major and trace element geochemistry of neutral and acidic thermal springs at el chichon volcano mexico implications for monitoring of the volcanic activity abstract four groups of thermal springs with temperatures from 50 to 80 c are located on the s sw w slopes of el chichon volcano a composite dome tephra edifice which exploded in 1982 with a 1 km wide 160 m deep crater left very dynamic thermal activity inside the crater variations in chemistry and migration of pools and fumaroles drastic changes in the crater lake volume and chemistry contrasts with the stable behavior of the flank hot springs during the time of observations 1974 2005 all known groups of hot springs are located on the contact of the basement and volcanic edifice and only on the w sw s slopes of the volcano at almost same elevations 600 650 m asl and less than 3 km of direct distance from the crater three groups of near neutral ph 6 springs at sw s slopes have the total thermal water outflow rate higher than 300 l s and are similar in composition the fourth and farthest group on the western slope discharges acidic ph 2 saline 10 g kg of cl water with a much lower outflow rate water rock interaction modeling of main types of the el chichon thermal waters using regular log q k graphs saturation indices vs temperature showed maximum equilibrium temperature slightly higher than 200 c acidic waters are equilibrated with some clay minerals at about 120 c three main sources of the salinity of thermal water are suggested on the basis of mixing plots and isotopic data a magmatic source for co2 boron sulfur and a limited part of cl volcanic rock source for the major cations and trace elements the oil bearing evaporitic basement source oil field brine for nacl br a part of ca and some trace elements all flank thermal springs end up in the river rio magdalena that has a variable seasonal flow rates from 4 to 20 m3 s any changes in the chemistry of springs must notably change the composition of the streams draining hot springs and eventually rio magdalena a monthly geochemical monitoring of rio magdalena and streams draining main hot springs would be a useful tool for surveying the activity of the volcano

halogen and ar ar age determinations of inclusions within quartz veins from porphyry copper deposits using complementary noble gas extraction techniques abstract extension of ar ar methodology has been used to determine mineralisation ages from mica inclusions and to simultaneously evaluate the noble gas and halogen composition of inclusion fluids within irradiated quartz vein samples from five porphyry copper deposits samples have been collected from the potassic and propylitic zones of bingham canyon utah and four arizonan deposits silverbell globe miami pinto valley and ray data obtained using three noble gas extraction techniques laser ablation in vacuo crushing and stepped heating are compared with each other laser ablation provides a means for the analysis of individual fluid inclusions but is limited by blank levels and detection limits stepped heating and in vacuo crushing are bulk extraction techniques that preferentially release gases from solid and fluid inclusion phases respectively and can be used in combination to obtain accurate and meaningful ages of mineralisation ages obtained for porphyry copper deposits are as follows bingham canyon 37 1 0 5 ray 65 3 1 5 globe miami 61 7 3 4 pinto valley 63 2 8 0 and silverbell 55 8 1 8 the age of mineralisation at ray is of particular interest as it enables a reported discrepancy in k ar ages to be understood halogen data for the bingham canyon samples gives insight into the partitioning of the heavy halogens br and i between solid and liquid phases

commentary on jgr sold earth paper deep seismic structure across the southernmost mariana trench implications for arc rifting and plate hydration by wan et al

uptake of elements from seawater by ferromanganese crusts solid phase associations and seawater speciation marine fe mn oxyhydroxide crusts form by precipitation of dissolved components from seawater three hydrogenetic crust samples one phosphatized and two hydrothermal mn oxide samples were subjected to a sequential leaching procedure in order to determine the host phases of 40 elements those host phase associations are discussed with respect to element speciation in seawater the partitioning of elements between the two major phases mn oxide and fe oxyhydroxide can in a first order approximation be explained by a simple sorption model related to the inorganic speciation of the elements in seawater as has been proposed in earlier models free and weakly complexed cations such as alkali and alkaline earth metals mn co ni zn tl i and partly y are sorbed preferentially on the negatively charged surface of the mno2 in hydrogenetic crusts the driving force is a strong coulombic interaction all neutral or negatively charged chloro cd hg tl carbonate cu y pb and u and hydroxide be sc ti fe zr nb in sn sb te hf ta bi th and tl iii complexes and oxyanions v cr as se mo and w bind to the slightly positively charged surface of the amorphous feooh phase while coulombic interaction can explain the sorption of the negatively charged species the binding of neutral species is based on specific chemical interaction organic complexation of elements in deep ocean water seems to be at most of minor importance surface oxidation can explain some strong metal associations e g of co and tl with the mno2 and te with the feooh sorption reactions initially driven by coulombic forces are often followed by the formation of specific bonds between the adsorbate and the atoms of the oxide surface differences in the associations of some metals between the non phosphatized and phosphatized hydrogenetic crusts and between the hydrogenetic and the hydrothermal samples reflect the different physico chemical environments of formation and speciations in oxic seawater vs less oxic fluids especially for the redox sensitive metals such as mo and v these environmental related differences indicate that the methodology of chemical speciation used here in combination with spectroscopic methods may allow for the detection of changes in paleoceanographic conditions recorded during the several tens of millions of years of crust growth

