Chapter 3. Release of geothermal energy: hot springs and tufa–travertines

The aqueous geochemistry of the rare earth elements and yttrium. Part 7. REE, Th and U contents in thermal springs associated with the Idaho batholith

Partitioning experiments of rare earth elements (REEs) between calcite and aqueous (CaCl2 + NaCl) solution at 25°C and 1 atm have been made in order to elucidate the incorporation process of seawater REE into marine limestones. Calcite-supersaturated solution doped with REE was constantly pumped into a reactor, in which calcite seeds and the solution were mixed and CO2 + N2 gas was bubbled to allow calcite overgrowths. Absolute values of REE partition coefficients, Kd(REE) = (XREE/XCa)calcite/([REE]total/[Ca])solution, could not be determined because of very small calcite overgrowths and difficulty in evaluating XCa. The relative values of Kd(REE) like Kd(REE)/Kd(Gd), however, were determined successfully. Kd(REE) given by [REE]total depends on REE(III)-carbonate complexation in solution, and does not correspond to a reaction incorporating a specific dissolved REE species into calcite. Hence, here we used Kd(REE)ω = (XREE/XCa)calcite/([REECO3+]/[Ca])solution, which is given by Kd(REE) and REE(III)-carbonate complexation constants. Kd(REE)ω relates directly to ΔGr. for the reaction incorporating REECO3+(aq) into calcite. The series variation of experimental logKd(REE)ω shows a convex tetrad effect, suggesting larger Racah parameters of REECO3+(aq) relative to REE(III) in calcite. The variation also shows a kink at around Pm, Sm and Eu, possibly reflecting a coordination change of REE(III) in calcite across the series. Yttrium is definitely enriched in solution relative to heavy REEs. Using the relative values of experimental logKd(REE)ω and REE analyses of upper Paleozoic Japanese Ishimaki and Tahara limestones, REE abundance patterns for seawater coexistent with the marine limestones have been calculated provided that pH, ΣCO2 and salinity are the same in the ancient and present times. The calculated patterns are quite similar to those for relatively deep waters at around 400 to 1000 m in the modern Pacific. Ishimaki and Tahara limestones are of the seamount-type. Hence, the calculated seawater REE patterns with large negative Ce anomalies suggest that the incorporation of seawater REE into the limestones occurred in moderately deep water, probably because of subsidence of volcanic seamounts that were capped by Ishimaki and Tahara limestones.

<p>Groundwater originating from great depths provide a valuable geochemical sampling medium for exploring the development of the Earth's crust, geological, and hydrogeological resources. This particularly applies to sites of natural springs, where favorable hydrogeological conditions enabled regional discharge. Despite the numerous occurrences of mineral and thermal waters in Serbia, the current understanding of the regional groundwater flow is associated with many open questions that need to be addressed. From a geological standpoint, Serbia is part of the Alpine-Mediterranean mountain belt. From the middle of the Mesozoic to the present, this area underwent processes of subduction, collision, and extensions with accompanying voluminous magmatism and volcanism. As a result of the mentioned geodynamic events, the Serbian territory was a zone of intensive tectonomagmatic processes which had a significant impact on the formation of the hydrogeological structures for forming groundwater enriched with specific elements and elevated temperatures.</p><p>Understanding groundwater origin and characterization of a deep circulation is a big challenge since the groundwater pathways and aqueous chemistry are significantly influenced by various factors. To contribute to the characterization of the hydrogeological systems in which the mineral and thermal waters of Serbia are formed, a general hydrochemical study was conducted. During this research 190 of the most significant sources of mineral and thermal waters were sampled, belonging to different geological (geotectonic) units all over Serbia. The applied hydrochemical approach of recognition of deep circulation patterns is based on an analysis of rare earth elements (REE) and natural radioactivity. REE and long-lived radionuclides <sup>40</sup>K, <sup>238</sup>U, <sup>232</sup>Th, <sup>226,228</sup>Ra, gross alpha, and beta radioactivity, have proven to be significant fingerprints of water-rock interaction as well as groundwater flow tracers.</p><p>The integrated approach of the hydrogeochemical analysis and multivariate statistical method, including spatial mapping of obtained results, was an important process for meaningful interpretation of the data set. The applied approach summarized the complex hydrochemical properties on a general level defining specific hydrochemical fingerprints of hydrogeological systems with distinct geochemical characteristics and flow patterns. Geochemical behavior of natural tracers (REE) and radioactivity contributed to further characterization of deep hydrogeological systems in basins structures, hard rocks (igneous and metamorphic rocks), as well as carbonate environments.</p><p>Rare-earth element data (including abundances and fractionation patterns along with anomalies of Ce and Eu and interelement ratios), relationships of U and Th as elements with different geochemical behavior, and the content of Ra in groundwaters have been singled out as important indicators of deep hydrogeological systems. The results showed that the isolated regional hydrogeological systems are in the function of significant tectonic structures/dislocations, but also hydrogeological characteristics and circulation conditions. Further use of the proposed methodology will provide important data from the assessment of the origin of hydro-geofluids in Serbia and contribute to the wider picture in the understanding of the hydrogeological evolution of regional groundwater flow.</p><p><strong>Keywords:</strong> natural radioactivity, rare earth elements, hydrogeochemical fingerprints, regional groundwater flow</p>

