Fluids Of Meteoric Origin Research Articles

Cerro Prieto Geothermal Field (Baja California, Mexico) – A fossil system? Insights from a noble gas study

Results of a survey of noble gases, water stable isotopes (δD and δ18O), and chlorine (Cl) and bromine (Br) contents measured in geothermal waters from the high-enthalpy, liquid-dominated Cerro Prieto Geothermal Field (CPGF) are reported. Helium isotopic ratios (3He/4He) help to identify two distinct fluids: a magmatic fluid, with 3He/4He (R) ratios of up to 7.3 times that of the atmospheric ratio (Ra = 1.384 × 10−6), and a 4He-rich fluid, with 3He/4He ≤ 3.5 Ra. The helium isotopic systematics point to limited modern freshwater recharge in the CPGF, and thus to the presence of a nearly fossil geothermal system. U-Th/4He-estimated minimum residence times for the 4He-rich fluid component vary from 1.5 to 1.8 Ma, corresponding to the age of the Colorado River paleo-delta sediments, suggesting the presence of connate waters. Cl and Br concentrations indicate that this connate water component is seawater with minor halite dissolution. Together with Cl and Br, the isotopic signature of the water (δD, δ18O) indicates the presence of a third old fluid of meteoric origin, from Late Quaternary to Holocene, corresponding to recharge during colder and wetter periods than today. This is identified as being old groundwater from the Colorado Delta unconsolidated sediments, which cap the Cerro Prieto reservoir. Our results suggest little direct recharge to the CPGF. The spatial distribution of helium isotopes in the reservoir shows that connate waters dominate the central portion of the field and mix with the magmatic fluid containing mantle He, with both fluids rising at the center of the basin where the heat source is located. Deep magmatic fluids containing mantle helium enter laterally into the reservoir, through the main lateral strike-slip faults (i.e., the Cerro Prieto and Imperial faults).

Геохимические особенности и условия образования медистых песчаников Оренбургского Пред­уралья

Object. The article describes a new geological and geochemical data for Permian host rocks and copper sandstones (CS) in Orenburg’s Pre-Urals. Methods . X-ray fluorescence, atomic absorption for Au and Ag, and ICP-MS analysis were used during investigations. Results. The cupriferous sandstones are enriched in a quite broad range of microelements: Cu, Ag, Au, Cd, Сr, Ni, Mn, Co, V, U, Sc, and Pb, compared to the average values of the upper crust. The Co/Ni ratio in the CS is very low, which is typical of low-thermal fluids of meteoric origin. The CS are characterized by a REE spectrum without Eu-minima and maxima, which is close to the chondrite spectrum. Like in the host rocks, the “cerium” group of REE dominates in the CS over the “yttrium” and “scandium” groups. The spectra of REE of the CS and the host rocks have definitely similar morphology. The δCe and δEu combination indicates that CS was formed under oxidizing conditions. On geological and genetic characteristics and geochemical indicators installed the similarity of the CS in the southern Pre-Urals deposits and the Manto-type Cu-Ag deposits of Chile and Iran, and also with the CS of Iran and Cu-shales of Kupferschiefer. Conclusion. Proposed geological-genetic model of CS, points to possible high rise development of the Cu-Ag mineralization at depth as in the fields of the Manto-type copper deposits in Chile and Iran. Geochemical data show that accommodating the Permian strata could serve as a source of REE and other trace elements for ore-forming fluids. Perm CS of Pre Urals can be considered as a very promising new (“old”) source of raw materials for the development of the copper industry of the region. The obtained results can be used to predict new ore fields in the Eastern Russia region.