behaviour of rare earth elements and yttrium in ferromanganese concretions gibbsite spots and the surrounding terra rossa over dolomite during chemical weathering abstract the behaviour of rare earth elements rees and yttrium y during chemical weathering processes has been investigated on a 4 05 m thick terra rossa profile over dolomite on the yunnan guizhou plateau china in this profile ferromanganese concretions and gibbsite spots coexist in the terra rossa solum analyses of rees y zr f s and toc as well as mineralogical studies were conducted on a suite of ferromanganese concretions gibbsite spots terra rossas dolomites and insoluble residues from the underlying dolomite these analyses helped us to understand the mobilization redistribution and fractionation of rees and y during chemical weathering the rees and y are mobilized and redistributed during the terra rossa formation rees except for ce are removed from the upper and middle profiles transferred downwards and then precipitated in the base profile resulting in remarkable enrichment in the terra rossa near the weathering front the significant increase of ph near the weathering front was responsible for ree excluding ce and y enrichment in the base profile y is quite mobile during extreme chemical weathering and most of it was carried away from the profile because of very efficient oxidative fractionation of ce a significant positive ce anomaly in terra rossa was found in the middle of the profile whereas the terra rossa near the weathering front exhibited notably negative ce anomalies moreover the presence of cerianite and its content in the ferromanganese concretions can explain the markedly positive ce anomaly and the variation of ce ce values with depth in profile these ce anomalies are characteristic of the geochemical environment especially the redox condition studies of ree distribution in the ferromanganese concretions gibbsite spots and surrounding terra rossa revealed that significant ree fractionation occurred rees and y were preferentially concentrated in the ferromanganese concretions rather than in the gibbsite spots the water rock interaction resulted in m type tetrad effects in some of the ferromanganese concretions gibbsite spots and terra rossa samples in addition the tetrad effect in terrestrial weathering processes likely played an important role in the fractionation of rees and y such as y ho sm nd and the eu anomaly change

the interpretation of inverse isochron diagrams in 40 ar 39 ar geochronology abstract the concepts involved in the construction and interpretation of inverse isochron diagrams used in 40 ar 39 ar geochronology are reviewed the diagrams can be useful as a means of recognising atmospheric argon and excess 40 ar incorporated in the mineral lattice which cannot be recognised from 40 ar 39 ar spectra the age established using an inverse isochron plot unlike that yielded by a spectrum is not affected by trapped argon 40 ar 36 ar ratios that are different from the atmospheric argon ratio e g due to excess 40 ar and may contribute to a better age interpretation however a heterogeneous distribution of excess 40 ar or heterogeneous argon loss can cause false isochrons with axial intercepts indicating an incorrect age and an incorrect trapped argon composition inconsistency between the ages from a spectrum and from the associated inverse isochron plot may indicate the degree of inaccuracy of isochrons however it is possible that both the spectrum and inverse isochron yield the same incorrect age the importance of considering all possible interpretations before assigning an age to a specimen is stressed

new constraints on the release of noble gases during in vacuo crushing and application to scapolite br cl i and 40ar 39ar age determinations abstract the release of irradiation produced noble gas isotopes 38arcl 80krbr 128xei and 39ark during in vacuo crushing scapolite has been investigated and is compared to quartz three thousand crushing strokes released 98 of fluid inclusion hosted noble gas from quartz in comparison 3000 crushing strokes released only 4 of the lattice hosted 38arcl from a scapolite gem in vacuo crushing released lattice ar preferentially relative to lattice kr or xe and prolonged crushing released 88 of the lattice hosted noble gas in 96 000 crushing strokes we suggest fast diffusion pathways generated by crushing are an important noble gas release mechanism and we demonstrate two applications of prolonged in vacuo crushing on irradiated scapolite firstly scapolite molar br cl and i cl values are shown to vary over a similar range as crustal fluids the cl rich scapolite gem from hunza pakistan has br cl of 0 5 0 6 10 3 and i cl values of 0 3 2 10 6 that are similar to fluids that have dissolved evaporites in contrast three out of four skarn related scapolites from the canadian grenville province have molar br cl values of 1 5 2 4 10 3 and i cl values of 11 24 10 6 that are broadly consistent with skarn formation by magmatic fluids the fourth grenvillian scapolite with only 0 02 wt cl has an exceptionally elevated molar br cl value of up to 54 10 3 and i cl of 284 10 6 it is unclear if these values reflect the composition of fluids formed during metamorphism or preferential incorporation of br and i in cl poor meionitic scapolite secondly the grenvillian scapolites give plateau ages of between 830 ma and 400 ma the oldest ages post date regional skarn formation by 200 myr but are similar to feldspar cooling ages in the province the age variation in these samples is attributed to a combination of factors including variable thermal history and the presence of mineral sub grains in some of the samples these sub grains control the release of 39ark 38arcl and 40ar during in vacuo crushing as well as the samples 40ar retentivity in nature scapolite is suggested as a possible analogue for k feldspar in thermochronologic studies

