sills associated with the bushveld complex south africa an estimate of the parental magma composition abstract four distinct ages of sills intrude the floor rocks under the bushveld complex the first is a metadolerite and pre dates the bushveld complex the middle two are generally related to the complex itself one has quench textured olivine and orthopyroxene crystals and chemically equates to the parental magma of the bushveld complex the second suite is a hypersthene microgabbro representative of the second major injection of magma into the complex the last is doleritic and does not obviously correlate with any portion of the layered sequence the sills genetically related to the complex display several features 1 lack of chilled margins coarse grain size ability to melt country rock xenoliths extreme heterogeneity 2 atypical of normal sills but explicable in their present context

a clinoenstatite bearing cumulate olivine pyroxenite from howqua victoria the howqua olivine pyroxenite of eastern victoria australia intrudes a metamorphosed sequence of cambrian high mg lavas it crystallized an unusual mineral assemblage cr rich magnesiochromite olivine fo94 and protoenstatite now inverted to polysynthetically twinned clinoenstatite residual liquid crystallized strongly zoned interstitial pyroxenes followed by pargasite pargasite often showing quench habit crystallized in interstitial glass which is now altered to serpentine

the j m platinum palladium reef of the stillwater complex montana ii origin by double diffusive convective magma mixing and implications for the bushveld complex sequences of cumulates form concurrently by downdip accretion from a column of liquid layers that are primarily separated by diffusive interfaces the low cumulates grow in advance of the upper cumulates in accord with their higher crystallization temperatures an important observation is that mixing of the two parent liquids lowers their crystallization temperatures and consequently should produce unsaturated hybrids that could dissolve earlier cumulates the repetition of cyclic units above the j m reef is explained by having periodic additional injections of dense magma beneath the subsiding column of crystallizing liquid layers neither the j m reef nor the bushveld ore zones should ever have been continuous across the floor of their respective magma chambers and for bushveld the circumstances resulted in zones that are actually minable modified journal abstract

the origin of fluoride in groundwater supply to hermosillo city sonora mexico anomalous high fluoride concentration up to 7 59 mg dm3 is found in groundwater from la victoria area this water is used to supply drinking water to hermosillo city sonora geochemistry of groundwater relationship between physicochemical parameters hydrogeology and geologic setting were correlated to define the origin and the geochemical mechanisms of groundwater fluorine enrichment high fluoride concentration is associated with high bicarbonates ph and temperature and it decreases toward the west and south of the area fluoride is in negative correlation to calcium concentration sodium sulphate facies of regional deep water flow are related to high fluoride concentration high electric resistivity rocks associated with granites from the sierra bachoco basement might be the deep source of fluoride outcropping of sierra bachoco in the west causes upward regional flow groundwater of longer residence time can be pumped there the anomalous area is restricted to la victoria because calcareous paleozoic rocks outcrop to the south

investigation of fluoride contamination and its mobility in groundwater of simlapal block of bankura district west bengal india the occurrence of dental skeletal fluorosis among the people in the study area provided the motivation to assess the distribution severity and impact of fluoride contamination in groundwater of bankura district at simlapal block west bengal india to meet the desired objective groundwater samples were collected from different locations of laxmisagar machatora and kusumkanali regions of simlapal block at different depths of tube wells in both pre and post monsoon seasons geochemical results reveal that the groundwaters are mostly moderate to hard water type of total groundwater samples 37 are situated mainly in relatively higher elevated region containing fluoride above 1 5 mg l indicating that host aquifers are severely affected by fluoride contamination machatora region is highly affected by fluoride contamination with maximum elevated concentration of 12 2 mg l several symptoms of fluorosis among the different age groups of people in laxmisagar and machatora areas are indicating consumption of fluoridated water for prolonged period the groundwater samples were mainly na ca hco3 type and rock dominance indicating the dissolution of minerals taking place ion exchange between oh ion and f ion present in fluoride bearing mineral is the most dominant mechanism of fluoride leaching high concentration of na and hco3 increases the alkalinity of the water providing a favorable condition for fluoride to leach into groundwater from its host rocks and minerals

experimental data at 3 kbars pressure on parental magma to the bushveld complex experimental studies mainly under 3 kbars pressure have been undertaken on representative samples to determine if any of these compositions could be parental magma to the bushveld complex one such composition with 12 5 mgo mg mg fe of 0 72 and quartz normative crystallizes olivine fo88 as liquidus mineral at about 1 300 c followed at only slightly lower temperature by orthopyroxene at 3 kbars pressure there is a temperature drop of over 100 c before the appearance of plagioclase and finally clinopyroxene this crystallization sequence is in excellent agreement with the observed sequence in the lower part of the bushveld complex

factors affecting arsenic concentration in groundwaters from northwestern chaco pampean plain argentina the concentration of arsenic measured in groundwater from three aquifers in the study area located in the eastern tucuman province argentina mostly depends on the lithology but the spatial and temporal variations of concentrations seem to be also controlled by ph changes climatic factors and human perturbations the highest concentrations of as more than 1 000 g l 1 were found in the shallow aquifer made of as rich loess while the lowest concentrations were measured in the deep confined aquifer consisting of alternating layers of alluvial sands gravels and clays intermediate values were measured in the semiconfined aquifer made of the fluvial sediments deposited in the sali river valley that alternate in the upper part of the sedimentary sequence with layers of loess because most of as in the loess is considered to be adsorbed onto fe oxyhydroxide coatings the increase of ph in the flow direction west east leads to increasing arsenic concentrations towards the eastern border of the study area the decomposition of organic wastes poured into the sali river or associated with local and diffuse sources of contamination in the eastern part of the study area depletes dissolved oxygen which leads to the reductive dissolution of fe and mn oxyhydroxides and to the subsequent release of the adsorbed and co precipitated as this process mainly affects shallow groundwater and the upper part of the semiconfined aquifer geochemical and hydrological data also suggest that rising water table levels at the end of the wet season may also lead to reductive dissolution of as rich fe oxyhydroxides in the shallow aquifer