bazenAbstractCold mineral and thermal waters from Tertiary aquifers in the Mura Basin mainly belong to the Ca-(Mg)-(Na)-HCO3 and Na-HCO3 hydrogeochemical facies, respectively, and the concentrations of yttrium (Y) and lanthanides or rare earth elements (REEs) are far below (10-2 – 10-4) the abundances in the aquifer sediments. Mineral waters are high pCO2, and the plots of concentrations of YREEs normalised to Post Archean Australian Shale (PAAS) show fractionation of Y and heavy REEs (HREEs) over light REEs (LREEs), and a significant positive europium (Eu) anomaly. Thermal water from regionally developed aquifer Thermal I (recently also termed the Mura/Ujfalu Formation aquifer) shows a similar PAAS-normalised pattern with an obvious positive Eu anomaly and the tendency of enrichment with middle REEs (MREEs). The plots of PAAS-normalised YREE concentrations in thermal waters from the underlying low-permeability aquifers with poorly developed fracture porosity and abundant CO2 are flat with insignificant positive Eu anomaly. The abundance and fractionation of YREEs in mineral and thermal waters seems to be mainly controlled by the presence of carbonate complexing ligands, permeability of the aquifers and the related time of water-rock interaction. YREEs have been used for geochemical recognition of overexploitation of the Sob-1 well that yields mixed waters from Thermal I and the underlying low-permeability aquifers. The well overexploitation has resulted in continuous 30-to-80-minute changes in hydrodynamic pressure in Thermal I, and the related change in temperature and chemical composition of abstracted water. Leakage from clayey-silty layers rich in coal and organic matter has been recognised over a several-year time scale by increased abundances of total organic carbon (TOC), YREEs, gallium (Ga), thallium (Tl) and selenium (Se). PAAS-normalised plots of YREE concentrations have shown significant positive anomalies of samarium (Sm), terbium (Tb) and holmium (Ho) and indicate the YHREE complexing ligands could be, beside carbonate species, humic and/or fulvic acids.

