geochemistry of geothermal waters from the gonghe region northwestern china implications for identification of the heat source the gonghe geothermal region located in the northeastern part of qinghai tibet plateau is the most geothermally active in qinghai province the geothermal waters from three hydrothermal areas qiabuqia guide and xinghai of gonghe are characterized with different hydrochemical types nevertheless their d and 18o data suggest that they are all of meteoric origin most gonghe samples are far away from the full equilibrium line in na k mg triangular diagram implying that na k geothermometer is generally not suitable for calculating the reservoir temperatures in comparison silica geothermometers perform much better and give more accurate temperature estimations the hydrochemistry of the gonghe geothermal waters is distinctively different from that of the hot springs from rehai a well known magmatic hydrothermal area located in the tengchong volcanic region of yunnan province southwestern china indicating that the geothermal anomaly in gonghe is not related to an underlying magma chamber instead the strong hydrothermal manifestation there is more likely to be supported by the intense deep tectonic activities moreover the possible existence of radioactive heat source can not be ruled out at this stage

the bimodal ph distribution of volcanic lake waters abstract volcanic lake waters have a bimodal ph distribution with an acidic mode at ph 0 5 1 5 and a near neutral mode at ph 6 6 5 with relatively few samples having ph 3 5 5 to investigate the reasons for this distribution the irreversible water rock mass exchanges during the neutralization of acid so4 cl waters with andesite under both low and high temperature conditions were simulated by means of the eq3 6 software package version 7 2 reaction path modeling under low temperature and atmospheric pco2 and fo2 suggests that several homogeneous and or heterogeneous ph buffers exist both in the acidic and neutral regions but no buffer is active in the intermediate central ph region again the same titration under high temperature hydrothermal magmatic conditions is expected to produce comparatively infrequent aqueous solutions with ph values in the 3 5 5 range upon their cooling below 100 c substantially different ph values are obtained depending on the cooling paths either through boiling or conductive heat losses these distinct ph values are governed by either hso4 and hcl aq in poorly neutralized aqueous solutions or the co2 aq hco3 couple and the pco2 value as well in neutralized aqueous solutions finally mixing of the acid lake water with the aqueous solutions produced through high temperature titration and cooled below 100 c is unlikely to generate mixtures with ph values higher than 3 unless the fraction of the acidic water originally present in the lake becomes very small which means its virtually complete substitution summing up the evidence gathered through reaction path modeling of the neutralization of acid lake waters with andesite both at low and high temperatures explains the scarcity of volcanic lake waters with measured ph values of 3 5 5

geochemistry of hot springs in the tengchong hydrothermal areas southwestern china abstract as an important volcanic geothermal region in china tengchong belongs to the mediterranean himalayas geothermal belt and is characterized by wide distribution of volcanic rocks fifty eight hydrothermal areas have been identified in tengchong among which the rehai hydrothermal system is the most geothermally active the geothermal waters from rehai are mainly na hco 3 cl and na hco 3 types whereas those from the other hydrothermal areas are mainly na hco 3 na ca hco 3 ca hco 3 ca mg hco 3 mg na ca hco 3 and mg ca hco 3 types both quartz geothermometer and k mg geothermometer indicate that the rehai geothermal field has higher subsurface temperatures than the other hydrothermal areas except for three rehai samples most geothermal water samples collected from tengchong are far from the full equilibrium line in giggenbach s triangular diagram suggesting that the complete chemical re equilibrium has not been achieved as these geothermal waters flow upward from reservoirs towards spring vents and possibly mix with cooler waters statistical analysis shows that cl b li rb and cs are the characteristic constituents of the tengchong geothermal waters and the good linear relations among these elements in the rehai geothermal waters reflect the existence of a deep parent geothermal liquid pgl below rehai an enthalpy chloride diagram of the rehai geothermal waters suggests that the parent geothermal liquid has cl concentration of 291 mg l and enthalpy of 1495 j g the pgl ascends to the surface through different channels and may cool by conduction of heat to reservoir host rocks by boiling or by mixing with cooler shallow groundwaters