the scourie dyke suite petrogenesis and geochemical nature of the proterozoic sub continental mantle the petrogenesis of bronzite picrite olivine gabbro norite and quartz tholeiite dykes which make up the 2 39 b y scourie dyke swarm cutting the archaean lewisian gneisses of n w scotland is interpreted on the basis of their major and trace element geochemistry most of the dykes bear primary amphibole and or phlogopite and with one exception are all hypersthene or quartz normative apart from one tholeiite dyke which shows relative light rare earth element depletion all the dykes show enrichment in light rare earths and large ion lithophile elements they do not however show an equivalent enrichment in other incompatible high field strength ions such as nb and ta and in this respect resemble island arc and calc alkaline basalts the different dyke types have distinctive rare earth patterns and other trace element ratios which are maintained over a range of major element compositions

groundwater arsenic variations the role of local geology and rainfall high concentrations of as were detected in the aquifer system of zimapan valley mexico arsenic is related to a multisource system both natural and anthropogenic the main source is as bearing rocks groundwater as variations were detected in the more polluted urban deep well variations were correlated with the precipitation regime and with the hydrogeologic and geologic framework an induced as transport mechanism related mainly with the rainfall regime is proposed

tectonic and petrogenetic implications of major and rare earth element chemistry of troodos glasses cyprus chilled pillow margins dike margins and interpillow hyaloclastites from the extrusive sequences of the troodos ophiolite cyprus reveal two compositional groups of glasses 1 andesites to dacitic andesites containing plagioclase ca rich pyroxene and ca poor pyroxene as phenocrysts occur in a stratigraphically low position and 2 basaltic andesites containing olivine and ca rich pyroxene phenocrysts occur in an upper position in the lava sequence the glasses contain between 52 and 62 wt sio2 and have mg numbers between 65 and 27 the troodos glasses are very similar to basaltic andesite or boninitic glasses from the mariana trench and together these two groups define a trend intermediate between typical calcalkaline and tholeiite evolutions the troodos glasses are inferred by difference to contain 3 4 5 wt h2o which is taken to be of primary origin and to reflect the ocean depth of extrusion and quenching based on normative projections in the basalt phase diagram there are indications that elevated water pressures during formation of the phenocryst assemblages may have shifted the isobaric pseudo quaternary peritectic towards silica quantitative crystal fractionation models fail to explain the observed chemical variation it is suggested that the chemical variation may result from high pressure melts equilibrated to lower pressure 2 and 3 phase cotectic relations some mariana and the troodos glasses have similar ree patterns with relatively low abundances depletion in lree and flattening in the hree region the close similarities between the troodos and the mariana glasses point to an identical tectonic and petrogenetic control on their origin

the fluoride in the groundwater of guarani aquifer system the origin associated with black shales of parana basin this work presents petrological and geochemical results of the black shales interval from permian and devonian strata of the parana basin brazil and its relationships with fluoride of groundwater from guarani aquifer system the guarani aquifer located in south brazil uruguay paraguay and argentine presents contents of fluoride higher than the brazilian accepted potability limits several hypotheses have been presented for the origin of the fluoride in the groundwater of the guarani aquifer microcrystalline fluorite was registered in black shales of ponta grossa and irati formations from parana basin the results shown in this work suggest that fluoride present in groundwater of guarani aquifer can be originated in deeper groundwater that circulates in ponta grossa and irati formations the interaction of the groundwater coming from deeper black shales with the groundwater bearing aquifer guarani system occurs through regional fragile structures faults and fractures that constitute excellent hydraulic connectors between the two sedimentary packages the microcrystalline fluorite registered in ponta grossa and irati formations can be dissolved promoting fluoride enrichment in groundwater of these black shales and guarani aquifer system

groundwater arsenic in the chaco pampean plain argentina case study from robles county santiago del estero province in large parts of rural argentina people depend on groundwater whose as content exceeds the argentine drinking water standards 0 05 mg l 1 the most affected areas are located in the chaco pamp

two high precision u pb zircon ages for the sudbury nickel irruptive two independent u pb zircon ages were measured using norite samples from the north and south ranges of the sudbury nickel irruptive ages of and ma were obtained with a probability of fit within experimental error of 51 and 57 respectively previous determinations by the rb sr whole rock method gave ages between about 1700 and 2000 ma with errors of the order of 100 ma the difference in precision is inherent in the two methods zircons from the norite are highly radiogenic and almost concordant whereas rb sr whole rock ages are determined by very small increments in radiogenic 87sr the two zircon ages have completely different discordia so that all simple models for lead loss by continuous diffusion can be excluded

water salt and sodium dynamics in a natraquoll in argentina abstract the influence of soil and environmental factors on water and salt dynamics in a typic natraquoll of the center of the flooding pampa argentina was studied in phreatimeters the water table reached the soil surface during floods but in the soil profile it was never above the bottom of the b31 horizon 0 65 m this horizon and the over laying b22 one showed a permanent unsaturation the a1 b1 and b21 horizons however often became saturated with water the typical floods in the region are caused by the accumulation of rainwater on the previously saturated upper horizons simultaneously phreatic water undergoes an abrupt increase in electrical conductivity ecw these saline peaks ecw of up to 45 00 ds m 1 caused the immediate salinization of the deep horizons probably by diffusion the arrival of salts at the soil surface was episodic and by convection however salt leaching prevailed in the course of time in the upper horizons the soil saturation extracts showed a balanced proportion of anions but among cations na prevailed over mg ca and k soil alkalinity was low and with some significant variations in the surface horizons that depended on episodic salt rises or salt leaching processes in the deep horizons soil remained permanently natric this dynamic balance of water and salt showed that in this part of the region the soil profile exhibits two zones which are relatively independent of each other each represents different stages of the evolution as stated by gedroiz s theory the deep horizons undergo a continuous salinization and alkalinization process the upper horizons tend to be similar to zonal soils the slight halomorphism in this profile zone is due to the episodic salt rises