Migration and controlling factors of rare earth elements in geothermal systems on the southern Tibetan Plateau

Advanced characterization of hydrothermal flows within recharge and discharge areas using rare earth elements, proved through a case study of two-phase reservoir geothermal field, in Southern Bandung, West Java, Indonesia

Rural inhabitants depend on groundwater for their drinking water in the Lakes region of central Cote d’Ivoire. The aim of this study is to identify the factors responsible of the water mineralisation and the sources of major ions in groundwater within the area. 123 groundwater samples were collected and analysed for various physico-chemical parameters. Multivariate statistical techniques including Principal Component Analysis (PCA) and Cluster Analysis (CA) were applied on the dataset to evaluate the geochemical processes that control the hydrogeochemistry of groundwater. Ca-HCO3 and Mg-Ca-HCO3 hydrochemical facies predominate the groundwater samples. The first 4 factors explain 79.139% of the total variance, their loading allowing the interpretation of hydrogeochemical processes in the area. The sources of ions in the groundwater are due to two main factors: natural mineralisation and anthropogenic activities. The silicates mineral weathering such as acid hydrolysis of silicates provide the major part of the ions in groundwater such as Ca2+, Mg2+, and HCO3-. The concentrations of NO-3 and Cl- in groundwater were due to anthropogenic activities such as farming. Reduction-oxidation process produced Mn and Fe. The results of this study show the usefulness of multivariate statistical techniques in hydrochemical studies.

Rare earth elements geochemistry in springs from Taftan geothermal area SE Iran

Rare earth elements, yttrium and Pb isotope ratios in thermal spring and well waters of West Anatolia, Turkey: a hydrochemical study of their origin

The report presents original data on the isotope and chemical composition of the nitric thermal, cold underground, and surface natural waters, along with the water-enclosing rocks, of the Ulsk occurrence of thermal mineral waters (coasts of the Sea of Okhotsk, Khabarovsk krai). The data on the concentrations of oxygen and nitrogen isotopes and rare-earth elements, as well as on the volume activity of radon, in the treated underground and surface waters are obtained for the first time. Based on the data of automated monitoring of the physical parameters, the hydrogeological characteristics of the thermal waters are determined and the balneal properties are evaluated. The results obtained show the atmospheric origin of the nitric thermal waters of the Ulsk spring; however, the indicative chemical elements occurring in the considered waters represent the effects of deep-seated high-temperature processes as well. It is found that the waters warmed to 31°C within fractured Paleocene granites do not show significant variations of temperature, and the chemical composition varies exclusively under the interaction with the water-enclosing rocks. The profiles of the distribution of rare-earth elements (REEs) in the thermal waters represent the REE distribution in the water-enclosing granitoids and point to the limitation of the thermal water circulation with the area of the occurrence of the Paleocene granites of the Bekchi–Ul Massif. The temperature of the deep-seated reservoir measured by geothermometers was 80°C or below, which may indicate a depth of water circulation of 1–2 km or less.

بررسی منشأ و شرایط شکل گیری آگات های خور و بیابانک (استان اصفهان)

This study investigates water–rock interactions of Taiwan hot springs by analyzing rare earth elements (REEs) concentrations and strontium (Sr) isotopes. REEs were separated from samples using RE resin, and their concentrations were measured by HR-ICPMS. Strontium was isolated using SrSPEC resin, and the strontium isotopic ratio was determined by MC-ICPMS. The ΣREE in the hot springs ranges from 3.17 ng/L to 29.7 µg/L, with the highest levels found in the Tatun Volcano Group, followed by springs from sedimentary and metamorphic regions. The primary factors controlling REE compositions are lithology and pH. REE patterns of hot springs can be categorized into five types, indicating that the hot springs were affected by various mechanisms. The most distinct hot spring samples are from Tatun Volcano, Ginshan, and Kuantzuling. The 87Sr/86Sr ratios range from 0.70468 to 0.71730, with the most radiogenic samples originating from metamorphic regions, reflecting the nature of the parent rock interacting with the hot spring water. Seawater intrusion and preferential weathering of carbonate also have minor effects on Sr isotope composition. The findings indicate that the types of surrounding rocks and the pH values of the hot springs significantly influence REE patterns and Sr isotope compositions in Taiwan’s hot springs.

