groundwater composition hydrochemical evolution and mass transfer in a regional detrital aquifer baza basin southern spain abstract the physical chemical characteristics of the groundwater in the baza caniles detrital aquifer system indicate that a wide diversity of hydrochemical conditions exists in this semiarid region defining geochemical zones with distinct groundwater types the least mineralized water is found closest to the main recharge zones and the salinity of the water increases significantly with depth towards the center of the basin geochemical reaction models have been constructed using water chemistry data along flow paths that characterize the different sectors of the aquifer system namely quaternary aquifer unconfined sector and shallow and deep confined sectors of the mio pliocene aquifer geochemical mass balance calculations indicate that the dominant groundwater reaction throughout the detrital system is dedolomitisation dolomite dissolution and calcite precipitation driven by gypsum dissolution this process is highly developed in the central part of the basin due to the abundance of evaporites apart from this process there are others which influence the geochemical zoning of the system in the quaternary aquifer which behaves as a system open to gases and which receives inputs of co 2 gas derived from the intensive farming in the area the interaction of the co 2 with the carbonate matrix of the aquifer produces an increase in the alkalinity of the water in the shallow confined sector of the mio pliocene aquifer the process of dedolomitisation evolves in a system closed to co 2 gas ca 2 na cation exchange and halite dissolution processes are locally important which gives rise to a relatively saline water finally in the deep confined sector a strongly reducing environment exists in which the presence of h 2 s and nh 4 in the highly mineralized groundwater can be detected in this geochemical zone the groundwater system is considered to be closed to co 2 gas proceeding from external sources but open to co 2 from oxidation of organic matter the geochemical modeling indicates that the chemical characteristics of this saline water are mainly due to so 4 dissolution dedolomitisation and so 4 reduction coupled with microbial degradation of lignite

geochemistry origin and recharge mechanisms of groundwaters from the garoua sandstone aquifer northen cameroon this paper presents results of the geochemical and isotopic studies on groundwater samples from the garoua sandstone basin in northern cameroon chemical and environmental isotope data are presented and discussed in terms of the origin of dissolved species and of groundwater all of the investigated groundwaters are categorized into two chemical types low mineralized and acidic waters of ca na hco3 type and relatively high mineralized waters of na hco3 type with relatively high ph between 7 40 and 8 22 interpretation of chemical data based upon both thermodynamic calculations and stability diagrams suggests that the chemical evolution of groundwater is primarily controlled by water rock interactions involving 1 acidic weathering of aluminosilicates 2 dissolution of secondary carbonate minerals and 3 cation exchange of na for ca2 however the original composition of groundwater may have been modified by further secondary processes such as mixing of chemically different water masses and anthropogenic no 3 pollution tritium contents in the considered groundwaters are very heterogeneous suggesting differences in the water turnover time or in the recharge conditions or both on the basis of the geographical distribution of 3h contents a hydrogeological relation between river and the groundwater systems has been proposed for the study site interpretation of both 18o and 2h as well as 3h suggests that the recharge of the investigated groundwaters may result from three major mechanisms 1 direct infiltration of local precipitation 2 lateral inflow of river waters 3 probably upward leakage of old groundwaters

optically stimulated luminescence osl dating of coastal aeolian sand accumulation in sanday orkney islands scotland optically stimulated luminescence osl dating of sand has been used to identify periods of enhanced aeolian activity at two coastal archaeological sites in orkney that coincide with periods of holocene climatic deterioration recorded elsewhere in both scotland and w europe areas of tofts ness sanday were settled from the neolithic abandoned in the late neolithic early bronze age reoccupied and permanently abandoned in the iron age sand layers above the neolithic soils have been osl dated to about 4000 bp correlating well with a period of increased aeolian activity elsewhere in w europe osl dating of aeolian sands above midden deposits and a bronze age burial at lopness on sanday suggest dune development by 3000 bp although both sites also contain sand that was deposited during the little ice age several possible mechanisms may have contributed to an increase in aeolian activity during the holocene that led to the abandonment of these sites although volcanic eruptions in iceland cannot be disc

the use of hydrochemical sections to identify recharge areas and saline intrusions in alluvial aquifers southeast queensland australia abstract alluvial ground waters used for irrigation in the southwest lockyer valley queensland experience varying salinity problems samples were taken on three occasions along transects in the valleys of the tenthill and ma ma creeks during the dry season august 1984 the wet season february 1985 and during a period of drought january 1987 the waters are categorized by chemical type and hydrochemical sections are plotted for major cation data magnesium calcium and sodium the interpretation of the sections permits the identification of recharge areas for the alluvial aquifers and the location of saline intrusions into the alluvium from underlying sandstone aquifers it is also possible with the assistance of chemical type to correlate some saline intrusions in adjacent valleys as issuing from the same sandstone aquifers a diagram to summarize the locations and magnitudes of salinity changes along transects is given

surface water and groundwater contaminations and the resultant hydrochemical evolution in the yongxiu area west of poyang lake china major ion and stable hydrogen and oxygen isotopic compositions were employed in this study of surface water and groundwater contaminations and their impacts on intrinsic hydrochemical evolution in the yongxiu area west of poyang lake south china a total of 36 samples were collected from surface water and groundwater in the study area where water pollution risk is high due to the fertilizer use for farmland and the waste drainage from a nearby silicon industry site the results show that the surface water bodies have been badly polluted and are characterized by low ph values minimum 2 85 and high concentrations of chemical compounds such as cl na nh4 n no3 n and tds groundwater has also been polluted with the similar specific contaminates as both surface water and groundwater may have similar contamination sources and groundwater is recharged from the precipitation infiltration and surface water leakage as indicated by oxygen 18 and deuterium compositions due to the thin unsaturated zone in the area the acidification and the intrusion of contamination further lead to hydrogeochemical reactions and changed hydrochemical type of groundwater from ca mg hco3 to ca mg na cl the data evaluation methods and results of this study could be useful to the water sustainable usage management in this area and other environmental vulnerable areas

geochemical and statistical evaluation of groundwater in imphal and thoubal district of manipur india abstract in order to identify the hydrogeochemical process controlling the quality of groundwater an extensive study was carried out in imphal and thoubal district of manipur india the objectives of the studies were to delineate the spatial and temporal variability in groundwater quality and understand its suitability for human uses in the study area groundwater samples from 45 location have been collected during the pre monsoon monsoon and post monsoon seasons and analyzed for the major ions such as ca2 mg2 na k hco 3 cl so 4 2 no 3 po 4 3 f fe and silica the water quality of both districts was good for domestic and agricultural uses except for few samples these saline samples were localized and were due to the inherent lithology of the study area three major hydrochemical facies ca hco3 type mixed ca na hco3 and ca mg cl types in imphal district and ca hco3 mixed ca mg cl and ca cl type in thoubal district were identified the mineral stability diagrams indicated that the groundwater is in equilibrium with kaolinite and ca montmorillonite whereas gibbs plot showed that the chemical composition of ground water in both districts is controlled by the natural weathering processes irrespective of seasons among the chemical weathering processes silicate weathering was dominant the results were supported by wilcox plot and ussl diagrams the study reflected the overall suitability of groundwater for anthropogenic use

origin of the ug2 chromitite layer bushveld complex chromitite layers are common in large mafic layered intrusions a widely accepted hypothesis holds that the chromitites formed as a consequence of injection and mixing of a chemically relatively primitive magma into a chamber occupied by more evolved magma this forces supersaturation of the mixture in chromite which upon crystallization accumulates on the magma chamber floor to form a nearly monomineralic layer to evaluate this and other genetic hypotheses to explain the chromitite layers of the bushveld complex we have conducted a detailed study of the silicate rich layers immediately above and below the ug2 chromitite and another chromitite layer lower in the stratigraphic section at the top of the lower critical zone the ug2 chromitite is well known because it is enriched in the platinum group elements and extends for nearly the entire 400 km strike length of the eastern and western limbs of the bushveld complex where we have studied the sequence in the central sector of the eastern bushveld the ug2 chromitite is embedded in a massive 25 m thick plagioclase pyroxenite consisting of 60 70 vol granular cumulus orthopyroxene with interstitial plagioclase clinopyroxene and accessory phases throughout the entire pyroxenite layer orthopyroxene exhibits no stratigraphic variations in major or minor elements mg number1 4 79 3 81 1 however the 6 m of pyroxenite below the chromitite footwall pyroxenite is petrographically distinct from the 17 m of hanging wall pyroxenite among the differences are 1 phlogopite k feldspar and quartz are ubiquitous and locally abundant in the footwall pyroxenite but generally absent in the hanging wall pyroxenite and 2 plagioclase in the footwall pyroxenite is distinctly more sodic and potassic than that in the hanging wall pyroxenite an45 60 vs an70 75 the lower critical zone chromitite is also hosted by orthopyroxenite but in this case the rocks above and below the chromitite are texturally and compositionally identical for the ug2 we interpret the interstitial assemblage of the footwall pyroxenite to represent either interstitial melt that formed in situ by fractional crystallization or chemically evolved melt that infiltrated from below in either case the melt was trapped in the footwall pyroxenite because the overlying ug2 chromitite was less permeable if this interpretation is correct the footwall and hanging wall pyroxenites were essentially identical when they initially formed however all the models of chromitite formation that call on mixing of magmas of different compositions or on other processes that result in changes in the chemical or physical conditions attendant on the magma predict that the rocks immediately above and below the chromitite layers should be different this leads us to propose that the bushveld chromitites formed by injection of new batches of magma with a composition similar to the resident magma but carrying a suspended load of chromite crystals the model is supported by the common observation of phenocrysts including those of chromite in lavas and hypabyssal rocks and by chromite abundances in lavas and peridotite sills associated with the bushveld complex indicating that geologically reasonable amounts of magma can account for even the massive 70 cm thick ug2 chromitite the model requires some crystallization to have occurred in a deeper chamber for which there is ample geochemical evidence