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

hydrogeochemistry and rare earth element behavior in a volcanically acidified watershed in patagonia argentina abstract the rio agrio watershed in northern patagonia argentina is naturally acidic due to discharges of volcanic h 2 so 4 hcl and hf at its headwaters near the summit of copahue volcano a suite of water samples was collected from the summit of the volcano to a point roughly 40 km downstream where the ph of the rio agrio rose above 6 0 this suite included a sample of the hyperacidic ph the concentrations of ree in the rio agrio decreased by several orders of magnitude through the study area as a result of dilution and chemical attenuation a subtle shift in the slope of shale normalized profiles of dissolved ree concentration was observed from being weakly positive near the source of the rio agrio to showing a weak middle ree enrichment trend in lake caviahue to being weakly negative in the lower reaches of the river the trend to a negative slope across the lanthanide series in the lower river is explained by selective partitioning of the heavier ree to hydrous oxides of fe and al suspended in the water column and accumulating on the riverbed most of the decrease in ree load occurred immediately downstream of the confluence with a tributary that increased the ph of the rio agrio from 4 3 to 6 1 although the mixed water was supersaturated with ree phosphate compounds precipitation of lnpo 4 is not believed to have been a dominant process because the predicted pattern of inter element fractionation from phosphate deposition is inconsistent with the observed trends instead ree attenuation most likely occurred from adsorption onto freshly precipitated hydrous aluminum oxide the behavior of ree in the rio agrio watershed is broadly similar to what has been observed in watersheds that owe their acidity to oxidation of sulfide minerals

the rare earth element geochemistry of acid sulphate and acid sulphate chloride geothermal systems from yellowstone national park wyoming usa rare earth element ree concentrations have been determined by inductively coupled plasma mass spectrometry icp ms in acid sulphate and acid sulphate chloride waters and the associated sinters and volcanic rocks from the yellowstone national park ynp wyoming usa geothermal system ree concentrations in the volcanic rocks range from 222 to 347 ppm their chondite normalised ree patterns are typical of upper continental crust with lree hree and negative eu anomalies total ree concentrations in the fluids range from 3 to 1133 nmol kg 1 162 ppm and ree concentrations in sinter are 181 ppm ree abundances and patterns in drill core material from ynp indicate some ree mobility normalisation of ree concentrations in altered lava creek tuff lct from y 12 drill core to ree concentrations in fresh lct indicate that the ree overall have been depleted with the exception of eu which has been decoupled from the ree series and concentrated in the altered rocks relative to the host rocks the ree patterns of the fluids are variably depleted in hrees and lrees and usually have a pronounced positive eu anomaly this decoupling of eu from the ree suite suggests that 1 eu has been preferentially removed either from the host rock glass or from the host rock minerals or 2 the waters are from a high temperature or reducing environment where eu2 is more soluble than the trivalent rees since the latter is inconsistent with production of acid sulphate springs in a low temperature oxidising near surface environment we suggest that the positive eu anomalies in the fluids result from preferential dissolution of a eu rich phase in the host rock spatial and temporal variations in major element chemistry and ph of the springs sampled from norris geyser basin and crater hills accompany variations in ree concentrations and patterns of individual geothermal springs these are possibly related to changes in subsurface plumbing which results in variations in mixing and dilution of the geothermal fluids and may have lead to changes in the extent and nature of ree complexing

the behavior of rare earth elements zr and hf during biologically mediated deposition of silica stromatolites and carbonate rich microbial mats abstract venere lake in the pantelleria island thermal system central mediterranean sea consists of a mix of seawater and hydrothermal volcanic fluids containing high levels of dissolved sio 2 close to the lake s thermal springs siliceous stromatolites are deposed under high bacterial activity conditions whereas roughly interlaminated ca carbonates and microbial mats are widely scattered in the lake the dissolved ree speciation in lake waters is dominated by ree co 3 2 ree co 3 and ree h 3 sio 4 2 complexes on the contrary the most abundant zr and hf species are hydroxyl and fluoride complexes the behavior of ree zr and hf in the venere lake waters is controlled by precipitation of amorphous silica carbonates and bacterial activity chondrite normalized ree patterns in stromatolites are characterized by positive la anomalies superchondritic y ho ratios and negative eu anomalies the eu depletion is also found in microbial mats where is associated to a chondritic y ho signature zr and hf differently behave in dissolved phase and in newly formed siliceous and carbonatic material hf reacts easily into amorphous silica surfaces whereas zr is preferentially partitioned onto phosphate binding sites on microbial cell surfaces similar to the observed behavior of heavy ree hree we suggest that the zr hf relationship reflect the interface processes between mineral phases and bacterial membranes or compounds produced by bacterial activity

