influence of the temperature of co2 rich springs on their aluminium and rare earth element contents abstract in a set of thermomineral waters of about constant major element composition al fe and rare earth element ree concentrations are strongly dependent on the spring temperature al and ree concentrations are not affected by co2 degassing at the outflow of the waters al concentrations vary by one order of magnitude between the coldest and the hottest waters this change in total concentration is related to a change in the speciation fluoride complexes mainly alf03 are the dominant species in cold waters hydroxide or fluoro hydroxide complexes are more important at higher temperature ree patterns vary smoothly as a function of the atomic number from a regular decrease for the hottest water ce yb 30 to a large increase from ce to dy followed by a slight decrease from dy to yb for the coldest waters ce yb 0 3 ce dy 0 15

multiphase formation of the obři důl polymetallic skarn deposit west sudetes bohemian massif geochemistry and re os dating of sulfide mineralization the ob i d l fe cu as polymetallic sulfide skarn deposit is developed in a metamorphic series in the west sudetes bohemian massif it consists of lenses of marble calc silicate rocks and skarns we studied the gustav orebody which is located few hundred meters away from the contact with a large late orogenic variscan krkonose jizera plutonic complex kjpc emplaced into shallow crust mineralogical and fluid inclusion study evidence indicates that the main sulfide stage dominated by pyrrhotite arsenopyrite and chalcopyrite originated from aqueous hydrothermal fluids with salinity up to 8 wt nacl eq with minimum homogenization temperatures ranging from 324 to 358 c these fluids mainly replaced carbonate rich lithologies carbon oxygen and strontium isotope data in ca rich rocks imply total overprinting by channelized metasomatic fluid flow which is most probably related to the intrusion of the kjpc whereas 34s values of sulfides argue for a magmatic source of sulfur the re os age of arsenopyrite overlaps published age data for the kjpc and suggests synchronous formation of the main sulfide mineralization and pluton emplacement

nd isotopic and geochemical constraints on provenance of sedimentary rocks in the eastern officer basin australia implications for the duration of the intracratonic petermann orogeny sm nd isotopic and geochemical data from neoproterozoic to cambrian sedimentary rocks in the intracratonic eastern officer basin in central australia highlight the evolving provenance roles of the basement complexes that underlie and bound the basin initial e nd values of around 12 for the basal units indicate that both were largely derived from the late archaean to mesoproterozoic gawler craton which bounds the basin to the south at c 720 ma an influx of juvenile glacially derived sediment indicates partial uplift of the mesoproterozoic musgrave block along the basin9s northern margin in a regime interpreted to be broadly extensional at around 600 ma synchronous with the development of a foreland architecture there was a large influx of musgrave block derived sediments this is interpreted to mark the onset of the intracratonic petermann orogeny which was a long lived event or series of events spanning more than 70 ma subsequent to c 600 ma the nd isotopic composition of sequences within the officer basin indicates an increasing contribution from the gawler craton despite up to 45 km of denudation of part of the musgrave block this suggests that the majority of sediment derived from the petermann orogen bypassed the eastern officer basin for much of the history of the petermann orogeny

nd sr isotopic and ree geochemical compositions of late quaternary deposits in the desert loess transition north central china implications for their provenance and past wind systems abstract the nd sr isotopic and ree geochemical compositions of the dishaogouwan profile in the desert loess transition between the ordos desert and the chinese loess plateau were investigated to identify the provenance of the sediments and to reconstruct the regional wind systems of the past the 87 sr 86 sr ratios of 0 7158 0 7175 nd 0 values of 8 9 to 16 8 ree values between 133 g g and 277 g g and roughly flat paas normalized ree patterns which differs from the 75 m fractions in the dishaogouwan profile this is most likely due to mineral sorting and or source features isotopic and geochemical comparisons of the dishaogouwan profile with potential sources show that 1 coarse eolian deposits resulted from wind erosion of the highlands in the adjacent west central ordos and the coarse fluvio lacustrine deposits originated chiefly from water erosion of the underlying eolian deposits in the dishaogouwan profile 2 fine particles of eolian deposits with absolute nd 0 values of 1 originated completely from the highland erosion in west central ordos and the fining of in situ coarse particles but the fine particles of the eolian deposits with absolute nd 0 values of 1 have more complex sources 3 fine fluvio lacustrine deposits were fed from the central loess plateau by water for the chengchuan and middle lower salawusu formations but for the upper salawusu formation they were significantly fed from the east central ordos desert by wind according to the source identification of the dishaogouwan profile the wind systems have been re established over the ordos and surrounding areas in the past 200 ka 1 the northwesterly was the dominant wind for eolian deposits in the dishaogouwan profile and the northeasterly simultaneously affected fine eolian deposits in certain periods the middle part of mis 6 and the lower part of mis 4 2 the summer monsoon was a predominant wind in periods during which most of the fluvio lacustrine deposits developed in the salawusu river valley but was thoroughly displaced by the cold dry northeasterly wind during the transition between mis 5 and 4 this study is helpful for further understanding the evolution of the desert loess transition and the related climate change

rare earth element geochemistry and nd isotope composition of stream sediments south han river drainage basin korea abstract chemical analyses of parent rock soil and stream sediments were done to determine to what extent the river sediments retain the geochemical signature of the parent rocks the study area consists mainly of mesozoic biotite granite and precambrian biotite gneiss located in the central korean peninsula the drainage system consists of tributaries of the south han river such as bokhacheon shinduncheon and yanghwacheon stream sediments were collected every march during 2004 2006 the sediments collected were divided into coarse gravel to sand size and fine silt to clay size more than 90 is coarse sediment the major element composition of the coarse and fine sediments are not identical to the weathering trend of granite however molar proportions of al2o3 cao na2o and k2o in the sediments show that they were derived from granitoids rather than from biotite gneiss the total fe2o3 cao mgo na2o and mno contents and ree concentrations of the fine sediments are higher than those of the coarse sediments in a weathering profile from the granite and gneiss area there was no change of ree distribution pattern from the fresh rock to soil compared to biotite granite normalized ree pattern for the sediment both coarse and fine sediments have relatively flattened ree patterns and all the coarse sediment have positive eu anomalies whereas in the fine sediments negative eu anomalies prevail nd isotopic composition of the sediments is similar to that of the biotite granite rather than the biotite gneiss stream sediments in the icheon area were derived from the granite nd isotope geochemistry as well as ree geochemistry is useful tool for tracing the provenance of the river sediments

rare earth elements in the surface sediments of the yarlung tsangbo upper brahmaputra river sediments southern tibetan plateau abstract the yarlung tsangbo yt is the tibetan portion of the brahmaputra river it transports a large amount of sediment annually to the indo gangetic plain and thus contributes significantly to the quaternary evolution of the plain eighteen surface sediment samples were collected from the yt and the compositions of rare earth elements rees were analyzed for the bulk sediments

gold mineralization in the paleozoic appalachian orogen constraints from geologic u pb and stable isotope studies of the hammer down prospect newfoundland the hammer down gold prospect occurs in an accretionary tectonic setting in the paleozoic appalachian orogen it has many geologic and geochemical features in common with other shear hosted mesothermal gold deposits the gold prospect is located about 25 km to the east of an exposed continental oceanic suture zone and is near a major fault the green bay fault of regional extent the main mineralized zones consist of structurally controlled quartz veins with abundant pyrite chalcopyrite sphalerite and carbonate hosted by volcanic and sedimentary rocks of the ordovician catchers pond group gold bearing veins postdate a regional subgreenschist metamorphism and an early phase of deformation mineralization occurred synchronously with a locally intense s 2 fabric within narrow brittle ductile high strain zones in and adjacent to early silurian felsic porphyry dikes carbonate and chlorite alteration is widespread and in part predates the mineralization however there is increasing chloritization near the gold bearing zones and the mineralized veins contain abundant carbonate strong sericite pyrite rutile hydrothermal alteration is restricted to narrow zones adjacent to veins isotopic compositions of quartz delta 18 o 11 4 or 0 7 and carbonate delta 13 c 6 2 or 0 7 from gold bearing veins at hammer down are typical of shear hosted mesothermal gold deposits of archean and younger age oxygen isotope thermometry using quartz chlorite and muscovite yields temperatures of vein formation between 245 degrees and 320 degrees c the ore forming fluids have calculated delta 18 o and delta d values between 1 1 and 5 8 and 36 and 54 per mil respectively and are interpreted to be of mixed origin dominantly from a metamorphic reservoir with a small component of low 18 o meteoric water in the hammer down area felsic tuff in the host arc related sequence the catchers pond group has an igneous u pb zircon age of 480 super 4 sub 3 ma this allochthonous sequence is intruded by felsic dikes which are correlative with granodiorite of the burlington intrusive suite a major regional unit of the eastern baie verte

uranium and rare earth elements in co2 rich waters from vals les bains france abstract waters from springs at vals les bains result from the mixing of a co2 rich highly mineralized water with dilute shallow subsurface water total content of dissolved species vary from 5 mmol 1 to 100 mmol 1 for many elements mixing of these waters is non linear non conservative and further water rock reactions take place the ph is controlled by co2 outgassing redox conditions are controlled by both the iron hydroxide siderite buffer and the introduction of oxygen with shallow subsurface waters among the major elements concentrations of ca mg mn fe are related to mixing co2 outgassing and carbonate precipitation uranium shows a complex behaviour controlled by carbonate complexing redox conditions mixing of waters and leaching from the rocks the 234 u 238 u activity ratio is near secular equilibrium in the more dilute waters dissolved rare earth element ree patterns are almost flat with a slight negative eu anomaly in the concentrated waters heavy rare earth elements gd yb hree are strongly enriched relative to light rare earth elements ce eu lree we relate the enrichment in hree to water chemistry and to complexing with carbonate species

an interpretation of the alteration assemblages at sulphur springs valles caldera new mexico sulphur springs located near the western edge of the valles caldera north central new mexico is the only vapor dominated surface manifestation of any significance found in the valles the percolating acid sulfate waters and fumarolic gases have leached and oxidized the country rock near the hot springs to a bleached wasteland the near surface mineral assemblages at 90 c are restricted to one and two phases occurring in contact with a variety of solutions and gases the conditions of local equilibrium at 90 g are approximately halotrichite alunogen log fo2 45 log fs2 12 ph 0 3 szomolnokite pyrite log fo2 46 log fs2 16 ph 0 8 alunite log fo2 50 log fs2 10 ph 1 2 kaolinite sulphur log fo2 53 log fs2 10 ph 1 2 log ak 0 0012 m log asio2 0 0033 m and pyrite log fo2 60 log fs2 19 ph 4 3 this study has demonstrated that local equilibrium is closely approached even under the low temperature and pressure conditions found near the surface