natural pollutants of northern lake baikal hot and cold springs in the northwestern shore of lake baikal are investigated as natural pollutants of the lake which can interfere with its chemistry the study includes chemical analyses of lake water samples from different depths in the north baikal basin as well as waters of hot and cold onshore springs and baikal tributaries collected in 2007 through 2013 thermal waters in the shore of lake baikal have much higher so4 cl f na and sio2 concentrations than those in the lake water as well as ten to hundred times greater enrichments in li rb cs ga as and w mineral water in cold springs is generally similar to the baikal water with respect to total dissolved solids tds and major and trace element chemistry however the milky cold spring discovered in the lower reaches of the b cheremshan river within a few km from the lake stands out in its unusual ca mg so4 composition low ph 3 57 and high tds 535 mg l and trace element enrichments in al mn ni co zn y and ree the concentrations of these elements are still higher up to one or two orders of magnitude in suspended solids abundant in the spring water this water composition is typical rather of mine drainage in sulfide mineralization provinces and prompts the existence of a sulfide orebody in the area mn co ni zn and cd occur in the dissolved form and their concentrations in stream water near the b cheremshan inlet into baikal are only slightly lower than immediately downstream of the spring ree and y are ten times lower because of precipitation from the river water however all metals the spring water leaches from the surrounding rocks eventually end up in lake baikal although the spring has much greater enrichments relative to the baikal water in a number of elements it hardly can cause any significant change to the lake composition only local chemical anomalies of mn al co ni zn cd ree and y can be expected in the bottom sediments where the lake uptakes the b cheremshan stream

acid hot springs discharged from the rehai hydrothermal system of the tengchong volcanic area china formed via magmatic fluid absorption or geothermal steam heating across mainland china tengchong is geothermally unique because both magmatic hydrothermal systems and late cenozoic volcanic activities have been observed there rehai located in the tengchong volcanic area is the only hydrothermal system in mainland china discharging acid springs with very low ph values two types of acid geothermal waters were identified one is sulfate waters with low chloride concentrations and ph levels as low as around 2 the other has slightly higher chloride concentrations and is marked with diversified hydrochemical types both types of acid springs at rehai are immature waters and far from being equilibrated with a thermodynamically stable mineral assemblage comprising albite k feldspar muscovite and clinochlore characteristic for felsic rock hosted reservoirs in contrast to those neutral chloride springs at rehai that are formed via boiling conductive cooling or mixing with cold groundwaters of a parent geothermal liquid pgl the sulfate rich acid waters discharged from the diretiyan area the dagunguo area and the shizitou spring of rehai are essentially locally perched groundwaters heated by h2s rich steam separated from deep geothermal fluid the acidity of these waters originates from the oxidation of h2s in near surface environment in contrast the acid waters with higher chloride concentrations are the results of mixing between steam heated waters and neutral chloride waters the geochemical geneses of the rehai geothermal springs inferred based on stable hydrogen and oxygen isotopes are generally identical unlike active volcanic areas across the world there is a lack of acid waters at rehai formed through partial neutralization of magmatic fluid possibly owing to the comparatively deep seated magma chamber there no less than 7 km deep

chemical characteristics of the crater lakes of popocatetetl el chichon and nevado de toluca volcanoes mexico abstract three crater lakes from mexican volcanoes were sampled and analyzed at various dates to determine their chemical characteristics strong differences were observed in the chemistry among the three lakes nevado de toluca considered as dormant el chichon at a post eruptive stage and popocatepetl at a pre eruptive stage not surprisingly no influence of volcanic activity was found at the nevado de toluca volcano while the other volcanoes showed a correlation between the changing level of activity and the evolution of chemical trends low phs so 4 2 and f decreased irregularly at el chichon from 1983 until 1997 major cations concentrations also diminished at el chichon a 100 increase in the so 4 2 content was measured at popocatepetl between 1985 and 1994 an increase in the mg cl ratio between 1992 mg cl 0 085 and 1994 mg cl 0 177 was observed at popocatepetl before the disappearance of the crater lake in 1994 it is concluded that chemical analysis of crater lakes may provide a useful additional tool for active volcano monitoring