excess argon crustal fluids and apparent isochrons from crushing k feldspar using a combination ofin vacuo crushing and stepped heating the40ar39ar technique has been applied to two k feldspar bearing sedimentary rocks from the proterozoic of north china with a view to studying ancient fluids trapped in these rocks and their chronology correlations between natural ar isotopes and those produced by neutron irradiation permitted a clear distinction to be made between different components of natural argon crushing released cl correlated excess40ar and palaeoatmospheric36ar trapped in moderately saline fluid inclusions in quartz and possibly the k feldspar the very high40ar cl ratios of these fluids 2 7 10 4 and1 7 10 4 is interpreted as indicating a metamorphic source for the40ar more surprisingly crushing also released from the k feldspar a k correlated component with a very well defined40ar k ratio which for both samples corresponded formally to an apparent age comparable to or slightly less than the stratigraphic age in contrast stepped heating yielded40ar k ratios corresponding to significantly younger ages which are interpreted as low grade metamorphic ages the explanation of the k correlated component released on crushing and the significance if any of the distinct40ar k ratio is obscure although several effects involving microporosity and a combination of39ar recoil and diffusion are suggested there is a contribution of this component to the stepped heating release pattern which may have implications for attempts to use k feldspar as a40ar39ar thermochronometer

amphibolite facies retrograde metamorphism of the zhujiachong eclogite se dabieshan 40ar 39ar age constraints from argon extraction using uv laser microprobe in vacuo crushing and stepwise heating the zhujiachong eclogite in the south eastern dabieshan ultra high p terrane has been overprinted during retrograde metamorphism with the development of garnet amphibolite mineral assemblages in most rocks in the outcrop this study is focused on providing age constraints for the retrograde amphibolite facies and greenschist facies mineralogy by 40 ar 39 ar dating by applying a novel approach of combining three different techniques for extracting argon laser stepwise heating of single grains and small separates a spot fusion technique by uv laser ablation microprobe on polished sections and an in vacuo crushing technique for liberating radiogenic argon from fluid inclusions it is demonstrated that an internally consistent thermal history can be derived the 40 ar 39 ar ages indicate that phengite formed before 265 ma probably during the ultra high p event ages associated with amphibolite facies retrograde metamorphism range from 242 to 217 ma by the analyses of amphibole ages of c 230 ma were found for the symplectite matrix that formed during retrogression from eclogite pyroxene late stage hydrothermal activity leading to the formation of coarse grained paragonite and fluid inclusions in vein amphibole was dated at c 200 ma these age results agree well with the mineral crystallization sequence observed from thin sections of the retrograded eclogite phengite fi paragonite and amphibole in matrix fi amphibole in the corona

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

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

the chemistry of fumarolic vapor and thermal spring discharges from the nevado del ruiz volcanic magmatic hydrothermal system colombia on the basis of three sets of gas samples taken during the three months preceding the november 13 1985 eruption of nevado del ruiz from fumaroles on the crater floor the composition of the vapors discharged following minor eruptive activity in september corresponded to that of an essentially magmatic gas during the subsequent quiet period in october the proportion of a hydrothermal component in the vapor discharge increased steadily up until the major eruption the gases were found to be exceptionally high in total sulfur and are super saturated with respect to elemental sulfur their thermodynamic equilibration temperatures range from 200 to 600 c gases and waters from fumaroles and thermal springs on the flanks of the volcano are likely to be derived from a two phase vapor brine envelope surrounding the magmatic system the chemistry of the fumarole discharges is compatible with the assumption of an eruptive mechanism involving the build up of pressure in an extensive vapor zone by gas released from an essentially stagnant already extensively degassed body of magmatic material at depth production of such a residual gas over extended periods may account for the large amount of so2 discharged from the volcano in relation to the small amount of ejected solids

sphalerite 40ar 39ar progressive crushing and stepwise heating techniques abstract it is difficult to determine the mineralization ages of sulfide deposits because no suitable minerals can be selected for the traditional isotopic dating methods the 40ar 39ar method rarely applies well to sulfide minerals because of their trace potassium content and strong radioactivity after irradiation this preliminary study investigates the possibility of dating the hydrothermal sphalerites by 40ar 39ar using crushing and heating techniques the 40ar 39ar crushing experiments of two sphalerite samples from the fankou lead zinc deposit yield well defined and concordant isochron ages of 265 8 1 0 1 ma and 269 7 6 2 ma corresponding to initial 40ar 36ar ratios of 290 7 2 4 and 294 6 8 1 respectively the crushed powders of the later sphalerite yields with stepwise heating a flat age spectrum with 40ar 39ar plateau age of 267 2 2 5 ma which define a good isochron with an age of 271 3 5 4 ma and initial 40ar 36ar ratio of 294 0 1 7 this is the first report to distinguish secondary and primary fluid inclusions within sphalerite to obtain their ages using the crushing technique and to obtain good concordant ages both of fluid inclusions by crushing and heating of k containing minerals we expect progressive crushing and stepwise heating techniques will become an effective approach to 40ar 39ar dating of the mineralization ages of hydrothermal sulfide deposits

