Infiltration Of Meteoric Water Research Articles

Hydrogeochemical assessment of Moradabad city, an important industrial town of Uttar Pradesh, India

An attempt has been made to understand the hydrochemistry of Moradabad city, a major industrial town of western Uttar Pradesh. For this purpose a total of 188 samples for both the seasons (pre- and post-monsoon of 2012 and 2013) were collected and analyzed for major cations (Na+, K+, Ca2+ and Mg2+) and anions (Cl−, HCO3 −, SO4 −, NO3 − and F−) and 14 samples collected in 2013 were analyzed for trace elements. The groundwater is slightly acidic to alkaline in nature and moderately hard to very hard. Elevated concentration of most of the major ions and trace elements is observed in the area. On the basis of Piper Trilinear plot groundwater has been identified as Na–Cl–SO4 type in pre-monsoon and Na–HCO3 type in post-monsoon season. Base-exchange indices along with meteoric genesis indices demonstrate that groundwater in all the four seasons belong to alkali bicarbonate type and are of shallow meteoric water percolation type. The concentration of the trace elements like (Al, Fe, Se and As) is higher than the permissible limits. Correlation of SiO2 with Cl and TDS was done to assess the processes responsible for altering the groundwater chemistry. Water quality index maps show that the groundwater in the north eastern and central parts of the study area is unsuitable for drinking purpose. A comparison of spatial distribution of EC and Cl with those of WQI depicts a strong correlation. The study, thus, suggests the poor groundwater quality of Moradabad city. Urban sprawl, population explosion, industrial expansion heavily affected the water quality of the study area.

Multiple dolomitization and later hydrothermal alteration on the Upper Cambrian-Lower Ordovician carbonates in the northern Tarim Basin, China

Thick Upper Cambrian-Lower Ordovician carbonates were deposited on a shallow marine platform in the northern Tarim Basin, which were extensively dolomitized, particularly for the Upper Cambrian carbonates. The resulting dolomite rocks are predominantly composed of matrix dolomites with minor cement dolomites. Based on petrographic textures, matrix dolomites consist of very finely to finely crystalline, nonplanar-a to planar-s dolomite (Md1), finely to medium crystalline, planar-e(s) dolomite (Md2), and finely to coarsely crystalline, nonplanar-a dolomite (Md3). Minor cement dolomites include finely to medium crystalline, planar-s(e) dolomite (Cd1) and coarsely crystalline, nonplanar saddle dolomite (Cd2), which partially or completely fill dissolution vugs and fractures; these cements postdate matrix dolomites but predate later quartz and calcite infills. Origins of matrix and cement dolomites and other diagenetic minerals are interpreted on the basis of petrography, isotopic geochemistry (O, C and Sr), and fluid inclusion microthermometry. Md1 dolomite was initially mediated by microbes and subsequently precipitated from slightly modified brines (e.g., evaporated seawater) in near-surface to very shallow burial settings, whereas Md2 dolomite was formed from connate seawater in association with burial dissolution and localized Mg concentration (or cannibalization) in shallow burial conditions. Md3 dolomite, however, was likely the result of intense recrystallization (or neomorphism) upon previously-formed dolomites (e.g., Md1 or Md2 dolomite) as the host carbonates were deeply buried, and influenced by later hydrothermal fluids. Subsequent cement dolomite and quartz crystals precipitated from higher-temperature, hydrothermal fluids, which were contributed more or less by the extensive Permian large igneous province (LIP) activity in Tarim Basin as evidenced by less radiogenic Sr in the cement and parts of matrix dolomites. This extensive abnormal hydrothermal activity could also have resulted in recrystallization (or neomorphism) on the previous matrix dolomites. Faults/fractures likely acted as important conduit networks which could have channeled the hydrothermal fluids from depths. However, the basin uplift triggered by the Late Hercynian Orogeny from the Late Permian would have facilitated downward infiltration of meteoric water and dilution of hydrothermal fluids, resulting in precipitation of later calcites in which lighter C and more radiogenic Sr components demonstrate such a switch of fluid properties. This study provides a useful analogue to understand the complicated dolomitizing processes and later hydrothermal alteration intimately related to the Permian LIP activity within Tarim Basin and elsewhere.