Origin, evolution and geothermometry of the thermal waters in the Gölemezli Geothermal Field, Denizli Basin (SW Anatolia, Turkey)

The Gölemezli Geothermal Field (GGF) is one of the best known geothermal fields in western Anatolia (Turkey). The exploited fluids are of meteoric origin, mixed with deep magmatic fluids, which interacted with the metamorphic rocks of the Menderes Massif. The geothermal fluids are channeled along Quaternary faults belonging to the main normal faults system delimiting the northern side of the Denizli Basin and their associated transfer zones. In this study, hydrochemical and isotopic analyses of the thermal and cold waters allow us to determine water-rock interactions, fluid paths and mixing processes.Two groups of thermal waters have been distinguished: (i) Group 1A, comprising Na-SO4 type and Ca-SO4 type and (ii) Group 1B, only consisting Ca-HCO3 type waters. Differently, two groups were recognized in the cold waters: (i) Group 2A, corresponding to Ca-HCO3 type and (ii) Group 2B, including Mg-HCO3 type. Their geochemical characteristics indicate interactions with the Paleozoic metamorphic rocks of the Menderes Massif and with the Neogene lacustrine sedimentary rocks. Dissolution of host rock and ion-exchange reactions modify thermal water composition in the reservoir of the GGF. High correlation in some ionic ratios and high concentrations of some minor elements suggest an enhanced water-rock interaction. None of the thermal waters has been reached a complete chemical re-equilibrium, possibly as a result of mixing with cold water during their pathways. Geothermal reservoir temperatures are calculated in the range of 130-210°C for the Gölemezli field.Very negative δ18O and δ2H isotopic ratios are respectively between −8.37 and −8.13‰ and −61.09 and −59.34‰ for the SO4-rich thermal waters, and ca. −8.40 and −8.32‰ and −57.80 and −57.41‰ for the HCO3-rich thermal waters. Low tritium (<1 TU) and low oxygen isotope values reflect a deep circuit and fluids of meteoric origin. Positive δ13CDIC ratios (+5.11 to +7.54‰) of all thermal waters imply a contribution of metamorphic origin. Heating is guaranteed by a deep circuit within an overheated continental crust, mainly affected by damaged rock volumes. Volatile ascent from deep magmatic sources through crustal structures can explain the occurrence of mantle volatiles at shallow depth in the Denizli Basin. The NW- and NE-trending fault systems, associated with their related fractures, played as hydraulic conduits underlining the strict link existing between fractures and fluid convection in the extensional settings. In this view, the GGF is a very good example of geothermal field associated to active tectonic setting and magmatism, as it is the case of the other geothermal fields occurring in the Denizli Basin.

Investigating fossil hydrothermal systems by means of fluid inclusions and stable isotopes in banded travertine: an example from Castelnuovo dell’Abate (southern Tuscany, Italy)

Southern Tuscany (Italy) hosts geothermal anomalies with associated widespread CO2 gas-rich manifestations and active travertine-deposing thermal springs. Geothermal anomalies have been active since the Late Miocene and have led to the formation of widespread Late Miocene–Pleistocene travertine deposits and meso- and epithermal mineralizations. This study investigates the travertine deposit exposed in the Castelnuovo dell’Abate area of southern Tuscany. Here, a fissure-ridge type travertine deposit and its feeding conduits, currently filled with banded calcite veins (i.e. banded travertine), represent a spectacular example of fossil hydrothermal circulation in the peripheral area of the exploited Monte Amiata geothermal field. The Castelnuovo dell’Abate travertine deposit and associated calcite veins were analysed to establish the characteristics of the parent hydrothermal fluids, and the age of this circulation. The focus of the study was on fluid inclusions, rarely considered in travertine studies, but able to provide direct information on the physico-chemical characteristics of the original fluid. Uranium–thorium geochronological data provided further constraints on the: (1) age of tectonic activity; (2) age of the hydrothermal circulation; and (3) evolution of the Monte Amiata geothermal anomaly. Results indicate that brittle deformation (NW- and SE-trending normal to oblique-slip faults) was active during at least the Middle Pleistocene and controlled a hydrothermal circulation mainly characterized by fluids of meteoric origin, and as old as 300–350 ka. This is the oldest circulation documented to date in the Monte Amiata area. The fluid chemical composition is comparable to that of fluids currently exploited in the shallow reservoir of the Monte Amiata geothermal field, therefore suggesting that fluid composition has not changed substantially over time. These fluids, however, have cooled by about 70 °C in the last 300–350 ka, corresponding to a cooling rate of the Monte Amiata geothermal area of about 20 °C 100 ka−1.

