estimate distinguishes the ural alaskan type dunites and progressively reduces in pyroxenites and gabbros in the lherzolite harzburgite complexes of mindyak and nurali layered wehrlites and pyroxenites as well as rocks from the gabbro diorite units have fractionated pge patterns pd ir 2 94 92 39 and positive pt anomaly as in the ural alaskan complexes conversely the pt anomaly is negative in the peridotites and increases from lherzolites and harzburgites to dunites similarly to residual mantle from alpine type orogenic massifs the pd ir 0 71 3 7 is higher than in ophiolites and resembles that of lherzolite massifs of the western mediterranean representing sub continental mantle variation of the pt anomaly versus pd ir in ural alaskan type complexes and in the layered sequences overlaying lherzolite harzburgite mantle suites is consistent with magmatic fractionation in which pt behaves as a compatible element it reflects a progressive depletion by partial melting in mantle peridotites the pt becoming incompatible in the last stage of melting in which pt poor residual dunites are formed the positive pt anomaly in ural alaskan type complexes is striking and would appear as a distinctive feature of the parent magma probably inherited from its mantle source

characteristics and genesis of kanggur gold deposit in the eastern tianshan mountains nw china evidence from geology isotope distribution and chronology abstract the kanggur gold deposit lies in east tianshan mountains eastern section of central asia orogenic belt the gold mineralization occurs on the northern margin of the aqishan yamansu island arc in the tarim plate it is mainly hosted in lower carboniferous volcanic rocks and controlled by syn tectonic intrusions and the ductile shear zone the host rock is a calc alkaline volcanic rock series consisting of andesite dacite tuff and subvolcanic rocks the gold ore bodies were distributed in transition zone from strong ductile deformation to weak deformation ore controlling structure is ew trending normal brittle ductile shear zone the gold ore bodies are composed of au bearing altered rocks and a few au bearing sulfide quartz veins the mineralization shows vertical zonation in which au was enriched in the upper orebodies au pb zn were enriched in the middle and au cu were enriched in the lower orebodies according to mineral assemblages and alteration intensity hydrothermal alteration could be divided into three zones silicification chloritization pyritization and magnetization zone major ore body pyrite phyllic rock and or sericite alteration zone and sericite chlorite alteration zone five mineralization stages are identified on the basis of mineral assemblage and crosscutting relationship of veins the 34 s values of sulfide in the ores range from 0 9 to 3 3 similar to those of the volcanic and subvolcanic rocks 3 21 1 3 indicating that the sulfur isotope composition is characterized by unfractionated mantle sulfur the lead isotope compositions of ores are between those of the volcanic rocks and subvolcanic rocks the initial 87 sr 86 sr ratios of the ores vary between 0 7077 and 0 7106 similar to those of the host rocks 0 7079 0 7125 according to the sr s and pb isotopic data it is indicated that the ore forming materials were derived from the surrounding volcanic rocks and feature deep source the 18 o values of the ore fluids vary from 3 83 to 1 77 and the d values from 46 to 66 the 18 o vs d and 18 o vs 87 sr 86 sr diagrams indicate that ore fluids were derived from dynamic metamorphic water magmatic water and meteoric water the ore forming ages of kanggur gold deposit are determined by rb sr and sm nd isochron methods the results show that the main ore forming stages of kanggur gold deposit are 290 282 ma secondary mineralization stages are 275 254 ma studies on regional geology ore geology isotope geochemistry and ore forming ages have proved that the kanggur gold deposit was formed in the compression extension transition stage during the latest paleozoic continental collision and is characterized by orogenic gold deposits

fluid inclusion rb sr isochrons for dating mineral deposits the precise dating of mineral deposits has important implications for understanding the lifetime of ore forming systems and their temporal relationship to various geological events not all deposits provide material suitable for conventional radiometric dating or data which are amenable to unequivocal interpretation nor is it easy to verify that such samples have remained isotopically closed since their formation fluid inclusions provide an alternative closed system approach by analysing the isotopic composition of rband sr in inclusions within quartz from the carrock fell tungsten vein deposits cumbria we demonstrate here the feasibility of obtaining rb sr fluid inclusion isochrons the age for the mineralization 392 5 myr is in good agreement with the mean k ar age 387 6 myr for the vein micas and confirms the significance of fluid inclusions as precise rb sr geochronometers