The distribution of thermogenic, bacterial and inorganic fluid sources in the petroleum systems of the Llanos Basin (Colombia) – Insights from the noble gases and carbon stable isotopes

The Colombian Andean foreland is a rich petroleum province, where various source rocks and an active circulation of fresh water are present in the subsurface, resulting in a complex fluid mixture within the reservoirs. Moreover, some of the traps are shallow, and low °API gravity oils are found. Massive meteoric water infiltration and local biodegradation have been proposed to explain these observations, but require some in-depth investigation to be confirmed. In order to provide some new insights into the Llanos Basin petroleum system, we performed a natural gas geochemical survey over different areas of the basin, including stable isotopes of hydrocarbon, non-hydrocarbon and noble gases. Results show that the influence of meteoric water infiltration is dominant in the shallow area eastward, but decreases towards the deepest part of the basin westward. A general gas/oil phase separation differentiates gas-depleted biodegraded, shallow reservoirs from deep gas-rich less-altered reservoirs. Data suggest that there is a shallow biodegradation associated with meteoric water circulation in the Carbonera Fm, while some of the deeper heavy oils (Mirador, Une fms) were more likely produced by an early mature source rock. However, biodegraded oil later mixed with less altered oil and associated gas are plausible. This study also indicates a contribution of mantle fluids in the deepest parts of the basin near the contact with the Guaycaramo Fault System. There, older rift sequences may have recorded mantle fluid fluxes, or alternately the presence of diffuse mantle fluxing along the deep-rooted thrust front during the formation of the Llanos Basin.

Origin and evolution of geothermal fluids from Las Tres Vírgenes and Cerro Prieto fields, Mexico – Co-genetic volcanic activity and paleoclimatic constraints

Major and trace elements, noble gases, and stable (δD, δ18O) and cosmogenic (3H, 14C) isotopes were measured from geothermal fluids in two adjacent geothermal areas in NW-Mexico, Las Tres Vírgenes (LTV) and Cerro Prieto (CP). The goal is to trace the origin of reservoir fluids and to place paleoclimate and structural-volcanic constraints in the region. Measured 3He/4He (R) ratios normalized to the atmospheric value (Ra = 1.386 × 10−6) vary between 2.73 and 4.77 and are compatible with mixing between a mantle component varying between 42 and 77% of mantle helium and a crustal, radiogenic He component with contributions varying between 23% and 58%. Apparent U–Th/4He ages for CP fluids (0.7–7 Ma) suggest the presence of a sustained 4He flux from a granitic basement or from mixing with connate brines, deposited during the Colorado River delta formation (1.5–3 Ma). Radiogenic in situ4He production age modeling at LTV, combined with the presence of radiogenic carbon (1.89 ± 0.11 pmC – 35.61 ± 0.28 pmC) and the absence of tritium strongly suggest the Quaternary infiltration of meteoric water into the LTV geothermal reservoir, ranging between 4 and 31 ka BP. The present geochemical heterogeneity of LTV fluids can be reconstructed by mixing Late Pleistocene – Early Holocene meteoric water (58–75%) with a fossil seawater component (25–42%), as evidenced by Br/Cl and stable isotope trends. CP geothermal water is composed of infiltrated Colorado River water with a minor impact by halite dissolution, whereas a vapor-dominated sample is composed of Colorado River water and vapor from deeper levels. δD values for the LTV meteoric end-member, which are 20‰–44‰ depleted with respect to present-day precipitation, as well as calculated annual paleotemperatures 6.9–13.6 °C lower than present average temperatures in Baja California point to the presence of humid and cooler climatic conditions in the Baja California peninsula during the final stage of the Last Glacial Pluvial period. Quaternary recharge of the LTV geothermal reservoir is related to elevated precipitation rates during cooler-humid climate intervals in the Late Pleistocene and Early Holocene. The probable replacement of connate water or pore fluids by infiltrating surface water might have been triggered by enhanced fracture and fault permeability through contemporaneous tectonic–volcanic activity in the Las Tres Vírgenes region. Fast hydrothermal alteration processes caused a secondary, positive δ18O-shift from 4‰ to 6‰ for LTV and from 2‰ to 4‰ for CP geothermal fluids since the Late Glacial infiltration.