estuarine distributions of zr hf and ag in the hudson river and the implications for their continental and anthropogenic sources to seawater 1 zirconium and hf in seawater are derived from continental weathering and are transported to the oceans by rivers but the modification of this flux with estuaries is largely unknown furthermore there is no information as to whether there is a pollutant source of these metals that might affect their budget calculations in the modern ocean to address the riverine flux and potential anthropogenic sources the distributions of dissolved zr and hf have been measured in surface and bottom water through the hudson river estuary the distribution of ag is included because it is sensitive to urban sources and has partial similarities in its distribution to those of zr and hf there is about 50 removal of zr and hf in surface water relative to their freshwater end member concentrations of 243 and 3 1 pmol kg as salinity starts to increase but an urban source of these metals midestuary may obscure greater removal silver concentrations in surface water are below the detection limit until salinity of 3 5 is reached the concentrations of zr and hf 0 5 m above the bottom are 1 5 to 3 times higher than their surface water concentrations throughout the estuary and may result from input of groundwater diffusion from pore fluids or inclusion of colloidal phases in our analyses downstream of the turbidity maximum bottom water ag concentrations are high due to release from particles that originally formed within the estuary and were moved inland following the spring freshet this process may also affect zr and hf the increase in the freshwater atomic zr hf ratio from 70 to 80 characteristic of terrestrial rocks to the elevated zr hf 110 ratio of seawater takes place at middle to high salinity due to enhanced release of zr from resuspended particles and slower removal rates compared to hf a main implication of this study is that estuaries are a sink for zr and hf the reduction of the predicted export of continental zr and hf to the oceans increases their previously calculated seawater residence by as much as 2 to 4 times assuming rivers dominate the supply of zr and hf to seawater

40ar39ar dating of the quartz samples from two mineral deposits in western yunnan sw china by crushing in vacuum abstract the primary aim of this study is to investigate the possibility of dating fluid inclusions of quartz samples using the 40 ar 39 ar method by crushing in vacuo the samples are from the lushui tin tungsten deposit and the shangmanggang gold deposit in western yunnan sw china coexisting muscovite s 90ms and quartz s 90qw in a piece of tungsten ore from the former deposit were selected and the isochron age of s 90qw by crushing 38 6 1 9 ma shows excellent coincidence with that of s 90ms by stepped heating 38 6 0 8 ma the isochron age and plateau age by crushing of the quartz smg 8qz from the latter deposit indicate that the gold mineralization occurred at 144 ma these ages are respectively agreeable with the evaluated ages from the geologic facts in addition since the potassium concentration calculated from 39 ar released by crushing in the quartz sample smg 8qz was as high as 0 24 electron probe analysis was applied to investigate the occurrence of potassium and the results reveal that the majority of potassium scattered in the microcrystal quartz grains

bathymetric and geochemical investigation of kawah ijen crater lake east java indonesia abstract a bathymetric survey of kawah ijen crater lake was conducted by acoustic sounding in 1996 to compare the lake morphology with those measured in 1922 1925 and 1938 and to calculate the present lake volume even though the lake experienced several hydrothermal eruptions the maximum depth became shallower 182 m than before 200 m resulting in a reduced lake volume 3 0 10 7 m 3 fifty two major and minor constituents including rare earth elements and polythionates pt of the lake waters at various depths were determined by icp aes icp ms and hplc respectively these ions except for several volatile elements are taken up by lake fringe through congruent dissolution of pyroclastics of kawah ijen volcano most ions are homogeneously distributed throughout the lake although pt showed a considerable vertical variation rare earth elements ree in the kawah ijen water as well as those from other hyper acidic crater lakes show distribution patterns likely due to the three rock dissolution preferential congruent and residual types and their logarithmic concentrations linearly depend upon the ph values of the lake waters using the pt degradation kinetics data production rates of pt injection rates of so 2 and h 2 s into the lake were estimated to be 114 86 and 30 tons day respectively also travel time of the spring water at the banyupahit riverhead from kawah ijen was estimated to be 600 1000 days through the consideration of decreasing rates of pt molten sulfur stocks containing sn cu bi sulfides and pb barite exposed on the inner crater slope were presumed to be extinct molten sulfur pools at the former lake bottom this was strongly supported by the barite precipitation temperature estimated through the consideration of the temperature dependence of pb chlorocomplex formation

high precision 40ar 39ar age of the gas emplacement into the songliao basin the problem of determining an exact isotopic age of hydrocarbon emplacement is complex because minerals suitable for dating with common isotopic methods are often lacking in the sedimentary domain however the igneous quartz from the cretaceous volcanic rocks that host the gas reservoir in the songliao basin northeastern china contains abundant secondary fluid inclusions with high concentrations of k and high partial pressures of methane trapped during gas emplacement quartz with abundant k rich fluid inclusions provides an excellent closed system well suited for 40 ar 39 ar dating three igneous quartz samples were measured by stepwise crushing to release the inclusion based argon gas all three samples yielded well defined isochrons with ages in close agreement precisely constraining the gas emplacement at 42 4 0 5 ma 2 below the daqing oil field in the songliao basin extending possible gas reservoirs from the upper cretaceous to the middle eocene

the paleozoic metamorphic history of the central orogenic belt of china from 40ar 39ar geochronology of eclogite garnet fluid inclusions abstract the pressure temperature time evolution of the uhp eclogites of dabie sulu in the eastern sector of the central orogenic belt of china shows a complex pattern of predominantly triassic and to a lesser extent early paleozoic ages 40 ar 39 ar stepwise crushing analysis of eclogitic garnets yielded consistently paleozoic ages because our initial results from the bixiling eclogite were of limited areal extent their significance required further testing data for garnet bearing gneiss and eclogites from new locations in northern and southern dabieshan shuanghe ganghe and hongmiao confirm the paleozoic garnet results obtained from bixiling eclogite we also tested the technique on a garnet sample of known paleozoic age from altyn tagh in the western central orogenic belt these new results indicate that light colored garnets from dabieshan and altyn tagh yield concordant 40 ar 39 ar ages ranging from 445 465 ma by in vacuo crushing and confirm that a paleozoic u hp metamorphic event took place in the central orogenic belt from altyn tagh in western china to dabieshan in eastern china in contrast dark colored garnets from mafic metavolcanics do not yield 40 ar 39 ar plateaux or isochrons ages