the temporal distribution of evolutionary and migrational events in pelagic systems episodic or continuous the evolutionary and ecological dynamics of origination immigration and extinction emigration patterns of two pelagic groups planktic foraminifera and calcareous nannofossils within two paleoceanographic regions over the past 40 m y are compared with predictions of the turnover pulse hypothesis that speciation extinction and migration are pulsed or episodic and synchronous with change in the physical environment the specific species dynamics examined of the records of 918 species include expected time to extinction origination immigration as a function of geologic time extinction emigration as a function of biologic age and geologic time and the interactive effects of time of origination immigration and geologic time on the probability of extinction emigration overall there is little empirical support for times of evolutionary quiescence or ecological stability rather the dominant pattern is one of continuous rather than episodic evolutionary and ecological activity there is little evidence of synchroneity of response among cohorts or with major change in the physical environment coeval species experience the same time periods differently in terms of the probability of speciation immigration and extinction emigration the empirical patterns support the hypothesis that at this taxonomic and temporal resolution the controlling factors on evolutionary and ecological turnover are more omnipresent than pulsed or episodic

potassium distribution and metasomatism in pelites and schists how and when relation to postdepositional events a large global database for over 9000 archean to holocene pelites in numerous basins has been developed to evaluate diagenetically unaltered and altered compositions the mineralogy and geochemistry of quaternary muds and ancient mudstones provide first order controls on diagenetic potassium metasomatism in pelites clay mineralogy of quaternary muds is dominated by smectite and kaolinite with minor detrital mica and illite thus k2o is 4 k al is 0 25 and k rb is 220 in most quaternary muds with diagenetic alteration of clays to illite smectite and illite k2o content increases to 4 8 and k al rises to 0 2 0 5 or more in extreme potassium metasomatism authigenic k feldspar develops sources of potassium are internal to shale sandstone units wherein detrital k feldspar is dissolved during diagenesis providing k for clay illitization in closed system isochemical alteration as in some gulf coast and north sea basin cases potassium in amounts greater than that available from closed system alteration is provided from extraformational circulating brines in open system diagenesis k rb with diagenesis varies according to whether the metasomatizing fluid was relatively poor in rb seawater derived brines or richer in rb as in many hydrothermal waters diagenetic fluids may originate from seawater or meteoric water enriched in cations by water rock interactions along their subsurface migration paths and or by dissolution of evaporites potassium metasomatizing fluids penetrate low permeability pelites through faults fractures and microfractures and by diffusion in the mineral matrix typically k metasomatism possibly with pb zn cu ba and f mineralization occurs long after sediment deposition and burial at temperatures of 50 to 150 c related to tectonic activity and fluid movement different modes of metasomatism are recognized and correlated with geological setting in the passive margin gulf coast tertiary basin open system k metasomatism where present is limited to areas adjacent to steeply dipping growth faults which act as conduits for episodic pulses of altering fluids migrated upward from deeper basin sources in contrast widespread pervasive open system k metasomatism produced by continuous long term gravity advective and diffusive flow of brine from the late paleozoic appalachian ouachita wichita mountains highland to altered earlier paleozoic shales plus sandstones bentonites and carbonates in the illinois and anadarko ardmore foreland basins this mode of k alteration following major mountain building events is characteristic of many precambrian and paleozoic collision orogens and associated foreland basins another mode is in rift basins with no external drainage in which indigenous waters are evaporated to brines these brines cause albitization of k feldspar to yield potassium for illitization of detrital clays

a detrital model for the origin of gold and sulfides in the witwatersrand basin based on re os isotopes abstract the re os systematics of gold and sulfides from the witwatersrand basin were utilized to determine whether the gold is detrital or was introduced by hydrothermal solutions from outside the basin gold from a gravity concentrate from the western areas gold plant and gold from the vaal reef have very high os concentrations of approximately 73 to 10000 ppb and 3 to 32 ppb re resulting in 187re 188os ratios of 0 010 to 0 185 the gold has subchondritic 187os 188os ratios between 0 1056 to 0 1099 and an average value of 0 1067 rhenium depletion ages trd range from 3 5 ga to 2 9 ga with a median age of 3 3 ga pyrite from the vaal reef have os concentrations ranging from 0 26 to 0 68 ppb re concentrations of 1 7 to 2 8 ppb and187re 188os ratios of approximately 14 to 87 the pyrite samples have measured 187os 188os ratios of 0 84 to 4 7 and define an isochron with an age of 2 99 0 11 ga mswd 0 77 the os isotopic data from the direct measurement of gold preclude introduction of gold to the witwatersrand basin from crustally derived metamorphic or hydrothermal fluids between 2 7 to 2 0 ga the unradiogenic 187os 188os ratios old trd ages of the western areas and vaal reef gold samples as well as the contemporaneously old age of the vaal reef pyrite are consistent with detrital deposition of gold during the formation of the witswatersrand basin the os data will allow for minor hydrothermal remobilization and or overprinting of hydrothermal gold on preexisting detrital gold grains but does not support the introduction of gold solely by hydrothermal fluids

stratigraphic relations and lithologic variations in the jemez volcanic field new mexico over 100 radiometric dates and recent detailed geologic mapping allow some refinements of the stratigraphic relations of major units and generalization of temporal lithologic variations in the jemez volcanic field volcanism had begun in the area by about 16 5 ma with episodic eruptions of alkaline basalts by 13 ma alkaline volcanism had been replaced with eruptions of more voluminous olivine tholeiite high silica rhyolite derived from melts of lower crust also was erupting by about 13 ma basalt and high silica rhyolite continued to be erupted until about 7 and 6 ma respectively but effusions of dominantly andesitic differentiates of basalt that began as early as about 12 ma volumetrically overshadowed all other eruptive products between 10 and 7 ma from 7 to 3 ma the dominant erupted lithology was dacite which appears to have been generated by mixing of magmas whose compositions are approximated by earlier andesites and high silica rhyolites less than 4 3 ma volcanism was dominated by eruption of rhyolitic tuffs field relations geochemistry and dates specifically indicate the following with regards to stratigraphie relations 1 distinctions among basalt of chamisa mesa paliza canyon formation basalts and lobato basalt for other than geographic reasons are artificial basaltic volcanism was continuous in volcanic field from 13 to 7 ma 2 canovas canyon and bearhead rhyolites form a continuum of high silica rhyolite volcanism from 13 to 6 ma 3 hypabyssal and volcanic rocks of the cochiti mining district probably represent the exhumed interior of a keres group volcano s 4 temporal overlaps exist among the major stratigraphie groups which may imply some genetic relations and 5 the tewa group formation cerro rubio quartz latite may more appropriately be considered part of the tschicoma formation of the polvadera group preliminary analysis of hydrothermal alteration in the context of the volcanic stratigraphy suggests at least three distinct hydrothermal events have occurred in the volcanic field s history

rare earth geochemistry in sediments of the upper manso river basin rio negro argentina abstract the abundance distribution and fractionation of rare earth elements was studied in solid material transported by the upper manso river and in the sediments deposited in lake mascardi argentina the pristine condition of the area offers an ideal environment for assessing geochemical processes and the seasonal cycles to which the basin is subjected permit us to study seasonal variations that are mainly influenced by glacial pulses the most remarkable characteristics observed in the ree normalized patterns are a strong hree enrichment and a positive eu anomaly these normalized patterns are atypical as compared to those considered representative of the world s major rivers and are caused by drainage basin geology due to the dissected topography and the small size of the basin intense mixing phenomena are not favoured and the weathering reactions are inhibited by the fast flowing river these physicochemical conditions and near neutral ph values have an important influence on the ree patterns of the sediments which mainly originated by glacial erosion that are transported by the river the feldspars and their secondary products which are both enriched in eu might be the cause of the eu anomaly hree enrichment which is mainly associated with high ph systems or with the presence of accessory phases shows a clear dependence on source rocks the calculated la yb n ratios oscillate between 0 5 and 0 6 contrasting with the values reported in the literature as average values for suspended load material nevertheless these values are consistent with the dependence of la yb n values on the age of drainage area rocks as was observed by goldstein and jacobsen 3 seasonal variations are not manifested in ree concentrations and additional elemental determinations showed coherent behaviour during weathering for all elements except sr and ba which exhibited selective elemental mobilization during periods of minimum discharge

the remarkable re os chronometer in molybdenite how and why it works the re os rhenium osmium chronometer applied to molybdenite mos2 is now demonstrated to be remarkably robust surviving intense deformation and high grade thermal metamorphism successful dating of molybdenite is dependent on proper preparation of the mineral separate and analysis of a critical quantity of molybdenite unique to each sample such that recognized spatial decoupling of 187re parent and 187os daughter within individual molybdenite crystals is overcome highly precise accurate and reproducible age results are derived through isotope dilution and negative thermal ion mass spectrometry id ntims spatial decoupling of parent daughter precludes use of the laser ablation icp ms microanalytical technique for re os dating of molybdenite the use of a reference or control sample is necessary to establish laboratory credibility and for interlaboratory comparisons the rb sr k ar and 40ar 39ar chronometers are susceptible to chemical and thermal disturbance particularly in terranes that have experienced subsequent episodes of hydrothermal magmatic activity and therefore should not be used as a basis for establishing accuracy in re os dating of molybdenite as has been done in the past re os ages for molybdenite are almost always in agreement with observed geological relationships and when available with zircon and titanite u pb ages for terranes experiencing multiple episodes of metamorphism and deformation molybdenite is not complicated by overgrowths as is common for some minerals used in u pb dating e g zircon monazite xenotime nor are re and os mobilized beyond the margins of individual crystals during solid state recrystallization moreover inheritance of older molybdenite cores incorporation of common os and radiogenic os loss are exceedingly rare whereas inheritance common pb and pb loss are common complications in u pb dating techniques therefore molybdenite ages may serve as point in time markers for age comparisons

ree distribution in the clay fraction of pelites from the southern apennines italy abstract in order to evaluate whether clay minerals or accessory phases control the ree pattern of the only illite is correlated with ree while a smectite rich sample is characterized by the lowest content in ree strong correlations exist between ree and tio2 nb zr and a less significant one with sr no correlations exist between these elements and y r mode factor analysis indicated that three factors account for 87 of the total variance the first factor var 43 2 seems to express mainly the tendency of some resistate minerals to concentrate ree in the fine fraction the second factor var 30 0 may be related to the effect of circulating fluids responsible for dickite genesis the third factor may be linked to the weathering of micaceous phases the ree do not have a significant weight in the second and third factors resistate minerals appear dominant in controlling at least the lree and nb it is proposed that in the studied samples illite likely conveyed ree via the included minerals