revealing mineralization and subsequent hydrothermal events insights from 40ar 39ar isochron and novel gas mixing lines of hydrothermal quartzs by progressive crushing abstract increasingly more data have indicated that the 40ar 39ar crushing technique provides a very useful approach to determine the mineralization ages of hydrothermal ore deposits in this study novel gas mixing lines are proposed based on the data of two quartz samples by 40ar 39ar crushing electron microprobe analyses indicate that the quartz grains contain k rich silicate microlites both quartzs by crushing yield two mixing lines with ages corresponding respectively to those of k feldspar or sericite post mineralization fluids and muscovite samples ore forming fluids this is the first report that both ages of secondary and primary fluid inclusions sfis and pfis are confirmed correspondingly by those of the k rich minerals this study strongly indicates that the 40ar 39ar crushing technique is very useful to determine the ages of geofluid activities the newly proposed gas mixing patterns are shown on the inverse and normal isochron diagrams indicating 1 the mixtures are in different proportions of the pfis and sfis in different crushing steps 2 the gas mixing lines yield pfi ages with low initial 40ar 36ar ratios 3 an intermediate age between pfi and sfi ages cannot be obtained because the progressive crushing technique never release gas mixtures with a constant pfi sfi proportion for each step the gas mixing lines are thus interpreted to yield significant geological ages the mixing patterns will help us better understand the 40ar 39ar dating results and be used for references to other isotopic mixing isochron systems

geochronology and isotope geochemistry studies of an epithermal gold deposit in the northern lesser khingan range ne china the gaosongshan example abstract the gaosongshan epithermal gold au deposit is located in the northern margin of the lesser khingan range polymetallic ore belt northeast ne china and contains au resources of more than 23 tons at an average grade of 6 3 g t gold orebodies are mainly hosted in intensely altered volcanic rocks of the lower cretaceous banzifang formation and as exploration has continued gold has also been discovered in extensively altered porphyritic intrusions with the highest au grade of 70 g t however the ages of metallogenesis and related magmatism have not been well constrained yet which have hindered the summary of metallogenic regularities in this study laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb dating from the granite porphyry yields a weighted mean 206pb 238u age of 101 6 1 2 ma slightly older than the rb sr isotope age of 98 1 6 ma for the auriferous quartz samples indicating that the gaosongshan au mineralization is genetically related to the granite porphyry the fluid d and 18oh2o values vary from 136 to 111 and from 9 3 to 2 5 respectively and the 4he and 40ar isotope compositions range from 15 7 10 9 to 35 5 10 9 cm3 stp g and 13 4 10 7 cm3 to 34 1 10 7 cm3 stp g respectively the obtained isotopic data show that the ore forming fluids were mixtures of magmatic and meteoric water but were dominated by meteoric water the 206pb 204pb 207pb 204pb and 208pb 204pb ratios of ores in the gaosongshan deposit are 17 752 18 856 15 514 15 674 and 38 005 39 921 respectively which are similar to those of the gaosongshan granite porphyry implying that pb and possibly au originated primarily from late early cretaceous magmatic intrusions combining these results with data from previous studies we propose that the gaosongshan au deposit formed in an extensional tectonic setting during the rollback of the paleo pacific oceanic plate in ne china