the origin of fluoride in the granitic aquifer of porto alegre southern brazil the porto alegre region southern brazil comprises a fractured aquifer system constituted by pre cambrian granitic and gneissic rocks and a porous aquifer system formed by cenozoic muddy sandy to sandy sediments a model is presented for the origin of the fluoride in the groundwater of the fractured aquifer system based on ionic interrelations a statistical analysis of physicochemical parameters and geochemical modeling the fluoride is present at levels of up to 6 13 mg l in groundwater and it arises due to the dissolution of secondary fluorite filling fractures in the granitic and gneissic rocks the dissolution of fluorite occurs at the same time as calcite and dolomite solubilization the statistical analysis identified three chemically distinct groups named 1 2 and 3 and two subgroups 1a and 1b of groundwater in the fractured aquifer the most significant differences between these groups are the different concentration ranges of fluoride calcium bicarbonate magnesium total dissolved solids and chloride and ph values as well as the correlations between them the compositional evolution of each groundwater group is governed mainly by how much high salinity groundwater from the porous aquifer system is mixed with them and the different thermodynamic equilibrium conditions of calcite dolomite and fluorite

field relations and strontium isotope systematics of the marginal rocks of the eastern bushveld complex the well exposed basal contact of the eastern bushveld complex was mapped at scales of 1 10 000 and 1 20 000 along 130 km of strike and through a 9 km vertical section field relations petrography and geochemistry of the marginal rocks and associated sills have aided their subdivision into two main groups a broadly pyroxenitic group rims the complex from its base to the top of the pyroxenitic subzone of the critical zone a gabbroic group occurs above this level each group consists of a number of closely related rock types most of which have sill analogs rocks of the first group b1 include pyroxenites norites and peridotites all of which may have quench textures all contain orthopyroxene en 78 plagioclase an 65 and chromite with subordinate clinopyroxene and biotite rare earth element patterns are mostly strongly fractionated ce n yb n approximately 10 and have 40x chondritic abundances at ce their initial strontium isotope ratios at 2 05 b y fall in the range 0 7032 to 0 7057 and rb sr ratios approximate 0 2 the gabbroic group consists of microcrystalline two pyroxene gabbros b2n and b3n and their coarser grained equivalents b2 and b3 that border the upper critical and main zones respectively mineral assemblages are dominated by plagioclase approximately an 55 clinopyroxene and orthopyroxene approximately en 63 with abundant magnetite and traces of ilmenite and biotite their rare earth element patterns are less fractionated than b1 rocks the b2n and b2 family have ce n yb n approximately 6 and 30x chondritic abundances at ce the b3n and b3 rocks have ce n yb n approximately 3 6x chondritic abundances at ce and pronounced positive eu anomalies strontium isotope initial ratios at 2 05 b y fall in the range 0 706 to 0 708 and the rb sr ratios are approximately 0 02 whole rock and sr isotope compositions of the peridotitc sills can be successfully simulated by a model involving olivine fractionation from a liquid with an initial sr isotope ratio r 0 similar to that of the transition zone 0 7056 a fraction of such liquid enriched in cumulus olivine crystals when mixed with up to 30 percent of a pyroxenitic liquid with low r 0 0 7034 yields a product having the isotopic and compositional characteristics of the peridotite sills a continuum exists in the initial sr ratios through the pyroxenitic and gabbroic marginal rocks suggesting that these represent mixtures of at least two sources with distinct initial sr isotope ratio characteristics it is argued that neither magma aging nor crustal contamination adequately accounts for the sr isotope characteristics of the marginal rocks or their derived cumulates the unusual chemistry of the pyroxenitic early liquids sio 2 approximately 55 mgo approximately 13 coupled with high concentrations of incompatible elements should be considered primary

recovering permanent displacements from seismic records of the june 9 1994 bolivia deep earthquake 1 ground displacements of the 1994 deep bolivia earthquake are recovered from six on scale velocity records of a temporary array located 600 km south of the epicenter i first removed the instrument sts 2 response using a time domain deconvolution to correct for baseline drift in the deconvolutions i used two separate windows of the trace one before and one after the transient motion from the earthquake and fit them simultaneously with a 4th order polynomial the amount of permanent displacement is included in the post transient signal window and is determined together with the polynomial coefficients by a least squares inversion the polynomial is then subtracted from the displacement to remove the drift i found that this technique produces robust displacement waveforms as demonstrated by similar results at all stations the obtained vertical permanent subsidences range from 5 5 to 6 4 mm which agree well with predictions by using normal mode summation

a review of the source behaviour and distribution of arsenic in natural waters the range of as concentrations found in natural waters is large ranging from less than 0 5 g l 1 to more than 5000 g l 1 typical concentrations in freshwater are less than 10 g l 1 and frequently less than 1 g l 1 rarely much higher concentrations are found particularly in groundwater in such areas more than 10 of wells may be affected defined as those exceeding 50 g l 1 and in the worst cases this figure may exceed 90 well known high as groundwater areas have been found in argentina chile mexico china and hungary and more recently in west bengal india bangladesh and vietnam the scale of the problem in terms of population exposed to high as concentrations is greatest in the bengal basin with more than 40 million people drinking water containing excessive as these large scale natural as groundwater problem areas tend to be found in two types of environment firstly inland or closed basins in arid or semi arid areas and secondly strongly reducing aquifers often derived from alluvium both environments tend to contain geologically young sediments and to be in flat low lying areas where groundwater flow is sluggish historically these are poorly flushed aquifers and any as released from the sediments following burial has been able to accumulate in the groundwater arsenic rich groundwaters are also found in geothermal areas and on a more localised scale in areas of mining activity and where oxidation of sulphide minerals has occurred the as content of the aquifer materials in major problem aquifers does not appear to be exceptionally high being normally in the range 1 20 mg kg 1 there appear to be two distinct triggers that can lead to the release of as on a large scale the first is the development of high ph 8 5 conditions in semi arid or arid environments usually as a result of the combined effects of mineral weathering and high evaporation rates this ph change leads either to the desorption of adsorbed as especially as v species and a range of other anion forming elements v b f mo se and u from mineral oxides especially fe oxides or it prevents them from being adsorbed the second trigger is the development of strongly reducing conditions at near neutral ph values leading to the desorption of as from mineral oxides and to the reductive dissolution of fe and mn oxides also leading to as release iron ii and as iii are relatively abundant in these groundwaters and so4 concentrations are small typically 1 mg l 1 or less large concentrations of phosphate bicarbonate silicate and possibly organic matter can enhance the desorption of as because of competition for adsorption sites a characteristic feature of high groundwater as areas is the large degree of spatial variability in as concentrations in the groundwaters this means that it may be difficult or impossible to predict reliably the likely concentration of as in a particular well from the results of neighbouring wells and means that there is little alternative but to analyse each well arsenic affected aquifers are restricted to certain environments and appear to be the exception rather than the rule in most aquifers the majority of wells are likely to be unaffected even when for example they contain high concentrations of dissolved fe