use of reaction path modeling to identify the processes governing the generation of neutral na cl and acidic na cl so4 deep geothermal liquids at miravalles geothermal system costa rica abstract the eq3 6 software package was used to investigate the irreversible water rock mass exchanges governing the production of neutral na cl and acidic na cl so 4 geothermal liquids circulating at depth into the miravalles geothermal system first we reconstructed the in situ reservoir composition including ph we evaluated the boundary conditions p co 2 p h 2 s and or p o 2 which are necessary for the implementation of reaction path modeling we estimated the thermodynamic affinity of the reservoir liquids with respect to relevant hydrothermal solid phases and we identified possible compositions of the initially acidic meteoric magmatic liquids then we modeled both the interaction between meteoric magmatic fluids and calc alkaline volcanic rocks and the interaction between neutral na cl waters and highly altered volcanic rocks reaction path modeling was performed through a purely stoichiometric approach without considering the kinetics of irreversible mass exchanges results of reaction path modeling suggest that the neutral na cl liquids hosted in the miravalles geothermal reservoirs are produced through interaction between initially acidic magmatic meteoric aqueous solutions and volcanic rocks and represent the final product of this process however the deep acid na cl so 4 liquids of miravalles are not intermediate products in this process they are instead generated through interaction of neutral na cl waters with volcanic rocks affected by advanced argillic alteration representing old solfataras buried by later volcanics as suggested by robert o fournier about 10 years ago

methods for calculating frechet derivatives and sensitivities for the non linear inverse problem a comparative study1 a fundamental step in the solution of most non linear inverse problems is to establish a relationship between changes in a proposed model and resulting changes in the forward modelled data once this relationship has been established it becomes possible to refine an initial model to obtain an improved fit to the observed data in a linearized analysis the frechet derivative is the connecting link between changes in the model and changes in the data in some simple cases an analytic expression for the frechet derivative may be derived in this paper we present three techniques to accomplish this and illustrate them by computing the frechet derivative for the id resistivity problem for more complicated problems where it is not possible to obtain an expression for the frechet derivative it is necessary to parameterize the model and solve numerically for the sensitivities partial derivatives of the data with respect to model parameters the standard perturbation method for computing first order sensitivities is discussed and compared to the more efficient sensitivity equation and adjoint equation methods extensions to allow for the calculation of higher order directional and objective function sensitivities are also presented finally the application of these various techniques is illustrated for both the 1d and 2d resistivity problems

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

the application of geochemistry to bicarbonate thermal springs with high reservoir temperature a case study of the batang geothermal field western sichuan province china abstract the batang geothermal field located at the north eastern margin of the qinghai tibet plateau is a high temperature geothermal system with two main geothermal areas namely bogexi and rekeng the rehai geothermal field is also a high temperature geothermal system with a magmatic heat source which shows geothermal manifestations similar to those in batang especially in the rekeng area in this study we compared the chemical compositions of different thermal springs in the batang geothermal field with those in the rehai geothermal field to ascertain whether the thermal spring waters in batang are also influenced by magma degassing or not further we investigated the hydrogeochemical processes involved in forming the various thermal springs in the batang geothermal field we find that the thermal waters in the batang geothermal field are not influenced by magma degassing although inorganic carbon including hco3 and co32 is the dominant anion component of most of the thermal waters in the batang geothermal field so42 is present in variable amounts in this area the mixing of the thermal waters with steam containing some amount of h2s generated by metamorphism probably causes the relatively high so42 concentration in the neutral thermal springs also beneath the rekeng area there is a deep reservoir with the temperature of about 180 c a shallow reservoir of a relatively low temperature of about 75 c was also identified in the eastern part about half of the thermal spring waters in rekeng directly originate in the deep reservoir mixing with little or no snow melt water and steam conversely no steady reservoir exists beneath the bogexi area we attribute the high levels of ca2 mg2 and tic total inorganic carbon in the thermal spring waters in the bogexi area to the carbonate geologic stratum distributed at the outlets of the springs