sand drift and soil formation along an exposed north atlantic coastline 14 000 years of diverse geomorphological climatic and human impacts this paper sets out the history of aeolian deposition and soil formation over the last 14 15 000 calendar years along the exposed and gale prone atlantic coastlines of the southern isles of the outer hebrides of scotland detailed palaeoenvironmental interpretation and chronological control have been provided by field mapping soil micromorphological analyses and radiocarbon and optically stimulated luminescence osl dating programmes two dominant types of aeolian sands are described in this region quartzose sands are shown to originate mainly as periglacial wind blown sands derived from glacial and periglacial deposits of late devensian age which were formerly exposed on the present continental shelf this aeolian deposition did however continue into the early holocene with re working perhaps by slope wash taking place as recently as the 4th millenniumbp quartzose sands mantle valley floors and hillslopes by the end of the devensian and early holocene a variety of soil types with extensive horizonation had developed upon them including podzolic brown earths peaty gleys and peat soils radiocarbon and osl dating demonstrate that the carbonate sands of the machair sand sheets which characterize the present atlantic shorelines began to accumulate very early for a european shoreline from approximately 8700 calendar years ago on benbecula and north uist whereas further south deposition began later osl dating suggests that non sequences and diastems are common in greater part these machair sand sheets are best interpreted as a composite of separate slivers of sand reflecting small scale and local episodes of sand drift rather than distinct layers of region wide distribution which might reflect past major storms or significant palaeoclimatic fluctuations the new evidence presented here provides little support for the following explanatory geomorphic or stratigraphic models which have previously sought to explain the development of these coastal machair landscapes continuous development layer cake or step wise prograding coastal barrier qualified support is given for the explanations that emphasize i the long term spasmodic input and re cycling of sands and ii that the present smoothed landscapes and distinctive machair grassland vegetation are essentially recent in age and reflect the interactions of natural and human processes in a stormy environment characterized by re working widespread layers of thick organic materials within the carbonate sands in the study area which have previously been regarded as dune palaeosols dating to the bronze age and iron age are suggested by soil micromorphological analysis to be in significant part anthropogenic in origin they are organically enriched layers or midden soils the consequence of human activities notably the disposal of organic wastes and other forms of soil modification during times of significant settlement in these coastal sands these periods of relatively intense human activity are therefore shown to be associated at least locally with periods of soil formation and stability not universal instability and dune drift along these shorelines in general these extensive layers of midden soil do not necessarily imply periods of decreased storminess relatively widespread soil formation in these coastal dunes did however take place in the period between 400 and 100 years ago essentially within the period of increased storminess associated with the little ice age it is suggested that at some point s within the following periods of time broadly defined in calendar yearsbp notable sand drift affecting the quartzose sands the carbonate sands or both took place within the study area 13 700 13 000 11 000 10 500 9000 8300 7500 7000 6900 6400 5800 4200 one of the most notable episodes of drift in the outer hebrides as well as elsewhere on the coast of north west europe 3800 3300 1700 1300 600 200 with individual great storms being recorded in the 17th and 18th centuries and 100 present day limited drift associated with machair stratification

sill intrusion into pyroxenitic mush and the development of the lower upper critical zone boundary of the bushveld complex implications for the origin of stratiform anorthosites and chromitites in layered intrusions

hydrochemical processes governing groundwater quality of sedimentary aquifers in central saudi arabia and its environmental implications the present study deals with the interpretation of the major processes governing the groundwater chemistry in parts of qassim and riyadh province of saudi arabia the study area that is dominated by agricultural activities is represented by a multi layered aquifer system with sedimentary formations ranging from cambrian to the quaternary present as outcrops groundwater samples from 97 agricultural bore wells in the area were collected and analyzed for 16 physio chemical parameters the evaluation of the main hydrochemical processes affecting the groundwater quality was carried out by interpreting the ionic relationships and hydrochemical facies analysis the interpretation pointed toward evaporation gypsum dissolution and ion exchange as main factors controlling the major ion groundwater chemistry the piper plot showed so4 cl type of groundwater with majority of the samples falling in the zone of permanent hardness due to the formation of non carbonate salts principal component analysis that helps to understand the underlying natural and anthropogenic factors controlling the groundwater chemistry in an area was used in the present study based on which four principal components pcs were extracted the first pc as expected was dominated by the major ions and was attributed to natural processes whereas the extracted components mainly heavy metals in pc 2 3 and 4 pointed toward anthropogenic activities playing an active role in affecting the trace element hydrochemistry

hydrogeochemical processes and contaminants enrichment with special emphasis on fluoride in groundwater of birbhum district west bengal india the hydrogeochemistry of groundwater in rural parts of birbhum district west bengal india has been studied to understand the contaminants and prime processes involved in their enrichment with a focus on f concentration the lithological units consist of quaternary alluviums with underlying rajmahal basaltic rocks of middle jurassic age groundwater occurs in the alluviums weathered residuum and fracture zone of rajmahal rocks studies show elevated concentration of cl sio2 fe and f excess cl is attributed to anthropogenic inputs sio2 is ascribed to high degree of weathering of silica rich host rocks and high fe is due to the interaction of water with fe rich sediments under reducing condition the f concentration is found high 1 20 mg l mainly in water from rajmahal rocks revealing a lithological control on f enrichment the weathering of silicates and ion exchange are the leading controlling processes for major ions in groundwater the f enrichment is due to the dissolution of f bearing minerals and perhaps also through anion exchange oh for f on clay minerals at high alkaline conditions precipitation of caco3 favours caf2 dissolution leading to elevated f concentration cahco3 the dominant water type contains low f while nahco3 and nacl types exhibit high f concentrations among the three spatial associations cluster 1 and cluster 2 are cahco3 type cluster 3 shows nahco3 and nacl waters with low ca2 and mg2 and high na contents cluster 1 and cluster 2 waters are in general drinkable barring the elevated fe content while cluster 3 water is unsafe for drinking due to the high f concentration

an appraisal of groundwater quality in seymour and blaine aquifers in a major agro ecological region in texas usa aquifer based groundwater quality assessment offers critical insight into the major hydrochemical processes and aids in making groundwater resources management decisions the texas rolling plains trp spanning over 22 counties is a major agro ecological region in texas from where highest groundwater nitrate no3 levels in the state have been reported in this study we present a comparative assessment of major hydrochemical facies pertaining to no3 contamination and a host of species such as sulfate so42 chloride cl and total dissolved solids tds in different water use classes in the seymour and blaine aquifers underlying the trp aquifer stratified groundwater quality information from 1990 to 2010 was obtained from the texas water development board and aggregated over decadal scale high groundwater salinization was found in the municipal water use class in the blaine aquifer with about 100 87 and 50 of observations exceeding the secondary maximum contaminant level for tds so42 and cl respectively in the 2000s 2000 2010 the no3 contamination was more alarming in the seymour aquifer with 82 and 61 of observations respectively exceeding the maximum contaminant level mcl in the irrigation and municipal water use classes in the 2000s salinization was more influenced by so42 and cl in the blaine aquifer and by no3 in the seymour aquifer high no3 mcl observations in the seymour aquifer occurred in the ca hco3 and ca mg hco3 facies the domains of fresh water recharge and anthropogenic influences e g agricultural activities waste disposal high so42 cl and tds observations in the blaine aquifer dominated the ca cl na cl and mixed ca mg so4 cl facies indicating evaporite dissolution mixing and solute exchange and lack of fresh recharge

the origin of chromitites and related pge mineralization in the bushveld complex new mineralogical and petrological constraints this article reports a study of chromitites from the lg 1 to the ug 2 3 from the bushveld complex chromite from massive chromitite follows two compositional trends on the basis of cation ratios trend a decreasing mg mg fe with increasing cr cr al trend b decreasing mg mg fe with decreasing cr cr al the chromitites are divided into five stages on the basis of which trend they follow and the data of eales et al chemical geology 88 261 278 1990 on the behaviour of the mg fe ratio of the pyroxene and whole rock sr isotope composition of the environment in which they occur following eales et al chemical geology 88 261 278 1990 the different characteristics of the stages are attributed to the rate at which new magma entered the chamber and the effect of this on aal2o3 and in the case of stage 5 the appearance of cumulus plagioclase buffering the aal2o3 the similarity of pge profiles across the mg 3 and mg 4 chromitites that are separated laterally by up to 300 km and the variation in v in the ug 2 argue that the chromitites have largely developed in situ modelling using the programme melts shows that increase in pressure mixing of primitive and fractionated magma felsic contamination of primitive magma or addition of h2o do not promote crystallization of spinel before orthopyroxene in general they hinder it and that the cr2o3 content of the magma was of the order of 0 25 wt less than 20 of the chromite in the magma is removed before orthopyroxene joins chromite which implies a 13 km thickness of magma for the critical zone it is suggested that the large excess of magma has escaped up marginal structures such as the platreef the pge profile of chromitites depends on whether sulphide accumulated or not along with chromite modelling shows that contamination of critical zone magma with a felsic melt will induce sulphide immiscibility although not chromite precipitation the lg 1 to lg 4 chromitites developed without sulphide whilst those from the lg 5 upwards had associated liquid sulphide much of the sulphide originally in the lg 5 and above has been destroyed as a result of reaction with the chromite