arkose subarkose quartz sand and associated muds derived from felsic plutonic rocks in glacial to tropical humid climates abstract in the range of climates from high latitude glacial to equatorial tropical the mineral and chemical compositions of over 600 modern nonmarine first cycle sands and muds produced from felsic crystalline basement provenance in various tectonic settings were studied under glacial conditions sediments are developed by mostly mechanical weathering and thus are mineralogically and chemically similar to their source rocks humid tropical climates yield quartz rich sands kaolinite rich muds along with si mg ca na and k in solution between these extremes a wide range of detrital sediment compositions are developed in arid to wet climates in arid climate and semi arid climate sands feldspar is commonly more abundant than quartz and plagioclase k feldspar except in the cases of granite source rocks the muds are feldspathic with smectite dominant in the clays with increasing temperature and moisture in temperate to subtropical climates mafic silicates and feldspars are destroyed so that the sands range from arkoses with plagioclase as the major feldspar to subarkoses with dominant k feldspar through this range of climate muds become more kaolinitic and thus more aluminous with increasingly severe weathering typically feldspathic sands are associated with feldspathic muds with decreasing feldspar in sands there is less feldspar in muds with increasingly intense chemical weathering rare earth elements ree are more fractionated into muds typically sands contain 150 ppm ree with much of the ree in heavy minerals abundance differences are greatest between humid tropical sands and muds in many samples the ree are mostly in monazite allanite sphene and apatite more intensely weathered samples contain more xenotime and zircon evidenced by yb enrichment

ree and other trace elements in a granitic weathering profile from serre southern italy abstract ree v cr ni rb sr y zr and nb behaviour in a granitic weathering profile in southern italy is studied in the saprolites of the considered profile depletion of v cr ni rb sr zr and nb is observed this is quite remarkable for sr and cr whereas ree and y are enriched in the more altered portion of the profile and especially in its m fraction such enrichment is associated with the lree hree fractionation and the positive ce anomaly the former results from an increased solubility of hree in a non acid environment as well as from the removal of the hree rich phases from the residual component the latter is related to the redox chemistry of ce which as ceo 2 is less soluble than the other ree no analogy is observed between the behaviour of ce and fe mn and cr saprolites also exhibit a negative eu anomaly which is mostly inherited from the parental material finally the influence of accessory minerals in the ree distribution of weathering products and in sediments calls for a careful evaluation of preferential settling phenomena of heavy minerals during transportation and deposition processes this is especially true in the parent material sediment relationships

quantitative biostratigraphy of the taranaki basin new zealand a deterministic and probabilistic approach a quantitative biostratigraphic analysis of the paleocene to lower miocene of the taranaki basin has enabled high precision in correlation zonation and assessment of depositional history biostratigraphic range end events based on 493 taxa in cuttings samples from eight wells representing foraminifera nannofossils dinoflagellates and miospores were culled to 87 range top events that were then analyzed by deterministic constrained optimization conop and probabilistic ranking and scaling rasc techniques all except 16 of the events are found to have relatively good biostratigraphic reliability the rasc probable sequence and probabilistic zonation give the best estimate of the sequence of events and zones to be encountered in any new well in the basin and a precise biostratigraphic scale for future exploration the conop composite section which matches well with that derived by conventional graphic correlation graphcor is readily related to previous zonations based on maximum ranges of taxa but gives an order of magnitude greater precision conop provides a precise correlation framework and reveals marked variation in thickness of stages across the basin when the composite section is calibrated against the time scale basinwide changes in depositional rate are revealed the upper eocene and oligocene mark an interval of slow deposition whereas the miocene marks a sharp increase in deposition the time calibrated composite section enables unconformities and changes in depositional rate found in individual wells to be precisely estimated many new unconformities are indicated particularly in the paleocene and eocene

mobility of rare earth elements during weathering of till in northern sweden abstract continuous volume controlled sampling from the surface down to a depth of 130 cm was conducted at two stations on weathered till typic haplocryods all the samples were analysed for major and trace elements including the rare earth elements ree eight thousand seven hundred years of weathering since the glacial ice left the area has resulted in a strong depletion of ree in the e horizon this loss decreases as atomic number increases so that 80 85 of the la and 54 60 of the yb have been lost europium has been lost to a greater degree than have the neighbouring elements possible explanations for the release of ree are weathering of common silicates such as hornblende and epidote and plagioclase in the case of eu weathering of apatite weathering of rare but ree rich minerals such as allanite and monazite and release of ree adsorbed on clay minerals further studies on various size fractions and minerals are needed to quantify the importance of the various possible mechanisms of ree release the release of ree continues within and below the bs1 horizon but the results from one station show that light ree can be enriched in the bs1 horizon this secondary enrichment could be caused by adsorption on secondary oxy hydroxides on clay minerals or on organic material however the net result of the weathering is that all ree have been released to the groundwater

two stage gold mineralization of the axi epithermal au deposit western tianshan nw china evidence from re os dating s isotope and trace elements of pyrite the axi gold deposit is one of the largest epithermal deposits in northwestern china and is characterized by multistage generations of pyrite associated with gold mineralization genetic models for superjacent epithermal au and porphyry cu systems involve either contemporaneous or episodic mineralization implying different metal sources and ore forming events nine pyrite separates from disseminated ores associated with pyrite sericite quartz alteration in the axi deposit yield a re os isochron age of 350 10 ma mswd 5 1 initial 187os 188os ios 0 20 0 11 this age likely reflects a mixed contribution of two subtypes of disseminated pyrite py1 based on zoned pyrite crystals the isochron age of 353 6 ma mswd 1 6 ios 0 107 0 021 n 6 excluding samples with pyrite cores overlaps previous ages for andesite from the dahalajunshan formation ca 356 ma indicating that the early mineralization event occurred shortly after the formation of host rocks ca 353 ma pyrite from disseminated ores shows little variation of sulfur isotopic compositions 2 9 to 4 0 and has high cu co ni and v contents which favors a magmatic hydrothermal origin pyrite grains from gray quartz veins yield a younger re os isochron age of 332 8 ma mswd 0 22 n 4 vein hosted pyrite shows characteristics of a mantle derived magma source ios 0 171 0 024 34s 0 10 3 10 which result from the intrusion driven convective hydrothermal circulation accompanying fluid exsolution and metal remobilization from basement and wallrocks our data demonstrate that the axi gold deposit was formed during two temporally separated hydrothermal events this model of ore formation may apply to other epithermal porphyry deposits within the axi tawuerbieke district disseminated au and porphyry style au cu mineralization occurred shortly after magmatic activity 356 353 ma whereas epithermal style au mineralization occurred at ca 332 ma

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

a re os isotope study of sedimentary rocks and copper gold ores from the ertsberg district west papua indonesia abstract the ores of the ertsberg district consist of both porphyry stockwork and contact controlled mineralization related to the grasberg and ertsberg intrusion centers high grade copper mineralization with gold occurs in skarns on the periphery of each of the intrusion centers the periphery mineralization includes the kucing liar skarn related ores the massive sulfide lenses on the borders of the grasberg intrusive complex and the giant skarn bodies of the deep and intermediate ore zones together with the ores of the dom complex on the margin of the ertsberg diorite the ertsberg orebody the basis of discovery of the district is a copper gold roof pendant of sedimentary strata in the diorite in order to clarify genetic and geochronologic links between the peripheral sediment hosted ore bodies and the intrusion hosted ore bodies re os isotopes of the ores and subjacent precambrian and phanerozoic crust were analyzed re os geochronology of molybdenites was used to resolve the age relationships of the ore bodies the grasberg and kucing liar molybdenites have older molybdenite mineralization ages of 2 88 0 02 ma and 3 01 0 02 ma respectively whereas the ertsberg molybdenite has a younger age of 2 54 0 02 ma these data agree with ar chronologies of the alteration associated with mineralization pollard and taylor 2000 pollard p j taylor r 2000 geochronology of intrusive rocks and cu au mineralization in the ertsberg district in proceedings of freeport institut teknologi bandung itb geological symposium bandung java pp 17 19 and also indicate that the grasberg and kucing liar molybdenites are closely similar in age and older than the ertsberg intrusive system re os data from pyrite chalcopyrite magnetite gold and the surrounding sedimentary rocks from the district define a mixing relationship between samples from the initial stockwork mineralization and peripheral ores of each intrusion center sulfide and oxide minerals from primary stockwork mineralization are isotopically homogeneous and define trends on isochron diagrams with distinct os initial ratios whereas sulfides and oxides taken from peripheral ores are isotopically heterogeneous and define trends on mixing diagrams one possible end member for the mixing is sedimentary rock surrounding the porphyries the measured os ratios of the sedimentary rocks range from 0 52 to 2 21 and overlap the os initial ratios of the sulfides and oxides sampled from both stockwork and contact mineralization the data suggest a model in which the continental crust supplied some of the os and by inference other metals during magma genesis in the lower crust and the remainder came from sedimentary rocks near the intrusion centers

