toward direct micron scale xrf elemental maps and quantitative profiles of wet marine sediments 1 here we describe a chemical analysis technique for ca fe k sr ti and s using a recently developed micro xrf analyzer micro xrf with a 100 m resolution and an xrf whole core scanner xrf s with a 5 mm resolution for selected sediment sections from a continental margin sediment core the micro xrf produces highly resolved element maps of individual sections and the calculation of individual continuous element profiles is based on overlap measurements of successive sections by means of discrete subsamples analyzed by icp oes the two xrf data sets are successfully calibrated to provide quantitative profiles of ca fe k sr and ti we discuss the advantages and limitations of both xrf techniques a comparison of the two independent xrf data sets demonstrates the overall high consistency and accuracy of both techniques the resulting element profiles and detailed xrf maps clearly show that the micro xrf is a powerful tool for studying at high resolution the chemical transitions linked to paleoenvironmental changes for example the discrimination between provenance changes and diagenetical effects on the fe profile can be achieved by the combined inspection of the fe ti profile and s maps this highlights the usefulness of the xrf maps for clarification of profile ambiguities and clearly distinguishes the micro xrf from other technical devices producing elemental profiles only

chemical element imaging for speleothem geochemistry application to a uranium bearing corallite with aragonite diagenesis to opal eastern siberia russia abstract two complementary image based microanalysis methods digital autoradiography of radioactive elements and x ray fluorescence microspectroscopy micro xrf were used to study the geochemistry of a speleothem from eastern siberia our objective was to show the interest of these micro chemical methods to investigate the distribution of u and some other elements as ca sr and si in speleothems the sample studied was a corallite concretion that formed slowly by the precipitation of minerals from moisture that had condensed underground polished sections of the sample revealed alternating laminas of gray calcite and white aragonite the concretion which is older than 400 kyr u th tims showed no signs of detrital contamination 230 th 232 th 10 000 digital autoradiography and xrf analyses indicated exceptionally high uranium contents ranging from 3 10 to more than 1300 g g 1 in different areas of the sample element maps for calcium ca uranium u strontium sr and silicon si showed inverse correlations between ca and u and between ca and si but there is a strong correlation between si and u under the optical microscope the low ca appears as corrosion voids which were found to contain uranium enriched amorphous silica replacing areas of aragonite and in some cases calcite this postgenetic amorphous and uraniferous silica is composed of two kinds of opal opal a formed by large microspheres of 30 40 m in diameter and a gray opal ct with irregular lepispheres this late opal dated around 385 412 kyr is probably due to a special volcanic event formed by uraniferous glass ashes easily soluble by meteoric waters as suggested by the presence of volcanic suite in the fine fraction of the opal opal precipitated after speleothem crystallization by evaporation or cryogenic supersaturation the study of this exceptional concretion shows the value of direct chemical imaging methods as they easily revealed the presence and distribution of u in the concretion and allowed an unusual case of opal diagenesis in a carbonate speleothem to be described given the value of speleothems as geo chronometers and recorders of environmental changes at different time scales from season to isotopic stage this methodology opens new perspectives in understanding the geochemical system and consequently the validity of radiometric datings u th and u pb especially in speleothem samples

2000 year environmental history of a karstic lake in the mediterranean pre pyrenees the estanya lakes spain abstract the sediment record of the estanya lakes pre pyrenees spain indicates that this region was intensely affected by land use during the middle and modern ages which contrasts with the present day poor socioeconomic development of the region the correlation between sediment and biotic data and well known historical events suggests a reliable history of environmental changes in this area during the last 2000 years changes in lake level were mainly controlled by climatic factors whereas properties such as lithology organic carbon ostracods and pollen content are mainly associated with lake management and land use major sedimentological changes resulted from the use of the lake for hemp retting at the start of the xivth century subsequent depopulation of the area in the xxth century led to the progressive recovery of the lacustrine ecosystem