Novel applications of fluid inclusions and isotope geochemistry in unravelling the genesis of fossil travertine systems

AbstractThe Denizli Basin is a fault‐bounded Neogene–Quaternary depression located in the Western Anatolian Extensional Province, Western Turkey. The basin is a unique geological site with abundant active and fossil (Quaternary) travertine and tufa deposits. Fluid inclusion microthermometry and isotopic analysis were applied to study the genesis of the Ballık fossil travertine deposits, located in the south‐eastern part of the basin. Microthermometry on fluid inclusions indicates that the main travertine precipitating and cementing fluids are characterized by low salinity (&lt;0·7 wt% NaCl equivalent) and variable temperatures that cluster at &lt;50°C and ca 100°C. Fluids of meteoric origin have been heated by migration to the deeper subsurface, possibly in a local high geothermal gradient setting. A later uncommon cementation phase is related to a fluid with a significantly higher salinity (25·5 to 26·0 wt% bulk). The fluid obtained its salinity by interaction with Late Triassic evaporite layers. Strontium isotopes indicate that the parent carbonate source rock of the different travertine precipitates is very likely to be the Triassic limestone of the Lycian Nappes. Carbon isotopes suggest that the parent CO2 gas originated from thermal decarbonation of the Lycian limestones with minor contributions of magmatic degassing and organic soil CO2. Oxygen isotopes confirm the meteoric origin of the fluids and indicate disequilibrium precipitation because of evaporation and degassing. Results were integrated within the available geological data of the Denizli Basin in a generalized travertine precipitation model, which enhanced the understanding of fossil travertine systems. The study highlights the novel application of fluid inclusion research in unravelling the genesis of continental carbonates and provides several recommendations for hydrocarbon exploration in travertine‐bearing sedimentary basins. The findings suggest that travertine bodies and their parent carbonate source rocks have the potential to constitute interesting subsurface hydrocarbon reservoirs.

Geochemical processes in an active shallow submarine hydrothermal system, Bahía Concepción, México: mixing or boiling?

Hydrothermal activity at Bahía Concepción, on the western coast of the Gulf of California, is not linked to present volcanic activity. This site is a potential energy source; however, geothermal modelling of the system is needed in order to determine the processes that generated this activity. Two processes might lead to the formation of the secondary fluids that were sampled in this submarine hydrothermal system: the thermal endmember might be undergoing either boiling or mixing with a fluid trapped within the sedimentary strata. However, boiling was ruled out as this process would not produce a highly saline fluid within the temperature range determined for the Bahía Concepción system (∼87°C). We modelled the mixing of a highly saline fluid with a geothermal fluid of meteoric origin. Our results suggest that the composition of the thermal water representing the hot endmember at Bahía Concepción consists of 20–30% highly saline fluid and 70–80% aqueous fluid of meteoric origin. The computed fluid has a chemical composition similar to that determined for the submarine vents. Its derived contents of calcium, chloride, and silica are similar to those we measured for the vent discharge. Our hypothesis of saline water addition is supported by the mineralizing fluid characteristics determined from fluid inclusion microthermometric study of a fossil intertidal system that discharges in the vicinity of the vent areas. This intertidal spring fluid at ∼40°C, according to the geochemical model, would be supersaturated in opaline silica and calcite, consistent with the mineralogy of the stromatolitic sinter encircling the discharges.

Assessing the geochemical and tectonic impacts of fluid-rock interaction in mid-crustal shear zones: a case study from the intracontinental Alice Springs Orogen, central Australia