re os dating of low level highly radiogenic llhr sulfides the harnas gold deposit southwest sweden records continental scale tectonic events to obtain geologically meaningful and precise results on low level sulfides that are highly radiogenic blank corrections that account for the extreme difference in the os isotope composition of sample and blank are necessary and the resulting data is best plotted in 187 re 187 os space much like the approach used for molybdenites we here introduce the acronym llhr as a means of characterizing low level and highly radiogenic sulfides use of the traditional 187 re 188 os vs 187 os 188 os plot for llhr sulfides leads to large analytical uncertainties and highly correlated errors as 188 os is poorly determined and can generally be accounted for by the blank we now recognize that llhr sulfides such as those encountered at the harnas au deposit are a common occurrence and characteristic of many crustally affiliated ore systems the harnas au deposit in southwest sweden is located in the mjosa vanern mineral belt that transects from northwest to southeast the prominent geologic fabric of the sveconorwegian province including the mylonite zone the deposit is hosted in a strongly sheared and locally brecciated sulfide bearing quartz vein that crosscuts the foliation of orthogneisses belonging to the 1600 maa mal granitoid suite a 187 re 187 os isochron of 973 34 ma 2 for samples of pyrite and chalcopyrite from outcrops of the harnas alma and silvergruvan veins was obtained the harnas and subsidiary alma veins are au bearing whereas the silvergruvan 2 5 km to the southeast is not of the au bearing type four replicate analyses of an additional pyrite sample from the harnas vein yield a model age of 616 40 ma 95 c l in all samples re and 187 os concentrations are extremely low 0 35 to 7 1 and 0 005 to 0 074 ppb respectively and total common os 0 002 0 028 ppb is less than half the calculated radiogenic 187 os two samples of galena from the harnas vein yielded blank level re and os neither the 973 nor 616 ma time of mineralization is related to development of the mylonite zone at 920 ma or intrusion of the anorogenic bohus blomskog granites at 920 to 900 ma previously proposed sources for generating mjosa vanern mineral belt ore fluids an age of 973 ma for harnas alma silvergruvan suggests that sulfide deposition was associated with the waning stages 0 97 0 90 ga of the sveconorwegian grenvillian orogeny 1 15 0 90 ga postdating metamorphism and deformation that produced a regionally overthickened crust in the northern part of the sveconorwegian province the vein systems for these and numerous other small deposits in the mjosa vanern mineral belt could have resulted from regional exhumation in the late sveconorwegian with associated extension and the development of fracture systems at cooler middle to upper crustal levels in the southern part of the sveconorwegian province dominated by granulitic facies rocks no mineralization is present perhaps due only to increased exhumation and erosion that has exposed deeper crustal levels the late sveconorwegian age 973 ma records the main period of sulfide deposition for the harnas alma silvergruvan vein systems and indicates the robustness of the chronometer within tectonically complex terranes the late neoproterozoic age 616 ma records a later time of pyrite deposition probably associated with shearing and reopening of the harnas vein system because the au mineralization at harnas has been described as associated with shearing and occurring in fracture fillings in early pyrite we suggest that part or all of the au mineralization could have been introduced at 616 ma during reactivation of the vein system the 616 ma age for pyrite suggests a previously unrecognized and much younger mineralizing episode in the harnas region most likely reflecting continental scale extension and the late neoproterozoic opening of the iapetus ocean

re os isotope and pge constraints on the timing and origin of gold mineralisation in the witwatersrand basin abstract analyses of the re os isotope system and pge abundances have been used to investigate the timing and origin of mineralisation in the vaal reefs section of the witwatersrand basin the world s largest gold deposit consistent interelement pge fractionation in both organic and sulphide phases intimately associated with gold mineralisation suggests that the re os isotope system was fractionated during gold mobilisation the re os isotope data on organic separates intimately associated with the gold in this part of the basin indicate open system behaviour until 2 26 0 19 ga 2 of the order of 450 myr younger than the minimum age of sedimentation the overlying ventersdorp volcanics preserve a re os isochron age of 2 43 0 21 ga 250 ma younger than their u pb zircon emplacement age these data indicate substantial post sedimentary noble metal mobility within portions of the witwatersrand basin re os model age calculations on os rich fractions suggest that noble metals were derived from a 3 0 3 1 ga terrain of granite greenstone affinities significantly younger than the barberton greenstone belt these data support a hybrid model involving post depositional mobilisation of ancient probably detrital noble metals for the origin of mineralisation in this part of the witwatersrand basin such a model is applicable to other areas of gold mineralisation in the basin that display similar textural characteristics and geochemistry

beyond whole rock geochemistry of shales the importance of assessing mineralogic controls for revealing tectonic discriminants of multiple sediment sources for the ouachita mountain flysch deposits the origin of the ouachita mountains has been the focus of significant debate for decades considerable confusion also exists concerning the provenance of the carboniferous flysch of the ouachitas trace element geochemistry of shales from the stanley group delineates the provenance of the sediments and provides clues to the plate tectonic evolution of the southern continental margin during mississippian time th sc and cr th ratios indicate a cratonic source for the majority of the stanley group sedimentary rocks however in several samples low th sc ratios and high cr th ratios suggest a contribution from a mafic source using element ratio diagrams all of the samples plot along a curve consistent with a two component mixing model consisting of a dominant felsic and a subordinate mafic source the heavy mineral fraction of these shales sequester many of the trace elements used in whole rock studies monazite is ubiquitous in trace amounts and is the probable site for much of the rare earth elements in the whole rock the occurrence of monazite almost exclusively in sialic igneous rocks implies that sm nd isotopic signatures are not sensitive to sediment input from more mafic sources in some stanley shale samples chromite and mn oxides were identified and positively identify an oceanic crustal component as a source of stanley group sediment the results of this study emphasize the importance of determining the mineralogic sites of trace elements and realization of specific mineralogic contributions from mafic or sialic tectonic provenances

lithostratigraphy of the state 2 14 borehole salton sea scientific drilling project sedimentary rocks from the california state 2 14 research borehole of the salton sea scientific drilling project located in the imperial valley of southern california were deposited in the continental basin of the salton trough lacustrine shale and siltstone are the dominant lithologies sandstones were deposited in lake margin meander channel fill and lacustrine delta environments framework modal clast compositions of the sandstones indicate a dominant colorado river provenance rare pebbly mudstones were deposited as storm induced debris flows primary depositional structures in the sediments are commonly disrupted by seismic disturbances nonmarine gastropods and ostrocods are relatively uncommon and occurrences of stratabound sulfides suggest periods of brackish water conditions bedded anhydrite and centimeter scale mudcracks record intervals of dessication the state 2 14 sedimentary rocks are interpreted as the basinward facies of the borrego and brawley formations which range from pliocene to pleistocene in age

the timing of epigenetic gold mineralization on the baie verte peninsula newfoundland canada new evidence from re os pyrite geochronology the absolute timing of epigenetic mineralization including most types of gold deposits is difficult to resolve due to the absence of suitable minerals in veins and replacement zones however gold is commonly closely associated with pyrite and arsenopyrite which may be amenable to re os geochronology providing sufficient re and os are present within them this short paper outlines the use of this method to date two gold deposits in newfoundland using pyrite although the os contents of the pyrites are extremely low 0 1 ppb the os is almost exclusively radiogenic 187os and data are amenable to model age calculations as used in re os molybdenite dating the pyrites from these deposits correspond to low level highly radiogenic sulphides as defined by other studies the stog er tight and pine cove gold deposits yield mean re os model ages of 411 7 ma n 4 and 420 7 ma n 5 respectively which agree with isochron regression of 187os against 187re the re os age for stog er tight is within uncertainty of a previous u pb age from hydrothermal zircon 420 5 ma in spatially related alteration a latest silurian earliest devonian age for the mineralization is consistent with indirect age constraints from some other gold deposits in central newfoundland and suggests a broad temporal link to the mid silurian salinic orogeny however the gold mineralization appears to be younger than most plutonic activity associated with this event the results illustrate the potential value of re os pyrite geochronology in understanding the temporal framework of epigenetic mineralization especially if future improvements in analytical precision and reductions in procedural blanks allow wider application to material with similarly low re and os concentrations

rare earth element systematics in hydrothermal fluids abstract rare earth element concentrations have been measured in hydrothermal solutions from geothermal fields in italy dominica valles caldera salton sea and the mid atlantic ridge the measured abundances show that hydrothermal activity is not expected to affect the ree balance of either continental or oceanic rocks the ree enrichment of the solutions increases when the ph decreases high temperature solutions 230 c percolating through different rock types may show similar ree patterns

sources of stream sediments in the granulite terrain of the walawe ganga basin sri lanka indicated by rare earth element geochemistry abstract thirty eight samples of stream sediments draining high grade metamorphic rocks in the walawe ganga river basin sri lanka were analysed for their ree contents together with samples of metamorphic suites from the source region the metamorphic rocks are enriched in light ree lree compared to heavy ree hree and are characterised by high la lu ratios and negative eu anomalies the chondrite normalised patterns for these granulite grade rocks are similar to that of the average post archaean upper crust but they are slightly enriched with la and ce the ree contents of the n sm n and lower la n lu n ratios relative to other fractions the lower la n lu n ratio is related to the depletion of heavy minerals in the

chemical evolution of mid ocean ridge hot springs abstract chemical analyses yielding elemental concentrations of major and minor elements of four hot springs on the east pacific rise at 21 n and 10 hot springs from the southern trough of the guaymas basin gulf of california provide a basis for thermodynamic modeling of conductive cooling of the hydrothermal endmembers mixing of the hydrothermal endmember with seawater and reaction of an epr type fluid with sediment of bulk chemical composition corresponding to unaltered sediment from dsdp hole 477 in the guaymas basin results of the calculations indicate that conductive cooling of endmember fluids within closed chimneys and conduits accounts for the solution composition of one vent on the east pacific rise and several vents in guaymas basin mixing of the hydrothermal fluids with seawater yields a prediction of mineral assemblages closely approximating those observed in samples of chimneys from the east pacific rise and drill cores in guaymas basin the hypothesis that guaymas basin hydrothermal fluids result from interaction of an epr type fluid with sediment cover in guaymas basin is supported by calculations which predict an increase in ph to a value similar to guaymas basin fluids an order of magnitude decrease in metal concentrations and an excellent agreement between predicted mineral assemblages as a function of extent of interaction with sediment and observed mineral assemblage distribution with depth

pb sr nd isotopes in surficial materials at the pebble porphyry cu au mo deposit southwestern alaska can the mineralizing fingerprint be detected through cover the cretaceous pebble porphyry cu au mo deposit is covered by tundra and glacigenic sediments pb sr nd measurements were done on sediments and soils to establish baseline conditions prior to the onset of mining operations and contribute to the development of exploration methods for concealed base metal deposits of this type pebble rocks have a moderate range for 206pb 204pb 18 574 to 18 874 207pb 204pb 15 484 to 15 526 and 208pb 204pb 38 053 to 38 266 mineralized granodiorite shows a modest spread in 87sr 86sr 0 704354 0 707621 and 143nd 144nd 0 512639 0 512750 age corrected 89 ma values for the granodiorite yield relatively unradiogenic pb e g 207pb 204pb 15 52 low values of 87sr 86sr and positive values of nd 1 00 4 52 that attest to a major contribution of mantle derived source rocks pond sediments and soils have similar pb isotope signatures and 87sr 86sr and 143nd 144nd values that resemble the mineralized granodiorites glacial events have obscured the recognition of isotope signatures of mineralized rocks in the sediments and soils baseline radiogenic isotope compositions prior to the onset of mining operations reflect natural erosion transport and deposition of heterogeneous till sheets that included debris from barren rocks mineralized granodiorite and sulfides from the pebble deposit and other country rocks that pre and postdate the mineralization events isotopic variations suggest that natural weathering of the deposit is generally reflected in these surficial materials the isotope data provide geochemical constraints to glimpse through the extensive cover and together with other geochemical observations provide a vector to concealed mineralized rocks genetically linked with the pebble deposit