part ii evaluation of 40ar 39ar quartz ages implications for fluid inclusion retentivity and determination of initial 40ar 36ar values in proterozoic samples the argon isotope systematics of vein quartz samples with two different k reservoirs have been evaluated in detail potassium is hosted by ultra high salinity fluid inclusions in quartz samples from the eloise and osborne iron oxide copper gold iocg deposits of the mt isa inlier australia in contrast k is hosted by accidentally trapped mica within lower salinity fluid inclusions of a sample selected from the railway fault 13 km south of the mt isa copper mine australia imprecise apparent ages have been obtained for all of the samples studied and conclusively demonstrate that quartz fluid inclusions are retentive to ar and have not leaked over billions of years iocg samples that host k in fluid inclusions only have k cl values of 1 and the ages obtained represent the maximum ages for mineralization in contrast the railway fault samples that include accidentally trapped mica have k cl values of 1 excess 40 are plus cl hosted by fluid inclusions and radiogenic 40 arr plus k are strongly correlated in these samples and define a plane in 3d 40 ar 36 ar k cl space in this case the plane yields an excess 40 are corrected age of 1030 ma that is 100 s of ma younger than nearby cu mineralization at mt isa the age is interpreted to reflect 40 ar loss from the accidentally trapped mica into the surrounding fluid inclusions and is not related to the samples age of formation the initial 40 ar 36 ar value of fluid inclusions is widely used to provide information on fluid origin for the iocg samples that host k in fluid inclusions only the initial 40 ar 36 ar values are close to the measured values at every temperature of stepped heating experiments for samples that include accidentally trapped mica the correction for post entrapment radiogenic 40 arr production is significant furthermore because 39 ark present in accidentally trapped mica crystals is released at different temperatures to radiogenic 40 arr lost to the surrounding fluid inclusions intra sample 40 ar 36 ar variation cannot be reliably documented the results demonstrate that noble gas analysis is readily applicable to proterozoic or older samples but that if k mineral impurities are present within quartz the abundance of k must be determined before calculation of mean 40 ar 36 ar values that are

rheological conditions for emplacement of ural alaskan type ultramafic complexes article i nfo ural alaskan or alaskan type complexes correspond to a particular class of ultramafic intrusions that attract particular attention due to their deep mantle origin and their platinum group element pge mineralization when defined as massifs of dunite clinopyroxenite only forty six complexes are reported in the literature these large scale dunite pipe like structures are rarely isolated and they even can appear in clusters to better understand genesis of these relatively young b460 ma complexes a worldwide compilation has been built and three categories have been defined single circular or elliptical bodies twin bodies with similar shapes and dismembered dunite bodies pge enrichment in alaskan type complexes is highest for the second category where twin bodies are interpreted as horizontal sections of y shaped dunite pipes to constrain mechanical properties of the lithosphere allowing emplacement of the alaskan type complexes the forceful diapiric ascent hypothesis is investigated through numerical thermo mechanical models one hundred high resolution experi ments accounting for realistic phase changes and softening mechanisms have been performed the experiments show that with no rheological softening of the host rock and in case of a relatively weak ductile lower crust the uprising magma tends to spread laterally without reaching the surface to account for the forceful ascent of deep magmas it is hence necessary to assume a strong lower crust rheology and strong local softening mechanisms besidesreproducingtheclustereddistributionoftheweaknesszonesrepresentingmagmapathways theselatter experiments reproduce large scale pipe like cylindrical structures y shaped and funnel shaped bodies and laterally shifted structures interestingly zones of highest strain rates are located at the bottom parts of the inclined edges of y shaped and funnel shaped bodies the restricted age range of alaskan type complexes b460 ma would mean that prior to this time the lower crust was less resistant due to the hotter geotherm prohibiting the possibility of alaskan type magmatism

determination of anisotropy of spatial correlation structure in a three dimensional permeability field accompanied by shallow faults 1 structural planes such as fractures bedding planes schistosity and so on induce heterogeneity of permeability field in geologic bodies one of the ways to demonstrate the heterogeneity is to geostatistically infer the spatial correlation structure this paper presents a newly developed geostatistical technique for estimating the three dimensional heterogeneous permeability field in the presented method the plane directional anisotropy of spatial correlation structure of the three dimensional permeability field is determined by estimating semivariograms in multiplane directions using limited in situ measurement data of basement rock permeability a case study of a dam site shows that the spatial correlation of permeability in the direction parallel to the fault planes is greater than that perpendicular to it direction of the largest anisotropy of the spatial correlation of the permeability field is concordant with the strike of the major faults