partition of arsenic in soils sediments and the origin of naturally elevated concentrations in groundwater of the southern pampa region argentina excessive arsenic concentrations above the argentinean and who guidelines for drinking water 10 g l 1 affects shallow aquifers of the southern pampean plain argentina hosted in the pampean and the post pampean formations loess and reworked loess plio pleistocene holocene health problems related to high as concentrations in drinking waters are known as endemic regional chronic hydroarsenicism hydrochemistry of shallow groundwaters and soil geochemistry were investigated aiming to 1 understand the partition of as in the solid phase and its relationship with unacceptable as concentrations in waters 2 identify the provision source of as to groundwaters only 5 of the samples had as concentrations 10 g l 1 in 27 as concentrations ranged from 10 to 50 g l 1 and in 58 it reached 60 500 g l 1 the coarse fraction 50 2 000 m hosts about 27 of the total as in the solid phase being positively correlated to ba p 0 01 r2 0 93 about 70 is included in the 2 m fraction and had positive correlations of as fe p 0 05 r2 0 85 and as cr p 0 05 r2 0 68 soils and sediment sand fractions of vadose zones are the primary sources of as in shallow groundwater while adsorption desorption processes codisolution coprecipitation and evaporation during the dry seasons raise as concentrations in waters exceeding the guideline value for drinking water

strontium isotope evidence for preserved density stratification in the main zone of the bushveld complex south africa the bushveld complex formed from two isotopically distinct magmas magma addition and mixing can be tracked by measuring initial strontium isotope ratios of cumulates rocks with ratios of 0 7065 lie below the lower 2 2 km of the main zone ratio 0 7085 whereas those with ratios of 0 7073 lie above it this unit represents a liquid layer intruded into the density stratified magma pile near the base of the chamber the merensky reef was produced by mixing of the pile with underlying trapped liquid enriched in precious metals

hydrogeochemistry of arsenic and other inorganic constituents in groundwaters from la pampa argentina groundwaters from quaternary loess aquifers in northern la pampa province of central argentina have significant quality problems due to high concentrations of potentially harmful elements such as as f no3 n b mo se and u and high salinity the extent of the problems is not well defined but is believed to cover large parts of the argentine chaco pampean plain over an area of perhaps 106 km2 groundwaters from la pampa have a very large range of chemical compositions and spatial variability is considerable over distances of a few km dissolved as spans over 4 orders of magnitude 4 5300 g l 1 and concentrations of f have a range of 0 03 29 mg l 1 b of 0 5 14 mg l l v of 0 02 5 4 mg l 1 no3 n of 0 2 140 mg l 1 mo of 2 7 990 g l 1 and u of 6 2 250 g l 1 of the groundwaters investigated 95 exceed 10 g as l 1 the who guideline value and 73 exceed 50 g as l 1 the argentine national standard in addition 83 exceed the who guideline value for f 1 5 mg l 1 99 for b 0 5 mg l 1 47 for no3 n 11 3 mg l 1 39 for mo 70 g l 1 32 for se 10 g l 1 and 100 for u 2 g l 1 total dissolved solids range between 730 and 11400 mg l 1 the high values resulting mainly from evaporation under ambient semi arid climatic conditions the groundwaters are universally oxidising with high dissolved o2 concentrations groundwater phs are neutral to alkaline 7 0 8 7 arsenic is present in solution predominantly as as v groundwater as correlates positively with ph alkalinity hco3 f and v weaker correlations are also observed with b mo u and be desorption of these elements from metal oxides especially fe and mn oxides under the high ph conditions is considered an important control on their mobilisation mutual competition between these elements for sorption sites on oxide minerals may also have enhanced their mobility weathering of primary silicate minerals and accessory minerals such as apatite in the loess and incorporated volcanic ash may also have contributed a proportion of the dissolved as and other trace elements concentrations of as and other anions and oxyanions appear to be particularly high in groundwaters close to low lying depressions which act as localised groundwater discharge zones concentrations up to 7500 g l 1 were found in saturated zone porewaters extracted from a cored borehole adjacent to one such depression concentrations are also relatively high where groundwater is abstracted from close to the water table presumably because this zone is a location of more active weathering reactions the development of groundwaters with high ph and alkalinity results from silicate and carbonate reactions facilitated by the arid climatic conditions these factors together with the young age of the loess sediments and slow groundwater flow have enabled the accumulation of the high concentrations of as and other elements in solution without significant opportunity for flushing of the aquifer to enable their removal

origin of high magnesian andesites in the setouchi volcanic belt southwest japan i petrographical and chemical characteristics high magnesian andesites of middle miocene age occur in southwest japan forming an obvious volcanic belt these andesites have low feo mgo ratios 0 546 0 931 and are rich in ni 101 312 ppm co 30 0 45 1 ppm and cr 208 756 ppm they are relatively aphyric phenocrysts 10 vol and the phenocrysts of magnesian olivine fo88 are in equilibrium with the host high magnesian andesite magmas on the basis of the fe mg exchange partitioning these features suggest that the high magnesian andesites are not differentiated or accumulative they appear to represent primary andesites generated in the upper mantle these southwest japanese high magnesian andesites are rich in incompatible elements and show light rare earth enrichment relative to boninites suggesting that the former is derived from a less depleted mantle source than the latter