mineralogical crystal morphological and isotopic characteristics of smooth slope travertine deposits at reshuitang tengchong china abstract reshuitang is an important active hydrothermal area in the tengchong geothermal field and is characterized by many hot springs and their associated deposits detailed mineralogical crystal morphological and stable isotopic investigations of the smooth slope fossil travertines at reshuitang and hydrochemical studies of two active springs around the fossil travertines were conducted to study their genesis the results show that 1 the modern springs discharge waters with high temperature 70 c near neutral ph 6 3 8 34 and high saturation indices of calcite and aragonite 2 the fossil travertines contain calcite and small amounts of mn fe oxides halite thenardite and non carbonate debris 3 the calcite include ray crystals dendrite crystals platy crystals and spike crystals and 4 13c and 18o of the fossil travertines at reshuitang range from 1 59 to 0 87 and 6 48 to 7 80 respectively according to comparison between the travertines at reshuitang and other travertines in tengchong all these travertines are thermogene travertines with a large contribution of mantle degassing to their parent co2 but are formed at different temperatures the fossil travertines at reshuitang similar to those at shuzhishi are formed at high temperatures near 100 c which results in weak microbial activities during the formation of the fossil travertines most of the calcite crystals at reshuitang were non equilibrium products precipitated directly from the spring waters during the deposition process while the spike crystals originated from diagenetic dissolution of large calcite crystals comparison between the fossil travertines at reshuitang and other smooth slope travertines from other areas shows these smooth slope travertines have different lithofacies and fabrics in smooth slope environments temperature may control the distribution and development of microbes and the intensity of co2 degassing and consequently cause the precipitation of contrasting fabrics and lithofacies

magmatic fluid input explaining the geochemical anomaly of very high arsenic in some southern tibetan geothermal waters abstract tibet is characterized by extremely high terrestrial heat flow and widely distributed hydrothermal systems among which many are discharging geothermal waters with extremely high arsenic concentrations from over 10 mg l to up to 126 mg l the distribution of these high arsenic waters is basically in accordance with the location of the indian continental subduction zone a detailed analysis indicates that host rock leaching alone cannot explain the observed arsenic anomaly instead substantial contribution of arsenic from the underlying magma chambers is postulated which are likely mantle derived intrusions that have been severely contaminated by the very thick crustal material below southern tibet possibly including deep seated arsenic rich sedimentary rocks alternatively the partial melts at crustal depths reflected by the detected low velocity and or high conductivity anomalies in southern tibet serving as the magmatic heat source of the high arsenic hydrothermal systems may also form indirectly under the high temperature conditions generated by mantle upwelling or due to crustal thickening low sulfide concentrations further promote high dissolved arsenic concentrations with little formation of thioarsenates and no precipitation of limiting arsenic sulfide phases in contrast mantle magmas less affected by crustal contamination serving as the heat source of many hydrothermal systems in rift zones and hot spots worldwide where the crust is thinner are releasing magmatic fluids lower in arsenic and higher in mantle sulfur species overall the existence of a magmatic heat source alone does not ensure the formation of geothermal waters with very high arsenic concentrations and geothermal waters from sedimentary rock hosted systems are neither necessarily arsenic rich the most critical factor controlling the arsenic concentration of geothermal water discharging from a magmatic hydrothermal system is the geological genesis of the magma fluid and its chemical composition