planktic foraminiferal events in early miocene zones n 6 and n 7 at southwest pacific dsdp site 593 relation with climatic changes in oxygen isotope zone milb abstract oxygen isotope data are compared with relative abundances of selected planktic foraminifera through a ca 15 m interval at dsdp site 593 tasman sea southwest pacific 40 s in which there are prominent changes in population sizes as well as several evolutionary events we focus on the relation between faunal and climatic histories the base of early miocene oxygen isotope zone milb uppermost planktic foraminiferal zone n 6 is identified from close sampled 14 kyr isotope records of globigerina woodi and cibicides kullenbergi chronostratigraphic interpolations using the first occurrences of globorotalia praescitula g miozea and praeorbulina curva give an age estimate of ca 18 4 ma cf 18 1 18 3 ma for the base of the zone at dsdp site 608 type level north atlantic 43 n another significant benthic 18o enrichment event informally designated as the base of zone milc is identified 10 m higher in the sequence at ca 17 8 ma populations of globoquadrina dehiscens and globigerinoides trilobus inferred to be near the southern margin of their distributions either reduced considerably or withdrew particularly in the vicinity of zone milc a bioseries linking globorotalia incognita with g zealandica developed following the benthic 18o enrichment spike at the base of zone milb the latter species became extinct at least regionally just above the base of zone milc in contrast the apparently opportunistic globorotalia praescitula increased dramatically in abundance at this time there were also transformations in its architecture leading to the evolutionary appearance of g miozea while planktic foraminifera abundances often do not closely covary with the detailed isotope records and tend to be more stable through time the near coincidence of evolutionary and biogeographic events with isotopic events suggests at least indirect adaptive responses to climatic changes early miocene middle latitude planktic foraminiferal evolution biogeography and biostratigraphy may be intimately connected with climatic history

apatite liquid partition coefficients for the rare earth elements and strontium abstract sixteen sets of apatite liquid partition coefficients dap liq for the rare earth elements ree la sm dy lu and six values for sr were experimentally determined in natural systems ranging from basanite to granite the apatite melt glass assemblages were obtained from starting glasses artificially enriched in ree sr and fluorapatite components these were run under dry and hydrous conditions of 7 5 20 kbar and 950 1120 c in a solid media piston cylinder apparatus an sem equipped electron microprobe was used for subsequent measurement of ree and sr concentrations in coexisting apatites and quenched glasses the resulting partition coefficient patterns resemble previously determined apatite phenocryst groundmass concentration ratios in the following respects 1 the rare earth patterns are uniformly concave downward i e the middle ree are more compatible in apatite than the light and heavy ree 2 dreeap liq is much higher for silicic melts than for basic ones and 3 strontium and therefore eu2 is less concentrated by apatite than are the trivalent ree the effects of both temperature and melt composition on dreeap liq are systematic and pronounced at 950 c for example a change in melt sio2 content from 50 to 68 wt causes the average ree partition coefficient to increase from 7 to 30 a 130 c increase in temperature on the other hand results in a two fold decrease in dreeap liq partitioning of sr is insenstitive to changes in melt composition and temperature and neither the sr nor the ree partition coefficients appear to be affected by variations in pressure or h2o content of the melt the experimentally determined partition coefficients can be used not only in trace element modelling but also to distinguish apatite phenocrysts from xenocrysts in rocks reported apatite megacryst host basalt ree concentration ratios 12 for example are considerably higher than the equilibrium partition coefficients which suggest that in this particular case the apatite is actually xenocrystic a reversal experiment incorporated in our study yielded diffusion profiles of ree in apatite from which we extracted a ree ca interdiffusion coefficient of 2 4 10 14 cm2 s at 1120 c extrapolated downward to crustal temperatures this low value suggests that complete ree equilibrium between felsic partial melts and residual apatite is rarely established

re os molybdenite pyrite and chalcopyrite geochronology lupa goldfield southwestern tanzania tracing metallogenic time scales at midcrustal shear zones hosting orogenic au deposits a detailed re os molybdenite pyrite and chalcopyrite geochronology at five shear hosted au occurrences kenge mbenge porcupine konokono and dubwana in the lupa goldfield southwestern tanzania is reported in this paper au occurrences within the lupa goldfield share many geologic similarities with the orogenic au deposit type and are situated within a paleoproterozoic magmatic arc that intruded the archean tanzanian cratonic margin pyrite chalcopyrite molybdenite bearing fault fill veins and mylonitic shear zones crosscut granitic host rocks and are associated with the highest au grades re os sulfide ages are deemed a suitable proxy to constrain the timing of au based on the occurrence of au bearing minerals as inclusions within pyrite and chalcopyrite whereas au bearing minerals filling pyrite fractures may represent a younger and undated metallogenic event molybdenite at kenge occurs as ultrafine disseminations within fault fill veins 1953 6 ma n 3 that possess nominally older weighted average re os ages than molybdenite hosted by stylolite like veins 1937 8 ma n 7 both sample sets are ca 70 m y older than a weighted average re os pyrite age from the mylonitic shear zones at kenge and mbenge 1876 10 ma n 13 which contain fault fill veins and record the timing of mylonitization molybdenite at porcupine occurs as ultrafine disseminations within quartz veins and mylonitized granite samples 1886 6 ma n 4 that are broadly equivalent in age to weighted average re os ages of molybdenite occurring as stylolite like veins 1873 5 ma n 6 and pyrite within oblique extension veins 1894 45 ma n 2 weighted average re os pyrite model ages at konokono 1880 14 ma n 9 and dubwana 1905 25 ma n 2 are also consistent with the ca 1 88 ga event observed at kenge mbenge and porcupine gold occurrences in the lupa goldfield therefore record a protracted hydrothermal history 1 95 1 87 ga comprising at least three temporally distinct hydrothermal events ca 1 95 1 94 and 1 88 ga which are each represented in detail by a complex vein history that occurred at a time scale less than the resolution of the re os method the sampling of broadly contemporaneous sulfides from five shear zones suggest that mylonitic shear zones represented an interconnected network of midcrustal permeable fluid conduits at ca 1 88 ga that permitted the transportation and deposition of gold comparison between re os sulfide and high precision u pb zircon ages for the granitic host rocks provides unequivocal evidence for sulfidation concomitant with magmatism however the range of re os ages argues against an intrusion related deposit model whereby metallogenic fluids are solely derived from an individual intrusion the regional ca 1 88 ga metallogenic event identified as part of this study occurred concurrently with eclogite facies metamorphism during the ubendian orogenic cycle and provides one of earth s earliest temporal links between subduction zone processes and orogenic au deposit formation during the paleoproterozoic

early and middle miocene stable isotopes implications for deepwater circulation and climate the middle miocene 18o increase represents a fundamental change in the ocean atmosphere system which like late pleistocene climates may be related to deepwater circulation patterns there has been some debate concerning the early to early middle miocene deepwater circulation patterns specifically recent discussions have focused on the relative roles of northern component water ncw production and warm saline deep water originating in the eastern tethys our time series and time slice reconstructions indicate that ncw and tethyan outflow water two relatively warm deepwater masses were produced from 20 to 16 ma ncw was produced again from 12 5 to 10 5 ma another feature of the early and middle miocene oceans was the presence of a high 13c intermediate water mass in the southern hemisphere which apparently originated in the southern ocean miocene climates appear to be related directly to deepwater circulation changes deep waters warmed in the early miocene by 3 c 20 to 16 ma and cooled by a similar amount during the middle miocene 18o increase 14 8 to 12 6 ma corresponding to the increase 20 ma and subsequent decrease 16 ma in the production of ncw and tethyan outflow water large 0 6 relatively rapid 0 5 m y 18o increases in both benthic and planktonic foraminifera i e the mi zones of miller et al 1991a and wright and miller 1992a were superimposed in the long term deepwater temperature changes they are interpreted as reflecting continental ice growth events seven of these m y glacial interglacial cycles have been recognized in the early to middle miocene two of these glacial interglacial cycles mi3 and mi4 combined with a 2 to 3 c decrease in deepwater temperatures to produce the middle miocene 18o shift

drilling the snake pit hydrothermal sulfide deposit on the mid atlantic ridge lat 23 sup 0 22 n a major high temperature hydrothermal area has been discovered in the mid atlantic ridge rift valley about 25 km south of the kane fracture zone the vent field consists of a wide area 40 000 m sup 2 of dark hydrothermal deposits numerous sulfide chimneys and mounds some up to 11 m high and high temperature black smoker vents ten shallow holes the first ever drilled in an active submarine hydrothermal area recovered friable unconsolidated fe cu fe and zn sulfides and several large fragments of massive sulfide mainly chalcopyrite from the locally thick 13 m hydrothermal deposits the vents are also associated with an unusual biological community of smaller more mobile organisms than reported from the east pacific rise

geochemistry of rare earth elements in the mainstream of the yangtze river china abstract water suspended matter and sediment samples were taken from 8 locations along the yangtze river in 1992 the concentration and speciation exchangeable bound to carbonates bound to fe mn oxides bound to organic matter and residual forms of rare earth elements la ce nd sm eu tb yb and lu were determined by instrumental neutron activation analysis inaa the contents of the soluble fraction of rees in the river are low and rees mainly reside in particulate form in the particles the chondrite normalized distribution patterns show significant lree enrichment and eu depletion while normalized to shales both sediments and suspended matter samples show relative lree enrichment and hree depletion rees are relatively enriched in fine grained fractions of the sediments the speciation characteristics of rees in the sediments and suspended matter are very similar the amount of the five forms follows the order residual bound to organic matter bound to fe mn oxides bound to carbonates exchangeable about 65 to 85 of rees in the particles exist in the residual form and the exchangeable form is very low high proportions of residual rees reveal that rees in sediments and suspended matter are controlled by their abundances in the earth s crust carbonate fe mn oxide and organic fractions of rees in sediments account for 2 4 6 9 5 2 11 1 and 7 3 14 0 of the total contents respectively they are similar to those in the suspended matter this shows that carbonates fe mn oxides and organic matter play important roles during the particle water interaction processes by normalization to shales the 3 forms of rees follow convex shapes according to atomic number with middle ree sm eu and tb enrichment while light ree and heavy ree are depleted