hydrogeology and geochemistry of the ogallala aquifer southern high plains the ogallala aquifer which underlies the southern high plains consists of saturated sediments of the ogallala formation neogene that are deposited mainly as a set of humid type alluvial fans derived from the rocky mountains the ogallala aquifer the main source of water for the high plains of texas and new mexico has been severely depleted by extensive pumpage the hydrology and geochemistry of the aquifer are controlled by the surface topography of the underlying formations and by the thickness and permeability of the alluvial fan deposits axes of three major alluvial fans trend from northwest to southeast the fans have increased thickness and permeability compared with interfan areas flow lines follow the orientation of the alluvial fans along these major axes the saturated section is thick and the chemical composition is relatively constant ca hco3 to mixed cation hco3 water depleted in 18o d and tritium external effects on the chemical composition are less pronounced the aquifer is thinner and less permeable in areas between major fan axes and along the caprock escarpment in these areas groundwater can discharge from aquifers in the cretaceous triassic and permian formations into the ogallala formation cross formational movement of water and low permeabilities in the ogallala formation result in varying hydrochemical facies and in isotopic compositions that differ from those of the major depositional areas areas where upward cross formational flow occurs are evident by the presence of permeable contacts between the ogallala and the underlying formations water level head differences and chemical and isotopic similarities secondary factors that locally affect the chemical composition of ogallala formation groundwater include contamination from evaporating saline lakes agricultural chemicals and fertilizers and oil field brines impact of chemicals and brines may increase in the future because much of these contaminants may still be moving through the unsaturated zone toward the water table

early anthropogenic soil formation at tofts ness sanday orkney abstract a buried dark coloured loam soil horizon embedded between calcareous wind blown sand deposits is identified in three areas of the tofts ness landscape the close association with early settlement sites and enhanced total phosophate levels suggests that this soil horizon is anthropogenic in origin radiocarbon dating and stratigraphic relationships with settlement sites indicate that the horizon is associated with bronze age cultural landscape activity and may have commenced formation during the late neolithic period horizon formation is interpreted through a synthesis of thin section micromorphology stable carbon isotope analysis and analysis of free soil lipids these analytical methods indicate that formation was through the application of grassy turf material together with domestic waste midden while cultivation was moderately intense as evidenced by the movement of fine material through the horizon the closest parallels to these soil horizons are the cultural plaggen soils of continental north west europe with the tofts ness soils amongst the earliest known of these soil types application of this manuring technique at tofts ness allowed arable activity in what was a highly marginal farming environment emerging evidence from other parts of the northern isles of scotland suggests that these manuring strategies were commonly used in early arable systems

the impact of hydrogeological settings on geochemical evolution of groundwater in karstified limestone aquifer basin in northwest sri lanka the geochemical and isotope analysis of groundwaters from the murunkan basin in north western sri lanka was carried out to examine their evolution and recharge sources in order to shed light to enhance the current knowledge of the hydro geochemical processes in a karst geological setting a total of 40 water samples from ground and surface water bodies were collected from the miocene limestone terrain nearby metamorphic and from unconsolidated quaternary terrains for major anions cations and environmental isotopes ratios 18ovsmow and 2hvsmow distinct geochemical differences were noted between waters from limestone terrain and nearby metamorphic terrain indicating the modification of groundwater flow paths bicarbonate chloride rich water is dominated in the limestone terrain in which water flows through a less mineralized aquifer system and is modified by the sea water intrusion groundwater in the metamorphic terrain is modified by dissolving of ca mg rich mineral phases and subsequent ion exchange processes the environmental isotopes of groundwater from both limestone and metamorphic terrains vary from 0 38 to 6 68 and 2 41 to 42 3 for 18ovsmow and 2hvsmow respectively however slightly enriched isotope signatures and low d excess values from limestone terrain indicate an excessive evaporation compared to that of the metamorphic terrain where rapid infiltration occurs through the overlying highly permeable grumusols soil layers

crustally contaminated komatiite primary source of the chromitites and marginal lower and critical zone magmas in a staging chamber beneath the bushveld complex in the lowermost rocks of the rustenburg layered suite bushveld complex levels of total cr 2 o 3 are up to ten times higher than its putative solubility 0 16 cr 2 o 3 in the magmas that many investigators have accepted as parental to the dunites harzburgites pyroxenites and norites of the lower lower critical and upper critical zones various existing models fail to explain this chromium paradox in so far as they may explain why chromite is precipitated but do not account for its abundance in many cumulates simple mixing calculations and quantitative adiabat 1ph runs support our model in which a heterogeneous liquid crystals system was evolved in a staging chamber beneath the complex by mixing of komatiitic melts with 20 to 30 of crustal melts at depths appropriate to pressures between 10 and 4 5 kbars we contend that crystal settling and the effects of elutriation during magma ascent had generated a high sio 2 cap with modal olivine orthopyroxene and chromite increasing with depth in the staging chamber the magma from the high sio 2 cap of the staging chamber was first injected into the largely sedimentary transvaal supergroup generating what is now termed the marginal zone slurries of crystals plus liquid from the spasmodically rejuvenated main body of the staging chamber were then injected into the shallower bushveld chamber to form the lower and critical zones chromite within the slurries introduced in this way could account for their high gross cr content frequent reversals of normal evolutionary trends evident in the cumulates are attributable to the episodic nature of the influxes from the staging chamber the lithologically diverse nature of the floors upon which the chromitite layers accumulated peridotites pyroxenites norites and anorthosites was therefore more a function of the timing of emplacement of the cr rich slurries generated in the deeper reservoir than of specific evolutionary processes within the bushveld chamber itself

hydrogeochemical characterization and groundwater quality assessment in the intensive agricultural zone of the upper cheliff plain algeria the alluvial aquifer of upper cheliff northern algeria is known for its intensive agricultural activities which is based especially on groundwater exploitation this aquifer is now facing a dual problem of quantity and quality with a decrease in the groundwater levels and an increase in mineralization twenty monitoring samples were collected and analyzed for major ion during the dry season 2014 in the present study we try to characterize the hydrogeochemical processes and to assess the impact of natural and anthropogenic conditions on groundwater mineralization the analytical results of the dry season 2014 show a groundwater quality slightly alkaline ph 7 and indicate that the majority of samples have a values exceeding the limits of potability fixed by who in 2008 due to the various sources of anthropogenic pollution the piper diagram shows the dominance of groundwater types ca cl the mixed facies cl so4 ca mg and ca hco3 the mineralization process in this aquifer is mainly controlled by the lithology of the aquifer exchange water rock and weathering of calcareous crust dissolution in the unsaturated zone by anthropogenic factors discharges of untreated urban sewage intensive use of fertilizers in agriculture and the use of domestic septic tanks by rural inhabitants and also by geoclimatic conditions semiarid climate suitability of groundwater shows more than 80 of samples have very poor quality for drinking and more than 20 of samples indicate a quality unsuitable for irrigation

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

identification of groundwater contamination zones and its sources by using multivariate statistical approach in thirumanimuthar sub basin tamil nadu india hydrogeochemical studies have been made in the study area by using multivariate statistical analysis which is mainly helpful for interpretation of complex data matrices to better understand the geochemical evolution of the area and it allows identifying the possible factors sources that influence water systems the spatial distribu tion of electrical conductivity reveals that an untreated industrial effluents landfill and anthropogenic activities affecting their groundwater quality in its vicinity and the surrounding area the dominance of ions was in the order of na ca 2 mg 2 k cl hco3 so4 2 no3 and ca 2 mg 2 na k hco3 cl no3 so4 2 during pre monsoon prm and post monsoon pom respectively the statistical results reveals that the groundwater chemistry gets altered by silicate weathering ion exchange leaching anthropogenic input from agricultural return flow and longer distance of migrating groundwater the hydrogeochemical regimes are distributed along the upstream side northwestern western and eastern parts of the study area the study highlights the descriptive capabilities of conventional and multivariate techniques as effective tools in groundwater evaluation

geochemical and isotope characterization of geothermal spring waters in sri lanka evidence for steeper than expected geothermal gradients summary seven geothermal springs from the precambrian high grade metamorphic terrain of sri lanka were investigated to assess their formation processes and to determine reservoir temperatures based on their chemical compositions silica based geothermometric calculations for the marangala and nelumwewa springs showed the highest average reservoir temperatures of 122 c and 121 c respectively samples of low temperature

a marine isotope stage 4 age for pleistocene raised beach deposits near fethard southern ireland raised beach deposits around the irish coast have been interpreted as interglacial or last glacial in age on the south coast of ireland the courtmacsherry formation raised beach cfb near fethard county wexford was dated using optically stimulated luminescence osl this site was previously dated to marine isotope stage mis 6 5 but more recent dating of the cfb elsewhere along the south coast shows it is considerably younger mis 4 3 the osl analyses in this paper aimed to determine if new dating would support the greater age of the fethard raised beach or realign it with the cfb the new osl ages place the formation of the fethard raised beach between 57 6 and 45 6 ka with 53 5 ka the most likely age if a single depositional event is assumed this is consistent with osl dates of the cfb elsewhere an mis 4 3 age has important implications in understanding the palaeogeography and timing of glaciation in ireland and requires a reassessment of regional relative sea level history as the eustatic response to global ice volume resulted in lowered relative sea level during mis 4 2 a crustal response to glaciation is implied by the new dates