platinum group element geochemistry of sulfide rich horizons in the ural alaskan type ultramafic complex of duke island southeastern alaska the duke island ultramafic complex in southeastern alaska is a ural alaskan type complex that hosts sulfide rich horizons primarily in the olivine clinopyroxenite unit although placer deposits hosting platinum group elements pges have been found in association with ural alaskan type complexes in several locations around the world these ultramafic complexes have traditionally been viewed as sulfide poor systems and therefore unlikely hosts of economic ni cu sulfide deposits sulfide mineralization in the duke island complex consists of massive net textured and disseminated assemblages that formed as a result of the interaction between magma and sulfidic graphitic country rocks the sulfide mineralization at duke island is characterized by strong depletion in ir os and ru ipges and relative enrichment in pt pd and cu the sulfide bearing olivine clinopyroxenites formed from a derivative magma produced as a result of the fractional crystallization of olivine and chromite although ipges may be compatible within olivine and chromite fractional crystallization of up to 20 cannot explain the observed ipge depletion we propose that early crystallization of laurite and ir alloys accompanied the accumulation of olivine and chromite r factor modeling indicates that much of the inter element variation in the sulfide mineralization can be attributed to variations in the degree of equilibration between sulfide and silicate liquids mixing between monosulfide solid solution and fractionated sulfide liquid may also have contributed to the variability the modeling suggests that the pre sulfide saturation concentrations of os pt and pd in the magmas were approximately 0 03 2 and 3 ppb respectively the concentration of pd is near that of primitive mantle and the low pt concentration can be explained by the crystallization of pt alloy with early formed dunites and chromitites this is consistent with models for pt rich placers in the urals that have been derived from chromitites and dunites the relative enrichments in pd and cu are the results of fractional crystallization before sulfide saturation was achieved taken together the ni cu pge elemental characteristics at the duke island complex are similar to those shown by flood basalt related sulfide deposits and cu rich sulfide veins studied in different locations around the world

chromite and pge geochemistry of the elekdag ophiolite kastamonu northern turkey implications for deep magmatic processes in a supra subduction zone setting abstract the geochemistry of chromium spinel and platinum group elements pge provides significant information about conditions in the mantle during the emplacement and genesis of ophiolitic complexes the elekdag ophiolite is a greenschist to amphibolite facies ophiolite that was emplaced onto the sakarya zone in the central part of the pontides of northern turkey nw se trending elekdag ophiolite hosts small scale chromitite occurrences in serpentinized harzburgite and dunite and have maximum resource of several thousands t cr2o3 the chromitites the elekdag ophiolite can be divided in to high cr and high al types the calculated melt composition of the high cr chromitites is 9 4 13 2 wt al2o3 0 2 0 4 wt tio2 with feo mgo ratios of 0 4 1 9 which are indicative of boninitic compositions however the high al chromitites have 14 7 17 3 wt al2o3 and 0 3 0 8 wt tio2 with feo mgo ratios of between 0 3 and 0 8 which are consistent with morb like tholeiitic affinities the total pge content of the chromitites range between 82 and 1466 ppb and the average pge content of the high cr and high al chromitites are 267 ppb and 195 ppb respectively the chromitites are characterized by low pd ir ratios of 0 02 0 20 that is characteristic of non fractionated chromitites the chondrite normalized pge pattern of the chromitites resemble those of mantle derived cr rich chromitites in ophiolites of the supra subduction zone ssz elsewhere mineral and bulk rock pge data for the elekdag chromitites indicate that high cr chromitites formed from cr rich and al and ti poor boninitic melts most probably in the fore arc setting in the deeper part of the mantle this was succeeded by the mineralization of high al chromitites from a differentiated boninitic melt at shallow depths close to the moho discontinuity