hydrogeochemistry and environmental impact of geothermal waters from yangyi of tibet china abstract the yangyi geothermal field located 72 km northwest to lhasa city capital of tibet has a high reservoir temperature up to at least 207 2 c the geothermal waters from both geothermal wells and hot springs belong to the hco 3 co 3 na type factor analysis of all the chemical constituents shows that they can be divided into two factors f 1 factor receives the contributions of so 4 2 cl sio 2 as b na k and li whereas f 2 factor is explained by hco 3 f co 3 2 ca 2 and sr 2 the f 1 factor can be regarded as an indicator of the reservoir temperature distribution at yangyi but its variable correlation with the results of different geothermometers na k quartz and k mg does not allow one to draw further inferences different from f 1 the f 2 factor is an indicator of a group of hydrogeochemical processes resulting from the co 2 pressure decrease in geothermal water during its ascent from the deep underground including transformation of hco 3 to co 3 2 precipitation of ca 2 and sr 2 and release of f from some fluoride bearing minerals of reservoir rocks the plot of enthalpy vs chloride prepared on the basis of na k equilibrium temperatures suggests that a parent geothermal liquid pgl with cl concentration of 185 mg l that of sample yyt 8 and enthalpy of 1020 j g corresponding to a temperature of 236 237 c i e somewhat higher than that of sample yyt 6 is present in the geothermal reservoir of the yangyi area below both the qialagai valley and the bujiemu valley although the samples less affected by mixing and cooling yyt 6 and yyt 7 come from the second site the discharge of geothermal waters with high contents of toxic elements such as b as and f into the luolang river the only drinking water source for local residents has caused slight pollution of the river water great care should therefore be taken in the geothermal water resource management at yangyi

physical boundaries of intrathermocline ulleung eddies in the east japan sea abstract a new eddy detection algorithm is developed based on the particle tracking experiment pte to determine the spatial extent of the intrathermocline ulleung eddies iue in the east japan sea ejs the new eddy detection method enables us to identify three regions of interests the iue transitional regions between the iue and mean currents and mean current regions around iue the estimated spatial boundary of the iue is expressed as least square fitted elliptic characteristics from february to september 2015 accordingly we could obtain three main results after analyzing the iue 1 the center and the highest sea level height of the iue are not co located suggesting that the iue is sustained by potential vorticity through the relative vorticity in response to bathymetry changes 2 the highest sea level is always anchored around ulleung island which is associated with the relatively high chlorophyll concentration chl around the edge of the iue and 3 the shape of the iue is strongly influenced by the current systems in the ulleung basin furthermore the semi major and semi minor axes and its ratios are determined as well as the mean areas and the highest sea surface height of the iue to understand the spatio temporal characteristics of the iue and the dominant frequencies on it

hydrogeochemistry of high temperature geothermal systems in china a review as an important part of the mediterranean himalayas geothermal belt southern tibet and western yunnan are the regions of china where high temperature hydrothermal systems are intensively distributed of which rehai yangbajing and yangyi have been investigated systematically during the past several decades although much work has been undertaken at rehai yangbajing and yangyi to study the regional geology hydrogeology geothermal geology and geophysics the emphasis of this review is on hydrogeochemical studies carried out in these geothermal fields understanding the geochemistry of geothermal fluids and their environmental impact is critical for sustainable exploitation of high temperature hydrothermal resources in china for comparison the hydrogeochemistry of several similar high temperature hydrothermal systems in other parts of the world are also included in this review it has been confirmed by studies on cl and stable isotope geochemistry that magma degassing makes an important contribution to the geothermal fluids from rehai yangbajing and yangyi though meteoric water is still the major source of recharge for these hydrothermal systems however the mechanisms of magma heat sources appear to be quite different in the three systems as recorded by the 3he 4he ratios of escaping geothermal gases a mantle derived magma intrusion to shallow crust is present below rehai although the intruding magma has been heavily hybridized by crustal material by contrast the heat sources below yangbajing and yangyi are inferred to be remelted continental crust besides original sources the geochemistry of characteristic constituents in the geothermal fluids have also been affected by temperature dependent fluid rock interactions boiling and redox condition changes occurring in the upper part of hydrothermal systems and mixing with cold near surface waters the geothermal fluids from rehai yangbajing and yangyi contain very high concentrations of some toxic elements since local drinking water sources may be mixed with geothermal water and irrigation with water containing geothermally derived harmful elements possibly leading to accumulation in crops consumed by human beings the natural geothermal spring discharge or anthropogenic geothermal wastewater drainage of these fields poses a threat to the environment and human health future research work should focus on estimation of stable o and h isotope compositions of magmatic water related to high temperature hydrothermal systems in china which is of significance for the quantitative source study of geothermal fluid recharged by degassed magmatic waters attention should also be paid to some constituent species in geothermal fluid of strong environmental significance such as thioarsenate that is crucial for the fate of as discharged from geothermal springs especially sulfidic hot springs