rapid and quantitative major element analysis method for wet fine grained sediments using an xrf microscanner several types of x ray fluorescence xrf core scanners have been developed to fulfill the demands for high resolution rapid chemical analysis of wet sediment cores however their application to quantitative analysis has been hampered by the difficulty of evaluating the xrf absorption effect of water in a water film on the sediment surface and interstitial water within the sediments especially for lighter elements in this study we established a non destructive rapid high resolution and quantitative chemical analysis method for wet fine grained sediment samples using an xrf microscanner results of our experiments suggest that the degree of xrf absorption by the water film which develops on the wet sample surface covered with mylar film shows a clear positive correlation with the water content of the sediments under the measurement area a clear positive correlation also exists between the degree of xrf absorption by the interstitial water and the water content of the sediments under the measurement area we evaluated the xrf absorption by the thin water film using the relationship between the water content and thickness of the thin water film and the xrf absorption by the interstitial water using its relation with the water content the water content under the measurement area is estimated from the average transmitted x ray intensity that is measured on the same measurement area simultaneously with the measurement of xrf intensities the dry sample equivalent xrf intensities of major elements al si k ca ti and fe which are the xrf intensities of wet samples corrected for the xrf absorption by the thin water film and the interstitial water show better correlation with the major element concentrations determined by conventional xrf methods using this new method it is possible to measure the average water content and average concentrations of the 6 major elements simultaneously for a square area as small as 0 5 0 5 mm on the wet fine grained sediment within 6 min which is nearly ten times faster than the conventional xrf method

reconstructing hydrological variability in lake baikal during mis 11 an application of oxygen isotope analysis of diatom silica in this paper we reconstruct hydrological variability in lake baikal during marine isotope stage 11 mis 11 427 362 ka bp from oxygen isotope analysis of diatom silica highest d 18 odiatom values are found during mis 11 3 highlighting the dominance of hydrological input from rivers flowing into the south and central basins of lake baikal especially the selenga river hydrological input from south basin rivers dominated for over 30 ka however there is evidence from both biogenic silica and d 18 odiatom records for an abrupt cooling event at ca 390 ka bp stadial conditions at this time are coincident with an iceberg discharge event into the north atlantic the decline in d 18 odiatom values suggests increasing proportion of hydrological input from rivers to the north of lake baikal due to greater influence of winter precipitation and snow melt after a period of interstadial conditions during the early stages of mis 11 1 biogenic silica and d 18 odiatom values decline mirroring the slow growth in northern hemisphere ice sheets despite rigorous cleaning procedures palaeoclimatic inferences need to be treated with caution due to contamination of the d 18 odiatom record during stadial and glacial periods contamination of the d 18 odiatom record is even more significant natural environment research council nerc copyright 2008 reproduced with the permission of nerc published by john wiley sons ltd

electrical resistivity investigation of potential cavities underlying a proposed ash disposal area measurements of electrical resistivity anomalies using a wenner electrode array in a profiling mode were conducted over a 105 acre area near crystal river florida analyzed results of collected data were used to determine the likelihood of subsurface solution cavities beneath a proposed ash disposal area sounding measurements with electrode spacing values extending up to 100 feet and lee electrode measurements were used to identify and locate specific anomaly maxima identified anomalies on the order of 200 chms feet contrasted with expected values of 300 to 400 ohms feet and were attributed to lower resistivities inherent in water filled solution cavities below a shallow water table prominent cavity complexes at 5 to 15 feet depth were predicted in areas of low resistivity anomalies in the otherwise geoelectrically uniform eocene ocala limestone shallow test borings confirmed the presence of a significant concentration of shallow cavities in the predicted areas this study demonstrated the feasibility of electrical resistivity measurements as a reconnaissance tool to economically determine subsurface cavities and to aid in developmental and environmental planning