constraining the age and formation of stone runs in the falkland islands using optically stimulated luminescence the stone runs of the falkland islands are thought to be periglacial blockfields but their age and detailed origin remain enigmatic we examine the fine sediments that underlie two stone runs in order to establish whether optically stimulated luminescence osl dating is an appropriate technique to constrain the date of emplacement of the fine sediments and hence the stone runs six samples were collected from two accessible sections during the scotia centenary antarctic expedition in 2003 all samples were used to explore the main luminescence characteristics of the sediment followed by quartz sar dating procedures on four of the samples age estimates range from in excess of 54 ka to 16 ka suggesting that the overlying stone runs remained active until 16 ka or later saturation of luminescence from quartz limits age estimates for the oldest samples in the sequences however these are not critical to define the upper limit to the emplacement age for the overlying stone runs the sediments also contain feldspars and initial results suggest that these may be useful in extending the timescale further but require further samples to be obtained from other parts of the sequence extending the method to other stone runs in the port stanley formation may allow estimates of the age of stabilisation of the stone runs to be extended into the 1 250 ka timescale luminescence dating of the underlying sediments used in conjunction with cosmogenic isotope dating of the surface boulders from a range of locations along the stone runs appears to offer a useful route towards decoding the depositional history of these impressive deposits

solute and isotopic geochemistry and ground water flow in the central wasatch range utah ground water flow systems in the rugged central wasatch range utah were investigated by solute and isotopic methods six types of ground water systems were identified on the basis of rock type and structure the systems are broadly grouped into four categories 1 granitic systems 2 non granitic systems a unconsolidated alluvial systems b consolidated sedimentary rock systems and c fault controlled systems 3 thermal systems 4 mine drainage systems these ground water systems have distinctive solute and isotopic chemistries based on an analysis of 3h and 14c data all of the ground waters have a component of post 1952 recharge water and most of the ground waters are composed almost entirely of post 1952 recharge water a few of the ground water systems contain some water which is hundreds to perhaps thousands of years old the 18o and 2h data plot on a local meteoric water line and none of the data exhibit a positive 18o shift the absence of a positive 18o shift suggests maximum aquifer temperatures are approximately 100 c granitic terrains are dominated by fracture controlled local ground water flow systems which respond rapidly to recharge events the granitic ground water systems have estimated maximum circulation depths of about 160 m below land surface all the alluvial most of the consolidated sedimentary bedrock and some of the fault controlled ground water systems are shallow circulating local flow systems with short travel times ground water circulation of most of the local flow systems is within 200 m of land surface and is bedding plane controlled some of the consolidated bedrock and many of the fault controlled ground water systems are of the intermediate type and have circulation depths to 500 m four thermal ground water systems have been identified the thermal systems are heated by the geothermal gradient and have not circulated deeper than 2 2 5 km the thermal systems are of the intermediate and regional type the solute chemistry of most of the non granitic ground waters may be attributed to the dissolution of carbonate minerals and minor amounts of gypsum contributions of external co2 g to some of the thermal systems from either metamorphic or silicate hydrolysis processes is suspected

groundwater quality assessment and its suitability in celtikci plain burdur turkey the celtikci burdur plain is located in the southwest of turkey and is a semi closed basin groundwater is densely used as drinking irrigation and domestic water in the plain hydrogeochemical processes controlling groundwater chemistry and geochemical assessment of groundwater were investigated in the celtikci burdur turkey plain in this study groundwater samples for two seasons were analyzed and major ion chemistry of groundwater was researched to understand the groundwater geochemistry two major hydrochemical facies ca hco3 and ca mg hco3 were determined in the area various graphical plots and multivariate statistical analysis were used for identifying the occurrence of different geochemical processes in the study area weathering is one of the key geochemical processes which controlled the solute concentration in groundwater chemical indexes such as sodium adsorption ratio na residual sodium carbonate magnesium hazard and permeability index were calculated and results show that groundwater is suitable for irrigation purpose except for permeability index values concentrations of mn no3 and total hardness exceed the prescribed limits of who and are the major limiting parameters of groundwater use for potable and domestic purposes

influence of hydrogeochemical processes on temporal changes in groundwater quality in a part of nalgonda district andhra pradesh india geochemical processes that take place in the aquifer have played a major role in spatial and temporal variations of groundwater quality this study was carried out with an objective of identifying the hydrogeochemical processes that controls the groundwater quality in a weathered hard rock aquifer in a part of nalgonda district andhra pradesh india groundwater samples were collected from 45 wells once every 2 months from march 2008 to september 2009 chemical parameters of groundwater such as groundwater level ec and ph were measured insitu the major ion concentrations such as ca2 mg2 na k cl and so42 were analyzed using ion chromatograph co3 and hco3 concentration was determined by acid base titration the abundance of major cation concentration in groundwater is as na ca2 mg2 k while that of anions is hco3 so42 cl co3 ca hco3 na cl ca na hco3 and ca mg cl are the dominant groundwater types in this area relation between temporal variation in groundwater level and saturation index of minerals reveals the evaporation process the ion exchange process controls the concentration of ions such as calcium magnesium and sodium the ionic ratio of ca mg explains the contribution of calcite and dolomite to groundwater in general the geochemical processes and temporal variation of groundwater in this area are influenced by evaporation processes ion exchange and dissolution of minerals

a 7600 year sedimentary record of climatic instability in dunnet bay north scotland abstract we present a partial reconstruction of ne atlantic climatic variability the first based on stratigraphic evidence obtained from a vegetated dune system of the northern scottish coast the dune system at dunnet bay is fringed by prominent submerged peat deposits exposed only at low tide which record stable climatic periods when lower energy wind regimes prevailed allowing the formation of organic soils by contrast periods of sand influx are associated with high energy conditions the majority of sand material tested had a narrow range of particle sizes and major element composition supporting the interpretation of a common aeolian origin sand layers were dated with optically stimulated luminescence osl and peat layers were 14 c dated in four cores c1 c4 and seven sample sections s1 s7 the results from the two master sections s1 and s2 1 km apart indicate synchronous episodes of climatic stability 7650 6310 4340 4000 2690 2290 100 0 cal a bp and instability 6310 4340 4000 2690 2290 2000 170 100 cal a bp in spite of very different mean accumulation rates at the two sites 1 mm a 1 at s1 and 0 2 mm a 1 at s2 phases of sand deposition i e aeolian activity at dunnet tend to be associated with high average levels of chloride in the greenland ice sheet project 2 ice core gisp2 phases of peat development show a fairly good correspondence with low ice rafting activity in the ne atlantic and with indicators of wetness measured from a peat bog in sw sweden by contrast comparison of the dunnet depositional timeline with other regional studies e g hebrides and orkney shows little synchronicity this suggests that a local scale variables have a strong effect on regional patterns of dune instability and b the geological and geographic settings of dunnet bay mean that only large climatic regime shifts in the ne atlantic are capable of triggering instability and being preserved in the depositional record

application of luminescence dating and geomorphological analysis to the study of landscape evolution settlement and climate change on the channel island of herm abstract the optically stimulated luminescence osl dating of sands and palaeosol horizons sampled as part of an archaeological investigation and supported by geomorphological analysis has been applied to identify critical stages in the development of the landscape on herm one of the channel islands that lies off the coast of guernsey on which megalithic monuments were constructed during the neolithic period in particular there were three phases of significant aeolian activity during the prehistoric period the onsets dated by osl in this study to ca 4 3 and 2 3 ka ago where the first phase marked a significant change in the long term trend of aggradation of soils that persisted during the next two millennia osl ages were also obtained for palaeosols in which there was evidence of ploughing placing this activity in the late 2nd millennium bc and the 4th and 13th centuries ad the osl ages for basal deposits of dune sands that cover the northern part of the island indicate that they were formed by phases of intense aeolian activity during the medieval period commencing in the 13th century ad and continuing for several hundred years which can be correlated with documented high intensity storms in the north atlantic within the period 13th 15th centuries ad the phases of significant aeolian activity dated by osl to ca 4 and 2 ka ago can be linked with those detected in different regions of the north atlantic coastal areas the availability of chronologies for aeolian horizons provides a valuable tool in the study of the evolution of coastal landscape and how past coastal communities responded to climate change

assessment of hydrogeochemistry and contamination of varamin deep aquifer tehran province iran the present study investigates the hydrogeochemistry and contamination of varamin deep aquifer located in the southeast of tehran province iran the study also evaluates groundwater suitability for irrigation uses the hydrogeochemical study was conducted by collecting and analyzing 154 groundwater samples seasonally during 2014 based on evolutionary sequence of chebotarev the aquifer is in the stage of so4 hco3 in the north half of the plain and it has evolved into so4 cl in the south half the unusual increase in tds and cl toward the western boundaries of the aquifer indicates some anomalies these anomalies have originated from discharge of untreated wastewater of tehran city in these areas the studied aquifer contains four dominant groundwater types including na ca so4 55 na ca hco3 22 na cl 13 and ca cl 10 the spatial distributions of na cl and ca cl water types coincide with observed anomalies ionic relationships of so4 2 versus cl and na versus cl confirm that water rock interaction and anthropogenic contribution are main sources of these ions in the groundwater the main processes governing the chemistry of the groundwater are the dissolution of calcite dolomite and gypsum along the flow path and direct ion exchange reverse ion exchange controls the groundwater chemistry in the areas contaminated with untreated wastewater based on na and sar 10 3 and 27 of water samples are unsuitable for irrigation purposes respectively regarding residual sodium carbonate there is no treat for crop yields only 6 of water samples represent magnesium adsorption ratios more than 50 which are harmful and unsuitable for irrigation