further evaluation of the re os geochronometer in organic rich sedimentary rocks a test of hydrocarbon maturation effects in the exshaw formation western canada sedimentary basin abstract re os isotopic analyses of a single organic rich sedimentary rock unit ors of known depositional age and at three levels of regional hydrocarbon maturity show that hydrocarbon maturation does not affect the ability the 187re 187os chronometer to yield a depositional age for such rocks we present re os isotope analyses from the late devonian exshaw formation in the subsurface of the western canada sedimentary basin alberta and obtain a re os isochron age of 358 10 ma 2 model 3 1 666 10 11 a 1 for samples ranging from hydrocarbon immature to overmature this age is within uncertainty of the established absolute age for the exshaw formation hydrocarbon immature and mature plus overmature samples show no significant age differences if regressed individually indicating that hydrocarbon maturation did not greatly disturb the re os isotope system in the exshaw formation as such we propose that the re os geochronometer may be used as a reliable tool for measuring the depositional ages of ors regardless of their level of hydrocarbon maturity we find that minimizing natural variation in the initial 187os 188os ratio is more important than avoiding hydrocarbon maturation in obtaining precise re os ages in particular the exshaw formation appears to contain a nonhydrogenous component of unradiogenic os in addition to the hydrogenous os load a subset of exshaw formation samples with 5 total organic carbon toc which should best reflect the hydrogenous os load alone yields a very well fitted isochron having a depositional age of 358 9 ma 2 1 666 10 11 a 1 with an initial 187os 188os ratio of 0 59 0 05 model 3 mean square of weighted deviates mswd 1 8 the initial 187os 188os ratio of this regression may provide an estimate of the os isotopic composition of local seawater at the time of deposition

element redistribution during hydrothermal alteration of rhyolite in an active geothermal system yellowstone drill cores y 7 and y 8 abstract hydrothermal alteration of the 0 54 ma biscuit basin rhyolite flow in yellowstone drill cores y 7 and y 8 has involved significant changes in ti normalized whole rock concentrations of li mg ca na k mn rb sr sb cs ba and u whereas such changes have generally not occurred for al fe sc co y zr ree hf ta and th the relatively mobile elements have been redistributed over distances from 2 5 cm to more than 10 100 m and are associated mainly with zeolites and clays in thoroughly altered samples average whole rock changes in ti normalized mass range from about 0 5 17 g kg 9 49 for major elements and 0 1 280 mg kg 19 4260 for minor and trace elements compositional changes correlate with hydrothermal mineralogy the relatively immobile elements have been redistributed over a distance of at least 10 100 m but less than 2 5 cm and are associated mainly with clays in thoroughly altered samples addition of sio2 ranges from 110 890 g kg in samples where porosity has been thoroughly sealed by silica deposition thermal water is not in oxygen isotopic equilibrium with any primary or secondary phases analyzed except calcite modest depletions of 18o 1 2 due to exchange with thermal water apparently have occurred in y 8 plagioclase and obsidian oxygen isotope ratios in obsidian replacing smectite and in veinlet celadonite and cristobalite suggest that these phases precipitated from water locally enriched in 18o up to 8 heavier than present thermal water the minimum integrated water rock mass ratio in y 7 and y 8 is 103 104 assuming advective transport

sequence of late jurassic early cretaceous magmatic hydrothermal events in the xiong ershan region central china an overview with new zircon u pb geochronology data on quartz porphyries recent investigations have revealed several large au and mo deposits in the xiong ershan region central china most quartz porphyries associated with the mineralization occur as dikes and apophyses or as rubbles cemented in mineralized breccia pipes three types of quartz porphyries were sampled from the leimengou mo deposit the qiyugou au deposit and the niutougou au deposit la icp ms zircon u pb analysis was performed in zircons from two quartz porphyries the results yielded ages of 125 4 0 77 ma for leimengou mo deposit and 150 1 1 1 ma for qiyugou au deposit the magma source of leimengou quartz porphyry is similar to that of the mineralized cementing material in breccia pipes of the qiyugou au deposit whereas the magma source of qiyugou quartz porphyry is the same as that of quartz porphyries in niutougou au deposit based on the new u pb isotopic ages of granitic plutons reported in this study together with the age data in the literature we identify distinct magmatic pulses in the xiong ershan region at ca 160 150 143 133 125 and 115 ma during the late jurassic early cretaceous the ages of au and mo mineralization coincide with the thermal events at about 115 125 133 and 143 ma are considered to be co eval with granitic magmatism no mineralization ages of 150 and 160 ma thermal events have been previously reported our study demonstrates late jurassic early cretaceous multiple magmatic pulses and mineralization in the xiong ershan region

factors controlling the trace element distribution in fine grained rocks the albian kaolinite rich deposits of the oliete basin ne spain abstract this paper combines mineralogical data x ray diffraction petrographic and scanning electron microscopy techniques and geochemical analyses in order to investigate the composition of a set of samples claystones siltstones and sandstones which belong to the albian deposits of the oliete basin in spain the aims of the study are to characterize the distribution of major and trace elements in kaolinite rich rocks to infer the role played by accessory phases and clay minerals on the trace element distribution and to assess the source area composition of these materials mineralogical analyses show that these rocks are mainly composed of different proportions of quartz and clay minerals kaolinite and illite with minor feldspar micron accessory minerals such as monazite zircon pyrite marcasite fe oxides and ti oxides have also been detected the sandstone framework implies that the source area of these sediments was probably a granitoid source which underwent low rank metamorphism the major element distribution reflects the mineralogy of the rocks plots in the a cn k diagram as well as their cia values indicate that these sediments were generated from an intensely weathered source area this produced the development of relatively cation poor clays such as kaolinite and claystones with large rare earth elements ree contents the fact that transition element contents in claystones are greater than in siltstones and sandstones suggests that they are preferentially linked to clay minerals probably by surficial sorption in comparison with other lithologies the high abundances of high field strength elements in siltstones imply that accessory minerals such as zircon and nb bearing phases are mainly concentrated in siltstones it should be noted that siltstones are also the lithology which displays the highest ree abundances the statistical analysis of the geochemical data suggests that ree are mainly controlled by ti and nb bearing phases such as titanite and nb and ti oxides although clay minerals are not the main phases in the ree control they probably also have some influence as the analyses show in addition other accessory phases such as monazite secondary phosphates and zircon also contribute to the ree contents although much less than amorphous fe oxides in some samples according to the ree patterns and elemental ratios such as la sc th sc th co etc the source area of the studied outcrops was probably felsic and with intermediate composition between granite and granodiorite

intracaldera volcanic activity toledo caldera and embayment jemez mountains new mexico the toledo caldera was formed at 1 47 0 06 ma during the catastrophic eruption of the lower member bandelier tuff the caldera was obscured at 1 12 0 03 ma during eruption of the equally voluminous upper member of the bandelier tuff that led to formation of the valles caldera earlier workers interpreted a 9 km diameter embayment located ne of the valles caldera toledo embayment to be a remnant of the toledo caldera drill hole data and new k ar dates of toledo intracaldera domes redefine the position of toledo caldera nearly coincident with and of the same dimensions as the younger valles caldera the toledo embayment may be of tectonic origin or a small tschicoma volcanic center caldera this interpretation is consistent with distribution of the lower member of the bandelier tuff and with several other field and drilling related observations explosive activity associated with cerro toledo rhyolite domes is recorded in tuff deposits located between the lower and upper members of the bandelier tuff on the northeast flank of the jemez mountains recorded in the tuff deposits are seven cycles of explosive activity most cycles consist of phreatomagmatic tuffs that grade upward into plinian pumice beds a separate deposit of the same age and consisting of pyroclastic surges and flows is associated with rabbit mountain located on the southeast rim of the valles toledo caldera complex these are the surface expression of what may be a thicker more voluminous intracaldera tuff sequence the combined deposits of the lower and upper members of the bandelier tuff toledo and valles intracaldera sediments tuffs and dome lavas form what we interpret to be a wedge shaped caldera fill this sequence is confirmed by deep drill holes and gravity surveys this fill accumulated in depressions formed during precaldera rifting and episodes of caldera collapse we interpret the toledo valles caldera complex to be a pair of nearly coincident trapdoor calderas with the hinge on the west side and thick caldera fill in the east

mobilization and re distribution of major and trace elements during extreme weathering of basalt in hainan island south china major trace and organic elements of a laterite profile developed on neogene basalts in northern hainan island south china were reported in this paper the aim of which was to investigate element mobilization and re distribution during extreme weathering the results indicate that most of the elements have been mobilized and transferred downwards along the profile by aqueous solution organic matter om can significantly improve the transport of insoluble elements among all the elements th is the least mobile as for the general conservative elements during incipient chemical weathering such as fe ti zr hf nb and ta the removals are up to 20 40 in the upper profile however these elements behave as conservatively as th in the lower profile in the middle profile oxic environment occurs accompanied with significant om decomposition the mn and ce transferred downward are readily oxidized into insoluble mn iv and ce iv and precipitate in the oxic front important om decomposition decreases the capacity of transfer of insoluble elements in aqueous solution consequently al significantly precipitates in the oxic front and rees with the exception of ce precipitate largely in the omdepleted layers co and u are also concentrated in the oxic front in association with mn and ce respectively however cr shows a negative correlation with mn because its response to redox condition changes is reversed from that of mn mn oxides hydroxides fe oxides hydroxides and secondary phosphate minerals other than clay minerals are potential hosts for rees except for ce in the profile rees with high concentrations in the profile seem closely associated with mn oxides hydroxides remarkable highly correlated ce and gd anomalies are observed in the profile ce anomalies are caused by ce precipitation in the oxic environment and successive decomposition of organic matter gd anomalies are likely to have resulted from lower stability constants of gd om complexes compared to those of neighboring rees the overall elemental behaviors in this profile suggest that organic matter plays a very important role in the mobilization and re distribution of the elements during extreme weathering