geochemical appraisal of fluoride contamination of groundwater in the nayagarh district of orissa india the occurrence of high concentrations of fluoride in groundwater 1 5 mg l in the villages of singhpur and sagaragan in the nayagarh district of orissa and its relation with the fluoride rich hot spring water 10 mg l located nearby have been studied the composition of the hot spring water is very comparable to the other thermal waters of the world thermodynamic considerations show that more than 65 of the groundwater and hot spring water samples are oversaturated with calcite and only four samples are oversaturated with fluorite fluoride concentration shows a positive relation to sodium bicarbonate and ph and a negative relation to calcium and magnesium in fluoride rich groundwater and hot spring water principal component analysis shows that the fluoride rich groundwater was produced due to a mixing of hot spring water with the surrounding groundwater studies of the saturation index of fluorite with log electrical conductivity also indicate mixing of hot spring water with the surrounding groundwater the spatial distribution of fluoride in groundwater follows the topography of the area

enrichment of fluoride in groundwater under the impact of saline water intrusion at the salt lake area of yuncheng basin northern china long term intake of high fluoride groundwater causes endemic fluorosis this study for the first time discovered that the salt lake water intrusion into neighboring shallow aquifers might result in elevation of fluoride content of the groundwater two cross sections along the groundwater flow paths were selected to study the geochemical processes controlling fluoride concentration in yuncheng basin northern china there are two major reasons for the observed elevation of fluoride content one is the direct contribution of the saline water the other is the undersaturation of the groundwater with respect to fluorite due to salt water intrusion which appears to be more important reason the processes of the fluorine activity reduction and the change of na ca ratio in groundwater induced by the intrusion of saline water favor further dissolution of fluorine bearing mineral and it was modeled using phreeqc with the increase in na concentration by adding nacl or na2so4 as na source calcium content kept invariable the increase of naf concentration was rapid at first and then became slower and the concentrations of hf hf2 caf and mgf were continuously decreasing the geochemical conditions in the study area are advantageous to the complexation of f with na and the decline of saturation index of caf2 regardless of the water type cl na or so4 na type water

spatial variation in arsenic and fluoride concentrations of shallow groundwater from the town of shahai in the hetao basin inner mongolia abstract twenty nine wells were selected for groundwater sampling in the town of shahai in the hetao basin inner mongolia four multilevel samplers were installed for monitoring groundwater chemistry at depths of 2 5 20 m results show that groundwater as exhibits a large spatial variation ranging between 0 96 and 720 g l with 71 of samples exceeding the who drinking water guideline value 10 g l fluoride concentrations range between 0 30 and 2 57 mg l there is no significant correlation between as and f concentrations greater as concentrations were found with increasing well depth however f concentrations do not show a consistent trend with depth groundwater with relatively low eh has high as concentrations indicating that the reducing environment is the major factor controlling as mobilization low as concentrations 2 into the aquifers and lead to reducing conditions that favor as release sediment composition is an additional factor in determining dissolved as concentrations in aquifers composed of yellowish brown fine sands at depths around 10 m groundwater generally has low as concentrations which is attributed to the high as adsorption capacity of the yellow brown fe oxyhydroxide coatings fluoride concentration is positively correlated with ph and negatively correlated with ca 2 concentration all groundwater samples are over saturated with respect to calcite and under saturated with respect to fluorite dissolution and precipitation of ca minerals such as fluorite and calcite and f adsorption desorption are likely controlling the concentration of f in groundwater

age and origin of early proterozoic dolerite dykes in south west greenland samples of three dolerite dykes from south west greenland give a pooled weighted mean rb sr whole rock isochron age of 2 130 65 ma initial 87sr 86sr ratios are 0 70155 0 00018 for one of the dykes naujat and 0 70277 0 00012 for the other two torssut and akinaq a fourth dyke qaqarssuaq did not yield an isochron torssut samples have significantly lower initial 207pb 204pb ratios than samples from the naujat dyke indicating that the torssut dyke has been affected by crustal contamination

fluoride variations in groundwater of an area in buenos aires province argentina spatial variations of fluoride concentration in groundwater in the town of saldungaray argentina affect water quality for human supply and decrease the aquifer reserves the study region is a piedmont area located near a hill area west and the fluvial valley of the sauce grande river east two hydrogeological units can be identified bedrock and clastic sediments these sediments consist of sandy silt with a variable amount of calcium carbonate its greatest thickness occurs near the river where it is 60 m groundwater flow coincides with topography fresh water is exploited from this unit and it has low salt contents dissolved solids 400 to 800 mg l fluoride concentration varies between 0 2 and 5 mg l the groundwater flow and hydrogeological characteristics related to spatial variations of fluoride content are analyzed the quality of water is a critical parameter in determining the overall quality of human lives and the occurrence of high fluoride concentrations can have a pronounced impact on groundwater quality

arsenic and fluoride in a loess aquifer in the central area of argentina the objective of this study is to analyze the geochemical conditions associated with the presence of arsenic as and fluoride f in the phreatic aquifer of coronel moldes in the central sector of the argentine chacopampean plain the studied aquifer is composed of silty sand sediments of aeolian origin typically loess like sediments the geochemical composition of water varies from sodium bicarbonate to sodium sulfate chloride water as contents range from low concentrations below detec tion level to 250 lg l high values of f up to 12 mg l were recorded a high as f correlation was found r 2 0 84 the ph varied from 7 31 to 8 85 and the nitrates reached concentrations up to 200 mg l indicating an oxidant environment the highest values of as and f agreed with sodium bicarbonate waters as well as with the highest values of ph recorded there was a high correlation between as and f as well as between as and the na ca ratio the composition and texture of loess low permeability and hydraulic gradients together with the geochemical features of sodium bicarbonate waters are proper conditions for the mobilization of as and f in groundwater in the central area of argentina

incompatible trace element behavior in the bushveld complex borehole core from the uppermost 500 m of the rustenburg layered suite of the bushveld complex has been analyzed for rb sr zr y and nb plots of absolute trace element abundance and trace element ratios against stratigraphic height are presented these are used to test for multiple injection of magma and postcumulus migration of residual liquid these and previously published data are used to support the hypotheses that there was a new injection of magma above the merensky reef and that large scale infiltration metasomatism did not occur no evidence from incompatible element data exists for an addition of magma near the pyroxenite marker where a distinct reversal in cumulus mineral composition occurs however this may be the result of relatively small degrees of fractionation of the host magma prior to the addition of new magma the ability to recognize the entry of new magma may be restricted by the analytical precision the uppermost 500 m of the layered sequence appears to behave as a single broadly homogeneous magma in showing a systematic predictable upward increase in incompatible element abundances consistent with a model assuming 10 to 30 percent trapped liquid in the cumulate deviations from the predicted trends for zr y and nb are attributed to these elements being compatible in magnetite for zr and apatite for y and nb which are present in the uppermost rocks