Origin and evolution of palaeokarst within the Lower Ordovician (Ibexian) Goodwin Formation (Pogonip Group)

AbstractPalaeokarst within the Lower to Middle Ordovician Goodwin Formation, Pogonip Group (upper Ibexian-lower Whiterockian) was examined in detail at Meiklejohn Peak, Nevada USA in order to determine its origin, evolution, and relationship to sea level change. Detailed outcrop and petrographic examination of dolostone breccias and host rock reveals that palaeokarst was formed and affected by two distinct cycles of sea level change. A relative transgression resulted in deposition of lagoonal, ooid shoal, and shallow subtidal facies as sea level rose. Exposure of the carbonate platform led to the formation of multiple phreatic caves below the water table, as well as the development of numerous vadose conduits from the downward percolation of meteoric waters. Vadose water flow through early cave-wall and cave-roof collapse breccias resulted in rounding of smaller breccias clasts via physical transport and corrosion, while subsidence of subsurface karst led to the formation of a palaeodoline at the exposure surface. A second relative transgression deposited lagoonal sediments over the older karst; subsequent re-exposure of the carbonate platform resulted in the development of small breccia pockets as well as grikes within the youngest lagoonal sediments, and may have led to further corrosion of the older, deeper subsurface karst. The distal location of the study area within the carbonate platform suggests karst formation was the result of a substantial drop in relative sea level; the presence of multiple generations of palaeokarst imply that at least two higher-frequency cycles of sea-level change overprint the larger regression.

Stable isotope constraints on the origin of kaolin deposits from Variscan granitoids of Galicia (NW Spain)

Kaolinite-rich fractions of <45, <2 and <1μm size from deposits of Galicia (NW Spain) at Ramón-Fazouro and Nuevo Montecastelo to the north, Vimianzo, Barilongo and Lendo in the center, and Santa Tecla to the south show significant ranges in δ18O from 16.5 to 22.4‰ and in δD from −99 to −40‰. These widely spread values question a single crystallization process as no statistically significant overall correlation between δ18O and δD can be obtained. The analytical spread is such that 11 of the 43 analyzed separates plot below the kaolinite weathering line, and one at the line separating the supergene from hypogene evolution field. Noteworthy for this wide scatter is the fact that some separated size fractions, especially from Ramón-Fazouro deposit contain also up to 65% halloysite, as well as varied amounts of contaminating minerals generally considered as relicts from parental igneous rocks, such as quartz, illite (=muscovite) and feldspars. However, the addition of these minerals does not appear to significantly bias the isotopic data of the <2μm size fractions. Mean values for the <1μm kaolin fractions of the five deposits for which there is more than a single sample have linearly correlated δ18O and δD values with a best-fit line: δD=8.75 δ18O−248 (R=0.896, n=5, >95%) rather similar to the kaolinite weathering line of δD=7.5 δ18O−220. However, the overall spread of values and particularly those for coarser material, together with occurrences of halloysite, strongly suggest that higher temperature process(es) also occurred.Kaolinite, and also likely halloysite, crystallized from waters, whose δ18O values were of meteoric signature from about −5 to −1‰, at temperatures ranging from about 20°C to 50°C. The higher crystallization temperatures, especially at the sedimentary Lendo deposit, imply fluids at higher temperatures than during a climatic-controlled weathering process, probably of a low-temperate hydrothermal character with a fluid isotopically close to meteoric origin. However, interaction with fluids at higher temperatures and with higher δ18O cannot be ruled out, because the relatively wide ranges of kaolin δ18O and δD values are difficult to reconcile with a narrow range of δ18O and δD for the interacting parental fluids. The most likely scenario for the kaolinite and halloysite precipitation is then a two-stage process of interaction with meteoric waters at close Earth-surface temperature, but with one of the two episodes occurring at temperatures slightly above those of weathering processes even under tropical conditions. There is no compelling evidence for an episode of significantly high temperature, such as in most hydrothermal fluid–rock interactions, but a low-temperature episode of about 50°C cannot be ruled out unequivocally, especially for the <2μm material. Following local continental weathering, percolation of meteoric waters at temperatures up to ~50°C, and even higher, through the granitoids and felsites could have favored halloysite crystallization and affected the isotopic composition of earlier precipitated kaolinite.