fluid geochemistry and geothermometry applications of the kangding high temperature geothermal system in eastern himalayas abstract high temperature geothermal systems hold an enormous capacity for generating geothermal energy the kangding area is a typical high temperature geothermal field in the himalayan geothermal belt hydrogeochemical gas geochemical and isotopic investigations were performed to identify and qualify the main hydrogeochemical processes affecting thermal water composition including mixing and degassing and then to estimate a reliable reservoir temperature nine water samples and four geothermal gas samples were collected and analysed for chemical and isotopic components the results demonstrate the alkaline deep geothermal water is the mixtures of approximately 75 snow melt water and 25 magmatic water it is enriched in na k f li and other trace elements indicating the granite reservoir nature the shallow geothermal water is the mixtures of approximately 30 upward flow of deep geothermal water and 70 meteoric cold water high concentrations of ca mg and hco3 indicate the limestone reservoir nature there is no remarkable oxygen isotope shift in the geothermal water since the rapid circulation is difficult to trigger off strong water rock interaction co2 is the predominant geothermal gas accounting for more than 97 of total gases in volume percentage the concentration of co2 degassing ranged from 0 4 mol l 1 to 0 8 mol l 1 via geothermometrical modelling as a result the geothermal water ph increased from 6 0 to 9 0 and approximately 36 of the total sio2 re precipitate the sources of co2 are the metamorphism of limestone and magmatic degassing based on the composition of carbon isotope the appropriate geothermometers of na k and na li yield reservoir temperature of 280 c the geothermometrical modelling developed to eliminate the effects of co2 degassing yields temperature of 250 c the silica enthalpy mixing model yields temperature of 270 c with no steam separation before mixing

arsenic and thioarsenic species in the hot springs of the rehai magmatic geothermal system tengchong volcanic region china abstract rehai is the sole geothermal area in mainland china that discharges both acidic and alkaline hot springs with phs ranging from 1 4 to 10 0 the hot springs in rehai are also characterized by a wide range of arsenic concentrations with the highest being 1 35 mg l analysis of the arsenic geochemistry indicates that the alkaline and neutral hot springs in rehai have high arsenic concentrations the alkaline hot springs represent arsenic rich boiled reservoir fluids and the neutral hot springs represent mixtures of these reservoir fluids with non thermal waters and or condensed steam the enrichment of arsenic in the deep reservoir fluids also called primary fluids is primarily attributable to the leaching of reservoir rocks at high temperatures but a possible arsenic contribution from magmatic fluids cannot be ruled out the acidic springs in contrast have much lower arsenic concentrations because they are a mixture of non thermal oxygenated waters and condensed steam both of which are depleted in arsenic in addition to arsenite and arsenate mono di and tri thioarsenates have been detected in the rehai geothermal waters the arsenic speciation in the rehai hot springs is primarily linked to the formation processes of the various secondary fluids at the surface and their sulfide concentrations in addition the speciation is also affected by the ph values and the redox potentials of the waters compared to the springs along secondary e w trending faults the chloride rich springs along the main n s trending faults are generally much less affected by mixing with non thermal waters and or condensed steam they are also more enriched in sulfide and thioarsenates consequently represent a greater proportion of the total arsenic this is the first study to report the thioarsenic geochemistry of hot springs in china