analytical solutions for whirling groundwater flow in two dimensional heterogeneous anisotropic aquifers analytical solutions are derived for steady state groundwater flow in a heterogeneous anisotropic semiconfined aquifer the aquifer consists of a number of horizontal layers while each layer consists of a number of homogeneous cells with different hydraulic conductivity tensors an exact solution for an arbitrary number of layers and cells is derived using a multilayer approach hypothetical models are used to study how flow is affected by heterogeneity in the anisotropy when the major principal direction of the transmissivity tensor varies between layers streamlines have the shape of spirals bundles of spiraling streamlines rotating in the same direction are called groundwater whirls analytical and numerical models of hypothetical cases produce the same flow patterns of groundwater whirls projected streamlines may be represented by stream function contours which allows for easy interpretation of the main characteristics of complex whirl patterns typical whirl patterns may be identified in relatively simple models clockwise and counterclockwise whirl axes occur at the interfaces of adjacent layers one or more clockwise whirls may occur within one counterclockwise whirl and vice versa the practical consequence of groundwater whirls is that the exchange of water between aquifer layers is intensified this may have a significant impact on contaminant spreading

transient well flow in vertically heterogeneous aquifers abstract a solution for the general problem of computing well flow in vertically heterogeneous aquifers is found by an integration of both analytical and numerical techniques the radial component of flow is treated analytically the drawdown is a continuous function of the distance to the well the finite difference technique is used for the vertical flow component only the aquifer is discretized in the vertical dimension and the heterogeneous aquifer is considered to be a layered stratified formation with a finite number of homogeneous sublayers where each sublayer may have different properties the transient part of the differential equation is solved with stehfest s algorithm a numerical inversion technique of the laplace transform the well is of constant discharge and penetrates one or more of the sublayers the effect of wellbore storage on early drawdown data is taken into account in this way drawdowns are found for a finite number of sublayers as a continuous function of radial distance to the well and of time since the pumping started the model is verified by comparing results with published analytical and numerical solutions for well flow in homogeneous and heterogeneous confined and unconfined aquifers instantaneous and delayed drainage of water from above the water table are considered combined with the effects of partially penetrating and finite diameter wells the model is applied to demonstrate that the transient effects of wellbore storage in unconfined aquifers are less pronounced than previous numerical experiments suggest other applications of the presented solution technique are given for partially penetrating wells in heterogeneous formations including a demonstration of the effect of decreasing specific storage values with depth in an otherwise homogeneous aquifer the presented solution can be a powerful tool for the analysis of drawdown from pumping tests because hydraulic properties of layered heterogeneous aquifer systems with partially penetrating wells may be estimated without the need to construct transient numerical models a computer program based on the hybrid analytical numerical technique is available from the author

an exact analytical solution for steady seepage from a perched aquifer to a low permeable sublayer kirkham brock s legacy revisited an analytical solution is obtained for steady 2 d potential seepage flow from a nonclogged and nonlined soil channel into a highly permeable porous layer with phreatic surfaces tapering toward a horizontal interface with a subjacent low permeable formation along this boundary a vertical component of the darcian velocity vector equals the formation saturated hydraulic conductivity the image of the physical flow domain in the hodograph plane is a circular polygon a triangle or digon in a limiting case of a phreatic jet impinging on the low permeable substratum the polygon is mapped onto an auxiliary half plane where the complex physical coordinate and complex potential are reconstructed by the polubarinova kochina method i e by solution of a riemann bvp the seepage flow rate from the channel free surfaces and a saturated water logged area are found for different thicknesses of the top layer channel widths and conductivity ratios of the two strata in particular the earlier results of brock kirkham and youngs which are based on a numerical solution dupuit forchheimer df approximation and approximate potential model are confirmed in the full 2 d models sufficiently far from the channel the phreatic surface and interface make a wedge for a sufficiently deep substratum three zones are analytically distinguished an almost vertical 1 d descending flow an almost wedge configured 1 d flow and an essentially 2 d zone in between where neither a standard infiltration theory nor df analysis are valid

an analytical solution for leakage rate and depletion of aquitard influenced by the delayed yield phenomenon delayed yield phenomenon dyp occurs when the drawdown of an aquitard is no longer in equilibrium owing to previous changes in the level of water in adjacent aquifers in this study an analytical solution to determine the distribution of the drawdown at any time and at any point in an aquitard in which the water level was not in equilibrium at the initial time and the water level of the aquifers immediately above and below the aquitard was time dependent was developed the analytical solution for the flow rate at any time and location was presented based on variations in drawdown in the aquitard in addition the effects of the dyp on the leakage rate and depletion of the aquitard were studied subsequent comparison of the proposed analytical and numerical solutions revealed that they were in good agreement the results of this study will be useful to future studies of groundwater flow and environmental problems such as water budgets rising sea levels solute transport heat conduction and ground subsidence