a strontium isotope study of the vc 1 core hole and associated hydrothermal fluids and rocks from valles caldera jemez mountains new mexico chemical and strontium isotopic analyses have been performed on 10 geothermal waters from the valles caldera jemez mountain region as well as 10 rock samples collected in the vc 1 scientific core hole the 87sr 86sr values of other rocks sampled in the jemez mountains have also been used in this study to understand relations between the fluids and rocks of the volcanically driven geothermal system and the lateral outflow plume discharging down the jemez fault zone the strontium content of groundwater is linked to the host rock composition the aquifer temperature and therefore the solubility of sr containing minerals low sr concentrations in the fluid are found with a high temperature and or volcanic host rocks whereas high sr concentrations are characteristic of a low temperature and or a paleozoic sedimentary aquifer important variations of the 87sr 86sr value in hydrothermal waters 0 70842 0 72193 are related to chemical composition sr content and host rocks for vc 1 core samples the sr isotopic ratios are also markedly variable 0 70459 0 75686 low for the quaternary volcanics and high for the paleozoic sedimentary rocks the same observation is made for other jemez mountains rocks 0 70465 0 8163 with in addition high 87sr 86sr values for precambrian crystalline rocks a good correspondence is generally found between the waters and the reservoir rocks studied here which indicates that isotopic equilibrium is rapidly attained the following suite of hydraulically related fluids displays a progressive enrichment in radiogenic strontium baca wells 87sr 86sr 0 7084 0 7094 vc 1 core hole at 483 m 0 7152 0 7154 main jemez spring 0 7217 and soda dam 0 7219 this trend is associated with flow through paleozoic rocks and with the length of the flow path from the center of valles caldera primary geothermal fluids toward san diego canyon along the jemez fault zone derivative waters

the phlegraean fields structural evolution volcanic history and eruptive mechanisms abstract the main event within the volcanic history of the phlegraean fields was the eruption about 35 000 years ago of a huge alkali trachytic ignimbrite 80 km 3 dre followed by caldera collapse the pre caldera activity evidence from geothermal wells and surface outcrops changed from submarine to subaerial shortly before the ignimbrite eruption the caldera was subsequently invaded by the sea and became progressively filled with tuffites and subordinate submarine flows in its northern half the last submarine explosive activity dates back to 12000 10500 yr with the eruption of mostly hydroplinian yellow tuffs recent mostly subaerial activity consists of a series of explosive eruptions whose volume decreases with time until the last eruption of mt nuovo in 1538 a d two peaks in recent activity occur at 10000 8000 and 4700 3000 years ago during post caldera activity eruptive vents migrated from the caldera rim toward the center where there are two distinct zones of recent vents minor collapses occurred within the caldera after the main eruptions often they are eccentric to the vent and displaced toward the caldera center phlegraean explosive activity is characterized by water magma interaction eruptive events without a hydromagmatic component are extremely rare in most cases the evolved trachytic magmas interacted with surface water either the sea or intracaldera lakes however there is evidence of interaction of magma with deep seated aquifers for some plinian events explosivity i e the efficiency of the transformation of thermal into kinetic energy during magma water interaction is largely controlled by the primary fragmentation of the magmatic melt

clastic metasediments of the early proterozoic broken hill group new south wales australia geochemistry provenance and metallogenic significance whole rock analyses of samples of pelite psammite and psammopelite from the early proterozoic broken hill group willyama supergroup in the broken hill block new south wales australia reveal distinctive geochemical signatures major element data show high al2o3 and k2o low mgo and na2o and relatively high fe2o3tmgo ratios compared to average early proterozoic clastic metasediments high field strength elements hfse are especially abundant including nb most 15 27 ppm ta most 1 0 2 2 ppm th 17 36 ppm hf 4 15 ppm and zr most 170 400 ppm y 33 74 ppm is also high concentrations of ferromagnesian elements are generally low sc 20 ppm ni 62 ppm co 26 ppm cr most 100 ppm data for rare earth elements rees show high abundances of light rees lacn 116 250 chondrite lacn 437 in one sample high lacnybcn ratios 5 6 13 9 and large negative eu anomalies eueu 0 32 0 57 the geochemical data indicate derivation of the metasedimentary rocks of the broken hill group by the erosion mainly of felsic igneous or meta igneous rocks high concentrations of hfse y and rees in the metasediments suggest a provenance dominanted by anorogenic granites and or rhyolites including those with a type chemistry likely sources of the metasediments were the rhyolitic to rhyodacitic protoliths of local quartz feldspar biotite garnet gneisses e g potosi type gneiss that occur within the lower part of the willyama supergroup or chemically similar basement rocks in the region alternative sources may have included early proterozoic anorogenic granites and or rhyolites in the mount isa and or pine creek blocks of northern australia or in the gawler craton of south australia metallogenic considerations suggest that the metasediments of the broken hill block formed enriched source rocks during the generation of pegmatite hosted deposits and concentrations of la ce nb ta th and sn in the region li be b w and u in pegmatite minerals of the district may have been acquired during granulite facies metamorphism of the local metasediments

geochemistry of precambrian and paleozoic siliciclastic rocks from the iberian range ne spain implications for source area weathering sorting provenance and tectonic setting abstract the major and trace element chemical composition of precambrian and paleozoic shales and sandstones from the iberian range spain has been investigated to determine the provenance and tectonic setting of these rocks as well as to appraise the influence of the weathering hydraulic sorting and recycling processes upon source rock signature the samples studied belong to a prograde sequence from diagenesis to anchizonal grade and are mainly composed of quartz illite mica phases and or kaolinite with chlorite feldspars and carbonates as minor components the major element distribution chemical index of alteration cia indices reflects that recycling processes have been important in homogenizing the composition of shales and sandstones the higher cia indices observed in the silurian and devonian shales 80 and 85 respectively compared with those of precambrian to ordovician and the carboniferous age about 70 indicate that their source area underwent more intense chemical weathering processes possibly due to climatic and or tectonic variations alternatively the source area of the silurian and devonian shales may have been composed of recycled sedimentary materials mineral fractionation is mainly observed in coarser rocks through zircon apatite and xenotime accumulation although the shales are not free of these phases the zircon content of the fine grained rocks is not high enough to affect rare earth element ree contents but phosphate minerals apatite and xenotime at least partially control the ree distribution the influence of apatite and xenotime are slightly higher in the precambrian shales as the phosphate concentration produces a decrease in the la sm ratios chondrite normalized ree patterns and negative eu anomaly size of the studied rocks are similar to that of post archean australian shales paas indicating that they originally come from a differentiated silicic source the higher ree contents in the studied shales in relation to paas indicate that recycling processes in the iberian range sources were probably more intense than that of paas the slight differences among the ree patterns of the different groups of shales probably do not reflect changes in source area composition but instead suggest variations in mineral sorting chemical weathering and or sediment recycling the th sc co th cr th cr v v ni ratios support a primitive silicic source for these rocks with the higher th sc and lower co th in cambrian and ordovician shales indicating a higher proportion of felsic material in their primitive source area the compositional maturity of analyzed sandstones is typical of cratonic environments and their la sc th and zr contents reflect their passive continental margin setting

re os isotopic systematics of the voisey s bay ni cu co magmatic ore system labrador canada abstract re and os concentrations and os isotopic compositions have been obtained for massive matrix and disseminated sulphide ores from three environments within the voisey s bay intrusion the ovoid eastern deeps and discovery hill zone in order to assess the role of crustal contamination in the genesis of this large cu ni co deposit these samples have high re concentrations 148 to 288 ppb in 100 sulphide for their common os concentrations 4 8 to 24 ppb in 100 sulphide yielding high re os ratios 12 to 33 these data confirm that the magma parental to the voisey s bay ore system was broadly basaltic in major element chemistry rather than picritic consistent with the low ni cu ratio of the ores 1 5 re os isotopic data exhibit a limited spread in 187 re 188 os 57 to 157 and define an imprecise 1323 135 ma model 3 isochron likely the result of small r factor variations within the ore system the re os isochron age is within error of 1334 ma u pb ages obtained for baddeleyite from the ore bearing troctolites demonstrating that whole rock re os isotopic systematics have remained closed since crystallisation the initial os isotopic composition of the isochron os 1040 200 implies significant magma interactions with radiogenic os that most likely resides in the nain churchill province crust these data are therefore consistent with the parental magma achieving sulphide saturation as a result of contamination by radiogenic crustal components with further addition of base and precious metals as a function of r factor analyses of sulphide separates from the proterozoic tasiuyak churchill and archaean nain gneisses confirm that both units contained significant os 8 6 ppb and 0 38 ppb respectively that was very radiogenic at 1334 ma os 1908 and 5202 respectively yielding crustal residence tchur model ages of 2200 to 2400 ma however these model ages may have been affected by re and or os mobility during the 1 85 ga torngat and 1 1 ga grenville orogeny re os isotopic modelling suggests that a reasonable fit to the ore data may be obtained via bulk crustal contamination of magmas parental to the nain plutonic suite nps with either tasiuyak 2 contamination or nain 16 contamination gneiss followed by an r factor process 200 to 1000 which improved the tenor of the sulphide liquid during transport in active magma conduits or after deposition in an active replenished voisey s bay intrusion magma chamber however the dominance of plagioclase rich high al2o3 magmas in the mafic members of the nps troctolites and anorthosites may indicate that other deeper forms of lithospheric interaction potentially involving mafic lower crust may be crucial to understanding this style of magmatic sulphide ore system

re os dating of sulfides associated with gold mineralization in central victoria australia we report re os isotope ages that are the first for sulfides closely associated with gold mineralization at the bendigo and maldon goldfields in central victoria two arsenopyrite samples from bendigo contain 11 ppb re and 0 08 ppb highly radiogenic os llhr samples stein et al 2000 and have model ages of 444 7 and 447 7 ma with a mean model age of 446 5 ma a five point isochron based on these arsenopyrite analyses plus three pyrite analyses including one replicate gives an age of 438 6 ma molybdenite associated with au te cu and sb mineralization at maldon gives an re os age of 376 2 ma similar to the age of the nearby har court granite these results support previous 40 ar 39 ar data indicating that initial emplacement of gold mineralization in central victoria occurred in the late ordovician during the earliest stages of accretionary development of the southern lachlan fold belt the molybdenite data are also consistent with the mobilization and or introduction of gold during late devonian magmatism