seasonal variations in sr mg and p in modern speleothems grotta di ernesto italy sub annual variations in trace element chemistry and luminescence have recently been demonstrated from speleothems and offer the potential of high resolution palaeoclimatic proxies however no studies have yet examined microscopic trace element variations in relation to modern cave conditions in this study the spatial variations in trace element sr mg and p concentrations in speleothems a stalagmite and a soda straw stalactite from the alpine ernesto cave temperature 6 6 0 1 c in a forested catchment in ne italy have been studied using secondary ion mass spectrometry sims and compared with environmental parameters and waters in the modern cave an annual lamination exists in the stalagmite and soda straw stalactite in the form of clear calcite with narrow visible layers which are uv fluorescent and interpreted to contain soil derived humic fulvic acids washed into the cave during autumn rains microanalyses were undertaken of seven annual laminae probably deposited during the 1960s in the stalagmite and seven laminae in the 1990s for the stalactite the analysis results show that sr consistently has a trough and p a peak centred on the inclusion rich layer mg shows mainly a negative covariation with sr in laminae formed in the 1990s but a positive covariation in the stalagmite formed in 1960s the spatial scale of the main geochemical variations is the same as that of annual laminae of inclusion poor and inclusion rich couplets mass balance arguments are used to show that the p is inorganic in form and presumably occurs as individual phosphate ions within the calcite most drip waters show limited chemical variations but a summer peak in trace elements in 1995 and a decrease in mg ca in the following winter are notable more pronounced covariations in mg ca and sr ca are shown by a site with highly variable drip rates where ratios increase at slow drip rates the strongest seasonal variations are found in pool waters where ratios increase reflecting significant ca removal from the water into the calcite during the winter in response to seasonal pco2 variations in cave air thus the cave waters compositions tend to reflect climate conditions such that mg ca and sr ca are tentatively interpreted to be higher when climate conditions are dry combining results from the speleothems and cave water along with the behaviour of each trace species mg ca variations in the speleothems are considered to reflect their variation in the cave waters whereas sr incorporation is also dependent on precipitation rate in this case mainly controlled by temporal variations in pco2 in the cave and conceivably also by inhibitors such as phosphate p adsorption a fraction of which is subsequently incorporated within calcite depends on aqueous phosphate concentration and water flux both of which should increase during the autumn therefore multiple trace element profiles in speleothems reflect multiple aspects of environment seasonality and conditions and hence a calibration against weather records is desirable to establish their palaeoclimatological meaning the strong annual variation of trace elements and particularly p can provide chronological markers for high resolution studies of other climate proxies such as stable isotopes

annual trace element variations in a holocene speleothem high resolution secondary ionization mass spectrometry sims analysis along the growth axis of a holocene speleothem from northern scotland reveals high frequency oscillations and longer term trends in mg ca sr ca and ba ca at the scale of the high frequency oscillations mg ca and sr ca display a well defined anticorrelation while sr ca and ba ca are positively correlated imaging of elemental ratios in two dimensions reveals that the high frequency signal is well preserved and laterally continuous across the sample tims 230th ages and annual ultraviolet luminescence banding provide chronological control and demonstrate that the high frequency cyclicity is annual trace element variations in speleothem calcite are a reflection of hydrochemical processes in the unsaturated zone overlying the cave supply effects and partitioning at the water calcite interface mg partitioning between water and calcite is temperature dependent calculations suggest that the annual mg ca oscillations may be caused by seasonal temperature changes however the longer timescale variations in mg ca are too great to be explained by this mechanism seasonal variations in water residence time in the unsaturated zone which reflect effective precipitation provide a more probable explanation for the observed annual oscillations and also explain the inverse relationship between mg ca and sr ca this record suggests that trace elements in speleothems have the potential to provide the high resolution insights into interannual palaeoclimatic variability required for assessment of general circulation models

cryogenic opal a deposition from yellowstone hot springs sub zero winter temperatures on the yellowstone plateau alter the opal a precipitation pathway offluid erupting from hot springs and geysers frozen fluid often only meters from boiling pools contains abundant opal a particles comprising sheet and filamentlike aggregations of opal a microspheres which are formed by opal a precipitation in brine pockets channels and veins by natural cryogelling unconsolidated cryogenic opal a sediment accumulates in and below water ice where it is locked until spring thaw conditions sediment is then either remobilized contributing large volumes of opal a particulate to geothermally influenced wetlands or becomes adhered in situ by dehydration and cementation this strongly seasonal opal a precipitation regime has been overlooked in investigations of sinter deposition accretion rates and microbe mineral interactions natural opal a textures recorded fromyellowstonemaybereplicatedsimplybyfreezingandthawingsyntheticsilica saltsolutioninthelaboratory cryogenicprocess may have influenced mineral precipitation and sediment accumulation in many other geothermal areas particularly active terrestrial springs located at high altitude latitude fossil systems influenced by ancient glaciations plus potential astrobiological targets e g mars and europa 2007 elsevier b v all rights reserved