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

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

oceanography chemical twins separated how the chemical composition of sea water changes on its journey through the world s oceans is poorly understood systematic measurements of dissolved trace metals across the pacific ocean suggest that these metals may help track sources and mixing of water masses

geochemistry of ree zr and hf in a wide range of ph and water composition the nevado del ruiz volcano hydrothermal system colombia the geochemical behaviour of rare earth elements zr and hf was investigated in the thermal waters of nevado del ruiz volcano system a wide range of ph between 1 0 and 8 8 characterizes these fluids the acidic waters are sulphate dominated with different cl so4 ratios the important role of the ph and the ionic complexes for the distribution of ree zr and hf in the aqueous phase was evidenced the ph rules the precipitation of authigenic fe and al oxyhydroxides producing changes in ree zr hf amounts and strong anomalies of cerium the precipitation of alunite and jarosite removes lree from the solution changing the ree distribution in acidic waters y ho and zr hf twin pairs have a different behaviour in strong acidic waters with respect to the water with ph near neutral yttrium and ho behave as zr and hf in waters with ph near neutral to neutral showing super chondritic ratios the twin pairs showed to be sensitive to the co precipitation and or adsorption onto the surface of authigenic particulate fe al oxyhydroxides suggesting an enhanced scavenging of ho and hf with respect to y and zr leading to superchondritic values in acidic waters a different behaviour of twin pairs occurs with chondritic y ho ratios and sub chondritic zr hf ratios for the first time zr and hf were investigated in natural acidic fluids to understand the behaviour of these elements in extreme acidic conditions and different major anion chemistry zr hf molar ratio changes from 4 75 to 49 29 in water with ph 3 6 in strong acidic waters the fractionation of zr and hf was recognized as function of major anion contents cl and so4 suggesting the formation of complexes leading to sub chondritic zr hf molar ratios

40ar 39ar dating of mica bearing pyrite from thermally overprinted archean gold deposits previous studies have suggested that pyrite may armor potassium bearing mineral inclusions from alteration induced argon loss thus providing improved 40ar 39ar age results to test this hypothesis matrix muscovite and pyrite crystals hosting muscovite inclusions were selected from two variably overprinted yilgarn gold deposits western australia and analyzed by combined single crystal 40ar 39ar laser probe and in vacuo crushing methods pyrite grains from the ca 2 60 ga mount charlotte gold deposit exhibit evidence of minor argon loss but give concordant high temperature ages averaging 2594 8 ma 2 indistinguishable from previous age estimates matrix mica from the ca 2 63 ga kanowna belle gold deposit yielded a discordant age spectrum with all ages younger than 2 5 ga indicating substantial 40ar loss related to middle proterozoic thermal overprinting crushing and low temperature heating experiments on pyrite crystals from kanowna belle produced anomalously old apparent ages up to 7 0 ga however in contrast to the matrix mica total gas pyrite ages generally approach or overlap the inferred time of gold mineralization this behavior is attributed to diffusion of 40ar to internal muscovite pyrite grain boundaries in response to the middle proterozoic thermal event with limited external loss of argon it is concluded that pyrite acts as a partially closed system for argon but that the 40ar 39ar pyrite dating method has the potential to see through later thermal and or alteration events and resolve controversial aspects of ore deposit geochronology