origin of groundwater salinity current seawater vs saline deep water in a coastal karst aquifer based on sr and cl isotopes case study of the la clape massif southern france origin of groundwater salinity current seawater vs saline deep water in a coastal karst aquifer based on sr and cl isotopes case study of the la clape massif southern france a b s t r a c t in this study a typical coastal karst aquifer developed in lower cretaceous limestones on the western med iterranean seashore la clape massif southern france was investigated a combination of geochemical and isotopic approaches was used to investigate the origin of salinity in the aquifer water samples were collected between 2009 and 2011 three groundwater groups a b and c were identified based on the hydrogeological setting and on the cl a concentrations average and maximum cl a concentrations in the recharge waters were calculated cl ref and cl ref max to be 0 51 and 2 85 mmol l respectively group a includes spring waters with cl a concentrations that are within the same order of magnitude as the cl ref concentration group b includes groundwater with cl a concentrations that range between the cl ref and cl ref max concentrations group c includes brackish groundwater with cl a concentrations that are significantly greater than the cl ref max concentration overall the chemistry of the la clape groundwater evolves from dominantly ca hco 3 to nacl type on binary diagrams of the major ions vs cl most of the la clape waters plot along mixing lines the mixing end members include spring waters and a saline component current seawater or fossil saline water based on the br cl molar ratio the hypothesis of halite dissolution from triassic evaporites is rejected to explain the origin of salinity in the brackish groundwater groundwaters display 87 sr 86 sr ratios intermediate between those of the limestone aquifer matrix and current mediterranean seawater on a sr mixing diagram most of the la clape waters plot on a mixing line the end members include the la clape spring waters and saline waters which are similar to the deep geo thermal waters that were identified at the nearby balaruc site the 36 cl cl ratios of a few groundwater samples from group c are in agreement with the mixing hypothesis of local recharge water with deep saline water at secular equilibrium within a carbonate matrix finally phreeqc modelling was run based on cal cite dissolution in an open system prior to mixing with the balaruc type saline waters modelled data are consistent with the observed data that were obtained from the group c groundwater based on several trac ers i e concentrations and isotopic compositions of cl and sr calculated ratios of deep saline water in the mixture are coherent and range from 3 to 16 and 0 to 3 for groundwater of groups c and b respectively with regard to the la clape karst aquifer the extension of a lithospheric fault in the study area may favour the rise of deep saline water such rises occur at the nearby geothermal balaruc site along another lithospheric fault at the regional scale several coastal karst aquifers are located along the gulf of lion and occur in mezosoic limestones of similar ages the 87 sr 86 sr ratios of these aquifers tend toward values of 0 708557 which suggests a general mixing process of shallow karst waters with deep saline fossil waters the occurrence of these fossil saline waters may be related to the introduction of seawater during and after the flandrian transgression when the highly karstified massifs invaded by seawater formed islands and peninsulas along the mediterranean coast

an assessment of groundwater salinization in haryana state in india using hydrochemical tools in association with gis unplanned abstraction of groundwater due to various land use land cover activities and variations in monsoonal rainfall have greatly affected the availability and quality of groundwater resources in semi arid regions of india in the present study a study of the hydrogeochemical characteristics of groundwater was undertaken in the sonipat district of haryana in india together with the use of stable isotope 18o and d measurements and gis analysis a total of 53 groundwater samples were collected from seven blocks of the district and 14 water quality parameters and stable isotopes 18o and d were analysed to infer hydrogeochemical processes taking place in the area the integration of hydrochemistry with gis is very helpful to understand the factors governing in the area the majority of the samples showed na cl type of hydrochemical facies the trilinear plot for major cations and anions in groundwater indicates dominance of sodium calcium chloride and bicarbonate ions nitrate plumes in the groundwater appear to be migrating in groundwater from the central and south western parts of the area towards the urbanized areas a total of 64 of the samples exceed the maximum permissible limit of 1 5 mg l given by who for fluoride besides natural sources such as silicate and carbonate weathering ion exchange and reverse ion exchange the leaching of surficial salts and untreated industrial wastes along with unregulated abstraction are contributing to poor groundwater quality in the study area an assessment of saturation indices has shown that groundwater in the area is unsaturated with respect to anhydrite halite and gypsum suggesting significant contribution of ca2 mg2 and other ions in the groundwater a scatter plot of 18o versus cl also suggests mixing of saline water with fresh groundwater

identification and evolution of hydrogeochemical processes in the groundwater environment in an area of the palar and cheyyar river basins southern india the palar and cheyyar river basins in tamil nadu state of southern india are characterised by different geological formations and groundwater is the major source for domestic agricultural and other water related activities hydrogeochemical studies were carried out in this area with the objective of identifying the geochemical processes and their relation to groundwater quality groundwater samples were collected once a month from 43 groundwater wells in this area from january 1998 to july 1999 sampling procedures and chemical analysis were carried out as per the standard methods chemical data are used for mathematical calculations and graphical plots to understand the chemical process and its relation to the groundwater quality the chemical composition of groundwater in the central part of the study area mainly depends on the recharge from lakes and the river which is explained by a mixing mechanism in addition weathering of silicate minerals controls the concentration of major ions such as sodium calcium magnesium and potassium in the groundwater of this area further the activity ratios indicate that the groundwater is in equilibrium with kaolinite smectite and montmorrillonite the reverse ion exchange process controls the concentration of calcium magnesium and sodium in hard rock formations and dissolution of carbonate minerals and accessory minerals is the source of ca and mg in addition to cation exchange in the sedimentary formations in general the chemical composition of the groundwater in this area is influenced by rock water interaction dissolution and deposition of carbonate and silicate minerals ion exchange and surface water interactions

recharge mechanisms and geochemical processes in a semi arid sedimentary basin eastern cape south africa abstract stable isotope 18 o and 2 h and geochemical signatures are used to gain some insight into recharge processes and groundwater salinization mechanisms in a semi arid rangeland catchment the 665 km 2 catchment is underlain by fractured lower beaufort sandstones and mudstones and is intruded by several dolerite dykes chloride and isotopic relationships suggest that chloride ions in ground water are of meteoric origin the hypothesized recharge and salinization mechanism is that large storm events periodically dissolve accumulated surficial meteoric salts and after a period of evaporative enrichment at or near the soil surface leach them into the ground water geochemical variations imply that spatial differences exist in recharge volumes in evaporative enrichment or in the extent of leaching of surficial salts meteoric sodium chloride contributes greater than 90 of the dissolved sodium except at low salinities where cation exchange processes yield additional sodium inputs in exchange for dissolved calcium and magnesium at high salinities this process reverses and sodium is adsorbed releasing calcium and magnesium this process accounts for up to 40 of the dissolved calcium and magnesium contributions from geochemical weathering are relatively uniform in spite of highly variable salinities which implies that residence times are also relatively uniform

re os isotope and pd ru variations in chromitites from the critical zone bushveld complex south africa abstract rhenium osmium isotope measurements of selected chromitites from the critical zone of the bushveld igneous complex reveal that a significant component of radiogenic os was present in the magma when it formed 2 06 ga ago measured 187 os 188 os ratios increase with stratigraphic height and individual layers have similar values across the complex initial 187 os 188 os ratios for chromitites from the western bushveld decrease from 0 140 at the lg to 0 129 at the mg2 chromitite increasing to 0 153 at the ug2 chromitite the inflection at mg2 mg3 is the boundary between the lower and upper critical zone consistent with previous mineralogical and geochemical studies indicating a shift in magma composition at this point chromite separates have os values of 12 35 at 2 06 ga and are too radiogenic for a purely mantle derivation assimilation of 5 mafic granulitic lower crust in a tholeiitic parent magma can explain the radiogenic values pd ru ratios for the intergranular and chromite separate components of each layer differ by orders of magnitude but relative shifts from layer to layer are similar combined with the re os data the results suggest that pge were concentrated into chromitites by magmatic or early deuteric processes that were specific to each layer post layering upward mobilization of pge by hydrothermal processes probably did not play a significant role in pge enrichment

assessment of hydrogeochemistry and the quality of groundwater in 24 parganas districts west bengal hydrogeochemistry of an area helps in understanding the geological processes which control the chemistry of water and play an important role in determining the suitability of groundwater for various purposes in the present study an attempt has been made to understand the geological processes controlling the quality of water in a part of north and south 24 parganas districts of west bengal 39 representative groundwater samples were collected from the study area and physico chemical parameters were analyzed for all the samples schoeller and durov diagram were used to understand the hydrochemical nature of water results obtained from water chemistry were used in the interpretation of controlling processes using different conventional graphs and determining the quality of groundwater silicate weathering and ion exchange are the dominant processes controlling the chemistry of groundwater in the study area where calcium and magnesium in the water are replaced by the sodium and potassium in the minerals from the host rock as chloro alkaline indices are negative at most of the places saturation index was calculated to understand the mineralogy of the subsurface the groundwater is oversaturated with iron containing minerals like fe oh 3 goethite and hematite while undersaturated with anhydrite and gypsum the groundwater suitability was determined by calculating water quality index for drinking purpose while sar and residual sodium carbonate indices for the agricultural purpose the groundwater in the study area is not suitable for drinking but can be used for other household use and in irrigation for agriculture