206pb 230th 234u 238u and 207pb 235u geochronology of quaternary opal yucca mountain nevada abstract u th pb isotopic systems have been studied in submillimeter thick outermost layers of quaternary opal occurring in calcite silica fracture and cavity coatings within tertiary tuffs at yucca mountain nevada usa these coatings preserve a record of paleohydrologic conditions at this site which is being evaluated as a potential high level nuclear waste repository the opal precipitated from groundwater is variably enriched in 234u measured 234u 238u activity ratio 1 124 6 179 and has high u 30 313 ppm low th 0 008 3 7 ppm and low common pb concentrations measured 206pb 204pb up to 11 370 it has been demonstrated that the laboratory acid treatment used in this study to clean sample surfaces and to remove adherent calcite did not disturb u th pb isotopic systems in opal the opal ages calculated from 206pb 238u and 207pb 235u ratios display strong reverse discordance because of excess radiogenic 206pb derived from the elevated initial 234u the data are best interpreted using projections of a new four dimensional concordia diagram defined by 206pb 238u 207pb 235u 234u 238uactivity and 230th 238uactivity ages and initial 234u 238u activity ratios have been calculated using different projections of this diagram and tested for concordance the data are discordant that is observed 207pb 235u ages of 170 32 2 to 1772 40 ka are systematically older than 230th u ages of 34 1 0 6 to 452 32 ka the age discordance is not a result of migration of uranium and its decay products under the open system conditions but a consequence of noninstantaneous growth of opal combined u pb and 230th u ages support the model of slow mineral deposition at the rates of millimeters per million years resulting in layering on a scale too fine for mechanical sampling in this case u pb ages provide more accurate estimates of the average age for mixed multiage samples than 230th u ages because ages based on shorter lived isotopes are nonlinearly biased by younger mineral additions use of the combined u th pb technique to date yucca mountain quaternary opals significantly extends the age range beyond that of the 230th u dating method and shows that selected fracture pathways in the unsaturated zone felsic tuffs of yucca mountain have been active throughout the quaternary

long term time lapse microgravity and geotechnical monitoring of relict salt mines marston cheshire u k the area around the town of northwich in cheshire u k has a long history of catastrophic ground subsidence caused by a combination of natural dissolution and collapsing abandoned mine workings within the underlying triassic halite bedrock geology in the village of marston the trent and mersey canal crosses several abandoned salt mine workings and previously subsiding areas the canal being breached by a catastrophic subsidence event in 1953 this canal section is the focus of a long term monitoring study by conventional geotechnical topographic and microgravity surveys results of 20 years of topographic time lapse surveys indicate specific areas of local subsidence that could not be predicted by available site and mine abandonment plan and shaft data subsidence has subsequently necessitated four phases of temporary canal bank remediation ten years of microgravity time lapse data have recorded major deepening negative anomalies in specific sections that correlate with topographic data gravity 2d modeling using available site data found upwardly propagating voids and associated collapse material produced a good match with observed microgravity data intrusive investigations have confirmed a void at the major anomaly the advantages of undertaking such long term studies for near surface geophysicists geotechnical engineers and researchers working in other application areas are discussed

controls on trace element sr mg compositions of carbonate cave waters implications for speleothem climatic records abstract at two caves clamouse s france and ernesto ne italy cave drip and pool waters were collected and sampled at intervals over a 2 3 year period mg ca and sr ca concentration ratios corrected for marine aerosols are compared with those of bedrocks and in some cases aqueous leachates of soils and weathered bedrocks cave waters do not lie along mixing lines between calcite and dolomite of bedrock carbonate but typically show enhanced and covarying mg ca and sr ca four factors are considered as controlling processes 1 the much faster dissolution rate of calcite than dolomite allows for the possibility of increase of mg ca if water rock contact times are increased during drier conditions a theoretical model is shown to be comparable to experimental leachates 2 prior calcite precipitation along a flow path is a powerful mechanism for generating enhanced and covarying mg ca and sr ca ratios this mechanism requires the solution to lose co 2 into pores or caverns 3 incongruent dolomite dissolution has only limited potential and is best regarded as two separate processes of dolomite dissolution and calcite precipitation 4 selective leaching of mg and sr with respect to ca is shown to be important in leachates from ernesto where it appears to be a phenomenon of calcite dissolution in general selective leaching can occur whenever ca is sequestered into precipitates due to freezing or drying of soils or if there is derivation of excess sr and mg from non carbonate species the ernesto cave has abundant water supply which in the main chamber is derived from a reservoir with year round constant p co 2 of around 10 2 4 and no evidence of calcite precipitation in the karst above the cave two distinct but overlying trends of enhanced and covarying mg ca and sr ca away from the locus of bedrock compositions are due to calcite precipitation within the cave and at a variable drip site due to enhanced selective leaching at slow drip rates mg enhancement in the first chamber is due to a more dolomitic bedrock and longer residence times the clamouse site has a less abundant water supply and presents geochemical evidence of prior calcite precipitation both in the cave and in overlying porous dolomite dedolomitized limestone bedrock initial p co 2 values as high as 10 1 are inferred experimental incubations of clamouse soils which generated enhanced p co 2 and precipitated caco 3 had compositions similar to the karst waters calcite precipitation is inferred to be enhanced in drier conditions hydrological controls on cave water chemistry imply that the trace element chemistry of speleothems may be interpretable in palaeohydrological terms drier conditions tends to promote not only longer mean residence times enhancing dolomite dissolution and hence mg ca but also enhances degassing and calcite precipitation leading to increased mg ca and sr ca