hydrothermal fluids argon isotopes and mineralization ages of the fankou pb zn deposit in south china insights from sphalerite 40ar 39ar progressive crushing abstract hydrothermal fluid geochemistry and mineralization timing are two important factors in the genesis of a hydrothermal deposit 40 ar 39 ar analyses of fluid inclusions not only provide time constraints for the mineralization but also help to clarify the k ca cl ar characteristics for the ore forming fluids in this study six sphalerite samples collected from the fankou lead zinc sulfide deposit are investigated by 40 ar 39 ar in vacuo crushing gases liberated from the early and late crushing steps exhibit distinct ar isotopic compositions and 40 ar 39 ar apparent ages argon released in the early steps has much higher 40 ar and 38 ar cl and lower 37 ar ca contents than those in the late steps the significant excess ar 40 ar e extracted in the early crushing steps shows a strong correlation with 38 ar cl with very high 40 ar e 38 ar cl ratios in contrast those of the late steps mainly consist of atmospheric ar and k correlated radiogenic ar with a constant 40 ar r 39 ar k ratio and the atmospheric initial 40 ar 36 ar ratio as a result all samples yield similar declining age spectra the fore segments with anomalously old apparent ages decline quickly in the early crushing steps and the rear ones are flat with concordant apparent ages in the late crushing steps the data points of the early steps define linear correlations in plots of 40 ar na 39 ar k vs 38 ar cl 39 ar k and 38 ar cl 40 ar na vs 39 ar k 40 ar na na for non atmospheric and most yield ages of 240 230 ma on the other hand the data of the late steps always construct well defined isochrons in the plots of 36 ar a 40 ar na vs 39 ar k 40 ar na with consistent ages of 300 ma we interpret that gases released in the early steps were from the secondary fluid inclusions sfis due to their distribution characteristics along cracks leading to be easily extracted and those released in the later steps represented the contribution of the primary fluid inclusions pfis the initial 40 ar 36 ar ratios of sfis much higher than the modern atmospheric ratio suggest that their fluids were most likely from deep sources however these ratios of pfis close to the modern atmospheric ratio might imply that the ore forming fluids were mainly meteoric accordingly our results show that a major lead zinc mineralization occurred at about 300 ma and a subsequent hydrothermal interruption at 240 230 ma the sphalerite 40 ar 39 ar crushing results suggest that the ore forming fluid might strongly interact with the sedimentary rocks resulting in the enrichment of ore deposit

geochronological constraints on the baguamiao gold deposit west qinling orogen central china implications for ore genesis and geodynamic setting abstract the baguamiao gold deposit located in the fengxian taibai ore district is one of the largest gold deposits in the west qinling orogen central china the poor age constraints on the gold mineralization event at the baguamiao has caused strong debate on ore genesis and associated geodynamic controls we carried out sm nd and 40ar 39ar geochronological studies to determine more precise age constraints on the god deposition the gold mineralization at baguamiao deposit was developed during four hydrothermal stages that formed sequentially i nw trending ankerite quartz veins ii deformed and folded nw trending sulfide ankerite quartz veins iii joint hosted ne trending sulfide ankerite quartz veinlets and iv nw and ne trending quartz fissure veins stages ii and iii define the main gold mineralization the sm nd dating of dolomite ankerite and calcite yielded isochron ages of 209 3 4 2 ma mswd 1 80 and 208 1 3 1 ma mswd 0 50 for gold mineralization of stages and iii respectively the 40ar 39ar dating of muscovite intergrown with sulfides of stage yielded a plateau age of 209 5 1 4 ma mswd 0 30 the age data obtained from the two geochronological methods are consistent with each other within uncertainties indicating clearly the baguamiao gold deposit formed at ca 209 ma integrating deposit geology from this and previous studies geochronological data and regional tectonics we classify baguamiao as an orogenic gold deposit which was resulted from a number of fluid pulses but during a single ore forming episode in late norian rhaetian time of the late triassic the ore forming fluids and metals are suggested to have been derived from both metamorphic and magmatic processes in a post collisional regime of the west qinling orogen

dissolved zirconium and hafnium distributions across a shelf break in the northeastern atlantic ocean abstract dissolved zr and hf distributions have been determined for five stations located across the shelf break in the northeastern atlantic ocean on the celtic approaches for stations in deep water the range in zr concentrations has been found to be 70 180 pmol kg and the range in hafnium concentrations 0 4 1 1 pmol kg the distributions with depth are indicative of a nutrient like scavenging regeneration behavior in seawater although the dissimilarity with silicate and nitrate for samples below the nutricline suggest that other mechanisms are also important in defining the oceanic distribution of these elements in contrast the concentrations of zr and hf at the station located closest to land are highest in surface waters and decrease with depth although salinity does not indicate dilution of seawater with freshwater with high zr and hf concentrations the ratio of dissolved zr to hf in seawater is higher and more variable than is found for the majority of terrestrial rocks or predicted from thermodynamic considerations fractionation due to small differences in their interactions with particulate material is implicated

combined zircon and cassiterite u pb dating of the piaotang granite related tungsten tin deposit southern jiangxi tungsten district china abstract the large low grade piaotang w sn deposit in the southern jiangxi tungsten district of the eastern nanling range south china is related to a hidden granite pluton of jurassic age the magmatic hydrothermal system displays a zonation from an inner greisen zone to quartz veins and to peripheral veinlets stringers five floor zonation model most mineralization is in quartz veins with wolframite cassiterite the hidden granite pluton in underground exposures comprises three intrusive units i e biotite granite two mica granite and muscovite granite the latter unit is spatially associated with the w sn deposit combined la mc icp ms u pb dating of igneous zircon and la icp ms u pb dating of hydrothermal cassiterite are used to constrain the timing of granitic magmatism and hydrothermal mineralization zircon from the three granite units has a weighted average 206pb 238u age of 159 8 0 3 ma 2 mswd 0 3 the cathodoluminescence cl textures indicate that some of the cassiterite crystals from the wolframite cassiterite quartz vein system have growth zonations i e zone i in the core and zone ii in the rim dating on cassiterite zone ii yields a weighted average 206pb 238u age of 159 5 1 5 ma 2 mswd 0 4 i e the magmatic and hydrothermal systems are synchronous this confirms the classical model of granite related tin tungsten mineralization and is against the view of a broader time gap of 6 myr between granite magmatism and w sn mineralization which has been previously proposed for the southern jiangxi tungsten district the elevated trace element concentrations of zr u nb ta w and ti suggest that cassiterite zone ii formed in a high temperature quartz vein system related to the piaotang granite pluton