The Reynolds–Anmatjira Ranges, central Australia, form part of a high-grade basement terrane dissected by intensely metasomatized transpressional shear zones active during the Ordovician–Carboniferous Alice Springs Orogeny. Unlike typical retrograde structures associated with discrete fluid flow, the mid-crustal setting and intracontinental nature of these shear systems present significant problems for the source and ingress mechanism of the fluid involved in their rehydration. To address these issues, we describe two detailed traverses across deformed and metasomatized basement rocks in this region, and interrogate their record of fluid–rock interaction from various perspectives. Both traverses combine structural and petrological observations with Zr-in-rutile and Ti-in-quartz thermobarometry, oxygen and hydrogen stable isotope analysis, and major, trace and rare earth element mobility trends. Each technique is critically evaluated for its utility in this study and its more widespread applicability to alternative field areas, providing a strategic framework for the general investigation of fluid-affected shear zones. Ultimately, the integrated data sets specify pressure–temperature conditions of ∼530 °C and 4–5 kbar, implying average apparent thermal gradients of 29–36 °C km−1 and depths of 14–18 km. Other characteristic features to emerge include strongly variable element mobilities and pronounced isotopic depletion fronts consistent with the alteration effects of an externally derived, non-equilibrium fluid. This is confirmed by calculated fluid compositions indicative of contributions from a fluid of meteoric origin, with estimated δ18O and δD values as low as 2.3‰ and −59.8‰, respectively. We propose that these surficial fluid signatures are imposed on the mid-crust by the prograde burial and dehydration of hydrothermally altered fault panels produced during pre-orogenic basin formation. Progressive fluid release with continued subsidence then leads to the accumulation of increasing fluid volumes in the vicinity of the brittle–ductile transition, promoting extensive hydration, metasomatism and reaction softening at the locus of stress transmission from plate-boundary sources. The sustained injection of externally derived fluids into refractory crustal material may thus stimulate a critical reduction in the long-term strength of the lithosphere, providing strong impetus for the initiation and advancement of intracontinental orogenesis.

A fluid inclusion and stable isotope study of 200 Ma of fluid evolution in the Galway Granite, Connemara, Ireland

Fluid inclusions in granite quartz and three generations of veins indicate that three fluids have affected the Caledonian Galway Granite. These fluids were examined by petrography, microthermometry, chlorite thermometry, fluid chemistry and stable isotope studies. The earliest fluid was a H2O-CO2-NaCl fluid of moderate salinity (4–10 wt% NaCl eq.) that deposited late-magmatic molybdenite mineralised quartz veins (V1) and formed the earliest secondary inclusions in granite quartz. This fluid is more abundant in the west of the batholith, corresponding to a decrease in emplacement depth. Within veins, and to the east, this fluid was trapped homogeneously, but in granite quartz in the west it unmixed at 305–390 °C and 0.7–1.8 kbar. Homogeneous quartz δ18O across the batholith (9.5 ± 0.4‰n = 12) suggests V1 precipitation at high temperatures (perhaps 600 °C) and pressures (1–3 kbar) from magmatic fluids. Microthermometric data for V1 indicate lower temperatures, suggesting inclusion volumes re-equilibrated during cooling. The second fluid was a H2O-NaCl-KCl, low-moderate salinity (0–10 wt% NaCl eq.), moderate temperature (270–340 °C), high δD (−18 ± 2‰), low δ18O (0.5–2.0‰) fluid of meteoric origin. This fluid penetrated the batholith via quartz veins (V2) which infill faults active during post-consolidation uplift of the batholith. It forms the most common inclusion type in granite quartz throughout the batholith and is responsible for widespread retrograde alteration involving chloritization of biotite and hornblende, sericitization and saussuritization of plagioclase, and reddening of K-feldspar. The salinity was generated by fluid-rock interactions within the granite. Within granite quartz this fluid was trapped at 0.5–2.3 kbar, having become overpressured. This fluid probably infiltrated the Granite in a meteoric-convection system during cooling after intrusion, but a later age cannot be ruled out. The final fluid to enter the Granite and its host rocks was a H2O-NaCl-CaCl2-KCl fluid with variable salinity (8–28 wt% NaCl eq.), temperature (125–205 °C), δD (−17 to −45‰), δ18O (−3 to + 1.2‰), δ13CCO2 (−19 to 0‰) and δ34Ssulphate (13–23‰) that deposited veins containing quartz, fluorite, calcite, barite, galena, chalcopyrite sphalerite and pyrite (V3). Correlations of salinity, temperature, δD and δ18O are interpreted as the result of mixing of two fluid end-members, one a high-δD (−17 to −8‰), moderate-δ18O (1.2–2.5‰), high-δ13CCO2 (> −4‰), low-δ34Ssulphate (13‰), high-temperature (205–230 °C), moderate-salinity (8–12 wt% NaCl eq.) fluid, the other a low-δD (−61 to −45‰), low-δ18O (−5.4 to −3‰), low-δ13C (<−10‰), high-δ34Ssulphate (20–23‰) low-temperature (80–125 °C), high-salinity (21–28 wt% NaCl eq.) fluid. Geochronological evidence suggests V3 veins are late Triassic; the high-δD end-member is interpreted as a contemporaneous surface fluid, probably mixed meteoric water and evaporated seawater and/or dissolved evaporites, whereas the low-δD end-member is interpreted as a basinal brine derived from the adjacent Carboniferous sequence. This study demonstrates that the Galway Granite was a locus for repeated fluid events for a variety of reasons; from expulsion of magmatic fluids during the final stages of crystallisation, through a meteoric convection system, probably driven by waning magmatic heat, to much later mineralisation, concentrated in its vicinity due to thermal, tectonic and compositional properties of granite batholiths which encourage mineralisation long after magmatic heat has abated.