a geophysical survey routine for the detection of doline areas in the surroundings of zaragoza ne spain abstract alluvial karst represents a complex system where cavities collapses subsidence and suffusion processes are the main result of dissolution of soluble rocks in the substratum underlying the detrital cover different states of filling of subsiding areas or paleocollapses and the anthropogenic filling of these areas provide a wide range of variability of physical properties resulting in ambiguities in the interpretation of geophysical surveys this complex system can be analyzed from a historical approach by means of aerial photographs old maps and farmers interviews permitting a regional planning however local analysis for building purposes needs a change on the working scale especially when karst activity is not self evident from superficial indicators as it is the case of sudden collapses related to near surface cavities below carbonate crusts in this case geophysical methods are especially useful the application of geophysical techniques in urban and building planning must deal with equilibrium between resolution ambiguity discrimination capacity and budget in this work we propose a geophysical routine to be applied in alluvial karst areas to obtain a final model based on the integration of different techniques for each technique the geophysical properties involved and its resolutions and ambiguities were analyzed the proposed sequence of applied techniques represents a progressive increase of time consumption in surveys decrease of ambiguities and higher resolution the first step is related to fast techniques magnetometry and electromagnetic em multifrequency radiation that permit to examine the whole survey area to determine anomalous subsoil behaviours the objective of the second step is to get an indirect view of subsoil structure by means of ground penetrating radar gpr electric tomography or seismic methods the last and more time consuming step concerns the development of microgravimetric surveys on anomalies identified by other techniques

anatomy of biologically mediated opal speleothems in the world s largest sandstone cave cueva charles brewer chimanta plateau venezuela abstract siliceous speleothems can be formed in sandstone caves recently opal biospeleothems have been found in the world s largest cave in precambrian sandstones on the chimanta tepui in venezuela the speleothems although reminiscent of normal stalactites and stalagmites from limestone caves are in fact large microbialites more than a dozen forms were distinguished but they share a common structure and origin they consist of two main types 1 fine laminated columnar stromatolite formed by silicified filamentous microbes either heterotrophic filamentous bacteria or cyanobacteria and 2 a porous peloidal stromatolite formed by nostoc type cyanobacteria the first type usually forms the central part and the second type the outer part of speleothems fungal hyphae metazoan and plant remains also subordinately contribute to speleothem construction the speleothems occur out of the reach of flowing water the main source of silica is the condensed cave moisture which is the main dissolution reprecipitation agent speleothems which originated by encrustation of spider threads are unique

duripans of idaho u s a in situ alteration of eolian dust loess to an opal a x ray amorphous phase abstract micromorphological techniques were used to study the silicification process in a wide range of duripans from idaho u s a investigations indicated that once loess was incorporated into a carbonaterich pan it was altered in situ to an opal a x ray amorphous phase loess became incorporated by at least two pathways each of which had a distinctive micromorphic signature the first pathway began immediately above the duripan as calcite encapsulated eolian materials to create sand sized loess agglomerates incorporation was completed either as the upward developing duripan enveloped the agglomerates or as they filled fractures in the duripans and were subsequently cemented by calcite after encasement of the loess agglomerates within the duripan aluminosilicate minerals were embayed by reaction with the calcareous soil solution the most altered loess agglomerates consisted of opal a x ray amorphous material and calcite the second pathway was initiated when fractures in the duripan were filled by eolian dust to create pedotubules the tops of pedotubules had a fabric similar to unaltered loess silasepic plasmic however the bottoms of pedotubules were invariably altered to a microgranular array of opal a and calcite impetus for alteration appears to have been high ph created by closed system conditions combined with increased surface free energy of minerals caused by elevated grain to grain pressures which led to enhanced solubility of aluminosilicate minerals the incorporation of loess and its subsequent alteration may be an important process in the silicification of calcareous pans