an approximate analytical solution for well flow in anisotropic layered aquifer systems abstract the mathematical problem of steady groundwater flow toward a pumping well in an aquifer system consisting of layers or aquifers with anisotropy of the horizontal conductivity is solved analytically for the first time the solution is an approximation for relatively weak anisotropy if more than one layer is horizontally anisotropic the method requires that the principal directions of anisotropy are the same in all layers the presented solution is based on a first order perturbation technique comparison with numerical calculations shows a good agreement as long as tmin is nowhere less than 0 6tmax layers with stronger anisotropy are also allowed provided these are embedded in a system with layers of weaker anisotropy

drawdown around a well in a heterogeneous leaky aquifer system abstract real leaky multiaquifer systems are composed of several aquifers separated by aquitards all layers have non uniform hydraulic parameters and irregular lateral extension following natural boundaries in this study wells are replaced by point sources and storativity of aquitards is neglected the proposed synthesized analytical numerical san method is based on the analytical solution that extends hydraulic parameters of the well site to an appropriate regular flow field effects of heterogeneity and real no flow boundaries are estimated separately by numerical methods numerical tests show a low level of numerical error of the coupled san procedure vs available analytical solutions

steady groundwater flow in leaky multiple aquifer systems abstract the hydraulic properties of stratified formations usually vary from layer to layer within the area of influence of a pumped well drain or section of a river the subsoil can often be schematized into a limited number of aquifers each separated by less pervious layers a general method has been developed for the analytical solution of steady flow problems in leaky multiple aquifer systems comprising any number of aquifers this method has been used to investigate potential distributions in multilayered aquifers of infinite extent being pumped or recharged at a constant rate using completely penetrating wells and drains in one or more of the aquifers the same approach is applicable to groundwater flow problems with more complicated boundary conditions such as the influence of a wide river partially penetrating the leaky top layer the well flow solution has been applied to evaluate hydraulic properties of several aquifers and aquitards from pumping tests in a six layer leaky aquifer system in a general sense the method presented may be regarded as a combined analytical numerical technique

implications for mechanical properties of brittle faults from observations of the punchbowl fault zone california field observations of the punchbowl fault zone an inactive trace of the san andreas are integrated with results from experimental deformation of naturally deformed punchbowl fault rocks for a qualitative description of the mechanical properties of the fault and additional information for conceptual models of crustal faulting the punchbowl fault zone consists of a single continuous gouge layer bounded by zones of extensively damaged host rock fault displacements were not only localized to the gouge layer but also to discrete shear surfaces within the gouge deformation in the exposure studied probably occurred at depths of 2 to 4 km and was dominated by cataclastic mechanisms textural data also suggest that significant amounts of pore fluids were present during faulting and that fluid assisted mechanisms such as dissolution diffusion and precipitation were operative the experimental data on specimens collected from the fault zone suggest that there is a gradual decrease in strength and elastic modulus and an increase in relative ductility and permeability toward the main gouge zone the gouge layer has fairly uniform mechanical properites and it has significantly lower strength elastic modulus and permeability than both the damaged and the undeformed host rock for the punchbowl fault and possibly other brittle faults the variations in loading of the gouge zone with time are primarily governed by the morphology of the fault and the mechanical properties of the damaged host rock in addition the damaged zone acts as the permeable unit of the fault zone and surrounding rock it appears that the gouge primarily governs whether displacements are localized and it therefore may have a significant influence on the mode of slip