Genesis of Li-donbassite and tosudite in Echassieres granitic cupola, Massif Central, France.

Lithium-bearing donbassite and tosudite occur in veins in the Echassieres granitic cupola (Massif Central, France). The two minerals are characterized by high Li contents and very low Fe and Mg contents; their structural formulae are :(Si3.81Al0.19)4.00(Al3.81Li0.52Fe2+0.01Ca0.02Mg0.01Mn0.01)4.38O10(OH)8(Na0.07K0.04)0.11 for donbassite and(Si3.50Al0.50)4.00(Al2.95Li0.22Fe3+0.01Ti0.01)3.19O10(OH)5(Ca0.01Na0.15K0.18)0.34 for tosudite. Petrographic investigations of drill cores from the Echassieres area indicate that these two minerals were formed in intermediate stages of a hydrothermal alteration series, muscovite-pyrophyllite-donbassite-tosudite-kaolinite, which occurred successively in the post-magmatic stage of granite. Fluid inclusion and stable isotope studies indicate that these aluminosilicates were formed at 400-150°C by interactions between low salinity (1-8 wt% NaCl) fluids of meteoric origin and the alkali granite.Thermodynamic calculations assured that Li-donbassite possessed the stability field from 300 to 200°C under acid conditions (3 < pH < 5) in the Echassieres hydrothermal system.

Fluid inclusions and rare earth element geochemistry of fluorite from south-central Idaho

Epithermal fluorite mineralization of Tertiary age occurs in a northeast-trending belt within the Challis 2 degrees quadrangle of south-central Idaho. Fluorite was collected from the Meyers Cove area and the Bayhorse, Yankee Fork, and Stanley mining districts. Host rocks include the Eocene Challis Volcanics, the Cretaceous Idaho batholith, and the Ordovician(?) Bayhorse Dolomite. Mineralization is structurally controlled and is present as fault and fracture fillings and breccia cements. Argillization and silicification of the wall rocks is common and locally intense.Microthermometric measurements on nearly 400 two-phase (H 2 O + vapor), water-rich inclusions with low vapor to liquid ratios yielded mean homogenization temperatures of 160 degrees C for the Meyers Cove area, 150 degrees C for the Stanley district, and 130 degrees C for the Bayhorse and the Yankee Fork districts. Salinities range from 0 to 1.4 equiv wt percent NaCl.The rare earth element content of the fluorite is quite variable, ranging from 2.6 to 130 ppm, and Ce/Yb ratios reflect the dominant trend of light rare earth element enrichment. Fluorite from the Meyers Cove area and the Bayhorse and Stanley districts have similar Tb/La ratios, indicating crystallization at about the same time. Fluorite from the Yankee Fork district has a lower mean Tb/La ratio which is indicative of earlier crystallization. Chondrite-normalized plots and rare earth element ratios reveal persistent negative Ce anomalies, indicating high oxygen fugacities at the source area. Positive Eu anomalies indicate the release of Eu (super +2) during feldspar destruction, oxidation to Eu (super +3) at the deposition site, and subsequent incorporation in the fluorite. Samples with negative Eu anomalies indicate the presence of divalent Eu.The fluid inclusion, geochemical, geologic, geochronologic, and stable isotope data support deposition in Tertiary hydrothermal systems dominated by fluids of meteoric origin. The most important depositional mechanism is believed to be an increase in the pH of the ore-bearing fluids upon interaction with the wall rocks.