Source, transport, and evolution of saline groundwater in a shallow Holocene aquifer on the tidal deltaplain of southwest Bangladesh

AbstractDeltaic groundwater resources are often vulnerable to degradation from seawater intrusion or through interaction with saline paleowaters. The Ganges‐Brahmaputra‐Meghna River delta, in Bangladesh and West Bengal, India, is a particularly vulnerable area with an estimated 20 million coastal inhabitants directly affected by saline drinking water. The shallow groundwater of the coastal regions is primarily brackish with pockets of fresher water. A small‐scale hydrologic investigation of groundwater salinity beneath an embanked tidal channel island was undertaken to explore possible hydrogeological explanations of the distribution of water salinities in the shallow aquifer. This study employs a combination of 3H and 14C dating, electromagnetic subsurface mapping, and a 2‐D solute transport model. The authors conclude that the shallow groundwater salinity can best be explained by the slow infiltration of meteoric water into paleo‐brackish estuarine water that was deposited during the early‐mid Holocene.

Geochemistry of pore water and associated diagenetic reactions in the diapiric area of Yinggehai Basin, northwestern South China Sea

This study examined the geochemical features of pore water in the diapiric area of the Yinggehai Basin, northwestern South China Sea, and illuminated the origin and evolution of basin fluids. Pore water with low salinity occurs in marine sediments in the diapiric area even without meteoric water infiltration. The presence of low-salinity water within deep, overpressured compartments is assumed to be due to smectite-illite transformation. Howerver, in shallow portions (less than 2 000 m) of diapiric areas with normal pressure, pore water has a much wider variation and much lower salinity than that in the overpressured intervals. Its total dissolved solid (TDS) content is ∼5 336 to 35 939 mg/L. Moreover, smectite and chlorite content sharply decreases as kaolinite and illite content increase in shallower intervals. The geochemical variation of pore water in diapiric structures indicates the expulsion of low-salinity, overpressured fluids along vertical faults. Strong injection of hot fluids from deep overpressured sediments results in rapid clay mineral transformation in shallow reservoirs. Consequently, fluid mixing due to fluid expulsion from deeper overpressured deposits leads to variation in salinity and ionic composition as well as some diagenetic reactions. This includes transformation of clay minerals caused by the higher temperatur of deeper hot fluids, e.g., the transfromation of smectite to illite and chlorite to kaolinite. Therefore, variations in salinity and ionic compositions in various pressured systems provide a clue to flow pathways and associated diagenetic reactions.

Ore-forming timing of polymetallic-fluorite low temperature veins from Central Pyrenees: A Pb, Nd and Sr isotope perspective

Vein fluorite deposits (Tebarray, Lanuza, Bielsa-Parzán, Bizielle and Yenefrito) as well as one MVT-style fluorite mineralization (Portalet) in the Central Pyrenees are the focus in this contribution. These deposits are made up of fluorite, barite, base metal sulphides, calcite, and quartz and are hosted in sedimentary rocks and granites of Palaeozoic age. Generally, these mineral occurrences, typically associated with Late Palaeozoic steeply dipping faults are similar with respect to geologic setting, mineralogy and geochemical trends to other fluorite and base metal veins located in the Central Pyrenees. Veins occurring along such faults most likely represent channelways used by mineralizing solutions that were expelled from the basement. Previous work argued for genetic processes involving circulation of mineralising fluids during the Triassic–Lower Cretaceous period, which is often considered to represent a period of heat, fluid, and mass transfers related to rifting events in the western European basins, which is related to the opening of the Atlantic.A major goal of this study was to decipher the timing of fluid flow and ore formation on the basis of Nd–Sm dating of fluorite sampled from a number of deposits sharing a similar geological framework. No precise age(s) could be obtained due to a scatter in data, but results from the Portalet MVT-style deposit point to a mid-Triassic age (around 220Ma) for this mineralization. The model that best explains the diagenetic stratabound mineralization at Portalet is gravity-driven fluid flow involving basinal brines during a rifting stage. Indeed, the formation of horst and graben structures during Early Alpine extensional tectonics favoured the infiltration of meteoric water into uplifted blocks, followed by fluid migration through the deeper parts of the basins whereby heat and dissolved components were acquired. This model also explains diagenetic changes recorded in the host limestone at Portalet. Also, overall Pb, Sr and Nd isotopic ratios measured in galena and fluorite suggest that differences in host rock and in the lithology of the basement seem to have exerted control on the chemistry of mineralizing fluids providing each deposit with distinctive characteristics.