analytical solutions for pressure perturbation and fluid leakage through aquitards and wells in multilayered aquifer systems 1 large scale groundwater pumping or deep fluid injection in a multilayered subsurface system may generate pressure perturbation not only in the target formation s but also in over and underlying units hydraulic communication in the vertical direction may occur via diffuse leakage through aquitards and or via focused leakage through leaky wells existing analytical solutions for pressure perturbation and fluid flow in such systems consider either diffuse leakage or focused leakage but never in combination with each other in this study we developed generalized analytical solutions that account for the combined effect of diffuse and focused leakage the new solutions solve for pressure changes in a system of n aquifers with alternating leaky aquitards in response to fluid injection extraction with any number ni of injection pumping active wells and passive leakage recharge in any number nl of leaky wells the equations of horizontal groundwater flow in the aquifers are coupled by the vertical flow equations in the aquitards and by the flow continuity equations in the leaky wells the solution methodology described in detail in this paper involves transforming the transient flow equations into the laplace domain decoupling the resulting ordinary differential equations odes coupled by diffuse leakage via eigenvalue analysis solving a system of nl n linear algebraic equations for the unknown rates of flow through leakage wells and superposing the solution of pressure buildup drawdown in aquifers and aquitards resulting from flow in the ni active and nl leaky wells verification of the new methodology was achieved by comparison with existing analytical solutions for diffuse leakage and for focused leakage and against a numerical solution for combined diffuse and focused leakage application to an eight aquifer system with leaky aquitards and one leaky well demonstrates the usefulness and efficiency of the approach and illustrates the pressure behavior over a spectrum of leakage scenarios and parameters

analytic elements for multiaquifer flow abstract the objective of this paper is to present an analytic element formulation for groundwater flow in multiaquifer systems analytic element equations are presented for wells line sinks and circular infiltration areas each analytic element is a solution to the governing system of differential equations and thus simulates the leakage between aquifers exactly the head discharge and leakage may be computed analytically at any point in the aquifer superposition of these analytic elements allows for the simulation of regional multiaquifer flow a hypothetical example is presented of a system with three aquifers a river network and three pumping wells it is demonstrated that the leakage between aquifers may vary significantly over short distances and that each aquifer has its own water divide

experimental study of the solubility of platinum and iridium in basic silicate melts implications for the differentiation of platinum group elements during magmatic processes this study presents evidence for the dissolution of two platinum group elements pge s pt and ir in silicate melts of basic composition in the absence of any associated fluid phase the dissolution of these pge s is attributed to the formation of a complex ion in which the noble metal is uncharged an increase in oxygen fugacity in equilibrium with the melt brings about a considerable decrease in ir solubility in this way we can explain the early enrichment in ir group pge s ipge s ir ru os observed during the crystallization of ultrabasic cumulates by contrast however pt remains soluble in the melt an increase in the fs2 results in a pronounced increase in the solubility of pt in the silicate melt the sulfur saturation which leads to the precipitation of the base metal sulfides bms s also brings about the fixation of pt group pge s ppge s pt pd rh which are dissolved in bms s this accounts for the presence of ppge s in the nickel sulfide horizons of stratiform deposits the occurrence of platiniferous fe crystallizing with chromite in alaskan type complexes at oxygen fugacities of 10 6 bar can be explained by the low activity of fe in fe pt alloys such alloys have been formed in our laboratory at such fo2

spatial correlation structure estimation using geophysical and hydrogeological data the large spatial variability of hydraulic properties in natural geologic systems over a wide range of scales and the difficulty of collecting representative and sufficient hydraulic property measurements using conventional sampling techniques render estimation of spatial correlation parameters difficult further compounding the estimation problem is the observation that the integral scale estimate is a function of the measurement support scale to mitigate these problems we investigate the use of tomographic geophysical data in combination with hydrogeological data in the spatial correlation estimation procedure two synthetic case studies were investigated where the scale of the geophysical measurements were varied relative to the scale of the hydrogeological properties the spatial correlation structure parameter estimation procedure was performed in the spectral domain where analysis of data having different support scales and spatial sampling windows was facilitated comparison of the spatial correlation structure parameters estimated from measured data with those of the synthetic aquifers revealed which type of data tomographic hydrogeological or a combination of both was most effective for recovering spatial correlation statistics under different sampling heterogeneity conditions these synthetic case studies suggest that collection of a few tomographic profiles and interpretation of these profiles together with limited well bore data can yield correlation structure information that is otherwise obtainable only from extensive hydrological sampling