the chronology of magma influxes to the eastern compartment of the bushveld complex as exemplified by its marginal border groups the floor contact of the eastern compartment of the bushveld complex has been mapped in detail for 130 km field relations petrographical and geochemical data have enabled 3 important marginal border groups and a possible parent to the lower zone to be demarcated these represent the 4 main magma influxes which formed the malic phase of the bushveld complex and are in chronological order 1 a contaminated magnesian basalt b1 which gave rise to a saucer shaped laminated marginal zone at the base of the complex with diverse related sills 2 a harrisitic peridotite representing quenched lower zone magma 3 a border group to the more evolved probably basaltic critical zone magma which was intruded in two phases an early quenched norite facies n being followed by a chilled bulk critical zone facies b2 which forms a skin to the whole critical zone finally 4 a border group to the main and upper zone b3 which represents an early magnesian pulse of this last immense volume of tholeiitic liquid there is also evidence for minor influxes of magma within the critical zone and main zone

emplacement and cooling of komatiite lavas we propose that komatiite lavas were emplaced as turbulent flows accompanied by vigorous forced convection with cooling rates often in excess of hundreds of c h 1 they melted and assimilated up to 10 of the ground over which they flowed forming deep channels nickel sulphide mineralization may have resulted from incorporation of sulphur rich sediment after emplacement high cooling rates persisted resulting in spinifex textures due to compositional convection

petrology of the apollo 11 highland component new data for 38 highland fragments hand picked from apollo 11 coarse fines are reported petrographic mineralogic and bulk chemical data show that 1 the apollo 11 highland component is non kreepy and like that of apollo 16 2 poikilitic rocks granulitic breccias and the anorthosite norite troctolite suite are the most abundant rock types followed by polymict breccias and glasses 3 both the ferroan anorthosite and mg rich plutonic suites are represented in the apollo 11 highland component 4 except for one sample the intermediate k fra mauro and high k fra mauro groups are not represented the data and observations are consistent with local derivation of the highland material from beneath relatively thin basalt flows and addition to the regolith via vertical mixing

trace element variations in atlantic ocean basalts and proterozoic dykes from northwest scotland their bearing upon the nature and geochemical evolution of the upper mantle abstract trace element data on ocean floor and ocean island basalts from the atlantic and from early proterozoic dyke swarms are considered in relation to the nature and causes of upper mantle heterogeneity studies of dredged and drilled basalts from the north atlantic have enabled the compositions of erupted ridge basalts to be monitored in space and time and have revealed the following features a that while melting processes may give rise to appreciable ree variation at a particular site ratios of the more incompatible elements remain remarkably consistent in basalts erupted at a particular ridge segment for tens of millions of years and b that there are major differences in incompatible element ratios in basalts erupted at different ridge segments the relationships suggest that the volumes of mantle with these characteristic incompatible element ratios must be large but that the processes associated with basalt generation are not capable of significantly changing incompatible element ratios nevertheless the processes which have produced these incompatible element variations must be incorporated into any model for mantle evolution our preferred model invokes both crustal extraction and incipient mantle melting as the major mechanisms for changing incompatible element mantle source regions both represent very small degrees of mantle melting a depleted upper mantle variably veined with incompatible element enriched liquids or fluids derived through incipient melting at greater depths is most consistent with the trace element and isotopic compositions of north atlantic basalts many of which are not normal mid ocean ridge basalts n type morb ocean island basalts may represent more intensely veined and in some cases at least more refractory sources sampled at lower degrees of partial melting mantle from which incipient melts have been removed probably represents the n type morb source extraction of crustal material having high contents of the large ion lithophile elements but low contents of the high field strength ions ie ta and nb from a veined metasomatized mantle source leaves the upper mantle residue enriched in ta and nb relative to the large ion lithophile elements this might explain the enrichment of ta and nb in most mantle sources of continental and ocean island basic lavas mantle sources enriched by incipient melting processes are continually dissipated by mantle convection but may be preserved for a significant time beneath stable continents trace element data on early proterozoic tholeiitic to picritic dyke swarms from scotland suggest that short term mantle heterogeneities may have existed beneath the region at that time and could have been related to the processes of crustal generation 600 m y earlier

early late cretaceous ca 93 ma norites and hornblendites in the milin area eastern gangdese lithosphere asthenosphere interaction during slab roll back and an insight into early late cretaceous ca 100 80 ma magmatic flare up in southern lhasa tibet abstract at more than 500 km in length the mainly jurassic early eocene gangdese batholith is one of the most important constituents of the southern lhasa sub block and provides an ideal site for study of tibetan orogenesis recent studies on gangdese intermediate felsic intrusive rocks mainly granites demonstrate that remarkable crustal growth as well as an early late cretaceous ca 100 80 ma magmatic flare up event occurred in southern tibet however the mechanism that drove this magmatic event and its relationship to crustal growth event are not yet clear here we report detailed petrological geochronological geochemical and sr nd hf isotopic data for recently identified norites and hypersthene bearing hornblendites in the milin area southern lhasa sub block these mafic rocks are dated at early late cretaceous ca 93 ma and are characterized by relatively uniform sr nd hf isotopic compositions 87sr 86sr i 0 7042 to 0 7047 end t 2 9 to 3 6 and ehf t zircon 10 9 to 17 0 suggesting that they evolved from similar parental magmas the milin norites and hornblendites are likely to be the products of mineral fractionation and accumulation from a common parental magma during the early and late stages of the magma evolution respectively thermometric calculations indicate that pyroxenes from the milin norites have high crystallization temperatures 1240 1349 c the parental magmatic compositions calculated from pyroxene trace element compositions in the milin norites show slightly flat to enriched light rare earth element lree patterns la yb n 2 9 3 4 la gd n 2 1 2 9 with variable negative nb anomalies nb la n 0 18 0 81 indicating their dual or hybrid geochemical characteristics we suggest that their parental magmas may have been generated by the interaction of upwelling asthenospheric and metasomatized lithospheric mantle taking into account the spatial and temporal distribution of the mesozoic magmatic rocks and regional paleomagnetic data we further suggest that the early late cretaceous magmatic flare up in the southern lhasa sub block was also triggered by the asthenospheric upwelling which resulted from roll back of subducted tethyan oceanic slab