opal as a u pb geochronometer search for a standard we report structural geochemical and tims u th pb and u series isotopic data for several samples of precious and common opal which we tested as potential standards for ion microprobe and la icpms isotopic studies the precious opals are low in u contain high concentration of common pb and are not suitable for u pb age determinations in contrast all studied samples of common opal are enriched in uranium and contain sufficiently radiogenic pb for precise calculations of 206pb 238u and 207pb 235u dates complications in the u pb systematics are due to the presence of ubiquitous unsupported 206pb probably derived from initial excess 234u and possibly other intermediate products of 238u decay elevated concentrations and possibly anomalous isotopic composition of initial pb in some of the opals and the presence of two opal generations of different ages in one of the samples despite these imperfections two out of five studied common opals are acceptable as u pb and u series standards at least in the interim the data obtained in this study can be used to guide further search for a better opal standard

comparison of high resolution sub annual records of trace elements in a modern 1911 1992 speleothem with instrumental climate data from southwest australia high spatial resolution measurements of mg p u sr ba and na using 193 nm excimer laser ablation inductively coupled plasma mass spectrometry has revealed clearly resolvable annual cycles in a modern speleothem from southwestern australia the age of this stalagmite is established by the dates of emplacement and removal of the boardwalk where it grew 1911 1992 this chronological constraint allows for the first confident comparison between the instrumental climate record and speleothem trace element content eleven laser ablation transects across a 0 5 mm wide section of the speleothem growth axis were measured cycles that could be matched between adjacent transects were stacked into a master record to minimise variability between tracks and permit greater confidence in comparing the trace elements to the instrumental climate record p and u positively and mg inversely mimic the sudden 20 decrease in annual rainfall experienced by this region since 1965 we argue that p from seasonal vegetation decay is transported to the speleothem before it is mineralised in the soil owing to the low p retention capacity of southwest australian soils both vegetation activity and the transport of vegetation derived hpo42 are sensitive to rainfall groundwater p concentration may also influence the transport of u through the strong affinity between phosphate and uranyl ions mg appears to be sensitive to groundwater residence time as this affects drip water mg ca composition by preferential loss of ca during drier episodes when calcite precipitates before reaching the stalagmite the effects of groundwater residence time may also be important for sr on inter annual scales however the behaviour of sr on the annual cycle is opposite to mg but compatible with ba and na which are shown to depend on speleothem growth rate

geothermal reservoir monitoring with a combination of absolute and relative gravimetry microgravity monitoring is a valuable tool for mapping the redistribution of subsurface mass and for assessing changes in fluid recharge from reservoir boundaries associated with geothermal exploitation to further the development of a high precision absolute relative hybrid gravity measurement technique we conducted measurements using an absolute gravimeter in two geothermal fields in japan the absolute gravity measurements were performed in the central production areas to directly measure gravity changes caused by fluid withdrawal we succeeded in measuring long term trends within an accuracy of a few microgals in the okuaizu and ogiri fields which have been producing electricity for several years absolute measurements in the center of the field provide reliable and local reference datum anchor points for more widely distributed relative gravity measurements in the ogiri field we carried out time lapse hybrid measurements with this combination of absolute and relative gravimetry and delineated the

formation temperatures of natural coke in the lower silesian coal basin poland evidence from pyrite and clays by sem edx abstract the purpose of this paper is to show how sem edx can be applied in a study of coals altered to coke by a magnetic intrusion sem photographs reveal some textural features of a natural coke which would not be detectable using optical microscopy the similarity between images of natural and artificial coke is proof that temperatures over 350 c were experienced during contact metamorphosis crystal shapes of minerals are presented as evidence of hydrothermal activity in the contact zone and an average temperature level below 575 c pyrite is used as a geological thermometer its shape and composition showing the occurrence of incidental hot spots 750 c in contact with the dyke