the source and significance of argon isotopes in fluid inclusions from areas of mineralization argon isotopes in fluid inclusions in quartz veins associated with granite hosted tungsten mineralization in the southwest and north of england have been investigated in detail by the40ar 39ar technique the natural argon is present as a number of discrete components which can be identified through correlations with39ar 38ar and 37ar induced by neutron bombardment of potassium chlorine and calcium the potassium correlated component arises principally from in situ decay of potassium in solid phases in the inclusions in the case of the hemerdon tungsten deposit of southwest england the phases responsible are small 25 m captive authigenic micas which are shown to have been deposited from a fluid 268 20 ma ago shortly after the emplacement of the host granite the chlorine correlated component is present in the brines which constitute the fluid phase of the inclusions the argon in these hydrothermal fluids is made up in part of parentless or excess 40ar leached from surrounding crustal rocks and in part of dissolved ancient atmospheric argon absolute concentrations of both atmospheric and excess components in the brine can be estimated from 40arcl ratios and independent determinations of the salinity of the inclusions the absolute concentrations of the atmospheric argon are close to those found in modern meteoric water while those of the excess component can be interpreted in terms of the degree of interaction betwen the circulating fluids and country rock a calcium correlated component with a much higher ratio of excess to atmospheric argon than that in the brine was found to be a dominant phase in one sample from the hemerdon deposit indicating the presence of a solid phase probably a caso4 daughter mineral inclusions of this composition represent fluids which have had a more prolonged interaction with crustal rocks the results obtained from this study provide a systematization and a framework for future multi component argon studies of fluid inclusions together with an indication of the wide range of information which can be inferred

paleozoic ages and excess 40ar in garnets from the bixiling eclogite in dabieshan china new insights from 40ar 39ar dating by stepwise crushing abstract the 40 ar 39 ar stepwise crushing technique is applied for the first time to date garnet from ultra high pressure metamorphic uhpm eclogites three garnet samples from the bixiling eclogites analyzed by 40 ar 39 ar stepwise crushing yield regular predictable age spectra and a clear separation between excess 40 ar and concordant plateau and isochron ages all three age spectra begin with high apparent ages followed by step by step decreasing ages and finally age plateaux with apparent ages in the range from 427 20 to 444 10 ma the data points constituting the age plateaux yield excellent isochrons with radiogenic intercept ages ranging from 448 34 to 459 58 ma corresponding to initial 40 ar 36 ar ratios from 292 1 4 5 to 294 5 6 7 statistically indistinguishable from the modern air the high initial ages are interpreted to derive from secondary fluid inclusions containing excess 40 ar whereas the plateau ages are attributed to gas from small primary fluid inclusions without significant excess 40 ar the plateau ages are interpreted to approximate the time of garnet growth during initial uhpm metamorphism phengite analyzed by laser stepwise heating yielded a complicated two saddle age spectrum with a scattered isochron corresponding to age of 463 116 ma and initial 40 ar 36 ar ratio of 1843 1740 indicative of the presence of extraneous 40 ar within phengite these concordant isochron ages measured on minerals diagnostic of eclogite grade metamorphism strongly suggest that dabie uhpm eclogites were first formed in the early paleozoic during the same event that caused the qinling northern qaidam basin altyn tagh eclogites

naturally acid waters from copahue volcano argentina volcanic acid sulfate chloride brines form through absorption of volcanic vapors in shallow reservoirs of meteoric water reaction with surrounding volcanic rocks leads to partial neutralization of the fluids and precipitation of secondary minerals chemical data of such acid waters from copahue volcano argentina covering 8 years of observations show evidence for changes in composition related to water rock interaction at depth prior to emergence of the fluids at the surface the chemical composition changed dramatically during the 2000 eruption of copahue with enhanced concentrations and fluxes of mg na fe and al followed in 2001 by rapidly declining concentrations and element fluxes the subsequent 5 years saw more variable element ratios and strong depletions in k and al most incompatible elements are released from the rock matrix stochiometrically whereas some elements are enriched through vapor input from the magma as pb zn most fluids have lree enrichments relative to the rock matrix but during periods of new magma intrusion the lree enrichment decreases as does the magnitude of the negative eu anomaly in the fluids these observations are interpreted assuming early dissolution of plagioclase olivine and volcanic glass that occurs during intrusion of new magma into the hydrothermal system the high field strength elements are virtually immobile even in these hot acid fluids with nb and ta more so than hf and zr the mobility of u and th in these fluids is comparable at variance with th behavior in neutral fluids the local rivers and lakes of copahue are fertilized by volcanic dissolved p and most surface waters with ph 3 have high levels of as the acid fluids from copahue may be surficial analogs for deep subduction fluids that evolve below zones of arc magma generation as well as for early mars environments that are thought to have had large acid lakes