Groundwater at Shmakovka Spa: Chemical Composition and Element Sources

This study presents new data on major element contents, trace and REE concentration of groundwater in Shmakovka Spa, located in the western part of Primorye, in the Far East of Russia. The studied area is characterized by two types of groundwater issuing from springs and wells: fresh water with low mineralization (TDS up to 100 mg/l), and high pCO2 water with high mineralization (TDS up to 3,000 mg/l). Our new data on the chemical composition of groundwater and δC(TIC), oxygen (δO) and hydrogen (δH) isotope data, indicate that these waters are the result of meteoric water infiltration into the Sikhote-Alin mountain, circulating at shallow depths in sedimentary rocks. CO2 gas in groundwater may be derived from mantle (magmatic origin), and its role is crucial to high pCO2 groundwater origination. KeywordsHydrogeochemistry; High pCO2 Water; Leaching Test; Isotopes; Far East of Russia

DIAGENETIC ALTERATIONS AND RESERVOIR QUALITY EVOLUTION OF LOWER CRETACEOUS FLUVIAL SANDSTONES: NUBIAN FORMATION, SIRT BASIN, NORTH‐CENTRAL LIBYA

Lower Cretaceous meandering and braided fluvial sandstones of the Nubian Formation form some of the most important subsurface reservoir rocks in the Sirt Basin, north‐central Libya. Mineralogical, petrographical and geochemical analyses of sandstone samples from well BB6–59, Sarir oilfield, indicate that the meandering fluvial sandstones are fine‐ to very fine‐grained subarkosic arenites (av. Q91F5L4), and that braided fluvial sandstones are medium‐ to very coarse‐grained quartz arenites (av. Q96F3L1). The reservoir qualities of these sandstones were modified during both eodiagenesis (ca. &lt;70°C; &lt;2 km) and mesodiagenesis (ca. &gt;70°C; &gt;2 km). Reservoir quality evolution was controlled primarily by the dissolution and kaolinitization of feldspars, micas and mud intraclasts during eodiagenesis, and by the amount and thickness of grain‐coating clays, chemical compaction and quartz overgrowths during mesodiagenesis. However, dissolution and kaolinitization of feldspars, micas and mud intraclasts resulted in the creation of intercrystalline micro‐ and mouldic macro‐porosity and permeability during eodiagenesis, which were more widespread in braided fluvial than in meandering fluvial sandstones. This was because of the greater depositional porosity and permeability in the braided fluvial sandstones which enhanced percolation of meteoric waters. The development of only limited quartz overgrowths in the braided fluvial sandstones, in which quartz grains are coated by thick illite layers, retained high porosity and permeability (12–23% and 30–600 mD). By contrast, meandering fluvial sandstones underwent porosity loss as a result of quartz overgrowth development on quartz grains which lack or have thin and incomplete grain‐coating illite (2–15% and 0–0.1 mD). Further loss of porosity in the meandering fluvial sandstones occurred as a result of chemical compaction (pressure dissolution) induced by the occurrence of micas along grains contacts. Other diagenetic alterations, such as the growth of pyrite, siderite, dolomite/ankerite and albitization, had little impact on reservoir quality. The albitization of feldspars may have had minor positive influence on reservoir quality through the creation of intercrystalline micro‐porosity between albite crystals.The results of this study show that diagenetic modifications of the braided and meandering fluvial sandstones in the Nubian Formation, and resulting changes in reservoir quality, are closely linked to depositional porosity and permeability. They are also linked to the thickness of grain‐coating infiltrated clays, and to variations in detrital composition, particularly the amounts of mud intraclasts, feldspars and mica grains as well as climatic conditions.

Detecting Surface Structures after Large Eruption of Mt. Merapi in 2010 Using ALOS/PALSAR Data

Mt. Merapi located in central Java is one of the most active volcanoes in Indonesia. Its activity is characterized by small eruptions with periodicities ranging from one to five years. Eruptions of the last century were characterized by effusive lava dome growth and collapse to produce “Merapi type” pyroclastic flows. However, the characteristics of Merapi eruptions have changed in November 2010. The eruptions are more explosive (VEI 4), involving exceptionally rapid dome growth and collapse that produced extensive pyroclastic flows and heavy ash fall. Following the extra-ordinary eruption, we evaluated the changes of surface structures by quantifying the Linear Features Density (LFD) related to the geological structures before and after eruption using dual observation of ALOS/PALSAR data. An automatic extraction of linear feature density from Synthetic Aperture Radar (lifedSAR) was applied to quantify the LFD. Statistically, the LFD increased to about 85% after the eruption with the location of maximum density at Southern flank. The high fractured zones were located at NW and NE from the summit. The zones could be served as fluid path of meteoric water infiltration to the subsurface. Therefore, the path may connect the water to the hot materials beneath the surface.