consequences of slow growth for 230th u dating of quaternary opals yucca mountain nv usa thermal ionization mass spectrometry and data are reported for uranium rich opals coating fractures and cavities within the silicic tuffs forming yucca mountain nv the potential site of a high level radioactive waste repository high uranium concentrations up to 207 ppm and extremely high activity ratios up to about 106 make microsamples of these opals suitable for precise dating conventional ages range from 40 to greater than 600 ka and initial activity ratios between 1 03 and 8 2 isotopic evidence indicates that the opals have not experienced uranium mobility however wide variations in apparent ages and initial ratios for separate subsamples of the same outermost mineral surfaces positive correlation between ages and sample weights and negative correlation between ages and calculated initial are inconsistent with the assumption that all minerals in a given subsample was deposited instantaneously the data are more consistent with a conceptual model of continuous deposition where secondary mineral growth has occurred at a constant slow rate up to the present this model assumes that individual subsamples represent mixtures of older and younger material and that calculations using the resulting isotope ratios reflect an average age ages calculated using the continuous deposition model for opals imply average mineral growth rates of less than 5 mm m y the model of continuous deposition also predicts discordance between ages obtained using different radiometric methods for the same subsample differences in half lives will result in younger apparent ages for the shorter lived isotope due to the greater influence of younger materials continuously added to mineral surfaces discordant and u pb ages obtained from outermost mineral surfaces at yucca mountain support this model

mining subsidence and its effect on the environment some differing examples the impact of mining subsidence on the environment can occasionally be very catastrophic destroying property and even leading to the loss of life usually however such subsidence gives rise to varying degrees of structural damage that can range from slight to very severe different types of mineral deposits have been mined in different ways and this determines the nature of the associated subsidence some mining methods result in contemporaneous subsidence whereas with others subsidence may occur long after the mine workings have been abandoned in the latter instance it is more or less impossible to predict the effects or timing of subsidence a number of different mineral deposits have been chosen to illustrate the different types of associated subsidence that result and the problems that arise the examples provided are gold mining in the johannesburg area bord and pillar mining of coal in the witbank coalfield south africa longwall mining of coal in the ruhr district mining of chalk and limestone in suffolk and the west midlands respectively and solution mining of salt in cheshire these mineral deposits have often been worked for more than 100 years and therefore a major problem results from abandoned mines especially those at shallow depth the presence of which is unrecorded abandoned mines at shallow depth can represent a serious problem in areas that are being developed or redeveloped abstraction of natural brine has given rise to subsidence with its own particular problems and cannot be predicted although such abstraction is now inconsequential in cheshire dereliction associated with past subsidence still remains

hydrothermal alteration of deep fractured granite effects of dissolution and precipitation abstract this paper investigates the mineralogical effects of hydrothermal alteration at depth in fractures in granite a fracture accompanied by an alteration halo and filled with clay was found at a depth of 200 m in a drill core through toki granite gifu central japan microscopic observation xrd xrf epma and sxam investigations revealed that the microcrystalline clays consist of illite quartz and pyrite and that the halo round the fracture can be subdivided into a phyllic zone adjacent to the fracture surrounded by a propylitic zone in which fe phyllosilicates are present and a distinctive outer alteration front characterized by plagioclase breakdown the processes that result in these changes took place in three successive stages 1 partial dissolution of plagioclase with partial chloritization of biotite 2 biotite dissolution and precipitation of fe phyllosilicate in the dissolution pores 3 dissolution of k feldspar and fe phyllosilicate and illite precipitation associated with development of microcracks these hydrothermal alterations of the granite proceed mainly by a dissolution precipitation process resulting from the infiltration of hydrothermal fluid along microcracks such infiltration causes locally high mobility of al and increases the ratio of fluid to rock in the alteration halo these results contribute to an understanding of how granitic rock becomes altered in orogenic fields such as the japanese island arc

complex speleothem growth processes revealed by trace element mapping and scanning electron microscopy of annual layers closely spaced transects measured by excimer laser ablation inductively coupled plasma mass spectrometry ela icpms at 5 and 32 m spatial resolution are used to generate trace element composition maps ba sr mg u na p and al from mnd s1 a previously studied modern stalagmite from southwest australia treble et al 2003 epsl216 141 rainfall at the site is highly seasonal and trace elements in mnd s1 show strong seasonal variation trace element maps show that ba sr u and na concentrations coherently follow annual growth layers identified from scanning electron microscopy sem images the sem images also reveal that stalagmite growth did not proceed uniformly growth layers vary in thickness and locally pinch out highly preferential crystal growth determined by nucleation sites left by the previous year s growth may be responsible for this uneven growth layering differential crystal growth apparently causes variability of trace element concentrations along each annual layer although additional disequilibrium processes affect mg which is less distinctly banded than ba sr u and na uneven and discontinuous growth layers influence the number of annual cycles their wavelengths and seasonal amplitudes measured in any one transect this has clear implications for studies that use annual trace element cycles as chronological markers growth rate or seasonality proxies