structural setting and geochronology of auriferous quartz veins at the high rock island gold deposit northwestern superior province manitoba canada the high rock island gold deposit occurs across the intrusive contact between a granitoid pluton and a mafic metavolcanic rock at the southern margin of the island lake greenstone belt the main structure at the deposit is a 5 m wide north trending and steeply dipping dextral ductile brittle fault zone the main fault that cuts at a right angle across the pluton greenstone contact and the contact parallel foliation total horizontal displacement along the fault is 9 m of which 3 m is accomplished by ductile shearing and 6 m by brittle faulting the gold deposit consists of steeply dipping auriferous quartz veins that are hosted in and were emplaced during the dextral shearing along the main fault they include 1 the main vein a fault fill vein that occurs in the center of and is parallel to the main fault 2 en echelon veins extensional veins that occur on both sides of the main vein and cut across the foliation and 3 foliation parallel veins that occur locally detailed analysis of the geometry of the en echelon veins partly based on a new mohr circle construction method shows that the deformation in the main fault was transtensional the faulting and quartz vein emplacement were controlled by the contacts of a north trending mafic dike they took place under greenschist facies conditions postdating amphibolite facies metamorphism in the host rock the mineralized quartz veins contain both monazite and titanite which yield u pb ages of 2687 2 ma and 2658 5 ma respectively although the exact interpretation of the two ages remains somewhat uncertain it is likely that gold could have been introduced during a secondary event at 2658 ma in a vein originally formed at 2687 ma or earlier this is supported by the isotopic affinity of pb in titanite with that in galena that is spatially closely associated with gold the interpretation that gold was introduced after the emplacement of the quartz veins is also consistent with the observation that the main vein only contains significant gold and sulfide where it is cut by a vein parallel fault in any case the mineralization at the deposit took place at the latest stages of orogenic development in the northwestern superior province

re os isotopic and trace element compositions of pyrite and origin of the cretaceous jinchang porphyry cu au deposit heilongjiang province ne china abstract the jinchang cu au deposit in northeast china contains more than 76 tons of au and 4683 tons of cu with average ore grades of 11 34 g t au and 1 44 cu the deposit is typical of porphyry types and consists of gold orebodies mainly hosted in a 113 ma granitic porphyry and breccia pipes within the porphyry intrusion mineralization is closely associated with early potassic alteration and late phyllic alteration pyrite is the main au bearing mineral and contains 1 48 18 9 ppb re and 11 4 38 ppt common os extremely low common os concentrations and high re os ratios are indicative of derivation of ore forming materials from the crust low re in pyrite from the jinchang deposit may indicate a mixing source of mantle and crust or a crustal source five re os isotopic analyses yield a model 1 isochron age of 114 22 ma 2 mswd 0 15 similar to the age of the host porphyry pyrite contains detectable co ni cu zn as ag au sb pb and bi pyrite has co ni ratios similar to that of volcanogenic and hydrothermal sulfide deposits indicating a magmatic hydrothermal origin and has au and as contents similar to that of porphyry epithermal systems pyrite grains from potassic and phyllic alteration stages have different trace element contents reflecting the evolution of ore forming fluids from magmatic dominated to magmatic mixed with meteoric water in combination with regional geology our new results are suggestive of origin of the jinchang cu au deposit from contemporary intrusions of granitic porphyries related to the early cretaceous subduction of the paleo pacific plate

change of sm nd isotope composition during weathering of till weathering of till in northern sweden results in the formation of well developed spodosols the till is dominated by 1 9 1 8 ga granitic material the ree are among the elements most strongly depleted during weathering and the loss of ree from the e horizon decreases as the atomic number increases to study if weathering leads to a change of the nd isotope composition we have analysed the nd isotopic composition of the various horizons including living plants and humus of two profiles of weathered till typic haplocryods in northern sweden as much as between 65 6 and 75 3 of the sm and nd in the 0 2 mm fraction has been lost from the e horizon and between 32 5 and 54 7 from the b horizon nd has been lost to a slightly greater extent than sm the two c horizon samples have end 0 values of 22 1 and 23 2 corresponding e horizon values are 18 1 and 20 2 the b horizon values are intermediate between the values of the e and c horizons it is concluded that the weathering leads to a change in the sm nd ratio resulting in a change of the sm nd isotope composition the plant and humus samples deviate even more from the unweathered till for one station the results could be interpreted as if the sm and nd taken up by the plants had similar isotope characteristics as the amounts of these elements released by weathering in the e horizon for the other station it is probable that the nd isotope composition of the organic samples is dominated by nd released by till weathering which however is mixed with another nd source possibly an airborne component the explanation to the change of isotope compostion in the till is that a larger proportion of the nd released by weathering is released from minerals with a lower sm nd ratio than the bulk soil compared with the amount released from minerals with a higher sm nd ratio although the various ree carrying minerals had the same initial nd isotopic composition 1 8 1 9 ga of decay of 147sm to 143nd has resulted in a higher present 143nd 144nd ratio in the minerals with a higher sm nd ratio

unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on antarctica since the earliest oligocene circa 35 ma the growth and decay of ice sheets during the oligocene to modern ice house world caused glacioeustatic sea level changes the early eocene was an ice free greenhouse world but it is not clear if ice sheets existed during the middle to late eocene doubt house world benthic foraminiferal 18o records place limits on the history of glaciation suggesting the presence of ice sheets at least intermittently since the earliest oligocene the best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic 18o records although planktonic isotope records from the western equatorial regions are limited subtropical planktonic foraminifera may also record such ice volume changes it is difficult to apply these established principles to the cenozoic 18o record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events we improved oligocene to miocene correlations of 18o records and erected eight oxygen isotope zones oi1 oi2 mi1 mi6 benthic foraminiferal 18o increases which are associated with the bases of zones oil circa 35 8 ma oi2 circa 32 5 ma and mil circa 23 5 ma can be linked with 18o increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near antarctica our new correlations of middle miocene benthic and western equatorial planktonic 18o records show remarkable agreement in timing and amplitude we interpret benthic planktonic covariance to reflect substantial ice volume increases near the bases of zones mi2 circa 16 1 ma mi3 circa 13 6 ma and possibly mi5 circa 11 3 ma possible glacioeustatic lowerings are associated with the 18o increases which culminated with the bases of zone mi4 circa 12 6 ma and mi6 circa 9 6 ma although low latitude planktonic 18o records are required to test this these inferred glacioeustatic lowerings can be linked to seismic and rock disconformities for example we link 12 oligocene early late miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries inferred eustatic lowerings of haq et al 1987

paleo oceanography global ocean evolution paleoceanography one of the youngest branches of earth sciences is concerned with the development of oceanic circulation through geologic time this is a multifaceted and integrated endeavor since none of the subdisciplines is easily separated from the others the field is holistic in character and includes the history and effects of bottom intermediate and surface circulation patterns planktonic and benthonic biogeographic development and rates of organic evolution the history of biogenic productivity and dissolution and their effect on sediment distribution and the consequences of sea level change paleoceanography was largely born of the deep sea drilling project dsdp and continues to be nourished by it because problems are of global scope the appetite for new sediment core material is large and is being supplied by numerous expeditions of dsdp this article is a brief overview of a number of advances that have occurred in paleoceanography and related fields during the period from 1979 to 1982 because of page limitations all publications cannot be cited which is not meant to indicate any lack of importance

manganese geochemistry near high temperature vents in the mid atlantic ridge rift valley in july 1985 the first high temperature hydrothermal vents ever discovered on the mar were found at 26 n tag a transponder navigated survey of a 4 8 km area was begun when on board measurements of manganese revealed concentrated hydrothermal plumes in the water column comparable in size and intensity to those found over geothermal fields on the epr these plumes also possess anomalously high light scattering properties and anomalously warm potential temperatures using relay transponder navigation with a rosette ctd system it was possible to sample bottom waters with temperature anomalies of several decidegrees samples collected near vent orifices possessed silica anomalies of up to 17 m and dissolved manganese anomalies as large as 360 nmol kg these manganese and silica anomalies are linearly related and predict amn si ratio of 20 mmol mol for these mar vent fluids a value essentially identical to that measured in 350 c fluid from the epr at 21 n the distribution of temperature anomalies in the water column over this area requires the presence of more than one active vent site a rough estimate of the convective heat loss from this section of the mar based on z profiles is 1 2 108 cal s which is similar to the heat loss estimated for the vent field on the epr at 21 n

rhenium osmium geochronology of arsenopyrite in meguma group gold deposits meguma terrane nova scotia canada evidence for multiple gold mineralizing events rhenium osmium geochronology using arsenopyrite was undertaken for three gold deposits in the meguma terrane nova scotia canada in order to better constrain their age of formation and to assess the utility of arsenopyrite for dating similar deposits globally analyses of arsenopyrite from bedding concordant veins from the ovens locality southwest meguma terrane yield a precise re os isochron age of 409 5 ma arsenopyrite analyses from a bedding discordant vein at this locality indicate an identical re os age of 407 4 ma saddle reef veins from the dufferin deposit northeast meguma terrane contain arsenopyrite with a precise re os isochron age of 380 3 ma the lack of common os in some arsenopyrite samples from both the ovens and dufferin permit calculation of single mineral model ages for each deposit which are identical to those determined using the isochron method initial os compositions for the two vein types at the ovens suggest a predominately crustal source of os in the mineralizing fluids whereas a less radiogenic initial os composition for arsenopyrite from dufferin does not as clearly define a crustal metal source at a third locality the touquoy deposit the re os systematics of arsenopyrite associated with disseminated gold mineralization do not define a precise formation age possibly as a result of mixing of re and os derived from the mineralizing fluid and the shale host rock the re os ages of arsenopyrite indicate that there were at least two distinct periods of gold deposition in the meguma terrane coinciding with widespread tectonothermal events regional deformation and metamorphism associated with acadian orogenesis and widespread generation of meta and peraluminous granites and high grade metamorphism within the basement rocks under the meguma terrane the ca 407 ma age for the ovens arsenopyrite provides the best estimate for the timing of regional acadian deformation in the meguma terrane and is slightly older than previous estimates based solely on 40ar 39ar dating

chemistry of thermal springs in the larderello travale geothermal region southern tuscany italy abstract thirty two thermal spring eleven cold spring and six steam condensates in the larderello travale geothermal region have been studied from a geochemical point of view the aim of this work was to delineate the relation between the chemical composition of the natural thermal manifestations and the thermal anomaly which is among the best known in the world the larderello spring both hot and cold are characterized by low salinity total dissolved solids generally lower than 1000 mg kg and alkaline earth bicarbonate composition in contrast an alkaline earth sulfate composition characterizes the thermal springs of the travale area this difference is due to the fact that the underground pathways of the larderello hot springs are only in shallow flyschoid caprock formations whereas at travale the paths are longer and in carbonate anhydritic mesozoic rocks which constitute the main reservoir formations in both the larderello and travale areas the thermal character of larderello springs is therefore mainly due to rock conduction whereas in travale it is mostly due to inflows of hot fluid phases from the geothermal reservoir comparison between ammonia li and b in fluid phases both steam condensates and hot springs in the larderello area suggests that in some of them their temperatures might be partly due to direct vapor inflows