Meteoric Burial Diagenesis of Pennsylvanian Arkosic Sandstones, Southwestern Anadarko Basin, Texas

Pennsylvanian arkosic sandstones at Mobeetie field were deposited in fan deltas that prograded onto a shallow shelf in the southern Anadarko basin. The detrital minerals of the sandstones reflect the composition of the Precambrian granites and granodiorites that were exposed in the nearby Amarillo uplift. Distal margins of some fan-delta lobes were reworked by marine processes, and carbonate fossil fragments and oolites were mixed with terrigenous clastics. The diagenetic history and, hence, reservoir quality of the distal, marine-reworked sandstones differ from those of the more proximal, nonreworked sandstones. The earliest diagenetic events--formation of chlorite ooids and precipitation of fibrous submarine Mg-calcite cement--took place in the depositional environment of the marine-reworked sandstones. On the basis of isotopic data, the remainder of the diagenesis evidently occurred in fluids of meteoric origin. Shallow, early meteoric diagenesis induced precipitation of iron-poor calcite spar in reworked sandstones; nonreworked sandstones lack calcite spar but contain early pore-lining chlorite cement. Dissolution of aragonite by fresh meteoric ground water created moldic porosity within reworked sandstones. As burial increased, porosity in both the reworked and nonreworked fan-delta sandstones was reduced by precipitation of authigenic quartz, feldspar, kaolinite, Fe-calcite, and ankerite. Oxygen isotope data suggest that these cements also precipitated from fluids of meteoric origin that became increasingly hot but remained relatively constant in isotopic composition. The last diagenetic events were influenced by the overlying Permian evaporites. Sodium-rich fluids caused partial albitization of detrital plagioclase, and sulfate derived from the evaporites precipitated as anhydrite and celestite.

Origin and Distribution of Fractures in Tertiary and Cretaceous Rocks, Piceance Basin, Colorado, and Their Relation to Hydrocarbon Occurrence: ABSTRACT

Gas production in the lower Tertiary Wasatch Formation and Upper Cretaceous Mesaverde Group, Piceance basin, Colorado, is controlled by a network of open and partly mineralized natural fractures. These fractures formed in response to high pore-fluid pressures that developed during hydrocarbon generation, and to widespread tectonic stress associated with periods of uplift and erosion that occurred during the late Tertiary. Sandstone beds commonly contain vertical extension fractures that are cemented with fine to coarsely crystalline calcite and locally with quartz, barite, and dickite. These minerals cut detrital grains, authigenic cements, and secondary pores, indicating that fracture mineralization occurred during later stages of diagenesis. Isotopic compositions for fr cture-fill calcite in the Wasatch vary from -5.0 ^pmil to -11.6 ^pmil for ^dgr13C and from -9.5 ^pmil to -14.9 ^pmil for ^dgr180. In the Mesaverde, calcite ranges from -0.7 ^pmil to -10.4 ^pmil for ^dgr13C and from -13.3 ^pmil to -17.7 ^pmil for ^dgr180. These isotopic data indicate that fractures were mineralized during burial by fluids of meteoric origin, with temperatures that remained fairly constant, or by fluids that circulated at a rate that End_Page 860------------------------------ prohibited significant cooling. The wide range in ^dgr13C compositions reflects mixtures of organically derived carbon and dissolved marine carbonate. In reservoir rocks that are extensively fractured, gas generated in situ from carbonaceous and coaly shales and tongues of lacustrine rock may have migrated locally along open faults and fractures. End_of_Article - Last_Page 861------------