hydrochemical characteristics of groundwater and surface water for domestic and irrigation purposes in vea catchment northern ghana the vea catchment mainly underlain by crystalline basement rocks is located in northern ghana hydrogeochemical studies were carried out in this area with the objective of identifying the geochemical processes influencing water quality and suitability of surface and groundwater for agricultural and domestic uses sixty one groundwater and four surface water samples were collected from boreholes dams and rivers and analysed for ca2 mg2 na k hco3 cl and so4 2 fetot po4 3 mntot nh4 no3 no2 in addition ph total dissolved solids electrical conductivity total hardness turbidity colour salinity and dissolved oxygen were analysed chloro alkaline indices 1 and 2 and characterization of weathering processes suggest that the chemistry of groundwater is dominated by the interaction between water and rocks cation exchange and silicate weathering are the dominant processes controlling the chemical composition of the groundwater in the area studied mineral saturation indices indicate the presence of at least three groups of groundwater in the vea catchment with respect to residence time the meteoric genesis index suggests that 86 of the water samples belong to the shallow meteoric water percolation type the findings further suggest that the groundwater and surface water in the basin studied are mainly ca mg hco3 water type regardless of the geology compared to the water quality guidelines of who the study results on sodium absorption ratio sodium percentage magnesium hazard permeability index and residual sodium carbonate indicate that groundwater and surface water in the vea catchment are generally suitable for drinking and irrigation purposes

assessment of groundwater quality for irrigation and drinking purposes and identification of hydrogeochemical mechanisms evolution in northeastern tunisia oligocene and mio plio quaternary siliciclastic deposits constitute the most important deep aquifers of the kairouanai sahel region considering the over exploitation and contamination of the surface groundwater recourse to use deep groundwater was crucial these aquifers revealed three major hydrochemical facies hco3 mg hco3 na and so4 mg water types rock water interaction showed the main mechanisms are rock weathering and evaporation different parameters such as water quality index wqi sodium absorption ratio sar percentage of sodium residual sodium carbonate rsc magnesium hazard mh and permeability index pi were used to evaluate groundwater suitability for drinking and irrigation purposes results highlighted that groundwater is unsafe for irrigation based on pi mh rsc and salinity diagram according to the wqi values 10 25 of the water samples had good water quality 69 23 were considered as poor water 12 82 were very poor water and 7 69 were considered unsuitable for drinking purpose

seasonal disparity in the co occurrence of arsenic and fluoride in the aquifers of the brahmaputra flood plains northeast india arsenic as and fluoride f in groundwater are increasing global water quality and public health concerns the present study provides a deeper understanding of the impact of seasonal change on the co occurrence of as and f as both contaminants vary with climatic patterns groundwater samples were collected in pre and post monsoon seasons n 40 in each season from the brahmaputra flood plains bfp in northeast india to study the effect of season on as and f levels weathering is a key hydrogeochemical process in the bfp and both silicate and carbonate weathering are enhanced in the post monsoon season the increase in carbonate weathering is linked to an elevation in ph during the post monsoon season a piper diagram revealed that bicarbonate type water with na k ca2 and mg2 cations is common in both seasons correlation between cl and no3 r 0 74 p 0 01 in the post monsoon indicates mobilization of anthropogenic deposits during the rainy season as was within the 10 g l 1 who limit for drinking water and f was under the 1 5 mg l 1 limit a negative correlation between oxidation reduction potential and groundwater as in both seasons r 0 26 and 0 49 respectively for pre monsoon and post monsoon p 0 05 indicates enhanced as levels due to prevailing reducing conditions reductive hydrolysis of fe hydr oxides appears to be the predominant process of as release consistent with a positive correlation between as and fe in both seasons r 0 75 and 0 73 for pre and post monsoon seasons respectively at p 0 01 principal component analysis and hierarchical cluster analysis revealed grouping of fe and as in both seasons f and sulfate were also clustered during the pre monsoon season which could be due to their similar interactions with fe hydr oxides higher as levels in the post monsoon appears driven by the influx of water into the aquifer which drives out oxygen and creates a more reducing condition suitable for reductive dissolution of fe hydr oxides an increase in ph promotes desorption of as oxyanions aso4 3 arsenate and aso3 3 arsenite from fe hydr oxide surfaces fluoride appears mainly released from f bearing minerals but fe hydr oxides can be a secondary source of f as suggested by the positive correlation between as and f in the pre monsoon season

characterization and evaluation of processes governing the groundwater quality in parts of the sabarmati basin gujarat using hydrochemistry integrated with gis intense agricultural and industrial activities in any area are likely to make groundwater vulnerable with respect to its quality in one such area which is a part of sabarmati river basin of gujarat factors influencing the groundwater hydrochemistry in pre and post monsoon season were evaluated groundwater samples were collected from 5 km 5 km grids on the basis of spectral signature of vegetation and soil observed on satellite image integration of conventional graphical plots piper plot saturation index values estimated using phreeqc and gis was helpful not only to create the database for analysis of spatial variation in respective water quality parameters but also to decipher the hydrogeochemical process occurring in such a large area ussl diagram and sodium were used to characterise the suitability of groundwater for irrigation it was observed that leaching of wastes disposed from anthropogenic activities and agrichemicals is the major factor influencing the groundwater quality in addition to the natural processes such as weathering dissolution and ion exchange sea water relics are also impacting the groundwater quality control of indiscriminate and unplanned exploitation of groundwater application of fertilizers and disposal of industrial wastes in the affected areas can possibly ensure groundwater protection from further pollution and depletion copyright 2011 john wiley sons ltd

concentrations of rare earth elements in silicate rocks of the lower critical and main zones of the bushveld complex concentrations of rare earth elements in the lower critical and main zones of the bushveld complex at union section show distinct variation with stratigraphic height in that lower and lower critical zone cumulates are lree and th enriched ce sm 10 25 ce smn 3 65 th smn 6 17 over main zone cumulates ce sm 4 10 ce smn approximately 2 th smn 1 57 the upper critical zone constitutes a transitional interval in terms of ree concentrations ce sm 9 17 this pattern is broadly coupled albeit in a contraposed manner to that in initial sr isotopic ratio and confirms earlier studies that the bushveld complex crystallized from at least two compositionally distinct parental magmas mixing between the two magmas occurred as early as in the lower zone and is sensitively reflected by variation in ce sm th sm modal plagioclase and chromite while ree contents of the lower and critical zones are approximately 15 those of the corresponding b1 and b2 marginal rocks the main zone cumulates have similar ree contents to the b3 marginal rocks this suggests that the main zone rocks either crystallized from a highly viscous crystal mush without appreciable fractionation or from magma strongly ree enriched over the marginal rocks which would imply that the main zone is not represented in the suite of marginal rocks

geochemistry water balance and stable isotopes of a clean pit lake at an abandoned tungsten mine montana usa abstract the calvert mine is a small tungsten rich scheelite skarn deposit in a remote mountainous region of southwest montana usa the open pit mine closed in the 1970s and subsequently flooded to form a pit lake that is roughly conical in shape 30 m deep and 120 m in diameter with no surface inlet or outlet the lake is holomictic with a groundwater flow through hydrology and an estimated residence time of 2 5 5 y water isotopes show that the lake is at an approximate steady state with respect to water balance and has experienced 30 evaporation the lake has a near neutral ph exceptional clarity and extremely low concentrations of nutrients sulfate and most metals including tungsten manganese concentrations are slightly elevated and increase with depth towards the sediment water interface despite seasonally anoxic conditions in the deep water dissolved fe concentrations are orders of magnitude lower than mn suggesting that insufficient organic carbon is present in the sediment of this oligotrophic lake to drive bacterial fe reduction based on stable isotope fingerprinting diffuse seepage that enters a nearby headwater stream at the base of a large waste rock pile can be directly linked to the partially evaporated pit lake however this seepage has neutral ph and low metal concentrations and poses no threats to the environment stable isotopes of dissolved inorganic carbon dic and dissolved oxygen do are used to track the relative importance of photosynthesis and respiration with depth in summer a zone of high productivity exists near the base of the chemocline releasing do that is isotopically light respiration exceeds photosynthesis below the secchi depth which causes do concentrations to approach zero towards the bottom of the lake in winter thick ice and snow cover prohibits photosynthesis however because of the low nutrient content most of the volume of the lake remains oxic through the winter overall the calvert lake is a good example of a pit lake formed from metal mining that has excellent water quality which is a result of its favorable geology paucity of sulfide minerals and hydrology flow through lake with short residence time in a temperate climate

saline groundwater in israel its bearing on the water crisis in the country abstract one of the major causes for the deterioration of water quality bearing heavily on the water crisis in israel is the ongoing contamination of its water resources by saline water bodies the present paper reviews the geochemical processes forming saline water lists and explains certain chemical and isotopic parameters which enable understanding these processes and describes the saline groundwater bodies and various salinization phenomena occurring in the country s various aquifers deterioration of groundwater in israel is caused by numerous natural processes such as encroachment of sea water migration of connate highly pressurized brines penetrating into fresh groundwater by subsurface dissolution of soluble salts originating in surrounding country rocks and by water rock interaction in addition to sea water two saline water bodies were identified as the main factors causing salinization of fresh groundwater a ca chloride brines encountered in the jordan dead sea rift valley in various parts of the negev and of the coastal plain and b na chloride saline water identified in the subsurface of the negev and in the southern part of the coastal plain intensive exploitation of groundwater in israel has disturbed the natural equilibrium which prevailed between fresh and saline water the newly established groundwater flow regimes have facilitated the migration of saline water bodies their participation in the active hydrological cycle and the progressive contamination of fresh groundwater these processes which were not anticipated by planners and water resources managers emphasize that large scale groundwater exploitation was undertaken without giving sufficient consideration to the occurrence and subsurface migration of saline water and brines