Major and trace element compositions (including REE) of mineral, thermal, mine and surface waters in SW Germany and implications for water–rock interaction

Comparison of hydrogeological characteristics and genesis of the Xiaguan Hot Spring and the Butterfly Spring in Yunnan of China

China has been the world’s leading rare earth element (REE) and yttrium producer for more than 20 years and hosts a variety of deposit types. Carbonatite-related REE deposits are the most significant REE deposit type, with REY (REE and yttrium)-bearing clay deposits, or ion adsorption-type deposits, being the primary source of the world’s heavy REEs. Other REY resources in China include those hosted in placers, alkaline granites, pegmatites, and hydrothermal veins, as well as in additional deposit types in which REEs may be recovered as by-product commodities. Carbonatite-related REE deposits in China provide nearly all the light REE production in the world. Two giant deposits are currently being mined in China: Bayan Obo and Maoniuping. The carbonatite-related REE deposits in China occur along the margins of Archean-Paleoproterozoic blocks, including the northern, southern, and eastern margins of the North China craton, and the western margin of the Yangtze craton. The carbonatites were emplaced in continental rifts (e.g., Bayan Obo) or translithospheric strike-slip faults (e.g., Maoniuping) along reactivated craton margins. The craton margins provide the first-order control for carbonatite-related REE resources. Four REE metallogenic belts, including the Proterozoic Langshan-Bayan Obo, late Paleozoic-early Mesozoic eastern Qinling-Dabie, late Mesozoic Chishan-Laiwu-Zibo, and Cenozoic Mianning-Dechang belts, occur along cratonic margins. Geologic and geochemical data demonstrate that the carbonatites in these belts originated from mantle sources that had been previously enriched, most likely by recycled marine sediments through subduction zones during the assembly of continental blocks. Although the generation of carbonatite magma is debated, a plausible mechanism is by liquid immiscibility between silicate and carbonate melts. This process would further enrich REEs in the carbonatite end member during the evolution of mantle-derived magma. The emplacement of carbonatite magma in the upper crust, channeled by translithospheric faults in extensional environments, leads to a rapid decompression of the magma and consequently exsolution of a hydrothermal fluid phase. The fluid is characterized by high temperature (600°–850°C), high pressure (up to 350 MPa), and enrichment in sulfate, CO2, K, Na, Ca, Sr, Ba, and REEs. Immiscibility of sulfate melts from the aqueous fluid, and phase separation between CO2 and water may take place upon fluid cooling. Although both sulfate and chloride have been called upon as important ligands in hydrothermal REE transport, results of our studies suggest that sulfate is more important. The exsolution of a sulfate melt from the primary carbonatite fluid would lead to a significant decrease of the sulfate activity in the fluid and trigger REE precipitation. The subsequent unmixing between CO2 and water may also play an important role in REE precipitation. Because of the substantial ability of the primary carbonatite fluid to contain REEs, a large-volume magma chamber or huge fluid flux are not necessary for the formation of a giant REE deposit. A dense carbonatite fluid and rapid evolution hinder long distance fluid transportation and distal mineralization. Thus, carbonatite-related alteration and mineralization occur in or proximal to carbonatite dikes and sills, and this is observed in all carbonatite-related REE deposits in China. Ion adsorption-type REE deposits are primarily located in the South China block and are genetically linked to the weathering of granite and, less commonly, volcanic rocks and lamprophyres. Indosinian (early Mesozoic) and Yanshanian (late Mesozoic) granites are the most important parent rocks for these REE deposits. Hydrothermal alteration by fluids exsolved from late Mesozoic granites or related alkaline rocks (e.g., syenite) may have enriched the parent rocks in REEs, particularly the heavy REEs. Furthermore, this alteration process led to the transformation of some primary REE minerals to secondary REE minerals that are more readily broken down during subsequent weathering. During the weathering process, the REEs are released from parent rocks and adsorbed onto kaolinite and halloysite in the weathering profile, and further enriched by the loss of other material to form the ion adsorption-type REE deposits. A warm and humid climate and a low-relief landscape are important characteristics for development of ion adsorption REE deposits.