geochemistry of platinum group elements of the zoned ultramafic alto condoto complex northwest colombia the alto condoto complex dated at 20 ma is a zoned ultramafic intrusion with a magmatic rock sequence ranging from dunite to hornblendite the different petrographic units are cumulates formed by fractional crystallization processes parts of the central dunite are anomalously enriched in ptfe alloys and to a minor degree in iros alloys all other lithologic units of the complex display normal fractionation trends of platinum group elements pge with a general increase of total pge from wehrlite to horn blende clinopyroxenite and hornblendite this normal trend is best described by increasing pd and decreasing ir abundances the controlling factor for pge mineralization in zoned ultramafic complexes is probably an effective ptfe alloy precipitation during the crystallization of olivine this may be initiated by rapid tectonic movements causing pressure decrease and overheating of the magma with pge alloy formation as a result of the f sub o 2 shift during olivine crystallization

alteration of platinum group minerals and dispersion of platinum group elements during progressive weathering of the aguablanca ni cu deposit sw spain the distribution mineralogy and mobility of the platinum group elements pge in the surface environment are poorly understood this study of the lower less altered and upper more altered gossan overlying the aguablanca ni cu pge magmatic deposit spain has shown that the platinum group minerals pgm are progressively oxidised and dispersed into iron oxides that form the gossan a combination of the characterization of pge in host pgm using a scanning electron microscope and measurement of pge at lower concentrations in host iron oxides using laser ablation inductively coupled plasma mass spectrometry la icp ms has for the first time allowed the total distribution of the pge within a gossan to be documented this study has revealed a complete in situ alteration and dispersion sequence of the pgm including 1 breakdown of both the more stable pt arsenides pt pd tellurides and the less stable bismuthotellurides 2 formation of partially oxidised pgm 3 development of a wide range of oxidised pt and pd bearing phases 4 subsequent formation of fe pge oxides and pge hydroxides 5 incorporation of pge into ferruginous supergene products and lastly 6 concentration of pge at the edges of veins and iron oxides dispersion of pd is greater than for the other pge with pd being widely distributed throughout the iron oxides this oxidising environment produced pge oxides rather than pge alloys also commonly found in the surface environment especially in placers these results provide critical evidence for the stages of mineralogical change from pge host mineralogy in magmatic ores to surface weathering producing pge oxides

spinel compositions of mantle hosted chromitite from the eastern anatolian ophiolite body turkey implications for deep and shallow magmatic processes abstract the eastern anatolian accretionary complex includes several ophiolitic megablocks and or tectonic slivers within a 150 180 km long east west trending complex formed during the late cretaceous tertiary in eastern turkey the alabayir mollatopuz yukaribalcikli and mehmetalan ophiolites are megablocks or tectonic slivers containing locally massive nodular or schlieren banded chromitite layers these podiform chromitites formed in mantle sequences and are classified as high cr chromitites cr 0 63 0 88 mg 0 50 0 64 0 01 0 5 wt tio 2 5 7 18 8 wt al 2 o 3 calculated parental melt compositions of these chromitites indicate boninite magma characteristics 8 2 13 4 wt al 2 o 3 0 64 1 50 feo mgo the pge patterns also support the view that they crystallized from a boninitic melt the total pge contents of chromitites vary between 79 and 390 ppb pd ir ratios of chromitites vary from 0 07 to 0 28 and are consistent with an ipge fractionated nature the examined chromitites were divided into two groups in terms of their mineral chemistry group i alabayir mollatopuz yukaribalcikli and mehmetalan i chromitites group ii mehmetalan ii chromitites mineral chemistry of these chromitites and their parental melt composition indicate that group i chromitites were probably formed at shallow mantle depths and that group ii chromitites formed in deeper parts of the mantle mineral chemistry of these eastern anatolia high cr chromitites indicate that they formed not only in the deeper mantle but also in shallower parts of the moho transition zone