identifying source and evaluation of hydrogeochemical processes in the hard rock aquifer system geostatistical analysis and geochemical modeling techniques in order to quantify spatio temporal changes in the hydrogeochemistry of swarnamukhi river basin andhra pradesh india a total of 239 groundwater samples have been collected for pre and post monsoon seasons of 2014 and 2015 the geology of the study area is comprised of granite granitic gneisses shales quartzites laterites and recent alluvium along the river course based on the study of geochemical processes of different seasons it is found that the occurrence of na and hco3 in 2014 shifted toward ca and hco3 in 2015 due to cation exchange process fe shows the higher concentration value than safe limit due to dissolution of ferruginous minerals and domestic sewage discharges bivariate plots of various ions and ratios depict the predominance of silicate weathering over carbonate and evaporite dissolution apart from anthropogenic activities in the enrichment of groundwater constituents high nitrate concentration was observed in the urbanized regions of the basin followed by intense agricultural areas geochemical modeling was carried out using mineral saturation index and thermodynamic stability plots to deduce major weathered products most of the groundwater samples in the study area are saturated with carbonate minerals but are undersaturated with silicate minerals thermodynamic stability plots suggest the formation of kaolinite secondary mineral and presence of aluminosilicate minerals fuzzy calculation is applied to determine the water quality index which categorizes a majority of the samples as excellent to good category for human use factor analysis points toward the mixed source identification of ionic constituents saline water mixing index model calculation suggests the effect of salinization in coastal areas due to heavy withdrawal of the fresh groundwater resources for various uses whereas in the mainland it is due to agricultural runoff and domestic waste water

the hydrochemical identification of groundwater flowing to the bet she an harod multiaquifer system lower jordan valley by rare earth elements yttrium stable isotopes h o and tritium abstract the bet she an and harod valleys in israel are regional recipients and mixing zones for groundwater draining from a multiple aquifer system which includes carbonate and basalt aquifers and deep seated pressurized brines the aquifers drain through two types of outlets distinct and mixed the latter type is mainly conditioned by the occurrence of fault blocks related to the jordan rift system which act as connecting media between the aquifers and facilitate interaquifer flow conjoint application of rare earth element distribution and water isotopes enables detection of the local areas replenishment by rainfall infiltration and in connection with the position of wells or springs the identification of groundwater flow paths once stationary equilibria are established changes of rey composition between rey in groundwater and their surface adsorption are negligible in areas with little soil coverage and vegetation even recharge over young tertiary and diagenetic cretaceous limestones is distinguishable by their rey distribution patterns groundwater recharged over tertiary limestones show higher rey abundance and more significant ce anomalies than those derived from the cretaceous limestones weathering of alkali olivine basalts leads to rey patterns in groundwater depleted in the middle ree the improved knowledge of the hydrological systems is thought to be useful for regional hydrogeological modeling and for designing rational water management schemes

investigation of the hydrogeochemical processes in an alluvial channel aquifer located in a typical karoo basin of southern africa an investigation was conducted to assess the hydrogeochemical processes of an alluvial channel aquifer located in a typical karoo basin of southern africa the investigation was aimed at identifying and describing the groundwater chemistry evolution and its contribution to the overall groundwater quality x ray fluorescent spectrometry xrf and x ray diffractometry xrd analyses were performed on geological samples to identify and quantify the major element oxides and minerals the study utilises the conventional piper diagram bivariate plots and phreeqc hydrogeochemical model to analyse groundwater chemistry data obtained during the wet february and may and dry seasons august and december of 2011 the xrf and xrd results show that the channel deposits are dominated by sio2 element oxides and quartz minerals thus elevated concentrations of silicon si4 were found in the groundwater dolomite and calcite minerals were also detected in the unconsolidated aquifer sediments the detailed study of the alluvial aquifer system has shown that dissolution of dolomite and calcite minerals and ion exchange are the dominant hydrogeochemical processes influencing the groundwater quality the groundwater evolves from ca2 mg2 hco3 recharge water that goes through ion exchange with na in the clay silt sediment to give a na hco3 water type the groundwater is supersaturated with respect to quartz dolomite and calcite minerals the study shows the potential usefulness of simple bivariate plots as a complimentary tool to the conventional methods for analyzing groundwater hydrogeochemical processes

quantification of groundwater seawater interaction in a coastal sandy aquifer system a study from panama sri lanka the panama coastal aquifer system is an important water resource in the southeast coast of sri lanka that provides adequate supplies of water for agriculture and domestic uses one of the biggest threats to these fragile aquifers is the sea water intrusion in this study recharging mechanism and geochemical evaluation of groundwater in the coastal sandy aquifer of panama were evaluated using chemical and stable isotope techniques thirty groundwater samples were collected and analyzed for their major ion concentrations and stable isotope ratios of oxygen 18o 16o and hydrogen d h all studied samples showed a ranking of major anions in the order cl hco 3 so 4 2 n no3 while cations showed a decreasing order of abundance with na ca2 mg2 k dominant groundwater hydrogeochemical types were na cl and mixed ca mg cl results of saturation index calculations indicate that the investigated groundwater body was mostly saturated with respect to calcite dolomite and gypsum in addition stable isotope and geochemical data suggest that fresh groundwater in the aquifer is recharged mainly by local precipitation with slight modification from evaporation and saline water intrusions isotope data suggest that mixing of salt water with freshwater occurs in aquifers which are located towards the lagoon since the communities in the study area depend entirely on groundwater an understanding of the hydrogeochemical characteristics of the aquifer system is extremely important for the better water resource management in the region

luminescence characterisation of quartz rich cover sands from ne thailand abstract the genesis of a several meter thick cover sand layer which is widely distributed in mainland se asia has been the subject of much debate being considered by some to be an aeolian mantle of late pleistocene early holocene origin and by others to represent a holocene biomantle samples were collected from three sites in nw thailand in 1998 to assess the potential of luminescence studies for characterisation and chronometric studies of the layer the material is a quartz rich iron stained sand with high luminescence sensitivities a pronounced 325 c tl peak and high sensitivity to phototransfer and osl a number of methods for estimating stored dose were assessed of which additive tl and regenerative osl procedures produced good laboratory results these methods have been used to produce stored dose and apparent age profiles for one of the sites the data are consistent with a late pleistocene holocene aeolian deposition process possibly modified in the upper layers by bioturbation however the possibility that the recorded profiles are the result of heterogeneous mixing of bleached and unbleached grains within the biomantle model cannot at this stage be excluded the material has excellent luminescence properties and it is likely that further luminescence studies will be able to distinguish between the formation models and contribute significantly to understanding of these regionally significant sediments

sodium calcium ion exchange in the weathering of shales implications for global weathering budgets unpolluted rivers and streams that drain marine shales show an excess of sodium compared to chloride and a deficiency of calcium and magnesium compared to sulfate and alkalinity this is due in part to cation exchange of sodium for divalent cations on clay minerals consideration of the global weathering budget suggests that up to 34 of the sodium in the total dissolved stream load may be due to cation exchange rather than sodium production via silicate dissolution weathering reactions these results suggest that the weathering budgets for sodium and calcium are in need of revision because of the inclusion of cation exchange processes in the weathering cycle this implies that silicate dissolution is less important in determining the composition of global river water than was previously thought

hydrogeochemical controls on shallow alluvial groundwater under agricultural land case study in central portugal a hydrogeochemical study employing graphical multivariate statistical and modeling tools was conducted in an area of alluvial deposits in the mondego river basin to determine the factors and processes controlling the shallow groundwater chemistry groundwater was collected from 29 observation wells in six sampling campaigns between march 2001 and september 2002 samples were analyzed for basic physicochemical parameters major ions and some minor ions hierarchical cluster analysis was applied to the data set including both the spatial and temporal monitoring data and resulted in the definition of eight distinct water types with the aid of hydrochemical and physicochemical scatter plots it was possible to identify the main processes controlling the groundwater chemistry 1 evapotranspiration and recharge 2 calcium and magnesium carbonate and co2 dissolution 3 nitrate leaching from agriculture 4 oxidation and reduction and 5 cation exchange these processes are frequently common to more than one water type but unique in combination and or extent in space and or time geochemical modeling of the water types using phreeqc allowed the validation and to a certain extent quantification of the processes that affect the shallow groundwater evolution these tools can provide an essential support for the assessment of groundwater vulnerability to contamination and for the elaboration of groundwater resource management strategies