isotopic and chemical composition of water and steam discharges from volcanic magmatic hydrothermal systems of the guanacaste geothermal province costa rica the guanacaste geothermal province encompasses three major geothermal systems each centered on its respective volcanic structure rincon de la vieja to the nw miravalles in the center and tenorioto the se each shows corresponding sets of surface manifestations vapor discharges from fumaroles and steam heated pools at altitudes 500 m lower temperature so4cl springs on the lower slopes of the respective volcano and cooler neutral cl springs to the s of the volcanic chain at altitudes 500 m the production of hco3 rich waters is limited to a narrow belt stretching to the s of miravalles volcano chemical and isotopic evidence suggests that the neutral cl waters also discharged from deep wells are derived from a more primitive clso4 water formed by transfer of readily mobilised originally magmatic constituents to deeply circulating groundwater isotopic evidence suggests that this groundwater is derived largely from areas to the north of the volcanic chain the presence of immature waters within drillable depth is indicated by the incursion of an acid so4 water into a well at miravalles after deepening to 2000 m as the cl waters rise they start to boil the separated vapors feed the fumaroles and steam heated features at the surface the residual water travels underground to be discharged some 5 25 km to the s the uniformity in chemical and isotopic compositions of the neutral cl waters is compatible with the assumption that the individual thermal systems are linked at depth to form large contiguous geothermal reservoirs beneath the guanacaste geothermal province

environmental impacts of geothermal waters with extremely high boron concentrations insight from a case study in tibet china abstract boron is a potentially toxic element in the environment and commonly enriched in high temperature geothermal waters in this study seven typical boron rich geothermal areas in tibet china were selected as the study areas for comprehensively investigating the geochemistry of geothermal boron and its environmental impact the geothermal waters were classified into four types acid low boron waters acid high boron waters neutral alkaline low boron waters and neutral alkaline high boron waters the enrichment of boron in the neutral alkaline high boron geothermal waters is attributed to the input of magmatic fluids whereas the host rock leaching is the primary boron source for the neutral alkaline low boron geothermal waters the acid low boron waters are essentially locally perched groundwaters heated by geothermal vapors separated from flashed deep geothermal fluids and thereby their boron comes mainly from the limited leaching of the host rocks of the shallow aquifers as for the acid high boron waters they could be formed via a mixing between acid low boron waters and neutral alkaline geothermal waters with the latter as the primary boron source the boron species in these geothermal waters comprise mainly h3bo3 b oh 4 polyborate ions and fluoroborate complexes all of which are affected by the ph temperature and f and b concentrations of the waters when the geothermal waters flow out of the hot spring vents the rapid changes in unstable parameters like ph and water temperature will lead to the conversion of b oh 4 and polyborate ions to h3bo3 the discharge of the boron rich geothermal waters has contaminated the surface waters and sediments in and around the investigated geothermal areas in turn the boron sorbed onto into the hot spring sediments is liable to be released either in short term if it is originally exchangeable boron or in long term if carbonates fe mn oxides or organic matters sulfides combined boron this study enhances the understanding of geothermal boron speciation and its environmental impact and provides insights for rational exploitation of hydrothermal resource without inducing geothermal boron pollution

major hydrogeochemical processes in the two reservoirs of the yangbajing geothermal field tibet china abstract the yangbajing geothermal field with the highest reservoir temperature in china is located about 90 km northwest to lhasa city capital of tibet where high temperature geothermal fluids occur both in shallow and deep reservoirs the geophysical survey by the indepth international deep profiling of tibet and the himalayas project group proved the existence of magmatic heat source at yangbajing in the study area the hydrochemistry of cold surface waters and groundwaters and that of thermal groundwaters from both reservoirs are distinctively different however analysis of the relationship between enthalpy values and cl concentrations of cold groundwaters and geothermal fluids indicates that the geothermal fluids from the shallow reservoir were formed as a result of mixing of cold groundwaters with geothermal fluids from the deep reservoir in other words the geothermal fluids from the deep reservoir flowed upwards into the shallow reservoir where it was diluted by the shallow cold groundwaters to form the shallow geothermal fluids with much lower temperature a binary mixing model with two endmembers the cold groundwaters and the deep geothermal fluids was proposed and the mixing ratios for the geothermal fluid from each shallow well were estimated using the mixing ratios the concentrations of some constituents in shallow geothermal fluids such as as b sio 2 so 4 2 and f were calculated and their differences with the actual concentrations were estimated the results show that the differences between estimated and actual concentrations of as and b are small the average absolute values being only 1 9 and 7 9 respectively whereas those of sio 2 so 4 2 and f are much bigger indicating that other hydrogeochemical processes are responsible for the concentrations of these constituents it is postulated that sio 2 precipitation due to water temperature decrease h 2 s oxidation and ion exchange between oh in geothermal waters and exchangeable f in fluoride bearing silicate minerals during the geothermal fluid upflow might be the causes for the observed concentration differences