ancient subcontinental mantle a source for k rich orogenic volcanics active island arc volcanoes west of the arc continent collision between the sunda arc and northwest australia are erupting mafic volcanics that range from calc alkaline basalts through shoshonitic trachybasalts to leucitites these mafic arc volcanics display a threefold enrichment in k rb sr ba la and nb contents along the arc from bali to flores increasing toward the collision zone the enrichment is very well correlated with increasing 87sr 86sr and decreasing 143nd 144nd values the geochemical and isotopic data imply that the arc volcanics are being generated from two source materials one yielding material poor in k group elements with relatively low 87sr 86sr 0 707 values and low 143nd 144nd values the k rich material appearing in the arc volcanoes is being derived from ancient subcontinental mantle involved in the collision zone eastern sunda k rich mafic volcanism first appeared after the collision began before the collision ancient northwest australian mantle erupted k rich diamond bearing ultramafics with high 87sr 86sr values and low 143nd 144nd values these form part of a typical ultrapotassic continental volcanic association yet they have ba la and ba nb values characteristic of arc volcanism showing their parent mantle to be geochemically and isotopically capable of supplying the k rich material appearing in the eastern sunda arc volcanoes terranes possibly underlain by similar gondwanaland mantles surround the collision zone which is the site of large scale mixing between oceanic and continental lithospheres other petrogenetic theories seem incapable of accounting for the regional variations in eastern sunda arc geochemistry striking geochemical and isotopic resemblances between eastern sunda leucitites and k rich orogenic volcanics elsewhere in the world such as those of the roman region imply similar origins involving k rich subcontinental mantle material where a k h correlation occurs it might only be a signal that subduction of a lithospheric slab beneath a continental margin is inducing melting in old mantle deep in the continental lithosphere

geochemical evolution and unusual pyroxene chemistry of the md tholeiite dyke swarm from the archaean craton of southern west greenland

genesis and geochemistry of high fluoride bearing groundwater from a semi arid terrain of nw india occurrence of fluoride in natural water resources and the associated health hazards have been reported from many parts of india during the last decade with the objective of organizing a systematic scientific programme to understand the geochemical behaviour of fluoride in natural water resources in relation to the local hydrogeological climatic conditions and agricultural use a typical semi arid terrain in the northwestern part of india was chosen for detailed study the present work is an attempt to study the fluoride contamination in groundwater in parts of jaipur district rajasthan state and to assess the origin and genesis of fluoride in groundwater the area falling under the semi arid tract of central rajasthan is geologically occupied by alluvial formations and precambrian rocks gneisses and schists where groundwater occurs under unconfined to semi confined conditions a total of 66 groundwater samples was collected during the pre monsoon period and analysed which gave a concentration of fluoride in water in the range of 0 35 to 9 3 mg l with 62 of the samples in excess of permissible limit of 1 5 mg l as compared to alluvial formations fluoride enrichment in groundwater is higher in hard rock areas the samples collected from the granite gneissic terrain show higher values when compared to those in the schist the groundwater of the shallow aquifers soil clay complex weathered zone has a higher concentration of fluoride than the deep fractured hard rock aquifer does the possible sources of fluoride are chemical weathering and leaching of fluorine bearing minerals present in hard rocks and alluvial formations under the alkaline environment in arid to semi arid conditions high ph as well as alkalinity and low levels of ca mg and total hardness suggest favourable chemical conditions for the fluoride dissolution process a higher rate of evapotranspiration intensive and long term irrigation and heavy use of fertilizers are the supplementary factors that further increase the fluoride content in the groundwater a groundwater management programme is suggested

assessment of processes controlling the regional distribution of fluoride and arsenic in groundwater of the pampeano aquifer in the del azul creek basin argentina abstract groundwater in the upper 50 m of the pampeano aquifer in the del azul creek basin argentina has f and as contents above the who safe drinking levels this basin is situated to the se of the chaco pampean plain in buenos aires province the pampeano aquifer is a major water source for all uses the aim of the study is to assess the primary processes controlling the regional distribution of f and as in the most exploited part of the aquifer the study involved sampling for chemical and isotopic analyses interpretation of data with different methods diagrams bivariate analyses mineral saturation states principal component analysis and deduction of leading processes information about aquifer mineralogy and hydrogeochemical processes involved in f and as solubilization in the aquifer has been taken from previous works of the same and other authors groundwater salinity increases to the ne in the direction of the regional groundwater flow chemical types evolve from ca mg hco 3 in the upper part of the basin to na hco 3 in the middle part and to na clso 4 and na cl in the lower part the regional distribution of f is controlled by hydrogeochemical processes the distribution of as is controlled by two types of processes dominating in different areas hydrogeochemical controls prevail in the low to moderately mineralized groundwater of the middle and lower parts of the basin hydrogeological controls lead to the ne of the lower basin and beyond it in the last zone there are abundant lagoons and seasonal flooding is frequent making evapoconcentration an important process for groundwater mineralization the main hydrogeochemical processes involved in both f and as distribution are cation exchange with na release and ca uptake carbonate dissolution and ph increase arsenic release induced by redox processes may play to the ne but its results would be masked by the effect of evaporation