Possible natural fluid pathways from gravity pseudo-tomography in the geothermal fields of Northern Alsace (Upper Rhine Graben)

BackgroundThis study aims on investigating the regional flow field of the Soultz and adjacent geothermal fields located on the western side of the central Upper Rhine Graben and thus to provide insight into the origin of the 70% of the geothermal fluid coming from the regional inflow in the deep reservoir of the Soultz site. In an integrative approach, we consolidate conceptual models on fluid flow in the central Upper Rhine Graben.MethodsBased on a 3D geological model and a new 3D temperature interpolation, we tackle the relation between tectonic structures and the occurrence of advection/convection along favourably oriented fault zones. Using sequential Butterworth filters, we study the distribution of negative residual anomalies in a pseudo-tomography down to a depth of about 6 to 8 km.ResultsWe derived N-S-striking V-shaped negative anomalies that are consistent with the orientation of fault zones revealing major temperature anomalies to their east.ConclusionsFollowing the concept of negative anomalies revealing zones of increased fracture porosity, and in agreement with fluid-chemistry, our findings suggest infiltration of meteoric water through the graben boundary fault and along preferential flow pathways that merge at intermediate depth. Up-flow of thermal water mixed most likely with brine from the deeper eastern part of the graben occurs along W-dipping typically rather steep structures.

Anomalous arsenic concentrations in the Ďurkov carbonate geothermal structure, eastern Slovakia

Concentrations of As in carbonate reservoirs in Slovakia are relatively low, with an average value of 0.72 mg/l in typical waters of Ca–Mg–HCO3 type. In factor analysis, arsenic is in Factor 1 with Na and Cl, separated from carbonate aquifer species Ca and Mg in Factor 2. A principal exception is the Ďurkov site in eastern Slovakia, where As concentration reaches 36.7 mg/l (median 30 mg/l) in geothermal waters of the Na–Cl type. The δ2H and δ18O isotopes indicate a primary meteoric origin of the water. Low δ2H and 14C reflect infiltration of surface water during a warmer climatic period in the Early Holocene, meanwhile positive δ18O shift (about 5 ‰) suggests enhanced water–rock interactions. The conceptual model of As-rich water formation includes the following steps: (a) Infiltration of meteoric waters and dissolution of evaporates, especially halite, in the overlying Neogene formation (b) reaction of the highly mineralized water with Hg–As–Sb type of mineralization, related to the Neogene volcanism, and, (c) accumulation of As-rich geothermal water in Triassic carbonates with an additional input of CO2. Geochemical modeling of the reaction between water and arsenopyrite reproduced measured As concentrations for a typical range of reservoir temperatures. Analogous to similar geothermal sites around the world, concentrations of arsenic in carbonate reservoirs in Slovakia are low except for cases where As is enriched by previous water–rock interaction related to Neogene volcanic activity outside the carbonate reservoirs, which then serve exclusively for a secondary accumulation of As-rich waters.

Metal and fluid sources in a potential world-class gold deposit: El-Sid mine, Egypt