fluid geochemistry of the cuopu high temperature geothermal system in the eastern himalayan syntaxis with implication on its genesis abstract high temperature geothermal fluids dissolve constituents pertinent to water rock interaction and magmatic volatile absorption resulting in high total dissolved solid tds values however this study focuses on the hydrochemical evolution of the low salinity hco3 na type high temperature geothermal fluid in cuopu eastern himalayas the geothermal water is recharged by local precipitation and glacier water from surrounding mountains the tds values are below 834 mg l and the constituents are mainly products of the water carbon dioxide rock interactions lacking magmatic volatile dissolved in the fluid the geothermal water reaches an almost complete chemical equilibrium with the feldspar or plagioclase enriched reservoir rock in a reducing condition the reservoir temperature is between 175 c 200 c while the temperature could reach up to 400 c in the deep crustas indicated by the carbon isotopic exchange equilibrium between co2 and ch4 the infiltrated glacier water was heated during its circulation within the hot thickened crust and continued dissolving the crustal metamorphic gas such as radiogenic helium and limestone metamorphic co2 until the junction of the two sets of faults provided an ascending channel for it upon rising along the conduit the geothermal water mixed with cold groundwater to different degrees approximately 0 015 mol l co2 escaped from the geothermal fluid when it scattered as bubbling hot springs on the surface of the anisotropic porous quaternary sediments such kind ofhydrochemical evolution of lowsalinity alkaline hco3 na type water represents a typical formation mechanism of the high temperature geothermal systems along the himalayas

magnetotelluric images of deep crustal structure of the rehai geothermal field near tengchong southern china broadband 0 004 4096 s magnetotelluric mt soundings have been applied to the determination of the deep structure across the rehai geothermal field in a quaternary volcanic area near the indo eurasian collisional margin tensorial analysis of the data show evidence of weak to strong 3 d effects but for approximate 2 d imaging we obtained dual mode mt responses for an assumed strike direction coincident with the trend of the regional scale faults and with the principal impedance azimuth at long periods the data were subsequently inverted using different approaches the rapid relaxation inversion models are comparable to the sections constructed from depth converted invariant impedance phase data the results from full domain 2 d conjugate gradient inversion with different initial models are concordant and evoke a picture of a dome like structure consisting of a conductive 50 1000 m cap which is about 5 6 km thick in the central part of the known geothermal field and thickens outwards to about 15 20 km the anomalous structure rests on a mid crustal zone of 20 30 m resistivity extending down to about 25 km depth where there appears to be a moderately resistive 30 m substratum the mt images are shown to be in accord with published geological isotopic and geochemical results that suggested the presence of a magma body underneath the area of study

meteoric interaction with magmatic discharges in japan and the significance for mineralization the andesitic volcanoes kirishima kyushu and esan hokkaido discharge 94 to 225 c hcl bearing vapors from summit fumaroles at kirishima a geothermal system exists on the flanks of the large volcanic massif 1500 m relief and 12 km radius in contrast esan is a small dome 600 m relief and 1 km radius with ephemeral hot springs the chemical and isotopic compositions of the fumarole gases and condensates and of waters from hot springs indicate that esan discharges are dominated by magmatic water and gases whereas those at kirishima are mainly meteoric the kirishima geothermal system contains acid fluids that are neutralized by interaction with the host rock and dilution by meteoric ground water the acidity is probably of magmatic origin a large ground water carapace at kirishima condenses a majority of magmatic volatiles and metals before they can discharge to the surface in contrast to esan where the volatiles including metals degas to the atmosphere this suggests that a meteoric system may be necessary to condense metals in this high level volcanic environment to provide a situation conducive to hydrothermal mineralization at epithermal depths