assessment of the hydrogeochemical characteristics of groundwater in two aquifer systems in cumra plain central anatolia located in a semi arid climate cumra konya plain is one of the most important agricultural regions in turkey groundwater is the major source for agricultural domestic and other water related activities due to the insufficiency of surface water as groundwater is the only major source of water in this area it is important to know the effects of geological formations and anthropogenic activities on groundwater chemistry this study was carried out with the objective of identifying the hydrogeochemical characteristics and processes controlling the groundwater chemistry in cumra plain central anatolia turkey the study area is comprised of two main aquifers which are the semi confined aquifer of the neogene age and the unconfined aquifer of the quaternary age to identify the hydrogeochemical characteristics of groundwater in two aquifer systems and to understand the major factors and mechanisms controlling the groundwater chemistry graphical plots mineral saturations and multivariate statistical analysis of chemical constituents in the groundwater were used study results show that groundwater is generally neutral to slightly alkaline in nature with a ph ranging from 6 67 to 8 10 and the dominance of ions is in the order of ca2 mg2 na k for the neogene aquifer and hco3 so4 2 cl no3 mg2 ca2 na k and so4 2 hco3 cl no3 for the quaternary aquifer while the chemical composition of groundwater in the neogene aquifer is mainly controlled by water rock interaction including dissolution of carbonates and gypsum calcite precipitation and de dolomitization the main geochemical processes in the quaternary aquifer are reverse ion exchange evaporation dissolution of carbonates gypsum and soil salts calcite precipitation and silicate weathering the mechanism controlling groundwater chemistry in the neogene aquifer is actually regulated by the geogenic processes water rock interaction rather than by anthropogenic activities however the mechanism controlling groundwater chemistry in the quaternary aquifer is regulated by both geogenic processes and anthropogenic activities in addition anthropogenic nitrogen pollution in the study area is currently not serious but evaporation and leaching of soil salts due to anthropogenic activities increase the concentrations of ions in the quaternary aquifer

natural zeolites enhance groundwater quality evidences from deccan basalts in india the zeolite minerals characterized with hydrated aluminosilicates negative ionic charge and 3d framework structure are well known for purifying the groundwater occurring in basaltic aquifer systems however the filtering mechanism at in situ field conditions is a complex process which is rarely studied and hence it needs to be demonstrated this paper explores the mechanism of hydrochemical processes and evolution of natural zeolites associated with basaltic rock to enhance groundwater quality we present the hydrochemical findings and evolution processes derived from 46 groundwater samples nt 46 belong to zeolitic nz 25 and non zeolitic nnz 21 zones of a micro watershed 4 4 km2 beset over basaltic terrain deccan volcanic province dvp india the groundwater samples collected for one hydrological cycle pre and post monsoons are examined for major ion chemistry to determine the aqueous solution mechanism and ion exchange process occurred in zeolitic and non zeolitic zones further the hydrochemical parameters are appraised by means of dominancy of ions rock water interactions silicate weathering chloro alkaline indices cation exchange bivariate plots and the mechanism controlling groundwater chemistry the results show that 1 the purifying efficiency of zeolites for total ionic strength is observed as 63 85 and 68 58 during pre and post monsoons respectively 2 the significant reduction 36 51 in total hardness attributed to the positive trend of chloro alkaline indices depicting the ion exchange phenomenon between na and k alkalies and ca2 and mg2 alkali earth elements in the zeolitic zone 3 gibbs plot shows the rock water interaction as the predominant mechanism controlling groundwater chemistry in the zeolitic zone and 4 the groundwater quality parameters from zeolitic zone are found within the permissible limit of who drinking water standards

luminescence dating of aeolian sands from archaeological sites in northern britain a preliminary study luminescence dating of aeolian sands from archaeological sites has potential to contribute to regional chronologies for sediment deposition and to provide a greater understanding of climatic influences on early communities the northern and western isles of scotland provide important opportunities for sampling archaeologically intercalated sands for these purposes and to provide constrained samples for method validation a wide range of modern beaches have been sampled in the western and orkney isles of scotland to examine regional variations in luminescence sensitivity residuals and ease of bleaching these modern sands have negligible residuals for infra red stimulated luminescence irsl small optically stimulated luminescence osl residuals and significant thermoluminescence residuals the relationship between these signals and laboratory bleaching results may indicate the initial depositional environment and hence lead to a means of identifying well bleached dating samples both sensitivities and residuals show regional differences reflecting local geology preliminary ages obtained from aeolian sands associated with archaeological sites at amble northumbria and tofts ness sanday orkney using regenerative blue osl techniques on extracted quartz are broadly consistent with external age controls from the first and third millennium bc

the bushveld complex south africa formation of platinum palladium chrome and vanadium rich layers via hydrodynamic sorting of a mobilized cumulate slurry in a large relatively slowly cooling subsiding magma chamber platinum group element pge deposits in the bushveld complex and other layered intrusions form when large incompletely solidified magma chambers undergo central subsidence in response to crustal loading resulting in slumping of semi consolidated cumulate slurries to the centres of the intrusions and hydrodynamic unmixing of the slurries to form dense layers enriched in sulfides oxides olivine and pyroxene and less dense layers enriched in plagioclase the most economic pge cr and v reefs form in large multiple replenished intrusions because these cool relatively slowly and their central portions subside prior to termination of magmatism and complete cumulate solidification the depth of emplacement has to be relatively shallow as otherwise ductile crust would not be able to flex and collapse in smaller intrusions cooling rates are faster subsidence is less pronounced and where it occurs the cumulate may be largely solidified resulting in insignificant mush mobility and mineral sorting layering is thus less pronounced and less regular and continuous and the grades of the reefs are lower but the reefs can be relatively thicker an additional factor controlling the pge cr and v prospectivity of intrusions is their location within cratons intra cratonic environments offer more stable emplacement conditions that are more amenable to the formation of large layered igneous bodies furthermore intrusions sited within cratons are more readily preserved because cratons are underlain by thick buoyant keels of harzburgite that prevent plate tectonic recycling and destruction of crust

factors influencing the major ion chemistry in the tihama coastal plain of southern saudi arabia evidences from hydrochemical facies analyses and ionic relationships coastal aquifers across the globe have been a subject of extensive research mainly because of problems related to saline water intrusion as a consequence of global climate changes and overabstraction of groundwater the present work deals with the assessment of factors which affects the groundwater chemistry in parts of the tihama coastal plains in the jazan province of southern saudi arabia hydrochemical parameters ph ec tds major ions no3 and sio2 were obtained from 263 wells and were interpreted hydrochemical facies analyses revealed two main types of groundwater facies i e the mixed groundwater facies predominantly confined to the eastern and central part of the study area away from the coast and groundwater facies dominated by so4 cl no3 ions found mostly in the coastal zones in the western part of the study area the average tds value of the mixed groundwater facies is 945 7 mg l whereas the average tds value is 3149 7 mg l for the so4 cl no3 anionic species greater influence of rainfall recharge can be observed in the mixed water species while saline water mixing or rock water interaction can be seen in the so4 cl no3 type of anionic species however ionic ratios point more toward rock water interaction rather than saline water mixing in the groundwater facies dominated by so4 cl no3 ions this interpretation is also supported by the presence of sabkhas salt flats in the coastal zones where its interaction with the groundwater has resulted in high cl and so4 concentration cl br ratios which have often been used to detect saline water intrusion in coastal zones also do not support saline water intrusion in the study area ionic ratios point toward dissolution and base ion exchange as the main factors influencing the groundwater chemistry silicate weathering and silica dissolution are also found in the area saturation indices point toward gypsum and halite dissolution the average no3 concentration is 157 80 mg l and is mostly attributed to the agricultural practices in the region the presence of shallow unconfined aquifers facilitate the easy percolation of irrigation return flows enriched in no3 concentration from the application of inorganic fertilizers on the agricultural farms

seasonal variation of the solute and suspended sediment load in gangotri glacier meltwater central himalaya india abstract a systematic study on the seasonal variation of major cations and anions was carried out to understand the source of dissolved ions as well as the geochemical weathering processes controlling the meltwater chemistry of gangotri glacier calcium and magnesium are the major cations while sulphate is the dominant anion followed by bicarbonate the high ratios of ca mg na k ca na mg na hco3 na and low ratio of na k tz for pre monsoon monsoon and post monsoon seasons indicate the dominance of carbonate weathering which is a major source of the dissolved ions in the meltwater of gangotri glacier followed by silicate weathering high equivalent ratios of na cl and k cl as compared to sea water indicate relatively lesser contribution from atmospheric input to the chemical composition of meltwater correlation matrix and factor analysis were used to identify various factors controlling the major ion chemistry marked seasonal and diurnal variations were observed in the dissolved ions and suspended sediment concentration daily mean suspended sediment concentration for pre monsoon monsoon and post monsoon was observed as 1719 3281 and 445 mgl 1 respectively highest suspended sediment load was observed in monsoon season followed by pre monsoon and post monsoon seasons the cation denudation rates of gangotri glacier meltwater were calculated to be 42 2 46 5 and 15 9 t km 2 y 1 for pre monsoon june only monsoon and post monsoon respectively these values are higher than that of other himalayan glaciers whereas physical weathering rate of the gangotri glacier catchment was observed to be 7056 15 344 and 588 t km 2 y 1 for pre monsoon june only monsoon and post monsoon respectively much higher than the indian and world averages of river

the ug2 merensky reef interval of the bushveld complex northwest of pretoria northwest of pretoria the ug2 merensky reef interval overlies a critical zone lower zone sequence that contains numerous large blocks of floor material nevertheless individual layers can be correlated with equivalent units at crocodile river mine the rustenburg impala union and amandelbult sections concentrations of platinum group elements in two borehole intersections of the ug2 chromitite are 4 ppm over 1 2 m and 2 4 ppm over 2 2 m therefore bulk pge levels appear to be only moderately lower than those at western platinum mine this renders models explaining pge enrichment by upward percolating melt or fluids problematic the merensky reef although containing sulphides is only weakly mineralized with pge 0 6 ppm the ug2 pyroxenite is separated from the ug2 chromitite by a 15 m noritic layer the introduction of feldspathic cumulates between two units that elsewhere directly overly each other may be explained by the more evolved composition of resident magma in those parts of the chamber distally located with regard to a major feeder zone at union section it also suggests that the ug2 unit is a multiple rather than a single cyclic unit