Lode gold mineralization at the El-Sid mine area is associated with the ca. 600 Ma Fawakhir granite intrusion, which cuts the ~737 Ma ophiolite nappes in the Central Eastern Desert of Egypt. The mineralized quartz veins are hosted by ~E- and NE-trending fault/fracture sets cutting the western boundary of the intrusion and sheared ophiolites. The results of electron microprobe analyses of gold-associated hydrothermal sulfide and silicate minerals suggest that Au was mobilized alongside Ni, Co, Cr and As from the adjacent ophiolitic serpentinite. After granite emplacement, hydrothermal fluids interacted with the sheared serpentinite, leaching metals and re-depositing them in the faults/fractures and adjacent wall rock in a cyclic process. Low-salinity aqueous-carbonic fluids with significant quantities of volatile species (CO2, CH4, and N2 ± H2S) leached and transported Au from deep to shallow crustal levels. Carbon dioxide had a buffering effect on the Au-bearing hydrothermal solution, maintaining its pH within a narrow near-neutral range, where elevated gold concentration was transported by complexation with reduced magmatic sulfur in a reducing environment. Gold deposition along fault/fracture conduits in the Fawakhir granite and adjacent serpentinite resulted from interplay of pressure drop, fluctuations in oxygen and sulfur fugacities, and exsolution of the volatile phases. Infiltration of meteoric water may have contributed to the formation of the late stage gold-sulfide mineralization that formed at shallower levels during terrane uplift. Sulfidation of the Fe-rich magmatic minerals was, on the other hand, the overriding process in the wall rock as evidenced by abundant disseminated sulfides with gold inclusions. Considering the structural control by regional shear zones (fluid conduits) and the voluminous granitic and ophiolitic rocks (metal sources), a high tonnage gold deposit amenable to open pit mining at the El-Sid mine area is very likely.

Strain and permeability gradients traced by stable isotope exchange in the Raft River detachment shear zone, Utah

Combined geochronological and stable isotope data of quartzite mylonite from the footwall of the Raft River detachment shear zone (NW Utah, USA) reveal that an important phase of ductile deformation and infiltration of meteoric water in the shear zone occurred in Miocene time. 40Ar/39Ar release spectra are complex, and plateau ages decrease systematically from 31.1 ± 0.8 Ma at the top to 20.2 ± 0.6 Ma at the bottom of the quartzite mylonite section, capturing a segment of the ∼40–15 Ma geochronologic record that has been documented regionally and is likely related to partial to total overprinting of Eocene white mica 40Ar/39Ar ages in the Miocene. Hydrogen stable isotope values of syn-kinematic muscovite range from −123‰ to −88‰ and suggest that meteoric water infiltrated the detachment shear zone during mica (re)crystallization and mylonite development. Bulk stable isotope analyses from fluid inclusions in quartz support a meteoric origin for the fluid (low D/H and 18O/16O ratios). Quartz and muscovite oxygen isotope analyses show varying degrees of 18O depletion, suggesting spatially variable time-integrated interaction of meteoric fluids with recrystallizing shear zone minerals. The overall pattern of D/H and 18O/16O ratios indicates that fluids were channelized along restricted layers or shear zones within the deforming detachment system. The variability in 18O/16O ratios of both quartz and muscovite and the fluid-rock isotopic exchange results can be explained by variations in the shear zone permeability (confined versus diffuse flow) along with strain variations along the transport direction (from flattening to constriction).

Paleo-modeling of coastal saltwater intrusion during the Holocene: an application to the Netherlands

Abstract. Coastal groundwater reserves often reflect a complex evolution of marine transgressions and regressions, and are only rarely in equilibrium with current boundary conditions. Understanding and managing the present-day distribution and future development of these reserves and their hydrochemical characteristics therefore requires insight into their complex evolution history. In this paper, we construct a paleo-hydrogeological model, together with groundwater age and origin calculations, to simulate, study and evaluate the evolution of groundwater salinity in the coastal area of the Netherlands throughout the last 8.5 kyr of the Holocene. While intended as a conceptual tool, confidence in our model results is warranted by a good correspondence with a hydrochemical characterization of groundwater origin. Throughout the modeled period, coastal groundwater distribution never reached equilibrium with contemporaneous boundary conditions. This result highlights the importance of historically changing boundary conditions in shaping the present-day distribution of groundwater and its chemical composition. As such, it acts as a warning against the common use of a steady-state situation given present-day boundary conditions to initialize groundwater transport modeling in complex coastal aquifers or, more general, against explaining existing groundwater composition patterns from the currently existing flow situation. The importance of historical boundary conditions not only holds true for the effects of the large-scale marine transgression around 5 kyr BC that thoroughly reworked groundwater composition, but also for the more local effects of a temporary gaining river system still recognizable today. Model results further attest to the impact of groundwater density differences on coastal groundwater flow on millennial timescales and highlight their importance in shaping today's groundwater salinity distribution. We found free convection to drive large-scale fingered infiltration of seawater to depths of 200 m within decades after a marine transgression, displacing the originally present groundwater upwards. Subsequent infiltration of fresh meteoric water was, in contrast, hampered by the existing density gradient. We observed discontinuous aquitards to exert a significant control on infiltration patterns and the resulting evolution of groundwater salinity. Finally, adding to a long-term scientific debate on the origins of groundwater salinity in Dutch coastal aquifers, our modeling results suggest a more significant role of pre-Holocene groundwater in the present-day groundwater salinity distribution in the Netherlands than previously recognized. Though conceptual, comprehensively modeling the Holocene evolution of groundwater salinity, age and origin offered a unique view on the complex processes shaping groundwater in coastal aquifers over millennial timescales.