geochemistry of high mg andesites from cape vogel papua new guinea abstract a detailed geochemical investigation of high mg andesites from cape vogel papua new guinea shows that these rocks are chemically as well as mineralogically unusual they are nonetheless important to our understanding of the earth s mantle since they represent primary magmas possibly derived in an island arc environment two groups of high mg andesites are recognized at cape vogel type c characterized by a concave ree pattern la yb n and zr nb 35 and type e with la yb n of 3 7 and zr nb 19 the origin of the two groups and their unique trace element patterns is attributed to a complex series of enrichment events superimposed on a previously depleted mantle source in general the enrichment events do not seem similar to those represented in island arc volcanics while some similarities are noted for oceanic ridge and island settings a marked depletion in ti relative to zr and y amongst high mg andesites is a unique facet of their geochemistry trends in the major and trace element geochemistry of type e high mg andesites were modelled orthopyroxene fractionation and or accumulation can explain much of the variation although decoupling of major and selected trace elements is noted source heterogeneity may also be a factor the origin of these rocks and their tectonic setting remains enigmatic however enough geochemical and petrographic evidence is available to suggest they are distinct from most low ti basalts associated with ophiolites

hydrogeochemistry of fluoride in the quequen river basin natural pollutants distribution in the argentine pampa fluoride pollution is a widespread problem in argentina as it is in many areas of the world former investigations have demonstrated that the dissolution of volcanic glass disseminated in the loess like sediments is the main source of fluoride in the argentine pampas nevertheless fluoride distribution is erratic and the factors controlling it are not yet well known a large amount of hydrochemical data collected in the quequen grande river catchment is used in order to contribute to the understanding of fluoride distribution and mobility in groundwater in the argentine pampas the quequen grande river catchment is 10 000 km2 it extends between two low hills ranges of precambrian metamorphic rocks and sedimentary paleozoic rocks filled by a thick sequence of cenozoic sediments mainly silts and silt clayed with sand layers these sediments form a multilayer phreatic aquifer which is recharged from precipitation infiltration discharging through streams directly into the sea fluoride concentration in surface water n 353 ranges between 0 and 6 5 mg l with an average value of 2 14 mg l groundwater concentration n 135 is from 0 up to 5 7 mg l with an average of 1 84 mg l considering the statistic distribution of fluoride two groups of samples can be determined a dominant group between 0 and 3 mg l with a mean value around 1 5 mg l corresponding to samples widely distributed in the catchment and a second one group with fluoride contents between 3 and 6 mg l corresponding to a smaller area in the central west border two different sources are proposed volcanic glass dissolution is responsible for dominant values in the catchment while the weathering of biotite from the paleozoic bedrock can be assumed to account for the higher concentrations in the second group

noritic dykes of southern west greenland early proterozoic boninitic magmatism two major swarms of early proterozoic ca 2 1 ga basic dykes occur within the archaean craton of southern west greenland one swarm comprises ophitic and sub ophitic tholeiitic dolerites while the other the bn dyke swarm constitutes mainly norites in which pyroxenes and olivine are enclosed by plagioclase oikocrysts the close geochemical similarity between a quenched norite and the coarser grained varieties indicates that the composition of the latter type has not been significantly modified by crystal accumulation the bn dykes are geochemically distinctive most having high mgo ca 16 cr and ni contents in conjunction with relatively high sio2 light rare earth ree and large ion lithophile lil element concentrations the texture mineral chemistry and petrochemistry of the quenched noritic dyke all bear strong resemblances to those features in modern boninitic lavas the bn dykes also correspond to proposed parental liquids of the bushveld complex and other major layered basic igneous intrusions the two dyke swarms are petrogenetically distinct the tholeiitic dolerites were derived from a relatively undepleted primordial mantle while the noritic dykes originated from a metasomatized harzburgitic source the wide spread distribution of similar proterozoic intrusions suggests crustal underplating by harzburgitic mantle on a world wide scale at this time

role of a thin komatiite rich oceanic crust in the archean plate tectonic process in the archean tectonic regime the time available for oceanic lithosphere to cool on its journey from ridge to convergent plate boundary was far less than at present under these conditions only an inherently dense lithosphere could have acquired the negative buoyancy necessary for it to subduct at this time plate tectonics could have operated only if 1 the oceanic crust was rich in komatiite lava and 2 the thickness of this crust was not much greater than the thickness of modern oceanic crust

arsenic associations in sediments from the loess aquifer of la pampa argentina groundwater from the quaternary loess aquifer of la pampa central argentina has significant problems with high concentrations of as up to 5300 g l 1 as well as other potentially toxic trace elements such as f b mo u se and v total as concentrations in 45 loess samples collected from the aquifer have a range of 3 18 mg kg 1 with a mean of 8 mg kg 1 these values are comparable to world average sediment as concentrations five samples of rhyolitic ash from the area have as concentrations of 7 12 mg kg 1 chemical analysis included loess sediments and extracted porewaters from two specially cored boreholes results reveal a large range of porewater as concentrations being generally higher in the horizons with highest sediment as concentrations the displaced porewaters have as concentrations ranging up to 7500 g l 1 as well as exceptionally high concentrations of some other oxyanion species including v up to 12 mg l 1 the highest concentrations are found in a borehole located in a topographic depression which is a zone of likely groundwater discharge and enhanced residence time comparison of sediment and porewater data does not reveal unequivocally the sources of the as but selective extract data acid ammonium oxalate and hydroxylamine hydrochloride suggest that much of the as and v is associated with fe oxides primary oxides such as magnetite and ilmenite may be partial sources but given the weathered nature of many of the sediments secondary oxide minerals are probably more important extract compositions also suggest that mn oxide may be an as source the groundwaters of the region are oxidising with dissolved o2 no3 and so4 normally present and as v usually the dominant dissolved as species under such conditions the solubility of fe and mn oxides is low and as mobilisation is strongly controlled by sorption desorption reactions desorption may be facilitated by the relatively high ph conditions of the groundwaters in the region 7 0 8 8 and high concentrations of potential competitors e g v p hco3 phreeqc modelling suggests that the presence of v at the concentrations observed in the pampean porewaters can suppress the sorption of as to hydrous fe iii oxide hfo by up to an order of magnitude bicarbonate had a comparatively small competitive effect oxalate extract concentrations have been used to provide an upper estimate of the amount of labile as in the sediments a near linear correlation between oxalate extractable and porewater as in one of the cored boreholes investigated has been used to estimate an approximate kd value for the sediments of 0 94 l kg 1 this low value indicates that the sediments have an unusually low affinity for as