Application of environmental tracers to study groundwater recharge in a semi-arid area of Central Tunisia

Groundwater of the Tertiary-Quaternary Formations in the Jeloula basin (Central Tunisia), together with rain and surface waters, were analysed to investigate the mineralization processes, the origin of the water and its recharge sources. The water samples present a large spatial variability of chemical facies which is related to their interaction with the geological formations. The main sources of the water mineralization are the dissolution of evaporitic and carbonate minerals and cation exchange reactions. Stable isotopes indicate that most groundwater samples originate from infiltration of modern precipitation. Surface water samples from small dam reservoirs show a 18O/2H enrichment, which is typical of water exposed to open-surface evaporation in a semi-arid region. Considerable data of 3H and 14C allow the qualitative identification of the present-day recharge that is probably supplied by infiltration of recent flood waters in the Wadi El Hamra valley, and by direct infiltration of meteoric water through the local carbonate outcrops.Editor D. Koutsoyiannis; Associate editor S. Faye

Assessing the Environmental Hazard of Using Seawater for Ore Processing at the Lasail Mine Site in the Sultanate of Oman

The Lasail mining area (Sultanate of Oman) was contaminated by acid mine drainage during the exploitation and processing of local and imported copper ore and the subsequent deposition of sulphide-bearing waste material into an unsealed tailings dump. In this arid environment, the use of seawater in the initial stages of ore processing caused saline contamination of the fresh groundwater downstream of the tailings dump. After detection of the contamination in the 1980s, different source-controlled remediation activities were conducted including a seepage water collection system and, in 2005, surface sealing of the tailings dump using an HDPE-liner to prevent further infiltration of meteoric water. We have been assessing the benefits of the remediation actions undertaken so far. We present chemical and isotopic (δ18O, δ2H, 3H) groundwater data from a long-term survey (8–16 years) of the Wadi Suq aquifer along a 28 km profile from the tailings dump to the Gulf of Oman. Over this period, most metal concentrations in the Wadi Suq groundwater decreased below detection limits. In addition, in the first boreholes downstream of the tailings pond, the salinity contamination has decreased by 30 % since 2005. This decrease appears to be related to the surface coverage of the tailings pond, which reduces flushing of the tailings by the sporadic, but commonly heavy, precipitation events. Despite generally low metal concentrations and the decreased salinity, groundwater quality still does not meet the WHO drinking water guidelines in more than 90 % of the Wadi Suq aquifer area. The observations show that under arid conditions, use of seawater for ore processing or any other industrial activity has the potential to contaminate aquifers for decades.

Chemical stabilization of metals in mine wastes by transformed red mud and other iron compounds: laboratory tests

A series of static and kinetic laboratory-scale tests were designed in order to evaluate the efficacy of transformed red mud (TRM) from bauxite refining residues, commercial zero-valent iron, and synthetic iron (III) hydroxides as sorbents/reagents to minimize the generation of acid drainage and the release of toxic elements from multi-contaminant-laden mine wastes. In particular, in some column experiments the percolation of meteoric water through a waste pile, alternated with periods of dryness, was simulated. Wastes were placed in columns together with sorbents/reagents in three different set-ups: as blended amendment (mixing method), as a bed at the bottom of the column (filtration method), or as a combination of the two previous methods. The filtration methods, which simulate the creation of a permeable reactive barrier downstream of a waste pile, are the most effective, while the use of sorbents/reagents as amendments leads to unsatisfactory results, because of the selective removal of only some contaminants. The efficacy of the filtration method is not significantly affected by the periods of dryness, except for a temporary rise of metal contents in the leachates due to dissolution of soluble salts formed upon evaporation in the dry periods. These results offer original information on advantages/limits in the use of TRM for the treatment of multi-contaminant-laden mine wastes, and represent the starting point for experimentation at larger scale.